CN107800444B - Multi-frequency multi-mode GNSS radio frequency signal recording and playing system and method - Google Patents
Multi-frequency multi-mode GNSS radio frequency signal recording and playing system and method Download PDFInfo
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- H—ELECTRICITY
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- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/005—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission adapting radio receivers, transmitters andtransceivers for operation on two or more bands, i.e. frequency ranges
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/13—Receivers
- G01S19/33—Multimode operation in different systems which transmit time stamped messages, e.g. GPS/GLONASS
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- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/005—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission adapting radio receivers, transmitters andtransceivers for operation on two or more bands, i.e. frequency ranges
- H04B1/0053—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission adapting radio receivers, transmitters andtransceivers for operation on two or more bands, i.e. frequency ranges with common antenna for more than one band
- H04B1/006—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission adapting radio receivers, transmitters andtransceivers for operation on two or more bands, i.e. frequency ranges with common antenna for more than one band using switches for selecting the desired band
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- H—ELECTRICITY
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- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/005—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission adapting radio receivers, transmitters andtransceivers for operation on two or more bands, i.e. frequency ranges
- H04B1/0067—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission adapting radio receivers, transmitters andtransceivers for operation on two or more bands, i.e. frequency ranges with one or more circuit blocks in common for different bands
- H04B1/0082—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission adapting radio receivers, transmitters andtransceivers for operation on two or more bands, i.e. frequency ranges with one or more circuit blocks in common for different bands with a common local oscillator for more than one band
- H04B1/0085—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission adapting radio receivers, transmitters andtransceivers for operation on two or more bands, i.e. frequency ranges with one or more circuit blocks in common for different bands with a common local oscillator for more than one band where one band is the image frequency band of the other and the band selection is done by image rejection
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/06—Receivers
- H04B1/10—Means associated with receiver for limiting or suppressing noise or interference
- H04B1/12—Neutralising, balancing, or compensation arrangements
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/06—Receivers
- H04B1/16—Circuits
- H04B1/1638—Special circuits to enhance selectivity of receivers not otherwise provided for
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
- Y02D30/00—Reducing energy consumption in communication networks
- Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks
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Abstract
The invention discloses a multi-frequency multi-mode GNSS radio frequency signal recording and playing system and a method, wherein the system comprises a receiving antenna, a low noise amplifier, a first radio frequency switch, a second radio frequency switch, a third radio frequency switch, a mixer, a local oscillator, a first filter, a second filter, a temperature compensation clock, an SDR platform, a control and storage computer, an I/O expander, a program-controlled adjustable attenuator and a transmitting antenna, wherein the receiving antenna is used for receiving L1 and L2 frequency bands of a GPS and B1 frequency bands of Beidou; the control and storage computer controls the first radio frequency switch, the second radio frequency switch and the third radio frequency switch to switch the recording and playback functions and controls the program-controlled adjustable attenuator through the I/O expander so as to adjust the intensity of playback signals. The system has the advantages of low cost, ingenious structure, stable work, small occupied space of recorded files and the like.
Description
Technical Field
The invention relates to the technical field of GNSS related course teaching and GNSS receiver research and development production test instruments, in particular to a multi-frequency multi-mode GNSS radio frequency signal recording and playing system and method.
Background
GNSS (global navigation satellite system Global navigation satellite System) receivers are widely used and play an important role in various fields such as civilian use, military use, mapping, water conservancy, geology, electric power, forests and the like. In the research and development process of the GNSS receiver, recording and playback equipment of GNSS signals is often used, so as to repeatedly form identical GNSS radio frequency signal scenes, so as to test the GNSS receiver, and compare and verify different receivers or different algorithms of the same receiver. With the development of Beidou systems in China, the research and development force of teaching scientific research institutions and manufacturers on the multi-frequency multi-mode GNSS receivers is increased, and the function of the multi-frequency multi-mode GNSS radio frequency signal recording and playing device in the research and development production process is very important. The current GNSS radio frequency signal recording and replaying device is generally divided into two types, one type is single frequency and single mode, and the price is lower, but the current GPS/Beidou multi-constellation multi-frequency point receiver test needs cannot be met. The other type is a multi-frequency multi-mode GNSS signal recording and playing device, which adopts a synchronous acquisition recording mode of a plurality of ADCs or a high-speed and high-bandwidth ADC acquisition mode, and the common defects of the two are that the generated signal acquisition file is huge. The former has the problem of synchronization, and poor synchronization can cause time dislocation among a plurality of signals, so that the signals cannot be played back completely; the latter is costly and complex in construction.
