CN113938177B - Low orbit satellite mobile communication random access method based on LTE - Google Patents
Low orbit satellite mobile communication random access method based on LTE Download PDFInfo
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- 239000013256 coordination polymer Substances 0.000 claims description 15
- 238000013468 resource allocation Methods 0.000 claims description 10
- 125000004122 cyclic group Chemical group 0.000 claims description 4
- 101150039363 SIB2 gene Proteins 0.000 claims 2
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- 229910052741 iridium Inorganic materials 0.000 description 8
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W74/00—Wireless channel access
- H04W74/08—Non-scheduled access, e.g. ALOHA
- H04W74/0833—Random access procedures, e.g. with 4-step access
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/14—Relay systems
- H04B7/15—Active relay systems
- H04B7/185—Space-based or airborne stations; Stations for satellite systems
- H04B7/1853—Satellite systems for providing telephony service to a mobile station, i.e. mobile satellite service
- H04B7/18532—Arrangements for managing transmission, i.e. for transporting data or a signalling message
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/14—Relay systems
- H04B7/15—Active relay systems
- H04B7/185—Space-based or airborne stations; Stations for satellite systems
- H04B7/1853—Satellite systems for providing telephony service to a mobile station, i.e. mobile satellite service
- H04B7/18539—Arrangements for managing radio, resources, i.e. for establishing or releasing a connection
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W56/00—Synchronisation arrangements
- H04W56/004—Synchronisation arrangements compensating for timing error of reception due to propagation delay
- H04W56/0045—Synchronisation arrangements compensating for timing error of reception due to propagation delay compensating for timing error by altering transmission time
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W72/00—Local resource management
- H04W72/04—Wireless resource allocation
- H04W72/044—Wireless resource allocation based on the type of the allocated resource
- H04W72/0446—Resources in time domain, e.g. slots or frames
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W72/00—Local resource management
- H04W72/04—Wireless resource allocation
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Abstract
A low orbit satellite mobile communication random access method based on LTE belongs to the technical field of satellite communication, and comprises the following steps: the base station periodically transmits a random access configuration message through a system information block SIB 2; when the terminal UE needs to initiate random access, selecting a proper RA preamble sequence according to the configuration message and sending the RA preamble sequence to the base station; the base station correspondingly executes a preamble sequence detection algorithm to acquire whether a random access request is initiated by the terminal UE, acquires propagation delay between the terminal UE and the base station, performs timing advance TA estimation, and is used for establishing uplink synchronization by the terminal UE; for each random access request, the base station feeds back a random access response RAR; after receiving the random access response RAR, the terminal adjusts the sending time sequence accordingly to finish the uplink synchronization.
Description
Technical Field
The invention relates to a low orbit satellite mobile communication random access method based on LTE, belonging to the technical field of satellite communication.
Background
A Random Access (RA) technology is one of key technologies of uplink Access of LTE (Long Time Evolution, long term evolution technology), and a terminal can establish connection with a cell and acquire uplink synchronization only through a Random Access procedure, and acquire a unique user identifier of the terminal in the cell. The random access shares two modes of contention and non-contention access, wherein under the condition of contention random access, a preamble sequence sent by UE (user equipment) and time-frequency resources occupied by the preamble sequence are randomly selected by the UE. Different UEs may initiate random access on the same time-frequency resource, causing collision, and then decide which UE wins by contention. Under the non-competitive random access condition, the leading sequence sent by the UE and the time-frequency resources occupied by the leading sequence are distributed by the base station, the base station sends random access configuration information through the downlink, the UE sends leading signals on the appointed time-frequency resources according to the appointed leading sequence of the base station, and the base station can ensure that the leading sequences or the time-frequency resources of different UEs are different, so that collision can not happen.
