CN115297560A - Random access method and device for low-orbit constellation and electronic equipment - Google Patents

Random access method and device for low-orbit constellation and electronic equipment Download PDF

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Publication number
CN115297560A
CN115297560A CN202210920809.0A CN202210920809A CN115297560A CN 115297560 A CN115297560 A CN 115297560A CN 202210920809 A CN202210920809 A CN 202210920809A CN 115297560 A CN115297560 A CN 115297560A
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random access
parameter
frequency offset
frequency
satellite
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谢涛
马长链
付艳艳
罗建松
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Beijing Commsat Technology Development Co Ltd
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Beijing Commsat Technology Development Co Ltd
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W74/00—Wireless channel access, e.g. scheduled or random access
    • H04W74/002—Transmission of channel access control information
    • H04W74/006—Transmission of channel access control information in the downlink, i.e. towards the terminal
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/01—Reducing phase shift
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
    • H04L25/03006—Arrangements for removing intersymbol interference
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W74/00—Wireless channel access, e.g. scheduled or random access
    • H04W74/08—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access]
    • H04W74/0833—Non-scheduled or contention based access, e.g. random access, ALOHA, CSMA [Carrier Sense Multiple Access] using a random access procedure
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W84/00—Network topologies
    • H04W84/02—Hierarchically pre-organised networks, e.g. paging networks, cellular networks, WLAN [Wireless Local Area Network] or WLL [Wireless Local Loop]
    • H04W84/04—Large scale networks; Deep hierarchical networks
    • H04W84/06—Airborne or Satellite Networks

Abstract

The embodiment of the application discloses a random access method, a device and electronic equipment for a low-orbit constellation, wherein the method comprises the following steps: receiving a random access pilot frequency sent by a ground terminal; detecting the frequency of the received random access pilot frequency, and determining the Doppler frequency offset between the ground terminal and the satellite; and issuing a random access pilot response message to the ground terminal based on the Doppler frequency offset, wherein the random access pilot response message comprises a frequency offset parameter, and the random access pilot response message is used for indicating the ground terminal to transmit an uplink signal after carrying out frequency offset according to the frequency offset parameter. The technical scheme can ensure that the ground terminal realizes uplink frequency synchronous transmission, avoids multi-user interference or intersymbol interference caused by frequency asynchronism during multi-user uplink transmission, and further successfully finishes the random access process.

Description

Random access method and device for low-orbit constellation and electronic equipment
Technical Field
The present application relates to the field of satellite communications technologies, and in particular, to a random access method and apparatus for a low earth orbit constellation, and an electronic device.
Background
Currently, there are various problems in using the radio access procedure of the existing 4G Long Term Evolution (LTE) and 5GNR systems in a low orbit (LEO) satellite communication system. Fig. 1A and 1B show a random access procedure in the existing 4GLTE and 5GNR systems, which includes: a first User Equipment (UE) transmits a random access pilot 11 in uplink, where a carrier frequency of the random access pilot 11 is a predefined frequency. After detecting the random access pilot 11 sent by the first user equipment in an uplink, the base station sends a random access pilot response (RAR) message 12 to the first user equipment in a downlink, where the RAR message includes Timing Advance (TA) information and transmission resource information allocated to the first user equipment. After receiving the random access pilot response message in the downlink, the first user equipment may send an uplink signal 13 in advance according to the timing advance on the allocated transmission resource, so that when the uplink signal 13 of the first user equipment reaches the base station, the base station may receive the uplink signal of the first user equipment in an uplink frame, and as can be seen from fig. 1B, the uplink signal 13 of the first user equipment and the uplink signal 14 of the second user do not interfere with each other, so that uplink synchronous transmission between the multi-user equipment and the base station may be achieved, and the random access process is completed.
However, when the terrestrial terminal accesses the satellite in the low earth orbit satellite communication system according to the random access procedure, the doppler shift in the low earth orbit satellite communication system is much more severe than that in the terrestrial cellular system (4 GLTE or 5 GNR) due to the high-speed movement of the low earth orbit satellite, which causes the uplink signal of the terrestrial terminal and the uplink signal of other terrestrial terminals received by the satellite on the same uplink frame to overlap in frequency and generate serious interference.
Disclosure of Invention
The embodiment of the application provides a random access method and device for a low-orbit constellation and electronic equipment.
In a first aspect, an embodiment of the present application provides a random access method for a low earth constellation, which is applied to a satellite, and includes:
receiving a random access pilot frequency sent by a ground terminal;
detecting the frequency of the received random access pilot frequency, and determining the Doppler frequency offset between the ground terminal and the satellite;
and issuing a random access pilot response message to the ground terminal based on the Doppler frequency offset, wherein the random access pilot response message comprises a frequency offset parameter, and the random access pilot response message is used for indicating the ground terminal to transmit an uplink signal after carrying out frequency offset according to the frequency offset parameter.
Further, the frequency offset parameter includes a first parameter and a second parameter, both of which are integers, the first parameter is used to indicate a multiple of a subcarrier spacing in the doppler frequency offset, the second parameter is used to indicate a multiple of a minimum offset unit in a residual amount, and the residual amount is an offset obtained by subtracting the subcarrier spacing of the multiple indicated by the first parameter from the doppler frequency offset.
Further, before issuing a random access pilot response message to the ground terminal based on the doppler frequency offset, the method further includes:
calculating the first parameter n and the second parameter m according to the following formulas:
Δf＝nf s +mf u +f d ；
wherein Δ f is the Doppler frequency offset, f s The subcarrier spacing of the satellite communication system, said f u For a preset minimum offset unit of the satellite communication system, f d In order to be the residual frequency offset,
Figure BDA0003777483190000021
further, the frequency offset parameter includes a third parameter, the third parameter is used to indicate a multiple of a minimum offset unit in the doppler frequency offset, and the third parameter is an integer.
Further, before issuing a random access pilot response message to the ground terminal based on the doppler frequency offset, the method further includes:
the third parameter x is calculated according to the following formula:
Δf＝xf u +f d ；
Δ f is the Doppler frequency offset, f s The subcarrier spacing of the satellite communication system, said f u For a preset minimum offset unit of the satellite communication system, f d In order to be the residual frequency offset,
Figure BDA0003777483190000022
further, the method further comprises:
and sending an indication message to the ground terminal, wherein the indication message is used for indicating the time period and the carrier frequency band of the random access pilot frequency sent by the ground terminal.
Further, the carrier frequency band includes a random access channel and a guard band, and the guard band includes an upper guard band located above a frequency of the random access channel or a lower guard band located below the frequency of the random access channel.
Further, when the satellite and the ground terminal are in a relative motion state in a period of time indicated by the indication message for sending a random access pilot, a carrier frequency band indicated by the indication message includes an upper guard band; and when the satellite and the ground terminal are in a back-to-back motion state in the period of sending the random access pilot frequency indicated by the indication message, the carrier frequency band indicated by the indication message comprises a lower guard band.
Further, the method further comprises:
and determining the bandwidth of an upper guard band and the bandwidth of a lower guard band of a carrier frequency band indicated by the indication message according to the relative speed of the satellite and the ground terminal in the period of sending the random access pilot frequency indicated by the indication message.
Further, the random access pilot response message further includes a timing advance and a transmission resource, and the random access pilot response message is used to instruct the ground terminal to perform frequency offset in the transmission resource according to a frequency offset parameter and then to transmit an uplink signal based on the timing advance; the method further comprises the following steps:
detecting the time of receiving the random access pilot frequency, and determining the transmission time delay between the ground terminal and the satellite;
determining the timing advance based on the transmission delay.
In a second aspect, an embodiment of the present application provides a random access method for a low-orbit constellation, which is applied to a ground terminal, and includes:
sending a random access pilot frequency to a satellite;
receiving a random access pilot response message issued by the satellite, wherein the random access pilot response message comprises a frequency offset parameter;
and transmitting the uplink signal after carrying out frequency offset according to the frequency offset parameter.
Further, the frequency offset parameter includes a first parameter and a second parameter, both of which are integers, the first parameter is used to indicate a multiple of a subcarrier spacing in the doppler frequency offset, the second parameter is used to indicate a multiple of a minimum offset unit in a residual amount, and the residual amount is an offset obtained by subtracting the subcarrier spacing of the multiple indicated by the first parameter from the doppler frequency offset.
Further, the sending the uplink signal after performing the frequency offset according to the frequency offset parameter includes:
the first frequency offset amount Δ f is calculated according to the following equation 1 ：Δf 1 ＝nf s +mf u Wherein, said f s The subcarrier spacing of the satellite communication system, said f u The n is a first parameter and the m is a second parameter, and the n is a preset minimum offset unit of the satellite communication system;
and transmitting an uplink signal after carrying out frequency offset according to the first frequency offset.
Further, the frequency offset parameter includes a third parameter, the third parameter is used to indicate a multiple of a minimum offset unit in the doppler frequency offset, and the third parameter is an integer.
Further, the sending the uplink signal after performing the frequency offset according to the frequency offset parameter includes:
the second frequency offset amount Δ f is calculated according to the following equation 2 ：Δf 2 ＝xf u Wherein, said f u The x is the third parameter and is the preset minimum offset unit of the satellite communication system;
and transmitting the uplink signal after carrying out frequency offset according to the second frequency offset.
Further, the method further comprises:
receiving an indication message issued by the satellite, wherein the indication message is used for indicating the time period and the carrier frequency band of the random access pilot frequency sent by the ground terminal;
the sending of the random access pilot to the satellite includes:
and transmitting the random access pilot to the satellite on the carrier frequency band within the time period indicated by the indication message.
Further, if the carrier frequency band includes a random access channel and a guard band, and the guard band includes an upper guard band located above a frequency of the random access channel or a lower guard band located below the frequency of the random access channel, then the random access pilot is sent to the satellite on the carrier frequency band within a time period indicated by the indication message, including:
and transmitting the random access pilot frequency to the satellite on a random access channel in the carrier frequency band in a time period indicated by the indication message.
Further, the random access pilot response message further includes timing advance and transmission resources, and the sending an uplink signal after performing frequency offset according to the frequency offset parameter includes:
and after carrying out frequency offset according to a frequency offset parameter in the transmission resource, transmitting an uplink signal based on the timing advance.
