What is the baseband and do i need to update mine? I have a Samsung galaxy note which I've rooted and installed Cyanogenmod. I've always been using Cyanogenmod and always used the inbuilt updater. 

My radio has been giving me trouble. For example I can't see the signal strength anymore and I've not been able to resolve it. No one on this forum had an answer either. 

Why is device not showing the phone signal bars anymore?

I thought I'd update my phone's baseband but I don't know what it is and whether I should update it? My current baseband is XXALIE and my phone is a Samsung Galaxy Note 2 (GSM. Intl. edition).

Here's a list of basebands I found on XDA but I'm not sure if it's a good idea to update it. I can't even find my baseband on the list. Since I'm using the XX baseband, can I download any of the XX basebands for Android 4.3 basebands from the XDA page.

(If someone could shed some light on this whole baseband thing, it would be great.)
The way I understand it is that the baseband or radio partition is firmware used by the baseband processor, which is physically different from the application processor. The BP also has its own RAM and communicates with the android kernel via a process called the RIL (Radio Interface Layer).

When you install/update a new ROM this should not touch the baseband. So if your android ROM is having trouble communicating with the cellular hardware, the RIL part of the kernel might be to blame. This may be because the newer RIL expects  a more modern baseband version. 

So basically your baseband becomes an outdated dependency if you upgrade your ROMs long enough. To fix either downgrade the ROM (Kernel) or upgrade the baseband. Note there are risks involved with flashing the baseband. See also What is radio.