United States Patent £19J
`Gilhousen et al.
`
`[11] Patent Number:
`[45] Date of Patent:
`
`4,901,307
`Feb. 13, 1990
`
`[54] SPREAD SPECI'RUM MULTIPLE ACCESS
`COMMUNICATION SYSTEM USING
`SATELLITE OR TERRESTRIAL REPEATERS
`Inventors: Klein S. Gilhousen, San Diego; Irwin
`M. Jacobs, La Jolla; Lindsay A.
`Weaver, Jr., San Diego, all of Calif.
`
`[75]
`
`[73] Assignee: Qualcomm, Inc., San Diego, Calif.
`[21] Appl. No.: 921,261
`[22] Filed:
`Oct. 17, 1986
`[51]
`Int. Cl.4 .............................................. H04J 13/00
`[52] U.S. CI ............................................ 370/18; 375/1
`[58] Field of Search .................. 370/18, 19, 95; 375/1
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`3,596,002 7/1971 Ohnsorge et al ..................... 179/15
`3,761,813 9/1973 Perrin ...................................... 325/4
`4,030,033 6/1977 Bib! et al ............................... 325/30
`4,114,155 9/1978 Raab .................................... 343/105
`4,164,628 8/1979 Ward eta!. ........................... 179/15
`4,172,257 10/1979 Mahner ............................... 343/854
`4,189,677 2/1980 Cooper et al ....................... 325/321
`4,191,410 9/1981 Caples et al ............................ 375/1
`4,222,115 9/1980 Cooper et al ........................... 375/1
`4,291,409 9/1981 Weinberg et al ....................... 375/1
`4,359,733 11/1982 O'Neill ................................. 343/6.5
`4,426,712 1/1984 Gorski-Popiel ....................... 375/96
`4,455,651 6/1984 Baran .................................. 370/104
`4,470,138 9/1984 Gutleber ............................... 370/18
`4,494,228 1/1985 Gutleber ............................... 370/21
`4,512,024 4/1985 Gutleber ............................... 370/18
`4,703,474 10/1987 Foschini et al ....................... 370/18
`
`FOREIGN PATENT DOCUMENTS
`2125654 3/1984 United Kingdom .................. 370/18
`
`OTHER PUBLICATIONS
`IEEE Communications, vol. 24, No. 2, Feb. 1986, pp.
`8-15, Cellular System Design: An Emerging Engineer(cid:173)
`ing Discipline, James F. Whitehead.
`IEEE Transactions on Aerospace and Electronic Sys(cid:173)
`tems, vol. AES-4, No. 5, Sep. 1968, Air-Ground,
`Ground-Air Communications Using Pseudo-Noise
`Through a Satellite, Blasbalg, Najjar, D'Antonio, Had-:
`
`dad, IBM Center for Exploratory Studies, IBM Space
`Systems Center.
`IEEE Transactions on Vehicular Technology, vol.
`VT-27, No.4, Nov. 1978, A Spread-Spectrum Tech(cid:173)
`nique for High-Capacity Mobile Communications,
`George R. Cooper, Raymond W. Nettleton.
`Article from Telecommunication Journal, vol. 45, Jan.
`1978 titled Spread-Spectrum Principles and Possible
`Application To Spectrum Utilization and Allocation by
`W. F. Utlaut.
`-Article· from-IEEE Communications Magazine, Mar.
`1978 titled Cellular Land-Mobile Radio: Why Spread
`(List continued on next page.)
`Primary Examiner-Douglas W. Olms
`Attorney, Agent, or Firm-Brown, Martin, Haller &
`McClain
`[57]
`.
`ABSTRACI'
`A multiple access, spread spectrum communication
`system and method for providing high capacity com(cid:173)
`munications to, from, or between a plurality of system
`users, using code-division-spread-spectrum communica(cid:173)
`tion signals. The communication system uses means for
`providing marginal isolation between user communica(cid:173)
`tion signals. The marginal isolation is provided by gen(cid:173)
`erating simultaneous multiple steerable beams; using an
`omni-directional antenna with polarization enhance(cid:173)
`ment; using power control devices to adjust the output
`power-for user generated communication signals either
`in response to their input activity level, or in accor(cid:173)
`dance 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(cid:173)
`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 terres(cid:173)
`trial or satellite repeaters. Multiple satellite repeaters
`are operable in a new communication mode to obtain
`further gains in signal isolation.
`
`46 Claims, 11 Drawing Sheets
`
`Cisco Systems, Inc., Exhibit 1026
`Page 1
`
`

