Intrusion Detection System using Wireless Sensor Networks
Contents
1. on Security Technology pp 75 77 October 1993 5 Crossbow Inc s MicaZ sensor platform http courses ece ubc ca 494 files MICAz Data sheet pdf 6 Crossbow Inc s MIB520 USB Interfacing board http www astiautomation ro produse Mems ic mib520 en html 7 Microchip PIC18F452 Microcontroller wwI1 microchip com downloads en devicedoc 3 9564 c pdf 8 Telegesis ETRX2 AT Command Manual http www telegesis com downloads general TG ETRX R212 Commands pdf EJSE Special Issue Wireless Sensor Networks and Practical Applications 2010 9 Telegesis ETRX2 Zigbee Module http www telegesis com downloads general TG ETRX2PA PM 003 107 pdf 10 Hygrosens PIR motion sensor Low Power Art No 172526 http shop hygrosens de out media 172526 pir Ip dbe pdf 11 Infrared Fresnel http www murata com catalog s2le pdf 12 D Gay P Levis R von Behren M Welsh E Brewer and D Culler The nesc language a holis tic approach to networked embedded systems In Proc of ACM Conference on Programming Lan guage Design and Implementation PLDI03 vol 38 pp 1 11 2003 13 TinyOS http www tinyos net 14 TinyOs Tutorial Lesson 1 Getting started with TinyOS and nesC http www tinyos net tinyos 1 x doc tutorialNesson html 15 N Lee M Welshd and D Culler TOSSIM Accurate and Scalable Simulation of Entire TinyOS Applications In Proc of t2. International vertical distance of the intruder increases from the sensor At 1 82 m 6 ft the detection probability is as high as 85 and degrades gracefully to 22 at maximum distance of 9 1 m 30 ft The results do 12 f 10 Horizontal Detection range meters fen 0 2 4 6 8 10 Vertical distance from PIR Sensor meters Fig 9 Horizontal detection range by varying vertical distance not correspond to speed changes and we expect the results to vary if the speed of the intruder is chang ing rapidly Thus the sensor is capable of binary de tection even at long range which can be used as a significant threshold for intrusion detection 1 0 0 9 0 8 0 7 0 6 0 5 0 4 0 3 0 2 0 1 OO be pg al 0O 1 2 3 45 6 7 8 9 10 Vertical Distance from PIR Sensor meters Event Detection Probability Fig 10 Detection probability by changing the vertical dis tance 6 ENERGY CONSUMPTION The energy consumption for the MicaZ sensor plat form are as follows the current draw for the micro controller is 8 mA in active mode and 15 uA in sleep mode The CC2420 radio on the MicaZ mote draws 19 7 mA in Rx mode and between 11 17 4 mA in Tx mode While in idle mode the current draw for the radio is 20 uA The PIR sensor draws 1 mA current in ON state The sensor platform is po wered by 2 x AA batteries which provide 2700 mAh of current Considering the energy require ments for reporting one event d
3. network from over the air attacks Also the PIR sensor has its limita tions which can be overcome by using better mod ules or even by entirely replacing the PIR sensor with an alternate means of monitoring Multimedia sensor platforms are now available in the market 26 which have low powered camera systems for more reliable and efficient monitoring We shall also explore the usability of multimedia sensors in our monitoring application Also the entire GUI can be ported on a web server with complete database man agement to provide a global access to the deployed network Node localization issues also need to be solved and finally a scalable architecture can be de veloped to allow thousands of nodes in one network while maintaining the performance requirements of the application REFERENCES 1 I Akyildiz W Su Y Sankarasubramaniam and E Cayirci Wireless sensor networks a survey Computer Networks vol 38 No 4 2002 pp 393 422 2 A Hac Wireless Sensor Network Designs Wiley amp Sons ISBN 0470867361 1 Ed pp 213 234 2003 3 S Ram J Sharf The People Sensor A Mobili ty Aid for the Visually Impaired In Proc of 2nd International Symposium on Wearable Computers pp 166 167 October 1998 4 Keller Hans J Advanced Passive Infrared Presence Detectors as Key Elements in Integrated Security and Building Automation Systems in Proc of IEEE International Carnahan Conference
4. run on Ti nyOS 13 an event driven operating system devel oped for wireless embedded sensor platforms Ti nyOS is written in nesC a programming language 92 eJSE International with a C like syntax for programming network em bedded systems nesC applications consist of one or more components linked together to form an execut able A component provides and uses interfaces In terfaces declare a set of functions called commands that the provider of the interface must implement Another set of functions called events that the user of the interface must implement nesC has two types of components modules and configurations Modules implement one or more interfaces Confi gurations are used to assemble other components to gether connecting interfaces to their implementa tion This is called wiring 14 The TinyOS tools are available for Linux and Microsoft Windows un der Cygwin and contain various tools nesC compi ler AVR compiler and utilities for Atmel micro controllers etc and a sensor network simulator TOSSIM AII our simulations for nesC based appli cations are done in TOSSIM 15 TOSSIM simu lates the entire TinyOS network stack at the bit lev el allowing experimentation with low level protocols in addition to top level application sys tems It works by replacing components with simulation implemen tations When it runs it pulls events of the event queue which is sorted by time and executes them Depen
