Single Relay Selection Scheme Research Articles

N – R th dual best relays opportunistic cooperation schemes and performance analyses over Nakagami‐ m fading channels

To overcome the performance loss caused by the N th single best relay selection schemes, in this study, the authors present the N-R th dual best relays selection schemes. In the proposed schemes, there are two relays selected out of the available relays to forward the received signals to the destination by using the decode-and-forward protocol. The statistical descriptions of instantaneous end-to-end received signal-to-noise ratios (SNR) are investigated over independent and non-identically distributed Nakagami- m fading channels. By using the appropriate mathematical proof, the authors firstly obtain the closed-form expressions to the probability density function and cumulative distribution function of instantaneous end-to-end SNR. Then, based on the derived results, the outage probability and average symbol error rate (SER) of the proposed N-R th dual best relays selection schemes are investigated. The comparison analyses between the N th schemes and the N-R th schemes show that the proposed N-R th dual best relays selection schemes can improve greatly the performance of opportunistic relaying systems such as outage probability and average SER. Especially, the proposed dual best relays selection scheme can obtain more outstanding improvement on SER.

Two- and four-relay selection schemes for application in interference limited legacy networks

The limiting effect of multi-user interference from an adjacent cell upon the relays used for cooperative transmission is considered in the context of legacy networks which adopt max(min(·,·)) type relay selection policies. We extend previous work which considered single relay selection to the selection of two or four such relays, as is required in distributed space–time coding. We obtain new analytical expressions for outage probability over Rayleigh frequency flat fading channels for two signal-to-noise ratio regimes. We confirm by simulation that such a relay selection scheme has robustness to relay selection feedback error and outperforms a single relay selection scheme.

Two-Way Amplify-and-Forward Relaying with Gaussian Imperfect Channel Estimations

In this letter, we study the effect of channel estimation errors on the reception reliability of two-way relaying. For a network with two users that exchange information with each other through multiple amplify-and-forward relays, we investigate a single-relay selection scheme. Since the communication is two-way, the selection scheme aims at optimizing the worse performance of the two communication tasks between the pair of users. The signal-to-noise ratio (SNR) at the users' nodes of the relaying network is formulated and upper bounded. Then, the probability density function (PDF) of the upper bounded SNRs are determined. Subsequently, expressions for the error probabilities are obtained. Furthermore, an approximate PDF of the output instantaneous SNRs are derived, based on which simple and general asymptotic expressions for the error probabilities are presented and discussed. Numerical and simulation results are provided to verify the analysis and compare the performance of the two-way relaying network for different operating conditions and scenarios.

Opportunistic Multiple Relay Selection With Outdated Channel State Information

The quality of channel state information (CSI) plays a significant role in the performance of relay selection (RS) schemes in cooperative communications. Particularly in a highly mobile environment when there exists delay between the selection and data transmission instants, the quality of CSI often degrades, given to what is known as outdated CSI phenomena. In this paper, we first outline several single RS schemes that achieve full diversity when using perfect CSI and prove that the diversity order of these schemes reduces to unity if outdated CSI exists. To deal with the performance deterioration due to the outdated CSI phenomena, we propose a new multiple RS scheme for both amplify-and-forward (AaF) and decode-and-forward (DaF) relay systems, namely, the plus normalized threshold opportunistic RS . In particular, we first opportunistically select best relays from all candidate relays with respect to end-to-end signal-to-noise ratios (SNRs) for AaF and relay-to-destination SNRs for DaF. Then, the ratios of the SNRs on the rest of the candidate relays to that of the th highest SNR are tested against a normalized threshold , and only those relays passing this test are selected in addition to the best relays. The performance of the scheme is theoretically analyzed in terms of outage probability, and its asymptotic diversity order is also examined. In addition, we outline a distributed selection protocol that makes no assumption of the global CSI at each relay. Numerical results confirm the analysis and show the advantage of the proposed scheme against existing counterparts in highly dynamic networks.

