HK1106630A

HK1106630A - Method and apparatus for canceling pilot interference in a wireless communication system

Info

Publication number: HK1106630A
Application number: HK07111894.7A
Authority: HK
Inventors: J.A.莱文; T．B．维尔包恩; B．K．布特勒; P．E．本纳
Original assignee: 高通股份有限公司
Priority date: 2001-06-06
Filing date: 2007-11-02
Publication date: 2008-03-14

Description

Method and apparatus for canceling pilot interference in a wireless communication system

The present application is a divisional application of chinese patent application entitled "method and apparatus for pilot interference cancellation in a wireless communication system" as filed on 6/2002.

Background of the invention

This application claims the benefit of provisional U.S. application serial No. 60/296,259 entitled "method and apparatus for multiple pilot signal cancellation" filed 6/2001, which is incorporated herein by reference in its entirety for all purposes.

Background

FIELD

The present invention relates generally to data communications, and more specifically to techniques for canceling interference due to pilots in a wireless (e.g., CDMA) communication system.

Background

Wireless communication systems are widely deployed to provide various types of communication such as voice, packet data, and so on. These systems may be based on Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), or some other multiple access technique. CDMA systems may provide certain advantages over other types of systems, including increased system capacity. CDMA systems are generally designed to implement one or more standards, such as the IS-95, CDMA2000, IS-856, W-CDMA, and TS-CDMA standards, all of which are known in the art.

In some wireless (e.g., CDMA) communication systems, a pilot may be transmitted from a transmitter device (e.g., a terminal) to a receiver device (e.g., a base station) to assist the receiver device in performing some functions. For example, the pilot may be used at the receiver device as a synchronization of timing and frequency of the transmitter device, an estimation of channel response and communication channel quality, coherent demodulation of data transmissions, and so on. The pilot is typically generated based on a known data pattern (e.g., an all-zero sequence) and using a known signal processing scheme (e.g., channelized with a particular channelization code and spread with a known spreading sequence).

On the reverse link in a cdma2000 system, the spreading sequence for each terminal is generated based on (1) a complex pseudo-random noise (PN) sequence that is common to all terminals, and (2) a scrambling sequence that is specific to that terminal. In this manner, pilots from different terminals may be identified by their different spreading sequences. On the forward link in cdma2000 and IS-95 systems, each base station IS assigned an offset of a particular PN sequence. In this manner, pilots from different base stations may be identified by their different assigned PN offsets.

At the receiver device, a "rake" receiver is often used to recover transmitted pilot, signaling, and traffic data from a transmitter device that has established communication with the receiver device. A signal transmitted from a particular transmitter device may be received at a receiver device via multiple signal paths, and each received signal instance (or multipath) of sufficient length may be individually demodulated by a "rake" receiver. Each such multipath is processed in a manner complementary to that performed at the transmitter device to recover the data and pilot received via that multipath. The amplitude and phase of the recovered pilot is determined by, and represented by, the channel response of the multipath. The pilot is typically used to coherently demodulate various types of data transmitted with the pilot, which is also distorted by the channel response. For each transmitter device, the pilots for some multipaths of the transmitter device may also be used to combine demodulated symbols derived from those multipaths to obtain combined symbols with improved quality.

On the reverse link, the pilot from each transmitting terminal acts as interference to signals from other terminals. For each terminal, the aggregate interference due to pilots transmitted by all other terminals may be a large percentage of the total interference experienced by this terminal. This pilot interference can degrade performance (e.g., higher packet error rates) and further reduce reverse link capacity.

There is therefore a need for techniques to cancel interference due to pilots in wireless (e.g., CDMA) communication systems.

SUMMARY

Aspects of the present invention provide techniques for estimating and canceling pilot interference in a wireless (e.g., CDMA) communication system. The received signal typically includes some signal instances (e.g., multipath). For each multipath to be demodulated (e.g., each desired multipath), the pilots in all multipaths are interference to the data in the desired multipath. If the pilot is generated according to a known data pattern (e.g., an all-zero sequence) and channelized with a known channelization code (e.g., a zero Walsh code), the pilot in the interfering multipath can simply be estimated as a spreading sequence having a phase corresponding to the time of arrival of that multipath at the receiver device. The pilot interference from each interfering multipath may be estimated from the spreading sequence and an estimate of the channel response for that multipath, which may be estimated from the pilot. The total pilot interference due to some interfering multipaths may be derived and subtracted from the received signal to provide a pilot-canceled signal with pilot interference removed.

In a particular example, a method for canceling pilot interference at a receiver device (e.g., a base station) in a wireless (e.g., cdma2000) communication system is provided. According to this method, a received signal is composed of signal instances, each of which includes a pilot, that are initially processed to provide data samples. The data samples are then processed to derive an estimate of the pilot interference due to one or more (interfering) signal instances, and the pilot interference estimates are further combined to derive the total pilot interference. The total pilot interference is then subtracted from the data samples to provide pilot-canceled data samples, which are further processed to derive respective demodulated data for at least one (desired) signal instance in the received signal.

The pilot interference due to each interfering signal instance may be estimated by (1) despreading the data samples with a spreading sequence for the signal instance, (2) channelizing the despread samples with a pilot channelization code to provide pilot symbols, (3) filtering the pilot symbols to provide an estimated channel response for the signal instance, and (4) multiplying the spreading sequence for the signal instance and the estimated channel response to provide an estimated pilot interference, among other things. Data demodulation for each desired multipath may be accomplished by (1) despreading the pilot-canceled data samples with a spreading sequence for the signal instance, (2) channelizing the despread samples with a data channelization code to provide data symbols, and (3) demodulating the data symbols to provide demodulated data for the signal instance. For performance improvement, pilot estimation and cancellation may be performed at a sample rate higher than the PN chip rate.

Various aspects, examples, and features of the invention are described in further detail below.

Brief description of the drawings

The features, nature, and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings. In the drawings, like reference characters designate corresponding parts throughout the several views.

Fig. 1 is a diagram of a wireless communication system.

Fig. 2 is a simplified block diagram of an example of a base station and terminal.

Fig. 3 is a block diagram of an example of a modulator for the reverse link in cdma 2000.

Fig. 4 is a block diagram of an example of a rake receiver.

Fig. 5 is a block diagram of a specific example of a searcher processor in a "rake" receiver that is capable of estimating and canceling pilot interference in addition to performing data demodulation.

Fig. 6A and 6B are diagrams illustrating processing of data samples to derive an estimate of pilot interference, in accordance with a specific example.

Fig. 7 is a flow diagram of an example of a process of deriving total pilot interference for some multipaths.

Fig. 8 is a flow chart of an example of a process for data demodulation of some multipaths using a pilot interference cancellation method.

Detailed Description

Fig. 1 is a diagram of a wireless communication system 100 supporting a number of subscribers in which various aspects and examples of the invention may be implemented. The system 100 provides communication to a number of cells, each of which is being served by a respective base station 104. A base station is also generally referred to as a Base Transceiver System (BTS), access point, or node B. A variety of terminals 106 are dispersed throughout the system. Each terminal 106 may communicate with one or more base stations 104 on the forward and reverse links at any given moment, depending on whether the terminal is active and in soft handoff. The forward link (e.g., downlink) refers to transmission from the base station to the terminal, and the reverse link (e.g., uplink) refers to transmission from the terminal to the base station.

