Indoor Location System based on 802.15.4

9112636 戴毓廷9112029 吳信賢9112029 許碩仁

Outline

Introduction Methodology Simulation Hardware equipment Related work Reference

Introduction

“Sensing data without location is meaningless.” [2]

Using Global Position System (GPS) for every sensor is expensive.

Local Position System (LPS): using Received signal strength (RSS) or time of arrival (TOA) to get location information

Introduction

Combining GPS and LPS can give a low cost location system.

In this project, we would like to implementation a fine indoor location estimation based on RSS.

Methodology

Reference Devices (RD) Measuring BD’s RSS value, and push RSSI value to coordinator. RD have clear information of their position.

Blindfolded devices (BD) Broadcast a packet so RD can get RSSI value. BD do not know where he is.

Methodology

Coordinator Collecting the RSSI values form every RD, and then push them to server.

Server Running a program that can get value from COM port, getting RSSI values and performing location algorithm.

Methodology

Reference

Reference

Router / Reference

Reference

Blindfolded

Blindfolded

PAN coordinator

PC

Wireless link

Physical wire

Methodology

Location algorithm:

1. RSSI and power relationship. 2. Power and distance relationship. 3. Distance and location relationship.

Methodology

1. RSSI and power relationship: By experimental measuring.

2. Power and distance relationship:

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Methodology

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Methodology

3. Distance and location relationship: Here we use a method called Geometry method. The Geometry Location Algorithm has some different types:

Gravity of Area Apexes Method. Line of Position Method. Section of Area Method. Weighted Area Apexes Method.

Methodology

Gravity of Area Apexes Method:

Step1:Plotting Cycles.Center: The three positions of reference devices.Radius: The measured distance between RD and BD.

Step2: Find the six intersection points.

RD RD

RD

Methodology

Step3: Find the “meaningful” intersection points.

Step4: So far, we have three “meaningful” intersection points. Calculate the gravity of the three points and the position of gravity is our location estimation result.

BD

Simulation

Consider a right triangular area with three RD which locate at (0,0), (0,10), (5, ) and a single BD locates at some unknown position.

We random choose the position of BD, and add some random noise on the actual distances between the three RDs.

75

Simulation

0 2 4 6 8 100

1

2

3

4

5

6

7

8

9

10

x

y

(x-5)2+(y-8.6603)2=8.87322 = 0

B.D. @ (1,1)

Estimation result: (1.1127, 0.7729)

B.D. @ (5,5)

Estimation result: (4.8548,5.0718)

0 2 4 6 8 100

1

2

3

4

5

6

7

8

9

10

x

y

(x-5)2+(y-8.6603)2=3.68372 = 0

Assume the measurement error of RSS is between -5% and +5%

Hardware equipment

UZ2400 RF chip, UBEC, Taiwan. 8051 platform.

Related work

Create a program to handle RSSI and location estimation on server.

A filter or some solution to deal with RSSI jumping when BD stay at the same position.

Channel access problem.

Related work

We plan to complete one dimension first, and than using the algorithm discussed above to challenge two dimension.

Reference

[1] Neal Patwari, Alfred O. Hero, Matt Perkins, Neiyer S. Correal, Robert J. O’Dea, “Relative Location Estimation in Wireless Sensor Networks” IEEE TRANSACTIONS ON SIGNAL PROCESSING, VOL. 51, NO. 8, AUGUST 2003

[2]J. M. Rabaey, M. J. Ammer, J. L. da Silva, Jr., D. Patel, and S. Roundy, “Picorodio supports ad hoc ultra-low power wireless networking,” IEEE Comput., vol. 33, pp. 42–48, July 2000.

Thank you !!