Performance Evaluation of Tandem Spreading Multiple Access with Polar Code System for IoT-Railways

With the rapid development of high-speed railways, intelligent railways have attracted much attention in railway industries and research institutes all over the world. The internet of things for railways (IoT-R) plays an important role for intelligent railways. In order to use limited radio resources to support massive low-cost and low-energy users in IoT-R, advanced multiple access technology becomes important. Tandem spreading multiple access (TSMA) is a recently proposed non-orthogonal multiple access scheme that uses a non-iterative receiver to solve the problem of data collision. In addition, TSMA can improve data transmission reliability and user connection capability at the expense of user data rate. Therefore, TSMA shows its potential in IoT-R. However, IoT-R has high requirements for data transmission reliability. In order to further improve data transmission reliability in IoT-R, TSMA with polar code system is proposed in this paper. Different from channel pre-compensation method used in the original TSMA system, the least squares channel estimation is applied in TSMA with polar code system. In addition, zero-forcing (ZF) equalizer and minimum mean square error (MMSE) equalizer are applied in TSMA with polar code system. Simulation results show that block error rate of TSMA with polar code system in both additive white Gaussian noise channel and Rayleigh fading channel is lower than that of TSMA system. In addition, TSMA with polar code system using MMSE equalizer has better performance than TSMA with polar code system using ZF equalizer.