FM spam: soon the posters will “grow wiser” and start broadcasting the FM signal, scoring our favorite radio station
Last year, a very interesting presentation was presented at the conference “USENIX Symposium on Networked Systems Design and Implementation”. How to turn a T-shirt or billboard into an FM radio station. The presentation author explains how to “fit” digital data and arbitrary audio tracks onto an FM signal already flying over the air. Through the effect of backscattering radio waves. The presentation seemed so interesting to me that I could not refrain from preparing a brief retelling.
What is the practical value of such "FM-jerking"? Are they generally real, or is it from science fiction? And if real, then how about licensing radio transmitters? About all about it - below.
smart posters at bus stops and smart street signs that can digitally transmit (1) local sights or (2) advertisements. Directly to our FM-receiver (to the driver’s radio tape recorder or to a passer’s smartphone).
smart posters that, advertising artists, broadcast their audio tracks to our smartphone. Or they encourage us to buy tickets for the upcoming concert by sending contextual advertising on our smartphone.
smart street signs that (1) broadcast information about the name of the intersection and (2) tell people with disabilities when you can safely cross the street.
smart clothes, made of smart fabric, which tracks the speed of a runner and the main indicators of his state of health, and then directly transmits this data to his smartphone.
How to achieve this? 3r3164.
At the presentation mentioned at the beginning of the article, the speaker demonstrated three technological innovations that enabled him to make an FM replanting: 3r-3219.
3r3183. Cotton T-shirt with machine embroidery of conductive thread, which serves as an antenna, transmitting the signal to the smartphone.
3r3183. The design of a flat antenna made of copper tape, suitable for placement on the back side of an advertising poster.
3r3183. The prototype of the device that implements the software logic of the FM replenishment, and the corresponding chip for this prototype.
What are the technical characteristics of this chip? 3r3164.
3r3183. Data transfer rate: up to 3.2 kilobits per second
3r3183. Range (with antenna): up to 18 meters. 3r3191.
3r3183. Power consumption: up to 11 µW. 3r3191.
3r3183. The battery charge in a smart poster lasts at least 12 hours. 3r3191.
3r3111. What are the technical limitations? 3r3164.
FM shuffling can only be done if the following three conditions are met: 3r-3219.
3r3183. The surrounding radio signals, for which we make FM replenishment, must be ubiquitous in outdoor urban environments. 3r3191.
3r3183. Target receivers (smartphones of passers-by and car stereos) must be equipped with FM radio receivers. 3r3191.
3r3183. Backscattering at the frequencies we need should be within the framework of legal use (so that it is not required to obtain a license); and therefore the possibility of using the cellular range immediately disappears. 3r3191.
Do FM radio signals really satisfy these limitations? 3r3164.
The short answer is yes. Technical answer:
3r3183. FM radio stations operate on a broadcasting principle and are already deployed in all cities. 3r3191.
3r3183. Radio towers transmit signals at high power (several hundred kilowatts), which is quite enough for communications based on backscattering. 3r3191.
3r3183. FM receivers are integrated into almost all modern LTE and Wi-Fi chips. This means that in order to receive information transmitted via FM infusion, no additional equipment is needed. 3r3191.
3r3183. The Federal Communications Commission allows low-power FM transmitters to operate on the FM band — without licensing. 3r3191.
3r3163. Real examples 3r3164.
The pride of the author of the above presentation is the following achievements: 3r33232.
I programmed a smart poster in such a way that he sat down an advertising audio track on an FM signal already on the air. As a result, the radio receivers of cars passing by (of course, if they are turned on and tuned to the same wavelength through which the FM replanting is performed) began to play this advertising audio track.
I found a way to transmit contextual advertising to passersby smartphones through the FM donation.
So, today there is already a technical possibility to turn static objects of urban infrastructure into FM radio stations. The signals propagated by them can be used as carriers for communications based on the effect of backscattering. The radio signals transmitted by such communications can be decoded by any FM receiver, including those that are placed in car radio and smartphones.
An example of such an audio signal can be heard here:
Your browser does not support HTML5 video. 3r3208.
If someone is interested in the technical details of the implementation of the mechanism of FM-add-ons and the materiel on backscattering, read the original source. There they are given in abundance.
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