Downlink signal sending method and downlink signal processing method

Abstract

The embodiment of the invention provides a downlink signal sending method and a downlink signal processing method, which are characterized in that a downlink signal is obtained on the satellite side based on a supplementary synchronization sequence, and then time-frequency synchronization is carried out on the terminal equipment side by using the downlink signal from the satellite. In the application, the terminal device can realize time-frequency offset tracking compensation without acquiring satellite ephemeris information and using GNSS (Global Navigation Satellite System) equipment, so that the influence of ephemeris errors and GNSS errors on time-frequency synchronization performance after the terminal device is shut down for a long time is eliminated, and the problem that the time-frequency synchronization performance of the terminal device is influenced in the related technology is solved. The problem of low precision of time-frequency offset tracking compensation in the satellite-ground communication process is solved, and the time-frequency synchronization success rate of satellite-ground communication under the conditions of inaccurate ephemeris and high speed is improved.

Description

TECHNICAL FIELD

[0001] Embodiments of the present application relate to the field of signal processing of satellite physical layer, in particular, to a downlink signal sending method and a downlink signal processing method. BACKGROUND

[0002] Currently, in the communication scenario of low-orbit satellite network, the large range of frequency offset and high time delay caused by high dynamic between satellite and ground makes the performance of conventional time-frequency synchronization algorithm based on synchronization sequence greatly decline. Therefore, the existing technology mainly adopts a time-frequency pre-compensation scheme based on terminal GNSS (Global Navigation Satellite System) and satellite ephemeris, which calculates the frequency offset value based on terminal GNSS and satellite ephemeris, and completes the frequency offset compensation at the terminal device side. The residual frequency offset after compensation is mainly determined by satellite ephemeris error, crystal oscillator error of satellite and terminal.

[0003] At present, the influence of residual frequency offset on signal demodulation is suppressed by further completing frequency offset compensation and tracking based on primary / secondary synchronization signals, reference signals and the like. Since the time-frequency synchronization scheme based on primary synchronization signal PSS can tolerate residual frequency offset of 1 / 2 subcarrier bandwidth, the frequency offset estimation range is small, and the terminal device needs to update satellite ephemeris once every 10 days to reduce the influence of ephemeris error on frequency offset compensation. However, if the terminal device is in a high-speed moving state for a long time, the expired satellite ephemeris and high-speed movement of the terminal device will cause the residual frequency offset to exceed the frequency offset range that can be tolerated by the existing scheme, which will reduce the success rate of time-frequency synchronization. It can be seen that due to the influence of large range of frequency offset and high time delay caused by high-speed movement of the terminal device, the accuracy of time-frequency offset tracking compensation in the process of satellite-ground communication is reduced.

[0004] Therefore, in the related art, there is a problem of low accuracy of time-frequency offset tracking compensation in the process of satellite-ground communication. SUMMARY

[0005] Embodiments of the present application provide a downlink signal sending method and a downlink signal processing method to at least solve the problem of low accuracy of time-frequency offset tracking compensation in the process of satellite-ground communication in the related art.

[0006] According to an embodiment of the present application, a downlink signal processing method is provided, applied to a terminal device, comprising: receiving a downlink signal from a satellite, wherein the downlink signal carries a supplementary synchronization sequence.

[0007] According to another embodiment of the present application, a downlink signal sending method is provided, applied to a satellite, comprising: sending a downlink signal to a terminal device, wherein the downlink signal carries a supplementary synchronization sequence.

[0008] According to a further embodiment of the present application, a processing device of a downlink signal is provided, applied to a terminal device, comprising: a receiving module configured to receive a downlink signal from a satellite, wherein the downlink signal carries a supplementary synchronization sequence.

[0009] According to a further embodiment of the present application, a transmitting device of a downlink signal is provided, applied to a satellite, comprising: a transmitting module configured to transmit a downlink signal to a terminal device, wherein the downlink signal carries a supplementary synchronization sequence.

[0010] According to a further embodiment of the present application, a computer readable storage medium is further provided, wherein the computer readable storage medium stores a computer program, and the computer program is configured to implement the steps of the method in any of the above embodiments when executed by a processor.

[0011] According to a further embodiment of the present application, an electronic device is further provided, comprising a memory and a processor, wherein the memory stores a computer program, and the processor is configured to run the computer program to perform the steps in any of the above method embodiments.

[0012] According to a further embodiment of the present application, a computer program product is further provided, comprising a computer program, and the computer program is configured to implement the steps of the method in any of the above embodiments when executed by a processor.

[0013] According to the present application, the supplementary synchronization signal is configured on the satellite side, and the time-frequency synchronization process is realized by the terminal device side using the signal. Specifically, the supplementary synchronization sequence is designed based on the excellent correlation characteristics of the conjugate ZC sequence on the satellite side, the downlink signal is obtained based on the supplementary synchronization sequence, and then the time-frequency synchronization is realized by the terminal device side using the downlink signal from the satellite. In the present application, the terminal device can realize the time-frequency offset tracking compensation without obtaining the satellite ephemeris information and using the GNSS device, eliminating the influence of the ephemeris error and the GNSS error on the time-frequency synchronization performance after the terminal device is powered off for a long time, solving the problem of low precision of the time-frequency offset tracking compensation in the satellite-ground communication process, providing a technical solution capable of meeting the high-precision time-frequency offset tracking compensation requirement, and improving the time-frequency synchronization success rate of the satellite-ground communication in the ephemeris inaccuracy and high-speed state. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a communication system structure diagram of the embodiment of the present application;

[0015] Figure 2 is a principle diagram of the supplementary synchronization signal design scheme according to the embodiment of the present application;

[0016] Figure 3 is a principle diagram of the supplementary synchronization signal transmitting end according to the embodiment of the present application;

[0017] Figure 4 is a schematic diagram of a supplementary synchronization signal receiving end according to an embodiment of the application;

[0018] Figure 5 is a flow chart of a downlink signal transmitting method according to an embodiment of the application;

[0019] Figure 6 is a schematic diagram of a CSS sequence time-frequency resource grid placement relationship according to an embodiment of the application;

[0020] Figure 7 is a format schematic diagram of a supplementary synchronization signal based on a symmetric ZC sequence according to an embodiment of the application;

[0021] Figure 8 is a flow chart of a downlink signal processing method according to an embodiment of the application;

[0022] Figure 9 is a schematic diagram of a time synchronization algorithm based on symmetric time domain signal autocorrelation according to an embodiment of the application;

[0023] Figure 10 is a processing flow schematic diagram of an autocorrelation module according to an embodiment of the application;

[0024] Figure 11 is a schematic diagram of a terminal device implementing time-frequency offset estimation according to an embodiment of the application;

[0025] Figure 12 is a structural block diagram of a downlink signal transmitting device according to an embodiment of the application;

[0026] Figure 13 is a structural block diagram of a downlink signal processing device according to an embodiment of the application. DETAILED DESCRIPTION

[0027] Hereinafter, the embodiments of the application will be described in detail with reference to the accompanying drawings and in conjunction with embodiments.

[0028] It should be noted that the terms "first", "second", etc. in the specification and claims of the application and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily describe a specific order or sequence.

[0029] It should be noted that the user information (including but not limited to user equipment information, user personal information, etc.) and data (including but not limited to data for analysis, stored data, displayed data, etc.) involved in the present application are all information and data authorized by the user or authorized by all parties, and the collection, use and processing of related data need to comply with relevant laws, regulations and standards, and provide corresponding operation portal for user to choose authorization or refusal.

