CA2167709A1 - A method and apparatus for identifying a coded communication signal - Google Patents
A method and apparatus for identifying a coded communication signalInfo
- Publication number
- CA2167709A1 CA2167709A1 CA002167709A CA2167709A CA2167709A1 CA 2167709 A1 CA2167709 A1 CA 2167709A1 CA 002167709 A CA002167709 A CA 002167709A CA 2167709 A CA2167709 A CA 2167709A CA 2167709 A1 CA2167709 A1 CA 2167709A1
- Authority
- CA
- Canada
- Prior art keywords
- signal
- signals
- multipath
- coded communication
- multipath signals
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- 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
- H04B1/709—Correlator structure
-
- 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
- H04B1/7073—Synchronisation aspects
- H04B1/7075—Synchronisation aspects with code phase acquisition
- H04B1/70754—Setting of search window, i.e. range of code offsets to be searched
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- 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
- H04B1/7073—Synchronisation aspects
- H04B1/7075—Synchronisation aspects with code phase acquisition
- H04B1/70755—Setting of lock conditions, e.g. threshold
Abstract
A receiver (900) employs a method (1100) for identifying a particular coded communication signal (301) from received coded communication signals (303, 305). The receiver (900) comprises a memory device (905) and a processor (907). The memory device (905) stores information contained in the received coded communication signals (303, 305) during multiple modulation symbol time intervals (210) to produce stored information. The processor (907) then searches the stored information to identify the particular coded communication signal (301).
Description
.
A Method and A~ c For Identifying A Coded t'c,.. ~.. ir~tion Signal Field of the Invention The present invention relates generally to the reception of coded co.. ~ ir-~tion signals and, in particular, to a method and a~ LuS for idc~lLiry~g a particular coded c~.. ...ic~tion from a 15 plu~lity of received coded c~ .;r~tiQn si~n~l.c.
R~r~ground of the Invention ~"""--";r~tion systems that utilize coded cs~ ic~tion 2 0 signals are known in the ar~ One such system is a direct sequence code division mnl*rle access (DS-CDMA) ce~ r commlmir~tion system, such as that set forth in the TelrcQ.. ir~tions Tn-illctry ~csoci~tion/Electronic Indust~ies Association I~l~e~ l Standard 95 (IIA/EIA IS-95), hereinafter l~fell~d to as IS-95. In accordance 2 ~ with IS-95, the coded cornm-lnir~tion signals used in the DS-CDMA
system comprise DS-CDMA signals that are transmitted in a common 1.25 MHz bandwidth to the base sites of the system from cq.~.. ;c~tioIl units, such as mobile or portable radiotelephones, that are collllllllllir~tirlg in the coverage areas of the base sites. Each 3 0 DS-CDMA signal incl~ es~ inter alia, a pseudo-noise (PN) sequence associ~trd with a particular base site and an i-l~ntific~tion number of a cq.. ~ ir~ting c~.. ic~tion unit.
During a typical co..,...l...ir~tion, the cornmlmicating co.... ic~tion unit often travels within the coverage area of the base site that is ~U~O~ lg the co"""~",ir~sion Such movemenl typically results in fading of the co.. -.. ication signal transmitted 5 from the co" " ~ tion unit to the base site due to multipath propagation of the L~ `---;LI- ~ signal. As is known, multipath propagation results from reflections of the transmitted signal off of nearby scatterers, such as b~ ling.c or large stones. These r~fl~ctionc produce replicas of the originally tr~ncmitted signal that 1 0 arrive at the base site at various times depen-ling on the effective prop~E~tion ~lict~nr,es traveled by the replicas. The originally tr~ncmitte(l signal and the mnl*r~th replicas are typically referred to as mnltir~th signals of the originally tpncmitte~l signal.
In a DS-CDMA system, such as that descnbed by IS-95, mnltir~th prop~g~*Qn typically results in mlll*r~th signals from each L~ ---ill;--g col~"~ "ir~tinn unit arriving at the base site at slll,s~ lly the same time, or at least vithin a commQn time interval. The IS-95 system divides the DS-CDMA signals into 20 2 0 millicecQnd ~ms) frames that contain six~ee.. power control groups.
Each power control group is fu~lcr divided into six modulation--or so-called Walsh--syrnbol time intervals. Each Walsh symbol time interval is approximately 208 microsecon~ls. Thus, with this frarne configuration, several multipath signals from each tr~n.cmitting 2 5 co...~ ..;cation unit might arrive at the base site during one of the Walsh symbol tirne intervals. Each Walsh symbol time interval generally contains one WaLch symbol of digital information as is known in the art.
3 0 To demodulate ~e t~ncmicsions from each colnml-nic~tion unit, the base site receiver must first identify the mllltip~th signals from each c~ tion unit and then select the best multipath signals to demodulate. To identify a particular mnl~ir~th signal, the base site initially receives and stores the information contained in one 2 1 6770q Walsh syrnbol. The base site then g.,l,elates its colles~onding PN
sequence and correlates it to the PN sequence cont~inr-d in the signal received at an initial tirne offset within the Walsh syrnbol to produce a correlation energy. The initial time offset is typically selected 5 based on the theoretical --i--;-------- rlict~nce between a comm--nication unit and the base site.
Upon obt~ining the first correlation energy, the base site advances to the same offset in the ne~t Walsh symbol and calculates a 10 coll.,s~ollding correlation energy. This advance and c~lr~ te, or search, process c~ e,c for a select .~ r of Walsh symbols, typically up to the mlmhlor c~ .ed in a power control group. The n-lmber of Walsh syrnbols to which a particular offset is applied is depen~ nt upon wllelLcr the signal being searched for is a traffic 15 signal (i.e., voice or data) or a pre~mhle signal used during the ~gisLIdLion of a cGl.~ .;c~ti~n unit in the DS-CDMA system.
When t~he signal being s~l~cd for is a t~ffic signal, the offset is applied to all six Walsh s,vrnbols in the power control group;
~l~cl~as, when the signal being scalched for is a prearnble signal, the 2 0 offset is only applied to two Walsh syrnbols.
Upon applying the initial offset to ~e a~lu~liate nllmber of Walsh symbols, the base site changes the offset and repeats the procedure until it locates one or more multipath signals that have 2 5 been transmitted from a co.. ,.. ~ication unit within its service coverage area. Depending on the initial offset and the propagation rii~t~nreS traversed by the comm-lnication unit's tr~n.cmicsion, the base site typically has to iterate through several offsets before obt~inin~ multipath signals to demo~ tr Thus, this search process 3 0 can often result in high effective demodulation times (i.e., the time to search and subsequently demodulate), especially for received traffic sigT~ . The high effective demodulation times impose an lln~lesired upper limit on the bit energy to noise ratio perform~nce required to m~int~in a particular received bit error rate. Such a limit prevents the DS-CDMA system from increasing its capacity without degradin the base site's .ecei~,ed bit error rate (i.e., signal quality).
Tllcl~fol._, a need exists for a m~thod and a~ dLus that identify a particular coded CC.. ~.. ;C~ rl signal from a plurality of received coded cu"~ r~tinn s~ , while significantly reducing the search time required to perform the identification. Further, such a method and al.~ala~us that i~ roves the received bit energy to noise ratio for a given bit error rate would be an improvement over 10 the prior art.
Brief Description of the Drawings FIG. 1 illustrates a co..... ~.. ;r-~*on system that might employ the ~l~sell~ invention.
l:IG. 2 i~ st~tes the power control groups tr~n~mitt~i by a co... ~.. ;c~tion unit at particular CDMA frame rates in accordance with the ~l~,senl invention.
FIG. 3 illustrates lef~ ce and received pseudo-noise sequences used to (iet~ ~...;..~- associ~te~l signal metrics of received mllltip~th signals in acco~ ce with the present invention.
2 5 FIG. 4 illustrates exemplary correlation energy levels of mllltip~th signals obtained in a single search window over a power control group in accordance with prior art methodologies.
FIG. 5 iIlustrates the total correlation energy obtained in the 3 0 single search window of FIG. 4.
FIG. 6 illustrates exemplary correlation energy levels of mlll*p?~th signals obtained in multiple search windows over a power control group in accordance with the present invention.
2 1 6 ~709 s PIG. 7 illustrates the total correlation energies obt~ined in the n~nltirle search windows of FIG. 6.
S FIG. 8 illustrates total correlation energies obt~ined in multiple search windows to ~ dtc the acquisition of peak energies and local energy ...~ in accordance with the present invention.
1 0 FIG. 9 illustrates a receiver that receives coded co.n....~ tion signals in accol~ance with the ~l~S~llL invention.
FIG. 10 illustrates ~l~fcll~d emboA;...P-..lc of the memory device and the ~locessor incl~lded in the l~,cei~- of FIG. 6.
FIG. 11 illll~tr~t~s an exemplary logic flow ~ gr~m of steps e~cllt~ by a lecei~el in accord~ce with the present invention.
2 0 Description of a P~ d Embotlim~-nt Generally, the present invention encoInr~cses a method and ap~d~s for identifying a particular coded co~ .ic~tion signal from a plurality of received coded co.... l~,.;cation signals. A
2 5 receiver that receives coded co~ ic~tion sign~l~ comprises a mernory means and a processin~ m~n~ The memory means stores inform~tion cont~ine~ in the received coded co.. l~.. ic~tion signals during multiple mo~ tion symbol time intervals to produce stored information. The processing means then searches the stored 3 0 inform~tion to identify the particular coded commllnic~tion signal.
By identifying the particular coded co,.. n.. i~tion signal in this m~nn~.r, the l l~senL invention signific~ntly reduces the average time re~uired to identify one or more mllltip~th si~l~ of the particular received coded co.. lll.ication signal. Thus, the present invention . 2167709 decreases the effective time ~quired for demodulation of the particular coded co~ .,ic~ttiQn signal as co",l,~.ed to the effective time for irmot~ tion of a coded co~ ;c~ttion signal using prior art search and tlrmo~ltlsttto te~hni-lues.
The present invention can be more fully described with ~f~,cnce to FIGs. 1-11. FIG. 1 illustrates a co.,..".~ ttion system 100 that might employ the ~l~ s~ invention. The comm--nication system 100 in~hltles a base site 101 and one or more comm--nication 10 units 103, 104 (two shown). The co",..,.",it~ttion system 100 dbly colll~llses a direct seqll~-nr~ code division multiple access (DS-CDMA) ce-lhll~tr cct-..~ ..ir~ttion system, such as that set forth in TIA/ELA IS-95. Ho~e~ r, the ~l~S~ invention is equally applicable to a frequency hopping col"~..,...;r~tic-n system, such as some of those 1 5 proposed for the ~irmrstir Pe~son~l t'o~ ir~tion System (PCS).
In a celllll~r co~ ll;r~tinn system, the base site lO1 is coupled to the public ~wi~ched telephone ~ lwul~ (PSTN) 105 using known ~rhnirlueS.
2 0 The base site 101 ~le~ldbly comprises a receiver that receives coded co~ tion signals from the co...""~ tion units 103, 104 within a coverage area of the base site 101, a tn~n~ er that Ll~.,~.l,il~ coded co.. ~.. ir~tion signals to the co~ tion units 103, 104, and the ~ro~liate interfaces between the PSTN 105 and 2 5 the receiver and tr~n~mitter. A piefclled base site receiver is discussed in detail below with regard to FIG. 9. Each of the co.. l.. ;c~tion units 103, 104 pief~ldbly co~ ises a mobile or portable radiotelephone, a mobile or portable two-way radio, or other two-way co..~ ...ic-~tin~ device, such as a conl~ r with radio 3 0 frequency (RF) tr~ncmi.csion and reception capabilities.
