SDR multichannel phase calibration system based on radio frequency transceiving

Abstract

The invention provides an SDR multichannel phase calibration system based on radio frequency transceiving, the system comprises a main control module, an acquisition playback module SDR and a portable computer, the software composition comprises an MATLAB algorithm, the characteristic that a radio frequency transceiver can transmit and receive is utilized to acquire and calculate a transmitting loop-back phase difference and a receiving phase difference, and the SDR multichannel phase calibration system comprises a main control module, an acquisition playback module SDR and a portable computer. The method comprises the following steps of: calculating a phase difference of a cable, adding the calculated phase difference and the measured phase difference of the cable to obtain an issued calibration phase difference, performing secondary calibration by using the phase difference on the oscilloscope, and after the oscilloscope is powered on again, not performing secondary calibration work, and finishing calibration only through a program control interface of MATLAB, and meanwhile, improving the calibration efficiency. In order to compensate the phase error caused by the vector modulation phase shifter, an iterative phase calibration method is adopted, and the precision meets the calibration requirement by collecting and issuing phase difference data for multiple times. Through the scheme of the invention, multi-channel high-precision phase calibration can be realized, and the calibration efficiency and the calibration precision are greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of SDR (Software Defination Radio) amplitude and phase calibration, and in particular to an SDR multi-channel phase calibration system based on radio frequency transceiver. Background Art

[0002] In the field of modern wireless communication technology, in order to create an efficient and convenient experimental condition for related scientific research and testing activities, it is necessary to reconstruct a specific electromagnetic environment in a specific area. This technology has attracted much attention because it can simulate the interaction of multiple electromagnetic radiation fields under the same space-time conditions, helping researchers to gain insight into possible interference to radio equipment in the area and find countermeasures.

[0003] In order to simulate a space-time electromagnetic environment that is close to reality, and to accurately generate electromagnetic signals with diverse distributions, dynamic ranges, and modulation methods in a specific electromagnetic environment, a high-performance RF transceiver is essential. Compared with traditional RF systems, RF transceivers have the advantages of high integration, configurability, high performance, and high reliability. Combined with the parallel computing advantages of FPGA (Field-Programmable Gate Array), a multi-frequency self-transceiver system can be built based on the RF transceiver. The system can simulate a specific electromagnetic environment in a specified area by accurately controlling the amplitude and phase of the signal, thereby accurately simulating the characteristics of the electromagnetic field in the time domain, space domain, and energy domain, and studying the dynamic behavior of the electromagnetic in a given area. However, when processing the synchronization of multiple channels, the existing SDR platform does not fully consider the errors caused by the random phase of the local oscillator and the vector phase modulation, which results in low phase calibration efficiency and calibration accuracy. Summary of the invention

[0004] In view of the above problems, the present invention applies the self-transmitting and self-receiving characteristics of the RF transceiver to the SDR platform, and proposes an SDR multi-channel phase calibration system based on RF transceiver, the system includes a main control module, an SDR module and a portable computer, and the software composition includes a MATLAB algorithm;

[0005] The main control module serves as the system control center, providing the SDR module with synchronous reference clock, second pulse, correction source, local oscillator signal, etc. for data acquisition / playback synchronization;

[0006] The SDR module realizes the acquisition and playback of RF signals. The SDR module includes an FPGA (field programmable gate array), multiple RF transceivers, multiple switches, multiple amplifiers, a memory, and a network port. The FPGA is responsible for the control of the RF transceiver and the interaction of collected data. The RF transceiver is responsible for the generation, modulation, filtering, mixing and digital-to-analog conversion of RF signals. The switch controls the working state of the SDR, and the amplifier amplifies the signal. The memory includes FLASH and DDR3. FLASH is used for onboard information storage, and DDR3 is used for sampled data storage. The network port is a Gigabit network interface for high-speed transmission of sampled data.

