By: Kevin LaMantia COSC 380

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

 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

 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

 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.

 Ambient source (TV Tower) sends out RF waves  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”

 Leverages RF signals from TV, radio, or cellular  TV Towers ◦ Transmit up to 1MW 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

 TV transmissions broadcast uninterrupted ◦ Reliable power and signal  8-level vestigial sideband (8VSB) ◦ 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

 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 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 has two stages: an envelope detection and averaging stage that produces an average envelope of the signal, and a compute- threshold stage that compares the averaged signal with a threshold value computed by taking a longer-term average of the signal

 A method that UW Engineers came up with to detect the signals from another A.B. Device  Detects power levels to distinguish between devices ◦ 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

Antenna Touchpad Buttons Device Scheme

Prototype in action

 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

 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

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

Questions?

 Vincent Liu, A. P. (2013, August). Ambient Backscatter: Wireless Communication Out of Thin Air.  Washington, U. O. (2013). Ambient Backscatter. Retrieved from Youtube.com: