We consider the uplink of a hardware-impaired intelligent reflective surfaces (IRS) aided multi-cell massive multiple-input multiple-output (mMIMO) system with mobile user equipments, whose channel age with time. For this system, we design a novel distortion-and-aging-aware MMSE (DAAMMSE) receiver that not only provides a higher spectral efficiency (SE) than conventional maximal ratio and distortionunaware MMSE (DU-MMSE) receivers, but also reduces the pilot overhead. We develop a novel low-complexity IRS phase optimization framework based on minorization-maximization (MM) technique, which requires only channel statistics to calculate the optimal phase. We also show that the SE gain of the DAA-MMSE receiver over DU-MMSE receiver increases with hardware impairments, and channel aging. Along with DAAMMSE receiver, the IRS is also shown to reduce the pilot overhead in a mMIMO system with channel aging.

We consider the uplink of a hardware-impaired intelligent-reflective surfaces (IRS)-aided multi-cell massive multiple-input multiple-output (mMIMO) system with mobile user equipments, whose channels age with time. We propose a novel distortion-and-aging-aware minimum-mean-square-error (DAA-MMSE) receiver that not only provides a higher spectral efficiency (SE) than conventional maximal ratio combiner (MRC) and distortion-unaware MMSE (DU-MMSE) receivers, but also reduces the pilot overhead. We also derive an SE lower bound for this system with MRC and DAA-MMSE receivers. We develop a novel low-complexity SE optimization framework using the weighted-MMSE and minorization-maximization (MM) techniques, which provide closed-form expressions for optimal power and phase allocations. The MM technique requires construction of a surrogate function, which we do in this work. We numerically characterize the i) UE velocities for which IRS deployment can tangibly increase their SE; ii) reduced pilot overhead with DAA-MMSE receiver along with IRS.

We consider two-way full-duplex (FD) massive multiple-input multiple-output decode-and-forward (DF) relaying with ultra-reliable low-latency communication (URLLC) users. The FD relay employs hybrid architecture with a fewer radio frequency (RF) chains than the antennas. Further, the users observe spatially-correlated Rician channels. For this system, we propose a novel optimal bilinear equalizer (OBE) that not only provides a much higher spectral efficiency (SE) than the conventional maximal ratio (MR) combiner, but also has better multi-user-interference (MUI) cancellation capability, which translates to low latency, as the system can schedule a large number of URLLC users. The OBE achieves this gain by exploiting spatial correlation in the system, an aspect we analytically demonstrate. We also derive a SE lower bound for this system, which is used to maximize the global energy efficiency (GEE) metric. The objective of GEE is a fractional function of the optimization variables, and is non-convex. We extend the fractional programming tools – Lagrangian dual and Quadratic transforms – to optimize the GEE. We show that a hybrid DF relay has a higher GEE, and a similar SE as that of a digital amplify-and-forward relay. We also show the higher GEE provided by a combination of OBE design and hybrid architecture, when compared with conventional combiners and digital architecture.

We consider two-way massive multiple-input multiple-output (mMIMO) relaying with ultra-reliable low-latency communication (URLLC) users. The full-duplex (FD) relay employs hybrid architecture, with a lesser number of radio frequency chains than the antennas. For this system, we first propose a novel digital optimal bilinear equalizer which not only provides a much higher spectral efficiency (SE) than the conventional maximal ratio combiner, but also yields a lower latency when a large number of URLLC users are scheduled. We also derive a SE lower bound for this system by considering spatially-correlated Rician fading channels. We also show that the hybrid decode-and-forward relay provides much higher SE to its URLLC users than a full-RF chain amplify-and-forward relay, which only serves non-URLLC users.