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input complex waveform specifies the QAM-modulated complex baseband waveform data.
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t0 specifies the trigger (start) time of the Y array. The default is 0.0.
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dt specifies time interval between data points in the acquired
Y array. The default is 1.0.
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Y specifies the complex-valued signal-only baseband modulated
waveform. The real and imaginary parts of this complex data array correspond to
the in-phase (I) and quadrature-phase (Q) data, respectively.
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QAM system parameters specifies parameter values defining the QAM system. Wire the
QAM system parameters cluster returned by the QAM (M) or QAM (Map) instance of the MT Generate System Parameters VI to this cluster. Do
not alter the values.
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samples per symbol specifies an even, positive number of samples dedicated to
each symbol. Multiply this value by the symbol rate to determine the sample
rate. The default is 16.
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Note The Modulation Toolkit demodulation and detector VIs use timing recovery, which is optimized for four or more samples per symbol. |
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symbol map specifies an ordered array that maps each symbol value to its
desired coordinates in the complex plane. The number of QAM states in the array
must be 2N, where N is the number of bits per symbol. The length of
the vector for the symbol(s) farthest from the origin must be 1.
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matched filter coefficients specifies an ordered array containing the desired matched
filter coefficients. Wire the matched filter
coefficients parameter of the MT Generate Filter Coefficients VI to this parameter. When
generating the filter coefficients, ensure that the value of the matched samples per symbol parameter of the MT Generate
Filter Coefficients VI is equal to the value of the samples
per symbol element of the QAM system
parameters cluster passed to this VI.
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Note When reset? is set to TRUE, there is a transient
response of half the filter length at the start of the demodulated signal, and
the returned data is shortened by approximately half the filter length.
When reset? is set to FALSE, the VI uses data from
the previous iteration to eliminate the transient. |
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Tip When reset? is set to TRUE, the number of trailing
symbols that are carried over to the next iteration during demodulation is upper
bounded by [L + 4(13 + K)]/K, where L is the matched filter length in taps and K is the number of samples per symbol. For typical values of
L = 25 (4 samples per symbol, filter length
of 6 symbols) and K = 4, this value equals 23.25
symbols. Therefore when reset? is set to TRUE, a
total of 1,024 QAM symbols must be passed to the demodulator to obtain at least
1,000 symbols at the output. This formula does not account for truncation caused by
any specified synchronization parameters. |
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synchronization parameters specifies parameter values describing the synchronization
sequence and the range of bits over which to search for this sequence. Wire the
QAM synchronization parameters cluster returned by the QAM bit array or number array instances of the
MT Generate Synchronization Parameters VI to this cluster.
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Note If the synchronization parameters cluster is
not wired, the demodulator does not attempt to synchronize, and the
constellation of the demodulated waveform has a 90° carrier phase ambiguity.
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expected sync location specifies the expected location of the first symbol of the
sync sequence. This value is an index to the
input complex waveform. A value of -1 searches the entire input
complex waveform and ignores the sync location
uncertainty parameter.
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sync sequence specifies the mapped symbol pattern used to synchronize the
bit stream. To prevent false synchronization, select this pattern such that
there is a low probability of accidental correlation to nonsynchronized
parts of the data stream. If this parameter is left empty (default), the signal
is still demodulated, but there is a phase ambiguity in the recovered symbols.
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sync location uncertainty specifies the number of symbols before or after the expected sync location where the first symbol of
the sync sequence may be located.
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sync indent specifies the distance that the sync
sequence is indented into the information block. The distance is the
number of demodulated symbols preceding the sync sequence. For example, a value of 10
indicates that the output bit stream consists
of 10 data symbols, followed by the sync sequence,
followed by the remaining data symbols.
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reset? specifies whether the VI continues demodulating using the
previous iteration states. reset? must be TRUE
whenever you want to restart the demodulator. The VI resets on the first call
and when reset? is set to TRUE. Set reset? to FALSE if the input complex waveform is
contiguous with the input complex waveform
from the previous iteration of this VI. The default is TRUE.
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flush buffers? forces out samples from the input complex waveform that are delayed due to the FIR filters used in the demodulation algorithm. Set this parameter to TRUE during single-shot operations and during the last iteration of continuous operations. The default is FALSE.
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Note Setting flush buffers? to TRUE destroys the internal states of the algorithms such that you cannot perform continuous processing on the signal during subsequent iterations. If flush buffers? is set to TRUE, you must set reset? to TRUE on the subsequent iteration. |
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error in (no error) can accept error information wired from
previously called VIs. Use this information to decide if any functionality
should be bypassed in the event of errors from other VIs. Right-click the front
panel error in control and select Explain Error or Explain
Warning from the shortcut menu for more information about the error.
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status is TRUE (X) if an error occurred or FALSE (checkmark) to
indicate a warning or that no error occurred. Right-click the front panel
error in control and select Explain Error or Explain
Warning from the shortcut menu for more information about the
error.
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code identifies the error or warning code. Right-click the front
panel error in control and select Explain Error or Explain
Warning from the shortcut menu for more information about the
error.
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source describes the origin of the error or warning. Right-click the
front panel error in control and select Explain Error or Explain
Warning from the shortcut menu for more information about the
error.
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output bit stream returns the demodulated information bit stream.
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Note For QAM systems with more than 1 bit per symbol, such as 4-QAM, the symbols are
converted to bits in least significant bit (LSB) first order. For example, if
the detected symbols are 2,1,... the generated
bits are 0,1,1,0...
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sync found index returns the symbol index within the input
complex waveform where the peak correlation to the sync sequence was found. If no sync sequence is specified in the synchronization parameters cluster, this parameter returns
the offset from the start of the input complex
waveform to the first complete symbol.
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error out passes error or warning information out of a VI to be used by
other VIs. Right-click the front panel error out indicator and select
Explain Error or Explain
Warning from the shortcut menu for more information about the
error.
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status is TRUE (X) if an error occurred or FALSE (checkmark) to
indicate a warning or that no error occurred. Right-click the front panel
error out indicator and select Explain Error or Explain
Warning from the shortcut menu for more information about the
error.
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code is the error or warning code. Right-click the front panel
error out indicator and select Explain Error or Explain
Warning from the shortcut menu for more information about the
error.
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source describes the origin of the error or warning. Right-click the
front panel error out indicator and select Explain Error or Explain
Warning from the shortcut menu for more information about the
error.
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Successful locking depends on many factors, including signal quality, modulation type,
filtering parameters, and acquisition size. Locking also requires a fairly uniform
distribution of symbols in the signal. The demodulator lock rate increases (and failures
decrease) as the number of symbols demodulated increases. In general, you can expect to
achieve a better than 95% lock when demodulating 10 × M number of symbols, where M is
2bits per symbol.