Impact of Channel Estimation Error on the Performance of Amplify-and-Forward Two-Way Relaying

In this paper, the impact of channel-state information (CSI) estimation error on the performance of an amplify-and-forward two-way multiple relay network has been investigated. In contrast to the existing literature, which assumes perfect self-interference cancellation, we consider imperfect self-interference cancellation at both sources that exchange information through multiple relays, and maximal-ratio combining is then applied to improve the decision statistics under imperfect signal detection. We derive the effective signal-to-noise ratio (SNR) subject to noisy channel estimation, and based on this SNR, the system outage probability is given. In addition, we derive the closed-form expression of the average system bit error rate (BER) and the asymptotic expressions for both outage probability and BER. Furthermore, instead of employing all relays, we examine the impact of imperfect CSI on a single relay selection (RS) scheme. To mitigate the negative impact of imperfect CSI, we show that power allocation (PA), by minimizing either the outage probability or the BER, can suitably be cast as the geometric-programming problem. Numerical results validate the correctness of the derived expressions and show that the adaptive-PA scheme outperforms the equal-PA scheme under the aggregated effect of imperfect CSI.

Single Relay Selection for Bidirectional Cooperative Networks with Physical-Layer Network Coding

To serve the growing demand of the bidirectional information exchange, we propose a single relay selection (RS) scheme for physical-layer network coding (PNC) in a bidirectional cooperative network consisting of two sources and multiple relays. This RS scheme selects a single best relay by maximizing the bottleneck of the capacity region of both information flows in the bidirectional network. We show that the proposed RS rule minimizes the outage probability and that it can be used as a performance benchmark for any RS rules with PNC. We derive a closed-form exact expression of the outage probability for the proposed RS rule and show that it achieves full diversity gain. Finally, numerical results demonstrate the validity of our analysis.

Single Relay Selection for Bidirectional Cooperative Networks with Physical-Layer Network Coding

To serve the growing demand of the bidirectional information exchange, we propose a single relay selection (RS) scheme for physical-layer network coding (PNC) in a bidirectional cooperative network consisting of two sources and multiple relays. This RS scheme selects a single best relay by maximizing the bottleneck of the capacity region of both information flows in the bidirectional network. We show that the proposed RS rule minimizes the outage probability and that it can be used as a performance benchmark for any RS rules with PNC. We derive a closed-form exact expression of the outage probability for the proposed RS rule and show that it achieves full diversity gain. Finally, numerical results demonstrate the validity of our analysis.

Optimal energy-efficient scheme for two-way relay channel using physical layer network coding

Systems are always designed and optimized based on full traffic load in the current literatures. However, practical systems are seldom operating at full load, even at peak traffic hours. Instead of maximizing system rate to achieve the full load, an optimal energy-efficient scheme to minimize the transmit power with required rates is investigated in this article. The considered scenario is a two-way relay channel using amplify-and-forward protocol of physical layer network coding, where two end nodes exchange messages via multiple relay nodes within two timeslots. A joint power allocation and relay selection scheme is designed to achieve the minimum transmit power. Through convex optimization theory, we firstly prove that single relay selection scheme is the most energy-efficient way for physical layer network coding. The closed-form expressions of power allocation are also given. Numerical simulations demonstrate the performance of the designed scheme as well as the comparison among different schemes.

Performance analysis of dual-hop relay systems with single relay selection in composite fading channels

Abstract In this paper, we present novel and easy-to-evaluate expressions for the performance of dual-hop relaying with best relay selection operating over generalized- K fading channels. Since it is hard to find a closed-form expression for the probability density function (PDF) of the exact end-to-end signal-to-noise ratio (SNR) at the destination node even for the single dual-hop system with amplify-and-forward (AF) relaying, we use a tight upper bound value instead. Using the approximate value for the end-to-end SNR, closed-form expressions for the statistics of the SNR, the average bit and symbol error probabilities, and the ergodic capacity for the single dual-hop AF relay system, are derived. Moreover, assuming independent nonidentical fading conditions across multiple dual-hop relay links, we derive lower performance bounds for the single relay selection scheme with AF relaying. The final expressions are useful in the performance evaluation of AF opportunistic relaying in a generalized composite radio environment. Simulation results are also given to verify the analytical results.

