CN114916088A

CN114916088A - Low-earth-orbit-satellite-based non-ground network random access method and device

Info

Publication number: CN114916088A
Application number: CN202210495312.9A
Authority: CN
Inventors: 孙耀华; 朱剑锋; 彭木根
Original assignee: Beijing University of Posts and Telecommunications
Current assignee: Beijing University of Posts and Telecommunications
Priority date: 2022-05-07
Filing date: 2022-05-07
Publication date: 2022-08-16

Abstract

The application provides a non-ground network random access method based on a low earth orbit satellite, which comprises the following steps: searching a synchronous block broadcasted by the satellite-borne base station at the air interface and analyzing the searched synchronous block to obtain analysis data; after the number of the analyzed synchronous blocks reaches a threshold value, carrying out user coarse positioning based on the analyzed data to obtain a coarse positioning result; calculating the distance between the user and the satellite by using the analytic data and the coarse positioning result, and selecting the closest satellite as a service satellite; selecting a time point and a frequency point from time points and selectable frequency points which are provided by the analysis data and used for initiating random access to prepare for initiating a random access process; the random access process comprises the following steps: and judging whether the user meets the condition of 2-step random access or not according to the analyzed data, if so, initiating 2-step random access, and otherwise, initiating 4-step random access. By adopting the scheme, the method and the device realize that the user only needs to measure data once for each satellite, and simultaneously support simultaneous access of a large number of users.

Description

Low-earth-orbit-satellite-based non-ground network random access method and device

Technical Field

The present application relates to the field of non-terrestrial network technologies, and in particular, to a method and an apparatus for low-earth satellite-based random access to a non-terrestrial network.

Background

Compared with a land mobile communication system, the satellite communication has the advantages of wide coverage and no influence of ground natural disasters, and can provide services in scenes with missing ground communication facilities such as disaster areas, polar regions, oceans, deserts, forests and the like. In order to enhance and expand the coverage of the terrestrial 5G network, 3GPP discusses the architecture of the non-terrestrial network after 5G and satellite fusion, air interface protocol enhancement, mobility management, and the like in Release15 and Release16, wherein the situations that the satellite carries transparent loads and renewable loads are considered. In addition, the European SATis5 project verifies the feasibility of satellite infrastructure as a backhaul between a base station and a core network by building a satellite-ground fusion test platform.

3GPP proposes a satellite-based non-terrestrial network, in which the cell range is extended to tens or even hundreds of kilometers, and in addition, the fast movement of the low-orbit satellite relative to the ground brings about a large doppler shift, both of which cause the satellite-borne base station to enlarge the preamble receiving window in random access and to adopt more bits to indicate the amount of Timing Advance (TA), and at the same time, more preamble sequence repetition times and larger cyclic shift intervals are required. However, prolonging the uplink preamble receiving window will cause the spectrum efficiency of the network to decrease, increasing the number of TA value indicating bits will bring extra signaling overhead, and using a larger cyclic shift interval will cause the available preamble resources to decrease, and the user access contention to the network to be aggravated.

Disclosure of Invention

The present application is directed to solving, at least to some extent, one of the technical problems in the related art.

Therefore, a first objective of the present application is to provide a non-terrestrial network random access method based on low-earth orbit satellites, which realizes that a user can estimate a TA value and an uplink frequency offset value with higher accuracy by measuring downlink frequency offset data for each satellite only once, and finally increases available preamble resources through a newly designed preamble sequence format, thereby supporting simultaneous access of a large number of users.

A second objective of the present application is to provide a non-terrestrial network random access apparatus oriented to a low earth orbit satellite.

A third object of the present application is to propose a non-transitory computer-readable storage medium.

In order to achieve the above object, a first embodiment of the present application provides a method for random access to a non-terrestrial network based on a low earth orbit satellite, including: searching a synchronization block broadcasted by the satellite-borne base station at the air interface, and then analyzing the searched synchronization block to obtain analysis data; after the number of the analyzed synchronous blocks reaches a threshold value, carrying out user coarse positioning based on the analyzed data to obtain a user coarse positioning result; calculating the distance between the user and the satellite by using the analytic data and the user coarse positioning result, and selecting the satellite with the closest distance as a service satellite; randomly selecting a time point and a frequency point from time points and selectable frequency points which are provided by the analysis data and used for initiating random access to prepare for initiating a random access process; wherein, the random access process comprises: and judging whether the user meets the condition of 2-step random access or not according to the analyzed data, if so, initiating 2-step random access to the service satellite, and otherwise, initiating 4-step random access.

In the embodiment of the application, a non-terrestrial network random access method based on a low earth orbit satellite is oriented, a user obtains frequency offset values and ephemeris data of downlink signals of a plurality of satellites to perform self coarse positioning in an initial cell search stage, based on the frequency offset values and the ephemeris data, a TA value and a frequency offset value of preamble sequence transmission precompensation are calculated, and random access is initiated to a satellite-borne base station through a new preamble format. The method has the advantages that a user can estimate the TA value and the uplink frequency offset value with higher precision only by measuring downlink frequency offset data once for each satellite, and finally, the available lead code resources are increased through a newly designed lead code sequence format, so that simultaneous access of a large number of users is supported.

Optionally, in an embodiment of the present application, parsing the data includes: a cell identifier, a satellite coordinate under a geocentric geostationary coordinate system, a satellite speed, a downlink frequency offset measurement value of a satellite-borne base station, a Radio Resource Control (RRC) configuration parameter and a channel state parameter; wherein, the RRC parameter comprises: a root sequence number selection range, a Cyclic shift interval range, a preamble format, a Cyclic Prefix (CP) length of a random access preamble ZC (Zadoff-Chu) sequence, a frame number and a slot number of a satellite-borne base station allowing a user to initiate Uplink 2-step and 4-step random access, a frequency range for bearing the preamble sequence, and a mapping relationship between a root sequence number and a Physical Uplink Shared Channel (PUSCH) resource in the 2-step random access; the channel state parameters include a Signal-to-noise Ratio (SNR).

Optionally, in an embodiment of the present application, performing coarse positioning based on the parsed data includes:

based on a downlink frequency offset measurement value of a satellite-borne base station, a satellite coordinate and a satellite speed under a geocentric geostationary coordinate system, solving an optimization problem by using an optimization algorithm to obtain a user coarse positioning result, wherein the optimization problem is as follows:

wherein:

for the result of the coarse positioning of the user,

in order to obtain the error of the crystal oscillator,

to estimate the downlink frequency offset, f, of satellite i from the coarse positioning result _off,i Is a downlink frequency offset measurement of satellite i, c is the speed of light, f _c,i Is the downlink signal carrier frequency of satellite i,

in order to estimate the downlink Doppler frequency offset of the satellite i according to the coarse positioning result, the coordinate of the satellite i in the geocentric geostationary coordinate system is (x) _i ,y _i ,z _i )，(v _x,i ,v _y,i ,v _z,i ) Is the velocity vector of the satellite i under the geocentric geostationary coordinate system.

Optionally, in an embodiment of the present application, the distance between the user and the satellite is calculated by using the coarse positioning result and the satellite coordinates in the geocentric/geostationary coordinate system, and the satellite closest to the coarse positioning result is selected as the serving satellite.

