CA1294074C - Spread spectrum multiple access communication using satellite or terrestrial repeaters - Google Patents

Abstract

SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM
USING SATELLITE OR TERRESTRIAL REPEATERS
Abstract of the Disclosure A multiple access, spread spectrum communication system and method for providing high capacity communications to, from, or between a plurality of system users, using code-division-spread-spectrum communication signals. The communication system uses means for providing marginal isolation between user communication signals. The marginal isolation is provided by generating simultaneous multiple steerable beams; using an omni-directional antenna with polarization enhancement; using power control devices to adjust the output power for user generated communication signals either in response to their input activity level or in accordance with a minimum allowable power for maintaining a communication link. The communication system can also employ a means for transmitting a predetermined pilot chip sequence contiguous with the code-division-spread-spectrum communication signals. In further embodiments the communication system employs a plurality of user terminals linked to each other or to other services through one or more terrestrial or satellite repeaters. Multiple satellite repeaters are operable in a new communication mode to obtain further gains in signal isolation.

Description

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SPREAD SPECTR~M MULTIPLE ACCESS COMM~NICATION SYSTEM
USING SATELLITE OR TERRESTRIAL REPEATERS
Background of the Invention Te_h~cal Eiel~
The present invention relates to multiple access communication systems and more particularly to a method and apparatus for employing Code Division Multiple Access (CDMA~
spread spectrum signals to provide communication services ; for mobile or remote user terminals using satellite or terrestrially based repeater apparatus. The present invention further relates to utilizing CDMA spread spectrum signals with multiple beam phased array repeater antennas, polarization enhanced omni-directional mobile antennas, voice or data activity switching, adjustable user terminal power control, and L frequency band communication links.
Bac~rou~d There has been a long-standing need to provide quality communication services to many groups o~ service users that are classified as remote or mobile or both. These users include rural telephone systems, police and other governmental agencies, commercial dispatching and paging systems, emergency services, and marine telephone. In the past these needs were partially satisfied by land mobile radio. ~owever, these services have always been faced ~i~h more potential users than system capacity. The frequency or spectral bandwidth allocations do not provide enough capacity to simultaneously handle the total number of potential users.
Even so, private individuals, businesses, and new classès of users, ~uch as aeronautical communications, are , [QUAFPA2.J15]
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~reating an ever increasing demand for services for both mobile and remote users. A large increase in the number or remotely accessible computers and data systems has also created a demand for remote and mobile digital data communications in addition to voice communications. In addition, new types of remote data collection or sensing/
and alphanumeric keypad or keyboard entry systems are being proposed which can not be serviced by current communication systems. Thererore, new communication systems are being proposed and built to serve these demanQs for service.
In building or implementing any new communication system, the key issue for both the designer and tne end user is the channel capacity of the system. In a commercial system, capacity translates directly into income or economic ~easibility which is important to the system operator, since capacity determines the number o~ revenue generating users that can be accommodated. The number of allowable users is in turn important to the potential service users. The - number of simultaneous users and, therefore, capacity supported by any communication system is determined by the amount o~ mutual interference between users.
Current mobile radio services operate as frequency division multiplexed (FDM) or frequency ~ivision multiple access !FDMA) systems which div-ide the ay~ilahl~ ~an~ h into smaller bands or channels. To decrease mutual interference some of the bandwidth is also assigned to "guard bands" between channels to provide attenuation or isolation between users. Full duplex communication requires two channels. The total number of channels is generally divided in half, one hal~ being for uplink and call control [QUAFPA2.J15]

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to a central base repeater and the other for downlink and control signals to users. In addition, some channels may be allocated for additional user protocol and call control.
There~ore, the number of simultaneous users is much lower than the apparent number of channels.
System capacity can be increased by increasing the number of channels but this decreases channel bandwidth which limits voice quality and the use of high speed data transfers. Instead, the preferred technique for increasing system capacity is frequency reuse. Frequency reuse is the process of using the same frequency in two separate geographic regions for two distinct communication links as long as the two regions are attenuated or isolated trom each other by a minimum value for signal rejection by the two user receivers.
~ ypical isolation or attenuation requirements for ad0~uate rejection of unwanted signals are on the order of 15 dB (FM type) to 30 dB (AM) or more down from the desired signals. Therefore, a communication system can be su~-diviaed into geographical regions and the same frequency cansimultaneously be "reused" in neign~oring regions which are isolated from each other by the appropriate attenuation.
This technique is easily applied in land moGile radio systems since radio waves are inherently attenuated proportional to the square of the distance from the radiating source (in free space). Systems operating in large urban areas actually appear to experience l/r3 to 1/r5 attenuation due to buildings and other absorbing structures.
Users geographically removed from each other by an appreciable distance naturally have their communication [QUAFPA2.J15]

~ILZ~ 4 signals attenuated with respect to each other. Thererore, a communication system can be constructed using several interconnected base stations positioned so that signals from adjacent stations experience a 15 to 30 dB attenuation with S respect to each other. To further increase capacity the ; geographical regions served by base transceivers are divided into successively smaller sizes which are separated by the appropriate attenuation or isolation, to allow for increased frequency reuse.
10This is the basis for cellular telephone technology whicn is the current approach to accommodating large numbers of mobile users. Here, each cell comprises a geographical region serviced by a central base station wnich uses land based communication lines and switching systems to form an interlinked system with other base stations so that the only airborne transmissions are localized across the cell. To decrease mutual interference and increase system capacity, frequency use is controlled to assure a minimum amount of isolation between users by assigning channels so that at least one "guard" cell is positioned between two users using the same channel. Each cell is large enough so that signals ;~crossing a cell are attenuated a substantial amount so that they are perceived as lower level noise in distant cells.
The cellular system employs a cqnt~al ~Qn~rnl-le~ that ~es ~;25 a~vanced processing technology to keep track of all the ;channel assignments within the system to maintain the required channel isolation. However, hand-off now becomes a problem. In hand-off, a mobile user crosses from one cell where the current frequency is allowed into a cell where it ~30 is not. This requires the system to change the rrequencies :' [QUAFPA2.J15J

used for the communication link. If a channel is unavailable in an adjacent cell, the call fails abruptly at cell borders.
A relate~ problem of current channel assignment scnemes is the inability to have instant access to the communication system at any time. Channel assignments increase the time the central controller requires to establish a communication link and may even prevent calls rrom being established.
Cellular systems also su~fer rrom multipath problems, especially near cell borders, where users receive desired signals both from a central transmitter and sources such as re~lections from buildings. I~- the signals add out of phase then they may cancel and become severely degraded. This problem is also encountered in radio telephone and other current mobile systems.
A similar problem occurs for mobile users moving away from central transmitters at speeds that give rise to Doppler effects and phase shifts. Here tbe standing wave pattern from the transmitter appears to fade every half wavelength creating continual reception problems. In addition, motion on the order of 70 mph can produce Doppler shifts on the order of +/- ~0 Hz at frequencies of 800 MHz which can increase inter-channel interference.
The F~ typç ~ la~ ~nd radio -~:el eFhQne syst~m broadcasts are not efficient techniques for transferring digital data signals. Current user demands call for data transmission links that are high quality exhibiting very low bit error rates on the order of 10-6 or 10-8 at data transfer rates on the order of 2400 to 4800 baud witn future data transrer rates extending up to 19l200 ~aud.

[QUAFPA2.J153 ` ~Z~4~ i~ 66128-196 Increasing capacity by using smaller cells is useful in large, high user density, metropolitan or urban regions but not in low user density rural regions. Increased capacity is not likely to be achieved economically (cost of base station versus number of users served in region) in rural areas. Therefore, while cellular telephone meets some of the demands of large metropolitan areas it does not meet the demands of rural areas which comprise 25 percent of the population and 84 percent of the land mass for countries like the United States. In addition, larger rural cells can decrease the frequency reuse in adjacent urban areas. This occurs because a single large cell is adjacent to several small cells which cannot use the same frequency. This and other design con-siderations and problems for cellular systems are discussed in further detail in IEEE COMMWNICATIONS MAGAZINE, Vol. 24, No. 2, February, 1986, especially pages 8-15.
It has previously been assumed that satelli-te systems are required to economically provide service to low density, rural or remote areas. However, satellite systems generally utilize high volume communication links to transfer otherwise terrest-rially based telephone communications over single large distancesbetween terrestrial relay stations for further transfer. This does not address the needs of mobile users or system users already without local telephone service.
Some satellite systems have been proposed to address single users through individual antennas instead of central relay stations, but the frequencies at which satellites .

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operate and the methods of transmission have led to the the use of rather large fixed antennas which are expensive and not amenable to use in mobile systems.
Proposed satellite services generally operate as FDMA
systems employing UHF frequency repeaters and AM modulation schemes such as Amplitude Companàe~ Single Sideband (ACSSB).
Frequency reuse can be used for satellite systems similar to cellular systems discussed above. The continental ~.S. can be divided into geographic~ regions or cells by using a multiple beam antenna where a separate beam is used for each region. Ir the signals in each region or antenna pattern experience an attenuation on the order of say 10 db with respect to those in the nearest nelghbor region and 20 dB
with respect to the next adjacent regions and so forth, then a given frequency can be reused two regions away based on 20 dB sensitivity rejection. This roughly doubles the num~er o~ users allowed at any time within a transcontinental communication system. However, this does not match demand for services.
Antenna designs have been proposed which would scan the antenna patterns across the target geographic regions using advanced frequency scanning techniques. These antenna schemes take advantage of the fact that different ~requencies c~ Gted ~ eren~ 2ngles hy a given antenna reflector as used on communication satellites. This means that as the frequencies transmitted ~y the antenna ; radiator system change, the virtual spot created on the earth by the antenna reflector will move. In this manner the same antenna structure is made to alter the beam location. However, such techniques use the antenna [QUAFPA2.J15~

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structure to direct oifferent ~requencies to di~ferent regions, thus failing to fully take advantage or frequency reuse by allocating only a portion o~ the total spectrum to each region.
Satellite systems do not use terrestrially based repeaters that communicate directly with users or a series of multiple satellites that communicate with the same user.
Thererore, current systems do not provide universal service, that is, the ability for users to change position over a large geographical range and still be able to communicate without using alternate transmission equipment or new frequency bands. In multiple satellite systems ~req~ency reuse would be limited by the isolation between geographic target regions. Satellite systems also experience ~ 15 multipath, blocking, and fading problems similar to mobile - radio and telephone systems.
Alternate methods o~ decreasing user inter~erence include time division multiple access ~TDMA) or m~ltiplexed (TDM) systems. Such systems use a central receiving station to multiplex or interleave separate user signals in time so that each signal only uses a portion o~ the total outgoing ; signal to the satellite. The time division approach divides the total spectrum up into predetermined temporal increments~ All signals -in the commu~i~-a~i~n r~nea~er system are allocated portions of tnis time controlled sequence Therefore, no other user is using the link at the same exact time. The allocated portions are very small and the interleaving very large so that it appears simultaneous to all users. However, this time based synchronization o~
signals creates a natural limit to the number of users that .
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:' k7 4 can be coordinated "simultaneously" which is lower than desired. Also synchronizing a large number of simultaneous users greatly increases the complexity and cost of the system.
; 5 What is needed is a communication system that accommodates a larger number of users throughou~ a variety of user environments from high density urban to very low density rural. The communication system needs to exhibit increased capacity within standard spectral allocation bandwidths but with the same or better communication quality than presently available. In addition, a need also exists for a communication system capable of han~ling high speed low bit error rate digital data transfers at low power densities~
SUMM~RY
~herefors, with the above disadvantages present in the art in mind, it is an object of the present invention to provide a mul~iple access communication system having high simultaneous user capacity.
It is another object o~ the present invention to provide a communication system having automatic Doppler shift and fade control.
It is a purpose of tne present invention to provide a communication system capable o~ expan~ion to meet ~ut~ure needs and interface with ~uture alternative communication systems.
It is a further purpose of the present invention to ~, provide an inexpensive communication system user terminal capa~le of meeting the needs of a variety of mobile o~r remote users ; :
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It is yet another purpose of the present invention to provide for transmission and receipt o~ hign speed digital data signals with very low bit error rates.
These and other objects, purposes, and advantages are provided in a multiple access, spread spectrum communication system, having means for communicating information signals to, ~rom, or between a plurality of users, using code-division-spread-spectrum communication signals and isolation means ror providing marginal isolation between said user communication signals. The isolation means can comprise a phased array antenna couple~ to means for generating substantially simultaneous multiple steeraDle beams; an antenna structure con~igured to obtain either one or both of two circular polarization states; transceiver means ~or transmitting or receiving the same communication signals by two or more locations to create constructive interference maximized slgnal reception; ~irst power control means for adjusting an output power duty cycle for said code-division-- spread-spectrum communication signals in response to a predetermined activity level for said inrormation signals;
or secona power control means for ad~usting said output power level for said code-division-spread-spectrum communication signals in response to a minimum power level reguired to complet-- a communication link.
The preferred embodiment of the multiple access, spread spectrum communication system o~ the present invention further comprises means for transmitting a predetermined : pilot chip saquence to users contiguous with said code-division-spread-spectrum communication signals.

