CA2158269A1 - Method and apparatus for time division multiplexing the use of spreading codes in a communication system - Google Patents
Method and apparatus for time division multiplexing the use of spreading codes in a communication systemInfo
- Publication number
- CA2158269A1 CA2158269A1 CA002158269A CA2158269A CA2158269A1 CA 2158269 A1 CA2158269 A1 CA 2158269A1 CA 002158269 A CA002158269 A CA 002158269A CA 2158269 A CA2158269 A CA 2158269A CA 2158269 A1 CA2158269 A1 CA 2158269A1
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- CA
- Canada
- Prior art keywords
- coded
- user data
- data
- user
- spreading
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J13/00—Code division multiplex systems
- H04J13/16—Code allocation
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J13/00—Code division multiplex systems
- H04J13/0007—Code type
- H04J13/004—Orthogonal
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- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Mobile Radio Communication Systems (AREA)
Abstract
A communication system time division multiplexes the use of spreading codes. The communication system accepts information (301, 302) from at least two users and codes each users information utilizing error correction coders (303, 306). The coded information is then time multiplexed by a multiplexer (312) into timeslots. The output of the multiplexer (312) is spread by a common spreading (Walsh) code, scrambled with a pseudo-noise sequence, and conveyed to a modulator for transmission. In this manner, information for two users may be transmitted utilizing only a single spreading (Walsh) code.
Description
~ 2158269 L'` 1 ND APP~TUS FO~ T~E LJ~V~l~N
MULIInEaNG T~ USE OF SPRE~DING CODES
IN.~ r~1Ur'UNr~'~nONSYS~
Field of the Llvé~lliOn The illvt~ ion relates generally to c~ .-ication ~ys~--s, and more particularly to time division multiplexing the use of 1 0 spre~i~ codes in such Cc~ ;r~*rln ayah.~ 5.
Back~lou.~d of the L.v~.lion C~o---~ ication ~ySlell1S take many forms. In general, the ~u~ose of a communication :~y:.L~I is to ~ ;t il~...ation-I,ea.il~ 5ign~1c from a source, lor~t~l at one point, to a user dea~ ;orl, located at another point some ~icPrlc~ away. A
communication system generally consists of three basic 20 CQ.~ ls; transmitter, channel, and r~eeiv~n The h.l..~...;ll~.
has the function of processing the mf~cç~ge signal into a form suitable for transmission over the channel. This ~rocêssil~ of the m~cs~ge signal is .cfe..ed to as modulation. The function of the channel is to provide a physical connection between the 25 tral~,~ l output and the receivel input. The function of the ~eceiv~. is to process the received signal so as to produce an estimate of the original message signal. This ~ cec~ g of the rèceiv~:d signal is referred to as demodulation.
Analog and digital trar~cmicsion methods are used to 3 0 transmit a message signal over a communication channel. The use of digital methods offers several c,yc~ Lonal advantages over analog methods, including but not l;~ e~ to~ eased il~ Ul ily to chalu~el noise and inlL.r~ ce, flexible o~_.ali;)n of the ~ysle..-, L ~ ~ ~ 1 5 8 2 ~ ~
commorl fonn~t for the ~ C~ c~;on of dir~.e~ll kinds of mPcc~e sigls, i,l~.o-ved sec~ily of ccs~ u~ication through the use of el,~ly~tion~ and il~s~d r~r~rity.
To l-~-L~---;l a m~cs~p signal (either analog or digital) over a 5 co~ rA*on ~ nnPl ~-vi,.~, an ~c~ci~pd cl a,u,el bandwidth, the mess~ge signal must be ~u~llated into a form suitable for PffiriPnt trarlcmission over the c~nnP1 Mo~lific~tion of the meSS~e signal is achieved by means of a process termed modulation. This process involves Vd~yil~ some par~metp~ of a 10 carrier wave in accordance with the mesS?~e signal in such a way that the s~e.hu"l of the morlnl~tefl wave matches the ~ssig~prl .1.~.1..~1 bandwidth. P~.-...et~-s of a carrier wave that can be varied include amplitude, frequency, and or phase.
Co~cs~u~lLllgly, the receiv~ is l~Uil.,d to recreate the original 15 mpscs~ge signal from a degraded version of the trarlcmitte~l signal after propagation through the c~nnPl. The re-creation is accc,ll,ylished by using a process known as rl~moc~ Qn, which is the inverse of the modulation ~rDcess used in the tral~
A spread s~e-Llulll ~y~Lèlll provides, among other things, 2 0 robllc~nPcs to jamming, good il.Lelrerel,ce and mlll*p~th rejec*Qn, and inhLlelllly secure communications from eavesdf~ . In a spread spectrum ~y~Lélll, a modulation têchnique is utilized in which a Ll.~ itted signal is spread over a wide frequency band within the communication channel. The frêquency band is much 25 wider than the minimum bandwidth required tû transmit the il~lll,ation being sent. A voice sign~l, for example, can be sent with ~mE~ e modulation (AM) in a bandwidth only twice that of the ~Ifol...~tion itself. Other forms of modulation, such as low deviation frequency modulation (FM) or single si~ nd AM, also 3 0 ~l.llit il,fol~l,ation to be trancmitte~l in a bandwidth comparable to the bandwidth of the information itself. However, in a spread s~e.hulll ayaLelll, the modulation of a signal to be trarlcmitterl often includes taking a b~ceb~n~ signal (e.g., a voice channel) with a bandwidth of only a few l~iloh~rtz, and dish;L uh~l~ the signal to be t~ e~ over a frequency band that may be many megahertz wide. This is accomplished by modulating the signal to be h~ æll with the ;~.~o~ *on to be sent and with a wideband S ~nror~ signal (c~mmorlly hlo~ l as a spr~ i~ code).
Thus, a spread s~e~l.u l. sr~le..l must have two ~,o~ ies:
(1) the hd~ æ~ balldwidth sh~ be much g~æal., than the bandwidth or rate of the ;~ro~ tion being sent and (2) some function other than the i.~,l,lation being sent is employed to 10 let~- -.i-P the resulting modulated cl,a~ulel bandwidth.