Signals transmitted from a terminal may reach a base station via one or more signal paths. These signal paths may include through paths (e.g., signal path 110a) and reflected paths (e.g., signal path 110 b). A reflected path is established when the transmitted signal reflects off a reflection source and reaches the base station via a path other than the line-of-sight path. The source of reflection is typically an object in the environment in which the terminal is operating (e.g., a building, tree, or some other structure). The signal received by each antenna of a base station may thus contain some signal instances (or multipaths) from one or more terminals.

In the system 100, a system controller 102, which may also be referred to as a Base Station Controller (BSC), is coupled to the base stations 104, provides coordination and control for the base stations coupled thereto, and further controls the routing of calls to the terminals 106 via the coupled base stations. The system control engine 102 may be further coupled to a Public Switched Telephone Network (PSTN) via a Mobile Switching Center (MSC) and to a packet data network via a Packet Data Serving Node (PDSN), which are not shown in fig. 1. System 100 may be designed to support one or more CDMA standards, such as CDMA2000, IS-95, IS-856, W-CDMA, and TS-CDMA, some other CDMA standard, or a combination thereof. These CDMA standards are known in the art and are incorporated herein by reference.

Various aspects and examples of the disclosure may be used for the forward and reverse links in a wide variety of wireless communication systems. For clarity, this pilot interference cancellation technique is described specifically for the reverse link in a cdma2000 system.

Fig. 2 is a simplified block diagram of an example of a base station 104 and a terminal 106. On the reverse link, at terminal 106, a Transmit (TX) data processor 214 receives various types of "traffic," such as user-specific data, messages, etc., from a data source 212. TX data processor 214 then formats and codes the different types of traffic according to one or more coding schemes to provide coded data. Each coding scheme may include any combination of Cyclic Redundancy Check (CRC), convolutional, Turbo, block, and other coding, or no coding at all. When error correction coding is used in an attempt to reduce fading, a crossover method is generally used. Other coding schemes may include automatic repeat request (ARQ), hybrid ARQ, and incremental redundancy retransmission. Generally, different coding schemes are used. Different types of traffic coding. A Modulator (MOD)216 then receives the pilot data and coded data from TX data processor 214 and further processes the received data to generate a modulated signal.

Fig. 3 is a block diagram of an example of a modulator 216a, which modulator 216a may be used as modulator 216 in fig. 2. For the reverse link in cdma2000, the processing by modulator 216a includes encoding with respective Walsh codes, C_chxData to cover each of a number of code channels (e.g., traffic, sync, paging, and pilot channels) is passed through multiplier 312 to channelize user-specific data (packet data), messages (control data), and pilot data to their respective code channels. The channelized data for each code channel may be provided with a respective gain, G, by device 314_iScaling is performed to control the associated transmit power of the code channel. The scalar data for all code channels of the in-phase (I) path are then summed by adder 316a to provide I channel data, and the scalar data for all code channels of the quadrature (Q) path are summed by adder 316b to provide Q channel data.

Fig. 3 also illustrates an example of a spreading sequence generator 320 for the reverse link in cdma 2000. In the generator 320, a long code generator 322 receives a long code mask assigned to a terminal and generates a long pseudo-random noise (PN) sequence having a phase determined by the long code mask. The long PN sequence is then multiplied by the I-channel PN sequence by multiplier 326a to generate an I-spread sequence. The long PN sequence is also delayed by delay unit 324, multiplied by the Q-channel PN sequence by multiplier 326b, decimated by a factor of 2 by unit 328, and coded with Wal sh (C)_sPlus-) is covered and further spread with an I spreading sequence by multiplier 330 to generate a Q spreading sequence. The I-channel and Q-channel PN sequences from the composite short PN sequence are used by all channels. From the complexI and Q spreading sequences of a composite spreading sequence, S_kSpecific to the channel.

In modulator 216a, the sequence (S) is spread with I and Q_KI+jS_KQ) I channel data and Q channel data (D) via complex multiplication performed by multiplier 340_chI+jD_chQ) Is expanded to generate I expanded data and Q expanded data (D)_spI+jD_spQ). The complex despreading operation can be expressed as:

D_spI+jD_spQ＝(D_chI+jD_chQ)·(S_KI+jS_KQ)

＝(D_chIS_KI-D_chQS_KQ)+j(D_chIS_KQ+D_chQ S_KI) Equation 1

The I and Q spread data comprise modulated data provided by a modulator 216 a.

The modulated data is then provided to and conditioned by a transmitter (TMTR)218 a. Transmitter 218a is an example of transmitter 218 in fig. 2. Signal conditioning includes filtering the I and Q spread data with filters 352a and 352b, respectively, and with cos (ω) by multipliers 354a and 354b_ct) and sin (ω)_ct) up-converting the filtered I and Q data, respectively. The I and Q components from multipliers 354a and 354b are then summed by summer 356 and further applied by multiplier 358 with a gain, G₀And amplified to generate a reverse link modulated signal.

Returning to fig. 2, the reverse link modulated signal is then transmitted via antenna 220 and over a wireless communication link to one or more base stations.

At base station 104, the reverse link modulated signals from some terminals are received by each of one or more antennas. Multiple antennas 250 may be used to provide spatial diversity that cancels out deleterious path effects such as fading. For example, for a base station supporting three sectors, two antennas for each sector, the base station may include six antennas. Any number of antennas may be used by the base station.

Each received signal is provided to a respective receiver (RCVR)252 that conditions (e.g., filters, amplifies, downconverts) and digitizes the received signal to provide data samples of the received signal. Each received signal may include one or more signal instances (e.g., multipath) for each of a number of terminals.

A demodulator (DEMOD)254 then receives and processes the data samples for all received signals to provide recovered symbols. For cdma2000, the processing by demodulator 254 to recover a data transmission from a particular terminal includes (1) despreading the data samples with the same spreading sequence used by the terminal to spread the data, (2) channelizing the despread samples to separate or channelize the received data and pilot into their respective code channels, and (3) coherently demodulating the channelized data with the recovered pilot to provide a demodulated signal. Demodulator 254 may implement a "rake" receiver that processes multiple signal instances for each of a number of terminals, as described above.

A Receive (RX) data processor 256 then receives and decodes the demodulated signals for each terminal to recover the user-specific data and messages sent by the terminals on the reverse link. The processing by demodulator 254 and RX data processor 256 is complementary to the processing performed by modulator 216 and TX data processor 214, respectively, at the terminal.

Fig. 4 is a block diagram of an example of a rake receiver 254a, the rake receiver 254 being capable of receiving and demodulating reverse link modulated signals from some terminals 106. The "rake" receiver 254a includes one or more (L) sample buffers 408, one or more (M) finger handlers (finger processors) 410, a searcher 412, and a symbol combiner 420. The example in fig. 4 shows all finger handlers 410 coupled to the same symbol combiner 420.

