Higher order modulation scheme with more strict EVM requirement ??

[criterion456]

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~!!

 

[tyassin]

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