`
`4,901,307
`
`Page 2
`
`OTHER PUBLICATIONS
`
`Spectrum? by G. Cooper, R. Nettleton and D. Grybos.
`Paper from I.E.E. International Conference on Land
`Mobile Radio, Spread Spectrum Communication Sys(cid:173)
`tems for the Land Mobile Service by R. Ormondroyd,
`B. Eng and M. Shipton, Sep. 1979.
`Article from AIAA 7th Communications Satellite Sys(cid:173)
`tems Conference titled Communications Satellite Sys(cid:173)
`tem Concept Based on the AMP A Experiment by S.
`Durrani and F. Keblawi, Apr., 1978.
`Article from Electronics & Power titled The Spread
`Spectrum Controversy, Mar. 1980, pp. 222 and 224.
`Excerpts from the book Communications Satellite Sys(cid:173)
`tems, 1978 by Martin, pp. 142-147, 189, 358-359,
`-- 365-367 by Prentice Hall, Inc.
`Paper titled Low Cost Satellite Data Transmission Net-
`
`·works-Using Demand Assigned TDMA by J. Husted
`and S. Dinwiddy.
`Paper titled DYNAC: A Low Cost Data/Voice Com(cid:173)
`munications Network by S. Salamoff, D. Ross and J.
`Steinhorn.
`Excerpt from book titled Digital Communications by
`Satellite, 1977, Delay-Lock Tracking of Pseudonoise
`Signals, chapter 18, p. 578.
`Ad by Equatorial Communications Co. entitled Satel(cid:173)
`lite Network For Point-To-Multipoint Data Distribu(cid:173)
`tion.
`Excerpt from book entitled Spread Spectrum Systems,
`1976, Applications of Spread Spectrum Methods, Chap-
`. ter 9.
`Paper titled Subjective Evaluation of Dedicated Multi(cid:173)
`ple-Hop Satellite Communications for Government
`and Military Users by S. Campanella, H. Suyderhoud
`and M. Onufry.
`
`Cisco Systems, Inc., Exhibit 1026
`Page 2
`
`

`
`U.S. Patent
`
`Feb.13,1990
`
`Sheet 1 ofll
`
`4,901,307
`
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`Cisco Systems, Inc., Exhibit 1026
`Page 3
`
`

`
`U.S. Patent
`
`Feb.13,1990
`
`Sheet 2 ofll
`
`4,901,307
`
`ANTENNA MARGINAL GAl N
`D. ANGLE
`# USERS WTD#USERS
`ATTN. RANGE CUM. ANGLE
`( 0)
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`7.4
`
`FDMA REUSE FACTOR
`2.64
`
`FIG. lb
`
`189
`188.59
`126
`99.87
`79.33
`126
`126
`63.01
`29.82
`94
`[8.81
`94
`126
`12.57
`3.98
`126
`4.17
`1320
`2326
`500.17
`COMA REUSE FACTOR
`4.65
`
`RELATIVE CAPACITY INCREASE AND
`POLARIZATION ISOLATION vs. ELLIPTICITY
`ELLIPTICITY
`AXIAL
`CAPACITY
`POLARIZATION
`t dB)
`RATIO
`I NCR EASE
`I SOLATION (dB)
`
`o.oo
`2.o·o
`4.00
`6.00
`8.00
`10.00
`12.00
`14.00
`16.00
`18.00
`20.00
`
`1.00
`0.63
`0.40
`0.25
`0.16
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`0.06
`0.04
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`o.o1
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`100%
`79%
`63%
`50%
`40%
`32%
`25%
`20%
`16%
`13%
`10%
`
`- 00
`
`-18.81
`-12.91
`-9.57
`-7.32
`-5.69
`-4.46
`-3.51
`-2.78
`-2.20
`-1.74
`
`FIG. 14
`
`Cisco Systems, Inc., Exhibit 1026
`Page 4
`
`

`
`SATELLITE
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`
`Cisco Systems, Inc., Exhibit 1026
`Page 5
`
`

`
`50
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`FIG.3
`
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`
`Cisco Systems, Inc., Exhibit 1026
`Page 6
`
`

