Cooperative MAC Design in Multi-Hop Wireless Networks—Part II: When Source and Destination are Two-Hops Away from Each Other

Ubiquitous and pervasive computing and networking are envisaged as part of the future 5G wireless communication landscape where devices which are multi-hops away from each other are connected in a cooperative way. In this paper, we investigate a challenging case in cooperative communications where source and destination are two-hops away from each other. From the perspective of MAC design, we propose a novel MAC protocol which enables two-hop cooperative communications by involving one or more one-hop neighbors of both source and destination as the relays for cooperative communication. To do so, a concept referred to as Multiple Relay Points (MRPs) has been introduced and the MRPs are selected by jointly considering the link quality of both hops. In addition to employing a static scheme which always uses a fixed number of relays for cooperative communication, we have also proposed an adaptive scheme which can optimally adjust the number of relays flexibly according to channel conditions. Through performance evaluation and comparison with the original IEEE 802.11 based scheme, we demonstrate that more reliable communications, reduced transmission power and significant throughput improvement can be achieved by using our two-hop cooperative MAC protocol, especially when operated in the adaptive mode.     

Geographic random forwarding (GeRaF) for ad hoc and sensor networks: multihop performance

In this paper, we propose a novel forwarding technique based on geographical location of the nodes involved and random selection of the relaying node via contention among receivers. We focus on the multihop performance of such a solution, in terms of the average number of hops to reach a destination as a function of the distance and of the average number of available neighbors. An idealized scheme (in which the best relay node is always chosen) is discussed and its performance is evaluated by means of both simulation and analytical techniques. A practical scheme to select one of the best relays is shown to achieve performance very close to that of the ideal case. Some discussion about design issues for practical implementation is also given.     

A Non-Orthogonal Selection Cooperation Protocol with Interference in Multi-Source Cooperative Networks

This work proposes a non-orthogonal selection cooperation scheme with interference for multi-source and single destination cooperative networks. In our model, the source nodes can cooperate for one another, i.e., each source node plays the dual role of a source and a relay, thus there is no need for relays. In addition, the source nodes can be continuously transmitted and without dedicated timeslots for cooperative transmissions, which can save system resources and improve spectral efficiency. However, by this way, it will introduce interference with the non-orthogonal transmission mechanism. To overcome this problem, we use general reception scheme in source nodes and successive interference cancellation technology in the destination node, which can reduce the effect of interference effectively. For interference-limited networks, we also derive the theoretical upper bound and lower bound of outage probability of our method. Through the outage probability analysis and comparison, the results show that the spectral efficiency is improved while the system still keeps acceptable transmission reliability.

     

基于非对称信道状态信息的协作通信：一种契约理论建模方法

In relay-assisted cooperative com-munication, relay nodes help forwarding the information of a source node in case of link failure between the source and a destination. Although user cooperation improves the over-all efficiency of the network, it requires incen-tive to stimulate potential relay nodes to assist the source by forwarding its data to the desti-nation. Moreover, the potential relays are bet-ter informed than the source about their chan-nel conditions to destination, which results in asymmetric information between the source and the relays. In this paper, we study the problem of lack of forwarding incentive in cooperative communication when channel state information of relays is private infor-mation and not known by the source. To tackle this problem, we apply the principle of contract theory to a cooperative wireless system. Source first designs incentive compatible and individually rational contract, consisting of a set of power-credit pairs. Then it broadcasts contract items to nearby nodes. Once the source node receives reply messages from the volunteer relays, it chooses one or more relays based on its re-quirements and communication starts. Simulation results show how credit assignment works in order to stimulate relays to cooperate and prevents relays from cheating behavior.     

