Performance Analysis of OTSM under Hardware Impairments and Imperfect CSI

TL;DR

This paper analyzes the performance of Orthogonal Time Sequency Multiplexing (OTSM) considering multiple hardware impairments and imperfect channel information, demonstrating its robustness and advantages over traditional waveforms in complex wireless environments.

Contribution

It provides the first comprehensive analysis of OTSM under combined hardware impairments and imperfect CSI, deriving analytical error probabilities and validating performance through simulations.

Findings

OTSM outperforms OFDM by 29% in energy efficiency.

OTSM performs comparably to OTFS in high mobility doubly-spread channels.

Hardware impairments cause specific interference patterns and sparsity in the effective channel.

Abstract

Orthogonal time sequency multiplexing (OTSM) has been recently proposed as a single-carrier waveform offering similar bit error rate to orthogonal time frequency space (OTFS) and outperforms orthogonal frequency division multiplexing (OFDM) in doubly-spread channels (DSCs); however, with a much lower complexity making it a potential candidate for 6G wireless networks. In this paper, the performance of OTSM is explored by considering the joint effects of multiple hardware impairments (HWIs) such as in-phase and quadrature imbalance (IQI), direct current offset (DCO), phase noise, power amplifier non-linearity, carrier frequency offset, and synchronization timing offset for the first time in the area. First, the discrete-time baseband signal model is obtained in vector form under all mentioned HWIs. Second, the system input-output relations are derived in time, delay-time, and delay-sequency (DS) domains in which the parameters of all mentioned HWIs are incorporated. Third, analytical expressions are derived for the pairwise and average bit error probability under imperfect channel state information (CSI) as a function of the parameters of all mentioned HWIs. Analytical results demonstrate that under all mentioned HWIs, noise stays additive white Gaussian, effective channel matrix is sparse, DCO appears as a DC signal at the receiver interfering with only the zero sequency, and IQI redounds to self-conjugated sequency interference in the DS domain. Simulation results reveal the fact that by considering the joint effects of all mentioned HWIs and imperfect CSI not only OTSM outperforms OFDM by 29% in terms of energy of bit per noise but it performs same as OTFS in high mobility DSCs.