CN114326362B - Wireless time service system and method parasitic on frequency modulation radio station - Google Patents
Wireless time service system and method parasitic on frequency modulation radio station Download PDFInfo
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- CN114326362B CN114326362B CN202111663436.5A CN202111663436A CN114326362B CN 114326362 B CN114326362 B CN 114326362B CN 202111663436 A CN202111663436 A CN 202111663436A CN 114326362 B CN114326362 B CN 114326362B
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Abstract
The application relates to a wireless time service system and a wireless time service method parasitic on a frequency modulation radio station. The system comprises: a transmitting end and a receiving end; the transmitting end is obtained by adding a time encoder and a signal synthesizer on the basis of the original transmitting end of the frequency modulation radio station, and the carrier frequency signal of the transmitting end is a sine wave with the frequency of 1 kHz; the time encoder is used for encoding the UTC time signal by adopting a self-defined encoding mode to obtain a time encoded signal with the frequency of 10Hz and the code element length of 10 whole periods, and the signal synthesizer is used for synthesizing the time encoded signal and the voice signal to be modulated into a synthesized signal; the demodulator at the receiving end is used for demodulating the modulated synthesized signal to obtain a demodulated synthesized signal, and the demodulated synthesized signal comprises a time coding signal and an audio signal. The time service system is used for time service of local equipment, and has the advantages of low construction cost, wide coverage and high time service accuracy.
Description
Technical Field
The present disclosure relates to the field of time synchronization, and in particular, to a system and method for wireless time service parasitic on a fm radio station.
Background
Time service is to transmit time information, or strictly speaking, to transmit a standard time signal to users (including but not limited to mobile phones, computers, televisions, etc.) needing time information, so as to synchronize the time of the whole system. In short, when you find that the mobile phone time is slower by a few seconds, the process of calibrating the reference computer time is also known as a time service. We need time service and a unified standard time. Meanwhile, time service technology is also accompanied by the continuous development of our human society. The current time service method mainly comprises the following aspects: radio time service, network time service, satellite time service and optical fiber time service.
At present, special equipment or a transmission route, or special professional frequency band resources, or special optical fiber transmission are needed in the time service technologies, and a method for carrying out time service by adopting a frequency modulation radio station is also proposed, namely an SCA1 additional channel of the frequency modulation radio station is utilized, and frequency resources are also needed to be occupied independently. The conventional wired transmission mode has limited distance and high cost if the transmission distance is long, and the wireless transmission mode generally adopts a long-wave or short-wave fixed-frequency transmission mode, so that a special long-wave and short-wave transmission base is needed, the cost is high, and the coverage area is limited.
Disclosure of Invention
Accordingly, it is necessary to provide a system and a method for wireless timing parasitic to a fm radio, which can realize high-precision timing by using a fm radio parasitic signal without occupying additional frequency resources and bandwidth.
A wireless time service system parasitic on a frequency modulation radio, the system comprising: a transmitting end and a receiving end; the transmitting end and the receiving end perform data transmission through radio waves.
The transmitting end is improved on the basis of the original transmitting end of the frequency modulation radio station, and the improvement points are as follows: adding a time encoder and a signal synthesizer; the carrier frequency signal of the transmitting end is a sine wave with the frequency of 1 kHz.
The time encoder is used for encoding the UTC time signal by adopting a self-defined encoding mode to obtain a time encoded signal, and inputting the time encoded signal and a voice signal to be modulated of a radio station into the signal synthesizer; the time-coded signal has a frequency of 10Hz and a symbol length of 10 full cycles.
The signal synthesizer is used for synthesizing the received voice signal to be modulated of the radio station and the time coding signal into a path of synthesized signal, and inputting the synthesized signal into the modulator.
The receiving end comprises a demodulator; the demodulator is used for demodulating the received synthesized signal modulated by the modulator to obtain a demodulated synthesized signal, and the demodulated synthesized signal comprises a demodulated time code signal and an audio signal.