Optionally, in an embodiment of the present application, when the signal-to-noise ratio is higher than a preset threshold, 2-step random access is initiated to the serving satellite, otherwise 4-step random access is initiated.

Optionally, in an embodiment of the present application, the 2-step random access includes: sending data to a service satellite, processing the received data at a service satellite end to obtain a processing result, and judging whether the access is successful according to the processing result;

wherein transmitting data to the service satellite comprises:

step S1: according to RRC configuration parameters, randomly selecting a root sequence number u and a cyclic shift interval N from a root sequence number selection range and a cyclic shift interval range _cs A plurality of leading ZC sequences are generated, and then a Discrete Fourier Transform (DFT) and an Inverse Discrete Fourier Transform (IDFT) are performed on all leading ZC sequences to generate a time-domain leading signal y in a cascade manner _r ；

Step S2: randomly selecting an available frequency point and a sending time point for transmitting uplink data according to the mapping relation between the root sequence number and the PUSCH resource;

step S3: using user identity information UE-ID and user selfInitial TA value

Forming PUSCH data, then performing addition of cyclic redundancy check bits, channel coding, scrambling, four-phase shift keying modulation and IDFT on the PUSCH data to generate PUSCH time domain data, wherein UE-ID is specified by a network or generated by a user in a mode of generating a random number sequence, scrambling identifiers used in the scrambling process are generated by calculating available frequency points and sending time points, cell identifiers and leader root sequence numbers,

calculating and generating a user coarse positioning result and a satellite coordinate under a geocentric geostationary coordinate system;

step S4: after the CP is added to the time domain preamble signal and the PUSCH time domain data, the available frequency point and the sending time point are used for advancing

Sending to a service satellite and precompensating for the uplink frequency offset f _pre-c Wherein f is _pre-c The sum of the downlink frequency deviation measurement value of the satellite-borne base station and the double crystal oscillator error estimation is equal to;

processing the received data at the service satellite terminal to obtain a processing result, wherein the processing result comprises the following steps:

step S5: will time domain preamble signal y _r After CP removal, the number of samples L is counted in one symbol _IDFT Dividing the interval into at least one sub-segment, and performing L on the sampled data of each sub-segment _IDFT After point DFT operation, decoding frequency domain resource mapping to obtain a frequency domain ZC sequence, and then correspondingly summing the frequency domain ZC sequence to obtain a summed sequence Y _sum ；

Step S6: DFT is carried out on the leader sequence with the local root sequence number u to generate a local sequence Y _local Performing IDFT after conjugate multiplication of the local sequence and the summation sequence to obtain a first sequence;

step S7: performing peak detection on the first sequence, the optional RRC specified interval when detecting the presence of three pulses in the first sequenceCyclic shift interval N _cs When the preamble sequence of a user is detected, it is noted that the result of the pulse interval calculation needs to be N _zc Taking the remainder, the mode of the distance between one pulse and the next pulse in the three pulses is far more than N _cs The position of the pulse is denoted as N _peak According to N _peak Number of points and sampling points L _IDFT Length N of ZC sequence _ZC Calculating to obtain a decimal multiple estimation error delta ta _f ；

Step S8: will time domain preamble signal y _r Leftward shift by a decimal multiple of the estimation error Δ ta _f Removing CP, and performing L on the time domain preamble signal sub-segment in each detection window _IDFT Obtaining sequence Y after point DFT and frequency-domain resource mapping _k After which the sequence Y is _k With the local sequence Y _local Performing IDFT after conjugate multiplication to generate a second sequence, performing peak detection on the second sequence and calculating to obtain an integral multiple estimation error delta ta _i ；

Step S9: according to the number L of sampling points _IDFT Decimal multiple estimation error delta ta _f And integer multiple estimation error Δ ta _i Calculating the TA estimation error Delta TA of the user _ue Simultaneously extracting user identity identification information UE-ID and user self initial TA value from received PUSCH time domain data

Step S10: the TA estimation error and the user self initial TA value are compared

Summing to obtain the user real TA value TA _full-ue ；

Step S11: user identity identification information UE-ID detected by a base station, TA estimation error of a user, a root sequence number u and a cyclic shift interval N are broadcasted to all users through a Physical Downlink Shared Channel (PDSCH) _cs A Cell Radio Network Temporary Identifier (C-RNTI);

step S12: judging whether the access is successful according to the processing result, comprising the following steps:

step S13: starting a random access response timer, analyzing the PDSCH, and if the transmitted user identity identification information UE-ID and the root sequence number u adopted by the transmitted preamble signal and the cyclic shift interval N are successfully extracted _cs After the successful competitive access is considered, the C-RNTI and the TA value of the true TA of the user are set _full-ue And finishing the 2-step random access.

Optionally, in an embodiment of the present application, if the user information is not extracted yet when the corresponding timer for random access expires, the 2-step random access is regarded as unsuccessful, and the 4-step random access is executed again.

Optionally, in an embodiment of the present application, the 4-step random access includes: transmitting the first data to a serving satellite; sending a random access response to the user terminal after the service satellite terminal receives the first data; sending second data to the service satellite at the user side according to the random access response; receiving and processing the second data at the service satellite terminal to obtain a processing result, and judging whether the access is successful according to the processing result;

wherein transmitting the first data to the serving satellite comprises:

step S81: step S1 is executed, and the generated time domain preamble signal is added to the CP and then advanced by the available frequency point and the transmission time point

sending a random access response to the user terminal after the service satellite terminal receives the first data, wherein the random access response comprises the following steps:

step S82: the service satellite terminal executes the steps S5-S8 according to the received time domain preamble signal, completes the detection of the time domain preamble signal and obtains the TA estimation error delta TA of the user _ue Then, broadcasting the received root sequence number u and cyclic shift interval N to all users through PDSCH _cs TA estimation error Δ TA of user _ue PUSCH modulationDegree authorization and Temporary Cell Radio Network Temporary identity (TC-RNTI);

transmitting, at the user terminal, second data to the service satellite based on the random access response, comprising:

step S83: starting a random access response timer, monitoring the PDSCH until receiving PDSCH data sent by a service satellite and including a root sequence number u and a cyclic shift interval N _cs Stopping monitoring, if the random access response timer is expired, the root sequence number u and the cyclic shift interval N sent by the service satellite are not received yet _cs If the access is failed, performing steps S81, S82, S83 again;

step S84: executing the step S3, and transmitting the generated PUSCH time domain data through the PUSCH resource of the PUSCH scheduling authorization, wherein the transmission time is the PUSCH transmission time point of the serving satellite authorization and advances the TA _full-ue A scrambling identifier used in the scrambling procedure is calculated and generated by the TC-RNTI and the cell identifier, TA _full-ue Timing advance estimation error delta TA provided by PDSCH for the user's true TA value _ue And the user's own initial TA value

Summing to obtain;

receiving and processing the second data at the service satellite terminal to obtain a processing result, wherein the processing result comprises:

step S85: receiving PUSCH time domain data from a service satellite terminal, and extracting user identity identification information (UE-ID) and user self initial TA value contained in the PUSCH time domain data

Then the satellite-borne base station calculates the real timing advance value TA of the user _full-ue And broadcasting the user identity identification information UE-ID, the root sequence number u and the cyclic shift interval N detected by the base station to all the users through the PDSCH _cs ；

Judging whether the access is successful according to the processing result, comprising the following steps:

step S86: start timer and resolvePDSCH, if successfully extracting the transmitted user ID information UE-ID and the root sequence number u adopted for transmitting the preamble signal, and the cyclic shift interval N _cs And if the timer expires, the user information sent in the PDSCH is still not received, and the contention access is regarded as failure, and a new 4-step random access process is restarted.

