Wireless sensor network for berth supervision in marinas
Contents
1. The analysis of these graphs concludes that for Tyee of 3 minutes estimated boat tag runtime is from 1 3 to 15 years and berth sensor node over three years Having in mind that boat berthing and departure takes over 10 minutes these results are entirely satisfactory Finally we can roughly estimate node prices based on deRFmegal28 module 33 waterproof sensor Maxsonar 73 and IP67 case prices Sensor nodes are the most expensive part of the system and should cost about 130 while tag price estimate is 50 These are retail prices for one piece order IV CONCLUSION Automatized berth supervision system is described Tests have proven that system is beneficial and meets predetermined requirements With Tice set to 3 min boat tag battery is estimated to last over year and half and sensor node over three years The main limit for the network size is available reader RAM Battery powered infrastructure except readers ensures low cost and fast installation Developed system solves various logistics problems in a marina especially with the reservation of transit berths First field test of prototype network was carried out so the next step should be permanent system installation for a long term in field testing ACKNOWLEDGEMENT This research has been partly supported by the ACROSS project 285939 FP7 REGPOT 2011 1 The authors would like to thank Sailing Club Uskok from Zadar for in field test support REFERE2. po nodes change mers A ee a Reader Computer Children E table Tags _Application timeout _Newtag l Boat Polling timers tag left inventory Algorithm otuput Sensor Berth status ______ Berth status nodes change change Poo 3 Algorithm no b Reader Computer Berth owner e table Tags Application gt gt Application Boat inventory Algorithm timeout otuput Sensor Berth status Berth status timers nodes change change B c Fig 3 Boat inventory management approaches a on the reader lever b distributed between reader and computer c on the computer level messages to be more energy efficient 2 Managing boat inventory Regardless of the message types used boat inventory management can be implemented in three ways Fig 3 The first approach is to manage inventory and berth owner table on the reader level using ZigBee children table The problem with this approach is that every reader manages its own children table partial inventory so berth sensor node and its corresponding boat tag should connect to the same reader for the system to operate correctly The second approach is that every reader manages its own children table and sends messages to the computer via the coordinator only when a tag leaves or a new tag enters the network The computer uses these messages to manage the complete boat inventory of the marina without using timeout timers they are u
3. topology and routing 4 Networks are mainly based on 802 15 4 protocol and ZigBee is often used as a proven solution for fast development 5 6 In such networks boat identification could be optimally done by radio identification RFID In addition position of the wireless tag could also be estimated using network s localization capabilities 7 9 Current localization solutions require custom development and training whereas reported maximum localization accuracy is around 1 8 m Without localization a system can only provide an inventory of all boats in the marina Nevertheless if a berth state changes to occupied and the berth holder s boat is in the marina at the same time we can assume with a certainty that the holder has docked at his own berth Summing all advantages and drawbacks we have chosen to use ultrasonic sensors for occupancy detection and ZigBee tags for boat identification The goal of this article is to evaluate the use of ZigBee for RFID considering the marina specific requirements The berths are usually leased for a year long period so the runtime of all battery powered devices in boats should be at least one year All other battery powered devices should last as long as possible A typical marina has 500 berths which means that large scale network support should also be ensured Additionally system infrastructure should be kept simple and cost effective System layout and hardware RFID implementati
4. NCES 1 H Ichihashi A Notsu K Honda T Katada and M Fujiyoshi Vacant parking space detector for outdoor parking lot by using surveillance camera and fcm classifier in Fuzzy Systems 2009 FUZZ IEEE 2009 IEEE International Conference on aug 2009 pp 127 134 2 J Chinrungrueng U Sunantachaikul and S Triamlumlerd Smart park ing An application of optical wireless sensor network in Applications and the Internet Workshops 2007 SAINT Workshops 2007 International Symposium on jan 2007 p 66 3 S eun Yoo P K Chong T Kim J Kang D Kim C Shin K Sung and B Jang Pgs Parking guidance system based on wireless sensor network in Wireless Pervasive Computing 2008 ISWPC 2008 3rd International Symposium on may 2008 pp 218 222 4 J Benson T O Donovan P O Sullivan U Roedig C Sreenan J Bar ton A Murphy and B O Flynn Car park management using wireless sensor networks in Local Computer Networks Proceedings 2006 31st IEEE Conference on nov 2006 pp 588 595 5 S Lee D Yoon and A Ghosh Intelligent parking lot application using wireless sensor networks in Collaborative Technologies and Systems 2008 CTS 2008 International Symposium on may 2008 pp 48 57 6 Meshnetics Parking Lot Gets Smart with ZigBee 2007 Online Available http www meshnetics com netcat_files Image ZigBee 20Parking 20Automation 20Case 20Study pd
