An all-digital satellite demodulator automatic gain control system and method

Abstract

A fully digital satellite demodulator automatic gain control (AGC) system and method, belonging to the field of communication technology. The traditional AGC loop is implemented by analog circuits, with high hardware costs, insufficient precision in the operation process, and poor versatility. The system provided by the present invention includes a pre-level detector, a variable gain amplifier, a gain error detector, and a loop filter, which can reduce hardware overhead, support flexible configuration of loop parameters, and maintain high-precision calculation results at the same time.

Description

Technical Field

[0001] The present invention belongs to the field of communications, and particularly relates to an all-digital satellite demodulator automatic gain control (AGC) system and method. Background Art

[0002] With the advancement of satellite miniaturization technology and the rapid reduction of the launch cost of a single satellite, countries around the world have increasingly emphasized the resource investment and industrial construction of satellite communication systems. The number of on-orbit satellites has seen an explosive growth globally. However, this has also made satellite communication channels increasingly congested and the interference between them more severe.

[0003] As an important part of a satellite receiver, the automatic gain control (AGC) loop can enhance the anti-interference ability of the entire system and improve the system's adaptability to complex and rapidly changing channel environments. Specifically, the functions of the AGC loop include: (1) maximizing the dynamic range of the input signal; (2) compensating for changes in the channel signal-to-noise ratio; (3) maintaining the amplitude of the input signal to the decision maker within an optimal range.

[0004] To achieve the above functions, the AGC loop includes modules such as a variable gain amplifier, a gain error detector, and a gain control signal generator. The gain error detector generates a gain error signal by comparing the amplitude information of the input signal with a desired threshold. The gain control signal generator processes the gain error signal to generate a gain control signal to control the gain of the amplifier, thereby completing the automatic feedback adjustment of the gain. The traditional AGC loop is implemented using analog circuits, with high hardware costs, insufficient precision in the operation process, and poor versatility. Once deployed, parameters such as the AGC dynamic range and desired threshold cannot be flexibly configured. Summary of the Invention

[0005] In view of one or more of the above defects or improvement requirements of the prior art, the present invention provides an all-digital satellite demodulator automatic gain control system, which includes: a pre-level detector, a variable gain amplifier, a gain error detector, and a loop filter;

[0006] The pre-level detector is used to estimate the amplitude of the input complex signal and compare it with the magnitude of a user-predefined level threshold value to obtain a level indication signal;

[0007] The variable gain amplifier is used to amplify or attenuate the signal obtained by matching filtering the input complex signal according to the gain control signal;

[0008] The gain error detector is used to compare the output signal of the control system with the user-predefined threshold value to generate a gain error signal and a power indication signal;

[0009] The loop filter is configured to filter the gain error signal to generate the gain control signal, thereby controlling the variable gain amplifier to form a closed-loop feedback structure.

[0010] Preferably, the signal after the input complex signal is matched and filtered refers to: a local oscillation signal generated by a local oscillator signal generator that is of the same frequency and in-phase with the carrier in the input complex signal, and then the mixer uses the local oscillation signal to remove the carrier existing in the input complex signal, and then the out-of-band noise and interference are filtered out by the matched filter, and the target signal component in the received signal is retained.

[0011] The present invention also provides a method for gain control using the above system, including the following steps:

[0012] Step S1: The pre-level detector generates a level indication signal by comparing the amplitude of the input complex signal with the magnitude of a user-predefined level threshold;

[0013] Step S2: A mixer and a local oscillator signal generator are used to remove the carrier in the input signal;

[0014] Step S3: A matched filter is used to perform matched filtering on the signal with the carrier removed to maximize its signal-to-noise ratio;

[0015] Step S4: The variable gain amplifier is used to amplify or attenuate the signal after matched filtering according to the gain control signal;

[0016] Step S5: The gain error detector is used to generate a gain error signal and a power indication signal, and the gain error signal is used as the input to the loop filter;

[0017] Step S6: The loop filter is used to filter the gain error signal to generate a gain control signal.

[0018] Preferably, in step S4, the linear gain of the amplifier and the logarithmic gain of the amplifier are calculated according to the following formula:

[0019]

[0020] G AGC-dB =20×[log(1.0+m AGC )+e AGC log(2)]

[0021] where m AGC and e AGC are respectively the base part and the exponent part of the gain control signal.

