Space-Air-Ground Integrated Network Frequency Offset Estimation Method, Device and Medium

Abstract

The present invention provides a method, apparatus, and medium for frequency offset estimation in a space-ground integrated network. The method includes: obtaining synchronization information blocks for downlink synchronization in OFDM systems of different sub-networks in the space-ground integrated network; for multiple sub-networks in the space-ground integrated network, respectively obtaining parameter information of each sub-network from the synchronization information blocks; according to the obtained parameter information, establishing a system of equations for linearly estimating the carrier frequency offset; and solving the system of equations by the least squares method to obtain estimation results of each component of the carrier frequency offset. The frequency offset estimation method, apparatus, and medium provided by the present invention can solve the problem of estimating each component of the frequency offset under the conditions of low signal-to-noise ratio, large propagation delay, high Doppler frequency shift, and rapid change of Doppler frequency shift faced by the space-ground integrated network architecture.

Description

Technical Field

[0001] The present invention belongs to the field of wireless communication technologies, and particularly relates to a method, apparatus, and medium for estimating frequency offset in a space-ground integrated network. Background Art

[0002] Carrier frequency offset (CFO) is a common problem in wireless communication systems, mainly composed of two parts: the instability of the local crystal oscillator and the Doppler frequency offset generated by the relative motion between the communication parties. In a wireless communication system using orthogonal frequency division multiplexing (OFDM), OFDM is very sensitive to carrier frequency offset (CFO). Once the CFO reaches 20%-30% of the subcarrier spacing (SCS), the orthogonality between subcarriers will be destroyed, resulting in serious inter-carrier interference (ICI), inter-symbol interference (ISI), and timing errors, severely degrading the performance of the communication system.

[0003] In a space-ground integrated network, non-terrestrial network platforms such as low-earth orbit satellites and user terminals have a greater relative operating speed and higher communication carrier frequencies than terrestrial cellular networks. This results in a Doppler frequency offset much larger than that in terrestrial cellular communication, and the Doppler frequency offset is time-varying. At the same time, the carrier frequency offset caused by crystal oscillator instability will also be larger. However, most traditional frequency offset estimation algorithms are for terrestrial systems and cannot adapt to the situations of low signal-to-noise ratio, large propagation delay, high Doppler frequency shift, and rapid change of Doppler frequency shift in a space-ground integrated network. Moreover, they can only estimate the superposition value of the two. In the case where GNSS signals are incorrect or absent, traditional frequency offset estimation algorithms cannot separate the two, so correct uplink frequency offset pre-compensation cannot be achieved. For example, Figure 1 it can only be separated through a closed-loop feedback mechanism during the random access process, which will generate additional network overhead. Summary of the Invention

[0004] The purpose of the present invention is to provide a method, apparatus, and medium for estimating frequency offset in a space-ground integrated network, which can solve the problem of frequency offset estimation in the case of low signal-to-noise ratio, large propagation delay, high Doppler frequency shift, and rapid change of Doppler frequency shift faced by the space-ground integrated network architecture.

[0005] To achieve the above purpose, in the first aspect, the present invention provides a method for estimating frequency offset in a space-ground integrated network, the method comprising:

[0006] For the multi-connection scenario of a space-ground integrated network, use the synchronization information blocks of M sub-networks to establish an equation system to estimate N frequency offset parameters, where M >= 2, N >= 2, and M >= N.

[0007] To achieve the above purpose, in the second aspect, the present invention further provides a device for estimating frequency offset in a space-ground integrated network, the device comprising:

[0008] An estimation module, for the multi-connection scenario of the space-ground integrated network, uses the synchronization information blocks of M sub-networks to establish a system of equations to estimate N frequency offset parameters, where M >= 2, N >= 2, and M >= N.

[0009] To achieve the above object, in a third aspect, the present invention also provides an electronic device, which includes: a processor, a memory, and a communication bus;

[0010] The processor is used to execute one or more programs stored in the memory to implement the steps of the space-ground integrated network frequency offset estimation method as described above.

