Time synchronization method for direct satellite connection of existing 4G FDD terminals

Abstract

This invention discloses a time synchronization method for direct satellite connection of existing 4G FDD terminals. First, the base station delays the start of the preamble sequence detection window and expands the window size. Within the expanded window, the base station receives the preamble sequence and detects the delay by decoding it. After determining the delay, the base station divides the delay into integer parts τ in milliseconds. i and the decimal part τ f Based on whether the fractional delay is greater than 0.66ms, terminals are divided into two types. The uplink frame structure of the base station is then modified accordingly. The base station then determines the uplink subframe scheduling strategy based on the uplink frame structure, i.e., the fractional part of the delay τ. f Used to determine the TA value, the integer part τ i This scheduling strategy is used to delay the reception of uplink information and is applied to the subsequent transmission and reception of Msg3, downlink HARQ, and other uplink information. It enables existing 4G terminals to directly connect to the satellite by modifying only the base station-side protocol without changing the terminal-side protocol, allowing the 4G communication system to support greater latency and reducing upgrade costs for operators and users.

Description

Technical Field

[0001] This invention relates to the field of satellite communication technology, and more specifically to a time synchronization method for direct satellite connection of existing 4G FDD terminals. Background Technology

[0002] The technology for direct satellite connection to existing 4G terminals stems from the need for global communication coverage and the advancements in satellite and mobile communication technologies. With the development of the 3GPPPNTN (non-terrestrial network) standard, the rapid growth of low-Earth orbit satellite constellations, and the active promotion by commercial enterprises, this technology has been advanced. It aims to utilize existing 4G terminals to achieve direct communication via satellite, solving the problem of insufficient terrestrial network coverage, while simultaneously promoting the construction of an integrated space-ground communication network.

[0003] Existing direct satellite connection solutions for terminals mostly rely on customized terminals, meaning modifications to the protocols between the terminal and the base station to achieve direct satellite connection. However, these methods are not suitable for existing terminals. Starlink and AST are currently developing direct satellite connection services for existing terminals, attempting to achieve direct satellite connection for 4G and 5G terminals through customized satellites. The core approach of Starlink and AST is: how to deceive the terminal into believing that the satellite is on the ground. Figure 2 As shown, an offset is added between uplink and downlink to send downlink information in advance in order to compensate for large latency. Taking uplink DATA as an example, a fixed offset is added between DATA and ACK, that is, ACK is sent in advance, so that the terminal thinks that the satellite latency is within the normal range, thereby offsetting the large latency.

[0004] Currently, most direct satellite communication solutions for terminals rely on specific equipment or communication protocols, which limits the use of existing terminals. While Starlink and AST's direct satellite communication solutions for existing terminals can offset large latency, they still have several problems. First, the base station sends HARQ before receiving DATA, which prevents HARQ from providing adequate feedback to the DATA. Second, because the base station does not truly handle the large latency but only offsets it through offset, this method still cannot achieve a large coverage area.

[0005] Chinese patent application CN116406022A discloses a method for 5G terminals to directly connect to satellites in a low-Earth orbit (LEO) satellite FDD configuration. However, this method uses a TA (Transitional Time Acquisition) mechanism to adjust the fractional part τ of the latency. f In the 4G context, the maximum latency adjustment by the TA mechanism is 0.66ms, which is less than the fractional part of the latency τ. f The latency is 1ms, so this solution is not applicable to 4G communication networks. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a time synchronization method for direct satellite connection of existing 4G FDD terminals. Under the FDD system, without changing the 4G terminal, only the protocol on the base station side is modified to solve the problem of large latency in direct satellite connection of terminals.

[0007] Specifically, during uplink synchronization, i.e., the random access Msg1 stage, the protocol on the base station side is modified to expand the preamble sequence detection window of the base station, so that it can support the detection of greater latency while ensuring smooth uplink synchronization. At the same time, in the subsequent random access and data transmission stages, the uplink frame structure and uplink subframe scheduling strategy on the base station side are modified so that greater latency can also be supported, thereby significantly improving the flexibility and reliability of communication.

[0008] This method enables existing 4G terminals to communicate directly with satellites, which not only reduces the complexity of the communication system but also significantly reduces costs, bringing new development directions and business opportunities to the communications industry.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A time synchronization method for direct satellite connection of existing 4G FDD terminals includes the following steps:

[0011] The time synchronization method for direct satellite connection of existing 4G FDD terminals requires no modification to the terminal during the Msg1 stage of random access. Only by delaying and expanding the preamble sequence detection window on the base station side, a foundation is provided for supporting the detection of larger delays. In the subsequent steps of random access and the data transmission stage, no modification to the terminal is required. On the base station side, by setting appropriate uplink frame structures and uplink subframe scheduling strategies, correct random access and normal data transmission under large delay conditions are achieved.

[0012] A time synchronization method for direct satellite connection of existing 4G FDD terminals includes the following steps:

[0013] Step 1: In the first step of random access, the terminal sends the preamble sequence Msg1 to the base station, while the base station delays and expands the preamble sequence detection window;

[0014] Step 2: The base station receives the preamble sequence Msg1 through the preamble sequence detection window expanded in Step 1, then decodes the preamble sequence Msg1 to estimate the delay, and divides the delay into an integer part τ. i and the decimal part τ f ;

[0015] Step 3: The base station uses the integer part of the delay τ from Step 2 as a basis. i and the decimal part τ f And based on the fractional delay τ fWhether the delay is greater than 0.66ms determines whether the terminal is classified into two types. The base station calculates the corresponding TA value based on the two types and resets the uplink frame structure. Based on the uplink frame structure, TA value, and integer delay part τ, the system determines the type of terminal. i Execute the corresponding uplink subframe scheduling strategy;

[0016] Step 4: After receiving the preamble sequence Msg1 in step 2, the base station sends a random access response Msg2 to the terminal in the second step of random access and transmits the TA value calculated in step 3 to the terminal through the random access response Msg2. After receiving the random access response Msg2, the terminal determines the transmission time of Msg3 based on the received TA value. In the third step of random access, the terminal sends Msg3 to the base station. At the same time, the base station calculates the uplink reception time of Msg3 based on the uplink subframe scheduling strategy determined in step 3, so that the base station can correctly receive the Msg3 sent by the terminal.

[0017] Step 5: In the fourth step of random access, the base station sends Msg4 to the terminal. The terminal receives Msg4 and sends the corresponding HARQ. At the same time, the base station calculates the uplink reception time of HARQ according to the uplink subframe scheduling strategy given in step 3, so as to correctly receive HARQ.

