Positioning Energy-Neutral Devices: Technological Status and Hybrid RF-Acoustic Experiments
Round 1
Reviewer 1 Report
The article is well written and the direction of the research is appropriate.
However, the mixed results and the anomalies on the variouis CDF plots are not adequately justified.
The authors should investigate the causes of the errors more closely and correct them.
Regarding the components on the board, why are there two different RF switches? The part number of the component is not reported, however, the authors state that the component has multiple channels available that could be exploited.
It is unclear how the power and energy consumption shown in Table 2 was calculated and what the power source and input voltage are.
Are the values theoretical or measured?
Is the RF switch consumption for a single IC?
Table 3: please, add units of measurement.
Fig. 11: please, add a description of the orange and red line in the caption.
Author Response
Please see the attachment
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The authors provide an insight into the field of energy-neutral positioning technologies and propose a hybrid RF-acoustic method for indoor positioning. In my opinion the article is generally well written and interesting, it provides enough information to understand and evaluate the scientific results. I only have a few questions.
A) The authors use the Vesper VM1000 microphone way above the provided specifications. What guaranties that different baches of the microphone will behave similarly to the ones used in the experiments?
(Note: the microphone may have a resonance peak somewhere above the graph given in the specification, it may be used for increased sensitivity or selectivity.)
B) The authors stated that the RF wake-up detector is not yet implemented. It would be interesting to know what the average consumption of the mobile device is, e.g. how long could it operate on a simple battery in the current state.
C) The experiments were performed in the Techtile infrastructure. Based on the article I do not see the role of this special infrastructure.
D) I do not see the role of using Raspberry PI as a signal generator (if there is already a high-cost instrument in the setup). A proper signal generator could be used for audio signal generation, this could provide a more precise synchronization.
E) Figure 10. Is there a reason why the distance error is the highest at 350 cm?
Note: for the first sight it looks like the error is quite small, but only because it is given in meters, not centimeters. It would be better to have the same prefixes in the legend and the scale (e.g. cm).
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Reviewer 3 Report
1.The article involves a comprehensive overview of the active research in low-power, indoor positioning systems.
2.The problem of 3D positioning of energy-neutral devices is condifered. The authors examine hybrid acoustic-RF approaches for positioning energy-neutral devices.
3.The results of the paper demonstrate the very promising potential of the combination of slower propagating acoustic waves with low-power backscatter RF communication technology to enable this sought-after feature in location based services.
4.The authors explain how the combination of adequate signaling realizing a late wake up of the devices with backscattering could position energy-neutral devices. Experiments in a real-life testbed confirm the potential 10 cm-accuracy based on RF-harvested energy.
5.Presentation and analysis of ranging experiments demonstrating the opportunities and open challenges on the way to accurate 3D positioning
6.In the future, it will be useful to consider some combinatorial optimization models for the positioning problem.
Author Response
We would like to thank the reviewer for reading our work and giving some suggestions for future positioning research. As no major remarks were given in this review, we did not alter or add text to this journal paper other than some language-based improvements after a thorough revision.
