A digital rotating downconversion system for satellite signals based on SOC

Abstract

This invention discloses a satellite signal digital rotating downconversion system based on a System-on-Chip (SOC). Targeting satellite navigation applications for agile aircraft, it employs a reset multiplication, Doppler frequency signal shifting, and combined digital downconversion method to complete the complex-phase rotating downconversion function of satellite signals, improving out-of-band noise suppression and increasing the carrier-to-noise ratio of the satellite signal receiver. Furthermore, an agile aircraft satellite receiver is constructed based on the aerospace electronic system computing center and a multi-frequency fusion integrated circuit RF front-end. The downconversion method is designed and implemented using software IP + integrated RF front-end. The software IP implementation includes a digital resampling function module, a local carrier NCO function module, and a multi-level complex-phase rotating digital downconversion function module. Compared with traditional spacecraft receiver downconversion methods, this method and design have advantages such as low power consumption and less logic unit resource usage.

Description

Technical Field

[0001] This invention relates to the field of satellite navigation signal radio frequency signal processing and down-conversion technology, and in particular to an implementation of a digital rotation down-conversion system for satellite signals based on a System-on-Chip (SOC). Background Technology

[0002] The general workflow of a satellite navigation receiver based on radio technology involves digitizing the analog signal at radio frequency (RF) or intermediate frequency (IF), and then using digital logic programming to implement some functions of traditional radio, such as digital down-conversion, digital filtering, digital frequency synthesis, and digital modulation and demodulation. After these steps, the digital signal output from the logic unit is supplied to a digital signal processor for information processing.

[0003] Digital down-conversion technology is a key technology in the field of communications, and its quality directly affects the performance of satellite navigation receivers. The main function of digital down-conversion technology in satellite navigation receivers is to convert analog-to-digital conversion to digital intermediate frequency (IF) and to extract the Doppler information from the digital IF into a zero-frequency signal.

[0004] With continuous technological innovation, FPGAs have achieved unprecedented breakthroughs in various fields requiring logic operations, making leaps in process technology, power consumption, size, and functional integration. This has improved the processing power of FPGAs, especially in the field of communications, making it possible to implement low-cost, high-performance digital down-conversion modules. However, implementing digital down-conversion functions in satellite navigation receivers using the traditional DSP+FPGA architecture results in relatively large size and power consumption, high design complexity, and improving out-of-band noise suppression capabilities to increase the carrier-to-noise ratio of satellite signal receivers remains a challenge. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and propose a satellite signal digital rotary downconversion system based on SOC, which reduces size and power consumption, reduces design difficulty, improves out-of-band noise suppression capability, and provides high-quality zero-frequency digital signals for satellite navigation receiver information processing circuits.

[0006] The technical solution adopted in this invention is as follows:

[0007] This design utilizes a hardware platform based on a System-on-a-Chip (SoC) and radio frequency integrated chip to achieve digital rotating down-conversion of satellite signals. Specifically, it proposes a SoC-based digital rotating down-conversion system for satellite signals, comprising: an RF signal conditioning and down-conversion module, a digital resampling module, a local carrier numerically controlled oscillator module, and a multi-stage complex-phase rotating down-conversion module.

[0008] The radio frequency signal conditioning and downconversion module includes a conditioning preselection module and a radio frequency integrated chip. The conditioning preselection module performs bandpass filtering on the weak radio frequency signal input at the antenna end, retains the selected radio frequency signal, filters out carrier signals of other frequency bands, and amplifies the retained signal at high frequency and low noise. The radio frequency integrated chip shifts the radio frequency signal to an intermediate frequency signal.

[0009] The digital resampling module resamples, quantizes, latches, and sends the RF intermediate frequency signal to the multi-stage complex phase rotating downconverter module;

[0010] The local carrier numerically controlled oscillator module is used to generate a single-frequency complex sine wave with adjustable output frequency, which is supplied to the multi-stage complex phase rotating downconverter module as an input signal.

