Uplink array transmission method and system based on phase-locked loop control

Abstract

The invention belongs to the technical field of deep space exploration, satellite communication and wireless communication, and discloses a phase-locked loop control-based uplink array transmission method, which comprises the following steps of: S1, transmitting an initial uplink signal by a ground station; s2, the target receives the uplink signals and superposes the uplink signals to form aliasing signals, and the target forwards the aliasing signals to a ground station; and S3, the ground station phase-locked loop performs uplink signal phase adjustment according to the aliasing signal. According to the invention, the phase-locked loop is used for automatically calibrating the phase of the uplink signal, so that the defects of complex flow, many limiting conditions and low flexibility in an open-loop correction method are effectively overcome, the phase of the uplink signal can automatically change along with the change of a channel and a ground station, and a special reference signal does not need to be transmitted.

Description

Technical Field

[0001] The invention belongs to the technical fields of deep space exploration, satellite communication and wireless communication, and relates to an uplink array transmission method and system based on phase-locked loop control. Background Art

[0002] In the fields of deep space exploration, satellite communications, wireless communications, etc., since the target is very far away from the ground station, the signal transmission between the target and the ground station faces huge transmission path loss, which puts forward very demanding performance requirements on the communication system. At present, the task of transmitting signals to deep space targets or satellites is generally completed by large-aperture antennas. The larger the antenna aperture, the better the communication performance. However, it is very difficult to improve the performance by continuing to increase the antenna aperture.

[0003] Compared with the downlink array technology, the uplink array technology must solve the problem of phase adjustment of the ground station transmitter. By performing phase compensation at the ground station, the uplink signal can be superimposed in phase at the target. Currently, the open-loop calibration method is mostly used.

[0004] The typical representative of the open-loop calibration method is the uplink array calibration technology based on Very Long Baseline Interferometry (VLBI), such as Figure 1As shown in the figure, the ground station consists of a VLBI receiver and a transmitter, and is divided into three working modes: Mode 1 is the observation mode, using the VLBI receiver to receive the downlink signal; Mode 2 is the transmission channel calibration mode, the ground station transmitter transmits the signal and the VLBI receiver receives the signal; Mode 3 is the uplink working mode, using the transmitter to transmit the uplink signal. Its disadvantages are mainly reflected in the following aspects: (1) It requires close cooperation between the target and the ground station. For example, in the VLBI calibration technology, in order to obtain the geographical location information of each ground station, the target transmits a downlink reference signal to each ground station, and each ground station receives the reference signal and calculates the delay difference of the reference signal reaching each station. In the process of transmitting the reference signal and being received by the ground station, in order to ensure that the signal can be accurately captured and identified, both parties in the air-to-ground communication need to know the prior information such as the signal carrier frequency, symbol rate, and signal waveform. (2) It is necessary to use a specially designed reference signal as a reference to calculate the delay of the propagation link. For example, in VLBI calibration technology, the sum of the geometric delay and the receiving device delay is measured by receiving a reference signal. Then, the sum of the transmitting device delay and the receiving device delay is measured by using a self-transmitting and self-receiving method. Then, the geometric delay is measured. Finally, an algebraic operation is performed to obtain the sum of the geometric delay and the transmitting device delay, which is the calibration value. (3) After the calibration is completed, the transmission parameters will not change with environmental changes within a certain period. For example, the uplink array calibration technology of VLBI belongs to the open-loop calibration method. The significant feature of this method is that its calibration parameters are designed according to the environmental conditions at the time of calibration, and these parameters remain unchanged until the next calibration process arrives. However, environmental conditions are difficult to maintain constant. Using fixed transmission parameters for a period of time will lead to calibration errors. (4) Ground stations need to exchange information, and each station needs to communicate with the reference station. For example, in VLBI calibration technology, after the ground station receives the reference signal, it uses the baseline interference principle to measure the downlink signal delay difference between each station and the reference station. During the calculation process, each station must establish communication with the reference station. Whether using wired communication technology or wireless communication technology will affect the layout of the ground station.

