Relay Selection Method Research Articles

A Relay-Aided Device-to-Device-Based Load Balancing Scheme for Multitier Heterogeneous Networks

As a key feature of the next generation wireless networks (5G), heterogeneous networks (HetNets) architecture is embraced as the fundamental network technology to meet the immensely diverse service requirements and characteristics of various devices. By introducing underlaying device-to-device (D2D) communication into HetNets, it is possible to offload the unevenly distributed load from the overloaded macrocell to the uncongested femtocell in multitier HetNets. However, the performance of load balancing (LB) scheme heavily depends on the D2D relay selection method as well as the potential resource reuse interference brought by underlay D2D relaying. In order to improve resources utilization ratio and mitigate the resource reuse interference, an LB strategy based on D2D relaying is proposed. To accommodate more new users into the already overloaded macrocell, the macro user equipment with poor link quality will be first transferred into nearby uncongested femtocells by D2D relaying. Then, the released macrocell resource can be allocated to new users who cannot access femtocell due to location restriction. Furthermore, we also propose a two-stage relay selection and resource allocation scheme which not only minimizes the potential interference caused by resource reuse but also guarantees the transmission requirement of different users. Extensive simulation results demonstrate that by taking advantage of D2D relaying, the proposed LB algorithm can effectively adjust the unbalanced load between macrocell and femtocells, which achieves improved performance of the whole HetNets.

Channel quantization-based physical-layer network coding for two-way relay STBC system

Wireless multiple-input multiple-output (MIMO) two-way relay systems have received increasing attention recently. In a simple two-hop relay system, physical-layer network coding (PNC) is an effective scheme for relay to map the transmitted symbols from two terminal nodes into the network coded symbol. This paper considers a two-hop two-way relay system which uses the Alamouti space-time code for signaling between all nodes and channel quantization for PNC mapping at the relay. Specifically, based on the concept of CQ-PNC we derive a PNC mapping rule for two pairs of network coded symbols. An adaptive mapping scheme based on minimum residual interference power is introduced to reduce the effect of quantization error. Finally, a relay selection method based on minimum residual interference power is proposed as a means to increase the system performance.

Relay Selection in Full-Duplex Energy-Harvesting Two-Way Relay Networks

In this paper, we investigate the relay selection (RS) problem in full-duplex (FD) two-way relay networks, where the relays are wirelessly powered by harvesting a portion of the received signal power from the sources. To the best of the authors’ knowledge, this is the first investigation of FD two-way relays with simultaneous wireless and information transfer capabilities. For each relay, we prove the quasi convexity of the power splitting (PS) factor optimization, and obtain the optimal PS factor in terms of the outage probability by linear search. Both single relay selection (SRS) and general relay selection (GRS) without the limit on the number of cooperating relays are investigated and the corresponding RS methods are proposed. Since the optimal GRS problem is computationally intractable with exponential complexity, we propose several low-complexity heuristic GRS methods based on various relay ordering and greedy selection criteria. Simulations indicate that the proposed GRS methods perform better than the SRS methods and achieve very similar performance compared with the optimal RS method achieved by exhaustive search but with dramatically reduced complexity.

Chọn lựa nút chuyển tiếp nâng cao hiệu năng mạng vô tuyến nhận thức dạng nền với sự xuất hiện của nút nghe lén và khiếm khuyết phần cứng

In this paper, we study physical-layer security issue of secondary networks in cognitive radio (CR). In the considered system model, a secondary source communicates with a secondary destination with assistance of multiple secondary relays in presence of multiple secondary eavesdroppers. The secondary users operate on an underlay mode, where they must adjust their transmit power to satisfy interference constraints required by primary users. Moreover, we propose three efficient relay selection methods to improve outage performance for the data links as well as to reduce decoding probability (DP) of the eavesdropping links. For performance evaluation and comparison, we derive exact closed-form expressions of outage probability (OP) and decoding probability (DP) over Rayleigh fading channel under impact of imperfect hardware transceiver. Finally, Monte Carlo simulations are performed to verify our theoretical derivations. The results present that with the presence of the eavesdroppers, there always exists a trade-off between security and reliability.

