Pengyu Zhang, Jeremy Gummeson, Deepak Ganesan
Backscatter communication offers an ultra-low power alternative to active radios in urban sensing deployments --- communication is powered by a reader, thereby making it virtually ''free''. While backscatter communication has largely been used for extremely small amounts of data transfer (e.g. a 12 byte EPC identifier from an RFID tag), sensors need to use backscatter for continuous and high-volume sensor data transfer. To address this need, we describe a novel link layer that exploits unique characteristics of backscatter communication to optimize throughput. Our system offers several optimizations including 1) understanding of multi-path self-interference characteristics and link metrics that capture these characteristics, 2) design of novel mobility-aware probing techniques that use backscatter link signatures to determine when to probe the channel, 3) bitrate selection algorithms that use link metrics to determine the optimal bitrate, and 4) channel selection mechanism that optimize throughput while remaining compliant within FCC regulations. Our results show upto 3$\times$ increase in goodput over other mechanisms across a wide range of channel conditions, scales, and mobility scenarios.
Public Review uploaded by sseshan:
This public review was prepared by Srinivasan Seshan.
As stated in the introduction of this paper, backscatter communication holds the promise of dramatically reducing the energy cost of communications. Unfortunately, there has been little work from our community on incorporating this technology effectively in mobile systems. This paper takes an important step towards making backscatter-based links more useful by improving their data transfer performance.
The paper uses techniques similar to those that have been widely used in other wireless networks to perform rate-adaptation and channel selection on backscatter links. As a result, the proposed techniques are not incredibly sophisticated or novel. However, as the first work exploring this area, the paper does a great job in showing how backscatter links differ from other wireless technologies for the problems related to bandwidth optimization. In addition, the paper provides a valuable experimental study showing how well these links perform, how well more traditional WiFi-based solutions work on these links and how much performance can be obtained using the proposed techniques. I suspect that many follow-on efforts will use these results from this paper to design techniques that improve upon the BLINK design.
The main weakness of this paper is that it fails to show even a single simple application that can be enhanced significantly by the proposed link improvements. However, the technology is promising enough that I am confident that these applications of will be found. Assuming that such applications are found, this paper will be seen as a highly influential kick-start for this topic area.
BLINK is a link layer protocol designed to support high throughput data transfer between RFID sensors and readers. We want to give a brief review on the applications supported by BLINK and its unique design methodology.
Applications: We want to point out that there are several RFID sensors that are currently available in the market. For example, TagSense manufactures proximity, physiology, and other sensors with an RFID analog front end instead of an active radio. Other companies including CAEN systems, Evigia EV3 system, etc provide similar RFID sensors. These tags have a small on-board buffer, and transfer data when connected to a reader. While we do not explicitly evaluate our work with a specific RFID sensor, BLINK is designed for improving throughput for data transfer from such devices to a reader.
Novelty of techniques: The reviewers are right in pointing out that we use well-known link metrics (RSSI, packet loss rate) for rate adaptation and channel selection. However, we feel that the key novelty in our approach is providing an in-depth and empirically-validated measurement study that illustrates the differences between backscatter and traditional active radio links, and shows how to use standard link metrics to do mobility-aware rate adaptation/channel selection.