On the benefits of location-based relay selection in mobile wireless networks

We consider infrastructure-based mobile networks that are assisted by a single relay transmission where both the downstream destination and relay nodes are mobile. Selecting the optimal transmission path for a destination node requires up-to-date link quality estimates of all relevant links. If the relay selection is based on link quality measurements, the number of links to update grows quadratically with the number of nodes, and measurements need to be updated frequently when nodes are mobile. In this paper, we consider a location-based relay selection scheme where link qualities are estimated from node positions; in the scenario of a node-based location system such as GPS, the location-based approach reduces signaling overhead, which in this case only grows linearly with the number of nodes. This paper studies these two relay selection approaches and investigates how they are affected with varying information update interval, node mobility, location inaccuracy, and inaccurate propagation model parameters. Our results show that location-based relay selection performs better than SNR-based relay selection at typical levels of location error when medium-scale fading can be neglected or accurately predicted.     

Extending the Lifetime of Wireless Sensor Networks Through Mobile Relays

We investigate the benefits of a heterogeneous architecture for wireless sensor networks (WSNs) composed of a few resource rich mobile relay nodes and a large number of simple static nodes. The mobile relays have more energy than the static sensors. They can dynamically move around the network and help relieve sensors that are heavily burdened by high network traffic, thus extending the latter's lifetime. We first study the performance of a large dense network with one mobile relay and show that network lifetime improves over that of a purely static network by up to a factor of four. Also, the mobile relay needs to stay only within a two-hop radius of the sink. We then construct a joint mobility and routing algorithm which can yield a network lifetime close to the upper bound. The advantage of this algorithm is that it only requires a limited number of nodes in the network to be aware of the location of the mobile relay. Our simulation results show that one mobile relay can at least double the network lifetime in a randomly deployed WSN. By comparing the mobile relay approach with various static energy-provisioning methods, we demonstrate the importance of node mobility for resource provisioning in a WSN.      

Relay Placement for Coverage Extension in Cellular Wireless Networks Under Composite Fading Model

In relay-assisted cellular networks, mobile stations are connected to base station through two or more single-hop communication links, where the intermediate nodes act as relay stations (RSs). The focus of this paper is on two-hop relay assisted cellular networks, where optimal relay placement is a crucial issue for achieving maximum extension of the cell coverage. However, the location of RS has significant impact on signal-to-interference plus noise ratio (i.e., SINR) and outage probability experienced on the access and backhaul links. Moreover, the frequency re-use factor also has significant influence on the SINR. In this paper, we develop analytical models for computing the SINR and outage probability performance of a two-hop relay assisted cellular network for both downlink (DL) as well as uplink (UL) transmission scenarios, considering the impact of path loss, shadowing, Nakagami fading and co-channel interference. We then investigate optimal placement of RS while satisfying the required criterion on probability of correct decoding, initially by considering the DL scenario alone and then by considering both DL and UL scenarios jointly. Through extensive evaluations, we report the impact of realistic propagation models on outage probability, optimal relay position and the cell coverage radius. Further, the model can be used to find the impact of co-channel re-use factor on optimal relay positioning in two-hop cellular networks.     

基于NOMA的协作中继网络安全性能分析

由于非正交多址接入(Non-orthogonal Multiple Access,NOMA)能够显著提升系统的频谱资源利用率,在下一代移动通信中得到广泛应用。对NOMA环境下多中继协作网络的最优中继选择方案和系统安全性能进行了分析和讨论,其中包含窃听者仅窃听中继和窃听者同时窃听中继及源节点这2种情况下的系统安全性能表现,并与相同场景下正交多址接入(Orthogonal Multiple Access,OMA)网络进行了对比。最终的理论分析和仿真结果表明,在所提出系统模型中,当信道条件相同时,NOMA网络总能取得相较于OMA网络更好的安全性能,同时随着系统中继节点数目的增多,NOMA网络在物理层安全性能上获得更大的优势。     

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).     

