5/4) ?— 8
= 11 Mcps
FIGURE 1.29 A 5.5-Mbps CCK transmission block diagram.
Group
8 Bits
Spread
by 8 Chips
11 Mbps
11/8
Mbps
(11/8) ?— 8
= 11 Mcps
FIGURE 1.30 An 11-Mbps CCK transmission block diagram.
Sync
Start Frame
Delimiter
PLW PSF CRC
1 Mbps
PSDU
FIGURE 1.31 FHSS PLCP PPDU format.
Data
Whitening
Symbol
Mapping
PSDU
Gaussian
LPF
2- or 4-
Level
GFSK
FIGURE 1.32 An FHSS transmission block diagram.
The modulation scheme is GFSK 2 level and 4 level. AGaussian filter with the BT product 0.5
is used. The frequency deviation is greater than 110 kHz, thus having a modulation index of
.
A simplified block diagram of the transmit section is shown in Fig. 1.32.
b
2 110 kHz
1 Mbps
0.22
IEEE802.11a. This WLAN system was targeted for use in the 5.15??“5.35 GHz and 5.725??“5.825
GHz unlicensed bands. The standard is based on the orthogonal frequency division multiplexing
(OFDM) physical layer. The data rates supported are 6, 9, 12, 18, 24, 36, 48, and 54 Mbps, where 6,
12, and 24 Mbps are mandatory.
The OFDM physical layer uses 52 subcarriers using BPSK/QPSK, 16-QAM (quadrature amplitude
modulation), and 64-QAM, with the FEC technique being convolutional coding with code rates
of 1/2, 2/3, and 3/4.
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