CN115835407A - Method for reducing access time delay of low-orbit satellite communication system - Google Patents

Abstract

The invention relates to the technical field of satellite communication, in particular to a method for reducing access time delay of a low-earth-orbit satellite communication system, which comprises the following steps: the random access process is completed through two-step signaling interaction, and the terminal sends a random access request to a satellite communication system through a resource which is indicated by a system message for the terminal and is used for transmitting the random access request in the first step; the terminal receives the random access response sent by the satellite communication system in the second step and completes competition resolution according to the received random access response, and the network allocates special burst configuration for the terminal through the random access response message; the invention completes the random access process through two-step signaling interaction, and ensures that the terminal is quickly accessed to the network, thereby reducing the time delay of the terminal accessing the satellite communication system.

Description

Method for reducing access time delay of low-orbit satellite communication system

Technical Field

The invention relates to the technical field of satellite communication, in particular to a method for reducing access time delay of a low-earth-orbit satellite communication system.

Background

Low earth orbit satellite communications is a very important application in today's social life. The low-orbit satellite communication system has the advantages of wide coverage range, insensitivity to ground conditions and the like, the low-orbit satellite communication channel has good quality, stable transmission performance and strong disaster tolerance, and the cost of communication equipment cannot be increased due to the increase of distance. Nowadays, low earth orbit satellite communication has become an important component in the field of terrestrial mobile communication, especially in places difficult to be covered by terrestrial networks such as gobi, air and ocean. In addition, the low-orbit satellite communication channel is in a microwave frequency range, and frequency resources are relatively rich.

Due to the fact that links of the low-orbit satellite voice communication system are complex, the low-orbit satellite communication has the characteristic of being large in time delay compared with ground communication, the influence of the signaling process and the voice service process on the use experience of a user is large, and therefore the method has important significance for time delay optimization of the signaling process.

Disclosure of Invention

The invention mainly aims to shorten the time delay of a terminal accessing a satellite communication system, provides a new random access design method, adopts two-step signaling interaction to complete the process of the terminal randomly accessing the satellite communication system, and comprises the following steps:

the first step is as follows: the terminal sends RACH burst to the satellite communication system through the initial system message; wherein the initial system message contains resources for instructing the terminal to transmit a RACH burst; RACH denotes a random access channel;

the second step is that: and the terminal receives the random access response message through the resource which is indicated by the system message for the terminal and is used for receiving the random access response message, completes the competition solution according to the received random access response message and completes the process of accessing the terminal into the satellite communication system.

Preferably, the RACH burst transmitted by the terminal includes a pilot sequence and a data payload; the terminal sends RACH burst to a satellite communication system in a burst mode through a pilot frequency sequence at the random access sending timing advance time indicated by the initial system message; the pilot sequence is a random number or a sequence code, and the data payload is data of a common control channel or data of a media access control layer control unit and is distinguished by a logical channel identifier LCID in the MAC header.

Further, the initial system message indicating the resources for transmitting the RACH burst for the terminal includes: frequency band identification, carrier identification, radio frame allocation mode identification, time slot position in a radio frame used for transmitting RACH burst and RACH timing advance information.

Further, the initial system message indicates a resource mode for transmitting the RACH burst to the terminal, including:

reserving random access resources by setting a plurality of carriers;

indicating available random access request transmission carriers by a bitmap configuration mode, wherein the bitmap length depends on the number of the carriers divided by the frequency band;

indicating a wireless frame distribution mode through a table index of a predefined mapping table, and defining a required wireless frame mode according to the user number requirement of an access network;

determining a corresponding frame division mode through a system information block SIB indication table index value so as to determine an available wireless frame;

and sending the RACH burst according to the timing advance time indicated by the determined time domain resource advance system message.

Preferably, after the terminal sends the RACH burst, the system message indicating, to the terminal, a resource for receiving the random access response message includes:

frequency band identification, carrier identification, wireless frame allocation mode identification, time slot position and response window length in a wireless frame used for transmitting physical burst of random access response.

Further, the system message indicates to monitor the starting timeslot index of the random access response channel in the process that the terminal indicates the resource for receiving the random access response message.

