CN109039471B - Digital-analog hybrid demodulation method applied to high-speed laser communication - Google Patents
Digital-analog hybrid demodulation method applied to high-speed laser communication Download PDFInfo
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Abstract
The invention discloses a digital-analog hybrid demodulation method applied to high-speed laser communication, which comprises the following steps: carrying out coarse compensation on the obtained carrier optical signal; performing photoelectric conversion on the carrier optical signal after compensation is obtained to generate an electric signal; carrying out quadrature frequency mixing on the generated electric signal and the local oscillation signal to obtain a baseband quadrature signal; dividing the baseband orthogonal signal into two paths of signals; providing the first path of signal to the FPGA through an amplitude limiter, and demodulating the first path of signal by the FPGA to obtain baseband data; performing analog processing on the second path of signals to obtain phase discrimination signals of residual carriers; the phase discrimination signal of the residual carrier wave is provided for the FPGA after A/D conversion; and the FPGA carries out carrier reconstruction after capturing and tracking the phase discrimination signal of the residual carrier after A/D conversion, and carries out orthogonal modulation based on the reconstructed carrier and the analog phase-locked loop PPL to obtain a local oscillator signal.
Description
Technical Field
The invention relates to the technical field of satellite communication, in particular to a digital-analog hybrid demodulation method applied to high-speed laser communication.
Background
The space laser communication system requires high-speed communication between space-based terminals by adopting laser as a medium, needs to deal with a scene of large dynamic high-speed signal processing, and requires to reduce complexity and power consumption as much as possible so as to adapt to a power-limited system.
At present, a space high-speed laser communication receiver has two systems, namely coherent and incoherent: the incoherent is mainly represented by intensity modulation and direct detection, and has low receiving sensitivity and low frequency spectrum utilization rate; the coherent communication has the advantage of sensitivity due to the amplification effect of the local oscillator light, and a high-order modulation mode can be selected to improve the utilization rate of the frequency spectrum.
Coherent demodulation techniques are mainly divided into two categories: analog homodyne optical phase-locked loop technology and digital optical heterodyne technology. The technical scheme of the analog homodyne optical phase-locked loop is similar to the scheme of a traditional microwave receiver, but the traditional Voltage Controlled Oscillator (VCO) is replaced by a tunable optical local oscillator, and the frequency estimation, the phase frequency discrimination and the phase discrimination, the loop filtering and the local oscillator light regulation of a carrier ring are all controlled by an analog device, so that the scheme has higher requirements on the stability and the drift rate of a laser and is easily influenced by the environment; according to the digital optical heterodyne technical scheme, an intermediate frequency signal is obtained through optical mixing, and then is sampled into a digital chip through a high-speed analog-to-digital converter (ADC) to complete a series of operations such as capturing, tracking, clock recovery and data demodulation.
In addition, the carrier doppler frequency of laser communication between low-earth orbit satellites can reach about 10GHz, the corresponding system symbol rate needs to reach dozens of Gbps magnitude, and the sampling rate of an analog-to-digital converter (ADC) needs to meet the nyquist theorem (that is, the sampling frequency of the ADC is at least 2 times of the signal frequency) to sample the transmission symbol, so that the traditional digital processing method is not applicable, and the traditional carrier synchronization method is difficult to apply.
Therefore, a novel digital-analog hybrid demodulation device and method applied to high-speed laser communication are urgently needed to solve the problems that in the prior art of laser communication, high-efficiency demodulation of large dynamic high-speed laser signals is difficult to realize, a high-speed analog-to-digital converter (ADC) and a high-speed parallel processing chip are needed, algorithm complexity is high, power consumption is high, and the like.