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12~ t4 In a preferred embodiment the means for communicating comprises chip generation means for generating a plurality o~ quasl-orthogonal spreading ~unctions; code selection means for assigning one of tne spreading functions to a user; and a plurality of mobile user terminals capable of transmitting or receiving code-division-spread-spectrum communication signals. Each of the user terminals uses a transmitter ~or generating a code-division-spread-spectrum communication signal according to an assigned spreading ~unction in response to an input in~ormation signal; a receiver for detecting a code-division-spread-spectrum communication signal and generating an output information signal according to said assigned spreading ~unction; and an omni-directional antenna. At least one repeater is used ~or receiving communication sign~ s from the plurality o~ user ; terminals and for translating the code-division-spread-spectrum communication sign~ s to a form suitable for transfer to an intended recipient.
In a further aspect of the invention the repeater preferably employs means for transmitting a predetermined pilot cnip seq~ence to users contiguous with a communication ,~ link and the receivers include a pilot sequence tracking loop. An activity detector is included in the repeater for - s~n~ing ~ign~l ~a~i~-i~y 1~Y~ n -B~i~ inform~ion ~n~lS
and decreasing repeater transmission power duty cycle in response to a decrease in sensed activity below a predetermined threshold level for a predetermined sampling time.
The user terminals can also comprise an activity detection means ~or sensing signal activity levels in the :
:
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:~l2~¢~4 input information signals and decreasing user terminal ; transmission power duty cycle in response to a decrease in sensed activity below a predetermined threshold level.
Tne terminals can furtner comprise power control means S for sensing a received power level present in received code-division-spread-spectrum communication signals and for adjusting the output level power applied to an antenna for transmitting code-division-spread-spectrum communication signals in response to the sensed power level, The antenna of the preferred embodiment further comprises polarization control means for adjusting the antenna so as to select a predeterminea polarization mode.
; In further aspects of the invention the repeater means can comprise at least one terrestrially based repeater or lS at least one satellite based repeater or Doth. The communication system pretera~ly employs at least two satellites and earth base~ repeaters. Generally ~he satellite repeaters are interconnected to other communication systems using a central control station known as a hub. ~sers can access either type of repeater based on their location and assigned communication links~ In this ~; manner universal service is obtained in a manner previously unavailable and terrestrial repeaters in high user density regions can of~load loc~l us~rs to ~,re~~ ~he pow~ ~r~ln on satellites or increasa their capacity, The repeaters preferably use a phased array antenna structure to create simultaneous multiple steerable beams.
In still furtner aspects of the invention the communication system further comprises a demodulator, using a radio frequency mixer to correlate a local reference ;~ ~QUAFPA2.J15]

signal with input code-division-spread-spectrum communication signals. The resulting intermediate frequency spread spectrum signal is riltered to remove undesirable frequency components~ A phase division means connected in series with the filter divides the spread spectrum signal into an analog in-phase signal and an analog quadrature signal which are then converted into digital in-phase and quadrature signals at a variable rate. Combiner means transfers the digital in-phase and quadrature signals onto a single data line in serial rashion ~or processing by other components within the demodulator.
A pilot chip reference means generates a local bit sequence corresponding to a predetermined pilot chip sequence transmitted contiguous with communication signals received by the demodulator. Carrier tracking means connected to the com~iner and the pilot rererence means compares the local pilot chip sequence to received signals in a timed relationship to determine the timing o~ the code-division-spread-spectrum communication signals with respect to the said local pilot chip sequence. A decision is ~hen made to adjust the ~requency o~ the local mixer ~requency source. Chip synchronization means connected to the combiner ana the pilot reference means compares the local pilot chip sequ~nc~ ~o reGe~Ye~ nal-~ -~n a plural1ty o~ ~lmed relationships to determine the timing o~ code-division-spread-spectrum communication signals with respect ~o the local pilot chip sequence. The comparison determines if the rate for the analog-to-diyital conversion needs adjusting.
Unit chip means generates a bit sequence corresponding to an assigne~ spreading ~unction wnich is use~ by ~QUAFPA2.J15~

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despreading means connected to the combiner for generating despread-spectrum in-phase and quadrature information signals.
These signals are then combined in an output means to from an output information signal.
The present invention provides a method of providing high capacity multiple access communications to a plurality of communication service users, by converting a plurality of narrow band analog input or digital data input signals into a plurality of wide band code-division-spread-spectrum communication signals, using an assigned spreading function and a predetermined carrier frequency; applying marginal isolation to the plurality of code-division-spread-spectrum communication signals; transmitting the code-division-spread-spectrum communication signals to or ~rom users; and converting a code-division-spread-spectrum communication signal received by a user to a narrow band analog or digital information signal.
The method of the present invention may also comprise the steps of transmitting a pilot chip sequenca and transmitting and receiving signals through repeaters. The repeaters can include at least one terrestrial and/or at least one satellite based repeater.
In accordance with the present invention a spread spectrum multiple access communication system having high system user capacity is disclosed. The system comprises means for communicating and isolation means. The means for communicating communicates system user addressable information signals between at least two of a plurality of system users using address , ~1' '~ ~'.

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14a 66128-196 corresponding code-division-spread-spectrum communication signals.
The means for communicating genera~es mutual interference in communications between at least two system users by contemporaneously communicating code-division-spread-spectrum communication signals between other system users. The means for communicating has a processing gain for reducing the mutual interference. The isolation means, coupled to the means for communicating, provide~ an increase in system user realized average signal power for the system user address corresponding code-division-spread-spectrum communication signals in communicatlons ~etween the at least two system users relative to mutual interference signal power of the contemporaneous communications between the other sy~tem users.
Further in accordance with the present invention a method of providing high system user capacity in a spread spectrum multiple access communication system is disclosed. In the employed method, system users communicate user addressable information signals using address corresponding code-division-spread-spectrum communication signals. In communications between at least two system users, other system users generate mutual interference by contemporaneously communicating code-division-spread-spectrum communication signals. Although the system has a processing gain for reducing mutual in~erference, the method of the present invention provides high system user capacity by further reducing mutual interference in communications between the at least two system users. The method comprises the steps of:
~roviding a plurality of system user addressable narrow band ~3 :~

~l~9~(~74 14b 66128-196 information signals; converting the plurality of system user addressable narrow band information signals into a corresponding plurality of system user address corresponding wide band code-division-spread-spectrum communication signals; transmitting the plurality of code-division-spread-speictrum communicatlon signals between system users; receiving, at each respective system user, system user address corresponding code-division-spread-spectrum communication signals and other respective system user addressed code-division-spread-spectrum communication signals as mutual interference; providing for each respective system user an increase in system user realized average signal power for the system user address corresponding code-division-spread-spectrum communication signals with respect to mutual interference signal power of the other system user adress corresponding code-division-spread-spectrum signals; and converting, at each respective system user, received address corresponding code-division-spread-spectrum communication signals into corresponding user addressable : information signals.
BRIEF DESCRIPTI0~ 0~ TH~ DRAWINGS
The novel features of the present invention may be better understood from the a~companying description when taken in conjunction with the accompanying drawings in which like chara~ters refer to like parts and in which:
FIG. la is a plot of antenna gain versus angular deviation from boresight center for an exemplary antenna used in a satellite communication system;

~;~9~C~74 FIG. lb is a table of actual and "weighted" users versus antenna gain and angular deviation for the antenna of FIG. la when used in the communication system of the present invention;
FIG. 2 is an overview of a communication system con-; structed according to the principles of the present invention;
FIG. 3 is a schematic of a repeater employed in thesystem of FIG. l using an omni-directional antenna;
FIG. 4 i5 a graphic plot of average user power to esta-bli.sh a communication link versus the distance from a terrestrial repeater;
FIG. 5 is a schematic of another repeater employed in the system of FIG. 2 using a phased array antenna structure;
FIG. 6 is a graphic plot of average user power versus the distance fro~ a repeater;
: FIG. 7 is a schematic of an orbital repeater and a communication system hub used in the system of FIG. 2;
FIG. 8 is a plot of relative signal strength versus position for a satellite interference pattern;
FIG. 9 is a schematic view of a hub interferometer communication link;
: FIG. lO is a schematic of the user terminal employed in the system of FIG. 2;
FIG. ll, on the fifth sheet of drawings, is a view of an antenna for use in the system of FIG. 2;
FIG. 12 is an illustration of elliptical ratio;
FIG. 13 is a graphic presentation of capacity versus antenna ellipticity;

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FIG. 14, on the second sheet o-f drawings, is a tabular listing of capacity versus ellipticity and axial ratio;
FIG~ 15 is a schematic of a demodulator used in the user terminal of FIG. 10; and FIG. 16 is a schematic of a modulator used in the user terminal of the FIG. 10.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The present invention comprises a new communication system employing one or more satellite or terrestrially based repeater stations to provide communication links among a large number of mobile or fixed, and local or remote users. To obtain a large number of users, the user terminals within the communica-tion system employ new modulators and demodulators to transmit forward-error-correcting-coded communication signals using Code Division Multiple Access (CDMA) spread spectrum transmission sig-nals. In addition, system capacity and communication is further enhanced by using means for providing marginal isolation between users comprising multiple beam phased array repeater antennas, polarization enhanced mobile antennas, means for generating inter ference patterns for reception and transmission of communication signals, voice or data activity switching, or adjustable user terminal power control. Additionally, independent pilot chip sequence signals are used to improve acquisition and tracking.
Traditionally, CDMA has been held to be inferior as a multiple access technique in comparison to FDMA and TDMA because it appeared to provide inferior spectral utilization. This was based on the argument that for TDMA or FDMA, the number of equal bandwidth channels that a given X t band can be divided into is approximately equal to tne total banawiath divided ~y the bandwidth per user channel.
Whereas, CD~A provides fewer channels according to the ; ~ollowing argument.
In a bandwidth limited environment where a number of ; equal users desire to share a common ~requency band using CDMA, the number of such equal users is determined by the ~ollowing formula:
I/S = W/R - Eb/~o (1) where I is the total inter~erence power seen by each user's receiver and is equal to tne total power o~ all the users, which is equal to the number of users times the power per user;
S is the power o~ one user's signal, thus I/S
equals the e~fective number or users;
W is tbe ban~wiath occupied by the spread spectrum signals;
R is the data rate of each user; and E~/No is the signal-to-noise ratio required for the modulation and coding system employed.
Since it can be seen that W/R is the TDMA and FDMA
capacity, the CDMA capacity would seem to be always less by - an ~mount equ~l to ~bJNo~ r practical ~s~
approximately 3 - 5 dB, ~epending on the particulars of the modulation and coding system employed.
The present invention greatly increases the capacity of CDMA systems by employing means for producing marginal isolation. The term, marginal isolation, will be defined herein. The key idea is that the spread spectrum receiver [QUAFPA2.J15]

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sees the welghted sum of all the users' incident power as interrerence to the one desired signal. If the system includes means to provide non-uniform weighting, then increases in capacity can be o~tained rrom differences in ; 5 weighting. Differences too small to be of use to FDMA or TDMA systems are quite valuable to a CDMA system.
In previously proposed CDMA satellite systems, a wide band transponder with earth coverage antenna has been employed. Such an antenna provides nearly tbe same gain to all users, no marginal isolation is realized and performance is, in fact, worse for CD~A tnan ~or TDMA or FDMA. The ; present invention, however, utilizes a multiple steerable beam antenna which provides the capability to realize marginal isolation. Such an antenna also increases the capacity of FDMA and TDMA systems, but provides far more capacity gain for CDMA. Tnis is because FDMA and TDMA
systems require at least 15 dB isolation of co-channel signals in order to provide accepta~le performance, while the CDMA system o~tains useful capacity increases from isolation as small as 1 dB.
-Marginal isolation is derined as a system characteristic that provides unequal weighting of the incident received power or inter~ering user signals.
~mbo~m~ts o~ th~ p~e6~nt -inYen~on util i~e se~7eral mechanisms for providing marginal isolationr including multiple steerable beam antennas, antenna polarization, formation of interference beam patterns from multiple satellites, path loss difrerentials ~or in~erferors at di~ferent distances, and less than continuous transmit duty cycle. A~ditional methods o~ producing marginal isolation [QUAFPA2.J15~
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-4 137~a may be devised by those skille~ in the art o~ communications system design An exemplary rommunication system 30 woul~ use a spread : spectrum bandwidth, W~of 8 M~z and an in~ormation signal bandwidth, R ~of 5 kHz ~or a bandwidth ratio o~ 1600 and a processing gain of 32 dB. I~ we assume Eb/No to be 5 dB, the number of users can be computed rrom equation 1. Under these conditions I/S is 27 dB. The total number of users (I
+ S) is, therefore, approximately 500. This means that the communication system supports 500 users under these conditions. But these are users all operating under the same conditions and with equal power and isolation within the system.
I~ instead the system users are isolated or contribute unequally to the interference in the system communication link, new users can be added. This can be illustrated using an antenna pattern that exhibits a relatively ~lat "response" or gain across the middle of a beam width and tnen falls o~f sharply on the edges. If we assume an equal distribution or users over an area larger than the central high gain portion o~ the antenna beamwidth, then each user is "weighted" by tne relative gain e~fected ~or its signal because of a roll-off in gainO E~IG. 1, shows the impact of - ~h-ifi ~ or~ o~-~ ÇQmmlln ~ Qn sy _t ~.m. .
FIG. la shows a plot o~ the actual, maximum, and minimum gains versus single-sided angle from boresight o~ a typical satellite antenna used for L-Band transmission ~rom synchronous orbit. This antenna pattern represents an antenna optimized for an FDMA system, not a CDMA system.
FIG. lb shows the minimum and maximum gain data in a taDular ~QUAFPA2.J15]

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form with gain regions and angles expressed as double-sided or total angle from the center of the boresight. I~ we use the maximum gain in eacn region and the gain f actor f or the entire region and assume that there is a uniform distribution o~ users across the typical 7.4~ width of the United States, than FIG. lb shows how a total population of 2326 users has the same effective interrerence as 500 users having the strength o~ the user of interest.
The " Q Angle" column giYes the angle size o~ each gain range, The "~ of ~sers" column is calculated by multiplying the total number of users by the fraction of users at this gain. The followlng equation is used:
~ Angle # of Users ~ Total ~sers (2) Total Angle of US
~'he "Weighted ~ of Users" column is calculated by multiplying the "# of Users" column ~y the maximum gain of ~' that range. This calculates the equivalent num~er of users at 0 dB that would produce tne same interrerence as the users in this region at this maximum gain. The following equation is ~sed:
Weighte~ ~ of ~sers = ~ of Users lO -(MaxGain/lO) (3) It is important to note how even attenuations of as small as l dB reduce the weighte~ total. Lastly, the "Wei~hted ~ of Users" is totaledO The number of users in the U. S. was adjusted for purposes o~ illustration so that the "Weightea Total" was approximately 500 users as used above.
The "CDMA Reuse Factor" of 4.65 was calculated as the ratio of 2326:500. The "FDMA Reuse Factor" or 3.70 was calculate~ as 7.4~/(1.0~ 2). 7.4~ is the width of the ~.S., [QUAFPA2.Jl53 `:

l~g~74 1.0~ is the 2 dB beamwid~h of the antenna, and one needs to use one half of the frequencies in one beam and then the otner hal~ in the next beam; so it takes two beamwidths before the frequencies. ~sing the antenna optimizeo ~or ~DMA, CDMA shows a better reuse factor. If tbe same size antenna is optimized ~or CDMA -- minimum noise beamwidth --then the CDMA reuse tactor can ~e further increased to 6.67 giving a reuse gain of 6.67/3.70 = 1.80.
As can be seen, the total number of "errective" users is 500 while tne system is actually supporting 2326 users if multiple beam positions are provided so that all users can be received near the center or a beam. Tnerefore, the system uses marginal isolation o~ a few dB, which is useless to otner systems, to provide ~requency reuse. ~his ability to increase the eL~ective adjacent user attenuation allows the present communication system to provide greatly increase~
~requency reuse as compared to other communica~ion systems.
An overall schematic or a communica~ion system operating according to tne principles o~ the present invention is illustrated in FIG~ 2. In FIG. 2, a sprea~
spectr~m communication system 10 employs terrestrial repeaters 12 or or~ital repeaters 14 with one or more central s~ations 16, to transmit and receive iniormation to ~ or from mobile terminals 20,or 22,and ~ixe~ terrinals 24 or 26.
The term information is used to encompass botn digital data and voice since some terminals will transmit, or ~e ~ equipped to transmit, signals in the form of digital data as - well as the typical analog or voice signals. Transmission of digital data is generally accomplisheà using an ' [QUAFPA2.J15]

appropriate interface ~or linking a data generation source 28, such as a TTY device or computer, with the user terminal 22 or 26 circuitry. Modems and other data communication inter~ace devices are readily designed and understood by those skilled in the art and are not described in detail here, The pre~erred embodiment of the communication system 10 ma~es extensive use of the mobile terminals 20 or 22 since the fixed terminals 24 or 26 provide less of an advantage in large urban areas where high quality "wire borne"
communication lin~s are easily an~ cheaply accessed.
~owever, rixed terminals 24 and 26 located in distant or remote locations will gain great advantage ~rom the communication system 10 since terrestrial wire or cable based links are prohibitively expensive, difficult to ins~all, or even non-existent in many areas.
The communication system 10 uses, or evolves in stages to use, several alternative paths ~or communica~ion. An initial communication system 10 installation would perhaps use exclusively terrestrially based repeaters 12 which communicate with and relay information between the terminals 20, 22, or 24. Tnis is illustrated by the portion or system to the right of the double dashed line dividing the system -10 ~into ~wo par~s, a ~errestrial portion and a satellite portion. The earth based repeater 12 or tbe present invention advances the communication art by providing improved high quality, high capacity communications. However, the terrestrial portion o~ the ` communication system lQ is also constructed to inter~ace witn an orbital satellite repeater 14.

