# A Low-Power WLAN Communication Scheme for IoT WLAN Devices Using Wake-Up Receivers
## 1 Introduction
By using the proposed effective AP selection mechanisms, STAs with mobility are able to reduce the number of handoffs, leading to reduced power consumption. In the IEEE 802.11h group, the IEEE 802.11 ah standard has been developed recently for low-power and long-range operation [9; 10]. The main features of IEEE 802.11 ah is narrow band transmission and scheduled wake-up operation called target wake time (TWT). IEEE 802.11 ah effectively manages power consumption and a large number of STAs, but there is a trade-off between latency and power consumption. Since power management operation is based on a scheduled wake-up procedure, trade-off occurs because the latency for STAs to receive data depends on the length of the wake-up cycle. In order to achieve the low-power operation and short communication delay required for battery powered WLAN devices, wake-up receivers were proposed in [11; 12; 13; 14]. The wake-up receiver is a simple structured receiver which detects on-off keying (OOK) signals, enabling low-power operation and short transmission delay, simultaneously. The previous power-saving operations using wake-up receivers are primarily for conventional sensor networks. The main scenario involves a large number of devices with a low traffic ratio and a simple structure. In [15], the authors proposed the two-channel-based wake-up protocol. In the two-channel wake-up protocol, one channel is used to transmit data, and the other channel is used only to wake up neighboring STAs. In this protocol, the sender node may wake up all neighboring nodes through a wake-up channel when the sender has more data to transmit than the threshold. However, by using two channels without any indication, power may be wasted because all nodes which sense a signal in the wake-up channel should wake up and sleep including the nodes without data to receive, and other devices that operate at similar frequencies with the wake-up channel may wake up the sensor nodes. In [16], the wake-up receiver protocol was proposed using a low-power operating wake-up receiver, based on the duty-cycled operation of the wake-up receiver. In the proposed operation, the duty-cycle wake-up receiver operation is proposed in order to achieve further power saving. The scenario in [16] is also a distributed sensor network, and the operation includes the acknowledgment of a wake-up frame in order to ensure that the wake-up receiver in the receiving node awakes and successfully receives the wake-up frame. However, since those works assumed a low traffic arrival rate, in the dense communication scenario where a large number of communication devices are involved in communication with high traffic ratio or in the scenario where the collection of information from multiple nodes is required, these approaches may result in large delays. In the IEEE 802.11 group, as the demand for IoT communication has evolved, the IEEE 802.11 amendment standard, IEEE 802.11 ba has initiated standardization. IEEE 802.11 ba defines WLAN wake-up radio operation for low-power WLAN devices like IoT devices. Because the wake-up radio using a wake-up receiver resolved the trade-off problem of duty-cycled operations in previous works, various applications with different traffic patterns, as well as delay and power-consumption requirements, are considered as the scenarios for IEEE 802.11 ba. The wake-up radio operation developed in IEEE 802.11 ba may be paired with any other IEEE 802.11 standards, including IEEE 802.11a/b/g/n/ac/ax. However, although the IEEE 802.11 ba standard includes various scenarios for IoT applications, it does not consider a traffic scenario where a mobile device requests sensed data from a large number of users. Moreover, the long wake-up delay of a STA causes large transmission delays in the case of the multi-user transmission scenario. In this paper, transmission methods for massive transmission scenarios are proposed. The proposed schemes are based on the joint design of uplink multiuser (MU) operation in IEEE 802.11 ax and the wake-up radio operation of IEEE 802.11 ba.