Sung-Yeop Pyun

Power-saving scheduling for multiple-target coverage in wireless sensor networks

We address the multiple-target coverage problem (MTCP) in wireless sensor networks (WSNs). We also propose an energy-efficient sensor-scheduling algorithm for multiple-target coverage (MTC) that considers both the transmitting energy for collected data and overlapped targets. We introduce two algorithms: one optimal, the other heuristic. Simulation results show that the proposed algorithms can contribute to extending the lifetime of network and that the heuristic algorithm is more practical than the optimal algorithm with respect to complexity.

Efficient resource allocation for rapid link recovery and visibility in visible-light local area networks

Visible-light communication provides many advantages over other forms of communications, such as visibility, high SNR (Signal to Noise Ratio), easy installation, freedom of interference from radio or electromagnetic waves, usage of license free frequency band, and high security. Furthermore, the exponentially increasing requirements and quality of LEDs (Light Emitting Diodes) have encouraged the development of visible-light communication that makes use of LEDs. In a visible-light communication system, an LOS (Line of Sight) link between two transceivers should be guaranteed due to the straightness of the visible-light signal. However, link failure caused by temporary blocking or poor orientation of a transmitter frequently occurs, causing burst frame errors. In this paper, we focus on how to let a user know about link failure as quickly as possible, in order that the link failure problem may be solved by realigning the transmission signal towards the receiver. This is furthermore a relatively straightforward matter, by the very nature of this system being a visible means of communication. It is also required that the visibility should be supported when a user attempts initial access procedure. Nevertheless, by supporting visibility, system performance can be degraded because some additional resources are required for the visibility to be enabled. In this paper, we propose three schemes for supporting visibility without reducing system performance in a visible-light local area network.

Interference Mitigation Based on Femtocells Grouping in Low Duty Operation

Since a large number of femtocells may coexist in one macrocell area, interference management becomes a major issue in the deployment of femtocells, and therefore has been researched actively. In the IEEE 802.16m, one way to mitigate interference is Low Duty Operation (LDO) Mode for femtocells. Femtocell in the LDO mode changes alternately between available interval and unavailable interval. During available interval, femtocell may become active on air interface by transmitting control messages, while during unavailable interval, femtocell becomes inactive on air interface. However, the operation of femtocell in the LDO mode is not efficient, since it still has available intervals even though there are no MSs will access the femtocell in anytime soon. In this case, the available intervals may not be necessary and can further cause interference to neighbor cells. In this paper, we propose an interference mitigation scheme based on the grouping of femtocells in one neighborhood area. The unnecessary available intervals in LDO can be decreased by the proposed scheme and results in decreasing interference to neighbor cells. The analysis and simulation results show that the proposed scheme has superior advantages compared to the conventional LDO scheme in IEEE 802.16m, in terms of interference reduction and energy saving aspects.

Downlink Resource Allocation Scheme for Smart Antenna Based V2V2I Communication System

In this paper, we propose a vehicle-to-vehicle-to-infrastructure (V2V2I) communication system which utilizes a smart antenna technology. In the proposed V2V2I communication system, both an infrastructure and a vehicle can form multiple directional beams by using multiple antennae in order to transmit multiple data streams simultaneously. Since vehicle-to-infrastructure (V2I) and vehicleto-vehicle (V2V) communications exist together in the V2V2I communication system, the co-channel interference between V2I and V2V communications causes severe system performance degradation. To solve this problem, we propose a downlink resource allocation scheme for the smart antenna based V2V2I system by considering the interference between V2I and V2V communications so that overall system capacity can be improved. Through simulation results, we show that our proposed scheme can contribute to increase the overall capacity of V2V2I communication system.

