CN110708131A - Circuit structure and method for realizing rapid calibration of transmitter power of MIMO channel simulator based on digital-to-analog block division - Google Patents
Circuit structure and method for realizing rapid calibration of transmitter power of MIMO channel simulator based on digital-to-analog block division Download PDFInfo
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Abstract
The invention relates to a circuit structure for realizing the rapid calibration of the transmitter power of an MIMO channel simulator based on digital-analog block division, which comprises a digital-analog converter unit, a digital-analog converter unit and a control unit, wherein the digital-analog converter unit is used for converting a digital signal of a channel model into an analog signal and regulating the output power; the analog circuit module comprises a first filter, a first frequency mixer, a second filter, a second frequency mixer, a numerical control attenuator and a large step attenuator which are sequentially connected, and the analog circuit module further comprises a first local oscillator and a second local oscillator. The invention also relates to a method for realizing the rapid calibration of the transmitter power of the MIMO channel simulator based on the digital-analog block division. The circuit structure and the method for realizing the rapid calibration of the transmitter power of the MIMO channel simulator based on the digital-analog block type solve the problem that the time for calibrating the transmitter power of the large-scale MIMO channel simulator is too long. By using the method, the calibration time of the single-channel simulator transmitter is increased by 10-20 times, and the method is particularly suitable for power calibration of a large-scale MIMO transmitter.
Description
Technical Field
The invention relates to the technical field of instrument measurement and calibration, in particular to the field of transmitter power measurement and calibration, and specifically relates to a circuit structure and a method for realizing rapid calibration of transmitter power of an MIMO channel simulator based on digital-analog block division.
Background
The channel simulator is a testing instrument for simulating relevant characteristics such as path loss, multipath fading and the like in a wireless environment, and realizes the function of verifying the influence of the wireless environment on the system performance under various complex scenes of system equipment and terminals in a laboratory. With the rapid advance of the development and industrialization of 5G mobile communication technology, the number of channels to be simulated in real time in a 5G MIMO channel simulator is increased by several orders of magnitude (e.g. 128x4) compared to the multi-antenna of MxN in the 4G era (e.g. 4x 4).
In the MIMO channel simulator transmitter system, the transmitter system mainly includes a main control unit, a baseband unit, a digital-to-analog converter unit group and a transmitter, and the configuration of the transmitter system is as shown in fig. 1. Wherein the transmitter comprises (M + N) transmission channels.
The digital-analog block-type fast calibration method for the transmitter power of the MIMO channel simulator is mainly aimed at a multi-channel super-heterodyne transmitter, and a main architecture block diagram of the transmitter power is shown in figure 2. When the channel simulator transmitter works, the baseband unit converts the low-frequency signal superposed with the channel model into an analog intermediate-frequency signal through the digital-to-analog converter unit and transmits the analog intermediate-frequency signal to the transmitter, and the transmitter expands the frequency to a full frequency range supported by the channel simulator through twice frequency conversion. The first-stage mixing is performed by mixing dot frequency intermediate frequency and dot frequency first local oscillator to dot frequency, filtering is performed, then mixing is performed with frequency sweeping second local oscillator to radio frequency output, and radio frequency signals are adjusted to a power range meeting user requirements through a large dynamic attenuator.
The accuracy of the transmission power of the channel simulator is one of the important indexes for measuring the performance of the channel simulator, and is mainly determined by the radio frequency circuit of the transmitter part. Theoretically, the power accuracy of the transmitter of the channel simulator can be ensured most accurately by traversing and calibrating different frequencies and different powers one by one. Then, it is a very time consuming process, which is only applicable to channel simulator transmitters with a small number of antennas. When a MIMO channel simulator transmitter meeting the 5G requirement is produced, only a single channel simulator needs to be calibrated 128+ 4-132 times, and the above method of traversing calibration cannot be repeated in mass production.
Most channel simulator transmitters use a Voltage Variable Attenuator (VVA) to adjust the Attenuator of the path, which can ensure both precise stepping and power accuracy. However, VVA belongs to analog devices, the nonlinear effect is very serious, and the nonlinear effect drops sharply as the attenuation value is larger, and for wide-band spectrum signals with high peak-to-average ratio, the vector performance will be very serious after VVA. Meanwhile, VVA is a negative feedback loop, the stabilization process of VVA is slow, generally it takes us-magnitude time to adjust from one power to another and stabilize, and such a long stabilization time is not suitable for the channel simulator to simulate the requirement of 5G communication wireless channel.
