Wednesday, August 19, 2015

Session 5 (Wireless) Paper 3: BackFi: High Throughput WiFi Backscatter

Authors: Dinesh Bharadia, Kiran Joshi, Manikanta Kotaru, Sachin Katti
from Stanford University

Link to the public review

According to the authors, for the Internet of Things (IoT) to become a reality, the IoT devices need to satisfy three requirements: sufficient range & throughput, low power design, and reuse of ambient signals. In order to achieve these goals, the authors propose a backscattering-based approach where the IoT devices piggyback their data on the ambient signals.

The presenter explained that this is done by modulating the data on the received downlink signals from Wi-Fi APs to clients and then backscattering the signal to the APs. The authors designed an AP that can receive backscatter signals even when transmitting data. In order to achieve this, they rely on recently-proposed self-interference cancellation techniques for full-duplex radios and modify them so that the backscatter itself signal does not get canceled.

The presenter showed that BackFi provides low energy consumption for the IoT devices, and delivers 1Mbps of throughput for 5m range and 1Mbps for 1m range. BackFi also improves spectral efficiency.

Q: What happens when all the IoT devices respond at the same time since there is no MAC protocol? How do you handle that?
A: We are working on a protocol to actually do it.

Q: Since there are multiple APs and many clients, a lot of them will trigger the backscatter signals. How do the sensors know when to reply and to which AP they’re associated with?
A: The AP sends a CTS message and then the sensors know that the next message will be backscattered to this AP.