Towards Optimal Broadcasting Policies for HARQ based on Fountain Codes in Underwater Networks

This paper explores hybrid ARQ policies based on fountain codes for the transmission of multicast messages in underwater channels. These rateless codes are considered because of two nice properties, namely, they are computationally lightweight and do not require to know the channel erasure probabilities at the receivers prior to transmission. In this paper, these codes are used together with a Stop and Wait ARQ to enhance the performance of broadcast communications. First, we present a dynamic programming model for the characterization of optimal broadcasting policies. The derived broadcasting rules are then compared against plain ARQ schemes via Monte-Carlo simulation. Our results show that digital fountain codes are a promising technique for the transmission over underwater channels as their performance, in terms of delay, reliability and energy efficiency, clearly dominates that of plain ARQ solutions. This paper is a preliminary study on the topic and encourages us towards the design of practical HARQ protocols for the underwater medium.