CN109788548B - Satellite mobile communication random access method, system and medium with time advance compensation - Google Patents

Satellite mobile communication random access method, system and medium with time advance compensation Download PDF

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CN109788548B
CN109788548B CN201910124298.XA CN201910124298A CN109788548B CN 109788548 B CN109788548 B CN 109788548B CN 201910124298 A CN201910124298 A CN 201910124298A CN 109788548 B CN109788548 B CN 109788548B
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prach
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CN109788548A (en
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夏斌
张朝贤
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Shanghai Jiaotong University
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Abstract

The invention provides a satellite mobile communication random access method, a system and a medium with time advance compensation, comprising the following steps: a downlink broadcast sending step: obtaining a cell formed by a satellite beam on the ground, and obtaining a minimum TA in the cell, which is recorded as TAminLet the satellite transmit the satellite position information and TA in the downlink broadcastmin(ii) a Calculating transmission time delay: the UE receives the downlink broadcast, and obtains the satellite position information and TA according to the received downlink broadcastminCalculating the TA relative to the TA estimated by the UEminDifference value TA ofdiff. In the random access process of the satellite, the invention solves the problem of large time overhead caused by long time delay in the random access of the satellite by estimating the transmission time delay in advance at the UE side and compensating when the PRACH is sent, thereby greatly reducing the consumption of the PRACH to uplink resources.

Description

Satellite mobile communication random access method, system and medium with time advance compensation
Technical Field
The invention relates to the technical field of satellite communication, in particular to a satellite mobile communication random access method, a system and a medium with time advance compensation.
Background
Satellite mobile communications have gradually attracted attention in the industry, and most companies and communication organizations consider the convergence of satellite and terrestrial network infrastructures to have great market potential. The importance of satellite communication in 5G has been confirmed in 3GPP Release 14, while the study of 5G technology for satellite communication has been conducted in Release 15. As part of the 5G access technology, satellites are particularly well suited for serving mission critical and industrial applications in ubiquitous coverage.
The provision of wireless access by satellites may help facilitate the launch of 5G services in areas that are out of service or under-served to make up for coverage gaps in terrestrial networks and provide service continuity for user equipment or mobile platforms (e.g., automobiles, airplanes, ships, high-speed rails, etc.) to enhance reliability. By virtue of the superior broadcast/multicast capability of the satellite, efficient data distribution services can be provided for the network edge and the user terminals.
Satellites include space vehicles in Low Earth Orbit (LEO), Medium Earth Orbit (MEO), geostationary orbit (GEO), or High Elliptic Orbit (HEO). Unlike a mobile communication system based on a ground infrastructure, a satellite is far from the ground, and transmission delay is large. The LEO satellite runs on an orbit 500 km-1500 km away from the ground, while the orbit of the GEO satellite is up to 36000km away from the ground, and the distance between a user and the satellite is far beyond the value when the satellite antenna is declined for a small angle. The Round-Trip delay of a satellite transmission is generally expressed in terms of an absolute RTT (Round-Trip Time), which refers to the Round-Trip Time required for a signal to travel between the satellite and a user, and a relative RTT, which refers to the difference between the maximum Round-Trip Time and the minimum Round-Trip Time within the coverage of the satellite. Table 1 gives typical RTT values for GEO and LEO, and it can be seen that GEO has an absolute RTT of up to 500ms, and LEO also has 28 ms.
TABLE 1 typical RTT of GEO and LEO
Figure GDA0002422803710000011
Figure GDA0002422803710000021
Taking an uplink prach (physical random Access channel) channel of the LTE system as an example, the time overhead includes a Preamble and a guard interval (denoted as TGT), where the Preamble includes CP (Cyclic Prefix) time (denoted as TCP) and ZC sequence time (denoted as TSEQ) of OFDM. The UE PRACH signal time received by the base station is shown in fig. 1.
According to the existing design criteria, the following relationships need to be satisfied:
TCP>RTT+τd，TSEQ>RTT+τd，TGT>RTT.
wherein tau isdIs the channel maximum delay spread. Can be used forIt is seen that even if τ is not taken into accountdTotal time overhead T of PRACH channelRACHAt least 3 times the RTT is reserved.
When absolute RTT is used, TRACHIs almost unacceptably large and with relative RTT this problem can be mitigated to some extent. Although the satellite is far away from the users, the path difference between the users closest to the satellite and the users farthest from the satellite in the satellite beam coverage cell is much smaller than the absolute distance, as shown in fig. 2, only L1 is needed to be considered when the random access time of the users is considered, and L1+ L2 is not needed to be considered. The relative RTTs of GEO and LEO in table 1 are 4ms and 2ms, respectively, much smaller than their corresponding absolute RTTs.
Even if relative RTT is adopted, typically 4ms under GEO, the total time overhead of PRACH should be reserved at least for more than 12ms to meet the requirements, which is still much higher than the PRACH requirement of terrestrial transmission. In the most extreme case the relative RTT of the GEO will exceed 4ms, the time overhead of the PRACH will also be greater.
The technical scheme of the prior art I related to the invention is as follows:
the random access process of the existing ground LTE system is shown in fig. 3, and is divided into 4 steps:
step 1, the user sends a random access preamble signal on the PRACH, so that the base station can correctly estimate the transmission delay of the terminal and establish uplink synchronization.
And step 2, the feedback information sent to the terminal by the base station comprises the transmission delay required by uplink synchronization, namely the uplink sending time advance TA.
