Mobile phone direct connection satellite system transmission method

Abstract

The invention discloses a mobile phone direct connection satellite system transmission method, which solves the problem of limited time sequence adjustment capability caused by long time delay characteristic of a satellite channel through time delay pre-compensation, and solves the problem of limited time-frequency synchronization capability caused by large Doppler frequency shift of the satellite channel through Doppler pre-compensation. The time delay pre-compensation comprises uplink post-delay processing, downlink timing advance, timer enhancement and HARQ enhancement, and the Doppler pre-compensation comprises narrowband Doppler frequency offset pre-compensation and broadband Doppler spread pre-compensation. The maximum beam width allowed to be designed by specific beam pointing is further determined through beam optimization, and the problem of residual time-frequency offset caused by position differences of different users in a satellite cell is solved. According to the method, the ground 5G terminal can be accessed to the satellite network in a non-inductive manner under the Rel-15 protocol standard framework, the hardware / algorithm of the mobile phone is prevented from being upgraded, the mobile phone can be compatible with the ground base station and the satellite-borne base station at the same time, and the method has high engineering practical significance.

Description

Technical Field

[0001] The present invention belongs to the field of satellite mobile communication, and relates to a transmission method for a mobile phone direct satellite system compatible with the Rel-15 standard. Background Art

[0002] In recent years, with disruptive technological innovations such as multi-satellite launches and rocket recycling, as well as the effective improvement of the service capabilities and numbers of single satellites, the cost of satellite launches has been significantly reduced, making mobile phone direct satellite a focus of attention from all walks of life. In addition, with the generational evolution of terrestrial mobile communication technologies, terrestrial cellular mobile communication technologies can also be applied to satellites to provide communication capacity for satellite communication systems. The mobile phone direct satellite technology redefines traditional satellite mobile communication that relies on dedicated terminals and mainly focuses on voice and low-rate services. It is an effective means to achieve global 5G coverage and an important support for shaping the physical world of 6G. The mobile phone direct low-earth orbit satellite technology is highly favored by the industry due to the existing large number of mobile phone terminals.

[0003] The non-terrestrial networks (NTN) project led by the 3rd Generation Partnership Project (3GPP) has carried out standardization work to support mobile phone direct satellite, aiming to incorporate satellite communication technology into the standard framework. In addition, terminal manufacturers such as Huawei and Apple have set up satellite communication modules and mobile communication modules for mobile phones, and achieved the integration of satellite Internet and terrestrial networks through a hardware combination method, enabling mobile phones to have the communication capabilities with both satellites and terrestrial base stations.

[0004] However, although the direct satellite technology for multi-mode mobile phones has been commercialized, its application capabilities are still limited to short message messages; the research on the direct satellite technology for NTN mobile phones currently mainly focuses on the transparent relay mode, and the discussion on the regenerative payload mode is restricted by the NTN standardization process. Considering the global commercial application process of 5G technology, in the current and quite a long period in the future, 5G terminals based on the Rel-15 version will become the mainstream in the market, and the above two technical routes cannot support Rel-15 5G mobile phone direct satellite, thus restricting the commercial markets of both. Therefore, it is particularly important to further explore the mobile phone direct satellite technology compatible with the Rel-15 version. Summary of the Invention

[0005] Object of the Invention: The object of the present invention is to propose a transmission method for a mobile phone direct satellite system compatible with the Rel-15 standard, which can achieve direct connection between terrestrial terminals and satellite networks without involving the enhancement of mobile phone capabilities and the modification of protocol standards, so as to break through the limitations of the standardization process and avoid terminal hardware upgrades.

[0006] Technical solution: To achieve the above object, a transmission method for a mobile phone direct connection satellite system provided by the present invention includes the following steps:

[0007] Determine the common delay pre-compensation value and the common Doppler pre-compensation value for the satellite beam cell;

[0008] Introduce delay pre-compensation and Doppler pre-compensation on the satellite-based base station side to solve the problem of limited terminal capabilities in the mobile phone direct connection system; the delay pre-compensation includes: the satellite-based base station adjusts the uplink reception logic of the scheduler to delay the uplink signal reception and processing time slot to achieve time slot-level delay pre-compensation; adjusts the downlink frame timing to advance the downlink signal transmission timing to achieve sampling point-level delay pre-compensation; and timer enhancement and HARQ enhancement; the Doppler pre-compensation includes narrowband Doppler frequency offset pre-compensation and broadband Doppler spread pre-compensation.

