5/11-Mbps data rate services will use CCK modulation.
The 1- and 2-Mbps data rate services will be discussed first (see Figs. 1.27 and 1.28). Since
this is a DSSS system, with a chip rate of 11 Mcps, we need to discuss the PN code sequence, which
in this case is a Barker sequence and is given as
(1.8)
Here, each symbol (or bit) of DQPSK (or DBPSK) shall be spread by this 11-chip sequence given
in Eq. (1.8). The DBPSK encoding phase state table is given as
Input Output
0 0
1
The DQPSK encoding phase state table is given as
Input Output
00 0
01 /2
11
10 /2
For the higher??“data rate services, CCK modulation is used. Each symbol shall be spread by 8 chips
that are complex valued. The 5.5-Mbps data rate groups 4 bits to transmit per symbol. The CCK
spreading code is derived as follows (8 complex-valued chips):
(1.9)
Here we take the input 5.5-Mbps data stream and group incoming bits into groups of 4 bits.
These 4 bits are used to determine the phase values used in the PN codes described above. Thus
every group of 4 bits leads to different complex values of the PN shown above. The block diagram
is shown in Fig. 1.29.
Lastly, the 11-Mbps data rate is accomplished by grouping 8 bits together to transmit a symbol
(see Fig.
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