Fawaz S. Al-Qahtani

Performance Analysis of Dual-Hop AF Systems With Interference in Nakagami-

In this letter, we investigate the performance of dual-hop channel state information-assisted amplify-and-forward relaying systems over Nakagami-m fading channels in the presence of multiple interferers at the relay. Assuming integer fading parameter m, we derive closed-form expressions for the exact outage probability and accurate approximation for symbol error rate of the system. Furthermore, we look into the asymptotical high signal to noise ratio regime, and characterize the diversity order achieved by the system. All the analytical results are validated via Monte Carlo simulations.

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In this paper, we present a comprehensive investigation on the secrecy performance of opportunistic relay selection systems employing the decode-and-forward protocol over Rayleigh fading channels. Considering a practical setting where direct link between the source node (Alice) and the destination node (Bob) is available, we study the secrecy performance of three different diversity combining schemes, namely, maximum ratio combining (MRC), distributed selection combining (DSC), and distributed switch-and-stay combining (DSSC). Throughout the analysis, we consider two different scenarios based on the availability of the eavesdroppers channel state information (CSI), i.e., Scenario A, where the eavesdroppers CSI is not available at Alice and the relay, and Scenario B, where Alice and the relay have knowledge about the eavesdroppers CSI. For Scenario A, we derive exact closed-form expressions for secrecy outage probability and simple asymptotic approximations for the secrecy outage probability, which enable the characterization of the achievable secrecy diversity order and coding gains. For Scenario B, we derive closed-form expressions for the achievable secrecy rates. For both scenarios, we investigate the impact of feedback delay (outdated CSI) on the secrecy performance wherein exact and asymptotic secrecy outage probability and closed-form expressions of the secrecy achievable rates are obtained. Our analytical findings suggest that both the MRC and DSC schemes achieve the maximum diversity order of K+1 where K is the number of relays. In addition, the feedback delay has a significant impact on the achievable secrecy performance by reducing the achievable diversity order to two.

Fading Channels

This paper presents a comprehensive performance analysis of multiuser multiple antenna amplify-and-forward relaying networks employing opportunistic scheduling with feedback delay and co-channel interference over Rayleigh fading channels. Specifically, we derive exact as well as approximate closed-form expressions for the outage probability and average symbol error rate (SER) of the system. In addition, simple asymptotic expressions at the high signal-to-noise ratio (SNR) regime are obtained, which facilitate the characterization of the achievable diversity order and coding gain of the system. Moreover, two novel ergodic capacity bounds valid for general systems with arbitrary number of antennas and users are proposed. Finally, the optimum power allocation scheme in terms of minimizing the average SER is studied, and simple analytical solutions are obtained. Simulation results are provided to corroborate the derived analytical expressions, and it is demonstrated that the ergodic capacity bounds remain sufficiently tight across the entire range of SNRs and the proposed power allocation scheme offers significant improvements on the SER performance. The findings of the paper suggest that the full diversity order can only be achieved when there is ideal feedback, i.e., no feedback delay, and the diversity order always reduces to one in the presence of feedback delay. Also, the impact of key parameters such as the number of antennas and users on the system performance is intimately dependent on the level of feedback delay.

Opportunistic Relay Selection for Secrecy Enhancement in Cooperative Networks

In this paper, we propose general-order transmit antenna selection to enhance the secrecy performance of multiple-input-multiple-output multieavesdropper channels with outdated channel state information (CSI) at the transmitter. To evaluate the effect of the outdated CSI on the secure transmission of the system, we investigate the secrecy performance for two practical scenarios, i.e., Scenarios I and II, where the eavesdroppers CSI is not available at the transmitter and is available at the transmitter, respectively. For Scenario I, we derive exact and asymptotic closed-form expressions for the secrecy outage probability in Nakagami-m fading channels. In addition, we also derive the probability of nonzero secrecy capacity and the ε-outage secrecy capacity, respectively. Simple asymptotic expressions for the secrecy outage probability reveal that the secrecy diversity order is reduced when the CSI is outdated at the transmitter, and it is independent of the number of antennas at each eavesdropper NE, the fading parameter of the eavesdroppers channel mE, and the number of eavesdroppers M. For Scenario II, we make a comprehensive analysis of the average secrecy capacity obtained by the system. Specifically, new closed-form expressions for the exact and asymptotic average secrecy capacity are derived, which are valid for general systems with an arbitrary number of antennas, number of eavesdroppers, and fading severity parameters. Resorting to these results, we also determine a high signal-to-noise ratio power offset to explicitly quantify the impact of the main channel and the eavesdroppers channel on the average secrecy capacity.

