Efficient multipath centroid tracking circuit for a code division multiple access (cdma) system

Abstract

A method implemented in a communication device for tracking a spread spectrum signal having an associated code at a receiver is claimed. Components of the spread spectrum signal are despread using locally generated versions of the associated code, each component having a different code phase. A tracking error is determined based on a quadratic function of the components and a weighting factor relating the signal to the tracking error. The weighting factor is a function of a time shift. A minimum in the tracking error is determined by adjusting the time shift.

1 . A method implemented in a communication device for tracking a spread spectrum signal having an associated code at a receiver, the method comprising:
 despreading a plurality of components of the spread spectrum signal using locally generated versions of the associated code, each of the plurality of components having a different code phase than all others of the plurality of code phases;   determining a tracking error based on:
 a quadratic function of the components, and 
 a weighting factor relating the signal to the tracking error; the weighting factor being a function of a time shift; and 
   determining a minimum in the tracking error by adjusting the time shift.   
   
   
       2 . The method of  claim 1 , comprising maximizing a ratio of:
 a slope of the error signal in the neighborhood of the value of the time shift yielding the minimum to   an average noise power.   
   
   
       3 . The method of  claim 1 , wherein the quadratic function is obtained by truncating an infinite quadratic form. 
   
   
       4 . The method of  claim 3 , wherein the truncating comprises the application of an exponential decay function of the time shift. 
   
   
       5 . The method of  claim 2 , wherein the ratio is maximized by performing the operation of forming a product of:
 a vector representing the components,   a matrix, and   a transpose of the vector,   
     wherein elements of the matrix are adjusted to maximize the ratio. 
   
   
       6 . The method of  claim 1 , further comprising a subsequent coherent tracking method.