• The Journal of the Korea Contents Association
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• v.8 no.10
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• pp.20-26
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• 2008

The quality of stream remaking is decided the load of a server and Jitter through the traffic of the transmission path between end to end. In order to improve these problems in this paper, I propose tree construction method of low-delay-level-multicast. In this case which the network congestion will be occurred by streaming quality, I also propose the technique which dynamically changes the transmission path. This technique first constructs the overlay structure for relaxing the overload of server. Secondly, in order to decrease Jitter of client, it makes upload bandwidth and low latency balanced. In the evaluation of the performance, this paper showed better enhancement of about $15%{\sim}24%$ than P2CAST[4] in the simulation about node average join count, average bandwidth, service request refusal ratio, RTT measurement of nodes, and node average join count by defect ratio.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.3
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• pp.292-299
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• 2012

This paper proposes the design of circularly polarized multi band antenna for a non-linear junction detector (NLJD) system. In order to design for broad bandwidth, the CPW (Co-Planar Waveguide) feeding method is considered in this design. In order to realize the circular polarization, the axial ratio was controlled by inserting a $45^{\circ}$ inclined slot on radiating element and by cutting an edge of the radiating patch. Measurement results of return loss, bandwidth, axial ratio, polarization pattern and gain are agreed well with their simulation results in interested frequency band at 2.4~ 2.44 GHz, 4.84~4.92 GHz, and 7.28~7.32 GHz.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.6
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• pp.1127-1136
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• 2017

In wireless networks, the packet loss due to the bit error is misinterpreted as loss due to the congestion state, so TCP congestion control occurs frequently and performance degradation occurs. This degradation also occurs in MPTCP(Multipath TCP), which is an extension protocol of original TCP. In MPTCP, the overall performance of the multipath is degraded. In this paper, we propose a congestion control scheme which measures the bandwidth on each path of MPTCP and reduces the congestion window size by the measured bandwidth when packet loss occurs, in order to solve the MPTCP performance degradation in the wireless environment. We also implemented the proposed congestion control in the Linux kernel and compared it with the original MPTCP in the testbed and real wireless networks. Experimental results show that the proposed congestion control has better throughput performance than original MPTCP congestion control in the wireless environment.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.2 s.105
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• pp.184-192
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• 2006

Synthetic Aperture Radars(SAR) are used mainly for high-resolution imaging of the terrain. This paper describes the $16{\times}16$ array antenna designed for an X-band, automobile-based SAR(AutoSAR) system. This antenna has the structure of several layers such as radome, radiators, slots, feed network, and honeycomb cores. Each layer is adhesively bonded to meet different combination of structural and electrical design requirements. Using the Strip-Slot-Foam-Inverted-Patch(SSFIP) structure and honeycomb cores, a wide bandwidth and a structural hardness were achieved. Measurement results were compared with simulation results. It was observed that this antenna had a bandwidth of 1.7 GHz, side-lobe levels of less than -20 dB, half-power beamwidth of $5^{\circ}$ and $5^{\circ}$, and gains of 25.0 dBi. The observed results show that the designed array antenna will be applicable to the wideband SAR system.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.7
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• pp.664-672
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• 2009

In this paper we propose an on-glass antenna which consists of conducting dual center striplines and multi-loaded striplines. Multi-loaded striplines and dual center lines were employed for achieving a broad matching bandwidth and improving a vertical radiation gain, respectively. The detail design parameters were determined using the Pareto genetic algorithm with an full wave EM simulator. The optimized design was built and installed on a commercial vehicle, and the antenna performances such as the return loss and the radiation gain were measured in a semi-anechoic chamber. The measurement results showed the matching bandwidth($S_{11}$<-3 dB) of about 49 % in the T-DMB frequency band, the vertical gain of about -3 dBi along the bore-sight direction, and the average gain of about -10 dBi along the azimuth direction.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.6
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• pp.698-705
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• 2010