The essence of the spread s~ec~, um communication involves ~cp~i~ the l~".lwitth of a sign~ .a~.~...ill;.lg the e~ signal and l~CCsv~ the desired signal by remapping the received spread specl, u,,. into the ori~in~l i,lfo."lation 15 bandwidth. Furthermore, in the ~,ocess of c~..y,.~ out this series of bandwidth trades, the purpose of spread s~.hulll techni~ues is to allow the sy~lel" to deliver error-free il~o,ll.ation in a noisy signal e,l~i,wullent.
With digital communication, user i,lfcsl"lation such as 20 speech is encoded into sequences of binary il~ lation. This encoding is convenient for modulation and is easily error-co.,ecLon coded for tr~ncmicsion over a ~o~ lly degrading co...~ ..;c~tion channel. Such binary il~o....~*s~n is part~ rly amenable to transmission using "direct sequence" spread ~ecL, 2 5 modulation. With direct sequence, digital illfG"llation is spread with a spreading code whose bit rate is much higher than the il,forlllation signal itself. Although the spreading can be ~rCQmpliched by several methods, the most co~nmon is to add each bit of inform~tion (generally after a~ .iale error colle-lion 3 0 ~ ,) to a sequence of bits of the spr~ i~ code. Thus as desired for the sprP~Ai~ process, many bits are grnPr~ted for each coded information bit that is desired to be ~ e~
.~ 2IS8269 Advantages from direct sequence spread spech ul~l communication sysleùls are obtained since the receiver is knowlerlgPA~le of the sprPA~ code used to spread the user signal. As is well known in the art the ~c~;v._., after a~,u~,;ate 5 synchrorli7~*on to the ~eceive signal, is able to decode the wide ~all.lwidth spread signal using a replica of the spreA~li~ sequence.
A~lotl.~ adv~ ge of spread s~chu~l cC~ Ation sy~ s is the ability to provide multiple access capability. Specif C~PlllllAr telephone ~ommlmirAtion :iyal~u~s have been designed to 10 incûr~orate the characteristic of communicating with many remote units on the same cQm~ nir~tion channel.
One type of multiple access spreat spectrum communication ~ysLelll utilized with direct sequence spread spectrum is a code division multiple access (CDMA) commnni~A*on sy:,L~ . In a CDMA co.. ~.. ;rAtion sy:~le communication between two communication units is cQmplished by spre~ing each tral~c~ e~ signal over the frequency band of the co~ t~l;rAtion rh~nnPl with a unique user spreading code. As a result, trallc....lle~ signals are in the same 2 0 frequency band of the communication charmel and are separated only by unique user spreading codes. Particular tran~ lle(l signals are retrieved from the communication channel by desprPA~ing a signal representative of the sum of sign~lc in the ro....u...ucation charmel with a user spreading code related to the 25 particular transmitted signal which is to be retrieved from the - commurucation channel. Specially suited spreading codes may be employed to reduce the il~Le~fe,.:llce created by the sum of all the other 5ign~1c present on the same channel. OrthogonaI codes are typically used for this purpose, and of these, the Walsh codes are 3 0 most roTnmon.
Many digital cellular pleco~ irAtion ~y~le~l~s have the ability to provide reduced data rate traffic rhAnnPlc. These ~ysle~ls have traffic channels designed to o~elale at a particular data rate and also have rer~ e~l data rate kaffic rh~nrlPlc which provide more kafflc data r~rarity than that at the designed data rate. ~is il,.lcased kafflc data r~ rity in a~l~e~ed at the cost of reduced quality and/or ~l~leased co~ yity a~l~ coders and ~lero~
Thus, a need exists for a ro.. ~.. ;c~tion :,y~Le~l~ which provides increased or high data rate trafflc channels which allow for tral.c...icsion of data at a rate higher than ~e designed data rate traffic c~ lc without ~lt~ri~ .;u~.~,L l~a~lw."~ ~esi~r~c and air-; "1~ . ~a~æ spnr~rds.
Brief Des..;~tion of the D.a-vu~s FIG. 1 generally depicts, in block ~ F~m form, a prior art 15 spread s~e.~ " transmitter.
FIG. 2 generally depicts, in bloclc di~F~m form, a prior art spread s~ecl~ l transmitter for l~ ittirlg il~fG~ tion for two users.
FIG. 3 generally depicts, in block rli~ m form, a ylëLe~ed 20 emboflirn~rlt spread spectrum traI~cmitte- which ye~LGlllls timê
division multiplexing of spreading codes for two users in accordance with the invention.
FIG. 4 is a chart showing how a spreading (Walsh) code is shared ~mongct two users to provide a rate 1/2 capability for each 2 5 user in accordance with the invention.
Detailed Description of a r~eLe.,ed Embo~lim~rlt A communication sy:,Lelll time division multiplexes the use of spreading codes. The coll,l~,u~ucation ~y~lelll accepts in~rmAtion (301, 302) from at least h~ro users and codes each users il~ro~ on utilizing error co.-~.lion coders (303, 306). The coded info.l..a*on is then time mlll*plP~e~l by a mlll*rlexer (312) into *nnPslots. The ol,lyul of the mnl*plexer t312) is spread by a common sprr~ ~ (Walsh) code, srr~mhl~ with a pseudo-noise sequence, and ccl~ ed to a mo~ tor for ~ ...;qciott. In this 5 manner, i.~o,...~*on for two users may be transmitted utilizing only a single spr~iin~ (Walsh) code.
Many embo~imenb exist. In the ~refe..ed embodiment, first (USER 1) and second (USER 2) user i..ro~ tion 301, 302 is mall*~ prl in at least partially non-ove.l~y~ time pPno~s by a 10 multiplexer 312 to produce m~ll*rlexed first and second user il~o...-~*o-l The mlll*rleYerl first and sec~ user ;~.f.~ *Qn is then spread with a coInmon spr~ ~ code. In an ~lter~te emboAim~rlt, the first and seco~ user ;.. fc.. ~*~n 301, 302 may first be spread by a common spre~ling code, then mtll*pl~Ye~ into at least partially non-overlapping time periods. In either embodiment, the common spreading code is a common orthogonal spreading, and typically a Walsh code. As one of ordinary skill in the art will appreciate, the first and seco~l user ation may be coded or llnro~P-I, Any Pmhorlim~nt chosen 2 0 may be implemented in either a base-station or a mobile unit which is compatible with the spread specl~ulll corn~ lnication ~y~l~.l Referring now to FIG. 1, a prior art spread spectrum trar~cmitter is shown. In the prior art spread spe~u.l~ trar~cm~ r 2 5 of PIG. 1, USEl~ 1 data bits 100 are input to an encoder 102 at a partirlllPr bit rate ~e.g., 9.6 kbps). USER 1 data bits 100 can include either voice converted to data by a vocoder, pure data, or a rc-mh;rlation of the two types of data. F.nrnrl~r 102 convolutionally encodes the USER 1 data bits 100 into data symbols at a fixed 3 o ~ncorling rate. For example, encoder 102 ptlrorlpc ~ecei.~ed data bits 100 at a fixed ~nro~-rlg rate of one data bit to two data symbols such that the encoder 1~2 o.lL~ul~ data symbols 104 at a 19.2 ksym/s rate.
