2327-4662 (c) 2019 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/JIOT.2019.2943030, IEEE Internet of Things Journal JOURNAL OF L A T E X CLASS FILES, VOL. 14, NO. 8, AUGUST 2015 1 AnyCharge: An IoT-based Wireless Charging Service for the Public Kuan-Ting Lai, Member, IEEE, Fu-Chiung Cheng, Seng-Cho T. Chou, Yi-Chun Chang, Guo-Wei Wu, and Jung-Cheng Tsai Abstract—Mobile phones have become a necessity of modern life and are used for various tasks including audio calls, text messaging, web surfing, video streaming, gaming, and pay- ments. Most of these tasks consume significant battery power, which makes public charging services increasingly important. Therefore, many public places and private stores have started to provide free charging services. However, there are several issues that restrict the popularity of public charging service. First, people cannot easily find charging spots. Second, there is no effective way to monitor charging status and manage the chargers. Third, a free charging service increases business expenses. To address these issues, we developed an IoT-based wireless charging service system, which is called AnyCharge. There are five major components of AnyCharge: a Wi-Fi enabled wireless charger, an IoT gateway, a cloud-based management platform, a secure Wi-Fi auto-connection algorithm, and a mobile app. The charger is connected to an IoT gateway through Wi-Fi using our secure auto-connection algorithm, and the gateways are linked to the cloud server using MQTT. The administrators can monitor and control chargers using the management platform. In addition, Android and iOS apps have been created to allow users to locate free chargers and find the shortest route to the nearest charging spot. We initiated a large-scale experimental deployment in Taiwan, Thailand, Singapore, and Japan. More than 200 chargers have been installed in different places, includ- ing restaurants, hospitals, telecom stores, and hotels. Statistics show that there is a strong demand for public charging services. Index Terms—Internet of Things (IoT), wireless charging, MQTT, Wi-Fi automatic connection, IoT security, CoAP I. I NTRODUCTION M OBILE devices are ubiquitous nowadays. In addition to making phone calls, people use cell phones to browse web pages, buy products, pay bills, play video games, and even for live broadcast. Most mobile applications are heavy consumers of battery power. As a result, phones still run low on battery power over the course of a day despite advances in battery and power-saving technology. Because mobile phone functions have become so important to our daily activities, people are more willing to visit places with charging services. Some public places and private stores have noticed the need for K.-T. Lai, G.-W. Wu, and J.-C. Tsai are with the Department of Electronic Engineering, National Taipei University of Technology, Taipei City 10608, Taiwan (e-mail: ktlai@ntut.edu.tw; t107368004@ntut.edu.tw; t107368009@ntut.edu.tw). F.-C. Cheng is with the Department of Computer Science and Engineering, Tatung University, Taipei City 10452, Taiwan (e-mail: fccheng@ttu.edu.tw) S.-C. T. Chou and Y.-C. Chang are with the Department of Information Management, National Taiwan University, Taipei City 10617, Taiwan. (e-mail: chou@ntu.edu.tw, d03725001@ntu.edu.tw) Manuscript received January 3, 2019; revised August 30, 2019. Fig. 1: An overview of AnyCharge’s architecture. The system consists of five major components: Wi-Fi enabled wireless charger, IoT gateway, cloud-based management platform, se- cure Wi-Fi auto-connection algorithm and mobile app. charging, and have started to provide free charging. However, there are several issues that limit the widespread adoption of public charging services. First, there is no search engine to look up charging spots, so people cannot find the nearest place to charge in an emergency. Second, there is no effective way to monitor and control the chargers. Thus, it is hard to replace broken chargers or limit the usage of certain users. Third, a free charging service increases operation costs, which reduces the motivation of business owners to provide such services. To solve these issues, we leveraged the latest IoT technology and developed an IoT-based wireless charging system to manage chargers. This novel service is called AnyCharge. We designed a Wi-Fi enabled wireless charger, which can automatically connect to an IoT gateway using our automatic and secure Wi-Fi connection algorithm. After the connection is established, the Constrained Application Protocol (CoAP) [1] is used to communicate between the gateway and chargers. The IoT gateway is in charge of managing local chargers and connecting to the cloud server using the Message Queue Telemetry Transport (MQTT) protocol [2]. By connecting all the chargers to the cloud, we can monitor the charging status and control the chargers in real-time. Therefore, AnyCharge knows where and when the chargers are available, and can