Abstract:
A receiving device is provided that comprises: a channel estimator adapted to receive an input; and an equalizer adapted to receive the input and generate an equalized output, wherein the equalized output is used by the channel estimator for at least one subsequent channel estimation.

Description:
CROSS-REFERENCE TO OTHER APPLICATIONS 
       [0001]    The following applications of common assignee are related to the present application, and are hereby incorporated herein by reference in their entireties: 
         [0002]    U.S. patent application Ser. No. 11/687,689 to YANG, et al entitled “METHOD AND APPARATUS FOR CHANNEL INTERPOLATION IN A TDS-OFDM SYSTEM OR DVB T/H SYSTEM” with attorney docket number LSFFT-047. 
         [0003]    U.S. patent application Ser. No. 11/687,693 to YANG, et al entitled “METHOD AND APPARATUS FOR ROBUST FREQUENCY EQUALIZATION” with attorney docket number LSFFT-048. 
     
    
     FIELD OF THE INVENTION 
       [0004]    The present invention relates generally to communication devices or receivers. More specifically, the present invention relates to a mobile receiver equalizer structure for use in a digital television (DTV) standard such as the ATSC standard. 
       BACKGROUND 
       [0005]    Digital receivers such as DTV receivers requires channel estimation for later processing. In addition, digital receivers are known to use an equalizer such as decision-feedback equalizers (DFE). The use of DFE in digital demodulation is known. 
         [0006]    However, DFE equalization is not suitable for enabling the initial acquisition of digital modulation that is severely distorted by multipath-induced intersymbol interference. Therefore, a reference waveform or reference sequence is typically introduced. 
         [0007]    In the United States, an 8-level vestigial sideband modulation (8-VSB) is proposed for the terrestrial broadcast of digital television transmission by the Advanced Television Systems Committee ATSC. The 8-level vestigial sideband modulation is a special single carrier technique. As in most wireless transmission, multipath propagation is one of the major challenging problems in VSB signal transmission. Multipath propagation degrades the receiver performance by introducing inter-symbol interference (ISI). Often, time-domain decision-feedback equalization (DFE) is required. U.S. Pat. No. 7,230,983 to Yousef describes a DFE means for determine coefficients of a decision feedback equalizer from a sparse channel estimate. However, the result of the equalization is not used for later channel estimation purposes. 
         [0008]    U.S. Pat. No. 5,886,748 to Lee describes an Equalizing method and equalizer using reference signal. However, the cited work does not address the multipath issues relevant to ATSC DTV reception. 
         [0009]    In summary, previous work concentrates on continuous adaptive DFE and is not suited for mobile application. For a receiver in a mobile context such a moving automobile, channel conditions may change at a rate greater than that of a non-mobile context. Therefore, it is desirous to have a mobile receiver equalizer structure that possesses an improved means for modeling channel conditions. 
       SUMMARY OF THE INVENTION 
       [0010]    An improved equalizer structure for modeling channel conditions is provided. 
         [0011]    A mobile receiver having an improved equalizer structure for modeling channel conditions is provided. 
         [0012]    A receiving device is provided that comprises: a channel estimator adapted to receive an input; and an equalizer adapted to receive the input and generate an equalized output, wherein the equalized output is used by the channel estimator for at least one subsequent channel estimation. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0013]    The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention. 
           [0014]      FIG. 1  is an example of a receiver in accordance with some embodiments of the invention. 
           [0015]      FIG. 2  is an example of a first detailed part of  FIG. 1 . 
           [0016]      FIG. 3  is an example of a second detailed part of  FIG. 1 . 
           [0017]      FIG. 4  is an example of a receiver in accordance with some embodiments of the invention. 
       
    
    
