Measure signal-to-noise ratio (SNR) in digital modulation applications
The MER Measurement block outputs the modulation error ratio (MER). MER is a measure of the signal-to-noise ratio (SNR) in digital modulation applications. The block measures all outputs in dB.
The MER Measurement block accepts a received
signal at input port
Rcv. It may use an ideal input
signal at reference port
Ref or, optionally, a
reference constellation. The MER block then outputs a measure of the
modulation accuracy by comparing these inputs. The modulation error
ratio is the ratio of the average reference signal power to the mean
square error. This ratio corresponds to the SNR of the AWGN channel.
The block output always outputs MER in dB, with an option to output minimum MER and X-percentile MER values. The minimum MER represents the best-case MER value per burst. For the X-percentile option, you can select to output the number of symbols processed in the percentile computations.
The table shows the output type, the parameter that selects the output type, the computation units, and the corresponding measurement interval.
|Output||Activation Parameter||Units||Measurement Interval|
|MER||None (output by default)||dB|
|Minimum MER||Output minimum MER||dB|
|Percentile MER||Output X-percentile EVM||dB|
|Number of symbols||Output X-percentile EVM and Output the number of symbols processed||None|
The block accepts double, single, and fixed-point data types.
The output of the block is always
Specifies the reference signal source as either
Estimated from reference constellation.
Specifies the reference constellation points as a vector. This
parameter is available only when Reference signal is
from reference constellation. The default is
Specify the measurement interval as:
with periodic reset. This parameter affects the RMS
and minimum MER outputs only.
To calculate MER using only the current samples, set
this parameter to
To calculate MER for all samples, set this parameter
To calculate MER over an interval you specify and
to use a sliding window, set this parameter to
To calculate MER over an interval you specify and
to reset the object each time the measurement interval is filled,
set this parameter to
'Custom with periodic reset'.
Specify the custom measurement interval in samples as a real
positive integer. This is the interval over which the MER is calculated.
This parameter is available when Measurement interval is
with periodic reset. The default is
Specify the dimensions over which to average the MER measurements
as a scalar or row vector whose elements are positive integers. For
example, to average across the rows, set this parameter to
The default is
This block supports var-size inputs of the dimensions in which
the averaging takes place. However, the input size for the nonaveraged
dimensions must be constant. For example, if the input size is
3 2] and Averaging dimensions is
3], then the output size is
[1 3 1].
The number of elements in the second dimension is fixed at 3.
Outputs the minimum MER of an input vector or frame.
Enables an output X-percentile MER measurement. When you select this option, specify X-percentile value (%).
This parameter is available only when you select Output X-percentile MER. The Xth percentile is the MER value above which X% of all the computed MER values lie. The parameter defaults to the 95th percentile. That is, 95% of all MER values are above this output.
Outputs the number of symbols that the block uses to compute the Output X-percentile MER. This parameter is available only when you select Output X-percentile MER.
Select the simulation mode.
On the first model run, simulate and generate code. If the structure of the block does not change, subsequent model runs do not regenerate the code.
If the simulation mode is
System objects corresponding to the blocks accept a maximum of nine
Simulate model without generating code. This option results in faster start times but can slow subsequent simulation performance.
Measure the MER of a noisy 8-PSK signal.
Load the model by typing doc_mer_example at the command line.
Run the model. The MER is shown in the Display block and is approximately equal to the SNR, which is set by using the Constant block. Experiment with different SNR values, and observe the effect on the estimated MER.
MER is a measure of the SNR in a modulated signal calculated in dB. The MER over N symbols is
The MER for the kth symbol is
The minimum MER represents the minimum MER value in a burst, or
Ik = In-phase measurement of the kth symbol in the burst
Qk = Quadrature phase measurement of the kth symbol in the burst
Ik and Qk represent ideal (reference) values. and represent measured (received) symbols.
The block computes the X-percentile MER by creating a histogram of all the incoming MERk values. The output provides the MER value above which X% of the MER values fall.
 DVB (ETSI) Standard ETR290. Digital Video Broadcasting (DVB): Measurement guidelines for DVB systems. May 1997.