Frequency offset estimation method, terminal equipment and storage medium

Abstract

The invention discloses a frequency offset estimation method, terminal equipment and a storage medium, and relates to the technical field of wireless communication. The method comprises the following steps: acquiring first time slot data in M continuous subframe signals, and performing modulation information elimination on the first time slot data to obtain corresponding spectrum data; according to the receiving time sequence, grouping the corresponding spectrum data in pairs, and adding a preset sequence in each group of spectrum data to obtain N groups of sequences; processing the N groups of sequences to obtain corresponding frequency offset estimation values; calculating frequency offset estimation values of M sub-frame signals based on the frequency offset estimation values of the N groups of sequences; and performing frequency offset compensation based on the frequency offset estimation values of the M sub-frame signals. According to the method and the device, the frequency offset estimation value of the subframe signal is jointly calculated through the first time slot data of the continuous multiple subframe signals, so that the accuracy of frequency offset estimation is improved to a certain extent, frequency offset compensation is effectively realized, and the condition of inaccurate frequency offset estimation caused by a relatively large frequency offset change rate is avoided.

Description

Technical Field

[0001] The present application relates to the field of wireless communication technology, and in particular to a frequency offset estimation method, terminal equipment, and storage medium. Background Art

[0002] With the rapid development of communications technology, the use of satellite communications is becoming increasingly widespread. Satellite communication systems use satellites as relay stations to forward radio waves, enabling wireless communication between devices. Satellite communication systems enable global communication in various forms, including voice, data, and video. They offer high communication capacity, wide coverage, seamless global connectivity, and strong anti-interference capabilities.

[0003] Synchronization is a crucial factor influencing wireless communication performance. Correct coherent demodulation of the signal is only possible when both the local carrier frequency and phase are synchronized with the received signal. Frequency synchronization is an essential step in this process. In satellite communication systems, where large frequency shifts and low signal-to-noise ratios exist, how terminal devices estimate the frequency offset after receiving signals from the satellite transmitter, thereby achieving carrier synchronization, is a worthy research issue.

[0004] In current technology, the commonly used frequency offset estimation method for satellite communications is generally a data-assisted method. The terminal device uses known data to perform frequency offset estimation. For example, the terminal device performs frequency offset estimation based on a locally known synchronization sequence. The known synchronization sequence is generally a sequence with good autocorrelation characteristics.

[0005] However, in the frequency offset estimation method commonly used in current technology, the accuracy of frequency offset estimation is low, so that frequency offset compensation cannot be effectively implemented, and thus subsequent coherent demodulation of the signal cannot be correctly implemented. Summary of the Invention

[0006] The present application provides a frequency offset estimation method, terminal device, and storage medium, which improve the accuracy of frequency offset estimation to a certain extent, thereby effectively realizing frequency offset compensation so that coherent demodulation of the signal can be correctly realized subsequently.

[0007] To achieve the above objectives, this application adopts the following technical solutions:

[0008] The present application provides a frequency offset estimation method, including: obtaining the first time slot data in M ​​consecutive subframe signals, and performing modulation information elimination on the first time slot data in the M subframe signals to obtain spectrum data corresponding to the first time slot data in the M subframe signals; grouping the spectrum data corresponding to the first time slot data in the M subframe signals in pairs according to the reception time sequence of the M subframe signals, and adding a preset sequence to each group of spectrum data to obtain N groups of sequences corresponding to the M subframe signals; processing the N groups of sequences to obtain frequency offset estimation values ​​corresponding to the N groups of sequences; calculating the frequency offset estimation values ​​of the M subframe signals based on the frequency offset estimation values ​​corresponding to the N groups of sequences; and performing frequency offset compensation on the M subframe signals based on the frequency offset estimation values ​​of the M subframe signals. Specifically, frequency offset compensation can be performed on all M subframe signals, or on part of the M subframe signals. The frequency offset estimation values ​​of the subframe signals are jointly calculated using the first time slot data of multiple subframe signals. The present application calculates the frequency offset estimate of the subframe signal based on the first time slot data of the subframe signal itself. Compared with the frequency offset estimate obtained by the current technology based only on a known synchronization sequence, the frequency offset estimate is more accurate. Moreover, based on the first time slot data of multiple subframe signals, the frequency offset estimate relies on more prior information, which improves the accuracy of the frequency offset estimate to a certain extent, thereby effectively achieving frequency offset compensation so that the coherent demodulation of the signal can be correctly achieved later. Furthermore, by jointly calculating the frequency offset estimate of the subframe signal through multiple subframe signals, the large frequency offset change rate in satellite communications is also taken into account, which to a certain extent avoids the situation where the frequency offset estimate is inaccurate due to the large frequency offset change rate.

[0009] In one possible implementation, the length of the preset sequence added to each set of spectrum data is the difference between the length of one subframe signal and the length of the first time slot. The length of the preset sequence added to each set of spectrum data is the absolute value of the difference between the length of one subframe signal and the length of the first time slot. This allows for better integration of the two subframe signals and prevents the influence of other time slot data on frequency offset estimation.

[0010] In one possible implementation, when first acquiring the first time slot data from M consecutive subframe signals, it is necessary to continuously receive M subframe signals and extract the first time slot data from the M subframe signals to acquire the first time slot data from the M consecutive subframe signals. Furthermore, the first time slot data from the M subframe signals can be stored. This facilitates direct acquisition of the first time slot data from the stored data during subsequent frequency offset estimation, simplifying the steps for acquiring the first time slot data.

[0011] In one possible implementation, when acquiring the first time slot data of M consecutive subframe signals, but not for the first time, only the first subframe signal (the Mth subframe signal among the M subframe signals) is received, and the first time slot data of the first subframe signal is extracted. The first time slot data of the first subframe signal through the Nth subframe signal among the M subframe signals is then acquired to acquire the first time slot data of the M consecutive subframe signals. Furthermore, the received first time slot data of the first subframe signal can be stored so that the first time slot data of the first subframe signal can be directly acquired from the storage when frequency offset estimation is subsequently performed.

[0012] In one possible implementation, when first acquiring the first time slot data of M subframe signals, the frequency offset estimate of the first subframe signal among the M subframe signals is a preset constant, namely, a standard frequency offset estimate. The frequency offset estimate of the second subframe signal among the M subframe signals is obtained based on the average of the frequency offset estimates of the first and second sequences. Subsequently, the frequency offset estimate of the yth subframe signal is calculated based on the frequency offset estimate of the xth sequence and the frequency offset estimate of the xth subframe signal. This differential iterative calculation method can effectively improve the accuracy of the frequency offset estimation.

[0013] In one possible implementation, frequency offset estimation is performed on each of the M subframe signals using the frequency offset estimation values ​​of the M subframe signals. For example, the frequency offset estimation value of the first subframe signal is used to compensate for the frequency offset of the first subframe signal; the frequency offset estimation value of the second subframe signal is used to compensate for the frequency offset of the second subframe signal; and so on, the frequency offset estimation value of the Mth subframe signal is used to compensate for the frequency offset of the Mth subframe signal.

[0014] In one possible implementation, frequency offset compensation is performed on the first subframe signal based on the frequency offset estimate (constant) of the first subframe signal; and frequency offset compensation is performed on the remaining subframe signals based on the frequency offset estimate of the Mth subframe signal. This effectively implements frequency offset compensation while simplifying the complexity of the frequency offset compensation steps.

[0015] In one possible implementation, a frequency offset estimate value of an M-th subframe signal among the M subframe signals is calculated based on the frequency offset estimate value of the N-th sequence among the N groups of sequences and the frequency offset estimate value of the N-th subframe signal among the M subframe signals. When this is not the first time that the frequency offset estimate values ​​of the M subframe signals are acquired, only the frequency offset estimate value of the M-th subframe signal among the M subframe signals may be calculated.

[0016] In one possible implementation, when the frequency offset estimation values ​​of M subframe signals are not obtained for the first time, the frequency offset estimation value of the Mth subframe signal is used to perform frequency offset compensation on the Mth subframe signal, because the frequency offset compensation has been completed for the remaining subframe signals.

[0017] In one possible implementation, a frequency offset compensation value for a phase-locked loop (PLL) is calculated by summing the known frequency offset estimates of all subframe signals. Based on the frequency offset compensation value, the frequency of the PLL's oscillator is adjusted to achieve PLL frequency offset compensation. Because the accuracy of the subframe signal frequency offset estimation is improved, the accuracy of the PLL frequency offset compensation value calculated based on the subframe signal frequency offset estimate is also improved, thereby enabling more efficient PLL frequency offset compensation.