[0005] Another typical open-loop calibration method is the carrier phase parallel calibration method, which mainly uses pseudo-random sequences to distinguish signals transmitted by different ground stations, such as Figure 2As shown. Its disadvantages are mainly reflected in the following aspects: (1) The uplink signal transmitted by the ground station must be a signal modulated with different pseudo-random sequences. For example, in the carrier phase parallel calibration method, in order to separate the uplink signals of each channel at the target, the uplink signal must be a signal modulated with different pseudo-random sequences. Using other non-orthogonal signals cannot achieve signal separation. In addition, in order for the target to accurately receive the signal transmitted by the ground station, close cooperation is required between the air and the ground, and both parties must know the signal prior information. (2) The target needs to have the function of receiving and processing reference signals, which puts higher performance requirements on the target. For example, in the carrier phase parallel calibration method, the ground station transmits an uplink reference signal modulated with different pseudo-random sequences, and the target receives the mixed signals of each channel, uses the good orthogonal performance of the pseudo-random sequence to separate the signals of each channel, and calculates the phase difference. In this process, different from the ordinary receiving and forwarding function, the target must have the ability to separate signals and calculate the phase difference, which puts higher performance requirements on the target. (3) After the target calculates the phase of each uplink signal, it needs to design an air-to-ground communication system to complete the transmission of phase information. For example, in the carrier phase parallel calibration method, in deep space, after the target successfully separates each uplink signal and accurately calculates the phase difference of each signal, the result must be accurately fed back to the ground station for phase compensation operations. In order to ensure that the phase information is accurately transmitted to the ground, a communication system dedicated to transmitting phase information must be built, which is independent of the conventional air-to-ground communication system. This communication system must ensure that the phase information broadcast signal sent by the target can be accurately received by all ground stations, and any error will affect the accuracy of the phase standard. (4) In order to achieve signal separation, it is necessary to sacrifice power to transmit a pseudo-random sequence. For example, in the carrier phase parallel calibration method, the pseudo-random sequence does not carry any useful information, but in order to achieve the separation of the uplink signals at the target, a reference signal modulated with a pseudo-random sequence must be periodically transmitted, which causes the channel that should transmit useful information to transmit the pseudo-random sequence, resulting in a waste of power.

[0006] In summary, the main disadvantages of the two methods are: (1) high requirements for air-ground coordination; (2) high requirements for processing hardware and processing power; (3) poor environmental adaptability; (4) complex calibration equipment and calibration process; (5) limited scope of application. Summary of the invention

[0007] In view of the technical problems existing in the above-mentioned open-loop calibration method, the present invention provides an uplink array transmission method and system based on phase-locked loop control, which uses a phase-locked loop to automatically calibrate the phase of the uplink signal, effectively overcoming the shortcomings of the open-loop correction method, such as complex procedures, many restrictions and low flexibility, so that the phase of the uplink signal can automatically change with the change of the channel and the ground station, and there is no need to transmit a special reference signal.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides an uplink array transmission method based on phase-locked loop control, comprising the following steps:

[0010] S1: The ground station transmits the initial uplink signal;

[0011] S2: The target receives the uplink signal and superimposes it to form an aliased signal, and then forwards the aliased signal to the ground station;

[0012] S3: The ground station phase-locked loop adjusts the uplink signal phase according to the aliased signal.

[0013] The step S3 described in the above technical solution specifically includes:

[0014] S301: a multiplier calculates an error signal between an aliased signal and one of the output signals of a voltage controlled oscillator;

[0015] S302: The error signal is filtered out by a low-pass filter to remove high-frequency components and then enters a phase error detector to obtain an instantaneous phase error signal;

[0016] S303: the instantaneous phase error signal is filtered out again by the loop filter to remove the high frequency component and then enters the voltage controlled oscillator and outputs a signal; the output signal of the voltage controlled oscillator is divided into two paths, one path is used as the ground station transmission signal to be uplinked to the target, and the other path is fed back to the loop input end to calculate the error signal with the aliasing signal;

[0017] S304: The loop is continuously adjusted following the change of the input reference signal, and finally the loop is locked, and the uplink signals of each channel are superimposed in phase at the target.

[0018] The step S301 in the above technical solution specifically includes:

[0019] The aliased signal received by the target is divided into two paths and sent to the multiplier. The two aliased signals are multiplied with the in-phase branch signal and the orthogonal branch signal of one of the output signals of the voltage-controlled oscillator to obtain the error signal of the in-phase branch and the error signal of the orthogonal branch.

