CN113484549B - EVM measuring method suitable for OTA test - Google Patents
EVM measuring method suitable for OTA test Download PDFInfo
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Abstract
The invention discloses an EVM measuring method suitable for OTA test, which comprises the following steps: the method comprises the following steps of firstly, building different error vector magnitude measurement systems, wherein each error vector magnitude measurement system comprises a first measurement system, a second measurement system and a third measurement system; step two, measuring the error vector magnitude under different error vector magnitude measuring systems; step three, obtaining error vector magnitude measurement values of different error vector magnitude measurement systems; and step four, calculating the error vector amplitude value caused by the device to be measured according to the error vector amplitude measured values obtained under different measuring systems. The measuring method is suitable for OTA testing conditions, vector modulation errors caused by instrument factors and vector modulation errors caused by environment factors are calculated and obtained by building three testing links, and the two interferences are eliminated by vector difference calculation, so that the vector modulation errors of the device to be tested are more accurate through measurement and calculation.
Description
Technical Field
The invention relates to the technical field of radio frequency terminal testing in the field of wireless communication, in particular to an EVM measuring method suitable for OTA testing.
Background
Error Vector Magnitude (EVM) is the Vector difference between an ideal reference signal and a measurement signal in a given moment, is an important index for evaluating the signal quality after Vector modulation in a communication system, and can intuitively reflect the Magnitude Error and the phase Error between the measurement signal and the reference signal. The error vector magnitude can be calculated by comparing the difference between the vector values of the measurement signal and the reference signal, as shown in fig. 1.
The Air interface radiation (OTA) test is to simulate The wireless transmission environment in a microwave darkroom and test The performance of The device to be tested in The simulated wireless transmission environment. The new generation of 5G wireless communication technology includes a 5G active antenna system, the 5G active antenna system integrates an antenna and a radio frequency RRU module, and an output port of the radio frequency RRU module becomes an internal interface of the system, so that the EVM measurement of a device to be measured cannot be performed by a conventional conduction method but by a far-field OTA test method.
For EVM testing of Vector modulated signals, measurements must be made on the transmitter and receiver sections using a Vector Signal Generator (VSG) and a Vector Signal Analyzer (VSA), respectively. Under the conditions of different output power and receiving power, nonlinear components (a mixer and an amplifier) in a vector signal generator and a vector signal analyzer can introduce different equipment measurement errors to the EVM measurement of a device to be measured, so that the EVM measurement of the device to be measured cannot be accurately performed, and particularly in OTA (over the air) test, due to the fact that the insertion loss of a test system is extremely large, the power of a signal received by a VSA (voltage-dependent amplifier) is low, a preamplifier inside the VSA is required to amplify the received signal, the nonlinear influence from the equipment is introduced, and the EVM measurement of the device to be measured is interfered.
In the prior art, error vector amplitude compensation is performed on an EVM test instrument only by a conduction method, and measurement and compensation of error vector amplitude errors caused by the EVM test instrument under an OTA test condition are lacked (publication No. CN 102546036 a, an error vector amplitude compensation method); in addition, only the error vector amplitude error introduced by the vector signal analyzer VSA is considered, but the error vector amplitude error also introduced by the vector signal generator VSG is not considered, so that the measurement result is inaccurate, and an instrument error exists (CN 110518988A, an apparatus and a method for measuring a device vector modulation error).
Disclosure of Invention
In view of the above drawbacks of the prior art, an object of the present invention is to provide an error vector magnitude measuring method under an OTA test condition, which is used to solve the problem that the EVM measurement result is inaccurate due to instrument factors and environmental factors under the OTA test condition, so as to measure and calculate an accurate EVM value of a device under test.
The invention is realized by at least one of the following technical schemes.
An EVM measurement method suitable for OTA test comprises the following steps:
the method comprises the following steps of firstly, constructing different error vector magnitude measurement systems, wherein each error vector magnitude measurement system comprises a first measurement system, a second measurement system and a third measurement system;
step two, measuring the error vector magnitude under different error vector magnitude measuring systems;
step three, obtaining error vector magnitude measured values of different error vector magnitude measuring systems;
and step four, calculating the error vector amplitude value caused by the device to be measured according to the error vector amplitude measured values obtained by different measuring systems.
