Abstract:
A method for initializing an equalizer in an Orthogonal Frequency Division Multiplexing (“OFDM”) receiver includes generating a desired equalizer tap setting based on an adaptive algorithm. An initial setting for the adaptive algorithm corresponds to an approximate inverse of a channel estimate, and the desired tap setting corresponds to an ideal inverse of the channel estimate. In an alternative embodiment, a method includes generating a channel estimate, generating an equalizer tap setting based on a complex conjugate of the estimate and a quantized magnitude squared of the estimate, and repeatedly generating subsequent tap settings until an error falls within limits. In another alternative embodiment, an apparatus includes a tap initialization controller configured to: generate a channel estimate, generate an equalizer tap setting based on a complex conjugate of the estimate and a quantized magnitude squared of the estimate, and repeatedly generate subsequent tap settings until an error falls within limits.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to processing orthogonal frequency division multiplexed (“OFDM”) signals.  
         BACKGROUND OF THE INVENTION  
         [0002]    A local area network (“LAN”) may be wired or wireless. A wireless local area network (“wireless LAN” or “WLAN”) is a flexible data communications system implemented as an extension to, or as an alternative for, a wired local area network (“wired LAN”) within a building or campus. Using electromagnetic waves, WLANs transmit and receive data over the air, minimizing the need for wired connections. Thus, WLANs combine data connectivity with user mobility, and, through simplified configuration, enable movable LANs. Some industries that have benefited from the productivity gains of using portable terminals (e.g., notebook computers) to transmit and receive real-time information are the digital home networking, health-care, retail, manufacturing, and warehousing industries.  
           [0003]    Manufacturers of WLANs have a range of transmission technologies to choose from when designing a WLAN. Some exemplary technologies are multicarrier systems, spread spectrum systems, narrowband systems, and infrared systems. Although each system has its own benefits and detriments, one particular type of multicarrier transmission system, orthogonal frequency division multiplexing (“OFDM”), has proven to be exceptionally useful for WLAN communications.  
           [0004]    OFDM is a robust technique for efficiently transmitting data over a channel. The technique uses a plurality of subcarrier frequencies (“subcarriers”) within a channel bandwidth to transmit data. These subcarriers are arranged for optimal bandwidth efficiency as compared to conventional frequency division multiplexing (“FDM”), which can waste portions of the channel bandwidth in order to separate and isolate the subcarrier frequency spectra and thereby avoid inter-carrier interference (“ICI”). By contrast, although the frequency spectra of OFDM subcarriers overlap significantly within the OFDM channel bandwidth, OFDM nonetheless allows resolution and recovery of the information that has been modulated onto each subcarrier. In addition to the more efficient spectrum usage, OFDM provides several other advantages, including a tolerance to multi-path delay spread and frequency selective fading, good interference properties, and relatively simplified frequency-domain processing of the received signals.  
           [0005]    For processing, an OFDM receiver typically converts a received signal from the time-domain into frequency-domain representations of the signal. Generally, conventional OFDM receivers accomplish this by sampling the timedomain signal and then applying Fast Fourier Transforms (“FFTs”) to blocks of the samples. The resulting frequency-domain data generally includes a complex value (e.g., magnitude component and phase component, or real component and imaginary component) for each respective subcarrier. The receiver typically applies an equalizer to the frequency-domain data before recovering the baseband data that was modulated onto each subcarrier. Primarily, the equalizer corrects for multi-path distortion effects of the channel through which the OFDM signal was transmitted. Some receivers may also use the equalizer to correct for other problems encountered with OFDM communications, such as, for example, carrier frequency offset (i.e., a difference between the transmitter and receiver frequencies), and/or sampling frequency offset (i.e., a difference between the transmitter and receiver sampling clock frequencies). Carrier frequency offset and sampling frequency offset can result in a loss of orthogonality between the subcarriers, which results in inter-carrier interference (“ICI”) and a severe increase in the bit error rate (“BER”) of the data recovered by the receiver. In any event, the equalizer of the OFDM receiver typically has one or more taps which receive a tap setting corresponding to the complex correction (e.g., real correction and imaginary correction, or magnitude correction and phase correction) for each subcarrier.  
