A method for time division duplex terrestrial network terminal direct connection satellite

Abstract

The application provides a method for time division duplex ground network terminal direct connection satellite, which comprises the following steps: a satellite base station generates a first uplink / downlink matching scheme according to a standard ground network protocol; the satellite base station generates a second uplink / downlink matching scheme by using a calculation method; the satellite base station broadcasts the first uplink / downlink matching scheme to a ground network terminal according to the standard ground network protocol; the ground network terminal executes the first uplink / downlink matching scheme, and the satellite base station executes the second uplink / downlink matching scheme. The application enables the ground terminal to communicate with the satellite base station normally in a time division duplex mode under the premise of complying with the ground cellular network protocol without modification.

Description

Technical Field

[0001] This invention relates to the field of satellite communication technology, and more specifically, to a method for a time-division duplex terrestrial network terminal to directly connect to a satellite. Background Technology

[0002] The access network portion of a mobile phone direct-connect satellite communication system consists of two types of equipment: base stations (BS) and terminals, also known as user equipment (UE). Base stations are deployed on-board, while terminals operate on the ground. There are two main technical approaches to implementing this access network portion. One is the non-terrestrial network (NTN) standardized by 3GPP, which evolves from the traditional terrestrial network (TN). However, NTN base stations and terminals differ from TN base stations. The other approach involves existing terminals directly connecting to onboard base stations. This requires modifications to the communication protocols of the onboard base stations, while the terminals only need to comply with the TN protocol and do not require modification.

[0003] On a Time Division Duplex (TDD) TN air interface, the base station's transmission and the terminal's reception, as well as the terminal's transmission and the base station's reception, all use the same frequency band. The TN air interface is divided into equal-length time slots in the time domain. Several time slots constitute a frame, and the length of a frame is typically 10 milliseconds. Frame numbers are sequentially incremented from 0 to 1023 and cycle through the network. Within each frame, time slots are numbered sequentially starting from 0. Radio signal transmission directions are divided into downlink and uplink. Downlink is from the base station to the terminal, and uplink is from the terminal to the base station. Each frame contains three types of time slots in the time domain: several downlink time slots, one special time slot, and several uplink time slots. The radio signal direction in the downlink time slot is downlink, and the radio signal direction in the uplink time slot is uplink. The special time slot consists of several downlink symbols, several blank symbols, and several uplink symbols appearing sequentially in the time domain. The base station transmits radio signals on the downlink symbols, and the terminal transmits radio signals on the uplink symbols. During the time occupied by blank symbols, neither the base station nor the terminal transmits anything. The configuration of an intra-frame uplink / downlink mode described above is called the uplink / downlink ratio. Typically, each frame uses the same uplink / downlink ratio scheme. The base station informs the terminal of the uplink / downlink ratio information via a broadcast channel, and the terminal executes according to this ratio information upon receiving it.

[0004] The base station periodically transmits synchronization signals in the downlink time slot. Upon receiving the synchronization signal, the terminal can determine the boundaries and slot number of the downlink time slot. Because there is a certain distance between the base station and the terminal, and radio wave propagation takes time, the downlink time slot boundaries of the terminal and the base station are generally not aligned; the terminal's downlink time slot boundary lags behind the base station's. The terminal needs to adjust the length of the blank symbols in its special time slots in the time domain to ensure that the radio signals emitted by the terminal in its own uplink time slot, after being affected by propagation delay, can fall into the uplink time slot of the base station with the same slot number, maintaining normal communication. Therefore, the duration of blank symbols in the terminal's special time slots is usually shorter than the duration of blank symbols in the base station's special time slots. The difference between these two blank symbol durations is called the Timing Advance (TA). It is typically the round-trip time (RTT) of the radio signal between the base station and the terminal. The greater the distance between the base station and the terminal, the larger the required TA value. In a TN system, the maximum distance between the base station and the terminal that the TA can handle is generally around 100 kilometers. The distance between the satellite and the ground is usually much greater than the distance that the TA can handle. This causes the boundary of the uplink timeslot sent by the terminal to be unable to align with the boundary of the uplink timeslot of the base station, and the two numbers are also inconsistent, so the base station and the terminal cannot communicate normally.