5. Wireless sensor network for berth supervision in marinas Roko Krpetic Dinko Oletic Vedran Bilas University of Zagreb Faculty of Electrical Engineering and Computing Zagreb Croatia Email roko krpetic gmail com dinko oletic fer hr vedran bilas fer hr Abstract In this paper a berth supervision system for marinas is presented Berth occupancy is detected using wireless ultrasonic sensor nodes installed on every berth ZigBee RFID tags installed on each boat are used for its identification RFID readers installed along marina wharfs route tag messages to a central computer Prototype system is implemented using Atmel ZigBee development kits and Atmel Bitcloud stack Power consumption and large scale network support are analysed and tested System functionality was successfully demonstrated in a marina field test Kstimated run times of the boat tag and the berth sensor node are over two and three years respectively Index Terms wireless sensor networks marina berth super vision RFID ZigBee I INTRODUCTION Berth supervision is important for marina logistics manage ment It consists of two functions berth occupancy control and boat identification It s often necessary to determine the number of free berths at a given time and to verify whether a berth is occupied by its holder Berth occupancy check and boat identification are usually performed manually An employee has to patrol the marina visually inspect berths and ve
6. ag in and out of the network The first state comprises of sending tag ID and the latter state is an attempt to connect to the network As described in Section I subsections B and C various combinations of waiting time and number of beacon requests were tested and measured Tests have shown that using two beacon requests and a medium waiting time is optimal for reliable reconnection upon a boat tag s return to the marina Berth sensor node power consumption was also measured using sensor SRFO5 This measurement was used as a base for consumption estimation of Maxsonar MB7067 sensor suitable for final installation Power consumptions are shown in Table I Finally these measurements were used for node runtime estimation assuming the use of a standard 1100 mAh alkaline battery Boat tag runtime is shown in Fig 7 depending on how long the boat remains in the marina p and how long outside the marina p2 Boats stay docked in the marina most of the time so situations with p gt 0 5 are realistic Berth sensor node runtime is shown in Fig 8 Node Runtime years T min sleep Fig 7 Boat tag runtime in years as a function of Tsicep p refers to the percentage of time that boat remains in the marina and p2 outside the marina Node Runtime years Ja A 0S l 2 3 4 5 6 7 8 T min sleep Fig 8 Berth sensor node runtime in years as a function of Tsleep
7. connection Send boat ID Notify reader a b Incoming message Berth state occupied Berth state empty Boat ID Reset timeout timer add new timeout timer Check boat inventory Owner docked or issue a warning Delete boat record Timer runs out ee in inventory c a Berth sensor node b boat tag and c central computer software Berth empty Fig 2 flowchart 1 ID messages There are two ways the tag can transmit its ID The first one is through 802 15 4 polling mechanism which is normally used to inform the parent that the child is awake and ready to receive data buffered while sleeping 11 In our scenario we can use polling messages just to manage the children table on the reader The alternative is to simply use application layer messages Polling messages use COMMAND frame instead of DATA which is shorter 12 Also they are transparent to the upper layers making the communication process less resource intensive Hence we expect the polling Reader Computer Berth owner table r Application Partial boat aBS bolli gt inventory l oling Algorithm eee Algorithm ia Children otuput otuput Sensor Berth status
8. d waterproof IP67 rating Specific beam geometry is an important requirement as well Having in mind that the smallest berths are 3 m wide the beam should be roughly 3 m wide at a 3 m distance from the waterside Beam range should be at least 5 m System prototype was developed using Robot Electronics SRFO5 ultrasonic sensor and Meshnetics MeshBean Amp development boards The boards are equipped with Meshnetics Zigbit module based on Atmel ATmegal281 microcontroller Developed software uses Atmel Bitcloud stack 10 B RFID implementation Given the described layout RFID system is implemented by managing a table of boat tags connected to the network real time inventory of boats in marina Every record in this inventory should have a timeout timer As long as the boat tag is in the network it sends its ID which resets the corresponding timer and the boat record remains in the inventory Timeout timer is responsible for deleting the record if the tag boat exits the marina When a specific berth sensor node detects berthing the system should find an owner in the berth owner table and then look up the boat inventory with the owner ID If the owner is in the inventory the system can assume the berth owner has docked on his berth Otherwise the system can warn that unidentified boat has docked Ultrasonic detection Boat in marina Boat outside Berth state marina changed Attempt network