           [0006]    Historically, the equalizer taps have been initialized with (X/Y), which represents a division of a predetermined, stored frequency-domain representation of an expected OFDM signal (i.e., a “training symbol” or “X”) by the frequency-domain representation of the corresponding actual received signal (“Y”). Such initialization schemes are based on a simplified frequency-domain channel model that assumes orthogonality among the subcarriers, in which Y=C*X, where an actual received signal (Y) is merely a transmitted predetermined signal (X) times the channel response (C). In such a case, C=Y/X and thus, to compensate for the channel response, the equalizer is initialized with the inverse of the channel response (i.e., 1/C, or X/Y).  
           [0007]    However, in digital data processing systems division operations are generally slower and require more memory than multiplication operations. Accordingly, some OFDM receivers implement the necessary division by divider circuits in hardware. But hardware divider circuits are undesirably expensive. Alternatively, other receivers approximate the division by resort to a lookup table. There, multiplication operations can be employed when the received training symbol (Y) is the input to the table and the output of the table is the inverse of the received training symbol (1/Y). The inverse (1/Y) is then multiplied by the actual training symbol (X) to form the tap initialization (X/Y), thus avoiding division operations. However, in order to get good results, the lookup tables must have undesirably large numbers of storage locations, which is also undesirably expensive. The present invention is directed to the correction of this problem.  
         SUMMARY OF THE INVENTION  
         [0008]    A method for initializing an equalizer in an Orthogonal Frequency Division Multiplexing (“OFDM”) receiver includes generating a desired equalizer tap setting based on an adaptive algorithm. An initial setting for the adaptive algorithm corresponds to an approximate inverse of a channel estimate, and the desired tap setting corresponds to an ideal inverse of the channel estimate. In an alternative embodiment, a method includes generating a channel estimate, generating an equalizer tap setting based on a complex conjugate of the estimate and a quantized magnitude squared of the estimate, and repeatedly generating subsequent tap settings until an error falls within limits. In another alternative embodiment, an apparatus includes a tap initialization controller configured to: generate a channel estimate, generate an equalizer tap setting based on a complex conjugate of the estimate and a quantized magnitude squared of the estimate, and repeatedly generate subsequent tap settings until an error falls within limits. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    The aforementioned advantages of the invention, as well as additional advantages thereof, will be more fully understood as a result of a detailed description of the preferred embodiment when taken in conjunction with the accompanying drawings in which:  
         [0010]    [0010]FIG. 1 is a block diagram of an OFDM receiver according to the present invention;  
         [0011]    [0011]FIG. 2 is a block diagram of the adaptive equalizer of FIG. 1;  
         [0012]    [0012]FIG. 3 is a flowchart for a method of generating a tap seed for an adaptive algorithm according to the present invention;  
         [0013]    [0013]FIG. 4 is a flowchart for a method of operating an adaptive algorithm according to the present invention; and  
         [0014]    [0014]FIG. 5 is an illustration of various operational modes for the adaptive equalizer of FIG. 2. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]    The characteristics and advantages of the present invention will become more apparent from the following description, given by way of example.  
         [0016]    It should be appreciated that “1”, “one”, and/or “unity” as used in the description of the present invention and the claims means any suitable number or amount taken as that for which 1 is meant to stand in a formula, calculation, computation, or otherwise, and in practice the actual number or amount may not be exactly 1 due to accuracy limitations or other features of the hardware and/or software in which the invention is embodied. Similarly, it should be appreciated that “0” and/or “zero” as used in the description of the present invention and the claims means any suitable number or amount taken as that for which 0 is meant to stand in a formula, calculation, computation, or otherwise, and in practice the actual number or amount may not be exactly 0 due to accuracy limitations or other features of the hardware and/or software in which the invention is embodied.  
         [0017]    Referring to FIG. 1, a block diagram of an OFDM receiver  20  according to the present invention is shown. OFDM receiver  20  includes a sampler  24 , an FFT processor  28 , a training symbol extractor  32 , an adaptive equalizer  36 , and downstream processors  40 . In general, OFDM receiver  20  is configured to receive OFDM transmissions and recover baseband data therefrom. The received transmissions may conform to the proposed ETSI-BRAN HIPERLAN/2 (Europe) and/or the IEEE 802.11a (USA) wireless LAN standards, which are herein incorporated by reference, or they may conform to any other suitable protocols or standard formats. It should be noted that OFDM receiver  20  may be embodied in hardware, software, or any suitable combination thereof. Additionally, OFDM receiver  20  may be integrated into other hardware and/or software. For example, OFDM receiver  20  may be part of a WLAN adapter that is implemented as a PC card for a notebook or palmtop computer, as a card in a desktop computer, or integrated within a hand-held computer. Further, it should be readily appreciated that various components of OFDM receiver  20  may suitably be interconnected by various control inputs and outputs (not shown) for the communication of various control settings. For example, FFT processor  28  may include a suitable input for receiving window synchronization settings.  
