# Interference-Aware Opportunistic Dynamic Energy Saving Mechanism for Wi-Fi Enabled IoTs
## 4 Proposed Dynamic Energy Saving Mechanism  
A wireless communication system consumes more power with a larger bandwidth because a larger bandwidth requires a higher processing speed, that is, the operation frequency, of a wireless communication circuit. Therefore, in this paper, we propose dynamic power saving mechanism to determine the communication sub-channels and operating clock frequencies to be performed based on the clear channel assessment (CCA) of each of the selected communication sub-channels. Figure 3 is a flowchart illustrating the proposed dynamic energy saving operation. The proposed method uses RTS/CTS frames for dynamic bandwidth operation between a transmitter and a receiver. At least one communication sub-channel is selected from the multiple communication sub-channels that have received the RTS, based on a CCA of set of communication channels. When all channels are affected by the interference signal and therefore the transmission PHY data rate is low, the absence of a good quality channel for high PHY data rate is noted through the CTS frame and the power save mode begins. As a result, the receiver selects the sub-channels and feedbacks the decision to transmitter, then the transmitter bonds the sub-channels that have received the CTS from the receiver. Here, the data packet is not transmitted on a communication channel that has not received the CTS among set of communication channels.  
Figure 4 illustrates a multi-channel low power communication method according to the proposed energy saving operation. The left side of Figure 4 shows an example of the proposed energy saving mechanism that aggregates four bands and transmits RTS to four bands, but performs communication with only two bands. The receiver requests the energy saving operation through the dynamic bandwidth operation information field of the CTS. Thus, by transmitting the CTS, the receiver notes the transmitter reduction in channels and operating clock frequencies in order to save power. In the right side of Figure 4, there is a request to use a channel of a smaller width for transmission of a data packet during transmission of the CTS. During exchange of the RTS and CTS, the CCAs are measured. The power saving efficiency can be increased by using the RTS and the C  
Figure 3: Flowchart for dynamic energy saving operation.  
battery capacity and the channel state of the wireless communication network. The main idea of the proposed dynamic energy saving mechanism is to improve the energy efficiency by reducing the operating clock frequency of ADC and digital front-end circuits including digital filters if the wireless system determines to use narrower channel bandwidth. Core digital modem maintains the operating clock frequency because clock rate converter transforms the clock rates between the digital front-end circuits and core digital modem. Thus, the transmission time is the same regardless the operating clock rate of ADC and digital front-end circuits. As the ADC and digital front-end circuits are major energy consumers in WLANs, the adaptive operating clock scheme is an effective way to save power.