[0007] Furthermore, the working principle of the SDR multi-channel phase calibration system based on RF transceiver is:

[0008] By adjusting the clock synchronization interface and synchronization register state of the main control module, the clock source on the main control module is connected to the XTALP (crystal positive end) and XTALN (crystal negative end) pins of the RF transceiver, and the clock synchronization of multiple RF transceivers is controlled, so that the phase calibration can be more efficient;

[0009] When the main control module controls the SDR module to work in the transmitting state, multiple RF transceivers generate I and Q signals at the same time. For each RF transceiver, the generated I and Q signals are recombined and modulated at the carrier frequency for transmission to the output stage. At the same time, the RF transceiver is configured to output in differential LVDS (low voltage differential signal) format to generate differential RF signals. The differential RF signals are then passed through an analog filter, which provides band shaping processing. The differential RF signals processed by the band shaping are amplified by the amplifier and output to the transmitting SMA, i.e., RF connector. The transmitting signal is then divided into two parts through a one-to-two power divider, one part is connected to the oscilloscope, and the other part is connected to the S At the receiving end of the DR module, in the receiving part, the RF transceiver supports a differential LVDS interface and can receive differential RF signals. The RF transceiver first amplifies the received signal through a low noise amplifier LNA, then mixes it with the local oscillator signal, and digitizes it after filtering to obtain a digital signal, thus realizing the self-transmission and self-reception of the RF transceiver. The portable computer collects the digital signals obtained by all RF transceivers through FPGA, and selects the transmission channel of one of the RF transceivers as the reference transmission channel. The digital signal generated by it is set as the transmission reference digital signal, and the phase of the digital signal generated by each of the remaining transmission channels is subtracted from the phase of the transmission reference digital signal to obtain the transmission loop phase difference.

[0010] When the main control module controls the SDR module to work in the receiving state, for each RF transceiver, a PE42442 single-pole four-throw (SP4T) RF switch is used to adjust to the receiving state. The first switch is in internal coupling mode, that is, the coupling of the transmitting channel to the receiving channel is realized through the RF line. The SMA from the second to the fourth is external reception. The receiving signal generated by the external source is input to the RF switch, and then input to the RF transceiver in the form of a differential signal for demodulation, filtering and digital processing to obtain a digital signal. The portable computer collects the digital signals obtained by all RF transceivers through FPGA, selects the receiving channel of one of the RF transceivers as the reference receiving channel, and sets the digital signal generated by it as the receiving reference digital signal. The phase of the digital signal generated by each of the remaining receiving channels is subtracted from the phase of the receiving reference digital signal to obtain the receiving phase difference.

[0011] Finally, the portable computer subtracts the transmit loop phase difference from the receive phase difference, and adds the measured cable phase difference to obtain a set of calibrated phase differences as phase calibration coefficients, and sends the calibrated phase differences to the RF transceiver through the FPGA.

[0012] Furthermore, when the FPGA sends down the calibration phase difference, due to the error in the phase orthogonality of the orthogonal power divider of the RF transceiver, the phase shift accuracy of the vector modulator of the RF transceiver will be affected, thereby generating a phase control error of the vector modulator. The iterative phase calibration method is used to repeatedly collect and calculate the calibration phase difference sent down to eliminate the phase control error caused by vector phase modulation. The process of the iterative phase calibration method is to first send down the calculated calibration phase difference, then collect the transmission loop phase difference again, compare the actual corrected phase difference with the sent calibration phase difference, calculate the error between the actual corrected phase difference and the sent calibration phase difference, and then add the error to the sent calibration phase difference and send it down again, and perform multiple iterations until the set accuracy requirement is met.

[0013] Furthermore, the phase shift, i.e., the device error, generated by the power divider and other devices inside the board is difficult to measure, and the phase difference of this part needs to be sent to the RF transceiver through the reading of the oscilloscope. After the sending, the phase synchronization can be completed on the oscilloscope.

[0014] When the system of the present invention is implemented by using the MATLAB algorithm, the transmitting frequency and receiving frequency of the radio frequency transceiver are first configured in the MATLAB program control interface, and the receiving gain and transmitting attenuation are configured at the same time. The receiving gain can improve the sensitivity of the received signal. A highly sensitive receiver can capture the phase information more accurately, thereby improving the accuracy of the phase calibration. The appropriate transmitting signal strength helps to obtain a more accurate phase measurement result. Too strong or too weak signals may affect the accuracy of the phase calibration. Then the signal of the receiving end is collected, and the receiving phase difference between the remaining channels of the receiving end and channel 1 is calculated. Then the transmitting switch of the radio frequency transceiver is turned on, the reception of the external source is stopped, and the receiving switch is switched to self-reception. By using self-transmission and self-reception, the signal of the receiving end is also collected, and the transmitting loop phase difference between the remaining channels of the receiving end and channel 1 is calculated. Then subtract the transmitting loop phase difference from the receiving phase difference. Theoretically, if the phase difference of the cable is zero, the phase difference at this time is the calibration phase difference of the transmitting signal. However, the actual cable has a phase difference, so the phase difference of the cable needs to be taken into account in the phase difference. Due to the error caused by vector phase modulation, the iterative phase calibration method is used to send the phase. The number of iterations can be modified in the program to meet the iteration requirements.

