Iterative Versus Adaptive Equalizers in Time-Variant Channels

This paper discusses the application of iterative versus adaptive equalizers to a Universal Mobile Telecommunications System (UMTS) High Speed Downlink Packet Access (HSDPA) receiver. Among the investigated algorithms are the Least Mean Square (LMS) and Recursive Least Square (RLS) algorithms and their adaptions to Code Division Multiple Access (CDMA), such as Griffith's algorithm, as well as the conjugate gradient (CG) algorithm. We show that adaptive algorithms do not perform well in HSDPA scenarios at medium to high mobile speed, and that the conjugate gradient algorithm achieves higher performance at the same or even lower complexity than any of the investigated adaptive algorithms. We also discuss the necessity to consider oversampling.