CN114567923A - Uplink synchronization method in satellite communication system - Google Patents

Abstract

The present invention provides an uplink synchronization method in a satellite communication system, which includes: a base station and a terminal maintain time synchronization with the same timing system, and map a downlink frame reference time through the same rules; the terminal measures the arrival time of the downlink frame and the reference time by itself The deviation is taken as the one-way transmission delay from the base station to the terminal; 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. This application can complete the transmission delay measurement from the base station to the terminal without relying on any ephemeris and geographic location information, avoiding the air interface overhead caused by the location update of the base station and the complex processing of the terminal; for the base station in the transparent forwarding processing mode, the terminal does not need to be processed differently, simplifying Terminal operation; accurate terminal uplink delay pre-compensation mechanism can greatly reduce the length of the RACH receiving window, thereby reducing uplink overhead and shortening access delay.

Description

A kind of uplink synchronization method in satellite communication system

technical field

The invention relates to the field of satellite communication, in particular to an uplink synchronization method in a satellite communication system.

Background technique

A key issue of satellite communication system is uplink synchronization. Uplink synchronization of satellite communication means that the terminal adjusts the signal transmission time so that the signal arrives at the satellite base station at the specified time. The general steps include: the ground terminal sends a random access RACH signal; the satellite base station By detecting the arrival time of the RACH signal, the signal transmission delay from the terminal to the base station is measured; the base station adjusts the TA command to the terminal by issuing timing; the terminal adjusts the signal transmission time so that the signal arrives at the satellite base station at the specified time point.

According to the terrestrial 5G scheme, the RACH signal detection window length needs to be 2 times the coverage distance of the base station divided by the speed of light. For example, if the cell coverage distance is 600km, the RACH window length is more than 4ms, which will result in a large time domain overhead. To reduce this overhead, the industry has proposed two methods.

One method is called a closed-loop method. The satellite broadcasts the advance of the transmitted signal at the edge of the coverage area to the terminal according to its orbit height and coverage area. The terminal first adjusts the RACH transmission time according to the information, and the RACH window length can be configured to 2 *(D2-D1)/C; where D2 is the farthest distance between the on-board base station and the terminal within the coverage area, and D1 is the shortest distance between the on-board base station and the terminal within the coverage area, as shown in Figure 1. Calculated with a track height of 600km and a cell diameter of 400km, the RACH duration is about 0.8ms. The closed-loop scheme has a larger RACH window and a larger system overhead.

Another method is called the open-loop method. The terminal calculates the distance between the terminal and the base station on the satellite according to its own location information and ephemeris information, so as to adjust the RACH transmission time in advance. At this time, the window length of the RACH can be configured to be shorter. . This open-loop scheme has a smaller RACH window and lower overhead, but it depends on terminal positioning and ephemeris information. For the on-satellite transparent forwarding processing mode, the terminal needs to obtain the location information and ephemeris information of the ground base station, and the error of the ephemeris and geographical position information needs to be controlled in a small range, and the ground base station is constructed frequently, and the initial information of the terminal also needs to be updated frequently. Maintenance The price is high.

SUMMARY OF THE INVENTION

In view of the above problems, the present application proposes an uplink synchronization method in a satellite communication system, including: the base station and the terminal maintain time synchronization with the same timing system, and map the reference time of the downlink frame through the same rules; the terminal measures the arrival time of the downlink frame by itself. The deviation of the reference time is used as the one-way transmission delay from the base station to the terminal; 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.

Further, the terminal measures the deviation between the arrival time of the downlink frame and the reference time by itself, which specifically includes: the terminal detects the downlink frame sent by the base station at time T1, records the time when the downlink frame is detected as T2, and calculates the difference between the two as T2. The one-way transmission delay D=T2-T1.

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: the terminal takes the expected receiving time T3 as a reference, and sends the uplink signal one time earlier. The transmission delay D sends the uplink signal, so that the start position of the uplink signal is earlier than T3 and the end position is greater than T3+

The expected receiving time window of T_duration arrives at the base station side; wherein, the T_duration is the duration of the uplink signal.

Further, the expected reception time T3 is issued by the base station side through broadcast information as explicit information or implied information, or 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 time, absolute time or a certain time slot within a certain frame number.

Further, the base station and the terminal maintain time synchronization with the same timing system, and map the downlink frame reference time through the same rules, including: the base station and the terminal are synchronized with GNSS or 1588V2 to obtain 1PPS timing; both the base station and the terminal are based on 1PPS information. Frame boundary timing is generated, and frame numbers are assigned in sequence.

