High-order modulation based on repeat-accumulate codes for underwater acoustic communications

Several characteristics of underwater acoustic (UWA) communication channels-limited bandwidth, extended multipath and severe fading-impede UWA data transmissions. To solve this problem, we propose to set up a receiver combining repeat-accumulate (RA) coding and high-order modulation, and calculate the channel soft information for RA decoding with high-order modulation. A multipath fading acoustic channel model for the southern Taiwan Strait channel is established based on BELLHOP ray model and its real sound speed profile. The paper also discusses the error correction capability of the different combination of RA coding and high-order modulation. Simulation results show that the system performance may be improved by using error correction coding; however, its data rate will be reduced. While the frequency efficiency grows significantly, the reliability cannot be improved remarkably.