In the ~ d DS-CDMA system 100, the coded cc...~..l...i~tion signals comprise DS-CDMA commllni~tion signals 107, 108 that are conveyed between the cc,~ .ication units 103, 104 and the base site 101 through an RF chAnn~l In an altemate freqll~.nr,y~opping commlmirAti()n system, the coded comm-mication signals might comrri.ce slow fi~lv ..-ry hopping (SFH) cQ~ ..irAtion signals (multiple morlnlAtio~ symbol time intervals S per hop) or fast frequency hopping (F~:H) co... ~.icAtion signals (multiple hops per modulation symbol time interval). The RF
chAnnel inrllldes an uplink (co...~ ...;rAIion units 103, 104 to base site 101) and a downlink (base site 101 to co.. .i~Ation units 103, 104). In a l~l.,rcll~d embo~im~-nt, t-h-e uplink colll~lises a prescribed 1 0 bandwidth (e.g., 1.25 MHz for IS-95) coll~ctively used by the co.l...... ;rAti~n units 103, 104 to tr~ncmit multiple coded co.~...... ir.Ation signals 107, 108 (DS-CDMA si~nAlc in this case) toward the base site 101. Each DS-CDMA co...... .~-irAtion signal 107, 108 inr.hl~es, inter alia, a pse~do-noise sequence associated with 1 5 the base site 101 and an i~ientifirAtion code for the particular co........ i~.Ation unit 103, 104.
As described above, movement of each col~ ication unit 103, 104 typically results in fading and multipath propagation of the 2 0 DS-CDMA co~ ..ic-Ation signals 107, 108--for example, due to reflection of the t~ncmitte-l signals 107, 108 off of nearby scauerc 109, 110, such as bnil~lin~.c The fading and m--ltipAth propagation ph~nom~n~ produce mlll*pAth signal replicas 119, 120 of the DS-CDMA co... ~ Ation signals 107, 108 llAII~I2littP.~i by the 2 5 co.... ~.. icAtion units 103, 104. Due to the inherent nature of mllltipAth propagation, the trncmitte~ signAlc 107, 108 and the mllltipAth replicas l l9, 120 arrive at the base site 101 at varying times coll~;,yonding to the propagation rlictAnces 111-113, 115-117 of the ~IA.~.c~ e-l signals 107, 108 and the multipath replicas 119, 3 0 120. For example, mllltipAth replica 119 effectively propagates over propA~tion ~lictAnces 112 and 113 prior to arriving at the base site 101; wllcl~as, tr~n.cmitte~l signal 107 propAg~tes over propagation tAnee. 111. Therefore, when the base site 101 receives the DS-CDMA col".,.l."ic~tion signals 107, 108, 119, 120, it searches the -B
collection of received signaLc 107, 108, 119, 120 to distinguish each CC~ lllir~tiQ~l unit's tr~ncmicsions (e.g., 107, 119) from the collrction, as later described. Note that in a mllltip~th environment, the tr~ncmi~e~l signals 107, 108 together with their respective S mlll*r~th signal replicas 119, 120 are generally referred to as mnltirA~h signals (e.g., 107, 119 and 108, 120) of the transrnitted co..,.,~.,ir-~tion signals 107, 108.
Refernng now to FIGs. 2-8, the mnltip~th sign~l.c (e.g., 107, 1 0 119) of a particular DS-CDMA cc..,ll..~ ;c~tio~ signal 107 received at the base site 101 r~n be id~o-ntifie~l in acw~d~lce with a preferred embo-limrnt of the ~l~S~llL invention in the following manner.
During a co,.. ~ ic~tion~ the cc.. ~l-;r~l;on units 103, 104 co!lec-*vely tn~n.cmit their l~s~;Li~e DS-CDMA co~ .ir~tion 1 5 signals 107, 108 on the uplink of the RF çl.A...~r] during one or more time frames 201. In a ~lefcll~d embo~limrnt~ each time frame 201 is divided into s;~l~,e~ power control groups (0-15) of illfollllation, wllel~ill each power control group oc.;ul,;cs one-s;~ , of the time frame 201 as illustrated in FIG. 2. Each power control group (e.g., 2 0 203) is further divided into a plurality of orthogonal symbol sets, such as mod~ tiQn symbols or Walsh symbols (WS(n)).
In a preferred embo-limrnt~ each power control group 203 inrl~lde,c six Walsh symbols (e.g., 210), wherein each Walsh symbol 2 5 210 occupies a modulation symbol time interval of approximately 208 microseconds. Each Walsh symbol 210 further comprises 64 Walsh chips or, equivalently, 256 pseudo-noise (PN) chips, wherein each PN chip preferably colll~lises appro~im~teiy 813 nanoseconds in accold~lce with IS-95. Depentling on the amount of 3 0 cn.. ~.. ic~tion activity (e.g., voice activity), the DS-CDMA
co~ --;r~tion signals might be t~ ."ille-l from the co--~ ication units 103, 104 using one of four possible frame rates 205-208. For e~cample, full rate tr~n.cmi.csion 205, which provides for tr~ncmission of DS-CDMA co~ ..ic~tion signals during all sixteen power 2 ~ 6 7709 control groups, might be used while a user of the co.,....~...ir~-ion unit 103, 104 is actually conversing, while one-eighth rate tr~n~mi.csion 208, which provides for tn~n.cmi.csion only during power control groups 2 and 9, might be use~during periods of 5 sllhst~nti~l silence.
Upon receiving the coded mlll*r~th si~n~ 107, 108, 119, 120 from the co"""l~"i~ti~n units 103, 104, the receiver at the base site 101 stores the i~ llation (e.g., tligi*7e~ voice or data) contained in 1 0 the received mlllhr~th signals 107, 108, 119, 120 during a plurality of mo(~ *orl symbol time intervals (e.g., Walsh syrnbols 210). In a fcll~,d embo~lim~nt~ the receiver stores the information cont~in~d in a complete power control group 203. Upon storing the informa*on, the receiver sealches the stored .l~lll ation to identify 1 5 the mnl*r~th signals (e.g., 107, 119) associated with a tr~n~mi.~sion from a particular col.. ~.. ic~*on unit 103. In a l.l.,f~ d emhorlimf~nt the search is ~lro,~ed se ~ -t;~lly over a plurality of search windows, each search window being offset in tirne with respect to the previous search window. The searching process is 2 0 described below with regard to FIGs. 3-8.
FIG. 3 illustrates r~fel~,nce and received PN sequences 301, 303, 305 used to determine associated signal metrics of the received multipath signals 107, 108, 119, 120 during the afolclllentioned 2 5 searching process in accordance with the present invention. The associated signal metrics ~rcfelably comprise correlation energies of the received PN sequences 303, 305. The correlation energy ~iete~in~tion process is initiated by generating a base site l~fclGllce - PN sequence 301 and correlating the ~efel~llce sequence 301 with the 3 0 PN sequences (e.g., 303, 305) of the mllltip~th signals 107, 108, 119, 120 received at particular offsets in time to obtain correlation energies for the received PN sequences 303, 305. The correlation energies are l,lefe~ably detclll~i,lcd by sampling the base site lefclcnce PN sequence 301 and the received PN sequences 303, 305 at partiClllar sarnpling tirnes (to - tl3) over a predeterrnined period of tirne (e.g., a m~ tion symbol time interval) and Col~ uLillg a coll~ollding energy at each sampling tirne. For e~carnple, at s~mrling time 4 the correlation energy between the reference 5 sequence 301 and the m~tch~ or in-phase, received PN sequence 303 is 1 (i.e., +1 x +1), while the correlation energy between the lefelellce PN sequence 301 and the offset received PN sequence 30S
is -1 ~i.e., -1 ~ +1).
1 0 The correlation energies obt~in~d at the particular sarnpling tirnes are then s.. ~l over the sarnpling period to obtain the correlation energy for each l.,cei~d PN sequence 303, 305. Thus, for the received PN sequences 303, 30S shown in FIG. 3, the correlation energy for the ..~Atel~ed PN sequence 303 is 14, while the 1 5 correlation energy for the PN se4u~"lce offset by 1 PN chip 305 is -2. Therefore, when a l~,cei~d PN sequence 305 is offset in time from the lef.,lellce PN sequence 301, the correlation energy ~soci~ted with t-h-at sequence 305 will be snbst~nti~lly less than the correlation energy for the m~trhe~l sequence 303.
FIG. 4 illustrates exemplary correlation energy levels 401-406 of mlll*p~th signals obtained over a power control group in accordance with prior art methodologies. As shown in FIG. 4 and briefly described in the background section above, the prior art 2 5 techniques of identifying one or more multipath signals 107, 119 tr~n~mitte~ from a co.~ tion unit 103 consist of receiving a first Walsh symbol 210 of information and tletemlining the offset in time 408 associated with the co~ --ication unit's theoretical ~list~nce with respect to the base site 101. The correlation energy 3 0 401 for one of the multipath signals (e.g., 119) received at the offset in time 408 is deteImined by delaying the reference PN sequence 301 by the offset in time 408 and c~lc~ ting the correlation energy as described above with regard to FIG. 3.
The receiver at the base site 101 then seq-~nti~lly deterrnines the correlation energies 402-406 in dle rem~ininE Walsh symbols of the power control group as they are received at the base site 101.
The subsequent correlation energies 402-406 are deterrnined ~y advancing the previously iete~...;..~d offset in time 408 by the corresponding modulation symbol tirne interval (e.g., Walsh symbol). Thus, dhe prior art approach obtains correlation energies 401406 in all Walsh syrnbols of the power control group at the same time offset in each Walsh symbol. Concequendy~ dhe search window 1 0 used to search for mnl-ir~-h signals of a particular transmitted traffic (e.g., voice) signal in the prior art t~o~hnique cclll~lises a single time offset 408 applied to each Walsh symbol in the power control group.
Upon obtaining all six correlation energies 401406, the 1 5 correlation energies 401406 are s~ --P-~ to ~ccllm~ -e the total correlation energy (501 in FIG. 5) at the chosen offset 408 in the power control group. Ho~ ,r, it should be noted that the correlation energies 401-406 o~J~aillcd over the power control group at the sel~-ct~l time offset 408 may not ..~-cess~. ily provide the 2 0 high~t total correlation energy 501 in each power control group.
Therefore, with prior art techniques, the correlation energies 401-406 for multiple offsets (i.e., search windows) might need to be obtained in order to identify a mllltip~-h signal of a particular tr~ncmitte~ DS-CDMA co~ ...c~-ion signal. For example, if the 2 ~ location in time of a mlll~ip~-h signal is such that the correlation energies must be obtained for ten offsets (a typical scenario), then the prior art method would require a search time approximately equal to ten power control groups, or approximately 12.S
milliccconds (ms) for a 20 ms frame tirne in accordance with IS-95.
FIG. 6 illustrates exemplary correlation energy levels 601-606, 610-615, 620-625 of received multipath signals obtained over a power control group in accordance with the present invention. In contrast to the prior art, the present invention receives and stores the informa*on corlt~in~d in multiple modulation symbol time intervals (e.g., si~c Walsh symbols) and sca.ches the multiple modulation symbol time intervals by 11çtennining correlation energies for the multiple modulation symbol time intervals at various offsets in tirne 608, 618, 628. The correla*on energies are obtained at each tirne offset 608, 618, 628 by delaying the base site lcfc~ ce PN sequence by the corresponding offset in time 608, 618, 628 (e.g., by one-half of a PN chip) and c~lc~ *ng ~e correlation energy (e.g., 601) in each Walsh symbol as described above with regard to FIG. 3.
The correlation energies 601-606, 610-615, 620-625 are acc~m--l~te~l and ~ t.~.r-d together with the respective correlation energies obtained at co~ .po~ding offsets 608, 618, 628 to produce the total correlation e,lcl~ies (701-703 in FIG. 7) in multiple search 1 5 windows (i.e., at multiple offsets 608, 618, 628) over the power control group. In a pl~fell~d emboAim~nt, only the set of correlation energies that meet or e~cee~ a prer3~-~e~ -d threshold (E~) are used to dt-l --~ the total correlation energies. For e~cample, the total correlation energy 701 in a search window 2 0 coll~s~onding to offset 608 is l~etC-lll----~'-~ by s--mming the correlation energies 601, 605 obtained at that offset 608 over the power control group that meet or e~ree~ the threshold level.