[QUAFPA2.J15]

.; . .

3~2~

The initial system accommodates many remote or mobile users with communication lin~s 30 through terrestrial repeaters 12 that are interlinked by existing telephone networ~s 32, or through dedicated ~iber optic or radio communication links 34. Then when a satellite is launched, the communication system 10 uses satellite links 36 to interconnect users, especially rural users. Later on addi~ional satellite repeaters 14 are launched to provide improved communications and higher system capaci~y.
A~ditional control and signal processing is pre~erably providea in the satellite portion by using central ground stations or hubs 16 via satellite lin~s 38.
This makes tne communication system 10 highly rlexible and advantageous ror handling a variety of communication lS needs and services. The communication system~ 10 accommoaates a larger user base or geographical service area commensurate with governmental agency approval and satellite development and launch timing~
T~is dual system has additional aàvantages over current systems, both in terms o~ universal service and interference9 Universal service allows users to move ~reely throughout the system and have communications regaraless o~
location. That is, mobile access is provided to users that switch between rural, s~bu~b~n~ or urban area6~ and land, aeronautical, or water based ~orms o~ travel. Tnis service is provided on individual, low cost user terminals without equipment alteration. This also means that users have communication system 10 access even when out or normal "home coverage" area provided by a cellular arrangement.

[QUAFPA2.J15~

~2~4~t7~L

The communication system 10 can be configured as a cellular system using varied cell sizes with larger cells positioned adjacent to many smaller cells. While this decreases the amount of ~requency reuse, it will not be a substantial limitation for the communication system 10 due to its greatly increased frequency reuse capabilities. It can accommodate such a limitation or loss of reuse and still serve more users than previous communication systems. The t communication system 10 does not require the same guard cells or spaces for frequency reuse as previously seen in cellular systems.
; As previously discussed, current communication sys~ems such as cellular telephone, or mobile radio, are SCPC or single channel per carrier FDMA systems that divide the overall spectrum into discrete channels or rrequencies for each user or communication link. These communication systems employ AM or FM modulation techniques that generally require minimum attenuation between users on the order of 15 dB for FM to 30 dB or more for AM.
The communication system 10 uses spread spectrum signal transmission techniques to increase user capacity by establishing coded digital communication signals that use ~` quasi-orthogonal bit sequences to decrease mutual inter~erence~ At the s~me ~i~e, the communi~atien shannels are spread across or occupy the entire allocation bandwidth, which improves communication quality, allows for increased ~andwidth signals and decreases the erfects of frequency selective fading.
~ Sprea~ spectrum communication involves processing the ;~ 30 outgoing inrormation signal with a spreading function which ,~
[QUAFPA2.J15]

.

, 4~7~

changes or expands a narrow bandwidth signal into a broad band-width signal. The spreading function is a reproducible function which spreads the narrow bandwidth transmission signal over a broader bandwidth and reduces the peak spectral density of the signal. This is direct sequence spread spectrum coding. Alterna-tively, the carrier frequency can be pseudo-randomly hopped over the spread bandwidth. Direct sequence spread spectrum is prefer-red for applications addressing multipath impairments.
In the communication system 10, this is accomplished by converting analog input information signals, such as voice, into digital form and multiplying them by a high bandwidth high fre-quency digital spreading signal. Digital input signals can be directly spread. The resulting spread spectrum signal is then used to modulate a carrier and create a communication signal. It is also possible to modulate the carrier first and then apply the spreading function but for the preferred embodiment the first approach is used for ease in digital processing.
The high bandwidth spreading signal comprises a deter-ministic series of bits of period Tc referred to in the art as chips. The chips or chip sequences are generated using electronic apparatus and techniques known to those skilled in the art. There are a variety of techniques as well as known coding formulas for generating spread spectrum chip sequences. Exemplary techniques or methods are described in further detail in SPREAD SPECTRUM
COMMUNICATIONS, Volume l by M. K. Simon et al, Chapter 5, pages 262-358.

;

2 ~ ~ ~ 7 -26~

The chips are generated at a much higher rrequency than ;the input voice or data signal. By generating the chips at this higher ~requency, a series of chips are generateà for every single information bit. The specific chip frequency use~ depends on the allocation bandwidth for the communication system 10. It is desirable to spread the communication signal to cover the entire allocated bandwidth where possible and achieve a high processing gain, as discussed below. Also, the higher the chip rate the more users a spread spectrum communication system can service since higher rates generate more chips per information ~it and more quasi-orthogonal codes with which to differentiate between users.
For a spectral allocation bandwidth of 9 MHz and using 15 ~ a fifth order elliptical ~ilter to process the spreading signal, a chip rrequency of approximately 8 MHæ would be used to provi~e a signal having a 2 aB pass bana ripple and 30 aB stop band attenuation. This frequency provides long chip sequences, whicn proviaes a large number or discrete addresses or codes for dif~erentiating between users.
~The communication system 10 uses Code Division Multiple ; Access (CDNA) signals to increase the user capacity or the system. This is done by assigning each user a speci~ic code in the chip sequences so that the cross-correlation function ~etween users is small and the users are said to ~e quasi-orthoyonal to each other. As previously stated, there are known coding functions which can be used to determine or generate a family of codes or chip sequences. An exemplary set would be the GOLD codes which are also discussed in the [QUAFPA2.J15]

~;25a4~7~

previously mentioned SPREAD SPECTRUM CO~MUNICATIONS
re~erence.
The chip sequences can be generated or chosen so that a predetermined or unique chip sequence is assigned to a specific user ~or the entire time a user terminal is used in the communication system 10 or assigned each time the user starts a communication link as part o~ the call setup protocol. This, of course, means maintaining a central log or listing of all user chip sequence assignments.
The earth based or terrestrial repeater 12 o~ the communication system 10 is illustrated schematically in FIG.

3. In FIG. 3, the repeater 12, whicn can be located in a rural or urban region, employs an antenna 40 to receive or transmit communication signals. The antenna 40 is coupleà
to a duplexer 42 which allows coupling the antenna to both the transmit ana receive sections or modes o~ tne repeater 12. This simplifies the antenna design and installation by using a single antenna structure as opposed to two, However, it is not necessary for the function or the present invention to use a single antenna.
Tbe duplexer 42 trans~ers incoming or received communication signals through a receive power splitter 44 to spread spectrum receivers 46, each of which will handle a specific user or communication lin~O Tnere~ore, eacn repeater will employ as many spread spectrum receivers as users or communication links it is expected to accommodate at a given time. The receivers 46 contain circuitry to ~ change the incoming communication signals to a lower IF
- ~requency and track and lock onto the signal. The receivers 46 then r~nove the carrier and despread the signals to [QUAFPA2.J15~

~;~9413;7~
, provide a digitally enco~e~ signal. The enco~ed signal is then trans~errea to data-to-voice decoders 48 where they are changed to analog or voice signals for use over a terrestrially ~ased linK. In FIG. 3 a telepnone network interface 50 is used to couple the voice signals to telephone lines ror trans~er to o~her locations. In the alternative, a riber optic coupler, not shown, could be used to couple signals into a fiber optic communication ; cable. The interface and riber optic couplers represent devices that are commercially availa~le and designed by those skilled in the art o~ terrestrial communication systems.
The repeater 12 may also communicate incoming signals directly with other mobile users within the region it is servicing. In this case, a repeater controller 52, which can comprise microprocessor controllers and circuitry, routes the decoded communication signal to the user that is specified in the communication protocol (cnip sequence assignment). Both users for this communication link are assigned speci~ic receivers and transmitters. Previously each user was assigned a specific channel. The term channel can still be used for the communication system 10 DUt it now refers to a percentage of the overall power of the system.
Every user generally occupies the whole spectrum used by the repeater but is allocated only a portion o~ the power available to the repeater, determined by the minimum amount of power required to establish and maintain a communication link. In the preferred em~odiment the overall spectral allocation is divide~ in half with one half ~sed for tne [QUAFPA2.J15]

,..... .. .

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uplink portion and the other for the downlin~ portion of communication links.
By usiny this type of power control the amount of power required for maintaining communications witn users decreases as the users are closer to the repeater based on the attenuation of radio waves over distance. The e~fect of the power decrease is illustrated in FIG. 4 where a plot of average power used to maKe a communication lin~ versus distance rrom tne repeater is shown. It can be rurther shown that for this type of distribution the total power required for tne repeater is decreased almost by a factor or 2. This decrease can be used to reduce the power requirements for the repeater or to increase the capacity by a ractor or 2 for the same power requirements.
This reduction o~ power also reduces inter~erence in neighboring calls.
Returning to FIG. 3, information signals~ either from the terrestrial link or another "local" user, are transferred back through voice to data encoders 54 to transmitters 56~ In the transmitters 56 the digitally coded signals are spread and used to modulate a carrier ~o form the desired communication signal. The communication signal is now transferred through the transmitter power combiner 58 and duplexer 42 to antenna 40, For communication siynals remaining within the region serviced ~y the repeater,l2, the preferred system o~ tne present invention would not route intermediate versions of the signals through the digital decoders 48 and encoders 54, Instead tne signals are transferred directly between the receivers 46 and transmitters 56 only providing so much of [QUAFPA2.J15~

' ... .. .. ...
, .

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the decoding as necessaxy tO cnange the spread spectrum code assignment rather than actual conversion to analog ~orm.
The repeater of the present invention can trans~er a single communication signal to as many users as desired without requiring duplication of the signal. In tnis regard the protocol used for tne sen~ing of messages can accommodate an indication of multiple users in the address.
Thererore, for some services one message can be detected ~y the receivers 46 and quickly transrerred directly to several transmitters 56 for reception Dy several users. Tnis is the so called one to many ~orm o~ transrer use~ul for some types or dispatch and data transrers. The repeater can also easily accom~o~ate the reverse, where several communication signals are transferred to a single receiver~ The many to one type or trans~er.
Anotner advance over the art ~or the repeater 12 is the ; inclusion o~ a voice activity detector in the circuitry.
This detector moni~ors tne activity of signals processed by the circuit to decrease the power utilized in the absence o~
communication. In a CDMA communication system it iS
possible to employ rast attac~, threshold sensitive, detectors tnat can decrease tne signal level, energy, or transmitter power used auring periods as brief as between syllables in conversation. FDMA and TDMA communication systems cannot reassign channels or ta~e similar steps in this short a time perioa. For pauses during digital data transmission this is equally applica~le. The power re~uction is accomplishea by gating off the transmitter except ~or brief, periodic bursts to maintain syncnronization. This [QUAFPA2.J15]

can ~e accomplished by generating a control signal which alters the duty cycle o~ power ou~put circuitry.
The activity detection and power control results in a net savings o~ energy usage ~or the communication system 10.
It is estimated that as much as 40 percent o~ the total time consumed by a typical conversation can ~e treated as "dead"
time, The bit error rate an~ signal quality for each user is determined by Eb/Io on an instantaneous ~asis.
There~ore, if some of the interference is gated o~ tnen Io decreases and the remaining user interference also decreases whicn in turn increases system capacity. The resulting reduction in average power per user is also important for tne orbital repeaters 14 which operate in a power limiteà
environment, Tne elimination of about 40 percent ot the "conversational" dead time in the communication system 10 increases the system capaci~y by as much as 2 1/2 times.
This increase in system capacity or number o~ communication channels is not possible with FDMA and TDMA communication systems because o~ the dirriculty in switching busy or active channels into idle channels during conversational pauses. In addition, the inherent time delay imposed by signal transit times, makes cooroination o~ such signal switching for use in the uplink portion o~ a communication lin~ impossible in satellite FDMA or TD~A systems, Additional advantages are realized ir an antenna array is used for the repeater 12. The antenna array o~ the preferred embodiment forms multiple steerable beams that are directe~ to specific users which increases the isolation between users. This is shown schematically in FIG. 5 where [QUAFPA2.J15]

.

a phasea array repeater 60 uses the intrinsic properties o~
a phase~ array to create beam directionality and also multiple beams which can be directed to speciric users or user regions. The modems 64 comprise the circuitry previously shown in FIG. 3 aLove, with the exception o~ the ~- antenna 40. Tne antenna now employs a dif~erent structure and some new control elements.
Siynals tnat were previously transferred to a single antenna 40 are now trans~erred to a beam former 62. The number or beam ~ormers 62 used in tne repeater 60 ~epends ; upon the amount or control desire~ over the communications to indivi~ual users versus tne cost and complexity that can ~e accommodated. The more beam formers used, ~he greater amount o~ control tnat can be exercised over each communication link from tne modems. The maximum number o~
beam formers used would correspond to the number or modems and provide optimal control over user communications.
However, tnis is overly complex for most communication uses.
Each beam former transfers signals ~rom its associated transmitters in the modems 64 to a series of antenna elements 66 comprising a phased array 68. As will be apparent to those skilled in the art, tne phase~ array antenna r~nctions by controlling tne relative pnase o~ the signals transmitted by tne indiviGual elernents 66 to ~orm a beam along a speci~ic direction. By controlling the relative phase o~ tne transmission or signals from the elements 66, tne transmissions are summed in space to form a single beam traveling along a particular direction Controlling the phase of the elements controls the resulting beam direction.
:

~; lQUAFPA2.J15]
:
.
' :~29~7~

Each beam former 62 is ~esigned to transmit signals along a specific beam pattern or patterns. The beam formers 62 accept signals from the modems 64 and create as many duplicate or parallel signals from each single communication signal as there are antenna elements 66. In FIG. 7 three elements are shown for purposes o~ illustration only. The pre~erred embodiment of the communication system 10 uses from 6 to 15 elements in a two dimensional array or pattern, but is not limited to these numbers. Tne number used depen~s upon the amount of frequency reuse that is desired, realistic attenuation limi~ations, and the allowa~le complexity o~ the repeater 60.
The beam formers 62 then alter the pnase of the parallel signals using techniques known in the electronics arts and transfer these signals to the antenna elements 660 At the same time, t~e outputs ~rom each o~ tne beam formers 62 is summed by digital combiners 70. This is done so that all of the power inten~ed ror each element is summed and transferre~ to that element and the transfer is isolated from returning through adjacent ~eam formers. Tnis allows for multiple beams to be formea and directed by the array simultaneously by the beam formers 62.
It is furtner possible to permanently assign receivers and transmitters to the beam formers so that they function to handle communications within preselected regions or along dedicated communication links. While dedicated communication links tend to decrease tne capacity or the communication system 10, there are priority users such as emergency services that orten require or demand this kind o~
service.