2I58~69 -~ 7 l~e encoder 102 may ~c~ orl~te the input of USER 1 data bit_ 100 at variable lower rates by e~ ~rn~ on. That L, when the data bit rate is slower than the particular bit rate at which the ~ncorler 102 is .l~ci~ to o~e,al~, Pnc~r 102 repeats USER 1 - S data bits 100 such that the USER 1 dah Wts 100 are provided the f~n~o~ g Phmentc within the ~ncorl~r 102 at the desired full rate.
For eY~mple, if the input rate were 1/2 rate, the inforrnation would be repeated twice (i.e., to 5im~ te a full rate). If the input rate were 1/4 rate, the il~ro~ nrl would be ~ four times, and so on. Thus, the encoder 102 ou~ ls data symbols 104 at a the same fixed rate regardless of the rate at which data bits 100 are input to the encoder 102.
The data symbols 104 are then input into an interleaver 106.
Tnt~rle~ver 106 interleaves the input data symbols 104. The l 5 interleaved data syrnbols 108 are uul~-li by the interleaver 106 at the same data symbol rate that they were input (e.g., 19.2 ksyrn/s) to one input of an exclusive-OR combiner 112.
A long pseudo-noise (PN) generator 110 is operatively coupled to the other input of exclusive-OR combiner 112 to 2 0 enhance the security of the cc~ ?tion .l~a~u~cl by 5~r~mhli~
data symbols 108. The long PN generator 110 uses a long PN
sequence to generate a user specific sequence of symbols or unique user code at a fixed rate equal to the data symbol rate of the data symbols 108 input to exclusiv~OR gate 112 (e.g., 19.Z ksym/s). The 2 5 scrambled data symbols 114 are output from exclusive-OR
combiner 112 at a fixed rate equal to the rate that data symbols 108 are input to the exclusive-OR combiner 112 (e.g., 19.2 ksym/s).
Scrambled data symbols 114 are then input into exclusiYe-OR
combiner 118.
3 0 A code division channel s~lec*~n generator 116 provides a particular predetermined length spreading (Walsh) code to another input of exclusive-OR combiner 118. The code division d~lulel s~lection generator 116 can provide one of 64 orthogonal ~=
.` 2158269 _ 8 codes c~ O~G~ to 64 Walsh codes from a 64 by 64 ~Ad~mArd matrix, wherein a Walsh code is a single row or column of the m~triy ~ . l,.e;v~OR comhin~r 118 uses the particular Walsh code input by the code division .l~alulel gel~ 116 to spread the input scrambled data symbols 114 into Walsh code spread data symbols 120. The Walsh code spread data symboLc 120 are oul~
from ~y~ c;v~oR combiner 118 at a fixed chip rate (e.g., 1.2288 Mchips/s).
The Walsh code spread data symbols 120 are provided to an 1 0 input of two eYcll~cive-OR comhirlers 122 and 128. A pair of short PN sequences (i.e. short when ro ~ ed to the long PN sequence used by the long PN g-..e.dlor 110) are ~ .e" l~l by I-charmel PN
generator 124 and Q-channel PN generator 130. These PN
ge~ Q~ 124 and 130 may ~,~ ...o., te the same or diLL.e.ll short 1 5 PN seq~ r~e F~ cive~oR combiners 122 and 128 further spread the input Walsh code spread data 120 with the short PN sequences generated by the PN I-channel generator 124 and PN Q-channel generator 130, respectively. The resulting I-channel code spread sequence 126 and Q-channel code spread sequence 132 are used to 2 0 bi-phase modulate a quadrature pair of sin~lcoi~ls by driving the power level controls of a the- pair of si~?lcoi~C. The sinusoid's ouL~ ci~Alc are summed, bandpass filtered, trAnclAted to an RF
~requency, amplified, filtered and radiated by an anlel.lla to complete transmission of USER 1 data bits 100 via a 2 5 communication channel.
FIG 2 shows the typical confi~uration used to Accc,~ orlAte two users. In essence, the apparatus of FIG 1 is replicated for the - second user. Each apparatus' q~lA~rAtllre oul~ut signals are combined together by combiner 134 prior to modulation and radio 3 o tr~nen~ieeion. Each user always uses a rlictinct Walsh code to spread its i~.fo~.l.ation 114. This is true even when the input data 100 rate is reduced, for example, to 4.8 kbps max. As previously mentioned, .~eLLon coding expands this data rate to an eL~e.Lve ,`~ 21S826g 9.6 kbps rate so that the Walsh code spr~i~ always results in the desired 1.2288 Mchips/s desired oult,u~. Thus, to trancmit the il.fc,.l..ation of any two users, for cx~u,~le USER 1 and USER 2, re~lUil~S the use of two (of the m~ ---. 64) Walsh codes.
S ~IG. 3 ~PnPrAlly r~epictS, in block ~ m form, a ~lere~èd embodiment spread s~ecll ù~l transmitter apparatus which ~.lru~ll s time division mlll*pl~Yirl~ of spreading codes for two users in accordance with the u,~ n The l ~a..~ . a~a~alus of PIG. 3 ill~iC~v~ s upon the prior art s~ e~hull~ tral~
10 shown in PIG. 2 when used for ~ , the i.~folll,ation of two users. As can be seen, FIG. 3 does not .~quir~ the dup~ AtiQn of trAncmitter hardware to transmit ;..fol...A*on for two users while only requiring a single spreA~lin~ (Walsh) code for .icsion of the il,[c~ Atior~
I2Ff~-,;-,~, to FIG. 3, USER 1 data bits 301 and USER 2 dah bits 302 enter respective error cûll~cLion coders 303, 306. Time division multiplexing of spreading codes is acco~,~lished by cor~ first user data 301 to prûduce coded first user data 304 and codil.g second user data 302 to produce coded secul,.i user data 307.
