In order to appreciate the capacity benefits A-MAS software can enable, some background in spectral efficiency may be appropriate.
The radio frequency medium has been used for communications for about a hundred years. When Guglielmo Marconi conducted his first transmissions in 1895, the energy from his spark gap transmitter occupied a huge band of radio spectrum. By 1901, the first Transatlantic transmission blanketed an area of millions of square miles, and was capable of sending a pitifully small amount of information. In fact, using that technology, only about 50 separate conversations, whether broadcast or personal communication, could be accommodated on the surface of the earth.
How things have changed! We can now conduct a million conversations in the usable radio spectrum in one location, assuming that the entire usable spectrum was used for such communications. Of course it isn’t, but compare that with Marconi’s one communication that wasn’t even voice.
A more interesting way to look at the improvement in the way we use the spectrum is to compare the number of “conversations” (voice or data) that can theoretically be conducted over a given area in all of the useful radio spectrum. It turns out that this number has doubled every two-and-a-half years for the past 104 years. This observation was made by Martin Cooper, Chairman Emeritus of ArrayComm, and is dubbed “Cooper’s Law.”
It is certainly remarkable that the rate of improvement in use of the radio spectrum for personal communications has been essentially uniform for 104 years. Further, the cumulative improvement in the effectiveness of personal communications total spectrum utilization has been over a trillion times in the last 90 years, and a million times in the last 45 years.
How was this improvement in the effectiveness of personal communication achieved? The technological approaches can be loosely categorized as:
- Frequency division
- Modulation techniques
- Spatial division
- Increase in magnitude of the usable radio frequency spectrum
How much of the improvement can be attributed to each of these categories? Of the million times improvement in the last 45 years, roughly 25 times were the result of being able to use more spectrum, 5 times can be attributed to the ability to divide the radio spectrum into narrower slices — frequency division. Modulation techniques like FM, SSB, time division multiplexing, and various approaches to spread spectrum can take credit for another 5 times or so. The remaining sixteen hundred times improvement was the result of confining the area used for individual conversations to smaller and smaller areas — what we call spectrum re-use.
The importance of spectrum re-use for making more effective use of the spectrum is even greater than reflected in these figures. Frequency division and the various modulation techniques have yielded about as much as we can ever expect. The gains we get are costly and these gains often compromise voice quality. Shannon’s Law teaches us that there is only so much information that can be delivered in a given bandwidth with a given signal-to-noise ratio.
There is no such limitation on re-use of radio spectrum. We already have a lot of experience with spatial technology in our wireline networks. These networks can be expanded indefinitely by merely running more lines, more bandwidth, to more terminals. Imagine how effective our use of the spectrum would be if we could create a reliable, broadband wireless connection between any two points. And if we further imagine that independent conversations could be conducted to points separated by only a few feet, the potential would exist to increase effectiveness of spectrum use by 10 million times over today’s capabilities. If this happened at a rate of doubling every 2.5 years, it would be another 60 years before we would have the capability of delivering the entire radio frequency spectrum to every single individual — this is the ultimate goal of A-MAS.