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Mobile Computing and Wireless Sensor Networks

Mobile Ad-hoc Network

Inter-Contact Time Study for MANETs with Random Walk Mobility

In mobile ad hoc networks (MANETs), the inter-contact time, the time interval between two consecutive contacts of two mobile nodes, has been shown to have significant impact on network performances. Analyzing the inter-contact time in MANETs serves as the foundation for network performance evaluation and efficient network design. Despite lots of research efforts, accurate analytical results of the inter-contact time still remain elusive. As a step toward this direction, this paper provides theoretical analysis on the inter-contact time in a MANET with random walk mobility. Specifically, we first develop a powerful theoretical framework based on quasi-birth-and-death (QBD) process to characterize the mobility process of mobile nodes in the concerned MANET. With the help of this theoretical framework, we then derive accurate analytical results of the cumulative distribution function as well as mean and variance of the inter-contact time. Finally, we carry out numerical studies to investigate the impact of network parameters on inter-contact time performance.

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Consideration of A Mobile Payment System Using Endorsement in MANETs for A Disaster Area

Payment system in the disaster area is essential for people to buy necessary amenities, like groceries, cloth- ing, medical supplies. However, due to the lack of infrastructures in disaster areas, existing payment systems cannot be applied directly to such scenarios because they either require direct connection to the payment authorities or cannot prevent fraudulent transactions. In this paper, we propose a mobile payment system by adopting infrastructureless mobile ad-hoc networks (MANETs), which can allow users to purchase amenities in disaster areas while providing secure transactions. Specifically, we propose an endorsement-based scheme to verify each transaction and location information based monitoring scheme to achieve transaction validity and reliability. By employing blind signature and one-time session token techniques, our mobile payment system can also prevent double spending and replay attacks.

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A demand-oriented information retrieval method on MANET

In urban areas including shopping malls and stations with many people, it is important to utilize various information which those people have obtained. In this paper, we propose a method for information registration and retrieval in MANET which achieves small communication cost and short response time. In our method, we divide the whole application field into multiple sub-areas and classify records into several categories so that mobile terminals in an area holds records with a category. Each area is associated with a category so that the number of queries for the category becomes the largest in the area. Thus, mobile users search records with a certain category by sending a query to nodes in the particular area using existing protocol such as LBM (Location-Based Multicast). Through simulations supposing actual urban area near Osaka station, we have confirmed that our method achieves practical communication cost and performance for information retrieval in MANET.

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Video Ads Dissemination through WiFi-Cellular Hybrid Networks

In this paper, we propose a method for video ads dissemination through a hybrid network consisting of WiFi and cellular networks, in order to provide timely delivery of video ads with preferred content to users according to the users’ contexts. In recent years, video download/streaming services for cellular phones have already become popular. Among various video delivery services, a service for disseminating video ads according to the users’ contexts is expected to achieve high advertising effects. However, context-aware video ads dissemination will consume large bandwidth since the size of video ad is rather large and the same ad is required at different time from various users. We propose a new video ads dissemination method for mobile terminals which utilizes both WiFi and cellular networks. In the proposed method, a file of video ad is divided into pieces and each node exchanges the pieces with neighbor nodes using WiFi ad hoc communication so that the usage of cellular network is reduced. In order to make the method works effectively for a large number of nodes, we propose an algorithm where mobile nodes autonomously and probabilistically decide their actions without a central control. Through simulations, we confirmed that our method reduces cellular network usage by about 93% compared with a case that all nodes download video ads via cellular network, and works effectively in cases with a large number of nodes and high mobility.

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A Method for Distributed Computaion of Semi-Optimal Multicast Tree in MANET

In this paper, we propose a new method to construct a semi-optimal QoS-aware multicast tree on MANET using distributed computation of the tree based on Genetic Algorithm (GA). This tree is sub-optimal for a given objective (e.g., communication stability and power consumption), and satisfies given QoS constraints for bandwidth and delay. In order to increase scalability, our proposed method first divides the whole MANET to multiple clusters, and computes a tree for each cluster and a tree connecting all clusters. Each tree is computed by GA in some nodes selected in the corresponding cluster. Through experiments using network simulator, we confirmed that our method outperforms existing on-demand multicast routing protocol in some useful objectives.

