Real Time Location Sensing (RTLS) using Passive RFID tagshome.iitk.ac.in/~rohan/Real Time Location System... · Real time location sensing (RTLS) is a technique of tracking and identifying

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Real Time Location Sensing (RTLS) using Passive RFID tags

Amit Bansal

Himanshu Rai

Rohan Mandala

Project Guide :

Professor A. R. Harish

Department of Electrical Engineering

Indian Institute of Technology - Kanpur, India

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CONTENTS Page No.

INTRODUCTION 7

Alien Reader--ALR8800 7

Passive RFID tags-ALL9640 7

RFID Reader External circular polarized Antenna 7

LITRATURE SURVEY 8

Real Time Location Sensing 8

1) Nearest Neighbor Algorithm 8

2) Triangulation 10

PROJECT WORK 11

1) Study of the properties of environment, antennae, Tags 11

Experiment 1.1: Threshold power level v/s distance from transmitter 11

Experiment 1.2 Tag Read V/s Background 12

Experiment 1.3: Power contour as antenna moves 13

Experiment 1.4: No. of tags read v/s distance from center of the tag grid 14

2) RTLS in 2D grid using Nearest Neighbor Algorithm with 1 transmitter 15

Experiment 2.1: RTLS in a 2 dimensional grid using Nearest Neighbor Algorithm 15

(Transmitter in front of one corner of grid)

Experiment 2.2: RTLS in a 2 dimensional grid using nearest neighbor Algorithm 17

(Transmitter in front of center of grid)

3) Effect on increasing antenna on RTLS in 2D 19

Experiment 3.1 RTLS using Random Arrangement of 4 antennae 19

Experiment 3.2 RTLS using Symmetrical placement of 4 antennae 20

Experiment 3.3 Effect of increasing no. of antennae further (Up to 28 antennae) 22

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4) RTLS in 3D using Nearest Neighbors Algorithm 24

Experiment 4.1 RTLS in 3D using 4 antennae 24

Experiment 4.2.1 RTLS in 3D using 8 antennae (All antennae not in one plane) 25

Experiment 4.2.2 RTLS in 3D using 8 antennae (all antennae in one plane) 27

Experiment 4.3.1 effect of increasing working area on RTLS in 3D using 8 antennae 29

(All 8 antennae not in one plane)

Experiment 4.3.2 Effect of increasing working area on RTLS in 3D using 8 antennae 30

(All 8 antennae in one plane)

Experiment 4.4.1 RTLS in 3D using 8 antennae on increasing no. of tags 32

(All 8 antennae not in one plane)

Experiment 4.4.2 RTLS in 3D using 8 antennae on increasing no. of tags 34

(All 8 antennae in one plane)

5) Triangulation 36

Experiment 5.1 Triangulation using 3 antennae 36

Experiment 5.2 Triangulation using 4 antennae 38

6) RTLS in 2D Random Setup 43

Experiment 6.1 Random setup in 2D for RTLS (Random orientations of tags) 43

Note: All the experiments we have done have following sections:

Objective of experiment

Experimental Setup

Measurements

Results

Conclusion

OVERALL CONCLUSION 44

LIMITATIONS 44

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List of figures

Figure No. Caption Page No.

1 Nearest Neighbors 8

2 Triangulation 10

1.1.1 Experimental setup to measure Threshold power with distance 11

1.1.2 Threshold power v/s distance of tag from antenna 12

1.2.1 Tag on different background 12

1.3.1 Power contour on horizontal movement of antenna 13

1.4.1 Experimental Setup for no. of tags read as antenna moves away 14

1.4.2 No. of tags read v/s distance of transmitter from center 15

2.1.1 Experimental setup for RTLS in 2D using nearest neighbor algorithm 16

(Transmitter Antenna In front of corner of grid)

2.2.1 Experimental setup for RTLS in 2D using nearest neighbors algorithm 17

(Transmitter Antenna placed in front of center of the grid.)

3.1.1 RTLS in 2D using Nearest Neighbors Algorithm with Four Antennae 19

(Random Arrangement of Antennae)

3.2.1 RTLS in 2D using Nearest Neighbors Algorithm 20

3.2.2 Antennae placement (on a circle around grid) 21

3.3.1 Different setups each at angle of 15 degree with previous setup 23

3.3.2 MEE v/s No. of antennae 24


(All Antennae placed in one plane in working area)


(Tags are randomly distributed in 3D in random orientations)


(All 8 antennae placed in one plane)

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(Working area more than in experiment 4.2)


(Working area more than in experiment 4.2& all 8 antennae placed in one plane)


(Working area same as in experiment 4.3, No. of tags are increased to 48)


(All 8 antennae placed in one plane &Working area same as in experiment 4.3, No. of tags=48)

5.1.1 Triangulation using 3 Transmitter antennae 36

5.1.2 Location of a tag using Triangulation with 3 antennae 37

5.2.1 Triangulation using 4 antennae 38

5.2.2 Threshold power v/s distance from antenna 1 39




5.2.6 RTLS using Triangulation for curve from friis formula 41

5.2.7 RTLS using Triangulation for curve from experimental data 42

6.1.1 RTLS using nearest neighbors in 2D Random tag arrangement in a large working area 43

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List of Tables

Table No. Title Page No.

