CN114867095A - Time slot synchronization method for TDMA/MF-TDMA satellite communication system - Google Patents
Time slot synchronization method for TDMA/MF-TDMA satellite communication system Download PDFInfo
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Abstract
The invention discloses a time slot synchronization method of a TDMA/MF-TDMA satellite communication system, wherein a random competition mechanism is adopted in an initial synchronization stage, and a strategy of sending in a timing period is adopted in a time slot synchronization maintaining stage; the process includes step S1, using the time of the central station as the reference, the central station uses the forward link to time each remote station through the TOD frame, so that each remote station and the central station are kept uniform in time; s2, calculating the path time delay of each remote station by the central station auxiliary closed loop mode, and making each remote station complete burst communication in the allocated time slot; s3, time slot synchronization keeping stage, the remote station calculates the current frame number and time slot number according to the local TOD counter value and path time delay, and makes service burst communication on the allocated time slot. The time slot synchronization of the system does not depend on the position information of a remote station, and does not need a third-party time service system to carry out time service, and the TDMA synchronization frame carries out data communication in a way of channel associated service, so that the complexity of the design of a satellite communication system can be effectively reduced.
Description
Technical Field
The invention relates to satellite communication technology, in particular to a time slot synchronization technology and scheme of a TDMA/MF-TDMA satellite communication system.
Background
Satellite communication is a communication means widely used in military and civil use at present, and in terms of an access mode, a multiple access mode of satellite communication mainly includes Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Code Division Multiple Access (CDMA), and the like, wherein TDMA is an important communication system in current satellite communication. A TDMA satellite communication system is comprised primarily of a central station, high-throughput satellites, and remote stations, as shown in fig. 1. TDMA satellite communication systems are generally divided into forward links and return links in terms of communication links. The forward link refers to the communication link from the central station to the remote stations, generally using a continuous single carrier TDM stream, each remote station can receive the data transmitted by the central station, and the return link refers to the communication link from the remote stations to the central station, generally using the TDMA/MF-TDMA communication system, each remote station performs burst communication on its assigned time slot.
For TDMA satellite communication systems, the slot synchronization (also called system synchronization/time synchronization) problem has been one of the key issues studied and solved. At present, most of TDMA satellite communication systems adopt Beidou or GPS time service positioning or use an independent calibration station to complete time slot synchronization, and an independent channel is required to complete the analysis of signals of the Beidou/GPS/calibration station, which undoubtedly increases the complexity of system design.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a method for synchronizing time slots of a TDMA/MF-TDMA satellite communication system based on the assistance of a central station. The TDMA satellite communication time slot synchronization can be completed without depending on third-party equipment, and the effect is excellent by application in practical projects.
The technical scheme adopted by the invention is as follows:
a TDMA/MF-TDMA satellite communication system time slot synchronization method, the time slot synchronization process is divided into 2 stages of initial synchronization stage and time slot synchronization maintenance stage, the initial synchronization stage adopts the mechanism of random competition, the time slot synchronization maintenance stage adopts the strategy of timing cycle transmission; the method specifically comprises the following steps:
s1, using the time of the central station as the reference, the central station uses the forward link to time each remote station through TOD frame, and aligns the time of each remote station with the time of the central station, so that each remote station and the central station keep uniform in time;
s2, calculating the path time delay of each remote station by the central station auxiliary closed loop mode, and making each remote station complete burst communication in the allocated time slot;
s3, time slot synchronization keeping stage, the remote station calculates the current frame number and time slot number according to the local TOD counter value and path time delay, and makes service burst communication on the allocated time slot.
In the time slot synchronization method of the TDMA/MF-TDMA satellite communication system, in step S2, in the initial synchronization stage, the remote station returns to burst and takes frame as time unit for scheduling, and the remote station randomly sends a TDMA synchronization frame at a certain time in each scheduling period; after receiving the TDMA synchronous frame sent by the remote station, the central station takes the TOD counting value of the captured TDMA synchronous frame as a central station time stamp, fills the TDMA synchronous frame and returns the TDMA synchronous frame to the remote station through a forward link; after receiving the synchronous frame returned by the central station, the remote station calculates the path time delay through the remote station sending time stamp and the central station receiving time stamp in the TDMA synchronous frame, and adjusts the time of each burst of the remote station according to the path time delay to complete the initial time slot synchronization.
