Technologies radio Wifi

Détails théoriques

Pour les détails théoriques on lira les documents suivants :

• Wireless Technologies
• Cisco Aironet Antennas and Accessories
• Capacity Coverage & Deployment Considerations for IEEE 802.11g
• Multipath and Diversity

802.11b does not use FHSS (Frequency Hopping Spread Spectrum) !

Multipath Distortion
- definition : High signal Strength and low quality
- DSSS is more sensible than OFDM

802.11b/g -2.4GHz

Maximum Power level 802.11b
- in Europe : 20 dBm (100 mW)
- in USA : 24 dBm (250 mW)

Maximum 3 non-overlapping channels (33Mbps in 802.11b and 162Mbps in 802.11g)

Bandwidth of each channels
- 802.11g : 22MHz

Total bandwidth of 2.4Ghz = 83MHz (2.400 to 2.483)

QPSK Quadrature Phase Shift Keying

CCK Complementary Code Keying

BPSK Biphase Shift Keying

DSSS Direct Sequence Spread Spectrum

QAM Quadrature Amplitude modulation

802.11a - 5GHz

Aironet client maximum outpout : 20mW (UNII-1 and UNII-2)

UNII bands
1. UNII-1 5.150GHz to 5.250GHz

• indoor only
• 40mW max transmit power
• 4 non-overlapping channels
• integrated antenna 6dBi in Cisco AP

2. UNII-2 5.25G0Hz to 5.350GHz

• indoor/outdoor
• 200mW max transmit power
• 4 non-overlapping channels

3. UNII-3 5.725GHz to 5.825GHz

• outdoor only
• 1W with 6dBi antenna (multipoint)
• 1W with 23dBi antenna (point-to-point)
• 4 non-overlapping channels

Each channel of 20MHz is divided in 52 subchannels (each 300KHz of bandwidth). 48 of 52 are used for data transmission

8 non-overlapping channels (4 UNII-1 + 4 UNII-2)

802.11a Orthogonal Frequency Division Multiplexing (OFDM)