Taku Noguchi

Broadcasting with Randomized Network Coding in Dense Wireless Ad Hoc Networks

In this paper, we consider the broadcast storm problem in dense wireless ad hoc networks where interference among densely populated wireless nodes causes significant packet loss. To resolve the problem, we apply randomized network coding (RNC) to the networks. RNC is a completely different approach from existing techniques to resolve the problem, and it reduces the number of outstanding packets in the networks by encoding several packets into a single packet. RNC is a kind of linear network coding, and it is suited to wireless ad hoc networks because it can be implemented in a completely distributed manner. We describe a procedure for implementing the wireless ad hoc broadcasting with RNC. Further, with several simulation scenarios, we provide some insights on the relationship between the system parameters and performance and find that there is the optimal length of coding vectors for RNC in terms of packet loss probability. We also show a guideline for the parameter setting to resolve the broadcast storm problem successfully.

Construction of a robust multicast tree for application-level multicast

Application-level multicast (ALM) is a feasible alternative to IP multicast. In ALM, multicast related features, such as group membership management, multicast routing and packet replication, are implemented at end-hosts instead of routers. A multicast distribution tree is constructed in the application layer, so all nodes in this tree are end-hosts. Packet transmission between end-hosts uses conventional IP unicast service. Therefore, all end-hosts can enjoy multicast communications without IP multicast service. However, ALM has a serious problem that the multicast distribution tree is intrinsically fragile and an end-host failure causes tree partitions. In this paper, to deal with this problem, we propose a new tree construction protocol which makes outdegrees of intermediate nodes be balanced. The degree-balanced distribution tree can reduce the average number of nodes decoupled by tree partitions. To investigate performance of our protocol, it is compared with an existing ALM protocol. Our simulation results show that our protocol outperforms the existing protocol from the viewpoints of robustness, loss probability and receiver-perceived delay.

Localization scheme for large scale Wireless Sensor Networks

Localization of Wireless Sensor Networks (WSNs) is an issue for location-based services. This paper proposes a new Wireless Sensor Network Localization Scheme based on Self-Organizing Maps (SOM) to deal with this issue. Our scheme utilizes only connectivity information and information from some heard anchors in the network to determine the location of nodes. With anisotropic topologies or topologies having obstacles, localization schemes tend to get higher error. Our scheme not only solves well the isotropic networks, but also minimizes the error in anisotropic networks and networks having obstacles by filtering the information from heard anchors. From our intensive simulations, the results show that the proposed scheme achieves very good accuracy in most cases.

Maximizing Aggregate Throughput of Wireless Ad Hoc Networks Using Enhanced Physical Carrier Sensing

Aggregate throughput of wireless ad hoc networks is diminished by the presence of hidden terminal problem which can cause packet collisions at the receiver and exposed terminal problem which can degrade spatial reuse of the network. As reducing one problem increases the other, the aggregate throughput will be improved only if tradeoff between these two problems is achieved. In this paper, we propose a medium access control scheme which utilizes enhanced physical carrier sensing with tunable carrier sense range based on transmitter-receiver distance. Two analytical formulations for deriving optimal carrier sense ranges: one for interference mitigation and the other for reducing exposed terminal problem have been proposed and the optimal carrier sense range for balancing these two problems has also been estimated based on these formulations. Effectiveness of enhanced physical carrier sensing with tunable carrier sense range on achieving the highest aggregate network throughput has been demonstrated and the optimal carrier sense ranges for different transmitter-receiver distances have been investigated through extensive simulations. Comparisons between simulation results and theoretical results have been presented to validate our proposed scheme.

Robust application-level multicast tree construction for wireless/mobile hosts

IP multicast is an effective technology to distribute identical data simultaneously to multiple users. However, for technical and administrative reasons, IP multicast has not been globally deployed on the Internet. Another approach to multicast is application-level multicast (ALM). In ALM, multicast related features, such as group membership management, multicast routing and packet replication, are implemented at end-hosts instead of routers. Multicast delivery tree is constructed in the application layer, so all nodes in this tree are end-hosts. Packet transmission between end-hosts uses conventional IP unicast service. Therefore, ALM is a promising alternative to IP multicast. However, application-level multicast relying on end-hosts is more fragile than IP multicast relying on routers. Especially, when a mobile host forwards packets to downstream hosts, a handover causes performance degradations on downstream hosts. In this paper, to alleviate the impact of a handover, we propose a new tree building protocol which locates mobile hosts on leaves of multicast tree. A handover of the mobile host on a leaf does not affect other end-hosts. To investigate performance of our protocol, it is compared with existing application-level multicast protocols. Our simulation results show that our protocol outperforms existing protocols from the viewpoints of loss probability, throughput and delay performance.