FIG. 8 illustrates total correlation energies 801-808, 810-813 2 5 obtained in multiple search windows to demonstrate the acquisition of peak energies and local energy maxirna in accordance with the present invention. After obt~ining the total correlation energies 801-808, 810-813 over multiple search windows, a set of the total correlation energies 801-808, 810-813 are selected based on their 3 0 energy values. In a ~lcfell~,d embo~lim~nt, the best eight total correlation energies 801-808 are in~ d in the set and represent the peak energies from the search. The peak energies in the set c~ ond to the multipath signals received by the receiver at particular time offsets. In addition to identifying the peak energies, the total correlation energies are also used to identify a set of local energy m~im~ (e.g., 802, 804, 806-808, 810-813). Each local energy m~imnm is lJlc~lably ~el~ l...;.~r-d by selecting the best energy level over a pre~ete. ~ d interval of time (e.g, over three S time offsets). The local energy ma~cima are used to identify possible starting offsets for subsequent se&c~les when the total correlation energy levels at the ~;ull~nt offsets degrade due to movement of a tr~n~mittin~ co.,l~ ir~tion unit in a fading envirorlm~nt In a ~l~,rell~d embotlim~-nt~ the peak energies and the energies 10 coll~sponding to the local m~lrim~ are processed to obtain the offsets for demor~ tion By using the ..~r-lhrJ~l of the ~.csenL invention, the mllki~th signals received during multiple modulation symbol time intervals 1 5 can be ev~hl~tç~l over multiple offsets to identify the best offsets from which to demor~ at~ in, at most, the time collll,lising a power control group (i.e., 1.25 ms per IS-95). Thus, in the ten offset search e~ample provided above with regard to the ~ c~lssion of FIG.
A Method and A~ c For Identifying A Coded t'c,.. ~.. ir~tion Signal Field of the Invention The present invention relates generally to the reception of coded co.. ~ ir-~tion signals and, in particular, to a method and a~ LuS for idc~lLiry~g a particular coded c~.. ...ic~tion from a 15 plu~lity of received coded c~ .;r~tiQn si~n~l.c.
R~r~ground of the Invention ~"""--";r~tion systems that utilize coded cs~ ic~tion 2 0 signals are known in the ar~ One such system is a direct sequence code division mnl*rle access (DS-CDMA) ce~ r commlmir~tion system, such as that set forth in the TelrcQ.. ir~tions Tn-illctry ~csoci~tion/Electronic Indust~ies Association I~l~e~ l Standard 95 (IIA/EIA IS-95), hereinafter l~fell~d to as IS-95. In accordance 2 ~ with IS-95, the coded cornm-lnir~tion signals used in the DS-CDMA
system comprise DS-CDMA signals that are transmitted in a common 1.25 MHz bandwidth to the base sites of the system from cq.~.. ;c~tioIl units, such as mobile or portable radiotelephones, that are collllllllllir~tirlg in the coverage areas of the base sites. Each 3 0 DS-CDMA signal incl~ es~ inter alia, a pseudo-noise (PN) sequence associ~trd with a particular base site and an i-l~ntific~tion number of a cq.. ~ ir~ting c~.. ic~tion unit.
During a typical co..,...l...ir~tion, the cornmlmicating co.... ic~tion unit often travels within the coverage area of the base site that is ~U~O~ lg the co"""~",ir~sion Such movemenl typically results in fading of the co.. -.. ication signal transmitted 5 from the co" " ~ tion unit to the base site due to multipath propagation of the L~ `---;LI- ~ signal. As is known, multipath propagation results from reflections of the transmitted signal off of nearby scatterers, such as b~ ling.c or large stones. These r~fl~ctionc produce replicas of the originally tr~ncmitted signal that 1 0 arrive at the base site at various times depen-ling on the effective prop~E~tion ~lict~nr,es traveled by the replicas. The originally tr~ncmitte(l signal and the mnl*r~th replicas are typically referred to as mnltir~th signals of the originally tpncmitte~l signal.
In a DS-CDMA system, such as that descnbed by IS-95, mnltir~th prop~g~*Qn typically results in mlll*r~th signals from each L~ ---ill;--g col~"~ "ir~tinn unit arriving at the base site at slll,s~ lly the same time, or at least vithin a commQn time interval. The IS-95 system divides the DS-CDMA signals into 20 2 0 millicecQnd ~ms) frames that contain six~ee.. power control groups.
Each power control group is fu~lcr divided into six modulation--or so-called Walsh--syrnbol time intervals. Each Walsh symbol time interval is approximately 208 microsecon~ls. Thus, with this frarne configuration, several multipath signals from each tr~n.cmitting 2 5 co...~ ..;cation unit might arrive at the base site during one of the Walsh symbol tirne intervals. Each Walsh symbol time interval generally contains one WaLch symbol of digital information as is known in the art.
3 0 To demodulate ~e t~ncmicsions from each colnml-nic~tion unit, the base site receiver must first identify the mllltip~th signals from each c~ tion unit and then select the best multipath signals to demodulate. To identify a particular mnl~ir~th signal, the base site initially receives and stores the information contained in one 2 1 6770q Walsh syrnbol. The base site then g.,l,elates its colles~onding PN
sequence and correlates it to the PN sequence cont~inr-d in the signal received at an initial tirne offset within the Walsh syrnbol to produce a correlation energy. The initial time offset is typically selected 5 based on the theoretical --i--;-------- rlict~nce between a comm--nication unit and the base site.
Upon obt~ining the first correlation energy, the base site advances to the same offset in the ne~t Walsh symbol and calculates a 10 coll.,s~ollding correlation energy. This advance and c~lr~ te, or search, process c~ e,c for a select .~ r of Walsh symbols, typically up to the mlmhlor c~ .ed in a power control group. The n-lmber of Walsh syrnbols to which a particular offset is applied is depen~ nt upon wllelLcr the signal being searched for is a traffic 15 signal (i.e., voice or data) or a pre~mhle signal used during the ~gisLIdLion of a cGl.~ .;c~ti~n unit in the DS-CDMA system.
When t~he signal being s~l~cd for is a t~ffic signal, the offset is applied to all six Walsh s,vrnbols in the power control group;
~l~cl~as, when the signal being scalched for is a prearnble signal, the 2 0 offset is only applied to two Walsh syrnbols.
Upon applying the initial offset to ~e a~lu~liate nllmber of Walsh symbols, the base site changes the offset and repeats the procedure until it locates one or more multipath signals that have 2 5 been transmitted from a co.. ,.. ~ication unit within its service coverage area. Depending on the initial offset and the propagation rii~t~nreS traversed by the comm-lnication unit's tr~n.cmicsion, the base site typically has to iterate through several offsets before obt~inin~ multipath signals to demo~ tr Thus, this search process 3 0 can often result in high effective demodulation times (i.e., the time to search and subsequently demodulate), especially for received traffic sigT~ . The high effective demodulation times impose an lln~lesired upper limit on the bit energy to noise ratio perform~nce required to m~int~in a particular received bit error rate. Such a limit prevents the DS-CDMA system from increasing its capacity without degradin the base site's .ecei~,ed bit error rate (i.e., signal quality).
Tllcl~fol._, a need exists for a m~thod and a~ dLus that identify a particular coded CC.. ~.. ;C~ rl signal from a plurality of received coded cu"~ r~tinn s~ , while significantly reducing the search time required to perform the identification. Further, such a method and al.~ala~us that i~ roves the received bit energy to noise ratio for a given bit error rate would be an improvement over 10 the prior art.
Brief Description of the Drawings FIG. 1 illustrates a co..... ~.. ;r-~*on system that might employ the ~l~sell~ invention.
l:IG. 2 i~ st~tes the power control groups tr~n~mitt~i by a co... ~.. ;c~tion unit at particular CDMA frame rates in accordance with the ~l~,senl invention.
FIG. 3 illustrates lef~ ce and received pseudo-noise sequences used to (iet~ ~...;..~- associ~te~l signal metrics of received mllltip~th signals in acco~ ce with the present invention.
2 5 FIG. 4 illustrates exemplary correlation energy levels of mllltip~th signals obtained in a single search window over a power control group in accordance with prior art methodologies.
FIG. 5 iIlustrates the total correlation energy obtained in the 3 0 single search window of FIG. 4.
FIG. 6 illustrates exemplary correlation energy levels of mlll*p?~th signals obtained in multiple search windows over a power control group in accordance with the present invention.
2 1 6 ~709 s PIG. 7 illustrates the total correlation energies obt~ined in the n~nltirle search windows of FIG. 6.
S FIG. 8 illustrates total correlation energies obt~ined in multiple search windows to ~ dtc the acquisition of peak energies and local energy ...~ in accordance with the present invention.
1 0 FIG. 9 illustrates a receiver that receives coded co.n....~ tion signals in accol~ance with the ~l~S~llL invention.
FIG. 10 illustrates ~l~fcll~d emboA;...P-..lc of the memory device and the ~locessor incl~lded in the l~,cei~- of FIG. 6.
FIG. 11 illll~tr~t~s an exemplary logic flow ~ gr~m of steps e~cllt~ by a lecei~el in accord~ce with the present invention.
2 0 Description of a P~ d Embotlim~-nt Generally, the present invention encoInr~cses a method and ap~d~s for identifying a particular coded co~ .ic~tion signal from a plurality of received coded co.... l~,.;cation signals. A
2 5 receiver that receives coded co~ ic~tion sign~l~ comprises a mernory means and a processin~ m~n~ The memory means stores inform~tion cont~ine~ in the received coded co.. l~.. ic~tion signals during multiple mo~ tion symbol time intervals to produce stored information. The processing means then searches the stored 3 0 inform~tion to identify the particular coded commllnic~tion signal.
By identifying the particular coded co,.. n.. i~tion signal in this m~nn~.r, the l l~senL invention signific~ntly reduces the average time re~uired to identify one or more mllltip~th si~l~ of the particular received coded co.. lll.ication signal. Thus, the present invention . 2167709 decreases the effective time ~quired for demodulation of the particular coded co~ .,ic~ttiQn signal as co",l,~.ed to the effective time for irmot~ tion of a coded co~ ;c~ttion signal using prior art search and tlrmo~ltlsttto te~hni-lues.
The present invention can be more fully described with ~f~,cnce to FIGs. 1-11. FIG. 1 illustrates a co.,..".~ ttion system 100 that might employ the ~l~ s~ invention. The comm--nication system 100 in~hltles a base site 101 and one or more comm--nication 10 units 103, 104 (two shown). The co",..,.",it~ttion system 100 dbly colll~llses a direct seqll~-nr~ code division multiple access (DS-CDMA) ce-lhll~tr cct-..~ ..ir~ttion system, such as that set forth in TIA/ELA IS-95. Ho~e~ r, the ~l~S~ invention is equally applicable to a frequency hopping col"~..,...;r~tic-n system, such as some of those 1 5 proposed for the ~irmrstir Pe~son~l t'o~ ir~tion System (PCS).
In a celllll~r co~ ll;r~tinn system, the base site lO1 is coupled to the public ~wi~ched telephone ~ lwul~ (PSTN) 105 using known ~rhnirlueS.
2 0 The base site 101 ~le~ldbly comprises a receiver that receives coded co~ tion signals from the co...""~ tion units 103, 104 within a coverage area of the base site 101, a tn~n~ er that Ll~.,~.l,il~ coded co.. ~.. ir~tion signals to the co~ tion units 103, 104, and the ~ro~liate interfaces between the PSTN 105 and 2 5 the receiver and tr~n~mitter. A piefclled base site receiver is discussed in detail below with regard to FIG. 9. Each of the co.. l.. ;c~tion units 103, 104 pief~ldbly co~ ises a mobile or portable radiotelephone, a mobile or portable two-way radio, or other two-way co..~ ...ic-~tin~ device, such as a conl~ r with radio 3 0 frequency (RF) tr~ncmi.csion and reception capabilities.
In the ~ d DS-CDMA system 100, the coded cc...~..l...i~tion signals comprise DS-CDMA commllni~tion signals 107, 108 that are conveyed between the cc,~ .ication units 103, 104 and the base site 101 through an RF chAnn~l In an altemate freqll~.nr,y~opping commlmirAti()n system, the coded comm-mication signals might comrri.ce slow fi~lv ..-ry hopping (SFH) cQ~ ..irAtion signals (multiple morlnlAtio~ symbol time intervals S per hop) or fast frequency hopping (F~:H) co... ~.icAtion signals (multiple hops per modulation symbol time interval). The RF
chAnnel inrllldes an uplink (co...~ ...;rAIion units 103, 104 to base site 101) and a downlink (base site 101 to co.. .i~Ation units 103, 104). In a l~l.,rcll~d embo~im~-nt, t-h-e uplink colll~lises a prescribed 1 0 bandwidth (e.g., 1.25 MHz for IS-95) coll~ctively used by the co.l...... ;rAti~n units 103, 104 to tr~ncmit multiple coded co.~...... ir.Ation signals 107, 108 (DS-CDMA si~nAlc in this case) toward the base site 101. Each DS-CDMA co...... .~-irAtion signal 107, 108 inr.hl~es, inter alia, a pse~do-noise sequence associated with 1 5 the base site 101 and an i~ientifirAtion code for the particular co........ i~.Ation unit 103, 104.