[0009] Further, the calculation method of the common delay pre-compensation value for the satellite beam cell is:

[0010]

[0011] where R is the average radius of the earth, h s is the satellite orbit altitude, v c is the speed of light, θ min = max{θ - θ BW / 2, 0}, θ is the satellite beam elevation angle, θ BW is the satellite beam width.

[0012] Further, the calculation method of the common Doppler pre-compensation value for the satellite beam cell is:

[0013]

[0014] where v s is the satellite speed, f c is the operating frequency, and α is the satellite beam azimuth angle.

[0015] Further, the uplink delay processing includes: the satellite-based base station calculates the uplink signal reception window delay processing amount comp based on the common delay pre-compensation value T slot of the beam cell and the system time slot length T and correspondingly adjusts the uplink reception scheduling logic to equivalently achieve that the uplink frame timing lags behind the downlink frame timing, completing the satellite-ground delay pre-compensation at the time slot level of the satellite beam cell;

[0016] The downlink timing advance includes: the satellite-based base station calculates the downlink timing advance amount comp based on the common delay pre-compensation value T And correspondingly adjust the downlink signal transmission timing to make the downlink frame timing at the spaceborne base station ahead of the uplink frame timing, and complete the sampling point-level delay pre-compensation for the beam-oriented cell;

[0017] Timer enhancement includes: the spaceborne base station adjusts the value of the upper-layer timer based on the common delay pre-compensation value: where T timer represents the value of the timer, which is the set of timer values specified by the Rel-15 protocol;

[0018] HARQ enhancement includes: the spaceborne base station scheduler always sets the HARQ process to the available state, continuously transmits new data regardless of the feedback status, and equivalently disables the HARQ mechanism.

[0019] Furthermore, the narrowband Doppler frequency shift pre-compensation is that the spaceborne base station performs carrier frequency offset correction on the baseband transceiver signals in the time domain based on the Doppler pre-compensation value; the wideband Doppler spread pre-compensation is that the spaceborne base station performs phase correction on the baseband transceiver signals in the frequency domain based on the Doppler pre-compensation value.

[0020] Furthermore, the method further includes:

[0021] Determine the maximum differential delay and the maximum differential frequency offset of the satellite beam cell;

[0022] Based on the constraint conditions of the ground 5G network protocol on the maximum differential delay of the cell and the constraint conditions of the ground 5G terminal capabilities on the maximum differential frequency offset of the cell, determine the maximum beam width allowed for the specific beam pointing design.

[0023] Furthermore, the maximum differential delay of the cell under specific satellite beam parameters is:

[0024]

[0025] where R is the average radius of the earth, h s is the satellite orbital altitude, v c is the speed of light, The constraints of the ground network protocol on the maximum differential delay of the cell include the constraints of the random access preamble format, the zero correlation coefficient, and the timing advance mechanism on the maximum differential delay of the cell.

[0026] Furthermore, the maximum differential frequency offset of the cell under specific satellite beam parameters is:

[0027]

[0028] The constraints of the ground 5G terminal capabilities on the maximum differential frequency offset of the cell include the constraints of the frequency offset resistance capability of the ground terminal on the maximum differential frequency offset of the cell.

[0029] Based on the same inventive concept, the present invention also provides a mobile direct satellite connection system, comprising:

[0030] A compensation value calculation module for determining a common delay pre-compensation value and a common Doppler pre-compensation value for the satellite beam cell;

[0031] A pre-compensation module for introducing delay pre-compensation and Doppler pre-compensation on the spaceborne base station side to solve the problem of limited terminal capabilities in the mobile direct connection system; the delay pre-compensation includes: the spaceborne base station adjusts the uplink reception logic of the scheduler to delay the uplink signal reception and processing time slot to achieve time slot-level delay pre-compensation; adjusts the downlink frame timing to advance the downlink signal transmission timing to achieve sampling point-level delay pre-compensation; and timer enhancement and HARQ enhancement; the Doppler pre-compensation includes narrowband Doppler frequency offset pre-compensation and broadband Doppler spread pre-compensation.

[0032] Further, the system further includes a beam optimization design module for determining the maximum differential delay and the maximum differential frequency offset of the satellite beam cell; and determining the maximum beam width allowed for the specific beam pointing based on the constraint conditions of the maximum differential delay of the cell in the ground 5G network protocol and the constraint conditions of the maximum differential frequency offset of the cell on the ground 5G terminal capabilities.

