US 6,792,031 B1
`a2) United States Patent
`(10) Patent No.:
`
`(45) Date of Patent: Sep. 14, 2004
`Sriram etal.
`
`US006792031B1
`
`(54) METHOD FOR MAINTAINING TIMING IN A
`CDMA RAKE RECEIVER
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`(75)
`
`Inventors: Sundararajan Sriram, Dallas, TX
`(US); Yuan Kang Lee, Richardson, TX
`(US); Katherine G. Brown, Coppell,
`ag Zhenguo Gu, Plano, TX
`(US)
`(73) Assignee: Texas Instruments Incorporated,
`Dallas, TX (US)
`
`(*) Notice:
`
`Subject to any disclaimer, the term ofthis
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 618 days.
`
`(21) Appl. No.: 09/691,576
`
`Oct. 18, 2000
`Filed:
`(22)
`(51) UntC17 cceccccssscsssesseeees HO4B 1/69; HO4B 1/707;
`HO4B 1/713
`32) US.CI
`375/147. 370/320: 370/335:
`3"0/342: 3.8/78
`(52)
`US.
`Che eee (147;
`?
`(58) Field of Search ....... 375/147; 370/320;
`341/50; 708/190; 714/732
`
`8/2001 Brown et al. .........0. 375/140
`6,282,230 B1 *
`
`5/2003 Medlocketal. ...
`.... 341/50
`6,567,017 B2 *
`6,639,907 B2 * 10/2003 Neufeld et al.
`.....00..... 370/342
`* cited by examiner
`Primary Examiner—Stephen Chin
`.
`Assistant Examiner—Harry Vartanian
`(74) Attorney, Agent, or Firm—Ronald O. Neerings; Wade
`James Brady, III; Frederick J. Telecky, Jr.
`(57)
`ABSTRACT
`
`A system and method for maintaining timing in a CDMA
`rake receiver has a global chip counter that counts CDMA
`signal chips as they arrive at the CDMA rake receiver. A
`local pseudo-noise (PN) sequence replica of the incoming
`CDMAsignal is generated and used to perform a sliding
`window correlation of the locally generated PN sequence
`T@Plica with the incoming signal to correlate the CDMA
`signal timing relative to stored CDMAsignal chip counts.
`The PN sequence timing is maintained relative to GCC,
`which avoids having to keep track of absolute time within
`
`each Rakefinger.
`
`23 Claims, 5 Drawing Sheets
`
`Rxsource 0
`
`Rxsource 1
`
`20°
`
`]o2
`
`100 .
`
`GCC
`
`Input Buffers
`0
`1
`
`
`
`ENEreas
`Correlator
`eae|CoProcessor
`
`Data Path
`
`Controller
`
`Task Buffer
`
`
`rue 48|Finger PSC [pPé|sse FOL a Configuration Configuration
`
`
`
`
`
`Symbol|Search neut put bat TT Tables Tables
`
`
`
`4 4.
`QL
`Buffer
`Buffer yy
`do, 2
`aiBus
`
`
`
`Finger Symbol Buffer
`Extemal Bus
`
`Interupt
`
`21,
`
`EXHIBIT 1016
`
`1
`
`EXHIBIT 1016
`
`

`

`U.S. Patent
`
`Sep. 14, 2004
`
`Sheet 1 of 5
`
`US 6,792,031 B1
`
`co)
`
` Global Chip Counter
`
`current contents of input buffer
`
`Figure 1. Global chip counter
`
`Global Chip Counter
`
`PF long code with an L chip periodforfinger “i”
`
`offset i
`
`“spr_factor” chips symbol boundary
`
`300
`
`302.
`
`Figure 3
`
`2
`
`

`

`U.S. Patent
`
`Sep. 14, 2004
`
`Sheet 2 of 5
`
`US 6,792,031 B1
`
`OOt
`
`999
`
`
`
`saqe]
`
`uogesnByuoz)Tey
`
`veeZt,|Utsit||Teddy
`JOssaoaigo’)812VO}EIBUSD
`joyeaLN05USIEM9Nd
`.*00|ZOl
`srwayu|sngjewa)x3
`
`Ne
`
`sngvant
`
`}SUNOSxyOQsanosxy
`Zandy
`L0sayngyndu|
`yedeeq
`youeas|joquAS
`Jayng"]seyng
`
`OSd_|Jabury
`
`
`JayngjoquuAsyabury
`
`i
`
`3
`
`
`
`
`

