Research On The Anti-Fading Performance Of EBPSK Communication System

Available wireless spectrum resource is increasingly scarce. Efficient use of the resource is in favor of sustainable development, and higher requirement of system's anti-fading performance is put forward in wireless transmission environment. To this end, the performance of efficient ultra-narrow spectrum extended binary phase shift keying(EBPSK) modulation in fading channel is discussed in detail in the thesis, which has important theoretical significance and practical value.Firstly, the characteristics of wireless fading channel are analyzed. The simulation modeling methods of flat fading channel and frequency selective fading channel are studied.Secondly, the EBPSK communication system is studied, as well as its inherent anti-fading performance. At the modulation end, the essential modulation parameters and their influence on the power spectrum are analyzed. At the demodulation end, the existing impacting demodulation and coherent demodulation are analyzed. And a new delay superposition method is proposed, by which the signal is converted to 2ASK modulation signal and envelope detection can be used to demodulation, but the performance is not satisfactory. Special amplitude limiting (SAL) method is proposed, through which the phase jump information is highlighted and there are varied degrees of improvement on the performances of impacting demodulation and other demodulation methods based on full code delay superposition. The proposed demodulation methods using coherent carrier have better anti-noise performance, but they are difficult against fading. Neither are the methods using envelop detection. Furthermore, a delay multiplication demodulation method is proposed. It demands no coherent carrier and can overcome the amplitude fluctuation by zero threshold. Consequently the ability against Doppler spread is superior to other methods.Then, the anti-fading scheme of EBPSK system is researched. In flat Rayleigh fading channel, Automatic Gain Control (AGC) is proposed against the signal amplitude fluctuation when fixed threshold is used in impacting demodulation and envelope detection based on delay superposition. A series of diversity combining schemes suitable for EBPSK system is proposed, which can eliminate the influence of both deep fading and AWGN and improve the performance of impacting demodulation and delay multiplication demodulation. In multipath delayed channel, a multipath estimation method based on impacting filter is proposed and simulated by typical shortwave model of DRM standard. The results illustrate that the high accuracy of the estimation is realized in high SNR conditions or when enough symbols is adopted. Strengths and weaknesses of the existing multipath separation method are analyzed and the improved separation algorithm is proposed to obtain the optimal modulation parameter N, so as to realize sectional or complete separation of all the paths in channel. In order to take full advantage of multipath information, three common combined detection methods are employed. The simulation results show the correctness and effectiveness of the proposed schemes.Finally, since the envelop fluctuation makes that the accurate decision threshold cannot be set, a new Symmetric-EBPSK modulation system is proposed. Its theoretical power spectrum and BER expression in AWGN channel are derived. Without fixed threshold, the detection can be accomplished by comparison. It is illustrated by simulation that the BER performance of S-EBPSK system is better than EBPSK system with same modulation parameters and same demodulation methods in the same channel.