Parallel Cross-technology Transmission from IEEE 802.11ax to Heterogeneous IoT Devices

Cross-Technology Communication (CTC) is an emerging technique that enables direct interconnection among incompatible wireless technologies. However, for the downlink from WiFi to multiple IoT technologies, serially emulating and transmitting the data of each IoT technology has extremely low spectrum efficiency. Recent parallel CTC uses IEEE 802.11g to send emulated ZigBee signal and let the BLE receiver decodes its data from the emulated ZigBee signal with a dedicated codebook. It still has a low spectrum efficiency because IEEE 802.11g exclusively uses the whole channel. Besides, the codebook design hinders the reception on commodity BLE devices. In this paper, we propose WiCast, a parallel CTC that uses IEEE 802.11ax to emulate a composite signal that can be received by commodity BLE, ZigBee, and LoRa devices. By taking advantage of OFDMA in 802.11ax, WiCast uses a single Resource Unit (RU) for parallel CTC and sets other RUs free for high-rate WiFi users. But such a sophisticated composite signal is very easily distorted by emulation imperfections, dynamic channel noises, cyclic prefix, and center frequency offset. We propose a CTC link model that jointly models the emulation errors and channel distortions. Then we carve the emulated signal with elaborate compensations in both time and frequency domains to solve the above distortion problem. We implement a prototype of WiCast on the USRP platform and commodity devices. The extensive experiments demonstrate WiCast can achieve an efficient parallel transmission with the aggregated goodput up to 390.24kbps.