CN114867095B - 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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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W56/00—Synchronisation arrangements
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- H04B7/185—Space-based or airborne stations; Stations for satellite systems
- H04B7/1851—Systems using a satellite or space-based relay
- H04B7/18515—Transmission equipment in satellites or space-based relays
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- H04J3/0638—Clock or time synchronisation among nodes; Internode synchronisation
- H04J3/0652—Synchronisation among time division multiple access [TDMA] nodes, e.g. time triggered protocol [TTP]
- H04J3/0655—Synchronisation among time division multiple access [TDMA] nodes, e.g. time triggered protocol [TTP] using timestamps
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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 timing periodic transmission is adopted in a time slot synchronization maintaining stage; the process includes the steps that S1, the central station uses the time of the central station as a reference, and the central station uses a forward link to time service each remote station through TOD frames, so that each remote station and the central station keep uniform in time; s2, calculating the path delay of each remote station in a central station auxiliary closed loop mode, so that each remote station completes burst communication in an allocated time slot; and S3, in the time slot synchronization maintaining stage, 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 business burst communication on the time slot allocated by the remote station. The time slot synchronization of the system does not depend on the position information of the remote station, and a third party time service system is not needed to perform time service, and the TDMA synchronous frame performs data communication in a way of the channel-associated service, so that the complexity of the design of the satellite communication system can be effectively reduced.
Description
Technical Field
The invention relates to satellite communication technology, in particular to a technology and a scheme for time slot synchronization of a TDMA/MF-TDMA satellite communication system.
Background
Satellite communication is a communication means widely used in military and civil at present, and in terms of access modes, 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. TDMA satellite communication systems consist essentially of a central station, high-throughput satellites, and remote stations, as shown in fig. 1. TDMA satellite communication systems are generally divided into forward and reverse links in terms of communication links. The forward link refers to the communication link from the central station to the remote stations, typically using a continuous single carrier TDM stream, and the data transmitted by the central station may be received by each of the remote stations, and the reverse link refers to the communication link from the remote stations to the central station, typically using a TDMA/MF-TDMA communication scheme, where each of the remote stations communicates in bursts over its assigned time slot.
For TDMA satellite communication systems, the problem of time slot synchronization (also known as system synchronization/time synchronization) has been one of the key issues to be studied and addressed. Most TDMA satellite communication systems currently use either beidou or GPS time service positioning, or an independent calibration station to complete slot synchronization, which requires an independent channel to complete the resolution of the beidou/GPS/calibration station signals, which undoubtedly increases the complexity of the 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 time slot synchronization of the TDMA satellite communication can be completed without depending on third party equipment, and the effect is excellent by being applied to practical projects.
The invention adopts the technical scheme that:
A time slot synchronization method of TDMA/MF-TDMA satellite communication system, the time slot synchronization process is divided into an initial synchronization stage and a time slot synchronization holding stage 2 stages, the initial synchronization stage adopts a random competition mechanism, and the time slot synchronization holding stage adopts a strategy of timing periodic transmission; the method specifically comprises the following steps:
S1, taking the time of a central station as a reference, the central station uses a forward link to time service each remote station through a TOD frame, and the time of each remote station is aligned with the time of the central station, so that the time of each remote station and the time of the central station are kept uniform;
s2, calculating the path delay of each remote station in a central station auxiliary closed loop mode, so that each remote station completes burst communication in an allocated time slot;
And S3, in the time slot synchronization maintaining stage, 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 business burst communication on the time slot allocated by the remote station.
In the time slot synchronization method of the TDMA/MF-TDMA satellite communication system, in the step S2, in the initial synchronization stage, a remote station returns to a burst to be scheduled by taking a frame as a time unit, and the remote station randomly transmits a TDMA synchronization frame at a certain moment in each scheduling period; after receiving the TDMA synchronous frame sent by the remote station, the central station takes the TOD count value of the captured TDMA synchronous frame as a central station time stamp, fills the time stamp into the TDMA synchronous frame and transmits the time stamp back to the remote station through a forward link; after receiving the synchronization frame returned by the central station, the remote station calculates the path delay through the remote station sending time stamp and the central station receiving time stamp in the TDMA synchronization frame, and adjusts the time of each burst of the remote station according to the path delay, thus completing the initial time slot synchronization.
