A random access enhancement method for non-terrestrial networks based on RedCap technology

Abstract

The present invention provides a non-ground network random access enhancement method based on RedCap technology, which relates to the field of wide-area Internet of Things in satellite Internet. The present invention includes: initializing a non-ground network RedCap system access scenario, the ground RedCap terminal sends Msg1 to the non-ground network base station, and the non-ground network base station estimates the current network load; the non-ground network base station restricts the access of some RedCap terminals, forms Msg2 and sends it to the ground; the RedCap terminal receives Msg2 from the non-ground network base station, and completes corresponding operations according to Msg2; the non-ground network base station receives Msg3, and feeds back Msg4 to complete contention resolution. The present invention takes into account the load condition of the system, restricts the access of some RedCap terminals, prevents network overload, ensures the performance of the wide-area Internet of Things based on the NTN network, and saves the signaling resources of the system.

Description

Technical Field

[0001] The present invention relates to the field of wide area Internet of Things in satellite Internet, and in particular to a non-terrestrial network (NTN) random access enhancement method based on RedCap technology. Background Art

[0002] As an IoT technology in 5G NR, RedCap (Reduced Capability) focuses on how to reduce the performance and complexity of 5G networks to accommodate a large number of widely distributed IoT device terminals.

[0003] In the RedCap communication scenario, the random access of large-scale RedCap terminals will affect the performance of the system. The IoT communication system including RedCap technology is composed of a large number of Machine Type Communication (MTC) terminals. For RedCap communication, general devices only need to transmit a large amount of small data, but when a large number of devices arrive at the network at the same time, it will cause serious congestion and delay.

[0004] Applying RedCap technology to non-ground network communication systems, especially satellite communication systems, will also bring new problems. Satellites or unmanned aerial platforms, drones, etc. have a wide communication coverage range and can provide solutions for wide-area IoT coverage. However, compared with ground cellular communications, satellite-to-ground / air-to-ground communication links have problems such as extended communication time, large link loss, and unstable links. The RedCap terminal on the ground needs to enhance uplink transmission to ensure that the RedCap terminal can stably access the network.

[0005] In the four-step initial access process, the RedCap terminal first selects the preamble in the broadcast channel and sends Msg1. After receiving Msg1, the satellite or airborne base station feeds back Msg2 to the terminal. Msg2 contains instructions for the terminal to continue sending Msg3 and instructions for uplink enhancement. After receiving Msg3, the satellite or airborne base station feeds back Msg4 to complete the initial access process. When multiple terminals use the same preamble to make access requests at the same time, contention resolution is achieved through Msg3 and Msg4.

[0006] Currently, there are two solutions for enhancing uplink coverage of RedCap terminals: joint channel estimation and repeated transmission technology.

[0007] Joint channel estimation, such as DMRS configuration scheme optimization, is a method in which the transmitter sends a DMRS signal to the receiver, and uses DMRS in different time slots together to perform channel estimation to improve the uplink and downlink channel estimation and demodulation capabilities, thereby effectively improving the coverage performance of the corresponding channel and achieving coverage enhancement.

[0008] Repeated transmission technologies such as TTI (Transmission Time Interval) repetition are implemented based on the principle of integer multiples of TTI. The transmitter repeatedly sends the same data frame according to the protocol. Although this reduces the bit rate and rate of data transmission, resulting in higher transmission delay, it achieves additional soft combination gain and incremental redundancy gain, improves the demodulation performance of the receiving end, improves the receiving signal-to-noise ratio, and achieves coverage enhancement.

[0009] However, joint channel estimation methods such as DMRS configuration scheme optimization are not applicable in non-terrestrial network RedCap scenarios. In terrestrial communication systems, base station energy consumption is not restricted and channel characteristics change little. In non-terrestrial network communication systems with satellites and drones as carrier platforms, due to the high dynamic characteristics of satellite-to-ground / air-to-ground links, the difference in channel characteristics reflected between DMRS in different time slots will increase with the increase of time difference. This scheme will further increase the complexity of DMRS channel estimation processing, and the performance gain obtained in the overall transmission task is not ideal.

