Wireless Communication FundamentalsPhysical Properties of WirelessWireless = WavesPublic Use BandsFree-space Path-lossMulti-path PropagationMulti-Path EffectOther Path-loss ExponentsDigital ModulationExamples of Digital ModulationMulti-transmitter InterferenceWireless Communication FundamentalsDavid [email protected] Properties of WirelessMakes wireless network different from wired networksShould be taken into account by all layersWireless = WavesElectromagnetic radiationSinusoidal wave with a frequency/wavelengthEmitted by sinusoidal current running through a wire (transmitting antenna)Induces current in receiving antennacf Public Use BandsC (speed of light) = 3x108 m/sName 900 Mhz 2.4 Ghz 5 GhzRange 902 - 928 2.4 - 2.48355.15 - 5.35Bandwidth26 Mhz 83.5 Mhz 200 MhzWavelength.33m / 13.1”.125m / 4.9”.06 m / 2.4”Free-space Path-loss Power of wireless transmission reduces with square of distance (due to surface area increase)Reduction also depends on wavelengthLong wave length (low frequency) has less lossShort wave length (high frequency) has more loss24DPLMulti-path PropagationElectromagnetic waves bounce off of conductive (metal) objectsReflected waves received along with direct waveMulti-Path EffectMulti-path components are delayed depending on path length (delay spread)Phase shift causes frequency dependent constructive / destructive interferenceAmplitudeTimeAmplitudeFrequencyOther Path-loss ExponentsPath-Loss Exponent Depends on environment: Free space 2 Urban area cellular 2.7 to 3.5 Shadowed urban cell 3 to 5 In building LOS 1.6 to 1.8 Obstructed in building 4 to 6 Obstructed in factories 2 to 3Digital ModulationModulation allows the wave to carry information by adjusting its properties in a time varying wayDigital modulation using discrete “steps” so that information can be recovered despite noise/interferenceExamples of Digital ModulationBPSKQPSKODFMMulti-transmitter InterferenceSimilar to multi-pathTwo transmitting stations will constructively/destructively interfere with each other at the receiverReceiver will “hear” the sum of the two signals, which usually means
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