Masahito Iwai

Energy-efficient WLAN with on-demand AP wake-up using IEEE 802.11 frame length modulation

This paper considers a radio-on-demand (ROD) wireless LAN (WLAN) in which access points (APs) are put into a sleep mode during idle periods and woken up by stations (STAs) upon communications demands. The on-demand wake-up is realized by a wake-up receiver which is equipped with each AP and is used to detect a wake-up signal transmitted by STA. In order to reduce the hardware installation cost at STA, we advocate to utilizing wireless LAN frames transmitted by each STA as a wake-up signal. We generate a wake-up signal based on frame length modulation (FLM) where each STA creates a series of WLAN frames with different length to which the information on wake-up ID is embedded. The simple and low-power wake-up receiver extracts the wake-up ID from the received frames. In this paper, we design and develop a prototype of the wake-up receiver and propose a wake-up protocol which defines a procedure to realize the on-demand AP wake-up in ROD WLAN. We evaluate system-level performance of ROD WLAN based on our prototype and our proposed wake-up protocol, and investigate appropriate settings of parameters for our proposed FLM to achieve the required system-level performance. Our numerical results confirm that the proposed wake-up protocol with FLM achieves smaller delay than a conventional AP employing passive scanning while maintaining small probability to be falsely woken up by continuous interference.

Receiver design for realizing on-demand WiFi wake-up using WLAN signals

In this paper, we design a simple, low-cost, and low-power wake-up receiver which can be used for an IEEE 802.11-compliant device to remotely wake up the other devices by utilizing its own wireless LAN (WLAN) signals. A typical usage scenario of such a wake-up receiver is energy management of WiFi device: a device equipped with the wake-up receiver turns WiFi interface off when there is no communication demand, which is powered-on only when the wake-up receiver detects a wake-up signal transmitted by the other WiFi device. The employed wake-up mechanism utilizes the length of 802.11 data frame generated by a WiFi transmitter to differentiate the information conveyed to the wake-up receiver. The wake-up receiver is designed to reliably detect the length of transmitted data frame only with simple envelope detection and limited signal processing. We develop a prototype of the wake-up receiver and investigate the detection performance of the envelope of 802.11 signals. Based on the obtained experimental results, we select appropriate parameters employed by the wake-up receiver to improve the detection performance. Our numerical results show that the proposed wake-up receiver achieves much larger detection range than the off-the-shelf, commercial receiver having the similar functionality.

Wake-up radio using IEEE 802.11 frame length modulation for Radio-On-Demand wireless LAN

In this paper, we introduce Radio-On-Demand (ROD) wireless LAN (WLAN) in which access points (APs) are put into a sleep mode during idle periods and woken up by stations (STAs) upon communications demands. The on-demand wake-up is realized by a wake-up receiver which is equipped with each AP and is used to detect a wake-up signal transmitted by STA. In this paper, in order to reduce the hardware installation cost at STA, we advocate to utilize wireless LAN frames transmitted by each STA as a wake-up signal to awake the target AP. The STA generates a wake-up signal by devising WLAN signal: each STA creates a series of WLAN frames with different length to which the information on wake-up ID is embedded. The wake-up receiver extracts the wake-up ID from the received frames with a simple detector which ensures its low-power operation. We evaluate false negative (STA fails to wake up the target AP) and false positive (AP falsely wakes up without an intended wake-up signal) probabilities of our proposed on-demand wake-up scheme with computer simulations. The numerical results show that the proposed scheme achieves the false negative probability of about 10−2 when the detection error ratio of ‘1’ is less than 10−3. We also show that the false positive probability can be largely reduced by employing long WLAN frames to generate each wake-up signal. These results confirm that the proposed wake-up scheme is a promising approach to reducing wasteful energy consumed by idle APs in WLAN.