A Two-Stages Relay Selection and Resource Allocation with Throughput Balance Scheme in Relay-Assisted D2D System

Introducing relay node to Device-to-Device (D2D) technology can extend the cell coverage range and improve the system performance. In this paper, we discuss a relay-assisted D2D communication underlaying cellular network from two aspects. Firstly, we discuss relay selection problem. A two-stages relay selection and resource allocation method is proposed. The stage 1 determines the range of candidate relay UEs through an area division method. Through this way, signaling overhead and measurement overhead can be reduced. The stage 2 selects an optimal relay UE from candidate relay UEs and determines the resource allocation method using an optimal bipartite matching theory with a pretty low complexity. Secondly, we find that the two-stages method causes a throughput unbalance and resource waste problem. Therefore, throughput balance is investigated in this paper. Eight throughput balance options are discussed in details. Then, three throughput balance schemes are proposed. The two-stages method and three throughput balance schemes are evaluated by simulation. Simulation results show that the proposed two-stages method can improve the throughput of relay-assisted D2D communication with a low signaling overhead and measurement overhead. Three proposed throughput balance schemes can improve system throughput performance further.

Joint Clustering Relay Selection and Beamforming in Cooperative Cognitive Radio Networks

This paper proposes a joint clustering relay selection and beamforming method for a more realistic cooperative cognitive radio network, in which a secondary network of multiple secondary links and a relay network coexist with a primary network of one primary link. We aim to improve performance of the system in terms of maximizing the received signal power of the secondary destinations, subject to the constraint of received interference plus noise power of the primary destination using the proposed method. Since different relays cooperate differently towards the signals at the secondary and primary destinations, the proposed method can improve the performance of the system and enables the relay network to simultaneously transmit signals of all secondary links toward the destinations by clustering the relays. Results of simulations confirm validity of the method and improve the system performance compared to the existing cooperative beamforming and Zero-Forcing beamforming, in which no relay selection strategy is used.

A Safety Relay Selection Method Based on Network Coding

A method of cooperative relay selection based on network coding security is proposed for relay selection problem of cooperative communication system security in networked multi-relay scenarios, which is different from the existing relay node selection method. The algorithm not only merged with timestamp and homomorphic signature to construct the node degree of safety to find reliable relay, at the same time to considers the received signal to noise ratio at all relay nodes value and the channel gain to the source node. The simulation results show that the proposed method can improve the achievable rate of the destination node and reduce the outage probability on the basis of guaranteeing the safety of the relay node.

Power Allocation and Relay Selection for Multisource Multirelay Cooperative Vehicular Networks

In wireless distributed networks, multisource multirelay cooperative techniques can be used to exploit the spatial and temporal diversity gains to increase the performance or reduce the transmission energy consumption, which is very useful for intelligent transport system (ITS) networks. In this paper, we propose a power allocation method to optimize the hybrid decode–amplify–forward cooperative transmission for multisource multirelay ITS networks as a means to reduce the total power consumption while minimizing outage probability. Specifically, we derive closed-form outage probability expressions and present an energy-efficient relay selection method to form an optimal relay set. It is proven that the proposed methods can solve the joint power allocation and relay selection problem under outage probability constraint. Our performance analysis is supplemented by numerical simulation results to illustrate the significant energy savings of the proposed optimal power allocation and the relay selection methods.

Cooperation Methods for Cognitive Radio Systems

This paper deals with a joint relay selection and spectrum sensing problem for multi-relay Cognitive Radio Networks. The aim is to determine optimum relays to achieve sufficient performances of both cooperative transmission and spectrum sensing for the secondary network, while ensuring the quality of service of primary user. In the first stage, best relay selection method investigated for cooperative transmission and cooperative spectrum sensing in Cognitive Radio Networks. Thereafter, a multiple relay selection method proposed to improve the performance of the system. This jointly optimized method is capable of selecting "multiple best" relays for transmission as well as spectrum sensing. The proposed method provides cooperative communication and cooperative spectrum sensing performed at the same multiple terminals. As such, individually selected best relays for transmission and for spectrum sensing may be used cooperatively. Simulation results are given to demonstrate that our proposed optimum relay selection method provides beneficial performances for both transmission and spectrum sensing in Cognitive Radio Networks.

랜덤한 릴레이를 갖는 추가 기회전송 협동 릴레이 시스템의 릴레이 선택법에 따른 성능비교

Cooperative relaying systems have been studied actively to improve the system performance effectively in wireless fading channels. Most of the cooperative relay studies are assumed fixed relay, recently the performance analysis of the cooperative relaying systems with spatially random relays considering the practical mobile environment are introduced. However the comparative studies for relay selection methods of incremental cooperative relay systems, the performance of which is influenced by the selection methods, have not been studied. Therefore we derive the performance of the system which has MRC(Maximal-ratio combining) with Max SNR(signal-to-noise ratio) selection or Max-min SNR selection, respectively. And the outage performances of the system with Max or Max-min selection method are compared for different transmit power allocation to the source and to the relays. The analytical results serve as useful tools for relay selection and power allocation to transmit nodes for opportunistic incremental relaying systems.

