Kwang-il Hwang

Enhanced self-configuration scheme for a robust ZigBee-based home automation

In recent, ZigBee is considered as a potential solution for a scalable and flexible home automation systems. However, several constraints of the ZigBee might create node failure or frequent link breakages and thus some nodes in the network might become orphans. This orphan problem of ZigBee might bring a big confusion to a home automation environment in which a number of consumer devices are interconnected in the multi-hop manner. Therefore, in this paper, an enhanced self-configuration (ESC) scheme is proposed, which can improve the robustness of the conventional ZigBee-based home automation systems by coping well with orphan propagation problem and dynamic error environments. Through experiments on real system implementation, it is demonstrated that the ESC is superior to the conventional ZigBee network in terms of delay and robustness.

Distributed Fast Beacon Scheduling for Mesh Networks

Despite its many benefits, the use of the beacon-enabled mode in multi-hop communications has been limited due to beacon collision problems. In addition, although there has been a lot of research on the beacon scheduling for a tree topology, only a few studies have dealt with the beacon scheduling for a mesh network, which enables more reliable communication by maintaining multiple paths. For a beacon enabled mesh network, the IEEE802.15.4e standard, an emerging new standard for enhanced 802.15.4 MAC, more specifically DSME capability provides a concrete specification about a bitmap-based distributed beacon scheduling. However, it still has some limitations and additional problems which can happen during operation. Therefore, in this paper, we introduce a novel beacon scheduling algorithm to construct a scalable, reliable mesh network. The proposed approach manages efficiently beacon slots of neighboring nodes by means of a fixed length of single variable, RINSD, rather than a bitmap, achieves fast network construction via active allocation of devices, and resolves the potential beacon collision. The experimental results demonstrate that the DFBS achieves faster beacon scheduling and is more efficient in memory usage and beacon frame size than 15.4e DSME standard.

Tiny module-linking for energy-efficient reprogramming in wireless sensor networks

The remote and automatic reprogramming is an indispensable part in the wireless sensor networks. Especially, the energy saving problem is an important challenge because of a limited energy characteristics. Many kinds of conventional researches about reprogramming have tried to solve the energy saving problem. But they do not consider the energy consumption model and still have inefficient memory access times. In this paper, we propose a tiny module-linking scheme. It performs module relocation to decrease program code shifts and connects the relocated module with a tiny module-linker to eliminate module caller changes. This proposed scheme reduces access times to Electrically Erasable Programmable Read-Only Memory (EEPROM) and program memory during the decoding procedure of the reprogramming. Experimental results show that our scheme outperforms the previous reprogramming schemes in terms of the energy consumption.

Analysis and Enhancement of IEEE 802.15.4e DSME Beacon Scheduling Model

In order to construct a successful Internet of things (IoT), reliable network construction and maintenance in a sensor domain should be supported. However, IEEE 802.15.4, which is the most representative wireless standard for IoT, still has problems in constructing a large-scale sensor network, such as beacon collision. To overcome some problems in IEEE 802.15.4, the 15.4e task group proposed various different modes of operation. Particularly, the IEEE 802.15.4e deterministic and synchronous multichannel extension (DSME) mode presents a novel scheduling model to solve beacon collision problems. However, the DSME model specified in the 15.4e draft does not present a concrete design model but a conceptual abstract model. Therefore, in this paper we introduce a DSME beacon scheduling model and present a concrete design model. Furthermore, validity and performance of DSME are evaluated through experiments. Based on experiment results, we analyze the problems and limitations of DSME, present solutions step by step, and finally propose an enhanced DSME beacon scheduling model. Through additional experiments, we prove the performance superiority of enhanced DSME.

AVSR: Asynchronous virtual slot-based ranging for user-oriented location services

In general, the asynchronous ranging is preferred over synchronous ranging since it does not require global synchronization and an expensive and precise oscillator. However, conventional asynchronous ranging requires two or more messages per ranging session for a reference node. This requirement might increase the network traffic considerably. For this reason, conventional ranging schemes are not suitable for user-oriented location service. In this paper, we propose (AVSR) asynchronous virtual slot-based ranging utilizing broadcast ranging request. The utilized virtual slot is accomplished in a fully distributed manner among reference nodes. The evaluation result demonstrates that in spite of very low traffic intensity, AVSR is more robust against ranging error than conventional ranging schemes: TWR and SDS-TWR.

