Patent Publication Number: US-7903728-B2

Title: Equalize training method using re-encoded bits and known training sequences

Description:
CROSS REFERENCE TO RELATED PATENTS/PATENT APPLICATIONS 
     Continuation Priority Claim, 35 U.S.C. §120 
     The present U.S. Patent Application claims priority pursuant to 35 U.S.C. §120, as a continuation, to the following U.S. Patent Application which is hereby incorporated herein by reference in its entirety and made part of the present U.S. Patent Application for all purposes: 
     1. U.S. application Ser. No. 11/271,692, entitled “Equalizer training method using re-encoded bits and known training sequences,” filed Nov. 10, 2005, scheduled to issue as U.S. Pat. No. 7,529,297 on May 5, 2009, which claims priority pursuant to 35 U.S.C. §119(e) to the following U.S. Provisional Patent Applications which are hereby incorporated herein by reference in their entirety and made part of the present U.S. Patent Application for all purposes: 
     a. U.S. Provisional Application Ser. No. 60/657,564, entitled “Single antenna interference cancellation in a cellular telephone,” filed Mar. 1, 2005, now expired. 
     b. U.S. Provisional Application Ser. No. 60/678,997, entitled “Equalizer training method using re-encoded bits and known training sequences,” filed May 9, 2005, now expired. 
     Incorporation by Reference 
     The following U.S. Provisional Patent Application is hereby incorporated herein by reference in its entirety and is made part of the present U.S. Patent Application for all purposes: 
     c. U.S. Provisional Application Ser. No. 60/603,148, entitled “Method and system improving reception in wireless receivers through redundancy,” filed Aug. 20, 2004, now expired. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field of the Invention 
     The present invention relates generally to cellular wireless communication systems, and more particularly to the cancellation of interference associated with received data communications processed by a wireless terminal within a wireless communication system. 
     2. Description of Related Art 
     Cellular wireless communication systems support wireless communication services in many populated areas of the world. While cellular wireless communication systems were initially constructed to service voice communications, they are now called upon to support data communications as well. The demand for data communication services has exploded with the acceptance and widespread use of the Internet. While data communications have historically been serviced via wired connections, cellular wireless users now demand that their wireless units also support data communications. Many wireless subscribers now expect to be able to “surf” the Internet, access their email, and perform other data communication activities using their cellular phones, wireless personal data assistants, wirelessly linked notebook computers, and/or other wireless devices. The demand for wireless communication system data communications continues to increase with time. Thus, existing wireless communication systems are currently being created/modified to service these burgeoning data communication demands. 
     Cellular wireless networks include a “network infrastructure” that wirelessly communicates with wireless terminals within a respective service coverage area. The network infrastructure typically includes a plurality of base stations dispersed throughout the service coverage area, each of which supports wireless communications within a respective cell (or set of sectors). The base stations couple to base station controllers (BSCs), with each BSC serving a plurality of base stations. Each BSC couples to a mobile switching center (MSC). Each BSC also typically directly or indirectly couples to the Internet. 
     In operation, each base station communicates with a plurality of wireless terminals operating in its cell/sectors. A BSC coupled to the base station routes voice communications between the MSC and the serving base station. The MSC routes the voice communication to another MSC or to the PSTN. BSCs route data communications between a servicing base station and a packet data network that may include or couple to the Internet. Transmissions from base stations to wireless terminals are referred to as “forward link” transmissions while transmissions from wireless terminals to base stations are referred to as “reverse link” transmissions. 
     Wireless links between base stations and their serviced wireless terminals typically operate according to one (or more) of a plurality of operating standards. These operating standards define the manner in which the wireless link may be allocated, setup, serviced, and torn down. One popular cellular standard is the Global System for Mobile telecommunications (GSM) standard. The GSM standard, or simply GSM, is predominant in Europe and is in use around the globe. While GSM originally serviced only voice communications, it has been modified to also service data communications. GSM General Packet Radio Service (GPRS) operations and the Enhanced Data rates for GSM (or Global) Evolution (EDGE) operations coexist with GSM by sharing the channel bandwidth, slot structure, and slot timing of the GSM standard. The GPRS operations and the EDGE operations may also serve as migration paths for other standards as well, e.g., IS-136 and Pacific Digital Cellular (PDC). 
     In order for EDGE to provide increased data rates within a 200 KHz GSM channel, it employs a higher order modulation, 8-PSK (octal phase shift keying), in addition to GSM&#39;s standard Gaussian Minimum Shift Keying (GMSK) modulation. EDGE allows for nine different (autonomously and rapidly selectable) air interface formats, known as Modulation and Coding schemes (MCSs), with varying degrees of error control protection. Low MCS modes, (MCS 1-4) use GMSK (low data rate) while high MCS modes (MCS 5-9) use 8-PSK (high data rate) modulation for over the air transmissions, depending upon the instantaneous demands of the application. 
     To a cellular telephone operating in a receive mode, co-channel and adjacent channel GMSK/8PSK signals appear as colored noise. In order to better receive the information intended for the cellular telephone, the cellular telephone must attempt to cancel these interference signals. Prior techniques for canceling such interference included channel equalization for received symbols. However, existing channel equalization techniques fail to typically remove co-channel and adjacent channel noise sufficiently. Thus, a need exists for improvements in interference cancellation. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is directed to apparatus and methods of operation that are further described in the following Brief Description of the Several Views of the Drawings, the Detailed Description of the Invention, and the claims. Other features and advantages of the present invention will become apparent from the following detailed description of the invention made with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings in which like reference numerals indicate like features and wherein: 
         FIG. 1  is a system diagram illustrating a portion of a cellular wireless communication system that supports wireless terminals operating according to the present invention; 
