萬代 雅希

This paper discusses a buffering strategy for a delay-tolerant multimedia sensor network (DTMSN), whose typical application is video surveillance. In DTMSN, a sensor node observes events around it and stores the data in its own buffer memory. All the data is collected to the sink. Sensor nodes have restrictions on buffer memory as well as battery capacity. The entire data size is much larger than a single node's memory size. Thus, developing a strategy for buffering satisfying these restrictions is a critical issue for DTMSN. In this paper, we propose a novel buffering scheme for DTMSN called cooperative buffering (CB). In the proposed CB, the sensor node which has a large amount of data cooperates with its neighbor nodes to buffer the data in a distributed manner. CB uses mobile sinks. The cooperatively buffered data are transmitted directly to the mobile sink when it arrives. After proposing CB, this paper discusses extension for easy collection of the sink, extension for multi source nodes, and some sink mobility strategies of sink mobility. It evaluates the power consumption performance of CB via theoretical formulation and computer simulation. As a result, we show from the results that the proposed CB can handle multimedia data while operating at low-power.

In this paper, we propose a multi-lobe directional transmission for network coding in multi-rate ad hoc networks to improve throughput performance of XOR-based WNC. The proposed scheme uses directional antennas that can make antenna beam forms with multiple main lobes. In the proposed scheme, a node transmits uncoded packets with a beam form of one or multiple main lobes for realizing high-rate unicast transmissions. In addition a node transmits XORed packets and native packets with a beam form of multiple main lobes with directional antenna to realize high-rate multicast transmissions. We evaluated and investigated the performance of the proposed scheme in terms of throughput via intensive computer simulations. The simulated results show that the proposed scheme can improve throughput performance of XOR-based WNC in some simple topologies such as 5 nodes straight line topology and X topology. In the fundamental evaluation, we have confirmed that the proposed scheme can achieve higher throughput than the conventional XOR-based WNC without using directional antennas in the same topologies. The proposed scheme is also applicable for other smart/directional antennas.

This paper discusses a buffering strategy for a delay-tolerant multimedia sensor network (DTMSN), whose typical application is video surveillance. In DTMSN, a sensor node observes events around it and stores the data in its own buffer memory. All the data is collected to the sink. Sensor nodes have restrictions on buffer memory as well as battery capacity. The entire data size is much larger than a single node’s memory size. Thus, developing a strategy for buffering satisfying these restrictions is a critical issue for DTMSN. In this paper, we propose a novel buffering scheme for DTMSN called cooperative buffering (CB). In the proposed CB, the sensor node which has a large amount of data cooperates with its neighbor nodes to buffer the data in a distributed manner. CB uses mobile sinks. The cooperatively buffered data are transmitted directly to the mobile sink when it arrives. After proposing CB, this paper discusses extension for easy collection of the sink, extension for multi source nodes, and some sink mobility strategies of sink mobility. It evaluates the power consumption performance of CB via theoretical formulation and computer simulation. As a result, we show from the results that the proposed CB can handle multimedia data while operating at low-power.

近年,指向性アンテナの使用を仮定した指向性MAC(Medium Access Control)プロトコルが提案されている.従来の指向性MACプロトコルでは,理想的なアンテナビームパターンが仮定されていた.しかし,実際のアンテナを用いた場合,サイドローブ,バックローブ等のマイナーローブの存在により,理想アンテナでは考慮されていなかった問題が発生することが考えられる.本論文では,マイナーローブが存在するアンテナビームパターンを用いて既存のMACプロトコルを評価し,問題点を定量的に明らかにする.問題点として,NAV(Network Allocation Vector)が適切に設定されないために発生する四つの問題を明らかにし,それらの問題について考察する.続いて,指向性アンテナのマイナーローブを考慮した指向性MACプロトコルを提案する.提案方式では,指向性巡回受信,NAVリクエストフレーム送信により,周辺端末との衝突を回避する.シミュレーション評価により,理想的なアンテナビームパターンを仮定して設計された従来のMACプロトコルと比較し,提案方式のスループット性能が向上することを示す.

Although the use of directional antennas in ad hoc networks is expected to provide significant improvements, directional MAC protocols inherently introduce new kinds of problems. Deafness is one of the major problems caused when a transmitter repeatedly attempts to communicate with its intended receiver, but it fails because the receiver has its beam pointed away from the transmitter. This paper proposes Receiver-Initiated Directional MAC (RI-DMAC) to handle the deafness problem. RI-DMAC is a combination of sender- and receiver-initiated operations. The sender-initiated mode is the default mode and the receiver-initiated mode is triggered when the transmitter experiences deafness. Each node maintains a polling table and polls a deafness node using the Ready to Receive (RTR) frame after the completion of every dialogue. Simulation results show that RI-DMAC outperforms other directional MAC protocols (e.g. Basic DMAC and Circular RTS MAC) in terms of throughput, fairness, overhead and packet drop ratio.

