Ad hoc networks are comprised of MAC, routing protocols and physical environments. In this paper, optimum MTU (Maximum Transmission Unit) sizes are studied in the ad hoc network environment. For a performance index, the "throughput rate" is defined. The throughput rate is the ratio between the number of packets received and packets sending through the overall systems. MTUs with the sizes between 250 bytes and 750 bytes have been shown to have better throughput rates in the environment without noise. MTUs with the size of 500 bytes have been found to generate the optimum throughput rate in the environments of 10-4 BER or less. Similar results are obtained in lower BER environments. AODV has slightly better performance than DSR without noise. These results found to be true for practical mobile environment.

In this paper, a novel carrier-sense multiple-access (CSMA) scheme for UWB ad-hoc network is proposed and evaluated. UWB is a kind of spread spectrum communication and it is possible to detect the distance between the nodes. With this positioning capability of the UWB systems, DS-CDMA (DS-UWB) scheme with variable spreading factor is used. In this paper, a novel CSMA scheme that employs the correlation of the spreading code is proposed.

We investigate the effects of DoS (Denial of Service) attacks in wireless ad hoc networks using simulations, concentrating on the problem of energy availability. Our results show that the damages due to the DoS attack may quite different with those in wired networks: First, the nodes along the transmission route mostly suffer damages rather than the victim node itself. Second, if the mobile nodes are crowded and close together, the damage becomes more severe. Lastly, if the nodes have random mobility, the attacker itself consumes more energy.

A multi-hop wireless local area network (LAN) is an ad-hoc wireless network that connects to the Internet backbone via an access point. Routing paths between mobile hosts and a fixed host can be divided into two sub-paths, wireless and wired. In this paper, we apply the Hierarchical Routing Tree (HRT) concept to finding wireless sub-paths. That is, by constructing an HRT, each mobile host can find a routing path to an access point (i.e., the HRT root) quickly and thus gain the access to Internet. In addition, we choose the Ad-hoc On-demand Distance Vector (AODV) routing protocol as a point-to-point routing method for sources and destinations located in the same ad-hoc network in order to improve upon a weakness in the HRT method. Numerical experiments are given to show the effectiveness of the hybrid routing method.

Since IEEE 802.11 has many problems such as hidden node, exposed node problem, larger sensing function and BEB (Binary Exponential Back-off), it is not suitable for use in multi-hop wireless ad hoc network. When an on-demand routing protocol is used with 802.11 DCF (Distributed Coordination Function), the route to transmit the packet will be formed by nodes which have less competition (fewer neighbors) than others for the medium access. This effect will make that the routing path will be longer and decrease network performance. Therefore, we propose a new MAC (Medium Access Control) protocol that makes a shorter routing path, enabling better performance in multi-hop wireless ad hoc networks. The protocol modifying IEEE 802.11 DCF gives priority to the node with more neighbors and with less transmission. Through simulations, we have demonstrated that the proposed algorithm improves performance in terms of transmission rate, transmission delay and total consumption energy.

The unfairness problem among TCP connections has been proved to be very severe in the IEEE 802.11-based wireless ad hoc networks because the hidden station problem still exists and the binary exponential backoff algorithm always favors the latest successful station. In this paper, a novel protocol, neighbor-medium-aware MAC (NEMA-MAC), is proposed to improve the TCP fairness. By adding a medium (channel) state field in the head of the traditional IEEE 802.11 MAC frame, the NEMA-MAC protocol provides a communication mechanism to resolve the hidden station problem. In addition, when a collision occurs, the new backoff algorithm makes the senders cooperatively adjust the contention window according to their local and neighbors' channel usage indexes. The simulation results show that TCP sessions can acquire satisfying fairness and increase the throughput in the NEMA-MAC-based multihop ad hoc networks.

