CA2102082C - Despreading technique for cdma systems - Google Patents
Despreading technique for cdma systemsInfo
- Publication number
- CA2102082C CA2102082C CA002102082A CA2102082A CA2102082C CA 2102082 C CA2102082 C CA 2102082C CA 002102082 A CA002102082 A CA 002102082A CA 2102082 A CA2102082 A CA 2102082A CA 2102082 C CA2102082 C CA 2102082C
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- code
- sequence
- coded
- symbol
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/14—Relay systems
- H04B7/15—Active relay systems
- H04B7/204—Multiple access
- H04B7/216—Code division or spread-spectrum multiple access [CDMA, SSMA]
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B1/707—Spread spectrum techniques using direct sequence modulation
- H04B1/7097—Interference-related aspects
- H04B1/7103—Interference-related aspects the interference being multiple access interference
- H04B1/7105—Joint detection techniques, e.g. linear detectors
- H04B1/71052—Joint detection techniques, e.g. linear detectors using decorrelation matrix
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04K—SECRET COMMUNICATION; JAMMING OF COMMUNICATION
- H04K1/00—Secret communication
- H04K1/02—Secret communication by adding a second signal to make the desired signal unintelligible
Abstract
Despreading of the received signal in a CDMA system is provided using code coefficient sequences which are derived from those utilized by the system users to encode their respective symbols. Each derived code coefficient sequence is a function of the correlation between a different user's code coefficient sequence and the code coefficient sequences of all other users. Advantageously, this technique substantially reduces interference effects and is suitable for use in the despreader of differentially or nondifferentially coded CDMA systems.
Description
2 ~
DESPREADING TECHNIQUE FOR CDMA SYSTEMS
Te~ Field The present invention pertains to recovering tr~ngmit~ed data in the receiver of a Code Division Multiple Access (CDMA) system and, more particularly, S to such a system wherein the symbols of each user are recovered by despreading a received signal which is a co~ o~i~e of all users' symbols.
Ba~ uu~ld vf the I~
CDMA is a signal mo~ ti~n technique used in a variety of applications, such as cellular and wireless cc~ ",~,ir~ti-lns systems. In such 10 systems, multiple users co".. ~ r at will with a base station over a common ~
frequency band, with each user trtln~mit~ing a uniquely coded signal. Consequently, the received signal at the base station is a composite of many dirr.,~ ly coded slgnals.
At each user's L~ ;ltl,l, that user's coded signal is formed using a 15 sequence of code coeffi~ ntg in ei~her of two ways. In non~1irr~ .~ntially encoded CDMA systems, each user's symbol is multiplied by a sequence of code coefficients.
In dirr~ ially coded systems, instead of multiplying each user symbol by a code sequenre, the ~lirrt;l~,nce between cer ain symbols and preceding symbols is mllltirliPd by the se~ e of code coefficients. In either arr~ngPm~nS, the 2û mllltirlir~ti~n process is known as spreading since the signal spectrum of the coded output symbols extends across a wider frequency range than that of the uncoded user symbols. At the receiver, each user's encoded digital symbols are recovered fromthe in~oming co.llposile signal using a signal despreader. In the dcs~Jlc,adel, each user's symbols are l~cov~,lGd by multiplying the incoming colllposil~ signal with an 25 ~oci~tsd one of a plurality of different code coefficient sequences. In ~he prior art, the code sequenre ~so~ ted with each user is a replica of the code sequence used to encode that user's symbols.
It has long been recogni7ed that during ~:~n~mi~ n a substantial amount of illltilr~ ,nce can be introduced into each coded signal from the other30 coded signals and co...l~en ~ on for this illLt; rel5;-lce must be provided for intelli~ihl~ co,,,,,~ oni. To reduce this in~elrt;lcllce, a number of different in~ f~,nce reduction t~chni~lues have been devised. In one prior art technique, us is used in the receiver which operates on each user's symbols outputted by a despreader using priorly recovered other users' symbols. See, for example, U.S.
35 Paten~ No. 5,136,612, issued August 4, 1992 and entitled "Method and ApparahJs for 2 ~
Reducing Effects of Multiple Access Interference in a Radio Receiver in a Code Division Multiple Access Commnni~atinns System". Another class of prior art systems uses an approach which operates on the received composite signal over a time interval using blocks of code coefficients where;n each block includes the code 5 coeffi~iPnts of each user corresponding to this time interval. See, for example, a publication entitled "Near-Far Resistance of Multiuser Detectors in Asynchronous~h Inn~15'', I.E.E.E. Transactions on Commnnir~ions, Vol. 38, No. 4, April 1990,and, more recently, a pending patent application entitled Data Recovery Technique for Asynchronous CDMA Systems, Serial No. 982,168, filed on November 24, 1992, 10 and assigned to the present assignee. The potential sho}tcoming with all of these prior art arrSln~PmPnt~ is that they require the adclition of hl~elr~,lcnce canceller ' circuitry in the receiver and thus incur the cost of implem~onting such circuitry. In ~1(1iti~n, they are not readily suitable for improving the pelru~ll-al~ce capabilities of existing CDMA systems on a retrofit basis.
It would, ~h~lGru~e, be desirable if a low-cost, data recovery technique could be developed for CDMA systems which can be readily added to existing systems.
Summary of the I~ liul~
Broadly, the sh~ O~ of the prior art CDMA data recovery 20 techniques are OVt;1~;0111G, in accordance with the present invention, by despreading the ~eceived signal using code coeffiri~nt seqn~nres which are different from those utilized by the users to generate their respective coded signals. More particularly, a coded user signal is ir~n~mitted for each of a plurality of users by processing that user9s symbol by an associated sequence of code coefficients. Accordingly, the 25 received signal is a composite of all coded user signals. In the receiver, each coded user signal is recovered using a different derived code cobrrlcielll sequence. Each derived code coGrLciellL sequence i3 a function of the correlation of the code coçffici~nt sequence associated with one of the system wsers and those code coeffirient sequences associated with the other system users. Advantageously, this 30 technique s~lbst~ntially reduces int~,l~bncb-induced decoding elTors and is suitable for use in the des~readbi in either differentially or nnn(liff~rentially coded CDMA
systems.
In the disclosed embo~im~nt~, each derived code coefficient sequence is formed by multiplying the code coeffi-~ient~ in an associated seqn~n~e by weighting 35 factors.
~2~38~
DESPREADING TECHNIQUE FOR CDMA SYSTEMS
Te~ Field The present invention pertains to recovering tr~ngmit~ed data in the receiver of a Code Division Multiple Access (CDMA) system and, more particularly, S to such a system wherein the symbols of each user are recovered by despreading a received signal which is a co~ o~i~e of all users' symbols.
Ba~ uu~ld vf the I~
CDMA is a signal mo~ ti~n technique used in a variety of applications, such as cellular and wireless cc~ ",~,ir~ti-lns systems. In such 10 systems, multiple users co".. ~ r at will with a base station over a common ~
frequency band, with each user trtln~mit~ing a uniquely coded signal. Consequently, the received signal at the base station is a composite of many dirr.,~ ly coded slgnals.