2.1.1 Threshold Power Level of the Tag grid having transmitter in front of origin 16

2.1.2 Results for RTLS in a 2 dimensional grid using Nearest Neighbour Algorithm 17


2.2.1 Threshold Power Level of the Tag grid having transmitter in front of center of the grid 18

2.2.2 Results for RTLS in a 2 dimensional grid using nearest neighbour Algorithm 18

(Transmitter in front of centre of grid)

3.1.1 Result for RTLS in 2D using 4 antennae (Random Arrangement of antennae) 20

3.2.1 Result for RTLS in 2D using 4 antennae (Symmetrical placement of antennae) 21

3.3.1 Results for MSE for all tags and mean estimation error for every setup individually 23

3.3.2 Results for MEE using different no. of combination of antennae 23

4.1.1 Results for RTLS in 3D using 4 antennae 25


4.2.2 Results for RTLS in 3D using 8 antennae (Symmetrical Antennae) 27

4.3.1 Results for RTLS in 3D using 8 antennae (Larger Working Area & 32 tags) 30


(Larger Working Area & Symmetrical Antennae placement)

4.4.1 Results for RTLS in 3D using 8 antennae (Larger Working Area & 48 tags) 33


(Larger Working Area & 48 tags &Symmetrical Antennae placement)

5.1.1 Results for Triangulation using 3 antennae 37

6.1.1 Results for RTLS in 2D using 4 antennae and Nearest neighbors algorithm 44

(Larger Working Area and Tags are randomly distributed)

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Introduction

RFID is an automatic remotely operated identification mechanism based on storing and retrieving identification

data on RFID tags which are similar to transponders, through radio wave propagation. It provides non-contact,

non-line-of-sight operation .It is a highly capable and proven technology for a wide range of applications. RTLS

using passive RFID tags consists of Passive RFID tags, Antenna, Middleware. Using these we can only get data

for Threshold power. We can calculate the position using this threshold power and some known tags position.

These RFID tags can be implanted on consumables, animals and humans for the purpose of positioning or

identification too. The RFID technology is largely being used for replacing barcode technology. RFID

technology is primarily based on reflecting back a received radio signal by encoding it with the desired

information. We send a command to reader threw a middleware interface .Reader sends power to antenna

according to that command and antenna transmits power, part of which is received by the RFID tag. Hence tag

is charged with enough energy to send back an identifying response. This response is received by the receiver

antenna which is also connected to the reader.

Passive RFID tags-ALL9640

Tag Dimension= 76.2 mm x 76.2 mm

Read Range 3-5 meters

Tag Type: Passive

Memory Capacity 96 bits user programmable - 128 bits total

Memory Type Read/Write

Orientation Sensitivity Good performance for challenging operations

No internal battery , Energy is transferred using RF from reader

Alien Reader-ALR8800

Model No : ALR 8800

Operating Frequency: 865.7 to 867.5 MHz

RF power level: 15.7 to 30.7 dBm

Power Consumption: 45 Watts

Communication Interface : RS232,TCPI/IP

Weight: 1.8 Kg

RFID Reader External circular polarized Antenna

Circularly polarized

Operating Frequency: 850-875 MHz

Theoretical gain-6dBi

Power Consumption: 45 Watts

Dimensions:25.6cm*25.6cm*2.8cm

Weight: 0.77 Kg

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Literature Survey

Real Time Location Sensing

Real time location sensing (RTLS) is a technique of tracking and identifying the location of objects in an area in real

time. The determination of location is called Localization. For locating an object in Real time there are many

standard algorithms which can be used like Nearest Neighbor Algorithm, Triangulation etc.

1) Nearest Neighbour Algorithm Principle - there are many reference tags spread across a room. These tags act as landmarks in a city. The readers

keep track of the reference tag locations by storing their power levels, which indicate their distance readability to the

readers due to other factors. Now when unknown tags need to be detected, their power levels detected by the readers

are compared to the reference tags (Euclidian distance between power levels recorded by numerous readers of the

reference tag and the unknown tag). The reference tag showing the smallest distance is assumed to be the closest to

the unknown tag and so some such closest neighbors are selected. Once the closest neighbors have been obtained, a

weighted sum of their respective positions is carried out (i.e. the highest weight to the closest reference tag position

and so on) to estimate the unknown tag location.

Figure 1: NEAREST NEIGHBORS

Mathematical Formulation

Let we have

No. of antennae=N

No. of Known tags=P

No. of unknown tags=K

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Signal strength of kth unknown tag (N antennae)

Sk= (S1k,S2k,..........SNk)

Signal strength of mth reference tag(N antennae)

θ m= (θ 1m, θ 2m,........... θ Nm)

Euclidian distance of kth unknown tag from mth reference tag

Euclidian set Ek= (Ek1,Ek2,...........….EkP) for an unknown tag

Now we choose M nearest neighbors from this set.