[0018] Step 6: After step 5 is completed, the base station calculates the reception times of the channel sounding reference signal (SRS), uplink control channel (PUCCH), and uplink shared channel (PUSCH) according to the uplink subframe scheduling strategy given in step 3, and ensures that the channel sounding reference signal (SRS), uplink control channel (PUCCH), and uplink shared channel (PUSCH) sent by the terminal are correctly received without modifying the terminal.

[0019] Step 1 includes the following steps:

[0020] Step 1.1: In the first step of random access, the terminal sends a preamble sequence Msg1 to the base station. The base station determines the closest and farthest points of the terminal based on ephemeris information and beam coverage, and determines the minimum delay τ based on the distance between the closest and farthest points. min and maximum value τ max ;

[0021] Step 1.2: After determining the delay range in step 1.1, the base station postpones the start position of the preamble sequence detection window by τ. min Time, window size increased to τ max -τ min This allows the base station to correctly receive the preamble sequence Msg1.

[0022] Step 2 includes the following steps:

[0023] Step 2.1: The base station correctly receives the preamble sequence Msg1 within the expanded preamble sequence detection window and estimates the delay.

[0024] Step 2.2: Under FDD, a single 4G subframe is 1ms. Based on the latency estimated in Step 2.1, the latency is divided into integer parts τ in 1ms increments. i and the decimal part τ f The integer part τ i The full number of milliseconds representing the latency, with the fractional part τ. f Indicates excluding the integer part τ i The remaining delay size.

[0025] Step 3 includes the following steps:

[0026] Step 3.1: Since the maximum adjustable latency value supported by the LTE standard is 0.66ms, the latency is determined based on the fractional part τ. f Terminals are classified into two types: type 1 and type 2.

[0027] If the fractional part of the delay is 0ms≤τ f If ≤0.66ms, then TA is τ. f At this time, the uplink information sent by the terminal arrives at the base station synchronously, indicating that it is a type 1 terminal;

[0028] If the fractional part of the delay is 0.66ms < τ f If the time interval is less than 1ms, then the value of TA is τ. f -0.5, at this time the uplink information sent by the terminal arrives at the base station with an offset of 0.5ms, which is a type 2 terminal;

[0029] Step 3.2: The LTE standard specifies that the uplink frame period for base stations is 10ms, and each frame contains 10 subframes. For the two types identified in Step 3.1, to avoid interference between the uplink information of the two terminal types, the base station adopts a new uplink frame structure to ensure simultaneous and correct reception of uplink information from both terminal types. Specifically, there are two types:

[0030] Structure 1: In the uplink frames of the base station, subframes with atomic frame numbers 0, 3, 6, and 9 are dedicated to receiving type 1 information, and subframes with atomic frame numbers 1, 2, 4, 5, 7, and 8 are dedicated to receiving type 2 information.

[0031] Structure 2: In the uplink frames of the base station, subframes with atomic frame numbers 0, 1, 2, 3, 4, and 5 are dedicated to receiving type 1 information, and subframes with atomic frame numbers 6, 7, 8, and 9 are dedicated to receiving type 2 information.

[0032] Step 3.3: The base station executes the corresponding uplink subframe scheduling strategy according to the uplink frame structure divided in Step 3.2. Through scheduling, it ensures that both type 1 and type 2 uplink information arrive at the time specified in the new uplink frame structure. The base station then determines the arrival time based on the scheduling information and the integer part of the delay τ. i To calculate the correct reception time of uplink information for different types of terminals, since the timing of uplink information transmission is determined by the corresponding downlink control information, the transmission time of the corresponding downlink control information is calculated based on the arrival time of the uplink information.

[0033] Step 4 includes the following steps:

[0034] Step 4.1: After receiving Msg1, in the second step of random access, the base station sends Msg2 to the terminal. Msg2 contains the TA value and the scheduling information of Msg3.

[0035] Step 4.2: After receiving Msg2 from the base station in Step 4.1, in the third step of random access, the terminal, according to the LTE standard, first determines the uplink subframe transmission time based on the TA value, and then transmits Msg3 in the specified uplink subframe according to the Msg3 scheduling information; the base station, based on the integer part of the delay τ... i The correct reception time of Msg3 is calculated by delaying the base station's reception time of Msg3 by an integer part τ, based on the LTE-specified Msg3 reception time. i Each subframe receives Msg3 to ensure normal reception of Msg3.

[0036] Step 5 specifically includes:

[0037] After receiving Msg3, the base station sends Msg4 to the terminal in the fourth step of random access. The terminal calculates the HARQ transmission subframe according to LTE specifications and sends the HARQ to the base station at that subframe time. Simultaneously, the base station determines the transmission time based on the integer part τ of the delay. i Calculating the HARQ reception time means that the base station, based on the HARQ timing specified in LTE, delays the integer part τ. i Each subframe receives HARQ to ensure normal HARQ reception.

[0038] Step 6 includes the following steps:

[0039] After random access is completed, the base station determines the uplink reception times for the Channel Sounding Reference Signal (SRS), Uplink Control Channel (PUCCH), and Uplink Shared Channel (PUSCH), as follows:

[0040] For the Channel Sound Reference Signal (SRS), the base station determines the time delay integer part τ based on the SRS. i Determine the Channel Sounding Reference Signal (SRS) reception time, which is the time when the base station delays the original uplink scheduled reception subframe by an integer part τ. iEach subframe receives the Channel Sounding Reference Signal (SRS) to ensure normal reception of the SRS.

[0041] For the uplink control channel PUCCH, the base station determines the delay based on the integer part τ. i The uplink control channel (PUCCH) reception time is determined by the base station delaying the original uplink scheduled reception subframe by an integer part τ. i Each subframe receives the uplink control channel PUCCH to ensure normal reception of the uplink control channel PUCCH;

[0042] For the uplink shared channel PUSCH, the base station determines the delay based on the integer part τ. i Determine the uplink shared channel (PUSCH) reception time, which means that the base station delays the original uplink scheduled reception subframe by the integer part τ. i Each subframe receives the uplink shared channel (PUSCH) to ensure normal reception of the PUSCH.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0044] First: In Msg1, i.e. uplink synchronization, the base station expands the preamble sequence detection window, enabling the base station to support greater latency during the uplink synchronization phase. This allows synchronization to be maintained even with significant signal propagation delay, thereby improving the network's synchronization capability and communication quality.

