CN110708131A - Circuit structure and method for fast calibration of transmitter power of MIMO channel simulator based on digital-analog block - Google Patents

Abstract

The invention relates to a circuit structure for realizing fast calibration of transmitter power of a MIMO channel simulator based on a digital-analog split type, comprising a digital-to-analog converter unit for converting a digital signal of a channel model into an analog signal and adjusting the output power; The analog circuit module includes a first filter, a first mixer, a second filter, a second mixer, a digitally controlled attenuator and a large step attenuator connected in sequence, and the analog circuit module further includes a first vibration and a second local oscillator. The invention also relates to a method for realizing fast calibration of the transmitter power of the MIMO channel simulator based on the digital-analog block type. The circuit structure and method for realizing fast calibration of the transmitter power of the MIMO channel simulator based on the digital-analog block type of the present invention solves the problem of too long time for the transmitter power calibration of the massive MIMO channel simulator. Using the method of the present invention, the calibration time of the single-channel channel simulator transmitter is increased by 10-20 times, which is especially suitable for the transmitter power calibration of massive MIMO.

Description

Realization of fast calibration of transmitter power of MIMO channel simulator based on digital-analog block Circuit structure and method thereof

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, in particular to a circuit structure and a method for realizing fast calibration of transmitter power of a MIMO channel simulator based on a digital-analog block method.

Background technique

The channel simulator is a test instrument that simulates the path loss, multipath fading and other related characteristics in the wireless environment. With the rapid advancement of 5G mobile communication technology research and development and industrialization, compared with the MxN multi-antenna (such as 4x4) in the 4G era, the number of channels simulated in real time in the 5G MIMO channel simulator will increase by an order of magnitude (such as 128x4).

In the MIMO channel simulator transmitter system, it mainly includes a main control unit, a baseband unit, a digital-to-analog converter unit group and a transmitter, and its main structure is shown in Figure 1. The transmitter includes (M+N) transmission channels.

The digital-to-modular block type realizes the fast calibration of the transmitter power of the MIMO channel simulator mainly for the multi-channel superheterodyne transmitter, and its main structural block diagram is shown in FIG. 2 . When the channel simulator transmitter is working, the baseband unit converts the low-frequency signal superimposed with the channel model into an analog intermediate frequency signal through the digital-to-analog converter unit and transmits it to the transmitter. full frequency range. Among them, the first stage of mixing is the point frequency intermediate frequency and the point frequency first local oscillator mixed to the point frequency, and then mixed with the sweep frequency second local oscillator to the RF output, and the RF signal is adjusted by a large dynamic attenuator to meet the The power range required by the user.

The transmit power accuracy of the channel simulator is one of the important indicators to measure the performance of the channel simulator, which mainly depends on the radio frequency circuit of the transmitter part. In theory, traversing and calibrating different frequencies and different powers one by one can most accurately ensure the power accuracy of the channel simulator transmitter. Then, it is a very time-consuming process to traverse, which is only applicable to channel simulator transmitters with a small number of antennas. When producing a MIMO channel simulator transmitter that meets the requirements of 5G, only a single channel simulator needs to be calibrated 128+4=132 times. In mass production, the above traversal calibration method must not be repeated.

Most channel simulator transmitters use an attenuator (Voltage Variable Attenuator, VVA) to adjust the attenuator of the channel, which can ensure precise stepping and power accuracy. However, VVA is an analog device, and the nonlinear effect is very serious, and as the attenuation value increases, the nonlinear effect decreases sharply. For broadband spectrum signals with high peak-average ratio, after VVA, the vector performance will deteriorate very seriously. At the same time, VVA is a negative feedback loop, and its stabilization process is slow. Generally, it takes us time to adjust from one power to another and stabilize. Such a long stabilization time is not suitable for channel simulators to simulate 5G communication. Wireless channel requirements.

Therefore, using VVA to adjust and traverse the calibration transmitter output power has disadvantages such as nonlinearity and long time, and is no longer suitable for the transmitter power calibration of massive MIMO channel simulators supporting 5G communication. Under the premise of ensuring power accuracy and channel linearity, how to shorten the transmitter power calibration time of massive MIMO channel simulators and ensure efficient production of channel simulators needs to be solved urgently.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art, and to provide a circuit structure that satisfies the requirements of high precision, simple operation and wide application range based on the digital-analog block type to realize the rapid calibration of the transmitter power of the MIMO channel simulator and the same. method.

