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  Smart Dust (Wireless sensor network) Prathamesh N. Patil, Ajinkya A. Powale, Prashant A. Yadav, Abhishek Vichare   Don Bosco Institute of Technology, Kurla    Abstract   —Huge sensors and their installation overheadscan be avoided by designing a wireless communicationsystem for sending and receiving data from distributedsensor networks, or Smart Dust systems. The devices forcommunication on the dust motes are subject to size andpower constraints, which can collect various informationby sensing the environment.  Keywords  — Wireless Sensor Networks, MEMS, motes, basestation. I. INTRODUCTIONIn the late 1990s, the vision of “smart-dust” wasarticulated by the research community. This vision was predicated on advances in microelectronics, wirelesscommunications, and microfabricated (MEMS) sensing thatwere enabling computing platforms of rapidly diminishingsize. The early proponents imagined devices one cubicmillimeter in size with capabilities sufficient to power themselves, sense the environment, perform computation,and communicate wirelessly [7]. Large-scale deploymentsof such devices would enable a wide range of applicationssuch as dense environmental monitoring, sensor rich homeautomation and smart environments, and self-identificationand context awareness for everyday objects.The past decade has seen significant effort and progress towards the srcinal motivating applications. In particular, wireless sensor networks (WSNs) based on“mote” sensing platforms have been applied to many real-world problems. Remote monitoring applications havesensed animal behavior and habitat, structural integrity of  bridges, volcanic activity, and forest fire danger [5], to nameonly a few successes. These networks leveraged therelatively small form-factor (approximately 1” x 2”) of motes and their multihop wireless communication to provide dense sensing in difficult environments. Due totheir low power design and careful networking protocolsthese sensor networks had lifetimes Measured in weeks or months, which was generally sufficient for the applications.This paper focuses on business applications of smart dust, its architecture and various communicationtechniques those can be used to communicate with themotes.II. ARCHITECTURE AND OPERATION While dust-sized sensing and communication unitsare the goal of the project, macro-scale units called moteshave been successfully developed and are in use for avariety of research projects. The motes are based on acommon architecture, but each mote has a unique set of communication and sensor capabilities [1,6]. Smart motesconsist of a microcontroller, sensors and a communicationunit. The communication unit is one of the following: an RFtransceiver, a Laser Module, or a corner cube reflector. Thesensors measure a number of physical or chemical stimulisuch as temperature, humidity, ambient light, vibration,acceleration, or air pressure.Periodically the microcontroller receives a readingfrom one of the sensors, processes the data, and stores it inmemory. A receiver is used to receive incomingcommunications from other motes or from the base station.Sensor data and messages can be transmitted back to the base station or to other motes in the network with the use of the corner cube reflector, laser or RF transceiver. The microcontroller determines the tasks performed by the mote, and controls power distribution tothe various components of the system in order to minimizetotal consumption. Power conservation is achieved largelythrough the use of timers. When a timer expires, it signals a part of the mote to carry out a task, then powers off. Uponcompletion of the task, everything is powered down and thetimer begins counting again. The microcontroller canreceive several types of packets, including new programcode that is stored in the program memory. This capabilityenables remote modification of the mote’s behavior.Incoming packets may also contain messages from the basestation or other motes. The message may contain specificinstructions for the mote, or it may simply be a message thatis in transit to some other destination.Some of the timers mentioned above are dedicatedto control of the sensors. When one of these timers expires,it powers up the corresponding sensor, takes a sample, andconverts it to a digital word. If data are interesting, themicrocontroller can assemble it into a packet for transmission. Alternatively, the sensor data may be storeddirectly in the mote’s SRAM.  