Wireless networks
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Wireless Networks. 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

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Wireless Networks

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Wireless networks

Wireless Networks


Wireless technologies

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


Wireless networks

WiFi

  • Base Standard 802.11

  • Utilises unlicensed spectrum

    • 2.4 GHz ISM range

    • 5 GHz UNII range

  • Access technology


802 11 1997

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)


Dsss channel frequencies

DSSS Channel Frequencies


Dsss channel

≥30 dB

≥50 dB

Centre

Frequency

-22MHz

-11MHz

+11MHz

+22MHz

DSSS Channel


Dsss channel overlap

4

8

9

6

7

10

1

2

5

11

3

12

13

DSSS Channel Overlap


802 11b

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


802 11a 1999

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


Wireless networks

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


802 11g

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


Beyond 802 11g

Beyond 802.11g

  • 802.11e - QoS extensions

  • 802.11f - hand-off for roaming

  • 802.11i – improved security

  • 802.11s – Mesh Networks

  • 802.11n - MIMO


Common issues in wifi

Common Issues in WiFi

  • Interference; other hotspots, other equipment in same band, microwave ovens.

  • Near/Far

  • Hidden Node

  • Multipath


Wimax

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.


Wireless mesh

Wireless Mesh


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