Direct communication method between ground network terminal and satellite base station and satellite base station

Abstract

The present invention discloses a direct communication method between a ground network terminal and a satellite base station and a satellite base station. The direct communication method includes: determining the advance time Δt of the base station's downlink transmission time slot; adjusting the time of the satellite base station's downlink transmission time slot according to the advance time of the base station's downlink transmission time slot, advancing the time when the satellite base station starts sending the downlink transmission time slot numbered n to the time when the satellite base station starts receiving the uplink reception time slot numbered n, with an advance time of Δt; and advancing the time when the satellite base station generates the data to be sent in the downlink transmission time slot numbered n to the time when the satellite base station starts receiving the uplink reception time slot numbered n, with an advance time of not less than Δt. The direct communication method and satellite base station of the present invention align the beginning and end of the signal received by the satellite base station with the boundary of the uplink reception time slot, thereby ensuring normal communication between the satellite base station and the ground network terminal.

Description

Technical Field

[0001] The present invention relates to a ground terminal and satellite communication technology, and in particular to a ground network terminal and satellite base station direct communication method and a satellite base station. Background Art

[0002] At present, with the advancement of technology, the mobile phone direct connection satellite communication system has shown great practical potential. Specifically, the access network part of the mobile phone direct connection satellite communication system consists of two types of equipment: base stations and terminals. The base stations are deployed on the satellite and the terminals work on the ground. There are two main technical routes for the implementation of this access network part. One is the non-terrestrial network (NTN) standardized by 3GPP. It is based on the evolution of the traditional terrestrial network (TN), but the NTN base station is different from the TN base station, and the NTN terminal is also different from the TN terminal. The other technical route is for the existing terminal to directly connect to the base station on the satellite. The communication protocol of the TN base station needs to be modified and placed on the satellite as a satellite base station, while the terminal only needs to comply with the TN protocol and does not need to be modified.

[0003] On the frequency division duplexing (FDD) TN air interface, base stations transmit and terminals receive using one frequency band as the downlink channel; terminals transmit and base stations receive using another frequency band as the uplink channel. The TN air interface is divided into equal-length time slots in the time domain. Several slots form a frame, and the slots within each frame are numbered incrementally, starting at 0. On the FDD air interface, the downlink transmit time slot boundaries on the base station side are aligned with the uplink receive time slot boundaries, and the downlink transmit time slot numbers are also consistent with the uplink receive time slot numbers. For example, the time period during which the base station transmits time slot 0 on the downlink channel is also the time period during which it receives time slot 0 on the uplink channel.

[0004] The base station periodically transmits a synchronization signal on the downlink channel. After receiving the synchronization signal, the terminal can learn its own downlink receive slot boundary and downlink receive slot number. There is a certain distance between the base station and the terminal, and it takes a certain amount of time for radio waves to propagate over this distance. Therefore, the boundary of the terminal's downlink receive slot numbered n is generally not aligned with the boundary of the base station's downlink transmit slot numbered n. The boundary of the terminal's downlink receive slot numbered n will lag behind the boundary of the base station's downlink transmit slot numbered n. The boundary of the terminal's uplink transmit slot numbered n is usually ahead of the boundary of the terminal's downlink receive slot numbered n. This timing advance (TA) is generally the radio propagation time of the round-trip distance between the base station and the terminal. This ensures that the signal sent by the terminal in its own uplink transmit slot numbered n falls within the base station's uplink receive slot numbered n when it arrives at the base station, and the signal is aligned with the base station's uplink receive slot boundary, ensuring normal communication. The greater the distance between the base station and the terminal, the larger the TA value needs to be.

[0005] Placing TN base stations directly on satellites presents a problem: the maximum distance between base stations and terminals that can be handled by the TA method in TN systems is generally around 100 kilometers. The distance between satellite and ground is often much greater than the distance handled by the TA method. As a result, the signal emitted by a terminal in its own uplink transmit timeslot n, after long-distance propagation, cannot land in the base station's uplink receive timeslot n. Furthermore, the beginning and end of the signal do not align with the boundaries of the base station's uplink receive timeslot, preventing normal communication between the base station and the terminal. Therefore, the communication protocol of the TN base station must be modified to enable it to communicate properly with TN terminals onboard the satellite. Summary of the Invention

[0006] The object of the present invention is to provide a direct communication method between a ground network terminal and a satellite base station and a satellite base station, wherein the direct communication method and the satellite base station align the beginning and end of a signal received by the satellite base station with the boundary of an uplink receiving time slot, thereby ensuring normal communication between the satellite base station and the ground network terminal.