The single path routing protocol, known as the Ad Hoc On-demand Distance Vector, has been widely studied for use in mobile ad hoc networks. AODV requires a new route discovery whenever a path breaks. Such frequent route discoveries cause a delay due to route discovery latency. To avoid such inefficiency, a multipath routing protocol has been proposed that attempts to find link-disjoint paths in a route discovery. However, when there are two or more common intermediate nodes on the path, the protocol can not find a pair of link-disjoint paths even if the paths actually exist. To reduce this route discovery latency, it is necessary to increase the opportunities for finding a pair of link-disjoint paths. In this paper, we focus on AODV and propose an AODV-based new multipath routing protocol for mobile ad hoc networks. The proposed routing protocol uses a new method to find a pair of link-disjoint paths by selecting a route having a small number of common intermediate nodes on its path. Using simulation models, we evaluate the proposed routing protocol and compare it with AODV and the existing multipath routing protocol. Results show that the proposed routing protocol achieves better performance in terms of delay than other protocols because it increases the number of cases where a pair of link-disjoint paths can be established.

Since a radio channel is shared among terminals in an ad hoc network, packet collisions are frequent. In case of transmitting packets especially using TCP, data and ACK packets are transmitted in opposite directions on the same radio channel. Therefore, frequent collisions are unavoidable, and this seriously degrades TCP throughput. It is possible to transmit to two or more nodes which adjoin from a certain node simultaneously on the radio channel. To reduce the likelihood of packet collisions when an intermediate node transmits both data and ACK packets, these two types of packet can be combined and transmitted at the same time to increase the efficiency of radio channel utilization. In this paper, we propose a new technique to improve TCP performance by combining data and ACK packets. Our proposed technique is applicable to generic ad hoc networks easily. By means of a simulation using networks with various topologies, we have found that throughput can be improved by up to 60% by applying our proposed technique.

This paper presents a path compression protocol for on-demand ad hoc network routing protocols, which is called dynamic path shortening (DPS). In DPS, active route paths adapt dynamically to node mobility based on the "local" link quality estimation at each own node, without exchanging periodic control packets such as Hello messages. Each node monitors its own local link quality only when receiving packets and estimates whether to enter the "proximity" of the neighbor node to shorten active paths in a distributed manner. Simulation results of DPS in several scenarios of various node mobility and traffic flows reveal that adding DPS to DSR which is the conventional prominent on-demand ad hoc routing protocol significantly reduces the end-to-end packet latency up to 50-percent and also the number of routing packets up to 70-percent over the pure DSR, in heavy traffic cases. We also demonstrate the other simulation results obtained by using our two novel mobility models which generate more realistic node mobility than the standard random waypoint mobility model: Random Orientation Mobility and Random Escape Mobility models. Finally, simple performance experiments using DPS implementation on FreeBSD OS demonstrate that DPS shortens active routes in the order of milliseconds (about 5 ms).

We propose an efficient IP address assignment protocol in mobile ad hoc networks, which use a proactive routing protocol. In this method, which is termed the Bisected-Range based Assignment (BRA), a node repeatedly broadcasts an Agent Request to ask for address assignment. If there are one or more neighbor MANET nodes, one of them becomes an agent to select and assign an IP address to the requesting node. We use address location in the IP address space so that each agent maintains its own exclusive address range to be used for address selection, resulting to decrease the possibility of address conflict. If the requesting node cannot discover any neighbor MANET node over pre-determined random agent-search time, it selects by itself an IP address at random from the given address block. We evaluate performance of the basic and enhanced BRAs by computer simulation. It is shown that the basic and enhanced BRAs can reduce address conflict compared with random assignment. It is also shown that the enhanced BRA is superior in terms of control traffic overhead as well as address assignment delay over the random assignment with the strong Duplicate Address Detection.