[0005] Meanwhile, in direct satellite connection scenarios, time-division duplex (TDD) ground terminals have significant advantages in direct satellite connections. According to 3GPP standard document TS 38.101-1, the maximum transmit power of a ground terminal operating in frequency division duplex (FDD) mode is limited to 200 mW, while the maximum transmit power of a ground terminal operating in time-division duplex mode is limited to 400 mW. The higher transmit power of the ground terminal in time-division duplex mode can increase the uplink signal strength received by the satellite by up to 3 dB, which is beneficial for successful uplink signal reception by the satellite. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a method for a time-division duplex terrestrial network terminal to directly connect to a satellite, enabling the terrestrial network terminal to communicate normally with the satellite base station in time-division duplex mode without modification, while adhering to the terrestrial cellular network protocol.

[0007] To solve the above problems, the technical solution of the present invention is as follows:

[0008] A method for a time-division duplex terrestrial network terminal to directly connect to a satellite includes the following steps:

[0009] The satellite base station generates the first uplink / downlink configuration scheme according to the standard terrestrial network protocol;

[0010] The satellite base station uses a calculation method to generate a second uplink / downlink ratio scheme;

[0011] According to the standard terrestrial network protocol, the satellite base station will broadcast the first uplink / downlink configuration scheme to the terrestrial network terminal;

[0012] The terrestrial network terminal implements the first uplink / downlink configuration scheme, while the satellite base station implements the second uplink / downlink configuration scheme.

[0013] Preferably, the first uplink / downlink allocation scheme includes M downlink time slots, 1 special time slot, and N uplink time slots; the downlink time slots are numbered sequentially as 0, 1, ..., M-1, the special time slot is numbered as M, and the uplink time slots are numbered sequentially as M+1, M+2, ..., M+N; the number of uplink symbols in the special time slot is 0.

[0014] Preferably, in the second uplink / downlink configuration scheme, a new time slot type, the flexible time slot, is defined; the base station determines the time domain location of the flexible time slot and, during operation, determines whether the transmission direction of the radio signal within the flexible time slot is downlink or uplink.

[0015] Preferably, in the step of generating the second uplink / downlink ratio scheme using a calculation method by the on-board base station, the calculation method is defined as: (n + L × 2 / c / T) slot Divide by The integer quotient is x, and the remainder is y; where n is the input variable, the shortest distance from the satellite base station to the ground coverage cell is L, the speed of light between the satellite and the ground is c, and the time slot duration is T. slot The subcarrier spacing used by the system is f. SCS .

[0016] Preferably, in the step of generating the second uplink / downlink ratio scheme by the on-board base station using the calculation method, the set of integers D=[0, 1, ..., M-1] and the set of integers U=[M+1, M+2, ..., M+N] are defined. The process is to traverse n∈U, use calculation method 1 to calculate x and y corresponding to each n, and generate the second uplink / downlink ratio scheme according to the following rules based on the x and y corresponding to each n.

[0017] If y∈D or y=M, the time slot with time slot number y is marked as a flexible time slot;

[0018] Determining the direction of flexible time slot transmission: If the on-board base station schedules the terminal to perform uplink transmission in time slot with frame number fx and time slot number n, then the on-board base station will use the flexible time slot with frame number f and time slot number y as uplink transmission, and will treat the signal received there as the signal received in time slot with frame number fx and time slot number n for subsequent processing; if the on-board base station uses the flexible time slot with frame number f and time slot number y as downlink transmission, then it will keep its frame number f and time slot number y unchanged, and generate and send downlink signals accordingly.

[0019] If y∈U, then the time slot with time slot number y is marked as an uplink time slot; the base station will treat the signal received in it as the signal received in the time slot with frame number fx and time slot number n for subsequent processing.

[0020] Preferably, the step of the satellite base station broadcasting the first uplink / downlink configuration scheme to the ground network terminal according to the standard terrestrial network protocol specifically includes: the base station filling the first uplink / downlink configuration scheme into the parameter tdd-UL-DL-ConfigurationCommon of the system information block, and all ground terminals can learn about the first uplink / downlink configuration scheme by parsing the system information block.

[0021] Preferably, the steps of the ground network terminal executing the first uplink / downlink configuration scheme and the satellite base station executing the second uplink / downlink configuration scheme specifically include: the ground network terminal determining the reference direction of each time slot and the number of downlink and uplink symbols in a special time slot according to the first uplink / downlink configuration scheme obtained by parsing the system information block, and strictly constraining its own receiving and transmitting behavior according to this direction; the satellite base station directly determining the reference direction of each time slot according to the second uplink / downlink configuration scheme, and strictly constraining its own receiving and transmitting behavior according to this direction.