         [0018]    Sampler  24  is configured to receive transmitted OFDM signals and generate time-domain samples or data therefrom. To this end, sampler  24  includes suitable input signal conditioning and an analog-to-digital converter (“ADC”).  
         [0019]    FFT processor  28  is coupled to sampler  24  to receive time-domain data therefrom. FFT processor  28  is configured generate frequency-domain representations or data from the time-domain data by performing FFT operations on blocks of the time-domain data.  
         [0020]    Training symbol extractor  32  is coupled to FFT processor  28  to receive frequency-domain data therefrom. Training symbol extractor  32  is configured to extract training symbols from training sequences that have been included in the transmitted OFDM signals. A training sequence contains predetermined transmission values for all of the subcarriers of the OFDM carrier. Here, it should be noted that for clarity of exposition, much of the description of the present invention is presented from the point of view of a single subcarrier. In this context, a “training symbol” may be viewed as the predetermined frequency-domain value for a particular subcarrier. Nevertheless, it should be readily appreciated that the present invention may be used to sequentially process data for a plurality of subcarriers, and/or various components of the present invention may be suitably replicated and coupled to parallel process data for a plurality of subcarriers.  
         [0021]    Adaptive equalizer  36  is coupled to training symbol extractor  32  to receive training symbols therefrom and is coupled to FFT processor  28  to receive frequency-domain data therefrom. In general, adaptive equalizer  36  is configured to reduce the multi-path distortion effects of the channel through which the OFDM signals have been transmitted. The configuration and operation of adaptive equalizer  36  is discussed in further detail below.  
         [0022]    Downstream processors  40  are coupled to adaptive equalizer  36  to receive equalized frequency-domain data therefrom. Downstream processors  40  are configured to recover baseband data that was included in the transmitted OFDM signals.  
         [0023]    In operation of the OFDM receiver  20 , sampler  24  receives OFDM signals and generates time-domain data therefrom. FFT processor  28  generates frequency-domain data from the time-domain data by performing FFT operations on blocks of the time-domain data, and training symbol extractor  32  extracts training symbols from training sequences that have been included in the OFDM signals. Generally, adaptive equalizer  36  reduces multi-path distortion effects of the OFDM transmission channel. The operation of adaptive equalizer  36  is discussed in further detail below. Downstream processors  40  recover baseband data that was included in the transmitted OFDM signals.  
         [0024]    Referring now to FIG. 2, a block diagram of adaptive equalizer  36  of FIG. 1 is shown. Adaptive equalizer  36  includes channel estimator  50 , seed generator  54 , reference training symbol storage  58 , equalizer tap storage  64 , switch  68 , equalizer filter  72 , switch  76 , switch  92 , tap adapter  96 , switch  100 , slicer  104 , and tap initialization controller  108 . As noted above, OFDM receiver  20  (FIG. 1) may be embodied in hardware, software, or any suitable combination thereof. Accordingly, it should be readily appreciated that adaptive equalizer  36  may be embodied in hardware, software, or any suitable combination thereof. In general, adaptive equalizer  36  is configured to generate an initial equalizer tap setting based on a training symbol and an adaptive algorithm, and to generate subsequent tap settings based on data symbols and an adaptive algorithm.  
         [0025]    Channel estimator  50  is coupled to training symbol extractor  32  (FIG. 1) to receive training symbols therefrom. Further, channel estimator  50  is coupled to reference training symbol storage  58  to receive a predetermined reference training symbol therefrom. Channel estimator  50  is configured to generate a channel estimate based on a training symbol and the reference training symbol. Further details regarding the operation of channel estimator  50  are discussed below.  
         [0026]    Seed generator  54  is coupled to channel estimator  50  to receive the channel estimate therefrom. Seed generator  54  is configured to generate a tap seed based on the channel estimate as discussed further below.  
         [0027]    Reference training symbol storage  58  is coupled to channel estimator  50  to provide the reference training symbol thereto. Reference training symbol storage  58  is configured to store the reference training symbol (real part and imaginary part, or magnitude and phase).  