[0011] The multi-stage complex phase rotating downconverter module uses a reset multiplication calculation to remove the Doppler frequency from the baseband signal, shifting the spectrum in the required frequency band to the zero-frequency signal.

[0012] Furthermore, the adjustment preselection module includes a filter, a low-noise amplifier, and an attenuator;

[0013] The filter performs bandpass filtering, retaining the selected RF signal and filtering out carrier signals from other frequency bands. The retained signal is then amplified at high frequency and low noise by passing it through a low-noise amplifier and attenuator.

[0014] Furthermore, the filter is a surface acoustic wave (SAW) filter.

[0015] Furthermore, the radio frequency integrated chip integrates a four-frequency dual-channel receiver (GPS_L1, BD_B1, BD_B2, BD_B3) that supports simultaneous independent operation of both channels.

[0016] Furthermore, the local carrier numerically controlled oscillator module generates the single-frequency complex sine wave signal required for down-conversion according to the set carrier frequency control word and a lookup table.

[0017] Furthermore, the local carrier numerically controlled oscillator module includes an accumulator, registers, and a lookup table; based on the system reference clock f clk The phase accumulator accumulates once according to the NCO control word K, stores the value calculated by the accumulator, and looks up the waveform in the waveform lookup table according to the value to obtain the corresponding waveform.

[0018] Furthermore, the system reference clock, NCO control word, and phase accumulator bit depth all control the clock value f generated by the local NCO. LO The specific formula is as follows:

[0019] f LO =f clk ·K / 2 n .

[0020] Furthermore, the multi-stage complex phase rotating digital down-converter module shifts the Doppler frequency signal to the zero-frequency signal by removing the carrier frequency component of the resampled complex signal, that is, subtracting the center frequency of the real signal from the original complex signal. Let the intermediate frequency f of the signal be... cent Then, after transformation, it becomes:

[0021]

[0022] Where Y(n) is the radio frequency intermediate frequency signal, Let X(n) be the quadrature local oscillator signal generated by the local carrier numerically controlled oscillator, and let X(n) be the resampled quadrature complex signal. Its expression can be expressed as:

[0023] X(n) = I(n) + i*Q(n)

[0024] Where I(n) and Q(n) are orthogonal complex signals, with I(n) and Q(n) being 90° out of phase, and i representing the imaginary part;

[0025] but

[0026]

[0027] Furthermore, the satellite signal digital rotating downconversion system is implemented through a System-on-Chip (SOC).

[0028] The significant advantages of this invention compared to existing technologies are:

[0029] (1) The downconversion system of this invention breaks the traditional DSP+FPGA architecture and adopts SOC platform instead of traditional DSP+FPGA platform. This reduces the size and the complexity of hardware circuit design. It uses fewer components and adopts complex phase rotation downconversion method to improve out-of-band noise suppression capability and improve the carrier-to-noise ratio of satellite signal receiver.

[0030] (2) The frequency conversion system of the present invention has a simple structure, which can shorten the system development cycle and reduce development risks;

[0031] (3) The present invention uses complex phase rotating downconversion technology to strip Doppler frequency, improve out-of-band noise suppression capability, and improve the carrier-to-noise ratio of satellite signal receiver. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of a digital rotating downconversion system for satellite signals.

[0033] Figure 2 This is a schematic diagram of the radio frequency signal adjustment and downconversion function module;

[0034] Figure 3This is the functional schematic diagram of a local carrier numerically controlled oscillator. Detailed Implementation

[0035] This invention discloses a satellite signal digital rotating downconversion system based on a System-on-Chip (SOC). Targeting satellite navigation applications for agile aircraft, it employs a reset multiplication, Doppler frequency signal shifting, and combined digital downconversion methods to achieve complex-phase rotating downconversion of satellite signals, improving out-of-band noise suppression and increasing the carrier-to-noise ratio of the satellite signal receiver. Furthermore, an agile aircraft satellite receiver is constructed based on the aerospace electronic system computing center and a multi-frequency fusion integrated circuit RF front-end. The downconversion method is designed and implemented using software IP and an integrated RF front-end. The software IP implementation includes a digital resampling module, a local carrier NCO module, and a multi-stage complex-phase rotating digital downconversion module. Compared with traditional spacecraft receiver downconversion methods, this method and design have advantages such as low power consumption and minimal logic unit resource usage.

