HK1148130A - Minimum finger low-power demodulator for wireless communication - Google Patents

Abstract

Techniques for assigning multipaths to finger processors to achieve the desired data performance and low power consumption are described. A search is initially performed to obtain a set of multipaths for a transmission from at least one base station. At least one multipath (e.g., the minimum number of multipaths) having a combined performance metric (e.g., a combined SNR) exceeding a threshold is identified. The at least one multipath is assigned to, and processed by, at least one finger processor to recover the transmission from the base station(s).

Description

Minimum finger low power demodulator for wireless communications

Technical Field

The present disclosure relates generally to communication, and more specifically to techniques for receiving signals in a wireless communication system.

Background

Wireless communication systems are widely deployed to provide various communication services such as voice, packet data, video, broadcast, messaging, and so on. These systems may be multiple-access systems capable of supporting communication for multiple users by sharing the available system resources. Examples of such multiple-access systems include Code Division Multiple Access (CDMA) systems, Time Division Multiple Access (TDMA) systems, and Frequency Division Multiple Access (FDMA) systems.

Wireless devices, such as cellular telephones, in CDMA systems typically use rake receivers. A rake receiver includes one or more searchers and a plurality of finger processors or fingers. Due to the relatively wide bandwidth of CDMA signals, wireless communication channels are assumed to be composed of a limited number of resolvable signal paths or multipaths. Each multipath is characterized by a particular complex gain and a particular time delay. The searcher searches for stronger multipaths in the received signal and provides multipaths having signal strengths that exceed a particular threshold. The available finger processors are then assigned to the multipaths found by the searcher. Each finger processor processes its assigned multipath and provides symbol estimates for the multipath. The symbol estimates from all assigned finger processors are then combined to obtain combined symbol estimates.

The quality of the combined symbol estimates is typically improved by processing more multipaths and combining the symbol estimates of all of these multipaths. Thus, each multipath with sufficient signal strength is typically assigned to a finger processor (if available) so that as many multipaths as possible are combined. However, each assigned finger processor consumes battery power. In some applications, it is desirable to conserve battery power as much as possible in order to extend battery life.

There is therefore a need in the art for techniques to efficiently operate a rake receiver to achieve good performance while reducing power consumption.

Disclosure of Invention

Techniques for processing multipath with a finger processor in a manner to achieve desired data performance and low power consumption are described herein. In an embodiment, a search is initially performed to obtain a set of multipaths for transmission from at least one base station. At least one multipath (e.g., a minimum number of multipaths) having a combined performance metric that exceeds a threshold is identified. The performance metric may relate to a signal-to-noise ratio (SNR), a signal strength, or some other quantity. The at least one multipath is assigned to and processed by at least one finger processor to recover the transmissions from the base station.

In an embodiment, SNRs for the multipaths in the group are determined, and the multipaths are ordered based on their SNRs. One multipath is assigned at a time, starting with the multipath with the highest SNR, until the combined SNR of all assigned multipaths exceeds a threshold. Such an embodiment may result in a minimum number of multipaths being assigned, and may also provide a maximum margin between the combined SNR and the minimum SNR needed to reliably receive the transmission. The amount of power consumed by the finger processors may scale linearly with the number of finger processors assigned. Power savings may be maximized by assigning the minimum number of finger processors that can achieve the desired data performance.

Various aspects and embodiments of the disclosure are described in further detail below.

Drawings

Aspects and embodiments of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout.

Fig. 1 shows a wireless communication system.

Fig. 2 shows a block diagram of a base station and a wireless device.

Fig. 3 shows the multipath in the received signal on a PN circle.

Fig. 4 shows a block diagram of a rake receiver at a wireless device.

Fig. 5 shows a process for performing minimum finger assignment.

Fig. 6A and 6B show the finger processor implemented in a TDM fashion.

Fig. 7 shows a process for assigning finger processors.

Detailed Description

The word "exemplary" is used herein to mean "serving as an example, instance, or illustration. Any embodiment or design described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments or designs.

Fig. 1 shows an exemplary wireless communication system 100. For simplicity, fig. 1 shows only one base station 110 and one wireless device 120. A base station is typically a fixed station that communicates with the wireless devices and may also be referred to as an access point, a node B, or some other terminology. A wireless device may be stationary or mobile and may also be referred to as a mobile station, a terminal, an access terminal, a User Equipment (UE), a subscriber unit, or some other terminology. The wireless device may be a cellular telephone, a Personal Digital Assistant (PDA), a wireless modem, or some other device or apparatus.

