Performance Analysis of MIMO K-user Interference Channels with Hardware Impairments.

Next generation of wireless systems will employ many antenna branches with low-cost devices and hence, may suffer from severe hardware impairments (HWI) like I/Q imbalance, phase noise, etc. With I/Q imbalance, the received signal is a widely linear transformation of the transmitted signal and noise. Thus, the effective noise may be improper, which means that its real and imaginary parts are not independent and identically distributed. Improper Gaussian signaling (IGS) can improve system performance with improper noise and/or improper interference. This paper studies IGS for multiple-input, multiple-output (MIMO) $K$-user interference channels (IC) with imperfect devices in terms of two performance metrics: achievable rate and energy efficiency (EE). We also define an optimization framework for interference-limited systems when treating interference as noise. This framework obtains a stationary point of any optimization problem in which either the objective function and/or constraints are linear functions of rates. These include the optimization of the rate region, the sum-rate, the EE region, or the global EE, among others. Our numerical results show that IGS can improve the performance of MIMO $K$-user IC with HWI and I/Q imbalance, where its benefits increase with $K$ and the imbalance level and decrease with the number of antennas.