[0033] Advantageous effects: Compared with the prior art, the present invention has the following advantages:

[0034] 1. In response to the satellite-ground Doppler and long delay problems, the present invention proposes a method of performing pre-compensation only on the spaceborne base station side. By introducing narrowband Doppler frequency shift pre-compensation, broadband Doppler spread pre-compensation, uplink delay processing mechanism, downlink timing advance mechanism, timer enhancement mechanism, and HARQ enhancement mechanism, the anti-frequency offset ability and timing adjustment ability of the system are enhanced, ensuring that ordinary ground 5G mobile phones can seamlessly access the satellite network within the framework of the Rel-15 protocol standard. This method transfers the complexity of modifying the 5G protocol to the spaceborne base station side, avoiding the need to upgrade the hardware / algorithm of the mobile phone, enabling the mobile phone to be compatible with both ground base stations and spaceborne base stations, and having strong engineering practical significance.

[0035] 2. Through the uplink delay processing mechanism and the downlink timing advance mechanism, the present invention completes the delay pre-compensation at the time slot level and the sampling point level respectively, so that the spaceborne base station can configure and use all random access preamble formats in the 5G protocol according to actual needs, avoiding the limitation of the preamble sequence format by the long delay characteristics of the satellite channel.

[0036] 3. The pre-compensation technology and protocol enhancement scheme adopted by the present invention are applicable to both the mobile direct connection scenarios for low-earth orbit satellites and geostationary satellites, providing a unified technical solution for mobile direct connection communication for different types of satellites, and having wide applicability and generality.

[0037] 4. The present invention proposes a satellite beam optimization design method for multi-user scenarios. After determining the Doppler pre-compensation value and time-delay pre-compensation value for the beam cell, by constraining the satellite beam width, the time-delay and frequency-offset differences within the beam cell are controlled within the tolerances of the terrestrial 5G standard protocol and the capabilities of terrestrial 5G terminals, thereby improving the synchronization and access stability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is the architecture diagram of the mobile direct satellite system according to the embodiment of the present invention.

[0039] Figure 2 It is the system timing diagram under the uplink delay processing mechanism according to the embodiment of the present invention.

[0040] Figure 3 It is the system timing diagram under the downlink timing advance mechanism according to the embodiment of the present invention.

[0041] Figure 4 It is the implementation block diagram of the downlink HARQ disabling mechanism according to the embodiment of the present invention.

[0042] Figure 5 It is the implementation block diagram of the uplink HARQ disabling mechanism according to the embodiment of the present invention.

[0043] Figure 6 It is the implementation block diagram of the Doppler pre-compensation according to the embodiment of the present invention.

[0044] Figure 7 It is the simulation result diagram of the beam width constraint conditions for the preamble format according to the embodiment of the present invention.

[0045] Figure 8 It is the simulation result diagram of the beam width constraint conditions for the zero correlation zone coefficients according to the embodiment of the present invention.

[0046] Figure 9 It is the simulation result diagram of the beam width constraint conditions for the timing advance mechanism according to the embodiment of the present invention.

[0047] Figure 10 It is the simulation result diagram of the beam width constraint conditions for the terminal frequency offset resistance ability according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] The following further describes the present invention in conjunction with the accompanying drawings and specific embodiments. These embodiments are only used to illustrate the present invention and do not limit the protection scope of the present invention.

[0049] An embodiment of the present invention discloses a transmission method for a mobile phone direct satellite system, which mainly includes: determining a common delay pre-compensation value and a common Doppler pre-compensation value for a satellite beam cell; introducing delay pre-compensation and Doppler pre-compensation on the spaceborne base station side to respectively solve the problem of limited timing adjustment ability caused by the long delay characteristic of the satellite channel and the problem of limited time-frequency synchronization ability caused by the large Doppler frequency shift of the satellite channel. Among them, the delay pre-compensation includes uplink delay processing, downlink timing advance, timer enhancement, and HARQ enhancement; the Doppler pre-compensation includes narrowband Doppler frequency offset pre-compensation and broadband Doppler spread pre-compensation. Specifically, the delay pre-compensation includes that the spaceborne base station adjusts the uplink reception logic of the scheduler to delay the uplink signal reception processing time slot to achieve time slot-level delay pre-compensation; adjusts the downlink frame timing to advance the downlink signal transmission timing to achieve sampling point-level delay pre-compensation; adjusts the selection values of the random access response timer, the contention resolution timer, the radio link control protocol (RLC) layer timer, and the packet data convergence protocol (PDCP) layer timer; equivalently disables the HARQ mechanism by setting the HARQ process to an available state and continuously sending new data; the Doppler pre-compensation includes that the spaceborne base station performs carrier frequency offset correction on the baseband transceiver signal in the time domain to complete narrowband Doppler frequency offset pre-compensation, and performs phase correction on the baseband transceiver signal in the frequency domain to complete broadband Doppler spread pre-compensation.

