Abstract:
The present disclosure describes a wireless user equipment (UE) device that can receive a communication signal that may be transmitted along a wireless channel. The wireless user equipment device can include a sleep deactivator that periodically activates wireless user equipment from a sleep mode periodically in advance of a periodically transmitted message, such as a paging indicator or a control message that is expected to be received within a slot of time. The wireless user equipment device can also include an element that can extract the message during multiple sub-intervals, a signal quality assessor that can a) assess the quality of the indicator in the sub-intervals and b) assign a signal quality metric for the sub-intervals. The wireless UE device can also include a channel estimator that can estimate a physical channel over which the communication signal is transmitted. The wireless UE device can also assign a quality metric to the extracted message at each sub-interval to select a sub-interval that is most consistent with timing of the paging indicator or control message.

Description:
INCORPORATION BY REFERENCE 
     This application claims the benefit of U.S. Provisional Application No. 60/916,431, “Increasing Stand-by Time in OFDM Handsets” filed on May 7, 2007, No. 60/916,926, “Increasing Stand-by Time in OFDM Handsets” filed on May 9, 2007, and No. 60/952,779, “Increasing Stand-by Time in OFDM Handsets” filed on Jul. 30, 2007 including all cited references which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     A cellular handset or user equipment (UE) is a battery-powered wireless device that communicates with one or more base stations (BSs), such as an eNodeB. A cellular handset can be in one of two modes, an idle or a connected mode. In the idle mode, the UE can operate in a discontinuous reception (DRX) mode. In accordance with some standards governing cellular handset operation, in the connected mode, the UE can operate in a continuous reception mode or DRX mode. During the DRX mode, the handset can enter a sleep mode and can wakeup to detect periodic control messages. When a cellular handset or UE enters the sleep mode, the UE can conserve the energy stored in the battery and extend the standby and connect time of a cellular handset. 
     A cellular handset may periodically awaken or exit the sleep mode to test for a paging indicator or control message from a base station. The indicator or message can show that a message from a base station is available for the cellular handset. The cellular handset may make brief, repeated transitions from the sleep mode to an active or connect mode, and vice versa, when checking for messages. The cycle of sleep and connect mode transitions can be called standby mode. 
     A cellular handset consumes a relatively small amount of power during the sleep mode. When a cellular handset exits the sleep mode, the increased power consumption shortens the remaining standby and connect time. 
     SUMMARY 
     The present disclosure describes a wireless user equipment (UE) device that can receive a communication signal that may be transmitted along a wireless channel. The wireless user equipment device can include a sleep deactivator that periodically activates the wireless user equipment device from a sleep mode periodically in advance of a periodically transmitted message, such as a paging indicator or a control message that is expected to be received within a slot of time. The wireless user equipment device can also include an element that can extract the message during multiple sub-intervals, a signal quality assessor that can a) assess the quality of the indicator in the sub-intervals and b) assign a signal quality metric for the sub-intervals. The wireless UE device can also include a channel estimator that can estimate a physical channel over which the communication signal is transmitted. The wireless UE device can also assign a quality metric to the extracted message at each sub-interval to select a sub-interval that is most consistent with timing of the paging indicator or control message. 
     The present disclosure describes a wireless device that can include a receiver that receives and samples a transmitter signal that has a periodically transmitted message such as a paging indicator or a control message, a sample selector unit that selects signals at multiple delays, a hypothesis testing unit that uses a predetermined criterion to demodulate and score the samples of the received signal at the multiple delays, and a controller that determines the message timing based on the scores. 
     The present disclosure describes a wireless device that can include a receiver that samples a periodically transmitted message such as a paging indicator or a discontinuous reception (DRX) control message, a sample demodulation unit that demodulates the received samples at multiple delays and forms a corresponding set of delayed sampled received signals, a hypothesis testing unit that scores the offset received signal samples using a predetermined scoring criterion, and a controller that determines the present symbol timing based on the present scores. 
