A method and device for eliminating Doppler frequency shift of medium and low orbit satellites

Abstract

The present application discloses a method for eliminating the Doppler shift of medium and low orbit satellites, comprising the following steps: calculating the user link Doppler shift and the feeder link Doppler shift according to the satellite position and movement speed at the compensation moment. The sum of the user link Doppler shift and the feeder link Doppler shift is taken as the total Doppler shift, and a single-tone signal is generated according to a frequency deviation value opposite to the total Doppler shift. The received signal of the gateway is down-converted into a baseband signal, the baseband complex signal and the single-tone signal are multiplied, and then up-converted into a radio frequency signal for output. The present application also includes an apparatus for implementing the method. The solution of the present application solves the problem that existing equipment cannot cope with the Doppler shift caused by the high-speed movement of low-orbit satellites in the communication link test based on medium and low orbit satellites.

Description

Technical Field

[0001] The present application relates to the field of satellite communications, and in particular to a method and device for eliminating Doppler frequency shift of medium and low orbit satellites. Background Art

[0002] Satellite communications refer to communications between radio communication equipment on Earth's surface and in the lower atmosphere, using satellites as relays. Within the field of satellite communications, satellites can be categorized as high-, medium-, and low-orbit satellites, depending on their altitude. High-orbit satellites are 35,786 kilometers from Earth, low-orbit satellites are 300–1,500 kilometers from Earth, and medium-orbit satellites are typically 7,000–25,000 kilometers from Earth. High-orbit satellites rotate synchronously with the Earth and are also known as geosynchronous orbit satellites. Both medium- and low-orbit satellites orbit the Earth at high speeds and are considered asynchronous satellites. Except for geosynchronous satellites, medium- and low-orbit satellites experience relative motion with ground terminals and gateways, causing the receiving frequency to shift relative to the transmitting frequency, introducing a Doppler shift.

[0003] In satellite communication systems, the Doppler shift varies with frequency and satellite orbit altitude. The closer the satellite is to the ground, the faster the relative motion. For example, a low-Earth orbit satellite at an altitude of 1000 km, operating at a speed of 7.56 km / s, produces a Doppler shift exceeding 1 MHz for Ka-band signals. Furthermore, the movement of satellite terminals also causes Doppler shift. For example, terminals placed on vehicles such as airplanes and high-speed trains experience significant Doppler shift due to their high speed. Furthermore, because the relative distance and speed between the satellite and terminal change in real time, the Doppler shift is dynamic.

[0004] Doppler shift severely impacts the synchronization mechanisms of wireless communication systems and processes related to signal demodulation and handoff, causing devices to lose network access or even communication interruption. To overcome Doppler shift, satellite communication protocols include procedures for Doppler shift compensation, and communication devices must perform Doppler compensation according to these procedures. The Doppler compensation mechanism is complex, involving estimation and pre-compensation techniques based on ephemeris and orbital information, as well as estimation and compensation techniques based on auxiliary signals. Typically, network-side compensation is combined with user-side compensation, implemented through both physical layer underlying and higher-layer protocol processes. Summary of the Invention

[0005] The present application provides a method and device for eliminating Doppler frequency shift of medium and low orbit satellites on orbit, which can solve the problem that existing equipment is unable to cope with the Doppler frequency shift caused by the high-speed movement of low-orbit satellites in medium and low orbit satellite communication link testing.

[0006] On the one hand, an embodiment of the present application provides a method for eliminating Doppler shift of a medium- and low-orbit satellite, characterized in that it includes the following steps:

[0007] Calculate the user link Doppler shift and feeder link Doppler shift according to the satellite position and movement speed at the compensation time;

[0008] Taking the sum of the user link Doppler frequency shift and the feeder link Doppler frequency shift as the total Doppler frequency shift, generating a single tone signal according to a frequency offset value opposite to the total Doppler frequency shift;

[0009] The signal received by the gateway is down-converted to a baseband signal, the baseband complex signal and the single-tone signal are multiplied, and then up-converted to a radio frequency signal for output.

[0010] Preferably, before the above steps, the following steps are included:

[0011] The satellite position and movement speed at the compensation time are determined based on the satellite trajectory represented by the ephemeris.

