Wireless Communication past question

Prove that for a hexagonal geometry the co-channel reuse ratio is given by Q = sqrt(3N); Where N = i^2 + j^2 + ij. A cellular service provider decides to use a digital TDMA scheme which can tolerate a Signal-to-Interference Ratio of 15 dB in the worst case. Find the optimal value of N for (a) Omni directional antennas, (b) 120 Degree Sectoring, (c) 60 Degree Sectoring [Use path loss exponent of 4 and consider trunking efficiency]