A Modified CSMA/CA Protocol for OFDM Underwater Networks: Cross Layer Design

TL;DR

This paper proposes a cross-layer modified CSMA/CA protocol for OFDM underwater networks, jointly optimizing PHY parameters and MAC strategies to improve throughput in challenging acoustic channels.

Contribution

It introduces a novel cross-layer approach combining adaptive OFDM PHY link adjustments with a modified CSMA/CA protocol for underwater sensor networks.

Findings

Enhanced network throughput in simulations

Effective joint PHY/MAC optimization

Improved handling of packet loss causes

Abstract

The underwater acoustic channel continues to present significant challenges to efficient throughput performance of underwater acoustic sensor networks (UASNs) in varying scenarios. As a result, cross-layer approaches that explore joint PHY/MAC strategies are worthy of further exploration. We consider a recent high-speed OFDM modem and propose a new cross-layer solution based on modified CSMA/CA, for a canonical star network topology with few nodes (the most common scenario in UASNs). Some innovations to an adaptive OFDM PHY link are developed to jointly select the modulation, convolutional coding and frequency diversity order (different transmission modes) for matching varying channel conditions. Additionally, receiver logic that disambiguates the cause of packet loss between a) that caused by channel vs. b) that due to collisions is used to modify the ARQ/backoff logic for retransmissions with CSMA/CA random access. Simulation results reveal that the cross-layer design can effectively increase network throughput.