Disclosure of Invention
Aiming at the problems that the high-efficiency demodulation of a large dynamic high-speed laser signal is difficult to realize in the prior art of laser communication, a high-speed analog-to-digital converter (ADC) and a high-speed parallel processing chip are needed, the algorithm complexity is high, the power consumption is high and the like, according to one embodiment of the invention, a digital-to-analog hybrid demodulation method applied to the high-speed laser communication is provided, and the method comprises the following steps:
carrying out coarse compensation on the obtained carrier optical signal;
performing photoelectric conversion on the carrier optical signal after compensation is obtained to generate an electric signal;
carrying out quadrature frequency mixing on the generated electric signal and the local oscillation signal to obtain a baseband quadrature signal;
dividing the baseband orthogonal signal into two paths of signals;
the first path of signal is provided to the FPGA through a limiter,
the FPGA demodulates the first path of signal to obtain baseband data;
performing analog processing on the second path of signals to obtain phase discrimination signals of residual carriers;
the phase discrimination signal of the residual carrier wave is provided for the FPGA after A/D conversion; and
and the FPGA captures and tracks the phase discrimination signal of the residual carrier after A/D conversion, then carries out carrier reconstruction, and carries out orthogonal modulation on the basis of the reconstructed carrier and the analog phase-locked loop PPL to obtain a local oscillator signal.
In an embodiment of the present invention, the method for performing coarse compensation on the acquired carrier optical signal further includes;
satellite orbit information obtains carrier Doppler signals;
amplifying the obtained carrier Doppler signals by an optical amplifier; and
and roughly compensating the amplified carrier Doppler signal in the optical mixer by adjusting the optical local oscillator generated by the local oscillator laser.
In the embodiment of the present invention, the method for performing photoelectric conversion on the compensated carrier optical signal to generate an electrical signal is to perform photoelectric conversion on the optical signal output by the optical mixer through the balanced detector, the band-pass filter and the low-noise amplifier to generate an electrical signal.
In the embodiment of the present invention, the dividing the baseband orthogonal signal into two paths is to divide the baseband orthogonal signal into two paths by using a power divider.
In the embodiment of the present invention, the specific method for the FPGA to demodulate the first path of signal to obtain the baseband data is to demodulate the first path of signal by using a Decision Feedback Equalizer (DFE) and a Clock Data Recovery (CDR) module to obtain the baseband data.
In an embodiment of the present invention, the method for capturing the phase detection signal of the residual carrier after the a/D conversion by the FPGA further includes:
setting a frequency control word through software to control the frequency of the D/A output carrier;
detecting error signals on two local oscillator frequencies;
if no error signal is detected in both local oscillator frequencies, adjusting the local oscillator frequencies and continuing to scan in the whole processing bandwidth; and
and if the error signals are continuously detected at the two local oscillation frequencies, judging to obtain the frequency of the error signals.
In an embodiment of the present invention, the frequency control word is
Where M is the phase control word length.
In an embodiment of the present invention, the method for detecting an error signal in two local oscillation frequencies includes performing N-point FFT on the error-shaped signal, searching for a peak point m exceeding a threshold, and determining that an error signal is detected if the amplitude ratio of the peak point to the sub-peak point is greater than 10, where the frequency may be represented as
Wherein N, M denotes the FFT length and phase control word length, respectively, fsFor A/D miningThe sample frequency.
In an embodiment of the present invention, the method for determining and obtaining the frequency of the error signal is as follows:
let the local oscillator frequencies be fref,1And fref,2(fref,2>fref,1) The corresponding peak value is P1And P2Error signal estimation frequency of f1And f2；
If P1>P2If the frequency f of the error signal is equal to fref,1+f1；
If P1<P2If the frequency f of the error signal is equal to fref,2－f2。
The invention provides a digital-analog hybrid demodulation method applied to high-speed laser communication, which comprises the steps of firstly, obtaining carrier Doppler information by utilizing satellite orbit information, carrying out coarse compensation on the carrier Doppler by adjusting an optical local oscillator, and carrying out photoelectric conversion on a laser signal output by an optical mixer to generate an electric signal; then, orthogonal frequency mixing is carried out on the local oscillation signal generated locally to obtain a baseband orthogonal signal; the baseband orthogonal signal is divided into two paths, one path is sent into a GTX module of the FPGA through a limiter for processing, baseband data is demodulated through modules such as a Decision Feedback Equalizer (DFE) and a Clock Data Recovery (CDR), the other path is subjected to analog processing to obtain a phase demodulation signal of a residual carrier, the phase demodulation signal is collected into the FPGA through an A/D (analog/digital) circuit to generate a reconstructed residual carrier, and the local oscillation frequency is adjusted to achieve the purpose of carrier synchronization. The digital-analog hybrid demodulation method based on the invention can realize the high-efficiency demodulation of the large dynamic high-speed laser signal without high-speed A/D conversion.