In order to achieve the above-mentioned purpose, the circuit structure and the method thereof for realizing the fast calibration of the transmitter power of the MIMO channel simulator based on the digital-analog block type are as follows:

The circuit structure for realizing fast calibration of transmitter power of a MIMO channel simulator based on a digital-modular block type is mainly characterized in that the circuit structure includes a digital circuit module and an analog circuit module, and the analog circuit module and the digital circuit module connected;

The digital circuit module includes a digital-to-analog converter unit, which is connected to the analog circuit module and is used to convert the digital signal of the channel model into an analog signal, adjust the output power, and control the power step and accuracy;

The analog circuit module includes a first filter, a first mixer, a second filter, a second mixer, a numerically controlled attenuator and a large step attenuator connected in sequence, and the analog circuit module further includes a first local oscillator and a second local oscillator, the first local oscillator is connected to the first mixer, the second local oscillator is connected to the second mixer, the The digitally controlled attenuator is used to adjust and calibrate the error of attenuation characteristics on different frequency channels, and the large step attenuator is used to expand the output power dynamic range of the channel simulator transmitter.

Preferably, the analog circuit module further includes a power meter, which is connected to the large step attenuator for receiving the output signal and feeding back the power level.

Preferably, the circuit structure further includes a control unit, which is respectively connected with the control unit, the first local oscillator, the second local oscillator, the numerically controlled attenuator, the large step attenuator and the power meter for controlling the circuit. And carry out the reading back record operation.

Preferably, the digital circuit module calculates the output power, specifically:

Calculate the output power according to the following formula:

Among them, V _pp is the output full scale, M is the digital-to-analog converter unit control word, and N is the bit position.

Preferably, the digital circuit module calculates the output power accuracy, specifically:

Calculate the output power accuracy according to the following formula:

Among them, V _pp is the output full scale, M is the digital-to-analog converter unit control word, and N is the bit position.

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 corresponding output power of different digital-to-analog converter units. the value of M.

The method of utilizing the above-mentioned circuit structure to realize the fast calibration of the transmitter power of the MIMO channel simulator based on the digital-analog block type is mainly characterized in that the method comprises the following steps:

(1) Perform analog circuit module calibration;

(2) Change the frequency and perform further calibration to obtain the calibration table of the full frequency range;

(3) Carry out digital circuit module calibration to improve the power calibration within the step range of the large-step power attenuator;

(4) Carry out the output power calibration of the single-channel channel simulator transmitter according to the formula.

Preferably, the step (1) specifically includes the following steps:

(1.1) Initialize the configuration signal source, the frequency of the first local oscillator and the value of the numerically controlled attenuator, and determine the signal of frequency and power;

(1.2) Set the current output power that needs to be calibrated, calculate and configure the initial value of the digital attenuator and the value of the large step attenuator;

(1.3) Set the output frequency of the channel simulator transmitter, calculate and configure the frequency of the second local oscillator;

(1.4) Measure the output signal of the channel simulator transmitter through the power meter, and feed back the measured power signal to the control unit;

(1.5) Calculate the power error, determine whether the power error meets the accuracy requirements, if so, continue to step (6); otherwise, substitute the power error into the numerically controlled attenuator, and reconfigure the numerically controlled attenuator, continue to step (4);

(1.6) Record the current output power value, the value of the large step attenuator, the numerical control attenuator value, the measured output power value, and the power error value;

(1.7) Switch the frequency and continue step (3) until all frequency points are traversed;

(1.8) Switch the frequency and continue step (2) until all powers are traversed.

Preferably, the step (3) specifically includes the following steps:

(3.1) Calculate the maximum output power of the digital-to-analog converter unit;

(3.2) Calculate the control word value corresponding to the attenuation value of the digital-to-analog converter unit.