In order to achieve the above object, a second aspect of the present invention provides a random access apparatus for a non-terrestrial network, including a parsing module, a coarse positioning module, a first selecting module, a second selecting module, and an access module,

the analysis module is used for searching the synchronous block broadcasted by the satellite-borne base station at the air interface, and then analyzing the searched synchronous block to obtain analysis data;

the coarse positioning module is used for carrying out user coarse positioning based on the analysis data after the number of the analyzed synchronous blocks reaches a threshold value, and obtaining a user coarse positioning result;

the first selection module is used for calculating the distance between the user and the satellite by using the analytic data and the user coarse positioning result, and selecting the satellite with the closest distance as a service satellite;

the second selection module is used for randomly selecting a time point and a frequency point from the time point and the selectable frequency points which are provided by the analysis data and used for initiating the random access to prepare for initiating the random access process;

and the access module is used for judging whether the user meets the condition of 2-step random access or not according to the analysis data, if so, initiating 2-step random access to the service satellite, and otherwise, initiating 4-step random access.

To achieve the above object, a third embodiment of the present invention proposes a non-transitory computer readable storage medium, wherein instructions of the storage medium, when executed by a processor, enable the non-terrestrial network-oriented random access method to be performed.

Additional aspects and advantages of the present application will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the present application.

Drawings

The foregoing and/or additional aspects and advantages of the present application will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

fig. 1 is a schematic flowchart of a random access method for a non-terrestrial network according to an embodiment of the present application;

fig. 2 is a schematic diagram illustrating user preamble generation according to an embodiment of the present application;

fig. 3 is a PUSCH data format diagram of user uplink transmission according to an embodiment of the present application;

fig. 4 is a schematic diagram of an uplink frequency precompensation method according to an embodiment of the present application;

fig. 5 is a flowchart illustrating an estimation process of a TA value of a user multiplied by a decimal number by a base station according to an embodiment of the present application;

fig. 6 is a schematic diagram illustrating peak estimation in a fractional TA value estimation process according to an embodiment of the present application;

fig. 7 is a flowchart illustrating an estimation process of a TA value of a user by a base station according to an embodiment of the present application;

fig. 8 is a flow chart of 2-step random access in an embodiment of the present application;

fig. 9 is a flowchart of 4-step random access in an embodiment of the present application;

FIG. 10 is a schematic diagram of an application scenario according to an embodiment of the present application;

fig. 11 is a schematic structural diagram of a random access device for a non-terrestrial network according to an embodiment of the present application.

Detailed Description

Reference will now be made in detail to embodiments of the present application, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are exemplary and intended to be used for explaining the present application and should not be construed as limiting the present application.

The following describes a random access method and apparatus for a non-terrestrial network according to an embodiment of the present application with reference to the drawings.

Fig. 1 is a flowchart illustrating a random access method for a non-terrestrial network according to an embodiment of the present disclosure.

As shown in fig. 1, the method for random access to a non-terrestrial network based on a low earth orbit satellite comprises the following steps:

step 101, searching a synchronization block broadcasted by a satellite-borne base station at an air interface, and then analyzing the searched synchronization block to obtain analysis data;

102, after the number of the analyzed synchronous blocks reaches a threshold value, carrying out user coarse positioning based on the analyzed data to obtain a user coarse positioning result;

103, calculating the distance between the user and the satellite by using the analytic data and the user coarse positioning result, and selecting the satellite with the closest distance as a service satellite;

104, randomly selecting a time point and a frequency point from time points and selectable frequency points which are provided by the analysis data and used for initiating random access to prepare for initiating a random access process; wherein, the random access process comprises: and judging whether the user meets the condition of 2-step random access or not according to the analyzed data, if so, initiating 2-step random access to the service satellite, and otherwise, initiating 4-step random access.

According to the non-terrestrial network random access method based on the low orbit satellite, a user estimates an initial TA value And an uplink Signal frequency offset value of the user by using a Synchronization Signal And Physical Broadcast Channel (SSB) And a downlink frequency offset value of n (n is larger than or equal to 3) low orbit satellites, And initiates random access to a satellite-borne base station through a new lead code format, And finally the method can realize normal user access of the satellite-borne 5G base station on the premise of not expanding the length of a lead code receiving window of the satellite-borne base station And the indication range of the TA value specified by the existing 5G protocol.

Optionally, in an embodiment of the present application, the user searches the SSB broadcast by the satellite-based base station at the air interface _i And i is 1,2, …, and n is the number of the transmitting satellite. The user then parses the SSB _i Obtaining analytical data, including: satellite coordinates (x) under cell identification and earth-centered earth-fixed coordinate system _i ,y _i ,z _i ) Satellite velocity (v) _x,i ,v _y,i ,v _z,i ) Satellite borne baseDownlink frequency offset measurement f for a station _off,i RRC configuration parameters, channel state parameters; the RRC configuration parameters comprise a root sequence number selection range of a random access leader sequence, a cyclic shift interval range, a preamble code format, a CP length, a frame number and a time slot number of a satellite-borne base station allowing a user to initiate uplink 2-step and 4-step random access, a frequency range for bearing the preamble code sequence and a mapping relation between the root sequence number and a PUSCH in the 2-step random access; the channel state parameters include signal-to-noise ratio.

satellite coordinates (x) under earth-centered earth-fixed coordinate system based on downlink frequency deviation measurement value of satellite-borne base station _i ,y _i ,z _i ) And satellite velocity (v) _x,i ,v _y,i ,v _z,i ) The following optimization problem is solved by using an optimization algorithm such as a grid search method, a sparrow search method or a least square method and the like to obtain the user coordinate estimation

And crystal oscillator error estimation

Wherein:

for the result of the coarse positioning of the user,

in order to obtain the error of the crystal oscillator,

for estimating the downlink Doppler frequency offset of the satellite i according to the coarse positioning result, the coordinate of the satellite i in the geocentric geostationary coordinate system is (x) _i ,y _i ,z _i )，(v _x,i ,v _y,i ,v _z,i ) The velocity vector of the satellite i under the geocentric geostationary coordinate system is shown.

Optionally, in one embodiment of the present application, the coarse positioning result is utilized

With satellite coordinates (x) _i ,y _i ,z _i ) And calculating to obtain the distance between the user and the satellite, and selecting the satellite with the closest distance as a service satellite.

Optionally, in an embodiment of the present application, when the signal-to-noise ratio is higher than a preset threshold, a 2-step random access is initiated to the serving satellite, otherwise a 4-step random access is initiated.