As shown in fig. 1, the eNB (Evolved Node B) periodically issues a random access configuration message through SIB2 (System Information Block ), and then the terminal selects an appropriate preamble sequence according to the configuration message to initiate random access on an appropriate time-frequency resource. After receiving the preamble sequence, the eNB detects the TA (Timing Advance) value corresponding to the terminal and the preamble sequence index used by the same, and because a plurality of terminals may initiate random access requests at the same time, the eNB may detect a plurality of random access requests, and for each random access request, the eNB needs to feed back a random access response RAR (Random Access Response ). After receiving the RAR, the terminal needs to correspondingly adjust the sending time sequence to finish the uplink synchronization. For non-contention random access, the random access procedure ends up, but multiple terminals in contention random access initiate random access at the same time may cause collisions, so that subsequent steps are required to resolve (i.e. RRC message round trip in fig. 1) the collisions.
When the UE needs to initiate random access, the RA preamble sequence is required to be sent first, the eNB correspondingly executes a preamble sequence detection algorithm, through the algorithm, the eNB can know whether the UE initiates the random access request or not, and can also calculate the propagation delay between the UE and the eNB, namely, perform timing advance TA estimation, wherein the purpose of TA estimation is to help the UE to establish uplink synchronization.
The random access preamble sequence under the LTE system comprises a cyclic prefix CP, a sequence SEQ and a guard interval GT, the duration time of the cyclic prefix CP, the sequence SEQ and the guard interval GT is respectively marked as T CP、TSEQ and T GT, and the time domain form is shown in figure 2.
In LTE, the duration of CP and GT is typically the largest difference in round trip delay within a cell, and the duration of the sequence T SEQ should be as long as possible and greater than the largest difference in round trip delay within a cell. For FDD (Frequence Division Duplexing, frequency division duplex) mode, LTE defines four different random sequence formats according to different application scenarios of terrestrial mobile communication, as shown in fig. 3.
In general, the larger the cell coverage, the longer the sequence duration, and longer CPs and GTs are needed to compensate for the longer round trip delay due to the cell radius.
Because the LEO-LTE system has larger satellite-ground link time delay and wider beam coverage, the coverage radius and the maximum round trip time delay difference of a cell are larger than those of the land LTE system, and the random access in the land LTE system is not suitable for the LEO-LTE system.
[ Patent number: 201210019547.7, a method and a device for implementing initial synchronization in a satellite communication system, which aim at the time delay of a larger satellite-to-ground link in a satellite mobile communication system, are provided, and a method for determining the time delay difference of the terminal according to the system longitude and latitude related configuration information carried by a network side broadcast message is provided. However, this method requires acquiring the location information of the terminal through GPS, and is not applicable to the satellite mobile communication system when the location information of the terminal cannot be acquired.
[ Patent number: 201310271772.4, in the initial random access two-step delay measurement method compatible with the LTE mode satellite communication, aiming at the larger satellite-to-ground link delay in the satellite mobile communication system, the two-step delay measurement method is adopted to solve the problem of large delay. Firstly dividing a cell in a satellite communication system into a plurality of sub-regions according to time delay values, and when the first step of random access is performed, a user terminal sends an uplink random access signal to reach a satellite side receiving end through transmission time delay; when the second step is random access, the user sends a preamble in advance, and the advanced time is the first round trip delay difference measured in the first step; obtaining a third round trip delay difference between the terminal and the center of the satellite communication system cell according to the first round trip delay difference and the second round trip delay difference; and according to the third round trip delay difference, measuring the transmission delay difference of the current user relative to the user nearest to the satellite. However, the method increases the number of random access times of the system, and increases the system overhead.
Therefore, for the larger satellite-to-ground link delay and wider beam coverage in the LEO-LTE system, a random access method suitable for being applied to the LEO-LTE system needs to be designed.
The main disadvantages of the current technology are: because the LEO-LTE system has larger satellite-ground link time delay and wider beam coverage, the coverage radius and the maximum round trip time delay difference of a cell are larger than those of the land LTE system, and the random access scheme of the land LTE system is not suitable for the LEO-LTE system. However, in the first method, the terminal position information needs to be acquired through the GPS, but when the GPS is not available or the terminal position information is unknown due to other problems, the delay difference cannot be calculated. The second method increases the number of random accesses of the system, and increases the system overhead.
