Shaped OQPSK (Digital Demod)

Menu Path:

is similar to Offset QPSK and can be thought of dually as:

an OQPSK scheme using a special differential bit mapping and frequency-pulse shaping filter

CPM using a special set of symbols with restrictions on bit ordering (and a special frequency-pulse filter). The I and Q streams of bits are separately restricted state transitions of +1/-1/0 and then the I and Q streams are combined.

The demodulator behaves like the 89600 VSA OQPSK demodulator (IQ traces), instead of like the CPM demodulator (FSK traces).

To automatically configure the VSA for measuring signals that conform to the IRIG 106-04 standard, on the Format tab, click Preset to Standard > Other and select SOQPSK-TG (IRIG 106-04). Note that the SOQPSK-TG preset sets the symbol rate to 5 MHz although the standard does not define a specific symbol rate.

For more information about SOQPSK-TG, see the following document: http://www.irig106.org/docs/106-05/chapter2.pdf

To automatically configure the VSA for measuring signals that conform to the SOQPSK-A or SOQPSK-B standards, on the Format tab, click Preset to Standard > Other and select SOQPSK-A or SOQPSK-B.

Things to note

When using , note the following:

An even number must be specified for Points / Symbol.

The metrics in the Error Summary table use the same computations as other demodulation formats with the following exceptions:

Amplitude droop is not computed for Shaped OQPSK.
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.

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 points as the , at twice the symbol rate.