4G FDD stock terminal direct connection satellite-oriented time synchronization method

Abstract

The invention discloses a 4G FDD stock terminal direct connection satellite-oriented time synchronization method, which comprises the following steps: firstly, a base station delays a starting point of a preamble sequence detection window and enlarges the window size, the base station receives a preamble sequence in the enlarged window and detects the size of time delay by decoding the preamble sequence, and after the base station determines the size of the time delay, the base station delays the starting point of the preamble sequence detection window; according to the method, time delay is divided into an integer part tau i and a decimal part tau f by taking milliseconds as a unit, terminals are divided into two types according to whether the decimal time delay is greater than 0.66 ms or not, so that an uplink frame structure of a base station is modified, the base station determines an uplink subframe scheduling strategy according to the uplink frame structure, the decimal part tau f of the time delay is used for determining a TA value, and the TA value is used for scheduling the uplink subframe. The integer part tau i is used for delaying receiving of uplink information, and the scheduling strategy is applied to subsequent receiving and transmitting of Msg3, downlink HARQ and other uplink information; the stock 4G terminal is directly connected with the satellite under the condition that only the base station side protocol is modified and the terminal side protocol is not changed, so that the 4G communication system supports larger time delay, and meanwhile, the upgrading cost of an operator and a user is reduced.

Description

Technical Field

[0001] The present invention relates to the field of satellite communication technology, and in particular to a time synchronization method for 4G FDD existing terminals directly connected to satellites. Background Art

[0002] The technology of connecting 4G stock terminals directly to satellites stems from the demand for global communication coverage and the progress of satellite and mobile communication technologies. With the formulation of the 3GPP NTN (non-terrestrial network) standard, the rapid development of low-orbit satellite constellations, and the active promotion of commercial enterprises, this technology has been promoted. It aims to use existing 4G terminals to achieve direct communication through satellites, solve the problem of insufficient ground network coverage, and promote the construction of a space-ground integrated communication network.

[0003] Most of the existing terminal direct satellite connection solutions are through customized terminals, that is, modifying the terminal and base station side protocols to achieve terminal direct satellite connection. However, these methods are not applicable to existing terminals. Starlink and AST are currently developing existing terminal direct satellite connection services, attempting to achieve 4G and 5G terminal direct satellite connection services through customized satellites. The core approach of Starlink and AST is: how to deceive the terminal and make the terminal think that the satellite is on the ground. Figure 2 As shown in the figure, an offset is added between the uplink and downlink, and the downlink information is sent in advance to compensate for the large delay. Taking the 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 delay is within the normal range, thereby offsetting the large delay.

[0004] At present, most terminal direct satellite communication solutions rely on specific equipment or specific communication protocols, which limit the use of existing terminals. Starlink and AST's existing terminal direct satellite technology solutions can offset large delays, but there are still many problems. First, the base station sends HARQ before receiving DATA, which makes HARQ unable to make reasonable feedback to DATA. Secondly, since the base station side does not really handle large delays, but only offsets the delay through offsets, this method still cannot achieve a large coverage area.

[0005] The Chinese patent application with publication number CN116406022A discloses a method for 5G terminals to directly connect to satellites under the low-orbit satellite FDD system. However, since this method uses the TA mechanism to adjust the fractional part of the delay τ f In the case of 4G, the maximum delay adjusted by the TA mechanism is 0.66ms, which is smaller than the fractional part of the delay τ f , that is, 1ms, so this solution cannot be applied to 4G communication networks. Summary of the invention

[0006] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a time synchronization method for 4G FDD existing terminals directly connected to satellites. Under the premise of not changing the 4G terminals under the FDD system, only the protocol on the base station side is modified to solve the problem of large delay when the terminals are directly connected to the satellites.

[0007] Specifically, in the uplink synchronization, that is, the random access Msg1 stage, the protocol on the base station side is modified to expand the base station's preamble sequence detection window so that it can support the detection of a larger delay 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 a larger delay can be supported subsequently, thereby significantly improving the flexibility and reliability of communications.

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

[0009] In order to achieve the above object, the technical solution adopted by the present invention is:

[0010] The time synchronization method for 4G FDD stock terminals directly connected to satellites includes the following steps:

[0011] The time synchronization method for 4G FDD existing terminals directly connected to satellites does not require any modification to the terminals in the Msg1 stage of random access. The base station side only postpones and expands the preamble sequence detection window to provide a basis for supporting the detection of larger delays. In the subsequent steps of random access and the data transmission stage, the terminal does not need to be modified. The base station side completes correct random access and normal data transmission under large delay conditions by setting a suitable uplink frame structure and uplink subframe scheduling strategy.

