Maximizing the Effective Channel Capacity of Power Controlled WCDMA Systems under Rayleigh Fading Environments

This paper studies the optimization of the effective channel capacity of wideband code division multiple access (WCDMA) systems under Rayleigh fading environments. Firstly, the results for Shannon capacity of fading channels with channel side information are reviewed, where the capacity is achieved by using an optimal power control scheme. Secondly, an optimal interference threshold α0 is set for a given system outage probability Pout to minimize total interference. Finally, the effective channel capacity of WCDMA is defined and a target SIR level γ∗ is derived with the Lagrangian multiplier method to maximize the effective channel capacity. It is shown that α0 is dependent on the power control interference ratio (PCIR) ρ, the number of diversity paths identified by the receiver M, and the outage probability of the system. Simulation results are provided to validate the theoretical deductions. We conclude that the total effective channel capacity will be maximized as long as M ≥ 4, and ρ ≤ 0.5 for a proper value of α0. key words: channel capacity, power control, WCDMA, Rayleigh fading