         FIG. 2  is a block diagram functionally illustrating a wireless terminal constructed according to the present invention; 
         FIG. 3  is a block diagram illustrating the general structure of a GSM frame and the manner in which data blocks are carried by the GSM frame; 
         FIG. 4  is a block diagram illustrating the formation of down link transmissions; 
         FIG. 5  is a block diagram illustrating the stages associated with recovering a data block from a series of RF bursts; 
         FIG. 6  is a block diagram illustrating the stages associated with recovering a voice data from a series of RF bursts; 
         FIG. 7  is a block diagram illustrating the stages associated with recovering a burst from a data or voice frame; 
         FIGS. 8A and 8B  are flow charts illustrating operation of a wireless terminal in receiving and processing a RF burst; 
         FIG. 9  is a block diagram illustrating components of a multi-branch burst equalization component according to an embodiment of the present invention; and 
         FIG. 10  is a block diagram illustrating components of a burst equalization component according to an embodiment of the present invention; and 
         FIG. 11  is a block diagram illustrating components of a burst equalization component according to an embodiment of the present invention; and 
         FIG. 12  is a flow chart illustrating operation according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Preferred embodiments of the present invention are illustrated in the FIGs., like numerals being used to refer to like and corresponding parts of the various drawings. 
     Gaussian Minimum Shift Keying (GMSK) modulation systems can be modeled as a single-input two-output system in real domain. This model is a virtual single transmit 2 receive system. Interference cancellation techniques for multiple antennas can be applied to GMSK systems as provided by embodiments of the present invention that substantially addresses the above identified needs as well as other needs. The present invention provides a multi-branch equalizer processing module operable to cancel interference associated with received radio frequency (RF) burst(s). This multi-branch equalizer processing module includes multiple equalizer processing branches. One equalizer processing branch is operable to be trained based upon known training sequences and equalize the received RF burst. These results are then further processed and used to train a second equalizer processing branch. The second equalizer processing branch then equalizes the received RF burst to produce an output based on canceling the interfering signals that results in improved processing of the received RF bursts. 
       FIG. 1  is a system diagram illustrating a portion of a cellular wireless communication system  100  that supports wireless terminals operating in accordance with embodiments of the present invention. Cellular wireless communication system  100  includes a Mobile Switching Center (MSC)  101 , Serving GPRS Support Node/Serving EDGE Support Node (SGSN/SESN)  102 , base station controllers (BSCs)  152  and  154 , and base stations  103 ,  104 ,  105 , and  106 . The SGSN/SESN  102  couples to the Internet  114  via a GPRS Gateway Support Node (GGSN)  112 . A conventional voice terminal  121  couples to the PSTN  110 . A Voice over Internet Protocol (VoIP) terminal  123  and a personal computer  125  couple to the Internet  114 . The MSC  101  couples to the Public Switched Telephone Network (PSTN)  110 . 
     Each of the base stations  103 - 106  services a cell/set of sectors within which it supports wireless communications. Wireless links that include both forward link components and reverse link components support wireless communications between the base stations and their serviced wireless terminals. These wireless links can result in co-channel and adjacent channel signals that may appear as noise which may be colored or white. As previously stated, this noise may interfere with the desired signal of interest. Hence, the present invention provides techniques for canceling such interference in poor signal-to-noise ratio (SNR) or low signal-to-interference ratio (SIR) environments. 
     These wireless links may support digital data communications, VoIP communications, and other digital multimedia communications. The cellular wireless communication system  100  may also be backward compatible in supporting analog operations as well. The cellular wireless communication system  100  may support the Global System for Mobile telecommunications (GSM) standard and also the Enhanced Data rates for GSM (or Global) Evolution (EDGE) extension thereof. The cellular wireless communication system  100  may also support the GSM General Packet Radio Service (GPRS) extension to GSM. However, the present invention is also applicable to other standards as well, e.g., TDMA standards, CDMA standards, etc. In general, the teachings of the present invention apply to digital communication techniques that address the identification and cancellation of interfering communications. 
     Wireless terminals  116 ,  118 ,  120 ,  122 ,  124 ,  126 ,  128 , and  130  couple to the cellular wireless communication system  100  via wireless links with the base stations  103 - 106 . As illustrated, wireless terminals may include cellular telephones  116  and  118 , laptop computers  120  and  122 , desktop computers  124  and  126 , and data terminals  128  and  130 . However, the cellular wireless communication system  100  supports communications with other types of wireless terminals as well. As is generally known, devices such as laptop computers  120  and  122 , desktop computers  124  and  126 , data terminals  128  and  130 , and cellular telephones  116  and  118 , are enabled to “surf” the Internet  114 , transmit and receive data communications such as email, transmit and receive files, and to perform other data operations. Many of these data operations have significant download data-rate requirements while the upload data-rate requirements are not as severe. Some or all of the wireless terminals  116 - 130  are therefore enabled to support the EDGE operating standard. These wireless terminals  116 - 130  also support the GSM standard and may support the GPRS standard. 
       FIG. 2  is a block diagram functionally illustrating wireless terminal  200 . The wireless terminal  200  of  FIG. 2  includes an RF transceiver  202 , digital processing components  204 , and various other components contained within a housing. The digital processing components  204  includes two main functional components, a physical layer processing, speech COder/DECoder (CODEC), and baseband CODEC functional block  206  and a protocol processing, man-machine interface functional block  208 . A Digital Signal Processor (DSP) is the major component of the physical layer processing, speech COder/DECoder (CODEC), and baseband CODEC functional block  206  while a microprocessor, e.g., Reduced Instruction Set Computing (RISC) processor, is the major component of the protocol processing, man-machine interface functional block  208 . The DSP may also be referred to as a Radio Interface Processor (RIP) while the RISC processor may be referred to as a system processor. However, these naming conventions are not to be taken as limiting the functions of these components. 
