Measure error vector magnitude
Thecomm.EVM
(error vector magnitude) System object™ measures the modulator or demodulator performance of an impaired signal.
To measure error vector magnitude:
Define and set up your EVM object. SeeConstruction.
Callstep
测量调制器和解调器performance according to the properties ofcomm.EVM
. The behavior ofstep
is specific to each object in the toolbox.
Note
Starting in R2016b, instead of using thestep
method to perform the operation defined by the System object, you can call the object with arguments, as if it were a function. For example,y = step(obj,x)
andy = obj(x)
perform equivalent operations.
EVM = comm.EVM
creates an error vector magnitude object,EVM
. This object measures the amount of impairment in a modulated signal.
EVM = comm.EVM(
creates anName
,Value
)EVM
object with each specified property set to the specified value. You can specify additional name-value pair arguments in any order as (Name1
,Value1
,...,NameN
,ValueN
).
Example:EVM = comm.EVM('ReferenceSignalSource','Estimated from reference constellation')
creates an object,EVM
, that measures the RMS EVM of a received signal by using a reference constellation.
|
Normalization method Normalization method used in EVM calculation, specified as one of the following: |
|
Average constellation power Average constellation power, specified in watts as a positive real scalar. This property is available when |
|
Peak constellation power Peak constellation power, specified in watts as a positive real scalar. This property is available when |
|
Reference signal source Reference signal source, specified as either |
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Reference constellation Reference constellation, specified as a vector. This property is available when the The default is |
|
Measurement interval source Measurement interval source, specified as one of the following:
|
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Measurement interval 测量时间间隔对挣值管理的都是它ted, specified in samples as a real positive integer. This property is available when |
|
Averaging dimensions Averaging dimensions over which to average the EVM measurements, specified as an integer or row vector of integers with element values in the range [1, 3]. For example, to average across the rows, set this property to The object supports variable-size inputs over the dimensions in which the averaging takes place. However, the input size for the nonaveraged dimensions must remain constant between calls of the object. For example, if the input has size |
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Maximum EVM measurement output port Maximum EVM measurement output port, specified as a logical scalar. To create an output port for maximum EVM measurements, set this property to |
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X-percentile EVM measurement output port X-percentile EVM measurement output port, specified as a logical scalar. To create an output port forX-percentile EVM measurements, set this property to |
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X-percentile value X-percentile value below whichX% of the EVM measurements fall, specified as a real scalar from |
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Symbol count output port Symbol count output port, specified as a logical scalar. To output the number of accumulated symbols used to calculate theX-percentile EVM measurements, set this property to |
step | Measure error vector magnitude |
Both the EVM block and the EVM object provide three normalization methods. You can normalize measurements according to the average power of the reference signal, average constellation power, or peak constellation power. Different industry standards follow one of these normalization methods.
The block or object calculates the RMS EVM value differently for each normalization method.
EVM Normalization Method | Algorithm |
---|---|
Reference signal |
|
Average power |
|
Peak power |
|
Where:
ek=
Ikis the in-phase measurement of the kth symbol in the burst
Qkis the quadrature phase measurement of the kth symbol in the burst
Nis the input vector length
Pavgis the average constellation power
Pmaxis the peak constellation power
IkandQkrepresent ideal (reference) values. and represent measured (received) symbols.
The max EVM is the maximum EVM value in a frame or where k is the kth symbol in a burst of lengthN.
The definition for EVMkvaries depending upon which normalization method you select for computing measurements. The block or object supports these algorithms.
EVM Normalization | Algorithm |
---|---|
Reference signal |
|
Average power |
|
Peak power |
|
The block or object computes theX-percentile EVM by creating a histogram of all the incomingEVMkvalues. The output provides the EVM value below which X% of the EVM values fall.