[0007] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0008] A direct communication method between a ground network terminal and a satellite base station, the direct communication method comprising:

[0009] Determine the advance time Δt of the downlink transmission time slot of the base station;

[0010] The starting time of the downlink transmission time slot of the satellite base station is adjusted according to the advance time of the downlink transmission time slot of the base station, and the starting time of the downlink transmission time slot numbered n of the satellite base station is advanced before the starting time of the uplink reception time slot numbered n of the satellite base station, and the advance time length is Δt, so that the downlink transmission time slot of the satellite base station is advanced in the time domain before the uplink reception time slot with the same number.

[0011] Furthermore, the direct communication method further includes:

[0012] The moment when the satellite base station generates the data to be sent in the downlink sending time slot is adjusted according to the advance length of the downlink sending time slot of the base station, and the moment when the satellite base station generates the data to be sent in the downlink sending time slot numbered n is advanced to the starting moment of the uplink receiving time slot numbered n of the satellite base station, and the advance length is not less than Δt.

[0013] Furthermore, the direct communication method further includes:

[0014] The ground terminal follows the standard TN communication protocol, regards the satellite base station as a standard TN base station, and performs uplink and downlink synchronization and communication with it. The ground network terminal receives the synchronization signal from the satellite base station, and determines its own downlink receiving time slot number and downlink receiving time slot boundary based on the synchronization signal, and follows the standard TN protocol to exchange signaling and data with the satellite base station.

[0015] Furthermore, the base station downlink transmission time slot transmission advance time length Δt, which is calculated by the formula:

[0016] Δt=H / c×2

[0017] Where Δt represents the advance time of the base station's downlink transmission time slot, H represents the shortest straight-line distance from the satellite to the coverage area on the Earth's surface generated by the radio signal transmitted by the satellite, and c represents the speed of light in a vacuum.

[0018] A satellite base station, wherein the satellite base station is provided with a downlink transmission time slot advance module;

[0019] The downlink transmission time slot advance module is used to adjust the starting time of the downlink transmission time slot of the satellite base station according to the predetermined base station downlink transmission time slot transmission advance time length, and advance the starting time of the downlink transmission time slot numbered n of the satellite base station to the starting time of the uplink reception time slot numbered n of the satellite base station, with an advance time length of Δt, so that the downlink transmission time slot of the satellite base station is advanced in the time domain to the uplink reception time slot with the same number.

[0020] Furthermore, the satellite base station is further provided with a downlink transmission time slot data advance generation module;

[0021] The downlink transmission time slot data advance generation module is used to adjust the moment when the satellite base station completes generating the data to be sent in the downlink transmission time slot according to a predetermined advance time of the base station downlink transmission time slot, and advance the moment when the satellite base station completes generating the data to be sent in the downlink transmission time slot numbered n to the starting moment of the uplink reception time slot numbered n of the satellite base station, and the advance time is not less than Δt.

[0022] Furthermore, the base station downlink transmission time slot transmission advance time length Δt, which is calculated by the formula:

[0023] Δt=H / c×2

[0024] Where Δt represents the advance time of the base station's downlink transmission time slot, H represents the shortest straight-line distance from the satellite to the coverage area on the Earth's surface generated by the radio signal transmitted by the satellite, and c represents the speed of light in a vacuum.