The circuit structure and method for realizing fast calibration of MIMO channel simulator transmitter power based on the digital-analog block type of the present invention are adopted, the nonlinear problem introduced by the channel simulator transmitter analog device is solved, and the digital-to-analog converter unit is adopted. The calculation ensures the continuity of the output power of the transmitter, which not only improves the vector performance of the channel simulator transmitter, but also ensures the accuracy of its transmission power. This solution solves the problem that the transmitter power calibration time of massive MIMO channel simulator is too long. Using the method of the present invention, the calibration time of the single-channel channel simulator transmitter is increased by 10-20 times, which is especially suitable for the transmitter power calibration of massive MIMO.

Description of drawings

Figure 1 is a block diagram of the main components of a MIMO channel simulator transmitter.

FIG. 2 is an architecture diagram of a superheterodyne transmitter of a MIMO channel simulator.

FIG. 3 is a schematic diagram of a fast calibration scheme of a MIMO channel simulator transmitter.

FIG. 4 is a single-channel analog partial circuit calibration system of the present invention based on a circuit structure for realizing fast calibration of transmitter power of a MIMO channel simulator based on a digital-analog block type.

FIG. 5 is a flow chart of the circuit calibration of the 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 according to the present invention.

FIG. 6 is a schematic diagram of calibration formed after the method for realizing fast calibration of transmitter power of a MIMO channel simulator based on a digital-analog block type according to the present invention.

Detailed ways

In order to describe the technical content of the present invention more clearly, further description will be given below with reference to specific embodiments.

The circuit structure of the present invention for realizing fast calibration of the transmitter power of the MIMO channel simulator based on the digital-analog block type includes:

a digital circuit module and an analog circuit module, the analog circuit module is connected with the digital circuit module;

The digital circuit module includes a digital-to-analog converter unit, which is connected to the analog circuit module and is used to convert the digital signal of the channel model into an analog signal, adjust the output power, and control the power step and accuracy;

The analog circuit module includes a first filter, a first mixer, a second filter, a second mixer, a numerically controlled attenuator and a large step attenuator connected in sequence, and the analog circuit module further includes a first local oscillator and a second local oscillator, the first local oscillator is connected to the first mixer, the second local oscillator is connected to the second mixer, the The digitally controlled attenuator is used to adjust and calibrate the error of attenuation characteristics on different frequency channels, and the large step attenuator is used to expand the output power dynamic range of the channel simulator transmitter.

As a preferred embodiment of the present invention, the analog circuit module further includes a power meter, which is 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 digitally controlled attenuator, the large step attenuator and the power meter, It is used to control the circuit and carry out the operation of reading back and recording.

As a preferred embodiment of the present invention, the digital circuit module calculates the output power, specifically:

Calculate the output power according to the following formula:

Among them, V _pp is the output full scale, M is the digital-to-analog converter unit control word, and N is the bit position.

As a preferred embodiment of the present invention, the digital circuit module calculates the output power accuracy, specifically:

Calculate the output power accuracy according to the following formula:

Among them, V _pp is the output full scale, M is the digital-to-analog converter unit control word, and N is the bit position.

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 numerically controlled attenuator value, the large-step attenuator value, the power error value and different digital-to-analog converters. The M value corresponding to the output power of the unit.

The present invention utilizes the above-mentioned circuit structure to realize the method for fast calibration of the transmitter power of the MIMO channel simulator based on the digital-modular block type, which comprises the following steps:

(1) Perform analog circuit module calibration;

(1.1) Initialize the configuration signal source, the frequency of the first local oscillator and the value of the numerically controlled attenuator, and determine the signal of frequency and power;

(1.2) Set the current output power that needs to be calibrated, calculate and configure the initial value of the digital attenuator and the value of the large step attenuator;

(1.3) Set the output frequency of the channel simulator transmitter, calculate and configure the frequency of the second local oscillator;

(1.4) Measure the output signal of the channel simulator transmitter through the power meter, and feed back the measured power signal to the control unit;

(1.5) Calculate the power error, determine whether the power error meets the accuracy requirements, if so, continue to step (6); otherwise, substitute the power error into the numerically controlled attenuator, and reconfigure the numerically controlled attenuator, continue to step (4);

(1.6) Record the current output power value, the value of the large step attenuator, the numerical control attenuator value, the measured output power value, and the power error value;

(1.7) Switch the frequency and continue step (3) until all frequency points are traversed;

(1.8) Switch the frequency and continue step (2) until all powers are traversed;

(2) Change the frequency and perform further calibration to obtain the calibration table of the full frequency range;

(3) Carry out digital circuit module calibration to improve the power calibration within the step range of the large-step power attenuator;

(3.1) Calculate the maximum output power of the digital-to-analog converter unit;

(3.2) Calculate the control word value corresponding to the attenuation value of the digital-to-analog converter unit;

(4) Carry out the output power calibration of the single-channel channel simulator transmitter according to the formula.

