Abstract:
Decision metrics used to decode wireless communication payloads are combined for successive frames to improve decoding of the later received frames. A bitwise payload difference between successive frames is encoded in the same manner the payloads are encoded. Decision metrics determined for the earlier received frame are combined with the encoded payload difference to generate adjusted decision metrics. The adjusted decision metrics are combined with decision metrics determined for the later received frame. The combined decision metrics are decoded to generate a payload for the later received frame. If the decoding is not successful the combined decision metrics are carried forward and the process is repeated based on the payload difference between the following frames.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 61/242,307, entitled “METHOD AND APPARATUS FOR COMBINING DECISION METRICS FOR DECODING BASED ON PAYLOAD DIFFERENCE,” filed on Sep. 14, 2009, the disclosure of which is expressly incorporated by reference herein in its entirety. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    Aspects of the present disclosure relate generally to wireless communication systems, and more particularly, to techniques for decoding in wireless communication systems. 
         [0004]    2. Background 
         [0005]    Wireless communication networks are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, and the like. These wireless networks may be multiple-access networks capable of supporting multiple users by sharing the available network resources. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources. One example of such a network is the Universal Terrestrial Radio Access Network (UTRAN). The UTRAN is the radio access network (RAN) defined as a part of the Universal Mobile Telecommunications System (UMTS), a third generation (3G) mobile phone technology supported by the 3rd Generation Partnership Project (3GPP). Examples of multiple-access network formats include Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, and Single-Carrier FDMA (SC-FDMA) networks. 
         [0006]    A wireless communication network may include a number of base stations or evolved node Bs that can support communication for a number of user equipments (UEs). A UE may communicate with a base station via downlink and uplink. The downlink (or forward link) refers to the communication link from the base station to the UE, and the uplink (or reverse link) refers to the communication link from the UE to the base station. 
         [0007]    A base station may transmit data and control information on the downlink to a UE and/or may receive data and control information on the uplink from the UE. On the downlink, a transmission from the base station may encounter interference due to transmissions from neighbor base stations or from other wireless radio frequency (RF) transmitters. On the uplink, a transmission from the UE may encounter interference from uplink transmissions of other UEs communicating with the neighbor base stations or from other wireless RF transmitters. This interference may degrade performance on both the downlink and uplink. 
         [0008]    As the demand for mobile broadband access continues to increase, the possibilities of interference and congested networks grows with more UEs accessing the long-range wireless communication networks and more short-range wireless systems being deployed in communities. Research and development continue to advance the UMTS technologies not only to meet the growing demand for mobile broadband access, but to advance and enhance the user experience with mobile communications. 
       SUMMARY 
       [0009]    In one aspect of the disclosure, a method of wireless communication includes determining first decision metrics for a first frame carrying a first payload, determining second decision metrics for a second frame carrying a second payload, and determining payload difference between the second payload and the first payload. The method combines the first and second decision metrics based on the payload difference to obtain combined decision metrics; and decodes the combined decision metrics to obtain a decoded second payload. 
         [0010]    In an additional aspect of the disclosure, an apparatus for wireless communication includes means for determining first decision metrics for a first frame carrying a first payload, means for determining second decision metrics for a second frame carrying a second payload, and means for determining a payload difference between the second payload and the first payload. The apparatus also includes means for combining the first and second decision metrics based on the payload difference to obtain combined decision metrics; and means for decoding the combined decision metrics to obtain a decoded second payload. 
         [0011]    In an additional aspect of the disclosure, a computer program product has a computer-readable medium having program code recorded thereon. This program code includes code to determine first decision metrics for a first frame carrying a first payload, code to determine second decision metrics for a second frame carrying a second payload, and code to determine a payload difference between the second payload and the first payload. The program code also includes code to combine the first and second decision metrics based on the payload difference to obtain combined decision metrics, and code to decode the combined decision metrics to obtain a decoded second payload. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a block diagram conceptually illustrating an example of a mobile communication system. 
           [0013]      FIG. 2  is a block diagram conceptually illustrating an example of a downlink frame structure in a mobile communication system. 
           [0014]      FIG. 3  is a block diagram conceptually illustrating an exemplary frame structure in uplink LTE/-A communications. 
           [0015]      FIG. 4  is a block diagram conceptually illustrating a design of a base station/eNB and a UE configured according to one aspect of the present disclosure. 
           [0016]      FIG. 5  is a block diagram conceptually illustrating an exemplary payload for a PBCH according to one aspect of the present disclosure. 
           [0017]      FIG. 6  is a block diagram conceptually illustrating processing at an eNB for a PBCH transmission according to one aspect of the present disclosure. 