无线网络中基于DSDV的最大化吞吐量的协作路由算法

为最大化无线自组织网络的吞吐量,提出一种自适应的协作路由算法。在算法中,协作分集技术与路由选择相结合,通过在路由的每一跳选择最佳的中继节点协作发送节点传输信息来改善网络吞吐量。首先通过目的序列距离矢量路由协议（DSDV）初步建立最短路由路径,在每条链路的发送节点和接收节点根据邻节点表选出公共邻居节点,建立候选中继集合;进一步,每一跳根据链路吞吐量,在候选中继集合中自适应选择最多两个中继来协助发送节点进行传输,并根据选出的中继节点数动态分配节点发射功率。在保证系统发射功率一定的情况下,最大化网络吞吐量。仿真结果表明,在相同的发射功率下,相对于非协作路由DSDV算法,采用固定数量中继的协作路由算法提高了整个网络的吞吐量,而自适应的协作路由算法可进一步提高吞吐量;同时仿真了网络吞吐量与网络规模和节点最大移动速度的变化关系。      

Multi-hop routing with cooperative transmission: a cross-layer approach

Cooperative diversity techniques have received a lot of attention recently due to their ability to provide spatial diversity in fading wireless environment without the requirement of implementing multiple antenna on the same device. It increases link reliability, provides higher capacity, reduces transmit power, and extends transmission range for the same level of performance and modulation rate. In this paper, we study the achievable gain of cooperative communications from a wireless cross-layer point of view in multi hop networks. We propose two routing algorithms applicable for wireless ad hoc networks. First, we propose an edge node based on a greedy cooperative routing (ENBGCR) algorithm, where we modify the geographic routing algorithm to incorporate the cooperative transmission and extend the coverage range of the nodes. The main objective of ENBGCR algorithm is to minimize the number of hops that messages transverse to reach their destination. Then the energy-efficient cooperative routing algorithm is proposed to minimize the end-to-end total transmission power subject to end-to-end target data rate. Simulation results for both algorithms show that the proposed strategies have great improvement in terms of delay and power saving respectively for the same quality of service requirement as compared to traditional algorithms.     

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.     

车载自组织网中基于车辆密度的可靠性路由协议

为了降低转发节点在转发范围内直接寻找一个最优或次优节点的复杂度、减少平均跳数和提高链路的可靠性,提出一种车载自组织网络中基于车辆密度的可靠性路由协议,转发节点首先根据道路车辆密度设置最优块的大小,并将转发范围分割成若干大小相等的块,然后选择其中一个距离转发节点最远的块,最后在被选中的块里根据可靠性原则选择连接时间最长的邻居节点作为中继节点进行转发。仿真结果表明,与EG-RAODV 相比,所提路由协议的平均跳数较少,平均每跳前进距离较大,能够使数据分组快速到达目的节点。     

IPool-ADELIN: An extended ADELIN based on IPool node for reliable transport of Underwater Acoustic Sensor Networks

ADELIN (ADaptive rELIable traNsport) protocol is a reliable transport protocol only based on FEC (Forward Error Correction) for UASN (Underwater Acoustic Sensor Networks). In cooperative scenario, ADELIN improves its reliability of data packet transmission further by forwarding node redundancy, which wastes the limited energy and bandwidth of nodes. In this paper, the IPool-ADELIN protocol is proposed and shown to help reduce energy consumption. In IPool-ADELIN, by overhearing the data transmissions, the IPool node not only relays the data packets, which are not implicitly acknowledged, but also does local link maintenance when the BER (Bit Error Rate) of the monitored link is high. The results of mathematical analysis and simulations show that IPool-ADELIN has a higher data delivery ratio and lower energy consumption.     

Impact of relative speed on node vicinity dynamics in VANETs

Communication protocols generally rely on the existence of very long multihop paths to reach distant nodes. They disregard, however, how often such paths indeed occur, and how long they persist, especially in highly dynamic mobile networks. In this direction, this paper evaluates quantitatively the influence of node relative speed on path establishment and maintenance, using real and synthetic vehicular network traces. We propose a methodology for vehicular network analysis where both relative speeds and hop distances are used as parameters to characterize node vicinity. Results show that contact opportunities highly depend on the relative speed and the hop distance between nodes. In sparser scenarios, the number of contacts between nodes separated by more than 3 hops or even between neighbors with relative speed above 40 km/h is negligible. This confirms the intuition that contacts at lower relative speeds and at few hop distances happen more often. In addition, contacts last longer as the number of hops between nodes decreases. Nevertheless, we can still find multihop paths able to transmit messages at high relative speeds, even though less often. We also demonstrate that relative speeds reduce the number of useful contacts more severely when compared to the hop distance. For last, we show that it is possible to increase the number of successful packet transmissions by simply applying the outcomes of this work, without any sophisticated model, avoiding the waste of resources, such as energy and bandwidth.