In the specific embodiment of the present invention, the technical problem to be solved by the present invention is to solve the nonlinear problem introduced by the channel simulator transmitter analog device. Channel emulator transmitters using VVA degrade the performance of the channel emulator due to the nonlinearity of the VVA, which leads to the deterioration of the transmitter vector performance. The invention also needs to solve the algorithm problem of the transmitter power calibration of the massive MIMO channel simulator. Using the traditional frequency and power traversal calibration method, the calibration time is too long, which is not suitable for the calibration of massive MIMO channel simulator transmitters and the mass production of channel simulators.

The invention provides a fast calibration system and method for realizing the transmitter power of a MIMO channel simulator based on a digital-analog block. Using the point-frequency input characteristics of the superheterodyne structure of the transmitter, the digital-to-analog converter unit IF power calibration and the RF attenuation power calibration are performed on the channel simulator transmitter in blocks. While ensuring the power accuracy of the channel simulator transmitter, the calibration efficiency of the single channel channel simulator transmitter is greatly improved. Using the multi-channel consistency of the MIMO channel simulator transmitter, it only needs to calibrate a few frequency points to realize the multi-channel transmitter power calibration, which greatly improves the power calibration efficiency of the MIMO channel simulator transmitter. The inventive method is a brand-new digital-analog split method to realize the fast calibration method of the transmitter power of the MIMO channel simulator. The block diagram of the single-channel circuit scheme is shown in Figure 3, and the technical scheme includes two parts:

The analog circuit part mainly includes two mixers, two local oscillators, two filters, a digitally controlled attenuator and a large step attenuator. The point-frequency first intermediate frequency signal output by the digital-to-analog converter unit is mixed with the point-frequency first local oscillator to the point-frequency second intermediate frequency, filtered and then mixed with the sweep-frequency second local oscillator to a full-band radio frequency output. The digitally controlled attenuator is used to adjust the error of calibrating the attenuation characteristics on different frequency channels, while the large step attenuator is used to extend the output power dynamic range of the channel simulator transmitter.

The digital circuit part mainly includes a digital-to-analog converter unit. The digital signal superimposed on the channel model is converted into an analog signal by the digital-to-analog converter unit, and its output power can be adjusted by the digital-to-analog converter unit. Super-heterodyne channel simulator transmitter, the output of the digital-to-analog converter unit is a point frequency and intermediate frequency signal, and the digital-to-analog converter unit can accurately control its power step and accuracy. For N bits, the output full scale is Vpp The digital-to-analog converter unit is configured with different values of M, M∈[0, 2 ^N -1], and its output power (converted to dBm) is calculated as follows:

The output power accuracy (dB) is calculated as follows:

At present, most of the digital-to-analog converter units on the market reach N=10 bits or more, and in the actual use process, for the signal-to-noise ratio of the signal, the configuration value of the digital-to-analog converter unit will not take a small value, then From the above formula, it can be concluded that when M gradually increases from small to 2N-1, ΔP _out-DAC will be infinitely close to 0, which shows that the output power accuracy of the digital-to-analog converter unit is very high.

The traditional channel simulator transmitters all use an attenuator (Voltage Variable Attenuator, VVA) to adjust the attenuator of the channel, which has the advantages of small steps and high power accuracy. However, VVA is an analog device, and the nonlinear effect is very serious, and as the attenuation value increases, the nonlinear effect decreases sharply. For broadband spectrum signals with high peak-average ratio, after VVA, the vector performance will deteriorate very seriously. At the same time, VVA is a negative feedback loop, and its stabilization process is slow. Generally, it takes us time to adjust from one power to another and stabilize. Such a long stabilization time is not suitable for channel simulators to simulate 5G communication. Wireless channel requirements.