5. sink The core MicaZ sensor node application is the De tection Interrupt module a multiple mode event ge nerator for human detection and node availability The sensing application relies on various services and subsystems that facilitate network management and interaction Figure 5 22 describes the software services on the MicaZ sensor platform The DetectionInterrupt module relies on the Collec tion Tree Protocol CTP 23 which enables relia ble robust and efficient data collection It works by building one or more collection trees each of which is rooted at a base station When a node has data eJSE Internanonal EJSE Special Issue Wireless Sensor Networks and Practical Applications 2010 Reliability C Medium Low Aeee erometer oa e e TABLE I PROPERTIES OF DIFFERENT TYPES OF SENSING MODULES FOR HUMAN DETECTION which needs to be collected it sends the data up the tree and forwards collected data that other nodes send to it Each node in our system can perform four different roles in collection producer snooper in network processor and consumer Depending on their role the odes use different interfaces to interact with the collection component which in our case 1s the base station node The configurations of the routing stack of CTP are shown in Figure 6 24 RootControl Send Receive SnoopPacket CollectionC Y Yy i A cpp vw Roe we we ee ee ee ee d St ee eee ee aaa wesw ee
6. to it and EJSE Special Issue Wireless Sensor Networks and Practical Applications 2010 viewing the responses received from remote ETRX2 devices 19 3 Base Station Monitoring The monitoring ap plication at the base station is developed using the C programming language with Microsoft Visual Studio 2008 C is a modern general purpose object oriented programming language suitable for devel opment of software components in distributed envi ronments It is also suitable for writing applications for embedded systems and uses strong type check ing array bounds checking and other features to bring software robustness durability and productivi ty 20 Gateway Node Base Station App Code Nesc App Code C pf _ Patch of Sensors Gateway Node Base Station PC Fig 4 MicaZ sensor platform setup IV SYSTEM IMPLEMENTATION The system is implemented using the MicaZ and custom designed nodes cooperatively to monitor the human presence through a base station application The MicaZ based sensor devices communicate with each other and traverse their data to the base station whereas the custom designed sensor nodes also communicate with the base station which has the ga teway node for both the MicaZ and custom sensor nodes The entire setup is shown in Figure 4 Detectioninterrupt Module Fig 5 Application architecture It uses a timer to act PIR sen sor to collect data and CTP routing layer to deliver data to
7. were communicating with the default power levels defined for their radios in TinyOS We believe that increasing the power level for the radio transmission range can be en hanced to much closer than the theoretical maximum EJSE Special Issue Wireless Sensor Networks and Practical Applications 2010 value which is 100 m The custom designed sensor platform has the Telegesis ETRX2 transceiver which uses ZigBee protocol to communicate It also de pends on almost the same factors as MicaZ motes since ZigBee protocol is developed over IEEE 802 15 4 protocol 25 Same assumptions were made for the custom sensor platform s radio and re sults achieved were similar The single hop commu nication distance between two nodes is between 70 80 m 5 2 Evaluation of PIR Sensor The capabilities of PIR sensors were thoroughly tested for effective human detection range of the PIR sensor We place a MicaZ sensor node with a PIR sensor at the elevation m above the ground and perform several tests At this height with sensor s opening angle of 120 degree with variation of 20 de gree we achieve the maximum detection range of 9 1 m 30 ft This value is about 24 lesser than what is described in the data sheet of the PIR sensor 10 The next experiment is done with the PIR sen sor to evaluate its horizontal coverage range with the same opening angle A test subject moves in front of the PIR sensor at varying vertical distances and we measure
