• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.41 no.3
• /
• pp.15-20
• /
• 2004

In this paper, a wideband two-layer H-shaped microstrip antenna for WLAN is designed. To increase the bandwidth of microstrip patch antenna a configuration of stacked type using parastic element is used. Furthermore, to reduce the size of microstrip patch antenna, two techniques are employed . the first one is H-shaped patch type and the second one is that the main radiator and parastic patch are shorted to the ground plane using ten shorting posts. The antenna bandwidth and radiation characteristics are calculated by ENSEMBLE ver. 5.0 simulation software, and compared with the experimental results. Experiment results show that the bandwidth of antenna in 740MHz centered at 5.46㎓(13.5%), which is close agreement with the calculations, 770MHz(13%). Also, the antenna size can be reduced by 71.5% compared with the half wavelength rectangular microstrip antenna using the same substrate at the same frequency.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.29 no.10
• /
• pp.817-820
• /
• 2018

In this letter, a compact multiple-input multiple-output(MIMO) antenna design for a 2.4 GHz wireless local area network(WLAN) band is proposed for use in smart glasses. To miniaturize the MIMO antenna system, a ground plane is employed within the antenna and a T-shaped ground is proposed. To achieve wideband isolation, dual resonance is formed by the ground mode. One resonance is created by the T-shaped ground and the second resonance is created by adding a slot and a capacitor between the two feed lines. The measurements show that the reflection coefficient characteristic was less than -5.1 dB, whereas the isolation obtained was less than -20 dB. The diversity performance was evaluated using the measured two-dimensional radiation patterns, and the envelope correlation coefficient(ECC) values achieved in the target band(2.4~2.5 GHz) were less than 0.1.

• Journal of Advanced Navigation Technology
• /
• v.14 no.5
• /
• pp.632-639
• /
• 2010

Ground Transportation is one of the most required field that users need positioning information Especially, more precise position can make smart traffic management possible and bring convenience to users. By advanced wireless network, cars can receive the GPS information of reference station in any tim e and any where. Thus land vehicles are possible to process precise positioning. In general, for precise positioning code and phase measurements are used. But receivers provide not only code and phase measurements but also doppler measurements and Doppler is direct measurement of velocity. In this paper, because velocity is very important information required in Ground Transportation, precise positioning for Ground Transportation is studied. For precise positioning RTK(Real-Time Kinematic) was used and double differenced doppler measurements were added, As a Result, positioning error by multipath and cycle slip was soften. However there still remained Positioning error. Thus smoothing technique using doppler measurement in position domain is used for softening positioning error.

• Journal of Korea Multimedia Society
• /
• v.13 no.3
• /
• pp.349-358
• /
• 2010

Adaptability is an important issue in video streaming over mobile environments, since the clients may request videos with great differences in their workload. In this paper, we propose the issues in limited bandwidth scheduling for efficient MPEG-4 video stream transmission over a mobile or wireless network. In the phase of admission control, the amount of bandwidth allocated to serve a video request is the mean bandwidth requirement of its requested video. The dynamic allocation of bandwidth in the phase of scheduling depends on the playback buffer levels of the clients with an objective to make it more adaptive to the playback situation of individual clients. In the proposed RTA scheduling protocol, more bandwidth may be allocated temporarily to the client whose buffer level is low. By employing the buffer level based scheduling policy, this protocol attempts to maximize the real-time performance of individual playback while minimizing the impact of transient overloading. Extensive simulation experiments have been performed to investigate the performance characteristics of the RTA protocol as comparing with BSBA protocol. This RTA protocol shows the better performance by transferring more frames than BSBA protocol.Computer simulations reveals that the standard deviation of the bit rate error of the proposed scheme is 50% less than that of the conventional method.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.5 no.5
• /
• pp.892-901
• /
• 2001

Despite of many advantages over conventional radio paths, application of the Meteor Burst Path in commercial communication system is so far limited to a few extent because of its low duty rate, which is, less than several percent at best. In order to get through maximum number of data bits during the short interval of each burst, which normally lives a fractions of a second, a sophisticated communication protocol is called for. In this paper, author introduces a communication protocol which can effectively locate and fetch burst signal by sending out periodic detection signal from master station and, with minimal delay, switch over to transmission states so as to put as many data bits through the detected burst as the burst length permits. By analyzing time period required for each transaction steps, the author derives optimal packet length for various bursts which assures to get a message string through in minimum delay. According to the analysis, the author proposes a protocol including a routine which automatically accesses average length of bursts at each environment and automatically adapt length of data packet so as to maximize data throughput under Riven burst conditions.

