Patent Publication Number: US-2013251013-A1

Title: Dynamic receiver switching

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 61/615,146, entitled, “DYNAMIC RECEIVER SWITCHING”, filed on Mar. 23, 2012, which is expressly incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     1. Field 
     Aspects of the present disclosure relate generally to wireless communication systems, and more particularly, to dynamic receiver switching. 
     2. Background 
     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. 
     A wireless communication network may include a number of base stations or 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. 
     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. 
     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. 
     SUMMARY 
     In one aspect of the disclosure, a method of wireless communication that includes determining a channel quality of a channel associated with one or more data transmissions, selecting a first receiver to decode one or more data transmissions, wherein the first receiver is associated with higher performance at the determined channel quality than a second receiver, and selecting the second receiver to decode one or more data re-transmissions of the one or more data transmissions. 
     In one aspect of the disclosure, a method of wireless communication that includes determining availability of soft metrics for a data transmission, obtaining an error rate for first data transmissions over a plurality of preceding subframes, and selecting a receiver from a plurality of available receivers, at a mobile device, based, at least in part, on the availability of soft metrics and the error rate, wherein at least one receiver of the plurality of available receivers has different operating characteristics than at least another receiver of the plurality of available receivers. 
     In an additional aspect of the disclosure, an apparatus configured for wireless communication that includes means for determining a channel quality of a channel associated with one or more data transmissions, means for selecting a first receiver to decode one or more data transmissions, wherein the first receiver is associated with higher performance at the determined channel quality than a second receiver, and means for selecting the second receiver to decode one or more data re-transmissions of the one or more data transmissions. 
     In an additional aspect of the disclosure, an apparatus configured for wireless communication that includes means for determining availability of soft metrics for a data transmission, means for obtaining an error rate for first data transmissions over a plurality of preceding subframes, and means for selecting a receiver from a plurality of available receivers, at a mobile device, based, at least in part, on the availability of soft metrics and the error rate, wherein at least one receiver of the plurality of available receivers has different operating characteristics than at least another receiver of the plurality of available receivers. 
     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 for causing at least one computer to determining a channel quality of a channel associated with one or more data transmissions, code for causing at least one computer to select a first receiver to decode one or more data transmissions, wherein the first receiver is associated with higher performance at the determined channel quality than a second receiver, and code for causing at least one computer to select the second receiver to decode one or more data re-transmissions of the one or more data transmissions. 
     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 for causing at least one computer to determine availability of soft metrics for a data transmission, code for causing at least one computer to obtain an error rate for first data transmissions over a plurality of preceding subframes, and code for causing at least one computer to select a receiver from a plurality of available receivers, at a mobile device, based, at least in part, on the availability of soft metrics and the error rate, wherein at least one receiver of the plurality of available receivers has different operating characteristics than at least another receiver of the plurality of available receivers. 
     In an additional aspect of the disclosure, an apparatus includes at least one processor and a memory coupled to the processor. The processor is configured to determining a channel quality of a channel associated with one or more data transmissions, to select a first receiver to decode one or more data transmissions, wherein the first receiver is associated with higher performance at the determined channel quality than a second receiver, and to select the second receiver to decode one or more data re-transmissions of the one or more data transmissions. 
     In an additional aspect of the disclosure, an apparatus includes at least one processor and a memory coupled to the processor. The processor is configured to determine availability of soft metrics for a data transmission, to obtain an error rate for first data transmissions over a plurality of preceding subframes, and to select a receiver from a plurality of available receivers, at a mobile device, based, at least in part, on the availability of soft metrics and the error rate, wherein at least one receiver of the plurality of available receivers has different operating characteristics than at least another receiver of the plurality of available receivers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating an example of a mobile communication system. 
         FIG. 2  is a block diagram illustrating a design of a base station/eNB and a UE configured according to one aspect of the present disclosure. 
         FIG. 3  is a functional block diagram illustrating example blocks executed to implement one aspect of the present disclosure. 
         FIG. 4  is a block diagram illustrating a receiving device configured according to one aspect of the present disclosure. 
