CA2077343C

CA2077343C - Method and apparatus for providing high data rate traffic channels in a spread spectrum communication system

Info

Publication number: CA2077343C
Application number: CA002077343A
Authority: CA
Inventors: Eugene J. Bruckert; Vedat Eyuboglu; David D. Falconer
Original assignee: Motorola Inc
Current assignee: Motorola Mobility LLC
Priority date: 1991-03-13
Filing date: 1992-02-13
Publication date: 1998-08-18
Anticipated expiration: 2012-02-13
Also published as: CA2077343A1; IL101044A; EP0529051A1; EP0529051B1; KR960000460B1; DE69230710D1; WO1992017011A1; JPH05506763A; EP0529051A4; JP2632596B2; IL101044A0; US5204876A; DE69230710T2

Abstract

A method and apparatus is provided for transmitting spread spectrum signals. The transmitter receives data bits (200) at a particular rate. Subsequently, the transmitter encodes (202) the received data bits (200) at a predetermined encoding rate into data symbols (204).
Subsequently, the transmitter derives (210) predetermined length orthogonal codes (212) from the data symbols (208). The transmitter accommodates variable received data bit rates by setting the predetermined encoding rate and the predetermined orthogonal code length in response to the received data bit rate. Subsequently, the transmitter spreads (216) the derived orthogonal codes (212) with a user PN spreading code (214).
An alternative method and apparatus is provided for transmitting spread spectrum signals. The transmitter receives data bits (230) at a particular rate. Subsequently, the transmitter encodes (232) the received data bits (230) at a predetermined encoding rate into data symbols (234). Subsequently, the transmitter determines (248) a particular channel to transmit the data symbols (244) by spreading (248) the data symbols (244) with a predetermined length orthogonal code (246). The transmitter accommodates variable received data bit rates by setting the predetermined encoding rate and the predetermined orthogonal code length in response to the received data bit rate.

Description

._ IJETHOD AND APPARATUS FOR PROVIDING HIGH DATA
RATE TRAFFIC CHANNELS IN A SPREAD SPECTRUI'JI
COMMUNICATION SYSTEUI

Field of the Inverl~ion The pr~sent invention relates to communication systems which employ spread-spectrum signals and, more particularly to a method 10 and apparatus for providing high data rate tramc channels in a sprdad spectrum communication system.

Background of the InventiGn Communication systems take many torms. In general, the purpose of a communication system is to transmit information-bea,ing signals from a source, lo~l at one point to a user de~ti"dtion l~t~
at ~.~)otl,er point some di~lance away. A communication system generally consists of three basic co-"ponents: transmitter channel and 20 r~ceiver. The l-dns",itler has the function of processing the message signal into a form suitable for trans",ission over the channel. This p,ucescing of the n,essaga signal is ~e~"~ to as modu'~tion. The function of the channel is to provide a physical conne- tion between the trans."itler output and the recGiver input. The function of the r~iver is 25 to pl~cess the received signal so as to produce an e:,ti,n~te of the 2~77~ 3 _ -2-original ~,-es~ signal. This processing of the recGived signal is refe..~ to as de.--c..hJ'--ion.
- Two types of two-way communication channels exist, namely, point-to-point ehannals and point-to-multipoint channels. Examples of 6 point-to-point channels include wirelines (e.g., local telephone lranslll;ssion), microwave links, and optical fibers. In co,lt,~sl, point-to-multipoint channels provide a capability where many receivin~ ~lations may be reacheJ simultaneously from a sin~le transmitter (e.g. cellular radio telephone communication syste."s). These point-to-mulli,~oinl 10 systems are also ter,--ed Multiple Access Systems (MAS).
Analo~ and di~ital trans---;ssion ,.-etl.Gds are used to transmit a ",esseg~ signal over a communication channel . The use of di~ital nl~ttlG~ls offers -~over~l opGr~lionat advantages over anatog ~--eti-GJs, inctuding but not limited to: increaseJ immunity to channel noise and 1 5 i- ,terferdnce, ftexible operatio" of the system, CG~ 1 ,Gn format for the trans..-;ssion of dift~rent kinds of llles~B si~anal5, illlpru~od security of communication through the use of encryption, and inclease.l u~c-;ty.
These advantages are attained at the cost of ;ncreased system compîexity. However, through the use of very lar~ scale i-~t~rdtiGn 20 (VLSI) technology, a cost-effective way of building the hardware has been dev~loped To l~ns,.,il a ",ess~ge signal (either analo~ or digital) over a bandp~ss communication channel, the message signal must be man;~u'~ted into a form suitable for efficient l,a.~s" ssion over the 25 channel. Modification of the message signal is achieved by means of p,~cess ter",~ modu~tion. This pr~cess involves varying some pard,--v~er of a carrier wave in acco,clance with the ",ess~e signal in such a way that the spectrum of the modu~e~ wave ."d~hes the assiyned channel bandwidth. Corlespofi~ingly, the receiver is required 30 to re-create the original message signal from a d~r~led ve.~ion of the transmitted signal after pn,p~g~1iGn through the channel. The re-c~ea~ion is acco",plished by using a process known as demodu'~-ion, which is the inverse of the modu~tion prûcess used in the l,~.ns",itler.
In aJdilion to providing efficient lr~"sn, ssion, there are other 35 leasons for performing modul- ion. In particular, the use of modu'--ion permits multiplexing, that is, the simultaneous trans",ission of signals from several "~ess~e sources over a common channel. Also, - 2077~3 mo~u'-~ion may be used to convert the ",essa~a signal into a form less su~ptible to noise and i,lte~fer~nce.
For mult plexed communication systems, the system typically consists of many remote units (i.e. subscriber units) which require active 5 ~elvice over a communic~tiG. ohannel for a short or discrete intervals of time rather than continuous service on a communication channel at all times. Tharefore communication systems have been desi~ne.J to in~",orate the char~o.istic of communicating with many remote units for brief intervals of time on the same communication cl,annel. These 10 systems are ter",ed multiple Ac~ess communication systems.
One type of multiple A~cess communication system is a spread spectrum sys~e.". In a spread spectrum system a mo~u'~t-on technique iS U~il;79~ in which a trans",;lted signal is spread over a wide frelu~n~
band within the communication channel. The frequency band is wider 15 than the minimum bandwidth required to II'dnS~ the info""alion being sent. A voice signal, for example, can be sent with amplitude mod~ on (AM) in a bandwidth only twice that of the info""ation itself.
Other forms of modul~tion such as low deviation frequency mod~ ;Qn (FM ) or single siJeL~nd AM also pemmit inlor",dt;on to be t~..ns",iUecl in a bandwidth col"pal~le to the bandwidth of the ;nfor",dtion itself.
However in a sprb~l spectrum system the mod~ tion of a signal to be trans",ill~ often includes taking a lA-sebend signal (e.g. a voice channel) with a bandwidth of only a few kilohe.k, and distributing the signal to be lm.)s",;lteJ over a fr~uency band that may be many megahertz wide. This is accoi"plished by modu'-'ing the signal to be l,lns",itled with the infol",dtion to be sent and with a wiJebar,d oncoJing signal.
Three general types of spread spectrum communication techniques exist including:
The modu~-~ion of a carrier by a digital code sequence whose bit rate is much higher than the infor",~tion signal bandwidth. Such systems are refer,~l to as ~direct sequence~ modu~-'~ systems.

