There are many standards of modulation; the most commonly used are;DSSS (Direct-Sequence Spread Spectrum), which is a transmission technology that combines the data signal with a higher data rate bit sequence, called a chipping code this improves noise resistance and data integrity.
OFDM (Orthogonal Frequency Division Multiplexing) transmits digital data over a radio wave by splitting a radio signal into multiple sub-signals that are then transmitted simultaneously at different frequencies. OFDM's modulation technique reduces the amount of crosstalk in signal transmissions.
CCK (Complementary Code Keying) uses a set of 64 eight-bit code words to encode data for 5.5 and 11Mbps data rates in the 2.4GHz band of 802.11b standard. The code words have unique mathematical properties; this allows them to be correctly distinguished from one another by a receiver even in the presence of substantial noise or multipath interference.