Due to the multipath environment, the reverse link modulated signals transmitted from each terminal 106 may reach base stations 104 via a number of signal paths (shown in FIG. 1), and each base stationThe received signal for the antenna typically comprises a combination of different instances of the reverse link modulated signal from each of several terminals. Each signal instance (or multipath) in a received signal is typically associated with a particular amplitude, phase, and arrival time (e.g., a time delay or time offset associated with CDMA system time). If there are more than one PN chip difference between the arrival times of the base station multipaths, then at the input of the respective receiver 252, each received signal, y₁(t), expressible as:

img id="idf0001" file="A20071008774900121.GIF" wi="272" he="35" img-content="drawing" img-format="GIF"/equation 2

Therein, the

x_j(t) is the jth reverse link modulated signal transmitted by the jth terminal.

Is at the 1 st antenna, is in communication with the jth reverse link modulated signal, x_j(t) the arrival time of the ith multipath in relation to the time of transmission.

p_i，j，l(t) is the j-th antenna at the 1 st antennaThe channel gain and phase of the ith multipath of the terminal and is a function of the attenuation process.

Is the sum of all reverse link modulated signals in the 1 st received signal.

Is the sum of all multipaths of each reverse link modulated signal in the 1 st received signal; and

n (t) represents the real-valued channel noise at RF plus internal receiver noise.

Each receiver 252 amplifies and frequency downconverts a respective received signal, y₁(t) and further filtering the signal with a receive filter that is generally matched to the transmit filter used at the terminal, such as filter 352, to provide a conditioned signal. Each receiver device 252 then digitizes the conditioned signal to provide a respective stream of data samples, which is then provided to a respective sample buffer 408.

Each sample buffer 408 stores received data samples and further provides the appropriate data samples at the appropriate time to the appropriate processing device (e.g., finger processor 410 and/or searcher 412). In one design, each buffer 408 may provide data samples to a respective set of finger processors 410 assigned to process multipath in the received signal associated with the buffer. In another design, some buffers 408 may provide data samples to a particular finger processor (e.g., in a time-multiplexed manner), which may have the ability to handle some multipaths in a time-multiplexed manner. The buffers 408a through 4081 may also be implemented as a single buffer of suitable size and speed.

Searcher 412 is used to search for strong multipaths in the received signal and provide an indication of the length and timing of each discovered multipath that meets a set of criteria. The search for multipaths of a particular channel is typically accomplished by correlating the data samples of each received signal with the terminal spreading sequence, which is locally generated at various chip or sub-chip offsets (or phases). Due to the pseudo-random nature of the spreading sequence, the correlation of the data samples and the spreading sequence should be low, except when the phase of the locally generated spreading sequence is time aligned with the phase of the multipath, in which case the correlation result is a high value.

For each reverse link transmitted modulated signal, x_j(t), searcher 412 may provide a set of one or more time offsets to a set of one or more multipaths discovered (possibly accompanied by the length of the signal for each discovered multipath) for the reverse link modulated signal, t_i，j，lTime offset, t, provided by searcher 412_i，j，lTime offset, t, related to base station timing or CDMA time, and related to signal transmission time as shown in equation (2)_i，j，lAnd (4) correlation.

Searcher 412 may be designed with one or more searcher devices, each of which may be designed to search for multipaths over a respective search window. Each search window includes a range of spreading sequence phases to be searched. The searcher devices may work in parallel to speed up the search operation. Additionally or alternatively, the searcher 412 may be operated at a high clock rate to speed up the search operation. The searcher and search method are described in further detail in U.S. Pat. Nos. 5,805,648, 5,781,543, 5,764,687, and 5,644,591, all of which are incorporated herein by reference.

Each finger processor 410 may then be assigned to process a respective set of one or more multipaths of interest (e.g., multipaths of sufficient length, as determined by control engine 260 based on signal length information provided by searcher 412). Each finger processor 410 then receives the following for each assigned multipath: (1) data samples of the received signal including the assigned multipath, (2) or the time offset, t, of the assigned multipath_i，j，lOr a beltWith an offset in time, t_i，j，l(which may be generated by spreading sequence generator 414) a spreading sequence, S, of the corresponding phase_i，j，lAnd (3) channelization coding (e.g., Walsh coding) of the code channel to be recovered. Each finger processor 410 then processes the received signal and provides a demodulated signal to each assigned multipath. The processing of finger processor 410 is described in further detail below.

A symbol combiner 420 receives and combines demodulated data (e.g., demodulated symbols) for each terminal. In particular, symbol combiner 420 receives demodulated symbols for all assigned multipaths for each terminal, and, depending on the design of the finger processor, may time align (or de-phase shift) the symbols to calculate the difference in time offset for the assigned multipaths. Symbol combiner 420 then combines the time-aligned demodulated symbols for each terminal to provide recovered symbols for the terminal. Multiple symbol combiners may be provided to combine symbols for multiple terminals simultaneously. The recovered symbols for each terminal are then provided to an RX data processor 256 and decoded.

The processing of the multipath may be performed according to different demodulator designs. In a first demodulator design, a finger processor is assigned to process some of the multipaths in the received signal. For this design, data samples from the sample buffer may be processed in "segments" that cover a duration of a particular time (e.g., a particular number of PC slices) and are launched at some determined time boundary. In a second demodulator design, multiple finger processors are assigned to process multiple multipaths in the received signal. Various aspects and embodiments of the present invention are described with respect to a first demodulator design.

The pilot interference cancellation method may also be accomplished according to various schemes. In a first pilot interference cancellation scheme according to the first demodulator design, the channel response for a particular multipath is estimated from a segment of the data samples, and the estimated channel response is then used to derive an estimate of the pilot interference due to that same segment of the multipath. This scheme may improve pilot interference cancellation. However, because the data samples are first processed to estimate and cancel pilot interference before data demodulation can begin on the same segment, additional processing delays in data demodulation for multipath can be introduced with this scheme.

In a second pilot interference cancellation scheme, also based on the first demodulator design, the channel response for a particular multipath is estimated from one segment of data samples, and the estimated channel response is then used to derive an estimate of the pilot interference due to multipath for the next segment. This scheme may be used to reduce (or possibly eliminate) additional processing delay in data demodulation due to pilot interference estimation and cancellation. However, the link adjustment may be continuously changing at all times, and the time delay between the current and next segments should be kept short enough that the channel response estimate for the current segment is still accurate in the next segment. For clarity, the pilot interference estimation and cancellation method is described in a second scheme as follows.

Fig. 5 is a block diagram of a particular embodiment of a finger processor 410x that can estimate and cancel pilot interference in addition to performing data demodulation. The finger processor 410x may be used as each finger processor 410 in the "rake" receiver 254a shown in fig. 4. In the following description, fig. 5 shows a processing unit, and fig. 26A and 6B graphically show timing sequences for pilot interference estimation and cancellation.

Finger processor 410x is assigned to demodulate one or more desired multipaths in a particular received signal. Sample buffer 408x stores data samples of a received signal that contains multipath assigned to finger processor 410 x. Buffer 408x then provides the appropriate data samples (in segments) to the finger processor when they are needed. In the embodiment shown in fig. 5, finger processor 410x includes a resampler 522, a pilot estimator 520 (or channel estimator), a summer 542, a data demodulation device 550, and a pilot interference estimator 530.