Further, the receiving end further comprises a signal splitter, a 20Hz low-pass filter and a time service signal decoding module.
The signal splitter is configured to split the demodulated composite signal into two paths of demodulated composite signals, take the first path of demodulated composite signal as an audio signal for subsequent processing, and input the second path of demodulated composite signal into a 20Hz low-pass filter.
The 20Hz low-pass filter is used for carrying out low-pass filtering on the received second path of demodulated synthesized signal to obtain a demodulated time coding signal.
The time service signal decoding module is used for decoding the received demodulated time code signal to obtain a decoded UTC time signal.
Further, the self-defined coding mode adopted by the time encoder is as follows: the initial bit is 1bit, the last two bits of the year occupy 7bits, the month occupies 4bits, the day occupies 5bits, the total seconds in the day occupy 17bits, and 34bits are needed in total; the symbols of the time-coded signal include: the system comprises P code elements, H code elements and L code elements, wherein the P code elements represent the beginning of frame data, are starting points of a whole minute and are used for accurately aligning time points; the H symbol represents the number 1; l symbols represent the number 0; the symbol length is fixed to 1 second, and consists of 10Hz signals with 10 whole periods; p symbol when the ratio of the high level duration to the low level duration of the amplitude is 4:1, H symbol when the ratio of the high level duration to the low level duration of the amplitude is 1:1, L symbol when the ratio of the high level duration to the low level duration of the amplitude is 1:4; an ASK modulation mode is adopted in the code element, and the modulation proportion is configurable.
Further, the pair of orthogonal signals includes: sine signals and cosine signals.
The time service signal decoding module comprises two decoding branches consisting of a first multiplier, 1 low-pass filter and a second multiplier, 1 adder, 1 comparator and 1 decoding module in a counting mode;
and the first decoding branch is used for receiving the sinusoidal signal and the demodulated time code signal, multiplying the sinusoidal signal and the demodulated time code signal through the first multiplier, filtering the obtained multiplied signal through the low-pass filter, and squaring the filtered signal through the second multiplier to obtain a sinusoidal demodulation signal.
And the second decoding branch is used for carrying out cosine demodulation on the demodulated time coding signal by adopting the cosine signal, so as to obtain a cosine demodulation signal.
And the adder is used for adding the sine demodulation signal and the cosine demodulation signal to obtain an added signal.
The comparator is used for comparing the summation signal with a preset threshold level.
The decoding module of the counting mode is used for carrying out high-level counting on the signal output by the comparator, determining the code element type according to the obtained counting value, decoding the code element of the time coding signal according to the code element type, and obtaining time service information according to the obtained decoded time coding signal.
Further, obtaining time service information according to the obtained decoded time code signal includes:
and determining an original starting moment point from the rising edge of the P code element of the demodulated time code signal, and compensating the original starting moment of the minute to obtain the starting moment point.
Decoding is carried out according to 33 code elements which are immediately behind the P code in the demodulated time coding signal, and an accurate UTC time value corresponding to the starting moment point is obtained.
And forming the starting moment and the corresponding accurate UTC time value into complete time service information, and completing time service on the local equipment.
Further, the 20Hz low-pass filter is a switched capacitor filter.
Further, the signal synthesizer includes an adder.
The method is used for carrying out time service on a user by adopting any one of the wireless time service systems parasitic on the frequency modulation radio station; the method comprises the following steps:
transmitting end:
and (3) adopting a sine wave with the frequency of 1kHz as a carrier frequency signal, and adopting a self-defined coding mode to code the UTC time signal to obtain a time coding signal with the frequency of 10Hz and the code element length of 10 whole periods.
And synthesizing the time coding signal and the voice signal to be modulated of the radio station by adopting a signal synthesizer to obtain a synthesized signal.
And modulating the synthesized signal to obtain a modulated synthesized signal, and transmitting the modulated synthesized signal to a receiving end through radio waves.