Carrier frequency shilling in discrete increments in a p~tler"
dictated by a code sequence. These systems are called ~frequency hoppers.~ The transn,iller jumps from frequen-:y to frequency within some predete,n,;n6d set; the order of frequency usage is determined by a code sequence. Similarly ~time hopping# and ~time-frequency hoppin~' have times of t,ans",- si~n which are regulated by a code sequence.

Pulse-FM or ~chirp- mo~u'~Yon in which a carrier is swept over a wide band during a given pulse interval.

Infor",ation (i.e. the ",ess~e signal) can be o.,-~ in the spectnum signal by several n,etl,c~. One ",etl~l is to add the infor",dtion to the spreading code before it is used for spre~Jing modulation. This technique can be used in direct sequence and frequency howing systems. It will be noted that the info""dtion being sent must be in a digital forrn prior to addin~ it to the spr~ding code because the cG"~bination of the sp,esJing code, typically a binary code, involves modulo-2 s~hlition. Altematively, the ;nfor",dtion or message signal may be used to mo~ {e a carrier before spreading it.
Thus a spre6 J spectrum system must have two prup~. ties: (1 ) the trans,nitlecl bandwidth should be much ~r~at~r than the bandwidth or rate of the info""dtion being sent and (2) some function other than the infor",ation being sent is employed to cleter",ine the resulting mod~ ts~ channel bandwidth.
The esoence ot the spre~l spectrum communication involves the art of expanding the bandwidth of a signal, ln~.ns",;tling the expanded signal and recovering the desired signal by r~ ."apping the l~ceiv~J
:,pre~J spectrum into the original infon,,atiûn bandwidth. Fu,ll,er"~ore in the p,ocess of carrying out this series of bandwidth trades the purpose of sprea ~ spectrum techniques is to allow the system to deliver error-free info""ation in a noisy signal envi-~n",E.)t.
Spread spectrum communication systems can be multiple ~ess communication systems. One type of multiple ~ess s~r~ spectrum system is a code ~ ision multiple ~ss (ÇDMA) system. In a CDMA
system, communication between two communication units is accomplished by spr~6~i, 9 each transmitted signal over the frequency band of the communication channel with a unique user spreading code.
As a result transmmed signals are in the same frequency band of the communication channel and are separated only by unique user spre~ing codes. Particular l,~ns"~itled siyn~ls are retrieved from the -5- ~ n ~ 7 3 ~ 3 ~
',=.,, communication channel by ~Jespre~ing a signal r~presenl~ e of the sum of si~nals in the communication channel with a user spreadin~
code r~lal~l to the particular trans-.-itleJ signal which is to be retrieved trom the communication ~nnel. A CDMA system may use direct 5 sequence or frequency hoppin~ spres~ling techniques.
Many di~ital cellular telecG"--"unication systems have the ability to provide redu~ data rate traffic channek. These systems have traffic channels desi~ned to operate a particular da~ rate and also have re~uced data rate traffic channels which p~vide more traffic data 10 G~ than that at the ~Je~n~ data rate. This in~ase~l traffic data ~ity in achieved at the cost of redu~ quality and/or ;n~dase~
complexity speech coders and ~lec~ers. However in spre~d spectrum communication sy~te.l,s there is also a need for systems which pro~iJa in~dased or high data rate traffic channels which allow the ~,dns.., ssion 15 of data at a rate higher than the Jesi~ned data rate traffic channels.

Summary of the Invention A method and apparatus is provided for transmitting spread spectrum 20 signals. The l.a~a".ill~r rt:ceives data bits input thereto at a particular rate.
- Subsequently the transmitter encodes the input data bits at a pr6dete."lined encoding rate into data sy.-~bols. ~SIubse~luently, the transmitter derives pr~eter..lined length ~J.lho~on~l codes from the datasy--~l~ols. Thetransmittera~---.)~ svariable inputdatabit 25 rates by settin~ the pr~te....in~ encodin~ rate and the predetermined ~l~ol al code length in rdspo.~se to the input data bit rate.
~Jbse~uently, the tr~ns-.-itler spreads the derived o,ll-~onal codes with a user PN spr~aJing code.
An ~e."~i~e ",etl,~J and apparatus is p.~ided for l,a,)sn~ilti.-g 30 spre~ spectrum si,an~s. The l-d-,sl"itler r~,es data bits input thereto at a particular rate. Subse~llJently, the l-ans",;tl&r encodes the input data bits at a pr~eter",ined encocling rate into data symbols. Su~se~uently the transmitter d~en"ines a particular channel to tr~ns,nil the data sy.nbols by spreading the data symbols with a preJet&r nined length 35 G.ll,~onal code. The transmitter accel"l"c~ es variable input data bit rates by setting the pr~Jetermined encoJin~ rate and the -6- 2 0 7 7 ~ 4 3 predel~r"lined G,ll)o~onal code length in res,oonse to the input data bit rate.
Briet Desc~i~ffion of the Drawin~s FIG. 1 is a diagram sl ,~vr.~ a prior a t spre~d spectnJm Ir~.~sll)i~l~r.
FIG. 2 is a diagram showing an alternathe prior art spre~d spectrum transmffler.
FIG. 3 is a diagram showing an preferred elllboJ;,--enl spre~d spectrum transmitter.
FIG. 4 is a ~;ay.~-. showin~ an alternative preferred e"~li",enl spread spectrum transmffler.

