Sungjin Lee

Joint Energy Management System of Electric Supply and Demand in Houses and Buildings

In this paper, a joint scheduling scheme for the electric supply and demand of Home Energy Management System (HEMS) and Building Energy Management System (BEMS) via energy management in houses and buildings is presented. To reflect ongoing policy, the Korea Electric Power COoperation (KEPCO) tariff is employed to formulate the optimization problem in terms of the sequential management procedure of prediction, supply control and demand control. As a result, an optimal electric supply pattern to produce the minimum energy cost can be obtained under a given curtailment. From simulation, the proposed scheduling scheme demonstrates greater reliability and adaptation for the interruptible load (IL) than the day-ahead method.

Coexistence Performance Evaluation of IEEE 802.15.4 Under IEEE 802.11B Interference in Fading Channels

The IEEE 802.15.4 standard specifies the physical and medium access control layers designed for low-rate wireless personal area networks. Its operational frequency band includes the 2.4 GHz industrial, scientific and medical band, which is also used by other IEEE 802 wireless standards. This paper presents the coexistence model of IEEE 802.15.4 with IEEE 802.1 lb interference in fading channels and proposes two adaptive channel allocation schemes. The first avoids the IEEE 802.15.4 interference only and the second avoids both of the IEEE 802.15.4 and the IEEE 802.11b interferences. Numerical results show that by selecting a channel which gives the maximum signal to noise ratio to the system, the proposed algorithms are effective for avoiding the interferences and for max-imizing the network capacity.

Node distribution-based localization for large-scale wireless sensor networks

Distributed localization algorithms are required for large-scale wireless sensor network applications. In this paper, we introduce an efficient algorithm, termed node distribution-based localization (NDBL), which emphasizes simple refinement and low system-load for low-cost and low-rate wireless sensors. Each node adaptively chooses neighboring nodes, updates its position estimate by minimizing a local cost-function, and then passes this updated position to neighboring nodes. This update process uses a node distribution that has the same density per unit area as large-scale networks. Neighbor nodes are selected from the range in which the strength of received signals is greater than an experimentally based threshold. Based on results of a MATLAB simulation, the proposed algorithm was more accurate than trilateration and less complex than multi-dimensional scaling. Numerically, the mean distance error of the NDBL algorithm is 1.08–5.51 less than that of distributed weighted multi-dimensional scaling (dwMDS). Implementation of the algorithm using MicaZ with TinyOS-2.x confirmed the practicality of the proposed algorithm.

Optimization of Delay-Constrained Video Transmission for Ad Hoc Surveillance

Recent increases in demand by militaries and disaster relief operations has greatly accelerated research on delay-constrained video surveillance with low-delay and high-quality video transmission. The following factors should be systematically analyzed due to the tradeoff between low delay and high quality: the visual importance of surveillance objects, quality degradation due to wireless channel dynamics, and variant end-to-end delay. We propose and optimize a low-delay video transmission technique for video surveillance over an ad hoc network. The proposed protocol is composed of intercommunication and intraprocessing parts. Through intercommunication optimization, we identify an optimal routing path and an associated relaying in terms of channel throughput that meet the source-rate, the flow-rate, and delay constraints. Through intraprocessing optimization, we identify an optimal packet length and an associated number of packets to adapt to the delay in the variant dynamic channel. Through simulations, we demonstrate that delay and throughput control significantly contribute to improvements in visual quality of up to 1.7-3 dB compared with conventional schemes.

BUCKET: Scheduling of Solar-Powered Sensor Networks via Cross-Layer Optimization

Renewable solar energy harvesting systems have received considerable attention as a possible substitute for conventional chemical batteries in sensor networks. However, it is difficult to optimize the use of solar energy based only on empirical power acquisition patterns in sensor networks. We apply acquisition patterns from actual solar energy harvesting systems and build a framework to maximize the utilization of solar energy in general sensor networks. To achieve this goal, we develop a cross-layer optimization-based scheduling scheme called binding optimization of duty cycling and networking through energy tracking (BUCKET), which is formulated in four-stages: 1) prediction of energy harvesting and arriving traffic; 2) internode optimization at the transport and network layers; 3) intranode optimization at the medium access control layer; and 4) flow control of generated communication task sets using a token-bucket algorithm. Monitoring of the structural health of bridges is shown to be a potential application of an energy-harvesting sensor network. The example network deploys five sensor types: 1) temperature; 2) strain gauge; 3) accelerometer; 4) pressure; and 5) humidity. In the simulations, the BUCKET algorithm displays performance enhancements of ~12-15% over those of conventional methods in terms of the average service rate.