[0030] The technical solutions of the embodiments of the present application can be applied to various communication systems, such as: Long Term Evolution (LTE) system, LTE Frequency Division Duplex (FDD) system, LTE Time Division Duplex (TDD), Universal Mobile Telecommunication System (UMTS), Worldwide Inter-operability for Microwave Access (WiMAX) communication system, 5th Generation (5G) mobile communication system, 6th Generation (6G) mobile communication system, future 7th Generation (7G) mobile communication system, NTN (Non-Terrestrial Network) communication system, Device-to-Device (D2D) system, vehicle-to-X (V2X) system, Internet of Vessels, etc., wherein V2X can include vehicle to network (V2N), vehicle to vehicle (V2V), vehicle to infrastructure (V2I), vehicle to pedestrian (V2P), etc., LTE-V (Long Term Evolution-Vehicle), Internet of Vehicles, machine type communication (MTC), Internet of Things (IoT), Long Term Evolution-Machine (LTE-M), Machine to Machine (M2M), etc.

[0031] To facilitate understanding of the embodiments of the present application, first, in combination with Figure 1This application describes in detail the communication system applicable to the embodiments of this application. For example... Figure 1 As shown, the communication system 100 may include at least one access network device, such as Figure 1 The access network device 110 shown may also include core network devices, such as... Figure 1 The core network equipment 120; the communication system 100 may also include at least one terminal device, such as Figure 1 The terminal device 130 shown can be mobile or fixed. The access network device 110 is a device that can communicate with the terminal device 130 via a wireless link, such as a base station or an access controller (AC). Each access network device can provide communication coverage for a specific geographical area and can communicate with the terminal device 130 located within that coverage area (cell).

[0032] In some embodiments, the core network device 120 is a functional network element in the core network, such as a policy control function network element, which corresponds to the policy control function (PCF) network element in the 5G core network, or a mobility management network element, which corresponds to the access and mobility management function (AMF) network element in the 5G core network, etc. There are no specific limitations here. It can be understood that the network element of the core network can also be a network element with corresponding functions in the 4G (fourth generation mobile communication technology) core network, or a network element with corresponding functions in the 6G (sixth generation mobile communication technology) core network. There are no specific limitations here either.

[0033] The access network device 110 in this application embodiment is a network-side entity used for transmitting or receiving signals. This network device can be referred to as a network-side device. For example, the access network device 110 can be an evolved NodeB (eNB), a transmission reception point (TRP), a next-generation NodeB (gNB) in an NR system, a base station in other future mobile communication systems, or an access node in a wireless fidelity (WiFi) system. The embodiments of this application do not limit the specific technology or device form used in the network device.

[0034] The access network device 110 provided in the embodiments of the present application can also be composed of a central unit (CU) and a distributed unit (DU), wherein the CU can also be referred to as a control unit, and the CU-DU structure can split the protocol layers of the network device, for example, a base station, and place the functions of part of the protocol layers in the CU for centralized control, and place the functions of the remaining part or all of the protocol layers in the DU for distributed control.

[0035] In some embodiments, the access network device 110 is a network device, which can include a non-ground network device, for example, a satellite, which can be regarded as a mobile network device, and is not specifically limited here.

[0036] The terminal device 130 in the embodiments of the present application is an entity for receiving or transmitting signals on the user side, for example, a mobile phone. The terminal device can also be referred to as a terminal, a user equipment (UE), a mobile station (MS), a mobile terminal (MT), a user side device, etc. The terminal can be a car, a smart car, a mobile phone, a wearable device, a tablet computer (Pad), a computer with wireless transceiver function, a virtual reality (VR) terminal, an augmented reality (AR) terminal, a wireless terminal in industrial control, a wireless terminal in self-driving, a wireless terminal in remote medical surgery, a wireless terminal in smart grid, a wireless terminal in transportation safety, a wireless terminal in smart city, a wireless terminal in smart home, etc.

[0037] In some embodiments, the terminal device 130 supports a non-terrestrial network (NTN) connection.

[0038] In some embodiments, the terminal device 130 camps in the access network device 110, for example, camps in the network where the access network device 110 is located, and the terminal device 130 is in an idle state.

[0039] In some other embodiments, the terminal device 130 can access the access network device 110 to perform service transmission.

[0040] It can be understood that, Figure 1 The structure of only one network system is shown in the embodiments, and the embodiments of the present application do not limit the specific technology and specific device form adopted by the terminal device / access network device / core network device.

[0041] It can be understood that the communication system described in the embodiments of the present application is for more clearly illustrating the technical solutions of the embodiments of the present application, and does not constitute a limitation on the technical solutions provided by the embodiments of the present application. It can be known by those skilled in the art that, with the evolution of system architecture and the appearance of new service scenarios, the technical solutions provided by the embodiments of the present application are also applicable to similar technical problems.

[0042] In the present application, a complementary synchronization signal compatible with the existing system and a corresponding physical frame structure are designed. As shown in Figure 2 For the newly proposed complementary synchronization sequence, a receiver time-frequency synchronization method is designed to achieve large frequency offset estimation and compensation without using ephemeris and GNSS information. It can be divided into two parts: the sending end and the receiving end. In short, at the sending end, it involves the generation of a new signal frame structure design of the complementary synchronization sequence, and at the receiving end, it involves the processing of the complementary synchronization sequence, time-frequency synchronization processing such as sliding autocorrelation processing, etc.

[0043] Among them, the steps of "resource mapping", "IFFT (Inverse Fast Fourier Transform)", "adding cyclic prefix (CP)" in the sending end are consistent with the existing system processing flow, which reflects the compatibility of the scheme design and the respect for the existing technical framework. A brief description of these steps is as follows.

[0044] Optionally, the downlink signal can directly carry the complementary synchronization sequence, or it can also be carried by the complementary synchronization signal (CSS, Complemental Synchronization Signal) included in the downlink signal. Among them, the full name of the complementary synchronization sequence in English is Complementary Secondary Synchronization Sequence.

[0045] For resource mapping, after the supplementary synchronization signal is generated, the signal needs to be mapped onto physical resource blocks for transmission over the air interface. Specifically, the center frequency point of the supplementary synchronization sequence carried by the CSS is placed at the center frequency point position of the synchronization signal block (SSB), ensuring its relative position relationship with the primary synchronization signal (PSS) and the secondary synchronization signal (SSS) in the frequency domain, which helps the receiving end to perform time-frequency synchronization processing. In the frequency domain, the supplementary synchronization sequence is placed at intervals, and the same subsequence can be obtained before and after IFFT, so that the receiving side (corresponding to the terminal device) uses this feature to perform time-frequency synchronization.

[0046] For IFFT, the supplementary synchronization sequence after resource mapping needs to be transformed by IFFT for conversion to the time domain for transmission. IFFT is a key technology in the generation process of OFDM (Orthogonal Frequency Division Multiplexing) signals. Through IFFT, the signal in the frequency domain is converted to the time domain to form an OFDM symbol, which is a standard operation in the OFDM modulation process and is necessary for the modulation of SSB signals and other data signals in existing systems.

[0047] For adding CP: After the time-domain signal is generated, in order to reduce the inter-symbol interference caused by multipath effects and simplify the equalization algorithm at the receiving end, a cyclic prefix is added at the front end of each OFDM symbol, which is usually a repetition of the end part of the symbol. The length of the CP is generally set to be greater than the maximum delay spread of the channel to ensure that the complete information of the OFDM symbol can be avoided from being disturbed even in the presence of multipath. In this application, the supplementary synchronization sequence is placed in the fourth OFDM symbol position of the first subframe in the half frame with the SSB block, which means that it will follow the same CP addition rule as the SSB signal, i.e., the CP length is determined by the maximum delay spread of the system, which is usually a fixed value in existing systems. Through the above steps, the supplementary synchronization sequence of the present application fully considers the compatibility with existing systems in the generation, modulation and preparation for transmission process, not only ensuring the reliability of the signal, but also avoiding the introduction of additional complexity, so that the terminal in the high-speed mobile scenario can more effectively use the supplementary synchronization sequence carried by the CSS for time-frequency synchronization, thereby improving the quality and efficiency of communication.

