CN114025422B - Open loop uplink frequency synchronization method and device for low orbit satellite communication system - Google Patents
Open loop uplink frequency synchronization method and device for low orbit satellite communication system Download PDFInfo
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- CN114025422B CN114025422B CN202111413211.4A CN202111413211A CN114025422B CN 114025422 B CN114025422 B CN 114025422B CN 202111413211 A CN202111413211 A CN 202111413211A CN 114025422 B CN114025422 B CN 114025422B
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- H04W56/0005—Synchronisation arrangements synchronizing of arrival of multiple uplinks
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
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- H04B7/00—Radio transmission systems, i.e. using radiation field
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- H04B7/1851—Systems using a satellite or space-based relay
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- H—ELECTRICITY
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- H04W56/0035—Synchronisation arrangements detecting errors in frequency or phase
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
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- H04W56/0055—Synchronisation arrangements determining timing error of reception due to propagation delay
- H04W56/0065—Synchronisation arrangements determining timing error of reception due to propagation delay using measurement of signal travel time
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Abstract
The invention discloses an open loop uplink frequency synchronization method and device of a low orbit satellite communication system, which are applicable to the satellite communication system and belong to the technical field of satellite communication; estimating downlink frequency deviation according to each measured frequency deviation between a satellite and a terminal; calculating an uplink frequency deviation according to the downlink frequency deviation; calculating an uplink frequency precompensation value according to the uplink frequency deviation; and according to the uplink frequency precompensation value, realizing uplink frequency synchronization of the satellite and the terminal. Compared with the closed-loop synchronization process, the method has the advantages that the time delay is short, the open-loop synchronization is not needed by ephemeris information, the problem that the satellite link resource waste is large due to frequent ranging in the traditional synchronization method is avoided, the accuracy is high, the realization flow is simple, and the problem of uplink synchronization of a low-orbit satellite communication system can be rapidly and efficiently solved.
Description
Technical Field
The invention relates to an open loop uplink frequency synchronization method and device of a low-orbit satellite communication system, and belongs to the technical field of satellite communication.
Background
The low orbit satellite communication system can realize communication link at any place and any moment in the global scope, and solves the problem of coverage blind areas of the ground communication network. As a backup and supplement to the terrestrial communication network, the low-orbit satellite communication system becomes an important component of the future personal communication system due to the advantages of global coverage, low power consumption and the like. The low orbit satellite is in a high-speed motion state relative to the ground, and the Doppler frequency offset, the Doppler frequency change rate, the transmission delay and the delay change rate show rapid time-varying characteristics along with the movement of the satellite. In order to avoid time-frequency interference between uplink users, the low-orbit satellite system with inter-satellite links adopts satellites as frequency references for uplink, and needs time-frequency offset precompensation before uplink transmission, the smaller the time-frequency offset of a terminal reaching the satellites is, the smaller the time-frequency guard interval of a channel can be set, thereby improving the frequency spectrum efficiency and reducing the complexity of satellite processing. But the high doppler rate of change, high time delay rate of change of the low orbit satellites present a significant challenge to uplink time-frequency synchronization of the terminal.
At present, in order to solve the problem of uplink frequency synchronization of a low-orbit satellite communication system, a closed-loop synchronization method can be used for referencing a ground mobile communication system, and the closed-loop synchronization needs the satellite to carry out statistics and closed-loop adjustment according to the time-frequency offset difference of an uplink physical channel. Therefore, research on how to quickly and efficiently realize uplink synchronization of a low-orbit satellite communication system becomes a technical difficulty to be solved.
Disclosure of Invention
The invention aims to provide a method and a device for synchronizing open loop uplink frequency of a low-orbit satellite communication system. The invention pre-compensates the uplink frequency offset based on the downlink physical channel measurement process, firstly, the terminal estimates the downlink frequency offset according to the measured frequency offset and the downlink frequency pre-compensation, then converts the uplink frequency offset according to the downlink frequency offset, and finally calculates the uplink frequency pre-compensation value according to the uplink frequency offset. Compared with the closed-loop synchronization process, the method has the advantages that the time delay is short, the open-loop synchronization is not needed by ephemeris information, the problem that the satellite link resource waste is large due to frequent ranging of the traditional synchronization method is avoided, the implementation process is simple, and the problem of uplink synchronization of a low-orbit satellite communication system can be quickly and efficiently solved.
