Feasibility and limits of wi-fi imaging

Abstract

We explore the feasibility of achieving computational imaging using Wi-Fi signals. To achieve this, we leverage multi-path propagation that results in wireless signals bouncing off of objects before arriving at the receiver. These reflections effectively light up the objects, which we use to perform imaging. Our algorithms separate the multi-path reflections from different objects into an image. They can also extract depth information where objects in the same direction, but at different distances to the receiver, can be identified. We implement a prototype wireless receiver using USRPN210s at 2.4 GHz and demonstrate that it can image objects such as leather couches and metallic shapes in line-of-sight and non-line-of-sight scenarios. We also demonstrate proofof-concept applications including localization of static humans and objects, without the need for tagging them with RF devices. Our results show that we can localize static human subjects and metallic objects with a median accuracy of 26 and 15 cm respectively. Finally, we discuss the limits of our Wi-Fi based approach to imaging.

Reusing 60GHz Radios for Mobile Radar Imaging

“…Like [25], we found that the imaging quality depends on the imaging angle, defined by the relative location of TX to the object and the trajectory of RX. Specifically, to identify the object, TX's beam should cover the object and the reflected signal should reach RX along its trajectory.…”

“…We summarize RSA here and present the detailed algorithm in §4. RSA offers two advantages over prior work on RF imaging [25,29,52]:…”

“…Like existing works on radar imaging [25,36,21,20], we evaluate the utility and accuracy of our proposed design by imaging real objects of different size, curvature, and material. In addition to the objects listed in Figure 3 which are of 5cm-30cm in width, we also test smaller objects including a keyring and a small wrench (2.5cm in width).…”

“…A recent work built WiFi imaging using OFDM and large phased arrays (available on APs) and discussed the resolution limitation due to its large wavelength [25]. Our work considers 60GHz (mmwave) communications because it offers several desirable qualities for mobile imaging when compared with WiFi: tiny wavelength, high directionality, stable and predictable signal propagation.…”

“…But they require costly specialized hardware or large antennas unsuitable for mobile devices. A recent project reuses WiFi communication devices with multiple antennas to image objects, but its precision is fundamentally limited by WiFi's large wavelength [25]. Finally, while today's millimeterwave imaging systems can offer accurate object imaging [6,10,34,42], they all require specialized hardware, e.g.…”