[0018] In one possible implementation, the first time slot data is valid time slot data. Although the non-data-assisted frequency offset estimation method has higher frequency offset estimation accuracy than the data-assisted frequency offset estimation method, due to the low signal-to-noise ratio in the current non-data-assisted frequency offset estimation method, the first time slot data may introduce more noise, thereby affecting the accuracy of the frequency offset estimation. The present application only extracts valid time slot data, thereby avoiding the impact of the noise data on the accuracy of the frequency offset estimation and further improving the accuracy of the frequency offset estimation.

[0019] In a second aspect, the present application provides a terminal device comprising a processor and a memory; the memory stores computer-executable instructions; the processor executes the computer-executable instructions stored in the memory, so that the processor executes the method of the first aspect above.

[0020] In a third aspect, the present application provides a computer-readable storage medium, in which a computer program or instruction is stored. When the computer program or instruction is executed, the method of the first aspect described above is implemented.

[0021] In a fourth aspect, the present application provides a computer program product, comprising a computer program or instructions, which, when executed by a processor, implements the method of the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A flowchart of an overall signal processing method on the receiver side provided in an embodiment of the present application;

[0023] Figure 2 A flowchart of a frequency offset estimation method provided in an embodiment of the present application;

[0024] Figure 3 A schematic diagram of the length of a set of fourth power data with zeros added in the middle provided in an embodiment of the present application;

[0025] Figure 4 A schematic diagram of a subframe signal of a frequency offset estimation method provided in an embodiment of the present application;

[0026] Figure 5A flowchart of another frequency offset estimation method provided in an embodiment of the present application;

[0027] Figure 6 This is an example diagram of the composition of an electronic device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0028] The terms "first", "second" and "third" in the specification, claims and drawings of this application are used to distinguish different objects rather than to limit a specific order.

[0029] In the embodiments of this application, words such as "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of this application should not be interpreted as being preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0030] To make the description of the following embodiments clear and concise, a brief introduction to the related technologies is first given:

[0031] Frequency offset, in wireless communication systems, refers to the difference between the carrier frequency of the received signal and the carrier frequency of the transmitted signal. Due to multipath fading, the Doppler effect, and other influences during signal propagation, the received signal's frequency may be offset from the transmitted signal's frequency. This frequency offset can cause errors in demodulation of the received signal, thus affecting the performance of the communication system.

[0032] The purpose of frequency offset estimation is to estimate the deviation between the carrier frequency of the received signal and the carrier frequency of the transmitted signal, and to perform frequency compensation based on the estimation result to ensure correct demodulation of the received signal.

[0033] Frequency offset compensation (FOC) is a compensation measure designed to eliminate or reduce signal distortion or interference caused by frequency offset. It can be simply understood as implementing frequency offset compensation based on frequency offset estimation to eliminate or reduce the difference between the received signal's frequency and the transmitted signal's frequency.

[0034] As can be seen from the above introduction to related technologies, to reduce the impact of frequency offset on communication system performance, frequency offset estimation and compensation are required at the receiver side to achieve frequency synchronization, thereby avoiding problems such as signal distortion, high bit error rates, and reduced transmission rates caused by frequency offset. In communication systems, frequency offset estimation is an indispensable step in achieving frequency synchronization. The accuracy of frequency offset estimation directly affects the accuracy of subsequent frequency offset compensation, frequency offset synchronization, and even subsequent channel decoding, thereby affecting the performance of the entire communication system.

[0035] Before introducing the embodiments of this application, Figure 1 Briefly introduce the overall signal processing flow on the receiver side.

[0036] After a receiver (e.g., a terminal device) receives a signal, it first separates and extracts the useful signal from the received signal through the digital front-end (DFE). The digital front-end (DFE) is part of the Remote Radio Unit (RRU) system, which consists of two parts: the remote radio unit (RRU) and the baseband processing unit (BPU). The RRU is defined as all transceiver circuits and various processing units between the antenna and the baseband processing unit. The transceiver circuits and processing units between the ADC / CDA and the baseband processing unit are defined as the DFE.

[0037] The signal output by the digital front-end is then synchronized, including time and frequency synchronization. Synchronization is a critical factor affecting wireless communication performance. Only when the frequency and phase of the local carrier are synchronized with the received signal can correct coherent demodulation of the signal be achieved.

[0038] After synchronizing the signal output from the digital front-end, the synchronized signal undergoes channel equalization, soft demodulation, channel decoding, and CRC check to obtain the valid signal from the received signal, completing the overall signal processing process. Channel equalization aims to offset multipath interference, frequency-selective fading, and other effects on the signal during propagation, thereby improving the quality of the received signal. Soft demodulation aims to recover the original bit sequence from the received signal. Channel decoding aims to restore the original data as accurately as possible. CRC (Cyclic Redundancy Check) is a commonly used method for detecting data transmission errors and is used to detect errors or corruption in the data carried by the signal during transmission.

[0039] In such Figure 1An overall signal processing process is shown, and a frequency offset estimation method provided in this application is applied to the frequency synchronization process in the entire signal processing process, that is, the frequency offset of the received signal is estimated, and the frequency offset of the received signal is compensated according to the frequency offset estimation, thereby achieving frequency synchronization.

[0040] The advantages of a frequency offset estimation method provided by the present application are described below in combination with the frequency offset estimation method in the current technology.

[0041] During satellite communications, the characteristics of satellite communications result in signals received by terminal devices experiencing large frequency deviations, low signal-to-noise ratios, and short-lived and bursty signals. The specific reasons for this include at least three aspects: First, due to the extremely high speed of the satellite relative to the terminal device, there is a significant Doppler shift (a large frequency offset) between the frequency of the signal received by the terminal device and the carrier frequency of the satellite transmitter, as well as a high rate of change in the frequency offset. Second, due to the long distance between the satellite and the terminal device, the signal-to-noise ratio of the signal received by the terminal device is very low. Third, due to the small data volume and low symbol rate of satellite communications, the signals received by the terminal device are bursty and short-lived. Doppler shift refers to the phenomenon in which the frequency of the observed wave shifts relative to the frequency emitted by the source when there is relative motion between the wave source and the observer. In short-duration burst communication systems such as satellite communication systems, when the received signal has a large frequency offset and a low signal-to-noise ratio, the frequency offset estimation used in current technologies is inaccurate and has large errors. Furthermore, the low signal-to-noise ratio renders the frequency offset estimation ineffective, making it impossible to achieve subsequent signal synchronization and correctly implement coherent demodulation. The specific reasons for this are explained below, combined with commonly used frequency offset estimation methods in current technologies:

[0042] The first type of frequency offset estimation is data-assisted, where the terminal device performs frequency offset estimation based on known data. For example, the terminal device estimates the frequency offset of the received signal based on a locally known synchronization sequence. This allows the terminal device to compensate for the signal's frequency offset based on the estimated frequency offset and achieve frequency synchronization. Generally, the known synchronization sequence is a sequence with good autocorrelation characteristics. Convolving this synchronization sequence with the received signal yields a peak. The position of this peak indicates the offset between the synchronization sequence and the signal, and frequency offset estimation can be performed based on this offset. The relationship between the length of the known synchronization sequence and the signal length is: signal length = known synchronization sequence length * m, where m is a positive integer, i.e., the signal length is an integer multiple of the known synchronization sequence length. In satellite communications, the signal received by the terminal device is bursty and short-lived. This burstiness and short-lived nature mean that the signal received by the terminal device is limited in time, and the length of the received signal is short and discontinuous. Since the received signal length is short, according to the equation signal length = known synchronization sequence length * m (m is a positive integer), the corresponding known synchronization sequence length is also short. Therefore, there is less prior information for frequency offset estimation, resulting in a larger frequency offset estimation error and lower accuracy.

[0043] The second type of frequency offset estimation method is a non-data-assisted method. In this method, the terminal device does not rely on any known data, but instead performs frequency offset estimation based on the received data itself. It should be noted that this non-data-assisted frequency offset estimation method does not restrict the type of subframe signal. For example, after receiving a signal transmitted by a satellite, the terminal device performs frequency offset estimation for each subframe signal in the signal. For frequency offset estimation of a subframe signal, the terminal device performs frequency offset estimation based on the target time slot data in the subframe signal, so that frequency offset compensation for the corresponding subframe signal can be performed based on the frequency offset estimation, thereby achieving frequency synchronization. To address the low frequency offset estimation accuracy of data-assisted frequency offset estimation methods, the target time slot length is truncated to a larger value in the non-data-assisted frequency offset estimation method, thereby increasing prior information. However, due to the low signal-to-noise ratio of the signal received by the terminal device in satellite communications, the target time slot data in the subframe signal carries a large amount of noise (i.e., the target time slot data contains less valid data), resulting in large errors and low accuracy in frequency offset estimation based on the target time slot data of the subframe signal. Furthermore, when the signal-to-noise ratio of the signal received by the terminal device is too low, the frequency offset estimation may even fail, making it impossible to perform frequency synchronization of the signal (ie, the frequency synchronization function fails as a whole), and coherent demodulation of the signal cannot be achieved.