[0045] Second: To address the issue that the TA mechanism does not support large latency, this invention uses milliseconds as the unit and divides the latency into an integer part τ. i and the decimal part τ f Given that the maximum adjustment range of the TA mechanism is 0.66ms, which is less than one subframe, and considering that the fractional part τ... f There are two types, type 1 (decimal part τ) f (less than 0.66ms) and type 2 (decimal part τ) f (greater than 0.66ms), which improves the support range of 4G latency. By subdividing the latency, the TA mechanism can work more effectively, maintaining the accuracy and efficiency of communication even in the case of high latency.

[0046] Third: This invention provides two base station uplink frame structures. The first frame structure has a higher coverage range, and the second frame structure has higher spectral efficiency. Each structure has its advantages and disadvantages. The appropriate frame structure can be selected according to the actual situation, which can adapt to different scenarios and provide greater flexibility and adaptability.

[0047] Fourth: This invention, without changing the terminal protocol, only changes the base station side protocol to complete random access and data transmission and reception, solving the problem that the time delay between the satellite and the ground is much greater than the TA adjustment range. It can be applied to existing 4G terminals under the FDD system, improving the system's compatibility and practicality, and reducing the upgrade costs for operators and users.

[0048] In summary, this invention, in 4G scenarios, expands the preamble sequence detection window, refines latency processing, and provides two frame structure options, enabling modification of the base station-side protocol without altering the terminal-side protocol. This allows for greater latency support, improves the synchronization capability, communication efficiency, and adaptability of 4G networks, while reducing upgrade costs for operators and users and enhancing system compatibility. Attached Figure Description

[0049] Figure 1 This is a flowchart illustrating the implementation of the present invention.

[0050] Figure 2 This is a schematic diagram of the existing latency handling strategies for AST and Stalink.

[0051] Figure 3 This is a diagram of the architecture of an existing direct-connect satellite system for terminals.

[0052] Figure 4 This is a schematic diagram of the existing cell search and four-step random access process.

[0053] Figure 5 This is a schematic diagram of the existing timed advance TA concept.

[0054] Figure 6 This is a schematic diagram of the dual-type division of the first base station uplink subframe structure of the present invention.

[0055] Figure 7 This is a schematic diagram of the dual-type division of the second type of base station uplink subframe structure of the present invention.

[0056] Figure 8 This is a schematic diagram of the subframe delay scheduling strategy based on latency optimization according to the present invention.

[0057] Figure 9 This is a timing diagram of the type 1 delay Msg2 / Msg3 of the present invention.

[0058] Figure 10 This is a timing diagram of the type 2 delay Msg2 / Msg3 of the present invention.

[0059] Figure 11 This is a schematic diagram of the downlink HARQ timing of the present invention.

[0060] Figure 12 This is a schematic diagram of an existing RAR window.

[0061] Figure 13 This is a schematic diagram of the existing Msg4 receiver window.

[0062] Figure 14 This is a schematic diagram illustrating the maximum latency supported by the first frame structure of the present invention.

[0063] Figure 15 This is a schematic diagram illustrating the maximum latency supported by the second frame structure of the present invention. Detailed Implementation

[0064] The present invention will now be described in detail with reference to the accompanying drawings.

[0065] Reference Figure 3 It is a system architecture that directly connects existing terminals to satellites. The satellite communication system consists of three parts: space segment, user segment, and ground segment. The space segment consists of satellite constellations in orbit and inter-satellite links. The ground segment includes ground gateway stations and ground network facilities. The user segment covers terminal equipment connected to the satellite.

[0066] This invention employs FDD (Free-Depth) duplex mode. Satellite communication systems typically employ two main implementation architectures: transparent payload and regenerative payload. In the transparent payload architecture, the satellite primarily acts as a relay link between user terminals and gateway stations, without processing signal content. In the regenerative payload architecture, the satellite not only relays signals but also functions as a base station, processing signals and thus reducing transmission latency. This invention supports both regenerative and transparent payload modes to meet the needs of different users and application scenarios.

[0067] Reference Figure 4 In a communication system, for a base station and a terminal to communicate, they must first complete a cell search and random access process, which is as follows:

[0068] During cell search, the user terminal, within its supported frequency bands, first searches for downlink synchronization signals, including the primary synchronization signal (PSS) and secondary synchronization signal (SSS), based on its own frequency and bandwidth. Subsequently, the terminal obtains basic network information by decoding the physical broadcast channel (PBCH). The PBCH carries the main network information block (MIB), which provides the parameters needed to decode other system information blocks (SIBs). The terminal uses the SIB information to search for and select the most suitable cell for communication, thus completing the cell search.

[0069] After the cell search is completed, the random access process begins, which consists of four steps, as follows:

[0070] In the first step of random access, the terminal sends Msg1 using the Physical Random Access Channel (PRACH). The main purpose of this step is to achieve uplink synchronization and assign a unique Connection Identifier (RNTI) to the terminal. Msg1 contains a preamble sequence randomly generated by the terminal. After receiving this preamble sequence, the base station will parse out the value of the preamble sequence and the corresponding delay.

[0071] In the second step of random access, the base station sends a random access response to the terminal via Msg2, which includes the TA and scheduling information for Msg3.

[0072] In the third step of random access, in Msg3, the terminal uses the scheduling information carried in Msg2 to send a Radio Resource Control (RRC) connection request on the resources scheduled by the base station.

[0073] In the fourth step of random access, in Msg4, the base station completes conflict resolution, and random access is completed.

[0074] See Figure 1 A time synchronization method for direct satellite connection of existing 4G FDD terminals includes the following steps:

[0075] Step 1: In the first step of random access, the terminal sends the preamble sequence Msg1 to the base station, while the base station delays and expands the preamble sequence detection window;

[0076] Step 1.1: In the first step of random access, the terminal sends a preamble sequence Msg1 to the base station. The base station determines the closest and farthest points of the terminal based on ephemeris information and beam coverage, and determines the minimum delay τ based on the distance between the closest and farthest points. min and maximum value τ max ;

[0077] Step 1.2: After determining the delay range in step 1.1, the base station postpones the start position of the preamble sequence detection window by τ. min Time, window size increased to τ max -τ min This allows the base station to correctly receive the preamble sequence Msg1.

[0078] That is: after determining the delay range, the base station postpones the start position of the preamble sequence detection window by τ. min Time, window size τ max -τ min This ensures that the preamble sequence Msg1 sent by all users is within τ. min Arrive after the time, and all are in τ. max -τ min Within the window, this allows the base station to correctly receive the preamble sequence Msg1.

