Optimization Framework and Graph-Based Approach for Relay-Assisted Bidirectional OFDMA Cellular Networks

TL;DR

This paper introduces a novel relay-assisted bidirectional OFDMA cellular network framework with a new TDD protocol, formulating an NP-complete resource allocation problem and solving it efficiently using a graph-based approach and ACO metaheuristic, leading to significant throughput improvements.

Contribution

It proposes a new three-time-slot TDD protocol and an optimization framework for resource allocation using a graph-based approach and ACO, advancing relay-assisted bidirectional OFDMA network performance.

Findings

Significant throughput gains demonstrated in simulations.

Effective resource allocation via graph-based maximum clique approach.

Metaheuristic ACO algorithm efficiently solves NP-complete problem.

Abstract

This paper considers a relay-assisted bidirectional cellular network where the base station (BS) communicates with each mobile station (MS) using OFDMA for both uplink and downlink. The goal is to improve the overall system performance by exploring the full potential of the network in various dimensions including user, subcarrier, relay, and bidirectional traffic. In this work, we first introduce a novel three-time-slot time-division duplexing (TDD) transmission protocol. This protocol unifies direct transmission, one-way relaying and network-coded two-way relaying between the BS and each MS. Using the proposed three-time-slot TDD protocol, we then propose an optimization framework for resource allocation to achieve the following gains: cooperative diversity (via relay selection), network coding gain (via bidirectional transmission mode selection), and multiuser diversity (via subcarrier assignment). We formulate the problem as a combinatorial optimization problem, which is NP-complete. To make it more tractable, we adopt a graph-based approach. We first establish the equivalence between the original problem and a maximum weighted clique problem in graph theory. A metaheuristic algorithm based on any colony optimization (ACO) is then employed to find the solution in polynomial time. Simulation results demonstrate that the proposed protocol together with the ACO algorithm significantly enhances the system total throughput.