Tracking compensation method and device for satellite channel Doppler frequency shift under low signal-to-noise ratio

Abstract

The invention discloses a tracking compensation method and device for satellite channel Doppler frequency shift under a low signal-to-noise ratio, and the method comprises the steps: firstly, employing a spreading code sequence corresponding to a data signal, and employing a precise estimation mode to estimate a Doppler frequency offset initial value of each frame of data signal; then estimating an inter-frame Doppler frequency offset variable quantity according to the Doppler frequency offset initial value of each frame to compensate the inter-frame Doppler frequency offset variable quantity, estimating the Doppler frequency offset initial value of each frame by using the signal after the inter-frame Doppler frequency offset variable quantity is compensated and adopting an accurate estimation mode, and repeating the steps until the Doppler frequency offset initial value of each frame is obtained. And the algorithm is considered to be convergent until the Doppler frequency offset initial values of two times of precise estimation meet a preset condition. According to the method, Doppler frequency offset can be accurately compensated before spread spectrum de-spreading under the condition of low signal-to-noise ratio, the spread spectrum gain is released, and the decoding precision is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless communication, and in particular relates to a tracking and compensation method and device for Doppler frequency shift of a satellite channel under low signal-to-noise ratio. Background Art

[0002] With the rapid development of wireless communication technology, satellite communication, as a communication method with wide coverage, rich frequency band resources and huge transmission capacity, has rapidly become an important part of today's global communication network. Driven by the increasing demand for human connectivity, the widespread application of satellite communication technology not only provides support in traditional fields such as television broadcasting, meteorological monitoring, and geographic surveying and mapping, but also plays a vital role in many emerging fields such as the Internet of Things, smart cities, military defense, and emergency communications.

[0003] Under this development trend, low-orbit satellite systems have become one of the key research directions. Compared with geosynchronous orbit satellite systems, low-orbit satellites have the advantage of low latency, can achieve faster response speed and higher data transmission efficiency, and are suitable for services with high requirements for latency and bandwidth. However, low-orbit satellite systems also bring new technical challenges, especially in highly dynamic satellite-to-ground and inter-satellite links. The high-speed movement of satellites will cause Doppler frequency deviation, which will interfere with signal transmission. The existence of Doppler frequency deviation not only affects the accurate reception of signals, but also significantly weakens the anti-interference performance of the system.

[0004] Spread spectrum technology, as a modulation technology widely used in satellite communications, can effectively improve the reliability of information transmission and has excellent anti-interference capabilities. However, when the system is in a low signal-to-noise ratio environment, due to the interference of Doppler frequency offset, the spread spectrum gain cannot be fully released, resulting in a significant reduction in the decoding accuracy of the data at the receiving end. Summary of the invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a tracking compensation method and device for Doppler frequency shift of satellite channels under low signal-to-noise ratio. The technical problem to be solved by the present invention is achieved by the following technical solutions:

[0006] The present invention provides a tracking and compensation method for Doppler frequency shift of a satellite channel under low signal-to-noise ratio, which is applied to a spread spectrum system under low signal-to-noise ratio. The method comprises:

[0007] S1, obtaining N frames of data signals sn(m) that require frequency offset compensation, the synchronization header and the spread spectrum code sequence of each frame of data signal;

[0008] S2, based on the spread spectrum code sequence corresponding to the data signal sn(m), estimates the initial value of the Doppler frequency deviation of each frame of data signal

[0009] S3, based on the initial value of the Doppler frequency deviation of each frame of data signal Estimate the inter-frame Doppler frequency deviation variation of each frame of data signal According to the change of Doppler frequency deviation between frames Performing a first frequency offset compensation on the data signal sn(m) to obtain s′n(m);

[0010] S4, replacing sn(m) with s′n(m), and cyclically executing steps S2 and S3 until the initial values ​​of the Doppler frequency offsets of the adjacent times meet the preset conditions, and outputting the initial values ​​of the Doppler frequency offsets and the inter-frame Doppler frequency offset variation that meet the preset conditions as the Doppler frequency offset estimation convergence results;

[0011] S5, performing a second frequency offset compensation on the data signal sn(m) according to the Doppler frequency offset estimation convergence result, to obtain an output signal

[0012] In one embodiment of the present invention, the expression of sn(m) is as follows:

[0013]

[0014] Among them, PN i (m) represents the spreading code sequence, m represents time, j represents the imaginary unit, is the initial phase deviation of the channel, fs represents the sampling rate of the spread spectrum system, Indicates the phase deviation caused by the Doppler frequency deviation corresponding to the n-th frame data signal, Indicates the phase deviation caused by the frequency deviation variation between bits of the nth frame, n i (m) is the channel noise, and U represents the number of bits of the “1” and “0” sequences in the SYN sequence.

