Satellite navigation signal quality adaptive correction system and method

Abstract

The application discloses a kind of adaptive correction system and method of satellite navigation signal quality, the system includes navigation signal generation unit, DA conversion and up-conversion circuit, power amplifier, filter and coupler and DA conversion and down-conversion circuit;Navigation signal generation unit is used to generate baseband navigation signal, and pre-distortion algorithm is used to carry out pre-distortion processing to transmitter channel non-ideality;DA conversion and up-conversion circuit are used to convert digital baseband signal into radio frequency signal;Power amplifier carries out high-power amplification to radio frequency signal;Filter and coupler are used to carry out out-of-band suppression to input high-power signal, while coupling out small-power signal into down-conversion and AD conversion circuit;Down-conversion and AD conversion circuit are used to convert input coupling signal into digital baseband signal.The application can effectively improve navigation signal quality.

Description

Technical Field

[0001] This invention relates to the field of spacecraft technology, and in particular to an adaptive correction system and method for satellite navigation signal quality. Background Technology

[0002] Global Navigation Satellite Systems (GNSS) provide positioning, velocity, and timing (PVT) services to users by broadcasting navigation signals to the ground. The quality of the navigation signal directly affects the receiving performance of the receiver terminal. Non-idealities in the navigation transmitter channel (including channel linear response primarily due to filter characteristics and non-linear response primarily due to power amplifier characteristics) are the main sources of navigation signal quality degradation. Currently, navigation signal quality can be evaluated using indicators such as time-domain waveform distortion, synthesized power spectrum deviation, correlation loss, and zero-crossing offset of the discrimination curve. Pre-distortion of the signal within the navigation signal baseband generation unit is a commonly used technique, and its effectiveness can be assessed using signal quality evaluation techniques.

[0003] The characteristics of the transmitter channel of a navigation satellite payload change in orbit due to temperature variations and degradation of device parameters. The pre-distortion parameters fixed before satellite launch may no longer be suitable for these channel characteristics, leading to a deterioration in navigation signal quality. How to adaptively adjust the pre-distortion parameters based on the actual transmitter channel characteristics is currently an unsolved problem. Summary of the Invention

[0004] In view of this, the present invention provides an adaptive correction system and method for satellite navigation signal quality.

[0005] This invention discloses an adaptive correction system for satellite navigation signal quality, comprising: a navigation signal generation unit, a DA converter and up-conversion circuit, a power amplifier, a filter and coupler, and a DA converter and down-conversion circuit; the output terminal of the navigation signal generation unit is sequentially connected to the DA converter and up-conversion circuit, the power amplifier, the filter and coupler, and the DA converter and down-conversion circuit; the output terminal of the DA converter and down-conversion circuit is connected to the input terminal of the navigation signal generation unit.

[0006] The navigation signal generation unit is used to generate baseband navigation signals, and a predistortion algorithm is used to predistort the non-idealities of the transmitter channel.

[0007] The DA converter and upconversion circuit is used to convert digital baseband signals into radio frequency signals;

[0008] The power amplifier amplifies the radio frequency signal at high power.

[0009] Filters and couplers are used to suppress high-power input signals out of band, while coupling out low-power signals to enter the down-conversion and AD conversion circuits.

[0010] The downconversion and AD conversion circuit is used to convert the input coupled signal into a digital baseband signal.

[0011] Furthermore, the navigation signal generation unit includes a navigation signal generation module, a channel filter predistortion module, a power amplifier nonlinear predistortion module, a channel characteristic residual estimation module, and a channel filter predistortion parameter calculation module; the output of the navigation signal generation module is sequentially connected to the channel filter predistortion module and the power amplifier nonlinear predistortion module; the output of the power amplifier nonlinear predistortion module is connected to the DA converter and up-conversion circuit; the input of the channel characteristic residual estimation module is connected to the output of the DA converter and down-conversion circuit; the output of the channel characteristic residual estimation module is connected to the channel filter predistortion module through the channel filter predistortion parameter calculation module.