[0012] The time synchronization method for 4G FDD stock terminals directly connected to satellites includes the following steps:

[0013] Step 1: In the first step of random access, the terminal sends a preamble sequence Msg1 to the base station, and the base station postpones 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 the integer part τ i and the fractional part τ f ;

[0015] Step 3: The base station calculates the integer part of the delay τ based on the time delay divided in step 2 i and the fractional part τ f , and according to the fractional delay τ fWhether it is greater than 0.66ms, the terminal is divided into two types; the base station side calculates the corresponding TA value according to the two types of division, and resets the uplink frame structure, based on the uplink frame structure, TA value and the integer part of the delay τ i Execute 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 sending time of Msg3 according to the received TA value. In the third step of random access, the terminal sends Msg3 to the base station, and the base station calculates the uplink receiving time of Msg3 based on the uplink subframe scheduling strategy determined in step 3, so that the base station correctly receives 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 receiving 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 time of the channel sounding reference signal SRS, the uplink control channel PUCCH, and the uplink shared channel PUSCH according to the uplink subframe scheduling strategy given in step 3, and ensures the correct reception of the channel sounding reference signal SRS, the uplink control channel PUCCH, and the uplink shared channel PUSCH sent by the terminal without modifying the terminal.

[0019] The step 1 comprises 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 nearest and farthest points of the terminal from the base station based on the ephemeris information and the beam coverage, and determines the minimum delay value τ based on the distance between the nearest and farthest points. min and the maximum value τ max ;

[0021] Step 1.2: After determining the delay range in step 1.1, the base station postpones the starting position of the preamble sequence detection window by τ min time, the window size is expanded to τ max -τ min , so that the base station can correctly receive the leading sequence Msg1.

[0022] The step 2 comprises the following steps:

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

[0024] Step 2.2: Under FDD, a single 4G subframe is 1 ms. Based on the delay estimated in step 2.1, divide the delay into integer parts τ in units of 1 ms. i and the fractional part τ f , the integer part τ i Represents the complete number of milliseconds of the delay, and the fractional part τ f Indicates that except for the integer part τ i The remaining delay.

[0025] The step 3 comprises the following steps:

[0026] Step 3.1: Since the maximum adjustable delay of the TA value supported by the LTE standard is 0.66ms, the fractional part of the delay τ f Terminals are divided into two types: type 1 and type 2:

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

[0028] If the fractional part of the delay is 0.66ms<τ f <1ms, then the TA value is τ f -0.5, 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 base station uplink frame period is 10ms, and each frame contains 10 subframes. For the two types divided in step 3.1, in order to avoid interference between the uplink information of the two terminal types, the base station adopts a new uplink frame structure so that the uplink information of the two terminal types can be correctly received at the same time. There are two specific types:

[0030] Structure 1: In the uplink frame 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 frame 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, and ensures that both type 1 and type 2 uplink information arrive at the time specified in the new uplink frame structure through scheduling. The base station i Calculate the correct reception time of uplink information of different types of terminals. Since the sending timing of uplink information is determined by the corresponding downlink control information, the corresponding downlink control information sending time is calculated according to the uplink information arrival time.

[0033] The step 4 comprises the following steps:

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

[0035] Step 4.2: After the terminal receives Msg2 sent by the base station in step 4.1, in the third step of random access, the terminal first determines the uplink subframe transmission time according to the TA value according to the LTE standard, and then sends Msg3 in the specified uplink subframe according to the Msg3 scheduling information; the base station sends Msg3 according to the integer part of the delay τ i Calculate the correct reception time of Msg3, that is, the base station delays the integer part τ based on the Msg3 reception time specified by LTE i The subframe receives Msg3 to ensure the normal reception of Msg3.

[0036] The 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 sending subframe according to the LTE regulations and sends HARQ to the base station at the subframe time. At the same time, the base station calculates the delay integer part τ i Calculate the HARQ reception time, that is, the base station delays the integer part τ based on the HARQ timing specified by LTE i HARQ is received in each subframe to ensure normal reception of HARQ.

[0038] The step 6 comprises the following steps:

[0039] After random access is completed, the base station determines the uplink reception time of the channel sounding reference signal SRS, the uplink control channel PUCCH, and the uplink shared channel PUSCH, as follows:

[0040] For the channel sounding reference signal SRS, the base station calculates the delay integer part τ i Determine the channel sounding reference signal SRS reception time, that is, the base station postpones the integer part τ based on the original uplink scheduling reception subframe ireceiving a channel sounding reference signal SRS in each subframe to ensure normal reception of the channel sounding reference signal SRS;

[0041] For the uplink control channel PUCCH, the base station calculates the delay integer part τ i Determine the uplink control channel PUCCH reception time, that is, the base station postpones the integer part τ based on the original uplink scheduling reception subframe i The uplink control channel PUCCH is received in each subframe to ensure normal reception of the uplink control channel PUCCH;

[0042] For the uplink shared channel PUSCH, the base station calculates the delay integer part τ i Determine the uplink shared channel PUSCH reception time, that is, the base station postpones the integer part τ based on the original uplink scheduling reception subframe i The uplink shared channel PUSCH is received in each subframe to ensure normal reception of the uplink shared channel PUSCH.

