what is cck modulation?

what is cck modulation?
is it belong to spread spectrum modulation?
how is its processing gain.

if input data rate is 2Mbps, after cck modulation, how the
chip rate is? 2M chips/s ? or others?

http://www.microsoft.com/windowsxp/e...80211gspec.asp

rgds

See following Application Note to describe Complementary Code Keying.

thanks for all help,
but i am still confused:

is it belong to spread spectrum modulation?
how is its processing gain.

if input data rate is 2Mbps, after cck modulation, how the chip rate is? 2M chips/s ? or others?

Yes CCK is some kind of spread spectrum modulation. You begin with a data signal with a certain bitrate. Next the stream is chopped in pieces of 1,2,... bit, symbols. For every symbol, we have an equivalent code. Now, instead of sending the bits for the symbol, we send a code consisting of more bits. This means the transmitted bit data rate is higher, but the information data rate keeps the same. In the frequency domain: a broader bandwidth.

Then why the heck is this interesting? Because we can define orthogonal codes. If different transmitters send their data with orthogonal codes on the same carrier, a receiver can distinct them although their spectra overlap! And the receiver is much less sensitive to zeroes in the receiving antenna pattern, caused by destructive interference!

A key difference between 802.11b and 802.11g wireless technologies is the modulation type. Complementary Code Keying (CCK) is used for 802.11b. Orthogonal Frequency Division Multiplexing (OFDM) is used for the higher data rates of 802.11g and CCK is used for the lower 802.11g data rates. Optional support for another modulation called Packet Binary Convolutional Code (PBCC) is also included in the 802.11g standard (22 Mbps to 33 Mbps). Texas Instruments included this modulation in 802.11b+ products that are available from some vendors (D-Link, USR for example). PBCC was unsuccessfully proposed as the official standard for 802.11g.

as we know, general spread specturm can realize CDMA. can CCK do that?