Disclosure of Invention
In order to solve the technical problems, the invention provides a multi-frequency multi-mode GNSS radio frequency signal recording and playing method and system, which have the advantages of low cost, ingenious structure, stable work, small occupied space of recorded files and the like.
The technical scheme adopted by the invention is as follows:
a multi-frequency multimode GNSS radio frequency signal recording and reproducing system comprising: the GPS receiving device comprises a receiving antenna, a low noise amplifier, a first radio frequency switch, a second radio frequency switch, a third radio frequency switch, a mixer, a local oscillator, a first filter, a second filter, a temperature compensation clock, an SDR platform, a control and storage computer, an I/O expander, a program-controlled adjustable attenuator and a transmitting antenna, wherein the receiving antenna is used for receiving the L1 and L2 frequency bands of a GPS and the B1 frequency band of the Beidou;
the receiving antenna, the low noise amplifier, the first radio frequency switch, the mixer, the second radio frequency switch, the first filter, the third radio frequency switch and the SDR platform are sequentially connected, the local oscillator is connected with the mixer, the third radio frequency switch is connected with the first radio frequency switch, the second filter, the program-controlled adjustable attenuator and the transmitting antenna are sequentially connected, the temperature compensation clock is connected with the SDR platform, the SDR platform is connected with the control and storage computer, and the control and storage computer controls the first radio frequency switch, the second radio frequency switch and the third radio frequency switch to conduct recording and playback function switching and controls the program-controlled adjustable attenuator through the I/O expander so as to adjust the strength of playback signals.
The receiving antenna is an active antenna which can at least receive the L1 and L2 frequency bands of the GPS and the B1 frequency band of the Beidou, and has a gain of 30db and is used for receiving signals of the three frequency bands.
The low-noise amplifier is a microwave low-noise amplifier, the effective frequency band is between 1200Mhz and 1600Mhz, and the gain is 25db; the multistage microwave triode is adopted to design and build or select an amplifier module with the model of ZX60-P162LN+.
The first radio frequency switch, the second radio frequency switch and the third radio frequency switch adopt single-pole double-throw radio frequency switches with the model ZX80-DR230+ and are used for switching recording and playback functions.
The frequency mixer adopts a broadband high-performance frequency mixer with the model number of ADE-35 MH.
Wherein, the local oscillator adopts a temperature compensation crystal oscillator, and the oscillation frequency is 170Mhz.
The first filter adopts a filter with the model of VBFZ-1400+, and the second filter adopts three filters with different frequency bands CBP-1228C+, BFCN-1575+, BFCN-1560+ to be combined.
The SDR platform selects HackrfONE, and the temperature compensation clock adopts TCXO with the working frequency of 10 Mhz;
the program-controlled adjustable attenuator is a model ZX76-31-PN-S attenuator;
the I/O expander is composed of a singlechip ATMEGA128 and a UART-USB interface conversion chip FDTI FT232R, and the singlechip ATMEGA128 and the UART-USB interface conversion chip FDTI FT232R are matched to receive and control and store instructions of a computer so as to control a first radio frequency switch, a second radio frequency switch, a third radio frequency switch and a program-controlled adjustable attenuator.
A recording and playing method adopting the multi-frequency multi-mode GNSS radio frequency signal recording and playing system comprises the following steps:
s1, selecting the frequency of a local oscillator;
step S2, recording signals: amplifying the signal from the receiving antenna through the low noise amplifier, generating a high-frequency local oscillation signal by the local oscillation, sending the amplified signal and the local oscillation signal into the mixer to mix, and obtaining f 1 、f 2 、f 3 、f 4 、f 5 、f 6 6 signals, f is passed through a first filter 1 、f 3 、f 5 Filtering three mirror image signals with larger frequency band interval, and reserving f 2 、f 4 、f 6 Three signals with smaller frequency band spacing, so that the spacing of the three frequency points is reduced, invalid frequency spectrum parts are squeezed out, and then the filtered signals are put againFinally, the signals are sent to ADC equipment for sampling, and the sampled digital data are sent to a control and storage computer for storage for signal playback;
step S3, signal playback: converting the sampled and stored digital data by DAC equipment to obtain analog signal, wherein the analog signal contains f 2 、f 4 、f 6 Mixing the high-frequency signal generated by the local oscillator with the obtained analog signal again to obtain f 7 、f 8 、f 9 、f 10 、f 11 、f 12 6 signals, and passing the image signal f through a second filter 7 、f 11 、f 12 Filtering to retain only reduced f 8 、f 9 、f 10 And finally, the strength of the signals is adjusted by using a program-controlled adjustable attenuator to enable the signals to meet the use requirements.
