United States Patent [t9J
`Gilhousen et al.
`
`[54] SYSTEM AND METHOD FOR GENERATING
`SIGNAL WAVEFORMS IN A CDMA
`CELLULAR TELEPHONE SYSTEM
`
`[75]
`
`Inventors: Klein S. Gilhousen, San Diego; Inrin
`M. Jacobs, La Jolla; Roberto
`Padovani; Lindsay A. Weaver, Jr.,
`both of San Diego; Charles E.
`Wheatley, III, Del Mar; Andrew J.
`Viterbi, La Jolla, all of Calif.
`
`[73] Assignee: Qualcomm Incorporated, San Diego,
`Calif.
`
`[21) Appl. No.: 543,496
`
`[22] Filed:
`
`Jun.2S, 1990
`
`Int. Cl.s ............................................. H04L 27/30
`[51]
`[52] u.s. Cl ........................................... 375/1; 375/68;
`380/34; 370/18; 370/21; 370/22; 379/59;
`455/33.1; 455/54.1
`[58] Field of Search ......................... 375/1, 37, 59, 68;
`380/28, 33, 34, 49; 370/18, 19, 21, 22; 379/59;
`455/33, 54
`
`[56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`4,052,565 10/1977 Baxter eta!. ......................... 380/28
`4,730,340 3/1988 Frazier, Jr .............................. 375/1
`4,933,952 6/1990 A1brieux eta!. ........................ 375/1
`
`111111111111111111111111111111111111111111111111111111111111111111111111111
`US005103459A
`[It] Patent Number:
`[45] Date of .Patent:
`
`5,103,459
`Apr. 7, 1992
`
`OTHER PUBLICATIONS
`Erwin Kreyszig, Advanced Engineering Mathematics;
`(John Wiley & Sons, 1979; Section 4.7, pp. 186-190).
`Primary Examiner-Bernarr E. Gregory
`Attorney, Agent, or Firm-Russell B. Miller
`[57)
`ABSTRACT
`A system and method for communicating information
`signals using spread spectrum communication tech(cid:173)
`niques. PN sequences are constructed that provide or(cid:173)
`thogonality between the users so that mutual interfer(cid:173)
`ence will be reduced, allowing higher capacity and
`better link performance. With orthogonal PN codes, the
`cross-correlation is zero over a predetermined time
`interval, resulting in no interference between the or(cid:173)
`thogonal codes, provided only that the cOde time
`frames are time aligned with each other. In an exem(cid:173)
`plary embodiment, signals are communicated between a
`cell-site and mobile units using direct sequence spread
`spectrum communication signals. In the cell-to-mobile
`link, pilot, sync, paging and voice channels are defined.
`Information communicated on the cell-to-mobile link
`channels are, in general, encoded, interleaved, bi-phase
`shift key (BPSK) moduiated with orthogonal covering
`of each BPSK symbol along with quadrature phase shift
`key (QPSK) spreading of the covered symbols. In the
`mobile-to-cell link, access and voice channels are de(cid:173)
`fined. Information communicated on the mobile-to-cell
`link channels are, in general, encoded, interleaved, or(cid:173)
`thogonal signalling along with QPSK spreading.
`
`49 Claims, 13 Drawing Sheets
`
`FROt.t
`USER
`DIGITAL
`BASEBAND
`
`ENCODER
`
`r - - - - - - - - - - - - l
`608
`614
`I
`I
`
`PN
`GENERATOR
`PNu
`
`MOBILE
`UNIT
`ADDRESS I
`I
`r-.J
`I
`WALSH
`I NTERLEAVER ~---+"..,.
`ENCODER
`I
`I
`I
`45~
`616
`GENERATOR
`L ______________ _j
`
`602
`
`604
`
`TO
`TRANSMIT
`POWER
`CONTROL
`
`Cisco Systems, Inc., Exhibit 1110
`Page 1
`
`

`
`U.S. Patent
`
`Apr. 7, 1992
`
`Sheet 1 of 13
`
`5,103,459
`
`TO/FROM
`TO/FROM OTHER
`PSTN
`CELL-SITES
`~ r - - - - - - - - -w / .
`SYSTEU
`CONTROLLER
`AND SWITCH
`
`10_)
`
`12
`
`FIG. 1
`
`Cisco Systems, Inc., Exhibit 1110
`Page 2
`
`