Preferably, the random access response message includes: MAC sub-head, competition resolution identification, time offset adjustment information and frequency offset adjustment information, burst time frequency domain resource allocation information of special channel receiving and transmitting and synchronous channel burst time frequency domain resource allocation information; the MAC subheader comprises a random access transmission opportunity indication field used for distinguishing user groups, a competition resolution mark used for distinguishing user random access response messages in groups and an L field used for indicating the length of the random access response messages.

Further, the ROID in the MAC subheader format of the random access response message is a random access opportunity ID determined according to the RACH burst transmission time-frequency domain resource, and the ROID is determined jointly by the carrier number, the radio frame number, and the time slot position where the RACH burst transmission is located.

Preferably, the method for the terminal to perform contention resolution according to the random access response message includes: the terminal identifies and determines the random access response message through pilot sequence RAND information carried by RACH burst, ROID in response message MAC header and competition resolution identification in response message.

Further, the step of the terminal determining its own random access response message is:

s1: the terminal determines a random access time ROID according to the time-frequency domain resource position for sending RACH burst, if the ROID domain value in the MAC head of the random access response message received by the terminal in the response window is not matched with the determined value, the terminal UE discards the received random access response message, otherwise, the terminal UE firstly retains the received random access response message and executes S2;

s2: verifying whether the competition resolution identification in the response message is the same as the data payload content in the sent random access physical burst, if so, successfully solving the competition, successfully completing the random access process, otherwise, failing to solve the competition, and executing S3;

s3: and continuing to receive the random access response message in the response window, and executing S1 and S2 until the response window is ended.

The beneficial effects of the invention are as follows: the invention completes the random access process through two steps of signaling interaction, and redefines the transmission format of the random access response message, the terminal indicates the resource for transmitting the random access request for the terminal through the system message in the first step and sends the random access request to the satellite communication system; the terminal receives the random access response sent by the satellite communication system in the second step and completes competition resolution according to the received random access response, and the network distributes special burst configuration for the terminal through the random access response message to ensure that the terminal is quickly accessed to the network, so that the time delay of the terminal accessing the satellite communication system is reduced.

Drawings

FIG. 1 is a schematic illustration of frequency division in the present invention;

FIG. 2 is a diagram illustrating allocation of radio frame timeslots in the present invention;

FIG. 3 is a diagram illustrating RACH burst structure design in the present invention;

FIG. 4 is a diagram illustrating a first MAC subheader format of a random access response message in the present invention;

FIG. 5 is a diagram illustrating a second MAC subheader format of a random access response message in accordance with the present invention;

FIG. 6 is a diagram illustrating a format design of a random access response message in the present invention;

FIG. 7 is a diagram illustrating the time domain location of RACH burst transmission in the present invention;

FIG. 8 is a diagram illustrating the time domain transmission of a random access response message in the present invention;

FIG. 9 is a diagram illustrating a contention resolution process according to the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

A method for reducing access delay in a low earth orbit satellite communication system, the method comprising: the process that the terminal randomly accesses the satellite communication system is completed by adopting two steps of signaling interaction; the method comprises the following specific steps:

the first step is as follows: the terminal sends RACH burst to the satellite communication system through the initial system message; wherein the initial system message contains resources for instructing the terminal to transmit a RACH burst; RACH denotes a random access channel;

the second step is that: the terminal receives the random access response message through the resource which is indicated by the system message for the terminal and is used for receiving the random access response message, completes competition resolving according to the received random access response message, and completes the process that the terminal accesses the satellite communication system.

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

Furthermore, a plurality of carriers are arranged to reserve random access resources, so that the terminal has enough random access resources to access the satellite communication system; in order to reduce the signaling overhead, the available random access request transmission carriers can be indicated in a bitmap configuration mode, and the bitmap length depends on the number of the carriers divided by the frequency band.

A specific implementation mode for indicating random access resources through a bitmap configuration mode comprises the following steps in the process of setting frequency band identification: if the bit corresponding to the carrier wave is set to be 1, indicating that the carrier wave corresponding to the carrier wave has random access resources; if the bit corresponding to the carrier wave is set to be 0, the carrier wave corresponding to the carrier wave is indicated to have no random access resource. Preferably, in the process of setting the frequency band identifier, a plurality of bits can be set to 1 at the same time. As shown in fig. 1, if the frequency band is divided into 3 carriers, and both carrier 1 and carrier 3 have random access resources, the bitmap is configured as 101.

