CA2322543A1 - Apparatus for incorporating multiple data rates in an orthogonal direct sequence code division multiple access (ods-cdma) communications system - Google Patents
Apparatus for incorporating multiple data rates in an orthogonal direct sequence code division multiple access (ods-cdma) communications system Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J13/00—Code division multiplex systems
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Abstract
An ODS-CDMA communications system is disclosed with at least one hub station and a plurality of user terminals. Each user is assigned a code which is orthogonal to all of the other user codes. The orthogonal code period is chosen such that the code repeats an integer number of times in a data symbol time and the code is synchronized with the symbol transitions so that no data transitions occur within the code. Thus, the selection of an orthogonal code book which enables a high rate data to be spread using shorter code words, and conversely, low data rate to be spread using longer code words, all or which remain mutually orthogonal.
Description
WO 99/45669 ~ PCT/US99103722 APPARATUS FOR INCORPORATING MULTIPLE DATA RATES IN AN ORTHOGONAL DIRECT
SEQUENCE CODE
DIVISION MULTIPLE ACCESS (ODS-CDMA) COMMUNICATIONS SYSTEM
BacJcgmund and 8rlet Oesafption of Prior Art Sproad spectrum oortrmunica:ions is being used for a number of commert~at applications and is profrferatinp at a rapid rate. Synchronous orthogortaJ
dirsci soquence coda division multiple access (ODS-CDMA) has been proposed (sue U.S. Patent No. 5,375.140. 'Wlni~ Direct S~qu~oa Sp~c~ad Sp~ctrvm Digital Gliular Telephone Systertz', incorporated herein by refe~nce) as an effective technique for improving the capacity, i.e., bandwidth effsciency, of the rtsor~a conventions! quasj-orthogonal CDMA.
In conventional direct sequence (DS) spread spectrum CDMA systems, the irfdividual users ttanatrttit on the same frequency using different pseudo-noise (PN) codes. The PN codes are quasi-orthogonal, i.e. they have retativeiy low but nontoro cross.corratation values with each other.
oDS~COMA aysterns are designed such that alt signets are rived in tame and ~q~y sy~~. rnus all users remain orthogonal to each other and, in an idea! world, any user can be recovered with no mu~iplo access noise from otttrr users. This is most practice.! in a star configur~rd networfc whoa a multiplicity of users tran:mtt to and receive from a single Hub Si~ation. This oocsfrpuration is used in cellular as well as satellite netwottcs.
In an ODS-CDMA system, oac:h user is assigned a code which is ortnopona! to alt of the other user codas (t.e. the orthoflonal codes have a cross-comelatiott vatw of zero with each other). Further, the orthogonal code period is d~oaart such that the code repeats 8n integer number of times in a data symbol time (wualry once, since this results in the ma~dmum number of available ortnoQonal SUBSTITUTE SHEET (RULE 26~
functions). The code epoch is syncttrontzed with the symbol trans~ion= so that no data transitions occur within the code. The number of users Is limited by the number of orthogonal codes available, which is equal, at most, to the length of the code. Thersfor~e, the chipping rate is equal to the maximum number of orthogonal user~a times the symbol rate.
Efficient use of the available bandwidth is accomplished by using bi-phase sprasading and MPSK data modulation as taught In U.S. Patent Number 5,687,166, "~Aodulation System for Sproad Spectrum CD~A
Communication," incorporated herein by reference.
It is often desirable to accommodate a mix of different rata users where the rates are related by 2" where n is a positive integer. One coos-efficient way to do this is to size the system for the lowest user rate and then demutLplex higher rate data onto mu~ipie orthogonal codes, l.e. data of a user at 4 times the nominal rate would be demuttiplexed and spread onto 4 codes which are then summed for transmission. This scheme, while efficient in the use of orthogonal cods, ptoduoes a signal with a wide dynamic range which is a disadvantage for the subscriber terminal power amplifier efficiency. It also requires mutdple correl~a~tora and mutbple~onA to recover the original data stream. This technique is discussed by EJzak, et al in 'BALI: A Solution for High-Speed CDMA Data,' in 8eA Labs Tec~mical JoumaJ, vol. 2, no. 3, Summer i 987.
Another technique is disclosed in tT.S. Patent ~pplicatioa Serial Rio. 08/352,313, now o.S. Batent No. 5,57a,?21, entitled 'Orthogonal Code Division Multiple Access Commuaicatioa System having Multicarrier Modulation incorporated herein by refereaae. Za this disclosure, it is suggested that multiple ODS-CD~A signals be transmitted on orthogoaally spaced carriers (i.e. spaced at the chipping rate) and the data from a single high rate user is demultiplexed onto the multiple carriers. Once again, this results is a signal with wide amplitude variation.
SUBSTITUTE SHEET (RULE 26) In U.S. Patent Numuer 5,47 6,797 "System and Method for Generating Signal Wavefonns In a CDMA Cellular Telephone System," incorporated herein by reference, lower data rates than the nominal are supported on the celt~to-mobile link (which is orihogonat), by repeating data symbols of a low rate user a number of times to obtain the nominal symbol rate. This sequence of symbols is then spread by an orthogonal code and tn3nsmitted at a tower power proportional to the lower rate. This technique has the disadvantage of not being orthogonal code space efficient, l.e. each low rate user uses the same amount of code space as a high rate user.
In 'Design Study for a CDMA~Based Third Generation Mobile Radio System,' IEEE Joumat on Selected Areas in Communication, vol. 12, no. 4, May 19A4, Baler, et al, propose to use variable length spreading codes to support variable data rates in a CDMA system. However, they propose to use PN codes that are not necessarily orthogonal.
0bjeets of the Invention M object of this invention is to provide a means by which an ODS-CDMA
communications system can function efficiently with data races that are not all equal. This non~homogeneity in data rates allows diffenant users to communicate with different data bandwidths while the ODS-CDMA communications system signaling rate and orthogonal nature remain the same as in a homogeneous data J1 tnrthsr object of this invention i~a to provide an ODS~CD~iJ1 system which supports a mix of users, ~tith data rates related by 2', t~hich makes efficient use of the available orthogonal code space, i.e. a user with symbol rate R/k uses 1/k of the code space of a user ~rith symbol rate R.
tt a a further object of thin invention to ensure that users of all nstea tranamk a relatively cons~tt ampiirirde signal. This is of particular importance to the SUBSTITUTE SHEET (RULE 26) subscriber terminal where high transmitter power eff~cisrwy (at or near satura#on) is desicabie due to the impact on cost and power consumption.
tt is a further object of this invention to keep signal processing complexity to a Win.