At each user's L~ ;ltl,l, that user's coded signal is formed using a 15 sequence of code coeffi~ ntg in ei~her of two ways. In non~1irr~ .~ntially encoded CDMA systems, each user's symbol is multiplied by a sequence of code coefficients.
In dirr~ ially coded systems, instead of multiplying each user symbol by a code sequenre, the ~lirrt;l~,nce between cer ain symbols and preceding symbols is mllltirliPd by the se~ e of code coefficients. In either arr~ngPm~nS, the 2û mllltirlir~ti~n process is known as spreading since the signal spectrum of the coded output symbols extends across a wider frequency range than that of the uncoded user symbols. At the receiver, each user's encoded digital symbols are recovered fromthe in~oming co.llposile signal using a signal despreader. In the dcs~Jlc,adel, each user's symbols are l~cov~,lGd by multiplying the incoming colllposil~ signal with an 25 ~oci~tsd one of a plurality of different code coefficient sequences. In ~he prior art, the code sequenre ~so~ ted with each user is a replica of the code sequence used to encode that user's symbols.
It has long been recogni7ed that during ~:~n~mi~ n a substantial amount of illltilr~ ,nce can be introduced into each coded signal from the other30 coded signals and co...l~en ~ on for this illLt; rel5;-lce must be provided for intelli~ihl~ co,,,,,~ oni. To reduce this in~elrt;lcllce, a number of different in~ f~,nce reduction t~chni~lues have been devised. In one prior art technique, us is used in the receiver which operates on each user's symbols outputted by a despreader using priorly recovered other users' symbols. See, for example, U.S.
35 Paten~ No. 5,136,612, issued August 4, 1992 and entitled "Method and ApparahJs for 2 ~
Reducing Effects of Multiple Access Interference in a Radio Receiver in a Code Division Multiple Access Commnni~atinns System". Another class of prior art systems uses an approach which operates on the received composite signal over a time interval using blocks of code coefficients where;n each block includes the code 5 coeffi~iPnts of each user corresponding to this time interval. See, for example, a publication entitled "Near-Far Resistance of Multiuser Detectors in Asynchronous~h Inn~15'', I.E.E.E. Transactions on Commnnir~ions, Vol. 38, No. 4, April 1990,and, more recently, a pending patent application entitled Data Recovery Technique for Asynchronous CDMA Systems, Serial No. 982,168, filed on November 24, 1992, 10 and assigned to the present assignee. The potential sho}tcoming with all of these prior art arrSln~PmPnt~ is that they require the adclition of hl~elr~,lcnce canceller ' circuitry in the receiver and thus incur the cost of implem~onting such circuitry. In ~1(1iti~n, they are not readily suitable for improving the pelru~ll-al~ce capabilities of existing CDMA systems on a retrofit basis.
It would, ~h~lGru~e, be desirable if a low-cost, data recovery technique could be developed for CDMA systems which can be readily added to existing systems.
Summary of the I~ liul~
Broadly, the sh~ O~ of the prior art CDMA data recovery 20 techniques are OVt;1~;0111G, in accordance with the present invention, by despreading the ~eceived signal using code coeffiri~nt seqn~nres which are different from those utilized by the users to generate their respective coded signals. More particularly, a coded user signal is ir~n~mitted for each of a plurality of users by processing that user9s symbol by an associated sequence of code coefficients. Accordingly, the 25 received signal is a composite of all coded user signals. In the receiver, each coded user signal is recovered using a different derived code cobrrlcielll sequence. Each derived code coGrLciellL sequence i3 a function of the correlation of the code coçffici~nt sequence associated with one of the system wsers and those code coeffirient sequences associated with the other system users. Advantageously, this 30 technique s~lbst~ntially reduces int~,l~bncb-induced decoding elTors and is suitable for use in the des~readbi in either differentially or nnn(liff~rentially coded CDMA
systems.
In the disclosed embo~im~nt~, each derived code coefficient sequence is formed by multiplying the code coeffi-~ient~ in an associated seqn~n~e by weighting 35 factors.
~2~38~
Brief Description of the Drawin~
FIG. 1 is a block-schematic diagram of receiver circuitry in accordance with alternative embodiments of the present invention for nondifferentially encoded CDMA systems;
FIG. 2 is a block-schem~tir diagram of each of the objective function nel~lol~ in FIG. l;
FIG. 3 is a block-schematic diagram of receiver circuitry in accordance with alLtlllalivc embor1im~nt~ of the present invention for dirr~,.GIltially encoded CDMA systems;
FIG. 4 is a block-schçm~ic diagram of each of the objective function gelle~ ol~ in FIG. 3; and FIGS. 5, 6 and 7 are block-schematic diagrams of alternative additional circuitry which can be used with the circuitry of either FIG. 1 or 3.
I)etailed Description The present invention will be described in reference to an illustrative CDMA system in which the chip streams of n users, where n is a pre,~let~,rmin.o,d integer greater than 1, arrive at a base station. As is well-known, each user tr:~n~mit~
coded symbols, at will, to the base station. At each user's tr~nsmitter, each user's chip stream is ge~ ed by multiplying each symbol by a sequence of code 20 coçffic;Pnt~ or spreading code which includes a plllrality of code co' M~ien~ As a result, if there are m code coeffi~ient~ in each sequence, where m is a prerlt termined integer greater than l, there are m chips Ll~ c,.,il~ ~d for each symbol. Each symbol is one of a plurality of discrete user-supplied signal amrlit~l~le values and each symbol is ~ ,i,e~lL~liv~ of a bit or a plurality of such bits. Typically, each 25 coefficient in a spreading code is either -1 or +1 and is generated using a psell(1or~qn(lc m ge~ .L~l. It should be noted that the spreading code is both unique for each user and varies from symbol interval to symbol interval fi~r any user.
At the base station receiver, the incoming signal includes a Co~ o~i~c of all user chip streams. These chip streams are typically delayed relative to one 30 another due to the asynchluilous nature of the cf""""~"~ on~ between any user and the base station. To recover each user's symbols, each user's chip st~eam must be extracted from the received signal. This is accomplished by a signal despreader which, in the prior aTt, multiplies the received signal during a symbol interval by a replica of each user's sequence of code coefficien~ for that interval. Pursuan~ to the 35 present invention, it has been recognized that in CDMA systems of the type ~escrihed above, white (3;~ n noise is negligible co~ cd to the inte~rclcnce in 2J 02~32 each user's chip stream introduced by other user chip strcams. It is further recognized that the h~G~rt;lcllce in any user chip stream in any symbol interval is a function of the correlation between that user's sequence of code coefficients and the sequences of code coefficients for all other users for that symbol interval. TheS present invention utilizes this principle by the utili~ation of a signal despreader which multiplies the received signal in a symbol interval by a sequence of code coeffi~ n~s for each user which is an alteration of a replica of that user's code coefficient sequence in the symbol interval. The alteration is a function of theabove-recited correlation. Therefore, the alteration is user-specific, i.e., it varies 10 from user to user and, in ~cklitiQn, since th~ correlation varies from symbol interval to symbol interval, it follows that the alteration for any user also varies from symbol interval to symbol interval.