         [0028]    Equalizer tap storage  64  is coupled to switch  68  to selectively receive either the tap seed from seed generator  54  or a new tap setting from tap adapter  96 . Further, equalizer tap storage  64  is coupled to tap adapter  96  to provide an old tap setting thereto. Also, equalizer tap storage  64  is coupled to equalizer filter  72  to provide the new tap setting thereto. Additionally, equalizer tap storage  64  is coupled to switch  76  to selectively provide the new tap setting to tap adapter  96 . Equalizer tap storage  64  is configured to store a tap setting (real part and imaginary part, or magnitude and phase).  
         [0029]    Equalizer filter  72  includes a first input port  80 , a second input port  84 , and an output port  88 . Input port  80  is coupled to equalizer tap storage  64  to receive the new tap setting therefrom. Input port  84  is coupled to switch  92  to selectively receive either the channel estimate from the channel estimator  50  or a data symbol from FFT processor  28  (FIG. 1). Equalizer filter  72  is configured to generate an equalizer output at output port  88  that represents a frequency-domain multiplication of the data received through its two input ports.  
         [0030]    Tap adapter  96  is coupled to output port  88  of equalizer filter  72  to receive the equalizer output therefrom. Further, tap adapter  96  is coupled to switch  76 , which is coupled to input port  80  of equalizer filter  72  and input port  84  of equalizer filter  72  such that tap adapter  96  also selectively receives either the data provided to input port  80  or the data provided to input port  84 . Also, tap adapter  96  is coupled to switch  68  to selectively provide the new tap setting to equalizer tap storage  64 . Additionally, as noted above, tap adapter  96  is coupled to equalizer tap storage  64  to receive an old tap setting therefrom. Further, tap adapter  96  is coupled to tap initialization controller  108  to provide an “update completed” signal thereto. The update completed signal is discussed in further detail below. Meanwhile, tap adapter  96  is also coupled to switch  100  to selectively receive either 1 (real part=1 and imaginary part=0, or magnitude=1 and phase=0) or a slicer output. In general, tap adapter  96  is configured to generate tap settings based on an adaptive algorithm. Operation of the tap adapter  96  is discussed in further detail below.  
         [0031]    Slicer  104  is coupled to output port  88  of equalizer filter  72  to receive the equalizer output therefrom. Further, slicer  104  is coupled to switch  100  to provide the slicer output thereto. Slicer  104  is configured to generate the slicer output based on a decision as to which of a plurality of predetermined possible data values is closest to the actual equalizer output.  
         [0032]    Tap initialization controller  108  is coupled to tap adapter  96  to receive the update completed signal therefrom (the update completed signal is discussed in further detail below). Further, tap initialization controller  108  is coupled to switch  68 , switch  76 , switch  92 , and switch  100  (indicated by the dashed lines) to selectively control the operation of these switches. Tap initialization controller  108  is configured to cause the present invention to switch between various operational modes as is discussed in further detail below (see FIG. 5).  
         [0033]    In operation, adaptive equalizer  36  executes the methods and modes discussed below in connection with FIG. 3, FIG. 4, and FIG. 5.  
         [0034]    Referring now to FIG. 3, a flowchart for a method  200  of generating a tap seed for an adaptive algorithm according to the present invention is shown. In general, the following description of method  200  assumes execution by adaptive equalizer  36  (FIG. 1 and FIG. 2). Accordingly, it should be readily appreciated that the description of method  200  assumes frequency-domain operations. However, it is noted that method  200  is not necessarily limited to adaptive equalizer  36  and, accordingly, method  200  also may be executed by any suitable alternative hardware, software, or combination thereof.  
         [0035]    At step  210 , channel estimator  50  receives a training symbol from training symbol extractor  32 .  
         [0036]    At step  220 , channel estimator  50  generates a channel estimate. In general, channel estimator  50  generates the channel estimate by multiplying the received training symbol by a predetermined quantity. The predetermined quantity represents an inverse of a predetermined referenced training symbol. To this end, at step  220  channel estimator  50  may also retrieve the predetermined quantity from reference training symbol storage  58  or, in a case where the received training sequence includes all ones (“1s”) and negative ones (“−1s”) (for example, OFDM transmissions conforming to HIPERLAN/2) channel estimator  50  may generate the channel estimate by simply inverting the sign of the received training symbol.  
