Performance of ad hoc routing using directional antennas

This paper evaluates the tradeoffs involved in using directional antennas in ad hoc routing. Although problems with utilizing directional antennas have been visited in the past, the research has been confined mostly to medium access control. To determine whether directional antennas are beneficial to ad hoc networks, it is necessary to evaluate the impact of directional antennas on the performance of routing protocols as well. In this paper, we evaluate the performance of DSR (dynamic source routing) using directional antennas. We identify several issues that emerge from executing DSR (originally designed for omnidirectional antennas) over directional antennas. Using insights gained from simulations, we propose routing strategies that adapt the routing protocol to directional communication. Our analysis shows that by using directional antennas, ad hoc networks may achieve better performance. However, scenarios exist in which using omnidirectional antennas may be more appropriate.     

随机移动模型下移动自组网无序传输端到端延迟闭解分析

针对移动自组网端到端延迟在封闭形式分析方面的局限性,该文提出一种有效的针对无序传输,单副本两跳中继算法的网络延迟建模方案,并给出其严格的理论延迟上界。首先针对多种随机移动模型,证明了移动节点的相遇间隔时间可归纳为统一表达式。然后,综合分析了媒介竞争、流量竞争、排队延迟等问题,合理划分并精确求解出了各延迟关键时间段,从而构造了数据包排队服务模型。最后推导出移动自组网端到端延迟的封闭形式理论上界。仿真结果表明,该理论延迟与实验数据紧密吻合。     

基于可靠稳定性评价的MANET多路径路由优化算法

针对移动Ad hoc网络动态拓扑特性,该文提出一种以可靠路径稳定度估计为基础的多路径路由优化算法。该算法从路径剩余生存期统计特性出发,充分考虑相邻链路生存期相关性,从而消除已有算法在路径稳定度估计中存在的理论误差,并利用优化后的稳定度准则实现路由发现进程的多路径选取和基于备用路径支持的快速路由修复。仿真对比结果表明,该算法具有较快的收敛速度,能够有效提高网络吞吐量,缩短数据传输时延并降低路由开销,更好地保证较高节点移动度下的数据传输稳定性。     

Power-efficient topology control for static wireless networks with switched beam directional antennas

Topology control problems are associated with assignment of power levels to nodes of a wireless network so that the resulting graph topology satisfies certain properties. In this paper we consider the problem of power-efficient topology control with switched beam directional antennas taking into account their non-uniform radiation pattern within the beamwidth. Previous work in the area have all assumed a uniform gain model with these antennas which renders antenna orientation insignificant as a parameter in topology control algorithms. We present algorithms that take into account a model of non-uniform gain with the objectives of minimizing the total power and maximum power to keep the network connected. We consider two cases: one where the antenna orientation is assumed given and another where the antenna orientation needs to be derived as well. For the first case, we present optimal and approximation algorithms for constructing power-efficient topologies. For the second case, we prove the problem to be NP-complete and present heuristic solutions along with approximation bounds. Through comparison of the two cases by simulation, significant reductions are shown in the maximum as well as total power required to keep the network connected for the second case, thus demonstrating the benefits of using antenna orientation as parameter in topology construction.     

A range-adaptive directional MAC protocol for wireless ad hoc networks with smart antennas

Using smart antennas in wireless ad hoc networks can offer tremendous potential for improving the network performance. This paper proposes a range-adaptive MAC protocol, called Ra-MAC, for wireless ad hoc networks using smart antennas. In contrast to the previous MAC protocols with only single-fold directional transmission range, we propose to use multi-fold transmission ranges, i.e., LD (Low-distance), MD (Mid-distance) and HD (High-distance), to arrange efficient communications between the senders and receivers. The transmission range is selected dynamically according to the distance between the communicating node-pair. Building on the multiple transmission ranges, we extend directional network allocation vector (DNAV) to range-based DNAV (R-DNAV) to make full use of wireless channels. Moreover, in order to deal with the basic problems (i.e., hidden terminals, deafness and capture) within smart antenna-based wireless networks, we further equip some optimizations such as half-sweeping start of dialog (SOD), extended directional virtual carrier sensing (DVCS) and so on to Ra-MAC, and then detailedly discuss how these optimizations contribute to address the problems. Simulation results indicate that Ra-MAC outperforms the existing directional MAC protocols and 802.11 DCF. Finally, we also make a brief qualitative comparison between all these protocols.     

