Bandpass processing of a spread spectrum signal

Abstract

A digitally sampled spread spectrum signal is received, despread, and accumulated at a center frequency lower than the sampling rate and higher than zero.

What is claimed is:  
     
         1 . An apparatus for use in processing a spread spectrum signal digitally sampled at a selected sampling rate, the apparatus comprising: 
 a despreading element configured to receive and despread the digitally sampled signal at a center frequency lower than the sampling rate and higher than zero; and    an accumulation element configured to accumulate the despread signal at the center frequency.    
     
     
         2 . The apparatus of  claim 1 , wherein the center frequency is no greater than approximately one-half the sampling rate.  
     
     
         3 . The apparatus of  claim 1 , wherein the center frequency is equal to approximately one-quarter the sampling rate.  
     
     
         4 . The apparatus of  claim 1 , further including a DC filter configured to filter any DC offset from the digitally sampled spread spectrum signal.  
     
     
         5 . The apparatus of  claim 4 , wherein the center frequency is selected so that no data embedded in the spread spectrum signal is blocked by the DC filter.  
     
     
         6 . The apparatus of  claim 1 , wherein the spread spectrum signal includes a pseudo-noise (PN) spreading sequence.  
     
     
         7 . The apparatus of  claim 6 , wherein the despreading element is configured to multiply the digitally sampled signal with a reference signal containing the PN spreading sequence.  
     
     
         8 . A method of processing a spread spectrum signal digitally sampled at a selected sampling rate, the method comprising: 
 receiving the digitally sampled signal at a center frequency lower than the sampling rate and higher than zero;    despreading the digitally sampled signal to produce a despread signal centered at the center frequency; and    accumulating the despread signal at the center frequency.    
     
     
         9 . The method of  claim 8 , wherein the center frequency is no greater than approximately one-half the sampling rate.  
     
     
         10 . The method of  claim 8 , wherein the center frequency is equal to approximately one-quarter the sampling rate.  
     
     
         11 . The method of  claim 8 , further including filtering any DC offset from the digitally sampled spread spectrum signal.  
     
     
         12 . The method of  claim 11 , further including selecting the center frequency so that filtering any DC offset does not destroy data embedded in the spread spectrum signal.  
     
     
         13 . The method of  claim 8 , wherein the spread spectrum signal includes a pseudo-noise (PN) spreading sequence.  
     
     
         14 . The method of  claim 13 , wherein despreading the digitally sampled signal includes multiplying the digitally sampled signal with a reference signal containing the PN spreading sequence.  
     
     
         15 . A receiver for use in processing a spread spectrum signal digitally sampled at a selected sampling rate, the receiver comprising: 
 accumulation devices, each including: 
 a despreading element configured to receive the digitally sampled signal at a center frequency lower than the sampling rate and higher than zero and to produce an output signal by applying a despreading function to the signal; and  
 an accumulation element configured to receive the output signal from the despreading element at the center frequency and to accumulate the output signal to produce an accumulation output.