Will GSM Network Influence the RF equipment

I have Faced some serious Problem in Network.. I am facing some Latency issue and Packet Drops in My sector. I am observed that where ever i am faced the Problem near by my Equipment GSM tower was available. I am reduced the sector Height it was working Fine. I dont know what is the issue. Reducing the Height how the my access Point working properly(Through Sector).

GSM Network can introduce interference with other wireless system.
Reducing the height, the signal power of the interference is lower at the input of your system.
Most probably the GSM signal acts as an out-of-band blocker to your system. You have to do an RF system analysis, and see what kind of front-end filters you need to suppress/minimize the interference.

If possible, you can receive and test the GSM MASK, maybe GSM MASK do not comply the standards.

Could u explain in deep what is meant by out-of-Band blocker could explain briefly how we can find this this Exactly we need any device like spectrum anlayzer?what are front-end filters available to suppress it.