【单选题】If the cluster size N of a cellular system is 7 and the path loss exponent n is 4, assume that there are six co-channel cells in the first tier, determine the signal-to-interference ratio______.
【简答题】For a cellular system, if the cluster size is 7 and the distance between two adjacent cells is 1 km, then the distance between two nearst co-channel cells is________km.