Information Technology Reference
In-Depth Information
The IEEE 802.11n standard was ratified in 2009. It added multiple-input multiple-output
(MIMO) antennas and expected maximum data rate up to 600 Mbps using four spatial
streams, each with a 40-MHz width. In addition to DSSS, it uses orthogonal frequency-di-
vision multiplexing (OFDM) as a digital carrier modulation method. IEEE 802.11n uses
both the 2.4-GHz and 5-GHz bands.
ISM and UNII Frequencies
ISM frequencies are set aside by ITU-R radio regulations 5.138 and 5.150. In the United
States, the Federal Communications Commission (15.247) specifies the ISM bands for un-
licensed use. ISM bands are specified in the following ranges:
900 MHz to 928 MHz
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2.4 GHz to 2.5 GHz
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5.75 GHz to 5.875 GHz
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Of these, channels located in the 2.4-GHz range are used for 802.11b and 802.11g. As
shown in Figure 5-1, 11 overlapping channels are available for use. Each channel is 22
MHz wide. It is common to use channels 1, 6, and 11 in the same areas because these
three channels do not overlap.
Frequency
2.402 GHz
2.483 GHz
2.441 GHz
6
11
1
2
7
3
8
4
9
5
10
ISM Channels
Figure 5-1
ISM 2.4 Channels
The UNII radio bands were specified for use with 802.11a wireless. UNII operates over
three ranges:
UNII 1:
5.15 GHz to 5.25 GHz and 5.25 GHz to 5.35 GHz.
■
UNII 2:
5.47 GHz to 5.725 GHz. This range is used by High Performance Radio LAN
(HiperLAN) in Europe.
■
UNII 3:
5.725 GHz to 5.875 GHz. This range overlaps with ISM.
■
UNII provides 12 nonoverlapping channels for 802.11a.
