Network coding for underwater acoustic networks of butterfly topology

Underwater network technologies are of growing interest for applications in marine research, oceanography, marine commercial operations, offshore oil industry and defense. Long propagation delays and low bit rates of underwater acoustic networks is the nature of underwater acoustic channels. This necessitates a research of underwater network protocols that show benefits in success probability and robustness of data transmission. Application of network coding approach can give significant advantage consisting in increasing channel throughput and decreasing data loss. In the paper an underwater acoustic network with a modified butterfly topology is considered, consisting of surface nodes, access points and nodes in the water column. The purpose of such topology is to provide delivery of data packages from nodes on the surface to the underwater nodes and vice versa. Transmission distances between these nodes can be very large, so that access points are required to relay packages. When transmitting sequentially in loaded networks the access points become vulnerable to overloads, what can lead to bottleneck problem. This problem can be yet improved when using network coding technique with several messages transmitted at once. This can help to reduce data loss and provide benefits in data throughput of the network. The objective of this paper is to demonstrate the increase of underwater acoustic network performance by means of implementation of the network coding algorithm on-board of underwater acoustic modems composing the network. To demonstrate the increase of the data throughput, there have been compared the network coding algorithm and the conventional data transmission algorithm based on a standard queuing approach. The results of experimental comparison of these two approaches are in details demonstrated in the paper.