[0012] Preferably, the method further comprises the following steps:

[0013] Real-time ephemeris information or pre-stored ephemeris information is provided by the satellite tracking and control system.

[0014] Preferably, in any embodiment of the present application, the following steps are further included:

[0015] The gateway obtains the compensated Doppler residual value through real-time data analysis and signal quality analysis;

[0016] The residual value analysis result is fed back to the Doppler frequency shift elimination device to change the frequency deviation value and improve the accuracy of Doppler frequency shift elimination.

[0017] Preferably, in any embodiment of the present application, the steps are implemented respectively according to the forward link frequency and the reverse link frequency.

[0018] On the other hand, an embodiment of the present application further provides an on-orbit Doppler shift elimination device for medium and low-orbit satellites, comprising:

[0019] A Doppler frequency shift calculator, used to calculate the user link Doppler frequency shift and the feeder link Doppler frequency shift according to the satellite position and movement speed at the compensation time;

[0020] A signal generator, configured to generate a single-tone signal according to a frequency deviation value opposite to the total Doppler frequency shift;

[0021] The downconverter, complex multiplier, and upconverter connected in sequence are used to downconvert the signal received by the gateway into a baseband signal, perform multiplication processing on the baseband complex signal and the single-tone signal, and upconvert the signal into a radio frequency signal output.

[0022] Preferably, the Doppler frequency shift calculator comprises a feedback data interface for receiving a Doppler residual value from a signal processing unit of a gateway; and the Doppler frequency shift calculator corrects the frequency offset value according to the Doppler residual value.

[0023] Preferably, the Doppler shift calculator comprises an ephemeris data interface for receiving ephemeris information from a computing device, a storage device or a satellite measurement and control system.

[0024] Preferably, the on-orbit Doppler shift elimination device for medium and low orbit satellites is divided into a forward link Doppler shift elimination device and a reverse link Doppler shift elimination device; the forward link Doppler shift elimination device or the reverse link Doppler shift elimination device is connected between the gateway station antenna and the gateway station signal processing unit through a switching switch.

[0025] Preferably, in response to a forward link test instruction, the Doppler shift calculator calculates the frequency deviation value under the forward link frequency condition; in response to a reverse link test instruction, the Doppler shift calculator calculates the frequency deviation value under the reverse link frequency condition.

[0026] At least one of the above technical solutions adopted in the embodiments of the present application can achieve the following beneficial effects:

[0027] The present invention primarily uses ephemeris to calculate the Doppler shift of a low- and medium-orbit satellite during its transit, and uses a Doppler shift cancellation device to reversely simulate the Doppler shift, thereby eliminating Doppler shift within the system. Using this method and device to test low- and medium-orbit satellite communication links simplifies the testing process, improves test efficiency, and avoids misjudgments of test results due to an imperfect Doppler compensation process. It also simplifies test system configuration and reduces costs. If the Doppler compensation mechanism is not verified, other testing projects can be carried out in advance, shortening the development cycle of the communication system. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0029] Figure 1 This is a schematic diagram of the satellite communication on-orbit test system;

[0030] Figure 2 Schematic diagram of the angle between the satellite and the ground equipment;

[0031] Figure 3 This is a flow chart of an embodiment of the method of this application;

[0032] Figure 4This is a structural diagram of a Doppler shift elimination device;

[0033] Figure 5 This is the connection diagram of the on-orbit test system. DETAILED DESCRIPTION

[0034] To make the purpose, technical solutions, and advantages of this application more clear, the technical solutions of this application will be clearly and completely described below in conjunction with the specific embodiments of this application and the corresponding drawings. Obviously, the embodiments described are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0035] The following describes in detail the technical solutions provided by various embodiments of the present application in conjunction with the accompanying drawings.

[0036] Figure 1 Schematic diagram of the satellite communication in-orbit test system.