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

[0044] First: in Msg1, i.e., uplink synchronization, the base station side expands the preamble sequence detection window so that the base station supports a larger delay in the uplink synchronization phase and can maintain synchronization even when the signal propagation delay is large, thereby improving the synchronization capability and communication quality of the network.

[0045] Second: To address the problem that the TA mechanism does not support large delays, the present invention divides the delay into integer parts τ in milliseconds: i and the fractional part τ f , given that the maximum adjustment range of the TA mechanism is 0.66ms, which is less than one subframe, and the fractional part τ f Divided into two categories, type 1 (decimal part τ f Less than 0.66ms) and type2 (fractional 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 and maintain communication accuracy and efficiency even in the case of large latency.

[0046] Third: The present invention provides two base station uplink frame structures. The first frame structure has a higher coverage range, and the second frame structure has a higher spectrum efficiency. The two structures have their own advantages and disadvantages. The appropriate frame structure can be selected according to actual conditions. It can adapt to different scenarios and provides greater flexibility and adaptability.

[0047] Fourth: The present invention only changes the base station side protocol without changing the terminal protocol, completes random access and the reception and transmission of data information, solves the problem that the time delay between the satellite and the ground is far greater than the TA adjustment range, and can be applied to 4G existing terminals under the FDD system, thereby improving the compatibility and practicality of the system and reducing the upgrade costs of operators and users.

[0048] In summary, in the 4G scenario, the present invention expands the preamble sequence detection window, subdivides the delay processing, and provides two frame structure options, thereby realizing the modification of only the base station side protocol without changing the terminal side protocol. It can support a larger delay, improve the synchronization capability, communication efficiency and adaptability of the 4G network, and at the same time reduce the upgrade costs of operators and users and enhance system compatibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a flow chart for implementing the present invention.

[0050] Figure 2 Schematic diagram of the existing AST and Stailink delay processing strategy.

[0051] Figure 3 This is the architecture diagram of the existing stock terminal direct-connected satellite system.

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

[0053] Figure 5 Schematic diagram of the existing timing advance TA concept.

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

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

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

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

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

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

[0060] Fig.12 This is the schematic diagram of the existing RAR window.

[0061] Fig.13 This is a schematic diagram of the existing Msg4 receiving window.

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

[0063] Fig.15 This is a schematic diagram of the maximum delay supported by the second frame structure of the present invention. DETAILED DESCRIPTION

[0064] The present invention will be described in detail below in conjunction with the accompanying drawings.

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

[0066] The duplex mode of the present invention adopts the FDD mode. There are two main implementation architectures in the satellite communication system: transparent load and regenerative load. In the transparent load architecture, the satellite mainly serves as a relay link between the user terminal and the gateway station and does not process the signal content. In the regenerative load architecture, the satellite not only forwards the signal, but also has the function of a base station and can process the signal, thereby reducing the delay of signal transmission. The present invention not only supports the regenerative load mode, but is also compatible with the transparent load mode to meet the needs of different users and application scenarios.

[0067] Reference Figure 4 In the communication system, the base station and the terminal need to complete the cell search and random access process first for communication. The specific process is as follows:

[0068] During the cell search process, the user terminal first searches for downlink synchronization signals, including the primary synchronization signal (PSS) and the secondary synchronization signal (SSS), within the supported frequency band according to its own frequency and bandwidth. Subsequently, the terminal obtains basic information about the network by decoding the physical broadcast channel (PBCH). The PBCH carries the network's main information block (MIB), which provides the parameters required to decode other system information blocks (SIBs). The terminal searches and selects cells based on the SIB information, determines the most suitable cell for communication, and completes the cell search.

[0069] After the cell search is completed, the random access process begins. There are four steps in random access, as follows:

[0070] In the first step of random access, the terminal uses the physical random access channel PRACH to send Msg1. 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 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 through 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 the random access is completed.

[0074] See also Figure 1 , a time synchronization method for 4G FDD stock terminals directly connected to satellites, comprising the following steps:

[0075] Step 1: In the first step of random access, the terminal sends a preamble sequence Msg1 to the base station, and the base station postpones 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 nearest and farthest points of the terminal from the base station based on the ephemeris information and the beam coverage, and determines the minimum delay value τ based on the distance between the nearest and farthest points. min and the maximum value τ max ;

[0077] Step 1.2: After determining the delay range in step 1.1, the base station postpones the starting position of the preamble sequence detection window by τ min time, the window size is expanded to τ max -τ min , so that the base station can correctly receive the leading sequence Msg1.

[0078] That is, after the base station determines the delay range, it postpones the starting position of the preamble sequence detection window by τ min time, the window size is τ max -τ min , thus ensuring that all leading sequences Msg1 sent by users are within τ min Arrived after time and all within τ max -τ min The window allows the base station to correctly receive the leading 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 the integer part τ i and the fractional part τ f :

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

[0081] Step 2.2: Under FDD, a single 4G subframe is 1 ms. Based on the delay estimated in step 2.1, divide the delay into integer parts τ in units of 1 ms. i and the fractional part τ f , the integer part τ i Represents the complete number of milliseconds of the delay, and the fractional part τ f Indicates that except for the integer part τ i The remaining delay size;

[0082] Reference Figure 5 The terminal uses the TA mechanism to determine the time to send the uplink subframe. The TA value actually represents a negative offset, that is, how much time in advance the terminal sends the uplink subframe after receiving the downlink subframe from the base station. The base station calculates the TA value of each terminal to ensure that even for a terminal that is far away, its uplink information can reach the base station almost at the same time as the uplink information of a terminal that is close to it.

