Showing papers on "Wireless mesh network published in 2004"

Routing in multi-radio, multi-hop wireless mesh networks

Abstract: We present a new metric for routing in multi-radio, multi-hop wireless networks. We focus on wireless networks with stationary nodes, such as community wireless networks.The goal of the metric is to choose a high-throughput path between a source and a destination. Our metric assigns weights to individual links based on the Expected Transmission Time (ETT) of a packet over the link. The ETT is a function of the loss rate and the bandwidth of the link. The individual link weights are combined into a path metric called Weighted Cumulative ETT (WCETT) that explicitly accounts for the interference among links that use the same channel. The WCETT metric is incorporated into a routing protocol that we call Multi-Radio Link-Quality Source Routing.We studied the performance of our metric by implementing it in a wireless testbed consisting of 23 nodes, each equipped with two 802.11 wireless cards. We find that in a multi-radio environment, our metric significantly outperforms previously-proposed routing metrics by making judicious use of the second radio.

Centralized channel assignment and routing algorithms for multi-channel wireless mesh networks

Abstract: The IEEE 802.11 Wireless LAN standards allow multiple non-overlapping frequency channels to be used simultaneously to increase the aggregate bandwidth available to end-users. Such bandwidth aggregation capability is routinely used in infrastructure mode operation, where the traffic to and from wireless nodes is distributed among multiple interfaces of an access point or among multiple access points to balance the traffic load. However, bandwidth aggregation is rarely used in the context of multi-hop 802.11-based LANs that operate in the ad hoc mode. Most past research efforts that attempt to exploit multiple radio channels require modifications to the MAC protocol and therefore do not work with commodity 802.11 interface hardware. In this paper, we propose and evaluate one of the first multi-channel multi-hop wireless ad-hoc network architectures that can be built using standard 802.11 hardware by equipping each node with multiple network interface cards (NICs) operating on different channels. We focus our attention on wireless mesh networks that serve as the backbone for relaying end-user traffic from wireless access points to the wired network. The idea of exploiting multiple channels is particularly appealing in wireless mesh networks because of their high capacity requirements to support backbone traffic. To reap the full performance potential of this architecture, we develop a set of centralized channel assignment, bandwidth allocation, and routing algorithms for multi-channel wireless mesh networks. A detailed performance evaluation shows that with intelligent channel and bandwidth assignment, equipping every wireless mesh network node with just 2 NICs operating on different channels can increase the total network goodput by a factor of up to 8 compared with the conventional single-channel ad hoc network architecture.

A multi-radio unification protocol for IEEE 802.11 wireless networks

Abstract: We present a link layer protocol called the multi-radio unification protocol or MUP. On a single node, MUP coordinates the operation of multiple wireless network cards tuned to non-overlapping frequency channels. The goal of MUP is to optimize local spectrum usage via intelligent channel selection in a multihop wireless network. MUP works with standard-compliant IEEE 802.11 hardware, does not require changes to applications or higher-level protocols, and can be deployed incrementally. The primary usage scenario for MUP is a multihop community wireless mesh network, where cost of the radios and battery consumption are not limiting factors. We describe the design and implementation of MUP, and analyze its performance using both simulations and measurements based on our implementation. Our results show that under dynamic traffic patterns with realistic topologies, MUP significantly improves both TCP throughput and user perceived latency for realistic workloads.

Establishing trust in pure ad-hoc networks

Abstract: An ad-hoc network of wireless nodes is a temporarily formed network, created, operated and managed by the nodes themselves. It is also often termed an infrastructure-less, self-organized, or spontaneous network. Nodes assist each other by passing data and control packets from one node to another, often beyond the wireless range of the original sender. The execution and survival of an ad-hoc network is solely dependent upon the cooperative and trusting nature of its nodes.However, this naive dependency on intermediate nodes makes the ad-hoc network vulnerable to passive and active attacks by malicious nodes. A number of protocols have been developed to secure ad-hoc networks using cryptographic schemes, but all rely on the presence of an omnipresent, and often omniscient, trust authority. As this paper describes, dependence on a central trust authority is an impractical requirement for ad-hoc networks. We present a model for trust-based communication in ad-hoc networks that also demonstrates that a central trust authority is a superfluous requirement. The model introduces the notion of belief and provides a dynamic measure of reliability and trustworthiness in an ad hoc network.