Wherein the steps are as follows
S1 specifically comprises the following steps: setting the frequency of the local oscillator as f lo And f lo <L2 frequency band of GPS;
the step S2 specifically includes: step a, after mixing by a mixer, the L1/L2/B1 signal and the local oscillator signal generate the following signals:
sum frequency:
f 1 ＝L1+f lo ；f 2 ＝L2+f lo ；f 3 ＝B1+f lo ；
difference frequency:
f 4 ＝L1-f lo ；f 5 ＝L2-f lo ；f 6 ＝B1-f lo ；
step b, the generated 6 mixed signals pass through a first filter to obtain 3 signals with smaller frequency band interval, namely sum frequency f 2 And two difference frequencies f 4 、f 6 ；
The step S3 specifically includes: in the signal playback phase, these three frequency points f are again set 2 、f 4 、f 6 Signal and f of (2) lo Mixing, so as to restore the signals, and at the moment, the mixed signals have 6:
sum frequency:
f 7 ＝f 2 +f lo ＝L2+2f lo ；
f 8 ＝f 4 +f lo ＝L1-f lo +f lo ；
f 9 ＝f 6 +f lo ＝B1-f lo +f lo ；
difference frequency:
f 10 ＝f 2 -f lo ＝L2+f lo -f lo ；
f 11 ＝f 4 -f lo ＝L1-f lo -f lo ；
f 12 ＝f 6 -f lo ＝B1-f lo -f lo ；
it can be seen that the sum frequency f 8 、f 9 And difference frequency f 10 It is the desired L1, B1, L2, and in addition three additional image signals are filtered out by the second filter.
The beneficial effects are that:
according to the multi-frequency multi-mode GNSS radio frequency signal recording and playing system and method provided by the invention, the phenomenon that two mixing results (namely mirror images) of sum frequency and difference frequency are generated during frequency conversion is utilized, different sum frequency signals and difference frequency signals are used during signal recording and playback, and the purpose of mixing is to reduce the spacing between effective frequency points during the signal recording stage, so that the collection is convenient; in the playback stage, the purpose of mixing is to stretch the distance between the effective frequency points so as to achieve the purpose of restoring the signal. And for signals of different frequency points, sum frequency signals and difference frequency signals are adopted respectively, so that the image signals are fully utilized, the effective bandwidth is greatly compressed, the device requirements and the system complexity are reduced, and the cost is reduced. The system has the advantages of low cost, ingenious structure, stable work, small occupied space of recorded files and the like.
Drawings
Fig. 1: the flo=160 Mhz spectrum schematic diagram with the bandwidth of 38.82Mhz after compression is provided by the invention.
Fig. 2: the flo=170 Mhz, and the bandwidth after compression is 28.82 Mhz.
Fig. 3: the invention provides a structure block diagram of a multi-frequency multi-mode GNSS radio frequency signal recording and playing system.
In the figure:
a 101-receiving antenna; 102-a low noise amplifier; 103-a first radio frequency switch; 106-a second radio frequency switch; 108 a third radio frequency switch; 104-a mixer; 105-local oscillation; 107-a first filter; 109-temperature compensation clock; a 110-SDR platform; 111-control and storage computer; 112-a second filter; 113-program controlled adjustable attenuator; 114-a transmitting antenna; 115-I/O extender.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. In addition, the technical features of the embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
The technical scheme of the invention is described in detail below with reference to the accompanying drawings and examples.
Example 1
Current GNSS signals mainly include Beidou (BDS), GPS, GLONASS, galileo, QZSS, and IRNSS. Currently, the application of the GPS system is wider, and the prospect of the BDS system is more attractive. The device is therefore designed mainly for GPS and BDS systems.
