# A Low-Power WLAN Communication Scheme for IoT WLAN Devices Using Wake-Up Receivers
## 1 Introduction  
The Internet of Things (IoT) has become more widely used in various applications, such as home networks, wearable devices, cattle farms, and warehouses. In most IoT applications, IoT devices are battery powered, and low-power operation is therefore one of the key requirements of IoT devices. Moreover, there are various applications for IoT devices, and there exist a variety of communication scenarios as well as power and delay requirements. The research on low-power communication has focused on sensor networks. Most of the previous works have focused on distributed sensor networks, which include tree construction, duty-cycled operation, and wireless energy harvesting operations [1,2]. In duty-cycled operation, sensors turn on and off their transceivers at predetermined times in order to reduce unnecessary power consumption when not transmitting or receiving data. Duty-cycled operation includes a synchronized approach [3] and an asynchronous duty-cycled operation [4,5]. In [3], a sending node scheduled transmission to a receiving node during a Data period, and performed a transmission procedure during a Sleep period. In [4], a receiving node first transmitted a Beacon frame after it woke up, and a sendingnode transmitted data as a response to the Beacon frame. The power saving protocol in [5] is an improvement on [4] which considers multiple traffic flows. In [5], each sensor woke up at randomized times using a pseudo-random number generator to avoid collision. In this method, if a sensor node wants to know the wake-up interval of the receiving node, it requests and receives the parameters of the pseudo-random number generator, and uses them to predict the awake time of the receiving node. Duty-cycled power saving protocols handle various systems and traffic models in sensor networks with a small overhead. However, since the previous duty-cycled power saving protocols were based on relay operation from a source node to a destination node, tree construction should be part of the framework. Therefore, the previous duty-cycled power saving methods in wireless sensor networks were not efficient for IoT devices with mobility. Moreover, the duty-cycled operation requiring wireless devices to turn on and off at scheduled times causes trade-offs between latency and power consumption. The IoT scenarios are different from sensor network scenarios in several aspects, although they may appear similar. First, in sensor networks, once the devices are implemented, the sensors are static and rarely move, while IoT devices may move around. Second, while low traffic arrival is assumed in sensor networks, in IoT applications, there are various traffic patterns with different delay requirements. In order to deal with such dynamic IoT communication environments and various IoT traffic types, centralized network structures, such as in wireless local area networks (WLANs), are more efficient than distributed sensor network structures. Several power saving methods and control systems for IoT operation have been proposed based on WLAN. In [6], an AP power saving method based on the distance value of a station (STA) has been proposed. Whereas the idea of managing AP operation by average distance calculated by received signal strength indicator (RSSI) is simple and effective in the dense AP scenario, such an AP power saving method cannot reduce the power consumption of STAs. In [7], a management system to control home appliances was proposed which takes into account the coexistence of heterogeneous networks. However, client nodes (home appliances) were only turned off and on based on their utilization. The proposed system in [7] does not provide a power efficient communication method. In [8], the authors have proposed an effective handoff procedure and AP selection mechanisms based on a certain medium access control (MAC) protocol called distributed queueing with collision avoidance (DQCA).