         FIG. 5  is a call flow diagram illustrating example communication between a UE and an eNB according to one aspect of the present disclosure. 
         FIG. 6  is a functional block diagram illustrating example blocks executed to implement one aspect of the present disclosure. 
         FIG. 7  is a functional block diagram illustrating example blocks executed to implement one aspect of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     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 limit the scope of the disclosure. Rather, the detailed description includes specific details for the purpose of providing a thorough understanding of the inventive subject matter. It will be apparent to those skilled in the art that these specific details are not required in every case and that, in some instances, well-known structures and components are shown in block diagram form for clarity of presentation. 
     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. 
       FIG. 1  shows a wireless network  100  for communication, 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. 
     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. 
     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. 
     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 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 tablet computer, 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. 
     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 72, 180, 300, 600, 900, and 1200 for a corresponding system bandwidth of 1.4, 3, 5, 10, 15, 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 1.4, 3, 5, 10, 15, or 20 MHz, respectively. 
     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 station  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-200 mW) than the macro eNBs  110   a - c.    
     Channel conditions experienced by UEs  120  may vary significantly throughout wireless network  100 . A UE  120  may detect channel conditions with various measurements such as a signal-to-noise ratio (SNR), signal-to-interference-plus-noise ratio (SINR), carrier-to-interference-plus-noise ratio (CINR), etc. Information about the channel conditions, also referred to as channel state information (CSI), may be sent to a serving base station  110  and used to determine a transmission mode and other communication parameters. A hybrid automatic repeat request (HARQ) mechanism may also be used to manage the transmission and re-transmissions of data between eNBs  110  and UEs  120 . 
     As described herein, it may be advantageous for a UE  120  to select different receivers depending upon channel conditions, transmission modes, retransmission rates, and other factors. In one aspect, a UE  120  may use a different receiver for demodulation in a high SNR environment than it uses in a low SNR environment. An initial receiver may be selected according to one or more predetermined performance characteristics. The UE  120  may then be vary its receiver dynamically (i.e. subframe-to-subframe) based on additional criteria such as CSI, MCS (modulation and coding scheme), a number of retransmissions, etc. In one particular example, each UE  120  may include a first receiver having a Linear Minimum Mean Square Error (LMMSE) de-mapper engine and a second receiver having an MLD de-mapper engine. The MLD receiver may be selected for MIMO demodulation in high SNR environments whereas the LMMSE receiver may be utilized in low SNR environments. 
       FIG. 2  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 eNB  110  may be the macro eNB  110   c  in  FIG. 1 , and the UE  120  may be the UE  120   y.  The eNB  110  may also be a base station of some other type. The eNB  110  may be equipped with antennas  234   a  through  234   t,  and the UE  120  may be equipped with antennas  252   a  through  252   r.    
     At the eNB  110 , a transmit processor  220  may receive data from a data source  212  and control information from a controller/processor  240 . The control information may be for the physical broadcast channel (PBCH), physical control format indicator channel (PCFICH), physical hybrid automated repeat request channel (PHICH), physical downlink control channel (PDCCH), etc. The data may be for the physical downlink shared channel (PDSCH), etc. The transmit processor  220  may process (e.g., encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. The transmit processor  220  may also generate reference symbols, e.g., for the primary synchronization signal (PSS), secondary synchronization signal (SSS), and cell-specific or “common” reference signal (CRS). A transmit (TX) multiple-input multiple-output (MIMO) processor  230  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)  232   a  through  232   t.  Each modulator  232  may process a respective output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Each modulator  232  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  232   a  through  232   t  may be transmitted via the antennas  234   a  through  234   t,  respectively. 