As described above, movement of each col~ ication unit 103, 104 typically results in fading and multipath propagation of the 2 0 DS-CDMA co~ ..ic-Ation signals 107, 108--for example, due to reflection of the t~ncmitte-l signals 107, 108 off of nearby scauerc 109, 110, such as bnil~lin~.c The fading and m--ltipAth propagation ph~nom~n~ produce mlll*pAth signal replicas 119, 120 of the DS-CDMA co... ~ Ation signals 107, 108 llAII~I2littP.~i by the 2 5 co.... ~.. icAtion units 103, 104. Due to the inherent nature of mllltipAth propagation, the trncmitte~ signAlc 107, 108 and the mllltipAth replicas l l9, 120 arrive at the base site 101 at varying times coll~;,yonding to the propagation rlictAnces 111-113, 115-117 of the ~IA.~.c~ e-l signals 107, 108 and the multipath replicas 119, 3 0 120. For example, mllltipAth replica 119 effectively propagates over propA~tion ~lictAnces 112 and 113 prior to arriving at the base site 101; wllcl~as, tr~n.cmitte~l signal 107 propAg~tes over propagation tAnee. 111. Therefore, when the base site 101 receives the DS-CDMA col".,.l."ic~tion signals 107, 108, 119, 120, it searches the -B
collection of received signaLc 107, 108, 119, 120 to distinguish each CC~ lllir~tiQ~l unit's tr~ncmicsions (e.g., 107, 119) from the collrction, as later described. Note that in a mllltip~th environment, the tr~ncmi~e~l signals 107, 108 together with their respective S mlll*r~th signal replicas 119, 120 are generally referred to as mnltirA~h signals (e.g., 107, 119 and 108, 120) of the transrnitted co..,.,~.,ir-~tion signals 107, 108.
Refernng now to FIGs. 2-8, the mnltip~th sign~l.c (e.g., 107, 1 0 119) of a particular DS-CDMA cc..,ll..~ ;c~tio~ signal 107 received at the base site 101 r~n be id~o-ntifie~l in acw~d~lce with a preferred embo-limrnt of the ~l~S~llL invention in the following manner.
During a co,.. ~ ic~tion~ the cc.. ~l-;r~l;on units 103, 104 co!lec-*vely tn~n.cmit their l~s~;Li~e DS-CDMA co~ .ir~tion 1 5 signals 107, 108 on the uplink of the RF çl.A...~r] during one or more time frames 201. In a ~lefcll~d embo~limrnt~ each time frame 201 is divided into s;~l~,e~ power control groups (0-15) of illfollllation, wllel~ill each power control group oc.;ul,;cs one-s;~ , of the time frame 201 as illustrated in FIG. 2. Each power control group (e.g., 2 0 203) is further divided into a plurality of orthogonal symbol sets, such as mod~ tiQn symbols or Walsh symbols (WS(n)).
In a preferred embo-limrnt~ each power control group 203 inrl~lde,c six Walsh symbols (e.g., 210), wherein each Walsh symbol 2 5 210 occupies a modulation symbol time interval of approximately 208 microseconds. Each Walsh symbol 210 further comprises 64 Walsh chips or, equivalently, 256 pseudo-noise (PN) chips, wherein each PN chip preferably colll~lises appro~im~teiy 813 nanoseconds in accold~lce with IS-95. Depentling on the amount of 3 0 cn.. ~.. ic~tion activity (e.g., voice activity), the DS-CDMA
co~ --;r~tion signals might be t~ ."ille-l from the co--~ ication units 103, 104 using one of four possible frame rates 205-208. For e~cample, full rate tr~n.cmi.csion 205, which provides for tr~ncmission of DS-CDMA co~ ..ic~tion signals during all sixteen power 2 ~ 6 7709 control groups, might be used while a user of the co.,....~...ir~-ion unit 103, 104 is actually conversing, while one-eighth rate tr~n~mi.csion 208, which provides for tn~n.cmi.csion only during power control groups 2 and 9, might be use~during periods of 5 sllhst~nti~l silence.
Upon receiving the coded mlll*r~th si~n~ 107, 108, 119, 120 from the co"""l~"i~ti~n units 103, 104, the receiver at the base site 101 stores the i~ llation (e.g., tligi*7e~ voice or data) contained in 1 0 the received mlllhr~th signals 107, 108, 119, 120 during a plurality of mo(~ *orl symbol time intervals (e.g., Walsh syrnbols 210). In a fcll~,d embo~lim~nt~ the receiver stores the information cont~in~d in a complete power control group 203. Upon storing the informa*on, the receiver sealches the stored .l~lll ation to identify 1 5 the mnl*r~th signals (e.g., 107, 119) associated with a tr~n~mi.~sion from a particular col.. ~.. ic~*on unit 103. In a l.l.,f~ d emhorlimf~nt the search is ~lro,~ed se ~ -t;~lly over a plurality of search windows, each search window being offset in tirne with respect to the previous search window. The searching process is 2 0 described below with regard to FIGs. 3-8.
FIG. 3 illustrates r~fel~,nce and received PN sequences 301, 303, 305 used to determine associated signal metrics of the received multipath signals 107, 108, 119, 120 during the afolclllentioned 2 5 searching process in accordance with the present invention. The associated signal metrics ~rcfelably comprise correlation energies of the received PN sequences 303, 305. The correlation energy ~iete~in~tion process is initiated by generating a base site l~fclGllce - PN sequence 301 and correlating the ~efel~llce sequence 301 with the 3 0 PN sequences (e.g., 303, 305) of the mllltip~th signals 107, 108, 119, 120 received at particular offsets in time to obtain correlation energies for the received PN sequences 303, 305. The correlation energies are l,lefe~ably detclll~i,lcd by sampling the base site lefclcnce PN sequence 301 and the received PN sequences 303, 305 at partiClllar sarnpling tirnes (to - tl3) over a predeterrnined period of tirne (e.g., a m~ tion symbol time interval) and Col~ uLillg a coll~ollding energy at each sampling tirne. For e~carnple, at s~mrling time 4 the correlation energy between the reference 5 sequence 301 and the m~tch~ or in-phase, received PN sequence 303 is 1 (i.e., +1 x +1), while the correlation energy between the lefelellce PN sequence 301 and the offset received PN sequence 30S
is -1 ~i.e., -1 ~ +1).
1 0 The correlation energies obt~in~d at the particular sarnpling tirnes are then s.. ~l over the sarnpling period to obtain the correlation energy for each l.,cei~d PN sequence 303, 305. Thus, for the received PN sequences 303, 30S shown in FIG. 3, the correlation energy for the ..~Atel~ed PN sequence 303 is 14, while the 1 5 correlation energy for the PN se4u~"lce offset by 1 PN chip 305 is -2. Therefore, when a l~,cei~d PN sequence 305 is offset in time from the lef.,lellce PN sequence 301, the correlation energy ~soci~ted with t-h-at sequence 305 will be snbst~nti~lly less than the correlation energy for the m~trhe~l sequence 303.
FIG. 4 illustrates exemplary correlation energy levels 401-406 of mlll*p~th signals obtained over a power control group in accordance with prior art methodologies. As shown in FIG. 4 and briefly described in the background section above, the prior art 2 5 techniques of identifying one or more multipath signals 107, 119 tr~n~mitte~ from a co.~ tion unit 103 consist of receiving a first Walsh symbol 210 of information and tletemlining the offset in time 408 associated with the co~ --ication unit's theoretical ~list~nce with respect to the base site 101. The correlation energy 3 0 401 for one of the multipath signals (e.g., 119) received at the offset in time 408 is deteImined by delaying the reference PN sequence 301 by the offset in time 408 and c~lc~ ting the correlation energy as described above with regard to FIG. 3.
The receiver at the base site 101 then seq-~nti~lly deterrnines the correlation energies 402-406 in dle rem~ininE Walsh symbols of the power control group as they are received at the base site 101.
The subsequent correlation energies 402-406 are deterrnined ~y advancing the previously iete~...;..~d offset in time 408 by the corresponding modulation symbol tirne interval (e.g., Walsh symbol). Thus, dhe prior art approach obtains correlation energies 401406 in all Walsh syrnbols of the power control group at the same time offset in each Walsh symbol. Concequendy~ dhe search window 1 0 used to search for mnl-ir~-h signals of a particular transmitted traffic (e.g., voice) signal in the prior art t~o~hnique cclll~lises a single time offset 408 applied to each Walsh symbol in the power control group.
Upon obtaining all six correlation energies 401406, the 1 5 correlation energies 401406 are s~ --P-~ to ~ccllm~ -e the total correlation energy (501 in FIG. 5) at the chosen offset 408 in the power control group. Ho~ ,r, it should be noted that the correlation energies 401-406 o~J~aillcd over the power control group at the sel~-ct~l time offset 408 may not ..~-cess~. ily provide the 2 0 high~t total correlation energy 501 in each power control group.
Therefore, with prior art techniques, the correlation energies 401-406 for multiple offsets (i.e., search windows) might need to be obtained in order to identify a mllltip~-h signal of a particular tr~ncmitte~ DS-CDMA co~ ...c~-ion signal. For example, if the 2 ~ location in time of a mlll~ip~-h signal is such that the correlation energies must be obtained for ten offsets (a typical scenario), then the prior art method would require a search time approximately equal to ten power control groups, or approximately 12.S
milliccconds (ms) for a 20 ms frame tirne in accordance with IS-95.
FIG. 6 illustrates exemplary correlation energy levels 601-606, 610-615, 620-625 of received multipath signals obtained over a power control group in accordance with the present invention. In contrast to the prior art, the present invention receives and stores the informa*on corlt~in~d in multiple modulation symbol time intervals (e.g., si~c Walsh symbols) and sca.ches the multiple modulation symbol time intervals by 11çtennining correlation energies for the multiple modulation symbol time intervals at various offsets in tirne 608, 618, 628. The correla*on energies are obtained at each tirne offset 608, 618, 628 by delaying the base site lcfc~ ce PN sequence by the corresponding offset in time 608, 618, 628 (e.g., by one-half of a PN chip) and c~lc~ *ng ~e correlation energy (e.g., 601) in each Walsh symbol as described above with regard to FIG. 3.
The correlation energies 601-606, 610-615, 620-625 are acc~m--l~te~l and ~ t.~.r-d together with the respective correlation energies obtained at co~ .po~ding offsets 608, 618, 628 to produce the total correlation e,lcl~ies (701-703 in FIG. 7) in multiple search 1 5 windows (i.e., at multiple offsets 608, 618, 628) over the power control group. In a pl~fell~d emboAim~nt, only the set of correlation energies that meet or e~cee~ a prer3~-~e~ -d threshold (E~) are used to dt-l --~ the total correlation energies. For e~cample, the total correlation energy 701 in a search window 2 0 coll~s~onding to offset 608 is l~etC-lll----~'-~ by s--mming the correlation energies 601, 605 obtained at that offset 608 over the power control group that meet or e~ree~ the threshold level.