• Journal of Broadcast Engineering
• /
• v.16 no.2
• /
• pp.360-371
• /
• 2011

T-DMB hybrid data service provides advanced data services while maintaining backward compatibility with legacy T-DMB receivers by using hybrid BIFS technology enabling distributed delivery of scene description information and object description information. This paper presents the hybrid service authoring framework implementing hybrid BIFS technology for creating contents for distributed delivery, and the results of experiments by using it. Hybrid service authoring framework is comprised of service creation system, service management system, and contents offering system. It enables the creation of combined hybrid data service and the splitting of the contents into two parts for ecah delivery network, data for broadcasting network and the data for mobile network. It also enables the managements of the contents. The feasibility of advanced data services while maintaining backward compatibility with the legacy T-DMB receiver has been proved by the contents created by using the hybrid authoring framework presented in this paper.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2007.10a
• /
• pp.153-158
• /
• 2007

The INMARSAT is able to long range maritime communications that can not use for expensive charge in non-SOLAS ship. Therefore, international discussion for the question that replacements use of MF/HF band for maritime distress and safety communications in maritime. HF data communications system may be effectively utilized for SOLAS ships as well as for the existing non-SOLAS vessels including the fishing boats, which navigate A2 and A3 sea areas. The HF data communications may have various functions such as e-mail services, broadcasting services of up-to-date information related to marine safety, position reporting services, polling services etc. However, the present HF e-mail communications protocols have a problem of increasing calling redundancy as the number of channels in operation increases. This paper new protocol and communication sequence proposed in this submission establishes a proper radio link automatically and adaptively by taking channel traffic into account.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.35 no.5A
• /
• pp.440-446
• /
• 2010

Convergence of IT and BT is considered in many area, especially in medical care industry. The example of this trend is a capsule endoscope. But in a capsule endoscope, communication through human body has a few restrictions. At first, the transmit power should be limited not to have a bad effect on human organs and for the battery capacity. Second, the channel characteristic of human body has not been examined exactly. Third, general modulation / demodulation techniques which require a channel estimation cannot be used because of battery limit. There also may be a lot of interference signals because a capsule endoscope uses UWB bandwidth. In this paper, we introduce Chirp Spread Spectrum Differential Binary Phase Shift Keying(CSS-DBPSK) and propose Chirp Spread Spectrum On-Off Keying(CSS-OOK) which don't require a channel estimation and robust to interference signals. Using CSS-DBPSK or CSS-OOK, we can get 5 dB or 2~3 dB of Eb/N0 gain at 10-5 target BER. And if there are interference signals, those gains of CSS-DBPSK and CSS-OOK are increased.

• Journal of KIISE
• /
• v.43 no.2
• /
• pp.246-255
• /
• 2016

The orthogonal frequency-division multiple access (OFDMA) systems are well suited to multi-rate multicast transmission, as they allow flexible resource allocation across both frequency and time, and provide adaptive modulation and coding schemes. Unlike layered video coding, the multiple description coding (MDC) enables flexible decomposition of the raw video stream into two or more substreams. The quality of the video stream is expected to be roughly proportional to data rate sustained by the receiver. This paper describes a mathematical model of resource allocation and throughput in the multi-rate video multicast for the OFDMA wireless and mobile networks. The impact on mean opinion score (MOS), as a measurement of user-perceived quality (by employing a variety of scheduling disciplines) is discussed in terms of utility maximization and proportional fairness. We propose a pruning algorithm to ensure a minimum video quality even for a subset of users at the resource limitation, and show the optimal number of substreams and their rates can sustain.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2007.06a
• /
• pp.188-194
• /
• 2007

We propose a new ad hoc multicast routing protocol for based on the ontology scheme called inference network. Ontology knowledge-based is one of the structure of context-aware. We will have developed an algorithm that will design multi-hierarchy Layered networks to simulate a desired system.