Many understand that millimeter wave spectrum offers much-higher bandwidths than signals transmitted at low-band and mid-band frequencies. To be sure, we see the confluence of several trends including use of small cells, spectrum aggregation, spectrum sharing, new spectrum and better radios and modulation techniques, each of which helps increase usable bandwidth.
What typically is less well understood is why the increase in bandwidth from millimeter wave frequencies is possible.
The answer lies in the physics of radio waves at different frequencies. Consider a simple explanation. Assume that the ability to code symbols hinges on the oscillation of a radio signal from high to low.
As a simple example, assume that every zero crossing of any wave represents the opportunity to code a bit (one or zero). Using a very simple coding method, the total amount of bits that can be represented in one second of time hinges on the number of oscillations a wave makes over that period of time.
A slightly more complex method able to code on four different amplitudes of a wave would yield four symbols per second.
Of course, modern coding and modulation techniques are far more substantial than that. But looking only at the number of zero crossings per second, millimeter wave spectrum increases potential capacity simply because there are so many more “zero crossings” per second of time.
To the real extent that each oscillation of a radio wave in a second of time dictates the number of symbols which can be represented, increasing the number of oscillations necessarily increases the potential symbol representation, whether the coding uses signal amplitude or phase modulation.
That also means radio channels can be much higher. Where 2G and 3G channels might have used as little as 5 MHz, and 4G could use channels of 20 MHz, 5G allows channels that are routinely 100 MHz wide. Wider channels means more bandwidth; more bandwidth more speed.
Roughly speaking, compared to low-band radio signals, millimeter wave spectrum can support at least an order of magnitude higher bandwidth.
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