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  • Babatunde Ojetunde, Naoki Shibata, Juntao Gao, Minoru Ito : Consideration of a Mobile Payment System using Endorsement in MANETs for a Disaster Area, 2014-CSEC-66, No. 5, pp. 1-8, 2014-06-26 [ PDF ]
  • Juntao Gao, Xiaohong Jiang : Inter-Contact Time Study for MANETs with Random Walk Mobility, DICOMO2014シンポジウム論文集, pp. 804 - 808, 2014.7.10.
  • Enomoto, M., Shibata, N., Yasumoto, K., Ito, M. and Higashino, T.: A demand-oriented information retrieval method on MANET, International Workshop on Future Mobile and Ubiquitous Information Technologies (FMUIT'06). [ PDF ]
  • Hanano, H., Murata, Y., Shibata, N., Yasumoto, K., Ito, M.: Video Ads Dissemination through WiFi-Cellular Hybrid Networks, Proc. of PerCom2009, pp. 322-327 (2009)[ PDF ].
  • Takashima, E., Murata, Y., Shibata, N., Yasumoto, K. and Ito, M.: A Method for Distributed Computaion of Semi-Optimal Multicast Tree in MANET, IEEE Wireless Communications and Networking Conference (WCNC 2007), pp. 2570-2575, DOI:10.1109/WCNC.2007.478 (March 2007). [ PDF ]

Wireless Sensor Network

Minimizing Localization Cost with Mobile Anchor in Underwater Sensor Networks

In underwater sensor networks (UWSNs), it is important to know the position of each sensor node to identify the place of event in the target ocean field. In this research, we propose a new localization technique for underwater sensor nodes which utilizes a ship-type mobile anchor. Our method estimates the position of each sensor node based on trilateration by measuring relative distances to the sensor node from three linear independent points on the water surface. For accurate estimation for sensor nodes in deep ocean, the distance between measurement points should be larger than the threshold predefined from the depth and other factors. We need to decide at least three measurement points for each sensor node and let the mobile anchor visit all the measurement points of all sensor nodes for estimating their positions. The localization cost will be reduced by shortening the total distance to visit the points. The cost can also be reduced by finding points where the mobile anchor can communicate with multiple sensor nodes at the same time. We propose a heuristic algorithm to find the near best measurement points and the route to visit all the points on the water surface.



  • Matsumoto, K., Katsuma, R., Shibata, N., Yasumoto, K., Ito, M.: Minimizing Localization Cost with Mobile Anchor in Underwater Sensor Networks, Proc. pf 4th ACM International Workshop on UnderWater Networks (WUWNet'09), Article No. 14, DOI:10.1145/1654130.1654144 (Nov. 2009). [ PDF ]

Delay Tolerant Network

In case of disaster like a massive earthquake, communication infrastructure (e.g., cellular phone network, WLAN, etc.) may completely fail due to damage of facilities or communication congestion. Delay/Disruption Tolerant Network(DTN) is a promising technique for such environment, and there have been a lot of research activities to realize data delivery/dissemination with DTN. Most of existing studies on DTN focus on improving data delivery success ratio and reduction of delay, and there are little studies for data delivery taking into account data priority and deadline. In this research, we proposed a DTN-based data delivery method for an environment without communication infrastructures (e.g., disaster area, event place, etc) that takes into account relative importance and deadline of users' data requests. As a target application, we suppose a system that allows users in the target service area to retrieve word-of-mouth information such as photos on sightseeing spots. We assume that multiple portable servers called ``InfoBoxes that collect/disseminate data from/to user terminals via short range wireless communication (e.g., Bluetooth) are deployed in the service area. In our proposed system, each user terminal sends, to an InfoBox, a query specifying (1) a destination spot on which the user wants to get information, (2) the importance of the query (to what extent the user satisfies when getting the query response), and (3) a receiving spot where the user wants to receive the query response. We propose a carry-and-forward based technique for delivering queries/responses so that the overall user satisfaction is maximized. Depending on a given probability of user movement between two spots, the proposed method appropriately adjusts the number of data replicas copied from each InfoBox to user terminals. In addition, we introduced a method that each InfoBox does not accept data upload from user terminals when the data is likely to exceed the delivery deadline, and discards the data in its queue which cannot meet the delivery deadline, for efficient bandwidth utilization. Through computer simulations, we confirmed that the proposed method achieves 20 - 50% better overall user satisfaction than other conventional methods such as FIFO and EDF(early deadline first).

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Ishimaru, Y., Sun, W., Yasumoto, K., Ito, M.:DTN-based Delivery of Word-of-Mouth Information with Priority and Deadline, Proc. of 5th Int'l. Conf. on Mobile Computing and Ubiquitous Networking (ICMU2010) (27th, Apr. 2010). [ PDF ]