[0025] Compared with the prior art, the direct communication method and satellite base station of the present invention have the following beneficial effects: the starting time of the downlink transmission time slot of the satellite base station is advanced before the starting time of the uplink reception time slot with the same number of the satellite base station, so that the downlink transmission time slot of the satellite base station is advanced in the time domain before the uplink reception time slot with the same number, so that the signal sent by the ground network terminal in its own uplink transmission time slot numbered n can fall into the uplink reception time slot numbered n of the satellite base station after being transmitted through the satellite-to-ground distance, and the beginning and end of the signal received by the satellite base station are aligned with the boundary of the uplink reception time slot, thereby ensuring normal communication between the satellite base station and the ground network terminal. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of communication between a satellite and a ground terminal in a specific embodiment of the method for direct communication between a ground network terminal and a satellite base station according to the present invention;

[0027] Figure 2 This is a schematic diagram of air interface timing errors caused by satellite-to-ground distance in the prior art;

[0028] Figure 3 The figure is a schematic diagram of the air interface timing of the direct connection communication method and satellite base station of the present invention. DETAILED DESCRIPTION

[0029] The present invention will be further described below with specific embodiments:

[0030] This embodiment provides a method for direct communication between a ground network terminal and a satellite base station. This direct communication method addresses the issue of the ground-to-satellite distance being significantly greater than the base station-to-terminal distance supported by the ground network terminal. This method ensures that the signal transmitted by the ground network terminal during its own uplink transmit time slot, numbered n, falls within the uplink receive time slot, numbered n, of the satellite base station, and that the beginning and end of the signal received by the satellite base station are aligned with the boundary of the satellite base station's uplink receive time slot, numbered n. This direct communication method of this embodiment enables effective communication between the ground network terminal and the satellite base station without modifying the ground network terminal, overcoming the challenges posed by satellite-to-ground propagation delay.

[0031] It should be noted that the direct communication method of this embodiment is implemented when a TN base station is placed on a satellite as a satellite base station. Due to the extremely long distance between the satellite and the ground-based TN terminal, the uplink signal emitted by the TN terminal cannot correctly fall into the corresponding uplink receive time slot of the satellite base station. It should be noted that the uplink signal is emitted by a ground-based network terminal, such as a mobile phone, tablet, laptop, etc.

[0032] The direct communication method of this embodiment includes the following steps S1 to S4:

[0033] S1, calculate a time amount according to the formula, which is called "base station downlink transmission time slot transmission advance length" and is represented by Δt;

[0034] Specifically,

[0035] The calculation formula for the advance time of the base station downlink transmission time slot is:

[0036] Δt=H / c×2

[0037] Where Δt represents the advance time of the base station's downlink transmission time slot, H represents the shortest straight-line distance from the satellite to the coverage area on the Earth's surface generated by the radio signal transmitted by the satellite, and c represents the speed of light in a vacuum.

[0038] S2, adjusting the start time of the downlink transmission time slot of the satellite base station according to the advance time length Δt of the downlink transmission time slot of the base station determined in step S1.

[0039] Specifically,

[0040] The starting time of the downlink transmission time slot numbered n of the satellite base station is advanced before the starting time of the uplink reception time slot numbered n of the satellite base station. The specific advance time length is the base station downlink transmission time slot transmission advance time length Δt determined in the previous step S1. In this way, the downlink transmission time slot of the satellite base station is advanced in the time domain before the uplink reception time slot with the same number.

[0041] S3, adjusting the time when the satellite base station completes generating the data to be sent in the downlink transmission time slot according to the base station downlink transmission time slot transmission advance time length Δt determined in step S1.

[0042] Specifically,

[0043] The time when the satellite base station generates the data to be sent in the downlink transmission time slot numbered n is advanced to the start time of the uplink reception time slot numbered n of the satellite base station, and the specific advance time length is not less than the base station downlink transmission time slot transmission advance time length Δt determined in the previous step S1.

[0044] It should be noted that, except for the above steps S1, S2, and S3, the satellite base station does not make any other modifications and still follows the communication protocol of the TN base station; in particular, the way the satellite base station generates and sends downlink synchronization signals, and the signaling and data interaction process between the satellite base station and the ground terminal are the same as those of the TN base station.

[0045] In step S4, the ground terminal follows the standard TN communication protocol, treating the satellite base station as a standard TN base station and performing uplink and downlink synchronization and communication with it without any modification. Specifically, the ground network terminal receives the synchronization signal from the satellite base station, determines its own downlink receive timeslot number and downlink receive timeslot boundary based on the synchronization signal, and then exchanges signaling and data with the satellite base station according to the standard TN protocol.

