Research On Key Technique For Frequency Hopping Communication System With BICM Over High Frequency Channel

The High Frequency frequency-hopping communication systems have an important position and role in the modern military communications, and it is an important means of the communication interference, and one of the focus study areas currently in the Western military power. With the development needs of the modern high-tech warfare, it is positive significance to improve and enhance the performance of the HF frequency-hopping communication systems to adapt to the modern electronic warfare, so the development of the more high-performance HF frequency-hopping communication system is an important research topic. This dissertation discusses the coded modulation scheme of the HF frequency-hopping communication systems, called the bit-interleaved coded modulation scheme, to improve and enhance the performance of the HF frequency-hopping communication system.After studying the communication features of the high frequency channels, such as multi-path effects, channel fading, Doppler effects, etc, a frequency hopping communication system based on the bit-interleaved coded modulation and iterative decoding techniques (BICM-ID) is constructed over the high frequency channel. The factors that affect the performance have been analyzed in the system. It is focus on the key technologies in this system, such as the synchronization, carrier estimation, channel equalization, and channel estimation, which have been researched deeply.At the problem of synchronization, a frequency hopping synchronization method is proposed based on the BICM-ID-FH system. The chaotic sequence and the TOD sequence were used as the key to encrypt the frequency hopping sequence. Then the synchronization of the frequency hopping sequences in complexity system was transformed to the synchronization of the TOD sequence. So the anti-interception of the synchronous information was enhanced at the same time.About the estimation of carrier frequency, the carrier frequency offset iterative estimation algorithm is proposed based on the Turbo iteration theory in the BICM-ID-FH system. At the initial iteration of the algorithm, the Kay algorithm was used, and the L&R algorithm was used in the iterative process. So the algorithm has the advantages of the large scope and the high precision, obtained good performance. Using this algorithm, the scheme of the iterative estimation and correction carrier offset was designed in the system. In addition, the scheme of the iterative estimation and correction phase offset was designed in the system.The equalization is the very important problem in the communication systems. The Decision Feedback Equalization has been improved based on the iteration theory in the BICM-ID-FH system. In the Turbo equalization structure of the BICM-ID-FH system, the SIC equalization algorithm has been improved, by using the priori probability estimation of the received signal instead of the traditional assumption that the signal probability was uniformly distribution, which effectively improves the BER performance. Otherwise, a joint algorithm is proposed by combining the MAP algorithm and the SIC algorithm in the Turbo equalization scheme of the system. In the initial iteration of the algorithm, using MAP algorithm to estimate the prior probability distribution of the received signal, it is more accurate than using the SIC algorithm. The SIC algorithm was used in the iterative process, to facilitate the calculation and implementation. The simulation results show that the algorithm effectively improve the system equalizing.Finally, the problem of the channel estimation was discussed. The semi-blind iterative scheme of the channel estimation and equalization was designed based on the iterative theory in the BICM-ID-FH system. At the initial iteration of the scheme, the training sequences was used to estimate the channel information, and then combining with the Turbo equalization iterative process, and the output of the decoder was fully used to achieve the unification of the channel estimation, channel equalization and decoding. The simulation results show that the scheme has good adaptability for the high frequency channel. In addition, the blind iterative scheme of the channel estimation and equalization was designed and implemented in the BICM-ID-FH system, and the simulation results show that the scheme has a convergence when channel fading is not serious.