Method and apparatus for wireless communication in a mesh network

Abstract: A method and apparatus for communication in a wireless sensor network. In one embodiment, one or more routers in a network may be available for communication with one or more star nodes at a randomized time and/or frequency. A connectivity assessment, which may be performed at several different frequencies and/or times, may be performed to evaluate the quality of communications between devices in the network. Primary and secondary communication relationships may be formed between devices to provide for system redundancy. One or more proxies may be maintained where each proxy includes a status of one or more devices in the network, e.g., one or more star nodes or routers. Proxies may be used to handle information requests and/or status change requests, e.g., a proxy may be requested to change a communication relationship between devices in the network and may generate command signals to cause the corresponding devices to make the change.

On the Connectivity of Ad Hoc Networks

Abstract: This paper presents a framework for the calculation of stochastic connectivity properties of wireless multihop networks. Assuming that n nodes, each node with transmission range r0, are distributed according to some spatial probability density function, we study the level of connectivity of the resulting network topology from three viewpoints. First, we analyze the number of neighbors of a given node. Second, we study the probability that there is a communication path between two given nodes. Third, we investigate the probability that the entire network is connected, i.e. each node can communicate with every other node via a multihop path. For the last-mentioned issue, we compute a tight approximation for the critical (r0 ,n )pairs that are required to keep the network connected with a probability close to one. In fact, the problem is solved for the general case of a k-connected network, accounting for the robustness against node failures. These issues are studied for uniformly distributed nodes (with and without ‘border effects’), Gaussian distributed nodes, and nodes that move according to the commonly used random waypoint mobility model. The results are of practical value for the design and simulation of wireless sensor and mobile ad hoc networks.

Plug-in network appliance

Abstract: A plug-in network appliance is disclosed. In one aspect, a network appliance performs a bridge between two wireless communication formats. In another aspect, a network appliance is deployed to perform position location services. In another aspect, a mesh network comprising one or more network appliances is deployed. A mesh network comprising one or more network appliances may be deployed to perform position location services. A plug-in form factor is described. A network appliance may convert power received from a plug in a first format to power in a second format for powering various components. A network appliance may connect with a wireless network and/or a network connected through a plug. A plug-in network appliance may connect to a weight-bearing outlet. Various other aspects are also presented.

Diagnosis of embedded, wireless mesh networks with real-time, flexible, location-specific signaling

Abstract: A system for optimizing the security of data communication on wireless mesh networks invention uses existing mesh network nodes to control new nodes that attempt to join the network. In a preferred embodiment, this is achieved by (1) testing that a new node is “clean” before allowing it to join the wireless mesh network by scanning the new node for viruses, checking for security patches, etc., (2) quarantining an “infected” node from joining the wireless mesh network until it is cleaned, (3) signaling other nodes in the existing mesh network that a node is either “infected” or “clean”, (4) cleaning a new node by supplying it with antivirus software, vendor patches, etc. from nearby nodes in the existing wireless mesh network, (5) updating the wireless mesh network in real time with a list of clean and infected nodes, and (6) performing the above steps without the need for a central, controlling server.

A review of fault management in WDM mesh networks: basic concepts and research challenges

Abstract: The article first presents a broad overview of the fault management mechanisms involved in deploying a survivable optical mesh network which employs optical crossconnects. We review various protection and restoration schemes, primary and back-up route computation methods, shareability optimization, and dynamic restoration. We then describe different parameters that can measure the quality of service provided by a WDM mesh network to upper protocol layers (e.g., IP network backbones, ATM network backbones, leased lines, virtual private networks), such as service availability, service reliability, restoration time, and service restorability. We review these concepts, the factors that affect them, and how to improve them. In particular, we present a framework for cost-effective availability-aware connection provisioning to provide differentiated services in WDM mesh networks. Through the framework, the more realistic scenario of multiple near-simultaneous failures can be handled. In addition, the emerging problem of protecting low-speed connections of different bandwidth granularities is also reviewed.

Ad Hoc wireless node and network

Abstract: A node is suitable for a wireless network. A wireless network comprises one or more sensor nodes and/or one or more control nodes. In the wireless network, the sensor node transmits in response to a sensed event and/or a request from a control node. A transmission/routing of data between a sensor node and/or a control node may be subject to a policy constraint and a resource constraint.

