Transcript Doctoral Program Meeting - Oregon State University

FE 640 : Term Project Presentation
RFID Network Planning using Particle
Swarm Optimization (PSO)
Atipong Suriya
School of MIME
March 16, 2011
Suriya, A.
July 17, 2015, Slide 0
Outline





Introduction
Problem Description
Problem Solution
Results and Discussions
Conclusions
Suriya, A.
July 17, 2015, Slide 1
Introduction
Barcode
RFID
Fig 1. An infrastructure of typical RFID System
(http://www.anbitarabia.com/RFID_overview.jpg)
Benefits:
o Not require line of sight (Non-LOS)
o Multiple tag can be read in one time,
o Reduce time and operators in processing,
o Can be used for tracking of physical objects in real time
such as inventory and asset tracking.
The benefits of RFID in term of inventory monitoring and tracking can
improve the performance of inventory management system in the
warehouse. -> Focus on the placement of RFID readers in warehouse.
Suriya, A.
July 17, 2015, Slide 2
Problem Description
Problem Statement



RFID readers are expensive. The effective placement of RFID readers
in the warehouse is needed. (high implementation cost)
Currently, the placement of RFID readers are based on trial and
error basis; therefore, the automated tool is required. (trial and
error)
With the trial and error method, it often results in less than optimal
signal coverage and high level of interference. This directly affect the
reliability of RFID system in term of reader-tag communication and
tag reading. (lack of RFID system reliability)
Suriya, A.
July 17, 2015, Slide 3
Problem Description

Start implementing from the simple scenario (indoor free space
environment) with small facility 10*10m with 50 tags (items)
which are randomly added to the system.
Suriya, A.
July 17, 2015, Slide 4
Problem Description


Antennas with circular coverage pattern are used. Radius of the
coverage is derived from Friis’s equation
From the concept of the hexagonal packing -> the initial number
of readers = 7 readers
Select the location for 7 readers from
121 locations = 121!/(7!*114!)
= 6.314e10 combinations !!!
Suriya, A.
July 17, 2015, Slide 5
Problem Solution

Apply the optimization techniques (Particle Swarm
Optimization: PSO) to find the optimum placement of
RFID reader antennas in warehouse to :




Maximize the coverage area within the warehouse facility
(max. coverage area).
Minimize the number of RFID reader antenna (min.
implementation cost).
Minimize the degree of overlap (min. interference).
Balancing the loads (tags) for each reader in the system
(max. load balance)
Multi-Objective functions
Suriya, A.
July 17, 2015, Slide 6
Objective Function
fitness = 0.4*coverage+ 0.2*interference + 0.2*cost + 0.2*load balance
Multi-Objective functions -> Weighted Sum
Suriya, A.
July 17, 2015, Slide 7
Results and Discussions

