CN113612523B - Uplink time precompensation algorithm, terminal synchronization method and system - Google Patents
Uplink time precompensation algorithm, terminal synchronization method and system Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/14—Relay systems
- H04B7/15—Active relay systems
- H04B7/185—Space-based or airborne stations; Stations for satellite systems
- H04B7/1851—Systems using a satellite or space-based relay
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/14—Relay systems
- H04B7/15—Active relay systems
- H04B7/185—Space-based or airborne stations; Stations for satellite systems
- H04B7/1851—Systems using a satellite or space-based relay
- H04B7/18519—Operations control, administration or maintenance
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W56/00—Synchronisation arrangements
- H04W56/0005—Synchronisation arrangements synchronizing of arrival of multiple uplinks
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- Y02D30/00—Reducing energy consumption in communication networks
- Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks
Abstract
The invention provides an uplink time precompensation algorithm, a terminal synchronization method and a system, wherein the uplink time precompensation algorithm of a low-earth orbit satellite communication system comprises the following steps: acquiring initial lead of a terminal sending uplink signal according to the fact whether the terminal has a positioning function or not; the satellite calculates the time deviation between the time of receiving the uplink signal and the theoretical receiving time and sends the time deviation to the access network, the access network calculates a time adjustment value according to the time deviation, and the terminal receives the downlink frame and adjusts the time advance. The method considers the high dynamic characteristic of the low-orbit satellite, acquires the initial lead of the terminal sending uplink signal according to the condition whether the terminal has the positioning function, then calculates the time adjustment value accurately in a closed loop manner, and realizes the uplink time synchronization quickly and accurately. Collision among terminal signals is avoided, and efficient and orderly transmission of multiple terminal signals in limited resources is guaranteed.
Description
Technical Field
The invention belongs to the technical field of satellite mobile communication, and particularly relates to an uplink time precompensation algorithm of a low-earth-orbit satellite communication system, a terminal synchronization method and a terminal synchronization system.
Background
As wireless communication applications penetrate into various fields of human activities, in some communication fields such as large range, cross-region and severe environment, a ground network has no function due to limitations of space, environment and the like, and a phenomenon of service and demand mismatch occurs. The reason for this is that the communication network, which mainly depends on the ground for laying base stations and connecting base stations, is limited: base stations cannot be built in large-area oceans, deserts and other areas; the cost of building base stations in the region with rare footprints is high; ground networks are easily damaged when natural disasters occur. The satellite communication network is established to supplement and extend the ground network, so that the defects can be effectively overcome, and the effects of full coverage, large access, destruction resistance, safe communication and the like can be realized. In recent years, due to the huge application value of satellite communication in the fields of military, internet of things and the like, and the limited frequency domain and orbit resources in the near-space field of the earth, each country has developed intense competition in the field of global satellite constellations.
In the aspect of satellite orbit selection, compared with the adoption of a geostationary high-orbit satellite, the adoption of a low-orbit satellite can reduce transmission delay and improve timeliness; the transmission loss is reduced, and the miniaturization of the terminal is facilitated; the establishment of polar orbit constellations can cover the global scope. The particularity of low earth orbit satellite communication mainly lies in the difference of transmission channels, the low earth orbit satellite moves at a high speed around the earth, satellite beams sweep over the ground at a speed of thousands of meters per second, large Doppler frequency shift is caused, dynamic change and frequent switching of network connection relation are caused, and time synchronization is a difficult point and a key point.
Compared with a high-orbit satellite which is static relative to the earth surface and a low-orbit satellite which runs at a high speed relative to the ground, the time delay from the terminal to the satellite mainly depends on the motion and the change of the satellite, the influence of the low-speed motion of the terminal on the time delay can be ignored, but the influence of the motion of the terminal which moves fast (such as in the scenes of riding high-speed rails, airplanes and the like) on the time delay has a certain influence and cannot be ignored. Therefore, how to pre-compensate the uplink time of the low-orbit satellite communication system is more complex and valuable.
Disclosure of Invention
The invention aims to solve the technical problems in the prior art, and aims to provide an uplink time precompensation algorithm, a terminal synchronization method and a terminal synchronization system.
