CN114567923A - Uplink synchronization method in satellite communication system - Google Patents
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W56/00—Synchronisation arrangements
- H04W56/0005—Synchronisation arrangements synchronizing of arrival of multiple uplinks
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
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- H04W56/004—Synchronisation arrangements compensating for timing error of reception due to propagation delay
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W84/00—Network topologies
- H04W84/02—Hierarchically pre-organised networks, e.g. paging networks, cellular networks, WLAN [Wireless Local Area Network] or WLL [Wireless Local Loop]
- H04W84/04—Large scale networks; Deep hierarchical networks
- H04W84/06—Airborne or Satellite Networks
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- Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
- Y02D30/00—Reducing energy consumption in communication networks
- Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks
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Abstract
The invention provides an uplink synchronization method in a satellite communication system, which comprises the following steps: the base station and the terminal keep time synchronization with the same time service system, and the reference time of the downlink frame is mapped through the same rule; the terminal measures the deviation between the arrival time of the downlink frame and the reference time by itself as the one-way transmission time delay from the base station to the terminal; and the terminal sends an uplink signal in advance according to the one-way transmission time delay so that the uplink signal reaches the base station side in the expected receiving time window. According to the method and the device, transmission delay measurement from the base station to the terminal can be completed without depending on any ephemeris and geographical position information, and air interface overhead and terminal complex processing caused by base station position updating are avoided; for the base station with the transparent forwarding processing mode, the terminal does not need to perform differential processing, so that the terminal operation is simplified; the accurate uplink time delay precompensation mechanism of the terminal can greatly reduce the length of an RACH receiving window, thereby reducing uplink overhead and shortening access time delay.
Description
Technical Field
The invention relates to the field of satellite communication, in particular to an uplink synchronization method in a satellite communication system.
Background
A key problem of a satellite communication system is uplink synchronization, which means that a terminal adjusts the signal transmission time so that a signal reaches an on-satellite base station at a specified time, and generally includes the following steps: the ground terminal sends random access RACH signals; the satellite base station calculates the signal transmission time delay from the terminal to the base station by detecting the arrival time of the RACH signal; the base station sends a timing adjustment TA command to the terminal; and the terminal adjusts the signal sending time so that the signal reaches the satellite base station at the specified time point.
If the duration of the RACH signal detection window needs to be 2 times the coverage distance of the base station divided by the speed of light according to the terrestrial 5G scheme, if the cell coverage distance is 600km, the RACH window length is more than 4ms, which results in a large time-domain overhead. To reduce this overhead, two approaches have been proposed.
A method is called closed-loop method, the satellite broadcasts the signal advance of the edge of the coverage area to the terminal according to the orbit height and the coverage area, the terminal adjusts the RACH sending time according to the information, at this time, the RACH window length can be configured to be 2 (D2-D1)/C; where D2 is the farthest distance between the satellite base station and the in-coverage terminal, and D1 is the closest distance between the satellite base station and the in-coverage terminal, as shown in fig. 1. The RACH duration is about 0.8ms measured by the height of 600km rail and the diameter of a cell of 400 km. The closed-loop scheme has a large RACH window and high system overhead.
Another method is called an open loop method, and the terminal measures and calculates the distance between the terminal and the satellite base station according to the self-position information and the ephemeris information, so as to adjust the RACH transmission time in advance, wherein the window length of the RACH can be configured to be shorter. The RACH window of the open-loop scheme is smaller, the overhead is also smaller, but the method depends on terminal positioning and ephemeris information. For the on-satellite transparent forwarding processing mode, the terminal needs to acquire the position information of the ground base station, the ephemeris information, and the error of the ephemeris and the geographical position information needs to be controlled in a small range, the ground base station is frequently constructed, the initial information of the terminal also needs to be frequently updated, and the maintenance cost is very high.
Disclosure of Invention
In order to solve the above problem, the present application provides an uplink synchronization method in a satellite communication system, including: the base station and the terminal keep time synchronization with the same time service system, and the reference time of the downlink frame is mapped through the same rule; the terminal measures the deviation between the arrival time of the downlink frame and the reference time by itself as the one-way transmission time delay from the base station to the terminal; and the terminal sends an uplink signal in advance according to the one-way transmission time delay so that the uplink signal reaches the base station side in the expected receiving time window.
