Method and apparatus for generating complex four-phase sequences for a CDMA communication system

Abstract

A transmission apparatus for generating a complex four-phase pseudo-random sequence having I and Q portions includes a shift register and an accumulator. The shift register has a plurality of positions. The accumulator has a first input for receiving an output from the shift register and a second input for receiving a predetermined value. The accumulator combines the data received via the first and second inputs and outputs the combined data to the shift register. Bits from a first predetermined position within the shift register are used to generate the I portion of the sequence and bits from a second predetermined position within the shift register are used to generate the Q portion of the sequence.

1 . A method for mapping a pseudo-random code sequence to a quadrature phase shift keying (QPSK) signal constellation, the method comprising: 
 (a) determining a first multi-bit number by dividing a parameter M by a parameter N, wherein M and N are integers and M is selected to be relatively prime to N;    (b) combining the first multi-bit number with a second multi-bit number to produce a resulting sum;    (c) extracting a first bit and a second bit from the resulting sum of step (b); and    (d) generating an I value and a Q value based on at least one of the first and second bits.    
   
   
       2 . The method of  claim 1  wherein the second multi-bit number is greater than the first multi-bit number by a factor of two.  
   
   
       3 . The method of  claim 1  wherein the I value is equal to one when the first bit is equal to zero.  
   
   
       4 . The method of  claim 1  wherein the I value is equal to negative one when the first bit is equal to one.  
   
   
       5 . The method of  claim 1  further comprising: 
 (e) setting the Q value to one by performing a logical function on the first and second bits resulting in a value equal to zero.    
   
   
       6 . The method of  claim 1  further comprising: 
 (e) setting the Q value to negative one by performing a logical function on the first and second bits resulting in a value equal to one.    
   
   
       7 . A method for mapping a pseudo-random code sequence to a quadrature phase shift keying (QPSK) signal constellation, the method comprising: 
 (a) storing initial parameters M and N in a memory, wherein M and N are integers and M is selected to be relatively prime to N;    (b) dividing the parameter M by the parameter N to produce a resulting quotient input;    (c) combining a first number equal to the resulting quotient with a second number to produce a resulting sum;    (d) extracting a first bit and a second bit from the resulting sum of step (c); and    (e) generating an I value and a Q value based on at least one of the first and second bits.    
   
   
       8 . The method of  claim 7  wherein the second number is greater than the first number by a factor of two.  
   
   
       9 . The method of  claim 7  wherein the I value is equal to one when the first bit is equal to zero.  
   
   
       10 . The method of  claim 7  wherein the I value is equal to negative one when the first bit is equal to one.  
   
   
       11 . The method of  claim 7  further comprising: 
 (f) setting the Q value to one by performing a logical function on the first and second bits resulting in a value equal to zero.    
   
   
       12 . The method of  claim 1  further comprising: 
 (f) setting the Q value to negative one by performing a logical function on the first and second bits resulting in a value equal to one.