Therefore, the VVA is used for adjusting and traversing the output power of the calibration transmitter, and the adverse factors such as nonlinearity, long time and the like exist, so that the VVA is not suitable for the transmitter power calibration of the massive MIMO channel simulator supporting 5G communication. On the premise of ensuring power accuracy and channel linearity, the problem of how to shorten the power calibration time of a transmitter of a large-scale MIMO channel simulator and ensure high-efficiency production of the channel simulator needs to be solved urgently.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a circuit structure and a method for realizing the rapid calibration of the transmitter power of the MIMO channel simulator based on digital-analog block division, which have the advantages of high precision, simple and convenient operation and wide application range.
In order to achieve the above purpose, the circuit structure and method for realizing the fast calibration of the transmitter power of the MIMO channel simulator based on the digital-analog block type of the invention are as follows:
the circuit structure for realizing the rapid calibration of the transmitter power of the MIMO channel simulator based on the digital-analog block type is mainly characterized in that the circuit structure comprises a digital circuit module and an analog circuit module, wherein the analog circuit module is connected with the digital circuit module;
the digital circuit module comprises a digital-to-analog converter unit which is connected with the analog circuit module and used for converting the digital signal of the channel model into an analog signal, adjusting the output power and controlling the power step and the accuracy;
the analog circuit module comprises a first filter, a first frequency mixer, a second filter, a second frequency mixer, a numerical control attenuator and a large step attenuator which are sequentially connected, the analog circuit module further comprises a first local oscillator and a second local oscillator, the first local oscillator is connected with the first frequency mixer, the second local oscillator is connected with the second frequency mixer, the numerical control attenuator is used for adjusting and calibrating errors of attenuation characteristics on different frequency channels, and the large step attenuator is used for expanding the dynamic range of output power of a channel simulator transmitter.
Preferably, the analog circuit module further includes a power meter connected to the large step attenuator for receiving the output signal and feeding back the power level.
Preferably, the circuit structure further comprises a control unit, which is respectively connected with the control unit, the first local oscillator, the second local oscillator, the numerical control attenuator, the large step attenuator and the power meter, and is used for controlling the circuit and performing reading, returning and recording operations.
Preferably, the digital circuit module calculates the output power, specifically:
the output power is calculated according to the following formula:
wherein, VppTo output the full scale, M is the dac cell control word and N is the bit.
Preferably, the digital circuit module calculates the output power accuracy, specifically:
the output power accuracy is calculated according to the following formula:
wherein, VppTo output the full scale, M is the dac cell control word and N is the bit.
Preferably, the control unit stores the output frequency, the output power of the large step attenuator, the measured power, the numerical control attenuator value, the large step attenuator value, the power error value and the M value corresponding to the output power of different digital-to-analog converter units.
The method for realizing the fast calibration of the transmitter power of the MIMO channel simulator based on the digital-analog block division by utilizing the circuit structure is mainly characterized by comprising the following steps of:
(1) calibrating the analog circuit module;
(2) changing the frequency, and further calibrating to obtain a calibration table of the full frequency band;
(3) calibrating the digital circuit module to perfect the power calibration in the stepping range of the large-step power attenuator;
(4) and calibrating the output power of the single-channel simulator transmitter according to a formula.
Preferably, the step (1) specifically comprises the following steps:
(1.1) initializing a configuration signal source, the frequency of a first local oscillator and the value of a numerical control attenuator, and determining signals of the frequency and the power;
(1.2) setting the output power which needs to be calibrated at present, and calculating and configuring the initial value of the numerical control attenuator and the value of the large-step attenuator;
(1.3) setting the output frequency of the channel simulator transmitter, and calculating and configuring the frequency of a second local oscillator;
(1.4) measuring an output signal of the channel simulator transmitter through a power meter, and feeding back the measured power signal to the control unit;
(1.5) calculating a power error, judging whether the power error meets the precision requirement, and if so, continuing to perform the step (6); otherwise, substituting the power error into the numerical control attenuator, reconfiguring the numerical control attenuator, and continuing the step (4);
(1.6) recording the current output power value, the value of the large step attenuator, the value of the numerical control attenuator, the actually measured output power value and the power error value;
(1.7) switching the frequency, and continuing the step (3) until all frequency points are traversed;
and (1.8) switching the frequency, and continuing the step (2) until all power is traversed.