[0050] To further solve the problem of residual time-frequency offset caused by the difference in the positions of different users within a satellite cell, the transmission method for a mobile phone direct satellite system further includes beam optimization design; the beam optimization design includes that the spaceborne base station determines the maximum differential delay and the maximum differential frequency offset under a specific beam direction based on ephemeris data and beam pointing; determines the random access preamble format, zero correlation coefficient, and the constraint of the timing advance mechanism on the cell differential delay according to the ground 5G standard protocol, determines the constraint of the ground terminal's anti-frequency offset ability on the cell differential frequency offset according to the ground 5G standard protocol, and then determines the maximum beam width allowed to be designed for a specific beam direction.

[0051] Accordingly, a mobile direct satellite system includes: a compensation value calculation module for determining a common delay pre-compensation value and a common Doppler pre-compensation value for the satellite beam cell; a pre-compensation module for introducing delay pre-compensation and Doppler pre-compensation on the satellite base station side to solve the problem of limited terminal capabilities in the mobile direct satellite system. The pre-compensation module includes an uplink delay processing unit, a downlink timing advance unit, a timer enhancement unit, a HARQ enhancement unit, and a Doppler pre-compensation unit; the uplink delay processing unit is used to adjust the uplink reception logic of the scheduler on the satellite base station side and delay the uplink signal reception processing time slot to achieve time slot-level delay pre-compensation; the downlink timing advance unit is used to adjust the downlink frame timing on the satellite base station side and advance the downlink signal transmission timing to achieve sampling point-level delay pre-compensation; the timer enhancement unit is used to adjust the selection values of the random access response timer, the contention resolution timer, the radio link control protocol (RLC) layer timer, and the packet data convergence protocol (PDCP) layer timer on the satellite base station side; the HARQ enhancement unit is used to set the HARQ process to an available state and continuously send new data on the satellite base station side, equivalently disabling the HARQ mechanism; the Doppler pre-compensation unit is used to perform carrier frequency offset correction on the baseband transceiver signal in the time domain to complete narrowband Doppler frequency offset pre-compensation, and perform phase correction on the baseband transceiver signal in the frequency domain to complete broadband Doppler spread pre-compensation. Further, the system further includes a beam optimization design module, which is used to determine the maximum differential delay and the maximum differential frequency offset under a specific beam direction, determine the random access preamble format, the zero correlation coefficient, and the constraint of the timing advance mechanism on the cell differential delay according to the ground 5G standard protocol, determine the constraint of the ground terminal's anti-frequency offset ability on the cell differential frequency offset according to the ground 5G standard protocol, and then determine the maximum beam width allowed for design under a specific beam direction.

[0052] According to the non-negativity constraint of the timing advance amount in the access phase according to the ground 5G standard protocol, when the beam direction and the beam width are determined, the common delay pre-compensation value for the satellite beam cell can be expressed as:

[0053]

[0054] Where R is the average radius of the earth, h s is the satellite orbital altitude, v c is the speed of light, θ is the satellite beam elevation angle, θ BW is the satellite beam width, θ min = max{θ - θ BW / 2, 0}.

[0055] Further, the calculation method of the common Doppler pre-compensation value for the satellite beam cell is:

[0056]

[0057] where v s is the satellite velocity, f c is the operating frequency, and α is the satellite beam azimuth angle.

[0058] Figure 1 The architecture diagram of the mobile direct satellite system is given. Combining Figure 1 , an embodiment of the present invention discloses a transmission method for a mobile direct satellite system compatible with the Rel-15 standard, including delay pre-compensation and Doppler pre-compensation; among them, the delay pre-compensation design includes uplink delay processing, downlink timing advance, timer enhancement, and HARQ enhancement.