     This disclosure can provide a method of determining the symbol timing of a periodically transmitted orthogonal frequency division multiple access signal. The disclosed method can include 1) sampling a transmitter signal that has a paging indicator or DRX connected mode control message, 2) providing a set of delayed samples of the received signals, 3) demodulating selected sets of delayed samples, 4) scoring each set using a predetermined scoring criterion, and 5) selecting the symbol timing based on the delay that corresponds to the maximum or selected score. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will make reference to the accompanying figures, wherein like numerals represent like elements, and wherein: 
         FIG. 1A  shows a diagram of an example of a message timing determination unit in a wireless device in accordance with an embodiment; 
         FIG. 1B  shows a block diagram of a hardware implementation of the message timing determination unit of  FIG. 1A ; 
         FIG. 2  shows a flowchart of a method for increasing the standby time of a wireless device in accordance with an embodiment; 
         FIG. 3  shows a flowchart of a method for increasing the standby time of a wireless device in accordance with an embodiment; and 
         FIG. 4  shows a flowchart of a method for increasing the standby time of a wireless device in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIG. 1A  shows a diagram of a message timing determination unit  100  which is part of a wireless device schematically represented by reference numeral  102 . In accordance with an embodiment, message timing determination unit  100  includes a receiver front end  105 , a sample selector unit  110 , a hypothesis testing unit  120 , a controller  130 , and a channel estimator  140 . In accordance with an embodiment, wireless device  102  may be a mobile user equipment (UE) that is compatible with third generation partnership program (3GPP) standards, such as a long term evolution (LTE) mobile UE. In accordance with an embodiment, timing determination unit  100  can test the timing hypotheses of received paging indicators or other suitable messages that are transmitted with several frequency components and determine a timing of when the indicator or message was received. 
     The receiver front end  105  can receive a radio frequency (RF) communication signal and can couple samples of the received signal to the sample selector unit  110 . The sample selector unit  110  can couple the signal samples to the hypothesis testing unit  120 . The hypothesis testing unit  120  can couple hypothesis results and decoded signals to the controller  130 . The controller  130  can couple control signals, clock signals, and demodulation parameters, including signal structure and channel estimations or propagation path parameters, to the hypothesis testing unit  120 , the sample selector unit  110 , and the receiver front end  105 . 
     The receiver front end  105  can receive a radio frequency (RF) transmitter signal, such as a WiMax signal, a long term evolution (LTE) signal, such as an LTE advance signal, or a frequency division multiplex (FDM) signal, such as an orthogonal frequency domain multiple access signal, denoted OFDM or OFDMA, from a base station or a Node B. The RF transmitter signal can include a paging signal, a paging channel, a paging indicator, such as an enhanced universal terrestrial radio (E-UTRA) paging indicator or a third generation partnership program (3GPP) long term evolution (LTE) paging indicator, a reference signal (RS), a periodic control message transmitted on a control channel during a DRX transmission in a connected mode, and other signals. The receiver front end  105  can receive the RF signal on one or more antennas and can downconvert the RF signal to an intermediate frequency (IF) or a baseband received signal. 
     The receiver front end  105  can include mixers, local oscillators, filters, amplifiers, and other elements that downconvert RF signals to an IF or baseband received signal. Some of the analog, RF, and digital elements of receiver front end  105  may be de-powerable upon receipt of a sleep mode command from controller  130 . 
     The receiver front end  105  may include one or more analog to digital converters (ADC) that sample the received signal or convert the analog IF or complex baseband signal to a real or complex digital data stream. The receiver front end  105  can combine downconversion and sampling. For example, the receiver front end  105  can use subsampling or intentionally aliasing to fold a subsampled IF signal to generate a sampled baseband signal. The signal samples or digital stream can be coupled via a serial digital bus, a parallel digital bus, and the like, to the sample selector unit  110 . 
     The elements of receiver front end  105  can be configured by control signals from controller  130 . The controller  130  may include a sleep deactivator functionality that can activate other elements of the wireless device  102 , including the receiver front end  105 . For example, the controller  130  may exit a sleep mode at a wake-up time or pre-frame time, and may apply power to analog and/or digital sections of the receiver front end  105  before an impending paging signal. The controller  130  may adjust receiver front end  105  elements such as the bandwidth of filters, the frequency of local oscillators, the gain of amplifiers, and the like. For example, the controller  130  can supply a sample clock signal to the receiver front end  105  that can determine the sampling rate and sample-timing phase of an ADC. 
