Adaptive path selection for interference cancellation

Adaptive path selection for interference cancellation is provided for wireless communication devices. Signal strength metrics are obtained for each of multiple signal paths. One or more of the signal paths are selected as cancellation candidates in response to determining that the signal paths are associated with a strong interfering path based at least in part on the signal strength metrics for the signal paths and threshold criteria. Cancellation is enabled for an estimated signal generated using the signal paths in response to the signal paths being selected as cancellation candidates.

BACKGROUND

Wideband code division multiple access (WCDMA) is a third generation (3G) cellular technology that enables the concurrent transmission of a plurality of distinct digital signals via a common RF channel. WCDMA supports a range of communications services that include voice, high speed data and video communications. One such high speed data communications service, which is based on WCDMA technology, is the high speed downlink packet access (HSDPA) service.

WCDMA is a spread spectrum technology in which each digital signal is coded or “spread” across the RF channel bandwidth using a spreading code. Each of the bits in the coded digital signal is referred to as a “chip.” A given base transceiver station (BTS), which concurrently transmits a plurality of distinct digital signals, may encode each of a plurality of distinct digital signals by utilizing a different spreading code for each distinct digital signal. At a typical BTS, each of these spreading codes is referred to as a Walsh code. The Walsh coded digital signal may in turn be scrambled by utilizing a pseudo-noise (PN) bit sequence to generate chips. An example of a PN bit sequence is a Gold code. Each of a plurality of BTS within an RF coverage area may utilize a distinct PN bit sequence. Consequently, Walsh codes may be utilized to distinguish distinct digital signals concurrently transmitted from a given BTS via a common RF channel while PN bit sequences may be utilized to distinguish digital signals transmitted by distinct BTSs. The utilization of Walsh codes and PN sequences may increase RF frequency spectrum utilization by allowing a larger number of wireless communications to occur concurrently within a given RF frequency spectrum. Accordingly, a greater number of users may utilize mobile communication devices, such as mobile telephones, Smart phones and/or wireless computing devices, to communicate concurrently via wireless communication networks.

A user utilizing a mobile communication device may be engaged in a communication session with a user utilizing a first mobile communication device via a base transceiver station within a wireless communication network. For example, the mobile communication device may transmit a digital signal to the base transceiver station, which the base transceiver station may then transmit to a second mobile communication device. The base transceiver station may encode signals received from the second mobile communication device and transmitted to the mobile communication device by utilizing a Walsh code and a PN sequence. The second mobile communication device may receive signals transmitted concurrently by multiple base transceiver stations in addition to the base transceiver station within a given RF coverage area. The second mobile communication device may process the received signals by utilizing a descrambling code that is based on the PN sequence and a despreading code that is based on the Walsh code. In doing so, the second mobile communication device may detect a highest relative signal energy level for signals received from base transceiver station, which comprise a digital signal corresponding to the first mobile communication device.

However, the second mobile communication device may also detect signal energy from the digital signals, which correspond to signals from mobile communication devices other than the first mobile communication device. The other signal energy levels from each of these other mobile communication devices may be approximated by Gaussian white noise, but the aggregate noise signal energy level among the other mobile communication device may increase in proportion to the number of other mobile communication devices whose signals are received at the second mobile communication device. This aggregate noise signal energy level may be referred to as multiple access interference (MAI). The MAI may result from signals transmitted by the base transceiver station, which originate from signal received at the base transceiver station from mobile communication devices other than the first mobile communication device. The MAI may also result from signals transmitted by the base transceiver stations BTSs other than the base transceiver station. The MAI and other sources of noise signal energy may interfere with the ability of the second mobile communication device to successfully decode signals received from the first mobile communication device.

An additional source of noise signal energy may result from multipath interference. The digital signal energy corresponding to the second mobile communication device, which is transmitted by the base transceiver station may disperse in a wavefront referred to as a multipath. Each of the components of the multipath may be referred to as a multipath signal. Each of the multipath signals may experience a different signal propagation path from the base transceiver station to the second mobile communication device. Accordingly, different multipath signals may arrive at different time instants at the second mobile communication device. The time duration, which begins at the time instant that the first multipath signal arrives at the second mobile communication device and ends at the time instant that the last multipath signal arrives at the second mobile communication device, is referred to as a delay spread. The second mobile communication device may utilize a rake receiver that allows the second mobile communication device to receive signal energy from a plurality of multipath signals received within a receive window time duration. The receive window time duration may comprise at least a portion of the delay spread time duration. Multipath signals that are not received within the receive window time duration may also contribute to noise signal energy.

DETAILED DESCRIPTION

The present disclosure relates to adaptive path selection for interference cancellation in a spread-spectrum wireless communication system such as WCDMA and HSDPA. Interference cancellation may be employed to improve the performance of spread-spectrum wireless communication receivers using code division multiple access (CDMA). Interfering signals from other cells using different scrambling codes may be detected and reconstructed. The reconstructed interfering signal may then be subtracted from the desired signal, thereby increasing the quality of the desired signal. Various techniques for such interference cancellation are described in U.S. Patent Application entitled “METHOD AND SYSTEM FOR PROCESSING SIGNALS UTILIZING A PROGRAMMABLE INTERFERENCE SUPPRESSION MODULE,” having Ser. No. 12/612,272, and filed on Nov. 4, 2009, which is incorporated by reference herein in its entirety.