8. 2 serial interface 8 It has small form factor measuring at 37 5 x 20 5 x 3 2 mm and supports data rate up to 250 kbps with 16 channels 802 15 4 Channel 11 to 26 Also the device sup ports four different power modes for extended bat tery life which we have extensively used The device has very flexible input voltage requirements and can operate between 2 1 3 6 V DC input with current draw as low as 1A in deep sleep mode This makes it an ideal choice for low powered energy efficient node design 9 3 Sensor for Human Detection In outdoor condi tions the sensor network needs to detect the pres ence of stationary as well as walking or running hu man beings Other properties of the sensor for such a scenario are lower power operations with lesser processing power requirements The size and cost of the sensor should be reasonable so as to make the to tal size and cost per node under check for maximum cost and size effectiveness At the same time the sensor should be powerful enough to detect objects at long range while being reliable they should not give false positive or negative readings Considering the design requirements different sensors could have been used for human detection and tracking The sensors which came under our consideration were accelerometer seismic ultrasound ultrason ic and infrared thermal Based on the analysis re ported in Table I ultrasound sensor is excluded since low power property is require
9. EEE 802 115 4 a wireless communication technology for large scale ubiquitous computing applications http ubicomp algoritmi uminho pt csmu proc koub aa 129 pdf 26 MEMSIC iMote Multimedia WSN Mote in formation document http www memsic com support documentation wire less sensornetworks cate gory datasheets html download 139 3Aimote2 multimedia
10. SNs has been very ac tive Our efforts describe the development of an in trusion detection monitoring application not only us ing the standard sensor platform but focuses on the design of a custom sensor platform at a much lower cost keeping in view the application requirements Moreover the ability to integrate both platforms into one standard WSN application is the highlight of our efforts The field evaluation results of the system with 30 sensor nodes half of which are MicaZ and half our own custom designed platform correspond to the cost efficient intrusion detection Field expe riments result show that the system is reliable with up to 85 successful human detection rate and can be deployed keeping in view the environmental is sues The major lesson learned from this effort is that practical considerations and real time factors must be taken into account while building such a monitoring application so it can perform well not only in simulation but also during practical deploy ment 8 FUTURE WORK The system described in this paper is still a proto type with room for several improvements for better elSE Meern There are many design issues which can be solved to enhance the overall usability relia bility and efficiency of the system This includes improving the power consumption and energy con sumption of the system design of robust WSN routing algorithms for efficient data communication and securing the entire wireless
11. and also our custom built low cost sensor nodes Performance results show that how the custom designed sensor nodes perform equally well and coexist with MicaZ motes Finally through this paper we share our experiences and the valuable lessons learned in de veloping such a complete running system 1 INTRODUCTION Security is today one of the primary concerns around the world Recent trends have shown that surveil lance of tactically important areas for suspicious ac tivities is a high priority for organizations Despite technological advances the major threat that still lurks is from unauthorized humans who can gain access to a target location and compromise its inte grity This results in surveillance of key areas for possible intrusion to be one of the most desired goals for security Wireless Sensor Networks WSNs are one of the most contemporary and suc cessful technique used for environmental monitoring of certain physical parameters WSNs can be effec tively used to gather useful data from the physical environment they are deployed in and communicat ing that information wirelessly to base stations which can process it and extract useful information WSNs are envisioned to reduce and eventually completely eliminate human involvement in infor mation gathering in certain applications 1 Howev er they have their own limitations the most impor tant of which is the amount of energy available to a sensor node With slow prog
12. d Comparing the accelerometer and the infrared sensor the infra red sensor has better detection properties for move ment PINS 1 2 ON A HORIZONTAL PLANE FRESNEL LENS DETECTING AREA Fig 2 Illustration of movement detection with PIR sensor 11 Thus the sensor used in this project is a thermal sen sor more precisely a passive infrared sensor PIR Another advantage is that the analog output signal of a PIR sensor can give an indication of the direction EJSE Special Issue Wireless Sensor Networks and Practical Applications 2010 of movement We have used Hygrosens low power PIR motion sensor which operates with pyro electric sensors and shows maximum sensitivity un der the effect of heat radiation from living bodies 10 At 37 degree Celsius body temperature the spectral sensitivity lies between 7 and 14 A The PIR sensor is segmented form inside 1 e two or more individual elements are interconnected within the unit so that they mutually compensate with each other With this the self temperature of the sensor is compensated A MOSFET is integrated in the sensor as an impedance converter because the pyro elements can only be driven by high ohmic value As depicted in Figure 2 a change in output voltage occurs only when the part segments of sensors expe rience different levels of infrared radiation A person passing the sensor will first activate one element and then the other which gives a positive or negative
