23-Wireless - Wireless - Yahel Ben-David - EE 122: Intro to...

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Wireless - Yahel Ben-David - EE 122: Intro to Communication Networks Materials with thanks to Scott Shenker, Jennifer Rexford, Ion Stoica, Vern Paxson and other colleagues at Princeton and UC Berkeley
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2
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3 Metrics for evaluation / comparison of wireless technologies Bitrate or Bandwidth Range - PAN, LAN, MAN, WAN Two-way / One-way Multi-Access / Point-to-Point Digital / Analog Applications and industries Frequency – Affects most physical properties: Distance (free-space loss) Penetration, Reflection, Absorption Energy proportionality Policy: Licensed / Deregulated Line of Sight (Fresnel zone) Size of antenna h Determined by wavelength – )
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5 Modern art?
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6 Modern art? Old mess!
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7 The Wireless Spectrum
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Wireless Communication Standards • Cellular ( 800/900/ 1700 /1800/1900Mhz ): – 2G: GSM / CDMA / GPRS /EDGE – 3G: CDMA2000/UMTS/HSDPA/EVDO – 4G: LTE, WiMax • IEEE 802.11 (aka WiFi): – b: 2.4Ghz band, 11Mbps (~ 4.5 Mbps operating rate ) – g: 2.4Ghz , 54-108Mbps (~ 19 Mbps operating rate ) – a: 5.0Ghz band, 54-108Mbps (~ 25 Mbps operating rate ) – n: 2.4/5Ghz , 150-600Mbps (4x4 mimo). • IEEE 802.15 – lower power wireless: – 802.15.1: 2.4Ghz , 2.1 Mbps (Bluetooth) – 802.15.4: 2.4Ghz , 250 Kbps (Sensor Networks) 8
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Wireless Link Characteristics 9 (Figure Courtesy of Kurose and Ross)
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Antennas / Aerials • An electrical device which converts electric currents into radio waves, and vice versa. 11 h Q: What does “higher-gain antenna” mean? h A: Antennas are passive devices – more gain means focused and more directional. h Directionality means more energy gets to where it needs to go and less interference everywhere. h What are omni-directional antennas? 2-3dB 8-12dB 15-18dB 28-34dB
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What has changed? 12
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How many radios/antennas ? • WiFi 802.11n (maybe MiMo?) • 2G - GSM • 3G – HSDPA+ • 4G – LTE • Bluetooth (4.0) • NFC • GPS Receiver • FM-Radio receiver (antenna is the headphones cable) 13
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What Makes Wireless Different? • Broadcast and multi-access medium… • Signals sent by sender don t always end up at receiver intact – Complicated physics involved, which we won t discuss – But what can go wrong? 14
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Path Loss / Path Attenuation • Free Space Path Loss: d = distance λ = wave length f = frequency c = speed of light • Reflection, Diffraction, Absorption • Terrain contours (Urban, Rural, Vegetation). • Humidity 15
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Multipath Effects • Signals bounce off surface and interfere with one another • Self-interference 16 S R Ceiling Floor
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Ideal Radios (courtesy of Gilman Tolle and Jonathan Hui, ArchRock)
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Real Radios (courtesy of Gilman Tolle and Jonathan Hui, ArchRock)
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19 The Amoeboed cell (courtesy of David Culler, UCB) Signal Noise Distance
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Interference from Other Sources • External Interference – Microwave is turned on and blocks your signal – Would that affect the sender or the receiver? • Internal Interference
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23-Wireless - Wireless - Yahel Ben-David - EE 122: Intro to...

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