2 0 Coded first user data 304 and coded second user data 307 are then m~ plexed in at least partially non-overlapping time periods by multiplexer 312. The partially non-overla~il,g time periods are given by l/fc~ where fc is the frequency of a clock signal 309 input into mlll*plexer 312. The multiplexed coded first user data and 2 5 the coded second user data is then spread, by spreader 315, with a common spreading code (Wj) to create modulator data 316.
Important to note is that only a single, common orthogonal spreading (or Walsh) code is required in this implem~rltAt;Qn.
Modulator data 316 is then srrAmhled by s~r~mhler 318. In 3 0 the ~le~cl~ed embodiment, scrambler 318 scrambles modulator data 316 with a psel~o-noise s~r~mhli~ se~uence. The s~ramhl~
modulator data 319 is then collveyed to a mo~ tor where it is transmitted via a wireless il.lel~ace to a destination. In the ~ ` 2158269 ~el~e;l embo~lim~nt, the c,l~ui~ of FIG. 3 and the method f may be imrl~m~nte~l in either a ~a~e st~ion or a mobile unit ~o~ ;hle with the spread s~ o~ ication Syale--~
It is well known in the art to ay~..lu~.~e the mlll*plexingof mlll*ple data streams on an ~lt~ ting basis to the Walsh spreader. Of course, this method and synchronization illfo~ll.ation must also be known at the feceivel (i.e., the deslil~lion) to allow sllcc~csr~ ieco~ of the ;--rol---~*Qn D~
CDMA sy~l~ms have very well ~Ct~ clock signals, through 10 use of synchronization sequence and PN tracking, thus no ~itior~ 3, il,fo.~ tion is l~r~c5~ . Again, through this method, it is seen that only a single Walsh code is l~t~ er1 for the tr~ncmicsiQn of two user's i~ l.ation.
FIG. 4 shows a timing chart of how a single Walsh code, Wl, 1~ is shared for transmitting the i~ ation of two users. In alternate trarlcmicsion blocks, the il~~ tion for USER 1 and then USER 2 is repetitively transmitted in partially non-overla~ æ time periorlc given by fc-While the invention has been particularly shown and 20 described with ,ere~ .ce to a particular embori~ t~ it will be1ln~rctoo-l by those skilled in the art that various changes in form and details may be made therein without d~a~ , from the spirit and scope of the invention.
What I claim is:
MULIInEaNG T~ USE OF SPRE~DING CODES
IN.~ r~1Ur'UNr~'~nONSYS~
Field of the Llvé~lliOn The illvt~ ion relates generally to c~ .-ication ~ys~--s, and more particularly to time division multiplexing the use of 1 0 spre~i~ codes in such Cc~ ;r~*rln ayah.~ 5.
Back~lou.~d of the L.v~.lion C~o---~ ication ~ySlell1S take many forms. In general, the ~u~ose of a communication :~y:.L~I is to ~ ;t il~...ation-I,ea.il~ 5ign~1c from a source, lor~t~l at one point, to a user dea~ ;orl, located at another point some ~icPrlc~ away. A
communication system generally consists of three basic 20 CQ.~ ls; transmitter, channel, and r~eeiv~n The h.l..~...;ll~.
has the function of processing the mf~cç~ge signal into a form suitable for transmission over the channel. This ~rocêssil~ of the m~cs~ge signal is .cfe..ed to as modulation. The function of the channel is to provide a physical connection between the 25 tral~,~ l output and the receivel input. The function of the ~eceiv~. is to process the received signal so as to produce an estimate of the original message signal. This ~ cec~ g of the rèceiv~:d signal is referred to as demodulation.
Analog and digital trar~cmicsion methods are used to 3 0 transmit a message signal over a communication channel. The use of digital methods offers several c,yc~ Lonal advantages over analog methods, including but not l;~ e~ to~ eased il~ Ul ily to chalu~el noise and inlL.r~ ce, flexible o~_.ali;)n of the ~ysle..-, L ~ ~ ~ 1 5 8 2 ~ ~
commorl fonn~t for the ~ C~ c~;on of dir~.e~ll kinds of mPcc~e sigls, i,l~.o-ved sec~ily of ccs~ u~ication through the use of el,~ly~tion~ and il~s~d r~r~rity.
To l-~-L~---;l a m~cs~p signal (either analog or digital) over a 5 co~ rA*on ~ nnPl ~-vi,.~, an ~c~ci~pd cl a,u,el bandwidth, the mess~ge signal must be ~u~llated into a form suitable for PffiriPnt trarlcmission over the c~nnP1 Mo~lific~tion of the meSS~e signal is achieved by means of a process termed modulation. This process involves Vd~yil~ some par~metp~ of a 10 carrier wave in accordance with the mesS?~e signal in such a way that the s~e.hu"l of the morlnl~tefl wave matches the ~ssig~prl .1.~.1..~1 bandwidth. P~.-...et~-s of a carrier wave that can be varied include amplitude, frequency, and or phase.
Co~cs~u~lLllgly, the receiv~ is l~Uil.,d to recreate the original 15 mpscs~ge signal from a degraded version of the trarlcmitte~l signal after propagation through the c~nnPl. The re-creation is accc,ll,ylished by using a process known as rl~moc~ Qn, which is the inverse of the modulation ~rDcess used in the tral~
A spread s~e-Llulll ~y~Lèlll provides, among other things, 2 0 robllc~nPcs to jamming, good il.Lelrerel,ce and mlll*p~th rejec*Qn, and inhLlelllly secure communications from eavesdf~ . In a spread spectrum ~y~Lélll, a modulation têchnique is utilized in which a Ll.~ itted signal is spread over a wide frequency band within the communication channel. The frêquency band is much 25 wider than the minimum bandwidth required tû transmit the il~lll,ation being sent. A voice sign~l, for example, can be sent with ~mE~ e modulation (AM) in a bandwidth only twice that of the ~Ifol...~tion itself. Other forms of modulation, such as low deviation frequency modulation (FM) or single si~ nd AM, also 3 0 ~l.llit il,fol~l,ation to be trancmitte~l in a bandwidth comparable to the bandwidth of the information itself. However, in a spread s~e.hulll ayaLelll, the modulation of a signal to be trarlcmitterl often includes taking a b~ceb~n~ signal (e.g., a voice channel) with a bandwidth of only a few l~iloh~rtz, and dish;L uh~l~ the signal to be t~ e~ over a frequency band that may be many megahertz wide. This is accomplished by modulating the signal to be h~ æll with the ;~.~o~ *on to be sent and with a wideband S ~nror~ signal (c~mmorlly hlo~ l as a spr~ i~ code).