To achieve the above object, according to a first aspect of the present invention, there is provided an uplink time precompensation algorithm for a low earth orbit satellite communication system, comprising the following steps:
s1, determining whether a terminal in communication with a low-orbit satellite has a positioning function, and acquiring initial lead of an uplink signal sent by the terminal according to whether the terminal has the positioning function;
s2, the satellite calculates the time deviation between the time of receiving the uplink signal and the theoretical receiving time and sends the time deviation to an access network, and the access network calculates a time adjustment value according to the time deviation;
s3, judging whether the time adjustment value is smaller than a threshold value, if so, judging that the uplink time precompensation of the terminal meets the requirement, and quitting; if the time adjustment value is larger than the threshold value, the access network sends a downlink frame to the terminal according to the adjustment time, the terminal adjusts the time lead, the uplink time compensation is carried out again, and the step S2 is returned.
The method effectively estimates the uplink time delay of the low-earth-orbit satellite communication, pre-compensates to achieve uplink time synchronization, and the satellite antenna port realizes the alignment of the time of the terminal signal and the satellite reference time, thereby avoiding the collision among the terminal signals and ensuring the efficient and ordered transmission of the multi-terminal signal in the limited resource. The reference point of time is selected as a satellite, and the time reference of sending and receiving must be under the same reference, so that the method is more accurate.
The method considers the high dynamic characteristic of the low-orbit satellite, obtains the initial lead of the terminal sending uplink signal according to whether the terminal has the positioning function, then precisely calculates the time adjustment value in a closed loop, and rapidly and accurately realizes the uplink time synchronization.
According to a preferred embodiment of the present invention, a terminal without a positioning function searches for paging information at a fixed frequency point to obtain an uplink transmission timeslot and a distance from a satellite to a beam center, and calculates an initial advance of an uplink signal.
According to another preferred embodiment of the present invention, for a terminal with a positioning function, a satellite position vector and a terminal position vector are obtained through ephemeris information and terminal position information, a variation relationship between a satellite-ground distance and time is obtained, and a time delay is calculated, that is, an initial advance of an uplink signal is obtained.
Aiming at two types of terminals without a positioning function and with the positioning function, the uplink time compensation method is designed, and the method is simple and easy to implement.
According to a preferred embodiment of the present invention, step S2 specifically includes: by adopting a feedback timing estimation algorithm, the satellite carries out physical layer analysis on the received uplink signal, calculates the time deviation between the time of receiving the uplink signal and the theoretical receiving time, and sends the measured time deviation and analysis data to an access network; and the access network maintains uplink time control for each terminal, and filters within t time according to the time deviation to obtain a relative uplink time adjustment value, wherein t is the total filtering time length.
The closed-loop time adjustment control process designed by the invention carries out filtering processing on the measured value, so that the time adjustment is more reliable. The feedback timing estimation algorithm is convenient for hardware to realize quickly, has high synchronization precision and can realize 1/8 symbol precision.
According to another preferred embodiment of the invention, this is achieved by consecutive multi-frame bursts if the time adjustment range exceeds the maximum range of one adjustment.
If the continuous multi-frame burst adjustment is carried out, the access network sends a new time adjustment value to the terminal once again after the last burst frame is sent and adjusted.
The invention avoids the repeated adjustment of the terminal caused by time delay through repeated adjustment waiting.
To achieve the above object, according to a second aspect of the present invention, there is provided a terminal synchronization method, including the steps of:
s1, determining whether a terminal has a positioning function, and acquiring initial lead of an uplink signal sent by the terminal according to whether the terminal has the positioning function;
s2, receiving a time adjustment value sent by an access network, wherein the time adjustment information calculation method comprises the following steps: according to the time deviation of the receiving time of the uplink signal calculated by the satellite and the theoretical receiving time, the access network calculates a time adjustment value according to the time deviation;
s3, judging whether the time adjustment value is smaller than a threshold value, if so, judging that the uplink time precompensation of the terminal meets the requirement, and quitting; if the time adjustment value is larger than the threshold value, receiving the downlink frame sent by the access network to the terminal according to the adjustment time, and the terminal again performs uplink time compensation and returns to the step S2.
