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This standard is developed in accordance with the rules given in GB/T 1.1-2009.
This standard replaces GB/T 26684-2011 Methods of Measurement for Digital Terrestrial Set-top Box. In addition to a number of editorial changes, the following technical deviations have been made with respect to the GB/T 26684-2011 (the previous edition):
— "Symbols" are added to Terms, Definitions, Symbols and Abbreviations (see 3.2 );
— "Measurement mode" is added in the basic requirements of measurement (see 4.3);
— "Change in working mode and modulation parameters" (see 5.2.2), "suppression capability of two-path long-echo" (see 5.2.16), "suppression of three-path long-echo" (see 5.2.17), "suppression 1 of channel disturbance under fixed receiving conditions" (see 5.2.18), "suppression 2 of channel disturbance under fixed receiving conditions" (see 5.2.19), "suppression of other multipath channel performance " (see 5.2.21), "suppression of echo outside the guard interval" (see 5.2.22) and "output gain of radio frequency loop circuit" (see 5.2.23) are added in the requirements of radio frequency demodulation and channel decoding;
— Annex C (Informative) Models of Other Multipath Channels is added (see Annex C).
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. The issuing body of this document shall not be held responsible for identifying any or all such patent rights.
This standard was proposed by the Ministry of Industry and Information Technology of the People's Republic of China.
This standard is under the jurisdiction of SAC/TC 242 (National Technical Commitee 242 on Audio, Video and Multimedia Systems and Equipment Standardization Administration of China).
The previous editions of this standard are as follows:
— GB/T 26684-2011.
Methods of Measurement for Digital Terrestrial Set-top Box
1 Scope
This standard specifies the measurement conditions, electrical performance measurement items and methods of measurement for digital terrestrial set-top box (hereinafter referred to as "set-top box") that supports the terrestrial digital TV receiving function specified in GB 20600-2006.
This standard is applicable to the standard definition and high defination set-top box that supports the terrestrial digital TV receiving function specified in GB 20600-2006.
2 Normative References
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB 3174 Specifications of PAL-D Television System
GB 20600-2006 Framing Structure, Channel Coding, and Modulation for Digital Television Terrestrial Broadcasting System
GB/T 22122-2008 Methods of Measurement of Surround Audio for Digital TV
GB/T 26270-2010 Standard Test Signals for Digital Television Receiving Equipment
GB/T 26681-2011 Technical Requirements and Methods of Measurement for Standard Testing Transmitter of Digital Terrestrial Television
GB/T 26683-2017 General Specification for Digital Terrestrial Set-top Box
GB/T 26685-2017 Methods of Measurement for Digital Terrestrial Set-top Box
SJ/T 11324-2006 Terminology of Digital Television Receiving Equipment
3 Terms, Definitions, Symbols and Abbreviations
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 Basic Requirements for Measurement
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℃ to 35℃;
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℃±2℃;
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
1 C=3780 0.4 16QAM PN945 Yes 720 — 9.626
2 C=1 0.8 4QAM PN595 — 720 No 10.396
3 C=3780 0.6 16QAM PN945 Yes 720 — 14.438
4 C=1 0.8 16QAM PN595 — 720 No 20.791
5 C=3780 0.8 16QAM PN420 Yes 720 — 21.658
6 C=3780 0.6 64QAM PN420 Yes 720 — 24.365
7 C=1 0.8 32QAM PN595 — 720 No 25.989
8 C=3780 0.8 16QAM PN945 Yes 720 — 19.251
9 C=3780 0.6 64QAM PN945 Yes 720 — 21.658
10 C=3780 0.8 64 PN420 Yes 720 — 32.486
11 C=1 0.8 4QAM-NR PN945 No 240 Yes 4.813
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
3 Spectrum analyzer Frequency range: 40MHz to 1GHz; average noise level: ≤ 150 dBc/Hz
4 Network analyzer Frequency range: 40MHz to 1GHz; reflection loss measurement precision: ≤0.1 dB; impedance: 75
5 Video analyzer Measure the baseband video signal level, frequency, delay, phase difference, etc.; bandwidth: ≥ 6 MHz
6 High defination video analyzer Analyze and measure the baseband video signal level, frequency, delay, phase difference, etc.; bandwidth: ≥ 30 MHz
7 Audio analyzer Achieve the functions of audio measurement amplifier, distortion meter and others, and has a 1 kHz, l/3 oct bandpass filter, and a A-weighted filter that meets O-type tolerance
8 Power meter Measurement precision 0.1W
9 Bitstream generator Bitstream required for the output test
10 Gaussian noise generator Noise bandwidth: ≥ 20 MHz; radio frequency output power (8MHz bandwidth): ≥ -50 dBm
11 Channel simulator Analog channel: ≥ 20 path; Doppler type, delay, amplitude, Doppler shift and phase of each channel are independent adjustable
12 Multiplexer Multi-input bitstream signal is digitally multiplexed and output as multi-program transmission stream
13 SI generator Edit and generate service information
14 Mixer Frequency range: 30MHz to 1GHz
15 Color monitor Conform with the signal aspect requirements of set-top box
16 Oscilloscope Bandwidth: ≥30MHz
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.
Foreword II
1 Scope
2 Normative References
3 Terms, Definitions, Symbols and Abbreviations
3.1 Terms and Definitions
3.2 Symbols
3.3 Abbreviations
4 Basic Requirements for Measurement
4.1 General Description
4.2 Test Signal
4.3 Measurement Mode
4.4 Measuring System and Test Apparatus
4.5 Standard Measurement Conditions
5 Measurement Items and Methods
5.1 System Block Diagram
5.2 Requirements of Radio Frequency Demodulation and Channel Decoding
5.3 Decoding Feature Requirements of Transport Stream
5.4 Performance Requriements of Baseband Video Output
5.5 Audio Output Characteristic
5.6 Functional Requirements
5.7 Power Supply Adaptability Requirements
5.8 Consumed Power
5.9 Standby Consumed Power
Annex A (Normative) Multipath Channel Model
Annex B (Normative) Acceptable Error Free
Annex C (Informative) Other Multipath Channel Model