A vehicle antenna for AM, FM, TDMB, GPS systems was designed and implemented. Omnidirectional AM antenna was designed by ferrite turn style antenna. For the FM and TDMB antenna, folded monopole antenna which helical is folded was applied. GPS antenna for the bandwidth achievement was designed by trapezoidal microstrip patch that has air substrate. Receiving signal strengths by the measurement were presented for the AM, FM and TDMB antenna. AM signal strength was -65.7 dBm, this strength is almost as same conventional pole antenna as -63.4 dBm. It can be replaced conventional pole or glass antenna by the studied antenna. Signal strengths for FM and TDMB were -55.66 and -43.50 dBm at center frequency, they are 5~10 dB higher than conventional antenna. Measurements of bandwidth and gain for the GPS antenna showed 135 MHz under VSWR 2 : 1 and 4.31 dBi, gains over GPS band were 3~5 dB higher than ceramic patch antenna.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.7
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• pp.1537-1543
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• 2010

This paper describes a compact microstrip antenna with dual polarization characteristics. The antenna, receiving both a left-hand circularly polarized(LHCP) wave and a right-hand circularly polarized(RHCP) wave, can be used for a polarization diversity. A diamond-shaped patch with internal empty room is designed for impedance matching as well as size reduction. And slots are added around feeding point to improve input matching. The proposed antenna has been applied to GPS(global positioning system), operating at 1.57GHz. And, the proposed idea has been verified and estimated by simulation. The measurement results show that it has VSWR 2:1 bandwidth of 83MHz, 3dB axial bandwidth of about 58MHz, 3dB beamwidth of 90degree, and gain of 0dBi, respectively, for RHCP. Also, it has similar performances for LHCP.

• Journal of Advanced Navigation Technology
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• v.13 no.2
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• pp.244-251
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• 2009

In this paper, a compact slot antenna for 2.4GHz ISM band applications has been designed. The folded slot with some additional meander sections are used in the design of the antenna within the restricted PCB space. The operating frequency band and the fractional bandwidth of the antenna is about 2.32~2.58 GHz and 11%, and the radiation patterns within the operation bandwidth are almost same. Also, the radiation efficiency and gain of the antenna is more than 49% and 1.2 dBi respectively. To check the validity of the design result, the measurement and simulation results are compared and presented.

• Journal of Institute of Control, Robotics and Systems
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• v.20 no.8
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• pp.890-894
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• 2014

In this paper, we derive the CRLB (Cramer-Rao Lower Bound) of effective carrier-to-noise power ratio ($C/N_0$) estimation for a GPS (Global Positioning System) L1 C/A (Coarse/Acquisition) signal under band-limited white noise jamming environments. The quality of a received GPS signal is commonly described in terms of its $C/N_0$, implying that the noise is white and thus can be described by scalar noise density. However, if some intentional interference is received to a victim GPS receiver, then the $C/N_0$ is no longer the efficacious performance indicator. The correct and straightforward measurement to analyze the receiving situation is the effective $C/N_0$. In this paper, we consider a band-limited white noise jamming whose bandwidth is 2MHz and is the same as one of the first null-to-null bandwidth of the GPS L1 C/A signal.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.17 no.5
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• pp.128-134
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• 2018

In this paper, two ports feeding a microstrip patch antenna using a quadrature hybrid circuit was proposed to enhance the bandwidth for the global positioning system(GPS). The square patch was designed, and the probe feeding was applied. The quadrature hybrid chip circuit for two-port feeding was designed, and output ports that have a 90-degree phase difference feed to the patch antenna. The designed patch and quadrature hybrid circuit were implemented on an FR4 board, and were combined. The measurement of the bandwidth within a voltage standing wave ratio(VSWR) of 2:1 and axial ratio(AR) in 3dB were wide band as 29% BW (1,230~1,700 MHz) and 15.87% BW (1,400~1,650 MHz), respectively. Antenna gain were measured 2.75dBi at the center frequency.