The receiving end:
and receiving the modulated composite signal, and demodulating the modulated composite signal by adopting a pair of orthogonal signals with the same frequency as the carrier frequency signal of the transmitting end to obtain a demodulated composite signal, wherein the demodulated composite signal comprises a demodulated time coding signal and an audio signal.
When the receiving end needs to normally receive the time signal, dividing the demodulated synthesized signal into two paths of signals, and inputting the first path of signals as audio signals to an audio signal subsequent processing module; and filtering the second path of signal by adopting a 20Hz low-pass filter to obtain a demodulated time code signal, and decoding the demodulated time code signal to obtain a UTC time signal.
The system and the method for wireless time service parasitic on the frequency modulation radio station comprise the following steps: a transmitting end and a receiving end; the transmitting end and the receiving end perform data transmission through radio waves; the transmitting end is improved on the basis of the original transmitting end of the frequency modulation radio station, and the improvement points are as follows: adding a time encoder and a signal synthesizer; the carrier frequency signal of the transmitting end is a sine wave with the frequency of 1kHz, and the receiving end comprises a demodulator. The time encoder is used for encoding the UTC time signal by adopting a self-defined encoding mode to obtain a time encoded signal, and the signal synthesizer is used for synthesizing the time encoded signal and a voice signal to be modulated of the radio station to obtain a synthesized signal; wherein the time-coded signal has a frequency of 10Hz and a symbol length of 10 full cycles. The demodulator is used for demodulating the modulated composite signal to obtain a demodulated composite signal, and the demodulated composite signal comprises a demodulated time code signal and an audio signal. The system can generate sub-millisecond level under the condition of not occupying extra frequency and bandwidth resourcesTime service signals are used for time service for local equipment; the system can realize the time service mode of national coverage by slightly modifying under the existing basic design condition, and reduces the cost.
Drawings
FIG. 1 is a block diagram of a wireless timing system parasitic on a FM station in one embodiment;
FIG. 2 is a spectrum structure of a synthesized signal according to another embodiment;
FIG. 3 is a block diagram of a receiver in another embodiment;
FIG. 4 is a diagram of three symbols in another embodiment, where (a) is a P symbol, (b) is an H symbol, and (c) is an L symbol;
FIG. 5 is a block diagram of a timing signal decoding module according to another embodiment;
fig. 6 is a flow chart of a method of wireless timing parasitic on a fm radio in one embodiment.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application will be further described in detail with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the present application.
Generally, the frequency range of the speech signal is: 300 Hz-3.4 kHz, and is widened to the professional audio field, and the frequency range of the audio signal is as follows: 20 Hz-20 kHz, which means the frequency lower than 20Hz, cannot be heard at all by the human ear, and no way is provided for transmitting voice signals, but from another angle, the frequency band lower than 20Hz can be used for transmitting some other available information, and the low-frequency band of the frequency modulation radio station is adopted for transmitting time signals.
The time service signal generally needs to transmit accurate and perfect time information, which contains information of two aspects, namely an accurate time alignment signal, namely a time point, and information of the other aspect, namely an accurate UTC time value corresponding to the time point. The channel is divided into unidirectional time service and bidirectional comparison time service according to whether the channel is unidirectional or bidirectional, and only the unidirectional time service is considered because the signal transmitted by the radio station is unidirectional. The most common mode in unidirectional time service is a wire transmission 1pps+tod transmission mode, which is transmitted by dividing a time point and a time code into two channels. There are many transmission modes for combining the time point and the time code to transmit by using one channel, for example, the B code is divided into an alternating current B code and a direct current B code, and the two information are fused into one channel to transmit. The coding mode of the invention refers to the design thought of the alternating current B code, the signal frequency of the alternating current B code is 1kHz, but the frequency signal is in the audio frequency range, the frequency of the alternating current B code can be correspondingly reduced to 10Hz, the coding mode adopts self-defined coding, and the corresponding time service frequency is expanded to be 60 seconds time service once.
