极化码在OFDM水声通信中的应用研究

极化码（Polar code）因其高可靠性、实用的线性编、译码复杂度和理论上唯一可达香农极限等特点，成为信道编码领域新的研究热点。其编、译码方法的研究扩展至多种信道类型和应用领域，但在水声信道中的理论证明和应用研究相对较少且滞后。针对具有显著多途、多普勒扩散和有限带宽等复杂特性的水声信道，文章提出了与之相匹配的极化码信道编码机制；并结合正交频分复用（Orthogonal Frequency Division Multiplexing，OFDM）技术搭建水声通信仿真系统，研究极化码在OFDM水声通信系统中的性能表现；同时研究极化码在不同的水声信道模型、信道参数、码长、码率下的性能。仿真结果表明，在信噪比为4 dB时，码率为1/2的极化码在水声时变信道中的误码率可达10^-4～10^-5，优于低密度校验（Low density Parity Check，LDPC）、Turbo码，约有0.5～1 dB的性能增益，该极化码信道编码机制与水声信道相匹配，可有效提高水声通信的可靠性。

Research on the application of Polar codes to underwater acoustic OFDM communication system

Polar code is a new research hotspot in the field of channel coding due to its high reliability and lower encoding and decoding complexity, and it can reach the Shannon capacity limit in theory. The ongoing researches on Polar codes have provided numerous code construction algorithms and decoding methods for several kinds of channel types and application fields. However, the theoretic proofs and the performances of Polar codes in underwater acoustic (UWA) channels are relatively less concerned. In this paper, a Polar code channel coding mechanism is established, which matches the UWA channel with significant multipath, strong Doppler spreading, limited bandwidth, and other complex random transmission characteristics. Then the performance of Polar codes is studied in the UWA communication system with the orthogonal frequency division multiplexing (OFDM) technique by theoretical analysis and simulation. Meanwhile, the BER performances of Polar codes under different UWA channel models, channel parameters, code lengths, and code rates are also compared. The simulation results show that the BER of Polar codes with a code rate of 1/2 in the underwater time-varying channel can reach 10^-4~10^-5 when the signal-to-noise ratio (SNR) is 4 dB, which is about 0.5~1 dB better than LDPC and Turbo codes. The results demonstrate that the proposed mechanism matches the UWA channel well, thus the application of Polar codes is suitable and reliable in UWA communication systems.