Revisiting relay assignment in cooperative communications

Wireless Networks - 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...     

Joint relay assignment and power allocation for cooperative communications

In the recent years, cooperative communication is shown to be a promising technology to improve the spatial diversity without additional equipments or antennas. With this communication paradigm, energy can be saved by effective relay assignment and power allocation while achieving the required bandwidth for each transmission pair. Thus, this paper studies the joint relay node assignment and power allocation problem which aims to minimize the total power consumption of the network while providing the efficient bandwidth service. We first analyze the minimum power consumption under the bandwidth requirement for different communication modes. Based on the analytical results, we present a polynomial-time algorithm JRPA to optimally solve this problem. The algorithm first constructs a weighted bipartite graph G based on the given transmission pairs and relay nodes. Then, we adopt the KM method to find out a saturated matching M, and assign the relay nodes to the transmission pairs based on the matching. The optimality of the algorithm is also proved. The simulation results show that JRPA algorithm can save about 34.2% and 18.9% power consumptions compared with the direct transmission and ORA schemes in many situations.     

Lifetime maximization via cooperative nodes and relay deployment in wireless networks

Extending lifetime of battery-operated devices is a key design issue that allows uninterrupted information exchange among distributed nodes in wireless networks. Cooperative communications has recently emerged as a new communication paradigm that enables and leverages effective resource sharing among cooperative nodes. In this paper, a general framework for lifetime extension of battery-operated devices by exploiting cooperative diversity is proposed. The framework efficiently takes advantage of different locations and energy levels among distributed nodes. First, a lifetime maximization problem via cooperative nodes is considered and performance analysis for M-ary PSK modulation is provided. With an objective to maximize the minimum device lifetime under a constraint on bit-error-rate performance, the optimization problem determines which nodes should cooperate and how much power should be allocated for cooperation. Since the formulated problem is NP hard, a closed-form solution for a two-node network is derived to obtain some insights. Based on the two-node solution, a fast suboptimal algorithm is developed for multi-node scenarios. Moreover, the device lifetime is further improved by a deployment of cooperative relays in order to help forward information of the distributed nodes in the network. Optimum location and power allocation for each cooperative relay are determined with an aim to maximize the minimum device lifetime. A suboptimal algorithm is developed to solve the problem with multiple cooperative relays and cooperative nodes. Simulation results show that the minimum device lifetime of the network with cooperative nodes improves 2 times longer than the lifetime of the non-cooperative network. In addition, deploying a cooperative relay in a proper location leads up to 12 times longer lifetime than that of the non-cooperative network     

Full-rate cooperative communications with spatial diversity for half-duplex uplink relay channels

This paper proposes a full-rate cooperative communication technique with spatial diversity for single-carrier transmissions. In order to achieve both the spatial diversity and the full-rate, data streams are simultaneously transmitted through all direct and relay channels with different phase rotation and cyclic delay patterns. The phase rotation and cyclic delay patterns are derived in the sense of minimizing interlayer interference and a corresponding destination structure is presented for decoupling each layer at the destination. Simulation results show that the proposed technique achieves spatial diversity without sacrificing spectral efficiency and outperforms conventional full-rate cooperative communication techniques.     

Joint relay selection and resource allocation in cooperative device-to-device communications

Device-to-device (D2D) communications allow proximate cellular user equipments (UEs) to communicate with each other directly under the control of base station (BS). In this paper, considering the selection relaying (SR) rule which allows a subset of potential relays to forward the source’s data to the corresponding destination, we first establish a multi-relay system model where a D2D UE can act as not only a source but also a potential relay for another D2D link, and then analyze the cooperation behaviors among selfish UEs. Next a simple strategy is proposed to deal with the relay selection problem, and then the fair and efficient resource sharing problem among cooperating D2D UEs is formulated as a bargaining game. Since the game function is non-convex, we turn to an iterative method by introducing an auxiliary function to get the proportional fair resource allocation results. The system efficiency and fairness are proved by numeral simulation results.     

Secrecy capacity maximization for untrusted UAV-assisted cooperative communications with wireless information and power transfer

Wireless Networks - This article addresses the problem of secure communication in an unmanned aerial vehicle (UAV)-aided wireless communication system in which a source sends confidential messages...     