`
`U.S. Patent
`
`Feb. 13, 1990
`
`Sheet 5 of11
`
`4,901,307
`
`USER
`POWER
`
`Dl STANCE
`FIG.4
`
`\
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`
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`
`FIG. II
`
`Cisco Systems, Inc., Exhibit 1026
`Page 7
`
`

`
`64
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`Cisco Systems, Inc., Exhibit 1026
`Page 8
`
`

`
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`Cisco Systems, Inc., Exhibit 1026
`Page 9
`
`

`
`U.S. Patent
`
`Feb. 13,1990
`
`108 ~,
`
`4,901,307
`
`TO
`El
`SATELLIJ
`"'::>
`
`104 ~-~
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`Sheet 8 of11
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`
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`
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`
`Cisco Systems, Inc., Exhibit 1026
`Page 10
`
`

`
`OATA TO
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`
`Cisco Systems, Inc., Exhibit 1026
`Page 11
`
`

`
`222
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`
`..&;;.
`....
`
`\C = ~ w =
`
`......,J
`
`Cisco Systems, Inc., Exhibit 1026
`Page 12
`
`

`
`162
`
`300~
`304
`
`TRANSMIT CHIP
`SEQUENCE
`GENERATOR
`
`308
`
`TRANSMIT
`
`316
`
`318
`
`TRANSMIT
`
`TRANSMIT
`POWER
`CONTROL
`
`~
`V1
`;p
`ft a
`
`~
`~
`....... w
`...
`.......
`~ Q
`
`....... -
`
`TJl =-m.
`.......
`.......
`e,
`.......
`.......
`
`~ -...
`
`\C = ~ w =
`
`......,J
`
`SYMBOL CLOCKS
`BIT CLOCKS
`OTHER TIMING
`SIGNALS
`DOPPLER CORRECTED
`UPLINK CHIP CLOCK
`FROM RECEIVE
`CHIP-TIME TRACKING LOOP
`
`310
`
`-320
`
`FR EQ UEN CY
`SYNTHESIZER
`212
`
`INITIAL ACQUISITION
`AND FADE
`POWER CONTROL
`
`DOPPLER CORRECTED
`UPLINK CARRIER FREQUENCY
`FROM RECEIVE
`CARRIER LOOP
`302
`
`TRANSMIT
`CLOCK
`GENERATION
`
`"326
`
`278
`
`FREQUENCY
`SYNTHESIZER
`
`FIG. 16
`
`100
`
`80
`
`60
`% DECREASE
`IN CAPACITY 40
`
`FIG. 12
`
`FIG. 13
`
`0~--.--.---.--.--.---.--.--.--.-~
`0
`2
`4
`6
`8
`I 0
`12
`14
`I 6 18 20
`ELLIPTICITY (dB)
`
`Cisco Systems, Inc., Exhibit 1026
`Page 13
`
`

