science

Very minimum shift keying

Very minimum shift keying is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Very minimum shift keying rather than just read about it. In short: Very minimum shift keying, or VMSK, modulation, is one of several ultra-narrow-band modulation (UNBM) methods indeterminately claimed to send high-speed digital data through very low bandwidth (or narrowband) channels. VMSK is a type of phase-shift keying, not related to minimum shift keying.

Key takeaways

Very minimum shift keying belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Very minimum shift keying to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Very minimum shift keying from memory before moving on to harder problems.

Reference excerpt

Very minimum shift keying, or VMSK, modulation, is one of several ultra-narrow-band modulation (UNBM) methods indeterminately claimed to send high-speed digital data through very low bandwidth (or narrowband) channels. VMSK is a type of phase-shift keying, not related to minimum shift keying.

Claims versus analysis 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 "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; however, VMSK, like all ultra-narrow band modulation methods uses negative- or zero-delay filters. Walker claims that with VMSK, "Efficiencies up to 15 bits/s/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 Tomazic) 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", regardless of the filter used.

Personalities VMSK is promoted primarily by H. R. Walker, owner of the "Welcome to the Ultra Narrowband Club" website, and author of several papers and publications on the arguments. Mr. Walker has written about his ideas in telecommunications sector publications such as Microwaves & RF, as well as in a co-authored book chapter.

Legal issues It was reported in 2000 that "AlphaCom Communications holds patent rights to the non-Nyquist filters and other aspects of VMSK and VMSK/2 technology. The company claimed to have secured these rights as a result of a contract with H.R. Walker, doing business as Pegasus Data Systems, to purchase the patents and fund further R&D. AlphaCom defaulted on the contract and a legal dispute over ownership arose. A 2003 Securities and Exchange Commission charge against AlphaCom and its principals alleges that "defendants raised these funds by falsely representing that AlphaCom owned exclusive rights to novel Internet technologies, Network Utilities (NU) and Very Minimal Shift Keying (VMSK), that were supposed to increase Internet downloading speeds and the speed of access to the Internet. Many of these claims could not be supported." In order to avoid further legal costs, Walker agreed to surrender the ownership of the VMSK patents US 5,930,303 and US 6,748,022 to AlphaCom in return for AlphaCom making no further claims against Walker or Pegasus regarding any newer methods. The special near zero group delay filters required are claimed by Walker to be non patentable due to prior publication. In 2002, "Walker said the company (Pegasus Data Systems) was delayed when one of its financial backers (AlphaCom) went out of business in late 2000. Now armed with new backers, the company is again moving forward with a new method, he said." In 2007, Compress Technologies, Inc., announced on their web site that they had "acquired VMSK Technology." Their domain name has since been acquired by someone else.

References

External links Welcome to the Ultra Narrowband Club Archived 2005-02-14 at the Wayback Machine VMSK developer's website

Worked examples

Example 1 — a first encounter with Very minimum shift keying

Start with the simplest possible case. Write down what Very minimum shift keying claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Very minimum shift keying before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Very minimum shift keying ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Very minimum shift keying

In research: Very minimum shift keying appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Very minimum shift keying in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Very minimum shift keying is common in secondary-school and first-year university syllabi. It links to neighbouring topics Pseudoscience, Quantized radio modulation modes, so understanding it makes those chapters shorter.
In everyday life: Look for Very minimum shift keying outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Very minimum shift keying in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Very minimum shift keying means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Very minimum shift keying out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Very minimum shift keying in simple terms?

Why does Very minimum shift keying matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Very minimum shift keying?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Very minimum shift keying.