Performance Analysis of Multi-user OTFS, OTSM, and Single carrier in Uplink

In this paper, we develop a multiple access (MA) mechanism where users transmit upsampled and circularly shifted orthogonal frequency division multiplexing (OFDM) signals in the uplink. These signals pass through MA doubly-dispersive channel and get combined at the base station (BS). We show that the composite signal received at the BS forms an equivalent single-user orthogonal time frequency space (OTFS) system. We show that such low-complexity transmission of OFDM symbols in the uplink from low-capability devices yields diversity gain as the OTFS. We extend this MA scheme for orthogonal time sequency multiplexing (OTSM) and block based single carrier (block SC) transmissions, where the composite received signal at the BS forms an equivalent single-user OTSM or block SC received signal depending on the transmission. We also develop successive interference cancellation (SIC) and turbo decoding principles-based receivers for multi-user OTFS, OTSM, and block SC transmissions, and a frequency domain SIC receiver for OFDM. We analyze their complexity with both analytical and simulation methods. Further, we compare the multi-user uncoded and coded performance of OTFS, OTSM, and block SC with multi-user OFDM. We also evaluate their performance under the effects of nonlinear high-power amplifiers in multi-user scenarios.