• Journal of Sensor Science and Technology
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• v.21 no.5
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• pp.352-358
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• 2012

A sensor network system can be an efficient tool for healthcare telemetry for multiple users due to its power efficiency. One drawback is its limited data size. This paper proposed a real-time application of data compression/decompression method in u-Health monitoring system in order to improve the network efficiency. Our high priority was given to maintain a high quality of signal reconstruction since it is important to receive undistorted waveform. Our method consisted of down sampling coding and differential Huffman coding. Down sampling was applied based on the Nyquist-Shannon sampling theorem and signal amplitude was taken into account to increase compression rate in the differential Huffman coding. Our method was successfully tested in a ZigBee and WLAN dual network. Electrocardiogram (ECG) had an average compression ratio of 3.99 : 1 with 0.24% percentage root mean square difference (PRD). Photoplethysmogram (PPG) showed an average CR of 37.99 : 1 with 0.16% PRD. Our method produced an outstanding PRD compared to other previous reports.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.3
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• pp.254-262
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• 2013

This paper proposes FMT(Filtered Multi-Tone)-based digital radio implementation algorithms and the results obtained by various field tests especially in terms of transmitter characteristics. In this study, we predefined frame structure and protocols used for the CSTDMA(Carrier Sensing Time Division Multiple Access) scheme, designed digital filters and RF front end to fulfill the system characteristics such as the spectral mask and processing delays given by the Recommendation ITU-R M.1842-1. The proposed system supports exchange of data for e-Navigation with the usage of wider channel of 50-100kHz bandwidth, Turbo coding and FMT modulation. Furthermore, the common Ethernet protocol makes connection to local WLAN(Wireless Local Area Network) on board the ship for other data services.

• The KIPS Transactions:PartC
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• v.12C no.4 s.100
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• pp.465-472
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• 2005

IEEE 802.11 wireless LAN technology is essential for wireless internet, next generation converged network and home network. But, it is certain that user's privacy must be provided to expand the applicable area in IEEE 802.11 WLAN. Recently, WEP and 802.11i security scheme can be used in MAC Layer. But with VPN technology which is applied to WLAN user, it means that suity mechanism is used redundantly. One bit authentication mechanism was already proposed to solve this redundancy. In this paper, we analyze problems of 1-bit Authentication mechanism which are failure of synchronization and waste of packet. And we propose new algorithm which synchronizes sender with receiver, at once, using duplicated-packet-count information. We show that our algorithm improves success probability of packet authentication up to $98\%$ and efficiency of authentication bit stream up to $97\%$.

• The Journal of the Korea Contents Association
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• v.9 no.7
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• pp.67-75
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• 2009

IEEE 802.11 WLAN(Wireless Local Area Network) standard is currently developing with increased wireless internet demand. Study trends of IEEE 802.11n for high throughput show two aspects, enhanced system throughput using aggregation among packets in MAC(Medium Access Control) layer, and better data rates adapting MIMO(Multiple-Input Multiple-Output) in PRY(Physical) layer. But, no one demonstrates IEEE 802.11n system performance results considering MAC and PRY connection. This paper adapts A-MPDU(Aggregation-MAC Protocol Data Unit) method in MAC layer and MIMO in PRY layer for IEEE 802.11n system. Consequently, Simulation results show enhanced throughput and data rates compared to existing system. Also, We use NS-2(Network Simulator-2) considering MAC and PRY connection for reality.

• Journal of Advanced Navigation Technology
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• v.20 no.5
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• pp.490-495
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• 2016

In the present study, a microstrip-fed monopole antenna is proposed for wireless local area network (WLAN) operations which cover dual band of 2.4 GHz (2.4 ~ 2.484 GHz) and 5 GHz (5.15 ~ 5.825 GHz). In order to obtain its compact structure and good omnidirectional radiation patterns, a modified inverted L-shaped slot separated from ground for impedance matching in 5 GHz band is etched on 2.4 GHz printed monopole antenna. The proposed antenna is designed and fabricated on a FR4 substrate with dielectric constant 4.3, thickness of 1.6 mm, and size of $30{\times}45mm^2$. The measured impedance bandwidths (${\mid}S_{11}{\mid}{\leq}-10dB$) of fabricated antenna are 270 MHz (2.22 ~ 2.48 GHz) in 2.4 GHz band and 890 MHz (5.08 ~ 5.97 GHz) in 5 GHz band respectively. In particular, high gain of more than about 4 dBi and good omnidirectional radiation patterns have been observed over the entire frequency band of interest.

