Measure signal-to-noise ratio (SNR) in digital modulation applications

Utility Blocks

The Modulation Error Ratio (MER) is a measure of the signal-to-noise ratio (SNR) in digital modulation applications. You can use these types of measurements to determine system performance in communications applications. For example, determining if an EDGE system conforms to 3GPP radio transmission standards requires accurate MER, Minimum MER, and 95th percentile for the MER measurements. The block measures all outputs in decibels (dB).

The MER block receives an ideal input signal (at reference port, `Ref`

)
and an AWGN corrupted signal (at input port, `In`

).
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 defaults to MER in decibels (dB), with an option
of `Output minimum MER`

or ```
Output
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 following table shows the output type, the activation (what selects the output computation), computation units, and the corresponding computation duration.

Output | Activation | Units | Computation Duration |
---|---|---|---|

MER | Default | Decibels | Per burst |

Min MER | Parameter setting | Decibels | Per burst |

Percentile MER | Parameter setting | Decibels | Continuous |

Number of symbols | Parameter setting if you select Output X-percentile
MER | None | Continuous |

The block computes measurements for bursts of data. The data
must be of length *N* symbols, where *N* is
the size of the burst. The block computes a unique output for each
incoming burst; therefore, the computation duration is per burst.

The input signals must be 1-D or 2-D sample-based column vectors or 2-D frame-based column vectors. The input and reference signals must have identical dimensions.

The output is always a scalar value.

The block accepts double, single, and fixed-point data types. The output of the block is always double type.

MER is a measure of the SNR in a modulated signal calculated
in dB. MER over *N* symbols is

$$MER=10*\text{}{\mathrm{log}}_{10}\left(\frac{{\displaystyle \sum _{n=1}^{N}\left({I}_{k}^{2}+{Q}_{k}^{2}\right)}}{{\displaystyle \sum _{n=1}^{N}\left({e}_{k}\right)}}\right)dB$$

The MER for the *k _{th}* symbol
is

$$ME{R}_{k}=10*\text{}{\mathrm{log}}_{10}\left(\frac{\frac{1}{N}{\displaystyle \sum _{n=1}^{N}\left({I}_{k}^{2}+{Q}_{k}^{2}\right)}}{{e}_{k}}\right)db$$

The minimum MER represents the minimum MER value in a burst or

$$ME{R}_{\mathrm{min}}=\underset{k\in [1,\mathrm{...},N]}{\mathrm{min}}\left\{ME{R}_{k}\right\}$$

where

*e _{k}* = $${({I}_{k}-\stackrel{~}{{I}_{k}})}^{2}+{({Q}_{k}-{\stackrel{~}{Q}}_{k})}^{2}$$

*I _{k}* = In-phase measurement
of the

*Q _{k}* = Quadrature phase
measurement of the

*I _{k}* and

The block computes X-percentile MER by creating a histogram
of all the incoming *MER _{k}* values.
The output provides the MER value above which X% of the MER values
lay.

**Output Minimum MER**Outputs the minimum MER of an input vector or frame.

**Output X-percentile MER**Enables an output X-percentile MER measurement. When you select this option, specify

**X-percentile value (%)**.**X-Percentile value (%)**This parameter only appears 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. Therefore, 95% of all MER values are above this output.**Output the number of symbols processed**Outputs the number of symbols that the block uses to compute the

**Output X-percentile MER**. This parameter only appears when you select**Output X-percentile MER**.

[1] *Digital Video Broadcasting (DVB): Measurement
guidelines for DVB systems*, DVB (ETSI) Standard ETR290,
May 1997.

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