[0037] Low- and medium-orbit broadband satellite communication systems are a rapidly emerging satellite communication technology in recent years. Currently, the communication system and many key technologies are still in the research and development phase, requiring extensive testing to verify the relevant technologies. In-orbit testing utilizes actual satellites in space, along with ground-based gateways, satellite terminals, and other equipment. Measuring instruments are connected to both the ground gateways and satellite terminals to conduct technical verification. In-orbit testing fully recreates the satellite communication environment and scenarios, making it an effective means of system verification.

[0038] For some on-orbit test scenarios, due to limitations in test methods and equipment capabilities, or to prevent the impact of Doppler compensation on test results, it is necessary to eliminate the Doppler shift in the test environment. This invention provides a method and apparatus for eliminating Doppler shift for on-orbit technology testing of medium and low-orbit satellites.

[0039] Figure 2 The angles between the satellite and the ground equipment are shown in Figure 2. The angles between the satellite and the terminal and the gateway are defined as 、 .

[0040] Figure 3 This is a flow chart of an embodiment of the method of this application.

[0041] The present invention provides a method for eliminating Doppler shift of a low-orbit satellite on-orbit, which includes the following steps:

[0042] Step 10: Determine the satellite position and movement speed at the compensation time based on the satellite trajectory represented by the ephemeris.

[0043] Satellite motion is represented by ephemeris. Using this data, we can determine the satellite's coordinates, position, velocity, and other parameters at any given moment. Ephemeris offers exceptional accuracy. It can also be used to determine the angle between the satellite and ground equipment, such as terminals and gateways, and thus calculate the corresponding Doppler.

[0044] Preferably, the method further comprises the following steps: providing real-time ephemeris information or pre-stored ephemeris information through a satellite measurement and control system.

[0045] Step 20: Calculate the user link Doppler shift and the feeder link Doppler shift based on the satellite position and velocity at the compensation time.

[0046] The Doppler shift of the user link is calculated based on the angle. The calculation formula is as follows

[0047] (1)

[0048] in is the satellite moving speed, is the user link operating frequency, The speed of light

[0049] The Doppler shift of the feed link is calculated based on the angle. The calculation formula is as follows

[0050] (2)

[0051] in is the satellite moving speed, is the feeder link operating frequency, The speed of light

[0052] Calculate the total Doppler shift and time curve using the following formula:

[0053] (3)

[0054] In step 20, the compensation moments are formed into a time sequence according to the set time intervals.

[0055] Step 30: Taking the sum of the user link Doppler frequency shift and the feeder link Doppler frequency shift as the total Doppler frequency shift, generate a single tone signal according to a frequency offset value opposite to the total Doppler frequency shift.

[0056] It should be noted that the frequency offset value is time-varying. This is because, as the satellite moves, the compensation moments in step 20 form a time series at set time intervals, and the calculated user link Doppler shift, feeder link Doppler shift, and total Doppler shift are time-varying.

[0057] Step 40: Down-convert the signal received by the gateway into a baseband signal, perform multiplication on the baseband complex signal and the single-tone signal, and then up-convert it into a radio frequency signal for output.

[0058] In step 40, the I and Q signals of the baseband complex signal are multiplied with the single tone signal respectively.

[0059] Step 50: Obtain the compensated Doppler residual value through real-time data analysis and signal quality analysis.

[0060] The gateway feeds back the residual value analysis results to the Doppler shift elimination device to change the frequency deviation value and improve the accuracy of Doppler shift elimination.

[0061] Preferably, in any embodiment of the present application, steps 10 to 50 are respectively implemented according to the forward link frequency and the reverse link frequency to perform the forward link test or the reverse link test.

[0062] Figure 4 This is a structural diagram of the Doppler shift elimination device.

[0063] On the other hand, an embodiment of the present application further provides an on-orbit Doppler shift elimination device for medium and low-orbit satellites, comprising:

[0064] The Doppler shift calculator calculates the Doppler shift of the user link and the feeder link based on the satellite's position and velocity at the compensation time. For example, the Doppler shift calculator uses ephemeris information to calculate the sum of the Doppler shifts of the user link and the feeder link. This sum is then output to the signal generator to set its operating frequency. Ephemeris information can be obtained from two sources: 1. Prestored ephemeris information; 2. Real-time ephemeris information provided by the satellite's tracking and control system.

