# Interference-Aware Opportunistic Dynamic Energy Saving Mechanism for Wi-Fi Enabled IoTs
## 1 Introduction  
As demand for high data rate and low power mobile applications has increased, many efforts have been made to increase the data rate and energy efficiency in wireless communication systems. In order to obtain a high data rate and high reliability, wireless local area network (WLAN) chipsets got more complex and supported a wider channel bandwidth [1; 2; 3]. Since data is transmitted using a wider bandwidth to support high throughput, the required operating clocks of the circuits have had to be increased, which causes an increase in power consumption. In addition, the required energy efficiency levels of RF, analog and digital circuitry design are more constrained. However, battery technology has not kept up with these demands. Therefore, the energy budget of a wireless communication interface with a limited battery capacity is extremely limited because wireless communication devices are rapidly developing to accept additional elements and technologies to add new functions and increase the performance [4]. Accordingly, there is a desire for a method for using the limited battery capacity longer and more efficiently [5].  
Since the battery capacity is limited in the mobile terminal or the sensor, a technology for minimizing energy consumption is necessary [6; 7]. A wireless interface may reduce power consumption by two methods. First, the wireless interface is awake only when there is data to be exchanged with another wireless device [8]. Otherwise, a power save mode is maintained to reduce energy consumption. Second, when a received packet does not correspond to an identifier (ID) of the wireless interface, data processing is not performed to reduce energy consumption [1]. According to these conventional technologies, the energy efficiency may deteriorate when the mobile station is actively processing in the maximum operating clock mode of the circuits to accept the widest channel bandwidth signal. In particular, since the WLAN is required to perform high speed digital processing to support a high performance service, a high frequency clock is used and a large hardware size is required. In addition, since a relatively high voltage scale is used, power consumptionis extremely high. However, this is not always true because mobile station adapts transmission bandwidth using dynamic bandwidth operation. In a typical WLAN chipset, it has analog and digital filters for 20/40/80 MHz signal bandwidths for IEEE 802.11 ac, and 1/2/4/8 MHz signal bandwidths for IEEE 802.11 ah [1; 3]. Nyquist sampling theorem states that the minimum sampling-rate is two times to the signal bandwidth [9]. Therefore, the dynamic bandwidth operation is proposed to save power if the device needs to process a narrower signal bandwidth than the maximum operatable signal bandwidth.  
WLANs have been a good solution for the internet of things (IoTs) because there are various IoTs applications which have different requirements, such as throughput, service coverage, and power consumption [8]. However, in IoTs networks, the dynamic channel access and heterogeneous network conditions lead to partial sub-channel operation, which is not the widest operatable channel bandwidth, so it is possible to optimize signal processing in the transceivers in order to improve its energy efficiency. For example, a typical WLAN supports 80 MHz channel bandwidth operation, and it can support 20 MHz, 40 MHz, or 80 MHz bandwidth operation. Here, 20 MHz and 40 MHz channels are the sub-channels for 80 MHz channel bandwidth operation. This paper proposes a dynamic power saving mechanism to improve energy efficiency for Wi-Fi enabled IoTs utilizing multiple sub-channels. The remainder of this paper is organized as follows. In Section 2, related works are described. In Section 3, a dynamic bandwidth operation is introduced and a dynamic power saving mechanism is proposed in Section 4. Section 5 presents the evaluation results, and finally Section 6 draws conclusions.