Satellite signal digital rotation down-conversion system based on SOC

Abstract

The invention discloses an SOC-based satellite signal digital rotation down-conversion system, and aims at agile aircraft satellite navigation application, a reset multiplication method, a Doppler frequency signal moving method and a combined digital down-conversion method are adopted to complete a satellite signal complex phase rotation down-conversion function, improve the out-of-band noise suppression capability and improve the airborne noise ratio of a satellite signal receiver. An agile aircraft satellite receiver is constructed based on an agile aircraft spaceflight electronic system computing center and a multi-frequency-point fusion integrated circuit radio frequency front end, and design implementation of the down-conversion method is completed in a software IP + integrated radio frequency front end mode. The software IP specifically comprises a digital resampling function module, a local carrier NCO function module and a multistage complex phase rotation digital down-conversion function module, and compared with a traditional spacecraft receiver down-conversion method, the method and the design have the advantages of being low in power consumption and small in occupied logic unit resource quantity.

Description

Technical Field

[0001] The invention relates to the technical field of satellite navigation signal radio frequency signal processing and down-conversion, in particular to a realization of a satellite signal digital rotation down-conversion system based on SOC. Background Art

[0002] The working process of satellite navigation receiver based on radio technology is roughly to digitize analog signals at RF or IF frequencies, and use 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 the above work, the digital signal output by the logic unit is supplied to the digital signal processor for information processing.

[0003] Among them, digital down-conversion technology is a key technology in the field of communications, and the quality of this technology directly affects the performance of satellite navigation receivers. The biggest function of digital down-conversion technology in satellite navigation receivers is to convert analog-to-digital conversion to digital intermediate frequency and strip the Doppler information of the digital intermediate frequency into a zero-frequency signal.

[0004] With the continuous innovation of science and technology, FPGA has made unprecedented breakthroughs in various fields that require logical operations, and has made leaps and bounds in terms of process, power consumption, volume, and functional integration, thereby improving the processing capabilities of FPGA, especially in the field of communications, making it possible to realize low-cost and high-performance digital down-conversion modules. However, the traditional DSP+FPGA architecture realizes the digital down-conversion function of satellite navigation receivers, which is relatively large in size and power consumption, and has a high design complexity. In addition, how to improve the out-of-band noise suppression capability and improve the carrier-to-noise ratio of satellite signal receivers is also one of the problems faced. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art, propose a satellite signal digital rotation down-conversion system based on SOC, reduce the volume and power consumption, reduce the design difficulty, improve the out-of-band noise suppression capability, and provide high-quality zero-frequency digital signals for the satellite navigation receiver information processing circuit.

[0006] The technical solution adopted by the present invention is:

[0007] This design is a hardware platform based on SOC and RF integrated chip architecture to realize digital rotary down-conversion of satellite signals. Specifically, a satellite signal digital rotary down-conversion system based on SOC is proposed, including: RF signal adjustment and down-conversion module, digital resampling module, local carrier digital controlled oscillator module, multi-stage complex phase rotary down-conversion module;

[0008] The RF signal adjustment and down-conversion module includes an adjustment pre-selection module and an RF integrated chip; the adjustment pre-selection module performs bandpass filtering on the weak RF signal input from the antenna end, retains the selected RF signal, filters out the carrier signals of other frequency bands, and performs high-frequency and low-noise amplification on the retained signal, and the RF integrated chip moves the RF signal to an intermediate frequency signal;

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

[0010] The local carrier digitally controlled oscillator module is used to generate a single-frequency complex sinusoidal signal with adjustable frequency output, which is supplied to the multi-stage complex phase rotation down-conversion module as an input signal quantity;

[0011] The multi-stage complex phase rotation down-conversion module uses reset multiplication calculation to remove the baseband signal after the Doppler frequency is removed, and the spectrum on the frequency band needs to be moved to move the Doppler frequency signal to the zero-frequency signal.