`
`U.S. Patent
`
`Apr. 7, 1992
`
`Sheet 2 of 13
`
`5,103,459
`
`, - - - - - - - - - - - - - - - - - ,
`r-------~38
`I
`I
`I DIGITAL ~--------------,
`I
`I
`I
`DATA
`r--...-.t
`I RECEIVER t------,
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`34
`I
`l
`I
`SEARCHER
`. I
`I
`I, 5o
`1
`~-+-~
`I
`RECEIVER
`'"\
`J
`1
`...---"----'"-----.
`I
`I
`I
`DIVERSITY
`I
`I
`COMBINER
`!
`I
`I
`& DECODER
`J
`I
`r---f---
`1
`cir~~~
`1
`I
`I
`1
`DlECODERS
`I
`I 52,
`I
`I
`)
`1
`I
`DIGITAL foo-
`l
`I
`LINK
`.
`I
`1
`I
`I
`GPS
`1
`I
`'- RECEIVER
`1
`CELL-SITE
`FROM
`SYSTEM ------~ CONTROL
`PROCESSOR ---1---..a L -:-~ ~- - l
`CONTROL
`I
`PROCRSSOR
`1"--__,..1 ----..,
`I
`I
`I
`I
`I
`TRANSMIT
`I
`t---+-!---i TRANSMIT
`POWER
`j MODULATOR
`:
`CONTROL
`'-56 L __ 54J ___ --'
`
`L -L -- tr=-_:~
`
`_
`
`TO OTHER
`TRANSMIT
`MODULATORs·
`
`30~
`
`ANTENNA
`TO ADDITIONAL
`ANALOG---i
`RECEIVERS
`
`_r-
`32
`
`ANALOG
`RECEIVER
`
`40
`
`ANTENNA
`
`TO ADDITIONAL
`ANALOG---i
`RECEIVERS
`
`ANALOG
`RECEIVER
`
`ANTENNA
`
`6
`
`6t
`
`I
`
`L--------J
`
`-
`
`I
`
`I
`
`36
`"-... DIGITAL
`DATA
`RECEIVER
`4~.------.
`'- DIGITAL 1-+---'
`DATA
`RECEIVER ~f--
`44,
`...---....~..---
`SEARCHER
`RECEIVER
`
`1
`
`I
`
`PILOT/CONTROL
`CHANNEL TRANSMIT
`MODULATOR AND
`TRANSMIT
`POWER CONTROL
`
`F ROM OTHER TRANSMIT
`MODULATOR AND
`.TRANS MIT POWER CONTROL
`CIRCUITS
`
`60\
`
`ANTENNA J -
`
`:- SUtAtER
`
`57
`TO/FROM t.tTSO
`DIGITAL. SWITCH
`
`TRANSMITT lis
`
`POWER
`AMPLJ F I ER
`
`FIG. 2
`
`Cisco Systems, Inc., Exhibit 1110
`Page 3
`
`

`
`U.S. Patent
`
`Apr. 7, 1992
`
`Sheet 3 of 13
`
`5,103,459
`
`L------------------~
`
`TO
`DIVERSITY
`COMBINER &
`DECODER
`--l
`
`PNo
`
`PNi
`
`PN
`PNt
`J - - - - - - -1 GENERATOR
`130
`
`136
`
`120
`
`PN
`PNQ
`.,.._-+-------1 GENERATOR
`
`122
`
`PN
`PNu
`1.....------'------1 GENERATOR
`124
`
`L-:r----------- ---- __ J
`
`36
`
`UOBILE
`UNIT
`ADDRESS
`
`FHT
`
`I'IG. 3
`
`FROM
`CONTROL
`PROCESSOR
`
`Cisco Systems, Inc., Exhibit 1110
`Page 4
`
`

`
`U.S. Patent
`
`Apr. 7, 1992
`
`Sheet 4 of 13
`
`5,103,459
`
`19l
`
`PN
`GENERATOR
`
`PN
`GENERATOR
`
`~
`196
`
`SECTOR OR
`CELL ADDRESS
`FROM CONTROL
`PROCESSOR
`
`SYNC
`CHANNEL
`DATA FROM
`CONTROL
`PROCESSOR
`
`~
`~
`
`~---
`I
`I
`I
`
`d -...
`
`0 .....
`
`218
`
`PAGING
`CHANNEL
`DATA FROM
`CONTROL ---.....-!
`I '-----'
`PROCESSOR
`I
`I
`GENERATOR
`.
`L
`------------------l
`I
`L __ _
`
`VOICE
`CHANNEL (i)
`DATA
`MOBILE UNIT __ _.
`ADRESS FROM
`CONTROL
`PROCESSOR
`
`VOICE
`CHANNa (j)
`DATA
`MOBILE UNIT __ ..
`ADRESS FROM
`CONTROL
`PROCESSOR
`
`PN
`GENERATOR
`253J
`
`nG. "-
`
`255j
`
`2541
`
`254j
`
`~
`
`FUNCTION
`SELECT
`FROM
`CONTROL
`PROCESSOR
`
`.
`
`.
`1 5252J ~
`
`~
`~
`
`.
`
`0
`.....
`FUNCTION
`SELECT
`FROM
`CONTROL
`PROCESSOR
`
`Cisco Systems, Inc., Exhibit 1110
`Page 5
`
`

`
`U.S. Patent
`
`Apr. 7, 1992
`
`Sheet 5 of 13
`
`5,103,459
`
`c2ss
`
`c27o
`
`0/A t-1--
`0/A t-1--
`c272
`o;AI ..... --
`c274
`0/A t-1--
`
`0/A
`
`0/A
`c2s21
`o;AI~---
`
`c2soJ
`o;AI~---
`c2s21
`0/A .It---
`
`Cisco Systems, Inc., Exhibit 1110
`Page 6
`
`