Optimal relay functionality for SNR maximization in memoryless relay networks

We explore the SNR-optimal relay functionality in a mernoryless relay network, i.e. a network where, during each channel use, the signal transmitted by a relay depends only on the last received symbol at that relay. We develop a generalized notion of SNR for the class of memoryless relay functions. The solution to the generalized SNR optimization problem leads to the novel concept of minimum mean squared uncorrelated error (MMSUE) estimation. For the elemental case of a single relay, we show that MMSUE estimate is a scaled version of the MMSE estimate. This scheme, that we call estimate and forward (EF), performs better than the best of amplify and forward (AF) and demodulate and forward (DF) in both parallel and serial relay networks. We determine that AF is near-optimal at low transmit power in a parallel network, while DF is near-optimal at high transmit power in a serial network. For hybrid networks that contain both serial and parallel elements, the advantage of EF over the best of AF and DF is found to be significant. Error probabilities are provided to substantiate the performance gain obtained through SNR optimality. We also show that, for Gaussian inputs, AF, DF and EF are identical     

ADS‐B aided robust relay selection for cooperative communications in aircraft approach

The ground‐to‐air communications in the aircraft approach stage suffer from multipath fading. We propose to combat this problem using cooperative communication technique. The relay selection problem is formulated to minimize the spectrum cost while preserving the signal‐to‐noise‐ratio (SNR) outage requirement of the approaching aircraft. By leveraging the position and velocity information in the automatic dependent surveillance‐broadcast messages, the average channel gains can be derived with uncertainty sets based on the Ricean channel model. Because the outage probability of the received SNR is intractable, we transform the outage constraint into a simple but efficient reliability requirement. The formulated problem is a mixed integer nonlinear optimization problem, with robustness in the worst‐case average SNR. A robust greedy relay selection algorithm is proposed as a solution, whereby a Kalman filter based trace prediction algorithm is adopted to determine the order of relays. Simulation results are given to show the effectiveness of the proposed scheme.Copyright © 2014 John Wiley & Sons, Ltd.     

QoS provisioning in energy-efficient cooperative networks with power assignment and relay deployment planning

Wireless Networks - The cooperative network is an energy-efficient technology to provide ubiquitous broadband access and quality-of-service (QoS). This paper investigates the tradeoffs among QoS,...     

Sum-rate maximization for UAV-enabled two-way relay systems

In this paper, an Unmanned Aerial Vehicle (UAV)-enabled two-way relay system with Physical-layer Network Coding (PNC) protocol is considered. A rotary-wing UAV is applied as a mobile relay to assist two ground terminals for information interaction. Our goal is to maximize the sum-rate of the two-way relay system subject to mobility constraints, propulsion power consumption constraints, and transmit power constraints. The formulated problem is not easy to solve directly because it is a mixed integer non-convex optimization problem. Therefore, we decompose it into three sub-problems, and use the mutation arithmetic of the Genetic Algorithm (GA) and Successive Convex Approximation (SCA) to dispose. Besides, a high-efficiency iterative algorithm is proposed to obtain a locally optimal solution by jointly optimizing the time slot pairing, the transmit power allocation, and the UAV trajectory design. Numerical results demonstrate that the proposed design achieves significant gains over the benchmark designs.     

Improving energy efficiency of incremental relay based cooperative communications in wireless body area networks

In this paper, we investigate the energy efficiency of an incremental relay based cooperative communication scheme in wireless body area networks (WBANs). We derive analytical expressions for the energy efficiency of direct and cooperative communication schemes taking into account the effect of packet error rate. The following communication scenarios specific to a WBAN are considered: (i) in‐body communication between an implant sensor node and the gateway, and (ii) on‐body communication between a body surface node and the gateway with line‐of‐sight (LOS) and non‐LOS channels. The results reveal a threshold behavior that separates regions where direct transmission is better from regions where incremental relay cooperation is more useful in terms of energy efficiency. It is observed that, compared with direct communication, incremental relay based cooperative communication schemes improves the energy efficiency significantly. Further, cooperation extends the source‐to‐destination hop length over, which energy efficient communication can be achieved as compared with direct communication. We also observe that, for both direct as well as cooperative transmission schemes in error prone channels, an optimal packet size exists that result in maximum energy efficiency. Copyright © 2013 John Wiley & Sons, Ltd.     

