A method for reducing access latency of a low earth orbit satellite communication system

Abstract

The present application relates to the technical field of satellite communication, in particular to a method for reducing access delay of low-orbit satellite communication system, comprising: completing random access process through two-step signaling interaction, wherein the terminal sends random access request to the satellite communication system through the resource for transmitting random access request indicated by the system message for the terminal in the first step; the terminal receives the random access response sent by the satellite communication system in the second step and completes contention resolution according to the received random access response; and the network allocates dedicated burst configuration for the terminal through the random access response message; the present application completes random access process through two-step signaling interaction, ensures that the terminal accesses to the network quickly, and thus reduces the access delay of the terminal to the satellite communication system.

Description

Technical Field

[0001] This invention relates to the field of satellite communication technology, and in particular to a method for reducing access latency in low-Earth orbit satellite communication systems. Background Technology

[0002] Low Earth Orbit (LEO) satellite communication plays a vital role in modern life. LEO satellite communication systems offer advantages such as wide coverage, insensitivity to ground conditions, high channel quality, stable transmission performance, strong disaster tolerance, and the cost of communication equipment does not increase with distance. Currently, LEO satellite communication has become an important component of terrestrial mobile communication, especially in areas where terrestrial networks are difficult to cover, such as deserts, the air, and oceans. Furthermore, LEO satellite communication channels operate in the microwave frequency range, where frequency resources are relatively abundant.

[0003] Because low-Earth orbit (LEO) satellite voice communication systems have complex links and are characterized by greater latency compared to terrestrial communication, the signaling and voice service processes have a significant impact on the user experience. Therefore, optimizing the latency of the signaling process is of great importance. Summary of the Invention

[0004] This invention primarily aims to shorten the latency of a terminal accessing a satellite communication system. It proposes a novel random access design method that employs a two-step signaling interaction to complete the process of a terminal randomly accessing a satellite communication system, including:

[0005] Step 1: The terminal sends a RACH burst to the satellite communication system via an initial system message; the initial system message contains resources to instruct the terminal to transmit the RACH burst; RACH stands for Random Access Channel;

[0006] Step 2: The terminal receives the random access response message through the system message indicating the resource for receiving the random access response message, and completes the contention resolution based on the received random access response message, thus completing the process of the terminal accessing the satellite communication system.

[0007] Preferably, the RACH burst sent by the terminal includes a pilot sequence and a data payload; the terminal sends the RACH burst to the satellite communication system in burst form via the pilot sequence at the random access transmission timing advance indicated by the initial system message; the pilot sequence is a random number or sequence code, and the data payload is common control channel data or media access control layer control unit data, which are distinguished by the logical channel identifier (LCID) in the MAC header.

[0008] Furthermore, the initial system message indicates to the terminal the resources used for transmitting the RACH burst, including: frequency band identifier, carrier identifier, radio frame allocation mode identifier, time slot position within the radio frame used to transmit the RACH burst, and RACH timing advance information.

[0009] Furthermore, the initial system message indicates to the terminal the resource method used for transmitting RACH bursts, including:

[0010] By reserving random access resources by setting multiple carriers;

[0011] The available random access request transmission carriers are indicated by the bitmap configuration method, and the bitmap length depends on the number of carriers in the frequency band division;

[0012] The wireless frame allocation mode is indicated by a predefined mapping table index, and the required wireless frame mode is defined according to the number of users accessing the network.

[0013] The corresponding frame division mode is determined by the index value of the System Information Block (SIB) indicator table, thereby determining the available radio frames;

[0014] RACH bursts are sent at the time indicated by the system message advance based on the determined time-domain resources.

[0015] Preferably, after the terminal sends a RACH burst, the system message indicates to the terminal the resources used to receive the random access response message, including:

[0016] Frequency band identifier, carrier identifier, radio frame allocation mode identifier, time slot position and response window length within the radio frame used for the physical burst of the random access response.

[0017] Furthermore, the system message indicates the starting timeslot index for listening to the random access response channel during the process of the terminal instructing the resources used to receive the random access response message.

[0018] Preferably, the random access response message includes: a MAC subheader, a contention resolution identifier, time offset adjustment information and frequency offset adjustment information, burst time-frequency domain resource configuration information for dedicated channel transmission and reception, and burst time-frequency domain resource configuration information for synchronization channel; wherein, the MAC subheader contains a random access transmission timing indication field for distinguishing user groups, a contention resolution identifier for distinguishing random access response messages of users within the same group, and an L field for indicating the length of the random access response message.

