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16QAM EVM and IQ Imbalance
This example demonstrates the impact of phase imbalance, amplitude imbalance, and dc-offset on the RMS Max EVM measurement.
The resulting constellation of the RF link is shown in "16QAM IQ after RF link".
The best EVM (approximately 1.0%) is achieved when all imbalances are set to zero. The EVM measurement can be monitored in the "EVM Measured in percentage" table.
The example makes use of the VSS RMS EVM measurement, and the I_Q imbalance model. The I_Q imbalance model is a subcircuit and can be found in the elements tree under Libraries/RF Blocks.
In this example, you can tune on the average signal power (PWR), phase imbalance (PHASE) and amplitude imbalance (AMPLITUDE).
To update the MWO Filter Response graph you have to click the Analyze button.
The DLYCMP block is used to compensate for the group delay of the filter.
The ALIGN block applies a constant gain and phase correction to the distorted signal from the RF link. The correction is determined from an initial block of reference and distorted samples.
Please read the online help for each block and measurement along with the VSS Getting Started Guide. You can find the VSS Getting Started Guide under Help --> Getting Started.
System Diagram - 16QAM Signal EVM Test Bench
Schematic - Filter
Graph - 16 QAM IQ after RF link
Graph - Average Signal Power in dBm
|DB(PWR_vsT(TP.64QAM_IN,0,0,0,0,1,1000,0,30,1,-1,0,-1,10,1,0,0.5,0,0,0,0,0)) (us) 16QAM Signal EVM Test Bench Time||DB(PWR_vsT(TP.64QAM_IN,0,0,0,0,1,1000,0,30,1,-1,0,-1,10,1,0,0.5,0,0,0,0,0)) (dBm) 16QAM Signal EVM Test Bench|
Graph - EVM Measured in percentage
|EVM(VSA.M1,0,1,1,100,1,0,10,0,0,0,1,1,0,0,0,0) (us) 16QAM Signal EVM Test Bench Time||EVM(VSA.M1,0,1,1,100,1,0,10,0,0,0,1,1,0,0,0,0) 16QAM Signal EVM Test Bench|