[0012] Furthermore, the navigation signal generation module is used to generate baseband navigation signals; the channel filter predistortion module is used to compensate for the linear distortion of the transmitter channel through a complex filter; the power amplifier nonlinear predistortion module is used to compensate for the nonlinear distortion of the channel; the channel characteristic residual estimation module is used to run an adaptive filter algorithm to estimate the channel characteristic residual; and the channel filter predistortion parameter calculation module is used to recalculate new filter parameters.

[0013] This invention also discloses an adaptive correction method for satellite navigation signal quality, applicable to the adaptive correction system for satellite navigation signal quality described in any of the above claims, comprising:

[0014] Step 1: Initialize the channel filter predistortion module of the satellite transmitter;

[0015] Step 2: Predistort the nonlinearity of the power amplifier in the satellite transmitter channel;

[0016] Step 3: Use an adaptive filter to estimate the channel characteristic residuals and obtain the filter parameters that compensate for them;

[0017] Step 4: Update the predistortion filter parameters of the channel filter predistortion module at fixed intervals.

[0018] Further, step 1 includes:

[0019] The transfer function of the complex FIR filter is designed as H(z) = a(1) + a(2)z -1 +a(3)z -2 +...+a(N)z -(N-1), where a(1), a(2), ..., a(N) are all filter coefficients and are all complex numbers. The filter coefficient matrix A(m) = [a(1), a(2), ..., a(N)], where A(m) represents the filter coefficient matrix at time m. Its initial state is set to an all-pass filter, i.e., A(0) = [1, 0, ..., 0].

[0020] Further, step 2 includes:

[0021] On the ground, a vector network analyzer is used to scan the AM-AM and AM-PM characteristics of the channel, extracting the channel's nonlinear parameters. The inverse functions of the AM-AM and AM-PM characteristic curves are used as a lookup table, and the baseband signal is pre-distorted. Alternatively,

[0022] The power amplifier model is learned by directly or indirectly learning the structure to obtain predistortion parameters, and the signal is predistorted.

[0023] Further, step 3 includes:

[0024] Step 3-1: The signal output by the navigation signal generation module is a distortion-free signal. Use the signal output by the navigation signal generation module as the reference signal for the adaptive filter.

[0025] Step 3-2: Use the signal after passing through the filter and coupler as the output of the unknown channel;

[0026] Step 3-3: Design an FIR filter with N taps, and use the recursive least squares algorithm to adjust its tap weight vector W = [w1, w2, w3, ..., w N ] T Make an estimate.

[0027] Further, step 3-3 includes:

[0028] Step 3-3-1: Initial value of the tap weight vector at time 0. Initial value of the inverse matrix P(0) = δ -1 I, where I is an N×N identity matrix, and δ is a regularization parameter, which is a small positive constant;

[0029] Step 3-3-2: For a given time n, update the relevant parameters;

[0030] Step 3-3-3: By iterating multiple times according to step 3-3-2, the tap weight vector W can be converged. W is the filter parameter that compensates for the channel characteristic residual.

[0031] Further, step 3-3-2 includes:

[0032] Input vector u(n) = [s(n), s(n-1), s(n-2), ..., s(n-N+1)] T , where s(n) represents the sampled signal at time n;

[0033] Calculation error N0 is the estimated time delay of the signal after passing through predistortion and the transmitter link, and its value is [value missing]. and the sum of transmitter link delay; where, For a rough estimate of the filter group delay, the sum of the transmit link delays needs to be quantized to integer multiples of the sampling point time.

[0034] Calculate the gain vector Wherein, the exponential weighting factor λ takes values ​​in the interval (0, 1], u H (n) is the conjugate transpose of u(n);

[0035] Calculate the inverse matrix P(n) = λ -1 P(n-1)-λ -1 k(n)u H (n)P(n-1);

[0036] Calculate the weight vector ξ * (n) is the conjugate matrix of ξ(n).

[0037] Further, step 4 includes:

[0038] At time m, the predistortion filter parameters are A(m), the FIR filter weight vector obtained by the channel characteristic residual estimation module is W(m), and the convolution of A(m) and W(m) is conv(A(m),W(m)). After truncating it to a length N, it is used as the predistortion filter coefficient for the next time step.

