• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.10 no.9
• /
• pp.2340-2349
• /
• 2009

In this paper we proposed a hopping routing scheme to resolve the hot spot problem for periodic monitoring services in wireless sensor networks. Our hopping routing scheme constructs load balanced routing path, where an amount of energy consumption of all nodes in the sensor networks is predictable. Load balanced routing paths can be obtained from horizontal hopping transmission scheme which balances the load of the sensor nodes in the same area, and also from vertical hopping transmission scheme which balances the load of the sensor nodes in the other area. The direct transmission count numbers as load balancing parameter for vertical hopping transmission are derived using the energy consumption model of the sensor nodes. The experimental results show that the proposed hopping scheme resolves the hot spot problem effectively. The efficiency of hopping routing scheme is also shown by comparison with other routing scheme such as multi-hop, direct transmission and clustering.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.9 no.2
• /
• pp.237-241
• /
• 2005

In Bluetooth version 1.0, the frequency hopping algorithm was such that there was one piconet, using a specific frequency, resolving the frequency depending on the part of the digits of the device clock and the Bluetooth address. Basic pattern was a kind of a round-robin using 79 frequencies in the ISM band. At this point, a problem occurs if there were more than two devices using the same frequency within specific range. In this paper, we proposed a software-based adaptive frequency hopping method so that more than two wireless devices can stay connected without frequency crash. Suggested method was implemented with HDL(Hardware Description Language) and automatically synthesized and laid out. Implemented adaptive frequency hopping circuit operated well in 24MHz correctly.

• Proceedings of the Korean Society of Broadcast Engineers Conference
• /
• 2012.07a
• /
• pp.195-198
• /
• 2012

MB-OFDM UWB시스템은 TFC(Time-Frequency Code)를 이용하여 시간/주파수 호핑을 수행한다. 이를 통해 주파수 영역에서 다이버시티 효과를 갖는 동시에 사용되는 다른 piconet간의 간섭을 최소할 수 있다. 송신단에서는 프리앰블을 전송할 때부터 해당 TFC에 맞게 호핑을 하면서 전송을 하기 때문에 수신단에서는 신호의 시작을 추정하는 패킷 검출은 매우 중요한 과제이다. 따라서 본 논문에서는 MB-OFDM UWB시스템을 위한 간단하고 효율적인 패킷 검출 방법을 제안하였다. 시뮬레이션 수행 결과 제안된 방법은 기존 방법보다 약 0.5 dB의 SNR 개선 결과가 있는 것으로 밝혀졌다.

• Korean Journal of Optics and Photonics
• /
• v.17 no.6
• /
• pp.548-555
• /
• 2006

We investigate the effect of the reflectivity of both facets and the phase of a phase tuning section on the self-pulsation (SP) characteristics of multisection index-coupled (IC) DFB lasers composed of two index-coupled DFB sections and a phase tuning section between them in terms of yield. In the case of weak coupling strength, as the reflectivity of both facets increases, the effect of reflected fields from both facets and the other DFB section on the mode characteristics of one DFB section increases. Thus the number of mode hoping increases and yield decreases for the variation of phases of both facets. In the case of strong coupling strength, as the reflectivity of both facets increases, the spatial hole burning effect increases, so that the yield decreases. The maximum yield and the range of the phase of a phase tuning section with yield more than 40% decrease as the facet reflectivity increases irrespective of coupling strength. As the coupling strength increases, the variation of yield for the variation of the phase of a phase tuning section increases and the variation of the phase of a phase tuning section with the maximum yield for the variation of the reflectivity of both facets decreases. The yield characteristics of the cases with the coupling strengths of 2 and 3 are better than those with the coupling strengths of 1.2 and 4.

• Korean Journal of Optics and Photonics
• /
• v.16 no.1
• /
• pp.85-98
• /
• 2005

As the number of compound cavity modes within the stopband of DFB sections decreases, the frequency of mode hopping decreases for the variation of $\Delta$λ$_{B}$, which represents the difference between the Bragg wavelengths of two DFB sections, so that the number of abrupt changes of pulsation frequencies decreases. In addition, the pulsation frequency varies continuously for the variation of the phase in a phase tuning section for a fixed $\Delta$λ$_{B}$. The number of compound cavity modes within the stopband decreases as the length of DFB sections increases and the length of a phase tuning section decreases. Thus stable self-pulsation operations for the variation of $\Delta$λ$_{B}$ and the phase in a phase tuning section could be obtained by proper selection of the coupling strength and the length of each section.ction.

• Journal of the Korean Society for Precision Engineering
• /
• v.13 no.1
• /
• pp.143-152
• /
• 1996

The vibratory bowl feeder is the most versatile of all hopper feeding devices for small engineering parts, and the typical nonlinear dynamic system experiencing repeated impacts with friction. We model and analyze the dynamic behavior of a single part on the vibrating track of the bowl feeder. While the previous studies are restricted to the sliding regime, we focus our analysis on the hopping regime where the high conveying rate is available. We present the numerical analysis results for conveying rate and frictional impact process both in periodic and chaotic regimes. We examined the dynamic effects from the variation of several physical parameters, and presented the important features for the design of the vibratory bowl feeder. This research holds much potential for leverage over design problems of wide range of mechanisms and tools with repeated collisions.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.29 no.10A
• /
• pp.1177-1188
• /
• 2004

This paper describes and analyzes the performance of MB-OFDM UWB system that is suggested as one of standards in IEEE 802.15 TG3a for UWB application. UMBchannel model that has been contributed in IEEE 802.15 SG3a is a wideband channel model of 6Ghz bandwidth, so we modify it to have 3 subband channels that are obtained by filtering conventional U Channel, considering center frequency hopping and system bandwidth. From simulations, we compare performances of MB-OFDM system in AWGN and WB channel and verify the frequency and time domain diversity gains from time End frequency spreading technique. We also compare and analyze the performance of proposed SFBC MB-OFDM with that of conventional MB-OFDM system. Simulation results show SFBC MB-OFDM system outperforms conventional MB-OFDM system about 1.5dB of Eb/No at target BER of 10$^{-m4}$./.