Opportunities for Adaptivity in the UMTS Terminal Receiver: The Path-Search Function

Wireless communication systems will have to become more and more exible. In the Adaptive Wireless Networking project we try to develop such a exible wireless communication system by developing algorithms for adaptive implementation of the digital signal processing functions in wireless communication systems. Within the limits of a wireless communication system standard there are two kinds of adaptivity: algorithm-selection adaptivity and algorithm-parameter adaptivity. In this paper we focus on algorithm-selection adaptivity in the UMTS path search function. Therefore we describe two path search algorithms: a Power Delay Prole (PDP) based algorithm and a Maximum Likelihood Estimate (MLE) based algorithm. We study and compare the performance of these algorithms under a number of multipath channel conditions by means of simulations. The MLE based algorithm is able to resolve a larger number of paths, especially when the paths are closely spaced, at the cost of an increased computational complexity. Therefore, using algorithm-selection adaptivity in the UMTS path search function seems to be useful. The MLE based algorithm is used when there are strong closely spaced path and the PDP based algorithm is used in all other conditions, appears to be useful. However, in order to be conclusive a few points will still have to be studied.