Performance Analysis and Compensation of Joint TX/RX I/Q Imbalance in Differential STBC-OFDM

TL;DR

This paper investigates the impact of I/Q imbalance on differential STBC-OFDM systems and proposes blind, decision-directed compensation algorithms to mitigate performance degradation caused by hardware imperfections.

Contribution

It is the first to quantify IQ imbalance effects on differential STBC-OFDM and introduces adaptive, blind compensation algorithms that do not require pilot signals.

Findings

Proposed algorithms effectively mitigate IQI effects.

Compensation improves system performance under high mobility.

Algorithms operate blindly without training sequences.

Abstract

Differential space time block coding (STBC) achieves full spatial diversity and avoids channel estimation overhead. Over highly frequency-selective channels, STBC is integrated with orthogonal frequency division multiplexing (OFDM) to efficiently mitigate intersymbol interference effects. However, low-cost implementation of STBC-OFDM with direct-conversion transceivers is sensitive to In-phase/Quadrature-phase imbalance (IQI). In this paper, we quantify the performance impact of IQI at both the transmitter and receiver radio frequency front-ends on differential STBC-OFDM systems which has not been investigated before in the literature. In addition, we propose a widely-linear compensation algorithm at the receiver to mitigate the performance degradation caused by the IQI at the transmitter and receiver ends. Moreover, a parameter-based generalized algorithm is proposed to extract the IQI parameters and improve the performance under high-mobility. The adaptive compensation algorithms are blind and work in a decision-directed manner without using known pilots or training sequences. Numerical results show that our proposed compensation algorithms can effectively mitigate IQI in differential STBC-OFDM.