On Alleviating Reader Collisions Towards High Efficient RFID Systems

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1 Δεκ 2013 (πριν από 3 χρόνια και 6 μήνες)

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On Alleviating Reader Collision
s

Towards High Efficient
RFID
Systems


Ching
-
Hsien Hsu
1

and
Chia
-
Hao Yu
2

1
Department of Computer Science and Information Engineering

2
College of
Engineering

Chung Hua University, Hsinchu, Taiwan 300, R.O.C.

{
r
obert
,

yu
}@grid.chu.edu.tw


Abstract.


With the emergence of
wireless

technologies,
RFID is
increasingly used in many applications such as inventory management,
object tracking, retail checkout etc.
In an
RFID system
,

readers are centered
in a finite area within which they can communicate with tags.

B
ecause the
same radio frequency is us
ed for communication
,

r
eaders may also interfere
with the operations of other readers even if their interrogation zones do not
overlap.
Thus

the problem of scheduling
multiple
reader
s to
tag
s

transmissions in dynamic systems has been arousing attention.
This paper
presents a priority

based
transaction method
to coordinate simultaneous
communications among multiple readers in order

to increase the overall read rate
in dynamic RFID systems. Through a contention
-
free scheduling,

the reader
-
tag
transmissions
can be performed without collisions even the environment has

hidden terminal. To evaluate the effectiveness of the proposed techniques, both
network density

and mobility of readers’ join and leave are conducted in the tests.
Experimental results show that

the proposed techniques provide superior system
throughput in both static and dynamic

circumstances.

1.

Introduction

The Radio Frequency Identification (RFID) system is an

automatic technology that aids
machines or computers in

identifying, recording or
controlling individual targets

through radio waves. It is regarded as one of the leading

technologies for realizing
so
-
called ubiquitous computing

and its services. Recently it has also starting to attract
much

attention from research communities and vario
us industries.

An RFID system consists of three components, RFID reader, RFID tag and the
back
-
end database.

The electronics in the RFID reader use an outside power

resource to
generate a signal to drive the reader’s antenna

and turn it into a radio wave.
The radio
wave will be

received by a RFID tag which will reflect the energy in

the way of
signaling its identification and other related

information. To access the reflection, the
RFID reader

works as a receiver on sensing and decoding the signal

to identi
fy the tag.
In simple RFID system, RFID tag is

passive and powered by the energy of the reader’s
signals.

In some matured systems, the reader’s RF can also instruct

the memory of tag to
be read or write.

Since communications between the RFID tag and

reader

are executed on public RF
channels, the systems

could face many problems in accuracy, reliability, security

and
communication collisions. As a
n

RFID reader

is designed to accept the tiny signal
reflected from a tag,

it will be particularly influenced by a
ny relatively powerful

transmissions from other readers that happen at the same

time. Therefore, it will be
necessary to install RFID readers

at appropriated distances from each other. Otherwise

the interference could be caused when the frequency band

is s
hared by other potential
users.

In order to prevent mutual interference among readers,

there are possible reactions.
With the distributed scheme,

RFID readers switch the communication state with each

other to avoid simultaneous transactions. The centralize
d

control mode means that
appropriate coordination is

handled by a specific reader.

In this
paper
, we combine

the
virtues of both centralized and distributed schemes

and propose a Priority Based
Transaction with Multiple Prime (
PBT
-
MP
)

mechanism, aimed to
efficiently perform
reader
-
tag

transmissions and to avoid communication collisions that

are caused by
hidden terminals
[2,

3].

Employing dual channel scheme, in
PBT
-
MP
,

communications
among readers are established through

control channel while the actual da
ta
transmission between

reader and tag is carried out in the data channel
[4]
. The proposed
PBT
-
MP

scheduling mechanism is

applicable in the arbitrary RFID network, in which
readers

may frequently join and leave, forming an ad
-
hoc network,

and have
unrestri
cted mobility. The
PBT
-
MP

is a simple

mechanism for coordinating
simultaneous transmission

among multiple readers. A significant improvement of this

approach is that
PBT
-
MP

can prevent reader collisions based on

a contention free
communication scheduling.
The second

advantage of the present technique is that
PBT
-
MP

is adaptive

in both static and dynamic RFID environments.