[0020] In a second aspect, the present invention further provides an uplink array transmission system based on phase-locked loop control, comprising: a plurality of ground stations and a target, each of the ground stations being provided with a phase-locked circuit, the phase-locked circuit comprising two multipliers, a low-pass filter, a phase error detector, a loop filter and a voltage-controlled oscillator;

[0021] Two multipliers are used to calculate an error signal between the aliased signal and one of the output signals of the voltage controlled oscillator;

[0022] The low-pass filter is used to filter out the high-frequency components in the error signal;

[0023] The phase error detector is used to obtain an instantaneous phase error signal;

[0024] The loop filter is used to filter out the high frequency components in the instantaneous phase error signal;

[0025] A voltage controlled oscillator is used to output the signal.

[0026] In the above technical solution, one of the multipliers is used to multiply one of the aliased signals with the in-phase branch signal of one of the output signals of the voltage-controlled oscillator to obtain an error signal of the in-phase branch, and the other multiplier is used to multiply another aliased signal with the orthogonal branch signal of one of the output signals of the voltage-controlled oscillator to obtain an error signal of the orthogonal branch.

[0027] In a third aspect, the present invention further provides an electronic device, comprising a memory and a processor, wherein the processor and the memory communicate with each other via a bus; the memory stores program instructions executable by the processor, and the processor can execute the above method by calling the program instructions.

[0028] In a fourth aspect, the present invention further provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program is executed by a processor to perform the above method.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The present invention utilizes the advantages of array technology, such as superior performance, flexibility, reliability and low cost, and uses a small-aperture antenna array to transmit uplink signals. The phase of each uplink signal is controlled and adjusted through a phase-locked loop to achieve spatial in-phase superposition enhancement at the target. The present invention is suitable for processing uplink signal phase calibration in the fields of deep space exploration, deep space communication, wireless communication, etc., and can be applied to communication scenarios with fast moving targets and changing atmospheric environments.

[0031] The present invention uses the signal formed by aliasing the uplink signals of each channel through the target repeater as the reference signal for uplink signal alignment, and uses the ground station phase-locked loop to automatically calibrate the uplink signal phase. Each ground station works independently, and there is no need for information interaction and communication between stations, and no need for additional information communication (such as instructions, signaling, etc.) between the air and the ground except for normal communication. The shortcomings of the open-loop correction method, such as complex procedures, many restrictions, and low flexibility, are effectively overcome, so that the uplink signal phase can automatically change with the change of the channel and the ground station, and the uplink signal phase calibration and alignment is automatically realized, and there is no need to set up a ground reference station, transmit a special reference signal, and no special signal specifications or waveforms are required when applied. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of VLBI-based uplink array calibration technology.

[0033] Figure 2 Schematic diagram of the carrier phase calibration method.

[0034] Figure 3 The figure is a schematic diagram of the uplink signal transmission principle based on phase-locked loop control of the present invention.

[0035] Figure 4 The diagram is a schematic diagram of the structure of the phase-locked loop controlling the phase of the uplink signal in the ground station of the present invention. DETAILED DESCRIPTION

[0036] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. Unless otherwise specified, the technical means used in the examples are conventional means known to those skilled in the art. The test methods in the following examples are conventional methods unless otherwise specified.

[0037] Embodiment 1

[0038] Combined with Figure 3 The schematic diagram of the uplink signal transmission principle based on phase-locked loop control of the present invention is shown. In this embodiment, an uplink array transmission method based on phase-locked loop control specifically includes the following steps:

[0039] S1: The ground station transmits the initial uplink signal.

[0040] Each ground station transmits the same uplink signal, but due to the existence of phase error, the signals cannot be superimposed in phase when they are uplinked to the target.

[0041] S2: The target receives the uplink signal and superimposes it to form an aliased signal, and then forwards the aliased signal to the ground station.

[0042] The target receives the uplink signals transmitted by the ground station. These signals are frequency converted, power amplified, and aliased in the target's communication repeater. The target then forwards the aliased signals to the ground station.

[0043] S3: The ground station phase-locked loop (PLL) adjusts the phase of the uplink signal according to the aliased signal. Figure 4 As shown, the specific method is as follows:

[0044] S301: The aliased signal received by the target is divided into two paths and sent to the multiplier. The two aliased signals are multiplied with the in-phase branch signal and the orthogonal branch signal of one of the output signals of the voltage-controlled oscillator (VCO) (i.e., the uplink signal transmitted by the ground station) to obtain the error signal of the in-phase branch and the error signal of the orthogonal branch.

