Research On Multiple-input Multiple-output OTFS Modulation Systems

In the future,wireless networks are envisioned to provide global coverage for intelligent digital society,specially,with high-speed ubiquitous connectivity as well as space-air-groundsea integration.With the vision of the next generation of wireless communication networks to support full-connection and full-frequency band,how to achieve reliable transmission in high mobility scenarios at high carrier frequency is undoubtedly a major bottleneck for the current communication systems.In general,it will introduce severe Doppler spread in high carrier frequency and high mobility communications.Thus,the channel will be fast time-varying,resulting in the failure of current channel estimation technology and adaptive technology;besides,the traditional orthogonal frequency division multiplexing(OFDM)technology will also suffer a significant degradation of demodulation performance caused by inter-carrier interference.Orthogonal time frequency space(OTFS)modulation is a twodimensional modulation scheme,proposed recently to accommodate the channel with high Doppler spread.It mainly multiplexes information symbols in the delay-Doppler domain,which has strong robustness of delay and Doppler shift,while providing the potential to obtain time-frequency full diversity.Consider the increasingly high data rate needs as well as diversified scenario requirements of future wireless communications,this thesis combines multiple-input multipleoutput(MIMO)technology with OTFS(MIMO-OTFS),and deeply studies MIMO-OTFS systems with different multi-antenna technologies.The main contents and results are summarized as follows:(1)Consider high carrier frequency and high mobility communications with high Doppler spread,this thesis deeply studies the basic principle of OTFS modulation technology,including the system model and its implementation.Besides,advantages and disadvantages of OTFS as well as several low-complexity detection schemes in delay-Doppler domain are explored.Simulation results show that OTFS modulation has stronger robustness of time and frequency offset than the traditional OFDM modulation.In addition,with the potential to obtain time-frequency full diversity,no matter in slow fading channel or fast fading channel,no matter high mobility or low mobility scenarios,no matter low carrier frequency and high carrier frequency communication,OTFS has a more superior performance than OFDM.(2)Aiming at the requirements of ultra-high data transmission rate,this thesis studies the MIMO-OTFS system based on spatial multiplexing,analyzes the transmission model of the system in detail,carries out in-depth research on several typical signal detection schemes,discusses and deduces the traversal capacity of the system.Simulation results show that the MIMO-OTFS system based on spatial multiplexing will sacrifice performance for transmission efficiency to a certain degree.But compared with the traditional MIMO-OFDM system under the same simulation sets,MIMO-OTFS system still has obvious performance improvement.(3)In order to further improve the transmission reliability of the wireless communication systems,this thesis studies the OTFS system based on space-time block code(STBCOTFS).We design the space-time coding scheme,system model and receiver detection scheme.The study shows that STBC-OTFS can further improve the transmission reliability of OTFS system by providing extra spatial diversity.(4)The MIMO-OTFS system based on spatial multiplexing has a higher spectral efficiency but requires to deal with the inter-antenna interference,which induces the high complexity of receiver.Meanwhile,STBC-OTFS system’s spectral efficiency is only one symbol per second per Hertz.To resolve the problems mentioned above,a high spectral efficiency MIMO-OTFS transmission scheme based on spatial modulation(SM-OTFS)is proposed.In this thesis,the spatial mapping criterion and system model of SM-OTFS system are analyzed,and the maximum likelihood detection scheme based on antenna index and information symbol joint detection is discussed.Simulation results show that SM-OTFS system,carrying information through antenna index,can achieve higher spectral efficiency compared to STBC-OTFS system.In addition,SM-OTFS system also has obvious performance improvement compared with single-input single-output OTFS system due to its receive diversity.