     The sample selector unit  110  can store samples of the received signal and can transfer stored samples in a serial or parallel form to the hypothesis testing unit  120 . The sampled received signal can be arranged in multiple blocks or intervals. The intervals may be offset in time and partially overlap or abut each other, or may be non-overlapping with gaps. In one embodiment, the intervals abut each other. For example, sample selector unit  110  can distribute or de-multiplex stored samples in blocks. Each block of samples or intervals can represent a different hypothesized time slot in which a paging indicator or control message is received. For example, the designated indicator or message can be one or more OFDM symbols, which can be temporally overlapping or non-overlapping samples. In an embodiment, each block can include 2 k  sequential samples of the received signal, where k is a positive integer. 
     The hypothesis testing unit  120  can include a demodulation functionality  120   a ,  120   b , and  120   c  and corresponding metric calculation functionality  120   d ,  120   e , and  120   f . The demodulation functionality  120   a - c  can demodulate the sampled received signals that may be plural frequency components and may apply the channel coefficients and equalization parameters to the sampled received signals. In other words, the demodulation functionality  120   a - c  may perform both FFT-based signal separation as well as equalization functions. For example, the demodulation functionality  120   a - c  can include equalization by adjusting multiplier coefficients, such as equalization and channel coefficients using a multiplication stage that precedes or follows a conventional set of FFT stages. It may be noted that the sample received signals may be processed serially or in parallel. 
       FIG. 1B  shows a block diagram of a hardware implementation  150  of the message timing determination unit  100  of  FIG. 1A  in accordance with an embodiment. The elements and structure of the hardware implementation  150  will be discussed in detail to convey an embodiment that can allow serial sample processing, then the discussion will resume with the structure and function of the message timing determination unit  100 . 
     The hardware implementation  150  can receive an RF signal  151  at an orthogonal frequency division multiplex (OFDM) receiver front end  155 . The RF signal  151  can bear a paging indicator on a paging channel or a control message on a control channel. The hardware implementation  152  may wake up at a wake up time  153 . 
     The receiver front end  155  can receive the RF signal  151  at one or more antennas, downconvert, and sample the downconverted signals, and transfer the downconverted signals to the sample selector  160 . The sample selector  160  can select samples to be demodulated by the demodulator  170 . The demodulator  170  can include a transform unit  172 , a channel estimator  174 , and a channel equalizer  176  for example. The demodulator  170  may be a single block that demodulates each selected sample cyclically or there may be several demodulator blocks, each of which can demodulated a different sample corresponding to a timing hypothesis as discussed with respect to  FIG. 1A . In other words, the demodulator  170  may operate serially upon samples to demodulate all of the sampled OFDM signal or in parallel, as shown with respect to demodulation functionality  120   a - c  of  FIG. 1A . 
     The transform unit  172  can be a fast Fourier transform (FFT) unit. The channel estimator  174  can be an estimator that determines channel propagation parameters and other signal parameters. The channel equalizer  176  can compensate the output of the transform unit  172  so that the RF signal  151  is equalized in the sense of Nyquist. For example, the channel equalizer  176  may accept channel propagation parameters from the channel estimator  174  and may process the output of the transform unit  172  to generate a demodulated, equalized output signal that exhibits minimal inter-symbol interference. 
     The demodulator  170  can transfer the demodulated, equalized signals corresponding to multiple timing hypotheses to the metric calculator  178 . The metric calculator  178  can determine a quality metric  181  for each timing hypothesis. The metric calculator  178  may include a decoder  179 , such as a Viterbi decoder, a low density parity check (LDPC) decoder, and the like that can decode a message that includes forward error correction (FEC). The decoder  179  may be optionally, and if included, can output a decoded message  183 . 
     As discussed, the hardware implementation  150  may be controlled by a controller (not shown) such as the controller  130  discussed with respect to  FIG. 1A . The controller may serially process samples, such as sample blocks corresponding to a given timing hypothesis for the time of arrival of the RF signal  151  with respect to a wake up time  153 . The functionality of hardware implementation  150  may be understood equally well in terms of a parallel arrangement of timing hypotheses per the following resumed discussion of  FIG. 1A . 