センサネットワークにおいて,観測データの発生が地理的に偏る場合には,センサノードの電力消費に差が生じ,シンク付近のノードが他のノードに比べて早期にバッテリ枯渇を起こす.これが原因となり,長いネットワーク寿命を達成できない.この問題に対し,本論文では,複数のシンクを用い,各ノードが複数のシンクを届け先とするバケット分配送信方式(DispersiveCast方式)を提案する.DispersiveCast方式は,各シンクヘのホップ数をもとに各ノードが分散的にバケット送信割合を決定するB-DOP(Basic DispresiveCast Of Packet)送信方式と,複数のシンクに到達するトラヒックを均衡化させるようにシンクが集中的にバケット送信割合を決定するO-DOP(Optima1 DispersiveCast Of Packet)送信方式からなる.シミュレーションによって,両送信方式の性能を評価し,DispersiveCast方式がネットワーク寿命の延長を可能とすることを示す.

In this paper, a routing protocol referred to as Directed Diffusion with Stepwise Interest Retransmission (DD/SIR) for wireless sensor networks is proposed to mitigate power consumption considering node mobility. In DD/SIR, a sink retransmits interest. The propagation areas of the interest are narrowed stepwisely. In addition, according to the number of hops between the sink and sensor nodes, the data transmission timing is controlled sequentially. By both theoretical analysis and computer simulation, we evaluate the performance of DD/SIR. We show that DD/SIR can mitigate control overhead and realize low power operation without degrading data reachability to the sink. Especially, at a small number of data sending nodes, DD/SIR is more effective than the conventional routing.

ワイヤレスマルチホップネットワークでは,端末のアクセス数の増加やホップ数の増加に伴い,著しくスループットが低下する問題点がある.我々は,この問題を解決するために,IEEE802.11をベースとしたAsymmetric Wireless Multi-hop Access Network(以下AWiMA Net)を提案している.AWiMA Netではアクセスポイント(以下AP)と携帯端末(以下端末)の通信を上りリンク配信区間と下りリンク配信区間に分離するノンコンテンションデータ転送方式によってデータパケットのふくそうを抑止する.更に下りリンク配信区間においてAPの信号出力を高めAPから端末へは1ホップでデータ送信を行いAPのサービス領域の拡大とスループット向上を行っている.本論文ではAWiMA Netに対するシミュレーションによって得られたスループットの特性評価を行った上で,ネットワークのスループット向上のための下りデータのバースト転送による高速化を提案する.シミュレーションにより提案方式を評価した結果,端末からAPへのデータ配信の要求間隔と,上りリンク配信区間と下りリンク配信区間で構成するサイクルタイム長の設定を適切に行うことで,提案方式によるスループットが3倍から4倍向上することを確認した.

In this paper, we propose a novel energy-efficient route-discovery scheme with transmission power control (TPC) for ad hoc networks. The proposed scheme is very simple and improves energy efficiency without any information about neighbor nodes. In the proposed scheme, when a node receives a route request (RREQ), the node calculates the routing-level backoff time as being inversely proportional to the received power of the RREQ. After the route discovery, source and intermediate nodes transmit packets by the power-controlled medium access control (MAC) protocol. In addition, we propose an extended version of the proposed scheme for discrete power control devices. Simulation results demonstrate the proposed schemes can discover more energy efficient routes than the conventional schemes.

本論文では,データ送信における電力効率を高める目的で送信電力と送信レートを適応制御するアドホックネットワークメディアアクセス制御(MAC)プロトコルを提案する.提案プロトコルでは,あらかじめ送信電力と送信レートのすべての組合せに対して,電力消費の効率を算出した送信電力レート制御テーブルを作成する.提案プロトコルでは制御フレームの交換によって得られた受信電力を用いて,送信電力レート制御テーブルを参照して,二つの送信シーケンスを使い分ける.送受信間の直接送信よりも他のノードが中継を行った方が電力効率が高い場合,リレーシーケンスを適用する.計算機シミュレーションによって提案プロトコルを評価し,提案方式の電力効率が向上できることを示す.

This paper describes a protocol testbed system called UNAGI/ESPAR for ad hoc networks, which enables the evaluation of communication protocols with a gain-controlled antenna. It incorporates ESPAR as a practical smart antenna, IEEE802.15.4/ZigBee, GPS and gyro modules to allow easy installation of different protocols. Some experimental results are also shown.

