一种基于信道利用状况的无线Mesh路由判据

无线Mesh网络,又称无线因特网,融合了无线局域网和移动Ad Hoe网络的优势,它已经成为下一代无线网络的关键技术之一.路由技术对Mesh网络性能起着至关重要的作用.现有用于Ad Hoc的路由协议不能充分体现WlVlN的特殊性,在现有WCETT及CCM判据的基础上,提出一种新的用于Mesh网络的多信道路径判据Weighted Cumulative CCM-L(WCCCM-L),该判据主要根据信道利用状况选择干扰低的路径发送消息.     

Enhancing channel utilization by improving media access coordination in wireless local area networks

Distributed coordination function (DCF) is the basis protocol for IEEE 802.11 standard wireless local area networks. It is based on carrier sense multiple access with collision avoidance (CSMA/CA) mechanism. DCF uses backoff process to avoid collisions on the wireless channel. The main drawback with this process is that packets have to spend time in the backoff process which is an additional overhead in their transmission time. The channel is rendered idle when all the stations defer their transmissions due to their backoff process. Therefore, the channel utilization and the total throughput on the channel can be improved by reducing the average time spent by the packets in the backoff process. In this paper, we propose a new media access coordination function called proposed media access protocol (PMAP) that will improve the channel utilization for successful packet transmission and therefore, the total achievable throughput. In addition, we propose an analytical model for PMAP under saturated conditions. We use this model to analyze the performance of PMAP under saturated conditions. To substantiate the effectiveness of our model, we have verified the model by simulating PMAP in NS‐2. Simulation and analytical results show that under saturated conditions, PMAP shows profound improvement in the throughput performance compared to DCF. In addition, the throughput performance of PMAP under unsaturated conditions is presented. We have also presented the delay performance of PMAP and DCF through simulation in both saturated and unsaturated conditions. Simulation results show that the average delay experienced by the packets is less in PMAP compared to DCF. Further, the variance in the packet delay is same for both PMAP and DCF protocols under unsaturated conditions. From the performance results obtained for PMAP under both saturated and unsaturated conditions, it can be concluded that PMAP is superior in performance compared to DCF. Copyright © 2006 John Wiley & Sons, Ltd.     

Dynamic channel allocation in wireless ATM networks

During the last few years extensive research has been carried out to extend fixed ATM networks to mobile users. Currently the European Telecommunications Standards Institute (ETSI) is standardising new types of Broadband Radio Access Networks (BRAN): HIPERLAN/2 and HIPERACCESS. In cellular systems like HIPERLAN/2 the aspect of channel allocation plays an important role. In this paper two approaches for channel allocation are introduced and compared with each other concerning the spectrum efficiency and their influence on the implementation of wireless ATM networks and wireless LANs. This revised version was published online in July 2006 with corrections to the Cover Date.     

蜂窝通信网络中的分布式无线信道分配方法

文中提出了一种适用于蜂窝通信网的分布式无线信道分配方法。当网络部署环境中出现干扰后,终端用户通过控制信道,发送反馈信息至基站;基站接收到反馈信息后,对可用信道进行扫频,利用广播帧通知受干扰的终端用户可用信道信息;然后终端用户收到基站发送的广播帧后,根据优先级机制,选择新的信道重新建立与基站的通信,当蜂窝通信网中终端用户受外部干扰而信道中断后,该方法可减少终端用户和基站之间信令的开销。     

Dynamic channel assignment in wireless communication networks

We propose a new Cochannel information based Dynamic Channel Assignment (CDCA) strategy for small and microcell systems and a new Group Dynamic Channel Assignment (GDCA) strategy which handles multichannel traffic in wireless networks. Copyright © 1999 John Wiley & Sons, Ltd.     