`

`U.S. Patent
`
`Sep. 14, 2004
`
`Sheet 3 of 5
`
`US 6,792,031 B1
`
`
`Controller ——___ids
`
`4OL
`
`CCP Data Path
`
`~
`
`ra
`
`440
`
`
`
`\
`
`
`Finger
`
`
`Input
`Symbol
`FSB Ext I/F
`
`
`Data
`Buffer
`
`(from Input
`
`buffers)
`
`+
`DPE &
`EOL
`Buffer
`
`
`
`RHEABus
`
`i{
`i
`
`
`Noncoherent
`Scratch
`
`Memory
`hwy 4h
`
`Figure 4 CCP Data Path
`
`4
`
`

`

`U.S. Patent
`
`Sep. 14, 2004
`
`Sheet 4 of 5
`
`US 6,792,031 B1
`
`
`
`Cambined
`
`Channe!
`
`OPE/Search
`
`Instructions
`
`
`Symbol
`Estimation
`Sufter
`
`
`
`
`Buffer
`
`Buffer
`Coefficients
`
`1&Q Samples
`tom A/O be :
`
`
`
`
`
`~< CRP-ASIC
`
`506
`
`5
`
`

`

`U.S. Patent
`
`Sep. 14, 2004
`
`Sheet 5 of 5
`
`US 6,792,031 B1
`
`CDMA
`SIGNAL
`
`600
`
`OL
`v
`Generate Local
`6
`Count chips
`
`
`
`
`
`Modulo The
`PN code
`
`
`
`Period of spreadi d
`(CDMA Signal Replive
`at GCC offset
`
`PN code. at
`input buffer
`
`
`
`6oF
`
`
`Conelatt
`Vary PN Code
`
`
`Received CDMA
`Ofkset
`Signal w/PN Code.
`Corvespondiisg fo
`Search W'adow 9/22.
`
`
`
`
`
`
`
`
`
`608
`
`612
`
`
` Assign ach
`distioed offset
`
`joa Finger
`
`
`
`Multipath
`
`614
`Determire
`
`Absolute Time
`for tach
`Moltipath
`Compone
`
`
`
`616
`
`Figure. j
`
`6
`
`