In this paper, to realize the low delay and high throughput route discovery in multi-rate ad hoc networks, we propose a novel on demand routing using signal strength, called signal strength aware routing (SSR). SSR is based on the on-demand routing with the route request (RREQ) and route reply (RREP) procedure. In SSR, a node measures the signal strength of a received RREQ, and calculate the appropriate data transmission rate. Nodes also calculate the standby time for the RREQ forwarding proportionally to the medium time at the data transmission rate. A RREQ through higher data rate links arrives at the destination earlier, and the destination can select a low delay and high throughput route easily. We evaluate the performance of SSR in terms of delay, throughput and route discovery delay by means of QualNet network simulator. As a result, we show that SSR can discover the lower delay and higher throughput route than the conventional shortest hop routing without increasing control overhead in multi-rate ad hoc networks.

Recently, wireless sensor networks have been seen as a key technology for a ubiquitous computing society. In sensor networks, many network technologies have been developed, whose main concern is reduction of power consumption of sensor nodes. Moreover, these conventional approaches assume that a node in a sensor network operate in a finite quantity and initial battery of a node. However, if we use the sensor network in the natural environment, it means that the batteries of nodes must be exchanged to long term operation. From a viewpoint of the environmental sustainability it is also necessary for sensor nodes to be easily collected and replaced. This paper proposes a routing protocol for sensor networks with high node exchangeability in order to realize the continuous long-term operations of sensor networks. In the proposed routing protocol, power consumption of nodes is partially biased and the region is rotated in order to exchange a set of nodes easily. We evaluate the proposed routing protocol comparing with DSR, and a routing protocol where all nodes try to consume the battery equally. We use evaluation metrics biased toward transmitting data, the battery residue of nodes at the exchange time, the transition of operating nodes. The results show that the difference of the battery residue between the largest and the smallest nodes is 88% and node exchangeability improves by restricting the geographical area of exchanging nodes.

This paper addresses the issue of deafness in MAC (Medium Access Control) protocols for wireless ad hoc networks using directional antennas. Directional antennas are expected to provide significant improvements over omni-directional antennas in ad hoc networks, such as high spatial reuse and range extension. Recently, several MAC protocols using directional antennas, typically referred to as directional MAC protocols, have been proposed for ad hoc networks. However, directional MAC protocols inherently introduce new kinds of problems arising from directivity. One major problem is deafness, caused by a lack of state information of neighbor nodes, whether idle or busy. This paper proposes DMAC/DA (Directional MAC with Deafness Avoidance) to overcome the deafness problem. DMAC/DA modifies the previously proposed MAC protocol, MDA (MAC protocol for Directional Antennas), to reduce the number of control messages and also maintain the ability to handle deafness. In DMAC/DA, WTS (Wait To Send) frames are simultaneously transmitted by the transmitter and the receiver after the successful exchange of directional RTS (Request To Send) and CTS (Clear To Send) to notify the on-going communication to potential transmitters that may experience deafness. The experimental results show that DMAC/DA outperforms existing directional MAC protocols, such as DMAC (Directional MAC) and MDA, in terms of throughput, control overhead and packet drop ratio under the different values of parameters such as the number of flows and the number of beams. In addition, qualitative evaluation of 9 MAC protocols is presented to highlight the difference between DMAC/DA and existing MAC protocols.

Several directional MAC protocols for ad hoc networks using directional antennas have been proposed recently. Although directional antennas have great potential such as high spatial reuse and range extension, directional MAC protocols inherently introduce new problems arising from directivity. Deafness is one of the major problems and reduces the performance, caused by a lack of state information from neighbor nodes. This paper presents two directional MAC protocols, DMAC/DA (Directional MAC with Deafness Avoidance) and RI-DMAC (Receiver-Initiated Directional MAC), which handle the deafness problem, and mainly evaluates these protocols through extensive simulation study. DMAC/DA is a proactive handling method for deafness. In DMAC/DA, WTS (Wait To Send) frames are transmitted to notify the on-going communication to potential transmitters that may experience deafness. In this paper, DMAC/DA is enhanced by the next packet notification, called DMAC/DA with NPN, to distinguish transmitters from neighbors. On the other hand, RI-DMAC handles deafness reactively using a combination of sender-initiated and receiver-initiated operations. In RI-DMAC, each node polls a potential deafness node using RTR (Ready To Receive) after the completion of every dialog. The experimental results show that our proposed protocols outperform existing directional MAC protocols in terms of throughput, control overhead and packet drop ratio.