Relay Selection Schemes for Cooperative Communications Systems Sensor Networks

Due to being so effective to mitigate the fading effect of wireless channels relay networks have received so much attention recently. Especially because relays are typically small, power limited and low cost and also can remove the problem of attenuation of signal due to propagation loss. Moreover increasing the number of relays improves the system performance and also using more power. The system efficiency can be enhanced by selecting relays in better conditions. In this paper single and multiple relay selection schemes is proposed applying Principal Component Analysis (PCA) method. The main idea of PCA method is selecting relays according to the eigenvector corresponding to the largest eigenvalue of channels from source to the destination. The PCA method provides an acceptable tradeoff between better power and Bit Error Rate (BER) performances. The higher efficiency is achieved by Appling PCA which demonstrated in power performance and this management of total power usage makes relay networks more practical.

A General Diversity Gain Function and Its Application in Amplify-and-Forward Cooperative Networks

The diversity gain function is a unified metric for the asymptotic error performance of wireless communication systems. In this correspondence, we propose a theorem that relates the diversity gain function and the coding gain to the probability density function of the instantaneous signal-to-noise ratio (SNR) at the origin. It provides a general framework for analyzing the asymptotic reliability of wireless communication systems in the presence of fading. As two applications of the proposed theorem, we evaluate two relay selection schemes in fixed-gain amplify-and-forward (AF) cooperative networks. The results show that even if not all channel state information is available at the destination, fixed-gain AF relay selection schemes can still achieve full cooperative diversity and near optimal error performance. This is an outstanding merit that instantaneous-gain AF relay selection schemes do not possess [Y. Jing and H. Jafarkhani, “Single and multiple relay selection schemes and their achievable diversity orders,” IEEE Trans. WIRELESS COMMUN., vol. 8, no. 3, pp. 1414-1423, Mar. 2009].

Outage-optimal opportunistic relaying for two-way amplify and forward relay channel

Presented is a simple opportunistic amplify and forward (AF) relaying for the two-way relay channel, where two nodes want to exchange information with each other at the same transmission rate with the help of relay nodes. In particular, the opportunistic relay can be selected in a distributed manner requiring only local channel knowledge. It is shown that opportunistic AF relaying is outage-optimal among single relay selection schemes and significantly outperforms an AF strategy based on equal-power multiple-relay transmission with local channel knowledge. Numerical and simulation results verify the analysis.

Signal transmission with unequal error protection in relay selection networks

A relaying technique based on single-relay selection is studied for multiple-relay networks when hierarchical modulation is employed for unequal error protection. A single-relay selection scheme achieves a higher bandwidth efficiency while maintaining the same diversity order as when all the relays are selected in a multiple-relay network. Specifically, a cooperative network with one source, K relays, and one destination is considered in which two different protection information classes are modulated by a hierarchical 2/4-amplitude shift keying (ASK) constellation at the source. After selecting a relay to cooperate with the source, based on the instantaneous received signal-to-noise ratio, the selected relay decides to retransmit both classes by using a hierarchical 2/4-ASK constellation, or the more protection class by using a 2-ASK constellation, or remains silent. The approximated bit error rate (BER) of each information class is derived. Optimal thresholds are chosen to minimise the BER of one class while the BER of the other class satisfies a requirement. Numerical and simulation results are provided to validate the analysis. The results also show that the optimal thresholds can improve the error performance significantly.

Single and multiple relay selection schemes and their achievable diversity orders

This paper is on relay selection schemes for wireless relay networks. First, we derive the diversity of many single-relay selection schemes in the literature. Then, we generalize the idea of relay selection by allowing more than one relay to cooperate. The SNR-optimal multiple relay selection scheme can be achieved by exhaustive search, whose complexity increases exponentially in the network size. To reduce the complexity, several SNR-suboptimal multiple relay selection schemes are proposed, whose complexity is linear in the number of relays. They are proved to achieve full diversity. Simulation shows that they perform much better than the corresponding single relay selection methods and very close to the SNR-optimal multiple relay selection scheme. In addition, for large networks, these multiple relay selection schemes require the same amount of feedback bits from the receiver as single relay selection schemes.