The invention realizes the alignment of the time of the terminal signal and the satellite reference time, avoids the collision among the terminal signals and ensures the efficient and orderly transmission of the multi-terminal signal in the limited resources.
To achieve the above object, according to a third aspect of the present invention, there is provided a low-earth-orbit satellite communication system including a low-earth-orbit satellite, an access network, and at least one terminal communicating with the low-earth-orbit satellite; the low-orbit satellite communication system realizes the uplink time synchronization of the terminal by utilizing the uplink time precompensation algorithm of the low-orbit satellite communication system.
The low-orbit satellite communication system ensures that the time of the terminal signal is aligned with the satellite reference time, avoids collision among the terminal signals and ensures efficient and orderly transmission of the multi-terminal signal in limited resources.
To achieve the above object, according to a fourth aspect of the present invention, there is provided a terminal that performs the terminal synchronization method of the present invention.
The terminal uplink time is aligned with the satellite reference time, so that collision among terminal signals is avoided, and efficient and ordered transmission of multiple terminal signals in limited resources is guaranteed.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
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The above and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
FIG. 1 is a flow chart of an uplink time precompensation algorithm for a low earth orbit satellite communication system in a preferred embodiment of the present invention;
fig. 2 is a schematic diagram illustrating the estimation of the timing advance of a terminal without a positioning function according to a preferred embodiment of the present invention;
FIG. 3 is a flow chart of a closed loop time adjustment control in a preferred embodiment of the present invention;
FIG. 4 is a timing synchronization diagram for a preferred embodiment of the present invention using a Gardner based algorithm;
fig. 5 is a diagram of an interpolation process of the interpolation filter shown in fig. 4.
Detailed Description
Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention and are not to be construed as limiting the present invention.
In the description of the present invention, it is to be understood that the terms "longitudinal", "lateral", "vertical", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, indicate orientations or positional relationships based on those shown in the drawings, and are used only for convenience in describing the present invention and for simplicity in description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed in a particular orientation, and be operated, and thus, should not be construed as limiting the present invention.
In the description of the present invention, unless otherwise specified and limited, it is to be noted that the terms "mounted," "connected," and "connected" are to be interpreted broadly, and may be, for example, a mechanical connection or an electrical connection, a communication between two elements, a direct connection, or an indirect connection via an intermediate medium, and specific meanings of the terms may be understood by those skilled in the art according to specific situations.
For the time when the uplink signal reaches the satellite, the timing reference point is the time when the signal reaches the satellite, and the purpose of timing synchronization is to make the time when the uplink signal reaches the satellite reference point meet the nominal time by adjusting the time when the terminal transmits the signal.
The invention provides an uplink time precompensation algorithm of a low earth orbit satellite communication system, which comprises the following steps as shown in figure 1:
s1, determining whether a terminal in communication with a low earth orbit satellite has a positioning function, and acquiring initial lead of an uplink signal transmitted by the terminal according to whether the terminal has the positioning function. And performing primary coarse synchronization on the terminals without the positioning function and with the positioning function, and then performing closed-loop time accurate adjustment on the basis of preliminary time precompensation.
In this embodiment, a terminal without a positioning function searches for paging information at a fixed frequency point to obtain an uplink transmission time slot and a distance from a satellite to a beam center, and calculates an initial advance of an uplink signal.
Fig. 2 shows a schematic diagram of timing advance estimation of a terminal without a position location. After a terminal without a positioning function is started, firstly, a paging signal is searched and captured on a fixed frequency point to establish a local time reference. Through the paging signal, the terminal obtains parameters such as an uplink transmission time slot, a distance from the satellite to the beam center and the like, and calculates to obtain a time advance 2 (L/c) from the satellite to the beam center, wherein L is the distance from the satellite to the beam center, and c is the light speed. As shown in fig. 2, after the satellite downlink burst is transmitted, the terminal receives the downlink signal after a certain delay, which is caused by the satellite-to-ground distance and can be denoted as L/c. After the downlink transmission is completed, the satellite is ready to receive the uplink signal. However, since the terminal is intended to start uplink transmission after the signal reception is completed, the satellite cannot correctly receive the uplink signal at a predetermined timing. The difference between the actual arrival time of the uplink burst at the satellite and the expected arrival time is 2 (L/c) due to the time offset caused by the distance. Therefore, in order for the satellite to receive the uplink signal on time, it should transmit 2 (L/c) ahead of time.