FIG. 8 illustrates total correlation energies 801-808, 810-813 2 5 obtained in multiple search windows to demonstrate the acquisition of peak energies and local energy maxirna in accordance with the present invention. After obt~ining the total correlation energies 801-808, 810-813 over multiple search windows, a set of the total correlation energies 801-808, 810-813 are selected based on their 3 0 energy values. In a ~lcfell~,d embo~lim~nt, the best eight total correlation energies 801-808 are in~ d in the set and represent the peak energies from the search. The peak energies in the set c~ ond to the multipath signals received by the receiver at particular time offsets. In addition to identifying the peak energies, the total correlation energies are also used to identify a set of local energy m~im~ (e.g., 802, 804, 806-808, 810-813). Each local energy m~imnm is lJlc~lably ~el~ l...;.~r-d by selecting the best energy level over a pre~ete. ~ d interval of time (e.g, over three S time offsets). The local energy ma~cima are used to identify possible starting offsets for subsequent se&c~les when the total correlation energy levels at the ~;ull~nt offsets degrade due to movement of a tr~n~mittin~ co.,l~ ir~tion unit in a fading envirorlm~nt In a ~l~,rell~d embotlim~-nt~ the peak energies and the energies 10 coll~sponding to the local m~lrim~ are processed to obtain the offsets for demor~ tion By using the ..~r-lhrJ~l of the ~.csenL invention, the mllki~th signals received during multiple modulation symbol time intervals 1 5 can be ev~hl~tç~l over multiple offsets to identify the best offsets from which to demor~ at~ in, at most, the time collll,lising a power control group (i.e., 1.25 ms per IS-95). Thus, in the ten offset search e~ample provided above with regard to the ~ c~lssion of FIG.
4, the present invention reduces the prior art search time, and the 2 0 effective demodulation time, by a factor of more than 10. In addition, the search and demodulate techniqll~ of the present invention provides an i~ lo~ed bit energy to noise ratio (Eb/No) at a particular bit error rate (BER) as compared to its prior art coullL~l~arts due to the more expedient identific~tion of the best 2 s mllltip~th signals for use in demodulation. This improvement in Eb/No is ~tt~ine~ bec~ e the faster searching process of the ~esellt invention reduces the oppol~ulliLies for acquiring additional noise in the received signals due to fading during the search tirne. Fo e~mple, to m~int~in a received BER of 1%, the method of the 3 0 present invention requires 0.6 dB less Eb/No than does the methods of ~e prior art. This reduction in required Eb/No correlates tO an increased system c.~p~city for that BER.
It should be noted that although the above tliccl~ssion is du~d at ide.~ julg mllltip~th ci~n~ls at the base site 101 of uplink -issionc from the ~ tion units 103, 104, the ~sellt invention is also applicable in iden~fying mlllti~th signals at the 5 co~ ;r~ti~n unit 103, 104 of downlink tPncmiccions from the base site 101 (e.g., when using LI~S .I diversity techniques at the base site 101). It should be Çulll~cr noted that although the prefer~d embo~im~nt uses energy levels to identify desired offsets for demo~ tion, the m~nillldes of received Walsh symbols might o ~h~rn~*vely CGlll~liSC the ~csoci~d signal metrics that are used to idc,lli~ received mlll*rath si~lc. The l,-oced~ for deh....i..in~
the m~nitude of a Walsh symbol is known in dle art.
FIG. 9 ill..c~ s a l~;~el 900 that l~i~'es coded 15 co~ -ic~*on signals in accor~lce with the y~S~ invention.
The .~i~er 900 inrln~es an ~ structure 901, a signal receiver 903, a memory device 905, a yloccss~r 907, a sc~ling device 909, a ~emo~ tor911,andacombiner913. ~ez-.~ structure901 l,icf~.dbly inrllldes t vo di~.cl~ z.~ n..~s, ~l~holl~h a single ~nte~n~
2 0 may ~hprn~tively be used. The signal receiver 903 yl~fcndbly inrltl~es known receiver front end and ~r~entl circuitry, such as amplifiers, filters, oscill~tors, do vn mi~ers and analog-to-digital converters. The memory device 905, the processor 907, the sc~lin~
device 909, the demo~ tor 911, and the combiner 913 preferably 2 5 reside in an application specific integrated circuit (ASIC). Preferred embo~ of the memory device 905 and the processor 907 are dcsc-ibcd in det il below with regard to PIG. 10. The sc~ling device 909 is coupled to the yr~cessor 907 via a control line 915 and r~ably co..~ylises a mukiplier, a ~egister, and a state m~t~hinP.
3 0 The dP-mod~ tor 911 is also coupled to the processor 907 via a con~ol line 917 and ynerclably comprises known digital hardware ~ssoci~ted with performing a Past H~ m~rd Transforrn (PHT).
Ope~tion of the receiver 900 in accordance wi~ the present invcntion occurs in the following m~nner. The mllltip~-h si~l.c are rcceived by the z~ structure 901 and subsequently supplied to the signal receiver 903. The signal ,ccci~cr 903 processes the S received sign~lc and ~ ably s~rplies a power control group of sampled b~ce~n~ sc..l~l;nnc of the rcceived sigr~lc to the m~.mo2y device 905. The ~e .~o.~ device 905 stores the information cc,~ d in ~e t!~eb~nd represe-nt~ti~n~ during two or more modulation symbol time intervals as described above with regard to 10 FIG. 2. Tbe memory device 905 then provides the stored illfo ...~l;cn to the ~.oc~ssor 907 where the stored infom ~tion is sca.~llcd to obtain the time offsets and c,lc.~;ies ~csoc;~tf-A with the ,d m~ltip~th signals as described above. l~t~ d operation of the l,luc~ssor is provided below with regard to FIG. 10.
In ~dAition to supplying ~,~nd lC~CSÇ ~I~I;r~n~ to the m~mory device 905, the signal l~i~el 903 also de;,~l~ads the coded c~ .;c~ rl signals based on the time offsets supplied by the l,loccssor 907 to e~ctract the 64 Walsh chips cc~ -d in each Walsh 2 0 symbol. The signal lecei~,er 903 provides the despread signals (Walsh chips) to the scaler 909. The scaler 909 weights each des~.~ad mnltip~th signal based on the total correlation energy ollt~L.ed in a corresponding search window. The scaler 909 then provides the weighted despread nlllltirath si~ls to the demodulator 2 ~ 911 where each despl-,ad signal is de-mQd~ tP-d and subsequently provided to the combiner 913. The combiner 913 combines the demodlll~ted mllltip~th signals in accol~,cc with known techni~
to l~,clJ-er the particular coded co~ ..;c~tiQn signal ~soci~tPd with the received mllltip~th sign~ls The combiner 913 supplies the 3 0 reco~ ,d coded cQ...~ ic~tion signal to the rem~ining reverse c1~nne] circui~ (e.g., soft tlecici~n cilcui~ry, convohltit~
~leco~l~r, etc.) for ful~lel processing In a preferred embodiment the scaler 909 is not used and ~e despread sign~l~ are provided from the signal receiver 903 dil~,clly to the ~lemodlll~tQr 911.
FIG. 10 illusLla~s ~ fc"~d emhloAimçntc of the memory device 905 and the ~,ocessor 907 incluAe-d in ~e receiver 900 of FIG. 9. In the ~.efel-c,d emboAim~nt, the memory device 905 S COl~ iSES a l~ldo,ll access ~t~mory 1001 (RAM) used to store the infonnation co~ i.-e(l in one or more power control groups (PCG(n)) or two or more Walsh symbols. However, the memory device 905 might ~hern~tively collllJl;se a register file, an array of l~trhes7 or any other means for storing digital illfolmation. The 1 0 lJ,efell~d ~ ssor 907 inrht~es a dc~l~ader 1004, an F~IT block 1006, an energy RAM 1008, a combined ellc,~ RAM 1010, a multiplier 1012, an adder/subtractor 1014, a co~ a~or 1016, a search result RAM 1018, and a PN se~çnce g~lclator 1020.
Operation of ~e ~lef~ ,d m.onnory device 905 and the ~,~"~d l"uccssor 907 occurs in the following m~nn~r. The sampled b~ceb~nd S -~t:~l;C!I~ of the mllhip~th sign~lC provided by the signal receiver 903 to the m~mory device 905 are stored in the RAM 1001. The RAM 1001 provides an equivalent amount of 2 0 the sampled represont~tions as is cu~ d in a Walsh symbol to the des~l~ader 1004. The des~,cader 1004 also receives a r~iel~nce PN
se~enGe (e.g., the l~iel~"lce sequence of FIG. 3) from the PN
seq-~ nc~ g~ or 1020 and uses the l~r~l~"lce PN sequence in a known m~nn-or to obtain the 64 Walsh chips that cou-~lise the 2 5 il-~Jul~d Walsh symbol. In a ~fell~d emboAiment~ each Walsh symbol corresponds to an in-phase (I) col-l~oll~llL or a quadrature (Q) com~ of a Aigit~lly moA-ll~te~ M-ary signal.
The Walsh chips are provided to t~he F~lT block 1006 where 3 0 they are clernod~ te~ using ~e afor~ ;on~-~ FHT. The F~lT
block 1006 effec~vely ~ rOlllls the inputted Walsh chips (either I
or Q) into a t~ble of inAe~eA m~hll~es having associ~te.~ signs (i.e., either positive or negative) that depen~ on, inter alia, the signs of the originally tr~n~mine~ digital information and characteristics of ~e 21 6770q ...el. The in~lç~es coll~sy~lld to the code symbols used for a particuLar cn~o~lin~ldeco~ing confi~ration as is known in the art.
The F~lT block 1006 provides thc Walsh chips sequçnti~lly to 5 the multiplier 1012. The mlll*plier 1012 squares each inde~ed m~gnitll-l~ and provides thc s~u~cd magri~hl~es to the adder/
subtractor 1014. When using M-ary digital mo~ tion, the multiplier 1012 yl~fcldbly COlllylllCS I2 for each index (i.e., Il2, I22, I32, etc.) in the output table of the FHT block 1006 and provides 10 thcse squared ma~itl~Aes to thc adder/sul~àctor 1014. The adder/subtractor 1014 passes the I2 valucs to the cnergy RAM 1008 wherc they are stored. S-~uc~lt to CG~ ~g the I2 values, the m ll*plier 1012 squares cach in~ ed m~ ih~flP for the Walsh chips ~cscci~ with thc Q co~ onc,l~. As each Qi2 is produced by the 15 mnl*rlier 1012 and provided to the adder/s~lb~ctor 1014, the energy RAM 1008 provides a coll~s~o~ ing Ii2value to the adder/subtractor 1014. Thc adder/~ ~bh~or 1014 adds the coll~sl,o..tling I2 and Q2 valucs and sellnçnti~lly provides the s~mm~tions (Ii2 + Qi2) to the energy RAM 1008 where the 2 0 s~ ....AIinnc, or energies, are stored until all 64 have been conlyllLed.
Thc encrgy RAM 1008 provides the stored energies to the ccl~ JAIator 1016 where the ellcr~its are seqllçnti~lly col.ly&l~d to each other to identify the inde~ h-aving the highest associated energy 2 ~ (i.e., correlation energy) for the particular offset. This first correlation energy is then cn...p~ed to upper and lower thresholds I~u~ Tl). When the first correlation energy is less d~an the lower threshold (Tl), the energy is ignored (i.e., weighte~ by zero) and the ;ll;llg search at that offset is ~iicco~ etl When dle first 3 0 correlation energy level resides ~~ cl- the upper and lower thresholds, the energy is stored in the combined energy RAM 1010 and the search is allowed to co~ e at that offset for dle rem~ining Walsh symbols in the power control group. When the first correlation energy level e~ce~s the upper threshold (Tu), the energy 2 1 6770q level is stored in the combined energy RAM 1010 and the offset at which t~he e.lc~y was ol)t~ is then provided to the scaler 909 and/or the ~mot~ tor 911 for f."lllcr ~luc~s~ng of the m-lltip~th signal received at that offset.
Upon obt~inin~ t~he first correlation energy, the above process is l~e~ A for each offset in each Walsh symbol until all the Walsh syrnbols of the stored power control group have been sca.~hcd.
However, during these repe~teA ~loc~sses, the correlation energies 10 ~~ ed at co,-~s~unding offsets are rccllm~ d and co...~ d to updated upper and lower ILl~-sl.nl~lc. For c~ample, when the correl~tio~ c nclgics are aGc~nmll~ted for a parlicular offset over ~ree Walsh symbols, ~e acc~ ht~ el,el~;y (i.e., the sum of the tl~e correl~tinn tnCf~iCS) iS co~ 5;-cd to upper and lower 15 th~esl~nl~ls that are a~ t~ly threc t~nes higher than those which were co~ d to the first correlation ellclgy. The c~m~ tiorl of this it,lali~ y~dule cffcctively rcsults in the g of the corrclation encrgies shown in FIG. 6, thereby olJtS';~ g the total correlation ellelgies depicted in FIGs. 7 and 8.