9. e will be in case the parent node is currently busy with some other operation We have tested and measured power consumption of various combinations to determine the optimal ratio as shown in Section III Ultrasonic berth sensor nodes are always connected to the network so the power consumption depends only on the characteristics of the ultrasonic sensor D Large network support Average marina has 500 berths which means the average number of nodes in the network is about 1000 To analyse potential node number limits we have to consider network topology Our network has a maximum of 2 hops with many nodes directly connected to routers readers and several dozen readers connected to the coordinator ZigBee protocol uses 16 bit network addresses so it theo retically supports network with as many as 65536 nodes 12 Bitcloud stack doesn t define the maximum number of nodes but the user s manual 10 claims support for hundreds of devices Atmel s development team has unofficially tested a network with 112 nodes 14 Furthermore the limits on reader level are defined by the amount of RAM available for children table management Bitcloud uses 49 B per child record in this table 10 Newer Atmel chips ATmegal28RFA1 have 16 kB of RAM The stack uses about 7 kB which means the rest is available for 188 children node records Thus this is a serious limitation only when older chips are used with only 8 kB of RAM Another potential li
10. erth sensor nodes to the computer which manages boat inventory as shown in Fig 2c and provides information to the user Fig 5 C Power management There are two types of battery powered nodes in this system boat tags and berth sensor nodes As usual in wireless sensor networks reducing endnode energy consumption is a key challenge Node runtime directly depends on the duty cycle Longer node sleep period Tsteep prolongs node runtime but introduces lag to system operation which decreases quality of service Therefore node runtime will be measured as a function of variable Tsicep As seen in Fig 2b there are two possible states after the tag wakes up boat tag connected to the network boat in the marina and boat tag not connected boat out of the marina In the first case boat tag should send boat ID As presented in Section IIB tests have shown that application messages are more energy efficient In the second case boat tag has to try to connect to the network once This wake state consumes a lot of power Bitcloud uses active channel scan Connection is initiated by sending a beacon request and waiting for beacons from potential parent nodes 13 Both the waiting time and the number of beacon requests are configurable Shorter scanning time results with longer runtime and also with greater risk the radio will turn off before the beacon is received Also the fewer the number of attempts the more probable the connection failur
11. f 7 A I Noh W Lee and J Ye Comparison of the mechanisms of the zigbee s indoor localization algorithm in Software Engineering Artificial Intelligence Networking and Parallel Distributed Computing 2008 SNPD 08 Ninth ACIS International Conference on aug 2008 pp 13 18 8 F Sottile R Giannantonio M Spirito and F Bellifemine Design deployment and performance of a complete real time zigbee localization system in Wireless Days 2008 WD 08 Ist IFIP nov 2008 pp 1 5 9 Nanotron Loss Protection Solutions 2011 http www nanotron com 10 BitCloud User Guide Atmel November 2009 Online Available http www atmel com dyn resources prod_documents doc8199 pdf S C Ergen Zigbee ieee 802 15 4 summary 2004 Online Available http staff ustc edu cn ustcsse papers SR10 ZigBee pdf ZigBee Specification r17 ed ZigBee Standards Organiza tion October 2007 Online Available http www zigbee org ZigBeeSpecificationDownloadRequest tabid 3 1 Default aspx 13 ZEEE Std 802 15 4 2006 Part 15 4 Wireless Medium Access Con trol MAC and Physical Layer PHY Specifications for Low Rate Wire less Personal Area Networks WPANs IEEE SA Standards Board June 2006 Bitcloud team 100 node ZigBee PRO network w BitCloud stack and WSN Monitor 2011 Online Available http www youtube com watch v bkH_kJO_DVY Online Available 11 12 14