[0022] Preferably, in step S5, the gain error detector includes three modules: a Cartesian coordinate - polar coordinate converter, a gain error signal generator, and a power comparator.

[0023] Preferably, in step S5, the gain error detector includes a gain error signal generator, which is used to compare the amplitude of the output signal of the variable gain amplifier with a user - preset threshold value, so as to obtain a gain error signal as the input of the loop filter.

[0024] Preferably, in step S6, the loop filter allows the user to configure three parameters: the filter coefficient, the minimum AGC gain, and the maximum AGC gain.

[0025] Generally speaking, compared with the prior art, the beneficial effects of the above - mentioned technical solution conceived by the present invention include:

[0026] (1) The embodiment of the present invention provides a full - digital satellite demodulator AGC design method. The AGC loop designed by this method can reduce the hardware overhead, support flexible configuration of loop parameters, and at the same time maintain high - precision calculation results.

[0027] (2) The embodiment of the present invention realizes the automatic gain control function of the input signal of the satellite demodulator by designing a full - digital satellite demodulator AGC loop. While keeping the amplitude of the input signal of the decision - maker within the optimal range, it maximizes the dynamic range of the input signal and compensates for the change of the channel signal - to - noise ratio, solving the problems of large hardware overhead, low operation accuracy, and inflexible configuration of the AGC loop on traditional satellite demodulators. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a flowchart of a full - digital satellite demodulator automatic gain control (AGC) design method provided by an embodiment of the present invention;

[0029] Figure 2 is a flowchart of a pre - level detector provided by an embodiment of the present invention;

[0030] Figure 3 is a schematic diagram of a mixer provided by an embodiment of the present invention;

[0031] Figure 4 is a flowchart of a gain error detector provided by an embodiment of the present invention;

[0032] Figure 5 is a schematic diagram of a Cartesian coordinate - polar coordinate converter provided by an embodiment of the present invention;

[0033] Figure 6 is a flowchart of a loop filter provided by an embodiment of the present invention;

[0034] Figure 7 It is a schematic diagram of the numerical format and bit weight of a gain control signal provided by an embodiment of the present invention;

[0035] Figure 8 It is a relationship diagram between the high eight - bit value of the gain control signal and the AGC loop gain provided by an embodiment of the present invention. Detailed implementation manners

[0036] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0037] Embodiment:

[0038] As Figure 1 shown, it is a flowchart of a design method for an all - digital satellite demodulator automatic gain control (AGC). The AGC loop includes:

[0039] A pre - level detector 101, which is used to quickly estimate the amplitude of the input complex signal r(n) and compare it with the magnitude of the user - preset level threshold A d to obtain a level indication signal d(n) with a bit width of 1 bit.

[0040] A mixer 102, which is used to remove the possible carrier in the input signal by using the oscillation signal generated locally.

[0041] A local oscillator signal generator 103, which is used to generate a local oscillator signal with the same frequency and phase as the carrier in the input complex signal.

[0042] A matched filter 104, which is used to filter out the out - of - band noise and interference in the received signal and retain only the target signal component in the received signal as much as possible.

[0043] A variable - gain amplifier 105, which is used to amplify or attenuate the signal s(n) after matched filtering according to the gain control signal c(n).

[0044] A gain error detector 106, which is used to compare the AGC loop output signal with the user - preset threshold value to generate a gain error signal e(n) and a power indication signal p(n).

[0045] A loop filter 107, which is used to filter the gain error signal e(n) to generate a gain control signal c(n), thereby controlling the variable - gain amplifier to form a closed - loop feedback structure.

[0046] The automatic gain control loop (AGC) 108 adjusts the gain of the amplifier circuit in a closed-loop feedback regulation manner to keep the amplitude of the output signal of the amplifier circuit near the expected value.

[0047] Figure 2 The following is a flowchart of a pre-level detector provided by an embodiment of the present invention. As Figure 2 shown, the pre-level detector module includes:

[0048] The amplitude fast estimator 201 obtains an estimated value of the amplitude of the input complex signal using formula (1).

[0049] The amplitude comparator 202 compares the estimated value of the amplitude Mag(r(n)) of the complex signal r(n) with the threshold A d . If Mag(r(n)) is less than the user-defined level threshold A d , then d(n) is set to "1" (high level); otherwise, d(n) is set to "0" (low level).