In the time slot synchronization method of the TDMA/MF-TDMA satellite communication system, in the step S3, in the time slot synchronization maintaining stage, the remote station periodically sends a TDMA synchronization frame on the allocated time slot in a timing mode, the sending method of the TDMA synchronization frame is similar to the initial time slot synchronization stage, and a new path delay L is obtained RTT Maintaining local frame number and time slot number according to updated path delayThe problem that the remote station causes the change of path delay due to the difference of motion and crystal oscillation is solved, and the central station and the remote station keep synchronization in time all the time.
Specifically, step S1, the central station uses the forward link to time each remote station through TOD frames, so that each remote station and the central station are kept uniform in time, including the following steps:
after the central station and the remote station are started, a 32-bit wide TOD counter is maintained locally and is driven by a clock to count by taking a superframe as a period;
the central station periodically generates a TOD frame and broadcasts on a forward link; wherein, the TOD frame is fixedly arranged behind the unique word of the physical frame, and the filling value of the central station time stamp field is the TOD counter value corresponding to the first unique word symbol of the physical frame;
after receiving the TOD frame, the remote station updates the local TOD counter value by using the received TOD time stamp of the central station and counts the time under the driving of the clock.
In step S2, the time slot synchronization process in the initial synchronization stage is as follows:
s21, the far-end station of the return link takes the frame as the dispatching cycle, each frame is composed of N time slots, the far-end station needs to carry out the return burst communication on the time slot allocated to each frame; in the initial time slot synchronization stage, the remote station transmits a TDMA synchronization frame once in each scheduling period in random time slot, the TDMA synchronization frame carries the ID number of the remote station and the value of the TOD counter of the remote station when the remote station transmits the TDMA synchronization frame, namely the remote station transmits a time stamp L remote (ii) a If the remote station TDMA synchronous frame is collided, which causes the central station not to receive the TDMA synchronous frame, the next frame period sends the TDMA synchronous frame by a time slot again at random.
S22, the central station takes the value of the counter for capturing the synchronization head time TOD of the TDMA synchronization frame transmitted by the remote station as the receiving time stamp L of the central station master Value of (2), remote station-sent timestamp L remote Filled by remote stations, the central station only needs to analyze out, does not make any change, and then fills other fields to form a TDMA synchronous frame which is transmitted back to the central station through a forward linkA remote station;
s23, after the remote station analyzes the TDMA synchronous frame returned by the central station, the remote station can obtain the time stamp L sent by the remote station remote And the central station receives the time stamp L master Then, the path delay value L can be obtained through the two pieces of information RTT
In step S3, the specific process of the time slot synchronization maintaining stage includes the following steps:
s31, after completing the initial time slot synchronization, the remote station according to the local TOD counter value L CNT Sum path delay L RTT Calculating the current frame number and time slot number as the time reference of far-end station burst;
and S32, after calculating the time slot number, the remote station performs the service burst communication on the allocated time slot. After a plurality of frame periods are spaced, a TDMA synchronous frame is periodically transmitted once on an allocated time slot, the transmission method of the TDMA synchronous frame is similar to the initial time slot synchronization stage, and a new path time delay L is obtained RTT And maintaining the local frame number and the time slot number according to the updated path delay, thereby solving the problem that the path delay changes due to the difference of motion and crystal oscillator of the remote station, and keeping the central station and the remote station synchronized in time.
The invention has the beneficial effects that:
1. the time slot synchronization method of the TDMA/MF-TDMA satellite communication system of the invention does not depend on the position information of the remote stations, does not need a third-party time service system such as Beidou/GPS to carry out time service, does not need an independent system time slot synchronization channel, aligns the time of each remote station with the time of the central station by taking the time of the central station as a reference in a central station auxiliary mode, and then calculates the path time delay of each remote station in a central station auxiliary closed-loop mode, thereby ensuring that each remote station can finish burst communication in the allocated time slot.