[0015] In one embodiment of the present invention, the phase deviation caused by the Doppler frequency deviation corresponding to the n-th frame data signal The expression is as follows:

[0016]

[0017] Among them, f n It represents the frequency deviation of the first bit corresponding to the nth frame data signal, and fs represents the sampling rate of the spread spectrum system.

[0018] In one embodiment of the present invention, the phase deviation caused by the inter-bit frequency deviation variation of the nth frame The expression is as follows:

[0019]

[0020] Wherein, fn+1 represents the frequency deviation of the first bit corresponding to the (n+1)th frame data signal, L represents the length of each frame data signal, and fs represents the sampling rate of the spread spectrum system.

[0021] In one embodiment of the present invention, the S2 comprises:

[0022] S21, according to the preset frequency deviation value Select h different spreading code sequences from all spreading code sequences for correlation calculation, and obtain the corresponding g correlation quantities. According to the relevant quantity corresponding to each preset frequency deviation value Get the average of the preset frequency deviation values Where, h∈[1,U], p∈[1,g], g=U / h, U represents the number of bits of “1” and “0” sequences in the SYN sequence;

[0023] S22, the mean of all The frequency deviation value corresponding to the maximum value in is taken as the initial value of Doppler frequency deviation

[0024]

[0025] In one embodiment of the present invention, the expression of s′n(m) is as follows:

[0026]

[0027] Where m represents time, exp represents the natural exponential function, and j represents the imaginary unit. Indicates the inter-frame Doppler frequency deviation change corresponding to the n-th frame data signal.

[0028] In one embodiment of the present invention, the S4 comprises:

[0029] S41, replace sn(m) with s′n(m), and execute step S2 to obtain the initial value of Doppler frequency deviation

[0030] S42, based on the initial value of Doppler frequency deviation Get the inter-frame Doppler frequency deviation change

[0031] S43, determining whether the initial value of the Doppler frequency deviation meets the preset conditions If the conditions are met, the initial value of the Doppler frequency offset and the change in the Doppler frequency offset between frames that meet the preset conditions are output as the Doppler frequency offset estimation convergence result; if the conditions are not met, the Doppler frequency offset between frames is calculated based on the change in the Doppler frequency offset between frames. Perform a first frequency offset compensation on the data signal sn(m) to obtain s′n′(m), use s′n′(m) to replace sn(m), and execute S2 and S3 repeatedly until the initial values ​​of the Doppler frequency offset of adjacent times meet the preset conditions, and output the initial value of the Doppler frequency offset that meets the preset conditions and the change in the Doppler frequency offset between frames as the Doppler frequency offset estimation convergence result; wherein ε represents the preset threshold.

[0032] In one embodiment of the present invention, the output signal The expression is as follows:

[0033]

[0034] Where m represents time, exp represents the natural exponential function, and j represents the imaginary unit. Indicates the initial value of Doppler frequency deviation that meets the preset conditions, Indicates the inter-frame Doppler frequency deviation change that meets the preset conditions.

[0035] In a second aspect, the present invention provides a tracking and compensating device for Doppler frequency shift of a satellite channel under low signal-to-noise ratio, the device comprising:

[0036] Acquisition module, calculation module and compensation module; wherein,

[0037] The acquisition module is used to acquire N frames of data signals sn(m) that require frequency offset compensation, the synchronization header and the spread spectrum code sequence of each frame of data signal;

[0038] The calculation module is used to estimate the initial value of the Doppler frequency deviation of each frame of data signal according to the spread spectrum code sequence corresponding to the data signal sn(m). According to the initial value of Doppler frequency deviation of each frame data signal Estimate the inter-frame Doppler frequency deviation variation of each frame of data signal According to the change of Doppler frequency deviation between frames Performing a first frequency offset compensation on the data signal sn(m) to obtain s′n(m); replacing sn(m) with s′n(m), cyclically executing the process of obtaining the initial value of the Doppler frequency offset and the change amount of the Doppler frequency offset between frames until the initial value of the Doppler frequency offset of adjacent times meets a preset condition, and outputting the initial value of the Doppler frequency offset and the change amount of the Doppler frequency offset between frames that meet the preset condition as the Doppler frequency offset estimation convergence result;

