Complementary code keying (CCK) is a modulation scheme used with wireless networks (WLANs) that employ the IEEE 802.11b specification.
In 1999, CCK was adopted to supplement the Barker code in wireless digital networks to achieve data rate higher than 2 Mbit/s at the expense of shorter distance.
This is due to the shorter chipping sequence in CCK (8 bits versus 11 bits in Barker code) that means less spreading to obtain higher data rate but more susceptible to narrowband interference resulting in shorter radio transmission range.
CCK is a variation and improvement on M-ary Orthogonal Keying and uses 'polyphase complementary codes'.
They were developed by Lucent Technologies and Harris Semiconductor and were adopted by the 802.11 working group in 1998.
CCK was selected over competing modulation techniques as it used approximately the same bandwidth and could use the same preamble and header as pre-existing 1 and 2 Mbit/s wireless networks and thus facilitated interoperability.
Networks using the 802.11g specification employ CCK when operating at 802.11b speeds.
In 5.5 Mbit/s and 11 Mbit/s modes respectively 4 and 8 bits are modulated onto the eight chips of the symbol c0,...,c7, where and