Further, in order to reduce the frame allocation signaling overhead, the radio frame for transmission of the random access request may be indicated in a short-period repetition allocation manner. A mapping table is predefined, a wireless frame distribution mode is indicated through a table index, and a required wireless frame mode is defined according to the user number requirement of an access network. And determining a corresponding frame division mode through the index value of the system information block SIB message indication table, thereby determining an available radio frame.

A specific embodiment of a radio frame indicating random access request transmission through short-period repeat allocation comprises the following steps: when various data transmission is carried out, in order to avoid the interference of different data transmission, the length of a wireless frame comprises Y slots. When the RACH burst data is transmitted, N slots are occupied, and N may be configured by a fixed protocol or dynamically (indicated by a network management configuration or a master information block MIB). Specifically, with N slots as one unit, it is possible to calculate how many units Y slots contain, and display and indicate which units can be used for RACH transmission in a bitmap manner, or determine which units can be used for RACH transmission by using an index value. For example, if the radio frame includes 4 cells and the bitmap mode indicator is 1010, it indicates that the first N consecutive slots and the 3 rd N consecutive slots from the radio frame may be used to transmit the RACH.

A specific embodiment of indicating a radio frame allocation mode through a table index includes: and taking N continuous solats as a unit, and setting an indication parameter according to the number by using all the N continuous solats as the number to indicate the unit for RACH transmission. Specifically, as shown in fig. 2, for example, there are 4 cells, index values are required to indicate RACH cells available for transmission, 0 indicates a first consecutive N slots, 1 indicates a second consecutive N slots, 2 indicates a third consecutive N slots, 3 indicates a fourth consecutive N slots, 4 indicates a first and a second consecutive N slots, and 5 indicates a first and a third consecutive N slots; by analogy, enumerating 4 elements may indicate a single element for RACH transmission, may indicate a consecutive plurality of elements for RACH transmission, and may also indicate a hop element for RACH transmission.

The terminal sends RACH burst to a satellite communication system in a burst mode through a pilot frequency sequence at the random access sending timing advance moment indicated by the initial system message; preferably, for the design of the RACH burst structure as shown in fig. 3, the random access request message is transmitted in the form of a physical RACH burst, where the RACH burst includes a pilot sequence and a data payload, where RAND is the pilot sequence, supports a random number or a sequence code, 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 a logical channel identifier LCID in the MAC header, and can also be used for contention resolution.

An embodiment of the initial system message indicating RACH burst resource, as shown in fig. 4, includes: the initial system message indicates that the RACH burst resource is frequency band identifier =4, carrier identifier =0110, radio frame allocation pattern identifier =1, and time slot =10 in a radio frame used for transmitting the RACH burst; and indicating that the carrier 2 and the carrier 3 of the frequency band 4 have random access resources according to the initial system message. Defining an index and random access radio frame allocation pattern mapping table, a system information block SIB indication table index, which specifies that multiframe N within superframe m and all radio frames within multiframe N +2 can be used for RACH burst transmission and that the RACH burst transmission slot indication parameter is set to 00, meaning that RACH bursts can be transmitted in the first N consecutive slots within a certain radio frame. If the UE determines that the radio frame 8 in the multiframe N transmits the random access request message according to the RACH resource configuration and the timing advance information indicated by the system message, and randomly generates a random number of 15, the UE sends a random access burst message in the first N slots of the radio frame 8, wherein the RAND in the message is 15.

An embodiment of indicating resources for receiving a random access response message includes: and indicating resource information for receiving the random access response message for the terminal through the system message, wherein the resource information comprises a frequency band identifier, a carrier identifier, a wireless frame allocation mode identifier, a time slot position in a wireless frame used for transmitting a physical burst of the random access response and a response window length. The carrier identifier needs to indicate which carrier is used for transmitting the response message, and the wireless frame allocation mode identifier is similar to a random access request message transmission wireless frame allocation indication mode and determines an available wireless frame by adopting a predefined table indication table index depending on the parameter length determined by the number of the frequency-divided carriers.

Further, the system message indicates to monitor the initial time slot index of the random access response channel in the process that the terminal indicates the resource for receiving the random access response message; for a physical burst transmission slot for downlink transmission, in order to avoid interference of other beams with MIB (master information block) transmission, the starting time slots of other data transmissions should be indicated within P time slots excluding the time slot occupied by the MIB. Assuming that each response message transmission occupies M slots, M may be configured either fixed or dynamically in protocol (network management configuration or MIB indication). The continuous M slot positions of transmission can be determined through a bitmap mode or an index mode of indicating the initial slot.

