CN114143411A - Meteorological fax digital receiving system based on FPGA - Google Patents
Meteorological fax digital receiving system based on FPGA Download PDFInfo
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- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
- H04N1/32—Circuits or arrangements for control or supervision between transmitter and receiver or between image input and image output device, e.g. between a still-image camera and its memory or between a still-image camera and a printer device
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Abstract
The invention provides a weather fax digital receiving system based on FPGA, comprising: the system comprises a digital down-conversion module, an FSK demodulation module, a weather fax signal identification module, a weather fax data framing module and a radio frequency interaction module. And the digital down-conversion module is used for performing decimation and filtering processing on the sampling signal. The FSK demodulation module is used for carrying out phase and frequency discrimination processing. The weather facsimile signal identification module is used for carrying out signal identification according to the format of the signal. And the meteorological fax data framing module is used for framing the identified demodulation signal and sending the signal to the interior of the upper computer. The radio frequency interaction module is used for carrying out radio frequency interaction with an upper computer, transmitting a radio frequency control command and carrying out radio frequency state feedback. The weather fax digital receiving system based on the FPGA can overcome the defects of nonlinearity, low precision, poor anti-interference capability and the like of analog demodulation and improve the processing convenience of weather fax information.
Description
Technical Field
The invention belongs to the technical field of communication, and particularly relates to a weather fax digital receiving system based on an FPGA (field programmable gate array).
Background
The wireless weather fax adopts the short-wave broadcast fax diagram, which not only can provide the live analysis reports of various meteorology and hydrology related to the ground, high altitude and ocean, but also can provide the short-term and medium-term forecast diagrams of various atmospheric pressure situations, atmospheric pressure elements, sea surface conditions and other physical quantities, thereby improving the timeliness and service quality of weather forecast. The traditional meteorological fax machine hardware circuit is too complex and huge, the digital integration level is lower, the system performance is not superior, and when signal processing is carried out, the defects of low precision, poor anti-interference capability and the like generally exist, so that the identification rate of fax signals can be reduced, and the difficulty of subsequent signal processing is increased.
Disclosure of Invention
In view of the above, the present invention provides a weather fax digital receiving system based on FPGA to solve the above technical problems.
In order to achieve the purpose, the technical scheme of the invention is realized as follows:
a weather fax digital receiving system based on FPGA comprises: the system comprises a digital down-conversion module, an FSK demodulation module, a weather fax signal identification module, a weather fax data framing module and a radio frequency interaction module; the digital down-conversion module is used for extracting and filtering the sampling signal to generate a variable frequency signal; the FSK demodulation module is used for receiving the frequency conversion signals and carrying out phase and frequency discrimination processing on the frequency conversion signals to generate demodulation signals; the weather facsimile signal identification module is used for receiving the demodulation signal and identifying the signal according to the format of the signal; the weather fax data framing module is used for framing the identified demodulation signal and sending the signal to the interior of an upper computer; the radio frequency interaction module is used for carrying out radio frequency interaction with an upper computer, transmitting a radio frequency control command and carrying out radio frequency state feedback.
Further, the demodulation signal received by the weather fax signal identification module includes:
the starting signal is a square wave signal with the frequency of 300Hz or a square wave signal with the frequency of 675 Hz;
the phase signals comprise 25ms low-level signals and 475ms high-level signals, the 25ms low-level signals represent white pixel points of a meteorological image, and the 475ms high-level signals represent black pixel points of the meteorological image;
the image signal is divided into lines according to a meteorological image, a line synchronizing signal of 25ms is arranged at the beginning of each line of the image signal, and the line synchronizing signal comprises a low-level signal of 4.5ms and a high-level signal of 20.5 ms;
and the end signal comprises a square wave signal with the frequency of 450Hz and a high-level signal.
Further, the signal identification according to the format of the signal includes:
detecting an initial signal, and if the initial signal exists, proving that the meteorological fax image starts to be transmitted;
after the transmission is started, detecting a phase signal, and if the phase signal is detected, acquiring the transmission speed of the weather fax image through the phase signal;
detecting image signals, acquiring line synchronization signals through the image signals, and starting to upload data of the image signals of each line;
and detecting an end signal, and stopping data uploading if the end signal exists.
Further, the phase and frequency discrimination processing is performed on the frequency-converted signal to generate a demodulated signal, including:
carrying out digital phase discrimination on the frequency conversion signals according to a CORDIC algorithm to obtain the phase of each point;
demodulation data is obtained through digital frequency discrimination, and level judgment and timing synchronization are carried out on the demodulation data to generate a demodulation signal.