In a third aspect, an embodiment of the present application provides a random access apparatus for a low earth constellation, which is applied to a satellite, and includes:
a first receiving module configured to receive a random access pilot transmitted by a ground terminal;
a first determining module configured to detect a frequency at which the random access pilot is received, and determine a doppler frequency offset between the ground terminal and the satellite;
a first sending module, configured to issue a random access pilot response message to the ground terminal based on the doppler frequency offset, where the random access pilot response message includes a frequency offset parameter, and the random access pilot response message is used to instruct the ground terminal to send an uplink signal after performing frequency offset according to the frequency offset parameter.
Further, the frequency offset parameter includes a first parameter and a second parameter, both of which are integers, the first parameter is used to indicate a multiple of a subcarrier spacing in the doppler frequency offset, the second parameter is used to indicate a multiple of a minimum offset unit in a residual amount, and the residual amount is an offset obtained by subtracting the subcarrier spacing of the multiple indicated by the first parameter from the doppler frequency offset.
Further, the first sending module is further configured to:
calculating the first parameter n and the second parameter m according to the following formulas:
Δf＝nf s +mf u +f d ；
wherein Δ f is DopplerAmount of frequency offset, said f s The subcarrier spacing of the satellite communication system, said f u For a preset minimum offset unit of the satellite communication system, f d In order to be the residual frequency offset,
Figure BDA0003777483190000041
further, the frequency offset parameter includes a third parameter, the third parameter is used to indicate a multiple of a minimum offset unit in the doppler frequency offset, and the third parameter is an integer.
Further, the first sending module is further configured to:
the third parameter x is calculated according to the following formula:
Δf＝xf u +f d ；
Δ f is the Doppler frequency offset, f s The subcarrier spacing of the satellite communication system, said f u For a predetermined minimum offset unit of the satellite communication system, f d Is a residual frequency offset and is a frequency offset,
Figure BDA0003777483190000051
further, the apparatus further comprises:
a second sending module, configured to send an indication message to the ground terminal, where the indication message is used to indicate a time period and a carrier frequency band when the ground terminal sends a random access pilot.
Further, the carrier frequency band includes a random access channel and a guard band, and the guard band includes an upper guard band located above a frequency of the random access channel or a lower guard band located below the frequency of the random access channel.
Further, when the satellite and the ground terminal are in a relative motion state within the period of sending the random access pilot indicated by the indication message, the carrier frequency band indicated by the indication message includes an upper guard band, and when the satellite and the ground terminal are in a reverse motion state within the period of sending the random access pilot indicated by the indication message, the carrier frequency band indicated by the indication message includes a lower guard band.
Further, the apparatus further comprises:
a second determining module configured to determine a bandwidth of an upper guard band and a bandwidth of a lower guard band of a carrier band indicated by the indication message according to a relative velocity of the satellite and the ground terminal in a period of transmitting a random access pilot indicated by the indication message.
Further, the random access pilot response message further includes timing advance and transmission resources, and the random access pilot response message is used to instruct the ground terminal to transmit an uplink signal based on the timing advance after performing frequency offset according to a frequency offset parameter in the transmission resources, where the apparatus further includes:
a third determining module configured to detect a time when the random access pilot is received, and determine a transmission delay between the ground terminal and the satellite;
a fourth determining module configured to determine the timing advance based on the transmission delay.
In a fourth aspect, an embodiment of the present application provides a random access apparatus for a low-orbit constellation, which is applied to a ground terminal, and includes:
a third transmitting module configured to transmit a random access pilot to the satellite;
a second receiving module, configured to receive a random access pilot response message issued by the satellite, where the random access pilot response message includes a frequency offset parameter;
and the fourth sending module is configured to send the uplink signal after performing frequency offset according to the frequency offset parameter.
Further, the frequency offset parameter includes a first parameter and a second parameter, both of which are integers, where the first parameter is used to indicate a multiple of a subcarrier spacing in the doppler frequency offset, the second parameter is used to indicate a multiple of a minimum offset unit in a residual amount, and the residual amount is an offset obtained by subtracting the subcarrier spacing indicated by the first parameter from the doppler frequency offset.
Further, the fourth sending module is configured to:
the first frequency offset amount Δ f is calculated according to the following equation 1 ：Δf 1 ＝nf s +mf u Wherein, the f s The subcarrier spacing of the satellite communication system, said f u The n is a first parameter and the m is a second parameter, and the n is a preset minimum offset unit of the satellite communication system;
and transmitting an uplink signal after carrying out frequency offset according to the first frequency offset.
Further, the frequency offset parameter includes a third parameter, the third parameter is used to indicate a multiple of a minimum offset unit in the doppler frequency offset, and the third parameter is an integer.
Further, the fourth sending module is configured to:
the second frequency offset amount Δ f is calculated according to the following equation 2 ：Δf 2 ＝xf u Wherein, said f u The x is a third parameter and is a preset minimum offset unit of the satellite communication system;
and transmitting the uplink signal after carrying out frequency offset according to the second frequency offset.
Further, the apparatus further comprises:
a third receiving module, configured to receive an indication message issued by the satellite, where the indication message is used to indicate a time period and a carrier frequency band at which a ground terminal sends a random access pilot;
the third transmitting module is configured to:
and transmitting the random access pilot to the satellite on the carrier frequency band within the time period indicated by the indication message.
Further, the carrier frequency band comprises a random access channel and a guard band, the guard band comprises an upper guard band located above a frequency of the random access channel or a lower guard band located below the frequency of the random access channel, and the part of the third transmitting module that transmits the random access pilot to the satellite on the carrier frequency band within the time period indicated by the indication message is further configured to:
and transmitting the random access pilot frequency to the satellite on a random access channel in the carrier frequency band in a time period indicated by the indication message.
Further, the random access pilot response message further includes a timing advance and a transmission resource, and the third sending module is further configured to:
and after carrying out frequency offset according to a frequency offset parameter in the transmission resource, transmitting an uplink signal based on the timing advance.
The functions can be realized by hardware, and the functions can also be realized by executing corresponding software by hardware. The hardware or software includes one or more modules corresponding to the above-described functions.
In one possible design, the apparatus includes a memory configured to store one or more computer instructions that enable the apparatus to perform the corresponding method, and a processor configured to execute the computer instructions stored in the memory. The apparatus may also include a communication interface for the apparatus to communicate with other devices or a communication network.
In a fifth aspect, an electronic device is provided in an embodiment of the present application, where the electronic device includes a memory, a processor, and a computer program stored on the memory, where the processor executes the computer program to implement the method of any one of the above aspects.
In a sixth aspect, the present application provides a computer-readable storage medium for storing computer instructions for any one of the above apparatuses, wherein the computer instructions, when executed by a processor, are configured to implement the method according to any one of the above aspects.
In a seventh aspect, the present application provides a computer program product, which contains computer instructions, when executed by a processor, for implementing the method of any one of the above aspects.
The technical scheme provided by the embodiment of the application can have the following beneficial effects:
in the embodiment of the application, the satellite can issue the random access pilot response message carrying the frequency offset parameter to the ground terminal based on the Doppler frequency offset between the ground terminal and the satellite, and the ground terminal can transmit the uplink signal after carrying out frequency offset according to the frequency offset parameter so as to reduce the frequency interference between the satellite receiving the uplink signal of the ground terminal and receiving the uplink signals of other ground terminals, so that the ground terminal realizes uplink frequency synchronous transmission, thereby avoiding multi-user interference or intersymbol interference caused by frequency asynchronization during multi-user uplink transmission and further successfully completing the random access process.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the application.
Drawings
Other features, objects, and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments when taken in conjunction with the accompanying drawings. In the drawings:
fig. 1A is a flowchart of a random access method in existing 4GLTE and 5GNR systems;
fig. 1B is a schematic diagram of a random access uplink and downlink frame in a conventional 4GLTE and 5GNR system;
fig. 2A is a schematic diagram of a low earth orbit satellite constellation disclosed in an embodiment of the present application;
fig. 2B is a schematic diagram of a scenario in which a single low-earth satellite provides wireless access services to a ground terminal;
fig. 2C is a schematic diagram of a corresponding system uplink and downlink frame when the existing random access method is used in a low-orbit constellation;
fig. 3 is a flowchart of a random access method applied to a satellite according to an embodiment of the present application;
fig. 4 is a block diagram illustrating a structure of a random access pilot response message according to an embodiment of the present disclosure;
fig. 5 is a block diagram illustrating another random access pilot response message according to an embodiment of the present disclosure;
fig. 6 is a schematic flow chart of an uplink and downlink frame corresponding to a random access method disclosed in an embodiment of the present application;
fig. 7 is a schematic diagram illustrating a frequency band allocation structure in a random access frame according to an embodiment of the present application;
fig. 8 is a schematic diagram illustrating a frequency band allocation structure in another random access frame according to an embodiment of the present application;
fig. 9 is a schematic diagram illustrating a frequency band allocation structure in a random access frame according to another embodiment of the present disclosure;
fig. 10 is a flowchart of a random access method applied to a ground terminal according to an embodiment of the present application;
fig. 11 is an overall flowchart of a random access method disclosed in an embodiment of the present application;
fig. 12 is a block diagram of a random access apparatus applied to a satellite according to an embodiment of the present disclosure;
fig. 13 is a block diagram of a random access apparatus applied to a ground terminal according to an embodiment of the present application;
fig. 14 is a schematic structural diagram of an electronic device suitable for the random access method disclosed in the embodiment of the present application.
Detailed Description
Hereinafter, exemplary embodiments of the present application will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement them. Also, for the sake of clarity, parts not relevant to the description of the exemplary embodiments are omitted in the drawings.
