Multi-pair Massive Multiple-input Multiple-output Research Articles

Performance Optimization of Multipair Massive MIMO Polarized Relay Systems

In this paper, we analyze the challenges faced by multipair massive Multiple-input-multiple-output (MIMO) relay channels in 5G wireless communication systems, where high path loss and severe shadow fading between different user nodes can cause poor channel quality. To overcome these limitations, we propose a polarization selection scheme for antenna arrays combining multipair massive MIMO relay and beamforming to improve MIMO relay channel quality. Specifically, our main goal is to exploit the potential of polarization diversity to maintain and improve the link quality while maintaining the compact size of the MIMO antenna array. To achieve this goal, we introduce a dynamic weighted particle swarm optimization algorithm with contraction factor (CF-DWPSO) to select the polarization direction. In addition, we employ distributed beamforming to effectively suppress or eliminate inter-pair interference. The performance of the simulation analysis shows that CF-DWPSO combined with beamforming provides significant performance improvement of the multipair massive MIMO polarized relay channels, which further indicates that it is of great necessity for improving the performance of this system to optimize the polarization selection by combining beamforming techniques.

Spectral Efficiency of Multipair Massive MIMO Two-Way Relaying With Hardware Impairments

We consider a multipair massive multiple-input multiple-output (MIMO) two-way relaying system, where multiple pairs of single-antenna devices exchange data with the help of a relay employing a large number of antennas $N$. The relay consists of low-cost components that suffer from hardware impairments. A large-scale approximation of the spectral efficiency (SE) with maximum ratio (MR) processing is derived in closed form, and the approximation is tight as $N \to \infty$. It is revealed that for a fixed hardware quality, the impact of the hardware impairments vanishes asymptotically when $N$ grows large. Moreover, the impact of the impairments may even vanish when the hardware quality is gradually decreased with $N$, if a scaling law is satisfied. Finally, numerical results validate that multipair massive MIMO two-way relaying systems are robust to hardware impairments at the relay.

Secure Performance Analysis for Multi-Pair AF Relaying Massive MIMO Systems in Ricean Channels

This paper investigates the secure communication in a multi-pair massive multiple-input multiple-output (MIMO) amplify-and-forward (AF) relay network over Ricean fading channels in the presence of an eavesdropper. With the imperfect estimated channel state information, maximum ratio combining (MRC)/maximal ratio transmission (MRT) are employed for AF relaying. Based on random matrix theory, we first derive tractable analytical expressions of the end-to-end signal-to-interferenceplus-noise ratios (SINRs) at the intended user and Eve, respectively. Then, some asymptotic results for infinite Ricean K-factor, unbounded transmit power, and relay power are provided, which show that the SINRs at target user and Eve are both limited by some bounds and the effects of estimation error, relay noise, or received additive noise will be eliminated in these extreme cases. Meanwhile, power scaling laws for transmit power and relay power are studied that they should satisfy to maintain a desirable rate level. Analytical results indicate that the power can largely be cut down in inverse proportion to the number of relay antennas in Ricean fading channels. Moreover, by exploiting successive approximations, geometric programming, and iterative computation, a power control scheme is proposed to maximize the achievable sum secrecy rate. Numerical results are presented to demonstrate the effectiveness of this secure multi-pair massive MIMO relaying system.