     At the UE  120 , the antennas  252   a  through  252   r  may receive the downlink signals from the eNB  110  and may provide received signals to the demodulators (DEMODs)  254   a  through  254   r,  respectively. Each demodulator  254  may condition (e.g., filter, amplify, downconvert, and digitize) a respective received signal to obtain input samples. Each demodulator  254  may further process the input samples (e.g., for OFDM, etc.) to obtain received symbols. A MIMO detector  256  may obtain received symbols from all the demodulators  254   a  through  254   r,  perform MIMO detection on the received symbols if applicable, and provide detected symbols. A receive processor  258  may process (e.g., demodulate, deinterleave, and decode) the detected symbols, provide decoded data for the UE  120  to a data sink  260 , and provide decoded control information to a controller/processor  280 . Receive processor  258  may support different types of demodulation and dynamic switching according to channel conditions, performance characteristics, and the like. 
     On the uplink, at the UE  120 , a transmit processor  264  may receive and process data (e.g., for the PUSCH) from a data source  262  and control information (e.g., for the PUCCH) from the controller/processor  280 . The transmit processor  264  may also generate reference symbols for a reference signal. The symbols from the transmit processor  264  may be precoded by a TX MIMO processor  266  if applicable, further processed by the demodulators  254   a  through  254   r  (e.g., for SC-FDM, etc.), and transmitted to the eNB  110 . At the eNB  110 , the uplink signals from the UE  120  may be received by the antennas  234 , processed by the modulators  232 , detected by a MIMO detector  236  if applicable, and further processed by a receive processor  238  to obtain decoded data and control information sent by the UE  120 . The processor  238  may provide the decoded data to a data sink  239  and the decoded control information to the controller/processor  240 . 
     The controllers/processors  240  and  280  may direct the operation at the eNB  110  and the UE  120 , respectively. The controller/processor  240  and/or other processors and modules at the eNB  110  may perform or direct the execution of various processes for the techniques described herein. The controllers/processor  280  and/or other processors and modules at the UE  120  may also perform or direct the execution of the functional blocks illustrated in FIGS.  3  and  6 - 7 , and/or other processes for the techniques described herein. The memories  242  and  282  may store data and program codes for the eNB  110  and the UE  120 , respectively. A scheduler  244  may schedule UEs for data transmission on the downlink and/or uplink. 
     For MIMO signaling, a receiving device will have multiple receivers. Dynamic switching of these multiple receivers may be used to increase the efficiency of transmission decoding.  FIG. 3  is a functional block diagram illustrating example blocks executed to implement one aspect of the present disclosure. In one aspect, blocks  300 - 302  may be performed by a receive processor  258  or a combination of the elements shown for UE  120  in  FIG. 2 . At block  300 , a channel quality is determined for a channel associated with one or more data transmissions. With reference to  FIG. 4 , for purposes of illustrating an example implementation of the operations illustrated in blocks  300 - 302 , data transmission signals  406  may be received by receiving device  400  at any of receivers Rx 1  403  or Rx 2  404 . Receivers Rx 1 and Rx 2 may include a variety of receiver-types, including a maximum log map (MLM), such as a maximum likelihood detector (MLD) receiver, a means square-based receiver, such as a linear minimum means square error (LMMSE) receiver, a sphere decoding receiver, and the like. Each type of receiver may have an operating region over which it produces more reliable results. Under control of processor  401 , channel quality logic  409 , stored in memory  402 , is executed. The executing environment of channel quality logic  409  is able to analyze and determine the quality of the downlink channels. The combination of these acts and components may provide means for determining a channel quality of a channel associated with one or more data transmissions. 
     At block  301 , a first receiver to decode one or more data transmissions, wherein the first receiver is associated with higher performance at the determined channel quality than a second receiver. For example, processor  401 , at receiving device  400 , executes receiver selector logic  405 , stored in memory  402 . The operating environment of receiver selector logic  405  selects whichever of receiver 1 (Rx 1)  403  or receiver 2 (Rx 2)  404  that is associated with higher performance at the determined channel quality. In operation, an LMMSE receiver has been shown to work better when the signal-to-noise ratio (SNR) is low. Conversely, an MLD receiver has been shown to work better when the SNR is high. However, based on a given channel quality indicator (CQI) the MLD receiver may have a potential available MCS assignment that would support a higher throughput or better performance, should the decoding operation successfully decode received data transmissions. Thus, if Rx 1  403  is an MLD-type receiver, while Rx 2  404  is an LMMSE-type receiver, then receiving device  400  will select Rx 1  403 . Receiving device  400  then uses Rx 1  403  to decode data transmissions  406 . The combination of these acts and components may provide means for selecting a first receiver to decode one or more data transmissions, wherein the first receiver is associated with higher performance at the determined channel quality than a second receiver. 