[0010] Considering the processing capacity of RedCap terminals, repeated transmission is adopted to enhance uplink. The uplink enhancement of RedCap terminal Msg3 transmission is indicated by Msg2. However, when a large number of RedCap terminals are collectively connected, network congestion and delay will be caused.

[0011] At this time, no matter whether the RedCap terminal to be connected will perform Msg3 enhancement with more or fewer repetitions, it will cause the network load to increase further. In addition, for multiple RedCap terminals that select the same preamble code for access at a time, even if the uplink transmission is performed according to the instructions in Msg2, only one RedCap terminal can complete the access process in the end, and the remaining RedCap terminals need to re-access. Therefore, for the RedCap terminals that have not accessed, more resources are wasted. In addition, it will also increase the difficulty of data processing by satellite or airborne base stations, which is not helpful for alleviating the load condition of the system.

[0012] The Chinese patent with publication number CN117377124A discloses a random access enhancement method, device and equipment for RedCap UE, which is used to solve the random access problem of RedCap terminals. The technical solution of the invention is: RedCap UE obtains the Msg2 message sent by the base station, and determines whether it can send the Msg3 message to the base station according to the UL grant information in Msg2 to complete the random access process. In the technical solution of the invention, the bandwidth processing capability of the RedCap UE is taken into consideration. When the Msg3 frequency domain resources indicated by the UL grant information exceed the bandwidth processing capability of the RedCap UE, the RedCap UE resends the preamble and allocates the UL grant information to it again, thereby enhancing the success rate of random access of the RedCap terminal. However, this method only considers the bandwidth processing capability of the RedCap UE and lacks consideration for the system load. For IoT systems with a large number of terminals, it is more important to complete the RedCap random access enhancement under the premise of considering the system load.

[0013] The Chinese patent with publication number CN114071777A discloses a method, network device and terminal for random access enhancement. The technical solution of the invention is: Msg2 indicates the resources of PUSCH time domain repetition of the terminal, and the resources of PUSCH time domain repetition are indicated by the reserved field or the padding field in the second message; the terminal repeatedly sends Msg3 to the network device according to the number of repetitions indicated by the resources of PUSCH time domain repetition. In this way, uplink random access enhancement is achieved, but the method does not take into account the system load status, which may cause network congestion.

[0014] The document "Random access enhancement method, device and equipment for RedCap UE" (CN202311394945.1[P]. 2024-01-09.) published by China United Network Communications Group Co., Ltd. and China Telecom Consulting and Design Institute Co., Ltd. only considers the need for uplink enhancement of RedCap terminals to complete access, without considering the network load conditions. Summary of the invention

[0015] In view of this, the present invention proposes a random access enhancement method for non-terrestrial networks based on RedCap technology. The present invention is aimed at non-terrestrial RedCap systems such as satellite-borne or airborne systems, and proposes a random access enhancement scheme for non-terrestrial networks (NTN). The present invention takes into account the load condition of the system, restricts the access of some RedCap terminals, prevents network overload, ensures the performance of the wide area Internet of Things based on the NTN network, and saves the signaling resources of the system.

[0016] The technical solution adopted by the present invention is:

[0017] A non-terrestrial network random access enhancement method based on RedCap technology comprises the following steps:

[0018] S1: Initialize the non-ground network RedCap system access scenario. The ground RedCap terminal completes the initial synchronization and sends Msg1 to the non-ground network base station. The non-ground network base station estimates the current network load based on the received preamble code.

[0019] S2: The non-ground network base station determines the required number of uplink enhancement retransmissions of Msg3 according to the received signal strength of each preamble and the uplink enhancement request, and restricts the access of some RedCap terminals according to the network load status obtained in step S1, forms Msg2 and sends it to the ground;

[0020] S3: The RedCap terminal receives Msg2 from the non-terrestrial network base station. If the RedCap terminal receives the uplink authorization of Msg2, it performs uplink enhancement on Msg3 according to the requirements in Msg2; if Msg2 indicates that the access is restricted, it performs random fallback, and after the fallback is completed, it initiates the access request again and returns to step S1;

[0021] S4: The non-terrestrial network base station receives Msg3 from the RedCap terminal and feeds back Msg4 to complete the contention resolution. The RedCap terminal receives Msg4, and the random access process of the non-terrestrial network RedCap system ends.

