WO2017016321A1 - 基于数字调频广播的时钟同步方法和调频广播接收机 - Google Patents

基于数字调频广播的时钟同步方法和调频广播接收机 Download PDF

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Publication number
WO2017016321A1
WO2017016321A1 PCT/CN2016/085079 CN2016085079W WO2017016321A1 WO 2017016321 A1 WO2017016321 A1 WO 2017016321A1 CN 2016085079 W CN2016085079 W CN 2016085079W WO 2017016321 A1 WO2017016321 A1 WO 2017016321A1
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broadcast receiver
broadcast
time
clock
local
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PCT/CN2016/085079
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English (en)
French (fr)
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陈曦
张光华
李立
彭铁雁
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深圳思凯微电子有限公司
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L7/00—Arrangements for synchronising receiver with transmitter

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  • the present invention relates to the field of wireless navigation technologies, and in particular, to a clock synchronization method based on digital FM broadcasting and an FM broadcast receiver.
  • GNSS Global Navigation Satellite System
  • a pseudo-satellite (Pseudo-Satellite or Pseudolite, abbreviated as PL) is a transmitter that is deployed on the ground to transmit some kind of positioning signal, and usually emits signals similar to GPS.
  • the pseudolite can replace the satellite for navigation and positioning, for example, indoors, underground parking lots and tunnels.
  • pseudo-satellite systems or pseudo-satellite systems are usually equipped with a temperature-compensated crystal oscillator clock. The accuracy is not high, and clock drift occurs. The standard time signal of the reference station cannot be accurately synchronized during the sampling time. However, in the positioning model, all pseudolites in the system must be synchronized.
  • the clock synchronization of the pseudolite is generally realized by the navigation satellite. However, if the clock synchronization of the pseudolite depends on the satellite navigation, when the satellite navigation fails, the clock precision of the pseudolite cannot reach the navigation requirement and the pseudolite fails. The clock of the pseudolite system is over-synchronized by relying on satellite navigation.
  • the main object of the present invention is to provide a clock synchronization method based on digital FM broadcasting and a frequency modulation broadcast receiver, which aims to solve the technical problem that the clock synchronization of a pseudo satellite system or a pseudolite system is too dependent on satellite navigation.
  • the present invention provides a clock synchronization method based on digital FM broadcasting, and the clock synchronization method based on digital FM broadcasting includes:
  • the FM broadcast receiver receives the wireless data broadcast signal broadcast by the FM broadcast transmitter synchronized with the standard time;
  • the FM broadcast receiver demodulates a time synchronization signal in the wireless data broadcast signal
  • the FM broadcast receiver acquires local time information of the time synchronization signal it receives;
  • the FM broadcast receiver synchronizes the time and frequency of the local clock of the FM broadcast receiver according to its local location information, the time synchronization signal, and local time information.
  • the time synchronization signal includes a ranging code, a remote time information of the FM broadcast transmitter broadcasting the ranging code, and remote location information of the FM broadcast transmitter,
  • the step of synchronizing the time and frequency of the local clock of the FM broadcast receiver according to the time synchronization signal, the local time information and the local location information by the FM broadcast receiver includes:
  • the FM broadcast receiver estimates estimated time information of the ranging code received by the FM broadcast receiver and a relative frequency difference between the FM broadcast receiver and the FM broadcast transmitter according to the local time information;
  • the FM broadcast receiver calculates a time difference between the clock of the FM broadcast receiver and the clock of the FM broadcast transmitter according to the remote location information, local location information, remote time information, and estimated time information;
  • the FM broadcast receiver synchronizes the time and frequency of the local clock of the FM broadcast receiver based on the time difference and the relative frequency difference.
  • the step of the FM broadcast receiver acquiring local time information of the time synchronization signal received by the FM broadcast receiver includes:
  • the FM broadcast receiver generates a local ranging code identical to a pulse signal waveform of a ranging code transmitted by the FM broadcast transmitter;
  • the FM broadcast receiver acquires a local clock value when a pulse waveform of the local ranging code is aligned with a pulse waveform of a ranging code transmitted by the FM broadcast transmitter;
  • the step of estimating, by the FM radio receiver, the estimated time information of the ranging code received by the FM broadcast receiver and the relative frequency difference between the FM broadcast receiver and the FM broadcast transmitter according to the local time information include:
  • the FM broadcast receiver estimates that the FM broadcast receiver receives the ranging according to a nominal delay of each pulse of the ranging code transmitted by the FM broadcast transmitter and a nominal value of the first clock and the local clock value The estimated clock value of the first pulse of the code and the relative frequency difference between the FM broadcast receiver and the FM broadcast transmitter.
  • the FM broadcast receiver calculates a time difference between the clock of the FM broadcast receiver and the clock of the FM broadcast transmitter according to the remote location information, local location information, remote time information, and estimated time information.
  • the steps include:
  • the FM broadcast receiver calculates a propagation time of the signal from the FM broadcast transmitter to the FM broadcast receiver according to the remote location information and the local location information;
  • the FM broadcast receiver calculates a time difference between the FM broadcast receiver clock and the FM broadcast transmitter clock according to the remote time information, the estimated time information, and the transmission time.
  • the step of adjusting, by the FM radio receiver, the time and frequency of the self clock according to the time difference and the relative frequency difference comprises:
  • the step of adjusting, by the FM radio receiver, the time and frequency of the self clock according to the time difference and the relative frequency difference comprises:
  • the FM broadcast receiver adjusts a frequency of the clock of the FM broadcast receiver according to the relative frequency difference and a frequency nominal value of the FM broadcast receiver;
  • the FM broadcast receiver adjusts a timing of the FM broadcast receiver clock based on the time difference and a frequency nominal value of the FM broadcast receiver.
  • the present invention further provides an FM broadcast receiver, characterized in that the FM broadcast receiver comprises:
  • a signal receiving module configured to receive a wireless data broadcast signal broadcast by an FM broadcast transmitter synchronized with a standard time
  • a demodulation module configured to demodulate a time synchronization signal in the wireless data broadcast signal
  • a local time acquisition module configured to acquire local time information that the FM broadcast receiver receives the time synchronization signal
  • a synchronization module configured to synchronize a time and a frequency of the local clock of the FM broadcast receiver according to the local location information, the time synchronization signal, and the local time information.
  • the time synchronization signal includes a ranging code, a remote time information of the FM broadcast transmitter broadcasting the ranging code, and remote location information of the FM broadcast transmitter,
  • the synchronization module includes:
  • an estimating unit configured to estimate, according to the local time information, estimated time information that the FM broadcast receiver receives the ranging code, and a relative frequency difference between the FM broadcast receiver and the FM broadcast transmitter;
  • a time difference calculation unit configured to calculate, according to the remote location information, the local location information, the remote time information, and the estimated time information, a time difference between the clock of the FM broadcast receiver and the clock of the FM broadcast transmitter;
  • a synchronization unit configured to synchronize a time and a frequency of the local clock of the FM broadcast receiver according to the time difference and the relative frequency difference.
  • the local time acquisition module includes:
  • a pulse generating unit configured to generate a local ranging code that is the same as a pulse signal waveform of the ranging code sent by the FM broadcast transmitter;
  • a clock value acquiring unit configured to acquire a local clock value when a pulse waveform of the local ranging code is aligned with a pulse waveform of a ranging code sent by the FM broadcast transmitter;
  • the estimating unit is further configured to: according to a nominal delay of each pulse of the ranging code sent by the FM broadcast transmitter and a first pulse thereof, and the local clock value, estimate that the FM broadcast receiver receives the An estimated clock value of the first pulse of the ranging code and a relative frequency difference between the FM broadcast receiver and the FM broadcast transmitter.
  • the time difference calculation unit is further configured to:
  • the synchronization unit is further configured to:
  • the present invention receives a wireless data broadcast signal in a signal broadcast by a frequency modulated broadcast transmitter synchronized with a standard time by an FM broadcast receiver, and then extracts a time synchronization signal in the wireless data broadcast signal and acquires local time information of the FM broadcast receiver and Local location information, and finally synchronizing the time and frequency of the local clock of the FM broadcast receiver according to the local location information, the time synchronization signal and the local time information, thereby parasiticizing the wireless data broadcast signal in the vacant resource of the conventional FM signal, due to
  • the data broadcasting of the FM band has the characteristics of long propagation distance, high diffraction and transmission capability, and thus the present invention realizes synchronization of clocks in a pseudo-satellite system or a pseudo-satellite system through FM FM broadcasting, that is, the standard time is passed through the FM broadcasting transmitter.
