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.

Overall Approach

Trilateration is the method of determining location of an object through relative distances of points and geometry of spheres. It is a method that is used in Global Positioning Systems but we intend to use the same principle in indoor localization. As illustrated below, knowing an object's relative distance from Boise, Minneapolis and Tucson, one can derive that that object is in Denver. Similarly, knowing a person's location from three USRPs enables us to roughly estimate his position in an indoor place.

Resources

USRP:

ESG Signal Regenerator:

Wiserd:

Spectrum Analyzer:

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.

Trilateration

The location of the transmitter and the various receivers

Experiment one: Detecting noise and signals using the nodes

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.

Experiment two: I/Q Samples

The noise in the ORBIT lab	the signal received by a node
Analysis: The left image shows signal reception when there is no signal transmitted. This is the noise that is present while we conduct experiments in the ORBIT room. The peak that is visible in the right image is the frequency that the transmitted signal is received at the receiver nodes.

IQ samples are often used in RF applications. In signal processing, I/Q samples are the real and imaginary components of a transmitted signal. The in-phase component is the "i" and the out of phase component, shifted by 90 degrees, is "q". These samples were used to calculate the power of the signal and figure out the relationship between signal power and distance.

Analysis: We used USRPs to collect the IQ samples that are portrayed in Figure 1. The graph has time on the x axis and amplitude on the y axis for both the real and imaginary components of the signal. Figure 2 verifies the reception of this signal using Fast Fourier Transform in Matlab. IQ samples are often used for modulation and demodulation of the signal that is being analyzed. We used these samples to calculate the power of the signal at known distances.

Experiment four: Relating Signal to noise ratio to distance

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


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 shown below.

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

​Week 2
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​Week 9
​Final Week

Team

Real and Imaginary Signals	Verifying Reception using FFT
Analysis: As shown in this experiment, the line of best fit follows a generally negative and exponential curve but some of the points are no where close to the curve. The scattering of the data points signify either an error in signal processing or simply not enough data points. We believed the latter might have had a hand in this error.

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