[0044] Furthermore, both types of frequency offset estimation methods suffer from large frequency offset variations in the frequency of the signal received by the terminal in satellite communications, leading to larger frequency estimation errors and lower accuracy. For example, data-assisted frequency offset estimation uses a locally known synchronization sequence to estimate the frequency of the received signal. If the frequency offset variation is large, the signal's frequency offset will have significantly changed during the estimation process. The resulting frequency offset estimate will then differ significantly from the current signal's frequency offset, resulting in inaccurate frequency offset estimation. Therefore, current technologies struggle to achieve rapid frequency offset synchronization in the face of the high dynamic frequency offset variation found in satellite communications.

[0045] In summary, in satellite communication systems, the frequency offset estimation results obtained by the current frequency offset estimation methods have low accuracy, large errors, and may even fail to be estimated.

[0046] The present application provides a frequency offset estimation method, which obtains first time slot data from multiple consecutive subframe signals, and performs modulation information elimination (for example, quartic processing, quadratic processing, etc.) on the first time slot data in the multiple subframe signals to obtain spectrum data corresponding to the first time slot data in the multiple subframe signals; groups the spectrum corresponding to the first time slot data in the multiple subframe signals in pairs according to the reception time sequence of the multiple subframe signals, adds a preset sequence to each group of spectrum data to obtain multiple corresponding groups of sequences, processes the multiple groups of sequences to obtain frequency offset estimation values ​​corresponding to the multiple groups of sequences; calculates frequency offset estimation values ​​for multiple subframe signals based on the frequency offset estimation values ​​of the multiple groups of sequences; and performs frequency offset compensation on the multiple subframe signals based on the frequency offset estimation values ​​of the multiple subframe signals. That is, the present application jointly calculates the frequency offset estimation value of the subframe signal through the first time slot data of multiple consecutive subframe signals, and calculates the frequency offset estimation value of the subframe signal based on the first time slot data of the subframe signal itself. Compared with the frequency offset estimation value obtained only based on the known synchronization sequence in the current technology, the frequency offset estimation is more accurate; and based on the first time slot data of multiple subframe signals, the frequency offset estimation relies on more prior information, which improves the accuracy of the frequency offset estimation to a certain extent, and can effectively realize frequency offset compensation, so that the coherent demodulation of the signal can be correctly realized subsequently.

[0047] Furthermore, by jointly calculating the frequency offset estimation value of the subframe signal through multiple subframe signals, the large frequency offset change rate in satellite communication is also taken into account, which to a certain extent avoids the situation where the frequency offset estimation is inaccurate due to the large frequency offset change rate.

[0048] Furthermore, the first time slot can be selected as a valid time slot, that is, based on the valid time slot data of multiple consecutive subframe signals, the frequency offset estimation value of the current subframe signal is jointly calculated. Although the non-data-assisted frequency offset estimation method in the current technology can improve the accuracy of frequency offset estimation compared with the data-assisted frequency offset estimation method, in the non-data-assisted frequency offset estimation method in the current technology, due to the low signal-to-noise ratio, the target time slot data may introduce noise data, affecting the accuracy of the frequency offset estimation. The present application extracts the valid time slot data, avoids the influence of the noise data on the accuracy of the frequency offset estimation, further improves the accuracy of the frequency offset estimation, and avoids the failure of the frequency offset estimation.

[0049] Example 1:

[0050] The following combination Figure 2-Figure 4 , a frequency offset estimation method provided in an embodiment of the present application is introduced in detail.

[0051] Before introducing in detail a frequency offset estimation method provided in an embodiment of the present application, the frame, subframe, time slot and effective time slot are first introduced.

[0052] A frame is the largest unit of organization in wireless communication systems, containing a set of related data and control information. A frame is typically composed of multiple subframes or time slots, the length of which depends on the specific wireless communication standard or protocol.

[0053] A subframe is a portion of a frame, typically shorter than a frame. In some wireless communication systems, a frame is divided into several subframes, each with its own specific function. The use of subframes can increase the flexibility of data transmission.

[0054] A time slot is a small time interval in a frame or subframe, usually used for finer-grained resource allocation and data transmission. A frame or subframe can contain multiple time slots, each of which contains a certain number of symbols or sampling points. For example: a subframe usually lasts 1ms, and each time slot lasts 0.5ms, so a completed subframe is transmitted within two consecutive time slots. Furthermore, an effective time slot usually refers to a time slot in a frame or subframe that can be used to transmit actual data (for example, voice, video, etc.), excluding time slots used for synchronization, control signals or other non-data information transmission. That is, an effective time slot refers to a time slot that can be used to transmit valid data. In actual applications, not all time slots can be used for data transmission, and time slots that are not used for data transmission are not effective time slots.

[0055] As can be seen from the above concepts, the relationship between frames, subframes, and time slots can be simply understood as a hierarchical structure from the overall to the local. That is, a frame contains multiple subframes, and a subframe contains one or more time slots. The effective time slot is the time slot used to transmit valid data.

[0056] like Figure 1 As can be seen from the overall signal processing flow shown, frequency synchronization includes: frequency offset estimation and frequency offset compensation, so the frequency offset estimation process is located after the time synchronization of the signal. Therefore, a frequency offset estimation method provided in the embodiment of the present application is performed on the signal after time synchronization. For the convenience of description, the signals described in the first embodiment are all signals after time synchronization is completed. Figure 2 , a frequency offset estimation method provided in an embodiment of the present application includes the following steps:

[0057] S201. The terminal device sets initialization parameters.

[0058] The terminal device sets the initialization parameters n=0, F n =F0=F initial .

[0059] Where n is a time index, which characterizes the temporal sequence of subframe signals and uniquely identifies a subframe signal. For example, if the time index of a subframe signal is n = 0, the subframe signal with time index 0 is the first subframe signal received by the terminal device. Furthermore, because the time index uniquely identifies a subframe signal, it serves as a unique identifier for the subframe signal.

[0060] It should be noted that n can also be the subframe ID of the subframe signal. The subframe ID is also one of the unique identifiers of the subframe signal. The applicable unique identifier can be selected according to the actual situation. In the embodiment of this application, only the unique identifier of the subframe signal is used as the time index as an example for illustration, but this application does not specifically limit the type of unique identifier of the subframe signal.

[0061] Among them, F n For the frequency offset estimate of the subframe signal corresponding to time index n, the initialization parameter F is set n =F0=F initial , that is, the frequency offset estimation value corresponding to the first subframe signal received by the terminal device is F0, F0=F initial , the F initial The standard frequency deviation value is set according to the frequency difference between the transmitting and receiving ends of the signal.

[0062] Specifically, the terminal device first sets the time index of the first subframe signal currently received to n=0, and the corresponding F0 is the frequency offset estimation value corresponding to the first subframe signal currently received.

[0063] S202: When the terminal device receives three consecutive sub-frame signals for the first time, it extracts and stores valid time slot data from the three sub-frame signals.

[0064] The valid time slot data is the data carried by the signal in the valid time slot in the subframe signal.

[0065] Specifically, the terminal device receives three consecutive subframe signals for the first time, and the corresponding time indexes are n, n+1, and n+2, respectively, where n=0, that is, the time indexes of the first reception of three consecutive subframe signals are 0, 1, and 2, respectively; the valid time slot data of the first reception of three consecutive subframe signals are extracted to obtain the valid time slot data corresponding to the three subframe signals, and the valid time slot data corresponding to the three subframe signals are represented by FID0, FID1, and FID2, respectively.

[0066] The effective time slot data of three consecutive subframe signals are extracted, and the noise data in the subframe signals are removed, so as to obtain only the effective time slot data of the subframe signals, thereby avoiding the influence of subsequent noise data on the accuracy of frequency offset estimation.

[0067] Furthermore, valid time slot data FID0, FID1, and FID2 of three consecutive subframe signals received for the first time are stored.

[0068] S203 : The terminal device performs a fourth power operation on the valid time slot data in the three sub-frame signals respectively to obtain fourth power data corresponding to the three sub-frame signals.

