Research On Techniquues For Improving The HF Low Rate Data Transmission

The HF low rate data transmission systems based on America military standard110B are mainly analyzed in this thesis. In order to improve the system performance of anti-multipath, anti-fading and anti-jamming, the key techniques, including the signal de-spread, multipath combining and anti-single-tone jamming, are chiefly discussed.Firstly, the length and format of synchronization preamble sequence is modified,because the capture time of old low rate data transmission system is too long. Secondly, multi-sampling points method for signal detection is discussed and realized on the hardware platform, respectively using the optimal sampling points, three and five sampling points for detection. Thirdly, based on the characteristics of the shortwave communication systems, three merging methods for multi-path signals are presented and implemented on the DSP hardware platform, which are selective combining, equal gain combining and the maximum ratio combining.Finally, starting with the estimate of signal parameter, for the integer and non-integer harmonic jamming, the direct algorithm, improved FFT algorithm and windowing algorithm are researched. And then removing method based on frequency domain, trapping method based on frequency domain and removing method based on time domain to restrain strong single sine wave interfere from the angle of the frequency domain and time domain are discussed and analyzed.