The code coefficients within each sequence in a symbol interval will now be ~i~Cll~se(1 At the outset, it will be noted ~hat the code coefficients for the i'h 15 user, where 1 < i ~ n, folms a sequence of code coeffi~i~nt~ c; in a symbol interval which can be written as:
Ci = (Cil,Ci2, ~ ~ ~, Cim) where the ~ul~e~ T ~ G;,e~ the transpose of a vector and the second subscript of each code coefficient in the sequence c i ~ e~ the position of that coefficient 20 in the sequence of m coeffirienti.
The composite of all n vectors ci can be expressed as an m by n matrix C, where C = (cl,c2, . ~ ~, Cn)~ (2) and the matrix C contains the code coeffi~iPnt~ for all users in one symbol interval.
25 Each vector ci can be eYrantlt.d into an m by m diagonal matrix C i which can be sst,d as Ci = diag(cil,ci2, ~ ~ ~, Cirn) ~ (3) : : ~
%10~
FIG. 1 is a block-schematic diagram of receiver circuitry in accordance with alternative embodiments of the present invention for nondifferentially encoded CDMA systems;
FIG. 2 is a block-schem~tir diagram of each of the objective function nel~lol~ in FIG. l;
FIG. 3 is a block-schematic diagram of receiver circuitry in accordance with alLtlllalivc embor1im~nt~ of the present invention for dirr~,.GIltially encoded CDMA systems;
FIG. 4 is a block-schçm~ic diagram of each of the objective function gelle~ ol~ in FIG. 3; and FIGS. 5, 6 and 7 are block-schematic diagrams of alternative additional circuitry which can be used with the circuitry of either FIG. 1 or 3.
I)etailed Description The present invention will be described in reference to an illustrative CDMA system in which the chip streams of n users, where n is a pre,~let~,rmin.o,d integer greater than 1, arrive at a base station. As is well-known, each user tr:~n~mit~
coded symbols, at will, to the base station. At each user's tr~nsmitter, each user's chip stream is ge~ ed by multiplying each symbol by a sequence of code 20 coçffic;Pnt~ or spreading code which includes a plllrality of code co' M~ien~ As a result, if there are m code coeffi~ient~ in each sequence, where m is a prerlt termined integer greater than l, there are m chips Ll~ c,.,il~ ~d for each symbol. Each symbol is one of a plurality of discrete user-supplied signal amrlit~l~le values and each symbol is ~ ,i,e~lL~liv~ of a bit or a plurality of such bits. Typically, each 25 coefficient in a spreading code is either -1 or +1 and is generated using a psell(1or~qn(lc m ge~ .L~l. It should be noted that the spreading code is both unique for each user and varies from symbol interval to symbol interval fi~r any user.
At the base station receiver, the incoming signal includes a Co~ o~i~c of all user chip streams. These chip streams are typically delayed relative to one 30 another due to the asynchluilous nature of the cf""""~"~ on~ between any user and the base station. To recover each user's symbols, each user's chip st~eam must be extracted from the received signal. This is accomplished by a signal despreader which, in the prior aTt, multiplies the received signal during a symbol interval by a replica of each user's sequence of code coefficien~ for that interval. Pursuan~ to the 35 present invention, it has been recognized that in CDMA systems of the type ~escrihed above, white (3;~ n noise is negligible co~ cd to the inte~rclcnce in 2J 02~32 each user's chip stream introduced by other user chip strcams. It is further recognized that the h~G~rt;lcllce in any user chip stream in any symbol interval is a function of the correlation between that user's sequence of code coefficients and the sequences of code coefficients for all other users for that symbol interval. TheS present invention utilizes this principle by the utili~ation of a signal despreader which multiplies the received signal in a symbol interval by a sequence of code coeffi~ n~s for each user which is an alteration of a replica of that user's code coefficient sequence in the symbol interval. The alteration is a function of theabove-recited correlation. Therefore, the alteration is user-specific, i.e., it varies 10 from user to user and, in ~cklitiQn, since th~ correlation varies from symbol interval to symbol interval, it follows that the alteration for any user also varies from symbol interval to symbol interval.
The code coefficients within each sequence in a symbol interval will now be ~i~Cll~se(1 At the outset, it will be noted ~hat the code coefficients for the i'h 15 user, where 1 < i ~ n, folms a sequence of code coeffi~i~nt~ c; in a symbol interval which can be written as:
Ci = (Cil,Ci2, ~ ~ ~, Cim) where the ~ul~e~ T ~ G;,e~ the transpose of a vector and the second subscript of each code coefficient in the sequence c i ~ e~ the position of that coefficient 20 in the sequence of m coeffirienti.
The composite of all n vectors ci can be expressed as an m by n matrix C, where C = (cl,c2, . ~ ~, Cn)~ (2) and the matrix C contains the code coeffi~iPnt~ for all users in one symbol interval.
25 Each vector ci can be eYrantlt.d into an m by m diagonal matrix C i which can be sst,d as Ci = diag(cil,ci2, ~ ~ ~, Cirn) ~ (3) : : ~
%10~
where the term diag ~ .,se~ . the diagonal of the matrix and such diagonal inclucles the m values of the vector c j respectively distributed across the diagonal positions from left to right. The other matrix positions of C i have zero values.
The received signal in each symbol interval, whether analog or digital, S can be represented by a vector y having a pre~et~nine(l number of vector colllponellL.. For purposes of simplicity, we shall assume that the number of compnnents of vector y is m and that m is a number of samples which satisfies the Nyquist theorem, Accordingly, the vector y can be e~ ,ssed as Y = ~Yl Y2 ym) r (4) In the prior art, the operation of a despreader can be expressed as being m~th.qm:~tir~11y equivalent to yTC where the superscript T indicates the transpose of a vector.
In such prior art systems, the int~,lrc,lence is related to a vector R', which in an n user CDMA system forming m chips per symbol interval, has n x I
15 11imenSioni and can be ;;~ ,ssed as Ri = ~TCi (S) or, in other words, m (C lL) (C iL ) Lm l ~ (C2L) (CiL) Ri = . , (6) (C ~ C iL ) where L is a ~ lpol~y variable in a s~mm~ ion .~ ~ . - ! , 2 ~ 2 Ex:-mining equation (6), the n comporlents of vector Rj l~,.,sclll a cross-co~elation of the code coefficient sequence ~or the i~ user in any symbol interval and the code coefficients of all other users in this same interval.