[0015] The beneficial technical effects of the present invention are:

[0016] The present invention receives signals from an external source, adjusts the receiving channel by switching a switch, calculates the phase difference between the receiving waveform and the transmitting waveform, and eliminates the receiving local oscillation by collecting the transmitting loopback signal and the receiving signal.

[0017] The present invention also uses an iterative phase calibration method to correct the phase control error caused by vector phase modulation, without the need for complex device design and excessive correction times, and provides a new idea for solving the problem of random phase of local oscillators in multi-channel reception.

[0018] The present invention also sends the device error on the oscilloscope that is inconvenient to measure to the radio frequency transceiver for calibration, and the phase difference does not need to be calibrated again in the next calibration after power failure because it has been stored in the calibration coefficient, that is, the present invention greatly improves the calibration efficiency and calibration accuracy by calibrating the calculated calibration phase difference, the phase control error of the vector modulator and the device error that is inconvenient to measure;

[0019] The present invention makes full use of the transmitting and receiving characteristics of the radio frequency transceiver, uses the radio frequency transceiver to receive the signal transmitted by itself, eliminates the random phase difference caused by the receiving local oscillator, and does not require a lot of calibration work each time the power is turned on again. The phase calibration can be completed by operating on the MATLAB program control interface.

[0020] The present invention integrates a large number of code programs into a MATLAB program-controlled interface, through which the radio frequency transceiver is controlled to transmit and receive signals, collect transmit and receive signals, compensate transmit and receive links, and calculate and calibrate phases, thereby avoiding excessive programs and cumbersome manual operations. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 It is a structural schematic diagram of an SDR multi-channel phase calibration system based on radio frequency transceiver provided by an embodiment of the present invention;

[0023] Figure 2 is a schematic diagram of the structure of an SDR module provided by an embodiment of the present invention;

[0024] Figure 3 is a schematic diagram of an interactive process of phase calibration provided by an embodiment of the present invention;

[0025] Figure 4 is a time domain waveform diagram of 8 channels before calibration provided by an embodiment of the present invention;

[0026] Figure 5 is a time domain waveform diagram of 8 channels without iterative calibration provided by an embodiment of the present invention;

[0027] Figure 6 It is a time domain waveform diagram of 8 channels after iterative calibration provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] The present invention proposes a SDR multi-channel phase calibration system based on radio frequency transceiver, such as Figure 1As shown, the system includes: a main control module, an SDR module and a portable computer, and the software composition includes a MATLAB algorithm. The key to realizing phase calibration in the present invention is to eliminate the random phase difference of the receiving local oscillator through theoretical derivation and calculate the calibration phase difference required to be sent and the error caused by the correction vector phase modulation.

[0030] As the system control center, the main control module provides the SDR module with synchronous reference clock, second pulse, correction source, local oscillator signal, etc. for synchronous data acquisition / playback.

[0031] The SDR module realizes the acquisition and playback of RF signals. The SDR module includes an FPGA (field programmable gate array), multiple RF transceivers, multiple switches, multiple amplifiers, a memory, and a network port. The FPGA is responsible for the control of the RF transceiver and the interaction of collected data. The RF transceiver is responsible for the generation, modulation, filtering, mixing and digital-to-analog conversion of RF signals. The switch controls the working state of the SDR, and the amplifier amplifies the signal. The memory includes FLASH and DDR3. FLASH is used for onboard information storage, and DDR3 is used for sampled data storage. The network port is a Gigabit network interface for high-speed transmission of sampled data.

[0032] Furthermore, the working principle of the SDR multi-channel phase calibration system based on RF transceiver is:

[0033] By adjusting the clock synchronization interface and synchronization register status of the main control module, the clock source on the main control module is connected to the XTALP (crystal positive end) and XTALN (crystal negative end) pins of the RF transceiver, and the clock synchronization of multiple RF transceivers is controlled, making the phase calibration more efficient.