For a terminal with a positioning function, a satellite position vector and a terminal position vector are obtained through ephemeris information and terminal position information, the change relation of the satellite-ground distance along with time is obtained, time delay is calculated, and an initial uplink time precompensation value of random access burst is obtained, namely the initial lead of an uplink signal. The terminal adjusts the uplink burst time to allow the uplink signal to arrive at the satellite exactly at the assigned time slot with higher accuracy.
The time delay calculation method comprises the following steps:
ΔR＝Rs-Ru
ΔV＝Vs-Vu
wherein Rs is a satellite position vector, ru is a terminal position vector, vs is a satellite velocity vector, vu is a velocity vector of the terminal, Δ V is a relative velocity between the satellite and the terminal, and α is an included angle between the relative velocity between the satellite and the terminal and a connection line between the satellite and the terminal.
And S2, the satellite calculates the time deviation between the time of receiving the uplink signal and the theoretical receiving time and sends the time deviation to the access network, and the access network calculates a time adjustment value according to the time deviation.
After the terminal is subjected to preliminary uplink time precompensation, the uplink information is subjected to accurate closed-loop time synchronization in a specified time slot. As shown in fig. 3, a feedback timing estimation algorithm, which may be but not limited to a Gardner feedback timing estimation algorithm, is specifically used for performing closed-loop time adjustment according to an uplink signal, and a satellite performs physical layer measurement and analysis on the received uplink signal, calculates a time deviation between the time of receiving the uplink signal and a theoretical receiving time, and sends the measured time deviation and analysis data to an access network, where the specifically analysis data is bit information that needs to be uploaded by a terminal; and the access network maintains uplink time control for each terminal, and filters within t time according to the time deviation to obtain a relative uplink time adjustment value, wherein a specific filtering factor can be adjusted according to actual conditions, and t is the total filtering time length.
S3, judging whether the time adjustment value is smaller than a threshold value, if so, judging that the uplink time precompensation of the terminal meets the requirement, and quitting; if the time adjustment value is larger than the threshold value, the access network sends a downlink frame to the terminal according to the adjustment time, the terminal adjusts the time lead, the uplink time compensation is carried out again, and the step S2 is returned.
According to an embodiment, if the time adjustment range is too large, exceeding the maximum range of one adjustment, this is achieved by consecutive multi-frame bursts, e.g. up to 3 consecutive frames of one adjustment.
In order to avoid repeated adjustment, if continuous multi-frame burst adjustment is performed, after the last burst frame is adjusted, the access network sends a new time adjustment value to the terminal again, and when the time adjustment value is specifically performed, the interval between two times of adjustment is T, and T should be greater than the return delay.
The invention can adopt a Gardner feedback-based timing estimation algorithm, and the satellite measures the deviation of the received uplink burst time and the theoretical receiving time. And filtering the uplink time deviation by the access network, and calculating to obtain a time adjustment value. The threshold value can be selected to be 1/8 symbol, whether the adjustment value is smaller than 1/8 symbol or not is judged, and if the adjustment value is within 1/8 symbol, the uplink time precompensation of the terminal meets the requirement; if the deviation exceeds the threshold, the uplink time pre-compensation is carried out again according to the adjustment value, and the synchronization precision of 1/8 symbols is realized.
The method considers the high dynamic characteristic of the low-orbit satellite, obtains the initial lead of the terminal sending uplink signal according to whether the terminal has the positioning function, then precisely calculates the time adjustment value in a closed loop, and rapidly and accurately realizes the uplink time synchronization.