In one embodiment, as shown in fig. 1, there is provided a wireless time service system parasitic to a frequency modulation radio, the system comprising: a transmitting end 10 and a receiving end 20; the transmitting end 10 and the receiving end 20 perform data transmission by radio waves.
The transmitting end 10 is improved on the basis of the original transmitting end of the frequency modulation radio station, namely, only the voice signal to be modulated of the radio station and the time coding signal are synthesized and then changed into a synthesized signal, and the synthesized signal is input to the modulator, and the spectrum structure of the synthesized signal is shown in fig. 2. The concrete improvement points are as follows: adding a time encoder 101 and a signal synthesizer 102; the carrier frequency signal of the transmitting end 10 is a sine wave with the frequency of 1 kHz.
The time encoder 101 is configured to encode the UTC time signal by using a custom encoding manner, obtain a time encoded signal, and input the time encoded signal and a voice signal to be modulated of the radio station into the signal synthesizer; the time-coded signal has a frequency of 10Hz and a symbol length of 10 full cycles.
The signal synthesizer 102 is configured to synthesize the received voice signal to be modulated and the time-coded signal of the radio station into a composite signal, and input the composite signal to the modulator.
The receiving end 20 includes a demodulator 201; the demodulator 201 is configured to demodulate the received composite signal modulated by the modulator to obtain a demodulated composite signal, where the demodulated composite signal includes a demodulated time-coded signal and an audio signal.
Specifically, at the receiving end, if a common radio receives a signal, no change can be made, because the signal is a composite signal of a radio audio signal and a time coding signal after demodulation, the spectrum structure of the composite signal is shown in fig. 2, the frequency dimension of the composite signal of the time coding signal is 10Hz, the frequency dimension of the composite signal is not in the audio frequency range, the ear does not feel any, only the audio signal of the radio is heard,
in the above-mentioned wireless time service system parasitized in the frequency modulation radio station, the system includes: a transmitting end and a receiving end; the transmitting end and the receiving end perform data transmission through radio waves; the transmitting end is improved on the basis of the original transmitting end of the frequency modulation radio station, and the improvement points are as follows: adding a time encoder and a signal synthesizer; the carrier frequency signal of the transmitting end is a sine wave with the frequency of 1kHz, and the receiving end comprisesA demodulator. The time encoder is used for encoding the UTC time signal by adopting a self-defined encoding mode to obtain a time encoded signal, and the signal synthesizer is used for synthesizing the time encoded signal and a voice signal to be modulated of the radio station to obtain a synthesized signal; wherein the time-coded signal has a frequency of 10Hz and a symbol length of 10 full cycles. The demodulator is used for demodulating the modulated composite signal to obtain a demodulated composite signal, and the demodulated composite signal comprises a demodulated time code signal and an audio signal. The system can generate sub-millisecond level under the condition of not occupying extra frequency and bandwidth resourcesTime service signals are used for time service for local equipment; the system can realize the time service mode of national coverage by slightly modifying under the existing basic design condition, and reduces the cost.
Further, as shown in fig. 3, the receiving end further includes a signal splitter 202, a 20Hz low-pass filter 203, and a timing signal decoding module 204; a signal splitter 202, configured to split the demodulated composite signal into two paths of demodulated composite signals, and subsequently process the first path of demodulated composite signal as an audio signal, and input the second path of demodulated composite signal into a 20Hz low-pass filter 203; a 20Hz low-pass filter 203, configured to perform low-pass filtering on the received second demodulated composite signal, to obtain a demodulated time-coded signal; the time service signal decoding module 204 is configured to decode the demodulated time code signal to obtain a decoded UTC time signal.
Specifically, if the receiving end needs to normally receive the time signal, the demodulated synthesized signal is divided into two paths, one path is directly an audio signal and is sent to the audio signal for subsequent processing, and the other path is passed through a low-pass filter, and the cut-off frequency of the low-pass filter can be set to be 20Hz, so that a switched capacitor filter is preferably adopted. The filtered audio signal is removed at a rate leaving only a 10Hz time-coded signal. And then the UTC time signal is recovered by decoding.
