Ahmed M. Almradi

Ergodic Capacity Analysis of MIMO Full Duplex Relaying with Imperfect CSI

In this paper, with the aid of new analytical method, we present a new closed-form expression for the ergodic capacity of full-duplex relaying (FDR) systems, with multiple antenna amplify-and-forward (AF) cooperative networks and imperfect channel state information (CSI). At the relay, the loopback self-interfernce (LI) is mitigated by using receive zero-forcing (ZF) precoding scheme, then steering the signal to the destination by using the maximum-ratio transmission (MRT) technique. To facilitate comparison, a closed-form expression for the ergodic capacity of half-duplex relaying (HDR) systems with multiple antenna AF cooperative networks is also addressed, when maximum-ratio combining (MRC)/MRT precoding schemes are performed at the relay input/output, respectively. Therefore, since perfect CSI is not available in practice, this paper investigates the impact of channel estimation errors on the performance of receive ZF/MRT and MRC/MRT schemes. These expressions are exact in the case of perfect CSI and form a very tight indistinguishable lower-bound in the case of imperfect CSI. Numerical results sustained by Monte-Carlo simulations show the exactness of the proposed analytical expressions in perfect CSI and the tightness of the lower-bounds in imperfect CSI. In addition, it is seen here that the FDR AF cooperative systems outperforms the HDR AF cooperative systems in terms of capacity. Furthermore, in contrast to perfect CSI, in the presence of imperfect CSI, an ergodic capacity ceiling is seen as SNR increases. Besides, it is seen that the ergodic capacity degradation due to imperfect CSI is higher in the FDR case because of the extra LI estimation errors.

Spectral Efficiency of OFDM Systems With Random Residual CFO

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.

Ergodic capacity analysis of correlated MIMO full-duplex relaying

This paper analyzes the performance of full-duplex (FD) relaying with multiple-antenna amplify-and-forward (AF) relay. The system performance due to practical wireless transmission impairments of spatial fading correlation, cross-correlation due to correlated links is investigated. To this end, new exact closed-form expressions for the ergodic capacity are derived in the case of arbitrary correlations for both, the spatial and cross correlations. 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 the maximum-ratio transmission (MRT) technique. Numerical results sustained by Monte Carlo simulations show the exactness of the proposed closed-form analytical expressions. In addition, it is seen that the ergodic capacity performance of FD relaying systems outperforms that of half-duplex (HD) relaying systems. Furthermore, the system performance insights reveal the negative and positive impact of the spatial and cross correlation on the ergodic capacity performance, respectively. Surprisingly therefore, an improvement in the ergodic capacity is seen as the cross-correlation between the two links increases. As a result, the ergodic capacity is not maximized by independent links as fully correlated links with uncorrelated spatial correlation results in the maximum ergodic capacity.

The performance of wireless powered MIMO relaying systems with energy beamforming

This paper analyzes the performance of energy beamforming in multiple-input multiple-output (MIMO) relaying systems, where the source and destination nodes are equipped with multiple antennas and communicating via a dual-hop amplify-and-forward (AF) single antenna energy-constrained relay, and the destination is subject to co-channel interference (CCI). The wirelessly powered relay scavenge energy from the source information radio-frequency (RF) signal through energy beamforming, using the time-switching receiver, and 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 of the considered system are presented in closed-form, through which the throughput of the delay-constrained and delay-tolerant transmission is investigated, respectively. Numerical results sustained by Monte Carlo simulations show the tightness of the proposed analytical expressions. The impact of various parameters such as the energy harvesting time, source transmit power and the number of antennas on the system throughput is also considered. It is seen that the system throughput increases as the number of antenna and/or the source transmit power increases. In addition, energy beamforming increases the harvested energy and hence reduces the optimal energy harvesting ratio, as a result, more time is left for information transmission.

On the Performance of MIMO Full-Duplex Relaying in the Presence of Co-Channel Interference

This paper studies the deployment of multiple- input multiple-output (MIMO) full-duplex (FD) relaying systems in a multi-cell environment, where a multi-antenna amplify-and-forward (AF) FD relay station serves multiple half-duplex (HD) multi-antenna users. The fundamental challenges of loopback self-interference (LI) and multiple co-channel interferers (CCI) at the relay and destination when incorporating FD relaying in cellular systems are addressed. Due to the higher frequency reuse in FD relaying compared to its HD relaying counterpart, the number of CCI is expected to double as the FD relay station simultaneously schedule uplink and downlink transmission on the same channel. In this paper, the optimal design of transmit/receive precoding/decoding weight vectors which maximizes the overall signal-to- interefernce-plus-noise ratio (SINR) is formulated by a proper optimization problem, then a closed-form sub-optimal solution is proposed. The proposed hop-by-hop zero-forcing (ZF) beamforming vectors are based on added ZF constraints used to suppress the LI and CCI channels at the relay and destination. To this end, new exact expressions for the outage probability and ergodic capacity are derived in closed-form. Numerical results sustained by Monte-Carlo simulations show the exactness of the proposed analytical expressions. In addition, our results show that while multi- antenna terminals improve the system performance, the detrimental effect of the number of interferers on FD relaying is clearly seen. Furthermore, our findings reveal that MIMO FD relaying could substantially boost the system performance compared to its conventional MIMO HD relaying counterpart.

