Uplink capacity optimization by power allocation for multimedia CDMA networks with imperfect power control

A closed-form capacity quasi-optimal power allocation scheme is presented for the uplink of multimedia code-division multiple-access (CDMA) systems with randomized received signal-to-interference ratio (SIR) resulted from the errors of power control. The optimality in capacity comes from that this scheme provides class-dependent SIR margins subject to the constraint of differentiated outage requirements. The statistics of signal under imperfect power control is modeled as lognormal random variable. The objective of capacity maximization is formulated as the minimization of total average received powers since the capacity of a CDMA system is interference limited. Under this model, we first derive the necessary conditions that a capacity-optimal power allocation should satisfy. By using conservative bounds, we provide a closed-form approximate solution to this optimization problem. This approximate solution provides nearly the same admissible region for multimedia traffic under imperfect power control as the accurate solution (the optimal one) does. The closed-form quasi-optimal power allocation scheme proposed in this paper is just based on this approximate solution. By numerical example we verify our analysis and show that great capacity gain (e.g., 92% as a maximum in the example) can be achieved by our scheme over its counterpart.