First, before specifically describing the technical solution of the embodiment of the present application, a technical background on which the embodiment of the present application is based is described. As shown in fig. 2A, the constellation 2 is composed of a plurality of orbits 21, each orbit 21 running a plurality of low earth orbit satellites 22 (also referred to as satellites), the orbits 21 meeting near north and south poles. Each low earth satellite 22 provides wireless access services to a terrestrial region via a communication link, wherein the individual low earth satellite 22 remains mobile relative to the ground and, therefore, the terrestrial region covered by its communication link changes over time. As shown in fig. 2B, the ground terminal 23 (including the gateway station) and the low-orbit satellite 22 perform two-way communication through the communication link 24, the gateway station can provide a telemetry and control service of the low-orbit satellite after accessing the low-orbit satellite, perform communication and control on the on-board computer of the low-orbit satellite, and implement services of low-orbit satellite operation, such as temperature management, attitude adjustment, positioning, and the like, and the ground terminal directly used by the user can access the network after accessing the low-orbit satellite, and communicate with other devices in the network. The carrier frequency of a communication link between the low-earth satellite and the ground terminal is usually a KA or KU band, and the low-earth satellite transmits and receives wireless signals to and from the ground terminal through beamforming realized by the phased array antenna array (since the communication frequency of the low-earth satellite is in the KA or KU band, the path loss of the band is large, and if the phased array antenna is not used for beamforming radio waves, an effective signal-to-noise ratio cannot be realized at the ground terminal). When the wave beam is narrow, the range of the included angle between the low-orbit satellite and the ground terminal is fixed, and the included angle can be approximate to the included angle between the central direction of the wave beam and the connecting direction. The absolute velocity of the low earth orbit satellite is again related to the orbital altitude and is relatively fixed, as determined by newton's third law. Therefore, the specific calculation formula of the flight speed of the low earth orbit satellite can be calculated by the following formula:
Figure BDA0003777483190000081
therefore, the flight speed of the low-orbit satellite on a low earth orbit with the height of 1000km can reach about 7 km/s. Although the relative velocity between the ground terminal and the low-earth satellite is also related to the elevation angle of the ground terminal relative to the low-earth satellite, i.e., the above-mentioned angle, and the autorotation speed of the earth, it can be understood that the relative velocity between the ground terminal and the low-earth satellite is much greater than the upper limit of the velocity supported by terrestrial cellular (e.g., 4G lte and 5 GNR) systems, e.g., the 500km/h velocity of a high-speed rail is the highest time velocity supported by 4G and 5G systems, and the velocity of the low-earth satellite is 50 times this highest time velocity, which means a significant doppler shift for the communication link. And low earth orbit satelliteThe carrier frequencies used are relatively high, e.g. the carrier frequencies in the Ka band are between 20GHz and 30GHz, due to the Doppler shift being equal to v/c f 0 Where v is the relative moving speed, c is the speed of light, f 0 Is the carrier frequency. It can be seen that the carrier frequency f 0 Higher means larger doppler shift. For example, in a satellite communication system with an orbital constellation of 1000km and a carrier frequency of 30GHz, the frequency deviation due to doppler shift is between-675 KHz and 675KHz, and if the satellite communication system employs a mature OFDM system, even if the subcarrier spacing employs 120KHz defined in a terrestrial cellular system, the doppler shift cannot be absorbed as a residual frequency deviation smaller than one subcarrier spacing, which means that an OFDM system with a subcarrier spacing of 120KHz will suffer from a subcarrier offset of more than-6 to 6 integers. In addition, the transmission distance between the low earth orbit satellite and the ground terminal is much larger than that between the base station and the terminal in the traditional ground cellular system. One of the problems associated with this long transmission distance is the increase in transmission delay. The bidirectional transmission delay τ can be calculated according to the following formula without considering the processing delay:
Figure BDA0003777483190000091
wherein d is the orbit height, theta is the elevation angle of the low orbit satellite relative to the ground terminal, and c is the vacuum light velocity. For example, when d =500km and θ =30 degrees, the bidirectional transmission delay τ can be calculated to be 6.6ms.
In summary, the doppler shift and the two-way transmission delay in the low earth orbit satellite system are much more severe than those in the terrestrial cellular system, and if the time and frequency difference of the uplink signals of a plurality of terrestrial terminals reaching the low earth orbit satellite are controlled within a certain range in the random access process, the requirement of uplink transmission synchronization cannot be satisfied only by using the random access process of the existing 4g lte or 5g nr system in the low earth orbit satellite communication system. As shown in fig. 2C, using the conventional random access procedure shown in fig. 1B in the low-orbit satellite communication system, a first terrestrial terminal transmits a random access pilot 25 in uplink, and after detecting the random access pilot 11 transmitted by the first terrestrial terminal in uplink, a base station transmits a random access pilot response message 26 in downlink to the first terrestrial terminal, where the random access pilot response message 26 carries only a timing advance and a transmission resource allocated to a user equipment, and only considers synchronization of uplink time but not uplink frequency, because in a 4g lte or 5g nr system, even if the user equipment moves relative to the base station at the highest speed, a generated doppler shift is small and can be absorbed by a well-designed subcarrier spacing; however, in the low-earth satellite system, the doppler shift between the satellite and the ground terminal is very large, and the sub-carrier distance cannot be absorbed, so that as shown in fig. 2C, the frequency shift of the uplink signal 27 of the first ground terminal received by the satellite at the corresponding time is large, and the frequency of the uplink signal 28 of the second ground terminal received by the satellite at the same time overlaps with each other, causing serious interference, and further causing random access failure.
In order to solve the technical problem, the present application provides a random access method for a low earth constellation, where a satellite may issue a random access pilot response message carrying a frequency offset parameter to a ground terminal based on a doppler frequency offset between the ground terminal and the satellite, and the ground terminal may perform frequency offset according to the frequency offset parameter and then transmit an uplink signal, so as to reduce frequency interference between the satellite receiving the uplink signal of the ground terminal and receiving uplink signals of other ground terminals, so that the ground terminal implements uplink frequency synchronous transmission, thereby avoiding multi-user interference or inter-symbol interference caused by frequency asynchronization during multi-user uplink transmission, and further successfully completing a random access process.
The details of the embodiments of the present application are described in detail below with reference to specific embodiments.
Satellite side embodiment
As shown in fig. 3, the random access method is applied to a satellite, and may include the following steps:
in step S301, a random access pilot sent by the ground terminal is received;
in step S302, detecting a frequency of receiving the random access pilot, and determining a doppler frequency offset between the ground terminal and the satellite;
in step S303, based on the doppler frequency offset, a random access pilot response message is issued to the ground terminal, where the random access pilot response message includes a frequency offset parameter, and the random access pilot response message is used to instruct the ground terminal to perform frequency offset according to the frequency offset parameter and then send an uplink signal.
In this embodiment, the satellite is any low-orbit satellite in a satellite communication system constructed by a constellation, for example, the constellation may be the constellation shown in fig. 2A, and of course, the constellation may also be other types of constellations, which is not limited herein, and the ground terminal includes any ground device capable of receiving a satellite signal, and is not necessarily a device directly used by a user, and may also be a device such as a gateway station.
In this embodiment, the satellite operates along an orbit in a constellation, a ground area covered by a communication link of the satellite changes with time, the satellite can broadcast a broadcast message to the ground area at regular time, the broadcast message carries resource information that can be used by a ground terminal in the ground area covered by the satellite and indicated by the satellite, and the satellite is informed that the satellite can provide a random access service for the ground terminal in some time-frequency resources. If the ground terminal needs to access the network provided by the satellite, the random access process can be started, and the corresponding random access pilot frequency is sent in the time frequency resource.
In this embodiment, the ground terminal sending a random access pilot to the satellite may tell the satellite the doppler frequency offset between the ground terminal and the satellite. After the satellite receives the random access pilot frequency, the frequency of receiving the random access pilot frequency can be detected, and the satellite prestores the non-offset frequency of receiving the random access pilot frequency when no Doppler frequency shift exists, so that the Doppler frequency offset between the ground terminal and the satellite can be obtained according to the detected frequency of receiving the random access pilot frequency and the prestore non-offset frequency.
In this embodiment, in order to ensure that the satellite can receive the uplink signal of the terrestrial terminal at the predetermined frequency, the uplink signal needs to be transmitted with a certain amount of offset based on the predetermined frequency in consideration of the doppler offset between the terrestrial terminal and the satellite, so that the uplink signal is received by the satellite at the predetermined frequency when reaching the satellite after the doppler offset at the time of transmission. The amount of the offset is the doppler frequency offset between the ground terminal and the satellite, and can be represented by a frequency offset parameter, so that the satellite can receive the uplink signal on the predetermined frequency and realize uplink frequency synchronization as long as the uplink signal is transmitted after being subjected to frequency offset on the basis of the predetermined frequency according to the frequency offset parameter before being transmitted.
In this embodiment, the random access may be contention-based random access or non-contention-based random access, which is not limited herein. When the random access is non-contention based random access, the steps S301 to S303 are only required to complete the random access procedure. When the random access is contention-based random access, the uplink signal may be Msg3 (message 3), the Msg3 includes a unique identifier of the ground terminal, the satellite, after receiving the Msg3, sends Msg4 (message 4) to the ground terminal to inform the ground terminal whether the contention is successful, and if the contention is successful, the random access of the ground terminal is successful.
In this embodiment, after receiving the random access pilot response message, the ground terminal acquires initial uplink synchronization, and may start to send an uplink signal (which may carry Msg3 or other uplink data) to the satellite, and the ground terminal may send the uplink signal after performing frequency offset according to the frequency offset parameter, so that the satellite may receive the uplink signal at a predetermined frequency, thereby implementing synchronous transmission of the uplink frequency, facilitating elimination of mutual interference with uplink signals of other ground terminals in a frequency domain, and avoiding multi-user interference or inter-symbol interference caused by frequency asynchronization.
In this embodiment, the satellite may issue a random access pilot response message carrying a frequency offset parameter to the ground terminal based on a doppler frequency offset between the ground terminal and the satellite, and the ground terminal may perform frequency offset according to the frequency offset parameter and then transmit an uplink signal, so as to reduce frequency interference between the satellite receiving the uplink signal of the ground terminal and receiving uplink signals of other ground terminals, so that the ground terminal realizes uplink frequency synchronous transmission, thereby avoiding multi-user interference or inter-symbol interference caused by frequency asynchronization during multi-user uplink transmission, and further successfully completing a random access process.
In an optional implementation manner of this embodiment, the frequency offset parameter includes a first parameter and a second parameter, where the first parameter and the second parameter are both integers, the first parameter is used to indicate a multiple of a subcarrier spacing in the doppler frequency offset, the second parameter is used to indicate a multiple of a minimum offset unit in a residual amount, and the residual amount is an offset obtained by subtracting an integer multiple of the subcarrier spacing from the doppler frequency offset.
In this alternative implementation, the doppler frequency offset may be divided into an integer multiple of subcarrier spacing and a fractional multiple of the smallest offset unit, and the integer multiple of the doppler frequency offset may be indicated by a first parameter and the fractional multiple of the doppler frequency offset may be indicated by a second parameter.
In an optional implementation manner of this embodiment, before the step S303, that is, based on the doppler frequency offset, the step of issuing a random access pilot response message to the ground terminal, the method may further include the following steps:
calculating the first parameter n and the second parameter m according to the following formulas:
Δf＝nf s +mf u +f d ；
wherein Δ f is a Doppler frequency offset, f s The subcarrier spacing of the satellite communication system, said f u For a preset minimum offset unit of the satellite communication system, f d For residual frequency deviation
Figure BDA0003777483190000111
In this optional implementation manner, when the satellite issues the random access pilot response message to the ground terminal, it is necessary to calculate the frequency offset parameter in the random access pilot response message based on the doppler frequency offset, and then carry the frequency offset parameter in the random access pilot response message for transmission.
