Niwat Thepvilojanapong

On the construction of efficient data gathering tree in wireless sensor networks

A wireless sensor network can be an effective tool for gathering data in a variety of environments. The data gathering process must be designed to conserve the limited resources of the sensors. We propose an Efficient Data GathEring (EDGE) protocol which satisfies such requirement because it avoids both flooding and periodic updating of routing packets. The tree created by EDGE is reconstructed upon node failures or the addition of new nodes. Simulation results compared to directed diffusion, DSR, AODV, and OLSR demonstrated that EDGE achieves a higher delivery ratio and shorter delay on various scenarios.

HAR: hierarchy-based anycast routing protocol for wireless sensor networks

In this paper, we present hierarchy-based any-cast routing (HAR), a routing protocol for collecting data over multihop, wireless sensor networks. The design of the protocol aims to satisfy the requirements of sensor networks that every sensor transmits sensed data to the base station periodically or spontaneously. The base station constructs hierarchical tree by finding its child nodes which in turn discover their own child nodes and so on. HAR avoids both flooding and periodic updating of routing information but the tree will be reconstructed upon node failures or adding of new nodes. By knowing only its own parent and grandparent, each sensor can make forwarding decisions regardless of the knowledge on other neighboring nodes or geographical information. We evaluate the performance of HAR by using the ns-2 simulator and comparing with those of both DSR and AODV. The simulation results demonstrate that HAR achieves much higher delivery ratio and lower latency on various scenarios.

Askus: Amplifying Mobile Actions

Information sharing has undeniably become ubiquitous in the Internet age. The global village created on the Internet provides people with instant access to information and news on events occurring in a remote area, including access to video content on websites such as YouTube . Thus, the Internet has helped us overcome barriers to information. However, we cannot conceive an event happening in a remote area and respond to it with relevant actions in a real-time fashion. To overcome this problem, we propose a system called Askus , a mobile platform for supporting networked actions. Askus facilitates an extension of the conceivable space and action by including humans in the loop. In Askus , a persons request is transmitted to a suitable person who will then act in accordance with the request at a remote site. Based on a diary study that led to detailed understanding about mobile assistance needs in everyday life, we developed the Askus platform and implemented the PC-based and mobile phone-based prototypes. We also present the results from our preliminary field trial.

A Deployment of Fine-Grained Sensor Network and Empirical Analysis of Urban Temperature

Temperature in an urban area exhibits a complicated pattern due to complexity of infrastructure. Despite geographical proximity, structures of a group of buildings and streets affect changes in temperature. To investigate the pattern of fine-grained distribution of temperature, we installed a densely distributed sensor network called UScan. In this paper, we describe the system architecture of UScan as well as experience learned from installing 200 sensors in downtown Tokyo. The field experiment of UScan system operated for two months to collect long-term urban temperature data. To analyze the collected data in an efficient manner, we propose a lightweight clustering methodology to study the correlation between the pattern of temperature and various environmental factors including the amount of sunshine, the width of streets, and the existence of trees. The analysis reveals meaningful results and asserts the necessity of fine-grained deployment of sensors in an urban area.

Opportunistic collaboration in participatory sensing environments

The proliferation of networked mobile devices that can capture and communicate various kinds of data provides an opportunity to design novel man-machine sensing environments of which this paper considers participatory sensing. To achieve energy efficiency and reduce data redundancy, we propose Aquiba protocol that exploits opportunistic collaboration of pedestrians. Sensing activity is reduced according to the number of available pedestrians in nearby area. The paper investigates the benefit of opportunistic collaboration in large-scale scenarios through simulation studies. To take microscopic interaction of social crowds into consideration, we adapt the social force model and include it as one of three mobility models applied in our studies. Though the simulation results depend on mobility models, they validate the benefit of opportunistic collaboration employed by Aquiba protocol.

A human probe for measuring walkability

Recent mobile devices are integrated with various kinds of sensors, thereby allowing people to capture what stationary sensing devices cannot easily acquire. We term the systems that exploit the ubiquity of the users of such devices Human Probes. To realize a Human-Probe environment, our research group has examined the usefulness of pressure sensors embedded in shoes [2]. In this demonstration, we present our recent work that extends our previous research on embedded pressure sensors by considering complimentary uses of accelerometers so as to measure walkability in our everyday spaces. Pressure sensors and accelerometers are similarly useful for capturing the motion of pedestrians; however, the close examination of the signals from both sensors reveals the strengths and the weaknesses of each, and suggests the possibility of their complimentary use to support Human Probes.