Thus, a spread s~e~l.u l. sr~le..l must have two ~,o~ ies:
(1) the hd~ æ~ balldwidth sh~ be much g~æal., than the bandwidth or rate of the ;~ro~ tion being sent and (2) some function other than the i.~,l,lation being sent is employed to 10 let~- -.i-P the resulting modulated cl,a~ulel bandwidth.
The essence of the spread s~ec~, um communication involves ~cp~i~ the l~".lwitth of a sign~ .a~.~...ill;.lg the e~ signal and l~CCsv~ the desired signal by remapping the received spread specl, u,,. into the ori~in~l i,lfo."lation 15 bandwidth. Furthermore, in the ~,ocess of c~..y,.~ out this series of bandwidth trades, the purpose of spread s~.hulll techni~ues is to allow the sy~lel" to deliver error-free il~o,ll.ation in a noisy signal e,l~i,wullent.
With digital communication, user i,lfcsl"lation such as 20 speech is encoded into sequences of binary il~ lation. This encoding is convenient for modulation and is easily error-co.,ecLon coded for tr~ncmicsion over a ~o~ lly degrading co...~ ..;c~tion channel. Such binary il~o....~*s~n is part~ rly amenable to transmission using "direct sequence" spread ~ecL, 2 5 modulation. With direct sequence, digital illfG"llation is spread with a spreading code whose bit rate is much higher than the il,forlllation signal itself. Although the spreading can be ~rCQmpliched by several methods, the most co~nmon is to add each bit of inform~tion (generally after a~ .iale error colle-lion 3 0 ~ ,) to a sequence of bits of the spr~ i~ code. Thus as desired for the sprP~Ai~ process, many bits are grnPr~ted for each coded information bit that is desired to be ~ e~
.~ 2IS8269 Advantages from direct sequence spread spech ul~l communication sysleùls are obtained since the receiver is knowlerlgPA~le of the sprPA~ code used to spread the user signal. As is well known in the art the ~c~;v._., after a~,u~,;ate 5 synchrorli7~*on to the ~eceive signal, is able to decode the wide ~all.lwidth spread signal using a replica of the spreA~li~ sequence.
A~lotl.~ adv~ ge of spread s~chu~l cC~ Ation sy~ s is the ability to provide multiple access capability. Specif C~PlllllAr telephone ~ommlmirAtion :iyal~u~s have been designed to 10 incûr~orate the characteristic of communicating with many remote units on the same cQm~ nir~tion channel.
One type of multiple access spreat spectrum communication ~ysLelll utilized with direct sequence spread spectrum is a code division multiple access (CDMA) commnni~A*on sy:,L~ . In a CDMA co.. ~.. ;rAtion sy:~le communication between two communication units is cQmplished by spre~ing each tral~c~ e~ signal over the frequency band of the co~ t~l;rAtion rh~nnPl with a unique user spreading code. As a result, trallc....lle~ signals are in the same 2 0 frequency band of the communication charmel and are separated only by unique user spreading codes. Particular tran~ lle(l signals are retrieved from the communication channel by desprPA~ing a signal representative of the sum of sign~lc in the ro....u...ucation charmel with a user spreading code related to the 25 particular transmitted signal which is to be retrieved from the - commurucation channel. Specially suited spreading codes may be employed to reduce the il~Le~fe,.:llce created by the sum of all the other 5ign~1c present on the same channel. OrthogonaI codes are typically used for this purpose, and of these, the Walsh codes are 3 0 most roTnmon.
Many digital cellular pleco~ irAtion ~y~le~l~s have the ability to provide reduced data rate traffic rhAnnPlc. These ~ysle~ls have traffic channels designed to o~elale at a particular data rate and also have rer~ e~l data rate kaffic rh~nrlPlc which provide more kafflc data r~rarity than that at the designed data rate. ~is il,.lcased kafflc data r~ rity in a~l~e~ed at the cost of reduced quality and/or ~l~leased co~ yity a~l~ coders and ~lero~
Thus, a need exists for a ro.. ~.. ;c~tion :,y~Le~l~ which provides increased or high data rate trafflc channels which allow for tral.c...icsion of data at a rate higher than ~e designed data rate traffic c~ lc without ~lt~ri~ .;u~.~,L l~a~lw."~ ~esi~r~c and air-; "1~ . ~a~æ spnr~rds.
Brief Des..;~tion of the D.a-vu~s FIG. 1 generally depicts, in block ~ F~m form, a prior art 15 spread s~e.~ " transmitter.
FIG. 2 generally depicts, in bloclc di~F~m form, a prior art spread s~ecl~ l transmitter for l~ ittirlg il~fG~ tion for two users.
FIG. 3 generally depicts, in block rli~ m form, a ylëLe~ed 20 emboflirn~rlt spread spectrum traI~cmitte- which ye~LGlllls timê
division multiplexing of spreading codes for two users in accordance with the invention.
FIG. 4 is a chart showing how a spreading (Walsh) code is shared ~mongct two users to provide a rate 1/2 capability for each 2 5 user in accordance with the invention.
Detailed Description of a r~eLe.,ed Embo~lim~rlt A communication sy:,Lelll time division multiplexes the use of spreading codes. The coll,l~,u~ucation ~y~lelll accepts in~rmAtion (301, 302) from at least h~ro users and codes each users il~ro~ on utilizing error co.-~.lion coders (303, 306). The coded info.l..a*on is then time mlll*plP~e~l by a mlll*rlexer (312) into *nnPslots. The ol,lyul of the mnl*plexer t312) is spread by a common sprr~ ~ (Walsh) code, srr~mhl~ with a pseudo-noise sequence, and ccl~ ed to a mo~ tor for ~ ...;qciott. In this 5 manner, i.~o,...~*on for two users may be transmitted utilizing only a single spr~iin~ (Walsh) code.