           [0018]      FIG. 7  is a block diagram conceptually illustrating characteristic of a linear code according to one aspect of the present disclosure. 
           [0019]      FIG. 8  is a block diagram conceptually illustrating decoding PBCH transmissions with decision metric combining according to one aspect of the present disclosure. 
           [0020]      FIG. 9  is a block diagram conceptually illustrating a process for performing decoding in a communication system according to one aspect of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    The detailed description set forth below, in connection with the appended drawings, is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of the various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form in order to avoid obscuring such concepts. 
         [0022]    The techniques described herein may be used for various wireless communication networks such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA and other networks. The terms “network” and “system” are often used interchangeably. A CDMA network may implement a radio technology, such as Universal Terrestrial Radio Access (UTRA), Telecommunications Industry Association&#39;s (TIA&#39;s) CDMA2000®, and the like. The UTRA technology includes Wideband CDMA (WCDMA) and other variants of CDMA. The CDMA2000® technology includes the IS-2000, IS-95 and IS-856 standards from the Electronics Industry Alliance (EIA) and TIA. A TDMA network may implement a radio technology, such as Global System for Mobile Communications (GSM). An OFDMA network may implement a radio technology, such as Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDMA, and the like. The UTRA and E-UTRA technologies are part of Universal Mobile Telecommunication System (UMTS). 3GPP Long Term Evolution (LTE) and LTE-Advanced (LTE-A) are newer releases of the UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described in documents from an organization called the “3rd Generation Partnership Project” (3GPP). CDMA2000® and UMB are described in documents from an organization called the “3rd Generation Partnership Project 2” (3GPP2). The techniques described herein may be used for the wireless networks and radio access technologies mentioned above, as well as other wireless networks and radio access technologies. For clarity, certain aspects of the techniques are described below for LTE or LTE-A (together referred to in the alternative as “LTE/-A”) and use such LTE/-A terminology in much of the description below. 
         [0023]      FIG. 1  shows a wireless communication network  100 , which may be an LTE-A network. The wireless network  100  includes a number of evolved node Bs (eNBs)  110  and other network entities. An eNB may be a station that communicates with the UEs and may also be referred to as a base station, a node B, an access point, and the like. Each eNB  110  may provide communication coverage for a particular geographic area. In 3GPP, the term “cell” can refer to this particular geographic coverage area of an eNB and/or an eNB subsystem serving the coverage area, depending on the context in which the term is used. 
         [0024]    An eNB may provide communication coverage for a macro cell, a pico cell, a femto cell, and/or other types of cell. A macro cell generally covers a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscriptions with the network provider. A pico cell would generally cover a relatively smaller geographic area and may allow unrestricted access by UEs with service subscriptions with the network provider. A femto cell would also generally cover a relatively small geographic area (e.g., a home) and, in addition to unrestricted access, may also provide restricted access by UEs having an association with the femto cell (e.g., UEs in a closed subscriber group (CSG), UEs for users in the home, and the like). An eNB for a macro cell may be referred to as a macro eNB. An eNB for a pico cell may be referred to as a pico eNB. And, an eNB for a femto cell may be referred to as a femto eNB or a home eNB. In the example shown in  FIG. 1 , the eNBs  110   a ,  110   b  and  110   c  are macro eNBs for the macro cells  102   a ,  102   b  and  102   c , respectively. The eNB  110   x  is a pico eNB for a pico cell  102   x . And, the eNBs  110   y  and  110   z  are femto eNBs for the femto cells  102   y  and  102   z , respectively. An eNB may support one or multiple (e.g., two, three, four, and the like) cells. 
         [0025]    The wireless network  100  also includes relay stations. A relay station is a station that receives a transmission of data and/or other information from an upstream station (e.g., an eNB, a UE, or the like) and sends a transmission of the data and/or other information to a downstream station (e.g., another UE, another eNB, or the like). A relay station may also be a UE that relays transmissions for other UEs. In the example shown in  FIG. 1 , a relay station  110   r  may communicate with the eNB  110   a  and a UE  120   r , in which the relay station  110   r  acts as a relay between the two network elements (the eNB  110   a  and the UE  120   r ) in order to facilitate communication between them. A relay station may also be referred to as a relay eNB, a relay, and the like. 
         [0026]    The wireless network  100  may support synchronous or asynchronous operation. For synchronous operation, the eNBs may have similar frame timing, and transmissions from different eNBs may be approximately aligned in time. For asynchronous operation, the eNBs may have different frame timing, and transmissions from different eNBs may not be aligned in time. The techniques described herein may be used for either synchronous or asynchronous operations. 
         [0027]    A network controller  130  may couple to a set of eNBs and provide coordination and control for these eNBs. The network controller  130  may communicate with the eNBs  110  via a backhaul  132 . The eNBs  110  may also communicate with one another, e.g., directly or indirectly via a wireless backhaul  134  or a wireline backhaul  136 . 