[0069] The fourth power data is a calculation result obtained by performing a fourth power calculation on the valid time slot data.

[0070] The purpose of performing the fourth power operation on the effective time slot data is to eliminate the modulation information, thereby extracting the phase information in the effective time slot data, so as to facilitate the subsequent frequency offset estimation.

[0071] It should be noted that, in general, the signal modulation and demodulation method in satellite communications is generally orthogonal phase shift keying (Quadrature Phase Shift Keying, QPSK), which is a quaternary phase modulation and demodulation method, so in order to eliminate the modulation, the effective time slot data is subjected to a fourth power operation. In addition, the signal modulation and demodulation method in satellite communications can also be binary phase shift keying (Binary Phase Shift Keying, BPSK), which is a binary phase modulation and demodulation method, so in order to eliminate the modulation, the effective time slot data is subjected to a quadratic operation. In the embodiment of the present application, the modulation and demodulation method is described as QPSK as an example, and this application does not make any specific limitations.

[0072] Specifically, when the terminal device receives three consecutive subframe signals for the first time, it performs a fourth power operation on FID0, FID1, and FID2 to obtain the corresponding fourth power data.

[0073] S204 , the terminal device groups the fourth power data corresponding to the three sub-frame signals into two groups, and adds 0 to each group of fourth power data to obtain two groups of sequences corresponding to the three sub-frame signals.

[0074] The length of the added zeros is the interval slot length, where interval slot length = one subframe signal length - effective slot length. Specifically, the zeros added to each set of quartic data form an all-0 sequence. An all-0 sequence is a sequence consisting entirely of zeros, and its length is the difference between one subframe signal length and the effective slot length.

[0075] Specifically, when the terminal device receives three consecutive subframe signals for the first time, Group them in pairs according to the order of time index, and get and Two sets of data. and Add 0 to the two sets of fourth power data to get two sets of sequences respectively. and in It represents a sequence of all zeros consisting of 0s added to each set of fourth power data.

[0076] In order to facilitate the understanding of the length of adding 0 in the middle of each set of fourth power data, the following is combined Figure 3 Give an example.

[0077] Assume that the subframe signal A with time index 1 and the subframe signal B with time index 2 include 5 time slots, and the valid time slot is the first time slot in the subframe signal. Then the set of fourth power data corresponding to the subframe signal A and the subframe signal B is Depend on Figure 3 It can be seen that the subframe signal length of subframe signal A and subframe signal B is 5 time slots, and the effective time slot length of subframe signal A and subframe signal B is 1 effective time slot, then the interval time slot length = subframe signal length (5 time slots) - effective time slot length (1 time slot) = 4 time slots, then the length of adding 0 is 4 time slots, then Add 4 time slots of length 0 to get the corresponding sequence:

[0078] S205: The terminal device performs fast Fourier transform operations on the two groups of sequences corresponding to the three subframe signals to obtain frequency offset estimation values ​​corresponding to the two groups of sequences.

[0079] The Fast Fourier Transform (FFT) is an efficient algorithm for calculating the Discrete Fourier Transform (DFT). The FFT solves complex computational problems by breaking the DFT down into smaller subproblems, achieving a higher speed than directly calculating the DFT.

[0080] Specifically, when the terminal device receives three consecutive sub-frame signals for the first time, the two groups of sequences corresponding to the three sub-frame signals are and Perform FFT operations respectively to obtain the spectrum peaks corresponding to the two groups of sequences; perform frequency offset estimation based on the spectrum peaks corresponding to the two groups of sequences to obtain the frequency offset estimation values ​​f1 and f2 corresponding to the two groups of sequences. The subscript of the frequency offset estimation value f can be simply used to indicate which group of sequences the frequency offset estimation value corresponds to. That is, according to the order of receiving the subframe signal (time order), the sequence For the first group of sequences, the corresponding frequency offset estimate can be represented by f1, and the sequence For the second group of sequences, the corresponding frequency offset estimation value can be represented by f2.

[0081] Since the frequency offset change rate in satellite communications is relatively high (approximately 300 Hz / s), the time intervals between the effective time slots in the three subframe signals result in different frequency offsets, which can even differ significantly. Therefore, the two frequency offset estimates f1 and f2 obtained by the spectrum peaks corresponding to the two sets of sequences can only represent the frequency offset values ​​at the middle position of the two sets of sequences. The specific reasons are as follows:

[0082] In wireless communications (especially satellite communications), terminal devices have the same sampling frequency, or sampling period. Furthermore, each subframe signal contains the same number of time slots, each time slot lasts the same amount of time, and the intervals between valid time slots in adjacent subframe signals are the same, meaning the number of time slots between valid time slots in adjacent subframe signals is the same. Because the intervals between valid time slots are the same, the spectrum distribution obtained by performing a fast Fourier transform on each sequence is periodic, with the spectrum peak generally located in the middle.

[0083] For ease of understanding, the following describes in detail the calculation process of obtaining the spectrum peak corresponding to the sequence by combining formula (1) and formula (2). Take a set of sequences for example to perform fast Fourier transform calculations and obtain the corresponding spectrum peak.

[0084] The input sequence z(m) is FFT-ed to Z(k), and its calculation expression is shown in formula (1). Where z(m) is a sequence with a total length of M, that is, z(m) is an M-point sequence. For example: When is an M-point sequence.

[0085]

[0086] Where m = 0, 1, ..., M-1, z(m) is the m+1th data in the sequence, which may be the fourth power of the valid time slot signal or 0. For example: And when m=0, k represents the number of spectral points after fast Fourier transformation. For an M-point sequence z(m), k = 0, 1, ..., M-1.

[0087] When the sequence z(m) is subjected to FFT operation, the resulting Z(k) is a complex sequence of length M. The real and imaginary parts of Z(k) represent the amplitudes of the sine and cosine components of z(m) at the kth spectrum point, respectively, which can represent the spectrum of the kth spectrum point. After obtaining the FFT operation result Z(k) corresponding to the sequence z(m), the frequency offset estimation value f corresponding to the sequence z(m) is obtained based on Z(k). d , its calculation expression is shown in formula (2)

[0088]

[0089] Among them, f d The frequency offset estimation value corresponding to the number sequence z(m) is obtained by the FFT spectrum peak, and d is used to indicate that the sequence is the dth sequence in the two groups of sequences. For example, the time indexes of three consecutive subframe signals are 0, 1, and 2 respectively, then the sequence is the first sequence in the two sequences, that is, d = 1, and the sequence It is defined as the second sequence in the two sequences, that is, d = 2. M is the total number of symbols in the sequence z(m), which can also be understood as the number of time slots contained in the sequence z(m). s The duration of one symbol can also be understood as the duration of one time slot. Since the fourth-order nonlinear operation is performed on the valid time slot signal in S203, the phase information of the signal is amplified by 4 times. Therefore, when calculating the frequency offset estimate corresponding to z(m), the numerical value needs to be scaled to obtain a frequency offset estimate with the correct multiple.

[0090] S206. The terminal device calculates the frequency offset estimation values ​​of the three subframe signals based on the frequency offset estimation values ​​corresponding to the two groups of sequences.

[0091] When the terminal device receives three consecutive subframe signals for the first time, it calculates the frequency offset estimation values ​​of the three subframe signals based on the frequency offset estimation values ​​corresponding to the two groups of sequences corresponding to the three subframe signals, and represents them by F0, F1, and F2 respectively.

[0092] Specifically, the two groups of sequences corresponding to the three subframe signals are and The frequency offset estimates corresponding to the two sequences are f1 and f2, respectively. Since each subframe signal includes the same number of time slots, each time slot lasts the same amount of time, and the effective time slots are located in the same position within the subframe signal (i.e., the time intervals between effective time slots in adjacent subframe signals are the same), F1 = (f1 + f2) / 2, and f2 = (F1 + F2) / 2. Solving these two equations yields F2 = 1.5f2 - 0.5f1.

[0093] In a possible implementation, for the subframe signal with a time index of 0 (ie, the first subframe signal received by the terminal device), the subframe signal with a time index of 0 is set during initialization, ie, F0=F initial For a subframe signal with a time index of 1, F2 = (f1 + f2) / 2. For a subframe signal with a time index of 2, F2 = 1.5f2 - 0.5f1.

[0094] In another possible implementation, for the subframe signal with a time index of 0 (ie, the first subframe signal received by the terminal device), the subframe signal with a time index of 0 is set during initialization, ie, F0=F initial For the subframe signal with a time index of 1 and the subframe signal with a time index of 2, F1 = F2 = 1.5f2 - 0.5f1.