Now, equation ~5) can be written as S Ri = ~T(~jwj, (7) or m ~ (CIL) (CiL) (WjL) L=t m ~, (C2L) (CiL) (WL) L=1 ~Ri = ~ ~ (8) m L~;l (CnL) (C iL ) (W iL ) _ That is, the vector Ri can be ~ ssed as the above-mentiQned cross-correlation times a weighting vector w j. The weighting vector w j can be t;A~ ,ed as ., ~Vi = (Wil~wi2~ Wim) 7 (9) where wi is an m times 1 vector and the ~U~ T is the ~l~r.s~ose of this vector.
In equation (6), this weighting vector is a unity or all ones vector. From equation (8~, it shs)uld be noted that the e1~m~nts of R j, i.e., the h~ r~,. c;nce from other users, can be reduced if one can find the appropriate nonzero values of w j such 15 tha~ each of the n ~erms of R j is reduced co.llp~.,d to its unweighted c:ount~ in equa~ion (6).
It can be shown that ~ the n terms of R j can be e~ ,sscd by either one of the following objective functions T m J = lRiRi - ai ~, WiL, (10) L=l 2 ~ 3 ~ ~
The received signal in each symbol interval, whether analog or digital, S can be represented by a vector y having a pre~et~nine(l number of vector colllponellL.. For purposes of simplicity, we shall assume that the number of compnnents of vector y is m and that m is a number of samples which satisfies the Nyquist theorem, Accordingly, the vector y can be e~ ,ssed as Y = ~Yl Y2 ym) r (4) In the prior art, the operation of a despreader can be expressed as being m~th.qm:~tir~11y equivalent to yTC where the superscript T indicates the transpose of a vector.
In such prior art systems, the int~,lrc,lence is related to a vector R', which in an n user CDMA system forming m chips per symbol interval, has n x I
15 11imenSioni and can be ;;~ ,ssed as Ri = ~TCi (S) or, in other words, m (C lL) (C iL ) Lm l ~ (C2L) (CiL) Ri = . , (6) (C ~ C iL ) where L is a ~ lpol~y variable in a s~mm~ ion .~ ~ . - ! , 2 ~ 2 Ex:-mining equation (6), the n comporlents of vector Rj l~,.,sclll a cross-co~elation of the code coefficient sequence ~or the i~ user in any symbol interval and the code coefficients of all other users in this same interval.
Now, equation ~5) can be written as S Ri = ~T(~jwj, (7) or m ~ (CIL) (CiL) (WjL) L=t m ~, (C2L) (CiL) (WL) L=1 ~Ri = ~ ~ (8) m L~;l (CnL) (C iL ) (W iL ) _ That is, the vector Ri can be ~ ssed as the above-mentiQned cross-correlation times a weighting vector w j. The weighting vector w j can be t;A~ ,ed as ., ~Vi = (Wil~wi2~ Wim) 7 (9) where wi is an m times 1 vector and the ~U~ T is the ~l~r.s~ose of this vector.
In equation (6), this weighting vector is a unity or all ones vector. From equation (8~, it shs)uld be noted that the e1~m~nts of R j, i.e., the h~ r~,. c;nce from other users, can be reduced if one can find the appropriate nonzero values of w j such 15 tha~ each of the n ~erms of R j is reduced co.llp~.,d to its unweighted c:ount~ in equa~ion (6).
It can be shown that ~ the n terms of R j can be e~ ,sscd by either one of the following objective functions T m J = lRiRi - ai ~, WiL, (10) L=l 2 ~ 3 ~ ~
or J = I~Ri aj ~, w~, (11) where ai is a scaling factor and 0 ~ o~; S 1. If we attempt to ",;l~i."i,~ J in either equation (10) or (11), we will minimi7e the interference in any recovered user's chip S stream. Indeed,theRT~ erm It;plbS~ thisi~ ,,r~ ce. Moreover,a ",i"i".i,;~lion of J in either of these equations will respectively Illcl~ iL~; the term m m WiL or ~, w2L. A ~AXi"~ ion of either of these sums represen~s a selection L=l L=l of w j values which will reduce the received signal energy as little as possible.
The objective functions governed by eqn~ ns (10) and (11) differ only 10 in the COllSIloin~:i on the permissible nonzero value of each col~onenl of the vector w j. In equation (10), 0 ~ w jL ~; 1 and in equation (11) -1 5 wiL 5 1.
Once the appropriate weighting vector w j is found, then the i~ r~ l~;nce will be reduced in the despreader if this apparatus operates with code coefficient seqn~1 c es expressible as ci = Ci ~i ~ (12) As will be ~ cll~se~1~ the objective functions t;,-p~ssed by equations (10) and (11) are utilized by the ~ sed embodiments of the present invention and, once a ,.,i~ value of 3 is found, the collG~pollding nonzero values of ~vi are used to generate the altered code seqllenre ci ~ sed by 20 equation (12) for each of $he n users.
Refer now to FIG. 1 which shows an illustrative receiver 10V which inct,l~ul~lt~s the present i~vt;lllion. It will be assumed that sampling apparatus (not shown) forms m samples of the received signal in each symbol interval on lead 101.
These samples are coupled to despreader 102 which multiplies each sample by a 25 different code coefficient in one of n different code sequences. Each of these code sequences is coupled to the despleade~ via an associated lead of bus 103.
Code sequencei ge~ vl 104 provides the n code sequences to despreader 102. A replica of each of the code se(lu~ ces used by each of the n users in his or her ~ . . is provided by code sequence gen.,l~ 105-1 through 30 10~-n. The outputs of all of these generators is provided to matrix generator 106 2~2()~
The objective functions governed by eqn~ ns (10) and (11) differ only 10 in the COllSIloin~:i on the permissible nonzero value of each col~onenl of the vector w j. In equation (10), 0 ~ w jL ~; 1 and in equation (11) -1 5 wiL 5 1.
Once the appropriate weighting vector w j is found, then the i~ r~ l~;nce will be reduced in the despreader if this apparatus operates with code coefficient seqn~1 c es expressible as ci = Ci ~i ~ (12) As will be ~ cll~se~1~ the objective functions t;,-p~ssed by equations (10) and (11) are utilized by the ~ sed embodiments of the present invention and, once a ,.,i~ value of 3 is found, the collG~pollding nonzero values of ~vi are used to generate the altered code seqllenre ci ~ sed by 20 equation (12) for each of $he n users.
Refer now to FIG. 1 which shows an illustrative receiver 10V which inct,l~ul~lt~s the present i~vt;lllion. It will be assumed that sampling apparatus (not shown) forms m samples of the received signal in each symbol interval on lead 101.
These samples are coupled to despreader 102 which multiplies each sample by a 25 different code coefficient in one of n different code sequences. Each of these code sequences is coupled to the despleade~ via an associated lead of bus 103.