And 3, the user sends the user identification C-RNTI of the user on the appointed uplink resource.
And step 4, the base station feeds the conflict resolution information back to the user terminal.
The technical details relating to the present invention are embodied in the 1 st and 2 nd steps. The Zadoff-Chu sequence of the Preamble sequence cyclic shift sent by the user on the uplink PRACH is generated by adding a cyclic prefix, because the sequence has good autocorrelation and cross-correlation characteristics, the base station is convenient to detect random signals, and the interference of random access signals of adjacent cells is reduced. In LTE systems per definitionThe number of random access preamble sequences available in a cell is 64. The preamble is a pulse signal in time domain, and comprises a pulse signal with a length of TCPCyclic prefix of length TSEQAnd a length TGTAs shown in fig. 4.
The LTE defines 5 random access preamble formats, as shown in table 2, and respectively corresponds to different cell radii, wherein LTE-FDD supports preamble formats 0 to 3, and LTE-TDD supports preamble formats 0 to 4. As can be seen from TCP and TSEQ in the table, the number of subframes occupied by the 5 formats is 1,2, 3, and 1, and the maximum PRACH time overhead of LTE is 3ms if each subframe time is 1 ms.
Table 2 LTE random access preamble format
Preamble formats TCP/μs TSEQ/μs
0 About 100 About 800
1 About 684 About 800
2 About 200 About 1600
3 About 684 About 1600
4 About 14.6 About 133.3
After receiving the Preamble signal, the base station determines the time position sent by the user through related operations, estimates a Timing Advance (TA, i.e., time Advance) value, and sends the value to the UE through a Timing Advance Command field (total 11 bits, and the range of the corresponding TA index value is 0-1282).
In the above process, the user does not participate in TA calculation, but is estimated by the base station, so T in PRACHGTIt must not be less than the maximum TA of the cell to ensure that interference is not caused and to support the base station to estimate the TA. When the TA is large, the corresponding PRACH channel time overhead may also be large.
The first prior art has the following defects:
in the existing LTE random access process, the time lead of a user is not estimated in advance when the user initiates access, all TA calculation is carried out at a base station, and the PRACH time overhead cannot be borne when the method is used for satellite access. Due to the fact that GEO and LEO satellites are long in transmission distance, large in cell radius and large in time delay difference, the time cost of the PRACH adopting the existing LTE protocol is far higher than that of a ground access system, and the existing random access protocol cannot support satellite scenes and needs to be solved through a certain mechanism.
The technical problems to be solved by the invention are as follows:
the invention provides a method for compensating Timing Advance (TA) by self-estimation of a user when a user randomly accesses between a ground user and a satellite and quantitatively feeding back the TA to the satellite. The method can keep the time overhead of the satellite uplink PRACH close to that of a ground system, and effectively reduces the consumption of the satellite PRACH channel on uplink transmission resources.
Patent document CN107197517A (application number: 201710651008.8) discloses an LTE satellite uplink synchronization method based on TA packets.
The abbreviations and key terms of the present invention are shown in the following table:
Figure GDA0002422803710000041
disclosure of Invention
In view of the defects in the prior art, the present invention aims to provide a time advance compensated satellite mobile communication random access method, system and medium.
The satellite mobile communication random access method with time advance compensation provided by the invention comprises the following steps:
a downlink broadcast sending step: obtaining a cell formed by a satellite beam on the ground, and obtaining a minimum TA in the cell, which is recorded as TAminLet the satellite transmit the satellite position information and TA in the downlink broadcastmin；
Calculating transmission time delay: the UE receives the downlink broadcast, and obtains the satellite position information and TA according to the received downlink broadcastminCalculating the TA relative to the TA estimated by the UEminDifference value TA ofdiff；
And a relative time delay quantization step: according to the obtained difference TAdiffTo TAdiffQuantizing to obtain quantized difference TAdiff_qAnd a quantization level k;
and a PRACH sending step: making UE according to obtained quantized difference value TAdiff_qAnd the quantized difference TA of the quantization level kdiff_qAnd quantizing the grade k, and selecting a Preamble sequence in advance to send the PRACH to the satellite;
and a PRACH receiving step: the time for receiving PRACH is measured by the satellite to obtain the corresponding measured TA offset which is recorded as TAmeasuredDetecting the Preamble sequence at the same time, obtaining the quantization grade k according to the detected Preamble sequence, calculating to obtain the real TA, and recording as TAreal。
Preferably, the downlink broadcast transmitting step:
obtaining the formation of the satellite beam on the ground according to the position of the satellite, the downward inclination angle of the beam and the coverage radiusObtaining the minimum TA in the cell, and recording as TAminLet the satellite transmit the satellite position information and TA in the downlink broadcastmin。
Preferably, the transmission delay calculating step:
the UE receives the downlink broadcast, and obtains the satellite position information and TA according to the received downlink broadcastminThe UE estimates the position of the UE itself and calculates the transmission time delay TA between the UE and the satelliteestLet the coordinates of the satellite and the UE be (x) respectively1,y1,z1) And (x)2,y2,z2) If so, the transmission delay TAestThe calculation formula is as follows:
Figure GDA0002422803710000051
wherein the content of the first and second substances,
TAestrepresenting the transmission delay between the UE and the satellite;
c represents the speed of light in vacuum;
according to the transmission time delay TA between UE and satelliteestCalculating the TA relative to the TA estimated by the UEminDifference value TA ofdiffThe calculation formula is as follows:
TAdiff＝TAest–TAmin
wherein the content of the first and second substances,
TAdiffTA vs. TA representing UE self-estimationminThe difference of (a).