To evaluate the performance of the proposed technique, we have

implemented
PBT
-
MP

along with other previously proposed protocols
. We stud
y the

impact of the
density of RFID readers and the frequency

of readers joining or leaving on system
throughput and

efficiency.

The experimental results show that the
PBT
-
MP

can achieve
better
efficiency than the
previously proposed
PBT

scheme.
The easy
-
implementation
is also advantage of the
proposed
scheme.

The pa
per is organized as follows.
Section 2 briefly
introduces
h
idden terminal
problem.
A Priority Based Transaction (
PBT
)
method

is
introduced

in Section 3, where
we also define notations
and

terminologies used in this paper.
An enhanced
PBT

scheme,
term as
PBT
-
MP

will

be
explained

in Section 4. The performance comparison

is
given

in Section 5. Section 6 concludes this paper.


2.
Hidden T
erminal

on RFID Network

To simplify the presentation
of the following sections,

we first explain some terminologies
used in this paper.


Figure 1 shows an example of
hidden terminal problem

in
RFID
network. In this example, Tag T
1

is surrounded

by two readers. Each of the readers is
located beyond

the sensin
g range of the others in the RFID network.

Therefore, these
two readers are not able to communicate

with each other and reader collision might
happen.

The situation is known as the hidden terminal problem, and

has the following
features:




R
eader

doesn

t
reside

in
other
s


sensing range

might interfere with tags and cause
carrier sensing to

become ineffective.



When queries or transmissions from multiple readers

collide on a tag, signals can
be distorted and the queries

might be incorrect.



RFID tags can
communicate only when they are

activated by readers because it is
a passive element.

Therefore, RFID tags will not able to pro
-
actively

communicate with readers for avoiding collisions.


Figure 1
:

Hidden terminal in RFID network


Interferences in RFID
system are usually classified into

reader to reader frequency
interference and reader
-
to
-
tag

interference

[
5,

6]
.

We further describe these two type
in the following subsections.


2
.1 Reader frequency interference


Reader to reader frequency interference i
s also called

frequency interference,
which

occurs when readers interfere

with others
in
communicating with tags. Figure 2 shows

that RFID reader R
2

resides in the frequency interference

range of reader R
1

which

has
a wider interference signal range

(the d
otted line).
When

tag T
1

responds to reader R
2
,
it might

be influenced by the interference signal of reader R
1
. Such

hidden terminal
problem occurs even when the range of the

two readers do not overlap.



Figure 2
:

Reader frequency interference

2
.
2

Multiple readers to tag interference


Also referred

as simply tag interference, it occurs when

two or more readers in the
transmission zone attempt

to communicate with one tag simultaneously. In this

situation, each reader performs a one to one
communication

with the tag. However, it
is not known by the readers

that the tag is responsible for multiple readers,

simultaneously
, as a result, r
eader collision
might

happen in this

undesirable way.
Figure 3 indicates
an

overlapping

of three readers
,
R
1
, R
2

and R
3

are
not
able to detect

other
s

when
communicati
ng

with tag T
1
. Such interference is
also referred as
part of
the hidden

terminal problem.


Figure 3
:

Multiple readers to tag interference

with

read

range overlapped


Many methods have been
proposed

to
resolve

the hidden terminal problem
.


Nan
Li et al. [
7
] present
DCMA

(Dual Channel Multiple Access) protocol
for active RFID
systems with low power advantage
.


S Jain et al. [
8
]
developed a
CSMA
-
based MAC
protocol to

avoid reader
-
reader and rea
der
-
tag collisions in a dense RFID

network. The
network is implemented using mote
-
based

RFID readers.
Performance comparison was
conducted with a Naive, a Random and the
CSMA

protocol. The
evaluation shows

much superior performance relative to a naive and

a randomized protocol in dense
deployment environments both

in regards to accuracy and time per tag read.

Xu Huang
et al
.
[
9
] present an efficient dynamic framed slotted
ALOHA

protocol, which improves the
performance of conventional
ALOHA

in high

density

e
nvironment.


