CN113708872A - Forward link time delay estimation method of low-orbit satellite TDMA static-medium-communication system - Google Patents

Forward link time delay estimation method of low-orbit satellite TDMA static-medium-communication system Download PDF

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CN113708872A
CN113708872A CN202110972855.0A CN202110972855A CN113708872A CN 113708872 A CN113708872 A CN 113708872A CN 202110972855 A CN202110972855 A CN 202110972855A CN 113708872 A CN113708872 A CN 113708872A
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贺俊文
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Abstract

The application provides a forward link time delay estimation method of a transparent forwarding low-orbit satellite TDMA static center-through system, which comprises the following steps: pre-calculating a function of satellite/main station transmission delay and ephemeris time and a function of satellite/end station transmission delay and ephemeris time; estimating the ephemeris time of the forward information reaching the satellite according to the ephemeris time of the forward information sent by the main station; and respectively estimating free space transmission time delays of a forward uplink and a forward downlink according to a function of the transmission time delay of the satellite/main station and ephemeris time, a function of the transmission time delay of the satellite/end station and ephemeris time of forward information reaching the satellite, and adding the free space transmission time delays to the forward uplink and the forward downlink to obtain the free space transmission time delay of the forward link. The method adopts an extrapolation estimation method based on linear approximation, and is simple and convenient to calculate; under the condition that the satellite ephemeris information is accurate, good estimation performance can be obtained.