In this alternative implementation, the doppler frequency offset may be described as an integer multiple portion of one subcarrier spacing and a fractional multiple portion of one subcarrier spacing, Δ f = nf s +f r Wherein n is an integer, f s Is the subcarrier spacing, f r Frequency offset of a fractional multiple of the subcarrier spacing due to high velocity movement of low earth orbit satellites, f r Is a continuous variable and s /2＜f r ＜f s 2 and therefore cannot be directly indicated by signaling. The doppler frequency offset can be divided into integer multiples of the subcarrier spacing (nf) s ) And integer multiple of minimum offset units (mf) u ) And a residual frequency offset f d At this time, the frequency offset parameter in the random access pilot response message may be two integers of the first parameter n and the second parameter m. For example, as shown in fig. 4, the random access pilot response message 4 includes two parts, a first part 41 is information of a timing advance, and a second part 42 is information of a frequency offset parameter, where the information of the frequency offset parameter includes two parts, one part is used to indicate the first parameter n, and the other part is used to indicate the second parameter m. The information of the frequency offset parameter may be a binary string of a predetermined number of bits, the first few strings indicating the first parameter n, and the second few strings indicating the second parameter m.
In this optional implementation manner, after receiving the random access pilot response message, the ground terminal may shift the uplink signal by a certain amount nf on the basis of the predetermined frequency according to the frequency shift parameter, that is, the first parameter n and the second parameter m, in combination with the pre-stored subcarrier spacing and the minimum shift unit s +mf u Then sending to the satellite, at this time, there is still a certain residual frequency offset f between the frequency of the uplink signal received by the satellite and the predetermined frequency d . And the residual frequency offset f d If the uplink signal is small enough, the uplink signal will not cause serious interference to the uplink signals of other ground terminals. And due to-f u /2＜f d ＜f u 2, so, only the minimum offset unit f is chosen carefully u The influence caused by Doppler frequency shift due to high-speed satellite movement can be controlled to a controllable range, and f is u The degree of interference caused in the satellite communication system by the frequency offset.
In this optional implementation, a residual frequency offset f exists between the uplink signal of the ground terminal and a predetermined frequency when the uplink signal reaches the satellite d F of the u The selection value of (A) is to achieve the following effects: even if residual frequency offset f exists d The uplink signal of the ground terminal may overlap with the uplink signals of other ground terminals that arrive synchronously in frequency, and no serious interference, i.e., residual frequency offset f, is caused to the uplink signals of other ground terminals d Even if f is reached u The interference level caused by/2 will also be small, much less than the noise of the satellite communication system itself.
In this alternative implementation, the minimum offset unit f u It can be an empirical value, for example, the maximum moving speed supported by the existing 4G LTE system is 500km/h, and the corresponding maximum doppler shift occupies about 6% of the subcarrier spacing, within this maximum doppler shift range, the system still has good receiving performance, and the signal between multiple users will not generate serious multi-user interference. Thus, f can be set u ＝f s 10, the frequency offset f of the uplink signal received by the satellite d No more than f u The/2 =5% subcarrier spacing is close to the performance at the maximum moving speed in the 4G LTE system, and signals among multiple users cannot generate serious multi-user interference. When setting f u ＝f s At/10, m ∈ [0,1, 2. ].9]The m corresponding information occupies 4 bits in the character stringA bit. Of course, f can be further reduced u Such as f u ＝f s 12 to obtain smaller frequency offset and better synchronization result, the number of bits of the second parameter m needs to be further increased.
In the implementation mode, the satellite communication system can realize sensitive time and frequency synchronization under the condition that the satellite moves at a high speed through the minimum signaling overhead, and ensure that the satellite can realize high-frequency spectrum utilization rate among a plurality of ground terminals.
In an optional implementation manner of this embodiment, the frequency offset parameter includes a third parameter, the third parameter is used to indicate a multiple of a minimum offset unit in the doppler frequency offset, and the third parameter is an integer.
In this alternative implementation, the doppler frequency offset may be represented by an integer multiple of the smallest offset unit, and then a third parameter may be used to indicate how many multiples of the smallest offset unit exist in the doppler frequency offset.
In an optional implementation manner of this embodiment, step S303, namely the step of issuing a random access pilot response message to the ground terminal based on the doppler frequency offset, may further include the following steps:
the frequency offset parameter x is calculated according to the following formula: Δ f = xf u +f d ；
Δ f is the Doppler frequency offset, f s The subcarrier spacing of the satellite communication system, said f u Is a preset minimum offset unit of the satellite communication system,
Figure BDA0003777483190000131
in this implementation, the doppler frequency offset may also be divided into an integer multiple of the minimum offset unit xf u And a residual frequency offset f d At this time, the frequency offset parameter in the random access pilot response message may be an integer of x. Illustratively, as shown in fig. 5, the random access pilot response message 5 includes two parts, the first partThe portion 51 is timing advance information and the second portion 52 is frequency offset parameter information, wherein the frequency offset parameter information only includes a portion for indicating the third parameter x.
In an optional implementation manner of this embodiment, the method may further include the following steps:
and sending an indication message to the ground terminal, wherein the indication message is used for indicating the time period and the carrier frequency band of the random access pilot frequency sent by the ground terminal.
In this optional implementation manner, the indication message may be a broadcast message broadcasted by the satellite, or may also be some downlink messages issued by the satellite, where the indication message is used to indicate a time period and a carrier frequency band at which the ground terminal sends the random access pilot. Therefore, the ground terminal can send the random access pilot frequency to the satellite on the carrier frequency band in the period of time, and the time and the frequency of receiving the random access pilot frequency when no transmission delay or Doppler frequency shift exists in the satellite are prestored, so that the satellite can obtain the transmission delay and the Doppler frequency offset between the ground terminal of the satellite and the satellite after detecting the time and the frequency of receiving the random access pilot frequency.
Here, fig. 6 is a schematic flowchart of an uplink and downlink frame corresponding to a random access method disclosed in an embodiment of the present application; as shown in fig. 6, with the above solution, after the terrestrial terminal UE #1 transmits the random access pilot U1 to the satellite uplink, the satellite receives the random access pilot U1 transmitted by the UE #1 uplink, then the satellite downlink transmits the random access pilot response message D1 to the UE #1, after the random access pilot response message D1 is received by the UE #1 downlink, the random access pilot response message D1 uses the indicated frequency offset parameter to transmit the uplink signal U2, the U2 reaches the satellite after the transmission delay h1, and after the uplink signal U2 and the uplink signal U3 of other terrestrial terminal UE #2 synchronously reach the satellite, the uplink signal U2 and the uplink signal U3 of other terrestrial terminal UE #2 both receive at the satellite by being multiplied by the respective predetermined frequency, so that overlapping and interference in the frequency domain are avoided. However, since the frequency offset parameter is not obtained until the UE #1 receives the random access pilot response message D1, the random access pilot U1 of the UE #1 may overlap with the uplink signal U4 of the UE # 2. In order to further avoid interference of the random access pilot due to doppler shift, in an optional implementation manner of this embodiment, the carrier frequency band carried in the indication message includes a random access channel and a guard band, where the guard band includes an upper guard band located above a frequency of the random access channel and/or a lower guard band located below the frequency of the random access channel.
In this alternative implementation, as shown in fig. 7, the satellite may allocate the carrier band 7 of the random access pilot on a reserved random access frame for receiving the random access pilot, and the carrier band is periodically arranged at a specific position of the random access frame, where the carrier band 7 includes the random access channel 71 and the guard band. The guard band may comprise an upper guard band 72 located above the frequency of the random access channel and a lower guard band 73 located below the frequency of the random access channel, within which guard bands terrestrial terminals are scheduled to transmit any uplink signals. The bandwidths of the upper guard band 72 and the lower guard band 73 may be the maximum doppler frequency offset between the satellite and the ground terminal, for example, assuming that the doppler frequency offset between the satellite and the ground terminal is between-6 and 6 sub-carrier spacings, the maximum doppler frequency offset is 6 sub-carrier spacings, and 6 null sub-carriers may be respectively set on both sides of the random access channel as guard bands. In this way, no matter where the position of the terrestrial terminal transmits the random access pilot, as long as the random access pilot is transmitted on the random access channel 71, no matter how shifted in the transmission process, the random access pilot finally falls within the guard band range, and no interference is caused to the uplink signals of other terrestrial terminals.
In this alternative implementation, the doppler shift refers to a change in phase and frequency due to a propagation path difference when the mobile station moves in a certain direction at a constant speed, and this change is generally referred to as doppler shift. It reveals the law that the wave properties change during motion. When moving in front of the wave source, the wave is compressed, the wavelength becomes shorter, and the frequency becomes higher; when the motion is behind the source, the opposite effect occurs, the wavelength becomes longer and the frequency becomes lower. Therefore, the ground terminal transmits the random access pilot frequency at a predetermined frequency in a certain period of time, and the frequency when the random access pilot frequency reaches the satellite becomes large, and at this time, only a guard band needs to be set above the frequency of the random access channel, so that the random access pilot frequency can be ensured to fall within the range of the guard band, and no interference is caused to uplink signals of other ground terminals. In other periods, the random access pilot frequency is transmitted at a predetermined frequency, and the frequency when the random access pilot frequency reaches the satellite becomes smaller, and at this time, only a lower guard band needs to be set below the frequency of the random access channel, so that the random access pilot frequency can be ensured to fall within the range of the guard band, and no interference is caused to uplink signals of other ground terminals.
In an optional implementation manner of this embodiment, when the satellite and the ground terminal are in a relative motion state in the period that is indicated by the indication message and used for sending the random access pilot frequency, the carrier frequency band indicated by the indication message includes an upper guard band, and when the satellite and the ground terminal are in a reverse motion state in the period that is indicated by the indication message and used for sending the random access pilot frequency, the carrier frequency band indicated by the indication message includes a lower guard band.
In this implementation, as shown in fig. 8, in the first phase 81, the low-earth satellite 22 and the ground terminal 23 are in a relative motion state, and both are closer to each other, so that the phase may also be referred to as a near phase, in which the doppler shift only causes the frequency of the random access pilot reaching the satellite to be higher, and therefore, in the near phase, only the upper guard band 72 needs to be set above the frequency of the random access channel 71 of the random access frame. In the second phase 82, the low-earth satellite 22 and the ground terminal 23 move away from each other, and the distance therebetween gradually increases, so that the phase may also be referred to as a far-away phase, in which the doppler shift only causes the frequency of the random access pilot arriving at the satellite to decrease, and therefore the lower guard band 73 only needs to be set below the frequency of the random access channel 71 of the random access frame in the far-away phase.