[0079] Step 2: The base station receives the preamble sequence Msg1 through the preamble sequence detection window expanded in Step 1, then decodes the preamble sequence Msg1 to estimate the delay, and divides the delay into an integer part τ. i and the decimal part τ f :

[0080] Step 2.1: The base station correctly receives the preamble sequence Msg1 within the expanded preamble sequence detection window and estimates the delay.

[0081] Step 2.2: Under FDD, a single 4G subframe is 1ms. Based on the latency estimated in Step 2.1, the latency is divided into integer parts τ in 1ms increments. i and the decimal part τ f The integer part τ i The full number of milliseconds representing the latency, with the fractional part τ. f Indicates excluding the integer part τ i The remaining delay;

[0082] Reference Figure 5 The terminal uses the TA mechanism to determine the time when it sends uplink subframes. The TA value actually represents a negative offset, that is, how much time the terminal sends uplink subframes after receiving downlink subframes from the base station. The base station calculates the TA value of each terminal to ensure that even for terminals that are far away, their uplink information can arrive at the base station almost simultaneously with the uplink information of terminals that are closer.

[0083] In 4G, after receiving the preamble sequence Msg1, the base station determines the TA value by decoding and sends the calculated TA value to the terminal through the random access response message Msg2. The terminal determines the transmission time of its uplink information based on the received TA value.

[0084] In 4G, the TA value ranges from 0 to 1282, the uplink synchronization granularity is 16Ts, and the actual time corresponding to the TA value is:

[0085] N TA =T A ×16 (Unit: T) s )

[0086] Among them, T A N represents the TA value. TA The TA value represents the time delay. 16Ts = 0.52μs. Therefore, the maximum adjustable time delay of TA is approximately 0.66ms. A round-trip time delay of 0.66ms represents a maximum transmission distance of approximately 99km. This range is only applicable to ground environments and not to satellite-to-ground transmission. The estimated time delay in the preamble sequence Msg1 is represented by τ (in milliseconds). When the time delay is less than 0.66ms, the relationship between time delay and TA is as follows:

[0087]

[0088] Where τ represents the magnitude of the time delay, T A This indicates the TA value corresponding to the delay.

[0089] Low-Earth orbit satellites typically operate at altitudes between 200 and 2000 km, while the range supported by 4G's TA mechanism is only 99 km, far less than the round-trip distance between the terminal and the satellite.

[0090] In the first step of random access, the terminal sends a preamble sequence Msg1 to the base station. After correctly receiving Msg1, the base station decodes it to obtain the latency (τ). However, since the adjustment range of the TA (Time Acquisition) is limited to within 0.66ms, which is much smaller than the satellite-to-ground latency, the TA mechanism needs to be modified. Specifically, the estimated latency is divided into two parts, using subframes (i.e., 1 milliseconds) as units: the integer part τ... i and the decimal part τ f , where τ=τ i +τ f The integer part τ i The base station stores this information to determine the uplink reception time; the fractional part τ f The TA value is then sent to the terminal, but the terminal does not know the integer part of the delay τ. i The existence of.

[0091] Step 3: The base station uses the integer part of the delay τ from Step 2 as a basis. i and the decimal part τ f And based on the fractional delay τ f Whether the delay is greater than 0.66ms determines whether the terminal is classified into two types. The base station calculates the corresponding TA value based on the two types and resets the uplink frame structure. Based on the uplink frame structure, TA value, and integer delay part τ, the system determines the type of terminal. i Execute the corresponding uplink subframe scheduling strategy;

[0092] Step 3.1: Since the maximum adjustable latency value supported by the LTE standard is 0.66ms, the latency is determined based on the fractional part τ. f Terminals are classified into two types: type 1 and type 2.

[0093] If the fractional part of the delay is 0ms≤τ f If ≤0.66ms, then TA is τ. f At this time, the uplink information sent by the terminal arrives at the base station synchronously, indicating that it is a type 1 terminal;

[0094] If the fractional part of the delay is 0.66ms < τ f If the time interval is less than 1ms, then the value of TA is τ. f-0.5, at this time the uplink information sent by the terminal arrives at the base station with an offset of 0.5ms, which is a type 2 terminal;

[0095] Step 3.2: The LTE standard specifies that the uplink frame period for base stations is 10ms, and each frame contains 10 subframes. For the two types identified in Step 3.1, to avoid interference between the uplink information of the two terminal types, the base station adopts a new uplink frame structure to ensure simultaneous and correct reception of uplink information from both terminal types. Specifically, there are two types:

[0096] like Figure 6 As shown, Structure 1: In the uplink frames of the base station, subframes with atomic frame numbers 0, 3, 6, and 9 are dedicated to receiving type 1 information, and subframes with atomic frame numbers 1, 2, 4, 5, 7, and 8 are dedicated to receiving type 2 information.

[0097] like Figure 7 As shown, Structure 2: In the uplink frames of the base station, subframes with atomic frame numbers 0, 1, 2, 3, 4, and 5 are dedicated to receiving type 1 information, and subframes with atomic frame numbers 6, 7, 8, and 9 are dedicated to receiving type 2 information.

[0098] Considering that the starting points of type 1 and type 2 uplink information are at the beginning and middle of the subframe respectively, they will inevitably cause some interference if no intervention is made. In order to optimize data reception, and considering that after random access is completed, the frame structure of the base station also needs to match the transmission period of CSI, SRS, and SR (5ms, 10ms, 20ms, 40ms, 80ms, etc.), the uplink frame structure of the base station needs to be modified. The uplink frame structure of the base station adopts a one-frame-per-cycle strategy, while the downlink frame structure does not need to be changed. This periodic subframe allocation can effectively reduce the interference between type 1 and type 2 uplink information.

[0099] The first frame structure has a total of 4 type 1 subframes and 3 type 2 subframes, while the second frame structure has a total of 6 type 1 subframes and 3 type 2 subframes. Compared to the first frame structure, the second frame structure has a greater number of type 1 subframes, resulting in higher spectral efficiency. However, due to the limitations of the RAR window, the second frame structure results in a significantly shorter maximum supported transmission distance, which will be explained in detail later. In the following figures, unless otherwise specified, the first frame structure is used as an example, but all techniques can be applied to both frame structures.