sunurtary of t~ inwntlon In an ODS-COMA system, each user is assigned a code Hfilch is orthogonal to a!I of the other user codas (i.e. the orthogonal codes have a cross-correlation value of soro with oad~ other. Further, the orthogonal code period is chosen such that the code repeats an integer number of times in a data symbol time (usually once, sir~cv this r~wrtts !n the m~udmum numoer of avaltsbie orthogonal sanctions) and the code epoch is synchronized with the symbol transitions so that no data transitions occur within the code. Thus, in a perfectly sytu~tronlzsd sys:rm, the individual users can be demodulated with no lnterfen~nce from other Ths number of users is Limited by the number of orthogonal codes available, which is equal, ai most, to the length of the code. Note that the chipping rate is equal to the ma~dmum number of orthogonal users times the symbol rate. This 4npliss that, for a fixed chipping rate, a system transmitting data at a rate Qf R/4 shovid be able to accommodate 4 times ss many users as a system with rats R
Ef~rtt use of oods space in a system with a mix of user rstes ensures that a uar with rate R/4 will only oaupy 1/4 of the orthogonal function space of a user wkh rats f~ The irw~ention disclosed herein teaches an effictertt way to oonstnxt such otthoponat codes by selection of an orthogonal codebook whsnin subs~Quertoea of the codewords are also orthogonal. With such a oodsbook, short codes for high rate users are determined directly by the wbsectuecxos, and bng codes for low rate users are determined by the Kronedcer product of the subsequettoes wish an orthogonal codeword allocated to these users. I1s a SUBSTITUTE SHEET (RULE 26) pr~afen~rd embodiment, the Sytvester construction of a Haoarnard matti~c Is used to generate the orthogonal codebook Thus, this invention discloses how to effidently support variable data rates in a synchronous OOS-CDMA
communication system with const8nt chip rate.
The novelty of this invention lies in the selection of an orthogonal codebook which enables high rate data to be spread using shorter codewords, and conversely, low rate data to be spread using longer codewords, aJt of which rort~ain mutually orthogonal.
Further, using this invention, each user tn~nsm'rts a single code that is constant in amplitude and n3qulres no data multiplexing or demutupiexing. The disclosed technique r~asuits in tow receiver and tn3nsmitter complexity since no additional coda generators or comelators are required to accommodate rates that are higher or lowor than the nominal data rate. Further, the constant amplitude nature of the signal allows efficient power amplification.
Desalption o! the Drawirtps Figure 7. Diagntm of mufti-rate ODS-CDMA Return Unk Stturxure with M users Figure 2. Diagn~rn of an Exemplary ODS-CDMA Receiver at the Hub Statirort Did Description of the inwnf3on .A generalized atruc4rre for an OOS-ODMA communications system is itfusttat~d in F~a~e 1. A Return Unk structure is shown to facilitate the invention de:cxiptton, however, the concept can be applied to the Forward Link as well.
In the Return Link , many users communicate with the Hub Station by nwans of a modulator and transmitter process that uses some medium for transmission. The most common medium for transmission is radio frsquarxy el~tromagnotic radiation. In this example, all users in the Return Link transmit on the same carrier frequency using the same type of modulator. it is necessary that the users transmit at time instances such that all signals nxeived at the flub SUBSTITUTE SHEET (RULE 26) Station are time ayrxhronous. The waveform uansmitted by each user comprises of MPSK modulated data spread w'rth an orthogonal ODS-COMA code.
in order to axommodate muttiple data rates while maintaining a constant chip rate for all assns, the length of spreading code for each user is varied. M
orthogonal codebook is constructed which enables high note data to be spread usMg shorter codewords, and conversely, low rate data to be spread using longer codevrorris, all of which remain mutually orthogonal. In a preferred embodiment, the Syivester conswctlon of a Hadamard matrix is used to generate the codebook.
It is well known . in the art that a Sytvester Hadamard matrix of dimension N
Is defuwd recursively as N(11I )s 'N(N/1) H(NI2) N(N/1) -H(NII) where H~t) ~ ~ ~ and N = 2", where n is a positive integer. The N news of the Ha~dertw~d matrix H(N) define an orthogonal codebook !=or convenience, the rows are indexed from 0 tv IW 1, starting from the top row. It can be seen from the recursive construction of H(N) that it is composed of SyivestehNadamard sutxnatrices of the form tH(11~), where k is a positive integer ranging from 1 to n-t. Since the rows of H(NI~') are orthogonal, tt follows that the codeworda of H(IY) consist of subsequsnoes of length N/2'" that arse orthogonal as well.
Conewst a mufti-rate OOS-00MA communications system with fixed chip rats ta, some fundaments! data symbol rate t,, and a codebook of N orthogonal sequences such that f~~ All,. tf there exist M Retum tJnk users with data streams at the fundamental symbol hate, each user may be assigned one of the N
otthopon$I oodeworda as long as M S N . However, it there exist users that re4ues! higher or lower data rates compared to the fundaments) rate. they may be as:~sd shorter or Longer codewords, respectlv~ety. These shorter (ionperj cafes are coed from the codeword in a fashion such that the orlhogortal SUBSTITUTE SHEET (RULE 26) WO 99/45669 ~ PCT/US99/03722 nature of the OOS-CDMA system is maintained and tt~e code space !s used efficiently. An illustrative example is considered first to motivate the general approach for constructing these variable length codewords.
Suppose one of the users request a higher symbol rate, say at twice the fundamental rate 2f,. Since the chip rate, which is the product of the spreading sequence length and the symbol rate, is fixed, it follows from f~
=(IY~'2)(2f,~, that the spreading sequence length per symbol must be reduced to NI2. This can be implemented by spreading attemate symbols of the high rate user by the first chips of a codeword and the last N/'2 chips of the same codeword. Since this codeword is sub-divided into two N/~ subsequences, the remaining codewords must be orthogonal over each of these two subsequences such that the users at fundamental rate f, and the high rate user at 2f, do not mutually interfere, thereby maintaining otthogonality in the ODS-CDMA system. Consider allocating the k°' codeword to this user (k = O,1,...,N~1). If a Sytvester~Hadamard matrix is used as the orthogonal codebook, the (k+(N~2))~"o~v~ codeword does not possess the rsqufred llfl'2 subsequence orthogonalityr since it contains the same two subsequences (up to a t sign) and therefore cannot be allocated to other users.
For example, if the high rate user is assigned the ka' code word ck = [S~ S~j, the oodeword q s [S~n -S~j .for j ~ (k+(11t12))",o,~,v~ cannot be assigned to another user, and vice versa. Note that if a user at rate 2f, Is assigned a single short subsequence in Afl2 space (say subsequence Sue, this is equivalent to usirtp two codewords in the N space codebook. Hence, in an attemative implementation, a rate 2!, user may be supported by assigning the user a shorter subsequence of length fYl2, and removing the codewocds which contain this subsequence from the list of allocable codewords.
In gsnstal, a mufti-rate ODS-CDMA system with a codebook of N Syiveater-Hadamard sequences (N = 2° for some integer p), fundamental data symbol rate f,~ and a faced chip rate f~ ~ Nf,, can support users with higher data rates than the fundamental rate. The users may reques~i to transmit data at notes 2'f,, whets r SUBSTITUTE SHEET (RULE 26) ranges from 0 to p. This is achieved by reducing the length of the spr~aading code to IYr1' such tnat the chipping rate, ~_ =(NI1')(2't,J, remains constant.