Optionally, in an embodiment of the present application, the 2-step random access includes: sending data to a service satellite, processing the received data at a service satellite terminal to obtain a processing result, and judging whether the access is successful according to the processing result;

wherein transmitting data to the service satellite comprises:

step S1: according to RRC configuration parameters, randomly selecting a root sequence number u and a cyclic shift interval N from a root sequence number selection range and a cyclic shift interval range _cs Generating a plurality of leading ZC sequences, then performing DFT and IDFT post-concatenation on all leading ZC sequences to generate a time domain leading signal y _r The specific way of cascading is shown in FIG. 2, wherein the cyclic shift interval of the ZC sequence is

N

_cs 0, 1, or 2 times of, the length N of the total number K, ZC of concatenated ZC sequences _zc Length N of CP _cp And a guard interval length N _gp Searching for SSB at a user _s And obtaining in the analysis process, wherein s is the service satellite number;

step S3: using user identity information UE-ID and user own initial TA value

Forming PUSCH data, then performing cyclic redundancy check bit addition, channel coding, scrambling, quadrature phase shift keying modulation and IDFT on the PUSCH data to generate PUSCH time domain data, wherein the UE-ID is specified by a network or generated by a user in a mode of generating a random number sequence, and a scrambling identifier c used in the scrambling process _init Generated by available frequency points and sending time points, cell identification calculation and leader root sequence number index,

the data is generated by calculation of satellite coordinates under the user coarse positioning result and a geocentric geostationary coordinate system, and the PUSCH data is generated by c _init The generated gold sequence is scrambled,

c _init ＝n _RNTI *2 ¹⁶ +N _RAPID *2 ¹⁰ +n _ID

wherein, c _init Length of 31bit, n _RNTI RA-RNTI with length of 16bit, n given for the time frequency resource position for initiating 2-step random access _RAPID Is the index of the root sequence number of the leader sequence, the length is 6 bits, n _ID Identify for cell (by resolving SSB) _s Obtained) of the first step,length of 10bit, slot _s Time slot number, f, to initiate random access for a user _id Sending index numbers of time-frequency resources occupied by the preamble sequences to users;

step S4: after the cyclic prefix CP is added to the time domain preamble signal and the PUSCH time domain data, the time domain preamble signal and the PUSCH time domain data are advanced through the available frequency point and the sending time point

Sending to a service satellite and precompensating for the uplink frequency offset f _pre-c Wherein, the PUSCH data format transmitted by the user is shown in figure 3, f _pre-c Equal to the downlink frequency offset measurement f _off,s And 2 times crystal oscillator error estimation

Sum, as in FIG. 4;

as shown in fig. 5, the satellite-borne base station performs a fractional TA estimation procedure:

step S5: the satellite-borne base station receives the time domain preamble signal y _r After CP removal, the number of samples L is counted in one symbol _IDFT Is a spacing of y _r Divided equally into K + N _gp /L _IDFT Sub-sequence y _r，k And for all subsequences y _r，k Executing L _IDFT Point DFT and resource demapping to finally obtain K + N _gp /L _IDFT Each length is N _zc The frequency domain sub-sequence of (1). Summing all subsequences to obtain sequence Y _sum ；

Step S6: the satellite-borne base station carries out DFT on the ZC sequence without the cyclic shift locally to generate a sequence Y _local Then, Y is added _local And Y _sum Conjugate multiplication and execution of IDFT to generate sequence y _cor ；

Step S7: subsequently, the satellite carries the base station pair sequence y _cor Execution peakValue detection, peak detection procedure as shown in fig. 6, when the satellite-borne base station observes 3 pulses above the detection threshold and the interval between the pulses is optional cyclic shift interval N specified by RRC _cs Then, the leader sequence of a user is determined to be detected and the root sequence number u of the leader sequence is equal to the root sequence number of the local ZC sequence, and it is noted that the result of the pulse interval calculation needs to be performed on N _zc Taking the remainder, the mode of the distance between one pulse and the next pulse in the three pulses is far more than N _cs The position of the pulse is denoted as N _peak According to N _peak Number of points and sampling points L _IDFT 、N _zc Calculating to obtain a decimal multiple estimation error delta ta _f ，

Wherein T is _s The interval of two adjacent sampling points is shown;

as shown in fig. 7, the satellite-borne base station performs an integer-times TA error estimation procedure:

step S8: satellite-borne base station transmits time domain preamble signal y _r Leftward movement by a decimal multiple of the estimation error Δ ta _f Removing CP, and performing L on the time domain preamble signal sub-segment in each detection window _IDFT Obtaining sequence Y after point DFT and frequency-domain resource mapping _k K is a detection window number, K is 1,2 _gp /L _IDFT After which the sequence Y is _k With the local sequence Y _local Performing IDFT after conjugate multiplication to generate a second sequence y _cor，k For all second sequences y _cor，k Carrying out peak value detection and calculating to obtain integral multiple TA estimation error delta TA _i Wherein, the size of the detection window is LIDFT sampling points, and when the base station is in the slave window

Is started for the first time at

Midpoint N _zc -N _cs A peak is observed and in the window

Observe point N _zc -2N _cs A peak appears, which can be considered as

Step S9: satellite-borne base station calculation user TA estimation error delta TA _ue ＝Δta _i *L _IDFT *T _s +Δta _f Meanwhile, extracting user identity identification information UE-ID and user self initial TA value from received time domain data of PUSCH

Step S10: delta ta of satellite-borne base station passing user _ue And

value calculation user true TA value

Step S11: broadcasting user identity identification information UE-ID, user TA estimation error, root sequence number u and cyclic shift interval N detected by a base station to all users through PDSCH _cs A combination of C-RNTI;

step S13: the user starts a random access response timer and analyzes a PDSCH channel, and if the user identity identification information UE-ID sent by the user and the root sequence number u and the cyclic shift interval N adopted by the sending of the preamble signal are successfully extracted _cs After the successful competitive access, the user sets C-RNTI and TA value of true TA of the user _full-ue And finishing the 2-step random access. When the timer expires, the user still does not receive the transmitted user information in the PDSCH channel, and the contention access is considered to fail.

Optionally, in an embodiment of the present application, if the 2-step random access is unsuccessful, the 4-step random access is re-executed.

Optionally, in an embodiment of the present application, the 4-step random access includes:

Sending to a service satellite and precompensating for the uplink frequency offset f _pre-c Wherein f is _pre-c Equal to the sum of the downlink frequency offset measurement value of the satellite-borne base station and the double crystal oscillator error estimation, and the format of the preamble signal is shown in fig. 2;

step S82: the service satellite terminal executes the steps S5-S8 according to the received time domain preamble signal, completes the detection of the time domain preamble signal and obtains the user TA estimation error value delta TA _ue Then, broadcasting the received root sequence number u and cyclic shift interval N to all users through PDSCH _cs User TA estimation error value Δ TA _ue A combination of a PUSCH scheduling grant and a TC-RNTI;

step S83: the user starts a random access response timer and monitors the PDSCH until receiving PDSCH data sent by a service satellite and including a root sequence number u and a cyclic shift interval N _cs When the timer expires, the user still does not receive the root sequence number u and the cyclic shift interval N sent by the serving satellite _cs If the user is determined to have failed the access, the user performs the steps S81, S82, S83 again;

step S84: step S3 is executed, and the generated PUSCH time domain data is sent through the PUSCH resource authorized by the PUSCH scheduling, and the sending time is TA advanced for the PUSCH transmission time point authorized by the service satellite _full-ue A time point, wherein the time point of uplink data transmission authorized by uplink PUSCH scheduling to the user is not earlier than the sum of the time point of transmitting the current PDSCH and the maximum round-trip transmission delay of the cell, TA _full-ue Timing advance estimation error delta TA provided by PDSCH for the user's true TA value _ue And the user's own initial TA value

