Throughput improvement of ieee 802.15.4 based medical


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Throughput improvement of ieee 802.15.4 based medical

  1. 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: Impact Factor (2012): 3.5930 (Calculated by GISI) © 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: 2 Department of E&T/C, Zeal Education Society’s DCOER, Pune, India. Email: 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 43
  2. 2. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 3, October- December (2012), © IAEMEhome monitoring of patients with chronic diseases and the home monitoring of the health ofthe elderly persons. These Medical Ad-Hoc Sensor networks records the health parameterslike body temperature, heart rate and the ECG of the patients during their normal activitywithout curtaining their freedom to move inside their homes. These sensor networks consistof sensor nodes which acquire the health data from the patient, transmit the acquired healthdata to a local healthcare server present in the patient’s home. This local healthcare server, inturn, transmits the data to the remote healthcare server located at the hospital usinginfrastructure networks [2][3]. The rest of the paper is organized as follows: the related work is presented in section2, the clear channel Assessment in section 3, the experimentation, experimental setup havebeen described in the section 4, the results in section 5, the result analysis in section 6,and thepaper is concluded in section 7.2. RELATED WORKThe 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 causinginterference on IEEE 802.15.4 WPANs used in healthcare applications[4]. The original IEEE802.15.4 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 channelsare left without any overlap. With the co-location of similar IEEE 802.15.4 WPANs, thesefour channels also prone to have interference. The overlap of the channels of the variouswireless 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 ch262405MH 2430MH 2450MHz 2480MHz z zFig.1. The channels overlap between the co-existed Wireless Technologies [5].There are mainly two ways to achieve interference avoidance: global channel assignment andthe local channel assignment. Ruitao Xu et al., in [6], have proposed global and local channelassignment schemes to improve the throughput by avoiding Wi-Fi interference. The increasednode 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 collisionprobability 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. TheCCA offers two services. They are 1. Incoming packet detection and 2.ensuring free channelbefore transmission. The CCA processes the received radio signal in the CCA window and 44
  3. 3. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 3, October- December (2012), © IAEMEreports the channel state based on either energy detection or feature detection. The energybased CCA compares the received signal strength with the set threshold. The feature basedCCA looks for a known feature of the signal like modulation and signal spreading. Thefeature based CCA performs better than the energy based CCA. However, prior knowledge ofthe signal characteristics of all the co-existent technologies is required, which needs morecomplex hardware and draws more energy [8]. Here in this study, we have used the energybased CCA which is a more suitable solution for the medical ad–hoc sensor networks as, it issimple needs no complex hardware, and the energy consumption is also very less.4. EXPERIMENTATIONThe Experiments were conducted in Electronics and Telecommunication Engineeringdepartment, Vishwakarma Institute of Technology, Pune, India.4.1. Interference Level MeasurementThe RSSI level of Wi-Fi Access points at different places in the campus are recorded usinginSSIDer Wi-Fi tracker tool. The signal strength and the channels in which these Wi-Fisystems are operating is given in Table.1.Channel Frequency Center RSSI Description IEEE802.15.4No. Frequency channels affected Band (dB) (Mhz) (Mhz)3 2411-2433 2422 -70 Interfering AP outside 12,13,14,15,16, 17 the campus5 2421-2443 2432 -50 Interfering AP outside 15, 16, 17, 18 the campus7 2431-2453 2442 -50 VIT Campus 17,18,19, 20, 21Table.1. the Wi-Fi interference at V.I.T. CampusThere are three Wi-Fi access points have their range spread across the campus. The Accesspoints with their channel numbers, frequency band, center frequency along with the powerlevels are recorded in the table1.The interference affected channels of the IEEE 802.15.4 arelisted 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 GhzISM band.4.2. Experimental setup Fig.2. Experimental Setup 45
