Energy-efficient data transmission over multiple-access channels with QoS constraints

Energy efficiency and quality-of-service (QoS) have been two key considerations in the design of modern multi-user communication systems. In this paper, we study optimal rate control over the multiple-access channel to minimize the sum transmission energy under general QoS constraints. We model the data flows and QoS constraints using a cumulative curves methodology and formulate the optimization problem as a continuous-time control problem. We analyze the optimality properties and show that the optimization problem has a dynamic programming (DP) structure induced by successive interference cancellation (SIC). Based on the DP structure, we propose a low-complexity solution, which is amenable to an appealing graphical visualization and has the same order of complexity as the single user energy minimization problem. We bound the energy gap between the low-complexity solution and the optimal solution, and show that the energy gap diminishes to zero in the symmetric high SNR regime.