`

`US 6,792,031 B1
`
`1
`METHOD FOR MAINTAINING TIMING IN A
`CDMA RAKE RECEIVER
`
`RELATED PATENT APPLICATIONS
`
`This application is related to U.S. patent application Ser.
`No. 09/607,410 entitled Correlator Co-Processor For
`CDMARAKE Receiver Operations, filed on Jun. 9, 2000,
`by Katherine G. Brownetal.
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`This invention relates generally to data communication
`systems and methods, and moreparticularly to a method for
`maintaining timing in a CDMArakereceiver.
`2. Description of the Prior Art
`Whenusing a data communication system based on bursts
`(packets),
`the generic format of a frame consists of a
`preamble at the beginning of each burst. Some communi-
`cation protocols additionally include data and end-of-frame.
`The preamble is used to signify (recognize) the start of
`transmission. All nodes on a network traditionally use the
`same preamble and the same end-of-frame. Each node,
`therefore, is required to decode at least the beginning of the
`data to identify if this message is addressed to itself.
`Decoding efforts importantly require a real-time computa-
`tional complexity. Further, traditional data communication
`processes are made even more complex and time consuming
`dueto the necessity to utilize collision detection and resolve
`techniques.
`in code division multiple access (CDMA)
`Further,
`systems, as well as others, there are overlaying coded data
`streams, each having its own frame timing. In view of the
`foregoing,it is therefore desirable to provide a technique to
`maintain timing in a CDMA rakereceiver.
`SUMMARYOF THE INVENTION
`
`The conventional method for maintaining timing in a
`CDMAreceiveris to let each Rake finger maintain absolute
`time, and count out chip, slot, and frame boundaries. Each
`component has its own free running counter that maintains
`path offset information. In this situation, the control device
`(usually a microcontroller or programmable DSP) then must
`explicitly load the path timing information obtained from the
`searcher hardware into each Rake finger. Since all timing is
`absolute, the microcontroller software must determine the
`values of various hardware counters that maintain finger
`timing.
`The present invention on the other hand maintains a single
`counter (GCC) that tracks the chip samples as they come
`into the receiver; and all timing in the system is specified in
`terms of timing offsets from this global(or central) counter.
`This avoids the problem of software having to determine the
`hardware state of various counters that may be running at
`several Gigahertz speeds. All finger timings are specified in
`termsofoffsets, and the hardware fingers use the value of the
`GCCcounter to infer their absolute time. This eases system
`design, and allows a very flexible implementation of the
`receiver(e.g. the numberoffingers can beeasily scaled,the
`search window can be increase, etc. with minimal system
`level changes).
`One embodiment of the present invention is more spe-
`cifically directed to a system and method for maintaining
`timing ina CDMA rakereceiver for supporting high bit rate
`data communication systems such as the correlator
`co-processor (CCP) disclosed in U.S. patent application Ser.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`No. 09/607,410 entitled Correlator Co-Processor For
`CDMA RAKE Receiver Operations, docket no. TI-30639,
`filed on Jun. 9, 2000, by Katherine G. Brownet al., incor-
`porated by reference herein. The CCP is capable of receiving
`multiple in-phase (I) and quadrature (Q) signal samples from
`multiple sources to accommodate antenna diversity wherein
`I and Q samples may be 6-bits or more. The I and Q samples
`further represent multiple overlaying channels, each of
`which have several multi-path elements, the aggregate data
`rate being possibly greater than the chip rate. According to
`one embodiment, a hardware counter counts the incoming
`CDMAsignal samples (or “chips”). The counter is called a
`“Global Chip Counter” or GCC. The GCC counts modulo
`the period of the pseudo-noise (PN) sequence used to spread
`the CDMAsignal.It counts the samples of the CDMA signal
`(“chips”) as they arrive at the receiver and are written into
`an input buffer such as described in US. patent application
`Ser. No. 09/648,184, entitled Triple Data Buffer System for
`High Data Rate Communication Systems, docket no.
`TI-30696, filed on Aug. 25, 2000, by Katherine G. Brown,
`incorporated by reference herein. All timing in the CDMA
`receiver is then specified relative to the GCC. The searcher
`provides path timing,also relative to the GCC. These path
`timings may then be transferred to RAKE fingers. In the
`event that the finger allocation is performed in software, the
`software process does not need to know the precise timing
`in the hardware. Since the path timingsare specified relative
`to GCC, the hardware can compute the precise timing by
`addingthe relative timing value to the current value of GCC.
`According to one embodiment, a method of maintaining
`timing in a CDMA rakereceiver comprises the steps of:
`a) providing a GCC counter;
`b) counting via the GCC counter, CDMAsignal chips as
`they arrive at a CDMArake receiver;
`c) generating a local pseudo-noise sequencereplica ofthe
`incoming CDMAsignal;
`d) performing a sliding window correlation ofthe locally
`generated PN sequencereplica with the incoming sig-
`nal to correlate the CDMAsignal timing relative to
`stored CDMAsignal sample count values; and
`e) specifying finger timing offsets relative to the stored
`CDMAsignal sample count values to allocate RAKE
`fingers to the strongest multipath components.
`According to yet another embodiment, a system for
`maintaining timing in a CDMArake receiver comprises:
`a correlator co-processor including a pseudo-noise (PN)
`generator for generating a PN sequence replica of an
`incoming CDMAsignal; a Walsh code generator for
`generating Walsh codes; at
`least one chip counter
`(GCC) configured to count CDMAsignal samples; at
`least one data input buffer configured to receive and
`store CDMAchips; a data path configured to receive
`and process samples of the PN sequence replica
`samples of the Walsh codes and CDMAchip samples;
`at least one task buffer configured to store a list of
`programmably executable tasks; an interrupt generator;
`at least one configuration table buffer in communica-
`tion with the at least one task buffer and configured to
`store a plurality of configuration tables that specify how
`each task within the list of programmably executable
`tasks is implemented; at least one configuration table
`buffer having at least one input in communication with
`an external system interface bus; at least one output
`data buffer; and a controller in communication with the
`data path; and
`an algorithmic software, wherein the controller in com-
`munication with the data path, the at least one task
`
`7
`
`

