802.11g, referred to in full as IEEE 802.11g, is an amendment to the IEEE 802.11 standard created by the Institute of Electrical and Electronics Engineers LAN/MAN Standards Committee (IEEE 802) which governs wireless networking transmission methods.
It was ratified in 2003. Along with 802.11b, it is the most widely used amendment in the 802.11 family. It uses the same 2.4 GHz band as 802.11b, but has a data rate of up to 54 Mbps for a throughput of about 19 Mbps. This is because of its heritage to 802.11a. It is identical to the 802.11a core, but it features some additional legacy overhead for backward compatibility.
The hardware of 802.11g is completely backwards compatible with that of 802.11b, making the two amendments interoperable. However, the speed of the overall 802.11g network will be significantly reduced if there is a legacy 802.11b participant present. Since it operates in the 2.4 GHz range, it is prone to interference by devices in the same band, such as Bluetooth devices, microwave ovens, baby monitors, and cordless telephones.
Like in 802.11a, a 52-subcarrier coded orthogonal frequency-division multiplexing (COFDM) is used as the 802.11g modulation scheme. COFDM is able to reduce multipath effects in reception and increase spectral efficiency. The COFDM has a symbol duration of 4 microseconds and a guard interval (also known as a "cyclic prefix") of 0.8 microseconds.
Of the 52 COFDM sub-carriers, 48 are used for data transmission and the remaining 4 are pilot sub-carriers with a carrier separation of 0.3125 MHz. The sub-carriers may employ the following digital modulation schemes: binary phase-shift keying (BPSK) for 6 and 9 Mbps, quadrature phase-shift keying (QPSK) for 12 and 18 Mbps, 16-quadrature amplitude modulation (16-QAM) for 24 and 36 Mbps, or 64-QAM for 48 and 54 Mbps.
Orthogonal components are generated and decoded in baseband using digital signal processing (DSP). At the transmitter, the components are then upconverted to 5 GHz. Generation of the time domain signal is done by taking an Inverse Fast Fourier Transform (IFFT). The receiver will then downconvert, sample at 20 MHz before doing an FFT to retrieve the original coefficients.
For 5.5 and 11 Mbps, 802.11g makes use of complementary code keying (CCK). For 1 and 2 Mbps, it uses either differential binary phase-shift keying (DBPSK) or differential quadrature phase-shift keying (DQPSK) in combination with direct-sequence spread spectrum (DSSS).
The demand for higher speeds and lower manufacturing costs led to the 802.11g standard quickly being adopted by consumers in January 2003, before its ratification. Most dual-band 802.11a/b products became dual-band/tri-mode, able to support a, b and g in a single mobile adapter card or access point, in the summer of 2003.
The success of the 802.11g standard has caused usage and density problems related to crowding in urban areas, making the network less efficient since the protocol works better with only a few users per channel. A solution for the crowding and interference problems is to deploy an 802.11 network with a unique service set identifier (SSID).