For each desired multipath to be demodulated by finger processor 410x, the data in all other multipaths and the pilot in all multipaths in the same received signal act as interference to this multipath. Because the pilots are generated from a known data pattern (e.g., a generally all-zero sequence) and processed in a known manner, the pilots in the "interfering" multipaths can be estimated and removed from the desired multipath to improve the signal quality of the data component in the desired multipath. Finger processor 410x can estimate and cancel pilot interference due to some of the multipaths found in the received signal that contain the pilot for the desired multipath, as described below.

In an embodiment, pilot interference estimation and cancellation and data demodulation are done in "short bursts". For each short pulse (e.g., processing period), a segment of data samples for a particular number of PN chips is processed to estimate the pilot interference due to a particular multipath. In a particular example, each segment contains data samples for one symbol period, which may be 64 PN chips for cdma 2000. However, other segment sizes may be used (e.g., for data symbols of other durations), and this is within the scope of the invention. As described below, data demodulation may be done in parallel and in a pipelined fashion with pilot interference estimation to increase processing throughput and possibly reduce overall processing time.

To derive an estimate of the pilot interference due to the mth multipath (where m is (i, j, l), and is the label of the ith multipath of the jth reverse link modulated signal found in the 1 st received signal), a segment of data samples is initially provided by buffer 408x to a resampler 522 in the finger processor. The re-sampler 522 may then perform decimation, interpolation, or a combination thereof to provide decimated sampled data samples at the slice rate and at the appropriate "fine-grained" timing phase.

Fig. 6A illustrates an example of resampling performed by the resampler 522. The received signal is typically resampled at a sample rate that is a multiple of the chip rate to provide higher temporal resolution. The data samples are stored in a sample buffer 408x, which thereafter provides a segment (e.g., 512) of the data samples for each processing cycle. Resampler 522 then "resamples" the data samples received from buffer 408a to provide samples at the chip rate and at the appropriate timing phase.

As shown in fig. 6A, if the received signal has been sufficiently re-sampled (e.g., at 8 times the chip rate), then re-sampling of the mth multipath may be accomplished by providing each, e.g., 8 th, data sample that has been received from the buffer, the selected data samples, which are those that are most closely aligned with the peak timing of the mth multipath. The mth multipath is generally the multipath assigned to the data demodulation call, and the multipath time offset, t_mAnd may be determined and provided by the search engine 412. However, pilot interference due to multipaths not allocated for data demodulation can also be estimated and cancelled, provided that the time offset for each such multipath is known. Time offset, t, per multipath_mCan be considered to include an integer number of symbol periods and a fractional portion of a symbol period (e.g., t)_m＝t_full，m+t_frac，m) In one aspect, the symbol period is related to the base station timing or CDMA system time, where the symbol period is determined by the length of the channelization code (e.g., 64 PN chips for CDMA 2000). Fractional part of the time offset, t_frac，mWhich may be used to select data samples for a particular segment to provide to the resampler 522 and for decimation. In the example shown in fig. 6A, the fractional part of the time offset of the mth multipath is t_frac，mData sample segment 622 is provided by buffer 408x, and the decimated data samples provided by resampler 522 are represented by the shaded boxes.

For some other receiver designs in which the received signal is not sufficiently re-sampled, interpolation may alternatively or additionally be done with decimation to derive new samples at the appropriate timing phase, as is known in the art.

In pilot estimator 520, a despreader 524 receives the decimated sampled data samples and a (complex conjugate) spreading sequence, S_m ^*(k) Expanding, expandingSpreading sequence having time offset, t, with mth multipath_mAnd the pilot frequency interference of the mth multipath is to be estimated according to the corresponding phase. Spreading sequence, S_m ^*(k) And may be provided by a spreading sequence generator 414. For the reverse link in cdma2000, the spreading sequence, S_m ^*(k) May be generated as shown by the spreading sequence generator in fig. 3. As shown in FIG. 6A, a spreading sequence, S, of the same length and the same timing phase as the data sample segment_m ^*(k) Can be used for despreading (e.g., spreading sequence, S)_m ^*(k) Are time aligned with the decimated data samples).

Despreader 524 (which may be implemented as a complex multiplier such as multiplier 340 shown in fig. 3) uses a spreading sequence, S_m ^*(k) The decimated data samples are despread, and despread samples are provided. The pilot channelizer 526 then combines the despread sequence with the channelization code used for pilot at the terminal (e.g., the zero Walsh code for cdma2000), C_pilot，mMultiply by each other. The decovered pilot samples are then accumulated over a particular accumulation time interval to provide pilot symbols. The accumulation time interval is typically an integer multiple of the pilot channelization code length. If the pilot data is covered by a channelization code of zero (as in cdma2000), then sum channelization code, C_pilot，mThe multiplication of (d) may be omitted and the pilot channelizer 526 simply completes the accumulation of the despread samples from the despreader 524. In a particular example, one pilot symbol is provided for each segment, each segment having a size of one symbol period.

The pilot symbols from the pilot channelizer 526 are then provided to a pilot filter 528 and filtered according to a particular low pass filter response to remove noise. The pilot filter 528 may be implemented by a Finite Impulse Response (FIR) filter, an Infinite Impulse Response (IIR) filter, or some other filtering structure. The pilot filter 528 provides a pilot estimate, P_m(k) Which represents the channel response (e.g., gain and phase, a) of the mth multipath_me^jθ). Each one of which isPilot estimation value, P_m(k) And is therefore complex. Pilot estimates are provided at a rate sufficient so that non-null changes in the channel response of the multipath are acquired and reported. In a particular example, one pilot estimate may be provided for each segment, each segment having a size of one symbol period.

The pilot interference estimator 530 then estimates the pilot interference due to the mth multipath for the next segment. For estimating the pilot interference, pilot data and pilot channelization codes for the mth multipath, C_pilot，mAnd provided to a pilot channelizer 532, which pilot channelizer 532 channelizes the pilot data with a pilot channelization code to provide channelized pilot data. Spreader 534 then accepts and uses the spreading sequence, S_m(k + N), spreading the channelized pilot data to generate spread pilot data (e.g., processed pilot data). Spreading sequence, S_m(k + N) with a time offset from the mth interfering multipath, t_mThe corresponding phase and is further advanced by N PN chips for the next segment as shown in fig. 6A. If the pilot data is an all-zero sequence and the pilot channelization code is also an all-zero sequence (as in cdma2000), then the pilot channelizer 532 and spreader 534 may be omitted and the spread pilot data is simply the spread sequence S_m(k+N)。

Multiplier 536 then receives and combines the spread pilot data with the pilot estimate, P, from pilot filter 528_m(k) Multiplied to provide an estimate of the pilot interference due to the mth multipath, I, for the next segment_pilot，m(k + N). Because of the pilot estimate, P_m(k) Is derived from the current segment and is used to derive an estimated pilot interference for the next segment, so a prediction technique may be used to derive a pilot prediction value for the next segment based on the pilot estimate. These pilot predictions are then used to derive the estimated pilot interference for the next segment.