     At block  302 , the second receiver is selected to decode one or more data re-transmissions  of the data transmissions. For example, when Rx 1  403 , of receiving device  400 , fails to properly decode data transmissions  406 , the operating environment of receiver selector logic  405 , executed by processor  401 , operates to select Rx 2  404  to receive and decode data re-transmissions  407 . As noted in the description above, Rx 2  404  is an LMMSE-type receiver, for purposes of the described example, that generally works better when SNR is low. Moreover, receiving device  400  will have soft metrics produced by the de-mapper of Rx 1  403  in the first attempt to decode data transmissions  406 . While Rx 2  404  operates better at low SNR, it will also have a very high decode success rate when using the soft metrics to conduct HARQ combining. The combination of these acts and components may provide means for selecting the second receiver to decode one or more data re-transmissions of the one or more data transmissions. 
     It should be noted that, for purposes of this disclosure, SNR includes other noise measurement ratios, such as signal-to-interference-plus-noise (SINR), carrier-to-interference-plus-noise (CINR), and the like. The various aspects of the present disclosure are not limited to a single noise measurement. 
     As referenced above,  FIG. 4  is a block diagram illustrating a receiving device  400  configured according to one aspect of the present disclosure. The receiving device  400  may be a UE, similar to the UEs  120  illustrated in  FIGS. 1 and 2 . In alternative aspects, the receiving device  400  may be an eNB, similar to the eNBs  110  illustrated in  FIGS. 1 and 2 . The process and structure defining the various aspects of the present disclosure are similar for both UEs and eNBs in their operation as a receiving device of signals. 
     Receiving device  400  includes a processor  401  which controls the various functions and features of the receiving device  400 . Accessing memory  402 , processor  401  may execute program code or logic to operate receiving device  400 . Receiving device  400  also includes multiple receivers, Rx 1  403  and Rx 2  404 . Receivers Rx 1 and Rx 2 have different operating characteristics and may, therefore, be of various different types, such as an MLM receiver, an MLD receiver, an LMMSE receiver, a sphere decoding receiver, and the like, as noted above. Each of receivers Rx 1- 403  and Rx 2- 404  may also have different optimal operating regions in which each one works best. 
     Receiver selector logic  405  is stored in memory  402  of receiver device  400 . When executed by the processor  401 , the receiver selector logic  405  makes a selection of one of receivers Rx 1- 403  and Rx 2- 404  to perform decoding of a received signal in a subframe. Receiver selector logic  405  may be configured to select such receivers in various different ways. In one such operational example, receiver Rx 1- 403  is an MLD-type receiver that has an optimal operating region in a high-SNR environment, while receiver Rx 2- 404  is an LMMSE-type receiver that has an optimal operating region in a low-SNR environment. In the first operational example, receiver selector logic  405  determines that the first transmission  406  will be decoded by receiver Rx 1- 403 , as the first transmission  406  may generally occur in a higher SNR environment. During subsequent HARQ re-transmissions  407 , the receiver selector logic  405  switches to decoding the re-transmissions  407  using receiver 2- 404 . The subsequent HARQ re-transmissions  407  may generally occur in a lower SNR environment. Thus, switching to receiver Rx 2- 404 , which, in the described first operational example, is an LMMSE-type receiver, should operate better at the lower SNR. Not only producing better results that an MLD-type receiver at the given SNR environment, but also displaying more efficient power management. The decoding results from receivers Rx 1- 403  and Rx 2- 404  are provided as input to the back-end of demodulator(s)  408  for further processing of the received signals. 