2. The time slot synchronization method of the TDMA/MF-TDMA satellite communication system of the invention adopts a mode of sending TDMA synchronization frames in a random competition and timing period to complete the time slot synchronization of the whole satellite communication system, and the strategy can still ensure that each remote station is synchronous on the time slot under the condition of minimum resource consumption. In the initial synchronization stage, the remote stations complete initial synchronization by adopting a random competition mechanism, and in the time slot synchronization maintaining stage, the time slot synchronization of the whole satellite communication system is completed by periodically sending a TDMA synchronization frame at fixed time.
3. The time slot synchronization method of the TDMA/MF-TDMA satellite communication system does not need to establish an independent time slot synchronization channel between the central station and the remote station, and TDMA synchronization frames carry out data communication in a channel associated service mode, thereby effectively reducing the complexity of the design of the satellite communication system.
4. The time slot synchronization method of the TDMA/MF-TDMA satellite communication system is a method which can complete the time slot synchronization of the TDMA satellite communication without depending on third-party equipment, is applied to practical projects and has excellent effect.
Drawings
FIG. 1 is a block diagram of a TDMA satellite communications system;
FIG. 2 is a TOD frame format diagram;
FIG. 3 is a diagram of a TDMA synchronization frame format;
fig. 4 is a flowchart illustrating the overall slot synchronization process according to the present invention.
Detailed Description
In order to make the technical idea and advantages of the invention for realizing the purpose of the invention more clear, the technical solution of the invention is further described in detail with reference to the accompanying drawings. It should be understood that the following examples are only for illustrating and explaining preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention as claimed in the claims.
Example 1
The invention discloses a TDMA satellite communication system time slot synchronization method based on central station assistance, wherein the time slot synchronization process is divided into 2 stages of an initial synchronization stage and a time slot synchronization maintenance stage, the initial synchronization stage adopts a random competition mechanism, and the time slot synchronization maintenance stage adopts a strategy of timing period transmission; the overall processing flow is shown in fig. 4, and includes:
step S1, using the time of the central station as the reference, the central station uses the forward link to time each remote station through TOD frame, and aligns the time of each remote station with the time of the central station, so that each remote station and the central station keep uniform in time;
step S2, calculating the path time delay of each remote station by the central station auxiliary closed loop mode, and making each remote station complete the burst communication in the allocated time slot;
step S3, the remote station calculates the current frame number and time slot number according to the local TOD counter value and the path delay, and performs the service burst communication in the allocated time slot.
Example 2
The TDMA/MF-TDMA satellite communication system time slot synchronization method of the present embodiment is different from embodiment 1, and further: in step S2, in the initial synchronization stage, the remote station schedules the backward burst in a frame time unit, and the remote station randomly transmits a TDMA synchronization frame at a certain time in each scheduling period; after receiving the TDMA synchronous frame sent by the remote station, the central station takes the TOD counting value of the captured TDMA synchronous frame as a central station time stamp, fills the TDMA synchronous frame and returns the TDMA synchronous frame to the remote station through a forward link; after receiving the synchronous frame returned by the central station, the remote station calculates the path time delay through the remote station sending time stamp and the central station receiving time stamp in the TDMA synchronous frame, and adjusts the time of each burst of the remote station according to the path time delay to complete the initial time slot synchronization.
Example 3
The TDMA/MF-TDMA satellite communication system time slot synchronization method of the present embodiment is different from the embodiments 1 and 2, and further comprises: in step S3, in the time slot synchronization maintaining stage, the remote station periodically transmits a TDMA synchronization frame in its allocated time slot, and the transmission method of the TDMA synchronization frame is similar to the initial time slot synchronization stage, and acquires a new path delay L RTT And maintaining the local frame number and the time slot number according to the updated path delay, thereby solving the problem that the path delay is changed due to the difference of motion and crystal oscillation of the remote station, and keeping the central station and the remote station synchronous in time.