  • the data broadcast of the FM band is transmitted to the corresponding FM broadcast receiver to complete the synchronization of the receiver clock, and solves the technical problem that the clock synchronization of
  • FIG. 1 is a schematic structural diagram of an embodiment of a clock synchronization method corresponding system based on digital FM broadcasting according to the present invention
  • FIG. 2 is a schematic flow chart of a first embodiment of a clock synchronization method based on digital FM broadcasting according to the present invention
  • FIG. 3 is a diagram showing an in-band spectral relationship between a frequency modulated signal and a parasitic digital signal
  • FIG. 4 is a diagram showing an out-of-band spectrum relationship between a frequency modulated signal and a parasitic digital signal
  • 5 is a signal format of a frequency modulated data broadcast signal D(t) in a clock synchronization method based on digital FM broadcasting;
  • FIG. 6 is a schematic diagram showing the performance of a method for measuring a pulse arrival time in a clock synchronization method based on digital FM broadcasting according to the present invention
  • FIG. 7 is a schematic diagram of functional modules of a first embodiment of an FM broadcast receiver according to the present invention.
  • the model of the clock synchronization method based on the digital FM broadcasting of the present invention includes at least one FM broadcasting transmitter A0 and a plurality of FM broadcasting receivers. (For example, three, A1, A2, and A3), the clock synchronization process of the FM broadcast receiver is similar.
  • the following embodiments take the FM broadcast receiver A1 as an example.
  • the present invention provides a clock synchronization method based on digital FM broadcasting.
  • the clock synchronization method based on digital FM broadcasting includes:
  • Step S10 the FM broadcast receiver receives the wireless data broadcast signal broadcast by the FM broadcast transmitter synchronized with the standard time;
  • the FM broadcast transmitter A0 synchronizes its own time to standard time.
  • the most commonly used standard time is Coordinated Universal.
  • the synchronization method uses a timing-based global navigation satellite receiver to receive signals from GNSS, and time-synchronized global navigation satellites to synchronize the time of FM transmitter A0.
  • To standard time When the global navigation satellite system is not available, the FM broadcast transmitter A0 can operate according to its own clock. At this time, there is an error between the time of the FM broadcast transmitter A0 and the standard time, but it is still visible as long as the error is within the allowable range. Is "in sync". Different applications have different requirements for the allowable range. In the case of a pseudo-satellite system, the time between the system FM radio transmitter A0 and the world coordination time is usually less than one second.
  • the FM broadcast transmitter A0 (hereinafter referred to as the transmitter A0), in addition to broadcasting the conventional FM signal FM(t), simultaneously broadcasts a wireless data broadcast signal D(t) parasitic to the FM broadcast, the signal with a ranging code, Transmitter A0 broadcasts the far-end time information of the ranging code and the remote location information of transmitter A0.
  • an analog sound broadcast signal and a digital sound broadcast signal are combined into one analog digital mixed signal, and an analog sound broadcast channel is shared, and the mixed modulated signal is amplified, and then transmitted by an antenna system to obtain a radio frequency signal of a predetermined spectrum mode.
  • the analog sound broadcasting signal and the digital sound broadcasting signal are superimposed and simultaneously transmitted in the same frequency band.
  • the spectrum design of the D(t) signal is based on the reception quality of the existing FM radio that does not significantly affect the general radio.
  • Figure 3 shows the full-band spectrum form, also known as the in-band form, where D(t) can be seen.
  • the spectrum B2 overlaps with the spectrum B1 of FM(t).
  • Figure 4 shows a non-full-band spectral form, also known as the out-of-band form, where it can be seen that there is no overlap between the spectrum B2 of D(t) and the spectrum B1 of FM(t). Both of these forms have advantages and disadvantages and are visible in the actual system.
  • the US HDRadio uses the out-of-band form shown in Figure 4, while the Chinese CDRadio uses the in-band form shown in Figure 3.
  • the D(t) signal can actually achieve a data communication function of several tens of Kbps.
  • the signal format of D(t) according to the present invention is as shown in FIG.
  • a ranging code periodically in the D(t) signal, and between adjacent ranging codes is a data block.
  • the modulation mode of the data block is usually an Orthogonal Frequency Division Multiplexing (OFDM) signal.
  • OFDM Orthogonal Frequency Division Multiplexing
  • the ranging code may be a pseudo random code, a Gold code or the like, and in the present invention, the ranging code is not continuous, but a data block is stored between adjacent ranging codes.
  • Step S20 the FM broadcast receiver demodulates a time synchronization signal in the wireless data broadcast signal
  • the FM broadcast receiver A1 demodulates D(t) from RF(t). If the spectrum of D(t) does not overlap with the FM signal FM(t), the filtering method can be used to separate. Otherwise, the spectrum of D(t) overlaps with the FM signal FM(t), and an in-band separation method is needed. For example, a separation method of an intra-band analog-frequency analog-mode audio broadcast signal is disclosed in the patent CN201510011206. method. The FM broadcast receiver A1 then removes the carrier from the separated D(t) and performs digital sampling to obtain D(n). In digital communications, removing carriers is a conventional technique.
  • Step S30 the FM broadcast receiver acquires local time information of the time synchronization signal it receives
  • the FM broadcast receiver A1 records the local time information of the FM broadcast receiver A1 at the time when receiving the time synchronization signal transmitted by the transmitter A0.
  • the receiver A1 generates the same local ranging code as the pulse signal waveform of the ranging code transmitted by the transmitter A0 at the local end, and the receiver A1 acquires the pulse waveform of the local ranging code and the ranging code transmitted by the transmitter.
  • the local clock value when the pulse waveform is phase aligned that is, local time information, this local clock value is multiple).
  • Step S40 The FM broadcast receiver synchronizes the time and frequency of the local clock of the FM broadcast receiver according to its local location information, the time synchronization signal, and local time information.
  • the time synchronization signal includes a ranging code, the remote time information of the FM broadcast transmitter broadcasting the ranging code, and the remote location information of the FM broadcast transmitter,
  • Step S40 includes:
  • Step S41 The FM broadcast receiver estimates, according to the local time information, estimated time information that the FM broadcast receiver receives the ranging code and a relative frequency difference between the FM broadcast receiver and the FM broadcast transmitter;
  • the FM broadcast receiver estimates that the FM broadcast receiver receives the ranging according to a nominal delay of each pulse of the ranging code transmitted by the FM broadcast transmitter and a nominal value of the first clock and the local clock value The estimated clock value of the first pulse of the code and the relative frequency difference between the FM broadcast receiver and the FM broadcast transmitter.
  • the FM broadcast receiver A1 generates a local ranging code CL(n) identical to the waveform of the transmitter A0 signal c(t).
  • the CL(n) and D(n) are subjected to a sliding correlation operation.
  • the correlation result is maximum at this time, that is, a correlation peak is obtained.
  • Tsel the sliding correlation operation obtains M correlation peaks
  • the mth correlation peak is the correlation peak corresponding to the mth ranging code in this period, assuming the mth correlation peak
  • the corresponding local clock value is ⁇ m . Take the maximum correlation peak where M is multiplied by rate (a given percentage) to perform the following estimation operation:
  • the local clock value corresponding to the mth correlation peak is ⁇ m , that is, the mth observation equation can be expressed as:
  • k is the frequency difference coefficient of the transmit and receive clocks to be sought
  • ⁇ is the optimal estimate of the arrival of the pulse corresponding to the first correlation peak to be sought
  • ⁇ m is the measurement of the arrival time of the mth pulse noise
  • ⁇ is the arrival time of the obtained ranging code
  • the frequency difference coefficient k is a relative frequency difference from the self-clocked broadcast transmitter A0.
  • the technique of obtaining ⁇ m is a mature technology in communication, and generally takes the sampling point with the largest correlation peak and the adjacent sampling point with a leading lag (a total of three sampling points) for calculation.
  • Step S42 the FM broadcast receiver calculates a time difference between the clock of the FM broadcast receiver and the clock of the FM broadcast transmitter according to the remote location information, local location information, remote time information, and estimated time information.
  • the receiver A1 obtains the distance S between the receiver A1 and the transmitter A0 according to its local position information and the remote position information of the transmitter A0, and the transmission speed of the FM broadcast signal in the air is close to the speed of light, thereby obtaining the signal from The propagation time of the transmitter A0 to the receiver A1; thus, the receiver calculates the distance between the receiver A1 and the transmitter A0 clock based on the remote time information, the estimated time information (ie, the above-mentioned ranging code arrival time ⁇ ) and the transmission time. The time difference.
  • Step S43 the FM broadcast receiver synchronizes the time and frequency of the local clock of the FM broadcast receiver according to the time difference and the relative frequency difference.
  • Receiver A1 typically maintains local time on a digital circuit with a digital second counter that has an operating clock that has a frequency that is fluctuating, but the frequency nominal is known (frequency) The rate nominal value is set to Fdef).
  • the receiver A1 thinks that when the digital second counter increases the Fdef, it considers that the time has passed one second, that is, the second overflows once.
  • the corresponding time difference of the value of the second timer ie, the time of the receiver A1 is multiplied by the frequency nominal value; when the relative frequency difference (ie, the frequency difference coefficient is detected) k), adjust the actual operating clock frequency of the digital circuit to Fdef/(1+K).