Preferably, the relative delay quantizing step:
according to the obtained difference TAdiffWill TAdiffQuantified as TAdiff_qThe calculation formula is as follows:
Figure GDA0002422803710000052
ΔTA＝TAdiff_max/K
wherein the content of the first and second substances,
Figure GDA0002422803710000053
represents a rounding down, i.e. the largest integer not greater than a given value;
TAdiff_maxrepresents the system-defined maximum TA difference;
k represents the maximum quantization level;
Δ TA denotes a quantization step;
and (3) calculating the quantization level k according to the following calculation formula:
Figure GDA0002422803710000061
wherein the content of the first and second substances,
k denotes quantization level, K is 0,1,2, …, K-1.
Preferably, the PRACH transmitting step:
feeding back the quantization level k to obtain a quantized difference value TAdiff_qFeeding back to a satellite, numbering Preamble sequences in advance and dividing the Preamble sequences into K groups, wherein K is the maximum quantization level, the serial number of the Preamble sequence is denoted as Preamble index, and UE randomly selects a sequence from the kth group of sequences satisfying the Preamble index% K ═ K to send PRACH;
% represents the modulus operation, and the Preamble sequence refers to the information sequence sent to the satellite when the UE randomly accesses, namely the Preamble sequence.
Preferably, the PRACH receiving step:
the time for receiving PRACH is measured by the satellite to obtain the corresponding measured TA offset which is recorded as TAmeasured；
Detecting a Preamble sequence, obtaining a Preamble index of the Preamble sequence according to the detected Preamble sequence, and calculating to obtain a quantization grade k, wherein the calculation formula is as follows:
k＝preambleIndex％K
according to the quantization grade k, calculating to obtain a quantized difference value TAdiff_qThe calculation formula is as follows:
TAdiff_q＝ΔTA×k
according to the obtained quantized difference value TAdiff_qCalculating to obtain a true TA, is denoted as TArealThe calculation formula is as follows:
TAreal＝TAmin+TAdiff_q+TAmeasured
the invention provides a satellite mobile communication random access system with time advance compensation, which comprises:
a downlink broadcast sending module: obtaining a cell formed by a satellite beam on the ground, and obtaining a minimum TA in the cell, which is recorded as TAminLet the satellite transmit the satellite position information and TA in the downlink broadcastmin；
A transmission delay calculation module: the UE receives the downlink broadcast, and obtains the satellite position information and TA according to the received downlink broadcastminCalculating the TA relative to the TA estimated by the UEminDifference value TA ofdiff；
A relative time delay quantization module: according to the obtained difference TAdiffTo TAdiffQuantizing to obtain quantized difference TAdiff_qAnd a quantization level k;
a PRACH sending and TA quantification feedback module: making UE according to obtained quantized difference value TAdiff_qAnd the quantized difference TA of the quantization level kdiff_qAnd quantizing the grade k, and selecting a Preamble sequence in advance to send the PRACH to the satellite;
a PRACH receiving module: the time for receiving PRACH is measured by the satellite to obtain the corresponding measured TA offset which is recorded as TAmeasuredDetecting the Preamble sequence at the same time, obtaining the quantization grade k according to the detected Preamble sequence, calculating to obtain the real TA, and recording as TAreal。
Preferably, the downlink broadcast transmitting module:
according to the position of the satellite, the downward inclination angle of the wave beam and the coverage radius, obtaining a cell formed by the wave beam of the satellite on the ground, obtaining the minimum TA in the cell and recording as TAminLet the satellite transmit the satellite position information and TA in the downlink broadcastmin。
The transmission delay calculation module:
the UE is enabled to receive the downlink broadcast and, according to the received downlink broadcast,obtaining satellite position information and TAminThe UE estimates the position of the UE itself and calculates the transmission time delay TA between the UE and the satelliteestLet the coordinates of the satellite and the UE be (x) respectively1,y1,z1) And (x)2,y2,z2) If so, the transmission delay TAestThe calculation formula is as follows:
Figure GDA0002422803710000071
wherein the content of the first and second substances,
TAestrepresenting the transmission delay between the UE and the satellite;
c represents the speed of light in vacuum;
according to the transmission time delay TA between UE and satelliteestCalculating the TA relative to the TA estimated by the UEminDifference value TA ofdiffThe calculation formula is as follows:
TAdiff＝TAest–TAmin
wherein the content of the first and second substances,
TAdiffTA vs. TA representing UE self-estimationminThe difference of (a).
The relative time delay quantization module:
according to the obtained difference TAdiffWill TAdiffQuantified as TAdiff_qThe calculation formula is as follows:
Figure GDA0002422803710000072
ΔTA＝TAdiff_max/K
wherein the content of the first and second substances,
Figure GDA0002422803710000073
represents a rounding down, i.e. the largest integer not greater than a given value;
TAdiff_maxrepresents the system-defined maximum TA difference;
k represents the maximum quantization level;
Δ TA denotes a quantization step;
and (3) calculating the quantization level k according to the following calculation formula:
Figure GDA0002422803710000074
wherein the content of the first and second substances,
k denotes quantization level, K is 0,1,2, …, K-1.
