參數(shù)資料
型號(hào)： HFA3824A
廠商： Intersil Corporation
元件分類(lèi)： 基帶處理器
英文描述： Direct Sequence Spread Spectrum Baseband Processor
中文描述： 直接序列擴(kuò)頻基帶處理器
文件頁(yè)數(shù)： 17/40頁(yè)
文件大?。?/td> 271K
代理商： HFA3824A
2-115
sequences.
sequences the PG range of the HFA3824A is:
From 10.41dB (10 LOG(11)) to 12.04dB (10 LOG(16))
The transmitter and receiver PN sequences can are pro-
grammed independently. This provides additional flexibility to
the network designer.
The TX sequence is set through CR 13 and CR 14 while the
RX PN sequence is set through CR 20 and CR 21. A maximum
of 16 bits can be programmed between the pairs of these con-
figuration registers. For TX Registers CR13 and CR14 contain
the high and low bytes of the sequence for the transmitter. In
addition Bits 5 and 6 of CR 4 define the sequence length in
chips per bit. CR 13, CR 14 and CR 4 must all be programmed
for proper functionality of the PN generator. The sequence is
transmitted MSB first. When fewer than 16 bits are in the
sequence, the MSBs are truncated.
Given
the
length
of
these
programmable
Scrambler and Data Encoder Description
The data coder the implements the desired DQPSK coding as
shown in the DQPSK Data Encoder table. This coding scheme
results from differential coding of the dibits. When used in the
DBPSK modes, only the 00 and 11 dibits are used. Vector rota-
tion is counterclockwise. This rotation sense can be reversed
by programming CR16 <7> and CR5 <7>.
TABLE 8. DQPSK DATA ENCODER
The data scrambler is a self synchronizing circuit. It consist
of a 7-bit shift register with feedback from specified taps of
the register, as programmed through CR 16. Both transmitter
and receiver use the same scrambling algorithm. All of the
bits transmitted are scrambled, including data header and
preamble. The scrambler can be disabled.
Scrambling provides additional spreading to each of the spec-
tral lines of the spread DS signal. The additional spreading due
to the scrambling will have the same null to null bandwidth, but
it will further smear the discrete spectral lines from the PN code
sequence. Scrambling might be necessary for certain allocated
frequencies to meet transmission waveform requirements as
defined by various regulatory agencies.
In the absence of scrambling, the data patterns could con-
tain long strings of ones or zeros. This is definitely the case
with the a DS preamble which has a stream of up to 256
continuous ones. The continuous ones would cause the
spectrum to be concentrated at the discrete lines defined by
the spreading code and potentially cause interference with
other narrow band users at these frequencies. Additionally,
the DS system itself would be moderately more susceptible
to interference at these frequencies. With scrambling, the
spectrum is more uniform and these negative effects are
reduced, in proportion with the scrambling code length.
Figure 11 illustrates an example of a non scrambled trans-
mission using an 11-bit code with DBPSK modulation with
alternate 1’s and 0’s as data. The data rate is 2 MBPS while
the spread rate or chip rate is at 11 MCPS. The 11 spectral
lines resulting from the PN code can be clearly seen in Fig-
ure 11. In Figure 12, the same signal is transmitted but with
the scrambler being on. In this case the spectral lines have
been smeared.
Another reason to scramble is to gain a small measure of
privacy. The DS nature of the signal is easily demodulated
with a correlating receiver. Indeed, the data modulation can
be recovered from one of the discrete spectral lines with a
narrow band receiver (with a 10dB loss in sensitivity). This
means that the signal gets little security from the DS
spreading code alone. Scrambling adds a privacy feature to
the waveform that would require the listener to know the
scrambling parameters in order to listen in. When the data
is scrambled it cannot be defeated by listening to one of the
scrambling spectral lines since the unintentional receiver in
this case is too narrow band to recover the data modula-
tion. This assumes though that each user can set up differ-
ent scrambling patterns There are 9 maximal length codes
that can be utilized with a generator of length 7. The differ-
ent codes can be used to implement a basic privacy
scheme. It needs to be clear though that this scrambling
code length and the actual properties of such codes are not
a major challenge for a sophisticated intentional interceptor
to be listening in. This is why we refer to this scrambling
PHASE SHIFT
DIBITS
0
00
+90
01
+180
11
-90
10
CENTER 280MHz
RES BW 300kHz
FIGURE 11. UNSCRAMBLED DBPSK DATA OF ALTERNATE
1’s/0’s SPREAD WITH AN 11-BIT SEQUENCE
VBW 100kHz
SPAN 50MHz
SWP 20ms
REF -24dBm
ATTEN 10dB
CENTER 280MHz
RES BW 300kHz
VBW 100kHz
SPAN 50MHz
SWP 20ms
REF -25dBm
ATTEN 10dB
FIGURE 12. SCRAMBLED DBPSK DATA OF ALTERNATE
1’s/0’s SPREAD WITH AN 11-BIT SEQUENCE
HFA3824A
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
HFA3824AIV 制造商:Rochester Electronics LLC 功能描述:BASEBAND PROCESSOR - Bulk
HFA3824AIV WAF 制造商:Harris Corporation 功能描述:
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HFA3824EVAL 制造商:Rochester Electronics LLC 功能描述:- Bulk
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