Distributed Sensor Networks

Abstract: An Overview, S.S. Iyengar, Ankit Tandon, and R.R. Brooks Microsensor Applications, David Shepherd A Taxonomy of Distributed Sensor Networks, Shivakumar Sastry and S.S. Iyengar Contrast with Traditional Systems, R.R. Brooks Digital Signal Processing Background, Yu Hen Hu Image-Processing Background Lynne Grewe and Ben Shahshahani Object Detection and Classification, Akbar M. Sayeed Parameter Estimation David Friedlander Target Tracking with Self-Organizing Distributed Sensors R.R. Brooks, C. Griffin, D.S. Friedlander, and J.D. Koch Collaborative Signal and Information Processing: An Information-Directed Approach Feng Zhao, Jie Liu, Juan Liu, Leonidas Guibas, and James Reich Environmental Effects, David C. Swanson Detecting and Counteracting Atmospheric Effects Lynne L. Grewe Signal Processing and Propagation for Aeroacoustic Sensor Networks, Richard J. Kozick, Brian M. Sadler, and D. Keith Wilson Distributed Multi-Target Detection in Sensor Networks Xiaoling Wang, Hairong Qi, and Steve Beck Foundations of Data Fusion for Automation S.S. Iyengar, S. Sastry, and N. Balakrishnan Measurement-Based Statistical Fusion Methods For Distributed Sensor Networks, Nageswara S.V. Rao Soft Computing Techniques, R.R. Brooks Estimation and Kalman Filters, David L. Hall Data Registration, R.R. Brooks, Jacob Lamb, and Lynne Grewe Signal Calibration, Estimation for Real-Time Monitoring and Control, Asok Ray and Shashi Phoha Semantic Information Extraction, David Friedlander Fusion in the Context of Information Theory Mohiuddin Ahmed and Gregory Pottie Multispectral Sensing, N.K. Bose Coverage-Oriented Sensor Deployment Yi Zou and Krishnendu Chakrabarty Deployment of Sensors: An Overview S.S. Iyengar, Ankit Tandon, Qishi Wu, Eungchun Cho, Nageswara S.V. Rao, and Vijay K. Vaishnavi Genetic Algorithm for Mobile Agent Routing in Distributed Sensor Networks, Qishi Wu, S.S. Iyengar, and Nageswara S.V. Rao Computer Network - Basic Principles, Suresh Rai Location-Centric Networking in Distributed Sensor Networks, Kuang-Ching Wang and Parameswaran Ramanathan Directed Diffusion, Fabio Silva, John Heidemann, Ramesh Govindan, and Deborah Estrin Data Security Perspectives, David W. Carman Quality of Service Metrics, N. Gautam Network Daemons for Distributed Sensor Networks Nageswara S.V. Rao and Qishi Wu Designing Energy-Aware Sensor Systems N. Vijaykrishnan, M.J. Irwin, M. Kandemir, L. Li, G. Chen, and B. Kang Operating System Power Management Vishnu Swaminathan and Krishnendu Chakrabarty An Energy-Aware Approach for Sensor Data Communication, H. Saputra, N. Vijaykrishnan, M. Kandemir, R. Brooks, and M.J. Irwin Compiler-Directed Communication Energy Optimizations for Microsensor Networks, I. Kadayif, M. Kandemir, A. Choudhary, M. Karakoy, N. Vijaykrishnan, and M.J. Irwin Sensor-Centric Routing in Wireless Sensor Networks Rajgopal Kannan and S.S. Iyengar Query Processing in Sensor Networks Samuel Madden and Johannes Gehrke Autonomous Software Reconfiguration, R.R. Brooks Mobile Code Support, R.R. Brooks and T. Keiser The Mobile-Agent Framework for Collaborative Processing in Sensor Networks, Hairong Qi, Yingyue Xu, and Teja Phani Kuruganti Distributed Services, Alvin S. Lim Adaptive Active Querying, Bhaskar Krishnamachari Need for Self-Configuration, R.R. Brooks Emergence, R.R. Brooks Biological Primitives, M. Pirretti Physics and Chemistry, Mengxia Zhu, Richard Brooks, Matthew Pirretti, and S.S. Iyengar Collective Intelligence for Power-Aware Routing in Mobile Ad Hoc Sensor Networks Vijay S. Iyer, S.S. Iyengar, and N. Balakrishnan Random Networks and Percolation Theory R.R. Brooks On the Behavior of Communication Links in a Multi-Hop Mobile Environment , Prince Samar and Stephen B. Wicker Example Distributed Sensor Network Control Hierarchy Mengxia Zhu, S.S. Iyengar, Jacob Lamb, R.R. Brooks, and Matthew Pirretti SenSoft: Development of a Collaborative Sensor Network Gail Mitchell, Jeff Mazurek, Ken Theriault, and Prakash Manghwani Statistical Approaches to Cleaning Sensor Data Eiman Elnahrawy and Badri Nath Plant Monitoring with Special Reference to Endangered Species, K.W. Bridges and Edo Biagioni Designing Distributed Sensor Applications for Wireless Mesh Networks, Robert Poor and Cliff Bowman Beamforming, J.C. Chen and K. Yao