Choi
et al
. [
10
]
present
ed

performance comparison of another class of anti
-
collision protocol i.e. tree
based protocols; bi
-
slotted query tree algorithm (
BSQTA
) and bi
-
slotted collision
tracking tree algorithm (
BSCTTA
). Performance
was

measure
d on the basis of minimum
time required to identify users accessing a common source.

Maselli
et al
. [
11
]
proposed

a
n optimized
slotted
ALOHA

protocol for dynamic t
ag estimation in RFID networks.

Muhammad U. Farooq
ey al
.
[12] investigate
d

the performance of multiple access
protocols

(
ALOHA

and
CSMA

protocols)
use
d

in RFID environment
s
.


3.
Priority Based Transaction Scheduling

To avoid reader

collision in a high density environment, the nature of time

division
multiple access is employed t
o enforce reading

RFID tags at different time slots and
guarantee that readers

do not interfere with each other. In addition, through

registering
the presence of new join/leave readers (in control

channel) to a coordinating agent
which is associated

with t
he target RFID tag, all transactions between readers

and tags
can be performed in a contention
-
free manner.

In this section, we introduce

the

PBT

scheduling algorithm aimed at avoiding communication

contention in a dynamic RFID
system.

3.1
Motivating
example

Figure
4

shows an example of four readers R
1
, R
2
, R
3

and R
4

residing within the
communication range reachable to the

tag. However, each of them unable to
communicate with

others because it is beyond its sensing range. The hidden

terminal
problem, t
herefore, exists. It is expected that if the

readers know existence of others,
communications

with tags will not
be
collide
d
. Therefore, a coordinator reader

(R
5
)
could be, on demand, associated with the
target
tag. Meanwhile, the coordinator can

communica
te with all of the readers who attempt to read the

target tag. Namely, in this
case the request readers (R
1

~ R
4
)

can notify the coordinator (R
5
) of their existence by
sending

beacon information.

The coordinator keeps track of the total

amount of readers
and makes readers

be informed in order to build their own transaction schedule

locally.


Figure
4:

An RFID network with coordinating reader (R
5
)

T
he information of the RFID network is handled by

a centrali
z
ed coordinator

while
scheduling reader
-
tag
transactions

is distributed and self
-
determined
locally,

the proposed
technique

is classified as a semi
-
distributed algorithm, which has

the following
characteristics. Each request reader sends a

beacon through the control channel to the
corresponding

coor
dinator, notifying its attempt to communicate with a tag

before
transmitting data. The coordinating reader learns the

beacon’s source address according to the
received frame.

Then, it informs existing readers of the fact that a new prime

number (i.e.,
repr
esenting a priority factor) is assigned by

sending a reply to the beacon. In this way, if two
or more

readers transmit data with a tag at the same time slot and

cause communication
conflict, the time slot with the larger

prime number will have higher prior
ity than small ones.

Figure
5
(a) gives an example showing tha
t R
1

has been

assigned time slots with
multiples of prime number 2

for performing transactions, while R
2

uses multiples of

prime number 3. Namely, R
1

t
ransmits data with
tag at

time slots t
2
, t
4
,

t
6

and t
8
, etc.
while R
2

transmits data with a

tag every three time units (i.e., t
3
, t
6
, t
9
, t
12
, etc…). The
complete interaction between RFID readers and

coordinator is shown in Figure
5
(b).

It
is

obvious that

reader
s

joined
the network earlier
will be a
ssigned a

lower prime number,
representing the use of a lower priority

time slot. This strategy reflects the fact that the
PBT
design

is based on a consideration of maintaining a fairness

transaction and to prevent
starvation that could have

happened to
RFID readers which joined late. Regarding the

concept of larger prime number with higher priority, reader

R
2

will have the ordinary
transmission schedule based on

prime number 3. For reader
R
1
, multiples of the
lcm
(2, 3),

e.g.,
t
6

and
t
12

are regarded as c
onflict slots and will be

preempted by reader
R
2

as it collided
with higher priority

slots. The complete interaction between RFID readers and

coordinator is
shown in Figure 5(b).