The Performance of Wireless Powered MIMO Relaying With Energy Beamforming

This paper analyzes the performance of energy-constrained dual-hop amplify-and-forward relaying systems with multi-antenna nodes in the presence of multiple co-channel interferers at the destination. To maximize the overall signal-to-interference-plus-noise ratio, 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 scavenges energy from the source information radio frequency signal through energy beamforming, where both the time-switching receiver and power-splitting receiver are considered, and 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 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.

Outage probability of spatially correlated MIMO full-duplex relaying with imperfect CSI

This paper analyzes the performance of full-duplex relaying (FDR) with multiple-antenna amplify-and-forward (AF) relay. The system performance due to practical wireless transmission impairments of spatial fading correlation and imperfect channel state information (CSI) is investigated. 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-bounds are also included. 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 the maximumratio transmission (MRT) technique. Numerical results sustained by Monte Carlo simulations show the exactness and tightness of the proposed exact closed-form and lower-bound expressions, respectively. In addition, it is seen that the outage probability performance of FD relaying outperforms that of HD relaying at low to medium signal-to-noise ratio (SNR). Furthermore, in the presence of channel estimation errors, an outage probability error floor is seen as SNR increases.

Information and Energy Beamforming in MIMO Wireless Powered Systems

This paper analyzes the performance of information and energy beamforming in multiple-input multiple- output (MIMO) wireless communications systems, where a self-powered multi-antenna hybrid access point (AP) coordinates wireless information and power transfer (WIPT) with an energy-constrained multi-antenna user terminal (UT). The wirelessly powered UT scavenge energy from the hybrid AP radio-frequency (RF) signal in the downlink (DL) using the harvest-then-transmit protocol, then uses the harvested energy to send its information to the hybrid AP in the uplink (UL). To maximize the overall signal-to-noise ratio (SNR) as well as the harvested energy so as to mitigate the severe effects of fading and enable long-distance wireless power transfer, information and energy beamforming is investigated by steering the transmitted information and energy signals along the strongest eigenmode. To this end, exact and lower-bound expressions for the outage probability and ergodic capacity are presented in closed-form, through which the throughput of the delay- constrained and delay-tolerant transmission modes are analyzed, respectively. Numerical results sustained by Monte Carlo simulations show the exactness and tightness of the proposed analytical expressions. The impact of various parameters such as energy harvesting time, hybrid AP transmit power and the number of antennas on the system throughput is also considered.

DA and NDA SINR estimation in non Gaussian noise

In this paper, the problem of signal-to-interference plus noise ratio estimation over flat fading channels in non-Gaussian noise is addressed. Most previously published estimators assume the additive noise to be Gaussian. These estimation algorithms performs significantly worse when the additive noise is non-Gaussian. The additive non-Gaussian noise is modeled by a mixture of Gaussians distribution. Both data aided (DA) and non data aided (NDA) estimators are studied. The second and forth order moment based (M2M4) estimator is derived. Besides, the expectation maximization (EM) algorithm is proposed to iteratively estimate the maximum likelihood (ML) signal to interference plus noise ratio (SINR) estimate for both DA and NDA cases. The performance of the proposed estimators are compared in terms of their mean square error (MSE). Simulation results show remarkable performance improvements of the DA and NDA EM based ML SINR estimator over the M2M4 moment based estimator. Besides, it reveals the degradation in accuracy due to the impulsive noise components over Additive white Gaussian noise (AWGN).

Wireless Powered Spatially Correlated MIMO AF Relaying Systems with Energy Beamforming

This paper analyzes the performance of energy beamforming in spatially correlated multiple-input multiple-output (MIMO) relaying systems, where the source and destination nodes are equipped with multiple spatially correlated antennas and communicating via a dual-hop amplify-and-forward (AF) single antenna energy-constrained relay. To maximize the overall harvested energy so as to enable long-distance wireless power transfer, the wirelessly powered relay scavenge energy from the source radio-frequency (RF) signal through energy beamforming, then uses the harvested energy to forward the source message to the destination. To facilitate wireless information and power transfer at the relay, time-switching receiver (TSR) protocol is considered. To this end, tight lower and upper bound expressions for the outage probability and ergodic capacity are derived in closed-form, through which the throughput of the delay-constrained and delay-tolerant transmission modes are investigated, respectively. Numerical results sustained by Monte Carlo simulations show the tightness of the proposed analytical expressions. The impact of various parameters such as energy harvesting ratio, source transmit power, number of antennas and spatial fading correlation on the system throughput is also considered.