`
`U.S. Patent
`
`Apr. 7, 1992
`
`Sheet 6 of 13
`
`5,103,459
`
`---~
`I
`I
`I
`I
`I
`I
`I
`
`
`FROM
`TRANSMIT
`POWER
`~ 58
`CONTROL
`L ____________________ l
`
`II
`
`BPF
`
`298
`
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`_j
`
`TO ANTENNA
`
`cos ( 2 1'1' ft)
`
`FIG. 4c
`
`r---.----
`1
`I
`I
`I
`r------------__J
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`__ _ _j
`
`Cisco Systems, Inc., Exhibit 1110
`Page 7
`
`

`
`U.S. Patent
`
`Apr. 7, 1992
`
`Sheet 7 of 13
`
`5,103,459
`
`64 CHIP
`SHIFT
`1
`
`1
`
`N PILOT r ·: co
`
`CHANNEL
`
`I
`I
`I
`N+1 PILOT ·1 C' 1
`I
`CHANNEL
`I
`tx
`
`I
`ty
`
`C'O
`
`C1
`
`co
`
`C'O
`
`TIME
`
`FIG. 5
`
`• • •
`
`C1
`• • •
`
`I
`
`I
`
`I
`I
`I
`
`C'O
`
`Cl~
`
`I
`
`I
`SYNC CHANNEL
`OTHOGONAL
`COVER
`
`I
`I•
`
`co
`
`p b
`
`I
`I
`I
`
`N PILOT
`CHANNEL
`
`N SYNC
`CHANNEL
`
`I
`I
`N+1 PILOT:
`CHANNEL I
`
`I
`I
`
`tx
`
`n n D n n n n ~
`'
`'
`N+1 SYNC D f=J n n D p n n D p •••
`CHANNEL I 64
`...
`ICHIP~
`.. I
`ty
`
`I
`1 ..
`I
`
`co
`
`C'O
`
`•1C1--..
`•••
`
`TIME
`
`riG. 8
`
`Cisco Systems, Inc., Exhibit 1110
`Page 8
`
`

`
`U.S. Patent
`
`Apr. 7, 1992
`
`Sheet 8 of 13
`
`5,103,459
`
`USERS LONG (42-BIT) PN
`GENERATOR IN STATE X
`4 SEC
`2 SEC
`1 SEC
`lpps --1------.J.--~.1 ----If-----...::114----+---
`75 PILOT CYCLES•2 SECS
`
`I
`SYNC MESSAGE
`fN+l
`I
`I
`
`I
`SYNC CHANNEL MESSAGE
`LENGTH MULTIPLE OF 80 MSEC
`I
`I
`I
`SYNC MESSAGE fN
`LONG PN GENERATOR
`I
`I
`IS LOADED WITH X
`I
`FOR SCRAMBLING
`
`SYNC
`CHANNEL
`
`PAGING
`OR
`VOICE
`
`80 mSEC EQUAL TO
`2 INTERLEAVER CYCLES OR
`4 VOCODER FRAMES
`
`1ST CODE SYMBOL OF NEW BIT
`DEINTERLEAVER WRITE ADDRESS 0
`DEINTERLEAVER READ ADDRESS J
`NEW INTERLEAVER CYCLE
`
`TIME
`
`I'IG. 7
`
`Cisco Systems, Inc., Exhibit 1110
`Page 9
`
`

`
`U.S. Patent
`
`Apr. 7, 1992
`
`Sheet 9 of 13
`
`5,103,459
`
`TO/FROM
`PSTN
`
`308
`
`DIGITAL
`SWITCH
`
`TO/FROM
`CELL-SITES
`CONTROL PROCESSORS
`
`t
`
`SYSTEM
`CONTROL
`PROCESSOR
`
`~300
`
`1
`/306
`......, DIGITAL
`VOCODER
`
`(304
`
`DIVERSITY
`COMBINER .._--I
`
`•
`•
`•
`
`•
`•
`•
`TO OTHER ----~
`DIVERSITY COMBINERS
`~TO/FROM OTHER
`~ VOCODERS
`
`TO/FROM
`CELL-SITES
`DIGITAL LINKS
`
`DIGITAL
`SWITCH
`
`FROM OTHER_....,.
`VOCODERS
`'--------'
`
`FIG. 8
`
`Cisco Systems, Inc., Exhibit 1110
`Page 10
`
`

