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Wi Vi technology

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Researchers have always tried to build a device capable of seeing people through walls. However, previous efforts to develop such a system have involved the use of expensive and bulky radar technology that uses a part of the electromagnetic spectrum only available to the military. Now a system is being developed by Dina Katabi and Fadel Adib, could give all of us the ability to spot people in different rooms using low-cost Wi-Fi technology. The device is low-power, portable and simple enough for anyone to use, to give people the ability to see through walls and closed doors. The system, called “Wi-Vi,” stands for "Wi-Fi" and "vision." is based on a concept similar to radar and sonar imaging. But in contrast to radar and sonar, it transmits a low-power Wi-Fi signal and uses its reflections to track moving humans. It can do so even if the humans are in closed rooms or hiding behind a wall.

Simple definition for Wi-Vi is, as a Wi-Fi signal is transmitted at a wall, a portion of the signal penetrates through it, reflecting off any humans on the other side. However, only a tiny fraction of the signal makes it through to the other room, with the rest being reflected by the wall, or by other objects. Wi-Vi cancels out all these other reflections, and keeps only those from the moving human body. Previous work demonstrated that the subtle reflections of wireless inter signals bouncing off a human could be used to track that person's movements, but those previous experiments either required that a wireless router was already in the room of the person being tracked. Wi-Fi signals and recent advances in MIMO communications are used to build a device that can capture the motion of humans behind a wall and in closed rooms. Law enforcement personnel can use the device to avoid walking into an ambush, and minimize casualties in standoffs and hostage situations. Emergency responders can use it to see through rubble and collapsed structures. Ordinary users can leverage the device for gaming, intrusion detection, privacy-enhanced monitoring of children and elderly, or personal security when stepping into dark alleys and unknown places.

The concept underlying seeing through opaque obstacles is similar to radar and sonar imaging. Specifically, when faced with a non-metallic wall, a fraction of the RF signal would traverse the wall, reflect off objects and humans, and come back imprinted with a signature of what is inside a closed room. By capturing these reflections, we can image objects behind a wall.

Wi-Vi is a see-through-wall technology that is low-bandwidth, low-power, compact, and accessible to non-military entities. Wi-Vi is a see-through-wall device that employs Wi-Fi signals in the 2.4 GHz ISM band.

