GB/T 20851 consists of the following five parts under the general title Electronic toll collection - Dedicated short range communication:
——Part 1: Physical layer;
—— Part 2: Data link layer;
——Part 3: Application layer;
——Part 4: Equipment application;
——Part 5: Test methods of the main parameters in physical layer.
This is part 5 of GB/T 20851.
This part is developed in accordance with the rules given in GB/T 1.1-2009.
This part replaces GB/T 20851.5-2007 Electronic toll collection - Dedicated short range communication - Part 5: Test methods of the main parameters in physical layer. In addition to editorial changes, the following main technical changes have been made with respect to GB/T 20851.5-2007:
——the test signal requirements are modified and added (see 5.2; 5.2 of Edition 2007);
——"Requirements for test state of equipment under test" is added (see 5.3);
——the expressions of test methods are modified (see 6.2, 6.3 and 6.4; 6.2, 6.3, 6.4, 6.5, 6.6, 6.7 and 6.8 of Edition 2007);
—— the test methods for receiving sensitivity, receiving bandwidth, maximum input signal power, cochannel interference rejection ratio, adjacent channel interference rejection ratio and blocking interference rejection ratio of roadside unit are added (see 6.2);
——the test methods for wakeup sensitivity, wakeup time, receiving sensitivity, receiving bandwidth, maximum input signal power, cochannel interference rejection ratio, adjacent channel interference rejection ratio and blocking interference rejection ratio of on board unit are added (see 6.3);
——the test method of initialization equipment for on board unit is modified and added (see 6.4; 6.4 of Edition 2007).
This part was proposed by and is under the jurisdiction of the National Technical Committee on Intelligent Transportation Systems of Standardization Administration of China (SAC/TC 268).
The previous edition replaced by this part is as follows:
——GB/T 20851.5-2007.
Electronic toll collection - Dedicated short range communication - Part 5: Test methods of the main parameters in physical layer
1 Scope
This part of GB/T 20851 specifies the recommended characteristics, test conditions and test methods of the main test equipment and accessories for the main parameters in physical layer of dedicated short range communication for electronic toll collection.
This part is applicable to electronic toll collection system for highways and urban roads, and may be used as a reference for fields of automated vehicle identification, vehicle access control system, etc.
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/T 9254 Information technology equipment - Radio disturbance characteristics - Limits and methods of measurement
GB/T 12190-2006 Method for measuring the shielding effectiveness of electromagnetic shielding enclosures
GB/T 20851.1-2019 Electronic toll collection - Dedicated short range communication - Part 1: Physical layer
3 Symbols and abbreviations
3.1 Symbols
For the purposes of this document, the following symbols apply.
D: the maximum diameter of antenna.
d: the distance between equipment under test and test antenna.
dBc: the ratio of representation power to carrier signal power.
dBm: the ratio of representation power to 1mW.
e.i.r.pcon: the spurious equivalent isotropically radiated power.
e.i.r.pmax: the maximum equivalent isotropically radiated power.
f1: the lower limit frequency of receiving bandwidth.
f2: the upper limit frequency of receiving bandwidth.
fc: the center frequency of signal emitted by signal source.
fTx: the nominal carrier frequency.
fTxa: the actual carrier frequency.
GRx: the gain of receiving antenna of equipment under test.
GT: the gain of test antenna.
GTx: the gain of transmitting antenna of equipment under test.
h: the height of equipment under test and test antenna from the ground.
PA: the test signal power of adjacent channel interference.
PB: the test signal power of blocking interference.
PC: the test signal power of co-channel interference.
Pcon: the spurious emission power.
Pcw: the single frequency signal power of the equipment under test.
Pcwo: the single frequency signal power of signal source and test antenna.
Pi,max: the maximum input signal power.
P0: the output power of signal source.
PR: the measured power of the signal received by the test antenna replacing the equipment under test.
RA: the adjacent channel interference rejection ratio.
RB: the blocking interference rejection ratio.
