Figure 2: (a) Distribution of the SINR at the cellular cell borders. The simulations are compared to the calculations. In our calculations the aggregate interference is modelled by the log-normal distribution. Different secondary cell radiuses are tested. The standard deviation is taken equal to 𝜎 S U = 5  dB. (b) Transmission power level required to achieve SINR target 𝛾 𝑡 = 3 . 5  dB at the cellular cell border with outage probability 𝑂 S U = 1 0 % for different cell radiuses and reuse distance 𝐾 = 3 . The results obtained by using the actual interference margin (10) are compared to the results obtained by using the lower bound of the interference margin (11). The rest of the parameter setting can be found in Section 4.1.