         [0028]    The UEs  120  are dispersed throughout the wireless network  100 , and each UE may be stationary or mobile. A UE may also be referred to as a terminal, a mobile station, a subscriber unit, a station, or the like. A UE may be a cellular phone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a laptop computer, a cordless phone, a wireless local loop (WLL) station, or the like. A UE may be able to communicate with macro eNBs, pico eNBs, femto eNBs, relays, and the like. In  FIG. 1 , a solid line with double arrows indicates desired transmissions between a UE and a serving eNB, which is an eNB designated to serve the UE on the downlink and/or uplink. A dashed line with double arrows indicates interfering transmissions between a UE and an eNB. 
         [0029]    LTE/-A utilizes orthogonal frequency division multiplexing (OFDM) on the downlink and single-carrier frequency division multiplexing (SC-FDM) on the uplink. OFDM and SC-FDM partition the system bandwidth into multiple (K) orthogonal subcarriers, which are also commonly referred to as tones, bins, or the like. Each subcarrier may be modulated with data. In general, modulation symbols are sent in the frequency domain with OFDM and in the time domain with SC-FDM. The spacing between adjacent subcarriers may be fixed, and the total number of subcarriers (K) may be dependent on the system bandwidth. For example, K may be equal to 128, 256, 512, 1024 or 2048 for a corresponding system bandwidth of 1.25, 2.5, 5, 10 or 20 megahertz (MHz), respectively. The system bandwidth may also be partitioned into sub-bands. For example, a sub-band may cover 1.08 MHz, and there may be 1, 2, 4, 8 or 16 sub-bands for a corresponding system bandwidth of 1.25, 2.5, 5, 10 or 20 MHz, respectively. 
         [0030]      FIG. 2  shows a downlink frame structure used in LTE/-A. The transmission timeline for the downlink may be partitioned into units of radio frames. Each radio frame may have a predetermined duration (e.g., 10 milliseconds (ms)) and may be partitioned into 10 subframes with indices of 0 through 9. Each subframe may include two slots. Each radio frame may thus include 20 slots with indices of 0 through 19. Each slot may include L symbol periods, e.g., 7 symbol periods for a normal cyclic prefix (as shown in  FIG. 2 ) or 14 symbol periods for an extended cyclic prefix. The 2L symbol periods in each subframe may be assigned indices of 0 through 2L−1. The available time frequency resources may be partitioned into resource blocks. Each resource block may cover N subcarriers (e.g., 12 subcarriers) in one slot. 
         [0031]    In LTE/-A, an eNB may send a primary synchronization signal (PSS) and a secondary synchronization signal (SSS) for each cell in the eNB. The primary and secondary synchronization signals may be sent in symbol periods  6  and  5 , respectively, in each of subframes  0  and  5  of each radio frame with the normal cyclic prefix, as shown in  FIG. 2 . The synchronization signals may be used by UEs for cell detection and acquisition. The eNB may send a Physical Broadcast Channel (PBCH) in symbol periods  0  to  3  in slot  1  of subframe  0 . The PBCH may carry certain system information, as discussed in further detail below. 
         [0032]    The eNB may send a Physical Control Format Indicator Channel (PCFICH) in the first symbol period of each subframe, as seen in  FIG. 2 . The PCFICH may convey the number of symbol periods (M) used for control channels, where M may be equal to 1, 2 or 3 and may change from subframe to subframe. M may also be equal to 4 for a small system bandwidth, e.g., with less than 10 resource blocks. In the example shown in  FIG. 2 , M=3. The eNB may send a Physical HARQ Indicator Channel (PHICH) and a Physical Downlink Control Channel (PDCCH) in the first M symbol periods of each subframe. The PDCCH and PHICH are also included in the first three symbol periods in the example shown in  FIG. 2 . The PHICH may carry information to support hybrid automatic retransmission (HARQ). The PDCCH may carry information on resource allocation for UEs and control information for downlink channels. The eNB may send a Physical Downlink Shared Channel (PDSCH) in the remaining symbol periods of each subframe. The PDSCH may carry data for UEs scheduled for data transmission on the downlink. 
         [0033]    In addition to sending PHICH and PDCCH in the control section of each subframe, i.e., the first symbol period of each subframe, the LTE-A may also transmit these control-oriented channels in the data portions of each subframe as well. As shown in  FIG. 2 , these new control designs utilizing the data region, e.g., the Relay-Physical Downlink Control Channel (R-PDCCH) and Relay-Physical HARQ Indicator Channel (R-PHICH) are included in the later symbol periods of each subframe. The R-PDCCH is a new type of control channel utilizing the data region originally developed in the context of half-duplex relay operation. Different from legacy PDCCH and PHICH, which occupy the first several control symbols in one subframe, R-PDCCH and R-PHICH are mapped to resource elements (REs) originally designated as the data region. The new control channel may be in the form of Frequency Division Multiplexing (FDM), Time Division Multiplexing (TDM), or a combination of FDM and TDM. 
         [0034]    The eNB may send the PSS, SSS and PBCH in the center 1.08 MHz of the system bandwidth used by the eNB. The eNB may send the PCFICH and PHICH across the entire system bandwidth in each symbol period in which these channels are sent. The eNB may send the PDCCH to groups of UEs in certain portions of the system bandwidth. The eNB may send the PDSCH to specific UEs in specific portions of the system bandwidth. The eNB may send the PSS, SSS, PBCH, PCFICH and PHICH in a broadcast manner to all UEs, may send the PDCCH in a unicast manner to specific UEs, and may also send the PDSCH in a unicast manner to specific UEs. 
         [0035]    A number of resource elements may be available in each symbol period. Each resource element may cover one subcarrier in one symbol period and may be used to send one modulation symbol, which may be a real or complex value. Resource elements not used for a reference signal in each symbol period may be arranged into resource element groups (REGs). Each REG may include four resource elements in one symbol period. The PCFICH may occupy four REGs, which may be spaced approximately equally across frequency, in symbol period  0 . The PHICH may occupy three REGs, which may be spread across frequency, in one or more configurable symbol periods. For example, the three REGs for the PHICH may all belong in symbol period  0  or may be spread in symbol periods  0 ,  1  and  2 . The PDCCH may occupy 9, 18, 32 or 64 REGs, which may be selected from the available REGs, in the first M symbol periods. Only certain combinations of REGs may be allowed for the PDCCH. 