Description

Forward link time delay estimation method of low-orbit satellite TDMA static-medium-communication system
Technical Field
The invention relates to a time synchronization technology of a TDMA satellite communication system, in particular to a forward link time delay estimation method of a transparent forwarding low-orbit satellite TDMA static-neutral communication system.
Background
The full-network time synchronization of the TDMA system comprises two parts: forward link time synchronization and return link time synchronization. The forward link time synchronization has the function of realizing Network Clock Reference (NCR) synchronization, namely establishing a mapping relation between an end station timing system and a master station timing system, and further achieving the purpose that an end station identifies the time slot position of the master station through a local timing system.
The forward link transmission delay typically includes: the method comprises the steps of forward link sending side processing time delay, forward link receiving side processing time delay, on-satellite processing time delay and forward link free space transmission time delay. For a transparent forwarding satellite, the satellite-borne transponder only performs simple processing such as filtering, amplification, frequency conversion and the like on a signal, and the time delay of the satellite-borne transponder is far less than the free space transmission time delay of a forward link and can be ignored; both the transmit side processing delay and the receive side processing delay of the forward link can be accurately estimated according to a specific processing mechanism. Therefore, the present application mainly discusses an estimation method of forward link free space transmission delay.
The forward link in a transparent transponded satellite TDMA communication system is a transmission link from a master station to a satellite and then to an end station, consisting of two parts, a forward uplink and a forward downlink, as shown in fig. 1. Where forward uplink refers to the transmission link from the master station to the satellite and forward downlink refers to the transmission link from the satellite to the end station. The free space transmission delay of the forward link can be obtained by estimating the free space transmission delay of the forward uplink and the forward downlink respectively and adding the free space transmission delay of the forward uplink and the free space transmission delay of the forward downlink.
In a low earth orbit satellite communication system, the forward link is not a fixed, constant transmission link, but varies with time, since the position of the satellite varies with time. The first prerequisite for accurately estimating the free space transmission delay of the forward link is to correctly find which forward link to be estimated is.
In a static communication scene, the positions of a master station and an end station are fixed and unchanged, and a forward link is uniquely determined by the position of a satellite; the position of the satellite is a function of time, and if the time of the forward information reaching the satellite is determined, the position of the satellite at the corresponding moment can be determined, so that the forward link for transmitting the forward information is uniquely determined. In the scenario shown in FIG. 1, the forward information D [ n ]]At tnIs sent from the master station at time t'nThe time of day arrives at the satellite and is then forwarded by the satellite to the end station. At t'nAt time, the position of the satellite is P (t'n) Transmitting Dn]The forward link of (c) is H → P (t'n)→R。
Therefore, determining the time of arrival of the forward information at the satellite is key to accurately estimating the forward link free space transmission delay.
Disclosure of Invention
In order to solve the related technical problems, the invention provides a forward link time delay estimation method of a transparent forwarding low-orbit satellite TDMA static-neutral communication system, which adopts an extrapolation estimation method based on linear approximation and is simple and convenient to calculate; under the condition that the satellite ephemeris information is accurate, good estimation performance can be obtained.
In order to achieve the purpose of the invention, the invention is realized by the following technical scheme:
a forward link time delay estimation method of a transparent forwarding low orbit satellite TDMA static center-through system comprises the following steps:
s1, using ephemeris time t as abscissa, and sending forward information D [ n ]]Ephemeris time tnIs an origin of an abscissa and takes the transmission delay tau between the satellite and the master station'SAT/HUB(t) is a vertical coordinate, and a rectangular coordinate system is established by taking 0 as the origin of the vertical coordinate
Figure BDA0003226523650000021
S2, rectangular coordinate system
Figure BDA0003226523650000022
In (1), two linear equations are established: one is the equation of an identical straight line l1:τ′SAT/HUB(t) t, the other being a function τ of satellite/master station transmission delay and ephemeris timeSAT/HUB(t)＝g1Coordinate-translated version of (t) 'τ'SAT/HUB(t)＝τSAT/HUB(t+tn)＝g1(t+tn) In the interval [0, T]Equation of local approximate straight line segment of
Figure BDA0003226523650000023
T is a time increment, and
Figure BDA0003226523650000024
Figure BDA0003226523650000025
represents the maximum value of the forward uplink free space transmission delay;
wherein, equation of straight line segment l2The establishing method comprises the following steps:
at curve τ'SAT/HUB(t)＝g1(t+tn),t∈[0,T]Two adjacent points (0, g) are selected1(tn) And (T, g)1(tμ) Wherein t) isμ＝tn+T；
According to (0, g)1(tn) And (T, g)1(tμ) Two points) to establish a straight-line equation to obtain
Figure BDA0003226523650000031
S3 solving straight line l1And straight line segment l2Coordinates of the intersection point of
Figure BDA0003226523650000032
S4, estimating the ephemeris time of the forward information D [ n ] reaching the satellite to obtain
t′n＝tn+tintersect；
S5, according to two groups of pre-calculated parameters: function tau of satellite/master station transmission delay and ephemeris timeSAT/HUB(t) and a function τ of satellite/end station transmission delay and ephemeris timeSAT/RCST(t), and forward information D [ n ]]Ephemeris time t 'to satellite'nSeparately estimating the free space transmission delay tau of the forward uplinkFL/UL(t′n) And free space transmission delay tau of forward downlinkFL/DL(t′n)：
Figure BDA0003226523650000033
S6, uplink forwardAdding the free space transmission time delay of the path and the forward downlink to obtain the free space transmission time delay tau of the forward linkFL/FS(t′n) I.e. by
τFL/FS(t′n)＝τFL/UL(t′n)+τFL/DL(t′n)。
The invention has the beneficial effects that:
the forward link time delay estimation method of the transparent forwarding low-orbit satellite TDMA static center-pass system is provided, and the method adopts an extrapolation estimation method based on linear approximation, so that the calculation is simple and convenient; under the condition that the satellite ephemeris information is accurate, good estimation performance can be obtained.
Drawings
Fig. 1 is a schematic diagram of the forward link of a transparent transponded low earth orbit satellite TDMA communication system.
FIG. 2 shows the estimation of the forward information D [ n ] in the present application]Ephemeris time t 'to satellite'nSchematic diagram of the method of (1).