The invention adopts the following technical scheme for solving the technical problems:
in a first aspect of the present invention, the present invention provides a method for synchronizing an open loop uplink frequency of a low-orbit satellite communication system, comprising:
estimating downlink frequency deviation according to each measured frequency deviation between the satellite and the terminal;
calculating an uplink frequency deviation according to the downlink frequency deviation;
calculating an uplink frequency precompensation value according to the uplink frequency deviation;
and according to the uplink frequency precompensation value, realizing uplink frequency synchronization of the satellite and the terminal.
Further, the downstream frequency offset includes summing respective frequency offsets between the downstream frequency satellite and the terminal, the downstream frequency offset expressed as:
f D ＝f d1 +f csat +f cue +f a
wherein f D Representing a downlink frequency offset between the satellite and the terminal; f (f) d1 Indicating Doppler frequency deviation generated by relative motion of the satellite and the terminal; f (f) csat Representing the frequency deviation caused by the satellite crystal oscillator; f (f) cue Representing the frequency deviation caused by the terminal crystal oscillator, f a And the frequency deviation caused by the terminal frequency deviation estimation algorithm is represented.
Further, the downlink frequency deviation further includes pre-compensating and summing each frequency deviation between the satellite and the terminal and the downlink frequency of the terminal, where the downlink frequency deviation is expressed as:
f D ＝f d1 +f csat +f cue +f a +f dpre
wherein f D Representing a downlink frequency offset between the satellite and the terminal; f (f) d1 Indicating Doppler frequency deviation generated by relative motion of the satellite and the terminal; f (f) csat Representing the frequency deviation caused by the satellite crystal oscillator; f (f) cue Representing frequency deviation caused by terminal crystal oscillator; f (f) a Representing frequency deviation caused by a terminal frequency deviation estimation algorithm; f (f) dpre Indicating the downlink frequency precompensation of the terminal.
Further, the calculating method of the downlink frequency precompensation of the terminal includes calculating the Doppler change rate of the previous moment according to ephemeris information, multiplying the Doppler change rate by the time difference between the current moment and the previous moment to obtain the downlink frequency precompensation of the terminal, which is expressed as:
f dpre ＝a(t i -t i-1 )
wherein a represents the Doppler change rate at the previous time, t i Indicating the current time, t i-1 Indicating the previous moment.
Further, the downlink frequency precompensation of the terminal is expressed as:
wherein f Di-1 Representing a downlink frequency offset between the satellite and the terminal at a previous time instant; f (f) Di-2 Representing the downlink frequency deviation between the satellite and the terminal at the previous two moments; t is t i Indicating the current time, t i-1 Indicating the previous time, t i-2 Indicating the first two moments.
Further, the uplink frequency deviation is expressed as:
f U ＝-(f D )*f u0 /f d0
wherein f u0 Representing the uplink carrier center frequency; f (f) d0 Representing the downlink carrier center frequency.
Further, the uplink frequency precompensation value is expressed as:
f upre ＝-(f d2 +f csat +f cue )*f u0 /f d0
wherein f upre Representing upstream frequency precompensation; f (f) d2 Doppler frequency offset for the downlink and uplink time difference T.
In a second aspect of the present invention, there is also provided an open loop uplink frequency synchronization apparatus for a low orbit satellite communication system, the apparatus comprising:
a measurement unit for measuring each frequency deviation between the satellite and the terminal;
the estimating unit is used for estimating downlink frequency deviation according to each measured frequency deviation between the satellite and the terminal;
the conversion unit is used for calculating the uplink frequency deviation according to the downlink frequency deviation;
the calculation unit is used for calculating an uplink frequency precompensation value according to the uplink frequency deviation;
and the synchronization unit is used for realizing the uplink frequency synchronization of the satellite and the terminal according to the uplink frequency precompensation value.
