Research On Transmission Performance Optimization Of GFDM Satellite System

ABSTRACTGeneralized frequency division multiplexing(GFDM)is a nonorthogonal multicarrier technology based on block data modulation.Compared with the orthogonal frequency division multiplexing technology,it has many advantages such as low radiation out of band,high spectrum utilization efficiency and good multiple services compatibilities.GFDM can be flexibly compatible with the uplink and downlink waveforms of 5G mobile communication system or other new multi-carrier waveforms.The application of GFDM technology in satellite mobile communication system can improve spectrum efficiency,increase system capacity,promote the integration of satellite communication system and cellular mobile communication system,and realize the hybrid satellite-terrestrial networks.Although GFDM has many advantages,its inherent self-interference,high peak to average ratio(PAPR),timing synchronization sensitivity reduce the transmission and reception performance of satellite communication,so it is necessary to propose correponding solutions.Aiming at the problem that the self interference of GFDM affects the receiving performance of satellite,this dissertation deeply studies the self interference model of GFDM system,and puts forward three kinds of self interference performance optimization algorithms of GFDM,which are data-aided single-sided interference cancellation algorithm in frequency domain,double-sided interference cancellation algorithm based on the optimized matched filter and the parallel interference cancellation algorithm based on the active interference cancellation algorithm.The simulation results show that the self interference suppression effect of the three algorithms is obvious,which effectively improves the symbol error rate performance of GFDM receiver in satellite channel.Aiming at the problem that the PAPR of GFDM and GFDMA is too high to reduce the transmission performance of satellite communication link,this dissertation deduces the CCDF theoretical expression of PAPR,which is the unified architecture of GFDM/GFDMA.Then,in the condition of low SNR for satellite communication,two new PAPR waveform for satellite GFDM system are proposed,which are constant amplitude zero autocorrelation(CAZAC)sequence expansion GFDM-CDMA waveform and GFDMA waveform with sub symbol expansion and optimized precoding.The simulation results show that the PAPR performance of the two new waveform is improved by about 10 dB compared with the original waveform,and the anti noise performance is enhanced.Aiming at the problem that the traditional GFDM timing synchronization algorithm can't be used in the satellite communication system with large frequency offset,this dissertation analyzes the influence of time offset and frequency offset on the GFDM system firstly.The closed expression of SINR varying with time offset and frequency offset is derived,and the sensitivity of GFDM to timing offset is clarified.An anti frequency offset GFDM timing synchronization algorithm based on differential cross correlation is proposed.The simulation results show that the timing performance of the algorithm is not affected by frequency offset.Aiming at the problem that GFDM-CDMA waveform has poor performance with frequency offset,this dissertation proposes a new anti frequency offset GFDM-CDMA waveform based on PN weighted ZC sequence.The comprehensive simulation and complexity analysis results show that the new PAPR waveform optimizes the synchronous performance in the environment with high frequency offset.Because the frequency offset estimation and compensation is omitted,the receiving complexity is greatly reduced compared with the traditional GFDM receiver,which can meet the requirements of satellite communication system for complexity and frequency offset robustness.