Preferably, the step (3) specifically includes the following steps:
(3.1) calculating the maximum output power of the digital-to-analog converter unit;
and (3.2) calculating a control word value corresponding to the attenuation value of the digital-to-analog converter unit.
The circuit structure and the method for realizing the rapid calibration of the transmitter power of the MIMO channel simulator based on the digital-analog block type solve the problem of nonlinearity introduced by a simulation device of the transmitter of the channel simulator, and ensure the continuity of the output power of the transmitter through the calculation of the digital-analog converter unit, thereby not only improving the vector performance of the transmitter of the channel simulator, but also ensuring the accuracy of the transmission power of the transmitter of the channel simulator. The scheme solves the problem that the time for calibrating the transmitter power of the large-scale MIMO channel simulator is too long. By using the method, the calibration time of the single-channel simulator transmitter is increased by 10-20 times, and the method is particularly suitable for power calibration of a large-scale MIMO transmitter.
Drawings
Fig. 1 is a block diagram of a MIMO channel simulator transmitter.
Fig. 2 is a diagram of a super heterodyne transmitter architecture for a MIMO channel simulator.
Fig. 3 is a schematic diagram of a MIMO channel simulator transmitter fast calibration scheme.
Fig. 4 is a circuit calibration system of a single-channel analog part of the circuit structure for realizing the fast calibration of the transmitter power of the MIMO channel simulator based on digital-analog block division.
Fig. 5 is a circuit calibration flow chart of a single-channel analog part of the method for realizing the fast calibration of the transmitter power of the MIMO channel simulator based on the digital-analog block type of the present invention.
Fig. 6 is a calibration schematic diagram formed after calibration by the method for realizing fast calibration of the transmitter power of the MIMO channel simulator based on the digital-analog block division.
Detailed Description
In order to more clearly describe the technical contents of the present invention, the following further description is given in conjunction with specific embodiments.
The circuit structure for realizing the fast calibration of the transmitter power of the MIMO channel simulator based on the digital-analog block division comprises:
the circuit comprises a digital circuit module and an analog circuit module, wherein the analog circuit module is connected with the digital circuit module;
the digital circuit module comprises a digital-to-analog converter unit which is connected with the analog circuit module and used for converting the digital signal of the channel model into an analog signal, adjusting the output power and controlling the power step and the accuracy;
the analog circuit module comprises a first filter, a first frequency mixer, a second filter, a second frequency mixer, a numerical control attenuator and a large step attenuator which are sequentially connected, the analog circuit module further comprises a first local oscillator and a second local oscillator, the first local oscillator is connected with the first frequency mixer, the second local oscillator is connected with the second frequency mixer, the numerical control attenuator is used for adjusting and calibrating errors of attenuation characteristics on different frequency channels, and the large step attenuator is used for expanding the dynamic range of output power of a channel simulator transmitter.
As a preferred embodiment of the present invention, the analog circuit module further includes a power meter connected to the large step attenuator for receiving the output signal and feeding back the power level.
As a preferred embodiment of the present invention, the circuit structure further includes a control unit, which is respectively connected to the control unit, the first local oscillator, the second local oscillator, the numerical control attenuator, the large step attenuator, and the power meter, and is used for controlling the circuit and performing reading, returning, and recording operations.
As a preferred embodiment of the present invention, the digital circuit module calculates the output power, specifically:
the output power is calculated according to the following formula:
wherein, VppTo output the full scale, M is the dac cell control word and N is the bit.
As a preferred embodiment of the present invention, the digital circuit module calculates the output power accuracy, specifically:
the output power accuracy is calculated according to the following formula:
wherein, VppTo output the full scale, M is the dac cell control word and N is the bit.
As a preferred embodiment of the present invention, the control unit stores the output frequency, the output power of the large step attenuator, the measured power, the numerical control attenuator value, the large step attenuator value, the power error value, and the M value corresponding to the output power of different digital-to-analog converter units.
