• 한국ITS학회:학술대회논문집
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• 한국ITS학회 2010년도 춘계학술대회
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• pp.53-55
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• 2010

• ETRI Journal
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• 제29권5호
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• pp.676-678
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• 2007

In this letter, we propose a cognitive ultra-wideband radio scheme which is based on a modified chirp waveform. Therefore, it requires only time domain processing in the cognitive radio systems and reduces system complexity and power consumption.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 C
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• pp.2386-2388
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• 2005

As anti-crash and pre-crash systems in vehicles become more extensively used, the need for high performance short-range radars is playing an increasing role. This paper presents the design of a micromachined, ultra-wideband beamformer centered at 24 GHz for automotive short-range radar systems. This beamformer is a Butler matrix designed using ultra-wideband transmission-line couplers, which consist of a multilayered structure that exhibits wider bandwidth compared to conventional microstrip branch-line couplers. The circuit has been designed on a quartz substrate, and to achieve the desired coupling, lines suspended on BCB layers located at specific parts of the circuit were used, achieving a three metal layered structure in form of wide microstrips, that give low loss and a wideband response. In this paper the design and fabrication procedure of the proposed beamformer are fully described.

• Journal of Communications and Networks
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• 제9권4호
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• pp.482-489
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• 2007

In this paper, two frequency domain signal processing techniques for pulse shape modulation(PSM) ultra wideband(UWB) systems are presented. Firstly, orthogonal detection of UWB PSM Hermite pulses in frequency domain is addressed. It is important because time domain detection by correlation-based receivers is severely degraded by many sources of distortion. Pulse-shape, the information conveying signal characteristic, is deformed by AWGN and shape-destructive addition of multiple paths from the propagation channel. Additionally, because of the short nature of UWB pulses, timing mismatches and synchronism degrade the performance of PSM UWB communication systems. In this paper, frequency domain orthogonality of the Hermite pulses is exploited to propose an alternative detection method, which makes possible efficient detection of PSM in dense multipath channel environments. Secondly, a ranging method employing the Cepstrum algorithm is proposed. This method is partly processed in the frequency domain and can be implemented without additional hardware complexity in the terminal.

• ETRI Journal
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• 제32권1호
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• pp.44-52
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• 2010

Ultra-wideband (UWB) systems have witnessed a debate over whether they may cause interference to other existing and future narrowband systems sharing their band of operation. The detect and avoid (DAA) mechanism was developed as a solution to reduce interference to narrowband systems in order to ease regulatory concerns. It works by adaptively reducing the transmitted power at the overlapping bands upon detecting an active narrowband link. However, employing DAA degrades the performance of UWB transmissions. In this paper, we present the Korean UWB regulations as an example of regulations that require DAA in certain bands. We investigate DAA's impact on performance and propose a method to mitigate it, which provides UWB with the more efficient support of the DAA mechanism and enables it to avoid a larger number of narrowband users while sustaining the data rate. Results show significant improvement in performance with the application of our technique compared to conventional performance.

• 한국전자파학회논문지
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• 제19권8호
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• pp.913-919
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• 2008

본 논문에서는 밀리미터파 시스템에 응용이 가능한, 마이크로스트립으로 급전되는 초광대역 테이퍼 슬롯 안테나의 새로운 설계법을 제시하고 그 실험결과를 보여주고 있다. 초광대역 특성을 가지는 마이크로스트립-CPS 전이 구조 혹은 발룬을 적용하여 테이퍼 슬롯 안테나 고유의 초광대역 특성을 얻었고, 안테나와 발룬의 연결은 임피던스 정합의 방법을 이용함으로 테이퍼 슬롯 안테나 설계를 간단하게 하였다. 테이퍼 슬롯 안테나 설계에는 페르미-디락(Fermi-Dirac) 테이퍼 함수와 corrugation을 적용하였다. 제안된 안테나는 23 GHz에서 58 GHz까지의 초광대역 주파수 특성을 가졌으며, 12에서 14 dBi의 비교적 높고 평탄한 이득과 낮은 부엽 레벨을 가졌다. 또한, 4개의 소자로 이루어진 간단한 선형 배열 안테나를 통하여 광대역 위상 배열 및 밀리미터파 센서에 응용될 수 있음을 보였다.

• 한국통신학회논문지
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• 제32권8A호
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• pp.836-846
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• 2007

유비쿼터스 사회가 도래함에 따라 모든 사회가 무선통신과 밀접한 연관성을 가지게 되었다. 하지만 늘어나는 주파수 수요는 주파수 자원의 고갈을 야기하였다. 이와 같이 주파 주파수 자원의 중요성이 부각되어 주파수 공유 기술이 필요하게 되었다. 제안한 Cognitive UWB 시스템은 넓은 주파수 대역을 사용하는 UWB(Ultra Wideband) 기술과 채널 환경을 인지하여 사용하지 않는 비어있는 주파수 대역을 이용하는 CR(Cognitive Radio) 기술이 합해진 기술이다. 본 논문에서는 Cognitive UWB 시스템의 세부 기술을 설명하고 시뮬레이션을 통하여 원하는 마스크를 충족시키고 타 시스템의 간섭을 회피하여 성능향상을 보였다.

• Journal of Communications and Networks
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• 제8권2호
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• pp.151-157
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• 2006

In a continuously expanding wireless world, the number of radio systems increases every day and efficient spectrum usage becomes a more significant requirement. Ultra-wideband (UWB) and cognitive radio are two exciting technologies that offer new approaches to the spectrum usage. The main objective of this paper is to shed the first light on the marriage of these two important approaches. The strength of orthogonal frequency division multiplexing (OFDM) based UWB in co-existing with licensed systems is investigated. The opportunity concept is defined, and the requirements of the opportunistic spectrum usage are explained. It is proposed to take the UWB-OFDM from the current underlay implementation, and evolve it to a combined underlay and opportunistic spectrum usage technology, leading to cognitive UWB-OFDM. This way, we aim at making UWB more competitive in the wireless market with extended range, higher capacity, better performance, and a wide variety of applications.

• Journal of Advanced Marine Engineering and Technology
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• 제32권4호
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• pp.603-610
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• 2008

In this paper, analytical methods for calculating the average probability of bit error of direct sequence pulse amplitude modulation ultra wideband (DS-PAM UWB) system and time hopping pulse position modulation ultra wideband (TH-PPM UWB) system are given. For the multi-user DS-PAM UWB system, the bipolar pulse amplitude modulation is used in order to achieve better performance. As we know, more attention is paid to the TH-PPM UWB systems recently. In this paper. we first introduce the accurate BER calculation methods of the multi-user DS-PAM UWB and TH-PPM UWB systems and then give the performance analysis over the ideal AWGN channel and a correlation receiver. Furthermore, we also introduce their applications in image transmission and data transmission and give the simulation results. The analytical method yields simple and exact formulas relating the performance to the system parameters.

• ETRI Journal
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• 제31권4호
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• pp.472-474
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• 2009

In this letter, an ordered successive interference cancellation (OSIC) scheme is applied for multiple-input multiple-output (MIMO) detection in ultra-wideband (UWB) communication systems. The error rate expression of an OSIC receiver on a log-normal multipath fading channel is theoretically derived in a closed form solution. Its bit error rate performance is analytically compared with that of a zero forcing receiver in the UWB MIMO detection scheme followed by RAKE combining.