[0046] In the direct communication method of this embodiment, since the downlink transmission time slot of the satellite base station is advanced, the satellite base station can receive uplink data from the ground network terminal in the correct uplink reception time slot.

[0047] When adopting the direct communication method of this embodiment, the original Timing Advance (TA) mechanism can still be retained to compensate for the deviation caused by the distance between the satellite and the terminal not being completely equal to the shortest straight-line distance from the coverage area generated by the radio signal transmitted by the satellite on the surface of the earth to the satellite, thereby ensuring normal communication.

[0048] In order to implement the above-mentioned direct communication method, this embodiment further provides a satellite base station, in which a downlink transmission time slot advance module and a downlink transmission time slot data advance generation module are provided.

[0049] The downlink transmission time slot advance module is used to implement the function of step S2 of the above-mentioned direct communication method, namely:

[0050] The start time of the downlink transmission time slot of the satellite base station is adjusted according to the determined advance time length Δt of the downlink transmission time slot of the base station.

[0051] Specifically,

[0052] The starting time of the downlink transmission time slot numbered n of the satellite base station is advanced before the starting time of the uplink reception time slot numbered n of the satellite base station. The specific advance time length is the base station downlink transmission time slot transmission advance time length Δt determined in the previous step S1, so that the downlink transmission time slot of the satellite base station is advanced in the time domain before the uplink reception time slot with the same number.

[0053] The downlink transmission time slot data advance generation module is used to implement the function of step S3 of the above-mentioned direct communication method, namely:

[0054] The time when the satellite base station completes generating the data to be sent in the downlink sending time slot is adjusted according to the determined advance time length Δt of the downlink sending time slot of the base station.

[0055] Specifically,

[0056] The moment when the satellite base station generates the data to be sent in the downlink transmission time slot numbered n is advanced to the starting moment of the uplink reception time slot numbered n of the satellite base station, and the specific advance time length is not less than the base station downlink transmission time slot send advance time length Δt determined in the previous step S1.

[0057] It should be noted that:

[0058] The downlink timeslot mentioned in this article refers to the time domain in which the downlink channel is divided into time periods of equal length. The end time of the previous time period is the start time of the next time period. Any time period is called a downlink timeslot.

[0059] The uplink timeslots mentioned in this document refer to the time domain division of the uplink channel into equal-length time segments. The end time of the previous time segment is the start time of the next time segment. Any of these time segments is called an uplink timeslot. The duration of an uplink timeslot is equal to the duration of a downlink timeslot.

[0060] The base station transmit time slots mentioned in this document refer to downlink time slots as understood by the base station. That is, the base station divides the downlink channel into downlink time slots in the time domain based on its local time. Each downlink time slot is a base station transmit time slot. The base station starts sending signals to the terminal at the start time of the base station transmit time slot and stops sending signals to the terminal at the end time of the base station transmit time slot.

[0061] The base station receive timeslots mentioned in this document refer to uplink timeslots as understood by the base station. That is, the base station divides the uplink channel into uplink timeslots in the time domain based on its local time. Each uplink timeslot is a base station receive timeslot. The base station begins receiving signals from the terminal at the start time of the base station receive timeslot and stops receiving signals from the terminal at the end time of the base station receive timeslot.

[0062] The terminal transmit timeslots mentioned in this document refer to uplink timeslots as understood by the terminal. That is, the terminal divides the uplink channel into uplink timeslots in the time domain based on its local time. Each uplink timeslot is a terminal transmit timeslot. The terminal begins transmitting signals to the base station at the start of the transmit timeslot and stops transmitting signals to the base station at the end of the transmit timeslot. The boundaries of the terminal transmit timeslots do not necessarily align with the boundaries of the base station receive timeslots.

[0063] The term "terminal receive slot" in this document refers to the downlink slot as understood by the terminal. This means that the terminal divides the downlink channel into downlink slots in the time domain based on its local time. Each downlink slot is a terminal receive slot. The terminal begins receiving signals from the base station at the start of the receive slot and stops receiving signals at the end of the receive slot. The boundaries of the terminal receive slot do not necessarily align with the boundaries of the base station transmit slot.