[0034] When the main control module controls the SDR module to work in the transmitting state, multiple RF transceivers generate I and Q signals at the same time. For each RF transceiver, the generated I and Q signals are recombined and modulated at the carrier frequency for transmission to the output stage. At the same time, the RF transceiver is configured to output in differential LVDS (low voltage differential signal) format to generate differential RF signals. The differential RF signals are then passed through an analog filter, which provides band shaping processing. The differential RF signals processed by the band shaping are amplified by the amplifier and output to the transmitting SMA, i.e., RF connector. The transmitting signal is then divided into two parts through a one-to-two power divider, one part is connected to the oscilloscope, and the other part is connected to the S At the receiving end of the DR module, in the receiving part, the RF transceiver supports a differential LVDS interface and can receive differential RF signals. The RF transceiver first amplifies the received signal through a low noise amplifier LNA, then mixes it with the local oscillator signal, and digitizes it after filtering to obtain a digital signal, thus realizing the self-transmission and self-reception of the RF transceiver. The portable computer collects the digital signals obtained by all RF transceivers through FPGA, and selects the transmission channel of one of the RF transceivers as the reference transmission channel. The digital signal generated by it is set as the transmission reference digital signal, and the phase of the digital signal generated by each of the remaining transmission channels is subtracted from the phase of the transmission reference digital signal to obtain the transmission loop phase difference.

[0035] When the main control module controls the SDR module to work in the receiving state, for each RF transceiver, a PE42442 single-pole four-throw (SP4T) RF switch is used to adjust to the receiving state. The first path of the switch is the internal coupling mode, that is, the coupling of the transmitting channel to the receiving channel is realized through the RF line. The SMA from the second to the fourth path is external reception. The receiving signal generated by the external source is input to the RF switch, and then input to the RF transceiver in the form of a differential signal for demodulation, filtering and digital processing to obtain a digital signal. The portable computer collects the digital signals obtained by all RF transceivers through FPGA, selects the receiving channel of one of the RF transceivers as the reference receiving channel, and sets the digital signal generated by it as the receiving reference digital signal. The phase of the digital signal generated by each of the remaining receiving channels is subtracted from the phase of the receiving reference digital signal to obtain the receiving phase difference. The interactive process is as follows: Figure 3 shown.

[0036] Finally, the portable computer subtracts the transmit loop phase difference from the receive phase difference, and adds the measured cable phase difference to obtain a set of calibrated phase differences as phase calibration coefficients, and sends the calibrated phase differences to the RF transceiver through the FPGA.

[0037] Furthermore, when the FPGA sends down the calibration phase difference, due to the error in the phase orthogonality of the orthogonal power divider of the RF transceiver, the phase shift accuracy of the vector modulator of the RF transceiver will be affected, thereby generating a phase control error of the vector modulator. The iterative phase calibration method is used to repeatedly collect and calculate the calibration phase difference sent down to eliminate the phase control error caused by vector phase modulation. The process of the iterative phase calibration method is to first send down the calculated calibration phase difference, then collect the transmission loop phase difference again, compare the actual corrected phase difference with the sent calibration phase difference, calculate the error between the actual corrected phase difference and the sent calibration phase difference, and then add the error to the sent calibration phase difference and send it down again, and perform multiple iterations until the set accuracy requirement is met.

[0038] Furthermore, the phase shift, i.e., the device error, generated by the power divider and other devices inside the board is difficult to measure, and the phase difference of this part needs to be sent to the RF transceiver through the reading of the oscilloscope. After the sending, the phase synchronization can be completed on the oscilloscope.

[0039] Preferably, the present invention selects 4 RF transceivers with a total of 8 transceiver channels, uses channel 1 as a reference signal, and uses a vector network analyzer to measure the cable phase difference caused by the transmitting cable before calibration.

[0040] When the system of the present invention is implemented by using the MATLAB algorithm, the transmitting frequency and receiving frequency of the radio frequency transceiver are first configured in the MATLAB program control interface, and the receiving gain and transmitting attenuation are configured at the same time. The receiving gain can improve the sensitivity of the received signal. A highly sensitive receiver can capture the phase information more accurately, thereby improving the accuracy of the phase calibration. The appropriate transmitting signal strength helps to obtain a more accurate phase measurement result. Too strong or too weak signals may affect the accuracy of the phase calibration. Then the signal of the receiving end is collected, and the receiving phase difference between the remaining channels of the receiving end and channel 1 is calculated. Then the transmitting switch of the radio frequency transceiver is turned on, the reception of the external source is stopped, and the receiving switch is switched to self-reception. By using self-transmission and self-reception, the signal of the receiving end is also collected, and the transmitting loop phase difference between the remaining channels of the receiving end and channel 1 is calculated.