     RF transceiver  202  couples to an antenna  203 , to the digital processing components  204 , and also to battery  224  that powers all components of wireless terminal  200 . The physical layer processing, speech COder/DECoder (CODEC), and baseband CODEC functional block  206  couples to the protocol processing, man-machine interface functional block  208  and to a coupled microphone  226  and speaker  228 . The protocol processing, man-machine interface functional block  208  couples to various components such as, but not limited to, Personal Computing/Data Terminal Equipment interface  210 , keypad  212 , Subscriber Identification Module (SIM) port  213 , a camera  214 , flash RAM  216 , SRAM  218 , LCD  220 , and LED(s)  222 . When camera  214  and LCD  220  are present, these components may support either/both still pictures and moving pictures. Thus, the wireless terminal  200  of  FIG. 2  may be operable to support video services as well as audio services via the cellular network. 
       FIG. 3  is a block diagram illustrating the general structure of a GSM frame and the manner in which data blocks are carried by the GSM frame. The GSM frame, 20 ms in duration, is divided into quarter frames, each of which includes eight time slots, time slots  0  through  7 . Each time slot is approximately 625 us in duration, includes a left side, a right side, and a midamble. The left side and right side of an RF burst of the time slot carry data while the midamble is a training sequence. 
     RF bursts of four time slots of the GSM frame carry a segmented RLC block, a complete RLC block, or two RLC blocks, depending upon a supported Modulation and Coding Scheme (MCS) mode. For example, data block A is carried in slot  0  of quarter frame  1 , slot  0  of quarter frame  2 , slot  0  of quarter frame  3 , and slot  0  of quarter frame  3 . Data block A may carry a segmented RLC block, an RLC block, or two RLC blocks. Likewise, data block B is carried in slot  1  of quarter frame  1 , slot  1  of quarter frame  2 , slot  1  of quarter frame  3 , and slot  1  of quarter frame  3 . The MCS mode of each set of slots, i.e., slot n of each quarter frame, for the GSM frame is consistent for the GSM frame but may vary from GSM frame to GSM frame. Further, the MCS mode of differing sets of slots of the GSM frame, e.g., slot  0  of each quarter frame vs. any of slots  1 - 7  of each quarter frame, may differ. The RLC block may carry voice data or other data. 
       FIG. 4  generally depicts the various stages associated with mapping data into RF bursts. Data is initially uncoded and may be accompanied by a data block header. Block coding operations perform the outer coding for the data block and support error detection/correction for data block. The outer coding operations typically employ a cyclic redundancy check (CRC) or a Fire Code. The outer coding operations are illustrated to add tail bits and/or a Block Code Sequence (BCS), which is/are appended to the data. In CS-1, the header and data are coded together using block coding and convolutional coding. In non-CS-1 coding schemes, the header and data information are often coded separately. 
     Fire codes allow for either error correction or error detection. Fire Codes are a shortened binary cyclic code that appends redundancy bits to bits of the data Header and Data. The pure error detection capability of Fire Coding may be sufficient to let undetected errors go through with only a probability of 2 −40 . After block coding has supplemented the Data with redundancy bits for error detection, calculation of additional redundancy for error correction to correct the transmissions caused by the radio channels. The internal error correction or coding scheme is based on convolutional codes. 
     Some redundant bits generated by the convolutional encoder may be punctured prior to transmission. Puncturing increases the rate of the convolutional code and reduces the redundancy per data block transmitted. Puncturing additionally lowers the bandwidth requirements such that the convolutional encoded signal fits into the available channel bit stream. The convolutional encoded punctured bits are passed to an interleaver, which shuffles various bit streams and segments the interleaved bit streams into the 4 bursts shown. 
       FIG. 5  is a block diagram that generally depicts the various stages associated with recovering a data block from a RF burst(s). Four RF bursts typically make up a data block. These bursts are received and processed. Once all four RF bursts have been received, the RF bursts are combined to form an encoded data block. The encoded data block is then depunctured (if required), decoded according to an inner decoding scheme, and then decoded according to an outer decoding scheme. The decoded data block includes the data block header and the data. Depending on how the data and header are coded, partial decoding may be possible to identify data. 
       FIG. 6  is a block diagram that depicts the various stages associated with recovering data from a transmitted voice frame. This is similar to the process described with reference to  FIG. 5 . Typically a 20 millisecond voice frame is transmitted, wherein the first half of the 20 millisecond voice frame is transmitted within a first series of RF bursts and the second half of the voice frame is transmitted with a second series of RF bursts. A series of four RF bursts is shown as being off-set by 10 milliseconds from the first voice frame, Voice Frame n , wherein the second half of Voice Frame n  and the first half of the subsequent voice frame, Voice Frame n+1 , are coded and interleaved into the series of four RF bursts. When the four RF bursts are processed, the coded block produced produces a data stream that comprises the second half of Voice Frame n  and the first half of Voice Frame n+1 . The first half of Voice Frame, stored within memory, may be combined with the second half of Voice Frame n  to produce the data associated with a valid Voice Frame n . 
     Re-encoding the data associated with a valid Voice Frame n , as described with reference to  FIG. 7 , may result in an at least partially re-encoded data bursts that may be used to train the second equalizer processing branch. As previously stated, the first half of the voice frame recovered from a previous set of RF bursts and the second half of the voice frame recovered from the current set of RF bursts are combined to produce the data associated with a voice frame. This voice frame may be validated and corrected using cycle redundancy checks in order to produce a valid voice frame. This valid voice frame may then be re-encoded. However, only the second half of the re-encoded Voice Frame n  is used to partially recreate the burst(s). The second half of re-encoded Voice Frame n  may be segmented and interleaved to produce a series of partially encoded RF bursts. Since the processing of the second half of the Voice Frame n+1  has not occurred, the RF bursts are only partially re-encoded. Since Voice Frame n+1  has not been validated, the first half of a re-encoded Voice Frame n+1  is not possible and is not used to recreate the burst(s). The partially re-encoded burst(s), based on Voice Frame n , taken together with the known training sequences are operable to better train the second equalizer-processing branch in accordance with an embodiment of the present invention. 