Detailed DGS~;~ tion Rebrring now to flG. 1, a prior art spn~a~ spectrum l~ans---itl~r, as p~ tially Jes~il~ in ~On the System Design ~c~c of Code Division Multiple Access (CDMA) Applied to Digital Cellular and 20 r~.;.on~l Communication Networks~, Allen Salmasi and Klein S.
Gilhousen, pr~s~nt~J at the 41 ~t IFFF Vehicup~ Technol~y ~'~nference on May 19-22, 1991 in St. Louis, MO, pages 57-62, is shown. In the prior art sple~J spectrum ~ r, traffic ~annel data - bits 100 are input to an e~er 102 at a particular bit rate (e.g., 9.6 kbit/s). The tramc channel data bits can include either voice converted to data by a voc~er, pure data, or a combination of the two types of data Cnco~ier 102 convolutionally G.-c~es the input data bits 100 into data sy.-lbols at a fixed onc~lin~ rate. For example, encodu 102 onc~Jes receive_l data bits 100 at a ffxed enc~;n~ rate of one data bit to three data sy"~l,ols such that the encG Jer 102 outrlnS data sy.nbols 104 at a 28.8 ksym/s rate. The encoder 102 a~G"""~es the input of data bits 100 at variable rates by encoding repetition. That is, when the data bit rate is slower than the particular bit rate at which the Gncoder 102 is ~Jesi~ned to oper~te, then the encoder 102 repea~ the input data bits 100 such that the input data bits 100 are provided to the oncod;ng elements within the encoder 102 at the equivalent of the input data bit rate at which the encG lin~ elements are designed to operdte. Thus, the r -20773~3 encoder 102 outputs data symbols 104 at the same fixed rate regardless of the rate at which data bits 100 are input to the encoder 102.
The data s~ bols 104 are then input into an i"tGrledver 106.
Interleaver 106 block interleaves the input data sy."bGls 104. In the interleaver 106, the data sy.-lbols are input column by column into a matrix and output from the matrix row by row. The inte, led~ed data sy."t~ls 108 are output by the interleaver 106 at the same data symbol rate that they were input (e.g., 28.8 ksym/s).
The inte,le~ed data symbols 108 are then input to a modu'~or 110. The modu'~Qr 110 derives a sequence of fixed length Walsh codes 112 (e.g., 64-ary G- IhGyOnal codes) from the inte. Ied/ed data sy,n~ls 108. In 64-ary G,ll,o~onal code signalling, the interleaved data s~llbGls 108 are grouped into sets of six to select one out of the 64 C,ll,G~onal codes to r~pr~~Gnl the set of six data sy"lbols. These 64 Gltllo9onal codes conespol,J to Walsh codes from a 64 by 64 Hadamard matrix wherein a Walsh code is a single row or column of the matrix. The modu~tor 1 10 o~ Itputs a se~l~J6.xe of Walsh codes 112 which cor,esponcl to the input data sy",bols 108 at a fixed symbol rate (e.g., 307.2 ksym/s) to one input of an exclusive-OR combiner 116.
A long pse~ldo-noise (PN) generator 114 is op&rdti~ely coupled to the other input of the exclusive-OR co"lbiner 116 to provide a sprd~.ling sequence to the exclusive-OR combiner 116. The long PN
generator 114 uses a long PN se(~u~nce to generate a user specific sequence of symbols or unique user spre~Jing code at a fixed chip rate (e.g., 1.228 Mchp/s). In a~lition to providing an identification as to which user sent the trafRc channel data bits 100 over the communication channal, the unique user code enhances the security of the communication in the communication channel by scrambling the traffic channel data bits 100. Fxcl~Jsive-OR combiner 116 uses the unique user code input by long PN ~enerator 1 14 to s~r~l the input Walsh coded data symbols 112 into user code spre~J data symbols 118. The user code spreacJ data symbols 118 are output~rom the exclusive-OR
combiner 116 at a fixed chip rate (e.g., 1.2288 Mchp/s).
The user code spre~ data symbols 118 are provided to an input of two exclusive-OR combiners 120 and 126, r~spe.. 1i~ely. A pair of short PN sequences (i.e. short when co"~pared to the long PN sequence used by the long PN generator 114) are generated by l-channel PN

