UI ECE 5995 - Introduction to Wireless Sensor Networks

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Introduction to Wireless Sensor NetworksOrganizationalSlide 3Review QuestionsWireless TermsSlide 6BER and Effective Channel CapacityRadio Propagation MechanismsRadio PropagationSlide 10Slide 11Fresnel Zone and LOSExampleLoss ModelsIndoor PropagationSlide 16Received Signal Strength Indicator (RSSI)RSSISlide 19Slide 20Slide 211The University of Iowa. Copyright© 2005A. KrugerIntroduction to Wireless Sensor Networks Wireless Terms, FAQ & Glossary27 January 20052The University of Iowa. Copyright© 2005A. KrugerOrganizationalMonday 4:30-5:20 Room 4511 SCThursday 12:30-1:20 Room 3220 SCPlease note that the room numbers are different for Mondays and Thursdays.Monday 5:20-6:20 Room 1126 SCThursday 1:30-2:30 Room 1126 SCOther By appointment Room 523C SHL Class Websitewww.engineering.uiowa.edu/~ece195/2005/Class TimeOffice Hours3The University of Iowa. Copyright© 2005A. KrugerOrganizationalNo Class on Monday January 314The University of Iowa. Copyright© 2005A. KrugerReview Questions•Name and explain the differences and similarities between the concept of a WSN and traditional telemetry•Explain what the Argos system is•Explain what the acronym SCADA stands for•True or false – wireless fleet management is an example of WSNs•Explain what the term “ISM” means5The University of Iowa. Copyright© 2005A. KrugerWireless Terms–Decibel (dB). Ratio of two powers–dBm. The reference power is in mW–SNR. Signal-to-Noise Ratio. Power, expressed in dB–Attenuation. Power loss (dB)–CDMA. Code Division Multiple Access–Simplex communication. One direction at a time–Duplex communication . Transmit and receive simultaneously–FCC. Federal Communications Commission–Antenna gain. How much more power the antenna received compared to reference (half wave). Expressed in dB–MAC. Medium/Media Access Control21log10dBin to of Ratio1021PPPP6The University of Iowa. Copyright© 2005A. KrugerWireless Terms–Circuit Switched. Dedicated (virtual) link between parties. Connection held even when no data transmitted.–Packet Data. Split information into packets and route independently through network. Use of spectrum only when data are transmitted.–Spread Spectrum. A wideband modulation which imparts noise-like characteristics to an RF signal. –Frequency-hopping and Direct Sequence Examples of Spread Spectrum–TDMA. Time-Division Multiple Access–FDMA. Frequency Division Multiplex Access7The University of Iowa. Copyright© 2005A. KrugerBER and Effective Channel Capacity•Analog vs. Digital links•BER – Bit Error Rate increases as SNR decreases–Error detection and correction mechanisms–Repeated transmission–Reduce channel capacity8The University of Iowa. Copyright© 2005A. KrugerRadio Propagation Mechanisms•Free Space•Reflection–Wave impinges on large (compared to wavelength) objects.•Diffraction–Waves bends around obstacle (no LOS)•Scattering–Objects much smaller that wavelength9The University of Iowa. Copyright© 2005A. KrugerRadio Propagation•Simple (but useful) models exist for–Free Space–Common geometries (flat, curved earth, wall)•Radio propagation in many real environments is complex–Multipath propagation–Shadowing–Attenuation•Environment changes => fluctuations in received power10The University of Iowa. Copyright© 2005A. KrugerRadio Propagation•Free space modelReceiverTransmitterhthrRPt , GtPr , Gr2RGGPPrttr11The University of Iowa. Copyright© 2005A. KrugerRadio Propagation•Two-beam/ray ground reflection model, large R•The “breakpoint” distance R at which the model changes from 1/R2 to 1/R4 is  4hthr/ReceiverTransmitterhthrPhase shiftRPt , GtPr , Gr422RhhGGPPrtrttr12The University of Iowa. Copyright© 2005A. KrugerFresnel Zone and LOS2121DDDDnFnConsistent Units60% rule-of-thumb•Diffraction13The University of Iowa. Copyright© 2005A. KrugerExample•A 1-km 2.4 GHz link has two antennas that are 2 m above the ground. Do we have LOS? 60% of this is 3.3 m, so we don’t have clearance. Answer is “NO”m 59.5500500500500125.012121DDDDnFn14The University of Iowa. Copyright© 2005A. KrugerLoss ModelsThis graph does not reflect temporal changes•Why need model?•Hybrid models (physics and empirical)15The University of Iowa. Copyright© 2005A. KrugerIndoor Propagation•Signal decays much faster•Coverage contained by walls (waveguides)•Very complicated dynamic (people move) attenuation and multipathPath Loss = Unit Loss + 10nlog(R) = kF+lW•Unit Loss = power loss @ 1 m (say 30 dB)•n = power delay index•R •k = # of floors, F = # of floors•l = # of walls, W = loss per wall16The University of Iowa. Copyright© 2005A. KrugerIndoor PropagationBuilding Freq (MHz)nSigma (dB)Retail Store 914 2.2 8.7Grocery Store 914 1.8 5.2Office 1500 3.0 7.0Textile Factory 1300 2.0 3.0Home 900 3.0 7.0Path Loss = Unit Loss + 10nlog(R) = kF+lW17The University of Iowa. Copyright© 2005A. KrugerReceived Signal Strength Indicator (RSSI)•Measure of received signal strength of radio•Indicator of link quality•Radio can be interrogated for RSSI•On-board Software use RSSI•Typically a number 23, 19, etc.•Consult manufacturer for mapping to power level dBm18The University of Iowa. Copyright© 2005A. KrugerRSSIOS determines RSSI is too small for reliable link19The University of Iowa. Copyright© 2005A. KrugerRSSIRadio with serial interfaceController+++ATRS<CR> ATCN<CR> 40nW01.0W10mW10dBm80118Small!20The University of Iowa. Copyright© 2005A. KrugerNo Class on Monday January 3121The University of Iowa. Copyright© 2005A. KrugerIntroduction to Wireless Sensor Networks Energy Considerations in Wireless Sensor Networks2 February


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UI ECE 5995 - Introduction to Wireless Sensor Networks

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