Moving Object Detection System: Wi-Vi

By: Kunwardeep Singh Gujral

Can Wi-Fi in our homes help us to see through walls? From many years, people have thought about supernatural vision and production with the concepts of science fiction movies. But this can be achieved with Wi-Vi technology by using it in two different modes. The first phase of the system will find objects that have movement behind the wall, and the second phase is a gesture-based interface. Wi-Vi is the only device which is capable in identifying gestures behind the wall or to convey the message. The fundamental concept of examining through an opaque obstacle is kindred to the old concepts of RADAR and SONAR. Using Wi-Vi in front of a non-metallic wall will result in small amount of the Radio Frequency signal passes through the wall, get reflected by objects or living beings, and reinstate with the impression of what is in a closed room. By apprehending these reflected signals and analyzing them, we can create an image-map of the object behind the wall.

Existing Systems and their comparison with Wi-Vi

1. Ultra-Wideband Systems (Through Wall Radar)

Earlier attempts have been made to develop such systems which are highly expensive and have huge sizes. These consists of bulky radars, that were dependent on electromagnetic spectrum, which was provided only to the military. Their were mainly focused on modeling and simulation. To eliminate flash effect, the system assists by differentiating the reflected signal from the wall and from the objects behind the wall. This separation can be achieved by using a very short pulse (approximately 1 nano second) due to the delay between arrival time of both the reflected signals i.e. from the wall and from the moving object behind the wall. Hence, this old technique requires an ultra-wideband (UWB) of around 2GHz to operate properly[1].

However, Wi-Vi systems have different operational characteristics because it works on less bandwidth and in the same range as Wi-Fi. Wi-Vi exceeds UWB requirements by knocking out the flash effect using MIMO (Multi Input Multi Output) nulling. The Wi-Vi system operates to distinguish reflected signals from the wall and from reflections caused by objects behind it, which is dependent on their arrival time. Therefore, it becomes necessary to identify the delay (that is, nanoseconds) to filter the effects of the flash.

In operational mode, Wi-Vi makes use of two antennas on the transmitter aspect and one receiving antenna. The two antennas transmit approximately the equal signal, besides that the second antenna signal is the inverse of the primary antenna signal, leading to the inference.

2. WISEE (note-based interfaces)

The gesture based recognition system based on wireless signals which has ability to identify and analyze the human gestures is known as WISEE. The system can detect human gestures without using a sensor on the human body. Several systems can detect human movement through the camera or by attaching a sensor to the human body. Currently recents models use micro-Dopler signatures that can detect human sightline activity while working on 2.4 GHz bandwidth [3]. Wi-Vi offers gesture-based system that is used as an interface in invisible cases and also through the wall, which eliminates the need of wireless devices and sensors to be used by moving human.

3. Infrared and Thermal Imaging

Infrared signals and thermal power imaging based frameworks broaden the human visualization past the apparent electromagnetic range and permitting us to recognize objects in presence of fog/smoke and dimness. This framework works by catching thermal power or infrared signals received back from the main obstruction in the sightline of their sensors. However, this innovation doesn’t permit us to see through opaque objects due to having a short frequency, though the Wi-Vi system has a frequency in the scope of 12.5 cm [5].

Working of Wi-Vi

To apply theoretical concept of Wi-Vi in real life, it is necessary to work on two major issues:

• The reflected signal is essentially more fragile than the obstacle which is bigger than the object of study, having a higher reflection coefficient [5].
• The signal from transmitter antenna to the recieving antenna, is notably bigger than the impressions of actual obstacles (flash effect)

The Wi-Vi system uses MIMO(Multi Input Multi Output) nulling technique to get over the above two issues and it also increases the focus on the reflection of real objects. The system eliminates the flash effect by using a cancellation technique (the received signal counts to zero) on the receiving antenna. The WI-VI system majorly has three antennas, which consists of two broadcasting antennas and  one receiving antenna. Firstly, the system estimates the channel recieved by the broadcasting antenna to the receiving antenna. In second stage, the system uses the channel estimation technique to cancel out the signal at the receiving antenna.

As shown in Figure 1, Inverse Synthetic Aperture Radar (ISAR) is used to detect moving objects using Wi-Vi. Earlier, a series of antennas(antenna array) is used in spatially spaced antennas to detect moving objects and it processes this information to calculate their orientation (Figure 2). ISAR, on the other hand, uses only one receiving antenna to detect moving objects, so the system makes only one measurement at a time [3]. When the person starts moving in the room, it filters the received signal from adjoining positions in space. This has a comparable effect on the set of antennas. Wi-Vi can mimic different antennas and use them to detect movement behind the wall by treating continuous-time samples as spatial samples.

Tracking Multiple Humans

The Wi-Vi system can be extended for tracking process of several moving objects/humans. To detect human movement, a series of antennas can be tracked, as in the case of individual human detection. However, each human mimics a separate antenna array. Due to presence of single antenna in Wi-Vi, the received signal can be accessed with the moving person’s antenna array. Also, with multiple people, the noise increases significantly. To avoid this problem, Wi-Vi use Smoothed Music Algorithm to catch up with different people. This algorithm computes the correlation matrix (w x w) on R[n]. To remove the noise and to maintain the strongest eigen-vectors, eigen decomposition on R[n] is executed [1]. This corresponds to some moving eigen-vectors and DC values ​​in this case.

Applications of Wi-Vi based System

• It can be used in military operations replacing previous bulky systems.
• Can be effectively used during the time of natural disasters like earthquake to track human movement behind walls or in between a debris.
• It can be used as a smart sensing device in smart home systems and also as security system for homes.

To sum up, Wi-Vi uses wireless technology i.e. a Wi-Fi signal, to sense people moving behind walls or inside shrouded rooms. Unlike previous systems, where the area unit was military, now  Wi-Vi enables a small, inexpensive, transparent wall device that works within the bounds of the idea, and its usage by general public is possible. Wi-Vi will help us to communicate channels with people behind the wall without having to carry a transmission device with us. The upcoming Wi-Fi networks generation will not only be functional in tele-communication mode, but will also be able to detect, control and localize objects within buildings.

References

[1] Vidyasagar S D, Seema, “A Study on Applications of Wi-Vi Technology,” International Journal of Computer Sciences and Engineering, 2019

[2] Sudarshan Adeppa, “Detection of Objects across the Walls with Wi-Fi Technology”, International Journal on Emerging Technologies, 2015.

[3] Adib, Fadel, and Dina Katabi, “See through Walls with Wi-Fi,” Proceedings of the ACM SIGCOMM Conference, 2013.

[4] Arpitha Shankar S I “MIMO Cognitive Radio with Low-Cost Reception Using Beam Forming and Antenna Sub Array Formation” International Journal of Computer Sciences and Engineering (IJCSE), 2016

[5] G. Char vat, L. Keppel, E. Rothwell C. Coleman, and E. Mohole. An ultra-wideband (UWB) switched-antenna-array radar imaging system in IEEE ARRAY, 2010

Cite this article as:

Kunwardeep Singh Gujral (2021) Moving Object Detection System: Wi-Vi, Insights2Techinfo, pp.1

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