The objective of the interference cancellation is to improve the desired signal quality at the receiver. The interference within the received signal may be divided, for example, into two categories: intra-cell interference, where the interference comes from the multipath signals originally transmitted from the desired cell; and inter-cell interference, where the interference comes from multipath signals originally transmitted from cells other than the desired cell. Interference cancellation logic may be configured to carry out both intra-cell and inter-cell interference cancellation. In this scenario, the interference cancellation logic may be used as a standalone block in the receiver or in conjunction, for example, with a rake and/or equalizer. The interference cancellation logic may alternatively be configured to carry out only inter-cell interference cancellation. In this scenario, the interference cancellation logic may be used in conjunction, for example, with either a rake and/or an equalizer, which may be configured to suppress the intra cell interference. In either case, the interference cancellation logic is provided channel estimates by a source such as a rake, cluster path processor, or other source of channel estimates.

In the scenario where the interference cancellation logic is used standalone, the interference cancellation logic reconstructs the desired signal while suppressing the interfering signals and provides a clean signal to a despreader for further processing. In the scenario where the interference cancellation logic is used at the front end of the overall receiver, the interference cancellation logic provides a signal that is clean of inter-cell interference at the input of the rake receiver and/or at the input of the HSDPA receiving chain, which may, for example, contain an equalizer. In both of these scenarios, the block error rate performance and/or HSDPA throughput (i.e., data rate) may be improved for a given signal-to-noise ratio.

Under some conditions, however, if the interference cancellation logic is configured to cancel inter-cell and/or intra-cell interference unconditionally, the interference cancellation may result in a suboptimal performance gain compared to a configuration for conditional interference cancellation. Under such conditions or other conditions where the interference cancellation logic is used with a rake and/or equalizer, the interference cancellation may result in performance degradation rather than gain. In such cases, it may be desirable to operate with either the rake and/or equalizer without the interference cancellation until conditions again become favorable for interference cancellation to be used at the front end. For example, an interfering signal path may be too weak or too noisy to enable accurate reconstruction of the interfering signal within the interference cancellation logic. Cancellation of the reconstructed signal in such a case may adversely impact the desired signal.

Various embodiments of the present disclosure introduce path admission logic to selectively control the interference cancellation. To this end, various gating factors may be employed between the path management and the path cancellation as part of the interference cancellation system. Interfering signal paths that are too weak or too noisy may be left in the signal. The signal paths may be assessed individually (per finger) or jointly (per cell). Additionally, the interference cancellation logic, when used with a rake and/or equalizer, may be disabled or bypassed when it is not being used, which may reduce power consumption.

FIG. 1is a drawing of an exemplary wireless communication system, in accordance with an embodiment of the present disclosure. Referring toFIG. 1, there is shown a cell100and a base station C106. The cell100comprises base station A102, mobile communication device MU_1112and mobile communication device MU_2114. The base station106may be located outside of the cell100.

The mobile communication devices MU_1112and MU_2114may be engaged in a communication via the base station A102. The mobile communication device MU_1112may transmit signals to the base station A102via an uplink RF channel122. In response, the base station A102may transmit signals to the mobile communication device MU_2114via a downlink RF channel124. Signals transmitted by the base station A102may communicate chips that are generated utilizing a scrambling code PN_A. The signals transmitted via RF channel124may be spread utilizing a spreading code WC_12. The spreading code WC_12may comprise an orthogonal variable spreading factor (OVSF) code, for example, a Walsh code, which enables the mobile communication device MU_2114to distinguish signals transmitted by the base station A102via the downlink RF channel124from signals transmitted concurrently by the base station A102via other downlink RF channels, for example downlink RF channel126.

The base station A102may utilize one or more OVSF codes, WC_other, when spreading data transmitted via downlink RF channel126. The one or more OVSF codes, WC_other, may be distinct from the OVSF code WC_12. The base station A102may also transmit broadcast signals which may be received by all mobile communication devices. The broadcast signals, spread by OVSF code, WC_broadcast, may be sent simultaneously on downlink RF channels124and126.

The mobile communication device MU_2114may receive multiple access interference (MAI) signals from RF channel126and/or RF channel130. As stated above, the signals received via RF channel126may be transmitted by the base station A102. The signals received via RF channel130may be transmitted by the base station C106. The signals transmitted by the base station C106may be scrambled based on a scrambling code PN_C.

The mobile communication device MU_2114may be operable to perform a soft handoff from the current serving base station A102to a base station, which is outside of the cell100, for example, the base station C106. Accordingly, the mobile communication device MU_2114may be operable to process received signals based on scrambling code PN_C. In this regard, MU_2114may listen for signals from base station C106.

In various embodiments, the mobile communication device MU_2may comprise suitable logic, circuitry and/or code that are operable to receive signal energy via the RF channels124,126, and/or130, and suppress interference signal energy received via the RF channels126and/or130. The mobile communication device MU_2may utilize an iterative method for interference cancellation. The iterative method may comprise a weighting iteration, one or more addback, weighting, and un-addback iterations, and an addback iteration.

AlthoughFIG. 1depicts communication between two mobile devices via a single BTS, the present disclosure is not so limited. For example, aspects of the present disclosure may be equally applicable regardless of the origin of data communicated wirelessly to the mobile communication device114.

FIG. 2is a diagram of an exemplary wireless communication device, which may utilize interference suppression, in accordance with various embodiments. Referring toFIG. 2, there is shown a transceiver system200, a receiving antenna222and a transmitting antenna232. The transceiver system200may comprise at least a receiver202, a transmitter204, a processor206, an interference cancellation module210and a memory208. Although a separate receiver202and transmitter204are illustrated byFIG. 2, the present disclosure is not limited. In this regard, the transmit function and receive function may be integrated into a single transceiver block. The transceiver system200may also comprise a plurality of transmitting antennas and/or a plurality of receiving antennas, for example to support diversity transmission and/or diversity reception. Various embodiments may comprise a single antenna, which is coupled to the transmitter204and receiver202via a transmit and receive (T/R) switch. The T/R switch may selectively couple the single antenna to the receiver202or to the transmitter204under the control of the processor206, for example.

