## 1 Introduction  
Nowadays, _Internet of Things (IoT)_ is gaining popularity all over the world with increasing the number of devices connected to the Internet. IoT has been widely deployed in various applications, including smart factories, smart cities, smart homes, smart grid systems, smart farms, smart warehouses, and smart healthcare systems [1, 2, 3, 4, 5, 6]. In IoT application systems, device-to-device connections are usually made through wireless networks, such as Wireless Sensor Networks (WSNs), Wireless Local Area Networks (WLANs), Long Term Evolution (LTE), and Global System for Mobile Communication (GSM) [7, 8, 9, 10, 11]. Among them, many IoT application systems adopt IEEE 802.11 WLANs, as shown in Figure 1[8, 12, 13, 14]. Currently, a huge number of IoT devices are connected to the Internet through IEEE 802.11 WLANs, because their popularity has remarkably increased around the world due to high-speed data transfer, flexible coverage ranges, low costs, and easy installation. In WLAN, hosts are connected to the _access point (AP)_ wirelessly, which makes it extensible and flexible compared with wired LAN. As a result, WLAN services are available in offices, schools, and public places, such as hotels, airports, malls, stations, and even trains and airplanes [15, 16, 17]. In traditional WLANs, hosts communicate with servers over the Internet,while IoT devices communicate with servers. In this paper, a _host_ represents a smartphone, a PC, a tablet, or an IoT device that will be accessed to the Internet through WLAN. In a network field, multiple APs are often deployed to support a large number of users. Such situations are called _dense WLAN environments_. In dense WLAN environments, network performance can be degraded by radio-signal interference between nearby APs and hosts. To avoid the performance degradation as best as possible, the network configuration of the WLAN, such as activations/deactivations of APs and associations of hosts with active APs, should be properly optimized, according to traffic demands. If redundant APs exist, they should be deactivated to reduce energy consummations [18; 19; 20; 21]. Therefore, we have proposed the active AP configuration algorithm to dynamically optimize the network configuration by activating or deactivating APs according to traffic demands [22]. The throughput performance in a WLAN is affected by various factors in an indoor environment. Therefore, we have studied the _throughput estimation model_ with the _parameter optimization algorithm_[23], and the _AP setup optimization approach_ in terms of the orientation and the height of the device [24]. The number of users using WLANs to access the Internet is increasing, resulting in fast growth of traffic. In order to meet the ever-increasing traffic, _channel bonding (CB)_ was introduced in the _IEEE 802.11n_ amendment for improving the network performance of WLANs. In the CB, two adjacent 20 \(MHz\) channels are bonded together to form one 40 \(MHz\) channel [16; 25; 26]. The _IEEE 802.11 ac_ and the _IEEE 802.11 ax_ may further extend the channel-boding feature by allowing 80 \(MHz\) or 160 \(MHz\) channels with four or eight single channels, respectively, refs. [27; 28; 29]. However, we did not consider them, since they are still not common in WLAN. In addition, our experiments using IEEE 802.11 ax devices [30] show that the throughput performance does not reach the expected level. Therefore, their use will be in future works. In [31], using _orthogonal frequency division multiplexing (OFDM)_, the CB raises the number of sub-carriers from 52 to 108. To get higher throughput in this wide-band CB, the OFDM can transmit data using a multiple of narrow-band carriers. However, the CB reduces the number of non-interfered channels and may increase interference between nearby APs and hosts due to wider channel bands in dense WLANs. In [32], [PERSON] et al. demonstrated that a CB link can decrease the _signal-to-interference-plus-noise ratio (SINR)_ at a distant host from the AP due to the wider channel bandwidth.