On the fairness and throughput tradeoff of multi-user uplink scheduling in WCDMA systems

It has been demonstrated that the problem of efficient and fair uplink transmission scheduling in CDMA systems differs significantly from its counterparts in the time-division multiple-access (TDMA) wireless systems or the conventional wireline systems, where only one user is scheduled in a time slot. In this paper we study, analyze and demonstrate the tradeoffs between the achievable throughput and fairness that occur in the realization of multi-user uplink transmission scheduling in CDMA systems. The fundamental problem of optimal transmission scheduling in order to maximize the uplink system throughput, while maintaining the fairness among the various users despite their different varying channel conditions is expressed as a weighted, throughput maximization problem, under certain power and QoS constraints, where the weights are the control parameters that reflect the fairness constraints. A stochastic approximation method is presented in order to effectively identify the required control parameters. It is demonstrated that by controlling the process of estimating the mean total system throughput, the stochastic approximation method is able to tradeoff between the throughput and fairness.