  • the FM broadcast receiver receives the wireless data broadcast signal in the signal broadcast by the FM broadcast transmitter synchronized with the standard time, and then extracts the time synchronization signal in the wireless data broadcast signal and acquires the local of the FM broadcast receiver. Time information and local location information, and finally synchronizing the time and frequency of the local clock of the FM broadcast receiver according to the local location information, the time synchronization signal and the local time information, thereby parasiticizing the wireless data broadcast signal to the vacant resource of the conventional FM FM signal
  • the data broadcast has the characteristics of long propagation distance, high diffraction and transmission capability, so that the present invention realizes synchronization of clocks in a pseudo satellite system or a pseudo-satellite system through FM FM broadcasting, that is, through an FM broadcast transmitter.
  • the standard time is transmitted to the corresponding FM broadcast receiver through the data broadcast of the FM band to complete the synchronization of the receiver clock, and solves the technical problem that the clock synchronization of the pseudo satellite system or the pseudo-satellite system is too dependent on satellite navigation.
  • the step S30 includes:
  • Step S31 the FM broadcast receiver generates a local ranging code that is the same as the pulse signal waveform of the ranging code transmitted by the FM broadcast transmitter;
  • Step S32 the FM broadcast receiver acquires a local clock value when the pulse waveform of the local ranging code is aligned with the pulse waveform of the ranging code sent by the FM broadcast transmitter;
  • the FM broadcast receiver A1 generates a local ranging code CL(n) identical to the waveform of the transmitter A0 signal c(t).
  • CL(n) and D(n) are subjected to a sliding correlation operation.
  • the correlation result is the largest at this time, that is, a correlation peak is obtained, and the local clock value at the time of generation of each correlation peak is recorded (ie, the current time). ).
  • Step S41 includes:
  • Step S411 the FM broadcast receiver estimates the frequency modulation according to the nominal delay of each pulse of the ranging code sent by the FM broadcast transmitter and the local clock value and the local clock value.
  • the broadcast receiver receives an estimated clock value of the first pulse of the ranging code and a relative frequency difference between the FM broadcast receiver and the FM broadcast transmitter.
  • the FM broadcast receiver A1 generates a local ranging code CL(n) identical to the waveform of the transmitter A0 signal c(t).
  • the CL(n) and D(n) are subjected to a sliding correlation operation.
  • the correlation result is maximum at this time, that is, a correlation peak is obtained.
  • Tsel the sliding correlation operation obtains M correlation peaks
  • the mth correlation peak is the correlation peak corresponding to the mth ranging code in this period, assuming the mth correlation peak
  • the corresponding local clock value is ⁇ m . Take the maximum correlation peak where M is multiplied by rate (a given percentage) to perform the following estimation operation:
  • the local clock value corresponding to the mth correlation peak is ⁇ m , that is, the mth observation equation can be expressed as:
  • k is the frequency difference coefficient of the transmit and receive clocks to be sought
  • ⁇ is the optimal estimate of the arrival of the pulse corresponding to the first correlation peak to be sought
  • ⁇ m is the mth pulse arrival time measurement noise
  • ⁇ is the arrival time of the obtained ranging code
  • the frequency difference coefficient k is a relative frequency difference from the self-clocked broadcast transmitter A0. It should be explained that the technique of obtaining ⁇ m is a mature technology in communication, and generally takes the sampling point with the largest correlation peak and the adjacent sampling point with a leading lag (a total of three sampling points) for calculation.
  • the bandwidth generally reaches 2Mhz or more, and the ranging code is continuous, and the code phase resolution can reach the sub-meter code phase resolution, and in the present invention
  • the medium ranging code is not continuous, and the data block is stored between adjacent ranging codes.
  • the bandwidth of the D(t) signal is only a few hundred KHz (narrow bandwidth), and is usually sampled by a sampling clock of 1 Msps. The resolution is only 1us, and the synchronization error is obviously too large.
  • the optimal estimate ⁇ of the arrival of the pulse corresponding to the first correlation peak to the local time is estimated by using a plurality of correlation peaks in combination, and the transmitter A0 and the receiver A1 (here, the receiver) A1 is an example) the frequency difference coefficient k of the clock, thereby adjusting the local clock time and frequency of the receiver A1 to synchronize with the transmitter A0, achieving high in the case of a relatively low frequency sampling clock and narrowband signal.
  • Accurate time synchronization refer to Figure 6, Figure 6 shows the optimal estimate ⁇ mean square error using 48 pulses with pulse rate rates of 0.6, 0.8, and 1, respectively.
  • the accuracy of the measured synchronization can usually reach 10 nanometers.
  • the abscissa Eb/N0 in FIG. 6 is the ratio of the energy per bit of data of the received radio signal to the noise power density, and is a general method in the art for indicating the quality of the received radio signal;
  • the ordinate RMSE of 6 is the root mean square error between the estimated value of ⁇ and the true value, in nanoseconds, and is a general method in the art for expressing the quality of the estimate.
  • step S42 includes:
  • Step S421 the FM broadcast receiver calculates, according to the remote location information and the local location information, a propagation time of the signal at the FM broadcast transmitter and the FM broadcast receiver;
  • the propagation time T prop
  • Step S422 the FM broadcast receiver calculates a time difference between the clock of the FM broadcast receiver and the clock of the FM broadcast transmitter according to the remote time information, the estimated time information, and the transmission time.
  • the propagation time of the signal between the transmitter and the receiver is calculated according to the local location information of the receiver and the remote location information of the transmitter, and then according to the remote time information of the transmitter, the receiver.
  • the estimated time information and transmission time are calculated, and the time difference between the receiver clock and the transmitter clock is calculated, and the time difference between the receiver clock and the transmitter clock is obtained in a simple calculation manner.
  • Step 43 includes:
  • Step S431 the FM broadcast receiver adjusts a frequency of the clock of the FM broadcast receiver according to the relative frequency difference and a frequency nominal value of the FM broadcast receiver;
  • Step S432 the FM broadcast receiver adjusts the timing of the FM broadcast receiver clock according to the time difference and the frequency nominal value of the FM broadcast receiver.
  • the FM broadcast receiver usually uses a digital second counter to maintain the local time on the digital circuit.
  • the digital circuit has an operating clock whose frequency fluctuates, but the frequency nominal value (unit: MHz) is known. , set the frequency nominal value to Fdef.
  • the receiver A1 is started by default, if the digital seconds timer of the receiver A1 increases the Fdef, the time exceeds one second, that is, the second overflows once.
  • T E time difference between the transmitter A0 and the receiver A1
  • the value of the second counter is correspondingly reduced by ⁇ T E *Fdef ⁇ (requires rounding or negative).
  • the FM broadcast receiver A1 should adjust the second overflow mechanism to become when the digital second counter reaches the frequency nominal
  • the value is increased by Fdef/(1+K) (requires rounding) and the time is considered to be one second.
  • the present invention provides an FM broadcast receiver.
  • the FM broadcast receiver includes:
  • the signal receiving module 10 is configured to receive a wireless data broadcast signal broadcast by the FM broadcast transmitter synchronized with the standard time;
  • the FM broadcast transmitter A0 synchronizes its own time to standard time.
  • the most commonly used standard time is Coordinated Universal.
  • the synchronization method uses a timing-based global navigation satellite receiver to receive signals from GNSS, and time-synchronized global navigation satellites to synchronize the time of FM transmitter A0.
  • To standard time When the global navigation satellite system is not available, the FM broadcast transmitter A0 can operate according to its own clock. At this time, there is an error between the time of the FM broadcast transmitter A0 and the standard time, but it is still visible as long as the error is within the allowable range. Is "in sync". Different applications have different requirements for the allowable range. In the case of a pseudo-satellite system, the time between the system FM radio transmitter A0 and the world coordination time is usually less than one second.
  • the FM broadcast transmitter A0 (hereinafter referred to as the transmitter A0), in addition to broadcasting the conventional FM signal FM(t), simultaneously broadcasts a wireless data broadcast signal D(t) parasitic to the FM broadcast, the signal with a ranging code, Transmitter A0 broadcasts the far-end time information of the ranging code and the remote location information of transmitter A0.
  • an analog sound broadcast signal and a digital sound broadcast signal are combined into one analog digital mixed signal, and an analog sound broadcast channel is shared, and the mixed modulated signal is amplified, and then transmitted by an antenna system to obtain a radio frequency signal of a predetermined spectrum mode.
  • the analog sound broadcasting signal and the digital sound broadcasting signal are superimposed and simultaneously transmitted in the same frequency band.
  • the spectrum design of the D(t) signal is based on the reception quality of the existing FM radio that does not significantly affect the general radio.
  • Figure 3 shows the full-band spectral form, also known as the in-band form, where it can be seen that the spectrum B2 of D(t) overlaps the spectrum B1 of FM(t).