Spatial channel reuse in wireless sensor networks

Wireless sensor networks (WSN) are formed by network-enabled sensors spatially randomly distributed over an area. Because the number of nodes in the WSNs is usually large, channel reuse must be applied, keeping co-channel nodes sufficiently separated geographically to achieve satisfactory SIR level. The most efficient channel reuse configuration for WSN has been determined and the worst-interference scenario has been identified. For this channel reuse pattern and worst-case scenario, the minimum co-channel separation distance consistent with an SIR level constraint is derived. Our results show that the two-hop co-channel separations often assumed for sensor and ad hoc networks are not sufficient to guarantee communications. Minimum co-channel separation curves given various parameters are also presented. The results in this paper provide theoretical basis for channel spatial reuse and medium access control for WSN s and also serve as a guideline for how channel assignment algorithms should allocate channels. Furthermore, because the derived co-channel separation is a function of the sensor transmission radius, it also provides a connection between network data transport capacity planning and network topology control which is administered by varying transmission powers. Xiaofei Wang is born on July 31st, 1974, in Jilin, People’s Republic of China. He received the M.S. degree in Electrical Engineering from Delft University of Technology, Delft, The Netherlands in 1992, and the Ph.D. degree in Electrical and Computer Engineering from Cornell University, Ithaca, New York in 2005. From 1997 to 1998, he was selected as one of the twenty best master graduate candidates in all fields to participate in the Japan Prizewinners Programme, an international leadership exchange program established by the Dutch Ministry of Culture, Science and Education. From 1998 to 1999, he worked as a researcher at the Department of Electrical Engineering and Applied Mathematics of Delft University of Technology in the areas of Secondary Surveillance Radar and Ground Penetrating Radar. His research interests include wireless sensor networks, wireless mesh networks, wireless networking, error control coding, communication theory and information theory. He is currently working at Qualcomm Incorporated in San Diego, CA. Toby Berger was born in New York, NY on September 4, 1940. He received the B.E. degree in electrical engineering from Yale University, New Haven, CT in 1962, and the M.S. and Ph.D. degrees in applied mathematics from Harvard University, Cambridge, MA in 1964 and 1966, respectively. From 1962 to 1968 he was a Senior Scientist at Raytheon Company, Wayland, MA. From 1968 through 2005 he he held the position of Irwin and Joan Jacobs Professor of Engineering at Cornell University, Ithaca, NY where in 2006 he became a professor in the ECE Deportment of the University of Virginia, Charlottesville, VA. Professor Berger’s research interests include information theory, random fields, communication networks, wireless communications, video compression, voice and signature compression and verification, neuroinformation theory, quantum information theory, and coherent signal processing. Berger has served as editor-in-chief of the IEEE Transactions on Information Theory and as president of the IEEE Information Theory Group. He has been a Fellow of the Guggenheim Foundation, the Japan Society for Promotion of Science, the Ministry of Education of the People’s Republic of China and the Fulbright Foundation. In 1982 he received the Frederick E. Terman Award of the American Society for Engineering Education, he received the 2002 Shannon Award from the IEEE Information Theory Society and has been designated the recipient of the IEEE 2006 Leon K. Kirchmayer Graduate Teaching Award. Berger is a Fellow and Life Member of the IEEE, a life member of Tau Beta Pi, and an avid blues harmonica player.     

On the connectivity of wireless multi-hop networks with arbitrary wireless channel models

Considering a wireless multi-hop network where a total of n nodes are randomly, independently and uniformly distributed in a unit square in R² and each node has a uniform transmission power, a fundamental problem is to investigate the connectivity of such networks. In this letter, we prove that the probability of having a connected network and the probability of having no isolated node asymptotically converges to the same value as n goes to infinity for an arbitrary wireless channel model satisfying certain intuitively reasonable conditions.     

