Radio spectrum is similar to land: it is a finite resource. We cannot generally create new land, and frequencies able to support mobile or wireless communications--radio frequencies--cannot be manufactured at all.
That constraint noted, various technological means are available to increase effective usage of spectrum. Mobile networks increase usage of a fixed amount of spectrum by increasing the amount of reuse: building smaller cells instead of relatively few big cells. By decreasing cell radii by 50 percent, four smaller cells are created where there once was one original cell, allowing four times the use of any fixed amount of radio spectrum.
Spatial division, time division and frequency division are other traditional ways of reusing a fixed amount of spectrum. Newer ways involve licensing mechanisms that allow multiple classes of users (a license holder and other sub-licensees; a license holder and other unlicensed users) to share use of a fixed spectrum resource.
“Listen before talk” protocols allow many unlicensed users of Wi-Fi spectrum to access a finite number of channels. Newer database approaches monitor channels in real time, allowing additional users to transmit when the license holder of record is not using the channels.
Historically, use of smaller cells has arguably driven most mobile industry effective spectrum increase. New spectrum allocations have been the second driver of capacity increases. Some benefit also comes from better signal modulation and radio techniques.
There is a reason so much attention now is being paid to “non-traditional” radio frequencies higher in frequency that have not been used for mobile applications because of poor signal propagation. Above 10 GHz and up to perhaps 300 GHz, point-to-point applications have dominated.
But millimeter (30 GHz to 300 GHz) and teraHertz spectrum (300 GHz to 3000 GHz) is where most of the unassigned radio frequency spectrum remains. Aside from availability, the other issue is that radio frequency and capacity are directly related.
Higher frequencies feature higher capacity. The simple matter is that mobile data rates (capacity or “bandwidth”) increase with frequency because it is precisely frequency that underpins data rates. The faster a radio wave oscillates, the more data it can carry.
In other words, the more times a radio wave oscillates between its +1 and -1 conditions, the more symbols can be represented, all other things being equal.
Spectrum sharing has not been as popular a concept elsewhere in the world as in the United States, but the United Kingdom seems headed towards greater use of spectrum sharing.
The advantages are many. It takes time and costs money to relocate existing users of any spectrum when that resource is reallocated to some new use. Allowing new users and uses when those resources are unused is more efficient. It avoids the effort and cost of moving users to new frequencies.
Spectrum sharing also is a faster way of bringing new capacity to market, as it intensifies use of already-allocated resources without harming the interests of existing license holders.
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