In a third aspect of the invention, the invention also provides an apparatus comprising at least one processor for performing an open loop uplink frequency synchronization method of a low orbit satellite communication system according to the first aspect of the invention and at least one memory coupled to the processor.
The invention has the beneficial effects that:
compared with the closed-loop synchronization process, the method has the advantages that the time delay is short, the open-loop synchronization is not needed by ephemeris information, the problem that the frequent ranging of the traditional synchronization method wastes large satellite link resources is avoided, the downlink frequency deviation is estimated through the frequency deviation between the satellite and the terminal, and the uplink frequency deviation is calculated according to the downlink frequency deviation; calculating an uplink frequency precompensation value according to the calculated uplink frequency deviation, and finally realizing uplink frequency synchronization of the satellite and the terminal according to the uplink frequency precompensation value; the method fully utilizes the relation between the uplink frequency deviation and the downlink frequency deviation to finish the correction of the uplink synchronization, has high accuracy and simple realization flow, and can rapidly and efficiently solve the problem of the uplink synchronization of the low-orbit satellite communication system.
Drawings
FIG. 1 is a flow chart of an open loop uplink frequency synchronization method for a low orbit satellite communication system according to an embodiment of the present invention;
FIG. 2 is a flow chart of an open loop uplink frequency synchronization method of a low orbit satellite communication system according to the preferred embodiment of the invention;
FIG. 3 is a schematic diagram of a downlink frequency deviation measurement interpolation process according to an embodiment of the present invention;
FIG. 4 is a block diagram of an open loop uplink frequency synchronization apparatus for a low-orbit satellite communication system according to an embodiment of the present invention;
fig. 5 is a block diagram of an apparatus in an embodiment of the invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Fig. 1 is a flowchart of an open loop uplink frequency synchronization method of a low-orbit satellite communication system according to an embodiment of the present invention, as shown in fig. 1, where the method includes:
101. estimating downlink frequency deviation according to each measured frequency deviation between the satellite and the terminal;
in this step, the terminal estimates the downlink frequency deviation according to the received downlink synchronization channel, broadcast channel, dedicated channel, wherein each frequency deviation between the measured satellite and the terminal includes Doppler deviation f generated by the relative motion of the satellite and the terminal d1 Frequency deviation f caused by satellite crystal oscillator csat Frequency deviation f caused by terminal crystal oscillator cue And frequency deviation f caused by a terminal frequency deviation estimation algorithm a Etc., the calculation formula is expressed as:
f D ＝f d1 +f csat +f cue +f a
wherein f D Representing the downlink frequency offset between the satellite and the terminal.
Doppler deviation f generated by relative motion of satellite and terminal d1 The calculation formula is as follows:
wherein f represents a carrier frequency; c represents the speed of light; v denotes the relative movement speed between the satellite and the terminal; θ represents the angle between the satellite and the moving direction of the terminal.
In one embodiment, the satellite crystal induced frequency deviation f csat The maximum deviation was 1.995kHz, calculated as 1.995G,1 ppm. Frequency deviation f caused by terminal crystal oscillator cue The maximum deviation was 1.995kHz. Frequency deviation f caused by terminal frequency deviation estimation algorithm a Smaller, typically no higher than 20Hz.
102. Calculating an uplink frequency deviation according to the downlink frequency deviation;
the terminal generates a downlink frequency deviation f according to the step 101 D Calculating the uplink frequency deviation f U The method comprises the steps of carrying out a first treatment on the surface of the The calculation formula is as follows:
f U ＝-(f D )*f u0 /f d0
f U ＝-(f d1 +f csat +f cue +f a )*f u0 /f d0
wherein f u0 Representing the uplink carrier center frequency; f (f) d0 Representing the downlink carrier center frequency.