Figure 1 Smart Dust Mote III. C OMMUNICATION   TECHNOLOGIES A viable wireless communication architecture for smart dust must satisfy a number of requirements. It mustsupport half- or full-duplex, bidirectional communication between a central transceiver and up to 1000 dust motes.The downlink (central transceiver to dust motes) must broadcast to all of the dust motes at a bit rate of severalkbps. The uplink (dust motes to central transceiver) must permit each of 1000 dust motes to convey about 1 kb of datawithin 1 s, an aggregate throughput of 1 Mbps. Options for uplink multiplexing include time-, frequency-, code- andspace-division multiplexing, as described below. The centraltransceiver must be able to resolve the position of each dustmote with an angular resolution of the order of 1/100 of thefield of view. The link should operate over a range of atleast several hundred meters. The dust mote transceiver must occupy a volume of the order of 1 mm3, and consumean average power not exceeding 1 mW. If possible, theuplink and downlink should afford a low probability of interception. It should be noted that we do not envision performing direct communication between dust motes.We will perform a detailed comparison of severalalternative system designs based on radio frequency (RF)and free-space optical transmission. This study will revealthe best downlink and uplink designs, and permit us tooptimize the design of the relevant components. Optimumdownlink and uplink designs are likely to be rather different.Indeed, optimized designs of both should exploit thesystem’s asymmetry, i.e., the larger power consumption,complexity, size and cost permissible in the centraltransceiver unit, as compared to a dust mote.RF transmission can be employed for the uplink and/or the downlink. In principle, uplink multiplexing can be achieved using time-, frequency- or code-divisionmultiplexing (TDMA, FDMA or CDMA) [2], but eachtechnique may be problematic in this application. TDMArequires each dust mote to transmit at an excessively high bit rate, as high as the aggregate uplink capacity in theabsence of other multiplexing techniques. Moreover, TDMArequires each dust mote to coordinate its transmission withall the other dust motes. FDMArequires accurate control of the dust-mote oscillator frequency, while CDMA requires high-speed digitalcircuitry to operate for a relatively extended time interval, potentially consuming excessive power. In order to avoidcoordination between dust motes, both FDMA and CDMArequire individual dust motes to be preprogrammed withunique frequencies or codes. If RF transmission is to beused, it is probably necessary to employ an judiciouscombination of two or more of these multiplexingtechniques. In principle, space-division multiplexing (SDMA)represents another means to multiplex uplink RFtransmissions. In SDMA, the central transceiver employs anantenna array to separate transmissions from different dustmotes. Given the limited size of the central transceiver,however, it would be difficult for SDMA to achieve therequired spatial resolution. For similar reasons, it would bedifficult for a RF uplink to provide information on thelocation of the dust motes. The resolution of RF-based location determinationcan also be degraded by multipath propagation. Free-spaceoptical transmission at visible or near-infrared wavelengths(400-1600 nm) represents an attractive alternative for thedownlink and uplink. On the downlink, a single laser transmitter can broadcast an on off- keyed signal to thecollection of dust motes. Each dust mote would be equippedwith a very simple receiver consisting of a bandpass opticalfilter, a photodiode, a preamplifier and a slicer. This receiver would involve only low-speed baseband electronics, makingit far simpler than its RF counterpart.On the uplink, optics offers two alternatives for transmission. Each dust mote can be equipped with anactive laser-diode-based transmitter. This has thedisadvantage of requiring excessive power. To minimize the power consumption, the dust mote should employ adirectional beam and an active beam-steering mechanism, but this complicates the dust-mote design, and adds the needfor beam-tracking protocols. Alternatively, each dust motecan employ an optically passive transmitter consisting of acorner-cube retroreflector (CCR). By displacing one of themirrors, the CCR reflectivity can be modulated at bit ratesup to 10 kbps. The collection of dust motes can beilluminated