Preferably, the PRACH transmission and TA quantization feedback module:
feeding back the quantization level k to obtain a quantized difference value TAdiff_qFeeding back to a satellite, numbering Preamble sequences in advance and dividing the Preamble sequences into K groups, wherein K is the maximum quantization level, the serial number of the Preamble sequence is denoted as Preamble index, and UE randomly selects a sequence from the kth group of sequences satisfying the Preamble index% K ═ K to send PRACH;
% represents the modulus operation, and the Preamble sequence refers to the information sequence sent to the satellite when the UE randomly accesses, namely the Preamble sequence.
The PRACH receiving module:
the time for receiving PRACH is measured by the satellite to obtain the corresponding measured TA offset which is recorded as TAmeasured；
Detecting a Preamble sequence, obtaining a Preamble index of the Preamble sequence according to the detected Preamble sequence, and calculating to obtain a quantization grade k, wherein the calculation formula is as follows:
k＝preambleIndex％K
according to the quantization grade k, calculating to obtain a quantized difference value TAdiff_qThe calculation formula is as follows:
TAdiff_q＝ΔTA×k
according to the obtained quantized difference value TAdiff_qCalculating to obtain the true TA, and recording as TArealThe calculation formula is as follows:
TAreal＝TAmin+TAdiff_q+TAmeasured
according to the present invention, there is provided a computer readable storage medium storing a computer program which, when executed by a processor, implements the steps of the time advance compensated satellite mobile communication random access method according to any of the above.
Compared with the prior art, the invention has the following beneficial effects:
1. in the random access process of the satellite, the invention solves the problem of large time overhead caused by long time delay in the random access of the satellite by estimating the transmission time delay in advance at the UE side and compensating when the PRACH is sent, thereby greatly reducing the consumption of the PRACH to uplink resources.
2. The invention realizes the implicit feedback of TA quantization level by selecting preambleIndex in the random access process, does not need to increase extra feedback signaling overhead, ensures that the satellite can obtain the advanced compensation quantity of UE when in random access, and solves the feedback problem of UE transmission delay.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
fig. 1 is a schematic diagram of UE PRACH signal time received by a base station according to a preferred embodiment of the present invention;
FIG. 2 is a schematic diagram of the relative distances between users and satellites within the coverage area of a satellite according to a preferred embodiment of the invention;
fig. 3 is a schematic diagram of an overall LTE random access process provided in a preferred embodiment of the present invention;
fig. 4 is a schematic diagram of a PRACH time domain configuration according to a preferred embodiment of the present invention;
fig. 5 is a diagram illustrating a random access scenario between a terrestrial user and a satellite link according to a preferred embodiment of the present invention;
fig. 6 is a flowchart of a random access method for satellite mobile communication with time advance compensation according to a preferred embodiment of the present invention.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.
The satellite mobile communication random access method with time advance compensation provided by the invention comprises the following steps:
a downlink broadcast sending step: obtaining a cell formed by a satellite beam on the ground, and obtaining a minimum TA in the cell, which is recorded as TAminLet the satellite transmit the satellite position information and TA in the downlink broadcastmin；
Calculating transmission time delay: the UE receives the downlink broadcast, and obtains the satellite position information and TA according to the received downlink broadcastminCalculating the TA relative to the TA estimated by the UEminDifference value TA ofdiff；
And a relative time delay quantization step: according to the obtained difference TAdiffTo TAdiffQuantizing to obtain quantized difference TAdiff_qAnd a quantization level k;
and a PRACH sending step: making UE according to obtained quantized difference value TAdiff_qAnd the quantized difference TA of the quantization level kdiff_qAnd quantizing the grade k, and selecting a Preamble sequence in advance to send the PRACH to the satellite;
and a PRACH receiving step: the time for receiving PRACH is measured by the satellite to obtain the corresponding measured TA offset which is recorded as TAmeasuredDetecting the Preamble sequence at the same time, obtaining the quantization grade k according to the detected Preamble sequence, calculating to obtain the real TA, and recording as TAreal。
Preferably, the downlink broadcast transmitting step:
according to the position of the satellite, the downward inclination angle of the wave beam and the coverage radius, obtaining a cell formed by the wave beam of the satellite on the ground, obtaining the minimum TA in the cell and recording as TAminLet the satellite transmit the satellite position information and TA in the downlink broadcastmin。
Preferably, the transmission delay calculating step:
the UE receives the downlink broadcast, and obtains the satellite position information and TA according to the received downlink broadcastminThe UE estimates the position of the UE itself and calculates the transmission time delay TA between the UE and the satelliteestLet the coordinates of the satellite and the UE be (x) respectively1,y1,z1) And (x)2,y2,z2) If so, the transmission delay TAestThe calculation formula is as follows:
Figure GDA0002422803710000101
wherein the content of the first and second substances,
TAestrepresenting the transmission delay between the UE and the satellite;
c represents the speed of light in vacuum;
according to the transmission time delay TA between UE and satelliteestCalculating the TA relative to the TA estimated by the UEminDifference value TA ofdiffThe calculation formula is as follows:
TAdiff＝TAest–TAmin
wherein the content of the first and second substances,
TAdiffTA vs. TA representing UE self-estimationminThe difference of (a).