In step S3, in the time slot synchronization maintaining stage, the remote station periodically sends a TDMA synchronization frame periodically on its allocated time slot, the TDMA synchronization frame sending method is similar to the initial time slot synchronization stage, a new path delay L RTT is obtained, and the local frame number and time slot number are maintained 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 keep synchronous in time all the time.
Specifically, in step S1, the central station uses the forward link to time service each remote station through the TOD frame, so that each remote station and the central station maintain the uniformity in time, and the method includes the following steps:
after the central station and the remote station are started, respectively maintaining a TOD counter with 32-bit width locally, and counting by taking a super frame as a period under clock driving;
periodically generating a TOD frame by the central station and broadcasting on the forward link; the TOD frame is fixedly placed behind the unique word of the physical frame, and the filling value of the timestamp field of the central station 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 with the received TOD timestamp of the central station, and performs time counting under clock driving.
Step S2, the time slot synchronization process in the initial synchronization stage is as follows:
S21, the far-end station of the backward link takes frames as a dispatching period, each frame consists of N time slots, and the far-end station needs to carry out backward burst communication on the time slots allocated by the far-end station of each frame; in the initial time slot synchronization stage, the remote station transmits a TDMA synchronization frame once in each scheduling period in a random time slot, and the TDMA synchronization frame carries the ID number of the remote station and the TOD counter value of the remote station when the remote station transmits the TDMA synchronization frame, namely, the remote station transmits a time stamp L remote; if the TDMA synchronous frame of the remote station collides, and the central station does not receive the TDMA synchronous frame, the next frame period is again random for one time slot to send the TDMA synchronous frame.
S22, the central station takes the value of a counter for capturing the time TOD of the synchronous head of the TDMA synchronous frame sent by the remote station as the value of a central station receiving time stamp L master, the remote station sending time stamp L remote is filled by the remote station, the central station only needs to analyze without any change, and then the central station is filled with other fields to form the TDMA synchronous frame to be 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 sending time stamp L remote and the central station receiving time stamp L master can be obtained, and then the path delay value L can be obtained through the two information RTT
Step S3, the specific process of the time slot synchronization maintaining stage comprises the following steps:
S31, after the initial time slot synchronization is completed, the remote station calculates the current frame number and time slot number according to the local TOD counter value L CNT and the path delay L RTT, and uses the current frame number and time slot number as the time reference of the remote station burst;
S32, after calculating the time slot number, the remote station performs business burst communication on the time slot allocated by the remote station. After a plurality of frame periods are separated, a TDMA synchronous frame is periodically transmitted on an allocated time slot, the transmission method of the TDMA synchronous frame is similar to that of an initial time slot synchronous stage, a new path delay L RTT is obtained, a local frame number and a time slot number are maintained according to the updated path delay, and therefore the problem that the path delay changes due to the difference of motion and crystal oscillator of a remote station is solved, and the central station and the remote station keep synchronous in time all the time.
The invention has the beneficial effects that:
1. the time slot synchronization method of the TDMA/MF-TDMA satellite communication system 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 perform 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 an auxiliary mode of the central station, and calculates the path delay of each remote station in an auxiliary closed-loop mode of the central station, thereby ensuring that each remote station can complete burst communication in the assigned time slot.
2. The time slot synchronization method of the TDMA/MF-TDMA satellite communication system adopts a mode of random competition and timing period transmission of the TDMA synchronization frame to complete time slot synchronization of the whole satellite communication system, and the strategy can still ensure that all remote stations are synchronous on time slots under the condition of minimum resource consumption. The remote stations in the initial synchronization stage complete initial synchronization by adopting a random competition mechanism, and the time slot synchronization maintaining stage completes the time slot synchronization of the whole satellite communication system by periodically transmitting the TDMA synchronization frame at regular 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 the TDMA synchronization frame carries out data communication in a way of channel-associated service, so that the complexity of the design of the satellite communication system can be effectively reduced.
4. The time slot synchronization method of the TDMA/MF-TDMA satellite communication system is designed to complete time slot synchronization of the TDMA satellite communication without depending on third-party equipment, and is applied to practical projects, so that the effect is excellent.
