• Journal of Communications and Networks
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• 제5권4호
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• pp.374-385
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• 2003

The growing interest towards ultra-wideband (UWB) communications stems from its unique features such as baseband operation, ample multipath diversity, and the potential of enhanced user capacity. But since UWB has to overlay existing narrowband systems, multiple access has to be achieved in the presence of narrowband interference (NBI). However, existing baseband spreading codes for UWB multiple access are not flexible in handling NBI. In this paper, we introduce two novel spreading codes that not only enable baseband UWB multiple access, but also facilitate flexible NBI cancellation. We construct our codes using a single carrier or multiple carriers (SC or MC), which can be implemented with standard discrete-cosine transform (DCT) circuits. With our SC/MC codes, NBI can be avoided by simply nulling undesired digital carriers. Being digital, these SC/MC codes give rise to multiband UWB systems, without invoking analog carriers. In addition, our SC/MC codes enable full multipath diversity, and maximum coding gains. Equally attractive is their capability to reduce the number of interfering users, with simple matched filter operations. Comprehensive simulations are also carried out to corroborate our analysis.

• Journal of Communications and Networks
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• 제5권4호
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• pp.365-373
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• 2003

This paper investigates the performance of M-ary pulse position modulation (PPM) multiuser ultra-wideband (UWB) communication systems in terms of symbol error rate (SER) over fading and additive white Gaussian noise (AWGN) channel. Based on Gaussian approximation for the multiple access interference, an expression for the signal-to-noise ratio (SNR) is derived for the UWB system. This expression is used to derive exact SER expressions for coherent UWB receivers. The effect of pulse selection on the SER of multiuser UWB system is studied. In addition to rectangular pulse, the 2nd derivative Gaussian waveform and Rayleigh pulses were considered. We show that the system capacity and/or SER performance can be significantly increased by using the monocycle pulse in fading channels.

• Journal of Communications and Networks
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• 제5권4호
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• pp.328-343
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• 2003

Orthogonal pulse-shape modulation using Hermite pulses for ultra-wideband communications is reviewed. Closedform expressions of cross-correlations among Hermite pulses and their corresponding transmit and receive waveforms are provided. These show that the pulses lose orthogonality at the receiver in the presence of differentiating antennas. Using these expressions, an algebraic model is established based on the projections of distorted receive waveforms onto the orthonormal basis given by the set of normalized orthogonal Hermite pulses. Using this new matrix model, a number of pulse-shape modulation schemes are analyzed and a novel orthogonal design is proposed. In the proposed orthogonal design, transmit waveforms are constructed as combinations of elementary Hermites with weighting coefficients derived by employing the Gram-Schmidt (QR) factorization of the differentiating distortion model’s matrix. The design ensures orthogonality of the vectors at the output of the receiver bank of correlators, without requiring compensation for the distortion introduced by the antennas. In addition, a new set of elementary Hermite Pulses is proposed which further enhances the performance of the new design while enabling a simplified hardware implementation.

• 한국통신학회논문지
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• 제26권7B호
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• pp.1021-1033
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• 2001

본 논문에서는 초광대역 시간 도약 임펄스 무선 전송 (ultra wideband time hopping impulse radio) 다원 접속 시스템을 위한 잡음 부호 기반의 새로운 시간 도약 시퀀스를 제안한다. 임펄스 무선 전송 시스템에 대한 지금까지의 연구에서는 대부분 이상적인 랜덤 시간 도약 시퀀스를 사용하여 여러 사용자가 다원 접속한다고 가정하였다. 본 논문에서는 동일 차수의 다수 m-시퀀스와 십진화기를 이용하여 구현 가능한 시간 도약 시퀀스를 제안하고, 여러 사용자의 동기식 및 비동기식 접속 상황에 대한 모의 실험을 통해 이상적인 랜덤 시퀀스와 유사한 우수한 비트오율 성능을 얻을 수 있음을 확인하였다. 또한 제안된 시간 도약 시퀀스를 사용하는 경우 좀 더 일반적인 상황인 비동기식 다원 접속이 동기식 다원 접속에 비해 우수한 성능을 얻을 수 있음을 분석한다.