103. Calculating an uplink frequency precompensation value according to the uplink frequency deviation;
the uplink frequency precompensation value is expressed as:
f upre ＝-(f d2 +f D -f d1 -f a )*f u0 /f d0
f upre ＝-(f d2 +f csat +f cue )*f u0 /f d0
wherein f upre Representing an uplink frequency precompensation, which is to achieve zero frequency offset of the satellite after terminal compensation in an ideal case; f (f) d2 Doppler frequency offset for the downlink and uplink time difference T.
104. And according to the uplink frequency precompensation value, realizing uplink frequency synchronization of the satellite and the terminal.
In order to achieve uplink frequency synchronization, f is needed according to the above analysis U ＝f upre Since the Doppler shift increases with increasing frequency, the low-orbit satellite Doppler frequency change rate is assumed to take on a value of 500Hz/s. When the value of T is 0.5s, the Doppler frequency deviation is 500Hz/s, 0.5s=250 Hz.
According to the S frequency band n70, the uplink frequency is 1695 MHz-1710 MHz, the downlink frequency is 1995 MHz-2020 MHz, f u0 Highest taken at 1710MHz, f d0 The minimum is 1995MHz.
The satellite crystal oscillator has small change within 0.5s, and is generally sealed and insulated, so that the deviation generated by the satellite crystal oscillator is offset after the downlink conversion. Similarly, the deviation generated by the terminal crystal oscillator is offset after being converted with the downlink.
That is to say that- (f) d1 +f a )＝-(f d2 ) Equal, therefore there is: f (f) d2 ＝f d1 +f a The method comprises the steps of carrying out a first treatment on the surface of the The core needs to counteract the frequency deviation f caused by the frequency deviation estimation algorithm a Doppler frequency deviation f generated by relative motion between satellite and terminal d1 The method comprises the steps of carrying out a first treatment on the surface of the Therefore, the invention generates Doppler frequency offset f by the time difference T between the downlink and the uplink d2 To achieve uplink frequency synchronization of the satellite and the terminal.
The deviation of the frequency offset estimation is 20Hz/f d0 *f u0 = (20/1995 x 1710) hz=17 Hz, total upstream frequency deviation f U ＝(250+17)Hz＝267Hz。
Therefore, in this embodiment, the uplink frequency of the terminal is adjusted according to the uplink frequency deviation calculated in 0.5s, that is, the uplink frequency precompensation value, and the error 267Hz, so as to achieve uplink frequency synchronization between the satellite and the terminal.
Fig. 2 is a flowchart of an open loop uplink frequency synchronization method of a low-orbit satellite communication system according to an embodiment of the present invention, and as shown in fig. 2, the method includes:
201. pre-compensating and estimating downlink frequency deviation according to each measured frequency deviation between the satellite and the terminal and the downlink frequency;
in this step, the terminal estimates the downlink frequency deviation according to the received downlink synchronization channel, broadcast channel, dedicated channel, wherein each frequency deviation between the measured satellite and the terminal includes Doppler deviation f generated by the relative motion of the satellite and the terminal d1 Frequency deviation f caused by satellite crystal oscillator csat Frequency deviation f caused by terminal crystal oscillator cue And frequency deviation f caused by a terminal frequency deviation estimation algorithm a Besides, the invention also performs downlink frequency precompensation on the satellite side, so that the actual downlink frequency deviation=measured frequency deviation+downlink frequency precompensation, and the calculation formula of the downlink frequency deviation is expressed as:
f D ＝f d1 +f csat +f cue +f a +f dpre
wherein f D Representing a downlink frequency offset between the satellite and the terminal; f (f) d1 Indicating Doppler frequency deviation generated by relative motion of the satellite and the terminal; f (f) csat Representing the frequency deviation caused by the satellite crystal oscillator; f (f) cue Representing frequency deviation caused by terminal crystal oscillator; f (f) a Representing frequency deviation caused by a terminal frequency deviation estimation algorithm; f (f) dpre Indicating the downlink frequency precompensation of the terminal.