`

`US 6,792,031 B1
`
`3
`buffer, the at least one configuration table, the interrupt
`generator,
`the PN code generator,
`the Walsh code
`generator, the GCC and the at least one output buffer
`and directed by the algorithmic software is operational
`to correlate a locally generated PN sequence replica
`with an incoming CDMAsignal such that CDMA
`signal timingis correlated relative to GCC chips counts
`and further operational to specify finger offsets relative
`to GCC chip counts such that RAKE fingers are allo-
`cated to the strongest multipath components.
`In one aspect of the invention, a Global Chip Counteris
`implemented to accommodate CDMAreceiver timing func-
`tions.
`In still another aspect of the invention, a method is
`implemented to more easily maintain timing in a COMA
`rake receiver.
`
`In yet another aspect of the invention, a Global Chip
`Counter is implemented that allows a software process to
`allocate RAKE fingers to the strongest multipath compo-
`nents simply by specifying finger offset relative to GCC,
`without making an explicit reference to the current value of
`the time-base maintained in hardware.
`Still another aspect of the invention is associated with a
`method that allows determination of CDMAsignal param-
`eters such as current slot number within a frame, and
`occurrenceof slot and frame boundaries through knowledge
`of the current value within a Global Chip Counter and
`knowledge of the finger timing offset.
`As used herein, “algorithmic software” means an algo-
`rithmic program used to direct the processing of data by a
`computer or data processing device; wherein data processing
`device refers to a CPU, DSP, microprocessor, micro-
`controller, or other like device and an interface system in
`which the interface system provides access to the data
`processing device such that data can be entered and pro-
`cessed by the data processing device.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`Other aspects and features of the present invention and
`many of the attendant advantages of the present invention
`will be readily appreciated as the same become better
`understood by reference to the following detailed descrip-
`tion when considered in connection with the accompanying
`drawings in which like reference numerals designate like
`parts throughout the figures thereof and wherein:
`FIG. 1 is a diagram illustrating a Global Chip Counter
`(GCC),
`FIG. 2 is a diagram illustrating timing offset (“offset i”) of
`“finger 1”, that tracks a particular multipath component;
`FIG. 3 is a top level block diagram illustrating a correlator
`co-processor (CCP) system in communication with a GCC;
`FIG. 4 is a simplified block diagram illustrating a CCP
`Data Path structure;
`FIG. 5 illustrates one implementation of a CDMA
`receiver comprising the CCP shown in FIG. 3, a digital
`signal processor (DSP), and a maximal-ratio combining
`(MRC) ASIC and that is suitable to implement the present
`method; and
`FIG. 6 is a flow diagram illustrating a method according
`to one embodiment of the present invention.
`While the above-identified drawing figure sets forth a
`particular embodiment, other embodiments of the present
`invention are also contemplated, as noted in the discussion.
`In all cases, this disclosure presents illustrated embodiments
`of the present invention by way of representation and not
`limitation. Numerous other modifications and embodiments
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`can be devised by those skilled in the art which fall within
`the scope and spirit of the principles of this invention.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`FIG. 1 is a diagram illustrating a Global Chip Counter
`(GCC) buffer 10 that can be used to maintain timing in a
`CDMArakereceiver. As stated herein before, a CDMA rake
`receiver keeps track of timing between various multipath
`components, wherein the multipath timing is determined
`using a path search or delay profile estimation function
`familiar to those skilled in the art of CDMAsignals and
`communication techniques. There are several well known
`search techniques (generally hardware based) that provide
`the multipath profile information. Such hardware provides
`multipath information to a data processing device such as a
`DSP, that in turn determines which paths to despread and the
`path offsets from the delay profile information provided by
`the searcher hardware. The strongest multipath components
`are assigned to RAKE “fingers” that perform a despreading
`operation on each multipath component.
`In order to maintain timing between the various CDMA
`rake receiver components, a Global Chip Counter (GCC)
`100 such as depicted in FIG. 2 is introduced. FIG. 2 is a
`top-level block diagram illustrating a correlator
`co-processor (CCP) system 200 in communication with a
`GCC 100. The GCC 100 counts modulo the period of the
`pseudo-noise (PN) sequence used to spread the CDMA
`signal (this period is “L” in FIG. 1). Specifically the GCC
`100 counts the samples of the CDMAsignal (“chips”) as
`they arrive at the receiver and are written into an input buffer
`102, discussed above. All timing in the receiver is specified
`relative to the GCC 100. The searcher, discussed above,
`provides path timing, also relative to the GCC 100. These
`path timings can then be transferred to RAKE fingers. As
`also stated herein before, in the event that the finger allo-
`cation is performed in software, the software process does
`not need to know the precise timing in the hardware. The
`path timings are specified relative to the GCC 100 count
`value; and the hardware can compute the precise timing by
`addingthe relative timing value to the current count value of
`GCC 100. All
`timing in the coprocessor (CCP) 200 is
`relative to the GCC 100 count value, including the searcher
`and RAKE fingeroffsets.
`FIG. 3 is a diagram illustrating the timing offset (“offset
`i” 300) of “finger i”,
`that
`tracks a particular multipath
`component. The timing offsets (e.g. offset i 300) are deter-
`mined by meansof a search function that performsa sliding
`window correlation of a locally generated PN sequence
`replica with the incoming signal. The searcher reports its
`timingsrelative to the GCC 100 count value as well; and this
`allows a software process to allocate RAKE fingers to the
`strongest multipath components simply by specifying finger
`offsets relative to the GCC 100 count value without making
`an explicit reference to the current value of the time-base
`maintained in hardware.
`
`Using the stored GCC 100 count value and the offset
`value (e.g. offset i 300), it can then be determinedif there is
`a symbol boundary for “finger i” in the input buffer 102 at
`any given time, and if so, to determinethetree partitions. If
`each symbol spans spreadingfactor chips 302, then the
`condition for existence of a symbol boundary can be defined
`as:
`
`Symbol boundary present if [GCC-offset(#)] modulo spreading_
`factor<buff_size
`(4)
`
`where buff_size is the size of the input buffer 102.
`
`8
`
`