[0036] like Figure 1 As shown, this invention proposes a satellite signal digital rotating downconversion system based on a System-on-Chip (SOC). Based on a hardware platform with an SOC and integrated radio frequency (RF) chip architecture, it achieves digital rotating downconversion of satellite signals. It mainly includes: an RF signal adjustment and downconversion module, a digital resampling module, a local carrier numerically controlled oscillator module, and a multi-stage complex-phase rotating downconversion module. This downconversion system is implemented using an SOC and serves as the computing center of an agile aircraft.

[0037] The radio frequency signal conditioning and downconversion module includes a conditioning preselection module and a radio frequency integrated chip. The conditioning preselection module performs bandpass filtering on the weak radio frequency signal input at the antenna end, retains the selected radio frequency signal, filters out carrier signals of other frequency bands, and amplifies the retained signal at high frequency and low noise. The radio frequency integrated chip shifts the radio frequency signal to an intermediate frequency signal.

[0038] The digital resampling module resamples, quantizes, latches, and sends the RF intermediate frequency signal to the multi-stage complex phase rotating downconverter module;

[0039] The local carrier numerically controlled oscillator module is used to generate a single-frequency complex sine wave with adjustable output frequency, which is supplied to the multi-stage complex phase rotating downconverter module as an input signal.

[0040] The multi-stage complex phase rotating downconverter module uses a reset multiplication calculation to remove the Doppler frequency from the baseband signal, shifting the spectrum in the required frequency band to the zero-frequency signal.

[0041] like Figure 2 As shown, the radio frequency signal adjustment and downconversion module of the present invention includes an adjustment preselection module and a radio frequency integrated chip, and mainly consists of a low noise amplifier, a filter, an attenuator and a radio frequency integrated chip.

[0042] The pre-selection module includes filters, low-noise amplifiers, and attenuators. It primarily uses filters for bandpass filtering, retaining the selected RF signal while filtering out carrier signals from other frequency bands. The retained signal is then amplified at high frequency and low noise using low-noise amplifiers and attenuators. The RF integrated chip amplifies the previous stage bandpass-filtered signal with low noise and shifts the RF signal to an intermediate frequency (IF) signal.

[0043] Preferably, the low-noise amplifier in the RF signal conditioning and down-conversion function module is simple in design, requires few external circuits, and is a low-noise, high-gain broadband low-noise amplifier designed using SiGe technology. This device can achieve low-noise, high-gain low-noise amplifier functions using only 4 to 5 external bias devices.

[0044] Preferably, the filter is a surface acoustic wave filter, which is small in size and has low insertion loss.

[0045] The RF integrated chip completes the RF signal to digital down-conversion. This chip highly integrates a four-frequency dual-channel receiver (GPS_L1, BD_B1, BD_B2, BD_B3) and supports simultaneous independent operation of both channels.

[0046] Preferably, the chip integrates a mixer with image rejection, an intermediate frequency bandpass filter, a variable gain amplifier, an analog-to-digital converter, a voltage-controlled oscillator, a fractional-order frequency-locked loop, and a low-dropout linear regulator, requiring only a few external components to operate. The RF integrated chip can be configured using SPI communication, allowing selection of satellite signal types and channel gain matching information according to specific needs.

