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 replace the Barker code in wireless digital networks. Complementary codes, first introduced by Golay in 1961 are sets of finite sequences of equal length, such that the number of pairs of identical elements with any given separation in one sequence is equal to the number of pairs of unlike elements having the same separation in the other sequences.