13. dentifier as its payload All in coming radio packets from MicaZ motes are re ceived by the gateway node which simply forwards the message received on its radio link to the serial communication port of the PC from where the moni toring application takes over a MicaZ sensor mote b Custom designed node Fig 7 PIR sensor integrated with two different platforms The custom nodes also work in the same way albeit different components are used to perform the same tasks The PIR sensor integrated with the custom node is shown in Figure 7 b To process the infor mation provided by the sensor PIC18F452 micro controller is used It has bi directional ports which can be declared as inputs or outputs according to their purpose PORT B is an 8 bit wide bi directional port The corresponding data direction register is TRISB Setting a TRISB bit to 1 it makes the corresponding PORT B pin an input Clearing a TRISB to 0 makes the corresponding PORT B pin an output i e put the contents of the output latch on the selected pin Whenever the sensor detects an in truder RBO which is configured to INTO will give a digital interrupt to the micro controller It is a nega tive edge triggered interrupt and when this occurs the micro controller comes out of the sleep mode Once awake internal interrupts are called it converts analog data of the sensor at ANO pin to digital data which is then compared to a pre defined threshold value for decidi
14. difference between the elements depending on which element is activated first As soon as the signal level indicating the difference between the elements exceeds a certain limit a digital switching signal is generated This is further processed by the micro controller that handles it as an interrupt Fig ure 3 shows the changes in the voltage reading of the sensor as the person passes through the detection area of the sensor The pyro elements of the PIR sensor are covered by Fresnel lens 11 which en hances the capability of the sensor by dividing the space in front of the sensor element into segments The sensor has operating voltage of 3 5 V DC with 80 A current input This makes the PIR sensor ideal for battery powered operations The sensing range of PIR sensor is 12 m with an opening angle of 120 de gree Also the sensor can operate at temperatures upto 70 degree Celsius 10 Since the PIR sensor is made as a separate unit it needs to interface to the 51 pin expansion connector of MicaZ motes and the pins of micro controller Analog Sensor Output Ss SCSCSCSCS SFS S SSCSSC SCsSCSS SSS 3 0 Analog Signal 2 5 P 2 0 k 1 5 oe 1 1 0 0 5 0 0 0 Sensor value V 10 15 20 25 30 35 time s Fig 3 Analog output signal of PIR sensor 10 3 2 Software 1 TinyOS The software running on the MicaZ sensor nodes is written in nesC 12 and
15. ding on the level of simulation simulation events can represent hardware interrupts or high level system events such as packet reception Additionally tasks are simulation events so that posting a task causes it to run a short time in the fu ture 16 2 Custom Node Implementation Application program for custom node is written in C program ming language and compiled and burned on the mi cro controller using the Microchip MPLab IDE 17 and C18 compiler 18 C was used as a program ming language to develop detection application be cause it provides time and management efficiency with the micro controller The same application code written in assembly would be much longer with subsequent changes and code maintenance be ing difficult Application development was done us ing the tools available in the MPLAB Integrated De velopment Environment IDE which is a free toolset for embedded application development with PIC micro controller The MPLAB editor and de bugger tool are used to write the C code for our ap plication and then compiled using the C18 compiler For controlling the RF transceiver we used the Te legesis Terminal PC Software HyperTerminal which accesses the command line of the ETRX2 module This is a utility designed to manage a ZigBee wire less network consisting of Telegesis ETRX2 devices using the Telegesis AT command set Telegesis Terminal enables connection to ETRX2 wireless meshing modules sending commands