Base station 110 transmits Radio Frequency (RF) signals to wireless device 120. Such an RF signal may reach wireless device 120 via one or more signal paths, which may include direct paths and/or reflected paths. The reflected path is formed by the reflection of radio waves due to obstacles in the wireless environment (e.g., buildings, trees, vehicles, and other structures). Wireless device 120 may receive multiple instances or copies of the transmitted RF signal. Each received signal instance is obtained via a different signal path and has a particular complex gain and a particular time delay determined by the signal path. The RF signal received at the wireless device 120 is a superposition of all received signal instances at the wireless device. The received signal instance is commonly referred to as multipath. The received RF signal may therefore include many multipaths, where the number of multipaths and the strength of each multipath depends on the wireless environment. Wireless device 120 may also receive interfering transmissions from other transmitting stations. One interfering transmission is shown by the dashed line in fig. 1.

The wireless device 120 is also capable of receiving signals from satellites in a satellite positioning system, such as the well-known Global Positioning System (GPS). For simplicity, only one satellite 130 is shown in FIG. 1. Each GPS satellite transmits a GPS signal encoded with information that allows GPS receivers on earth to measure the time of arrival of the GPS signal. Measurements of a sufficient number of GPS satellites may be used to accurately estimate a three-dimensional (3-D) position of a GPS receiver.

The techniques described herein may be used for CDMA systems as well as other systems in which a rake receiver may be used. A CDMA system may implement one or more radio technologies such as CDMA2000, wideband-CDMA (W-CDMA), and so on. cdma2000 covers IS-2000, IS-856, and IS-95 standards. The cdma2000 family of standards is described in a document from an organization named "third generation partnership project 2" (3GPP 2). IS-2000 releases 0 and A are commonly referred to as CDMA20001X (or 1X for short), IS-2000 release C IS commonly referred to as CDMA20001xEV-DV (or 1xEV-DV for short), and IS-856 IS commonly referred to as CDMA20001xEV-DO (or 1xEV-DO for short). W-CDMA is described in a document from an organization named "third generation partnership project" (3 GPP). 3GPP and 3GPP2 use different terminology. For clarity, the techniques are described below for a cdma2000 system, which may be a 1X system, a 1xEV-DO system, or some other system.

Fig. 2 shows a block diagram of a base station 110 and a wireless device 120. At base station 110, a Transmit (TX) data processor 210 receives traffic data and control data/signaling for the wireless device being served, processes (e.g., formats, codes, interleaves, and symbol maps) the traffic and control data to generate data symbols, and provides the data symbols to a CDMA modulator 220. As used herein, a data symbol is a symbol for data, a pilot symbol is a symbol for pilot, and a symbol is typically a complex value. The data symbols and pilot symbols may be modulation symbols from a modulation scheme such as Phase Shift Keying (PSK) or Quadrature Amplitude Modulation (QAM). A pilot is data that is known a priori by both the base station and the wireless device.

CDMA modulator 220 processes the data symbols and pilot symbols and provides output chips. For 1X and 1xEV-DO, the processing by CDMA modulator 220 includes: (1) for each of a plurality of code channels (e.g., traffic, synchronization, paging, and pilot channels), data symbols or pilot symbols are channelized or covered with a different walsh code to channelize the traffic data, control data, and pilot onto their respective code channels, (2) the channelized data for all code channels is summed, and (3) the summed data is spread with a pseudo-random number (PN) sequence at a particular PN offset assigned to the base station. The pilot is typically channelized with an all-zero walsh code. A transmitter (TMTR)230 receives the output chips from CDMA modulator 220, processes (e.g., converts to analog, amplifies, filters, and frequency upconverts) the output chips, and generates an RF signal, which is transmitted from an antenna 232.

At wireless device 120, antenna 252 receives RF signals from base station 110 and possibly from other base stations via direct paths and/or via reflected paths. The antenna 252 provides a received RF signal containing various multipaths to a receiver (RCVR) 254. Receiver 254 processes (e.g., filters, amplifies, frequency downconverts, and digitizes) the received RF signal and provides input samples. The rake receiver 260 processes the input samples in a manner complementary to the processing by the CDMA modulator 220 and provides combined symbol estimates, which are estimates of the data symbols sent by the base station 110 to the wireless device 120. A Receive (RX) data processor 270 processes (e.g., symbol demaps, deinterleaves, and decodes) the combined symbol estimates and provides decoded data. The processing by RX data processor 270 is complementary to that performed by TX data processor 210 at base station 110.

Controllers/processors 240 and 280 direct the operation of various processing units at base station 110 and wireless device 120, respectively. Memories 242 and 282 store data and program codes for base station 110 and wireless device 120, respectively.