[0050] For example, the input of the pre-level detector is a signed fixed-point 16-bit complex signal r(n) (including the I channel and the Q channel), and the absolute value of a single-channel signal does not exceed 1. I r =-0.0108530111 (FE9C, hexadecimal), Q r =0.051550484 (0699, hexadecimal). According to the fast estimation algorithm, the estimated value of the amplitude of the complex signal r(n), Mag(r(n)), is 0.0555118330515 (071B, hexadecimal).

[0051] The user-defined level threshold is an unsigned fixed-point 8-bit decimal number, and the specific format is:

[0052] 2 0 .2 -1 2 -2 2 -3 2 -4 2 -5 2 -6 2 -7

[0053] The maximum representation range is from 0 to 1.9921875 (00-FF, hexadecimal). The user-defined level threshold A d is 0.0625 (08, hexadecimal). Taking the first eight bits of Mag(r(n)) (07, hexadecimal) and comparing with A d , we get d(n)=1.

[0054] Figure 3 The following is a schematic diagram of a mixer provided by an embodiment of the present invention. Refer toFigure 3 , the mixer is essentially a complex multiplier, and the two multipliers are the input complex signal and the locally generated oscillation signal respectively. The relationship between the input signal r(n) and the output signal x(n) is described by Equations (2) and (3).

[0055] The matched filter filters the output signal x(n) of the mixer to suppress out-of-band noise and interference signal components. In the embodiment of the present invention, an RRC filter (α = 0.25) is adopted.

[0056] Figure 4 It is a flowchart of a gain error detector provided by an embodiment of the present invention. See Figure 4 , the gain error detector includes:

[0057] A Cartesian coordinate - polar coordinate converter 301, which is used to extract the amplitude information of the output signal z(n) of the AGC loop. The relationship between the input and output signals of the Cartesian coordinate - polar coordinate converter is described by Equations (6) and (7), and its principle is as Figure 5 shown. The Cartesian coordinate - polar coordinate converter provided by the embodiment of the present invention specifically adopts the CORDIC algorithm to extract the amplitude information of the output signal z(n) and use it as the input of the gain error signal generator. Using the CORDIC algorithm can greatly reduce the computational complexity and is convenient for hardware implementation. If the absolute values of the I-channel and Q-channel of the input signal are both 1, the output amplitude value of the Cartesian coordinate - polar coordinate converter is that is, the gain of the Cartesian coordinate - polar coordinate converter is G C-P = 1.4142.

[0058] A gain error signal generator 302, which is used to generate a gain error signal e(n) as the input of the loop filter, as Figure 4 shown. The gain error signal generator is essentially a subtractor, and A e is the expected amplitude of the output signal of the AGC loop.

[0059] A power comparator 303, which is used to compare Mag(z(n)) with the user - preset level threshold A p , and obtain a power indication signal p(n). If Mag(z(n)) is less than the user - preset level threshold A p , then set p(n) to 1, otherwise, set p(n) to 0.

[0060] Figure 6 It is a flowchart of a loop filter provided by an embodiment of the present invention. See Figure 6 , the loop filter includes:

[0061] A scaler 401, which is used to scale the gain error signal e(n) with the filter coefficient K input by the user iThe scaling degree can be controlled, thereby directly affecting the AGC loop tracking speed, and the filter coefficient K i is divided into an exponential part e K and a base part m K in two parts. For example, the base part m K has a bit width of 3 bits and a value range of 0 to 7. The mapping relationship between the binary value of the base part m of the filter coefficient and the scaled decimal value is shown in Table 1 below: K Table 1:

[0062] Table 1:

[0063] Binary value Scaled decimal value Binary value Scaled decimal value 000 0.000 100 0.500 001 0.125 101 0.625 010 0.250 110 0.750 011 0.375 111 0.875

[0064] The exponential part e K has a bit width of 2 bits and a value range of 0 to 3. The mapping relationship between the binary value of the exponential part e of the filter coefficient and the scaled decimal value is shown in Table 2 below: K Table 2:

[0065] Table 2:

[0066]

[0067]

[0068] Combining the exponential part e K and the base part m K , the loop filter gain G LPF can be obtained as follows:

[0069]

[0070] It can be obtained from formula (9) that the loop filter gain G LPF has a value range of 0 to 0.875×2 -6 .