Preferably, the first measurement system comprises a first vector signal generator VSG, a first vector signal analyzer VSA, a first radio frequency cable No. 1, a first radio frequency cable No. 2, a first test antenna No. 1 and a first test antenna No. 2;
the second measurement system comprises a second vector signal generator VSG, a second vector signal analyzer VSA, a second No. 1 radio frequency cable, a second No. 2 radio frequency cable, a second test antenna and a device to be tested DUT;
the third measurement system comprises a third vector signal generator VSG, a third vector signal analyzer VSA, a third No. 1 radio frequency cable and a third No. 2 radio frequency cable.
Preferably, the performance and the appearance of the first test antenna No. 1, the first test antenna No. 2 and the second test antenna are completely consistent; the first No. 1 radio frequency cable, the first No. 2 radio frequency cable, the second No. 1 radio frequency cable, the second No. 2 radio frequency cable, the third No. 1 radio frequency cable and the third No. 2 radio frequency cable are isometric cables of the same type, and the performance and the appearance are completely consistent.
Preferably, in the first measurement system, the direct measurement value of the EVM is represented by:
wherein EVM OTA,S1 Is a direct measure of EVM under the first measurement System, P TX1 Is the magnitude of the power of the signal transmitted by the first vector signal generator VSG in dBm, P RX1 The value of the power of the received signal, in dBm,to transmit at a signal power of P TX1 Received signal power of P RX1 Under the condition that the error vector magnitude jointly introduced by the first vector signal generator VSG and the first vector signal analyzer VSA,the error vector magnitude introduced for the first test antenna No. 1 under the first measurement system OTA test condition,error vector magnitude introduced for the No. 2 first test antenna under the OTA test condition of the first measurement system;
in the second measurement system, the direct measurement value of the EVM is represented as:
wherein EVM OTA,S2 Is a direct measure of EVM under the second measurement system,for transmitting a signal with a power P at a second vector signal generator VSG TX2 Under the condition, the error vector amplitude introduced by the device to be tested,the error vector magnitude introduced by a second test antenna under the OTA test condition of a second measurement system;representing the magnitude of the error vector introduced by the rf module of the device under test,representing the magnitude of the error vector introduced by the antenna module of the device under test,anderror proper amplitude EVM (error variation modeling) jointly forming instrument to be measured DUT (P TX2 )。
In the third measurement system, the direct measurement of the EVM is represented as:
wherein EVM OTA,S3 Is a direct measure of EVM under a third measurement system, P RX3 The magnitude of the power of the transmitted signal, P, for the third vector signal generator VSG TX3 The power of the VSA receiving signal of the third vector signal analyzer is measured by three measuring systems to obtain the direct measurement value EVM of the EVM OTA,S1 、EVM OTA,S2 、EVM OTA,S3 。
Preferably, the distance L1 measured by the first measurement system is the same size as the distance L2 measured by the second measurement system.
Preferably, the VSG emission signal power of each measurement system vector signal generator is consistent, P TX1 =P TX2 =P TX3 (ii) a Keeping the VSA received signal power of each measurement system consistent, P RX1 =P RX2 =P RX3 。
preferably, the first measurement system operates as follows:
setting a first vector signal generator VSG to output a digital modulation signal with output power P1; opening a first vector signal analyzer VSA, and setting analysis signal parameters of the first vector signal analyzer VSA, so that the first vector signal analyzer VSA can normally demodulate a received signal, and the power of the received signal is P2; recording the EVM value measured by the VSA of the first vector signal analyzer as the EVM OTA,S1 。
Preferably, the second test system operates as follows:
setting a second vector signal generator VSG to output a digital modulation signal with the output power of P1; opening a second vector signal analyzer VSA, and setting analysis signal parameters of the second vector signal analyzer VSA, so that the second vector signal analyzer VSA can normally demodulate a received signal, and the power of the received signal is P3; adjusting the attenuator of the second vector signal analyzer VSA to be Gatt1(Gatt1 ≈ P3-P2), so that the power of the signal received by the second vector signal analyzer VSA is equal to P2 after passing through the attenuator; recording the EVM value obtained by the VSA measurement of the current second vector signal analyzer as EVM OTA,S2 。
Under the third test system, the digital modulation signal generated by the third vector signal generator VSG directly enters the receiving port of the third vector signal analyzer VSA through the third radio frequency cable No. 1 and the third radio frequency cable No. 2 in a conduction method.