Subsequences of length NI~ can be generated by sub-dividing an allocated codeword of ieneth N into 2'sub-codes. These sub-codes are used to spread 2' consecutive symbols of a data stream at rate 2'.; . Note that in the case of the Syivester-Hadamard sequences, any codeword of length N is a repeated subsequence of length NI2' (up to a t sign), which is orthogonal to the other non-idenZjccal subsequences of the same length.
Further, if the k~' codeword is composed of a repeated subsequence of length NI~' (up to a t sign), tnen the codewords (k+I(NI~');"ae~,,r~. for alt i =
t,Z.....2'-1 and r s 0, are also composed of the same subsequence (up to a t sign), and are no longer available for atlocatlon, if system orihogonality is to be preserved.
Indeed, supporting t user at data rate 2'f, is effectively equivalent to supporting 2rtusrs at rate f, since 2'~t codes are rendered unusable.
irt a network setting where muulple users are transmuting ai different data rates, appropriate provisions must be made for accommodating the data rate request of a new user in terms of checking for allocable subsequences. tn fact, the network corttrolier must. before assigning a subsequence. make certain first, a is not cor>binsd in the tongersubsequence of a lower note user (since the lower rate user would not be orthopona! over the subsequence length). Further, a must not oor~n a subsequence of shorter length that is already in use.
It is advantageous for the network controller to have the capability to change orthvponal sequence assignments periodically in order to most efficiently use the code space as the mix of user rates changes. tn addi~on, since the symbol ireerval of data at rate 2'f, is reduced to tI2'times the symbol interval of data at rstl to it may be desired, depending on the application, to Increase the trnnatnlt power by'2'to maMtaln the same level of perto:manos.
SUBSTITUTE SHEET (RULE 26) Conversely, a mutti.rsie OOS-COMA communkatjon sys~t~sm with a oode~boolc of N orthogonal sequences, fundamental data rate t, , and a faced chip rate to ~
Nto , can support users with lower data notes than the fundaments! note. The assts may request to transmit data at rates tl~', where r is a positive Integer ranging from 0 to q. A bwer rate user, at rate t,12', is assigned a beget spreading code of length 2'N such that ripe chipping rate. to ~(2~IV)(ll~'). ren»ins cor~Wtt.
The long coda is ~ns~ctsd ham the codeword allocated to this user, c,~ k~r 0,...,N~), as First, an ortho~onat function set G(2') of slzs 2' is constructed. This could be, but is not necessarily, a Syhrester~Hadamaud matrsx. The tCronecker product of the f' row of G(2') with the codeword_crr Produces a member L,,,d j s 0.....2''~1 of a set of 2r mutually orthogonal codes of length 2'N. Each of ~ese long sequerxes is orthoponaJ to codewords p, where l ~ J~ as well ,es longer code words l.~
tom~d by the ttronecker product of each row of G(2') with the codeworda c~. Thus, up to 2~ assts of rate ll~ can be assigned to a single code word ar by assigning each user a different row of G(~'). This code constructjon technique can be ~neta~ted to~accommodate a mix of users with dffferent n~tss of the form l,/~', whh ttta rruuamum aggrapate symbol rate bounded by !, .
Ttw proposed :dtsme :appeals that the symbol interval of data at rata tl~ Is inaaa:od to 2'timos the symbol Intenrat Ot data at n~ t,. tt may be dosired that a urer at the lower data rate reduce transmit power by 2~ In order to malrttaln the same aymbo!-to~noiw.imarDy ratio (FaINo~.
Tha Hub Stadon nosiwa a auperposJdon of signal wavefortna tranwnltttd by the R~lum kink uss~rs. Tho rs~h~ed signet to demodulated and despnad by thr mui4.rate OOS-CDMA rs~hrer. The ~iespr~eadlnp operation lrw~ohres oomolatinp tho noshed wawtorm with the sproadinp sequence of the desirod user aver a .symbol tntsrval. Hence, In a mutti~rate ayssem that supports users at higher data rasps than !,, the waveform of a user at rate 2't, is despread by correladrtp k SUBSTITUTE SHEET (RULE 26) against the uses allocated 1111'' chip subsequence. Conversely, in a muhi-rate system that supports users at lower data, rates than t,, t#~e wavefom~ of a user at nits l,~' is despread by cometatinp rt with the users allocated 2'N chip Kronecker-product code. In both cases, the despreadinp operation requires that the codewords of ail users be time aligned at the code boundaries in order to proserve orthoflonality, and that the data symbol rates of ail users be known at the reoerver. Furthermore, tn a system supporting lower rates, the row index of G~2'), used in fom~ing the Krcneckerproduct coda, must be known at the reviver. Appropriate provisions are to be made in a mufti-rate ODS-CDMA
system to satisfy these requiremen3s.
A functional block diapn~m of the Retum Unk stnrcture in the proposed mufti-rate ODS-CDMA system is showy tn Figure 1. in this figure, M users transmit data to the Hub Station at data symbol rates 2r'f,, 2~t,..... 2''~t, , where rj, J =
1,...,M, ranges from 0 to p for a system supporting higher rates than f,, from -q to 0 fog a system supporting tower rates than f,, and -q to p for a system supporting both high rate and bw rates. tf the ~ user requests a higher rate (r~ z 0), the users cods generator peneratos a codeword of length N ai rate f,, whkh is equhral~nt to peneratlnA 2'~ sub~codes of length 2''~N in dime-division mu~ipiex at rate 2'~t,.
On the other hand, it the ~th user requests a lower rate (r~ S 0~, ~e user's code penerstor generates a Kronecicer-product code of length 2''dN ai rate 2~f,.
Hence, at ~ symbol interval, Tj = 1/(2'Jf,~, the data symbol of the ~th user is muttipUed by the codeword from the code generator, and the resulting chip sequence is modulated and:ransrnfttad to the Hub station.
Ttta Hub Station reoeiwss the composite signal wavefortn of the M Retum Lhk users. The functional bbck diagram of an exemplary mutii.rate ODS-CDMA
receiver at the Hub Station is shown in !=figure 2. The receiver demodulate' the noeivod waveform and despresds tt i=or the ~th user with r~ z 0. despreading irtv~olves fomtatdnp oach bbck of N chips of demodulated data into su~quances of length 2'~N. and correlating each of these subsequenoes with SUBSTITUTE SHEET (RULE 2fi) the sub-code from the code generator. If rj S D, each block of 2"dN chips is correlated with the long code from the code generator. In the absence of channel distortions, the correiator output yields the user data.
A simple illustrative example which embodies the present invention is as follows.