The distance-2 matching problem and its relationship to the MAC-Layer capacity of ad hoc wireless networks

Abstract: We consider the problem of determining the maximum capacity of the media access (MAC) layer in wireless ad hoc networks. Due to spatial contention for the shared wireless medium, not all nodes can concurrently transmit packets to each other in these networks. The maximum number of possible concurrent transmissions is, therefore, an estimate of the maximum network capacity, and depends on the MAC protocol being used. We show that for a large class of MAC protocols based on virtual carrier sensing using RTS/CTS messages, which includes the popular IEEE 802.11 standard, this problem may be modeled as a maximum Distance-2 matching ( D2EMIS) in the underlying wireless network: Given a graph G(V,E), find a set of edges E'/spl sube/E such that no two edges in E' are connected by another edge in E. D2EMIS is NP-complete. Our primary goal is to show that it can be approximated efficiently in networks that arise in practice. We do this by focusing on an admittedly simplistic, yet natural, graph-theoretic model for ad hoc wireless networks based on disk graphs, where a node can reach all other nodes within some distance (nodes may have unequal reach distances). We show that our approximation yields good capacity bounds. Our work is the first attempt at characterizing an important "maximum" measure of wireless network capacity, and can be used to shed light on previous topology formation protocols like Span and GAF that attempt to produce "good" or "capacity-preserving" topologies, while allowing nodes to alternate between sleep and awake states. Our work shows an efficient way to compute an upper bound on maximum wireless network capacity, thereby allowing topology formation algorithms to determine how close they are to optimal. We also outline a distributed algorithm for the problem for unit disk graphs, and briefly discuss extensions of our results to: 1) different node interference models; 2) directional antennas; and 3) other transceiver connectivity structures besides disk graphs.

Ad Hoc UAV Ground Network (AUGNet)

Abstract: *† ‡ § , This paper describes an implementation of a wireless mobile ad hoc network with radio nodes mounted at fixed sites, on ground vehicles, and in small (10kg) UAVs. The ad hoc networking allows any two nodes to communicate either directly or through an arbitrary number of other nodes which act as relays. We envision two sce narios for this type of network. In the first, the UAV acts as a prominent radio node that connects disconnected ground radios. In the second, the networking enables groups of UAVs to communicate with each other to extend small UAVs' operational scope and range. The network consists of mesh network radios assembled from low -cost commercial off the shelf components. The radio is an IEEE 802.11b (WiFi) wireless interface and is controlled by an embedded computer. The network protocol is an implementation of the Dynamic Source Routing ad hoc networking protocol. The radio is mounted either in an environmental enclosure for outdoor fixed and vehicle mounting or directly in our custom built UAVs. A monitoring architecture has been embedded into the radios for de tailed performance characterization and analysis. This paper describes these components and performance results me asured at an outdoor test range .

Characterising the use of a campus wireless network

Abstract: We present the results of an analysis of the usage of our new campus-wide wireless network. A week-long traffic trace was collected in January 2003, recording address and protocol information for every packet sent and received on the wireless network. A centralised authentication log was used to match packets with wireless access points. The trace was analysed to answer questions about where, when, how much, and for what our wireless network is being used. Such information is important in evaluating design principles and planning for future network expansion.