In this implementation, the phase corresponding to the period of sending the random access pilot indicated by the satellite for the ground terminal may be obtained based on ephemeris data, so that it can be known in advance whether the satellite and the ground terminal are in a relative motion state or a reverse motion state in the period of sending the random access pilot indicated by the indication message, and thus, the satellite may set in advance whether the carrier frequency band indicated by the indication message includes an upper guard band or a lower guard band. Compared with the upper guard band and the lower guard band in fig. 7, only the upper guard band or the lower guard band is set in fig. 8, which reduces the frequency domain overhead by half, but still enables the random access pilot not to interfere with the uplink signals of other ground terminals.
However, the two schemes also have a disadvantage that 12 or 6 subcarriers in each random access frame cannot be used by any ground terminal, thereby causing huge resource overhead. And this resource overhead is periodic and can reduce the spectrum utilization of the entire system. In order to fully utilize the characteristics of satellite movement and divide the bandwidth of the guard band into finer granularity, in an optional implementation manner of this embodiment, the method may further include the following steps:
and determining the bandwidth of an upper guard band and/or a lower guard band of a carrier frequency band indicated by the indication message according to the relative speed of the satellite and the ground terminal in the period of sending the random access pilot frequency indicated by the indication message.
In this implementation, when the relative velocity between the satellite and the ground terminal is relatively high, the doppler shift during the random access pilot transmission will be relatively high, and at this time, a relatively large guard bandwidth needs to be set.
In this implementation, if the carrier frequency band of the random access pilot indicated by the indication message includes an upper guard band and a lower guard band, the bandwidths of the upper guard band and the lower guard band of the carrier frequency band indicated by the indication message may be determined based on the correspondence between the relative speed range and the bandwidth according to the relative speed (which may be obtained based on ephemeris data) of the satellite and the ground terminal in the period of sending the random access pilot indicated by the indication message.
In this implementation, if the period of sending the random access pilot indicated by the indication message is in the near-forward stage and the carrier frequency band includes an upper guard band, the bandwidth of the upper guard band of the carrier frequency band indicated by the indication message may be determined based on the correspondence between the relative speed range and the bandwidth according to the relative speed between the satellite and the ground terminal in the period of sending the random access pilot indicated by the indication message. If the period of sending the random access pilot indicated by the indication message is in the away stage, and the carrier frequency band includes a lower guard band, the bandwidth of the lower guard band of the carrier frequency band indicated by the indication message may be determined based on the correspondence between the relative speed range and the bandwidth according to the relative speed of the satellite and the ground terminal in the period of sending the random access pilot indicated by the indication message.
As shown in fig. 9, in the first phase 81, i.e., the approach phase, the low-orbiting satellite 22 gradually moves towards the ground terminal 23 from left to right in the transmission period of the random access pilot, and when the low-orbiting satellite 22 moves from the left side to the right side, the relative velocity between the low-orbiting satellite 22 and the ground terminal 23 is the largest, so that the bandwidth of 6 subcarriers may be configured above the frequency of the random access channel 71 at the random access frame #1 as the upper guard band 721, and when the low-orbiting satellite 22 moves from the left side to the right side, the relative velocity between the low-orbiting satellite 22 and the ground terminal 23 is the smallest, and the bandwidth of 3 subcarriers may be configured above the frequency of the random access channel 71 at the random access frame #2 as the upper guard band 722.
In the implementation mode, the satellite communication system can realize sensitive time and synchronization under the condition that the satellite moves at a high speed through minimum resource overhead, and the satellite can realize high-frequency spectrum utilization rate among a plurality of ground terminals.
In an optional implementation manner of this embodiment, the random access pilot response message further includes a timing advance and a transmission resource, and the random access pilot response message is used to instruct the ground terminal to perform frequency offset according to a frequency offset parameter in the transmission resource and then to send an uplink signal based on the timing advance; the method further comprises the steps of:
detecting the time of receiving the random access pilot frequency, and determining the transmission time delay between the ground terminal and the satellite;
determining the timing advance based on the transmission delay.
In this alternative implementation, the ground terminal sends the random access pilot to the satellite primarily to tell the satellite the transmission delay and doppler frequency offset between the ground terminal and the satellite. The satellite can detect the time and frequency of receiving the random access pilot frequency after receiving the random access pilot frequency, and the satellite prestores the non-delay time and non-offset frequency of receiving the random access pilot frequency when no transmission delay and Doppler frequency shift exist, so that the transmission delay between the ground terminal and the satellite can be obtained according to the detected time of receiving the random access pilot frequency and the prestored non-delay time, and the Doppler frequency offset between the ground terminal and the satellite can be obtained according to the detected frequency of receiving the random access pilot frequency and the prestored non-offset frequency.
In the optional implementation manner, the random access pilot response message carries transmission resources allocated to the ground terminal, where the transmission resources include time-frequency resources, that is, a satellite may provide a random access service for the ground terminal on the time-frequency resources (e.g., a predetermined subframe and a predetermined frequency), but because a transmission delay and a doppler shift exist between the ground terminal and the satellite, the satellite needs to provide a timing advance and a frequency shift parameter for the ground terminal, so as to ensure that the satellite can obtain an uplink signal sent by the ground terminal on the transmission resources.
In this alternative implementation, in order to ensure that the uplink signal of the ground terminal reaches the satellite and is synchronized with the predetermined uplink frame of the satellite (i.e., the uplink signal can be obtained within the time of the predetermined uplink frame), in consideration of the transmission delay between the ground terminal and the satellite, a timing advance is required to be sent before the start time of the uplink frame, the uplink signal can reach the satellite at the start time of the uplink frame, and the timing advance can be calculated according to the transmission delay between the ground terminal and the satellite.
In the optional implementation manner, the satellite may issue a random access pilot response message carrying a timing advance, a frequency offset parameter, and a transmission resource to the ground terminal based on a transmission delay and a doppler frequency offset between the ground terminal and the satellite, and the ground terminal may send an uplink signal based on the timing advance after performing frequency offset according to the frequency offset parameter in the transmission resource, so that the time when the satellite receives the uplink signal of the ground terminal is synchronized with the time when the satellite receives uplink signals of other ground terminals, and the receiving frequencies are located at different frequencies, so that the ground terminal implements uplink time-frequency synchronous transmission, thereby avoiding multi-user interference or inter-symbol interference caused by multi-user time-frequency asynchronization, and further successfully completing a random access process.
Terminal side access embodiments
As shown in fig. 10, the random access method is applied to a terminal and may include the following steps:
in step S101, a random access pilot is transmitted to a satellite;
in step S102, receiving a random access pilot response message issued by the satellite, where the random access pilot response message includes a frequency offset parameter;
in step S103, the uplink signal is transmitted after performing frequency offset according to the frequency offset parameter.
In this embodiment, the satellite operates along an orbit in a constellation, a ground area covered by a communication link of the satellite changes with time, the satellite can broadcast a broadcast message to the ground area at regular time, the broadcast message carries resource information that can be used by a ground terminal in the ground area covered by the satellite and indicated by the satellite, and the satellite is informed that the satellite can provide a random access service for the ground terminal in some time-frequency resources. If the ground terminal needs to access the network provided by the satellite, the random access process can be started, and the corresponding random access pilot frequency is sent in the time frequency resource.
In this embodiment, the terrestrial terminal sends a random access pilot to the satellite that tells the satellite the amount of doppler frequency offset between the terrestrial terminal and the satellite. After the satellite receives the random access pilot frequency, the frequency of the received random access pilot frequency can be detected, and the satellite prestores the non-offset frequency of the received random access pilot frequency when no Doppler frequency shift exists, so that the Doppler frequency offset between the ground terminal and the satellite can be obtained according to the detected frequency of the received random access pilot frequency and the prestore non-offset frequency.
In this embodiment, in order to ensure that the satellite can receive the uplink signal of the terrestrial terminal at the predetermined frequency, the uplink signal needs to be transmitted with a certain amount of offset based on the predetermined frequency in consideration of the doppler offset between the terrestrial terminal and the satellite, so that the uplink signal is received by the satellite at the predetermined frequency when reaching the satellite after the doppler offset at the time of transmission. The amount of the offset is the doppler frequency offset between the ground terminal and the satellite, and can be represented by a frequency offset parameter, so that the satellite can receive the uplink signal on the predetermined frequency only by performing frequency offset on the basis of the predetermined frequency before transmitting the uplink signal and then transmitting the uplink signal according to the frequency offset parameter, thereby realizing uplink frequency synchronization.
In this embodiment, the random access may be contention-based random access or non-contention-based random access, which is not limited herein. When the random access is non-contention based random access, the steps S301 to S303 are only required to complete the random access procedure. When the random access is contention-based random access, the uplink signal may be Msg3 (message 3), where the Msg3 includes a unique identifier of a ground terminal, and the satellite, after receiving the Msg3, sends Msg4 (message 4) to the ground terminal to inform the ground terminal whether contention is successful, and if the contention is successful, the random access of the ground terminal is successful.
In this embodiment, after receiving the random access pilot response message, the ground terminal acquires initial uplink synchronization, and may start to send an uplink signal (which may carry Msg3 or other uplink data) to the satellite, and the ground terminal may send the uplink signal after performing frequency offset according to the frequency offset parameter, so that the satellite may receive the uplink signal at a predetermined frequency, thereby implementing synchronous transmission of the uplink frequency, facilitating elimination of mutual interference with uplink signals of other ground terminals in a frequency domain, and avoiding multi-user interference or inter-symbol interference caused by frequency asynchronization.
In this embodiment, the satellite may issue a random access pilot response message carrying a frequency offset parameter to the ground terminal based on a doppler frequency offset between the ground terminal and the satellite, and the ground terminal may perform frequency offset according to the frequency offset parameter and then transmit an uplink signal, so as to reduce frequency interference between the satellite receiving the uplink signal of the ground terminal and receiving uplink signals of other ground terminals, so that the ground terminal realizes uplink frequency synchronous transmission, thereby avoiding multi-user interference or inter-symbol interference caused by frequency asynchronization during multi-user uplink transmission, and further successfully completing a random access process.