`
`U.S. Patent
`
`Apr. 7, 1992
`
`Sheet 10 of 13
`
`5,103,459
`
`(430
`
`ANTENNA
`
`444
`------1)
`SEARCHER
`RECEIVER
`
`FIG. 9
`
`432_)
`
`(442
`
`(448
`
`~ DIPLEXER
`
`DIGITAL
`DATA
`RECEIVER
`
`DIVERSITY
`COMBINER
`AND
`DECODER
`
`(434
`
`(440
`
`;-450
`
`ANALOG
`RECEIVER
`
`DIGITAL
`DATA
`RECEIVER
`
`-
`
`USER
`DIGITAL
`BASEBAND
`
`(446
`
`CONTROL
`PROCESSOR
`
`"'--'
`
`...._
`
`TRANSMIT
`POWER
`AMPLIFIER
`
`TRANSMIT
`POWER
`CONTROL
`
`TRANSMIT
`MODULATOR
`
`Cisco Systems, Inc., Exhibit 1110
`Page 11
`
`

`
`U.S. Patent
`
`Apr. 7, 1992
`
`Sheet 11 of 13
`
`5,103,459
`
`FREQUENCY
`SYNTHESIZER
`L-----------
`TO TRANSMIT
`POWER CONTROL
`
`....--~To
`SEARCHER
`RECEIVER
`
`..... -~To
`DATA
`RECEIVER
`442
`
`TO
`DIVERSITY
`COMBINER
`AND
`DECODER
`-5a2l
`
`PHASE
`DETECTOR
`
`524
`
`522
`
`PN1
`
`PNl
`
`PN
`GENERATOR
`
`PN
`GENERATOR
`
`WALSJ.f
`GENERATOR
`
`TO
`DIVERSITY
`COMBINER
`AND
`DECODER
`
`FROM
`CONTROL
`PROCESSOR
`
`MOBILE UNIT
`ADDRESS
`FUNCTION
`SELECT ------'
`
`_j
`
`riG. 10
`
`I
`I
`I
`I
`I
`I
`I
`I
`452
`"-i
`I
`I
`I
`I
`
`L - ______________ ..;
`
`520
`
`PN
`534_,.- GENERATOR
`~-
`
`Cisco Systems, Inc., Exhibit 1110
`Page 12
`
`

`
`U.S. Patent
`
`Apr. 7, 1992
`
`Sheet 12 of 13
`
`5,103,459
`
`FROM
`USER
`DIGITAL
`BASEBAND
`
`602
`
`FIG. 11
`
`604
`
`FULL RATE~~~
`
`I
`I
`
`I
`I
`
`1/2 RATE ~ ~ I ~ I ~ ~ . ~
`
`I
`I
`I
`
`I
`I
`I
`
`~ I
`1/4 RATE I
`m
`~
`l l l l rzo / " i i i iM I
`I
`I
`I
`I
`tftRAT_E+;~+~~~1~1~1~1~1~~~+1~1~1~1 41~~
`I
`I
`t = 20 mSEC
`t - 0
`
`FIG. 12
`
`Cisco Systems, Inc., Exhibit 1110
`Page 13
`
`

`
`U.S. Patent
`
`Apr. 7, 1992
`
`Sheet 13 of 13
`
`5,103,459
`
`USERS LONG {~2-BIT) PN
`GENERATOR IN STATE X
`1 SEC
`2 SEC
`4 SEC
`1pps --!-------~1----~~------~-----t-----
`75 PILOT CYCLES-2 SECS
`
`1ST CODE SYMBOL OF NEW
`BIT INTERLEAVER WRITE
`ADDRESS 0 DEI~TERLEAVER
`READ ADDRESS J NEW INTER-
`
`. LONG PN GENERATOR I LEAVER CYCLE
`
`IS LOADED WITH X I
`FOR SCRAMBLING
`CELL PAGING_ 1---------J..-,4---+---------3!Httt---t---(cid:173)
`OR VOICE -
`CHANNEL
`1ST CODE SYMBOL OF NEW
`80 rnSEC EQUAL TO
`BIT AND NEW WALSH SYMBOL
`2 I TERLEAVER CYCLES OR
`INTERLEAVER WRITE ADDRESS
`4 VOCODER FRAMES
`0 INTERLEAVER READ ADDRESS
`0 NEW INTERLEAVER CYCLE AND
`I
`NEW V CODER FRAME
`LONG PN GENERATOR
`I
`IS LOADED WITH X
`I
`
`MOBILE
`VOICE
`CHANNEL
`
`MOBILE
`ACCESS
`CHANNEL.
`
`riG. 13
`
`I
`I
`I
`120 rnSEC
`1 FRAME
`I
`
`1ST CODE SYMBOL OF NEW
`BIT AND NEW WALSH
`SYMBOL INTERLEAVER
`WRITE ADDRESS 0
`INTERLEAVER READ
`I ADORE
`0
`
`~~~E PACKET~BURST
`
`N FRAMES
`
`LONG PN GENERATOR
`IS LOADED WITH X
`
`Cisco Systems, Inc., Exhibit 1110
`Page 14
`
`

