Visible Light based Activity Sensing using Ceiling Photosensors

Introduction

Activity sensing on a building at a wide scale can support a broad spectrum of applications for indoor environments. In smart homes, for example, it could enhance controls on lighting, heating, ventilation, and air conditioning based on sensed and predicted activities across rooms. Useful information ranges from basic occupancy and movement tracking, to activity inference (e.g., sleeping, cooking, eating, watching TV or media).

These kinds of activities can currently be detected by a number of dedicated sensing systems. One approach leverages sensing devices continuously and physically connected with the user (wearable sensing) like smart watches and smart phones, that users continuously carry, wear, and usually charge. Device-free solutions have relied on cameras or wifi-based activity sensing. These systems have privacy and security issues, even for RF-based systems, since RF signals penetrate walls. Wifi-based activity sensing systems have been found to have interference problems while coexisting with ISM band operating devices like microwaves and cordless phones.

Infrared (IR) sensing is one of the most prevalent techniques for motion sensing, starting with detecting motion by the blocking of transmission between an IR sender and receiver. Afterwards, passive or Pyroelectric infrared (PIR) sensors were introduced that detect the radiated IR energy from humans and animals. PIR sensors can suffer from reliability problems whenever a sudden heat change happens, like a window or door opening. Moreover, PIR sensors require line-of-sight to the moving object, which limits the range of such sensors.

More recently, VLS has been considered for indoor motion and activity tracking. VLS is appealing because of the following properties: it can leverage existing lighting infrastructure as transmitters (with no building wiring overhead), it does not penetrate walls (preserves privacy and security and makes it easier to determine in which room an activity occurred), and unlike RF techniques it does not cause or suffer from radio interference. With nanometer wavelengths, it is highly sensitive to small motions and small objects compared to RF waves. Moreover, VLS is not affected by temperature changes.

Many current visible light localization techniques are active techniques that require the user to carry a sensor/device (smart phone/light sensor) and localize using standard trilateration leveraging three anchors (light sources) or by sweeping a light beam. Among passive (device-free) techniques , researchers have used visible light to locate fingers within the workspace of mobile devices. Other works demonstrate fine-grained gesture and human skeleton reconstruction using visible light sensing but require deploying photodiodes on the floor, which limits the scalability of such a motion sensing system.

System Overview

2.Synchronization and Signaling

Implementation

3.1 Prototype 3.2 Experimental Setup

Preliminary Results

4.1 Location Differentiation 4.2 Detecting Open Doors

Conclusion and Future Work