In an earlier post titled “The dark secret of mobile broadband wireless” I briefly mentioned a recent invention called SMax. Because a number of readers wanted to know more about this, I am posting here a brief introduction.
SMax is a revolutionary new invention in wireless communication based on a surprisingly simple idea. As is well known conventional communication systems are all based on the transmission of sinusoidal signals. These sinusoidal signals are modulated in different ways to convey information. Sinusoidal waves have dominated communications for about a hundred years. However, a few original thinkers have attempted to break away from this tradition and advocate non-sinusoidal waves. The best known of these pioneers is Henning F. Harmuth whose work on non-sinusoidal waves and square waves in particular was developed in the early 1960’s. There is an extensive literature on Harmuth’s work, we list here only a few key references:
1. Harmuth H. F., A Generalized Concept of Frequency and Some Applications, IEEE Transactions on Information Theory, Vol. 14, No. 3, May 1968, Page(s): 375-382
2. Harmuth H. F., Historical Background and Motivation for the Use of Nonsinusoidal Functions, Introduction, Transmission of Information by Orthogonal Functions, Second Edition, Springer Verlag, 1972
3. Harmuth H. F., Frequently Raised Objections, Electromagnetic waves with general time variation, Excerpt, Sequency Theory-Foundation and Applications, Academic Press, Inc., 1977
4. Harmuth H. F., Nonsinusoidal Waves for Radar and Radio Communications, Academic Press, New York,1981
5. Harmuth H. F., Antennas and Wave Guides for Nonsinusoidal Waves, Academic Press, New York, 1984
SMax has taken Harmuth’s work an important step further by developing a practical wireless communication system which can work in the same frequency channels as conventional communication systems without mutual interference. This makes it possible to re-use the spectrum currently occupied by existing wireless systems. More specifically, SMax makes it possible to effectively quadruple the capacity of the existing spectrum.
At the heart of this invention is the SMax filter, which attenuates sinusoidal waves while passing through unattenuated square wave signal. This is illustrated in the following figure.
At the filter input we have a mixture of sinusoidal and square waves. At the filter output we have an essentially clean square wave, having attenuated the sinusoidal waves by 50 dB or more. The design of this filter was the key breakthrough of our invention. We can not discuss it in any detail for obvious IP protection reasons. We can say however that this is a special non-linear and time-varying filter. It is well known that conventional filters, which are linear and time-invariant, can not effectively separate square waves from sinusoids. If one attempts to use a standard filter this would simply not work. Our filter is the “secret sauce” of the SMax technology.
Note that the square wave is smaller (i.e. weaker) than the sinusoidal waves. The idea is to transmit these square waves at sufficiently low power so that they will not interfere with existing conventional communication systems. In effect our square wave “whispers” among the sinusoids. Because the SMax filter essentially eliminates interference, the SNR at the filter output is sufficiently high so that reliable detection is possible. This works especially well in cellular systems which are interference dominated, where the thermal noise is not the limiting factor.
Information is transmitted by modulating the square wave in one of several ways. The simplest is conventional amplitude modulation applied to square waves. For example, we have initially used Squarewave Pulse Amplitude Modulation (SPAM). However, later we have discovered more efficient modulation techniques uniquely tailored for square waves and quite different from conventional modulation techniques. Again, we can not discuss the details without an NDA.
In future posting we will describe in more detail the performance advantages of the SMax system and some of the applications which can greatly benefit from this unique technology.