     The metric calculation functionality  120   d - 120   f  of  FIG. 1A  can decode the demodulated, equalized signal and can compute a signal quality metric or score that is based on predetermined criteria. For example, the metric calculation functionality  120   d - f  can perform decoding functions, such as log-likelihood ratio (LLR) calculations, Viterbi decoding, cyclic redundancy check (CRC) calculations, and the like. For example, the metric calculation functionality  120   d - 120   f  can use the decoded signal to compute a channel quality indicator CQI or other signal quality score. 
     The demodulation functionality  120   a ,  120   b , and  120   c  can apply Fourier transforms, chirp-Z transforms, filter-bank result vectors, and the like, that segregate each of the following into time-frequency bins: 1) modulated signal components, 2) un-modulated signals, tones or pilot signals, and 3) noise components. The demodulation functionality  120   a - c  may or may not track frequency shifts in carrier or sub-carrier frequencies of the RF signal. 
     Scores output by the hypothesis testing unit  120  can be used to determine the approximate time-of-arrival (TOA) of a paging signal. The exactness of the estimate or approximation can depend on the range or window of hypothesized arrival times of a designated symbol in a paging signal. 
     Each demodulation functionality  120   a - 120   c  can demodulate a signal, such as an OFDMA signal, by calculating Fourier transforms of blocks of samples. The demodulation functionality  120   a - 120   c  may be described as extractive elements that can extract a symbol from the communications signal. The demodulation functionality  120   a - 120   c  may use circular convolution, eigen decomposition, cyclic prefix padding, periodic sampling, overlap-add techniques, overlap-save techniques, windowing, and the like. For example, the demodulation functionality  120   a - 120   c  can decompose or demodulate an OFDMA signal having data padding that may be described as a cyclic prefix into separate frequency bins with small spectral leakage compared to zero-padded or unpadded FFT based decompositions. 
     Each metric calculation functionality  120   d - f  can calculate a signal quality metric for the given timing hypothesis represented by each corresponding hypothesis block  1  to n. The signal quality metric can include, for example, a cyclic redundancy check (CRC), a channel quality indicator (CQI) that is predicated on a known signal structure, a signal to noise ratio (SNR) of a RS or a paging signal, a signal power, a signal to interference ration (SIR), a signal power spectral density, and the like. The output of each metric calculation functionality  120   d - 120   f  can be stored as a signal quality metric or score in the controller  130 . The metric calculation functionality  120   d - f  may be performed in a signal quality measurement unit, such as metric calculator  178  as further discussed with respect to hardware implementation  150  of  FIG. 1B . The signal quality measurement units may be described as a signal quality assessor. The order of evaluation of the signal quality metrics may be determined by a loop control signal from the controller  130 . In this capacity, the controller  130  may act as a loop controller. For example, the controller  130  may arrange the order of evaluation in terms of probable priority, such as a prior probability determined by an application of Bayesian statistics. 
     The controller  130  can include a score memory  130   a  and a score selector  130   b  and can output a timing for when the paging indicator or control message arrived. The score memory  130   a  can include a random access memory (RAM), a first-in, first-out (FIFO) memory, and the like. The hypothesis testing unit  120  can overwrite the contents of the score memory  130   a  with hypothesis scores. The score memory  130   a  can transfer signal quality metrics or scores to the score selector  130   b . In an embodiment, the hypothesis testing unit  120  can be configured to decode received messages and the decoded messages can be stored, for example, in a memory in controller  130 . 
     The score selector  130   b  can process a set of scores corresponding to selected hypotheses from score memory  130   a  and can rank or prioritize each score relative to other scores. The score selector  130   b  can select and output the hypothesis or hypothesized time interval that corresponds to the highest score. The highest score can determine the timing of a designated timeslot or symbol timing of a paging signal. For example, the score selector  130   b  can select a hypothesized time-frequency bin that has a CQI score of 25 or more instead of time-frequency bins that have a CQI score of 15 or below. The score selector  130   b  may interpolate the time corresponding to a set of hypothesis scores. Interpolation can improve the effective time resolution of the symbol timing. The score selector  130   b  can include a central processing unit, a microprocessor, a programmable logic array, and the like that can compare scores and can generate control signals that control the sample selector unit  110  and the hypothesis testing unit  120 . 
     The controller  130  can determine an approximate timing of a paging signal from a set of channel metrics or scores from hypothesis testing unit  120 . In an embodiment, the controller  130  may, in addition to coarsely estimating the timing of the paging indicator, adjust the convergence rate of the channel estimation of the channel estimator  172  discussed with respect to  FIG. 1B . 