Further, the time encoder adopts a custom coding mode that: the initial bit is 1bit, the last two bits of the year occupy 7bits, the month occupies 4bits, the day occupies 5bits, the total seconds in the day occupy 17bits, and 34bits are needed in total; the symbols of the time-coded signal include: the system comprises P code elements, H code elements and L code elements, wherein the P code elements represent the beginning of frame data, are starting points of a whole minute and are used for accurately aligning time points; the H symbol represents the number 1; l symbols represent the number 0; the symbol length is fixed to 1 second, and consists of 10Hz signals with 10 whole periods; p symbol when the ratio of the high level duration to the low level duration of the amplitude is 4:1, H symbol when the ratio of the high level duration to the low level duration of the amplitude is 1:1, L symbol when the ratio of the high level duration to the low level duration of the amplitude is 1:4; an ASK modulation mode is adopted in the code element, and the modulation proportion is configurable.
Specifically, the H symbol is 800ms (8 full cycles) in length and 200ms (2 full cycles) in length, the H symbol is 500ms (5 full cycles) in length and 500ms (5 full cycles) in length, the L symbol is 200ms (2 full cycles) in length and 800ms (8 full cycles) in length and the ratio of the high to low of the amplitude (A H /A L ) Called modulation ratio, which can be configured according to actual requirements, as an alternative modulation ratio is 3:1, a step of; the signal amplitude can flexibly configure gain and attenuation according to the modulation requirement of the radio station, and specific symbols are shown in fig. 4, wherein (a) is a P symbol, (b) is an H symbol, and (c) is an L symbol.
Further, as shown in fig. 5, the timing signal decoding module is shown in a block diagram. The pair of orthogonal signals includes: sine signals and cosine signals. The time service signal decoding module comprises two decoding branches consisting of a first multiplier, 1 low-pass filter and a second multiplier, 1 adder, 1 comparator and 1 decoding module in a counting mode; the first decoding branch is used for receiving the sinusoidal signal and the demodulated time code signal, multiplying the sinusoidal signal and the demodulated time code signal through the first multiplier, filtering the obtained multiplied signal through the low-pass filter, and squaring the filtered signal through the second multiplier to obtain a sinusoidal demodulation signal; and so on, the second decoding branch is used for performing cosine demodulation on the demodulated time coding signal by adopting a cosine signal to obtain a cosine demodulation signal; an adder for adding the sine demodulation signal and the cosine demodulation signal to obtain an added signal; the comparator is used for comparing the summation signal with a preset threshold level; and the decoding module of the counting mode is used for counting the high level of the signal output by the comparator, determining the code element type according to the obtained count value, decoding the code element of the time coding signal according to the code element type, and obtaining time service information according to the obtained decoded time coding signal.
Specifically, the three symbol patterns described in FIG. 4, each symbol may be represented by a function S (t 1 ,t 2 )＝A H sin(2π·t 1 /T)+A L sin(2π·t 2 T), where T is the period of the symbol, t=100 milliseconds, T 1 ∈[t 0 ,t 0 +nT]，t 2 ∈[t 0 +nT,t 0 +10T]The schematic diagram of the timing signal decoding module at the receiving end is shown in fig. 5, where LPF represents a low-pass filter in fig. 5.
The receiving end generates a pair of orthogonal signals with the same frequency as the carrier frequency of the transmitting end,wherein (1)>For the initial phase, consider a method of demodulating one symbol, and multiply the orthogonal signal with the input symbol to obtain signal S I (t)、S Q And (t) the expression of which is shown in the formula (1).
Wherein t, t 1 、t 2 Are all time variables, t 0 For the start time, n is the number of cycles, n is an integer of 1 or more and 10 or less, and T is the symbol period.
Will beSubstituting the formula (1) to obtain the formulas (2) and (3).
And filtering the integrated sum and difference signals in the formulas (2) and (3) through a low-pass filter (filtering signals higher than 20 Hz), and obtaining the expressions of the signals as shown in formulas (4) and (5).