`

`US 6,792,031 B1
`
`5
`ACDMAsignalis typically divided into frames and slots
`as stated herein before. The present GCC-based timing
`allows the determination of parameters such as currentslot
`number within a frame, and occurrence of slot and frame
`boundaries. Such parameters can be determined,
`for
`example, through knowledge of the current count value of
`the GCC 300 and the knowledge of the finger timing offset
`(offset(i)); simple arithmetic manipulations similar to Equa-
`tion (1), using the current GCC 300 count value and offset(i)
`yield the desired information.
`FIG. 4 is a simplified block diagram illustrating a CCP
`200 Data Path structure 400 according to one embodiment of
`the present invention, and is described herein below with
`reference also to FIG. 2 in order to further exemplify a
`system according to one embodiment that is suitable to
`implement the present method for maintaining timing in a
`CDMArake receiver. The CCP 200 accumulates bits and
`
`writes despread symbols to memoryatdifferent stages of the
`Data Path 400. The input data 402 (from the input buffers
`102) is obtained via an A/D converter (not shown) of some
`number(typically 5-6 bits). After passing through Adder
`Trees 404, there are 17 data bits. At this point, somebits are
`discarded. Before writing symbols to the Finger Symbol
`Buffer 406, 9 MSB’s are discarded, with saturation, for
`symbolfinger=4; or 1 MSBis discarded, with saturation, for
`other symbolfingers. Regarding the symbols passed into the
`remainder of the Data Path 400 (e.g. DPE & EOL Buffer
`408), 4 MSB’s and 2 LSB’s are discarded, with saturation.
`Following coherent accumulation 410, there are 22 bits. Of
`these 22 bits, 18 bits are kept starting from (13+max(5,
`log2(Ns)))” LSB, wherein Ns is the number of symbols of
`coherent accumulation. Following non-coherent accumula-
`tion 412, there are 32 bits. Of these 32 bits, 24 bits are kept
`starting from (13+max(5, log2(Ny-<))) LSB, wherein Nyg is
`the number of non-coherent accumulations.
`
`The PSC Search Buffer 414 serves two purposes. First,it
`stores running energy values while the PSC search task is
`active. In this regard, it is used as accumulator memory by
`the CCP 200. Second, when the PSC searchtask is finished,
`it stores the final energy values, which can then be read by
`the host processor, i.e. DSP. One energy value per %-chip
`offset is returned, thereby resulting in a total of 5120 energy
`values for a time slot having 2560 chips. According to one
`embodiment, the PSC search task requires a post-processor
`(not shown), to acquire the 5120 energy values; where the
`PSC Search Buffer 414 is dedicated for intermediate first
`stage values which would be read by the aforesaid post-
`processor. While the PSC search task is active, the PSC
`Search Buffer 414 is accessible only by the CCP Data Path
`400. When the PSC search task is inactive, the PSC Search
`Buffer 414 is accessible only via DSP Bus 416(can be either
`RHEAor External Memory Interface(EMIF) communica-
`tion bus). An arbitrator 418 handles accessrights. Further, an
`interrupt may be generated upon completion of a PSC task.
`The DPE & EOL Buffer(s) 408 and LCI Buffer 202 store
`DPE and LCIsearch results respectively. They are directly
`readable via the DSP Bus 416 atall times. The DPE Buffer
`204 and LCI Buffer 202 (depicted in FIG. 2) are single-
`buffered, and new results over-write old ones. When new
`results are ready, they may be read on the DSP Bus 416
`directly by the host processor or by Controller 206. Task-
`based interrupts can be generated when new results are
`ready. When a DPEtaskfinishes, for example, an interrupt
`may be generated.
`The EOL Buffer 208 stores finger EOL measurement
`results. It is directly readable via the DSP Bus 416 atall
`times. The EOL Buffer 208 is also single-buffered, and as