  • Figure 4 shows a non-full-band spectral form, also known as the out-of-band form, where it can be seen that there is no overlap between the spectrum B2 of D(t) and the spectrum B1 of FM(t). Both of these forms have advantages and disadvantages and are visible in the actual system.
  • the US HDRadio uses the out-of-band form shown in Figure 4, while the Chinese CDRadio uses the in-band form shown in Figure 3.
  • the D(t) signal can actually achieve a data communication function of several tens of Kbps.
  • the signal format of D(t) according to the present invention is as shown in FIG.
  • a ranging code periodically in the D(t) signal, and between adjacent ranging codes is a data block.
  • the modulation mode of the data block is usually an Orthogonal Frequency Division Multiplexing (OFDM) signal.
  • OFDM Orthogonal Frequency Division Multiplexing
  • the ranging code may be a pseudo random code, a Gold code or the like, and in the present invention, the ranging code is not continuous, but a data block is stored between adjacent ranging codes.
  • a demodulation module 20 configured to demodulate a time synchronization signal in the wireless data broadcast signal
  • the demodulation module 20 of the FM broadcast receiver A1 demodulates D(t) from RF(t). If the spectrum of D(t) does not overlap with the FM signal FM(t), the filtering method can be used to separate. Otherwise, the spectrum of D(t) overlaps with the FM signal FM(t), and an in-band separation method is needed. For example, a separation method of an intra-band analog-frequency analog-mode audio broadcast signal is disclosed in the patent CN201510011206. method. The demodulation module 20 of the FM broadcast receiver A1 then removes the carrier from the separated D(t) and performs digital sampling to obtain D(n). In digital communications, removing carriers is a conventional technique.
  • the local time acquisition module 30 is configured to acquire local time information that the FM broadcast receiver receives the time synchronization signal
  • the local time acquisition module 30 of the FM broadcast receiver A1 records the local time information of the FM broadcast receiver A1 at the time when receiving the time synchronization signal transmitted by the transmitter A0.
  • the receiver A1 generates the same local ranging code as the pulse signal waveform of the ranging code transmitted by the transmitter A0 at the local end, and the receiver A1 acquires the pulse waveform of the local ranging code and the ranging code transmitted by the transmitter.
  • the local clock value when the pulse waveform is phase aligned that is, local time information, this local clock value is multiple).
  • the synchronization module 40 is configured to synchronize the time and frequency of the local clock of the FM broadcast receiver according to its local location information, the time synchronization signal, and local time information.
  • the time synchronization signal includes a ranging code, the remote time information of the FM broadcast transmitter broadcasting the ranging code, and the remote location information of the FM broadcast transmitter,
  • the synchronization module 40 includes:
  • the estimating unit 41 is configured to estimate, according to the local time information, estimated time information that the FM broadcast receiver receives the ranging code, and a relative frequency difference between the FM broadcast receiver and the FM broadcast transmitter;
  • the FM broadcast receiver is based on each pulse of a ranging code transmitted by the FM broadcast transmitter Estimating the estimated delay of the first pulse of the ranging code received by the FM broadcast receiver with the nominal delay of the first pulse and the local clock value, and the FM broadcast receiver and the FM broadcast transmission The relative frequency difference between the machines.
  • the FM broadcast receiver A1 generates a local ranging code CL(n) identical to the waveform of the transmitter A0 signal c(t).
  • the CL(n) and D(n) are subjected to a sliding correlation operation.
  • the correlation result is maximum at this time, that is, a correlation peak is obtained.
  • Tsel the sliding correlation operation obtains M correlation peaks
  • the mth correlation peak is the correlation peak corresponding to the mth ranging code in this period, assuming the mth correlation peak
  • the corresponding local clock value is ⁇ m . Take the maximum correlation peak where M is multiplied by rate (a given percentage) to perform the following estimation operation:
  • the local clock value corresponding to the mth correlation peak is ⁇ m , that is, the mth observation equation can be expressed as:
  • k is the frequency difference coefficient of the transmit and receive clocks to be sought
  • ⁇ is the optimal estimate of the arrival of the pulse corresponding to the first correlation peak to be sought
  • ⁇ m is the mth pulse arrival time measurement noise
  • ⁇ is the arrival time of the obtained ranging code
  • the frequency difference coefficient k is a relative frequency difference from the self-clocked broadcast transmitter A0.
  • the technique of obtaining ⁇ m is a mature technology in communication, and generally takes the sampling point with the largest correlation peak and the adjacent sampling point with a leading lag (a total of three sampling points) for calculation.
  • the time difference calculation unit 42 is configured to calculate, according to the remote location information, the local location information, the remote time information, and the estimated time information, a time difference between the clock of the FM broadcast receiver and the clock of the FM broadcast transmitter;
  • the time difference calculation unit 42 of the receiver A1 obtains the distance S between the receiver A1 and the transmitter A0 according to its local position information and the remote position information of the transmitter A0, and the transmission speed of the FM broadcast signal in the air is close to the speed of light. Thereby, the propagation time of the signal from the transmitter A0 to the receiver A1 is obtained; thus, the receiver calculates the receiver A1 and the transmission according to the remote time information, the estimated time information (ie, the above-mentioned ranging code arrival time ⁇ ) and the transmission time. The time difference between the A0 clocks of the machine.
  • the synchronization unit 43 is configured to synchronize the time and frequency of the local clock of the FM broadcast receiver according to the time difference and the relative frequency difference.
  • the synchronization unit 43 of the receiver A1 typically maintains the local time on a digital circuit with a digital second counter having an operating clock whose frequency fluctuates, but the nominal frequency value is known (frequency nominal value) Set to Fdef), when receiver A1 is started by default, receiver A1 thinks that when the digital seconds counter increases Fdef, it thinks that the time has passed one second, that is, the second overflows once.
  • the corresponding time difference of the value of the second timer ie, the time of the receiver A1
  • the frequency nominal value when the relative frequency difference is detected (ie, the frequency difference system)
  • the actual frequency of the operating clock of the digital circuit is adjusted to Fdef/(1+K).
  • the signal receiving module 10 of the FM broadcast receiver receives the wireless data broadcast signal in the signal broadcast by the FM broadcast transmitter synchronized with the standard time, and then the demodulation module 20 extracts the time synchronization signal in the wireless data broadcast signal.
  • the local time acquisition module 30 acquires the local time information and the local location information of the FM broadcast receiver, and the last synchronization module 40 synchronizes the time and frequency of the local clock of the FM broadcast receiver according to the local location information, the time synchronization signal, and the local time information. Therefore, the wireless data broadcast signal is parasitic in the vacant resource of the conventional FM frequency modulated signal.
  • the present invention implements a pseudo-satellite system through FM FM broadcasting.
  • the synchronization of the clock in a pseudo-satellite system that is, the FM radio transmitter transmits the standard time data broadcast through the FM band to the corresponding FM broadcast receiver to complete the synchronization of the receiver clock, and solves the pseudo-satellite system or the like pseudo-satellite.
  • the system's clock synchronization is too dependent on Wei The technical problem of star navigation.
  • the local time acquisition module 30 includes:
  • a pulse generating unit 31 configured to generate a local ranging code that is the same as a pulse signal waveform of the ranging code sent by the FM broadcast transmitter;
  • the clock value obtaining unit 32 is configured to acquire a local clock value when the pulse waveform of the local ranging code is aligned with the pulse waveform of the ranging code sent by the FM broadcast transmitter;
  • the pulse generation unit 31 of the FM broadcast receiver A1 generates the same local ranging code CL(n) as the waveform of the transmitter A0 signal c(t).
  • the clock value acquisition unit 32 performs a sliding correlation operation on CL(n) and D(n). According to the correlation of the ranging codes, when D(n) and CL(n) are phase-aligned, the correlation result is the largest at this time, that is, a correlation peak is obtained, and the local clock value at the time of generation of each correlation peak is recorded (ie, the current time). ).
  • the estimating unit 41 is further configured to: according to the nominal delay of each pulse of the ranging code sent by the FM broadcast transmitter and the first pulse thereof and the local clock value, estimate the FM broadcast receiver to receive the location An estimated clock value of the first pulse of the ranging code and a relative frequency difference between the FM broadcast receiver and the FM broadcast transmitter.
  • the FM broadcast receiver A1 generates a local ranging code CL(n) identical to the waveform of the transmitter A0 signal c(t).
  • the CL(n) and D(n) are subjected to a sliding correlation operation.
