Best-relay Selection Scheme Research Articles

Performance Analysis of Dual-Hop AF Cognitive Relay Networks with Best Selection and Interference Constraints

In this paper, a dual-hop underlay cognitive relay network (CRN) with a best-relay selection (BRS) scheme under spectrum-sharing constraints from the primary user (PU) is investigated. The system model in this work consists of one PU, one secondary user (SU) and a few SU relays. Both users exchange the information using a half-duplex mode through amplify-and-forward (AF) SU relays. Moreover, all channels are modelled using the Nakagami-m fading model. In this work, the outage probabilities (OPs) are derived for the proposed system model under several scenarios to investigate the network performance under interference power constraint Ip at the PU receiver. In addition, the impacts of the number of relays and the channel fading severity parameters are investigated as well. Furthermore, the system performance is investigated for several PU locations. The various numerical results are verified using a Monte Carlo simulation. Overall, the obtained results show that several factors such as the number of relays, channel fading severity parameters and PU location have a major impact on the outage performance of the SU. The simulation and analytical results are perfectly matched, confirming the accuracy of the analytical derivations.

Security Performance Analysis for Best Relay Selection in Energy-Harvesting Cooperative Communication Networks

In this paper, we investigate an energy-harvesting cooperative communication network, which comprises of a source, a destination, and multiple decode-and-forward (DF) relays in the presence of multiple passive eavesdropper (Es). Es attempt to intercept confidential information transmissions from the source to destination via DF relays. In this network, all the DF relays harvest energy from radio-frequency (RF) signals of a source through time-switching receivers. In order to improve the physical layer security of energy-harvesting cooperative communication networks, we propose a best relay selection (BRS) scheme, where the “best” relay is chosen to assist the source-destination transmission. For the purpose of comparison, we consider the classic direct transmission (DT) and equal relay selection (ERS) as benchmark schemes. We derive the exact closed-form expressions of outage probability (OP) and intercept probability (IP) for the ERS and BRS schemes over Rayleigh fading channels. Besides, the security-reliability tradeoff (SRT) is analyzed as a metric to evaluate the tradeoff performance of the proposed BRS scheme. Numerical results show that the SRT of the BRS scheme consistently outperforms that of the ERS scheme, which demonstrates the advantage of our proposed scheme against eavesdroppers. Besides, it is verified that total error rate (TER) defined as the sum of OP and IP can be minimized for both the ERS and BRS schemes through changing the time allocation factor between information transmission and energy harvesting phases. Moreover, there is a best energy conversation efficiency to obtain a maximal SRT value of the ERS and BRS schemes. In addition, as the number of DF relays increases, the SRT of BRS scheme improves notably, while that of ERS scheme remains unchanged. And as the number of Es increases, the SRT of both the ERS and BRS schemes become worse.

Relay Selection for Improved Physical Layer Security in Cognitive Relay Networks Using Artificial Noise

In this paper, the physical layer security of underlay cognitive decode-and-forward (DF) relay networks is investigated, wherein one secondary transmitter (ST) exchanges confidential information with one secondary destination with the assistance of multiple cognitive DF relays by sharing the licensed spectrum of an primary user, and the relayed transmission is intercepted by multiple passive eavesdroppers. To provide security guarantee for secondary transmission, we propose a novel cooperative scheme aided by artificial noise. In the absence of the eavesdroppers’ channel state information (CSI), two opportunistic relay selection schemes, namely best relay selection (BRS) and conventional relay selection (CRS), are proposed as an incentive to further enhance the physical layer security. To be specific, only the CSI of the main channel is employed in the CRS scheme, whereas the BRS scheme invokes both the CSI of the main channel and interference channel. We address the secrecy performance in terms of secrecy outage probability, for which the closed-form expressions for both the relay selection schemes are derived. Simulation results are provided to verify our analysis and show that the proposed BRS scheme significantly achieves a better secrecy outage performance compared with the CRS scheme as well as the conventional scheme without jamming.

Secrecy outage analysis and power allocation for decode‐and‐forward relay systems

The decode-and-forward multi-relay system with the presence of an eavesdropper is researched in this study. Two widely used transmission schemes are considered, namely, the best-relay selection scheme and the all-relay-based beamforming scheme. To be specific, the former scheme adopts only the single best relay among all the candidate relays that have succeeded in decoding the source signal to assist the transmission, whereas the all-relay-based beamforming scheme allows all the candidates to assist the source simultaneously in a beamforming manner. The authors reveal that in both schemes, if the total transmit power of the two hops is constrained, contradiction exists between the two means of improving physical-layer security: (i) letting more relays succeed in decoding the source signal; (ii) increasing the transmit power of the selected relay(s). The authors thus analyse the secrecy outage behaviour of the two schemes and derive expressions of secrecy outage probability (SOP), based on which, the optimal power allocation solutions are obtained. It is demonstrated that in both schemes, the analysis results match well with the simulation results. Moreover, the proposed power allocation solutions surpass the conventional average power solution in SOP in both schemes.