Techniques for ad-hoc mesh networking

Abstract: A wireless communications device includes a first radio and a second radio. The first radio is receives information regarding an ad-hoc mesh wireless network from at least one remote device. The second radio exchanges user data with the ad-hoc wireless mesh network. The wireless communications device also includes a buffer and a scheduler. The buffer stores user data for transmission to one or more remote devices in the ad-hoc wireless mesh network. The scheduler schedules transmissions by the second radio of the user data based on the received information. The first and second radios may employ various communications technologies. Examples of such technologies include Bluetooth, wireless local area network (WLAN), and ultra wideband (UWB). The information received from the remote device may include one or more of the following: configuration information (e.g., topology information) corresponding to the ad-hoc wireless mesh network; routing information; and information regarding communications capabilities of one or more nodes within the ad-hoc wireless mesh network.

Communication protocol for a wireless mesh architecture

Abstract: A wireless mesh communication protocol that dynamically assigns communication time-slots and frequencies to mesh nodes. A first node is established as a PC that sequentially polls other nodes. A second node responds at a predetermined time with information that includes database records, and then a third node responds similarly. The second node is then established as the PC and the first node is polled during dynamically allocated time-slots and on a frequency that depend on the second node's database records. The third node is then established as a PC and acts similarly. In both cases the first node responds by sending information and data records. The first node is then re-established as the PC. The first node then polls the second and third nodes at times and frequencies that depend on the first node's database records.

Capacity bounds for three classes of wireless networks: asymmetric, cluster, and hybrid

Abstract: We present capacity results for three classes of wireless ad hoc networks, using a general framework that allows their unified treatment. The results hold with probability going to 1 as the number of nodes in the network approaches infinity, and under a general model for channel fading.We first study asymmetric networks that consist of n source nodes and around nd destination nodes, communicating over a wireless channel. Each source node creates data traffic that is directed to a destination node chosen at random. When ½ ‹ d ‹ 1, an aggregate throughput that increases with n as n½ is achievable. If, however, 0 ‹ d ‹ ½, bottlenecks are formed and the aggregate throughput can not increase faster than nd.We also consider cluster networks, that consist of n client nodes and around nd cluster heads, communicating over a wireless channel. Each of the clients wants to communicate with one of the cluster heads, but the particular choice of cluster head is not important. In this setting, the maximum aggregate throughput is on the order of nd, and it can be achieved with no transmissions taking place between client nodes.We conclude with the study of hybrid networks. These consist of n wireless nodes and around nd access points. The access points are equipped with wireless transceivers, but are also connected with each other through an independent network of infinite capacity. Their only task is to support the operation of the wireless nodes. When ½ ‹ d ‹ 1, an aggregate throughput on the order of nd is achievable, through the use of the infrastructure. If, however, 0 ‹ d ‹ ½, using the infrastructure offers no significant gain, and the wireless nodes can achieve an aggregate throughput on the order of n½ by using the wireless medium only.

Node placement method within a wireless network, such as a wireless local area network

Abstract: The disclosure includes a method of and associated system for placing nodes in a wireless local area network (WLAN). The method includes receiving user-specified parameters regarding the network. The parameters can include a layout of a building or other space, and requirements for the WLAN. An algorithm then employs these parameters to automatically create and optimized layout of multiple wireless access points for the WLAN. The method can display the layout and provide various types of information to the user.

Wireless network monitoring system

Abstract: A plug-in network appliance is disclosed. In one aspect, a network appliance performs a bridge between two wireless communication formats. In another aspect, a network appliance is deployed to perform position location services. In another aspect, a mesh network comprising one or more network appliances is deployed. A mesh network comprising one or more network appliances may be deployed to perform position location services. A plug-in form factor is described. A network appliance may convert power received from a plug in a first format to power in a second format for powering various components. A network appliance may connect with a wireless network and/or a network connected through a plug. A plug-in network appliance may connect to a weight-bearing outlet. Various other aspects are also presented.

Predictive route maintenance in a mobile ad hoc network

Abstract: The mobile ad hoc network includes a plurality of wireless mobile nodes and a plurality of wireless communication links connecting the nodes together. A method for operating the network includes discovering and using routes in the network, predicting route failure in the network, and performing route maintenance in the network based upon the predicted route failure.