Weights

We know x and y positions of those M nearest neighbors and z position too if tags are in 3D

Hence Weighted sum

In 2D

In 3D

𝑥𝑘𝑒,𝑦𝑘𝑒, 𝑧𝑘𝑒 = 𝑊𝑘𝑖(𝑥𝑖,𝑦𝑖, 𝑧𝑖)

𝑀

𝑖=1

This is the estimated position of kth unknown tag

Mean square error

In 2D

In 3D

𝑀𝑆𝐸 𝑘 = 𝑥𝑘𝑒 − 𝑥𝑘𝑜 2 + 𝑦𝑘𝑒 − 𝑦𝑘𝑜 2 + 𝑧𝑘𝑒 − 𝑧𝑘𝑜 2

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Where xko, yko, zko are the original position of kth unknown tag.

Mean Estimated Error

2) Triangulation

Figure 2: Triangulation

Friis formula

When gain of transmitter=gain of receiver

Then friis formula becomes

In this gain of antenna i.e. G is known already and hence it can be set by us and from experiment we can obtain

Threshold power S. λ is 0.346 meter at 866 MHz and from friis formula we can get the distance R of a particular tag

from different antennae using threshold power. Hence we can draw circles of those radius and intersection of these

circles will give us a point or a region in which tag must lie.

RGG

P

Prt

t

r 4log20log10log10log10 10101010

RSG dBdB

4log202 10,21

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Project work

1) Study of the properties of environment, antennae, Tags

Experiment 1.1: Threshold power level v/s distance from transmitter

Objective of Experiment: This experiment was designed to observe the behaviour of threshold power of the

tags with the distance from transmitter in the environment where we will be conducting the experiments. This

experiment is also useful in measuring the deviation of friis formula from its ideal behaviour in our experimental

environment.

Experimental Setup

Here we have a tag which is moved perpendicular to the transmitter from 10 cms. To 490 cms .One position of the

tag is shown in the figure below.

Figure 1.1.1: Experimental setup to measure Threshold power with distance

Measurements: Tag is moved by 10 cms every time and the minimum power level at which tag is read is

measured. Hence for every distance we found the Threshold power level.

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Results

Blue line: From friis formula Red line: From Experiment

Figure 1.1.2: Threshold power v/s distance of tag from antenna

Conclusion: We conclude that friis formula does not hold in our environment ideally but it follows the ideal curve

approximately after a distance of about 0.8 meters.

Experiment 1.2 Tag Read V/s Background

Objective of Experiment: To study the effect of tag background on its readability.

Experimental Set Up:

Figure 1.2.1: Tag on different background

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Measurements: Threshold power was measured by putting antenna at the same distance in every case.

Results:

PVC: Power=30.6dBm

Wall: Power=19.6dBm

Wood: Power=25.5dBm

Metallic: No read

Conclusion: Tag read is affected by background. On metals tags are not read.

Experiment 1.3: Power contour as antenna moves

Objective of Experiment: This experiment was designed to measure maximum power contour around tag.

Maximum power contour represents the boundary lines up to which a tag is read when the reader is moved parallel

to the tag.

Experimental Set Up: Antenna moves horizontally and it is at same height as of the tag, as shown in figure

below.

Figure 1.3.1: power contour on horizontal movement of antenna.

Measurements: Black line represents the line on which antenna transmitted power=30.7dBm and after that it

does not read the tag at all.

Results: Black line in the image represents the maximum power contour.

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Conclusion: Read range of antenna is dependent on angle from the tag too. Maximum read range is obtained if

tag is in front of the antenna.

Experiment 1.4: No. of tags read v/s distance from center of the tag grid

Objective of Experiment: This experiment was designed to find the relation between the no. of tags read with

distance of transmitter from the grid center.

Experimental Set Up: Transmitter is moved perpendicular to the tag grid plane with the receiver fixed at its

place and no. of tag read were measured. Tag grid contains a total of 95 tags. For future experiments in 2D the same

grid was used.

Figure 1.4.1: Experimental Setup for no. of tags read as antenna moves away.

This is showing transmitter at a distance of 1 meter.

Measurements: No. of tag reads and distance of antenna from center of grid are measured every time.

Results: This is the graph between no. of tags read with distance of transmitter from grid.

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Figure 1.4.2: No. of tags read v/s distance of transmitter from center

Conclusion: No. of tags read decreases as distance increases because as distance increases so tags are not in the

read range of the transmitter.

2) RTLS in 2D grid using Nearest Neighbor Algorithm with 1 transmitter

Experiment 2.1: RTLS in a 2 dimensional grid using Nearest Neighbour Algorithm


Objective of Experiment: This experiment was designed to locate an unknown tag in a 2 dimensional grid of

1.4 meter*1 meter using some known tags position.

Experimental Set Up: In this experiment the tags were arranged symmetrically in a 2D grid and transmitter

was placed in front of left upper corner of the grid. There were a total of 95 tags.