[0071] The saturation accumulator 402 is used to integrate the scaled gain error signal to obtain the gain control signal c(n). The user can input parameters G max and G min as the upper and lower limits of the saturation accumulator respectively. When the value of the saturation accumulator reaches G max , the value will no longer increase; when the value of the saturation accumulator reaches G min , the value will no longer decrease. The user can set G min and G max to the same value to set the gain of the AGC loop to a fixed value.

[0072] Figure 7 is a schematic diagram of the numerical format and bit weight of a gain control signal c(n) provided by an embodiment of the present invention. SeeFigure 7 , the upper eight bits of the saturated accumulator output signal are the exponential part (eee) and the mantissa part (mmmmm) of the gain control signal, G min and G max That is, by controlling the value of the upper eight bits, the upper and lower limits of the saturated accumulator are controlled. The last 10 bits (represented by "g" in the figure) are the input accumulation bits of the saturated accumulator, and each bit has a different weight.

[0073] Analyzing the numerical format and bit weights of the gain control signal c(n), the mantissa part m of the gain control signal can be obtained AGC The mapping relationship between the binary value and the scaled decimal value is shown in Table III below:

[0074] Table III:

[0075]

[0076]

[0077] Exponential part e of the gain control signal AGC The mapping relationship between the binary value and the scaled decimal value is shown in Table IV below:

[0078] Table IV:

[0079] Binary value Decimal value Scaled decimal value 000 0 1 001 1 2 010 2 4 011 3 8 100 4 16 101 5 32 110 6 64 111 7 128

[0080] As can be seen from formulas (4) and (5), if G min and G max are not set, the AGC loop gain range is from 1 to 1.96875×128. In logarithmic form, it is from 0 dB to 48 dB. The representation form of the gain control signal c(n) is similar to that of the filter coefficient K i in that both have a mantissa part and an exponential part. The difference is that the gain control signal is used to control the gain of the amplifier, while the filter coefficient only affects the convergence speed of the loop filter.

[0081] Figure 8 is a relationship diagram between the upper eight-bit value of the gain control signal c(n) provided by the embodiment of the present invention and the AGC loop gain. Refer to Figure 8 , the upper eight-bit value of the gain control signal c(n) and the AGC loop gain G AGC-dBThere is an approximate log-linear relationship between them. This approximate log-linear relationship can be used to predict the AGC response time. At the same time, this approximate log-linear relationship also indicates that the AGC loop gain does not change uniformly with the gain error. When the AGC loop gain is large, the loop gain changes faster caused by the gain error signal. When the AGC loop gain is small, the loop gain changes slower caused by the gain error signal. Since the AGC loop consists of a fully digital structure, after the hardware deployment, the user can still set G min and G max values, intercept any segment on the curve as the dynamic range of the actual AGC loop gain, so as to achieve the purpose of flexibly configuring the AGC loop parameters and facilitating adaptation to different application requirements.

[0082] The AGC loop convergence time is affected by various factors, including: the user preset expected threshold A e , the loop filter coefficient K i , the Cartesian to polar converter gain G C-P , the gain control signal bit weight, the saturation accumulator lower limit G min and the upper limit G max .

[0083] Among them, the loop filter coefficient K i directly determines the rate of change of the saturation accumulator value, and the rate of change of the loop filter output gain control signal directly determines the rate of change of the AGC loop tracking signal. The AGC loop response represents the change amplitude of the AGC loop gain caused by each change in the gain control signal value, and its unit is dB / symbol. The AGC loop response reflects the amplitude that the AGC loop gain can change per unit time. During the actual AGC loop convergence process, when the AGC loop starts to capture the signal, the value will be large, and as the signal amplitude gradually converges near the user's expected amplitude, the value gradually decreases until it decreases to near 0 and oscillates.

[0084] According to formula (9), the loop response value continuously decreases during the convergence process until it finally stabilizes near 0. After the AGC loop parameters are determined, the maximum value of the loop response can be calculated. Specifically, using the base parts of different gain terms to estimate the maximum value, the results are as follows:

[0085] RSP max = 1×0.5×0.5×2 -6 ×48 = 0.1875dB / symbol (11)

[0086] Among them, the first 0.5 is the most significant bit weight of the base part of G C-P , the second 0.5 is the most significant bit weight of the base part corresponding to the loop gain, 2 -6is the maximum shift gain, and 48 is the maximum value of the AGC loop gain. Accordingly, different bit weights W can be calculated according to formula (9). s Under this condition, the RSP value of the AGC loop response is as follows in Table V:

[0087] Table V:

[0088]

[0089]

[0090] It can be obtained from Table V that when the AGC loop gain is the maximum value of 48 dB, the maximum value of the loop response RSP is RSP max is 0.1875 dB / symbol, and the minimum value of RSP min is 0.02344 dB / symbol. By setting the error gain signal e(n) and the gain control signal c(n) with different bit widths, different tables of loop response RSP values can be obtained.