       FIGS. 8A and 8B  are flow charts illustrating operation of a wireless terminal  200  in receiving and processing a RF burst. The operations illustrated in  FIGS. 8A and 8B  correspond to a single RF burst in a corresponding slot of GSM frame. The RF front end, the baseband processor, and the equalizer processing module perform these operations. These operations are generally called out as being performed by one of these components. However, the split of processing duties among these various components may differ without departing from the scope of the present invention. 
     Referring particular to  FIG. 8A , operation commences with the RF front end receiving an RF burst in a corresponding slot of a GSM frame (step  802 ). The RF front end then converts the RF burst to a baseband signal (step  804 ). Upon completion of the conversion, the RF front end sends an interrupt to the baseband processor (step  806 ). Thus, as referred to in  FIG. 8A , the RF front end performs steps  802 - 806 . 
     Operation continues with the baseband processor receiving the baseband signal (step  808 ). In a typical operation, the RF front end, the baseband processor, or modulator/demodulator will sample the analog baseband signal to digitize the baseband signal. After receipt of the baseband signal (in a digitized format), the baseband processor performs blind detection of a modulation format of the baseband signal of step  810 . This blind detection of the modulation format determines the modulation format of the corresponding baseband signal. In one particular embodiment according to the GSM standard, the modulation format will be either Gaussian Minimum Shift Keying (GMSK) modulation or Eight Phase Shift Keying (8PSK) modulation. The baseband processor makes the determination (step  812 ) and proceeds along one of two branches based upon the detected modulation format. 
     For GMSK modulation, the baseband processor performs de-rotation and frequency correction of the baseband signal at step  814 . Next, the baseband processor performs burst power estimation of the baseband signal at step  816 . Referring now to  FIG. 11  via off page connector A, the baseband processor next performs timing, channel, noise, and signal-to-noise ratio (SNR) estimation at step  820 . Subsequently, the baseband processor performs automatic gain control (AGC) loop calculations (step  822 ). Next, the baseband processor performs soft decision scaling factor determination on the baseband signal (step  824 ). After step  824 , the baseband processor performs matched filtering operations on the baseband signal at step  826 . 
     Steps  808 - 826  are referred to hereinafter as pre-equalization processing operations. With the baseband processor performing these pre-equalization processing operations on the baseband signal it produces a processed baseband signal. Upon completion of these pre-equalization processing operations, the baseband processor issues a command to the equalizer module. 
     The equalizer module, whose operation as a multi-branch equalizer will be discussed in further detail with reference to  FIG. 9  and following, upon receiving the command, prepares to equalize the processed baseband signal based upon the modulation format, e.g., GMSK modulation or 8PSK modulation. The equalizer module receives the processed baseband signal, settings, and/or parameters from the baseband processor and performs Maximum Likelihood Sequence Estimation (MLSE) equalization on the left side of the baseband signal at step  828 . As was shown previously with reference to  FIG. 3 , each RF burst contains a left side of data, a midamble, and a right side of data. Typically, at step  828 , the equalizer module equalizes the left side of the RF burst to produce soft decisions for the left side. Then, the equalizer module equalizes the right side of the processed baseband signal at step  830 . The equalization of the right side produces a plurality of soft decisions corresponding to the right side. The burst equalization is typically based of known training sequences within the bursts. However, the embodiments of the present invention may utilize re-encoded or partially re-encoded data to improve the equalization process. This may take the form of an iterative process wherein a first branch performs burst equalization and a second module performs a second equalization based on the result obtained with the first branch over a series of RF bursts. 
     The equalizer module then issues an interrupt to the baseband processor indicating that the equalizer operations are complete for the RF burst. The baseband processor then receives the soft decisions from the equalizer module. Next, the baseband processor determines an average phase of the left and right sides based upon the soft decisions received from the equalizer module at step  832 . The baseband processor then performs frequency estimation and tracking based upon the soft decisions received from the equalizer module at step  836 . The operations of step  832 , or step  854  and step  836  are referred to herein as “post-equalization processing.” After operation at step  836 , processing of the particular RF burst is completed. 
     Referring again to  FIG. 8A , the baseband processor and equalizer module take the right branch from step  812  when an 8PSK modulation is blindly detected at step  810 . In the first operation for 8PSK modulation, the baseband processor performs de-rotation and frequency correction on the baseband signal at step  818 . The baseband processor then performs burst power estimation of the baseband signal at step  820 . Referring now to  FIG. 8B  via off page connector B, operation continues with the baseband processor performing timing, channel, noise, and SNR estimations at step  840 . The baseband processor then performs AGC loop calculations on the baseband signal at step  842 . Next, the baseband processor calculates Decision Feedback Equalizer (DFE) coefficients that will be used by the equalizer module at step  844 . The process to produce these coefficients will be described in further detail This determination when using a multi-branch equalizer will be discussed with reference to  FIG. 9  and following. The baseband processor then performs pre-equalizer operations on the baseband signal at step  846 . Finally, the baseband processor determines soft decision scaling factors for the baseband signal at step  848 . Steps  818 - 848  performed by the baseband processor  30  are referred to herein as “pre-equalization processing” operations for an 8PSK modulation baseband signal. Upon completion of step  648 , the baseband processor issues a command to equalizer module to equalize the processed baseband signal. 