Performance analysis of energy harvesting cognitive relay networks with primary interference

This paper investigates the outage performance of multihop energy harvesting cognitive relay network (EH-CRN), in which the secondary nodes are powered by dedicated power beacons based on the time splitting strategy. Assuming a multihop secondary network, we derive an analytical expression for the outage probability experienced by a secondary user by taking into account the effect of interference power from primary source. The developed outage probability model can be used to assess the impact of some key parameters on the reliability of the secondary user’s link in an EH-CRN. We then investigate the optimal location of the relay node in a one dimensional two-hop secondary network that minimizes the outage probability. Next, we study how the various system parameters such as energy harvesting efficiency, path loss exponent, harvest-to-transmit time duration ratio and transmit power from primary source affect the optimal relay location. The outage improvement achieved when the relay is placed at the optimum location is also investigated. Furthermore, the sensitivity of optimal relay location to the variations in position of the primary receiver is examined. Extensive simulation results are used to corroborate the analytical findings.     

A myopic mobile sink migration strategy for maximizing lifetime of wireless sensor networks

Network lifetime maximization is challenging particularly for large-scale wireless sensor networks. The sensor nodes near the sink node tend to suffer high energy consumption due to heavy traffic relay operations, becoming vulnerable to energy depletion. The rationale of the sink mobility approach is that as the sink node moves around, such risk of energy depletion at some nodes can be alleviated. In this paper, we first obtain the optimal mobile sink sojourning pattern by solving a linear programming model and then we mathematically analyze why the optimal solution exhibits such sojourning pattern. We use the insights from this analysis to design a simple practical heuristic algorithm for sink mobility, which utilizes only local information. Our heuristic is very different from the existing algorithms which often use the traffic volume as the main decision factor, in that we consider the variance of residual energy of neighboring sensor nodes. The simulation results show that our scheme achieves near-optimal network lifetime even with the relatively low moving speed of the mobile sink.     

Performance Modeling for Relay Cooperation in Delay Tolerant Networks

Delay tolerant networks (DTNs) rely on the mobility of nodes and sequences of their contacts to compensate for lack of continuous connectivity and thus enable messages to be delivered from end to end in a “store-carry-forward” way, where multiple relay nodes are usually employed in the message delivery process. In this paper, we focus on such relay cooperation and analytically explore its impact on the delivery performance in DTNs. Specifically, we first develop a continuous time Markov chain-based theoretical framework to model the complicated message delivery process in delay tolerant networks adopting the two-hop relay algorithm. We then derive closed-form expressions for both the expected delivery delay and the corresponding expected delivery cost, where the important relay behaviors of forwarding traffic for itself or for other nodes are carefully incorporated into the analysis.     

Causality and the Spatial–Temporal Ordering in Mobile Systems

Several mobile computing applications require that both the order and location of occurrence of events be taken into account during decision making. Thus, processes need to track the location of nodes and synchronize their clocks. The Global Positioning System can be employed to mimic a global virtual clock that keeps the local clocks of participating nodes in synchrony with each other. The global virtual clock in conjunction with a space–time vector can track the mobility of nodes. Nodes can prioritize resource requests on the basis of request time as well as the requester's distance from the resource. Two distributed mutual exclusion algorithms that employ the space–time vector are presented. The error in the estimates of a mobile node, due to clock drift, about the region in which other mobile nodes may be present is formulated. Various resource allocation policies can react differently to such errors leading to performance differences. However, every policy should ensure that resource allocation has the properties of safety, deadlock freedom, liveness, and fairness.     

Contract design for relay incentive mechanism under dual asymmetric information in cooperative networks

Cooperative relay network can effectively improve the wireless spectrum efficiency and extend the wireless network coverage. However, due to the selfish characteristics of wireless nodes, spontaneous cooperation among nodes is challenged. Moreover, wireless nodes may acquire the different network information with the various nodes’ location and mobility, channels’ conditions and other factors, which results in information asymmetry between the source and relay nodes. In this paper, the incentive issue between the relay nodes’ cooperative service and the source’s relay selection is investigated under the asymmetric information scenarios. By modeling cooperative communication as a labour market, a contract-theoretic model for relay incentive is proposed to achieve the twin objectives of ability-discrimination and effort-incentive. Considering the feature of asymmetric information, the static and dynamic information of the relay nodes are systematically discussed. To effectively incentivize the potential relay nodes to participate in cooperative communication, the optimization problems are formulated to maximize the source’s utility under the multiple information scenarios. A sequential optimization algorithm is proposed to obtain the optimal wage-bonus strategy with the low computational complexity under the dual asymmetric information scenario. Simulation results show that the optimal contract design scheme is effective in improving the performance of cooperative communication.     