The third test system operates as follows:
setting a third vector signal generator VSG to output a digital modulation signal and output power P1; opening the third vector signal analyzer VSA, and setting the analysis signal parameters of the third vector signal analyzer VSA to enable the third vector signal analyzer VSA to analyze the signal parametersObtaining that the third vector signal analyzer VSA can normally demodulate a received signal, wherein the power of the received signal is P4; adjusting the attenuator of the third vector signal analyzer VSA to Gatt2, so that the power of the signal received by the third vector signal analyzer VSA is equal to P2 after passing through the attenuator Gatt2(Gatt2 is approximately equal to P4-P2); recording the EVM value measured by the VSA of the current third vector signal analyzer as the EVM OTA,S3 。
And substituting direct EVM measurement values obtained by measurement under the three measurement system conditions into a formula (4) to obtain an EVM measurement value of the device to be measured.
The measuring method is suitable for OTA testing conditions, vector modulation errors caused by instrument factors and vector modulation errors caused by environment factors are calculated and obtained by building three testing links, and the two interferences are eliminated by vector difference calculation, so that the vector modulation errors of the device to be tested are more accurate through measurement and calculation.
Compared with the prior art, the invention has the beneficial effects that:
an EVM measuring method based on OTA test conditions is provided for an integrated instrument to be tested at the front end of an antenna or a multi-channel instrument to be tested. Compared with the EVM measuring method applied under the conduction method condition, the invention is suitable for testing the instruments to be tested of a plurality of receiving and transmitting channels under the OTA measuring condition, thereby improving the EVM testing speed and leading the testing condition to be closer to the actual working condition of the instruments to be tested.
Drawings
FIG. 1 is a schematic diagram of the definition of vector modulation errors involved in the method of the present invention;
FIG. 2 is a schematic view of a first measurement system according to an embodiment of the present invention;
FIG. 3 is a schematic view of a second measurement system according to an embodiment of the present invention;
FIG. 4 is a schematic view of a third measurement system according to an embodiment of the present invention;
FIG. 5 is an EVM measurement flow diagram according to an embodiment of the present invention;
fig. 6 is a structural diagram of a DUT device under test according to embodiment 3 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail by the following examples.
Example 1:
an EVM measurement method suitable for OTA test comprises the following steps:
step one, EVM measuring systems of different building modes say; the EVM measuring system comprises a first measuring system, a second measuring system and a third measuring system;
the first measurement system is constructed in a manner shown in fig. 2, and S1 represents that the first measurement system S1 includes a first vector signal generator VSG, a first vector signal analyzer VSA, a first radio frequency cable No. 1, a first radio frequency cable No. 2, a first test antenna No. 1, and a first test antenna No. 2. The first vector signal generator VSG is connected with the first test antenna No. 1 through a first No. 1 radio frequency cable, and a modulation signal generated by the first vector signal generator VSG is transmitted to a free space through the first test antenna No. 1; the first vector signal analyzer VSA is connected with a first test antenna 2 through a first 2 # radio frequency cable, the horizontal distance between the 1 # aperture plane of the first test antenna and the 2 # aperture plane of the first test antenna is L, and the 2 # test antenna transmits the received modulation signal to the VSA for signal demodulation;
the second measurement system is constructed in a manner as shown in fig. 3, and the second measurement system S2 includes a second vector signal generator VSG, a second vector signal analyzer VSA, a second radio frequency cable No. 1, a second radio frequency cable No. 2, a second test antenna, and a device under test DUT. The second vector signal generator VSG is connected with a DUT (device under test) through a second No. 1 radio frequency cable, and a modulation signal generated by the second vector signal generator VSG is transmitted to a free space through the DUT; the second vector signal analyzer VSA is connected with a second test antenna through a second No. 2 radio frequency cable, the horizontal distance between the antenna aperture plane of the DUT and the aperture plane of the second test antenna is L, and the second test antenna transmits the received modulation signal to the VSA for signal demodulation;