The AODV (Ad Hoc On-Demand Distance Vector) protocol is one of the typical reactive routing protocols in Ad Hoc networks, in that mobile nodes initiate routing activities only in the presence of data packets in need of a route. In this paper, we focus upon the local repair mechanism of AODV. When a link is broken, the upstream node of the broken link repairs the route to the destination by initiating a local route discovery process. The process involves the flooding of AODV control messages in every node within a radius of the length from the initiating node to the destination. In this paper, we propose an efficient local repair scheme for AODV, called AELR (AODV-based Efficient Local Repair). AELR utilizes the existing routing information in the downstream intermediate nodes which have been on the active route to the destination before a link break occurs. AELR can reduce the flooding range of AODV control messages and the route recovery time for route recovery because it can repair a route through the nearby downstream intermediate nodes. The performance results show that AELR can achieve faster route recovery than the local repair mechanism of AODV.

Along with expansion of utilization of mobile ad hoc networks, it is expected that the network size becomes large. However, design of current typical routing protocols supposes at most several hop routes between source and destination nodes. When messages are delivered along long hop routes in the networks, such routing protocols tend to degrade performance. Previously, we have proposed an autonomous clustering scheme for constructing and maintaining hierarchical structure in mobile ad hoc networks, which are adaptive to node movement. This paper proposes a class of hierarchical routing protocols Hi-TORA, Hi-DSR and Hi-AODV, all of which are based on the autonomous clustering scheme, compares them with their corresponding flat routing protocols TORA, DSR and AODV, respectively, and shows effectiveness of these hierarchical routing protocols by simulation experiments.

In ad-hoc on-demand routing algorithm, when a route is broken a relay node must perform error transaction and the source node must do rerouting to discover an alternate route. It is important to construct a stable route when route discovery occurs. In this paper, we use relative speeds among nodes as a measure of node mobility. Our routing algorithm chooses nodes of lower relative speed as relay nodes. As a result of our simulation, when there is one session in the network, our proposing algorithm can reduce the number of route breaks: about 3 times smaller than DSR. And our proposing algorithm can deliver more packets than DSR: 18% higher rate. However, in the congested traffic situation our algorithm should be improved.

Ad Hoc Networks are transmission networks in the structure of wireless networks that consist of many mobile hosts. They do so without the support from other communication infrastructures like Base Stations, and directly use wireless networks for data-transmission. This paper provides a general explanation of related protocols for setting up routes and their possible problems. In addition, related researches are described with their method of solving problems and reducing the possibility of problems occurring. Then, a novel constructive protocol called Partition-Timing Routing Protocol (PTR) is presented. If any covered node needs to transmit data to others outside the scope, it has to be managed by a core node. This protocol is able to adjust neighboring nodes covered in the scope, to select certain nodes to be their own core node. In addition, the timing for updating and adjusting the data of the covered scope is different from other methods, and at the same time it reduces the load of the entire network and makes it more flexible.

We have been developing new cycling environments by using knowledge sharing and speech communication. We have offered multimodal knowledge contents to share knowledge on safe and exciting cycling. We accumulated 140 contents, focused on issues such as riding techniques, trouble shootings, and preparations on cycling. We have also offered a new way of speech communication using an ad-hoc wireless LAN technology for safe cycling. Group cycling requires frequent communication to lead the group safely. Speech communication achieves spontaneous communication between group members without looking around or speaking loudly. Experimental result through actual cycling has shown the effectiveness of sharing multimodal knowledge contents and speech communication. Our new developed environment has an advantage of increasing multimodal knowledge through the accumulation of personal experiences of actual cycling.

In this paper, we propose a modeling framework for supporting QoS routing in mobile ad-hoc wireless networks. The basic motivations of the proposed modeling approach stem from the commonality observed in the location uncertainty in mobile ad-hoc wireless networks and the concept of entropy. These common characteristics have motivated our work in developing an analytical modeling framework using entropy concepts and utilizing mobility information as the corresponding variable features, in order to support and evaluate route stability in self-organizing mobile ad-hoc wireless networks. The corresponding methodology, results and observations can be used by the routing protocols to select the most stable route between a source and a destination, in an environment where multiple paths are available, as well as to create a convenient performance measure to be used for the evaluation of the stability and connectivity in a mobile ad-hoc wireless networks.