Consider a mufti-rate ODS-CDMA system w'tth a codebook derived from Syivester-Hadamard matrix of dimension N = 4, +1 +1 +1 +1 c.~
N(4)= +1 -1 +i -1 s c, +1 +1 -1 -1 Cs +1 -1 -1 +1 fundamental data symbol rate f,, and fixed chip rate f~ ~4f,.
Suppose User 1 is assigned codeword 0, co a [+1 +1 +1 +1 ), and is transmitting at rate f,. Now, a new user, User 2, requests to transmit at rate Zl,.
From the codes available for allocation, c,, c? and ca only c, or c~ may be allocated to Uset 2 since the length 2 subsequences of ca namely [+1 +i j and [-1 -7 ), are not orthogonal to the corresponding subsequences of cd. Let code c, be assigned to User 2. The chip sequence tn3nsmitted by User 1 within the time interval T,= tlf, is xr'~ s sf'~(+1 +1 +1 +1 ), where s~'~ is the current data symbol.
Simttaf'iy, the chip sequence tn3nsmitted by User 2 within the same time interval is x~ ~ (sw[+t ~1l set[+t -1p, where s,~ and ab~ are the current data symbols. Note that with the current allocation scenario, only code c~ is available for allocation to a new user with symbol rate f, or tower. A user that requests a higher symbol note cannot be supported unless the codes are n~assigned.
The signal received at the Hub Station (after demodulation) is of the form r s xf ~~ + Jr~
= sf'~[+i +t +1 +1 ) + ~s,~[+1 -1 ) sow[+1 .1D.
SUBSTITUTE SHEET (RULE 26) The signal is despread by cometating n with the appropriate ~apnsading code.
For User 7, this is achieved by computing the foliowin8 inner product +i '~l~ ~ 4 ~~ +1 ' +i whkh yields the transmtt:fed data symbol. The data symbols of User 2 aro retrieved by first pattiboning the received chip sequence into 2 subsequences, t, . ~~+1 +1 j + s,~+1 ~1 J arid rb ~ ar"~+1 +1 ) + ~,~I+1 ~1 j and then computing the following inner products 1 +i s i=~ ~",.~ .
' 2 ' -1 and 1 +1 syr=~ ~,~~' , 2 -i Now, suppose a third user, User 3, requests to transmit at rate t,12 Let this user be astiprted codeword p and row 0 of G(Z), the Syhrester~Hadartvar~d of order 2.
Tt~ bnp sprwdtng codo for User 3 ~ given by the Kror~ecker pr~oduci of row 0 of Q~ with tho ood~w~ord os t,~,.r I+1 +tj ~ a, = I ~ al, whkh is a caps ions.
M additional user at rats l,I~ may be axanodated with the ot:hogotsai code con:Znx~ed by taking the Kronecker product of rvw 1 of G(2) with c~ to give Lr's I+; -~ l ~ ar I cs -c~ l, or 2 additional users can be supported at the rate t,I4 by taking the Kronecksr product of the rows of ,a(2) with Ln to construct L'a~
~+i ~tl~ ~ Lts s ~ C~ -~t c~ -~ and L i~ ~ I+~ -1 ) ~ Lr~ ~ I ca -C~ -C~ ~.
Noto that the codes L'm and L'~~ ane 1 ~ chips long.
SUBSTITUTE SHEET (RULE 26) At the Hub Station, the data symbols of User 3 are retrieved by correlating the signal received over time period T, = 2ff, with the long code Lm. It follows from the construction of the codes that the interterence from Users 1 and 2 is zero at the correiator output.
In summary, the example system described above can support higher rates than l, of 2f,, 4f,, and lower symbol rates of t,P2, fl4, .., l,I2Q.
It the mufti-rate system allows high hates only, at full capacity wish total system throughput 4t,, the following allocation scenarios can be supported:
a) 4 users tn3nsmit at f, b) 2 users transmit at t,, and 1 user transmits at 2f, cj 2 users transmit at 2t, dj 1 user transmits at 4f, Conversely, if the mutti~rate system allows low rates only, for each codeword cw k s D, t,2,3, some of the scenarios that can be supported are:
a) t user transmits at l, b) 2 users transmit at t,JZ
c) 2 users tn3nsmtt at 1d4, and i user tn3nsmits at 1,12 dj 4 users transmit at f,/4 ej 24 users transmit at 1,12 Note that a mauomum data rate of f, can be supported per codewotd, yielding, as befiote, a tote! system throughput of 4f,. Finally, if the muiu~rate system allows both high and low data rates, a variety of allocation scenarios are possible, end again the total system throughput is bounded by 4t,.
SUBSTITUTE SHEET (RULE 26)
SEQUENCE CODE
DIVISION MULTIPLE ACCESS (ODS-CDMA) COMMUNICATIONS SYSTEM
BacJcgmund and 8rlet Oesafption of Prior Art Sproad spectrum oortrmunica:ions is being used for a number of commert~at applications and is profrferatinp at a rapid rate. Synchronous orthogortaJ
dirsci soquence coda division multiple access (ODS-CDMA) has been proposed (sue U.S. Patent No. 5,375.140. 'Wlni~ Direct S~qu~oa Sp~c~ad Sp~ctrvm Digital Gliular Telephone Systertz', incorporated herein by refe~nce) as an effective technique for improving the capacity, i.e., bandwidth effsciency, of the rtsor~a conventions! quasj-orthogonal CDMA.
In conventional direct sequence (DS) spread spectrum CDMA systems, the irfdividual users ttanatrttit on the same frequency using different pseudo-noise (PN) codes. The PN codes are quasi-orthogonal, i.e. they have retativeiy low but nontoro cross.corratation values with each other.
oDS~COMA aysterns are designed such that alt signets are rived in tame and ~q~y sy~~. rnus all users remain orthogonal to each other and, in an idea! world, any user can be recovered with no mu~iplo access noise from otttrr users. This is most practice.! in a star configur~rd networfc whoa a multiplicity of users tran:mtt to and receive from a single Hub Si~ation. This oocsfrpuration is used in cellular as well as satellite netwottcs.
In an ODS-CDMA system, oac:h user is assigned a code which is ortnopona! to alt of the other user codas (t.e. the orthoflonal codes have a cross-comelatiott vatw of zero with each other). Further, the orthogonal code period is d~oaart such that the code repeats 8n integer number of times in a data symbol time (wualry once, since this results in the ma~dmum number of available ortnoQonal SUBSTITUTE SHEET (RULE 26~
functions). The code epoch is syncttrontzed with the symbol trans~ion= so that no data transitions occur within the code. The number of users Is limited by the number of orthogonal codes available, which is equal, at most, to the length of the code. Thersfor~e, the chipping rate is equal to the maximum number of orthogonal user~a times the symbol rate.
Efficient use of the available bandwidth is accomplished by using bi-phase sprasading and MPSK data modulation as taught In U.S. Patent Number 5,687,166, "~Aodulation System for Sproad Spectrum CD~A
Communication," incorporated herein by reference.