[0048] Among them, the "data payload generation" of the sending end is, for example, Figure 3Physical Downlink Control Channel / Physical Downlink Shared Channel generation, reference signal generation, Physical Broadcast Channel generation.

[0049] Further, on the terminal device side, in combination with the flow shown in Figure 3 The process of the supplementary synchronization sequence generation specifically includes: generating a supplementary synchronization sequence according to a local ZC sequence and a conjugate ZC sequence; mapping the frequency domain position of the supplementary synchronization sequence, i.e., placing the center frequency point of the generated supplementary synchronization sequence at the center frequency point position of an SSB (Synchronization Signal Block), and placing the sequence at intervals in the frequency domain; then mapping the time domain position of the supplementary synchronization sequence, i.e., placing the starting position of the supplementary synchronization sequence at the fourth OFDM (Orthogonal Frequency Division Multiplexing) symbol position of the first subframe in the half frame with the SSB block, and occupying 1 OFDM symbol in the time domain.

[0050] On the satellite side, in combination with the flow shown in Figure 4 The processing scheme of the supplementary synchronization sequence specifically includes: receiving a signal transmitted by a satellite; performing a sliding autocorrelation operation on the received signal to obtain a peak position and a phase value corresponding to the peak position, estimate a fractional frequency offset, then performing a correlation operation on a local ZC sequence and the supplementary synchronization sequence extracted from the signal, and performing a DFT (Discrete Fourier Transform) to obtain a position value corresponding to a first main peak; performing a correlation operation on a conjugate of the local ZC sequence and the supplementary synchronization sequence, and performing a DFT to obtain a position value corresponding to a second main peak; and obtaining a value of an integer frequency offset and a fine time delay according to the position values corresponding to the first main peak and the second main peak. Through the above, based on the excellent correlation characteristics of the conjugate ZC sequence, the application designs a time-frequency synchronization algorithm with large-range timing synchronization and frequency offset compensation characteristics, which can meet the high-precision frequency offset estimation and compensation requirements while being compatible with high-speed and low-speed scenarios.

[0051] In the field of communication (especially 5G / NR system), the full name of ZC sequence is Zadoff-Chu sequence, and the name comes from its inventors Solomon A. Zadoff and D. C. Chu. This sequence has excellent mathematical properties and is widely used in scenarios such as synchronization and random access.

[0052] In one embodiment, a method for transmitting a downlink signal of a satellite is provided, as shown in the flowchart, comprising the following steps: Figure 5 As shown in the flowchart, the process comprises the following steps:

[0053] In step S502, a downlink signal is transmitted to a terminal device, wherein the downlink signal carries a supplementary synchronization sequence.

[0054] According to the present application, the supplementary synchronization signal is configured on the satellite side, and the time-frequency synchronization process is realized by the terminal device side using the signal. Specifically, the supplementary synchronization sequence is designed based on the excellent correlation characteristics of the conjugate ZC sequence on the satellite side, the downlink signal is obtained based on the supplementary synchronization sequence, and then the downlink signal from the satellite is received on the terminal device side.

[0055] Further, the terminal device calculates a coarse time delay estimation value and a fractional frequency offset value of the downlink signal, and obtains a compensation signal of the downlink signal according to the coarse time delay estimation value and the fractional frequency offset value, and calculates a fine time delay estimation value and an integer frequency offset value of the compensation signal.

[0056] In the present application, the terminal device can realize time-frequency offset tracking compensation without obtaining satellite ephemeris information and using GNSS equipment, eliminating the influence of ephemeris error and GNSS error on time-frequency synchronization performance after the terminal device is powered off for a long time, solving the problem of low precision of time-frequency offset tracking compensation in the process of satellite-ground communication, providing a technical solution capable of meeting the demand of high-precision time-frequency offset tracking compensation, and improving the time-frequency synchronization success rate of satellite-ground communication in the case of inaccurate ephemeris and high speed.

[0057] In one exemplary embodiment, the supplementary synchronization sequence can be determined according to a symmetric ZC sequence.

[0058] In the present embodiment, the symmetric ZC sequence can be specifically composed of the superposition of the ZC sequence and the conjugate ZC sequence. Compared with the single ZC sequence, the symmetric ZC sequence has additional correlation characteristics.

[0059] In one exemplary embodiment, the scheme for determining the supplementary synchronization sequence according to the symmetric ZC sequence comprises: determining a local ZC sequence and a local conjugate ZC sequence having a conjugate relationship with the local ZC sequence according to the symmetric ZC sequence; performing discrete Fourier transform (DFT) on the sequence obtained by adding the local ZC sequence and the local conjugate ZC sequence to obtain a first sequence after transformation; configuring the frequency domain position and the time domain position of the first sequence respectively to obtain a second sequence after configuration, and performing inverse fast Fourier transform (IFFT) on the second sequence to obtain the supplementary synchronization sequence in the time domain.

[0060] In one exemplary embodiment, the supplementary synchronization sequence is divided into two sub-sequences of the same length in the time domain.

[0061] In an example embodiment, the implementation process of configuring the frequency domain position and time domain position of the first sequence respectively includes: placing the center frequency point of the first sequence at the center frequency point of the first SSB (Synchronization Signal Block) in the downlink signal; and setting the fourth OFDM (Orthogonal Frequency Division Multiplexing) symbol position of the first subframe in the half frame where the first SSB is located as the starting position of the first sequence.

[0062] In a wireless communication system, SSB is a signal structure containing key synchronization information, which is used to help terminal devices to synchronize when performing initial access to the network. SSB usually consists of a PSS (Primary Synchronization Signal), an SSS (Secondary Synchronization Signal), and a PBCH (Physical Broadcast Channel). PSS and SSS are used for time and frequency synchronization, while PBCH transmits key information of the system, such as system frame number and cell identification, so that the terminal can identify and access the correct network cell. This design of SSB ensures that the terminal can quickly obtain synchronization information and connect even without understanding the detailed configuration of the network.

[0063] In an example embodiment, the supplementary synchronization sequences are placed at intervals in the frequency domain, and the signal bandwidth of the supplementary synchronization sequences is consistent with the bandwidth occupied by the SSB.

[0064] In an example embodiment, the supplementary synchronization sequences occupy 1 OFDM symbol in the time domain.

[0065] The time-frequency synchronization algorithm of the present application needs to mobilize both ends of the satellite side and the terminal device side to jointly implement.

[0066] In an embodiment, the supplementary synchronization sequence is configured on the satellite side, and the terminal device side uses the signal to implement the time-frequency synchronization process. Among them, the satellite side needs to configure the supplementary synchronization sequence in front of the first SSB signal, which can be specifically described in combination with the following steps:

[0067] Step one: generate a supplementary synchronization sequence.

[0068] The supplementary synchronization sequence can be obtained according to the local ZC sequence and the conjugate ZC sequence (i.e. the above local conjugate ZC sequence). Specifically, the local ZC sequence and the conjugate ZC sequence are added, and then the DFT operation is performed on the added sequence to obtain the supplementary synchronization sequence.

[0069] Further, the supplementary synchronization sequence is represented as:

[0070] .

[0071] .

[0072] wherein, is a supplementary synchronization sequence, is a first ZC sequence (corresponding to the above local ZC sequence), is a conjugate of the first ZC sequence (corresponding to the above local conjugate sequence), u is a root index of the ZC sequence, N ZC is a length of the ZC sequence, DFT(·) represents a discrete Fourier transform, and the number of points n of the DFT is the same as the length of the ZC sequence.

[0073] For example, let u = 1, N ZC = 67, n = 0, 1, 2,..., 66, and the corresponding conjugate ZC sequence is generated according to the above formula.

[0074] Step 2: Supplementary synchronization sequence frequency domain position mapping.

