Jaesub Kim

Railroad: virtual infrastructure for data dissemination in wireless sensor networks

In this paper, we present Railroad, a data dissemination architecture for large-scale wireless sensor networks. Railroad system proactively exploits a virtual infrastructure called Rail, which is an area where all the metadata of event data are stored. There is only one Rail in the network and it acts as a rendezvous area of the events and the queries. Rail is placed in the middle area of the field so that every node can easily access it. Once a query is issued, it circulates around Rail and searches relevant data stored in Rail. When a relevant metadata is found, the source node of the data transmits the corresponding data to the sink node which has issued the query. By using Rail, Railroad achieves a scalable and energy-efficient data dissemination architecture under dynamic conditions with multiple mobile observers and targets. We evaluate and compare the communication cost and the hot spot message complexity of Railroad with previous approaches.

An energy-efficient, transport-controlled MAC protocol for wireless sensor networks

In wireless sensor networks (WSNs), one major cause of wasted energy is that the wireless network interface is always on to accept possible traffic. Many medium access control (MAC) protocols therefore adopted a periodic listen-and-sleep scheme to save energy, at sacrifice of end-to-end latency and throughput. Another cause is packet dropping due to network congestion, necessitating a lightweight transport protocol for WSNs. In this paper, we suggest a transport-controlled MAC protocol (TC-MAC) that combines the transport protocol into the MAC protocol with the aims of achieving high performance as well as energy efficiency in multi-hop forwarding. Although TC-MAC also works through a periodic listen-and-sleep scheme, it lowers end-to-end latency by reserving data forwarding schedules across multi-hop nodes during the listen period and by forwarding data during the sleep period, all while increasing throughput by piggybacking the subsequent data forwarding schedule on current data transmissions and forwarding data consecutively. In addition, TC-MAC gives a fairness-aware lightweight transport control mechanism based on benefits of using the MAC-layer information. The results show that TC-MAC performs as well as an 802.11-like MAC in end-to-end latency and throughput, and is more efficient than S-MAC in energy consumption, with the additional advantage of supporting fairness-aware congestion control.

An Energy-Efficient Scheduling MAC Protocol for Wireless Sensor Networks

This paper proposes a novel MAC protocol for sensor networks which is energy efficient and has a good performance as well. Energy is the most important resource in battery-operated sensor networks. Sensor nodes need the wireless network interface to forward data and it has to be always awake to handle possible traffics. This occupies most energy wastes in sensor nodes and pervious works solved this problem by periodic listen and sleep. However, periodic listen and sleep causes the loss of performance. Our protocol also uses periodic sleeping but listen period are used for multi-hop schedule reservations and data transmission is delayed until schedule time. Schedules are reserved as data are pipelined for energy efficiency and performance. In addition, we suggest an energy efficient error recovery mechanism for data transmissions. We evaluate our protocol and compare with previous MAC protocols through ns-2 simulations.

An event-aware MAC scheduling for energy efficient aggregation in wireless sensor networks

The data aggregation scheme of wireless sensor networks (WSNs) can reduce the number of transmitted packets by aggregating multiple packets in one packet; thus, it can reduce energy consumption at the same time. However, the energy consumption of idle listening in WSNs remains dominant in the total energy consumption for WSNs. Therefore, the duty cycle MAC protocols have been used to reduce idle listening. However, if aggregation is used on duty cycle MAC protocols, it has very low performance caused by the latency of the sleep-wake scheduling. The goal of the present work is to design energy efficient event-aware MAC scheduling that can be used by a data aggregation technique. In order to aggregate the packets spatially and temporally, two corresponding mechanisms are proposed: the event-aware and energy-aware routing (EE routing) protocol at the routing layer, and the aggregation scheduling MAC (A-MAC) protocol at the MAC layer. The EE routing protocol chooses the best path for better aggregation and for energy balance in WSNs. The A-MAC protocol adjusts schedules to aggregate more packets while maintaining a low latency. The performances of the proposed protocols are evaluated through ns2 simulations. The results indicate that the proposed protocols reduce energy consumption by 80-90% and have balanced energy consumption while maintaining similar latencies and aggregation rates compared with previous aggregation protocols.

Look-ahead scheduling for energy-efficiency and low-latency in wireless sensor networks

The operation of a sensor node is limited by the initially equipped battery which is hard to be recharged or replaced. Thus reducing unnecessary energy consumption is one of the most important requirements. Most energy waste is from the always-on wireless interface and many new MAC protocols have been suggested to solve the problem. However, they sacrifice the MAC latency, especially, with multi-hop forwarding.In our approach, we designed a novel MAC protocol which has both low latency and power efficiency by separating channel reservation process and data transmission process. The sensor nodes having data to forward are efficiently scheduled during reservation process. The other nodes with no schedule go to sleep to save energy and only scheduled nodes are awake during scheduled time and transmit data. The performance of our protocol is evaluated through simulations.