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Figure 2.1.1: Experimental setup for RTLS in 2D using Nearest neighbor algorithm

Transmitter Antenna In front of corner of grid

95tags (87 known, 8 unknown)

Measurements

15.7 16.5 18.2 18.9 22.0 27.2 30.7 28.8 26.9 30.7

15.7 16.5 16.8 20.0 22.6 28.8 30.2 30.7 30.7

18.6 18.8 19.0 21.2 25.9 30.3 XXX 30.7 30.7 30.7

15.7 16.7 20.0 22.5 26.7 29.0 30.7 30.7 30.7

20.3 20.3 22.2 23.4 24.9 29.0 30.7 30.7 30.3 30.7

19.4 17.8 21.2 23.5 30.1 30.7 29.9 30.7 30.7

20.9 22.2 23.9 26.3 29.8 30.7 28.8 30.7 30.7 30.7

23.6 22.2 23.9 29.0 29.0 30.7 30.7 30.7 30.7

27.7 24.2 28.8 30.7 30.7 30.7 XXX 28.8 30.7 29.2

16.5 18.2 28.8 22.0 28.8 30.7 30.7 30.7 30.7

Table 2.1.1: Threshold Power Level of the Tag grid having transmitter in front of origin

Yellow blocks-Unknown tags, White blocks-Known tags, XXX – tag is not read at all

In this experiment we know the position of known tags which is helpful in positioning an unknown tag .We also

note position of unknown tag to find the error in results. For every unknown tag 10 nearest neighbours are

selected on the basis of minimum Euclidian distance from that unknown tag.

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Results:

Actual position Calculated position MSE

All are in cms.

Table 2.1.2: Results for RTLS in a 2 dimensional grid using Nearest Neighbor Algorithm (Transmitter in front

of one corner of grid)

NaN => Not read at all

Mean Estimation Error = 33.3 cms

Experiment 2.2: RTLS in a 2 dimensional grid using nearest neighbor Algorithm

(Transmitter in front of center of grid)


1.4 meter*1 meter using some known tags position.

Experimental Setup: In this experiment the tags were arranged symmetrically in a 2D grid and transmitter was

placed in front of center of the grid. There were a total of 95 tags.

Figure 2.2.1: Experimental setup for RTLS in 2D using nearest neighbors algorithm

MSE

37.9

30.4

NaN

12.6

21.7

25.8

NaN

73.8

X Y

4 -8

41 -18

95 -28

34 -48

101 -58

41 -78

94 -88

131 -98

X Y

23 -40

21 -40

NaN NaN

46 -50

105 -37

43 -52

NaN NaN

111 -27

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( Transmitter Antenna placed in front of center of the grid)

Measurements:

24.3 21.3 22.3 20.7 20.0 20.5 16.6 22.2 22.8 23.9

24.6 20.7 20.7 17.5 17.2 18.8 17.7 20.8 22.5

30.7 23.7 21.3 20.0 18.2 19.6 17.7 22.4 20.8 20.7

22.9 22.8 22.5 19.0 16.4 17.7 17.7 20.7 22.0

22.5 23.5 20.7 21.8 17.4 16.5 16.7 23.4 22.5 26.2

23.2 19.6 18.9 18.7 16.1 17.1 18.4 22.6 28.0

22.5 22.5 22.5 21.3 20.2 20.0 23.9 26.5 25.0 22.6

23.7 20.7 21.6 21.3 20.5 23.6 22.5 24.8 26.2

25.8 26.2 24.6 22.4 22.3 23.5 22.8 25.7 24.2 24.9

21.3 22.3 22.5 20.0 22.2 22.7 23.8 30.7 XXX

Table2.2.1: Threshold Power Level of the Tag grid having transmitter in front of center of the grid

Yellow blocks-Unknown tags, White blocks-Known tags, XXX – tag is not read at all

In this experiment we know the position of known tags which is helpful in positioning an unknown tag .We also

note position of unknown tag to find the accuracy of results and error in results. For every unknown tag 10 nearest

neighbors are selected on the basis of minimum Euclidian distance from that unknown tag.

Results:

Actual position calculated position Mean Square Error

All are in cms.

Table 2.2.2: Results for RTLS in a 2 dimensional grid using nearest neighbour Algorithm (Transmitter in front of

center of grid)

NaN => Tag is not read at all.


Conclusion and Comparison: Results in the case when transmitter is in front of center is poor than in case

transmitter is in front of the corner. The Reason is that when transmitter is at center then power is equally distributed

around the center so when we apply nearest neighbours algorithm, nearest neighbours of a tag happens to lie in

circle of equal threshold power, we can say that the calculated nearest neighbors are not the actual nearest to the tag.

X Y

78 -64

78 -37

77 -36

78 -37

72 -36

56 -48

68 -53

NaN NaN

MSE

92.9

41.9

17.9

45.4

36.8

33.0

43.4

NaN

X Y

4 -8

41 -18

95 -28

34 -48

101 -58

41 -78

94 -88

131 -98

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While in first case nearest neighbors lie on a quarter circle so the error must decrease. Hence results are better when

transmitter is asymmetrically with respect to the tag grid. .So this can be the reason that error in a 1.4 meter*1 meter

grid is 33 and 44 cms. Results may improve if we have more antenna data so we performed same experiment using

more no. of antennae

3) Effect on increasing antenna on RTLS using nearest neighbor algorithm in

2D

Experiment 3.1 RTLS using Random Arrangement of 4 antennae


1.4 meter*1 meter using some known tags position using 4 antennae data.