In the example, multiplier 536 provides the estimated pilot interference due to the mth multipath at the sample rate (e.g., 8x chip rate) and at the timing phase of the mth multipath. This makes all ofThe estimated pilot interference for paths (multipath typically has different time offsets that are not aligned with PN chip timing boundaries) can be accumulated with higher time resolution. Estimated pilot interference of mth multipath, I_pilot，m(k + N) and then provided to an interference accumulator 538 where the pilot interference includes the same number of interference samples as the data sample segment. As shown in fig. 6A, the interference samples for the mth multipath are stored (or accumulated with stored interference samples) in accumulator 538 at a location determined by the fractional portion of the multipath time offset.

The above process may be iterated several times in order to derive the pilot interference for all multipaths in a given received signal, one iteration or one processing cycle in order to estimate and cancel each interfering multipath from the desired multipath. For multipath received by the same, non-intersecting antennas, pilot interference is typically cancelled because the channel estimate from one antenna is typically unreliable for the other antenna. If the same finger processor hardware is used for multiple iterations, the processing can be done in short pulses, with each short pulse being done on each data sample as determined by the multipath fractional time offset.

Before the first iteration, the accumulator 538 is cleared or reset. For each iteration, estimated pilot interference due to the current multipath, I_pilot，mAnd accumulated with the accumulated pilot interference for all pre-processed multipaths. However, as shown in FIG. 6A, the estimated pilot interference, I_pilot，mThe samples are accumulated together at a particular section of accumulator 538, as determined by the time offset of the current multipath. After all interfering multipaths have been processed, the accumulated pilot interference in accumulator 538 contains the total pilot interference, I, due to all processed multipaths_pilot。

Fig. 6A also shows an example of accumulator 538. When finger processor 410x completes the data demodulation for the mth multipath of the current segment (with the total pilot interference, I, earlier derived and stored in one sector of accumulator 538)_pilot(k) In time of the next segmentPilot interference due to mth multipath, I_pilot，m(k + N) may be estimated and accumulated in another section of the accumulator.

The pilot of the mth multipath is the interference of all multipaths in the received signal, including the mth multipath itself. For demodulator designs in which multiple finger processors are assigned to process some of the multipaths in the received signal for a given terminal, the estimated pilot interference, Ic, due to the mth multipath_pilot，mMay be provided to other finger processors assigned to process other multipaths in the same received signal.

For demodulation to recover the data on the mth multipath, a segment of data samples is provided from buffer 408x to resampler 522. Resampler 522 then resamples the received data samples to provide the decimated data samples to this multipath at the chip rate and at the appropriate timing phase. The decimated sampled data samples are processed as described above to provide pilot estimates, P_m(k)。

Thus, interference samples of the total pilot interference of the same segment, I_pilot(k) And from the accumulator 538 to the resampler 540. The re-sampler 540 also re-samples the received interference samples to provide the decimated interference samples to the mth multipath at the chip rate and at the proper timing phase. Summer 542 then receives and subtracts the decimated sampled interference samples from the decimated sampled data samples to provide pilot-canceled data samples.

In data demodulation apparatus 550, a despreader 544 receives and uses a (complex conjugate) spreading sequence, S_m ^*(k) The pilot-canceled data samples are despread to provide despread samples. Spreading sequence, S_m ^*(k) Having a time offset, t, from the mth multipath_mThe corresponding phase. The data channelizer 546 then despreads the samples and channelizes the code, C_ch，mThe multiplication, channelization code is used for the code channel recovered by the finger processor. The channelized data samples are then transmittedIn the case of channelization codes, C_ch，mAnd are accumulated over a length to provide data symbols.

A data demodulator 548 then receives and uses the pilot estimate, P_m(k) The data symbols are demodulated to provide demodulated symbols (e.g., demodulated data) for the mth multipath, which is then provided to symbol combiner 420. Data demodulation and symbol combining may be achieved as described in the aforementioned U.S. patent No.5,764,687. The' 687 patent describes BPSK data demodulation by IS-95 by performing a dot product between the despread data and the filtered pilot. Demodulation of QPSK modulation, used in CDMA2000 and W-CDMA, is an extension of the techniques described in the' 687 patent. That is, instead of dot products, both dot products and cross products are used to recover the in-phase and quadrature streams.

As noted above, data demodulation for the mth multipath may be done in parallel and in a pipelined fashion along with pilot interference estimation. When the despreader 544 and the data channelizer 546 are processing the pilot-canceled data samples for the current segment (using spreading sequence, S)_m ^*(k) And channelization coding, C_ch，m) To provide data symbols for the mth multipath, despreader 524 and pilot channelizer 526 may process the same data samples (using spreading sequence, S) for the current segment_m ^*(k) And pilot channelization coding, C_ch，m) To provide pilot symbols for this multipath. The pilot symbols are filtered by a pilot filter 529 to provide a pilot estimate, P, for the multipath_m(k) In that respect The pilot interference estimator 530 then derives the estimated pilot interference, I, due to this multipath for the next segment_pilot，m(k + N) as described above. In this manner, when the total pilot interference, I, derived from the previous segment is used_pilot(k) The pilot interference for the next segment is also estimated and stored in another section of accumulator 538 for use in the next segment while data demodulation is taking place.

In 1 example, as described above, the pilot for a particular multipath being demodulated is estimated based on the "original" received data samples (from sample buffer 408x), rather than the pilot-canceled data samples (from accumulator 538). In another example, if the total pilot interference includes some or all of the interfering pilots in addition to the pilot of the multipath being demodulated (e.g., the pilot of the multipath being demodulated is included in the "other pilot canceled" data samples), the pilot may be estimated from the pilot canceled data samples. This alternative example may provide an improved estimate of the channel response of the multipath being demodulated and is particularly advantageous for the reverse link, where pilot estimation is generally the limiting factor in dealing with weak multipaths. The same "other pilot canceled" data samples used for pilot estimation may also be processed to recover multipath data, which is advantageous for a finger processor architecture that performs pilot estimation and data demodulation in parallel on the same stream of data samples. The same concept can also be used to estimate the channel response for a particular interfering multipath (e.g., the estimated channel response can be based on the original data samples or "other pilot canceled" data samples having interfering pilots in addition to the pilot for that particular multipath that has been canceled).

Figures 6A and 6B are diagrams illustrating processing of data samples to derive pilot interference estimates, depending on a particular implementation. In the example shown in fig. 6A and 6B, the received signal includes an offset t from time₁，t₂，t₃Three multipaths are involved. The received signal is digitized at a sample rate of 8 times the chip rate to provide data samples, which are stored to a sample buffer. These multipaths may or may not be sampled at their peaks.

In the example shown in fig. 6A and 6B, each segment includes 512 data samples for a symbol period of 64 PN chips. The pilot interference is estimated for each of the three multipaths and for each symbol period. The symbol timing of each multipath is determined by the fractional time offset of the multipath. If the fractional time offsets of the multipaths are not identical, which is generally true, then the symbol timing of these multipaths will be different and correlated with different data sample segments. In the 1 instance, the multipaths are processed sequentially according to their fractional time offsets, the multipath with the smallest fractional time offset being processed first and the multipath with the largest fractional time offset being processed last. This processing order ensures that the total pilot is derived as it is processed and is available for each multipath.