Blocking probability and channel assignment in wireless networks

We consider a multi-hop wireless network with a connection-oriented traffic model and multiple transmission channels that can be spatially re-used. In such a network the blocking probability of a call that makes a channel request depends on (a) the channel assignment scheme and (b) the transmission radius of the nodes which affects the network link structure. In this work, we study these two aspects for simple wireless networks. Specifically, we develop blocking probability analysis for a wireless line and grid network and explore the tradeoff between transmission radius and blocking probability for multi-hop calls. We show that for a line network a larger transmission radius can substantially reduce the blocking probability of calls, while for a grid network with a more dense node topology using a smaller transmission radius is better. We then, investigate various channel assignment schemes and present a novel non-rearranging channel assignment algorithm for multi-hop calls in a general network. Our algorithm efficiently incorporates spatial channel re-use and significantly reduces call blocking probability when compared to other algorithms.     

Self-regulating network utilization in mobile ad hoc wireless networks

In mobile ad hoc wireless LANs, it is very difficult to maintain a targeted network utilization due to the time-varying nature of the contention-based medium access control protocol and the lack of a central control. Furthermore, previous research has been mainly focusing on the aspect of optimizing the performance at each station. But doing so may result in a very low overall network utilization. Therefore, self-regulating network utilization is very important to provide quality-of-service (QoS) in mobile ad hoc wireless networks. Through self-disciplining its own behaviors locally, each station will optimize its protocol parameters to meet the targeted overall network utilization, which is very important for QoS provisioning to multimedia services. This paper proposes and evaluates a fully distributed scheme for each station to self-regulate its behaviors through adapting the local protocol parameters to meet the targeted overall network utilization with the changes in the network environment such as the number of stations and channel quality.     

Multipath selection and channel assignment in wireless mesh networks

In wireless networks, it is very important to optimize the number of channels, due to the limit on the number of usable channels in a given network. In addition, multimedia services with high QoS requirements with respect to throughput and delay have recently become popular. To satisfy these requirements, it has become important to find a way of providing multipath transmission. A channel assignment algorithm is presented that minimizes the number of required channels while satisfying the throughput requirements of source–destination pairs in multichannel, multiradio, multirate wireless mesh networks. A mathematical model is proposed that considers interference effect, link capacity, and throughput requirements. A novel channel assignment algorithm is developed that takes into account multipath selection, channel reusability, link capacity sharing, and global optimization. The performance of the algorithm is compared with that of CPLEX, using 24 network scenarios. The maximum gap between the CPLEX solutions and those of the proposed algorithm is, on average, only 4.8%.     

Predictive mobile-oriented channel reservation schemes in wireless cellular networks

Provision of seamless service to multimedia applications in cellular wireless networks largely depends on the way calls are handled during handoff. Hence, sufficient resources must be provided for handoff (HO) connections when a mobile station (MS) moves from one cell to another. Effective allocation of resources can be achieved when the exact future trajectory of MSs is known in advance. However, such a scenario is unrealistic. The next best possibility is to employ user mobility prediction to determine the cell(s) a MS will likely visit in the near future. In this paper, we present an extensive survey and classification of channel (bandwidth) reservation schemes which employ user mobility prediction in the resource reservation process. We also present a survey and classification of call admission control (CAC) schemes, including discussion of prioritized and non-prioritized handoff schemes, which can be useful for researches both in academia and industry.     

Estimating the channel capacity of multi-hop IEEE 802.11 wireless networks

In IEEE 802.11 wireless networks, the residual capacity of the wireless links should be accurately estimated to realize advanced network services such as flow admission control or load balancing. In this paper, we propose an algorithm that estimates the packet delivery failure probability by collecting transmission statistics from nearby nodes, and by using a basic collision detection mechanism. This probability is then used in an analytical model to calculate the maximum allowable traffic needed to reach the saturation condition. We show by simulations that estimation error is within 0.5–5.0%, which is significantly lower than the best performance of prior estimation methods. We also demonstrate that the flow admission control is successfully achieved in a realistic wireless network scenario by the help of accurate link residual bandwidth estimation, where the unsatisfied traffic demand remain bounded at a negligibly low level. A routing algorithm that finds max–min residual bandwidth path between source and destination nodes is also implemented, and simulation results show that the network throughput achieved by this algorithm significantly exceeds that of other popular mesh routing protocols. Finally, we provide test results from the real implementation of our algorithm on 802.11 wireless equipment, which are consistent with the simulations.     