基于双向MIMO中继系统的一种预编码策略

为了克服已有的双向MIMO中继系统模型中预编码技术计算量大的缺点,提出了一种基于双向MIMO系统的三时段预编码策略,给出了该策略的模型和算法。该模型的中继节点预均衡各信道状态信息影响(CSI)后将合并信号分时段发送给不同通信节点,简化了传统中继转发矩阵对多信道信息的联合设计。理论计算和仿真结果表明,该策略在性能和复杂度之间得到了良好的折衷     

ARQ strategies for relay cooperative systems

We propose two novel automatic repeat request (ARQ) strategies for relay cooperative systems over Rayleigh fading channel one uses relay ARQ and the other destination ARQ. The BER performance of these two strategies is derived in fast block fading. Numerical analysis and simulation show the systems can get more performance gain when the inter-channel (the source to the relay) quality is bad in the relay ARQ strategy. In the destination ARQ strategy, when the uplink qualities of the source and relay to the destination are poor, the average received SNR of the destination is much low, the systems performance can be improved efficiently.     

Optimized distributed MIMO for cooperative relay networks

This paper presents an optimized distributed multiple-inputmultiple-output (OD-MIMO) for cooperative communication in wireless relay networks. The set of cooperating nodes is a priori unknown. In order to avoid the centralized stream and pilot allocation procedure, a fixed signature vector (SV) is assigned for each node in the network. We analyze the constraints of the proposed scheme, and derive an optimization criterion for the decision of the SVs. A gradient-based algorithm for SV design is provided. Simulation results show that the performance loss of OD-MIMO compared to centralized distributed MIMO is small for large number of cooperative relay nodes.     

Joint power allocation and relay selection for decode-and-forward cooperative relay in secure communication

In this paper, we investigate the cooperative strategy with total power constraint in decode-and-forward (DF) relaying scenario, in the presence of an eavesdropper. Due to the difference of channel for each source-relay link, not all relay nodes have constructive impacts on the achievable secrecy rate. Besides, the final achieved secrecy rate depends on both source-relay and relay-destination links in DF relaying scenario. Therefore, the principal question here is how to select cooperative strategy among relays with proper power allocation to maximize the secrecy rate. Three strategies are considered in this paper. First, we investigate the cooperative jamming (CJ) strategy, where one relay with achieved target transmission rate is selected as a conventional relay forwarding signal, and remaining relays generate artificial noise via CJ strategy to disrupt the eavesdropper. Two CJ schemes with closed-form solutions, optimal cooperative jamming (OCJ) and null space cooperative jamming (NSCJ), are proposed. With these solutions, the corresponding power allocation is formulated as a geometric programming (GP) problem and solved efficiently by convex programming technique. Then, to exploit the cooperative diversity, we investigate the cooperative relaying (CR) strategy. An iterative algorithm using semi-definite programming (SDP) and GP together with bisection search method is proposed to optimize the cooperative relaying weight and power allocated to the source and relays. Furthermore, to exploit the advantages of both CR and CJ, we propose an adaptive strategy to enhance the security. Simulation results demonstrate that the efficiency of the proposed cooperative strategies in terms of secrecy rate.     

Price-based resource allocation for revenue maximization with cooperative communication

In recent years, cooperative communication becomes a promising technology to improve the spatial diversity for the future mobile network. Under this communication paradigm, both relay assignment and power allocation will greatly impact the network performance. However, since each device may be selfish, a significant challenge is to make the joint resource allocation robust to node selfishness while pursuing the maximum system revenue in the commercial network. This paper mainly studies the price-based joint relay-power allocation problem which aims to maximize the revenue (JRP-RM) while satisfying the bandwidth requirement with cooperative communication. We first analyze the power allocation under the bandwidth and selfishness constraints for different communication modes. According to the analytical results, this paper presents a polynomial-time algorithm, namely MRPA, to solve the JRP-RM problem. We prove its correctness and show that it can achieve an approximation ratio of \(1 - \varepsilon\), where \(\varepsilon\) is an arbitrarily positive constant. Moreover, we study the JRP-RM problem under a special case where the cost and payment are both linear functions of the transmission power. The simulation results show that MRPA can increase the system revenue about 34.2 and 18.9 % compared with the OPRA Yang et al. (2011 IEEE International Conference on Communications (ICC). IEEE, pp 1–6, 2011) and JRPA Xu et al. (Wirel Netw pp 2209–2219, 2010) algorithms while satisfying the selfishness constraint in most situations.