Abstract:
An improved method of the adaptive signal processing for diversity signals is disclosed. Under normal adaptive signal processing conditions a plurality of input diversity signals would tend to cause undesirable coefficient interactions. By employing a plurality of diversity related errors the present invention tends to ameliorate these undesirable coefficient interactions.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This patent relates to adaptive signal processing. If the signal stream within an adaptive signal processor is correlated from delay tap to delay tap then the tap coefficient weights tend to interact; this cause one correlated tap to go more positive while the other tends to go more negative. Even though this situation may statistically null out, the noise within an instantaneous signal estimate can be greatly exacerbated by this condition. Under this condition, usually amelioration techniques such as “bleeds” to the coefficient weights are employed.  
           [0002]    In general adaptive processors function better if the signal within the processing pipeline has a very low degree of autocorrelation over the total processing time. This means that for data communications it is desirable to use a PN scrambler in order to reduce the autocorrelation that may occur from time-to-time in the data stream. Also, for repetitive patterns such as coronary heartbeat, it is desirable for the processing time to be less than the repetition rate of the heartbeat.  
           [0003]    [0003]FIG. 1 depicts the general topology for a standard adaptive signal processor with diversity signal inputs (derived from “Adaptive Signal Processing” FIG. 1. 4 , by Bernard Widrow and Samuel D. Stearns, Prentice-Hall Inc., 1985). The first diversity input signal  105  is sent to PROC 1   110  which produces partial estimate signal  125  output. The second diversity input signal  115  is sent to PROC 1   120  which produces partial estimate signal  135  output. These partial estimate signals  125  and  135  are added together within summer  130  to produce estimate signal  145  output. Estimate signal  145  is subtracted from the desired signal  155  within the summer  140  to produce an error signal  165  output. Error signal  165  is sent to ADAPT  150  wherein an adaptation algorithm such as the LMS algorithm is applied to the error signal  165  to produce adjustment group signals  175 . These adjustment group signals  175  are applied to PROC 1   110  and PROC 2   120  for coefficient weight adjustments. This method tend to have undesired interactions between PROC 1   110  and PROC 2   120  coefficients.  
           [0004]    For various military and commercial applications (e.g. troposcatter communications) signal diversities are employed. These diversities may be frequency, spatial, temporal, or combinations thereof (Herein, an example of temporal diversity could be where the adaptive signal processor has tap delays at fractional spacing of data timing period.) These diversity signals when present within the same adaptive signal processor are highly correlated and tend to cause the undesired tap coefficient interactions as explained above. The present invention addresses this problem of coefficient interaction.  
         BRIEF SUMMARY OF THE INVENTION  
         [0005]    The present invention takes a plurality of diversity signal inputs to produce a desired output as in normal adaptive signal processing. However, it does not producing only one error signal which would cause diversity coefficient interactions because of the high degree of correlation between the diversity signals. The present invention employs a corresponding set of diversity related error signals that ameliorates the interactions between the diversity processing coefficients. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    [0006]FIG. 1 depicts a customary (prior art) adaptive signal processor for diversity signals that has only one error signal.  
         [0007]    [0007]FIG. 2 depicts the present invention that produces a plurality of error signals for adaptive signal processing for diversity signals.  
         [0008]    [0008]FIG. 3 depicts the present invention that produces a plurality of error signals for decision directed adaptive signal processing for diversity signals. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0009]    An improved method for the adaptive signal processing for diversity signals is disclosed. In the following description for purposes of explanation, numerous details are set forward to provide a through understanding of the present invention. However, it will be apparent to one ordinarily skilled in the art that these details are not required in order to practice the invention. It should be noted that the present invention is an understandable variation of Widrow&#39;s FIG. 1. 4  (“Adaptive Signal Processing” as above) with more specifics in FIG. 1. 5 , plus detailed examples and explanations throughout; therefore, it should be apparent to one ordinarily skilled in the art as to how the present invention can be implemented. Thus extensive details related to adaptive signal processing are not presented herein, because adequate literature exists for that purpose. Also, it should be noted, for digital diversity signals simple examples are given; however, that does not preclude the application of the present invention to more complex modulated signals (e.g. m-ary signals). Herein, adaptive signal processing for only two diversity signals are given for illustrations; this should in no way be construed as to place a limit upon the number of the plurality of diversity signals to be processed.  