[0012] Further, the adjustment pre-selection module includes a filter, a low noise amplifier and an attenuator;

[0013] The filter performs bandpass filtering, retains the selected RF signal, filters out the carrier signals of other frequency bands, and amplifies the retained signal through a low noise amplifier and attenuator for high frequency and low noise.

[0014] Furthermore, the filter adopts a surface acoustic wave filter.

[0015] Furthermore, the RF integrated chip integrates GPS_L1, BD_B1, BD_B2, BD_B3 four-frequency dual-channel receivers, supporting dual channels to work independently at the same time.

[0016] Furthermore, the local carrier digitally controlled oscillator module generates the single-frequency complex sinusoidal signal required for down-conversion in a lookup table manner according to the set carrier frequency control word.

[0017] Furthermore, the local carrier digitally controlled oscillator module includes an accumulator, a register and a lookup table; according to 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.

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

[0019] f LO =f clk K / 2 n .

[0020] Furthermore, the multi-stage complex phase rotation digital down-conversion module moves the Doppler frequency signal to the zero-frequency signal by removing the carrier frequency component of the resampled complex signal, that is, subtracting the frequency component of the center frequency of the real signal from the original complex signal as a whole. Assume that the intermediate frequency f cent , then after transformation:

[0021]

[0022] Among them, Y(n) is the RF intermediate frequency signal, is the orthogonal local oscillator signal generated by the local carrier digitally controlled oscillator, X(n) is the resampled orthogonal complex signal, and 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, where I(n) and Q(n) differ in phase by 90°, and i represents the imaginary part;

[0025] but

[0026]

[0027] Furthermore, the satellite signal digital rotation down-conversion system is implemented by SOC.

[0028] Compared with the prior art, the present invention has the following significant advantages:

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

[0030] (2) The down-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 adopts complex phase rotation down-conversion technology to strip off the Doppler frequency, improve the out-of-band noise suppression capability, and increase the carrier-to-noise ratio of the satellite signal receiver. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is the schematic diagram of the satellite signal digital rotary down-conversion system;

[0033] Figure 2 It is the schematic diagram of the RF signal adjustment and down-conversion function module;

[0034] Figure 3This is the functional schematic diagram of the local carrier digitally controlled oscillator. DETAILED DESCRIPTION

[0035] The invention discloses a satellite signal digital rotation down-conversion system based on SOC. Aiming at the application of agile aircraft satellite navigation, the system adopts reset multiplication, Doppler frequency signal shifting and combined digital down-conversion methods to complete the satellite signal complex phase rotation down-conversion function, improve the out-of-band noise suppression capability and improve the carrier-to-noise ratio of the satellite signal receiver. An agile aircraft satellite receiver is constructed based on the aerospace electronic system computing center of the agile aircraft and the multi-frequency point fusion integrated circuit radio frequency front end, and the design and implementation of the down-conversion method are completed in the form of software IP+integrated radio frequency front end. The specific implementation of the software IP includes a digital resampling module, a local carrier NCO module and a multi-stage complex phase rotation digital down-conversion module. Compared with the down-conversion method of the traditional spacecraft receiver, the method and design have the advantages of low power consumption and less occupied logic unit resources.

[0036] like Figure 1 As shown, the present invention proposes a SOC-based satellite signal digital rotation down-conversion system, which realizes the digital rotation down-conversion of satellite signals based on a hardware platform with SOC and integrated radio frequency chip as the architecture. It mainly includes: radio frequency signal adjustment and down-conversion module, digital resampling module, local carrier digital controlled oscillator module, and multi-stage complex phase rotation down-conversion module. The down-conversion system is implemented in SOC mode as the computing center of the agile aircraft.

[0037] The RF signal adjustment and down-conversion module includes an adjustment pre-selection module and an RF integrated chip; the adjustment pre-selection module performs bandpass filtering on the weak RF signal input from the antenna end, retains the selected RF signal, filters out the carrier signals of other frequency bands, and performs high-frequency and low-noise amplification on the retained signal, and the RF integrated chip moves the RF signal to an intermediate frequency signal;

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

[0039] The local carrier digitally controlled oscillator module is used to generate a single-frequency complex sinusoidal signal with adjustable frequency output, which is supplied to the multi-stage complex phase rotation down-conversion module as an input signal quantity;

[0040] The multi-stage complex phase rotation down-conversion module uses reset multiplication calculation to remove the baseband signal after the Doppler frequency is removed, and the spectrum on the frequency band needs to be moved to move the Doppler frequency signal to the zero-frequency signal.

