Capacity of practical wireless multihop broadcast networks

In a wireless multihop broadcasting scenario, a number of relay nodes may cooperate the source node in order to improve the capacity of the network. However, the imposition of total energy and maximum hop constraints to this system in a practical setting. In this paper, we study an ad-hoc network with infinitely many nodes and analytically find the number and positions of rebroadcasting relay nodes to achieve the optimal broadcast capacity. The interference due to multiple transmissions in the same geographical area is taken into account. According to the results of this theoretical model, we propose two heuristics, one distributed and one centralized, as suboptimal but practical solutions to the relay selection problem in wireless multihop broadcasting. We discuss the broadcast capacity performances and CSI (channel state information) requirements of these algorithms. The results illustrate that the benefits of peer-assisted broadcasting are more pronounced in the centralized relay selection algorithm when compared to the fully randomized and distributed selection under a realistic system model.     

Energy-efficient joint relay node selection and power allocation over multihop relaying cellular networks toward LTE-Advanced

Cooperative relaying is emerging as an effective technology to fulfill requirements on high data rate coverage in next-generation cellular networks,like long term evolution-advanced (LTE-Advanced).In this paper,we propose a distributed joint relay node (RN) selection and power allocation scheme over multihop relaying cellular networks toward LTE-Advanced,taking both the wireless channel state and RNs’ residual energy into consideration.We formulate the multihop relaying cellular network as a restless bandit system.The first-order finite-state Markov chain is used to characterize the time-varying channel and residual energy state transitions.With this stochastic optimization formulation,the optimal policy has indexability property that dramatically reduces the computational complexity.Simulation results demonstrate that the proposed scheme can efficiently enhance the expected system reward,compared with other existing algorithms.     

Secure Energy Harvesting Communications with Relay Selection over Nakagami-m Fading Channels

In this paper, an energy harvesting relay network over Nakagami-m fading is investigated. In the considered system, the power beacon can provide wireless energy for the source and relays which deploy time-switching-based radio frequency energy harvesting technique. Two relay selection schemes, namely partial relay selection and optimal relay selection, are proposed in order to enhance the system performance. In the former, the source only has the channel state information of the first hop, while in the latter it has the full knowledge of the channel state information. The eavesdropper is able to wiretap to the signal transmitted from the source and the relays. The exact closed-form expressions of secrecy outage probability are derived. The results show that optimal relay selection performs better than partial relay selection. With increasing number of relays, the considered system shows better performance. In addition, the energy harvesting duration has a significant effect on the secrecy outage probability.     

High throughput relay policy in wireless cooperative relaying networks based on stochastic control theory

This paper proposes a distributed relay and modulation and coding scheme (MCS) selection in wireless cooperative relaying networks where the adaptive modulation and coding (AMC) scheme is applied. First-order finite-state Markov channels (FSMCs) are used to model the wireless channels and make prediction. The objective of the relay policy is to select one relay and MCS among different alternatives in each time-slot according to their channel state information (CSI) with the goal of maximizing the throughput of the whole transmission period. The procedure of relay and MCS selection can be formulated as a discounted Markov decision chain, and the relay policy can be obtained with recent advances in stochastic control algorithms. Simulation results are presented to show the effectiveness of the proposed scheme.     

Optimal reliable relay selection in multiuser cooperative relaying networks

In this paper, we investigate the problem of optimal reliable relay selection in multiuser cooperative wireless networks in the presence of malicious relay nodes. A general discrete time queueing model for such networks is introduced which takes into account the dynamic variations of the channel state, the dynamic malicious behaviour of relay nodes as well as stochastic arrival of data packets into the system. The model consists of a set of mobile users, one destination node and a set of relay nodes which may be either mobile or fixed. The system uses the benefit of cooperative diversity by relaying in the decode and forward mode. We assume that each user either transmits its packets directly to the destination (direct mode) or transmits them with the cooperation of a selected relay node (cooperative mode). It is assumed that a centralized network controller manages the relay selection process in the system. At each time slot, a malicious relay node in the system may behave spitefully and refuse to cooperate with a user deliberately when it is selected to cooperate with that user. A malicious relay node usually acts stochastically to hide its malicious behaviour for longer time. In such a system, at each time slot the network controller should decide whether a user has to cooperate with any relay node or not and if so, which relay node must be selected for cooperation. First, we show that the malicious behaviour of relay nodes makes the stable throughput region shrink. Then, we propose a throughput optimal secure relay selection policy that can stabilize the system for all the arrival rate vectors strictly inside the network stability region. We show that the optimal policy is equivalent to finding the maximum weighted matching in a weighted bipartite graph at each time slot. Finally, we use simulations to compare the performance of the proposed policy with that of four other sub-optimal policies in terms of average queue occupancy (or queueing delay).     