Fig. 3 shows a circle representing the entire code space of the PN sequence used by the base station 110 for spreading. In cdma2000, the PN sequence is a specific sequence of 32,768 chips. Each chip is assigned a particular index and corresponds to a different phase of the PN sequence. The first chip of the PN sequence is assigned an index of 0 and the last chip of the PN sequence is assigned an index of 32,767. The PN sequence can be conceptually viewed as being placed on the circumference 310 of the circle with the start of the PN sequence aligned to the top of the circle such that the PN chip index 0 is at the top of the PN circle. Although not shown in fig. 3, the circumference 310 is divided into 32,768 evenly spaced points, and each point corresponds to a different PN phase. The PN sequence is traversed by moving around the PN circle in a clockwise direction along the circumference 310.

Fig. 3 also shows an exemplary received signal 320 of wireless device 120. Received signal 320 includes a number of peaks corresponding to a number of multipaths or signal instances. Each multipath is associated with a particular magnitude, a particular phase, and a particular time of arrival, all of which are determined by the wireless environment. The arrival times T of four multipaths are shown in FIG. 3₁To T₄. The arrival time may be given in terms of PN phase or offset.

Fig. 4 shows a block diagram of an embodiment of a rake receiver 260 at the wireless device 120. Rake receiver 260 comprises a searcher 410, a plurality R of finger processors 430a through 430R, and a symbol combiner 450. The finger processors 430 are commonly referred to as fingers.

Searcher 410 searches for the stronger signal instances (or multipaths) in the received signal and provides the strength and timing of each discovered multipath that meets a set of criteria. To search for strong multipaths, the input samples are correlated with a locally generated PN sequence at various phases. Due to the pseudo-random nature of the PN sequence, the correlation of the input samples with the PN sequence should be low except when the phase of the locally generated PN sequence is approximately aligned with the PN phase of the multipath, where the correlation yields a high value. Searcher 410 evaluates various PN phases to search for multipath in the received signal.

Within searcher 410, a rotator 412 multiplies the input samples from receiver 254 with a complex sinusoidal signal and provides frequency converted samples to a sample buffer 414. Rotator 412 removes phase rotation in the input samples due to doppler shift and/or down conversion error. For each PN phase, a despreader 416 receives samples from sample buffer 414, multiplies the samples by a PN segment from a PN generator 418, and provides despread samples. The PN segment is a portion of the PN sequence that is at the PN phase being evaluated. A pilot decover 420 multiplies the despread samples with the walsh code for pilot and further accumulates Nc resulting samples for each group to obtain pilot symbol estimates, where Nc is an integer multiple of the pilot walsh code length. Unit 422 calculates the squared magnitude of the pilot symbol estimates. Accumulator (Acc)424 accumulates the Nnc squared magnitude values from unit 422 and provides a pilot energy estimate of the PN phase being evaluated to buffer 426.

After all PN phases have been evaluated, peak detector 428 examines the pilot energy estimates for all PN phases from buffer 426 and provides a set of detected peaks. Peak detector 428 may compare the pilot energy estimate for each PN phase to an energy threshold and provide the PN phase as the detected peak if the pilot energy estimate exceeds the energy threshold. Each detected peak corresponds to a multipath at a particular PN phase or time of arrival. Searcher 410 may again measure each detected peak to confirm the presence of multipath before providing search results.

Each finger processor 430 may be assigned to process a different multipath of interest, e.g., as determined by controller 280. Within each assigned finger processor 430, a sampler 432 resamples the input samples from the receiver 254 based on the timing error estimate from the time tracking loop 434 and provides the samples at the appropriate timing. Rotator 436 multiplies the samples from unit 432 with a complex sinusoidal signal from frequency control loop 438 and provides frequency converted samples. The time tracking loop 434 tracks the timing of the assigned multipath as it moves due to changes in channel conditions. The frequency control loop 438 tracks the residual frequency error due to doppler shift and down conversion error.

Despreader 440 multiplies the frequency-converted samples from rotator 436 with a PN sequence at a particular PN phase corresponding to the arrival time of the assigned multipath and provides despread samples. Pilot decover 446 multiplies the despread samples with the pilot walsh code and further accumulates Np resulting samples to obtain decovered pilot symbols, where Np is an integer multiple of the pilot walsh code length. Pilot filter 448 filters the decovered pilot symbols and provides pilot estimates, which indicate the complex channel gains of the assigned multipaths. A data decover 442 multiplies the despread samples with the walsh code for the traffic channel, accumulates the resulting samples over the length of the data walsh code, and provides decovered data symbols. A data demodulator (Demod)444 performs data demodulation on the decovered data symbols with the pilot estimates and provides symbol estimates. A symbol combiner 450 receives and combines the symbol estimates from all assigned finger processors and provides a combined symbol estimate. Although not shown in fig. 4 for simplicity, many of the quantities within the rake receiver 260 are complex values having in-phase (I) and quadrature (Q) components.