The receiver202may comprise suitable logic, circuitry, interfaces and/or code that may be operable to perform receive functions that may comprise PHY layer function for the reception or signals. These PHY layer functions may comprise, but are not limited to, the amplification of received RF signals, generation of frequency carrier signals corresponding to selected RF channels, for example uplink or downlink channels, the down-conversion of the amplified RF signals by the generated frequency carrier signals, demodulation of data contained in data symbols based on application of a selected demodulation type, and detection of data contained in the demodulated signals. The RF signals may be received via the receiving antenna222. The receiver202may be operable to process the received RF signals to generate baseband signals. A chip-level baseband signal may comprise a plurality of chips. The chip-level baseband signal may be descrambled based on a PN sequence and despread based on an OVSF code, for example a Walsh code, to generate a symbol-level baseband signal. The symbol-level baseband signal may comprise a plurality of data symbols. The receiver202may comprise a rake receiver, which in turn comprises a plurality of rake fingers to process a corresponding plurality of received multipath signals.

The transmitter204may comprise suitable logic, circuitry, interfaces and/or code that may be operable to perform transmit functions that may comprise PHY layer function for the transmission or signals. These PHY layer functions may comprise, but are not limited to, modulation of received data to generate data symbols based on application of a selected modulation type, generation of frequency carrier signals corresponding to selected RF channels, for example uplink or downlink channels, the up-conversion of the data symbols by the generated frequency carrier signals, and the generation and amplification of RF signals. The RF signals may be transmitted via the transmitting antenna232.

The memory208may comprise suitable logic, circuitry, interfaces and/or code that may enable storage and/or retrieval of data and/or code. The memory208may utilize any of a plurality of storage medium technologies, such as volatile memory, for example random access memory (RAM), and/or non-volatile memory, for example electrically erasable programmable read only memory (EEPROM).

The interference cancellation module210may comprise suitable logic, circuitry and/or code that are operable to suppress interference signals, relative to a desired signal, in a received signal. The received signal may comprise one or more desired signals and one or more interference signals. The interference cancellation module210may generate interference suppressed versions of the one or more signals in which the signal level for the interference signals is reduced relative to the signal level for the desired signal. The interference cancellation module210may include path admission logic240which is configured to selectively control cancellation of interfering signal paths.

In operation, the receiver202may receive signals via the receiving antenna222. In an exemplary embodiment, the receiver202may comprise a rake receiver. The receiver202may communicate signals to the processor206and/or to the interference cancellation module210.

The receiver202may generate timing information that corresponds to each of the fingers in the rake receiver portion of the receiver202. Each of the fingers in the rake receiver may process a distinct one of a plurality of multipath signals that are received within a delay spread time duration. Based on the received RF signals, the receiver202may generate chip-level baseband signals. The receiver202may communicate the chip-level baseband signals to the interference cancellation module210. The rake receiver within the receiver202may generate one or more symbol-level baseband signals based on a selected one or more OVSF codes and a selected one or more PN sequences. The symbol-level baseband signals may be communicated to the processor206. The OVSF codes may be selected based on a specified desired user signal. For example, referring toFIG. 1, the rake receiver within receiver202associated with mobile communication device MU_2may select an OVSF code, WC_12, or a broadcast OVSF code, WC_broadcast, and a PN sequence, PN_A, which may be utilized to generate the symbol-level baseband signal from the chip-level baseband signal.

The processor206may utilize common pilot channel (CPICH) information, communicated by the signals received from the receiver202, to compute a plurality of channel estimate values or, in various embodiments, the receiver202may compute the channel estimate values. The processor206and/or receiver202may compute one or more channel estimate values corresponding to each multipath signal, which was transmitted by a given transmit antenna of a given BTS and received at a finger in the rake receiver. The computed channel estimate values may be represented as a channel estimate parameter, H(bts, fgr), where bts represents a numerical index that is associated with a given BTS and fgr is a numerical index that is associated with a given rake finger. The processor206may be operable to communicate the computed channel estimate values to the receiver202and to the interference cancellation module210and/or to the memory208. The processor206may compute and/or select one or more interference cancellation parameter values, which control the signal interference cancellation performance of the interference cancellation module210. The processor206may also be operable to communicate the interference cancellation parameter values to the interference cancellation module210and/or to the memory208.

The processor206may also determine which BTSs are associated with a current cell100and which BTSs are not associated with the current cell100. For example, the processor206may determine that the base station A102and the base station B104are associated with the current cell100, while the base station C106is not associated with the current cell100. In an exemplary embodiment, the processor206may store PN sequences for at least a portion of the BTSs that are associated with the current cell100. For example, referring toFIG. 1, the processor206may generate and/or store corresponding PN sequences, for example PN_A and PN_B in the memory208. The PN sequences may be generated on the fly based on the code structure utilized by the BTS and/or based on timing information associated with the BTS. The PN sequences PN_A and PN_B may be associated with the current cell100.