  • the estimating unit 41 according to the correlation of the ranging codes, when the phases of D(n) and CL(n) are aligned, the correlation result is maximum at this time, that is, a correlation peak is obtained. It is assumed that in any given time period Tsel, the sliding correlation operation obtains M correlation peaks, and the mth correlation peak is the correlation peak corresponding to the mth ranging code in this period, assuming the mth correlation peak The corresponding local clock value is ⁇ m . Take the maximum correlation peak where M is multiplied by rate (a given percentage) to perform the following estimation operation:
  • the local clock value corresponding to the mth correlation peak is ⁇ m , that is, the mth observation equation can be expressed as:
  • k is the frequency difference coefficient of the transmit and receive clocks to be sought
  • ⁇ is the optimal estimate of the arrival of the pulse corresponding to the first correlation peak to be sought
  • ⁇ m is the mth pulse arrival time measurement noise
  • ⁇ is the arrival time of the obtained ranging code
  • the frequency difference coefficient k is a relative frequency difference from the self-clocked broadcast transmitter A0. It should be explained that the technique of obtaining ⁇ m is a mature technology in communication, and generally takes the sampling point with the largest correlation peak and the adjacent sampling point with a leading lag (a total of three sampling points) for calculation.
  • the bandwidth generally reaches 2Mhz or more, and the ranging code is continuous, and the code phase resolution can reach the sub-meter code phase resolution, and in the present invention
  • the medium ranging code is not continuous, and the data block is stored between adjacent ranging codes.
  • the bandwidth of the D(t) signal is only a few hundred KHz (narrow bandwidth), and is usually sampled by a sampling clock of 1 Msps. The resolution is only 1us, and the synchronization error is obviously too large.
  • the estimation unit 41 comprehensively uses a plurality of correlation peaks to estimate the optimal estimate ⁇ of the arrival of the pulse corresponding to the first correlation peak to the local time, and the transmitter A0 and the receiver A1 (this Taking the receiver A1 as an example) the frequency difference coefficient k of the clock, thereby adjusting the local clock time and frequency of the receiver A1 to synchronize with the transmitter A0, in the case of a relatively low frequency sampling clock and narrowband signal. High-accuracy time synchronization is achieved.
  • Figure 6 shows the optimal estimate ⁇ mean square error using 48 pulses with pulse rate rates of 0.6, 0.8, and 1, respectively.
  • the accuracy of the measured synchronization can usually be Up to the order of 10 nanoseconds, wherein the abscissa Eb/N0 in FIG. 6 is the ratio of the energy per bit of data of the received radio signal to the noise power density, which is a general expression in the art indicating the quality of the received radio signal.
  • Method; the ordinate RMSE of Fig. 6 is the root mean square error between the estimated value and the true value of ⁇ , in nanoseconds, which is a general method in the art for expressing the quality of the estimate.
  • the time difference calculation unit 42 is further configured to:
  • the propagation time T prop
  • the time difference calculation unit 42 calculates the propagation time of the signal between the transmitter and the receiver based on the local location information of the receiver and the remote location information of the transmitter, and then according to the remote time of the transmitter.
  • the information, the estimated time information of the receiver and the transmission time calculate the time difference between the receiver clock and the transmitter clock, and obtain the time difference between the receiver clock and the transmitter clock in a simple calculation manner.
  • the synchronization unit 43 is further configured to:
  • the FM broadcast receiver usually uses a digital second counter to maintain the local time on the digital circuit.
  • the digital circuit has an operating clock whose frequency fluctuates, but the frequency nominal value (unit: MHz) is known. , set the frequency nominal value to Fdef.