[0083] In 4G, after receiving the leading 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 sending time of its uplink information according to the received TA value;

[0084] In 4G, the TA value ranges from 0 to 1282, the granularity of uplink synchronization 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 Indicates TA value, N TA Indicates the delay corresponding to the TA value, 16Ts = 0.52μs, therefore, the maximum delay that TA can adjust is about 0.66ms, and the maximum transmission distance represented by the round-trip delay of 0.66ms is about 99km. This range is only applicable to the ground environment, but not to satellite-to-ground transmission. The estimated delay in the preamble sequence Msg1 is represented by τ (in milliseconds). When the delay is less than 0.66ms, the corresponding relationship between the delay and TA is as follows:

[0087]

[0088] Among them, τ represents the size of the delay, T A Indicates the TA value corresponding to the delay.

[0089] The altitude of low-orbit satellites is usually between 200-2000km. The support range of 4G's TA mechanism is only 99km, which is much smaller than the round-trip distance between the terminal and the satellite communication.

[0090] In the first step of random access, the terminal sends the preamble sequence Msg1 to the base station. After the base station correctly receives the preamble sequence Msg1, it decodes and obtains the delay (τ). However, since the adjustment range of TA is limited to 0.66ms, which is much smaller than the satellite-to-ground delay, the TA mechanism needs to be modified. Specifically, in units of subframes (i.e., 1 millisecond), the estimated delay is divided into two parts: the integer part τ i and the fractional part τ f , where τ = τ i +τ f , integer part τ i Saved by the base station itself, used to determine the uplink reception time, the decimal part τ f Then it is sent to the terminal to determine the TA value. The terminal does not know the integer part of the delay τ i existence.

[0091] Step 3: The base station calculates the integer part of the delay τ based on the time delay divided in step 2 i and the fractional part τ f , and according to the fractional delay τ f Whether it is greater than 0.66ms, the terminal is divided into two types; the base station side calculates the corresponding TA value according to the two types of division, and resets the uplink frame structure, based on the uplink frame structure, TA value and the integer part of the delay τ i Execute corresponding uplink subframe scheduling strategy;

[0092] Step 3.1: Since the maximum adjustable delay of the TA value supported by the LTE standard is 0.66ms, the fractional part of the delay τ f Terminals are divided into two types: type 1 and type 2:

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

[0094] If the fractional part of the delay is 0.66ms<τ f <1ms, then the TA value is τ f-0.5, 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 base station uplink frame period is 10ms, and each frame contains 10 subframes. For the two types divided in step 3.1, in order to avoid interference between the uplink information of the two terminal types, the base station adopts a new uplink frame structure so that the uplink information of the two terminal types can be correctly received at the same time. There are two specific types:

[0096] like Figure 6 As shown, structure 1: in the uplink frame of the base station, subframes with atomic frame numbers 0, 3, 6, and 9 specifically receive type 1 information, and subframes with atomic frame numbers 1, 2, 4, 5, 7, and 8 specifically receive type 2 information;

[0097] like Figure 7 As shown, structure 2: in the uplink frame of the base station, subframes with atomic frame numbers 0, 1, 2, 3, 4, and 5 specifically receive type 1 information, and subframes with atomic frame numbers 6, 7, 8, and 9 specifically receive type 2 information;

[0098] Considering that the starting points of type 1 and type 2 uplink information are at the beginning of the subframe and the middle of the subframe respectively, if no intervention is performed, type 1 and type 2 uplink information will inevitably cause certain interference. In order to optimize data reception, considering that after random access is completed, the frame structure of the base station must match the sending period of CSI, SRS, and SR. The sending period of CSI, SRS, and SR is 5ms, 10ms, 20ms, 40ms, 80ms, etc. Therefore, the uplink frame structure of the base station needs to be modified. The uplink frame structure of the base station adopts a one-frame-one-period strategy, and 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, and the second frame structure has a total of 6 type 1 subframes and 3 type 2 subframes. Compared with the first frame structure, the second frame structure has a larger number of type subframes, that is, higher spectrum efficiency, but due to the limitation of the RAR window, the second frame structure causes the maximum supported transmission distance to be much smaller, 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 technologies 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, and ensures that both type 1 and type 2 uplink information arrive at the time specified in the new uplink frame structure through scheduling. The base station i Calculate the correct reception time of uplink information of different types of terminals. Since the sending time of uplink information is determined by the corresponding downlink control information, the corresponding downlink control information sending time is calculated according to the arrival time of uplink information;