In other exemplary embodiments, the processor206may generate and/or store PN sequences for at least a portion of the BTSs that are associated with the current cell100and at least a portion of the BTSs that are not associated with the current cell100. For example, referring toFIG. 1, the processor206may generate and/or store corresponding PN sequences, for example PN_A, PN_B and PN_C in the memory208. In general, the processor206may store the PN sequences for the BTSs from which a mobile communication device, for example the mobile communication device MC_2114, may expect to receive signals and the processor206may store PN sequences from which the mobile communicating device may not expect to receive signals. The mobile communication device may expect to receive signals, for example common pilot channel (CPICH) signals, from a plurality of BTSs in anticipation of a soft handoff from a current service BTS to a subsequent serving BTS.

In instances in which the transceiver system200utilizes a plurality of receiving antennas, for example the receiving antennas222_1and222_2, the transceiver system200may utilize receive diversity. In a receive diversity system, the receiver202may receive a first set of signals via the receiving antenna222_1and a second set of signals via the receiving antenna222_2. The processor206may compute a first set of channel estimate values corresponding to receiving antenna222_1and a second set of channel estimate values corresponding to receiving antenna222_2. The computed channel estimate values may be represented as a channel estimate parameter, H(bts, rx, fgr), where rx represents a numerical index that is associated with a given receiving antenna. In various embodiments, which utilize receive diversity, the receiver202and/or the interference cancellation module210may also process signals that are transmitted by BTSs, which utilize signal transmission diversity.

The interference cancellation module210may receive signals from the receiver202, which correspond to received multipath signals. The signals received by the interference cancellation module210may comprise chip-level baseband signals. A plurality of chips, for example 256 chips, may be associated with a data symbol. The interference cancellation module210may be operable to determine a time duration that corresponds to a data symbol processing period. The interference cancellation module210may be operable to determine whether to perform iterations of a signal interference suppression on received chip-level baseband signals and/or symbol-level baseband signals, in accordance with an embodiment, during each data symbol processing period. The determination of whether to perform iterations of the signal interference suppression method may be based on, for example, the time instants at which chips, which are associated with a current data symbol and/or subsequent data symbol, arrive at the receiver202via received RF signals.

The interference cancellation module210may retrieve a plurality of channel estimate values, one or more PN sequences, a plurality of OVSF codes, and one or more interference cancellation parameter values from memory208. The interference cancellation module210may receive timing information from the receiver202that corresponds to each of the fingers in the rake receiver portion of the receiver202.

The interference cancellation module210may process received signals, utilizing received timing information and channel estimate values, to combine the multipath signals which are associated with corresponding fingers in the rake receiver. In various embodiments, the interference cancellation module210may combine the multipath signals, which were transmitted by a given BTS and associated with a given PN sequence, to generate a combined chip-level signal by utilizing, for example, maximal ratio combining (MRC) and/or equal gain combining (EGC). This combining may be performed on a per-cell basis if the fingers span more than one cell. The interference cancellation module210may process the per-cell combined chip-level signal, by utilizing a corresponding PN sequence and OVSF code, to determine a signal level associated with each of the plurality of OVSF codes for each of one or more selected PN sequences. In an exemplary embodiment, the plurality of OVSF codes comprises 256 Walsh codes. Each signal associated with an OVSF code may be referred to as a corresponding user signal although it should be noted that multiple OVSF codes may be associated with a single user and thus there is not necessarily a one-to-one correspondence between OVSF codes and users. For example, a signal associated with a jth OVSF code may be referred to as a jth user signal. Referring toFIG. 1, for example, the OVSF code WC_12may be associated with a user signal that is transmitted from base station A102to the mobile telephone MC_2114.

The interference cancellation module210may compute a signal power level value and a noise power level value corresponding to each of the user signals. Based on the computed signal power level value, noise power level value, and the one or more interference cancellation parameter values, the interference cancellation module210may compute a weighting factor value corresponding to each user signal. The plurality of weighting factor values associated with each BTS may be represented as a weighting factor matrix, A(bts), where bts represents a numerical index value that is associated with a given BTS. Each user signal may then be multiplied by the weighting factor before being transferred back into the chip-level domain and subtracted from the original received signal. After subtraction, the signal of interest may be reconstructed for further processing in the rake and/or equalizer receiver.

The interference cancellation module210may be operable to process chip-level signals received from each of a plurality of rake fingers in the receiver202to generate corresponding interference suppressed chip-level signals based on an iterative method for interference cancellation, in accordance with an embodiment. The interference suppressed chip-level signals may be output to each corresponding rake finger. Each of the rake fingers may then process its respective interference suppressed chip-level signals.

The weighting factor value z(j) is a function of the interference cancellation parameter values λ and γ. In various embodiments, the interference cancellation parameters λ and γ may comprise integer and/or non-integer values. In an exemplary embodiment, λ=1 and γ=1. The processor206may be operable to monitor the interference cancellation performance of the interference cancellation module210, for example by measuring SNR values for processed signals generated by the receiver202based on interference suppressed chip-level signals. Accordingly, the processor206may be operable to adjust one or both interference cancellation parameter values λ and γ.

FIG. 3is a diagram of an exemplary wireless communication receiver with interference suppression, in accordance with an embodiment of the present disclosure. Referring toFIG. 3, there is shown an interference cancellation module302, path admission logic303, a delay buffer304, a HSDPA processor306, an HSDPA switching device308, interference cancellation (IC) bypass switching device310, and a plurality of rake fingers312,314and316. The interference cancellation module302may correspond to the interference cancellation module210as presented inFIG. 2. The rake fingers312,314and316represent fingers in a rake receiver. In an exemplary embodiment, the HSDPA switching device308and the IC bypass switching device310may be configured by the processor206.

The delay buffer304may comprise suitable logic, circuitry, interfaces and/or code that may be operable to receive a burst of a chip-level signal324as input at a given input time instant and output it as a burst of a chip-level signal326at a subsequent output time instant. The time duration between the input time instant and the output time instant may be referred to as a delay time duration. In an exemplary embodiment, the delay time duration corresponds to 512 chips.

