Digital Compensation of IQ Imbalance, DC Offset for Zero-Padded OTFS Systems

Abstract

Next generation communication systems (e.g., 6G) foresee higher mobility, higher data rates with higher constellations and with high levels of integration in a small form factor. Direct conversion orthogonal time frequency space modulation (OTFS) systems suffer from hardware impairments such as in-phase and quadrature (IQ) imbalance, direct current (DC) offset causing image Doppler interference (IDI) among the sub-carriers in the delay Doppler (DD) domain. In this letter, we propose a novel method of estimation and compensation of hardware impairments for zero padded (ZP) OTFS systems in the delay time (DT) domain. A dual pilot approach with a phase difference of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\frac {\pi }{2}}$ </tex-math></inline-formula> between these symbols is followed in DD domain with which hardware impairments are estimated with less computational complexity in DT domain. It is found that the compensated system performs close to ideal system. The mean square error (MSE) of the estimated channel is computed and MSE reduces with increase in signal to noise ratio (SNR), pilot power ratio (PPR) and with reduction in mobility.