[0075] The generated supplementary synchronization sequence center frequency point is placed at the SSB center frequency point position as shown in Figure 6 , and the sequences are placed at intervals in the frequency domain to obtain the following sequences:

[0076] .

[0077] wherein, m is a frequency domain index after mapping of the CSS sequence, n is a supplementary synchronization sequence index, N ZC represents a length of the supplementary synchronization sequence. Similar to the number of REs occupied by the PSS / SSS reference signal, the number of REs occupied by the CSS in the frequency domain can be taken as N ZC = 67, so as to be compatible with the existing system.

[0078] represents a number of REs (Resource Elements) occupied by an SSB block, and the SSB block occupies 20 RBs (Resource Blocks) in the existing system, and the value is 240. The frequency domain index number after interval placement should be taken as 54-186, and a total of 133 REs.

[0079] It should be noted that the CSS center frequency point is placed in accordance with the SSB block center frequency point, so as to be compatible with the existing system.

[0080] wherein, the generated supplementary synchronization sequence bandwidth is the same as the bandwidth occupied by the SSB block, and 20 RBs are occupied.

[0081] Step three: mapping the time domain position of the supplementary synchronization sequence.

[0082] Reference Figure 7 The starting position of the supplementary synchronization sequence is placed at the fourth OFDM symbol position of the first slot of the subframe where the SSB is located, that is, the fourth OFDM symbol position of the first subframe in the half frame with the SSB block.

[0083] In this way, the supplementary synchronization sequence occupies 1 OFDM symbol in the time domain. Then, the supplementary synchronization sequences are placed at intervals in the frequency domain, and the processed CSS sequence is mapped in the 0 position offset 54, 56, 58…186, etc. for a total of 67 REs relative to the SSB subcarrier.

[0084] The IFFT transformation process is performed on the CSS (m) placed at intervals in the frequency domain, and the processed supplementary synchronization sequence presents two identical sub-sequences in the time domain, and each sub-sequence has a length of half the IFFT point number. That is, the supplementary synchronization sequence in the time domain generated after OFDM modulation can be represented as:

[0085] .

[0086] Where N represents the IFFT point number.

[0087] Step four: finally, the downlink signal can be obtained based on the supplementary synchronization sequence, and the downlink signal is sent to the terminal device. It can be understood that for the downlink signal, it can contain Figure 2 The baseband signal shown in the above. The baseband signal can be obtained by adding a cyclic prefix to the supplementary synchronization sequence in the time domain.

[0088] In one embodiment, a processing method of a downlink signal running on the above-mentioned mobile terminal (corresponding to the terminal device) is provided. As Figure 8 shown in the figure, the flow includes the following steps:

[0089] Step S802, receiving a downlink signal from a satellite, wherein the downlink signal carries a supplementary synchronization sequence.

[0090] Optionally, the execution subject of the above steps can be various terminal devices or components with corresponding signal processing capabilities.

[0091] These terminal devices are not limited to traditional communication devices such as mobile phones, tablets, laptops, but also include Internet of Things devices, vehicle-mounted communication systems, unmanned aerial vehicle communication modules, etc. that can receive and process satellite signals.

[0092] For example, the terminal device at least integrates a signal receiving device and a data processing device. The signal receiving device can include a high-sensitivity satellite signal receiving antenna, a radio frequency front-end module, etc., and is used to capture signals transmitted by satellites. The data processing device includes various types of processors, such as an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a digital signal processor (DSP), and a general-purpose microprocessor, etc., and is used to perform signal demodulation, synchronization, information extraction, etc. In addition, considering the needs of different application scenarios, the terminal device can also be equipped with a positioning module, a storage unit, a power management system, and an interface component for user interaction, etc. auxiliary components to enhance its functionality and user experience.

[0093] It is worth noting that with the development of technology, the design of terminal devices tends to be multi-functional and miniaturized. For example, mobile terminal devices such as smart watches, wearable health monitoring devices, and smart home control centers can also be terminal devices that directly communicate with satellites. For mobile terminal devices, in addition to integrating necessary signal processing hardware, power consumption management strategies need to be optimized to ensure long-term communication capabilities even when far away from power sources.

[0094] In one embodiment, further, the terminal device calculates a coarse time delay estimation value and a fractional frequency offset value of the downlink signal from the satellite, and obtains a compensation signal of the downlink signal according to the coarse time delay estimation value and the fractional frequency offset value; calculates a fine time delay estimation value and an integer frequency offset value of the compensation signal.

[0095] By this application, the supplementary synchronization signal is configured on the satellite side, and the terminal device side uses this signal to realize the time-frequency synchronization process. Specifically, the satellite side designs a supplementary synchronization sequence based on the excellent correlation characteristics of the conjugate ZC sequence, obtains the downlink signal based on the supplementary synchronization sequence, and the terminal device side calculates a coarse time delay estimation value and a fractional frequency offset value of the downlink signal from the satellite, and obtains a compensation signal of the downlink signal according to the coarse time delay estimation value and the fractional frequency offset value, and calculates a fine time delay estimation value and an integer frequency offset value of the compensation signal. In this application, the terminal device does not need to obtain satellite ephemeris information and does not need to use GNSS equipment to realize time-frequency offset tracking compensation, eliminating the influence of ephemeris error and GNSS error on time-frequency synchronization performance after the terminal device is turned off for a long time, solving the problem of low precision of time-frequency offset tracking compensation in the process of satellite-ground communication, providing a technical solution that can meet the demand for high-precision time-frequency offset tracking compensation, and improving the time-frequency synchronization success rate of satellite-ground communication under inaccurate ephemeris and high-speed state.

[0096] In an example embodiment, the process of calculating the coarse time delay estimation value of the downlink signal comprises: performing a sliding search on the downlink signal in time domain, and cutting a sliding window for each sampling point searched; performing autocorrelation calculation on a sub-sequence in a window sequence corresponding to the cut sliding window, to obtain an autocorrelation value; determining an autocorrelation peak value according to a maximum value in a plurality of autocorrelation values, and obtaining a coarse timing estimation value according to a first index position corresponding to the autocorrelation peak value.

[0097] In an example embodiment, the implementation step of performing autocorrelation calculation on the sub-sequence in the window sequence comprises: splitting the window sequence into a first sub-sequence and a second sub-sequence in time domain, the first sub-sequence preceding the second sub-sequence in time domain, and the sequence length of the first sub-sequence being the same as the sequence length of the second sub-sequence; performing autocorrelation calculation on the first sub-sequence and the second sub-sequence.

[0098] In an example embodiment, the process of calculating the fractional frequency offset value of the downlink signal can comprise: determining a phase corresponding to the autocorrelation peak value, and obtaining the fractional frequency offset value according to the phase.

[0099] In an example embodiment, the process of obtaining the compensated signal of the downlink signal according to the coarse time delay estimation value and the fractional frequency offset value comprises: performing time domain compensation on the downlink signal according to the coarse time delay estimation value in time domain, and performing frequency domain compensation on the downlink signal according to the fractional frequency offset value in frequency domain, to obtain the compensated signal.

[0100] In an example embodiment, the scheme of calculating the fine time delay estimation value and the integer frequency offset value of the compensated signal comprises: determining a local ZC sequence and a local conjugate ZC sequence, wherein the local conjugate ZC sequence has a conjugate relationship with the local ZC sequence; performing cross-correlation calculation on the compensated signal using the local ZC sequence and the local conjugate ZC sequence respectively, to obtain the fine time delay estimation value and the integer frequency offset value according to the cross-correlation values obtained by performing the cross-correlation calculation.