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

[0042] The adjustment preselection module includes filters, low noise amplifiers and attenuators. The filter is mainly used for bandpass filtering, retaining the selected RF signal, filtering out the carrier signals of other frequency bands, and amplifying the retained signal with high frequency and low noise through the low noise amplifier and attenuator. The RF integrated chip performs low noise amplification on the previous bandpass filter signal and moves the RF signal to the intermediate frequency signal.

[0043] Preferably, the low noise amplifier in the RF signal adjustment and down-conversion function module is simple in design, has few peripheral circuits, and is designed using SiGe technology to be a low noise, high gain broadband low noise amplifier. The device can complete the low noise, high gain low noise amplifier function using 4 to 5 external bias devices.

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

[0045] The RF integrated chip completes the digital down-conversion of RF signals. The chip is highly integrated with GPS_L1, BD_B1, BD_B2, and BD_B3 four-frequency dual-channel receivers, supporting dual channels to work independently at the same time.

[0046] Preferably, the chip integrates a mixer with image suppression function, an intermediate frequency bandpass filter, a variable gain amplifier, an analog-to-digital converter, a voltage-controlled oscillator, a fractional frequency phase-locked loop, and a low-dropout linear regulator, and other circuits, and only requires a few peripheral components to work. The SPI communication method can be used to configure the radio frequency integrated chip, and the satellite signal type and channel gain matching information can be selected according to one's own needs.

[0047] like Figure 3 As shown, the local carrier digitally controlled oscillator function module mainly generates orthogonal, frequency-controllable and stable sine and cosine signals. The stability of its function directly affects the correctness of 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 is the clock generated by the local NCO, f clk The reference clock of the system.

[0050] The local carrier digitally controlled oscillator module of the present invention comprises an accumulator, a register and a lookup table; 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 count all control the clock value f generated by the local NCO. LO , the specific expression formula is:

[0052] f LO =f clk K / 2 n (2)

[0053] The present invention adopts NCO control word K and accumulator are both 32 bits, the input address of the lookup table is 6 bits, and the output sine and cosine signal bit width is 6 bits. Assuming that the accumulator working 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 rotation digital down-conversion function module of the present invention adopts a reset multiplication operation method, which is used to move the spectrum on the frequency band that needs to be used and move the Doppler frequency signal to the zero-frequency signal. The Doppler frequency mainly includes the frequency components synthesized by the satellite motion Doppler frequency, the local clock deviation, and the receiver local motion Doppler.

[0055] The complex phase rotation digital down-conversion module moves the Doppler frequency signal to the zero-frequency signal by removing the carrier frequency component of the complex signal after AD resampling, that is, subtracting the frequency component of the center frequency of the real signal from the original complex signal as a whole. Suppose the intermediate frequency f cent , then after transformation:

[0056]

[0057] Among them, Y(n) is the RF intermediate frequency signal, is the orthogonal local oscillator signal generated by the local carrier digital controlled oscillator. X(n) is the complex signal of AD sampling orthogonality, and its expression can be expressed as:

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

[0059] Where, I(n) and Q(n) are orthogonal complex signals, where I(n) and Q(n) differ in phase by 90°, and i represents the imaginary part;

[0060] therefore,

[0061]

[0062] This method reduces the spectrum bandwidth by half within 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 collected by the front end of the RF integrated chip of the present invention is a complex signal of 62M data rate, which is I+i*Q. The signal generated by the local carrier NCO at the same 62M data rate is cos(w*n)+i*sin(w*n). The sampled complex signal is multiplied by the local carrier NCO signal to obtain:

[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, the present invention adopts a hardware platform with SOC and RF integrated chip as the architecture to realize digital rotation down-conversion processing of satellite signals, breaking the traditional DSP+FPGA architecture, reducing the volume while reducing the complexity of the design, and using complex phase rotation down-conversion to improve the out-of-band noise suppression capability and improve the carrier-to-noise ratio of the satellite signal receiver.

