VMSK/2 Promises 5 Times More Bandwidth

ksan writes "Acording to this article in EDN Magazine; VMSK/2, a new modulation technique may improve modem, FM, AM and other types of transmission. They say that its possible to transmit 100 channels of 128kbps MP3 over an FM channel. Anyone can say more about this?"Read below to find out the *major* problems with this article.

Comments

Re:how they do that?

[mesocyclone]

You can achieve very high spectral efficiencies if you use very high power. To send 2 bits/hz, just send the plain old signal single sideband AM (the bandwidth of a 1kbps baseband signal is 500hz). To send 4 bits/hz, you could (as an example), use four different voltage levels. For5 bits/Hz, use 8 levels, etc. Furthermore, you can modulate phase and amplitude independently. Doubling the data rate again.

There are a myriad of modulation schemes (and related coding schemes) for achieving spectral efficiency. Basically, beyond the simple stuff (filter off the extra sideband, use phase AND amplitude), they achieve that efficiency by encoding data in more subtle aspects of the signal (read: more noise sensitive). This VMSK/2 scheme appears to be one which generates smaller sidebands by modulating the signal less. As such, it requires higher power to achieve it's spectral efficienty (ignore the claims of lower power - that's *per carrier* in the signal, but they use more carriers).

Note also that increased spectral efficiency is only part of the issue. In the modern cellular world, you need increased efficiency in terms of bits per Hz per square kilometer (i.e. you share the frequencies over an area). A requirement for higher power (which really means a requirement for higher signal-to-noise ratio) reduces the areal sharing that you can achieve.

Ultimately, you can't beat Shannon's laws. If you can, you can also make perpetual motion machines and free energy (yeah, it's a stretch, but the connection is there).

Since this company is selling multilevel marketing, I am more than a bit suspicious of any claims. Multilevel marketing schemes are too often fraudulent and based on overblown claims. I am not saying these guys are wrong, just that their approach is suspicious.

As far as comments on here on FM signal bandwidth... FM stations use a 200kHz wide channel. A stereo signal uses a composite of simple FM for the Left+Right signal, and a subcarrier at 42kHz carrying Left-Right. There is still room left in the spectrum for an additional subcarrier (or more) - which is where you find service such as Muzak. Plain old FM mono is a *spread-spectrum* modulation scheme, in that the RF signal is occupies significantly more bandwidth than the modulating signal.