It is often desirable to accommodate a mix of different rata users where the rates are related by 2" where n is a positive integer. One coos-efficient way to do this is to size the system for the lowest user rate and then demutLplex higher rate data onto mu~ipie orthogonal codes, l.e. data of a user at 4 times the nominal rate would be demuttiplexed and spread onto 4 codes which are then summed for transmission. This scheme, while efficient in the use of orthogonal cods, ptoduoes a signal with a wide dynamic range which is a disadvantage for the subscriber terminal power amplifier efficiency. It also requires mutdple correl~a~tora and mutbple~onA to recover the original data stream. This technique is discussed by EJzak, et al in 'BALI: A Solution for High-Speed CDMA Data,' in 8eA Labs Tec~mical JoumaJ, vol. 2, no. 3, Summer i 987.
Another technique is disclosed in tT.S. Patent ~pplicatioa Serial Rio. 08/352,313, now o.S. Batent No. 5,57a,?21, entitled 'Orthogonal Code Division Multiple Access Commuaicatioa System having Multicarrier Modulation incorporated herein by refereaae. Za this disclosure, it is suggested that multiple ODS-CD~A signals be transmitted on orthogoaally spaced carriers (i.e. spaced at the chipping rate) and the data from a single high rate user is demultiplexed onto the multiple carriers. Once again, this results is a signal with wide amplitude variation.
SUBSTITUTE SHEET (RULE 26) In U.S. Patent Numuer 5,47 6,797 "System and Method for Generating Signal Wavefonns In a CDMA Cellular Telephone System," incorporated herein by reference, lower data rates than the nominal are supported on the celt~to-mobile link (which is orihogonat), by repeating data symbols of a low rate user a number of times to obtain the nominal symbol rate. This sequence of symbols is then spread by an orthogonal code and tn3nsmitted at a tower power proportional to the lower rate. This technique has the disadvantage of not being orthogonal code space efficient, l.e. each low rate user uses the same amount of code space as a high rate user.
In 'Design Study for a CDMA~Based Third Generation Mobile Radio System,' IEEE Joumat on Selected Areas in Communication, vol. 12, no. 4, May 19A4, Baler, et al, propose to use variable length spreading codes to support variable data rates in a CDMA system. However, they propose to use PN codes that are not necessarily orthogonal.
0bjeets of the Invention M object of this invention is to provide a means by which an ODS-CDMA
communications system can function efficiently with data races that are not all equal. This non~homogeneity in data rates allows diffenant users to communicate with different data bandwidths while the ODS-CDMA communications system signaling rate and orthogonal nature remain the same as in a homogeneous data J1 tnrthsr object of this invention i~a to provide an ODS~CD~iJ1 system which supports a mix of users, ~tith data rates related by 2', t~hich makes efficient use of the available orthogonal code space, i.e. a user with symbol rate R/k uses 1/k of the code space of a user ~rith symbol rate R.
tt a a further object of thin invention to ensure that users of all nstea tranamk a relatively cons~tt ampiirirde signal. This is of particular importance to the SUBSTITUTE SHEET (RULE 26) subscriber terminal where high transmitter power eff~cisrwy (at or near satura#on) is desicabie due to the impact on cost and power consumption.
tt is a further object of this invention to keep signal processing complexity to a Win.
sunurtary of t~ inwntlon In an ODS-COMA system, each user is assigned a code Hfilch is orthogonal to a!I of the other user codas (i.e. the orthogonal codes have a cross-correlation value of soro with oad~ other. Further, the orthogonal code period is chosen such that the code repeats an integer number of times in a data symbol time (usually once, sir~cv this r~wrtts !n the m~udmum numoer of avaltsbie orthogonal sanctions) and the code epoch is synchronized with the symbol transitions so that no data transitions occur within the code. Thus, in a perfectly sytu~tronlzsd sys:rm, the individual users can be demodulated with no lnterfen~nce from other Ths number of users is Limited by the number of orthogonal codes available, which is equal, ai most, to the length of the code. Note that the chipping rate is equal to the ma~dmum number of orthogonal users times the symbol rate. This 4npliss that, for a fixed chipping rate, a system transmitting data at a rate Qf R/4 shovid be able to accommodate 4 times ss many users as a system with rats R
Ef~rtt use of oods space in a system with a mix of user rstes ensures that a uar with rate R/4 will only oaupy 1/4 of the orthogonal function space of a user wkh rats f~ The irw~ention disclosed herein teaches an effictertt way to oonstnxt such otthoponat codes by selection of an orthogonal codebook whsnin subs~Quertoea of the codewords are also orthogonal. With such a oodsbook, short codes for high rate users are determined directly by the wbsectuecxos, and bng codes for low rate users are determined by the Kronedcer product of the subsequettoes wish an orthogonal codeword allocated to these users. I1s a SUBSTITUTE SHEET (RULE 26) pr~afen~rd embodiment, the Sytvester construction of a Haoarnard matti~c Is used to generate the orthogonal codebook Thus, this invention discloses how to effidently support variable data rates in a synchronous OOS-CDMA
communication system with const8nt chip rate.
The novelty of this invention lies in the selection of an orthogonal codebook which enables high rate data to be spread using shorter codewords, and conversely, low rate data to be spread using longer codewords, aJt of which rort~ain mutually orthogonal.
Further, using this invention, each user tn~nsm'rts a single code that is constant in amplitude and n3qulres no data multiplexing or demutupiexing. The disclosed technique r~asuits in tow receiver and tn3nsmitter complexity since no additional coda generators or comelators are required to accommodate rates that are higher or lowor than the nominal data rate. Further, the constant amplitude nature of the signal allows efficient power amplification.
Desalption o! the Drawirtps Figure 7. Diagntm of mufti-rate ODS-CDMA Return Unk Stturxure with M users Figure 2. Diagn~rn of an Exemplary ODS-CDMA Receiver at the Hub Statirort Did Description of the inwnf3on .A generalized atruc4rre for an OOS-ODMA communications system is itfusttat~d in F~a~e 1. A Return Unk structure is shown to facilitate the invention de:cxiptton, however, the concept can be applied to the Forward Link as well.
In the Return Link , many users communicate with the Hub Station by nwans of a modulator and transmitter process that uses some medium for transmission. The most common medium for transmission is radio frsquarxy el~tromagnotic radiation. In this example, all users in the Return Link transmit on the same carrier frequency using the same type of modulator. it is necessary that the users transmit at time instances such that all signals nxeived at the flub SUBSTITUTE SHEET (RULE 26) Station are time ayrxhronous. The waveform uansmitted by each user comprises of MPSK modulated data spread w'rth an orthogonal ODS-COMA code.
in order to axommodate muttiple data rates while maintaining a constant chip rate for all assns, the length of spreading code for each user is varied. M
orthogonal codebook is constructed which enables high note data to be spread usMg shorter codewords, and conversely, low rate data to be spread using longer codevrorris, all of which remain mutually orthogonal. In a preferred embodiment, the Syivester conswctlon of a Hadamard matrix is used to generate the codebook.