Disclosure of Invention
The invention solves the technical problems that: the random access method for the low orbit satellite mobile communication based on the LTE is provided for overcoming the defects of the prior art, and a random access scheme suitable for being applied to the LEO-LTE system is designed aiming at the characteristics of larger satellite-to-ground link time delay, wider beam coverage range and the like in the LEO-LTE system, and particularly, the random access scheme is designed to be an RA configuration method and a frame structure.
The technical scheme of the invention is as follows: the low orbit satellite mobile communication random access method based on LTE comprises the following steps:
the base station periodically transmits a random access configuration message through a system information block SIB 2;
when the terminal UE needs to initiate random access, selecting a proper RA preamble sequence according to the configuration message and sending the RA preamble sequence to the base station;
The base station correspondingly executes a preamble sequence detection algorithm to acquire whether a random access request is initiated by the terminal UE, acquires propagation delay between the terminal UE and the base station, performs timing advance TA estimation, and is used for establishing uplink synchronization by the terminal UE; for each random access request, the base station feeds back a random access response RAR;
after receiving the random access response RAR, the terminal adjusts the sending time sequence accordingly to finish the uplink synchronization.
Further, in the RA leader sequence, T CP＝TGT＝ΔTRTD is satisfied; wherein, T CP is cyclic prefix time, T GT is guard interval time, and Δt RTD is the difference between the maximum round trip delay and the minimum round trip delay of the cell in the LEO-LTE system.
Further, the system information block SIB2 includes a leoFlag value for identifying the LEO-LTE cell, a number for identifying the satellite to which the current beam belongs in the entire low orbit constellation, a position number for representing the current beam on the LEO satellite, and longitude and latitude where two values are used for representing the position of the point under the current satellite.
Further, when the terminal UE detects leoFlag in the system information block SIB2 as TRUE, the procedure and parameters for generating and transmitting the RA preamble sequence are operated and set according to the LEO-LTE mode.
Further, in the LEO-LTE mode, the RA preamble sequence further comprises a long preamble sequence; the RA configuration information includes a frequency domain start position of the long preamble sequence and a time-frequency resource configuration.
Further, in the RA configuration information, two fields of the PRACH configuration SIB and the PRACH configuration include a long preamble sequence PRACH configuration field, which is used to indicate a time-frequency resource configuration index and a frequency-domain offset value of the long preamble sequence; the prach-ConfigInfo field is used to indicate the time domain resource allocation index and the frequency domain offset value of the short preamble sequence.
Further, the terminal UE uses a long preamble sequence or a short preamble sequence, respectively, according to whether the location information is known.
Further, the long preamble sequence or the short preamble sequence occupies the same frequency domain resource, there is no overlap in time domain, and the long preamble sequence or the short preamble sequence appears in an interlaced manner.
Further, the long preamble sequence or the short preamble sequence occupies different frequency domain resources, overlap is allowed in the time domain, and the start time of the long preamble sequence or the short preamble sequence is different.
Further, in the random access response RAR, the time unit of TA Command is increased to 128T s, and the corresponding TA time range is [0,5.34ms ].
Compared with the prior art, the invention has the advantages that:
1) Depending on whether the terminal location is known, the terminal may itself send either a long preamble or a short preamble.
2) Improvements to SIB2 random access configuration information add LEO-LTE cell identification field (leoFlag) and long preamble PRACH configuration information field (PRACH-ConfigInfo _long).
3) A configuration scheme of preamble sequence time-frequency resource, an interleaving scheme and an overlapping scheme. The method has the beneficial effects that the base station can receive two preamble sequences simultaneously, so that the number of users supported by the system is increased.
4) In the time domain resource allocation scheme, the long and short preamble sequences cannot start at the same time. The beneficial effects brought by the method are that RA-RNTI calculated by the long and short leader sequences are different, so that the RAR responded by the eNB does not appear in the same subframe aiming at the long and short leader sequences, and the eNB does not need to indicate that the long leader sequence or the short leader sequence is detected in the RAR.