`
`1
`
`5,103,459
`
`5
`
`SYSTEM AND METHOD FOR GENERATING
`SIGNAL WAVEFORMS IN A CDMA CELLULAR
`TELEPHONE SYSTEM
`
`2
`differences in signals traveling on different paths may
`occur. The possibility for destructive summation of the
`signals may result, with on occasion deep fades occur(cid:173)
`ring.
`Terrestrial channel fading is a very strong function of
`the physical position of the mobile unit. A small change
`BACKGROUND OF THE INVENTION
`in position of the mobile unit changes the physical de-
`I. Field of the Invention
`lays of all the signal propagation paths, which further
`The present invention relates to cellular telephone
`results in a different phase for each path. Thus, the
`systems. More specifically, the present invention relates
`to a novel and improved system and method for com- 10 motion of the mobile unit through the environment can
`result in a quite rapid fading process. For example, in
`municating information, in a mobile cellular telephone
`system or satellite mobile telephone system, using
`the 850 MHz cellular radio frequency band, this fading
`can typical!y be as fast as one fade per second per mile
`spread spectrum communication signals.
`II. Description of the Related Art
`per hour of vehicle speed. Fading this severe can be
`The use of code division multiple access (COMA) 15 extremely disruptive to signals in the terrestrial channel
`modulation techniques is one of several techniques for
`resulting in poor communication quality. Additional
`facilitating communications in which a large number of
`transmitter power can be used to overcome the problem
`system users are present. Other multiple access commu-
`of fading. However, such power increases effect both
`nication system techniques, such as time division multi-
`the user, in excessive power consumption, and the sys-
`ple access (TDMA), frequency division multiple access 20 tern by increased interference.
`The COMA modulation techniques disclosed in U.S.
`(FDMA) and AM modulation schemes such as ampli-
`tude companded single sideband (ACSSB) are known in
`Pat. No. 4,901,307 offer many advantages over narrow
`the art. However the spread spectrum modulation tech-
`band modulation techniques used in communication
`nique of COMA has significant advantages over these
`systems employing satellite or terrestrial repeaters. The
`modulation techniques for multiple access communica- 25 terrestrial channel poses special problems to any com-
`munication system particularly with respect to multi-
`tion systems. The use of COMA techniques in a multi-
`ple access communication system is disclosed in U.S.
`path signals. The use of COMA techniques permit the
`Pat. No. 4,901,307, issued Feb. 13, 1990, entitled
`special problems of the terrestrial channel to be over-
`"SPREAD SPECTRUM MULTIPLE ACCESS
`COMMUNICATION SYSTEM USING SA TEL- 30 come by mitigating the adverse effect of multipath, e.g.
`LITE OR TERRESTRIAL REPEATERS", assigned
`fading, while also exploiting the advantages thereof.
`to the assignee of the present invention, of which the
`In a COMA cellular telephone system, the same fre-
`disclosure thereof is incorporated by reference.
`quency band can be used for communication in all cells.
`In the just mentioned patent, a multiple access tech-
`The COMA waveform properties that provide process-
`nique is disclosed where a large number of mobile tele- 3S ing gain are also used to discriminate between signals
`phone system users each having a transceiver communi-
`that occupy the same frequency band. Furthermore the
`cate through satellite repeaters or terrestrial base sta-
`high speed pseudonoise (PN) modulation allows many
`tions (also referred to as cell-sites stations, cell-sites or
`different propagation paths to be separated, provided
`for short, cells) using code division multiple access
`the difference in path delays exceed the PN chip dura-
`(CDMA) spread spectrum communication signals. In 40 tion, i.e. !/bandwidth. If a PN chip rate of approxi-
`using COMA communications, the frequency spectrum
`mately 1 MHz is employed in a COMA system, the full
`can be reused multiple times thus permitting an increase
`spread spectrum processing gain, equal to the ratio of
`in system user capacity. The use of COMA results in a
`the spread bandwidth to system data rate, can be em-
`much higher spectral efficiency than can be achieved
`played against paths that differ by more than one micro-
`using other multiple access techniques.
`45 second in path delay from the desired path. A one mi-
`The satellite channel typically experiences fading that
`crosecond path delay differential corresponds to differ-
`is characterized as Rician. Accordingly the received
`entia} path distance of approximately 1,000 feet. The
`signal consists of a direct component summed with a
`urban environment typically provides differential path
`multiple reflected component having Rayleigh fading
`delays in excess of one microsecond, and up to 10-20
`statistics. The power ratio between the direct and re- so microseconds are reported in some areas.
`In narrow band modulation systems such as the ana-
`fleeted component is typically on the order of 6-10 dB,
`depending upon the characteristics of the mobile unit
`log FM modulation employed by conventional tete-
`antenna and the environment about the mobile unit.
`phone systems, the existence of multiple paths results in
`Contrasting with the satellite channel, the terrestrial
`severe multipath fading. With wide band COMA mod-
`channel experiences signal fading that typically consists 55 ulation, however, the different paths may be discrimi-
`ofthe Rayleigh faded component without a direct com-
`nated against in the demodulation process. This discrim-
`ponent. Thus, the terrestrial channel presents a more
`ination greatly reduces the severity of multipath fading.
`se_vere fading environment than the satellite channel in Multipath fading is not totally eliminated in using
`COMA discrimination techniques because there will
`which Rician fading is the dominant fading characteris-
`tic.
`60 occasionally exist paths with delayed differentials of
`The Rayleigh fading characteristic in the terrestrial
`less than the PN chip duration for the particular system.
`channel signal is caused by the signal being reflected
`Signals having path delays on this order cannot be dis-
`from many different features of the physical environ-
`criminated against in the demodulator, resulting in some
`degree of fading.
`ment. As a result, a signal arrives at a mobile unit re-
`ceiver from many directions with different transmission 65
`It is therefore desirable that some form of diversity be
`delays. At the UHF frequency bands usually employed
`provided which would permit a system to reduce fad-
`for mobile radio communications, including those of
`ing. Diversity is one approach for mitigating the delete-
`rious effects of fading. Three major types of diversity
`cellular mobile telephone systems, significant phase
`
`Cisco Systems, Inc., Exhibit 1110
`Page 15
`
`