Cluster-based location service schemes in VANETs: current state,challenges and future directions

Vehicular Ad hoc Networks (VANETs) have drawn incredible interest in both academic and industrial sectors due to their potential applications and services. Vehicles’ position plays a significant role in many location-based applications and services such as public emergency, vehicles tracking, resource discovery, traffic monitoring and position-based routing. A location service is used to keep up-to-date records of current positions of vehicles. However, locating vehicles’ positions and maintaining an accurate view of the entire network are quite challenging tasks due to the high number of nodes, and high and fast nodes mobility which results in rapid topological changes and sudden network disconnections. In the past literature, various location-based services have been proposed to solve the above mentioned issues. Moreover, the cluster-based location service schemes have gained a growing interest due to their advantages over non-cluster-based schemes. The cluster-based schemes improve the network scalability, reduce the communications overhead and resolve the mobility issues within the clusters preventing them from propagating in the whole network. Therefore, this paper presents the taxonomy of the existing location service schemes, inspects the cluster-based location service by highlighting their strengths and limitations, and provides a comparison between location-based clustering and application specific clustering such as the one used in routing, information dissemination, channel access management and security. In addition, the existing clustering schemes, challenges and future directions for efficient cluster-based location service are also discussed.

     

Relaying in mobile ad hoc networks: The Brownian motion mobility model

Mobile ad hoc networks are characterized by a lack of a fixed infrastructure and by node mobility. In these networks data transfer can be improved by using mobile nodes as relay nodes. As a result, transmission power and the movement pattern of the nodes have a key impact on the performance. In this work we focus on the impact of node mobility through the analysis of a simple one-dimensional ad hoc network topology. Nodes move in adjacent segments with reflecting boundaries according to Brownian motions. Communications (or relays) between nodes can occur only when they are within transmission range of each other. We determine the expected time to relay a message and compute the probability density function of relaying locations. We also provide an approximation formula for the expected relay time between any pair of mobiles.     

Theoretical Limits for Time Delay Based Location Estimation in Cooperative Relay Networks

Node localization in wireless networks is crucial for supporting advanced location-based services and improving the performance of network algorithms such as routing schemes. In this paper, we study the fundamental limits for time delay based location estimation in cooperative relay networks. The theoretical limits are investigated by obtaining Cramer–Rao Lower Bound (CRLB) expressions for the unknown source location under different relaying strategies when the location of the destination is known and unknown. More specifically, the effects of amplify-and-forward and decode-and-forward relaying strategies on the location estimation accuracy are studied. Furthermore, the CRLB expressions are derived for the cases where the location of only source as well as both source and destination nodes are unknown considering the relays as reference nodes. In addition, the effects of the node topology on the location estimation accuracy of the source node are investigated. The results reveal that the relaying strategy at relay nodes, the number of relays, and the node topology can have significant impacts on the location accuracy of the source node. Additionally, knowing the location of the destination node is crucial for achieving accurate source localization in cooperative relay networks.     

Deadline-aware scheduling of cooperative relayers in TDMA-based wireless industrial networks

In this paper we consider a scenario in which a set of source nodes wishes to transmit real-time data packets periodically to a central controller over lossy wireless links, while using a TDMA-based medium access control protocol. Furthermore, a number of relay nodes are present which can help the source nodes with packet retransmissions. The key question we consider in this paper is how to schedule the TDMA slots for retransmissions while taking advantage of the relay nodes, so that the average number of packets missing their deadlines is minimized. We provide a problem formulation for the general deadline-aware TDMA relay scheduling problem. Since the design space of the general problem is large, we also present one particular class of restricted TDMA relay scheduling problems. We suggest and numerically investigate a range of algorithms and heuristics, both optimal and suboptimal, of the restricted scheduling problem, which represent different trade-offs between achievable performance and computational complexity. Specifically, we introduce two different Markov Decision Process (MDP) based formulations for schedule computation of the restricted TDMA relay scheduling problem. One MDP formulation gives an optimal schedule, another (approximate) formulation gives a sub-optimal schedule which, however, comes very close to the optimal performance at much more modest computational and memory costs.     

Evaluating performance of two-hop routing in DTN based on Home-MEG model

Performance analysis in delay tolerant networks (DTN) is often based on unrealistic mobility models. Recently, the Home-MEG model is proposed. This model is able to accurately reproduce the power law and exponential decay distribution of inter-contact times between mobile nodes which has been observed in many real motion traces. This letter proposes a theoretical framework to evaluate the performance of two-hop routing based on Home-MEG model for the first time. Simulation results show the accuracy of our theoretical model. Using the model, we explore the impact of some parameters (e.g. the number of relay nodes) on the routing performance.     