[0091] In the embodiment of the present invention, by designing an all-digital satellite demodulator AGC loop, the automatic gain control function of the input signal of the satellite demodulator is realized. While keeping the amplitude of the input signal of the decision maker within the optimal range, the dynamic range of the input signal is maximized, and the change of the channel signal-to-noise ratio is compensated, solving the problems of large hardware overhead, low operation accuracy, inflexible configuration, etc. of the AGC loop on the traditional satellite demodulator.

[0092] The automatic gain control method of the all-digital satellite demodulator provided by the present invention is as follows:

[0093] A pre-level detector is used to generate a level indication signal with a bit width of 1 bit. The pre-level detector obtains a level indication signal d(n) with a bit width of 1 bit by comparing the amplitude of the input complex signal r(n) with the user-predefined level threshold A d of the size.

[0094] The amplitude value of the fixed-point complex signal is quickly estimated according to the following formula:

[0095]

[0096] where n is the sampling time index, I r and Q r are the real part and the imaginary part of the input signal r(n) respectively. If Mag(r(n)) is less than the user-predefined level threshold A d, then set d(n) to "1" (high level); otherwise, set d(n) to "0" (low level). It can be found from the analysis and estimation process that by adopting the described fast estimation algorithm, the working delay of the pre-level detector can be greatly reduced, and at the same time, the system hardware overhead is not significantly increased.

[0097] The level indication signal d(n) generated by the pre-level detector can be integrated into an external or other AGC loop to ensure that when the amplitude of the input signal is lower than the lower limit of the dynamic range of the subsequent AGC loop, the system can be promptly prompted or warned, prompting other components of the system to take corresponding measures to ensure that the input of the subsequent AGC loop is within the dynamic range. When such a situation occurs in a traditional AGC loop, the system cannot be promptly reminded, but instead continues the subsequent automatic gain adjustment process, resulting in the demodulation end not being able to work in the best state, thus greatly reducing the demodulation performance of the system.

[0098] A mixer and a local oscillator signal generator are used to remove the possible carrier in the input signal. Due to the Doppler effect existing in the signal transmission process or the carrier component not being completely removed by the RF front end, there may be a frequency offset or a low-frequency carrier in the input signal at this time, which needs to be first sent into the mixer to eliminate the carrier. Essentially, a mixer is a complex multiplier, and its other input is an oscillation signal generated locally with the same frequency and phase as the carrier. In a digital circuit, the local oscillation is generally generated by an NCO.

[0099] The relationship between the input and output of the mixer can be described by the following formula:

[0100] I x = I r cos(ω c ) - Q r sin(ω c ) (2)

[0101] Q x = I r sin(ω c ) + Q r cos(ω c ) (3)

[0102] Among them, ω c is the frequency of the local oscillation signal, and I x and Q x are the real part and the imaginary part of the output signal x(n) of the mixer respectively.

[0103] A matched filter is used to maximize the signal-to-noise ratio at the sampling decision moment, thereby reducing the bit error rate of the entire system. After the mixer shifts the signal spectrum, the input baseband signal may contain the following several components:

[0104] 1. Target signal;

[0105] 2. Noise component;

[0106] 3. Interference signal component.

[0107] When the signal-to-noise ratio at the receiving end is relatively high, the component of the target signal will be much larger than other components. Conversely, when the signal-to-noise ratio at the receiving end is relatively low, the noise component or the interference signal component may be much larger than the target signal. Narrowing the bandwidth of the matched filter can effectively reduce the magnitudes of the noise component and the interference signal component, thereby improving the signal-to-noise ratio. Since the mixer, the local oscillator signal generator, and the matched filter are not the key focuses of this invention, no detailed elaboration will be provided here.