The invention discloses a method for realizing the fast calibration of the transmitter power of a MIMO channel simulator based on digital-analog block division by using the circuit structure, which comprises the following steps:
(1) calibrating the analog circuit module;
(1.1) initializing a configuration signal source, the frequency of a first local oscillator and the value of a numerical control attenuator, and determining signals of the frequency and the power;
(1.2) setting the output power which needs to be calibrated at present, and calculating and configuring the initial value of the numerical control attenuator and the value of the large-step attenuator;
(1.3) setting the output frequency of the channel simulator transmitter, and calculating and configuring the frequency of a second local oscillator;
(1.4) measuring an output signal of the channel simulator transmitter through a power meter, and feeding back the measured power signal to the control unit;
(1.5) calculating a power error, judging whether the power error meets the precision requirement, and if so, continuing to perform the step (6); otherwise, substituting the power error into the numerical control attenuator, reconfiguring the numerical control attenuator, and continuing the step (4);
(1.6) recording the current output power value, the value of the large step attenuator, the value of the numerical control attenuator, the actually measured output power value and the power error value;
(1.7) switching the frequency, and continuing the step (3) until all frequency points are traversed;
(1.8) switching the frequency, and continuing the step (2) until all power is traversed;
(2) changing the frequency, and further calibrating to obtain a calibration table of the full frequency band;
(3) calibrating the digital circuit module to perfect the power calibration in the stepping range of the large-step power attenuator;
(3.1) calculating the maximum output power of the digital-to-analog converter unit;
(3.2) calculating a control word value corresponding to the attenuation value of the digital-to-analog converter unit;
(4) and calibrating the output power of the single-channel simulator transmitter according to a formula.
In the specific implementation of the present invention, the technical problem to be solved by the present invention is to solve the problem of nonlinearity introduced by the analog device of the channel simulator transmitter. Channel simulator transmitters using VVAs suffer from degraded transmitter vector performance due to the non-linearity of the VVAs, reducing channel simulator performance. The present invention also needs to solve the algorithm problem of transmitter power calibration of massive MIMO channel simulators. The traditional traversing calibration method of frequency and power is adopted, the calibration time is too long, and the method is not suitable for the calibration of a large-scale MIMO channel simulator transmitter and the mass production of the channel simulator.
The invention provides a system and a method for realizing rapid calibration of transmitter power of an MIMO channel simulator based on digital-analog block division. By utilizing the dot frequency input characteristic of the super-heterodyne structure of the transmitter, the intermediate frequency power calibration and the radio frequency attenuation power calibration of the digital-to-analog converter unit are carried out on the channel simulator transmitter in blocks. The calibration efficiency of the transmitter of the single-channel simulator is greatly improved while the power accuracy of the transmitter of the channel simulator is ensured. By using the consistency of multiple channels of the transmitter of the MIMO channel simulator, the power calibration of the multi-channel transmitter can be realized only by calibrating a few frequency points, and the power calibration efficiency of the transmitter of the MIMO channel simulator is greatly improved. The method is a brand-new method for realizing the rapid calibration of the transmitter power of the MIMO channel simulator in a digital-analog block mode, the block diagram of the circuit scheme of a single channel is shown in figure 3, and the technical scheme comprises two parts:
the analog circuit part mainly comprises two frequency mixers, two local oscillators, two filters, a numerical control attenuator and a large step attenuator. The dot frequency first intermediate frequency signal output by the digital-to-analog converter unit is mixed with the dot frequency first local oscillator to the dot frequency second intermediate frequency, and then is mixed with the sweep frequency second local oscillator to be output in full-band radio frequency after filtering. The digitally controlled attenuator is used to adjust and calibrate the error in the attenuation characteristics over different frequency paths, while the large step attenuator is used to extend the dynamic range of the output power of the channel simulator transmitter.
The digital circuit part mainly comprises a digital-to-analog converter unit, the digital signal superposed with the channel model is converted into an analog signal by the digital-to-analog converter unit, and the output power of the digital signal can be adjusted by the digital-to-analog converter unit. The digital-to-analog converter unit outputs dot-frequency intermediate frequency signals, the digital-to-analog converter unit can accurately control the power stepping and the accuracy, for N bits, the digital-to-analog converter unit with the output full-range of Vpp is configured with different values M, M belongs to [0, 2 ]N-1]The output power (converted to dBm) is calculated as follows:
the output power accuracy (dB) is calculated as follows:
most of the digital-to-analog converter units on the market reach more than 10 bits, and in the practical use process, the configuration value of the digital-to-analog converter unit cannot take a very small value for the signal-to-noise ratio of the signal, and then the formula can show that when M is gradually increased from small to 2N-1, Δ P is obtainedout-DACApproaching infinity to 0, it can be seen that the output power accuracy of the digital-to-analog converter unit is very high.
