Efficient spreader for spread spectrum communication systems

Abstract

A spreading system and method for CDMA applications that requires fewer integer multiplications. User data is spread using real or complex integer based spreading codes of length SF to SF max chips. At least one of the codes is of the form j n ·v[n] where v[n] is a spreading code. The invention provides increased user separation using a plurality of spreading codes.

1 . A method for spreading a sequence of symbols using at least two spreading codes in a wireless communication system where the first spreading code is used for distinguishing users and the second spreading code is used for distinguishing base stations, the method comprising: 
 generating a single symbol spreading code from the at least two spreading codes;    generating a complex code sequence from the sequence of symbols; and,    generating a spread sequence by multiplying the symbol spreading code and the complex code sequence bit by bit.    
   
   
       2 . The method of  claim 1 , further comprising: 
 defining a plurality of groups, each group comprising N symbols, wherein spreading is conducted group by group.    
   
   
       3 . The method of  claim 2 , wherein the step of generating the symbol spreading code comprises multiplying the first spreading code and the second spreading code bit by bit.  
   
   
       4 . The method of  claim 3 , wherein the first spreading code is concatenated N times.  
   
   
       5 . The method of  claim 4 , wherein the number N is determined by dividing the maximum spreading factor (SF) of the system by the SF of the first code.  
   
   
       6 . The method of  claim 1 , wherein the complex code sequence is generated by adjusting a phase of the symbols, and rotating each phase-adjusted symbol SF times in the complex plane.  
   
   
       7 . The method of  claim 6 , wherein each rotation is determined by an integer multiple of 90 degrees counterclockwise, the integer being calculated by maximum SF modulo  4 .  
   
   
       8 . A sequence spreader for spreading a sequence of symbols using at least two spreading codes for transmission in a wireless communication system; where the first spreading code is used for distinguishing users and the second spreading code is used for distinguishing base stations, the spreader comprising: 
 a code generator for generating a spread code from the at least two spreading codes;    a complex code sequence generator for generating a complex code sequence from the spread code; and    two multipliers for generating a final spread code by multiplying the spread code and the complex code sequence bit by bit.    
   
   
       9 . The sequence spreader of  claim 8 , wherein the spread code comprises a plurality of groups of N symbols.  
   
   
       10 . The sequence spreader of  claim 9 , wherein the code generator generates the spreading code by multiplying the first spreading code and the second spreading code bit by bit.  
   
   
       11 . The sequence spreader of  claim 10 , wherein the first spreading code is concatenated N times.  
   
   
       12 . The sequence spreader of  claim 11 , wherein the number N is determined by dividing the maximum spreading factor (SF) of the system by the SF of the first code.  
   
   
       13 . The sequence spreader of  claim 12 , wherein the complex code sequence generator further comprises: 
 a phase adjuster for adjusting a phase of a symbol; and    a rotator for rotating each phase-adjusted symbol SF times in the complex plane.    
   
   
       14 . The sequence spreader of  claim 13 , wherein each rotation is determined by an integer multiple of 90 degrees counterclockwise, the integer being calculated by maximum SF modulo  4 .