[0045] S302: The error signal passes through a low-pass filter (LPF) to remove high-frequency components and then enters a phase error detector (PD) to obtain an instantaneous phase error signal.

[0046] S303: The instantaneous phase error signal is filtered out again through a loop filter and then enters a voltage-controlled oscillator and outputs a signal; the output signal of the voltage-controlled oscillator is divided into two paths, one path is used as a ground station transmission signal to be uplinked to the target, and the other path is fed back to the loop input end to calculate the error signal with the aliasing signal.

[0047] The loop filter has a low-pass characteristic, which can filter out the high-frequency components of the error signal, suppress the noise outside the loop band, and maintain the stability of the loop. The loop gain K of the phase-locked loop is calculated based on the phase-detection gain of the phase error detector and the voltage-controlled gain of the voltage-controlled oscillator (VCO). Design a suitable loop filter order based on the characteristics of the input error signal. Set the loop bandwidth according to the uplink and downlink delay of the signal to capture the signal. According to parameters such as the loop bandwidth and damping factor, use the relevant formula to calculate the component parameters of the loop filter. Perform multiple iterations and adjustments to obtain parameter values ​​that meet the requirements.

[0048] The voltage controlled oscillator requires a wide linear region of control characteristics, good linearity, high sensitivity, good frequency stability, and an output frequency range that meets the requirements. In the above process, the delay of the VCO output signal from the loop output end to the loop input end should be equal to the delay of the VCO output signal going up to the target, aliasing, and being forwarded down to the loop input end.

[0049] S304: The loop is continuously adjusted following the change of the input reference signal, and finally the loop is locked, and the uplink signals of each channel are superimposed in phase at the target.

[0050] Once the loop is locked, the uplink signals transmitted by each ground station are superimposed in phase at the target location to form a high-power signal.

[0051] In a specific implementation, MATLAB software is used to set the target to work in the Ku band, the number of ground stations is 5, and the distance between them is no more than 40 km. The center frequency of the satellite signal becomes f after down-conversion by the ground station. c =2×10 3 Hz (considering the frequency error); the low-pass filter order is set to 50, and the FIR structure is adopted with linear phase characteristics; the loop filter is set to an ideal second-order loop, the loop filter damping coefficient ξ=0.707, and the system sampling frequency f s =16×10 3 Hz, equivalent noise bandwidth BL = 100Hz, loop bandwidth ω n =188.57Hz, loop filter coefficient C 1 =0.0017C2 =1.3879×e -6 , loop gain K = 1, voltage controlled oscillator center frequency f 0 =2×10 3 Hz.

[0052] Embodiment 2

[0053] The present invention discloses an uplink array transmission system based on phase-locked loop control, comprising: a plurality of ground stations and a target, each of the ground stations is provided with a phase-locked circuit, the phase-locked circuit comprising two multipliers, a low-pass filter, a phase error detector, a loop filter and a voltage-controlled oscillator;

[0054] Two multipliers are used to calculate an error signal between the aliased signal and one of the output signals of the voltage controlled oscillator;

[0055] The low-pass filter is used to filter out the high-frequency components in the error signal;

[0056] The phase error detector is used to obtain an instantaneous phase error signal;

[0057] The loop filter is used to filter out the high frequency components in the instantaneous phase error signal;

[0058] A voltage controlled oscillator is used to output the signal.

[0059] The uplink array transmission system based on phase-locked loop control of the present invention has the following advantages:

[0060] ① Low coordination requirements between air and ground. It is not necessary for the target to transmit a specific reference signal to the ground station or the ground station to the target to measure parameters such as propagation delay. In the present invention, all ground station information is included in the uplink signal, which is aliased and forwarded at the target, and the ground station receives the aliased signal as a reference signal for phase-locked loop adjustment.

[0061] ② No special requirements for signal specifications. Compared with the existing methods, the present invention does not rely on the characteristics of the signal itself to perform signal separation. Therefore, the present method is not limited by signal specifications and is applicable to uplink phase calibration of various signals.

[0062] ③ No additional communication link guarantee is required between ground stations and between ground stations and targets. Different from the existing method which requires information exchange between ground stations and phase information transmission between air and ground, each ground station in the present invention works independently, and no information other than normal operation needs to be transmitted between air and ground.

