Performance Analysis of Multi-User OTFS, OTSM, and Single Carrier in Uplink

Abstract

In this paper, we develop a multiple access (MA) mechanism where users transmit upsampled and circularly shifted orthogonal frequency division multiplexing symbols in the uplink. These symbols pass through MA doubly dispersive channel and get combined at the base station. We show that the signal received from the users combine to form an equivalent single user orthogonal time frequency space (OTFS) system. Based on this system model, we further develop MA schemes for orthogonal time sequency multiplexing (OTSM), and block-based single carrier transmissions (block SC). We also develop two receivers based on successive interference cancellation and turbo decoding principles for multi-user OTFS, OTSM, and block SC transmissions. It is shown here that the uncoded bit error rate performance of multi-user uplink communication is worse than that of single user link, which is similar to earlier reported results. However, the coded block error rate performance in uplink is found to improve with increasing number of users. Since peak-to-average power ratio (PAPR) is an important characteristic of waveform for selection as air interface, we analyze the PAPR of OTFS, OTSM, and block SC as well as the effects of nonlinear high-power amplifiers on these three waveforms in multi-user scenarios.