         [0036]    A UE may know the specific REGs used for the PHICH and the PCFICH. The UE may search different combinations of REGs for the PDCCH. The number of combinations to search is typically less than the number of allowed combinations for the PDCCH. An eNB may send the PDCCH to the UE in any of the combinations that the UE will search. 
         [0037]    A UE may be within the coverage of multiple eNBs. One of these eNBs may be selected to serve the UE. The serving eNB may be selected based on various criteria such as received power, path loss, signal-to-noise ratio (SNR), etc. 
         [0038]      FIG. 3  is a block diagram  300  conceptually illustrating an exemplary frame structure in uplink long term evolution (LTE/-A) communications. The available resource blocks (RBs) for the uplink may be partitioned into a data section and a control section. The control section may be formed at the two edges of the system bandwidth and may have a configurable size. The resource blocks in the control section may be assigned to UEs for transmission of control information. The data section may include all resource blocks not included in the control section. The design in  FIG. 3  results in the data section including contiguous subcarriers, which may allow a single UE to be assigned all of the contiguous subcarriers in the data section. 
         [0039]    A UE may be assigned resource blocks in the control section to transmit control information to an eNB. The UE may also be assigned resource blocks in the data section to transmit data to the eNode B. The UE may transmit control information in a Physical Uplink Control Channel (PUCCH) on the assigned resource blocks in the control section. The UE may transmit only data or both data and control information in a Physical Uplink Shared Channel (PUSCH) on the assigned resource blocks in the data section. An uplink transmission may span both slots of a subframe and may hop across frequency as shown in  FIG. 3 . 
         [0040]    The PSS, SSS, CRS, PBCH, PUCCH, PUSCH, and other such signals and channels used in LTE/-A are described in 3GPP TS 36.211, entitled “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation,” which is publicly available. 
         [0041]    Referring back to  FIG. 1 , the wireless network  100  uses the diverse set of eNBs  110  (i.e., macro eNBs, pico eNBs, femto eNBs, and relays) to improve the spectral efficiency of the system per unit area. Because the wireless network  100  uses such different eNBs for its spectral coverage, it may also be referred to as a heterogeneous network. The macro eNBs  110   a - c  are usually carefully planned and placed by the provider of the wireless network  100 . The macro eNBs  110   a - c  generally transmit at high power levels (e.g., 5 W-40 W). The pico eNB  110   x  and the relay  110   r , which generally transmit at substantially lower power levels (e.g., 100 mW-2 W), may be deployed in a relatively unplanned manner to eliminate coverage holes in the coverage area provided by the macro eNBs  110   a - c  and improve capacity in the hot spots. The femto eNBs  110   y - z , which are typically deployed independently from the wireless network  100  may, nonetheless, be incorporated into the coverage area of the wireless network  100  either as a potential access point to the wireless network  100 , if authorized by their administrator(s), or at least as an active and aware eNB that may communicate with the other eNBs  110  of the wireless network  100  to perform resource coordination and coordination of interference management. The femto eNBs  110   y - z  typically also transmit at substantially lower power levels (e.g., 100 mW-2 W) than the macro eNBs  110   a - c.    
         [0042]    In operation of a heterogeneous network, such as the wireless network  100 , each UE is usually served by the eNB  110  with the better signal quality, while the unwanted signals received from the other eNBs  110  are treated as interference. While such operational principals can lead to significantly sub-optimal performance, gains in network performance are realized in the wireless network  100  by using intelligent resource coordination among the eNBs  110 , better server selection strategies, and more advanced techniques for efficient interference management. 
         [0043]    A pico eNB, such as the pico eNB  110   x , is characterized by a substantially lower transmit power when compared with a macro eNB, such as the macro eNBs  110   a - c . A pico eNB will also usually be placed around a network, such as the wireless network  100 , in an ad hoc manner. Because of this unplanned deployment, wireless networks with pico eNB placements, such as the wireless network  100 , can be expected to have large areas with low signal to interference conditions, which can make for a more challenging RF environment for control channel transmissions to UEs on the edge of a coverage area or cell (a “cell-edge” UE). Moreover, the potentially large disparity (e.g., approximately 20 dB) between the transmit power levels of the macro eNBs  110   a - c  and the pico eNB  110   x  implies that, in a mixed deployment, the downlink coverage area of the pico eNB  110   x  will be much smaller than that of the macro eNBs  110   a - c.    
         [0044]    In the uplink case, however, the signal strength of the uplink signal is governed by the UE, and, thus, will be similar when received by any type of the eNBs  110 . With the uplink coverage areas for the eNBs  110  being roughly the same or similar, uplink handoff boundaries will be determined based on channel gains. This can lead to a mismatch between downlink handover boundaries and uplink handover boundaries. Without additional network accommodations, the mismatch would make the server selection or the association of UE to eNB more difficult in the wireless network  100  than in a macro eNB-only homogeneous network, where the downlink and uplink handover boundaries are more closely matched. 
