Introduction
IEEE 802.11 (a/b/g)
17
Operating Manual 1171.5283.12 ─ 18
Dibit pattern (d0,d1) (d0 is first in time)
Phase change
00
0
01
pi/2
11
pi
10
3pi/2(-pi/2)
2.3.3
5.5 Mbps Data Rate with CCK Modulation
The standard specifies CCK modulation (complementary code keying) for a data rate
of 5.5
Mbps. To this end, in each modulation step, four successive bits (d
0
to d
3
) are
taken from the data stream which is already scrambled. The phases
φ
1
,
φ
2
,
φ
3
,
φ
4
are
determined by these four bits.
φ
1
is determined by the data bits d
0
and d
1
according to the following table, which
specifies different phases for even and odd modulation steps:
Dibit pattern (d0,d1) (d0 is first
in time)
Even symbols phase change
Odd symbols phase change
00
0
pi
01
pi/2
3pi/2(-pi/2)
11
pi
0
10
3pi/2(-pi/2)
pi/2
The phase
φ
1
must be interpreted relative to the phase of the previous symbol.
The other three phases are determined as follows:
φ
2
= (d
2
- pi ) + pi/2
φ
3
= 0
φ
4
= d
3
- pi
By means of these four phases, the CCK code word can now be determined; it is:
Data Spreading and Modulation CCK-PBCC