T
ime
-
slot

1

2

3

4

5

6

7

8

9

10

R
eader


R
1

R
2

R
1


R
2


R
1

R
2

R
1

T
ime
-
slot

11

12

13

14

15

16

17

18

19

20

R
eader


R
2


R
1

R
2

R
1


R
2


R
1

(a)


(b)

Figure
5
:

Priority based transaction scheduling: (a) example

of time slot allocation (b)
interaction between

reader and coordinator


For readers dynamically join a network,
f
ollowing the
circumstance

of
last
example given in
Figure 5, Figure
6
(
a
)

shows the
distribution of time slots after
reader
R
3

joined

the network.
Because

higher prime number
are with

higher priority, reader R
3

keeps an ordinary transaction schedule based on prime

number 5 and preempts time
slots that are multiples of

lcm
(2, 5) and
lcm
(3, 5) from readers R
1

and R
2
, respectively.


For reader leave, given
a snapshot of RFID system

with
n
readers,
R
1,
R
2, …,
Rn
residing in the network.

A
ssume that the associated time

slots for these readers

are
k
1,
k
2, …,
kn
, respectively
,

and
R
leave =
Ri
, where 1


i


n
.

The dynamic adjustment of
scheduling transactions will be

performed with synchroni
z
ation among the remaining

readers.
There are three different circumstances in
dynamic

scheduling.

Firstly, for reader
Rj
whose
id is smaller than
i
,

i.e.,
j < i
, it resets time slots that are multiples of
lcm
(
kj
,
kn
)

to ‘valid’.
Second
ly
, for reader
Rj
whose id is larger than
i
,

i.e.,
j
>
i
and
j


n
, it switches its time slot
from

kj
to
kj

1 and

sets all time slots that are in conflict with primes

kj
,
kj
+ 1, …,
kn


1 to
‘invalid’. Third
ly
, if
Rj
=
Rn
, the only

change is to switch its transaction from
kn
-
based time
slots

to
kn


1
-
based slots.



T
ime
-
slot

1

2

3

4

5

6

7

8

9

10

R
eader


R
1

R
2

R
1

R
3

R
2


R
1

R
2

R
3

T
ime
-
slot

11

12

13

14

15

16

17

18

19

20

R
eader


R
2


R
1

R
3

R
1


R
2


R
3

Figure 6
:

Distribution of time slots after reader
R
3

join
ed.

Given an example, r
eaders R
1
, R
2
,

R
3

and R
4

are considered as prior existing
readers in the

RFID network

as shown in Figure 7(a)
. Reader R
2

is assumed to be the
one

finished transaction with the tag

and going to leave
.
Once

R
2

leaves

the network,
reader R
1

enables time slots

that are multiples of
lcm
(2, 7) because prime number 7 will

be reclaime
d; reader R
3

switches its time slot from prime

number 5 to prime number 3
and disables all time slots

that conflict with prime 5. For reader R
4
, it reset its time slot
from prime number 7 to prime number 5

as shown in
Figure 7(
b
)
.


T
ime
-
slot

1

2

3

4

5

6

7

8

9

10

R
eader


R
1

R
2

R
1

R
3

R
2

R
4

R
1

R
2

R
3

T
ime
-
slot

11

12

13

14

15

16

17

18

19

20

R
eader


R
2


R
4

R
3

R
1


R
2


R
3

(a)

T
ime
-
slot

1

2

3

4

5

6

7

8

9

10

R
eader


R
1

R
3

R
1

R
4

R
3


R
1

R
3

R
4

T
ime
-
slot

11

12

13

14

15

16

17

18

19

20

R
eader


R
3


R
1

R
4

R
1


R
3


R
4

(b)

Figure 7
:

Distribution of time slots when reader leave
(
a
) before

R
2

leave
(
b
) after R
2

leave


4.

Priority Based Transaction With Multiple Prime
s

Owning the observations of low utilization of time slots in the
PBT

scheme, for example,
time slot t
1

is always idle
; time slots t
5
, t
7
, t
11
,

t
13
, t
17
, t
19
, remain idle in
low
-
density
environment
;

an enhanced algorithm
of
the
PBT

scheme is proposed which adds the
following characteristics:




Time slot
t
1

will be used by the one who was assigned to
use prim
e number 2.



Multiple prim
e numbers could be assigned to one

reader.


T
he idea of
taking
multiple prime
s is to fully utilize time slots
in

reader
-
tag
communications
.

