Relay Selection Method Research Articles

BER Minimization for AF Relay-Assisted OFDM Systems

We discuss bit error rate (BER) minimization problems in multiple amplify-and-forward (AF) relay-assisted orthogonal frequency-division multiplexing (OFDM) system over frequency-selective fading channels with total power and individual power constraints, respectively. A joint optimization method of power loading, relay selection and subcarrier pairing is solicited to solve the problems with respect to the above two power constraint conditions. Particularly, we transform subcarrier pairing into a linear assignment problem and apply Jonker-Volgenant (JV) algorithm to deal with it. A simulation result demonstrates superior performances of our algorithm to those of other schemes for different relay locations.

Secrecy Performance Analysis of Multihop Transmission Protocols in Cluster Networks

In this paper, we investigate the secured transmission in cluster-based multi-hop networks. In particular, we evaluate the secrecy performance of three various protocols over Rayleigh fading channel. In the first protocol, at each cluster, a relay is randomly selected to forward the source message to the next cluster. In the second and third ones, relay selection methods are applied to enhance secrecy performance. We derive closed-form expressions of secrecy outage probability and capacity, and then perform Monte Carlo simulations to verify the derivations.

A New Modification on Relay Selection by Considering the Effect of Relay Occupancy

Aims: Considering the effect of relay occupancy at relay selection schemes and also proposing a new approach which helps the selection schemes to find the best free relay. Study Design: Comparative study by simulation in MATLAB software. Place and Duration of Study: Digital Communications Signal Processing (DCSP) Lab. of Shahid Rajaee Teacher Training University (SRTTU), Since 1 st June 2012 up to 1 st August 2014. Methodology: In the existing research works, relay-based system is modeled by a pair of transmitter-receiver nodes and a number of relays. Also, it is assumed that the selected relays are always free. In this investigation, the effect of relay occupancy due to other pairs is considered. For this purpose, a uniform distribution is applied for all relays to show the effect of free or busy relay nodes. Then, the performance of the relay selection methods is obtained by using two well-known performance metrics, bit error rate (BER) and outage probability. As the main goal of this research, a new approach is proposed which first finds the free relays and then applies one of the selection

Relay Selection for Simultaneous Information Transmission and Wireless Energy Transfer: A Tradeoff Perspective

In certain applications, relay terminals can be employed to simultaneously deliver information and energy to a designated receiver and a set of radio frequency (RF) energy harvesters, respectively. In such scenarios, the relay that is preferable for information transmission does not necessarily coincide with the relay that is preferable for energy transfer, since the corresponding channels fade independently. Relay selection thus entails a tradeoff between the efficiency of the information transmission to the receiver and the amount of energy transferred to the energy harvesters. The study of this tradeoff is the subject on which this work mainly focuses. Specifically, we investigate the dependence of the ergodic capacity and the outage probability of the information transmission to the receiver on the amount of energy transferred to the RF energy harvesters. We propose a relay selection policy that yields the optimal tradeoff in a maximum capacity/minimum outage probability sense, for a given energy transfer constraint. We also propose two suboptimal relay selection methods that apply to scenarios with limited availability of channel state information. Additionally, we propose a suboptimal scheme which approximates the optimal scheme for the special case of two relays and facilitates performance analysis. Interesting insights on the aforementioned tradeoffs are unveiled.

Distributed load aware relay selection algorithm for cooperative relay networks

Cooperative relaying is accepted as a promising solution to achieve high data rates over large areas in the 4G wireless system. This paper presents a two-step distributed load aware relay selection algorithm LA-RS for relay-based cooperative networks. According to current user channel conditions as well as the user numbers that relay serves, LA-RS chooses the optimal relay node for each user in a distributed way. More specifically, in the first step each mobile station MS constructs relay selection functions for candidate relay node RN, and selects the appropriate RN accordingly. Furthermore, in the second step RNs also adopt a weighted channel dependent scheduling algorithm for resource allocation, so as to provide a flexible tradeoff between per-user fairness and aggregate throughput in each cell. Simulation results demonstrate that compared with other relay selection schemes, LA-RS achieves load balancing through effective relay selection method, so as to obtain a tradeoff between the system throughput and the user equity.