  • the receiver A1 is started by default, if the digital seconds timer of the receiver A1 increases the Fdef, the time exceeds one second, that is, the second overflows once.
  • T E time difference between the transmitter A0 and the receiver A1
  • the value of the second counter is correspondingly reduced by ⁇ T E *Fdef ⁇ (requires rounding or negative).
  • the FM broadcast receiver A1 should adjust the second overflow mechanism to become when the digital second counter reaches the frequency nominal
  • the value is increased by Fdef/(1+K) (requires rounding) and the time is considered to be one second.

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Abstract

本发明公开了一种基于数字调频广播的时钟同步方法，该方法包括：调频广播接收机接收与标准时间同步的调频广播发射机所广播的无线数据广播信号；调频广播接收机解调出无线数据广播信号中时间同步信号；调频广播接收机获取其接收到时间同步信号的本地时间信息；调频广播接收机根据自身的本地位置信息、时间同步信号和本地时间信息，同步该调频广播接收机本地时钟的时刻和频率。本发明还公开一种调频广播接收机。本发明通过FM调频广播实现伪卫星系统或类似伪卫星系统中时钟的同步，即通过调频广播发射机将标准时间通过FM频段的数据广播发送至对应的调频广播接收机，解决了伪卫星系统或类似伪卫星系统的时钟同步过于依赖卫星导航的技术问题。

Description

基于数字调频广播的时钟同步方法和调频广播接收机 技术领域
本发明涉及无线导航技术领域，尤其涉及一种基于数字调频广播的时钟同步方法和调频广播接收机。
背景技术
随着人类社会对卫星导航的日益依赖，现有全球卫星导航系统(北斗、全球定位系统(Global Positioning System，GPS)等，统称为全球卫星导航系统(Global Navigation Satellite System，GNSS))信号弱的缺点日益突出：在低层楼宇、丛林和峡谷环境下难以定位；城市高层楼宇内基本无法定位；以隐私保护为名义干扰无线电导航的事件越来越多，进一步降低了导航系统的日常可用性；在战争和对抗环境下，无线电导航对抗措施越来越成熟。故此，GNSS的可用性日益遭到质疑。
在这个背景下，世界上主要国家都已着手开展寻找GNSS增强和备份方案的工作，基本出发点都在于寻找和利用GNSS以外的更多导航源，达到增强或者备份现有GNSS的目的。其中，对卫星导航进行备份的应用最为广泛的是地面伪卫星技术。伪卫星(Pseudo-Satellite或Pseudolite，缩写为PL)，是布设于地面上发射某种定位信号的发射器，通常都是发射类似于GPS的信号。理论上，在任何威胁信号无效的地方，伪卫星都可以取代卫星进行导航定位，例如可以室内、地下停车场和隧道等场景进行导航。
但是，伪卫星系统或类似伪卫星系统面临的基本问题是需要不停地进行多个伪卫星节点之间的时钟同步。与GPS不同，伪卫星通常装备的是温度补偿晶振时钟，精度不高，会产生时钟漂移，在采样时间里与参考站的标准时间信号不能精确同步。但在定位模型中，系统中的所有的伪卫星必须要保持同步。现有技术中，一般通过导航卫星来现实伪卫星的时钟同步，但是，如果伪卫星的时钟同步依赖于卫星导航，当卫星导航失效时，伪卫星的时钟精度无法到达导航要求而导致伪卫星失效，导致伪卫星系统的时钟过同步于依赖卫星导航。
发明内容
本发明的主要目的在于提供一种基于数字调频广播的时钟同步方法和调频广播接收机，旨在解决伪卫星系统或类似伪卫星系统的时钟同步过于依赖卫星导航的技术问题。
为实现上述目的，本发明提供的一种基于数字调频广播的时钟同步方法，所述基于数字调频广播的时钟同步方法包括：
调频广播接收机接收与标准时间同步的调频广播发射机所广播的无线数据广播信号；
所述调频广播接收机解调出所述无线数据广播信号中时间同步信号；
所述调频广播接收机获取其接收到所述时间同步信号的本地时间信息；
所述调频广播接收机根据自身的本地位置信息、所述时间同步信号和本地时间信息，同步该调频广播接收机本地时钟的时刻和频率。
优选地，所述时间同步信号包括测距码、所述调频广播发射机广播所述测距码的远端时间信息和所述调频广播发射机的远端位置信息，
所述调频广播接收机根据所述时间同步信号、本地时间信息和本地位置信息，同步该调频广播接收机本地时钟的时刻和频率的步骤包括：
调频广播接收机根据所述本地时间信息，估算该调频广播接收机接收到所述测距码的估算时间信息以及所述调频广播接收机与调频广播发射机之间的相对频差；
调频广播接收机根据所述远端位置信息、本地位置信息、远端时间信息和估算时间信息，计算得出所述调频广播接收机时钟与调频广播发射机时钟之间的时间差；
调频广播接收机根据所述时间差和相对频差，同步该调频广播接收机本地时钟的时刻和频率。
优选地，所述调频广播接收机获取其接收到所述时间同步信号的本地时间信息的步骤包括；
所述调频广播接收机生成与所述调频广播发射机所发送的测距码的脉冲信号波形相同的本地测距码；
所述调频广播接收机获取所述本地测距码的脉冲波形与所述调频广播发射机所发送的测距码的脉冲波形相位对齐时的本地时钟值；
所述调频广播接收机根据所述本地时间信息，估算该调频广播接收机接收到所述测距码的估算时间信息以及所述调频广播接收机与调频广播发射机之间的相对频差的步骤包括：
所述调频广播接收机根据所述调频广播发射机所发送的测距码的各个脉冲与第其一个脉冲的标称延迟和所述本地时钟值，估算该调频广播接收机接收到所述测距码的第一个脉冲的估算时钟值以及所述调频广播接收机与调频广播发射机之间的相对频差。
优选地，所述调频广播接收机根据所述远端位置信息、本地位置信息、远端时间信息和估算时间信息，计算得出所述调频广播接收机时钟与调频广播发射机时钟之间的时间差的步骤包括：
所述调频广播接收机根据所述远端位置信息和本地位置信息，计算得出信号自所述调频广播发射机到调频广播接收机的传播时间；
所述调频广播接收机根据所述远端时间信息、估计时间信息和传输时间，计算得出所述调频广播接收机时钟与调频广播发射机时钟之间的时间差。
优选地，所述调频广播接收机根据所述时间差和相对频差，调整自身时钟的时刻和频率的步骤包括：
优选地，所述调频广播接收机根据所述时间差和相对频差，调整自身时钟的时刻和频率的步骤包括：
所述调频广播接收机根据所述相对频差和所述调频广播接收机的频率标称值，调整所述调频广播接收机时钟的频率；
所述调频广播接收机根据所述时间差和所述调频广播接收机的频率标称值，调整所述调频广播接收机时钟的时刻。
此外，为实现上述目的，本发明还提供一种调频广播接收机，其特征在于，所述调频广播接收机包括：
信号接收模块，用于接收与标准时间同步的调频广播发射机所广播的无线数据广播信号；
解调模块，用于解调出所述无线数据广播信号中时间同步信号；
本地时间获取模块，用于获取所述调频广播接收机接收到所述时间同步信号的本地时间信息；
同步模块，用于根据自身的本地位置信息、所述时间同步信号和本地时间信息，同步该调频广播接收机本地时钟的时刻和频率。
优选地，所述时间同步信号包括测距码、所述调频广播发射机广播所述测距码的远端时间信息和所述调频广播发射机的远端位置信息，
所述同步模块包括：
估算单元，用于根据所述本地时间信息，估算该调频广播接收机接收到所述测距码的估算时间信息以及所述调频广播接收机与调频广播发射机之间的相对频差；
时间差计算单元，用于根据所述远端位置信息、本地位置信息、远端时间信息和估算时间信息，计算得出所述调频广播接收机时钟与调频广播发射机时钟之间的时间差；
同步单元，用于根据所述时间差和相对频差，同步该调频广播接收机本地时钟的时刻和频率。
优选地，所述本地时间获取模块包括；
脉冲生成单元，用于生成与所述调频广播发射机所发送的测距码的脉冲信号波形相同的本地测距码；
时钟值获取单元，用于获取所述本地测距码的脉冲波形与所述调频广播发射机所发送的测距码的脉冲波形相位对齐时的本地时钟值；
所述估算单元，还用于根据所述调频广播发射机所发送的测距码的各个脉冲与其第一个脉冲的标称延迟和所述本地时钟值，估算该调频广播接收机接收到所述测距码的第一个脉冲的估算时钟值以及所述调频广播接收机与调频广播发射机之间的相对频差。
优选地，所述时间差计算单元还用于：
根据所述远端位置信息和本地位置信息，计算得出信号自所述调频广播发射机到调频广播接收机的传播时间；
根据所述远端时间信息、估计时间信息和传输时间，计算得出所述调频广播接收机时钟与调频广播发射机时钟之间的时间差。
优选地，所述同步单元还用于：
根据所述相对频差和所述调频广播接收机的频率标称值，调整所述调频广播接收机时钟的频率；
根据所述时间差和所述调频广播接收机的频率标称值，调整所述调频广播接收机时钟的时刻。
本发明通过调频广播接收机接收与标准时间同步的调频广播发射机广播的信号中的无线数据广播信号，然后提取无线数据广播信号中的时间同步信号以及获取该调频广播接收机的本地时间信息和本地位置信息，最后根据本地位置信息、时间同步信号和本地时间信息，同步该调频广播接收机本地时钟的时刻和频率，从而将无线数据广播信号寄生在传统的FM调频信号的空置资源中，由于FM频段的数据广播具有传播距离远、绕射和传输能力强的特点，从而本发明通过FM调频广播实现伪卫星系统或类似伪卫星系统中时钟的同步，即通过调频广播发射机将标准时间通过FM频段的数据广播发送至对应的调频广播接收机以完成接收机时钟的同步，解决了伪卫星系统或类似伪卫星系统的时钟同步过于依赖卫星导航的技术问题。
附图说明