G
iven an
example of
RFID systems in which a reader needs to
transmit data
m

times
w
ith
the

desire tag to complete a transaction
.


T
o guarantee
a
100% efficiency,
all time slots smaller than
m

could be

taken

by the same reader if only
one exists in the environment
.
As

time slots of the
PBT

scheme is
assigned

based on
prime numbers, that means all primes
smaller

than
m

should

be taken by the reader.
Considering the environment with multiple reader, for example,
n

readers, all of the
readers will need
n
*
m

time slots to complete the
n

transactions. Thus all pr
imes
smaller than
n
*
m

should be applied among the
n

readers. In the
P
BT
-
MP

scheme, a
round
-
robin distribution of the time slots is employed.


The algorithm of reader join in
PBT
-
MP

is given as follows
:


//
Coordinator procedure

seq

= total numbers of readers in the network; //inital zero


if (

new join beacon received

) { //new reader join

seq
++; //increase total number of readers

send
seq

to all readers; //notify presence readers

}



//
Reader procedure

//Activated upon new reader j
oin,
R
seq

is the rank of one reader, initial zero

//Assume primes of reader
R
1
,
R
2
,
R
3
,... are
k
1
[],
k
2
[],
k
3
[],..., respectively


if (

R
seq

== 0

) { //the new join reader

send

"join" beacon to coordinator;

receive

beacon reply associated with the serial number seq;

R
seq

=
seq
;

} else { //presence readers

receive

beacon reply associated with the serial number seq
;

}


myrank

=
R
seq
;


while ( tag transmission not complete ) {

if ( ts == 1 &&
myrank == 1
) { //
ts

is current time slot

receive

data packet from tag;

} else
if (
myrank

==
seq

) {
//new reader join

flag

=
ts

%

k
myrank
[];

//
k
seq
[] are the prime of reader R
myrank

//
flae

== 0, ts is reader R
myrank

s time slot

while (
flag

> 0); //skip lock

receive

data packet from tag;

}

else {

flag

=
ts

%
k
myrank
[];

//
flae

== 0, ts is reader
R
myrank

s time slot

suc_slot

=














;

//
suc_slot

== 0, ts is time slot one of reader
R
id

s successor readers

while (
flag

> 0 ||
suc_slot

== 0 ); // skip lock

receive

data packet from tag;

}

}




The algorithm of reader
leave

in
PBT
-
MP

is given as follows
:


//
Coordinator procedure

seq

= total numbers of readers in the network;


if (

receive

leace beacon from reader
R
i
) { //
reader
R
i

leave

seq
--
; //
de
crease total number of readers

send
(
seq
,i
)

to all readers; //notify presence readers

}


//
Reader procedure

//Activated upon reader
leave
,
myrank

is the rank of one reader


r
eceive

beacon reply (
seq
,
i
);


if (
myrank > i
) { //successor readers of
R
i

myrank
--
; //upgrade its priority

}


sync(); //reset time slot = 1


if (

R
seq

== 0

) { //the new join reader

send

"join" beacon to coordinator;

receive

beacon reply associated with the serial number seq;

R
seq

=
seq
;

} else {
//presence readers

receive

beacon reply associated with the serial number seq
;

}


myrank

=
R
seq
;


while ( tag transmission not complete ) {

if ( ts == 1 &&
myrank == 1
) {

receive

data packet from tag;

} else {

flag

=
ts

%
k
myrank
[];

suc_slot

=














;

while (
flag

> 0 ||
suc_slot

== 0 ); // skip lock

receive

data packet from tag;

}

}

5
.
Performance Evaluation

To evaluate the performance of proposed techniques,
we
have implemented the

PBT
-
MP

method along with the
PBT

scheduling
scheme.

Both static and dynamic circumstances
were

conducted in our simulations. Each test sample was

executed 30 times to obtain a
mean value.

5.1
Performance metrics

To simplify the presentation,
Table 1 summarizes
notations and

terminologies

used in
our experiment
s
.