         [0010]    [0010]FIG. 2 depicts how the present invention could be applied to the previous case (FIG. 1 above). The first diversity input signal  205  is sent to PROC 10   210  which produces partial estimate signal  225  output. The second diversity input signal  265  is sent to PROC 20   270  which produces partial estimate signal  285  output. These partial estimate signals  225  and  285  are added together within summer  240  to produce the estimate signal  245  output.  
         [0011]    Here is where the present invention deviates from the previous case. Partial estimate signal  225  is subtracted from desired signal  255  within summer  220  to produce an error signal  235  output. Error signal  235  is sent to ADAPT 10   230  wherein an adaptation algorithm is applied to error signal  235  to produce adjustment group signals  215  (group herein refers to one adjustment signal per coefficient—in a some cases there may be only one coefficient to adjust). These adjustment group signals  215  are applied to PROC 10   210  for coefficient weight adjustments. In like manner, partial estimate signal  285  is subtracted from desired signal  258  within summer  260  to produce an error signal  295  output. (It should be noted that desired signals  255  and  258  may be of the same value, but are not so constrained.) Error signal  295  is sent to ADAPT 20   250  wherein an adaptation algorithm (e.g. LMS algorithm) is applied to error signal  295  to produce adjustment group signals  275 . These adjustment group signals  275  are applied to PROC 20   270  for coefficient weight adjustments. These error signals ( 235  and  295 ) are diversity related, thus the coefficient interactions between PROC 10   210  and PROC 20   270  are substantial reduced for most cases.  
         [0012]    [0012]FIG. 3 depicts an alternate embodiment of the present invention. The first diversity input signal  305  is sent to PROC 30 A  310  which produces partial estimate signal  335  output. The second diversity input signal  405  is sent to PROC 40 A  410  which produces partial estimate signal  435  output. Partial estimate signals  335 ,  435 ,  365 , and  465  are added together within summer  330  to produce the estimated data signal  345  output. This estimated data signal  345  is sent to a slicer  340 . Slicer  340  makes the decision as to whether the estimated data signal is a logical ‘one’ or ‘zero’; then the slicer  340  outputs its decision signal  355  in the form of ideal data amplitudes that are quantized to represent ‘ones’ or ‘zeroes’. This decision signal  355  is sent to PROC 30 B  350  which produces partial estimate signal  365  output. Partial estimate signals  365  and  335  are subtracted from the quantized decision signal  355  within summer  320  to produce error signal  325  output. This error signal  325  is sent to ADAPT 30   360  wherein an adaptation algorithm is applied to error signal  325  to produce adjustment group signals  315 . These adjustment group signals  315  are applied to PROC 30 A  310  and PROC 30 B  350  for coefficient weight adjustments. Thus the loop is closed with the quantized decision  355  being the desired signal.  
         [0013]    In like manner, decision signal  355  is sent to PROC 40 B  450  which produces partial estimate signal  465  output. Partial estimate signals  465  and  435  are subtracted from the quantized decision  355  within summer  420  to produce error signal  425  output. This error signal  425  is sent to ADAPT 40   460  wherein an adaptation algorithm is applied to error signal  425  to produce adjustment group signals  415 . These adjustment group signals  415  are applied to PROC 40 A  410  and PROC 40 B  450  for coefficient weight adjustments.  
         [0014]    This embodiment (FIG. 3) could be implemented in digital, analog, or combinations thereof. However, it is preferred that the implementation be digital with the diversity input signals  305  and  405  being the digitized analog-to-digital (A/D) representation of the analog baseband signals; the processing delays would be obtained with digital registers as opposed to analog delays. An example of what we refer to as temporal diversity could be where diversity input signals  305  and  405  are derived from the same analog baseband signal. Diversity input signal  305  being derived from an A/D in synch with the data clock and the diversity input signal  405  being derived from an A/D that is clocked with the data clock offset by say half the period of the data clock.