The Application Research Of LDPC Code In Hf Wideband Spread Spectrum OFDM Communication System

HF communication is an important means of military communication. On account of thecomplex battlefield condition and the adverse electromagnetic environment, the modernhigh-tech military competition requires the information transmitted more accurately, timelyand confidentially, which proposed a higher demand for HF communication in terms ofinformation transmission rate and communication quality. For this reason, the new technologywas introduced to improve the performance of HF communication system in order to play amore significant role in the modern electronic warfare.This paper started with analyzing the characteristics of HF communication from theaspects of the maximum usable frequency, transmission mode, multipath effects, shadowfading, and interference etc. Three typical HF channel models were investigated: Wattersonmodel, extended Watterson model and ITS model, among which the focus is on the ITS HFwideband channel model.Second, this paper specifically introduced the principles of the spread spectrumtechnology, OFDM technology, and three means of combining the spread spectrum with theOFDM technology. Furthermore, a communication system was established by using thecombination of spread spectrum OFDM technology in frequency domain. And the paperresearched the effects of sub-carrier’s various number on the performance of system throughthe simulation analysis in the Gaussian channel and HF wideband ITS channel.At last, based on the spread spectrum OFDM communication system, a new system wasestablished by adding LDPC code which has excellent error correcting capability to improvethe effects of HF communication in the wideband ITS channel. According to thecharacteristics of HF communication, the system parameters being set, the modulation andequalization algorithm were selected through simulation analysis. The application of differentLDPC codes factors in the system was dealt with further, including the method ofconstructing check matrix, the length of the code, the rate of the code, the decoding algorithmand the iteration number. A reasonable scheme of LDPC code parameters was determinedbased on the analysis of the simulation result.In sum, the error rate was decreased attributed to the collaboration of the LDPC code designed here and the spread spectrum OFDM technology, achieving the goal of a high-speeddata transmission rate with the quality of HF communication improved, which provided areference scheme to improve the HF communication technology; and the selected reference ofLDPC codes served as a reference for the hardware implementation.