Further, the terminal measures the deviation between the downlink frame arrival time and the reference time by itself, and specifically includes: and the terminal detects a downlink frame sent by the base station at the time T1, records the time when the downlink frame is detected as T2, and calculates the deviation of the downlink frame and the time as the one-way transmission time delay D which is T2-T1.
Further, the terminal sends an uplink signal in advance according to the one-way transmission delay, so that the uplink signal reaches the base station side within the expected receiving time window, including: the terminal sends the uplink signal in advance by a transmission delay D with the expected receiving time T3 as the reference, so that the initial position of the uplink signal is earlier than T3, and the end position of the uplink signal is greater than T3+
The expected receiving time window of the T _ duration reaches the base station side; wherein the T _ duration is a duration of the uplink signal.
Furthermore, the expected receiving time T3 is issued by the base station side as explicit information or implicit information through broadcast information, or is calculated by the terminal and the base station according to the local time and the same rule.
Further, the T1, T2, and T3 are relative times, absolute times, or certain time slots within a certain frame number.
Further, the base station and the terminal keep time synchronization with the same time service system, and map the reference time of the downlink frame according to the same rule, including: the base station and the terminal are synchronous with GNSS or 1588V2 to obtain 1PPS time service; and the base station and the terminal generate frame boundary timing based on the 1PPS information and sequentially allocate frame numbers.
Furthermore, the terminal measures the deviation between the arrival time of the downlink frame and the reference time by itself as the one-way transmission time delay from the base station to the terminal; the method comprises the following steps: the terminal detects the downlink frame and records the time Trev when the downlink frame is detected; calculating the difference between the time and the boundary time Tbase of the latest downlink frame corresponding to the local reference timing, wherein Td is Trev-Tbase; and calculating the difference N between the frame number carried in the downlink frame broadcast channel and the frame number of the latest downlink frame corresponding to the local reference timing, and calculating the length of the unidirectional transmission time delay D-Td + N-frame.
Furthermore, the terminal measures the deviation between the arrival time of the downlink frame and the reference time by itself as the one-way transmission time delay from the base station to the terminal; the method comprises the following steps: the terminal detects the downlink frame and records the time Trev when the downlink frame is detected; calculating the difference between the time and the boundary time Tbase of the latest downlink frame corresponding to the local reference timing, wherein Td is Trev-Tbase; comparing the parity attribute of the frame number carried in the downlink frame broadcast channel with the frame number of the latest downlink frame corresponding to the local reference timing: if the parity attributes of the two are the same, the one-way transmission time delay D is Td; if the parity attributes of the two are different, the one-way transmission time delay D is Td + the frame length.
Further, the terminal sends the uplink signal in advance according to the one-way transmission delay, so that the uplink signal reaches the base station side within the expected receiving time window, including: and the terminal sends the uplink signal by advancing 2 unidirectional transmission time delays 2 x D by taking the Trev as a reference.
Further, the base station is a satellite base station or a ground base station or both.
The invention can finish the transmission delay measurement from the base station to the terminal without depending on any ephemeris and geographical position information, thereby avoiding the air interface overhead and the terminal complex processing caused by the updating of the position of the base station; for the base station with the transparent forwarding processing mode, the terminal does not need to perform differential processing, so that the terminal operation is simplified; the accurate uplink time delay precompensation mechanism of the terminal can greatly reduce the length of an RACH receiving window, thereby reducing uplink overhead and shortening access time delay.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and those skilled in the art can also obtain other drawings according to the drawings without creative efforts.
FIG. 1 is a diagram illustrating the advance of a signal transmitted at the edge of a coverage area of a satellite broadcast in the prior art;
fig. 2 is a schematic diagram of uplink synchronization proposed in embodiment 1 of the present application;
fig. 3 is a schematic diagram of uplink synchronization proposed in embodiment 2 of the present application;
fig. 4 is a schematic diagram of uplink synchronization proposed in embodiment 3 of the present application.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments; it should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
One embodiment of the present application provides an uplink synchronization method in a satellite communication system, including: the base station and the terminal keep time synchronization with the same time service system, and the reference time of the downlink frame is mapped through the same rule; the terminal measures the deviation between the arrival time of the downlink frame and the reference time by itself as the one-way transmission time delay from the base station to the terminal; and the terminal sends the uplink signal in advance according to the one-way transmission time delay so that the uplink signal reaches the base station side in the expected receiving time window.