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`6
`with the DPE Buffer 204, new result over-write old ones.
`Whennewresults are ready, they may be read on the DSP
`Bus 416 directly the host processor or by Controller 206.
`The finger task can issue various slot-based interrupt events
`that can be used to signal the availability of new EOL data.
`The Finger Symbol Buffer 406 stores complex I and Q
`“symbols” that result from finger tasks. All symbols such as
`pilot, TPC, data and the like, are stored here after they are
`received and processed by the CCP Data Path 400. The
`Finger Symbol Buffer 406 is implemented as a multi-slot
`circular buffer for each Walsh channel. The Finger Symbol
`Buffer 406 serves as intermediate storage for downstream
`symbol-rate processing. The size of the Finger Symbol
`Buffer 406 is preferably a compromise between area and the
`rate at which data must be moved to where downstream
`processing takes place. The Finger Symbol Buffer 406 is
`also accessible on a FSB External Bus 420 that may be used
`when downstream processing and/or storage take place
`outside of the host processor (e.g. DSP system).
`Regarding the PN Generator 422 and Walsh Code Gen-
`erator 424, a CCP 200 task specifies a PN code (“Gold
`code”) and a Walsh code to be generated as well as a code
`offset. The PN/Walsh Code generators 422, 424 then gen-
`erate a block of the specified PN/Walsh codesstarting from
`the specified code offset. Gold code generation is centralized
`and can be produced for any correlation cycle. No LFSR
`state nor “mask” need to be specified, as the code number
`and offset from a global chip counter (GCC 100)
`is
`available, as described herein above. Both “block” and
`“serial” Gold code generation methods are preferably
`employed to minimize power dissipation. The 16x16
`WCDMAPSC and SSC Buffers 414, 210 have program-
`mable parameters to be specified for use in association with
`PSC and SSC search operations.
`With continued reference to FIG. 2, the Controller 206 is
`responsible for actually implementing each of the CCP 200
`tasks, and generating appropriate control signals for the Data
`Path 400. Diverse correlations can importantly be imple-
`mented simply by varying the control sequence. Down-
`stream control and Data Path 400 pipeline stages are most
`preferably gated off to conserve power when notasks are
`running.
`Local timing reference for the CCP 200 is maintained via
`a global chip counter (GCC 100) discussed herein before,
`that counts the incoming chip samples as they are written
`into the input buffer(s) 102. The GCC 100 counts modulo the
`length of a WCDMAlong code. All timing in the CCP 200
`is relative to the GCC 100 count value, including offsets
`used in rake receiver operations.
`The CCP 200 uses a numberof configuration tables 212
`to specify how it executes each ofits tasks. Sometables are
`used globally, while others are associated with certain tasks.
`One configuration table, for example, contains the position
`and size of the pilot symbols for each spreading factor.
`Another configuration table contains the Walsh codes asso-
`ciated with a particular finger task. Configurations are pro-
`vided directly by the host processor.
`Interrupt Generator 214 generates three types of interrupts
`including task-based interrupts, system interrupts and error
`interrupts. Each CCP 200 task can generate at least one
`interrupt. When a DPEtask finishes, for example, it may
`generate an interrupt. Each finger task can generate a num-
`ber of interrupts, for example, to indicate the end of a radio
`slot or the reception of a transmit-power-control (TPC)
`symbol. Task-based interrupts are mainly used by the host
`processor for data retrieval, but may be for other software/
`hardware synchronization purposes. Task-based interrupts
`
`9
`
`

