Very minimum shift keying

Lore & Background

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 William C.Y. Lee, V.P. of Vodafone Airtouch, in a 2001 publication. H. R. Walker, owner of the 'Welcome to the Ultra Narrowband Club' website, has promoted VMSK through papers and publications in telecommunications sector magazines and a co-authored book chapter. Walker has claimed that with VMSK, efficiencies up to 15 bits/s/Hz are being achieved in usable hardware with carrier-to-noise ratios better than those obtainable using FM, BPSK or QPSK.

Analysis by third parties (Karn and Tomazic) concluded that no ultra narrow band modulation method, including VMSK, can have substantially greater efficiency than conventional methods. On a spectrum analyzer, a VMSK signal appears narrow, but the actual bandwidth required to avoid interference is much wider. One analyst stated that the spectral efficiency claims for VMSK are unsupported, regardless of the filter used. Individuals have made analyses based on positive group delay filters claiming the method does not work; however, VMSK uses negative- or zero-delay filters.

Reader's Guide

VMSK's significance lies in its status as a prominent example of ultra-narrow-band modulation, a category that has generated both strong claims and strong rebuttals. The method attracted attention from major telecommunications companies and was endorsed in a well-known reference work, yet independent analysis concluded it cannot achieve substantially greater efficiency than conventional methods. The legal history surrounding VMSK includes a dispute over patent ownership between H. R. Walker and AlphaCom Communications, which ended with Walker surrendering patent rights to avoid further legal costs. AlphaCom later faced a Securities and Exchange Commission charge alleging false representations about VMSK's capabilities. The special near zero group delay filters required for VMSK are claimed by Walker to be non-patentable due to prior publication. Despite ongoing promotion by its developer, the method remains controversial, with critics arguing that its apparent narrow bandwidth on a spectrum analyzer is misleading and that the actual occupied bandwidth is much wider. The legacy of VMSK is that of a technically disputed modulation scheme whose claims have not been broadly accepted by the engineering community.

Did You Know?

• A 2003 SEC charge alleged false representations about VMSK's capabilities.
• The special filters required are claimed to be non-patentable due to prior publication.