Some parameters of PSO need to be varied to achieve the best performance
1) Inertia (w) : Large => global search, Small => local search
The objective function during the search (w varied)
0.9
0.8
Objective function
0.7
w=0.4
w=0.5
w=0.6
w=0.7
w=0.8
w=0.9
0.6
0.5
0.4
w=0.9 gives
the best performance
0.3
0.2
0.1
0
0
20
40
60
80
Number of iterations
100
120
Suriya, A.
July 17, 2015, Slide 8
Results and Discussions
2) Global social component (c1) : how much global best influences movement
Local social component (c2) : how much local best influences movement
The objective function during the search (c1 and c2 varied)
The objective function during the search (c1 and c2 varied)
0.9
0.88
0.86
0.8
0.84
The objective function
0.7
0.6
0.5
0.4
The objective function
c1=c2=0.5
c1=c2=0.6
c1=c2=0.7
c1=c2=0.8
c1=c2=0.9
c1=c2=1.0
c1=c2=2.0
0.82
0.8
0.78
0.76
c1=c2=0.5
c1=c2=0.6
c1=c2=0.7
c1=c2=0.8
c1=c2=0.9
c1=c2=1.0
c1=c2=2.0
0.74
0.72
0.7
0.68
80
0.3
90
95
100
Number of iterations
105
c1=c2=0.7 gives
the best performance
0.2
0.1
0
85
0
20
40
60
80
Number of iterations
100
120
Suriya, A.
July 17, 2015, Slide 9
Results and Discussions
3) Number of Particles
The objective function during the search (# of particles varied)
The objective function during the search (# of particles varied)
0.9
0.82
0.8
0.8
nPar=10
nPar=20
nPar=30
nPar=50
nPar=100
0.7
The objective function
The objective function
0.78
0.6
0.5
0.76
nPar=10
nPar=20
nPar=30
nPar=50
nPar=100
0.74
0.72
0.7
0.68
0.66
0.64
0.62
0.4
75
80
85
90
Number of iterations
95
100
0.3
0.2
nPar=30 gives
the best performance
0.1
0
20
40
60
80
Number of iterations
100
120
Suriya, A.
July 17, 2015, Slide 10
nReader = 5 gives
the best performance
Results and Discussions
4) Number of readers
The objective function during the search (# of readers varied)
The objective function during the search (# of readers varied)
0.9
nReader=7
nReader=6
nReader=5
nReader=4
nReader=3
nReader=2
nReader=1
0.88
0.8
0.86
0.7
0.84
The objective function
0.6
0.5
The objective function
nReader=7
nReader=6
nReader=5
nReader=4
nReader=3
nReader=2
nReader=1
0.4
0.82
0.8
0.78
0.76
0.3
0.74
0.2
0.72
0.1
0
0.7
0.68
0
20
40
60
Number of iterations
80
100
Parameters
1. The number of particles
2. The value of w, c1, and c2
3. The fitness function
4. The process for rounding the value of
RFID placement location (coordinate)
5. The number of iteration
6. Total number of readers
120
80
85
90
95
Number of iterations
100
105
The most appropriate Values
30 particles
w = 0.9; c1 = c2 = 0.7
fitness = 0.4*coverage+ 0.2*interference + 0.2*cost +
0.2*load balance
Rounding up
1,000 iterations
5 readers
Suriya, A.
July 17, 2015, Slide 11
Results and Discussions
The optimum placement of RFID readers in the simple scenario with 5 readers and 50 tags
12
The objective function during the search with the mosr appropriate parameters setting
0.9
Fitness = 0.8209
0.8
At iteration=150
0.7
The objective function
10
(5,8)
Height of the facility (H=10m)
8
(0,7)
(9,7)
6
0.6
0.5
0.4
0.3
0.2
0.1
4
0
(8,2)
(3,2)
2
0
-2
-4
-2
0
2
4
6
Width of the facility (W=10m)
8
10
12
0
200
400
600
800
Number of iterations
1000
1200
Reader 1 at site = 31 ( 8,2 )
Reader 2 at site = 87 ( 9,7 )
Reader 3 at site = 94 ( 5,8 )
Reader 4 at site = 26 ( 3,2 )
Reader 5 at site = 78 ( 0,7 )
Computation time = 37.38 seconds
Coverage = 1
Interference = 0.96
Cost = 0.2857
Load Balance = 0.8586
Fitness = 0.8209
Suriya, A.
July 17, 2015, Slide 12
Conclusions
The developed PSO in this simple scenario, the small facility area 10*10m
consisting of 50 tags, can guide the search to a good solution with 100%
coverage, low level of interference, and high load balance.

These factor can improve the reliability of reader-tag communication and tags
reading process.

The optimum solution can be obtained with 5 readers -> less than the initial
number of readers, i.e. 7 readers, derived from the concept of hexagonal
packing. -> The company can save implementation cost.

Applying optimization technique save a lot of time and the near-optimum solution
can be achieved.
Recommendations for further study and research

All tags in the simple scenario are fixed location which sometimes is not practical
in the real warehouse because it also has the mobile tags. Therefore, covering
all entire area are needed.

The RFID reader antenna tends to be more directional; thus, the elliptical shape
of signal coverage have to be considered.

The real warehouse has some obstacles which directly affect the signal
propagation. This also needs to concern about to make the model more realistic.

Suriya, A.
July 17, 2015, Slide 13
Thank you for your attention
Questions and Suggestions
Suriya, A.
July 17, 2015, Slide 14