Estimation and Compensation of IQ Imbalance at the Receiver of IRS-Assisted SISO OTSM System Under Perfect Phase Optimization

Orthogonal time sequency multiplexing (OTSM) is a recently proposed modulation technique that outperforms orthogonal frequency division multiplexing (OFDM) in high-mobility and doubly spread channel conditions. Integrating intelligent reflecting surfaces (IRS) can further boost OTSM performance by effectively combining multi-path signals. This paper investigates the combination of OTSM and IRS to develop a generalized input-output relationship in both the time domain and delay-sequency (DS) domain, considering the presence of in-phase and quadrature-phase imbalances (IQI) at the receiver. To mitigate these imbalances, we apply a zero-padding (ZP) strategy in the DS domain, which not only suppresses time-domain interference but also enables dual pilot insertion for the estimation of IQI and channel parameters in the delay-time domain, followed by compensation in the time domain. Our analysis demonstrates that receiver IQI significantly degrades the bit error rate (BER) performance, particularly with increasing gain mismatch parameters. However, with the proposed compensation techniques, the BER performance approaches that of an ideal, imbalance-free scenario.