A multi-channel MAC protocol for AUV networks

This paper presents results from a study on using multiple communication channels simultaneously for effective networking in a small AUV network. AUVs can be highly mobile, leading to time-varying inter-node distances and a dynamic network topology. We try to exploit this mobility by using multiple acoustic modems operating at different frequency bands and suited for different ranges. We utilize a MAC protocol based on MACA that uses RTS / CTS / DATA / ACK handshaking along with carrier sensing. Data packet trains are used to greatly enhance the performance of this protocol and results show that this feature makes it a very viable protocol for underwater networks in general. The protocol exchanges AUV position information and uses this information to allocate traffic to the different modems. The study is oriented towards the use of multiple AUVs in highly co-operative missions where effective peer to peer data exchange is vital. The term "channel" is used to represent very different capability modems, and is different from the standard context of multi-channel communications where a single transceiver has the option to choose between multiple channels, as in FDMA or CDMA. In our model, we have multiple and very different transceivers being used simultaneously. We name the protocol MACA-MCP since it utilizes Multiple Channels and Positioning information.

1. Introduction

Communications in an underwater network comprising of Autonomous Underwater Vehicles (AUV), fixed sensor nodes and control vessels are commonly implemented using acoustic links. Typical acoustic modems used to establish these links operate at low data rates and ranges up to a few kilometers. At much shorter ranges of tens to hundreds of meters, higher performance communication links can be established using high frequency acoustics. If more than one of the nodes is at the surface, traditional radio links in air also become feasible. As AUVs move around during a collaborative mission, the inter-node separations may vary from few tens of meters to several kilometers. In this paper we explore the possibility of effectively using such multiple communication channels in an AUV network. The key objective is to maximize throughput and overall data rate per node using multiple channels.