[0101] In one example embodiment, the scheme of obtaining the fine time delay estimation value and the integer multiple frequency offset value from the cross-correlation value obtained by the cross-correlation calculation comprises: obtaining a first cross-correlation value and a second cross-correlation value from the cross-correlation value obtained by the cross-correlation calculation, the first cross-correlation value being obtained by cross-correlation calculation of the local ZC sequence and the compensation signal, and the second cross-correlation value being obtained by cross-correlation calculation of the local conjugate ZC sequence and the compensation signal; obtaining a second index position according to the first cross-correlation value, and obtaining a third index position according to the second cross-correlation value; determining the fine time delay estimation value and the integer multiple frequency offset value of the compensation signal according to the second index position and the third index position.

[0102] In one example embodiment, the process of obtaining the second index position according to the first cross-correlation value and the third index position according to the second cross-correlation value can comprise: performing discrete Fourier transform processing on the first cross-correlation value, determining a first main peak value, and searching for the second index position corresponding to the first main peak value in the frequency domain; and performing discrete Fourier transform processing on the second cross-correlation value, determining a second main peak value, and searching for the third index position corresponding to the second main peak value in the frequency domain.

[0103] In one example embodiment, the specific steps of determining the fine time delay estimation value of the compensation signal according to the second index position and the third index position comprise: obtaining a position difference value of the second index position and the third index position; and calculating the fine time delay estimation value of the compensation signal based on the position difference value, a root index of the local ZC sequence, a time delay value in a preset time delay range, and a point number of fast Fourier transform (FFT).

[0104] In one example embodiment, the scheme of determining the integer multiple frequency offset value according to the second index position and the third index position comprises: obtaining a position and value of the second index position and the third index position; and calculating the integer multiple frequency offset value of the compensation signal based on the position and value, a preset multiple corresponding to the position and value, and a point number of fast Fourier transform (FFT).

[0105] In one embodiment, the terminal side processes the supplementary synchronization sequence and implements the time-frequency synchronization process using the supplementary synchronization sequence, specifically comprising:

[0106] Step one: receiving the signal y sent by the satellite k (n) (corresponding to the above downlink signal).

[0107] Step two: using the property that the CSS is two identical sequences in the time domain, the autocorrelation method is used to calculate the coarse time delay and the decimal multiple frequency offset. The received signal can be autocorrelated to obtain the peak position and the corresponding value, and the decimal multiple frequency offset is estimated and compensated.

[0108] For details, please refer to Figure 9 The coarse timing estimation principle shown and Figure 10 The calculation process for coarse delay within the sliding autocorrelation module is as follows: Starting from the first sample point of the received data, the sliding window moves one sample point at a time, taking the signals within two windows for correlation calculation to obtain the correlation value. Assuming the length of two identical sequences within a symbol is L, the first sliding window is taken, and then a second sliding window is taken after a gap of L. Both sliding windows have a length of L, where L is the length of the CSS sequence, i.e., L = N / 2, where N is the number of IFFT points. In this way, coarse synchronization can be achieved using the autocorrelation of signals with two identical sequences. The formula for the calculated autocorrelation value is expressed as follows.

[0109] .

[0110] in, This represents the sequence preceding a symbol (corresponding to the first subsequence), i.e. Figure 10 The first half of the symbol, This represents the sequence following a symbol (corresponding to the second subsequence), i.e. Figure 10 The second half of the symbol.

[0111] By comparing the magnitude of each sliding autocorrelation value, the index position corresponding to the peak value of the autocorrelation value is extracted to obtain the position of the coarse synchronization point. This position is the coarse timing estimate. :

[0112] .

[0113] in, The area located on or to either side of the platform area.

[0114] Then, by finding the phase (i.e., the argument) at the peak value of the relevant value, we obtain:

[0115] .

[0116] in, If we take the phase at the peak of the correlation value, then the fractional octave frequency offset estimate is:

[0117] .

[0118] in, This indicates the duration of an OFDM symbol. The subcarrier spacing.

[0119] Based on the estimated coarse timing value and fractional frequency offset estimates The following compensation signal was obtained.

[0120] .

[0121] The received signal can also be expressed as:

[0122] .

[0123] wherein, denotes the received signal of user k, denotes the channel response gain of user k, denotes the coarse time delay estimation value, denotes the fractional frequency offset value, denotes the normalized integer frequency offset value, is the fine time delay of the kth user (corresponding to the fine time delay estimation value), and N denotes the FFT point number, denotes the zero-mean complex Gaussian white noise.

[0124] The compensated signal can be further expressed as:

[0125] .

[0126] wherein, denotes the residual phase offset after compensation, denotes the zero-mean complex Gaussian white noise, denotes the channel response gain of the kth user, denotes the fractional frequency offset estimation value after compensation of the signal the residual integer frequency offset, denotes the timing offset of the kth user after compensation of the coarse time delay the residual timing offset, N denotes the FFT point number, and u is the root index of the ZC sequence.

[0127] Next, the compensated received signal is respectively multiplied with the local ZC sequence and the conjugate of the local ZC sequence.

[0128] Step three: specifically, the local ZC sequence is correlated with the compensated received signal and DFT is performed to obtain the position value corresponding to the first main peak.

[0129] wherein, the local ZC sequence is cross-correlated with the compensated received signal, and the first cross-correlation value is:

[0130] .

[0131] .

[0132] .

[0133] wherein, represents the compensated residual phase deviation, represents the complex Gaussian white noise with zero mean, represents the channel response gain of the kth user, represents the compensated fractional frequency offset estimation value of the signal the residual integer frequency offset, represents the compensated coarse timing offset of the kth user the residual timing deviation, N represents the FFT point number, and u is the root index of the ZC sequence, represents the noise multiplied by the value after point multiplication, which only affects the level of noise during detection.

[0134] DFT operation is performed on the correlation result to obtain the following operation result:

[0135] .

[0136] The correlation peak value is searched according to the operation result, and the maximum peak value searched is determined as the first main peak position. The index position of the main peak can be represented as:

[0137] .

[0138] b is an integer, such that , and N represents the FFT point number.

[0139] Step four: the local ZC conjugate sequence is correlated with the compensated received signal, and DFT is performed to obtain the position value corresponding to the second main peak;

[0140] wherein, the compensated received signal is correlated with the local ZC conjugate sequence, and the second cross-correlation value is represented as:

[0141] .

[0142] .

[0143] .

[0144] represents the noise multiplied by the value after point multiplication, represents the compensated residual phase deviation.

[0145] DFT operation is performed on the correlation result to obtain the following operation result:

[0146] .

[0147] wherein, represents the channel response gain of the kth user, represents the signal compensation fractional frequency offset estimation value the integer multiple frequency offset of the post residual, represents the kth user compensation coarse time delay the timing offset of the post residual, N represents the FFT point number, u is the root index of the ZC sequence, and m is the time delay of the ZC sequence, only related to the background noise.

[0148] According to the operation result, a correlation peak value is searched, and a maximum value position, i.e. a second main peak position, is found. The index position of the main peak can be expressed as:

[0149] .

[0150] a is an integer, such that , and N is the FFT point number.

[0151] Through the above steps, by using the characteristics of the ZC sequence constituting the CSS, the received signal is cross-correlated with the local ZC sequence and the local conjugate ZC sequence to obtain two correlation peak values. Next, the relative position relationship of the two peak positions is calculated to realize fine time delay synchronization and integer multiple frequency offset estimation and compensation.

[0152] It should be noted that the index position of the first main peak and the index position of the second main peak can be calculated by steps three and four. However, the application does not limit the calculation order of the above steps three and four, i.e. step three can be performed first, or step four can be performed first, or steps three and four can be performed simultaneously.

[0153] wherein, in step four, it is further proved that the peak position is only related to .

[0154] By analyzing and , the following expression can be obtained by transforming the formula, wherein, :

[0155] .

[0156] Subsequently, the is subjected to N-point DFT transformation:

[0157] .

[0158] As can be seen from the formula, when :

[0159] ;

[0160] When ,

[0161] .