After the terminal sends RACH burst data on the selected resources, starting a random access response window after M wireless frames, and receiving a random access response message in the response window, wherein M is fixed by a protocol or indicated by a system message.

A random access response message comprising: MAC sub-head, competition resolution identification, time offset adjustment information and frequency offset adjustment information, burst time frequency domain resource allocation information of special channel receiving and transmitting and synchronous channel burst time frequency domain resource allocation information; the MAC subheader comprises a random access transmission opportunity indication field used for distinguishing user groups, a competition resolution mark used for distinguishing user random access response messages in the groups and an L field used for indicating the length of the random access response messages.

Preferably, the MAC subheader format is designed, including: the ROID is a random access opportunity ID determined according to RACH burst transmission time-frequency domain resources, is determined jointly through a carrier number, a radio frame number and a time slot position where RACH burst transmission is located, and is used for distinguishing user groups; the L field indicates a random access response message length.

There are two schemes for the length of L, the first is as shown in fig. 5, where the length of L is 7 bits, indicating the number of bytes of the response message; as shown in fig. 6, the second type, where the length of L is 2 bits, indicates whether the random access response message contains 1 burst configuration or 2 burst configurations, or does not carry a burst configuration, and the indication scheme is as follows:

00: indicating that the random access response message does not carry burst configuration;

01: indicating that the random access response message carries 1 burst configuration;

10: indicating that the random access response message carries 2 burst configurations.

As shown in fig. 7, in a format of the random access response message, each burst configuration has a length of 4 bytes, and at most 2 burst configurations can be performed, so that a configuration in which the response message includes several bursts can be indicated through an L field in the MAC header, thereby enabling determination of a final random access response message length.

As shown in fig. 8, the system message indicates, for the terminal, available resources for receiving the random access response message and a response window length, where the available resources include a carrier frequency band, an available radio frame, and a slot position used for transmitting a physical burst of the random access response message in the radio frame. For example, the SIB indicates a predefined radio frame allocation pattern mapping table index that specifies that multiframe n within superframe m and all radio frames within multiframe n +1 may be used for random access response message transmission. The protocol fixed response message transmission needs to use M slots, and the SIB indicates that the random access response message is transmitted from the second M slots in the determined radio frame. After the terminal selects the random access resource on the 2 nd carrier in the wireless frame 6 in the multiframe n to send the random access request message, the terminal starts a random access response window after P wireless frames, and the random access response message is prevented from being received in the wireless frame where the MIB and the SIB are located. And if the P is 3, starting a random access response window in a wireless frame 9 in the multiframe n, and receiving a random access response message in the response window according to a specified time slot position in the wireless frame determined by the random access burst resource indication.

Because the RACH burst transmission resource indicated by the system information is a shared resource, if a plurality of terminals select the same transmission resource, the base station cannot identify the terminal through the resource, and can only distinguish the terminal by the terminal identifier in the burst data transmitted by the terminal, and then send a response message. These terminals may receive the same response message and need to identify the terminal to which the response message belongs through contention resolution. The terminal identifies and determines the random access response message through the RAND information carried by the RACH burst, the ROID in the MAC header of the response message and the competition resolution identification in the response message.

As shown in fig. 9, the terminal determines whether the received random access response message is sent to itself through contention resolution, and the specific steps are as follows:

the first step is as follows: and the UE determines the ROID according to the time-frequency domain resource position for sending the RACH burst.

If the ROID domain value in the MAC header of the random access response message received by the UE in the response window is not matched with the determined value, the UE discards the received random access response message; otherwise, the received random access response message is reserved first, and the second step is carried out.

The second step is that: verifying whether the competition resolution identification in the response message is the same as the data payload content in the sent random access physical burst, if so, successfully solving the competition, and successfully finishing the random access process; otherwise, the competition resolving is failed, and the third step is executed.

The third step: and continuing to receive the random access response message in the response window, and executing the first step and the second step until the response window is finished. If no random access response is received in the random access response window, or all the received random access responses do not contain the ROID matched with the transmitted random access opportunity identification, or the received response message MAC header contains the ROID matched with the transmitted random access opportunity identification, but the competition resolution identification in the response message is not matched with the transmitted content, the random access process is considered to be failed.