Many embo~imenb exist. In the ~refe..ed embodiment, first (USER 1) and second (USER 2) user i..ro~ tion 301, 302 is mall*~ prl in at least partially non-ove.l~y~ time pPno~s by a 10 multiplexer 312 to produce m~ll*rlexed first and second user il~o...-~*o-l The mlll*rleYerl first and sec~ user ;~.f.~ *Qn is then spread with a coInmon spr~ ~ code. In an ~lter~te emboAim~rlt, the first and seco~ user ;.. fc.. ~*~n 301, 302 may first be spread by a common spre~ling code, then mtll*pl~Ye~ into at least partially non-overlapping time periods. In either embodiment, the common spreading code is a common orthogonal spreading, and typically a Walsh code. As one of ordinary skill in the art will appreciate, the first and seco~l user ation may be coded or llnro~P-I, Any Pmhorlim~nt chosen 2 0 may be implemented in either a base-station or a mobile unit which is compatible with the spread specl~ulll corn~ lnication ~y~l~.l Referring now to FIG. 1, a prior art spread spectrum trar~cmitter is shown. In the prior art spread spe~u.l~ trar~cm~ r 2 5 of PIG. 1, USEl~ 1 data bits 100 are input to an encoder 102 at a partirlllPr bit rate ~e.g., 9.6 kbps). USER 1 data bits 100 can include either voice converted to data by a vocoder, pure data, or a rc-mh;rlation of the two types of data. F.nrnrl~r 102 convolutionally encodes the USER 1 data bits 100 into data symbols at a fixed 3 o ~ncorling rate. For example, encoder 102 ptlrorlpc ~ecei.~ed data bits 100 at a fixed ~nro~-rlg rate of one data bit to two data symbols such that the encoder 1~2 o.lL~ul~ data symbols 104 at a 19.2 ksym/s rate.
2I58~69 -~ 7 l~e encoder 102 may ~c~ orl~te the input of USER 1 data bit_ 100 at variable lower rates by e~ ~rn~ on. That L, when the data bit rate is slower than the particular bit rate at which the ~ncorler 102 is .l~ci~ to o~e,al~, Pnc~r 102 repeats USER 1 - S data bits 100 such that the USER 1 dah Wts 100 are provided the f~n~o~ g Phmentc within the ~ncorl~r 102 at the desired full rate.
For eY~mple, if the input rate were 1/2 rate, the inforrnation would be repeated twice (i.e., to 5im~ te a full rate). If the input rate were 1/4 rate, the il~ro~ nrl would be ~ four times, and so on. Thus, the encoder 102 ou~ ls data symbols 104 at a the same fixed rate regardless of the rate at which data bits 100 are input to the encoder 102.
The data symbols 104 are then input into an interleaver 106.
Tnt~rle~ver 106 interleaves the input data symbols 104. The l 5 interleaved data syrnbols 108 are uul~-li by the interleaver 106 at the same data symbol rate that they were input (e.g., 19.2 ksyrn/s) to one input of an exclusive-OR combiner 112.
A long pseudo-noise (PN) generator 110 is operatively coupled to the other input of exclusive-OR combiner 112 to 2 0 enhance the security of the cc~ ?tion .l~a~u~cl by 5~r~mhli~
data symbols 108. The long PN generator 110 uses a long PN
sequence to generate a user specific sequence of symbols or unique user code at a fixed rate equal to the data symbol rate of the data symbols 108 input to exclusiv~OR gate 112 (e.g., 19.Z ksym/s). The 2 5 scrambled data symbols 114 are output from exclusive-OR
combiner 112 at a fixed rate equal to the rate that data symbols 108 are input to the exclusive-OR combiner 112 (e.g., 19.2 ksym/s).
Scrambled data symbols 114 are then input into exclusiYe-OR
combiner 118.
3 0 A code division channel s~lec*~n generator 116 provides a particular predetermined length spreading (Walsh) code to another input of exclusive-OR combiner 118. The code division d~lulel s~lection generator 116 can provide one of 64 orthogonal ~=
.` 2158269 _ 8 codes c~ O~G~ to 64 Walsh codes from a 64 by 64 ~Ad~mArd matrix, wherein a Walsh code is a single row or column of the m~triy ~ . l,.e;v~OR comhin~r 118 uses the particular Walsh code input by the code division .l~alulel gel~ 116 to spread the input scrambled data symbols 114 into Walsh code spread data symbols 120. The Walsh code spread data symboLc 120 are oul~
from ~y~ c;v~oR combiner 118 at a fixed chip rate (e.g., 1.2288 Mchips/s).
The Walsh code spread data symbols 120 are provided to an 1 0 input of two eYcll~cive-OR comhirlers 122 and 128. A pair of short PN sequences (i.e. short when ro ~ ed to the long PN sequence used by the long PN g-..e.dlor 110) are ~ .e" l~l by I-charmel PN
generator 124 and Q-channel PN generator 130. These PN
ge~ Q~ 124 and 130 may ~,~ ...o., te the same or diLL.e.ll short 1 5 PN seq~ r~e F~ cive~oR combiners 122 and 128 further spread the input Walsh code spread data 120 with the short PN sequences generated by the PN I-channel generator 124 and PN Q-channel generator 130, respectively. The resulting I-channel code spread sequence 126 and Q-channel code spread sequence 132 are used to 2 0 bi-phase modulate a quadrature pair of sin~lcoi~ls by driving the power level controls of a the- pair of si~?lcoi~C. The sinusoid's ouL~ ci~Alc are summed, bandpass filtered, trAnclAted to an RF
~requency, amplified, filtered and radiated by an anlel.lla to complete transmission of USER 1 data bits 100 via a 2 5 communication channel.
FIG 2 shows the typical confi~uration used to Accc,~ orlAte two users. In essence, the apparatus of FIG 1 is replicated for the - second user. Each apparatus' q~lA~rAtllre oul~ut signals are combined together by combiner 134 prior to modulation and radio 3 o tr~nen~ieeion. Each user always uses a rlictinct Walsh code to spread its i~.fo~.l.ation 114. This is true even when the input data 100 rate is reduced, for example, to 4.8 kbps max. As previously mentioned, .~eLLon coding expands this data rate to an eL~e.Lve ,`~ 21S826g 9.6 kbps rate so that the Walsh code spr~i~ always results in the desired 1.2288 Mchips/s desired oult,u~. Thus, to trancmit the il.fc,.l..ation of any two users, for cx~u,~le USER 1 and USER 2, re~lUil~S the use of two (of the m~ ---. 64) Walsh codes.