         [0045]    If server selection is based predominantly on downlink received signal strength, as provided in the LTE Release 8 standard, the usefulness of mixed eNB deployment of heterogeneous networks, such as the wireless network  100 , will be greatly diminished. This is because the larger coverage area of the higher powered macro eNBs, such as the macro eNBs  110   a - c , limits the benefits of splitting the cell coverage with the pico eNBs, such as the pico eNB  110   x , because, the higher downlink received signal strength of the macro eNBs  110   a - c  will attract all of the available UEs, while the pico eNB  110   x  may not be serving any UE because of its much weaker downlink transmission power. Moreover, the macro eNBs  110   a - c  will likely not have sufficient resources to efficiently serve those UEs. Therefore, the wireless network  100  will attempt to actively balance the load between the macro eNBs  110   a - c  and the pico eNB  110   x  by expanding the coverage area of the pico eNB  110   x . This concept is referred to as range extension. 
         [0046]    The wireless network  100  achieves this range extension by changing the manner in which server selection is determined. Instead of basing server selection on downlink received signal strength, selection is based more on the quality of the downlink signal. In one such quality-based determination, server selection may be based on determining the eNB that offers the minimum path loss to the UE. Additionally, the wireless network  100  provides a fixed partitioning of resources equally between the macro eNBs  110   a - c  and the pico eNB  110   x . However, even with this active balancing of load, downlink interference from the macro eNBs  110   a - c  should be mitigated for the UEs served by the pico eNBs, such as the pico eNB  110   x . This can be accomplished by various methods, including interference cancellation at the UE, resource coordination among the eNBs  110 , or the like. However, there are some cases when interference cancellation is not desirable. 
         [0047]      FIG. 4  shows a block diagram of a design of a base station/eNB  110  and a UE  120 , which may be one of the base stations/eNBs and one of the UEs in  FIG. 1 . For a restricted association scenario, the base station  110  may be the macro eNB  110   c  in  FIG. 1 , and the UE  120  may be the UE  120   y . The base station  110  may also be a base station of some other type. The base station  110  may be equipped with antennas  434   a  through  434   t , and the UE  120  may be equipped with antennas  452   a  through  452   r.    
         [0048]    At the base station  110 , a transmit processor  420  may receive data from a data source  412  and control information from a controller/processor  440 . The control information may be for the PBCH, PCFICH, PHICH, PDCCH, etc. The data may be for the PDSCH, etc. The processor  420  may process (e.g., encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. The processor  420  may also generate reference symbols, e.g., for the PSS, SSS, and cell-specific reference signal. A transmit (TX) multiple-input multiple-output (MIMO) processor  430  may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, and/or the reference symbols, if applicable, and may provide output symbol streams to the modulators (MODs)  432   a  through  432   t . Each modulator  432  may process a respective output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Each modulator  432  may further process (e.g., convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink signal. Downlink signals from modulators  432   a  through  432   t  may be transmitted via the antennas  434   a  through  434   t , respectively. 
         [0049]    At the UE  120 , the antennas  452   a  through  452   r  may receive the downlink signals from the base station  110  and may provide received signals to the demodulators (DEMODs)  454   a  through  454   r , respectively. Each demodulator  454  may condition (e.g., filter, amplify, downconvert, and digitize) a respective received signal to obtain input samples. Each demodulator  454  may further process the input samples (e.g., for OFDM, etc.) to obtain received symbols. A MIMO detector  456  may obtain received symbols from all the demodulators  454   a  through  454   r , perform MIMO detection on the received symbols if applicable, and provide detected symbols. A receive processor  458  may process (e.g., demodulate, deinterleave, and decode) the detected symbols, provide decoded data for the UE  120  to a data sink  460 , and provide decoded control information to a controller/processor  480 . 
         [0050]    On the uplink, at the UE  120 , a transmit processor  464  may receive and process data (e.g., for the PUSCH) from a data source  462  and control information (e.g., for the PUCCH) from the controller/processor  480 . The processor  464  may also generate reference symbols for a reference signal. The symbols from the transmit processor  464  may be precoded by a TX MIMO processor  466  if applicable, further processed by the demodulators  454   a  through  454   r  (e.g., for SC-FDM, etc.), and transmitted to the base station  110 . At the base station  110 , the uplink signals from the UE  120  may be received by the antennas  434 , processed by the modulators  432 , detected by a MIMO detector  436  if applicable, and further processed by a receive processor  438  to obtain decoded data and control information sent by the UE  120 . The processor  438  may provide the decoded data to a data sink  439  and the decoded control information to the controller/processor  440 . 
         [0051]    The controllers/processors  440  and  480  may direct the operation at the base station  110  and the UE  120 , respectively. The processor  440  and/or other processors and modules at the base station  110  may perform or direct the execution of various processes for the techniques described herein. The processor  480  and/or other processors and modules at the UE  120  may also perform or direct the execution of the functional blocks illustrated in  FIGS. 4 and 5 , and/or other processes for the techniques described herein. The memories  442  and  482  may store data and program codes for the base station  110  and the UE  120 , respectively. A scheduler  444  may schedule UEs for data transmission on the downlink and/or uplink. 