[0095] S207: The terminal device performs frequency offset compensation on the three subframe signals based on the frequency offset estimation values ​​of the three subframe signals.

[0096] Based on the frequency offset estimation value of the current subframe signal, the frequency offset compensation is performed on the current subframe signal to eliminate the frequency offset between the signal received by the terminal device and the signal sent due to the Doppler effect, clock deviation, etc., so as to achieve clock synchronization. In a possible implementation, when the terminal device receives three consecutive subframe signals for the first time, that is, the subframe signals corresponding to time indexes 0, 1, and 2 respectively. At this time, by setting the initialization parameter F0=F initial Frequency offset compensation is performed on the subframe signal with time index 0, and frequency offset compensation is performed on the subframe signals with time indexes 1 and 2 respectively through F1=F2=1.5f2-0.5f1, so that the entire frequency offset compensation process is implemented through a logical process.

[0097] In another possible implementation, when the terminal device receives three consecutive subframe signals for the first time, that is, the subframe signals corresponding to time indexes 0, 1, and 2, respectively. initialThe subframe signal with time index 0 is frequency offset compensated, the subframe signal with time index 1 is frequency offset compensated by F1=(f1+f2) / 2, and the subframe signal with time index 2 is frequency offset compensated by F2.

[0098] S208. The terminal device performs frequency offset compensation of the phase-locked loop based on the frequency offset estimation values ​​of the three subframe signals.

[0099] Specifically, while performing frequency offset compensation for the subframe signal, the terminal device calculates the frequency offset compensation value of the phase-locked loop (PPL) based on the frequency offset estimation values ​​of the three subframe signals, and adjusts the frequency of the terminal device's oscillator based on the frequency offset compensation value of the phase-locked loop to achieve frequency offset compensation of the phase-locked loop, thereby eliminating or reducing the frequency offset as much as possible.

[0100] A phase-locked loop (PPL) is a feedback control system consisting of a phase detector, a low-pass filter, and a voltage-controlled oscillator (VCO). After frequency offset compensation is performed on the subframe signal, the frequency of the PPL's ​​oscillator must also be compensated accordingly to minimize the frequency offset between the PPL's ​​input and output signals, thereby more accurately tracking the input signal's frequency variations.

[0101] Specifically, the phase-locked loop frequency offset compensation value is obtained by formula (3):

[0102]

[0103] Among them, F pll is the frequency offset compensation value of the phase-locked loop, F i is the frequency offset estimation value of the subframe signal with time index i. For example, when three consecutive subframe signals are received for the first time, n=0, then F pll =F0+F1+F2.

[0104] S209. The terminal device iterates n=n+1 and receives a subframe signal with a time index of n+2.

[0105] Specifically, after the terminal device completes frequency offset compensation for the subframe signal and the phase-locked loop, it needs to continue frequency offset estimation and frequency offset compensation for the next subframe signal. At this time, the terminal device iterates n = n + 1 and continues to receive the subframe signal with a time index of n = 2. For example: After the terminal device completes frequency offset compensation for the first three consecutive subframe signals received and the corresponding frequency offset compensation for the phase-locked loop, it iterates n = 0 + 1 = 1 and receives the subframe signal with a time index of 3, that is, the terminal device receives the fourth subframe signal.

[0106] S210. The terminal device extracts the valid time slot data of the subframe signal with time index n+2, and obtains the valid time slot data of the subframe signals with time indexes n and n+1, to obtain the valid time slot data of three consecutive subframe signals.

[0107] Specifically, the terminal device extracts the valid time slot data of the subframe signal with time index n+2, and stores the valid time slot data with time index n+2. And obtains the valid time slot data of the subframe signal with time index n and n+2 in the storage of the terminal device, and obtains the valid time slot data of three consecutive subframe signals. The valid time slot data of the three consecutive subframe signals is stored by FID. n 、FID n+1 、FID n+2 To express.

[0108] It should be noted that the three consecutive subframe signals corresponding to the subframe signal with a time index of n+2 are subframe signals with time indexes of n, n+1, and n+2.

[0109] Exemplarily, the terminal device iterates n=0+1=1. After the terminal device receives the subframe signal with a time index of 3, it extracts the valid time slot data of the subframe signal with a time index of 3, and stores the valid time slot data of the subframe signal with a time index of 3. And the valid time slot data of the subframe signals with time indexes of 1 and 2 are obtained in the storage of the terminal device to obtain the valid time slot data of three consecutive subframe signals. It should be noted that the valid time slot data of the subframe signals with time indexes of 1 and 2 are obtained when the three consecutive subframe signals (subframe signals with time indexes of 0, 1, and 2) are received for the first time, and the valid time slot data of the subframe signals with time indexes of 0, 1, and 2 are extracted and stored. Therefore, the valid time slot data of the subframe signals with time indexes of 1 and 2 have been stored in the terminal device.

[0110] S211. The terminal device performs a fourth power operation on the valid time slot data of the three consecutive sub-frame signals respectively to obtain the fourth power data corresponding to the three consecutive sub-frame signals.

[0111] Specifically, the terminal equipment respectively n 、FID n+1 、FID n+2 Perform a fourth power operation to obtain the corresponding fourth power data

[0112] S212: The terminal device groups the fourth power data corresponding to the three consecutive sub-frame signals into two groups, and adds 0 to each group of fourth power data to obtain two groups of sequences corresponding to the three consecutive sub-frame signals.

[0113] Specifically, the terminal device will Group them in pairs according to the order of time index and get and Two sets of sequences. Add 0 in the middle of each set of fourth power data to obtain two sets of sequences corresponding to three consecutive subframe signals. and To express.

[0114] S213: The terminal device performs fast Fourier transform operations on the two groups of sequences corresponding to the three consecutive subframe signals to obtain frequency offset estimation values ​​corresponding to the two groups of sequences.

[0115] Specifically, the two groups of sequences corresponding to the three subframe signals and Perform FFT operations respectively to obtain the spectrum peaks corresponding to the two groups of sequences; perform frequency offset estimation based on the spectrum peaks corresponding to the two groups of data to obtain the frequency offset estimation values ​​f1 and f2 corresponding to the two groups of sequences. The subscript of the frequency offset estimation value f can be simply used to indicate which group of sequences the frequency offset estimation value corresponds to. For example, the two groups of sequences corresponding to three consecutive subframe signals are and According to the order of receiving subframe signals (time sequence), the sequence For the second group of sequences, the corresponding frequency offset estimation value can be obtained by f2.

[0116] S214. The terminal device calculates a frequency offset estimation value of the subframe signal with a time index of n+2 based on the frequency offset estimation values ​​corresponding to the two groups of sequences.

[0117] When the terminal device receives three consecutive subframe signals for the non-first time, the three consecutive subframe signals are subframe signals with time indexes n, n+1, and n+2. The subframe signals with time indexes n and n+1 have already completed frequency offset compensation. For example: n=1, three consecutive subframe signals are subframe signals with time indexes 1, 2, and 3. The subframe signals with time indexes 1 and 2 have already completed frequency offset compensation in S201-S208, and there is no need to perform frequency offset compensation on the subframe signals with time indexes 1 and 2. Therefore, there is no need to calculate the frequency offset estimation value of the subframe signals with time indexes 1 and 2.

[0118] Specifically, two sets of sequences and The frequency offset estimation values ​​f1 and f2 correspond to each other, and the frequency offset estimation value of the effective time slot signal corresponding to the subframe signal with time index n+1 is F n+1 The frequency offset estimation value corresponding to the subframe signal with time index n+2 is expressed as F n+2Since each subframe signal includes the same number of time slots, each time slot lasts the same amount of time, and the time intervals between valid time slots in adjacent subframe signals are the same, F n+1 =(f1+f2) / 2, and f2=(F n+1 +F n+2 ) / 2, according to the above two equations, we can get F n+2 =1.5f2-0.5f1.

[0119] The frequency offset estimation value of the current subframe signal is calculated by the frequency offset estimation value corresponding to the two sets of sequences, that is, the frequency offset estimation value of the current subframe signal is jointly calculated by three consecutive subframe signals. Compared with the current technology that only relies on the local limited synchronization sequence or the data of the single subframe signal itself, the embodiment of the present application has more prior information for frequency offset estimation, which can improve the accuracy of frequency offset estimation to a certain extent. Further, according to the peak value of the fast Fourier transform of the sequence, after obtaining the frequency offset estimation value of the middle position (middle position in the time domain) in the sequence, the frequency offset estimation value of the current subframe signal is obtained by the differential algorithm based on the frequency offset estimation value of the two sequences corresponding to the three consecutive subframe signals. The frequency offset change rate during the signal transmission process is fully considered, thereby avoiding the error of the frequency offset estimation caused by the frequency offset change rate to a certain extent, and improving the accuracy of the frequency offset estimation of the subframe signal. And the frequency offset estimation value of the current subframe signal is obtained by the differential algorithm, which can reduce the error generated in the process of calculating the frequency offset estimation value to a certain extent.