[0039] The compensation module is used to perform a second frequency offset compensation on the data signal sn(m) according to the Doppler frequency offset estimation convergence result to obtain an output signal

[0040] In one embodiment of the present invention, when the calculation module outputs the Doppler frequency offset estimation convergence result, it is specifically used to:

[0041] Replace sn(m) with s′n(m) and obtain the initial value of Doppler frequency deviation according to the spreading code sequence corresponding to s′n(m):

[0042] According to the initial value of Doppler frequency deviation Get the inter-frame Doppler frequency deviation change

[0043] Determine whether the initial value of Doppler frequency deviation meets the preset conditions If the conditions are met, the initial value of the Doppler frequency offset and the change in the Doppler frequency offset between frames that meet the preset conditions are output as the Doppler frequency offset estimation convergence result; if the conditions are not met, the Doppler frequency offset between frames is calculated based on the change in the Doppler frequency offset between frames. A first frequency offset compensation is performed on the data signal sn(m) to obtain s′n′(m), and s′n′(m) is used to replace sn(m). The process of obtaining the initial value of the Doppler frequency offset and the change in the Doppler frequency offset between frames is executed repeatedly until the initial value of the Doppler frequency offset for adjacent times meets the preset conditions. The initial value of the Doppler frequency offset and the change in the Doppler frequency offset between frames that meet the preset conditions are output as the convergence result of the Doppler frequency offset estimation; wherein ε represents a preset threshold.

[0044] Beneficial effects of the present invention:

[0045] In the scheme provided by the present invention, the spread spectrum code sequence corresponding to the data signal is first used to estimate the initial value of the Doppler frequency deviation of each frame of the data signal by an accurate estimation method, and then the Doppler frequency deviation variation between frames is estimated according to the initial value of the Doppler frequency deviation of each frame to compensate for the Doppler frequency deviation variation between frames, and the signal after compensating for the Doppler frequency deviation variation between frames is used to estimate the initial value of the Doppler frequency deviation of each frame by an accurate estimation method, and this is repeated until the two accurately estimated initial values ​​of the Doppler frequency deviation meet the preset conditions, and then the algorithm is considered to converge. The present invention can realize accurate compensation of the Doppler frequency deviation before despreading under low signal-to-noise ratio conditions, release the spread spectrum gain, and improve the decoding accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 A schematic diagram of the steps of a method for tracking and compensating Doppler frequency shift of a satellite channel under low signal-to-noise ratio provided by an embodiment of the present invention;

[0047] Figure 2 A schematic flow chart of a method for tracking and compensating Doppler frequency shift of a satellite channel under low signal-to-noise ratio provided by an embodiment of the present invention;

[0048] Figure 3A constellation diagram of a QPSK modulation signal provided by an embodiment of the present invention;

[0049] Figure 4 A QPSK data constellation diagram for Doppler frequency offset compensation provided by an embodiment of the present invention;

[0050] Figure 5 A curve diagram showing the frequency offset estimation error changing with the number of iterations provided in an embodiment of the present invention;

[0051] Figure 6 A QPSK data constellation diagram after Doppler frequency offset compensation provided by an embodiment of the present invention;

[0052] Figure 7 A curve diagram showing the frequency offset estimation error as a function of frequency offset and signal-to-noise ratio provided by an embodiment of the present invention;

[0053] Figure 8 A schematic diagram of the structure of a tracking and compensating device for Doppler frequency shift of a satellite channel under low signal-to-noise ratio provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0054] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0055] The embodiment of the present invention provides a tracking and compensation method and device for Doppler frequency shift of a satellite channel under low signal-to-noise ratio.

[0056] Below, firstly, a tracking and compensation method for Doppler frequency shift of a satellite channel under low signal-to-noise ratio provided by an embodiment of the present invention is introduced.

[0057] like Figure 1 As shown, a tracking and compensation method for Doppler frequency shift of a satellite channel under low signal-to-noise ratio provided by an embodiment of the present invention may include the following steps:

[0058] S1, obtaining N frames of data signals sn(m) that require frequency offset compensation, the synchronization header and the spread spectrum code sequence of each frame of data signal.

[0059] Specifically, assume that the received N frames of data signal sn(m) have a frequency deviation of the first bit from the first frame to the Nth frame of f1, f2, f3, ..., f N Each transmission time slot contains three parts: synchronization header, data and protection interval. The synchronization header is formed by splicing two parts and spreading them. The first part is a filling sequence of '1' and '0', and the second part is a specific byte frame header. The spreading code sequence uses a specified sequence. Each spreading code sequence of the first part of the synchronization header after spreading is recorded as PN i (m), i∈(1,...,U), U represents the number of bits of the "1" and "0" sequences in the SYN sequence.