Characterisation of relay selection in cooperative multiple‐input multiple‐output‐orthogonal frequency division multiplexing systems

In this study, two relay selection methods in the half-duplex decode-and-forward relaying for cooperative multiple-input multiple-output-orthogonal frequency division multiplexing (MIMO-OFDM) systems have been introduced. The relay selections are implemented using the symbol-based and subcarrier-based methods. By considering different number of antennas for source, each relay, and destination, the authors have derived closed-form outage expressions for these proposed methods. The MIMO channel model for each subcarrier, between source–relay and relay–destination is considered as a MIMO Rician fading channel with independent but not necessary identically distributed. Moreover, the outage expressions for MIMO independent and identically distributed Rician and Rayleigh fading channels are derived as special cases. Furthermore, the correlation among the OFDM subchannels is analysed. In addition, the implementation issues of both relay selection methods are also investigated. Monte Carlo simulations are performed to validate the outage analysis where the excellent agreement between the analytical and simulation results is observed.

Joint relay selection and cooperative beamforming in two‐hop multi‐relay decode‐and‐forward networks

Cooperative communication can improve the performance of communication systems under multi-path fading conditions through relaying. Increasing the number of relays will also boost the performance of the system, but since relays transmit through orthogonal channels, this improvement is obtained at the cost of bandwidth or rate of the system. Best relay selection is a well-known technique to achieve full order of diversity and use bandwidth efficiently in a cooperative two-hop multi-relay network. A new beamforming at the relay is proposed that selects the best two among several relays and then the selected relays forward their detected symbols in a common channel to the destination. For achieving full diversity order at the destination, a modified maximal ratio combining detector is proposed. In the proposed beamforming scheme, the phase of the selected relays is adjusted in such a way to compensate the channel between the relays and the destination and achieve acceptable performance at the receiving end. The selected relays require two-bit quantised phase information of the channel gain between the relay and the destination, which can be sent to the relay by the destination. It is shown that the proposed method achieves full diversity order and has considerable performance gain in comparison with the best relay selection method.

On performance evaluation of hybrid decode-amplify-forward relaying protocol with partial relay selection in underlay cognitive networks

In this paper, we evaluate performance of a hybrid decode-amplify-forward relaying protocol in underlay cognitive radio. In the proposed protocol, a secondary relay which is chosen by partial relay selection method helps a transmission between a secondary source and a secondary destination. In particular, if the chosen relay decodes the secondary source's signal successfully, it will forward the decoded signal to the secondary destination. Otherwise, it will amplify the signal received from the secondary source and will forward the amplified signal to the secondary destination. We evaluate the performance of our scheme via theory and simulation. Results show that the proposed protocol outperforms the amplify-and-forward and decode-and-forward protocols in terms of outage probability.

Energy-Efficient Relay Selection and Resource Allocation in Nonregenerative Relay OFDMA Systems

Discrete modulation in multiuser nonregenerative relay systems is less investigated in current resource allocation but is more commonly used in practical systems. In this paper, based on a set of discrete modulation levels, we formulate a joint optimization of relay selection and resource allocation under rate requirements to minimize the system transmitting power consumption and to improve energy efficiency. Since the problem cannot be easily solved due to its NP-hardness, we decompose it into two subproblems, namely, a simple relay selection method and a resource allocation method, and we develop a heuristic algorithm to find suboptimal solutions. The two-step solutions are based on power saving and virtual direct transmission, and they can reduce the dimensionality and can simplify the resource allocation of the relay networks. In addition, the power constraints at the relay stations (RSs) are considered in a way that the subcarriers on overloaded RSs are adjusted according to the joint optimization. Our results show that a satisfactory suboptimal solution close to the optimal one could be achieved, and the power constraints at RSs may have a significant impact on the total power consumption.

Exact Outage Probability of Two-Way Decode-and-Forward Scheme with Opportunistic Relay Selection Under Physical Layer Security

The combination of cooperative communication and physical layer security is an effective approach to overcome the disadvantages of the fading environment as well as to increase the security capacity of the wireless network. In this paper, we propose a two-way decode-and-forward scheme with a relay selection method. In the proposed protocol, two source nodes communicate with each other with the help of intermediate relays under the eavesdropping of another wireless node, called the eavesdropper node. The best relay, which is chosen by the max---min strategy, uses digital network coding to enhance secure communication and spectrum use efficiency. The system performance is analyzed and evaluated in terms of the exact closed-form outage probability over Rayleigh fading channels. The Monte-Carlo simulation results are presented to verify the theoretical analysis. Finally, the proposed protocol is compared with the two-way protocol, which does not use digital network coding.

