Novel Subcarrier-pair based Opportunistic DF Protocol for Cooperative Downlink OFDMA

TL;DR

This paper introduces a new subcarrier-pair based opportunistic decode-and-forward protocol for cooperative downlink OFDMA, significantly improving sum rate performance through innovative resource allocation and beamforming strategies.

Contribution

The paper proposes a novel subcarrier-pair based protocol with beamforming, and develops a polynomial-time algorithm for near-optimal resource allocation in cooperative OFDMA systems.

Findings

The proposed protocol achieves higher sum rates than benchmark methods.

Beamforming at the relay enhances transmission efficiency.

Numerical results confirm substantial performance gains.

Abstract

A novel subcarrier-pair based opportunistic DF protocol is proposed for cooperative downlink OFDMA transmission aided by a decode-and-forward (DF) relay. Specifically, user message bits are transmitted in two consecutive equal-duration time slots. A subcarrier in the first slot can be paired with a subcarrier in the second slot for the DF relay-aided transmission to a user. In particular, the source and the relay can transmit simultaneously to implement beamforming at the subcarrier in the second slot for the relay-aided transmission. Each unpaired subcarrier in either the first or second slot is used by the source for direct transmission to a user without the relay's assistance. The sum rate maximized resource allocation (RA) problem is addressed for this protocol under a total power constraint. It is shown that the novel protocol leads to a maximum sum rate greater than or equal to that for a benchmark one, which does not allow the source to implement beamforming at the subcarrier in the second slot for the relay-aided transmission. Then, a polynomial-complexity RA algorithm is developed to find an (at least approximately) optimum resource allocation (i.e., source/relay power, subcarrier pairing and assignment to users) for either the proposed or benchmark protocol. Numerical experiments illustrate that the novel protocol can lead to a much greater sum rate than the benchmark one.