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Chapter 6 - TV Measuring Range
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BER measurement (Bit Error Rate)
6.2.2.4.6
The measurement of the bit error rate aids in the determination of the quality of a DVB-T2 signal.
To determine the bit error rate, the error correction mechanisms in the digital receiver are used.
The data stream is compared before and after correction and the number of corrected bits is
determined from that. This number is placed in a ration to the total throughput of bits and the BER
is calculated based on that.
For DVB-T2, two independent error protection mechanisms work together. LDPC (Low Density
Parity Check) is used for internal error protection, BCH (Bose Chaudhuri Hocquenghem) is used for
external error protection.
The equipment measures the bit error rates before LDPC (CBER) and after LDPC (LBER).
Both values are shown on the display in exponential form.
The depth of measurement for the CBER is1•10
6
bits, for the LBER it is 1•10
8
bits.
MER measurement (Modulation Error Rate)
6.2.2.4.7
In addition to measure the bit error rate, it is established practice with digital transmission to also
measure MER. It is defined in ETR290. MER is calculated from the constellation points.
It is the counterpart to S/N measurement with analogue transmission methods. The measuring
range goes up to 35 dB with a resolution of 0.1 dB.
Noise Margin (NM)
6.2.2.4.8
In case of white noise a limit value of MER for the minimum signal quality (QEF) can be determined
dependent on the modulation type and the FEC.
The difference of MER to this limit value corresponds to the system reserve NM (noise margin).
Just as MER it is displayed in dB with a resolution of 0.1 dB. For an easier assessment of the
signal quality the NM is shown in the colors red for bad, yellow for limited and green for good signal
quality. The limit values for the BER (>2e-4 for bad and <1e-6 for good) will also be included in this
assessment.
Important! The noise margin cannot be shown in DVB-T2 during active PE-measurement.