[0022] Furthermore, step S1 specifically includes:

[0023] Measurement The number of preambles M received in each SSB cycle and the number of idle preambles I are used to estimate the number of devices using preambles in the current time slot. :

[0024]

[0025] in, for The total number of preambles requested by RedCap terminals;

[0026] According to the maximum number of network access users and the number of devices applying the preamble in the current time slot , calculate the Access load of SSB cycle :

[0027]

[0028] According to the previous Access load within SSB cycle, estimate current network load :

[0029]

[0030] in, is the length of the buffer, For the weight of each access load, That is, the load information of the SSB cycle closer to the current time has a greater weight in the network load determination process.

[0031] Furthermore, step S2 specifically includes:

[0032] S21: After the RedCap terminal sends an uplink enhancement request to the non-ground network base station, the non-ground network base station sends an uplink enhancement request based on the number of retransmissions n and the retransmission gain. For all received Msg1, select The minimum configurable number of retransmissions n, where a is the signal-to-noise ratio of the non-terrestrial network base station receiving the RedCap terminal Msg1, in dB, and b is the minimum signal-to-noise ratio required to receive Msg3;

[0033] S22: For the received Msg1, after calculating the corresponding number of retransmissions according to step S21, The number of retransmissions is arranged in descending order to obtain the sequence ;

[0034] S23: If , is the maximum number of network access users, then for the sending sequence Center front For the RedCap terminal that receives the preamble corresponding to the part of the preamble, the non-terrestrial network base station restricts its access this time by configuring the physical control information UL grant in Msg2. For the RedCap terminal that sends the rest of the preamble, the non-terrestrial network base station grants its uplink normally in Msg2 and indicates the number of retransmissions required for the uplink enhancement of its Msg3;

[0035] like , then access to any RedCap terminal is not restricted.

[0036] The beneficial effects of the present invention are:

[0037] 1. Aiming at the uplink access enhancement requirement of NTN RedCap system, the present invention measures the signal strength of Msg1 and determines the appropriate uplink enhancement times of RedCap terminal by using the relationship between the retransmission times and the retransmission gain.

[0038] 2. The present invention estimates the network load status according to the preamble code, and limits the subsequent access of some RedCap terminals through Msg2 according to the network load status, thereby preventing further congestion of the system and effectively improving the access efficiency of large-scale IoT terminals.

[0039] 3. The present invention prevents the problem of energy loss caused by repeated transmission due to the RedCap terminal that fails to complete access due to competition due to excessive number of repetitions of Msg3, thereby saving the signaling resources of the system and reducing the power consumption of the IoT terminal. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a schematic flow diagram of the method of the present invention;

[0041] Figure 2 It is a flowchart of four-step random access;

[0042] Figure 3 is the system scenario graph;

[0043] Figure 4 It is a flow chart for calculating network load.

[0044] Figure 5 It is the flow chart sent by the satellite according to Msg2. DETAILED DESCRIPTION

[0045] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. However, this should not be understood as the scope of the above subject matter of the present invention being limited to the following embodiments, and all technologies realized based on the content of the present invention belong to the scope of the present invention.

[0046] In the following description, since the RedCap terminal will occupy independent communication resources after accessing the non-terrestrial network and does not need to access again, the following access represents the initial access process of the RedCap terminal accessing the network.