Hierarchical multichannel-based integrated smart metering infrastructure

The use of independent metering infrastructures overlapped in the same area may cause wastage in network resources. So, this paper proposes an integrated metering infrastructure, which is capable of accommodating several different home meters into a single metering infrastructure. In particular, to support stable and efficient data aggregation, hierarchical multichannel tree architecture is utilized. Through several experiments based on the developed prototype and test-bed, we prove out energy efficiency of hierarchical multichannel integrated metering infrastructure (Hi-MIMI). Furthermore, based on fast data aggregation capability, Hi-MIMI enables irregular server command processing in real time, so that it is possible for utility administrator to facilitate a variety of real-time services including check real-time status check, current meter reading of specific meter, and real-time control, etc.

A Distributed Reservation Protocol for Collision-Free Three-Hop Mobility Support in WiMedia MAC

A Distributed Medium Access Control (D-MAC) protocol has been proposed to support high-rate Wireless Personal Area Networks (HR-WPANs) by the WiMedia Alliance. The WiMedia D-MAC solves the problems of the IEEE 802.15.3 MAC caused its centralized architecture. However, due to mobility of WiMedia devices in multi-hop environment, DRP (Distributed Reservation Protocol) reservation conflicts happen frequently among devices within three-hop range distance. To solve this problem, we propose a new DRP reservation scheme using a new 2-hop range DRP Availability IE for three-hop mobility support in WiMedia MAC with ultrawideband (UWB) technology. It is shown by simulation results that throughputs of devices at frequent three-hop range DRP reservation conflicts are largely increased.

Experimental Study of Real-Time Comprehensive Indoor Air Quality

The growing concern about IAQ has accelerated the development of small, low cost Indoor Air Quality (IAQ) monitoring systems. These are capable of monitoring various indoor air pollutants in real-time. However, since most IAQ monitoring systems present the sensed value of the corresponding pollutant as a number, when we read the sensor values it is difficult for not experts but normal users to identify how polluted the air is or what is the pollution criteria of each pollutant. Therefore, for ambient air quality, a comprehensive Air Quality Index (AQI) is already being used in a number of nations to present the polluted level of the air, and thereby people can identify the current status of air quality easily. Nevertheless, since the index calculation is based on ambient air pollutants, and the index presents a section mean of sensed values collected for 1 or 24 h, the AQI used for presenting ambient air quality is not suitable for IAQ representation. Therefore, in this paper, we perform an experiment that applies the AQI directly to IAQ monitoring system that we developed, and derive some problems through the result analysis.

An Efficient Key Management Scheme for Advanced Metering Infrastructure

In this paper we focus on key management scheme for a specific WSN application such as Advanced Metering Infrastructure (AMI), which is based on hierarchical tree network and performs metering data aggregation along the tree. We utilize a novel identity based key generation and propose a hierarchical key management algorithm based on encapsulated encryption. Through experiments, we prove that the proposed key management scheme is suitable for small embedded networked systems which have energy, memory, and processing constraints.

An Adaptive Superframe Duration Allocation Algorithm for Resource-Efficient Beacon Scheduling.

Beacon scheduling is considered to be one of the most significant challenges for energy-efficient Low-Rate Wireless Personal Area Network (LR-WPAN) multi-hop networks. The emerging new standard, IEEE802.15.4e, contains a distributed beacon scheduling functionality that utilizes a specific bitmap and multi-superframe structure. However, this new standard does not provide a critical recipe for superframe duration (SD) allocation in beacon scheduling. Therefore, in this paper, we first introduce three different SD allocation approaches, LSB first, MSB first, and random. Via experiments we show that IEEE802.15.4e DSME beacon scheduling performs differently for different SD allocation schemes. Based on our experimental results we propose an adaptive SD allocation (ASDA) algorithm. It utilizes a single indicator, a distributed neighboring slot incrementer (DNSI). The experimental results demonstrate that the ASDA has a superior performance over other methods from the viewpoint of resource efficiency.