Network addressing scheme for reducing protocol overhead in an optical network

Abstract: A method for operating a network and a network architecture implementing the method are described. The method, in one embodiment, begins by grouping a plurality of nodes into zones, where the network includes the plurality of nodes. At least one of the nodes in each one of the zones is one of a plurality of boundary nodes, and each of the boundary nodes in each one of the zones is coupled to a boundary node in another of the zones by one of a first number of inter-zone optical links. One of the zones includes a number of nodes, each of which is coupled to at least one other of the nodes by one of a second number of intra-zone optical links. Next, a non-boundary node is configured to transmit network information to other of the nodes. The non-boundary node is a node in the zone that is not a boundary node. Finally, a boundary node in the zone is configured to limit transmission of the network information through itself to other of the boundary nodes. The network information so limited can be restoration information (in the event of a failure), network topology information, and/or other network information.

System and a node used in the system for wireless communication and sensory monitoring

Abstract: A system is provided for communication and sensory monitoring. The system comprises a plurality of nodes installed as a network in a structure. Each of the plurality of nodes comprises an internode transceiver for wireless communication between nodes, a wireless network transceiver for wireless communication with one or more wireless devices, one or more sensors for monitoring the environment of the structure and a processor coupled to the internode transceiver, the wireless network transceiver and the one or more sensors to exchange data with the internode transceiver, the wireless network transceiver and the one or more sensors devices coupled to the processor and process the data. The system also includes a wide area network bridge coupled to the plurality of network nodes. The network bridge receives data from the plurality of network nodes and passes the information to a computer network for processing.

Self-configuring, self-optimizing wireless local area network system

Abstract: A system and associated method provides for a wireless local area network (WLAN) that permits mobile units to communicate with an external, wired network. Nodes in the WLAN include multiple components, such as a base module, antenna module, and one or more wireless modules. Indeed, this system can employ two or more wireless modules that employ different short-range wireless protocols, such as IEEE 802.11-type and Bluetooth protocols. The nodes may perform self-discovery to determine modules within the node and associated functionality, as well as identify neighboring nodes to thereby establish a mesh-type network. Nodes can be configured to provide connectivity to the wired network, while others (access points) communicate wirelessly with mobile devices. The nodes may then be interconnected wirelessly, or via wires.

Channel assignments within a mesh network

Abstract: Embodiments of methods of assigning a channel to a link of an access node within a wireless mesh network, is disclosed The method includes the access node receiving beacons over multiple channels, from at least one upstream device, and the access node selecting an uplink channel based upon the received beacons Additional methods include the access node selecting a downlink channel so that different channels are assigned to consecutive links within a data path between a gateway and a down stream device The different channels can include non-overlapping channels, or a combination of non-overlapping and at least partially overlapping channels The method can further include selecting a downstream link channel based upon predetermined sequences of channel selections, and a hop count of the access node

TIDS: threshold and identity-based security scheme for wireless ad hoc networks

Abstract: As various applications of wireless ad hoc network have been proposed, security has received increasing attentions as one of the critical research challenges. In this paper, we consider the security issues at network layer, wherein routing and packet forwarding are the main operations. We propose a novel efficient security scheme in order to provide various security characteristics, such as authentication , confidentiality , integrity and non-repudiation for wireless ad hoc networks. In our scheme, we deploy the recently developed concepts of identity-based signcryption and threshold secret sharing . We describe our proposed security solution in context of dynamic source routing (DSR) protocol. Without any assumption of pre-fixed trust relationship between nodes, the ad hoc network works in a self-organizing way to provide key generation and key management services using threshold secret sharing algorithm, which effectively solves the problem of single point of failure in the traditional public-key infrastructure (PKI) supported system. The identity-based signcryption mechanism is applied here not only to provide end-to-end authenticity and confidentiality in a single step, but also to save network bandwidth and computational power of wireless nodes. Moreover, one-way hash chain is used to protect hop-by-hop transmission.

Mesh AMR network interconnecting to TCP/IP wireless mesh network

Abstract: A wireless system for collecting metering data that includes a plurality of meters, a collector and a central communications server. The meters communicate usage data to either the collector or the central server via a Wi-Fi and/or WiMax wireless communications network. The Wi-Fi and/or WiMax network can operate independently of, or in conjunction with, existing data gathering wireless networks.