Drawings
To further clarify the above and other advantages and features of embodiments of the present invention, a more particular description of embodiments of the invention will be rendered by reference to the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. In the drawings, the same or corresponding parts will be denoted by the same or similar reference numerals for clarity.
Fig. 1 is a schematic diagram of a receiver structure of a digital-analog hybrid demodulation method applied to high-speed laser communication according to an embodiment of the present invention.
Fig. 2 is a flowchart illustrating a digital-analog hybrid demodulation method applied to high-speed laser communication according to an embodiment of the present invention.
Fig. 3 shows a carrier capture flow chart of a digital-analog hybrid demodulation method applied to high-speed laser communication according to an embodiment of the present invention.
Detailed Description
In the following description, the invention is described with reference to various embodiments. One skilled in the relevant art will recognize, however, that the embodiments may be practiced without one or more of the specific details, or with other alternative and/or additional methods, materials, or components. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of embodiments of the invention. Similarly, for purposes of explanation, specific numbers, materials and configurations are set forth in order to provide a thorough understanding of the embodiments of the invention. However, the invention may be practiced without specific details. Further, it should be understood that the embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale.
Reference in the specification to "one embodiment" or "the embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.
It should be noted that, the method steps are described in a specific order in the embodiments of the present invention, however, this is only for convenience of distinguishing the steps, and the order of the steps is not limited, and in different embodiments of the present invention, the order of the steps may be adjusted according to the adjustment of the method.
The invention provides a digital-analog hybrid demodulation method applied to high-speed laser communication, which comprises the steps of firstly, obtaining carrier Doppler information by utilizing satellite orbit information, carrying out coarse compensation on the carrier Doppler by adjusting an optical local oscillator, and carrying out photoelectric conversion on a laser signal output by an optical mixer to generate an electric signal; then, orthogonal frequency mixing is carried out on the local oscillation signal generated locally to obtain a baseband orthogonal signal; the baseband orthogonal signal is divided into two paths, one path is sent into a GTX module of the FPGA through a limiter for processing, baseband data is demodulated through modules such as a Decision Feedback Equalizer (DFE) and a Clock Data Recovery (CDR), the other path is subjected to analog processing to obtain a phase demodulation signal of a residual carrier, the phase demodulation signal is collected into the FPGA through an A/D (analog/digital) circuit to generate a reconstructed residual carrier, and the local oscillation frequency is adjusted to achieve the purpose of carrier synchronization. The digital-analog hybrid demodulation method based on the invention can realize the high-efficiency demodulation of the large dynamic high-speed laser signal without high-speed A/D conversion.
A digital-analog hybrid demodulation method applied to high-speed laser communication according to an embodiment of the present invention will be described with reference to fig. 1-2. Fig. 1 is a schematic diagram illustrating a receiver structure of a digital-analog hybrid demodulation method applied to high-speed laser communication according to an embodiment of the present invention; fig. 2 is a flowchart illustrating a digital-analog hybrid demodulation method applied to high-speed laser communication according to an embodiment of the present invention; fig. 3 shows a carrier capture flow chart of a digital-analog hybrid demodulation method applied to high-speed laser communication according to an embodiment of the present invention.