• Journal of Advanced Navigation Technology
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• v.10 no.1
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• pp.63-69
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• 2006

Recently there are increasing needs for Internet and various kinds of contents. These traffics for various contents need more amount of data to provide high-quality information and require various QoS depending on the characteristics of contents. However, current Internet service supports BE (Best Effort) service only, therefore IntServ (Integrated Service) scheme and DiffServ (Differentiated Service) scheme are represented to support QoS in IP layer. Moreover, while wireless Internet is getting popular, MAC(Medium Access Control) is also becoming important. This is due to the fact that wireless access, resource allocation and packet scheduling, which are done in another layers before, are performed in MAC layer in many new wireless systems. This paper describes new scheme that provides QoS taking into account the traffic characteristics over Mobile IPv6 network based on IEEE 802.11e EDCF and evaluates the performance through computer simulation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37B no.11
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• pp.993-1003
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• 2012

In this paper, we propose a method that wireless mobile nodes can obtain high throughput in heterogeneous wireless networks using multiple connections and it has low packet loses under handover situation. Currently, a mobile node exchanges data with server for one network connection. The proposed method can use high throughput because it doesn't only use one network(WLAN, 3G, etc.) but also use multiple wireless networks. When mobile nodes move to area to use multiple connection, mobile nodes request heterogeneous wireless networks using multiple connections message from the server and the server transmit packets using multiple connections. Also, this method doesn't disconnect previous networks, so packets losses are decreased. Using the NS-2 simulation, we verify that the propose method enhances throughput.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.2
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• pp.397-406
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• 2009

A Wireless Access for Vehicular Environment (WAVE) system based on Orthogonal frequency Division Multiplexing (OFDM) is made for vehicle to vehicle wireless communications. The physical layer standard of the WAVE system is very similar to that of the IEEE802.1la wireless local area network (WLAN). Therefore, the performance of the WAVE system is degraded by continual timing delay in the WAVE multipath fading channels after starting initial timing synchronization. In this paper, the tracking algorithm that synchronizes symbol timing is proposed to continually compensate additional timing delay. Computer simulation of the proposed algorithm is performed in the worst communication environments that apply to maximum timing delay. Computer simulation shows that the proposed algorithm can improve the system performance in various channel conditions.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.46 no.4
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• pp.31-41
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• 2009

IEEE 802.11e proposed by IEEE 802.11 working group to guarantee QoS has contention based EDCA and contention free based HCCA. HCCA, a centralized polling based mechanism of 802.11e, needs a scheduling algorithm to allocate the network resource efficiently. The existing standard scheduler, however, is inefficient to support for QoS guarantee for real-time service having VBR traffic. To improve these limit, in this paper, we First, we propose priority polling algorithm which additionally considers the size of MSI and TXOP based on EDD algorithm to increase number of QSTAs. We also propose a dual token bucket TXOP allocation algorithm to reduce congestion caused by stations which enters network with considerable delay variance. TSPEC parameters, Maximum Burst Size (MBS) and Peak Data Rate (PR), are applied to design depth and token generation rate of two buckets. Simulation results show that the proposed algorithm has much higher performance compared with reference and SETT-EDD scheduler in terms of throughput and delay.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.9 s.351
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• pp.158-164
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• 2006

Mobile operators will face many challenges both economically and technically, as WLAN evolve through a bewildering number of different standards during the coming years. Potentially this will require several upgrades to the mobile infrastructure. A new approach for addressing these challenges is evaluated in this paper. It is based on a radio over fiber (RoF) technology that uses electro-absorption modulator (EAM) and optical single sideband (OSSB) modulation technique and it promises to provide solutions that will be transparent to changes in protocols and frequency of operation as well as reducing radio access infrastructure costs. This paper describes the development of prototype RoF system based on the 60GHz band CATV transport distribution system with EAM and the possibility of radio over fiber technology for use in the broadband convergence network (BcN) wireless access infrastructure.