The sum is obtained, and the PUSCH data is formed by c _init The generated gold sequence is scrambled, and the gold sequence is generated,

c _init ＝TC-RNTI*2 ¹⁵ +n _ID

wherein n is _ID To resolve SSB _s The obtained cell identification s is the service satellite number;

step S85: the service satellite receives the PUSCH time domain data and extracts the user identity identification information UE-ID and the user self initial TA value contained in the PUSCH time domain data

And calculate TA _full-ue Then, the user identity identification information UE-ID, the root sequence number u and the cyclic shift interval N detected by the base station are broadcasted to all users through the PDSCH _cs ；

Step S86: the user starts a timer and analyzes the PDSCH, and if the user identity identification information UE-ID and the root sequence number u adopted by the preamble signal are successfully extracted and sent, the cyclic shift interval N _cs And if the contention access is successful, setting the TC-RNTI as the C-RNTI to finish 4 steps of random access. And when the timer expires, the user still does not receive the transmitted user information in the PDSCH channel, the contention access is regarded as failure, and the user with the access failure restarts a new 4-step random access flow.

The following describes a practical use case of the random access method for non-terrestrial networks of the present application:

s1: after a user receives SSB signals of satellites 1-3 in an initial cell search stage and executes downlink time-frequency synchronization, the user obtains a downlink signal frequency offset value (f) of the satellites _off，i I-1, 2, 3 represents satellite number), cell identification of the satellite-borne base station, and uplink frame number frame of the satellite-borne base station allowing user to initiate random access _i And slot number slot _i 2, optional root sequence number of random access and mapping relation between the root sequence number and PUSCH resources, 4, multiple available frequency points for bearing lead code, interval of lead code cyclic shift, and lattice of lead codeEquation, duration of CP, and coordinates (x) of the satellite in the geocentric geostationary coordinate system _i ，y _i ，z _i ) And velocity vector (v) _x，i ，v _y，i ，b _z，i )；

S2: user utilization f _off，i 、(x _i ，y _i ，z _i ) And (v) _x，i ，v _y，i ，v _z，i ) Solving the following optimization problem and obtaining the position of the user to the user

And crystal oscillation error

The estimated value of (2) can adopt an optimization algorithm comprising a grid search method, a sparrow search method, a least square method and the like;

wherein

f _c，i Is the carrier frequency of satellite i, c is the speed of light,

to estimate the downlink frequency offset of satellite i based on the coarse positioning result,

is the downlink Doppler frequency offset of the satellite i estimated according to the coarse positioning result.

S3: after calculating the distances between the user and all satellites, selecting a satellite s closest to the user as a service satellite, and calculating the SNR of a downlink of the satellite s;

s4: the user calculates the frequency offset value to be pre-compensated for the uplink to satellite s, which is shown in fig. 4

S5: the user locates the result according to the rough

Calculating initial uplink timing advance to satellite s

S6: user judging received SSB _s Whether the SNR of (a) is higher than a certain preset threshold value

If the SNR is higher than

User slave SSB _s Randomly selecting one time point and one frequency point from the provided time points and selectable frequency points for initiating 2-step random access and advancing

A 2-step random access procedure is performed as shown in fig. 8. If the SNR is not higher than

User slave SSB _s Randomly selecting one time point and one frequency point from the provided time points and selectable frequency points for initiating 4-step random access and advancing

A 4-step random access procedure is performed as shown in fig. 9. Carrier frequency of user uplink signal transmission deviates f relative to reference frequency point _pre-c ；

Specifically, there are many optimization algorithms that can be used in S2, and here, the procedure of user position and crystal oscillator error pre-estimation is briefly described by taking a sparrow search algorithm as an example:

a. the coordinates of three satellites are converted from a rectangular coordinate system to a spherical coordinate system to obtain azimuth angles and polar angles of the satellites, and the conversion process is realized in the following mode:

azimuth angle:

polar angle:

b. calculating the center points of the azimuth and polar coordinates of the three satellites

It is briefly described as

c. Setting the maximum value of the difference between the azimuth of the central point and the azimuths of all the satellites as a critical value for updating the azimuth coordinate, and recording the critical value as theta _max Setting the maximum value of the difference between the polar angle of the central point and the polar angles of all satellites as the critical value of polar angle coordinate updating, and recording the critical value as

d. An array L of M x 2 is randomly generated, M being the total number of sparrows. The element of the mth row of the array is the coordinate of sparrow m and is recorded as

M1, 2, wherein M represents a sparrow number, and coordinates satisfy a constraint condition of theta _max ≤θ _m ≤θ _max 、

e. Adding the coordinates of each sparrow with the coordinates of the center point, and converting into three-dimensional coordinates (x) on the earth surface _m ，y _m ，z _m ) The radius of the earth is represented by R, and the conversion process is implemented by the following formula:

f. calculating the Doppler frequency offset of the position of the sparrow m relative to three satellites according to the three-dimensional coordinates of the sparrow

The calculation process is as follows:

in the formula f _c，i The carrier frequency of a downlink signal of the satellite-borne base station i and the speed of light c.

g. Calculating the fitness value of the sparrows, wherein the fitness value is calculated according to the following formula:

h. sequencing all sparrow fitness values;

i. updating the positions of discoverers in the sparrow population and updating the fitness value by using the following formula;

wherein L is _m，n A coordinate value of the nth dimension representing sparrow m, T represents the current iteration times, T is the preset highest iteration time, and alpha belongs to [0, 1 ]]And tau is a random number, SA is a random number, 0.5, 1]For a safety value generated in advance, gamma is a function following a normal distributionNumber of machines, X being the matrix [1, 1]。

j. Updating the positions of the participants in the sparrow population and updating the fitness value by using the following formula;

wherein

For the optimal position occupied by the finder at present, L _worst For the current global worst position, R is a 1 × 2 matrix, where each element is randomly assigned a value of 1 or-1.

k. Updating the position of the alerter in the sparrow population and updating the fitness value by using the following formula;

wherein the content of the first and second substances,

for the current global optimum position, ρ is a random number following a normal distribution with a mean of 0 and a variance of 1, f _m 、f _g 、f _w Respectively the fitness value of sparrow m, the current global optimal fitness value and the current global worst fitness value, and A belongs to [ -1, 1]Is a random number and δ is a constant other than 0.

1. Recording the best fitness value and the corresponding three-dimensional coordinate value (x) from the cutoff to the current iteration _m ，y _m ，z _m )；

And m, repeating e to 1 until a stopping condition is met, such as reaching the maximum iteration number and the like. Finally obtaining three-dimensional coordinate (x) corresponding to optimal fitness value _m ，y _m ，z _m ) I.e. coordinates estimated for the coarse positioning of the user

n. crystal oscillation error

Specifically, the detailed process of the 2-step random flow in S6 is as follows:

a: as shown in FIG. 2, the user passes SSB at the base station _s Randomly selecting a root sequence number u and a cyclic shift interval N in the selectable range of the root sequence number and the cyclic shift interval of the provided preamble code _cs Generating K length N _zc And performing DFT and IDFT and then cascading to generate a time domain preamble signal;

b: user presence at SSB _s And randomly selecting an available frequency point and a sending time point from the provided mapping relation between the root sequence number and the PUSCH resource to prepare for transmitting uplink data. At the same time, the user sends time point, frequency point and cell mark according to the root serial number of the preamble code to calculate the scrambling mark c for scrambling data _init ：

c _init ＝n _RNTI *2 ¹⁶ +n _RAPID *2 ¹⁰ +n _ID ，

Wherein, c _init The length is 31 bit. n is _RNTI RA-RNTI given by the time frequency resource position of initiating 2-step random access, the length is 16 bit. n is _RAPID The length is 6 bits for the leader sequence root sequence number index. n is _ID For cell identification, by resolving SSB _s Obtained, the length is 10 bits. slot _s Time slot number, f, for initiating random access for a user _id A user is sent an index number that the preamble sequence occupies time-frequency resources.

