Optimal power control law for multimedia multirate CDMA systems

This paper considers the optimal reverse-link power control law for multimedia multirate DS/CDMA systems which offer services with different transmission rates (VBR or CBR) and quality of service (QoS) requirements. In the multimedia multirate CDMA system, the transmission power of a mobile station (MS) is proportional to a power control law, which is a function of its distance to the base station (BS), the transmission rates and interference level (number of active users). Each transmitted signal from the MS will be affected by path loss, Rayleigh fading and log-normal shadowing in the reverse link. The bit error probability of the asynchronous multirate CDMA system that takes the MS locations into account is derived first in order to derive the optimum power control functions. By applying the optimal power control functions to mobile stations, the QoS (bit error probability) requirements can be met, the system capacity (number of simultaneously transmitted users) can be maximized, and the power consumption can be minimized. Since the difficulty of deriving the optimal power control law in a closed form, we discretize the power control function so that dynamic programming (DP) can be utilized to obtain the optimal solution. The numerical results show that the optimal power control law can increase the system capacity and decrease the power consumption compared with other power control laws (eg. equal received bit energy) in the multimedia multirate CDMA system.