图1为本发明基于数字调频广播的时钟同步方法对应系统的一个实施例的结构示意图；
图2为本发明基于数字调频广播的时钟同步方法第一实施例的流程示意图；
图3为调频信号与寄生数字信号的带内频谱关系图；
图4为调频信号与寄生数字信号的带外频谱关系图；
图5为本发明基于数字调频广播的时钟同步方法中调频数据广播信号D(t)的信号格式；
图6为根据本发明基于数字调频广播的时钟同步方法中测量脉冲到达时间方法的性能示意图；
图7为本发明调频广播接收机第一实施例的功能模块示意图。
本发明目的的实现、功能特点及优点将结合实施例，参照附图做进一步说明。
具体实施方式
应当理解，此处所描述的具体实施例仅仅用以解释本发明，并不用于限定本发明。
为了更好的理解本发明基于数字调频广播的时钟同步方法，如图1所示，运用本发明基于数字调频广播的时钟同步方法的模型包括至少一个调频广播发射机A0和多个调频广播接收机(例如三个，A1、A2、A3)，调频广播接收机的时钟同步流程相似，为方便叙述，以下各实施例以调频广播接收机A1为例。
本发明提供一种基于数字调频广播的时钟同步方法，在本发明基于数字调频广播的时钟同步方法的第一实施例中，参照图2，基于数字调频广播的时钟同步方法包括：
步骤S10，调频广播接收机接收与标准时间同步的调频广播发射机所广播的无线数据广播信号；
调频广播发射机A0将自己的时间同步到标准时间。一般来讲，最常用的标准时间是世界协调时，同步的方法是利用一个授时型全球导航卫星接收机接收全球导航卫星系统的信号，利用授时型全球导航卫星将调频广播发射机A0的时间同步到标准时间。当全球导航卫星系统不可用时，调频广播发射机A0可以依赖于自身时钟进行工作，此时，调频广播发射机A0的时间与标准时间会存在误差，但只要误差处于可允许的范围，仍然可视为“处于同步状态”。不同应用对可允许的范围的要求不同。伪卫星系统来讲，通常系统调频广播发射机A0的时间与世界协调时误差不超过1秒。
调频广播发射机A0(以下简称发射机A0)除广播传统调频信号FM(t)外，还同时广播一种寄生于调频广播的无线数据广播信号D(t)，该信号带有测距码、发射机A0广播测距码的远端时间信息和发射机A0的远端位置信息。因此发射机A0发射的信号可以表示为RF(t)＝FM(t)+D(t)，其中RF(t)为发射机A0发射的全部信号。例如现有技术中，将模拟声音广播信号和数字声音广播信号合成为一路模拟数字混合信号，共用一个模拟声音广播频道，混合调制信号放大后，经天馈系统发射，得到预定频谱模式的射频信号。在同一频段内模拟声音广播信号和数字声音广播信号叠加、同时传送。
D(t)信号的频谱设计以不显著影响一般收音机的对现有调频广播的接收音质为出发点。图3给出了全频带频谱形式，也称作带内形式，可以看到D(t) 的频谱B2与FM(t)的频谱B1存在交叠。图4给出了一种非全频带频谱形式，也称作带外形式，可以看到D(t)的频谱B2与FM(t)的频谱B1不存在交叠。这两种形式各有优缺点，在实际系统中均可见。美国HDRadio采用了图4所示的带外形式，而中国的CDRadio则采用了如图3的带内形式。
一般地，D(t)信号实际能够实现几十Kbps的数据通信功能。根据本发明的D(t)的信号格式如图5所示。根据本发明，我们在D(t)信号中周期的放置测距码，相邻测距码之间为数据块儿。数据块的调制方式通常为正交频分复用(OFDM)信号。具体地，D(t)可以在时间t＝[T0+nTp，T0+nTp+Tpn]时间内发送测距码c(t-nT)，其中T0为第一个测距码的起始时刻，Tp为相邻测距码出现的周期，Tpn为测距码持续时长。测距码可以是伪随机码、Gold码等，且在本发明中，测距码不是连续的，而是在相邻的测距码之间存储数据块。
步骤S20，所述调频广播接收机解调出所述无线数据广播信号中时间同步信号；
调频广播接收机A1将D(t)从RF(t)中解调出来。如果D(t)的频谱与调频信号FM(t)不重叠，则采用滤波方法就可以分开。否则D(t)的频谱与调频信号FM(t)存在重叠，则需要使用带内分离方法，如专利CN201510011206一种带内同频数模音频广播信号的分离方法就公开了一种具体的分离方法。然后调频广播接收机A1对分离后的D(t)去除载波，并进行数字化采样得到D(n)。在数字通信中，去除载波是常规技术。
步骤S30，所述调频广播接收机获取其接收到所述时间同步信号的本地时间信息；
调频广播接收机A1在接收到发射机A0发送的时间同步信号时，记录当时调频广播接收机A1的本地时间信息。接收机A1在本端生成与发射机A0所发送的测距码的脉冲信号波形相同的本地测距码，并且接收机A1获取本地测距码的脉冲波形与发射机所发送的测距码的脉冲波形相位对齐时的本地时钟值(即本地时间信息，此本地时钟值为多个)。
步骤S40，所述调频广播接收机根据自身的本地位置信息、所述时间同步信号和本地时间信息，同步该调频广播接收机本地时钟的时刻和频率。
时间同步信号包括测距码、所述调频广播发射机广播所述测距码的远端时间信息和所述调频广播发射机的远端位置信息，
步骤S40包括：
步骤S41，调频广播接收机根据所述本地时间信息，估算该调频广播接收机接收到所述测距码的估算时间信息以及所述调频广播接收机与调频广播发射机之间的相对频差；
所述调频广播接收机根据所述调频广播发射机所发送的测距码的各个脉冲与第其一个脉冲的标称延迟和所述本地时钟值，估算该调频广播接收机接收到所述测距码的第一个脉冲的估算时钟值以及所述调频广播接收机与调频广播发射机之间的相对频差。
调频广播接收机A1生成与发射机A0信号c(t)波形相同的本地测距码CL(n)。将CL(n)与D(n)进行滑动相关运算。根据测距码的相关性，当D(n)和CL(n)相位对齐时，此时相关结果最大，即得到一个相关峰。假设在任一给定时间段Tsel内，所述滑动相关运算获得了M个相关峰，第m个相关峰是这一时间段内第m测距码所对应的相关峰，假设第m个相关峰对应的本地时钟值为λm。取其中M乘以rate(一个给定的百分比)个最大的相关峰进行下述估值运算：
待估计的值为：
(1)第一个相关峰对应的脉冲的起始到达本地时刻的最优估值θ；
(2)发射机A0和接收机A1(此处以接收机A1为例)时钟的频差系数k。
已知：
任意第m个脉冲相对于第1个脉冲的标称延迟为tm(t1＝0)，有
T＝[t1，t2，...tm.....，tM]T
其中[]T表示矩阵转置。
现有观测值：
M个脉冲到达时间(本地时钟值)Ф＝[λ1，λ2，λ3，..λm....，λM]T，假设各脉冲到达时间测量噪声为ζ＝[υ1，υ2，υ3，..υm...，υM]T。
观测方程：
第m个相关峰对应的本地时钟值为λm，即第m观测方程可表示为：
λm＝(k+1)tm+θ+υm
或
λm-tm＝ktm+θ+υm
其中k是待求的发射和接收时钟的频差系数；θ是待求的第一个相关峰对应的脉冲的起始到达本地时刻的最优估值，υm是第m个脉冲到达时间测量 噪声
矩阵表示：上述观测方程可以表示矩阵形式。
令X＝[k，θ]T
则上述问题可表述为：
Ф-T＝Γ*X+ζ
其中
Figure PCTCN2016085079-appb-000001
即
Figure PCTCN2016085079-appb-000002
用最小二乘求解，有：
X＝(ΓTΓ)-1ΓT(Ф-T)
X＝[k，θ]T中的最优估值θ和频差系数k即为所求值。其中，θ为所求测距码到达时刻，频差系数k为与自身时钟调频广播发射机A0的相对频差。
需要解释的是，获取λm的技术在通信中是成熟技术，一般取相关峰最大的那个采样点以及超前滞后的相邻采样点(一共三个采样点)进行计算。
步骤S42，调频广播接收机根据所述远端位置信息、本地位置信息、远端时间信息和估算时间信息，计算得出所述调频广播接收机时钟与调频广播发射机时钟之间的时间差；
接收机A1根据其本地位置信息和发射机A0的远端位置信息，得出接收机A1与发射机A0之间的距离S，且调频广播信号在空气中传输速度接近光速，从而求得信号自发射机A0到接收机A1的传播时间；从而接收机根据远端时间信息、估计时间信息(即上述测距码到达时刻θ)和传输时间，计算得出接收机A1与发射机A0时钟之间的时间差。
步骤S43，调频广播接收机根据所述时间差和相对频差，同步该调频广播接收机本地时钟的时刻和频率。
接收机A1通常在数字电路上用数字秒计数器维护本地时间，该数字电路有一个工作时钟，该工作时钟的频率存在波动，但是频率标称值是已知的(频 率标称值设为Fdef)，接收机A1默认启动时，接收机A1认为当数字秒计数器每增加Fdef时认为时间过了一秒，即秒溢出一次。当检测到接收机A1与发射机A0存在时间差时，将秒计时器的值(即接收机A1的时刻)相应的减少时间差乘以频率标称值；当检测到相对频差(即频差系数k)时，将该数字电路的工作时钟实际频率调整为Fdef/(1+K)。
在本实施例中，调频广播接收机接收与标准时间同步的调频广播发射机广播的信号中的无线数据广播信号，然后提取无线数据广播信号中的时间同步信号以及获取该调频广播接收机的本地时间信息和本地位置信息，最后根据本地位置信息、时间同步信号和本地时间信息，同步该调频广播接收机本地时钟的时刻和频率，从而将无线数据广播信号寄生在传统的FM调频信号的空置资源中，由于FM频段的数据广播具有传播距离远、绕射和传输能力强的特点，从而本发明通过FM调频广播实现伪卫星系统或类似伪卫星系统中时钟的同步，即通过调频广播发射机将标准时间通过FM频段的数据广播发送至对应的调频广播接收机以完成接收机时钟的同步，解决了伪卫星系统或类似伪卫星系统的时钟同步过于依赖卫星导航的技术问题。
进一步地，在本发明基于数字调频广播的时钟同步方法第一实施例的基础上，提出基于数字调频广播的时钟同步方法的第二实施例，在第二实施例中，步骤S30包括：
步骤S31，所述调频广播接收机生成与所述调频广播发射机所发送的测距码的脉冲信号波形相同的本地测距码；
步骤S32，所述调频广播接收机获取所述本地测距码的脉冲波形与所述调频广播发射机所发送的测距码的脉冲波形相位对齐时的本地时钟值；
调频广播接收机A1生成与发射机A0信号c(t)波形相同的本地测距码CL(n)。将CL(n)与D(n)进行滑动相关运算。根据测距码的相关性，当D(n)和CL(n)相位对齐时，此时相关结果最大，即得到一个相关峰，记录每个相关峰产生时的本地时钟值(即当前的时刻)。