C: and generating PUSCH data content to be sent by a user, and generating time domain data of the PUSCH after adding cyclic redundancy check bits, channel coding, scrambling, quadrature phase shift keying modulation and IDFT to the data content. As shown in FIG. 3, the data content includes a UE-ID,

The value is obtained. When the network does not specify a UE-ID, the user generates the UE-ID by generating a random number sequence.

D: after the user adds CP to the time domain preamble signal and the PUSCH time domain data, the transmission time point of the PUSCH resource appointed by the antenna relative to the preamble root serial number is advanced

Transmitting to the base station and performing a size of f _pre-c In which f is pre-compensated _pre-c Equal to the downlink frequency offset measurement f _off，s And 2 times crystal oscillator error estimation

Summing;

e: as shown in fig. 5, the base station will obtain the preamble signal y of the time domain _r After CP removal, the number of samples L is counted in one symbol _IDFT Partitioning preamble signal into K + N for intervals _gp /L _IDFT Each segment, and executing L on the sampling data of each segment _IDFT After point DFT operation, frequency domain resource mapping is solved to finally obtain the length N _zc The frequency domain ZC sequence of (1). Adding K + N _gp /L _IDFT Obtaining a sequence Y after corresponding summation of ZC sequences in each frequency domain _sum ；

F: the satellite-borne base station carries out DFT on the leader sequence with the local root sequence number u to generate a sequence Y _local Is a reaction of Y _local And Y _sum Performing IDFT after conjugate multiplication to obtain sequence y _cor 。

G: as shown in FIG. 5, for y _cor Performing peak detection when y _cor With three pulses in the middle, providing an optional cyclic shift interval N for RRC parameters _cs When the base station detects the leader sequence of a user, the root sequence number is u, and the cycle interval is N _cs . The mode of the three pulses with the distance between one pulse and the next pulse is far more than N _cs The position of the pulse is denoted as N _peak Then the user estimates the error by a few times

Wherein T is _s The interval of two adjacent sampling points is shown;

h: as shown in fig. 7, the satellite-borne base station will be y _r Leftward movement by Δ ta _f Removing CP, and adding K + N _gp /L _IDFT Time domain preamble subsequence y in detection window _r，k Obtaining a sequence Y after both DFT and de-frequency domain resource mapping _k And k is the detection window number. Will Y _k And Y _local Performing IDFT after conjugate multiplication to generate sequence y _cor，k . For all y _cor，k Performing peak detection and calculating integral multiple estimation error delta ta _i ；

In H, when the base station is from the window

Is started for the first time at

Midpoint N _zc -N _cs A peak is observed and in the window

Observe point N _zc -2N _cs A peak appears, which can be considered as

I: calculating estimation error delta ta of user by satellite-borne base station _ue ＝Δta _i *L _IDFT *T _s +Δta _f Extracting UE-ID and UE-ID on corresponding PUSCH simultaneously

And calculates the user' s

J: the base station broadcasts the UE-ID, delta ta successfully detected in the PUSCH by the base station to all users through the PDSCH _ue 、u、N _cs And a combination of C-RNTI allocated to the user by the base station;

k: user' sAnd starting a random access response timer and monitoring the PDSCH. UE-ID, u and N transmitted by base station when user receives _cs After matching with the local information, the user sets C-RNTI and judges that the access is successful

Update to TA _full-ue . Otherwise, the access failure is transferred to 4 steps of access flow;

specifically, the detailed process of 4-step random access in S6 is as follows:

a: in the same way as 2-step random access preamble signal generation, the user passes SSB at the base station _k Randomly selecting a root sequence number u and cyclic shift times N in the selectable range of the provided preamble root sequence number and cyclic shift times _cs Generating K length N _zc Performing DFT and IDFT operation to generate time domain cascaded leading signals;

b: after the user adds the preamble signal to the CP, the slot is corresponding to _s Advance the time

Sending signals to the base station while f is proceeding _pre-c In which f is pre-compensated _pre-c Equal to the downlink frequency offset measurement f _off，s And 2 times crystal oscillator error estimation

Summing;

c: the same way as 2-step random access detection of the preamble signal, after the base station collects the random access signal data of the time domain, the decimal multiple estimation error delta ta of the user is estimated _f And integer multiple estimation error Δ ta _i And calculating Δ ta _ue ；

D: the base station sends PDSCH to the user, and the PDSCH comprises u and N detected by the base station _cs 、Δta _ue The TC-RNTI and the PUSCH scheduling authority, wherein the time for scheduling the uplink PUSCH of the authorized user is not earlier than the sum of the time node for sending the current PDSCH and the maximum round-trip transmission delay of the cell;

e: and 2 steps of randomizationThe access is similar, the user starts a random access response timer, and after the user receives the PDSCH, the user calculates the TA _full-ue And transmits the UE-ID and the UE-ID via the PUSCH

As shown in fig. 3. When the network does not provide the UE-ID, the UE-ID can be generated by generating a random number, and the user advances the TA relative to the time point of authorizing PUSCH transmission _full-ue Transmitting data, when a timer expires, the u, N not detected in PDSCH yet _cs The user regards as the competition access failure, and the user prepares for the next new 4-step access;

f: the base station detects the PUSCH and calculates TA _full-ue And will successfully receive the UE-ID, u and N _cs The combination is broadcast to all users through PDSCH;

g: the user starts a timer and monitors PDSCH, and when the user detects UE-ID, u and N sent by the base station _cs And after the local information is matched, if the access is successful, setting the TC-RNTI as the C-RNTI. And when the timer expires, the user still does not receive the transmitted user information in the PDSCH channel, the contention access is regarded as failure, and the user with the access failure restarts a new 4-step random access flow.

The random access method for the non-terrestrial network is applied to the problem that the probability of successful random access of a user is low due to the wide geographical range and the large Doppler frequency offset of a low-orbit satellite, the position of the user, the TA value of the user and the frequency offset value of an uplink signal are estimated based on downlink frequency offset data, satellite coordinates and satellite velocity vector data which are periodically sent by the satellite-borne base station by the user side and calculated by SSB, and random access is initiated through an enhanced lead code format to obtain the service of the satellite-borne base station, wherein the application scenario is shown in FIG. 10. The method has the advantages that the user can realize the estimation of TA (timing advance) and the uplink frequency offset precompensation of the uplink data of the user by only acquiring the downlink SSB (single serving cell) signal of each satellite once, so that the base station does not need to prolong the length of a preamble sequence receiving window and increase the indication range of the TA value, the frequency offset value of the preamble signal detected by the base station is relatively small, the characteristics of the preamble signal among different users are distinct, and the aims of improving the overall spectrum efficiency of a network and the success probability of random access are fulfilled.

