1. InternationalINTERNATIONAL JOURNAL OF ELECTRONICS AND
Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 3, October- December (2012), © IAEME
COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET)
ISSN 0976 – 6464(Print)
ISSN 0976 – 6472(Online)
Volume 3, Issue 3, October- December (2012), pp. 43-48
IJECET
© IAEME: www.iaeme.com/ijecet.asp
Journal Impact Factor (2012): 3.5930 (Calculated by GISI) ©IAEME
www.jifactor.com
THROUGHPUT IMPROVEMENT OF IEEE 802.15.4 BASED MEDICAL
AD-HOC SENSOR NETWORKS USING CLEAR CHANNEL
ASSESSMENT
Rambabu.A.Vatti1, Dr.A.N.Gaikwad2
1
Department of E&T/C, Vishwakarma Institute of Technology, Pune, , India.
Email: rambabuvatti.india@gmail.com.
2
Department of E&T/C, Zeal Education Society’s DCOER, Pune, India.
Email: Arungkwd47@gmail.com.
ABSTRACT
The Co-existence of the heterogeneous wireless Networks in the communication subnet is
degrading the throughput performance of Medical Ad-hoc Sensor Networks based on IEEE
802.15.4 Wireless Personal Area Networks. The degradation of the throughput performance
of these wireless Personal Area networks is mainly due to Interference from the co-existed
other similar wireless technologies operating in the 2.4 GHz license free ISM band, the
packet collisions due to increased traffic and Congestion at the link or at the node. In this
paper, we studied the impact of the interference of IEEE 802.11b/g Wi-Fi on the throughput
performance of the Medical Ad-Hoc Sensor Networks, the wireless Personal Area Networks
used in healthcare applications. . The Wi-Fi Access points operating in vicinity of the
patient’s home causes interference, due to which the Quality of Service of these Medical Ad-
hoc Sensor Networks is severely affected in terms of reduced throughput because of the
packet loss. We used Clear Channel Assessment technique to improve the throughput
performance. We have conducted experiments on Texas instruments ez430RF2530 motes,
which use MSP430 DSP Processor and CC2530 Radio. The experimental results show that
the throughput performance is improved by 63 percent by using the Clear Channel
Assessment.
Keywords: Clear Channel Assessment, interference, Medical Ad-hoc Sensor Networks,
Packet loss, Throughput.
1. INTRODUCTION
The IEEE 802.15.4 is an emerging standard for Low Rate Wireless Personal Area
Networks (WPANs). The main goal of this standard is to provide low rate, low power, cost
effective, flexible, reliable and scalable wireless Networks [1].The Medical Ad-hoc Sensor
Networks based on IEEE 802.15.4 wireless personal area networks are widely used in the
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2. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 3, October- December (2012), © IAEME
home monitoring of patients with chronic diseases and the home monitoring of the health of
the elderly persons. These Medical Ad-Hoc Sensor networks records the health parameters
like body temperature, heart rate and the ECG of the patients during their normal activity
without curtaining their freedom to move inside their homes. These sensor networks consist
of sensor nodes which acquire the health data from the patient, transmit the acquired health
data to a local healthcare server present in the patient’s home. This local healthcare server, in
turn, transmits the data to the remote healthcare server located at the hospital using
infrastructure networks [2][3].
The rest of the paper is organized as follows: the related work is presented in section
2, the clear channel Assessment in section 3, the experimentation, experimental setup have
been described in the section 4, the results in section 5, the result analysis in section 6,and the
paper is concluded in section 7.
2. RELATED WORK
The co-existence of the heterogeneous wireless technologies like IEEE 802.15.1 Bluetooth,
IEEE 802.11b/g/n Wi-Fi working in the license free 2.4Ghz ISM band are causing
interference on IEEE 802.15.4 WPANs used in healthcare applications[4]. The original IEEE
802.15.4 standard contains 16 channels in 2.4 GHz ISM Band. Channel 11 to channel 26.
Due to the overlapping of the channels by the co-existing technologies, only four channels
are left without any overlap. With the co-location of similar IEEE 802.15.4 WPANs, these
four channels also prone to have interference. The overlap of the channels of the various
wireless technologies is shown in Fig.1.
