Research On Performance Of QC-LEPC Codes In Adaptive Channel Coding For Underwater Acoustic Communication

With the rapid development of the information construction in such areas as sea exploitation, detection and ocean national security, the needs of using marine channels for information transmission increased significantly. So, underwater acoustic (UWA) communications have drawn more and more attention. UWA communication technique is a interdisciplinary research of marine science and information science, having extremely important applications values both in military and civilian. However, the UWA channels, especially shallow water acoustic channel, which characterize as high noise, multipath, large transmission time delay and fast time-varying, bring enormous challenges to highly reliable data transmission in UWA communication systems. Therefore, channel error correction coding is now an integral part of key technologies in both coherent and non-coherent modulation UWA communication system.LDPC codes with excellent performance of approaching the Shannon limit and low complexity have been a research topic in the field of error correction coding. But the superiority of LDPC codes can show only in long code-length, while underwater acoustic channels require as short code-length as possible. QC-LDPC codes have lower complexity and better performance in short code-length. Therefore QC-LDPC codes are more suitable for UWA communications. However, general design of regular QC-LDPC codes don’t consider rows related problem of check matrix, making construct generation matrix very difficultly. Basing on studying on sound propagation properties in the ocean and shallow water acoustic channels characteristic, this dissertation built shallow water acoustic channel multipath propagation model and then in-depth researched the design and performance of irregular QC-LDPC codes with both performance optimizations and coding simplification in UWA channels. Contraposing high dynamic range of UWA channel variation characteristics, adaptive channel coding techniques was been proposed to improve channel utilization of UWA channel. This dissertation focused on encoding of rate compatible QC-LDPC (RC QC-LDPC) and application in UWA channel combination with frequency-hopping UWA communication technique. In addition, for adaptive channel coding techniques, signal-to-noise ratio estimation algorithm in channel was also been researched, which was one of the vital parameters to switch code-rate of rate-compatible codes.The major work of this dissertation is as the following:1. From the perspective of improving the performance of UWA communication, it studied the main characteristics of UWA channels and the implications on UWA communication systems. Besides, modeling of water acoustic channel was also presented here. Two actual channel models were built according to the underwater blasting data of Wuyuan Bay, Xiamen and quangang xiaocuo, Quanzhou, Fujian.2. In order to increase the transmission reliability and real-time capability, irregular QC-LDPC codes were proposed as the channel coding scheme for UWA transmitting. The method of encoding and decoding of irregular QC-LDPC codes were studied. And the performance of irregular QC-LDPC codes in UWA channels was further analyzed with sea trial data.3. As for increasing the channel utilization, adaptive channel coding was proposed for UWA transmitting. The effects of design techniques for RC QC-LDPC codes were discussed. Jointing UWA frequency-hopping communication technology, research and analysis of the performance of RC QC-LDPC codes was showed using the two sea trial data. Furthermore, a lookup table was given for the RC QC-LDPC performance of different SNR in frequency hopping system.4. It researched SNR estimation method in UWA communication channel and then presented one SNR estimation method based on auxiliary data (DA) for PSK modulation, as well as one estimation method without auxiliary data (NDA) suitable for spread spectrum communication. Combining with multiple UWA channel model and sea trial data, accuracy comparison of the two estimation methods was also present here. Among them, the SNR estimation error of NDA algorithm was controlled by0.5dB within a-15dB to20dB, which was not sensitive to multipath interference in UWA channel. These two estimation algorithms were simple and suitable for hardware implementation with low complexity.The innovations of this dissertation are as follows:1. Constructing generate matrix of regular QC-LDPC codes was very difficult. To solve this problem, irregular QC-LDPC codes with performance optimizations and coding simplification were proposed as a channel error correction coding scheme in UWA communication system. 2. Since channel coding designed for the worst channel quality leads to inefficient channel utilization, adaptive channel coding technique in UWA transmitting system was proposed. This dissertation used RC QC-LDPC codes as adaptive channel coding schemes and analyzed the performance with sea trial data.3. SNR is an important parameter of assessment UWA channel quality. This dissertation proposed one SNR estimation method——NDA, which was suitable for UWA spread-spectrum communication. This algorithm had low complexity, high accuracy and wide estimating range.