Performance analysis of QAM in amplify-and-forward cooperative communication networks over Rayleigh fading channels

Performance analysis of quadrature amplitude modulation (QAM) schemes for cooperative amplify-and-forward (AF) dual-hop relaying system over independent and identically distributed (i.i.d.) Rayleigh fading channels are presented in this paper. Specifically, we derive closed-form lower-bound expressions of average symbol error rate (ASER) for general order rectangular QAM (RQAM) and cross QAM (XQAM) using well-known moment generating function (MGF) based approach with maximal ratio combining (MRC) scheme. Further, using best relay selection scheme (BRS), we also derive an ASER expression for XQAM. Numerical and simulated results are compared to validate the correctness of derived expressions. Furthermore, comparative analysis of RQAM and XQAM schemes is discussed which confirms that XQAM is better alternative over RQAM for transmission of odd number of bits per symbol for the considered system model. We also compare the ASER performance for MRC and BRS schemes in terms of SNR gain using different XQAM constellations. Moreover, the impact of system parameters on ASER is also highlighted.

Outage Performance of Hybrid Decode–Amplify–Forward Protocol with the nth Best Relay Selection

In this paper, we consider the Hybrid Decode---Amplify---Forward protocol with the $$n$$ n th best-relay selection scheme. In the best-relay selection scheme, the best relay only forwards the sourc...

On the Study of Outage Performance for Cognitive Relay Networks (CRN) with the Nth Best-Relay Selection in Rayleigh-fading Channels

Relay selection is an effective way to achieve considerable performance gains in cognitive relay networks (CRN). In practice, the best relay may not always be selected, thus the study of the small Nth best relay selection will be very beneficial for CRN design. In this paper, performance analysis for underlay cognitive decode-and-forward relay networks with the small Nth best-relay selection scheme is studied over independent and identically distributed (i.i.d.) Rayleigh fading channels. Closed-form expression for the exact outage probability is derived, which can be used to evaluate the impact of the relay selection scheme, the number of relays, the interference power constraint and the transmit power limit on the outage performance. The theoretical analysis is validated by Monte-Carlo simulations. The results show that both the relay selection scheme and the number of relays have great impact on the outage performance of cognitive relay networks.

Decode-and-Forward Relaying Systems with NthBest-Relay Selection over Rayleigh Fading Channels

In this paper, we evaluate performances of dual-hop decode-and-forward relaying systems with the <TEX>$N^{th}$</TEX> best-relay selection scheme. In some schemes, such as scheduling or load balancing schemes, the best relay is unavailable and hence the system must resort the second best, third best, or generally the <TEX>$N^{th}$</TEX> best relay. We derive the expressions of the outage probability and symbol error rate (SER) for this scenario over Rayleigh fading channels. Monte-Carlo simulations are presented to verify the analytical results.

Performance analysis of selective cooperation in amplify‐and‐forward relay networks over identical Nakagami‐m channels

ABSTRACTIn cooperative communications, multiple relays between a source and a destination can increase the diversity gain. Because all the nodes must use orthogonal channels, multiple‐relay cooperation becomes spectrally inefficient. Therefore, a bestrelay selection scheme was recently proposed. In this paper, we analyzed the performance of this scheme for a system with the relays operating in amplify‐and‐forward mode over identical Nakagami‐m channels using an exact source–relay–destination signal‐to‐noise ratio (SNR).We derived accurate closed‐form expressions for various system parameters including the probability density function of end‐to‐end SNR, the average output SNR, the bit error probability, and the channel capacity. The analytical results were verified through Monte Carlo simulations. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Performance of Amplify-and-Forward Cooperative Communications with the N^{th} Best-Relay Selection Scheme over Nakagami-m Fading Channels

This letter derives the asymptotic symbol error rate (SER) of amplify-and-forward (AF) cooperative communications with the Nth best-relay scheme over independent and non-identical Nakagami-m fading channels. The diversity gain has been analyzed and examined as well. Simulation and numerical evaluation show the tightness of such an approximation in the high SNR regions and the accuracy of our theoretical analysis.