DBLAR：A DISTANCE-BASED LOCATION-AIDED ROUTING FOR MANET

In location-aided routing of Mobile Ad hoc NETworks (MANET), nodes mobility and the inaccuracy of location information may result in constant flooding, which will reduce the network performance. In this paper, a Distance-Based Location-Aided Routing (DBLAR) for MANET has been proposed. By tracing the location information of destination nodes and referring to distance change between nodes to adjust route discovery dynamically, the proposed routing algorithm can avoid flooding in the whole networks. Besides, Distance Update Threshold (DUT) is set up to reach the balance between real-time ability and update overhead of location information of nodes, meanwhile, the detection of relative distance vector can achieve the goal of adjusting forwarding condition. Simulation results reveal that DBLAR performs better than LAR1 in terms of packet successful delivery ratio, average end-to-end delay and routing-load, and the set of DUT and relative distance vector has a significant impact on this algorithm.     

The design of a channel-access protocol for a wireless ad hoc network with sectored directional antennas

A packet scheduler and a medium access control (MAC) protocol are presented for a direct-sequence spread-spectrum, wireless ad hoc network that contains a mix of nodes with directional antennas and nodes with omnidirectional antennas. The scheduler and MAC protocol are designed to prevent the co-site interference problem that arises in some types of nodes employing directional antennas. It is shown that the presence of nodes with directional antennas exacerbates the vulnerability of the network to the receiver blocking problem. A modification of the MAC protocol is presented that mitigates the receiver blocking problem, and it is shown to improve the performance of a network that includes nodes with directional antennas.     

Heuristic optimization techniques for self-orientation of directional antennas in long-distance point-to-point broadband networks

A self-orientation system for a directional antenna is capable of determining the best orientation to receive the strongest wireless signal. In the event of two antennas being deployed randomly or deployed in a dense space where the effects of multipath and other wireless interference exist, efficient search algorithms are required to find the best orientation. Therefore, this paper presents four heuristic optimization techniques for the self-orientation of directional antennas in such events: Pattern Search method, Downhill Simplex method, DIRECT method, and Genetic Algorithm. The modification of each technique for this orientation problem is described, and the performance of each algorithm using different test cases with real world experiments is also described. From our study, we show that the Pattern Search method is the most suitable optimization technique for the self-orientation of directional antennas in long-distance point-to-point broadband networks.     

移动Ad hoc网络容量非合作规划博弈模型的稳定性

该文研究了非合作规划博弈移动Ad hoc网络容量分析模型的稳定性。首先求得非合作规划博弈移动Ad hoc网络容量分析模型的源节点流量发送速率演化方程,在此基础上构造Lyapunov函数,运用MakuH稳定性定理得到非合作规划博弈移动Ad hoc网络容量分析模型的稳定性。仿真试验验证了该模型具有优良的稳定性。     

Power efficient routing trees for ad hoc wireless networks using directional antenna

In ad hoc wireless networks, nodes are typically powered by batteries. Therefore saving energy has become a very important objective, and different algorithms have been proposed to achieve power efficiency during the routing process. Directional antenna has been used to further decrease transmission energy as well as to reduce interference. In this paper, we discuss five algorithms for routing tree construction that take advantage of directional antenna, i.e., Reverse-Cone-Pairwise (RCP), Simple-Linear (SL), Linear-Insertion (LI), Linear-Insertion-Pairwise (LIP), and a traditional approximation algorithm for the travelling salesman problem (TSP). Their performances are compared through a simulation study.     

MAC protocols using directional antennas in IEEE 802.11 based ad hoc networks

Using directional antennas can be beneficial for wireless ad hoc networks consisting of a collection of wireless hosts. The most important benefit includes a reduction of the radio interference. Thus, it can significantly increase the spatial reuse, thereby improving the network throughput. To best utilize directional antennas, a suitable Medium Access Control (MAC) protocol must be designed. Current MAC protocols, such as the IEEE 802.11 standard, do not benefit when using directional antennas, because these protocols have been designed for omnidirectional antennas. In this paper, we present modified MAC protocols suitable for 802.11 based ad hoc networks using directional antennas. Our comprehensive simulation results demonstrate the performance improvement obtained with the proposed protocols. Copyright © 2007 John Wiley & Sons, Ltd.     