The channel simulator transmitter system of the present invention converts the inherent problem of VVA into two parts. First, the numerical control attenuator is used to effectively avoid the nonlinear problem, and its linearity will not decrease with the increase of the attenuation. The continuous power output that cannot be achieved by the numerical control attenuator is realized by the digital-to-analog converter unit of the digital part, and the accuracy of the digital-to-analog converter unit fully meets the requirements of the transmission power accuracy of the channel simulator.

The channel simulator transmitter power calibration is divided into two parts, the analog part and the digital part. The power calibration of the analog part is the power calibration of the attenuation characteristic of the transmitter, and the power calibration of the digital part is the IF power calibration of the digital-to-analog converter unit.

First, the power calibration of the analog part is introduced. The connection method of the instrument is shown in Figure 4. The signal source sends out a point frequency signal with a fixed frequency and a fixed power, and simulates the first intermediate frequency signal of the channel simulator; the power meter is used to receive the output signal and feed back the power level; the control unit controls the signal source, the power meter, the first local oscillator, the second Local oscillator, numerical control attenuator and large step attenuator, and perform operations such as reading back and recording. The numerical control attenuator is used to adjust the channel frequency response corresponding to different large step attenuations on the analog part of the circuit, that is, only the step of the large step attenuator needs to be used as the output power step for calibration. The specific power calibration process is shown in Figure 5. The calibration method includes the following steps:

1. The signal source simulates a signal with a determined frequency/determined power;

2. Set the current output power that needs to be calibrated, and configure the initial value of the numerical control attenuator and the value of the large step attenuator accordingly;

3. Set the output frequency of the channel simulator transmitter, calculate and configure the frequency of the swept local oscillator;

4. Use the power meter to measure the output signal of the channel simulator transmitter, and feed back the measured power signal to the control unit;

5. The control unit calculates the power error, and sends an instruction to adjust the numerical control attenuator on the channel. After several iterations of the error value, the output power that needs to be calibrated is in one-to-one correspondence with the value of the large-step attenuator;

6. Record the current output frequency, output power, measured power, numerical control attenuator value, large step attenuator value, and power error value;

7. Switch the frequency and perform the above calibration operation to ensure that different frequencies and the same large step attenuator value can be calibrated to the same output power that needs to be calibrated;

8. Switch the output power again (the step is determined by the step of the large step attenuator), and repeat the above operation.

In the calibration table formed after performing the above calibration operations, the numerical control attenuator value or power error value is only related to the output frequency and output power, as shown in Figure 6. Different output power, different output frequency, there is a slight difference between the numerical control attenuator value; under different output frequency, the same large step attenuator configuration, the output power after calibration is the same.

After the power calibration of the analog circuit is completed, the power value within the step range of the large-step attenuator is still missing. This part of the power calibration is handed over to the digital-to-analog converter unit of the digital part for precise calculation and configuration. Next, the digital Partial power calibration.

Since the digital-to-analog converter unit outputs a point-frequency intermediate frequency signal, it is not necessary to consider the frequency response characteristics corresponding to different frequencies, and the digital-to-analog converter unit has many bits, and the power output accuracy is very high. The precise power control within the output power step range of the channel simulator transmitter is handed over to the digital-to-analog converter unit for calculation processing without redundant 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 calibration -S ~ 0dB. First, configure the digital-to-analog converter unit control word M=x, corresponding to '0dB' within the step range of the output large-step attenuator, configure the digital-to-analog converter unit control word M=y, corresponding to the output large-step attenuator step '-SdB' in the range, according to Equation 1:

For a certain digital-to-analog converter unit circuit and a large step attenuator, N, Vpp, and S in the above formula are all certain constants, and the x corresponding to '0dB' and the corresponding value of '-SdB' are quickly calculated. y.

Similarly, according to formula 1, the value of the control word M corresponding to any digital-to-analog converter unit between -S and 0 dB can be quickly calculated.