12. mitation is the overload due to excessive communication so application confirmations and communication are reduced as much as possible HI TESTS AND RESULTS A Field test Our prototype network was tested in a marina to check all functions and to demonstrate system performance in real conditions The test included ultrasonic sensor calibration Fig 6 and both tagged and untagged boat docking and departure Hy Ma i j H De 1 i akik Fig 6 Berth sensor mounted on the pontoon forefront as seen from above TABLE I BOAT TAG WAKE STATES POWER CONSUMPTION State Duration Consumption Tag in network 9 ms 0 73 mJ Tag outside network 789 ms 51 99 mJ Ultrasonic measurement 285 ms 19 32 mJ The test took place 6th June 2011 in Zadar Croatia Ultrasonic sensor was calibrated using a range threshold of 3 m The reader was set on a 3 m high base When a tag was placed in the boat cabin its range was about 50 m using the half of maximum transmitter power 5 dbm All situations were properly detected which proved accurate system performance B Power consumption and node runtime We measured power consumption of active node states to estimate node runtime Measurements were carried out using a Tektronix A6802 current probe and National Instruments NI 6211 acquisition card Sleep current was measured using Fluke 45 multimeter The results were obtained and calculated using Matlab There are two possible wake states for a boat tag t
13. on concept challenges regarding power management and large network support are described in Section II Tests and results are presented in Section III and conclusions are given in Section IV Il METHODS A System layout and hardware Wireless ultrasonic berth sensor nodes Fig 1 are mounted on every berth and used as occupancy detectors When awake a berth sensor node checks berth state and notifies the reader of any change Fig 2a Also every berth holder s boat is equipped with an active RFID boat tag Boat tags and berth sensor nodes are enddevices and do not communicate with each other They send messages directly to the readers mounted along marina docks Readers are responsible for Berth Berth sensor sensor node node Fig 1 Berth occupancy and boat identification system layout routing the messages to the coordinator which delivers in formation to the computer When the boat is in the marina the boat tag is connected to the ZigBee network and reports the boat ID every time it awakes Fig 2b When the boat leaves the marina it disconnects from the network As long as the boat remains away from the marina the boat tag will periodically attempt reconnecting to the network once every wake state The ultrasonic sensor should have a low power consumption few mA on average during the detection period less than 200 ms Also it should be CMOS 3 3 V compatible It s important that the sensor itself is robust an
14. rify boats This approach is obviously inefficient It is time consuming and expensive with increased probability of error Automatic berth supervision offers many advantages for marina management Such a system can automatically record boat arrivals and departures graphically present occupancy be used to send information to the boat owner and provide new billing policies Berth occupancy can be detected using a small number of sensors such as cameras which have proven adequate for parking space detection 1 Their advantage is low hardware cost since only a few cameras can cover the whole marina and image processing can be used for boat identification at the same time However since marina berths and boats come in various sizes and shapes false detection becomes more probable making such a solution require custom development and training Another approach is to use a large number of distance measurement sensors mounted on each berth A potential drawback of such an approach is the higher overall cost Ultrasonic and optical sensors are the strongest candidates with ultrasonic sensors being less susceptible to environmental conditions sunlight underwater operation Many experiences and solutions from the field of intelligent parking lot applications are applicable to such systems These systems normally use wireless sensor networks in favour of wired networks 2 Main research issues are energy con sumption versus duty cycle 3
15. sed on the reader level Both polling or application messages can be used The third approach is to use the ZigBee network only for forwarding the messages to the computer while complete processing is done on the computer level Only application messages can be used Polling message Current mA 0 5 10 15 20 25 30 35 40 45 Time ms Application message Current mA 15 20 25 30 35 40 45 Time ms Fig 4 Power consumption of the polling and application messages with wireless node operating at 3 3 V a MarinaView oje z Debug Tablica Router 01 Vez 001 1 lt Plovilo 0001 Send 7 Clear Cm Fig 5 Test application graphical user interface To find the optimal approach we have measured and compared power consumption between polling and application messages as seen in Fig 4 The results are unexpected polling and application message energy consumptions are measured at 2 9 mJ and 0 7 mJ respectively Such high polling message consumption stems from the long standby period following the transmission of the polling message During this period the node awaits the in coming parent messages Its duration is not user configurable This prolongs the wake state and consumes more power in the end Therefore we decided to use application messages and the third approach ZigBee network forwards periodical messages from the boat tags and messages from b
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