Power control techniques for CDMA-based mobile systems.

Code division multiple access (CDMA) is a well-known radio communication technique that allows multiple users to share the same spectrum simultaneously. It is an alternative to frequency division and time division multiple access scheme. Its numerous advantages have merited being the main air-interface choice for the third generation (3G) mobile communication system. Nevertheless, due to the use of same frequency, the capacity of CDMA air-interface is interference limited. This problem is minimised by use of power control scheme. Power Control reduces the interference in the system by adjusting the transmitted power according to the received Signal-to-Interference (SIR) ratio. The main difficulty to achieve this scheme is that mobile terminals experience different radio propagation channel. For success completion of this task, two objectives have been identified for power control. First assure that the received signal matches the required SIR at physical layer and secondly adjust the required SIR of users at system layer to an acceptable value so that the terminals in the system are capable of achieving. In this thesis both objectives are discussed and analysed through analytical and simulation methods. At physical layer, two analytical methods based on non-linear control theory are proposed to combat the fast fading channel propagation. The proposed methods are a fast solution to assess the performance of the Closed Loop Power Control compared to the usual lengthy simulation process. At system level, a new distributed power algorithm for reverse link that adjusts the SIR target of the mobile terminal at the base station is proposed. This algorithm brings the performance of the distributed algorithm closer to the optimal solution provided by the non-feasible centralised power control algorithm in current technology