Distributed semi-synchronous channel coordination for multi-channel wireless networks

In multi-channel wireless networks, multi-channel diversity can increase the number of concurrent transmissions and thus improve the throughput performance as data transmission on a wireless channel does not interfere with transmissions on the other non-overlapping channels. However, multi-channel coordination may cause severe performance degradation due to hidden terminals, missing receivers, or broadcast deafness problems if the channel usage information is not properly shared among the neighboring nodes. In this paper, we devise a semi-synchronous multi-channel coordination protocol that enables wireless nodes to: (i) efficiently exchange channel and coordination information, and (ii) reduce the overhead of channel switchings. In the proposed protocol, a rendezvous interval is set up in a distributed manner depending on the traffic rate and pattern, and each node independently switches its channel when it can complete its transmissions and then returns to the control channel within the rendezvous interval. This approach makes all nodes return to the control channel at almost the same time without incurring a severe synchronization overhead. Through subsequent analyses and simulation studies, we show that the proposed protocol effectively reduces the number of channel switchings, thereby achieving higher throughput in various multi-channel networking environments.     

Throughput analysis of multiple channel based wireless sensor networks

To improve the capacity of multi-hop wireless networks, protocols based on spatial reuse of frequencies with multiple orthogonal channels have been studied earlier. This paper focuses on the design, implementation and analysis of multiple-channel based wireless sensor networks (WSN). The objectives of the paper are two-fold. The first objective is to identify the sensor node bottlenecks in implementing multi-channel MAC protocols. In particular, a control channel based MAC protocol is implemented and analyzed. The analysis shows the gap between reality and simulation models due to system overheads in implementing these protocols. The second objective is to understand the capacity limits of multi-hop paths in a WSN with multiple channels. A generic channel allocation scheme based on k-distance coloring technique is developed. The protocols and mechanisms were implemented on a testbed consisting of Crossbow MicaZ and TelosB motes using IEEE 802.15.4 compliant radios. Throughput and delivery ratio measurements from the testbed are reported. Some of these measurements are incorporated in a discrete-event simulator model, based on OMNET++ 4.0 with Mobility Framework, for more detailed throughput analysis. The results show that it is possible to achieve 90 % delivery ratio over paths consisting of as many as 18 hops, in a 10 × 10 grid topology using 16 channels.     

Protocols and architectures for channel assignment in wireless mesh networks

The use of multiple channels can substantially improve the performance of wireless mesh networks. Considering that the IEEE PHY specification permits the simultaneous operation of three non-overlapping channels in the 2.4 GHz band and 12 non-overlapping channels in the 5 GHz band, a major challenge in wireless mesh networks is how to efficiently assign these available channels in order to optimize the network performance. We survey and classify the current techniques proposed to solve this problem in both single-radio and multi-radio wireless mesh networks. This paper also discusses the issues in the design of multi-channel protocols and architectures.     

Two‐stage channel assignment scheme in wireless networks

This paper presents a new channel assignment scheme that efficiently improves the spatial frequency–spectrum reuse in a wireless network with heterogeneous demands, in which the cells are partitioned into a lot of clusters. Since the channel demands of each cell are different, this scheme adopts two stages to effectively assign channels. In the first stage, the cluster‐based scheme allocates a number of channels to the cells of each cluster for satisfying the requirement of co‐channel reuse. The channel demand of majority cells will be satisfied in this stage. In the second stage, when the channel requirement of most cells has been fulfilled, the tree‐based assignment scheme allocates channels for the minority cells, which are still lacking of channels. Simulation results showed that the proposed scheme is superior to the previous schemes. Copyright © 2005 John Wiley & Sons, Ltd.     

A hybrid channel allocation method for wireless communication networks

In this paper a new hybrid channel allocation method is presented, which focuses on both nominal and dynamic channel allocation. Copyright © 2000 John Wiley & Sons, Ltd.