The GPS signal comprises three frequency bands L1, L2 and L5, and the BDS passive positioning system also comprises three frequency bands B1, B2 and B3. In these several bands, L1 and L2 for civilian use are mainly GPS with B1 for BDS. The center frequency, the signal bandwidth and the common bandwidth of the civil receiver are respectively:
table 1: GPS L1/L2 and BDS B1 frequency table
It can be seen that the bandwidth covered by three frequency bands is already over 350Mhz, and if a general direct sampling form is adopted, the requirements on the device are quite high, and the corresponding cost is also high.
After studying the relationship of the three frequency bands, it can be known that the three frequency bands are not continuous, the effective total bandwidth is only 26Mhz, and the middle 300 Mhz is not actually needed, and another fact is that, since the GPS and the beidou system both use CDMA coding systems, even if there is partial overlap at the edge part of the frequency spectrum, the influence on signal reception is very limited. Therefore, the following method for compressing bandwidth by a frequency conversion method is proposed:
the frequency conversion of signals by mixers is a common means in radio technology, and the purpose of frequency conversion is usually to convert the frequency spectrum to one intermediate frequency (one frequency conversion) or several intermediate frequencies (multiple frequency conversion), so as to avoid the self-excitation of the amplifier and to facilitate the design of the amplifier and the filter. In a typical radio, either only the difference frequency or only the sum frequency is used. The invention utilizes the phenomenon that two mixing results (namely mirror images) of sum frequency and difference frequency are generated during frequency conversion, different sum frequency signals and difference frequency signals are used during signal recording and playback, and the aim of mixing is to reduce the spacing between effective frequency points during the signal recording stage, so that the acquisition is convenient; in the playback stage, the purpose of mixing is to stretch the distance between the effective frequency points so as to achieve the purpose of restoring the signal. And for signals of different frequency points, sum frequency signals and difference frequency signals are adopted respectively, so that the image signals are fully utilized, the effective bandwidth is greatly compressed, the device requirements and the system complexity are reduced, and the cost is reduced.
As shown in fig. 3, the present embodiment includes: a receiving antenna 101 for receiving the L1 and L2 frequency bands of GPS and the B1 frequency band of Beidou, a low noise amplifier 102, a first radio frequency switch 103, a second radio frequency switch 106, a third radio frequency switch 108, a mixer 104, a local oscillator 105, a first filter 107, a second filter 112, a temperature compensation clock 109, an SDR platform 110, a control and storage computer 111, an I/O expander 115, a program-controlled adjustable attenuator 113 and a transmitting antenna 114;
the receiving antenna 101, the low noise amplifier 102, the first radio frequency switch 103, the mixer 104, the second radio frequency switch 106, the first filter 107, the third radio frequency switch 108 and the SDR platform 110 are sequentially connected, the local oscillator 105 is connected with the mixer 104, the third radio frequency switch 108 is connected with the first radio frequency switch 103, the second radio frequency switch 106, the second filter 112, the program-controlled adjustable attenuator 113 and the transmitting antenna 114 are sequentially connected, the temperature compensating clock 109 is connected with the SDR platform 110, the SDR platform 110 is connected with the control and storage computer 111, and the control and storage computer 111 controls the switching of recording and playback functions and controls the program-controlled adjustable attenuator 113 through the I/O expander 115 so as to adjust the intensity of playback signals.
The receiving antenna 101 is an active antenna capable of receiving at least the GPS L1/L2 frequency band and the Beidou B1 frequency band, and has a gain of about 30db and is used for receiving signals of the three frequency bands.
The low noise amplifier 102 is a general microwave low noise amplifier, the effective frequency band is 1200Mhz to 1600Mhz, and the gain is about 25 db. The multi-stage microwave triode self-design can be used to build or select an existing amplifier module, such as ZX60-P162LN+.
The first radio frequency switch 103, the second radio frequency switch 106 and the third radio frequency switch 108 adopt single-pole double-throw radio frequency switches ZX80-DR230+ for recording and playback function switching.
The mixer 104 employs a wideband high performance mixer model ADE-35 MH.
The local oscillator 105 adopts a temperature compensation crystal oscillator, and the oscillation frequency is 170Mhz.
The first filter 107 adopts a filter with the model number of VBFZ-1400+, and the second filter 112 adopts three filters with different frequency bands CBP-1228C+, BFCN-1575+ and BFCN-1560+ to be combined.