Extended reactance domain algorithms for DoA estimation onto an ESPAR antennas

Based on an extended reactance domain (RD) covariance matrix, this article proposes new alternatives for directions of arrival (DoAs) estimation of narrowband sources through an electronically steerable parasitic array radiator (ESPAR) antennas. Because of the centro symmetry of the classic ESPAR antennas, an unitary transformation is applied to the collected data that allow an important reduction in both computational cost and processing time and, also, an enhancement of the resolution capabilities of the proposed algorithms. Moreover, this article proposes a new approach for eigenvalues estimation through only some linear operations. The developed DoAs estimation algorithms based on this new approach has illustrated a good behaviour with less calculation cost and processing time as compared to other schemes based on the classic eigenvalues approach. The conducted simulations demonstrate that high-precision and high-resolution DoAs estimation can be reached especially in very closely sources situation and low sources power as compared to the RD-MUSIC algorithm and the RD-PM algorithm. The asymptotic behaviours of the proposed DoAs estimators are analysed in various scenarios and compared with the Cramer-Rao bound (CRB). The conducted simulations testify the high-resolution of the developed algorithms and prove the efficiently of the proposed approach.     

Angular MAC: a framework for directional antennas in wireless mesh networks

Capacity of wireless mesh networks can be enhanced through the use of smart directional antennas, which not only enable nodes to have high quality links but also increase network throughput by allowing spatial reuse. This paper proposes a new MAC protocol and framework, called Angular MAC (ANMAC) that enables directional antennas in wireless mesh networks. The protocols and algorithms of the ANMAC framework fit well with the requirements of mesh networks such as neighbor discovery and self-configuration, while providing significant throughput enhancements. The throughput enhancements are proven by comprehensive simulations with realistic antenna patterns, including performance comparisons of ANMAC with directional schemes using a similar node architecture and omni 802.11. Also, the effect of contention window size is analyzed and a dynamic contention window adaptation algorithm is proposed to maximize the throughput of the self-configuring mesh network, by taking instantaneous traffic conditions into account.     

基于仿真的有线/MANET混合网络TCP性能研究

MANET网络是未来民用和军事通信应用的理想选择,它和Internet的通信是必不可少的。该文分析研究了有线/MANET混合环境中的一些关键问题,比如,网关的隐藏终端和暴露终端、移动节点速度、流的数目等对TCP性能的影响,为有线/MANET混合网络在未来民用和军事领域的应用提供有益的参考。     

Routing and transmission scheduling for minimizing broadcast delay in multirate wireless mesh networks using directional antennas

Using directional antennas to reduce interference and improve throughput in multihop wireless networks has attracted much attention from the research community in recent years. In this paper, we consider the issue of minimum delay broadcast in multirate wireless mesh networks using directional antennas. We are given a set of mesh routers equipped with directional antennas, one of which is the gateway node and the source of the broadcast. Our objective is to minimize the total transmission delay for all the other nodes to receive a broadcast packet from the source, by determining the set of relay nodes and computing the number and orientations of beams formed by each relay node. We propose a heuristic solution with two steps. Firstly, we construct a broadcast routing tree by defining a new routing metric to select the relay nodes and compute the optimal antenna beams for each relay node. Then, we use a greedy method to make scheduling of concurrent transmissions without causing beam interference. Extensive simulations have demonstrated that our proposed method can reduce the broadcast delay significantly compared with the methods using omnidirectional antennas and single‐rate transmission. In addition, the results also show that our method performs better than the method with fixed antenna beams. Copyright © 2012 John Wiley & Sons, Ltd.     