Wherein S' I (t)、S' Q (t) is respectively the signal S I (t)、S Q (t) filtered signal, A H For high amplitude values of symbols, A L Is a low amplitude value of the symbol.
The expression of the signal obtained by squaring the signal represented by the expression (4) and the expression (5) is shown in the expression (6).
As can be seen from equation (6), two DC levels can be obtained for the result after demodulation of a single symbol, the high level beingLow level is +.>The ratio of time of high and low levels is 4: and 1 is a P code element, and the ratio of high level to low level is 1: and 1 is an H symbol, and the ratio of high level to low level is 1: and 4 is L code elements, the identification method is simpler, for example, a reasonable comparison threshold can be adopted, and only the high level trigger counter is used for counting, and the code element type is judged through the count value because the code element length is fixed. The comparator extracts the 800ms, 500ms and 200ms high level pulses of the P, H and L code elements for subsequent decoding and identification, and the decoding only needs to count the width of the pulse, namely the P code if the pulse is about 800ms, the H code if the pulse is about 500ms, and the L code if the pulse is about 200 ms. The preset threshold level is set in such a manner that the recognition degree of the code element is maximized and the intermediate value between the two levels is set to be optimal.
In the derivation of the formula, if a tiny frequency difference exists between the generation of the orthogonal carrier signal at the receiving end and the sine wave at the transmitting end, the two paths of signals are completely orthogonal, and the same result is not difficult to obtain.
In one embodiment, obtaining time service information according to the decoded time coded signal includes: determining an original starting moment point from the rising edge of the P code element of the demodulated time coding signal, and compensating the original starting moment of minutes to obtain the starting moment point; decoding according to 33 code elements immediately following the P code in the demodulated time coding signal to obtain an accurate UTC time value corresponding to the starting moment point; and forming the starting moment and the corresponding accurate UTC time value into complete time service information, and completing time service on the local equipment.
Specifically, for the demodulation of the time service code stream signal, two processes are divided, firstly, a starting signal of whole minutes is provided, the rising edge of the demodulated P code is the starting signal of the minutes, and of course, the signal processing has a certain time delay, but the time delay is changed into a fixed time delay, the fixed time delay can be compensated by a deduction mode, and the accuracy after compensation can reach the sub millisecond level. And then solving specific time, month, day, time, minute and second according to 33 code elements immediately behind the P code, thus obtaining complete time service information, having accurate time points and determined time codes and being capable of carrying out time service on local equipment.
Further, the 20Hz low pass filter is a switched capacitor filter.
Further, the signal synthesizer includes an adder.
In one embodiment, as shown in fig. 6, a method for wireless time service parasitic on a fm radio station is provided, where the method is used for time service to a user by using any of the wireless time service systems parasitic on the fm radio station; the method comprises the following steps:
transmitting end:
step 600: and (3) adopting a sine wave with the frequency of 1kHz as a carrier frequency signal, and adopting a self-defined coding mode to code the UTC time signal to obtain a time coding signal with the frequency of 10Hz and the code element length of 10 whole periods.
Step 602: and synthesizing the time coding signal and the voice signal to be modulated of the radio station by adopting a signal synthesizer to obtain a synthesized signal.
Step 604: the synthesized signal is modulated to obtain a modulated synthesized signal, and the modulated synthesized signal is transmitted to a receiving end through radio waves.
The receiving end:
step 606: and receiving the modulated composite signal, and demodulating the modulated composite signal by adopting a pair of orthogonal signals with the same frequency as the carrier frequency signal of the transmitting end to obtain a demodulated composite signal, wherein the demodulated composite signal comprises a demodulated time code signal and an audio signal.
Step 608: when the receiving end needs to normally receive the time signal, dividing the demodulated synthesized signal into two paths of signals, and inputting the first path of signals serving as audio signals to an audio signal subsequent processing module; and filtering the second path of signal by adopting a 20Hz low-pass filter to obtain a demodulated time code signal, and decoding the demodulated time code signal to obtain a UTC time signal.
