Abstract-This paper studies the deployment of multiple-input multiple-output (MIMO) full-duplex (FD) relaying systems in a multi-cell environment, where the source and destination nodes are equipped with single antenna and communicating via a dualhop amplify-and-forward (AF) relay station with multiple receive and transmit antennas in the presence of co-channel interference (CCI). This paper addresses the fundamental challenges of loopback self-interference (LI) and CCI when incorporating FD relaying in cellular systems. Due to the higher frequency reuse in FD relaying compared to its half-duplex (HD) relaying counterpart, the CCI is expected to double as the FD relay station simultaneously schedule uplink and downlink transmission on the same channel. The optimal design of relay receive and transmit precoding weight vectors which maximizes the overall signal-to-interefernce-plus-noise ratio (SINR) is formulated by a proper optimization problem, then a closed-form suboptimal solution based on null space projection is proposed. The proposed precoding vectors are based on the added receive and transmit zero-forcing (ZF) constraints used to suppress the co-channel interference and loopback self-interfernce, respectively. To this end, exact closed-form expressions for the outage probability and ergodic capacity are derived, where a simpler lower-bound expressions are also presented. In addition, the asymptotic high signal-to-noise ratio (SNR) outage probability approximation is also considered, through which the diversity order of the null space projection (ZF/ZF) scheme is found to achieve min (NR − M, NT − 1), where NR and NT are the number of relay receive and transmit antennas, respectively, and M is the number of CCI interferers. Numerical results sustained by Monte-Carlo simulations show the exactness of the proposed analytical expressions as well as the tightness of the proposed lower-bound expressions. In addition, simulation results for the minimum mean square error (MMSE)/ZF scheme is also considered for comparison purposes. Our results reveal that MIMO FD relaying could substantially boost the system performance compared to its conventional MIMO HD relaying counterpart.Index Terms-MIMO relaying, full-duplex relaying, halfduplex relaying, zero-forcing (ZF), minimum mean square error (MMSE), outage probability, ergodic capacity, co-channel interference.

Abstract-This paper analyzes the performance of energyconstrained dual-hop amplify-and-forward (AF) relaying systems with multi-antenna nodes, in the presence of multiple co-channel interferers (CCI) at the destination. To maximize the overall signal-to-interference-plus-noise ratio (SINR) as well as the harvested energy so as to mitigate the severe effects of fading and enable long-distance wireless power transfer, hop-by-hop information and energy beamforming is proposed where the transmitted signal is steered along the strongest eigenmode of each hop. The wirelessly powered relay scavenge energy from the source information radio-frequency (RF) signal through energy beamforming, where both the time-switching receiver (TSR) and power-splitting receiver (PSR) are considered, then uses the harvested energy to forward the source message to the destination. To this end, tight lower and upper bound expressions for the outage probability and ergodic capacity are presented in closed-form. These are employed to investigate the throughput of the delay-constrained and delay-tolerant transmission modes. In addition, the asymptotic high signal-to-noise ratio (SNR) outage probability and ergodic capacity approximations are derived, where the achievable diversity order is also presented. Numerical results sustained by Monte Carlo simulations show the tightness of the proposed analytical expressions. The impact of various parameters such as energy harvesting time, power-splitting ratio, source transmit power and the number of antennas on the system throughput is also considered.Index Terms-MIMO relaying, half-duplex relaying, beamforming, maximum ratio transmission (MRT), maximum ratio combining (MRC), zero-forcing (ZF), wireless power transfer, energy harvesting, outage probability, ergodic capacity.

This paper analyzes the performance of multipleinput multiple-output (MIMO) full-duplex (FD) relaying systems, where the source and destination nodes are equipped with single antenna and communicating via a dual-hop amplify-andforward (AF) relay with multiple receive and transmit antennas. The system performance due to practical wireless transmission impairments of spatial fading correlation and imperfect channel state information (CSI) is investigated. At the relay, the loopback self-interference (LI) is mitigated by using receive zero-forcing (ZF) precoding scheme, then steering the signal to the destination by using maximum-ratio transmission (MRT) technique. To this end, new exact closed-form expressions for the outage probability are derived, where the case of arbitrary, exponential, and no correlations are considered. Meanwhile, for a better system performance insights, simpler outage probability lower-bound expressions are also included, through which the acheiveable diversity order of the receive ZF/MRT scheme is shown to be min (NR − 1, NT), where NR and NT are the number of relay receive and transmit antennas, respectively. Numerical results sustained by Monte Carlo simulations show the exactness and tightness of the proposed closed-form exact and lower-bound expressions, respectively. In addition, it is seen that the outage probability performance of FD relaying outperforms that of the conventional half-duplex (HD) relaying at low to medium signalto-noise ratio (SNR). However, at high SNR, the performance of HD relaying outperforms that of the FD relaying. Furthermore, in the presence of channel estimation errors, an outage probability error floor is seen at high SNR. Therefore, for optimum outage performance, hybrid relaying modes is proposed which switches between HD and FD relaying modes. Index Terms-MIMO relaying, full-duplex relaying, halfduplex relaying, maximum-ratio combining (MRC), maximum ratio transmission (MRT), zero-forcing (ZF), outage probability. I. INTRODUCTION C OOPERATIVE relaying techniques have gained a great deal of attention due to their ability to extend network coverage, connectivity and attain higher capacity without sacrificing extra power resources. In a dual-hop relaying systems,

Abstract-In this paper, a comprehensive design and analysis of multiple-input multiple-output (MIMO) full-duplex (FD) relaying systems in a multi-cell environment are investigated, where a multi-antenna amplify-and-forward (AF) FD relay station serves multiple half-duplex (HD) multi-antenna users. The pivotal obstacles of loopback self-interference (LI) and multiple co-channel interferers (CCI) at the relay and destination when employing FD relaying in cellular networks are addressed. In contrast to the HD relaying mode, the CCI in the FD relaying mode is predicted to double since the uplink and downlink communications are simultaneously scheduled via the same channel. In this paper, the optimal layout of transmit (receive) precoding (decoding) weight vectors which maximizes the overall signal-to-interefernce-plusnoise ratio (SINR) is constructed by a suitable optimization problem, then a closed-form sub-optimal formula based on null space projection is presented. The proposed hop-by-hop rank-1 zero-forcing (ZF) beamforming vectors are based on added ZF constraints used to suppress the LI and CCI channels at the relay and destination, i.e., the source and relay perform transmit ZF beamforming, while the relay and destination employ receive ZF combining. To this end, unified accurate expressions for the outage probability and ergodic capacity are derived in closed-form. In addition, simpler tight lower-bound formulas for the outage probability and ergodic capacity are presented. Moreover, the asymptotic approximations for outage probability is considered to gain insights into system behavior in terms of the diversity order and array gain. Numerical and simulation results show the accuracy of the presented exact analytical expressions and the tightness of the lower-bound expressions. The case of hopby-hop maximum-ratio transmission/maximal-ratio combining beamforming is included for comparison purposes. Furthermore, our results show that while multi-antenna terminals improve the system performance, the detrimental effect of CCI on FD relaying is clearly seen. Therefore, our findings unveil that MIMO FD relaying could significantly improve the system performance compared to its conventional MIMO HD relaying counterpart.Index Terms-MIMO relaying, full-duplex relaying, halfduplex relaying, beamforming, zero-forcing (ZF), outage probability, ergodic capacity, co-channel interference.

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