Quality of Service (QoS) provisioning is a new but challenging research area in the field of Mobile Ad hoc Network (MANET) to support multimedia data communication. However, the existing QoS routing protocols in ad hoc network did not consider a major aspect of wireless environment, i.e., mutual interference. Interference between nodes belonging to two or more routes within the proximity of one another causes Route Coupling. This can be avoided by using zone-disjoint routes. Two routes are said to be zone disjoint if data communication over one path does not interfere with the data communication along the other path. In this paper, we have proposed a scheme for supporting priority-based QoS in MANET by classifying the traffic flows in the network into different priority classes and giving different treatment to the flows belonging to different classes during routing so that the high priority flows will achieve best possible throughput. Our objective is to reduce the effect of coupling between routes used by high and low priority traffic by reserving zone of communication. The part of the network, used for high priority data communication, i.e, high priority zone, will be avoided by low priority data through the selection of a different route that is maximally zone-disjoint with respect to high priority zones and which consequently allows contention-free transmission of high priority traffic. The suggested protocol in our paper selects shortest path for high priority traffic and diverse routes for low priority traffic that will minimally interfere with high priority flows, thus reducing the effect of coupling between high and low priority routes. This adaptive, priority-based routing protocol is implemented on Qualnet Simulator using directional antenna to prove the effectiveness of our proposal. The use of directional antenna in our protocol largely reduces the probability of radio interference between communicating hosts compared to omni-directional antenna and improves the overall utilization of the wireless medium in the context of ad hoc wireless network through Space Division Multiple Access (SDMA).

We propose adaptive variable-rate constant-power scheme for ad hoc wireless networks, employing the modification of Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol. Potential improvements in throughput and back-off probability are presented for different system parameters.

The multimedia applications have recently generated much interest in wireless network infrastructure with supporting the quality-of-service (QoS) communications. In this paper, we propose a lantern-tree-based QoS on-demand multicast protocol for wireless ad hoc networks. Our proposed scheme offers a bandwidth routing protocol for QoS support in a multihop mobile network, where the MAC sub-layer adopts the CDMA-over-TDMA channel model. The QoS on-demand multicast protocol determines the end-to-end bandwidth calculation and bandwidth allocation from a source to a group of destinations. In this paper, we identify a lantern-tree for developing the QoS multicast protocol to satisfy certain bandwidth requirement, while the lantern-tree is served as the multicast-tree. Our lantern-tree-based scheme offers a higher success rate to construct the QoS multicast tree due to using the lantern-tree. The lantern-tree is a tree whose sub-path is constituted by the lantern-path, where the lantern-path is a kind of multi-path structure. This obviously improves the success rate by means of multi-path routing. In particular, our proposed scheme can be easily applied to most existing on-demand multicast protocols. Performance analysis results demonstrate the achievements of our proposed protocol.

An Ad Hoc network is a collection of wireless mobile nodes dynamically forming a temporary network without the use of any existing network infrastructure or centralized administration. The choice of medium access is difficult in Ad Hoc networks due to the time-varying network topology and the lack of centralized control. In this paper, we propose a novel multichannel schedule-based Medium Access Control (MAC) protocol for Ad Hoc networks named Multichannel Reservation Protocol for TDMA-based networks (MRPT). MRPT ensures collision free in successfully reserved data links, even when hidden terminals exist. The reservation of MRPT is based a control channel and in order to improve throughput we propose Four-Phase-Two-Division (FPTD) as a media access scheme of the control channel for broadcasting control or reservation messages. In FPTD, the collision can be solved rapidly with an efficient backoff algorithm which results in that system block is avoided in case of high traffic. In this paper, we also present the throughput performance of MRPT, which shows a high value and no system block even in case of high traffic load.