[0108] A variable gain amplifier is used to amplify or attenuate the signal s(n) after matched filtering according to the gain control signal. Although the matched filter suppresses the interference signal component and out-of-band noise, it cannot handle the in-band noise component. When the channel environment or the signal power at the transmitting end changes, it is necessary to compensate for the change in the amplitude of the received signal. The variable gain amplifier makes timely feedback to the gain control signal. Regardless of how the amplitude of the input signal changes (within the dynamic range), the amplitude of the output signal z(n) always remains near the desired level and remains relatively stable. There is a positive correlation between the amplifier gain and the gain control signal, rather than a strictly linear relationship.

[0109] Calculate the amplifier gain according to the following formula:

[0110]

[0111] G AGC-dB = 20 × [log(1.0 + m AGC ) + e AGC log(2)] (5)

[0112] where m AGC and e AGC are respectively the base part and the exponent part of the gain control signal. By controlling the bit lengths of the base part and the exponent part, the maximum and minimum values of the amplifier gain can be controlled, thereby affecting the dynamic range of the AGC loop. However, controlling the dynamic range in this way is not flexible. Once deployed, the dynamic range cannot be adjusted.

[0113] A gain error detector is used to generate a gain error signal and a power indication signal. The gain error detector includes three modules: a Cartesian coordinate - polar coordinate converter, a gain error signal generator, and a power comparator.

[0114] The Cartesian coordinate - polar coordinate converter maps the I - channel and Q - channel data into an equivalent polar coordinate representation. The specific relationship between the I - channel and Q - channel data and the polar coordinate data can be expressed as:

[0115]

[0116] Phase(z(n))=tan -1 (Q z / I z ) (7)

[0117] where I z and Q z are the real part and the imaginary part of the output signal z(n) of the AGC loop respectively, and tan -1 (·) is the arctangent function. The sampling rate of the input data of the Cartesian coordinate - polar coordinate converter determines the data processing speed of the AGC loop.

[0118] The gain error signal generator is used to compare the magnitude Mag(z(n)) of the amplifier output signal with the user - preset threshold value A e to obtain the gain error signal e(n) as the input of the loop filter. The user can control the desired magnitude of the stable signal by changing the preset threshold value A ed .

[0119] The gain error signal e(n) is calculated according to the following formula:

[0120] a(n)=A e -Mag(z(n)) (8)

[0121] The gain error signal e(n) is used as the input of the loop filter, which directly affects the change direction and change rate of the gain control signal. Setting e(n) to 0 can lock the amplification gain of the AGC loop at a fixed value. The gain of the gain error signal generator is denoted as G E .

[0122] The power comparator is used to generate a power indication signal with a bit width of 1. The power comparator obtains a power indication signal with a bit width of 1 bit by comparing the magnitude Mag(z(n)) of the amplifier output signal with the user - preset threshold value A p . If Mag(z(n)) is less than the user - preset level threshold A p , then p(n) is set to "1" (high level); otherwise, p(n) is set to "0" (low level).

[0123] The power indication signal p(n) generated by the power comparator can be used for signal detection and power detection, and can be integrated into an external AGC loop to ensure that when the output signal power is higher than the upper limit of the dynamic range of the AGC loop, the system can be prompted or warned to prompt other components of the system to take corresponding measures. Different from the pre-level detector, the input signal of the power comparator needs to go through modules such as a Cartesian-polar coordinate converter and a matched filter. Therefore, compared with the input signal, the generated power indication signal p(n) has a certain delay.

[0124] The loop filter is used to filter the gain error signal e(n) to generate a gain control signal c(n). The loop filter first scales the gain error signal e(n), and then integrates the scaled signal to obtain an L-bit gain control signal c(n). The weight of the i-th bit is denoted as W i (i = 1, 2, 3…, L), where the weight of the first bit aligned with the shifted gain error signal e(n) is denoted as W s . Intuitively, the gain control signal c(n) controls the amplitude of the amplifier output signal to be maintained near the user-preset threshold A e by adjusting the gain of the variable gain amplifier, so that the gain error signal e(n) is maintained near zero.

[0125] As the core module in the AGC loop, the user can configure three parameters for the loop filter, which are: filter coefficient K i , minimum AGC gain G min and maximum AGC gain G max . Similar to the AGC loop gain control signal c(n), the above parameters all include a mantissa part and an exponent part. By controlling the minimum AGC gain G min and the maximum AGC gain G max , the dynamic range of the AGC loop can be directly affected, and this method is flexible in configuration. After the hardware is deployed, the dynamic range of the AGC loop can still be changed by programming and other methods to adapt to different application requirements. Setting G min and G max to the same value can lock the amplification gain of the AGC loop at a fixed value.

