Low earth orbit satellite communication bit timing method and device based on angle synthesis

Abstract

The invention discloses a low-orbit satellite communication bit timing method and device based on angle synthesis. The method comprises the following steps: extracting offset information of a current code element of an input signal according to the power of the input signal to obtain an offset angle characterization value of the current code element; correcting the offset angle characterization value of the current code element through the offset angle characterization value of the previous code element so as to expand the sampling space to obtain the corrected offset angle characterization value of the current code element; fitting the sampling center of the current code element through the corrected offset angle characterization value; and sampling in the fitting interval based on the sampling center of the current code element to obtain sampling data of the current code element. According to the method provided by the invention, the sampling interval and the sampling point can be expanded towards the optimal sampling point direction; therefore, the conditions of code element repetition and code element missing caused by sampling offset can be avoided at low cost, and the satellite positioning effect is enhanced.

Description

Technical Field

[0001] The present invention belongs to the technical field of signal processing, and particularly relates to a bit timing method and device for low-earth orbit satellite communication based on angle synthesis. Background Art

[0002] Satellites can provide efficient global coverage, especially in terms of communication capabilities in remote areas and over the ocean. With the rapid deployment and technological progress of low-earth orbit satellites, their application prospects in providing high-speed Internet, Internet of Things connections, and disaster relief are broad. Satellite communication systems face various technical challenges in operation. First, since signals need to be transmitted over extremely long distances and experience severe free space loss, the received signals are weak. Second, when signals pass through the atmosphere, they are affected by factors such as multipath effects, ionospheric and tropospheric delays, and are prone to distortion. Finally, the high-speed movement of low-earth orbit satellites brings high dynamic problems in signal transmission, requiring the communication system to have extremely high signal tracking sensitivity.

[0003] However, the current bit timing technology performs poorly in the face of the sampling point drift phenomenon caused by the high dynamic characteristics of satellite communication, and it is prone to the phenomenon of missing or repeating symbols. Summary of the Invention

[0004] An embodiment of the present invention provides a bit timing method for low-earth orbit satellite communication based on angle synthesis, which can solve the problem that the current bit timing technology is prone to the phenomenon of missing or repeating symbols in the scenario of satellite communication.

[0005] In a first aspect, a bit timing method for low-earth orbit satellite communication based on angle synthesis provided by an embodiment of the present invention includes:

[0006] Extracting offset information of the current symbol of the input signal according to the power of the input signal to obtain an offset angle characterization value of the current symbol;

[0007] Correcting the offset angle characterization value of the current symbol through the offset angle characterization value of the previous symbol to expand the sampling space and obtain a corrected offset angle characterization value of the current symbol, where the sampling space is the selectable space of sampling points;

[0008] Fitting the sampling center of the current symbol through the corrected offset angle characterization value;

[0009] Sampling on the fitting interval based on the sampling center of the current symbol to obtain sampling data of the current symbol.

[0010] In a second aspect, an embodiment of the present invention provides a bit timing device for low-earth orbit satellite communication based on angle synthesis, including:

[0011] An offset quantization unit, which is used to extract the offset information of the current symbol of the input signal according to the power of the input signal to obtain the offset complex representation value of the current symbol;

[0012] An offset correction unit, which is used to determine the offset angle representation value of the current symbol according to the offset complex representation value of the current symbol, and correct the offset angle representation value of the current symbol through the offset angle representation value of the previous symbol to expand the sampling space to obtain the corrected offset angle representation value of the current symbol, where the sampling space is the selectable space of sampling points;

[0013] A sampling unit, which is used to fit the sampling center of the current symbol through the corrected offset angle representation value; and sample on the fitting interval based on the sampling center of the current symbol to obtain the sampling data of the current symbol.