In an optional implementation manner of this embodiment, the frequency offset parameter includes a first parameter and a second parameter, where the first parameter and the second parameter are both integers, the first parameter is used to indicate a multiple of a subcarrier spacing in the doppler frequency offset, the second parameter is used to indicate a multiple of a minimum offset unit in a residual amount, and the residual amount is an offset obtained by subtracting an integer multiple of the subcarrier spacing from the doppler frequency offset. In this way, the frequency offset of the uplink signal is the sum of the subcarrier spacing of the multiple indicated by the first parameter and the minimum offset unit of the multiple indicated by the second parameter, and the uplink signal is offset by the frequency offset on the preset frequency and then transmitted, so that the satellite can receive the uplink signal approximately around the preset frequency, and uplink frequency synchronization is realized.
In an optional implementation manner of this embodiment, step S103 in the method, that is, the step of sending the uplink signal after performing frequency offset according to the frequency offset parameter, may include the following steps:
the first frequency offset amount Δ f is calculated according to the following equation 1 ：Δf 1 ＝nf s +mf u Wherein, said f s The subcarrier spacing of the satellite communication system, said f u Is a preset minimum offset unit of the satellite communication system; the n is a first parameter, and the m is a second parameter.
And transmitting an uplink signal after carrying out frequency offset according to the first frequency offset.
In this implementation, if the frequency domain resource in the transmission resource received by the ground terminal is a predetermined frequency, the ground terminal performs frequency offset compensation on the predetermined frequency according to the first parameter n and the second parameter m. I.e. shifting the predetermined frequency by nf s +mf u And transmitting the uplink signal. At this time, a certain residual frequency offset f still exists between the frequency of the uplink signal received by the satellite and the predetermined frequency d But the residual frequency offset f d Small enough, the uplink signal of the ground terminal will not cause serious interference to the uplink signals of other ground terminals.
In an optional implementation manner of this embodiment, the frequency offset parameter includes a third parameter, the third parameter is used to indicate a multiple of a minimum offset unit in the doppler frequency offset, and the third parameter is an integer. In this way, the frequency offset of the uplink signal is the minimum offset unit of the multiple indicated by the third parameter, and the uplink signal is offset by the frequency offset on the predetermined frequency and then transmitted, so that the satellite can receive the uplink signal approximately around the predetermined frequency, thereby realizing uplink frequency synchronization.
In an optional implementation manner of this embodiment, step S103 in the method, that is, the step of sending the uplink signal after performing frequency offset according to the frequency offset parameter, may include the following steps:
the second frequency offset amount Δ f is calculated according to the following equation 2 ：Δf 2 ＝xf u Wherein, said f u The x is the third parameter and is the preset minimum offset unit of the satellite communication system;
and transmitting the uplink signal after carrying out frequency offset according to the second frequency offset.
In this implementation, if the frequency domain resource in the transmission resource received by the ground terminal is a predetermined frequency, the ground terminal performs frequency offset compensation on the predetermined frequency according to the third parameter x. I.e. the predetermined frequency offset xf u And transmitting the uplink signal. At this time, a certain residual frequency offset f still exists between the frequency of the uplink signal received by the satellite and the predetermined frequency d But the residual frequency offset f d Small enough, the uplink signal of the terrestrial terminal will not cause significant interference to the uplink signals of other terrestrial terminals.
In an optional implementation manner of this embodiment, the method further includes:
receiving an indication message issued by the satellite, wherein the indication message is used for indicating the time period and the carrier frequency band of the random access pilot frequency sent by the ground terminal;
the sending of the random access pilot to the satellite includes: transmitting the random access pilot to the satellite on the carrier frequency band for a period of time indicated by the indication message.
In this optional implementation manner, the indication message may be a broadcast message broadcasted by the satellite, or may also be some downlink messages issued by the satellite, where the indication message is used to indicate a time period and a carrier frequency band at which the ground terminal sends the random access pilot. Therefore, the ground terminal can send the random access pilot frequency to the satellite on the carrier frequency band in the period of time, and the time and the frequency of receiving the random access pilot frequency when no transmission delay and Doppler frequency shift exist in the satellite are prestored, so that the satellite can obtain the transmission delay and the Doppler frequency offset between the ground terminal of the satellite and the satellite after detecting the time and the frequency of receiving the random access pilot frequency.
In an optional implementation manner of this embodiment, if the carrier frequency band includes a random access channel and a guard band, and the guard band includes an upper guard band located above a frequency of the random access channel and/or a lower guard band located below the frequency of the random access channel, then the sending the random access pilot to the satellite on the carrier frequency band within a time period indicated by the indication message includes: and transmitting the random access pilot frequency to the satellite on a random access channel in the carrier frequency band in a time period indicated by the indication message.
In this implementation manner, in order to avoid interference of the random access pilot due to doppler shift, the random access pilot received by the satellite falls within the carrier frequency band, where the carrier frequency band includes a random access channel and a guard band, and the guard band includes an upper guard band located above the frequency of the random access channel and/or a lower guard band located below the frequency of the random access channel, and after receiving the indication message, the ground terminal may send the random access pilot to the satellite on the random access channel in the carrier frequency band indicated by the indication message, so that the random access pilot finally falls within the range of the corresponding guard band after the corresponding doppler shift in the transmission process, and does not cause interference to uplink signals of other ground terminals.
In an optional implementation manner of this embodiment, the random access pilot response message further includes a timing advance and a transmission resource, in step S103, that is, the step of sending the uplink signal after performing frequency offset according to the frequency offset parameter, may further include the following steps: and after carrying out frequency offset according to a frequency offset parameter in the transmission resource, transmitting an uplink signal based on the timing advance.
In this alternative implementation, the ground terminal sends the random access pilot to the satellite primarily to tell the satellite the propagation delay and doppler frequency offset between the ground terminal and the satellite. The satellite can detect the time and frequency of receiving the random access pilot frequency after receiving the random access pilot frequency, and the satellite prestores the non-delay time and non-offset frequency of receiving the random access pilot frequency when no transmission delay and Doppler frequency shift exist, so that the transmission delay between the ground terminal and the satellite can be obtained according to the detected time of receiving the random access pilot frequency and the prestored non-delay time, and the Doppler frequency offset between the ground terminal and the satellite can be obtained according to the detected frequency of receiving the random access pilot frequency and the prestored non-offset frequency.
In the optional implementation manner, the random access pilot response message carries transmission resources allocated to the ground terminal, where the transmission resources include time-frequency resources, that is, a satellite may provide a random access service for the ground terminal on the time-frequency resources (e.g., a predetermined subframe and a predetermined frequency), but because a transmission delay and a doppler shift exist between the ground terminal and the satellite, the satellite needs to provide a timing advance and a frequency shift parameter for the ground terminal, so as to ensure that the satellite can obtain an uplink signal sent by the ground terminal on the transmission resources.
In the optional implementation mode, the satellite can issue a random access pilot response message carrying a timing advance, a frequency offset parameter and a transmission resource to the ground terminal based on the transmission delay and the doppler frequency offset between the ground terminal and the satellite, and the ground terminal can transmit an uplink signal based on the timing advance after performing frequency offset according to the frequency offset parameter in the transmission resource, so that the time when the satellite receives the uplink signal of the ground terminal is synchronous with the time when the satellite receives the uplink signals of other ground terminals, and the receiving frequency is located at different frequencies, so that the ground terminal realizes uplink time-frequency synchronous transmission, thereby avoiding multi-user interference or inter-symbol interference caused by multi-user time-frequency asynchronization and further successfully completing the random access process.
As shown in fig. 11, the method is applied to a satellite communication system formed by a satellite and a ground terminal, and may include the following steps:
in step S111, the satellite transmits an indication message to the ground terminal, where the indication message is used to indicate a time period and a carrier frequency band at which the ground terminal transmits a random access pilot;
in step S112, the ground terminal transmits the random access pilot to the satellite on the carrier frequency band within the time period indicated by the indication message;
in step S113, the satellite detects the time and frequency of receiving the random access pilot, and determines the transmission delay and the doppler frequency offset between the ground terminal and the satellite;
in step S114, the satellite issues a random access pilot response message to the ground terminal based on the transmission delay and the doppler frequency offset, where the random access pilot response message includes a timing advance, a frequency offset parameter, and a transmission resource, and the random access pilot response message is used to instruct the ground terminal to transmit an uplink signal based on the timing advance after performing frequency offset according to the frequency offset parameter in the transmission resource;
in step S115, after receiving the random access pilot response message, the ground terminal performs frequency offset according to the frequency offset parameter in the transmission resource, and then transmits an uplink signal based on the timing advance.
For details of the random access method in this embodiment, reference may be made to the above description, and details are not described herein again.
The following are embodiments of the apparatus of the present application that may be used to perform embodiments of the method of the present application.
According to the random access apparatus for low orbit constellation of an embodiment of the present application, the apparatus may be implemented as part or all of a satellite by software, hardware or a combination of both. As shown in fig. 12, the random access apparatus includes:
a first receiving module 121, configured to receive a random access pilot sent by a ground terminal;
a first determining module 122 configured to detect a frequency at which the random access pilot is received, and determine a doppler frequency offset between the ground terminal and the satellite;
a first sending module 123, configured to issue a random access pilot response message to the ground terminal based on the doppler frequency offset, where the random access pilot response message includes a frequency offset parameter, and the random access pilot response message is used to instruct the ground terminal to send an uplink signal after performing frequency offset according to the frequency offset parameter.
In an optional implementation manner of this embodiment, the frequency offset parameter includes a first parameter and a second parameter, where the first parameter and the second parameter are both integers, the first parameter is used to indicate a multiple of a subcarrier spacing in the doppler frequency offset, the second parameter is used to indicate a multiple of a minimum offset unit in a residual amount, and the residual amount is an offset obtained by subtracting the subcarrier spacing of the multiple indicated by the first parameter from the doppler frequency offset.
In an optional implementation manner of this embodiment, the first sending module 123 may be configured to:
calculating the first parameter n and the second parameter m according to the following formulas: Δ f = nf s +mf u +f d ；
Wherein Δ f is a Doppler frequency offset, f s The subcarrier spacing of the satellite communication system, said f u The minimum deviation unit of the satellite communication system is preset;
Figure BDA0003777483190000211
in an optional implementation manner of this embodiment, the frequency offset parameter includes a third parameter, the third parameter is used to indicate a multiple of a minimum offset unit in the doppler frequency offset, and the third parameter is an integer.