16. eJSE Intemational EJSE Special Issue Wireless Sensor Networks and Practical Applications 2010 Intrusion Detection System using Wireless Sensor Networks Absar ul Hasan Ghalib A Shah amp Ather Ali National University of Science and Technology Islamabad Pakistan Center for Advanced Research in Engineering Islamabad Pakistan ABSTRACT Ground monitoring of areas of high strategic value is necessary in today s security sensitive world Often military setups require tight security cordons to be established around large encampments to protect any intruder malicious attacker or saboteur from entering the premises and compromising its security Such monitoring requires 24 7 watch over the area for long durations and a high degree of stealthiest At the same time cost reliability and longevity are the fundamental requirements of such a monitoring system Hence the ability to monitor an area for intrusion detection by using Wireless Sensor Networks WSNs is of great practical importance In this paper we describe the design and implementation of a system capable of reliable robust and efficient monitoring for human intrusion detection The system allows a group of cooper ative but autonomous sensory devices forming a wireless network to detect human presence within the dep loyment area and also track the positions of moving target We evaluate the performance of the system con sisting up to 30 nodes that includes MicaZ motes
17. ect location on the screen which displays the map of the area under surveillance The node icon is placed at a position in the GUI depict ing the actual physical location of the sensor node In case of type 2 blue wireless bubble is drawn on mote ID x which shows that the mote is alive For packet type 3 same bubble is drawn but in red color that depicts the event detection at node x In order to track the intruder the proposed algorithm uses the information received from both the custom node platform and the MicaZ platform When a hu man is detected by either of the platforms it is re ported to the base station and visual notification 1s elSE International made through the GUI When the next detection is made assuming the intruder moved in range of another sensor the detection at new node ID is made and we compare the current detection ID from the previous detection ID to create a tracking arrow which gives a relatively reliable direction of move ment of intruder within the sensor network A single intruder in this way can be continuously tracked within the sensor network with respect to the physi cal placement of the network Since the application requirement is to place the sensor nodes over the wall in a line intruder can change positions from be ing in one sensor s range and then in another s the reby making this tracking strategy effective 5 PERFORMANCE EVALUATION In this section we present the experimental re
18. eeeeeeaneaeat j i Fig 6 Some CTP routing stack configurations 23 The PIR sensor is interfaced with the 51 pin expan sion connector of the MicaZ mote using the external interrupt pins of the MicaZ mote as shown in Figure 7 a Whenever the sensor generates a DC interrupt it is recognized and the DetectionEvent module trig gers the RadioMessage event which then forwards the interrupt along with the node id in a radio packet towards the root which is the base station node In order to distinguish the data packets we have used three packet types Type 1 packet is sent only once when the entire network is booted that contains node id from which the packet is being generated and also the node id s of all the immediate neighbors of the node along with the gateway identifier which is true if the node is in direct radio range of the base sta tion This is done to ensure at network startup time that all nodes correctly booted and have full infor mation about their neighboring nodes and can multi hop successfully to send their data to the root Type 2 packet is sent after a period of every 2 5 sec that contains the node id and a string identifier of the packet type as he payload and is recognized as a hel lo packet by the base station node in order to con firm node availability Type 3 packet is sent through the radio link when detection is made and the inter rupt variable is true that contains the interrupt value node id and packet i
19. erfaced to the MicaZ motes and custom designed sensor nodes PIR sensor responds to the infrared radiation of the human body and is quite reliable in determin ing human presence within its sensing range 3 4 The remainder of the paper is organized as follows Section II describes the application scenario 1 e ap plication requirements for which this system is im plemented Section II describes the hardware and This work is supported by TWAS Italy under the grant number 09 068 C 90 eJSE International software components and the system setup Section IV discusses the implementation details of the sys tem Section V provides system evaluation results and lessons learned from our experience Conclusion is presented in section VI 2 APPLICATION REQUIREMENTS The design of our system is motivated by the re quirements of a perimetric monitoring application The general objective of such an application is to monitor the perimeter in most cases a boundary wall for any human presence over the wall or within some distance of it The base station where all the information is sent needs to have a map of the entire security perimeter and human detection at any seg ment of the wall must be reported to the base station with acceptable latency Some applications require ments which must be satisfied to make our system useful in practice are following First continuous monitoring requires the sensor devices to be active all t
