Arthur C Clarke famously said, “Any sufficiently advanced technology is indistinguishable from magic”. Not too many years ago, the concept of pointing an antenna into the air and receiving hundreds or even thousands of megabits per second of data would have seemed like magic.
Of course like any good magic, there is a trick – and for fixed wireless, that trick lies in the placement of transmission sites.
In the communications world, all technologies are based on the simple fundamental concept of a signal-to-noise ratio.
If the noise is higher than the signal, then a communications receiver can’t identify what is signal and what is noise. No information can be passed.
But if the signal is sufficiently greater than the noise, then your link is in business.
In simple terms, the higher the signal-to-noise ratio—or the higher the signal when compared to noise—the greater the scope for putting more and more complex information into the signal.
The Shannon-Hartley theorem describes the maximum amount of information that can be stuffed down a communications channel based on a certain signal-to-noise ratio.
But in any case, a higher signal-to-noise ratio is a good thing. In the wireless world, it means that you can push more information over your links and that they will work reliably.
Ensuring a high signal to noise ratio can be done by increasing the signal, decreasing the noise, or preferably a combination of the two. There is some scope to achieve this through the use of antennas. A large antenna focusses power in one direction, increasing the signal. At the same time, it listens in a tight beam on the same direction, reducing the noise from any locations not in that beam.
The best solution, however, is through the placement of transmission sites.This is particularly important when using class-licensed frequencies that are shared and can be used by others.
Most CBD areas have tall buildings, sometimes hundreds of metres high. They are visible for tens of kilometres away. You might think that these are ideal transmission sites for wireless communications, because they ‘see’ so much. And indeed, there is often a lot of wireless equipment there because there is often high demand for communications services at that location.
But as a rule, they’re not much good for wireless communications.
Why? The signal-to-noise ratio.
Links over a significant distance will have a weaker signal. And there’s a lot of wireless noise in a CBD.
The key to a good wireless service is making links short so that the signal is strong. Ideally, transmission sites will be separated from other wireless users, keeping noise low.
Cirrus Communications actively deploys sites in locations that meet these criteria. It uses licensed spectrum in noisy locations.
If you are looking at a fixed wireless service, ask your provider how many sites they have. That will give you an idea whether they’re serious about quality.