GB/T 26684-2017Methods of measurement for digital terrestrial set-top box (English PDF)

3.1 Terms and Definitions

For the purpose of this document, the terms and definitions given in SJ/T 11324-2006 and the following apply.

3.1.1 acceptable error free

threshold of maximum uncorrected error events within the specified time while receiving signals

3.2 Symbols

tD,MAX: the maximum delay of 0dB echo withstandable to set-top box as specified in GB/T 26683-2017.

3.3 Abbreviations

For the purpose of this document, the following abbreviations apply.

AEF: Acceptable Error Free

EPG: Electronic Program Guide

PSI: Program Specific Information

SI: Service Information

UHF: Ultra High Frequence

VHF: Very High Frequence

4.1 General Description

4.1.1 Working conditions

Unless otherwise specified, the set-top box shall be tested in accordance with the standard measurement conditions specified in 4.5.

4.1.2 Measurement site

Measurements shall be made in a room that is not subject to interference from external radio frequency and low frequency electromagnetic fields. If external electromagnetic interference affects the measurement, the measurement shall be made in the shielded room.

4.1.3 Environmental conditions of measurement

4.1.3.1 Measurement conditions

The measurement conditions shall meet the following requirements:

Ambient temperature: 15°C to 35°C;

Relative humidity: 25% to 75%;

Atmospheric pressure: 86kPa to 106kPa;

Power supply: [220 × (1 ± 5%)]V, [50 × (1 ± 2%)]Hz.

4.1.3.2 Arbitration conditions

The arbitration conditions shall meet the following requirements:

Ambient temperature: 20°C±2°C;

Relative humidity: 60% to 70%;

Atmospheric pressure: 86kPa to 106kPa;

Power supply: [220 × (1 ± 2%)]V, [50 × (1 ± 1%)]Hz;

Power supply harmonics: 0 to 5%.

4.1.4 Stabilization time

To ensure that the performance of set-top box does not changed significantly over time after the start of the measurement, the set-top box shall be stable operation for at least 15 minutes under the standard measurement conditions.

4.2 Test Signal

See GB/T 26270-2010.

4.3 Measurement Mode

The measurement modes as shown in Table 1, where working mode 11 is applicable to "change in working mode and modulation parameters" only.

Table 1

Working mode Carrier numbers Forward error correction code rate Symbol constellation mapping Frame header mode Frame header phase variation Symbol interleaving option Double pilot insertion Net code rateMbps

4.4 Measuring System and Test Apparatus

See Table 2 for specific requirements.

Table 2

No. Device name Requirements

1 Digital television test transmitter Meet the relevant requirements of GB/T 26681-2011, MER >= 36 dB

2 Analog television test transmitter Carrier frequency range: 40MHz to 1GHz; amplitude: >= -10dBm; unwanted emission power in adjacent channels is less than carrier power: >= 50 dB

4.5 Standard Measurement Conditions

4.5.1 Measurement channel

For the performance of working mode 7, the minimum received signal power shall be measured on all VHF and UHF channels, and takes the worst result as the measurement result of working mode 7.

The reflection loss, the capacity to suppress the adjacent channel interference of analog television, and the capacity to suppress the adjacent channel interference of the digital television are measured at the channel 14 (482 MHz), the channel 31 (658 MHz), and the channel 47 (786 MHz).

Other items are measured on channel 31 (658 MHz).

4.5.2 Standard radio frequency input signal power

The radio frequency signal input to the set-top box is expressed by the average power in the channel (8 MHz).

The standard useful input signal power for radio frequency television signals shall be -60 dBm at the radio frequency input terminal.

4.5.3 Analog television signal

PAL-D radio frequency signal is used for the analog television signal for interference, and the modulated video signal is 100/0/75/0 color bar signal, and the audio signal is 1 kHz signal. Other requirements shall meet the requirements of GB 3174. The analog television signal power is expressed in terms of the peak power in the channel (8 MHz).

4.5.4 Gaussian noise

Gaussian noise shall cover the interfered channel. Gaussian noise power is expressed as the average power in the interfered channel (8 MHz).

4.5.5 Impulse noise

The principle of impulse noise generation as shown in Figure 1.

Figure 1

The impulse noise power is expressed as the average power of the Gaussian noise generated by the Gaussian noise generator in the interfered channel (8 MHz).

4.5.6 Multipath channel

See Annex A for the multipath channel model.

4.5.7 Standard bitstream

The test bitstream program shall not be less than 1 minute in time span and contain at least one video program and one audio program. The video program shall be a sequence of moving images.

When testing and evaluating the system net load data rate is greater than the working mode of 14 Mbps, the video program included in the test bitstream shall contain at least one set of HD programs with a basic stream data rate greater than 8 Mbps, a frame frequency of 25 Hz, an pixel aspect ratio of 16:9, the resolution is 1920 × 1080, and the chroma parameter is 4:2:0.

If the standard definition program is included in the test bitstream, the frame frequency is 25 Hz, the pixel aspect ratio is 4:3, the resolution is 720 × 576, and the chrominance parameter is 4:2:0.