     Upon receipt of the command from the baseband processor, the equalizer module receives the processed baseband signal, settings, and/or parameters from the baseband processor and commences equalization of the processed baseband signal. The equalizer module first prepares state values that it will use in equalizing the 8PSK modulated processed baseband signal at step  850 . In the illustrated embodiment, the equalizer module uses a Maximum A posteriori Probability (MAP) equalizer. The equalizer module then equalizes the left and right sides of the processed baseband signal using the MAP equalizer to produce soft decisions for the processed baseband signal at step  852 . Upon completion of step  854 , the equalizer module issues an interrupt to the baseband processor indicating its completion of the equalizing the processed baseband signal corresponding. 
     The baseband processor then receives the soft decisions from the equalizer module. Next, the baseband processor determines the average phase of the left and right sides of the processed baseband signal based upon the soft decisions (step  854 ). Finally, the baseband processor performs frequency estimation and tracking for the soft decisions (step  836 ). The operations of steps  854  and  836  are referred to as post-equalization processing operations. From step  836 , operation is complete for the particular RF burst depicts the various stages associated with recovering a data block from an RF Burst. 
     While the operations of  FIGS. 8A and 8B  are indicated to be performed by particular components of the wireless terminal, such segmentation of operations could be performed by differing components. For example, the equalization operations could be performed by the baseband processor or system processor in other embodiments. Further, decoding operations could also be performed by the baseband processor or the system processor in other embodiments. 
       FIG. 9  is a block diagram illustrating the structure of one embodiment of a multi-branch equalizer processing module  900  operable to perform single antenna interference cancellation (SAIC) in accordance with embodiments of the present invention. There are two types of SAIC equalizer methods: (1) joint-detection (JD); and (2) blind interference cancellation (BIC). According to one aspect of the present invention, BIC method is selected. The components illustrated in  FIG. 9  may be hardware components, software components executed by a processor, e.g.,  206  or  208  of  FIG. 2 , or a combination of hardware components and software components. Multi-branch equalizer processing module  900  includes a first equalizer processing branch  902  and second equalizer processing branch  904 . Derotation block  906  receives In phase (I) and Quadrature (Q) components of a baseband burst. This baseband burst corresponds to RF burst(s), which were described with reference to  FIGS. 3-7 . Derotation block  906  derotates received I and Q burst samples and produces I and Q burst samples (“bursts”). In one embodiment, first equalizer processing branch  902  may include a burst equalizer. These samples may be later equalized in accordance with the embodiments of the present invention with other samples making up a data packet, e.g., RLC packet. The iterative processes of the second equalizer processing branch may be performed in addition to the burst level equalization during certain operating conditions. 
     Burst equalizers, include I and Q Finite Impulse Response (FIR) filters  908  and  910  and Minimum Least Squares Estimation (MLSE) equalizer  912  that operate upon each burst received from derotation block  906 . These components are trained by training module  913  using known Training Sequence(s) (TS), within the midamble received with each burst. Alternately, these components could be trained over multiple bursts. First equalizer processing branch  902  produces soft decisions wherein multiple soft decisions represent each data bit prior to decoding. Each soft sample is provided to deinterleaver  914  which in turn provides the deinterleaved soft samples to channel decoder  916 . Channel decoder  916  decodes a data frame from the soft samples (i.e. the multiple soft sample(s) that represent each data bit are decoded by the channel decoder to produce hard bits after decoding). 
     The data frame produced by channel decoder  916  may be validated and re-encoded using re-encoder  918  in order to produce re-encoded data bits. Interleaver  920  receives the re-encoded data bits to produce a re-encoded data burst(s). The re-encoded data burst(s), along with known training sequence(s), may then be used to train second equalizer processing branch  310 . 
     Second equalizer processing branch  906  includes a buffer  922  operable to store multiple bursts in memory as well as an I and Q FIR filters  924  and  926 , respectively. I and Q filters  924  and  926  are operable to be trained by training module  928  using known training sequence and at least partially re-encoded bursts. In this way, the second equalizer processing branch takes at least partially re-encoded data and known training sequences to train the I and Q RF filters. This results in an improved SNR for the burst(s) processed from buffer  922 . After the I and Q filters have been trained and used to process the stored burst(s). The results are combined with adder  930 . This creates an alternate set of soft samples which are provided to deinterleaver  914  and channel Decoder  916  to produce an alternate set of data bits. 
       FIG. 10  may be used to describe the first branch of the multi-branch equalizer of  FIG. 9  in more detail. Since there are only 26 training symbols, the first processing branch as shown may train feed-forward filters  908  and  910  with 4 taps each and 4 taps feedback filter DFEs. 
       FIG. 11  may be used to describe the second branch of the multi-branch equalizer of  FIG. 9  in more detail. After channel decoding, the data is re-encoded and used to train 7 tap LEs  924  and  926 . The reason to choose LE for the second branch is because of the inter-frame interleaving. The re-encoded bits that relate to a voice frame may only provide half of the burst (even data bits). DFEs need consecutive samples for the feedback filter. In addition, LE is simpler than DFE (MLSE). Other embodiments that use fully re-encoded bits may chose DFEs over Les for the second branch. 
     The following discussion further describes the indirect training method that may be based on the least-square channel estimation (LS-CE) and is similar to that used in EDGE. First the channel is estimated using the training sequence. Then the pre-filter and MLSE parameters are calculated as if they are the feed-forward and feedback filters of a DFE. A problem of the indirect method is poor CE since SAIC is usually operated at low SIR. The CE error propagates in the calculation filter coefficients. 
     The signal model at the MLSE input in  FIG. 10  can be viewed as an ISI channel plus noise. Suppose the DFE feedback filter impulse response is {b(0), b(1), . . . , b(L b −1)}. The objective of training is to obtain pre-filter coefficients {f 1 (0), . . . f 1 (L f −1), f 2 (0), . . . f 2 (L f −1)}, and the MLSE parameters b for the given training symbols and corresponding received signal. 
     Based on above mode, the noise at the MLSE input is given by 
     