Example 4
Referring to fig. 1-4, the present invention discloses a method for TDMA satellite communication system time slot synchronization based on central station assistance, the overall processing flow of which is shown in fig. 4, and the method comprises the following steps:
s1, the central station uses the forward link to time each remote station through TOD frames, so that each remote station and the central station are kept uniform in time, the specific steps are as follows:
s11, after the central station and the remote station are powered on, a 32-bit TOD counter is maintained locally, and is driven by a clock to count a plurality of (e.g., 1024) frame periods.
S12, the central station generates a TOD frame spaced apart by a number (e.g., 32) of frame periods and broadcasts on the forward link. Wherein, the TOD frame is fixedly arranged behind the unique word of the physical frame, and the filling value of the central station time stamp field is the TOD counter value corresponding to the first unique word symbol of the physical frame. The TOD frame format is shown in fig. 2.
S13, after the remote station receives TOD frame, the remote station updates the value L of local TOD counter with the received TOD time stamp of the central station CNT And counting time under the driving of the clock.
S2, the far-end station return burst is scheduled by using frame as time unit, and at the initial time slot synchronization stage, the far-end station randomly transmits a TDMA synchronization frame at a certain time in each scheduling period, and the format of the TDMA synchronization frame is as shown in fig. 3. After receiving the TDMA synchronous frame sent by the remote station, the central station takes the TOD counting value of the captured TDMA synchronous frame as a central station time stamp, fills the TDMA synchronous frame and returns the TDMA synchronous frame to the remote station through a forward link; after receiving the synchronous frame returned by the central station, the remote station can calculate the path time delay through the remote station sending time stamp and the central station receiving time stamp in the TDMA synchronous frame, and adjust the time of each burst of the remote station according to the path time delay to complete the initial time slot synchronization.
Step S2 specifically includes the following steps:
s21, the remote station of the return link takes the frame as the dispatching cycle, each frame is divided into a plurality of time slots, the remote station needs to distribute in each framePerforms a backward burst communication on the time slot. In the initial time slot synchronization stage, the remote station sends a TDMA synchronization frame once at a random time point in each scheduling period, the TDMA synchronization frame carries the ID number of the remote station and the value of the TOD counter of the remote station when the remote station sends the TDMA synchronization frame, namely the remote station sends a time stamp L remote 。
S22, the central station takes the value of the counter for capturing the synchronization head time TOD of the TDMA synchronization frame transmitted by the remote station as the receiving time stamp L of the central station master Value of (2), remote station-sent timestamp L remote Filled by remote stations, the central station only needs to analyze out without any modification, and then fills other fields to form a TDMA synchronization frame which is transmitted back to the remote stations through the forward link.
S23, after the remote station analyzes the TDMA synchronous frame returned by the central station, the remote station can obtain the time stamp L sent by the remote station remote And the central station receives the time stamp L master Then, the path delay value L can be obtained through the two pieces of information RTT ，L RTT The calculation process of (a) is as follows.
Wherein T is Frame Is the time length of each frame, and has the unit of ms, f clk To count the frequency of the clock, N Frame For how many frames there are 1 counting period.
S3, time slot synchronization keeping stage, the remote station according to local TOD counter value L CNT Sum path delay L RTT And calculating the current frame number and time slot number, and performing service burst communication on the allocated time slot. After a plurality of frame periods are spaced, a TDMA synchronous frame is periodically transmitted once on an allocated time slot, the transmission method of the TDMA synchronous frame is similar to the initial time slot synchronization stage, and a new path time delay L is obtained RTT And maintaining local frame number and time slot number according to the updated path delay, thereby solving the problem that the path delay changes due to the difference of motion and crystal oscillator of the remote station, and the central station and the remote station always keep timeSynchronization is maintained.