In one embodiment, the calculating manner of the downlink frequency precompensation of the terminal includes:
calculating the Doppler change rate of the previous moment according to the ephemeris information, multiplying the Doppler change rate by the time difference between the current moment and the previous moment to obtain the downlink frequency precompensation of the terminal, which is expressed as:
f dpre ＝a(t i -t i-1 )
wherein a represents the Doppler change rate at the previous time, t i Indicating the current time, t i-1 Indicating the previous moment.
In another embodiment, the calculating manner of the downlink frequency precompensation of the terminal may further include:
the downlink frequency precompensation is expressed as:
wherein f Di-1 Representing a downlink frequency offset between the satellite and the terminal at a previous time instant; f (f) Di-2 Representing the downlink frequency deviation between the satellite and the terminal at the previous two moments; t is t i Indicating the current time, t i-1 Indicating the previous time, t i-2 Indicating the first two moments.
In some preferred embodiments, in addition to performing interpolation processing using the downlink frequency deviation at the past two times, this embodiment may also perform interpolation processing using the downlink frequency deviation measurement value at the past N times, and the interpolation manner may be referred to the above embodiments.
202. Calculating an uplink frequency deviation according to the downlink frequency deviation;
the terminal follows the downlink frequency deviation f of step 201 D Calculating the uplink frequency deviation f U The method comprises the steps of carrying out a first treatment on the surface of the The calculation formula is as follows:
f U ＝-(f D )*f u0 /f d0
f U ＝-(f d1 +f csat +f cue +f a +f dpre )*f u0 /f d0
in one embodiment, at t 2 Time sum t 3 Time of day, for example, t is calculated from ephemeris information 2 The Doppler change rate of time is a, t 3 Time downlink frequency offset f D3 The calculation method of (1) is as follows:
f D3 ＝f D2 +a(t 3 -t 2 )
in another embodiment, at t 1 Time t 2 Time sum t 3 For example, the time is obtained by linearly estimating the frequency deviation of the time point of transmitting the uplink signal according to the frequency deviation of the past 2 downlink bursts, and converting the frequency deviation into the uplink frequency deviation as an uplink frequency precompensation value. As shown in fig. 3, let t be 1 Time t 2 The downlink frequency offset at the moment is f D1 ，f D2 ，t 3 Time downlink frequency offset f D3 The calculation method of (1) is as follows:
f D3 ＝(f D2 -f D1 )(t 3 -t 1 )/(t 2 -t 1 )+f D1
203. calculating an uplink frequency precompensation value according to the uplink frequency deviation;
thus t 3 Time uplink frequency offset f U3 ：
f U3 ＝-f D3 *f u0 /f d0
The calculation method of the uplink frequency compensation value is expressed as follows:
f upre ＝-(f d2 +f csat +f cue )*f u0 /f d0
wherein f upre Representing upstream frequency precompensation; f (f) d2 Doppler frequency offset for the downlink and uplink time difference T.
204. And according to the uplink frequency precompensation value, realizing uplink frequency synchronization of the satellite and the terminal.
Likewise, uplink frequency synchronization of the satellite and the terminal is achieved by adjusting the uplink frequency compensation value.
The accuracy error of the embodiment of the invention is the sum of the change rate error, the algorithm error and the crystal oscillator error, so that the maximum deviation can be controlled to be not higher than 200Hz, and the requirement of uplink frequency synchronization is met.