It is well known . in the art that a Sytvester Hadamard matrix of dimension N
Is defuwd recursively as N(11I )s 'N(N/1) H(NI2) N(N/1) -H(NII) where H~t) ~ ~ ~ and N = 2", where n is a positive integer. The N news of the Ha~dertw~d matrix H(N) define an orthogonal codebook !=or convenience, the rows are indexed from 0 tv IW 1, starting from the top row. It can be seen from the recursive construction of H(N) that it is composed of SyivestehNadamard sutxnatrices of the form tH(11~), where k is a positive integer ranging from 1 to n-t. Since the rows of H(NI~') are orthogonal, tt follows that the codeworda of H(IY) consist of subsequsnoes of length N/2'" that arse orthogonal as well.
Conewst a mufti-rate OOS-00MA communications system with fixed chip rats ta, some fundaments! data symbol rate t,, and a codebook of N orthogonal sequences such that f~~ All,. tf there exist M Retum tJnk users with data streams at the fundamental symbol hate, each user may be assigned one of the N
otthopon$I oodeworda as long as M S N . However, it there exist users that re4ues! higher or lower data rates compared to the fundaments) rate. they may be as:~sd shorter or Longer codewords, respectlv~ety. These shorter (ionperj cafes are coed from the codeword in a fashion such that the orlhogortal SUBSTITUTE SHEET (RULE 26) WO 99/45669 ~ PCT/US99/03722 nature of the OOS-CDMA system is maintained and tt~e code space !s used efficiently. An illustrative example is considered first to motivate the general approach for constructing these variable length codewords.
Suppose one of the users request a higher symbol rate, say at twice the fundamental rate 2f,. Since the chip rate, which is the product of the spreading sequence length and the symbol rate, is fixed, it follows from f~
=(IY~'2)(2f,~, that the spreading sequence length per symbol must be reduced to NI2. This can be implemented by spreading attemate symbols of the high rate user by the first chips of a codeword and the last N/'2 chips of the same codeword. Since this codeword is sub-divided into two N/~ subsequences, the remaining codewords must be orthogonal over each of these two subsequences such that the users at fundamental rate f, and the high rate user at 2f, do not mutually interfere, thereby maintaining otthogonality in the ODS-CDMA system. Consider allocating the k°' codeword to this user (k = O,1,...,N~1). If a Sytvester~Hadamard matrix is used as the orthogonal codebook, the (k+(N~2))~"o~v~ codeword does not possess the rsqufred llfl'2 subsequence orthogonalityr since it contains the same two subsequences (up to a t sign) and therefore cannot be allocated to other users.
For example, if the high rate user is assigned the ka' code word ck = [S~ S~j, the oodeword q s [S~n -S~j .for j ~ (k+(11t12))",o,~,v~ cannot be assigned to another user, and vice versa. Note that if a user at rate 2f, Is assigned a single short subsequence in Afl2 space (say subsequence Sue, this is equivalent to usirtp two codewords in the N space codebook. Hence, in an attemative implementation, a rate 2!, user may be supported by assigning the user a shorter subsequence of length fYl2, and removing the codewocds which contain this subsequence from the list of allocable codewords.
In gsnstal, a mufti-rate ODS-CDMA system with a codebook of N Syiveater-Hadamard sequences (N = 2° for some integer p), fundamental data symbol rate f,~ and a faced chip rate f~ ~ Nf,, can support users with higher data rates than the fundamental rate. The users may reques~i to transmit data at notes 2'f,, whets r SUBSTITUTE SHEET (RULE 26) ranges from 0 to p. This is achieved by reducing the length of the spr~aading code to IYr1' such tnat the chipping rate, ~_ =(NI1')(2't,J, remains constant.
Subsequences of length NI~ can be generated by sub-dividing an allocated codeword of ieneth N into 2'sub-codes. These sub-codes are used to spread 2' consecutive symbols of a data stream at rate 2'.; . Note that in the case of the Syivester-Hadamard sequences, any codeword of length N is a repeated subsequence of length NI2' (up to a t sign), which is orthogonal to the other non-idenZjccal subsequences of the same length.
Further, if the k~' codeword is composed of a repeated subsequence of length NI~' (up to a t sign), tnen the codewords (k+I(NI~');"ae~,,r~. for alt i =
t,Z.....2'-1 and r s 0, are also composed of the same subsequence (up to a t sign), and are no longer available for atlocatlon, if system orihogonality is to be preserved.
Indeed, supporting t user at data rate 2'f, is effectively equivalent to supporting 2rtusrs at rate f, since 2'~t codes are rendered unusable.
irt a network setting where muulple users are transmuting ai different data rates, appropriate provisions must be made for accommodating the data rate request of a new user in terms of checking for allocable subsequences. tn fact, the network corttrolier must. before assigning a subsequence. make certain first, a is not cor>binsd in the tongersubsequence of a lower note user (since the lower rate user would not be orthopona! over the subsequence length). Further, a must not oor~n a subsequence of shorter length that is already in use.
It is advantageous for the network controller to have the capability to change orthvponal sequence assignments periodically in order to most efficiently use the code space as the mix of user rates changes. tn addi~on, since the symbol ireerval of data at rate 2'f, is reduced to tI2'times the symbol interval of data at rstl to it may be desired, depending on the application, to Increase the trnnatnlt power by'2'to maMtaln the same level of perto:manos.
SUBSTITUTE SHEET (RULE 26) Conversely, a mutti.rsie OOS-COMA communkatjon sys~t~sm with a oode~boolc of N orthogonal sequences, fundamental data rate t, , and a faced chip rate to ~
Nto , can support users with lower data notes than the fundaments! note. The assts may request to transmit data at rates tl~', where r is a positive Integer ranging from 0 to q. A bwer rate user, at rate t,12', is assigned a beget spreading code of length 2'N such that ripe chipping rate. to ~(2~IV)(ll~'). ren»ins cor~Wtt.
The long coda is ~ns~ctsd ham the codeword allocated to this user, c,~ k~r 0,...,N~), as First, an ortho~onat function set G(2') of slzs 2' is constructed. This could be, but is not necessarily, a Syhrester~Hadamaud matrsx. The tCronecker product of the f' row of G(2') with the codeword_crr Produces a member L,,,d j s 0.....2''~1 of a set of 2r mutually orthogonal codes of length 2'N. Each of ~ese long sequerxes is orthoponaJ to codewords p, where l ~ J~ as well ,es longer code words l.~
tom~d by the ttronecker product of each row of G(2') with the codeworda c~. Thus, up to 2~ assts of rate ll~ can be assigned to a single code word ar by assigning each user a different row of G(~'). This code constructjon technique can be ~neta~ted to~accommodate a mix of users with dffferent n~tss of the form l,/~', whh ttta rruuamum aggrapate symbol rate bounded by !, .
