Popular Usable Frequencies in the UK
Frequencies most commonly used for wireless (2.4Ghz and 5Ghz) are generally licence free. However, there are 3 bands for 5Ghz, A, B and C and Band C is a licenced frequency! Band A is typically used for indoor wireless, where Band B and C are used for outdoors. Band C means you can transmit with up to 4W of output power. This means when using a high gain antenna you can send data over longer distances with higher throughputs (Band A allows you to transmit at up to 200mW, Band B means you can transmit up to 1W). All wireless equipment sold I the UK, will ask you to enter a country code as part of the configuration, this will ensure that you are compliant! Ofcom with periodically assess what is going on in the airspace, and it will mean that if you are exceeding these limits, you will be contacted and asked why you are doing so, potentially under caution!
If you were looking to connect two buildings using a wireless bridge with capabilities of 1Gbps, you would most likely be looking to use the 80Ghz frequency. This would mean a licence fee of around £50 per year so the costs are not always particularly huge. Like with most things when it comes to wireless, there are limitations to this frequency, you would only really be able to send these throughputs up to around 5KM. When looking to send over a longer distance with good availability, the 7Ghz frequency is a good choice for quality but when it comes to the licence fee, you could face a bill of thousands of pounds a year. An alternative could be to look at the 13Ghz frequency, you may not achieve 99.999% availability but you would still be able to get a throughputs of up to 200Mbps over distance of around 15KM with a much lower annual fee.