[0060] Assuming that the frequency deviation changes continuously, the Doppler frequency deviation of each bit is equal to the initial frequency deviation of the current frame plus the uniformly changing Doppler frequency deviation change. The expression of each data signal sn(m) in this part of the nth frame at the receiving end is as follows:

[0061]

[0062] Among them, PN i (m) represents the spreading code sequence, m represents time, j represents the imaginary unit, is the initial phase deviation of the channel, fs represents the sampling rate of the spread spectrum system, Indicates the phase deviation caused by the Doppler frequency deviation corresponding to the n-th frame data signal, Indicates the phase deviation caused by the frequency deviation variation between bits of the nth frame, n i (m) is the channel noise, and U represents the number of bits of the “1” and “0” sequences in the SYN sequence.

[0063] The phase deviation caused by the Doppler frequency deviation corresponding to the nth frame data signal The expression is as follows:

[0064]

[0065] Among them, f n It represents the frequency deviation of the first bit corresponding to the nth frame data signal, and fs represents the sampling rate of the spread spectrum system.

[0066] Phase deviation caused by the frequency deviation variation between bits of the nth frame The expression is as follows:

[0067]

[0068] Wherein, fn+1 represents the frequency deviation of the first bit corresponding to the (n+1)th frame data signal, L represents the length of each frame data signal, and fs represents the sampling rate of the spread spectrum system.

[0069] S2, based on the spread spectrum code sequence corresponding to the data signal sn(m), estimates the initial value of the Doppler frequency deviation of each frame of data signal

[0070] For S2, this may include:

[0071] S21, according to the preset frequency deviation value Select h different spreading code sequences from all spreading code sequences for correlation calculation, and obtain the corresponding g correlation quantities. According to the relevant quantity corresponding to each preset frequency deviation value Get the average of the preset frequency deviation values Where, h∈[1,U], p∈[1,g], g=U / h, U represents the number of bits of “1” and “0” sequences in the SYN sequence;

[0072] S22, the mean of all The frequency deviation value corresponding to the maximum value in is taken as the initial value of Doppler frequency deviation

[0073]

[0074] Specifically, due to the frequency deviation component At the same time, the phase deviation caused by the frequency deviation variation between bits The phase deviation caused by the Doppler frequency deviation corresponding to the data signal This is related to the estimation of Doppler frequency deviation. The impact of each frame is estimated first. The phase deviation caused by the initial frequency deviation of each frame can be The original SYN sequence and the Gold sequence in each time slot at the receiving end are completely consistent and known. However, due to the influence of the channel, when the received signal is correlated with the transmitting signal, these phase deviation values ​​need to be corrected to add up to a correlation value. The expression is as follows:

[0075]

[0076] in, Indicates the spreading code sequence PN i (m), [-b, b] represents the preset frequency search range, Δα represents the frequency search accuracy, Indicates the preset frequency deviation value. Including all possible frequency deviation values ​​that meet the accuracy within the search range. Among them, the value of the preset frequency search range can be set according to specific needs.

[0077] S3, based on the initial value of the Doppler frequency deviation of each frame of data signal Estimate the inter-frame Doppler frequency deviation variation of each frame of data signal According to the change of Doppler frequency deviation between frames Performing a first frequency offset compensation on the data signal sn(m) to obtain s′n(m);

[0078] It can be understood that the Doppler frequency offset initial value of each frame data signal accurately estimated in step S2 is It can be used to preliminarily estimate the inter-frame Doppler frequency deviation change of each frame of data signal Then according to the change of Doppler frequency deviation between frames The first frequency offset compensation is performed on the data signal sn(m) to obtain s′n(m), and the expression of the obtained s′n(m) is as follows:

[0079]

[0080] Where m represents time, exp represents the natural exponential function, and j represents the imaginary unit. Indicates the inter-frame Doppler frequency deviation change corresponding to the n-th frame data signal.

[0081] S4, replace sn(m) with s′n(m), and repeat steps S2 and S3 until the initial values ​​of the Doppler frequency offset of adjacent times meet the preset conditions, and output the initial value of the Doppler frequency offset and the change in the Doppler frequency offset between frames that meet the preset conditions as the Doppler frequency offset estimation convergence result.

