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Chapter 10. Wireless Ethernet > Complementary Code Keying

10.4. Complementary Code Keying

Eight-chip Complementary Code Keying (CCK) is used as the modulation method for HRDSS (5.5 and 11 Mbps) transmissions. The CCK chip signaling rate is 11 MHz and is the same as that of DSSS. The signal bandwidth of CCK is therefore also 11 MHz and is compatible with DSSS systems. The HRDSSS basic packet format is the same as that of DSSS. An optional short packet format is also provided to reduce transmission overhead for 2-, 5.5-, and 11-Mbps rates. An optional HRDSSS packet binary convolutional coding (PBCC) modulation method can also be used in place of the CCK modulation.

10.4.1. Summary of 802.11b Standards

Two different preambles and headers are defined: the mandatory supported long preamble and header, which is interoperable with the 1- and 2-Mbps DSSS specification, and an optional short preamble and header. Figure 10.26 shows the long packet format for HRDSSS transceivers. The long packet format is the same as that used by DSSS transceivers. There are several new definitions in the Signal and Service fields. High rates and corresponding encodings are different in the Signal field. A bit is used in the Service field to indicate the length that is expressed in whole microseconds. Another bit is used in the Service field to indicate whether the optional PBCC mode is being used. One bit is used in the Service field to indicate that the transmit carrier frequency and bit clocks are locked.


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