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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 Minimum-shift keying ： ウィキペディア英語版 Minimum-shift keying In digital modulation, minimum-shift keying (MSK) is a type of continuous-phase frequency-shift keying that was developed in the late 1950s and 1960s.〔M.L Doelz and E.T. Heald, ''Minimum Shift Data Communication System'', US Patent 2977417, 1958, http://www.freepatentsonline.com/2977417.html〕 Similar to OQPSK, MSK is encoded with bits alternating between quadrature components, with the Q component delayed by half the symbol period. However, instead of square pulses as OQPSK uses, MSK encodes each bit as a half sinusoid. This results in a constant-modulus signal (constant envelope signal), which reduces problems caused by non-linear distortion. In addition to being viewed as related to OQPSK, MSK can also be viewed as a continuous phase frequency shift keyed (CPFSK) signal with a frequency separation of one-half the bit rate. In MSK the difference between the higher and lower frequency is identical to half the bit rate. Consequently, the waveforms used to represent a 0 and a 1 bit differ by exactly half a carrier period. Thus, the maximum frequency deviation is $\backslash delta\backslash$ = 0.25 ''fm'' where ''fm'' is the maximum modulating frequency. As a result, the modulation index ''m'' is 0.5. This is the smallest FSK modulation index that can be chosen such that the waveforms for 0 and 1 are orthogonal. A variant of MSK called GMSK is used in the GSM mobile phone standard. == Mathematical representation == The resulting signal is represented by the formula $s(t)\; =\; a\_(t)\backslash cos\backslash right)\}\backslash cost)\}-a\_(t)\backslash sin\backslash right)\}\backslash sint\backslash right)\}$ where $a\_(t)$ and $a\_(t)$ encode the even and odd information respectively with a sequence of square pulses of duration ''2T''. $a\_(t)$ has its pulse edges on $t=()$ and $a\_(t)$ on $t=()$. The carrier frequency is $f\_$. Using the trigonometric identity, this can be rewritten in a form where the phase and frequency modulation are more obvious, $$ s(t) = \cos\left(\pi f_c t + b_k(t) \frac + \phi_k\right ) where ''bk(t)'' is +1 when $a\_(t)\; =\; a\_(t)$ and -1 if they are of opposite signs, and $\backslash phi\_k$ is 0 if $a\_(t)$ is 1, and $\backslash pi$ otherwise. Therefore, the signal is modulated in frequency and phase, and the phase changes continuously and linearly. 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「Minimum-shift keying」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.