Offset-Resistant Physical-Layer Cross-Technology Acknowledgment: A General Approach and Its Case Studies

Physical-layer cross-technology communication (PHY-CTC) enables direct communications among heterogeneous devices by using different wireless technologies such as WiFi, ZigBee, and Bluetooth Low Energy (BLE). With the recent emergence of customizable physical-layer firmware, PHY-CTC is more efficient and flexible than ever, positioning it as one of the most promising techniques to concisely realize ubiquitous connectivity in the sixth generation (6G) wireless networks. However, transmission reliability in PHY-CTC remains a critical challenge, particularly due to the lack of robust acknowledgment (ACK) mechanisms. Existing ACK designs for PHY-CTC, while successfully becoming lightweight by focusing on the physical layer, are limited to ZigBee-WiFi pair and susceptible to sampling offsets inherent in PHY-CTC. To address these limitations, we propose a general approach to offset-resistant physical-layer cross-technology ACK. Our approach encodes ACK into specially designed offset-resistant signals (ORSs) that can be effortlessly and robustly conveyed across a wide range of heterogeneous technologies, even in the presence of sampling offsets. We present comprehensive guidelines for implementing ORS-based ACK across various heterogeneous technology pairs, further enhancing the approach's generality. To validate the efficacy and generality of our approach, we apply our method to ZigBee-to-BLE and ZigBee-to-WiFi ACKs. Real-world experiments validate the feasibility of our approach and its superiority over state-of-the-art solutions. This study contributes to advancing PHY-CTC, enhancing its practicality for the Internet-of-Things ecosystem in 6G networks.