the third measurement system is constructed in a manner as shown in fig. 4, and the third measurement system S3 includes a third vector signal generator VSG, a third vector signal analyzer VSA, a third radio frequency cable No. 1, and a third radio frequency cable No. 2. The modulation signal generated by the third vector signal generator VSG passes through the third radio frequency cable No. 1 and the third radio frequency cable No. 2 to reach a receiving port of a third vector signal analyzer VSA, and the third vector signal analyzer VSA demodulates the received signal;
in the measurement systems S1, S2, and S3, the performance and the shape of the first test antenna No. 1, the first test antenna No. 2, and the second test antenna are completely consistent; the first No. 1 radio frequency cable, the first No. 2 radio frequency cable, the second No. 1 radio frequency cable, the second No. 2 radio frequency cable, the third No. 1 radio frequency cable and the third No. 2 radio frequency cable are all identical isometric cables;
step two, establishing the relation between instrument factors, environment factors and EVM;
in the first measurement system, the direct measurement of the EVM is represented as:
wherein EVM OTA,S1 Is a direct measurement of EVM under the first measurement system, P TX1 Is the magnitude of the power of the signal transmitted by the first vector signal generator VSG in dBm, P RX1 The value of the power of the received signal, in dBm,to transmit at a signal power of P TX1 Received signal power of P RX1 Under the condition that the error vector magnitude jointly introduced by the first vector signal generator VSG and the first vector signal analyzer VSA,for the error vector magnitude introduced by the first test antenna No. 1 with OTA test distance L,test for the first test antenna No. 2 under the condition of distance L for OTAThe magnitude of the introduced error vector is that the first test antenna No. 1 and the first test antenna No. 2 are identical antennas, so thatSize equal to
In the second measurement system, the direct measurement value of the EVM is represented as:
wherein EVM OTA,S2 Is a direct measurement of the EVM under the second measurement system,for transmitting a signal with a power P at a second vector signal generator VSG TX2 Under the condition, the error vector magnitude introduced by the device to be tested.Representing the power of the transmitted signal at the second vector signal generator VSG as P TX2 Under the condition, the error vector magnitude introduced by the radio frequency module of the device to be tested,the error vector magnitude introduced by the antenna module of the device under test is represented, and the error vector magnitude together form the proper error magnitude of the instrument under test, as expressed by the formula (3).
In the third measurement system, the direct measurement value of the EVM is represented as:
wherein EVM OTA,S3 Is a direct measure of EVM under the third measurement system.
The EVM direct measurement value EVM is obtained through the measurement of the three measurement systems OTA,S1 、EVM OTA,S2 、EVM OTA,S3 The VSG transmitting power P in the vector signal generator is obtained through calculation of formulas (1) to (4) TX Under the condition of EVM measured value of the element to be measuredExpressed as:
step three, error vector magnitude EVM measurement is carried out under different measurement systems;
under a first measurement system, a digital modulation signal generated by a first vector signal generator VSG is converted into an electromagnetic wave propagating in a free space through a first test antenna No. 1 and is received by a first test antenna No. 2 with a distance L, wherein L is the horizontal distance between the caliber plane No. 1 of the first test antenna and the caliber plane No. 2 of the first test antenna, and the size of L must reach the far-field condition distance of the first test antenna No. 2,λ is the wavelength of the electromagnetic wave, and D is the aperture of the first test antenna No. 2. The first measurement system operates as follows:
setting a first vector signal generator VSG to output a digital modulation signal with output power P1; opening a first vector signal analyzer VSA, and setting analysis signal parameters of the first vector signal analyzer VSA, so that the first vector signal analyzer VSA can normally demodulate a received signal, and the power of the received signal is P2; recording the EVM value measured by the VSA of the first vector signal analyzer as the EVM OTA,S1 。
Under an S2 test system, a digital modulation signal generated by a second vector signal generator VSG is converted into an electromagnetic wave which is propagated in a free space through a device to be tested DUT, and the electromagnetic wave is received by a second measuring antenna No. 2 with a distance L, wherein L is the horizontal distance between the antenna aperture plane of the device to be tested DUT and the second measuring antenna aperture plane; the second vector signal generator VSG decomposes the received signal into I and Q component signals, and the I and Q component signals obtained by decomposition are compared with I in an ideal demodulation state to obtain a required EVM direct measurement value.