[0014] The beneficial effects of the embodiments of the present invention compared with the prior art are as follows: According to the method provided by the present invention, the position of the sampling point is dynamically adjusted by the difference between the offset values of two adjacent symbols, so that the sampling interval and the sampling points expand towards the optimal sampling point; thereby, it is possible to avoid the situation of symbol repetition and missed symbols caused by sampling offset at a lower cost and enhance the satellite positioning effect. Description of the Drawings

[0015] Figure 1 It is a flowchart of the implementation of a low-orbit satellite communication bit timing method based on angle synthesis provided by an embodiment of the present invention;

[0016] Figure 2 It is a schematic diagram of the effect of adjusting the sampling interval provided by an embodiment of the present invention;

[0017] Figure 3 It is a schematic structural diagram of a low-orbit satellite communication bit timing device based on angle synthesis provided by an embodiment of the present invention;

[0018] Figure 4 It is a comparison constellation diagram before and after bit timing provided by an embodiment of the present invention;

[0019] Figure 5 It is a comparison schematic diagram of error code curves provided by an embodiment of the present invention;

[0020] Figure 6 It is a schematic diagram of the relationship between deviation variance and signal-to-noise ratio provided by an embodiment of the present invention;

[0021] Figure 7 It is a schematic diagram of the relationship between the number of convergent symbols and the signal-to-noise ratio provided by an embodiment of the present invention. Detailed Embodiments

[0022] In the following description, specific details such as specific system architectures and technologies are presented for purposes of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present invention. However, those skilled in the art should understand that the present invention can also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to avoid unnecessary details from obscuring the description of the present invention.

[0023] It should be understood that when used in the specification of the present invention and the appended claims, the term "comprising" indicates the presence of the described features, wholes, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or their combinations.

[0024] It should also be understood that the term "and / or" used in the specification of the present invention and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0025] As used in the specification of the present invention and the appended claims, the term "if" can be interpreted as "when" or "once" or "in response to determining" or "in response to detecting" depending on the context. Similarly, the phrases "if determined" or "if detected [the described condition or event]" can be interpreted as meaning "once determined" or "in response to determining" or "once detected [the described condition or event]" or "in response to detecting [the described condition or event]" depending on the context.

[0026] In addition, in the description of the specification of the present invention and the appended claims, the terms "first", "second", "third", etc. are only used for distinguishing descriptions and cannot be understood as indicating or implying relative importance.

[0027] Reference to "one embodiment" or "some embodiments" or the like described in the specification of the present invention means that a specific feature, structure, or characteristic described in connection with that embodiment is included in one or more embodiments of the present invention. Thus, statements such as "in one embodiment", "in some embodiments", "in other some embodiments", "in still other embodiments", etc. that appear in different places in this specification do not necessarily all refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in another way. The terms "comprising", "including", "having", and their variants all mean "including but not limited to", unless otherwise specifically emphasized in another way.

[0028] The present invention will be further described in detail below in conjunction with specific embodiments, but the implementation manners of the present invention are not limited thereto.

[0029] Figure 1 The following is a flowchart showing the implementation of a bit timing method for low-earth orbit satellite communication based on angle synthesis provided by an embodiment of the present invention. By way of example and not limitation, the method may include steps S101 - S104, which are described below.

[0030] S101, Extract the offset information of the current symbol of the input signal according to the power of the input signal to obtain the offset angle characterization value of the current symbol.

[0031] In a possible implementation manner, the offset complex characterization value of the current symbol may be determined according to the power of the input signal and the quantization vector of the current symbol, and then the offset complex characterization value of the current symbol is subjected to smooth integration and angle synthesis to obtain the offset angle characterization value of the current symbol.

[0032] Exemplarily, the offset complex characterization value of the current symbol may satisfy the following formula:

[0033] θ = angle(α) (1.1)

[0034] θ is the offset angle characterization value of the current symbol, and α is the smoothing result of the current symbol;

[0035] Among them, the smoothing result of the (m + 1)-th symbol satisfies the following formula:

[0036] α(m + 1) = (temp(m + 1) - α(m)) / δ + α(m) (1.2)

[0037] δ is the smoothing coefficient, generally taking a power of 2 for easy hardware implementation; α(m + 1) is the smoothing result of the (m + 1)-th symbol, temp(m + 1) is the offset complex characterization value of the (m + 1)-th symbol, and angle is the function for obtaining the complex angle.

[0038] Specifically, the angle function can be directly called in the software code, or the Coordinate Rotation Digital Computer (cordic) algorithm can be selected for implementation in hardware.

