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Wireless Networks

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Wireless Networks

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  1. Wireless Networks

  2. Wireless Technologies • Bluetooth, ZigBee & Wireless USB • short range communication between devices typically controlled by a single person. • WiFi, DECT, HIPERLAN • WLAN. WiFi is the most widely implemented in this space. • UMTS over W-CDMA, UMTS-TDD, EVDO HSPA, WiMAX • Wide Area

  3. WiFi • Base Standard 802.11 • Utilises unlicensed spectrum • 2.4 GHz ISM range • 5 GHz UNII range • Access technology

  4. 802.11 (1997) • 1 or 2 Mbps • 2.4GHz Industrial, Scientific & Medical (ISM) band; or IR • Frequency Hopping Spread Spectrum (FHSS) or Direct-Sequence Spread Spectrum (DSSS) • CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance)

  5. DSSS Channel Frequencies

  6. ≥30 dB ≥50 dB Centre Frequency -22MHz -11MHz +11MHz +22MHz DSSS Channel

  7. 4 8 9 6 7 10 1 2 5 11 3 12 13 DSSS Channel Overlap

  8. 802.11b • Operates in the 2.4GHz ISM band • Utilises HR-DSSS to provide speeds up to 11Mbps • Rates are 1M, 2M, 5.5 M 11M

  9. UNII-1 (Low) UNII-2 (Mid) UNII-2 (High) 5.150GHz 5.825GHz 5.725GHz 5.350GHz 5.250GHz 802.11a (1999) • Operates in 5GHz UNII bands • Consumer equipment generally uses middle & low bands • 4 channels/band at 20m MHz spacing resulting in 8 non-overlapping channels • Utilises OFDM to produce speeds up to 54Mbps

  10. OFDM • Orthogonal Frequency Division Multiplexing • Communications channels is made up of many sub-carriers in parallel • Convolution coding used for error checking. • Utilises Quadrature Amplitude Modulation (QAM )to achieve data rates of 24Mbps-54Mbps

  11. 802.11g • Operates in the 2.4 GHz ISM band • Utilises OFDM and DSSS to provide speeds up to 54Mbps • Thus 802.11g equipment can act as 802.11b equipment • Presence of 802.11b equipment will reduce the throughput of an 802.11g WLAN

  12. Beyond 802.11g • 802.11e - QoS extensions • 802.11f - hand-off for roaming • 802.11i – improved security • 802.11s – Mesh Networks • 802.11n - MIMO

  13. Common Issues in WiFi • Interference; other hotspots, other equipment in same band, microwave ovens. • Near/Far • Hidden Node • Multipath

  14. WiMAX • Worldwide Interoperability for Microwave Access • Fixed WiMAX 802.16-2004 ('802.16d') • Mobile WiMAX 802.16e-2005 • OFMD / SOFDMA • As with DSL & WiFi more distance / interference = less throughput.

  15. Wireless Mesh