       
         
           
             
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                         + 
                         d 
                         - 
                         i 
                       
                       ) 
                     
                   
                 
               
               - 
               
                 
                   ∑ 
                   
                     i 
                     = 
                     0 
                   
                   
                     
                       L 
                       b 
                     
                     - 
                     1 
                   
                 
                 ⁢ 
                 
                   
                     b 
                     ⁡ 
                     
                       ( 
                       i 
                       ) 
                     
                   
                   ⁢ 
                   
                     s 
                     ⁡ 
                     
                       ( 
                       
                         k 
                         - 
                         i 
                       
                       ) 
                     
                   
                 
               
             
           
         
       
     
     where x 1  and x 2  are de-rotation output I &amp; Q, respectively, s is the training symbol, d is the system delay. In vector form: 
     
       
         
           
             
               [ 
               
                 
                   
                     
                       n 
                       ⁡ 
                       
                         ( 
                         k 
                         ) 
                       
                     
                   
                 
                 
                   
                     
                       n 
                       ⁡ 
                       
                         ( 
                         
                           k 
                           + 
                           1 
                         
                         ) 
                       
                     
                   
                 
                 
                   
                     ⋮ 
                   
                 
                 
                   
                     
                       n 
                       ⁡ 
                       
                         ( 
                         
                           k 
                           + 
                           N 
                         
                         ) 
                       
                     
                   
                 
               
               ] 
             
             = 
             
                 
               
                   
               
               ⁢ 
               
                   
                 
                   
                     [ 
                     
                       
                         
                           
                             
                               x 
                               1 
                             
                             ⁡ 
                             
                               ( 
                               
                                 k 
                                 + 
                                 d 
                               
                               ) 
                             
                           
                         
                         
                           … 
                         
                         
                           
                             
                               x 
                               1 
                             
                             ⁡ 
                             
                               ( 
                               
                                 k 
                                 + 
                                 d 
                                 - 
                                 
                                   L 
                                   
                                     f 
                                     ⁢ 
                                     
                                         
                                     
                                   
                                 
                                 + 
                                 1 
                               
                               ) 
                             
                           
                         
                         
                           
                             
                               x 
                               2 
                             
                             ⁡ 
                             
                               ( 
                               
                                 k 
                                 + 
                                 d 
                               
                               ) 
                             
                           
                         
                         
                           … 
                         
                         
                           
                             
                               x 
                               2 
                             
                             ⁡ 
                             
                               ( 
                               
                                 k 
                                 + 
                                 d 
                                 - 
                                 
                                   L 
                                   f 
                                 
                                 + 
                                 1 
                               
                               ) 
                             
                           
                         
                       
                       
                         
                           
                             
                               x 
                               1 
                             
                             ⁡ 
                             
                               ( 
                               
                                 k 
                                 + 
                                 d 
                                 + 
                                 1 
                               
                               ) 
                             
                           
                         
                         
                           … 
                         
                         
                           
                             
                               x 
                               1 
                             
                             ⁡ 
                             
                               ( 
                               
                                 
                                   
                                     
                                       k 
                                       + 
                                       d 
                                       + 
                                       1 
                                       - 
                                     
                                   
                                 
                                 
                                   
                                     
                                       
                                         L 
                                         f 
                                       
                                       + 
                                       1 
                                     
                                   
                                 
                               
                               ) 
                             
                           
                         
                         
                           
                             
                               x 
                               2 
                             
                             ⁡ 
                             
                               ( 
                               
                                 k 
                                 + 
                                 d 
                                 + 
                                 1 
                               
                               ) 
                             
                           
                         
                         
                           … 
                         
                         
                           
                             
                               x 
                               2 
                             
                             ⁡ 
                             
                               ( 
                               
                                 
                                   
                                     
                                       k 
                                       + 
                                       d 
                                       + 
                                       1 
                                       - 
                                     
                                   
                                 
                                 
                                   
                                     
                                       
                                         L 
                                         f 
                                       
                                       + 
                                       1 
                                     
                                   
                                 
                               
                               ) 
                             
                           
                         
                       
                       
                         
                           
                               
                           
                         
                         
                           ⋮ 
                         
                         
                           
                               
                           
                         
                         
                           
                               
                           
                         
                         
                           ⋮ 
                         
                         
                           
                               
                           
                         
                       
                       
                         
                           
                             
                               x 
                               1 
                             
                             ⁡ 
                             
                               ( 
                               
                                 k 
                                 + 
                                 d 
                                 + 
                                 N 
                               
                               ) 
                             
                           
                         
                         
                           … 
                         
                         
                           
                             
                               x 
                               1 
                             
                             ⁡ 
                             
                               ( 
                               
                                 
                                   
                                     
                                       k 
                                       + 
                                       d 
                                       + 
                                       N 
                                       - 
                                     
                                   
                                 
                                 
                                   
                                     
                                       
                                         L 
                                         f 
                                       
                                       + 
                                       1 
                                     
                                   
                                 
                               
                               ) 
                             
                           
                         
                         
                           
                             
                               x 
                               2 
                             
                             ⁡ 
                             
                               ( 
                               
                                 k 
                                 + 
                                 d 
                                 + 
                                 N 
                               
                               ) 
                             
                           
                         
                         
                           … 
                         
                         
                           
                             
                               x 
                               2 
                             
                             ⁡ 
                             
                               ( 
                               
                                 
                                   
                                     
                                       k 
                                       + 
                                       d 
                                       + 
                                       N 
                                       - 
                                     