The S2 test system operates as follows:
setting a second vector signal generator VSG to output a digital modulation signal with the output power of P1; opening a second vector signal analyzer VSA, and setting analysis signal parameters of the second vector signal analyzer VSA, so that the second vector signal analyzer VSA can normally demodulate a received signal, and the power of the received signal is P3; adjusting the attenuator of the second vector signal analyzer VSA to Gatt1(Gatt1 is approximately equal to P3-P2), so that the power of the signal received by the second vector signal analyzer VSA is approximately equal to P2 after the attenuator; recording the EVM value measured by the VSA of the current second vector signal analyzer as the EVM OTA,S2 。
Under the test system of S3, the digital modulation signal generated by the third vector signal generator VSG enters the receiving port of the third vector signal analyzer VSA directly through the third No. 1 radio frequency cable and the third No. 2 radio frequency cable in a conduction method.
The S3 test system operates as follows:
setting a third vector signal generator VSG to output a digital modulation signal, and outputting power P1; opening a third vector signal analyzer VSA, and setting analysis signal parameters of the third vector signal analyzer VSA, so that the third vector signal analyzer VSA can normally demodulate a received signal, and the power of the received signal is P4; adjusting the attenuator of the third vector signal analyzer VSA to Gatt2, so that Gatt2 is approximately equal to P4-P2, and the power of the signal received by the third vector signal analyzer VSA is approximately equal to P2 after passing through the attenuator; recording the EVM value measured by the VSA of the current third vector signal analyzer as EVM OTA,S3 。
Substituting EVM direct measurement values measured under the conditions of the three measurement systems into a formula (5), and calculating to eliminate vector modulation errors caused by instrument factors and vector modulation errors caused by environmental factors to obtain the vector modulation errors of the device to be measuredThe measuring mode of the invention eliminates the influence of instrument factors and environmental factors on the EVM measurement of the device to be measured under the OTA condition.
Example 2:
according to the schematic diagrams of the first measurement system (S1), the second measurement system (S2) and the third measurement system (S3) in fig. 2, fig. 3 and fig. 4, the EVM measurement system is built, the system parameters of the vector signal generator and the vector signal analyzer are set, and the specific configuration of the software and hardware conditions of the device is shown in table 1 and table 2:
(1) vector signal generator SMW200A
TABLE 1 SMW200A parameter configuration diagram
(2) Vector signal analyzer R & S FSW43
TABLE 2R & S FSW43 parameter configuration diagram
(3) The first test antenna 1 and the first test antenna 2 of the three measurement systems are respectively an English-Union microwave multi-octave horn antenna LB-180400-KF;
as shown in fig. 5, the method for operating EVM measurement suitable for OTA testing includes the following steps:
TABLE 3 Experimental measurements and calculations based on the procedure of step 101
TABLE 4 Experimental measurements and calculations based on the procedure of step 102
TABLE 5 Experimental measurements and calculations based on the procedure of step 103
For the present embodiment, the EVM is measured through steps 101 to 103 OTA,S1 =7.88%,EVM OTA,S2 =9.53%,EVM OTA,S3 7.20%. The vector error of the device to be tested under the OTA test condition is obtained by calculation of a formula (4)
Example 3:
in order to verify the accuracy of the EVM measurement result of the present invention, the DUT used in embodiment 2 is composed of three parts as shown in fig. 6: the device comprises a DUT radio frequency module, a DUT antenna and a DUT radio frequency cable; the DUT radio frequency cable is connected with the DUT radio frequency module and the DUT antenna, and the DUT radio frequency module and the DUT antenna can be separated by removing the DUT radio frequency cable, wherein the DUT radio frequency module is composed of an LNA power amplifier module, the DUT antenna is a multi-octave horn antenna LB-180400-KF of Union microwave and is consistent with the antenna adopted in embodiment 2, and the DUT radio frequency cable is consistent with the radio frequency cable adopted in embodiment 2.
