Power control and SIR estimation for DS-CDMA based cellular mobile communication systems and its effect on the system and link performance

Direct Sequence Code Division Multiple Access (DS-CDMA) has been widely accepted as the major wireless access technique for third generation mobile communication systems. DS-CDMA based systems are interference limited and suffer from an inherent near-far problems. Further, the transmitted signal is affected by the time varying radio channel, which introduces a variety of impairments such as attenuation, linear distortion, and time varying response in the desired user's signal. These effects of the time varying channel contribute to a high degree of Multiple Access Interference (MAI), which is the major cause of transmission impairments. To improve link and system performance, a combination of rake combining and power control is essential.; In this thesis, we have developed analytical and simulation methodology to study and analyze the system performance in terms of capacity and outage probability of multiple-cell DS-CDMA system with power control under dynamically fading channel conditions. We have derived a new expression for the signal-to-interference ratio (SIR) at the output of a DS-CDMA receiver including all time varying conditions of the mobile radio channel, and employed this expression to simulate network power control. The theoretical and simulation model presented can be used as a general framework for the simulation of reverse link coherent DS-CDMA cellular systems employing SIR based power control algorithms for different traffic types and under different traffic environments.; In this thesis, we have developed a new power control algorithm, which is based on proportional plus derivative based feedback loop (PD Controller). This algorithm performs better compared to the standard closed loop algorithm because it has an additional derivative based loop which tracks the change in the estimated signal-to-interference ratio (SIR). Link level performance of the system with power control is sensitive to the SIR estimation. We have outlined different methods for estimating the SIR for a WCDMA system.; For third generation mobile communication systems, there will be a demand for high data rate and packet based transmission. We have presented new protocols for packet transmission through a common control channel and a dedicated control channel for WCDMA system. We have derived the throughput of the system for the two protocols.