In FIG. 6A, for a value with t_frac，mThe resampler 522 receives data samples 5 through 516 from the sample buffer 408 and provides data samples 5, 13, 20, etc. and 509 to the despreader 524 for the nth symbol period of the mth multipath at 5 fractional time offsets, as indicated by the shaded boxes. Therefore, despreader 524 receives signals having an AND value of t_mOf the same time offset corresponding phase, S_m ^*(k) And the decimated sampled data samples are despread with the spreading sequence. A pilot estimate, P, is then derived based on the despread samples for that segment_m(k) As described above.

To derive the estimated pilot interference due to the mth multipath, spreader 534 receives spreading sequence S corresponding to the next segment_m(k + N) and spread the channelized pilot data. Multiplier 536 will then (by spreading sequence S)_m(k + N) extended pilot data and a pilot estimate, P, derived from the current segment_m(k) Multiplied to provide the estimated pilot interference, I, for the next segment_pilot，m(k + N). Estimated pilot interference, I_pilot，m(k + N), containing interference samples 517 through 1028, these and the same subscript samples 517 through 1028 are accumulated in interference accumulator 538, as shown in FIG. 6A. In this approach, the fractional time offset of the mth multipath is calculated in the derivation of the total pilot interference.

For data demodulation of the mth multipath for the nth symbol period, interference samples 5 through 516 of the same segment are provided from accumulator 538 to resampler 540. Resampler 540 then provides interference samples 5, 13, 20, etc. and 509 (these are also indicated by the shaded boxes) to summer 542, which correspond to the data samples of the same subscript provided by resampler 522. Data demodulation of the pilot-canceled data samples then proceeds as described above. Each multipath may be handled in a similar manner. However, because each multipath may be associated with a different time offset, different decimated data and interference samples may operate.

Fig. 6B shows three data sample segments, decimated data samples, and three spreading sequences used to derive the estimated pilot interference due to three multipaths.

In another demodulation design, pilot interference estimation/cancellation and data demodulation may be done in real-time (e.g., as data samples are received), if sufficient processing power is provided. For example, M finger processors may be assigned to process M multipaths in the received signal simultaneously. For each symbol period, each finger processor may derive a pilot estimate for that symbol period and then use the pilot estimates to derive an estimated pilot interference for the next symbol period due to multipath assigned to that finger processor. The summer then sums the estimated pilot interference from all M finger processors (taking into account their respective time offsets) and the total pilot interference for the next symbol period is stored in an interference accumulator.

When the total pilot interference is received in the next symbol period, they may then be subtracted from the data samples, and the same pilot-canceled data samples may be provided to all finger processors for data demodulation (non-pilot-canceled, received data samples that may be used to derive pilot estimates are also provided to the finger processors). In this manner, data demodulation may be performed in real time on pilot-canceled data samples, and possibly without a sample buffer. For schemes that use pilot estimation to derive an estimated pilot interference for the same segment (not for the next segment), the data samples may be temporarily stored (e.g., one symbol period) when the total pilot interference is derived.

For demodulation designs that process the same data samples multiple times (e.g., if a finger processor is assigned to process some multipath), the sample buffer 408 may be designed and operated on in a manner that ensures that data samples are not inadvertently dropped. In one example, the sample buffer is designed to receive input data samples while providing stored data samples to the finger processor. This may be achieved by implementing the data buffer in such a way that stored data samples may be read from one portion of the buffer while new data samples are written to another portion of the buffer. The sample buffer may be implemented as a double or multiple buffer, a multi-port buffer, a circular buffer, or some other buffer design. Interference accumulator 538 may be implemented in the same manner as sample buffer 408 (e.g., a circular buffer).

For the above demodulation design, to avoid duplicating writing samples that are still being processed, the size of the sample buffer 408 may be selected to be at least twice the time required to derive the total pilot interference for all M multipaths (the relationship between time and buffer size is determined by the sample rate). If a different data sample segment is available for each of the M multipaths, the size of the sample buffer may be selected to be at least (2N) of each received signal allocated to the sample buffer_os) Where N is the duration of the data samples used to derive the estimated pilot interference for a multipath, and N_oSIs the oversampling factor of the data samples (determined by the ratio of the sample rate to the chip rate). For the above example, where one symbol period (e.g., N ═ 64 PN chips) is processed for each multipath, a two symbol period buffer can provide one symbol period for one data sample per multipath regardless of its fractional time offset. If the oversampling rate is N_osThen the minimum size of the buffer is (2 · N ═ 8_os2 · 64 · 8 ═ 1024) data samples.

Similarly, the capacity of interference accumulator 538 can be selected to be at least (3N)_os). The extra symbol period of the interference accumulator (e.g., 3 · N instead of 2 · N) is considered a factor from the estimated pilot interference derived for the next segment.

As noted above, the estimated pilot interference derived from one data sample segment may be cancelled from a subsequent data sample segment. For mobile terminals, the channel response of the communication link and of the various multipaths is changing. Therefore, there is a need to reduce the delay between the data samples from which pilot interference is estimated and the data samples from which the estimated pilot interference is cancelled. This delay may be as large as 2 · N slices.

By selecting a sufficiently small value for N, the channel response for each multipath can be expected to remain relatively stable over a period of 2 · N chips. However, the value of N should be chosen large enough so that the channel response of each multipath to be processed has an accurate estimate.

Fig. 7 is a flow diagram of a process 700 for deriving total pilot interference for a number of multipaths, according to an example embodiment of the invention. Process 700 may be performed by finger processor 410 shown in FIG. 5.

Initially, the accumulator 538 for accumulating the estimated pilot interference is cleared, at step 712. The interfering multipaths that have not been processed are then selected, at step 714. In general, pilot interference is estimated for each multipath assigned for data demodulation. However, the pilot interference due to unassigned multipaths should also be estimated. In general, any number of interfering multipaths may be processed, as well as those multipaths for which pilot interference is estimated and accumulated to derive total pilot interference.

The data samples for the received signal in the selected multipath are then processed to derive an estimate of the channel response for the selected multipath, at step 716. The channel response may be estimated based on the pilots in the selected multipath, as described above. For cdma2000, this process involves: (1) despreading the data samples for the multipaths (e.g., with an appropriate phase corresponding to the time offset for the multipaths), (2) channelizing the despread data samples to provide pilot symbols (e.g., multiplying the despread samples with a pilot channelization code and accumulating the channelized data samples over a pilot channelization code length), and (3) filtering the pilot symbols to derive a pilot estimate representing the channel response for the selected multipath. It is within the scope of the invention that the channel response is estimated according to some other technique.

The pilot interference due to the selected multipath is then estimated, in step 718. The pilot interference may be estimated by generating processed pilot data and multiplying this data with the estimated channel response derived in step 716. The processed pilot data is simply the spreading sequence of the selected multipath if the pilot data is an all-zero sequence and the pilot channelization code is also all-zero. Typically, the processed pilot data is the pilot data after all signal processing at the transmitter device but before filtering and frequency upconversion (e.g., the data at the output of modulator 216a in fig. 3 of the reverse link in cdma 2000).

