Rake receiver and a method of providing a frequency error estimate

Abstract

An input signal is mixed with a scrambling code and with an OVSF code, and then accumulated over a period of time equal to one symbol of the pilot channel before being reset. The resultant complex signals are mixed with the conjugate of complex signals provided by a pilot pattern generator, with the result being fed to a delay line (). A multiplier multiplies the complex value at a location P(n) in the delay line () by the conjugate of a complex value at another location P(n+k), and provides the resulting complex number (which is a complex vector whose phase is a coherent measurement of the phase rotation occurring between the symbols corresponding to the two locations) at an output (). The real part of the complex signal provided at the output () is provided to a first combiner (), and the imaginary part is provided to a second combiner (). These combiners () also receive corresponding signals from all of the other fingers (not shown) of the rake receiver. Each combiner () coherently sums all of the signals at its inputs and provides the result to its respective accumulator (), which provide coherent filtering. The phase rotation of the combined and accumulated signals is then calculated. Once convergence of the frequency of an LO with the frequency of the received signals is achieved, the value of k is increased.