In general, if more multipaths of sufficient strength are processed and combined, thatBut the quality of the combined symbol estimates from the symbol combiner 450 improves. The signal quality may be represented by a signal-to-noise ratio (SNR), a signal-to-total noise-and-interference ratio (SNIR), an energy-per-symbol-to-total noise-and-interference ratio (E)_s/N_t) Or some other metric. The signal quality may also be determined by the received signal strength of the traffic data (traffic E)_s/I_o) Or pilot signal strength (pilot E)_s/I_o) And (4) approximation. The wireless device 120 typically performs Automatic Gain Control (AGC) such that the total received power (I)_o) Which includes the desired signal as well as noise and interference, is maintained at a fixed level. The signal strength is also referred to as received signal strength, received signal level, received power, etc. For clarity, SNR is used in much of the description below to represent signal quality.

To maximize the SNR of the combined symbol estimates, each detected multipath is assigned to a finger processor if its signal strength or SNR exceeds a certain threshold. The combined SNR (also referred to as the accumulated SNR or total SNR) of the combined symbol estimates is determined by the SNR of all assigned multipaths. In many operating scenarios, four or more multipaths may be assigned to the finger processors due to complex multipath channel conditions. Since the energy of the pilot, traffic data, and control data is typically combined across all assigned finger processors, the amount of battery power consumed by the assigned finger processors scales linearly with the number of assigned finger processors.

In many operating scenarios, a large portion of the signal energy resides in one or a few primary multipaths, and the remaining non-primary multipaths may be much smaller in amplitude than the primary multipaths, e.g., as shown in fig. 3. In these scenarios, a large portion of the combined SNR may come from the dominant multipath, and the non-dominant multipath may contribute less to the combined SNR. Each assigned finger processor consumes an approximately equal amount of battery power. Thus, processing non-dominant multipaths may yield a smaller improvement in data performance, but consume a relatively larger amount of battery power. For example, eight finger processors may be assigned to two primary multipaths and six non-primary multipaths. The two finger processors assigned to the two dominant multipaths may provide most of the combined SNR. The other six finger processors may contribute less to the combined SNR but consume three times the power of the other two finger processors.

For some applications, low power consumption may be highly desirable or necessary. For example, a wireless device may be used as a monitoring or tracking device that is attached to a precious object (asset) to be monitored or tracked. The wireless device may periodically receive a low rate control channel, for example, for system information or satellite information such as almanac and/or ephemeris information for GPS satellites. It may be desirable to have low power consumption so that the wireless device can operate on available battery power for long periods of time in the field.

In an embodiment, multipath is assigned to the finger processors so that desired data performance can be achieved while consuming as little battery power as possible. Finger assignment may be performed in various ways and using various criteria.

In an embodiment, a minimum number of multipaths are assigned to the finger processors to achieve reliable data reception. Wireless device 120 may receive transmissions sent at a particular rate on a traffic channel or a control channel. This rate is associated with a certain minimum signal quality required to reliably receive the transmission. For example, the rate may be associated with a certain minimum SNR needed to receive a transmission at a certain target Packet Error Rate (PER) in an Additive White Gaussian Noise (AWGN) channel. This minimum SNR is referred to as a desired SNR and may be determined by computer simulation, empirical measurements, and/or other means.

Fig. 5 shows an embodiment of a process 500 for performing a minimum finger assignment. A search is performed and a set of multipaths (or peaks) is obtained (block 512). The SNR for each multipath is estimated (block 514). The multipaths in the reached group are then ordered based on their SNRs, e.g., in descending order from highest SNR to lowest SNR (block 516).

The minimum number of multipaths is then assigned to the finger processor. The multipath with the highest SNR in the group is initially selected (block 518) and assigned to the finger processor (block 520). The combined SNR for all assigned multipaths is determined (block 522). For the first assigned multipath, the combined SNR is equal to the SNR of that multipath. For each subsequent assigned multipath, the combined SNR is determined by the SNRs of all assigned multipaths, as described below. A determination is then made whether the combined SNR is greater than or equal to the desired SNR for the transmission being received (block 524). If the answer is "yes," then the process terminates. Otherwise, if the combined SNR has not reached the desired SNR, then the just selected multipath is removed from the group (block 526). The group is thus updated to include only unassigned multipaths. The process then returns to block 518 to select and assign the multipath with the highest SNR in the updated set.

