Throughput Maximization under Rate Requirements for the OFDMA Downlink Channel with Limited Feedback

Abstract

The purpose of this paper is to show the potential of UMTS long-term evolution using OFDM modulation by adopting a combined perspective on feedback channel design and resource allocation for OFDMA multiuser downlink channel. First, we provide an efficient feedback scheme that we call mobility-dependent successive refinement that enormously reduces the necessary feedback capacity demand. The main idea is not to report the complete frequency response all at once but in subsequent parts. Subsequent parts will be further refined in this process. After a predefined number of time slots, outdated parts are updated depending on the reported mobility class of the users. It is shown that this scheme requires very low feedback capacity and works even within the strict feedback capacity requirements of standard HSDPA. Then, by using this feedback scheme, we present a scheduling strategy which solves a weighted sum rate maximization problem for given rate requirements. This is a discrete optimization problem with nondifferentiable nonconvex objective due to the discrete properties of practical systems. In order to efficiently solve this problem, we present an algorithm which is motivated by a weight matching strategy stemming from a Lagrangian approach. We evaluate this algorithm and show that it outperforms a standard algorithm which is based on the well-known Hungarian algorithm both in achieved throughput, delay, and computational complexity.