The SDR platform 110 is a HackrfONE, has low cost, is completely open, and is convenient to develop. However, the clock performance is poor, the frequency is unstable, the phase noise is large, and the overall performance cannot be ensured, so that the clock must be matched with the temperature compensation clock 109, and the working frequency is 10 Mhz. Higher performance OCXOs or atomic frequency standards may also be substituted if cost warrants.
The control and storage computer 111 is used to control the operation of the HackRF ONE and store the recorded signals, and also needs to control the switching of the recording and playback functions of the first RF switch 103, the second RF switch 106 and the third RF switch 108 through the I/O extender 115 and control the programmable adjustable attenuator 113 to adjust the strength of the playback signals.
The program controlled adjustable attenuator 113 is used for adjusting the playback signal intensity, and ZX76-31-PN-S is selected.
The I/O expander 115 is composed of a single-chip microcomputer ATMEGA128 and a UART-USB interface conversion chip FDTI FT232R, the ATMEGA128 has rich interfaces, the FT232R has stable performance, and the two cooperate to complete the function of receiving and controlling the instructions of the computer 111 to control the first radio frequency switch 103, the second radio frequency switch 106, the third radio frequency switch 1088 and the program-controlled adjustable attenuator 113.
Example 2
The selection of the frequency of the local oscillator 105 is critical to the quality of the sampling and playback and to the requirements of the device and equipment.
Let the local oscillator 105 frequency f lo And f lo <L2 is f lo <1227.6Mhz, the L1/L2/B1 signal and the local oscillator signal may generate the following signals after mixing:
sum frequency:
f 1 ＝L1+f lo ＝1575.42+f lo
f 2 ＝L2+f lo ＝1227.6+f lo
f 3 ＝B1+f lo ＝1561.098+f lo
difference frequency:
f 4 ＝L1-f lo ＝1575.42-f lo
f 5 ＝L2-f lo ＝1227.6-f lo
f 6 ＝B1-f lo ＝1561.098-f lo
so long as the proper f is selected lo Can obtain 3 frequency spacing feet in the 6 frequency mixing signals generated aboveA signal small enough. To shorten the pitch of the three frequency points, a sum frequency f should be selected 2 I.e. 1227.6+f lo And two difference frequencies f 4 1575.42-f lo 、f 6 Namely 1561.098-f lo . And the total bandwidth at this time is scaled to:
f 4 -f 2 +1+10＝358.82-2f lo
where 1 and 10 are half the effective bandwidth of L1 and L2, respectively.
At the time of playback, these three frequency points (f 2 、f 4 、f 6 ) Signal and f of (2) lo Mixing, thereby recovering the signal. The signals obtained by mixing at this time are also 6:
sum frequency:
f 7 ＝f 2 +f lo ＝1227.6+f lo +f lo ＝1227.6+2f lo
f 8 ＝f 4 +f lo ＝1575.42-f lo +f lo ＝1575.42Mhz
f 9 ＝f 6 +f lo ＝1561.098-f lo +f lo ＝1561.098Mhz
difference frequency:
f 10 ＝f 2 -f lo ＝1227.6+f lo -f lo ＝1227.6
f 11 ＝f 4 -f lo ＝1575.42-f lo -f lo ＝1575.42Mhz-2f lo
f 12 ＝f 6 -f lo ＝1561.098-f lo -f lo ＝1561.098Mhz-2f lo
it can be seen that the sum frequency f 8 、f 9 And difference frequency f 10 It is the required L1, B1, L2, and in addition there are three extra mirror signals. To reduce bandwidth requirements while ensuring signal recording and playback quality, f needs to be selected lo So that the following three conditions are satisfied:
1.f 1 、f 2 、f 3 、f 4 、f 5 、f 6 the spacing between them is reduced so thatBandwidth reduction;
2.f 1 、f 2 、f 3 、f 4 、f 5 、f 6 avoiding spectrum overlapping as much as possible;
3.f 7 、f 8 、f 9 、f 10 、f 11 、f 12 the spectrum overlap is avoided as much as possible.
