支持MIMO链路的Ad hoc网络中的链路激活型拓扑未知MAC协议

该文提出了支持多输入多输出(MIMO)链路的Ad hoc网络的链路激活型拓扑未知多址接入协议。该协议利用正交拉丁方来为网络链路分配传输时隙,保证每个链路在1帧中至少有1个时隙可以成功传输。推导了该协议的平均吞吐量,并以最大化平均吞吐量为准则给出了选择协议参数的方法。数值结果表明,与已有链路激活型和节点激活型拓扑未知协议相比,本文的协议可以提高网络节点的吞吐量。     

MIMO广播信道中联合多用户速率和延迟约束调度的研究

该文给出了一种多入多出高斯广播信道中具有延迟约束的多用户无线数据包的传输方案。首先,在信道的QR分解及脏纸编码基础上,通过贪婪算法获取多用户分集与包延迟约束之间的有效结合。其次,将包到达速率、可达服务速率、用户数以及传输天线数构成一优化问题,得到最佳的用户组合及调度周期。最后,在不同用户数及发射天线数情况下对该方案进行了性能仿真,仿真结果表明：在满足包传递最小延迟等待要求的同时,得到了传输容量的最大化。     

移动分布式无线网络中具有QoS保证的UPMA协议

该文基于有效竞争预约接入、无冲突轮询传输的思想提出了支持节点移动性、多跳网络结构和服务质量(QoS)的依据用户妥善安排的多址接入(UPMA)协议。它大大提高了信道的使用效率,保证了发送节点能快速接入信道,同时,最大程度地保证所有实时业务的时延和带宽要求。最后,我们考察了它对Internet数据业务的支持性能。     

Spatial compatible user grouping algorithm for multiuser MIMO systems

A spatial compatible user grouping algorithm is proposed to reduce CoChannel Interference （CCI） in Space Division Multiple Access （SDMA） multiuser Multiple Input Multiple Output （MIMO） systems. We evaluate the interferences among Users by use of distances between row spaces spanned by users＇ channel matrixes, then control frequency sharing according to the compatible user grouping algorithm. Results show that the row space distance algorithm outperforms others because it can fully utilize the information from users＇ channel matrixes, especially the matrix structure information. The results also prove that the algorithm based on channel matrix structure analysis is a better candidate for spatial compatibility approximation.     

MIMO广播系统中基于有限反馈的多用户选择新算法

在基于有限反馈多输入多输出(MIMO)广播系统的多用户选择研究中,目前已有的用户信噪干扰比(SINR)估计存在较大误差,这使得整个系统的性能受到制约。该文利用推导出的上下界来联合估计用户接收到的有用信号功率,得到了一种误差较小的SINR估计式,并基于该式给出了一种用户选择新算法。仿真结果表明,新的用户选择算法可以在低信噪比和高信噪比下同时达到较优性能,且复杂度较低。     

An efficient reliable broadcasting protocol for wireless mobile ad hoc networks

The mobile ad hoc network (MANET) has recently been recognized as an attractive network architecture for wireless communication. Reliable broadcast is an important operation in MANET (e.g., giving orders, searching routes, and notifying important signals). However, using a naive flooding to achieve reliable broadcasting may be very costly, causing a lot of contention, collision, and congestion, to which we refer as the broadcast storm problem. This paper proposes an efficient reliable broadcasting protocol by taking care of the potential broadcast storm problem that could occur in the medium-access level. Existing protocols are either unreliable, or reliable but based on a too costly approach. Our protocol differs from existing protocols by adopting a low-cost broadcast, which does not guarantee reliability, as a basic operation. The reliability is ensured by additional acknowledgement and handshaking. Simulation results do justify the efficiency of the proposed protocol.     