[0019] Furthermore, the ROID in the MAC subheader format of the random access response message is the random access opportunity ID determined based on the time-frequency domain resources of the RACH burst transmission. The ROID is jointly determined by the carrier number, radio frame number, and time slot position of the RACH burst transmission.

[0020] Preferably, the method by which the terminal resolves contention based on the random access response message includes: the terminal jointly identifies and determines its own random access response message by using the pilot sequence RAND information carried in the RACH burst, the ROID in the MAC header of the response message, and the contention resolution identifier in the response message.

[0021] Furthermore, the steps for a terminal to determine its own random access response message are as follows:

[0022] S1: The terminal determines the ROID of the random access opportunity based on the time-frequency domain resource location of the RACH burst. If the ROID field value in the MAC header of the random access response message received by the terminal in the response window does not match the determined value, the terminal UE discards the received random access response message. Otherwise, the received random access response message is retained and S2 is executed.

[0023] S2: Verify whether the contention resolution identifier in the response message is the same as the data payload content in the sent random access physical burst. If they are the same, the contention resolution is successful and the random access process is successfully completed. Otherwise, the contention resolution fails and S3 is executed.

[0024] S3: Continue receiving random access response messages within the response window, and execute S1 and S2 until the response window ends.

[0025] The beneficial effects of this invention are as follows: This invention completes the random access process through two-step signaling interaction and redefines the random access response message transmission format. In the first step, the terminal sends a random access request to the satellite communication system by instructing the terminal to use the resources for transmitting the random access request through system messages. In the second step, the terminal receives the random access response sent by the satellite communication system and completes the contention resolution based on the received random access response. The network allocates a dedicated burst configuration to the terminal through the random access response message to ensure that the terminal can quickly access the network, thereby reducing the latency of the terminal accessing the satellite communication system. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the frequency band division in this invention;

[0027] Figure 2 This is a schematic diagram of wireless frame time slot allocation in this invention;

[0028] Figure 3 This is a schematic diagram of the RACH burst structure design in this invention;

[0029] Figure 4 This is a schematic diagram of the design of the first random access response message MAC subheader format in this invention;

[0030] Figure 5This is a schematic diagram of the design of the second random access response message MAC subheader format in this invention;

[0031] Figure 6 This is a schematic diagram illustrating the design of the random access response message format in this invention;

[0032] Figure 7 This is a schematic diagram of the time-domain location of RACH burst transmission in this invention;

[0033] Figure 8 This is a schematic diagram of the time-domain transmission of the random access response message in this invention;

[0034] Figure 9 This is a schematic diagram of the contention resolution process in this invention. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] A method for reducing access latency to a low-Earth orbit satellite communication system, the method comprising: employing a two-step signaling interaction to complete the process of a terminal randomly accessing the satellite communication system; the specific steps are as follows:

[0037] Step 1: The terminal sends a RACH burst to the satellite communication system via an initial system message; the initial system message contains resources to instruct the terminal to transmit the RACH burst; RACH stands for Random Access Channel;

[0038] Step 2: The terminal receives the random access response message through the system message indicating the resource for receiving the random access response message, and completes the contention resolution based on the received random access response message, thus completing the process of the terminal accessing the satellite communication system.

[0039] The initial system message includes: frequency band identifier, carrier identifier, radio frame allocation mode identifier, time slot position within the radio frame used to transmit the RACH burst, and RACH timing advance information; the initial system message is used to indicate to the terminal the resources for transmitting the RACH burst.

[0040] Furthermore, by reserving random access resources for multiple carriers, terminals have sufficient random access resources to access the satellite communication system. To reduce signaling overhead, available random access request transmission carriers can be indicated through bitmap configuration, with the bitmap length depending on the number of carriers in the frequency band.

[0041] A specific implementation method for indicating random access resources via bitmap configuration includes the following steps in setting the frequency band identifier: if the corresponding bit is set to 1, it indicates that the corresponding carrier has random access resources; if the corresponding bit is set to 0, it indicates that the corresponding carrier does not have random access resources. Preferably, multiple bits can be set to 1 simultaneously during the frequency band identifier setting process. Figure 1 If the frequency band is divided into 3 carriers, and both carrier 1 and carrier 3 have random access resources, then the bitmap configuration is 101.