Ttw proposed :dtsme :appeals that the symbol interval of data at rata tl~ Is inaaa:od to 2'timos the symbol Intenrat Ot data at n~ t,. tt may be dosired that a urer at the lower data rate reduce transmit power by 2~ In order to malrttaln the same aymbo!-to~noiw.imarDy ratio (FaINo~.
Tha Hub Stadon nosiwa a auperposJdon of signal wavefortna tranwnltttd by the R~lum kink uss~rs. Tho rs~h~ed signet to demodulated and despnad by thr mui4.rate OOS-CDMA rs~hrer. The ~iespr~eadlnp operation lrw~ohres oomolatinp tho noshed wawtorm with the sproadinp sequence of the desirod user aver a .symbol tntsrval. Hence, In a mutti~rate ayssem that supports users at higher data rasps than !,, the waveform of a user at rate 2't, is despread by correladrtp k SUBSTITUTE SHEET (RULE 26) against the uses allocated 1111'' chip subsequence. Conversely, in a muhi-rate system that supports users at lower data, rates than t,, t#~e wavefom~ of a user at nits l,~' is despread by cometatinp rt with the users allocated 2'N chip Kronecker-product code. In both cases, the despreadinp operation requires that the codewords of ail users be time aligned at the code boundaries in order to proserve orthoflonality, and that the data symbol rates of ail users be known at the reoerver. Furthermore, tn a system supporting lower rates, the row index of G~2'), used in fom~ing the Krcneckerproduct coda, must be known at the reviver. Appropriate provisions are to be made in a mufti-rate ODS-CDMA
system to satisfy these requiremen3s.
A functional block diapn~m of the Retum Unk stnrcture in the proposed mufti-rate ODS-CDMA system is showy tn Figure 1. in this figure, M users transmit data to the Hub Station at data symbol rates 2r'f,, 2~t,..... 2''~t, , where rj, J =
1,...,M, ranges from 0 to p for a system supporting higher rates than f,, from -q to 0 fog a system supporting tower rates than f,, and -q to p for a system supporting both high rate and bw rates. tf the ~ user requests a higher rate (r~ z 0), the users cods generator peneratos a codeword of length N ai rate f,, whkh is equhral~nt to peneratlnA 2'~ sub~codes of length 2''~N in dime-division mu~ipiex at rate 2'~t,.
On the other hand, it the ~th user requests a lower rate (r~ S 0~, ~e user's code penerstor generates a Kronecicer-product code of length 2''dN ai rate 2~f,.
Hence, at ~ symbol interval, Tj = 1/(2'Jf,~, the data symbol of the ~th user is muttipUed by the codeword from the code generator, and the resulting chip sequence is modulated and:ransrnfttad to the Hub station.
Ttta Hub Station reoeiwss the composite signal wavefortn of the M Retum Lhk users. The functional bbck diagram of an exemplary mutii.rate ODS-CDMA
receiver at the Hub Station is shown in !=figure 2. The receiver demodulate' the noeivod waveform and despresds tt i=or the ~th user with r~ z 0. despreading irtv~olves fomtatdnp oach bbck of N chips of demodulated data into su~quances of length 2'~N. and correlating each of these subsequenoes with SUBSTITUTE SHEET (RULE 2fi) the sub-code from the code generator. If rj S D, each block of 2"dN chips is correlated with the long code from the code generator. In the absence of channel distortions, the correiator output yields the user data.
A simple illustrative example which embodies the present invention is as follows.
Consider a mufti-rate ODS-CDMA system w'tth a codebook derived from Syivester-Hadamard matrix of dimension N = 4, +1 +1 +1 +1 c.~
N(4)= +1 -1 +i -1 s c, +1 +1 -1 -1 Cs +1 -1 -1 +1 fundamental data symbol rate f,, and fixed chip rate f~ ~4f,.
Suppose User 1 is assigned codeword 0, co a [+1 +1 +1 +1 ), and is transmitting at rate f,. Now, a new user, User 2, requests to transmit at rate Zl,.
From the codes available for allocation, c,, c? and ca only c, or c~ may be allocated to Uset 2 since the length 2 subsequences of ca namely [+1 +i j and [-1 -7 ), are not orthogonal to the corresponding subsequences of cd. Let code c, be assigned to User 2. The chip sequence tn3nsmitted by User 1 within the time interval T,= tlf, is xr'~ s sf'~(+1 +1 +1 +1 ), where s~'~ is the current data symbol.
Simttaf'iy, the chip sequence tn3nsmitted by User 2 within the same time interval is x~ ~ (sw[+t ~1l set[+t -1p, where s,~ and ab~ are the current data symbols. Note that with the current allocation scenario, only code c~ is available for allocation to a new user with symbol rate f, or tower. A user that requests a higher symbol note cannot be supported unless the codes are n~assigned.
The signal received at the Hub Station (after demodulation) is of the form r s xf ~~ + Jr~
= sf'~[+i +t +1 +1 ) + ~s,~[+1 -1 ) sow[+1 .1D.
SUBSTITUTE SHEET (RULE 26) The signal is despread by cometating n with the appropriate ~apnsading code.
For User 7, this is achieved by computing the foliowin8 inner product +i '~l~ ~ 4 ~~ +1 ' +i whkh yields the transmtt:fed data symbol. The data symbols of User 2 aro retrieved by first pattiboning the received chip sequence into 2 subsequences, t, . ~~+1 +1 j + s,~+1 ~1 J arid rb ~ ar"~+1 +1 ) + ~,~I+1 ~1 j and then computing the following inner products 1 +i s i=~ ~",.~ .
' 2 ' -1 and 1 +1 syr=~ ~,~~' , 2 -i Now, suppose a third user, User 3, requests to transmit at rate t,12 Let this user be astiprted codeword p and row 0 of G(Z), the Syhrester~Hadartvar~d of order 2.
Tt~ bnp sprwdtng codo for User 3 ~ given by the Kror~ecker pr~oduci of row 0 of Q~ with tho ood~w~ord os t,~,.r I+1 +tj ~ a, = I ~ al, whkh is a caps ions.
M additional user at rats l,I~ may be axanodated with the ot:hogotsai code con:Znx~ed by taking the Kronecker product of rvw 1 of G(2) with c~ to give Lr's I+; -~ l ~ ar I cs -c~ l, or 2 additional users can be supported at the rate t,I4 by taking the Kronecksr product of the rows of ,a(2) with Ln to construct L'a~
~+i ~tl~ ~ Lts s ~ C~ -~t c~ -~ and L i~ ~ I+~ -1 ) ~ Lr~ ~ I ca -C~ -C~ ~.
Noto that the codes L'm and L'~~ ane 1 ~ chips long.
SUBSTITUTE SHEET (RULE 26) At the Hub Station, the data symbols of User 3 are retrieved by correlating the signal received over time period T, = 2ff, with the long code Lm. It follows from the construction of the codes that the interterence from Users 1 and 2 is zero at the correiator output.