S ~IG. 3 ~PnPrAlly r~epictS, in block ~ m form, a ~lere~èd embodiment spread s~ecll ù~l transmitter apparatus which ~.lru~ll s time division mlll*pl~Yirl~ of spreading codes for two users in accordance with the u,~ n The l ~a..~ . a~a~alus of PIG. 3 ill~iC~v~ s upon the prior art s~ e~hull~ tral~
10 shown in PIG. 2 when used for ~ , the i.~folll,ation of two users. As can be seen, FIG. 3 does not .~quir~ the dup~ AtiQn of trAncmitter hardware to transmit ;..fol...A*on for two users while only requiring a single spreA~lin~ (Walsh) code for .icsion of the il,[c~ Atior~
I2Ff~-,;-,~, to FIG. 3, USER 1 data bits 301 and USER 2 dah bits 302 enter respective error cûll~cLion coders 303, 306. Time division multiplexing of spreading codes is acco~,~lished by cor~ first user data 301 to prûduce coded first user data 304 and codil.g second user data 302 to produce coded secul,.i user data 307.
2 0 Coded first user data 304 and coded second user data 307 are then m~ plexed in at least partially non-overlapping time periods by multiplexer 312. The partially non-overla~il,g time periods are given by l/fc~ where fc is the frequency of a clock signal 309 input into mlll*plexer 312. The multiplexed coded first user data and 2 5 the coded second user data is then spread, by spreader 315, with a common spreading code (Wj) to create modulator data 316.
Important to note is that only a single, common orthogonal spreading (or Walsh) code is required in this implem~rltAt;Qn.
Modulator data 316 is then srrAmhled by s~r~mhler 318. In 3 0 the ~le~cl~ed embodiment, scrambler 318 scrambles modulator data 316 with a psel~o-noise s~r~mhli~ se~uence. The s~ramhl~
modulator data 319 is then collveyed to a mo~ tor where it is transmitted via a wireless il.lel~ace to a destination. In the ~ ` 2158269 ~el~e;l embo~lim~nt, the c,l~ui~ of FIG. 3 and the method f may be imrl~m~nte~l in either a ~a~e st~ion or a mobile unit ~o~ ;hle with the spread s~ o~ ication Syale--~
It is well known in the art to ay~..lu~.~e the mlll*plexingof mlll*ple data streams on an ~lt~ ting basis to the Walsh spreader. Of course, this method and synchronization illfo~ll.ation must also be known at the feceivel (i.e., the deslil~lion) to allow sllcc~csr~ ieco~ of the ;--rol---~*Qn D~
CDMA sy~l~ms have very well ~Ct~ clock signals, through 10 use of synchronization sequence and PN tracking, thus no ~itior~ 3, il,fo.~ tion is l~r~c5~ . Again, through this method, it is seen that only a single Walsh code is l~t~ er1 for the tr~ncmicsiQn of two user's i~ l.ation.
FIG. 4 shows a timing chart of how a single Walsh code, Wl, 1~ is shared for transmitting the i~ ation of two users. In alternate trarlcmicsion blocks, the il~~ tion for USER 1 and then USER 2 is repetitively transmitted in partially non-overla~ æ time periorlc given by fc-While the invention has been particularly shown and 20 described with ,ere~ .ce to a particular embori~ t~ it will be1ln~rctoo-l by those skilled in the art that various changes in form and details may be made therein without d~a~ , from the spirit and scope of the invention.
What I claim is:
Claims (10)
1. A method of time division multiplexing the use of spreading codes in a spread spectrum communication system, the method comprising the steps of:
time division multiplexing first and second user information in at least partially non-overlapping time periods to produce multiplexed first and second user information; and spreading the multiplexed first and second user information with a common spreading code.
time division multiplexing first and second user information in at least partially non-overlapping time periods to produce multiplexed first and second user information; and spreading the multiplexed first and second user information with a common spreading code.
2. The method of claim 1 wherein the common spreading code is a common orthogonal spreading code.
3. A method of time division multiplexing the use of spreading codes in a spread spectrum communication system, the method comprising the steps of:
coding first user data to produce coded first user data;
coding second user data to produce coded second user data;
multiplexing the coded first user data and the coded second user data in at least partially non-overlapping time periods to produce multiplexed coded first user data and the coded second user data; and spreading the multiplexed coded first user data and the coded second user data with a common spreading code to create modulator data.
coding first user data to produce coded first user data;
coding second user data to produce coded second user data;
multiplexing the coded first user data and the coded second user data in at least partially non-overlapping time periods to produce multiplexed coded first user data and the coded second user data; and spreading the multiplexed coded first user data and the coded second user data with a common spreading code to create modulator data.
4. The method of claim 3 further comprising the steps of:
scrambling the modulator data with a pseudo-noise scrambling sequence; and transmitting the scrambled modulator data via a wireless interface to a destination.
scrambling the modulator data with a pseudo-noise scrambling sequence; and transmitting the scrambled modulator data via a wireless interface to a destination.
5. The method of claim 3 wherein the method is implemented in either a base-station or a mobile unit compatible with the spread spectrum communication system.
6. An apparatus for time division multiplexing the use of spreading codes in a spread spectrum communication system; the apparatus comprising:
means for time division multiplexing first and second user information in at least partially non-overlapping time periods to produce multiplexed first and second user information; and means, coupled to the means for time division multiplexing, for spreading the multiplexed first and second user information with a common spreading code.
means for time division multiplexing first and second user information in at least partially non-overlapping time periods to produce multiplexed first and second user information; and means, coupled to the means for time division multiplexing, for spreading the multiplexed first and second user information with a common spreading code.
7. The apparatus of claim 6 wherein the common spreading code is a Walsh code.
8. The apparatus of claim 6 wherein the apparatus is implemented in either a radio compatible with the spread spectrum communication system.
