how can I determine interfering sectors

Hello all

I am doing on network MIMO. Using Matlab I am able to establish a network of two tier cells with 19 BS and each BS has three sectors. Each sector has one directional antenna. Now my question is that, let my sector of interest is 1 of BS 1. now other 18 BS are interfering sources but not all sectors belonging to them because they have directional antennas. how can I determine these interfering sectors. any method or algorithm to determine all interfering sectors?