Ambient Backscatter By Kevin La Mantia COSC 380

Ambient Backscatter By: Kevin La. Mantia COSC 380

Roadmap � What � How is Ambient Backscatter? it works and was designed � Potential applications of Ambient Backscatter

What is Ambient Backscatter? � Concept from Professors and Students at University of Washington ◦ ◦ ◦ Vincent Liu Aaron Parks Vamsi Talla Shyam Gollakota Joshua R. Smith David Wetherall � As devices get smaller, providing room for wires and batteries becomes more expensive � Came up with a novel concept that requires no batteries or wires

What is Ambient Backscatter (continued)… � Backscatter: A reflection of waves, or signals back to direction from which they came �A new communication primitive where devices communicate by backscattering ambient RF signals � No batteries

What is Ambient Backscatter (continued)… � Takes advantage of ambient RF waves ◦ TV, Cellular, and Radio � Small environmental footprint ◦ No additional energy is consumed since it uses what’s already in the air � Device to device communication ◦ Wireless communication

How Ambient Backscatter Works � Example: ◦ Two AB devices named Alice and Bob, and a TV Tower in an Urban environment as the ambient source. Alice wants to send a packet to Bob. She does this by backscattering the ambient RF signals to convey the bits in the packet.

How A. B. Works (continued)… � Ambient waves source (TV Tower) sends out RF � Ambient Backscatter devices can use these signals to power itself and reflect signals ◦ By reflecting or not, they transmit a 0 or a 1 � Bob can sense the backscattering signal changes and decode Alice’s packet � Also creates an “Additional Multipath”

How A. B. Works (continued)… � Leverages cellular � TV RF signals from TV, radio, or Towers ◦ Transmit up to 1 MW ERP (effective radiated power) ◦ Can serve up to 100 mi away in flat terrain or 45 mi in denser terrain � Provides Great coverage (urban) ◦ Top 4 broadcast TV channels reach up to 97% of Americans

How A. B. Works (continued)… � TV transmissions broadcast uninterrupted ◦ Reliable power and signal � 8 -level vestigial sideband (8 VSB) ◦ Transmit one of 8 amplitude values per symbol ◦ Symbols are sent over a 6 MHz wideband channel ◦ Very fast fluctuation in the signal � TV signal periodically encode special synchronization symbols ◦ Used to compute the multipath channel characteristics ◦ Ambient Backscatter devices create a multipath channel

Ambient Backscatter Design � Changes the impedance of the antenna � When a wave encounters an antenna with two different impedances, it reflects the wave � Controlling the strength of the reflection energy allows for information to be transmitted ◦ AB Devices control this energy with a switch that sets the states of the device (reflective ‘ 1’ and absorptive ‘ 0’)

What is it doing? What the signal looks like from the TV Tower and Backscattering Techniques After averaging the signals using the formula: y [n ] = x [n ] + B[n ]x [n ] + w [n ] You can get a on or off

The Demodulator Diagram � The demodulator has two stages: an envelope detection and averaging stage that produces an average envelope of the signal, and a computethreshold stage that compares the averaged signal with a threshold value computed by taking a longer-term average of the signal

Carrier Sense �A method that UW Engineers came up with to detect the signals from another A. B. Device � Detects devices power levels to distinguish between ◦ Compares 0’s and 1’s � Uses an equation for energy detection ◦ If D is close to 0, a device is near, if D is close to 1, a device is not near

A. B. Design (continued)… Antenna Touchpad Buttons Device Scheme

Prototype in action

Future Applications � Embed into building, bridges, infrastructure to alert Engineers about potential weaknesses � Because they are require no batteries, can be imbedded into materials like concrete � Example from video: ◦ Devices built into couches and can send an alert to the users phone that they left their keys on the couch or table

Future Applications (continued)… � Example from Research Paper: ◦ Grocery store: �Ambient Backscatter devices can be used for inventory systems. To alert when stock needs refilled. �Can also help customers locate items by transmitting the location to a users phone � More research needed to improve technology � Transfers are currently slow ◦ More research needed to speed up transmission ◦ Can be possible to improve this using different signal strengths

Conclusion � Covered what Ambient Backscatter is � How it works � How it was designed � Future applications

Questions?

Works Cited � � Vincent Liu, A. P. (2013, August). Ambient Backscatter: Wireless Communication Out of Thin Air. Washington, U. O. (2013). Ambient Backscatter. Retrieved from Youtube. com: http: //www. youtube. com/watch? feature=player_embedded&v=g. X 9 cbx. LSOk. E