The embodiment in fig. 5 assigns a minimum number of multipaths to the finger processor such that the combined SNR of the assigned multipaths meets or exceeds the SNR required by the transmission being received. This is achieved by ordering the multipaths and considering one multipath at a time starting with the multipath with the highest SNR. This embodiment also provides maximum SNR margin with a minimum number of multipaths. The SNR margin is the difference between the combined SNR and the desired SNR.

In another embodiment, multipath is assigned to the finger processor based on the combined signal strength of the traffic data or pilots. In this embodiment, the signal strength of each multipath may be determined in block 514, and the multipaths may be ordered based on their signal strengths. For each multipath selected in block 518 and assigned in block 520, a combined signal strength for all assigned multipaths is determined in block 522. The combined signal strength can then be compared to the signal strength required for the transmission being received. The desired signal strength may be determined by computer simulation, empirical measurements, and/or other means. One multipath is assigned at a time until the combined signal strength meets or exceeds the desired signal strength. Multipath may also be assigned based on other performance metrics.

In the embodiments described above, the number of multipaths assigned to the finger processors depends on the SNR or signal strength of the multipaths and the desired SNR of the transmission being received. A system (e.g., a 1X or 1xEV-DO system) may support a set of rates with different required SNRs for successful demodulation and decoding. The system may also support Low Duty Cycle (LDC) operation using a lower rate with a lower required SNR than in the conventional rate set. For example, a broadcast rate of 307.2 kilobits per second (kbps) for LDC may require an SNR of approximately-3.5 dB to successfully decode with a lower number of iterations. The rates of 38.4kbps and 78.8kbps may have even lower required SNRs. Fewer finger processors may be assigned for lower rates with lower required SNRs. This is beneficial for low power applications that utilize low rates. Wireless device 120 may store a look-up table of desired SNRs for different rates and may obtain the desired SNR for the rate of the transmission being received from this look-up table.

The finger processors may be assigned and operated in various ways. In an embodiment (also referred to as a fixed finger assignment scheme), detected multipaths are assigned to finger processors (e.g., as described above for fig. 5), and only the assigned multipaths are processed by the assigned finger processors and combined. In this embodiment, all assigned finger processors are enabled and operational. Whenever new search results are available, new multipaths may be assigned and existing multipaths may be de-assigned. In this embodiment, each finger processor is (1) assigned and enabled, or (2) unassigned and not enabled, or disabled.

In another embodiment, also referred to as a dynamic finger assignment scheme, detected multipaths are assigned to the finger processors in the normal manner. For example, a detected multipath may be assigned if its signal strength or SNR exceeds a threshold. Each finger processor may perform pilot processing and track the frequency and timing of its assigned multipath. However, only a subset of the assigned fingers may be enabled to perform data processing on the assigned multipaths. Pilot processing may include blocks 432 through 440 and 446 in fig. 4, data processing may include blocks 442, 444 and 448, and data and pilot processing may include blocks 432 through 448. If the pilot is Time Division Multiplexed (TDM) with traffic data and transmitted in short bursts (e.g., in 1xEV-DO), only a small amount of power may be consumed to perform pilot processing. In this embodiment, each finger processor is (1) assigned and enabled, (2) assigned but not enabled, or (3) unassigned and not enabled, or disabled.

In one embodiment, searcher 410 and finger processors 430a through 430r are implemented in dedicated hardware. In this embodiment, the finger processors 430 a-430 r may each be assigned to process different multipaths. Finger processors that are not assigned to any multipaths or assigned but not enabled may be powered down to conserve battery power.

In another embodiment, the finger processors 430a through 430r and (possibly) the searcher 410 are implemented in shared hardware. For example, a Digital Signal Processor (DSP) may implement finger processors 430a through 430r in a TDM manner. The timeline may be divided into time segments, and each time segment may be further divided into R slots 1-R. The DSP may perform the processing for finger processor 430a in time slot 1 for each time segment, the processing for finger processor 430b in time slot 2 for each time segment, and so on, and the processing for finger processor 430R in time slot R for each time segment. The DSP may be disabled during time slots for finger processors that are not assigned to any multipath or assigned but not enabled to conserve battery power. For digital circuits, power consumption is related to the number of clock cycles, and disabling digital circuits reduces power consumption. The DSP may also implement a sample/store/offline processing architecture in which samples are collected during the time slot in which the transmission is sent, and the collected samples are stored, and thereafter processed offline.