[0120] S215. The terminal device performs frequency offset compensation on the subframe signal with a time index of n+2 based on the frequency offset estimation value of the subframe signal with a time index of n+2.

[0121] Exemplarily, when the terminal device receives three consecutive subframe signals for the first time and n=2, the terminal device performs frequency offset compensation on the subframe signal with time index 4 based on the frequency offset estimation value F4 of the subframe signal with time index 4. The three consecutive subframe signals corresponding to the subframe signal with time index 4 are subframe signals with time indexes 2, 3, and 4. The subframe signals with time index 2 and time index 3 have already been frequency offset compensated, so there is no need to perform frequency offset compensation on the signals with time index 2 and time index 3 in this step. It should be noted that the frequency offset compensation for the subframe signal with time index 2 is achieved based on the three subframe signals with time indexes 0, 1, and 2, that is, based on the corresponding two groups of sequences. and The frequency offset estimation values ​​f1 and f2 of the subframe signal with time index 2 are used to obtain the frequency offset estimation value F2, and the frequency offset compensation is performed on the subframe signal with time index 2; similarly, the frequency offset compensation is achieved based on the three subframe signals with time indexes 1, 2, and 3 when the subframe signal with time index 3 is used. That is, based on the corresponding two groups of sequences and The frequency offset estimation values ​​f1 and f2 are used to obtain the frequency offset estimation value F3 of the subframe signal with time index 3, and frequency offset compensation is performed on the subframe signal with time index 3.

[0122] S216. The terminal device performs frequency offset compensation of the phase-locked loop based on the frequency offset estimation values ​​of all received subframe signals.

[0123] Specifically, while the terminal device is performing frequency offset compensation for the subframe signal with time index n+2, it calculates the frequency offset compensation value of the phase-locked loop based on the frequency offset estimation values ​​of all received subframe signals, and adjusts the frequency of the terminal device's oscillator based on the frequency offset compensation value of the phase-locked loop to achieve frequency offset compensation of the phase-locked loop.

[0124] After completing S216, the terminal device iterates n=n=1, that is, loops through S209-S216 until the terminal device no longer receives a subframe signal and stops looping.

[0125] The above combination Figure 2 and Figure 3 A frequency offset estimation method provided by an embodiment of the present application is described in detail. Figure 4 An example is given to introduce a frequency offset estimation method provided in an embodiment of the present application. The cycle of the frequency offset estimation method is described starting from the first time the terminal device receives three consecutive subframe signals, and the setting of the initialization parameters is completed, that is, setting n = 0 and F0 = F initial Each subframe signal includes 5 time slots, and the first time slot of each subframe signal is a valid time slot.

[0126] like Figure 4 As shown in (a), the terminal device receives three consecutive subframe signals for the first time. The time indexes of the three subframe signals are 0, 1 and 2 respectively. For the convenience of description, the three consecutive subframe signals are represented by S0, S1 and S2. The valid time slot data in S0, S1 and S2 are extracted to obtain FID0, FID1 and FID2. The valid time slot data FID0, FID1 and FID2 are subjected to the fourth power operation to obtain the fourth power data corresponding to the three subframe signals. The fourth power data corresponding to the three sub-frame signals are grouped in pairs to obtain two groups of data and Based on the interval time slot length between the effective time slot of S0 and the effective time slot of S1, Add 0 in the middle to get the corresponding first set of sequences Based on the interval time slot length between the effective time slot of S1 and the effective time slot of S2, Add 0 in the middle to get the corresponding second set of sequences right and The two sets of sequences are subjected to fast Fourier transform operations respectively to obtain the first set of sequences The corresponding frequency offset estimate f1 and the second set of sequences The corresponding frequency offset estimation value f2; Based on the frequency offset estimation values ​​f1 and f2 corresponding to the two sets of sequences, calculate the frequency offset estimation value F1 = (f1 + f2) / 2 corresponding to S1, and the frequency offset estimation value F2 = 1.5f2 - 0.5f1 corresponding to S2; Based on the frequency offset estimation value F1 corresponding to S1, frequency offset compensation is performed on S1, and based on the frequency offset estimation value F2 corresponding to S2, frequency offset compensation is performed on S2. Complete as Figure 4 The frequency offset compensation of (a) in the figure is performed, and the step is n=n+1, that is, n=1, then the valid time slot data of the subframe signal with time index n+2 is obtained, as shown in the following example: Figure 4 As shown in (b) in .

[0127] like Figure 4 As shown in (b) of FIG, the three consecutive subframe signals for jointly calculating the frequency offset estimation value are: subframe signals with time indexes 1, 2, and 3, which are represented by S1, S2, and S3, because Figure 4 In the process shown in (a), the valid time slot data corresponding to S1 and S2 have been extracted and are FID1 and FID2, then the valid time slot data FID3 corresponding to S3 is obtained; the valid time slot data FID1, FID2, and FID3 are subjected to a fourth power operation to obtain the fourth power data corresponding to the three subframe signals. The fourth power data corresponding to the three sub-frame signals are grouped in pairs to obtain two groups of data and Based on the interval time slot length between the effective time slot of S1 and the effective time slot of S2, Add 0 in the middle to get the corresponding first set of sequences Based on the interval time slot length between the effective time slot of S2 and the effective time slot of S3, Add 0 in the middle to get the corresponding second set of sequences right and The two sets of sequences are subjected to fast Fourier transform operations respectively to obtain the first set of sequences The corresponding frequency offset estimate f1 and the second set of sequences The corresponding frequency offset estimation value f2; according to the frequency offset estimation values ​​f1 and f2 corresponding to the two groups of sequences, calculate the frequency offset estimation value F3 corresponding to S3 = 1.5f2-0.5f1; based on the frequency offset estimation value F3 corresponding to S3, frequency offset compensation is performed on S3. It should be noted that since three consecutive subframe signals are received for the first time, frequency offset compensation needs to be performed on all three subframe signals; for the case where three consecutive subframe signals are not received for the first time, the frequency offset compensation has been completed for the first two subframe signals of the three subframe signals, so the frequency offset estimation value of the current subframe signal (the third subframe signal of the three subframe signals) obtained based on the combination of the three subframe signals can be used to perform frequency offset compensation on the current subframe signal. Complete as shown below. Figure 4 The frequency offset compensation of the subframe signal (current subframe signal) shown in (b) is performed, and the step is n=n+1, that is, n=2, and the valid time slot data of the subframe signal with time index n+2 is obtained. Specifically, Figure 4 As shown in (c) in .

[0128] like Figure 4 As shown in (c) in the figure, the three consecutive subframe signals for the joint calculation of the frequency offset estimation value are: the subframe signals with time indexes 2, 3, and 4 are represented by S2, S3, and S4, and the valid time slot data FID4 corresponding to S4 is obtained; the valid time slot data FID2, FID3, and FID4 are subjected to a fourth power operation to obtain the fourth power data corresponding to the three subframe signals. The fourth power data corresponding to the three sub-frame signals are grouped in pairs to obtain two groups of data and Based on the interval time slot length between the effective time slot of S2 and the effective time slot of S3, Add 0 in the middle to get the corresponding first set of sequences Based on the interval time slot length between the effective time slot of S3 and the effective time slot of S4, Add 0 to get the corresponding second set of sequences right and The two sets of sequences are subjected to fast Fourier transform operations respectively to obtain the first set of sequences The corresponding frequency offset estimate f1 and the second set of sequences The corresponding frequency offset estimation value f2; according to the frequency offset estimation values ​​f1 and f2 corresponding to the two sets of sequences, the frequency offset estimation value F4 corresponding to S4 is calculated = 1.5f2-0.5f1; based on the frequency offset estimation value F4 corresponding to S4, the frequency offset compensation of S4 is performed. Figure 4The frequency offset compensation of the subframe signal (current subframe signal) shown in (c) is performed, and stepping n=n+1, that is, n=3, then the valid time slot data of the next subframe signal is obtained, and the frequency offset estimation is continued. Figure 4 Furthermore, when frequency offset compensation is performed on the received subframe signal, frequency offset compensation is also performed on the oscillator of the phase-locked loop.