A dual reservation CDMA-based MAC protocol with power control for ad hoc networks

This paper proposes a new multi-channel Medium Access Control （MAC） protocol named as Dual Reservation Code Division Multiple Access （CDMA） based MAC protocol with Power Control （DRCPC）. The code channel is divided into common channel, broadcast channel and several data channels. And dynamic power control mechanism is implemented to reduce near-far interference. Compared with IEEE 802.11 Distributed Coordination Function （DCF） protocol, the results show that the proposed mechanism improves the average throughput and limits the transmission delay efficiently.     

Throughput analysis for interference limited TDMA and TDMA/CDMA wireless ad hoc networks

The node throughput, which is defined as the total rate received at each node, is evaluated for the interference limited TDMA and TDMA/CDMA wireless ad hoc networks. In the TDMA wireless ad hoc network, there is only one transmission link connected to each node in the same time slot, whereas in the TDMA/CDMA wireless ad hoc network there are multiple transmission links connected to each node in the same time slot. We first derive the node throughput for these two wireless ad hoc networks and then make a comparison of the node throughput between them. The theoretical results and simulation results both reveal that the TDMA wireless ad hoc network outperforms the TDMA/CDMA wireless ad hoc network in the node throughput. Copyright © 2008 John Wiley & Sons, Ltd.     

Performance of MIMO cross‐layer MAC protocol based on antenna selection in ad hoc networks

In this paper, we investigate the performance of a cross‐layer (physical and MAC) design for multiple‐input multiple‐output (MIMO) system that aims at maximizing the throughput of ad hoc networks by selecting the optimum antenna combination. Employing this cross‐layer design is shown to improve the overall network performance relative to the case where no antenna selection (AS) is used. To solve the node blocking problem associated with the IEEE 802.11 medium‐access control (MAC) protocol, the proposed protocol leverage the available degrees of freedom offered by the MIMO system to allow neighboring nodes to simultaneously communicate using the zero‐forcing (ZF) Bell‐labs layered space‐time (BLAST) architecture. Using the cross‐layer design, neighboring nodes share their optimum antenna selection (AS) information through control messages. Given this shared information, nodes set their decisions on the number of selected antennas based on the available spatial channels that guarantees collision‐free transmissions. At the destination node, the ZF receiver is employed to extract the desired user data while treating the data from neighboring users as interference. The performance of the proposed cross‐layer design is examined through simulations, where we show that the network throughput is significantly improved compared to conventional MAC protocols. Copyright © 2010 John Wiley & Sons, Ltd.     

Efficient broadcast for wireless ad hoc networks with a realistic physical layer

In this paper, we investigate the low coverage problem of efficient broadcast protocols in wireless ad hoc networks with realistic physical layer models. To minimize energy consumption, efficient protocols aim to select small set of forward nodes and minimum transmission radii. In ideal physical layer model, nodes within forward nodes’ transmission ranges can definitely receive packets; therefore energy efficient protocols can guarantee full coverage for broadcasting. However, in networks with a realistic physical layer, nodes can only receive packets with probability. We present an analytical model to show that the transmission radii used for nodes can be used to establish a tradeoff between minimizing energy consumption and ensuring network coverage. We then propose a mechanism called redundant radius, which involves using two transmission radii, to form a buffer zone that guarantees the availability of logical links in the physical network, one for broadcast tree calculation and the other for actual data transmission. With this mechanism, we extend well-known centralized protocols, BIP and DBIP, and corresponding localized protocols, LBIP and LDBIP. The effectiveness of the proposed scheme in improving network coverage is validated analytically and by simulation.     

Network mobility protocol for vehicular ad hoc networks

The goal of the network mobility management is to effectively reduce the complexity of handoff procedure and keep mobile devices connecting to the Internet. When users are going to leave an old subnet and enter a new subnet, the handoff procedure is executed on the mobile device, and it may break off the real‐time service, such as VoIP or mobile TV, because of the mobility of mobile devices. Because a vehicle is moving so fast, it may cause the handoff and packet loss problems. Both of the problems will lower down the throughput of the network. To overcome these problems, we propose a novel network mobility protocol for vehicular ad hoc networks. In a highway, because every car is moving in a fixed direction at a high speed, a car adopting our protocol can acquire an IP address from the vehicular ad hoc network through the vehicle‐to‐vehicle communications. The vehicle can rely on the assistance of a front vehicle to execute the prehandoff procedure, or it may acquire a new IP address through multihop relays from the car on the lanes of the same or opposite direction and thus may reduce the handoff delay and maintain the connectivity to the Internet. Simulation results have shown that the proposed scheme is able to reduce both the handoff delay and packet loss rate. Copyright © 2013 John Wiley & Sons, Ltd.     