       [0018]    Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention. 
       DETAILED DESCRIPTION 
       [0019]    Before describing in detail embodiments that are in accordance with the present invention, it should be observed that the embodiments reside primarily in combinations of method steps and apparatus components related to simultaneously use a set of coefficient for equalizing and training, as well as feeding back the equalized output to the channel estimator. Furthermore, instead of using both shuffle-in/shuffle-out circuitry associated with each row updating, only a modified shuffle-in circuitry is used, and the shuffle-out circuitry is eliminated. Accordingly, the apparatus components and method steps have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. 
         [0020]    In this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises . . . a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element. 
         [0021]    It will be appreciated that embodiments of the invention described herein may be comprised of one or more conventional processors and unique stored program instructions that control the one or more processors to implement, in conjunction with certain non-processor circuits, some, most, or all of the functions of relating to simultaneously use a set of coefficient for equalizing and training, as well as feeding back the equalized output to the channel estimator. In the exemplified embodiments, it is noted that the processors include Finite State Machines, which are used in the preferred embodiment. The non-processor circuits may include, but are not limited to, a radio receiver, a radio transmitter, signal drivers, clock circuits, power source circuits, and user input devices. As such, these functions may be interpreted as steps of a method with reduced memory requirements to perform simultaneously use a set of coefficient for equalizing and training, as well as feeding back the equalized output to the channel estimator. Alternatively, some or all functions could be implemented by a state machine that has no stored program instructions, or in one or more application specific integrated circuits (ASICs), in which each function or some combinations of certain of the functions are implemented as custom logic. Of course, a combination of the two approaches could be used. Thus, methods and means for these functions have been described herein. Further, it is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations, when guided by the concepts and principles disclosed herein will be readily capable of generating such software instructions and programs and ICs with minimal experimentation. 
         [0022]    Referring to  FIGS. 1-4 , depictions of the present invention are shown. In  FIG. 1 , received signal  102  coupled to an antenna (not shown) is fed to both a channel estimator  104  and a equalizer  106 . In channel estimator  104 , the estimated channel information h is generated and fed into an equalizer training block  110 . Further, a local pseudo noise (PN) sequence  112  is used as the training sequence for equalizer training block  110 . Equalizer training block  110  generates a set of coefficient a set of trained coefficient  114  that is used both for internal training and for equalizer  106 . At equalizer  106 , the equalized information is both used as output  116  and fed back  118  to channel estimator  104  as a reference for future channel estimation. It is noted that channel estimator  104  operates in one or a combination of ways described in the various patent applications to the same inventors, all of which are listed herein the document and are hereby incorporated herein by reference. 
         [0023]    An exemplified internal operation for channel estimator  104  is disclosed in U.S. Pat. No. 7,170,944 to Liu et al entitled “ITERATIVE ASSESSMENT OF MULTIPATH SIGNAL PRESENCE”, wherein a method and system disclosed for determining whether one or more multipath signals is present in a received signal frame that includes a reference symbol (RS) sequence as part of the frame, and for iteratively evaluating a multipath signal that is present. The RS sequence index (m1) for the frame is identified, and first and second Fourier transforms for the received frame are provided for a selected time segment IS that includes the RS sequence of the received frame. An inverse Fourier transform of the ratio of the transforms is computed and analyzed. If at least one multipath signal is present, the inverse Fourier transformed information is nonlinearly filtered, and the filtered function is convolved with the reference symbol (RS) sequence. This convolution represents a received signal extension, due to multipath signal(s) presence. A refinement procedure analyzes a contribution to multipath signals from the preceding frame(s). The procedure is iteratively driven toward an optimal representation of any multipath signal(s) present. 
         [0024]    In  FIG. 2 , a detailed depiction of equalizer  106  is shown. Received signal  102  along with a set of trained coefficients  114  feed into block  200  in which a feed forward coefficient f i  is selected. The set of trained coefficients  114  is also fed into feed backward coefficient block  208  in which a feed backward coefficient b i  is selected. The subscript i herein is a positive integer for both f i  and b i  that ranges between 1 to n and spans a time segment. Block  200  receives signal  102  and filters it with the feed-forward equalization coefficients fi. The feed-backward equalizer  208  filters signal  118  based on the feed-backward coefficients bi. The subtraction module  202  subtracts the feedback equalized signal from the feed-forward equalized signal to produce a equalized signal  204 . The  204  is further refined by a slicer  206 , wherein more accurate information is obtained. The sliced information is further fed back to channel estimator  104  via fed back line  118 . Further, sliced information is also fed to feed backward coefficient  208 . 
         [0025]    In  FIG. 3 , a depiction  300  of equalizer training block  110  with other elements is shown. Equalizer training block  110  comprises a training block  302 , a training decision feedback equalizer (DFE)  304 , and a feed forward and feed backward coefficient error generator  306 . The generated errors Efi and Ebi are fed into training DFE  304  for updating of f i  and b i . Estimated channel condition  108  is fed into a training block  302 , wherein together with training sequence  112  are used as inputs into training DFE  304 , wherein suitable f i  and b i  are updated. The coefficients of training DFE  304  is fed into EFE  106 , wherein a set of trained coefficients  114  such as f i  and b i  are used for equalization purposes. Further, feed forward and feed backward coefficient error generator  306  also uses training sequence  112  to generate f i  and b i . The generated f i  and b i  are first stored in a buffer or path and then used by equalizer  106 , which comprises a second DFE having received signal  102  as input. Equalizer  106  may comprise a feed forward DFE and a feed backward DFE (both not shown). Similarly, training DFE  304  may comprise a feed forward DFE and a feed backward DFE (both also not shown). As can be seen, in this invention, channel estimation, DFE training, and DFE are combined and looped together to form a new structure. 
         [0026]      FIG. 4 , an exemplified receiver  10  suitable for implementing the equalization structure of  FIG. 1  is shown. Analog RF signal is received wirelessly via antenna  12  and fed into a front end including a tuner  14  and an analog-to-digital converter (ADC)  16 , and an automatic gain control unit  18 . Within tuner  14  the analog RF signal is converted to base-band and adjusted by automatic gain control unit  18 . ADC  16  transforms the received analog signals into a digital signal. An automatic gain control unit  18  is used for maintaining the strength of signals coming from antenna  12  via tuner  14 . 
         [0027]    The transformed signal undergoes synchronization  20 . The synchronized digital information  102  undergoes equalization  100  as described in  FIGS. 1-3 . The equalized information  116  is further subjected to forward error control (FEC)  22 . In addition, equalized information  116  is also fed back  118  to equalization block  100  for subsequent processing. 
         [0028]    In the foregoing specification, specific embodiments of the present invention have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present invention. The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.