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Design Notes

QPSK  Multirate

This example demonstrates a multirate QPSK system in VSS. The term multirate is used to distinguish the fact that the data rate of the inphase (I) channel differs from that of the quadrature (Q) channel.

The DAC blocks after the random digital sources convert the different data rates to the same sampling frequency at the input to the two mixers.

The I-channel has a bit rate of 1024Kbps and its DAC has the sample per symbol parameter (SMPSYM) set to 20.

The Q-channel has a bit rate of 3200Kbps and its DAC has the sample per symbol parameter (SMPSYM) set to 6.4.

Therefore, 1/(1024e3*20) = 1/(3200e3*6.4) = 48.828125ns.

The resulting power spectrum can be seen in the “Power Spectrum” graph.

The raw Q and I data can be seen in its corresponding graph.

System Diagram - Quadrature QPSK System

Graph - Power Spectrum

Graph - Inphase Data

Graph - Quadrature Data