Performance Analysis of Multiuser Multiple Antenna Relaying Networks with Co-Channel Interference and Feedback Delay

In this paper, we propose transmit antenna selection with maximal ratio combining (TAS/MRC) in dual-hop decode-and-forward spectrum-sharing relaying networks with the primary users interference and outdated channel state information (CSI). In this network, a single antenna that maximizes the received SNR is selected at the secondary transmitter, and the MRC is adopted at the secondary receiver. To efficiently evaluate the impact of key parameters on the system performance, we derive the exact analytical expression for the outage probability of the secondary network in a Rayleigh fading channel. Moreover, we present simple asymptotic expressions for the outage probability in a high SNR regime, which reveal practical insights on the achievable diversity order and coding gain. The findings suggest that whether the outdated CSI concerning the secondary transmission links has significant impact on the outage probability of the system depends on the interference power constraint at primary receivers. Specifically, under the proportional interference power constraint, the achievable diversity order is affected by imperfect CSI regarding the secondary transmission links, and the diversity-multiplexing tradeoff is independent of the primary network. However, under the fixed interference power constraint, the error floor is displayed, and the achievable diversity order reduces to zero regardless of the CSI concerning the secondary transmission links.

Secure Transmission in MIMO Wiretap Channels Using General-Order Transmit Antenna Selection With Outdated CSI

Adaptive modulation can improve the performance of OFDM systems significantly. In Power Line Communication systems, impulsive noise has to be considered due to its severe effect in the system performance. This paper deals with the effect of impulsive noise in adaptive power loading in OFDM-based PLC systems. We present a simple power loading algorithm with uniform bit allocation and nonuniform BER distribution and test it by means of computer simulations in a widely-accepted power line channel model impaired with impulsive noise. Closed form expressions for BER and power allocation in the presence of impulsive noise are presented. Simulation results show that the proposed algorithm can achieve a considerable improvement over conventional OFDM with uniform power allocation.

Cognitive MIMO Relaying Networks With Primary User's Interference and Outdated Channel State Information

This letter investigates the outage behavior of a dual-hop N^{th}-best decode-and-forward (DF) relay system in which the relay and the destination undergo independent sources of co-channel interference (CCI). The fading envelopes associated with the desired and interfering users are assumed to follow independent but non-identically distributed (i.n.d.) Rayleigh fading models. Through the analysis, exact and approximate outage probability are derived based on which the diversity order and coding gain are obtained. Our findings suggest that the diversity order linearly increases with the number of relays and decreases with the order of the relay. Furthermore, results reveal that the system is still able to achieve full diversity gain in the presence of finite number of interferers with finite powers. The analytical results are supported and validated by Monte-Carlo simulations.

Adaptive power loading for OFDM-based power line communications impaired by impulsive noise

The performance of a dual-hop amplify-and forward relay system is analyzed in terms of outage probability and average symbol error rate. The source-relay and relay-destination channels experience mixed fading distributions namely, Rician and Nakagami-m. Analytical expressions for Cumulative Distribution Function (CDF) and Probability Density Function (PDF) of end-end signal-to-noise-ratio (SNR) are derived and confirmed with Monte-Carlo simulation. Approximate lower bound for outage probability is also derived, which becomes tight at high SNR values. The expressions are given in terms of infinite sum series of modified Bessel function, which converges after finite iterations. The derived expressions are valid for different fading scenarios (depending on m factor), and specialize to previously published results for m = 1.

Outage Analysis of N^{th}-Best DF Relay Systems in the Presence of CCI over Rayleigh Fading Channels

In this paper, we investigate the impact of multiuser diversity on the performance of secondary users (SUs) in dual-hop decode-and-forward (DF) spectrum sharing systems over Nakagami-

Performance analysis of amplify-forward relay in mixed Nakagami-m and Rician fading channels

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