Further, 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; including: the terminal detects the downlink frame, and records the time Trev when the downlink frame is detected; Calculate the difference between the boundary time Tbase of the latest downlink frame corresponding to this moment and the local reference timing, Td=Trev-Tbase; calculate the difference between the frame number carried in the broadcast channel of this downlink frame and the frame number of the latest downlink frame corresponding to the local reference timing N, calculate the one-way transmission delay D=Td+N*frame length.

Further, 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; including: the terminal detects the downlink frame, and records the time Trev when the downlink frame is detected; Calculate the difference between this moment and the boundary moment Tbase of the latest downlink frame corresponding to the local reference timing, Td=Trev-Tbase; compare the frame number carried in the broadcast channel of the downlink frame and the parity of the frame number of the latest downlink frame corresponding to the local reference timing Attribute: if the parity attributes of the two are the same, the one-way transmission delay D=Td; if the parity attributes of the two are different, the one-way transmission delay D=Td+frame length.

Further, the terminal sends the uplink signal in advance according to the one-way transmission delay, so that the uplink signal arrives at the base station side within the expected reception time window, including: the terminal uses the Trev as a reference, and sends the uplink signal two times in advance. Send the uplink signal with the one-way transmission delay 2*D.

Further, the base station is an on-board base station or a ground base station or an on-board base station and a ground base station.

The invention can complete the transmission delay measurement from the base station to the terminal without relying on any ephemeris and geographical position information, and avoid the air interface overhead caused by the location update of the base station and the complex processing of the terminal; Simplified terminal operation; accurate terminal uplink delay pre-compensation mechanism can greatly reduce the length of the RACH receiving window, thereby reducing uplink overhead and shortening access delay.

Description of drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description These are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to these drawings without creative efforts.

1 is a schematic diagram of the advance amount of the transmitted signal at the edge of the satellite broadcasting coverage area in the prior art;

FIG. 2 is a schematic diagram of uplink synchronization proposed in Embodiment 1 of the present application;

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 ways

In order to make the purposes, 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 accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments It is a part of the embodiments of the present invention, but not all of the embodiments; it should be noted that the embodiments in the present application and the features in the embodiments may be combined with each other under the condition of no conflict. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

An embodiment of the present application proposes an uplink synchronization method in a satellite communication system, including: the base station and the terminal maintain time synchronization with the same timing system, and map the reference time of the downlink frame through the same rule; the terminal measures the arrival time of the downlink frame by itself. The deviation of the reference time is regarded as the one-way transmission delay from the base station to the terminal; 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.

In an optional embodiment, it includes: the terminal detects the downlink frame sent by the base station at time T1, records the time when the downlink frame is detected as T2, and calculates the difference between the two as the one-way transmission delay D=T2-T1; Based on the expected receiving time T3, the terminal sends the uplink signal with a transmission delay D in advance, so that the uplink signal reaches the base station side in the expected receiving time window whose starting position is earlier than T3 and the ending position is greater than T3+T_duration; among them, T_duration is The duration of the upstream signal. The expected receiving time T3 may be issued by the base station side as explicit information or implied information through broadcast information, or may be calculated by the terminal and the base station according to local time and the same rules. T1, T2 and T3 can be relative time, absolute time, or a certain time slot in a certain frame number.

Example 1

In this embodiment, both the base station and the terminal are synchronized with the global navigation satellite system GNSS, and the same reference time point is used as the frame start time T1, and the base station sends the downlink synchronization signal at the reference time point. After receiving the downlink synchronization signal, the terminal calculates the time difference T_offset=T2-T1 between the arrival time T2 of the downlink synchronization signal and the reference time point T1 to obtain the transmission delay from the ground base station or the satellite base station to the terminal. According to the receiving time requirement of the base station, the terminal sends T_offset in advance, so that the signal arrives at the base station at the specified time T3, and the base station can complete the signal reception within a small detection window, please refer to Figure 2. The main steps include:

Step 1. Both the base station and the terminal obtain UTC time and 1PPS information through GPS, BD and other GNSS systems. The reference time points T1, T2, and T3 can be defined by UTC time, which can be relative time, absolute time, or a certain time in a certain SFN frame. slot;

Step 2, the base station sends synchronization and broadcast signals at time T1, wherein the frame number in the broadcast information can be calculated by T1;

Step 3. After the terminal detects the downlink synchronization signal, it obtains the time T2 at this time, and calculates T_offset, and the value is T2-T1, that is, the transmission delay between the base station and the terminal;

Step 4. The terminal obtains the time T3 when the base station expects to receive the uplink signal in the downlink broadcast signal, and sends the uplink signal in advance by T_offset, and the signal duration is T_duration;

Step 5: The starting position of the receiving window of the base station is slightly earlier than T3, and the ending position of the receiving window may be slightly greater than T3+T_duration, 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 GNSS or 1588V2 to obtain 1PPS timing; frame boundary timing is generated based on the 1PPS information, and frame numbers are assigned in sequence.

