Wireless data networks Why is wireless different?

Transcription

1 Wireless data networks Why is wireless different? Martin Heusse X L ATEX E

2 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: X L ATEX E

3 History what are we talking about? f λ Infrared IR WLAN 300GHz 1mm Twisted pair Coax EHF 30GHz SHF 3GHz UHF 300MHz VHF 30MHz HF 3MHz 1cm 10cm 1m Shortwave radio Walkie Talky Satellite (experimental) FM radio B&W TV CB radio AlohaNet Color TV Satellite communications Arpanet Cordless phone Mobile phone DECT Audio CD (82) IBM PC (81) IRIDIUM sat. to sat. WLAN Cell phone WiMAX G 4G / LTE DVB-T DAB Digital era Intro. 3

4 Wireless data networks Application HTTP DNS FTP SSH X11 Presentation MIME XDR Session HTTP Cookies SSL Session Transport TCP UDP SCTP Network Link Physical SLIP PPP (HDLC framing) Bluetooth RS-232 IP Ethernet baseT 100baseTX 11a 6Mb/s 9Mb/s 11b LLC MAC (adresses, security, channel access, ARQ) Phy. Layer Converg. Protocol Phy. medium dependent Intro. 4

5 The wireless channel Free space propagation Typical attenuation: λ = 0.1m, d = 1m -30dB (1/1000!) Attenuation # 1 d with 2 n n At best, the radiated power is projected on (a part of) a sphere 1 whose surface grows in the order of. 4πd 2 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

6 Propagation Ground wave f < 2MHz; ( ) AM radio Radio waves Sky wave (Reflection on the ionosphere) Line of sight Diffraction, refraction, absorption, scattering Multi-paths, fading Intro. 6

7 Radio waves (cont.) Intro. 7

8 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

9 Physical layer for wireless Antennas Why does an antenna radiate power? K2-3/ L39,4 K02- L39, Radiation pattern I08N L39, EHIJ O21, L39, P?== Example: cellular net. antennas point toward the ground Polarization Intro. 9

10 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

11 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

12 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, Code CDMA (3G) Frequency hopping (Bluetooth) Spatial Intro. 12

13 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

14 Applications of wireless networks Long distance links Cellular phones Wireless LAN (802.11) Internet access (802.11, WiMAX) Wireless personal area network ( Bluetooth) High rate, short range, low power consumption Sensor networks ( Zigbee) Low power consumption * Ad hoc networks (Mobile multihop network) Routing Performance issues * Mesh networks Intro. 14

15 AMATEUR AMATEUR SATELLIT FX SAT(E-S) FX SAT(E-S) EARTH EXPLORATION SPACE RESEARCH (E FI XED (E-S) Radio spectrum FCC Freq. alloc. SPACE RESEARCH (Passive) EARTH EXPLORATION (Passive) INTER- SAT EARTH EXPL-SAT (Pass SPACE RES. EARTH-ES INTER- S EARTH EXPLORATION - SAT SAT. (Passive) SPACE RES. INTER SPACE RES. EARTH EXPLORATION SAT. (Passive) SPACE RESEARCH (Passive) INTER- SATELLIT RADIO- LOCATION ACTIVITY CODE INTE SA SPACE RES.. EARTH EXPLORATION SAT. (Passive) INTER- SAT SPACE RES. EARTH- RADIO- LOC. INTER- SATELLIT ** INTER SATELL ** SPACE RESEARCH EARTH EXPLORATION GOVERNMENT EXCLUSIVE INTER SATELL RADIO NAVIGATION RADIO- NAVIGATION (E-S) (E-S) AMATEUR AMATEUR SATELLIT RADIOLOC. Amateur RADIOLOC. Amateur Amateur Sat RADIOLOC. AMATEUR AMATEUR SA RADIO- Amateur LOCATION Amateur Satellite (E-S) GOVERNMENT/ NON-GOVERNMENT SHARED SATELLIT (S-E) (S-E) BROAD- CASTING SATELLIT BROAD- CASTING EARTH EXPLORATION (Passive) SPACE RESEARCH (Passive) RADIO ASTRONOMY SATELLIT (E-S) RADIO- LOCATION ISM ±.250 GHz GHz NON-GOVERNMENT IS DESIGNATED FOR EXCLUSIVE UNLICENSED DEVICES 3 x 10 6 m 3 x 10 5 m 30,000 m 3,000 m 300 m 30 m 3 m 30 cm 3 cm 0.3 cm 0.03 cm 3 x 10 5 Å 3 x 10 4 Å FREQUENCY (VLF) LF MF HF VHF UHF SHF EHF INFRARED VISIBL Audible Range AM Broadcast FM Broadcast P L S C X Radar Bands Radar Sub-Millimeter Visible Sonics Ultra-sonics Microwaves Infrared 100 Hz 1 khz 10 khz 100 khz 1 MHz 10 MHz 100 MHz 1 GHz 10 GHz 100 GHz 1 THz Hz Hz THE RADIO SPECTRUM 3 khz MAGNIFIED ABOVE 300 GHz Intro. 15

16 Radio spectrum FCC Freq. alloc. (cont.) ILE ED Land Mobile BROADCASTING (TV CHANNELS 7-13) Radiolocation Radiolocation LAND AMATEUR 300 MHz AIDS (Radiosonde) Amateur F I X E D Fixed Mobile Radiolocation F I X E D (s-e) Fixed MET. SAT. (s-e) (E-S) SPACE RES. EARTH EXPL. SPACE OP. (E-S)(s-s) SAT. (E-S)(s-s) (E-S)(s-s) MOB. FX. S) (S-E) EARTH EXPLORATION SAT. (s-e)(s-s) SPACE OPERATION (s-e)(s-s) SPACE RESEARCH (s-e)(s-s) (LOS) (LOS) SPACE RES..(S-E) ** Amateur Amateur RADIOLOCATION ** Radiolocation Mobile Fixed MOB FX R- LOC. B-SAT Mobile Radiolocation Fixed BCST- Radiolocation Mobile Fixed MOB FX R- LOC. B-SAT RADIOLOCATION Fixed AMATEUR AMATEUR Amateur Radiolocation Radiolocation RADIODETERMINATION SAT. (S-E) (S-E) BCST - SAT. ** FX-SAT (S - E) E-Expl Sat Radio Ast Space res. MOB** B- SAT. FX FX-SAT RESEARCH EXPL SAT RADIO ASTRON. SPACE EARTH Radiolocation METEOROLOGICAL AIDS AERONAUTICAL RADIONAVIGATION Radiolocation MARITIME RADIONAVIGATION ISM ± 50 MHz 3 GHz Intro. 16