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Wi Vi technology

  1. 1. - Seeing through walls using Wi-Fi Technical Seminar On Presented by: Liju P Thomas 1HK10EC030
  2. 2. CONTENTS Introduction. Challenges faced in designing Wi-Vi Flash Effect. Tracking Human movements. Methods used to overcome the challenges. Implementation. Results. Advantages and limitations. Applications Conclusion and Future Scope
  3. 3. Wi-Vi - Wireless Device - Captures moving objects behind the wall - Through Wall Imaging - Relatively Low power - Low Cost - Low Bandwidth - It is 3 antenna MIMO Device - Two transmitting and one receiving antenna. - Limits itself to a 20 MHz- wide Wi-Fi channel, and avoids ultra-wide band solutions - Two modes of use: - Image moving objects behind the wall - Gesture based interface - Uses Wi-Fi signals in ISM band(2.4Ghz) - Typically Wi-Fi Hardware INTRODUCTION
  4. 4. KEY IDEA Wi-Vi Device
  5. 5. Challenges Faced in Designing Wi-Vi  Challenge #1: “Flash” Effect  RF signals penetrate walls: • Reflect off objects on other side of wall • Distinguish reflectors by their arrival times  At low bandwidth: • Wall reflection much stronger than reflections coming from behind the wall. • Flash effect: wall reflection saturates the ADC
  6. 6. Challenges Faced in Designing Wi-Vi  Challenge #2: Identifying and tracking Humans Traditional System:Array of Spaced Antennas  Previous attempts to track moving targets through walls have done so using an array of spaced antennas.  This would be too expensive and bulky. Angle of Arrival
  7. 7. How Can We Eliminate the Wall’s Reflection?  Wi-Vi uses interference nulling to cancel both the wall reflections and the direct signal from the transmitting to the receiving antenna, hence increasing its sensitivity to the reflections of interest. NULLING TO REMOVE THE FLASH  MIMO systems can pre-code their transmissions such that the signal received at a particular antenna is cancelled.  This property can be tailored to eliminate the flash effect as well as the direct signal from the transmitting to the receiving antenna, thereby enabling Wi-Vi to capture the reflections from objects of interest with minimal interference.  At a high level, Wi-Vi’s nulling procedure can be divided into three phases: • Initial nulling • Power boosting • Iterative nulling
  8. 8. Algorithm for Wi-Vi Nulling
  9. 9. h2 h1 px X y = h1‘ x + h2‘px p = -h1’ / h2‘ Static objects (wall, furniture, etc.) have constant channels People move, therefore their channels change y = h1‘ x + h2‘(- h1‘/ h2‘)x y = H1 ’ x + H2 ’(- h1‘/ h2‘)x Not Zero 0 MIMO Nulling
  10. 10. ISAR – Inverse Synthetic Aperture Radar  Inverse synthetic aperture radar uses the movement of the target to emulate an antenna array.  In ISAR, there is only one receive antenna; hence, at any point in time, we capture a single measurement. since the target is moving, consecutive measurements in time emulate an inverse antenna array – i.e., it is as if the moving human is imaging the Wi-Vi device.  By processing such consecutive measurements using standard antenna array beam steering, Wi-Vi can identify the spatial direction of the human. How Can We track the movement of Humans?
  11. 11. Direction of reflection θ Antenna Array Tracking Motion RF source
  12. 12. θ Antenna Array Direction of motion At any point in time, we have a single measurement Tracking Motion
  13. 13. θ Antenna Array Direction of motion θ Direction of motion Tracking Motion
  14. 14. IMPLEMENTATION USRPs connect to a host computer through a high-speed USB or Gigabit Ethernet link, Universal Software Radio Peripheral (USRP N210) Products are open source USRP models also integrate the general functionality of a host computer with an embedded processor Commonly used by research labs and universities etc. Comparatively inexpensive hardware platform for software radio Designed and sold by Ettus Research
  15. 15. IMPLEMENTATION MIMO nulling is implemented directly into the UHD driver, so that it is performed in real-time. • LP0965 directional antennas • 3 USRP’s are connected to an external clock and they act as one MIMO system. Application areas include:  Wi-Fi  Wi-Max  S-band transceivers  2.4 GHz ISM band transceivers Capable of MIMO and provides upto 40 MHz bandwidth Dual-band operation • Wide bandwidth transceiver • Power output: Upto 10mW • Noise Figure: 5dB SBX Transceiver
  16. 16. Wi-Vi Setup & Working Any objects that the signals hit including the wall create identical reflections, they too are cancelled out by this nulling effect. Only those reflections that change between the two signals, such as those from a moving object, arrive back at the receiver.
  17. 17. Tracking of 2 humans Tracking of 3 humans  Tracking of multiple people can be done by Smoothed Music Algorithm.  This algorithm computes w x w correlation matrix R[n]  It then performs an Eigen decomposition of R[n] to remove the noise and keep the strongest Eigen vectors, which in our case correspond to the few moving humans, as well as the DC value.
  18. 18.  For a human to transmit a message to a computer wirelessly, they typically has to carry a wireless device.  Wi-Vi can enable a human who does not carry any wireless device to communicate commands or short messages to a receiver using simple gestures.  Wi-Vi designates a pair of gestures as a ‘0’ bit and a ‘1’ bit.  At this stage, Wi-Vi’s interface is still very basic, yet we believe that future advances in through-wall technology can render this interface more expressive. Through-Wall Gesture-Based Communication
  19. 19. Gesture Encoding Gestures as Angles:Gestures as detected by Wi-Vi:
  20. 20. Gesture Decoding Output of matched filter: Decoded bits: Accuracy of Gesture Decoding as a Function of Distance
  21. 21. Results of Wi-Vi Using USRP N210 Detect movements behind opaque structural obstructions Wi-Vi device pointed at a closed room with 6” hollow walls supported by steel frames can distinguish between 0, 1, 2, and 3 moving humans in the room. Computed over 80 trials with 8 human subjects, Wi-Vi achieves an accuracy of 100%, 100%,90%, and 85% respectively in each of these cases. A single person sending gesture based messages, Wi-Vi correctly decodes all messages performed at distances equal to or smaller than 5 meters. The decoding accuracy decreases to 75% at distances of 8 meters, and the device stops detecting gestures beyond 9 meters. It also removes clutter from all static reflectors, rather than just one wall. This includes other walls in the environments as well as furniture inside and outside the imaged room.
  22. 22. Advantages  Wi-Vi is relatively a low-power, low-cost, low- bandwidth, and accessible to average users.  Wi-Vi requires only few MHz of bandwidth and operates in the same range as Wi-Fi. It operates in ISM band.  Wi-Vi can perform through-wall imaging without access to any device the other side of the wall.  Wi-Vi employs signals whose wavelengths are 12.5 cm.  Extend human vision beyond the visible electromagnetic range, allowing us to detect objects in the dark or in smoke. Limitations  Display has very low resolution.  We cannot detect humans behind concrete walls thicker than 8".  To achieve a narrow beam the human needs to move by about 4 wavelengths (i.e., about 50 cm).
  23. 23. Applications Law Enforcement Emergency Situations Personal Security Smart Sensing
  24. 24. ApplicationsUser Interface Design Intruder Detection Gaming
  25. 25. Conclusion  Wi-Vi, a wireless technology that uses Wi-Fi signals to detect moving humans behind walls and in closed rooms. In contrast to previous systems, which are targeted for the military, Wi-Vi enables small cheap see-through-wall devices that operate in the ISM band, rendering them feasible to the general public, without carrying any transmitting device. Wi-Vi could be built into a Smartphone or a special handheld device. Evolution of seeing humans through denser building material and with a longer range. High quality images. Future Scope
  26. 26. REFERENCES [1] Fadel Adib and Dina Katabi, "See through wall with WI-FI", Massachusetts Institute of Technology. In ACM SIGCOMM, 2013. [2] Q. Pu, S. Gupta, S. Gollakota, and S. Patel, "Whole-home gesture recognition using wireless signals", University of Washington. [3] T. Ralston, G. Charvat, and J. Peabody. “Real-time through-wall imaging using an ultra-wideband multiple-input multiple-output (MIMO) phased array radar system.” In IEEE ARRAY, 2010. [4] “Advanced trends in wireless communication” Edited by Dr. Mutamed Khatib [5] "Seeing through walls"- MIT's Lincoln Laboratory, http://www.youtube. com/watch?v=H5xmo7iJ7KA. [6] www.people.csail.mit.edu/fadel/wivi

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