2 0 These total correlation energies are then stored in the combined energy RAM 1010.
The cûll~l,ined energy RAM 1010 provides the total corrclation energies to the Cûllly~a~Ol 1016 where they are 2 5 co~ n~d to each other to detcl..~ a set of total correlation energies having energy values glcatel than the total correlation el~lE;ies not in the set~ In the yl~,Lll~,d embo~ the eight hi~h~ost total correlation energies are in~luded in the set. As described above with regard to I:IG. 8, the total correlation el,e,gies 3 0 in the set col~ ,olld to the mllltir~th s~ c received by the receiver 900 at l~sl,ec~ e tirne offsets. In ^d~lition to dc~,n~ g the offsets coll~ ullding to the greatest eight energies, the co~ z~àlor 1016 also det~ es a set of local rna~ima of the total correlation energies and ~ n*fies the offsets associated with those m~im~ as described above with regard to FIG. 8. The set of total correlation e,~rg;es, the set of local m~im~, and the offsets ~cs~-;Ated with both sets are provided to the search result RAM 1018 where they are stored and subs~ue~ y used for controlling the 5 ~loces~ ed by the scaler 909 andlor the demodulator 911.
The above i~ldLi~c process e~cemplifies a l lcfcll~d non-cohel~"~t demot~ tion approach used to identify the offsets from which to process the received mnltir~th signals. However, the use of 10 a coherent tlemod~ ticln tpthni~lue during the sealc~ling process is e~ually applicable to the ~.~S~t iu~elllion. The col~r~
mo~ tiQn ~locess ~,lc~lably occurs as follows. The FHT block 1006 receives the I and Q Walsh chips in a ~ r similar to that descnbed above for the non-coherent demoA~ tion approach. The 15 F~lT block 1006 then provides the I and Q Walsh chips of the first Walsh symbol in the power control group to the adder/ subtractor 1014. T,he adder/~ul)~aelor 1014 passes these I and Q values to the energy RAM 1008 where they are stored. The PHT block 1006 ~en provides the I and Q Walsh chips of the sllbsP~llPnt Walsh syrnbol, or 20 symbols~ ep~pn~ling on the l..~ "l~J of mod~ tion symbol time intervals stored in the RAM 1001--to the adder/ subtractor 1014.
The adder/~ub~,dctor 1014 adds the ,~s~ec1;.~e I values coll~sl,ol,ding to all 64 in~ S of all the Walsh symbols stored in the energy RAM 1008 (e.g., Il [WS(0)] + Il [WS(l)] + Il [WS(2)] +
2 5 ...; I2 [WS(0)] + I2 [WS(l)] + I2 [WS(2)] + ...; etc.)~ In a similar m~nner, the adder/subtractor 1014 adds the respective Q values coll~,s~onding to all 64 inrlexes of all the Walsh symbols stored in the energy RAM 1008. The 64 sllmmed I values ( [ ~I ] ) and the 64 s ~ ed Q values ( [ ~:Q ] ) are then provided to the multiplier 1012.
The mul~plier 1012 squares each s ~.. e~ I value and each s-~ .ed Q value, and provides the squared m~ s ( [ ~:I ]2, [ ~Q ]2) to the adder/ subtractor 1014. The adder/subtractor 1014 adds the collesl,ollding [ ~:I ]2 and [ ~.Q ]2 values and sequentially provides the s..... ~tinnc ([ ~Ii ]2 + [ ~;Qi ~2) to the energy RAM
1008 where the ~.. .n~tion~ or Chcl~;ics, are stored until all 64 have been co~ .uled The e.~,gies are provided to ~e cv~ dtor 1016 for fullher ~locesC;..g in a ..~ r analogous to that described above 5 with regard to non-colle.~ demod~ ti~n- It should be noted that the t~rhni11~es ~esc~i~d l.c,~illabove for non-coherent and coherent demQ~lnl~tion can also be applied to the final fl~mocllll~tion ~h,lrwllled by the ~em~~ tor 911 of FIG. 9.
FIG. 11 ilhl~tr~tes an e~emplary logic flow diagrarn 1100 of steps e~e~ted by a receiver in acco~ ce with the present invention. The logic flow begins (1101) when the receiver stores (1103) inform~tir.n co.~ ;..Pd in mnltirl.~ modl-l~tion symbol time intervals. The ~ el thcn searchcs (1105) the stored infonnation 1 ~ to id~l~if~ a set of mllltip~th signals of a particular coded cu~ c~tion signal in onc or more search windows (i.e., at one or morc time offsets in each mo~ tir~n symbol time interval) by llete----;--;--g the total correlation energy in each search window as described above. In a ~,efe,l~d embo~lim~-nt, the set of mllltip~th 2 0 signals are those signals received at the offsets that provide the eight best total correlation .,.l.,rgics.
Upon searclli,lg the stored information and det~rmining the set of mnl*rzth signzl~ the receiver de~llll;lles (1107) whether the 2 5 m ll*path signals in the set need to be adjusted to account for characteristics of the comple~ RF ch~ -l through which the mnltirzth signals propzg~t~d prior to reception. Such characteristics inrl--~le phase rotation or all~ ....z~;Qn of the multipath signzlc' mo~ tiQn symbols due to fa(lin~ When the mnltirzth signals in the 3 0 set need to be adjusted, the receiver es~ tes (1109) a characteristic of the ~z..~-l based on an ~csoci~te~ signal metric of a mllltipath signal in the set. For e~ample, to zcco~lnt for a phase rotation of the modulation symbols during tr~n~m~ on through the RF C~ -P1, the I and Q components of an M-ary mo~hllztiQn symbol that provide the correlation energy for a particular time offsct might be used to Aete~ a desilcd phase in the I, Q plane at that time offset for the ~m~inin~ stored moA~ tinn symbols.
Upon estim~tin~ the ch~ractenstic of the rh~ el, the receiver adjusts (1111) one or more mnltip~th si~ls in the set based on the coll~s~ol,ding cl.~ l es~im~te. In the above e~ample, this adjusting might colllylise rotating the phase of a ~-~l,se~ n~ stored moAlll~tion symbol such that the phase coll~syGllds to the previously detulllli..ed 1 0 desired phase.
~ o..l;l.~.;.~g down the logic flow diagram 1100, the receiver weights (1113) each mllltir~th signal in the set based on the ~Csoci~teA signal metric. In a l,l~fcl,~,d ~m~ the weiEhtinEs 1~ are de~....i.~fd in y~opo~Lion to ~e con~l~ti~ energy co...~ for each mllhir~th signal and are applied to the m~nitllA~s of each of tihe rr~lll*r~th si~n~lc~ Upon we,gh1;-.~ each m~ll*p~th signal in the set, the rece*er ~emo~Alll~tes (1115) the set of wei~ted mllhirath signals by ~lefeldbly applying an FHT to each weighted mllhir~th 2 0 signal. The receiver then comhin~os (1117) the AemoAl~l~t~A. signals using known combining !~-c~ ues to leco~e~ the particular coded c~ .ic~tion signal and the logic flow ends (1119).
The yl~S~ invention encomp~sses a method and al~p&l~L~ls for 2 ~ identifying a particular coded c~ .ic~tion signal from a plurality of received coded co~ ication sign~ls. With this invention, ~e time l~uil~d to search and identify the best mllltir~tll signals of the par~icular coded co~ ic~tiQn signal to use for Ae-moA~ tion is si~nifir~ntly reA~re~ as co,..~t~d to the prior art searching 30 l~c~ ues. Thissearchtirneilll~;o~ clllresultsbeç~æthe ~ilLSt~l~ invention provides a means for acquilillg energies at multiple offsets over a power control group; ~hcl~as, ~e prior art app~aches only acquire a single energy (i.e., one offset) over the power control group. Thus, the ~l~,selll invention more efficiently ntili7e the data cont-qin~A~ in a power control group during its mnltipqth signal æarch as cQ~ ed to the data u~ili7Ation of the prior art æarching t~hni~ os ru,~,cr, due to its e~peAient s~chillg ycl~o ...qnr~, the l,.ese.,~ invention provides an improved 5 Eb/No at a particular bit error rate as ccS~ d to its prior art co~ rl .l,~LS since faster sear~l~i,lg results in reAueed opportunities for acquiring -q-dditir~-q-l noiæ in the received mllltipAth signals due tO
fading during the tot. l search tirne interval.
1 0 What is cl-q-imed is:
It should be noted that although the above tliccl~ssion is du~d at ide.~ julg mllltip~th ci~n~ls at the base site 101 of uplink -issionc from the ~ tion units 103, 104, the ~sellt invention is also applicable in iden~fying mlllti~th signals at the 5 co~ ;r~ti~n unit 103, 104 of downlink tPncmiccions from the base site 101 (e.g., when using LI~S .I diversity techniques at the base site 101). It should be Çulll~cr noted that although the prefer~d embo~im~nt uses energy levels to identify desired offsets for demo~ tion, the m~nillldes of received Walsh symbols might o ~h~rn~*vely CGlll~liSC the ~csoci~d signal metrics that are used to idc,lli~ received mlll*rath si~lc. The l,-oced~ for deh....i..in~
the m~nitude of a Walsh symbol is known in dle art.
FIG. 9 ill..c~ s a l~;~el 900 that l~i~'es coded 15 co~ -ic~*on signals in accor~lce with the y~S~ invention.
The .~i~er 900 inrln~es an ~ structure 901, a signal receiver 903, a memory device 905, a yloccss~r 907, a sc~ling device 909, a ~emo~ tor911,andacombiner913. ~ez-.~ structure901 l,icf~.dbly inrllldes t vo di~.cl~ z.~ n..~s, ~l~holl~h a single ~nte~n~
2 0 may ~hprn~tively be used. The signal receiver 903 yl~fcndbly inrltl~es known receiver front end and ~r~entl circuitry, such as amplifiers, filters, oscill~tors, do vn mi~ers and analog-to-digital converters. The memory device 905, the processor 907, the sc~lin~
device 909, the demo~ tor 911, and the combiner 913 preferably 2 5 reside in an application specific integrated circuit (ASIC). Preferred embo~ of the memory device 905 and the processor 907 are dcsc-ibcd in det il below with regard to PIG. 10. The sc~ling device 909 is coupled to the yr~cessor 907 via a control line 915 and r~ably co..~ylises a mukiplier, a ~egister, and a state m~t~hinP.
3 0 The dP-mod~ tor 911 is also coupled to the processor 907 via a con~ol line 917 and ynerclably comprises known digital hardware ~ssoci~ted with performing a Past H~ m~rd Transforrn (PHT).
Ope~tion of the receiver 900 in accordance wi~ the present invcntion occurs in the following m~nner. The mllltip~-h si~l.c are rcceived by the z~ structure 901 and subsequently supplied to the signal receiver 903. The signal ,ccci~cr 903 processes the S received sign~lc and ~ ably s~rplies a power control group of sampled b~ce~n~ sc..l~l;nnc of the rcceived sigr~lc to the m~.mo2y device 905. The ~e .~o.~ device 905 stores the information cc,~ d in ~e t!~eb~nd represe-nt~ti~n~ during two or more modulation symbol time intervals as described above with regard to 10 FIG. 2. Tbe memory device 905 then provides the stored illfo ...~l;cn to the ~.oc~ssor 907 where the stored infom ~tion is sca.~llcd to obtain the time offsets and c,lc.~;ies ~csoc;~tf-A with the ,d m~ltip~th signals as described above. l~t~ d operation of the l,luc~ssor is provided below with regard to FIG. 10.
In ~dAition to supplying ~,~nd lC~CSÇ ~I~I;r~n~ to the m~mory device 905, the signal l~i~el 903 also de;,~l~ads the coded c~ .;c~ rl signals based on the time offsets supplied by the l,loccssor 907 to e~ctract the 64 Walsh chips cc~ -d in each Walsh 2 0 symbol. The signal lecei~,er 903 provides the despread signals (Walsh chips) to the scaler 909. The scaler 909 weights each des~.~ad mnltip~th signal based on the total correlation energy ollt~L.ed in a corresponding search window. The scaler 909 then provides the weighted despread nlllltirath si~ls to the demodulator 2 ~ 911 where each despl-,ad signal is de-mQd~ tP-d and subsequently provided to the combiner 913. The combiner 913 combines the demodlll~ted mllltip~th signals in accol~,cc with known techni~
to l~,clJ-er the particular coded co~ ..;c~tiQn signal ~soci~tPd with the received mllltip~th sign~ls The combiner 913 supplies the 3 0 reco~ ,d coded cQ...~ ic~tion signal to the rem~ining reverse c1~nne] circui~ (e.g., soft tlecici~n cilcui~ry, convohltit~
~leco~l~r, etc.) for ful~lel processing In a preferred embodiment the scaler 909 is not used and ~e despread sign~l~ are provided from the signal receiver 903 dil~,clly to the ~lemodlll~tQr 911.
FIG. 10 illusLla~s ~ fc"~d emhloAimçntc of the memory device 905 and the ~,ocessor 907 incluAe-d in ~e receiver 900 of FIG. 9. In the ~.efel-c,d emboAim~nt, the memory device 905 S COl~ iSES a l~ldo,ll access ~t~mory 1001 (RAM) used to store the infonnation co~ i.-e(l in one or more power control groups (PCG(n)) or two or more Walsh symbols. However, the memory device 905 might ~hern~tively collllJl;se a register file, an array of l~trhes7 or any other means for storing digital illfolmation. The 1 0 lJ,efell~d ~ ssor 907 inrht~es a dc~l~ader 1004, an F~IT block 1006, an energy RAM 1008, a combined ellc,~ RAM 1010, a multiplier 1012, an adder/subtractor 1014, a co~ a~or 1016, a search result RAM 1018, and a PN se~çnce g~lclator 1020.
Operation of ~e ~lef~ ,d m.onnory device 905 and the ~,~"~d l"uccssor 907 occurs in the following m~nn~r. The sampled b~ceb~nd S -~t:~l;C!I~ of the mllhip~th sign~lC provided by the signal receiver 903 to the m~mory device 905 are stored in the RAM 1001. The RAM 1001 provides an equivalent amount of 2 0 the sampled represont~tions as is cu~ d in a Walsh symbol to the des~l~ader 1004. The des~,cader 1004 also receives a r~iel~nce PN
se~enGe (e.g., the l~iel~"lce sequence of FIG. 3) from the PN
seq-~ nc~ g~ or 1020 and uses the l~r~l~"lce PN sequence in a known m~nn-or to obtain the 64 Walsh chips that cou-~lise the 2 5 il-~Jul~d Walsh symbol. In a ~fell~d emboAiment~ each Walsh symbol corresponds to an in-phase (I) col-l~oll~llL or a quadrature (Q) com~ of a Aigit~lly moA-ll~te~ M-ary signal.
The Walsh chips are provided to t~he F~lT block 1006 where 3 0 they are clernod~ te~ using ~e afor~ ;on~-~ FHT. The F~lT
block 1006 effec~vely ~ rOlllls the inputted Walsh chips (either I
or Q) into a t~ble of inAe~eA m~hll~es having associ~te.~ signs (i.e., either positive or negative) that depen~ on, inter alia, the signs of the originally tr~n~mine~ digital information and characteristics of ~e 21 6770q ...el. The in~lç~es coll~sy~lld to the code symbols used for a particuLar cn~o~lin~ldeco~ing confi~ration as is known in the art.
The F~lT block 1006 provides thc Walsh chips sequçnti~lly to 5 the multiplier 1012. The mlll*plier 1012 squares each inde~ed m~gnitll-l~ and provides thc s~u~cd magri~hl~es to the adder/
subtractor 1014. When using M-ary digital mo~ tion, the multiplier 1012 yl~fcldbly COlllylllCS I2 for each index (i.e., Il2, I22, I32, etc.) in the output table of the FHT block 1006 and provides 10 thcse squared ma~itl~Aes to thc adder/sul~àctor 1014. The adder/subtractor 1014 passes the I2 valucs to the cnergy RAM 1008 wherc they are stored. S-~uc~lt to CG~ ~g the I2 values, the m ll*plier 1012 squares cach in~ ed m~ ih~flP for the Walsh chips ~cscci~ with thc Q co~ onc,l~. As each Qi2 is produced by the 15 mnl*rlier 1012 and provided to the adder/s~lb~ctor 1014, the energy RAM 1008 provides a coll~s~o~ ing Ii2value to the adder/subtractor 1014. Thc adder/~ ~bh~or 1014 adds the coll~sl,o..tling I2 and Q2 valucs and sellnçnti~lly provides the s~mm~tions (Ii2 + Qi2) to the energy RAM 1008 where the 2 0 s~ ....AIinnc, or energies, are stored until all 64 have been conlyllLed.
Thc encrgy RAM 1008 provides the stored energies to the ccl~ JAIator 1016 where the ellcr~its are seqllçnti~lly col.ly&l~d to each other to identify the inde~ h-aving the highest associated energy 2 ~ (i.e., correlation energy) for the particular offset. This first correlation energy is then cn...p~ed to upper and lower thresholds I~u~ Tl). When the first correlation energy is less d~an the lower threshold (Tl), the energy is ignored (i.e., weighte~ by zero) and the ;ll;llg search at that offset is ~iicco~ etl When dle first 3 0 correlation energy level resides ~~ cl- the upper and lower thresholds, the energy is stored in the combined energy RAM 1010 and the search is allowed to co~ e at that offset for dle rem~ining Walsh symbols in the power control group. When the first correlation energy level e~ce~s the upper threshold (Tu), the energy 2 1 6770q level is stored in the combined energy RAM 1010 and the offset at which t~he e.lc~y was ol)t~ is then provided to the scaler 909 and/or the ~mot~ tor 911 for f."lllcr ~luc~s~ng of the m-lltip~th signal received at that offset.
Upon obt~inin~ t~he first correlation energy, the above process is l~e~ A for each offset in each Walsh symbol until all the Walsh syrnbols of the stored power control group have been sca.~hcd.
However, during these repe~teA ~loc~sses, the correlation energies 10 ~~ ed at co,-~s~unding offsets are rccllm~ d and co...~ d to updated upper and lower ILl~-sl.nl~lc. For c~ample, when the correl~tio~ c nclgics are aGc~nmll~ted for a parlicular offset over ~ree Walsh symbols, ~e acc~ ht~ el,el~;y (i.e., the sum of the tl~e correl~tinn tnCf~iCS) iS co~ 5;-cd to upper and lower 15 th~esl~nl~ls that are a~ t~ly threc t~nes higher than those which were co~ d to the first correlation ellclgy. The c~m~ tiorl of this it,lali~ y~dule cffcctively rcsults in the g of the corrclation encrgies shown in FIG. 6, thereby olJtS';~ g the total correlation ellelgies depicted in FIGs. 7 and 8.
2 0 These total correlation energies are then stored in the combined energy RAM 1010.
The cûll~l,ined energy RAM 1010 provides the total corrclation energies to the Cûllly~a~Ol 1016 where they are 2 5 co~ n~d to each other to detcl..~ a set of total correlation energies having energy values glcatel than the total correlation el~lE;ies not in the set~ In the yl~,Lll~,d embo~ the eight hi~h~ost total correlation energies are in~luded in the set. As described above with regard to I:IG. 8, the total correlation el,e,gies 3 0 in the set col~ ,olld to the mllltir~th s~ c received by the receiver 900 at l~sl,ec~ e tirne offsets. In ^d~lition to dc~,n~ g the offsets coll~ ullding to the greatest eight energies, the co~ z~àlor 1016 also det~ es a set of local rna~ima of the total correlation energies and ~ n*fies the offsets associated with those m~im~ as described above with regard to FIG. 8. The set of total correlation e,~rg;es, the set of local m~im~, and the offsets ~cs~-;Ated with both sets are provided to the search result RAM 1018 where they are stored and subs~ue~ y used for controlling the 5 ~loces~ ed by the scaler 909 andlor the demodulator 911.
The above i~ldLi~c process e~cemplifies a l lcfcll~d non-cohel~"~t demot~ tion approach used to identify the offsets from which to process the received mnltir~th signals. However, the use of 10 a coherent tlemod~ ticln tpthni~lue during the sealc~ling process is e~ually applicable to the ~.~S~t iu~elllion. The col~r~
mo~ tiQn ~locess ~,lc~lably occurs as follows. The FHT block 1006 receives the I and Q Walsh chips in a ~ r similar to that descnbed above for the non-coherent demoA~ tion approach. The 15 F~lT block 1006 then provides the I and Q Walsh chips of the first Walsh symbol in the power control group to the adder/ subtractor 1014. T,he adder/~ul)~aelor 1014 passes these I and Q values to the energy RAM 1008 where they are stored. The PHT block 1006 ~en provides the I and Q Walsh chips of the sllbsP~llPnt Walsh syrnbol, or 20 symbols~ ep~pn~ling on the l..~ "l~J of mod~ tion symbol time intervals stored in the RAM 1001--to the adder/ subtractor 1014.
The adder/~ub~,dctor 1014 adds the ,~s~ec1;.~e I values coll~sl,ol,ding to all 64 in~ S of all the Walsh symbols stored in the energy RAM 1008 (e.g., Il [WS(0)] + Il [WS(l)] + Il [WS(2)] +
2 5 ...; I2 [WS(0)] + I2 [WS(l)] + I2 [WS(2)] + ...; etc.)~ In a similar m~nner, the adder/subtractor 1014 adds the respective Q values coll~,s~onding to all 64 inrlexes of all the Walsh symbols stored in the energy RAM 1008. The 64 sllmmed I values ( [ ~I ] ) and the 64 s ~ ed Q values ( [ ~:Q ] ) are then provided to the multiplier 1012.
The mul~plier 1012 squares each s ~.. e~ I value and each s-~ .ed Q value, and provides the squared m~ s ( [ ~:I ]2, [ ~Q ]2) to the adder/ subtractor 1014. The adder/subtractor 1014 adds the collesl,ollding [ ~:I ]2 and [ ~.Q ]2 values and sequentially provides the s..... ~tinnc ([ ~Ii ]2 + [ ~;Qi ~2) to the energy RAM
1008 where the ~.. .n~tion~ or Chcl~;ics, are stored until all 64 have been co~ .uled The e.~,gies are provided to ~e cv~ dtor 1016 for fullher ~locesC;..g in a ..~ r analogous to that described above 5 with regard to non-colle.~ demod~ ti~n- It should be noted that the t~rhni11~es ~esc~i~d l.c,~illabove for non-coherent and coherent demQ~lnl~tion can also be applied to the final fl~mocllll~tion ~h,lrwllled by the ~em~~ tor 911 of FIG. 9.
FIG. 11 ilhl~tr~tes an e~emplary logic flow diagrarn 1100 of steps e~e~ted by a receiver in acco~ ce with the present invention. The logic flow begins (1101) when the receiver stores (1103) inform~tir.n co.~ ;..Pd in mnltirl.~ modl-l~tion symbol time intervals. The ~ el thcn searchcs (1105) the stored infonnation 1 ~ to id~l~if~ a set of mllltip~th signals of a particular coded cu~ c~tion signal in onc or more search windows (i.e., at one or morc time offsets in each mo~ tir~n symbol time interval) by llete----;--;--g the total correlation energy in each search window as described above. In a ~,efe,l~d embo~lim~-nt, the set of mllltip~th 2 0 signals are those signals received at the offsets that provide the eight best total correlation .,.l.,rgics.
Upon searclli,lg the stored information and det~rmining the set of mnl*rzth signzl~ the receiver de~llll;lles (1107) whether the 2 5 m ll*path signals in the set need to be adjusted to account for characteristics of the comple~ RF ch~ -l through which the mnltirzth signals propzg~t~d prior to reception. Such characteristics inrl--~le phase rotation or all~ ....z~;Qn of the multipath signzlc' mo~ tiQn symbols due to fa(lin~ When the mnltirzth signals in the 3 0 set need to be adjusted, the receiver es~ tes (1109) a characteristic of the ~z..~-l based on an ~csoci~te~ signal metric of a mllltipath signal in the set. For e~ample, to zcco~lnt for a phase rotation of the modulation symbols during tr~n~m~ on through the RF C~ -P1, the I and Q components of an M-ary mo~hllztiQn symbol that provide the correlation energy for a particular time offsct might be used to Aete~ a desilcd phase in the I, Q plane at that time offset for the ~m~inin~ stored moA~ tinn symbols.