The above-mentioned embodiments, which further illustrate the objects, technical solutions and advantages of the present invention, should be understood that the above-mentioned embodiments are only preferred embodiments of the present invention, and should not be construed as limiting the present invention, and any modifications, equivalents, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. A method for reducing the access time delay of a low earth orbit satellite communication system is characterized in that a process of randomly accessing a terminal to the satellite communication system is completed by two steps of signaling interaction, and the method comprises the following steps:

the first step is as follows: the terminal sends RACH burst to the satellite communication system through the initial system message; wherein the initial system message contains resources for instructing the terminal to transmit a RACH burst; RACH denotes a random access channel;

the second step is that: the terminal receives the random access response message through the resource which is indicated by the system message for the terminal and is used for receiving the random access response message, completes competition resolving according to the received random access response message, and completes the process that the terminal accesses the satellite communication system.

2. The method of claim 1, wherein the RACH burst transmitted by the terminal includes a pilot sequence and a data payload; the terminal sends RACH burst to a satellite communication system in a burst mode through a pilot frequency sequence at the random access sending timing advance time indicated by the initial system message; the pilot sequence is a random number or a sequence code, and the data payload is data of a common control channel or data of a media access control layer control unit and is distinguished by a logical channel identifier LCID in the MAC header.

3. The method of claim 1, wherein the initiating the system message comprises: frequency band identification, carrier identification, radio frame allocation mode identification, time slot position in a radio frame for transmitting RACH burst and RACH timing advance information; the initial system message is used to indicate to the terminal the resources to transmit the RACH burst.

4. The method as claimed in claim 1, wherein the initial system message indicates a resource manner for transmitting the RACH burst to the terminal, and comprises:

reserving random access resources by setting carriers;

indicating available random access request transmission carriers by a bitmap configuration mode, wherein the bitmap length depends on the number of the carriers divided by the frequency band;

indicating a wireless frame distribution mode through a table index of a predefined mapping table, and defining a required wireless frame mode according to the user number requirement of an access network;

determining a corresponding frame division mode through a system information block SIB indication table index value so as to determine an available wireless frame;

and sending the RACH burst according to the timing advance time indicated by the determined time domain resource advance system message.

5. The method as claimed in claim 1, wherein the system message indicates the resource for receiving the random access response message to the terminal after the terminal transmits the RACH burst, the method comprises:

frequency band identification, carrier identification, wireless frame distribution mode identification, time slot position in a wireless frame used for transmitting physical burst of random access response and response window length.

6. The method of claim 1, wherein the system message indicates a starting slot index of a listening random access response channel during the process of indicating the resource for receiving the random access response message for the terminal.

7. The method of claim 1, wherein the random access response message comprises: MAC sub-head, competition resolution identification, time offset adjustment information and frequency offset adjustment information, burst time frequency resource configuration information transmitted and received by a dedicated channel and burst time frequency resource configuration information of a synchronous channel; the MAC subheader comprises a random access transmission opportunity indication field used for distinguishing user groups, a competition resolution mark used for distinguishing user random access response messages in the groups and an L field used for indicating the length of the random access response messages.

8. The method as claimed in claim 7, wherein the random access occasion ID in the MAC subheader format of the random access response message is determined by the carrier number, the radio frame number, and the timeslot position where the RACH burst transmission is located.

9. The method of claim 1, wherein the performing contention resolution by the terminal according to the random access response message comprises: the terminal identifies and determines the random access response message by the pilot sequence carried by the RACH burst, the random access opportunity ID in the response message MAC header and the competition resolution identification in the response message.

10. The method of claim 9, wherein the step of the terminal determining its random access response message comprises:

s1: the terminal determines a random access time ROID according to the time-frequency domain resource position for sending RACH burst, if the ROID domain value in the MAC head of the random access response message received by the terminal in the response window is not matched with the determined value, the terminal UE discards the received random access response message, otherwise, the terminal UE firstly retains the received random access response message and executes S2;

s2: verifying whether the competition resolution identification in the response message is the same as the data payload content in the sent random access physical burst, if so, successfully solving the competition, successfully completing the random access process, otherwise, failing to solve the competition, and executing S3;

s3: and continuing to receive the random access response message in the response window, and executing S1 and S2 until the response window is ended.

Images