20773~3 generator 122 and Q-channel PN ~en~r~or 128. These PN ~enerators 122 and 128 may ~on~r~te the same or different short PN ss~luences.
The exclusive-OR combiners 120 and 126 further spreaJ the input user code spr~ad data 114 with the short PN sequences ~on6,at~J by the PN l-channel gonerator 1~ and PN Q channel generator 128, e~ti~ely. The resulting l~hann~l code spr~ sequence 124 and Q-~:ha"nel code spr~J sequence 125 are used to bi-phase mod~ tQ a quadrature pair of sinusoids by driving the power level c~,ltluls of the pair of sinusoids. The sinusoids' output signals are summed, banJ~,dss filtered, transl~ted to an RF frequency, amplified, filtered and r~ t~ by an antenna to complete trans",ission of the traffic channel data bits 100 in a communication channel.
Referrin~ now to FIG.2, a prior art spr~acl spectrum l.d,~s".;ll~r is shown. In the prior art spre~ spectrum lr~ns,-,itter, traffic cl,annel data bits 130 are input to an oncoder 132 at a particular bit rate (e.~.,9.6 kbit/s). The traffic chan,-el data bits can include either voice converted to data by a voc~er, pure data, or a co,nbination of the two types of data. Enc~r 132 convolutionally onc~es the input data bits 130 into data symbols at a fixed encodin~ rate. For example, enc~er 132 encocles re~iv0d data bits 130 at a fixed oncoJing rate of one data bit to two data symbols such that the oncoclu 132 o~tp~ltC data syl"L~ls 134 at a 19.2 ksym/s rate. The e,-coder 132 acool"l"~L~te6 the input ot - data bits 130 at variable rates by encGding repetition. That is, when the data bit rate is slower than the particular bit rate at which the GncGJer 132 is desi~n~l to opc.at~, then the ~ncod~r 132 ~peals the input data bits 130 such that the input data bits 130 are~ provided to the encoding elements within the e. cocler 132 at the equivalent of the input data bit rate at which the encoding elements are designad to opG.~te. Thus, the encoder 132 outputs data symbols 134 at the same fixed rate re~ardless of the rate at which data bits 130 are input to the oncoJer 132.
The data symbols 134 are then input into an interleaver 136.
Interleaver 136 inlerleaves the input data sy-"bols 134. The interleaved data symbols 138 are output by the interleaver 136 at the same data symbol rate that they were input (e.g.,19.2 ksym/s) to one input of an exdusive-OR combiner 142.
A long PN genardtùr 140 is operatively coupl~d to the other input of the exclusive~R combiner 142 to onha.1ce the security of the 2077~
g communication in the communication channel by scrambling the data sy--lbols 138. The long PN generator 140 uses a long PN se~ nce 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 138 which are input to the other input of the exclusive-OR gate 142 (e.g.,19.2 ksym/s). The scrambled data symbols 144 are output from the exclusive-OR co--~biner 142 at a fixed rate equal to the rate that the data symbols 138 are input to the exclusive-OR gate 142 (e.g.,19.2 ksym/s) to one input of an exclusive-OR combiner 148.
A code division channel s~l~ction gonar~tor 146 provides a particular pr~Jet6r",;neJ length Walsh code to the other input of the eYclusive-OR combiner 148. The code Ji~.sion channel ~slQction gG.-er~tor 146 can pru~iJe one ot 64 o-U,~Gnal codes cGr,espGfiJing to 64 Walsh codes from a 64 by 64 Hadamard matrix wherein a Walsh code is a single row or column of the matrix. The exclusive4R
combiner 148 uses the particular Walsh code input by the code Jiiision cl)annel go.l)er~tor 146 to spre~ the input scrambled data sy.,lb~ls 144 into Walsh code sprbad data sy"~ols 150. The Walsh code spre~J
data symbols 150 are output from the exclusive-OR combiner 148 at a fixed chip rate (e.g.,1.2288 Mchp/s).
The Walsh code spread data sy"lbols 150 are provided to an input of two exclusive-OR combiners 152 and 158, respe.,1i~ely. A pair of short PN se~ ences (i.e. short when cG",parecl to the long PN
sequence used by the long PN generator 140) are generaled by 1-channel PN ç,ane.~tor 154 and Q~hannel PN gener~tor 160. These PN
gener~to.~ 154 and 160 may generate the same or .Jiffe.~nl short PN
sequences. The exdusive-OR combiners 152 and 158 further spre~J
the input Walsh code spre~ data 150 with the short PN sequences generaleJ by the PN l-channel generator 154 and PN Q-channel gener~tor 160, res~ ely. The resulting l~hannel code spr~
sequence 156 and Q~hannel code spre~cl sequence 162 are used to bi-phase medu'~te a quadrature pair of sinusoids by driving the power - level contrûls of the pair of sinusoids. The sinusoids' output signals are summed, ban.l~,ass filtered, translated to an RF frequency, a",plified, ~
filtered and ~d; ?'elJ by an anlenna to complete lr~ns",;ssion of the traffic channel data bits 130 in a communication channel.

2077~43 Referring now to FIG. 3, a preferred embodiment sprd~J spectnum sn-itler is shown which improves upon the prior art spr~d spectrum tr~ns.-,itier shown in FIG.1. In the preferred embodiment sprd~J
spectn~m l-t.ns,.,iUer, traffic c~an"el daia bits 200 are input to an S oncoclar 202 at a particular bit rate ~e.g., 9.6 kbiUs). The traffic ch&nnel data bits can indude either a voice converted to data by a vocoder, pure data, or a c~,-,bination of the two types of data. Encoder 202 preferably convolutionally encodes the input data bits 200 into data sy.-~bols at a predetermined enco~lin~ rate and o~ s the data sy--,~ls 204. It will be appr~;~e~l by those skilled in the art that other types of G.-c~in~ can be used without depa,lin~ from the scope of the prvsont invention. In one example of a p,efer-~J embodiment impla.nont~tion, eno~er 202 onc~Jes leceived data bits 200 at a pr~leter---i,.
encoding rate of one data bit to three data sy.-lbols such that the enc~ler 202 outputs data symbols 204 at a 28.8 ksym/s rate.
The data sy--~bGls 204 are then input into an ;nte,leaver 206.
Ir,te.ledver 206 ,Gr~ferably block interleaves the input data sym~ols 204.
In the interleaver 206, the data sy.,lbols are input column by column into a matrix and output from the matrix row by row. It will be appr~c ated by those skilled in the art that other types of ;nte. Ieaving such as convolutional interloav;ng can be used in place of block interleaving without departing from the scope of the prdse,d inve.rtion. The - i"~e.ledved data sy.-~bGls 208 are output by the inte.leaver 206 at the same data symbol rate that they were input (e.g., 28.8 ksymls).
The inte,l6dved data symbols 208 are then input to a modulator 210. The mo~ cr 210 preferdbly derives a sequence of ~,re~Jute...lined length Walsh codes 212 (e.~., 64-ary ~.,ll-o~onal codes) from the interleaved data symbols 208. In 64-ary G,ll,o~onal code si~nalling, the interleaved data symbols 208 are grouped into sets of six 30 to select one out of the 64 orthogonal codes to represent the set of six data symbols. These 64 orthogonal codes cGr-~spond to Walsh codes from a 64 by 64 Hadamard matrix wherein a Walsh code is a single row or column of the matrix. lt will be appr~r: ~eJ by those skilled in the art that other types of Gl lllGjaGnal codes can be substituted for the Walsh 35 codes without departing from the scope of the prt,senl invention. For example, codes derived from a set of mutually ~,lll,o~onal sine waves could be substituted for the Walsh codes. In the pr~fer,~cJ e,-l~li-nent, 2a 7 7 ~ 4 ~
the modulator 210 outputs a sequence of Walsh codes 212 which correspond to the input data symbols 208 at a fixed symbol rate (e.s., 30~.2 ksym~s) to one input of an exclus~e OR c~mbiner 216.
A lon~ PN ~enerator 214 is opera~vely coupJed to the other input of the ex~usive~R combiner 216 to provide a spreading sequence to the exc~usive~R combiner 216. The long PN ~enerator 214 uses a long PN sequence to generate a user specific sequence of symbols or unique user code at a fixed chip rate (e.~., 1.228 MchpJs). In addition to providing an Ide.,tifi~ion as to which user sent the traffic channel data bits 200 over the communication channel, the unique user code enhances the security of the ~ommunication in the communication channel by s~r~."blin~ the traffic channe~ da~a bits 200. FYnlusNe-OR
combiner 216 uses the unique user code input by lon~ PN generator 214 to spread the input Walsh coded data symbols 212 into user code spread data symbols 218. This spreading by the exclusive-OR
combiner 218 provides a factor increase in the overall spreadin~ of the traffic channel data bits 200 to data symbols 218. The user code spread data symbols 218 are output fr~m the exclusive-OR combiner 216 at a fixed chip rate (e.g., 1.2288 Mchp/s).
The user code spread data symbols 218 are provided to an input of two exclusive-OR combiners 220 and 226, respectively. A pair of short PN sequences (i.e. short when cornpared to the long PN sequence used by the long PN generator 214) are generated by l-channel PN
generator 222 and ~channel PN generator 228. These PN generators 222 and 228 may generate the same or different short PN sequences.
The exdusive-OR combiners 220 and 226 further spread the input user code s~.re~d data 214 with the short PN sequences generated by the PN I channeJ ~enerator 222 and PN Q~channel generator 228, respectively. The resulting l-channel code spread sequence 224 and Q-channel c~de spread sequence 22~ are used to bi-phase mo~ul~te a ~u~dr~ture pair of sinusoids by driving the power level c~ntrols of the pair ~f sinusoids. The sinusoids' output signals are summed, bandpass filtered, translated to an Rf frequency, amplified, filtered and redi-~ed by an antenna to complete transmission of the traffic channel data bits 200 in a communication channel. -The prefer,~ ~mbodiment transn,iller ac~,l"nodates the input of data bits 200 at variable data bit rates by utilizin~ a controller 262 to B

