Space-time Coding For Hf Digital Communications

HF communication is important in wireless communication and applied widely for its low transmit power, establishing and maintenance cheaply, short establish period, device accomplished easily and simple operation. This paper presents the base theory and actuality of HF communication and indicates improving capability of channel and capability of anti-multipaths attenuation are development directions of HF communication.Recently,there has been growing interest in a new code scheme called space-time code.This paper will lay out the main concepts of space-time coding for flat Rayleigh fading channels.Specific space-time block code(STBC) for L=2 and L=3 antennas are given that provide coding gain as well as achieve full spatial diversity.The method of channel estimation for STBC is also presented.Since STBC is not fit to frequency-selective fading channels,we import orthogonal frequency division multiplexing (OFDM) to STBC,and then construct the model of STBC- OFDM system.Using matlab,this paper will simulate the situation of STBC- OFDM system under frequency-selective fading channels.According to these simulation results, we particularly analyze the reasons that affect the system performance, and indicate a new channel estimate method to OFDM-STBC system in the end of this paper.