In an optional implementation manner of this embodiment, the first sending module 123 may be configured to:
the third parameter x is calculated according to the following formula: Δ f = xf u +f d ；
Δ f is the Doppler frequency offset, f s The subcarrier spacing of the satellite communication system, said f u The minimum deviation unit of the satellite communication system is preset;
Figure BDA0003777483190000212
in an optional implementation manner of this embodiment, the apparatus further includes:
a second sending module, configured to send an indication message to the ground terminal, where the indication message is used to indicate a time period and a carrier frequency band when the ground terminal sends a random access pilot.
In an optional implementation manner of this embodiment, the carrier frequency band includes a random access channel and a guard band, and the guard band includes an upper guard band located above a frequency of the random access channel and/or a lower guard band located below the frequency of the random access channel.
In an optional implementation manner of this embodiment, when the satellite and the ground terminal are in a relative motion state in the period of sending the random access pilot indicated by the indication message, the carrier frequency band indicated by the indication message includes an upper guard band, and when the satellite and the ground terminal are in a reverse motion state in the period of sending the random access pilot indicated by the indication message, the carrier frequency band indicated by the indication message includes a lower guard band.
In an optional implementation manner of this embodiment, the apparatus further includes:
a second determining module configured to determine the bandwidth of the upper guard band and/or the lower guard band of the carrier band indicated by the indication message according to the relative speed of the satellite and the ground terminal in the period of sending the random access pilot indicated by the indication message.
In an optional implementation manner of this embodiment, the random access pilot response message further includes a timing advance and a transmission resource, and the random access pilot response message is used to instruct the ground terminal to perform frequency offset according to a frequency offset parameter in the transmission resource and then to send an uplink signal based on the timing advance; the device further comprises:
a third determining module configured to detect a time when the random access pilot is received, and determine a transmission delay between the ground terminal and the satellite;
a fourth determining module configured to determine the timing advance based on the transmission delay.
In this embodiment, the random access apparatus applied to the satellite corresponds to the random access method applied to the satellite, and specific details may refer to the description of the random access method, which is not described herein again.
According to an embodiment of the present application, the random access apparatus for low-orbit constellations may be implemented by software, hardware or a combination of the two to become part or all of the terrestrial terminal. As shown in fig. 13, the random access apparatus includes:
a third transmitting module 131 configured to transmit a random access pilot to the satellite;
a second receiving module 132, configured to receive a random access pilot response message sent by the satellite, where the random access pilot response message includes a frequency offset parameter;
a fourth sending module 133, configured to send the uplink signal after performing frequency offset according to the frequency offset parameter.
In an optional implementation manner of this embodiment, the frequency offset parameter includes a first parameter and a second parameter, where the first parameter and the second parameter are both integers, the first parameter is used to indicate a multiple of a subcarrier spacing in the doppler frequency offset, the second parameter is used to indicate a multiple of a minimum offset unit in a remaining amount, and the remaining amount is an offset obtained by subtracting the subcarrier spacing indicated by the first parameter from the doppler frequency offset.
In an optional implementation manner of this embodiment, the fourth sending module 133 is configured to:
the first frequency offset amount Δ f is calculated according to the following equation 1 ：Δf 1 ＝nf s +mf u Wherein, said f s The subcarrier spacing of the satellite communication system, said f u Is a preset minimum offset unit of the satellite communication system; n is a first parameter, and m is a second parameter;
and transmitting an uplink signal after carrying out frequency offset according to the first frequency offset.
In an optional implementation manner of this embodiment, the frequency offset parameter includes a third parameter, the third parameter is used to indicate a multiple of a minimum offset unit in the doppler frequency offset, and the third parameter is an integer.
In an optional implementation manner of this embodiment, the fourth sending module 133 is configured to:
the second frequency offset amount Δ f is calculated according to the following equation 2 ：Δf 2 ＝xf u Wherein, the f u The x is a third parameter and is a preset minimum offset unit of the satellite communication system;
and transmitting the uplink signal after carrying out frequency offset according to the second frequency offset.
In an optional implementation manner of this embodiment, the apparatus further includes:
a third receiving module, configured to receive an indication message issued by the satellite, where the indication message is used to indicate a time period and a carrier frequency band at which a ground terminal sends a random access pilot;
the third sending module 131 is further configured to: and transmitting the random access pilot to the satellite on the carrier frequency band within the time period indicated by the indication message.
In an optional implementation manner of this embodiment, the carrier frequency band includes a random access channel and a guard band, and the guard band includes an upper guard band located above a frequency of the random access channel and/or a lower guard band located below the frequency of the random access channel, then the portion of the third transmitting module 131 that transmits the random access pilot to the satellite on the carrier frequency band within the time period indicated by the indication message is further configured to:
and transmitting the random access pilot frequency to the satellite on a random access channel in the carrier frequency band in a time period indicated by the indication message.
In an optional implementation manner of this embodiment, the random access pilot response message further includes a timing advance and a transmission resource, and the fourth sending module 133 is further configured to:
and after carrying out frequency offset according to a frequency offset parameter in the transmission resource, transmitting an uplink signal based on the timing advance.
In this embodiment, the random access apparatus applied to the ground terminal corresponds to the random access method applied to the ground terminal, and specific details may refer to the description of the random access method, which is not described herein again.
Fig. 14 is a schematic structural diagram of an electronic device suitable for the random access method disclosed in the embodiment of the present application. The electronic device may be a satellite or a ground terminal.
As shown in fig. 14, electronic device 140 includes a processing unit 141, which may be implemented as a CPU, GPU, FPGA, NPU, or like processing unit. The processing unit 141 may execute various processes in the embodiment of any one of the methods described above in the present application according to a program stored in the Read Only Memory (ROM) 142 or a program loaded from the storage section 148 into the Random Access Memory (RAM) 143. In the RAM143, various programs and data necessary for the operation of the electronic apparatus 140 are also stored. The processing unit 141, the ROM142, and the RAM143 are connected to each other via a bus 144. An input/output (I/O) interface 145 is also connected to bus 144.
The following components are connected to the I/O interface 145: an input portion 146 including a keyboard, a mouse, and the like; an output section 147 including a display such as a Cathode Ray Tube (CRT), a Liquid Crystal Display (LCD), and the like, and a speaker; a storage section 148 including a hard disk and the like; and a communication section 149 including a network interface card such as a LAN card, a modem, or the like. The communication section 149 performs communication processing via a network such as the internet. The drive 1410 is also connected to the I/O interface 145 as needed. A removable medium 1411 such as a magnetic disk, an optical disk, a magneto-optical disk, a semiconductor memory, or the like is mounted on the drive 1410 as necessary, so that a computer program read out therefrom is installed into the storage section 148 as necessary.
In particular, according to embodiments of the application, any of the methods described above with reference to embodiments of the application may be implemented as a computer software program. For example, embodiments of the present application include a computer program product comprising a computer program tangibly embodied on a machine-readable medium, the computer program comprising program code for performing any of the methods of embodiments of the present application. In such embodiments, the computer program may be downloaded and installed from a network through the communication section 149, and/or installed from the removable medium 1411.
The flowchart and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present application. In this regard, each block in the flowcharts or block diagrams may represent a module, a program segment, or a portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.
The units or modules described in the embodiments of the present application may be implemented by software or hardware. The units or modules described may also be provided in a processor, and the names of the units or modules do not in some cases constitute a limitation of the units or modules themselves.
As another aspect, the present application also provides a computer-readable storage medium, which may be the computer-readable storage medium included in the apparatus described in the above embodiment; or it may be a separate computer readable storage medium not incorporated into the device. The computer readable storage medium stores one or more programs for use by one or more processors in performing the methods described herein.
The above description is only a preferred embodiment of the application and is illustrative of the principles of the technology employed. It will be appreciated by a person skilled in the art that the scope of the invention according to the present application is not limited to the specific combination of the above-mentioned features, but also covers other embodiments where any combination of the above-mentioned features or their equivalents is made without departing from the inventive concept. For example, the above features may be replaced with (but not limited to) features having similar functions disclosed in the present application.

Claims (39)

1. A random access method for a low earth orbit constellation, applied to a satellite, comprising:
receiving a random access pilot frequency sent by a ground terminal;
detecting the frequency of the received random access pilot frequency, and determining the Doppler frequency offset between the ground terminal and the satellite;
and issuing a random access pilot response message to the ground terminal based on the Doppler frequency offset, wherein the random access pilot response message comprises a frequency offset parameter, and the random access pilot response message is used for indicating the ground terminal to transmit an uplink signal after carrying out frequency offset according to the frequency offset parameter.
2. The method of claim 1, wherein the frequency offset parameters comprise a first parameter and a second parameter, the first parameter and the second parameter being integers, the first parameter indicating a multiple of a subcarrier spacing in the doppler frequency offset, the second parameter indicating a multiple of a smallest offset unit in a residual amount.
3. The method of claim 2, wherein before issuing a random access pilot response message to the ground terminal based on the doppler frequency offset, further comprising:
calculating the first parameter n and the second parameter m according to the following formulas:
Δf＝nf s +mf u +f d ；
wherein Δ f is a Doppler frequency offset, f s The subcarrier spacing of the satellite communication system, said f u For a preset minimum offset unit of the satellite communication system, f d In order to be the residual frequency offset,
Figure FDA0003777483180000011
4. the method of claim 1, wherein the frequency offset parameter comprises a third parameter indicating a multiple of a minimum offset unit in the doppler frequency offset, and wherein the third parameter is an integer.
5. The method of claim 4, wherein before issuing a random access pilot response message to the ground terminal based on the Doppler frequency offset, further comprising:
the third parameter x is calculated according to the following formula:
Δf＝xf u +f d ：
Δ f is the Doppler frequency offset, fs is the satellite communicationSubcarrier spacing of the system, said f u For a preset minimum offset unit of the satellite communication system, f d In order to be the residual frequency offset,
Figure FDA0003777483180000012
6. the method of claim 1, further comprising:
and sending an indication message to the ground terminal, wherein the indication message is used for indicating the time period and the carrier frequency band of the random access pilot frequency sent by the ground terminal.
7. The method of claim 6, wherein the carrier frequency band comprises a random access channel and a guard band, and wherein the guard band comprises an upper guard band located above a frequency of the random access channel or a lower guard band located below the frequency of the random access channel.
8. The method of claim 7,
when the satellite and the ground terminal are in a relative motion state in a period of sending a random access pilot frequency indicated by the indication message, a carrier frequency band indicated by the indication message comprises an upper guard band;
and when the satellite and the ground terminal are in a back-to-back motion state in the period of sending the random access pilot frequency indicated by the indication message, the carrier frequency band indicated by the indication message comprises a lower guard band.
