A coherent spread-spectrum RAKE-receiver with maximum-likelihood frequency estimation

A direct-sequence spread-spectrum receiver using M-ary phase shift keyed signaling is presented with digital algorithms for coherent data demodulation, diversity combining, and frequency offset estimation. These algorithms are derived by applying the maximum-likelihood rule. A RAKE-structure is used to resolve the time diversity due to multipath propagation of the frequency-selective fading channel. Such conditions are typically encountered in microcellular communication systems like personal communications networks, or wireless local area networks (LANs). The robust transient behavior of the present receiver with an automatic frequency control scheme, based on the non-biased frequency estimator, and the fairly low numerical complexity make these algorithms well suited for digital implementation