         [0052]    The techniques described herein may be used to decode various types of transmissions sent on the downlink and uplink, for example, when interference cancellation is not employed, and a low signal to noise ratio (SNR) exists. For clarity, much of the description below is for a Physical Broadcast Channel (PBCH) in LTE, although any known payload or payload having a predictable variation (e.g., deterministic variation) can be processed according to the disclosure. 
         [0053]      FIG. 5  shows an exemplary payload for each PBCH transmission. The PBCH payload includes a 6-bit Master Information Block (MIB), an 8-bit System Frame Number (SFN), and 10 reserved bits. The eNB may increment a 10-bit SFN by one in each 10 ms radio frame. The eNB transmits the PBCH periodically, e.g., every four radio frames and may use the eight most significant bits of the 10-bit SFN as the 8-bit SFN. The 8-bit SFN is incremented by one for each PBCH transmission. The MIB includes information that is semi-static, changing infrequently. Thus, redundant information is frequently re-sent. The reserved bits are set to fixed values (e.g., all zeros). Alternatively, one or more reserved bits may be used to convey information, which may be semi-static or dynamic. 
         [0054]    In general, the PBCH payload may include any number of fields, and each field can carry any type of information and may be of any size. The information in each field may be semi-static or dynamic. The information in a given field may also change in a deterministic manner, e.g., incremented by one in the case of the 8-bit SFN. 
         [0055]      FIG. 6  shows processing at the eNB for a PBCH transmission. In general, the PBCH payload may be processed with any combination of error detection code (e.g., CRC) and error correction code (e.g., tail biting convolutional code TBCC). In the illustrative embodiment, a PBCH payload is attached with a cyclic redundancy check (CRC) to obtain a data block. The CRC may be generated across the entire PBCH payload and may be 16 bits in LTE. The data block is the 24-bit payload and the 16-bit CRC and thus includes 40 data bits. The data block may be encoded with a rate 1/3 tail biting convolutional code (TBCC) to obtain a codeword of 120 code bits. The 120 code bits may be mapped to QPSK modulation symbols, which is further processed and transmitted in a PBCH transmission to UEs. 
         [0056]    A UE receives a PBCH transmission from the eNB and attempts to decode the received PBCH transmission. The UE may be able to correctly decode the received PBCH transmission if the channel conditions observed by the UE are not too poor. In certain scenarios, the UE is not be able to correctly decode the received PBCH transmission, and the CRC check would fail. The UE then receives the next PBCH transmission from the eNB and may again attempt to decode this received PBCH transmission. The UE may also not be able to correctly decode this received PBCH transmission if the channel conditions are poor, e.g., due to high interference. 
         [0057]    In an aspect, the UE combines decision metrics for multiple received PBCH transmissions whenever a received PBCH transmission is decoded in error. The UE may combine the decision metrics based on the difference between PBCH payloads, as described below. The UE may then decode the combined decision metrics instead of the decision metrics for each PBCH transmission. The combined decision metrics have more energy and may also provide time diversity. Consequently, the UE may be able to correctly decode the combined decision metrics even in poor channel conditions. 
         [0058]      FIG. 7  illustrates a characteristic of a linear code, such as a CRC or a TBCC. A first payload P 1  is encoded with the linear code to obtain a first codeword C 1 . A second payload P 2  is also encoded with the same linear code to obtain a second codeword C 2 . The difference between the second payload and the first payload is computed and denoted as ΔP=P 2 −P 1 . The payload difference is encoded with the same linear code to obtain a third codeword ΔC=C 2 −C 1 . The third codeword is the difference between the second codeword C 2  and the first codeword C 1 . 
         [0059]    As shown in  FIG. 7 , two payloads may be encoded separately with the linear code to obtain two codewords. For a linear code, the sum or difference of the two codewords is equal to a codeword obtained by encoding the sum or difference of the two payloads with the same linear code. This characteristic of the linear code may be exploited to combine decision metrics for different PBCH transmissions, as described below. 
         [0060]      FIG. 8  shows an exemplary design of decoding PBCH transmissions with decision metric combining to improve decoding performance. A UE receives a PBCH transmission with payload P 1  (e.g., MIB) in frame t (block  812 ). The UE computes log-likelihood ratios (LLRs) for code bits for payload P 1  based on the received PBCH transmission (block  814 ). LLRs are commonly used as soft decision metrics for decoding. Other types of decision metrics may also be used for decoding. The UE may obtain 120 LLRs for the 120 code bits for payload P 1 , one LLR for each code bit, and then store the LLRs. The LLRs for payload P 1  are denoted as LLR 1 . The UE decodes the LLRs to obtain a decoded payload P 1  (block  818 ). The UE may perform a CRC check to determine whether payload P 1  is decoded correctly. If the answer is yes, then the UE terminates the decoding of the PBCH. If the PBCH transmission in frame t is decoded in error, then the UE may store LLR 1  to improve decoding of the next PBCH transmission(s) as described below. 
         [0061]    The UE receives a PBCH transmission with payload P 2  (e.g., MIB) in frame t+1 (block  832 ). The UE may compute LLRs for code bits for payload P 2  based on the received PBCH transmission (block  834 ). The LLRs for payload P 2  are denoted as LLR 2 . The UE determines the binary difference (i.e., XOR) between payload P 2  and payload P 1 , which may be denoted as ΔP 2  (block  822 ). The UE encodes the payload difference ΔP 2  in the same manner as performed by the eNB for a PBCH payload to obtain a codeword having 120 code bits for the payload difference (block  824 ). For example, the UE may generate a CRC for the payload difference and encode the payload difference and the CRC with the TBCC to obtain the codeword. This codeword is denoted as ΔC 2 . The value ΔC 2  is the difference between the codeword C 1  generated by the eNB for frame t+1 and the codeword C 0  generated by the eNB for frame t. 
