Higher order modulation scheme with more strict EVM requirement ?

Hi,

In terms of PAR, higher order modulation scheme, more susceptible to nonlinearity distortion.

Besides, in terms of modulator, higher order modulation scheme, more susceptible to I/Q imbalance.

Thus, in theory, the EVM specification of higher order modulation scheme should be more relaxed.

Nevertheless, as shown in the figure below :

In LTE application, 64 QAM has more strict EVM requirement than QPSK ?

In other words,

For QPSK EVM test, it?s very easy to pass.
For 64 QAM EVM test, it?s very difficult to pass.

I am confused that why the specification is defined so.

Thanks~!

Hi

I guess, that since there are 4 constellation points in QPSK and these are far apart. A quite large EVM can be tolerated. However with 64QAM the constellation points can be quite close and therefore, there is no room for a large EVM.

Regards