     In general operation of a receiving device, a soft de-mapper engine may be used to produce final soft metrics in terms of bitwise log likelihood ratios (LLRs), which are then provided as an input to a demodulator back end of the receiving device. Two candidates for soft de-mapper are: (1) an LMMSE de-mapper/receiver, which is a simple linear vector weighted estimator; and (2) an MLD de-mapper/receiver, which is a sub-optimal maximum log receiver suited for MIMO demodulation at high SNR regimes. 
     In MIMO operations, a hard decision is made regarding which of the two de-mappers/receivers will be used during a subframe. In comparison, a MLD receiver generally works better than a LMMSE receiver at high SNR regimes. In contrast, an LMMSE receiver works better at low SNR regimes, especially when HARQ re-transmissions are involved. Moreover, LMMSE receivers are generally more power efficient. 
     From the comparison of LMMSE receivers and MLD receiver for MIMO operations, an observation may be made that the LMMSE and MLD curves diverge around half peak throughput, which suggests that the LMMSE receiver failed to decode the first transmission at high SNR range, where the MLD receiver succeeds. Thus, in the simplest aspect of the various aspects of the present disclosure, in switching between an LMMSE receiver and an MLD receiver, the receiving device first selects the MLD receiver to decode the first transmission and then falls back to the LMMSE for all the following transmissions. 
     During retransmissions, the receiver device  400  will retain the LLRs produced by the MLD soft de-mapper engine. Thus, in additional to the retransmitted signals, the receiver device  400  will have the LLRs, which will allow for a HARQ-combining decoding process that increases the likelihood of successfully decoding the retransmitted signal. In operation, on retransmissions, the MLD-type and LMMSE-type receivers may both have a high percentage success rate for decoding the retransmitted data. Accordingly, power consumption at the receiving device  400  may be improved by switching to the LMMSE-type receiver, which generally consumes less power, while still achieving a high decode success rate in the retransmission. 
       FIG. 5  is a call flow diagram illustrating communication interaction between an eNB  51  and a UE  50  configured according to one aspect of the present disclosure. UE  50  includes two different receivers Rx1, which is an advanced receiver, such as an MLM or MLD-type receiver, and Rx2, which may be a less complex receiver, such as an LMMSE-type receiver. Rx1 may have better operational performance at higher SNR, while Rx2 may have better operational performance at lower SNR. Additionally, the higher performance characteristics of Rx1 allow for UE  50  to report a CQI to eNB  51  that would allow eNB  51  to assign a higher MCS, which could result in a better performance or higher throughput when Rx1 is used. With the potentially higher MCS and potentially better performance/throughput, UE  50  initially selects to use Rx1 for decoding data transmissions. At  500 , UE reports to eNB  51  a CQI value that is associated with the use of Rx1. Based on the CQI value, eNB  51 , at  501 , assigns an MCS value to UE  500 . UE  500  then sets up operation based on the assigned MCS value. 
     At  502 , data transmissions begin with a first transmission of data to UE  50 . In the example of operation illustrated in  FIG. 5 , UE  50  fails to properly decode the data transmission, at  503 , using Rx1. In response to the failure to decode the data transmission, at  504 , UE  50  switches operation to Rx2. A re-transmission of the data is then sent by eNB  51 , at  505 . UE  50 , using Rx2, now decodes the re-transmission at  506 . The decoding process of Rx2 of the re-transmitted data includes HARQ combining, by using the LLRs that were generated by Rx2 during the failed decoding attempt at  503 . With a successful decoding of the re-transmission, UE  50  transmits an acknowledgement at  507  to eNB  51 . The next set of data is then transmitted by eNB  51  at  508 . With the acknowledgement transmitted, UE  50  will switch back to Rx1 for decoding first transmissions, such as at  509 , in attempting to decode the next set of data sent at  508 . 
     It should be noted that, in alternative operations of UE  50 , the first transmission of data at  502  may be successfully decoded by Rx1 at  503 . When the first transmissions are successfully decoded, UE  50  will maintain selection of Rx1 for further data transmissions. When Rx1 fails to decode a subsequent first transmission of data, such as at  503 , it will then selected to switch to Rx2, as at  504 , for the retransmissions of data and subsequent first transmissions. 