USD Protocol: Ubiquitous Service Discovery Protocol on Infrastructure-based architecture for Ubiquitous Fashionable Computer

Ubiquitous fashionable computer (UFC) is the wearable computer of next generation. Each modular component composing computer sinks in clothes and form UFC. This characteristics makes UFC has low computing power and small battery. With low computing power and small battery, UFC cannot show good functionality and high performance, but users should not feel inconvenience by them. So we suggested Infrastructure-based architecture. Infrastructure-based architecture assumes ubiquitous infrastructure (U-Infra), and UFC users request U-Infra to do some jobs and just get response. Then UFC does not need high computing power and does not spend much energy. In infrastructure-based architecture, service discovery charges finding available neighboring services and devices, and information delivery from U-Infra to UFC. But previous service discovery protocols have big overhead on mobile ubiquitous environment because they assume high computing power devices. We introduce ubiquitous service discovery protocol (USD protocol) which is fast, lightweight, energy efficient and supporting location free applications. Average USD protocols information delivery time is 1.3 seconds and USD Protocol reduces 46% of booting time of UFC. USD protocol can reduce energy consumption on UFC by using U-infra and also supports global area service discovery.

F-TCP: light-weight TCP for file transfer in high bandwidth-delay product networks

We describe F-TCP, a new TCP for file transfer in high bandwidth-delay product networks. TCP is not suitable for file transfer application in high bandwidth-delay product networks. There needs a protocol that should not take away too much bandwidth from standard TCP flows while utilizing the full bandwidth of high-speed networks. This paper presents another important constraint, namely small buffer problems. Small socket buffers at the end-hosts limit the effective window of the transfer, and the maximum throughput. Existing schemes have severe small buffer problems because high bandwidth-delay product networks need a large socket buffer. The proposed mechanism, called F-TCP, is based on direct kernel-to-kernel file transfer architecture. The key idea is that no need of in-order delivery in file transfer process. F-TCP needs only small buffer by allowing out-of-order file transfer with asynchronous loss recovery. Experimental results in several high bandwidth-delay product paths show that F-TCP provides consistently a significant throughput increase (18% to 80%) compared to previous TCP approach. We expect that F-TCP is mostly useful for application such as FTP and P2P in high-speed wide-area networks.

U-interactive: a middleware for ubiquitous fashionable computer to interact with the ubiquitous environment by gestures

In this paper we present a system, called U-interactive, that provides spontaneous interactions between human and surrounding objects in heterogenous ubiquitous computing environments. Our U-interactive system introduces a virtual map, which contains interactive objects around a user in each ubiquitous environment. In the virtual map, each interactive object is tagged with geographic information and attributes to interact with. Each user can create interactive objects in the virtual map corresponding to physical objects. Also the scope of the map is automatically adjusted according to users location (inside building or outdoors) by location services. U-interactive system runs on both mobile devices and infrastructures. U-interactive system provides interoperability with communication methods, such as UbiSpace, UPnP, and Web services. We developed our U-interactive system upon a prototype of ubiquitous environment. U-interactive system contains interactive kiosk, printer, sensor networks, and users.

Design and implementation of a look-ahead scheduling MAC protocol for wireless sensor networks

Energy is the most important resource in wireless sensor networks. The wireless interface of sensor node consumes most of the energy and therefore many MAC protocols are adopting the periodic listen-and-sleep scheme. However, the periodic listen-and-sleep approach results in high latency and low throughput. For low latency in multi-hop forwarding without sacrificing energy efficiency, we designed a look-ahead scheduling MAC (LAS-MAC) protocol, which also works on the periodic listen-and-sleep scheme, but it reserves multi-hop packet forwarding schedules across multi-hop nodes during the listen period and forwards data packets by awaking the nodes with the reserved schedules during the sleep period. For high throughput of LAS-MAC, in addition, we add the throughput enhancement mechanism which clones the current multi-hop forwarding schedules for the subsequent data packet forwarding. Our experimental results on the MICA2 platform show that LASMAC achieves lower latency, higher throughput, and higher energy efficiency than 802.11-like MAC without sleeping.

MTCP: A Transmission Control Protocol for Multi-Provider Environment

Transmission schemes that gain content from multiple servers concurrently have been highlighted due to their ability to provide bandwidth aggregation, stability on dynamic server departure, and load balancing. Previous approaches employ parallel downloading in the transport layer to minimize the receiver buffer size and maximize bandwidth utilization. However, they only focus on the receiver operations and induce considerable overhead at the senders in contradiction to the main goal of a multi-provider environment, offloading popular servers through replication. In the present work, the authors propose MTCP, a novel transport layer protocol that focuses on reduction of the sender overhead through the elimination of unnecessary disk I/Os and efficient buffer cache utilization. MTCP also balances trade-off objectives to minimize buffering at receivers and maximize the request locality at senders.