     The controller  130  can determine the number of hypotheses to test and can configure hypothesis testing unit  120  accordingly. The number of hypotheses to test or the timing window for the paging signal can depend, for example, on the rate of clock drift of the wireless device  102  relative to a base station clock. A larger clock drift between paging events can increase the number of hypotheses. The controller  130  can adjust the number of hypotheses dynamically and can change the order in which the hypotheses are evaluated, sorted, ranked, and compared. For example, the controller  130  can evaluate the hypotheses in serial order. The controller  130  can minimize the pre-frame interval or wake-up time that precedes a designated time-slot in a paging signal by adjusting the hypothesis window, granularity, as well as the order of evaluation. 
     The disclosed devices and methods can eliminate the need to perform multi-path searching and can minimize the pre-frame or interval between a wake-up time and the actual arrival of a designated time-slot in the paging signal, thereby increasing the standby time of a wireless device relative to other wireless devices. For example, the wireless device  102  can exit a sleep mode, rapidly re-acquire an OFDMA paging indicator timing, test for message availability, and resume the sleep mode if no message is pending. The disclosed devices and methods can eliminate the multi-path searcher of conventional wireless devices, reduce the pre-frame interval in the current and subsequent instances of exiting the sleep mode, reduce battery drain, and increase the standby time. 
     The disclosed devices and methods can be used for voice over internet protocol (VoIP), 3GPP UEs, including LTE cellular technology, DRX cellular handsets, and other communications technologies and systems. As an example, emerging 3GPP standards call for an OFDM symbol set having a 65 is symbol duration. The timing error tolerance for each OFDM symbol can span approximately 4% of the symbol period, or 2.5 μs. The timing error tolerance for OFDM signals can be much larger than CDMA, TDMA and certain other signals. The number of timing hypotheses can be reduced accordingly. 
     The timing error tolerance can be much smaller than the probable timing error or window of uncertainty for the arrival of a paging signal, which can be about 20 μs. The uncertainty can be due to clock drift in a wireless device relative to a base station, for example. The paging signal arrival uncertainty can be much smaller than the average interval between paging signals, which can be about 5 milliseconds (ms), for example. For these example tolerances and uncertainties, the hypothesis testing unit  120  and controller  130  can use about eight (=20 μs/2.5 μs) timing hypotheses and can select a hypothesized time that is tolerably close to the true paging signal symbol timing. Subsequently, the controller  130  may exit a sleep mode and check the paging signal by a pre-frame interval approximately equal to 20 μs plus a power-up interval of approximately 2 milliseconds (ms) for analog, RF, automatic gain control (AGC), digital circuits, and other circuits. 
     When the controller  130  1) tests the multiple timing hypothesis, 2) extracts the channel coefficients, 3) demodulates the paging signal, and, optionally, 4) decodes the bit streams for each hypothesis, then the controller  130  can compute a trial CRC for each hypothesis. If a trial CRC matches the CRC embedded in a paging signal, then the CRC matched time delay hypothesis can be used for 1) subsequent demodulation of the RF signal, 2) improving or refining the channel coefficient estimates, and 3) locking to or tracking the arrival time or frame time of subsequent paging signals. As discussed with respect to hardware implementation  150  and message timing determination  100 , hypothesis testing can be performed serially, i.e. one hypothesis after another, or sequentially. 
       FIG. 2  shows a flowchart of a method  200  for increasing the standby time of a wireless device in accordance with an embodiment. The program can begin at step S 210  and can proceed to step S 215  in which a wireless device, which is on standby, is awakened from a sleep mode. The wireless device may be awakened at a pre-frame interval or wake-up time that precedes a pre-defined time-slot for receipt of a paging indicator in idle mode or receipt of a control message on a control channel in a discontinuous reception mode of a connected state. Wakening the wireless device can include activating or powering analog, RF, and digital circuits, configuring a receiver, such as receiver front end  105 , and the like. 
     Wakening the wireless device can include configuring a hypothesis testing unit, such as hypothesis testing unit  120  with a hypothesis window, a hypothesis time resolution or granularity, the number of timing hypotheses to be tested, the order or priority for evaluating hypotheses, initializing a hypothesis counter, and the like. For example, wakening the wireless device can include setting a time granularity of 2.5 μs, setting the total number of hypotheses to eight, setting a hypothesis window of 25 μs, and selecting a chronological order of evaluation. 