FIG. 3 is a schematic geometric diagram of steps S1-S3 of the method of the present application.
Detailed Description
In order to make the purpose, technical scheme and specific implementation method of the application clearer, the application is further described in detail by combining with an example of the attached drawings.
The embodiment of the application provides a forward link time delay estimation method of a transparent forwarding low-orbit satellite TDMA static center-communication system, which is based on two preconditions:
1) and on the side of the primary station, a mapping relation between the NCR time and the ephemeris time is established.
2) The master station transmits the forward information D [ n ]]And its transmission time (here, the transmission time refers to the information D [ n ]]Time away from the primary station transmit antenna) corresponding to the ephemeris time tnAnd sent to the end station.
The design idea of the method is as follows:
firstly, a function tau of the transmission delay of the satellite/the main station and the ephemeris time in a satellite view window is calculated in advance according to the ephemeris information of the satellite and the GNSS position information of the main station and the end stationSAT/HUB(t)＝g1(t) and a function τ of satellite/end station transmission delay and ephemeris timeSAT/RCST(t)＝g2(t)。
Then, forward information D [ n ] is transmitted from the master station]Ephemeris time tn(known quantity) and function τSAT/HUB(t)＝g1(t) estimating the forward information D [ n ]]Ephemeris time t 'to satellite'n。
Then, by a function τSAT/HUB(t)＝g1(t) and τSAT/RCST(t)＝g2(t) separately estimating the free space transmission delays τ of the forward uplinksFL/UL(t′n)＝τSAT/HUB(t′n) And free space transmission delay tau of forward downlinkFL/DL(t′n)＝τSAT/RCST(t′n)。
And finally, adding the free space transmission time delay of the forward uplink and the forward downlink to obtain the free space transmission time delay of the forward link.
In order to simplify the computational complexity of the forward link delay estimation, two sets of parameters need to be prepared in advance: a function of satellite/master station transmission delay and ephemeris time and a function of satellite/end station transmission delay and ephemeris time.
The method for calculating the function of the satellite/main station transmission time delay and the ephemeris time is as follows:
1) a function of the position of the satellite in an earth-centered-earth-fixed (ECEF) coordinate system and ephemeris time within a satellite view window is calculated from the ephemeris information of the satellite.
2) And converting the GNSS position of the master station to obtain the position of the master station in the ECEF coordinate system.
3) Under an ECEF coordinate system, according to the position information of the satellite and the master station, calculating a function d of the distance between the satellite and the master station and the ephemeris timeSAT/HUB(t)＝f1(t)。
4) By dSAT/HUB(t)＝f1(t) dividing by the propagation velocity c of the electromagnetic wave to obtain a function tau of the satellite/master station transmission delay and ephemeris timeSAT/HUB(t)＝dSAT/HUB(t)/c。
By the use of the sameThe method can calculate the function tau of the satellite/end station transmission time delay and the ephemeris timeSAT/RCST(t) wherein τSAT/RCST(t)＝dSAT/RCST(t)/c，dSAT/RCST(t)＝f2(t) is a function of satellite/end station range and ephemeris time.
Under the above conditions, the estimation of the free space transmission delay of the forward link is carried out:
s1, using ephemeris time t as abscissa, and sending forward information D [ n ]]Ephemeris time tnIs an origin of an abscissa and takes the transmission delay tau between the satellite and the master station'SAT/HUB(t) is a vertical coordinate, and a rectangular coordinate system is established by taking 0 as the origin of the vertical coordinate
Figure BDA0003226523650000051
S2, rectangular coordinate system
Figure BDA0003226523650000052
In (1), two linear equations are established.
One is the equation of an identical straight line l1:τ′SAT/HUB(t)＝t；
The other is a function tau of the satellite/master station transmission delay and ephemeris timeSAT/HUB(t)＝g1Coordinate-translated version of (t) 'τ'SAT/HUB(t)＝τSAT/HUB(t+tn)＝g1(t+tn) In the interval [0, T]Equation of local approximate straight line segment of
Figure BDA0003226523650000061
The latter method of establishment is as follows: first, at curve τ'SAT/HUB(t)＝g1(t+tn),t∈[0,T]Two adjacent points (0, g) are selected1(tn) And (T, g)1(tμ) Wherein t) isμ＝tn+ T, T is a time increment, and
Figure BDA0003226523650000062
Figure BDA0003226523650000063
representing the maximum value of the forward uplink free space transmission delay. Then, establishing a straight-line equation according to the coordinates of the two points to obtain
Figure BDA0003226523650000064
S3 solving straight line l1And straight line segment l2Coordinates of the intersection point of
Figure BDA0003226523650000065
Fig. 3 is a geometrical diagram of steps S1-S3 of the method, which represents a scenario where the distance between the satellite and the primary station is gradually reduced, and therefore the transmission delay of the forward uplink is also gradually reduced.
S4, estimating the ephemeris time of the forward information D [ n ] reaching the satellite to obtain
t′n＝tn+tintersect。
Estimating forward information D [ n ]]Ephemeris time t 'to satellite'nThe method comprises the following steps: as shown in fig. 1, at tnAt the moment, the master station sends out forward information D [ n ]]At this time, the position of the satellite is P (t)n). Then, D [ n ]]In the forward uplink while the satellite continues to orbit in the direction pointed by the arrow. At t'nAt time, the satellite moves to a new position P (t'n) And at this time, D [ n ]]Also just to the satellite, i.e. with a time delay t'n-tnRear D [ n ]]Encounter a satellite. In the encounter problem described above, the satellite is in orbit P (t)n)→P(t′n) Time of motion and Dn]At forward uplink H → P (t'n) Exactly equal in transmission delay, i.e. straight line τSAT/HUB(t)＝t-tnAnd curve τSAT/HUB(t)＝g1(t) at tnThen must intersect, and the intersection point is t'n(as shown in fig. 2). Therefore, solving a system of non-linear equations
Figure BDA0003226523650000071
Forward information D n can be obtained]Ephemeris time t 'to satellite'n。
In general, in a low-earth orbit satellite communication system, the free space transmission delay of a forward uplink is small, the moving distance of a satellite in the time is short, and the motion track of the satellite can be approximate to a straight line segment. Thus, curve τSAT/HUB(t)＝g1(t) at tnThe nearby area may also be approximated by straight line segments. Let the equation for this straight line segment be
Figure BDA0003226523650000072
Where T is a time increment. Furthermore, the above problem can be simplified to the straight line τSAT/HUB(t)＝t-tnAnd straight line segment
Figure BDA0003226523650000073
The intersection problem of (a). In summary, solving a system of linear equations is described
Figure BDA0003226523650000074
Forward information D n can be obtained]Ephemeris time t 'to satellite'n。
S5 according to the following formula
Figure BDA0003226523650000075
Estimating the free space transmission delay tau of the forward uplink respectivelyFL/UL(t′n) And free space transmission delay tau of forward downlinkFL/DL(t′n)。
S6, adding the free space transmission time delay of the forward uplink and the forward downlink to obtain the free space transmission time delay tau of the forward linkFL/FS(t′n) I.e. by
τFL/FS(t′n)＝τFL/UL(t′n)+τFL/DL(t′n)。