[0082] For S4, Figure 2 As shown, it may include:

[0083] S41, replace sn(m) with s′n(m), and execute step S2 to obtain the initial value of Doppler frequency deviation

[0084] S42, based on the initial value of Doppler frequency deviation Get the inter-frame Doppler frequency deviation change

[0085] S43, determining whether the initial value of the Doppler frequency deviation meets the preset conditions If the conditions are met, the initial value of the Doppler frequency offset and the change in the Doppler frequency offset between frames that meet the preset conditions are output as the Doppler frequency offset estimation convergence result; if the conditions are not met, the Doppler frequency offset between frames is calculated based on the change in the Doppler frequency offset between frames. Perform a first frequency offset compensation on the data signal sn(m) to obtain s′n′(m), use s′n′(m) to replace sn(m), and execute S2 and S3 repeatedly until the initial values ​​of the Doppler frequency offset of adjacent times meet the preset conditions, and output the initial value of the Doppler frequency offset that meets the preset conditions and the change in the Doppler frequency offset between frames as the Doppler frequency offset estimation convergence result; wherein ε represents the preset threshold.

[0086] Specifically, due to The existence of The estimate is as follows: The smaller, the Therefore, we can use s′n(m) to repeat steps S2 and S3 to estimate and Reuse To compensate for the frequency deviation of sn(m), and then further estimate And so on, until the initial frequency offset of N frames estimated twice before and after is If the maximum difference is less than or equal to the preset threshold ε, the algorithm is considered to have converged. The value of the preset threshold ε can be set according to specific needs.

[0087] S5, performing a second frequency offset compensation on the data signal sn(m) according to the Doppler frequency offset estimation convergence result, and obtaining an output signal

[0088] Specifically, the output signal The expression is as follows:

[0089]

[0090] Where m represents time, exp represents the natural exponential function, and j represents the imaginary unit. Indicates the initial value of Doppler frequency deviation that meets the preset conditions, Indicates the inter-frame Doppler frequency deviation change that meets the preset conditions.

[0091] The embodiment of the present invention provides a tracking and compensation method for Doppler frequency shift of a satellite channel under low signal-to-noise ratio. First, the known synchronization header and its spread spectrum sequence are used to estimate the initial Doppler frequency deviation of each frame by an accurate estimation method. Then, the Doppler frequency deviation change rate between frames is estimated based on the initial Doppler frequency deviation of each frame, and the Doppler frequency deviation change between frames is compensated. The signal after compensating the Doppler frequency deviation change between frames is used to estimate the initial Doppler frequency deviation of each frame by an accurate estimation method. This is repeated until the initial values ​​of the Doppler frequency deviations accurately estimated twice before and after are less than a set threshold value, and the algorithm is considered to converge. The present invention can accurately compensate for the Doppler frequency deviation before despreading under low signal-to-noise ratio conditions and release the spread spectrum gain.

[0092] A flowchart of a method for tracking and compensating satellite channel Doppler frequency shift under low signal-to-noise ratio provided by an embodiment of the present invention is shown in FIG. Figure 2 ,from Figure 2 It can be seen that the tracking compensation method can include the following detailed process:

[0093] The transmitter can generate a standard QPSK modulated signal, QPSK modulated signal constellation diagram, such as Figure 3 shown.

[0094] For the receiving end, first, obtain the N frames of data signals that need to be compensated for frequency offset, as well as their synchronization header and spread spectrum code sequence. For the QPSK data constellation diagram for Doppler frequency offset compensation, please refer to Figure 4 ,from Figure 4 It can be seen that the acquired QPSK data constellation diagram for the Doppler frequency offset to be compensated forms a ring under the superposition of the Doppler frequency offset and the noise.

[0095] According to the spread spectrum code sequence corresponding to each frame of data signal, the initial value of the Doppler frequency deviation of each frame of data signal is estimated.

[0096] According to the initial value of the Doppler frequency deviation of each frame of data signal, the inter-frame Doppler frequency deviation variation of each frame of data signal is estimated.

[0097] Compare whether the difference between the two frequency offset estimation results is less than or equal to the preset threshold. If so, the Doppler frequency offset initial value and the inter-frame Doppler frequency offset change that meet the preset conditions are output as the Doppler frequency offset estimation convergence result. Otherwise, the Doppler frequency offset change between frames is used to estimate the convergence of the Doppler frequency offset. Perform a first frequency offset compensation on the data signal sn(m) to obtain s′n′(m), use s′n′(m) to replace sn(m), and execute S2 and S3 repeatedly until the initial value of the Doppler frequency offset of the adjacent times meets the preset condition, and output the initial value of the Doppler frequency offset that meets the preset condition and the change amount of the Doppler frequency offset between frames as the Doppler frequency offset estimation convergence result; wherein ε represents a preset threshold. The frequency offset estimation error curve diagram provided by the embodiment of the present invention is as follows: Figure 5 As shown, from Figure 5 It can be seen that the error of the first Doppler frequency offset estimation is relatively large, and the error result of the second estimation is close to 0.