[0059] The uplink delay processing is to adjust the uplink receiving logic of the scheduler on the satellite base station side, delay the uplink signal receiving processing time slot, and achieve time slot-level delay pre-compensation. Figure 2 Describes the system transceiver timing under the uplink delay processing mechanism, where RTT represents the round-trip transmission delay between the satellite and the ground, and T A represents the uplink timing advance amount on the terminal side. Different from the terrestrial 5G network, the satellite base station will delay the uplink signal receiving window according to the prior information of the channel delay, and define the uplink signal receiving window delay processing amount as Its calculation method is:

[0060]

[0061] where T slot represents the system time slot length, and T comp represents the common delay pre-compensation value of the beam cell.

[0062] In the process of receiving uplink data at the satellite base station, the interaction process between the PHY layer and the MAC layer through the FAPI interface is as follows: The MAC layer first generates a UL_TTI.request message according to the scheduling result, specifying the uplink resource block, time slot index, OFDM symbol position, etc.; after receiving the UL_TTI.request, the PHY layer opens the uplink receiving window within the specified time slot for signal demodulation and decoding; after completing the uplink signal reception, the PHY layer will send the data and the HARQ feedback result to the MAC layer through the RX.indication interface. In the FAPI interface, SlotIndex determines when the PHY layer starts the receiving process, so by increasing the value of SlotIndex, the receiving opportunity can be shifted backward as a whole. Therefore, it can be achieved by modifying the time slot index parameter in the UL_TTI.request message. Assuming that the original time slot for uplink data reception is K, then setting the SlotIndex of the UL_TTI.request message to can delay the PHY layer receiving window by A time slot is used to achieve slot-level pre-compensation for the long space-ground time delay.

[0063] Downlink timing advance is to pre-compensate the time delay at the sampling point level by adjusting the downlink frame timing on the satellite-based base station side and advancing the downlink signal transmission timing. Figure 3 The system transceiver timing sequence under the downlink timing advance mechanism is described. The satellite-based base station will simultaneously adjust its own downlink frame timing, and then adjust the downlink frame timing of the ground terminal to ensure the correct reception and demodulation of the uplink signal. On the basis of the uplink delay processing mechanism, the downlink timing advance amount of the satellite-based base station is further defined as The calculation method is as follows:

[0064]

[0065] When the satellite-based base station sends baseband IQ data, the sending time of the data can be flexibly controlled through the time_spec timestamp parameter. Therefore, the downlink data can be sent in advance by modifying the sending timestamp, so as to implement the downlink timing advance mechanism. Let the original downlink sending timestamp be t. In the case of introducing the uplink delay processing mechanism, the downlink sending timestamp is set to to achieve sampling point-level pre-compensation for the long space-ground time delay.

[0066] Timer enhancement is to adjust the selected values of the random access response timer, contention resolution timer, radio link control (RLC) layer timer, and packet data convergence protocol (PDCP) layer timer on the satellite-based base station side. During the user access and service transmission process, in order to improve the system performance and reliability, multiple timers are set in the high-layer protocol to manage the transmission and retransmission of protocol data units. However, compared with the terrestrial mobile communication system, the round-trip time delay between the ground terminal and the satellite in the mobile phone direct connection to low-earth orbit satellite system is significantly longer. Therefore, when configuring parameters for the satellite-based base station, the processing capabilities of the ground terminal need to be considered simultaneously, and the value range of the timer should be restricted according to the long time delay characteristics of the space-ground link, so as to ensure that the high-layer protocol can adapt to the long time delay environment. In this system, the value of the timer should follow the following rules:

[0067]

[0068] where T timer represents the timer value, It is the set of timer values specified in the Rel-15 protocol. At the MAC layer, the random access response reception window (ra-ResponseWindow) and the contention resolution timer (mac-ContentionResolutionTimer) respectively determine the maximum waiting duration after the mobile phone sends Msg1 and Msg3. The value sets of the two in the Rel-15 protocol are as follows:

[0069]

[0070] where SL represents the slot length and SF represents the subframe length.

[0071] At the RLC layer, the poll retransmission timer (t-PollRetransmit), the reassembly timer (t-Reassembly), and the status report prohibit timer (t-StatusProhibit) are respectively used to control the poll message sending frequency, detect out-of-order and packet loss situations of RLC PDUs, and limit the status report message sending frequency. The value sets corresponding to the three timers are as follows:

[0072]

[0073]

[0074] At the PDCP layer, the discard timer (discardTimer) determines the retention time of PDCP PDUs, and the reordering timer (t-Reordering) is used to maintain the reordering process of PDCP PDUs. The value sets of the two are as follows:

[0075]

[0076] In order to ensure the compatibility of high-layer timers with the long-delay environment of the satellite-terrestrial link, it is necessary to combine ephemeris information and beam information during the system implementation process and adjust the values of each high-layer timer according to the timer enhancement mechanism.