Since (L1+L2)/2 is about 174Mhz, f can be selected lo Near 174 Mhz. f (f) lo The closer to 174Mhz, the easier the first condition is to be satisfied, while the second and third conditions are less easily satisfied. f (f) lo The further from 174Mhz, the easier the second and third conditions are to be met, but the less easily the first condition is to be met. Thus f, where recording and playback device and device bandwidth permits lo Should be as far as possible from 174 Mhz. For example, f may be selected when the selected recording and playback device bandwidth is 40Mhz lo The spectrum at this time is shown in fig. 1, where fig. 1 (a) is the original signal, and the middle dashed line represents a bandwidth of about 350Mhz; FIG. 1 (b) is a mixed signal, f 2 ＝1387.6Mhz，f 4 ＝1415.42Mhz，f 6 1401.098Mhz, the total bandwidth is reduced to 38.82Mhz, the middle dotted line is squeezed out, only valid information remains, and it can be seen that f is satisfied at this time 1 、f 2 、f 3 、f 4 、f 5 、f 6 No spectral overlap (f) 1 、f 3 、f 5 Already out of band); FIG. 1 (c) is a playback signal in which the dash-dot line is a useless image signal, f 7 、f 8 、f 9 、f 10 、f 11 、f 12 There is no spectrum overlap between them, and the requirements of three conditions are satisfied. As another example, f may be selected when the recording and playback device bandwidth is selected to be 20Mhz lo =170 Mhz, at this time, f 2 ＝1397.6Mhz，f 4 ＝1405.42Mhz，f 6 The total bandwidth is reduced to 18.82Mhz, = 1391.098Mhz, and the spectrum at this time is shown in fig. 2, since the bandwidth has been compressed to an effective bandwidth of less than 26Mhz, it can be seen in fig. 2 (b), f 2 、f 6 Between which are locatedSlightly overlapping the frequency spectrum; in FIG. 2 (c) f can be seen 7 And f 9 ，f 10 And f 11 There is also a slight spectral overlap between the signals, where there is a loss of signal and interference between the signals, but the requirements are still met for a general test.
After the local oscillation frequency is selected, the recording and playback of the signals can be carried out.
The invention relates to a multi-frequency multi-mode GNSS radio frequency signal recording and playing method, which comprises the following working modes:
as shown in fig. 3, during signal recording, the control and storage computer 111 controls the first RF switch 103, the second RF switch 106, and the third RF switch 108 through the I/O expander 115 such that all three switches are located in the 1-path, so that the output terminal of the low noise amplifier 102 is connected to the RF input terminal of the mixer 104, the IF terminal of the mixer 104 is connected to the input terminal of the first filter 107, and the output terminal of the first filter 107 is connected to the RF terminal of the HACKRF ONE.
The receiving antenna 101 receives signals of the GPS L1/L2 and the Beidou B1, filters and amplifies the signals, then sends the signals to the low noise amplifier 102, the low noise amplifier 102 amplifies the signals, then sends the signals to the RF end of the mixer 104 through the first radio frequency switch 103, the mixer 104 mixes the signals with local oscillation signals with the frequency of 170Mhz from the local oscillation 105 at the LO end, and the mixing result is:
L1:1405.42Mhz
L2:1397.6Mhz
B1:1391.098Mhz
there are also three mirror signals:
1745.42Mhz，1057.6Mhz，1731.098Mhz。
it can be seen that the relative relationship of the three frequency points of L1, L2 and B1 is changed through frequency mixing, namely, the L2, B1 and L1 are in frequency increasing relationship, after frequency mixing, L2 is positioned in the middle, L1 and B1 respectively fall on two sides of L2, and the frequency center-to-center distance is 7.82Mhz and 6.502Mhz respectively. This distribution is more advantageous for equalizing the losses of the three frequency points, reducing the influence between them.
The mixed signal passes through the second rf switch 106 and enters the first filter 107, and the signal which is allowed to pass is only a signal with 1400Mhz as the center and 20Mhz as the bandwidth, namely three signals with 1405.42Mhz,1397.6Mhz and 1391.098Mhz as the center. Whereas the mirror signals (three signals centered around 1745.42mhz,1057.6mhz,1731.098 mhz) are filtered out here.
The filtered signal is sent to the RF end of the HackRF ONE through the third RF switch 108, and the control and storage computer 111 controls the HackRF ONE to sample and store the signal, where the sampling parameter is set to a center frequency 1397.6Mhz, the sampling bit width is 8 bits, the sampling rate is 20MSPS, and the sampling mode is IQ quadrature. The sample file is sent to the control and storage computer 111 via the USB bus for storage.