  4. 4. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 3, October- December (2012), © IAEMETo continuously monitor the patient, two nodes are placed in each room and one node in thetoilet of the 2 bed room flat of the patient and one node is with the patient and one node isconnected to the resident server located in the hall. We used Texas instruments ez430RF2530motes, which can be programmed using the IAR Embedded Workbench IntegratedDevelopment Environment (IDE). The rf-smart studio is used for configuring theIEEE802.15.4 channels and the data rate. PuTTY is used to read from the serial port. Thenode kept with the patient acts as the sensor node which collects the health parameters andrest of the nodes acts as relay nodes, which in turn, relay the data to the resident server. Thenodes are deployed as shown in fig.3. Two Wi-Fi enabled laptops are placed in between thenodes and interference is generated by a file transfer between the two laptops.4.3. The ExperimentsTwo sets of experiments are conducted to measure the throughput, one without using CCAand the other with using CCA, The results are then compared. 4.3.1.Experiment1. Transmission without Clear Channel Assessment20 data packets of 20 bytes each are transmitted. The packets received at the residenthealthcare server are measured. The experiment is conducted 10 times and the results arerecorded in table.2 4.3.2. Experiment 2. Transmission with Clear Channel AssessmentThe above experiment is repeated with implementing Energy based clear channel assessmentalgorithm at each node. The node dynamically tune it’s radio channel to free channel onsensing the received signal strength. The results are recorded in table.3.5. RESULTSTime interval (sec) 0 20 40 60 80 100 120 140 160 180Number of Packets 12 10 8 13 10 12 13 12 10 13Received Without CCATable.2. Packets successfully received without CCATime interval (sec) 0 20 40 60 80 100 120 140 160 180Number of Packets 18 18 17 17 18 17 18 18 18 18Received with CCATable. 3. Packets successfully received with CCA6. RESULT ANALYSISThe number of packets recieived succesfully with and without CCA , at each transmission arepresented in the in fig.4. and the relation between the cumulative packet loss is shown infig.5. 46
  5. 5. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 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 CCAFrom the fig.4, it is clear that the number of received packets are less in case of transmissionwithout CCA and also the variation in packet loss is more. With CCA, the nodes transmit thedata packets only after selecting the channel which is interference free.So the number ofpackets 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 CCA6.1. Mathematical Analysis ௉ோThe throughput λ = ்஻ ା ோ (1) ೞ೏ ା௅ା ௅ಲ಴಼ ା ௌூிௌା஽ூிௌ Where PR = number of Packets received successfully, Rsd = data rate between source anddestination, L = Length of the data packet, LACK = Length of the ACK packet, SIFS is ShortInter frame Spacing, DIFS = Data Inter frame Spacing, TB is the average back-off timebefore transmission.From the table.1 and table.2, we can calculate, ∑భబ ୔ୖ_୵୧୲୦୭୳୲ େେ୅ ೖసబMean number of packets received without CCA = ଵ଴ = 11.3 ∑భబ ୔ୖ_୵୧୲୦ େେ୅ ೖసబMean number of packets received with CCA = ଵ଴ = 17.9In the experiments conducted, the packet length, data rate are fixed. The packets aretransmitted in fixed time intervals. So, all the variables in the denominator are same for boththe experiments. Therefore, the only parameter on which the throughput depends on is thePR, the number of packets received [9]. λ α PR --------- (2) 47
  6. 6. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 3, October- December (2012), © IAEMEThe 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. CONCLUSIONThe experiments conducted using Texas instruments ez430RF2530 motes. The throughput ofthe Medical Ad-hoc Sensor Network is measured with and without using the Clear ChannelAssessment. 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(LR-WPANs)” , IEEE –SA Standards Board 2006.[2]. Rambabu.V, Dr.A.N.Gaikwad, Bhooshan Humane, “ Throughput Improvement inMedical 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 sensornetworks”,International Journal of Physical Sciences vol.6(4).pp.664-670, 18, Feb. 2011.[4]. Wail Mardini, Yaser Khamayseh, Reem Jaradatand and Rana Hijjawi, “InterferenceProblem between zigBee and WiFi”, 2012 IACSIT Honkong Conferences , IPCSIT, vol.30,pp.133-138. [5]. Marina Petrova, Lili Wu, Petri Mahonen and Janne Riihijarvi, “ InterferenceMeasurements on Performance Degradation between Colocated IEEE 802.11g/n and IEEE802.15.4 Networks”. Proceedings of the sixth international Conference on Networking(ICN’07). 2007. [6]. Ruitao Xu, Gaotao Shi, Jun Luo,Zenghua Zhao and Yantai Shu,“ MuZi: Multi ChannelZigBee Networks for avoiding WiFi interference”,IEEE -2011-International conferences onInternet of things,and cyber,Physical and Social Computing,pp.323-329.[7]. Tae Hyun Kim, Jae Yeol Ha and Sunghyun Choi., “Improving Spectral and TemporalEfficiency of Collocated IEEE 802.15.4 LR-WPANs”, IEEE Transactions on mobileComputing, Vol. 8, No. 12, Dec. 2009, pp 1596-1609.[8].Bin Zhen, Huan-Bang Li, Shinsuke Hara, and Ryuji Kohno, “Clear Channel Assessmentin Integrated Medical Environments”, EURASIP Journal on Wireless Communication andNetworking, volume 2008,pp. 1-8.[9]. Xin He and Frank Y.Li, “Throughput and Energy Efficiency Comparison One-hop,Two-hop, Virtual Relay and Cooperative Retransmission Schemes”, 2010 IEEE EuropeanWireless Conference., pp.580-587. 48