Scalable Wi-Fi Backscatter Uplink Multiple Access for Battery-Free Internet of Things

This paper presents a scalable uplink multiple access (SUMA) protocol for bistatic Wi-Fi backscatter systems, composed of a Wi-Fi reader, Wi-Fi helper, and multiple Wi-Fi backscatter tags. SUMA uses a Wi-Fi reader-initiated dynamic framed slotted ALOHA (DFSA)-based multiple access protocol to minimize collisions caused by simultaneous Wi-Fi backscatter uplink traffic from multiple Wi-Fi backscatter tags. In SUMA, the Wi-Fi helper first estimates the number of tags at the start of network operation and derives an appropriate slot-count parameter (i.e., Q), based on which the frame size is specified. Then, the Wi-Fi helper adaptively adjusts the value of Q to maximize network performance while continuously monitoring the number of remaining Wi-Fi backscatter tags to detect information. An experimental simulation was performed to verify the superiority of SUMA. The results demonstrated that SUMA obtained higher performance in terms of the number of collided and empty slots, delay, and throughput compared with the legacy DFSA approach adopted in the EPCglobal Class 1 Gen 2 standard.