[0098] The second frequency offset compensation is performed on the data signal according to the Doppler frequency offset estimation convergence result to obtain the output signal. The QPSK data constellation diagram after Doppler frequency offset compensation is as follows: Figure 6 As shown, from Figure 6 It can be seen that after compensating for the Doppler frequency offset, the four standard constellation points of the QPSK signal are restored.

[0099] In order to verify the beneficial effect of the tracking and compensation method for Doppler frequency shift of satellite channels under low signal-to-noise ratio proposed in the embodiment of the present invention, the robust tracking and compensation method for Doppler frequency shift of satellite channels under low signal-to-noise ratio proposed in the present invention is simulated and compared under the channel conditions of noise 0dB, -10dB, -20dB, and frequency offset set at 500-3000Hz. The obtained frequency offset estimation error changes with frequency offset and signal-to-noise ratio. Please refer to Figure 7 As shown, from Figure 7 It can be seen that the tracking compensation method provided in the embodiment of the present invention can estimate the Doppler frequency offset more accurately under the condition of 0dB, and still has a low frequency offset estimation error under the condition of -20dB. Therefore, the embodiment of the present invention can accurately estimate and compensate for the Doppler frequency offset before despreading under low signal-to-noise ratio conditions, thereby better releasing the spread spectrum gain.

[0100] In a second aspect, corresponding to the above method embodiment, the embodiment of the present invention further provides a tracking and compensation device for Doppler frequency shift of a satellite channel under low signal-to-noise ratio, such as Figure 8 As shown, the device may include:

[0101] Acquisition module, calculation module and compensation module; wherein,

[0102] An acquisition module, used to acquire N frames of data signals sn(m) that require frequency offset compensation, a synchronization header and a spread spectrum code sequence of each frame of data signal;

[0103] The calculation module is used to estimate the initial value of the Doppler frequency deviation of each frame of data signal according to the spread spectrum code sequence corresponding to the data signal sn(m) According to the initial value of Doppler frequency deviation of each frame data signal Estimate the inter-frame Doppler frequency deviation variation of each frame of data signal According to the change of Doppler frequency deviation between frames Performing a first frequency offset compensation on the data signal sn(m) to obtain s′n(m); replacing sn(m) with s′n(m), cyclically executing the process of obtaining the initial value of the Doppler frequency offset and the change amount of the Doppler frequency offset between frames until the initial value of the Doppler frequency offset of adjacent times meets a preset condition, and outputting the initial value of the Doppler frequency offset and the change amount of the Doppler frequency offset between frames that meet the preset condition as the Doppler frequency offset estimation convergence result;

[0104] The compensation module is used to perform a second frequency offset compensation on the data signal sn(m) according to the Doppler frequency offset estimation convergence result to obtain an output signal

[0105] Specifically, when the calculation module outputs the Doppler frequency offset estimation convergence result, it is specifically used to:

[0106] Replace sn(m) with s′n(m) and obtain the initial value of Doppler frequency deviation according to the spreading code sequence corresponding to s′n(m):

[0107] According to the initial value of Doppler frequency deviation Get the inter-frame Doppler frequency deviation change

[0108] Determine whether the initial value of Doppler frequency deviation meets the preset conditions If the conditions are met, the initial value of the Doppler frequency offset and the change in the Doppler frequency offset between frames that meet the preset conditions are output as the Doppler frequency offset estimation convergence result; if the conditions are not met, the Doppler frequency offset between frames is calculated based on the change in the Doppler frequency offset between frames. A first frequency offset compensation is performed on the data signal sn(m) to obtain s′n′(m), and s′n′(m) is used to replace sn(m). The process of obtaining the initial value of the Doppler frequency offset and the change in the Doppler frequency offset between frames is executed repeatedly until the initial value of the Doppler frequency offset for adjacent times meets the preset conditions. The initial value of the Doppler frequency offset and the change in the Doppler frequency offset between frames that meet the preset conditions are output as the convergence result of the Doppler frequency offset estimation; wherein ε represents a preset threshold.

[0109] It can be understood that the detailed working principle of the acquisition module can refer to the working process of step S1 in the method embodiment, the detailed working principle of the calculation module can refer to the working process of steps S2-S4 in the method embodiment, and the detailed working principle of the compensation module can refer to the working process of step S5 in the method embodiment, and no further details will be given here.