[0065] The signal generator is configured to generate a single tone signal according to a frequency offset value opposite to the total Doppler frequency shift. The signal generator sets a corresponding operating frequency point in real time according to the frequency shift value calculated by the Doppler frequency shift calculator.

[0066] The filter, downconverter, complex multiplier and upconverter connected in sequence are respectively used to filter out-of-band spurious signals of the received signal to avoid interference from out-of-band signals, downconvert the received signal of the gateway to a baseband signal, multiply the baseband complex signal and the single-tone signal, and upconvert it to a radio frequency signal for output. Preferably, the downconverter: downconverts the received signal to baseband to obtain I and Q data. The complex multiplier: performs complex multiplication on the I and Q data with the signal generated by the signal generator to achieve the Doppler frequency shift of the signal. The upconverter: upconverts the baseband signal to a radio frequency signal and outputs it.

[0067] In a further optimized embodiment, the Doppler shift calculator includes a feedback data interface for receiving a Doppler residual value from a signal processing unit at a gateway; the Doppler shift calculator corrects the frequency offset value based on the Doppler residual value. Furthermore, the Doppler shift setting value is modified using the Doppler residual error fed back by the gateway.

[0068] In a further optimized embodiment, the Doppler shift calculator includes an ephemeris data interface for receiving ephemeris information from a computing device, a storage device or a satellite measurement and control system.

[0069] To support the communication link test of medium and low orbit satellites, the on-orbit Doppler shift elimination device of medium and low orbit satellites is divided into a forward link Doppler shift elimination device and a reverse link Doppler shift elimination device; the forward link Doppler shift elimination device or the reverse link Doppler shift elimination device is connected between the gateway station antenna and the gateway station signal processing unit through a switching switch.

[0070] To support medium and low orbit satellite communication link testing, in response to a forward link test instruction, the Doppler shift calculator calculates the frequency deviation value under the forward link frequency condition; in response to a reverse link test instruction, the Doppler shift calculator calculates the frequency deviation value under the forward link frequency condition.

[0071] The Doppler shift cancellation device generates a frequency deviation value opposite to the Doppler introduced by satellite movement, which is used to offset the system's Doppler shift. In this invention, Doppler shift is achieved by multiplying a multiplier with a single-tone signal. Because the communication system transmits a complex signal, a complex multiplier is used to multiply the baseband complex signal with the single-tone signal to eliminate the Doppler shift. Complex multipliers cannot process radio frequency signals, so the input signal must first be down-converted to a baseband signal through a frequency converter. Similarly, the frequency-shifted signal is then up-converted to a radio frequency signal through a frequency converter.

[0072] Figure 5 This is a connection diagram of the on-orbit test system. Based on the Doppler shift elimination method and device of the present application, the present application proposes a method and system for testing a communication link of a medium- and low-orbit satellite.

[0073] The gateway station consists of a gateway antenna and a signal processing module, connected by an RF cable. A Doppler shift cancellation device is connected between the gateway antenna and the signal processing module via the RF cable. Because the forward and reverse links operate at different frequencies and have different Doppler shifts, two Doppler shift cancellation devices are required to offset the Doppler shift of the forward and reverse links, respectively. A switch controls the on / off function of the two devices.

[0074] like Figure 5The test system is constructed as shown. When testing the forward link characteristics, the forward link's Doppler shift cancellation device is connected via a switch. When testing the reverse link characteristics, the reverse link's Doppler shift cancellation device is connected via a switch.

[0075] In the Doppler shift elimination device, the Doppler shift amount is set based on time, and the compensation value is the total Doppler shift of the path. The opposite of . That is:

[0076] (4)

[0077] At the set starting time Activate the Doppler frequency shift compensation function to compensate for the Doppler frequency shift caused by the high-speed movement of low-orbit satellites;

[0078] Start the terminal and gateway and begin testing.

[0079] The gateway obtains the compensated Doppler residual value through real-time data analysis and signal quality analysis. This residual value analysis feeds the results back to the Doppler shift cancellation device, further improving the accuracy of Doppler shift cancellation.