一种基于802.11 DCF Basic Access机制的移动自组网动态速率控制模型

802.11移动自组网由于其固有的动态拓扑、分布式协作等特点,路由协议普遍采用多播方式以提高无线链接的传输效率,由此带来的拥塞使得移动自组网中多播拥塞控制至关重要。针对移动自组网中节点固有的随机特性,基于802.11 DCF协议,该文提出一种精确描述节点数据产生、排队、发送动态过程的拟生灭模型,并通过矩阵几何方法对其进行稳态分析,得出节点速率阈值方程组,并用OPNET进行了仿真实验,仿真结果与理论值拟合较好,为移动自组网中的拥塞控制提供了一个量化的指标。     

BeamMAC: A new paradigm for medium access in wireless networks

Medium access using the distributed coordination function of IEEE 802.11 is not efficient in wireless multihop networks if the devices are equipped with beamforming antennas. This paper proposes a distributed MAC protocol that goes completely away from the spatial reservation scheme of 802.11. It facilitates the use of beamforming antennas by following an announcement-objection scheme: a potential sender must “simulate” a transmission on a signaling channel before it can access the traffic channel. Based on this simulation, each receiving device estimates the expected interference and objects to the transmission if necessary. This paradigm overcomes the drawback of 802.11-based approaches that neighboring devices are silenced irrespective of whether or not they disturb signal reception. It benefits from a tight interaction of the MAC and physical layer.     

一种基于信誉的移动自组网区分服务激励机制

为了有效解决移动自组网节点在自觉提供服务方面的自私行为问题,该文提出了一种基于信誉的区分服务激励机制。该机制通过建立一种分簇全局信誉模型,并结合节点能力将服务与信誉进行等级关联,提供差异化服务;信誉级别越高的节点可以使用级别越高的服务,使用服务或者故意不提供服务会减少节点的信誉,节点需要积极提供可靠服务提高信誉才能保障服务的使用。仿真结果表明所提机制能有效抵制节点的自私行为,激励节点积极提供可靠服务。     

双基地分布式阵列MIMO雷达的DOA和DOD估计方法

结合分布式阵列和双基地多输入多输出(Multiple-Input Multiple-Output, MIMO)雷达的特点, 提出了一种新的双基地分布式阵列MIMO雷达的接收角(Direction of Arrival, DOA)和发射角(Direction of Departure, DOD)估计方法.根据发射阵列和接收阵列的空域旋转不变特性, 利用旋转不变估计技术(Estimation of Signal Parameters via Rotational Invariance Techniques, ESPRIT)获取无模糊DOA粗估计和高精度周期性模糊的DOA、DOD精估计; 再利用无模糊DOA粗估计、目标的双基地距离信息以及双基地MIMO雷达的几何特点, 解除DOA、DOD精估计的周期性模糊, 得到高精度且无模糊的DOA和DOD估计.最后, 根据ESPRIT算法原理和估计误差的概率统计特性进行算法的性能分析, 给出算法基线模糊门限的近似计算方法.该算法有效地放宽了发射阵列孔径扩展程度的限制, 从而提高了阵列在大孔径下的角度估计精度, 且能够实现DOA和DOD估计的自动配对.仿真结果验证了所提算法和性能分析方法的有效性.     

Joint carrier frequency offset and channel estimation for OFDM systems with two receive antennas

Carrier frequency offset (CFO) in OFDM systems results in loss of channel orthogonality and hence degrades the system's performance. In this paper, we propose a new method for joint CFO/channel estimation for OFDM systems with two receive antennas. Our method avoids the complexity of full search methods in one or two dimensions. Using one training OFDM symbol and utilizing the knowledge of the structure of the inter‐channel interference that results from CFO, we develop a two‐stage estimation procedure. The first stage derives an initial CFO/channel estimate based on a one shot minimization step. The second stage refines this joint estimate by conducting a small CFO search in the vicinity of the initial estimate. This procedure provides CFO estimates over a full range of −N /2–N /2, (N : number of subcarriers), as well as the channel estimates. Computer simulations show an excellent performance that is very close to the Cramer–Rao lower bound and superior to some existing methods. The effect of antenna correlation on performance is also investigated through computer simulations, showing small performance degradation even at medium correlation coefficients (0.3–0.6). Copyright © 2015 John Wiley & Sons, Ltd.