[0101] Reference Figure 8 , the base station uses the fractional part of the terminal's delay τ f The terminals are divided into two types. For this purpose, the uplink scheduling strategy needs to be modified to ensure that the uplink subframes of different users arrive at the base station at the correct type of subframe time. The transmission of uplink information is scheduled and guided by the corresponding downlink control information. The base station instructs the terminal when and how to send uplink information by sending downlink control information. Assuming that the downlink control information is sent in a subframe of n, the uplink information arrival subframe is n'=n+τ i +k, where τ i Indicates the integer part of the delay, and k represents the time interval from the terminal side receiving the downlink control information to sending the uplink information. In 4G, the value of k is specified by the protocol. For details, please refer to Chapter 8 and Chapter 10 of 3GPP protocol 36213. In FDD, the value of k is usually 4 and 6.

[0102] If the fractional part of the delay τ f <0.66ms, it is necessary to ensure that the uplink information arrives in the type1 subframe, the fractional part of the delay τ f When >0.66ms, it is necessary to ensure that the uplink information arrives in the type 2 subframe, so the base station should determine the appropriate n' value so that the uplink information can arrive in the specified type of subframe, according to n = n'-τ i -k determines the timing of sending the downlink control subframe, and then applies the scheduling strategy 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 sending time of Msg3 according to the received TA value. In the third step of random access, the terminal sends Msg3 to the base station, and the base station calculates the uplink receiving time of Msg3 based on the uplink subframe scheduling strategy determined in step 3, so that the base station correctly receives Msg3 sent by the terminal;

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

[0105] Step 4.2: After the terminal receives Msg2 sent by the base station in step 4.1, in the third step of random access, the terminal first determines the uplink subframe transmission time according to the TA value according to the LTE standard, and then sends Msg3 in the specified uplink subframe according to the Msg3 scheduling information; the base station sends Msg3 according to the integer part of the delay τ i Calculate the correct reception time of Msg3, that is, the base station delays the integer part τ based on the Msg3 reception time specified by LTE i Receive Msg3 in each subframe to ensure normal reception of Msg3;

[0106] Reference Fig. 9 , is a schematic diagram of the type 1 delay Msg2 / Msg3 timing. If the subframe in which Msg2 is sent is n, the subframe in which Msg3 arrives is n'=n+τ i +k, where τ i The integer part of the delay τ i , k represents the receiving and sending interval on the terminal side. According to the 3GPP 36213 protocol, in FDD, the value of k is 6. In order to ensure the fractional part of the delay τ f When the uplink subframes are less than 0.66ms, all the uplink subframes are received in the type 1 subframes. The base station first determines the n' value so that the arrival time of Msg3 belongs to the type 1 subframe, and then determines the sending subframe of Msg2 to be n = n'-k-τ i .

[0107] Reference Fig.10 , is a schematic diagram of the type 2 delay Msg2 / Msg3 timing, similar to the type 1 delay, in order to ensure the fractional part of the delay τ f When it is greater than 0.66ms, the uplink information is all received in the type2 subframe. The base station first determines the n' value so that the arrival time of Msg3 belongs to the type2 subframe. Since the uplink information is offset by 0.5τ at this time s Arrival, uplink information is distributed in two subframes, so the base station side needs to obtain the uplink information from the second half of the n' subframe and the first half of the n'+1 subframe. According to the n' value, the sending subframe of 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 receiving 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 sending subframe according to the LTE regulations and sends HARQ to the base station at the subframe time. At the same time, the base station calculates the delay integer part τ i Calculate the HARQ reception time, that is, the base station delays the integer part τ based on the HARQ timing specified by LTE i HARQ is received in each subframe to ensure normal reception of HARQ.

[0110] Reference Fig.11 After receiving Msg4, the terminal completes the fourth step of random access. After k subframes, it sends downlink HARQ to the base station through PUCCH, and the base station sends downlink data information after random access. After k subframes, it also sends downlink HARQ to the base station through PUCCH. Msg4 and downlink information are sent through PDSCH, and downlink HARQ is sent through PUCCH. Therefore, these two situations are divided into one category, where the k value represents the receiving and sending interval of PDSCH and HARQ on the terminal side. Referring to the 3GPP36213 protocol, in FDD, the k value is 4. Assuming that the sending time of PDSCH is n, the arrival time of downlink HARQ is n'=n+k+τ i Similarly, HARQ is also divided into two cases, type 1 (τ f <0.66ms) and type2 (τ f >0.66ms). The base station first determines the value of n' so that the downlink HARQ arrives in the specified type of 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 time of the channel sounding reference signal SRS, the uplink control channel PUCCH, and the uplink shared channel PUSCH according to the uplink subframe scheduling strategy given in step 3, and ensures the correct reception of the channel sounding reference signal SRS, the uplink control channel PUCCH, and the uplink shared channel PUSCH sent by the terminal without modifying the terminal:

[0112] After random access is completed, the base station determines the uplink reception time of the channel sounding reference signal SRS, the uplink control channel PUCCH, and the uplink shared channel PUSCH, as follows:

[0113] For the channel sounding reference signal SRS, the base station calculates the delay integer part τ i Determine the channel sounding reference signal SRS reception time, that is, the base station postpones the integer part τ based on the original uplink scheduling reception subframe i receiving a channel sounding reference signal SRS in each subframe to ensure normal reception of the channel sounding reference signal SRS;

[0114] SRS is a channel sounding reference signal. The base station evaluates the uplink channel quality by receiving the SRS signal. SRS is divided into two types: periodic and non-periodic.

