I. Introduction
The proliferation of the Internet of Things (IoT) applications enables ubiquitous connections among various wireless devices for bettering our daily life. According to a recent report [1], the number of IoT devices is expected to reach 55 billion by 2025, posing significant challenges on spectrum resources. Current IoT devices are using different wireless technologies, some of which share the same spectrum resources when they coexist in the common space. For example, IoT devices using the WiFi, ZigBee, and Bluetooth protocols occupying the Industrial, Scientific, and Medical (ISM) 2.4 GHz band, will lead to intense coexistence of wireless technologies. Due to their incompatibility, multiple costly and device-independent gateways are always needed to fully connect IoT devices deploying different protocols. However, the deployment of gateways not only incurs extra hardware costs but also introduces traffic overhead and communication delay. As one of the most promising paradigms, Cross-Technology-Communication (CTC) allows the direct communication among devices across different wireless technologies while bypassing the gateways, e.g., directly from WiFi to ZigBee devices or from WiFi to Bluetooth devices [2]–[4].