Yujin Nam

Optimal user selection algorithm for opportunistic space division multiple access systems

This paper proposes a user selection algorithm in space division multiple access (SDMA) systems. In the proposed algorithm, each user calculates signal to interference plus noise ratio (SINR) taking angle-of-departure, angle-of-arrival, and channel environment with clustering nature into consideration. The base station selects several users who have the high SINR to increase the system throughput. The simulation results show that the proposed algorithm achieves higher throughput compare to the conventional algorithm in SDMA systems.

An Energy-Efficient Data Reporting Scheme Based on Spectrum Sensing in Wireless Sensor Networks

Wireless sensor networks (WSNs) are widely used in a variety of fields including environmental and industrial monitoring. However, the battery-powered sensor devices in WSNs can suffer from a lack of energy resources problem because of their limited battery capacity. Although the energy harvesting (EH) sensor devices recently have become an attractive alternative to address the limited battery capacity problem, a small number of EH sensor devices can be deployed because of their high cost. To address this problem, we propose an energy-efficient data reporting scheme based on spectrum sensing. In the proposed scheme, each sensor device senses the spectrum over the air and then determines the transmission time of the access signal and the number of repetitions of access signal transmission. Also, the sink node resolves the collisions by detecting the variation of the received signal power. The simulation results show that the proposed scheme increases the total energy efficiency of the sensor devices and moreover it decreases the access failure probability of the sensor devices.

Sensing-based adaptive data reporting scheme in wireless sensor networks

Wireless sensor networks (WSNs) typically have a massive number of the sensor devices. The battery-powered (BP) sensor devices are the conventional type that has low transmission power due to the limited battery lifetime. The energy harvesting (EH) sensor devices can recharge their battery and therefore may transmit data with high transmission power. However, due to the low transmission power of the BP sensor device, the data reporting process can suffer from high access failure probability. To address this problem, we propose a sensing-based adaptive data reporting scheme. According to the spectrum sensing results, each sensor device determines the time and duration of data reporting. The sink node resolves the collisions by detecting the variation of the received signal power. The simulation results show that the proposed scheme decreases the access failure probability and increases the total number of successful reportings per frame.

Algorithms for ARQ feedback message transmission in IEEE 802.16m systems

This paper proposes two algorithms for automatic repeat request (ARQ) feedback message transmission in IEEE 802.16m systems. The proposed algorithms determine the transmission interval of an ARQ feedback message on the basis of the number of transmitted ARQ blocks or the number of received ARQ blocks. If the receiver frequently transmits ARQ feedback messages, the system throughput increases because there is no need to wait for ARQ feedback acknowledgements, though the feedback overhead also increases. Hence, determining the appropriate transmission time of an ARQ feedback message is very important for reaching a compromise between the throughput and the ARQ feedback overhead. The simulation results show that the proposed algorithms achieve a better throughput level than the conventional scheme described in the IEEE 802.16m standard.