Step S3 specifically includes the following steps:
s31, after completing the initial time slot synchronization, the remote station according to the local TOD counter value L CNT Sum path delay L RTT And calculating the current frame number and time slot number as the time reference of the remote station burst. The calculation process of the time slot number and the frame number is as follows
Frame number calculation process:
time slot number calculation process
Wherein L is SLOT Is the number of slots per frame.
And S32, after calculating the time slot number, the remote station performs the service burst communication on the allocated time slot. After a plurality of frame periods are spaced, a TDMA synchronous frame is periodically transmitted once on an allocated time slot, the transmission method of the TDMA synchronous frame is similar to the initial time slot synchronization phase, and a new path delay L is obtained RTT And maintaining the local frame number and the time slot number according to the updated path delay, thereby solving the problem that the path delay is changed due to the difference of motion and crystal oscillation of the remote station, and keeping the central station and the remote station synchronous in time.
At present, most of TDMA satellite communication systems adopt Beidou or GPS time service positioning or use an independent calibration station to complete time slot synchronization, and an independent channel is required to complete the analysis of signals of the Beidou/GPS/calibration station, which undoubtedly increases the complexity of system design. Aiming at the defects of the prior art, the invention provides a method for synchronizing time slots of a TDMA/MF-TDMA satellite communication system based on the assistance of a central station. The TDMA satellite communication time slot synchronization can be completed without depending on third-party equipment, and the effect is excellent by application in practical projects.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and should not be construed as limiting the invention. Other modifications of the invention will occur to those skilled in the art without the benefit of this disclosure and it is intended to cover within the scope of the invention any modifications that fall within the spirit and scope of the invention or the equivalents thereof which may be substituted by one of ordinary skill in the art without departing from the scope of the invention.
Claims (7)
1. A time slot synchronization method of a TDMA/MF-TDMA satellite communication system, the time slot synchronization process is divided into 2 stages of an initial synchronization stage and a time slot synchronization maintaining stage, and is characterized in that: the initial synchronization stage adopts a random competition mechanism, and the time slot synchronization maintenance stage adopts a strategy of timing period transmission; the specific process comprises the following steps:
s1, using the time of the central station as the reference, the central station uses the forward link to time each remote station through TOD frame, and aligns the time of each remote station with the time of the central station, so that each remote station and the central station keep uniform in time;
s2, calculating the path time delay of each remote station by the central station auxiliary closed loop mode, and making each remote station complete burst communication in the allocated time slot;
s3, time slot synchronization keeping stage, the remote station calculates the current frame number and time slot number according to the local TOD counter value and path time delay, and makes service burst communication on the allocated time slot.
2. The TDMA/MF-TDMA satellite communication system time slot synchronization method according to claim 1, wherein: in step S2, in the initial synchronization stage, the remote station schedules the backward burst in a frame time unit, and the remote station randomly transmits a TDMA synchronization frame at a certain time in each scheduling period;
after receiving the TDMA synchronous frame sent by the remote station, the central station takes the TOD counting value of the captured TDMA synchronous frame as a central station time stamp, fills the TDMA synchronous frame and returns the TDMA synchronous frame to the remote station through a forward link;
after receiving the synchronous frame returned by the central station, the remote station calculates the path time delay through the remote station sending time stamp and the central station receiving time stamp in the TDMA synchronous frame, and adjusts the time of each burst of the remote station according to the path time delay to complete the initial time slot synchronization.
3. The TDMA/MF-TDMA satellite communication system time slot synchronization method according to claim 1, wherein: in step S3, in the time slot synchronization maintaining stage, the remote station periodically transmits a TDMA synchronization frame in its allocated time slot, and the transmission method of the TDMA synchronization frame is similar to the initial time slot synchronization stage, and acquires a new path delay L RTT And maintaining the local frame number and the time slot number according to the updated path delay, thereby solving the problem that the path delay is changed due to the difference of motion and crystal oscillation of the remote station, and keeping the central station and the remote station synchronous in time.