[0100] Step 3.3: The base station executes the corresponding uplink subframe scheduling strategy according to the uplink frame structure divided in Step 3.2. Through scheduling, it ensures that both type 1 and type 2 uplink information arrive at the time specified in the new uplink frame structure. The base station then determines the arrival time based on the scheduling information and the integer part of the delay τ. i Calculate the correct reception time of uplink information for different types of terminals. Since the timing of uplink information transmission is determined by the corresponding downlink control information, the transmission time of the corresponding downlink control information is calculated based on the arrival time of the uplink information.

[0101] Reference Figure 8 The base station bases the time delay based on the fractional part τ of the terminal. f Terminals are divided into two types, requiring modifications to the uplink scheduling strategy to ensure that uplink subframes from different users arrive at the base station at the correct subframe time. Uplink information transmission is scheduled and guided by corresponding downlink control information. The base station instructs terminals when and how to transmit uplink information by sending downlink control information. Assuming the downlink control information transmission subframe is n, the uplink information arrival subframe is n' = n + τ. i +k, where τ i The integer part represents the delay, where k indicates the time interval from when the terminal receives downlink control information to when it sends uplink information. In 4G, the value of k is specified by the protocol; refer to Chapters 8 and 10 of 3GPP protocol 36213 for details. In FDD, the value of k is typically 4 or 6.

[0102] If the fractional part of the delay τ f For delays <0.66ms, it is necessary to ensure that uplink information arrives in type 1 subframes, with the fractional part of the delay τ. f When the latency is >0.66ms, it is necessary to ensure that the uplink information arrives in a type 2 subframe. Therefore, the base station should determine a suitable value for n' so that the uplink information can arrive in the specified type of subframe, according to n = n' - τ. i -k determines the timing of downlink control subframe transmission, and this scheduling strategy is then applied to the reception of Msg3, downlink HARQ, SRS, CSI, SR, and BSR.

[0103] Step 4: After receiving the preamble sequence Msg1 in step 2, the base station sends a random access response Msg2 to the terminal in the second step of random access and transmits the TA value calculated in step 3 to the terminal through the random access response Msg2. After receiving the random access response Msg2, the terminal determines the transmission time of Msg3 based on the received TA value. In the third step of random access, the terminal sends Msg3 to the base station. At the same time, the base station calculates the uplink reception time of Msg3 based on the uplink subframe scheduling strategy determined in step 3, so that the base station can correctly receive the Msg3 sent by the terminal.

[0104] Step 4.1: After receiving Msg1, in the second step of random access, the base station sends Msg2 to the terminal. Msg2 contains the TA value and the scheduling information of Msg3.

[0105] Step 4.2: After receiving Msg2 from the base station in Step 4.1, in the third step of random access, the terminal, according to the LTE standard, first determines the uplink subframe transmission time based on the TA value, and then transmits Msg3 in the specified uplink subframe according to the Msg3 scheduling information; the base station, based on the integer part of the delay τ... i The correct reception time of Msg3 is calculated by delaying the base station's reception time of Msg3 by an integer part τ, based on the LTE-specified Msg3 reception time. i Each subframe receives Msg3 to ensure normal reception of Msg3;

[0106] Reference Figure 9 This is a timing diagram of type 1 delay Msg2 / Msg3. If Msg2 sends subframe n, then Msg3 arrives at subframe n' = n + τ. i +k, where τ i Represents the integer part of the delay τ i k represents the terminal-side transmit / receive interval. Referring to the 3GPP 36213 protocol, in FDD, the value of k is 6 to ensure the fractional part of the delay τ. f When the time is less than 0.66ms, all uplink subframes are received in type 1 subframes. The base station first determines the value of n' so that the arrival time of Msg3 belongs to type 1 subframes, and then determines the transmission subframe of Msg2 as n = n' - k - τ. i .

[0107] Reference Figure 10 This is a timing diagram of type 2 delay Msg2 / Msg3. Similar to type 1 delay, to ensure the fractional part τ of the delay... f When the time is greater than 0.66ms, the uplink information is received in type 2 subframes. The base station first determines the value of n' so that the arrival time of Msg3 belongs to type 2 subframes. Since the uplink information is offset by 0.5τ at this time... s Upon arrival, the uplink information is distributed across two subframes. Therefore, when the base station acquires the uplink information, it needs to obtain the latter half of subframe n' and the first half of subframe n'+1. Based on the value of n', the transmission subframe for Msg2 is determined to be n'-k-τ. i .

[0108] Step 5: In the fourth step of random access, the base station sends Msg4 to the terminal. The terminal receives Msg4 and sends the corresponding HARQ. At the same time, the base station calculates the uplink reception time of HARQ according to the uplink subframe scheduling strategy given in step 3, so as to correctly receive HARQ.

[0109] After receiving Msg3, the base station sends Msg4 to the terminal in the fourth step of random access. The terminal calculates the HARQ transmission subframe according to LTE specifications and sends the HARQ to the base station at that subframe time. Simultaneously, the base station determines the transmission time based on the integer part τ of the delay. i Calculating the HARQ reception time means that the base station, based on the HARQ timing specified in LTE, delays the integer part τ. i Each subframe receives HARQ to ensure normal HARQ reception.

[0110] Reference Figure 11 After receiving Msg4, the terminal completes the fourth step of random access. After k subframes, it sends a downlink HARQ to the base station via PUCCH. Similarly, after random access is completed, the base station sends downlink data information, and after k subframes, it also sends a downlink HARQ to the base station via PUCCH. Both Msg4 and downlink information are sent via PDSCH, and downlink HARQs are sent via PUCCH. Therefore, these two cases are grouped together, where k represents the transmission interval of PDSCH and HARQ on the terminal side. Referring to the 3GPP 36213 protocol, in FDD, k is 4. Assuming the PDSCH transmission time is n, the arrival time of the downlink HARQ is n' = n + k + τ. i Similarly, HARQ is also divided into two cases, type 1 (τ f <0.66ms) and type 2 (τ) f >0.66ms). The base station first determines the value of n' to ensure that the downlink HARQ arrives in the specified type subframe, and then determines the PDSCH transmission subframe n = n' - k - τ. i .

[0111] Step 6: After step 5 is completed, the base station calculates the reception times of the Channel Sounding Reference Signal (SRS), Uplink Control Channel (PUCCH), and Uplink Shared Channel (PUSCH) according to the uplink subframe scheduling strategy given in step 3, ensuring correct reception of the SRS, PUCCH, and PUSCH sent by the terminal without modifying the terminal.