5) The time unit value of TA Command in the RAR field increases. The beneficial effect of the method is that 11-bit TA Command in the land LTE is continuously used, so that the compatibility with the land LTE is ensured.
Drawings
Fig. 1 is a schematic diagram of a random access procedure;
Fig. 2 is a time domain version of a random access preamble sequence;
Fig. 3 is an LTE FDD random access preamble sequence format;
FIG. 4 is a diagram of a time domain resource allocation (allocation indexes 0 and 1) of the interleaving scheme of the present invention;
FIG. 5 is a time domain resource allocation diagram (allocation index 0) of the overlapping scheme of the present invention;
FIG. 6 is a schematic diagram of a MAC RAR of the present invention;
fig. 7 is a random access procedure of the LEO-LTE system of the present invention.
Detailed Description
In order to better understand the above technical solutions, the following detailed description of the technical solutions of the present application is made by using the accompanying drawings and specific embodiments, and it should be understood that the specific features of the embodiments and the embodiments of the present application are detailed descriptions of the technical solutions of the present application, and not limiting the technical solutions of the present application, and the technical features of the embodiments and the embodiments of the present application may be combined with each other without conflict.
The random access scheme of the low orbit mobile satellite communication based on the LTE is to correspondingly improve the random access process of the LTE on land, and mainly improves the first three steps of the random access process, namely RA configuration information, a preamble sequence and a random access response, so that the random access scheme is suitable for an LEO-LTE system.
The following describes the LTE-based low-orbit satellite mobile communication random access method in detail with reference to the accompanying drawings, and the specific implementation manner may include (as shown in fig. 1 to 7):
designing a new preamble sequence, a long preamble sequence
For larger satellite-to-ground link delay and wider beam coverage in the LEO-LTE system, new preamble sequences need to be designed, so that T CP、TSEQ and T GT of the new preamble sequences can meet T CP＝TGT＝ΔTRTD, wherein DeltaT RTD is the difference between the maximum round trip delay and the minimum round trip delay of a cell in the LEO-LTE system, namely DeltaT RTD＝RTDmax-RTDmin, and the duration T SEQ of the sequences should be as long as possible and larger than the maximum round trip delay difference in the cell. Taking an iridium system as an example, the track height is 780km, the minimum communication elevation angle is 8.2 degrees, 48 spot beams can be provided for each star, 48 cells are formed on the earth, the radius of each cell is about 333.5km, the maximum round trip delay difference of the outermost cell is about 4.48ms, the maximum cell radius which can be supported in a land LTE system is 100km, the maximum round trip delay difference is 0.68ms, and the maximum round trip delay difference is smaller than the cell radius and the maximum round trip delay difference in the iridium system. Therefore, a new preamble sequence needs to be designed, and a specific new preamble sequence design and detection method are not in the scope of this patent, and only the duration of T CP and T GT of the new preamble sequence is 4.8ms, the duration of T SEQ is 6.4ms, and the total duration is 16 ms. In this patent, a new preamble sequence is referred to as a long preamble sequence, and an original preamble sequence in an LTE system is referred to as a short preamble sequence.
RA configuration information improvement
In the LEO-LTE system, the UE needs to acquire related information about satellites and beams, and SIB2 is used for transmitting cell access restriction information and common channel parameter information, so that the SIB2 of the land LTE is improved, specifically, a 1-bit Boolean type leoFlag is added in a SIB2 system message block to identify an LEO-LTE cell, if the UE detects that the bit is TRUE, the UE considers that the bit resides in the LEO-LTE cell, and all subsequent working parameters and flows are set according to the LEO-LTE system, otherwise, the UE is set according to the land LTE system; adding a 1-byte numerical value for identifying the number of the satellite to which the current beam belongs in the whole low orbit constellation; adding 1 byte to represent the position number of the current beam on the LEO satellite; two Double type values are added to represent the longitude and latitude of the current satellite's point-under-satellite position. The detailed SIB2 information element is shown in fig. 4, in which the bolded part is newly added satellite broadcast information.
