The original WLAN standard was released in 1997 by the IEEE as 802.11, which is now referred to as 802.11 Legacy. The 802.11 standard supported two data transfer speeds—1 or 2 megabits per second (Mbps)—on either infrared (IR) or radio frequency (RF) signals on the 2.4 GHz industrial, scientific, and medical (ISM) bands. This standard was later absorbed into the 802.11b standard.

The IEEE 802.11b WLAN standard, also known as 802.11 High Rate or Wi-Fi, extends the 802.11 standard by improving throughput and increasing data transfer rates to 5.5 Mbps and 11 Mbps. The 802.11b standard operates in the 2.4 to 2.483 GHz unlicensed RF ISM band for either infrastructure (devices communicate indirectly through an access point) or ad hoc (devices communicate directly) mode.

IEEE 802.11b defines the use of a number of technologies and methods, many of which were absorbed into later standards. These technologies include:

• DSSS—Direct sequence spread spectrum (DSSS) transmission is a modulation technique that spreads the transmitted signal over an entire bandwidth to fit the transmitted signal on the carrier.
• Unlicensed CCK—Complementary code keying (CCK) applies mathematical formulas to DSSS codes so they can represent more data per cycle and achieve the higher data rates defined in the 802.11b standard. CCK works only with DSSS.
• QAM—Quadrature amplitude modulation (QAM) combines two amplitude modulation (AM) signals onto a single channel, which effectively doubles the available bandwidth of the channel. The term quadrature refers to the 90-degree (one-quarter-of-a-cycle) phase shifts used to differentiate two carriers.
• DRS—Dynamic rate shifting (DRS) adjusts the transmission rate lower or higher depending on the signal strength or interference. In an electrically noisy environment, or as devices move into or out of range, an 802.11b transmitter adjusts the transmission speed down from 11 Mbps to 5.5 Mbps, 2 Mbps, or 1 Mbps.

An 802.11b infrastructure network includes at least one wireless station and one access point connected to a distribution system. The distribution system is any access device, such as a wired network interface, an Internet bridge or router, or the like.

The IEEE 802.11a WLAN standards actually preceded the other standards adapted from the 802.11 Legacy standard; however, the 802.11b standard was more widely adopted by manufacturers. The features that set 802.11a apart from 802.11b and 802.11 Legacy are:

• UNII—802.11a operates in the 5 GHz Unlicensed National Information Infrastructure (UNII)band, which eliminates most of the interference problems common to 2.4 GHz systems. Many microwave ovens, cordless telephones, Bluetooth devices, and other consumer electronic products also operate in the 2.4 GHz band.
• OFDM—Orthogonal frequency division multiplexing (OFDM) facilitates up to 54 Mbps of bandwidth, divides a 20 MHz RF channel into 48 narrowband subchannels, and then splits the data signal into 48 separate overlapped carriers—one on each subchannel. This arrangement, shown in FIGURE 10-1, enables OFDM to effectively deal with crosstalk and multipath propagation, which are transmission problems common to Frequency Division Multiplexing (FDM) and other 802.11 standards.
• Multipath propagation—OFDM supports multipath propagation, which is applied when the RF signal cannot take a clear and direct path between a wireless node and the access point. RF signals may not be able to take direct paths due to objects such as walls, chairs, and desks, which can deflect or diffuse the signal. When this happens, only a portion of a signal arrives at the receiver, with the remainder of the signal deflected to an indirect route. This may cause a delay between the two (or more) parts of the signal of as much as 50 to 300 nanoseconds, depending on the environment. When multipath propagation occurs, the delayed signal segments may overlap another discrete signal.
• IEEE 802.11a modulation—802.11a modulates digital data based on the data transfer rate in use:
  • Binary phase shift keying (BPSK)—This form of modulation allows higher data rates to be carried within a given bandwidth.
  • QAM—At 54 Mbps, the 802.11a applies QAM to vary the signal on different amplitude levels and phase shifting.

The IEEE 802.11g standard supports high-speed (up to 54 Mbps) wireless networking over relatively short distances. The 802.11g standard operates on the same RF bands as 802.11b, but incorporates OFDM to achieve the higher data transfer rates. When the communication distance increases or the signal becomes compromised, 802.11g can scale the transmission speeds back down to the 11 Mbps of the 802.11b standard or even lower. The 802.11b and 802.11g devices are compatible within a single WLAN because 802.11g hardware is fully backward compatible with 802.11b hardware.

The IEEE 802.11n standard increases the throughput of the 802.11g standard to 450 Mbps by using multiple wireless signals and antennas. IEEE 802.11n applies multiple-input and multiple-output (MIMO), an antenna technology that uses multiple antennas (to receive and transmit) at both ends of a transmission. Originally a broadcast radio technology, MIMO was integrated into WLAN communications to improve data throughput and range without changing the nominal bandwidth or transmission power of WLAN devices.

The IEEE 802.11ac standard provides another increase in speed, with up to 1300 Mbps throughput. It extends the design concepts of 802.11n with an RF bandwidth up to 160 MHz and more MIMO spatial streams, and adds high-density modulation in the form of 256 QAM. The 802.11ac standard provides a 33 percent improvement in data rate. The 802.11ac standard operates in the 5 GHz band, which is less crowded than the 2.4 GHz band.

The IEEE 802.11ax standard, also marketed as Wi-Fi 6, is the latest standard in the 802.11 family, providing up to 10,000 Mbps throughput. It extends the design concepts of 802.11n and 802.11ac with an RF bandwidth up to 160 MHz and more MIMO and MU-MIMO spatial streams (more on these later), and adds high-density modulation in the form of 1024 QAM. All Wi-Fi 6 802.11ax devices operate in the 2.4 GHz and 5 GHz bands, and Wi-Fi 6E devices also operate in the 6 GHz band.