Introduction to Ambient BackScatter, How it works?
In spite of many technological advances in wireless communications, whats the most annoying thing we face....battery drain, in fact more advanced technologies suck more battery !! For that reason for wireless devices like sensors, mobiles, swiping machines, all need a lot of maintenance...don't worry there is a way around ABS (ABC as they like to call it), Engineers from university of washington developed a prototype and demonstrated some applications.
BackScatter is an old technology used in RFID, but Ambient BackScatter differs from RFID in many ways (See below), main USP of ABS is, it Enableswireless devices with Power and Communications Medium without requiring batteries.....amazing isn't it..?? Its works on simple (Really!!) 2 principles
1) It gets powered on using the ambient RF signals around 2) It transmits/receives signals by reflect/absorbing ambient RF signals around
The ambient RF signals discussed were TV Signals.
It Uses
FM0 Coding (Data decoded by detecting change in transitions as 0 or 1)
Carrier Sensing
Own Network Stack (Similar Frame format as Ethernet)
At a high level, backscattering is achieved by changing the impedance of an antenna in the presence of an incident signal. Intuitively, when a wave encounters a boundary between two media that have different impedances/densities, the wave is reflected back
Energy Detection?
We show that one can perform energy detection by leveraging the property of the analog comparator, in the absence of a nearby backscattering transmitter, the comparator typically outputs either a constant sequence of ones or a constant sequence of zeros. A nearby transmission, on the other hand, results in changes that are greater than the comparator’s threshold and therefore bit transitions at the comparator’s output.
Since the transmitted bits have an equal number of ones and zeros (due to FM0 encoding), the comparator outputs the same number of ones and zeros. Thus comparing the number of ones and zeros allows the receiver to distinguish between the presence and absence of a backscatter transmission
How it is different from RFID?
Ambient backscatter differs from RFID-style backscatter in threekey respects.
Firstly, it takes advantage of existing RF signals so it does not require the deployment of a special-purpose power infrastructure—like an RFID reader—to transmit a high-power (1W) signal to nearby devices
Second, and related, it has a very small environmental footprint because no additional energy is consumed beyond that which is already in the air.
Finally, ambient backscatter provides device-to-device communication. This is unlike traditional RFID systems in which tags must talk exclusively to an RFID reader and are unable to even sense the transmissions of other nearby tags
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