Are you absolutely sure it’s an external interference? Sometimes a faulty TRX can cause what you described. Also make sure that all your hopping parameters are correct…it’s possible someone mistakenly changed something.
If you’re sure it’s an external interference, the only thing you can do is to identify where the interference is coming from, and ask the person to stop transmitting on those frequencies( ‘cos you’ve paid to use them). The big question is…how do you find where the interference is coming from? I will suggest you halt your cell(it it’s only one) and then use a spectrum analyzer to track it down. Generally, as you move towards the source, the received level will increase…it can be quite tough or frustrating….but you would be able to track it down with some hardwork and maybe luck. One of the main culprits in these cases are printing presses..so look out for those.
Anyway, if you’re able to track them down, then there are 2 things you can do
1. THE EASY WAY: politely ask the person to stop using your frequencies, and if he/she refuses, then you can use:
2. THE HARD WAY: Report the person to your regulator who will impose appropriate sanctions.
Hope this helps.