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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Orthogonal frequency division multiplexing (OFDM) over wireless channels is sensitive to carrier frequency offset (CFO), which destroys orthogonality amongst sub-carriers, giving rise to inter-carrier interference (ICI). Different techniques are available for estimating and compensating for the CFO at the receiver. However, in practice, a residual CFO remains at the receiver after CFO estimation, where the estimation accuracy depends primarily on the fractions of time and power used by the estimator. In this paper, we propose to measure the efficiency of OFDM systems with CFO estimation errors in terms of the spectral efficiency, which accounts for both, the degradation in signal-to-interference plus noise ratio (SINR) due to the residual CFO, and the penalty of the extra power and spectral resources allocated to achieve the desired CFO estimation accuracy. New accurate expressions are derived for the spectral efficiency of wireless OFDM systems in the presence of residual CFO and frequency-selective multipath fading channel. These are used to compare between two common CFO estimation methods in wireless OFDM systems, namely, the cyclic prefix based and the training symbols based CFO estimation techniques for fixed and variable pilot power. These results are further extended to include OFDM systems with transmit diversity techniques. In addition, the impact of imperfect channel estimation on the overall spectral efficiency is also included. Numerical results reveal that the cyclic prefix based CFO technique is more efficient than the training symbols based CFO technique when perfect channel state information (CSI) is known blindly at the receiver. Furthermore, fixed pilot power results in a spectral efficiency ceiling as SNR increases, whereas spectral efficiency increases with SNR without bound in the equal pilot and signal powers case.Index Terms-Orthogonal frequency division multiplexing (OFDM), signal to interference plus noise ratio (SINR), intercarrier interference (ICI), carrier frequency offset (CFO), multipath fading channels, spectral efficiency. 0090-6778

Accurate channel state information (CSI) is essential at the base station (BS) in order to serve multiple users simultaneously on the same time-frequency resources. Explicit low-rate CSI feedback from each user terminal to the BS is indispensable in frequency-division duplexing (FDD) multipleinput multiple-output (MIMO) hybrid precoding systems. In the presence of correlated Rician fading channels with arbitrary rank, and in order to reduce the feedback overhead, a unified adaptive statistical codebook is designed by leveraging the long-term first and second order channel statistics. Moreover, as the feedback overhead scales linearly with the number of BS antennas, which introduces a bottleneck in FDD massive MIMO systems, an adaptive two-stage reduced dimensionality codebook design is developed. The main idea stems from the fact that the high dimensional analog beamforming stage could get away with coarse CSI, e.g., statistical CSI, while the low dimensional baseband precoding stage acquires finite-rate quantized CSI of the reduced dimensionality channel to eliminate multiuser interference. These steps reduce significantly the CSI training and feedback overhead to scale linearly with the number of radio-frequency chains instead. For comparison purposes, the two extremes of full and statistical CSI at the BS are also included. The performance gap between these two extremes justifies the importance of the proposed two-stage reduced dimensionality adaptive statistical codebook.