RC: the cochannel interference rejection ratio.
SRx: the receiving sensitivity.
SW: the wakeup sensitivity.
T0: the start time of sending wake-up signal.
TR: the start time of sending response signal.
TW: the wakeup time.
Δf: the frequency tolerance.
λ: the wavelength.
3.2 Abbreviations
For the purposes of this document, the following abbreviations apply.
OBU: On Board Unit
RBW: Resolution Bandwidth
RSU: Roadside Unit
VSWR: Voltage Standing-Wave Ratio
4 Recommended characteristics of main test equipment and accessories
4.1 Power meter
The recommended characteristics of power meter shall meet the following requirements:
a) power measurement range: -60~+20dBm;
b) frequency range: 10MHz~18GHz;
c) power measurement error: ±3%.
4.2 Frequency meter
The recommended characteristics of the frequency meter shall meet the following requirements:
a) frequency range: 10Hz~20GHz;
b) frequency measurement error: ±10×10-9.
4.3 Microwave signal source
The recommended characteristics of microwave signal source shall meet the following requirements:
a) frequency range: 250kHz~20GHz;
b) frequency precision: fc×100×10-9;
c) phase noise: < -98dBc/Hz@10GHz, 1kHz offset.
4.4 Spectrum analyzer
The recommended characteristics of spectrum analyzer shall meet the following requirements:
a) frequency range: 3Hz~26.5GHz;
b) dynamic range: ≥70dB;
c) resolution bandwidth: 10Hz~3MHz;
d) background noise: ≤ -140dBm/Hz.
4.5 Vector signal analyzer
The recommended characteristics of vector signal analyzer shall meet the following requirements:
a) frequency range: direct current~6GHz;
b) vector modulation analysis type: amplitude modulation, frequency modulation and phase modulation analysis.
4.6 Digital oscilloscope
The recommended characteristics of digital oscilloscope shall meet the following requirements:
a) bandwidth: 1GHz;
b) sampling rate: 2Gsa/s;
c) memory depth: 2M points per channel;
d) trigger mode: edge, code pattern, time/event delay and pulse width, etc.
4.7 Test antenna
The recommended characteristics of the test antenna shall meet the following requirements:
a) frequency range: 30MHz~20GHz;
b) polarization mode: linear polarization;
c) VSWR: < 1.5:1;
d) impedance: 50Ω;
e) gain: available.
5 Test conditions
5.1 Test site and configuration
5.1.1 Test site
The radiation test may be conducted in anechoic chamber or open field.
The minimum dimension of anechoic chamber shall meet the test requirements in 3m method, the shielding effectiveness shall meet the requirements of GB/T 12190-2006, and the normalized site attenuation shall meet the requirements of GB/T 9254.
When tested in an anechoic chamber, the equipment under test shall be within the quiet zone of anechoic chamber.
The normalized site attenuation of open area shall meet the requirements of GB/T 9254.
5.1.2 Configuration
5.1.2.1 Configuration of conduction test system
The conduction test system consists of equipment under test, test equipment and connecting accessories, wherein, the connecting accessories include connectors, attenuators, etc. The connecting accessories are determined according to the interface of equipment under test and the strength of signal under test. Refer to Figure 1 for configuration of conduction test system.
Figure 1 Configuration of conduction test system
5.1.2.2 Configuration of radiation test system
The radiation test system consists of equipment under test, test equipment and connecting accessories, wherein, the connecting accessories include coaxial cable, test antenna, connector, attenuator, etc. The connecting accessories are determined according to the interface of equipment under test and the strength of signal under test. Refer to Figure 2 for configuration of radiation test system.
