HFA3861 データシートの表示（PDF） - Intersil
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HFA3861 Datasheet PDF : 35 Pages
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HFA3861
DATA
MODULATION
DBPSK
DQPSK
CCK
CCK
TABLE 3. BIT RATE TABLE EXAMPLES FOR MCLK = 44MHz
A/D SAMPLE CLOCK
(MHz)
TX SETUP CR 5
BITS 1, 0
RX SIGNAL CR 63
BITS 7, 6
DATA RATE (Mbps)
22
00
00
1
22
01
01
2
22
10
10
5.5
22
11
11
11
SYMBOL RATE
(MSPS)
1
1
1.375
1.375
DATA
802.11 DSSS BPSK
1Mbps
BARKER
IOUT
QOUT
CHIP
RATE
SYMBOL
RATE
1 BIT ENCODED TO
ONE OF 2 CODE
WORDS
(TRUE-INVERSE)
11 CHIPS
11 MC/S
1 MS/S
802.11 DSSS QPSK
2Mbps
BARKER
2 BITS ENCODED
TO ONE OF
4 CODE WORDS
11 CHIPS
11 MC/S
1 MS/S
I vs Q
5.5Mbps CCK
COMPLEX
SPREAD FUNCTIONS
11Mbps CCK
COMPLEX
SPREAD FUNCTIONS
4 BITS ENCODED
TO ONE OF 16
COMPLEX CCK
CODE WORDS
8 BITS ENCODED
TO ONE OF 256
COMPLEX CCK
CODE WORDS
8 CHIPS
11 MC/S
1.375 MS/S
8 CHIPS
11 MC/S
1.375 MS/S
FIGURE 7. MODULATION MODES
For the 1 and 2Mbps modes, the transmitter accepts data
from the external source, scrambles it, differentially encodes
it as either DBPSK or DQPSK, and spreads it with the BPSK
PN sequence. The baseband digital signals are then output
to the external IF modulator.
For the CCK modes, the transmitter inputs the data and
partitions it into nibbles (4 bits) or bytes (8 bits). At 5.5Mbps,
it uses two of those bits to select one of 4 complex spread
sequences from a table of CCK sequences and then QPSK
modulates that symbol with the remaining 2 bits. Thus, there
are 4 possible spread sequences to send at four possible
carrier phases, but only one is sent. This sequence is then
modulated on the I and Q outputs. The initial phase
reference for the data portion of the packet is the phase of
the last bit of the header. At 11Mbps, one byte is used as
above where 6 bits are used to select one of 64 spread
sequences for a symbol and the other 2 are used to QPSK
modulate that symbol. Thus, the total possible number of
combinations of sequence and carrier phases is 256. Of
these only one is sent.
The bit rate Table 3 shows examples of the bit rates and the
symbol rates and Figure 7 shows the modulation schemes.
The modulator is completely independent from the
demodulator, allowing the PRISM baseband processor to be
used in full duplex operation.
Header/Packet Description
The HFA3861 is designed to handle packetized Direct
Sequence Spread Spectrum (DSSS) data transmissions.
The HFA3861 generates its own preamble and header
information. It uses two packet preamble and header
configurations. The first is backwards compatible with the
existing IEEE 802.11-1997 1 and 2Mbps modes and the
second is the optional shortened mode which maximizes
throughput at the expense of compatibility with legacy
equipment.
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