[0039] In an example, the input signal may be two complex signals I(m) and Q(m), and the instantaneous power of the input signal can be obtained by the sum of the squares of the amplitudes to eliminate the information carried by the signal.

[0040] Exemplarily, the power of the m-th symbol of the input signal may satisfy the following formula:

[0041] P(m) = I(m) 2 + Q(m) 2 (1.3)

[0042] Among them, P(m) is the m-th symbol of the input signal.

[0043] In one example, the quantization interval can be generated according to the number of samples per symbol n first; then the quantization vectors are combined according to the quantization interval, and the unit complex value of the quantization vector is solved through Euler's formula; finally, the inner product of the unit complex value of the quantization vector and the instantaneous power of the previous symbol is taken to obtain the offset complex representation value of the current symbol.

[0044] Exemplarily, the quantization interval, the quantization vector, the unit complex value of the quantization vector, i.e., the offset complex representation value, can respectively satisfy the following formulas:

[0045] gap = 2π / n(1.4)

[0046]

[0047] Among them, gap, are respectively the quantization interval, the quantization vector, the unit complex value of the quantization vector, temp(m) is the offset complex representation value of the m-th symbol, and P(m - 1) is the instantaneous power of the (m - 1)-th symbol.

[0048] S102. Correct the offset angle representation value of the current symbol through the offset angle representation value of the previous symbol to expand the sampling space and obtain the corrected offset angle representation value of the current symbol.

[0049] Exemplarily, the sampling space is the selectable space of sampling points.

[0050] In one possible implementation, the offset angle representation value of the current symbol can be processed twice with the difference between the offset angle representation values of two adjacent symbols (i.e., the adjacent angle difference) as the judgment condition to ensure the stability and accuracy of the offset.

[0051] In one example, multiple correction preset ranges can be preset in advance, and a corresponding preset correction value is configured for each correction preset range. Then when correcting the offset angle representation value, the difference between the offset angle representation value of the previous symbol and the offset angle representation value of the current symbol can be determined first to obtain the adjacent angle difference; then the first preset range where the adjacent angle difference is located can be determined; finally, according to the positive or negative of the adjacent angle difference, the preset correction value corresponding to the first preset range is added to or subtracted from the offset angle representation value of the current symbol or the offset angle representation value of the previous symbol to obtain the corrected offset angle representation value of the current symbol.

[0052] Exemplarily, if 4 calibration preset ranges are preset, they can be denoted in the order of the size of the range boundaries as: #1, #2, #3, #4. Range #1 is the normal range. If the adjacent angle difference is within range #1, the offset angle characterization value of the current symbol can be directly output as the calibrated offset angle characterization value of the current symbol without processing.

[0053] If the adjacent angle difference is within #2 or #4, then the calibrated offset angle characterization value of the (m + 1)-th symbol can be obtained by adding or subtracting the preset calibration value corresponding to #2 or #4 to / from the offset angle characterization value θ(m) of the m-th symbol according to the adjacent angle difference.

[0054] If the adjacent angle difference is within #3, then the calibrated offset angle characterization value of the (m + 1)-th symbol can be obtained by adding or subtracting the preset calibration value corresponding to #3 to / from θ(m) according to the adjacent angle difference.

[0055] S103, fitting the sampling center of the current symbol through the calibrated offset angle characterization value.

[0056] In a possible implementation manner, before determining the sampling center, the fitting interval to be sampled can be determined first.

[0057] In an example, the fitting interval can include a plurality of consecutive symbol data, and the current symbol is not the first or the last symbol in the fitting interval.

[0058] In a possible implementation manner, after determining the fitting interval, the sampling center of the current symbol can be determined, and then the following step S104 is performed: selecting the sampling space through the value of the sampling center.

[0059] In an example, the difference between the first preset angle and the calibrated offset angle characterization value can be determined to obtain the first preset angle difference; the quotient of the first preset angle difference and the angle ratio is determined as the sampling center of the current symbol.

[0060] Exemplarily, the first preset angle can be used to determine the position of the sampling space.