`
`5,103,459
`
`25
`
`exist: time diversity, frequency diversity and space di(cid:173)
`versity.
`Time diversity can best be obtained by the use of
`repetition, time interleaving, and error detection and
`coding which is a form of repetition. The present inven- 5
`tion employes each of these techniques as a form oftime
`diversity.
`COMA by its inherent nature of being a wideband
`signle offers a form of frequency diversity by spreading
`the signal energy over a wide bandwidth. Therefore, 10
`frequency selective fading affects only a small part of
`the CDMA signal bandwidth.
`Space or path diversity is obtained by providing mul(cid:173)
`tiple signal paths through simultaneous links from a
`mobile user through two or more cell-sites. Further- !5
`more, path diversity may be obtained by exploiting the
`multipath environment through spread spectrum pro(cid:173)
`cessing by allowing a signal arriving with different
`propagation delays to be received and processed sepa(cid:173)
`rately. Examples of path diversity are illustrated in 20
`copending U.S. patent application entitled "SOFT
`HANDOFF IN A CDMA CELLULAR TELE(cid:173)
`PHONE SYSTEM", Ser. No. 07/433,030, filed Nov. 7,
`1989, and copending U.S. patent application entitled
`"DIVERSITY RECEIVER IN A COMA CELLU(cid:173)
`LAR TELEPHONE SYSTEM", Ser. No. 07/432,552,
`also filed Nov. 7, 1989, both assigned to the assignee of
`the present invention.
`The deleterious effects of fading can be further con- 30
`trolled to a certain extent in a CDMA system by con(cid:173)
`trolling transmitter power. A system for cell-site and
`mobile unit power control is disclosed in copending
`U.S. patent application entitled "METHOD AND AP(cid:173)
`PARATUS FOR CONTROLLING TRANSMIS- 35
`SION POWER IN A CDMA CELLULAR MOBILE
`TELEPHONE SYSTEM", Ser. No. 07/433,031, filed
`Nov. 7, 1989, also assigned to the present invention,
`now U.S. Pat. No. 5,056,109.
`The COMA techniques as disclosed in U.S. Pat. No. 40
`4,901,307 contemplated the use of coherent modulation
`and demodulation for both directions of the link in
`mobile-satellite communications. Accordingly, dis(cid:173)
`closed therein is the use of a pilot carrier signal as a
`coherent phase reference for the satellite-to-mobile link 45
`and the cell-to-mobile link. In the terrestrial cellular
`environment, however, the severity of multipath fad(cid:173)
`ing, with the resulting phase disruption of the channel,
`precludes usage of coherent demodulation technique
`for the mobile-to-cell link. The present invention pro- so
`vides a means for overcoming the adverse effects of
`multipath iii the mobile-to-cell link by using noncoher(cid:173)
`ent modulation and demodulation techniques.
`The COMA techniques as disclosed in U.S. Pat. No.
`4,901,307 further contemplated the use of relatively ss
`long PN sequences with each user channel being as(cid:173)
`signed a different PN sequence. The cross-correlation
`between different PN sequences and the autocrrelation
`of a PN sequence for all time shifts other than zero both
`have a zero average value which allows the different 60
`user signals to be discriminated upon reception.
`However, such PN signals are not orthogonal. Al(cid:173)
`though the cross-correlations average to zero, for a
`short time interval such as an information bit time the
`cross-correlation follows a binomial distribution. As 65
`such, the signals interfere with each other much the
`same as if they were wide bandwidth Gaussian noise at
`the same power spectral density. Thus the other user
`
`signals, or mutual interference noise, ultimately limits
`the achievable capacity.
`The existence ofmultipath can provide path diversity
`to a wideband PN CDMA system. If two or more paths
`are available with greater than one microsecond differ(cid:173)
`ential path delay, two or more PN receivers can be
`employed to separately receive these signals. Since
`these signals will typically exhibit independence in mul(cid:173)
`tipath fading, i.e., they usually do not fade together, the
`outputs of the two receivers can be diversity combined.
`Therefore a loss in performance only occurs when both
`receivers experience fades at the same time. Hence, one
`aspect of the present invention is the provision of two or
`more PN receivers in combination with a diversity
`combiner. In order to exploit the existence ofmultipath
`signals, to overcome fading, it is necessary to utilize a
`waveform that permits path diversity combining opera(cid:173)
`tions to be performed.
`It is therefore an object of the present invention to
`provide for the generation of PN sequences which are
`orthogonal so as to reduce mutual interference, thereby
`permitting greater user capacity, and support path di(cid:173)
`versity thereby overcoming fading.
`
`SUMMARY OF THE INVENTION
`The implementation of spread spectrum communica(cid:173)
`tion techniques, particularly CDMA techniques, in the
`mobile cellular telephone environment therefore pro(cid:173)
`vides features which vastly enhance system reliability
`and capacity over other communication system tech(cid:173)
`niques. CDMA techniques as previously mentioned
`further enable problems such as fading and interference
`to be readily overcome. Accordingly, CDMA tech(cid:173)
`niques further promote greater frequency reuse, thus
`enabling a subsiantial increase in the number of system
`users.
`The present invention is a novel and improved
`method and system for constructing PN sequences that
`provide orthogonality between the users so that mutual
`interference will be reduced, allowing higher capacity
`and better link performance. With orthogonal PN
`codes, the cross-correlation is zero over a predeter(cid:173)
`mined time interval, resulting in no interference be(cid:173)
`tween the orthogonal codes, provided only that the
`code time frames are time aligned with each other.
`In an exemplary embodiment, signals are communi(cid:173)
`cated between a cell-site and mobile units using direct
`sequence spread spectrum communication signals. In
`the cell-to-mobile link, pilot, sync, paging and voice
`channels are defmed. Information communicated on the
`cell-to-mobile link channels are, in general, encoded,
`interleaved, hi-phase shift key (BPSK) modulated with
`orthogonal covering of each BPSK symbol along with
`quadrature phase shift key (QPSK) spreading of the
`covered symbols.
`In the·mobile-to-celllink, access and voice channels
`are defmed. Information communicated on the mobile(cid:173)
`to-cell link channels are, in general, encoded, inter(cid:173)
`leaved, orthogonal signalling along with QPSK spread(cid:173)
`ing.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`The features, objects, and advantages of the present
`invention will become more apparent from the detailed
`description set forth below when taken in conjunction
`with the drawings in which like reference charcters
`identify correspondingly throughout and wherein:
`
`Cisco Systems, Inc., Exhibit 1110
`Page 16
`
`