[0162] Therefore, can be replaced by the formula:

[0163] .

[0164] Next, analyze parameters, assuming , the following formula can be derived:

[0165] .

[0166] When , the value is only related to the background noise.

[0167] Therefore, the above formula can be expressed as:

[0168] .

[0169] Where, only related to the background noise.

[0170] When q is an integer, .

[0171] When q is a decimal, related to the value of q.

[0172] And when , the maximum peak value can be obtained.

[0173] Similarly, and the local ZC sequence do cross-correlation and DFT transform, when , the maximum peak value can be obtained.

[0174] Step five: according to the position value corresponding to the first main peak and the second main peak, the value of integer multiple frequency offset and fine time delay is obtained. Specifically, it includes:

[0175] Calculate the difference between the main peak position d1 obtained in step three and the main peak position d2 obtained in step four:

[0176] .

[0177] The sum of the main peak position d1 obtained in step three and the main peak position d2 obtained in step four is calculated:

[0178] .

[0179] After simplifying, we get: , where c = a - b and g = a + b.

[0180] According to the position values corresponding to the first main peak and the second main peak, the value of the fine time delay is obtained:

[0181] .

[0182] (d1 - d2) corresponds to the above position difference value. u is the root index of the local ZC sequence. The maximum time delay estimation range (corresponding to the preset time delay range) of this method is [-L CP , L CP ), L CP represents the cyclic prefix (CP, Cyclic Prefix) length. c is an integer, and N represents the FFT point number.

[0183] Therefore, the value of c should be such that The value range of c is:

[0184] .

[0185] To avoid value ambiguity, the value of u should satisfy At this time, the value of c is determined by the following method:

[0186] .

[0187] According to the position values corresponding to the first main peak and the second main peak, the value of the integer multiple frequency offset is obtained:

[0188] .

[0189] g is an integer, (d1 + d2) takes a value in the range [0, N), and the integer multiple frequency offset value should be much smaller than the FFT point number N. Where (d1 + d2) corresponds to the above position sum value, and g corresponds to the above preset multiple.

[0190] The value of g can be determined by the following method:

[0191] .

[0192] Step six: compensate the signal according to the estimated integer multiple frequency offset and the fine time delay and output the compensated signal .

[0193] .

[0194] Further, in one embodiment, the process of terminal device handling the supplementary synchronization sequence is also explained with reference to the flowchart shown in Figure 11 . Figure 11 includes the following steps:

[0195] Step 1: The terminal device (may be referred to as terminal) is powered on to search for a satellite.

[0196] The terminal captures and parses the GNSS signal to obtain the terminal's own position and speed information. The terminal reads the pre-stored ephemeris information to derive the position and speed information of each satellite, and selects a visible target satellite in combination with its own position. Then the terminal adjusts the beam pointing to align with the target satellite, and calculates the frequency offset according to the relative relationship between its own position and the target satellite position, as well as the relative relationship between its own speed and the target satellite speed.

[0197] When the terminal GNSS is denied, a blind search can be used to search for a satellite.

[0198] Step 2: The terminal searches for a broadcast signal.

[0199] The terminal searches for a downlink broadcast signal at the corresponding frequency point, and the frequency offset search range is 1500 kHz.

[0200] Step 3: Through sequence autocorrelation, coarse timing synchronization and decimal multiple frequency offset compensation are performed.

[0201] The specific algorithm flow of this step can refer to the contents of Figure 4 , Figure 9 and Figure 10 .

[0202] Since the supplementary synchronization sequence is divided into two identical sequences in the time domain, it has good autocorrelation characteristics. After receiving the signal, the receiver performs sliding search in the time domain. Each time the sequence with a sliding window length of one OFDM symbol (4096 points) is intercepted, the front and back are divided into two parts for autocorrelation to find the correlation peak value, thereby achieving coarse timing synchronization and decimal multiple frequency offset compensation.

[0203] After step 3, the timing deviation can be limited within one CP, the residual frequency offset can be limited within 10 kHz, and the sample estimation error can be within 1024 points.

[0204] Step 4: Through cross-correlation of the sequence with the local CSS sequence, fine timing synchronization and integer multiple frequency offset compensation are achieved.

[0205] The specific algorithm flow of this step can refer to the contents of Figure 4 ,Figure 9 and Figure 10 the contents of.

[0206] This step utilizes the ZC sequence characteristics of the CSS to perform cross-correlation operations on the received signal with a local ZC sequence and a local conjugate ZC sequence to obtain two correlation peaks. Then, the relative position relationship between the two peak positions is calculated by using the formula to achieve fine timing synchronization and integer multiple frequency offset estimation and compensation.

[0207] Further, the following processes can also be implemented:

[0208] Step five: PSS / SSS signal detection. The local PSS sequence and SSS sequence are respectively correlated with the received signal to complete the PSS and SSS detection process.

[0209] Step six: residual frequency offset compensation. The PSS\SSS sequence of the receiver is extracted and correlated with the local PSS\SSS, respectively. Then, the PSS-correlated sequence and the SSS-correlated sequence are correlated again to estimate the residual frequency offset by using the phase information. This step is used to compensate for the residual fractional frequency offset after step three to ensure the demodulation performance of the signal.

[0210] Through the above steps, the present embodiment utilizes the supplementary synchronization sequence of the symmetric ZC sequence to implement large-range time delay and frequency offset estimation with low complexity, thereby improving the time-frequency synchronization success rate in the case of inaccurate ephemeris and high-speed state.

[0211] Through the description of the above implementation, those skilled in the art can clearly understand that the method according to the above embodiment can be realized by means of software and a necessary general hardware platform, and of course, it can also be realized by hardware, but in many cases, the former is a better implementation. According to such understanding, the technical solution of the present application can be embodied in the form of a software product, which is stored in a storage medium (such as a ROM / RAM, a magnetic disk, an optical disk), and includes a plurality of instructions for causing a terminal device (which can be a mobile phone, a computer, a server, or a network device, etc.) to execute the method described in each embodiment of the present application.

[0212] In the present embodiment, a downlink signal sending device and a downlink signal processing device are also provided, which are used to implement the above embodiments and preferred embodiments, and have been described above. As used below, the term "module" can be a combination of software and / or hardware that implements a predetermined function. Although the devices described in the following embodiments are preferably implemented in software, hardware, or a combination of software and hardware can also be implemented and conceived.

[0213] In one embodiment, as Figure 12As shown, the downlink signal processing device of the embodiment of the application is applied to a terminal device and comprises:

[0214] The receiving module 1202 is configured to receive a downlink signal from a satellite, wherein the downlink signal carries a supplementary synchronization sequence.

[0215] Further, the terminal device can calculate a coarse time delay estimation value and a fractional frequency offset value of the downlink signal from the satellite, and obtain a compensation signal of the downlink signal according to the coarse time delay estimation value and the fractional frequency offset value, and calculate a fine time delay estimation value and an integral frequency offset value of the compensation signal.

[0216] In the application, the supplementary synchronization signal is configured on the satellite side, and the terminal device side uses the signal to implement the time-frequency synchronization process. Specifically, the supplementary synchronization sequence is designed based on the excellent correlation characteristics of the conjugate ZC sequence on the satellite side, the downlink signal is obtained based on the supplementary synchronization sequence, and the terminal device side calculates a coarse time delay estimation value and a fractional frequency offset value of the downlink signal from the satellite, obtains a compensation signal of the downlink signal according to the coarse time delay estimation value and the fractional frequency offset value, and calculates a fine time delay estimation value and an integral frequency offset value of the compensation signal. In the application, the terminal device does not need to obtain satellite ephemeris information and does not need to use a GNSS device to achieve time-frequency offset tracking compensation, eliminates the influence of ephemeris error and GNSS error on time-frequency synchronization performance after the terminal device is powered off for a long time, solves the problem of low precision of time-frequency offset tracking compensation in the process of satellite-ground communication, provides a technical solution capable of meeting the high-precision time-frequency offset tracking compensation requirement, and improves the time-frequency synchronization success rate of satellite-ground communication in the ephemeris inaccuracy and high-speed state.