[0110] The tracking compensation method provided by the embodiment of the present invention first uses the spread spectrum code sequence corresponding to the data signal to estimate the initial value of the Doppler frequency deviation of each frame of the data signal in an accurate estimation manner, and then estimates the Doppler frequency deviation variation between frames based on the initial value of the Doppler frequency deviation of each frame to compensate for the Doppler frequency deviation variation between frames, and then uses the signal after compensating for the Doppler frequency deviation variation between frames to estimate the initial value of the Doppler frequency deviation of each frame in an accurate estimation manner, and repeats this process until the two accurately estimated initial values ​​of the Doppler frequency deviation meet the preset conditions, and then the algorithm is considered to converge. The present invention can accurately compensate for the Doppler frequency deviation before despreading under low signal-to-noise ratio conditions, release the spread spectrum gain, and improve the decoding accuracy.

[0111] It should be noted that in the description of the present invention, it should be understood that the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0112] Each embodiment in this specification is described in a related manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the device embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0113] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A tracking and compensation method for Doppler frequency shift of a satellite channel under low signal-to-noise ratio, characterized in that: Applied in a spread spectrum system under low signal-to-noise ratio, the tracking and compensation method for Doppler frequency shift of a satellite channel under low signal-to-noise ratio includes: S1, obtaining N frames of data signals sn(m) that require frequency offset compensation, the synchronization header and the spread spectrum code sequence of each frame of data signal; S2, based on the spread spectrum code sequence corresponding to the data signal sn(m), estimates the initial value of the Doppler frequency deviation of each frame of data signal S3, based on the initial value of the Doppler frequency deviation of each frame of data signal Estimate the inter-frame Doppler frequency deviation variation of each frame of data signal According to the change of Doppler frequency deviation between frames Performing a first frequency offset compensation on the data signal sn(m) to obtain s′n(m); S4, replacing sn(m) with s′n(m), and cyclically executing steps S2 and S3 until the initial values ​​of the Doppler frequency offsets of the adjacent times meet the preset conditions, and outputting the initial values ​​of the Doppler frequency offsets and the inter-frame Doppler frequency offset variation that meet the preset conditions as the Doppler frequency offset estimation convergence results; S5, performing a second frequency offset compensation on the data signal sn(m) according to the Doppler frequency offset estimation convergence result, to obtain an output signal 2. The tracking and compensation method for Doppler frequency shift of a satellite channel under low signal-to-noise ratio according to claim 1, characterized in that: The expression of sn(m) is as follows: Among them, PN i (m) represents the spreading code sequence, m represents time, j represents the imaginary unit, is the initial phase deviation of the channel, fs represents the sampling rate of the spread spectrum system, Indicates the phase deviation caused by the Doppler frequency deviation corresponding to the n-th frame data signal, Indicates the phase deviation caused by the frequency deviation variation between bits of the nth frame, n i (m) is the channel noise, and U represents the number of bits of the "1" and "0" sequences in the SYN sequence.

3. The tracking and compensation method for Doppler frequency shift of a satellite channel under low signal-to-noise ratio according to claim 2, characterized in that: The phase deviation caused by the Doppler frequency deviation corresponding to the nth frame data signal The expression is as follows: Among them, f n It represents the frequency deviation of the first bit corresponding to the nth frame data signal, and fs represents the sampling rate of the spread spectrum system.

4. The tracking and compensation method for Doppler frequency shift of a satellite channel under low signal-to-noise ratio according to claim 2, characterized in that: Phase deviation caused by the frequency deviation variation between bits of the nth frame The expression is as follows: Wherein, fn+1 represents the frequency deviation of the first bit corresponding to the (n+1)th frame data signal, L represents the length of each frame data signal, and fs represents the sampling rate of the spread spectrum system.

5. The tracking and compensation method for Doppler frequency shift of satellite channels under low signal-to-noise ratio according to claim 1, characterized in that: The S2 comprises: S21, according to the preset frequency deviation value Select h different spreading code sequences from all spreading code sequences for correlation calculation, and obtain the corresponding g correlation quantities. According to the relevant quantity corresponding to each preset frequency deviation value Get the average of the preset frequency deviation values Where, h∈[1,U], p∈[1,g], g=U / h, U represents the number of bits of "1" and "0" sequences in the SYN sequence; S22, the mean of all The frequency deviation value corresponding to the maximum value in is taken as the initial value of Doppler frequency deviation 6. The tracking and compensation method for Doppler frequency shift of satellite channels under low signal-to-noise ratio according to claim 1, characterized in that: The expression of s′n(m) is as follows: Where m represents time, exp represents the natural exponential function, and j represents the imaginary unit. Indicates the inter-frame Doppler frequency deviation change corresponding to the n-th frame data signal.