Estimating the value of co-operation approaches for multi-hop ad hoc networks

In multi-hop ad hoc networks, each node may be involved in forwarding data acting as a router. Unfortunately, in civilian scenarios with usually an open community, it is not obvious why nodes should forward foreign data and waste their battery power, CPU cycles, etc. Some work has already been done in proposing approaches to intensify participation in ad hoc networks. However, it is more or less a question of belief whether these approaches really benefit the community. This work gives a rational estimation of the effect of approaches that intensify participation in ad hoc networks. We present essential results assuming in particular low-dense networks that use on-demand routing protocols by applying some fundamental statistics to the problem.     

Capacity evaluation of multi-channel wireless ad hoc networks

In this paper, the capacity of multi-channel, multi-hop ad hoc network is evaluated.In particular, the performance of multi-hop ad hoc network with single channel IEEE 802.11 MAC utilizing different topologies is shown. Also the scaling laws of throughputs for largescale ad hoc networks and the theoretical guaranteed throughput bounds for multi-channel grid topology systems are proposed. The results presented in this work will help researchers to choose the proper parameter settings in evaluation of protocols for multi-hop ad hoc networks.     

Trading latency for energy in densely deployed wireless ad hoc networks using message ferrying

Wireless mobile ad hoc networks (MANETs) have the potential for use in important application environments, such as remote environmental monitoring, where energy resources are limited. Efficient power management is necessary to allow these networks to operate over a long period of time. One of the key factors affecting the design of power management mechanisms is the routing protocol in use within the network. In this paper, we investigate the Message ferrying (MF) routing paradigm as a means to save energy while trading off data delivery delay. In MF, special nodes called ferries move around the deployment area to deliver messages for nodes. While this routing paradigm has been developed mainly to deliver messages in partitioned networks, here we explore its use in a connected MANET. The reliance on the movement of ferries to deliver messages increases the delivery delay if a network is not partitioned. However, delegating message delivery to ferries provides the opportunity for nodes to save energy by aggressively disabling their radios when ferries are far away. To exploit this feature, we present a power management framework, in which nodes switch their power management modes based on knowledge of ferry location. We evaluate the performance of our scheme using ns-2 simulations and compare it with a multihop routing protocol, dynamic source routing (DSR). Our simulation results show that MF achieves energy savings as high as 95% compared to DSR without power management and still delivers more than 98% of messages. In contrast, a power-managed DSR delivers many fewer messages than MF to achieve similar energy savings. In the scenario of heavy traffic load, the power-managed DSR delivers less than 20% of messages. MF also shows robust performance for highly mobile nodes, while the performance of DSR suffers significantly. Thus, delay tolerant applications can use MF rather than a multihop routing protocol to save energy efficiently when both routing approaches are available.     

一种新的紫外光自组织网络的时分多址接入邻居发现算法

为了适应大 规模及拓扑变化较快的紫外光(UV)自组织网络,本文以提高邻居发现概率为目的,提出了一 种基于时分多址接入(TDMA, time division multiple access)的UV定向邻居发现新算法。新算法在DTRA(directional transmission and reception algorithm)协议的基础上采用了退避时延机制, 并通过邻居判断和维护机制让节点快速更新本地邻居表。实验结果表明,新 算法充分考虑了UV大气传输特性,能够有效地解决节点冲突问题,并通过找到一个最佳退避 时延使得节点冲突 概率和邻居发现时延之间达到一个较好的平衡。     