[0217] In one example embodiment, the downlink signal processing device further comprises a processing module configured to: perform a sliding search on the downlink signal in the time domain, and intercept a sliding window for each sampling point found in the search; perform autocorrelation calculation on a subsequence in a window sequence corresponding to the intercepted sliding window to obtain an autocorrelation value; determine an autocorrelation peak value according to a maximum value in a plurality of autocorrelation values, and obtain a coarse timing estimation value according to a first index position corresponding to the autocorrelation peak value.

[0218] In one example embodiment, the processing module is further configured to: split the window sequence into a first subsequence and a second subsequence in the time domain, the first subsequence precedes the second subsequence in the time domain, and the sequence length of the first subsequence and the sequence length of the second subsequence are the same; and perform autocorrelation calculation on the first subsequence and the second subsequence.

[0219] In an example embodiment, the processing module is further configured to determine a phase corresponding to the autocorrelation peak, and obtain the fractional frequency offset value according to the phase.

[0220] In an example embodiment, the processing module is further configured to perform time domain compensation on the downlink signal according to the coarse time delay estimation value in time domain, and perform frequency domain compensation on the downlink signal according to the fractional frequency offset value in frequency domain, to obtain the compensated signal.

[0221] In an example embodiment, the processing module is further configured to determine a local ZC sequence and a local conjugate ZC sequence, wherein the local conjugate ZC sequence has a conjugate relationship with the local ZC sequence; perform cross-correlation calculation on the compensated signal using the local ZC sequence and the local conjugate ZC sequence respectively, and obtain the fine time delay estimation value and the integer frequency offset value according to the cross-correlation values obtained by the cross-correlation calculation.

[0222] In an example embodiment, the processing module is further configured to obtain a first cross-correlation value and a second cross-correlation value from the cross-correlation values obtained by the cross-correlation calculation, the first cross-correlation value being obtained by cross-correlation calculation on the compensated signal using the local ZC sequence, and the second cross-correlation value being obtained by cross-correlation calculation on the compensated signal using the local conjugate ZC sequence; obtain a second index position according to the first cross-correlation value, and obtain a third index position according to the second cross-correlation value; and determine the fine time delay estimation value and the integer frequency offset value of the compensated signal according to the second index position and the third index position.

[0223] In an example embodiment, the processing module is further configured to perform discrete Fourier transform processing on the first cross-correlation value, determine a first main peak value, and search for a second index position corresponding to the first main peak value in frequency domain; and perform discrete Fourier transform processing on the second cross-correlation value, determine a second main peak value, and search for a third index position corresponding to the second main peak value in frequency domain.

[0224] In an example embodiment, the processing module is further configured to obtain a position difference value of the second index position and the third index position; and calculate the fine time delay estimation value of the compensated signal based on the position difference value, a root index of the local ZC sequence, a time delay value within a preset time delay range, and a point number of fast Fourier transform (FFT).

[0225] In an example embodiment, the processing module is further configured to obtain a position and value of the second index position and the third index position; and calculate the integer frequency offset value of the compensated signal based on the position and value, a preset multiple corresponding to the position and value, and a point number of fast Fourier transform (FFT).

[0226] As Figure 13 shown in the figure, the downlink signal sending device of the embodiment of the application is applied to a satellite, and comprises:

[0227] The sending module 1302 is configured to send a downlink signal to a terminal device, wherein the downlink signal carries a supplementary synchronization sequence.

[0228] Further, the terminal device calculates a coarse time delay estimation value and a decimal multiple frequency offset value of the downlink signal, and obtains a compensation signal of the downlink signal according to the coarse time delay estimation value and the decimal multiple frequency offset value, and calculates a fine time delay estimation value and an integer multiple frequency offset value of the compensation signal.

[0229] By the application, the supplementary synchronization signal is configured on the satellite side, and the terminal device side uses the signal to realize the time-frequency synchronization process. Specifically, the supplementary synchronization sequence is designed on the satellite side based on the excellent correlation characteristics of the conjugate ZC sequence, the downlink signal is obtained based on the supplementary synchronization sequence, and the terminal device side calculates a coarse time delay estimation value and a decimal multiple frequency offset value of the downlink signal from the satellite, and obtains a compensation signal of the downlink signal according to the coarse time delay estimation value and the decimal multiple frequency offset value, and calculates a fine time delay estimation value and an integer multiple frequency offset value of the compensation signal. In the application, the terminal device does not need to obtain satellite ephemeris information and does not need to use a GNSS device to realize time-frequency offset tracking compensation, eliminates the influence of ephemeris error and GNSS error on time-frequency synchronization performance after the terminal device is powered off for a long time, solves the problem of low precision of time-frequency offset tracking compensation in the process of satellite-ground communication, provides a technical solution capable of meeting the high-precision time-frequency offset tracking compensation requirement, and improves the time-frequency synchronization success rate of satellite-ground communication in the ephemeris inaccuracy and high-speed state.

[0230] In one example embodiment, the sending module is further configured to determine the supplementary synchronization sequence according to the symmetric ZC sequence, and determine the CSS according to the supplementary synchronization sequence.

[0231] In one example embodiment, the sending module is further configured to determine a local ZC sequence and a local conjugate ZC sequence having a conjugate relationship with the local ZC sequence according to the symmetric ZC sequence, perform discrete Fourier transform (DFT) on a sequence obtained by adding the local ZC sequence and the local conjugate ZC sequence to obtain a first sequence after transformation, configure the frequency domain position and the time domain position of the first sequence respectively to obtain a second sequence after configuration, and perform inverse fast Fourier transform (IFFT) on the second sequence to obtain the supplementary synchronization sequence in the time domain.

[0232] In one example embodiment, the supplementary synchronization sequence is divided into two sub-sequences of the same length in the time domain.

[0233] In an example embodiment, the sending module is further configured to: place a center frequency point of the first sequence at a center frequency point of a first synchronization signal block (SSB) in the downlink signal; and set a fourth orthogonal frequency division multiplexing (OFDM) symbol position of a first subframe in a half frame in which the first SSB is located as a starting position of the first sequence.

[0234] In an example embodiment, the supplementary synchronization sequences are placed at intervals in a frequency domain, and a signal bandwidth of the supplementary synchronization sequences is consistent with a bandwidth occupied by the SSB.

[0235] In an example embodiment, the supplementary synchronization sequences occupy 1 OFDM symbol in a time domain.

[0236] It should be noted that the above modules can be implemented by software or hardware, and for the latter, the following implementation manners can be used, but are not limited thereto: the above modules are located in the same processor; or the above modules are located in different processors in any combination.

[0237] Embodiments of the present application also provide a computer readable storage medium, which stores a computer program, and the computer program is executed by a processor to implement the steps of the method described in any of the above embodiments.

[0238] In an example embodiment, the computer readable storage medium can include, but is not limited to, a U disk, a read-only memory (ROM), a random access memory (RAM), a mobile hard disk, a magnetic disk or an optical disk, and various media that can store computer programs.

[0239] Embodiments of the present application also provide an electronic device, which includes a memory and a processor, the memory stores a computer program, and the processor is configured to run the computer program to perform the steps of the method in any of the above method embodiments.

[0240] In an example embodiment, the electronic device can further include a transmission device and an input / output device, wherein the transmission device is connected to the processor, and the input / output device is connected to the processor.

[0241] The specific examples in the present embodiment can refer to the examples described in the above embodiments and example embodiments, and the present embodiment will not be described here again.