[0011] To achieve the above object, in a fourth aspect, the present invention also provides a computer-readable storage medium, which stores one or more programs, and the one or more programs can be executed by one or more processors to implement the steps of the space-ground integrated network frequency offset estimation method as described above.

[0012] The frequency offset estimation algorithm for the OFDM system of the space-ground integrated network proposed by the present invention can collect the downlink synchronization information blocks SSB of the ground network and the non-ground network simultaneously through the dual-connection or multi-connection technology for frequency offset estimation, and can separate and estimate the Doppler frequency shift caused by movement and the frequency offset caused by crystal oscillator instability that cannot be separated only by relying on the non-ground network synchronization information block SSB, avoiding additional separation overhead of the network, improving the network spectrum efficiency, and being not limited by the system bandwidth at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic diagram of the uplink frequency offset pre-compensation mismatch provided by the prior art;

[0014] Figure 2 It is a network architecture diagram provided by an embodiment of the present invention;

[0015] Figure 3 It is a flowchart of the space-ground integrated network frequency offset estimation method provided by an embodiment of the present invention;

[0016] Figure 4 It is a flowchart of the space-ground integrated network frequency offset estimation method provided by an embodiment of the present invention;

[0017] Figure 5 It is a flowchart of the space-ground integrated network frequency offset estimation method provided by an embodiment of the present invention;

[0018] Figure 6 It is a flowchart of the space-ground integrated network frequency offset estimation method provided by an embodiment of the present invention;

[0019] Figure 7The structural diagram of the space-ground integrated network frequency offset estimation device provided by the embodiment of the present invention;

[0020] Figure 8 The structural diagram of the electronic device provided by the embodiment of the present invention. Specific embodiments

[0021] In order to make the invention objectives, features, and advantages of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present invention.

[0022] Figure 2 Shows the network environment to which the frequency offset estimation method provided by the embodiment of the present invention is applied. Refer to Figure 2 , the application environment of the frequency offset estimation method provided by the embodiment of the present invention lies in the space-ground integrated network integrating the terrestrial network and the non-terrestrial network. In this space-ground integrated network, it includes both satellites moving at high speed in the sky and various types of communication terminals on the ground. Among the ground terminals, there are terminals such as cars and rail vehicles that can also move at a relatively high speed by themselves, and also include terminals such as mobile phones that usually do not move at a high speed by themselves. In addition, the ground terminals also include some communication terminals such as NB, eNB, gNB, and WIFI access points that are usually fixed on the ground.

[0023] It should be understood that regardless of the types of terminals participating in communication in this network, OFDM communication using multiple subcarriers should be utilized when different terminals communicate with each other. Moreover, there should be real-time displacements between different terminals participating in communication. That is to say, there is a relative displacement speed v between two terminals participating in communication. Due to the existence of real-time displacements, Doppler frequency shifts will occur between different terminals.

[0024] Figure 3 Shows the flowchart of the space-ground integrated network frequency offset estimation method provided by the embodiment of the present invention. Refer to Figure 3 , the space-ground integrated network frequency offset estimation method includes the following steps:

[0025] S31, for the multi-connection situation of the space-ground integrated network, use the synchronization information blocks of M sub-networks to establish an equation set to estimate N frequency offset parameters, where M >= 2, N >= 2, and M >= N.

[0026] The core idea of the embodiments of the present invention is to establish a system of equations by using the information contained in the synchronization information blocks of multiple sub-networks, and estimate the frequency offset parameter by solving the established system of equations.

[0027] Through the above technical solution, the Doppler frequency shift caused by motion and the frequency offset caused by crystal oscillator instability that cannot be separated by relying solely on a single network synchronization information block SSB can be separated and estimated, avoiding additional separation costs of the network, improving the network spectrum efficiency, and being not limited by the system bandwidth at the same time.