Drawings
FIG. 1 is a diagram of a TDMA satellite communication system;
FIG. 2 is a diagram showing TOD frame formats;
FIG. 3 is a diagram of a TDMA synchronization frame format;
fig. 4 is a flowchart of the overall process of slot synchronization according to the present invention.
Detailed Description
In order to make the technical conception and advantages of the invention to achieve the objects of the invention more apparent, the technical scheme of the invention is further described in detail below with reference to the accompanying drawings. It is to be understood that the following examples are intended to illustrate and describe preferred embodiments of the invention and should not be construed as limiting the scope of the invention as claimed.
Example 1
The invention discloses a method for time slot synchronization of a TDMA satellite communication system based on the assistance of a central station, wherein the time slot synchronization process is divided into an initial synchronization stage and a time slot synchronization maintaining stage 2 stages, the initial synchronization stage adopts a random competition mechanism, and the time slot synchronization maintaining stage adopts a strategy of timing periodic transmission; the whole process flow is shown in fig. 4, and comprises the following steps:
step S1, taking the time of a central station as a reference, the central station uses a forward link to time service each remote station through a TOD frame, and the time of each remote station is aligned with the time of the central station, so that the time of each remote station and the time of the central station are kept uniform;
Step S2, calculating the path delay of each remote station in a central station auxiliary closed loop mode, so that each remote station completes burst communication in an allocated time slot;
and step S3, in the time slot synchronization maintaining stage, 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 business burst communication on the time slot allocated by the remote station.
Example 2
The TDMA/MF-TDMA satellite communication system time slot synchronization method of the present embodiment, unlike embodiment 1, further: in step S2, in the initial synchronization stage, the remote station returns burst to schedule with frame as time unit, and the remote station randomly transmits TDMA synchronization frame at a certain moment in each scheduling period; after receiving the TDMA synchronous frame sent by the remote station, the central station takes the TOD count value of the captured TDMA synchronous frame as a central station time stamp, fills the time stamp into the TDMA synchronous frame and transmits the time stamp back to the remote station through a forward link; after receiving the synchronization frame returned by the central station, the remote station calculates the path delay through the remote station sending time stamp and the central station receiving time stamp in the TDMA synchronization frame, and adjusts the time of each burst of the remote station according to the path delay, thus completing the initial time slot synchronization.
Example 3
The TDMA/MF-TDMA satellite communication system slot synchronization method of the present embodiment, unlike embodiment 1 and embodiment 2, further: in step S3, in the slot synchronization maintaining stage, the remote station periodically sends a TDMA synchronization frame on its allocated slot periodically, the TDMA synchronization frame sending method is similar to that in the initial slot synchronization stage, a new path delay L RTT is obtained, and the local frame number and slot number are maintained according to the updated path delay, so as to solve the problem that the path delay changes caused by the difference of motion and crystal oscillator of the remote station, and the central station and the remote station keep synchronous in time all the time.
Example 4
Referring to fig. 1-4, the invention discloses a method for synchronizing time slots of a TDMA satellite communication system based on the assistance of a central station, the whole processing flow is shown in fig. 4, and the method comprises the following steps:
s1, a central station uses a forward link to time service each remote station through a TOD frame, so that each remote station and the central station keep uniform in time, and the method comprises the following specific steps:
S11, after the central station and the remote station are started, a TOD counter with 32-bit width is maintained locally, and the clock is used for counting the period by taking a plurality of (for example 1024) frame periods as a time period.
S12, the central station generates one TOD frame at intervals of a plurality (e.g., 32) of frame periods and broadcasts on the forward link. The TOD frame is fixedly placed behind the unique word of the physical frame, and the filling value of the timestamp field of the central station 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.
And S13, after receiving the TOD frame, the remote station updates the value L CNT of the local TOD counter by using the received TOD timestamp of the central station, and performs time counting under clock driving.
S2, the remote station return burst is scheduled by taking a frame as a time unit, and in an initial time slot synchronization stage, the remote station randomly transmits a TDMA synchronization frame at a certain moment in each scheduling period, and the frame format of the TDMA synchronization frame is shown in figure 3. After receiving the TDMA synchronous frame sent by the remote station, the central station takes the TOD count value of the captured TDMA synchronous frame as a central station time stamp, fills the time stamp into the TDMA synchronous frame and transmits the time stamp back to the remote station through a forward link; after receiving the synchronization frame returned by the central station, the remote station can calculate the path delay through the remote station sending time stamp and the central station receiving time stamp in the TDMA synchronization frame, and adjust the time of each burst of the remote station according to the path delay, thus completing the initial time slot synchronization.
