System for processing digitized communication signals provided over plural RF channels

Abstract

A wireless digital subscriber communications system includes a base station and a subscriber unit and uses communications signals provided over a plurality of radio frequency channels. A processor provides an output phase signal corresponding to a selected output digital frequency, and a lookup table is used having two sets of predefined stored values pertaining to the amplitude of a signal for a single quadrant. In particular embodiments, predefined stored values include coarse angle approximations and fine angle approximations and a sine and cosine generator receives the phase signal and generates sine and cosine waveforms utilizing amplitude values obtained from the lookup table. In a further embodiment, the phase signal includes phase data and specifies the quadrant and the algebraic sign of the phase data, with the sine and cosine generator accessing the lookup table differently depending upon the quadrant and sine of the phase data, such that the lookup table provides an amplitude value from the sets of predefined stored values based on the phase data. A modulator combines the sine and cosine waveforms to produce the selected output digital frequency and modulates digital frequency.

What is claimed is:  
     
         1 . A system for processing communication signals which include a first information signal and a first communication signal which carries information contained in digital input symbols, and a second communication signal provides a second information signal, the communication signals provided over a plurality of radio frequency channels within a selected band of radio frequencies, the system comprising: 
 a circuit for generating a base radio frequency signal;    a circuit for generating a digital intermediate frequency signal such that the combination of the digital intermediate frequency signal with the base radio frequency signal produces a communication signal having a frequency within one of said radio frequency channels selected for communication;    a circuit for modulating the digital intermediate frequency signal with the digital input symbols to produce a modulated digital intermediate frequency signal, and combining the modulated digital intermediate frequency signal with the base radio frequency signal to produce the first communication signal; and    a circuit for combining the modulated digital intermediate frequency signal with the base radio frequency signal to produce the first communication signal.    
     
     
         2 . The system of  claim 1  further comprising a circuit for accumulating phase increment data to produce digitized phase values and generating the digital intermediate frequency signal based on the digitized phase values.  
     
     
         3 . The system of  claim 1  further comprising a demodulation circuit, the demodulation circuit using the digital intermediate frequency signal to demodulate the second communication signal.  
     
     
         4 . The system of  claim 3  further comprising a filter, including a noise shaping circuit, for filtering the digital intermediate frequency prior to demodulating the second communication signal received.  
     
     
         5 . The system of  claim 1  further comprising: 
 a memory; and  
 the circuit for generating the digital intermediate frequency signal based on the digitized phase values by using predefined values stored in the memory.  
 
     
     
         6 . The system of  claim 1  comprising: 
 a lookup table comprising a memory having a set of predefined stored values pertaining to the amplitude of a signal for a single quadrant;  
 a signal generator receiving an input signal and generating sine and cosine waveforms utilizing amplitude values obtained from said lookup tables, wherein the input signal includes phase data and specifies the quadrant and the algebraic sign of the phase data;  
 said signal generator accessing said lookup table differently depending upon the quadrant and sign of the phase data such that the lookup table provides an amplitude value from said set of values based upon the phase data; and  
 a circuit combining the sine and cosine waveforms to produce the digital frequency.  
 
     
     
         7 . The system of  claim 6  wherein the lookup table includes a first table having stored values pertaining to large angle approximations for coarse resolution frequency adjustment of the digital frequency and a second table for stored values pertaining to small angle approximations for fine resolution frequency adjustment.  
     
     
         8 . The system of  claim 6  wherein trigonometric decomposition is utilized to further reduce table size.  
     
     
         9 . The system of  claim 1  further comprising the circuit for modulating the digital intermediate frequency signal transcoding the first information signal into digital input symbols and modulating the digital intermediate frequency signal with the digital input symbols to produce the modulated digital intermediate frequency signal.  
     
     
         10 . The system of  claim 1  further comprising the circuit for generating the digital intermediate frequency signal using predefined sine and cosine waveform values stored in the memory to provide digitized phase values.  
     
     
         11 . The system of  claim 10  further comprising the circuit for generating the digital intermediate frequency using coarse and fine resolution frequency approximations stored in the memory.  
     
     
         12 . The system of  claim 11  further comprising the memory providing two lookup tables.  
     
     
         13 . The system of  claim 12  further comprising the circuit for generating the digital intermediate frequency signal reducing the table sizes by utilizing quadrant symmetry of the sine and cosine waveform values.  
     
     
         14 . The system of  claim 13  further comprising the circuit for generating the digital intermediate frequency signal utilizing trigonometric decomposition, thereby reducing required table sizes.  
     
     
         15 . The system of  claim 1  comprising: 
 a lookup table comprising a memory having a set of predefined stored values pertaining to the amplitude of a signal for a single quadrant;  
 a signal generator receiving an input signal and generating sine and cosine waveforms utilizing amplitude values obtained from said lookup tables, wherein the input signal includes phase data and specifies the quadrant and the algebraic sign of the phase data;  
 the lookup table providing an amplitude value from said set of values based upon the phase data; and  
 a circuit combining the sine and cosine waveforms to produce the digital frequency.  
 
     
     
         16 . The system of  claim 15  comprising: 
 the lookup table including a first table having stored values pertaining to large angle approximations for coarse resolution frequency adjustment of the digital frequency and a second table for stored values pertaining to small angle approximations for fine resolution frequency adjustment; and  
 the circuit for generating the digital intermediate frequency signal utilizing trigonometric decomposition, thereby reducing required table sizes.  
 
     
     
         17 . The system for processing communication signals which include a first information signal and a first communication signal which carries information contained in digital input symbols, and a second communication signal provides a second information signal, the communication signals provided over a plurality of radio frequency channels within a selected band of radio frequencies, the system comprising: 
 means for generating a base radio frequency signal;    means for generating a digital intermediate frequency signal such that the combination of the digital intermediate frequency signal with the base radio frequency signal produces a communication signal having a frequency within one of said radio frequency channels selected for communication;    means for modulating the digital intermediate frequency signal with the digital input symbols to produce a modulated digital intermediate frequency signal; and    circuit means for combining the modulated digital intermediate frequency signal with the base radio frequency signal to produce the first communication signal.    
     
     
         18 . The system of  claim 17  further comprising: 
 demodulation means, responsive to the digital intermediate frequency signal to demodulate the second communication signal; and  
 means for filtering the digital intermediate frequency by noise shaping prior to demodulating the second communication signal.  
 
     
     
         19 . The system of  claim 17  further comprising: 
 the means for generating a digital intermediate frequency signal generating the digital intermediate frequency signal based on predefined values stored in a memory store;  
 demodulation means, responsive to the digital intermediate frequency signal to demodulate the second communication signal;  
 the means for generating the digital intermediate frequency signal generating the signal based on the digitized phase values by using by utilizing quadrant symmetry of sine and cosine waveform values stored in the memory store;  
 the means for generating the digital intermediate frequency using coarse and fine resolution frequency approximations stored in the memory store.  
 
     
     
         20 . The system of  claim 17  comprising: 
 a lookup table comprising a memory having a set of predefined stored values pertaining to the amplitude of a signal for a single quadrant, the lookup table including a first table having stored values pertaining to large angle approximations for coarse resolution frequency adjustment of the digital frequency and a second table for stored values pertaining to small angle approximations for fine resolution frequency adjustment;  
 means for generating sine and cosine waveforms utilizing amplitude values and phase data obtained from said lookup tables; and  
 means for combining the sine and cosine waveforms to produce the digital frequency.  
 
     
     
         21 . The system of  claim 20  wherein trigonometric decomposition is utilized, thereby reducing table size.