The HSDPA processor306may comprise suitable logic, circuitry, interfaces and/or code that may be operable to provide HSDPA processing of received signals.

In operation, the HSDPA switching device308may comprise suitable logic, circuitry, interfaces and/or code that are operable to select an input signal to the HSDPA processor306. As illustrated with respect toFIG. 3, the HSDPA switching device308is configured so that it is operable to supply an interference suppressed signal328, generated by the interference cancellation module302, as an input to the HSDPA processor306. As indicated inFIG. 3, this configuration of the HSDPA switching device308may result in the HSDPA switching device308operating in a HSDPA interference cancellation (IC) mode.

The HSDPA switching device308may also be configured so that it is operable to supply the baseband signal324, generated by the receiver202, as an input to the HSDPA processor306. As indicated inFIG. 3, this configuration of the HSDPA switching device308may result in the HSDPA switching device308operating in a normal HSDPA mode.

The HSDPA switching device308may also be configured such that no input signal is supplied to the HSDPA processor306. As indicated inFIG. 3, this configuration of the HSDPA switching device308may result in the HSDPA switching device308operating in a HSDPA data path off mode.

The IC bypass switching device310may comprise suitable logic, circuitry, interfaces and/or code that are operable to select an input signal to the rake fingers312,314and316. As illustrated byFIG. 3, the IC bypass switching device310is configured so that it is operable to supply an interference suppressed signal322, generated by the interference cancellation module302, as an input to the rake fingers312,314and316.

The IC bypass switching device310may also be configured so that it is operable to supply a signal326, which is output from the delay buffer304, as an input to the rake fingers312,314and316. The signal326output from the delay buffer304may comprise a time-delayed, and possibly up-sampled or down-sampled, version of the signal324generated by the receiver202. As indicated inFIG. 3, the signal326output from the delay buffer304may comprise unsuppressed interference.

Each of the rake fingers312,314and316may receive, as input, the chip-level baseband signal324generated by the receiver202. Based on the input baseband signal324from the receiver202, each rake finger312,314and316may generate channel estimates and rake finger timing information. In various embodiments, each rake finger312,314and316may generate the channel estimates and/or rake finger timing information for selected multipath signals based on CPICH data received via the input baseband signal324received from the receiver202. In an exemplary embodiment, which comprises a receive diversity system, channel estimates and/or rake finger timing information may be generated for RF signals received at the receiver202via at least a portion of a plurality of receiving antennas. Each rake finger312,314and316may communicate, as one or more signals318, its respective channel estimates, rake finger timing information, scaling factors Kfgr, scrambling codes associated with one or more BTSs, and/or other information to the interference cancellation module302.

In various embodiments, the interference cancellation module302may receive chip-level signals326from the delay buffer304. Based on the channel estimates, rake finger timing, and/or other information communicated via the signal(s)318, the interference cancellation module302may select individual multipath signals from the chip-level signals326received via the delay buffer304. Based on the interference cancellation parameters320, which may be as described with respect toFIG. 2, the interference cancellation module302may process the received chip-level multipath signal326utilizing an iterative method for interference cancellation, in accordance with an embodiment.

The chip-level signals326received from the delay buffer304may comprise a plurality of multipath signals received via one or more receive antennas from one or more transmit antennas of one or more BTSs. The interference cancellation module302may be configurable to assign signal processing resources to perform the iterative method of interference cancellation for selected multipath signals. The processor206may configure the interference cancellation module302to receive multipath signals from one or more transmit antennas of one or more BTSs. In an exemplary embodiment, which comprises a receive diversity system, the selected multipath signals may be received via one or more of a plurality of receiving antennas. The processor206may configure the interference cancellation module302for receive diversity.

The interference cancellation module302may receive interference cancellation parameters320from the processor206and/or from the memory208. In an exemplary embodiment, the interference cancellation module302may generate and/or retrieve PN sequences and/or OVSF codes from the memory208. The PN sequences may be generated on the fly based on the code structure utilized by the BTS and/or based on timing information associated with the BTS. The interference cancellation module302may retrieve and/or generate a PN sequence for each of the one or more transmit antennas of the one or more BTSs from which the interference cancellation module302is configured to attempt to receive a signal.

In various embodiments in which the receiver202utilizes a plurality of receiving antennas and/or receives data from a plurality of transmit antennas, data received via the symbol-level signals corresponding to the plurality of receiving antennas and/or transmit antennas may be decoded by utilizing various diversity decoding methods. Various embodiments may also be practiced when the receiver202is utilized in a multiple input multiple output (MIMO) communication system. In instances where the receiver202is utilized in a MIMO communication system, data received via the symbol-level signals, received via the plurality of receiving antennas, may be decoded by utilizing various MIMO decoding and/or diversity decoding methods.

The path admission logic303obtains a plurality of finger parameters330corresponding to each of the fingers from the rake receiver202and generates path admission control signals333to control the interference cancellation module302, thereby enabling or disabling interference cancellation on a per-finger basis. The finger parameters330include a measure of finger strength for each of the fingers. For example, the measure of finger strength may be provided in energy per chip over total received power (Ec/Io). Here, the energy per chip may refer to the energy with respect to the CPICH channel. The operation of the path admission logic303will be described in further detail with respect to the following flowcharts.

