JOINT POWER CONTROL AND CODEWORD ADAPTATION FOR MULTICELL CDMA SYSTEMS

Abstract

With increase in demand for wireless data services, it becomes very essential to manage scarce radio resources. Especially in CDMA systems, where all the users share the same radio spectrum, mutual interference plays a crucial role in determining system capacity. Good codewords with small cross-correlation help in reducing mutual interference and power control mitigates near-far effect bringing energy efficiency. Joint codeword adaptation and power control can help users to achieve their desired Quality of Service (QoS) as well as in increasing the' system capacity. The QoS can be defined in terms of target Signal to Interference plus Noise Ratio (SINR), acceptable bit error rate. In this dissertation work non co-operative game theoretic approach has been used to deal with joint power control and codeword adaptation in wireless synchronous CDMA system. In CDMA system, every user tries to achieve its desired QoS with least possible transmitting power and best codeword sequence. Thus, all the users have conflicting interests and with their actions being interrelated. Non co-operative game theory can be used to model this scenario. In this dissertation, Non co-operative Joint power control and codeword adaptation game (NPCG) is considered where each user adjusts its codeword and power to minimize its cost while achieving its desired QoS. The NPCG is formulated as separable game with respect to codeword and power. Simulations have been carried out for continuous and quantized codeword and power profiles for single cell and multi-cell systems. Incremental update strategy has been used for power and codeword update so that receiver can follow changes in transmitter. The performance for dynamic wireless systems under varying QoS and varying number of users has been evaluated. The algorithm effectively tracks variable target SINR and variable number of users. In multi-cell systems, the algorithm reaches equilibrium with increase in signal dimension. For quantized codewords, different signal space dimensions with different quantization level have been used. Coarser quantization has been used for larger signal dimension to compensate for the bandwidth increment. Its effect on various performance parameters at equilibrium has been studied.