The estimated pilot interference for the selected multipath is then accumulated in interference accumulator 538 along with the estimated pilot interference for the previously processed multipath, in step 720. As noted above, the timing phase of the multipath is observed in performing steps 716, 718, and 720.

A determination is then made whether all interfering multipaths have been processed, at step 722. If not, processing returns to step 714 and other interfering multipaths are selected for processing. Otherwise, the contents of accumulator 538 represent the total pilot interference due to all processed multipaths, which may be provided by step 724. The process then terminates.

The pilot interference estimation of fig. 7 for all multipaths can be done in a time-division multiplexed manner using one or more finger processors. Alternatively, pilot interference estimation for multiple multipaths may be done in parallel using several finger processors. In this case, pilot interference estimation and cancellation may be done in real time with data demodulation (e.g., with minimal or no buffer when data samples are received, as described above) if the hardware has sufficient capacity

Fig. 8 is a flow diagram of a process 800 for data demodulation for some multipaths along with pilot interference cancellation, according to an example of the invention. Process 800 may also be performed by the finger processor shown in FIG. 5.

The total pilot interference due to all multipaths involved is initially derived, in step 812. Step 812 may be implemented using process 700 shown in fig. 7. The particular multipath is then selected for data demodulation, in step 814. In 1 instance and as described above, the total pilot interference is first cancelled from the selected multipath, in step 816. This may be accomplished by subtracting the interference samples of the total pilot interference (stored in accumulator 538) from the data samples of the received signal, which includes the selected multipath.

Data demodulation is then performed on the pilot-canceled signal in a conventional manner. For cdma2000, this involves: (1) despreading the pilot-canceled data samples, (2) channelizing the despread data to provide data symbols, and (3) demodulating the data symbols with pilot estimates. The demodulated symbols of the selected multipath (e.g., demodulated data) are then combined with the demodulated symbols of other multipaths of the same transmitter device (e.g., terminal). The demodulated signals of the multipaths in the multiple received signals (e.g., if receive diversity is used) may also be combined. Symbol combining may be accomplished by symbol combiner 420 shown in fig. 4.

A determination is then made whether all assigned multipaths have been demodulated, in step 822. If the answer is no, then the process returns to step 814 and another multipath is selected for data demodulation. Otherwise, the process terminates.

As noted above, data demodulation for all assigned multipaths for a given transmitter device may be accomplished in a time-division multiplexed manner using one or more finger processors. Alternatively, data demodulation of all assigned multipaths may be done in parallel using some finger processors.

Returning to fig. 4 and 5, searcher 412 may be designed and operated upon to search for new multipaths based on the pilot-canceled data samples (instead of the original received data samples from buffer 408). This may provide improved search performance because pilot interference from some or all known multipaths may be removed as described above.

The pilot interference cancellation techniques described herein can also provide significant performance improvements. Pilot sent by each terminal on the reverse link to react with background noise, N₀In a similar manner to the total pilot interference, I₀An influence is produced. The pilots from all terminals may be represented as a substantial portion of the total pilot interference level seen by all terminals. This may result in a lower signal to total noise plus interference ratio (SNR) for a single terminal. In fact, it is estimated that in cdma2000 systems (systems supporting pilots on the reverse link) that operate at similar capacities, approximately half of the interference seen at the base station may be due to pilots from the transmitting terminals. The cancellation of pilot interference thus improves the SNR for each individual terminal, which enables each terminal to transmit at a lower power level and increases the capacity of the reverse link.

The techniques for estimating and canceling pilot interference described herein may be advantageously used in a wide variety of wireless communication systems that transmit pilots with data. For example, the techniques may be used in a variety of CDMD systems (e.g., CDMA2000, IS-95, WOCDMA, TS-CDMA, etc.), Personal Communication Services (PCS) systems (e.g., ANSIJ-STD-008), and other wireless communication systems. The techniques described herein may be used to estimate and cancel pilot interference where multiple instances of each of one or more transmitted signals are received and processed (e.g., by a "rake" receiver or some other demodulator), and where multiple transmitted signals are received and processed.

For clarity, various aspects and examples of the disclosure are described with respect to the reverse link in cdma 2000. The pilot interference cancellation techniques described herein may also be used for the forward link from the base station to the terminal. The processing of the demodulator is determined by the particular CDMA standard being supported, and whether the inventive technique is used for the forward link or the reverse link. For example, "despreading" with spreading sequences in IS-95 and CDMA2000 and descrambling with scrambling sequences in W-CDMA are equivalent, and channelization with Walsh codes or quasi-orthogonal functions (QOFs) in IS-95 and CDMA2000 systems and despreading with OVSF in W-CDMA are equivalent. In general, the processing performed by the demodulator at the receiver is complementary to the processing performed by the modulator at the transmitter device.

For the forward link, the techniques described herein may approximately cancel other transmitted pilots in addition to, or possibly in lieu of, the "common" pilot transmitted to all terminals in one cell. For example, cdma2000 supports "transmit diversity" pilots and "auxiliary" pilots. These other pilots may utilize different Walsh codes (e.g., different channelization codes, possibly quasi-orthogonal functions). Different data patterns may also be used for pilot. To process any of these pilots, the despread samples are decovered using the same Walsh code used to channelize the pilot at the base station, and the pilot is further correlated with the same pilot data pattern at the base station. In addition to the common pilot, transmit diversity pilots and/or auxiliary pilots may be estimated and cancelled.

Also, W-CDMA supports a number of different pilot channels. First, a common pilot channel (CPICH) may be transmitted on the base station primary antenna. Second, a diversity CPICH may be generated from non-zero pilot data and transmitted on a diversity antenna of the base station, third, one or more secondary CPICHs may be transmitted on a limited portion of the cell, and the CPICHs of each secondary may be generated with a non-zero channelization code. Fourth, the base station may further send the decimated sampled pilots to a particular user with the same channelization code as the user data channel. In this case, the pilot symbols are time division multiplexed with the data symbols for that user. Accordingly, those skilled in the art will appreciate that the techniques described herein can be used to process all of the above different types of pilot channels, and that other pilot channels can also be transmitted in a wireless communication system.

Demodulators and other processing units used to implement various aspects and examples of the present invention may be implemented in hardware, software, firmware, or combinations thereof. In terms of hardware design, demodulators (including data demodulation devices and units for pilot interference estimation and cancellation, such as pilot estimators and pilot interference estimators), and other processing devices that may be implemented within one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), digital signal processing devices (DPSDs), Field Programmable Gate Arrays (FPGAs), processors, microprocessors, controllers, microcomputers, Programmable Logic Devices (PLDs) and other electronic devices, any combinations thereof, and the like.

For a software implementation, the means for pilot interference estimation and cancellation and data demodulation may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in a memory device (e.g., memory 262 in fig. 2) and executed by a processor (e.g., control engine 260). The memory device may be implemented within the processing machine or external to the processing machine, in which case it can be communicatively coupled to the processing machine via various means as is known in the art.