40MHz- 802.11n-
ch9
16
dBm
20MHz-
802.11g
0 dBm ch11-
IEEE802.15.4
channels(ISM)
ch11 ch16 ch20 ch26
2405MH 2430MH 2450MHz 2480MH
z z z
Fig.1. The channels overlap between the co-existed Wireless Technologies [5].
There are mainly two ways to achieve interference avoidance: global channel assignment and
the local channel assignment. Ruitao Xu et al., in [6], have proposed global and local channel
assignment schemes to improve the throughput by avoiding Wi-Fi interference. The increased
node density due to increased applications causes collisions, which reduces the throughput.
Tae Hyun Kim et al. in [7], introduced, the concept of virtual channel to reduce the collision
probability which improves the throughput performance.
3. THE CLEAR CHANNEL ASSESSMENT (CCA)
The CCA is a physical layer activity and is an essential element of the CSMA protocol. The
CCA offers two services. They are 1. Incoming packet detection and 2.ensuring free channel
before transmission. The CCA processes the received radio signal in the CCA window and
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3. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 3, October- December (2012), © IAEME
reports the channel state based on either energy detection or feature detection. The energy
based CCA compares the received signal strength with the set threshold. The feature based
CCA looks for a known feature of the signal like modulation and signal spreading. The
feature based CCA performs better than the energy based CCA. However, prior knowledge of
the signal characteristics of all the co-existent technologies is required, which needs more
complex hardware and draws more energy [8]. Here in this study, we have used the energy
based CCA which is a more suitable solution for the medical ad–hoc sensor networks as, it is
simple needs no complex hardware, and the energy consumption is also very less.
4. EXPERIMENTATION
The Experiments were conducted in Electronics and Telecommunication Engineering
department, Vishwakarma Institute of Technology, Pune, India.
4.1. Interference Level Measurement
The RSSI level of Wi-Fi Access points at different places in the campus are recorded using
inSSIDer Wi-Fi tracker tool. The signal strength and the channels in which these Wi-Fi
systems are operating is given in Table.1.
Channel Frequency Center RSSI Description IEEE802.15.4
No. Frequency channels affected
Band (dB)
(Mhz)
(Mhz)
3 2411-2433 2422 -70 Interfering AP outside 12,13,14,15,16, 17
the campus
5 2421-2443 2432 -50 Interfering AP outside 15, 16, 17, 18
the campus
7 2431-2453 2442 -50 VIT Campus 17,18,19, 20, 21
Table.1. the Wi-Fi interference at V.I.T. Campus
There are three Wi-Fi access points have their range spread across the campus. The Access
points with their channel numbers, frequency band, center frequency along with the power
levels are recorded in the table1.The interference affected channels of the IEEE 802.15.4 are
listed in the last column. The channels 12 to 21 are overlapped with the Wi-Fi interference.
Only five channels, 22-26 are available for interference free communication in the 2.4 Ghz
ISM band.
4.2. Experimental setup
Fig.2. Experimental Setup
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4. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 3, October- December (2012), © IAEME
To continuously monitor the patient, two nodes are placed in each room and one node in the
toilet of the 2 bed room flat of the patient and one node is with the patient and one node is
connected to the resident server located in the hall. We used Texas instruments ez430RF2530
motes, which can be programmed using the IAR Embedded Workbench Integrated
Development Environment (IDE). The rf-smart studio is used for configuring the
IEEE802.15.4 channels and the data rate. PuTTY is used to read from the serial port. The
node kept with the patient acts as the sensor node which collects the health parameters and
rest of the nodes acts as relay nodes, which in turn, relay the data to the resident server. The
nodes are deployed as shown in fig.3. Two Wi-Fi enabled laptops are placed in between the
nodes and interference is generated by a file transfer between the two laptops.
4.3. The Experiments
Two sets of experiments are conducted to measure the throughput, one without using CCA
and the other with using CCA, The results are then compared.
4.3.1.Experiment1. Transmission without Clear Channel Assessment
20 data packets of 20 bytes each are transmitted. The packets received at the resident
healthcare server are measured. The experiment is conducted 10 times and the results are
recorded in table.2
4.3.2. Experiment 2. Transmission with Clear Channel Assessment
The above experiment is repeated with implementing Energy based clear channel assessment
algorithm at each node. The node dynamically tune it’s radio channel to free channel on
sensing the received signal strength. The results are recorded in table.3.
