Faares,
The GOS is used only to design a cell.
You *decide* to use a GOS of 2% in your design, to dimension your cell capacity, vs. the offered traffic.
If you already have a live network, you actually look at the TCH CONGESTION RATE, which is a precise measurement of how many calls are blocked in your network.
The network congestion rate is indeed a kind of “weighted” average of all cells congestion (weight depends on traffic carried by each cell)
-pix