[0041] Then subtract the transmitting loop phase difference from the receiving phase difference. Theoretically, if the phase difference of the cable is zero, the phase difference at this time is the calibration phase difference of the transmitting signal. However, the actual cable has a phase difference, so the phase difference of the cable needs to be taken into account in the phase difference. Due to the error caused by vector phase modulation, the iterative phase calibration method is used to send the phase. The process of the iterative phase calibration method is to send the phase first, then collect the phase difference of the transmitting loop again, compare the actual corrected phase difference with the sent calibration phase difference, calculate the error between the actual corrected phase difference and the sent calibration phase difference, and then add the error to the sent calibration phase difference and send it again. Repeat this process for multiple iterations until the set accuracy requirement is met. The number of iterations can be modified in the program to meet the iteration requirements.

[0042] The scheme of the present invention is further described below in conjunction with specific embodiments.

[0043] This embodiment uses chip AD9361 as the RF transceiver. The AD9361 multi-chip synchronization mainly includes two parts: baseband synchronization and RF synchronization. The baseband synchronization is implemented by the MCS function of AD9361, and the RF synchronization is divided into two methods, namely the internal local oscillator method and the external local oscillator method. The present invention relates to multi-chip synchronization, which is implemented by using an external local oscillator and transceiver correction. According to the vector modulation principle of AD9361, the calibration of 8 channels of an SDR board is taken as an example. The other boards are similar. First, check the network connection between the portable computer and the main control module, and then configure the required transmission frequency and reception frequency, and then configure the transmission attenuation and reception gain to make the phase calibration more accurate. Then, the collected reception phase difference is calculated through the MATLAB program interface. To simplify the process description, only the phase of the I-channel signal of AD9361 is observed. The phase is The I-way signal expression can be obtained as:

[0044]

[0045] Where A represents the amplitude of the signal, is the initial phase of the main control source, all receiving channels are equal, ωt r is the sampling moment, all receiving channels are equal, To receive the local oscillator phase, each receiving channel is different. The phase of the remaining channels is subtracted from the phase of channel 1 to obtain the received phase difference, which is recorded as Then switch on all the transmit channels of AD9361, and the signal phase obtained after the transmit local oscillator and the receive local oscillator is The expression of the sampling signal at this time can be obtained as:

[0046]

[0047] Among them, wt t is the sampling moment, which is the same for each transmission channel. For receiving the local oscillator phase, each receiving channel is different. is the transmit local oscillator phase, which is different for each transmit channel. Therefore, the transmit loop phase difference is At this time, the signal expression on the oscilloscope is:

[0048]

[0049] Among them, α tx is the phase shift of the transmitting cable. Due to the differences in the transmitting cables, the phase difference of each transmitting cable is different. The phase difference of the cable is Δα tx Subtract the collected receiving phase difference from the collected transmitting loopback phase difference to obtain the calibration phase difference Therefore, each calibration only needs to send Δβ+Δα tx , you can calibrate the phase on the oscilloscope without considering the random phase of the transmitting and receiving local oscillators caused by power on and off.

[0050] The phase calibration process is implemented in MATLAB as follows:

[0051] Step 1, basic configuration: First, configure multiple AD9361s through the MATLAB program interface. It is necessary to configure the transmit frequency, receive frequency, receive gain, transmit attenuation, etc. of the four AD9361s.

[0052] Step 2, calculate the phase correction coefficient: collect orthogonal IQ data from the external source, directly use FPGA to process the IQ data of the SDR module, extract the amplitude and instantaneous phase of each channel under the trigger of the synchronous trigger signal, summarize the amplitude and instantaneous phase information of each channel to the main control module, select channel 1 as the reference channel, and calculate the receiving phase difference β between the remaining channels and the reference channel r ;

[0053] Then the transmit channel is calibrated, and the transmit loop phase difference β between the remaining channels and the reference channel is collected through the transmit loopback. t The phase difference Δα of the 1m cable between the transmitting channel and the oscilloscope is measured using a vector network analyzer. tx , and the phase is compensated. The phase correction coefficient at this time is the transmission loop phase difference of the transmission channel minus the receiving phase difference of the receiving channel plus the cable phase difference of the cable, and the calibration phase difference is obtained, that is, the phase correction coefficient Δγ′=β t -β r +Δα tx .