It should be understood that, although the steps in the flowchart of fig. 6 are shown in order as indicated by the arrows, the steps are not necessarily performed in order as indicated by the arrows. The steps are not strictly limited to the order of execution unless explicitly recited herein, and the steps may be executed in other orders. Moreover, at least some of the steps in fig. 6 may include multiple sub-steps or stages that are not necessarily performed at the same time, but may be performed at different times, nor do the order in which the sub-steps or stages are performed necessarily performed in sequence, but may be performed alternately or alternately with at least a portion of the sub-steps or stages of other steps or other steps.
The technical features of the above embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.
The above examples merely represent a few embodiments of the present application, which are described in more detail and are not to be construed as limiting the scope of the invention. It should be noted that it would be apparent to those skilled in the art that various modifications and improvements could be made without departing from the spirit of the present application, which would be within the scope of the present application. Accordingly, the scope of protection of the present application is to be determined by the claims appended hereto.
Claims (7)
1. A wireless time service system parasitic on a frequency modulation radio, the system comprising: a transmitting end and a receiving end; the transmitting end and the receiving end perform data transmission through radio waves;
the transmitting end is improved on the basis of the original transmitting end of the frequency modulation radio station, and the improvement points are as follows: adding a time encoder and a signal synthesizer; the carrier frequency signal of the transmitting end is a sine wave with the frequency of 1 kHz;
the time encoder is used for encoding the UTC time signal by adopting a self-defined encoding mode to obtain a time encoded signal, and inputting the time encoded signal and a voice signal to be modulated of a radio station into the signal synthesizer; the frequency of the time coding signal is 10Hz, and the code element length is 10 whole periods;
the signal synthesizer is used for synthesizing the received voice signal to be modulated of the radio station and the time coding signal into a path of synthesized signal, and inputting the synthesized signal into the modulator;
the receiving end comprises a demodulator; the demodulator is used for demodulating the received synthesized signal modulated by the modulator to obtain a demodulated synthesized signal, and the demodulated synthesized signal comprises a demodulated time code signal and an audio signal;
the receiving end also comprises a time service signal decoding module, wherein the time service signal decoding module comprises two decoding branches consisting of a first multiplier, 1 low-pass filter and a second multiplier, 1 adder, 1 comparator and 1 decoding module in a counting mode;
the first decoding branch is used for receiving the sinusoidal signal and the demodulated time code signal, multiplying the sinusoidal signal and the demodulated time code signal through the first multiplier, filtering the obtained multiplied signal through the low-pass filter, and squaring the filtered signal through the second multiplier to obtain a sinusoidal demodulation signal;
and so on, the second decoding branch is used for performing cosine demodulation on the demodulated time coding signal by adopting a cosine signal to obtain a cosine demodulation signal; the cosine signal and the sine signal are a pair of orthogonal signals;
the adder is used for adding the sine demodulation signal and the cosine demodulation signal to obtain an added signal;
the comparator is used for comparing the summation signal with a preset threshold level;
the decoding module of the counting mode is used for carrying out high-level counting on the signal output by the comparator, determining the code element type according to the obtained counting value, decoding the code element of the time coding signal according to the code element type, and obtaining time service information according to the obtained decoded time coding signal.
2. The system of claim 1, wherein the receiving end further comprises a signal splitter, a 20Hz low pass filter, and a timing signal decoding module;
the signal splitter is configured to split the demodulated composite signal into two paths of demodulated composite signals, take the first path of demodulated composite signal as an audio signal for subsequent processing, and input the second path of demodulated composite signal into a 20Hz low-pass filter;
the 20Hz low-pass filter is used for carrying out low-pass filtering on the received second path of demodulated synthesized signal to obtain a demodulated time coding signal.