Autonomous Relaying Scheme With Minimum User Power Consumption in Cooperative Multicast Communications

In this paper, we propose a probability-based relay selection and power control method in two-phase cooperative multicast communications to minimize the user power consumption for any given multicast data rate. Our method gives each user the ability to autonomously decide whether to participate in the relay transmission based on an active probability. In particular, we develop an optimal algorithm to calculate the optimal active probability and relay power by balancing the outage reduction efficiency. We also develop a sub-optimal algorithm by balancing the outage probability of the cell-center and the cell-edge users. Simulation results demonstrate that the proposed optimal and sub-optimal algorithms can reduce the user power consumption up to about 54% and 40%, respectively, compared with the conventional algorithm that requires all users to participate in the relay transmission.

Performance analysis of mixed amplify-and-forward and decode-and-forward protocol in underlay cognitive networks

In this paper, we propose and evaluate outage performance of a mixed amplify-and-forward (AF) and decode-and-forward (DF) relaying protocol in underlay cognitive radio. Different from the conventional AF and DF protocols, in the proposed protocol, a secondary source attempts to transmit its signal to a secondary destination with help of two secondary relays. One secondary relay always operates in AF mode, while the remaining one always operates in DF mode. Moreover, we also propose a relay selection method, which relies on the decoding status at the DF relay. For performance evaluation and comparison, we derive the exact and approximate closed-form expressions of the outage probability for the proposed protocol over Rayleigh fading channel. Finally, we run Monte Carlo simulations to verify the derivations. Results presented that the proposed protocol obtains a diversity order of three and the outage performance of our scheme is between that of the conventional underlay DF protocol and that of the conventional underlay AF protocol.

Relay selection and Optimization algorithm of Power allocation based on Channel Delay for UWSN

In the light of the characteristics of random change that underwater sensor change by time, space and frequency, select the best relay node to improve communication quality and get the diversity gain. A new optimal relay selection method is proposed in this paper, by considering two indexes synthetically that channel gain and underwater acoustic communication long time delay to select the best relay node. Based on the best relay node and minimization of bit error rate to take optimal power allocation of source node and relay node to realize network error rate’s reduction of 1.81 dB so then improve the overall performance of the network.

Revisiting relay assignment in cooperative communications

The performance gain of cooperative communications heavily depends on the selection of relay. Most of the existing relay selection methods for cooperative communications aim at maximizing cooperative gain by selecting appropriate relay, without taking into account the adverse effect brought by cooperative communications: extra interference introduced by relay transmission (called cooperation interference). Thus the derived performance gain could be inaccurate and/or the selected relay may be not optimal. In this paper, we address the assignment of relays for multiple communication sessions using cooperative communication mode in wireless networks. We first thoroughly investigate the adverse effect brought by using relays, and derive the cooperation gain with consideration of cooperation interference. Based on the insights of our investigation, we propose a method of assigning relays to individual transmission flows while taking into account cooperation interference. In order to tradeoff the advantage and adverse effect caused by relay transmissions, we use an auction approach to address relay assignment of cooperative communications. Specifically, we propose a single round double auction scheme (SAS) for centralized wireless network and a multiple rounds sequential auction scheme (MAS) for decentralized wireless network for relay assignment. We conduct extensive simulation experiments to validate the effectiveness of SAS and MAS. The significance of cooperation interference, the improvement of overall system throughput and energy efficiency of our proposed relay assignment schemes are demonstrated by numerical results.

SNR-based relay selection in cooperative wireless ad hoc networks

Cooperative communications aim to gain spatial diversity from stations cooperating during data transmission without requiring multiple transceiver antennas on the same station. However, performance from cooperative communications highly depends on the relay-selection method. This paper proposes and evaluates a distributed relay-selection method based on the signal-to-noise ratio of the communication links of candidate relay nodes. A node is selected as a relay node based on the signal-to-noise ratio of its communication link. Moreover, data might be delivered through a relay node that can support high transmission rate rather than through a direct link with a low transmission rate. This paper provides a detailed analysis of the collision probability in the proposed method as compared to a conventional random backoff method. Results demonstrate that the proposed relay-selection method reduces collision probability, and hence, enhances system throughput.