When UE detects leoFlag in SIB2 as TRUE, RA flow and parameters are operated and set according to LEO-LTE mode. In the LEO-LTE system, a long preamble sequence is added, so that the frequency domain starting position and time-frequency resource configuration of the long preamble sequence are needed in RA configuration information, two fields of PRACH configuration SIB (PRACH-ConfigSIB) and PRACH configuration (PRACH-Config) are improved, a long preamble sequence PRACH configuration (PRACH-ConfigInfo _long) field is added for indicating the time-frequency resource configuration index and the frequency domain offset value of the long preamble sequence, and an original PRACH-ConfigInfo field is used for indicating the time-domain resource configuration index and the frequency domain offset value of the short preamble sequence. The specific modification is shown in the bold portion of fig. 5.
The terminal uses different preamble sequences, long preamble sequences or short preamble sequences, respectively, depending on whether the location information is known or not.
When the terminal location information is known, a short preamble sequence or a long preamble sequence may be used; when the terminal location information is unknown, only a long preamble sequence can be used. The PRACH (Physical Random ACCESS CHANNEL Physical Random access channel) corresponding to each of the long and short preamble sequences is denoted as prach_l and prach_s, respectively. In LEO-LTE, in order to be able to support both types of terminals at the same time, time-frequency resources must be scheduled for prach_l and prach_s accordingly.
This patent proposes two time domain resource allocation schemes, respectively called an interleaving scheme and an overlapping scheme
The interleaving scheme means that prach_l and prach_s occupy the same frequency domain resource, but overlap is not allowed in the time domain, and prach_l and prach_s are interleaved. Since overlapping is allowed in the frequency domain, the interleaving scheme can be applied under any system bandwidth. As shown in table 1, some possible time domain resource allocation schemes for the interleaving scheme are shown in fig. 6, where the time domain allocation effects corresponding to the configuration schemes 0 and 1 are shown in fig. 6.
Table 1 interleaving scheme time domain resource configuration example
The overlapping scheme means that prach_l and prach_s occupy different frequency domain resources, and overlap is allowed in the time domain, but prach_l and prach_s cannot start at the same time, i.e. when prach_s occurs, prach_l must not occur at the same time, but prach_l may occur on a subsequent subframe. Since prach_l and prach_s occupy different frequency domain resources, the overlapping scheme is suitable for use in a larger system bandwidth. As shown in table 2, are some possible time domain resource allocation schemes for the overlapping scheme. The time domain configuration effect corresponding to the configuration scheme 0 is shown in fig. 7.
Table 2 example of overlapping scheme time domain resource configuration
Because prach_l and prach_s do not start at the same time, so that RA-RNTI (Random ACCESS RNTI, random access radio network identifier) calculated by the long and short preamble sequences is different, for the long and short preamble sequences, the RAR responded by the eNB does not appear in the same subframe, and because the base station can receive both preamble sequences at the same time, the number of support users can be increased by 1 time compared with the terrestrial LTE system.
The RAR is correspondingly improved.
In the terrestrial LTE protocol, the field of the RAR is shown in fig. 6, where the TA Command occupies 11 bits, the range of the TA Command is [0,1282], the unit is 16T s (the minimum sampling interval when the bandwidth is 1.4M), and the corresponding TA time range is [0,667.66 μs ], but the delay in the LEO-LTE system is larger, for example, the iridium system, the maximum round trip delay difference of the outermost cell is 4.48ms, and the TA Command of 11 bits in the original RAR is insufficient to represent such a large delay.
To ensure compatibility with terrestrial LTE, the patent continues to follow the 11-bit TA Command, but the time unit is increased to 128T s (which corresponds to a time length of 8 samples at a bandwidth of 1.4 MHz), and the corresponding TA time range is [0,5.34ms ], so that the delay in the iridium system can be represented by the 11-bit TA Command.