In order to implement the foregoing embodiments, the present application further provides a random access device for a non-terrestrial network.

As shown in fig. 11, the random access apparatus facing the non-terrestrial network includes a parsing module, a coarse positioning module, a first selection module, a second selection module, and an access module, wherein,

the analysis module is used for searching the synchronization block SSB broadcasted by the satellite-borne base station at the air interface, and then analyzing the searched SSB to obtain analysis data;

the coarse positioning module is used for carrying out user coarse positioning based on the analyzed data after the number of the analyzed SSBs reaches a threshold value, and obtaining a user coarse positioning result;

It should be noted that the foregoing explanation on the embodiment of the random access method for the non-terrestrial network is also applicable to the random access apparatus for the non-terrestrial network in this embodiment, and details are not described here.

In order to implement the above embodiments, the present invention also proposes a non-transitory computer-readable storage medium having stored thereon a computer program which, when executed by a processor, implements the method of the above embodiments.

In the description herein, reference to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the application. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present application, "plurality" means at least two, e.g., two, three, etc., unless explicitly specified otherwise.

Any process or method descriptions in flow charts or otherwise described herein may be understood as representing modules, segments, or portions of code which include one or more executable instructions for implementing steps of a custom logic function or process, and alternate implementations are included within the scope of the preferred embodiment of the present application in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art of the present application.

The logic and/or steps represented in the flowcharts or otherwise described herein, e.g., an ordered listing of executable instructions that can be considered to implement logical functions, can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. For the purposes of this description, a "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of the computer-readable medium would include the following: an electrical connection (electronic device) having one or more wires, a portable computer diskette (magnetic device), a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disc read-only memory (CDROM). Additionally, the computer-readable medium could even be paper or another suitable medium upon which the program is printed, as the program can be electronically captured, via for instance optical scanning of the paper or other medium, then compiled, interpreted or otherwise processed in a suitable manner if necessary, and then stored in a computer memory.

It should be understood that portions of the present application may be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, the various steps or methods may be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. If implemented in hardware, as in another embodiment, any one or combination of the following techniques, which are known in the art, may be used: a discrete logic circuit having a logic gate circuit for implementing a logic function on a data signal, an application specific integrated circuit having an appropriate combinational logic gate circuit, a Programmable Gate Array (PGA), a Field Programmable Gate Array (FPGA), or the like.

It will be understood by those skilled in the art that all or part of the steps carried by the method for implementing the above embodiments may be implemented by hardware related to instructions of a program, which may be stored in a computer readable storage medium, and when the program is executed, the program includes one or a combination of the steps of the method embodiments.

In addition, functional units in the embodiments of the present application may be integrated into one processing module, or each unit may exist alone physically, or two or more units are integrated into one module. The integrated module can be realized in a hardware mode, and can also be realized in a software functional module mode. The integrated module, if implemented in the form of a software functional module and sold or used as a stand-alone product, may also be stored in a computer readable storage medium.

The storage medium mentioned above may be a read-only memory, a magnetic or optical disk, etc. Although embodiments of the present application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present application, and that variations, modifications, substitutions and alterations may be made to the above embodiments by those of ordinary skill in the art within the scope of the present application.

Claims

1. A low-earth-orbit-satellite-based non-terrestrial network random access method is characterized by comprising the following steps of:

searching a synchronous block broadcasted by the satellite-borne base station at an air interface, and then analyzing the searched synchronous block to obtain analysis data;

after the number of the analyzed synchronous blocks reaches a threshold value, carrying out user coarse positioning based on the analyzed data to obtain a user coarse positioning result;

calculating the distance between the user and the satellite by using the analytic data and the user coarse positioning result, and selecting the satellite with the closest distance as a service satellite;

randomly selecting a time point and a frequency point from the time point and the selectable frequency points which are provided by the analysis data and initiate random access to prepare for initiating a random access process;

wherein the random access procedure comprises: and judging whether the user meets the condition of 2-step random access or not according to the analysis data, if so, initiating 2-step random access to the service satellite, and otherwise, initiating 4-step random access.

2. The method of claim 1, wherein parsing the data comprises: the method comprises the following steps of identifying a cell, satellite coordinates under a geocentric geostationary coordinate system, satellite speed, a downlink frequency offset measurement value of a satellite-borne base station, a radio resource control layer configuration parameter and a channel state parameter;

wherein the radio resource control layer parameters include: selecting a range of a root sequence number of a random access leader sequence, a range of cyclic shift intervals, a preamble code format, a cyclic prefix length, a frame number and a time slot number of a satellite-borne base station allowing a user to initiate uplink 2-step and 4-step random access, a frequency range for bearing the leader sequence, and a mapping relation between the root sequence number in the 2-step random access and physical uplink shared channel resources; the channel state parameter comprises a signal-to-noise ratio.

3. The method of claim 2, wherein the performing coarse positioning based on parsed data comprises:

based on the downlink frequency offset measurement value of the satellite-borne base station, the satellite coordinates and the satellite speed under the geocentric geostationary coordinate system, solving an optimization problem by using an optimization algorithm to obtain a user coarse positioning result, wherein the optimization problem is as follows:

wherein:

coarsely positioning for userAs a result of which,

in order to obtain the error of the crystal oscillator,

the coordinate of the satellite i in the geocentric geostationary coordinate system is (x) to estimate the downlink Doppler frequency offset of the satellite i according to the coarse positioning result _i ,y _i ,z _i )，(v _x,i ,v _y,i ,v _z,i ) The velocity vector of the satellite i under the geocentric geostationary coordinate system is shown.

4. The method of claim 2, wherein the coarse positioning result and the satellite coordinates in the geocentric/geostationary coordinate system are used to calculate the distance between the user and the satellite, and the closest satellite is selected as the serving satellite.

5. The method of claim 2, wherein 2-step random access is initiated to the serving satellite when the signal-to-noise ratio is above a preset threshold, and otherwise 4-step random access is initiated.

6. The method of claim 5, wherein the 2-step random access comprises: sending data to the service satellite, processing the received data at the service satellite end to obtain a processing result, and judging whether the access is successful according to the processing result;

wherein the sending data to the service satellite comprises:

step S1: according to the parameters of a radio resource control layer, randomly selecting one root sequence number and cyclic shift interval from the root sequence number selection range and the cyclic shift interval range to generate a plurality of preamble sequences, and then performing discrete Fourier transform and inverse discrete Fourier transform on all the preamble sequences to generate time domain preamble signals in a cascading manner;

step S2: randomly selecting an available frequency point and a sending time point for transmitting uplink data according to the mapping relation between the root sequence number and the physical uplink shared channel resource;

step S3: forming physical uplink shared channel data by using user identity identification information and a user self initial timing advance value, and then performing addition of a cyclic redundancy check bit, channel coding, scrambling, four-phase shift keying modulation and inverse discrete Fourier transform on the physical uplink shared channel data to generate physical uplink shared channel time domain data, wherein the user identity identification information is specified by a network or generated by a user in a mode of generating a random number sequence, a scrambling identification used in a scrambling process is generated by calculating available frequency points and sending time points, cell identifications and leader root sequence numbers, and the user self initial timing advance value is generated by calculating a user rough positioning result and satellite coordinates under a geocentric-geostationary coordinate system;

