• Title/Summary/Keyword: Band-limited Function

Search Result 43, Processing Time 0.025 seconds

A NOTE ON PROLATE SPHEROIDAL WAVE FUNCTIONS AND PROLATE FUNCTION BASED NUMERICAL INVERSION METHODS

  • Kim, Eun-Joo;Lee, June-Yub
    • Journal of the Korean Society for Industrial and Applied Mathematics
    • /
    • v.12 no.1
    • /
    • pp.41-53
    • /
    • 2008
  • Polynomials are one of most important and widely used numerical tools in dealing with a smooth function on a bounded domain and trigonometric functions work for smooth periodic functions. However, they are not the best choice if a function has a bounded support in space and in frequency domain. The Prolate Spheroidal wave function (PSWF) of order zero has been known as a best candidate as a basis for band-limited functions. In this paper, we review some basic properties of PSWFs defined as eigenfunctions of bounded Fourier transformation. We also propose numerical inversion schemes based on PSWF and present some numerical examples to show their feasibilities as signal processing tools.

  • PDF

PAPR reduction algorithm using Hadamard transform and phase shift in OFDM systems (Hadamard 변환과 위상 천이를 이용한 OFDM 시스템의 PAPR 감소 기법)

  • 구현철
    • Proceedings of the IEEK Conference
    • /
    • 2001.06a
    • /
    • pp.233-236
    • /
    • 2001
  • Orthogonal freqency division multiplexing (OFDM) is an attractive technique for achieving high-bit-rate wireless data transmission. However, the potentially large peak-to-average power ratio (PAPR) has limited its application; An OFDM signal with the large PAPR can cause power degradation (In-band distortion) and spectral spreading (Out-of-band distortion) by being clipped passing through a power amplifier. Thus, we propose the combining algorithm of Hadamard transform and phase shift, which is ascribed to the relation between the correlation of the IFFT input sequence function and PAPR. Extensive computer simulations show that the combining algorithm is an effective technique to reduce PAPR.

  • PDF

Robust seismic waveform inversion using backpropagation algorithm (Hybrid L1/L2 를 이용한 주파수 영역 탄성파 파형역산)

  • Chung, Woo-Keen;Ha, Tae-Young;Shin, Chang-Soo
    • 한국지구물리탐사학회:학술대회논문집
    • /
    • 2007.06a
    • /
    • pp.124-129
    • /
    • 2007
  • For seismic imaging and inversion, the inverted image depends on how we define the objective function. ${\ell}^1$-norm is more robust than ${\ell}^2$-norm. However, it is difficult to apply the Newton-type algorithm directly because the partial derivative for ${\ell^1$-norm has a singularity. In our paper, to overcome the difficulties of singularities, Huber function given by hybrid ${\ell}^1/{\ell}^2$-norm is used. We tested the robustness of our new object function with several noisy data set. Numerical results show that the new objective function is more robust to band limited spiky noise than the conventional object function.

  • PDF

Neural adaptive equalization of M-ary QAM signals using a new activation function with a multi-saturated output region (새로운 다단계 복소 활성 함수를 이용한 신경회로망에 의한 M-ary QAM 신호의 적응 등화)

  • 유철우;홍대식
    • Journal of the Korean Institute of Telematics and Electronics C
    • /
    • v.35C no.1
    • /
    • pp.42-54
    • /
    • 1998
  • For decreasing intersymbol interference (ISI) due to band-limited channels in digitalcommunication, the uses of equalization techniques are necessary. Among the useful adaptive equalization techniques, because of their ease of implementation and nonlinear capabilites, the neural networks have been used as an alternative for effectively dealing with the channel distortion. In this paepr, a complex-valued multilayer percepron is proposed as a nonlinear adaptive equalizer. After the important properties that a suitable complex-valued activation function must possess are discussed, a new complex-valued activation function is developed for the proposed schemes to deal with M-ary QAM signals of any constellation sizes. It has been further proven that by the nonlinear transformation of the proposed function, the correlation coefficient between the real and imaginary parts of input data decreases when they are jointly Gaussian random variables. Lastly, the effectiveness of the proposed scheme is demonstrated by simulations. The proposed scheme provides, compared with the linear equalizer using the least mean squares (LMS) algorith, an interesting improvement concerning Bit Error Rate (BER) when channel distortions are nonlinear.

  • PDF

Implementation of Power Control System for a Long Distance Transmission in Wireless Mesh Network (무선 메쉬 네트워크에서 장거리 전송을 위한 전력제어 시스템 구현)

  • Park, Tae-Jin;Park, Man-Gon
    • Journal of Korea Multimedia Society
    • /
    • v.10 no.4
    • /
    • pp.516-526
    • /
    • 2007
  • Wireless mesh network is not only WLAN technology but it says core technology for implementation of ubiquitous network and we have to application on a various field through connection with the sensor network. However, there are limited to 100mW in the maximum power because WLAN is used into transmission frequency band to ISM band. The mesh network based on WLAN is essential study for a long distance transmission in the limited maximum power that it is doing to cost-efficient network of backbone. Therefore, in this paper, we have presented an conquerable method to limitation of reaching distance of wireless mesh network and made several experiments to presentation the proposed method. The results show that it is possible to rise a long distance transmission and power efficiency into application of various antenna and function definition and implementation of device driver.