     

Localized energy efficient routing in mobile ad hoc networks

We consider the problem of localized energy aware routing in mobile ad hoc networks. In localized routing algorithms, each node forwards a message based on the position of itself, its neighbors and the destination. The objective of energy aware routing algorithms is to minimize the total power for routing a message from source to destination or to maximize the total number of routing tasks that a node can perform before its battery power depletes. In this paper we propose new localized energy aware routing algorithms called OLEAR. The algorithms have very high packet delivery rate with low packet forwarding and battery power consumption. In addition, they ensure good energy distribution among the nodes. Finally, packets reach the destination using smaller number of hops. All these properties make our algorithm suitable for routing in any energy constrained environment. We compare the performance of our algorithms with other existing energy and non‐energy aware localized algorithms. Simulation experiments show that our algorithms present comparable energy consumption and distribution to other energy aware algorithms and better packet delivery rate. Copyright © 2006 John Wiley & Sons, Ltd.     

一种能量平衡的无线体域网络AODV多播路由发现协议

在动态网络拓扑中,AODV协议通过数据源节点S泛洪广播RREQ消息请求到任意目标节点D的路由,而在无线体域网络中,只有一个sink目标节点,除最短跳数路由上的节点外,其他参与RREQ接收和转发的节点浪费了能量。提出了一种能量平衡的无线体域网络AODV多播路由发现协议,通过在节点广播的hello消息中增加到sink的最小跳数hops、到sink的下一跳节点next和节点本身是否具备转发能力isforward 3 个参数,只选择能到达sink节点的邻居节点参与转发RREQ消息,变广播为多播,有效地降低了路由发现的能量开销,并通过能量平衡延长了WBAN的使用寿命。性能分析与模拟实验表明,该协议在RREQ数量、数据传输率和能量消耗等方面优于相似协议EAAODV。     

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).     

Cooperative Strategies and Achievable Rate for Tree Networks With Optimal Spatial Reuse

In this paper, a low-complexity cooperative protocol that significantly increases the average throughput of multihop upstream transmissions for wireless tree networks is developed and analyzed. A system in which transmissions are assigned to nodes in a collision free, spatial time division fashion is considered. The suggested protocol exploits the broadcast nature of wireless networks where the communication channel is shared between multiple adjacent nodes within interference range. For any upstream end-to-end flow in the tree, each intermediate node receives information from both one-hop and two-hop neighbors and transmits only sufficient information such that the next upstream one-hop neighbor will be able to decode the packet. This approach can be viewed as the generalization of the classical three node relay channel for end-to-end flows in which each intermediate node becomes successively source, relay and destination. The achievable rate for any regular tree network is derived and an optimal schedule that realizes this rate in most cases is proposed. Our protocol is shown to dramatically outperform the conventional scheme where intermediate nodes simply forward the packets hop by hop. At high signal-to-noise ratio (SNR), it yields approximately 66% throughput gain for practical scenarios.     

Relay-Assisted Decorrelating Multiuser Detector (RAD-MUD) for Cooperative CDMA Networks

In this paper, we examine the uplink of a cooperative CDMA network, where users cooperate by relaying each other's messages to the base station. When spreading waveforms are not orthogonal, multiple access interference (MAI) exists at the relays and the destination, causing cooperative diversity gains to diminish. To address this issue, we adopt the multiuser detection (MUD) technique to mitigate MAI in achieving the full advantages of cooperation. Specifically, the relay-assisted decorrelating multiuser detector (RAD-MUD) is proposed to separate interfering signals at the destination with the help of preceding at the relays along with pre-whitening at the destination. Unlike the conventional zero-forcing (ZF) precoder or the decorrelating MUD, the proposed RAD-MUD experiences neither power expansion at the relays nor noise amplification at the destination. Three cooperative transmission strategies are considered on top of RAD-MUD; namely, transmit beamforming, selective relaying and distributed space-time coding. Since the reliability of each source-relay and/or relay-destination links are different, relay transmissions are weighted accordingly in our schemes to further combat MAI. The advantages of RAD-MUD over ZF precoding and other existing cooperative MUD schemes are shown through computer simulations.     

