Distributed transmitter adaptation for wireless CDMA systems

We consider some stability aspects of distributed transmitter adaptation in wireless CDMA systems. The transmitter adaptation problem is divided into two parts—power control and sequence adaptation.; Yates' power control framework has shown its importance in analyzing the convergence properties of a broad class of power control algorithms. However, algorithms that fall into this framework assume continuous power levels. We show that straightforward modifications to some algorithms when implemented in practical systems with quantized power levels may lead to instability. Alongside there are stable algorithms that assume quantized power levels; these algorithms do not fall into Yates' framework. Our contribution in the area of power control is to generalize Yates' framework so that the quantized-power algorithms are also included. We also show that the new framework may serve as a guideline in modifying existing continuous-power algorithms so that the stability properties are preserved when implemented in practical systems.; Another contribution of this thesis is to apply the idea of sequence adaptation to antenna array systems. We show that Nash equilibrium may not exist in such a system if the interference measure used to update sequences is based on traditional reception techniques. It means that no sequence adaptation algorithm can be both stable and distributed. To tackle this problem, we propose a generalized matched filter, which yields an interference measure that is suitable for sequence adaptation. We prove that Nash equilibrium always exists under this reception scheme. Furthermore, based on the new interference measure, we propose an adaptive sequence adaptation algorithm, which offers significant improvement in system throughput.; Finally, we analyze the stability issues on joint power and sequence adaptation schemes. We frame the problem in a very general setting such that the result can be applied to virtually all wireless systems that employ joint power and sequence control. The major contribution is the identification of three conditions that ensure the existence of Nash equilibria. To check whether these conditions hold in a particular system, decoupling sequence adaptation from power control is needed. This technique provides a methodology for analyzing the joint control problem. Some important examples are used to illustrate the idea. In particular, we point out that joint power and signature sequence control, in general, has no equilibrium point in two common situations—first, multi-cell systems, and second, single-cell systems in which the sequences are chosen from a discrete set.