EVM Measurement
Measures the magnitude of the error vector magnitude (EVM).
Description
The EVM Measurement unit measures the RMS (root mean square) EVM value, the maximum EVM value, and the EVM percentile of the received signal. EVM is an indication of the performance of the modulator or demodulator.
Ports
Input
Ref - reference signal
array
Reference signal as an array of up to three measurements. If you specify this input, the object measures the EVM of the Rcv input using this input as the reference constellation.
The dimensions of this input must match the dimensions of the Rcv input. The object uses each element of this input as a reference symbol for the corresponding element of the Rcv input.
Data types: Float16, Float32, Float64, Int8, Int16, Int32, Int64, UInt8, UInt16, UInt32, UInt64, Bool.
Rcv - received signal
array
Received signal as an array of up to three dimensions.
Data types: Float16, Float32, Float64, Int8, Int16, Int32, Int64, UInt8, UInt16, UInt32, UInt64, Bool.
Algorithms
The implementation supports three normalisation methods. You can normalise measurements according to the average power of the reference signal, the average power of the population, or the peak power of the population. Different industry standards follow one of these normalisation methods.
The algorithm calculates the RMS EVM differently for each normalisation method.
| EVM normalisation method | Algorithm |
|---|---|
Reference signal |
|
Average power |
|
Peak power |
|
In these equations:
-
-
represents the in-phase measurement of the k-th symbol in the packet.
-
represents the quadrature phase measurement of the k-th symbol in the packet.
-
- is the length of the input vector.
-
- is the average power of the constellation.
-
- peak power of the constellation.
-
and [Q_k] represent ideal (reference) values.
-
and * represent measured (derived) symbols.
The maximum EVM is the maximum EVM value in a frame or , where is the kth symbol in a packet of length N.
The definition of depends on which normalisation method you choose to compute the measurements. The implementation supports these algorithms.
| EVM normalisation method | Algorithm |
|---|---|
Reference signal |
|
Average power |
|
Peak power |
|
The implementation calculates the X percentile of EVM by creating a histogram of the incoming values . This output provides the EVM value below which X% of the EVM values fall.