       FIG. 6  is a functional block diagram illustrating example blocks executed to implement one aspect of the present disclosure. At block  600 , availability of soft metrics for a data transmission are determined. As noted above, soft metrics, such as LLRs, are produced by the soft de-mapper engines used while attempting to decode data transmissions. During an unsuccessful attempt to decode data transmissions, these soft metrics are still produced. If they are present and related to data transmissions that are being received, the receiving device will know that the data transmissions are. HARQ re-transmissions. With reference to  FIG. 4 , receiving device  400 , under control of processor  401 , accesses memory  402  to determine whether any soft metrics have been saved that were produced by either of Rx 1  403  or Rx 2  404  and used as input to demodulators  408 . The combination of these acts and components may provide means for determining availability of soft metrics for a data transmission. 
     At block  601 , an error rate is obtained for first data transmissions over a plurality of preceding subframes. For example, receiving device  400  may save information in memory  402 , under control of processor  401 , whenever a data transmission received at Rx 1  403  is unsuccessfully decoded demodulators  408 . This information may indicate that Rx 1  403  is not a suitable receiver choice for the particular area in which receiving device  400  is currently located. The combination of these acts and components may provide means for obtaining an error rate for first data transmissions over a plurality of preceding subframes. 
     At block  602 , a receiver is selected by a receiving device from multiple available receivers, based, at least in part, on the availability of soft metrics and the error rate. The multiple available receivers at the receiving device include at least one receiver that has different operating characteristics than another of the available receivers. For example, receiving device  400 , after checking memory  402  for both soft metrics associated with the data transmissions and an error rate experienced over a window of preceding first data transmissions or a count of the number of required HARQ re-transmissions over specific period of time, the receiving device  400 , under control of processor  401  executing receiver selector logic  405 , stored in memory  402 , will select the appropriate one of receivers Rx 1  403  or Rx 2  404 . 
     In example aspects where Rx 1  403  is an MLD-type receiver and Rx 2 is an LMMSE-type receiver, if receiving device  400  finds soft metrics stored in memory  402 , processor  401  will select Rx 2  404  for receiving the data transmissions, which will be HARQ re-transmissions, as the soft metrics will have been created at previous decoding attempts. Receiving device  400  will also select Rx 2  404  if no soft metrics are found in memory  402 , but the error rate in memory  402  indicates that decoding attempts of first data transmissions using Rx 1  403  have been unsuccessful at a rate higher than a particular threshold. In such aspects, receiving device determines it is better to initially select Rx 2  404 . When receiving device  400  does not find soft metrics in memory  402  and the error rate does not exceed the threshold, receiving device  400  will select Rx  1   403  for receiving the first data transmissions. The combination of these acts and components may provide means for selecting a receiver from a plurality of available receivers, at a mobile device, based, at least in part, on the availability of soft metrics and the error rate, wherein at least one receiver of the plurality of available receivers has different operating characteristics than at least another receiver of the plurality of available receivers. 
     With reference to the error rate identified in the example aspect of  FIG. 6 , this error rate information may be developed by the receiving device, such as a UE or by an eNB tracking the performance of a receiver UE to aid in the receiver selection process.  FIG. 7  is a functional block diagram illustrating example blocks executed to implement one aspect of the present disclosure. At block  700 , the receiving device calculates or determines the number of re-transmissions that occur when the first receiver, Rx1, is used. That number of re-transmissions  may provide the error rate of Rx1. A determination is made, at block  701 , whether the number of re-transmissions exceeds a given threshold. If so, then, the other receiver, Rx2, is selected for decoding the subsequent transmissions. If the number of re-transmissions does not exceed the threshold, however, then, at block  703 , Rx1 is selected to decode the subsequent transmissions. 
     The functional blocks and modules in FIGS.  3  and  6 - 7  may comprise processors, electronics devices, hardware devices, electronics components, logical circuits, memories, software codes, firmware codes, etc., or any combination thereof. 
     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. 
     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. 
     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. 
     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. 
     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.