[0077] Hybrid Automatic Repeat reQuest (HARQ) enhancement is to set the HARQ process to the available state at the satellite-based base station side and continuously send new data, which is equivalent to disabling the HARQ mechanism. Such as Figure 4As shown in the figure, during downlink data transmission, the spaceborne base station first sends a PDCCH carrying DL DCI to indicate the time-frequency position of the PDSCH received by the ground terminal and its corresponding HARQ information, and at the same time sends a PDSCH carrying downlink data. To achieve the effect of disabling the downlink HARQ mechanism, the spaceborne base station needs to indicate the data transmitted this time as newly transmitted data through the New data indicator field of the DLDCI every time it initiates downlink data transmission.

[0078] As Figure 5 shown in the figure, during uplink data transmission, the spaceborne base station first sends a PDCCH carrying UL DCI to indicate the time-frequency position of the PUSCH transmitted by the ground terminal and its corresponding HARQ information. For uplink data transmission, after the MAC layer of the spaceborne base station completes scheduling and delivers relevant scheduling information (HARQ information, coding and modulation methods, etc.) to the PHY layer, it is necessary to retain the relevant scheduling information until the corresponding uplink data is received and demodulated (downlink transmission can be directly discarded / overwritten). Therefore, it is necessary to increase the buffer length for retaining scheduling information in the satellite communication scenario. Further, since the scheduling information and the HARQ process are bound, the buffer for uplink scheduling information can be expanded by increasing the number of HARQ processes during the implementation of the uplink HARQ mechanism. When generating the UL DC, the HARQ process ID is modulo 16 and filled into the HARQ process number field to ensure compatibility with ground 5G terminals. Different from the downlink HARQ mechanism, the spaceborne base station does not need to send HARQ feedback to the ground terminal after completing uplink data demodulation. It only needs to indicate the data transmitted this time as newly transmitted data through the New data indicator field in the UL DCI when using the same HARQ process for uplink transmission next time.

[0079] Doppler pre-compensation is to perform carrier frequency offset correction on the baseband transceiver signals in the time domain to complete narrowband Doppler frequency offset pre-compensation, and perform phase correction on the baseband transceiver signals in the frequency domain to complete wideband Doppler spread pre-compensation. Figure 6 The system implementation structure of the Doppler pre-compensation function is shown in the figure. This structure divides the Doppler pre-compensation into two parts, including wideband Doppler effect pre-compensation and narrowband Doppler effect pre-compensation. During the wideband Doppler effect pre-compensation process, first, the common Doppler frequency shift pre-compensation f needs to be completed according to the satellite velocity v s in the satellite platform local coordinate system (SPL, Satellite Plane Local Coordinate), the beam pointing elevation angle Δ, and the azimuth angle α compThe calculation is performed, and broadband Doppler spread pre-compensation for the baseband digital signal x(n) is completed in the frequency domain to obtain the broadband Doppler pre-compensated signal x′(n). The broadband Doppler spread pre-compensation process based on the frequency domain can be expressed by the following formula:

[0080]

[0081] where S k represents the modulation symbol on the k-th subcarrier, represents the set of available subcarriers, and N is the number of system subcarriers.

[0082] Furthermore, narrowband Doppler effect pre-compensation is performed on the broadband Doppler pre-compensated signal in the time domain, and finally the Doppler pre-compensated signal x″(n) is obtained. The narrowband Doppler frequency shift pre-compensation process based on the time domain can be expressed by the following formula:

[0083]

[0084] where Δf represents the system subcarrier spacing.

[0085] Beam optimization design is used to determine the maximum differential delay and the maximum differential frequency offset under a specific beam direction. According to the terrestrial 5G standard protocol, the random access preamble format, the zero correlation coefficient, and the constraints of the timing advance mechanism on the cell differential delay are determined. According to the terrestrial 5G standard protocol, the constraints of the terrestrial terminal's anti-frequency offset ability on the cell differential frequency offset are determined, and then the maximum beam width allowed for a specific beam direction is determined.