-- -12- ~n 77 3 43 control encoder 202, interleaver 206 and modulator 210. The controller 262 acco~,-,~lPtes th~ variable data bit rates by inputting the traffic c~annel data bXs 2û~ and measuring the data b~t rate. Subsequently, controller 262 ser~s si~nals 264 and 268 to en~ oder 202 and 5 interleaver 206, respe~vely, to adjust the predetermined encoding rate to ac~ommodate the particular measured data bit rate. This adjustment of the encoding rate can be accomplished by implementing a puncture algorithm in the encoder 202 and interleaver 206 with the controller 262 .
A puncture al~orithm selectively deletes d~a syn~ols from the sequence of data symbols 208 eventually output by the interleaver 206.
Through the implementation of a puncture algorithm, an effectNe encoding rate of receiv~ data bXs to data symbols can be an integr~ or non-integral number (e.g., 1~2, tl2.4, or t/3 enc~dins rate is possiWe).
In addition to the controller 262 sending s;gnals to the enc~cter 202 and interleaver 206, controller 262 sends a signal 268 to m~u~q~or 210 to adjust the predetermined length of the Walsh codes to ~e used by the mo~ul~tor 210. Higher data rates can be accommodated within a spread spectrum system such as one based on the use of 64 symbol length Walsh codes by allowing a lower order Walsh code (e.g., 32 bit 20 length Walsh codes) to operate along with the 64 bit length Walsh c~des. In the preferred embodiment transmitter, the essential notion for providing a higher data rate traffic chanriel is to reduce the Walsh code for that channel from 64 bit length to 32 bit length while maintaining orthogonality between all of the Walsh codes used. This is 25 accomplished by prohibiting the use of the two 64 bit length Walsh codes (or ",axi-"um length Walsh codes for this preferred embodiment spread spectrum transmitter) that have the 32 bit length Walsh code as their building bloc~ An addition~ conslderation is that the higher data rate channel must be transmilled at a higher power to compensats for 30 the r~uced amour~ of spreading of the input data bit to a larger number of data symbols. Some possible controller implemented setlin~s of the predetermined encoding rate and the predetermined Walsh code lengtt in response to the input data bit rates are shown below in Table 1.

~' -t3- ~ ~ 7 7 ~ 4 ~ J

T~hle 1 Data Input Total Encodin~ Convert Walsh User Symbol Da~a Btt Spread Factor Fac~or Code Code Rate Limit Rate Factor (Walsh Factor Factor (Mchp/s) (kbiUs) code/bits~
1.2288 9.6 128 3 1/6 64 4 I .2288 4.8 2~6 6 1 /6 64 4 1.2288 19.2 64 2.5 1/5 32 4 1.2288 19.2 64 3 1/6 64 2 1.2288 16 76.8 3 1 /5 32 4 t.2288 16 76.8 3.6 1/6 64 2 An example of the controller262 using inforrnation from Table 1 is that 5 the controller determinss the rate of input of the traffic channel data bits 200 is 19.2 kbiWsecx~nd (see row 3 of Table 1~. Re~lJse the controller 262 is attempting to limit the final data symbol rate to 1.228~
Mchips/second, the controller 262 nesds to have an overall spreading factor of 64 (i.e. for each bit input to the sncoder 202 a maximum of 64 10 symbols representing the bit can be output by the mo~ul~tor 210).
Therefore, the controller 262 sets the predetermined encodin~ rate to 2.5 and the pr~Jelermined Walsh code length to 32 bits. Further, the controller is relyinS~ on the conversion factor in the use of a 32 bit ler~th Walsh code of 1/5 and a user code spreading factor of 4 inherent in the 15 exclusive-OR combiner: 216 of the user code from the long PN
generator 214 with the data symbols 212. Thus, the overall spreading factor of 64 is achieved by muttiplying 2.5, 1/5, 32 and 4 together. In a~liGI~, the controller must remember to eliminate the two 64 bit len~th Walsh codes which are related to the 32 bit length Wa~sh code. tt will be 20 appre~ets~l by those skilled in the art that the numerals shown in Table 1 are merely exa"~ples of po~sible numerals which can be used by a spread spectrum communication system and that ther~ many other po~:ble sets of numeraJs which can be used withou~ ~eparting from th scope of the present invention.
Referring now to FIG. 4, an altemative prefe.. ed embodiment spread spectrum tra"sl"iller is shown which improves upon the prior art spread spectrum transl"itler shown in FIG. 2. In the altemative embodiment spread spectrum transmitter, traffic channel data bits 230 ' ~

