Offset QPSK (Digital Demod)
CDMA digital cellular standard IS-95. To learn about these filters, see IS-95 base phase EQ and IS-95 baseband measured and reference filters.
demodulates like the other demodulation formats. With , two additional IS-95 filters are available to measure signals that conform to USTo 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.
- 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 EVM.
displays error data in the symbol table and uses the same computations as other
demodulation formats with the following exceptions: - 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)