Table 1
:

Definitions of notations and terminologies





Initially, the number of readers in a given RFID

network











Numbers of readers which joined the network

during time period tm ~ tn




















=




+














Number of time slots at which reader transmits

data with tag successfully





Number of time slots at which no reader

performs transaction





Number of time slots at which collision

happened








=



+







The completion time for all readers finished data

transmission with tag





A given time limit

for experiment





Number of time slots at which system is empty

before











=





(



+


),
i.e., number of

time slots during
time interval

(


,


)







The total number of time slots before









=



-







An integer value, representing the number of

transactions should be
performed by an RFID

reader

K

Every RDIF reader can used the number of
K

smallest prime numbers

P

RFID reader have a
P
% probability to join the network at each time slot

Throughput

The value of



before



Efficiency

In static network,

Efficiency =












In dynamic network,

Efficiency =
















5.2 Effect of




in S
tatic

Network

With the conditions of


=
9 and



= 1~80
,

Figure
9

gives the performance
comparisons of the
PBT
-
MP
(
k
)

and ordinary
PBT

scheme.

The y
-
axis presents

efficiency
(
%
)

and x
-
axis
represents
the number of readers in RFID network

(


).


The value of
k

in
PBT
-
MP
(
k
)

represents how many primes are assigned to each reader.

In low
-
density environment, the
PBT

achieves

only 50%~
80% efficiency.
In
high
-
density environment
, the

PBT

can reach 80%
-
90%
efficiency
.
It is
obvious that
the
PBT
-
MP
(
3
)

and
PBT
-
MP
(
4
)

present better efficiency than the ordinary
PBT

scheme.

In most cases, both
PBT
-
MP
(
3
)

and
PBT
-
MP
(
4
)

can achieve 100% efficiency due to the
fully utilized time slots with multiple primes.



Figure
9
: Effect of




in s
tatic

n
etwork


5.3 Effect of




in D
ynamic
Network

For
dynamic
circumstance
,
parameters
of


=
9,


= 60 and

P

= 5

are
set in our
experiments.
Figure
10

show
efficiency
(
%
)

of the
PBT

and
PBT
-
MP
(
k
) approaches.


The x
-
axis
represents 1000 time slots
.

T
he system read rate of
the
PBT
-
MP
(
4
)
maintains
100%
efficiency

at all
time slot from 1 to 1000.


Figure
s

11
and

12
are

given
to
describe
the stability of the
PBT
-
MP
(
k
) scheme in dynamic environments. The x
-
axis
in both figures represent the order of RFID readers join the network. The y
-
axis in
Figure 11 indicates the order a reader completes its work. From Figure 11 we can see
that
PBT
-
MP
(
k
) presents more stable res
ults
reflecting a FCFS principle
while the
PBT

method cannot guarantee the
completion
order
of the readers. Figure 12 reports the
waiting time of the two methods in
dynamic

RFID systems. It is also noticed that the
PBT
-
MP
(
k
) method has superior performan
ce to the ordinary
PBT

scheme.



Figure
10
: Effect of




in d
ynamic
n
etwork



Figure
11
:
Each
RFID reader to complete the work order

in d
ynamic
n
etwork



Figure
12:
RFID reader
total
waiting

time before complete the work
in d
ynamic
n
etwork


Table 2
outlines

the efficiency
of
the

PBT
-
MP

and
PBT

schemes
in
both
low
-
density and
high
-
density
environments
.

From the above observation, both
methods present its nature in avoiding reader collision. For read rate efficiency, the
PBT

achieves up to 80% efficien
cy in low density systems. In high density
environments, the
PBT

performs at least 90% efficiency which is much better than that
in low density environments. On the other hand,
the
PBT
-
MP

can maintain a 100%
efficiency
in both

low
-

and high
-
density environments.

Table
2

Comparisons of
the
PBT
-
MP

and
PBT

in term of efficiency

Method

Low
-
density

High
-
density

A
nti
-
collision

PBT
-
MP

100%

100%

Yes

PBT

< 80%

> 90%

Yes



6
.
Conclusions

RFID technologies help to advance next generation wireless communication. A RFID reader
could be planted into a cell phone or PDA after compressing to use as sensor to RFID tag for
information gathering. When a RFID tag is sensed, we can easily get the inf
ormation required
on a cell phone or PDA through the RFID tag at anytime and anywhere. With the increasing
use of RFID applications, high reader density and mobility are two major features in future
RFID systems. From this point of view, the condensed RFID

network incurs reader collision
problems, while the movement of readers brings out signal interference and prevents correct
information reading in a dynamic environment.