First, in step 201, a laser signal is coarsely compensated. As shown in fig. 1, after the satellite orbit information obtains carrier doppler signal information, the obtained carrier doppler signal is amplified by an optical amplifier, then an optical local oscillator is generated by adjusting a local oscillator laser, and the amplified carrier doppler signal is coarsely compensated in an optical mixer to obtain a compensated carrier doppler signal.
Next, in step 202, the carrier doppler signal obtained after the compensation is subjected to photoelectric conversion, and an electric signal is generated. In one embodiment of the present invention, as shown in fig. 1, the laser signal output by the optical mixer is photoelectrically converted by the balanced detector, the band-pass filter, and the low-noise amplifier to generate an electrical signal.
Then, in step 203, the generated electrical signal and the local oscillator signal generated locally are subjected to quadrature mixing by a quadrature mixer, so as to obtain a baseband quadrature signal. In an embodiment of the present invention, as shown in fig. 1, the local oscillation signal is generated by performing quadrature mixing modulation on a digital direct frequency synthesis DDS and an analog phase-locked loop PPL and then performing frequency multiplication, which has the advantages of a large dynamic range of frequency, low phase noise, and a fast adjustment speed.
Next, at step 204, the baseband quadrature signal is split into two paths. In one embodiment of the present invention, a power divider is used to divide the baseband quadrature signal into two paths. One path is output to a high-speed serial receiving module in the FPGA, and the other path is output to a carrier capturing and tracking module.
Then, in step 205, one of the signals is provided to a high-speed serial receiving module in the FPGA through a limiter.
Next, in step 206, the demodulation obtains baseband data. Since the data rate that the present invention needs to process reaches dozens Gbps, the conventional A/D chip and FPGA can not process the signal with such high rate at all. In an embodiment of the present invention, as shown in fig. 1, a processing scheme based on a high-speed serial receiving mode is designed, a baseband orthogonal signal enters a high-speed serial receiving module in an FPGA through a slicer, baseband data is obtained through module demodulation such as a Decision Feedback Equalizer (DFE) and a Clock Data Recovery (CDR), and is further processed in the FPGA, so that a/D sampling is omitted, and meanwhile, the data is processed in parallel through the high-speed serial receiving module, thereby reducing a requirement for processing a clock of the FPGA.
Then, in step 207, the other signal is subjected to analog processing to obtain a phase detection signal of the residual carrier. In one embodiment of the invention, the analog processing is performed by an analog multiplier and a low pass filter, as shown in FIG. 1.
Next, in step 208, the phase-detected signal of the residual carrier is a/D converted and then provided to the carrier capture and tracking module of the FPGA.
Finally, in step 209, the carrier capture and tracking module of the FPGA performs carrier reconstruction after capturing and tracking the phase-discriminated signal, and adjusts the local oscillator signal based on the reconstructed carrier to achieve the purpose of carrier synchronization.
According to an embodiment of the present invention, when providing the above-mentioned digital-analog hybrid demodulation method applied to high-speed laser communication, the main technical contents involved include:
1) intermediate frequency quadrature mixing technique
The method comprises the steps of inputting a broadband signal amplified by an amplifier and a local oscillation signal generated by a local oscillation laser into an optical mixer for orthogonal frequency mixing, carrying out down-conversion on the input signal and eliminating carrier Doppler frequency shift, and outputting two paths of baseband orthogonal signals. The local oscillation signal is generated by performing quadrature modulation on a digital direct frequency synthesis DDS and an analog phase-locked loop PPL, and has the advantages of large frequency dynamic range, low phase noise and high adjusting speed.
2) Power divider
The method is characterized in that a power divider is used for dividing baseband orthogonal signals into two paths. The quadrature mixer outputs baseband quadrature signals, the baseband quadrature signals are divided into two paths after passing through the power divider, one path of the baseband quadrature signals is output to a high-speed serial receiving module in the FPGA, and the other path of the baseband quadrature signals is output to a carrier capturing and tracking module.