Experimental Set Up: In this experiment the tags were arranged symmetrically in a 2D grid. There were a total

of 95 tags. Antennae are arranged randomly in the front of grid as shown

Figure 3.1.1: RTLS in 2D using Nearest Neighbors Algorithm

Four Antennae (Random Arrangement of Antennae)

Measurements: Threshold power for each tag is measured using 4 antennae. In this experiment we know the

position of known tags which is helpful in positioning an unknown tag .We also note position of unknown tag to

find the error in results. For every unknown tag 10 nearest neighbors are selected on the basis of minimum Euclidian

distance from that unknown tag.

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Results:


All are in cms.


Table 3.1.1: Results for RTLS in 2D using 4 antennae (Random Arrangement of antennae)

Conclusion: On comparing the results of single antenna with result of four antennae we can conclude that results

are far better in case of four antennae.

Experiment 3.2 RTLS using Symmetrical placement of 4 antennae


1.4 meter x1 meter using some known tags position using 4 antennae data.


of 95 tags. Antennae are arranged symmetrically on a circle with respect to grid as shown in set up.

Figure 3.2.1: RTLS in 2D using Nearest Neighbors Algorithm

X Y

23 -38

26 -36

88 -57

41 -40

84 -59

37 -52

104 --69

122 -74

MSE

35.7

23.7

29.6

10.8

17.4

26.9

21.4

26.0

X Y

4 -8

41 -18

95 -28

34 -48

101 -58

41 -78

94 -88

131 -98

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Four Antennae are placed symmetrical to the tag grid on a circle as shown below

Figure 3.2.2: Antennae placement (on a circle around grid)

Measurements: Threshold power for each tag is measured using each antenna. In this experiment we measured

the position of known tags which is helpful in positioning an unknown tag .We also note position of unknown tag to



Results:


All are in cms.

Table 3.2.1: Results for RTLS in 2D using 4 antennae (Symmetrical placement of antennae)

X Y

23 -39

21 -31

100 -35

45 -44

80 -49

66 -82

68 -83

82 -89

MSE

36.2

23.7

10.1

12.0

23.0

25.6

26.5

50.1

X Y

4 -8

41 -18

95 -28

34 -48

101 -58

41 -78

94 -88

131 -98

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Conclusion: On comparing the results of single antenna with result of four antennae we got that results are far

better in this case too. This gives us a hint that results may further increase on increasing no. of antennae. Hence we

further increased no. of antennae.

Experiment 3.3 Effect of increasing no. of antennae further (Up to 28 antennae)


1.4 meter*1 meter using some known tags position on increasing no. of antennae .Objective of this experiment was

to study the effect of increasing the number of antennae on the accuracy of location sensing.


of 95 tags. Antennae are arranged symmetrically on a circle with respect to grid as shown in set up and such

experiment is repeated by moving them in circle like give below. Set up1 was same as in experiment 3.2 and further

more setups were made by moving every antenna by 15 degree from its previous position. We created a circle with

radii 1.5 meter around the tag grid as shown in the figure with the center of the circle as the center of the grid, then

after we recorded the data. After this we moved the antennae on the circumference of this circle several times and

took the readings without disturbing the tag grid. In this way we had data for different number of antennae.

Set up 1 Set up 2 Set up 3

Set up 4 Set up 5 Set up 6

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Set up 7

Figure 3.3.1: Different setups each at angle of 15 degree with previous setup

Measurements: Thus by collecting data for 4 antenna 7 times we had data for 28 antennae.

Result: We collected data for all the antennae in every Set Up and calculated results for every set up individually

as well as combined with all previous setups.

Results for mean square error for all tags and mean estimation error for every setup

individually (all results in cms)

Set up 1 Set up 2 Set up 3 Set up 4 Set up 5 Set up 6 Set up 7

MSE(t1) 36.2 33.3 33.9 46.1 35.2 27.5 39.3

MSE(t2) 23.7 22.6 20.3 28.8 21.9 16.5 21.7

MSE(t3) 10.1 19.8 14.4 10.3 18.6 5.6 14.1

MSE(t4) 12.0 29.7 8.0 14.2 24.9 18.6 13.0

MSE(t5) 23.0 37.0 19.4 48.1 53.0 47.6 21.5

MSE(t6) 25.6 16.4 20.2 19.6 20.3 24.9 24.3

MSE(t7) 26.5 28.4 30.4 41.4 12.0 11.6 28.5

MSE(t8) 50.1 26.0 63.8 19.1 22.0 48.9 45.6

MEE 25.9 26.6 26.3 28.5 26.0 25.1 26.0

Table 3.3.1: Results for mean square error for all tags and mean estimation error for every setup individually (all

results in cms)

Now we combined the setups to increase no. of threshold power data per tag which is used to calculated Euclidian

distance.