[0112] After random access is completed, the base station determines the uplink reception times for the Channel Sounding Reference Signal (SRS), Uplink Control Channel (PUCCH), and Uplink Shared Channel (PUSCH), as follows:

[0113] For the Channel Sound Reference Signal (SRS), the base station determines the time delay integer part τ based on the SRS. i Determine the Channel Sounding Reference Signal (SRS) reception time, which is the time when the base station delays the original uplink scheduled reception subframe by an integer part τ. i Each subframe receives the Channel Sounding Reference Signal (SRS) to ensure normal reception of the SRS.

[0114] SRS stands for Channel Sounding Reference Signal. Base stations use SRS signals to assess the uplink channel quality. SRS is divided into two types: periodic and aperiodic.

[0115] For periodic SRS, the transmission time satisfies the following formula:

[0116]

[0117] Where, n f Indicates the system frame number, n s Indicates the timeslot number. T represents the subframe number. PERIODICITY N represents the transmission period. OFFSET It represents the subframe offset, indicating the specific subframe in which the SRS is transmitted.

[0118] The SRS transmission period is selectable from 2ms, 5ms, 10ms, 20ms, 40ms, 80ms, 160ms, and 320ms. Because it needs to correspond to the base station frame structure (which has a 10ms period), the SRS transmission period cannot be set to 2ms or 5ms. Users can freely choose other periods as needed. The subframe offset is based on the fractional part of the delay, τ. f Size selection, if the fractional part of the delay τ f <0.66ms, control SRS to arrive in type 1 subframe, if the fractional part of the delay τ f If the time is >0.66ms, the SRS will arrive in the type 2 subframe.

[0119] For the uplink control channel PUCCH, the base station determines the delay based on the integer part τ. i The uplink control channel (PUCCH) reception time is determined by the base station delaying the original uplink scheduled reception subframe by an integer part τ. i Each subframe receives the uplink control channel PUCCH to ensure normal reception of the uplink control channel PUCCH;

[0120] For the uplink shared channel PUSCH, the base station determines the delay based on the integer part τ. i Determine the uplink shared channel (PUSCH) reception time, which means that the base station delays the original uplink scheduled reception subframe by the integer part τ. i Each subframe receives the uplink shared channel (PUSCH) to ensure normal reception of the PUSCH.

[0121] CSI, SR, and downlink HARQ information are all carried on the uplink control channel PUCCH and sent to the base station through the uplink control channel PUCCH. The downlink HARQ information has been explained above.

[0122] CSI stands for Downlink Channel State Information. The base station sends CSI_RS as CSI reference information for measuring downlink channel state information. The terminal obtains downlink channel quality information, i.e., CSI, by measuring CSI_RS and reports the CSI information to the base station. CSI is divided into periodic and aperiodic types. For periodic CSI, the transmission time satisfies the following formula:

[0123]

[0124] Where, n f Indicates the system frame number, n s Indicates the timeslot number. Indicates subframe number, N OFFSET T represents the subframe offset. PERIODICITY N represents the transmission period. OFFSET This indicates the specific subframe in which the CSI is transmitted.

[0125] The CSI transmission period is selectable at 5ms, 10ms, 20ms, 40ms, and 80ms. Because it needs to correspond to the base station frame structure (which has a 10ms period), the CSI transmission period cannot be set to 5ms. Users can freely choose other periods as needed. Since CSI is transmitted via the uplink channel, the subframe offset needs to be calculated based on the fractional part of the delay, τ. f Choose if the fractional part of the delay τ f <0.66ms, control CSI to arrive in type 1 subframe, if the fractional part of the delay τ f If the time is >0.66ms, then the control CSI will arrive in the type 2 subframe.

[0126] For aperiodic CSI, it is necessary to consider the fractional part of the delay τ. f The type pre-calculates in which subframe the CSI information will arrive, thereby determining the downlink control information transmission time and calculating the TA value. The base station delays reception based on the scheduling information.

[0127] SR stands for Uplink Scheduling Request. For SR, the terminal tells the base station that it needs uplink resources for ULSCH transmission. The transmission of SR is periodic, and the period is controlled by sr-ConfigIndex. The specific correspondence is as follows.

[0128]

[0129] Where, n f Indicates the system frame number, n s Indicates the timeslot number. Indicates subframe number, SR PERIODICITY N represents the transmission period.OFFSET,SR This indicates the subframe offset, which specifies the subframe in which the SR is transmitted.

[0130] The SR transmission period is selectable from 1ms, 2ms, 5ms, 10ms, 20ms, 40ms, and 80ms. Because it needs to correspond to the base station frame structure (which has a 10ms period), the SR transmission period cannot be set to 1ms, 2ms, or 5ms. Users can freely choose other periods as needed. (Based on the fractional part of the delay τ...) f Size selection of subframe offset, if the fractional part of the delay τ f <0.66ms, control SR to arrive in type 1 subframe, if the fractional part of the delay τ f If the time is >0.66ms, the control SR will arrive in the type 2 subframe.

[0131] For the uplink shared channel PUSCH, the base station determines the delay based on the integer part τ. i Determine the uplink shared channel (PUSCH) reception time, which means that the base station delays the original uplink scheduled reception subframe by the integer part τ. i Each subframe receives the uplink shared channel (PUSCH) to ensure normal reception of the uplink shared channel (PUSCH).

[0132] Uplink data and terminal buffer status report (BSR) are both sent to the base station via PUSCH. The base station modifies the PUSCH according to the uplink subframe scheduling policy as follows:

[0133] The base station determines the timing of PUSCH transmission through scheduling and sends the scheduling information to the terminal via downlink control information. After receiving the downlink control information, the terminal transmits the PUSCH at the specified time. The base station delays the transmission by the integer part τ based on the original uplink scheduled reception subframe. i Each subframe receives the uplink shared channel (PUSCH) to ensure normal reception of the PUSCH.

[0134] By calculating the maximum delay supported by the two frame structures divided in step 3.2, the maximum transmission distance of information is discussed:

[0135] Reference Figure 12 , Figure 12The diagram illustrates the RAR window principle. The terminal opens the RAR window in the third subframe after sending the Msg1 subframe and continuously listens for ra-ResponseWindowSize subframes. During the RAR window, the terminal listens to the PDCCH to receive the Msg2 sent by the base station. If the terminal fails to receive Msg2 during the RAR window, the random access procedure fails. In the 3GPP protocol, the RAR window ranges from 2 to 10 subframes; therefore, the maximum duration of the RAR window is 10 subframes. This means that the total time from when the terminal sends Msg1 to when it receives Msg2 must be less than or equal to 13 subframes to ensure successful RAR reception.