9. The method according to claim 7 or 8, characterized in that the method further comprises:
and determining the bandwidth of an upper guard band and the bandwidth of a lower guard band of a carrier frequency band indicated by the indication message according to the relative speed of the satellite and the ground terminal in the period of sending the random access pilot frequency indicated by the indication message.
10. The method of claim 1, wherein the random access pilot response message further comprises a timing advance and a transmission resource, and wherein the random access pilot response message is used to instruct the ground terminal to transmit an uplink signal based on the timing advance after performing frequency offset according to a frequency offset parameter in the transmission resource, and wherein the method further comprises:
detecting the time of receiving the random access pilot frequency, and determining the transmission time delay between the ground terminal and the satellite;
determining the timing advance based on the transmission delay.
11. A random access method for a low-orbit constellation, applied to a ground terminal, includes:
sending a random access pilot frequency to a satellite;
receiving a random access pilot response message issued by the satellite, wherein the random access pilot response message comprises a frequency offset parameter;
and transmitting the uplink signal after carrying out frequency offset according to the frequency offset parameter.
12. The method of claim 11, wherein the frequency offset parameters comprise a first parameter and a second parameter, the first parameter and the second parameter being integers, the first parameter indicating a multiple of a subcarrier spacing in a doppler frequency offset, the second parameter indicating a multiple of a smallest offset unit in a residual amount.
13. The method of claim 12, wherein the transmitting the uplink signal after performing the frequency offset according to the frequency offset parameter comprises:
the first frequency offset amount Δ f is calculated according to the following equation 1 ：Δf 1 ＝nf s +mf u Wherein, said f s The subcarrier spacing of the satellite communication system, said f u The minimum offset unit of the satellite communication system is preset, n is a first parameter, and m is a second parameter;
and transmitting an uplink signal after carrying out frequency offset according to the first frequency offset.
14. The method of claim 11, wherein the frequency offset parameter comprises a third parameter indicating a multiple of a minimum unit of offset in doppler frequency offset, and wherein the third parameter is an integer.
15. The method of claim 14, wherein the transmitting the uplink signal after performing the frequency offset according to the frequency offset parameter comprises:
the second frequency offset amount Δ f is calculated according to the following equation 2 ：Δf 2 ＝xf u Wherein, the f u The x is the third parameter and is the preset minimum offset unit of the satellite communication system;
and transmitting the uplink signal after carrying out frequency offset according to the second frequency offset.
16. The method of claim 11, further comprising:
receiving an indication message issued by the satellite, wherein the indication message is used for indicating the time period and the carrier frequency band of the random access pilot frequency sent by the ground terminal;
the sending of the random access pilot to the satellite includes:
and transmitting the random access pilot to the satellite on the carrier frequency band within the time period indicated by the indication message.
17. The method of claim 16, wherein the carrier frequency band comprises a random access channel and a guard band, and wherein the guard band comprises an upper guard band located above a frequency of the random access channel or a lower guard band located below the frequency of the random access channel, then transmitting the random access pilot to the satellite on the carrier frequency band for a period of time indicated by the indication message comprises:
and transmitting the random access pilot frequency to the satellite on a random access channel in the carrier frequency band in a time period indicated by the indication message.
18. The method of claim 11, wherein the random access pilot response message further includes a timing advance and a transmission resource, and the transmitting the uplink signal after performing the frequency offset according to the frequency offset parameter includes:
and after carrying out frequency offset according to a frequency offset parameter in the transmission resource, transmitting an uplink signal based on the timing advance.
19. A random access apparatus for low earth constellation, applied to a satellite, comprising:
a first receiving module configured to receive a random access pilot transmitted by a ground terminal;
a first determining module configured to detect a frequency at which the random access pilot is received, and determine a doppler frequency offset between the ground terminal and the satellite;
a first sending module, configured to issue a random access pilot response message to the ground terminal based on the doppler frequency offset, where the random access pilot response message includes a frequency offset parameter, and the random access pilot response message is used to instruct the ground terminal to send an uplink signal after performing frequency offset according to the frequency offset parameter.
20. The apparatus of claim 19, wherein the frequency offset parameters comprise a first parameter and a second parameter, the first parameter and the second parameter being integers, the first parameter indicating a multiple of a subcarrier spacing in the doppler frequency offset, the second parameter indicating a multiple of a smallest offset unit in a residual amount.
21. The apparatus of claim 20, wherein the first sending module is further configured to:
calculating the first parameter n and the second parameter m according to the following formulas:
Δf＝nf s +mf u +f d ；
wherein Δ f is the Doppler frequency offset, f s The subcarrier spacing of the satellite communication system, said f u For a preset minimum offset unit of the satellite communication system, f d Is a residual frequency offset and is a frequency offset,
Figure FDA0003777483180000041
22. the apparatus of claim 19, wherein the frequency offset parameter comprises a third parameter indicating a multiple of a smallest unit of offset in the doppler frequency offset, and wherein the third parameter is an integer.
23. The apparatus of claim 22, wherein the first sending module is further configured to:
the third parameter x is calculated according to the following formula:
Δf＝xf u +f d ；
Δ f is the Doppler frequency offset, f s The subcarrier spacing of the satellite communication system, said f u For a preset minimum offset unit of the satellite communication system, f d In order to be the residual frequency offset,
Figure FDA0003777483180000042
24. the apparatus of claim 19, further comprising:
a second sending module, configured to send an indication message to the ground terminal, where the indication message is used to indicate a time period and a carrier frequency band when the ground terminal sends a random access pilot.
25. The apparatus of claim 24, wherein the carrier frequency band comprises a random access channel and a guard band, and wherein the guard band comprises an upper guard band above a frequency of the random access channel or a lower guard band below the frequency of the random access channel.
26. The apparatus of claim 25,
when the satellite and the ground terminal are in a relative motion state in a period of sending a random access pilot frequency indicated by the indication message, a carrier frequency band indicated by the indication message comprises an upper guard band;
and when the satellite and the ground terminal are in a back-to-back motion state in the period of sending the random access pilot frequency indicated by the indication message, the carrier frequency band indicated by the indication message comprises a lower guard band.
27. The apparatus of claim 25 or 26, further comprising:
a second determining module configured to determine bandwidths of an upper guard band and a lower guard band of a carrier band indicated by the indication message according to a relative speed of the satellite and the ground terminal in a period of sending a random access pilot indicated by the indication message.
28. The apparatus of claim 19, wherein the random access pilot response message further comprises a timing advance and a transmission resource, and wherein the random access pilot response message is configured to instruct the ground terminal to transmit an uplink signal based on the timing advance after performing frequency offset according to a frequency offset parameter in the transmission resource, the apparatus further comprising:
a third determining module configured to detect a time when the random access pilot is received, and determine a transmission delay between the ground terminal and the satellite;
a fourth determining module configured to determine the timing advance based on the transmission delay.
29. A random access apparatus for low-orbit constellation, applied to a ground terminal, comprising:
a third transmitting module configured to transmit a random access pilot to the satellite;
a second receiving module, configured to receive a random access pilot response message issued by the satellite, where the random access pilot response message includes a frequency offset parameter;
and the fourth sending module is configured to send the uplink signal after performing frequency offset according to the frequency offset parameter.
30. The apparatus of claim 29, wherein the frequency offset parameter comprises a first parameter and a second parameter, the first parameter and the second parameter being integers, wherein the first parameter is indicative of a multiple of a subcarrier spacing in a doppler frequency offset, and wherein the second parameter is indicative of a multiple of a smallest offset unit in the residual.
31. The apparatus of claim 30, wherein the fourth sending module is configured to:
the first frequency offset amount Δ f is calculated according to the following equation 1 ：Δf 1 ＝nf s +mf u Wherein, said f s The subcarrier spacing of the satellite communication system, said f u The n is a first parameter and the m is a second parameter, and the n is a preset minimum offset unit of the satellite communication system;
and transmitting an uplink signal after carrying out frequency offset according to the first frequency offset.
32. The apparatus of claim 29, wherein the frequency offset parameter comprises a third parameter indicating a multiple of a minimum unit of offset in doppler frequency offset, and wherein the third parameter is an integer.
33. The apparatus of claim 32, wherein the fourth sending module is configured to:
the second frequency offset amount Δ f is calculated according to the following equation 2 ：Δf 2 ＝xf u Wherein, the f u The x is a third parameter and is a preset minimum offset unit of the satellite communication system;
and transmitting the uplink signal after carrying out frequency offset according to the second frequency offset.
34. The apparatus of claim 29, further comprising:
a third receiving module, configured to receive an indication message issued by the satellite, where the indication message is used to indicate a time period and a carrier frequency band at which the ground terminal sends a random access pilot;
the third transmitting module is further configured to:
and transmitting the random access pilot to the satellite on the carrier frequency band within the time period indicated by the indication message.
35. The apparatus of claim 34, wherein the carrier frequency band comprises a random access channel and a guard band, wherein the guard band comprises an upper guard band located above a frequency of the random access channel or a lower guard band located below the frequency of the random access channel, and wherein the portion of the third transmitting module that transmits the random access pilot to the satellite on the carrier frequency band for the time period indicated by the indication message is further configured to:
and transmitting the random access pilot frequency to the satellite on a random access channel in the carrier frequency band in a time period indicated by the indication message.
36. The apparatus of claim 29, wherein the random access pilot response message further comprises a timing advance and a transmission resource, and wherein the fourth transmitting module is further configured to:
and after carrying out frequency offset according to a frequency offset parameter in the transmission resource, transmitting an uplink signal based on the timing advance.
37. An electronic device comprising a memory, a processor, and a computer program stored on the memory, wherein the processor executes the computer program to implement the method of any of claims 1-10 or 11-18.
38. A computer readable storage medium having stored thereon computer instructions, wherein the computer instructions, when executed by a processor, implement the method of any one of claims 1 to 10 or 11 to 18.
39. A computer program product comprising computer instructions, wherein the computer instructions, when executed by a processor, implement the method of any of claims 1 to 10 or 11 to 18.
CN202210920809.0A 2022-08-02 2022-08-02 Random access method and device for low-orbit constellation and electronic equipment Pending CN115297560A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116155369A (en) * 2023-04-20 2023-05-23 成都爱瑞无线科技有限公司 Satellite communication method, satellite device, terminal and storage medium

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116155369A (en) * 2023-04-20 2023-05-23 成都爱瑞无线科技有限公司 Satellite communication method, satellite device, terminal and storage medium
CN116155369B (en) * 2023-04-20 2023-08-29 成都爱瑞无线科技有限公司 Satellite communication method, satellite device, terminal and storage medium

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