Fig. 6A shows an embodiment of operating a DSP for a fixed finger assignment scheme. The DSP implements R finger processors 1 through R in a TDM manner. M finger processors 1 through M are assigned and enabled to process M multipaths, where 1 ≦ M ≦ R. The schedule for pilot and data processing may be sent to the DSP sequentially for only the M enabled finger processors. Scheduling is a command to perform pilot and/or data processing for the finger processor.

Fig. 6B shows an embodiment of operating a DSP for a dynamic finger assignment scheme. M finger processors 1 through M are assigned and enabled to process M multipaths, and N finger processors M +1 through M + N are assigned but not enabled. The schedule for pilot and data processing may be sent to the DSP sequentially for the M enabled finger processors. Scheduling for pilot processing (but not for data processing) may be sent to the DSP for the N assigned, but not enabled, finger processors. No schedule is sent to the DSP for unassigned finger processors.

In the embodiment shown in fig. 6A and 6B, the finger schedules may be ordered from highest to lowest SNR or signal strength. In an embodiment, a combined SNR or signal strength may be determined after each finger scheduling and compared to a desired SNR or signal strength. A minimum number of finger schedules may then be sent such that a desired SNR or signal strength is achieved. In another embodiment, a combined SNR or signal strength is determined in each time period and used to determine a finger assignment for the next time period. The finger processors may also be dynamically assigned in other ways. The number of finger processors enabled may be dynamically selected as channel conditions change.

In another embodiment, finger processors 430a through 430r are implemented with a combination of dedicated hardware and shared hardware. For all embodiments, unassigned or not enabled finger processors may be powered down to conserve battery power.

Multipath may be assigned based on various performance metrics such as SNR, signal strength, and the like. The SNR and signal strength may be estimated in various ways. For clarity, several exemplary estimation schemes are described below. In the following description, M finger processors 1 through M are assigned and enabled to process M multipaths. M may correspond to the number of multipaths selected and assigned in block 522 of fig. 5.

Referring back to fig. 4, the data demodulator 444 for finger processor m may perform data demodulation as follows:

S_I，m(n)+jS_Q，m(n)＝[D_I，m(n)+jD_Q，m(n)]·[H_I，m(n)+jH_Q，m(n)]^*equation (1)

Wherein D_I，m(n)+jD_Q，m(n) is the decovered complex data symbol from data decoverer 442 in finger processor m during symbol period n,

H_I，m(n)+jH_Q，m(n) is the complex pilot estimate from pilot filter 448 in finger processor m during symbol period n,

S_I，m(n)+jS_Q，m(n) is a complex symbol estimate from data demodulator 444 in finger processor m over symbol period n, and

"+" indicates the complex conjugate.

The subscripts I and Q represent the in-phase and quadrature components, respectively.

Symbol combiner 450 may combine the symbol estimates from the M assigned finger processors as follows:

equation (2)

Wherein S_I(n)+jS_Q(n) is the complex combined symbol estimate over symbol period n.

Data demodulation in equation (1) scales the symbol estimates for each finger processor according to the pilot signal strength of the multipath assigned to that finger processor. This pilot scaling results in the symbol estimates for the M finger processors being weighted appropriately prior to combining in equation (2). Pilot scaling results in the multipath with stronger pilot signal strength being given greater weight in the combined symbol estimate.

In an embodiment, the SNR of the symbol estimates (or traffic SNR) is used for finger assignment. The traffic SNR for finger processor m may be expressed as:

businessEquation (3)

Wherein the service E_s，mEnergy per data symbol for finger processor m, and

N_t，mis the total noise and interference of finger processor m.

Traffic E may be estimated in various ways_s，mAnd N_t，m. In an embodiment, traffic E may be estimated as follows_s，m：

BusinessEquation (4)

Where N is used to average to obtain a service E_s，mThe number of decovered data symbols.

In an embodiment, N may be estimated as follows_t，m：

Equation (5)

Wherein X_I，m(i)+jX_Q，m(i) Is a despread complex sample from despreader 440 in finger processor m within a sampling period i, and

l is for accumulating to obtain N_t，mThe number of samples of (a).

In another embodiment, N may be estimated as follows_t，m：

Equation (6)

Equation (6) calculates the difference between consecutive decovered pilot symbols, then calculates the power of the pilot difference, and then averages the pilot difference powers to obtain N_t，m。

Equation (3) gives the traffic SNR for each finger processor. In an embodiment, the combined SNR for all M finger processors may be estimated as follows:

combination ofEquation (7)

Wherein beta is_mAre weighting factors that are applied to the symbol estimates from finger processor m prior to combining by symbol combiner 450. For the symbol scaling and combining shown in equations (1) and (2), the weighting factor for finger processor m can be expressed as:

equation (8)

Where avg < > represents the averaging operation.