During signal playback, the control and storage computer 111 controls the first radio frequency switch 103, the second radio frequency switch 106, and the third radio frequency switch 108 via the I/O expander 115 such that the three radio frequency switches are all in a 2-way path, such that the RF terminal of the HackRFONE is connected to the RF input terminal of the mixer 104, and the IF output terminal of the mixer 104 is connected to the input terminal of the second filter 112. The control and storage computer 111 then sends the sample file obtained during recording to the HackRF ONE for playback, where the playback parameters are consistent with the recorded parameters, i.e. the center frequency 1397.6Mhz, bit width 8 bits, and the sampling rate 20MSPS. The RF signal obtained at the RF output of the HackRF ONE contains three signals with center frequencies 1405.42Mhz,1397.6Mhz and 1391.098Mhz, respectively. The signal is sent to the RF input end of the mixer 104 through the third RF switch 108 and the first RF switch 103, and mixed with the 170Mhz local oscillation signal from the local oscillation 105, so as to obtain three signals of 1575.42Mhz,1227.6Mhz and 1561.098Mhz after being restored, and three mirror image signals are provided at the same time: 1235.42mhz,1567.6mhz,1221.098, which are passed through a second rf switch 106 to a second filter 112, the three unwanted mirror amplitudes of 1235.42mhz,1567.6mhz,1221.098 are reduced after filtering. The filtered signal is sent to the programmable attenuator 113 and the attenuation amplitude of the programmable attenuator 113 is controlled by the control and storage computer 111 through the I/O expander 115 to obtain the appropriate signal strength. The attenuated signal is sent to the transmitting antenna 114. So far, the recorded signal is restored.
It should be understood that the foregoing embodiments are merely illustrative of the present invention and are not intended to limit the scope of the present invention, and that those skilled in the art, given the benefit of this disclosure, may make various substitutions and modifications to the described embodiments without departing from the scope of the invention as defined by the appended claims.
Claims (10)
1. A multi-frequency multi-mode GNSS radio frequency signal recording and reproducing system, comprising: a receiving antenna (101) for receiving the L1 and L2 frequency bands of the GPS and the B1 frequency band of the Beidou, a low noise amplifier (102), a first radio frequency switch (103), a second radio frequency switch (106), a third radio frequency switch (108), a mixer (104), a local oscillator (105), a first filter (107), a second filter (112), a temperature compensation clock (109), an SDR platform (110), a control and storage computer (111), an I/O expander (115), a program-controlled adjustable attenuator (113) and a transmitting antenna (114);
the low-noise radio frequency control system comprises a receiving antenna (101), a low-noise amplifier (102), a first radio frequency switch (103), a mixer (104), a second radio frequency switch (106), a first filter (107), a third radio frequency switch (108) and an SDR platform (110) which are sequentially connected, wherein the local oscillator (105) is connected with the mixer (104), the third radio frequency switch (108) is connected with the first radio frequency switch (103), the second radio frequency switch (106), the second filter (112), a program-controlled adjustable attenuator (113) and a transmitting antenna (114) are sequentially connected, a temperature compensation clock (109) is connected with the SDR platform (110), the SDR platform (110) is connected with a control and storage computer (111), and the control and storage computer (111) controls the first radio frequency switch (103), the second radio frequency switch (106) and the third radio frequency switch (108) to conduct switching of recording and playback functions and controls the program-controlled adjustable attenuator (113) so as to adjust the strength of playback signals.
2. The multi-frequency multi-mode GNSS radio frequency signal recording and reproducing system according to claim 1, wherein the receiving antenna (101) is an active antenna capable of receiving at least the L1 and L2 frequency bands of GPS and the B1 frequency band of beidou, and has a gain of 30db, for receiving signals of these three frequency bands.
3. The multi-frequency multi-mode GNSS radio frequency signal recording and reproducing system according to claim 1, wherein said low noise amplifier (102) is a microwave low noise amplifier with an effective frequency band of 1200Mhz to 1600Mhz and a gain of 25db; the multistage microwave triode is adopted to design and build or select an amplifier module with the model of ZX60-P162LN+.
4. The multi-frequency and multi-mode GNSS radio frequency signal recording and reproducing system according to claim 1, wherein the first radio frequency switch (103), the second radio frequency switch (106) and the third radio frequency switch (108) are single pole double throw radio frequency switches of the type ZX80-dr230+ for switching the recording and reproducing functions.