Fig. 4 is a block diagram of an open loop uplink frequency synchronization apparatus of a low-orbit satellite communication system according to an embodiment of the present invention, and as shown in fig. 4, the apparatus includes:
301. a measurement unit for measuring each frequency deviation between the satellite and the terminal;
the frequency deviation between the satellite and the terminal measured by the measuring unit comprises Doppler deviation f generated by the relative motion of the satellite and the terminal d1 Frequency deviation f caused by satellite crystal oscillator csat Frequency deviation f caused by terminal crystal oscillator cue And frequency deviation f caused by a terminal frequency deviation estimation algorithm a Etc. 302. The estimating unit is used for estimating downlink frequency deviation according to each measured frequency deviation between the satellite and the terminal;
the estimation unit estimates the measured frequency deviation to obtain a downlink frequency deviation, and the calculation formula is expressed as follows:
f D ＝f d1 +f csat +f cue +f a
the estimation unit may further estimate the measured frequency deviation and the downlink frequency precompensation at the satellite side together to obtain a downlink frequency deviation, where the calculation formula is expressed as:
f D ＝f d1 +f csat +f cue +f a +f dpre
303. the conversion unit is used for calculating the uplink frequency deviation according to the downlink frequency deviation;
the conversion unit converts the uplink frequency deviation according to the downlink frequency deviation to be expressed as:
f U ＝-(f D )*f u0 /f d0
that is, can be expressed as:
f U ＝-(f d1 +f csat +f cue +f a )*f u0 /f d0
or may be expressed as:
f U ＝-(f d1 +f csat +f cue +f a +f dpre )*f u0 /f d0
304. the calculation unit is used for calculating an uplink frequency precompensation value according to the uplink frequency deviation;
the calculating unit calculates an uplink frequency precompensation value according to the uplink frequency deviation, and the uplink frequency precompensation value is expressed as:
f upre ＝-(f d2 +f D -f d1 -f a )*f u0 /f d0
can also be expressed as:
f upre ＝-(f d2 +f csat +f cue )*f u0 /f d0
305. and the synchronization unit is used for realizing the uplink frequency synchronization of the satellite and the terminal according to the uplink frequency precompensation value.
The synchronization unit adjusts the uplink frequency compensation value f upre To achieve uplink frequency synchronization of the satellite and the terminal.
Fig. 5 is an apparatus in an embodiment of the invention comprising at least one processor 410 and at least one memory 430, the processor 410 being configured to perform an open loop uplink frequency synchronization method of a low orbit satellite communication system according to the invention, the memory 430 being coupled to the processor 410, preferably the memory 430 being coupled to the processor 410 via a bus 420.
Alternatively, it will be understood by those skilled in the art that the structure shown in fig. 5 is only schematic, and the electronic device may also be a terminal device such as a smart phone (e.g. an Android phone, an iOS phone, etc.), a tablet computer, a palm computer, and a mobile internet device (Mobile Internet Devices, MID), a PAD, etc. Fig. 5 is not limited to the structure of the electronic device and the electronic apparatus described above. For example, the electronic device may also include more or fewer components (e.g., network interfaces, etc.) than shown in FIG. 5, or have a different configuration than shown in FIG. 5.
The memory 430 may be used to store software programs and modules, such as program instructions/modules corresponding to an open loop uplink frequency synchronization method and apparatus of a low-orbit satellite communication system in the embodiment of the present invention, and the processor 410 executes various functional applications and data processing by running the software programs and modules stored in the memory 430, thereby implementing the open loop uplink frequency synchronization method of the low-orbit satellite communication system. Memory 430 may include high-speed random access memory, but may also include non-volatile memory, such as one or more magnetic storage devices, flash memory, or other non-volatile solid-state memory. In some examples, memory 430 may further include memory located remotely from processor 410, which may be connected to the terminal via a network. Examples of such networks include, but are not limited to, the internet, intranets, local area networks, mobile communication networks, and combinations thereof. The memory 430 may be, but is not limited to, a memory for storing information such as parameters of an open loop uplink frequency synchronization method of a low-orbit satellite communication system.
Finally, it is noted that the above-mentioned preferred embodiments are only intended to illustrate rather than limit the invention, and that, although the invention has been described in detail by means of the above-mentioned preferred embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention as defined by the appended claims.
In the description of the present invention, it should be understood that the terms "coaxial," "bottom," "one end," "top," "middle," "another end," "upper," "one side," "top," "inner," "outer," "front," "center," "two ends," etc. indicate or are based on the orientation or positional relationship shown in the drawings, merely to facilitate description of the invention and simplify the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and therefore should not be construed as limiting the invention.