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

[0116]

[0117] Among them, n f Indicates the system frame number, n s Indicates the time slot number, Indicates the subframe number, T PERIODICITY Indicates the sending cycle, N OFFSET It represents the subframe offset, indicating in which subframe the SRS is sent.

[0118] The SRS transmission period is available in 2ms, 5ms, 10ms, 20ms, 40ms, 80ms, 160ms, and 320ms. Since it needs to correspond to the base station frame structure, the base station frame structure period is 10ms, so the SRS transmission period cannot be set to 2ms and 5ms. For other periods, users can freely choose according to their needs. 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 type1 subframe, if the fractional part of the delay τ f >0.66ms, the SRS is controlled to arrive in the type 2 subframe.

[0119] For the uplink control channel PUCCH, the base station calculates the delay integer part τ i Determine the uplink control channel PUCCH reception time, that is, the base station postpones the integer part τ based on the original uplink scheduling reception subframe i The uplink control channel PUCCH is received in each subframe to ensure normal reception of the uplink control channel PUCCH;

[0120] For the uplink shared channel PUSCH, the base station calculates the delay integer part τ i Determine the uplink shared channel PUSCH reception time, that is, the base station postpones the integer part τ based on the original uplink scheduling reception subframe i The uplink shared channel PUSCH is received in each subframe to ensure normal reception of the uplink shared channel PUSCH.

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

[0122] CSI is the downlink channel state information. The base station sends CSI_RS as CSI reference information for measuring the downlink channel state information. The terminal obtains the downlink channel quality information, namely CSI, by measuring CSI_RS and reports the CSI information to the base station. CSI is divided into periodic and non-periodic types. For periodic CSI, the transmission time satisfies the following formula:

[0123]

[0124] Among them, n f Indicates the system frame number, n s Indicates the time slot number, Indicates the subframe number, N OFFSET Indicates the subframe offset, T PERIODICITY Indicates the sending cycle, N OFFSET Indicates in which subframe the CSI is sent.

[0125] The CSI transmission period is 5ms, 10ms, 20ms, 40ms, and 80ms. Since it needs to correspond to the base station frame structure, the base station frame structure period is 10ms, so the CSI transmission period cannot be set to 5ms. For other periods, users can freely choose according to their needs. At the same time, since CSI is sent through the uplink channel, the subframe offset needs to be based on the fractional part of the delay τ f Select, if the fractional part of the delay τ f <0.66ms, control CSI to arrive in type1 subframe, if the fractional part of delay τ f >0.66ms, the CSI is controlled to arrive in the type 2 subframe.

[0126] For non-periodic CSI, it is necessary to calculate the fractional part of the delay τ f The type pre-calculates in which subframe the CSI information arrives, and then determines the time to send the downlink control information and calculates the TA value. The base station delays reception according to the scheduling information;

[0127] SR is an uplink scheduling request. For SR, the terminal tells the base station through SR that uplink resources are needed for ULSCH transmission. The sending of SR is periodic, and the period is controlled by sr-ConfigIndex. The specific corresponding relationship is as follows.

[0128]

[0129] Among them, n f Indicates the system frame number, n s Indicates the time slot number, Indicates subframe number, SR PERIODICITY Indicates the sending cycle, NOFFSET,SR Indicates the subframe offset, indicating in which subframe the SR is sent.

[0130] The SR transmission period is available in 1ms, 2ms, 5ms, 10ms, 20ms, 40ms, and 80ms. Since it needs to correspond to the base station frame structure, the base station frame structure period is 10ms, so the SR transmission period cannot be set to 1ms, 2ms, and 5ms. For other periods, users can freely choose according to their needs. f The size selects the subframe offset. If the fractional part of the delay τ f <0.66ms, control SR to arrive in type1 subframe, if the fractional part of delay τ f >0.66ms, the SR is controlled to arrive in the type2 subframe.

[0131] For the uplink shared channel PUSCH, the base station calculates the delay integer part τ i Determine the uplink shared channel PUSCH reception time, that is, the base station postpones the integer part τ based on the original uplink scheduling reception subframe i The uplink shared channel PUSCH is received in each subframe to ensure normal reception of the uplink shared channel PUSCH;

[0132] The uplink data information and the terminal buffer status report BSR are sent to the base station through the PUSCH. The base station modifies the PUSCH according to the uplink subframe scheduling strategy as follows:

[0133] The base station determines the transmission time of PUSCH through scheduling, and sends the scheduling information to the terminal through downlink control information. After receiving the downlink control information, the terminal sends PUSCH at the specified time. The base station postpones the integer part τ based on the original uplink scheduling reception subframe i The uplink shared channel PUSCH is received in each subframe to ensure normal reception of the uplink shared channel PUSCH.