The step S2 specifically comprises the following steps:
S21, the far-end station of the backward link takes frames as a dispatching period, each frame is divided into a plurality of time slots, and the far-end station needs to carry out backward burst communication on the time slots allocated by the far-end station of each frame. In the initial time slot synchronization phase, the remote station transmits a TDMA synchronization frame once at a random time interval in each scheduling period, and the TDMA synchronization frame carries the ID number of the remote station and the TOD counter value of the remote station when the remote station transmits the TDMA synchronization frame, that is, the remote station transmission time stamp L remote.
S22, the central station takes the value of a counter for capturing the time TOD of the synchronous head of the TDMA synchronous frame sent by the remote station as the value of a central station receiving time stamp L master, the remote station sending time stamp L remote is filled by the remote station, the central station only needs to analyze without any change, and then the central station is filled with other fields to form the TDMA synchronous frame to be 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 sending time stamp L remote and the central station receiving time stamp L master can be obtained, and then the calculation process of the path delay value L RTT,LRTT can be obtained through the two information as follows.
Where T Frame is the length of time per frame in ms, f clk is the frequency of the count clock, and N Frame is how many frames are 1 count period.
S3, in the time slot synchronization maintaining stage, the remote station calculates the current frame number and time slot number according to the local TOD counter value L CNT and the path delay L RTT, and performs business burst communication on the time slot allocated by the remote station. After a plurality of frame periods are separated, a TDMA synchronous frame is periodically transmitted on an allocated time slot, the transmission method of the TDMA synchronous frame is similar to that of an initial time slot synchronous stage, a new path delay L RTT is obtained, a local frame number and a time slot number are maintained according to the updated path delay, and therefore the problem that the path delay changes due to the difference of motion and crystal oscillator of a remote station is solved, and the central station and the remote station keep synchronous in time all the time.
The step S3 specifically comprises the following steps:
S31, after the initial time slot synchronization is completed, the remote station calculates the current frame number and time slot number according to the local TOD counter value L CNT and the path delay L RTT, and uses the current frame number and time slot number as the time reference of the remote station burst. The time slot number and frame number calculation process is as follows
Frame number calculation process:
Remainder is L REM_1
Time slot number calculation procedure
Remainder is L REM_2
Wherein L SLOT is the number of slots in each frame.
S32, after calculating the time slot number, the remote station performs business burst communication on the time slot allocated by the remote station. After a plurality of frame periods are separated, a TDMA synchronous frame is periodically transmitted on an allocated time slot, the transmission method of the TDMA synchronous frame is similar to that of an initial time slot synchronous stage, a new path delay L RTT is obtained, a local frame number and a time slot number are maintained according to the updated path delay, and therefore the problem that the path delay changes due to the difference of motion and crystal oscillator of a remote station is solved, and the central station and the remote station keep synchronous in time all the time.
Most TDMA satellite communication systems currently use either beidou or GPS time service positioning, or an independent calibration station to complete slot synchronization, which requires an independent channel to complete the resolution of the beidou/GPS/calibration station signals, which undoubtedly increases the complexity of the 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 time slot synchronization of the TDMA satellite communication can be completed without depending on third party equipment, and the effect is excellent by being applied to practical projects.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention. Other modifications of the practice of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention without the need for inventive faculty, and any modification or substitution of equivalents which fall within the spirit and principles of the invention, or which are obvious to those skilled in the art, are intended to be encompassed within the scope of the invention.
