參數(shù)資料
型號： HFA3860A
廠商： Intersil Corporation
英文描述： Direct Sequence Spread Spectrum Baseband
中文描述： 直接序列擴(kuò)頻基帶
文件頁數(shù)： 15/39頁
文件大小： 251K
代理商： HFA3860A
2-145
Scrambling is done by a polynomial division using a
prescribed polynomial as shown in Figure 10. A shift register
holds the last quotient and the output is the exclusive-or of
the data and the sum of taps in the shift register. The taps
are programmable. The transmit scrambler seed is Hex 6C
and the taps are set with CR 7.
For the 1MBPS DBPSK data rates and for the header in all
rates, the data coder implements the desired DBPSK coding
by differential encoding the serial data from the scrambler
and driving both the I and Q output channels together. For
the 2MBPS DQPSK data rate, the data coder implements
the desired coding as shown in the DQPSK Data Encoder
table. This coding scheme results from differential coding of
dibits (2 bits). Vector rotation is counterclockwise although
bits 5 and 6 of configuration register CR2 can be used to
reverse the rotation sense of the TX or RX signal if needed.
For data modulation in the MBOK modes, the data is formed
into nibbles (4 bits). For Binary MBOK modulation
(5.5MBPS) one nibble is used per symbol and for
Quaternary MBOK (11MBPS), two are used. The data is not
differentially encoded, just scrambled, in these modes.
Spread Spectrum Modulator Description
The modulator is designed to generate DBPSK, DQPSK,
BMBOK, and QMBOK spread spectrum signals. The
modulator is capable of automatically switching its rate where
the preamble and header are DBPSK modulated, and the
data is differently modulated. The modulator can support date
rates of 1, 2, 5.5 and 11MBPS. The programming details to
set up the modulator are given at the introductory paragraph
of this section. The HFA3860A utilizes Quadraphase (I/Q)
modulation at baseband for all modulation modes.
In the 1MBPS DBPSK mode, the I and Q Channels are
connected together and driven with the output of the scrambler
and differential encoder. The I and Q Channels are then both
multiplied with the 11-bit Barker word at the spread rate. The I
and Q signals go to the Quadrature upconverter (HFA3724) to
be modulated onto a carrier. Thus, the spreading and data
modulation are BPSK modulated onto the carrier.
For the 2MBPS DQPSK mode, the serial data is formed
into dibits or bit pairs in the differential encoder as detailed
above. One of the bits in a dibit goes to the I Channel and
the other to the Q Channel. The I and Q Channels are then
both multiplied with the 11-bit Barker word at the spread
rate. This forms QPSK modulation at the symbol rate with
BPSK modulation at the spread rate.
For the 5.5MBPS Binary M-Ary Bi-Orthogonal Keying
(BMBOK) mode, the output of the scrambler is partitioned into
nibbles of sign-magnitude (4 bits LSB first). The magnitude
bits are used to select 1 of 8 eight bit modified Walsh
functions. The Walsh functions are modified by adding hex 03
to all members of a Walsh function set to insure that there is
no all 0 member as shown in table WAL. The selected
function is then XOR’ed with the sign bit and connected to
both I and Q outputs. The modified Walsh functions are
clocked out at the spread rate (nominally 11MCPS). The
symbol rate is 1/8th of this rate. The Differential Encoder
output of the last bit of the header CRC is the phase reference
for the high rate data. This reference is XOR’ed with the I and
Q data before the output. This allows the demodulator to
compensate for phase ambiguity without differential encoding
the high rate data.
For the 11MBPS QMBOK mode, the output of the scrambler
is partitioned into two nibbles. Each nibble is used as above
to select a modified Walsh function and set its sign. The first
of these modified Walsh spreading functions goes to the Q
Channel and the second to the I Channel. They are then
both XOR’ed with the phase reference developed from the
last bit of the header CRC from the differential encoder.
Clear Channel Assessment (CCA) and
Energy Detect (ED) Description
The clear channel assessment (CCA) circuit implements the
carrier sense portion of a carrier sense multiple access
(CSMA) networking scheme. The Clear Channel Assess-
ment (CCA) monitors the environment to determine when it
is feasible to transmit. The result of the CCA algorithm is
available 16
μ
s after RX_PE goes high through output pin 32
of the device. The CCA circuit in the HFA3860A can be pro-
grammed to be a function of RSSI (energy detected on the
channel), carrier detection, or both. The CCA output can be
ignored, allowing transmissions independent of any channel
TABLE 8. DQPSK DATA ENCODER
PHASE SHIFT
0
+90
+180
-90
DIBIT PATTERN (D0, D1)
D0 IS FIRST IN TIME
00
01
11
10
FIGURE 10. SCRAMBLING PROCESS
Z
-1
Z
-2
Z
-3
Z
-4
Z
-5
Z
-6
Z
-7
XOR
SERIAL DATA
IN
XOR
SERIAL
DATA OUT
TABLE 9. MODIFIED WALSH FUNCTIONS
MAG
0
1
2
3
4
5
6
7
mWAL
03
0C
30
3F
56
59
65
6A
DATA PATTERN
LSB.......MSB
11000000
00110000
00001100
11111100
01101010
10011010
10100110
01010110
HFA3860A
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