[0047] A non-terrestrial network random access enhancement method based on RedCap technology comprises the following steps:

[0048] S1: Initialize the NTN RedCap system access scenario. The ground terminal completes the initial synchronization and sends Msg1 to the NTN base station. The NTN base station estimates the current network load based on the received preamble code, including:

[0049] S11: Calculate the probability that a preamble is selected by only one RedCap terminal; for the number RedCap terminals, with equal probability ask preamble codes, the probability that a preamble code is selected by only one RedCap terminal is for:

[0050]

[0051] S12: According to probability , calculate the number of successful preamble codes The probability distribution of , and obtain the mathematical expectation of the success of the preamble :

[0052]

[0053]

[0054] Where m is a positive integer and E represents mathematical expectation;

[0055] S13: Calculate the probability that a preamble is not selected by any RedCap terminal :

[0056]

[0057] S14: According to , calculate the number of idle preambles The probability distribution of Expected number of free :

[0058]

[0059]

[0060] Where i is a positive integer and E represents mathematical expectation;

[0061] S15: Mathematical expectation of success through preamble and the expected number of idle , estimate the number of devices applying preamble in the current time slot :

[0062]

[0063]

[0064] S16: In the actual system, by measuring the The number of preambles received in an SSB cycle and the number of idle preambles are Make an estimate:

[0065]

[0066] S17: Maximum number of users connected to the network and It can be concluded that Access load of SSB cycle :

[0067]

[0068] S18: From the front The access load within an SSB cycle (where is the length of the buffer), estimating the current network load :

[0069]

[0070] in, For the weight of each access load, This ensures that the load information of the SSB cycle that is closer to the current time has a greater weight in the network load determination process.

[0071] S2: The NTN base station determines the required uplink enhancement retransmission times of Msg3 according to the received signal strength of each preamble and the uplink enhancement request, and restricts the access of some RedCap terminals according to the network load status obtained in step S1, and finally forms Msg2 to be sent to the ground, which specifically includes:

[0072] S21: The signal-to-noise ratio of Msg1 received by the NTN base station from the RedCap terminal is a dB, and the RedCap terminal sends an uplink enhancement request. relationship, choose (b is the minimum signal-to-noise ratio required to receive Msg3) The minimum configurable number of retransmissions;

[0073] S22: Calculate all received Msg1 according to the method of step S21, and The number of retransmissions is arranged in descending order, and we get ;

[0074] S23: If , for sending Center front For the RedCap terminal that sends the preamble corresponding to the part, the NTN base station restricts its access this time by configuring the UL grant in Msg2. For the RedCap terminal that sends the rest of the preamble, the NTN base station grants its uplink normally in Msg2 and indicates the number of retransmissions required for the uplink enhancement of its Msg3. The maximum number of retransmissions is 32, which needs to be determined according to the actual system capabilities. , then the access of any RedCap terminal is not restricted;

[0075] S3: The ground RedCap terminal receives Msg2 from the NTN base station. If the RedCap terminal receives the uplink authorization of Msg2, it will perform uplink enhancement on Msg3 according to the requirements in Msg2; if Msg2 indicates that the access is restricted, it will perform random fallback, and after the fallback is completed, it will initiate the access request again and return to S1;

[0076] S4: The NTN base station receives Msg3 from the RedCap terminal and feeds back Msg4 to complete the contention resolution. The ground RedCap terminal receives Msg4, and the random access process of the NTN RedCap system ends.

[0077] Here is a more specific example:

[0078] like Figure 1 As shown, a non-terrestrial network random access enhancement method based on RedCap technology includes the following steps:

[0079] S1: Initialize the NTN RedCap system access scenario, such as Figure 2 The ground RedCap terminal completes the initial synchronization and will follow Figure 3 In the 35th SSB cycle, the RedCap terminal sends Msg1 to the NTN base station. The NTN base station estimates the current network load based on the received preamble code. The calculation method is as follows: Figure 4 As shown, specifically including:

[0080] S11: Derivation of the probability of a preamble code value being selected by a RedCap terminal. Assume that there are 80 RedCap terminals with equal probability Request 64 preambles, then the probability that a preamble is selected by only one user is for:

[0081]

[0082] S12: According to probability , and further obtain the number of successful leading codes The probability distribution of , and obtain the mathematical expectation of the success of the preamble :

[0083]

[0084]

[0085] S13: The probability that a preamble is not selected by any RedCap terminal is :