Figure 2 Configuration of radiation test system
The distance between equipment under test and test antenna, d, shall conform to Equation (1):
(1)
The height of equipment under test and test antenna from the ground, h, conform to Equation (2):
h≥4D (2)
5.2 Test signal
The test system shall provide the following test signals:
a) test signal for bit rate, which is FM0-coded all-zero code modulated at the working frequency point;
b) interference test signals for cochannel and adjacent channel interference rejection ratios, which are modulated and uncoded pseudo-random binary sequence (PN9) signals with a cycle of 511 bits;
c) interference test signal for blocking interference rejection ratio, which is the continuous wave signal at a fixed frequency point out of the working frequency band (5725MHz~5850MHz) by (30MHz~20GHz);
d) wakeup response signal of OBU, which is the carrier signal transmitted in corresponding channel and lasting for 20ms.
5.3 Requirements for test state of equipment under test
5.3.1 RSU
The RSU under test shall be able to receive and transmit test signals according to the requirements of 5.2 and test demands, i.e., it is able to continuously transmit carrier, PN9 code and FM0-coded all-zero code modulated at working frequency point, and also able to extract the demodulated received data and clock signal and provide test points.
5.3.2 OBU
The OBU under test shall be able to receive and transmit test signals according to the requirements of 5.2 and test demands, i.e., it is able to transmit carrier, PN9 code and FM0-coded all-zero code modulated at the working frequency point, and send wakeup response signal after wakeup, and also able to extract the demodulated received data and clock signal and provide test points.
5.3.3 Initialization equipment for OBU
The initialization equipment for OBU under test shall be able to receive and transmit test signals according to the requirements of 5.2 and test demands. i.e., it is able to continuously transmit carrier, PN9 code and FM0-coded all-zero code modulated at working frequency point, and also able to extract the demodulated received data and clock signal and provide test points.
6 Test methods
6.1 General
For items with conduction test capability during test, conduction test method should be adopted.
6.2 RSU test
6.2.1 Carrier frequency and frequency tolerance
6.2.1.1 Test equipment
Frequency counter or spectrum analyzer with counter is used as the equipment for carrier frequency and frequency tolerance tests.
6.2.1.2 Test steps
This test may be completed under conduction or radiation test conditions, of which the steps are as follows:
a) set the working frequency of the transmitter of the equipment under test and set the equipment under test in non-modulation state, i.e., carrier state;
b) measure the actual carrier frequency fTxa of the equipment under test with frequency meter or spectrum analyzer with counter;
c) calculate the frequency tolerance Δf of the carrier frequency using Equation (3):
?f=|f_"Tx" -f_"Txa" |/(f_"Tx" ×10^6 ) (3)
d) repeat the above steps to test other carrier frequencies and their frequency tolerances.
6.2.2 Occupied bandwidth
6.2.2.1 Test equipment
Spectrum analyzer is used as the equipment for occupied bandwidth test.
6.2.2.2 Test steps
This test may be completed under conduction or radiation test conditions, of which the steps are as follows:
a) set the working frequency of the transmitter of the equipment under test and set the equipment under test in the state of continuously transmitting test signals;
b) set the transmitting power of the equipment under test to the maximum;
c) measure the occupied bandwidth of the test signal with spectrum analyzer;
d) repeat the above steps to measure the occupied bandwidth at other carrier frequencies.
6.2.3 Equivalent isotropically radiated power
6.2.3.1 Conduction test
6.2.3.1.1 Test equipment
Power meter is used as the equipment for conduction test of equivalent isotropically radiated power.
6.2.3.1.2 Test steps
Test steps are as follows:
a) set the working frequency of the transmitter of the equipment under test and set the equipment under test in non-modulation state, i.e., carrier state;
b) set the transmitting power of the equipment under test to the maximum;
c) use power meter to measure the power Pcw of transmitting antenna port of the equipment under test, and calculate the maximum equivalent isotropically radiated power e.i.r.pmax using Equation (4):
e.i.r.pmax=Pcw×GTx (4)
d) repeat the above steps to test the equivalent isotropically radiated power at other carrier frequencies.
6.2.3.2 Radiation test
6.2.3.2.1 Test equipment
The equipment for radiation test of equivalent isotropically radiated power includes power meter and microwave signal source.
