• Journal of electromagnetic engineering and science
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• 제1권2호
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• pp.120-125
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• 2001

The capacity improvement in the DS-CDMA system can be obtained by allowing spectrum-overlap between adjacent channels. In this paper, an analysis for capacity improvement is newly considered according to the various chip waveforms in the partial spectrum-overlapped DS-CDMA system. Optimum-overlapping ratio is numerically found to obtain maximum capacity improvement for each chip waveform. Assuming the bandwidth containing 95% of the total power, i.e., 95% power bandwidth, rectangular chip waveform has the largest capacity improvement in the considered chip waveforms and then the amount of improvement is 136.5% at overlapping ratio 1.5 for BER = $10^{-3}$TEX> . Furthermore, as the required BER becomes lower, the capacity improvement gets smaller for a1l of chip waveforms. For the unequal power channels, it is shown that the larger capacity improvement is achieved as the power of desired channel becomes larger than that of adjacent channels. And the capacity improvement can be obtained even though the desired channel power is lower than the adjacent channel power.

• Journal of Communications and Networks
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• 제13권5호
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• pp.518-524
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• 2011

A high assurance IP encryption (HAIPE) compliant protocol accelerator is proposed for military networks consisting of red (or classified) networks and black (or unclassified) networks. The boundary between red and black sides is assumed to be protected via a HAIPE device. However, the IP layer encryption introduces challenges for bandwidth on demand satellite communication. The problems experienced by transmission control protocol (TCP) over satellites are well understood: While standard modems (on the black side) employ TCP performance enhancing proxy (PEP) which has been shown to work well, the HAIPE encryption of TCP headers renders the onboard modem's PEP ineffective. This is attributed to the fact that under the bandwidth-on-demand environment, PEP must use traditional TCP mechanisms such as slow start to probe for the available bandwidth of the link (which eliminates the usefulness of the PEP). Most implementations recommend disabling the PEP when a HAIPE device is used. In this paper, we propose a novel solution, namely broadband HAIPE-embeddable satellite communications terminal (BHeST), which utilizes dynamic network performance enhancement algorithms for high latency bandwidth-on-demand satellite links protected by HAIPE. By moving the PEP into the red network and exploiting the explicit congestion notification bypass mechanism allowed by the latest HAIPE standard, we have been able to regain PEP's desired network enhancement that was lost due to HAIPE encryption (even though the idea of deploying PEP at the modem side is not new). Our BHeST solution employs direct video broadcast-return channel service (DVB-RCS), an open standard as a means of providing bandwidth-on-demand satellite links. Another issue we address is the estimation of current satellite bandwidth allocated to a remote terminal which is not available in DVBRCS. Simulation results show that the improvement of our solution over FIX PEP is significant and could reach up to 100%. The improvement over the original TCP is even more (up to 500% for certain configurations).

• 한국수산과학회지
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• 제50권5호
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• pp.605-615
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• 2017

A multi-resonant broadband acoustic transducer with six Tonpilz elements operating at different resonant frequencies in a transducer assembly was fabricated, tested, and analyzed. A compensated transducer, modified by adding series inductance to the developed multi-resonant broadband transducer, was shown to provide improved bandwidth performance with a relatively more uniform frequency response compared with the uncompensated transducer. By controlling the series inductance, flat frequency response characteristics at two frequency bands were obtained over the range 38-52 kHz with 1.1 mH inductance and 50-60 kHz with 0.4 mH inductance. These results suggest that the operating frequency of the developed multi-resonant broadband transducer in a chirp echo sounder can be shifted to a different frequency band that is optimized according to the environment for more effective echo surveys of fishing grounds.

• 전기학회논문지
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• 제65권2호
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• pp.329-334
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• 2016

In this paper, we demonstrate a Non-Foster matching method for an electrically small antenna to improve the signal-to-noise ratio (SNR) of communication link. For the experiment, we used a general FM antenna whose resonance frequency is about 52-57 MHz and a floating type Linvill negative impedance converter(NIC)-based circuit as a Non-Foster matching element. By implementing the Non-Foster circuit to cover FM band, we can achieve a wide bandwidth matching covers 40-200 MHz. Our measurement shows 3-7 dB improvement of SNR for the same bandwidth though there are several spikes which means no improvement of SNR in the band.