Referring next toFIG. 4, shown is a flowchart that provides one example of the operation of the path admission logic303according to various embodiments. It is understood that the flowchart ofFIG. 4provides merely an example of the many different types of functional arrangements that may be employed to implement the operation of the path admission logic303as described herein. As an alternative, the flowchart ofFIG. 4may be viewed as depicting an example of steps of a method implemented in the path admission logic303according to one or more embodiments.

Beginning with box403, the path admission logic303monitors the signal strengths of the fingers for an initial time period following finger assignment. In box406, the path admission logic303determines whether the finger strength meets a threshold criterion for being considered a false path. For example, if the finger strength measured over the predefined time period never exceeds a minimum threshold for being considered a true interfering path, the path associated with the finger may be deemed a false interfering path. If any of the finger strengths meet the false path criteria, the path admission logic303detects the false interfering paths in box409for the corresponding fingers. The fingers corresponding to the false interfering paths will not be cancellation candidates. The initial time period utilized for false path detection also enables a warm-up period for channel estimation.

In box412, the path admission logic303detects true interfering paths which are too weak for cancellation. The strength of each assigned finger is monitored to fulfill certain threshold criteria before the path associated with the finger can be a cancellation candidate. Various embodiments for detecting weak interfering paths are further described in connection with the flowcharts ofFIGS. 5-9. In the several embodiments, values for various thresholds may be empirically determined. In box415, the path admission logic303configures the interference cancellation module302(FIG. 3) not to cancel the detected false paths and not to cancel the detected weak true paths.

In box418, the path admission logic303determines whether no paths are canceled by the interference cancellation module302. If no paths are canceled, the path admission logic303disables the interference cancellation module302in box421. This may involve placing the interference cancellation module302into a bypass mode, e.g., by activating the bypass switch310(FIG. 3). The criteria discussed above for weak interfering paths and false paths may be checked at a desired rate. Thus, cancellation by the interference cancellation module302may be adapted at this rate, e.g., the 10 ms frame rate or another rate.

Moving on toFIG. 5, shown is a flowchart that provides one example of the operation of a portion of the path admission logic303(FIG. 3) according to a first embodiment. In particular,FIG. 5relates to box412ofFIG. 4, which involves detecting true interfering paths which are too weak for cancellation.FIG. 5pertains to enabling cancellation on a per-finger basis. It is understood that the flowchart ofFIG. 5provides merely an example of the many different types of functional arrangements that may be employed to implement the operation of the portion of the path admission logic303as described herein. As an alternative, the flowchart ofFIG. 5may be viewed as depicting an example of steps of a method implemented in the path admission logic303according to a first embodiment.

Beginning with box502, the path admission logic303determines the path signal strength (e.g., in Ec/Io or some other measure). In box504, the path admission logic303determines whether the path strength meets some absolute threshold (e.g., the path Ec/Io is at least Y dB, where Y is a threshold value). If the path strength does not meet the absolute threshold criteria, the path admission logic303moves to box506and disallows cancellation of the path. Thereafter, the portion of the path admission logic303ends.

If the path strength does meet the absolute threshold criteria, the path admission logic303moves from box504to box508and determines relative threshold criteria based at least in part on a reference signal strength metric for the serving cell. The reference signal strength metric may correspond, for example, to the signal strength (e.g., in Ec/Io or some other measure) for the strongest path of the serving cell (i.e., the desired signal), the total sum of signal strengths for all paths of the serving cell, the sum of signal strengths for a subset of strongest paths for the serving cell, and so on. In box510, the path admission logic303determines whether the path strength for the current finger meets relative threshold criteria. For example, the relative threshold criteria may be that the path Ec/Io is within X dB of the Ec/Io of the strongest path of the serving cell, where X is a threshold value. X may be selected such that X is much larger than Y. As a non-limiting example, X may be −5 dB, and Y may be −20 dB.

If the path strength does not meet the relative threshold criteria, the path admission logic303moves to box506and disallows cancellation of the path. Thereafter, the portion of the path admission logic303ends. If the path strength does meet the relative threshold criteria, the path admission logic303instead moves from box510to box512and allows cancellation of the path. Thereafter, the portion of the path admission logic303ends. The portion of the path admission logic303depicted inFIG. 5may be repeated for each candidate finger or path.

Turning now toFIGS. 6A and 6B, shown is a flowchart that provides one example of the operation of a portion of the path admission logic303(FIG. 3) according to a second embodiment. In particular,FIGS. 6A and 6Brelate to box412ofFIG. 4, which involves detecting true interfering paths which are too weak for cancellation.FIGS. 6A and 6Brelate to a conservative per-cell cancellation which may be enabled on a per-finger basis. It is understood that the flowchart ofFIGS. 6A and 6Bprovide merely an example of the many different types of functional arrangements that may be employed to implement the operation of the portion of the path admission logic303as described herein. As an alternative, the flowchart ofFIGS. 6A and 6Bmay be viewed as depicting an example of steps of a method implemented in the path admission logic303according to a second embodiment.

Beginning with box603inFIG. 6A, the path admission logic303determines the path signal strength (e.g., in Ec/Io or some other measure). In box606, the path admission logic303determines whether the path corresponds to a strongest path in an interfering cell (i.e., not the serving cell). If the path corresponds to the strongest path in the interfering cell, the path admission logic303transitions from box606to box609. In box609, the path admission logic303determines whether the path strength meets some absolute threshold (e.g., the path Ec/Io is at least Z dB, where Z is a threshold value). If the path strength does not meet the absolute threshold criteria, the path admission logic303moves to box612and disallows cancellation of the path and the other paths in the interfering cell. Thereafter, the portion of the path admission logic303ends.

