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VMSK, for very minimum shift keying modulation, is one of several "ultra narrow-band modulation" (UNBM) methods claimed to send high-speed digital data through very low bandwidth (or narrowband) channels. VMSK is a variant of phase-shift keying, not related to minimum shift keying. ==Claims versus analysis== The Facts: VMSK was introduced in 1998 as a Cellular Telephone modulating method. Hardware was sent to and tested by Vodafone, Sprint and AT&T. The method was reported on favorably by Dr. William C.Y. Lee, V.P. of Vodafone Airtouch, in “Lee’s Essentials of Wireless Communications”, McGraw Hill 2001. There have been individuals who have made an analysis based on 'positive' group delay filters that claim the method does not work. VMSK, like all Ultra Narrow Band modulation methods uses 'negative' or 'zero' delay filters, therefore their analysis should be disregarded. The Fantasy: Walker claims that with VMSK, "Efficiencies up to 15 bits/sec/Hz are now being achieved in usable hardware with C/N ratios better than that obtainable using FM, BPSK or QPSK." Analysis by third parties ( Karn and Tomasic ) have concluded that "no ultra narrow band modulation (UNBM) method, which includes very minimum shift keying (VMSK) and VPSK, can have substantially greater efficiency than conventional methods." On a spectrum analyzer, a VMSK signal looks narrow. However, the actual bandwidth required to avoid interference is much wider. One analyst says "the spectral efficiency claims being made for VMSK are hogwash", which they are if the wrong filter is used.〔Phil Karn. (The VMSK Delusion ). Phil Karn's analysis of ultra narrowband claims.〕 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「Very minimum shift keying」の詳細全文を読む スポンサード リンク
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