9. An apparatus for time division multiplexing the use of spreading codes in a spread spectrum communication system, the apparatus comprising:
a first coder for coding the first user data to produce coded first user data;
a second coder for coding second user data to produce coded second user data;
a multiplexer, coupled to the first and second coders, for multiplexing the coded first user data and the coded second user data in at least partially non-overlapping time periods to produce multiplexed coded first user data and the coded second user data;
a spreader, coupled to the multiplexer, for spreading the multiplexed coded first user data and the coded second user data with a common spreading code to create modulator data.
a first coder for coding the first user data to produce coded first user data;
a second coder for coding second user data to produce coded second user data;
a multiplexer, coupled to the first and second coders, for multiplexing the coded first user data and the coded second user data in at least partially non-overlapping time periods to produce multiplexed coded first user data and the coded second user data;
a spreader, coupled to the multiplexer, for spreading the multiplexed coded first user data and the coded second user data with a common spreading code to create modulator data.
10. The apparatus of claim 9 further comprising:
a scrambler for scrambling the modulator data with a pseudo-noise scrambling sequence; and an amplifier for transmitting the scrambled modulator data via a wireless interface to a destination.
a scrambler for scrambling the modulator data with a pseudo-noise scrambling sequence; and an amplifier for transmitting the scrambled modulator data via a wireless interface to a destination.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US20159694A | 1994-02-25 | 1994-02-25 | |
| US08/201,596 | 1994-02-25 |
Publications (1)
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| CA2158269A1 true CA2158269A1 (en) | 1995-08-31 |
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| CA002158269A Abandoned CA2158269A1 (en) | 1994-02-25 | 1995-01-09 | Method and apparatus for time division multiplexing the use of spreading codes in a communication system |
Country Status (4)
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| EP (1) | EP0700612A4 (en) |
| JP (1) | JPH08509590A (en) |
| CA (1) | CA2158269A1 (en) |
| WO (1) | WO1995023464A1 (en) |
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| ZA965340B (en) | 1995-06-30 | 1997-01-27 | Interdigital Tech Corp | Code division multiple access (cdma) communication system |
| US5930230A (en) * | 1996-05-28 | 1999-07-27 | Qualcomm Incorporated | High data rate CDMA wireless communication system |
| US5926500A (en) * | 1996-05-28 | 1999-07-20 | Qualcomm Incorporated | Reduced peak-to-average transmit power high data rate CDMA wireless communication system |
| US6678311B2 (en) | 1996-05-28 | 2004-01-13 | Qualcomm Incorporated | High data CDMA wireless communication system using variable sized channel codes |
| JP3409628B2 (en) * | 1996-06-19 | 2003-05-26 | 株式会社エヌ・ティ・ティ・ドコモ | CDMA communication method and group spread modulator |
| FR2750281B1 (en) * | 1996-06-19 | 1998-07-31 | Alcatel Espace | INTERFACE UNIT FOR MOBILE RADIO COMMUNICATIONS NETWORK |
| GB2320661B (en) * | 1996-12-20 | 2001-10-03 | Dsc Telecom Lp | Processing data transmitted and received over a wireless link connecting a central terminal and a subscriber terminal of a wireless telecommunications system |
| US6044103A (en) * | 1997-06-17 | 2000-03-28 | Qualcomm Inc. | Reduced peak-to-average amplitude dual channel link |
| EP0903871B1 (en) * | 1997-08-18 | 2004-06-30 | Samsung Electronics Co., Ltd. | Spread spectrum signal generating device and method |
| KR100369794B1 (en) * | 1997-08-18 | 2003-04-11 | 삼성전자 주식회사 | Apparatus and method for generating spread signal of transmitter of mobile communication system |
| KR100299148B1 (en) | 1998-03-14 | 2001-09-26 | 윤종용 | Apparatus and method for intermixing messages having different frame length and communicating in cdma communication system |
| DE19827701A1 (en) * | 1998-06-22 | 2000-01-05 | Siemens Ag | Method for the digital radio transmission of data from several participants |
| FI106896B (en) * | 1998-07-22 | 2001-04-30 | Nokia Networks Oy | Communication method, radio network subsystem and subscriber terminal |
| DE69832878T2 (en) * | 1998-10-05 | 2006-08-03 | Lucent Technologies Inc. | CDMA communication system and method |
| EP1001567A1 (en) * | 1998-11-13 | 2000-05-17 | TELEFONAKTIEBOLAGET LM ERICSSON (publ) | Combiner |
| EP1011281A3 (en) | 1998-12-18 | 2000-07-05 | TELEFONAKTIEBOLAGET L M ERICSSON (publ) | Flexible CDMA combiner |
| EP1039661A1 (en) * | 1999-03-03 | 2000-09-27 | Sony International (Europe) GmbH | Multicast channel for a CDMA system |
| CN1241450C (en) * | 2000-06-05 | 2006-02-08 | 连宇通信有限公司 | Method for assigning radio resources |
| EP1303997A4 (en) * | 2000-06-05 | 2004-04-28 | Linkair Comm Inc | A method for the air interface to support variable data rate |
| US7907574B2 (en) | 2004-01-29 | 2011-03-15 | Qualcomm Incorporated | Channel scheduling |
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| US4455651A (en) * | 1980-10-20 | 1984-06-19 | Equatorial Communications Company | Satellite communications system and apparatus |
| US5103459B1 (en) * | 1990-06-25 | 1999-07-06 | Qualcomm Inc | System and method for generating signal waveforms in a cdma cellular telephone system |
| US5239540A (en) * | 1990-11-27 | 1993-08-24 | Scientific-Atlanta, Inc. | Method and apparatus for transmitting, receiving and communicating digital data signals with corresponding program data signals which describe the digital data signals |
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- 1995-01-09 WO PCT/US1995/000233 patent/WO1995023464A1/en not_active Application Discontinuation
- 1995-01-09 EP EP95907342A patent/EP0700612A4/en not_active Withdrawn
- 1995-01-09 JP JP7522332A patent/JPH08509590A/en active Pending
- 1995-01-09 CA CA002158269A patent/CA2158269A1/en not_active Abandoned
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| WO1995023464A1 (en) | 1995-08-31 |
| EP0700612A4 (en) | 1998-09-30 |
| JPH08509590A (en) | 1996-10-08 |
| EP0700612A1 (en) | 1996-03-13 |
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