Combination of setups Total no. of antenna MEE(in cms)

1 4 25.9

1&2 8 22.8

1&2&3 12 20.4

1&2&3&4 16 22.2

1&2&3&4&5 20 20.5

1&2&3&4&5&6 24 20.8

1&2&3&4&5&6&7 28 22.3 Table 3.3.2: Results for MEE using different no. of combination of antennae

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MEE v/s No. of antennae graph:

Figure 3.3.2: MEE v/s No. of antennae

Conclusion: From this experiment we concluded that the accuracy in locating the position of the unknown tag

improves when we gradually increase the number of antennae and saturates after certain gradual increases. The

saturation point may vary depending on the conditions in which we do the experiment. In our case the saturation was

achieved at 12 antennae at which we could predict the location of the unknown tag with an error of 20.4 cms. Now

we extended our experiment to 3D.

4) RTLS in 3D using Nearest Neighbor Algorithm

Experiment 4.1 RTLS in 3D using 4 antennae

Objective of Experiment: This experiment was designed to locate an unknown tag in a 3 dimensional volume

using some known tags position using 4 antennae data.

Experimental Set Up: In this experiment the tags were placed randomly in 3D in random orientations as

shown below. There were a total of 32 tags. Antennae are placed at corners of that arrangement as shown.

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(Antennae placed symmetrically in working area)

Measurements: Threshold power for each tag is measured using all the antennae. In this experiment we

measured the position of known tags which is helpful in positioning an unknown tag .We also note position of

unknown tag to find the error in results. For every unknown tag 6 nearest neighbors are selected on the basis of

minimum Euclidian distance from that unknown tag.

Results:


All are in cms.

Table 4.1.1: Results for RTLS in 3D using 4 antennae


Conclusion: In 3D error is more than two dimension .Four antennae data is not a good option for 3D we should

have more antenna for locating an object in 3D so we increased no. of antennae further.

Experiment 4.2.1 RTLS in 3D using 8 antennae (All antennae not in one plane)



X Y Z

68 116 60

124 79 59

132 10 61

98 83 63

94 122 64

66 137 62

MSE

65.0

42.3

49.1

90.4

22.2

56.9

X Y Z

15 79 67

150 50 40

95 42 65

120 170 52

95 119 42

19 105 62

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Experimental Set Up: In this experiment the tags were placed in 3D in random orientations. There were a total

of 32 tags. Antennae are placed as shown in setup


Tags are randomly distributed in 3D in random orientations

Measurements: Threshold power for each tag is measured using each antenna. In this experiment we know the




Results:


All are in cms.

Table 4.2.1: Results for RTLS in 3D using 8 antennae


Mean Error in X= 20 cms

Mean Error in Y=10 cms

X Y Z

65 48 51

67 47 48

85 88 81

60 47 53

50 51 64

106 88 76

MSE

10.8

32.5

45.7

16.1

30.4

38.0

X Y Z

57 46 45

42 28 45

40 88 86

60 37 42

24 63 73

120 103 45

27

Mean Error in Z=11 cms

Conclusion: In 3D error is more than in 2D but it decreases drastically on increasing no. of antennae to 8.

Experiment 4.2.2 RTLS in 3D using 8 antennae (all antennae in one plane)




of 32 tags. Antennae are placed as shown in setup which is different from setup in experiment 4.2.1 in a way that all

antennae are at same height and at center of the chair height.


(All 8 antennae symmetrically placed)






28

Results:


All are in cms.

Table 4.2.2: Results for RTLS in 3D using 8 antennae (Symmetrical Antennae placement)


Mean Error in X= 6.5 cms


Mean Error in Z=16.5 cms

Conclusion: In 3D error is more than in 2D but it decreases drastically on increasing no. of antennae to 8.

Comparison of experiment 4.2.1 and 4.2.2

It can be seen that

Experiment 4.2.1

MEE=28.5 cms

In this case results for Z are better

Experiment 4.2.2

MEE=22.5 cms

In this case results for X and Y are better

Reason for this is when we put antennae at center Z i.e. Experiment 4.2.2 then nearest neighbor of a corner tag

will come out to be tags at tags at all different corner because they will have almost equal power so when we

apply nearest neighbor algorithm and Z result we get is weighted mean of those position will give poor result

because they are not actually the nearest neighbor. Similar Argument for Experiment 4.2.1 and X, Y position

will hold. Hence we applied a new approach that taking Z from the results from experiment 4.2.1 and X and Y

from experiment 4.2.2 and the results improved and we got MEE= 19.2 cms. This is similar to having 16

antennae where 8 are at center as in experiment 4.2.2 and 8 antennae as in experiment 4.2.1 and calculate X and

Y using 8 antennae data at center and Z from remaining 8 antennae data.

X Y Z

57 54 56

40 46 60

35 103 57

57 45 56

46 69 61

111 95 63

MSE

14.2

24.3

33.4

16.2

25.9

21.3

X Y Z

57 46 45

42 28 45

40 88 86

60 37 42

24 63 73

120 103 45

29

Experiment 4.3.1 effect of increasing working area on RTLS in 3D using 8 antennae (All 8

antennae not in one plane)


having data of some known tag positions using 8 antennae data.


of 32 tags. Antennae are placed as shown in setup. In this experiment we increased the working area.


Tags are randomly distributed in 3D in random orientations. (Working area more than in experiment 4.2)





30

Results:


All are in cms.