The traditional channel simulator transmitter uses a Voltage Variable Attenuator (VVA) to adjust the Attenuator of the path, and has the advantages of small step and high power accuracy. However, VVA belongs to analog devices, the nonlinear effect is very serious, and the nonlinear effect drops sharply as the attenuation value is larger, and for wide-band spectrum signals with high peak-to-average ratio, the vector performance will be very serious after VVA. Meanwhile, VVA is a negative feedback loop, the stabilization process of VVA is slow, generally it takes us-magnitude time to adjust from one power to another and stabilize, and such a long stabilization time is not suitable for the channel simulator to simulate the requirement of 5G communication wireless channel.
The channel simulator transmitter system of the invention converts the inherent problem of VVA into two parts, firstly uses a numerical control attenuator to effectively avoid the problem of nonlinearity, and the linearity of the numerical control attenuator is not reduced along with the increase of attenuation. The continuous power output which can not be achieved by the numerical control attenuator is realized by a digital-to-analog converter unit of the digital part, and the accuracy of the digital-to-analog converter unit completely meets the requirement of the transmission power accuracy of the channel simulator.
The channel simulator transmitter power calibration is divided into two parts, an analog part and a digital part. Wherein the power calibration of the analog part is the power calibration of the transmitter attenuation characteristic, and the power calibration of the digital part is the intermediate frequency power calibration of the digital-to-analog converter unit.
First, the analog part power calibration is described, and the instrument connection is shown in fig. 4. A signal source sends a fixed-frequency fixed-power dot-frequency signal to simulate a first intermediate-frequency signal of a channel simulator; the power meter is used for receiving the output signal and feeding back the power; the control unit controls the signal source, the power meter, the first local oscillator, the second local oscillator, the numerical control attenuator and the large-step attenuator and conducts reading, returning, recording and other operations. The numerical control attenuator is used for adjusting channel frequency response corresponding to different large-step attenuations on the analog part circuit, namely, the calibration is carried out only by taking the steps of the large-step attenuator as the steps of the output power. The specific power calibration process is shown in fig. 5, and the calibration method includes the following steps:
1. the signal source simulates a signal with determined frequency/determined power;
2. setting the output power which needs to be calibrated at present, and correspondingly configuring an initial value of the numerical control attenuator and a value of the large-step attenuator;
3. setting the output frequency of a channel simulator transmitter, and calculating and configuring the frequency of a frequency sweeping local oscillator;
4. measuring an output signal of a channel simulator transmitter by using a power meter, and feeding back an actually measured power signal to a control unit;
5. the control unit calculates power errors, sends out instructions to adjust the numerical control attenuators on the channel, and iterates error values for multiple times until the output power required to be calibrated at present corresponds to the values of the large-step attenuators one by one;
6. recording the current output frequency, the output power, the actually measured power, the numerical control attenuator value, the large step attenuator value and the power error value;
7. switching frequencies, executing the calibration operation, ensuring that different frequencies and the same large step attenuator value can be calibrated to the same output power to be calibrated;
8. the output power is switched again (the step is determined by the step of the large step attenuator) and the above operation is repeated.
In the calibration table formed after the above calibration operation is performed, the numerical control attenuator value or the power error value is only related to the output frequency and the output power, and the schematic diagram is shown in fig. 6. The numerical control attenuator has small difference between values of different output powers, different output frequencies and the numerical control attenuator; and under different output frequencies, the same large step attenuator is configured, and the calibrated output power is the same.
After the power calibration of the analog circuit part is executed, the power value in the step range of the large step attenuator is lacked, the power calibration criterion of the part is subjected to precise calculation processing and configuration by a digital-to-analog converter unit of the digital part, and the power calibration of the digital part is described next.
Because the digital-to-analog converter unit outputs the dot-frequency intermediate-frequency signal, the frequency response characteristics corresponding to different frequencies of the dot-frequency intermediate-frequency signal do not need to be considered, and the digital-to-analog converter unit has a plurality of bits and very high power output accuracy. The accurate power control within the output power stepping range of the channel simulator transmitter is processed by the digital-to-analog converter unit without extra instruments. Assuming that the step of the large step attenuator is SdB, the digital to analog converter unit only needs to calculate the output power between-S-0 dB of calibration. Firstly, configuring a digital-to-analog converter unit control word M as x, correspondingly outputting '0 dB' in a large step attenuator step range, configuring a digital-to-analog converter unit control word M as y, correspondingly outputting '-Sdb' in the large step attenuator step range, and according to a formula 1:
for certain digital-to-analog converter unit circuits and large step attenuators, N, Vpp and S in the above formula are all determined constants, and x corresponding to '0 dB' and y corresponding to '-SdB' are calculated quickly.
