Abstract:
Predetection combiners when properly implemented tend to function very well in combining diversity signals. However, they do not fair very well under some cases of interference sources (e.g. jamming). A novel method for using adaptive signal processing for interference canceling with a predetection combiner is disclosed.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This patent relates to adaptive signal processing and diversity combining. Predetection combiners when properly implemented tend to function very well in combining diversity signals. However, they do not fair very well under some cases of interference sources (e.g. military jamming). On the other hand, adaptive beamformers tend to handle these interference conditions better. However, they tend not to be as good a diversity combiner under some conditions. It is desired to have the combining advantages of the predetection combiner with the interference handle abilities of the adaptive signal processor.  
           [0002]    [0002]FIG. 1 depicts the general topology for a class of adaptive signal processors for diversity signal inputs (derived from “Adaptive Signal Processing” FIG. 14.4, by Bernard Widrow and Samuel D. Stearns, Prentice-Hall Inc., 1985). The first diversity input signal  200  is sent to delay function  100  which produces delayed signal  215 . The second diversity input signal  205  is sent to delay function  110  which produces delayed signal  220 . The last diversity input signal  210  is sent to delay function  120  which produces delayed signal  225  (other diversity inputs would be delayed in like manner). These delays  100 ,  110 ,  120  are selected such that their signal outputs  215 ,  220 ,  225  are in phase for the desired signal component that is to be demodulated. Collectively these delays  100 ,  110 ,  120  form what is oftentimes called the “look direction” of the array. These delayed signals  215 ,  220 ,  225  are added together within summer  130  to produce combined signal  230 .  
           [0003]    The summed signal  230  goes to optional filter  140  which produces filtered signal  235 . Additionally, the delayed signals  215 ,  220 ,  225  are, also, sent to adaptive interference processor  160  which produces processed signal  245 . This processed signal  245  is then subtracted from the filtered signal  235  within adjustment summer  150  to produce the interference adjusted output signal  240 . This interference adjusted output signal  240  is the error signal that is sent to adaptive interference processor  160  for tap weight adjustments for interference removal. It is an objective of the present invention to replace the delays  100 ,  110 ,  120  and the summer  130  with a predetection combiner.  
         BRIEF SUMMARY OF THE INVENTION  
         [0004]    The present invention takes a plurality of diversity signal inputs into a predetection combiner which phase aligns and then combines them into a single signal. Additionally, within the predetection combiner these phase aligned signals are sensed prior to combining and sent to an adaptive interference processor. The predetection combined signal is passed through an optional filter. The signal from the filter is sent to an adjustment summer wherein the signal from the adaptive interference processor is subtracted from it. The signal from this adjustment summer is the interference adjusted output signal; this output signal is also sent to the adaptive interference processor as an error input signal.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    [0005]FIG. 1 depicts a class (prior art) of adaptive signal processors for diversity signals for interference cancellation.  
         [0006]    [0006]FIG. 2 depicts the present invention that combines an adaptive interference processor with a predetection combiner.  
         [0007]    [0007]FIG. 3 depicts an alternate embodiment of the present invention that combines an adaptive interference processor with a modified predetection combiner. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0008]    A novel method for using adaptive signal processing interference canceling with a predetection combiner 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 contains understandable variations of Widrow&#39;s FIG. 14.4 (“Adaptive Signal Processing” as above) with Widrow&#39;s associated 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. Extensive details related to adaptive signal processing and predetection combining are not presented herein, because adequate literature exists for these subjects. Herein, a plurality of diversity input signals shall be construed to be more than one.  
         [0009]    [0009]FIG. 2 depicts a preferred embodiment of the present invention. It consists of a predetection combiner  400 , an adaptive interference processor  450 , an optional filter  430 , and an adjustment summer  440 . The diversity input signals  300 ,  305 ,  310  are received by the predetection combiner  400 ; it is preferred that the predetection combiner  400  be of the equal-gain type. These diversity signals  300 ,  305 ,  310  could be either RF or IF type signals; oftentimes they are IF types. In cases where different RF frequencies are involved (e.g. frequency diversity, frequency-hop, . . . ) one would usually prefer to use IF type for diversity signals  300 ,  305 ,  310 . It is preferred that the present invention be employed in frequency-hop applications. These diversity signals  300 ,  305 ,  310  first are processed by a phase alignment function  410  which produces phase aligned signals  320 ,  325 ,  330  (herein aligned, phase aligned, . . . refer to the desired modulated signal frequency). These phase aligned signals  320 ,  325 ,  330  are sent to detection summer  420  and adaptive interference processor  450 . These phase aligned signals  320 ,  325 ,  330  are added together within detection summer  420  to produce the combined signal  315 . This combined signal  315  is fed back to the phase alignment function  410  which derives a reference phase for alignment; also, it  315  is also fed to an optional filter  430 .  
         [0010]    This filter  430  could be in accordance with Widrow&#39;s FIG. 14.4 explanation, but it is not so constrained. This filter  430  produces a filtered signal  335  that is sent to adjustment summer  440 . Adjustment summer  440  takes the adaptive interference processor  450  processed signal  345  and subtracts it from the filtered signal  335  to produce the interference adjusted output signal  340 . The interference adjusted output signal  340  is also fed to the adaptive interference processor  450  as an error signal for tap weight adjustments. In general the adaptive interference processor  450  takes the phase aligned signals  320 ,  325 ,  330  and removes the bulk of the desired signal while retaining the interference signal(s). Then it can us any number of adaptive algorithms (e.g. LMS algorithm) to correlate the interference adjusted output signal  340  with these interference signal(s) to determine the tap weigh adjustment that determine the value of the processed signal  345 .  
         [0011]    The predetection combiner has another advantage in that it allows a variable “look direction” when the direction of the incoming signal is not know (e.g. there is relative motion between the transmitter(s) and the diversity array-mobile situations). The predetection combiner also has the advantage of performing better than some adaptive signal processors in the absence of any significant external interference signal(s). It should be noted that in the case where optional filter  430  is not used, processed signal  345  is then subtracted from combined signal  315  within adjustment summer  440 .  
         [0012]    [0012]FIG. 3 depicts an alternate embodiment of the present invention where in the predetection combiner is modified such that the feedback to the phase alignment function  410  is taken from the interference adjusted signal  340  instead of the combined signal  315 .