Table 4.3.1: Results for RTLS in 3D using 8 antennae (Larger Working Area)





Conclusion: In 3D error is more than two dimension but it decreases drastically on increasing no. of antennae to

8. But as we increase working area error increases too.

Experiment 4.3.2 Effect of increasing working area on RTLS in 3D using 8 antennae (All 8

antennae in one plane)




of 32 tags. Antennae are placed as shown in setup which is different from setup in experiment 4.3.1 in a way that all

antennae are at same height and at center of the chair height.

X Y Z

157 198 60

144 96 41

96 192 49

155 75 45

135 218 35

175 129 44

MSE

149.3

73.5

49.4

74.3

83.1

119.0

X Y Z

213 61 73

72 90 42

114 238 42

218 111 40

67 262 26

218 236 20

31


All 8 antennae are in one plane. Tags are randomly distributed in 3D in random orientations. (Working area

more than in experiment 4.2)

Measurements: Threshold power for each tag is measured using each antenna. In this experiment we know the




Results:


All are in cms.

Table 4.3.2: Results for RTLS in 3D using 8 antennae (Larger Working Area & Symmetrical Antennae

placement)

X Y Z

201 123 48

125 148 47

156 221 49

194 194 57

129 223 46

196 180 53

MSE

68

79

46

87

77

69

X Y Z

213 61 73

72 90 42

114 238 42

218 111 40

67 262 26

218 236 20

32






8. But error increases as we increase working area


It can be seen that

Experiment 4.3.1

MEE=91.4 cms


Experiment 4.3.2

MEE=70.7 cms





because they are not actually the nearest neighbor. Similar Argument for Experiment 4.2.1 and X ,Y position




Y using 8 antennae data at center and Z from remaining 8 antennae data.

Experiment 4.4.1 RTLS in 3D using 8 antennae on increasing no. of tags (all 8 antennae not

in one plane)



Experimental Set Up: In this experiment the tags were placed randomly in 3D in random orientations. There

were a total of 48 tags. Antennae are placed as shown in setup. In this experiment we increased the working area.

33


Tags are randomly distributed in 3D in random orientations. (Working area same as in experiment 4.3, No. of tags

are increased to 48)






Results:


All are in cms.

Table 4.4.1: Results for RTLS in 3D using 8 antennae (Larger Working Area & 48 tags)





X Y Z

171 96 38

151 54 69

130 134 56

103 129 43

133 143 50

118 60 56

MSE

99

140

87

76

57

44

X Y Z

219 180 62

12 56 40

167 56 64

40 141 14

95 101 55

109 50 87

34


8. But as we increase working area error increases too. But result improves as we increase no. of known tags.

Experiment 4.4.2 RTLS in 3D using 8 antennae on increasing no. of tags (all 8 antennae in

one plane)



Experimental Set Up: In this experiment the tags were placed randomly in 3D in random orientations. There

were a total of 48 tags. Antennae are placed as shown in setup which is different from setup in experiment 4.4.1 in a

way that all antennae are at same height and at center of the chair height.


All 8 antennae are in one plane. Tags are randomly distributed in 3D in random orientations. (Working area same as

in experiment 4.3, No. of tags=48)





35

Results:


All are in cms.

Table 4.4.2: Results for RTLS in 3D using 8 antennae (Larger Working Area & 48 tags &Symmetrical

Antennae placement)






8. But error increases as we increase working area


It can be seen that

Experiment 4.4.1

MEE=83.8 cms


Experiment 4.4.2

MEE=65.5 cms





because they are not actually the nearest neighbor. Similar Argument for Experiment 4.2.1 and X, Y position




Y using 8 antennae data at center and Z from remaining 8 antennae data

X Y Z

168 134 42

86 93 48

163 56 52

143 129 55

145 156 45

104 44 45

MSE

73

88

13

102

74

43

X Y Z

219 180 62

12 56 40

167 56 64

40 141 14

95 101 55

109 50 87

36

5) Triangulation

Experiment 5.1 Triangulation using 3 antennae

Objective of Experiment: This experiment was designed to locate an unknown tag in a 2 dimensional grid

position using 3 antennae data and using triangulation.

Experimental Set Up: In this experiment the tags were placed in a 2D grid of 95 tags. Out of which a total of 8

tags were randomly selected to locate. Antennae are placed as shown in setup in a way that all 3 transmitter antennae

are at same height as of grid.

Figure 5.1.1: Triangulation using 3 Transmitter antennae

This is the same grid as used in experiment 2 and 3

Three transmitter antennae placed in the same plane of the tag with one receiver.

Measurements: For each of the 8 unknown tags, their positions were measured using meter tape and threshold

power levels from each antenna were measured and then for those threshold power level distanced was calculated

using friis formula. Ideally the tag should lie on the circle of this distance calculated from the friis formula.

37

Result

For tag 1

Figure 5.1.2: Location of a tag using Triangulation with 3 antennae

The tag must be in the red region and its mean position is calculated as the center of this region.