[0064] The direct communication method and satellite base station provided in this embodiment have the following important innovations:

[0065] The starting time of the downlink transmission time slot of the satellite base station is advanced before the starting time of the uplink reception time slot with the same number of the satellite base station, so that the downlink transmission time slot of the satellite base station is advanced before the uplink reception time slot with the same number in the time domain, so that the signal sent by the ground network terminal in its own uplink transmission time slot numbered n can fall into the uplink reception time slot numbered n of the satellite base station after being transmitted through the satellite-to-ground distance, and the beginning and end of the signal received by the satellite base station are aligned with the boundary of the uplink reception time slot, thereby ensuring normal communication between the satellite base station and the ground network terminal.

[0066] The following provides a specific example to further illustrate the direct communication method of this embodiment:

[0067] See also Figure 1 Assume that the satellite carrying the satellite base station orbits at an altitude of 600 kilometers. The center of the coverage area on the Earth's surface produced by the satellite's radio signal is located at the satellite's sub-satellite point. This means that the shortest straight-line distance from the coverage area to the satellite is 600 kilometers. The NT ground network terminal is located at the sub-satellite point, meaning that the distance between the satellite and the ground network terminal is also 600 kilometers. The one-way radio propagation delay from the satellite to the ground is approximately 2 milliseconds. Similarly, the one-way radio propagation delay from the ground to the satellite is also approximately 2 milliseconds.

[0068] Assume that the air interface is FDD mode, the base station sends and the ground network terminal receives using the downlink frequency f DL , the ground network terminal sends and the base station receives using the uplink frequency f ULEach millisecond is a slot, 10 slots form a frame, and the slot numbers in each frame increase from 0 to 9 over time.

[0069] See also Figure 2 The figure shows the air interface timing disorder caused by satellite-to-ground propagation time when a ground base station is deployed directly on a satellite. The bottom time axis in the figure represents absolute time. The "Base Station Transmit Downlink" row shows the number of each base station downlink slot and the position of its start and end boundaries on the absolute time axis. Similarly, the "Base Station Receive Uplink" row shows the number of each base station uplink slot and the position of its start and end boundaries on the absolute time axis. The "Terminal Receive Downlink" row shows the number of each ground network terminal downlink slot and the position of its start and end boundaries on the absolute time axis. Similarly, the "Terminal Receive Uplink" row shows the number of each ground network terminal uplink slot and the position of its start and end boundaries on the absolute time axis. The base station sends a synchronization signal in its downlink slot 0, starting at absolute time 0 milliseconds and ending at absolute time 1 millisecond. After 2 milliseconds of propagation, the ground network terminal begins receiving the synchronization signal at an absolute time of 2 milliseconds and completes reception of the synchronization signal at an absolute time of 3 milliseconds. It then identifies the period between 2 and 3 milliseconds as its own slot 0, and the subsequent slot numbers for the ground network terminal follow accordingly. The ground network terminal then transmits uplink data in its own uplink slot 4, starting at an absolute time of 6 milliseconds and ending at an absolute time of 7 milliseconds. After 2 milliseconds of propagation, this uplink data can be received by the base station between an absolute time of 8 and an absolute time of 9 milliseconds. However, this time period is occupied by slot 8, the base station's uplink reception, and not slot 4. Therefore, a timing error occurs, preventing normal communication.

[0070] See also Figure 3 , the figure shows the correct air interface timing between the satellite base station and the ground network terminal after applying the direct communication method of this embodiment.

[0071] Based on the formula Δt = the shortest straight-line distance from the satellite to the Earth's coverage area of ​​the satellite's radio signal / the speed of light in a vacuum × 2, Δt = 4 milliseconds. This means that the base station must begin transmitting downlink slot n 4 milliseconds before it begins receiving uplink slot n. Where n is the slot number, which can be 0, 1, ..., 9. The base station must complete generating data to be transmitted in downlink slot n at least 4 milliseconds before it begins receiving uplink slot n. The base station sends a synchronization signal in its downlink slot 0, starting at absolute time -4 milliseconds and ending at absolute time -3 milliseconds. After 2 milliseconds of propagation, the ground network terminal begins receiving the synchronization signal at absolute time -2 milliseconds and completes reception at absolute time -1 millisecond. The ground network terminal then identifies the period between absolute time -2 milliseconds and -1 millisecond as its own slot 0. Subsequent slot numbers for the ground network terminal follow this pattern. The ground network terminal sends uplink data in its own uplink slot 4, starting at absolute time 2 milliseconds and ending at absolute time 3 milliseconds. After a propagation time of 2 milliseconds, this uplink data is received by the base station between absolute time 4 and absolute time 5 milliseconds. This time period is still occupied by slot 4 for uplink reception by the base station, allowing communication to proceed normally.