  • PDF

GENERALIZED HERMITE INTERPOLATION AND SAMPLING THEOREM INVOLVING DERIVATIVES

  • Shin, Chang-Eon
    • Communications of the Korean Mathematical Society
    • /
    • v.17 no.4
    • /
    • pp.731-740
    • /
    • 2002
  • We derive the generalized Hermite interpolation by using the contour integral and extend the generalized Hermite interpolation to obtain the sampling expansion involving derivatives for band-limited functions f, that is, f is an entire function satisfying the following growth condition |f(z)|$\leq$ A exp($\sigma$|y|) for some A, $\sigma$ > 0 and any z=$\varkappa$ + iy∈C.

Further seismic displacement PSDF results

  • Morales, C.A.
    • Structural Engineering and Mechanics
    • /
    • v.34 no.5
    • /
    • pp.663-666
    • /
    • 2010
  • The spectral content of ground displacement of the 10 largest last California earthquakes is studied. Specifically, the power spectral density function of the critical horizontal-component record of the closest-to-epicenter station is analyzed in each case. The results permit to state that horizontal ground displacement is a narrow-band process. This fact was previously noticed while trying to solve the large-base-displacement problem in isolated structures and it was fundamental in the solution of this issue; however, these preliminary results were limited in number to enable a statement like the foregoing one. Thus, the broader results presented herein were necessary.

A study of Full Width at Half Maximum(FWHM) according to the Filter's Cut off level in SPECT camera (SPECT filter의 cut off level에 따른 반폭치(FWHM) 크기에 관한 연구)

  • Park, Soung-Ock;Kwon, Soo-Il
    • Journal of radiological science and technology
    • /
    • v.26 no.2
    • /
    • pp.63-69
    • /
    • 2003
  • Filtering is necessary to reduce statistical noise and to increase image quality in SPECT images. Noises controled by low-pass filter designed to suppress high spatial frequency in SPECT image. Most SPECT filter function control the degree of high frequency supression by chosing a cut of frequency. The location of cut off frequency determines the affect image noise and spatial resolution. If select the low cut off frequency, its provide good noise suppression but insufficient image quantity and high cut off frequencies increase the image resolution but insufficient noise suppression. The purpose of this study was to determines the optimam cut off level with comparison of FWHM according to cut off level in each kiters-Band-limited, Sheep-logan, Sheep-logan Hanning, Generalized Hamming, Low pass cosine, Parazen and Butterworth filter in SPECT camera. We recorded image along the X, Y, Z-axis with $^{99m}TcO_4$ point source and measured FWHM by use profile curve. We find averaged length is $9.16\;mm{\sim}18.14\;mm$ of FWHM in X, Y, and Z-axis, and Band-limited and Generalized Hamming filters measures 9.16 mm at 0.7 cycle/pixel cut off frequency.

  • PDF

A Lock-Time Improvement for an X-Band Frequency Synthesizer Using an Active Fast-Lock Loop Filter

  • Heo, Yun-Seong;Oh, Hyun-Seok;Jeong, Hae-Chang;Yeom, Kyung-Whan
    • Journal of electromagnetic engineering and science
    • /
    • v.11 no.2
    • /
    • pp.105-112
    • /
    • 2011
  • In phase-locked frequency synthesizers, a fast-lock technique is frequently employed to overcome the trade-off between a lock-time and a spurious response. The function of fast-lock in a conventional PLL (Phased Lock Loop) IC (Integrated Circuit) is limited by a factor of 16, which is usually implemented by a scaling of charge pumper, and consequently a lock time improvement of a factor of 4 is possible using the conventional PLL IC. In this paper, we propose a novel external active fast-lock loop filter. The proposed loop filter provides, conceptually, an unlimited scaling of charge pumper current, and can overcome conventional trade-off between lock-time and spur suppression. To demonstrate the validity of our proposed loop-filter, we fabricated an X-band frequency synthesizer using the proposed loop filter. The loop filter in the synthesizer is designed to have a loop bandwidth of 100 kHz in the fast-lock mode and a loop bandwidth of 5 kHz in the normal mode, which corresponds to a charge pumper current change ratio of 400. The X-band synthesizer shows successful performance of a lock-time of below 10 ${\mu}sec$ and reference spur suppression below -64 dBc.

Study on the safety requirements identification method of the Commuication Based Train Cotrol (무선통신기반 열차제어의 지상무선통신장치 안전요구사항 도출방안에 관한 연구)

  • Lee, Kang-Mi;Shin, Duc-Ko;Lee, Jae-Ho
    • Proceedings of the KSR Conference
    • /
    • 2007.05a
    • /
    • pp.1023-1026
    • /
    • 2007
  • CBTC (Communication Based Train Control) is a railroad system, using wireless communication for data transmission between on-board units and ground units, that makes ground computer periodically collect position and speed data from each train and transmits the preceding train's distance data up to speed limit point so as to make on-board control unit control the optimum train speed. Due to the fact that wireless communication system for train control employs only limited frequency band and output frequency, a number of ground communication units should be installed at track-side; also a running train should carry out Handover function which maintains the communication by accessing a new communication channel of the adjacent on-board communication units in accordance with the output of received radio wave. Especially CBTC is largely dependent on Handoff function between ground communication units. Therefore, this paper provides the method of identification of hazard between ground communication units and on board units.

  • PDF