[0039] Because of the adoption of the above technical solution, the present invention has the following advantages:

[0040] 1. This invention can effectively improve navigation signal quality by pre-distorting the linear and nonlinear distortions of the transmitter channel;

[0041] 2. When predistorting the channel linear response, a recursive least squares adaptive filter algorithm was used to design the predistortion filter, which can quickly converge the parameters and has low implementation complexity.

[0042] 3. When the present invention is used in orbit, it can autonomously adjust the parameters of the predistortion filter according to the changes in the linear response characteristics of the channel. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in the embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0044] Figure 1 This is a flowchart illustrating an adaptive correction method for satellite navigation signal quality according to an embodiment of the present invention.

[0045] Figure 2 This is a schematic diagram of the hardware composition of an adaptive correction system for satellite navigation signal quality according to an embodiment of the present invention;

[0046] Figure 3 This is a schematic diagram of the software composition of an adaptive correction system for satellite navigation signal quality according to an embodiment of the present invention;

[0047] Figure 4 This is a block diagram illustrating the principle of using an adaptive filter to estimate channel characteristic residuals in an embodiment of the present invention.

[0048] Figure 5 This is a schematic diagram of the transmitter channel nonlinear characteristic curve measured using a vector network analyzer according to an embodiment of the present invention;

[0049] Figure 6 This diagram illustrates the improvement effect of the zero-crossing offset of the signal quality index discrimination curve after applying the adaptive filter-based satellite navigation signal quality correction system and method according to an embodiment of the present invention. Detailed Implementation

[0050] The present invention will be further described in conjunction with the accompanying drawings and embodiments. The described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art should fall within the protection scope of the present invention.

[0051] See Figure 2 This invention provides an embodiment of an adaptive correction system for satellite navigation signal quality, comprising a navigation signal generation unit, a DA converter and up-conversion circuit, a power amplifier, a filter and coupler, and a DA converter and down-conversion circuit. The navigation signal generation unit generates a baseband navigation signal and employs a pre-distortion algorithm to pre-distort the transmitter channel's non-ideals. The DA converter and up-conversion circuit converts the digital baseband signal into a radio frequency (RF) signal. The power amplifier amplifies the RF signal at high power. The filter and coupler perform out-of-band suppression on the input high-power signal and simultaneously couple out a low-power signal to the down-conversion and DA converter circuit. The down-conversion and DA converter circuit converts the input coupled signal into a digital baseband signal.

[0052] The on-board software system of this invention consists of, as follows: Figure 3 As shown, the implementation is primarily within an FPGA, including a navigation signal generation module, a channel filter predistortion module, a power amplifier nonlinear predistortion module, a channel characteristic residual estimation module, and a channel filter predistortion parameter calculation module. The navigation signal generation module generates the baseband navigation signal. The channel filter predistortion module compensates for the linear distortion of the transmitter channel using a complex filter. The power amplifier nonlinear predistortion module compensates for the nonlinear distortion of the channel. The channel characteristic residual estimation module runs an adaptive filter algorithm to estimate the channel characteristic residual. The channel filter predistortion parameter calculation module recalculates the new filter parameters.

[0053] See Figure 1 This invention provides an embodiment of an adaptive correction method for satellite navigation signal quality:

[0054] according to Figure 2 , Figure 3 An adaptive correction system for satellite navigation signal quality based on an adaptive filter is constructed for a transmitter channel with a signal operating frequency band of 1268.52±10.23MHz. The system includes both hardware and software components.

[0055] The specific implementation method is as follows:

[0056] Step 1: Initialize the satellite transmitter channel filter predistortion module.

[0057] Design a complex FIR filter, H(z) = a(1) + a(2)z -1 +a(3)z -2 +...+a(32)z -(N-1) , where A = [a(1), a(2), ..., a(32)] are filter coefficients, all of which are complex numbers. The initial state is set to an all-pass filter, with a(1) set to 1 and the other coefficients set to 0.

[0058] Step 2: Predistort the nonlinearity of the power amplifier in the satellite transmitter channel.

[0059] The AM-AM and AM-PM characteristics of the channel were scanned using a vector network analyzer on the ground to extract the channel's nonlinear parameters. The test results are as follows: Figure 5 As shown, the inverse functions of the AM-AM and AM-PM characteristic curves are used as a lookup table, and the baseband signal is pre-distorted.