i~ 2~773q3 are input to an onc~ler 232 at a particular bit rate (e.~., 9.6 kbit/s). The traffic channel data bits can include either a voice converted to data by a vo~s(Jer, pure data, or a co-,lbin~tion of the two types of data. Encoder 232 pr~fer~ly convolutionally oncoJ~ the input data bits 230 into data 5 sy"~ls at a p,ed~,ter"lined encodin~ rate and o~ts the data sy-,l~ls 234. It will be appre~qtsd by those skilled in the art that other types of enc~ding can be used without de~.tin~ from the scope of the prvsen invGntion. In one example of a prefe..~J altemative e"~l~iment implel"entation, onc~der 232 6nCO~JaS r~ived data bits 230 at a pr~cleten,-ined encoding rate of one data bitto two data sy--~ls such that the enc~Jer 232 ol~putç data sy--lbols 234 at a 19.2 ksym/s rate.
The data symbols 234 are then input into an inte.lea/er 236.
Interleaver 236 preferably convolutionally inte.led~es the input data sy."bols 234. It will be apprec: ~ted by those skilled in the art that other types of interle.lving such as block inte~lG~in9 can be used in place of convolutional inte.lea~ing ~thout departing from the scope of the present invention. The interleaved data sy--lbol-~ 238 are output by the interleaver 236 at the same data symbol rate that they were input (e.g., 19.2 ksym/s) to one input of an exclusive-OR combiner 242.
Optionally, a long PN gcne.dtor 240 is opcr~ti~ely coupled to the other input of the exclusive-OR combiner 242 to enhance the security of the communication in the communication channel by sc-a,.lblin~ the data symbols 238. The long PN gonor~tor 240 uses a long PN
sequence to gene,ale a user specific sequence of sy-n~ol-~ or unique user code. The user code 278 is input to a decimator 280 which limits the rate at which the user code is input to the other input of the exclusive-OR combiner 242 to the same data symbol rate that the interleaver 236 O~rlnc the data sy"l~l-~ to the other input of the exclusive~R co"llXner 242. The scrambled data symbols 238 are output trom the exclusive-OR colnbiner 242 at a fixed rate equal to the rate that the data sy-,lbGls 238 are input to the exdusive-OR gate 242 (e.g.,19.2 ksym/s) to one input of an exclusive-OR cG"Ibin~r 248.
- A code division channel ~ ction gonerator 246 preferabl~
provides a particular predetermined length Walsh code to the other input of the exdusive-OR combiner 248. The code division channel selection generator 246 can provide one of 64 olll,ogonal codes cGr.aspGr,Jing to 64 Walsh codes from a 64 by 64 Hadamard matrix 7 3 ~ 3 -'"..,.
wherein a Watsh code is a sir~le row or column ot the matrix. The exdusive-OR combiner 248 uses the par~cular Walsh code input by the cote division ch~nel generator 246 to spr~J the input scnd"lbled data symbols 244 into WaJsh code spread daIa~l..)bols 250. The Walsh code spre~J data sy.nbGls 250 are output from the exclusive-OR
combiner 248 at a fixed chip rate (e.g., 1.2288 Mchp/s).
The Walsh code spre~J data sy."~ols 250 are provided to an input of two exdusive-OR cG"Ibinera 252 and 258, .~ ely. A pair of short PN sequences (i.e. short when compared to the long PN
1 0 sequence used by the long PN generator 240) are generated by 1-cl,~nel PN generator 254 and a~,annel PN generator 260. These PN
~on~rdlor~ ?s4 and 260 may ~uner~e the same or di~fer~nl short PN
sequences. The exclusive4R combiners 252 and 258 h~rther spread the input Walsh code sprea~ data 250 with the short PN s~u~nces gonerat~ by the PN l~hannel generator 254 and PN achannel generator 260"~sp~ti~ely. The resulting h;l,a.lnel code spre~l sequence 256 and ~channel code spre~J sequ~nce 262 are used to bi~hase mo~ul~e a quadrature pair of sinusoids by driving the power level cont~ls of the pair of sinusoids. The sinusoids' output s;gnals are summed, L~,~4ass ~ r~l t,ansldt~J to an RF frequency ampliffed filtered and ~ J~el~.l by an antenna to complete tt~ns");ssion of the traffic o~,annel data bits 230 in a communication channel.
The altemate preferred e",~liment trans,''itter ac~m.,,ûd~tes the input of data bits 230 at variable data bit rates by utilizing a corlt~ullar270 to control encocler 232, intell6d./er 236, ~ ."dtor 280 and code division channel selection g~ner~tor 246. The controller 270 accom",oJ~es the variable data bit rates by inputting the traffic channel data bits 230 and measuring the data bit rate. ~u~seqlJently controller 270 sends signals 272 and 274 to encoder 232 and inlelleaver 236 re.specti./ely, to adjust the pre~ete",-ined enc~ing rate to a~cû,--m~Jale the particular measured data bit rate. This adjusl",e.lt of the Gnc~ii~
rate can be accomplished by imple",~nting a puncture algo.itl,-n in the encoder 232 and interleaver 236 with the controller 270. A puncture al~o.itl"" selectively ~IQtQs data symbols from the sequence of data symbols 238 eventually output by the interleaver 236. Through the implementation of a puncture algorithm an effective onc~in~ rate of received data bits to data symbols can be an integral or non-integral 207134~