`

`US 6,792,031 B1
`
`8
`7
`ence of signal multipaths. Offsets relative to the GCC
`place status information in one of four interrupt FIFO
`counter 100 are then associated with each signal multipath
`registers. Each interrupt FIFO register is tied to one of the
`as shown in block 610. Each multipath is assigned to a
`interrupt
`lines 216 coming from the CCP 200. System
`distinct finger as shown in block 612 in which the Rake can
`interrupts indicate global CCP 200 events. A task-based
`determine absolute time from the relative offset values as
`interrupt, for example, signals the host processor that task
`shown in block 614. Since the offsets are with respect to
`updates are completed. An error interrupt is generated when-
`ever an error condition is detected.
`GCC 100, the agent that sets up the rake (e.g., DSP) does not
`need to know the absolute hardware time, or even the GCC
`The Task Buffer 218 containsalist of tasks that the CCP
`count value.
`It simply specifies the offsets to the Rake
`200 executes. The Task Buffer 218 is read directly by the
`receiver; since the Rake has the GCC counter 100 value
`CCP 200 in order to determine the CCP’s current tasks. The
`available to it, the Rake can determine absolute time from
`the relative offset values (depicted in block 614). Having
`obtained the aforesaid timing information, the Rake receiver
`can then despread the CDMA multipath signal as shown in
`block 616.
`
`10
`
`15
`
`Task Buffer 218 is a ping/pong buffer with an individual
`control for the ping/pong status of each entry in the Task
`Buffer 218. Swapping from ping to pong or vice-versa
`occurs on a task-update boundary. A task-update interrupt
`tells the host processor whenthe transfer completes, and that
`the updated status bits are available for each task. This
`mechanism allows a synchronization between the host pro-
`cessor and the CCP 200 which prevents incomplete tasks
`being read by the CCP 200.
`FIG. 5 illustrates one implementation of a CDMA
`receiver 500 comprising the CCP 200 shown in FIG. 2, a
`digital signal processor (DSP) 502, and a maximal-ratio
`combining (MRC) ASIC 504 and that is suitable to imple-
`ment the present method. The MRC function can alterna-
`tively be implemented in software. The CCP 200 is respon-
`sible for 1) performing the de-spreading necessary to
`provide data symbols perfinger to the entity (e.g. DSP 502,
`ASIC 504) in charge of the MRCprocessing, 2) performing
`EOL energy measurements of a delay locked loop, 3)
`performing on-chip and %-chip correlations and energy
`measurements for DPE and search purposes, and 4) provid-
`ing raw pilot symbols per finger to the DSP 502. The DSP
`502 uses the computed raw pilot symbols to perform the
`channel estimation of eachfinger. Coefficients of the channel
`estimation are then sent to the entity in charge of the MRC
`processing (e.g. ASIC 504). Using those computed
`coefficients, the MRC ASIC 504 multiplies de-spread sym-
`bols with the channel estimation coefficients and then sums
`the symbols coming from variousfingers (paths) together to
`provide combined symbols in the Combined Symbol Buffer
`506.
`FIG. 6 is a flow diagram 600 illustrating a method for
`maintaining timing in a CDMArakereceiver according to
`one embodiment of the present invention and that can be
`implemented in a CDMArake receiver that employs the
`CCP 200 depicted in FIG. 2. The method begins by first
`counting chips modulo the period of the received CDMA
`signal spreading PN code as indicated at block 602. The
`received CDMAsignal is received into one or more data
`buffers 102 as described herein before in association with
`
`FIG. 2. The aforesaid chips are counted modulo the period
`of the received CDMAsignal spreading PN codevia a local
`GCCcounter 100, also described herein before in associa-
`tion with FIG. 2. A local PN code, being a CDMAsignal
