Siuli Roy

A network-aware MAC and routing protocol for effective load balancing in ad hoc wireless networks with directional antenna

Use of directional antenna in the context of ad hoc wireless networks can largely reduce radio interference, thereby improving the utilization of wireless medium. Our major contribution in this paper is to devise a routing strategy, along with a MAC protocol, that exploits the advantages of directional antenna in ad hoc networks for improved system performance. In this paper, we have illustrated a MAC and routing protocol for ad hoc networks using directional antenna with the objective of effective load balancing through the selection of maximally zone disjoint routes. Zone-disjoint routes would minimize the effect of route coupling by selecting routes in such a manner that data communication over one route will minimally interfere with data communication over the others. In our MAC protocol, each node keeps certain neighborhood status information dynamically in order that each node is aware of its neighborhood and communications going on in its neighborhood at that instant of time. This status information from each node is propagated periodically throughout the network. This would help each node to capture the approximate network status periodically that helps each node to become topology-aware and aware of communications going on in the network, although in an approximate manner. With this status information, each intermediate node adaptively computes routes towards destination. The performance of the proposed framework has been evaluated on QualNet Network Simulator with DSR (as in QualNet) as a benchmark. Our proposed mechanism shows four to five times performance improvement over DSR, thus demonstrating the effectiveness of this proposal.

Multipath Routing in Ad Hoc Wireless Networks with Omni Directional and Directional Antenna: A Comparative Study

Several routing schemes have been proposed in the context of mobile ad hoc network. Some of them use multiple paths simultaneously by splitting the information among multitude of paths, as it may help to reduce end-to-end delay and perform load balancing. Multipath routing also diminishes the effects of unreliable wireless links in the constantly changing topology of ad hoc networks to a large extent. Route coupling, caused by the interference during the simultaneous communication through multiple paths between a pair of source and destination, severely limits the performance gained by multipath routing. Using node disjoint multiple paths to avoid coupling is not at all sufficient to improve the routing performance in this context. Route coupling may be reduced to a great extent if zone disjoint or even partially zone disjoint paths are used for data communication. Two paths are said to be zone disjoint if data communication through one path does not interfere with other paths. Large path length (number of hops) also contributes to the performance degradation resulting in high end to end delay. So zone disjoint shortest multipath is the best choice under high traffic condition. However, it is difficult to get zone disjoint or even partially zone disjoint multiple routes using omni-directional antenna. This difficulty may be overcome if directional antenna is used with each mobile node. In this paper, we have done a comparative study on the performance of multipath routing using omni-directional and directional antenna. The result of the simulation study clearly shows that directional antenna improves the performance of multipath routing significantly as compared to that with omni-directional antenna.

Road traffic congestion monitoring and measurement using active RFID and GSM technology

In this paper, we present an intelligent Traffic Congestion Monitoring & Measurement System called TrafficMonitor to monitor and measure the road traffic congestions using probe vehicle. The concept of probe vehicle has come up in recent times for collecting real time traffic data. Our system provides an easy platform to analyze the traffic movement and congestion pattern. TrafficMonitor is a rapidly deployable, cost-effective and easily maintainable traffic congestion monitoring & measurement system that combines active RFID (based on IEEE 802.15.4 protocol, 2.4 GHz ISM band) and GSM technologies. The congestion detection algorithm is based upon calculation of vehicular speed over a stretch of road and the average waiting time of vehicles at road-crossing. Besides providing a complete description of our system and the concepts developed, the paper also provides a comprehensive description of on-road test results to support our concepts. We also provide a detailed description of all the field trials conducted, various traffic data gathered and finally the conclusions derived from such data. Government agencies, especially traffic control department, may use this system for realtime congestion monitoring by installing the system with probe vehicles. Road research organizations and NGOs may use this for studying and analyzing traffic mobility and congestion patterns.

Improving End-to-End Delay through Load Balancing with Multipath Routing in Ad Hoc Wireless Networks Using Directional Antenna

Multipath routing protocols are distinguished from single-path protocol by the fact that they use several paths to distribute traffic from a source to a destination instead of a single path. Multipath routing may improve system performance through load balancing and reduced end-to-end delay. However, two major issues that dictate the performance of multipath routing – how many paths are needed and how to select these paths. In this paper, we have addressed these two issues in the context of ad hoc wireless networks and shown that the success of multipath routing depends on the effects of route coupling during path selection. Route coupling, in wireless medium, occurs when two routes are located physically close enough to interfere with each other during data communication. Here, we have used a notion of zone-disjoint routes to minimize the effect of interference among routes in wireless medium. Moreover, the use of directional antenna in this context helps to decouple interfering routes easily compared to omni-directional antenna.

A Rotational Sector-Based, Receiver-Oriented Mechanism for Location Tracking and Medium Access Control in Ad Hoc Networks Using Directional Antenna

The use of directional antenna in wireless ad hoc networks potentially increases simultaneous communication by directing the transmitting and receiving beams towards the receiver and transmitter node as compared to omni-directional antenna, where nodes in the vicinity of a communication are kept silent. However, in order to implement effective directional MAC protocol using directional antenna, a node should know how to set its transmission direction to transmit a packet to its neighbors and to avoid transmission in other directions where data communications are already in progress. So, it becomes imperative to have a mechanism at each node to track the locations of its neighbors and to know the communication status of neighboring nodes. In this paper, we propose a receiver-centric approach for location tracking and MAC protocol. The performance evaluation on QualNet network simulator indicates that our protocol is highly efficient with increasing number of communications and increasing data rate.