[0028] Figure 4 The flowchart of the space-ground integrated network frequency offset estimation method provided by the embodiments of the present invention is shown. Refer to Figure 4 , the frequency offset estimation method includes the following steps:

[0029] S41, obtain the synchronization information blocks for downlink synchronization in the OFDM systems of different sub-networks in the space-ground integrated network.

[0030] S42, for multiple sub-networks in the space-ground integrated network, respectively obtain the parameter information of each sub-network from the synchronization information blocks.

[0031] S43, establish a system of equations for linearly estimating the carrier frequency offset according to the obtained parameter information.

[0032] S44, solve the system of equations by the least squares method to obtain the estimation results of the components of the carrier frequency offset.

[0033] The specific implementation manner of the frequency offset estimation algorithm for the space-ground integrated network proposed by the present invention includes the following steps:

[0034] First, it is necessary to determine the signal model according to the characteristics of the space-ground integrated network. In the space-ground integrated network, whether it is a terrestrial network or a non-terrestrial network, the air interface technology adopted is OFDM. Considering an OFDM system with a bandwidth of B Hz and a subcarrier spacing of Δf Hz, the baseband equivalent transmitted signal x[n] is:

[0035]

[0036] In the formula, N is the number of sampling points of the DFT, X[k] is the OFDM symbol on subcarrier k, and N cp is the length of the cyclic prefix code.

[0037] After passing through a tapped delay line (TDL) wireless channel model with multiple taps, the baseband equivalent received signal y[n] is:

[0038]

[0039] Where Δf0 is the frequency offset caused by the crystal oscillator mismatch between the transmitter and the receiver, is the Doppler shift generated by the relative motion of the receiver and the transmitter, T s is the sampling interval 1 / NΔf, is the complex channel coefficient without Doppler shift, λ is the carrier wavelength, v is the relative velocity of the transmitter and the receiver, and w[n] is the noise.

[0040] Assume that X[k] is a known reference signal, so x[n] is also known. Multiply the received signal y[n] by the conjugate of the known signal x[n] to obtain the sequence z[n]:

[0041]

[0042] Where x * [n] is the conjugate of x[n]. To eliminate the unknown phase rotation introduced by the complex channel perform a difference operation on z[n] to obtain the sequence d[n]:

[0043]

[0044] Where D is the difference distance, discard the terms containing noise, and sum the sequence d[n] over n to obtain:

[0045]

[0046] Due to the periodicity of the discrete-time exponent, the following conditions need to be satisfied for accurate estimation.

[0047]

[0048] Selecting a larger D can improve the estimation because it results in more noise averaging. However, selecting a larger D will reduce the estimable range. The impact of timing drift can be ignored.

[0049] Combined with a specific case, in the scenario of the dual-connection space-ground integrated network, such as Figure 2 , to solve the two unknowns in the equation, two estimation equations need to be constructed.

[0050]

[0051] Where c is the speed of light, f p represents the center frequency of the synchronization signal block SSB of different networks, v is the relative velocity of the transmitter and the receiver. Accordingly, we will have two estimation equations, and these linear estimation equations can be represented by matrices:

[0052]

[0053] When the user terminal is fixed in position, the two estimation equations are respectively:

[0054]

[0055]

[0056] When the user terminal is moving and its speed is known, the two estimation equations are respectively:

[0057]

[0058]

[0059] The present invention proposes a method for frequency offset estimation for the space-ground integrated network, which is used to more quickly and accurately separate and estimate the frequency offset parameters of the space-ground integrated network, so as to achieve correct uplink pre-compensation. This method is applicable to any scenario of the integration of ground and non-ground networks under the space-ground integrated network, provides a more reliable and accurate method for fields such as physical layer parameter estimation, and is expected to promote the research progress of the key technologies of the physical layer of the space-ground integrated network.

[0060] Figure 5 The flowchart of the frequency offset estimation method provided by the embodiment of the present invention is shown. Refer to Figure 5 , the frequency offset estimation method includes the following steps:

[0061] S51, obtain the synchronization information block for downlink synchronization in the OFDM systems of different sub-networks in the space-ground integrated network.