     From program step S 215 , the program can flow to program step S 220  in which a count of the hypotheses that have been tested can be compared with the total number of hypotheses. For example, there may be eight hypotheses or eight hypothetical paging signal symbol timings to evaluate. If the comparison indicates that the last hypothesis has already been tested, then program flow can proceed from step S 220  to step S 255  in which the wireless device can resume a sleep mode of standby. If the comparison in step S 220  indicates that an additional hypothesis needs to be tested, then program flow can proceed to step S 225 . For example, if seven out of eight hypotheses have been tested, then program flow can proceed from step S 220  to step S 225 . 
     In program step S 225 , the program can prepare to test the next or current timing hypothesis. The preparation can include, for example, selecting a subset of signal samples, setting up an FFT or other suitable demodulation such as an orthogonalizing transform, initializing memory locations, incrementing a hypothesis counter, and the like. A sample selector unit, such as sample selector unit  110 , can select and supply the subsets of signal samples to multiple demodulators, as directed in step S 225 . 
     From program step S 225 , program flow can continue to program step S 230  in which the paging signal can be demodulated. For example, the paging signal can be demodulated by decomposing the paging signal into different frequency components, equalizing and recombining the components. Demodulating the signal can include separating orthogonal signal components from each other and from other components such as noise, common channel signals, and interference. For example, FFT calculations can place the results in FFT frequency bins that correspond to a frequency grid. Some portions of the other components may be included in FFT bins that would otherwise only contain the orthogonal signal components. In other words, the separation of signal and noise may be incomplete. 
     From program step S 230 , program flow can proceed to program step S 235  in which the demodulated signal can be decoded to extract a symbol stream, bit stream, or data stream. Decoding can include extracting information and parity bits from a combined information and parity bit stream, decoding an estimated CRC, decoding a forward error corrected (FEC) encoded signal, and the like. 
     From program step S 235 , program flow can proceed to program step S 240  in which an estimated or candidate CRC of the decoded information and parity bits can be checked versus an embedded CRC from the demodulated, decoded paging signal. The estimated CRC can be based on demodulation and decoding of the signal samples using the current timing hypothesis as described with respect to program steps S 230  and S 235 . If the estimated CRC does not match the embedded CRC, then the CRC mismatch can cause the program flow to return to step S 220 , otherwise program flow can proceed to step S 245 . 
     When the program flow arrives at step S 245 , that is, when and if the detected and embedded CRCs match, then the program can test for a pending message. If no message is pending, program flow can proceed to step S 255  and re-enter the standby mode, otherwise the program flow can proceed to program step S 250 , exit the standby mode, and enter a connect mode. In other words, from program step S 250 , the program can proceed to active mode tasks. 
     Flowchart  200  may be part of an interrupt-driven program, for example. A clock, such as a system clock, can activate the interrupt-driven program. The program step S 250  can, when exiting standby mode, adjust the clock so that the receiver is awakened or pre-triggered in a subsequent step S 215  just before the arrival of a next paging signal. The time interval between the pre-trigger or wake-up time and the start of a designated time-slot in the paging signal can be called the pre-frame interval. 
     The wake-up time can vary due to the drift of a time base or clock in a wireless device relative to the time-of-arrival (TOA) of a repeated paging signal. The paging signal may or may not be strictly periodic. The wake-up time may be determined from an extended Kalman tracker, a Bayesian tracker, a gated phase locked loop, and the like. Program step S 255  can modify a wake-up time that closely precedes the next paging signal. For example, both steps S 250  and  255  can adjust the wake-up time to precede a designated symbol in the next paging signal frame by an interval that is approximately equal to the paging window uncertainty. For example, the paging window uncertainty due to drift in a wireless device clock relative to a base station clock can be 20 microseconds (μs). 
       FIG. 3  shows a flowchart of a method  300  for increasing the standby time of a wireless device in accordance with an embodiment. The program can start at step S 310  and can proceed to step S 315  in which the wireless device can be awakened as discussed with respect to program step S 215 . 