Wireless communication network architecture

Abstract: A heterogeneous wireless network topology is suited for low­ power, short-range and ubiquitous ad-hoc communication, said network topology being capable of integrating different wire­less transmission technologies, in particular to a wireless sensor network (WSN) including different node types (PUs, SAs and/or SPs) and communication technologies. The network is highly heterogeneous and can be operated according to the master-slave principle or in a distributed ad-hoc manner. The nodes (PUs, SAs and/or SPs) can have different wireless com­munication means tailored to their individual role in the network and other constraints, thus allowing different commu­ nication patterns. A remote polling and control system (430, 450, 460, or 470) in a heterogeneous wireless sensor network (WSN) comprises a master node (PU) having an RF transceiver (aTx and aRx) for sending (SOa) a wake-up signal to at least one remote slave node (SP, SA) of a first and/or second type for polling (Sob) information detected by said slave node (SP) or triggering functions to be executed, sending (SOc) control information for triggering a function to be executed by at least one re­ motely controllable slave node (SA) of a second type and re­ceiving (Sod) feedback information from the remotely control­lable slave node (SA) of said second type, said slave nodes (SAs, SPs) being in a stand-by mode before and after being called by the master node (PU).

Design and analysis of a cooperative medium access scheme for wireless mesh networks

Abstract: This paper presents the detailed design and performance analysis of MACA-P, a RTS/CTS based MAC protocol, that enables simultaneous transmissions in wireless mesh networks. The IEEE 802.11 DCF MAC prohibits any parallel transmission in the neighborhood of either a sender or a receiver (of an ongoing transmission). MACA-P is a set of enhancements to the 802.11 MAC that allows parallel transmissions in situations when two neighboring nodes are either both receivers or transmitters, but a receiver and a transmitter are not neighbors. The performance of MACA-P in terms of system throughput is obtained through a simulation of the protocol using ns and is compared with the 802,11 RTS/CTS MAC. Experiments with the base MACA-P protocol reveal the need for certain enhancements, especially to avoid the drawbacks associated with attempts at parallel transmissions in scenarios where such parallelism is not feasible. Studies with the enhanced MACA-P protocol also demonstrate how significant performance gains in wireless mesh network performance may be realized if the radio transceiver behavior is modified in tandem with the MAC protocol.

A reliable virtual backbone scheme in mobile ad-hoc networks

Abstract: In wireless ad-hoc networks, hosts communicate with each other without help of any physical infrastructure. Inevitably, the communication tends to be inefficient in terms of computational and network resources. Study on virtual infrastructures or backbones in wireless ad-hoc networks gets more attention in the hope of reducing the communication overhead. But the backbone structure is very vulnerable due to various factors like node mobility, unstable links, and so on. So a new scheme which is reliable and efficient both to construct and maintain the backbone structure is needed. We present our noble virtual backbone scheme which is reliable and efficient by considering stability and coverage of nodes.

An energy-efficient method for nodes assignment in cluster-based Ad Hoc networks

Abstract: One of the most critical issues in wireless ad hoc networks is represented by the limited availability of energy within network nodes. Thus, making good use of energy is a must in ad hoc networks. In this paper, we define as network lifetime the time period from the instant when the network starts functioning to the instant when the first network node runs out of energy. Our objective is to devise techniques to maximize the network lifetime in the case of cluster-based systems, which represent a significant sub-set of ad hoc networks. Cluster-based ad hoc networks comprise two types of nodes: cluster-heads and ordinary nodes. Cluster-heads coordinate all transmissions from/to ordinary nodes and forward all traffic in a cluster, either to other nodes in the cluster or to other cluster-heads. In this case, to prolong the network lifetime we must maximize the lifetime of the cluster-heads because they are the critical network element from the energy viewpoint. We propose an original approach to maximize the network lifetime by determining the optimal assignment of nodes to cluster-heads. Given the number of cluster-heads, the complexity of the proposed solution grows linearly with the number of network nodes. The network topology is assumed to be either static or slowly changing. Two working scenarios are considered. In the former, the optimal network configuration from the energy viewpoint is computed only once; in the latter, the network configuration can be periodically updated to adapt to the evolution of the cluster-heads energy status. In both scenarios, the presented solution greatly outperforms the standard assignment of nodes to cluster-heads, based on the minimum transmission power criterion.