[0042] Furthermore, to reduce frame allocation signaling overhead, short-cycle repetitive allocation can be used to indicate the radio frames transmitted for random access requests. A mapping table is predefined, and the radio frame allocation mode is indicated by the table index. The required radio frame mode is defined according to the number of users accessing the network. The corresponding frame allocation mode is determined by indicating the table index value through the System Information Block (SIB) message, thereby determining the available radio frames.

[0043] A specific implementation of a radio frame indicating random access request transmission using a short-cycle repetitive allocation method includes: When multiple data transmissions are performed, to avoid interference between different data transmissions, the radio frame length contains Y slots. RACH burst data occupies N slots during transmission, where N can be fixed or dynamically configured via the protocol (network management configuration or Master Information Block (MIB) indication). Specifically, using N slots as a unit, the total number of units contained in the Y slots can be calculated. This can be indicated using a bitmap or by using index values. For example, if the radio frame contains 4 units, and the bitmap indication is 1010, it means that the first N consecutive slots and the third N consecutive slots from the beginning of the radio frame are available for RACH transmission.

[0044] A specific implementation of indicating a radio frame allocation mode via a table index includes: using N consecutive solitaires as a unit, numbering all N consecutive solitaires, and setting indication parameters according to the numbers to indicate the unit used for RACH transmission. Specifically, as... Figure 2 As shown, for example, there are 4 units, and the index value is needed to indicate the RACH unit that can be used for transmission. 0 indicates the first consecutive N slots, 1 indicates the second consecutive N slots, 2 indicates the third consecutive N slots, 3 indicates the fourth consecutive N slots, 4 indicates the first and second consecutive N slots, 5 indicates the first and third consecutive N slots, and so on. By enumerating the 4 units, a single unit can be indicated for RACH transmission, multiple consecutive units can be indicated for RACH transmission, or a skipped unit can be indicated for RACH transmission.

[0045] At the initial system message indication of the random access transmission timing advance, the terminal transmits the RACH burst in burst form to the satellite communication system via pilot sequence; preferably, the RACH burst structure is designed as follows: Figure 3 As shown, random access request messages are transmitted in the form of physical RACH bursts. A RACH burst contains a pilot sequence and a data payload. The RAND is the pilot sequence, which supports random numbers or sequence codes and is used for user contention resolution. The data payload MAC SDU is common control channel data or media access control layer control unit (MAC CE) data, which is distinguished by the logical channel identifier (LCID) in the MAC header. The MAC SDU can also be used for contention resolution.

[0046] A specific implementation of an initial system message indicating RACH burst resources, such as... Figure 4 As shown, the specific process includes: the initial system message indicates that the RACH burst resources are frequency band identifier = 4, carrier identifier = 0110, radio frame allocation mode identifier = 1, and the time slot in the radio frame used to transmit the RACH burst = 10; according to the initial system message indication, carriers 2 and 3 of frequency band 4 have random access resources. An index and a random access radio frame allocation mode mapping table are defined, and a system information block (SIB) indicates the index of the table. This index specifies that all radio frames in superframe m and multiframe n and multiframe n+2 can be used for RACH burst transmission, and the RACH burst transmission time slot indication parameter is set to 00, meaning that the first N consecutive slots in the determined radio frame can transmit the RACH burst. If the UE determines to transmit a random access request message in radio frame 8 of multiframe n based on the RACH resource configuration and the timing advance information indicated by the system message, and randomly generates a random number of 15, then the UE sends a random access burst message in the first N slots of radio frame 8, with RAND = 15 in the message.

[0047] A specific implementation of indicating resources for receiving random access response messages includes: instructing a terminal via system messages to access resource information for receiving random access response messages. The resource information includes a frequency band identifier, a carrier identifier, a radio frame allocation mode identifier, the time slot position within the radio frame used to transmit the physical burst of the random access response, and the response window length. The carrier identifier indicates which carrier is used to transmit the response message and depends on the parameter length determined by the number of carriers in the frequency band allocation. The radio frame allocation mode identifier is similar to the radio frame allocation indication mode for random access request message transmission, and uses a predefined table index to determine the available radio frames.

[0048] Furthermore, the system message indicates the starting timeslot index of the listening random access response channel during the process of the terminal indicating resources for receiving random access response messages. For physical burst transmission timeslots used for downlink transmission, to avoid interference from other beams with MIB (Master Information Block) transmission, the starting timeslot of other data transmissions should be indicated within P timeslots after excluding the timeslot occupied by the MIB. Assuming each response message transmission occupies M slots, M can be fixed or dynamically configured via the protocol (network management configuration or MIB indication). The positions of the M consecutive slots for transmission can be determined using a bitmap method or by indicating the starting timeslot index.