An observer-based distributed scheme for selfish-node detection in a post-disaster communication environment using delay tolerant network

Aftermath of disaster causes severe destruction/damage to physical infrastructures. As a result, communication infrastructure gets disrupted for weeks. In such situations, smart-phone based adhoc opportunistic networks may be set up with the smart-phones carried by the relief workers (also referred as nodes) to communicate the situational information from different affected corners to some remote monitoring station. In such scenario, some malicious nodes may try to intercept and manipulate the sensitive situational data with the intention of corruption and fraud. One way of preventing such corruption is to devise an automated mechanism to detect and avoid the malicious nodes during data communication process. Reputation of nodes may be used as a measure to detect malicious nodes where reputation is estimated based on their degree of cooperation with other nodes in the network during data communication. In this paper, we propose an observer based dynamic reputation estimation technique for detection of selfish nodes where a group of independent roving observer nodes were introduced in the network to monitor the behavior of volunteer nodes as forwarder and receiver and to identify whether a node has any group-bias. Observers estimate the reputation of nodes based on their interaction patterns and group-biasness and periodically publishes global node reputation matrix based on which volunteer nodes may select an unselfish forwarder node during their data communication. The performance of the proposed scheme was evaluated on ONE simulator [19].

Multipath Routing in Ad Hoc Wireless Networks with Directional Antenna

Multipath routing protocols are distinguished from single-path routing by the fact that they look for and use several routes from a source to destination. Several routing schemes have been proposed in the context of mobile ad hoc networks that uses multiple paths simultaneously by splitting the information among the multitude of paths. However, the effect of route coupling in this environment can severely limit the gain offered by multipath routing strategies. Route coupling is a phenomenon of wireless medium and occurs when multiple routes are located physically close enough to interfere with each other during data communication. In this paper, we investigate the effect of directional antenna on multipath routing. We have shown that the effect of route coupling across multiple paths with directional antenna is much less compared to that with omni-directional antenna. As a result, the routing performance using multiple paths improves substantially with directional antenna compared to that with omni-directional antenna.

ACR: an adaptive communication-aware routing through maximally zone-disjoint shortest paths in ad hoc wireless networks with directional antenna

A fundamental problem that distinguishes wireless networks from wired networks is the mutual interference between routes within the proximity of each other. This phenomenon is known as route coupling and it restricts the possibility of occurrence of simultaneous communications along the coupled routes. In this context, the use of directional antenna, having smaller transmission beam-width compared to omni-directional antenna, helps to easily decouple interfering routes, and improves network performance through space division multiple access (SDMA). However, even if we have an efficient directional MAC protocol, it alone would not be able to guarantee good system performance, unless we have a proper routing strategy in place that exploits the advantages of directional antenna. So, in this paper, an adaptive routing strategy is proposed that exploits the advantages of directional antenna in ad hoc networks through the selection of maximally zone-disjoint shortest routes. Zone-disjoint routes would minimize the effect of route coupling and improve the overall network performance. The proposed strategy ensures effective load balancing and is applied to design and implement both single path and multipath routing protocols in ad hoc networks with directional antennas. Simulation results obtained on QualNet network simulator shows the effectiveness of the proposed routing protocols. Copyright

Service differentiation in multi-hop inter-vehicular communication using directional antenna

Inter-vehicular communication (IVC) on highways is one of the major application areas of ad hoc networks that enable multi-hop data exchange and forwarding between cars and between car and stationary gateways. In an IVC scenario, some emergency situations on highways may require an immediate communication with police, hospitals, highway assistance booth or with other cars. These messages should be forwarded on a top priority basis to the destination for immediate attention. So it is evident that, in an IVC scenario, some message flows are to be treated as high priority messages in order to ensure a timely and reliable delivery. We have proposed a priority-based communication scheme, which essentially selects shortest path for a high priority flow and reserves a zone known as high priority zone, along this path. Other low priority flows are forced to avoid this zone and take a longer diverse route to forward their messages to allow a contention-free communication to high priority flows. In this context, the use of directional antenna, having smaller transmission beam-width and larger transmission range compared to omni-directional antenna, helps to easily decouple interfering routes, and improves the overall utilization of the wireless medium through space division multiple access (SDMA).

A distributed feedback control mechanism for priority-based flow-rate control to support QoS provisioning in ad hoc wireless networks with directional antenna

We have proposed a scheme for supporting priority-based QoS in mobile ad hoc networks by classifying the traffic flows in the network into different priority classes, and giving different treatment to the flow-rates belonging to different classes. We have adopted a control-theoretic approach to adaptively control the low-priority flows so as to maintain the high priority flow-rates at their desired level, thus guaranteeing QoS to high-priority flow. At the same time, our objective is to adaptively maximize low priority flows while maintaining high priority flows at a desired level so that full utilization of wireless medium can be achieved through adaptive rate control. To provide this desired service guarantee to high priority flows, we need a distributed flow-control algorithm. Here, the low priority flows, causing interference to a high priority flow, detect and measure high priority flow-rate at each node on their routes and consequently adjust their flow-rates using a feedback control mechanism to maintain the high priority flow at its desired level. This detection and measurement is done at MAC layer of each node participating in routing from source to destination. We have proposed this protocol with a very nominal overhead using omni-directional antenna and modified the scheme to show the overall improvement in throughput using directional antenna. The performance has been evaluated using QualNet network simulator and the results indicate the effectiveness of our scheme.