         [0062]    The UE then combines the computed LLRs for payload P 1  with the computed LLRs for payload P 2  by taking into account the payload difference between payload P 2  and payload P 1 . The UE may obtain 120 code bits for codeword ΔC 2 , with each code bit having a binary value of either ‘0’ or ‘1’. The UE adjusts the sign/polarity of each computed LLR for payload P 1  based on the corresponding code bit in codeword ΔC 2  (via multiplier  826 ). The UE may perform sign adjustment for each computed LLR for payload P 1 , as follows: 
         [0063]    Flip the sign of the computed LLR for code bit k for payload P 1  if code bit k in codeword ΔC 2  has a value of ‘1’, or 
         [0064]    Retain the sign of the computed LLR for code bit k for payload P 1  if code bit k in codeword ΔC 2  has a value of ‘0’. 
         [0065]    The UE adjusts the computed LLRs for all 120 code bits (i.e., for 1&lt;k&lt;120) for payload P 1  in a similar manner. Each code bit k with a value of ‘1’ in codeword ΔC 2  may indicate code bit k for payload P 1  being different from code bit k for payload P 2 . Hence, the computed LLR for code bit k for payload P 1  may be flipped. 
         [0066]    The LLR adjustment may also be viewed as scrambling of the LLRs based on the codeword difference. The LLR adjustment converts the computed LLRs for payload P 1  into adjusted LLRs for payload P 2 . The UE then sums (with a binary operation) the adjusted LLRs for payload P 2  with the computed LLRs for payload P 2  to obtain combined LLRs for payload P 2  (adder  836 ). The combined LLRs include the energy in the received PBCH transmission with payload P 2  as well as the energy in the received PBCH transmission with payload P 1 . The UE decode the combined LLRs for payload P 2  to obtain a decoded payload P 2  (block  838 ). The likelihood of correct decoding is higher due to the higher energy in the combined LLRs. The UE may perform CRC check to determine whether payload P 2  is decoded correctly. If the answer is yes, then the UE terminates the decoding of the PBCH. 
         [0067]    If the PBCH transmission in frame t+1 is still decoded in error, then the UE receives a PBCH transmission with payload P 3  (e.g., MIB) in frame t+2 (block  852 ). The UE computes LLRs for code bits for payload P 3  based on the received PBCH transmission (block  854 ). The LLRs for payload P 3  are denoted as LLR 3 . The UE determines the difference between payload P 3  and payload P 2 , which is denoted as ΔP 3  (block  842 ). The UE encodes the payload difference ΔP 3  to obtain a codeword ΔC 3  having 120 code bits (block  844 ). 
         [0068]    The UE may then combine the combined LLRs for payload P 2  with the computed LLRs for payload P 3  by taking into account the payload difference between payload P 3  and payload P 2 . The combined LLRs for payload P 2  include the computed LLRs for payload P 1  (LLR 1 ) as well as the computed LLRs for payload P 2  (LLR 2 ). The UE may adjust the sign/polarity of each combined LLR for payload P 2  based on the corresponding code bit in codeword ΔC 3 , as described above (via multiplier  846 ). The sign adjustment converts the combined LLRs for payload P 2  into adjusted LLRs for payload P 3 . The UE then sums the adjusted LLRs for payload P 3  with the computed LLRs for payload P 3  to obtain combined LLRs for payload P 3  (adder  856 ). The combined LLRs for payload P 3  include the total energy in the three received PBCH transmissions for payloads P 1 , P 2  and P 3 . The UE decodes the combined LLRs for payload P 3  to obtain a decoded payload P 3  (block  858 ). The UE may perform CRC check to determine whether payload P 3  is decoded correctly. If the answer is yes, then the UE may terminate the decoding of the PBCH. If payload P 3  is decoded in error, then the UE receives the next PBCH transmission and may repeat the LLR combine and decode process. 
         [0069]    As shown in  FIG. 8 , the UE saves the latest combined LLRs (or the computed LLRs for the first PBCH transmission) when a PBCH transmission is decoded in error. The UE adjusts and combines the saved LLRs with the computed LLRs for the next PBCH transmission to obtain new combined LLRs having more energy. The higher energy improves the likelihood of correctly decoding the PBCH transmission. The UE combine LLRs for as many PBCH transmissions as desired until one is decoded correctly. The UE may save only one set of combined LLRs, which includes the computed LLRs for all PBCH transmissions decoded in error. 
         [0070]    The UE determines the difference between two payloads that change infrequently (e.g., MIBs) and uses the payload difference to combine LLRs for the two payloads. The payload difference is determined based on the known structure and characteristics of the payloads. 
         [0071]    Unlike the MIB, the system frame number (SFN) changes from one PBCH transmission to the next. In a synchronized network, all eNBs have the same frame timing and the same SFN. The UE may be able to obtain the SFN of the current frame from any eNB. The UE computes the SFN for the next frame by incrementing the known SFN for the current frame by one. The UE may determine the entire payload for the next frame by (i) using the computed SFN for the next frame and (ii) assuming that the MIB and reserved bits will not change in the next frame. The payload difference may then include (i) zeros for the MIB and the reserved bits and (ii) the difference between the computed SFN for the next frame and the known SFN for the current frame. The payload difference may be processed (e.g., attached with a CRC and encoded) to obtain code bits used for LLR adjustment, as described above. 
         [0072]    If the network is asynchronous, the UE may not know the SFN of the current frame. In one embodiment, the UE performs LLR combining and decoding for all possible SFN differences. If the SFN is incremented by one in each frame, then eight SFN differences are possible and are shown in Table 1. The values in Table 1 are given in binary, and each x may be either ‘0’ or ‘1’. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 SFN Difference 
                 Scenario 
               