[0072] The above are only preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for direct communication between a ground network terminal and a satellite base station, characterized by: The direct communication method includes: Determine the advance time Δt of the downlink transmission time slot of the base station; Adjusting the start time of the downlink transmission time slot of the satellite base station according to the advance time of the downlink transmission time slot of the base station, advancing the start time of the downlink transmission time slot numbered n of the satellite base station before the start time of the uplink reception time slot numbered n of the satellite base station by an advance time length of Δt, so that the downlink transmission time slot of the satellite base station is ahead of the uplink reception time slot with the same number in the time domain; The base station downlink transmission time slot transmission advance time length Δt, which is calculated by the formula: Δt=H / c×2 Where Δt represents the advance time of the base station's downlink transmission time slot, H represents the shortest straight-line distance from the satellite to the coverage area on the Earth's surface generated by the radio signal transmitted by the satellite, and c represents the speed of light in a vacuum. The direct communication method further includes: The ground network terminal follows the standard TN communication protocol, regards the satellite base station as a standard TN base station, and performs uplink and downlink synchronization and communication with it. The ground network terminal receives the synchronization signal from the satellite base station, and determines its own downlink receiving time slot number and downlink receiving time slot boundary based on the synchronization signal, and follows the standard TN protocol to exchange signaling and data with the satellite base station.

2. The method for direct communication between a ground network terminal and a satellite base station according to claim 1, characterized in that: The direct communication method further includes: The moment when the satellite base station generates the data to be sent in the downlink sending time slot is adjusted according to the advance length of the downlink sending time slot of the base station, and the moment when the satellite base station generates the data to be sent in the downlink sending time slot numbered n is advanced to the starting moment of the uplink receiving time slot numbered n of the satellite base station, and the advance length is not less than Δt.

3. A satellite base station, characterized in that: The satellite base station is provided with a downlink transmission time slot advance module; The downlink transmission time slot advance module is used to adjust the start time of the downlink transmission time slot of the satellite base station according to the predetermined base station downlink transmission time slot advance time length, and advance the start time of the downlink transmission time slot numbered n of the satellite base station to the start time of the uplink reception time slot numbered n of the satellite base station by an advance time length of Δt, so that the downlink transmission time slot of the satellite base station is ahead of the uplink reception time slot with the same number in the time domain; The base station downlink transmission time slot transmission advance time length Δt, which is calculated by the formula: Δt=H / c×2 Where Δt represents the advance time of the base station's downlink transmission time slot, H represents the shortest straight-line distance from the satellite to the coverage area on the Earth's surface generated by the radio signal transmitted by the satellite, and c represents the speed of light in a vacuum. The ground network terminal communicating with the satellite base station follows the standard TN communication protocol, regards the satellite base station as a standard TN base station, and performs uplink and downlink synchronization and communication with it. The ground network terminal receives the synchronization signal from the satellite base station, and determines its own downlink receiving time slot number and downlink receiving time slot boundary based on the synchronization signal, and follows the standard TN protocol to exchange signaling and data with the satellite base station.

4. The satellite base station according to claim 3, characterized in that: The satellite base station is also provided with a downlink transmission time slot data advance generation module; The downlink transmission time slot data advance generation module is used to adjust the moment when the satellite base station completes generating the data to be sent in the downlink transmission time slot according to a predetermined advance time of the base station downlink transmission time slot, and advance the moment when the satellite base station completes generating the data to be sent in the downlink transmission time slot numbered n to the starting moment of the uplink reception time slot numbered n of the satellite base station, and the advance time is not less than Δt.

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