Preferably, the relative delay quantizing step:
according to the obtained difference TAdiffWill TAdiffQuantified as TAdiff_qThe calculation formula is as follows:
Figure GDA0002422803710000102
ΔTA＝TAdiff_max/K
wherein the content of the first and second substances,
Figure GDA0002422803710000103
represents a rounding down, i.e. the largest integer not greater than a given value;
TAdiff_maxrepresents the system-defined maximum TA difference;
k represents the maximum quantization level;
Δ TA denotes a quantization step;
and (3) calculating the quantization level k according to the following calculation formula:
Figure GDA0002422803710000104
wherein the content of the first and second substances,
k denotes quantization level, K is 0,1,2, …, K-1.
Preferably, the PRACH transmitting step:
feeding back the quantization level k to obtain a quantized difference value TAdiff_qFeeding back to a satellite, numbering Preamble sequences in advance and dividing the Preamble sequences into K groups, wherein K is the maximum quantization level, the serial number of the Preamble sequence is denoted as Preamble index, and UE randomly selects a sequence from the kth group of sequences satisfying the Preamble index% K ═ K to send PRACH;
% represents the modulus operation, and the Preamble sequence refers to the information sequence sent to the satellite when the UE randomly accesses, namely the Preamble sequence.
Preferably, the PRACH receiving step:
the time for receiving PRACH is measured by the satellite to obtain the corresponding measured TA offset which is recorded as TAmeasured；
Detecting a Preamble sequence, obtaining a Preamble index of the Preamble sequence according to the detected Preamble sequence, and calculating to obtain a quantization grade k, wherein the calculation formula is as follows:
k＝preambleIndex％K
according to the quantization grade k, calculating to obtain a quantized difference value TAdiff_qThe calculation formula is as follows:
TAdiff_q＝ΔTA×k
according to the obtained quantized difference value TAdiff_qCalculating to obtain the true TA, and recording as TArealThe calculation formula is as follows:
TAreal＝TAmin+TAdiff_q+TAmeasured
the satellite mobile communication random access system with the time advance compensation can be realized by the step flow of the satellite mobile communication random access method with the time advance compensation. The time advance compensated satellite mobile communication random access method can be understood as a preferred example of the time advance compensated satellite mobile communication random access system by those skilled in the art.
The invention provides a satellite mobile communication random access system with time advance compensation, which comprises:
a downlink broadcast sending module: obtaining a cell formed by a satellite beam on the ground, and obtaining a minimum TA in the cell, which is recorded as TAminLet the satellite transmit the satellite position information and TA in the downlink broadcastmin；
A transmission delay calculation module: the UE receives the downlink broadcast, and obtains the satellite position information and TA according to the received downlink broadcastminCalculating the TA relative to the TA estimated by the UEminDifference value TA ofdiff；
A relative time delay quantization module: according to the obtained difference TAdiffTo TAdiffQuantizing to obtain quantized difference TAdiff_qAnd a quantization level k;
a PRACH sending and TA quantification feedback module: making UE according to obtained quantized difference value TAdiff_qAnd the quantized difference TA of the quantization level kdiff_qAnd quantizing the grade k, and selecting a Preamble sequence in advance to send the PRACH to the satellite;
a PRACH receiving module: the time for receiving PRACH is measured by the satellite to obtain the corresponding measured TA offset which is recorded as TAmeasuredDetecting the Preamble sequence at the same time, obtaining the quantization grade k according to the detected Preamble sequence, calculating to obtain the real TA, and recording as TAreal。
Preferably, the downlink broadcast transmitting module:
according to the position of the satellite, the downward inclination angle of the wave beam and the coverage radius, obtaining a cell formed by the wave beam of the satellite on the ground, obtaining the minimum TA in the cell and recording as TAminLet the satellite transmit the satellite position information and TA in the downlink broadcastmin。
The transmission delay calculation module:
the UE receives the downlink broadcast, and obtains the satellite position information and TA according to the received downlink broadcastminThe UE estimates the position of the UE itself and calculates the transmission time delay TA between the UE and the satelliteestLet the coordinates of the satellite and the UE be (x) respectively1,y1,z1) And (x)2,y2,z2) If so, the transmission delay TAestThe calculation formula is as follows:
Figure GDA0002422803710000121
wherein the content of the first and second substances,
TAestrepresenting the transmission delay between the UE and the satellite;
c represents the speed of light in vacuum;
according to the transmission time delay TA between UE and satelliteestCalculating the TA relative to the TA estimated by the UEminDifference value TA ofdiffThe calculation formula is as follows:
TAdiff＝TAest–TAmin
wherein the content of the first and second substances,
TAdiffTA vs. TA representing UE self-estimationminThe difference of (a).
The relative time delay quantization module:
according to the obtained difference TAdiffWill TAdiffQuantified as TAdiff_qThe calculation formula is as follows:
Figure GDA0002422803710000122
ΔTA＝TAdiff_max/K
wherein the content of the first and second substances,
Figure GDA0002422803710000123
represents a rounding down, i.e. the largest integer not greater than a given value;
TAdiff_maxrepresents the system-defined maximum TA difference;
k represents the maximum quantization level;
Δ TA denotes a quantization step;
and (3) calculating the quantization level k according to the following calculation formula:
Figure GDA0002422803710000124
wherein the content of the first and second substances,
k denotes quantization level, K is 0,1,2, …, K-1.