[0062] S52, for multiple sub-networks in the space-ground integrated network, respectively obtain the parameter information of each sub-network from the synchronization information block.

[0063] S53, according to the obtained parameter information, establish a system of equations for linearly estimating the carrier frequency offset.

[0064] S54, solve the system of equations by the least squares method to obtain the estimation results of the respective components of the carrier frequency offset.

[0065] S55, filter the estimation results.

[0066] Some existing technical solutions estimate the Doppler frequency shift based on the known reference signals at multiple frequency positions in the OFDM carrier. On the basis of the frequency points of the existing 5G synchronization information block SSB, a new SSB frequency point is added. Although this can complete the solution of two unknowns, this will inevitably lead to a reduction in the network spectrum efficiency, and it is also limited by the system bandwidth, and may fail or even be unable to work in some systems with narrow bandwidth and large frequency offset.

[0067] The present invention proposes a new solution, considering a scenario where a user terminal can be simultaneously connected to a terrestrial network base station and a non-terrestrial network satellite through dual-connection or multi-connection technology. Whether it is a terrestrial 5G NR network or a non-terrestrial network, the synchronization signal block (SSB) is used for downlink synchronization. Moreover, the carrier operating frequencies of the terrestrial network and the non-terrestrial network are different. Based on this feature, multiple estimation equations can be established.

[0068]

[0069] In the formula, c is the speed of light, f p represents the center frequency of the synchronization signal block (SSB) of different networks, and v is the relative speed between the transmitter and the receiver. Correspondingly, we will have P estimation equations, and these linear estimation equations can be represented by a matrix:

[0070]

[0071] It is usually assumed that P≥2, and A is a high-dimensional matrix determined by the system. In this case, we can seek an approximate solution of the least squares method (LS):

[0072] e LS =(A H A) -1 A H b

[0073] In the formula, A H represents the Hermitian transpose of A. Further, the estimated value can also be filtered over time, such as a first-order infinite impulse response filter:

[0074]

[0075] In the formula is the filtered estimate at time m, γ is the filtering parameter, ranging from [0,1], and e LS [m] is the estimate at the unfiltered time.

[0076] Figure 6 shows the flowchart of the frequency offset estimation method provided by the embodiment of the present invention. Refer to Figure 6 , the frequency offset estimation method includes the following steps:

[0077] S61, obtain the synchronization signal blocks for downlink synchronization in the OFDM systems of different sub-networks in the integrated terrestrial and non-terrestrial network.

[0078] S62, for multiple sub-networks in the integrated terrestrial and non-terrestrial network, respectively obtain the parameter information of each sub-network from the synchronization signal blocks.

[0079] S63. Based on the obtained parameter information, establish a system of equations for linearly estimating the carrier frequency offset.

[0080] S64. Solve the system of equations by the least squares method to obtain the estimation results of the components of the carrier frequency offset.

[0081] S65. Use the frequency offset estimated in the downlink to pre-compensate the frequency offset in the uplink.

[0082] After the pre-compensation process, the carrier frequency offsets between multiple terminals will be cancelled. This means that the carrier frequency offsets between terminals will no longer affect communication.

[0083] An embodiment of the present invention provides a space-ground integrated network frequency offset estimation device. Refer to Figure 7 As shown, the frequency offset estimation device includes: an estimation module 701.

[0084] The estimation module 701 is used to establish a system of equations to estimate N frequency offset parameters by using the synchronization information blocks of M sub-networks for the multi-connection scenario of the space-ground integrated network, where M >= 2, N >= 2, and M >= N.

[0085] In some embodiments, the estimation module 701 includes: an acquisition unit 7011, a separation unit 7012, a system of equations establishment unit 7013, and an estimation unit 7014.

[0086] The acquisition unit 7011 is used to acquire the synchronization information blocks for downlink synchronization in the OFDM systems of different sub-networks in the space-ground integrated network.

[0087] The separation unit 7012 is used to obtain the parameter information of each sub-network from the synchronization information blocks for multiple sub-networks in the space-ground integrated network respectively.