An Optimized Directional Distribution Strategy of the Incentive Mechanism in SenseUtil-Based Participatory Sensing Environment

This paper proposed an optimized strategy of the incentive mechanism for participatory sensing network on the basis of Sense Util which is our previous research work. For optimizing, the strategy considered the possibility of that some users actually cannot participate the current sensing task, so in order to avoid unnecessary energy and bandwidth consumption on server end, users were classified into different subsets according to their position, and server distributed the sensing tasks directionally. To evaluate the performance of the strategy, we conducted simulation study, and the results showed that the optimization work is energy efficient.

Performance Evaluation of Protocols for Inter-Vehicle Communications

Inter-vehicle communication (IVC) protocols have been studied to provide safe and comfortable driving. Each vehicle using the IVC protocols periodically broadcasts its current information (location, moving direction, speed, etc.), and other vehicles must receive such information exactly and in time. Other vehicles use received information to alert, advise, and navigate drivers, helping them become aware of the existence of other vehicles. This kind of application is helpful in various situations. For example, when a driver is approaching an intersection, the driver is not aware of vehicles that are also approaching the same intersection from another direction. To realize such inter-vehicle communication, we need to consider many issues such as protocol design, wireless standard, evaluation methodology, etc. Previous works on both mobile ad hoc networks and inter-vehicle communications used conventional metrics, e.g., packet delivery ratio, average delay, and path optimality, to study the performance of protocols. However, such metrics cannot be applied to inter-vehicle communications directly because the identities of the prospective receivers are a priori unknown. Moreover, many requirements must be considered to judge whether a IVC protocol satisfies the objectives of IVC applications. Although a vehicle get information properly, it is useless if that information arrives too late. This paper proposes new performance metrics to evaluate IVC protocols by the means of reliable and timely communications. We also introduce a methodology to perform realistic evaluation through simulation. Realistic vehicular traces and simulation models are required to get correct evaluation results. We then use the defined metrics to evaluate the previously proposed protocol [1]. According to the simulation results, the proposed protocol is a good candidate for real implementation because it passes all requirements of inter-vehicle communications.

Adaptive channel and time allocation for body area networks

Personal health care is a promising application of a body area network (BAN). The BAN for health care application consists of a data collector and multiple wearable sensors that send data to the collector according to a sampling interval determined by the application. The data collector may be any hand-held or portable device such as a mobile phone, a PDA or a wristwatch. An individual user needs a BAN to detect, track or manage his/her health. Multiple BANs for such purpose are likely to appear in a nearby area, especially a place where population density is high. Since multiple BANs must share wireless medium in this scenario, a problem of packet collisions among BANs is unavoidable. To deal with such problem, this study proposes an adaptive scheme to allocate channel and time for coexisting BANs. The proposed scheme distinguishes inter-BAN and intra-BAN communications, and adaptively allocates channel and time according to the current number of BANs that exist in a nearby area. As a salient feature, the proposed scheme allocates time by attempting to satisfy the requirement of sampling interval determined by the application. The evaluation results demonstrate that our scheme achieves much higher packet delivery rate than the existing scheme.

Resource Allocation for Coexisting ZigBee-Based Personal Area Networks

Personal healthcare is a promising market of a personal area network (PAN). The PAN consists of a data collector and multiple wearable sensors which must send data to the collector according to the frequency specified by each PAN. The data collector may be any hand-held or portable device, e.g., a mobile phone, a PDA, or a wristwatch. An individual user needs a PAN in order to detect, track, or manage his/her health. Multiple PANs for such purposes are likely to coexist in a same area, especially a place where a large number of users exist. Because multiple PANs must share resources (e.g., wireless channels, transmitting time) in this scenario, a problem of packet collisions among such PANs is unavoidable. As a result, the personal healthcare system using PAN cannot be provided as a service for the users because the data collector cannot collect sensing data from each sensor correctly. This paper proposes an adaptive scheme to allocate resources for coexisting PANs. The scheme distinguishes a PAN and a node when allocating resources such as wireless channel and transmitting time. Resources are dynamically allocated according to the current number of PANs that exist in the same area. In particular, the proposed scheme automatically reallocates resources when any PANs come into or leave from the coexisting area. As one of salient features, the scheme allocates transmitting time to meet a requirement on reporting interval determined by an application. Thus applications that are sensitive to delay can collect sensing data correctly and in time. The evaluation results show that our scheme achieves higher packet delivery rate than the standard ZigBee.