Preferably, the PRACH transmission and TA quantization feedback module:
feeding back the quantization level k to obtain a quantized difference value TAdiff_qFeeding back to a satellite, numbering Preamble sequences in advance and dividing the Preamble sequences into K groups, wherein K is the maximum quantization level, the serial number of the Preamble sequence is denoted as Preamble index, and UE randomly selects a sequence from the kth group of sequences satisfying the Preamble index% K ═ K to send PRACH;
% represents the modulus operation, and the Preamble sequence refers to the information sequence sent to the satellite when the UE randomly accesses, namely the Preamble sequence.
The PRACH receiving module:
the time for receiving PRACH is measured by the satellite to obtain the corresponding measured TA offset which is recorded as TAmeasured；
Detecting a Preamble sequence, obtaining a Preamble index of the Preamble sequence according to the detected Preamble sequence, and calculating to obtain a quantization grade k, wherein the calculation formula is as follows:
k＝preambleIndex％K
according to the quantization grade k, calculating to obtain a quantized difference value TAdiff_qThe calculation formula is as follows:
TAdiff_q＝ΔTA×k
according to the obtained quantized difference value TAdiff_qCalculating to obtain the true TA, and recording as TArealThe calculation formula is as follows:
TAreal＝TAmin+TAdiff_q+TAmeasured
according to the present invention, there is provided a computer readable storage medium storing a computer program which, when executed by a processor, implements the steps of the time advance compensated satellite mobile communication random access method according to any of the above.
The present invention will be described more specifically below with reference to preferred examples.
Preferred example 1:
the satellite mobile communication random access method with time advance compensation is suitable for a random access scene of a ground user and a satellite link, and is shown in figure 5. Each wave beam of the satellite forms a cell on the ground, when a mobile user in the cell accesses the network, a downlink broadcast signal of the satellite is received firstly, downlink synchronization is established, the time lead of the mobile user is estimated, then an uplink PRACH leader sequence is sent to the satellite according to the time lead, the satellite obtains the accurate time lead of the user by detecting the sequence number of the leader sequence, PRACH response is sent to the user, a TA value is informed, and the uplink synchronization is completed.
The invention proceeds according to the flow shown in fig. 6. The method comprises the following steps:
1. satellite transmission downlink broadcast
In order to enable the UE to calculate the transmission delay, the satellite will transmit satellite position information in a downlink broadcast. Meanwhile, in order to make the TA quantization reported by the UE more accurate, the satellite should calculate the minimum TA in the cell, i.e. the TAminAnd is transmitted in a downlink broadcast. The satellite can calculate TA through self position, beam downward inclination angle and coverage radiusmin。
UE calculates transmission delay
After receiving the downlink broadcast, the UE resolves the position of the satellite, and simultaneously, the UE needs to estimate its own position through a satellite positioning system or other positioning methods to calculate the transmission delay between the UE and the satellite. Let the coordinates of the satellite and the UE be (x) respectively1,y1,z1) And (x)2,y2,z2) Then delay of transmission
Figure GDA0002422803710000131
Wherein c is 3 × 108m/s is the speed of light in vacuum. Then, the UE calculates the self-estimationDifference of TA with respect to the cell minimum TA: TA (TA)diff＝TAest–TAmin。
3. Relative time delay quantization
In order for the satellite to estimate the timing advance selected by the UE (UE selects a certain amount of time to initiate uplink access in advance so that it can arrive synchronously with other UEs at satellite reception), TA needs to be estimateddiffQuantization is performed. In this step, the UE sends TA to the UEdiffQuantified as TAdiff_q. Let the maximum TA difference value defined by the system be TAdiff_maxWhen the maximum quantization level is K, the quantization step is Δ TA ═ TAdiff_maxK, then
Figure GDA0002422803710000141
Defining quantization levels
Figure GDA0002422803710000142
Figure GDA0002422803710000143
PRACH sending and TA quantization feedback of UE
True TA value TA of UErealThe UE cannot completely determine the TA, and needs to feed back the quantized TA to the satellite, and the satellite combines the quantized value and the actually measured TA offset to determine the true TA, where the actually measured TA offset is the time point when the satellite receives the uplink signal-the time point when the satellite uplink data frame is synchronized. The reason is that the position estimation of the UE may have errors, which causes TA calculation errors, and the TA is more reliable determined by satellite actual measurement; and the satellite must know the TA of the UErealOther processes used in the system, such as HARQ RTT (HARQ Round Trip Time), etc., therefore the UE must feed back the quantized TA.
Based on the above considerations, and in order to reduce the time overhead of PRACH, the UE will be based on the estimated TAestThe PRACH is sent in advance. Considering TAminIs a common part of the time delay of all users in a cell, so each UE can arrive at the base station (satellite) at the same time only by sending in advance according to the relative time delay, namely the advance time is TAdiff_q。
In order to calculate TArealIt is necessary to know the TA adopted by the UEdiff_q. Therefore, the UE feeds back the quantization level K in a certain manner, and when sending the PRACH, the UE numbers a Preamble sequence (the Preamble sequence refers to an information sequence sent to a satellite when the UE randomly accesses, and may also be referred to as a Preamble sequence, the satellite detects the sequence in a synchronous correlation manner, and can know a sequence number adopted by the sequence) and divides the sequence into K groups (where K is the maximum quantization level), and the sequence number of the Preamble is denoted as Preamble index, and the UE randomly selects one sequence from the kth group of sequences satisfying Preamble index% K ═ K to send the PRACH.