无线传感器网络中分区移动服务路由机制

在无线传感器网络中,利用节点的移动传输数据,可有效提高网络吞吐量和延时性能。文中提出了一种新的受控移动机制——分区移动服务路由机制。该机制根据移动节点个数划分服务区,采用最近邻点法对节点移动路径进行规划,利用移动节点对所在服务区的静止节点的数据传输提供中继服务。仿真结果表明,与不分区移动服务路由机制相比,分区移动服务路由机制可提高网络吞吐量,减少数据传输延时和延时抖动,更加适用于高服务质量要求的业务。     

A Mobility-Prediction-Based Relay Deployment Framework for Conserving Power in MANETs

There has been a growing interest in designing mobile systems consisting of special relay nodes whose mobility can be controlled by the underlying network. In this paper, we consider the design of a heterogeneous mobile ad hoc network (MANET) consisting of two kinds of mobile nodes-traditional nodes with limited energy and a few controllable mobile relay nodes with relatively abundant energy resources. We propose a novel relay deployment framework that utilizes mobility prediction and works in tandem with the underlying MANET routing protocol to optimally define the movement of the relay nodes. We present two instances of the relay deployment problem, together with the solutions, to achieve different goals. Instance 1, termed Min-Total, aims to minimize the total energy consumed across all the traditional nodes during data transmission, while instance 2, termed Min-Max, aims to minimize the maximum energy consumed by a traditional node during data transmission. Our solutions also enable the prioritization of individual nodes in the network based on residual energy profiles and contextual significance. We perform an extensive simulation study to understand the trade-offs involved in deploying an increasing fraction of such relay nodes in the network. We also investigate the performance of the proposed framework under different mobility prediction schemes. Results indicate that even when the relay nodes constitute a small fraction of the total nodes in the network, the proposed framework results in significant energy savings. Further, we observed that while both the schemes have their potential advantages, the differences between the two optimization schemes are clearly highlighted in a sparse network.     

A Privacy Preserving Method Using Privacy Enhancing Techniques for Location Based Services

The move towards service-oriented architectures and the increasing usage of mobile devices to access such services are two of the major changes in modern computing. Information about the user, their location and their trajectory can provide additional context information to a service, leading to useful applications such as directing a user to the nearest bus stop and displaying which buses are due to arrive in the next minutes. While this type of information can be useful, when the offered services are trusted, it also introduces privacy issues relating to gathering of location information for non-trusted applications like location-based marketing or user behaviour profiling. Users can limit their location information provided to a service but these controls are simple, making it important for the user to understand how their location information is being used by services. This paper reviews some of the methods currently being proposed to reduce the impact of location tracking on user privacy, and presents a novel encryption method for preserving the location and trajectory path of a user using Privacy-Enhancing Technologies.     

A Secure Relay-Assisted Handover Protocol for Proxy Mobile IPv6 in 3GPP LTE Systems

The LTE (Long Term Evolution) technologies defined by 3GPP is the last step toward the 4th generation (4G) of radio technologies designed to increase the capacity and speed of mobile telephone networks. Mobility management for supporting seamless handover is the key issue for the next generation wireless communication networks. The evolved packet core (EPC) standard adopts the proxy mobile IPv6 protocol (PMIPv6) to provide the mobility mechanisms. However, the PMIPv6 still suffers the high handoff delay and the large packet lost. Our protocol provides a new secure handover protocol to reduce handoff delay and packet lost with the assistance of relay nodes over LTE networks. In this paper, we consider the security issue when selecting relay nodes during the handoff procedure. During the relay node discovery, we extend the access network discovery and selection function (ANDSF) in 3GPP specifications to help mobile station or UE to obtain the information of relay nodes. With the aid of the relay nodes, the mobile station or UE performs the pre-handover procedure, including the security operation and the proxy binding update to significantly reduce the handover latency and packet loss. The simulation results illustrate that our proposed protocol actually achieves the performance improvements in the handoff delay time and the packet loss rate.     

A distributed location management strategy for next- generation IP-based wireless networks

1 Introduction Mobility management is a key technical aspect in mobile communication systems. The main purpose of mobility management is to enable mobile terminals or users to communicate with each other continuously while moving—— while minimizing data…