`
`1
`
`4,901,307
`
`SPREAD SPECI'RUM MULTIPLE ACCESS
`COMMUNICATION SYSTEM USING SATELUTE
`OR TERRESTRIAL REPEATERS
`
`BACKGROUND OF THE INVENTION
`Technical Field
`The present invention relates to multiple access com(cid:173)
`munication systems and more particularly to a method 10
`and apparatus for employing Code Division Multiple
`Access (CDMA) spread spectrum signals to provide
`communication services for mobile or remote user ter(cid:173)
`minals using satellite or terrestrially based repeater ap(cid:173)
`paratus. The present invention further relates to utiliz- 15
`ing COMA 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.
`
`25
`
`Background
`There has been a long-standing need to provide qual(cid:173)
`ity communication services to many groups of 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 satis(cid:173)
`fied by land mobile radio. However, these services have
`always been faced with more potential users than sys- 30
`tern capacity. The frequency or spectral bandwidth
`allocations do not provide enough capacity to simulta(cid:173)
`neously handle the total number of potential users.
`Even so, private individuals, businesses, and new
`classes of users, such as aeronautical communications, 35
`are creating an ever increasing demand for services for
`both mobile and remote users. A large increase in the
`number of remotely accessible computers and data sys(cid:173)
`tems has also created a demand for remote and mobile
`digital data communications in addition to voice com- 40
`munications. In addition, new types of remote data
`collection or sensing, and alphanumeric keypad or key(cid:173)
`board entry systems are being proposed which can not
`be serviced by current communication systems. There(cid:173)
`fore, new communication systems are being proposed 45
`and built to serve these demands for service.
`In building or implementing any new communication
`system, the key issue for both the designer and the end
`user is the channel capacity of the system. In a commer(cid:173)
`cial system, capacity translates directly into income or 50
`economic feasibility which is important to the system
`operator, since capacity determines the number of reve(cid:173)
`nue generating users that can be accommodated. The
`number of allowable users is in turn important to the
`potential service users. The number of simultaneous 55
`users and, therefore, capacity supported by any commu(cid:173)
`nication system is determined by the amount of mutual
`interference between users.
`Current mobile radio services operate as frequency
`division multiplexed (FDM) or frequency division mul- 60
`tiple access (FDMA) systems which divide the avail(cid:173)
`able bandwidth into smaller bands or channels. To de(cid:173)
`crease mutual interference some of the bandwidth is
`also assigned to "guard bands" between channels to
`provide attenuation or isolation between users. Full 65
`duplex communication requires two channels. The total
`number of channels is generally divided in half, one half
`being for uplink and call control to a central base re-
`
`2
`peater and the other for downlink and control signals to
`users. In addition, some channels may be allocated for
`additional user protocol and call control. Therefore, the
`number of simultaneous users is much lower than the
`5 apparent number of channels.
`System capacity can be increased by increasing the
`number of channels but this decreases channel band(cid:173)
`width which limits voice quality and the use of high
`speed data transfers. Instead, the preferred technique
`for increasing system capacity is frequency reuse. Fre(cid:173)
`quency 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 from each other by a minimum
`value for signal rejection by the two user receivers.
`Typical isolation or attenuation requirements for
`adequate 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
`20 can be subdivided into geographical regions and the
`same frequency can simultaneously be "reused" in
`neighboring regions which are isolated from each other
`by the appropriate attenuation. This technique is easily
`applied in land mobile 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 1fr3 to 1fr5 attenuation due to buildings
`and other absorbing structures.
`Users geographically removed from each other by an
`appreciable distance naturally have their communica(cid:173)
`tion signals attenuated with respect to each other.
`Therefore, 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 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.
`This is the basis for cellular telephone technology
`which is the current approach to accommodating large
`numbers of mobile users. Here, each cell comprises a
`geographical region serviced by a central base station
`which uses land based communication lines and switch(cid:173)
`ing systems to form an interlinked system with other
`base stations so that the only airborne transmissions are
`localized across the cell. To decrease mutual interfer-
`ence 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 central controller
`that uses advanced 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 is not. This requires the
`system to change the frequencies used for the communi(cid:173)
`cation link. If a channel is unavailable in an adjacent
`cell, the call fails abruptly at cell borders.
`A related problem of current channel assignment
`schemes is the inability to have instant access to the
`
`Cisco Systems, Inc., Exhibit 1026
`Page 14
`
`