Further, the digital down-conversion module includes: the digital synthesizer comprises a DDS, a first mixer, a first CIC decimation filter, a first narrow band filter, a second mixer, a second CIC decimation filter and a second narrow band filter; the first mixer and the second mixer respectively receive sampling signals; the first CIC decimation filter is in communication connection with the first mixer, and the first narrow band filter is in communication connection with the first CIC decimation filter; the second CIC decimation filter is in communication connection with the second mixer, and the second narrow band filter is in communication connection with the second CIC decimation filter; the DDS is used for dividing a system clock by programming a frequency control word so as to generate a cosine wave frequency and a sine wave frequency, and the cosine wave frequency is input into the first mixer, and the sine wave frequency is input into the second mixer.
Furthermore, the weather fax digital receiving system further comprises a carrier frequency offset processor, wherein the carrier frequency offset processor is used for calculating an average value of the initial signal in one period, removing the direct current component of the demodulated signal when the average value is the same as the direct current component of the demodulated signal, and sending the demodulated signal without the direct current component to the inside of the digital down-conversion module for extraction and filtering.
Compared with the prior art, the weather fax digital receiving system based on the FPGA has the following advantages that:
the weather fax digital receiving system based on the FPGA can overcome the defects of nonlinearity, low precision, poor anti-interference capability and the like of analog demodulation, eliminate carrier frequency offset and reduce the demodulation error rate. In addition, the weather fax digital receiving system can perform a plurality of times of relative processing, thereby improving the fax signal identification rate and the anti-interference capability, being convenient for storing weather fax data into a PC, and further providing convenience for subsequent image processing and application.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the invention without limitation.
In the drawings:
FIG. 1 is a flow chart of a weather fax digital receiving system according to an embodiment of the present invention;
fig. 2 is a schematic flow chart of a digital down conversion module according to an embodiment of the present invention;
FIG. 3 is a diagram illustrating a signal format according to an embodiment of the present invention;
fig. 4 is a schematic diagram of a signal identification process according to an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.
An FPGA-based weather fax digital receiving system, as shown in fig. 1, comprises: the system comprises a digital down-conversion module, an FSK demodulation module, a weather fax signal identification module, a weather fax data framing module and a radio frequency interaction module.
The digital down-conversion module is used for moving the sampling signal to the fundamental frequency aiming at the specific frequency point, and performing extraction and filtering processing, so that the signal rate is reduced, the bandwidth is reduced, and the frequency conversion signal is generated. Optionally, in this embodiment, the digital down-conversion module includes: the digital synthesizer comprises a DDS, a first mixer, a first CIC decimation filter, a first narrow band filter, a second mixer, a second CIC decimation filter and a second narrow band filter.
As shown in fig. 2, the first mixer and the second mixer respectively receive sampling signals; the first CIC decimation filter is communicatively coupled to the first mixer and the first narrowband filter is communicatively coupled to the first CIC decimation filter. The second CIC decimation filter is communicatively coupled to the second mixer and the second narrowband filter is communicatively coupled to the second CIC decimation filter. The DDS is used for dividing a system clock by programming a frequency control word so as to generate a cosine wave frequency and a sine wave frequency, and the cosine wave frequency is input into the first mixer, and the sine wave frequency is input into the second mixer.
At this time, the mixer can mix the frequency input by the DDS with the frequency of the sampling signal, and then the signal is sequentially subjected to integration, down-sampling and comb filter processing with the same number as the number of integration links in the CIC extraction filter and enters the narrow-band filter. The narrow-band filter can reduce the signal bandwidth, thereby outputting a variable frequency signal meeting the use requirement.
The FSK demodulation module is used for receiving the frequency conversion signals, carrying out phase discrimination and frequency discrimination processing on the frequency conversion signals and generating demodulation signals. Because the digital down-conversion module can obtain two paths of orthogonal I, Q signals through cosine wave frequency and sine wave frequency, the phase of each point can be calculated by carrying out digital phase discrimination on the signals. Then, demodulated data is obtained through digital frequency discrimination, and the demodulated data is subjected to level decision and timing synchronization, so that an FSK demodulation result, that is, a demodulated signal is generated.