7. The tracking and compensation method for Doppler frequency shift of satellite channels under low signal-to-noise ratio according to claim 1, characterized in that: The S4 comprises: S41, replace sn(m) with s′n(m), and execute step S2 to obtain the initial value of Doppler frequency deviation S42, based on the initial value of Doppler frequency deviation Get the inter-frame Doppler frequency deviation change S43, determining whether the initial value of the Doppler frequency deviation meets the preset conditions If the conditions are met, the initial value of the Doppler frequency offset and the change in the Doppler frequency offset between frames that meet the preset conditions are output as the Doppler frequency offset estimation convergence result; if the conditions are not met, the Doppler frequency offset between frames is calculated based on the change in the Doppler frequency offset between frames. Perform a first frequency offset compensation on the data signal sn(m) to obtain s′n′(m), use s′n′(m) to replace sn(m), and execute S2 and S3 repeatedly until the initial values ​​of the Doppler frequency offset of adjacent times meet the preset conditions, and output the initial value of the Doppler frequency offset that meets the preset conditions and the change in the Doppler frequency offset between frames as the Doppler frequency offset estimation convergence result; wherein ε represents the preset threshold.

8. The tracking and compensation method for Doppler frequency shift of satellite channels under low signal-to-noise ratio according to claim 1, characterized in that: The output signal The expression is as follows: Where m represents time, exp represents the natural exponential function, and j represents the imaginary unit. Indicates the initial value of Doppler frequency deviation that meets the preset conditions, Indicates the inter-frame Doppler frequency deviation change that meets the preset conditions.

9. A tracking and compensation device for satellite channel Doppler frequency shift under low signal-to-noise ratio, characterized in that: include: Acquisition module, calculation module and compensation module; wherein, The acquisition module is used to acquire N frames of data signals sn(m) that require frequency offset compensation, the synchronization header and the spread spectrum code sequence of each frame of data signal; The calculation module is used to estimate the initial value of the Doppler frequency deviation of each frame of data signal according to the spread spectrum code sequence corresponding to the data signal sn(m). According to the initial value of Doppler frequency deviation of each frame data signal Estimate the inter-frame Doppler frequency deviation variation of each frame of data signal According to the change of Doppler frequency deviation between frames Performing a first frequency offset compensation on the data signal sn(m) to obtain s′n(m); replacing sn(m) with s′n(m), cyclically executing the process of obtaining the initial value of the Doppler frequency offset and the change amount of the Doppler frequency offset between frames until the initial value of the Doppler frequency offset of adjacent times meets a preset condition, and outputting the initial value of the Doppler frequency offset and the change amount of the Doppler frequency offset between frames that meet the preset condition as the Doppler frequency offset estimation convergence result; The compensation module is used to perform a second frequency offset compensation on the data signal sn(m) according to the Doppler frequency offset estimation convergence result to obtain an output signal 10. The tracking and compensating device for satellite channel Doppler frequency shift under low signal-to-noise ratio according to claim 9, characterized in that: When outputting the Doppler frequency offset estimation convergence result, the calculation module is specifically used to: Replace sn(m) with s′n(m) and obtain the initial value of Doppler frequency deviation according to the spreading code sequence corresponding to s′n(m): According to the initial value of Doppler frequency deviation Get the inter-frame Doppler frequency deviation change Determine whether the initial value of Doppler frequency deviation meets the preset conditions If the conditions are met, the initial value of the Doppler frequency offset and the change in the Doppler frequency offset between frames that meet the preset conditions are output as the Doppler frequency offset estimation convergence result; if the conditions are not met, the Doppler frequency offset between frames is calculated based on the change in the Doppler frequency offset between frames. A first frequency offset compensation is performed on the data signal sn(m) to obtain s′n′(m), and s′n′(m) is used instead of sn(m). The process of obtaining the initial value of the Doppler frequency offset and the change in the Doppler frequency offset between frames is executed cyclically until the initial value of the Doppler frequency offset for adjacent times meets a preset condition, and the initial value of the Doppler frequency offset and the change in the Doppler frequency offset between frames that meet the preset condition are output as the Doppler frequency offset estimation convergence result; wherein ε represents a preset threshold.

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