Since the DUT antenna is identical to that used in example 2, it can be said that Calculating through formula (1) to formula (4) to obtain VSG transmitting power P in the vector signal generator TX Under the condition, the EVM value of the DUT radio frequency module in the device to be testedExpressed as:
the data measured in the embodiment 2 is calculated by the formula (5) to obtain the vector error caused by the DUT radio frequency module of the device to be tested under the OTA test condition
EVM measurement is carried out on the DUT radio frequency module by adopting a conduction method, and the measurement result is 5.23 percent
For the DUT rf module, the conduction EVM measurement results are compared with the EVM measurement results of the present invention, and the data pair ratio is shown in table 6:
TABLE 6 comparison of the EVM measurements by the conductive method with those of the present invention
conduction-EVM measurement | EVM measurement of the invention | Difference between them | |
EVM(%) | 5.23 | 5.36 | 0.13 |
The test result in embodiment 3 shows that, in the OTA test system, three different hardware connection modes are used to obtain the error vector value of the DUT radio frequency module in the instrument to be tested separately, and the difference between the result obtained by the conduction method measurement and the result obtained by the conduction method measurement is 0.13%, which can be considered to be within the experimental error range.
The embodiment adopts an EVM measuring method suitable for the OTA test environment. Through three different hardware connection modes, equipment factors and the influence of environmental factors on the measurement of the EVM of the device to be measured are eliminated, and the error vector magnitude caused by the device to be measured is obtained through calculation. A new EVM measuring method is provided for the device to be measured with the antenna and the radio frequency module integrated.
Although the present invention has been described with reference to the preferred embodiments, it is not intended to limit the present invention, and those skilled in the art can make possible variations and modifications of the present invention using the method and the technical contents disclosed above without departing from the spirit and scope of the present invention, and therefore, any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention are all within the scope of the present invention.
Claims (7)
1. An EVM measuring method suitable for OTA test is characterized by comprising the following steps:
the method comprises the following steps of firstly, constructing different error vector magnitude measurement systems, wherein each error vector magnitude measurement system comprises a first measurement system, a second measurement system and a third measurement system; the first measurement system comprises a first vector signal generator VSG, a first vector signal analyzer VSA, a first No. 1 radio frequency cable, a first No. 2 radio frequency cable, a first test antenna No. 1 and a first test antenna No. 2; the second measurement system comprises a second vector signal generator VSG, a second vector signal analyzer VSA, a second No. 1 radio frequency cable, a second No. 2 radio frequency cable, a second test antenna and a device to be tested DUT; the third measurement system comprises a third vector signal generator VSG, a third vector signal analyzer VSA, a third No. 1 radio frequency cable and a third No. 2 radio frequency cable;
step two, measuring the error vector magnitude under different error vector magnitude measuring systems;
step three, obtaining error vector magnitude measurement values of different error vector magnitude measurement systems;
step four, calculating the error vector amplitude value caused by the device to be measured according to the error vector amplitude measured values obtained under different measurement systems, wherein in the first measurement system, the direct measured value EVM of the EVM OTA,s1 Expressed as:
wherein EVM OTA,S1 Is a direct measure of the EVM under the first measurement system, P TX1 Is the magnitude of the power of the signal transmitted by the first vector signal generator VSG in dBm, P RX1 The value of the power of the received signal, in dBm,to transmit at a signal power of P TX1 Received signal power of P RX1 Under the condition that the error vector magnitude jointly introduced by the first vector signal generator VSG and the first vector signal analyzer VSA,the error vector magnitude introduced for the first test antenna No. 1 under the first measurement system OTA test condition,the error vector magnitude introduced for the first test antenna No. 2 under the OTA test condition of the first measurement system;