[0129] An embodiment of the present application provides a frequency offset estimation method that jointly calculates a frequency offset estimate of a subframe signal received by a terminal device using valid time slot data from three consecutive subframe signals. The frequency offset estimation method provided by the embodiment of the present application is a non-data-assisted frequency offset estimation method that can improve the accuracy of frequency offset estimation compared to data-assisted frequency offset estimation methods. Furthermore, the valid time slot data of the subframe signal is extracted, which, compared to non-data-assisted frequency offset estimation methods in the current technology, avoids the impact of noise data in the subframe signal on the accuracy of frequency offset estimation. However, since only valid time slot data is extracted in the embodiment of the present application, the prior information is reduced compared to non-data-assisted frequency offset estimation methods in the current technology. Therefore, by combining the valid time slot data of the three subframe signals, the prior information for frequency offset estimation is increased, that is, more valid prior information is relied upon compared to the current technology, which improves the accuracy of frequency offset estimation to a certain extent, reduces the error in frequency offset estimation, and avoids frequency offset estimation failure, thereby ensuring that frequency offset compensation can be effectively performed, so that coherent demodulation of the signal can be correctly achieved later.

[0130] Furthermore, the frequency offset estimation value of the current subframe signal is jointly calculated by three consecutive subframe signals, which also takes into account the large frequency offset change rate of the satellite communication system, and to a certain extent avoids the poor frequency offset estimation accuracy caused by the large frequency offset change rate.

[0131] Example 2:

[0132] The following combination Figure 5 , a frequency offset estimation method provided by an embodiment of the present application is described in detail. Figure 5 As shown, the method includes the following steps:

[0133] S501: Acquire first time slot data in M ​​consecutive subframe signals, and perform modulation information removal on the first time slot data in the M subframe signals to obtain spectrum data corresponding to the first time slot data in the M subframe signals.

[0134] Wherein, M is an integer not less than 3. For example, M can be 3, 4, 5, etc., which is not specifically limited in this application.

[0135] Among them, the subframe signal is a signal received by the terminal device that has completed time synchronization.

[0136] In one possible implementation, a method for removing modulation information from the first time slot data in the M subframe signals is determined based on the modulation mode of the subframe signals. For example, when the modulation mode of the subframe signals is QPSK, a fourth power operation is performed on the first time slot data in the M subframe signals to remove the modulation information.

[0137] In one possible implementation, the first time slot may be a valid time slot. Because current non-data-assisted frequency offset estimation methods often introduce significant noise into the first time slot data due to a low signal-to-noise ratio, thereby affecting the accuracy of frequency offset estimation, embodiments of the present application can extract valid time slot data, thereby avoiding the impact of noise on the accuracy of frequency offset estimation and further improving the accuracy of frequency offset estimation.

[0138] There are two cases for obtaining the first time slot data of M consecutive subframe signals, which are described below:

[0139] When first time slot data in M ​​consecutive subframe signals is acquired for the first time, specifically, M subframe signals are continuously received, and the first time slot data in the M consecutive subframe signals are extracted to acquire the first time slot data in the M consecutive subframe signals. Further, the first time slot data in the M consecutive subframe signals is stored.

[0140] When the first time slot data of M consecutive subframe signals is not acquired for the first time, specifically, the first subframe signal is received, and the first subframe signal is the Mth subframe signal among the M subframe signals; the first time slot data of the first subframe signal to the Nth subframe signal among the M subframe signals is acquired to acquire the first time slot data of the M consecutive subframe signals. Further, the first time slot data in the first subframe signal is stored. Where N = M-1.

[0141] S502 : Group the spectrum data corresponding to the first time slot data in the M sub-frame signals into groups of two according to the receiving time sequence of the M sub-frame signals, and add a preset sequence to each group of spectrum data to obtain N groups of sequences corresponding to the M sub-frame signals.

[0142] Wherein, N=M-1, that is, N is an integer not less than 2.

[0143] The length of the preset sequence is the difference between the length of a subframe signal and the length of the first time slot. In a possible implementation, the preset sequence may be an all-0 sequence.

[0144] S503: Process N groups of sequences to obtain frequency offset estimation values ​​corresponding to the N groups of sequences.

[0145] Specifically, fast Fourier transform operations are performed on N groups of sequences respectively to obtain frequency offset estimation values ​​corresponding to the N groups of sequences.

[0146] S504: Calculate frequency offset estimation values ​​of M subframe signals based on the frequency offset estimation values ​​corresponding to the N groups of sequences.

[0147] When M consecutive subframe signals are first received, a constant (i.e., a standard frequency offset value) is used as a frequency offset estimate for the first subframe signal in the M subframe signals; an average of the frequency offset estimates for the first and second groups of N sequences is calculated to obtain a frequency offset estimate for the second subframe signal in the M subframe signals; and a frequency offset estimate for the yth subframe signal in the M subframe signals is calculated based on the frequency offset estimate for the xth sequence in the N groups of sequences and the frequency offset estimate for the xth subframe signal in the M subframe signals to obtain frequency offset estimates for the third subframe signal to the Mth subframe signal in the M subframe signals. y is an integer not less than 3 and not greater than M, and x=y-1.

[0148] For example, let M=3, N=2, and let the frequency offset estimation values ​​of the three subframe signals be F a 、F b 、F c The frequency offset estimates corresponding to the two sequences are represented by f1 and f2. a = constant (standard frequency deviation value); F b =(f1+f2) / 2; by (F b +F c ) / 2=f2, we can see that F c =2f2-F b , that is, x=2, y=3, based on the frequency offset estimation value f2 of the second group of sequences and the frequency offset estimation value of the second subframe signal, the frequency offset estimation value of the third subframe signal is calculated.

[0149] When M consecutive subframe signals are not received for the first time, the frequency offset estimation value of the Mth subframe signal among the M subframe signals is calculated based on the frequency offset estimation value of the Nth group of sequences among the N groups of sequences and the frequency offset estimation value of the Nth subframe signal among the M subframe signals.

[0150] S505 : Perform frequency offset compensation on the M subframe signals based on the frequency offset estimation values ​​of the M subframe signals.

[0151] When first time slot data of M consecutive subframe signals is acquired for the first time, in one possible implementation, frequency offset compensation is performed on the M subframe signals using the frequency offset estimation values ​​of the M subframe signals in a one-to-one correspondence manner. For example, the frequency offset estimation value of the first subframe signal is used to compensate for the first subframe signal; the frequency offset estimation value of the second subframe signal is used to compensate for the second subframe signal; and so on, frequency offset compensation is performed on the Mth subframe signal using the frequency offset estimation value of the Mth subframe signal.

[0152] When first acquiring the first time slot data of M consecutive subframe signals, in another possible implementation, frequency offset compensation is performed on the first subframe signal among the M subframe signals using the frequency offset estimate of the first subframe signal; and frequency offset compensation is performed on the second through M subframe signals among the M subframe signals using the frequency offset estimate of the Mth subframe signal. That is, frequency offset compensation is performed on the first subframe signal based on a (constant), and frequency offset compensation is performed on the remaining subframe signals based on the frequency offset estimate of the Mth subframe signal. This effectively implements frequency offset compensation while simplifying the complexity of the frequency offset compensation steps.

[0153] When the first time slot data of M consecutive subframe signals is not acquired for the first time, the frequency offset estimation value of the Mth subframe signal is used to perform frequency offset compensation on the Mth subframe signal, because the frequency offset compensation has been completed for the remaining subframe signals.

[0154] Furthermore, in one possible implementation, after performing S504, the method further includes: calculating a frequency offset compensation value for a phase-locked loop (PLL) by summing the known frequency offset estimates of all subframe signals; and adjusting the frequency of an oscillator of the PLL based on the frequency offset compensation value of the PLL to achieve frequency offset compensation for the PLL. As the accuracy of the frequency offset estimation of the subframe signals is improved, the accuracy of the frequency offset compensation value of the PLL calculated based on the frequency offset estimate of the subframe signals is also improved, thereby enabling more efficient frequency offset compensation for the PLL.