QUAFPA2.J15]
' )7~

Tne phased array o~ the repeater 60 is also equally use~ul for scanning a region or directing a receiving pattern to detect speciric regions or users. The scan pattern ~or the array can be predetermined by the assignment o~ receivers to monitor specific regions or directions.
However, the array o~ the present invention is not limitea to static assignments. An antenna controller 72 provides signals to the beam formers 62 which alters the directional assignment used by each beam ~ormer. In this manner new steerable beams can be created or a~ditional beams directea into regions wnere increased user capacity is neede~. Also, incoming signals can be detected in terms o~ the phase relationship required for the highest strength. The phase of tne array can be periodically scannea or slightly adjusted to provide this information. Then the same phase relationship can be used in the array for the return signals to that user. In this manner not only can improved communication be obtained over the recep~ion link but also for the transmission link.
The communication system 10, as previously discussed in rela~ionship to the illustration o~ YIG. 2, can employ a series or terrestrial and satellite repeaters to ~orm a large interlinked communication system. As shown in FIG. 1, repeaters 12 can be subdivided into the xepeaters 12a and 12b as well as the satellites 14a and 14b.
The terrestrial basea repeaters 12a serve high user density urban Ol metropolitan areas while the terrestrial based repeaters 12b serve larger but lower density urban or sub-urban regions. The orbital repeaters or satellites 14a and 14b serve even larger geographical regions wnich are [QUAFPA2.J15]

7~

rural and low user density. While tnis is a preferrea allocation of resources for tne present invention, it is not the only possi~le allocation. For example, tbe orbital repeaters 14a or 14b can be used to service metropolitan areas where it is economically unreasonable to establish central base stations. This may also prove advantageous where it iB desirable to have direct communication links between certain metropolitan users and rural users without any intermediary communication service links.
Another important feature o~ the communication system is ability o~ the terrestrial repeaters, especially in the high user density metropolitan areas to "o~fload" local users from the satellite repeaters. Tnat is, as users come within range or terrestrial repeaters they are linKea through those repeaters preferentially. Note that the communication system 10 allows this to be a preferential transfer. If desirea the user can contin~e to use the orbital repeater even thougn the terrestrial repeater is close by. This allows for improved communications where ; 20 there is severe signal degradation due to ~ading, multipath, or direct blockage ~rom the nearby terrestrial repeater.
The switch over to a terrestrial repeater now means that as the user moves closer to a repeater, less pOW~I iS
r~quired for the communication lin~ due to the simple power versus distance relationships previously discussed. ~his is illustrated in FIG. 6, where a plot o~ power requirements ~or a~user link versus aistance rrom a repeater is shown.
In addition, an assumed user aensity is also plottea to provide an idea of the amount of power savin~s for the system. The ~act that less power is reguire~ for the [QUAFPA2 oJ15]

7~

communication link also means that less power is ~eing radiated in tne system to create inter~erence for other ~sers. This synergistic relationship between the repeaters and tne user access improves power considerations as well as capacity for the overall system 10.
The communication system 10 is very flexible and the or~ital repeater assignments as to regions served can be altered to match current market demands ~or services. This is another advance provi~ed by tne present invention.
The satellite or or~i~al repeaters 14 of FIG. 2 can be conr'igured in two diiferent modes o~' operation. The ~irst moae is tne direct user lin~ mode in which the satellite receives and transmits directly with users. The secon~ mode is the central hub moae in which communications to and from users are route~ through a terrestrially ~ased hu~.
In tne direc~ user mode tne satellite will employ a circuit similar to that shown ~'or the terrestrial repeater in FIGo 5. The di~'ferences being the specific types or antennas and the ~act that communication signals are not inter~aced directly to a terrestrial service such as a telephone sys~em. It' the satellite employs the circuitry or ;~ FIG. 5, advanced VLSI and hybrid circuit techniques would be used to reduce the size ana ~ower consumption o~ ~he circui~s.
Wnile the orbital repeaters 14 can use tbe same basic circuitry as used in the terrestrial repeater, it is very ~esirable to employ as few circuits as possi~le in a satellite. It is ~esira~le to have the satellite as much a passive relay as possible and use as little power as possible. Therer'ore, the preferable embodiment for the ' ~UAFPA2.J15]

~`

repeaters 14 utilizes a hub or control cen~er 16 tnrough which tne communications will be passed and processed. This allows decreasea power consumption in the satellite and greater system reliability by maintaining the banKs or receivers and transmitters needed for tne indiviaual communication lin~s on the grouna.
This is shown schematically in greater aetail in FIG.
7. In FIG. 7, hub 16 uses the same basic arrangement OI
transmitters ana receivers as seen in the repeater 60 as illustratea in FIG. 5. Spread spectrum receivers and transmitters as previously described, are snown as Spread Spectrum (SS) modem banks 74 Decause of tne manner in wnich they are grouped together as shown FIG. 5. Each bank or moaems is connectea on one hand to an interrace 50 for a terrestrial communication lin~ such as a telephone system or an optical fiber cable. Not illustratea in FIG. 7 are the voice and data encoders and decoaers tnat would be usea in association witn the modems of the modem ban~s 74.
Tne modem banKs 74 are connected to beam formers 76 which serve to generate the signals necessary to form ~irected or steerable multiple beams as seen in FIG. 5.
However, the output or tne beam $ormers 76 are connectea to an array or rrequency upconverters 78 rather than power com~iners or antenna elements. In essence, each satellite antenna element is provided with its own channel between tne hub Deam former and the antenna array. When polarization reuse is employe~, the horizontal and vertical array elements are proviaea with separate channels to the beam $ormer so that both right and lert handed circularly polarized beams can ~e formed.

[QUAFPA2.J15]

~Z~ 74 -3~-Tne signals provide~ by the upconverters 78 are communicated tnrough a K~ band antenna 80 to an associated Ku bana antenna 82 residing on an or~ital repeater 14. Tnis Ku band link between the satellite 14 and the hub 16 nas several advantages over an L band link. The Ru band ;~requencies which are on the order or 14GHz, do not inter~ere with the spectral allocations o~ the rest o~ the communication system 10. This helps maintain system capacity by not consuming a portion or tne power reguirements for the system in these lin~s. Another advantage of the present Ku bana link is that tne upconverters employ FM modulation techniques. Tnis allows improved phase control over the signals as they traverse ~he long distance to a satellite and decreases tbe necessary ~15 control, signal processing, and complexity require~ in the ;orbital repeater to maintain hiyh quality multiple in-phase communication links.
However, single sideband AM modulation is easier to implement where there are two or more hubs 16 which share the resources o~ the satellites. When two nubs communicate with the satellites at the same time, AM signals are easier to cooràinate in tne system.
-~In tne orbital repeater 14 the received Ku band signals are detectea and downconverted by Ku band transceiv~rs 84.
The signals are tnen transrerred to L band transmitters 86 where they are ampli~ied to controlled power levels and sent through duplexers 90 to the antenna elements 92.
As in tne case or the earth based repeater 12, the antenna elements 92 ~orm a two dimensional phased array 94 wbich provi~es multiple steerable beams for ~he [QUAFPA2.J15]

3~Z9~at74 communication system 10. It will be apparent to those sKillea in the art that direct radiation o~ tne earth by an array o~ 12 to 15 elements, as prererred, ~rom geosynchronous orbit is impractical. Tne solution is to use a reflector 96 to create tne desired pattern or ~ocused oeams at tne planet sur~ace.
It is possible to use a single antenna or even multiple antennas on the or~ital repeater 14 and have a functional repeater. However, the pre~erred antenna structure provi~es many advantages over previous communication system designs in terms of capacity, regional control, special users services, e~c., as discussed above. The multiple steerable ~eams formed by the array 94 can be directe~ to speciric regions, or classes o~ users. As in the case of the lS terrestrial repeater, the direction o~ the steerable beams can be controllea by the hub 16 to reassign satellite coverage to new regions (size or location).
Communication signals traveling to the orbital repeater 14 ~rom users will De detected by tne array 94 proviàed tney are in proper phase relationsnip to the tuning of the array - Received signals will be transrerrea through the duplexer gO
to the L band receivers 88. The signal is transrerred to the Ku band transceiver 84 wnere it is upconvertea and sent to the hu~ 16. Each o~ the receivers 88 is con~igured to receive tne ~ull ban~width or the spectrum allocated to the communication system 10. However, ~or speciric applications some receivers 88 could be limited to specific portions o~
the band to provide limited coverage of select regions or to accept or reject special dedicated services.

[QUAFPA2.J15~

129~

The nu~ 16 also employs the voice activity circuits previously descri~ed in order ~o decrease tne power consumed by "empty" communication signals an~ increase capacity.
Clearly tnis also decreases the power needlessly consumed by S an orbital repeater, helping to increase the ef~ective use of satellite power. The system capacity is increased due to the e~fects previously discussed with respect to activity detection and power control in the terrestrial repeater 12.
Anotner feature o~ the hu~ 16 is that it allows the communication system 10 to use multiple satellites or or~ital repeaters 14 in a new advantageous conriguration to achieve improved communication and orDital reuse. In addition, this is accomplished wi~hout increasing the complexity oX the user terminal or requiring alternate types of terminals.
In conventional reuse, the hub 16 directs the ~; satellites 14a and 14~ to cover ~i~rering geographical regions by directing multiple steera~le beams to specific locations simultaneously. In this manner the satellites are "reused" in that they can accommodate tne same ~requencies witnout concern for inter~erence ~ecause o~ the isolation provided by the antenna struc~ures.
Or~ital reuse is provide~ in the communication system even tnough the user terminals employ omni-directional antennas. Unli~e previo~s systemsl fixed directional antennas are not required because the system 10 uses two or more satellites in a new coincident transmission configuration that can ~e thought o~ as a very large scale interrerometer. This is made possible by the marginal [Q~AFPA2.J15]

~;~9~(37~

isolation proviaed ~y the two satellites in conjunction with spread-spectrum mo~ulation.
In tnis operational mode the satellites each transmit an appropriate communication signal to the earth, bot~
intenoe~ ror tne same user. The radio waves have relative phase variations due to patn dif~erences ~etween the tWO
satellites and the user. The two beams will form an interference pattern across the geographical target area with higher power densities where the beams constructively add and lower densities wnere they destructively add. This effect is illustrated graphically in FIG. 8 using a normalized value of 1 for the constructive addition or two satellite communication links. Ir a user is located in an ; in-phase, higher power density portion then the signal perceived by the user is errectively 3 dB higher than the other user interference WhiCh, on the average, receives no gain at the receivers location. Tnis improved signal to interference ratio gain a~ds additional isolation margin tO
tne communication system 10 and in turn increases tne overall capacity.
For purposes of clarity in illustration the tecnnique o~ the present invention is illustrated and ~iscussed utilizing tWO satellites operating in this mo~e. However, additional satellites can be employed to achieve additional ~ain, such as 4.8 dB ~or three satellites, 6 aB ror ~our, an~ so rorth.
To place a user in the nigher density portion o~ the inter~erence pattern, two in~epen~ent antenna beams are directed toward the user. Users can be "tuned" into the higher density portions o~ the antenna interference patterns [Q~AFPA2.J15]

. ' 3~29~

by a~justing the phase and time ~elay of their signals.
This same technique can ~e ~sed for the uplink side of communication as well as the downlink. Path diversity also proviaes additional advantases in terms of countering multipa~h and fading effects.
i The hub 16 circuitry for accomplishing the above operational mode is illustrated in FIG. 9. In FIG. 9 a modem or transmitter 100 provioes a communication signal to two beam formers 102 and 104 at the same timeO However, the delay devices 106 and 108 are disposed in the transmission links for the beam formers 102 and 104, respectively The beam formers operate as previously described. Only two beam ~ormers are shown for illustration, it being understood that the hub 16 may employ a larger number of beam formers as previously discussed.
One of the delay devices can provide a fixed delay while the other provides a variable length delay, since the relative delay is what is important. Alternatively, both delay devices 106, 108 can provide varia~le ~elay. The ; 20 delay devices 106, 108 esta~lish the relative time delay between the transmitte~ satellite signals. A phase adjuster 110 is also disposed in the communication lin~, here for beam former 104, to adjust the relative phase.
The signals from the beam formers 102, 104 are transmitted, as before, through frequency converters to the satellites. The signals from each beam former 102 or 104 are transmitted to dif~erent satellites where they are directed to a user, resulting in the desired inter~erence pattern.
:

[QUAFPA2.J15]

:
.

9~7~
~43-For the uplin~ communication signals lrom the respective system 10 users, the ~eam rormers 112 and 114 act as receiving elements ~`or t~e separate demodulators or receivers 116 and 118. Incoming communication signals are transferred to the demodulators where tney are despread into digital communication signals. In order to coherently combine the resulting signals a coherent combiner 120 is coupled to the output o~ tne demodulators 116 and 118.
Delay devices 122 anà 124 are positioned between the combiner 120 and the demodulators 116 and 118 to adjust the relative phase and timing o~ the signals into coherence.
Once tne signals are conerently combined into a single digital communication signal, ~he information is transferred to appropriate decodins circuitry ror ~urther processing.
The control over the phase and time delay for a given user depends on the quality or strength o~ the signals received by the hub 16. This in~ormation is derived ~rom tne demodulators 116, 118 and provi~ed to the varia~le delay devices 106, 122, 124, and the phase controller 110.
The hub 16 is capable of monitoring communication from both satellites simultaneously. In this case, each communication link between the user and a satellite is treated as a separate link whicb is assigned separate receivers, decoders, etc. The hub 16 determines tne 2S relative phase and time delay di~erence ~etween the two signals. This inrormation provides signals ~o delay and rotate the separately detected and decoded signals into coherence or phase with respect to each other and coherently summed to produce a single output. This process provides approximately an additional 3 dB of gain. Inter~erence ~rom ~QUAFPA2.J15~

other users' signals adcs inconerently producing 0 dB gain on the average.
Alternatively, the nub 16 utilizes the user assignment protocol in the communication llnks to determine that more ` 5 than one link is in use. T~en the hub compares the relative power or quality o~ each lin~. The link that provides the best error ~ree, high power signal is retained and the other communication link forced, under hub processor control, to terminate. The terminated link has its associated receivers, transmitters, ana steerable beam reassigned to a new user.
This technique chooses the DeSt communication path to account for path interrerence and ~ading without tying up additional equipment.
It shoul~ be readily understood by those skilled in the art that using a central control facility with tne terrestrially based repeaters ror monitoring and controlling the assignment o~ communication links will also provi~e the same multipath abilities. This is aovantageous in environments where such obstr~ctions as terrain, ~uil~ings and trees tend to alter tne best path and the nature o~ the communication pa~hs on a rrequent basis.
~ he communication signals used in t~e communication system 10 are trans~erred by ~ne repeaters 12 or 14 between the in~ivi~ual user terminals 20, 22, 24, or 26, as previously illustrated. Such terminals can in ~urn inter~ace to terrestrially based communication systems or other multi-user systems. An exemplary user terminal circuit employed in the system 10 is schematically illustrated in FIG. 10.