4. The TDMA/MF-TDMA satellite communication system time slot synchronization method according to claim 2, wherein: in step S3, in the time slot synchronization maintaining phase, the remote station periodically transmits a TDMA synchronization frame in its allocated time slot, the transmission method of the TDMA synchronization frame is similar to the initial time slot synchronization phase, and acquires a new path delay L RTT And maintaining the local frame number and the local time slot number according to the updated path delay, thereby solving the problem that the path delay changes due to the difference of motion and crystal oscillation of the remote station, and keeping the central station and the remote station synchronized in time.
5. The TDMA/MF-TDMA satellite communication system time slot synchronization method according to any one of claims 1-4, wherein: in step S1, the central station uses the forward link to time each remote station via TOD frames, so that each remote station and the central station are kept uniform in time, comprising the steps of:
after the central station and the remote station are started, a 32-bit wide TOD counter is maintained locally and is driven by a clock to count by taking a superframe as a period;
the central station periodically generates a TOD frame and broadcasts on a forward link; wherein, the TOD frame is fixedly arranged behind the unique word of the physical frame, and the filling value of the central station time stamp field is the TOD counter value corresponding to the first unique word symbol of the physical frame;
after receiving the TOD frame, the remote station updates the local TOD counter value by using the received TOD time stamp of the central station and counts the time under the driving of the clock.
6. The method for time slot synchronization of a TDMA/MF-TDMA satellite communication system according to claim 5, wherein:
in step S2, the time slot synchronization process in the initial synchronization stage is as follows:
s21, the far-end station of the return link takes the frame as the dispatching cycle, each frame is composed of N time slots, the far-end station needs to carry out the return burst communication on the time slot allocated to each frame; in the initial time slot synchronization stage, the remote station transmits a TDMA synchronization frame once in each scheduling period in random time slot, the TDMA synchronization frame carries the ID number of the remote station and the value of the TOD counter of the remote station when the remote station transmits the TDMA synchronization frame, namely the remote station transmits a time stamp L remote (ii) a If the remote station TDMA synchronous frame is collided, which causes the central station not to receive the TDMA synchronous frame, the next frame period sends the TDMA synchronous frame by a time slot again at random.
S22, the central station takes the value of the counter for capturing the synchronization head time TOD of the TDMA synchronization frame transmitted by the remote station as the receiving time stamp L of the central station master Value of (2), remote station-sent timestamp L remote The remote station is filled, the central station only needs to analyze and does not make any change, and then other fields are filled to form a TDMA synchronous frame which is transmitted back to the remote station through a forward link;
s23, after the remote station analyzes the TDMA synchronous frame returned by the central station, the remote station can obtain the time stamp L sent by the remote station remote And the central station receives the time stamp L master Then, the path delay value L can be obtained through the two pieces of information RTT ，L RTT In a calculation process such asShown below:
wherein T is Frame Is the time length of each frame, and has the unit of ms, f clk To count the frequency of the clock, N Frame For how many frames there are 1 counting period.
7. The method for time slot synchronization of a TDMA/MF-TDMA satellite communication system according to claim 6, wherein: in step S3, the specific process of the time slot synchronization maintaining stage includes the following steps:
s31, after completing the initial time slot synchronization, the remote station according to the local TOD counter value L CNT Sum path delay L RTT Calculating the current frame number and time slot number as the burst time reference of the remote station; the slot number and frame number calculation process is as follows:
frame number calculation process:
Time slot number calculation process
Wherein L is SLOT The number of time slots in each frame is the number of the time slots in each frame;
and S32, after calculating the time slot number, the remote station performs the service burst communication on the allocated time slot. After a plurality of frame periods are spaced, a TDMA synchronous frame is periodically transmitted once on an allocated time slot, the transmission method of the TDMA synchronous frame is similar to the initial time slot synchronization stage, and a new path time delay L is obtained RTT And maintaining local frame number and time slot number according to the updated path delay, thereby solving the problem of path delay variation caused by the difference of motion and crystal oscillator of the remote stationThe central station and the remote stations are kept synchronized in time.
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