Power-Efficient Resource Allocation for Time-Division Multiple Access Over Fading Channels

We investigate resource allocation policies for time-division multiple access (TDMA) over fading channels in the power-limited regime. For frequency-flat block-fading channels and transmitters having full channel state information (CSI), we first minimize power under a weighted sum average rate constraint and show that the optimal rate and time allocation policies can be obtained by a greedy water-filling approach with linear complexity in the number of users. Subsequently, we pursue power minimization under individual average rate constraints and establish that the optimal resource allocation also amounts to a greedy water-filling solution. Our approaches not only provide fundamental power limits when each user can support an infinite-size capacity-achieving codebook (continuous rates), but also yield guidelines for practical designs where users can only support a finite set of adaptive modulation and coding modes (discrete rates).

I. Introduction

With battery-operated communicating nodes, power efficiency has emerged as a critical issue in both commercial and tactical radios designed to extend battery lifetime, especially for wireless networks of sensors equipped with nonrechargeable batteries. Capitalizing on the fact that transmit power is an increasing and strictly convex function of the transmission rate [1], power-efficient resource allocation has been pursued in [2]–[8]. Among them, [2]–[5] dealt with designs over additive white Gaussian noise (AWGN) channels whereas [6] and [7] considered power-efficient scheduling for time-division multi-access (TDMA) networks over fading channels; see also [8] where transmit power is minimized for orthogonal frequency-division multiplexing (OFDM) systems using quantized channel state information (CSI).