[0086]

[0087] S14: According to , and further obtain the number of idle preamble codes The probability distribution of Expected number of free :

[0088]

[0089]

[0090] S15: The number of devices using the preamble code in the current time slot can be estimated by the expected success rate of the preamble code and the expected number of idle codes. :

[0091]

[0092] S16: In the actual system, the number of preambles received in the 35th SSB cycle and the number of idle preambles are measured to complete the Estimates

[0093]

[0094] S17: Maximum number of users connected to the network and The access load of the 35th SSB cycle can be obtained :

[0095]

[0096] S18: Estimate the current network load based on the access load in the previous 10 SSB cycles :

[0097]

[0098] S2: The NTN base station determines the required uplink enhanced retransmission times of Msg3 according to the received signal strength of each preamble, and restricts the access of some RedCap terminals according to the network load status obtained in S1, and finally forms Msg2 to be sent to the ground, such as Figure 5 As shown, specifically including:

[0099] S21: The signal-to-noise ratio of Msg1 received by the NTN base station from the RedCap terminal is 3 dB. According to the number of retransmissions n and the retransmission gain relationship, choose (b is the minimum signal-to-noise ratio required to receive Msg3, the value is 10) The minimum configurable number of retransmissions is 4;

[0100] S22: calculate all received Msg1s according to S21, and arrange the number of retransmissions in descending order: 12, 12, 8, 8, 8, 7, 7, 4, 4, 4, 4, 4, 3, 3, 3, 2, 2, 2, 2, 1, 1, 1;

[0101] S23: According to the current network load condition, for the RedCap terminals that send the first 5 preambles corresponding to 12, 12, 8, 8, 8, 7, 7, 4, 4, 4, 4, 4, 4, 3, 3, 3, 2, 2, 2, 2, 1, 1, 1, that is, the RedCap terminals corresponding to 12, 12, 8, 8, 8, the NTN base station restricts their access this time by configuring the uplink authorization indication in Msg2. For the RedCap terminals that send the remaining preambles, the NTN base station normally authorizes their uplink in Msg2, and indicates the number of retransmissions required for the uplink enhancement of their Msg3: 7, 7, 4, 4, 4, 4, 4, 3, 3, 3, 2, 2, 2, 2, 1, 1, 1;

[0102] S3: The ground RedCap terminal receives Msg2 from the NTN base station. If the RedCap terminal receives the uplink authorization of Msg2, it will perform uplink enhancement on Msg3 according to the requirements in Msg2; if Msg2 indicates that the access is restricted, it will perform random fallback, and after the fallback is completed, it will initiate the access request again and return to S1;

[0103] S4: The NTN base station receives Msg3 from the RedCap terminal and feeds back Msg4 to complete the contention resolution. The ground RedCap terminal receives Msg4, and the random access process of the satellite RedCap system ends.

[0104] The existing RedCap coverage enhancement technology can achieve the enhancement of Msg3 uplink transmission. However, the method of adopting such an enhancement scheme only considers whether the RedCap terminal can access, and does not consider the network performance of the RedCap system based on other unmanned non-ground platforms such as satellites or drones. To this end, the problem that the present invention first needs to solve is how to ensure the normal access of the RedCap terminals when large-scale RedCap terminals are collectively accessed while preventing the system from overloading.

[0105] In addition, since the RedCap terminal needs to perform Msg3 uplink enhancement when accessing, and the failure of competitive access will also lead to the waste of RedCap repeated transmission resources, the second key problem to be solved by the present invention is how to further reduce the waste of RedCap resources.

[0106] To this end, the present invention makes the following improvements to the random access enhancement of the NTN RedCap system:

[0107] 1. A low-complexity network load estimation scheme is proposed. According to the probability of the preamble being selected by the user and the probability of the preamble being idle, the number of successful preambles and the expected number of idle preambles are obtained respectively, and the number of preambles used in the current time slot is estimated, and the current network load status of the system is further obtained.