[0242] Embodiments of the present application also provide a computer program product, which includes a computer program, and the computer program is executed by a processor to implement the steps of the method described in the embodiments of the present application.

[0243] It should be apparent to those skilled in the art that the modules or steps of the application described above can be implemented with general computing devices, which can be centralized on a single computing device or distributed on a network of multiple computing devices, which can be implemented with program codes executable by the computing devices, so that they can be stored in storage devices and executed by the computing devices, and in some cases, the steps shown or described can be executed in different orders than shown, or made into individual integrated circuit modules, or made into a single integrated circuit module. Thus, the present application is not limited to any particular combination of hardware and software.

[0244] The preferred embodiments of the present application described above are only used to explain the principles of the present application and not limit the present application. Any modification, equivalent replacement, improvement, etc. within the principles of the present application should be included in the protection scope of the present application.

Claims

1. A method of processing a downlink signal, the method comprising: The application is applied to a terminal device, comprising: receiving a downlink signal from a satellite, wherein the downlink signal carries a supplementary synchronization sequence.

2. The method of claim 1, wherein, The method further comprises: calculating a coarse time delay estimation value and a fractional frequency offset value of the downlink signal, and obtaining a compensation signal of the downlink signal according to the coarse time delay estimation value and the fractional frequency offset value; calculating a fine time delay estimation value and an integral frequency offset value of the compensation signal.

3. The method of claim 2, wherein, The calculation of the coarse time delay estimation value of the downlink signal comprises: performing a sliding search on the downlink signal in the time domain, and cutting a sliding window for each sampling point searched; for the window sequence corresponding to the cut sliding window, performing autocorrelation calculation on the subsequence in the window sequence to obtain an autocorrelation value; determining an autocorrelation peak value according to the maximum value in the plurality of autocorrelation values, and obtaining a coarse timing estimation value according to the first index position corresponding to the autocorrelation peak value.

4. The method of claim 3, wherein, The autocorrelation calculation on the subsequence in the window sequence comprises: splitting the window sequence into a first subsequence and a second subsequence in the time domain, the first subsequence being prior to the second subsequence in the time domain, and the sequence length of the first subsequence being the same as that of the second subsequence; performing autocorrelation calculation on the first subsequence and the second subsequence.

5. The method of claim 3, wherein, The calculation of the fractional frequency offset value of the downlink signal comprises: determining a phase corresponding to the autocorrelation peak value, and obtaining the fractional frequency offset value according to the phase.

6. The method of claim 5, wherein, According to the coarse time delay estimation value and the fractional frequency offset value, the compensation signal of the downlink signal is obtained, comprising: performing time domain compensation on the downlink signal according to the coarse time delay estimation value in the time domain, and performing frequency domain compensation on the downlink signal according to the fractional frequency offset value in the frequency domain to obtain the compensation signal.

7. The method of claim 5, wherein, The calculation of the fine time delay estimation value and the integral frequency offset value of the compensation signal comprises: determining a local ZC sequence and a local conjugate ZC sequence, wherein the local conjugate ZC sequence has a conjugate relationship with the local ZC sequence; respectively using the local ZC sequence and the local conjugate ZC sequence to perform cross-correlation calculation on the compensation signal, and obtaining the fine time delay estimation value and the integral frequency offset value according to the cross-correlation value of the cross-correlation calculation.

8. The method of claim 7, wherein, The obtaining of the fine time delay estimation value and the integral frequency offset value according to the cross-correlation value of the cross-correlation calculation comprises: obtaining a first cross-correlation value and a second cross-correlation value from the cross-correlation value of the cross-correlation calculation, the first cross-correlation value being obtained by cross-correlation calculation of the local ZC sequence and the compensation signal, and the second cross-correlation value being obtained by cross-correlation calculation of the local conjugate ZC sequence and the compensation signal; obtaining a second index position according to the first cross-correlation value, and obtaining a third index position according to the second cross-correlation value; determining the fine time delay estimation value and the integral frequency offset value of the compensation signal according to the second index position and the third index position.

9. The method of claim 8, wherein, The obtaining of the second index position according to the first cross-correlation value and the third index position according to the second cross-correlation value comprises: The first cross-correlation value is processed by discrete Fourier transform to determine the first main peak value, and the second index position corresponding to the first main peak value is obtained by searching in the frequency domain. The second cross-correlation value is processed by discrete Fourier transform to determine the peak value of the second main peak, and the third index position corresponding to the peak value of the second main peak is obtained by searching in the frequency domain.

10. The method of claim 8, wherein, Determining the precise time delay estimate of the compensation signal based on the second index position and the third index position includes: Obtain the position difference between the second index position and the third index position; Based on the position difference, the root exponent of the local ZC sequence, the delay value within the preset delay range, and the number of points of the Fast Fourier Transform (FFT), the precise delay estimate of the compensated signal is calculated.

11. The method of claim 8, wherein, Determining the integer frequency offset value based on the second index position and the third index position includes: Obtain the position and value of the second index position and the third index position; Based on the position and value, the integer multiple of the compensation signal is calculated using the preset multiple corresponding to the position and value and the number of points of the Fast Fourier Transform (FFT).

12. A method of transmitting a downlink signal, the method comprising: Applied to satellites, including: A downlink signal is sent to the terminal device, wherein the downlink signal carries a supplementary synchronization sequence.

13. The method of claim 12, wherein, The method further includes: The supplementary synchronization sequence is determined based on the symmetric ZC sequence.

14. The method of claim 13, wherein, The supplementary synchronization sequence is determined based on the symmetric ZC sequence, including: The local ZC sequence is determined based on the symmetric ZC sequence, and the local conjugate ZC sequence is determined based on the conjugate relationship with the local ZC sequence. Perform a Discrete Fourier Transform (DFT) on the sequence obtained by adding the local ZC sequence and the local conjugate ZC sequence to obtain the first transformed sequence; The frequency domain position and time domain position of the first sequence are configured respectively to obtain the configured second sequence. The second sequence is then subjected to an inverse fast Fourier transform (IFFT) to obtain the supplementary synchronization sequence in the time domain.

15. The method of claim 14, wherein, The supplementary synchronization sequence is divided into two identical sub-sequences in the time domain.

16. The method of claim 14, wherein, Configure the frequency domain position and time domain position of the first sequence respectively, including: The center frequency point of the first sequence is placed at the center frequency point of the first synchronization signal block SSB in the downlink signal; Set the position of the fourth orthogonal frequency division multiplexing (OFDM) symbol in the first subframe of the half-frame containing the first SSB as the starting position of the first sequence.

17. The method of claim 16, wherein, The supplementary synchronization sequences are placed at intervals in the frequency domain, and the signal bandwidth of the supplementary synchronization sequences is consistent with the bandwidth occupied by the SSB.

18. The method of claim 16, wherein, The supplementary synchronization sequence occupies one OFDM symbol in the time domain.

19. A downlink signal processing apparatus, characterized in that, Applied to terminal devices, including: A receiving module is used to receive downlink signals from a satellite, wherein the downlink signals carry a supplementary synchronization sequence.

20. An apparatus for transmitting a downlink signal, the apparatus comprising: Applied to satellites, including: The transmitting module is used to send downlink signals to the terminal device, wherein the downlink signals carry a supplementary synchronization sequence.

21. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program, wherein the computer program, when executed by a processor, implements the method according to any one of claims 1 to 11, or the method according to any one of claims 12 to 18. 22.An electronic device comprising a memory and a processor, the electronic device characterized in that, The memory stores a computer program, and the processor is configured to run the computer program to perform the method according to any one of claims 1 to 11, or the method according to any one of claims 12 to 18.

23. A computer program product comprising a computer program, characterized in that, When the computer program is executed by a processor, it implements the method as described in any one of claims 1 to 11, or the method as described in any one of claims 12 to 18.

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