[0061] Exemplarily, the angle ratio is the quotient of the angle period and the proportional parameter.

[0062] In an example, if subsequent proportional quantization of the sinc function is to be implemented in hardware, since there are no negative values and decimals in hardware implementation, it is necessary to control the proportional parameter ω to be a factor of the angle period; and the sequence number of the maximum value position of the final result needs to be added to the calculation of the sampling center during sinc function quantization. Therefore, the difference between the second preset angle and the calibrated offset angle characterization value can be determined first to obtain the second preset angle difference; the quotient of the second preset angle difference and the angle ratio is determined as the sampling center of the current symbol.

[0063] Exemplarily, the second preset angle is the sum of the first preset angle and the maximum position serial number of the fitting interval.

[0064] Generally, the sampling space is the size of 1 symbol, and the offset angle representation value is also between 0 - 360 degrees. Therefore, referring to Figure 2 (a) in, when the receiving ends are far apart, the optimal sampling point exceeds the sampling interval. The traditional method will fix the sampling interval size and reset the offset value to zero and readjust it, so that the offset value is always within interval #1. For example, adjusting from 370 degrees to 10 degrees makes the sampling point unable to approach the optimal sampling point. In the present invention, through the correction in step S102, when the difference between two adjacent offset values is large, the sampling space is expanded, so that the sampling point can approach the optimal sampling point. Referring to Figure 2 (b) in, thereby enhancing the satellite positioning effect.

[0065] S104, sample the current symbol based on the sampling center of the current symbol on the fitting interval to obtain the sampling data of the current symbol.

[0066] In a possible implementation manner, the sampling data of the current symbol can be obtained by interpolating the current symbol data based on the sampling center of the current symbol.

[0067] In an example, when performing fitting interpolation sampling, sinc function proportional quantization can be performed first. After obtaining the fitting function value through the fitting function, multiply it by the fitting interval to obtain the sampling data of the current symbol.

[0068] Exemplarily, the fitting function value can satisfy: SINC = sinc(-4:1 / ω:4).

[0069] Exemplarily, the sampling data of the current symbol can satisfy the following formula:

[0070] out = SINC(i - 2n:i + 2n - 1)×X(1.8)

[0071] where out is the sampling data of the current symbol, i is the sampling center, and X is the fitting interval.

[0072] According to the method provided by the present invention, the position of the sampling point is dynamically adjusted by the difference between two adjacent symbol offset values, so that the sampling interval and the sampling point expand towards the optimal sampling point direction; thereby it can avoid the situation of symbol repetition and missed symbols caused by sampling offset at a lower cost and enhance the satellite positioning effect.

[0073] Furthermore, using a complex vector angle (i.e., the offset angle characterization value) to estimate the offset of a complex signal can make full use of the symbol waveform characteristics; using two simple measures, conditional limitation and simple integration, to determine the offset and sampling interval can achieve a faster convergence speed, lower resource overhead, and debugging cost.

[0074] Figure 3 The following is a schematic structural diagram of a low-earth-orbit satellite communication bit timing device based on angle synthesis provided by an embodiment of the present invention. By way of example and not limitation, device 300 can be used to implement the above method. Device 300 may include an offset quantization unit 310, an offset correction unit 320, and a sampling unit 330.

[0075] Exemplarily, the offset quantization unit 310 is configured to extract the offset information of the current symbol of the input signal according to the power of the input signal to obtain the offset complex characterization value of the current symbol; the offset correction unit 320 is configured to determine the offset angle characterization value of the current symbol according to the offset complex characterization value of the current symbol, and correct the offset angle characterization value of the current symbol through the offset angle characterization value of the previous symbol to expand the sampling space to obtain the corrected offset angle characterization value of the current symbol, where the sampling space is the selectable space of sampling points; the sampling unit 330 is configured to fit the sampling center of the current symbol through the corrected offset angle characterization value, and perform sampling on the fitting interval based on the sampling center of the current symbol to obtain the sampling data of the current symbol.

[0076] Specifically, the offset correction unit 320 can use a counter to record the data quantity, and reset the expanded sampling frame to its original position within the guard interval of the communication protocol to ensure continuous operation.