[0126] The three parameters of the loop filter will directly affect the convergence time of the AGC loop. The larger the filter coefficient, the smaller the dynamic range, and the faster the AGC loop captures and tracks the signal. However, if the filter coefficient is too large, it may cause system oscillation and seriously reduce the system performance; if the filter coefficient is too small, the convergence time may be too long, resulting in the data part being unable to be demodulated normally. In addition, the convergence time of the AGC loop is also related to the symbol rate of the input signal.

[0127] The loop response RSP value represents the value (dB) of the change in the AGC loop gain caused by each change in the gain control signal value. Its unit is dB / symbol. The AGC loop response reflects the amplitude by which the AGC loop gain can change per unit time.

[0128] According to the designed AGC loop structure, the loop response RSP value can be calculated according to the following formula:

[0129] RSP = |z(n)| × G C-P × G E × W s × G AGC-dB (9)

[0130] That is, the RSP value is equal to the product of the amplitude of the output signal z(n), the Cartesian-to-polar converter gain G C-P , the gain of the gain error signal generator G E , the first bit weight W after shifting e(n) s and the loop filter gain G AGC-dB Among the five. During the actual convergence process of the AGC loop, when the AGC loop starts to capture the signal, the RSP value will be relatively large. As the signal amplitude gradually converges near the user-expected amplitude, the RSP value gradually decreases until it decreases to near 0 and oscillates.

[0131] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included within the protection scope of the present invention.

Claims

1. An all-digital satellite demodulator automatic gain control system, characterized in that: The system consists of an all-digital structure, including: a pre-level detector, a variable gain amplifier, a gain error detector, and a loop filter; The pre-level detector is used to estimate the amplitude of the input complex signal and compare it with the magnitude of the user-predefined level threshold to obtain a level indication signal; The variable gain amplifier is used to amplify or attenuate the signal obtained by matching filtering the input complex signal according to the gain control signal. The linear gain of the amplifier and the logarithmic gain of the amplifier are calculated according to the following formulas: Among them, and are the mantissa part and the exponent part of the gain control signal respectively; The gain error detector is used to compare the amplitude of the output signal of the variable gain amplifier with the expected amplitude of the AGC loop output signal and the user-predefined level threshold to generate a gain error signal and a power indication signal; The loop filter includes a scaler and a saturating accumulator. The scaler is used to scale the gain error signal, and the filter coefficient input by the user is used to control the scaling degree. The filter coefficient is divided into two parts: an exponential part and a base part. The loop filter gain is: Among them, and are the base part and the exponent part of the filter coefficient respectively; The saturating accumulator is used to integrate the scaled gain error signal to generate the gain control signal, thereby controlling the variable gain amplifier to form a closed-loop feedback structure; the upper and lower limits of the saturating accumulator are configured by the user.

2. The control system according to claim 1, wherein: The signal obtained by matching filtering the input complex signal refers to: a local oscillation signal generated by a local oscillator signal generator that is of the same frequency and in-phase with the carrier in the input complex signal. Then, a mixer uses the local oscillation signal to remove the carrier existing in the input complex signal, and then a matching filter filters out out-of-band noise and interference to retain the target signal component in the received signal.

3. The automatic gain control method using any one of the control systems according to claims 1-2, characterized in that: The method includes the following steps: Step S1: The pre-level detector generates a level indication signal by comparing the amplitude of the input complex signal with the user-predefined level threshold; Step S2: A mixer and a local oscillator signal generator are used to remove the carrier in the input complex signal; Step S3: A matching filter is used to perform matching filtering on the signal from which the carrier has been removed to maximize its signal-to-noise ratio; Step S4: The variable gain amplifier is used to amplify or attenuate the signal after matching filtering according to the gain control signal; Step S5: The gain error detector is used to generate a gain error signal and a power indication signal. The gain error signal serves as the input to the loop filter; Step S6: The loop filter is used to filter the gain error signal to generate a gain control signal.

4. The control method according to claim 3, wherein: In step S5, the gain error detector includes three modules: a Cartesian coordinate - polar coordinate converter, a gain error signal generator, and a power comparator.

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