3) Analog phase-discrimination and low-pass filtering
The method is characterized in that analog phase discrimination is carried out on baseband orthogonal signals, then low-pass filtering is carried out on phase discrimination errors, and the baseband orthogonal signals can be respectively expressed as:
I＝cos(Δωt) (1)
Q＝sin(Δωt) (2)
where Δ ω is the frequency residual and t is time, the phase discrimination error can be expressed as:
Δθ(t)＝sin(2Δωt) (3)
after analog phase discrimination, low-pass filtering is carried out on the phase discrimination error to assist later carrier capture and tracking.
4) A/D sampling
The method refers to that the phase discrimination error of a phase discrimination signal is subjected to A/D sampling. After a/D sampling, the phase discrimination error can be expressed as:
wherein f issIs the A/D sampling frequency, n is the sampling point number, omega is the normalized digital frequency, epsilon is the DC offset.
5) Offset cancellation
Refers to the elimination of dc offset. Since carrier estimation and tracking are very sensitive to dc offset, it is necessary to first remove the dc offset before processing. The dc blocking process needs to be performed by a high-pass filter, and the digital phase discrimination error of the processed phase discrimination signal can be expressed as:
Δθ(n)＝sin(Ωn) (5)
6) carrier acquisition
The method refers to the carrier capture of the phase discrimination signal. In one embodiment of the invention, the operating frequency of A/D, D/A is too high for direct sampling and regeneration, taking into account the residual Doppler frequency range up to several hundred MHz, and is also a tremendous burden on FPGA processing. Therefore, the invention provides a scanning strategy, the whole frequency capture range is divided into a plurality of frequency sections in the analog part by a mode of controlling the local oscillation frequency through software, and the Doppler frequency is searched in each section, so that an A/D chip only needs to sample a single frequency section, and the pressure of A/D sampling and the FPGA processing rate are greatly reduced.
Because real signals are generated by complex signals during phase discrimination, frequency sign information is lost, so that only absolute deviation of frequency can be obtained during carrier capture by utilizing conventional FFT conversion, and whether the frequency is positive or negative cannot be judged. To this end, fig. 3 shows a carrier capture flow chart of a digital-analog hybrid demodulation method applied to high-speed laser communication according to an embodiment of the present invention, and as shown in fig. 3, the FFT-based frequency estimation algorithm is modified as follows:
A) the frequency control word is set through software to control the D/A output carrier frequency, and within the whole frequency range, the frequency control word is set step by step to control the D/A output carrier frequency, the step value is half of the bandwidth of the low-pass filter B, and can be expressed as:
Δθ(n)＝sin(Ωn) (5)
fref＝fc-fd,max,fc-fd,max+Δf,...,fc+fd,max-Δf,fc+fd,max(6)
Δf＝B/2 (7)
wherein f isrefIs the local oscillator frequency, f, of the quadrature mixercIs to set a carrier frequency, fd,maxIs the upper doppler frequency limit, Δ f is the frequency step value, and B represents the bandwidth of the low pass filter B.
B) Performing N-point FFT on the error shaping signal, searching a peak point m exceeding a preset threshold, and if the amplitude ratio of the peak point to the secondary peak point is more than 10, determining that the error signal is detected, wherein the frequency can be expressed as:
wherein f issIs the a/D sampling frequency.
C) If no error signal is detected in both local oscillator frequencies, adjusting the local oscillator frequencies and continuing to scan in the whole processing bandwidth;
D) if error signals are detected at both of the two local oscillator frequencies continuously, the local oscillator frequencies are set to be fref,1And fref,2(fref,2>fref,1) The corresponding peak value is P1And P2Error signal estimation frequency of f1And f2Then, the error signal frequency can be determined as follows:
if P1>P2Then, the error signal frequency:
f＝fref,1+f1(9)
on the contrary, if P1<P2Then frequency of error signal
f＝fref,2－f2(10)
E) The corresponding frequency control word is
Where M is the phase control word length.
