Research On Signal Demodulation Of 3G HF Communication System

In recent years, HF communication has been greatly developed because of the adaptive technology, digital signal processing technology, spread spectrum technology and error correction technology. HF is currently in its third generation HF communication system(3G-ALE), it is based on MIL-STD-188-141 B protocol, which announced by US military in March 1999. After that, NATO also put forward its own 3G-ALE protocol STANAG 4538. As a result of a series of waveform BW transmission technology, QPSK modulation scheme, the paging channel and the traffic channel separation technique, compared to the second-generation technology for Automatic Link Establishment, 3G-ALE has obvious advantages: faster speed link establishment, connection can be achieved at lower SNB conditions, high channel efficiency.This thesis is based on protocol STANAG 4538. Recognition BW1-BW5 waveform by sliding correlation peak power spectrum detection algorithm, While the center frequency of the signal also been detected, then use downconversion and matched filtering to move the signal to baseband, consequently achieve soft baseband demodulation of HF 3G-ALE signal.For orthogonal spreading modulation waveform using RAKE receiver algorithm diversity reception, so that the separated multipath signals properly combined with the main path signal, increasing the signal to noise ratio, thereby harmful multipath signal becomes advantageous the useful signal.Improved RLS adaptive equalization algorithm is directed against modulation waveform which has significantly frame. The algorithm is fast, robust, and can effectively eliminate the ISI, the maximum possible recovery distortion of symbols.Because various types of waveforms must specify certain parameters in the demodulation process, in order to achieve automatic demodulation without human intervention, this thesis using correlation peak energy detection algorithm to automatic calculation of the signal start and end time, using the traversal algorithm to automatically find the signal related to the initial state parameters. These algorithms improve the automation of demodulation, saving human resources.Finally, this paper discusses the design idea and system structure of HF signal demodulation software platform; and the platform is introduced. The demodulation algorithm is simulated; the validity of the algorithm is verified. For the requirements of the real time processing in engineering practice, the method of the implementation proposed in this paper has better applicable and reference value.