     From program step S 315 , the program can flow to step S 320  in which the program can prepare to estimate next or current timing hypothesis. The program step S 320  can include sub-steps such as selecting a subset of data samples, initializing demodulation functionality, initializing a hypothesis counter, and the like. 
     From program step S 320 , program flow can proceed to step S 330  in which demodulation of the signal can occur as discussed with respect to program step S 230 . 
     From program step S 330 , program flow can proceed to step S 340  in which a signal-structure dependent signal quality metric may be calculated. The signal quality metric calculation may or may not be based on decoding a bit stream from the signal. For example, the CQI can be calculated based on a known or pre-determined signal structure without decoding a bit stream. 
     Program step S 340  can include sub-steps for signal quality metric calculations, such as SNR calculations, signal to interference ratio (SIR) calculations, CQI calculations, and the like. Step S 330  may include parameter extraction routines that can determine channel coefficients that can equalize subsequent signal demodulation. 
     From program step S 340 , program flow can proceed to step S 350  in which a count of the number of hypotheses tested can be compared with the maximum or total number of hypotheses. If all hypotheses have been tested, program flow can proceed to step S 360 , otherwise program flow can proceed to back to step S 320 . 
     The best timing hypothesis can be selected in program step S 360 . The timing hypothesis selection can be based on one or more signal quality metrics, such as CQI, SNR, SIR, and the like. For example, the best timing hypothesis may be determined from a single hypothesis with the largest CQI or may be an interpolated or an extrapolated value from multiple hypotheses. In other words, the best timing hypothesis can be a single hypothesis selected using the maximum of the calculated signal quality metric, an interpolated value from multiple hypothesized times of arrival. The best timing hypothesis can be determined from the hypotheses using a maximum likelihood (ML) ratio or log likelihood ratio based estimate, a Bayesian estimate, and the like. 
     From program step S 360 , program flow can proceed to program step S 365  in which demodulation of the signal using the best timing hypothesis may be performed. The demodulation steps in program step S 365  can match the demodulation steps of program step S 330 , but with channel coefficients that are statistically conditioned on use of the best timing hypothesis. In other words, a set of channel coefficients can be associated with each timing hypothesis. The channel coefficients can fine-tune or equalize the demodulation to improve the quality of an IF or base band signal. The demodulation step can include selecting or averaging channel coefficients from each hypothesis to obtain an improved set of channel coefficient for the next awakening from the sleep mode. The improved coefficients may be realized by using an adaptive filter, a gradient search, a Kalman filter, a maximum likelihood sequence estimator or Viterbi decoder, and the like. 
     From program step S 365 , program flow can proceed to program step S 370  in which the demodulated signal for the selected hypothesis can be decoded to extract information bits and parity bits from an encoded data stream. Decoding the bit stream can include detecting, discriminating, hard limiting, decision thresholding, and the like, of the demodulated signal. For example, the decoded bit stream may be obtained using a CRC, a forward error correction code, a repetition code, and the like to detect and connect bit errors. 
     From program step S 370 , program flow can proceed to program step S 375  in which a test or check for pending messages from a base station may be performed. The pending message test can include examining the decoded data to determine if the base station has a message for the cellular handset. If a message is pending, program flow can proceed to program step S 380  in which the standby mode is exited and an active or connect mode is entered, otherwise program flow can proceed to program step S 385  in which a sleep mode of standby can be resumed. 
     Both program steps S 380  and S 385  can include sub-steps in which an alarm pre-trigger time or pre-frame interval hypothesis window size, and a hypothesis timing granularity can be evaluated or re-evaluated. The wake-up time or pre-trigger time calculated in program step S 380  and/or program step S 385  can establish a wake-up or pre-trigger time that precedes the likely arrival of a next paging signal from the base station. 
       FIG. 4  shows a flowchart of a method  400  that can increase the standby time of a wireless device in accordance with an embodiment. The program can start at program step S 410  and can proceed to program step S 415 . In program step S 415 , the receiver or cellular handset can be awakened as discussed with respect to program step S 215 . 
     From program step S 415 , program flow can proceed to program step S 420  in which preparations for testing a given timing hypothesis can be made. The given timing hypothesis can quantify an a priori estimate of a paging signal time-of arrival (TOA) relative to a clock in the wireless device. Each given timing hypothesis can differ from other hypotheses by an integer multiple of a time granularity. The program can evaluate an a posteriori or Bayesian estimate of the true TOA of the paging signal by demodulating the RF signal and calculating a signal metric for each hypothesis as described with respect to steps S 425  and S 430 . 