The following contents are stored in the control unit: output frequency, output power (large step), measured power, numerical control attenuator value, large step attenuator value, power error value, and M corresponding to the output power of different digital-to-analog converter units When the channel simulator transmitter is working normally, set the power required by the user. The control unit first splits the transmitting power required by the user into the actual calibrated output power, plus the small step power value after removing the large step. That is -S ~ 0dB output by the digital-to-analog converter unit. Using the method of the present invention, the amount of calibration data for a single-channel transmitter is increased by an order of magnitude.

Assume that the output frequency range of the transmitter is f _l ~ f _h , the output power range is P _l ~ P _h , the frequency calibration step is Δf, the power calibration step is ΔP, and the large step attenuator step on the transmitter path is ΔS (ΔS is generally about 10 to 20 times of ΔP), then, using the traditional frequency and power traversal method, the number of calibrations required is

However, using the method of the present invention, the number of calibrations required is only

It can be seen that, using the method of the present invention, the power calibration times are compared as follows

可以看作约等于1，因此，公式5可简化为The output power dynamic range of the channel simulator transmitter (ie, P _h -P _l ) is a relatively large range, in Equation 5

can be regarded as approximately equal to 1, therefore, Equation 5 can be simplified to

校准次数和时间降低为传统方法的10到20分之一，而校准的功率误差则为前文提到的步骤6中的功率误差，取决于数控衰减器的步进，一般为0.5dB，完全符合仪表的功率误差要求。Using the method of the present invention, the power calibration times of the single-channel channel simulator are improved compared with the traditional method

The calibration times and time are reduced to 10 to 20 times that of the traditional method, and the power error of the calibration is the power error in step 6 mentioned above, which depends on the step of the digital attenuator, generally 0.5dB, which is completely consistent with the The power error requirement of the meter.

For the massive MIMO channel simulator transmitter required by 5G, since the number of transmitter channels reaches more than 100, using the method of the present invention, the calibration times will be reduced to one thousandth of the traditional method, and the calibration time can be greatly shortened. promote. It can be seen that the method of the present invention is especially suitable for power calibration of a massive MIMO channel simulator transmitter.

Massive MIMO channel simulator transmitter supports 128x4, maximum input power -2dBm, output frequency range 0.4~6GHz, output power range -100~0dBm, digital attenuator dynamic 0~31.5dB step 0.5dB, high power attenuator dynamic 0 ~ 80dB step 20dB, 12 digital-to-analog converter unit full-scale output Vpp=1V.

The output power consists of the following parts:

Output power = - large step attenuation value - digital-to-analog converter unit attenuation value - numerically controlled attenuator value + frequency response value... (Equation 7)

According to formula 7, the method of the present invention is used to calibrate the output power. The numerical control attenuator mainly calibrates the frequency response of the transmitter channel, and the digital-to-analog converter unit attenuation is used to precisely calculate and adjust the power value outside the large step attenuation range.

The first is the analog section power calibration. For different frequencies, the calibration process of the method of the present invention is exactly the same, so the description of calibration of different frequencies is omitted in the description of the calibration steps. The specific process is as follows:

1. According to the step of the large step attenuator, the power calibration of the analog part of the output power of the channel simulator transmitter only needs to calibrate 0/-20/-40/-60/-80dBm;

2. First, set the output power of the channel simulator transmitter to be calibrated to 0dBm, configure the input power of the standard signal source to -2dBm, configure the initial value of the numerical control attenuator B0=0dB, and configure the large step attenuator value to be 0dB;

3. Read the power value received by the power meter, feed it back to the control module and calculate the power error value Aj = the received power value - the power value that needs to be calibrated;

4. Determine whether the power error value satisfies A _j ∈ [-0.5,+0.5], (0.5dB is determined by the numerical control attenuator, and has met the channel simulator transmitter output power accuracy requirements);

5. If Aj does not meet the requirements, substitute the error value of Aj into the numerical control attenuator, calculate B _j =A _j +B _j-1 , and configure the numerical control attenuator as Bj;

6. Repeat steps 3 to 5 until the requirements in step 4 are met;

7. If Aj meets the requirements, directly record the current power value, the value of the large step attenuator, the numerical control attenuator value, the measured output power value, and the power error value;

8. Change the output power of the channel simulator transmitter to be calibrated to -20dBm, and repeat steps 2 to 7 until the power point in step 1 is completed.