In another embodiment, the combined SNR is the sum of the individual SNRs of the M finger processors, and may be expressed as:

combination ofEquation (9)

Equation (9) gives the actual combined SNR at which the best combination occurs. Equation (9) may provide a sufficiently accurate estimate of the combined SNR even when the combination is not optimal.

In another embodiment, the SNR of the pilot estimate (or pilot SNR) is used for finger assignment. The pilot SNR for finger processor m may be expressed as:

pilot frequencyEquation (10)

Wherein the pilot frequency E_s，mThe energy per pilot symbol for finger processor m. Pilot E may be estimated as follows_s，m：

Pilot frequencyEquation (11)

The combined SNR for all M finger processors may then be estimated as shown in equation (7) or equation (9), but with pilot E_s，mTo replace service E_s，m。

In yet another embodiment, pilot signal strength is used for finger assignment. The pilot signal strength may be calculated as shown in equation (11). The combined pilot signal strength may then be calculated as follows:

equation (12)

Measurements of pilot and/or traffic data may be made before and/or after multipath is assigned to the finger processors. In embodiments that may be used for a fixed finger assignment scheme, measurements are made prior to finger assignment whenever a new detected multipath is available. In another embodiment, which may be used for a dynamic finger assignment scheme, measurements are made after finger assignment and used to determine which finger processors are enabled. In this embodiment, multiple thresholds may be used to provide hysteresis so that a given finger processor is not constantly enabled and disabled due to random fluctuations in measurements. For example, if the combined SNR is less than a first threshold, the finger processor may be enabled, and if the combined SNR is greater than a second threshold that is higher than the first threshold, the finger processor may not be enabled. Measurements may also be made both before and after finger assignment. For example, measurements may be made prior to finger assignment to determine which multipaths to assign to the finger processors, and measurements may also be made periodically after finger assignment to determine whether the combined SNR is too low, which may trigger a new search for multipaths.

Fig. 7 shows an embodiment of a process 700 for assigning finger processors. For example, a set of multipaths for transmission from at least one base station is obtained by performing a search to detect multipaths (block 712). At least one multipath (e.g., a minimum number of multipaths) in the set having a combined performance metric that exceeds a threshold is identified (block 714). The combined performance metric may relate to the SNR of the transmission from the base station, the SNR or signal strength of the pilot from the base station, or some other quantity. The at least one multipath is assigned to and processed by at least one finger processor to recover transmissions from the base station (block 716).

In the embodiments of blocks 714 and 716, SNRs for multipaths in the group are determined, and the multipaths are ordered based on their SNRs. One multipath at a time is assigned, starting with the multipath with the highest SNR, until the combined SNR of all assigned multipaths exceeds the threshold. Multipaths may be identified and assigned each time a new set of multipaths is obtained. Alternatively, multipaths may be identified and assigned in each time interval.

The techniques described herein may be implemented by various means. For example, these techniques may be implemented in hardware, firmware, software, or a combination thereof. For a hardware implementation, the processing units used to perform finger assignments and the finger processors may be implemented within one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, electronic devices, other electronic units designed to perform the functions described herein, or a combination thereof.

For a firmware and/or software implementation, the techniques may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The firmware and/or software codes may be stored in a memory (e.g., memory 282 in fig. 2) and executed by a processor (e.g., processor 280). The memory may be implemented within the processor or external to the processor.

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

Claims (28)

1. An apparatus, comprising:

at least one processor configured to obtain a set of multipaths for transmission from at least one base station, identify at least one multipath of the set having a combined performance metric that exceeds a threshold, and process the at least one multipath with at least one finger processor to recover the transmission from the at least one base station; and a memory coupled to the at least one processor.

2. The apparatus of claim 1, wherein the at least one processor is configured to perform a search for the set of multipaths.

3. The apparatus of claim 1, wherein the combined performance metric relates to a signal-to-noise ratio (SNR) of the transmissions from the at least one base station.

4. The apparatus of claim 1, wherein the combined performance metric relates to a signal-to-noise ratio (SNR) of pilots from the at least one base station.

5. The apparatus of claim 1, wherein the combined performance metric relates to signal strength of pilots from the at least one base station.