Optionally, the digital phase detection process in this embodiment may be implemented by a CORDIC algorithm. Specifically, when the digital CORDIC algorithm is used for word phase discrimination, the baseband I, Q signal is used to calculate the corresponding amplitude and phase, and the input signal is:
s(n)＝xi(n)·cosωcn-xQ(n)·sinωcn
in the above formula:
wherein xi(in) and xQAnd (n) respectively represent the in-phase component and the quadrature component of the baseband signal, and the two components jointly contain the information of the baseband signal. The instantaneous frequency is obtained according to the phase difference method:
the frequency obtained by differentiating the phase value obtained by the CORDIC algorithm can generate frequency jump, the frequency jump phenomenon can be eliminated by fully utilizing the characteristic of phase repetition under certain conditions, and accurate frequency discrimination output is obtained.
The weather facsimile signal identification module is used for receiving the demodulation signal and identifying the signal according to the format of the signal. As shown in fig. 3, in this embodiment, the demodulated signal received by the weather fax signal identification module includes: the starting signal, the phase signal, the image signal and the ending signal.
Wherein the start signal comprises a square wave signal with a duration of 10s and a frequency of 300Hz (corresponding to a cooperation factor of 576) or a square wave signal with a frequency of 675Hz (corresponding to a cooperation factor of 288), for a total of 20 lines.
The phase signal has a duration of 60s for 120 lines (also 32s, i.e. 64 lines). When each row of phase signals are sent, low-level signals of 25ms are sent firstly to represent white pixel points of the image signals, and then high-level signals of 475ms are sent to represent black pixel points of the image signals.
The image signal is divided into lines according to the meteorological images, and the size (i.e. the number of lines) of the whole meteorological image is changed, so the longest image signal is 20min, namely 2400 lines. At the beginning of each line of image signals, there is a line synchronizing signal of 25ms, which consists of a low level signal of 4.5ms and a high level signal of 20.5 ms.
The end signal is composed of two parts, namely a square wave lasting for 5s and with the frequency of 450Hz and a high level signal lasting for 10s (a full black signal).
Since the carrier frequency offset in the process of processing the weather fax signals is mostly caused by the inaccurate crystal oscillator or Doppler shift, the central carrier frequency in the process of processing the signals is unknown. For the FSK demodulation process, the carrier frequency offset can cause the errors of level judgment and timing synchronization results, so that demodulation misjudgment occurs, and the demodulation error rate is increased.
In order to solve the problem, the system includes a carrier frequency offset processor (not shown in the figure), the carrier frequency offset processor can calculate an average value of the initial signal in one period, when the average value is the same as a direct current component of the demodulated signal, the direct current component of the demodulated signal is removed, and the demodulated signal without the direct current component is sent to the inside of the digital down-conversion module for extraction and filtering, so as to reduce the influence of the carrier frequency offset on signal processing.
After the carrier frequency offset is eliminated, the system can identify the signal according to the format of the signal. As shown in fig. 4, the signal identification process in this embodiment includes:
detecting an initial signal, and if the initial signal exists, proving that the meteorological fax image starts to be transmitted;
after the transmission is started, detecting a phase signal, and if the phase signal is detected, acquiring the transmission speed of the weather fax image through the phase signal;
detecting image signals, acquiring line synchronization signals through the image signals, and starting to upload data of the image signals of each line;
and detecting an end signal, and stopping data uploading if the end signal exists.
Since the phase signal has a long duration, if it is not detected for the first time, the detection is continued until the phase signal is detected. In addition, to avoid the identification process being too redundant, the phase signal is detected at most 5 times, and if the phase signal is still not detected for the fifth time, the process is directly ended.
And after the signal identification is finished, the meteorological fax data framing module is used for framing the identified demodulation signal and sending the framed signal to the interior of the upper computer. And then, the upper computer can perform radio frequency interaction with the system through the radio frequency interaction module, so that a radio frequency control command is transmitted and radio frequency state feedback is performed, and a worker can conveniently adjust the system.
The following explains the effects of the above-described scheme:
the embodiment provides a weather fax digital receiving system based on an FPGA (field programmable gate array), which can overcome the defects of nonlinearity, low precision, poor anti-jamming capability and the like of analog demodulation, eliminate carrier frequency offset and reduce the demodulation error rate. In addition, the weather fax digital receiving system can perform a plurality of times of relative processing, thereby improving the fax signal identification rate and the anti-interference capability, being convenient for storing weather fax data into a PC, and further providing convenience for subsequent image processing and application.
It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.