Fig. 4 is a timing synchronization diagram based on Gardner algorithm in a preferred embodiment of the present invention, and for burst signals, a Gardner feedback timing estimation algorithm is used. After passing through the digital matching filter, the signal enters a Gardner timing synchronization recovery loop, and the Gardner timing synchronization recovery loop mainly comprises a timing error detection module, a loop filter, a numerical control oscillator and an interpolation filter, so that an optimal sampling signal is output. Through final fine compensation, 1/8 symbol precision can be achieved. The method comprises the following specific steps:
the interpolation filter implements a data rate conversion function. Fig. 5 is a diagram of an interpolation process according to an embodiment of the present invention, in which a plurality of zero points are first inserted between adjacent sampling points of an uplink signal sampling sequence x (n) at equal intervals, and then a low-pass filter is used for filtering. When the interpolation multiple is 2, the low-pass filter has the characteristic of a half-band filter, and a trigonometric polynomial function is selected to design a realizable low-pass half-band filter. Due to the fact that the coefficients are multiplexed and half of the coefficients are 0, compared with a common low-pass filter, the number of multipliers is reduced to 1/4 of the original number, interpolation is achieved efficiently, and the method is suitable for being implemented on a satellite.
The timing error detector only needs two sampling points per symbol, one is near the symbol decision point, and the other is near the middle of the two symbol decision points, and three sampling points are used continuously to solve the timing error, which is independent of the carrier phase deviation.
The output of the timing error detector is affected by high-frequency noise to generate certain error jitter, and the high-frequency noise is removed by adopting a loop filter.
In loop recovery, the interpolation filter is controlled using a numerically controlled oscillator. And after receiving the error signal, the numerical control oscillator calculates the deviation between the base point and the decimal, and can control the deviation by setting the step length of the numerical control oscillator.
The invention effectively estimates the uplink time delay of low earth orbit satellite communication, performs precompensation to achieve uplink time synchronization, and the satellite antenna port realizes the alignment of the time of terminal signals and the satellite reference time, thereby avoiding the collision among the terminal signals and ensuring the efficient and orderly transmission of the multi-terminal signals in limited resources. The time reference point is selected as a satellite, and the time reference of transmitting and receiving must be under the same reference, so that the time reference is more accurate.
The invention also provides a terminal synchronization method, which comprises the following steps:
s1, determining whether a terminal has a positioning function, and acquiring initial lead of an uplink signal transmitted by the terminal according to the fact whether the terminal has the positioning function;
s2, receiving a time adjustment value sent by an access network, wherein the time adjustment information calculation method comprises the following steps: according to the time deviation of the receiving time of the uplink signal calculated by the satellite and the theoretical receiving time, the access network calculates a time adjustment value according to the time deviation;
s3, judging whether the time adjustment value is smaller than a threshold value, if so, judging that the uplink time precompensation of the terminal meets the requirement, and quitting; if the time adjustment value is larger than the threshold value, receiving a downlink frame sent by the access network to the terminal according to the adjustment time, performing uplink time compensation again by the terminal, and returning to the step S2.
The invention realizes the alignment of the time of the terminal signal and the satellite reference time, avoids the collision among the terminal signals and ensures the efficient and orderly transmission of the multi-terminal signal in the limited resources.
The invention provides a low-orbit satellite communication system, which comprises a low-orbit satellite, an access network and at least one terminal which is communicated with the low-orbit satellite; the low-orbit satellite communication system realizes the uplink time synchronization of the terminal by utilizing the uplink time precompensation algorithm of the low-orbit satellite communication system. The low-orbit satellite communication system ensures that the time of the terminal signal is aligned with the satellite reference time, avoids collision among the terminal signals, and ensures efficient and ordered transmission of multiple terminal signals in limited resources.
The present invention provides a terminal which performs the terminal synchronization method of the present invention. The terminal uplink time is aligned with the satellite reference time, so that collision among terminal signals is avoided, and efficient and orderly transmission of multiple terminal signals in limited resources is guaranteed.
In the description herein, references to the description of the term "preferred embodiment," "one embodiment," "some embodiments," "an example," "a specific example" or "some examples" or the like are intended to mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
While embodiments of the invention have been shown and described, it will be understood by those of ordinary skill in the art that: various changes, modifications, substitutions and alterations can be made to the embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.
