Could you give me more details about CCK (complementary code keying)?
The Complementary Code Keying (CCK) modulation scheme was added to the 1999 High Rate Amendment to the 802.11 Wireless MAC and PHY standard, replacing the older Barker code used with DSSS. 802.11b WLANs use CCK modulation to operate at 5.5 or 11 Mbps, falling back to the Barker code to operate at 1-2 Mbps. 802.11g WLANs will soon use OFDM to operate at data rates up to 54 Mbps, falling back to CCK to interoperate with 802.11b at 11 Mbps.
According to an Intersil primer on CCK, complementary codes are binary complementary sequences with the mathematical property that their periodic auto-correlative vector sum is zero except at the zero shift. 8-bit complementary code words are used to spread data across a single carrier in 802.11b Direct Sequence Spread Spectrum (DSSS) systems. CCK can send more data using approximately the same bandwidth as the older Barker code because CCK generates complex symbols that carry more bits -- 8 bits at 11 Mbps, 4 bits at 5.5 Mbps.
Radio engineers that want to learn about CCK should read Intersil's excellent primer. Since I'm NOT a radio engineer, I'll stop here!
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