[0054] Step 3, loading the phase correction coefficient: The phase shifter designed based on vector modulation technology has a simple circuit structure and low cost. In theory, it is not limited by the phase shift step and accuracy. Ideally, the final output signal is:

[0055]

[0056] Among them, V I and V Q is the differential analog voltage component, ω c represents the angular frequency of the signal, represents the initial phase of the signal, For theoretical phase shift, the phase shifter can control the gain and phase of the signal at the same time, but this phase shifter has high requirements on device performance, because the performance of the device will directly affect its phase shift accuracy and gain stability.

[0057] The main consideration is the impact of the phase quadrature error on the phase shift accuracy of the vector modulation phase shifter. Assuming the phase quadrature error is Δθ, the output signal f OUT becomes:

[0058]

[0059] Since the theoretical phase shift is The actual phase shift is It can be seen that due to the existence of the vector phase adjustment error Δθ, the phase shifting accuracy is affected. Therefore, the measured IQ phase circle may be in the nonlinear region. The theoretical phase and the actual control phase are generally divided into two sections, the linear section and the nonlinear section. In the linear section, although there is still a difference between the control value and the actual value, the change is linear, and the difference is only reflected in a very small phase error, while the nonlinear section is manifested as a larger phase error. In order to solve the shortcomings of the phase shifter, an iterative phase calibration method or a phase circle phase correction method can be used to solve it. The present invention adopts an iterative phase calibration method.

[0060] First, normalize the obtained phase correction coefficient to between -180° and 180°, and then convert the offset phase degree Send it to the main control module and collect the phase difference of the transmission loop again Compare the actual corrected phase difference with the sent calibration phase difference, and calculate the error between the actual corrected phase difference and the sent calibration phase difference. Then, the error is added to the phase difference sent down, and the process is sent down again. This process may be repeated multiple times. Considering the time cost and accuracy requirements, this embodiment chooses to repeat 5 times to complete the preliminary correction.

[0061] Step 4, secondary calibration: Since the phase shift generated by the power divider and the board is difficult to measure, it is necessary to perform secondary calibration based on the initial calibration. When the initial calibration is completed, the phase difference on the oscilloscope is the phase difference generated by the power divider and the board. The phase difference on the oscilloscope is then used as the phase correction coefficient Δα that needs to be compensated. kx , the iterative phase correction method is also used to correct the compensation coefficient Δγ″=Δγ′+Δα kx It is sent to the RF transceiver, and the phase difference of multiple channels on the oscilloscope can be corrected at this time, thereby completing the phase correction.

[0062] The above steps require measuring the cable phase difference of the 1m cable of the transmitting channel in advance. Steps 1, 2, and 3 can be directly operated through the MATLAB user interface. After completing steps 1, 2, and 3, step 4 needs to be performed through the phase difference of the oscilloscope, but this only needs to be performed during the first calibration. After the second power-on, the phase calibration can be completed by operating in the MATLAB interface. The following takes the calibration of 8 channels as an example. Figure 4 The figure shows the time domain waveform of 8 channels after initialization before calibration. Figure 5 is the time domain waveform of the 8 channels after non-iterative calibration. Figure 6 It is the time domain waveform of the 8 channels after iterative calibration. It can be seen that the transmitter of AD9361 is basically calibrated, and the iterative calibration method can optimize the calibration accuracy from within 10° to within 3°. The phase difference before and after calibration of each transmitting channel is shown in Table 1:

[0063] Table 1 Phase difference of 8 transmission channels before and after calibration

[0064]

[0065] According to the data in Table 1, it can be found that through the SDR multi-channel phase calibration system based on RF transceiver provided by the present invention, using the MATLAB interface, the multi-channel signal phase can be calibrated to within 3°, and multi-channel phase calibration can be achieved to a large extent, so that the SDR can achieve the establishment of a specific electromagnetic environment standard.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An SDR multi-channel phase calibration system based on radio frequency transceiver, characterized in that: The system includes: a main control module, an SDR module and a portable computer; the main control module serves as the system control center and provides the SDR module with a synchronous reference clock, second pulse, correction source, local oscillator signal, etc. for synchronization of data acquisition / playback; The SDR module realizes the acquisition and playback of RF signals. The SDR module includes an FPGA, multiple RF transceivers, multiple switches, multiple amplifiers, a memory, and a network port. The FPGA is responsible for the control of the RF transceiver and the interaction of collected data. The RF transceiver is responsible for the generation, modulation, filtering, mixing and digital-to-analog conversion of RF signals. The switch controls the working state of the SDR, and the amplifier amplifies the signal. The memory includes FLASH and DDR3. FLASH is used for onboard information storage, and DDR3 is used for sampled data storage. The network port is a Gigabit network interface for high-speed transmission of sampled data.