6. The apparatus of claim 1, wherein the at least one processor is configured to determine signal-to-noise ratios (SNRs) of the multipaths in the set, and to identify a minimum number of multipaths in the set having a combined SNR that exceeds the threshold.

7. The apparatus of claim 6, wherein the at least one processor is configured to order the multipaths based on the SNRs, and to assign one multipath at a time to a finger processor starting with a multipath with highest SNR until the combined SNR of all assigned multipaths exceeds the threshold.

8. The apparatus of claim 1, wherein the at least one processor is configured to identify and assign the at least one multipath whenever a new set of multipaths is obtained.

9. The apparatus of claim 1, wherein the at least one processor is configured to identify and assign the at least one multipath in each of a plurality of time intervals.

10. The apparatus of claim 1, wherein the at least one finger processor is among a plurality of finger processors available for assignment, and wherein the at least one processor is configured to enable the at least one finger processor to process the at least one multipath and disable remaining ones of the plurality of finger processors.

11. The apparatus of claim 1, wherein the at least one processor is configured to perform pilot and data processing for the at least one multipath with the at least one finger processor, and to perform pilot processing for remaining multipaths in the set with at least one other finger processor.

12. The apparatus of claim 1, wherein the at least one processor is configured to: implementing a plurality of finger processors with Time Division Multiplexing (TDM), each finger processor being assigned a respective time slot; and processing by each of the at least one finger processor is performed in time slots allocated for the finger processor.

13. The apparatus of claim 12, wherein the at least one processor is configured to process one multipath at a time starting with a multipath with highest signal-to-noise ratio (SNR).

14. The apparatus of claim 12, wherein the at least one processor is configured to process one multipath at a time, to update a combined signal-to-noise ratio (SNR) after processing each multipath, and to skip processing of remaining multipaths when the combined SNR exceeds the threshold.

15. A method, comprising:

obtaining a set of multipaths for transmission from at least one base station;

identifying at least one multipath of the set having a combined performance metric that exceeds a threshold; and

processing the at least one multipath with at least one finger processor to recover the transmission from the at least one base station.

16. The method of claim 15, wherein the identifying the at least one multipath comprises:

determining a signal-to-noise ratio (SNR) of the multipaths in the group, an

Identifying a minimum number of multipaths in the group having a combined SNR that exceeds the threshold.

17. The method of claim 15, further comprising:

enabling the at least one finger processor to process the at least one multipath; and

finger processors not assigned to any multipath are disabled.

18. The method of claim 15, wherein the processing the at least one multipath comprises:

performing pilot and data processing for the at least one multipath with the at least one finger processor.

19. The method of claim 15, further comprising:

pilot processing for the remaining multipaths in the group is performed with at least one other finger processor.

20. An apparatus, comprising:

means for obtaining a set of multipaths for transmission from at least one base station;

means for identifying at least one multipath of the set having a combined performance metric that exceeds a threshold; and

means for processing the at least one multipath with at least one finger processor to recover the transmission from the at least one base station.

21. The apparatus of claim 20, wherein the means for identifying the at least one multipath comprises:

means for determining a signal-to-noise ratio (SNR) of the multipaths in the group, and

means for identifying a minimum number of multipaths in the group having a combined SNR that exceeds the threshold.

22. The apparatus of claim 20, further comprising:

means for enabling the at least one finger processor to process the at least one multipath; and

means for disabling finger processors that are not assigned to any multipath.

23. The apparatus of claim 20, wherein the means for processing the at least one multipath comprises:

means for performing pilot and data processing for the at least one multipath with the at least one finger processor.

24. The apparatus of claim 20, further comprising:

means for performing pilot processing for remaining multipaths in the group with at least one other finger processor.

25. A processor-readable medium for storing instructions operable to:

obtaining a set of multipaths for transmission from at least one base station;

identifying at least one multipath of the set having a combined performance metric that exceeds a threshold; and

assigning the at least one multipath to at least one finger processor for processing to recover the transmission from the at least one base station.

26. The processor-readable medium of claim 25, and further for storing instructions operable to:

obtaining signal-to-noise ratios (SNRs) of the multipaths in the group, an

Identifying a minimum number of multipaths in the group having a combined SNR that exceeds the threshold.

27. A wireless device, comprising:

a controller operative to identify at least one multipath from a set of multipaths having a combined performance metric that exceeds a threshold; and

a plurality of finger processors, wherein at least one of the finger processors is enabled to process the at least one multipath and remaining ones of the finger processors are disabled when not assigned to any multipath.

28. The wireless device of claim 27, wherein the controller identifies a minimum number of multipaths in the set having a combined signal-to-noise ratio (SNR) that exceeds the threshold.