20. etc 1 MicaZ Motes MicaZ is a crossbow Inc s flag ship commercial mote designed for applications to run in low power wireless sensor networks It fea EJSE Special Issue Wireless Sensor Networks and Practical Applications 2010 tures an Atmel ATmegal28L low powered micro controller with 128K bytes of program flash memo ry 512 Kbytes measurement Serial flash and 4K bytes configuration EEPROM The device also has a 250 kbps 2 4 GHz IEEE 802 15 4 standard com pliant MPR2400 radio The MicaZ motes provide low power operation 8 mA current draw in active mode and lesser than 15 A draw while in sleep and a radio range of up to 100 m It makes it an ideal platform for large scale long term deployment The MicaZ mote also has a 51 pin expansion connector which supports analog inputs Digital I O I2C SPI and UART interfaces These interfaces make it easy to connect to a wide variety of external peripherals The 51 pin expansion connector is used to interface the PIR sensor with the MicaZ mote The MicaZ is powered by two AA batteries 5 The cost of one MicaZ mote is approximately US 130 incl shipment cost The physical parameters of MicaZ motes help to achieve the stealthiness re quired by the application A MicaZ mote is also used as a gateway to aggregate the sensor network data onto a PC where base station monitoring application visually displays the data on a user friendly GUI For the gateway node a MicaZ mote is a
21. etection the total current draw in reporting to the base station 1s 26 4 mA Assuming one detection event is reported to the EJSE Special Issue Wireless Sensor Networks and Practical Applications 2010 base station within 1 sec and given the capacity of the power source the MicaZ sensor platform has the capability to report approximately 2700 3600 26 4 368 181 detect tions Obviously in practical deployment these results would be de graded because of factors like multi hop communi cation environment conditions random detections and false alarms etc In the experiments the average number of hops is reported to five and the MicaZ are able to report approximately 57156 detections The custom designed sensor node s energy consumption values gathered in a controlled environment are as follows The ETRX2 transceiver in sleep mode draws ap proximately 2 uA current During Tx Rx mode it draws 36 mA and the PIR sensor draws the same 1 mA current Again assuming that one detection event takes up to 1 sec to be reported to the base sta tion the total number of detections which can be made with 2700 mAh battery source turns out to be 255 790 It is noted that 1 sec is the worst case time for transmission of such a small data Again the cal culations may vary depending upon the physical condition or other above mentioned factors 7 CONCLUSION Research and implementation of diverse monitoring applications in the field of W
22. he Ist ACM Conference on Embedded Networked Sensor Systems SenSys 2003 16 TinyOS TOSSIM A Simulator for TinyOS Networks User s manual in TinyOS documenta tion http docs tinyos net index php TOSSIM 17 Microchip MPLAB Integrated Development Environment http www microchip com stellentidcplg IdcServic e SSGETPAGE amp nodeld 1406 amp dDocName en019 469 amp part SW007002 18 Microchip MPLAB C Compiler for PICI8 MCUs http www microchip com stellentidcplg IdcServic e SSGETPAGE amp nodeld 1406 amp dDocName en010 014 19 Telegesis Terminal PC Software http www telegesis com telegesis zigbee technolo gy technical support telegesis terminal htm 20 Wikipedia Online Encyclopedia entry on C Programming Language http en wikipedia org wiki CSharp 2sprogrammi ng language 29 21 Microsoft Visual Studio Homepage http msdn microsoft com enus vstudio default aspx 22 TinyOS programming April 2009 Ed Cam bridge University Press pp 8 2009 23 O Gnawali R Fonseca K Jamieson D Moss and P Levis CollectionTree Protocol in Proc of the 7th ACM Conference on Embedded Networked Sensor Systems SenSys 2009 24 TinyOS programming April 2009 Ed Cam Lens 98 elSE EJSE Special Issue Wireless Sensor Networks and Practical Applications 2010 International bridge University Press pp 49 2009 25 I Jawhar N Mohamed and K Shuaib I
23. he time Therefore energy conservation schemes are required so that lifetime of sensor devices can be extended for uninterrupted active sensing Second the perimeter must be entirely covered without any unattended spaces in between any two nodes This requires effective and acute positioning and orienta tion of the sensor devices Third it 1s crucial for the sensor nodes to have a very low possibility of being detected by the intruder which can then possibly find a way to bypass detection Small physical size of sensor nodes along with zero RF communication is desired in absence of significant events Fourth effective detection of human presence along with low reporting latency is also required so that active countermeasures can be deployed against the threat well in time Fifth the sensor nodes need to commu nicate with each other in a line topology since wall coverage is done by placing sensor nodes in a semi straight or straight line Thus the routing must be done in such a way to ensure that radio links are maintained even if any node goes down 3 SYSTEM COMPONENTS AND SETUP 3 1 Hardware The hardware platform used for the outdoor test bed consists of two sensor node types Firstly the indus try standard MicaZ motes are used and secondly in order to reduce the cost of each sensor node we have designed our own custom sensor node using discrete components micro controller voltage regu lating switches ZigBee transceivers
