interference
software problems…
but you know, if you have a problem like this in your network, it’s better to clearly state it, rather than trying to see what are the general causes of such problems.
you ask for “major causes”, now you are looking for “minor causes”, and soon you’ll ask for all possible causes for TCH assignment failures.
but radio troubleshooting is not that simple, it doesn’t work this way. you need to analyze all the problems in the cell, rather than focusing on just assignment failures. That’ll give you a global view about the cell, its surroundings, its covered subscribers, its neigbours, and so on. Then only you can see what is the root issue.