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

[0135] Reference Fig.12 , Fig.12This is the RAR window principle diagram. The terminal opens the RAR window in the third subframe after sending the Msg1 subframe, and continues to monitor ra-ResponseWindowSize subframes. During the RAR window, the terminal will monitor the PDCCH to receive the Msg2 sent by the base station. If the terminal fails to receive the Msg2 during the RAR window, the random access process fails. In the 3GPP protocol, the RAR window ranges from 2 to 10 subframes, so the maximum duration of the RAR window is 10 subframes. This means that the total time from the terminal sending Msg1 to receiving Msg2 must be less than or equal to 13 subframes to ensure that the terminal can successfully receive the RAR.

[0136] Reference Fig.13 , Fig.13 This is the 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 resolution is considered successful. In 4G, the Contention Resolution Timer can reach a maximum of 64ms.

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

[0138] Consider calculating the delay range supported by the two frame structures, and then get the longest transmission. Taking the leading sequence type as format 0 as an example, assuming that the round-trip propagation delay is τ, the sending time of Msg1 is n, and the receiving time is n+0.5τ, τ max Indicates the maximum value of the leading sequence detection window. The ending time of the leading sequence detection window is n+τ max , Δ represents the time interval from the end of the preamble sequence detection window to the sending of Msg2, and the sending time of Msg2 is n+τ max +Δ, the receiving time of Msg2 is 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 processed as 1 subframe, which needs to meet the following two conditions:

[0139] 1. The time when Msg1 reception ends must be within the leading sequence detection window, that is:

[0140] n+0.5τ+1≤n+τ max

[0141] 2. The time interval from sending Msg1 to the end of receiving Msg2 is less than the length of the RAR window, that is:

[0142] (n+τ max +Δ+0.5τ+1)-(n)≤13

[0143] By solving the above two equations, we can obtain that τ<11-Δ. When Δ takes the maximum value, the range of τ that is still supported is the supported range of the delay.

[0144] Reference Fig.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 sending of Msg2. If the fractional part of the delay τ f The type is type2, refer to Fig.14 As shown, at this time, 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 sending of Msg2 and send Msg2 3 subframes after the end of the preamble sequence detection window. At this time, the corresponding receiving subframe number of Msg3 is 1, which meets the frame structure requirements. At this time, the interval from the end of the preamble sequence detection window to the sending of Msg2 is 3 subframes. Similarly, according to this method, the interval from the end of the preamble sequence detection window to the sending of Msg2 in other cases can be obtained. Finally, it can be obtained that the interval is between 0 and 3 subframes, and the maximum value of Δ can be obtained as 3. From τ≤11-Δ, τ≤8, so the supported round-trip delay range is about 0 to 8ms, and the maximum transmission distance corresponding to the 8ms round-trip delay is about 1200km.

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

[0146] The altitude of low-orbit satellites is usually between 200 and 2000 km. It can be seen that the first base station frame structure has a larger coverage range, and the second frame structure has a higher spectrum efficiency. The appropriate frame structure can be selected based on the satellite orbit.

Claims

1. A time synchronization method for 4G FDD stock terminals directly connected to satellites, characterized in that: In the Msg1 phase of random access, no modification is required to the terminal. The base station side only postpones and expands the preamble sequence detection window to provide a basis for supporting the detection of larger delays. In the subsequent steps of random access and the data transmission phase, no modification is required to the terminal. The base station side sets a suitable uplink frame structure and uplink subframe scheduling strategy to complete correct random access and normal data transmission under large delay conditions.

2. A time synchronization method for 4G FDD stock terminals directly connected to satellites, characterized in that: The following steps are involved: Step 1: In the first step of random access, the terminal sends a preamble sequence Msg1 to the base station, and the base station postpones 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 the integer part τ i and the fractional part τ f ; Step 3: The base station calculates the integer part of the delay τ based on the time delay divided in step 2 i and the fractional part τ f , and according to the fractional delay τ f Whether it is greater than 0.66ms, the terminal is divided into two types; the base station side calculates the corresponding TA value according to the two types of division, and resets the uplink frame structure, based on the uplink frame structure, TA value and the integer part of the delay τ i Execute corresponding uplink subframe scheduling strategy; 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 sending time of Msg3 according to the received TA value. In the third step of random access, the terminal sends Msg3 to the base station, and the base station calculates the uplink receiving time of Msg3 based on the uplink subframe scheduling strategy determined in step 3, so that the base station correctly receives 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 receiving 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 time of the channel sounding reference signal SRS, the uplink control channel PUCCH, and the uplink shared channel PUSCH according to the uplink subframe scheduling strategy given in step 3, and ensures the correct reception of the channel sounding reference signal SRS, the uplink control channel PUCCH, and the uplink shared channel PUSCH sent by the terminal without modifying the terminal.