Code sequencei ge~ vl 104 provides the n code sequences to despreader 102. A replica of each of the code se(lu~ ces used by each of the n users in his or her ~ . . is provided by code sequence gen.,l~ 105-1 through 30 10~-n. The outputs of all of these generators is provided to matrix generator 106 2~2()~
which forms the matrix CT which, in turn, is coupled to objective function generators 107-1 through 107-n. Each of the outputs of code sequence generators 105-1 through 105-n is also respectively coupled to matrix gen~ tol~ 108-1 through 108-n. Each of these generators provides the diagonal 5 matrix associated with a particular code sequence. That is, code sequence ~,~,n~ ~ 105-2 provides the code sequence used by user 2 and matrix ~,vn~ . 108-2 provides the ~s(!ciAted diagonal matrix C2 cont~ining the code sequence for user 2 distributed across the diagonal of the matrix and having zero values elsewhere. The diagonal matrices provided by generators 108-1 through 10 108-n are respectively coupled to an ~oçi~ted one of objective function 107-1 through 107-n. Each objective function generator 107-1 through 107-n respectively performs a prGde~ ,ed process to optimize the objective function for users 1 through n. The predetermined process can be any of a variety of well-known optimi7:~ti~-n techniques, such as forming the ~ e..~ l derivative of15 the objective function and setting this derivative to zero, or by means of an iterative process. In either case, the objective function for each user is governed by either equation (lû) or (11) and, with the use of an iterative optimization process, more than one estimate of wi will be provided to each objective function g~;n~ldlol. To acc~ - --- - -n-i~te this, obJective functio~ generators 107-1 through 107-n are20 l~,;,pes;livGly lcsoc;!'tlod with Inll~ tion controllers lOg-l through 109-n. ~ach ..~;ni,.~; ..,.li~n controller receives the different values of J and the corresponding values of ~i provided by its ~csoc~ .d objective function ~;~,n~ ol during a y~,d~,t~ llh~ed portion of each symbol interval. These values are provided to each "~ n controller via an ~coci~t~.d one of buses 110-1 through 110-n. The 25 ...i.)i..".",;,i.~i- n controller, utilizing any one of a variety of well-known optimi7~ion t~hni~ s~ forms the next w; vector and couples this vector to the ~soci~t~d objective function ~,c;n~ll~ via an associated one of buses 111-1 through lll-n. Once per symbol interval, each ,~.illi,,.i,,.lion controller selects the ...ini..".."
value of J coupled to it and instmcts the associated objective function ~nel~lol to 30 output~hevectorwicuIt~o~ gtothe~ valueofJtobus 116. This instruction is provided via a control signal on bus 115. Accordingly, bus 116 couples the n different w i vectors to mnltirli~.rs 117- 1 through 117-n in each symbol interval. Thesç multipliers respectively form the products C 1 w 1, C2w2~ ~ ~, Cnwn, which ~re coupled via bus 103 to despreader 102.
: . , ~ . .-, .
..
; ~ . .-~ . ~ ' : . :: .
'.'. . ' , ' 2 ~0~ 3~/
g Despreader 102 includes multipliers 112-1 through 112-n which are respectively cnnnPctPd to summer 113-1 through 113-n. Each multiplier perforrns a different one of the n multiplications and provides the n products to an associated one of ~uln~ 113-1 through 113-n. Each swmmer outputs the sum of these 5 n products, expressible as yc,, each symbol interval.
FIG. 2 shows the circuitry within one embodiment of the objective function generator 107-1 in FIG. 1 wherein the objective function of either equation (10) or (11) is provided by a precletermined one of a variety of well-known optimi7:~tir~n techniques. The circuitry in each of the other objective function10 gen~,laLol~ is identical to that shown in FIG. 2.
As depicted in FIG. 2, multiplier 201 forms the product CTC 1 and ~
couples this product to multiplier 202. Multiplier 202 forms the vector R 1 or the product of the output of multiplier 201 and each c~n~ e or trial weighting vector w l provided via bus 111-1. Bus 111-1 provides at least one c~nt1~ te 15 weighting vectors w 1 within each symbol interval. Matrix Llans~oser 205 forms the transpose of the matrix product CTC 1 w 1 each symbol interval. Multiplier 203 forms the vector product RTR 1 for each can~ tf~ vector.
Objective function generator 107-1 can operate in acclj..l~c~ with either equation (10) or (11). In the f~rmer case, each cqn~ t~ vector provided by 20 the minimi7qtinn controller 109-1 on bus 111-1 is directly coupled to amplifier 208 which mllltirli.-s each c~n~ tç vector by a pre~lr., ..ii-~d scalar designqt~.d as a ~ .
In the latter case, each c~n~ ~ vec~or is coupled to circui~y 207 which squares each coll"~ollellt of each c~n~1irl~te vector and thence couples these squared components to amplifier 208. Consequently, the use of circuitry 207 is optional and 25 is shown in FIG. 2 as a dotted rect~n~l~. In either case, summer 204 algebraically subtracts the output of mn1tirli~r 208 from the ou~tput of multiplier 203 to form the objective function J. Controller and memory unit 209 receives each c~n~ t~ vector and the s~soriqt~d objective function which utili7es this c~nfli~l~tl weighting vector and stores these values. The plurality of formed objective functions J in each 30 symbol interval are successively coupled to minimi7~tion controller 109-1 vialead 110-1. The,..i~ ion controller then selects the .~ini",.~." value of J
formed in each symbol interval and co~ rqt~ s this selection via lead 115 to thecontroller and memory Ullit. In resp~nse to the control signal on lead 115, the cS~n~ te weighting vector coll~,sl,onding to the ,..i~ -.."~ value of J is outputted to 35 bus 116.
2:l.a2~s~
While the present invention has thus far been dexcribed relative to an illus~rative CDMA system which employs nondifferential coding, the present invention is also applicable to CDMA systems utilizing ~lirrt;,~ ial coding. For~lirrGl~ill~ial coding, it can be shown that the objective function set forth in5 equation (10) becomes m J = R~ Ri -- a; ~; WiL WiL ~ (13) where the telms in equation (13) have the same meaning as their count~ a~s in equation (10) and the term w L l~sign~tes the selected weighting vector for the ~th user in the symbol interval imm~ tely preceding the symbol interval for which the 10 o~ um weighting vector is being ~ete. ".i.~-l Similarly, the objective function set forth in equation (11) becomes L= 1 ( 14) Equafions (13) and (14), as with equations (10) and (11), differ only in the co~ ".;l.i~ on the pe~ h1~ nonzero value of each component of the vector w;. In 15 equation (13), 0 ~ wiL S 1 and in equation (14) -1 ~ wiL 5 1.
Refer now to FIG. 3. This FIG. shows an illustrative receiver 300 which illcol~silc~teS the present invention in a ~DMA system utilizing ~lirr~ilGillial coding.