         [0037]    At step  230 , seed generator  54  generates a magnitude squared of the channel estimate. In general, seed generator  54  generates the magnitude squared of the channel estimate by multiplying the real part of the channel estimate by the real part of the channel estimate and adding the result to the imaginary part of the channel estimate multiplied by the imaginary part of the channel estimate, as follows: 
           m   2 =( c*c )+( d*d ) 
         [0038]    where m 2  is the magnitude squared of the channel estimate, c is the real part of the channel estimate, and d is the imaginary part of the channel estimate.  
         [0039]    At step  240 , seed generator  54  generates a quantized magnitude squared of the channel estimate by quantizing the magnitude squared of the channel estimate to a power of two.  
         [0040]    At step  250 , seed generator  54  generates a complex conjugate of the channel estimate by inverting the sign of the imaginary part of the channel estimate.  
         [0041]    At step  260 , seed generator  54  generates a tap seed by right shifting the bits of the complex conjugate of the channel estimate as necessary to produce a practical equivalent of the complex conjugate of the channel estimate divided by the quantized magnitude squared of the channel estimate. For example: when the quantized magnitude squared of the channel estimate is 4 decimal (or 00000100 binary), tap seed generator  54  right shifts the bits of the real and imaginary parts of the complex conjugate of the channel estimate by two places; and when the quantized magnitude squared of the channel estimate is 8 decimal (or 00001000 binary), tap seed generator  54  right shifts the bits of the real and imaginary parts of the complex conjugate of the channel estimate by three places. Here, it should be noted that, since for a complex number, c+jd: 
         1/( c+jd )=( c−jd )/( c   2   +d   2 )={ c /[( c*c )+( d*d )]}−{ jd /[( c*c )+( d*d )]} 
         [0042]    the tap seed is an approximate inverse of the channel response. It should be appreciated that the tap seed is only an approximation because magnitude squared of the channel estimate, or [(c*c)+(d*d)], was quantized at step  240  above. However, it should also be appreciated that generating the quantized magnitude squared of the channel estimate to a power of two provides for the right shifting at step  260 , which avoids a hardware division circuit or a lookup table. In any event, seed generator  54  provides the tap seed to switch  68  and tap initialization controller  108  controls switch  68  to load the tap seed data into a variable (“TempTap”) that is stored in equalizer tap storage  64  (see “generate seed” mode of FIG. 5 and corresponding discussion below).  
         [0043]    Referring now to FIG. 4, a flowchart for a method  300  of operating an adaptive algorithm according to the present invention is shown. In general, the following description of method  300  assumes execution by adaptive equalizer  36  (FIG. 1 and FIG. 2). Accordingly, it should be readily appreciated that the description of method  300  assumes frequency-domain operations. However, it is noted that method  300  is not necessarily limited to adaptive equalizer  36  and, accordingly, method  300  also may be executed by any suitable alternative hardware, software, or combination thereof.  
         [0044]    At step  306 , tap adapter  96  sets a variable, ITERATION COUNTER, to zero. Tap adapter  96  uses ITERATION COUNTER to determine when a magnitude of the error generated at step  310  is less than a predetermined limit as discussed further below.  
         [0045]    At step  310 , tap adapter  96  generates an error according to the following: 
           E= 1−(TempTap*   C   ) 
         [0046]    where E is the error, TempTap is the new (or most recent) tap setting stored in equalizer tap storage  64  (and thus provided to input port  80  of equalizer filter  72 ), and C is the channel estimate generated at step  220  (FIG. 3) above. It should be readily appreciated that tap adapter  96  obtains TempTap data from equalizer tap storage  64  via switch  76  pursuant to the control of tap initialization controller  108  (see “update tap” mode of FIG. 5 and corresponding discussion below). Additionally, it should be readily appreciated that generation of the error in this manner makes sense because, ideally, the equalizer tap setting would be the exact inverse of the channel response, such that the product of the two values would be 1.  
         [0047]    At step  320 , tap adapter  96  updates TempTap in equalizer tap storage  64  according to the following: 
         TempTap=TempTap old +(stepsize*TempTap old   *E ) 
         [0048]    where TempTap old  is the previously generated TempTap data, and stepsize is the least-mean-squares stepsize value. Suitable ways of determining the stepsize are well known.  
         [0049]    At step  326 , tap adapter  96  increments ITERATION COUNTER. Thus, ITERATION COUNTER indicates the number of times that tap adapter  96  has updated TempTap during the present execution of method  300 .  
