## 4 Numerical Results
In the basic separation scheme, where SBSs manage both low and high rate data traffic, if the number of UEs is small, the energy consumption due to state switching increases if the number of UEs increases, because the state of SBSs changes from _off_ to _on_ state. However, if the number of UEs is sufficient, the number of SBSs in _on_ state is sufficient already, and thus, the effect of energy consumption increase due to state switching decreases. In the modified separation scheme, the SBSs only manage high rate data traffic and the increase of energy consumption due to state switching occurs more slowly than that in the basic separation scheme. Also, the decrease of energy consumption due to state switching also occurs more slowly. Figure 11 shows total energy consumption of BSs, which is the sum  
Figure 12 shows aggregate delay and reveals that the proposed energy saving scheme has the smallest delay, since the other two schemes have to move from _off_ state to _on_ state to accommodate traffic load, which takes relatively longer delay than the delay from _sleep_ state to _on_ state in the proposed energy saving scheme. There is a tradeoff between the basic separation scheme and the modified separation scheme. For small values of UE, the basic separation scheme has more aggregate delay since both low rate data traffic and high rate data traffic are managed by small cells and thus, SBSs have to awake to accommodate data traffic. However, in the modified separation architecture, since low rate data traffic is managed by an MBS, SBSs only need to awake to manage high rate data traffic. For large values of UE, most SBSs are already awake to accommodate both low rate data and high rate data traffic from UEs and have less delay compared to the modified separation scheme, where a part of SBSs should still wake up to manage high rate data traffic. Figure 11: Total energy consumption of BSs. Figure 12: Aggregate delay. Figures 13-15 show the energy consumption of BSs due to traffic processing, energy consumption of BSs due to state switching, and total energy consumption of BS by varying the ratio of high data. As shown in Figure 13, the energy consumptions of BSs due to traffic processing of the three schemes increase as the ratio of high rate data traffic increases, since more power is consumed to process high rate data traffic than low rate data traffic. The modified separation scheme and the proposed power saving scheme have lower energy consumption since low rate data traffic can be managed by a MBS and thus more SBSs can be turned off or put into sleep mode to save more energy. The difference is more significant for smaller values of ratio of high data traffic. As shown in Figure 14, the basic separation scheme has the largest energy consumption due to state switching and is not sensitive to the change of ratio of high data traffic since SBSs manage both low and high rate data traffic and thus more SBSs should change states. In the modified separation scheme and the proposed energy saving scheme, the energy consumption increases as the ratio of high data traffic increases since more SBSs should be turned on. For large values of ratio of high rate data traffic, the energy consumption of BSs due to state switching saturates because most SBSs are already turned on. The proposed energy saving scheme has the smallest energy consumption of BSs because of smaller power consumption due to switching between on and sleep states. Figure 15 shows the total energy consumption of BSs. As expected from Figures 13 and 14, the proposed energy saving scheme has the smallest energy consumption. Figure 16 shows aggregate delay. The proposed energy saving scheme has the smallest delay, as expected. There is a tradeoff between the basic separation scheme and the modified separation scheme. Except for large values of UE, the basic separation scheme has more aggregate delay since both low rate data traffic and high rate data traffic are managed by small cells and thus SBSs have to wake up to accommodate data traffic.