step S4: after adding a cyclic prefix to the time domain preamble signal and the time domain data of the physical uplink shared channel, sending the time domain preamble signal and the time domain data of the physical uplink shared channel to the service satellite through the available frequency point and the sending time point in advance of the initial timing advance value of the user, and pre-compensating uplink frequency offset, wherein the pre-compensated uplink frequency offset is equal to the sum of a downlink frequency offset measurement value of the satellite-borne base station and double crystal oscillator error estimation;

the processing of the received data at the service satellite terminal to obtain a processing result comprises:

step S5: after the cyclic prefix of the time domain preamble signal is removed, the time domain preamble signal is divided into at least one sub-segment by taking the number of sampling points of one symbol as an interval, the frequency domain resource mapping is decoded after the discrete Fourier transform operation is carried out on the sampling data of each sub-segment, a frequency domain preamble subsequence is obtained, and then the frequency domain preamble subsequence is correspondingly summed to obtain a summation sequence;

step S6: performing discrete Fourier transform on a local leader sequence to generate a local sequence, and performing inverse discrete Fourier transform after conjugate multiplication of the local sequence and the summation sequence to obtain a first sequence;

step S7: performing peak detection on the first sequence, and when detecting that the interval between three pulses in the first sequence is the optional cyclic shift interval provided by the parameters of the radio resource control layer, the satellite-borne base station determines to detect the leader sequence of one user, and calculates to obtain a decimal time advanced estimation error according to the position of the detected pulse, the number of sampling points and the length of the leader sequence;

step S8: moving the time domain pilot signal leftwards by the decimal estimation error, removing a cyclic prefix, performing discrete Fourier transform and de-resource mapping on a time domain pilot signal sub-segment in each detection window to obtain a frequency domain pilot sub-sequence segment, performing inverse discrete Fourier transform after performing conjugate multiplication on the frequency domain pilot sub-sequence segment and the local sequence to generate a second sequence, performing peak detection on the second sequence, and calculating to obtain an integral multiple timing advance estimation error;

step S9: calculating the timing advance estimation error of the user according to the sampling point number, the decimal time advance estimation error and the integral time advance estimation error, and extracting user identity identification information and the initial timing advance value of the user from the received time domain data of the physical uplink shared channel;

step S10: summing the timing advance estimation error and the user self initial timing advance value to obtain a user real timing advance value;

step S11: broadcasting the combination of user identity identification information, user timing advance estimation error, root sequence number, cyclic shift interval and cell wireless network temporary identification detected by a base station to all users through a physical downlink shared channel;

step S12: the judging whether the access is successful according to the processing result comprises the following steps:

step S13: starting a random access response timer, analyzing the physical downlink shared channel, if successfully extracting the transmitted user identity identification information and the root sequence number and the cyclic shift interval adopted by the transmitted preamble signal, and considering that the competitive access is successful, then setting a cell wireless network temporary identification of the user and a real timing advance value of the user, and completing the 2-step random access.

7. The method of claim 6, wherein if the user information is not extracted yet when the corresponding timer for random access expires, it is determined that the 2-step random access is unsuccessful, and the 4-step random access is performed again.

8. The method of claim 6, wherein the 4-step random access comprises: transmitting first data to the serving satellite; sending a random access response to the user terminal after the service satellite terminal receives the first data; sending second data to the service satellite at the user side according to the random access response; receiving and processing the second data at the service satellite end to obtain a processing result, and judging whether the access is successful according to the processing result;

wherein the sending the first data to the serving satellite comprises:

step S81: executing step S1, adding a cyclic prefix to the generated time domain preamble signal, sending the time domain preamble signal to the service satellite by advancing the user' S own initial timing advance value through the available frequency point and the sending time point, and pre-compensating the uplink frequency offset, wherein the pre-compensated uplink frequency offset is equal to the sum of the measured value of the downlink frequency offset of the satellite-borne base station and the error estimation of the double crystal oscillator;

the sending a random access response to the user terminal after the service satellite terminal receives the first data comprises:

step S82: executing steps S5-S8 at the service satellite terminal according to the received time domain preamble signal, and broadcasting the received root sequence number, cyclic shift interval, user timing advance estimation error, physical uplink shared channel scheduling authorization and temporary cell wireless network temporary identification to all users through a physical downlink shared channel after finishing the detection of the time domain preamble signal and obtaining the user timing advance estimation error;

the sending, at the user end, second data to the service satellite according to the random access response includes:

step S83: starting a random access response timer, monitoring the physical downlink shared channel, stopping monitoring until receiving the physical downlink shared channel data sent by the service satellite and containing a root serial number and a cyclic shift interval, and if the physical downlink shared channel data sent by the service satellite does not receive the root serial number and the cyclic shift interval when the random access response timer expires, determining that the access fails, and executing the steps of S81, S82 and S83 again;

step S84: executing step S3, and sending the generated time domain data of the physical uplink shared channel through the physical uplink shared channel resource authorized by the physical uplink shared channel scheduling, where the sending time is a value ahead of the user real timing advance of the transmission time point of the physical uplink shared channel authorized by the serving satellite, where the scrambling identifier used in the scrambling process is generated by calculating the temporary cell radio network temporary identifier and the cell identifier, and the user real timing advance can be obtained by summing the timing advance estimation error provided by the physical downlink shared channel and the user own initial timing advance;

the receiving and processing the second data at the service satellite end to obtain a processing result, including:

step S85: receiving the time domain data of the physical uplink shared channel from a service satellite terminal, extracting user identity identification information and an initial timing advance value of a user contained in the time domain data of the physical uplink shared channel, then calculating a real timing advance value of the user by a satellite-borne base station, and broadcasting the user identity identification information, a root sequence number and a cyclic shift interval detected by the base station to all users through the physical downlink shared channel;

the judging whether the access is successful according to the processing result comprises the following steps:

step S86: starting a timer and analyzing a physical downlink shared channel, if successfully extracting transmitted user identity identification information and transmitting a root sequence number and a cyclic shift interval adopted by a preamble signal, considering that the competitive access is successful, then setting the temporary cell wireless network temporary identification as a cell wireless network temporary identification to finish 4-step random access, and if the timer is overdue, not receiving the transmitted user information in the physical downlink shared channel, considering that the competitive access is failed, and restarting a new 4-step random access process.

9. A random access device facing to a non-ground network is characterized by comprising a parsing module, a coarse positioning module, a first selection module, a second selection module and an access module, wherein,

the analysis module is used for searching a synchronization block broadcasted by the satellite-borne base station at the air interface, and then analyzing the searched synchronization block to obtain analysis data;

the coarse positioning module is used for performing user coarse positioning based on the analytic data after the number of the analyzed synchronous blocks reaches a threshold value, and obtaining a user coarse positioning result;

the second selection module is used for randomly selecting a time point and a frequency point from the time points and the selectable frequency points which are provided by the analysis data and used for initiating the random access process;

and the access module is used for judging whether the user meets the condition of 2-step random access according to the analysis data, if so, initiating 2-step random access to the service satellite, and otherwise, initiating 4-step random access.

10. A non-transitory computer readable storage medium having stored thereon a computer program, wherein the computer program, when executed by a processor, implements the method of any one of claims 1-8.