5. Satellite reception PRACH
The satellite measures the time offset of receiving PRACH to obtain the corresponding measured TA, namely TAmeasuredMeanwhile, Preamble index is obtained in the process of detecting Preamble. The satellite obtains the quantization grade k and the corresponding TA according to preambendex selected by UEdiff_qThen the real TA of the UE is TAreal＝TAmin+TAdiff_q+TAmeasured。
When the satellite issues the TA indication, only the TA is required to be followedmeasuredThe corresponding TA is indicated, and the UE adds the TA when transmitting signals on the subsequent uplink data channel, uplink control channel, and other channelsdiff_qAnd (4) finishing.
In the prior art, the time advance of the UE is estimated on the network side, so that the PRACH time consumption is large. In the method adopted by the embodiment, in the random access process, the time advance is estimated in advance at the UE side, compensation is given when the PRACH is sent, and the compensation value is fed back to the satellite in a quantization mode. The process estimates TA cooperatively through the UE and the satellite, so that the PRACH time of the satellite link can be reduced to a degree equivalent to that of a ground system.
Those skilled in the art will appreciate that, in addition to implementing the systems, apparatus, and various modules thereof provided by the present invention in purely computer readable program code, the same procedures can be implemented entirely by logically programming method steps such that the systems, apparatus, and various modules thereof are provided in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers, embedded microcontrollers and the like. Therefore, the system, the device and the modules thereof provided by the present invention can be considered as a hardware component, and the modules included in the system, the device and the modules thereof for implementing various programs can also be considered as structures in the hardware component; modules for performing various functions may also be considered to be both software programs for performing the methods and structures within hardware components.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.

Claims (10)

1. A random access method for time advance compensated satellite mobile communication, comprising:
a downlink broadcast sending step: obtaining a cell formed by a satellite beam on the ground, and obtaining a minimum TA in the cell, which is recorded as TAminLet the satellite transmit the satellite position information and TA in the downlink broadcastmin；
Calculating transmission time delay: the UE receives the downlink broadcast, and obtains the satellite position information and TA according to the received downlink broadcastminCalculating the TA relative to the TA estimated by the UEminDifference value TA ofdiff；
And a relative time delay quantization step: according to the obtained difference TAdiffTo TAdiffQuantizing to obtain quantized difference TAdiff_qAnd a quantization level k;
and a PRACH sending step: making UE according to obtained quantized difference value TAdiff_qAnd quantizing the grade k, and selecting a Preamble sequence in advance to send the PRACH to the satellite;
and a PRACH receiving step: the time for receiving PRACH is measured by the satellite to obtain the corresponding measured TA offset which is recorded as TAmeasuredDetecting the Preamble sequence at the same time, and according to the detected Preamble sequence,calculating to obtain true TA, and recording as TAreal。
2. The time advance compensated satellite mobile communication random access method of claim 1, wherein the downlink broadcast transmitting step:
according to the position of the satellite, the downward inclination angle of the wave beam and the coverage radius, obtaining a cell formed by the wave beam of the satellite on the ground, obtaining the minimum TA in the cell and recording as TAminLet the satellite transmit the satellite position information and TA in the downlink broadcastmin。
3. The time advance compensated satellite mobile communication random access method of claim 2, wherein the transmission delay calculating step:
the UE receives the downlink broadcast, and obtains the satellite position information and TA according to the received downlink broadcastminThe UE estimates the position of the UE itself and calculates the transmission time delay TA between the UE and the satelliteestLet the coordinates of the satellite and the UE be (x) respectively1,y1,z1) And (x)2,y2,z2) If so, the transmission delay TAestThe calculation formula is as follows:
Figure RE-FDA0002422803700000011
wherein the content of the first and second substances,
TAestrepresenting the transmission delay between the UE and the satellite;
c represents the speed of light in vacuum;
according to the transmission time delay TA between UE and satelliteestCalculating the TA relative to the TA estimated by the UEminDifference value TA ofdiffThe calculation formula is as follows:
TAdiff＝TAest–TAmin
wherein the content of the first and second substances,
TAdiffTA vs. TA representing UE self-estimationminThe difference of (a).
4. The time advance compensated satellite mobile communication random access method of claim 3, wherein the relative delay quantizing step:
according to the obtained difference TAdiffWill TAdiffQuantified as TAdiff_qThe calculation formula is as follows:
Figure RE-FDA0002422803700000021
ΔTA＝TAdiff_max/K
wherein the content of the first and second substances,
Figure RE-FDA0002422803700000022
represents a rounding down, i.e. the largest integer not greater than a given value;
TAdiff_maxrepresents the system-defined maximum TA difference;
k represents the maximum quantization level;
Δ TA denotes a quantization step;
and (3) calculating the quantization level k according to the following calculation formula:
Figure RE-FDA0002422803700000023
wherein the content of the first and second substances,
k denotes quantization level, K is 0,1,2, …, K-1.
5. The time advance compensated satellite mobile communication random access method of claim 4, wherein the PRACH transmission step:
feeding back the quantization level k to obtain a quantized difference value TAdiff_qFeeding back to a satellite, numbering Preamble sequences in advance and dividing the Preamble sequences into K groups, wherein K is the maximum quantization level, the serial number of the Preamble sequence is denoted as Preamble index, and UE randomly selects a sequence from the kth group of sequences satisfying the Preamble index% K ═ K to send PRACH;
% represents the modulus operation, and the Preamble sequence refers to the information sequence sent to the satellite when the UE randomly accesses, namely the Preamble sequence.