In an alternative embodiment, the method comprises: the terminal detects a downlink frame sent by the base station at the time T1, records the time when the downlink frame is detected as T2, and calculates the deviation of the downlink frame and the time when the downlink frame is detected as the one-way transmission time delay D which is T2-T1; the terminal sends an uplink signal in advance by one transmission delay D by taking the expected receiving time T3 as a reference, so that the uplink signal reaches the base station side in an expected receiving time window with the starting position earlier than T3 and the ending position greater than T3+ T _ duration; wherein, the T _ duration is a duration of the uplink signal. The expected receiving time T3 may be sent by the base station side as explicit information or implicit information through broadcast information, or may be calculated by the terminal and the base station according to the local time and the same rule. T1, T2, and T3 may be relative time, absolute time, or a certain time slot within a certain frame number.
Example 1
In this embodiment, both the base station and the terminal are synchronized with a global navigation satellite system GNSS, and the same reference time point is used as a frame start time T1, and the base station transmits a downlink synchronization signal at the reference time point. After receiving the downlink synchronization signal, the terminal calculates a time difference T _ offset between an arrival time T2 of the downlink synchronization signal and a reference time point T1, which is T2-T1, and obtains a transmission delay from the ground base station or the satellite base station to the terminal. The terminal sends the signal in advance of T _ offset according to the receiving time requirement of the base station, which satisfies that the signal arrives at the base station at the specified time T3, and the base station can complete signal reception within a smaller detection window, please refer to fig. 2. The method mainly comprises the following steps:
step 3, after detecting the downlink synchronization signal, the terminal acquires time T2 at this time, and calculates T _ offset, whose value is T2-T1, that is, transmission delay from the base station to the terminal;
step 4, the terminal acquires time T3 when the base station expects to receive the uplink signal from the downlink broadcast signal, and sends the uplink signal in advance of T _ offset, wherein the signal duration is T _ duration;
step 5, the start position of the receiving window of the base station is slightly earlier than T3, and the end position of the receiving window may be slightly longer than T3+ T _ duration, so as to ensure that the uplink signal falls within the receiving window.
In an optional embodiment, both the base station and the terminal are synchronized with a GNSS or 1588V2 to obtain 1PPS time service; frame boundary timing is generated based on the 1PPS information, and frame numbers are sequentially allocated.
In an optional embodiment, the terminal detects a downlink frame, and records a time Trev when the downlink frame is detected; calculating the difference between the time and the boundary time Tbase of the latest downlink frame corresponding to the local reference timing, wherein Td is Trev-Tbase; and calculating the difference N between the frame number carried in the downlink frame broadcast channel and the frame number of the latest downlink frame corresponding to the local reference timing, and calculating the length of the unidirectional transmission time delay D-Td + N-frame.
In an optional embodiment, the terminal detects a downlink frame, and records a time Trev when the downlink frame is detected; calculating the difference between the time and the boundary time Tbase of the latest downlink frame corresponding to the local reference timing, wherein Td is Trev-Tbase; comparing the parity attribute of the frame number carried in the downlink frame broadcast channel with the frame number of the latest downlink frame corresponding to the local reference timing: if the parity attributes of the two are the same, the one-way transmission time delay D is Td; if the parity attributes of the two are different, the one-way transmission time delay D is Td + the frame length.
In an optional embodiment, the terminal sends the uplink signal 2 one-way transmission delays ahead of Trev.
In an alternative embodiment, the base station is an on-board base station or a ground base station or both.