[0108] 2. A scheme for restricting access to some RedCap terminals is proposed. The relationship between the number of retransmissions and the retransmission gain is considered, and a reasonable number of uplink enhanced retransmissions is set for each RedCap terminal according to the strength of the Msg1 signal. And according to the load condition of the system, access restrictions are imposed on some RedCap terminals in the sent Msg2, which prevents further congestion of the system and ensures the normal operation of the system.

[0109] 3. An uplink enhancement scheme for saving system signaling resources is proposed. In Msg2 sent by the NTN base station, the subsequent access process of the RedCap terminal, which is more difficult to access, is terminated in advance, thereby preventing the RedCap terminal that requires too many repetitions of Msg3 from completing the access due to competition, resulting in energy loss of repeated transmission, thus saving the system's signaling resources.

[0110] In summary, the present invention is oriented to non-terrestrial network RedCap communication scenarios, and designs a RedCap random access scheme that takes into account the system network load level, so as to prevent network overload and congestion while meeting the uplink enhancement of RedCap terminals. The present invention takes into account the load condition of the system, restricts the access of some RedCap terminals, saves the signaling resources of the system, and reduces the waste of resources.

Claims

1. A non-terrestrial network random access enhancement method based on RedCap technology, characterized in that: The following steps are involved: S1: Initialize the non-ground network RedCap system access scenario. The ground RedCap terminal completes the initial synchronization and sends Msg1 to the non-ground network base station. The non-ground network base station estimates the current network load based on the received preamble code. S2: The non-ground network base station determines the required number of uplink enhancement retransmissions of Msg3 according to the received signal strength of each preamble and the uplink enhancement request, and restricts the access of some RedCap terminals according to the network load status obtained in step S1, forms Msg2 and sends it to the ground; S3: The RedCap terminal receives Msg2 from the non-terrestrial network base station. If the RedCap terminal receives the uplink authorization of Msg2, it performs uplink enhancement on Msg3 according to the requirements in Msg2; if Msg2 indicates that the access is restricted, it performs random fallback, and after the fallback is completed, it initiates the access request again and returns to step S1; S4: The non-terrestrial network base station receives Msg3 from the RedCap terminal and feeds back Msg4 to complete the contention resolution. The RedCap terminal receives Msg4, and the random access process of the non-terrestrial network RedCap system ends.

2. According to claim 1, a non-terrestrial network random access enhancement method based on RedCap technology is characterized in that: Step S1 specifically includes: Measurement The number of preambles M received in each SSB cycle and the number of idle preambles I are used to estimate the number of devices using preambles in the current time slot. : in, for The total number of preambles requested by RedCap terminals; According to the maximum number of network access users and the number of devices applying the preamble in the current time slot , calculate the Access load of SSB cycle : According to the previous Access load within SSB cycle, estimate current network load : in, is the length of the buffer, For the weight of each access load, That is, the load information of the SSB cycle closer to the current time has a greater weight in the network load determination process.

3. The method for enhancing random access to non-terrestrial networks based on RedCap technology according to claim 2, characterized in that: Step S2 specifically includes: S21: After the RedCap terminal sends an uplink enhancement request to the non-ground network base station, the non-ground network base station sends an uplink enhancement request based on the number of retransmissions n and the retransmission gain. For all received Msg1, select The minimum configurable number of retransmissions n, where a is the signal-to-noise ratio of the non-terrestrial network base station receiving the RedCap terminal Msg1, in dB, and b is the minimum signal-to-noise ratio required to receive Msg3; S22: For the received Msg1, after calculating the corresponding number of retransmissions according to step S21, The number of retransmissions is arranged in descending order to obtain the sequence ; S23: If , is the maximum number of network access users, then for the sending sequence Center front For the RedCap terminal that receives the preamble corresponding to the part of the preamble, the non-terrestrial network base station restricts its access this time by configuring the physical control information UL grant in Msg2. For the RedCap terminal that sends the rest of the preamble, the non-terrestrial network base station grants its uplink normally in Msg2 and indicates the number of retransmissions required for the uplink enhancement of its Msg3; like , then access to any RedCap terminal is not restricted.

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