I've just been reading up in detail about how a mobile network works and I have a couple of questions if anyone can help...I can't seem to find out any info online.

Say my phone is communicating with mast A, but mast B in an adjacent cell can also pick up the signal from my phone. What does mast B do with the signal? Does it check and see that my phone is already communicating with mast B and ignore it?

Also, does each mast have to check every single signal it picks up from mobile phones so it can work out whether it has to deal with them or not (eg. it's an EE mast but picks up a signal from a Vodafone mobile)?

Hope it makes sense

Thanks in advance!

I could be wrong, but I think it's the phone that does the searching, not the mast.

ie. If you're on Vodafone, your phone will switch on and the sim will tell it to search for masts with the network code 23415 (vodafone UK).

It'll find one, and connect to it. The mast (or antenna I suppose, the mast is technically the structure that the antennae are on) will then allow the incoming connection.

If no 23415 (voda) is available, the phone will then connect to any roaming partners it can find. If it finds none, it will display No Service, and will use the nearest mast for emergency calls only.

(do not quote me! this is my understanding feel free to correct me.. )

The signal to/from each mast is coded in such a way that it is essentially unique in an area. This is done in various ways depending on the technology (2G/3G/4G).

2G is probably the easiest to understand, as each mast uses a different set of frequencies, so the signal to/from each mast uses a different frequency per mast, hence it is unique within a given area. The frequencies are reused between masts across the network, and if they are reused too close to each other, you can end up with interference between masts. The handset constantly measures these frequencies and when not doing anything, decides itself which mast to connect to. When you make a call the handset reports all of the frequencies it can see back to the network, which will then make a decision as to which mast you should be connected to, and perform a handover from one mast to the next if required.

Each network has a different set of frequencies, and codes (PLMN) to determine which cells make up part of that network and before a phone even tries to access a mast, it reads these codes to determine if it's allowed to, e.g. A vodafone phone would read the codes from an EE cell, and know that it is forbidden to access that mast (unless it's an emergency call).