[0077] In a possible implementation manner, as described in the above method, the fitting interval may include a plurality of consecutive symbol data, and the current symbol is not the first or last symbol in the fitting interval. Therefore, device 300 may further include a data combination unit 340. The data combination unit may be configured to perform interval combination on the serial data stream to obtain the symbol data in the fitting interval for use by the sampling unit 330.

[0078] In one example, based on the above formula (1.8), device 300 may further include a sinc storage module 350.

[0079] Exemplarily, the sinc storage module 350 may be configured to store the SINC values when i is different. This is convenient for subsequent calls by the sampling unit 330 and can simplify the structure of device 300.

[0080] In order to better illustrate the beneficial effects of the present invention, the following simulation experiments were carried out:

[0081] Exemplarily, in the simulation experiment, the device 300 is used as the bit timing module in the low-earth orbit satellite frequency-hopping communication system. The modulation method is DQPSK, the module operating clock is 122.88Mhz. The number of samples per symbol n is 12, the symbol rate is 10.24Mhz, and the sample rate is 122.88Mhz. ω is set to 30, β is 0, δ is 128, and the module processes in a pipelined manner throughout. Without a communication data storage link, congestion will not be caused. Its input is two paths to form a complex signal, and the quantization bit number is 16 bits.

[0082] Figure 4 The following shows a comparison constellation diagram before and after bit timing provided by an embodiment of the present invention.

[0083] See Figure 4 , where Figure 4 (a) in is the DQPSK signal constellation diagram before bit timing, Figure 4 (b) in is the DQPSK signal constellation diagram after bit timing.

[0084] See Figure 4 and Figure 5 In the error code curve diagram in, it can be seen that in the case of QPSK modulation, 12 samples per symbol, and using the hard decision method; when the signal-to-noise ratio is relatively high, the error code curve of the present invention basically overlaps with the error code curve that always maintains the optimal sampling point. When the signal-to-noise ratio drops below 0dB, the result of the present invention begins to fluctuate and deviate compared with the optimal sampling point.

[0085] Figure 6 The following shows a schematic diagram of the relationship between the deviation variance and the signal-to-noise ratio provided by an embodiment of the present invention.

[0086] See Figure 6 , it can be seen that the deviation variance of the sampling point deviation estimation result of the present invention is within a controllable range before -4dB, and the deviation increases significantly after -4dB.

[0087] Figure 7 The following shows a schematic diagram of the relationship between the convergence symbol number and the signal-to-noise ratio provided by an embodiment of the present invention. Among them, each signal-to-noise ratio point is repeatedly tested 50 times and the average value is taken.

[0088] See Figure 7 , it can be seen that the convergence speed of the present invention is slightly better than that of the general Gardner timing recovery loop, the Gardner loop. In the case of low signal-to-noise ratio, the reason for the significant increase in the convergence symbol number after -4dB is that on the one hand, the initial oscillation time is lengthened, and on the other hand, due to the influence of noise, the oscillation amplitude of itself increases and it is difficult to meet the variance standard recognized as convergence.

[0089] Therefore, according to the method provided by the present invention, the position of the sampling point is dynamically adjusted by the difference between the offset values of two adjacent code elements, so that the sampling interval and the sampling point are extended towards the optimal sampling point; thus, it is possible to avoid the situation of code element repetition and missed code elements caused by sampling offset at a lower cost, and enhance the satellite positioning effect.

[0090] In the above embodiments, the descriptions of the respective embodiments have their own emphases. For the parts not detailed or recorded in a certain embodiment, reference may be made to the relevant descriptions of other embodiments.

Claims

1. A low-orbit satellite communication position timing method based on angle synthesis, characterized in that: include: Extracting the offset information of the current symbol of the input signal according to the power of the input signal to obtain the offset angle representation value of the current symbol; Correcting the offset angle characterization value of the current code element by using the offset angle characterization value of the previous code element to expand the sampling space to obtain the corrected offset angle characterization value of the current code element, wherein the sampling space is a selectable space of sampling points; Fitting the sampling center of the current symbol by the corrected offset angle characterization value; Sampling is performed on a fitting interval based on the sampling center of the current symbol to obtain sampling data of the current symbol.