• Journal of electromagnetic engineering and science
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• 제14권1호
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• pp.31-35
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• 2014

An ultra-wideband (UWB) circular monopole antenna with a multiband-notched characteristic is proposed. The multiband-notched filter consists of three different sized folded slots, which are distinctly assigned for the notched band at the 3.5-GHz WiMAX, 5-GHz WLAN, and 8-GHz ITU bands. The proposed antenna results in a measured ${\mid}S_{11}{\mid}$ < -10 dB, which completely covers the UWB band (3.1 10.6 GHz) with three notched bands at 3.5, 5.5, and 8.0 GHz. The antenna yields an omnidirectional radiation pattern and high radiation efficiency.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권2호
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• pp.524-539
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• 2014

To investigate schemes of secret key generation from Ultra-wideband (UWB) channel, we study a statistical characterization of UWB outdoor channel for a campus playground scenario based on extensive measurements. Moreover, an efficient secret key generation mechanism exploiting multipath relative delay is developed, and verification of this algorithm is conducted in UWB Line-of-sight (LOS) outdoor channels. For the first time, we compare key-mismatch probability of UWB indoor and outdoor environments. Simulation results demonstrate that the number of multipath proportionally affects key generation rate and key-mismatch probability. In comparison to the conventional method using received signal strength (RSS) as a common random source, our mechanism achieves better performance in terms of common secret bit generation. Simultaneously, security analysis indicates that the proposed scheme can still guarantee security even in the sparse outdoor physical environment free of many reflectors.

• ETRI Journal
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• 제32권2호
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• pp.333-335
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• 2010

This letter proposes a non-coherent blind time-of-arrival (TOA) estimation scheme for impulse radio ultra-wideband systems. The TOA estimation is performed in two consecutive phases: the Rayleigh-quotient theorem-based coarse-signal acquisition (CSA) and the iterative-threshold-test-based fine time estimation (FTE). The proposed scheme serves in a blind manner without demanding any a priori knowledge of the channel and the noise. Analysis and simulations demonstrate that the proposed scheme significantly increases the signal detection probability in CSA and ameliorates the TOA estimation accuracy in FTE.

• ETRI Journal
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• 제29권3호
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• pp.322-328
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• 2007

We propose a direct-sequence pulse-amplitude modulation (DS-PAM) ultra-wideband (UWB) system which employs a non-linear chirp waveform instead of the conventional Gaussian monocycle in this paper. In the approved frequency for UWB, there exist myriad narrowband interferers. Specifically, we focus on the mutual interference between UWB systems and 802.11a WLAN. This paper offers a method to suppress this in-band narrowband interference by introducing a kind of non-linear chirp waveform. Using the proposed non-linear chirp waveform, the effects of one or more narrowband interference sources with different frequencies can be suppressed. System performance of UWB systems in the narrowband interference environment can be improved. Computer simulations with additive white Gaussian noise successfully demonstrate an increase in performance with the proposed system as compared to traditional linear chirp systems.

• ETRI Journal
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• 제35권3호
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• pp.397-405
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• 2013

In this paper, two sets of spectrally efficient ultra-wideband (UWB) pulses using zinc and frequency-domain Walsh basis functions are proposed. These signals comply with the Federal Communications Commission (FCC) regulations for UWB indoor communications within the stipulated bandwidth of 3.1 GHz to 10.6 GHz. They also demonstrate high energy spectral efficiency by conforming more closely to the FCC mask than other UWB signals described in the literature. The performance of these pulses under various modulation techniques is discussed in this paper, and the proposed pulses are compared with Gaussian monocycles in terms of spectral efficiency, autocorrelation, crosscorrelation, and bit error rate performance.

• 한국전자파학회지:전자파기술
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• 제3권1호
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• pp.11-19
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• 1992

본 연구에서는 초광대역증폭기를 설계하고자 GaAs MESFET 소신호 동가회로에 인덕터 피킹소자를 첨가하여 캐패시턴스의 영향을 감소시키는 주파수 피킹현상에 대하여 분석하였다. GaAs MESFET의 소신호 둥가회로의 전달함수로 부터 인턱터 피킹소자의 최적값을 유도하였으며, 매 우 균일이득을 갖는 귀환증폭모듈을 실현하였다. 실 주파수법에 의하여 입력과 출력단의 엄피던스정합회로를 설계하여 초광대역 마이크로파증폭기를 구현하였으며 컴퓨터 시률레이션에 의하여 셜계된 증폭기의 이득의 오차는 O.lGHz-12GHz에서 O.56dB의 매우 균일한 이득을 얻을 수 있었다.