Several directional MAC protocols for ad hoc networks using directional antennas have been proposed recently. Although directional antennas have great potential such as high spatial reuse and range extension, directional MAC protocols inherently introduce new problems arising from directivity. Deafness is one of the major problems and reduces the performance, caused by a lack of state information from neighbor nodes. This paper presents two directional MAC protocols, DMAC/DA (Directional MAC with Deafness Avoidance) and RI-DMAC (Receiver-Initiated Directional MAC), which handle the deafness problem, and mainly evaluates these protocols through extensive simulation study. DMAC/DA is a proactive handling method for deafness. In DMAC/DA, WTS (Wait To Send) frames are transmitted to notify the on-going communication to potential transmitters that may experience deafness. In this paper, DMAC/DA is enhanced by the next packet notification, called DMAC/DA with NPN, to distinguish transmitters from neighbors. On the other hand, RI-DMAC handles deafness reactively using a combination of sender-initiated and receiver-initiated operations. In RI-DMAC, each node polls a potential deafness node using RTR (Ready To Receive) after the completion of every dialog. The experimental results show that our proposed protocols outperform existing directional MAC protocols in terms of throughput, control overhead and packet drop ratio.

This paper addresses the issue of deafness in MAC (Medium Access Control) protocols for wireless ad hoc networks using directional antennas. Directional antennas are expected to provide significant improvements over omni-directional antennas in ad hoc networks, such as high spatial reuse and range extension. Recently, several MAC protocols using directional antennas, typically referred to as directional MAC protocols, have been proposed for ad hoc networks. However, directional MAC protocols inherently introduce new kinds of problems arising from directivity. One major problem is deafness, caused by a lack of state information of neighbor nodes, whether idle or busy. This paper proposes DMAC/DA (Directional MAC with Deafness Avoidance) to overcome the deafness problem. DMAC/DA modifies the previously proposed MAC protocol, MDA (MAC protocol for Directional Antennas), to reduce the number of control messages and also maintain the ability to handle deafness. In DMAC/DA, WTS (Wait To Send) frames are simultaneously transmitted by the transmitter and the receiver after the successful exchange of directional RTS (Request To Send) and CTS (Clear To Send) to notify the on-going communication to potential transmitters that may experience deafness. The experimental results show that DMAC/DA outperforms existing directional MAC protocols, such as DMAC (Directional MAC) and MDA, in terms of throughput, control overhead and packet drop ratio under the different values of parameters such as the number of flows and the number of beams. In addition, qualitative evaluation of 9 MAC protocols is presented to highlight the difference between DMAC/DA and existing MAC protocols. Copyright © 2007 The Institute of Electronics, Information and Communication Engineers.

In this paper, we propose Split Multi-path Routing protocol with Load Balancing policy (SMR-LB) to improve TCP performance in mobile ad hoc networks. In SMR-LB, each intermediate node records how many primary paths are attempted to construct as well as which source nodes attempt to construct the primary path. Each intermediate node decides which primary path should be constructed by using the primary path and the source node ID information. As a result, SMR-LB can balance the loads and so reduce the probability of congestion and avoid the continuous link breakage time between the specific source and destination pair. Computer simulation results show that SMR-LB can improve TCP performance compared with the conventional protocols.

In recent years, several MAC (Medium Access Control) protocols using directional antennas have been proposed for mobile ad hoc networks (MANETs) including our proposed MAC protocol called SWAMP (Smart antennas based Wider-range Access MAC Protocol). These are typically referred to as directional MAC protocols. This paper first summarizes the proposed directional MAC protocols and outlines these common issues, which reduce the probability of successful transmissions, such as location information staleness, deafness and directional hidden- and exposed-terminal problems arisen due to directional transmissions. This paper formulates and analyzes the issues of directional MAC protocols, and proposes solutions of these issues, especially for location information staleness. The experimental results show that the mobility prediction and the optimization of parameters associated with location information staleness, such as the beamwidth and lifetime of the table information, may mitigate location information staleness and improve the overall network performance.

単一の端末に複数の通信インタフェースを接続し, 複数経路を利用するマルチホーミング通信環境においては, 往路と復路で異なる経路を利用すれば, より効率的な情報通信が可能となる場合がある. これを可能とするためには, 片方向の遅延を考慮して適切なインタフェースを選択する必要がある. しかしながら, 通信経路の負荷が時間帯, 通信量などによって変動することや, 往路遅延と復路遅延を簡単には分離できないことなどから, 正確な片方向遅延を直接求めることは一般的には困難である. 本論文では, 複数のパターンの往復概遅延の組から片方向の概遅延差を簡便に求め, これに基づいて経路を選択する方式を提案する. 本方式は, 通信相手との時刻同期, 測定のための制御パケットが不要で, ネットワーク層に依存しないため拡張性があることなどの特徴をもつ. また, 提案方式をICMPで計算機上に実装し, 種々のマルチホーミング通信環境で実験評価する. その結果から片方向経路選択が可能であり, 提案方式が有効であることを示す.