On the optimal frequency selectivity to maximize multiuser diversity in an OFDMA scheduling system

TL;DR

This paper investigates the optimal frequency selectivity in OFDMA systems to maximize multiuser diversity, proposing a method to determine per-user cyclic delay for improved sum rate performance.

Contribution

It introduces a novel approach to optimize channel selectivity and cyclic delay in OFDMA systems, enhancing sum rate by balancing diversity and throughput.

Findings

Optimal channel selectivity maximizes user throughput.

Proposed cyclic delay method outperforms fixed schemes.

Achieves near-optimal sum rate with CDD.

Abstract

We consider an orthogonal frequency division multiple access (OFDMA) scheduling system. A scheduling unit block consists of contiguous multiple subcarriers. Users are scheduled based on their block average throughput in a proportional fair way. The multiuser diversity gain increases with the degree and dynamic range of channel fluctuations. %Lack of diversity in a limited frequency selective channel may decrease the sum rate. However, a decrease of the block average throughput in a too much selective channel may lessen the sum rate as well. In this paper, we first study optimal channel selectivity in view of maximizing the maximum of the block average throughput of an arbitrary user. Based on this study, we then propose a method to determine a per-user optimal cyclic delay when cyclic delay diversity (CDD) is used to enhance the sum rate by increasing channel selectivity for a limited fluctuating channel. We show that the proposed technique achieves better performance than a conventional fixed cyclic delay scheme and that the throughput is very close to the optimal sum rate possible with CDD.