Mobile network frequencies

[ravip]

When studying specs of a GSM device one comes across figures like these...

2G Network GSM 850 / 900 / 1800 / 1900

3G Network HSDPA 850 / 900 / 1900 / 2100

4G Network LTE 800 / 850 / 900 / 1800 / 2100 / 2600

My question is how could 3 systems work on the same frequency? Is it a 'regional' thing? or as the 850 spread from 824–849, each system uses a different channel?

e.g. 2G, 3G & 4G all work on 850MHz.

[RichCor]

Here's a slide show that shows the technical side of how it works.

Basically, many of the services can co-exist and share the same frequencies, doing so on a time-share or time-slice basis and detecting their required codec (compression/decompression) algorithms because their based on the same or compatible encoding techniques. Towers usual broadcast all outgoing data highly compressed on a couple of outgoing channels that every device listens to, while client devices uplink at a slower rate (limited by power available for output) on any of a number of pre-assigned channels on a time-share time-slice basis.

Incompatible technologies have to use separate bands. In the US, CDMA/EV-DO is not compatible with GSM/EDGE/W-CDMA(UMTS)/HSPA their newer 3G+ higher-speed variants so the service providers either split up the band or reside on different bands when in use in the same geographical locations.

Then there's LTE.

[lomatopo]

Within each of those designations there are multiple slices of 5 MHz, and each service provider has separate and distinct slices, usually contiguous, for both uplink and downlink. Some refer to this as spectrum.

In the most recent 3G auction here, the NBTC auctioned nine (9) separate bands of 2x5 MHz each (5 MHz for uplink and 5 MHz for downlink, so a total of 90 MHz in the 2100 MHz band), and AIS, DTAC and TrueMove each got three (3) contiguous bands for a total of 15 MHz each.

the NBTC allocated a total of 90MHz (nine lots of 2×5MHz) of UMTS spectrum, consisting of the bands 1920MHz-1965MHz paired with 2110MHz-2155MHz. The regulator divided the bandwidth into nine paired 5MHz slots

AIS paid a bit more for their slices as they wanted to be adjacent to TOT's 2100 MHz.

Service providers are free to offer any mobile voice/data service on their spectrum, hence TrueMove H as offering LTE/4G on some of their 2100 MHz spectrum. Likewise, DTAC is free to offer LTE/4G on their 1800 MHz spectrum, should they wish to do so.