Multipoint relay selection for robust broadcast in ad hoc networks

Broadcasting is a frequently used technique in a wireless ad hoc network not only to deliver protocol control information but also application data. Optimized Link State Routing (OLSR) uses Multipoint Relay (MPR) to flood Topology Control (TC) message while reducing redundant retransmissions. The downside of reducing duplicated retransmission is vulnerability of the transmitted packet to the packet error, collision, or hidden nodes. In this paper, we propose a multipoint relay selection method for robust broadcast in a wireless ad hoc network. The proposed method selects additional MPR nodes so that it can cover 2-hop MPR nodes m times not to cover all 2-hop neighbor nodes m times. The number of additional MPR nodes is analyzed using mathematical modeling and simulations. The proposed method can improve network throughput as well as delivery ratio compared with the original MPR selection method of OLSR.

An Opportunistic Relaying Selection Scheme Based on Relay Fairness

Opportunistic relaying scheme is a single cooperative relay selection method based on Channel State Information. However, the failure probability of the best relay selection may become unacceptable when the number of relays increases. Although most of the existing solutions can reduce the failure probability of relay selection, they ignore the fairness of the relay selection. In order to improve the fairness of the relay selection without affecting the failure probability of the best relay selection, we propose a modified practical best relay selection scheme in this paper, and by introducing proportional fair algorithm, the relay timer will be given a smaller correlation coefficient. The proposed method makes the probability of selection be improved. In the light of defined fairness factor, the relay fairness is represented. Simulation results show that the new algorithm can improve the fairness of the relay selection on the basis of maintaining the original failure probability of relay selection. DOI : http://dx.doi.org/10.11591/telkomnika.v12i1.3910

Selection Cooperation in Heterogeneous Cooperative Networks

Selection cooperation is an attractive cooperative strategy for wireless networks due to its simplicity and efficiency. In this paper, we consider a heterogeneous cooperative network consisting of different kinds of nodes with low-cost radios where the activities of one kind of nodes are triggered by the other kinds of nodes. This is a common scenario for many networks, such as wireless sensor networks. By exploiting the transmission relationship between heterogeneous nodes, we propose a selection cooperation protocol where inducing nodes can cooperate with the following nodes after their own transmissions for improving the communication reliability of the latter nodes. Through performance analysis, we show an interesting feature that the diversity-multiplexing tradeoff of the proposed protocol does not rely on the best relay selection method and the protocol always achieves the full diversity gain. We further develop an energy-efficient best relay selection method based on power control where the power consumption is minimized without decreasing the full diversity order. Simulation results demonstrate the good performance of the protocol and the remarkable energy reduction of the proposed best relay selection method.

Dependence of Outage Probability of Cooperative Systems with Single Relay Selection on Channel Correlation

The relay selection method is a promising technique for improving the performance of cooperative systems. Most of the existing studies assume that wireless channels are statistically independent. However, in reality, channel correlation is more likely to be non-negligible. In this study, we investigate the dependence of the performance of cooperative systems with single relay selection in equally correlated environments. A tight upper bound of the system outage probability is given as a function of the channel correlation coefficients. We show that even though the system performance is considerably degraded in the high signal-to-noise ratio (SNR) region when the channel correlations are sufficiently large, yet less than one, the system still achieves a diversity order equal to the number of available relays.

Local CSI Based Full Diversity Achieving Relay Selection for Amplify-and-Forward Cooperative Systems

This paper proposes a new relay selection method based on local channel state information (CSI) for a system consisting of a source, a destination and an arbitrary number of amplify-and-forward relay nodes. A set of candidate relays, whose source-relay (S-R) links are not in outage, is formed. An S-R link is in outage if its signal-to-noise ratio (SNR) is below the predefined threshold value of the destination SNR plus some adjustable margin. The candidate relay that yields the maximum second-hop SNR is then selected at the destination. Unlike the opportunistic relaying (OR) based on full CSI (F-CSI), the proposed method requires to equip the destination node with the instantaneous CSI of the S-R channel corresponding to only the selected relay. It is qualitatively shown that the training overhead of the proposed relay selection is less than or comparable to that of the partial relay selection (PRS) but can be much smaller than that of the OR with F-CSI. However, the proposed scheme requires to estimate a higher number of single-input single-output (SISO) channels than in the PRS scheme. The exact and asymptotic expressions of outage probability are derived and it is shown that the proposed method achieves full diversity. Simulation results verify theoretical analysis, and show that, for the optimized margin, the proposed scheme provides performance which is comparable to the method having F-CSI. The results also show that the proposed method significantly outperforms PRS, which may justify the linear order of the computational complexity associated with the estimation of the additional SISO channels and the low-cost one-dimensional line search used for optimizing the margin.