[0022] Compared with existing technologies, the method of flexible time slot design and location selection for the air interface and determining the transmission direction of flexible time slots during operation of the present invention changes some time slots with fixed transmission directions to time slots with flexible transmission directions. Furthermore, the base station determines the transmission direction of the flexible time slots based on the actual scheduling and transmission of uplink and downlink data during operation. This ensures that the uplink and downlink ratio of the ground network terminal itself is not disrupted by the radio propagation delay introduced by the satellite-to-ground distance. Without modifying the ground network terminal, it enables existing ground network terminals to communicate with the satellite base station in TDD mode, solving the problems of existing technologies and making full use of the terminal's transmission capability to improve the reliability of uplink signal transmission. Attached Figure Description

[0023] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0024] Figure 1 This is a flowchart of the method for direct connection of a time-division duplex terrestrial network terminal to a satellite according to the present invention;

[0025] Figure 2 This is a diagram illustrating the overall architecture of a terrestrial network terminal directly connected to a satellite, as shown in a specific embodiment.

[0026] Figure 3 This is a correct air interface timing diagram for a TN protocol TDD base station deployed on the ground according to a specific embodiment.

[0027] Figure 4 This is an error air interface timing diagram for a specific embodiment of a TN protocol TDD base station deployed on a satellite with TA=0.

[0028] Figure 5 In a specific embodiment, a TN protocol TDD base station is deployed on a satellite and TA=TA. max Error timing diagram of the air interface;

[0029] Figure 6 This is a correct air interface timing diagram for a TDD base station deployed on a satellite with TA=0, as shown in a specific embodiment.

[0030] Figure 7 This is a correct air interface timing diagram for a TDD-based base station deployed on a satellite and simultaneously serving terminals in different locations, as shown in a specific embodiment. Detailed Implementation

[0031] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0032] Specifically, the present invention provides a method for a time-division duplex terrestrial network terminal to directly connect to a satellite, such as... Figure 1 As shown, the method includes the following steps:

[0033] S1: The satellite base station generates the first uplink / downlink configuration scheme according to the standard terrestrial network protocol;

[0034] Specifically, the first uplink / downlink allocation scheme includes M downlink slots, 1 special slot, and N uplink slots; the downlink slots are numbered sequentially as 0, 1, ..., M-1, the special slot is numbered as M, and the uplink slots are numbered sequentially as M+1, M+2, ..., M+N; the number of uplink symbols in the special slot is 0.

[0035] S2: The satellite base station uses a calculation method to generate a second uplink / downlink ratio scheme;

[0036] Specifically, the calculation method is defined as (n + L × 2 / c / T) slot Divide by The integer quotient is x, and the remainder is y. Here, n is the input variable, L is the shortest distance from the satellite base station to the ground coverage cell, c is the speed of light between the satellite and the ground, and T is the time slot duration. slot The subcarrier spacing used by the system is f. SCS (Unit: kHz)

[0037] Define an integer set D = [0, 1, ..., M-1] and an integer set U = [M+1, M+2, ..., M+N]. Iterate through n ∈ U and calculate the x and y corresponding to each n using the aforementioned calculation method. Based on the x and y corresponding to each n, generate a second uplink / downlink allocation scheme according to the following rules.

[0038] If y∈D or y=M, the time slot with time slot number y is marked as a flexible time slot.

[0039] Determining the direction of flexible time slot transmission: If the on-board base station schedules the terminal to perform uplink transmission in the time slot with frame number fx and time slot number n, then the on-board base station will use the flexible time slot with frame number f and time slot number y as uplink transmission, and will treat the signal received there as the signal received in the time slot with frame number fx and time slot number n for subsequent processing; if the on-board base station uses the flexible time slot with frame number f and time slot number y as downlink transmission, then it will keep its frame number f and time slot number y unchanged, and generate and send downlink signals accordingly.

[0040] If y∈U, then the time slot with time slot number y is marked as an uplink time slot; the base station will treat the signal received in it as the signal received in the time slot with frame number fx and time slot number n for subsequent processing.

[0041] In the second uplink / downlink configuration scheme, a new time slot type, the flexible time slot, is defined. The base station determines the time domain location of the flexible time slot and, during operation, determines whether the transmission direction of the radio signal within the flexible time slot is downlink or uplink.

[0042] S3: According to the standard terrestrial network protocol, the satellite base station will broadcast the first uplink / downlink configuration scheme to the terrestrial network terminal;

[0043] Specifically, the base station fills the first uplink / downlink configuration scheme into the parameter tdd-UL-DL-ConfigurationCommon of the system information block, and all ground terminals can learn about the first uplink / downlink configuration scheme by parsing the system information block.

[0044] S4: The terrestrial network terminal implements the first uplink / downlink configuration scheme, and the satellite base station implements the second uplink / downlink configuration scheme.

