The channel frequencies and numbering defi ned in 802.11a start at 5 GHz and each
channel is spaced 5 GHz apart (see Table 21.8).
Three transmit RF power levels are specifi ed: 40 mW, 200 mW, and 800 mW
(see Table 21.9). The upper band defi nes RF transmit
power levels suitable for
bridging applications while the lower band specifi es a
transmit power suitable for
short-range indoor home and small offi ce environments.
Example 21.2
Consider an FH/MFSK
WLAN system, in which a pseudo-random noise (PN)
generator is defi ned by a 20-stage linear feedback shift
register with a maximal
length sequence. Each state of the register dictates a
new center frequency within
the hopping band. The minimum step-size between center frequencies (hop to
hop) is 200 Hz. The register clock rate is 2 kHz. 8-ary
FSK modulation is used
and the data rate is 1.2 kbps. (a) What is the hopping bandwidth? (b) What is
the chip-rate? (c) How many chips are there in each data symbol? (d) What is the
processing gain?
Table 21.8 Channel frequencies and channel numbers in the United States.
Regulatory domain
Frequency band
Channel number
Center frequencies
USA
Lower Band
5.15–5.25 GHz
36
40
44
48
5.180 GHz
5.220 GHz
5.220 GHz
5.240 GHz
USA
Middle Band
5.25–5.35 GHz
52
56
60
64
5.26 GHz
5.280 GHz
5.300 GHz
5.320 GHz
USA
Upper Band
149
153
157
161
5.745 GHz
5.765 GHz
5.785 GHz
5.805 GHz
21.5 IEEE 802.11 WLAN
733
Table 21.9 Transmit power levels for North American operation.