[0049] After the terminal sends RACH burst data on the selected resource, it starts a random access response window after M radio frames. Within the response window, it receives random access response messages. M is fixed by the protocol or indicated by system messages.

[0050] A random access response message includes: a MAC subheader, a contention resolution identifier, time offset adjustment information and frequency offset adjustment information, burst time-frequency domain resource configuration information for dedicated channel transmission and reception, and burst time-frequency domain resource configuration information for synchronization channel; wherein, the MAC subheader contains a random access transmission timing indication field for distinguishing user groups, a contention resolution identifier for distinguishing random access response messages of users within the same group, and an L field for indicating the length of the random access response message.

[0051] Preferably, the MAC subheader format is designed as follows: ROID is the random access opportunity ID determined according to the time-frequency domain resources of the RACH burst transmission. It is determined by the carrier number, radio frame number, and time slot position of the RACH burst transmission and is used to distinguish user groups; the L field indicates the length of the random access response message.

[0052] There are two solutions for the length L. The first is as follows: Figure 5 As shown, L is 7 bits long and indicates the number of bytes in the response message; the second type is as follows... Figure 6 As shown, L is 2 bits long and indicates whether the random access response message contains one burst configuration, two burst configurations, or no burst configuration. The indication scheme is as follows:

[0053] 00: Indicates that the random access response message does not carry burst configuration;

[0054] 01: Indicates that the random access response message carries one burst configuration;

[0055] 10: Indicates that the random access response message carries two burst configurations.

[0056] like Figure 7As shown, a random access response message format has a burst configuration length of 4 bytes and a maximum of 2 burst configurations. Therefore, the length of the final random access response message can be determined by indicating how many burst configurations the response message contains through the L field in the MAC header.

[0057] like Figure 8 As shown, the system message indicates to the terminal the available resources for receiving random access response messages and the response window length. Available resources include carrier frequency bands, available radio frames, and the time slot positions within a radio frame used for transmitting physical bursts of random access response messages. For example, the SIB indicates a predefined radio frame allocation mode mapping table index, which specifies that all radio frames within superframe m, subframe n, and subframe n+1 can be used for random access response message transmission. The protocol requires M consecutive slots for response message transmission, and the SIB indicates that the second consecutive M slots within the determined radio frame are used for transmitting random access response messages. After the terminal selects the random access resource on the second carrier in radio frame 6 of subframe n to send the random access request message, it starts the random access response window after P radio frames. Receiving random access response messages in the radio frames containing the MIB and SIB should be avoided. Assuming P is 3, the random access response window is started in radio frame 9 of subframe n, and the random access response message is received within the response window according to the time slot positions specified in the radio frame determined by the random access burst resource indication.

[0058] Because the RACH burst transmission resources indicated by the system information are shared resources, if multiple terminals select the same transmission resource, the base station cannot identify the terminals by the resource itself, but can only distinguish them by the terminal identifier in the burst data transmitted by the terminals, and then send a response message. These terminals may receive the same response message, and a contention resolution is required to identify the terminal to which the response message belongs. The terminal identifies and determines its own random access response message by jointly identifying the RAND information carried in the RACH burst, the ROID in the MAC header of the response message, and the contention resolution identifier in the response message.

[0059] like Figure 9 As shown, the terminal determines whether the received random access response message is addressed to itself through a contention-based resolution process. The specific steps are as follows:

[0060] Step 1: The UE determines the ROID based on the time-frequency domain resource location of the transmitted RACH burst.

[0061] If the ROID field value in the MAC header of the random access response message received by the UE within the response window does not match the determined value, the UE discards the received random access response message; otherwise, the received random access response message is retained, and the second step is performed.

[0062] Step 2: Verify whether the contention resolution identifier in the response message is the same as the data payload content in the sent random access physical burst. If they are the same, the contention resolution is successful and the random access process is successfully completed; otherwise, the contention resolution fails and step 3 is executed.

[0063] Step 3: Continue receiving random access response messages within the response window, performing steps 1 and 2 until the response window ends. If no random access response is received within the random access response window, or if none of the received random access responses contain an ROID matching the transmitted random access timing identifier, or if the received response message MAC header contains an ROID matching the transmitted random access timing identifier, but the contention resolution identifier in the response message does not match the transmitted content, then the random access procedure is considered to have failed.