In an optional embodiment, the terminal detects a downlink frame, and records the time Trev at which the downlink frame is detected; calculates the difference between the time and the boundary time Tbase of the latest downlink frame corresponding to the local reference timing, Td=Trev-Tbase; calculates 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 is calculated to calculate the one-way transmission delay D=Td+N*frame length.

In an optional embodiment, the terminal detects a downlink frame, and records the time Trev at which the downlink frame is detected; calculates the difference between the time and the boundary time Tbase of the latest downlink frame corresponding to the local reference timing, Td=Trev-Tbase; compares The parity attribute of the frame number carried in the broadcast channel of the downlink frame and 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 delay D=Td; if the parity attributes of the two are different, Then the one-way transmission delay D=Td+frame length.

In an optional embodiment, the terminal sends the uplink signal in advance of two one-way transmission delays based on Trev.

In an optional embodiment, the base station is an on-board base station or a terrestrial base station or an on-board base station and a terrestrial base station.

Embodiment 2: On-board processing base station uplink synchronization method

Please refer to FIG. 3 for a schematic diagram of the synchronization method proposed in this embodiment. It includes the following steps:

Both the base station and the terminal are synchronized with GNSS to obtain 1PPS timing, and the timing accuracy can generally meet the 1us deviation;

Both the base station and the terminal generate 10ms frame boundary timing based on 1PPS information:

The base station assigns odd-numbered frame numbers to the first 10ms wireless frame after 1PPS timing, and assigns odd-numbered frame numbers to the second 10ms wireless frame. The frame numbers are sequentially accumulated for each subsequent frame. The frame number ranges from 0 to 1023. Restart numbering from 0;

The terminal reference timing system defaults that the first 10ms radio frame after 1PPS is an even frame, and subsequent even frames and odd frames appear alternately.

After the terminal detects the downlink frame with the SFN number X, it first records the detected start time Trev_X of the X radio frame, and then obtains the latest 10ms frame boundary time Tbase_X and the parity frame attributes of the 10ms frame stored locally, and defines TDelay_X=Trev_X-Tbase_X , the unit is us.

If the wireless frame number X detected by the terminal is the same as the parity attribute of the latest 10ms frame corresponding to the reference timing of the terminal, that is, both are odd or even, then the transmission delay from the reference to the terminal TDelay=TDelay_X; The frame number X is different from the parity attribute of the latest 10ms frame corresponding to the reference timing of the terminal, so the transmission delay from the reference to the terminal TDelay=TDelay_X+10000, and the unit is us.

Based on Trev_X, the terminal sends 2*TDelay in advance to compensate for the downlink transmission delay and ensure that the uplink signals of all terminal signals under the satellite reach the base station on the satellite to achieve microsecond-level coarse synchronization.

Embodiment 3: Uplink synchronization method of transparent forwarding base station

Referring to FIG. 4 , in this embodiment, the on-board part is only used for transparent data forwarding. The uplink synchronization at this time mainly includes the following steps:

Both the ground base station and the terminal are synchronized with GNSS or 1588V2 to obtain 1PPS timing, and the on-board transparent forwarding unit does not need to be synchronized with GNSS.

Both the ground base station and the terminal generate 10ms frame boundary timing based on 1PPS information: the ground base station assigns odd-numbered frame numbers to the first 10ms radio frame after 1PPS timing, and assigns odd-numbered frame numbers to the second 10ms radio frame, and successively accumulates frame numbers for each subsequent frame. , the frame number ranges from 0 to 1023. After the accumulation reaches 1023, the numbering needs to start from 0 again; the terminal reference timing system defaults to the first 10ms wireless frame after 1PPS as an even frame, and subsequent even and odd frames appear alternately.