[0060] Step 3: Use an adaptive filter to estimate the channel characteristic residuals and obtain the filter parameters that compensate for them.

[0061] Step 3-1: Use the signal output by the navigation signal generation module as the reference signal for the adaptive filter.

[0062] Step 3-2: Use the signal after passing through the filter and coupler as the output of the unknown channel.

[0063] Step 3-3: Design a complex coefficient FIR filter with 32 taps, and use the recursive least squares algorithm to adjust its tap weight vector W = [w1, w2, w3, ..., w N ] T Make an estimate. See also Figure 4 The process is as follows:

[0064] (1) Initial value of the tap weight vector at time 0. Initial value of the inverse matrix P(0) = δ -1 I is an N×N identity matrix, and δ is a regularization parameter, which is a small positive constant, such as 10. -7 ;

[0065] (2) For a given time n, the parameters are updated as follows:

[0066] Input vector u(n) = [s(n), s(n-1), s(n-2), ..., s(n-31)] T , where s(n) represents the sampled signal at time n;

[0067] 1) Calculation error N0 is the estimated time delay of the signal after passing through predistortion and the transmitter link, and its value is [value missing]. and the sum of transmitter link delay; where, To provide a rough estimate of the filter group delay, the sum of the transmit link delays needs to be quantized to an integer multiple of the sampling point time; in this embodiment, the value of N0 is 20;

[0068] 2) Calculate the gain vector Wherein, the exponential weighting factor λ takes values ​​in the interval (0, 1], u H (n) is the conjugate transpose of u(n), and in this embodiment, λ is taken as 0.95;

[0069] 3) Calculate the inverse matrix P(n) = λ -1 P(n-1)-λ -1 k(n)u H (n)P(n-1);

[0070] 4) Calculate the weight vector ξ * (n) is the conjugate matrix of ξ(n);

[0071] (3) By iterating multiple times according to step (2), the tap weight vector W can be converged. W is the filter parameter that compensates for the channel characteristic residual.

[0072] Step 4: Update the predistortion filter parameters of the channel filter predistortion module every 1 second. At time m, the predistortion filter parameter is A(m), and the weight vector of the FIR filter obtained by the channel characteristic residual estimation module is W(m). The convolution of A(m) and W(m) is conv(A(m),W(m)). After truncating it to a length of 32, it is used as the predistortion filter coefficient for the next time step.

[0073] The signal acquisition instrument was used to acquire the signals before and after applying the predistortion algorithm. A signal quality analysis algorithm was then run to analyze each signal. The improvement effect on the zero-crossing offset of the signal quality index discrimination curve was as follows: Figure 6 As shown, the zero-crossing offset of the discrimination curve decreased from about 1.5 ns to less than 0.1 ns.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method of adaptive correction of satellite navigation signal quality, characterized in that, include: Step 1: Initialize the channel filter predistortion module of the satellite transmitter; Step 2: Predistort the nonlinearity of the power amplifier in the satellite transmitter channel; Step 3: Use an adaptive filter to estimate the channel characteristic residuals and obtain the filter parameters that compensate for them; Step 4: Update the predistortion filter parameters of the channel filter predistortion module at fixed intervals; Step 2 includes: scanning the AM-AM and AM-PM characteristics of the channel using a vector network analyzer on the ground, extracting the nonlinear parameters of the channel, using the inverse function of the AM-AM and AM-PM characteristic curves as a lookup table, and performing pre-distortion processing on the baseband signal; Step 3 includes: Step 3-1: The signal output by the navigation signal generation module is a distortion-free signal. Use the signal output by the navigation signal generation module as the reference signal for the adaptive filter. Step 3-2: Use the signal after passing through the filter and coupler as the output of the unknown channel; Step 3-3: Design an FIR filter with N taps, and use the recursive least squares algorithm to adjust its tap weight vector. Make an estimate; Step 3-3 includes: Step 3-3-1: Initial value of the tap weight vector at time 0. Initial value of the inverse matrix , It is an N×N identity matrix. For regularization parameters; Step 3-3-2: For a given time n, update the relevant parameters; Step 3-3-3: By iterating multiple times according to step 3-3-2, the tap weight vector can be completed. convergence, These are the filter parameters that compensate for the residuals of the channel characteristics; Step 3-3-2 includes: Input vector ,in, This represents the sampled signal at time n; Calculation error , The time delay estimate of the signal after passing through predistortion and the transmitter link is set to a value of and the sum of transmitter link delay; where, For a rough estimate of the filter group delay, the sum of the transmit link delays needs to be quantized to integer multiples of the sampling point time. Calculate the gain vector Among them, the index weighting factor The value is in the interval (0, 1). yes The conjugate transpose of ; Calculate the inverse matrix ; Calculate the weight vector ; yes The conjugate matrix.