Claims (4)
1.A time slot synchronization method of a TDMA/MF-TDMA satellite communication system is characterized in that the time slot synchronization process is divided into an initial synchronization stage and a time slot synchronization maintaining stage 2 stages, and is characterized in that: the initial synchronization stage adopts a random competition mechanism, and the time slot synchronization maintaining stage adopts a strategy of timing periodic transmission; the specific process comprises the following steps:
S1, taking the time of a central station as a reference, the central station uses a forward link to time service each remote station through a TOD frame, and the time of each remote station is aligned with the time of the central station, so that the time of each remote station and the time of the central station are kept uniform;
s2, calculating the path delay of each remote station in a central station auxiliary closed loop mode, so that each remote station completes burst communication in an allocated time slot;
s3, in the time slot synchronous holding stage, 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 business burst communication on the time slot allocated by the remote station;
The specific process of the time slot synchronization maintaining phase comprises the following steps:
S31, after the initial time slot synchronization is completed, the remote station calculates the current frame number and time slot number according to the local TOD counter value L CNT and the path delay L RTT, and uses the current frame number and time slot number as the time reference of the remote station burst; the slot number and frame number calculation process is as follows:
Frame number calculation process:
Remainder is L REM_1
Wherein, T Frame is the time length of each frame, the unit is ms, f clk is the frequency of the counting clock, and N Frame is how many frames are 1 counting period;
the time slot number calculation process comprises the following steps:
Remainder is L REM_2
Wherein, L SLOT is the number of time slots in each frame;
S32, after calculating the time slot number, the remote station performs business burst communication on the time slot allocated by the remote station; after a plurality of frame periods are separated, a TDMA synchronous frame is periodically transmitted on an allocated time slot, the transmission method of the TDMA synchronous frame is similar to that of an initial time slot synchronous stage, a new path delay L RTT is obtained, a local frame number and a time slot number are maintained according to the updated path delay, and therefore the problem that the path delay changes due to the difference of motion and crystal oscillator of a remote station is solved, and the central station and the remote station keep synchronous in time all the time.
2. The method for slot synchronization in a TDMA/MF-TDMA satellite communication system according to claim 1 wherein: in step S2, in the initial synchronization stage, the remote station returns burst to schedule with frame as time unit, and the remote station randomly transmits TDMA synchronization frame at a certain moment in each scheduling period;
After receiving the TDMA synchronous frame sent by the remote station, the central station takes the TOD count value of the captured TDMA synchronous frame as a central station time stamp, fills the time stamp into the TDMA synchronous frame and transmits the time stamp back to the remote station through a forward link;
after receiving the synchronization frame returned by the central station, the remote station calculates the path delay through the remote station sending time stamp and the central station receiving time stamp in the TDMA synchronization frame, and adjusts the time of each burst of the remote station according to the path delay, thus completing the initial time slot synchronization.
3. A TDMA/MF-TDMA satellite communication system time slot synchronization method according to claim 1 or 2 wherein: in step S1, the central station uses the forward link to transmit time to each remote station through the TOD frame, so that each remote station and the central station keep uniform in time, and the method comprises the following steps:
after the central station and the remote station are started, respectively maintaining a TOD counter with 32-bit width locally, and counting by taking a super frame as a period under clock driving;
periodically generating a TOD frame by the central station and broadcasting on the forward link; the TOD frame is fixedly placed behind the unique word of the physical frame, and the filling value of the timestamp field of the central station 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 with the received TOD timestamp of the central station, and performs time counting under clock driving.
4. A TDMA/MF-TDMA satellite communication system time slot synchronization method according to claim 1 or 2 wherein:
step S2, the time slot synchronization process in the initial synchronization stage is as follows:
S21, the far-end station of the backward link takes frames as a dispatching period, each frame consists of N time slots, and the far-end station needs to carry out backward burst communication on the time slots allocated by the far-end station of each frame; in the initial time slot synchronization stage, the remote station transmits a TDMA synchronization frame once in each scheduling period in a random time slot, and the TDMA synchronization frame carries the ID number of the remote station and the TOD counter value of the remote station when the remote station transmits the TDMA synchronization frame, namely, the remote station transmits a time stamp L remote; if the TDMA synchronous frame of the remote station collides, and the central station does not receive the TDMA synchronous frame, the next frame period is again random for a time slot to send the TDMA synchronous frame;
S22, the central station takes the value of a counter for capturing the time TOD of the synchronous head of the TDMA synchronous frame sent by the remote station as the value of a central station receiving time stamp L master, the remote station sending time stamp L remote is filled by the remote station, the central station only needs to analyze without any change, and then the central station is filled with other fields to form the TDMA synchronous frame to be 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 sending time stamp L remote and the central station receiving time stamp L master can be obtained, and then the calculation process of the path delay value L RTT,LRTT can be obtained through the two information is as follows:
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