Shinsuke Tanaka

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.

An adaptive framework for multipath routing via maximally zone-disjoint shortest paths in ad hoc wireless networks with directional antenna

Application of multipath routing techniques in mobile ad hoc networks has been explored earlier, as multipath routing may help to reduce end-to-end delay, perform load balancing and consequently improve throughput. However, it has also been shown that the success of multipath routing in ad hoc wireless network depends on network topology and channel characteristics can severely limit the gain offered by multipath routing strategies. The most significant challenge to making the use of multipath routing protocols effective in this environment involves considering the effects of route coupling. Route coupling in wireless medium occurs when two routes are located physically close enough to interfere with each other during data communication. As a result, the nodes in multiple routes are constantly contending for access to the medium they share and can end up performing worse than a single path protocol. In this paper, we propose a notion of zone-disjoint routes in wireless medium where paths are said to be zone-disjoint when data communication over one path will not interfere with data communication in other path. The notion of zone-disjointness is used as route selection criteria. However, zone-disjointness alone is not sufficient for performance improvement. If the path-length (number of hops) were large, that would increase the end-to-end delay even in the context of zone-disjointness. So, it is imperative to select maximally zone-disjoint shortest paths. However, getting zone-disjoint or even partially zone-disjoint routes in ad hoc network with omni-directional antenna is difficult, since the transmission zone of each node is larger compared to that with directional antenna. Hence, one way to reduce this transmission zone of a node is to use directional antenna. In this paper, we investigate the effect of directional antenna on zone-disjoint multipath routing and evaluated its effectiveness in QualNet network simulator.

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 Link Heterogeneity-Aware On-Demand Routing (LHAOR) Protocol Utilizing Local Update and RSSI Information

Many routing protocols have been proposed for mobile ad hoc networks. Among these protocols, the on-demand routing protocols are very attractive because they have low routing overhead. However, few of the existing on-demand routing protocols have considered the link heterogeneity, such as the different communication rate, different Packet Error Ratio (PER). As a result, the routes tend to have the shortest hop count and contain weak links, which usually provide low performance and are susceptible to breaks in the presence of mobility. In this paper, we analyze the existing on-demand routing protocols and propose a Link Heterogeneity Aware On-demand Routing (LHAOR) protocol, where the link quality and mobility are considered. Specifically, the Local Update (LU) is proposed and the link metric is inversely related with the Received Signal Strength Indicator (RSSI). By using the LU method and RSSI information, the routes adapt to the topology variation and link quality changes, and reach the local optimum quickly, which contains strong links and has a small metric. Simulation and experiment results show that our LHAOR protocol achieves much higher performance than the classical on-demand routing protocols. key words: ad hoc networks, link heterogeneity, on-demand, mobility, RSSI

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.

Admission control and simple class based QoS provisioning for mobile ad hoc network

In this paper, we present a network layer based admission control and simple class based service differentiation model to support QoS in mobile ad hoc networks. Our admission control procedure works along with the route finding phase of reactive routing protocols for mobile ad hoc networks (AODV, DSR etc). We also propose a simple class based service differentiation system to support QoS once a traffic is admitted by our admission controller. The proposed service differentiation is based on a DiffServ model and includes modifications like configuration of each node with edge and core functionality, dynamic selection of edge/core functionality, and use of minimal and simple classes. Simulation results show that our system allows seven times more real time traffic in the network than the proposed QoS for the AODV model while satisfying the demanded end-to-end delay and providing low jitter.

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.

A priority-based QoS routing protocol with zone reservation and adaptive call blocking for mobile ad hoc networks with directional antenna

Existing priority-based QoS routing protocols in ad hoc wireless networks did not consider the effect of mutual interference between routes in wireless medium during routing. We have investigated the effect of mutual interference on the routing performance in wireless environment and explored the advantage of using zone-disjoint routes to avoid mutual interference and to improve the network performance. In this paper, a priority based QoS routing scheme is proposed that uses the notion of zone-disjoint routes. Our protocol avoids the contention between high and low priority routes by reserving high priority zone of communication. Low priority flows tries to avoid this zone by selecting the routes that is maximally zone-disjoint with respect to the high priority reserved zone and consequently allows a contention-free transmission of high priority traffic in that reserved zone. If, under some unavoidable situations, a low priority flow has to go through high priority reserved zone causing interference, then it blocks itself temporarily to allow contention-free transmission of high priority flows and later may resume the blocked communication if possible. We have evaluated the effectiveness of our proposed protocol on QualNet network simulator.