Similarly, according to equation 1, the value of the control word M corresponding to any dac unit between-S and 0dB can be calculated quickly.
The control unit stores therein: the method comprises the steps of outputting frequency, output power (large step), actually measured power, a numerical control attenuator value, a large step attenuator value, a power error value and M values corresponding to the output powers of different digital-to-analog converter units, setting power required by a user when a channel simulator transmitter normally works, firstly splitting the transmission power required by the user into actually calibrated output power by a control unit, and adding a small step power value obtained after the large step is removed, namely-S-0 dB output by the digital-to-analog converter unit. By using the method, the calibration data volume of the single-channel transmitter is improved by orders of magnitude.
Assume that the transmitter has an output frequency range of fl～fhOutput power range of Pl～PhIf the frequency calibration step is Δ f, the power calibration step is Δ P, and the large step attenuator on the transmitter path is Δ S (Δ S is generally about 10-20 times of Δ P), then the calibration times are the same as those required by the conventional frequency and power traversal method
With the method of the present invention, the number of times of calibration is only required
It can be seen that using the method of the present invention, the power calibration times are compared as follows
Output power dynamic range (i.e., P) of a channel simulator transmitterh-Pl) Is a relatively large range, in equation 5
Can be considered to be approximately equal to 1, therefore, equation 5 can be reduced to
By using the method of the invention, the power calibration times of the single-channel simulator are improved compared with the traditional method
The calibration time and time are reduced by 10 to 20 times of the conventional method, and the calibrated power error is the aforementioned power error in step 6, which is generally 0.5dB depending on the step of the digitally controlled attenuator, and completely meets the power error requirement of the instrument.
For a large-scale MIMO channel simulator transmitter with 5G requirements, the number of transmitter channels reaches more than 100, and by using the method, the calibration frequency is reduced to one thousandth of that of the traditional method, and the calibration time can be greatly improved. Therefore, the method is particularly suitable for power calibration of the transmitter of the large-scale MIMO channel simulator.
The transmitter of the large-scale MIMO channel simulator supports 128x4, the input power is maximum-2 dBm, the output frequency range is 0.4-6 GHz, the output power range is-100-0 dBm, the dynamic 0-31.5 dB stepping of the numerical control attenuator is 0.5dB, the dynamic 0-80 dB stepping of the high-power attenuator is 20dB, and the full-scale output Vpp of the 12-bit digital-to-analog converter unit is 1V.
The output power is composed of the following parts:
output power-large step attenuation value-digital-analog converter unit attenuation value-numerical control attenuator value + frequency response value … … (equation 7)
According to the formula 7, the method is used for calibrating the output power, the numerical control attenuator is mainly used for calibrating the frequency response of a transmitter channel, and the attenuation of the digital-to-analog converter unit is used for precisely calculating and adjusting the power value outside a large stepping attenuation range.
First is the analog partial power calibration. The calibration process of the method of the present invention is the same for different frequencies, and therefore the description of the calibration process for different frequencies is omitted. The specific process is as follows:
1. the analog part power calibration of the channel simulator transmitter output power, determined from the large step attenuator step, requires only 0/-20/-40/-60/-80dBm calibration;
2. firstly, setting the output power of a channel simulator transmitter to be calibrated to be 0dBm, configuring-2 dBm of the input power of a standard signal source, configuring 0dB of an initial value B0 of a numerical control attenuator and configuring 0dB of a large step attenuator;
3. reading a power value received by the power meter, feeding the power value back to the control module, and calculating a power error value Aj which is the received power value-a power value required to be calibrated;
4. judging whether the power error value satisfies Aj∈[-0.5,+0.5](0.5dB is determined by the digitally controlled attenuator and has met the channel simulator transmitter output power accuracy requirement);
5. if Aj does not meet the requirement, substituting the error value of Aj into the numerical control attenuator, and calculating Bj＝Aj+Bj-1And the value of the numerical control attenuator is configured as Bj;
6. repeating the steps 3 to 5 until the requirements in the step 4 are met;
7. if Aj meets the requirement, directly recording the current power value, the value of the large step attenuator, the value of the numerical control attenuator, the actually measured output power value and the power error value;
8. changing the channel simulator transmitter to the output power of-20 dBm that needs to be calibrated, and repeating steps 2 through 7 until the power point in step 1 is completed.