Example 2: uplink synchronization method for satellite processing base station
Please refer to fig. 3 for a schematic diagram of the synchronization method in this embodiment. The method comprises the following steps:
the base station and the terminal are synchronous with the GNSS, 1PPS time service is obtained, and the time service precision can generally meet 1us deviation;
the base station and the terminal generate 10ms frame boundary timing based on 1PPS information:
the base station allocates even frame numbers for the first 10ms wireless frame after 1PPS timing, allocates odd frame numbers for the second 10ms wireless frame, sequentially accumulates the frame numbers of the subsequent frames, the range of the frame numbers is 0-1023, and numbering needs to be started from 0 again after the accumulation reaches 1023;
the first 10ms wireless frame after 1PPS is defaulted by the terminal reference timing system to be an even frame, and subsequent even frames and odd frames alternately appear.
After a terminal detects a downlink frame with an SFN number of X, the terminal firstly records the starting time Trev _ X of the detected X wireless frame, then acquires the boundary time Tbase _ X of the latest 10ms frame stored locally and the parity frame attribute of the 10ms frame, and defines TDelay _ X as Trev _ X-Tbase _ X with the unit of us.
If the parity attributes of the radio frame number X detected by the terminal and the latest 10ms frame corresponding to the reference timing of the terminal are the same, namely, the radio frame number X is both an odd number or both even numbers, the transmission delay TDelay from the reference to the terminal is TDelay _ X; if the parity attribute of the latest 10ms frame corresponding to the radio frame number X detected by the terminal and the terminal reference timing is different, the unit us is us where the transmission delay TDelay from the reference to the terminal is TDelay _ X + 10000.
The terminal takes Trev _ X as a reference, sends 2 times TDelay in advance, compensates downlink transmission time delay, and ensures that microsecond coarse synchronization is realized when uplink signals of all terminal signals under the satellite reach the base station on the satellite.
Example 3: uplink synchronization method of transparent forwarding base station
Referring to fig. 4, the on-board portion of the present embodiment only performs transparent forwarding of data. The uplink synchronization at this time mainly comprises the following steps:
the ground base station and the terminal are synchronous with the GNSS or 1588V2, 1PPS time service is obtained, and the on-board transparent forwarding unit does not need to be synchronous with the GNSS.
The ground base station and the terminal generate 10ms frame boundary timing based on 1PPS information: the ground base station allocates even frame numbers for the first 10ms wireless frame after timing of 1PPS, allocates odd frame numbers for the second 10ms wireless frame, sequentially accumulates the frame numbers of the subsequent frames, the range of the frame numbers is 0-1023, and numbering needs to be started from 0 again after the accumulation reaches 1023; the first 10ms wireless frame after the default 1PPS of the terminal reference timing system is an even frame, and subsequent even frames and odd frames alternately appear.
After a terminal detects a downlink frame with an SFN number of X, the terminal firstly records the starting time Trev _ X of the detected X wireless frame, then acquires the attribute of a parity frame locally storing the latest 10ms frame boundary time Tbase _ X and 10ms frame, and defines TDelay _ X as Trev _ X-Tbase _ X.
If the number X of the wireless frame detected by the terminal is the same as the parity attribute of the latest 10ms frame corresponding to the reference timing of the terminal, the transmission delay TDelay from the base station to the terminal is TDelay _ X; and if the parity attribute of the latest 10ms frame corresponding to the radio frame number X detected by the terminal and the reference timing of the terminal is different, the transmission delay TDelay from the reference to the terminal is TDelay _ X + 10000.
The terminal takes Trev _ X as a reference, sends 2 times TDelay in advance, compensates downlink transmission time delay, and ensures that microsecond coarse synchronization is realized when uplink signals of all terminal signals under the satellite reach the base station on the satellite.
The two embodiments can detect the transmission delay of 20ms at most, and can accurately measure the transmission delay when the total distance between the ground base station and the terminal is less than 6000 km.
It can be seen from the above embodiments that the transmission delay measurement from the base station to the terminal can be completed without depending on any ephemeris and geographical location information, thereby avoiding air interface overhead and terminal complex processing caused by base station location update; for the base station with the transparent forwarding processing mode, the terminal does not need to perform differential processing, so that the terminal operation is simplified; the accurate uplink time delay precompensation mechanism of the terminal can greatly reduce the length of an RACH receiving window, thereby reducing uplink overhead and shortening access time delay.
