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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Nyquist ISI criterion ： ウィキペディア英語版 Nyquist ISI criterion In communications, the Nyquist ISI criterion describes the conditions which, when satisfied by a communication channel (including responses of transmit and receive filters), result in no intersymbol interference or ISI. It provides a method for constructing band-limited functions to overcome the effects of intersymbol interference. When consecutive symbols are transmitted over a channel by a linear modulation (such as ASK, QAM, etc.), the impulse response (or equivalently the frequency response) of the channel causes a transmitted symbol to be spread in the time domain. This causes intersymbol interference because the previously transmitted symbols affect the currently received symbol, thus reducing tolerance for noise. The Nyquist theorem relates this time-domain condition to an equivalent frequency-domain condition. The Nyquist criterion is closely related to the Nyquist-Shannon sampling theorem, with only a differing point of view. ==Nyquist criterion== If we denote the channel impulse response as $h(t)$, then the condition for an ISI-free response can be expressed as: : for all integers $n$, where $T\_s$ is the symbol period. The Nyquist theorem says that this is equivalent to: :$\backslash frac\; \backslash sum\_^\; H\; \backslash left(\; f\; -\; \backslash frac\; \backslash right)\; =\; 1\; \backslash quad\; \backslash forall\; f$, where $H(f)$ is the Fourier transform of $h(t)$. This is the Nyquist ISI criterion. This criterion can be intuitively understood in the following way: frequency-shifted replicas of ''H(f)'' must add up to a constant value. In practice this criterion is applied to baseband filtering by regarding the symbol sequence as weighted impulses (Dirac delta function). When the baseband filters in the communication system satisfy the Nyquist criterion, symbols can be transmitted over a channel with flat response within a limited frequency band, without ISI. Examples of such baseband filters are the raised-cosine filter, or the sinc filter as the ideal case. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Nyquist ISI criterion」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.