                                   
                                 
                                 
                                   
                                     
                                       
                                         L 
                                         f 
                                       
                                       + 
                                       1 
                                     
                                   
                                 
                               
                               ) 
                             
                           
                         
                       
                     
                     ] 
                   
                   ⁢ 
                   
                       
                     
                         
                     
                     ⁢ 
                     
                         
                       
                           
                         
                             
                         
                         ⁢ 
                         
                           
                             [ 
                             
                               
                                 
                                   
                                     
                                       f 
                                       1 
                                     
                                     ⁡ 
                                     
                                       ( 
                                       0 
                                       ) 
                                     
                                   
                                 
                               
                               
                                 
                                   ⋮ 
                                 
                               
                               
                                 
                                   
                                     
                                       f 
                                       1 
                                     
                                     ⁡ 
                                     
                                       ( 
                                       
                                         
                                           L 
                                           f 
                                         
                                         - 
                                         1 
                                       
                                       ) 
                                     
                                   
                                 
                               
                               
                                 
                                   
                                     
                                       f 
                                       2 
                                     
                                     ⁡ 
                                     
                                       ( 
                                       0 
                                       ) 
                                     
                                   
                                 
                               
                               
                                 
                                   ⋮ 
                                 
                               
                               
                                 
                                   
                                     
                                       f 
                                       2 
                                     
                                     ⁡ 
                                     
                                       ( 
                                       
                                         
                                           L 
                                           f 
                                         
                                         - 
                                         1 
                                       
                                       ) 
                                     
                                   
                                 
                               
                             
                             ] 
                           
                           - 
                           
                             
                               [ 
                               
                                 
                                   
                                     
                                       s 
                                       ⁡ 
                                       
                                         ( 
                                         k 
                                         ) 
                                       
                                     
                                   
                                   
                                     … 
                                   
                                   
                                     
                                       s 
                                       ⁡ 
                                       
                                         ( 
                                         
                                           k 
                                           - 
                                           
                                             L 
                                             b 
                                           
                                           + 
                                           1 
                                         
                                         ) 
                                       
                                     
                                   
                                 
                                 
                                   
                                     
                                       s 
                                       ⁡ 
                                       
                                         ( 
                                         
                                           k 
                                           + 
                                           1 
                                         
                                         ) 
                                       
                                     
                                   
                                   
                                     … 
                                   
                                   
                                     
                                       s 
                                       ⁡ 
                                       
                                         ( 
                                         
                                           k 
                                           + 
                                           1 
                                           - 
                                           
                                             L 
                                             b 
                                           
                                           + 
                                           1 
                                         
                                         ) 
                                       
                                     
                                   
                                 
                                 
                                   
                                     
                                         
                                     
                                   
                                   
                                     ⋮ 
                                   
                                   
                                     
                                         
                                     
                                   
                                 
                                 
                                   
                                     
                                       s 
                                       ⁡ 
                                       
                                         ( 
                                         
                                           k 
                                           + 
                                           N 
                                         
                                         ) 
                                       
                                     
                                   
                                   
                                     … 
                                   
                                   
                                     
                                       s 
                                       ⁡ 
                                       
                                         ( 
                                         
                                           k 
                                           + 
                                           N 
                                           - 
                                           
                                             L 
                                             b 
                                           
                                           + 
                                           1 
                                         
                                         ) 
                                       
                                     
                                   
                                 
                               
                               ] 
                             
                             ⁡ 
                             
                               [ 
                               
                                 
                                   
                                     
                                       b 
                                       ⁡ 
                                       
                                         ( 
                                         0 
                                         ) 
                                       
                                     
                                   
                                 
                                 
                                   
                                     ⋮ 
                                   
                                 
                                 
                                   
                                     
                                       b 
                                       ⁡ 
                                       
                                         ( 
                                         
                                           
                                             L 
                                             b 
                                           
                                           - 
                                           1 
                                         
                                         ) 
                                       
                                     
                                   
                                 
                               
                               ] 
                             
                           
                         
                       
                     
                   
                 
               
             
           
         
       
     
     For convenience, boldface low-case letters are used for vectors, and boldface upper-case letter for matrix to represent the above equation:
 
 n=Xf−Sb  
 
     The criterion of equalizer is to find f and b that minimizes the MLSE input noise,
 
min∥n∥ 2  
 
     Since the number of training symbols is limited, joint optimization of f and b is sensitive to noise. The following discussion derives a sub-optimal approach that reduces the estimated parameter to pre-filer f only. 
     Cross-correlation between the pre-filter outputs (Xf) and training symbol may be by the ISI channel at the MLSE input (b). Thus b can be represented by f. Using LS CE at the pre-filter output, and let b be the channel estimate provides:
 
 b=S   +   Xf  
 
     where ( ) +  represents the pseudo-inverse. Substituting above will minimization the function, to yield:
 
min∥ Xf−SS   +   Xf∥   2 =min∥( I−SS   + ) Xf∥   2 =min f′Af  
 
     where A=X′(I−SS + )X, and ( )′ is the transpose operation. To avoid trivial solution, constraints are applied. Two types commonly used constraints are Unit-norm constraint and the Linear constraint. When this constrains the norm of 1, then the optimization solution is the eigen-vector of A corresponding to the least eigenvalue Provides:
 
 f=eigvec ( A )
 