3. The time synchronization method for 4G FDD stock terminals directly connected to satellites according to claim 2 is characterized in that: The step 1 comprises 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 nearest and farthest points of the terminal from the base station based on the ephemeris information and the beam coverage, and determines the minimum delay value τ based on the distance between the nearest and farthest points. min and the maximum value τ max ; Step 1.2: After determining the delay range in step 1.1, the base station postpones the starting position of the preamble sequence detection window by τ min time, the window size is expanded to τ max -τ min , so that the base station can correctly receive the leading sequence Msg1.

4. The time synchronization method for 4G FDD stock terminals directly connected to satellites according to claim 2 is characterized in that: The step 2 comprises the following steps: Step 2.1: The base station correctly receives the preamble sequence Msg1 in the expanded preamble sequence detection window and estimates the delay; Step 2.2: Under FDD, a single 4G subframe is 1 ms. Based on the delay estimated in step 2.1, divide the delay into integer parts τ in units of 1 ms. i and the fractional part τ f , the integer part τ i Represents the complete number of milliseconds of the delay, and the fractional part τ f Indicates that except for the integer part τ i The remaining delay.

5. The time synchronization method for 4G FDD stock terminals directly connected to satellites according to claim 2, characterized in that: The step 3 comprises the following steps: Step 3.1: Since the maximum adjustable delay of the TA value supported by the LTE standard is 0.66ms, the fractional part of the delay τ f Terminals are divided into two types: type 1 and type 2: If the fractional part of the delay is 0ms≤τ f ≤0.66ms, then the TA value is τ f At this time, the uplink information sent by the terminal arrives at the base station synchronously, which is a type 1 terminal; If the fractional part of the delay is 0.66ms<τ f <1ms, then the TA value is τ f -0.5, 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 base station uplink frame period is 10ms, and each frame contains 10 subframes. For the two types divided in step 3.1, in order to avoid interference between the uplink information of the two terminal types, the base station adopts a new uplink frame structure so that the uplink information of the two terminal types can be correctly received at the same time. There are two specific types: Structure 1: In the uplink frame 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 frame 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, and ensures that both type 1 and type 2 uplink information arrive at the time specified in the new uplink frame structure through scheduling. The base station i Calculate the correct reception time of uplink information of different types of terminals. Since the sending timing of uplink information is determined by the corresponding downlink control information, the corresponding downlink control information sending time is calculated according to the uplink information arrival time.

6. The time synchronization method for 4G FDD stock terminals directly connected to satellites according to claim 2, characterized in that: The step 4 comprises the following steps: Step 4.1: After receiving Msg1, the base station sends Msg2 to the terminal in the second step of random access. Msg2 includes the TA value and the scheduling information of Msg3; Step 4.2: After the terminal receives Msg2 sent by the base station in step 4.1, in the third step of random access, the terminal first determines the uplink subframe transmission time according to the TA value according to the LTE standard, and then sends Msg3 in the specified uplink subframe according to the Msg3 scheduling information; the base station sends Msg3 according to the integer part of the delay τ i Calculate the correct reception time of Msg3, that is, the base station delays the integer part τ based on the Msg3 reception time specified by LTE i The subframe receives Msg3 to ensure the normal reception of Msg3.

7. The time synchronization method for 4G FDD existing terminals directly connected to satellites according to claim 2, characterized in that: The 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 sending subframe according to the LTE regulations and sends HARQ to the base station at the subframe time. At the same time, the base station calculates the delay integer part τ i Calculate the HARQ reception time, that is, the base station delays the integer part τ based on the HARQ timing specified by LTE i HARQ is received in each subframe to ensure normal reception of HARQ.

8. The time synchronization method for 4G FDD stock terminals directly connected to satellites according to claim 2, characterized in that: The step 6 comprises the following steps: After random access is completed, the base station determines the uplink reception time of the channel sounding reference signal SRS, the uplink control channel PUCCH, and the uplink shared channel PUSCH, as follows: For the channel sounding reference signal SRS, the base station calculates the delay integer part τ i Determine the channel sounding reference signal SRS reception time, that is, the base station postpones the integer part τ based on the original uplink scheduling reception subframe i receiving a channel sounding reference signal SRS in each subframe to ensure normal reception of the channel sounding reference signal SRS; For the uplink control channel PUCCH, the base station calculates the delay integer part τ i Determine the uplink control channel PUCCH reception time, that is, the base station postpones the integer part τ based on the original uplink scheduling reception subframe i The uplink control channel PUCCH is received in each subframe to ensure normal reception of the uplink control channel PUCCH; For the uplink shared channel PUSCH, the base station calculates the delay integer part τ i Determine the uplink shared channel PUSCH reception time, that is, the base station postpones the integer part τ based on the original uplink scheduling reception subframe i The uplink shared channel PUSCH is received in each subframe to ensure normal reception of the uplink shared channel PUSCH.

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