in a second measuring system, direct measurement of EVM OTA,S2 Expressed as:
wherein EVM OTA,S2 Is a direct measure of EVM under the second measurement system,for transmitting at the second vector signal generator VSGPower of transmitted signal is P TX2 Under the condition, the error vector amplitude introduced by the device to be tested,the error vector magnitude introduced by the second test antenna under the OTA test condition of the second measurement system;representing the magnitude of the error vector introduced by the rf module of the device under test,representing the magnitude of the error vector introduced by the antenna module of the device under test,anderror proper amplitude EVM (error vector magnitude) jointly forming instrument to be measured DUT (P TX2 );
Direct measurement of EVM in a third measurement System, EVM OTA,S3 Expressed as:
wherein EVM OTA,S3 Is a direct measure of EVM under a third measurement system, P RX3 Magnitude of power of signal transmitted for third vector signal generator VSG, P TX3 The power of the VSA receiving signal of the third vector signal analyzer is measured by three measuring systems to obtain the direct measurement value EVM of the EVM OTA,S1 、EVM OTA,S2 、EVM OTA,S3 ;
2. the EVM measuring method suitable for OTA test according to claim 1, wherein the first test antenna No. 1, the first test antenna No. 2 and the second test antenna have completely consistent performance and appearance; the first No. 1 radio frequency cable, the first No. 2 radio frequency cable, the second No. 1 radio frequency cable, the second No. 2 radio frequency cable, the third No. 1 radio frequency cable and the third No. 2 radio frequency cable are isometric cables of the same type, and the performance and the appearance are completely consistent.
3. The EVM measurement method applicable to OTA tests according to claim 2, characterized in that the distance L1 measured by the first measurement system is the same size as the distance L2 measured by the second measurement system.
4. An EVM measurement method suitable for OTA tests according to claim 3, characterized in that each measurement system vector signal generator VSG has a uniform transmission signal power, P TX1 =P TX2 =P TX3 (ii) a Keeping VSA receiving signal power of each measuring system consistent, P RX1 =P RX2 =P RX3 。
5. The EVM measurement method applicable to OTA testing according to claim 4, wherein the first measurement system operates as follows:
setting a first vector signal generator VSG to output a digital modulation signal with output power P1; opening a first vector signal analyzer VSA, and setting analysis signal parameters of the first vector signal analyzer VSA, so that the first vector signal analyzer VSA can normally demodulate a received signal, and the power of the received signal is P2; recording the EVM value measured by the VSA of the first vector signal analyzer as the EVM OTA,S1 。
6. The EVM measurement method applicable to OTA testing according to claim 5, wherein the second testing system operates as follows:
setting a second vector signal generator VSG to output a digital modulation signal with the output power of P1; opening a second vector signal analyzer VSA, and setting analysis signal parameters of the second vector signal analyzer VSA, so that the second vector signal analyzer VSA can normally demodulate a received signal, and the power of the received signal is P3; adjusting the attenuator of the second vector signal analyzer VSA to Gatt1(Gatt1 ≈ P3-P2) so that the power of the signal received by the second vector signal analyzer VSA is equal to P2 after the attenuator; recording the EVM value measured by the VSA of the current second vector signal analyzer as the EVM OTA,S2 。
7. A method of EVM measurement suitable for OTA testing according to claim 6, wherein the third testing system operates as follows:
setting a third vector signal generator VSG to output a digital modulation signal and output power P1; opening a third vector signal analyzer VSA, and setting analysis signal parameters of the third vector signal analyzer VSA, so that the third vector signal analyzer VSA can normally demodulate a received signal, and the power of the received signal is P4; adjusting the size of an attenuator of the third vector signal analyzer VSA to Gatt2, so that Gatt2(Gatt2 ≈ P4-P2) can ensure that the power of a signal received by the third vector signal analyzer VSA is equal to P2; recording the EVM value measured by the VSA of the current third vector signal analyzer as EVM OTA,S3 。
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