Adaptive LDPC FEC for ZP-OFDM Underwater Acoustic Communication Systems

Research and exploration of the ocean environment face various challenges and engineering problems. One of them is data transmission underwater, which is vital for properly using autonomous underwater vehicles. Due to immensely higher attenuation, communication systems based on electromagnetics cannot be used on distances over several tens of meters. The only way to communicate with submerged vehicles is through underwater acoustic communication systems. Sound propagation underwater heavily depends on sound speed distribution and acoustic properties and the form of the sea surface and bottom. These parameters are non-stationary or suffer from local and unpredictable inhomogeneities, causing high variability of channel bit error rate (BER) and complicating the assessment of proper parameters of underwater acoustic communications systems (UACS), including forward error correction (FEC) coder. The paper presents an adaptation method for the code rate of the low-density parity-check (LDPC) coder without two-way channel estimation. The method for the design of parity-check and generator matrices, coding, and decoding processes are also described. The effectiveness of the proposed adaptive LDPC FEC is validated through simulations, and its results are provided.