2. The method according to claim 1, characterized in that The step of extracting the offset information of the current symbol of the input signal according to the power of the input signal to obtain the offset angle characterization value of the current symbol includes: Determine an offset complex representation value of the current symbol according to the power of the input signal and a quantization vector of the current symbol; The offset complex representation value of the current codeword is smoothly integrated and angle synthesized to obtain the offset angle representation value of the current codeword.

3. The method according to claim 2, characterized in that The offset angle characterization value of the current symbol satisfies the following formula: θ=angle(α) Wherein, θ is the offset angle representation value of the current code element, and α is the smoothing result of the current code element; The smoothing result of the m+1th symbol satisfies the following formula: α(m+1)=(temp(m+1)-α(m)) / δ+α(m) Wherein, δ is the smoothing coefficient, α(m+1) is the smoothing result of the m+1th codeword, temp(m+1) is the offset complex representation value of the m+1th codeword, and angle is the complex angle function.

4. The method according to claim 1, characterized in that: The step of correcting the offset angle characterization value of the current symbol by using the offset angle characterization value of the previous symbol to expand the sampling space to obtain the corrected offset angle characterization value of the current symbol includes: Determine the difference between the offset angle characterization value of the previous code element and the offset angle characterization value of the current code element to obtain an adjacent angle difference; Determine a first preset range in which the absolute values ​​of the adjacent angular differences are located, wherein the first preset range is one of the correction preset ranges, and each of the correction preset ranges corresponds to a preset correction value; According to the positive or negative sign of the adjacent angle difference, the preset correction value corresponding to the first preset range is added or subtracted from the offset angle characterization value of the current code element or the offset angle characterization value of the previous code element to obtain the corrected offset angle characterization value of the current code element.

5. The method according to claim 1, characterized in that The step of fitting the sampling center of the current symbol by the corrected offset angle characterization value comprises: Determine a difference between a first preset angle and the corrected offset angle characterization value to obtain a first preset angle difference, wherein the first preset angle is used to determine the position of the sampling space; The quotient of the first preset angle difference and the angle ratio is determined as the sampling center of the current code element, wherein the angle ratio is the quotient of the angle period and the ratio parameter.

6. The method according to claim 1, characterized in that The step of fitting the sampling center of the current symbol by the corrected offset angle characterization value comprises: Determine a difference between a second preset angle and the corrected offset angle characterization value to obtain a second preset angle difference, wherein the second preset angle is the sum of the first preset angle and the maximum position sequence number of the fitting interval; The quotient of the second preset angle difference and the angle ratio is determined as the sampling center of the current code element, wherein the angle ratio is the quotient of the angle period and the ratio parameter.

7. The method according to claim 1, characterized in that The sampling data of the current symbol satisfies the following formula: out=SINC(i-2n:i+2n-1)×X Wherein, out is the sampling data of the current symbol, i is the sampling center of the current symbol, n is the number of sample points per symbol, and X is the fitting interval; SINC=sinc(-4:1 / ω:4), ω is the proportional parameter.

8. The method according to claim 7, characterized in that The fitting interval includes a plurality of continuous symbol data, and the current symbol is not the first symbol or the last symbol in the fitting interval.

9. A low-orbit satellite communication position timing device based on angle synthesis, characterized in that: include: An offset quantization unit, the offset quantization unit being used to extract the offset information of the current symbol of the input signal according to the power of the input signal to obtain the offset complex representation value of the current symbol; An offset correction unit, the offset correction unit is used to determine the offset angle representation value of the current codeword according to the offset complex representation value of the current codeword, and correct the offset angle representation value of the current codeword by the offset angle representation value of the previous codeword, so as to expand the sampling space to obtain the corrected offset angle representation value of the current codeword, wherein the sampling space is a selectable space of sampling points; A sampling unit, the sampling unit is used to fit the sampling center of the current code element through the corrected offset angle characterization value; and to obtain sampling data of the current code element by sampling in a fitting interval based on the sampling center of the current code element.

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