After the power calibration of the steps is completed, the frequency is changed, and the calibration is further carried out, so that a complete calibration table of the full frequency band with the output power of the channel simulator transmitter being 0/-20/-40/-60/-80dBm can be obtained.
And then, the power calibration of the digital part is carried out, so that the power calibration in the stepping range of the large-step power attenuator is perfected. According to the above description, the digital-to-analog converter unit part only needs simple calculation, and does not need an external instrument for calibration. The specific process is as follows:
in order to ensure the peak-to-average ratio of the output signal of the transmitter, the highest bit of the dac unit is generally reserved to prevent signal saturation and nonlinearity, and at this time, the maximum output voltage peak-to-peak value of the dac unit is reduced to 1/2, that is, Vpp is 0.5V, the bit number N of the dac unit is 11, and based on these two data, the maximum output power of the dac unit is calculated according to equation 1 to be-2 dBm. This power of "-2 dBm" is the maximum input power corresponding to the channel simulator transmitter, corresponding to a channel simulator transmitter output power of 0/-20/-40/-60/-80dBm, i.e. the large step attenuator is configured to 0/20/40/60/80 dB.
According to equation 1, the dac unit control word M when the dynamic attenuation value of the dac unit is [0, 20) dB can be calculated, where M values corresponding to attenuation values of some dac units are listed as follows, and the calculation result is as follows:
similarly, the M value corresponding to the output power of other digital-to-analog converter units can be calculated according to formula 1.
And (3) finishing the power calibration of the analog part and the power calculation calibration of the digital part, and comparing a formula 7 to finish the output power calibration of the single-channel simulator transmitter.
Compared with the traditional frequency traversal and power traversal methods, the method has the advantage that the rapid calibration times of the transmitter power of the MIMO channel simulator are obviously improved based on the digital-analog block division. Assuming that the frequency calibration step is 20MHz, the frequency calibration time is 281 times, the power step in the conventional calibration method is generally 1dB, and assuming that the calibration time of each point is 1s, the calibration time and the calibration time are compared as follows:
it is obvious from the above table that, compared with the conventional method, the calibration method of the present invention has greatly increased calibration times and calibration time. It can be seen that the output power calibration time of the channel simulator transmitter is greatly shortened by using the method of the invention.
For a 5G channel simulator supporting 128x4, the calibration time of the transmitter output power is compared with the conventional method, and the calibration times and calibration times are as follows: (work continuously for 8 hours per day)
With the traditional calibration method, adverse factors in the actual process are not considered, and theoretically, 4 months of calibration time is needed, so that the calibration period can not meet the production requirements of the MIMO channel simulator at all. With the method of the present invention, only one week is needed and the power calibration of the 128x4 channel simulator transmitter can be completed.
It can be seen from the above two comparison tables that, when the calibration method of the present invention is used for calibrating the output power of the transmitter of the channel simulator, the calibration time is greatly increased, and the method is particularly suitable for calibrating the output power of the transmitter of the 5G large-scale MIMO channel simulator and the batch production of the channel simulator.
Meanwhile, by using the method of the invention, the calibration precision is the aforementioned power error value Aj, and the calibrated output power error value satisfies Aj∈[-0.5,+0.5]And the accuracy requirement of the output power of the transmitter of the MIMO channel simulator is completely met.
The circuit structure and the method for realizing the rapid calibration of the transmitter power of the MIMO channel simulator based on the digital-analog block type solve the problem of nonlinearity introduced by a simulation device of the transmitter of the channel simulator, and ensure the continuity of the output power of the transmitter through the calculation of the digital-analog converter unit, thereby not only improving the vector performance of the transmitter of the channel simulator, but also ensuring the accuracy of the transmission power of the transmitter of the channel simulator. The scheme solves the problem that the time for calibrating the transmitter power of the large-scale MIMO channel simulator is too long. By using the method, the calibration time of the single-channel simulator transmitter is increased by 10-20 times, and the method is particularly suitable for power calibration of a large-scale MIMO transmitter.
