Optimized Feedback Iterative Online Fountain Code Without Build-Up Phase for Underwater Acoustic Networks

Online fountain code (OFC) is a new type of fountain codes that can adjust the encoding strategy of the sender based on the decoding state feedbacked by the receiver. With the instant feedback of the decoding state, OFC offers advantages such as optimal encoding and low overhead, which are crucial for achieving low latency and high-reliability communication in underwater acoustic networks (UANs) with characteristics such as high error rate, long delay, and half-duplex communication. In this article, three optimization objectives for OFC in UANs are proposed through analyzing the characteristics of UANs and issues of OFC in UANs. Aiming at the three optimization objectives, an optimized feedback iterative OFC without build-up phase (OFI-OFCNB) is proposed to improve the intermediate decoding performance while reducing the coding and feedback overhead for UANs. Meanwhile, considering that the receivers with low-complexity requirements usually have limited buffer sizes to store partially encoded packets, the OFI-OFCNB dynamically adjusts the buffer occupancy to avoid buffer overflow. In addition, the number of encoded and feedback packets, the overhead, the complexity, and the buffer occupancy of OFI-OFCNB are analyzed. The analysis and simulation results validate the superior performance of OFI-OFCNB in terms of the coding and feedback overhead, the intermediate performance, and the buffer occupancy.