In the terrestrial LTE protocol, the receiving window starts from the 3 rd subframe after the subframe where the preamble is sent (if the preamble spans multiple subframes in the time domain, it is calculated as the last subframe), and compared with the terrestrial LTE, the scheme provides that the minimum satellite-to-ground transmission round trip delay is RTD min, the minimum satellite-to-ground transmission round trip delay is [ RTD min ] ([ ] means the whole down) subframes, the RAR receiving window start time is pushed back by [ RTD min ], the maximum round trip delay difference is Δt RTD, the whole down is [ Δt RTD ], and the size of the receiving window is increased by [ Δt RTD ] subframes on the basis of the terrestrial LTE.
This patent is further described below in connection with specific embodiments.
Taking an iridium satellite orbit parameter as an example, the orbit height is 780km, the minimum communication elevation angle is 8.2 degrees, the communication frequency band uses L frequency bands, the uplink frequency and the downlink frequency are 1610-1626.5 MHz, each satellite can provide 48 spot beams, 48 cells are formed on the earth, the radius of each cell is about 333.5km, the maximum round trip delay difference in the outermost cell is DeltaT RTD =4.48 ms, according to the previous analysis, the duration of the CP and GT of the random access preamble should be 2 times of the propagation delay difference, namely T CP＝TGT＝ΔTRTD, and the duration of the sequence T SEQ should be as long as possible and larger than the maximum round trip delay difference in the cell. The design parameter for the long preamble duration should be T CP＝TGT＝4.8ms,TSEQ =6.4 ms and the total duration should be 16ms.
The main content of the patent comprises the first three steps of the random access procedure, namely RA configuration information, a preamble sequence and random access response. The random access flow is shown in fig. 7.
As shown in fig. 7, step 1 is that the eNB sends random access configuration information, and the number field (leoSN) of the satellite in the whole low orbit constellation to which the beam belongs in SIB2, the position number field (cellLocSN) of the beam on the LEO satellite, and the latitude and longitude field (leoLoc) of the satellite point position are set according to the satellite related information, which is not described herein. The LEO-LTE cell indication flag bit leoFlag in SIB2 is set to TRUE for indicating that the subsequent operating parameters and procedures are set according to the LEO-LTE system. Both the interleaving scheme and the overlapping scheme may be used, and the PRACH-ConfigInfo _long field of the two PRACH-ConfigSIB and PRACH-Config fields may be set according to table 1 or table 2.
In step 2, the terminal selects either the long preamble sequence or the short preamble sequence according to whether the location information is known. If the terminal position information is known, a short preamble sequence or a long preamble sequence is selected, if the terminal position information is unknown, a long preamble sequence is selected, and time domain resource allocation is performed according to the random access configuration information in step 1, for example, the random access configuration information selects a time domain resource allocation scheme for configuring index 0 in table 2, that is, an overlapping scheme is adopted, the long preamble sequence is transmitted in a number 4 subframe of any system frame, the short preamble sequence is transmitted in any subframe except the number 4 subframe of any system frame, and the allocation scheme is shown in fig. 7.
In the terrestrial LTE protocol, the receiving window starts from the 3 rd subframe after the subframe where the preamble is sent (if the preamble spans multiple subframes in the time domain, it is calculated by the last subframe), the minimum transmission delay of the satellite-to-ground link in the iridium system is 2.6ms, the minimum round trip delay is 5.2ms, and the round trip delay is reduced by about 5 subframes, then the starting time of the RAR receiving window is pushed by 5 subframes, that is, the RAR receiving window starts from the 8 th subframe after the subframe where the preamble is sent. The maximum transmission delay of the satellite-ground link is 8.24ms, the maximum round-trip delay is about 16ms, the maximum round-trip delay and the minimum round-trip delay are different by about 11ms, and the size of a receiving window is increased by 11 subframes on the basis of terrestrial LTE.