[0155] An embodiment of the present application provides a frequency offset estimation method, including: obtaining the first time slot data in M ​​consecutive subframe signals, and performing modulation information elimination on the first time slot data in the M subframe signals to obtain spectrum data corresponding to the first time slot data in the M subframe signals; grouping the spectrum data corresponding to the first time slot data in the M subframe signals in pairs according to the receiving time sequence of the M subframe signals, and adding a preset sequence to each group of spectrum data to obtain N groups of sequences corresponding to the M subframe signals; processing the N groups of sequences to obtain frequency offset estimation values ​​corresponding to the N groups of sequences; calculating the frequency offset estimation values ​​of the M subframe signals based on the frequency offset estimation values ​​corresponding to the N groups of sequences; and performing frequency offset compensation on the M subframe signals based on the frequency offset estimation values ​​of the M subframe signals. Specifically, frequency offset compensation can be performed on all M subframe signals, or on part of the M subframe signals. The frequency offset estimation values ​​of the subframe signals are jointly calculated using the first time slot data of multiple subframe signals. The present application calculates the frequency offset estimate of the subframe signal based on the first time slot data of the subframe signal itself. Compared with the frequency offset estimate obtained by the current technology based only on a known synchronization sequence, the frequency offset estimate is more accurate. Moreover, based on the first time slot data of multiple subframe signals, the frequency offset estimate relies on more prior information, which improves the accuracy of the frequency offset estimate to a certain extent, thereby effectively achieving frequency offset compensation so that the coherent demodulation of the signal can be correctly achieved later. Furthermore, by jointly calculating the frequency offset estimate of the subframe signal through multiple subframe signals, the large frequency offset change rate in satellite communications is also taken into account, which to a certain extent avoids the situation where the frequency offset estimate is inaccurate due to the large frequency offset change rate.

[0156] In addition, the present application provides a terminal device. In some embodiments, the terminal device may be a mobile phone, tablet computer, desktop, laptop, notebook computer, ultra-mobile personal computer (UMPC), handheld computer, netbook, personal digital assistant (PDA), wearable terminal device, smart watch and other devices. The present application does not impose any special restrictions on the specific form of the above terminal devices. In this embodiment, the structure of the terminal device can be as follows: Figure 6 shown.

[0157] like Figure 6 As shown, the terminal device may include a processor 610, an internal memory 620, an antenna 1, an antenna 2, a mobile communication module 630, a wireless communication module 640, and the like.

[0158] The processor 610 may include one or more processing units, for example: the processor 610 may include an application processor (AP), a modem processor, an image signal processor (ISP), a controller, a video codec, a digital signal processor (DSP), a baseband processor, and / or a neural-network processing unit (NPU), etc.

[0159] The controller can be the nerve center and command center of the terminal device. It can generate operation control signals based on instruction opcodes and timing signals to complete the control of instruction fetching and execution.

[0160] The wireless communication function of the terminal device can be implemented through antenna 1, antenna 2, mobile communication module 630, wireless communication module 640, modem processor and baseband processor.

[0161] The mobile communication module 630 can provide wireless communication solutions including 2G / 3G / 4G / 5G applied on terminal devices.

[0162] The wireless communication module 640 can provide wireless communication solutions for application on terminal devices, including wireless local area networks (WLAN) (such as wireless fidelity (Wi-Fi) networks), Bluetooth (BT), global navigation satellite system (GNSS), frequency modulation (FM), near field communication technology (NFC), infrared technology (IR), etc.

[0163] In some embodiments, antenna 1 of the terminal device is coupled to the mobile communication module 630, and antenna 2 is coupled to the wireless communication module 640, so that the terminal device can communicate with the network and other devices through wireless communication technology.

[0164] This embodiment also provides a computer-readable storage medium, which includes instructions. When the above instructions are executed on a terminal device, the terminal device executes the relevant method steps in the above embodiments to implement the method in the above embodiments.

[0165] This embodiment further provides a computer program product containing instructions. When the computer program product is run on a terminal device, the user terminal executes the relevant method steps in the above embodiment to implement the method in the above embodiment.

[0166] The above is only a specific embodiment of the present application, but the scope of protection of this application is not limited to this. Any changes or substitutions within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A frequency offset estimation method, characterized in that: include: Obtaining first time slot data from M consecutive subframe signals, and performing modulation information removal on the first time slot data from the M subframe signals to obtain spectrum data corresponding to the first time slot data from the M subframe signals, where M is an integer not less than 3; and the subframe signal is a time-synchronized signal received by a terminal device; The first time slot data is data transmitted by the subframe signal in the first time slot; According to the receiving time sequence of the M sub-frame signals, the spectrum data corresponding to the first time slot data in the M sub-frame signals are grouped in pairs, and a preset sequence is added to each group of spectrum data to obtain N groups of sequences corresponding to the M sub-frame signals, where N=M-1; Processing the N groups of sequences to obtain frequency offset estimates corresponding to the N groups of sequences; Calculating frequency offset estimation values ​​of the M subframe signals based on the frequency offset estimation values ​​corresponding to the N groups of sequences; Frequency offset compensation is performed on the M subframe signals based on the frequency offset estimation values ​​of the M subframe signals.

2. The method according to claim 1, characterized in that The length of the preset sequence added to each set of spectrum data is the difference between a subframe signal length and the first time slot length.

3. The method according to claim 1, characterized in that The acquiring first time slot data in M ​​consecutive subframe signals includes: M subframe signals are continuously received, and first time slot data in the M continuously received subframe signals are extracted.

4. The method according to claim 1, wherein The acquiring first time slot data in M ​​consecutive subframe signals includes: receiving a first subframe signal and extracting first time slot data of the first subframe signal; the first subframe signal being the Mth subframe signal among the M subframe signals; Acquire first time slot data of the first subframe signal to the Nth subframe signal among the M subframe signals.

5. The method according to claim 1, wherein The calculating the frequency offset estimation values ​​of the M subframe signals based on the frequency offset estimation values ​​corresponding to the N groups of sequences includes: Using a constant as a frequency offset estimation value of a first subframe signal among the M subframe signals; Calculating an average of frequency offset estimation values ​​of a first group of sequences and a second group of sequences in the N groups of sequences to obtain a frequency offset estimation value of a second subframe signal in the M subframe signals; Based on the frequency offset estimation value of the xth sequence in the N groups of sequences and the frequency offset estimation value of the xth subframe signal in the M subframe signals, the frequency offset estimation value of the yth subframe signal in the M subframe signals is calculated to obtain the frequency offset estimation values ​​from the third subframe signal to the Mth subframe signal in the M subframe signals; y is an integer not less than 3 and not greater than M; x=y-1.

6. The method according to claim 5, characterized in that The performing frequency offset compensation on the M subframe signals based on the frequency offset estimation values ​​of the M subframe signals includes: The frequency offset estimation values ​​of the M sub-frame signals are used to perform frequency offset compensation on the M sub-frame signals in a one-to-one correspondence manner.

7. The method according to claim 5, characterized in that The performing frequency offset compensation on the M subframe signals based on the frequency offset estimation values ​​of the M subframe signals includes: Using the frequency offset estimation value of the first subframe signal, frequency offset compensation is performed on the first subframe signal among the M subframe signals; using the frequency offset estimation value of the Mth subframe signal, frequency offset compensation is performed on the second subframe signal to the Mth subframe signal among the M subframe signals.

8. The method according to claim 1, characterized in that The calculating the frequency offset estimation values ​​of the M subframe signals based on the frequency offset estimation values ​​corresponding to the N groups of sequences includes: The frequency offset estimation value of the Mth subframe signal among the M subframe signals is calculated based on the frequency offset estimation value of the Nth group of sequences among the N groups of sequences and the frequency offset estimation value of the Nth subframe signal among the M subframe signals.

9. The method according to claim 8, characterized in that The performing frequency offset compensation on the M subframe signals based on the frequency offset estimation values ​​of the M subframe signals includes: Frequency offset compensation is performed on the M-th subframe signal using the frequency offset estimation value of the M-th subframe signal.

10. The method according to claim 1, characterized in that After calculating the frequency offset estimation values ​​of the M subframe signals based on the frequency offset estimation values ​​corresponding to the N groups of sequences, the method further includes: Based on the known frequency offset estimation values ​​of all subframe signals, a frequency offset compensation value of the phase-locked loop is calculated by summing up; Based on the frequency offset compensation value of the phase-locked loop, the frequency of the oscillator of the phase-locked loop is adjusted to achieve the frequency offset compensation of the phase-locked loop.

11. The method according to claim 1, wherein The first time slot data includes: effective time slot data; the effective time slot data is data transmitted by the subframe signal in the effective time slot.

12. A terminal device, characterized in that: including processor and memory; The memory stores computer-executable instructions; The processor executes the computer-executable instructions stored in the memory, so that the processor performs the method according to any one of claims 1 to 11.

13. A computer-readable storage medium, characterized in that The computer-readable storage medium stores a computer program or instructions, and when the computer program or instructions are executed, the method according to any one of claims 1 to 11 is implemented.

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