`
`4,901,307
`
`4
`3
`each region. If the signals in each region or antenna
`communication system at any time. Channel assign-
`pattern experience an attenuation on the order of say lO
`ments increase the time the central controller requires
`db with respect to those in the nearest neighbor region
`to establish a communication link and may even prevent
`and 20 dB with respect to the next adjacent regions and
`calls from being established.
`Cellular systems also suffer from multipath problems, 5 so forth, then a given frequency can be reused two
`especially near cell borders, where users receive desired
`regions away based on 20 dB sensitivity rejection. This
`signals both from a central transmitter and sources such
`roughly doubles the number of users allowed at any
`as reflections from buildings. If the signals add out of
`time within a transcontinental communication system.
`phase then they may cancel and become severely de-
`However, this does not match demand for services.
`graded. This problem is also encountered in radio tele- 10 Antenna designs have been proposed which would
`phone and other current mobile systems.
`scan the antenna patterns across the target geographic
`A similar problem occurs for mobile users moving
`regions using advanced frequency scanning techniques.
`These antenna schemes take advantage of the fact that
`away from central transmitters at speeds that give rise
`to Doppler effects and phase shifts. Here the standing
`different frequencies can be reflected at different angles
`wave pattern from the transmitter appears to fade every 15 by a given antenna reflector as used on communication
`half wavelength creating continual reception problems.
`satellites. This means that as the frequencies transmitted
`In addition, motion on the order of 70 mph can produce
`by the antenna radiator system change, the virtual spot
`Doppler shifts on the order of +I- 80 Hz at frequen-
`created on the earth by the antenna reflector will move.
`cies of 800 MHz which can increase inter-channel inter-
`In this manner the same antenna structure is made to
`ference.
`20 alter the beam location. However, such techniques use
`The FM type cellular and radio telephone system
`the antenna structure to direct different frequencies to
`different regions, thus failing to fully take advantage of
`broadcasts are not efficient techniques for transferring
`digital data signals. Current user demands call for data
`frequency reuse by allocating only a portion of the total
`transmission links that are high quality exhibiting very
`spectrum to each region.
`low bit error rates on the order of lQ-6 or lQ-8 at data 25
`Satellite systems do not use terrestrially based repeat-
`transfer rates on the order of 2400 to 4800 baud with
`ers that communicate directly with users or a series of
`future data transfer rates extending up to 19,200 baud.
`multiple satellites that communicate with the same user.
`Increasing capacity by using smaller cells is useful in
`Therefore, current systems do not provide universal
`large, high user density, metropolitan or urban regions
`service, that is, the ability for users to change position
`but not in low user density rural regions. Increased 30 over a large geographical range and still be able to
`capacity is not likely to be achieved economically (cost
`communicate without using alternate
`transmission
`of base station versus number of users served in region)
`equipment or new frequency bands. In multiple satellite·
`in rural areas. Therefore, while cellular telephone meets
`systems frequency reuse would be limited by the isola-
`some of the demands of large metropolitan areas it does
`tion between geographic target regions. Satellite sys-
`not meet the demands of rural areas which comprise 25 35 tems also experience multipath, blocking, and fading
`problems similar to mobile radio and telephone systems.
`percent of the population and 84 percent of the land
`Alternate methods of decreasing user interference
`mass for countries like the United States. In addition,
`larger rural cells can decrease the frequency reuse in
`include time division multiple access (TDMA) or multi-
`adjacent urban areas. This occurs because a single large
`plexed (TDM) systems. Such systems use a central re-
`cell is adjacent to several small cells which cannot use 40 ceiving station to multiplex or interleave separate user
`signals in time so that each signal only uses a portion of
`the same frequency. This and other design consider-
`ations and problems for cellular systems are discussed in
`the total outgoing signal to the satellite. The time divi-
`further detail in IEEE COMMUNICATIONS MAG-
`sion approach divides the total spectrum up into prede-
`AZINE, Vol. 24, No. 2, February, 1986, especially
`termined temporal increments. All signals in the com-
`pages 8-15 which are incorporated herein by reference. 45 munication repeater system are allocated portions of
`It has previously been assumed that satellite systems
`this time controlled sequence. Therefore, no other user
`are required to economically provide service to low
`is using the link at the same exact time. The allocated
`density, rural or remote areas. However, satellite sys-
`portions are very small and the interleaving very large
`so that it appears simultaneous to all users. However,
`tems generally utilize high volume communication links
`to transfer otherwise terrestrially based telephone com- 50 this time based synchronization of signals creates a natu-
`rallimit to the number of users that can be coordinated
`munications over single large distances between terres-
`trial relay stations for further transfer This does not
`"simultaneously" which is lower than desired. Also
`address the needs of mobile users or system users al-
`synchronizing a large number of simultaneous users
`ready without local telephone service.
`greatly increases the complexity and cost of the system.
`Some satellite systems have been proposed to address 55 What is needed is a communication system that ac-
`commodates a larger number of users throughout a
`single users through individual antennas instead of cen-
`tral relay stations, but the frequencies at which satellites
`variety of user environments from high density urban to
`operate and the methods of transmission have led to the
`very low density rural. The communication system
`use of rather large fixed antennas which are expensive
`needs to exhibit increased capacity within standard
`60 spectral allocation bandwidths but with the same or
`and not amenable to use in mobile systems.
`Proposed satellite services generally operate as
`better communication quality than presently available
`FDMA systems employing UHF frequency repeaters
`In addition, a need also exists for a communication
`and AM modulation schemes such as Amplitude Com-
`system capable of handling high speed low bit error rate
`manded Single Sideband (ACSSB). Frequency reuse
`digital data transfers at low power densities.
`can be used for satellite systems similar to cellular sys- 65
`tems discussed above The continental U.S can be di(cid:173)
`vided into geographical regions or cells by using a mul(cid:173)
`tiple beam antenna where a separate beam is used for
`
`SUMMARY
`Therefore, with the above disadvantages present in
`the art in mind, it is an object of the present invention to
`
`Cisco Systems, Inc., Exhibit 1026
`Page 15
`
`