     A linear constraint may also be chosen for f. For example, we can fix i-th element of b to 1. In another word, the i-th tap of MLSE channel b is 1. When c is the i-th row vector of S + X. Then the linear constraint is given by:
 
cf=1
 
     This results in an optimization solution given by:
 
f=A −1 c′
 
     The linear constraint is often better than the unit-norm constraint. In the linear constraint, if the first tap is chosen to be one, the above minimization criterion is equivalent to the DFE criterion. Diagonal loading also helps at high SIR range. 
       FIG. 11  may be used to describe the second branch of the multi-branch equalizer of  FIG. 9  in more detail. After channel decoding, the data is re-encoded and used to train 7 tap LEs  924  and  926 . The reason to choose LE for the second branch is because of the inter-frame interleaving. The re-encoded bits that relate to a voice frame may only provide half of the burst (even data bits). DFEs need consecutive samples for the feedback filter. In addition, LE is simpler than DFE (MLSE). Other embodiments that use fully re-encoded bits may chose DFEs over LEs for the second branch. 
       FIG. 12  provides a logic flow diagram illustrating one embodiment of equalizing received RF burst(s). This involves a step  6   1200  receiving a number of burst(s), which are then de-rotated as previously described in step  1202 . In step  1204 , processing the RF burst(s) with a first equalizer, such as the first equalizer processing branch, of  FIG. 9  which is trained using the known training sequence in step  1206 . The received RF bursts may be supplied to both the first equalizer processing branch and second equalizer processing branch. Within the second equalizer processing branch, a buffer or other memory location stores the received RF burst(s), for further processing. The first equalizer processing branch equalizes the received RF burst in step  1208  using filters that have been trained based on a known training sequence. This equalized RF burst produces a series of samples or soft decisions which are de-interleaved in step  1210  and decoded in step  1212  to yield extracted data bits. A data frame may be decoded from the extracted data bits in step  1214 , which in turn may be re-encoded to produce re-encoded data bits in step  1216 . In the case of a voice frame, this requires that the data from the current set of RF burst(s) be combined with that of a previous set of RF bursts to produce a valid voice frame. The voice frame may them be re-encoded to produce re-encoded data bits. The re-encoded data bits may be interleaved in step  1218  to produce a re-encoded data burst. This re-encoded data burst may comprise partially re-encoded bits when applied to voice frames. 
     Step  1220  retrieves RF burst(s) from memory for processing using a second equalizer processing branch. This may involve the retrieval of one or more RF bursts, which are processed using the second equalizer branch. The re-encoded data burst is provided as a signal to train the second equalizer processing branch in step  1222 . This allows the RF burst stored in memory to be equalized in step  1224  using the second equalizer processing branch, wherein the second equalizer processing branch is trained not only on the known training sequence, but also at least some partially re-encoded data bits produced from the original output of the channel decoder. This allows the second processing branch to provide an improved output over the first processing branch by utilizing not only the known training sequence but also re-encoded data bits in order to better equalize or train the second equalizer processing branch. The second equalizer processing branch produces an alternate set of soft decisions, which may be de-interleaved in step  1226  and decoded in step  1228  in order to produce an alternate date frame in step  1230 . 
     In noise-limited scenarios, the single antenna interface cancel action may perform worse than the conventional receiver. In addition, channels having long delays such as those having hilly terrain can also cause large degradation due to the short pre-filter length. To solve the problem, a switch function may be added to enable the interactive single antenna cancellation process. The switch may be based on any combination of SNR, Colored noise discriminator and Channel profile detector. 
     In summary, the present invention provides a multi-branch equalizer processing module operable to cancel interference associated with received radio frequency (RF) burst(s). This multi-branch equalizer processing module includes both a first equalizer processing branch and a second equalizer processing branch. The first equalizer processing branch is operable to be trained based upon known training sequences and equalize the received RF burst. This results in soft samples or decisions which in turn may be converted to data bits. The soft samples are processed with a de-interleaver and channel decoder, where the combination is operable to produce a decoded frame of data bits from the soft samples. A re-encoder may re-encode the decoded frame to produce re-encoded or at least partially re-encoded data bits. An interleaver then processes the at least partially re-encoded data bits to produce and at least partially re-encoded burst. The second equalizer processing branch uses the at least partially re-encoded data bits to train linear equalizer(s) within the second equalizer processing branch. A buffer may initially store the received RF burst(s), which are retrieved and equalized by the second equalizer processing branch once the linear equalizer(s) are trained. This results in alternate soft samples or decisions which in turn may be converted to alternate data bits. The alternate soft samples are processed with the de-interleaver and channel decoder, where the combination is operable to produce an alternate decoded frame of data bits from the alternate soft samples. This allows interfering signals to be cancelled and more accurate processing of the received RF bursts to occur. 
     As one of average skill in the art will appreciate, the term “substantially” or “approximately”, as may be used herein, provides an industry-accepted tolerance to its corresponding term. Such an industry-accepted tolerance ranges from less than one percent to twenty percent and corresponds to, but is not limited to, component values, integrated circuit process variations, temperature variations, rise and fall times, and/or thermal noise. As one of average skill in the art will further appreciate, the term “operably coupled”, as may be used herein, includes direct coupling and indirect coupling via another component, element, circuit, or module where, for indirect coupling, the intervening component, element, circuit, or module does not modify the information of a signal but may adjust its current level, voltage level, and/or power level. As one of average skill in the art will also appreciate, inferred coupling (i.e., where one element is coupled to another element by inference) includes direct and indirect coupling between two elements in the same manner as “operably coupled”. As one of average skill in the art will further appreciate, the term “compares favorably”, as may be used herein, indicates that a comparison between two or more elements, items, signals, etc., provides a desired relationship. For example, when the desired relationship is that signal  1  has a greater magnitude than signal  2 , a favorable comparison may be achieved when the magnitude of signal  1  is greater than that of signal  2  or when the magnitude of signal  2  is less than that of signal  1 . 
     The foregoing description of a preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiment was chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents. Further, it should be understood that various changes, substitutions and alterations can be made hereto without departing from the spirit and scope of the invention as described by the appended claims.