The means for performing pilot interference estimation and cancellation as described herein may be incorporated in a receiver device or demodulator, which may be further incorporated in a terminal (e.g., handset, stand-alone device, etc.), a base station, or some other communication device or unit. These receiving devices or demodulators may be implemented with one or more integrated circuits.

The previous description of the disclosed examples is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these examples will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other examples without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the examples shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An apparatus for canceling pilot interference in a wireless communication system, comprising:

means for receiving a signal comprised of a plurality of signal instances, wherein each signal instance comprises pilot and data;

means for estimating pilot interference caused by each of the plurality of signal instances;

means for accumulating estimated pilot interference due to the plurality of signal instances in a buffer to provide total pilot interference;

means for subtracting the total pilot interference from a received signal to derive a pilot-canceled signal; and

means for processing the pilot-canceled signal to derive data for each signal instance in the received signal,

wherein pilot interference caused by each of the plurality of signal instances is estimated by

Means for processing the signal instance to derive an estimate of a channel response of the signal instance; and

means for multiplying pilot data of the signal instance and the estimated channel response to provide an estimated pilot interference.

2. The apparatus of claim 1, wherein the pilot data for each of the one or more signal instances is a spreading sequence for the signal instance.

3. The apparatus of claim 2, wherein the spreading sequence of signal instances has a phase corresponding to a time of arrival of the signal instances.

4. The apparatus of claim 1, wherein the estimated channel response for each of the one or more signal instances is derived by

Means for despreading data samples of a received signal with a spreading sequence of signal instances,

means for channelizing the despread samples with a pilot channelization code to provide pilot symbols, and

means for filtering the pilot symbols to provide an estimated channel response.

5. The apparatus of claim 1, wherein the estimated channel response for a signal instance is derived from data samples for a current segment of the received signal and the estimated pilot interference is for data samples for a subsequent segment.

6. The method of claim 1, wherein the estimated channel response for a signal instance is derived from data samples for a current segment of the received signal, and the estimated pilot interference is for data samples for the same segment.

7. The method of claim 1, wherein the estimated channel response for each of the one or more signal instances is derived from data samples of the received signal.

8. The method of claim 1, wherein the estimated channel response for each of the one or more signal instances is derived based on data samples that cause pilots from the signal instance to be not removed and pilots from other interfering signal instances to be removed.

9. An apparatus for canceling pilot interference in a wireless communication system, comprising:

means for deriving total pilot interference caused by one or more signal instances;

means for processing the pilot-canceled signal to derive demodulated data for each of at least one signal instance in the received signal,

wherein the means for processing the pilot-canceled signal for each of the at least one signal instance comprises

Means for despreading the samples of the pilot-canceled signal with a spreading sequence of the signal instance,

means for channelizing the despread samples with a data channelization code to provide data symbols, and

means for demodulating the data symbols with the pilot estimates to provide demodulated data for the signal instance.

10. The apparatus of claim 9, wherein the pilot estimate for each of the at least one signal instance is derived from data samples of the received signal.

11. The apparatus of claim 9, wherein the pilot estimate for each of at least one signal instance is derived from data samples that cause pilots from the signal instance not to be removed and cause pilots from other interfering signal instances to be removed.

12. An apparatus for canceling pilot interference in a wireless communication system, comprising:

means for processing the pilot-canceled signal to derive data for each of at least one signal instance in the received signal, wherein pilot interference caused by one or more signal instances is estimated in a time-multiplexed manner.

13. An apparatus for canceling pilot interference in a wireless communication system, comprising:

wherein the means for subtracting comprises means for subtracting samples of total pilot interference from data samples of the received signal, and

where the samples of total pilot interference and the data samples are both provided at a particular sample rate.

14. An apparatus for canceling pilot interference in a wireless communication system, comprising:

wherein pilot interference caused by signal instances being processed to derive data is excluded from the total pilot interference.

15. An apparatus for canceling pilot interference in a wireless communication system, comprising:

means for subtracting the total pilot interference from a received signal to derive a pilot-canceled signal;

means for processing the pilot-canceled signal to derive data for each of at least one signal instance in the received signal; and

means for processing the pilot-canceled signal to search for a new signal instance in the received signal.

16. The apparatus of claim 13, wherein the sample rate is a multiple of the chip rate.

17. The apparatus of claim 1, wherein deriving the total pilot interference is done based on data sample segments of the received signal.

18. The apparatus of claim 17, wherein each segment comprises data samples for one symbol period.

19. The apparatus of claim 1, wherein the process of deriving data is done based on segments of pilot-canceled data samples of a pilot-canceled signal.

20. An apparatus for canceling pilot interference in a wireless communication system, comprising:

wherein the process of deriving the total pilot interference and the pilot cancellation signal is performed in parallel.

21. The apparatus of claim 1, wherein the process of deriving the total pilot interference and the pilot cancellation signal is done in a pipelined manner.

22. The apparatus of claim 1, wherein the wireless communication system is a CDMA system.

23. The apparatus of claim 22, wherein the CDMA system supports CDMA2000 standard.

24. The apparatus of claim 22, wherein the CDMA system supports the W-CDMA standard.

25. The apparatus of claim 22, wherein the CDMA system supports IS-95 standard.

26. The apparatus of claim 22, wherein the received signal comprises one or more reverse link modulated signals in a CDMA system.

27. The apparatus of claim 22, wherein the received signal comprises one or more forward link modulated signals in a CDMA system.

28. An apparatus for canceling pilot interference in a wireless communication system, comprising:

means for processing a received signal comprised of a plurality of signal instances to provide data samples, wherein each signal instance comprises a pilot;

means for processing the data samples to derive an estimate of pilot interference caused by each of the one or more signal instances;

means for deriving total pilot interference caused by one or more signal instances from the estimated pilot interference;

means for subtracting the total pilot interference from the data samples to derive pilot-canceled data samples; and

means for processing pilot-canceled data samples to derive data for each of at least one signal instance in a received signal, wherein means for processing the data samples to derive estimated pilot interference caused by each of one or more signal instances comprises

Means for despreading the data samples with a spreading sequence of signal instances,

means for channelizing the despread samples with a pilot channelization code to provide pilot symbols,

means for filtering pilot symbols to provide an estimate of a signal instance or channel response, and

means for multiplying the spreading sequence of the signal instance and the estimated channel response to provide an estimated pilot interference caused by the signal instance.

29. An apparatus for canceling pilot interference in a wireless communication system, comprising:

means for processing the pilot-canceled data samples to derive demodulated data for each of at least one signal instance in the received signal, wherein processing the pilot-canceled data samples to derive demodulated data for each of the at least one signal instance comprises

Means for despreading the data samples of the pilot-canceled signal with a spreading sequence of the signal instance,

means for demodulating the data symbols to provide demodulated data for the signal instance.

30. The apparatus of claim 29, wherein subtracting comprises

Interference samples for subtracting total pilot interference from data samples of the received signal, wherein the interference samples and the data samples are both provided at a particular sample rate that is a multiple of the chip rate.