If the path strength does meet the absolute threshold criteria, the path admission logic303moves from box609to box615and determines relative threshold criteria based at least in part on a reference signal strength metric for the serving cell. The reference signal strength metric may correspond, for example, to the signal strength (e.g., in Ec/Io or some other measure) for the strongest path of the serving cell (i.e., the desired signal), the total sum of signal strengths for all paths of the serving cell, the sum of signal strengths for a subset of strongest paths for the serving cell, and so on. In box618, the path admission logic303determines whether the path strength for the current finger meets relative threshold criteria. For example, the relative threshold criteria may be that the path Ec/Io is within X dB of the Ec/Io of the strongest path of the serving cell, where X is a threshold value. X may be selected such that X is much larger than Z. As a non-limiting example, X may be −5 dB, and Z may be −20 dB.

If the path strength does not meet the relative threshold criteria, the path admission logic303moves to box612and disallows cancellation of the path and the other paths in the cell. Thereafter, the portion of the path admission logic303ends. If the path strength does meet the relative threshold criteria, the path admission logic303instead moves from box618to box621and allows cancellation of the path. Thereafter, the portion of the path admission logic303ends.

If the path is determined not to be the strongest path in an interfering cell in box606, the path admission logic303instead moves from box606to box624inFIG. 6B. In box624, the path admission logic303determines whether the strongest path in the interfering cell meets the absolute and relative threshold criteria. If the strongest path does not meet the criteria, the path admission logic303continues to box627and disallows cancellation of the path. Thereafter, the portion of the path admission logic303ends.

If the strongest path does meet the criteria, the path admission logic303moves from box624to box630. In box630, the path admission logic303determines whether the path strength meets some absolute threshold (e.g., the path Ec/Io is at least Z1dB, where Z1is a threshold value). If the path strength does not meet the absolute threshold criteria, the path admission logic303moves to box627and disallows cancellation of the path. Thereafter, the portion of the path admission logic303ends.

If the path strength does meet the absolute threshold criteria, the path admission logic303moves from box630to box633and determines relative threshold criteria based at least in part on a reference signal strength metric for the serving cell. The reference signal strength metric may correspond, for example, to the signal strength (e.g., in Ec/Io or some other measure) for the strongest path of the serving cell (i.e., the desired signal), the total sum of signal strengths for all paths of the serving cell, the sum of signal strengths for a subset of strongest paths for the serving cell, and so on. In box636, the path admission logic303determines whether the path strength for the current finger meets relative threshold criteria. For example, the relative threshold criteria may be that the path Ec/Io is within Y dB of the Ec/Io of the strongest path of the serving cell, where Y is a threshold value. Y may be selected such that Y is much larger than Z1. As a non-limiting example, Y may be −10 dB, and Z1may be −25 dB. Also, Y may be selected to be less than X (e.g., X=−5 dB, while Y=−10 dB), and Z1may be selected to be less than or equal to Z (e.g., Z=−20 dB, while Z1=−25 dB).

If the path strength does not meet the relative threshold criteria, the path admission logic303moves to box627and disallows cancellation of the path. Thereafter, the portion of the path admission logic303ends. If the path strength does meet the relative threshold criteria, the path admission logic303instead moves from box636to box639and allows cancellation of the path. Thereafter, the portion of the path admission logic303ends. The portion of the path admission logic303depicted inFIGS. 6A and 6Bmay be repeated for each candidate finger or path.

Continuing on toFIG. 7, shown is a flowchart that provides one example of the operation of a portion of the path admission logic303(FIG. 3) according to a third embodiment. In particular,FIG. 7relates to box412ofFIG. 4, which involves detecting true interfering paths which are too weak for cancellation.FIG. 7relates to an aggressive per-cell cancellation which may be enabled on a per-finger basis. It is understood that the flowchart ofFIG. 7provides merely an example of the many different types of functional arrangements that may be employed to implement the operation of the portion of the path admission logic303as described herein. As an alternative, the flowchart ofFIG. 7may be viewed as depicting an example of steps of a method implemented in the path admission logic303according to a third embodiment.

Beginning with box703, the path admission logic303determines the path signal strength (e.g., in Ec/Io or some other measure). In box706, the path admission logic303determines whether the path is one of the strongest N paths for the interfering cell. In other words, the path admission logic303determines whether the path is a member of a subset of the paths for the interfering cell containing the N strongest paths. If the path is not one of the strongest N paths for the interfering cell, the path admission logic303moves to box709and disallows cancellation of the path. Thereafter, the portion of the path admission logic303ends.

If the path is one of the strongest N paths for the interfering cell, the path admission logic303moves from box706to box712and determines a sum of the signal strength metrics (e.g., Ec/Io, etc.) for the N strongest paths of the interfering cell. In box715, the path admission logic303determines whether this sum of path strengths meets some absolute threshold (e.g., the Ec/Io is at least Y dB, where Y is a threshold value). If the sum does not meet the absolute threshold criteria, the path admission logic303moves to box709and disallows cancellation of the path. Thereafter, the portion of the path admission logic303ends.

If the sum of path strengths does meet the absolute threshold criteria, the path admission logic303moves from box715to box718and determines relative threshold criteria based at least in part on a reference signal strength metric for the serving cell. The reference signal strength metric may correspond, for example, to the signal strength (e.g., in Ec/Io or some other measure) for the strongest path of the serving cell (i.e., the desired signal), the total sum of signal strengths for all paths of the serving cell, the sum of signal strengths for a subset of strongest paths for the serving cell, and so on. In box721, the path admission logic303determines whether the sum of the strongest N path strengths for the interfering cell meets relative threshold criteria. For example, the relative threshold criteria may be that the sum Ec/Io is within X dB of the Ec/Io of the strongest path of the serving cell, where X is a threshold value. X may be selected such that X is much larger than Y. As a non-limiting example, X may be −5 dB, and Y may be −20 dB.