QoS routing through alternate paths in wireless ad hoc networks

Quality of service (QoS) routing plays an important role in QoS provisioning for mobile ad hoc networks. This work studies the issue of route selection subject to QoS constraint(s). Our method searches for alternate routes with satisfied QoS requirement(s) to accommodate each communication request when the shortest path connecting the source–destination pair of the request is not qualified. In order to effectively reduce protocol overhead, a directed search mechanism is designed to limit the breadth of the searching scope, which aims at achieving a graceful tradeoff between the success probability in QoS route acquisition and communication overhead. Efficient hop‐by‐hop routing protocols are designed for route selection subject to delay and bandwidth constraint, respectively. Simulation results show that the designed protocols can achieve high performance in acquiring QoS paths and in efficient resource utilization with low control overhead. Copyright © 2004 John Wiley & Sons, Ltd.     

天线选择对MIMO信道容量的影响

该文首先分析了多天线系统的信道容量,然后研究了当信道矩阵非满秩时,选择发射和接收天线对信道容量的影响。仿真试验结果表明,发射天线选择能提高系统容量,同时选择发射和接收天线虽然减小了复杂度和硬件成本,但对系统容量的增加低于单独进行发射天线选择时的情况。     

Defense against misbehavior in anonymous vehicular ad hoc networks

Vehicular ad hoc network (VANET) can offer various services and benefits to VANET users and thus deserves deployment effort. Misusing such network could cause destructive consequences. It is therefore necessary to discourage misbehavior and defend VANET systems against it, in order to ensure correct and smooth operations of the network. In this paper, we review the techniques for handling misbehavior in VANETs, particularly where anonymous communications are desired to conserve user privacy since it adds more complexity to the defense against misbehavior. A new scheme is proposed to punish misbehaving users and can be employed in both inter-vehicle and vehicle-to-infrastructure anonymous communications. Our scheme leverages some threshold authentication technique that dynamically revokes a user’s credential, while providing the flexibility of whether to reveal the user’s identity and tolerating unintentional misbehavior such as hardware malfunctioning.     

QoS-aware minimum energy multicast tree construction in wireless ad hoc networks

Energy conservation is a critical issue in wireless ad hoc networks since batteries are the only limited-life energy source to power the nodes. One major metric for energy conservation is to route a communication session along the routes which require the lowest total energy consumption. Most recent algorithms for the MEM (Minimum Energy Multicast) problem considered energy efficiency as the ultimate objective in order to increase longevity of such networks. However, the introduction of real-time applications has posed additional challenges. Transmission of video and imaging data requires both energy and QoS-aware routing in order to ensure efficient usage of the networks. In this paper, we only consider “bandwidth” as the QoS in TDMA-based wireless ad hoc networks that use omni-directional antennas and have limited energy resources. We present a constraint formulation model for the QoS-MEM (QoS-aware Minimum Energy Multicast) problem in terms of mixed integer linear programming (MILP), which can be used for an optimal solution of the QoS-MEM problem. Experiment results show that in a typical static ad hoc network with 20 nodes, the optimal solutions can always be solved in a timely manner.     

Joint scheduling and power control supporting multicasting in wireless ad hoc networks

This paper addresses the problem of power control in a multihop wireless network supporting multicast traffic. We face the problem of forwarding packet traffic to multicast group members while meeting constraints on the signal-to-interference-plus-noise ratio (SINR) at the intended receivers. First, we present a distributed algorithm which, given the set of multicast senders and their corresponding receivers, provides an optimal solution when it exists, which minimizes the total transmit power. When no optimal solution can be found for the given set of multicast senders and receivers, we introduce a distributed, joint scheduling and power control algorithm which eliminates the weak connections and tries to maximize the number of successful multicast transmissions. The algorithm allows the other senders to solve the power control problem and minimize the total transmit power. We show that our distributed algorithm converges to the optimal solution when it exists, and performs close to centralized, heuristic algorithms that have been proposed to address the joint scheduling and power control problem.