Indoor Localization

Introduction

The use of GPS services is growing just as fast as the development and accessibility of mobile devices. A GPS device, which used to be a significant investment, is now included in every smartphone that emerges on the market. These services have assisted many as they navigate themselves from place to place outdoors.

Although GPS is well-defined outdoors, localization indoors is still an active research problem. GPS signals indoors tend to be weaker; even if they are usable, the accuracy associated with GPS signals is not up to par. Large errors (on the order of meters) associated with GPS generally do not affect the user's ability to navigate to buildings, parks, landmarks, etc. Errors on the order of meters indoors, however, could mean that somebody is in a different room or different building altogether. A fine-grained service, down to the centimeter, is needed to localize indoors.

Motivation

An effective, low-cost, easy-to-implement solution to the indoor localization problem will have immediate impacts on everyday life, especially commercial retail. Based on movements of people in a store, retailers could determine where to place their best-selling items. They could place products effectively to accommodate shoppers and increase profits. In addition to commercial applications, indoor localization could help emergency responders efficiently respond to calls indoors, or help the elderly navigate inside a large building. Once the technology is fully developed, there are plenty of applications.

What is ORBIT Lab?

The ORBIT facility consists of a 20 x 20 grid of programmable radio nodes used to test wireless protocols and applications. Certain nodes in the facility, as well as certain sandboxes (part of the lab but not the grid), contain Universal Software Radio Peripherals (USRP), which are software defined radios that transmit and receive signals.

Founded in 2003 and launched in 2005, this lab provides the world's largest academic testbed for wireless communications. As of 2014, there are over 1000 registered users who have logged ~200,000 experimentation hours since the lab's founding.

Procedure

Using the USRPs as both transmitters and receivers, we measure the received signal power of a certain transmitted signal and plot this measurement against the distance between the node and transmitter. We hope to obtain many distance-power measurements, which would allow us to accurately predict the the distance (but not direction) between a transmitter and receiver based on the signal power.

The location of the transmitter and the various receivers

The photos below show what occurs before the signal is transmitted and after the signal is transmitted. The ASCII art below gives us a general idea of the signal amplitude, which is then measure directly with OMF (ORBIT Management Framework) commands.

Using the measured signal power, along with the distance between the transmitted and receiver, we obtained a signal amplitude-distance pair. We many of these pairs using different transmitters and receivers. We then plotted these items on a graph and found the exponential fit for the graph, as show below

(left) The noise in the ORBIT lab and (right) the signal received by a node	A received signal from the node

Signal-to-Noise ratio versus distance and the fitted curve(red)

Weekly Presentations

Presentations are done on a weekly basis before other research interns or professors. Presentations include the group's accomplishments over the past week as well as goals for the following week

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Team

Rahul Hingorani University of Michigan Industrial/Electrical	Vineet Shenoy Rutgers University Electrical and Computer Engineering	Karan Rajput Rutgers University Electrical and Computer Engineering