2. The SDR multi-channel phase calibration system according to claim 1, characterized in that: By adjusting the clock synchronization interface and synchronization register status of the main control module, the clock source on the main control module is connected to the XTALP and XTALN pins of the RF transceiver to control the clock synchronization of multiple RF transceivers; When the main control module controls the SDR module to work in the transmitting state, multiple RF transceivers generate I and Q signals at the same time. For each RF transceiver, the generated I and Q signals are recombined and modulated at the carrier frequency for transmission to the output stage. At the same time, the RF transceiver is configured to output in the low voltage differential signal LVDS format to generate a differential RF signal. The differential RF signal is then passed through an analog filter, which provides frequency band shaping processing. The differential RF signal processed by the frequency band shaping is amplified by the amplifier and output to the transmitting RF connector SMA. The transmitting signal is then divided into two parts through a one-to-two power divider, one part is connected to the oscilloscope, and the other part is connected to the SDR module. At the receiving end of the block, in the receiving part, the RF transceiver supports a differential LVDS interface and can receive differential RF signals. The RF transceiver first amplifies the received signal through a low noise amplifier LNA, then mixes it with the local oscillator signal, and digitizes it after filtering to obtain a digital signal, that is, the RF transceiver realizes self-transmission and self-reception. The portable computer collects the digital signals obtained by all RF transceivers through FPGA, and selects the transmission channel of one of the RF transceivers as the reference transmission channel. The digital signal generated by it is set as the transmission reference digital signal, and the phase of the digital signal generated by each of the remaining transmission channels is subtracted from the phase of the transmission reference digital signal to obtain the transmission loop phase difference.

3. The SDR multi-channel phase calibration system according to claim 2, characterized in that: When the main control module controls the SDR module to work in the receiving state, for each RF transceiver, a single-pole four-throw RF switch is used to adjust it to the receiving state. The first switch is in internal coupling mode, that is, the coupling of the transmitting channel to the receiving channel is realized through the RF line. The SMA from the second to the fourth is external reception. The receiving signal generated by the external source is input to the RF switch, and then input to the RF transceiver in the form of a differential signal for demodulation, filtering and digital processing to obtain a digital signal. The portable computer collects the digital signals obtained by all RF transceivers through FPGA, selects the receiving channel of one of the RF transceivers as the reference receiving channel, and sets the digital signal generated by it as the receiving reference digital signal. The phase of the digital signal generated by each of the remaining receiving channels is subtracted from the phase of the receiving reference digital signal to obtain the receiving phase difference.

4. The SDR multi-channel phase calibration system according to claim 3, characterized in that: Finally, the portable computer subtracts the transmit loop phase difference from the receive phase difference, and adds the measured cable phase difference to obtain a set of calibrated phase differences as phase calibration coefficients, and sends the calibrated phase differences to the RF transceiver through the FPGA.

5. The SDR multi-channel phase calibration system according to claim 4, characterized in that: When the FPGA sends the calibration phase difference, the phase orthogonality of the orthogonal power divider of the RF transceiver has errors, which affects the phase shift accuracy of the vector modulator of the RF transceiver, thereby generating a phase control error of the vector modulator. The iterative phase calibration method is used to repeatedly collect and calculate the calibration phase difference sent to eliminate the phase control error caused by vector phase modulation. The process of the iterative phase calibration method is to first send the calculated calibration phase difference, then collect the transmission loop phase difference again, compare the actual corrected phase difference with the sent calibration phase difference, calculate the error between the actual corrected phase difference and the sent calibration phase difference, and then add the error to the sent calibration phase difference and send it again. Repeated iterations are performed until the set accuracy requirements are met.

6. The SDR multi-channel phase calibration system according to claim 5, characterized in that: The phase shift, i.e., device error, generated by the power divider and other devices inside the board is difficult to measure. The phase difference of this part needs to be sent to the RF transceiver through the reading of the oscilloscope. After the transmission, the phase synchronization is completed on the oscilloscope.

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