In step 3, the eNB detects the Preamble sequence sent by the terminal, calculates RA-RNTI, preamble ID and TA value, encapsulates the RA-RNTI, preamble ID and TA value into RAR and sends the RAR to the terminal. Under the iridium satellite system, the maximum round trip delay difference of the outermost cell is 4.48ms, the patent continues to use TACommand of 11 bits in the RAR field, the time unit is increased from 16T S to 128T S, the corresponding TA time range is [0,5.34ms ], and the time delay under the iridium satellite system can be represented by TACommand of 11 bits.
Up to this point, the first three steps of the random access procedure specified in this patent, that is, the random access configuration information, the terminal sending preamble sequence and the random access response are all completed, and the subsequent random access procedure is still performed along the random access procedure of the terrestrial LTE system, which is not described herein again.
It will be apparent to those skilled in the art that various modifications and variations can be made to the present application without departing from the spirit or scope of the application. Thus, it is intended that the present application also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
What is not described in detail in the present specification is a well known technology to those skilled in the art.
Claims (6)
1. The low orbit satellite mobile communication random access method based on the LTE is characterized by comprising the following steps:
the base station periodically transmits a random access configuration message through a system information block SIB 2;
when the terminal UE needs to initiate random access, selecting a proper RA preamble sequence according to the configuration message and sending the RA preamble sequence to the base station;
The base station correspondingly executes a preamble sequence detection algorithm to acquire whether a random access request is initiated by the terminal UE, acquires propagation delay between the terminal UE and the base station, performs timing advance TA estimation, and is used for establishing uplink synchronization by the terminal UE; for each random access request, the base station feeds back a random access response RAR;
after receiving the random access response RAR, the terminal correspondingly adjusts the sending time sequence to finish uplink synchronization;
in the RA preamble sequence, T CP＝TGT＝ΔTRTD is satisfied; wherein, T CP is the cyclic prefix time, T GT is the guard interval time, and DeltaT RTD is the difference between the maximum round trip delay and the minimum round trip delay of a cell in the LEO-LTE system;
The system information block SIB2 comprises leoFlag values for identifying the LEO-LTE cell, a number for identifying the satellite to which the current beam belongs in the whole low-orbit constellation, a position number for representing the current beam on the LEO satellite and longitude and latitude of two values for representing the position of the point under the current satellite;
When detecting that leoFlag in a system information block SIB2 is TRUE, the terminal UE generates and transmits a flow and parameters of an RA preamble sequence to operate and set in an LEO-LTE mode;
In the LEO-LTE mode, the RA preamble sequence further comprises a long preamble sequence; the RA configuration information includes a frequency domain start position of the long preamble sequence and a time-frequency resource configuration.
2. The LTE-based low-orbit satellite mobile communication random access method according to claim 1, wherein the two fields of PRACH configuration SIB and PRACH configuration in RA configuration information include a long preamble sequence PRACH configuration field for indicating a time-frequency resource configuration index and a frequency domain offset value of the long preamble sequence; the prach-ConfigInfo field is used to indicate the time domain resource allocation index and the frequency domain offset value of the short preamble sequence.
3. The LTE-based low-orbit satellite mobile communication random access method according to claim 1, wherein the terminal UE uses a long preamble sequence or a short preamble sequence, respectively, according to whether the location information is known or not.
4. The random access method for LTE-based low-orbit satellite mobile communication according to claim 3, wherein the long preamble sequence or the short preamble sequence occupies the same frequency domain resource, there is no overlap in time domain, and the long preamble sequence or the short preamble sequence is staggered.
5. A low-orbit satellite mobile communication random access method according to claim 3, wherein the long preamble sequence or the short preamble sequence occupies different frequency domain resources, and overlap is allowed in time domain, and the start time of the long preamble sequence or the short preamble sequence is different.
6. The LTE-based low-orbit satellite mobile communication random access method according to claim 1, wherein: in the random access response RAR, the time unit of the TA Command is increased to 128T s, and the corresponding TA time range is [0,5.34ms ].
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