Fountain Codes and their Application to Broadcasting in Underwater Networks: Performance Modeling and Relevant Tradeoffs

Our aim in this paper is to study the performance of broadcasting algorithms for underwater acoustic sensor networks (UWASNs). The targeted scenario is very simple; we consider a source (the initiator of the broadcast transmission) and a number of nodes randomly placed within a given geographical area. For an efficient broadcast transmission we advocate the use of a hybrid ARQ scheme, where Fountain Codes (FC) are exploited to enhance the efficiency of the data dissemination process in the face of poor and possibly unknown channel conditions. FC codes, being rateless, are in fact able to adapt to diverse error rates and correct packet losses on the fly through the transmission of additional redundancy packets. The main contribution of this paper is a mathematical model to characterize the performance of fountain codes as applied to broadcasting in underwater networks. Our analysis allows us to find performance metrics such as transmission delay, reliability (e.g., percentage of covered users) and power consumption. Relevant tradeoffs are highlighted and quantified; in particular the implications of transmission power on covered distance, rate and delay are discussed. Even though we do not propose a practical broadcasting protocol here, the results and tradeoffs we obtain are essential to a proper design of practical schemes.