• Journal of electromagnetic engineering and science
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• 제14권3호
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• pp.299-305
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• 2014

A wideband circularly polarized (CP) antenna with a single feed is proposed for use in global navigation satellite systems. Its primary radiation elements are composed of two orthogonal bowtie dipoles, which are equipped with double-printed vacant-quarter rings to allow direct matching of the antenna to a single $50-{\Omega}$ coaxial line and to produce CP radiation. The crossed bowtie dipole is appropriately incorporated with a planar metallic reflector to produce the desired unidirectional radiation pattern as well as to achieve a wideband characteristic in terms of impedance matching and axial ratio (AR) bandwidths. The designed antenna was fabricated and measured. The prototype antenna with an overall 1.2-GHz frequency size of $0.48{\lambda}_o{\times}0.48{\lambda}_o{\times}0.25{\lambda}_o$ produced a measured ${\mid}S_{11}{\mid}$<-10 dB bandwidth of 1.05-1.79 GHz and a measured 3-dB AR bandwidth of 1.12-1.64 GHz. It also showed right-hand CP radiation with a small gain variation (${\pm}0.3dB$) and high radiation efficiency (>93%) over the operational bandwidth.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2005년도 하계학술대회
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• pp.427-430
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• 2005

A multi-code biorthogonal code keying (MBCK) system consists of multiple waveform coding blocks, and the sum of output codewords is transmitted. Drawback of MBCK is that it requires amplifier with high linearity because its output symbol is multi-level. MBCK with constant amplitude precoding block (CA-MBCK) has been proposed, which guarantees sum of orthogonal codes to have constant amplitude. The precoding block in CA-MBCK is a redundant waveform coder whose input bits are generated by processing the information bits. Redundant bits of constant amplitude coded CA-MBCK are not only used to make constant amplitude signal but also used to improve the BER performance at the receiver. In this paper, we proposed a transmission scheme which combines CA-MBCK with $Q^2PSK$ modulation to improve bandwidth efficiency of CA-MBCK and also uses chip interleaving to maintain a constant amplitude feature of CA-MBCK. bandwidth efficiency of a proposed transmission scheme is increased fourfold. And the BER performance of the scheme is same as that of CA-MBCK.

• 한국전기전자재료학회논문지
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• 제16권7호
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• pp.593-598
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• 2003

In this paper, 3rd overtone mode energy-trapped filter using modified PbTiO$_3$ system ceramics was manufactured to apply for intermediate frequency(IF) SMD type fillet with splitted electrode and gap size. To investigate the effects of splitted electrode and gap size on filter characteristics of 3rd overtone mode energy-trapped filter, ceramic wafers were fabricated by etching splitted rectangular electrode size(b$\times$d) of b=0.4, 0.6, 0.8, 1mm, d=0.3, 0.4, 0.5, 0.6mm and gap size(c) c=0.2, 0.3, 0.4, 0.6mm, respectively. And then, SMD type ceramic filter were fabricated with the size of 3.7$\times$3.1$\textrm{mm}^2$. SMD type ceramic filter with the size of b=0.8mm, d=0.4mm and gap(c)=0.4mm, which showed insertion loss of 2.951dB, 3dB bandwidth of 54.7kHz and 20dB stop bandwidth of 129.27kHz, was suitable for IF bandpass filter application.

• 로봇학회논문지
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• 제11권2호
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• pp.92-99
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• 2016

An electro-hydraulic actuator (EHA) is widely used in industrial motion systems and the increasing bandwidth of EHA position control is important issue. The model-inverse feedforward controller is known to extend the bandwidth of system. When the system has non-minimum phase (NMP) zeros, direct model inversion makes system unstable. To overcome this problem, an approximate model-inverse method is used. A representative approximate model inversion method is zero phase error tracking control (ZPETC). However, if zeros locate right half plane of z-plane, the approximate inverse model amplifies the high-frequency response. In this paper, to solve the problem of ZPETC, an adaptive model-inverse control is proposed. The adaptive algorithm updates feedforward term in real-time. The effectiveness of the proposed adaptive model-inverse position control strategy is verified by comparison with typical proportional-integral (PI) control and feedforward control by experiments. As a result, the proposed adaptive controller extends the bandwidth of EHA position control.

• 한국정보통신학회논문지
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• 제8권3호
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• pp.586-597
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• 2004

MAC (Medium Access Control) protocol is necessary for a OLT (Optical Line Termination) to allocate bandwidth to ONUs (Optical Network Units) dynamically in ATM PON (Passive Optical Network) operated in a kind of optical subscriber network having tree topology. The OLT collect information about ONUs and provide all permission with each ONU effectively by means of MAC protocol. Major functions of MAC protocol are composed of the algorism for distributing permission demanded by a ONU dynamically and allocation all permission used in APON properly. Sometimes MAC get to be a element of limiting the whole operation speed and occupy a most frequent operation part of the TC (Transmission Convergence) function module so it have to be designed to guarantee the best quality for each traffic. This paper introduce the way of implementation of a algorism which satisfy all of the upper renditions. This MAC algorism allocate bandwidth according to a number of working ONU and the information of the queue length dynamically and distribute permission for same interval to minimize delay variation of each ONU cell. MAC scheduler for the dynamic bandwidth allocation which is introduced in this paper has look-up table structure that makes programming possible. This structure is very suitable for implementation and operated in high speed because it require very simple and small chip size.