Adaptive Location-Aware Routing with Directional Antennas in mobile adhoc networks

In mobile ad hoc networks (MANETs), when information about the location of the destination node is known, efficient communication can be achieved by using location-based routing protocols. Even in location-based routing protocols, with omnidirectional antennas there is some redundant route discovery by blind flooding of route request packets outside the area between the source and destination. These redundant route discovery propagations can be reduced by using both a scheme of restricted flooding and directional antennas. In this paper, we propose a new location-based routing protocol using both restricted flooding and directional antennas, called Adaptive Location-Aware Routing with Directional Antennas (ALAR-DA). To investigate the performance of ALAR-DA, we compare it with existing location-aware routing protocols. Our simulation results show that ALAR-DA outperforms existing protocols from the standpoints of delay and route discovery traffic.

Construction of a Robust Multicast Tree for Application-Level Multicast

Application-level multicast (ALM) is a feasible alternative to IP multicast. In ALM, multicast related features, such as group membership management, multicast routing and packet replication, are implemented at end-hosts instead of routers. A multicast distribution tree is constructed in the application layer, so all nodes in this tree are end-hosts. Packet transmission between end-hosts uses conventional IP unicast service. Therefore, all end-hosts can enjoy multicast communications without IP multicast service. However, ALM has a serious problem that the multicast distribution tree is intrinsically fragile and an end-host failure causes tree partitions. In this paper, to deal with this problem, we propose a new tree construction protocol which makes outdegrees of intermediate nodes be balanced. The degree-balanced distribution tree can reduce the average number of nodes decoupled by tree partitions. To investigate performance of our protocol, it is compared with an existing ALM protocol. Our simulation results show that our protocol outperforms the existing protocol from the viewpoints of robustness, loss probability and receiver-perceived delay.

Enhancement of AODV Routing Protocol by Using Large Vehicles in VANETs on Highway

In recent years, many routing protocols that take into account particular vehicular ad hoc network (VANET) characteristics such as higher vehicle speeds and mobility patterns have been proposed. Most of the existing VANET routing protocols largely neglect vehicles as obstacles in VANETs. Obstacle shadowing caused by large vehicles such as trucks or buses more negatively affects packet transmission performance than some other type of fading affects the performance in highway scenarios because the direction of packet forwarding is limited only to that along the highway, i.e., the forward and backward directions on the highway. Large vehicles have not only the negative effect of obstacle shadowing but also a positive effect due to their higher antenna position. Antennas of large vehicles are placed at higher positions than those of standard-size vehicles. A higher antenna position can achieve a longer transmission distance. In this paper, we propose a new Ad hoc On-Demand Distance Vector (AODV) routing protocol using large vehicles (AODV-LV) that exploits the positive effect of large vehicles. AODV-LV preferentially selects large vehicles as nodes for rebroadcasting route request (RREQ) packets. To investigate the performance of AODV-LV, we compare it with an existing improved AODV routing protocol. Our simulation results show that AODV-LV outperforms the existing protocol from the standpoints of packet delivery ratio and delay.

Black hole attack prevention method using dynamic threshold in mobile ad hoc networks

A mobile ad hoc network (MANET) is a collection of mobile nodes that do not need to rely on a pre-existing network infrastructure or centralized administration. Securing MANETs is a serious concern as current research on MANETs continues to progress. Each node in a MANET acts as a router, forwarding data packets for other nodes and exchanging routing information between nodes. It is this intrinsic nature that introduces the serious security issues to routing protocols. A black hole attack is one of the well-known security threats for MANETs. A black hole is a security attack in which a malicious node absorbs all data packets by sending fake routing information and drops them without forwarding them. In order to defend against a black hole attack, in this paper we propose a new threshold-based black hole attack prevention method. To investigate the performance of the proposed method, we compared it with existing methods. Our simulation results show that the proposed method outperforms existing methods from the standpoints of black hole node detection rate, throughput, and packet delivery rate.

Simulation study of Maximum Amount Shortest Path routing in Wireless Sensor Networks using Ns-3

Spatially unbalanced energy consumption among sensors is the most important issue in Wireless Sensor Networks (WSNs). This uneven energy consumption can significantly reduce network lifetime. The use of sink mobility with constrained paths and decreasing the message flood by limiting the flood area can help to improve the energy efficiency in WSNs. Maximum Amount Shortest Path routing (MASP) is an efficient protocol using this idea. MASP is proactive (table-driven) in nature and tries to collect the largest amount of data with least energy. MASP makes use of constrained paths for the trajectories of mobile sinks and divides the deployed sensor nodes into independent zones to construct the routing tables. In this paper we discuss the implementation of MASP and conduct a performance evaluation of it using the ns-3 network simulator.