Wireless Standards
The IEEE 802.11 WLAN standards define how radio frequencies (RFs) are used for wireless links. To avoid interference, different channels within an RF can be used.
RF Spectrum
The RF spectrum, shown in Figure 22-1, includes all types of radio communications, including the 2.4-GHz and 5-GHz frequencies used by wireless devices.
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Figure 22-1 RF Spectrum
Channels
A frequency range is typically called a band of frequencies. For example, a wireless LAN device with a 2.4-GHz antenna can actually use any frequency from 2.4000 to 2.4835 GHz. The 5-GHz band lies between 5.150 and 5.825 GHz.
The bands are further subdivided into frequency channels. Channels become particularly important when the wireless devices in a specific area become saturated. Each channel is known by a channel number and is assigned to a specific frequency. As long as the channels are defined by a national or international standards body, they can be used consistently in all locations. Figure 22-2 and Figure 22-3 show the channel layouts for the 2.4- and 5-GHz bands, respectively.
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Figure 22-2 2.4-GHz Channels
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Figure 22-3 5-GHz Channels
Notice in Figure 22-3 that the 5-GHz band consists of nonoverlapping channels. Each channel is allocated a frequency range that does not encroach on or overlap the frequencies allocated for any other channel. The same is not true of the 2.4-GHz band in Figure 22-2. The only way to avoid any overlap between adjacent channels is to configure access points (APs) to use only channels 1, 6, and 11.
802.11 Standards
Most of the standards specify that a wireless device must have one antenna to transmit and receive wireless signals on the specified radio frequency (2.4 GHz or 5 GHz). Some of the newer standards that transmit and receive at higher speeds require APs and wireless clients to have multiple antennas using the multiple input, multiple output (MIMO) technology. MIMO uses multiple antennas as both the transmitter and receiver to improve communication performance. Up to four antennas can be supported.
Various implementations of the IEEE 802.11 standard have been developed over the years. Table 22-1 highlights these standards.
Table 22-1 Summary of 802.11 Standards
IEEE WLAN Standard |
Radio Frequency |
Description |
802.11 |
2.4 GHz |
Speeds of up to 2 Mbps |
802.11a |
5 GHz |
Speeds of up to 54 Mbps Small coverage area Less effective at penetrating building structures Not interoperable with 802.11b and 802.11g |
802.11b |
2.4 GHz |
Speeds of up to 11 Mbps Longer range than 802.11a Better able to penetrate building structures |
802.11g |
2.4 GHz |
Speeds of up to 54 Mbps Backward compatible with 802.11b with reduced bandwidth capacity |
802.11n |
2.4 GHz 5 GHz |
Data rates ranging from 150 Mbps to 600 Mbps with a distance range of up to 70 m (230 feet) APs and wireless clients require multiple antennas using MIMO technology Backward compatible with 802.11a/b/g devices with limiting data rates |
802.11ac |
5 GHz |
Provides data rates ranging from 450 Mbps to 1.3 Gbps (1300 Mbps) using MIMO technology Up to eight antennas can be supported Backward compatible with 802.11a/n devices with limiting data rates |
802.11ax |
2.4 GHz 5 GHz |
Released in 2019 (latest standard) Also known as High-Efficiency Wireless (HEW) Higher data rates and increased capacity Handles many connected devices Improved power efficiency 1 GHz and 7 GHz capable when those frequencies become available |