[0047] like Figure 3 As shown, the local carrier numerically controlled oscillator (NCO) module mainly generates orthogonal, frequency-controllable, and stable sine and cosine signals. The stability of its function directly affects the correctness of the digital down-conversion. Generally, a discrete expression is used to represent the carrier NCO:

[0048] N(n) = cos(2πnf) LO / f clk (1)

[0049] Among them, f LO For the clock generated by the local NCO, f clk This is the system reference clock.

[0050] The local carrier numerically controlled oscillator module involved in this invention includes an accumulator, a register, and a lookup table; based on the system reference clock f clk The phase accumulator accumulates once according to the NCO control word K, stores the value calculated by the accumulator, and looks up the waveform lookup table according to the value to obtain the corresponding waveform;

[0051] The system reference clock, NCO control word, and phase accumulator bit depth all control the clock value f generated by the local NCO. LO The specific formula is as follows:

[0052] f LO =f clk ·K / 2 n (2)

[0053] This invention employs a 32-bit NCO control word K and an accumulator, a 6-bit lookup table input address, and a 6-bit output sine and cosine signal width. Assuming the accumulator's operating clock is 62MHz, to generate a (+2kHz) complex sine signal output, the NCO control word K needs to be configured as 2^32*2e3 / 62e6 = 138548 (0x0021D34). To generate a (-2kHz) complex sine signal output, the NCO control word K needs to be configured as 2^32*-2e3 / 62e6 = -138548 (0xFFFDE2CC).

[0054] The multi-stage complex phase rotating digital down-conversion module of this invention employs a reset multiplication operation method. Its function is to shift the spectrum in the required frequency band, moving the Doppler frequency signal to a zero-frequency signal. The Doppler frequency mainly includes frequency components synthesized from satellite motion Doppler frequency, local clock deviation, and receiver local motion Doppler.

[0055] The complex phase rotating digital down-converter module shifts the Doppler frequency signal to a zero-frequency signal by removing the carrier frequency component of the complex signal after AD resampling. This means subtracting the center frequency component of the real signal from the original complex signal. Let the intermediate frequency f of the signal be... cent Then, after transformation, it becomes:

[0056]

[0057] Where Y(n) is the radio frequency intermediate frequency signal, X(n) is the quadrature local oscillator signal generated by the local carrier numerically controlled oscillator. X(n) is a complex signal sampled orthogonally by the AD converter, and its expression can be given as:

[0058] X(n)=I(n)+i*Q(n) (4)

[0059] Where I(n) and Q(n) are orthogonal complex signals, with I(n) and Q(n) being 90° out of phase, and i representing the imaginary part;

[0060] therefore,

[0061]

[0062] This method reduces the spectral bandwidth by half in a specific frequency range compared to the bandpass filtering used when sampling real signals, thereby reducing out-of-band noise suppression and improving the carrier-to-noise ratio.

[0063] The signal acquired by the front-end of the RF integrated chip of this invention is a complex signal with a data rate of 62M, denoted as I+i*Q. The local carrier NCO generates a signal with the same data rate of 62M, denoted as cos(w*n)+i*sin(w*n). Multiplying the sampled complex signal with the signal from the local carrier NCO yields:

[0064] (I+i*Q)*(cos(w*n)+i*sin(w*n))=

[0065] (I*cos(w*n)-Q*sin(w*n))+i*(I*sin(w*n)+Q*cos(w*n))(6)

[0066] I*cos(w*n)-Q*sin(w*n) is the new I branch, and I*sin(w*n)+Q*cos(w*n) is the new Q branch for subsequent processing.

[0067] In summary, this invention uses a hardware platform based on SOC and RF integrated chips to achieve digital rotation downconversion processing of satellite signals, breaking the traditional DSP+FPGA architecture, reducing the size and design complexity, and improving out-of-band noise suppression capability by using complex phase rotation downconversion method, thereby increasing the carrier-to-noise ratio of the satellite signal receiver.

[0068] The parts of this invention not described in detail are common knowledge to those skilled in the art.