[0086] The maximum cell differential delay under specific satellite beam parameters is:

[0087]

[0088] where

[0089] The maximum cell differential frequency offset under specific satellite beam parameters is:

[0090]

[0091] Based on the definition of different random access preamble formats in the standard 5G protocol, according to the preamble cyclic prefix and guard interval lengths, the constraint conditions of the preamble format on the cell differential delay are determined as:

[0092]

[0093] where is the random access preamble cyclic prefix length under the specified parameter set μ, is the random access preamble guard interval length under the specified parameter set μ. Figure 7The satellite beamwidth design constraints under different random preamble formats are given. During the simulation, the satellite orbit altitude is set to 530 km. It can be found from the simulation results that the satellite beamwidth design range under preamble format 1 is better than that of other preamble formats.

[0094] Based on the definition of the random access zero-correlation zone coefficient N cs in the standard 5G protocol, according to the corresponding zero-correlation zone length, the constraint condition of the zero-correlation zone coefficient on the maximum differential delay is determined as:

[0095]

[0096] where L RA is the length of the random access preamble root sequence, N cs is the zero-correlation zone coefficient, N u is the preamble sequence length, n is the number of preamble sequence repetitions, and T c = 1 / (480 kHz·4096) is the minimum time division unit of the 5G frame structure. Figure 8 The satellite beamwidth design constraints under different zero-correlation zone coefficients are given. During the simulation, the satellite orbit altitude is set to 530 km. It can be found from the simulation results that when N cs = 0, the satellite beamwidth can reach the maximum.

[0097] Based on the definition of the timing advance command bit width in the random access response (RAR) and MAC CE in the standard 5G protocol, according to the corresponding timing advance command indication range, the constraint condition of the timing advance mechanism on the maximum differential delay is determined as:

[0098]

[0099] where N TA,offset is the TA offset, and its value in different frequency bands is determined by the 5G standard protocol. Figure 9 The satellite beamwidth design constraints of the timing advance mechanism under different system parameter sets μ are given. During the simulation, the satellite orbit altitude is set to 530 km, and N TA,offset = 25600. It can be found from the simulation results that as the system parameter set μ changes, that is, the system subcarrier spacing becomes smaller, the satellite beamwidth design constraints of the timing advance mechanism are also relaxed accordingly.

[0100] Based on the requirements of the 5G terminal's 5 ppm anti-frequency offset ability in the standard 5G protocol, the constraint condition of the ground terminal ability on the maximum differential frequency offset is determined as:

[0101] Δf max ≤ f c × 5 × 10 -6

[0102] Figure 10 The 5G terminal's 5 ppm anti-frequency offset capability gives the design constraints for the satellite beamwidth. During the simulation, the satellite orbital altitude is set to 530 km. It can be found from the simulation results that, under the limitation of the ground terminal capabilities, the maximum beamwidth in the sub-satellite region can reach approximately 30°, while due to the limitation of the satellite half-angle, the maximum beamwidth gradually approaches zero at the edge of the satellite coverage area.

Claims

1. A method for transmitting a mobile phone directly connected to a satellite system, characterized in that: The steps include: Determine a common delay pre-compensation value and a common Doppler pre-compensation value for a satellite beam cell; Delay pre-compensation and Doppler pre-compensation are introduced on the satellite base station side to solve the problem of limited terminal capacity in the mobile phone direct connection system; the delay pre-compensation includes: the satellite base station delays the uplink signal reception and processing time slot by adjusting the scheduler uplink reception logic to achieve time slot-level delay pre-compensation; by adjusting the downlink frame timing and advancing the downlink signal sending timing, the sampling point-level delay pre-compensation is achieved; as well as timer enhancement and HARQ enhancement; the Doppler pre-compensation includes narrowband Doppler frequency offset pre-compensation and broadband Doppler extension pre-compensation.

2. A mobile phone direct connection satellite system transmission method according to claim 1, characterized in that: The calculation method of the common delay pre-compensation value for the satellite beam cell is: Where R is the average radius of the Earth, h s is the satellite orbit altitude, v c is the speed of light, θ min =max{θ-θ BW / 2,0}, θ is the satellite beam elevation angle, θ BW is the satellite beam width.

3. A mobile phone direct connection satellite system transmission method according to claim 1, characterized in that: The calculation method of the common Doppler pre-compensation value for the satellite beam cell is: where v s is the satellite velocity, v c is the speed of light, f c is the operating frequency, α is the satellite beam azimuth, θ is the satellite beam elevation, and θ BW is the satellite beam width.