24. ion A mobile end device only has a ETRX2 standard module which is interfaced with a sensor When the sensor detects it informs the ETRX2 RF module at I O11 Ref ETRX2 Command Manual which is physically its pin 31 It is a falling edge therefore bit 6 of SIO register is set to correctly configure ETRX2 When such external interrupt occurs an in ternal interrupt IRQ3 is generated for which the functionality register is S26 This register holds the code of specific functionality which we need the ETRX2 module to perform when an external inter rupt at I O11 occurs We set it to 8110 that sends the reading of the I O the two analogue ports and Vcc as well as an 8 bit transmission counter to the sink If no sink is known then the node searches for a EJSE Special Issue Wireless Sensor Networks and Practical Applications 2010 sink instead The router is responsible for delivering data of end devices to sink by collaborating with other routers present in the network managing the whole network while end devices are dedicated only to intrusion detection A standard module is declared as a mobile end de vice by changing the contents of S register OA bits F E to 11 By default it is 00 1 e a router The reason for declaring a mobile end device is that it cannot move around the network e g if its location is changed in the network it dynamically changes its parent to a nearby router Furthermore a mobile end device is kept in a low power m
25. ng whether it s a human or a small 94 eJSE International rodent or any other animal Due to this weak signals are discarded and once the detection comes out to be in the desired range of values the microcontroller gives a unicast command to ETRX2 RF module via a data string through its TX pin 25 which is con nected with the RX pin 28 of the ETRX2 module After that the microcontroller returns to sleep mode till next detection occurs PIC 18F 452 Reget H PEI 10 Bis m H ra ai r 7i r 76 25 24 J 22 2h x ALEE ERRTRGGDEE 1 UIEN Bom VCC ir TOF ae 2E 2 au E a oE Se eeee F a om M A a po E H ND Fig 8 PCB connection diagram To minimize overall power consumption of the net work the custom sensor platform consists of two kind of devices the first kind are declared as mobile end devices while others are fully functional devices to function as routers Each router has multiple usually 8 10 mobile end devices as its children PCB connection diagram of the router node is shown in Figure 8 All network related tasks are performed by the routers and the mobile end devices are asleep and wake up after an intrusion is detected only to notify its parent router After notifying they go back to sleep again There is no other task of a mobile end device therefore we do not need micro controllers on them thereby reducing power consumpt
26. ode to consume less battery This is done by changing the S register 39 contents to 0002 basically this enables the module to fall asleep If no polling and other timed actions are performed the power consumption can be as lit tle as 1 5 A in this mode However due to polling we expect this value to be little more The data is passed on to network sink which is serially con nected to the computer The sink is essentially the same module but it can connect serially to the com puter A node can be declared as sink by setting bit 4 of S register 10 Hence all data coming from the network can then be manipulated in any desired manner once it is at the serial port fig 9 displays the end device picture and MicaZ sensor node Note the same PIR sensor on both platforms The base station performs two tasks first it receives packet from MicaZ through other nodes connected to the MIB520 interfacing board Secondly it trans fers received packets from network to serial USB port The monitoring application parses the received packets over serial port and filters out relevant in formation such as packet type node ID interrupt va riable s value According to the packet type de tected specific action is taken by the monitoring application For packet type 1 in case of MicaZ based network the application displays a popup alert with the information that mote ID x has joined the network The user at the monitoring PC has to map the node to the corr