[0080] Implementation case: Building a test system; calculating the change in user link angle during satellite overpass based on ephemeris and terminal position , record the time point and angle value; calculate the change process of the feeder link angle during the satellite passing by based on the ephemeris and the position of the signal gateway station , record the time point and the angle value; calculate the user link Doppler frequency shift table and the feeder link Doppler frequency shift table based on the angle, and determine the compensation value of the Doppler frequency shift according to time .

[0081]

[0082] in , , the feeding frequency is , The speed of light.

[0083] It should also be noted that the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, commodity, or apparatus that includes a series of elements includes not only those elements but also other elements not explicitly listed, or includes elements inherent to such process, method, commodity, or apparatus. In the absence of further limitations, an element defined by the phrase "comprises a..." does not exclude the presence of other identical elements in the process, method, commodity, or apparatus that includes the element.

[0084] The foregoing is merely an embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application should all be included within the scope of the claims of the present application.

Claims

1. A method for eliminating Doppler shift of medium and low orbit satellites, characterized in that: The following steps are involved: Determine the satellite position and movement speed at the compensation time based on the satellite trajectory indicated by the ephemeris; Calculate the user link Doppler shift and feeder link Doppler shift according to the satellite position and movement speed at the compensation time; Taking the sum of the user link Doppler frequency shift and the feeder link Doppler frequency shift as the total Doppler frequency shift, generating a single tone signal according to a frequency offset value opposite to the total Doppler frequency shift; Down-convert the signal received by the gateway into a baseband signal, multiply the baseband complex signal and the single-tone signal, and then up-convert it into a radio frequency signal for output; The gateway obtains the compensated Doppler residual value through real-time data analysis and signal quality analysis; The residual value analysis result is fed back to the Doppler frequency shift elimination device to change the frequency deviation value and improve the accuracy of Doppler frequency shift elimination.

2. The method for eliminating Doppler shift of low- and medium-orbit satellites as claimed in claim 1, wherein: The following steps are involved: Real-time ephemeris information or pre-stored ephemeris information is provided by the satellite tracking and control system.

3. The method for eliminating Doppler shift of a low- and medium-orbit satellite as claimed in claim 1, wherein: The steps are implemented respectively according to the forward link frequency point and the reverse link frequency point.

4. A device for eliminating Doppler shift of a medium or low orbit satellite, used to implement the method according to any one of claims 1 to 3, characterized in that: Include: A Doppler frequency shift calculator, used to calculate the user link Doppler frequency shift and the feeder link Doppler frequency shift according to the satellite position and movement speed at the compensation time; A signal generator, configured to generate a single-tone signal according to a frequency deviation value opposite to the total Doppler frequency shift; The downconverter, complex multiplier, and upconverter connected in sequence are used to downconvert the signal received by the gateway into a baseband signal, perform multiplication processing on the baseband complex signal and the single-tone signal, and upconvert the signal into a radio frequency signal output.

5. The device for eliminating Doppler frequency shift of a medium or low orbit satellite as claimed in claim 4, characterized in that: The Doppler frequency shift calculator includes a feedback data interface for receiving a Doppler residual value from a signal processing unit of a gateway station; The Doppler shift calculator corrects the frequency offset value according to the Doppler residual value.

6. The device for eliminating Doppler frequency shift of a low-orbit satellite as claimed in claim 4, characterized in that: The Doppler frequency shift calculator comprises an ephemeris data interface for receiving ephemeris information from a computing device, a storage device or a satellite measurement and control system.

7. The device for eliminating Doppler frequency shift of a medium or low orbit satellite as claimed in claim 4, characterized in that: The device is divided into a forward link Doppler frequency shift elimination device and a reverse link Doppler frequency shift elimination device; The forward link Doppler frequency shift device or the reverse link Doppler frequency shift elimination device is connected between the gateway station antenna and the gateway station signal processing unit through a switching switch.

8. The device for eliminating Doppler shift of a low-orbit satellite as claimed in claim 4, wherein: In response to the forward link test instruction, the Doppler shift calculator calculates a frequency deviation value under a forward link frequency point condition; In response to the reverse link test instruction, the Doppler shift calculator calculates a frequency deviation value under a reverse link frequency point condition.

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