4. A mobile phone direct connection satellite system transmission method according to claim 1, characterized in that: Uplink delay processing includes: the satellite base station based on the common delay pre-compensation value T of the beam cell comp and system time slot length T slot , calculate the delayed processing amount of the uplink signal receiving window The uplink reception scheduling logic is adjusted accordingly, which is equivalent to making the uplink frame timing lag behind the downlink frame timing, and completing the satellite beam cell time slot level satellite-to-ground delay pre-compensation; Downlink timing advance includes: the common delay pre-compensation value T of the satellite base station based on the beam cell comp , calculate the downlink timing advance The downlink signal transmission timing is adjusted accordingly, so that the downlink frame timing on the satellite base station side is ahead of the uplink frame timing, and the sampling point level delay pre-compensation for the beam cell is completed; Timer enhancement includes: The satellite base station adjusts the upper layer timer value based on the common delay pre-compensation value: T timer ≥T comp , Where T timer Indicates the timer value. A set of timer values ​​specified in the Rel-15 protocol; HARQ enhancements include: the onboard base station scheduler always sets the HARQ process to an available state and continues to send new data regardless of the feedback status, which is equivalent to disabling the HARQ mechanism.

5. A mobile phone direct connection satellite system transmission method according to claim 1, characterized in that: Narrowband Doppler frequency shift pre-compensation is that the satellite-borne base station performs carrier frequency offset correction on the baseband transceiver signal in the time domain based on the Doppler pre-compensation value; Wideband Doppler spread precompensation is a method in which the satellite-borne base station performs phase correction on the baseband transmit and receive signals in the frequency domain based on the Doppler precompensation value.

6. A mobile phone direct connection satellite system transmission method according to claim 1, characterized in that: Also includes: Determine the maximum differential delay and maximum differential frequency deviation of the satellite beam cell; Based on the constraints of the terrestrial 5G network protocol on the maximum differential delay of the cell and the constraints of the terrestrial 5G terminal capabilities on the maximum differential frequency deviation of the cell, the maximum beam width allowed for the specific beam pointing is determined.

7. A mobile phone direct connection satellite system transmission method according to claim 6, characterized in that: The maximum differential delay of the cell under specific satellite beam parameters is: Where R is the average radius of the Earth, h s is the satellite orbit altitude, v c is the speed of light, θ is the satellite beam pitch angle, θ BW is the satellite beam width; the terrestrial network protocol's constraints on the maximum differential delay of the cell include the constraints of the random access preamble format, the zero correlation coefficient, and the timing advance mechanism on the maximum differential delay of the cell.

8. A mobile phone direct connection satellite system transmission method according to claim 6, characterized in that: The maximum differential frequency deviation of the cell under specific satellite beam parameters is: where v s is the satellite velocity, v c is the speed of light, f c is the operating frequency, α is the satellite beam azimuth, θ is the satellite beam elevation, and θ BW is the satellite beam width; the constraints of the ground 5G terminal capability on the maximum differential frequency deviation of the cell include the constraints of the ground terminal's anti-frequency deviation capability on the maximum differential frequency deviation of the cell.

9. A mobile phone direct satellite connection system, characterized in that: include: A compensation value calculation module, used to determine a common delay pre-compensation value and a common Doppler pre-compensation value for a satellite beam cell; The pre-compensation module is used to introduce delay pre-compensation and Doppler pre-compensation on the satellite base station side to solve the problem of limited terminal capacity in the mobile phone direct connection system; the delay pre-compensation includes: the satellite base station delays the uplink signal reception and processing time slot by adjusting the scheduler uplink reception logic to achieve time slot-level delay pre-compensation; by adjusting the downlink frame timing and advancing the downlink signal sending timing, the sampling point-level delay pre-compensation is achieved; as well as timer enhancement and HARQ enhancement; the Doppler pre-compensation includes narrowband Doppler frequency offset pre-compensation and broadband Doppler extension pre-compensation.

10. A mobile phone direct connection satellite system transmission system according to claim 9, characterized in that: It also includes a beam optimization design module, which is used to determine the maximum differential delay and maximum differential frequency deviation of the satellite beam cell; and based on the constraints of the terrestrial 5G network protocol on the maximum differential delay of the cell and the constraints of the terrestrial 5G terminal capabilities on the maximum differential frequency deviation of the cell, determine the maximum beam width allowed for the specific beam pointing design.

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