An Energy-Saving QoS-Based Resource Allocation for Multiuser TDMA Systems with Causal CSI

In this paper, we aim to develop an energy-efficient multiuser time-division multiple-access (TDMA) system in block-fading (BF), subject to individual user´s quality-of-service (QoS) requirements in terms of outage probability, by jointly-adaptive time-sharing and power allocation for the users in accordance with the causal channel side information (CSI) at the transmitter. We first propose a simple closed-form power allocation solution for a single-user BF channel to attain a given outage probability constraint with causal CSI. Then, we construct an optimization problem to permit a joint consideration of power consumptions and QoS requirements of the users, which we solve to obtain a near-optimal solution for users´ time-sharing. The two solutions are combined to provide a suboptimal joint solution for adaptive time-sharing and power allocation of the system. Results reveal that the proposed scheme is near-optimal and a significant energy saving of more than 15 (dB) is possible between systems with and without adaptation on time-sharing and/or power allocation.