`replica, is generated at the CDMArakereceiver via a PN
`Generator 422 discussed herein above in association with
`
`FIG. 4. The local PN code is generated having an offset
`determined by the GCC counter 100 as shownin block 604,
`and is subsequently correlated with the incoming CDMA
`chips as shown in block 606,
`to determine whether the
`incoming CDMAsignalis generatedat an offset equalto that
`established by the GCC counter 100. The PN offset associ-
`ated with the local PN codeis also varied in accordance with
`the search windowsize (offset not equal to GCCoffset) as
`shown in block 608 and then correlated as shown in block
`606 to determine peaks in the resulting correlation values
`obtained throughout the search window showing the pres-
`
`In view of the above, it can be seen the present invention
`presents a significant advancementin the art of CDMAand
`WCDMAinformation processing. A system and method
`have been described for maintaining timing in a CDMA rake
`receiver. Further, this invention has been described in con-
`siderable detail in order to provide those skilled in the data
`communication art with the information needed to apply the
`novel principles and to construct and use such specialized
`components as are required.
`In view of the foregoing
`descriptions, it should further be apparent that the present
`invention represents a significant departure from the priorart
`in construction and operation. However, while particular
`embodiments of the present invention have been described
`herein in detail, it is to be understood that variousalterations,
`modifications and substitutions can be made therein without
`departing in any way from the spirit and scopeofthe present
`invention, as defined in the claims which follow.
`Whatis claimedis:
`
`20
`
`25
`
`30
`
`35
`
`1. A method of maintaining timing in a Code Division
`Multiple Access(CDMA)rake receiver comprising the steps
`of:
`
`providing a CDMArake receiver global chip counter
`(GCC) that counts modulo the period of a spreading PN
`code;
`counting via the GCC counter CDMAsignalchips as they
`arrive at a CDMArakereceiver;
`generating a local CDMArake receiver pseudo-noise
`(PN) sequence replica of an incoming CDMAsignal;
`correlating received CDMAsignaltimingrelative to GCC
`counter CDMA chip counts via correlation of the
`locally generated PN sequence replica with the incom-
`ing CDMAsignal; and
`allocating RAKE fingers to the strongest multipath com-
`ponents via specifying finger timing offsets relative to
`GCC counter CDMAchip counts.
`2. The method according to claim 1 wherein the step of
`correlating received CDMAsignal timing relative to GCC
`counter CDMAchip counts comprises performing a sliding
`window correlation of the locally generated PN sequence
`replica with the incoming CDMAsignal.
`3. The method according to claim 1 wherein the step of
`generating a local CDMArake receiver pseudo-noise (PN)
`sequence replica of an incoming CDMAsignal comprises
`generating a PN code having a timing offset equal to a GCC
`count value.
`4. The method according to claim 1 wherein the step of
`generating a local CDMArake receiver pseudo-noise (PN)
`sequence replica of an incoming CDMAsignal comprises
`generating a PN code having a plurality of timing offset
`values corresponding to a search window size, wherein each
`timing offset value is specified relative to a GCC count
`value.
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`10
`
`10
`
`

`

`US 6,792,031 B1
`
`10
`a correlator co-processor having
`a pseudo-noise (PN) generator for generating a PN
`sequence replica of an incoming CDMAsignal; a
`Walsh code generator for generating Walsh codes;
`at least one global chip counter (GCC) configured to
`count CDMAsignal samples;
`at least one data input buffer configured to receive and
`store CDMAchips;
`a data path configured to receive and p