If the sum of path strengths does not meet the relative threshold criteria, the path admission logic303moves to box709and disallows cancellation of the path. Thereafter, the portion of the path admission logic303ends. If the sum does meet the relative threshold criteria, the path admission logic303instead moves from box721to box724and allows cancellation of the path. Thereafter, the portion of the path admission logic303ends. The portion of the path admission logic303depicted inFIG. 7may be repeated for each candidate finger or path.

Referring next toFIG. 8, shown is a flowchart that provides one example of the operation of a portion of the path admission logic303(FIG. 3) according to a fourth embodiment. In particular,FIG. 8relates to box412ofFIG. 4, which involves detecting true interfering paths which are too weak for cancellation.FIG. 8relates to per-cell cancellation that is enabled on per-cell basis. It is understood that the flowchart ofFIG. 8provides merely an example of the many different types of functional arrangements that may be employed to implement the operation of the portion of the path admission logic303as described herein. As an alternative, the flowchart ofFIG. 8may be viewed as depicting an example of steps of a method implemented in the path admission logic303according to a fourth embodiment.

Beginning with box803, the path admission logic303determines the path signal strength (e.g., in Ec/Io or some other measure) for all paths of an interfering cell. In box806, the path admission logic303determines a sum of the signal strength metrics (e.g., Ec/Io, etc.) for the N strongest paths of the interfering cell. In box809, the path admission logic303determines whether this sum of path strengths meets some absolute threshold (e.g., the Ec/Io is at least Y dB, where Y is a threshold value). If the sum does not meet the absolute threshold criteria, the path admission logic303moves to box812and disallows cancellation for all paths of the interfering cell. Thereafter, the portion of the path admission logic303ends.

If the sum of path strengths does meet the absolute threshold criteria, the path admission logic303moves from box809to box815and determines relative threshold criteria based at least in part on a reference signal strength metric for the serving cell. The reference signal strength metric may correspond, for example, to the signal strength (e.g., in Ec/Io or some other measure) for the strongest path of the serving cell (i.e., the desired signal), the total sum of signal strengths for all paths of the serving cell, the sum of signal strengths for a subset of strongest paths for the serving cell, and so on. In box818, the path admission logic303determines whether the sum of the strongest N path strengths for the interfering cell meets relative threshold criteria. For example, the relative threshold criteria may be that the sum Ec/Io is within X dB of the Ec/Io of the strongest path of the serving cell, where X is a threshold value. X may be selected such that X is much larger than Y. As a non-limiting example, X may be −5 dB, and Y may be −20 dB.

If the sum of path strengths does not meet the relative threshold criteria, the path admission logic303moves to box812and disallows cancellation of the path. Thereafter, the portion of the path admission logic303ends. If the sum does meet the relative threshold criteria, the path admission logic303instead moves from box818to box821and allows cancellation for all paths of the interfering cell. Thereafter, the portion of the path admission logic303ends. The variable N may be incremented until it is equal to the number of paths associated with the interfering cell.

With reference toFIG. 9, shown is a flowchart that provides one example of the operation of a portion of the path admission logic303(FIG. 3) according to a fifth embodiment. In particular,FIG. 9relates to box412ofFIG. 4, which involves detecting true interfering paths which are too weak for cancellation.FIG. 9relates to another form of per-cell cancellation, where cancellation is enabled on a per-cell basis. It is understood that the flowchart ofFIG. 9provides merely an example of the many different types of functional arrangements that may be employed to implement the operation of the portion of the path admission logic303as described herein. As an alternative, the flowchart ofFIG. 9may be viewed as depicting an example of steps of a method implemented in the path admission logic303according to a fifth embodiment.

Beginning with box903, the path admission logic303identifies the strongest path for an interfering cell. In box906, the path admission logic303determines the path signal strength (e.g., for CPICH in Ec/Io or some other measure). In box909, the path admission logic303determines whether the path strength meets some absolute threshold (e.g., the CPICH Ec/Io is at least Y dB, where Y is a threshold value). If the path strength does not meet the absolute threshold criteria, the path admission logic303moves to box912and disallows cancellation of all paths associated with the interfering cell. Thereafter, the portion of the path admission logic303ends.

If the path strength does meet the absolute threshold criteria, the path admission logic303moves from box909to box915and determines relative threshold criteria based at least in part on a reference signal strength metric for the serving cell. The reference signal strength metric may correspond, for example, to the signal strength (e.g., in Ec/Io or some other measure) for the strongest path of the serving cell (i.e., the desired signal), the total sum of signal strengths for all paths of the serving cell, the sum of signal strengths for a subset of strongest paths for the serving cell, and so on. In box918, the path admission logic303determines whether the path strength for the current finger meets relative threshold criteria. For example, the relative threshold criteria may be that the path Ec/Io is within X dB of the Ec/Io of the strongest path of the serving cell, where X is a threshold value. X may be selected such that X is much larger than Y. As a non-limiting example, X may be −7 dB, and Y may be −20 dB.

If the path strength does not meet the relative threshold criteria, the path admission logic303moves to box912and disallows cancellation of all of the paths associated with the interfering cell. Thereafter, the portion of the path admission logic303ends. If the path strength does meet the relative threshold criteria, the path admission logic303instead moves from box918to box921and allows cancellation of all of the paths associated with the interfering cell. Thereafter, the portion of the path admission logic303ends.