Research On OTFS Modulation And Tandem Spreading Multiple Access Technology For IoT-railways

With the rapid development of high-speed railways,the requirements of railways for safety and quality of service are constantly improving,and improving digital and intelligent level of railways has become an inevitable choice for railway development.Therefore,it is necessary to accelerate development of intelligent railway.The internet of things for railways(IoT-R)technology can support the realization of intelligent railway environment,state real-time perception and reliable transmission of information,has important applications in natural disaster monitoring,intrusion warning,railway infrastructure monitoring and other aspects,and plays an important role in the high-quality development of intelligent railway.The IoT-R has high requirements on the reliability of data transmission.The low bit error rate can ensure safety of railway traffic and reduce energy loss caused by data retransmission,thereby improving operating cycle of IoT-R terminal equipment.This paper focuses on the reliable transmission of single user and multi user data in IoT-R,and conducts research on modulation and multiple access technologies applicable to IoT-R.Orthogonal time frequency space(OTFS)modulation system can realize reliable communication in high mobility scenarios.In addition,OTFS modulation system can achieve lower peak-to-average power ratio(PAPR)than OFDM system,which can reduce the energy consumption of information transmission and improve the operation cycle of IoT-R terminal equipment.Tandem spreading multiple access(TSMA)uses non iterative receivers at the receiving end and can further improve data transmission reliability and user connectivity by sacrificing user data rates.Its relatively low data rate and high data transmission reliability are consistent with the design requirements of IoT-R.Therefore,this paper focuses on OTFS modulation and TSMA technology for IoT-R,and its specific research contents and achievements are summarized as follows:1.On the basis of summarizing the current modulation and multiple access technologies,and considering the characteristics of IoT-R,this paper explores the application of OTFS modulation and TSMA technology in IoT-R.Therefore,the simulation platforms of OTFS modulation system and TSMA system are built respectively,and the simulation platforms are used to evaluate and analyze bit error performance and PAPR performance of OTFS modulation,and user identification and data detection performance of TSMA system.The simulation results demonstrate the feasibility of applying OTFS modulation and TSMA technology to IoT-R.2.In order to further reduce the PAPR of OTFS modulation system,thereby improving battery life of IoT-R terminals and energy efficiency of system,this paper uses peak windowing technique to further reduce the PAPR of OTFS modulated signal.Therefore,peak windowing OTFS modulation system is designed in this paper.On this basis,the effects of different window types,window sizes and clipping ratios on bit error rate and PAPR performance of OTFS are compared and analyzed.The simulation results show that the peak windowing technique can significantly reduce the PAPR of OTFS modulation signal at the cost of reasonable bit error rate loss.For example,the peak windowing OTFS modulation system can achieve a reduction of approximately 4 d B in the PAPR of OTFS modulated signal with almost no loss of OTFS bit error performance.Compared with other existing technologies to reduce the PAPR of OTFS,peak windowing OTFS modulation system proposed in this paper is more suitable for IoT-R.3.In order to further improve the data transmission reliability of TSMA,polar coded TSMA(PC-TSMA)scheme is proposed in this paper.Different from the traditional TSMA scheme which uses channel pre-compensation method based on channel reciprocity,the least square channel estimation scheme is applied to PC-TSMA system.Meanwhile,the effects of zero-forcing(ZF)equalizer and minimum mean square error(MMSE)equalizer in the PC-TSMA system are compared and analyzed in this paper.The simulation results show that PC-TSMA scheme further improves the data transmission reliability of TSMA scheme.When the segment coding rate is 0.5,compared with TSMA system,PC-TSMA system has about 3 d B block error performance gain in additive white Gaussian noise channel and 2 d B block error performance gain in Rayleigh fading channel,respectively.In addition,MMSE equalizer is superior to ZF equalizer in PC-TSMA scheme.The PC-TSMA system can be used as a non-orthogonal multiple access solution for IoT-R.