Claims (6)
1. A weather fax digital receiving system based on FPGA is characterized in that: the method comprises the following steps: the system comprises a digital down-conversion module, an FSK demodulation module, a weather fax signal identification module, a weather fax data framing module and a radio frequency interaction module; the digital down-conversion module is used for extracting and filtering the sampling signal to generate a variable frequency signal; the FSK demodulation module is used for receiving the frequency conversion signals and carrying out phase and frequency discrimination processing on the frequency conversion signals to generate demodulation signals; the weather facsimile signal identification module is used for receiving the demodulation signal and identifying the signal according to the format of the signal; the weather fax data framing module is used for framing the identified demodulation signal and sending the signal to the interior of an upper computer; the radio frequency interaction module is used for carrying out radio frequency interaction with an upper computer, transmitting a radio frequency control command and carrying out radio frequency state feedback.
2. The weather fax digital receiving system based on the FPGA as claimed in claim 1, wherein: the demodulation signal received by the weather facsimile signal identification module comprises:
the starting signal is a square wave signal with the frequency of 300Hz or a square wave signal with the frequency of 675 Hz;
the phase signals comprise 25ms low-level signals and 475ms high-level signals, the 25ms low-level signals represent white pixel points of a meteorological image, and the 475ms high-level signals represent black pixel points of the meteorological image;
the image signal is divided into lines according to a meteorological image, a line synchronizing signal of 25ms is arranged at the beginning of each line of the image signal, and the line synchronizing signal comprises a low-level signal of 4.5ms and a high-level signal of 20.5 ms;
and the end signal comprises a square wave signal with the frequency of 450Hz and a high-level signal.
3. The weather fax digital receiving system based on the FPGA as claimed in claim 2, wherein: the signal identification according to the signal format comprises the following steps:
detecting an initial signal, and if the initial signal exists, proving that the meteorological fax image starts to be transmitted;
after the transmission is started, detecting a phase signal, and if the phase signal is detected, acquiring the transmission speed of the weather fax image through the phase signal;
detecting image signals, acquiring line synchronization signals through the image signals, and starting to upload data of the image signals of each line;
and detecting an end signal, and stopping data uploading if the end signal exists.
4. The weather fax digital receiving system based on the FPGA as claimed in claim 1, wherein: the phase discrimination and frequency discrimination processing of the frequency conversion signal to generate a demodulation signal includes:
carrying out digital phase discrimination on the frequency conversion signals according to a CORDIC algorithm to obtain the phase of each point;
demodulation data is obtained through digital frequency discrimination, and level judgment and timing synchronization are carried out on the demodulation data to generate a demodulation signal.
5. The weather fax digital receiving system based on the FPGA as claimed in claim 1, wherein: the digital down conversion module comprises: the digital synthesizer comprises a DDS, a first mixer, a first CIC decimation filter, a first narrow band filter, a second mixer, a second CIC decimation filter and a second narrow band filter; the first mixer and the second mixer respectively receive sampling signals; the first CIC decimation filter is in communication connection with the first mixer, and the first narrow band filter is in communication connection with the first CIC decimation filter; the second CIC decimation filter is in communication connection with the second mixer, and the second narrow band filter is in communication connection with the second CIC decimation filter; the DDS is used for dividing a system clock by programming a frequency control word so as to generate a cosine wave frequency and a sine wave frequency, and the cosine wave frequency is input into the first mixer, and the sine wave frequency is input into the second mixer.
6. The weather fax digital receiving system based on the FPGA as claimed in claim 1, wherein: the weather fax digital receiving system further comprises a carrier frequency offset processor, wherein the carrier frequency offset processor is used for calculating the average value of the initial signal in one period, removing the direct current component of the demodulation signal when the average value is the same as the direct current component of the demodulation signal, and sending the demodulation signal without the direct current component to the interior of the digital down-conversion module for extraction and filtering.
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| CN103248593A (en) * | 2012-02-09 | 2013-08-14 | 泰凌微电子（上海）有限公司 | Method and system for frequency offset estimation and elimination |
| CN103428401A (en) * | 2013-07-24 | 2013-12-04 | 南京虹航电子科技有限公司 | Digital meteorologic fax machine |
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- 2021-11-26 CN CN202111427467.0A patent/CN114143411A/en active Pending
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA2612122A1 (en) * | 2007-11-23 | 2009-05-23 | Research In Motion Limited | System and method for providing a variable frame rate and adaptive frame skipping on a mobile device |
| CN101261318A (en) * | 2008-04-03 | 2008-09-10 | 北京航空航天大学 | High dynamic state spread-spectrum precise distance measurement receiving machine |
| CN103248593A (en) * | 2012-02-09 | 2013-08-14 | 泰凌微电子（上海）有限公司 | Method and system for frequency offset estimation and elimination |
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