[0045] Specifically, the terrestrial network terminal determines the reference direction (downlink / uplink / special) for each time slot, as well as the number of downlink and uplink symbols in the special time slot, based on the first uplink / downlink configuration scheme obtained from the parsing system information block, and strictly constrains its receiving and transmitting behavior according to this direction. The on-board base station directly determines the reference direction (downlink / uplink / flexible) for each time slot based on the second uplink / downlink configuration scheme, and strictly constrains its receiving and transmitting behavior according to this direction.

[0046] In addition, since ground terminals may be located anywhere within the coverage area, the distance between the satellite and the terminal may be greater than the shortest distance from the satellite base station to the ground coverage cell. While applying the above mechanism, the base station can still enable the original timing advance mechanism in the ground network system, that is, measure the uplink signal time deviation and issue a timing advance adjustment command to compensate for the timing deviation caused by the distance between the satellite base station and the terminal being greater than the shortest distance from the satellite base station to the ground coverage cell.

[0047] The following specific embodiment illustrates the method of direct satellite connection between a time-division duplex terrestrial network terminal and the present invention.

[0048] like Figure 2 As shown, assuming the satellite carrying the onboard base station has an orbital altitude of 600 kilometers, and the ground network terminal is located at the sub-satellite point (i.e., the distance between the satellite and the ground network terminal is also 600 kilometers), then 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.

[0049] Assuming the air interface uses TDD mode, both the base station and the terminal use the same frequency for transmission and reception. Each millisecond is a time slot, and 10 time slots make up a frame. Within a frame, the time slot numbers increase from 0 to 9 over time. The uplink-to-downlink ratio is 7:1:2, meaning 7 downlink time slots, 1 special time slot, and 2 uplink time slots. Figure 3 This is a schematic diagram of the air interface timing when both the base station and the terminal are deployed on the ground. Figure 3The bottom timeline represents absolute time. The rectangles in the base station row represent a time slot on the base station side, with numbers above the slot indicating its number. Similarly, the rectangles in the terminal row represent a time slot on the terminal side, with numbers below the slot indicating its number. Letters within the time slot indicate its type: D for downlink, U for uplink, and S for special time slots. Due to the radio wave propagation delay caused by the distance between the base station and the terminal, the terminal's downlink time slot lags behind the base station's downlink time slot in absolute time. The terminal needs to shorten its special time slot length according to the base station's TA (Transmission Time) command to ensure that its uplink signal falls within the corresponding uplink time slot of the base station. The shortened length of the terminal's special time slot equals the TA value, which is equivalent to the RTT (Round-Trip Time) between the base station and the terminal. The maximum TA compensation capability is TA0. max , and TA max It is less than the original length of the special time slot. Therefore, it only applies when the RTT is less than the original length of the special time slot. <TA max Only then can base stations and terminals function properly in TDD mode.

[0050] Because the minimum RTT between satellite and ground exceeds the original length of the special time slot, which exceeds the compensation capability of the TA mechanism, ground base stations cannot work normally in TDD mode together with ground terminals when they are directly deployed on satellite.

[0051] Figure 4 This paper presents the air interface timing disorder caused by satellite-to-ground propagation delay when a ground base station is directly deployed on the satellite and TA=0. Time slots 8 and 9 of the terminal are uplink time slots, but the uplink signals emitted by the terminal will fall into time slots 2 and 3 of the next frame from the base station, respectively. This timing disorder on the base station side causes the TDD mode to malfunction.

[0052] Figure 5 The following conditions are given when the ground base station is directly deployed on the satellite, and TA=TA. max Even when the TA mechanism compensates for RTT at its maximum capacity, air interface timing can still be disrupted due to satellite-to-ground propagation delay. Time slots 8 and 9 of the terminal are uplink time slots, but the uplink signal sent by the terminal will fall between time slots 1 and 3 of the next frame from the base station. This timing disruption on the base station side causes TDD mode to malfunction.

[0053] After using the method of the present invention, the correct air interface timing can be maintained between the satellite base station and the ground terminal. Figure 6An example of air interface timing is given when a terminal is located on the shortest path from a satellite base station to a ground cell, i.e., TA=0. Time slots 2 and 3 of the base station are selected as flexible time slots. During operation, the base station can select these two flexible time slots as downlink directions, i.e., transmit downlink signals normally in time slots 2 and 3. The terminal can receive these downlink signals in its own time slots 2 and 3, as shown in time slots 2 and 3 of frame n. If the base station schedules the terminal to transmit uplink in time slots 8 and 9 in frame n via downlink control information, the base station needs to select time slots 2 and 3 of its own frame n+1 as uplink directions and process the signal received in time slot 2 of frame n+1 as the signal received in time slot 8 of frame n. Similarly, the signal received in time slot 3 of frame n+1 is processed as the signal received in time slot 9 of frame n.