`
`4,901,307
`
`45
`
`5
`provide a multiple access communication system hav(cid:173)
`ing high simultaneous user capacity.
`It is another object of the present invention to pro(cid:173)
`vide a communication system having automatic Dop(cid:173)
`pler shift and fade control.
`It is a purpose of the present invention to provide a
`communication system capable of expansion to meet
`future needs and interface with future alternative com(cid:173)
`munication systems.
`It is a further purpose of the present invention to 10
`provide an inexpel).sive communication system user
`terminal capable of meeting the needs of a variety of
`mobile or remote users.
`It is yet another purpose of the present invention to
`provide for transmission and receipt of high speed digi- 15
`tal data signals with very low bit error rates.
`These and other objects, purposes, and advantages
`are provided in a multiple access, spread spectrum com(cid:173)
`munication system, having means for communicating
`information signals to, from, or between a plurality of 20
`users, using code-division-spread-spectrum communica(cid:173)
`tion signals and isolation means for providing marginal
`isolation between said user communication signals. The
`isolation means can comprise a phased array antenna
`coupled to means for generating substantially simulta- 25
`neous multiple steerable beams; an antenna structure
`configured to obtain either one or both of two circular
`polarization states; transceiver means for transmitting
`or receiving the same communication signals by two or
`more locations to create constructive interference ·maxi- 30
`mized signal reception; first power control means for
`adjusting an output power duty cycle for said code-divi(cid:173)
`sion-spread-spectrum communication signals in re(cid:173)
`sponse to a predetermined activity level for said infor(cid:173)
`mation signals; or second power control means for ad- 35
`justing said output power level for said code-division(cid:173)
`spread-spectrum communication signals in response to a
`minimum power level required to complete a communi(cid:173)
`cation link.
`The preferred embodiment of the multiple access, 40
`spread spectrum communication system of the present
`invention further comprises means for transmitting a
`predetermined pilot chip sequence to users contiguous
`with said code-division-spread-spectrum communica-
`tion signals.
`In a preferred embodiment the means for communi(cid:173)
`cating comprises chip generation means for generating
`a plurality of quasi-orthogonal spreading functions;
`code selection means for assigning one of the spreading
`functions to a user; and a plurality of mobile user termi- 50
`nals capable of transmitting or receiving code-division(cid:173)
`spread-spectrum communication signals. Each of the
`user terminals uses a transmitter for generating a code(cid:173)
`division-spread-spectrum communication signal ac(cid:173)
`cording to an assigned spreading function in response to 55
`an input information signal; a receiver for detecting a
`code-division-spread-spectrum communication signal
`and generating an output information signal according
`to said assigned spreading function; and an omni-direc(cid:173)
`tional antenna. At least one repeater is used for receiv- 60
`ing communication signals from the plurality of user
`terminals and for translating the code-division-spread(cid:173)
`spectrum communication signals to a form suitable for
`transfer to an intended recipient.
`In a further aspect of the invention the repeater pref- 65
`erably employs means for transmitting a predetermined
`pilot chip sequence to users contiguous with a commu(cid:173)
`nication link and the receivers include a pilot sequence
`
`6
`tracking loop. An activity detector is included in the
`repeater for sensing signal activity levels in said infor(cid:173)
`mation signals and decreasing repeater transmission
`power duty cycle in response to a decrease in sensed
`5 activity below a predetermined threshold level for a
`predetermined sampling time.
`The user terminals can also comprise an activity de-
`tection means for sensing signal activity levels in the
`input information signals and decreasing user terminal
`transmission power duty cycle in response to a decrease
`in sensed activity below a predetermined threshold
`level.
`The terminals can further comprise power control
`means for sensing a received power level present in
`received code-division-spread-spectrum communica(cid:173)
`tion signals and for adjusting the output level power
`applied to an antenna for transmitting code-division(cid:173)
`spread-spectrum communication signals in r