3. The system of claim 2, wherein the time encoder employs a custom encoding scheme of: the initial bit is 1bit, the last two bits of the year occupy 7bits, the month occupies 4bits, the day occupies 5bits, the total seconds in the day occupy 17bits, and 34bits are needed in total; the symbols of the time-coded signal include: the system comprises P code elements, H code elements and L code elements, wherein the P code elements represent the beginning of frame data, are starting points of a whole minute and are used for accurately aligning time points; the H symbol represents the number 1; l symbols represent the number 0; the symbol length is fixed to 1 second, and consists of 10Hz signals with 10 whole periods; p symbol when the ratio of the high level duration to the low level duration of the amplitude is 4:1, H symbol when the ratio of the high level duration to the low level duration of the amplitude is 1:1, L symbol when the ratio of the high level duration to the low level duration of the amplitude is 1:4; an ASK modulation mode is adopted in the code element, and the modulation proportion is configurable.
4. A system according to claim 3, wherein obtaining time service information based on the decoded time coded signal comprises:
determining an original starting moment point from the rising edge of the P code element of the demodulated time coding signal, and compensating the original starting moment of minutes to obtain the starting moment point;
decoding according to 33 code elements immediately following the P code in the demodulated time coding signal to obtain an accurate UTC time value corresponding to the starting moment point;
and forming the starting moment and the corresponding accurate UTC time value into complete time service information, and completing time service on the local equipment.
5. The system of claim 2, wherein the 20Hz low pass filter is a switched capacitor filter.
6. The system of any of claims 1-5, wherein the signal synthesizer comprises an adder.
7. A method of wireless timing parasitic on a fm radio station, wherein the method is used for timing a user using the wireless timing system parasitic on a fm radio station of any one of claims 1-6; the method comprises the following steps:
transmitting end:
a sine wave with the frequency of 1kHz is adopted as a carrier frequency signal, and a self-defined coding mode is adopted to code UTC time signals, so that time coded signals with the frequency of 10Hz and the code element length of 10 whole periods are obtained;
synthesizing the time coding signal and the voice signal to be modulated of the radio station by adopting a signal synthesizer to obtain a synthesized signal;
modulating the synthesized signal to obtain a modulated synthesized signal, and transmitting the modulated synthesized signal to a receiving end through radio waves;
the receiving end:
the modulated composite signal is received, and the modulated composite signal is demodulated by adopting a pair of orthogonal signals with the same frequency as the carrier frequency signal of the transmitting end, so as to obtain a demodulated composite signal, wherein the demodulated composite signal comprises a demodulated time coding signal and an audio signal;
when the receiving end needs to normally receive the time signal, dividing the demodulated synthesized signal into two paths of signals, and inputting the first path of signals as audio signals to an audio signal subsequent processing module; filtering the second path of signal by adopting a 20Hz low-pass filter to obtain a demodulated time coding signal, and decoding the demodulated time coding signal by adopting a time service signal decoding module to obtain a UTC time signal, wherein the time service signal decoding module comprises two decoding branches consisting of a first multiplier, 1 low-pass filter and a second multiplier, 1 adder, 1 comparator and 1 decoding module in a counting mode; the first decoding branch is used for receiving the sinusoidal signal and the demodulated time code signal, multiplying the sinusoidal signal and the demodulated time code signal through the first multiplier, filtering the obtained multiplied signal through the low-pass filter, and squaring the filtered signal through the second multiplier to obtain a sinusoidal demodulation signal; and so on, the second decoding branch is used for performing cosine demodulation on the demodulated time coding signal by adopting a cosine signal to obtain a cosine demodulation signal; the cosine signal and the sine signal are a pair of orthogonal signals;
the adder is used for adding the sine demodulation signal and the cosine demodulation signal to obtain an added signal; the comparator is used for comparing the summation signal with a preset threshold level; the decoding module of the counting mode is used for carrying out high-level counting on the signal output by the comparator, determining the code element type according to the obtained counting value, decoding the code element of the time coding signal according to the code element type, and obtaining time service information according to the obtained decoded time coding signal.
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