Linear Single-Antenna Interference Cancellation Receiver

Abstract

System and method for interference cancellation in a digital wireless communications system. A preferred embodiment comprises sampling a received signal wherein the received signal is real-valued, rotating the sampled received signal by a specified amount, extracting in-phase and quadrature phase streams from the rotated, sampled received signal, applying an interference suppression filter and combining the filtered streams. The output of the combining operation can be de-correlated (by whitening) if there is excessive correlation.

1 - 38 . (canceled)  
   
   
       39 . A method for suppressing interference in a received signal comprising: 
 sampling the received signal to create a discrete time sequence representing the received signal;    rotating the discrete time sequence by a specified amount;    extracting in-phase and quadrature phase streams from the rotated, sampled received signal;    applying an interference suppression filter to the in-phase and quadrature phase streams; and    combining the filtered in-phase and quadrature phase streams.    
   
   
       40 . The method of  claim 39  further comprising after the combining, whitening the combined streams.  
   
   
       41 . The method of  claim 40 , wherein the whitening can be performed via a temporal filter.  
   
   
       42 . The method of  claim 41 , wherein the temporal filter can be implemented via a linear predictor.  
   
   
       43 . The method of  claim 39 , wherein the sampling is at a sampling rate essentially equal to a symbol rate of the received signal.  
   
   
       44 . The method of  claim 39 , wherein the in-phase stream is the real portion of the rotated, sampled received signal and the quadrature stream is the imaginary portion of the rotated, sampled received signal.  
   
   
       45 . The method of  claim 43 , wherein the interference suppression filter can be designed using a zero-forcing criteria.  
   
   
       46 . The method of  claim 43 , wherein the interference suppression filter can be designed using a minimum mean square error criteria.  
   
   
       47 . The method of  claim 43 , wherein the interference suppression filter can be designed using a maximum signal to interference plus noise (SINR) criteria.  
   
   
       48 . The method of claim  34 , wherein the sampling is at a sampling rate that is greater than a symbol rate of the received signal.  
   
   
       49 . A method for suppressing interference in a received signal comprising: 
 sampling the received signal to create a discrete time sequence representing the received signal, wherein the sampling is at a sampling rate that is not less than a symbol rate of the received signal;    rotating the discrete time sequence by a specified amount;    extracting in-phase and quadrature phase streams from the rotated, sample received signal; and    applying an interference suppression filter to the in-phase and quadrature phase streams.    
   
   
       50 . The method of  claim 49  further comprising after the applying, whitening the in-phase and quadrature phase streams.  
   
   
       51 . The method of  claim 50 , wherein the whitening can be performed by a spatial whitening transform, W, and wherein the spatial whitening transform is a function of an inverse of an interference convariance matrix estimate, wherein:  
     
       
         
           
             
               R 
               = 
               
                 
                   1 
                   
                      
                     Λ 
                      
                   
                 
                 ⁢ 
                 
                   
                     ∑ 
                     
                       m 
                       ∈ 
                       Λ 
                     
                   
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     
                       e 
                       m 
                     
                     ⁢ 
                     
                       e 
                       m 
                       T 
                     
                   
                 
               
             
             , 
           
         
       
     
     wherein e(z)=F(z)v(z) can be the residual interference after interference suppression, F(z) is the interference suppression matrix, Λ is an index set depending upon where v(z) is computed within a transmission burst, and R is the interference covariance matrix estimate.  
   
   
       52 . The method of  claim 51 , wherein the covariance matrix estimates can be derived from transmission training sequences.  
   
   
       53 . The method of  claim 51 , wherein the covariance matrix estimates can be derived via decision feedback.  
   
   
       54 . The method of  claim 51 , wherein W=R e   −1 .  
   
   
       55 . The method of  claim 51 , wherein W=R e   −1/2 .  
   
   
       56 . The method of  claim 51 , wherein the sampling is at a sampling rate that is greater than a symbol rate of the received signal.  
   
   
       57 . A circuit comprising: 
 a sampling and coupled to a signal input, the sampling unit containing circuitry to sample a received signal provided by the signal input at a specified sampling rate and to create a discrete time sequence representing the received signal;    a rotating unit coupled to the sampling unit, the rotating and containing circuitry to rotate the discrete time sequence by a specified amount;    a pair of extractors coupled to the rotating unit, the extractors containing circuitry to extract an in-phase and a quadrature phase steam from an output of the rotating unit; and    a filter coupled to the pair of extractors, the filter containing circuitry to suppress interference present in the received signal.    
   
   
       58 . The circuit of  claim 57  further comprising a whitening unit coupled to the filter, the whitening unit containing circuitry to de-correlate information present in the output of the filter.  
   
   
       59 . The circuit of  claim 57 , wherein the filter comprises: 
 a pair of filters, each filter to be applied separately to the in-phase and the quadrature phage streams; and    a combiner coupled to the pair of filters, the combiner to sum the outputs from the pair of filters.    
   
   
       60 . The circuit of  claim 57 , wherein the filter is a space-time interference suppression filter (STISF).  
   
   
       61 . The circuit of  claim 60  further comprising a whitening unit coupled to the STISF containing circuitry to de-correlate information present in the output of the STISF, wherein a transfer function of the STISF is computed from the output of the pair of extractors and captured training sequences from transmissions of a desired user.  
   
   
       62 . The circuit of  claim 61 , wherein the transfer function is the sum of the output of the pair of extractors and a convolution of a channel estimate with the captured training sequences.  
   
   
       62 . The circuit of  claim 61 , wherein the whitening unit applies a convolution of the transfer function of the STISF with a sum of the output of the pair of extractors and a convolution of a channel estimate with the captured training sequences.