[0064] The above-described embodiments further illustrate the purpose, technical solution, and advantages of the present invention. It should be understood that the above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the present invention within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for reducing access latency in a low-Earth orbit satellite communication system, characterized in that, The process of a terminal randomly accessing a satellite communication system using a two-step signaling interaction includes: Step 1: The terminal sends a RACH burst to the satellite communication system via an initial system message; the initial system message contains resources to instruct the terminal to transmit the RACH burst; RACH stands for Random Access Channel; Step 2: The terminal receives the random access response message using the resource specified by the system message, and resolves contention based on the received message, thus completing the terminal's access to the satellite communication system. The terminal resolves contention based on the random access response message by using the pilot sequence carried in the RACH burst, the random access opportunity ID in the MAC header of the response message, and the contention resolution identifier in the response message to identify and determine its own random access response message. The steps for the terminal to determine its own random access response message are as follows: S1: The terminal determines the ROID of the random access opportunity based on the time-frequency domain resource location of the RACH burst. If the ROID field value in the MAC header of the random access response message received by the terminal in the response window does not match the determined value, the terminal UE discards the received random access response message. Otherwise, the received random access response message is retained and S2 is executed. S2: Verify whether the contention resolution identifier in the response message is the same as the data payload content in the sent random access physical burst. If they are the same, the contention resolution is successful and the random access process is successfully completed. Otherwise, the contention resolution fails and S3 is executed. S3: Continue receiving random access response messages within the response window, and execute S1 and S2 until the response window ends.

2. The method for reducing access latency in a low-Earth orbit satellite communication system according to claim 1, characterized in that, The RACH burst sent by the terminal includes a pilot sequence and a data payload; the terminal sends the RACH burst to the satellite communication system in burst form via the pilot sequence at the random access transmission timing advance indicated by the initial system message. The pilot sequence is a random number or sequence code, and the data payload is common control channel data or media access control layer control unit data, which are distinguished by the logical channel identifier (LCID) in the MAC header.

3. The method for reducing access latency in a low-Earth orbit satellite communication system according to claim 1, characterized in that, The initial system message includes: frequency band identifier, carrier identifier, radio frame allocation mode identifier, time slot position within the radio frame used to transmit the RACH burst, and RACH timing advance information; the initial system message is used to indicate to the terminal the resources for transmitting the RACH burst.

4. The method for reducing access latency in a low-Earth orbit satellite communication system according to claim 1, characterized in that, The initial system message indicates to the terminal the resource method used to transmit RACH bursts, including: By reserving random access resources for carrier waves; The available random access request transmission carriers are indicated by the bitmap configuration method, and the bitmap length depends on the number of carriers in the frequency band division; The wireless frame allocation mode is indicated by a predefined mapping table index, and the required wireless frame mode is defined according to the number of users accessing the network. The corresponding frame division mode is determined by the index value of the System Information Block (SIB) indicator table, thereby determining the available radio frames; RACH bursts are sent at the time indicated by the system message advance based on the determined time-domain resources.

5. The method for reducing access latency in a low-Earth orbit satellite communication system according to claim 1, characterized in that, After the terminal sends a RACH burst, the system message indicates to the terminal the resources used to receive the random access response message, including: Frequency band identifier, carrier identifier, radio frame allocation mode identifier, time slot position within the radio frame used for transmitting random access response, and response window length.

6. The method for reducing access latency in a low-Earth orbit satellite communication system according to claim 1, characterized in that, The system message indicates the starting timeslot index for listening to the random access response channel during the process of the terminal instructing for the resources used to receive the random access response message.

7. The method for reducing access latency in a low-Earth orbit satellite communication system according to claim 1, characterized in that, The random access response message includes: MAC subheader, contention resolution identifier, time offset adjustment information and frequency offset adjustment information, burst time-frequency resource configuration information for dedicated channel transmission and reception, and burst time-frequency resource configuration information for synchronization channel; among them, the MAC subheader contains a random access transmission timing indication field for distinguishing user groups, a contention resolution identifier for distinguishing random access response messages of users within the same group, and an L field for indicating the length of the random access response message.

8. A method for reducing access latency in a low-Earth orbit satellite communication system according to claim 7, characterized in that, The random access opportunity ID in the MAC subheader format of the random access response message is determined by the carrier number, radio frame number, and time slot position of the RACH burst transmission.

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