Wireless data networks Why is wireless different? Martin Heusse X L A TEX E
General info • This is TLEN 5520, or ECEN 5032 • ECCS 1B12, WF, 3:00pm to 4:15pm • Please register to the class mailing list! ✓ send a mail to listproc@lists.Colorado.edu ✓ body: subscribe tlen5520-s09 <Your Full Name> • Web site: http://morse.colorado.edu/~tlen5520/ X L A TEX E
History — what are we talking about? f λ Infrared IR WLAN 300GHz 1mm EHF IRIDIUM 30GHz 1cm sat. to sat. Satellite WiMAX SHF communications Satellite 3GHz 10cm WLAN (experimental) Cordless 4G / LTE 3G DECT phone UHF AlohaNet Cell phone “Mobile” Coax DVB-T 300MHz 1m Color TV phone DAB FM radio Twisted pair VHF B&W 30MHz CB TV radio Audio CD (82) Shortwave HF Walkie radio Arpanet IBM PC (81) Talky 3MHz 1930 1940 1950 1960 1970 1980 1990 2000 2010 Digital era Intro. 3
Wireless data networks Application HTTP DNS FTP SSH X11 … Presentation MIME XDR HTTP SSL Session Session Cookies Transport TCP UDP SCTP Network IP LLC (adresses, security, Ethernet 802.11 MAC PPP Link SLIP channel access, ARQ) (HDLC framing) 11a 11b 100baseTX Phy. Layer Converg. Protocol 10baseT … … … Blue- Physical RS-232 6Mb/s 9Mb/s tooth Phy. medium dependent Intro. 4
The wireless channel • Free space propagation ✓ Typical attenuation: λ = 0 . 1 m , d = 1 m → -30dB (1/1000!) ✓ Attenuation # 1 d n with 2 ≤ n At best, the radiated power is projected on (a part of) a sphere whose surface grows in the order of 4 π d 2 . 1 ✓ May be worse! • The atmosphere is (mostly) transparent ✓ 10 − 2 dB/km attenuation for radio waves in the air ✓ Twisted pair: > 1dB/100m ✓ Attenuation is exponential! (and so it makes sense to measure attenuation in dB) ✓ Strong attenuation in concrete, metal; varies with λ → Good for long distance communications (if only the world was flat…) → Strong attenuation, even over short distances • No confinement ✓ … Intro. 5
Radio waves • Propagation ✓ Ground wave ◮ f < 2 MHz; (…) ◮ AM radio ✓ Sky wave (Reflection on the ionosphere) ★ Line of sight • Diffraction, refraction, absorption, scattering • Multi-paths, fading Intro. 6
Radio waves (cont.) Intro. 7
Digital transmission Channel capacity • Channel characteristics ✓ Bandwidth ✓ Signal to Noise power ratio (Signal power imited by regulation, amplifier performance, distance, antenna…) • Nyquist bandwidth ✓ Channel width B (Hz) → 2B (bauds) max trans. rate ✓ (bauds ⇔ symbols/s) ✓ POTS modems had a capacity of 56kb/s on a channel several kHz wide… ← multilevel signaling • Shannon capacity (How many levels can I use?) ✓ The signal is subject to noise. If levels are too close from each other, there is a risk of error! C = B log 2 (1 + SNR ) where SNR is the ratio of power in the signal to the power in the noise. Intro. 8
Physical layer for wireless • Antennas ✓ Why does an antenna radiate power? K2-3/ L39,4 K02- L39, EHIJ ✓ Radiation pattern I08N L39, O21, L39, P?== Example: cellular net. antennas point toward the ground ✓ Polarization Intro. 9
Physical layer for wireless (cont.) • Not baseband transmission! ( → modulation) • Synchronisation ( → preamble) (Ex.: for ASM, to which level does a logical “1” correspond?) • Spread spectrum ✓ Can help to reduce impact of noise ✓ Does not work for e.g. white noise • Error detection, correction • Scrambling Intro. 10
