this is typical “packet” dimensionning. Just sum up all the throughputs at BH (cs + ps + sig + o&m), take 30% (ex.) margin, and see if it all fits within 2mbps…
Yet, usually, you already have your E1 link. By switching from E1 to IPoE1, you will gain a lot of capacity. There is no need to do a dimensionning, because there is no risk of congestion. And then you can monitor your IP load thanks to BSS counters.
The next step is to gradually increase your radio capacity until you’re reaching your Abis IP capacity.