5. RESULTS
Time interval (sec) 0 20 40 60 80 100 120 140 160 180
Number of Packets 12 10 8 13 10 12 13 12 10 13
Received Without CCA
Table.2. Packets successfully received without CCA
Time interval (sec) 0 20 40 60 80 100 120 140 160 180
Number of Packets 18 18 17 17 18 17 18 18 18 18
Received with CCA
Table. 3. Packets successfully received with CCA
6. RESULT ANALYSIS
The number of packets recieived succesfully with and without CCA , at each transmission are
presented in the in fig.4. and the relation between the cumulative packet loss is shown in
fig.5.
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5. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 3, October- December (2012), © IAEME
20
No. of Packets
Received(PR)
15
10
5
0
0 20 40 60 80 100 120 140 160 180
Time interval (sec)
Fig.4. Number of packets recceived with CCA and without CCA
From the fig.4, it is clear that the number of received packets are less in case of transmission
without CCA and also the variation in packet loss is more. With CCA, the nodes transmit the
data packets only after selecting the channel which is interference free.So the number of
packets received are more and also the variation in packet loss is less.
Cum. Packet Loss Without CCA Cum. Packet Loss With CCA
Cumulative Packet Loss
100
80
60
40
20
0
0 20 40 60 80 100 120 140 160 180
Time interval (seconds)
Fig.5. Cumilative packet loss with CCA and without CCA
6.1. Mathematical Analysis
௉ோ
The throughput λ = ்஻ ା ோ (1)
ೞ೏ ା௅ା ௅ಲ಴಼ ା ௌூிௌା஽ூிௌ
Where PR = number of Packets received successfully, Rsd = data rate between source and
destination, L = Length of the data packet, LACK = Length of the ACK packet, SIFS is Short
Inter frame Spacing, DIFS = Data Inter frame Spacing, TB is the average back-off time
before transmission.
From the table.1 and table.2, we can calculate,
∑భబ ୔ୖ_୵୧୲୦୭୳୲ େେ୅
ೖసబ
Mean number of packets received without CCA = ଵ଴
= 11.3
∑భబ ୔ୖ_୵୧୲୦ େେ୅
ೖసబ
Mean number of packets received with CCA = ଵ଴
= 17.9
In the experiments conducted, the packet length, data rate are fixed. The packets are
transmitted in fixed time intervals. So, all the variables in the denominator are same for both
the experiments. Therefore, the only parameter on which the throughput depends on is the
PR, the number of packets received [9].
λ α PR --------- (2)
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6. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 3, October- December (2012), © IAEME
The percentage improvement in the throughput with CCA can be expressed as
୔ୖ_୬୭େେ୅
% throughput improvement = ( ୔ୖ_େେ୅
) X 100 ------- (3)
ଵଵ.ଷ
= (ଵ଻.ଽ) X 100 = (0.63) X 100 = 63%
7. CONCLUSION
The experiments conducted using Texas instruments ez430RF2530 motes. The throughput of
the Medical Ad-hoc Sensor Network is measured with and without using the Clear Channel
Assessment. The results show that the clear channel assessment technique gives 63%
improvement in throughput.
REFERENCES
[1]. IEEE. 802.15.4., Standard 2006.,Part 15.4: “ Wireless Medium Access Control (MAC)
and Physical Layer (PHY) Specifications for Low Rate Wireless Personal area Networks
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[2]. Rambabu.V, Dr.A.N.Gaikwad, Bhooshan Humane, “ Throughput Improvement in
Medical Ad-Hoc Sensor Networks: A Review, Challenges, Future scope for Research.”,
International Journal of Electronics and Communication Engineering & Technology
(IJECET), volume.3, Issue1. January-June (2012), pp. 23-28.
[3].Ahmed N.Abdalla, Muhammad Nubli,Tan Chien Slong, Fauzan Khairi and A. Noraziah,
“Enhancement of real-time multi-patient monitoring system based on wireless sensor
networks”,International Journal of Physical Sciences vol.6(4).pp.664-670, 18, Feb. 2011.
[4]. Wail Mardini, Yaser Khamayseh, Reem Jaradatand and Rana Hijjawi, “Interference
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[5]. Marina Petrova, Lili Wu, Petri Mahonen and Janne Riihijarvi, “ Interference
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[9]. Xin He and Frank Y.Li, “Throughput and Energy Efficiency Comparison One-hop,
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