         [0050]    At step  330 , tap adapter  96  determines whether a magnitude of the error generated at step  310  is less than a predetermined limit. Preferably, tap adapter  96  does this by simply determining whether ITERATION COUNTER indicates a predetermined number of iterations, where the predetermined number is that which is required to ensure a desirable minimization of the error. This technique provides a consistent number of iterations for each execution of method  300 . The predetermined number of iterations may be based on error convergence calculations, test trials, or a combination thereof. Suitable ways of determining this number are well known. Alternatively, tap adapter  96  may directly compare the magnitude of the error to a predetermined limit, in which case it should be readily appreciated that step  306  (resetting ITERATION COUNTER) and step  326  (incrementing ITERATION COUNTER) may be omitted. In any event, if tap adapter  96  determines that the magnitude of the error is less than the predetermined limit, then at step  340  tap adapter  96  signals tap initialization controller  108  and tap initialization controller  108  causes adaptive equalizer  36  to switch into a “track data” mode (see “track data” mode of FIG. 5 and corresponding discussion below); else, tap adapter  96  repeats step  310 , step  320 , step  326 , and step  330 .  
         [0051]    It should be appreciated from the foregoing description that the embodiments described herein generally follow a least-mean-squares (“LMS”) approach that starts with the tap seed and then recursively generates a more accurate (“desired”) initial equalizer tap setting. Further, it should also be appreciated that the desired tap setting is based on an ideal inverse of the channel estimate because as the error approaches zero, TempTap multiplied by the channel estimate approaches 1, and, thus, TempTap ideally becomes the inverse of the channel estimate. However, it is noted that alternative embodiments may employ any other suitable adaptive techniques in combination with or in lieu of LMS.  
         [0052]    Referring now to FIG. 5, an illustration of various operational modes for adaptive equalizer  36  of FIG. 2 is shown. In a “generate seed” mode, tap initialization controller  108  puts switch  68 , switch  76 , switch  92 , and switch  100  in the states shown in FIG. 2. That is, in the generate seed mode switch  68  couples seed generator  54  to equalizer tap storage  64 , switch  76  couples input port  80  of equalizer filter  72  to tap adapter  96 , switch  92  couples channel estimator  50  to input port  84  of equalizer filter  72 , and switch  100  couples 1 (one) to tap adapter  96 . Further, in the generate seed mode adaptive equalizer  36  generates the tap seed as discussed above (method  200 , FIG. 3). After the generate seed mode (i.e., after the tap seed is loaded into equalizer tap storage  64 ), tap initialization controller  108  initiates an “update tap” mode.  
         [0053]    In the update tap mode, tap initialization controller  108  puts switch  68  in its alternate state from that shown in FIG. 2, thereby uncoupling seed generator  54  from equalizer tap storage  64  and coupling tap adapter  96  to equalizer tap storage  64  through switch  68 . During the update tap mode, tap initialization controller  108  maintains switch  76 , switch  92 , and switch  100  in the states shown in FIG. 2. Further, in the tap update mode adaptive equalizer  36  executes the adaptive algorithm as discussed above (method  300 , FIG. 4). After the update tap mode (i.e., when the error becomes less than the limit), tap initialization controller  108  initiates a “track data” mode.  
         [0054]    In the track data mode, tap initialization controller  108  maintains switch  68  in its alternate state from that shown in FIG. 2, and tap initialization controller  108  puts switch  76 , switch  92 , and switch  100  all in alternate states from as they are shown in FIG. 2. That is, switch  68  couples tap adapter  96  to equalizer tap storage  64 , switch  76  couples input port  84  of equalizer filter  72  to tap adapter  96 , switch  92  couples the received data symbols to input port  84  of equalizer filter  72 , and switch  100  couples slicer  104  to tap adapter  96 . Further, it should be appreciated that during the track data mode, adaptive equalizer  36  adapts the data in equalizer tap storage  64  (which is coupled to input port  80  of equalizer filter  72 ) based on the received data symbols and LMS (or any other suitable technique).  
         [0055]    Thus, according to the principle of the present invention, an OFDM receiver generates an initial equalizer tap setting based on an adaptive algorithm.  
         [0056]    While the present invention has been described with reference to the preferred embodiments, it is apparent that that various changes may be made in the embodiments without departing from the spirit and the scope of the invention, as defined by the appended claims.