[0088] The system of equations establishment unit 7013 is used to establish a system of equations for linearly estimating the carrier frequency offset based on the obtained parameter information.

[0089] The estimation unit 7014 is used to solve the system of equations by the least squares method to obtain the estimation results of the components of the carrier frequency offset.

[0090] In some embodiments, the frequency offset includes: the frequency offset caused by the instability of the crystal oscillator and the Doppler frequency offset.

[0091] In some embodiments, use the synchronization information blocks of M sub-networks to obtain the correlation sequence through the correlation operation and then perform the difference operation on the correlation sequence to establish a system of equations to solve N frequency offset parameters.

[0092] In some embodiments, establishing the system of equations includes at least the following parameters: the phase of the differential sequence based on the synchronization signal block of each sub-network, the center frequency of the synchronization signal block (SSB) of each sub-network, the sampling interval, and the relative motion speed between the receiver and the transmitter.

[0093] In some embodiments, the estimation module 701 further includes: a filtering unit 7015.

[0094] The filtering unit 7015 is configured to filter the estimation result after solving the system of equations by the least squares method to obtain the estimation result of the carrier frequency offset.

[0095] In some embodiments, the estimation module 701 further includes: a pre-compensation unit 7016.

[0096] The pre-compensation unit 7016 is configured to pre-compensate the uplink frequency offset using the frequency offset estimated in the downlink after solving the system of equations by the least squares method to obtain the estimation results of the components of the carrier frequency offset.

[0097] An embodiment of the present invention provides an electronic device. Refer to Figure 8 As shown, it includes a processor 801, a memory 802, and a communication bus 803, where: the communication bus 803 is used to implement connection communication between the processor 801 and the memory 802; the processor 801 is configured to execute one or more computer programs stored in the memory 802 to implement at least one step in the frequency offset estimation method in the first embodiment above.

[0098] This embodiment also provides a computer-readable storage medium, which includes volatile or non-volatile, removable or non-removable media implemented in any method or technology for storing information (such as computer-readable instructions, data structures, computer program modules, or other data). The computer-readable storage medium includes, but is not limited to, RAM (Random Access Memory), ROM (Read-Only Memory), EEPROM (Electrically Erasable Programmable Read Only Memory), flash memory, or other memory technologies, CD-ROM (Compact Disc Read-Only Memory), digital versatile disc (DVD), or other optical disc storage, magnetic cassette, tape, magnetic disk storage, or any other medium that can be used to store the desired information and can be accessed by a computer.

[0099] The computer-readable storage medium in this embodiment can be used to store one or more computer programs, and the one or more computer programs stored therein can be executed by a processor to implement at least one step of the method in the first embodiment above.

[0100] This embodiment also provides a computer program, which can be distributed on a computer-readable medium and executed by a computable device to implement at least one step of the method in the first embodiment above; and in some cases, at least one step shown or described can be executed in a different order from that described in the above embodiment.

[0101] This embodiment also provides a computer program product, including a computer-readable device, on which the computer program as shown above is stored. In this embodiment, the computer-readable device can include the computer-readable storage medium as shown above.

[0102] It can be seen that those skilled in the art should understand that all or some of the steps in the method disclosed above, and the functional modules / units in the system and device, can be implemented as software (which can be realized by computer program code executable by a computable device), firmware, hardware, and their appropriate combinations. In the hardware implementation, the division between the functional modules / units mentioned above does not necessarily correspond to the division of physical components; for example, a physical component can have multiple functions, or a function or step can be executed by several physical components in cooperation. Some physical components or all physical components can be implemented as software executed by a processor, such as a central processing unit, a digital signal processor, or a microprocessor, or implemented as hardware, or implemented as an integrated circuit, such as an application-specific integrated circuit.

[0103] In addition, as is well known to those of ordinary skill in the art, a communication medium generally contains computer-readable instructions, data structures, computer program modules, or other data in a modulated data signal such as a carrier wave or other transmission mechanisms, and can include any information delivery medium. Therefore, the present invention is not limited to any specific combination of hardware and software.