Claims (3)

1. A forward link time delay estimation method of a transparent forwarding low orbit satellite TDMA static center-through system is characterized by comprising the following steps:
s1, using ephemeris time t as abscissa, and sending forward information D [ n ]]Ephemeris time tnIs an origin of an abscissa and takes the transmission delay tau between the satellite and the master station'SAT/HUB(t) is a vertical coordinate, and a rectangular coordinate system is established by taking 0 as the origin of the vertical coordinate
Figure FDA0003226523640000011
S2, rectangular coordinate system
Figure FDA0003226523640000012
In (1), two linear equations are established: one is the equation of an identical straight line l1:τ′SAT/HUB(t) t, the other being a function τ of satellite/master station transmission delay and ephemeris timeSAT/HUB(t)＝g1Coordinate-translated version of (t) 'τ'SAT/HUB(t)＝τSAT/HUB(t+tn)＝g1(t+tn) In the interval [0, T]Equation of local approximate straight line segment of
Figure FDA0003226523640000013
T is a time increment, and
Figure FDA0003226523640000014
Figure FDA0003226523640000015
represents the maximum value of the forward uplink free space transmission delay;
s3 solving straight line l1And straight line segment l2Coordinate t of intersection pointintersect；
S4, estimating the ephemeris time of the forward information D [ n ] reaching the satellite to obtain
t′n＝tn+tintersect；
S5, according to two groups of pre-calculated parameters: function tau of satellite/master station transmission delay and ephemeris timeSAT/HUB(t) and a function τ of satellite/end station transmission delay and ephemeris timeSAT/RCST(t), and forward information D [ n ]]Ephemeris time t 'to satellite'nSeparately estimating the free space transmission delay tau of the forward uplinkFL/UL(t′n) And free space transmission delay tau of forward downlinkFL/DL(t′n)：
Figure FDA0003226523640000016
S6, adding the free space transmission time delay of the forward uplink and the forward downlink to obtain the free space transmission time delay tau of the forward linkFL/FS(t′n) I.e. by
τFL/FS(t′n)＝τFL/UL(t′n)+τFL/DL(t′n)。
2. The forward link delay estimation method for the transparent retransmission low-orbit satellite TDMA static center-pass system according to claim 1, wherein the straight line segment l2The establishing method comprises the following steps:
at curve τ'SAT/HUB(t)＝g1(t+tn),t∈[0,T]Two adjacent points (0, g) are selected1(tn) And (T, g)1(tμ) Wherein t) isμ＝tn+T；
According to (0, g)1(tn) And (T, g)1(tμ) Two points) to establish a straight-line equation to obtain
Figure FDA0003226523640000021
3. The forward link delay estimation method for the transparent transponded low-earth-orbit satellite TDMA static-mid-communication system according to claim 2, wherein the line l1And straight line segment l2Coordinate t of intersection pointintersectSolving by the following formula:
Figure FDA0003226523640000022
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