`
`5,103,459
`
`5
`FIG. 1 is a schematic overview of an exemplary
`CDMA cellular telephone system;
`FIG. 2 is a block diagram of the cell-site equipment as
`implemented in the CDMA cellular telephone system;
`FIG. 3 is a block diagram of the cell-site receiver;
`FIGS. 4a-4c form a block diagram of the cell-site
`transmit modulator; and
`FIG. 5 is an exemplary timing diagram of sync chan(cid:173)
`nel symbol synchronization;
`FIG. 6 is an exemplary timing diagram of sync chan- 10
`nel timing with orthogonal covering;
`FIG. 7 is an exemplary timing diagram of the overall
`cell-to-mobile link timing;
`·
`FIG. 8 is a block diagram of the mobile telephone
`switching office equipment;
`FIG. 9 is a block diagram of the mobile unit tele(cid:173)
`phone configured for CDMA communications in the
`CDMA cellular telephone system;
`FIG. 10 is a block diagram of the mobile unit re-
`ceiver; and
`FIG. 11 is a block diagram of the mobile unit transmit
`modulator;
`FIG. 12 is an exemplary timing diagram of the mo(cid:173)
`bile-to-cell link for the variable data rate with burst
`transmission; and
`FIG. 13 is an exemplary timing diagram of the overall
`mobile-to-cell link timing.
`
`20
`
`6
`synchronization by a single search through all pilot
`signal code phases. The strongest pilot signal, as deter(cid:173)
`mined by a correlation process for each code phase, is
`readily identifiable. The identified strongest pilot signal
`5 generally corresponds to the pilot signal transmitted by
`the nearest cell-site. However, the strongest pilot signal
`is used whether or not it is transmitted by the closest
`cell-site.
`Upon acquisition of the strongest pilot signal, i.e.
`initial synchronization of the mobile unit with the stron(cid:173)
`gest pilot signal, the mobile unit searches for another
`carrier intended to be received by all system users in the
`cell. This carrier, called the synchronization channel,
`transmits a broadcast message containing system infor-
`15 mation for use by the mobiles in the system. The system
`information identifies the cell-site and the system in
`addition to conveying information which allows the
`long PN codes, interleaver frames, vocoders and other
`system timing information used by the mobile mobile
`unit to be synchronized without additional searching.
`Another channel, called the paging channel may also be
`provided to transmit messages to mobiles indicating that
`a call has arrived for them, and to respond with channel
`assignments when a mobile initiates a call.
`The mobile unit continues to scan the received pilot
`carrier signal code at the code offsets corresponding to
`cell-site neighboring sector or neighboring transmitted
`pilot signals. This scanning is done in order to determine
`if a pilot signal emanating from a neighboring sector or
`30 cell is becoming stronger than the pilot signal first de(cid:173)
`termined to be strongest. If, while in this call inactive
`mode, a neighbor sector or neighbor cell-site pilot sig(cid:173)
`nal becomes stronger than that of the initial cell-site
`sector or cell-site transmitted pilot signal, the mobile
`unit will acquire the stronger pilot signals and corre(cid:173)
`sponding sync and paging cha"lnel of the new sector or
`cell-site.
`When a call is initiated, a pseudonoise (PN) code
`address is determined for use during the course of this
`call. The code address may be either assigned by the
`cell-site or be determined by prearrangement based
`upon the identity of the mobile unit. After a call is initi(cid:173)
`ated the mobile unit continues to scan the pilot signal
`transmitted by the cell-site through which communica(cid:173)
`tions are established in addition to pilot signal of neigh(cid:173)
`boring sectors or cells. Pilot signal scanning continues
`in order to determine if one of the neighboring sector or
`cell transmitted pilot signals becomes stronger than the
`pilot signal transmitted by the cell-site the mobile unit is
`in communication with. When the pilot signal associ(cid:173)