[0104] The above content is a further detailed description of the embodiments of the present invention in combination with specific implementation manners, and it cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the concept of the present invention, several simple deductions or substitutions can be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. A method for estimating frequency offset in a space-ground integrated network, characterized in that Including: For the multi-connection scenario of the space-ground integrated network, simultaneously use the synchronization information blocks of M different sub-networks to establish an equation set to estimate N frequency offset parameters, where M >= 2, N >= 2, M >= N, and the M different sub-networks include a ground network and a non-ground network; Simultaneously using the synchronization information blocks of M different sub-networks to establish an equation set to estimate N frequency offset parameters includes: For multiple sub-networks in the space-ground integrated network, obtain the parameter information of each sub-network from the synchronization information block respectively; According to the obtained parameter information, establish an equation set for linearly estimating the carrier frequency offset; Solve the equation set to obtain the estimation results of the components of the carrier frequency offset.

2. The method according to claim 1, characterized in that For the multi-connection scenario of the space-ground integrated network, simultaneously use the synchronization information blocks of M different sub-networks to establish an equation set to estimate N frequency offset parameters, including: Obtain the synchronization information blocks for downlink synchronization in the OFDM systems of different sub-networks in the space-ground integrated network; Solve the equation set by the least squares method to obtain the estimation results of the components of the carrier frequency offset.

3. The method according to claim 1, characterized in that The frequency offset includes: the frequency offset caused by the instability of the crystal oscillator and the Doppler frequency offset.

4. The method according to claim 1, characterized in that Simultaneously use the synchronization information blocks of M different sub-networks to obtain correlation sequences through correlation operations, and then perform differential operations on the correlation sequences to establish an equation set to solve N frequency offset parameters.

5. The method according to claim 4, characterized in that Establishing the equation set includes at least the following parameters: the phase of the differential sequence based on the synchronization information block of each sub-network, the center frequency of the synchronization information block SSB of each sub-network, the sampling interval, and the relative motion speed between the receiver and the transmitter.

6. The method according to claim 4, characterized in that For the multi-connection scenario of the space-ground integrated network, simultaneously using the synchronization information blocks of M different sub-networks to establish an equation set to estimate N frequency offset parameters further includes: After solving the equation set by the least squares method to obtain the estimation result of the carrier frequency offset, filter the estimation result.

7. The method according to claim 1, characterized in that For the multi-connection scenario of the space-ground integrated network, simultaneously using the synchronization information blocks of M different sub-networks to establish an equation set to estimate N frequency offset parameters further includes: After solving the equation set by the least squares method to obtain the estimation results of the components of the carrier frequency offset, use the frequency offset estimated by the downlink to pre-compensate the frequency offset of the uplink.

8. A device for estimating frequency offset in a space-ground integrated network, comprising: An estimation module for, for the multi-connection scenario of the space-ground integrated network, simultaneously using the synchronization information blocks of M different sub-networks to establish an equation set to estimate N frequency offset parameters, where M >= 2, N >= 2, M >= N, and the M different sub-networks include a ground network and a non-ground network; Simultaneously using the synchronization information blocks of M different sub-networks to establish an equation set to estimate N frequency offset parameters includes: For multiple sub-networks in the space-ground integrated network, obtain the parameter information of each sub-network from the synchronization information block respectively; According to the obtained parameter information, establish an equation set for linearly estimating the carrier frequency offset; Solve the equation set to obtain the estimation results of the components of the carrier frequency offset.

9. An electronic device, comprising: A processor, a memory, and a communication bus; The processor is configured to execute one or more programs stored in the memory to implement the steps of the space-ground integrated network frequency offset estimation method according to any one of claims 1 to 7.

10. A computer-readable storage medium, wherein the computer-readable storage medium stores one or more programs, and the one or more programs can be executed by one or more processors to implement the steps of the method for estimating frequency offset in a space-ground integrated network according to any one of claims 1 to 7.

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