In this specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.
Claims (9)
1. A circuit structure for realizing the fast calibration of the transmitter power of an MIMO channel simulator based on digital-to-analog block division is characterized in that the circuit structure comprises a digital circuit module and an analog circuit module, wherein the analog circuit module is connected with the digital circuit module;
the digital circuit module comprises a digital-to-analog converter unit which is connected with the analog circuit module and used for converting the digital signal of the channel model into an analog signal, adjusting the output power and controlling the power step and the accuracy;
the analog circuit module comprises a first filter, a first frequency mixer, a second filter, a second frequency mixer, a numerical control attenuator and a large step attenuator which are sequentially connected, the analog circuit module further comprises a first local oscillator and a second local oscillator, the first local oscillator is connected with the first frequency mixer, the second local oscillator is connected with the second frequency mixer, the numerical control attenuator is used for adjusting and calibrating errors of attenuation characteristics on different frequency channels, and the large step attenuator is used for expanding the dynamic range of output power of a channel simulator transmitter.
2. The circuit structure according to claim 1, wherein the analog circuit module further comprises a power meter connected to the large step attenuator for receiving an output signal and feeding back power.
3. The circuit structure for implementing fast calibration of transmitter power of a MIMO channel simulator based on digital-to-analog block division according to claim 2, wherein the circuit structure further comprises a control unit, connected to the control unit, the first local oscillator, the second local oscillator, the digitally controlled attenuator, the large step attenuator, and the power meter, respectively, for controlling the circuit and performing the reading feedback recording operation.
4. The circuit structure for implementing fast calibration of the transmitter power of the MIMO channel simulator based on digital-to-analog block division according to claim 1, wherein the digital circuit module calculates the output power, specifically:
the output power is calculated according to the following formula:
wherein, VppTo output the full scale, M is the dac cell control word and N is the bit.
5. The circuit structure for implementing fast calibration of the transmitter power of the MIMO channel simulator based on digital-to-analog block division according to claim 1, wherein the digital circuit module calculates the output power accuracy, specifically:
the output power accuracy is calculated according to the following formula:
wherein, VppTo output the full scale, M is the dac cell control word and N is the bit.
6. The circuit structure for realizing fast calibration of the transmitter power of the MIMO channel simulator based on digital-to-analog block division according to claim 3, wherein the control unit stores the output frequency, the output power of the large step attenuator, the measured power, the numerical control attenuator value, the large step attenuator value, the power error value and the M value corresponding to the output power of different digital-to-analog converter units.
7. A method for implementing fast calibration of transmitter power for a MIMO channel simulator based on digital-to-analog block division using the circuit configuration of claim 1, said method comprising the steps of:
(1) calibrating the analog circuit module;
(2) changing the frequency, and further calibrating to obtain a calibration table of the full frequency band;
(3) calibrating the digital circuit module to perfect the power calibration in the stepping range of the large-step power attenuator;
(4) and calibrating the output power of the single-channel simulator transmitter according to a formula.
8. The method according to claim 7, wherein the step (1) comprises the following steps:
(1.1) initializing a configuration signal source, the frequency of a first local oscillator and the value of a numerical control attenuator, and determining signals of the frequency and the power;
(1.2) setting the output power which needs to be calibrated at present, and calculating and configuring the initial value of the numerical control attenuator and the value of the large-step attenuator;
(1.3) setting the output frequency of the channel simulator transmitter, and calculating and configuring the frequency of a second local oscillator;
(1.4) measuring an output signal of the channel simulator transmitter through a power meter, and feeding back the measured power signal to the control unit;
(1.5) calculating a power error, judging whether the power error meets the precision requirement, and if so, continuing to perform the step (6); otherwise, substituting the power error into the numerical control attenuator, reconfiguring the numerical control attenuator, and continuing the step (4);
(1.6) recording the current output power value, the value of the large step attenuator, the value of the numerical control attenuator, the actually measured output power value and the power error value;
(1.7) switching the frequency, and continuing the step (3) until all frequency points are traversed;
and (1.8) switching the frequency, and continuing the step (2) until all power is traversed.
9. The method according to claim 7, wherein the step (3) comprises the following steps:
(3.1) calculating the maximum output power of the digital-to-analog converter unit;
and (3.2) calculating a control word value corresponding to the attenuation value of the digital-to-analog converter unit.
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