- Much of the circuitry in FIG. 3 is identical in s~ucture and function to that shown in FIG. 1 and each such identical circuitry is (leiignslt~d by the same reference numeral 20 in FIG. 3 as its COUIlt~ in FIG. l. Indeed, despreader code sequen~es gen~,~al~,. 304 is identical to its COul~ 104 in FIG. 1 except for a modification of each of the objec~ive function ~,en~,la~ol~ required to carry out the objective function in acc~ ce with equation (13) or (14). These objective function j~,n~at ~l~ are flesigni~ted in FIG. 3 by reiference numerals 307-1 through 307-n.
25 Since the objective function of equation (13) or (14) requires the vector wi,buses 31b-1 through 316-n couple this vector between each minimi7i~fir~n controller and ils a~soci~t~d objective func~ion g~ f- u . Similarly, despreader 302 is quite similar to de~lc,ad~ 102 except for the addition of symbol interval delay units 317-1 through 317-n and multipliers 318-1 through 318-n. Each of the former 30 respectively delays the product of a different one of multipliers 112-1 through 112-n 11 21~ 2 by one symbol interval. As a result, multipliers 318-1 through 318-n respectively forms the products of two successive outputs of multipliers 112-1 through 112-n.Re~er now to FIG. 4. As be-fore, the circuitry of the objective function generator for user 1, ~le~i~n~tPd by reference numeral 307-1, has been shown andS such circuitry is utilized in each of the objective function ~ eld~ 307-2 through 307-n. To account -for the difference between the objective function set forth in equation (10) and that expressed by equation (13), vector transpose unit 303 andmnltiplif.r 304 ~re utilized. The vectors w 1 and w I are respectively supplied via buses 316-1 and 111-1 to objective function ~,~,n~,ld~ 307-1. Vector transpose 10 Ullit 303 forms the vector transpose wT which is multiplied by the vector w 1 via multiplier 304. If the objective function ~t;n~ ol is to implement the objective~
function governed by equation (14), then absolute value circuits 301 and 302 aredisposed as illustrated in FIG. 4 ~o respectively provide the absolute values of each of the m terms of vectors w I and w 1.
The circuitry in either FIG. 1 or FIG. 3 can be thought of as an estimator and the outputted e~ AIrs are real-valued signals. To convert these outputs to binary outputs, the circuitry shown in FIG. 5 or 6 could be coupled to output bus 114. FIG. 5 shows what is cc mmnnly referred to as a "hard" decision decoding arr~n~em--nt inf 11l~in~ a multi-input quantizer 501 which is serially connected to a 20 channel decoder 502. A "soft" decision dPcof1in~ arrangement is shown in FI(3. 6 and is provided by collneclillg channel decoder 601 to bus 114. Another use of the circuitry in FIGS. 1 and 3 can be realized by cnmbining either of these FIGS. with FIG. 7. In this regard, it should be noted that the outputs of FIGS. 1 and 3 arerepresentS~tinn.~ of the i~s~ alleous power of the received signal. By coupling either 25 one of these outputs to FIR filter 701 shown in FIG. 7, integration of the in.~t~nt:~n~.c~us power is provided. Therefore, the combination of FIGS. 1 and 7 or 3 and 7 forms a power estim~tnr.
It should, of course, be noted that while the present invention has been described in terms in reference to illustrative emb-~iments, other arr~nge~mf.nts will 30 be apparent to those of ordinary skill in the art. First, while the disclosed embodiments have been described r,lative to a CDMA system wherein user symbols, each symbol ~ Sel~ ive of a plurality of bits, are diLr~ l~ially or nc n~lir~ ially coded, the present invention is also applicable ts~ CDMA systemswherein user bits are dirr~ ially or nf)n(lifferentially coded. Se- ond, while in the 35 fli~lnsed embodiments, the number of received signal samples formed each symbol interval is equal to the number of chips tr~n~mitt~d each symbol interval by each -12- 2.~2~
user, the present invention is applicable in arrangements for any number of received signal samples per symbol interval which satisfies the Nyquist theorem. Finally,while the disclosed embodiments utili~ discrete devices, the devices can be impl~mf nted using one or more appropriately programmed general-purpose S processors or special-purpose integrated circuits or digital processors or an analog or hybrid coun~c~ u I of any of these devices.
value of J coupled to it and instmcts the associated objective function ~nel~lol to 30 output~hevectorwicuIt~o~ gtothe~ valueofJtobus 116. This instruction is provided via a control signal on bus 115. Accordingly, bus 116 couples the n different w i vectors to mnltirli~.rs 117- 1 through 117-n in each symbol interval. Thesç multipliers respectively form the products C 1 w 1, C2w2~ ~ ~, Cnwn, which ~re coupled via bus 103 to despreader 102.
: . , ~ . .-, .
..
; ~ . .-~ . ~ ' : . :: .
'.'. . ' , ' 2 ~0~ 3~/
g Despreader 102 includes multipliers 112-1 through 112-n which are respectively cnnnPctPd to summer 113-1 through 113-n. Each multiplier perforrns a different one of the n multiplications and provides the n products to an associated one of ~uln~ 113-1 through 113-n. Each swmmer outputs the sum of these 5 n products, expressible as yc,, each symbol interval.
FIG. 2 shows the circuitry within one embodiment of the objective function generator 107-1 in FIG. 1 wherein the objective function of either equation (10) or (11) is provided by a precletermined one of a variety of well-known optimi7:~tir~n techniques. The circuitry in each of the other objective function10 gen~,laLol~ is identical to that shown in FIG. 2.
As depicted in FIG. 2, multiplier 201 forms the product CTC 1 and ~
couples this product to multiplier 202. Multiplier 202 forms the vector R 1 or the product of the output of multiplier 201 and each c~n~ e or trial weighting vector w l provided via bus 111-1. Bus 111-1 provides at least one c~nt1~ te 15 weighting vectors w 1 within each symbol interval. Matrix Llans~oser 205 forms the transpose of the matrix product CTC 1 w 1 each symbol interval. Multiplier 203 forms the vector product RTR 1 for each can~ tf~ vector.
Objective function generator 107-1 can operate in acclj..l~c~ with either equation (10) or (11). In the f~rmer case, each cqn~ t~ vector provided by 20 the minimi7qtinn controller 109-1 on bus 111-1 is directly coupled to amplifier 208 which mllltirli.-s each c~n~ tç vector by a pre~lr., ..ii-~d scalar designqt~.d as a ~ .
In the latter case, each c~n~ ~ vec~or is coupled to circui~y 207 which squares each coll"~ollellt of each c~n~1irl~te vector and thence couples these squared components to amplifier 208. Consequently, the use of circuitry 207 is optional and 25 is shown in FIG. 2 as a dotted rect~n~l~. In either case, summer 204 algebraically subtracts the output of mn1tirli~r 208 from the ou~tput of multiplier 203 to form the objective function J. Controller and memory unit 209 receives each c~n~ t~ vector and the s~soriqt~d objective function which utili7es this c~nfli~l~tl weighting vector and stores these values. The plurality of formed objective functions J in each 30 symbol interval are successively coupled to minimi7~tion controller 109-1 vialead 110-1. The,..i~ ion controller then selects the .~ini",.~." value of J
formed in each symbol interval and co~ rqt~ s this selection via lead 115 to thecontroller and memory Ullit. In resp~nse to the control signal on lead 115, the cS~n~ te weighting vector coll~,sl,onding to the ,..i~ -.."~ value of J is outputted to 35 bus 116.