[0063] ④ No need to change the workflow of the original equipment or system. Unlike the existing method which requires designing an additional process outside the original workflow to complete the calculation of the phase compensation value, this method only needs to add a phase-locked loop guided processing link to the original workflow.

[0064] ⑤ Low requirements on the target signal processing capability. Different from the existing methods, which require the target to have the functions of separating signals and obtaining phases, the method of the present invention only requires the target to have the most basic transparent forwarding capability.

[0065] ⑥ The ground station can automatically adjust the phase of the uplink signal according to changes in the communication environment. As an automatic control device, the phase-locked loop has phase tracking capabilities. When the communication environment changes, the phase difference of the uplink changes. If the ground station still uses the parameters before the change for phase compensation, it will not be able to offset the phase error. The phase-locked loop receives the aliased signal as a reference signal, and the loop adjusts the transmission parameters in time to perform effective phase compensation, which can eventually offset the phase difference and achieve in-phase superposition of each signal at the target.

[0066] The embodiments described above are only preferred embodiments of the present invention and are only used to explain the present invention, not to limit the scope of implementation of the present invention. For those skilled in the art, other implementation methods can certainly be easily made by replacement or modification based on the technical contents disclosed in this specification. Therefore, all changes and improvements made on the principles of the present invention should be included in the scope of the patent application of the present invention.

Claims

1. An uplink array transmission method based on phase-locked loop control, characterized in that: The following steps are involved: S1: The ground station transmits the initial uplink signal; S2: The target receives the uplink signal and superimposes it to form an aliased signal, and then forwards the aliased signal to the ground station; S3: The ground station phase-locked loop adjusts the uplink signal phase according to the aliased signal.

2. The uplink array transmission method based on phase-locked loop control according to claim 1, characterized in that: The step S3 specifically includes: S301: a multiplier calculates an error signal between an aliased signal and one of the output signals of a voltage controlled oscillator; S302: The error signal is filtered out by a low-pass filter to remove high-frequency components and then enters a phase error detector to obtain an instantaneous phase error signal; S303: the instantaneous phase error signal is filtered out again by the loop filter to remove the high frequency component and then enters the voltage controlled oscillator and outputs a signal; the output signal of the voltage controlled oscillator is divided into two paths, one path is used as the ground station transmission signal to be uplinked to the target, and the other path is fed back to the loop input end to calculate the error signal with the aliasing signal; S304: The loop is continuously adjusted following the change of the input reference signal, and finally the loop is locked, and the uplink signals of each channel are superimposed in phase at the target.

3. The uplink array transmission method based on phase-locked loop control according to claim 2, characterized in that: The step S301 specifically includes: The aliased signal received by the target is divided into two paths and sent to the multiplier. The two aliased signals are multiplied with the in-phase branch signal and the orthogonal branch signal of one of the output signals of the voltage-controlled oscillator to obtain the error signal of the in-phase branch and the error signal of the orthogonal branch.

4. An uplink array transmission system for implementing the uplink array transmission method based on phase-locked loop control according to any one of claims 1 to 3, comprising: A plurality of ground stations and a target, characterized in that each of the ground stations is provided with a phase-locked circuit, wherein the phase-locked circuit comprises two multipliers, a low-pass filter, a phase error detector, a loop filter and a voltage-controlled oscillator; Two multipliers are used to calculate an error signal between the aliased signal and one of the output signals of the voltage controlled oscillator; The low-pass filter is used to filter out the high-frequency components in the error signal; The phase error detector is used to obtain an instantaneous phase error signal; The loop filter is used to filter out the high frequency components in the instantaneous phase error signal; A voltage controlled oscillator is used to output the signal.

5. The uplink array transmission system according to claim 4, characterized in that: One of the multipliers is used to multiply one of the aliased signals with the in-phase branch signal of one of the output signals of the voltage-controlled oscillator to obtain an error signal of the in-phase branch, and the other multiplier is used to multiply the other aliased signal with the orthogonal branch signal of one of the output signals of the voltage-controlled oscillator to obtain an error signal of the orthogonal branch.

6. An electronic device, characterized in that: It comprises a memory and a processor, wherein the processor and the memory communicate with each other via a bus; the memory stores program instructions executable by the processor, and the processor calls the program instructions to execute the method according to any one of claims 1 to 3.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method according to any one of claims 1 to 3 is implemented.

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