6. The time advance compensated satellite mobile communication random access method of claim 5, wherein the PRACH receiving step:
the time for receiving PRACH is measured by the satellite to obtain the corresponding measured TA offset which is recorded as TAmeasured；
Detecting a Preamble sequence, obtaining a Preamble index of the Preamble sequence according to the detected Preamble sequence, and calculating to obtain a quantization grade k, wherein the calculation formula is as follows:
k＝preambleIndex％K
according to the quantization grade k, calculating to obtain a quantized difference value TAdiff_qThe calculation formula is as follows:
TAdiff_q＝ΔTA×k
according to the obtained quantized difference value TAdiff_qCalculating to obtain the true TA, and recording as TArealThe calculation formula is as follows:
TAreal＝TAmin+TAdiff_q+TAmeasured。
7. a time advance compensated satellite mobile communications random access system, comprising:
a downlink broadcast sending module: obtaining a cell formed by a satellite beam on the ground, and obtaining a minimum TA in the cell, which is recorded as TAminLet the satellite transmit the satellite position information and TA in the downlink broadcastmin；
A transmission delay calculation module: the UE receives the downlink broadcast, and obtains the satellite position information and TA according to the received downlink broadcastminCalculating the TA relative to the TA estimated by the UEminDifference value TA ofdiff；
A relative time delay quantization module: according to the obtained difference TAdiffTo TAdiffQuantizing to obtain quantized difference TAdiff_qAnd a quantization level k;
a PRACH sending and TA quantification feedback module: making UE according to obtained quantized difference value TAdiff_qAnd quantizing the grade k, and selecting a Preamble sequence in advance to send the PRACH to the satellite;
a PRACH receiving module: the time for receiving PRACH is measured by the satellite to obtain the corresponding measured TA offset which is recorded as TAmeasuredDetecting the Preamble sequence at the same time, obtaining the quantization grade k according to the detected Preamble sequence, calculating to obtain the real TA, and recording as TAreal。
8. The time advance compensated satellite mobile communication random access system of claim 7, wherein the downlink broadcast transmitting module:
according to the position of the satellite, the downward inclination angle of the wave beam and the coverage radius, obtaining a cell formed by the wave beam of the satellite on the ground, obtaining the minimum TA in the cell and recording as TAminLet the satellite transmit the satellite position information and TA in the downlink broadcastmin；
The transmission delay calculation module:
the UE receives the downlink broadcast, and obtains the satellite position information and TA according to the received downlink broadcastminThe UE estimates the position of the UE itself and calculates the transmission time delay TA between the UE and the satelliteestLet the coordinates of the satellite and the UE be (x) respectively1,y1,z1) And (x)2,y2,z2) If so, the transmission delay TAestThe calculation formula is as follows:
Figure RE-FDA0002422803700000031
wherein the content of the first and second substances,
TAestrepresenting the transmission delay between the UE and the satellite;
c represents the speed of light in vacuum;
according to the transmission time delay TA between UE and satelliteestCalculating the TA relative to the TA estimated by the UEminDifference value TA ofdiffThe calculation formula is as follows:
TAdiff＝TAest–TAmin
wherein the content of the first and second substances,
TAdiffTA vs. TA representing UE self-estimationminA difference of (d);
the relative time delay quantization module:
according to the obtained difference TAdiffWill TAdiffQuantified as TAdiff_qThe calculation formula is as follows:
Figure RE-FDA0002422803700000041
ΔTA＝TAdiff_max/K
wherein the content of the first and second substances,
Figure RE-FDA0002422803700000042
represents a rounding down, i.e. the largest integer not greater than a given value;
TAdiff_maxrepresents the system-defined maximum TA difference;
k represents the maximum quantization level;
Δ TA denotes a quantization step;
and (3) calculating the quantization level k according to the following calculation formula:
Figure RE-FDA0002422803700000043
wherein the content of the first and second substances,
k denotes quantization level, K is 0,1,2, …, K-1.
9. The time advance compensated satellite mobile communications random access system of claim 8, wherein the PRACH transmission and TA quantization feedback module:
feeding back the quantization level k to obtain a quantized difference value TAdiff_qFeeding back to the satellite, numbering the Preamble sequence in advance and dividing the Preamble sequence into K groups, wherein K is the maximum quantization level, the serial number of the Preamble sequence is denoted as Preamble index, and the UE meets the requirement that the Preamble index% K is KRandomly selecting one sequence from the kth group of sequences to send the PRACH;
% represents the modulus operation, and the Preamble sequence refers to an information sequence sent to a satellite when the UE randomly accesses, namely a leader sequence;
the PRACH receiving module:
the time for receiving PRACH is measured by the satellite to obtain the corresponding measured TA offset which is recorded as TAmeasured；
Detecting a Preamble sequence, obtaining a Preamble index of the Preamble sequence according to the detected Preamble sequence, and calculating to obtain a quantization grade k, wherein the calculation formula is as follows:
k＝preambleIndex％K
according to the quantization grade k, calculating to obtain a quantized difference value TAdiff_qThe calculation formula is as follows:
TAdiff_q＝ΔTA×k
according to the obtained quantized difference value TAdiff_qCalculating to obtain the true TA, and recording as TArealThe calculation formula is as follows:
TAreal＝TAmin+TAdiff_q+TAmeasured。
10. a computer readable storage medium storing a computer program, wherein the computer program, when executed by a processor, performs the steps of the time advance compensated satellite mobile communication random access method of any one of claims 1 to 6.
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