2:l.a2~s~
While the present invention has thus far been dexcribed relative to an illus~rative CDMA system which employs nondifferential coding, the present invention is also applicable to CDMA systems utilizing ~lirrt;,~ ial coding. For~lirrGl~ill~ial coding, it can be shown that the objective function set forth in5 equation (10) becomes m J = R~ Ri -- a; ~; WiL WiL ~ (13) where the telms in equation (13) have the same meaning as their count~ a~s in equation (10) and the term w L l~sign~tes the selected weighting vector for the ~th user in the symbol interval imm~ tely preceding the symbol interval for which the 10 o~ um weighting vector is being ~ete. ".i.~-l Similarly, the objective function set forth in equation (11) becomes L= 1 ( 14) Equafions (13) and (14), as with equations (10) and (11), differ only in the co~ ".;l.i~ on the pe~ h1~ nonzero value of each component of the vector w;. In 15 equation (13), 0 ~ wiL S 1 and in equation (14) -1 ~ wiL 5 1.
Refer now to FIG. 3. This FIG. shows an illustrative receiver 300 which illcol~silc~teS the present invention in a ~DMA system utilizing ~lirr~ilGillial coding.
- Much of the circuitry in FIG. 3 is identical in s~ucture and function to that shown in FIG. 1 and each such identical circuitry is (leiignslt~d by the same reference numeral 20 in FIG. 3 as its COUIlt~ in FIG. l. Indeed, despreader code sequen~es gen~,~al~,. 304 is identical to its COul~ 104 in FIG. 1 except for a modification of each of the objec~ive function ~,en~,la~ol~ required to carry out the objective function in acc~ ce with equation (13) or (14). These objective function j~,n~at ~l~ are flesigni~ted in FIG. 3 by reiference numerals 307-1 through 307-n.
25 Since the objective function of equation (13) or (14) requires the vector wi,buses 31b-1 through 316-n couple this vector between each minimi7i~fir~n controller and ils a~soci~t~d objective func~ion g~ f- u . Similarly, despreader 302 is quite similar to de~lc,ad~ 102 except for the addition of symbol interval delay units 317-1 through 317-n and multipliers 318-1 through 318-n. Each of the former 30 respectively delays the product of a different one of multipliers 112-1 through 112-n 11 21~ 2 by one symbol interval. As a result, multipliers 318-1 through 318-n respectively forms the products of two successive outputs of multipliers 112-1 through 112-n.Re~er now to FIG. 4. As be-fore, the circuitry of the objective function generator for user 1, ~le~i~n~tPd by reference numeral 307-1, has been shown andS such circuitry is utilized in each of the objective function ~ eld~ 307-2 through 307-n. To account -for the difference between the objective function set forth in equation (10) and that expressed by equation (13), vector transpose unit 303 andmnltiplif.r 304 ~re utilized. The vectors w 1 and w I are respectively supplied via buses 316-1 and 111-1 to objective function ~,~,n~,ld~ 307-1. Vector transpose 10 Ullit 303 forms the vector transpose wT which is multiplied by the vector w 1 via multiplier 304. If the objective function ~t;n~ ol is to implement the objective~
function governed by equation (14), then absolute value circuits 301 and 302 aredisposed as illustrated in FIG. 4 ~o respectively provide the absolute values of each of the m terms of vectors w I and w 1.
The circuitry in either FIG. 1 or FIG. 3 can be thought of as an estimator and the outputted e~ AIrs are real-valued signals. To convert these outputs to binary outputs, the circuitry shown in FIG. 5 or 6 could be coupled to output bus 114. FIG. 5 shows what is cc mmnnly referred to as a "hard" decision decoding arr~n~em--nt inf 11l~in~ a multi-input quantizer 501 which is serially connected to a 20 channel decoder 502. A "soft" decision dPcof1in~ arrangement is shown in FI(3. 6 and is provided by collneclillg channel decoder 601 to bus 114. Another use of the circuitry in FIGS. 1 and 3 can be realized by cnmbining either of these FIGS. with FIG. 7. In this regard, it should be noted that the outputs of FIGS. 1 and 3 arerepresentS~tinn.~ of the i~s~ alleous power of the received signal. By coupling either 25 one of these outputs to FIR filter 701 shown in FIG. 7, integration of the in.~t~nt:~n~.c~us power is provided. Therefore, the combination of FIGS. 1 and 7 or 3 and 7 forms a power estim~tnr.
It should, of course, be noted that while the present invention has been described in terms in reference to illustrative emb-~iments, other arr~nge~mf.nts will 30 be apparent to those of ordinary skill in the art. First, while the disclosed embodiments have been described r,lative to a CDMA system wherein user symbols, each symbol ~ Sel~ ive of a plurality of bits, are diLr~ l~ially or nc n~lir~ ially coded, the present invention is also applicable ts~ CDMA systemswherein user bits are dirr~ ially or nf)n(lifferentially coded. Se- ond, while in the 35 fli~lnsed embodiments, the number of received signal samples formed each symbol interval is equal to the number of chips tr~n~mitt~d each symbol interval by each -12- 2.~2~
user, the present invention is applicable in arrangements for any number of received signal samples per symbol interval which satisfies the Nyquist theorem. Finally,while the disclosed embodiments utili~ discrete devices, the devices can be impl~mf nted using one or more appropriately programmed general-purpose S processors or special-purpose integrated circuits or digital processors or an analog or hybrid coun~c~ u I of any of these devices.
Claims (17)
1. Apparatus for use in a CDMA system which transmits a coded user signal for each of a plurality of users, each transmitted user signal being formed by processing that user's symbol with an associated sequence of code coefficients, and wherein a received signal includes a composite of all coded user signals, said apparatus comprising means for receiving samples of said received signal in a predetermined time interval; and means responsive to said received signal samples for estimating a symbol of a user using a derived sequence of code coefficients, said derived sequence being a function of a correlation of the code coefficient sequence associated with said user and those code coefficient sequences associated with the other users.
2. The apparatus of claim 1 wherein said time interval is one through which said symbol of said user extends.
3. The apparatus of claim 1 wherein said estimating means includes means for generating replicas of the code coefficient sequences associated with each of said plurality of users.
4. The apparatus of claim 3 wherein said generating means includes a pseudorandom number generator.
5. The apparatus of claim 1 wherein said derived sequence is derived from a replica of the code coefficient sequence associated with said user.
6. The apparatus of claim 5 wherein said derived code coefficient sequence is formed by multiplying each coefficient in said replica by an associated weighting factor.
7. The apparatus of claim 6 wherein said associated weighting factor varies from coefficient to coefficient in said replica.
