The 802.11 Physical Layer

The IEEE 802 standards committee formed the 802.11 Wireless Local Area Networks Standards Working Group in 1990. The 802.11 working group took on the task of developing a global standard for radio equipment and networks operating in the 2.4GHz unlicensed frequency band for data rates of 1 and 2 Mbps. The standard does not specify technology or implementation but simply specifications for the physical layer and Media Access Control (MAC) layer.
The Physical Layer in any network defines the modulation and signaling characteristics for the transmission of data. At the physical layer, two RF transmission methods and one infrared are defined. Operation of the WLAN in unlicensed RF bands requires the spread of spectrum modulation to meet the requirements for operation in most countries.
The 2 RF transmission modes specified in the 802.11 standard are:

1.Frequency Hopping Spread Spectrum (FHSS)

2.and Direct Sequence Spread Spectrum (DSSS).

Both architectures are defined for operation in the 2.4GHz frequency band, typically occupying the 83 MHz of bandwidth from 2.400 GHz to 2.483 GHz. Differential BPSK (DBPSK) and DQPSK is the modulation for the direct sequence. Frequency hopping uses 2-4 level Gaussian FSK as the modulation signaling method. The radiated RF power at the antenna is set by the rules governed by FCC part 15 for operation in the United States. Antenna gain is also limited to 6 dBi maximum. The radiated power is limited to 1W for the United States, 10mW per 1Mhz in Europe and 10mW for Japan. There are different frequencies approved for use in Japan, United States and Europe.