5. A multi-frequency multimode GNSS radio frequency signal recording and reproducing system according to claim 1, characterized in that said mixer (104) is a broadband high performance mixer of the type ADE-35 MH.
6. The system of claim 1, wherein the local oscillator (105) is a temperature compensated crystal oscillator with an oscillation frequency of 170Mhz.
7. A multi-frequency and multi-mode GNSS radio frequency signal recording and reproducing system according to claim 1, characterized in that said first filter (107) is a filter of the model VBFZ-1400+, and said second filter (112) is a combination of three filters CBP-1228c+, BFCN-1575+, BFCN-1560+.
8. The multi-frequency multi-mode GNSS radio frequency signal recording and reproducing system according to claim 1, wherein said SDR platform (110) is a HackrfONE, and said temperature compensation clock (109) is a TCXO with a working frequency of 10 Mhz;
the program-controlled adjustable attenuator (113) is an attenuator with the model of ZX 76-31-PN-S;
the I/O expander (115) is composed of a singlechip ATMEGA128 and a UART-USB interface conversion chip FDTI FT232R, and the singlechip ATMEGA128 and the UART-USB interface conversion chip FDTI FT232R are matched to receive and store instructions of a computer (111) so as to control a first radio frequency switch (103), a second radio frequency switch (106), a third radio frequency switch (108) and a program-controlled adjustable attenuator (113).
9. A recording and reproducing method using the multi-frequency multi-mode GNSS radio frequency signal recording and reproducing system according to any of the claims 1-8, comprising the steps of:
s1, selecting the frequency of a local oscillator (105);
step S2, recording signals: amplifying signals from a receiving antenna (101) through a low noise amplifier (102), generating a high-frequency local oscillation signal by a local oscillation (105), sending the amplified signals and the local oscillation signal to a mixer (104) for mixing to obtain f1, f2, f3, f4, f5 and f66 signals, filtering three mirror image signals f1, f3 and f5 with larger frequency band intervals through a first filter (107), reserving three signals f2, f4 and f6 with smaller frequency band intervals, enabling the intervals of the three frequency points to be smaller, squeezing out invalid frequency spectrum parts, amplifying the filtered signals again, finally sending the signals to an ADC device for sampling, and sending the sampled digital data to a control and storage computer (111) for signal playback;
step S3, signal playback: the digital data obtained by sampling and storing are converted through DAC equipment to obtain analog signals again, the analog signals at the moment comprise three signals f2, f4 and f6, the high-frequency signals generated by the local oscillator (105) are mixed with the obtained analog signals again to obtain f7, f8, f9, f10, f11 and f126 signals, the image signals f7, f11 and f12 are filtered through a second filter (112), only the three signals required by the restored f8, f9 and f10 are reserved, and finally the signals are subjected to intensity adjustment through a program-controlled adjustable attenuator (113) to meet the use requirements.
10. The recording and reproducing method according to claim 9, wherein said step S1 is specifically: setting the frequency of a local oscillator (105) as flo, wherein flo is L2 frequency band of a GPS;
the step S2 specifically includes:
step a, after mixing by a mixer (104), the signals of the L1/L2/B1 frequency band and the signals of the local oscillator (105) generate the following signals:
sum frequency:
f1＝L1+flo；f2＝L2+flo；f3＝B1+flo；
difference frequency:
f4＝L1-flo；f5＝L2-flo；f6＝B1-flo；
step b, 6 frequency mixing signals generated in the step b are subjected to a first filter (107) to obtain 3 signals with smaller frequency band intervals, namely a sum frequency f2 and two difference frequencies f4 and f6;
the step S3 specifically includes: in the signal playback phase, the signals of the three frequency points f2, f4 and f6 are mixed with flo again, so that the signals are restored, and at the moment, the mixed signals have 6:
sum frequency:
f7＝f2+flo＝L2+2flo；
f8＝f4+flo＝L1-flo+flo；
f9＝f6+flo＝B1-flo+flo；
difference frequency:
f10＝f2-flo＝L2+flo-flo；
f11＝f4-flo＝L1-flo-flo；
f12＝f6-flo＝B1-flo-flo；
it can be seen that the sum f8, f9 and the difference f10 are the required L1, B1, L2, and that in addition three unwanted image signals are filtered out by the second filter (112).
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