• 인터넷정보학회논문지
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• 제4권5호
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• pp.61-68
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• 2003

본 논문에서는 PRMA의 구조를 사용하여 ABR 형태의 데이터 서비스를 수행할 수 있는 알고리즘을 도입하므로서 그 개념을 확장하고, 채널의 이용효율을 극대화하도록 설계된 무선 MAC 알고리즘인 APRMA를 제안한다. 기존의 PRMA에서는 랜덤 데이터를 전송하고자 하는 단말들은 슬롯을 예약한 수 없다. 즉, 슬롯의 예약은 시간 지연에 엄격한 음성에만 국한된다. 그러나 데이터들도 요구하는 서비스 품질을 만족시켜주어야 하며, 이를 위해 데이터에 대해서도 예약을 가능하게 하므로서 채널의 처리율도 높일 수 있다. 따라서, APRMA에서는 초기에는 최소한의 대역만을 할당해주며, 잉여의 대역이 존재하면 계속 그 전송율을 높여나갈 수 있게 하므로서 채널의 이용율을 높이고, 음성과 같은 상대적으로 우선순위가 높은 서비스 요청에 대해서도 동시에 그 서비스 품질을 만족시킬 수 있다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제2권6호
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• pp.333-351
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• 2008

Transmission control protocols have to overcome common problems in wireless networks. TCP employing both packet loss discrimination mechanism and available bandwidth estimation algorithm, known as the good existing solution, shows significant performance enhancement in wireless networks. For instance, TCP New Jersey which exhibits high throughput in wireless networks intends to improve TCP performance by using available bandwidth estimation and congestion warning. Even though it achieves 17% and 85% improvements in terms of goodput over TCP Westwood and TCP Reno, respectively, we further improve it by exploring maximized available bandwidth estimation, handling bit-error-rate error recovery, and effective adjustment of sending rate for retransmission timeout. Hence, we propose TCP NJ+, showing that for up to 5% packet loss rate, it outperforms other TCP variants by 19% to 104% in terms of goodput when the network is in bi-directional background traffic.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권10호
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• pp.4977-4996
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• 2016

The existence of excessively large and too filled network buffers, known as bufferbloat, has recently gained attention as a major performance problem for delay-sensitive applications. Researchers have made three types of suggestions to solve the bufferbloat problem. One is End to End (E2E) congestion control, second is deployment of Active Queue Management (AQM) techniques and third is the combination of above two. However, these solutions either seem impractical or could not obtain good bandwidth utilization. In this paper, we propose a Transmission Control Protocol（TCP）delayed window update mechanism which uses a congestion detection approach to predict the congestion level of networks. When detecting the network congestion is coming, a delayed window update control strategy is adopted to maintain good protocol performance. If the network is non-congested, the mechanism stops work and congestion window is updated based on the original protocol. The simulation experiments are conducted on both high bandwidth and long delay scenario and low bandwidth and short delay scenario. Experiment results show that TCP delayed window update mechanism can effectively improve the performance of the original protocol, decreasing packet losses and queuing delay while guaranteeing transmission efficiency of the whole network. In addition, it can perform good fairness and TCP friendliness.

• 한국정보통신학회논문지
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• 제11권4호
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• pp.833-839
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• 2007

지속적인 데이터 전송이 필요한 센서네트워크의 경우 센서 노드가 증가할수록 네트워크의 요구 대역폭도 증가하게 되어 상대적으로 고속의 데이터 처리 및 전송이 필요하다. 본 논문에서는 이중채널 라우터를 사용하는 센서 네트워크에서 연속적인 데이터 스트림의 전송 속도를 최대화하기 위하여 여러 센서 노드로부터 싱크노드로의 다중경로를 설정하는 라우팅 알고리즘을 개발하고 제안하였다. 또한, 지그비 통신 모듈을 사용하는 이중채널 라우터에서 제안한 다중경로 알고리즘의 성능을 분석하였다. 실험을 통해 실제 통신 속도를 측정한 결과, 일반적인 단일 채널 라우터의 전송 성능의 2배에 가까운 150kbps 이상의 전송률을 안정적으로 얻을 수 있음을 확인하였다.

• ETRI Journal
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• 제41권2호
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• pp.167-175
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• 2019

A wideband dual-polarized antenna coupling cross resonator is proposed for LTE700/GSM850/GSM900 base stations. An additional resonance is introduced to obtain strong coupling between the dipole and resonator. Moreover, the input impedance of the proposed antenna is steadily close to $50{\Omega}$, which results in better impedance matching. Therefore, a wide bandwidth can be achieved with multiresonance. A prototype is fabricated to verify the proposed design. The measured results show that the antenna has a fractional bandwidth of 35.7% from 690 MHz to 990 MHz for ${\mid}S_{11}{\mid}$ < -15 dB. Stable radiation patterns as well as gain are also obtained over the entire operating band. Moreover, a five-element antenna array with an electrical downtilt of $0^{\circ}$to $14^{\circ}$ is developed for modern base station applications. Measurement shows that a wide impedance bandwidth of 34.7% (690 MHz to 980 MHz), stable HPBW (3-dB beamwidth) of $65{\pm}5^{\circ}$, and high gain of $13.8{\pm}0.6dBi$ are achieved with electrical downtilts of $0^{\circ}$, $7^{\circ}$, and $14^{\circ}$.