2. The adaptive correction method for satellite navigation signal quality according to claim 1, characterized in that, Step 1 includes: Design the transfer function of a complex FIR filter as follows: , where a(1), a(2), ..., a(N) are all filter coefficients and are all complex numbers. The filter coefficient matrix A(m) = [a(1), a(2), ..., a(N)], where A(m) represents the filter coefficient matrix at time m. Its initial state is set to an all-pass filter, i.e., A(0) = [1, 0, ..., 0].

3. The adaptive correction method for satellite navigation signal quality according to claim 1, characterized in that, Step 2 can also learn the power amplifier model by directly or indirectly learning the structure to obtain predistortion parameters and perform predistortion processing on the signal.

4. The adaptive correction method for satellite navigation signal quality according to claim 1, characterized in that, Step 4 includes: At time m, the predistortion filter parameters are: The weight vector of the FIR filter obtained by the channel characteristic residual estimation module is: , and The convolution is The coefficients are truncated to a length N and used as the predistortion filter coefficients for the next time step.

5. An adaptive correction system for satellite navigation signal quality, used to implement the adaptive correction method for satellite navigation signal quality according to any one of claims 1-4, characterized in that, include: Navigation signal generation unit, DA converter and up-conversion circuit, power amplifier, filter and coupler, and DA converter and down-conversion circuit; The output of the navigation signal generation unit is connected in sequence to the DA converter and up-conversion circuit, the power amplifier, the filter and coupler, and the DA converter and down-conversion circuit; the output of the DA converter and down-conversion circuit is connected to the input of the navigation signal generation unit. The navigation signal generation unit is used to generate baseband navigation signals, and a predistortion algorithm is used to predistort the non-idealities of the transmitter channel. The DA converter and upconversion circuit is used to convert digital baseband signals into radio frequency signals; The power amplifier amplifies the radio frequency signal at high power. Filters and couplers are used to suppress high-power input signals out of band, while coupling out low-power signals to enter the down-conversion and AD conversion circuits. The downconversion and AD conversion circuit is used to convert the input coupled signal into a digital baseband signal.

6. The adaptive correction system for satellite navigation signal quality according to claim 5, characterized in that, The navigation signal generation unit includes a navigation signal generation module, a channel filter predistortion module, a power amplifier nonlinear predistortion module, a channel characteristic residual estimation module, and a channel filter predistortion parameter calculation module. The output of the navigation signal generation module is connected to the channel filter predistortion module and the power amplifier nonlinear predistortion module in sequence. The output of the power amplifier nonlinear predistortion module is connected to the DA converter and up-conversion circuit. The input of the channel characteristic residual estimation module is connected to the output of the DA converter and down-conversion circuit. The output of the channel characteristic residual estimation module is connected to the channel filter predistortion module through the channel filter predistortion parameter calculation module.

7. The adaptive correction system for satellite navigation signal quality according to claim 6, characterized in that, The navigation signal generation module is used to generate baseband navigation signals; the channel filter predistortion module is used to compensate for the linear distortion of the transmitter channel through a complex filter; the power amplifier nonlinear predistortion module is used to compensate for the nonlinear distortion of the channel; the channel characteristic residual estimation module is used to run an adaptive filter algorithm to estimate the channel characteristic residual; and the channel filter predistortion parameter calculation module is used to recalculate new filter parameters.

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