SIMULATION OF POWER ADAPTATION SCHEMES FOR SUCCESSIVE INTERFERENCE CANCELLATION FOR DS-CDMA IN FADING CHANNEL

Abstract

The capacity of Code Division Multiple Access (CDMA) systems, using conventional single user correlator or matched filter receiver is primarily limited by the Multiple Access Interference (MAI), rather than noise. However, previous research has shown that capacity of CDMA systems can be considerably increased using some advanced signal processing techniques at the receiver, known mainly as Multi-User Detection (MUD). Interference Cancellation (IC) is one such multiuser detection technique. The IC techniques can be broadly broken into serial (successive) and parallel schemes for canceling MAI. Successive Interference Cancellation (SIC) is considered in this dissertation. SIC is a form of multiuser detection in which signals are detected in order of perceived reliability [1]. Once detection of a given signal is accomplished, that signal is regenerated and cancelled from the received signal, thus canceling its effect in the detection of subsequent user's signal. Therefore, a specific ordering of the users' power must be enforced for the users to achieve similar performance [2]. .. The focus of this dissertation is the study of some power adaptation scheme in the reverse link (mobile to base station) in Direct Sequence Code Division Multiple Access (DS-CDMA) communication that employs a SIC receiver. The Transmitted power is adapted so that, with channel variation, the received power levels of each user is arranged in appropriate order. The conventional power adaptation scheme in commercial cellular CDMA system such as IS-95, is to control the transmitted power with channel variation such that, all the users signal are received with equal power at the receiver. This is done mainly to combat the near-far effect. Nevertheless, we will study this power adaptation while employing SIC which enjoys the advantage of using the existing power control algorithms for commercial purpose. Studies are conducted for finding the received signal strengths under the constraint of average transmission power that give, after successive cancellation equal Bit-Error Rate (BER) for all the users [3]. Under the same constraint, we discuss another power adaptation scheme where the received powers of different users