by a single interrogating laser. Because of itssmall power consumption (of the order of 1 mW) and because it avoids the need for active beam-steering, theCCR-based transmitter seems much more promising thanthe laser-diode-based design. Because they involve onlylow-speed baseband digital electronics, both transmitter designs are much simpler than their RF-based counterparts.With either uplink optical transmitter design, theuplink receiver should employ an imaging receiver,consisting of a lens and a CCD or CMOS image sensor array. With either transmitter design, periodic pulsation of the downlink or interrogating laser beam can be used tosynchronize the transmissions from all dust motes to theframe clock of the imaging array. Such an uplink architecture offers several advantages over a RF solution.The short optical wavelength enables a reasonablysized camera to achieve high spatial resolution. Not onlydoes this easily yield information on the dust-motelocations, but it enables the uplink to rely solely upon  SDMA for multiplexing [4]. The 1000 dust motes cantransmit simultaneously and without any mutualcoordination, greatly simplifying their design and thesystem protocols.IV. R  ELATED   PROJECTS Several projects have recently been initiated toinvestigate a variety of communications research aspects of distributed sensor networks. The Factoid Project [9] at the Compaq PaloAltoWestern Research Laboratory (WRL) is developing a portable device small enough to be attached to a key chain.The device collects announcements from broadcastingdevices in the environment, and these can be uploaded to auser’s home basestation. In its first generation, the prototypedevices are much larger than smart dust motes,communications is accomplished via RF transmission, andthe networking depends on short-range point-to-point links.The Wireless Integrated Network Sensors (WINS)Project [10]. It is developing low power MEMS-baseddevices that in addition to sensing and actuating can alsocommunicate. The essential difference is that WINS haschosen to concentrate on RF communications over shortdistances. The Ultralow Power Wireless Sensor Project [11]at MIT is another project that focuses on low power sensingdevices that also communicate. The primary thrust isextremely low power operation. The prototype system willtransmit over a range of data rates, from 1 bps to 1 Mbps,with transmission power levels that span from 10  _  W to 10mW. The RF communications subsystem is being developedfor the project by Analog Devices.ACKNOWLEDGEMENT We extend our sincere thanks to Mr. Abishek Vichare, for providing us with the guidance and facilities for the Seminar.We express our sincere gratitude to Mrs. Nilakshi Joshi lecturers, for their cooperation and guidancefor preparing and presenting this seminar.We also extend our sincere thanks to all other faculty members of Computer Department and our friendsfor their support and encouragement.R  EFERENCES [1]Sotiris Nikoleteseas: Models and algorithms for Wireless Sensor Networks (Smart Dust). J. Weidermannet al. (Eds,): SOFSEM 2006, LNCS 3831, pp. 64-83,2006.[2]Michael Buettner, Ben Greenstein, Alanson Sample,Joshua R. Smith, David Wetherall: Revisiting SmartDust with RFID Sensor Networks.[3]Joseph M. Kahn, Randy Howard Katz, and Kristofer S.J. Pister: Emerging Challenges: Mobile Networking for “Smart Dust”.   June 2000.[4]V.S. Hsu, J.M. Kahn, and K.S.J. Pister: WirelessCommunications for Smart Dust. January 30, 1998.[5]Alice M. Agogino, Jessica Granderson, Shijun Qiu:Sensor Validation And Fusion With Distributed ‘SmartDust’ Motes For Monitoring And Enabling EfficientEnergy Use.[6]J. M. Kahn, R. H. Katz (ACM Fellow), K. S. J. Pister: Next Century Challenges: Mobile Networking for Smart Dust”. ACM 1999.[7]Doug Steel: Smart Dust (UHC ISRC TechnologyBriefing). March 2005.[8]Thomas Frey(2011). Tapping into the Secret LanguagePlants[Online].Available:http://www.futuristspeaker.com/2011/10/tapping-into-the-secret-language-of-plants/[9]Kris Pister(2010). Autonomous sensing andcommunication in a cubic millimeter. Available:http://robotics.eecs.berkeley.edu/~pister/SmartDust/[10]Thomas Hoffman(2003). Mighty motes for medicine,manufacturing, the military and more. Available:http://www.computerworld.com/s/article/79572/Smart_ Dust?taxonomyId=158&pageNumber=1[11]J. R. Link and M. J. Sailor(2003). Targeted Smart dustAvailable:http://sailorgroup.ucsd.edu/research/smartdust.html

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