A Pervasive Network Control Algorithm for Multicamera Networks

Owing to the increasingly large volume and complexity of captured videos, renewable energy systems based on solar energy are of particular interest in the design of energy harvesting (EH) wireless visual sensor networks (WVSNs). Since additional energy consumption following image capture occurs owing to image processing, mote operation, data transmission, and reception, the capture rate significantly affects the lifetime of a node. To this end, we explore a novel energy-efficient framework for EH-WVSN design by developing an optimal algorithm named capture rate and pervasive network control for multicamera networks where the quality of service is maximized by obtaining optimal values for the capture rate, allocated energy, and transmit power, based on field of view-based networking in the presence of event and power acquisition patterns. Through simulations, we demonstrate the feasibility of EH-WVSNs in terms of energy consumption, energy allocation, and capture rate in a realistic scenario (parking surveillance).

Reverse Link Capacity Analysis over Multi-Cell Environments

This paper presents a numerical analysis of reverse link capacity by obtaining a closed form of ICI (InterCell Interference) over OFDM (Orthogonal Frequency Division Multiplexing)-based broadband wireless networks. In the analysis, shadowing factors are taken into account for determining the home BS (Base Station) of each MS (Mobile Station) over multicell environments. Under the consideration, a more accurate analysis of link capacity can be performed compared to Gilhousens approximation. In the numerical results, it turns out that the actual interference is lower than Gilhousens approximation with a decrease of around 20% in the interference.

Outage Probability Analysis of WPAN under Coexistence Environments in Fading Channels

The IEEE 802.15.4 standard specifies the physical and medium access control layers designed for low-rate wireless personal area networks (LR-WPAN) with a focus on enabling the wireless sensor networks. Its operational frequency band includes the 2.4 GHz industrial, scientific and medical (ISM) band which is also used by other IEEE 802 wireless standards. This paper analyzes the performance of IEEE 802.15.4 in a coexistence environment with IEEE 802.11b in fading channels. The threshold used to obtain the outage probability is computed based on the mean packet error probability (PEP) which satisfies the performance requirement of IEEE 802.15.4. Numerical results show that the interference from IEEE 802.11b depends primarily on the frequency offset as well as on the receive signal power.

Optimal transmission methodology for QoS provision of multi-hop cellular network

In this paper, we present a framework of link capacity analysis for optimal transmission over uplink MCN (Multi-hop Cellular Network) environments. An overlaid architecture is employed as the network topology, i.e., single-hop transmission over the inner region and multi-hop transmission over the outer region. In particular, we analyzed the gain that accrued from grafting a relay method onto a conventional, SCN (Single-hop Cellular Network) and investigated the conditions for optimal performance through the numerical results. At high-user density, a MCN exhibits a much more reliable transmission than the SCN. For maximal link capacity, optimal region partitioning is approximately accomplished at the normalized cell radius of 0.6 in most of cases for region division. Finally, the link capacity can be improved 1.2–1.8 times better than the SCN when the number of relay hops is 1.6 and the half-duplex mechanism is used. In addition, the proposed MCN scheme demonstrates an effective reduction in transmission power relative to the SCN.

Channel Allocation Algorithms for Coexistence of LR-WPAN with WLAN

This paper presents a coexistence model of IEEE 802.15.4 with IEEE 802.11b interference in fading channels and proposes two adaptive channel allocation schemes. The first avoids the IEEE 802.15.4 interference only and the second avoids both of the IEEE 802.15.4 and IEEE 802.11b interferences. Numerical results show that the proposed algorithms are effective for avoiding interferences and for maximizing network capacity since they select a channel which gives the maximum signal to noise ratio to the system.