[0068] Parts of the present invention that are not described in detail belong to common knowledge among those skilled in the art.

Claims

1. A satellite signal digital rotation down-conversion system based on SOC, characterized in that include: RF signal adjustment and down-conversion module, digital resampling module, local carrier digitally controlled oscillator module, multi-stage complex phase rotation down-conversion module; The RF signal adjustment and down-conversion module includes an adjustment pre-selection module and an RF integrated chip; the adjustment pre-selection module performs bandpass filtering on the weak RF signal input from the antenna end, retains the selected RF signal, filters out the carrier signals of other frequency bands, and performs high-frequency and low-noise amplification on the retained signal, and the RF integrated chip moves the RF signal to an intermediate frequency signal; The digital resampling module resamples, quantizes and latches the RF intermediate frequency signal and sends it to the multi-stage complex phase rotation down-conversion module; The local carrier digitally controlled oscillator module is used to generate a single-frequency complex sinusoidal signal with adjustable frequency output, which is supplied to the multi-stage complex phase rotation down-conversion module as an input signal quantity; The multi-stage complex phase rotation down-conversion module uses reset multiplication calculation to remove the baseband signal after the Doppler frequency is removed, and the spectrum on the frequency band needs to be moved to move the Doppler frequency signal to the zero-frequency signal.

2. The satellite signal digital rotation down-conversion system based on SOC according to claim 1, characterized in that: The adjustment preselection module includes a filter, a low noise amplifier and an attenuator; The filter performs bandpass filtering, retains the selected RF signal, filters out the carrier signals of other frequency bands, and amplifies the retained signal through a low noise amplifier and attenuator for high frequency and low noise.

3. The satellite signal digital rotation down-conversion system based on SOC according to claim 2, characterized in that: The filter adopts a surface acoustic wave filter.

4. The satellite signal digital rotation down-conversion system based on SOC according to claim 2, characterized in that: The radio frequency integrated chip integrates GPS_L1, BD_B1, BD_B2, BD_B3 four-frequency dual-channel receivers, and supports dual channels to work independently at the same time.

5. The satellite signal digital rotation down-conversion system based on SOC according to claim 1, characterized in that: The local carrier digitally controlled oscillator module generates the single-frequency complex sinusoidal signal required for down-conversion in a lookup table manner according to the set carrier frequency control word.

6. The satellite signal digital rotation down-conversion system based on SOC according to claim 5, characterized in that: The local carrier digitally controlled oscillator module includes an accumulator, a register, and a lookup table; according to 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.

7. The SOC-based satellite signal digital rotation down-conversion system according to claim 6, characterized in that: The system reference clock, NCO control word, and phase accumulator bit count all control the clock value f generated by the local NCO. LO , the specific expression formula is: f LO =f clk ·K / 2 n 。 8. The satellite signal digital rotation down-conversion system based on SOC according to claim 1, characterized in that: The multi-stage complex phase rotation digital down-conversion module moves the Doppler frequency signal to the zero-frequency signal by removing the carrier frequency component of the resampled complex signal, that is, subtracting the frequency component of the center frequency of the real signal from the original complex signal as a whole. Suppose the intermediate frequency f cent , then after transformation: Among them, Y(n) is the RF intermediate frequency signal, is the orthogonal local oscillator signal generated by the local carrier digitally controlled oscillator, X(n) is the resampled orthogonal complex signal, and its expression can be expressed as: X(n)=I(n)+i*Q(n) Where, I(n) and Q(n) are orthogonal complex signals, where I(n) and Q(n) differ in phase by 90°, and i represents the imaginary part; but 9. The satellite signal digital rotation down-conversion system based on SOC according to any one of claims 1 to 8, characterized in that: The satellite signal digital rotation down-conversion system is implemented by SOC.

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