~QUAFPA2.J15~

12~ 74 Tne user terminal 130 o~ E`IG. 9 utilizes an antenna 132 to receive and transmit communication signals which are transferred through a duplexer 144 to or from a spread spectrum receiver 146 or transmitter 166, respectively.
5 These elements function in the same manner as those elements previously described in relation to tne repeater 12 or 14 circuitry of FIG,'s 2 through 7.
The antenna used by each system 10 user will vary according to the ~ype of service desired. A larger antenna 10 ~ructure can be used for ~ixed user ter~inals than for mo~ile users. In tnis case small to mediu~ sizea dish-type antennas are employea to isolate communication with one satellite and free the hub rrom having to ma~e tnis decision or assignment. However, tne communication system 10 is 15 intended to serve a large number o~ users that are either truly mobile or are unable to utilize even ~oderately sizea (2 to 4 ~oot diameter) antenna dishes.
In this latter application a small omni-directional antenna is contemplated. Omni-directional in tnis t ; 20 application means omni-~irectional in the horizontal direction. For satellite relay applications~ tnere is a slight gain on tne order of 5 dB isotropic at a~out 30 degrees elevation so tnat the antenna will direct its energy or be selective to receive energy from an elevated position.
25 This decreases interference ~rom energy sources that are at horizon level as woul~ be true for adjacent cells or unrelated satellite systems. An exemplary antenna configuration is the "droopy dipole" and is shown in FIG~
11. An antenna optimized for terres~rial repeaters would 30 preferably have more ~ain at lower elevation angles.

QUAFPA2.J15]

~2~7~

The antenna 132 of FIG. 11 employs four ~ipole arms 134, 136, 138, and 140 extending radially outward ~rom a support mast 142. The dipole arms are positioned every 90 degrees around the circumrerence o~ a support post and angled downward. The exact dimensions of tne antenna ele~ents depend upon the frequency to ~e transmitted as well as structural consiaerations for a mobile antenna subjected to wind drag, etc. This type or antenna is known in the communications art and it will be readily apparent to those s~i~led in the art how to choose the appropriate dimensions.
In order to improve the signal rejection o~ the antenna 112 and thereby also increase the capacity o~ the communication system 10, the antenna is preterably operated in a polarization selection mode. As previously discussed, the limiting ractor on the capacity o~ the communication ; system 10 is the sel~ noise or interference caused ~y ~other~ users. If some or tne users are operating on another polarization, then tne amount of self noise that tney contri~ute is attenuated by the polarization isolation.
If the radiation pattern of the transmi$ter is perrectly circularly polarized, then the axial ratio of tne receiving antenna pattern will determine tne amount or interference receivea from an undesired polarization. The axial ratio is defined as the ratio of tne minor axis to the major axis of the antenna reception pattern expresse~ in units of signal power. Figure 12 shows a typical pattern wi~h an axial ratio of AR~
Ellipticity (EL) expressed in dB is related to the axial ratio by the e~uation:
EL = -10 Loglu(AR) ~4) ,~
[QUA~PA2.J15 `::

~;~9~74 From thiS expression an increase in capacity for the communication system 10 as a runction o~ the axial ratio and ellipticity can ~e calculatea. If the voltage or a desirea polari~ation is detinea as l+ ~ then the vol~age of the undesired polarization is 1- ~
The increase in system capacity is the ratio o~ users in both polarizations to the total number of users when there is no polarization reuse. Because tne self noise seen ~y a terminal with polarization reuse at the system 10 capaci~y limit equals the sel~ noise with no polarization reuse at the system capacity limit, tne ~ollowing e~uations can be written and solved ~or the capacity increase K as a function or the axial ratio AR.
k k /1~
1 = ~ (5) 2 2 ~1~ ~ J

1 ~ 2 ~ + AR
k = ~ --- (6) ; l t ~

K = 1 + ~ (7) The relative increase in capacity for polarization reuse is k-l or ~ . Figure 12 presents a plot or k-l versus ellipticity in d~. Table I o~ FIG. 14 lists the axial ratio, capacity increase, and polarization isolation for ellipticity rrom 0 to 20 dB.
: Because o~ the unknown orientation of a mobile user and any vehicle it rnay located in and the need to have some [QUAFPA2.J15]

lZ~79~

directivity in elevation, ic is very di~ric~lt to get an ellipticity better than 6-10 dB. This provi~es a polariæation isolation of 9.6-5.7 dB. This is not enough to be usable for FDMA analog or digital systems. However, because or ~he sprea~ spectrum processing gain, polarization reuse can be used to increase the system 10 capacity even though the polarization isolation is quite small or unusable by other communication systems. This com~ination or CDMA
and polarization reuse can efrectively increase the capacity of communication system 10 on the order o~ 50 to 80 percent.
Circularly polarized antennas are desirable in a mobile system at L-Band or lower frequencies to combat problems with Fara~ay rotation of the signal. There~ore, the circular polarization technique of the present invention is well suited ~or the mobile ~ser terminals o~ the present communication system~
When the antenna 132 is operated in a polarization selection mode, tne repeater antenna structure must perform complimentary processing operations. Therefore, tne repeaters 12 or 14 may have additional control circuitry associated with tne antenna operation to control the polarization o~ tne transmitte~ and received signals.
As previously oiscussed, phase~ array antennas would ~employ separate beam rormer channels for norizon~al and ;25 vertical beam array elements so that le~t an~ right hande~
circularly polarized beams can be transmitted or received.
A polarization control signal, ~or selecting between tbe appropriate beam former used by a comrnunication signal and, therefore, polarization moaes can be generated according to the communication signal protocol designating [QUAFPA2.JlS]

.

,--C~4 speciric users. The user polarization mode can be iixed at the time or terminal installation or by optional control circuitryO
Communication signals received on the antenna 132 are transferrea to the spreaa spectrum receiver 146 where tney are demodulated and despread to yield a digital communication signal~ This digital signal is trans~erred tnrough a voice/data demultiplexer 148 whieh separates signals into digitized voice signals or digital data signals.
The digitized voice signals are in turn trans~errea to a data-to-voice decoder 150 where digitized analog signals are converte~ to analog rorm using techniques known in the art. The analog output or the decoder 150, which is generally a voice signal, can be presented to a variety o~
subsequent circuits through an interrace 152. The con~iguration or construction o~ the inter~ace 152 depends upon the applications required by the speci~ic user or user terminal. In typical mobile user terminals, analog signals are processed by pre-amplifiers, ampliriers, and other gain circuitry ror generating hign quality audible output to the system user, Such circuitry is constructed according to known principles or analog circuit design as appliea to portable radio or telepnone equipment and being known in the art is not descri~ed here.
Fixea user terminals would interrace to other communication sys~ems, therefore, requiring interface circuitry ~or connection to telephone systems, optical cable systems, or other equipment.

~QUAFPA2.J15]
'`

[174 The digital data is trans~erred out o~ tne user terminal on the data line 154 which can be connected to a modem or other inter~ace equipment for computers or other digital equipment. Circuits for interracing computers or other equipment ~or processing digital data signals are known in tne electronics arts and are not described here.
Outgoing voice or analog signals are received through the inter~ace 152 and transferred to a voice-to-data enco~er 156 wnicn generates a aigitized analog signal. This digi~ized signal is then transferred to a voice/data multiplexer 1580 The multiplexer 158 multiplexes together digitized analog siynals and digital ~ata signals to ~orm a digital communication signal. The term multiplexing is misleading in that most user terminals will handle either voice (analog) or data at one time and not both simultaneously, altnough tnis capability is built in to tne system. The need for this capability also depends on the capabilities of the receiving users.
The output of the multiplexer 158 forms tne input ~or a transmitter 166. The digital data is brought into the user terminal on a data bus line 160.
The voice-to-data or the data-to-voice encoders can be replacea witn a single element rererrea to in the art as a voice codec 162.
25The Demand Assignment Multiple Access (DAMA) module 164 acts in concert with central control racilities to determine the ability to access the system 10 ~y monitoring, air time, activity, account numbers, protocol, etc. A data ~us, such ~ as data bus 168 interconnects this module with the inter~ace c 30162, and additional buses sucn as data buses 170, 172, 174 [QUAFPA2.J15]

1;~9~ 74 an~ 176 couple the DAMA module ~o the voice/data multiplexing and demultiplexinq devices 148 and 158, and the receiver 146 and transmitter 166, respectively.
The communication system 10 allocates power to the particular user regardless of the actual activity level.
This means that ~or long pauses or ~or very low data bit rates a larger percentage o~ the power is being wasted in sending and receiving "empty~ signals. This energy also wastes capacity since the total power available in the system limits capacity and because of the nature in how each user forms inter~erence ~or o~ner users.
Therefore, within each user terminal 130 is one or more activity detectors or monitors ror sensing the data or voice activity level or the terminal user. Tnat is, the activity level o~ input signals are compared to a predetermined minimum tnresnola level useG to define an "active' input signal condition. Input signals below this threshold represent no activity and aG~ove this threshold represent activity. The transmission power is, as described previously, adjuste~ in response to the change in activity.
In this manner the relay sees no signal auring the low or non-activity time, except for occasional bursts, and can accommodate aaditional users.
The user terminal 130 has been ~escribed in the same terms as the repeaters 12 or 14. The user terminals utilize spread spectrum receivers and transmitters to process communication signals into and Irom digital data signals.
The spread spectrum receivers and transmitters are the heart o~ the communication system 10 in that they provide the spreading and despreading function which in turn provides tQUAFPA2.J15~

~Z~i34~

; the processing gain ana ability to use marginal isolation to achieve high quality, high capacity communications.
To achieve these results the spread spectrum receivers or the present invention use a particular demoàulator S circuit for despreading the incoming communication signals and generating a resulting digital signal. The demodulator circuit employed in t~e spread spectrum receiver 146 as shown in FIG. 10 is illustrate~ in ~urther detail in FIG~
15.
10In FIG. lS a demodulator 200 constructea according to the principles o~ the present invention is schematically illustrated. Tne demodulator 200 is proceeded by a downconverter 190 to cbange the rrequency of tne incoming communications signal to a lower intermediate ~requency ~or processing using techniques or apparatus known in the artO
An IF signal ~requency such as, but not limited to, about 70 MHz is generally employed ror communication signals in the L
Band altnougn this ~requency is determined by the demands o~
speciric applications. An incoming, RF frequency signal, 20202 from the repeater 12 or 14, is processed by the downconverter 190 to provide an input, IF ~requency, signal nich is fed into a gain control el~ment 204.
The gain control 204 compensates for ~ading and other energy alterations in the receiveà signal which lead to degradation in processingr Tbe gain element 204 provides a variable gain control ~unction over an input signal and can be an electronically controlled gain device, such as would ~e known to those skille~ in the electronics arts. For purposes of automatically controlling the gain provided by 30tne gain control 204, a gain control signal 206 is generated ~QUAFPA2.J153 .. . - . ....

~2g~L¢~4 by subsequent portions o~ tne demo~ulator 200 as ~iscussed ~urtner below.
This gain control ~unction allows the ~emoaulator 200 ~o operate without limiters an~ present the full band width to tne analog-to-digital converters as descri~ed below.
This prevents a loss or information during processing berore the conversion process. Also the gain control 204 can normalize the input signal to a predetermined level which allows the analog-to-digital conversion process to be more ef~`icient under changing conaitions and make maximum use of the bits in the analog-to-~igital conversion process. This is especially useful for purposes of the present invention since t~e transmission signals employed are generally power limited and the receiver may be called upon to compensate for a low energy signal level when tne system is handling a large number or users.
The ou~put o~ tne gain control 204 is connected to an ~; RF mixer 208 in which the IF irequency input signal is mixe~
with a predetermineo carrier frequency to yield a lower ~requency analog communications signal. Tne demodulation frequency is provided by a frequency synthesizer 210 which can be electronically controlled as in the case or a VCO, by a carrier input adjust signal 212. Therefore, ror purposes of providing a lower ~requency input signal, the synthesizer 210 provides the required mixer frequency. However, as the carrier is trac~e~ by the communication system lO and adjustments in tne carrier frequency are effectea by fading, Doppler shirting, etc, tbe demodulator can alter the synthesizer 210 output to also compensate. This is ; 30 accomplished by changing the value of the carrier input [QUAFPA2.Jl5]
;, ... , . . ~

fre~uency adjust signal 212. As will be shown below, other portions o~ the demodulatoL automatically provide this ~`unction.
Tne output of the RF mixer 208, which is an analog communications signal is passed through a band pass rilter 214 to remove unwanted mixer products and out o~ band ~requency components that may be present from the downconversion process, The resulting signal 216 is an intermediate frequency analog signal WhiCh represents a 1~ narrow ~and in~ormation signal spread over the allocatea spectral ~andwidth.
While still at baseband, the signal 216 is then divided into an in-phase (I) component and a quadrature (Q) component ~y the phase shift divider 220. The divider 220 can ~urther comprise a divider and phase-shifter combination as would be apparent to those skilled in the art The I and Q signals are also referred to in the art as the 0 degree and tne 90 degree components, respectively.
The I and Q signals are then transferred to separate Analog-to-Digital (A/D) converters 222 and 224, respectively. That is, the I or 0 degree component ~rom the ~ivi~er 220 provides an input to the first A/D converter device 222 and the Q component, which is 90 degrees out o~
phase with the I component~ provides an input ~or the A/D
converter device 224. This con~iguration is used to proviae more erficient conversion of tne analog signal into digital form as well as improved accuracy for the later signal processing stages ~y breaking the Analog-to-Digital conversion process into two components.