`ated with a neighboring cell or cell sector becomes
`stronger than the pilot signal of the current cell or cell
`sector; it is an indication to the mobile unit that a new
`cell or cell sector has been entered and that a handoff
`should be initiated.
`.
`An exemplary telephone system in which the present
`invention is embodied is illustrated in FIG. 1. The sys(cid:173)
`tem illustrated in FIG. 1 utilizes spread spectrum modu(cid:173)
`lation techniques in communication between the system
`mobile units or mobile telephones, and the cell-sites.
`Cellular systems in large cities may have hundreds of
`cell-site stations serving hundreds of thousands of mo(cid:173)
`bile telephones. The use of spread spectrum techniques,
`in particular CDMA, readily facilitates increases in user
`capacity in systems of this size as compared to conven(cid:173)
`tional FM modulation cellular systems.
`In FIG. 1, system controller and switch 10, also re(cid:173)
`ferred to as mobile telephone switching office (MTSO),
`
`25
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`In a CDMA cellular telephone system, each cell-site
`has a plurality of modulator-demodulator units or
`spread spectrum modems. Each modem consists of a
`digital spread spectrum transmit modulator, at least one
`digital spread spectrum data receiver and a searcher 35
`receiver. Each modem at the cell-site is assigned to a
`mobile unit as needed to facilitate communications with
`the assigned mobile unit.
`A soft handoff scheme is employed for a CDMA
`cellular telephone system in which a new cell-site 40
`modem is assigned to a mobile unit while the old cell(cid:173)
`site modem continues to service the call. When the
`mobile unit is located in the transition region between
`the two cell-sites, the call can be switched back and
`forth between cell-sites as signal strength dictates. Since 45
`the mobile unit is always communicating through at
`least one cell-site modem, fewer disrupting effects to the
`mobile unit or in service will occur. The mobile unit
`thus utilizes multiple receivers for assisting in the hand(cid:173)
`off process in addition to a diversity function for miti- SO
`gating the effects of fading.
`In the CDMA cellular telephone system, each cell(cid:173)
`site transmits a "pilot carrier" signal. Should the cell be
`divided into sectors, each sector has an associated dis(cid:173)
`tinct pilot signal within the cell. This pilot signal is used 55
`by the mobile units to obtain initial system synchroniza(cid:173)
`tion and to provide robust time, frequency and phase
`tracking of the cell-site transmitted signals. Each cell(cid:173)
`site also transmits spread spectrum modulated informa(cid:173)
`tion, such as cell-site identification, system timing, mo- 60
`bile paging information and various other control sig(cid:173)
`nals.
`The pilot signal transmitted by each sector of each
`cell is of the same spreading code but with a different
`code phase offset. Phase offset allows the pilot signals to 65
`be distinguished from one another thus distinguishing
`originating cell-sites or sectors. Use of the same pilot
`signal code allows the mobile unit to find system timing
`
`Cisco Systems, Inc., Exhibit 1110
`Page 17
`
`

`
`5,103,459
`
`25
`
`7
`typically includes interface and processing circuitry for
`providing system control to the cell-sites. Controller 10
`also controls the routing of telephone calls from the
`public switched telephone network (PSTN) to the ap(cid:173)
`propriate cell-site for transmission to the appropriate 5
`mobile unit. controller 10 also controls the routing of
`calls fromt he mobile units, via at least one cell-site, to
`the PSTN. Controller 10 may connect calls between
`mobile users via the appropriate cell-sites since the mo(cid:173)
`bile units do not typically communicate directly with !0
`one another.
`Controller 10 may be coupled to the cell-sites by
`various means such as dedicated telephone lines, optical
`fiber links or microwave communic