Upon estim~tin~ the ch~ractenstic of the rh~ el, the receiver adjusts (1111) one or more mnltip~th si~ls in the set based on the coll~s~ol,ding cl.~ l es~im~te. In the above e~ample, this adjusting might colllylise rotating the phase of a ~-~l,se~ n~ stored moAlll~tion symbol such that the phase coll~syGllds to the previously detulllli..ed 1 0 desired phase.
~ o..l;l.~.;.~g down the logic flow diagram 1100, the receiver weights (1113) each mllltir~th signal in the set based on the ~Csoci~teA signal metric. In a l,l~fcl,~,d ~m~ the weiEhtinEs 1~ are de~....i.~fd in y~opo~Lion to ~e con~l~ti~ energy co...~ for each mllhir~th signal and are applied to the m~nitllA~s of each of tihe rr~lll*r~th si~n~lc~ Upon we,gh1;-.~ each m~ll*p~th signal in the set, the rece*er ~emo~Alll~tes (1115) the set of wei~ted mllhirath signals by ~lefeldbly applying an FHT to each weighted mllhir~th 2 0 signal. The receiver then comhin~os (1117) the AemoAl~l~t~A. signals using known combining !~-c~ ues to leco~e~ the particular coded c~ .ic~tion signal and the logic flow ends (1119).
The yl~S~ invention encomp~sses a method and al~p&l~L~ls for 2 ~ identifying a particular coded c~ .ic~tion signal from a plurality of received coded co~ ication sign~ls. With this invention, ~e time l~uil~d to search and identify the best mllltir~tll signals of the par~icular coded co~ ic~tiQn signal to use for Ae-moA~ tion is si~nifir~ntly reA~re~ as co,..~t~d to the prior art searching 30 l~c~ ues. Thissearchtirneilll~;o~ clllresultsbeç~æthe ~ilLSt~l~ invention provides a means for acquilillg energies at multiple offsets over a power control group; ~hcl~as, ~e prior art app~aches only acquire a single energy (i.e., one offset) over the power control group. Thus, the ~l~,selll invention more efficiently ntili7e the data cont-qin~A~ in a power control group during its mnltipqth signal æarch as cQ~ ed to the data u~ili7Ation of the prior art æarching t~hni~ os ru,~,cr, due to its e~peAient s~chillg ycl~o ...qnr~, the l,.ese.,~ invention provides an improved 5 Eb/No at a particular bit error rate as ccS~ d to its prior art co~ rl .l,~LS since faster sear~l~i,lg results in reAueed opportunities for acquiring -q-dditir~-q-l noiæ in the received mllltipAth signals due tO
fading during the tot. l search tirne interval.
1 0 What is cl-q-imed is:
Claims (10)
1. In a receiver that receives a plurality of coded communication signals, a method for identifying a particular coded communication signal from a plurality of received coded communication signals, the method comprising the steps of:
a) storing information contained in the plurality of received coded communication signals during a plurality of modulation symbol time intervals to produce stored information; and b) searching the stored information to identify the particular coded communication signal.
a) storing information contained in the plurality of received coded communication signals during a plurality of modulation symbol time intervals to produce stored information; and b) searching the stored information to identify the particular coded communication signal.
2. The method of claim 1, wherein step (b) comprises the step of searching the stored information to identify a set of multipath signals of the particular coded communication signal, wherein each multipath signal in the set of multipath signals has an associated signal metric greater than an associated signal metric of any multipath signal of the particular coded communication signal not in the set of multipath signals.
3. The method of claim 2, further comprising the steps of:
c) weighting each multipath signal in the set of multipath signals based on the associated signal metric to produce a set of weighted multipath signals;
d) demodulating the set of weighted multipath signals to produce a set of demodulating multipath signals; and e) combining the set of demodulated multipath signals to recover the particular coded communication signal.
c) weighting each multipath signal in the set of multipath signals based on the associated signal metric to produce a set of weighted multipath signals;
d) demodulating the set of weighted multipath signals to produce a set of demodulating multipath signals; and e) combining the set of demodulated multipath signals to recover the particular coded communication signal.
4. The method of claim 2, wherein the particular coded communication signal propagates through a complex channel prior to reception by the receiver, the method further comprising the steps of:
c) estimating a characteristic of the complex channel based on the associated signal metric of a first multipath signal in the set of multipath signals to produce a channel estimate;
d) adjusting a second multipath signal in the set of multipath signals based on the channel estimate to produce an adjusted multipath signal; and e) demodulating the adjusted multipath signal.
c) estimating a characteristic of the complex channel based on the associated signal metric of a first multipath signal in the set of multipath signals to produce a channel estimate;
d) adjusting a second multipath signal in the set of multipath signals based on the channel estimate to produce an adjusted multipath signal; and e) demodulating the adjusted multipath signal.
5. The method of claim 1, wherein the step of searching comprises the steps of:
b1) performing a first search of the stored information in a first search window; and b2) performing a second search of the stored information in a second search window, the second search window being offset in time from the first search window.
b1) performing a first search of the stored information in a first search window; and b2) performing a second search of the stored information in a second search window, the second search window being offset in time from the first search window.
6. The method of claim 1, wherein each of the plurality of coded communication signals includes a plurality of orthogonal symbol sets, wherein at least two of the plurality of orthogonal symbol sets comprise a power control group, wherein step (a) comprises the step of storing information contained in a plurality of received orthogonal symbol sets to the produce stored information, and wherein step (b) comprises the step of searching the stored information contained in the power control group to identify the particular coded communication signal.
7. In a receiver that receives direct sequence code division multiple access (DS-CDMA) signals, each of the DS-CDMA signals including a plurality of Walsh symbols, at least two of the plurality of Walsh symbols comprising a power control group, a method for identifying a particular DS-CDMA signal from a plurality of received DS-CDMA signals, the method comprising the steps of:
a) storing information contained in the power control group to produce stored information;
b) searching the stored information to identify a set of multipath signals of the particular DS-CDMA signal, wherein each multipath signal in the set of multipath signals has an energy greater than an energy of any multipath signal of the particular DS-CDMA signal not in the set of multipath signals;
c) demodulating the set of multipath signals to produce a set of demodulated multipath signals; and d) combining the set of demodulated multipath signals to recover the particular DS-CDMA signal.
a) storing information contained in the power control group to produce stored information;
b) searching the stored information to identify a set of multipath signals of the particular DS-CDMA signal, wherein each multipath signal in the set of multipath signals has an energy greater than an energy of any multipath signal of the particular DS-CDMA signal not in the set of multipath signals;
c) demodulating the set of multipath signals to produce a set of demodulated multipath signals; and d) combining the set of demodulated multipath signals to recover the particular DS-CDMA signal.
8. A receiver for receiving a plurality of coded communication signals, the receiver comprising:
memory means for storing information contained in a plurality of received coded communication signals during a plurality of modulation symbol time intervals to produce stored information;
and processing means, operably coupled to the memory means, for searching the stored information to identify a particular coded communication signal.
memory means for storing information contained in a plurality of received coded communication signals during a plurality of modulation symbol time intervals to produce stored information;
and processing means, operably coupled to the memory means, for searching the stored information to identify a particular coded communication signal.
9. The receiver of claim 8, wherein the processing means comprises means for searching the stored information to identify a set of multipath signals of the particular coded communication signal, wherein each multipath signal in the set of multipath signals has an associated signal metric greater than an associated signal metric of any multipath signal of the particular coded communication signal not in the set of multipath signals, and wherein the receiver further comprises:
scaling means, operably coupled to the processing means, for weighting each multipath signal in the set of multipath signals based on the associated signal metric to produce a set of weighted multipath signals.
demodulating means, operably coupled to the scaling means, for demodulating the set of weighted multipath signals to produce a set of demodulated signals; and combining means, operably coupled to the demodulating means, for combining the set of demodulated signals to recover the particular coded communication signal.
scaling means, operably coupled to the processing means, for weighting each multipath signal in the set of multipath signals based on the associated signal metric to produce a set of weighted multipath signals.
demodulating means, operably coupled to the scaling means, for demodulating the set of weighted multipath signals to produce a set of demodulated signals; and combining means, operably coupled to the demodulating means, for combining the set of demodulated signals to recover the particular coded communication signal.
10. A receiver for receiving direct sequence code division multiple access (DS-CDMA) signals, each of the DS-CDMA signals including a plurality of Walsh symbols, at least two of the plurality of Walsh symbols comprising a power control group, the receiver comprising:
a memory device for storing information contained in the power control group to produce stored information;
a processor, operably coupled to the memory device, for searching the stored information to identify a set of multipath signals of a particular DS-CDMA signal, wherein each multipath signal in the set of multipath signals has an associated signal metric greater than an associated signal metric of any multipath signal of the particular DS-CDMA signal not in the set of multipath signals;
a demodulator, operably coupled to the processor, for demodulating the set of multipath signals to produce demodulated multipath signals; and a combiner, operably coupled to the demodulator, for combining the demodulated multipath signals to recover the particular DS-CDMA signal.
a memory device for storing information contained in the power control group to produce stored information;
a processor, operably coupled to the memory device, for searching the stored information to identify a set of multipath signals of a particular DS-CDMA signal, wherein each multipath signal in the set of multipath signals has an associated signal metric greater than an associated signal metric of any multipath signal of the particular DS-CDMA signal not in the set of multipath signals;
a demodulator, operably coupled to the processor, for demodulating the set of multipath signals to produce demodulated multipath signals; and a combiner, operably coupled to the demodulator, for combining the demodulated multipath signals to recover the particular DS-CDMA signal.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/269,403 US5530716A (en) | 1994-06-30 | 1994-06-30 | Method and apparatus for identifying a coded communication signal |
| US08/269,403 | 1994-06-30 |
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| CA2167709A1 true CA2167709A1 (en) | 1996-01-11 |
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| CA002167709A Abandoned CA2167709A1 (en) | 1994-06-30 | 1995-05-01 | A method and apparatus for identifying a coded communication signal |
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| EP (1) | EP0720794B1 (en) |
| JP (1) | JP3786422B2 (en) |
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| CN (1) | CN1087527C (en) |
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| CA (1) | CA2167709A1 (en) |
| FI (1) | FI119614B (en) |
| WO (1) | WO1996001012A1 (en) |
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- 1994-06-30 US US08/269,403 patent/US5530716A/en not_active Expired - Lifetime
-
1995
- 1995-05-01 BR BR9506022A patent/BR9506022A/en not_active IP Right Cessation
- 1995-05-01 EP EP95918341A patent/EP0720794B1/en not_active Expired - Lifetime
- 1995-05-01 CA CA002167709A patent/CA2167709A1/en not_active Abandoned
- 1995-05-01 KR KR1019960701004A patent/KR0173414B1/en not_active IP Right Cessation
- 1995-05-01 CN CN95190592A patent/CN1087527C/en not_active Expired - Lifetime
- 1995-05-01 JP JP50312096A patent/JP3786422B2/en not_active Expired - Lifetime
- 1995-05-01 WO PCT/US1995/005373 patent/WO1996001012A1/en active IP Right Grant
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1996
- 1996-02-15 FI FI960691A patent/FI119614B/en not_active IP Right Cessation
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| CN1087527C (en) | 2002-07-10 |
| JPH09502593A (en) | 1997-03-11 |
| EP0720794B1 (en) | 2007-08-15 |
| EP0720794A4 (en) | 2000-03-01 |
| US5530716A (en) | 1996-06-25 |
| EP0720794A1 (en) | 1996-07-10 |
| JP3786422B2 (en) | 2006-06-14 |
| FI960691A0 (en) | 1996-02-15 |
| CN1130003A (en) | 1996-08-28 |
| FI119614B (en) | 2009-01-15 |
| KR0173414B1 (en) | 1999-04-01 |
| BR9506022A (en) | 1997-10-14 |
| WO1996001012A1 (en) | 1996-01-11 |
| FI960691A (en) | 1996-02-15 |
| KR960705415A (en) | 1996-10-09 |
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