number (e.g.,1/2 1/2.4 or 1/3 encoding rate is possible). In ahlilion to the controller 270 sending signals to the encoder 232 and interlea~er 236, controller 270 sends a signal 276 to decimator 280 to adjust the rate at which the user code is input to the other input of the exclusive-OR
combiner 242. Further conl-uller 270 sends a signal to channel division selection gonur~lor 246 to adjust the preJete".,i,uJ length of the Walsh code to be used by the code division channel generator 246. Higher data rates can be ac~.""~o.J~1e.J within a spr~cl spectrum system such as one based on the use of 64 symbol length Walsh codes by allowing a lower order Walsh code (e.g. 32 bit length Walsh codes) to opGr~e along with the 64 bit length Walsh codes. In the alternative preferred o~lb~Jiment l,ansn,ill&r, the essential notion for providing a higher data rate traffic channel is to reduce the Walsh code for that channel from 64 bit length to 32 bit length while maintaining o,ll,ogonalitv between all of the Walsh codes used. This is a¢~",plished by prohibiting the use of the two 64 bit length Walsh codes (or ",acil"um length Walsh codes for this pr~fe..aJ e."b~lil-.ent spr~ spectrum l~ns,..;ller) that have the 32 bit length Walsh code as their buildin~ block. An additional consicieration is that the higher data rate channel must be lr~ns,-,ill6cl at 20 a higher power to cGI"pensate for the redlJc~ amount of spre~hling of the input data bit to a lar~er number of data symbols. Some possible controller implemented se~ings of the precleler--lined oncoJiilg rate and the preJetermined Walsh code length in response to the input data bi rates are shown below in Table 2.
Table 2 Data Symbol Input Data Total Spread Encoding Walsh Code Rate Limit Bit Rate Factor Factor Factor khp/s) (kbiVs) 1.2288 9.6 128 2 64 1.2288 4.8 256 4 64 1.2288 19.2 64 2 32 1.2288 1 6 76.8 2.4 32 An example of the controller 270 using information from Table 2 is that 30 the controller deter",ines the rate of input of the traffic channel data bits 207 73g~
.~.

230 is 19.2 kbiW~econcl (see row 3 of Table 1). Re~use the controller 270 is attempting to limit the tinal data s~ ol rate to 1.2288 Mchips/seco"J, the cont~vller 270 needs to have an overall spreading factor of 64 (i.e. for each bit input to the encoder 232 a ~--axi",um of 64 5 sy--~bols repr~senting the bit can be output by the sxclusive-OR
combiner 250). Ther~fore, the controller 270 sets the predelen";nec o.~in~ rate to 2 and the pr~Jele."dneJ Walsh code length to 32.
Thus, the overall spreading factor ot 64 is achieved by multiplyin~ 2 and 32 to~tl.er. In ~ ;tion, the-controller must remember to eliminate the 1 0 two 64 bit length Walsh codes which are related to the 32 bit length Walsh code. It will be a"prec "6-1 by those skilled in the art that the nu~erals shown in Table 2 are merely examples of possible numerals which can be used by a spr~J spectrum communication system and that there are many other possible sets of nun.er~ls which can be used 1 5 without ~Jepa. tin~ from the scope ot the pre50n~ inve. ltion.
Although the invo.~tion has been described and illus1r~teJ with a certain .le~,ee ot particularity, it is unde,~oocl that the prvson~
~ &rJoslJ~e ot e."~Jiments has been made by way ot exa")ple only and that numerous changes in the arrangement and combination ot parts as 20 well as steps may be r~sG~ leJ to by those skilled in the art without departing from the spirit and scope of the invention as claimed.

Claims

What is claimed is:

1. A spread spectrum channel apparatus which accommodates variable received data bit rates, comprising:
(a) forward error correction encoder means for receiving data bits at a particular bit rate and encoding the received data bits at a predetermined encoding rate into data symbols, the predetermined encoding rate being set in response to the received data bit rate; and (b) modulator means, operatively coupled to the forward error correction encoder means, for deriving predetermined length orthogonal codes from the data symbols, the predetermined length of the orthogonal codes being set in response to the received data bit rate.

2. The spread spectrum channel apparatus of claim 1 wherein the forward error correction encoder means comprises means for setting the predetermined encoding rate through implementation of a puncture algorithm.

3. The spread spectrum channel apparatus of claim 1 wherein the forward error correction encoder means comprises a symbol interleaver means for scrambling the data symbols prior to the modulator means deriving orthogonal codes from the data symbols.

4. The spread spectrum channel apparatus of claim 1 further comprising a transmitting means, operatively coupled to the modulator means, for transmitting the derived orthogonal codes over a communication channel, the transmitting means comprises spreading means for preparing the derived orthogonal codes for subsequent transmission by spreading the derived orthogonal codes with a spreading code.

5. The spread spectrum channel apparatus of claim 4 further comprising:
(a) despreading means for sampling the transmitted spread orthogonal codes received from over the communication channel into data samples by despreading the received orthogonal codes with a spreading code; and (b) decoding means, operatively coupled to the despreading means, for generating an estimated data bit by deriving the estimated data bit from the data samples.

6. A spread spectrum channel apparatus which accommodates variable received data bit rates, comprising:
(a) despreading means for sampling a signal received from over the communication channel into data samples by despreading the received signal with a spreading code, the received signal comprising spread orthogonal codes wherein the spread orthogonal codes were formed from data bits received at a particular bit rate and encoded at a predetermined encoding rate into data symbols, predetermined length orthogonal codes were derived from the data symbols, and subsequently the derived orthogonal codes were prepared for subsequent transmission by being spread with a spreading code, the predetermined encoding rate and the predetermined length of the orthogonal codes having been set in response to the received data bit rate: and (b) decoding means, operatively coupled to the despreading means, for generating an estimated data bit by deriving the estimated data bit from the data samples.

7. A spread spectrum channel apparatus which accommodates variable received data bit rates, comprising:
(a) forward error correction encoder means for receiving data bits at a particular bit rate and encoding the received data bits at a predetermined encoding rate into data symbols, the predetermined encoding rate being set in response to the received data bit rate; and (b) code division channel means, operatively coupled to the forward error correction encoder means, for determining a particular channel to transmit the data symbols by spreading the data symbols with a predetermined length orthogonal code, the predetermined length of the orthogonal code being set in response to the received data bit rate.

8. The spread spectrum channel apparatus of claim 7 wherein the forward error correction encoder means comprises means for setting the predetermined encoding rate through implementation of a puncture algorithm.

9. The spread spectrum channel apparatus of claim 7 wherein the forward error correction encoder means comprises scrambling means for scrambling the data symbols with a spreading code prior to the code division channel means determining a particular channel to transmit the data symbols by spreading the data symbols with a predetermined length orthogonal code.

