Eq. 5 is subject to the service quality constraint of Eq. 2, where λ_nis defined for each d ∈ D. With a larger coverage area of the WiMAX BS, it is assumed that the power consumption of each on channel in the WiMAX BS is not less than that of a cellular network BS (i.e., P_wv ≥ P_cv). In this case, to further improve the amount of energy saving, when the BSs of both networks are on, more channels from the cellular network are utilized. As a result, we let k_cn = C and k_wn = s_n – C when BSs from both networks are on; otherwise, the active number of channels from the on BS is equal to s_n. The time sequence of optimization events is illustrated in Fig. 2.