Fountain Coded Cooperative Communications for LTE-A Connected Heterogeneous M2M Network

Machine-to-machine communication over long-term evolution advanced (LTE-A) network has emerged as a new communication paradigm to support a variety of applications of Internet of Things. One of the most effective techniques to accommodate a large volume of machine type communication (MTC) devices in LTE-A is clustering where devices (nodes) are grouped into number of clusters and forward their traffics to the base station (e.g., LTE eNodeB) through some special nodes called cluster heads (CHs). In many applications, the CHs change location with time that causes variation in distances between neighboring CHs. When these distances increase, the performance of data transmission may degrade. To address this issue, we propose to employ intermediate non-CH nodes as relays between neighboring CHs. Our solution covers many aspects from relay selection to cooperative formation to meet the user’s QoS requirements. As the number of total relay plays a significant role in cooperative communications, we first design a rateless-coded-incremental-relay selection algorithm based on greedy techniques to guarantee the required data rate with a minimum cost. After that, we develop both source-feedback and non-source-feedback-based fountain coded cooperative communication protocols to facilitate the data transmission between two neighbor CHs. Numerical results are presented to demonstrate the performance of these protocols with different relay selection methods under Rayleigh fading channel. It shows that the proposed source-feedback-based protocol outperforms its non-source-feedbackprotocol counterpart in terms of a variety of metrics.

Secrecy Performances of Multicast Underlay Cognitive Protocols with Partial Relay Selection and without Eavesdropper’s Information

This paper considers physical-layer security protocols in multicast cognitive radio (CR) networks. In particular, we propose dual-hop cooperative decode-and-forward (DF) and randomize-and-forward (RF) schemes using partial relay selection method to enhance secrecy performance for secondary networks. In the DF protocol, the secondary relay would use same codebook with the secondary source to forward the source’s signals to the secondary destination. Hence, the secondary eavesdropper can employ either maximal-ratio combining (MRC) or selection combining (SC) to combine signals received from the source and the selected relay. In RF protocol, different codebooks are used by the source and the relay to forward the source message secretly. For each scheme, we derive exact and asymptotic closed-form expressions of secrecy outage probability (SOP), non-zero secrecy capacity probability (NzSCP) in both independent and identically distributed (i.i.d.) and independent but non-identically distributed (i.n.i.d.) networks. Moreover, we also give a unified formula in an integral form for average secrecy capacity (ASC). Finally, our derivations are then validated by Monte-Carlo simulations.

Energy-Efficient Joint Power Allocation and Relay Selection in Bit Error Rate Constrained Two-Way Relay Network

In this paper, the authors have proposed energy efficient power allocation and relay selection scheme in a two-way amplify-and-forward (AF) relay under bit error rate (BER) constrained network. They have derived an expression for the overall BER for Rayleigh fading channel. Based on minimum power consumption in the network, the authors have addressed the problem of power allocation by converting geometric programming to a convex optimization problem. A closed form solution of power allocation is found, which aims at minimizing total transmit power for the overall BER constrained network. The authors have evaluated minimum total transmit power for two-way AF relay network. Based on minimum total transmit power, a novel relay selection scheme has been proposed. Simulation results demonstrate that the proposed two-way power allocation and relay selection scheme can significantly minimize power consumption under BER constrained network as compared to the existing relay transmission. The proposed power allocation scheme gives 3 dBW gain than one-way relay transmission. The proposed relay selection method also outperforms the random relay selection by 24 dBW. The simulation results are corroborated with the analytical result

Secrecy performance analysis with relay selection methods under impact of co‐channel interference

In this study, the authors evaluate secrecy performance of cooperative protocols with relay selection methods under impact of co-channel interference. In particular, the authors propose an optimal selection scheme to maximise the secrecy capacity obtained at the cooperative phase. In addition, the authors also consider suboptimal and random selection schemes which reduce the complexity of implementation, when compared with the optimal one. For performance evaluation, the authors derive exact and asymptotic closed-form expressions of secrecy outage probability and probability of non-zero secrecy capacity for the considered schemes over Rayleigh fading channels. Monte Carlo simulations are performed to validate the derivations.

Inter-Relay Interference Management Schemes for Wireless Multi-User Decode-and-Forward Relay Networks

In this paper, two cooperative communications schemes with inter-relay interference (IRI) management are proposed for wireless multi-user decode-and-forward (DF) relay networks. The schemes are based on a DF half-duplex (HD) relaying protocol and a relay selection method which maximizes the signal-to-noise ratio (SNR) of the second hop. To minimize the IRI, the first scheme [constellation real part (CRP)] uses a new transmission scheme based on the constellation real parts of the modulated signals, and the second scheme [previous message buffering (PMB)] uses a buffering technique at the relays. To assess the performance, we derive the expressions of the average bit error rate (BER) for the proposed schemes. Numerical results are given to confirm the analytical expressions and the advantage of the proposed schemes in enhancing interference management for wireless cooperative networks.