~QUAFPA2.J15]

In the preferred embodiment of the present invention each A/D device 222 and 224 woul~ comprise a 4-~it converter TAat is, each would convert a given portion o~
the analog signal 216 into a digital signal having 4-bit precision. Since the I and Q components are each converted into 4 bits or digital information and they are temporally in series, the communication link accommodates 8 bits o~
effective information per conversion time. The analog-to-aigital conversion is diviaed into 4 bit increments to provide more efficient conversion since high speed 4-bit A/D
converters are well developea in tne art. However~ the present invention does not require 4 ~it increments to operate and other A/D converters may be employed where desired.
The A/D conversion process is clocked at a preaetermined rate by a syste~ clock 226 which also provides the appropriate timing signals used in the demodulator 200 as would be apparent to those skilled in the art who require a common in-phase clock source ~or other functions. The cloc~ source 226 comprises any of a number o~ known rrequency sources or synthesizers similar to rrequency synthesizer 210. The system clock must be provide~ with a rrequency driver so tnat the clocking rate is twice the chip' rrequency. The ~requency source is adjustable, as in the case of a VC0, so that variations in the signal link can be accommodated and the signal locked onto. For this reason a frequency adjustment input signal is provided ~rom a source 228 discussed below~
The output of the two A/D devices 222 and 224 are connected to a common output data bus 230 which transfers QUAFPA2.J15]

the O degree and the 90 degree related four data bit~ in serial ~asnion to other parts o~ the demodulator 200 circuitry. Tne digital communications signal on data bus 230 is input to a rirst ~our-pnase rotator 242 where it is combined witn a pilot chip sequence which is provided ~rom a pilot chip sequence generator 240. The resultant signal is trans~errea in to a ~irst summation means 260 where the and Q components are summea over a length of time when they are cOn erent.
Inserte~ into the transmittea signal is a phase coherent and chip synchronous, chip sequence that is detined as a pilot cnip sequence. Tnis pre-defined and generated chip sequence is a new method o~ providing phase and time acquisition and tracking, and multi-path correction.
In previous systems a code in the rorm of a tone might ~e usea. The tone was encoded along with input data and transmit~ea to the receiver. Each user required a di~ferent - tone. At the receiver the decoaing process would reproduce the tone whicn could ~e detected using a series o~ ~ ilters or other elements. Any variations in the desirea tone, phase or ~r~quency, were then adjusted for accordingly. In principle this technique provides a re~erence signal for tuning the frequency tracking and decoding stages o~ a demodulator. However, tne encoding and decoding of the signal and then subsequent active detection was slow, and reasonably inaccurate. Any errors in the detection or decoding o~ a chip sequence and/or propagation errors also create errors in a decoded tone decreasing the the ability ; to correctly compensate or adjust the carrier and chip synchronization tracking with this technique.

[QUAFPA2.J15~

The receiver of E`IG. 15 preferably uses a time tracking error detector known in the art as a ~laelay-locic" detector.
This detector ~'unctions by su~tracting the power in an early correlation o~' the received signal with the local re~erence 5 pilot sequence rrom the power in a late correlation or tne receivea signal with tne local re~erence pilot sequence. Ir there is no time txacking error, this airference signal will be zero. It the time error is such tnat the local reference signal leaas the correct timing, then a negative dirrerence 10 signal will be produced. Conversely, if the local rererence lags the correct timing, then a positive di~ference error signal will be produced. The error signal is used to correct the timing in chip-time tracking loop 276.
The early correlation is produced in correlator 242 c)y 15 correlating I and Q signals on bus 230 with tne pilot chip sequence. The result is integrated in integrator 260 and the power aetermined by circuit 270. Tne late correlation is produced in correlator 246 by correlating the twice delayed signals on ~us 238 with the pilot chip sequence 20 generator 240 output. This signal is integrated by integrator 264 and power determined by circuit 274. The outputs or' circuits 270 and 274 are difrerenced in the cnip time tracking loop 276.
The delay elements 232 and 236 determine the amount of 25 time di~erence between the ear~y and late correlations.
Preferably, these delays are set to a value equal to 1/2 chip duration, although other values may be pre~'erred in certain applications, The c~rrier tracking loop operates on the output o~ on-30 time correlator 244, which correlates the output ot' delay :`
[QUAFPA2.J15~

^:

~L~g~ 4 -5~-element 232 with tne pilot chip sequence generator 240. Tne correlator output is integrated in integrator 262 to provi~e an input to carrier tracking loop 280.
An alternate embodiment would proviae early, late and on-time correlations o~ the received signal with the pilot sequence by delaying the pilot chip sequence generator 240 output in two 1/2 chip time ~elay elements and then correlating with the signals on bus 230.
The correlator means 252, 242, 244 and 246 are comprised o~ four-phase rotator elements which serve to rotate the phase o~ the input signal by 0, 90, 180 or 270 degrees as determined by the pilot chip sequence input bits.
; Circuits ~or accomplisning this ~unction are readily apparent to those skillea in the communications art.
15Integrator means 260, 262, and 264 integrate ~he outputs of their respective correlators ~y summing samples over an interval equal to the length o~ the short pilot chip sequence. Integrator 282 integrates tne output o~ the unit chip sequence correlator 252 over an interval equal to the data symbol time. The I and Q signals output ~rom each correlator are summed in separate integrators.
The power in a signal is determineà ~y the circuits 284, 270 and 274. The I and Q outputs of tne integrators are each squared and then summed to provi~e a measure o~ the power in the signals. Integrator 284 measures the broad~and noise power on bus 234 for use in setting the receiver gain, while integrators 274 and 270 measure the power in the early and late correlations oI the pilot chip sequence~
The signal 278 is coupled to the rrequency synlhesizer 228 as previously described and serves to alter the [Q~AFPA2.J15]
.

rrequency generated in the syntnesizer 228. Tnis can be accomplished in several ways understood in tne art such as esta~lishing a predetermined voltage level in the signal 278 at tne input or the synthesizer 228 wnich operates as a VCO.
I~ the communication signal is late, then the tracking loop 276 establishes a lower voltage level for the signal 278 which decreases the trequency output by the synthesizer 228.
On the other hand, i~ the communication signal is early tnen the voltage level o~ the signal 278 increases and the output rrequency ot the syntnesizer 228 increases.
The alteration of the output ~requency for the syntnesizer 228 increases or decreases the timing provided by the system clocK generation element 226, which in turn alters tne rate at which the A/D converters 222 and 224 convert the analog data into tne digital signal chip patterns.
There~ore, as the system receives an incoming communication signal an~ also receives a pilot chip sequence, the portion o~ the circuit just descriDed allows the detection ot the relative timing o~ the user terminal with respect to the pilot chip sequence transmission and adjustment of the Analog-to-Digital rates to account for the variations in this timing. In addition, this circuitry is used to loc~ onto the correct carrier frequency.
By connecting tne output of the coherent summing means 262, ~or the "on-time", once-delayed, signal, to a carrier tracking loop 280 the carrier ~requency is acquirea and tracked. As the value o~ the summation for the on-time signal decreases it is assumed the local carrier ~requency needs to be decreased. As the summation ~or tne on-time ~QUAFPA2.J15]

~' :LZ~407 signal increases the local carrier irequency is increased.
To implement tnese changes, tne output of the tracking loop is proviaed as a signal 212 which is input to the ~requency synthesizer 210 as previously discussed. This changes the S ~requency used ~or the IF demodulation and causes the demoaulator 200 to track the incoming carrier, What has been described to this point is the initial operating function o~ the demodulator wherein the incoming communication signals are converted to a digital form and compared to the predetermine~ pilot chip sequence. This allows the determination of both the correct carrier ~requency as well as tne adjustment o~ the sample clock 278 to acquire the proper synchro~ization with tne chip rate.
Once tne tracking has Deen properly locked onto the incoming signal the actual aecoding or demodulation or the aata can occur to proviae the user terminal with the in~ormation being trans~errea in the communication signals along the communication link.
The actual data or voice spread spectrum decoding is accomplished by sending the on-time signal provided by the delay element 232 on t~e data bus 234 to a convoluiional decoder such as, but not limited to, a Viterbi algorithm decouer 290. However, the I and Q components are first summea using a summation means 282. The demodulators usea in tne hub 16 can also use a phase correction ~ilter to assure tnat the in~ormation remains in-phase with the appropriate convolutional decoding process during the hub translation and signal processing steps.
The demodulator 200 must demodulate CDMA spread spectrum signals which means that a unique chip sequence ~QUAFPA2.J15]

.

which is used to encode or spread the input signal must be generated and used to despread the communication signal.
There~ore, the incoming on-time signal provided by tne A/D
converters and through the delay element 232 onto bus 234 is mixe~ in a four-phase rotator 252 with a unit chip seguence to yield a signal only ~or tbat chip sequence corresponding to the correct user terminal.
~ he information is now decoded by the convolutional decoder 290 at the predetermined decoding rate to remove ~ne interleaved error detection ~its, and trans~erred to appropriate vocoder and other analog circui~ry such as pre-amplifiers, ampli~iers, and speaker systems where the user can utilize it. At this point the signal 292 can be further processed to provide additional demodulatiGn and conversion rrom a digital to an analog output as known in the art. The signal would be subject to conventional amplification and gain techniques as would ~e useful for the receiving station.
In order to provide automatic adjustment o~ the gain control 204, a square and summation means 284 also receives the in-phase and guadrature signals from the data bus 234 and processes them to provi~e a signal indicative of the relative energy or power level of the signals. Since the in-phase and quadrature signals can vary greatly and change signs during initial acquisition and tracking they are first squared and then summed together to prevent cancellation.
The results of this operation are transferred to an automatic gain control loop filter 286 where a control signal 206 is generated whicn increases or decreases the gain provided by the variable gain control 204 depending [QUAFPA2.J15]

4eI7~

upon the decrease or increase in relative signa~ strength for received communication signals.
The de~odulator 200 represents the basic demoaulator ; used in the pre~erred embodiment of the communication system 10. However, it will be apparent to those skilled in the art that demodulation of communication siynals in a repeater or a hu~ will not employ the pilot trac~ing circuitry.
Furthermore, repeater and hu~ circuits employ narrower band rilters and timing loops.
The demod~lator of FIG. 15 provides a narrow band information signal ~rom a received spread-spectrum communication signal. For the return transmission ir, a ~ communication link a modulator is required in the ; transmitter of the user terminals 20, 22, 24, 26, repeaters 12, 14, or hubs 16.
~ In the transmitter 166 or the user terminal 130 ;~ illustrated in FIG 10 is a ~odulator 300 ~or generating spread spectrum CDMA communication signals for transmission.
A moàulator circuit and methoa is provided which encodes and modulates input inr`ormation whicn can be data or voice as ~;~ previously described.
A modulator circuit constructed accoraing to t~e principles of the present invention is illustrated in FIG.
16. In FIG. 16 the modulator 300 receives incoming in~ormation signals 302 and inputs them into a convolutional encoder 304. The information siynals 302 are processed by a voice to digital encoder, here illustrated as voice codec 162, or multiplexed in as digital data. Tne signals 302 are previously amplified, ~iltered, or processed signals originating at tne user terminal and processed according to [QUA~PA2.J15~

.~ .

4~

typical analog processing ror communications prior to transmission.
The present invention contemplates using the latest in ~voice coding techniques to improve the quality of ;~5 communication and allow for decreased bandwidth where possible. This translates to decreased overall power when the signal is spread, which improves system 10 capacity.
For this reason current coding schemes planned for use in the embodiments of tne present invention include Linear Predictive Coding (LPC) ana Continuously Variable Sloped Delta (CVSD) modulation. These techniques can accommodate data rates on tne order of 4.8 to 16.0 KbpS (kilo-~its per secon~) which is very advantageous. Current integratea circuits exist ~or providing these high speed coding functions in a small package or space as would be reguired i for mobile user terminals. Tnis handles the demand for hign speed digital data encodins as well. Tbe high spread spectrum chip freguency also handles multiples of common data rates such as 56, 32, 16, 9.6, 4.8, 2.4 K~pS and aown to 75 bps, thus, addressing the most desired data ratesO
At a future time tne communication system 10 can be changed to use other types or even slower rate encoders/decoaers if desired without altering the entire communication system.
A~ter digital encoding the information signal is transferred to a convolutional encoder 304. A convolutional encoder is unaerstooa ~y those skilled in the art to provide interleaving of the actual data bits forming the input signal and additional bits ~o~ ascertaining, or monitoring errors and providing for correction. The present invention ,~
[QUAFPA2.J15 \
~2~

allows ~or a variety or coding rates ~rom 1/4 to 1/2 or more since the present invention is not constrained by tne data rates.
The output oi the convolutional encoder 304 is a digitally encoded in~ormation signal which is mixed with a spreading chip sequence in a ~our-phase rotator mixer 306.
The chip sequence is provided by a chip sequence generator 308 which generates or stores the chip sequence assigned to the user terminal 130~ The assignment of user terminal cnip sequences has been previously described above and is not repeated here. However, the transmit~ed communication signal also r~quires identi~ication o~ tne recipient in addition to the source terminal. This can be accomplished by using communication protocols known in the art.
In most communication systems the transmitting user sends a digital code representative ot a recipien~'s telephone, radio phone, user terminal, or other unique identi~ication number as part or an initiating communication signal. This number can be encoded in a speci~ic pattern o~
data bits with accompanying control codes whicn indicate that a communication siynal contains a receiver address and an initial communication link request. Since several protocol and link initiation code schemes which are compatible with the present invention are well understood in the art, additional circuitry used to implement them is not shown in FIG. 16.
The broad band spread in~ormation siynal produced by the mixer 306 operation is transferred to an RF mixer 31~
where it is mixed with a carrier Xrequency to produce the ' ~QUAFPA2.J15]
, 12 ~ 7 4 communication signals to be transmitted. The carrier rrequency is provided ~y or generated in a frequency synthesizer 310. The specific frequency used is predetermined by the spectral allocation ror the communication system 10 as well as any special spectral allocations for particular users. However, the frequency source 310 is adjustable so that the erIects or Doppler shifting can ~e compensated for on the uplin~ side of a communication lin~.
This is accomplishea by observing apparent changes in the carrier rrequency detected by the demodulator 200 in the receiver 146. As previously described, a carrier tracking signal 212 is generated in tne demodulator 200 which is in~icative of variations in the received carrier tracking rrequency in relation to a local carrier frequency. This same siynal can be coupled to the frequency synthesizer 310 to adjust the carrier ~requency used for transmission. As the carrier is observed by tne receiver tO vary due to a variety or effects, tne transmitter automatically adjus~s the return link to also compensate. In tbis manner, a repeater does not perceive a change, or very liltle change, in carrier tracking due to Doppler and other erfects.
Therefore, user terminals, even thougn mobile, appear substantially stationary to communication system 10 repeaters and do not require compensation in the repeater.
The communication signal provided by the mixer 312 is coupled int~ a transmit analog bandpass ~ilter 316 which acts to filtPr out undesirable frequencies which are outside - o~ the range o~ the target system and represent a loss of useful transmission power.

~QUAFPA2.J15]

.