Claims (7)
1. An uplink time precompensation algorithm for a low earth orbit satellite communication system is characterized by comprising the following steps of:
s1, determining whether a terminal in communication with a low-earth-orbit satellite has a positioning function, and acquiring initial lead of an uplink signal transmitted by the terminal according to the fact whether the terminal has the positioning function;
for a terminal without a positioning function, searching paging information at a fixed frequency point to obtain an uplink transmission time slot and a distance from a satellite to a beam center, and calculating an initial lead of an uplink signal;
for a terminal with a positioning function, acquiring a satellite position vector and a terminal position vector through ephemeris information and terminal position information, acquiring a change relation of a satellite-ground distance along with time, and calculating time delay, namely the initial advance of an uplink signal;
s2, the satellite calculates the time deviation between the time of receiving the uplink signal and the theoretical receiving time and sends the time deviation to an access network, and the access network calculates a time adjustment value according to the time deviation;
s3, judging whether the time adjustment value is smaller than a threshold value, if so, judging that the uplink time precompensation of the terminal meets the requirement, and quitting; if the time adjustment value is larger than the threshold value, the access network sends a downlink frame to the terminal according to the adjustment time, the terminal adjusts the time advance, the uplink time compensation is carried out again, and the step S2 is returned.
2. The algorithm for precompensation of uplink time for a low earth orbit satellite communication system as claimed in claim 1, wherein said time delay is calculated by:
ΔR＝Rs-Ru
ΔV＝Vs-Vu
in the formula, rs is a satellite position vector, ru is a terminal position vector, vs is a satellite velocity vector, vu is a velocity vector of the terminal, Δ V is a relative velocity between the satellite and the terminal, and α is an included angle between the relative velocity between the satellite and the terminal and a connection line between the satellite and the terminal.
3. The algorithm for pre-compensating uplink time in a low earth orbit satellite communication system as claimed in claim 1, wherein the step S2 specifically comprises:
by adopting a feedback timing estimation algorithm, the satellite carries out physical layer analysis on the received uplink signal, calculates the time deviation between the time of receiving the uplink signal and the theoretical receiving time, and sends the measured time deviation and analysis data to an access network;
and the access network maintains uplink time control for each terminal, and filters within t time according to the time deviation to obtain a relative adjustment value of the uplink time, wherein t is the total filtering time length.
4. The low earth orbit satellite communication system uplink time precompensation algorithm of claim 3, wherein if the time adjustment range exceeds the maximum range of one adjustment, the algorithm is implemented by continuous multi-frame bursts.
5. The algorithm of claim 4, wherein if the burst adaptation is performed for a plurality of consecutive frames, the access network sends a new time adaptation value to the terminal after the transmission adaptation for the last burst frame.
6. A terminal synchronization method is characterized by comprising the following steps:
s1, determining whether a terminal has a positioning function, and acquiring initial lead of an uplink signal sent by the terminal according to whether the terminal has the positioning function;
for a terminal without a positioning function, searching paging information at a fixed frequency point to obtain an uplink transmission time slot and a distance from a satellite to a beam center, and calculating the initial lead of an uplink signal;
for a terminal with a positioning function, acquiring a satellite position vector and a terminal position vector through ephemeris information and terminal position information, acquiring a change relation of satellite-to-ground distance along with time, and calculating time delay, namely initial lead of an uplink signal;
s2, receiving a time adjustment value sent by an access network, wherein the time adjustment information calculation method comprises the following steps: according to the time deviation of the receiving time of the uplink signal calculated by the satellite and the theoretical receiving time, the access network calculates a time adjustment value according to the time deviation;
s3, judging whether the time adjustment value is smaller than a threshold value, if so, judging that the uplink time precompensation of the terminal meets the requirement, and quitting; if the time adjustment value is larger than the threshold value, receiving a downlink frame sent by the access network to the terminal according to the adjustment time, performing uplink time compensation again by the terminal, and returning to the step S2.
7. A low-earth-orbit satellite communication system, comprising a low-earth-orbit satellite, an access network, and at least one terminal in communication with the low-earth-orbit satellite;
the low earth orbit satellite communication system uses the method of one of claims 1 to 5 to achieve uplink time synchronization of terminals.
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| CN114365016A (en) * | 2021-12-17 | 2022-04-15 | 北京小米移动软件有限公司 | Method and device for measuring Global Navigation Satellite System (GNSS) |
| CN114158128B (en) * | 2022-02-10 | 2022-05-17 | 北京理工大学 | Asymmetric dynamic time slot communication method and device for covert communication of synchronous orbit satellite |
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