27. ress in energy scaveng ing the current solutions need to be very energy efficient using the minimum amount of energy while having the maximum useful throughput Other major challenges faced by WSNs are tamper resistance unobtrusiveness and real time constraints Despite these limitations WSNs do have the advan tage of deploying sensors in hostile environments autonomously This fulfills a very important need for 1 any real time monitoring especially in remote sce narios These advantages and disadvantages of WSNs compel development of a system which can be deployed and tested in the real time environment Evaluations done through simulations tend to make simplified assumptions which fail to hold well in practice rendering the simulated systems incomplete Simulation does however give an in sight on the Operation of such systems under ideal conditions which can be a scale to measure the results achieved in real world scenarios 2 In this paper we describe our effort in designing and implementing a system on a network of up to 30 sensor nodes with at least half of them being MicaZ motes and the rest our own designed sensor nodes The primary goal is to build a system which is able to reliably and stealthily detect human presence and track the movement pattern of the human within the sensor network with minimum cost size and energy consumption The core of the system is use of the Passive Infrared PIR sensors which are int
28. sults that evaluate the performance of the system de scribed in the previous sections Results are obtained by deploying MicaZ and custom designed sensor nodes in a straight line on a grassy field depicting their deployment over the boundary wall For energy consumption experiments the system needed to be deployed unattended for long durations which could not be done due to security issues so energy con sumption experiments were conducted with a small er number of nodes in controlled environments Ex periments are divided into three categories The first set of experiments evaluates the transmission range of the MicaZ radio and the Telegesis ETRX2 tran sceiver The second set of experiments evaluates the sensor capabilities and finally the last set of experi ments evaluates the energy consumption calcula tions for both the MicaZ sensor nodes and custom designed sensor nodes 5 1 Evaluation of Sensor Node Radios The radio communication of the MicaZ motes de pends on several factors such as antenna length ele vation from the ground positioning of motes The conclusions drawn in experiments are based on the assumption that the antenna size is same for all Mi caZ motes same elevation above ground with simi lar line of sight Under these assumptions we have observed the radio range of single hop packet trans mission i e two MicaZ motes communicating with each other to be approximately 70 m This range is achieved when both nodes
29. the horizontal distance from the center of the lens until the first detection is made The results obtained comply with the fact that Fresnel lens en hances the sensor capability by segmentation and detection and the detection cone gets wider as dis tance from the center increases The graph in Figure 9 shows the plot of the results obtained The trend shows that as the vertical distance from the center of the PIR sensor lens increases the angle of detection horizontal distance of detection also increases This is due to the segmentation effect from Fresnel lens covering the pyro elements of the sensor As the vertical distance from the PIR sensor is increased the angle of detection increases thereby enabling the sensor to detect at a wider horizontal distance The last experiment performed with the PIR sensor was the detection ratio and reliability when a moving target passes in front of the sensor at varying dis tances A test subject moving at a constant speed of 1 feet sec passed in front of the sensor at varying vertical distances Assuming that the total detection and reporting time of one detection event is 1 second we evaluate the probability of events missed while the person is moving in front of the sensor The probabilities of detection events are plotted against the vertical distance of the test subject from the sensor and the results obtained are plotted in Figure 10 The detection probability decreases as the 96 eJSE
30. ttached to a MIB520 interfacing board via its 51 pin expansion connector which provides USB connectivity to Mi caZ motes for communication and in system pro gramming The MIB520CB offers two separate ports one dedicated to in system Mote program ming and a second for data communication over USB The MIB520CB has an on board processor that programs mote processor radio board USB bus power eliminates the need for an external power source 6 Transceiver Micro controller Sensor a2INOS l MO d Fig 1 Block diagram of custom designed sensor node 2 Custom Designed Sensor Node A new sensor network hardware platform is designed in order to reduce the cost up to US 50 per node which is half the cost of MicaZ platform For our application which requires dense sensor node deployments to increase system reliability and effectiveness sensory devices should be as much cost effective as possible while maintaining efficient detection and operation For RF communications we have used the Telegesis eJSE International be 2 PA module which is a power amplified 2 4GHz ISM band transceiver based on the Ember EM250 single chip ZigBeeR IEEE802 15 4 solu tion This transceiver enables us to communicate with the base station PC for reporting the sensor s detection data The module is based on AT style command line interface that allows us to communi cate with transceiver on the custom sensor node through RS 23
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