               
                   
                   
               
             
             
               
                   
                 00000001 
                 SFN going from xxxxxxx0 to xxxxxxx1 
               
               
                   
                 00000011 
                 SFN going from xxxxxx01 to xxxxxx10 
               
               
                   
                 00000111 
                 SFN going from xxxxx011 to xxxxx100 
               
               
                   
                 00001111 
                 SFN going from xxxx0111 to xxxx1000 
               
               
                   
                 00011111 
                 SFN going from xxx01111 to xxx10000 
               
               
                   
                 00111111 
                 SFN going from xx011111 to xx100000 
               
               
                   
                 01111111 
                 SFN going from x0111111 to x1000000 
               
               
                   
                 11111111 
                 SFN going from 01111111 to 10000000 
               
               
                   
                   
               
             
          
         
       
     
         [0073]    The UE performs LLR combining and decoding for each possible SFN difference. The UE then determines whether a given SFN difference is correct based on the CRC check. 
         [0074]    The UE may assume the same values for the MIB and reserved bits, as described above. In another embodiment, the UE assumes a reserved bit being used (i.e., varying across frames) and may then perform LLR combining and decoding for two hypotheses—one hypothesis for the reserved bit not changing across frames and another hypothesis for the reserved bit changing across frames. The UE may also assume multiple reserved bits being used and may perform LLR combining and decoding for each possible difference for the used reserved bits. 
         [0075]    In general, the UE may perform blind decoding and determine all possible payload differences or hypotheses based on the structure and characteristics of the payload. The UE performs LLR combining and decoding for each possible payload difference and may check whether the decoding is correct or in error for that payload difference based on the CRC check. The UE evaluates more hypotheses if more bits of the payload are unknown and can change. 
         [0076]      FIG. 9  shows a design of a process  900  for performing decoding in a communication system. The process  900  may be performed by a receiver, which may be part of a UE, a base station/eNB, or some other entity. The receiver may determine first decision metrics (e.g., LLR 1 ) for a first received transmission carrying a first payload (e.g., P 1 ) (block  912 ). The receiver determines second decision metrics (e.g., LLR 2 ) for a second received transmission carrying a second payload (e.g., P 2 ) (block  914 ). The first and second payloads may include system information and/or other types of information. The first and second received transmissions may be for the PBCH or some other channel. The receiver determines a payload difference (e.g., ΔP 2 ) between the second payload and the first payload (block  916 ). The receiver combines the first and second decision metrics based on the payload difference to obtain combined decision metrics (e.g., ΔC 2 ) (block  918 ). The decision metrics may be LLRs for code bits or some other metrics for decoding. The receiver decodes the combined decision metrics to obtain a decoded second payload (block  920 ). The receiver may determine whether the second payload is decoded correctly based on a CRC attached to the second payload. 
         [0077]    For block  916 , the receiver may determine the payload difference based on known structure and characteristics of the payloads. In one embodiment, each payload is a first part (e.g., MIB and reserved bits) and a second part (e.g., SFN). The receiver may determine the payload difference based on an assumption of (i) no change in the first part of the first and second payloads and (ii) the second part having a known variation (e.g., incrementing by one) from the first payload to the second payload. In another embodiment, the first and second payloads include a part having multiple possible differences between the first and second payloads (e.g., if the SFN is not known and/or if reserved bits are used). Multiple possible payload differences may be determined based on the multiple possible differences for the part. The receiver repeats the process (e.g., determines the payload difference, combines the decision metrics, and decodes the combined decision metrics) for each possible payload difference until the second payload is decoded correctly or all possible payload differences have been evaluated. 
         [0078]    In one embodiment of block  918 , the receiver processes the payload difference in the same manner as performed at a transmitter to obtain code bits. The receiver generates a CRC for the payload difference. The receiver then encodes the payload difference and the CRC based on the same linear code used by the transmitter to encode the first payload and the second payload to obtain the code bits. The receiver adjusts the sign of the first decision metrics based on the code bits to obtain adjusted first decision metrics. For each code bit obtained for the payload difference, the receiver may (i) flip the sign of a first decision metric for that code bit if the code bit has a first value (e.g., ‘1’) or (ii) retain the sign of the first decision metric if the code bit has a second value (e.g., ‘0’). The receiver then sums the adjusted first decision metrics and the second decision metrics to obtain the combined decision metrics. 
         [0079]    In one embodiment, the receiver decodes the first decision metrics to obtain a decoded first payload. The receiver may determine the second decision metrics, determine the payload difference, combine the first and second decision metrics, and decode the combined decision metrics in block  914  to  920  when the first payload is decoded in error. 
         [0080]    In another embodiment, if the second payload is decoded in error, then the receiver determines third decision metrics (e.g., LLR 3 ) for a third received transmission carrying a third payload (e.g., P 3 ). The receiver determines a second payload difference (e.g., ΔP 3 ) between the third payload and the second payload. The receiver combine the third decision metrics and the combined decision metrics based on the second payload difference to obtain second combined decision metrics (e.g., ΔC 3 ). The receiver then decodes the second combined decision metrics to obtain a decoded third payload. The receiver may repeat the process if the third payload is decoded in error. 
         [0081]    In one configuration, the UE  120 /eNB  110  configured for wireless communication includes means for determining first decision metrics, means for determining second decision metrics, and means for determining a payload difference between the second payload and the first payload. The UE/ 120 /eNB  110  may also include means for combining the first and second decision metrics, and means for decoding. In one aspect, the aforementioned means may be the processor(s), the controller/processor  480 , the memory  482 , the receive processor  458 , the MIMO detector  456 , the demodulators  454   a , and the antennas  452   a  configured to perform the functions recited by the aforementioned means. In another aspect, the aforementioned means may be a module or any apparatus configured to perform the functions recited by the aforementioned means. 
         [0082]    Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof. 
         [0083]    The functional blocks and modules in  FIG. 8-FIG .  9  may be processors, electronics devices, hardware devices, electronics components, logical circuits, memories, software codes, firmware codes, etc., or any combination thereof. 
         [0084]    Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the disclosure herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure. 
         [0085]    The various illustrative logical blocks, modules, and circuits described in connection with the disclosure herein may be implemented or performed with a general-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. 
         [0086]    The steps of a method or algorithm described in connection with the disclosure herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal. 
         [0087]    In one or more exemplary designs, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media. 
         [0088]    The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Thus, the disclosure is not intended to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.