7) Carrier tracking
Which refers to performing carrier tracking of the phase-detected signal. In an embodiment of the present invention, after the carrier acquisition is successful, the acquisition scanning is stopped, and the carrier tracking is started. Since the D/a operating clock should be more than 3 times the signal frequency, the D/a requirement for generating a carrier with a frequency of several hundred MHz is high. In order to reduce the D/a operation clock, in an embodiment of the present invention, the frequency of the regenerated carrier is compressed to one eighth of the original frequency in the digital domain by using an analog/digital combination method, and then the real frequency is reproduced by a frequency multiplication method in the analog processing, so that the requirement on the D/a operation frequency is reduced.
In one embodiment of the present invention, in order to reduce the D/a operating frequency, the frequency is specifically processed in the tracking by the following method:
A) setting the frequency control word of the carrier regeneration module E as the frequency control word determined by the capture unit;
B) inputting the error shaping signal into a loop filtering unit C for filtering;
C) the loop filter output is divided by 8 and input as a frequency control word to the carrier regeneration block E.
8) Quadrature modulation
After the carrier reconstruction is finished, the local oscillation signal is generated in an orthogonal modulation mode based on the reconstructed carrier signal and the analog phase-locked loop PPL, and the method has the advantages of large frequency dynamic range, low phase noise and high adjusting speed. Since the frequency control word is reduced by 8 times in carrier tracking, 4 times of frequency needs to be multiplied on the signal after quadrature modulation to generate a real control frequency.
9) High speed serial reception
The FPGA pair receives data in high-speed serial mode. Since the data rate that the present invention needs to process reaches dozens Gbps, the conventional A/D chip and FPGA can not process the signal with such high rate at all. In one embodiment of the invention, a processing scheme based on a high-speed serial receiving mode is designed, baseband orthogonal signals are processed in a high-speed serial receiving module in an FPGA through a limiter, and after processing such as decision feedback equalization, time synchronization and the like, baseband data are obtained and further processed in the FPGA, so that A/D sampling is omitted, and meanwhile, the data are processed in parallel through the high-speed serial receiving module, and the requirement on an FPGA processing clock is reduced.
Based on the digital-analog hybrid demodulation method applied to high-speed laser communication, carrier Doppler information is obtained by satellite orbit information, coarse compensation is carried out on the carrier Doppler by adjusting an optical local oscillator, and photoelectric conversion is carried out on laser signals output by an optical mixer to generate electric signals; then, orthogonal frequency mixing is carried out on the local oscillation signal generated locally to obtain a baseband orthogonal signal; the baseband orthogonal signal is divided into two paths, one path is sent into a GTX module of the FPGA through a limiter for processing, baseband data is demodulated through modules such as a Decision Feedback Equalizer (DFE) and a Clock Data Recovery (CDR), the other path is subjected to analog processing to obtain a phase demodulation signal of a residual carrier, the phase demodulation signal is collected into the FPGA through an A/D (analog/digital) circuit to generate a reconstructed residual carrier, and the local oscillation frequency is adjusted to achieve the purpose of carrier synchronization. The digital-analog hybrid demodulation method based on the invention can realize the high-efficiency demodulation of the large dynamic high-speed laser signal without high-speed A/D conversion.