The output o~ the banàpass filter 316 is couple~ to a transmit power control device 318 which proviaes the ~'inal amplirication and control o~ transmission power for the communication signal presented to an antenna. The power control device 318 is adjustable both in terms of overall power level and duty cycle or duration.
The relative strength o$ received communication signals can be determine~ in the demodulator 200 sucn as in the automatic gain control loop ~ilter 286. ~rom this a control signal can be provided to a r'ade and power adjust control circuit 320. The control circuit 320 detects the increase or ~ecrease in signal strength according to a signal 206 and provides an appropriate control signal 322 to the transmit power control device 318 to eitner increase or decrease output power. This allows the user terminal to compensate ~or changes in relative position with respec~ to a repeater as well as some degree of fading without requiring additional power compensation scnemes in the repeater circuitry. There~ore, the repeater observes the signal strength of the user terminal as if the terminal is in a ~ixed location. Alternatively, a repeater can of course, use a fixed control signal to in~icate fading of received signals and send inrormation to the control device 318 as part of tne pilot sequence or communication protocol to instruct it to compensate subs~quent communications.
As previously discussed the user terminals 20, 22, 24, and 26 employ a speech, voice, analog signal, or digital signal activity detector to decrease tne amount of unnecessary power consumed ano interference generated. To accomplish this an activity ~etector 324 is provided, here [QUAFPA2.J153 ~L25~

labeled as a voice activated switch (VOX), which is coupled to tbe input signal 302 or tne output o~ the convolutional encoder 304. For purposes or illustration a voice signal is ~escribed but a digital input signal can also be S accommodated ~y the modulator 300 and the VOX 324.
The VOX 324 detects the general activity level o~ the input inrormation signal and determines when the output transmission can ~e turne~ of~ due to a lack o~ activity.
T~e amount of power required or available in a communication system, as well as tne ~nount or capacity increase desired, aetermine the length of periods of "non-activity tnat are chosen. The VOX 324 provi~es a control signal to the power control device 318 which instructs it to alter the duty cycle for transmission signals. In this manner only short periodic bursts are sent by tbe transmitter when there is no activi~y. This allows tne communication system 10 to continue maintaining and tracKing the communication link ror the user terminal 130 while not wasting power and, tner-efore, communication system 10 capacity.
` 20 Tne output leaving the power control device 318 is transferred to the appropriate antenna structure employed ~y ~he user terminal 130. The modulator 300 has been descri~ed in terms of generating a communication signal at the desired carrier frequency. Alternatively, the frequency syntnesizer 310 provides an intermediate ~requency rrom tne mixer 312. In this case an upconvertor stage is disposed between the power control device 318 and any antenna to upconvert tne output communication signals to the appropriate carrier frequency for the communication system 10.

[Q~AEPA2.J15]

4~7~1L

In addition to the power control, ~he ~re~uency synthesis and the timing used ror the bit and symbol clocks are adjus~able to compensate for the Doppler shift anà
fading effects found primarily in mobile systems. That is, the demo~ulator 200 tracking loops are used to provide signals to the modulator 300 to alter the rrequency generate~ by a ~requency synthesizer 326 which in turn drives the modulator 300 clock generation device 328.
What has been described then is a new communication system employing CDMA spreaa spectrum processing techniques.
The user terminals and repeaters for the communication system use a new mo~ulator and demodulator design to transmit and receive communication signals. The user terminal~ and repeaters use means for creating marginal isolation between user communication signals such as, ~ut not limited to, multiple ~eam phased array repeater antennas, polarization enhanced omni-directional antennas, voice or activity switching, or aajustable user terminal power control to increase the capacity of the system.
Tne repeaters for tne communication links are orbital or terrestrially basea repeater stations that can provide a variety of communication patns to compensate ~or Doppler shi~ts, and multi-path proDlems found in other communication systems. The orbital and terrestrial repeaters can interconnect to o~loaa users ~rom each other and cov~r selecte~ geographical regions or user classes where desired.
The use o~ multiple beam antennas further increases system capacity and provides an ability to uniquely control communication links within the system.

[QUAFPA2.J15]

~ .

3~2~ 17~

I~ will be appreciate~ by those skilled in the art that additional means or methods or providing marginal isolation between users can be used WithOUt varying rrom the scope of the invention. Also alternate methods or providing spread spectrum waveforms other tnan those specirically discussed herein are contemplated by the present invention.
The pre~erred embodiment nas been described utilizing one or more repeaters ror ease or illustration that demonstrates the advantages as an initial system. However, a communication network employing direct user-to-user links with marginal isolation is also contemplated by the present invention.
The fo~egoing description of preferred embodiments has been presented for purposes or illustration and description.
It is not intende~ to be exhaustive nor to limit the invention tO the precise form disclosed, and many modifications and variations are possible in light o~ tne above teaching. The embodiments were chosen and described to best explain the principles or the invention and its practical application to there~y enable others skilled in tne art to best utilize the invention in various embodiments and with various modirications as are suited to the particular use contemplated. It is intended that the scope or the invention be deIined by the claims and their ~quivalents.
What we claim is:

¦QUAFPA2.J15]

.

Claims (51)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A multiple access, spread spectrum communication system, comprising:
means for communicating information signals between at least two of a plurality of system users using code-division-spread-spectrum communication signals;
isolation means, coupled to said means for communicating, for unequally weighting signal power of said code-division-spread-spectrum communication signals, wherein said isolation means comprises:
activity detection means for measuring signal activity levels for said information signals relative to a no activity level over a predetermined sampling time and for providing an activity signal corresponding to measured activity; and power control means coupled to said means for communicating for adjusting a transmission power duty cycle for said code-division-spread-spectrum communication signals in response to changes in said activity signal.

2. A multiple access, spread spectrum communication system, comprising:
means for communicating information signals between at least two of a plurality of system users using code-division-spread-spectrum communication signals;

isolation means, coupled to said means for communica-tion, for unequally weighting signal power of said code-division-spread-spectrum communication signals; and wherein said means for communicating further comprises:
chip generation means for generating a plurality of quasi-orthogonal spreading functions;
code selection means for assigning one of said spreading functions to a user, a plurality of mobile user terminals capable of transmitting and receiving said code-division-spread-spectrum communication signals, each of said user terminals comprising:
transmission means for generating a code-division-spread-spectrum communication signal in response to an input information signal according to an assigned spreading function;
receiver means for generating an output information signal by processing a receiving code-division-spread-spectrum communication signal according to said assigned spreading function; and at least one omni-directional antenna coupled to said transmission means and said receiver means; and at least one repeater means for receiving code-division-spread-spectrum communication signals from said plurality of user terminals and for translating said code-division-spread-spectrum communication signals to a form suitable for transfer to an intended recipient user.

3. The communication system of Claim 2 wherein said repeater means further comprises means for transmitting a predetermined pilot chip sequence to said users.

4. The communication system of Claim 2 wherein said at least one repeater means further comprises a phased array antenna structure capable of generating simultaneous multiple steerable beams.

5. The communication system of Claim 2 wherein said at least one repeater means comprises at least one terrestrially based repeater means centrally located within a geographical region.

6. The communication system of Claim 2, wherein said at least one repeater means comprises at least one satellite based repeater means.

7. The communication system of Claim 2 further comprising at least one central communication station for receiving communi-cation signals from said repeater means for transfer to an in-tended recipient user and for transmitting communication signals to said repeater means for translation and transfer to an intended recipient user.

8. The communication system of Claim 2, wherein said at least one repeater means comprises:

at least one terrestrially based repeater for receiving, translating and retransmitting said code-division-spread-spectrum communication signals;
at least one satellite based repeater for receiving, translating, and retransmitting said code-division-spread-spectrum communication signals; and wherein said user terminals transmit and receive code-division-spread-spectrum communication signals through at least one of said terrestrial based and satellite based repeaters and wherein each repeater receives and transmits code-division-spread-spectrum communication signals between user terminals.

9. The communication system of Claim 2 further comprising polarization control means coupled to said omni-directional antenna for selecting a predetermined polarization mode from a plurality of modes for transmission and reception of code-division-spread-spectrum communication signals.

10. A multiple access, spread spectrum communication system, comprising:
means for communicating information signals between at least two system users using code-division-spread-spectrum communication signals, said means for communicating comprising:
chip generation means for generating a plurality of quasi-orthogonal spreading functions;
code selection means for assigning at least one of said spreading functions to a system user;

a plurality of mobile user terminals capable of transmitting and receiving said code-division-spread-spectrum communication signals, each of said user terminals comprising:
transmission means for generating a code-division-spread-spectrum communication signal in response to an input information signal according to said assigned spreading function; and receiver means for generating an output information signal by processing a code-division-spread-spectrum communication signal according to said assigned spreading function, said receiver having a demodulator, comprising:
input means for receiving code-division-spread-spectrum communication signals;
a variable frequency source generating a local reference signal of predetermined frequency;
a radio frequency mixer connected to said input means and said variable frequency source for mixing the code-division-spread-spectrum communication signals with the local reference signal to provide an intermediate spread spectrum signal;
filter means connected in series with said radio frequency mixer for filtering undesirable frequency components from said intermediate spread spectrum signal;
phase division means connected in series with said filter means for dividing said spread spectrum signal into an analog in-phase signal and an analog quadrature signal;

converter means connected to said phase division means for converting said analog in-phase and quadrature signals to digital in-phase and quadrature signals at a variable rate;
combiner means connected to an output of said converter means for juxtaposing said digital in-phase and quadrature signals onto a single data line for transfer to other components within said demodulator in serial fashion;
pilot chip reference means for generating a local bit sequence corresponding to a predetermined pilot chip sequence transmitted contiguous with communication signals received by said demodulator, said local bit sequence being generated with a predetermined period;
carrier tracking means connected to said combiner means and said pilot chip reference means for comparing said local pilot chip sequence to received signals in a timed relationship to determine timing of said code-division-spread-spectrum communication signals with respect to said local pilot chip sequence and for adjusting the frequency of said variable frequency source;
chip synchronization means connected to said combiner means and said pilot reference means for comparing said local pilot chip sequence to received signals in a plurality of timed relationships to determine the timing of said code-division-spread-spectrum communication signals with respect to said local pilot chip sequence and for adjusting the rate for said converter means;

unit chip means for generating a bit sequence corresponding to said assigned spreading function;
despreading means connected to said combiner means and said unit chip means for generating in-phase and quadrature information signals;
output means connected to said despreading means for combining said despread-spectrum in-phase and quadrature signals into an output information signal; and at least one omni-directional antenna coupled to said transmission means and said receiver means; and at least one repeater means for receiving code-division-spread-spectrum communication signals from said plurality of user terminals and for translating said code-division-spread-spectrum communication signals to a form suitable for transfer to an intended recipient user.

11. The demodulator of Claim 10 wherein said carrier tracking means and said chip time tracking means further comprise:
first correlation means connected to said combiner means and said pilot reference means for comparing said in-phase and quadrature signals with said pilot chip sequence and providing an output representative of a first correlation pattern;
second correlation means connected to said combiner means and said pilot reference means for delaying said in-phase and quadrature signals an amount of time corresponding to said pilot chip period and comparing said in-phase and quadrature signals with said pilot chip sequence and providing an output representative of a second correlation pattern;
third correlation means connected to said combiner means and said pilot reference means for delaying said in-phase and quadrature signals an amount of time corresponding to half said pilot chip period and comparing said signals with said pilot chip sequence and providing an output representative of a third correlation pattern;
chip synchronization means connected to said first and third correlation means for adjusting the rate of conversion of said analog in-phase and quadrature to said digital in-phase and quadrature signals by said converter means in response to the output provided by said first correlation and third correlation means; and a carrier tracking loop connected to said second correlation means for adjusting said variable frequency source in response to the output provided by said second correlation means.

12. The demodulator of Claim 10 further comprising a variable gain control means disposed between and connected in series with said input means and said radio frequency mixer, and automatic gain control means connected to said combiner means for altering the gain of said variable gain control means in response to an absolute magnitude of said in-phase and quadrature signals.

13. The demodulator of Claim 10 wherein said converter means comprises first analog conversion means for converting said in-phase signal to a digital in-phase signal and second analog conversion means for converting said quadrature signal to a digital quadrature signal.

14. The demodulator of Claim 10 wherein said first correlation means comprises:
first means for multi-phase mixing said digital in-phase and quadrature signals with said pilot chip sequence;
first coherent summation means coupled to said means for multi-phase mixing, for generating the sum of said in-phase and said quadrature signals coherently over a predetermined period of time; and squared summation means for generating the sum of the square of said in-phase and said quadrature signals over a predetermined period of time.

15. The demodulator of Claim 10 wherein said second correlation means comprises:
second means for multi-phase mixing said in-phase and quadrature signals with said pilot chip sequence;
first delay means positioned between said combiner means and said second means for multi-phase mixing; and second coherent summation means coupled to said second means for multi-phase mixing, for generating the sum of said in-phase and said quadrature signals coherently over a predetermined period of time.

16. The demodulator of Claim 10 wherein said third correlation means comprises:
third means for multi-phase mixing said in-phase and quadrature signals with said pilot chip sequence;
second delay means positioned between said first delay means and said third means for multi-phase mixing;
third coherent summation means coupled to said third means for multi-phase mixing, for generating the sum of said in-phase and said quadrature signals coherently over a predetermined period of time; and second squared summation means for generating the sum of the square of said in-phase and said quadrature signals over a predetermined period of time.

17. The communication system of Claim 2 wherein said receiver means further comprises a demodulator, comprising:
input means for sampling substantially the entire bandwidth or said code-division-spread-spectrum signals;
phase division means connected in series with said input means for dividing said spread spectrum signal into an analog in-phase signal and an analog quadrature signal;
converter means connected to said phase division means for converting said analog in-phase and analog quadrature signals to digital in-phase and quadrature signals at a variable rate.

18. A method of providing high capacity multiple access communications to a plurality of communication service users, comprising the steps of:
converting a plurality of narrow band information input signals into a plurality of wide band user addressable code-division-spread-spectrum communication signals, using an assigned spreading function, and a predetermined carrier frequency;
transmitting said code-division-spread-spectrum communication signals between users;
receiving at said users said transmitted code-division-spread-spectrum communication signals;
weighting signal power unequally, upon at least one of transmission and reception, of said code-division-spread-spectrum communication signals for user addressed code-division-spread-spectrum communication signals as received by an address corresponding user with respect to other user addressed code-division-spread-spectrum communication signals also received by said same user, wherein said step of weighting signal power comprises the steps of receiving or transmitting said code-division-spread-spectrum communication signals through an antenna array forming multiple directive beams, and converting a received user addressed code-division-spread-spectrum communication signal corresponding to said user to a corresponding narrow band information signal.

19. A method of providing high capacity multiple access communications to a plurality of communication service users, comprising the steps of:
converting a plurality of narrow band information input signals into a plurality of wide band user addressable code-division-spread-spectrum communication signals, using an assigned spreading function, and a predetermined carrier frequency;
transmitting said code-division-spread-spectrum communi-cation signals between users;
receiving at said users said transmitted code-division-spread-spectrum communication signals;
weighting signal power unequally, upon at least one of transmission and reception, of said code-division-spread-spectrum communication signals for user addressed code-division-spread-spectrum communication signals as received by an address corresponding user with respect to other user addressed code-division-spread-spectrum communication signals also received by said same user, wherein said step of weighting signal power comprises the step of selecting a polarization mode from a plurality of polarization mode for an antenna used in transmitting and receiving said code-division-spread-spectrum communication signals; and converting a received user addressed code-division-spread-spectrum communication signal corresponding to said user to a corresponding narrow band information signal.

20. A method of providing high capacity multiple access communications to a plurality of communication service users, comprising the steps of:
converting a plurality of narrow band information input signals into a plurality of wide band user addressable code-division-spread-spectrum communication signals, using an assigned spreading function, and a predetermined carrier frequency;
transmitting said code-division-spread-spectrum communication signals between users;
receiving at said users said transmitted code-division-spread-spectrum communication signals, weighting signal power unequally, upon at least one of transmission and reception, of said code-division-spread-spectrum communication signals for user addressed code-division-spread-spectrum communication signals as received by an address corresponding user with respect to other user addressed code-division-spread-spectrum communication signals also received by said same user, wherein said step of weighting signal power comprises the step of decreasing transmission signal power for a user during periods of low input signal activity: and converting a received user addressed code-division-spread-spectrum communication signal corresponding to said user to a corresponding narrow band information signal.