In summary, the example system described above can support higher rates than l, of 2f,, 4f,, and lower symbol rates of t,P2, fl4, .., l,I2Q.
It the mufti-rate system allows high hates only, at full capacity wish total system throughput 4t,, the following allocation scenarios can be supported:
a) 4 users tn3nsmit at f, b) 2 users transmit at t,, and 1 user transmits at 2f, cj 2 users transmit at 2t, dj 1 user transmits at 4f, Conversely, if the mutti~rate system allows low rates only, for each codeword cw k s D, t,2,3, some of the scenarios that can be supported are:
a) t user transmits at l, b) 2 users transmit at t,JZ
c) 2 users tn3nsmtt at 1d4, and i user tn3nsmits at 1,12 dj 4 users transmit at f,/4 ej 24 users transmit at 1,12 Note that a mauomum data rate of f, can be supported per codewotd, yielding, as befiote, a tote! system throughput of 4f,. Finally, if the muiu~rate system allows both high and low data rates, a variety of allocation scenarios are possible, end again the total system throughput is bounded by 4t,.
SUBSTITUTE SHEET (RULE 26)
Claims (10)
1. In an ODS-CDMA communications system with at feast one Hub Station and a plurality of user terminals, a means for generating a codebook of N
orthogonal sequences where N = 2° for some integer p, a fundamental data symbol rate f s, and a fixed chip rate f c where f c = N f s, the improvement comprising:
means for supporting users with multiple data rates by assigning them mutually orthogonal codes of different lengths, while maintaining, the same chip rate, and the same peak-to-average ratio at the transmitter as in a homogeneous data rate system.
orthogonal sequences where N = 2° for some integer p, a fundamental data symbol rate f s, and a fixed chip rate f c where f c = N f s, the improvement comprising:
means for supporting users with multiple data rates by assigning them mutually orthogonal codes of different lengths, while maintaining, the same chip rate, and the same peak-to-average ratio at the transmitter as in a homogeneous data rate system.
2. In the system of Claim 1, where users desiring to tnansmit data at a rate of 2r f s, where r ranges from 0 to p, are assigned orthogonal subsequences of length N/2 r generated by sub-dividing the allocated codeword of length N, from the codebook of N orthogonal sequences, into 2 r subsequences.
3. In the system of Claim 1, the Sylvester construction of a Hadamard matrix is used to generate the orthogonal codebook such that select subsequences of the codewords in the codebook are also orthogonal.
4. The system of Claim 1, wherein users may request lower rates than the fundamental data symbol rate f s. The data symbols of a low rate user at rate f s/2r, where r may range from 0 to q, are spread using a longer code of length 2r N, which is constructed by the Kronecker product of a length 2 r orthogonal code and the N chip codeword allocated to this user.
5. The system of Claim 1, wherein users may request lower rates than the fundamental data symbol rate f s. The data symbols of a low rate user at rate f s/2 r, where r may range from 0 to q, are spread using a longer code of length 2r N, which is constructed by the Kronecker product of a row of the Syhrester-Hadamand matrix N(2r) and the N chip codeword allocated to this user.
6. In ah ODS-CDMA communications system with at least one Hub station and a plurality of user terminals. one or more satellites or other means for relaying the signals to and from the Hub Station, a means for generating a codebook of N orthogonal sequences where N = 2p for some integer.p, a fundamental data symbol rate f s, and a fixed chip rate f c where f c = N f s, the improvement comprising:
means for supporting users with multiple data rates by assigning them mutually orthogonal codes of different lengths, while maintaining, the same chip rate, and the same peak-to-average ratio at the transmitter as in a homogeneous data rate system.
means for supporting users with multiple data rates by assigning them mutually orthogonal codes of different lengths, while maintaining, the same chip rate, and the same peak-to-average ratio at the transmitter as in a homogeneous data rate system.
7. In the system of Claim 6, where users desiring to transmit data at a rate of 2r f s, where r ranges from 0 to p, are assigned orthogonal subsequences of length N/2 r generated by sub-dividing the allocated codeword of length N, from the codebook of N orthogonal sequences, into 2 r subsequences.
8. In the system of Claim 6, the Sylvester construction of a Hadamard matrix is used to generate the orthogonal codebook such that select subsequences of the codewords in the codebook are also orthogonal.
9. The system of Claim 6, wherein users may request lower rates than the fundamental data symbol rate f s. The data symbols of a low rate user at rate f s/2r, where r may range from 0 to q, are spread using a longer code of length 2 r N, which is constructed by the Kronecker product of a length 2r orthogonal code and the N chip codeword allocated to this user.
10. The system of Claim 6, wherein users may request lower rates than the fundamental data symbol rate f s. The data symbols of a low rate user at rate f s/2r, where r may range from 0 to q, are spread using a longer code of length 2r N, which is constructed by the Kronecker product of a row of the Sylvester-Hadamard matrix H(2r) and the N chip codeword allocated to this user.
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| PCT/US1999/003722 WO1999045669A1 (en) | 1998-03-04 | 1999-03-01 | Apparatus for incorporating multiple data rates in an orthogonal direct sequence code division multiple access (ods-cdma) communications system |
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| US6222832B1 (en) | 1998-06-01 | 2001-04-24 | Tantivy Communications, Inc. | Fast Acquisition of traffic channels for a highly variable data rate reverse link of a CDMA wireless communication system |
| US8134980B2 (en) | 1998-06-01 | 2012-03-13 | Ipr Licensing, Inc. | Transmittal of heartbeat signal at a lower level than heartbeat request |
| US6885691B1 (en) * | 1999-08-02 | 2005-04-26 | Lg Information & Communications, Ltd. | Scrambling codes and channelization codes for multiple chip rate signals in CDMA cellular mobile radio communication system |
| AU3673001A (en) | 2000-02-07 | 2001-08-14 | Tantivy Communications, Inc. | Minimal maintenance link to support synchronization |
| US6728225B1 (en) | 2000-02-10 | 2004-04-27 | Interdigital Technology Corporation | Asymmetrical forward/reverse transmission bandwidth |
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1999
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- 1999-03-01 AU AU27781/99A patent/AU748010B2/en not_active Ceased
- 1999-03-01 JP JP2000535113A patent/JP4361682B2/en not_active Expired - Fee Related
- 1999-03-01 CN CNB998058238A patent/CN1193528C/en not_active Expired - Fee Related
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- 1999-03-01 WO PCT/US1999/003722 patent/WO1999045669A1/en active IP Right Grant
- 1999-03-01 EP EP99908319A patent/EP1060588A4/en not_active Ceased
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| CN1299542A (en) | 2001-06-13 |
| JP2002506320A (en) | 2002-02-26 |
| WO1999045669A1 (en) | 1999-09-10 |
| CN1193528C (en) | 2005-03-16 |
| EP1060588A4 (en) | 2005-07-13 |
| AU748010B2 (en) | 2002-05-30 |
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