直达链路下的能量采集中继选择系统的吞吐量分析

针对三节点传输系统，研究了基于功率分配能量采集的全双工放大转发协作中继方案。考虑源和目的地之间存在直达链路，全双工中继节点采用天线选择技术以最小化中继自干扰，目的节点采用最大比合并技术以最大化目的地接收信噪比。在延迟受限传输模式下，运用高斯-切比雪夫积分推出了系统吞吐量的近似闭合表达式。在延迟容忍传输模式下，运用凸优化推出了系统吞吐量下界的闭合表达式。在多中继情况下考虑了最佳中继选择策略和机会式中继选择策略。数值分析和蒙特卡洛仿真表明，增加中继个数或者减小速率阈值均能提高系统吞吐量。      

Exploiting the attenuation of fiber-optic passive taps to createlarge high-capacity LANs and MANs

A local- or metropolitan-area network (LAN or MAN) that exploits the power losses of fiber-optic passive taps so that wavelengths can be reused in different portions of the network is proposed. This wavelength reuse makes it possible to design a large, high-capacity, multichannel network with many concurrent transmissions. An arbitrary number of nodes is supported by allowing packets to take multiple hops, when necessary, to reach their destinations. In one example configuration, there are two closed circular loops of fiber, one for transmissions in the clockwise direction and one for counterclockwise transmissions. Each node has one passive tap (per fiber), which is used for both a fixed-wavelength transmitter and a fixed-wavelength receiver     

BER-Constrained Incremental Relaying with Relay Selection in Cooperative Wireless Networks

One of the main drawbacks of cooperative communication systems with half-duplex relaying is inefficient use of spectrum. Incremental relaying is an effective technique that overcomes this limitation, particularly in the high-SNR regime. In this paper, for a multi-relay cooperative network with arbitrary number of relay nodes, we propose a spectrally-efficient incremental relaying scheme that eliminates redundant relay transmissions such that an average end-to-end bit error rate (BER) constraint is satisfied. For detect-and-forward relaying, under the assumption of error propagation from the relays to the destination, we analyze the performance of the system in terms of the end-to-end BER, the average spectral efficiency and the outage probability for Rayleigh fading environment. The performance of the system depends on a single threshold employed by the relays and the destination. We optimize this threshold such that the average spectral efficiency of the system is maximized under an average end-to-end BER constraint. This optimization criterion results in a constant-BER, variable-spectral efficiency relaying scheme. The proposed scheme makes use of spectrum as efficiently as possible, while providing the required quality of service at the destination.     

Security versus reliability analysis for multi-eavesdropper cooperation wireless networks with best relay

Physical-layer security could be used to effectively combat eavesdroppers and the transmission reliability of the main link could be improved.A wireless relay network with multiple both decode and forward eavesdroppers and relays were considered,in the presence of the link from source to destination.A best relay selection scheme based on multieavesdropper’s cooperation was proposed,and the outage probability and the intercept probability was deduced under both schemes without relay and with best relay.Then,the security and reliability influenced by different relay selection schemes were analyzed.The simulation results show that the achievable channel capacity at the destination node and the system outage probability are directly affected by different relay selection scheme.Lower system outage probability can be achieved by the proposed scheme,and the system outage probability and intercept probability are both decreased with the increase of the number of relays.The intercept probability increases with the increase of the number of eavesdroppers,which,however,can be reduced by increasing the number of relays to ensure the main link’s reliable transmission.     

基于任一随机选择转接节点的协作分集方法及其中断概率分析

 转接节点的选择是协作通信中的一个比较重要的问题.在许多实际情况中并不是所有节点都参与转接,本文研究了在所有潜在的转接节点中任选一个节点作为转接节点的协作分集方法,推导了这种协作分集方法中断概率的上界和下界.理论计算和仿真结果表明该协作分集的 中断概率的上界基本不随潜在的转接节点的数目的增加而变化,而下界却随潜在的转接节点的数目的增加而显著降低.