分布式环境中协作分集的移动中继动态选择和切换策略研究

在协作无线通信系统中,中继节点的移动会大大降低系统的性能,目前该方面的结果很少。本文探讨分布式环境中协作分集的移动中继选择算法,在放大转发（AF）协作通信模式下,给出了基于信道统计状态信息的功率分配和中继的动态选择策略。针对单中继情况提出了中继切换方案,针对多中继情况提出了动态剔除、补充中继的方案,并导出了分集增益及系统容量的计算公式。通过模拟仿真分析,该方案能有效的降低中断概率,提高系统分集增益,扩大系统容量,实现良好的整体性能。      

A game theoretic learning solution for distributed relay selection on throughput optimization

In this paper, we study the problem of distributed relay selection in wireless networks using a game theoretic approach. Specifically, we consider a system model where one relay node can be shared by multiple source-destination pairs. Our objective is to find the relay selections of source nodes to optimize the total capacity. The relay selection problem is formulated as a congestion game with player-specific payoff functions and the existence of Nash equilibrium (NE) is demonstrated. Then we propose a stochastic learning automata (SLA) based distributed relay selection approach to obtain the NE without information exchange among source nodes. Simulation results show that the proposed distributed relay selection approach achieves satisfactory performance, when compared with other solutions.     

A Store-and-Forward Cooperative MAC for Wireless Ad Hoc Networks

Cooperative communications are widely used to increase the throughput of wireless networks. It is important to select the appropriate relay nodes to enhance the performance of cooperative communications. In wireless ad hoc networks, such as IEEE802.11 WLAN, the distributed MAC is used to share the wireless channel to different nodes. In this work, a simple store-and-forward cooperative MAC (SFC-MAC) is proposed, which is fully compatible with IEEE 802.11 MAC. In SSF-MAC, the relay node just stores the packets received from the sender and forward them to the receiver after it successfully contend the channel. Furthermore, an model is built to analyze the performance of relay methods in the ideal channel and imperfect channel. We utilize throughput performance as a metric to determine whether a relay node is selected. The analysis and simulation results show that the proposed simple SSF-MAC can increase the system throughput.     

Distributed Relay Selection and Power Control for Multiuser Cooperative Communication Networks Using Stackelberg Game

The performance in cooperative communication depends on careful resource allocation such as relay selection and power control, but the traditional centralized resource allocation requires precise measurements of channel state information (CSI). In this paper, we propose a distributed game-theoretical framework over multiuser cooperative communication networks to achieve optimal relay selection and power allocation without knowledge of CSI. A two-level Stackelberg game is employed to jointly consider the benefits of the source node and the relay nodes in which the source node is modeled as a buyer and the relay nodes are modeled as sellers, respectively. The proposed approach not only helps the source find the relays at relatively better locations and "buy” an optimal amount of power from the relays, but also helps the competing relays maximize their own utilities by asking the optimal prices. The game is proved to converge to a unique optimal equilibrium. Moreover, the proposed resource allocation scheme with the distributed game can achieve comparable performance to that employing centralized schemes.     

Cross Layer Relay Selection in Device-to-Device Communication

Cross layer optimization for relay assisted wireless communication is important as it caters for parameters in more than one layer thereby a more holistic insight to the performance of proposed algorithms is realised. Due to the nature of the wireless channel, the availability of perfect channel state information may not be guaranteed. Moreover for relay selection algorithms, where mobile user equipment are used as relays, optimizing a relay defined utility can motivate relaying. This work proposes a cross layer stable matching based relay selection algorithm for relay assisted device-to-device communication. The cross layer parameter defined by this work is a function of data rate at the physical layer and queueing state information at the media access control sub-layer. The selection problem is modelled as an optimization problem for which stable matching is used to suitably allocate relay-enabled user equipment to source-destination pairs. To evaluate the performance of the proposed algorithm, spectral efficiency, energy efficiency and fairness were used as performance metrics. The proposed cross layer algorithm was compared with the best source-relay selection algorithm, best relay-destination selection algorithm and a random selection algorithm. Unlike other works, our proposed algorithm is channel uncertainty aware. The proposed cross layer selection algorithm was shown through simulations to offer improved spectral efficiency  performance of 16% over the random selection algorithm. Furthermore, there was a fairness improvement of 0.01 and 0.02 over the best source—relay and the best relay—destination selection algorithms respectively.