10. The spread spectrum channel apparatus of claim 7 wherein the forward error correction encoder means comprises a symbol interleaver means for scrambling the data symbols prior to the code division channel means determining a particular channel to transmit the data symbols by spreading the data symbols with a predetermined length orthogonal code.

11. The spread spectrum channel apparatus of claim 7 further comprising a transmitting means, operatively coupled to the code division channel means, for transmitting the orthogonal coded spread data symbols over a communication channel, the transmitting means comprises spreading means for preparing the orthogonal coded data symbols for subsequent transmission by spreading the orthogonal coded data symbols with a spreading code.

12. The spread spectrum channel apparatus of claim 11 further comprising:
(a) despreading means for sampling the transmitted spread orthogonal codes received from over the communication channel into data samples by despreading the received orthogonal codes with a spreading code; and (b) decoding means, operatively coupled to the despreading means, for generating an estimated data bit by deriving the estimated data bit from the data samples.

13. A spread spectrum channel apparatus which accommodates variable received data bit rates, comprising:
(a) despreading means for sampling a signal received from over the communication channel into data samples by despreading the received signal with a spreading code, the received signal comprising spread orthogonal codes wherein the spread orthogonal codes were formed from data bits received at a particular bit rate and encoded at a predetermined encoding rate into data symbols, predetermined length orthogonal codes spread the data symbols, and subsequently the orthogonal code spread data symbols were prepared for subsequent transmission by being spread with a spreading code, the predetermined encoding rate and the predetermined length of the orthogonal codes having been set in response to the received data bit rate; and (b) decoding means, operatively coupled to the despreading means, for generating an estimated data bit by deriving the estimated data bit from the data samples.

14. The spread spectrum channel apparatus of claim 7 wherein the code division channel means comprises means for limiting the number of orthogonal codes used when a less than maximum length orthogonal code is used such that orthogonality of the maximum length orthogonal codes is maintained with respect to the less than maximum length orthogonal code.

15. A method of communicating a spread spectrum signal while accommodating variable traffic data bit rates, comprising:
(a) determining the particular bit rate at which received traffic data bits were provided to a spread spectrum channel apparatus;
(b) setting a predetermined encoding rate and a predetermined length for an orthogonal code in response to the determined particular bit rate;
(c) encoding received data bits at the predetermined encoding rate into data symbols; and (d) deriving orthogonal codes of the predetermined length from the data symbols.

16. The method of claim 15 wherein the step of setting the predetermined encoding rate comprises implementation of a puncture algorithm.

17. The method of claim 15 further comprising the step of interleaving the data symbols prior to the step of deriving predetermined length orthogonal codes from the data symbols.

18. The method of claim 15 further comprising the step of transmitting the derived orthogonal codes over a communication channel, the transmitting step comprising preparing the derived orthogonal codes for subsequent transmission byspreading the derived orthogonal codes with a spreading code.

19. The method of claim 18 further comprising the steps of:
(a) sampling the transmitted spread orthogonal codes received from over the communication channel into data samples by despreading the received orthogonal codes with a spreading code; and (b) generating an estimated data bit by deriving the estimated data bit from the data samples.

20. A method of communicating a spread spectrum signal while accommodating variable traffic data bit rates, comprising:
(a) sampling a signal received from over the communication channel into data samples by despreading the received signal with a spreading code, the received signal comprising spread orthogonal codes wherein the spread orthogonal codes were formed from data bits received at a particular bit rate and encoded at a predetermined encoding rate into data symbols, predetermined length orthogonal codes were derived from the data symbols, and subsequently the derived orthogonal codes were prepared for subsequent transmission by being spread with a spreading code, the predetermined encoding rate and the predetermined length of the orthogonal codes having been set in response to the received data bit rate; and (b) generating an estimated data bit by deriving the estimated data bit from the data samples.

21. A method of communicating a spread spectrum signal while accommodating variable traffic data bit rates, comprising:
(a) determining the particular bit rate at which received traffic data bits were provided to a spread spectrum channel apparatus;
(b) setting a predetermined encoding rate and a predetermined length for an orthogonal code in response to the determined particular bit rate;
(c) encoding received data bits at the predetermined encoding rate into data symbols; and (d) determining a particular channel to transmit the data symbols by spreading the data symbols with a predetermined length orthogonal code.

22. The method of claim 21 wherein the step of setting the predetermined encoding rate comprises implementation of a puncture algorithm.

23. The method of claim 21 further comprising the step of scrambling the data symbols with a spreading code prior to the step of determining a particular channel to transmit the data symbols.

24. The method of claim 21 further comprising the step of interleaving the data symbols prior to the step of determining a particular channel to transmit the data symbols.

25. The method of claim 21 further comprising the step of transmitting the orthogonal coded spread data symbols over a communication channel, the step of transmitting comprising preparing the orthogonal coded data symbols for subsequent transmission by spreading the orthogonal coded data symbols with a spreading code.

26. The method of claim 25 further comprising the steps of:
(a) sampling the transmitted spread orthogonal codes received from over the communication channel into data samples by despreading the received orthogonal codes with a spreading code; and (b) generating an estimated data bit by deriving the estimated data bit from the data samples.

27. A method of communicating a spread spectrum signal while accommodating variable traffic data bit rates, comprising:
(a) sampling a signal received from over the communication channel into data samples by despreading the received signal with a spreading code, the received signal comprising spread orthogonal codes wherein the spread orthogonal codes were formed from data bits received at a particular bit rate and encoded at a predetermined encoding rate into data symbols, predetermined length orthogonal codes spread the data symbols, and subsequently the orthogonal code spread data symbols were prepared for subsequent transmission by being spread with a spreading code, the predetermined encoding rate and the predetermined length of the orthogonal codes having been set in response to the received data bit rate;
and (b) generating an estimated data bit by deriving the estimated data bit from the data samples.

28. The method of claim 21 further comprising the step of limiting the number of orthogonal codes used in the step of determining a particular channel to transmit the data symbols when a less than maximum length orthogonal code is used such that orthogonality of the maximum length orthogonal codes is maintained with respect to the less than maximum length orthogonal code.