After the terminal detects the downlink frame with the SFN number X, it first records the detected start time Trev_X of the X radio frame, and then obtains the latest 10ms frame boundary time Tbase_X and the parity frame attributes of the 10ms frame stored locally, and defines TDelay_X=Trev_X-Tbase_X .

If the radio frame number X detected by the terminal is the same as the parity attribute of the latest 10ms frame corresponding to the terminal reference timing, then the transmission delay from the base station to the terminal TDelay=TDelay_X; if the radio frame number X detected by the terminal corresponds to the terminal reference timing If the parity attributes of the latest 10ms frame are different, the transmission delay from the reference to the terminal TDelay=TDelay_X+10000.

Based on Trev_X, the terminal sends 2*TDelay in advance to compensate for the downlink transmission delay and ensure that the uplink signals of all terminal signals under the satellite reach the base station on the satellite to achieve microsecond-level coarse synchronization.

The above two embodiments can detect the maximum transmission delay of 20ms, and can accurately measure the transmission delay when the total distance between the ground base station and the terminal is less than 6000km.

It can be seen from the above embodiments that the present application can complete the transmission delay measurement from the base station to the terminal without relying on any ephemeris and geographic location information, avoiding the overhead of the air interface and the complex processing of the terminal caused by the location update of the base station; for transparent forwarding processing The base station of the method, the terminal does not need to be processed differently, which simplifies the terminal operation; the accurate terminal uplink delay pre-compensation mechanism can greatly reduce the length of the RACH receiving window, thereby reducing the uplink overhead and shortening the access delay.

Those of ordinary skill in the art can understand that all or part of the steps of implementing the above method embodiments can be completed by program instructions related to hardware, the aforementioned program can be stored in a computer-readable storage medium, and when the program is executed, execute It includes the steps of the above method embodiments; and the aforementioned storage medium includes: ROM, RAM, magnetic disk or optical disk and other media that can store program codes.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that it can still be The technical solutions described in the foregoing embodiments are modified, or some technical features thereof are equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (10)

1. an uplink synchronization method in a satellite communication system, is characterized in that, comprises: The base station and the terminal maintain time synchronization with the same timing system, and map the downlink frame reference time through the same rules; 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 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. 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, specifically comprising: The terminal detects the downlink frame sent by the base station at time T1, records the time when the downlink frame is detected as T2, and calculates the difference between the two as the one-way transmission delay D=T2-T1. 3. The method according to claim 2, wherein, according to the one-way transmission delay, the terminal sends an uplink signal in advance, so that the uplink signal reaches the base station side within an expected reception time window, comprising: The terminal takes the expected reception time T3 as a reference, and sends the uplink signal one transmission delay D in advance, so that the uplink signal reaches the base station side in the expected reception time window whose starting position is earlier than T3 and whose ending position is greater than T3+T_duration; Wherein, the T_duration is the duration of the uplink signal. 4. The method according to claim 3, wherein the expected reception time T3 is issued by the base station side with explicit information or implied information through broadcast information, or by the terminal and the base station according to local time and the same The rules are calculated individually. 5 . The method according to claim 1 , wherein the T1 , T2 and T3 are relative time, absolute time or a certain time slot in a certain frame number. 6 . 6. The method according to claim 1, wherein the base station and the terminal maintain time synchronization with the same timing system, and map the downlink frame reference time through the same rule, comprising: Both the base station and the terminal are synchronized with GNSS or 1588V2 to obtain 1PPS timing; Both the base station and the terminal generate frame boundary timing based on the 1PPS information, and assign frame numbers 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; comprising: The terminal detects the downlink frame, and records the time Trev when the downlink frame is detected; Calculate the difference between this moment and the boundary moment Tbase of the latest downlink frame corresponding to the local reference timing, Td=Trev-Tbase; Calculate 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, Calculate the one-way transmission delay D=Td+N*frame length. 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; comprising: The terminal detects the downlink frame, and records the time Trev when the downlink frame is detected; Calculate the difference between this moment and the boundary moment Tbase of the latest downlink frame corresponding to the local reference timing, Td=Trev-Tbase; Compare 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 delay D=Td; If the parity attributes of the two are different, the one-way transmission delay D=Td+frame length. 9. The method according to claim 7 or 8, wherein 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, comprising: : Using the Trev as a reference, the terminal sends the uplink signal two times in advance of the one-way transmission delay 2*D. 10 . The method according to claim 1 , wherein the base station is an on-board base station or a ground base station or an on-board base station and a ground base station. 11 .

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