While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to persons skilled in the relevant art that various combinations, modifications, and changes can be made thereto without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention disclosed herein should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
Claims (7)
1. A digital-analog hybrid demodulation method applied to high-speed laser communication comprises the following steps:
carrying out coarse compensation on the obtained carrier optical signal;
performing photoelectric conversion on the carrier optical signal after compensation is obtained to generate an electric signal;
carrying out quadrature frequency mixing on the generated electric signal and the local oscillation signal to obtain a baseband quadrature signal;
dividing the baseband orthogonal signal into two paths of signals;
providing the first path of signal to the FPGA through an amplitude limiter;
the FPGA demodulates the first path of signal to obtain baseband data;
performing analog processing on the second path of signals to obtain phase discrimination signals of residual carriers;
the phase discrimination signal of the residual carrier wave is provided for the FPGA after A/D conversion; and
the FPGA carries out carrier wave reconstruction after capturing and tracking the phase discrimination signal after A/D conversion, carries out orthogonal modulation based on the reconstructed carrier wave and an analog phase-locked loop PPL to obtain a local oscillation signal,
the method for capturing the phase detection signal after the a/D conversion by the FPGA further comprises:
setting frequency control words through software to control D/A output carrier frequency and further control the local oscillator frequency of the orthogonal mixer, realizing segmented scanning of phase discrimination signal frequency, and in the whole frequency range, controlling the D/A output carrier frequency according to the step-by-step setting frequency control words to obtain the local oscillator frequency f of the orthogonal mixerrefWherein f isref＝fc-fd,max,fc-fd,max+Δf,...,fc+fd,max-Δf,fc+fd,max，fcIs to set a carrier frequency, fd,maxIs the upper doppler frequency limit, Δ f is the frequency step value, B denotes the bandwidth of the low-pass filter, Δ f is B/2;
carrying out offset elimination on the phase discrimination signal subjected to A/D conversion to obtain a phase discrimination shaping signal;
in order to perform N-point FFT conversion on the phase discrimination shaped signal, searching peak values of all spectral lines of FFT, and if the amplitude ratio of the peak value to the secondary peak value is more than 10, determining that the phase discrimination signal is detected, wherein the frequency of the phase discrimination signal can be expressed as
Where N, m denotes the FFT length and the position of the spectral line at which the peak is located, respectively, fsIs the A/D sampling frequency;
during frequency scanning, if phase discrimination signals are not detected at least once on two adjacent local oscillator frequencies, adjusting the local oscillator frequency, and continuing to scan in the whole processing bandwidth; and
and during frequency scanning, if the phase discrimination signals are detected twice on two adjacent local oscillator frequencies, the frequency acquisition is confirmed to be successful, and the acquisition is finished.
2. The method of claim 1, wherein the method of coarsely compensating the acquired carrier optical signal further comprises;
satellite orbit information obtains carrier Doppler signals;
amplifying the obtained carrier Doppler signals by an optical amplifier; and
and roughly compensating the amplified carrier Doppler signal in the optical mixer by adjusting the optical local oscillator generated by the local oscillator laser.
3. The method of claim 1, wherein the compensating carrier optical signal is generated by performing optical-to-electrical conversion on the optical signal output by the optical mixer through a balanced detector, a band-pass filter and a low-noise amplifier.
4. The method of claim 1, wherein the splitting the baseband quadrature signal into two paths is performed by a power splitter.
5. The method as claimed in claim 1, wherein the FPGA demodulates the first signal to obtain the baseband data by demodulating through a decision feedback equalizer DFE and a clock data recovery CDR module.
6. The method of claim 1, wherein the frequency control word is
Where M is the phase control word length, fsIs the D/A clock frequency and f is the D/A output carrier frequency.
7. The method of claim 1, further comprising:
when the phase-discriminated signal is subjected to frequency scanning, the phase-discriminated signal is captured by two consecutive scans, and the local oscillator frequencies of the two adjacent scans are respectively fref,1And fref,2Wherein f isref,2>fref,1The frequencies of the spectral lines where the peaks are located after FFT estimation of the signals are respectively f1And f2The corresponding peak value is P1And P2Then the acquisition frequency is set as follows:
if P1>P2Then the quadrature mixer local oscillator frequency is set to f when the acquisition shifts to trackingref,1With D/A output frequency set to f1；
If P1<P2Then the quadrature mixer local oscillator frequency is set to f when the acquisition shifts to trackingref,1With D/A output frequency set to Δ f-f2。
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| CN114667717B (en) * | 2020-08-17 | 2024-02-09 | 湖南迈克森伟电子科技有限公司 | Satellite laser broadband demodulation method and device |
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