On the Performance of Cooperative-Diversity Networks with the Nth Best-Relay Selection Scheme

In this letter, we consider the adaptive decode-and-forward (DF) and amplify-and-forward (AF) cooperative-diversity systems with the N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> best-relay selection scheme. In the best-relay selection scheme, from the set of M relays the best relay only forwards the source signal to the destination. However, the best relay might be unavailable; hence we might resort to the second, third or generally the Nth best relay. We derive closed-form expressions for the symbol error probability, outage probability and asymptotic error probability. In particular, we derive a closed-form expression for the probability density function (PDF) of the signal-to-noise ratio (SNR) of the relayed signal at the destination node. Then, we find a closed-form expression for the moment generating function (MGF) of the output SNR at the destination. This MGF is used to derive the closed-form expressions of the performance metrics. All these expressions are derived over identical and non-identical Rayleigh fading channels. Results show that with the N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> best relay the diversity order is equal to (M - N + 2) where M is the number of relays.

A Relay Selection Based on Eigenvalue Decomposition for Cooperative Communications in Indoor Ubiquitous Sensor Networks

A new best-relay selection scheme is proposed in this letter in order to maintain a reliable cooperative communications for ubiquitous sensor networks in indoor environments. The suggested technique relies on eigenvalue decomposition to select the best relay. The simulation results confirm that the performance of the proposed approach is better than that of the previous scheme in indoor environments.

Performance analysis of adaptive decode-and-forward cooperative diversity networks with best-relay selection

Cooperative diversity is a relatively new technique that can be used to improve the performance of the wireless networks. The main advantage of this technique is that the diversity gain can be achieved without the need to install multiple antennas at the transmitter or the receiver. In this paper, we investigate the performance of the best-relay selection scheme where the "best" relay only participates in the relaying. Therefore, two channels only are needed in this case (one for the direct link and the other one for the best indirect link) regardless of the number of relays (M). The best relay is selected as the relay node that can achieve the highest signal-to-noise ratio at the destination node. A general mathematical probability model is developed to study the outage performance of the best-relay selection adaptive decode-and-forward cooperative networks. In particular, closed-form expressions for the outage probability and average channel capacity are derived. Results show that the best-relay selection not only reduces the amount of required resources but also can maintain a full diversity order.

Exact Error Probability and Channel Capacity of the Best-Relay Cooperative-Diversity Networks

Cooperative diversity networks have recently been proposed as a way to form virtual antenna arrays without using collocated multiple antennas. In this paper, we consider adaptive decode-and-forward cooperative diversity system where a source node communicates with a destination node directly and indirectly (through multiple relays). In this letter, we investigate the performance of the best-relay selection scheme where the best relay only participates in the relaying. Therefore, two channels only are needed in this case (one for the direct link and the other one for the best indirect link) regardless of the total number of relays. The best relay is selected as the relay node that can achieve the highest signal-to-noise ratio at the destination node. We developed a general analytical model to analyze the performance of the adaptive decode-and-forward cooperative networks with best-relay selection. In particular, exact closed-form expressions for the error probability and Shannon capacity are derived over independent and nonidentical Rayleigh fading channels. Results show that the best-relay selection not only reduces the number of required channels but also can maintain a full diversity order.

Performance of Multiple-Relay Cooperative Diversity Systems with Best Relay Selection over Rayleigh Fading Channels

We consider an amplify-and-forward (AF) cooperative diversity system where a source node communicates with a destination node directly and indirectly (through multiple relays). In regular multiple-relay cooperative diversity systems, all relay nodes relay the source signal using orthogonal channels (time slots, carriers, or codes) to avoid cochannel interference. Hence, for a regular cooperative diversity network with M relays, we need M+1 channels (one for the direct link and M for the M indirect links). This means that the number of required channels increases linearly with the number of relays. In this paper, we investigate the performance of the best-relay selection scheme where the "best" relay only participates in the relaying. Therefore, two channels only are needed in this case (one for the direct link and the other one for the best indirect link) regardless of the number of relays (M). The best relay is selected as the relay node that can achieve the highest signal-to-noise ratio (SNR) at the destination node. We show that the best-relay selection not only reduces the amount of required resources but also maintains a full diversity order (which is achievable by the regular multiple-relay cooperative diversity system but with much more amount of resources). We derive closed form expressions for tight lower bounds of the symbol error probability and outage probability. Since it is hard to find a closed-form expression for the probability density function (PDF) of SNR of the relayed signal at the destination node, we use an approximate value instead. Then, we find a closed-form expression for the moment generating function (MGF) of the total SNR at the destination. This MGF is used to derive the closed-form expressions of the performance metrics such as the average symbol error probability, the outage probability, the average SNR, the amount of fading, and the SNR moments. Furthermore, we derive the asymptotic behavior of the symbol error probability. From this asymptotic behavior, the diversity order and its dependence on the number of relays (M) can be explicitly determined. Simulation results are also given to verify the analytical results.