Those of ordinary skill in the art will understand that: all or part of the steps for implementing the method embodiments may be implemented by hardware related to program instructions, and the program may be stored in a computer readable storage medium, and when executed, the program performs the steps including the method embodiments; and the aforementioned storage medium includes: various media that can store program codes, such as ROM, RAM, magnetic or optical disks.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (10)
1. An uplink synchronization method in a satellite communication system, comprising:
the base station and the terminal keep time synchronization with the same time service system, and the reference time of the downlink frame is mapped through the same rule;
the terminal measures the deviation between the arrival time of the downlink frame and the reference time by itself as the one-way transmission time delay from the base station to the terminal;
and the terminal sends an uplink signal in advance according to the one-way transmission time delay so that the uplink signal reaches the base station side in the expected receiving time window.
2. The method according to claim 1, wherein the terminal measures the deviation between the arrival time of the downlink frame and the reference time by itself, and specifically comprises:
and the terminal detects a downlink frame sent by the base station at the time T1, records the time when the downlink frame is detected as T2, and calculates the deviation of the downlink frame and the time as the one-way transmission time delay D which is T2-T1.
3. The method according to claim 2, wherein the terminal sends the uplink signal in advance according to the one-way transmission delay, so that the uplink signal reaches the base station side within an expected receiving time window, including:
the terminal sends an uplink signal in advance by one transmission delay D by taking an expected receiving time T3 as a reference, so that the uplink signal reaches the base station side in an expected receiving time window with the starting position earlier than T3 and the ending position greater than T3+ T _ duration;
wherein the T _ duration is a duration of the uplink signal.
4. The method according to claim 3, wherein the expected receiving time T3 is issued by the base station side as explicit information or implicit information through broadcast information, or calculated by the terminal and the base station according to the local time and the same rule.
5. The method of any one of claims 1 to 4, wherein the T1, T2 and T3 are relative time, absolute time or a time slot within a frame number.
6. The method of claim 1, wherein the base station and the terminal maintain time synchronization with the same time service system, and map the reference time of the downlink frame according to the same rule, comprising:
the base station and the terminal are synchronous with GNSS or 1588V2 to obtain 1PPS time service;
both the base station and the terminal generate frame boundary timing based on the 1PPS information and allocate a frame number accordingly.
7. The method according to claim 6, wherein the terminal measures the deviation between the arrival time of the downlink frame and the reference time by itself as the one-way transmission delay from the base station to the terminal; the method comprises the following steps:
the terminal detects the downlink frame and records the time Trev when the downlink frame is detected;
calculating the difference between the time and the boundary time Tbase of the latest downlink frame corresponding to the local reference timing, wherein Td is Trev-Tbase;
calculating the difference N between the frame number of the downlink frame and the frame number of the latest downlink frame corresponding to the local reference timing,
and calculating the length of the unidirectional transmission time delay D-Td + N frame.
8. The method according to claim 6, wherein the terminal measures the deviation between the arrival time of the downlink frame and the reference time by itself as the one-way transmission delay from the base station to the terminal; the method comprises the following steps:
the terminal detects the downlink frame and records the time Trev when the downlink frame is detected;
calculating the difference between the time and the boundary time Tbase of the latest downlink frame corresponding to the local reference timing, wherein Td is Trev-Tbase;
comparing the frame number of the downlink frame with the parity attribute of the frame number of the latest downlink frame corresponding to the local reference timing:
if the parity attributes of the two are the same, the one-way transmission time delay D is Td;
if the parity attributes of the two are different, the one-way transmission time delay D is Td + the frame length.
9. The method according to claim 7 or 8, wherein the terminal sends the uplink signal according to the one-way transmission delay advance, so that the uplink signal reaches the base station side within the expected receiving time window, including:
and the terminal sends uplink signals by taking the Trev as a reference and advancing 2 unidirectional transmission time delays 2 x D.
10. The method according to any one of claims 1 to 9, wherein the base station is an on-board base station or a terrestrial base station or both.
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| CN117545062A (en) * | 2024-01-10 | 2024-02-09 | 中国电力科学研究院有限公司 | Time alignment method, system and related equipment in wireless communication |
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