Effect of Generalized Improper Gaussian Noise and In-Phase/Quadrature-Phase Imbalance on Quadrature Spatial Modulation

Quadrature spatial modulation (QSM) isa recently proposed multiple-input multiple-output (MIMO) wireless transmission paradigm that has garnered considerable research interest owing to its relatively high spectral efficiency. QSM essentially enhances the spatial multiplexing gain while maintaining all the inherent advantages of spatial modulation (SM). This work studies the effects of in-phase/quadrature-phase (I/Q) imbalance and improper Gaussian noise (IGN) on the performance of QSM. Considering a scenario where both receiver and transmitter operate under the effects of I/Q imbalance, we propose a novel receiver design that optimizes the system bit error rate (BER) when there is IGN at the receiver. Closed forms of the average pairwise error probability (APEP) and upper bound of the average BER formulas are derived. These formulas are derived considering the Beckmann fading channel model, where most well-known fading channel models can be considered special cases. The proposed designs demonstrate solid performance despite the effects of I/Q imbalance. In fact, these effects can be entirely eliminated if they exist at the receiver and significantly reduced at the transmitter. All analytical results were verified by computer simulations.