[0136] Reference Figure 13 , Figure 13 This is a schematic diagram of the Msg4 response receiving window. After sending Msg3, the terminal will open the Msg4 receiving window, which is called the contention resolution timer. If Msg4 is received within the contention resolution timer, the contention is considered to be resolved successfully. In 4G, the contention resolution timer can reach a maximum of 64ms.

[0137] LTE specifies that the Msg4 response receive window size is 64ms and the RAR window size is 13ms. Therefore, when considering the maximum supported round-trip time, only the smaller RAR window needs to be considered. It is necessary to ensure that the total time from when the terminal sends Msg1 to when it receives Msg2 must be less than or equal to 13 subframes.

[0138] Consider calculating the delay range supported by the two frame structures to obtain the longest transmission distance. Taking format 0 as an example, assuming the round-trip propagation delay is τ, the Msg1 transmission time is n, and the reception time is n+0.5τ, τ max This represents the maximum value of the leader sequence detection window, and the leader sequence detection window ends at time n+τ. max Δ represents the time interval from the end of the preamble detection window to the transmission of Msg2, and the transmission time of Msg2 is n+τ. max +Δ, the Msg2 receiving time is then n+τ max +Δ+0.5τ, considering that the duration of Msg2 is 1 subframe, and the duration of Msg1 is also close to 1 subframe, for simplicity, the duration of Msg1 is also treated as 1 subframe, which needs to satisfy the following two conditions:

[0139] 1. The moment Msg1 reception ends must be within the preamble sequence detection window, i.e.:

[0140] n+0.5τ+1≤n+τ max

[0141] 2. The time interval from Msg1 to the end of reception for Msg2 is less than the duration of the RAR window, i.e.:

[0142] (n+τ max +Δ+0.5τ+1)-(n)≤13

[0143] Solving the above two equations, we can obtain that τ < 11 - Δ. When Δ reaches its maximum value, the range of τ that is still supported is the range of time delay support.

[0144] Reference Figure 14 For the first base station frame structure, it is necessary to obtain the maximum value of the time interval from the end of the preamble sequence detection window to the transmission of Msg2. If the fractional part of the delay τ f The type is type2, see reference. Figure 14 As shown, if Msg2 is sent in the next subframe after the end of the preamble sequence detection window, the receiving subframe number of Msg3 is 8, which does not meet the frame structure requirements. Therefore, the base station needs to delay the transmission of Msg2 and send Msg2 3 subframes after the end of the preamble sequence detection window. At this time, the receiving subframe number of Msg3 is 1, which meets the frame structure requirements. The interval from the end of the preamble sequence detection window to the transmission of Msg2 is 3 subframes. Similarly, the interval from the end of the preamble sequence detection window to the transmission of Msg2 in other cases can be obtained according to this method. Finally, it can be found that the interval is between 0 and 3 subframes. The maximum value of Δ is 3. From τ≤11-Δ, we get τ≤8. Therefore, the supported round-trip delay range is about 0 to 8ms. The maximum transmission distance corresponding to the 8ms round-trip delay is about 1200km.

[0145] Reference Figure 15 For the second type of base station frame structure, similar to the first type, if the fractional part of the delay τ f The type is type2, see reference. Figure 15 As shown, if Msg2 is sent in the next subframe after the end of the preamble sequence detection window, then Msg3 is expected to receive 9 subframes, which does not meet the frame structure requirements. Msg2 is sent after 7 subframes from the end of the preamble sequence detection window, and Msg3 is expected to receive 6 subframes, which meets the frame structure requirements. At this time, the interval between the end of the preamble sequence detection window and the transmission of Msg2 is 7 subframes. Similarly, the interval between the end of the preamble sequence detection window and the transmission of Msg2 in other cases can be obtained according to this method. Finally, the interval is found to be between 0 and 7 subframes, and the maximum value of Δ is 7. From τ≤11-Δ, we get τ≤4. Therefore, the supported round-trip delay range is about 0 to 4ms, and the maximum transmission distance corresponding to a 4ms round-trip delay is about 600km.

[0146] Low-Earth orbit satellites typically operate at altitudes between 200 and 2000 km. It can be seen that the first type of base station frame structure has a wider coverage area, while the second type of frame structure has higher spectral efficiency. The appropriate frame structure can be selected based on a comprehensive consideration of the satellite's orbit.

Claims

1. A time synchronization method for direct satellite connection of existing 4G FDD terminals, characterized in that, During the Msg1 phase of random access, no modifications are required to the terminal. Only the preamble sequence detection window is delayed and expanded on the base station side to provide a foundation for supporting the detection of larger delays. In subsequent random access steps and data transmission phases, no modifications are required to the terminal. On the base station side, by setting appropriate uplink frame structures and uplink subframe scheduling strategies, correct random access and normal data transmission under high latency conditions are achieved. The specific steps are as follows: Step 1: In the first step of random access, the terminal sends the preamble sequence Msg1 to the base station, while the base station delays and expands the preamble sequence detection window; Step 2: The base station receives the preamble sequence Msg1 through the preamble sequence detection window expanded in Step 1, then decodes the preamble sequence Msg1 to estimate the delay, and divides the delay into an integer part τ. i and the decimal part τ f ; Step 3: The base station uses the integer part of the delay τ from Step 2 as a basis. i and the decimal part τ f And based on the fractional delay τ f Whether the delay is greater than 0.66ms determines whether the terminal is classified into two types. The base station calculates the corresponding TA value based on the two types and resets the uplink frame structure. Based on the uplink frame structure, TA value, and integer delay part τ, the system determines the type of terminal. i The corresponding uplink subframe scheduling strategy is executed, and the specific implementation process is as follows: Step 3.1: Since the maximum adjustable latency value supported by the LTE standard is 0.66ms, the latency is determined based on the fractional part τ. f Terminals are classified into two types: type 1 and type 2. If the fractional part of the delay is 0ms≤τ f If ≤0.66ms, then TA is τ. f At this time, the uplink information sent by the terminal arrives at the base station synchronously, indicating that it is a type 1 terminal; If the fractional part of the delay is 0.66ms < τ f If the time interval is less than 1ms, then the value of TA is τ. f -0.5, at this time the uplink information sent by the terminal arrives at the base station with an offset of 0.5ms, which is a type 2 terminal; Step 3.2: The LTE standard specifies that the uplink frame period for base stations is 10ms, and each frame contains 10 subframes. For the two types identified in Step 3.1, to avoid interference between the uplink information of the two terminal types, the base station adopts a new uplink frame structure to ensure simultaneous and correct reception of uplink information from both terminal types. Specifically, there are two types: Structure 1: In the uplink frames of the base station, subframes with atomic frame numbers 0, 3, 6, and 9 are dedicated to receiving type 1 information, and subframes with atomic frame numbers 1, 2, 4, 5, 7, and 8 are dedicated to receiving type 2 information. Structure 2: In the uplink frames of the base station, subframes with atomic frame numbers 0, 1, 2, 3, 4, and 5 are dedicated to receiving type 1 information, and subframes with atomic frame numbers 6, 7, 8, and 9 are dedicated to receiving type 2 information. Step 3.3: The base station executes the corresponding uplink subframe scheduling strategy according to the uplink frame structure divided in Step 3.