After completing the power calibration in the above steps, change the frequency and perform further calibration to obtain a complete channel simulator transmitter output power of 0/-20/-40/-60/-80dBm, the calibration table of the full frequency range.

Then carry out the power calibration of the digital part to improve the power calibration within the step range of the large-step power attenuator. According to the previous description, the digital-to-analog converter unit part only needs to perform simple calculations, and does not require external instruments 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 digital-to-analog converter unit is generally reserved to prevent signal saturation and nonlinear problems. At this time, the peak-to-peak value of the maximum output voltage of the digital-to-analog converter unit is reduced to 1/ 2, that is, Vpp=0.5V, and the number of digits of the digital-to-analog converter unit is N=11. Based on these two data, the maximum output power of the digital-to-analog converter unit calculated according to formula 1 is -2dBm. The power "-2dBm" is the maximum input power corresponding to the channel simulator transmitter, and the output power of the channel simulator transmitter is 0/-20/-40/-60/-80dBm, that is, the large step attenuator is configured as 0/20/40/60/80dB corresponds to.

According to formula 1, the digital-to-analog converter unit control word M can be calculated when the attenuation dynamic value of the digital-to-analog converter unit is [0, 20) dB. The M values corresponding to the attenuation values of some digital-to-analog converter units are listed below. Calculate The 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.

After completing the power calibration of the analog part and the power calculation and calibration of the digital part, and comparing with formula 7, the output power calibration of the single-channel channel simulator transmitter can be completed.

Compared with the traditional methods of frequency traversal and power traversal, the present invention realizes the rapid calibration times of the transmitter power of the MIMO channel simulator based on the digital-analog block method, and the number of times of rapid calibration is obviously improved. Assuming that the frequency calibration step is 20MHz, the frequency calibration times is 281 times. In the traditional calibration method, the power step is generally 1dB. Assuming that the calibration time of each point is 1s, the comparison between the calibration times and the calibration time is as follows:

It can be clearly seen from the above table that, compared with the traditional method, the calibration method of the present invention greatly improves the calibration times and calibration time. It can be seen that using the method of the present invention, the output power calibration time of the transmitter of the channel simulator is greatly shortened.

For a 5G channel simulator that supports 128x4, the transmitter output power calibration time is compared with the traditional method, the calibration times and the calibration time are as follows: (continuous work for 8 hours per day)

Using the traditional calibration method, regardless of the unfavorable factors in the actual process, theoretically requires a calibration time of 4 months. Such a calibration period cannot meet the production requirements of the MIMO channel simulator. By using the method of the present invention, only one week is required and the power calibration of the 128×4 channel simulator transmitter can be completed.

It can be seen from the above two comparison tables that the calibration method of the present invention is used to calibrate the transmitter output power of the channel simulator, and the calibration time is greatly improved, and it is especially suitable for 5G massive MIMO channel simulator transmitter output power calibration and channel simulator. of mass production.

At the same time, using the method of the present invention, the calibration accuracy is the power error value Aj mentioned above, and the calibrated output power error value satisfies A _j ∈ [-0.5,+0.5], which fully complies with the accurate output power of the MIMO channel simulator transmitter. degree requirements.

The circuit structure and method for realizing fast calibration of MIMO channel simulator transmitter power based on the digital-analog block type of the present invention are adopted, the nonlinear problem introduced by the channel simulator transmitter analog device is solved, and the digital-to-analog converter unit is adopted. The calculation ensures the continuity of the output power of the transmitter, which not only improves the vector performance of the channel simulator transmitter, but also ensures the accuracy of its transmission power. This solution solves the problem that the transmitter power calibration time of massive MIMO channel simulator is too long. Using the method of the present invention, the calibration time of the single-channel channel simulator transmitter is increased by 10-20 times, which is especially suitable for the transmitter power calibration of massive MIMO.

In this specification, the invention has been described with reference to specific embodiments thereof. However, it will be evident that various modifications and changes can still be made without departing from the spirit and scope of the invention. Accordingly, the specification and drawings are 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, V_ppTo 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, V_ppTo 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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