• 한국전자파학회논문지
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• 제19권3호
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• pp.304-310
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• 2008

이동 통신용 안테나로 PEC(Perfect Electric Conductor) 접지면을 갖는 U-slotted 패치 안테나가 널리 이용되고 있으나, 이동 통신 능력을 확대하기 위하여 대역폭의 개선이 요구되어 왔다. 본 논문에서는 대역폭을 확대하기 위하여 EBG(Electromagnetic Band-Gap) 접지면을 갖는 U-slotted 패치 안테나를 제안하고, 그 복사 특성을 고찰하였다. 본 논문에서 제안한 EBG 접지면을 갖는 U-slotted 패치 안테나의 대역폭이 개선됨을 보이기 위하여 EBG와 PEC 접지면을 갖는 두 가지 형태의 U-slotted 패치 안테나를 설계 제작하고 복사 특성을 측정하였다. 측정결과, EBG 접지면을 갖는 U-slotted 패치 안테나가 PEC 접지면을 갖는 안테나보다 대역폭이 넓은 것으로 확인되었다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 학술대회 논문집 정보 및 제어부문
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• pp.215-217
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• 2004

In wireless sensor networks, fair allocation of bandwidth among different nodes is one of the critical problems that effects the serviceability of the entire system. Fair bandwidth allocation mechanisms, like fair queuing, usually need to maintain state, manage buffers, and perform packet scheduling on a per flow basis, and this complexity may prevent them from being cost-effectively implemented and widely deployed. It is a very important and difficult technical issue to provide packet scheduling architecture for fairness in wireless sensor networks. In this paper, we propose an packet scheduling architecture for sensor node, called FISN (Fairness Improvement Sensor Network), that significantly reduces this implementation complexity yet still achieves approximately fair bandwidth allocations. Sensor node for sensing estimate the incoming rate of each sensor device and insert a label into each transmission packet header based on this estimate. Sensor node for forwarding maintain no per flow state; they use FIFO packet scheduling augmented by a probabilistic dropping algorithm that uses the packet labels and an estimate of the aggregate traffic at the gathering node. We present the detailed design, implementation, and evaluation of FISN using simulation. We discuss the fairness improvement and practical engineering challenges of implementing FISN in an experimental sensor network test bed based on ns-2.

• Journal of electromagnetic engineering and science
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• 제11권3호
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• pp.201-206
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• 2011

This paper presents a miniaturized epsilon negative (ENG) zeroth-order resonance (ZOR) patch antenna with an improved bandwidth. The miniaturization and the broad bandwidth of the ENG ZOR patch antenna are achieved by using a meandered via and a high permeability substrate instead of a straight via and a dielectric substrate. The use of a meandered via allows miniaturization of the ENG ZOR patch antenna without narrowing the bandwidth. The use of a high permeability substrate allows further miniaturization of the ENG ZOR patch antenna and improvement of the bandwidth. A high permeability substrate consisting of a multi-layered substrate is designed to have a small material loss. The antenna (kr=0.32) has a 10 dB fractional bandwidth of ~1 %, which is 1.74 times as broad as that of an antenna with a dielectric substrate.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2005년도 추계종합학술대회
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• pp.521-524
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• 2005

본 논문에서는 밀리미터파 대역에서 Giga-bit 모뎀을 위한 BASK 시스템의 성능개선을 위하여 수신단 low pass filter의 bandwidth를 자동으로 조절하는 방식을 제안하였다. 제안한 방식은 counter의 remainder 와 remainder의 합을 이용한 퍼지 논리 시스템으로 low pass filter의 bandwidth를 자동적으로 조절한다. 제안한 방식의 유용성을 BER 에 대한 시뮬레이션을 통하여 확인하였다.

• Journal of Power Electronics
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• 제10권4호
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• pp.382-387
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• 2010

This paper presents a novel design method for determining the PID gains of a speed controller for a servo system compensating variations in bandwidth at a low speed. The variations in bandwidth of a speed controller are measured at a low speed and the relationship between the bandwidth and the damping ratio are verified by determining the location of the closed loop pole. The proposed algorithm uses the z-transform of a plant and speed controller and applies the time-varying sampling method for determining the PID gains of the speed controller at low speed. The magnitude and the phase condition are considered for finding a suitable control gain. The usefulness and effectiveness of the proposed method is demonstrated through experimental results such as low speed control and robust disturbance responses.

• Journal of electromagnetic engineering and science
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• 제10권4호
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• pp.296-302
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• 2010

This paper proposes an approximate equation for broad bandwidth conditions in an antenna feeding probe design with a cylindrical magneto material structure (CMMS). The bandwidth calculation has been conducted according to the relation between the distance ($r_m$) between the magneto material and feeding probe, and the magneto material thickness ($t_m$) for a given ${\mu}_r$. The bandwidth of a proposed antenna with CMM feeding structure is improved about 182 %, when ${\mu}_r=20+j0.001$, in comparison with the bandwidth of an antenna without CMMS. The maximum error extent between the bandwidth calculated by the approximation equation and by the numerical calculation of the proposed antenna is about $\pm$3.2 % for ${\mu}_r=10+j0.001$. The approximation equation proposed in this study can solve the conventional problem of the complex process and the long time required for reiterative calculation, and allow simple and precise design with prediction. The accuracy of an approximated equation is compared with the results calculated by a commercial tool and verified by reasonable agreement between them.