In this paper, we have presented a
PBT

MP
scheduling technique for coordinating
simul
taneous transmissions among multiple readers and to increase the overall read rate
in
RFID system.

The

PBT
-
MP

is a semi
-
distributed mechanism
that employs a
dual channel
communication
scheme.

It overcomes the problem of hidden terminals in RFID systems
an
d provides a contention
-
free communication method based on priority scheduling.

The
experimental results show that the proposed technique provides superior and stable
performance in both static and dynamic environments. The
PBT
is shown to be effective in

terms of system throughput and efficiency. In addition, the
PBT
scheduling technique is
capable of scalability under high density and mobility networks.


References

[1]

Ching
-
Hsien Hsu,
Shih
-
Chang Chen and Chia
-
Hao Yu

(2009)

A Priority Based
Transaction Mech
anism towards High Reliable RFID Service
s’
,

International Journal
of Ad
-
Hoc and Ubiquitous Computing (IJAHUC
), pp.
323
-
333
.

[2]

Chen, W
-
T., Ho, T
-
W. and Chen, Y
-
C. (2005) ‘An MAC protocol

for wireless ad
-
hoc
networks using smart antennas’,

Proceedings of the
11th IEEE International
Conference

on Parallel and Distributed Systems (ICPADS’05),

pp.446

452.

[3]

You, T., Hassanein, H. and Yeh, C
-
H. (2005) ‘PIDC


towards an

ideal mac protocol
for multi
-
hop wireless LANs’,

Proceedings of the IEEE International Conference

on

Wireless Networks, Communications and Mobile Computing,

pp.655

660.

[4]

Jain, N., Das, S.R. and Nasipuri, A. (2001) ‘A multichannel

CSMA MAC protocol
with receiver
-
based channel selection

for multihop wireless networks’, Proceedings of
the 10
th

IEEE Intern
ational Conference on Computer

Communications and Networks,
pp.432

439
.

[5]

Engels, D.W. and Sarma, S.E. (2002) ‘The reader collision

problem’, Proceedings of
the 2002 IEEE International

Conference on Systems, Man and Cybernetics, p.6.

[6]

Ho, J.J., Engels, D.W. a
nd Sarma, S.E. (2006) ‘HiQ: a hierarchical

Q
-
learning
algorithm to solve the reader collision

problem’, Proceedings of the International
Symposium on

Applications and the Internet Workshops (SAINTW’06),

pp.88

91.

[7]

N. Li, X. Duan, Y. Wu, S. Hua and B. Jiao
(2006)

‘An Anti
-
Collision Algorithm for
Active RFID

,
Wireless Communications, Networking and Mobile Computing,

PP.1
-
4.

[8]

S. Jain, S. R
. Das.
(2006)
‘Collision

Avoidance in a Dense RFID Network, Stony
Brook

,

International Conference on Mobile Computing and
Networking
, PP.49
-
56.

[9]

X. Hang and S. Le
(2007)

‘Efficient dynamic framed

Slotted ALOHA for RFID
Passive tags

,

Advanced Communication Technology, The 9th International
Conference
, PP.94
-
97

[10]

J. H. Choi, D. Lee, H. Jeon,J. Cha, and H. Lee.

(2007)


Enhanced

Bin
ary Search with
Time
-
Divided Responses for Efficient RFID Tag Anti
-
Collision

,
Communications,
ICC '07. IEEE International Conference
, PP.3853
-
3858.

[11]

G. Maselli,C. Petrioli and C. Vicari.
(2008)

‘Dynamic

Tag Estimation for Optimizing
Tree Slotted Aloha in RF
ID Networks

,
International Workshop on Modeling Analysis
and Simulation of Wireless and Mobile Systems
, PP.315
-
322.

[12]

Muhammad U. Farooq, Muddassir Asif and Naeem Z. Azeemi (2009) ‘Performance
Evaluation of Multiple Access Protocols for RFID Testbed Environ
ment’,
Ultra
Modern Telecommunications & Workshops
, PP.1
-
7
.