Link layer for wireless • ARQ • Association information ✓ Which network am I connecting to? → Beacons / discovery • Multiplexing / channel sharing ✓ (Sub) Channel choice ✓ Channel access ◮ Centralized ◮ Localized ( � distributed) • Addressing (may include a relay address…) • Fragmentation/reassembly • Power management ✓ Idle listening is also power consuming Intro. 11
Multiplexing ☛ ✟ Multiplexing: several entities or flows share the same transmission channel ✡ ✠ • In time ✓ CSMA ✓ TDMA (GSM: 8 uni-directional connection/freq. band) • Frequency FDMA: GSM, DECT, 802.11 • Code ✓ CDMA (3G) ✓ Frequency hopping (Bluetooth) • Spatial Intro. 12
An example: DECT Digital Enhanced Cordless Telecommunications • 32kb/s; 1920 MHz–1930 MHz (US); (G)FSK • FDMA + TDMA • The base station transmits permanently in one slot ( → discovery) • Encryption • Several data profiles (e.g. HDLC framing etc.) Intro. 13
Applications of wireless networks • Long distance links • Cellular phones ★ Wireless LAN (802.11) ★ Internet access (802.11, 802.16—WiMAX) ★ Wireless personal area network (802.15.1—Bluetooth) ✓ High rate, short range, low power consumption ★ Sensor networks (802.15.4—Zigbee) ✓ Low power consumption * Ad hoc networks (Mobile multihop network) ✓ Routing ✓ Performance issues * Mesh networks Intro. 14
Sonics ENCY (VLF) e Range http://www.fcc.gov/oet/spectrum/table/fcctable.pdf http://www.ntia.doc.gov/osmhome/allochrt.pdf 3 x 10 5 m 1 kHz 3 kHz Radio spectrum—FCC Freq. alloc. 30,000 m 10 kHz AM Broadcast Ultra-sonics LF 100 kHz 3,000 m ACTIVITY CODE MF HF THE RADIO SPECTRUM 1 MHz 300 m NON-GOVERNMENT EXCLUSIVE GOVERNMENT EXCLUSIVE FM Broadcast MAGNIFIED ABOVE 30 m 10 MHz VHF UHF 100 MHz 3 m P L 1 GHz 30 cm GOVERNMENT/NON-GOVERNMENT SHARED S Microwaves C SHF X 10 GHz 3 cm EHF Radar Bands Radar 100 GHz 0.3 cm 300 GHz INFRARED Sub-Millimeter 0.03 cm 1 THz Infrared 3 x 10 5 Å 10 13 Hz Intro. 15
Radio spectrum—FCC Freq. alloc. (cont.) MOBILE FIXED SATELLITE (s-E) AIDS (Radiosonde) 1700 MET. SAT. FIXED Fixed 173.2 (s-E) FIXED Land Mobile 173.4 FIXED MOBILE 1710 174.0 FIXED MOBILE 1755 FIXED MOBILE 1850 FIXED MOBILE (TV CHANNELS 7-13) BROADCASTING 2000 MOBILE SATELLITE (E-S) 2020 FIXED MOBILE 2025 SPACE RES. EARTH EXPL. SPACE OP. MOB. FX. (E-S)(s-s) SAT. (E-S)(s-s) (E-S)(s-s) 2110 FIXED MOBILE 2155 S) FIXED 2160 FIXED MOBILE 2180 MOBILE SATELLITE (S-E) 2200 216.0 F i x e d M o b i l e R a d i o - SPACE F I X E D M O B I L E Amateur SPACE EARTH l o c a t i o n FIXED MOBILE RESEARCH OPERATION 220.0 (LOS) EXPLORATION (LOS) Radiolocation (s-E)(s-s) (s-E)(s-s) LAND MOBILE F I X E D SAT. (s-E)(s-s) 222.0 2290 AMATEUR Radiolocation FIXED MOBILE** 225.0 SPACE RES..(S-E) 2300 Amateur 2305 MOBILE Amateur RADIOLOCATION MOBILE** FIXED 2310 FIXED Mobile Fixed MOB FX R- LOC. Radiolocation B-SAT 2320 BCST-SATELLITE Mobile Radio- Fixed location 2345 235.0 Radiolocation Mobile FX R- LOC. B-SAT Fixed MOB ISM – 2450.0 ± 50 MHz 2360 MOBILE RADIOLOCATION Fixed 2385 MOBILE FIXED 2390 AMATEUR 2400 AMATEUR MOBILE SATELLITE 2417 Radiolocation Amateur 2450 MOBILE FIXED FIXED MOBILE Radiolocation 2483.5 RADIODETERMINATION SAT. (S-E) MOBILE SATELLITE (S-E) 2500 BCST - SAT. MOBILE** FX-SAT (S - E) FIXED 2655 Space res. E-Expl Sat Radio Ast MOB** B- SAT. FX FX-SAT 2690 RADIO ASTRON. SPACE RESEARCH EARTH EXPL SAT 2700 300 MHz AERONAUTICAL METEOROLOGICAL Radiolocation 3 GHz AIDS RADIONAVIGATION 2900 MARITIME Radiolocation RADIONAVIGATION 3000 300 Intro. 16
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