     From program step S 420 , program flow can proceed to program step S 425  in which demodulation, including channel estimation and/or equalization, can be performed. A demodulator, such as an demodulator functionality  120   a - 120   c , can separate the components of signal and noise in a paging signal. For example, an FFT and channel estimation may demodulate the reference signal or the paging indicator signal. The reference signal can be demodulated independently of the paging indicator signal. Demodulation of the reference signal or the paging indicator signal can prepare program step S 430  to calculate a score based on the reference signal CQI and the paging indicator signal SNR, respectively. 
     Demodulation of the paging indicator signal, such as with an FFT and channel estimation, may take into account the transmit signal structure. For example, the transmit signal may include space frequency block code (SFBC) properties that may be used to demodulate the paging indicator channel. 
     For example, the paging signal may include orthogonal signal components, such as OFDMA signal elements, that fall within a prescribed set of FFT time-frequency bins. 
     The program step S 425  can include single or multi-variate parameter estimation subroutines that can determine, for example, a center frequency of an FFT bin, a Doppler shift, a real or complex multi-path interference path loss, other signal parameters and channel coefficients. The channel coefficients can be used for equalization, demodulation, and decoding aspects of a paging signal. 
     From program step S 425 , program flow can proceed to program step S 430  in which a signal quality metric or score, such as a CQI, can be calculated. The signal quality score can include a SNR, a SIR, a CQI, a signal power level, and the like. The signal quality metric can be based on a combination of SNR, SIR, CQI, and the like. The signal quality metric can qualify the suitability of a current timing hypothesis for use in demodulating the signal in a subsequent step. 
     From program step S 430 , program flow can proceed to program step S 435  in which the calculated signal guide by score can be compared to a threshold score. For example, a CQI of 20 can be compared with a threshold CQI of 25. If the calculated score equals or exceeds the threshold, program flow can proceed to program step S 455 , otherwise program flow can proceed to program step S 440 . 
     In program step S 440 , a count or index of given hypotheses under evaluation can be compared against the maximum or total number of hypotheses. If the current hypothesis index equals or exceeds the total number of hypotheses, then program flow can proceed to program step S 445 , otherwise program flow can proceed to program step S 420 . 
     In program step S 445 , the best timing hypothesis can be selected and used to process the paging signal. For example, the selected or best timing hypothesis can be selected based on the largest score. The best timing hypothesis may include weighted combinations from hypotheses with sub-threshold scores. The signal quality metric and the timing and channel parameters that apply to the best timing hypothesis can be extracted from a memory, such as score memory  130   a.    
     From program step S 445 , program flow can proceed to program step S 450  in which the paging signal can be demodulated using best timing hypothesis and associated channel coefficients. For example, the paging signal can be demodulated using an FFT, a discrete Fourier transform (DFT), a chirp-Z transform, and the like. Program steps S 445  and S 450  can correspond to program steps S 420  and S 425 , respectively, but use a posteriori estimates of paging signal TOA and channel coefficients. 
     From program step S 450 , program flow can proceed to program step S 455  in which the demodulated signal can be decoded. The decoding process can include bit detection, hard limiting, discrimination, quantization, sequence estimation, and the like. For example, the decoding process can include applying a CRC decoder, a forward error correction (FEC) decoder, a ML decoder, a Viterbi decoder, a turbo decoder, and the like. 
     From program step S 455 , program flow can proceed to program step S 460  in which the availability of a message from a base station can be evaluated. The base station can indicate to the wireless device that a message or downlink communication is available. If a message is available, program flow can proceed from step S 460  to program step S 465  and the standby mode can be exited. Otherwise, program flow can proceed to program step S 470  in which the standby mode can be resumed. 
     In both program steps S 465  and S 470 , the program can calculate and store parameters used for subsequent wake-up operations in step S 415 . For example, S 465  and S 470  can include sub-steps that determine a next timing window width, a pre-trigger time that precedes the TOA of a next paging signal, a timing hypothesis granularity, and the like. 
     It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also, various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art, and are also intended to be encompassed by the following claims.