8. The apparatus of claim 1 wherein said estimating means includes means for forming an objective function associated with said user and means for minimizing said objective function using predetermined criteria.
9. The apparatus of claim 8 wherein said predetermined criteria reduces interference in said symbol of said user.
10. The apparatus of claim 8 wherein said predetermined criteria minimizes loss of received signal energy.
11. The apparatus of claim 1 wherein said estimating means includes signal despreading means.
12. The apparatus of claim 1 wherein each coded user signal is nondifferentially coded.
13. The apparatus of claim 1 wherein each coded user signal is differentially coded.
14. The apparatus of claim 1 further including decoding means connected to said estimating means for decoding said user symbol estimate.
15. The apparatus of claim 1 further including a serially connected quantizing means and decoding means connected to said estimating means.
16. The apparatus of claim 1 further including filtering means connected to said estimating means.
17. A method for use in a CDMA system which transmits a coded user signal for each of a plurality of users, each transmitted user signal being formed by processing that user's symbol with an associated sequence of code coefficients, and wherein a received signal includes a composite of all coded user signals, said method comprising the steps of receiving samples of said received signal in a predetermined time interval; and estimating a symbol of a user in said predetermined time interval in response to said received signal samples and a derived sequence of code coefficients, said derived sequence being a function of a correlation of the code coefficient sequence associated with said user and those code coefficient sequences associated with the other users.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US991,841 | 1992-12-16 | ||
| US07/991,841 US5345468A (en) | 1992-12-16 | 1992-12-16 | Despreading technique for CDMA systems |
Publications (2)
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|---|---|
| CA2102082A1 CA2102082A1 (en) | 1994-06-17 |
| CA2102082C true CA2102082C (en) | 1998-02-03 |
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| CA002102082A Expired - Fee Related CA2102082C (en) | 1992-12-16 | 1993-10-29 | Despreading technique for cdma systems |
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| US (1) | US5345468A (en) |
| EP (1) | EP0602843B1 (en) |
| JP (1) | JP3088227B2 (en) |
| KR (1) | KR100278727B1 (en) |
| CA (1) | CA2102082C (en) |
| DE (1) | DE69330740T2 (en) |
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| US5553062A (en) * | 1993-04-22 | 1996-09-03 | Interdigital Communication Corporation | Spread spectrum CDMA interference canceler system and method |
| KR100217715B1 (en) * | 1993-12-31 | 1999-09-01 | 윤종용 | Up-link system in ds/cdma |
| US5617088A (en) * | 1994-01-26 | 1997-04-01 | Sony Corporation | Sampling frequency converting device and memory address control device |
| DE69530259T2 (en) * | 1994-04-22 | 2003-12-24 | Nippon Telegraph & Telephone | METHOD FOR RECEIVING A CODE DIVISION MULTIPLEX SIGNAL |
| CN1059529C (en) * | 1994-06-23 | 2000-12-13 | Ntt移动通信网株式会社 | Method and device for receiving code-division multiplex signal |
| US5677930A (en) * | 1995-07-19 | 1997-10-14 | Ericsson Inc. | Method and apparatus for spread spectrum channel estimation |
| US5615209A (en) * | 1995-07-26 | 1997-03-25 | Ericsson Inc. | Method and apparatus for CDMA signal orthogonalization |
| US6047192A (en) * | 1996-05-13 | 2000-04-04 | Ksi Inc. | Robust, efficient, localization system |
| US5790537A (en) * | 1996-05-15 | 1998-08-04 | Mcgill University | Interference suppression in DS-CDMA systems |
| US6101178A (en) | 1997-07-10 | 2000-08-08 | Ksi Inc. | Pseudolite-augmented GPS for locating wireless telephones |
| US6229857B1 (en) * | 1998-06-02 | 2001-05-08 | Intel Corporation | Adaptive ingress filtering system |
| US6577658B1 (en) | 1999-09-20 | 2003-06-10 | E20 Corporation, Inc. | Method and apparatus for planar index guided vertical cavity surface emitting lasers |
| JP3514217B2 (en) | 2000-06-29 | 2004-03-31 | 日本電気株式会社 | Turbo decoding method and receiver |
| DE102005053301B3 (en) * | 2005-11-09 | 2007-02-22 | Atmel Germany Gmbh | Data symbols detection unit for transmit/receive device, has sequence provisioning unit providing group of sequences, which are stepped higher than sequences in transmission side, where chips of respective sequences store different values |
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| US4885757A (en) * | 1987-06-01 | 1989-12-05 | Texas Instruments Incorporated | Digital adaptive receiver employing maximum-likelihood sequence estimation with neural networks |
| US4995104A (en) * | 1989-05-08 | 1991-02-19 | At&T Bell Laboratories | Interference cancelling circuit and method |
| US5031173A (en) * | 1989-08-15 | 1991-07-09 | Unisys Corporation | Decoder for added asynchronous bit sequences |
| US5099493A (en) * | 1990-08-27 | 1992-03-24 | Zeger-Abrams Incorporated | Multiple signal receiver for direct sequence, code division multiple access, spread spectrum signals |
| JPH0779281B2 (en) * | 1990-09-21 | 1995-08-23 | 日本ビクター株式会社 | Spread spectrum modulation demodulator |
| EP0486834B1 (en) * | 1990-11-22 | 1995-11-22 | Ascom Tech Ag | Multi-access method and mobile radiocommunication system implementing said multi-access method |
| US5151919A (en) * | 1990-12-17 | 1992-09-29 | Ericsson-Ge Mobile Communications Holding Inc. | Cdma subtractive demodulation |
| US5218619A (en) * | 1990-12-17 | 1993-06-08 | Ericsson Ge Mobile Communications Holding, Inc. | CDMA subtractive demodulation |
| US5136612A (en) * | 1990-12-31 | 1992-08-04 | At&T Bell Laboratories | Method and apparatus for reducing effects of multiple access interference in a radio receiver in a code division multiple access communication system |
| US5177766A (en) * | 1991-06-03 | 1993-01-05 | Spectralink Corporation | Digital clock timing generation in a spread-spectrum digital communication system |
| US5237586A (en) * | 1992-03-25 | 1993-08-17 | Ericsson-Ge Mobile Communications Holding, Inc. | Rake receiver with selective ray combining |
| US5295153A (en) * | 1992-04-13 | 1994-03-15 | Telefonaktiebolaget L M Ericsson | CDMA frequency allocation |
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1992
- 1992-12-16 US US07/991,841 patent/US5345468A/en not_active Expired - Lifetime
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| JPH06261021A (en) | 1994-09-16 |
| KR940017331A (en) | 1994-07-26 |
| JP3088227B2 (en) | 2000-09-18 |
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| KR100278727B1 (en) | 2001-01-15 |
| CA2102082A1 (en) | 1994-06-17 |
| EP0602843A2 (en) | 1994-06-22 |
| DE69330740D1 (en) | 2001-10-18 |
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