This model shows how error vector magnitude (EVM) and modulation error rate (MER) measurements are made using Simulink blocks.
This example includes:
The model applies an I/Q imbalance to a QAM-modulated signal at which point MER and EVM measurements are made. The constellation diagram provides a visual representation of the effects the imbalance has on the modulation performance indicators.
The I/Q Imbalance block is set to that the I/Q amplitude imbalance (dB) is set to 1 and the I/Q phase imbalance (deg) is set to 15.
The MER Measurement block is set so that it outputs the X-percentile MER value which is set to 90%.
The EVM Measurement block is set to output the maximum and 75th percentile EVM values.
Run the model.
You can see that I/Q amplitude and phase imbalance has shifted the constellation diagram so that each symbol is not exactly equal to its reference symbol (shown in red). Change the I/Q Imbalance block to see the effects of differing imbalances on the constellation diagram.
Observe the EVM and MER values. For the default configuration of the model, the mean MER is approximately 16.9 dB and the 90th percentile MER is 13.9 dB. The RMS EVM is, approximately, 14.3%, the maximum EVM is 20.4%, and the 75th percentile EVM is 17.7%.
Change the I/Q amplitude imbalance (dB) value in the I/Q Imbalance block to 2 dB. You can see that the all the MER and EVM metrics degrade.