6.2.3.2.2 Test steps
Test steps are as follows:
a) the same as 6.2.3.1.2 a);
b) the same as 6.2.3.1.2 b);
c) measure the power Pcw with power meter;
d) under the same test conditions, replace the equipment under test with a microwave signal source and a test antenna with known gain GT, measure the power Pcwo with a power meter, and adjust the output power P0 of the microwave signal source until Pcwo is equal to Pcw;
e) calculate the maximum equivalent isotropically radiated power e.i.r.pmax using Equation (5):
e.i.r.pmax=P0×GT (5)
f) the same as 6.2.3.1.2 d).
6.2.4 Spurious emission
6.2.4.1 Conduction test
6.2.4.1.1 Test equipment
spectrum analyzer is used as the equipment for conduction test of spurious emission.
6.2.4.1.2 Test steps
Test steps are as follows:
a) set the working frequency of the transmitter of the equipment under test and set the equipment under test in the state of continuously transmitting test signals;
b) set the transmitting power of the equipment under test to the maximum;
c) set the modulation factor of the equipment under test to the maximum within its allowable range;
d) set RBW of spectrum analyzer in each test frequency band respectively and measure the spurious emission power Pcon of this frequency band, as required by Clauses 6 and 7, CB/T 20851.1-2019;
e) calculate the spurious equivalent isotropically radiated power e.i.r.pcon of this frequency band using Equation (6):
e.i.r.pcon=Pcon×GTx (6)
f) repeat the above steps to measure the spurious emissions at other carrier frequencies.
6.2.4.2 Radiation test
6.2.4.2.1 Test equipment
The equipment for radiation test of spurious emission includes spectrum analyzer and microwave signal source.
6.2.4.2.2 Test steps
Test steps are as follows:
a) the same as 6.2.4.1.2 a);
b) the same as 6.2.4.1.2 b);
c) the same as 6.2.4.1.2 c);
d) set RBW of spectrum analyzer in each test frequency band respectively and measure the spurious emission power Pcon in each frequency band, as required by Clauses 6 and 7, GB/T 20851.1-2019;
e) under the same test conditions, replace the equipment under test with a microwave signal source and a test antenna with known gain GT, measure the power with spectrum analyzer, and adjust the output power P0 of each frequency band of the microwave signal source until the power measured with spectrum analyzer is equal to Pcon;
f) calculate the spurious equivalent isotropically radiated power e.i.r.pcon of each frequency band using Equation (7):
e.i.r.pcon=P0×GT (7)
g) repeat the above steps to test the spurious emission of each frequency band at other carrier frequencies.
6.2.5 Modulation mode and modulation factor
6.2.5.1 Test equipment
Vector signal analyzer is used as the equipment for modulation mode and modulation factor tests.
6.2.5.2 Test steps
This test may be completed under conduction or radiation test conditions. Test steps are as follows:
a) set the working frequency of the transmitter of the equipment under test and set the equipment under test in the state of continuously transmitting test signals;
b) set the transmitting power of the equipment under test to the maximum;
c) set the modulation factor of the equipment under test to the minimum within its allowable range;
d) use the vector signal analyzer to measure the modulation factor of the equipment under test;
e) change the working frequency of the transmitter of the equipment under test, while keeping the rest of settings unchanged, and test the modulation factor at other carrier frequencies;
f) set the modulation factor of the equipment under test to the maximum within its allowable range;
g) use the vector signal analyzer to measure the modulation factor of the equipment under test;
h) change the working frequency of the transmitter of the equipment under test, while keeping the rest of settings unchanged, and test the modulation factor at other carrier frequencies;
6.2.6 Bit rate
6.2.6.1 Test equipment
Digital oscilloscope is used as the equipment for bit rate test.
Foreword i
1 Scope
2 Normative references
3 Symbols and abbreviations
4 Recommended characteristics of main test equipment and accessories
5 Test conditions
6 Test methods