21. A method of providing high capacity multiple access communications to a plurality of communication service users, comprising the steps of:
converting a plurality of narrow band information input signals into a plurality of wide band user addressable code-division-spread-spectrum communication signals, using an assigned spreading function, and a predetermined carrier frequency;
transmitting said code-division-spread-spectrum communication signals between users;
receiving at said users said transmitted code-division-spread-spectrum communication signals;
weighting signal power unequally, upon at least one of transmission and reception, of said code-division-spread-spectrum communication signals for user addressed code-division-spread-spectrum communication signals as received by an address corresponding user with respect to other user addressed code-division-spread-spectrum communication signals also received by said same user, wherein said step of weighting signal power comprises the step of adjusting transmission power applied to a code-division-spread-spectrum signal in response to a minimum power level required to establish a communication link, and converting a received user addressed code-division-spread-spectrum communication signal corresponding to said user to a corresponding narrow band information signal.

22. A method of providing high capacity multiple access communications to a plurality of communication service users, comprising the steps of:
converting a plurality of narrow band information input signals into a plurality of wide band user addressable code-division-spread-spectrum communication signals, using an assigned spreading function, and a predetermined carrier frequency;
transmitting said code-division-spread-spectrum communi-cation signals between users;
receiving at said users said transmitted code-division-spread-spectrum communication signals;
weighting signal power unequally, upon at least one of transmission and reception, of said code-division-spread-spectrum communication signals for user addressed code-division-spread-spectrum communication signals as received by an address corresponding user with respect to other user addressed code-division-spread-spectrum communication signals also received by said same user, wherein said step of weighting signal power comprises the steps of transmitting or receiving a same user addressed code-division-spread-spectrum communication signal by two or more spaced apart locations, so that interference patterns are generated which maximize a signal to noise ratio for said user addressed code-division-spread-spectrum communication signals received by an address corresponding user; and converting a received user addressed code-division-spread-spectrum communication signal corresponding to said user to a corresponding narrow band information signal.

23. A multiple access, spread spectrum communication system, comprising:
means for communicating information signals between at least two system users using user address corresponding code-division-spread-spectrum communication signals, said means for communicating comprising:
chip generation means for generating a plurality of quasi-orthogonal spreading functions;
code selection means for assigning at least one of said spreading functions to a system user a plurality of mobile user terminals capable of trans-mitting or receiving said code-division-spread-spectrum communica-tion signals, each of said user terminals comprising:
transmission means for generating a code-division-spread-spectrum communication in response to an input information signal according to said assigned spreading function;
activity detection means coupled to said transmission means for sensing signal activity levels in said input information signal and decreasing a user terminal transmission power duty cycle in response to a decrease in sensed activity below a pre-determined threshold level for a predetermined sampling period;
and receiver means for generating an output information signal by processing a code-division-spread-spectrum communication signal according to said assigned spreading function;

at least one omni-directional antenna; and at least one repeater means for receiving code-division-spread-spectrum communication signals from said plurality of user terminals and translating said code-division-spread-spectrum communication sig-nals to a form for transfer to an intended recipient user.

24. A multiple access, spread spectrum communication system, comprising:
means for communicating information signals between at least two system users using user address corresponding code-division-spread-spectrum communication signals, said means for communicating comprising:
chip generation means for generating a plurality of quasi-orthogonal spreading functions;
code selection means for assigning at least one of said spreading functions to a system user;
a plurality of mobile user terminals capable of trans-mitting or receiving said code-division-spread-spectrum communica-tion signals, each of said user terminals comprising:
transmission means for generating a code-division-spread-spectrum communication in response to an input information signal according to said assigned spreading function;
receiver means for generating an output information signal by processing a code-division-spread-spectrum communication signal according to said assigned spreading function;

at least one omni-directional antenna;
at least one repeater means for receiving code-division-spread-spectrum communication signals from said plurality of user terminals and translating said code-division-spread-spectrum communication signals to a form for transfer to an intended recipient user; and activity detection means coupled to said repeater means for sensing signal activity levels in said code-division-spread-spectrum communication signals and decreasing repeater trans-mission power duty cycle in response to a decrease in sensed acti-vity below a predetermined threshold level for a predetermined sampling period.

25. A multiple access, spread spectrum communication system, comprising:
means for communicating information signals between at least two system users using user address corresponding code-division-spread-spectrum communication signals, said means for communicating comprising:
chip generation means for generating a plurality of quasi-orthogonal spreading functions;
code selection means for assigning at least one of said spreading functions to a system user;
a plurality of mobile user terminals capable of trans-mitting or receiving said code-division-spread-spectrum communica-tion signals, each of said user terminals comprising:

transmission means for generating a code-division-spread-spectrum communication in response to an input information signal according to said assigned spreading function;
receiver means for generating an output information signal by processing a code-division-spread-spectrum communication signal according to said assigned spreading function;
link power control means connected to said receiver means for sensing a receiver power level present in received first code-division-spread-spectrum communication signals and for ad-justing power applied to an antenna for transmitting second code-division-spread-spectrum communication signals in response to the sensed power level;
at least one omni-directional antenna; and at least one repeater means for receiving code-division-spread-spectrum communication signals from said plurality of user terminals and translating said code-division-spread-spectrum communication signals to a form for transfer to an intended recipient user.

26. A spread spectrum multiple access communication system having high system user capacity, comprising:
means for communicating system user addressable informa-tion signals between at least two of a plurality of system users using address corresponding code-division-spread-spectrum communi-cation signals, said means for communicating generating mutual interference in communications between said at least two system users by contemporaneously communicating code-division-spread-spectrum communication signals between other system users, and said means for communicating having a processing gain for reducing said mutual interference; and isolation means, coupled to said means for communica-ting, for providing an increase in system user realized average signal power for said system user address corresponding code-division-spread-spectrum communication signals in communications between said at least two system users relative to mutual inter-ference signal power of said contemporaneous communications between said other system users.

27. The communication system of Claim 26 wherein said isola-tion means comprises an antenna system having an antenna beam pattern forming multiple directive beams.

28. The communication system of Claim 26 wherein said isola-tion means comprises an antenna system configured to obtain polarization mode selection between a plurality of polarization modes.

29. The communication system of Claim 26 wherein said isola-tion means comprises:
activity detection means for measuring signal activity levels for said information signals relative to a no activity level over a predetermined sampling time and for providing an activity signal corresponding to measured activity; and power control means coupled to said means for communica-ting for adjusting a transmission power duty cycle for said code-division-spread-spectrum communication signals in response to changes in said activity signal.

30. The communication system of Claim 26 wherein said isola-tion means comprises interference pattern means for generating interference patterns of maximum signal to noise ratio at a receive location in communicated code-division-spread-spectrum communication signals, said interference pattern means having transmission means for transmitting a same communication signal via at least two different communication paths to said receive location and control means coupled to said transmission means for adjusting at least one of signal phase and transmission start times in said transmissions of said same communication signal transmitted via said different communication paths.

31. The communication system of Claim 26 wherein said means for communicating further communicates a same communication signal via at least two different communication paths and said isolation means comprises signal combination means for coherently combining said same communication signal as received at a receive location from said different communication paths, said signal combination means having reception means for receiving each of said same communication signals as transmitted via each of said different communication paths and control means coupled to said reception means for adjusting at least one of signal phase and timing in receptions of said same communication signal via said different communication paths.

32. The communication system of Claim 26 wherein said means for communicating comprises:
a plurality of terrestrially based repeater means for transmitting said code-division-spread-spectrum communication signals;
a plurality of transceiver means each coupled to a respective one of certain system users for receiving said code-division-spread-spectrum communication signals and for trans-mitting system user addressed code-division-spread-spectrum communication signals;
said plurality of repeater means further for receiving transceiver means transmitted code-division-spread-spectrum communication signals; and wherein said isolation means comprises the placement of each repeater means at a predetermined position with respect to each other repeater means, each repeater means in communicating with at least one of said certain system users within a predeter-mined respective geographic region using said code-division-spread-spectrum communication signals with mutual interference signal power from communications in adjacent geographic regions attenuated as a function of distance therefrom.

33. The communication system of Claim 26 wherein said isola-tion means further comprises:
link control means for detecting a minimum power level required to maintain code-division-spread-spectrum communication signals in a user communication link above a predetermined incident power level and for providing a link control signal corresponding to said minimum power level;
power control means connected to said communication means and said link control means for adjusting a transmission power level for said code-division-spread-spectrum communication signals in response to said link control signal.

34. The communication system of Claim 26 wherein said means for communicating further comprises:
chip generation means for generating a plurality of quasi-orthogonal spreading functions;
code selection means for assigning one of said spreading functions to a user;
a plurality of mobile user terminals capable of transmitting and receiving said code-division-spread-spectrum communication signals, each of said user terminals comprising:
transmission means for generating, according to an assigned spreading function, a code-division-spread-spectrum communication signal in response to an input information signal;
receiver means for generating an output information signal by processing a received code-division-spread-spectrum communication signal according to said assigned spreading func-tion; and at least one omni-directional antenna for coupling to said transmission means and said receiver means; and at least one repeater means for receiving code-division-spread-spectrum communication signals from said plurality of user terminals and for translating said received code-division-spread-spectrum communication signals to a form suitable for transfer to an intended recipient user.

35. The communication system of Claim 26 wherein said code-division-spread-spectrum signals are transferred over one or more communication channels and said isolation means provides isolation between system user addressed signals in communications between said at least two system users and mutual interference signals in communications between said other system users in the range of about 1 dB to 15 dB.

36. The communication system of Claim 26 wherein said means for communicating transmits information signals from at least one central communication station to at least one remote system user.

37. The communication system of Claim 26 wherein said means for communicating transmits information signals from at least one remote system user to at least one central communication station.

38. In a spread spectrum multiple access communication system in which system users communicate user addressable infor-mation signals using address corresponding code-division-spread-spectrum communication signals wherein with respect to communica-tions between at least two system users other system users gener-ate mutual interference by contemporaneously communicating code-division-spread-spectrum communication signals with said system having a processing gain for reducing mutual interference, in said communication system a method for providing high system user capa-city by further reducing mutual interference in communications between said at least two system users comprising the steps of:
providing a plurality of system user addressable narrow band information signals;
converting said plurality of system user addressable narrow band information signals into a corresponding plurality of system user address corresponding wide band code-division-spread-spectrum communication signals;
transmitting said plurality of code-division-spread-spectrum communication signals between system users;
receiving, at each respective system user, system user address corresponding code-division-spread-spectrum communication signals and other respective system user addressed code-division-spread-spectrum communication signals as mutual interference;
providing for each respective system user an increase in system user realized average signal power for said system user address corresponding code-division-spread-spectrum communication signals with respect to mutual interference signal power of said other system user address corresponding code-division-spread-spectrum communication signals; and converting, at each respective system user, received address corresponding code-division-spread-spectrum communication signals into corresponding user addressable information signals.

39. The method of Claim 38 wherein said step of providing an increase in system user realized average signal power comprises the steps of:
providing an antenna system having an antenna beam pattern forming multiple directive beams with each beam corresponding to certain system users; and radiating each system user address corresponding code-division-spread-spectrum communication signals on each of said beams corresponding to each system user to which said radiated system user address corresponding communication signal cor-responds.

40. The method of Claim 38 wherein said step of providing an increase in system user realized average signal power comprises the steps of:
providing an antenna system having an antenna beam pattern forming multiple directive beams with each beam corres-ponding to certain system users; and collecting upon each beam code-division-spread-spectrum communication signals from said corresponding system users which correspond to each respective beam.

41. The method of Claim 38 wherein said step of providing an increase in system user realized average signal power comprises the step of providing each system user with a polarization mode selectable antenna set to receive transmitted code-division-spread-spectrum communication signals according to a predetermined one of a plurality of polarization modes where address correspond-ing code division-spread-spectrum communication signals are trans-mitted according to a polarization mode to which said antenna system of each address corresponding system user is set to receive.

42. The method of Claim 38 wherein said step of providing an increase in system user realized average signal power comprises the steps of:
measuring signal activity levels for said information signals relative to a no activity level over a predetermined samp-ling time;
providing an activity signal corresponding to said measured activity levels; and adjusting a transmission power duty cycle for said code-division-spread-spectrum communication signals in response to changes in said activity signal.

43. The method of Claim 38 wherein said step of providing an increase in system user realized average signal power comprises the steps of:
transmitting, in said step of transmitting, a same system user address corresponding code-division-spread-spectrum communication signal via at least two different communication paths to an address corresponding system user located at a receive location; and adjusting in said transmission of said same communica-tion signal one of signal phase and signal transmission delay time as transmitted upon said different communication paths, wherein an interference pattern occurs having a maximum signal to noise ratio in said transmitted same communication signals at said receive location.

44. The method of Claim 38 wherein said step of providing an increase in system user realized average signal power comprises the steps of:
receiving at a system user located at a receive location a same system user address corresponding code-division-spread-spectrum communication signal as transmitted upon at least two different communication paths in said step of transmitting; and coherently combining said same communication signal as received upon said different communication paths by adjusting at least one of signal phase and signal reception delay time of said same communication signal as received upon said different communi-cation paths.

45. The method of Claim 38 wherein said step of transmitting comprises the steps of:
providing a plurality o-f terrestrially based repeaters each capable of transmitting said code-division-spread-spectrum communication signals, providing for certain system users a transceiver capable of transmitting and receiving said code-division-spread-spectrum communication signals; and wherein said step of providing an increase in system user realized average signal power comprises the step of placing each repeater at a predetermined position with respect to other repeater wherein each repeater communicates with at least one of said certain system users within a predetermined respective geographic region using said code-division-spread-spectrum communication signals with mutual interference signal power from communications in adjacent geographic regions attenuated as a function of distance therefrom.

46. The method of Claim 38 further comprising the steps of:
detecting a minimum power level required to maintain system user address corresponding code-division-spread-spectrum communication signals in a system user communication link above a predetermined incident power level;
providing a link control signal corresponding to said detected minimum power level; and adjusting a transmission power level for said system user address corresponding code-division-spread-spectrum communi-cation signals in response to said link control signal.

47. The method of Claim 38 further comprising the step of transmitting a pilot chip sequence comprising a predetermined sequence of data bits.

48. The method of Claim 38 wherein said step of transmitting comprises the steps of transmitting to or from a plurality of users through a repeater.

49. The method of Claim 48 wherein said steps of transmitting to or from comprises the steps of transmitting to or from a terrestrial repeater.

50. The method of Claim 48 wherein said steps of transmitt-ing to or from comprises the steps of transmitting to or from at least one satellite repeater.

51. The method of Claim 48 wherein said steps of transmitt-ing to and from comprises the steps of transmitting to or from at least one satellite repeater and at least one terrestrially based repeater.