In the present invention, unless explicitly specified and limited otherwise, the terms "mounted," "configured," "connected," "secured," "rotated," and the like are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; either directly or indirectly through intermediaries, or in communication with each other or in interaction with each other, unless explicitly defined otherwise, the meaning of the terms described above in this application will be understood by those of ordinary skill in the art in view of the specific circumstances.
Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made therein without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (5)
1. A method for open loop uplink frequency synchronization in a low orbit satellite communication system, comprising:
estimating downlink frequency deviation according to each measured frequency deviation between the satellite and the terminal;
calculating an uplink frequency deviation according to the downlink frequency deviation;
calculating an uplink frequency precompensation value according to the uplink frequency deviation;
according to the uplink frequency precompensation value, uplink frequency synchronization of the satellite and the terminal is realized;
wherein estimating the downlink frequency deviation from the measured frequency deviations between the satellite and the terminal comprises pre-compensating and summing the downlink frequency deviations between the satellite and the terminal, wherein the downlink frequency deviation is expressed as:
f D ＝f d1 +f csat +f cue +f a +f dpre
wherein f D Representing a downlink frequency offset between the satellite and the terminal; f (f) d1 Indicating Doppler frequency deviation generated by relative motion of the satellite and the terminal; f (f) csat Representing the frequency deviation caused by the satellite crystal oscillator; f (f) cue Representing frequency deviation caused by terminal crystal oscillator; f (f) a Representing frequency deviation caused by a terminal frequency deviation estimation algorithm; f (f) dpre Indicating the downlink frequency pre-compensation of the terminal;
the downlink frequency of the terminal is precompensated f dpre Calculating the Doppler change rate of the previous moment according to ephemeris information, multiplying the time difference between the current moment and the previous moment by the Doppler change rate to obtain the downlink frequency precompensation of the terminal, wherein the downlink frequency precompensation is expressed as:
f dpre ＝a(t i -t i-1 )
wherein a represents the Doppler change rate at the previous time, t i Indicating the current time, t i-1 Representing the previous time;
or, the downlink frequency of the terminal is precompensated for f dpre The calculation method of (1) comprises the following steps:
wherein f Di-1 Representing a downlink frequency offset between the satellite and the terminal at a previous time instant; f (f) Di-2 Representing the downlink frequency deviation between the satellite and the terminal at the previous two moments; t is t i-2 Indicating the first two moments.
2. A method of open loop uplink frequency synchronization for a low orbit satellite communication system according to claim 1, wherein the uplink frequency deviation is expressed as:
f U ＝-(f D )*f u0 /f d0
wherein f u0 Representing the uplink carrier center frequency; f (f) d0 Representing the downlink carrier center frequency.
3. The method for open loop uplink frequency synchronization of a low orbit satellite communication system according to claim 2, wherein the uplink frequency precompensation value is expressed as:
f upre ＝-(f d2 +f csat +f cue )*f u0 /f d0
wherein f upre Representing upstream frequency precompensation; f (f) d2 Doppler frequency offset for the downlink and uplink time difference T.
4. An open loop uplink frequency synchronization device of a low orbit satellite communication system, which is applied to an open loop uplink frequency synchronization method of a low orbit satellite communication system according to any one of claims 1 to 3, characterized in that the device comprises:
a measurement unit for measuring each frequency deviation between the satellite and the terminal;
the estimating unit is used for estimating downlink frequency deviation according to each measured frequency deviation between the satellite and the terminal;
the conversion unit is used for calculating the uplink frequency deviation according to the downlink frequency deviation;
the calculation unit is used for calculating an uplink frequency precompensation value according to the uplink frequency deviation;
and the synchronization unit is used for realizing the uplink frequency synchronization of the satellite and the terminal according to the uplink frequency precompensation value.
5. An apparatus comprising at least one processor configured to perform an open loop uplink frequency synchronization method of a low orbit satellite communication system according to any one of claims 1-3 and at least one memory coupled to the processor.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202111413211.4A CN114025422B (en) | 2021-11-25 | 2021-11-25 | Open loop uplink frequency synchronization method and device for low orbit satellite communication system |
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