Actual position calculated position

X = 0.64m X=0.71m

Y=-0.08m Y =0.28m

Error in position

Serial No. Error(in meters)

1 0.37

2 0.59

3 1.60

4 1.43

5 0.90

6 0.69

7 0.90

8 0.83

Table 5.1.1: Results for Triangulation using 3 antennae

38

Mean Estimation Error = 0.91 meters

Conclusion and Reason for poor results

Using triangulation results were much poor than the nearest neighbor algorithm results. Reason for these poor results

is that friis formula is not valid in real time environment and antenna is not exactly circularly polarized but power

varies for different angles at same distance. But we tried to do the same experiment using 4 antennae.

Experiment 5.2 Triangulation using 4 antennae

Objective of Experiment: This experiment was designed to locate an unknown tag in a 2 dimensional grid

position using 4 antennae data and using triangulation.

Experimental Set Up: In this experiment the tags were placed in a 2D grid of 95 tags. Antennae are placed as

shown in setup in a way that all 4 transmitter antennae are at same height as of grid.

Figure 5.2.1: Triangulation using 4 antennae

This is the same grid as used in experiment 2 and 3

Four transmitter antennae placed in the same plane of the tag

Measurements: For each tag power levels was measured using every antenna.

39

Figure 5.2.2: Threshold power v/s distance from antenna1

Figure 5.2.3: Threshold power v/s distance from antenna 2

40



41

For each tag we know the power level from each antenna.

The blue curve is the ideal friis curve and the red curve is the the experimental curve between threshold power and

distance

Results

Power measured by antenna 1 for tag1=20.8dBm




Actual position of tag1

X=0.19,

Y=-0.08

For a single tag we calculated results using two approaches

Approach1: Using Friis curve

We calculated the distance of a tag from each antenna using friis formula and then applied triangulation.

Figure 5.2.6: RTLS using Triangulation for curve from friis formula

42

Red circle-Antenna1

Green circle-Antenna2

Blue circle-Antenna3

Yellow circle-Antenna4

About approach: One circle should cut other circle at 2 points hence we should have a total of 12 intersection

points for four circles but if they don’t intersect we take the intersection point to be the point which we get from

intersection of the line joining the center of those circles and those circles.Now out of these 12 intersection points

we take 6 intersection point which lies in our working range i.e quadrangle made using 4 antennae.For non cutting

circle we should take the mid point of the point of intersection obtained from above approach as the point in

working range.Using these 6 points we will get a common region that is marked as red above.

The red region have approximate area of 0.4 sq. Meter

Approach 2: Using calculated curve

We calculated the minimum and maximum distance of a tag from the curve obtained from our experiment from each

antenna and then we got a reason of confusion in which the tag must lie.

Figure 5.2.7: RTLS using Triangulation for curve from experimental data

43

The tag must be in the red region and its mean position is calculated as the center of this region. Approximate area

of confusion region is 0.8 sq. meter here. Area of confusion increases here.

Conclusion and Reason for poor results: Using triangulation, results were much poorer than the nearest

neighbor algorithm results. Reason for these poor results is that friis formula is not valid in real time environment

and antenna is not exactly circularly polarized but power varies for different angles at same distance.

6) RTLS in 2D Random Setup

Experiment 6.1 Random setup in 2D for RTLS (Random orientations of tags)

Objective of Experiment: This experiment was designed to locate an unknown tag in a random 2D setup.

Experimental Set Up: In this experiment the tags were placed in 2D setup of 30 tags. Antennae are placed as

shown in setup in a way that all 4 transmitter antennae are at same height as of tags.

Figure 6.1.1: RTLS using nearest neighbors in 2D Random tag arrangement in a large working area

Antennae are placed on chairs

Measurements: Threshold power was measured using every antenna for every tag. Positions of the tags were

also measured.

44

Results:


All are in cms.

Table 6.1.1: Results for RTLS in 2D using 4 antennae (Larger Working Area and Tags are randomly

distributed)

Mean Estimation Error = 93 cms.

Conclusion:

Results are not good as read range of antennae is not so good, some of the tags were not read. So for some of the

unknown tags we get less than 4 antennae data and also power is also angle variant.

OVERALL CONCLUSION

Symmetrical placement of antenna leads to poor results.

As no. of antennae increases mean estimation error decreases up to some point and then almost saturates.

Friis equation doesn’t hold because antenna field is not circular, it also varies with angle.

Environment has a great effect on triangulation results.

Symmetrical placement of antennae about a dimension leads to poor results for that dimension.

Mean Estimation Error increase on increasing working area

Mean Estimation Error depends on tag density, in a region having more tag error is less

Error is more in 3D than in 2D.

LIMITATIONS

All the tags are not similar. In same environment different tags behave differently.

Antenna field is not circular and also it is not known for different environments.

Properties of tags also decay with time.

Read range of antenna is very less i.e approximately 6 meters So not much useful for applications

Obstructions further decreases read range of antenna means in real time tag read is also affected by

movement of objects in read range of antenna.

X Y

154 112

153 130

131 117

151 139

134 148

181 150

MSE

125

85

59

104

125

64

X Y

37 66

76 93

125 58

230 70

253 111

214 206

Documents

Real Time Location Sensing (RTLS) using Passive RFID tagshome.iitk.ac.in/~rohan/Real Time Location System... · Real time location sensing (RTLS) is a technique of tracking and identifying