Offset QPSK (Digital Demod)
demodulates like the other demodulation formats. With , two additional IS-95 filters are available to
measure signals that conform to US digital cellular standard IS-95. To learn about these
filters, see IS-95 base phase EQ and IS-95 baseband measured and reference filters.
To automatically configure the VSA for mobile measurements,
display the dialog box, then click and select (for mobile measurements).
When using , note the following:
- An even number must be specified for Points / Symbol.
- displays error data in the symbol table and uses the same computations as other
demodulation formats with the following exceptions:
- Amplitude droop is not
computed for .
- The VSA uses two points-per-symbol (instead of one point-per-symbol) to
compute the following:
- Offset EVM is
computed in addition to the regular .
- The symbol rate is the frequency of the I (or Q) clock, not the 2x frequency sometimes
associated with the I to Q clock frequency.
- Demodulated traces show a symbol at every I and Q detection (decision) point. Therefore, all
demodulated traces (except the symbol table) show twice as many symbols as the Result
Length, at twice the symbol rate.
- When a Half-Sine reference filter is selected, the
constellation changes from a square to a circle and the ideal state circles are moved to the
I and Q axes.
- When Low SNR Enhancement is selected, does not support the Rotation parameter so the parameter will be grayed out.
- When Low SNR Enhancement is selected and the Adaptive Equilizer Filter is used, measurement speed can become very slow when the filter length is long.
- When Low SNR Enhancement is enabled, the maximum Result Length value is about 40000 symbols, otherwise it is 2048. In both cases this maximum may be limited by "Search Time" or by hardware capabilities.
See Also
Digital Demodulation System Block Diagrams (Digital Demod)
Available Digital Demodulation Formats (Digital Demod)
Half-Sine shaping (for OQPSK)
OQPSK Align I & Q
Shaped OQPSK
2024
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