TDMA-based channel access scheme for V2I communication system using smart antenna

In this paper, we propose a vehicle-to-infrastructure (V2I) communication system that utilizes a smart antenna technology to increase service coverage and system capacity. In the proposed V2I communication system, the infrastructure forms multiple directional beams to detect, in the shortest possible time, vehicles that have newly arrived within the area of its service coverage. We also propose a contention-based channel access procedure in the proposed V2I communication system. During channel access, collisions occur when more than two vehicles select the same mini-slot to transmit an access signal to an infrastructure. To solve this problem, we propose efficient channel access schemes with different approaches. Through performance analysis and simulation results, we show that our proposed schemes can contribute to reduce the number of collisions that occur during channel access. In addition, we also show that the proposed V2I communication system can increase the service coverage compared to a conventional V2I communication system that uses omni-directional antenna.

Energy-Efficient Scheduling for Multiple-Target Coverage in Wireless Sensor Networks

In wireless sensor network (WSN), scheduling and power management schemes have been researched as key techniques to extend a network lifetime. In conventional studies, it has commonly been assumed that sensors with the same sensing range would gather the same amount of data. Hence, the sensors consume the same amount of energy when transmitting the collected data, regardless of how many targets they observed. In this paper, we address a multiple target coverage problem (MTCP) of WSN in which different sensors will monitor different numbers of targets and a sensor that monitors more targets would gather more data; hence it will consume more transmission energy. In addition, in the MTCP, there exist overlapped targets that are monitored by more than two sensors at the same time. This results in energy being wasted by the sensors due to the overlapped targets. In this paper, we propose energy efficient sensor scheduling schemes for multiple target coverage (MTC) which maximize the network lifetime by considering both the number of targets covered by the sensor and the redundancy of overlapped targets. This paper introduces two sensor scheduling schemes: optimization scheme and heuristic scheme and verifies power saving results through simulation.

Resource Allocation Scheme for Minimizing Uplink Interference in Hierarchical Cellular Networks

Hierarchical cellular networks (HCNs), in which femtocells are deployed in the coverage of a conventional macrocell, offer a cost effective solution to achieve high user capacity and extended service coverage. Since a large number of femtocells can be installed by users without cell planning, interference between macrocells and femtocells causes a severe problem. Especially, the macro MS which is located near femtocells or transmits uplink data with large power may make strong uplink interference to neighbor femtocells. This uplink interference results in decreasing the system capacity of femtocells. In this paper, we propose novel resource allocation schemes which minimize the uplink interference from macro MSs to femtocells in TDMA (time division multiple access) based HCNs. This paper introduces two resource allocation schemes: optimization scheme and heuristic scheme. The simulation results show that our proposed schemes can contribute to increase the system capacity of femtocells. In addition, the heuristic scheme is more practical than the optimization scheme in view of computational time.

Group-Based Channel Access Scheme for a V2I Communication System using Smart Antenna

We propose a vehicle-to-infrastructure (V2I) communication system that utilizes a smart antenna technology to increase service coverage and system throughput. During contention-based channel access, a collision occurs when more than one vehicle selects the same minislot to transmit an access signal to an infrastructure. To solve this problem, we propose a group-based channel access scheme. Numerical analysis and simulation results show that the proposed scheme can help to reduce the number of collisions that occur during channel access.

Interference-aware topology control in wireless mobile ad-hoc networks

In this paper, we propose a distributed topology control scheme in wireless mobile ad-hoc networks in which the transmit power of each node is adaptively adjusted based on both the number of its neighbor nodes and the amount of interference that the node generates to the neighbors.

A novel fault recovery scheme for reliability of femtocell networks

Femtocell network is widely used for providing high data rate. However, there are some doubts about the reliability of femto base stations (BSs). When a fault occurs in a femto BS, MSs belonging to the faulted femto BS should handover to other BSs. Handover to inappropriate BS may decrease network efficiency. To make a smooth handover procedure, the usage of a candidate BS list is suggested. The candidate BS list consists of the recommended BSs based on received signal strength and cell load. By using the candidate BS list, MSs in the faulted femto BS can minimize the damage of failure.