[0054] Figure 7 An example of air interface timing for ground terminals located at different positions within a ground cell to operate normally simultaneously under the method of this invention is provided. A near terminal represents a terminal located on the shortest path from the satellite base station to the ground cell, and a far terminal represents a terminal located on the longest path from the satellite base station to the ground cell. The base station uses the original TA mechanism of the TN protocol, configuring TA=0 for the near terminal and TA=TA for the far terminal. max This ensures that terminals located in different locations can maintain the correct air interface timing.

[0055] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method for a time-division duplex terrestrial network terminal to directly connect to a satellite, characterized in that, The method includes the following steps: The satellite base station generates the first uplink / downlink configuration scheme according to the standard terrestrial network protocol; The on-board base station uses a calculation method to generate a second uplink / downlink ratio scheme, defined as: (n + L × 2 / c / T) slot Divide by The integer quotient is x, and the remainder is y; where n is the input variable, the shortest distance from the satellite base station to the ground coverage cell is L, the speed of light between the satellite and the ground is c, and the time slot duration is T. slot The subcarrier spacing used by the system is f. SCS ; Define an integer set D = [0, 1, ..., M-1] and an integer set U = [M+1, M+2, ..., M+N]. Iterate through n ∈ U, calculate x and y corresponding to each n using the calculation method described above, and generate a second uplink / downlink allocation scheme based on x and y corresponding to each n according to the following rules. If y∈D or y=M, the time slot with time slot number y is marked as a flexible time slot; the transmission direction of the flexible time slot is determined: if the on-board base station schedules the terminal to perform uplink transmission in the time slot with frame number fx and time slot number n, then the on-board base station uses the flexible time slot with frame number f and time slot number y as uplink transmission, and treats the signal received there as the signal received in the time slot with frame number fx and time slot number n for subsequent processing; if the on-board base station uses the flexible time slot with frame number f and time slot number y as downlink transmission, then its frame number f and time slot number y remain unchanged, and a downlink signal is generated and sent accordingly; If y∈U, then the time slot with time slot number y is marked as an uplink time slot; the base station will treat the signal received in it as the signal received in the time slot with frame number fx and time slot number n for subsequent processing; According to the standard terrestrial network protocol, the satellite base station will broadcast the first uplink / downlink configuration scheme to the terrestrial network terminal; The terrestrial network terminal implements the first uplink / downlink ratio scheme, while the satellite base station implements the second uplink / downlink ratio scheme.

2. The method for direct satellite connection of a time-division duplex terrestrial network terminal according to claim 1, characterized in that, The first uplink / downlink allocation scheme includes M downlink time slots, 1 special time slot, and N uplink time slots; the downlink time slots are numbered sequentially as 0, 1, ..., M-1, the special time slot is numbered as M, and the uplink time slots are numbered sequentially as M+1, M+2, ..., M+N; the number of uplink symbols in the special time slot is 0.

3. The method for direct satellite connection of a time-division duplex terrestrial network terminal according to claim 1, characterized in that, In the second uplink / downlink configuration scheme, a new time slot type, the flexible time slot, is defined. The base station determines the time domain location of the flexible time slot and, during operation, determines whether the transmission direction of the radio signal within the flexible time slot is downlink or uplink.

4. The method for direct satellite connection of a time-division duplex terrestrial network terminal according to claim 1, characterized in that, The step of broadcasting the first uplink / downlink configuration scheme to the ground network terminal according to the standard terrestrial network protocol specifically includes: the base station filling the first uplink / downlink configuration scheme into the parameter tdd-UL-DL-ConfigurationCommon of the system information block, and all ground terminals can learn about the first uplink / downlink configuration scheme by parsing the system information block.

5. The method for direct satellite connection of a time-division duplex terrestrial network terminal according to claim 1, characterized in that, The steps of the ground network terminal executing the first uplink / downlink configuration scheme and the satellite base station executing the second uplink / downlink configuration scheme specifically include: the ground network terminal determining the reference direction of each time slot and the number of downlink and uplink symbols in a special time slot according to the first uplink / downlink configuration scheme obtained by parsing the system information block, and strictly constraining its own receiving and transmitting behavior according to this direction; the satellite base station directly determining the reference direction of each time slot according to the second uplink / downlink configuration scheme, and strictly constraining its own receiving and transmitting behavior according to this direction.

Images