2. Through scheduling, it ensures that both type 1 and type 2 uplink information arrive at the time specified in the new uplink frame structure. The base station then determines the arrival time based on the scheduling information and the integer part of the delay τ. i Calculate the correct reception time of uplink information for different types of terminals. Since the timing of uplink information transmission is determined by the corresponding downlink control information, the transmission time of the corresponding downlink control information is calculated based on the arrival time of the uplink information. Step 4: After receiving the preamble sequence Msg1 in step 2, the base station sends a random access response Msg2 to the terminal in the second step of random access and transmits the TA value calculated in step 3 to the terminal through the random access response Msg2. After receiving the random access response Msg2, the terminal determines the transmission time of Msg3 based on the received TA value. In the third step of random access, the terminal sends Msg3 to the base station. At the same time, the base station calculates the uplink reception time of Msg3 based on the uplink subframe scheduling strategy determined in step 3, so that the base station can correctly receive the Msg3 sent by the terminal. Step 5: In the fourth step of random access, the base station sends Msg4 to the terminal. The terminal receives Msg4 and sends the corresponding HARQ. At the same time, the base station calculates the uplink reception time of HARQ according to the uplink subframe scheduling strategy given in step 3, so as to correctly receive HARQ. Step 6: After step 5 is completed, the base station calculates the reception times of the channel sounding reference signal (SRS), uplink control channel (PUCCH), and uplink shared channel (PUSCH) according to the uplink subframe scheduling strategy given in step 3, and ensures that the channel sounding reference signal (SRS), uplink control channel (PUCCH), and uplink shared channel (PUSCH) sent by the terminal are correctly received without modifying the terminal.

2. The time synchronization method for direct satellite connection of existing 4G FDD terminals according to claim 1, characterized in that, Step 1 includes the following steps: Step 1.1: In the first step of random access, the terminal sends a preamble sequence Msg1 to the base station. The base station determines the closest and farthest points of the terminal based on ephemeris information and beam coverage, and determines the minimum delay τ based on the distance between the closest and farthest points. min and maximum value τ max ; Step 1.2: After determining the delay range in step 1.1, the base station postpones the start position of the preamble sequence detection window by τ. min Time, window size increased to τ max -τ min This allows the base station to correctly receive the preamble sequence Msg1.

3. The time synchronization method for direct satellite connection of existing 4G FDD terminals according to claim 1, characterized in that, Step 2 includes the following steps: Step 2.1: The base station correctly receives the preamble sequence Msg1 within the expanded preamble sequence detection window and estimates the delay. Step 2.2: Under FDD, a single 4G subframe is 1ms. Based on the latency estimated in Step 2.1, the latency is divided into integer parts τ in 1ms increments. i and the decimal part τ f The integer part τ i The full number of milliseconds representing the latency, with the fractional part τ. f Indicates excluding the integer part τ i The remaining delay size.

4. The time synchronization method for direct satellite connection of existing 4G FDD terminals according to claim 1, characterized in that, Step 4 includes the following steps: Step 4.1: After receiving Msg1, in the second step of random access, the base station sends Msg2 to the terminal. Msg2 contains the TA value and the scheduling information of Msg3. Step 4.2: After receiving Msg2 from the base station in Step 4.1, in the third step of random access, the terminal, according to the LTE standard, first determines the uplink subframe transmission time based on the TA value, and then transmits Msg3 in the specified uplink subframe according to the Msg3 scheduling information; the base station, based on the integer part of the delay τ... i The correct reception time of Msg3 is calculated by delaying the base station's reception time of Msg3 by an integer part τ, based on the LTE-specified Msg3 reception time. i Each subframe receives Msg3 to ensure normal reception of Msg3.

5. The time synchronization method for direct satellite connection of existing 4G FDD terminals according to claim 1, characterized in that, Step 5 specifically includes: After receiving Msg3, the base station sends Msg4 to the terminal in the fourth step of random access. The terminal calculates the HARQ transmission subframe according to LTE specifications and sends the HARQ to the base station at that subframe time. Simultaneously, the base station determines the transmission time based on the integer part τ of the delay. i Calculating the HARQ reception time means that the base station, based on the HARQ timing specified in LTE, delays the integer part τ. i Each subframe receives HARQ to ensure normal HARQ reception.

6. The time synchronization method for direct satellite connection of existing 4G FDD terminals according to claim 1, characterized in that, Step 6 includes the following steps: After random access is completed, the base station determines the uplink reception times for the Channel Sounding Reference Signal (SRS), Uplink Control Channel (PUCCH), and Uplink Shared Channel (PUSCH), as follows: For the Channel Sound Reference Signal (SRS), the base station determines the time delay integer part τ based on the SRS. i Determine the Channel Sounding Reference Signal (SRS) reception time, which is the time when the base station delays the original uplink scheduled reception subframe by an integer part τ. i Each subframe receives the Channel Sounding Reference Signal (SRS) to ensure normal reception of the SRS. For the uplink control channel PUCCH, the base station determines the delay based on the integer part τ. i The uplink control channel (PUCCH) reception time is determined by the base station delaying the original uplink scheduled reception subframe by an integer part τ. i Each subframe receives the uplink control channel PUCCH to ensure normal reception of the uplink control channel PUCCH; For the uplink shared channel PUSCH, the base station determines the delay based on the integer part τ. i Determine the uplink shared channel (PUSCH) reception time, which means that the base station delays the original uplink scheduled reception subframe by the integer part τ. i Each subframe receives the uplink shared channel (PUSCH) to ensure normal reception of the PUSCH.

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