Cooperative Strategies for Wireless Relay Networks With Cochannel Interference Over Time-Correlated Fading Channels

Practical mobile communication systems suffer from time-variant channel fading and cochannel interference, both of which give rise to challenges concerning strategy design and performance analysis in wireless relay networks. Although these two aspects have attracted concerns in recent studies, most researchers still focused on dealing with a single problem and avoided intricate joint considerations. In this paper, we investigate the cooperative strategies for the communications of two cochannel pairs over time-correlated Rayleigh channels, and the system consists of a relay-assisted pair (Pair 1) along with a direct transmission pair (Pair 2). We begin with a theoretical evaluation on a conventional relay selection (RS) algorithm that maximizes outdated signal-to-interference-plus-noise ratio (M-SINR), and then develop a more sophisticated method that involves extra statistical and interference information based on the concept of minimizing outage probability (MOP). Closed-form outage probability expressions are derived for both pairs with each RS algorithm, and the MOP-type selection is confirmed to outperform M-SINR in robustness against channel fluctuation when the network operates on medium-to-high signal-to-noise ratio (SNR). Implementation issues of the RS methods are discussed to clarify their overhead and to support their practicability. Further, an interference control scheme is proposed to guarantee Pair 2 communication quality under either RS algorithm by disqualifying the relays that probably cause severe cochannel interference to Pair 2. The interference control mechanism is carried out via a novel threshold parameter e that represents the tolerance of outage performance degradation of Pair 2 resulting from interference. The closed-form analysis validates that the given e is rational for an arbitrary network scenario, and it can balance the two pairs' outage behavior under a proper configuration. We reveal the influence of factors such as average SNR, transmit rate, and network topology on system performance to make a comprehensive comparison between diverse cooperative strategies.

Multi-Path Relay Selection Based on Radio and Television Business

This paper presents a relay selection method for radio and television business, this method uses nodes time-delay and power information, obtains the value of network interrupt as decision threshold, then selects the relay node. At same time this paper proposes an optimal relay selection strategy which can minimize the network interrupt probability combination with power distributionMulti-Path Relay Routing Protocol, this protocol can change the appropriate route path according to the dynamic network. Simulation results show that this protocol can extend cells coverage area, reduce time-delay and increase system throughput, improve system spectral efficiency, and enhance Qos of radio and television business.

On Power Allocation and Relay Selection for a Two-Way Amplify-and-Forward Relaying System

In this paper, we investigate power allocation and relay selection problems for a two-way amplify-and-forward (AF) relaying system. We first derive asymptotic overall symbol error probabilities (AOSEPs) for the case of one relay cooperating with two sources with respect to the second-order channel statistics for both M-ary quadrature amplitude modulation (M-QAM) and M-ary phase-shift keying (M-PSK), and then present the corresponding optimal power allocation and relay selection schemes that minimize the AOSEPs. To achieve the full diversity order, we further propose alternative power allocation and relay selection methods by simply replacing the statistical channel information of the first scheme with instantaneous one. The diversity order of the second scheme is then verified by deriving the lower and upper bounds of the corresponding asymptotic overall outage probability. Computer simulation results are also given to support the analytical results.

A Lightweight Selection Cooperation Protocol with Multiple Available Best Relays

Selection cooperation has shown to be a practical cooperative strategy for wireless networks. In order to obtain full diversity gain, conventional selection cooperation schemes must select the node with the maximum relay-destination channel as the best relay, which restricts the choice of relay selection for the system. To overcome this limitation, we propose a lightweight selection cooperation protocol without requiring the radio of nodes to perform combining reception. Through outage probability and diversity-multiplexing tradeoff (DMT) analysis, we reveal an interesting fact that choosing any node that successfully receives the message from the source and the feedback frame from the destination as the best relay, the protocol always achieves the full diversity order and the optimal DMT. This result establishes a framework for obtaining multiple optimization objectives in selection cooperation networks. As an illustrative example, we then develop two best relay selection methods for relay balance without sacrificing the full diversity order. Simulation results demonstrate the remarkable performance and balance effect of the proposed protocol and selection methods.

Channel allocation and relay selection scheme in relay-based networks

It has been demonstrated that either Channel Allocation (CA) or Relay Selection (RS) can improve the performance in relaying networks separately. However, there is little work concerning their combination in multi-cell uplink scenarios. In this paper, we investigate the issue which considers the CA and RS to optimize the system transmission rate in an uplink scenario, while maintaining the resource distribution fairness among users. This is first formulated as an optimization problem for a linear cellular system, where the same frequency channels can be reused in different cells. Based on the link and co-channel interference conditions, two low-complexity CA and RS schemes are then proposed with different decomposition sequences. Finally, numerical results are conducted to verify the effectiveness of the proposed CA and RS methods. Simulations results show that the proposed methods can yield significant improvements in system performance in terms of average sum rate.