Claims

1. A satellite signal digital rotating downconversion system based on SOC, characterized in that... include: RF signal conditioning and downconversion module, digital resampling module, local carrier numerically controlled oscillator module, multi-stage complex phase rotating downconversion module; The radio frequency signal conditioning and downconversion module includes a conditioning preselection module and a radio frequency integrated chip. The conditioning preselection module performs bandpass filtering on the weak radio frequency signal input at the antenna end, retains the selected radio frequency signal, filters out carrier signals of other frequency bands, and amplifies the retained signal at high frequency and low noise. The radio frequency integrated chip shifts the radio frequency signal to an intermediate frequency signal. The digital resampling module resamples, quantizes, latches, and sends the RF intermediate frequency signal to the multi-stage complex phase rotating downconverter module; The local carrier numerically controlled oscillator module is used to generate a single-frequency complex sine wave with adjustable output frequency, which is supplied to the multi-stage complex phase rotating downconverter module as an input signal. The multi-stage complex phase rotating downconverter module uses a reset multiplication calculation to remove the Doppler frequency from the baseband signal, shifting the spectrum in the required frequency band to the zero-frequency signal.

2. The satellite signal digital rotating downconversion system based on SOC according to claim 1, characterized in that: The adjustment pre-selection module includes a filter, a low-noise amplifier, and an attenuator; The filter performs bandpass filtering, retaining the selected RF signal and filtering out carrier signals from other frequency bands. The retained signal is then amplified at high frequency and low noise by passing it through a low-noise amplifier and attenuator.

3. The satellite signal digital rotating downconversion system based on SOC according to claim 2, characterized in that: The filter is a surface acoustic wave filter.

4. A satellite signal digital rotating downconversion system based on SOC according to claim 2, characterized in that: The radio frequency integrated chip integrates a dual-channel receiver with four frequency points: GPS_L1, BD_B1, BD_B2, and BD_B3, supporting simultaneous independent operation of both channels.

5. A satellite signal digital rotating downconversion system based on SOC according to claim 1, characterized in that: The local carrier numerically controlled oscillator module generates the single-frequency complex sine wave signal required for down-conversion according to the set carrier frequency control word and a lookup table.

6. A satellite signal digital rotating downconversion system based on SOC according to claim 5, characterized in that: The local carrier numerically controlled oscillator module includes an accumulator, registers, and a lookup table; based on the system reference clock f clk The phase accumulator accumulates once according to the NCO control word K, stores the value calculated by the accumulator, and looks up the waveform in the waveform lookup table according to the value to obtain the corresponding waveform.

7. A satellite signal digital rotating downconversion system based on SOC according to claim 6, characterized in that: The system reference clock, NCO control word, and phase accumulator bit depth all control the clock value f generated by the local NCO. LO The specific formula is as follows: f LO =f clk ·K / 2 n 。 8. A satellite signal digital rotating downconversion system based on SOC according to claim 1, characterized in that: The multi-stage complex phase rotating digital down-converter module shifts the Doppler frequency signal to a zero-frequency signal by removing the carrier frequency component of the resampled complex signal. This means subtracting the center frequency component of the real signal from the original complex signal. Let the intermediate frequency f of the signal be... cent Then, after transformation, it becomes: Where Y(n) is the radio frequency intermediate frequency signal, Let X(n) be the quadrature local oscillator signal generated by the local carrier numerically controlled oscillator, and let X(n) be the resampled quadrature complex signal. Its expression can be expressed as: X(n) = I(n) + i*Q(n) Where I(n) and Q(n) are orthogonal complex signals, with I(n) and Q(n) being 90° out of phase, and i representing the imaginary part; but 9. The satellite signal digital rotating downconversion system based on SOC according to any one of claims 1-8, characterized in that: The satellite signal digital rotating downconversion system is implemented through a System-on-Chip (SOC).

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