步骤S41包括：
步骤S411，所述调频广播接收机根据所述调频广播发射机所发送的测距码的各个脉冲与第其一个脉冲的标称延迟和所述本地时钟值，估算该调频广 播接收机接收到所述测距码的第一个脉冲的估算时钟值以及所述调频广播接收机与调频广播发射机之间的相对频差。
调频广播接收机A1生成与发射机A0信号c(t)波形相同的本地测距码CL(n)。将CL(n)与D(n)进行滑动相关运算。根据测距码的相关性，当D(n)和CL(n)相位对齐时，此时相关结果最大，即得到一个相关峰。假设在任一给定时间段Tsel内，所述滑动相关运算获得了M个相关峰，第m个相关峰是这一时间段内第m测距码所对应的相关峰，假设第m个相关峰对应的本地时钟值为λm。取其中M乘以rate(一个给定的百分比)个最大的相关峰进行下述估值运算：
待估计的值为：
(1)第一个相关峰对应的脉冲的起始到达本地时刻的最优估值θ；
(2)发射机A0和接收机A1(此处以接收机A1为例)时钟的频差系数k。
已知：
任意第m个脉冲相对于第1个脉冲的标称延迟为tm(t1＝0)，有
T＝[t1，t2，...tm.....，tM]T
其中[]T表示矩阵转置。
现有观测值：
M个脉冲到达时间(本地时钟值)Ф＝[λ1，λ2，λ3，..λm....，λM]T，假设各脉冲到达时间测量噪声为ζ＝[υ1，υ2，υ3，..υm...，υM]T。
观测方程：
第m个相关峰对应的本地时钟值为λm，即第m观测方程可表示为：
λm＝(k+1)tm+θ+υm
或
λm-tm＝ktm+θ+υm
其中k是待求的发射和接收时钟的频差系数；θ是待求的第一个相关峰对应的脉冲的起始到达本地时刻的最优估值，υm是第m个脉冲到达时间测量噪声
矩阵表示：上述观测方程可以表示矩阵形式。
令X＝[k，θ]T
则上述问题可表述为：
Ф-T＝Γ*X+ζ
其中
Figure PCTCN2016085079-appb-000003
即
Figure PCTCN2016085079-appb-000004
用最小二乘求解，有：
X＝(ΓTΓ)-1ΓT(Ф-T)
X＝[k，θ]T中的最优估值θ和频差系数k即为所求值。其中，θ为所求测距码到达时刻，频差系数k为与自身时钟调频广播发射机A0的相对频差。需要解释的是，获取λm的技术在通信中是成熟技术，一般取相关峰最大的那个采样点以及超前滞后的相邻采样点(一共三个采样点)进行计算。
已有的导航技术中(例如GPS导航、北斗导航等)，带宽一般达到2Mhz以上，且测距码是连续的，通过码相位跟踪就可以达到亚米级的码相位分辨率，而在本发明中测距码不是连续的，相邻的测距码之间存储有数据块，D(t)信号的带宽只有几百KHz(带宽窄)，通常采用1Msps的采样时钟去采样，此时时钟的分辨率只有1us，这样的同步误差显然太大了。
在第二实施例中，通过综合使用多个相关峰估算出第一个相关峰对应的脉冲的起始到达本地时刻的最优估值θ，以及发射机A0和接收机A1(此处以接收机A1为例)时钟的频差系数k，从而对接收机A1的本地时钟时刻和频率进行调整，以与发射机A0同步，实现了在频率比较低的采样时钟和窄带信号的情况下取得了高精度的时间同步，参照图6，图6给出了使用48个脉冲，脉冲使用率rate分别为0.6，0.8，1时最优估值θ均方误差，经测量同步的精度通常可以达到10纳秒量级，其中，图6中的横坐标Eb/N0为接收到的无线电信号的每比特数据的能量与噪声功率密度的比，是本领域中表示接收到的无线电信号质量的通用方法；图6的纵坐标RMSE为θ的估计值与真实值之间的方均根误差，单位为纳秒，是本领域中表示估值质量的通用方法。
在本发明基于数字调频广播的时钟同步方法第二实施例的基础上，提出 基于数字调频广播的时钟同步方法的第三实施例，在第三实施例中，步骤S42包括：
步骤S421，所述调频广播接收机根据所述远端位置信息和本地位置信息，计算得出信号在所述调频广播发射机和调频广播接收机的传播时间；
设发射机A0的远端位置信息为Ptx＝[xtx，ytx，ztx]，接收机A1的本地位置信息为Prx＝[xrx，yrx，zrx]，计算信号自发射机A0到接收机A1的传播时间Tprop＝|Ptx-Prx|/C，其中C为光速。
步骤S422，所述调频广播接收机根据所述远端时间信息、估计时间信息和传输时间，计算得出所述调频广播接收机时钟与调频广播发射机时钟之间的时间差。
远端时间信息包括在预设时间内(如Tsel内)第一个脉冲对应的发射机A0时间为θtx，接收机接收到第一个脉冲对应的本地时间为θrx＝θ，发射机A0与接收机A1时钟的时间差TE＝θtx+Tprop-θrx。
在本实施例中，通过根据接收机的本地位置信息和发射机的远端位置信息计算得出信号在发射机和接收机之间的传播时间，再根据发射机的远端时间信息、接收机的估计时间信息和传输时间，计算得出接收机时钟与发射机时钟之间的时间差，以一种简单的计算方式获得接收机时钟与发射机时钟之间的时间差。
在本发明基于数字调频广播的时钟同步方法第三实施例的基础上，提出基于数字调频广播的时钟同步方法的第四实施例，在第四实施例中，
步骤43包括：
步骤S431，所述调频广播接收机根据所述相对频差和所述调频广播接收机的频率标称值，调整所述调频广播接收机时钟的频率；
步骤S432，所述调频广播接收机根据所述时间差和所述调频广播接收机的频率标称值，调整所述调频广播接收机时钟的时刻。
在本实施例中，调频广播接收机通常在数字电路上用数字秒计数器来维护本地时间，该数字电路有一个工作时钟，其频率存在波动，但是频率标称值(单位：MHz)是已知的，设定该频率标称值为Fdef。接收机A1默认启动时，若接收机A1的数字秒计时器每增加Fdef则时间过了一秒，即秒溢出一次。当检测到发射机A0与接收机A1存在时间差TE时，则将秒计数器的值相应的 减少{TE*Fdef}(需要四舍五入，也可能是负值)。当检测到频差系数k时，说明该数字电路的一个工作时钟实际频率为Fdef/(1+k)，因此调频广播接收机A1应调整秒溢出机制，变为当数字秒计数器达到频率标称值增加了Fdef/(1+K)(需要四舍五入)时认为时间过了一秒。
本发明提供一种调频广播接收机，在本发明调频广播接收机的第一实施例中，参照图7，调频广播接收机包括：
信号接收模块10，用于接收与标准时间同步的调频广播发射机所广播的无线数据广播信号；
调频广播发射机A0将自己的时间同步到标准时间。一般来讲，最常用的标准时间是世界协调时，同步的方法是利用一个授时型全球导航卫星接收机接收全球导航卫星系统的信号，利用授时型全球导航卫星将调频广播发射机A0的时间同步到标准时间。当全球导航卫星系统不可用时，调频广播发射机A0可以依赖于自身时钟进行工作，此时，调频广播发射机A0的时间与标准时间会存在误差，但只要误差处于可允许的范围，仍然可视为“处于同步状态”。不同应用对可允许的范围的要求不同。伪卫星系统来讲，通常系统调频广播发射机A0的时间与世界协调时误差不超过1秒。
调频广播发射机A0(以下简称发射机A0)除广播传统调频信号FM(t)外，还同时广播一种寄生于调频广播的无线数据广播信号D(t)，该信号带有测距码、发射机A0广播测距码的远端时间信息和发射机A0的远端位置信息。因此发射机A0发射的信号可以表示为RF(t)＝FM(t)+D(t)，其中RF(t)为发射机A0发射的全部信号。例如现有技术中，将模拟声音广播信号和数字声音广播信号合成为一路模拟数字混合信号，共用一个模拟声音广播频道，混合调制信号放大后，经天馈系统发射，得到预定频谱模式的射频信号。在同一频段内模拟声音广播信号和数字声音广播信号叠加、同时传送。
D(t)信号的频谱设计以不显著影响一般收音机的对现有调频广播的接收音质为出发点。图3给出了全频带频谱形式，也称作带内形式，可以看到D(t)的频谱B2与FM(t)的频谱B1存在交叠。图4给出了一种非全频带频谱形式，也称作带外形式，可以看到D(t)的频谱B2与FM(t)的频谱B1不存在交叠。这两种形式各有优缺点，在实际系统中均可见。美国HDRadio采用了图4所示的带外形式，而中国的CDRadio则采用了如图3的带内形式。
一般地，D(t)信号实际能够实现几十Kbps的数据通信功能。根据本发明的D(t)的信号格式如图5所示。根据本发明，我们在D(t)信号中周期的放置测距码，相邻测距码之间为数据块儿。数据块的调制方式通常为正交频分复用(OFDM)信号。具体地，D(t)可以在时间t＝[T0+nTp，T0+nTp+Tpn]时间内发送测距码c(t-nT)，其中T0为第一个测距码的起始时刻，Tp为相邻测距码出现的周期，Tpn为测距码持续时长。测距码可以是伪随机码、Gold码等，且在本发明中，测距码不是连续的，而是在相邻的测距码之间存储数据块。
解调模块20，用于解调出所述无线数据广播信号中时间同步信号；
调频广播接收机A1的解调模块20将D(t)从RF(t)中解调出来。如果D(t)的频谱与调频信号FM(t)不重叠，则采用滤波方法就可以分开。否则D(t)的频谱与调频信号FM(t)存在重叠，则需要使用带内分离方法，如专利CN201510011206一种带内同频数模音频广播信号的分离方法就公开了一种具体的分离方法。然后调频广播接收机A1的解调模块20对分离后的D(t)去除载波，并进行数字化采样得到D(n)。在数字通信中，去除载波是常规技术。
本地时间获取模块30，用于获取所述调频广播接收机接收到所述时间同步信号的本地时间信息；
调频广播接收机A1的本地时间获取模块30在接收到发射机A0发送的时间同步信号时，记录当时调频广播接收机A1的本地时间信息。接收机A1在本端生成与发射机A0所发送的测距码的脉冲信号波形相同的本地测距码，并且接收机A1获取本地测距码的脉冲波形与发射机所发送的测距码的脉冲波形相位对齐时的本地时钟值(即本地时间信息，此本地时钟值为多个)。
同步模块40，用于根据自身的本地位置信息、所述时间同步信号和本地时间信息，同步该调频广播接收机本地时钟的时刻和频率。
时间同步信号包括测距码、所述调频广播发射机广播所述测距码的远端时间信息和所述调频广播发射机的远端位置信息，
所述同步模块40包括：
估算单元41，用于根据所述本地时间信息，估算该调频广播接收机接收到所述测距码的估算时间信息以及所述调频广播接收机与调频广播发射机之间的相对频差；
所述调频广播接收机根据所述调频广播发射机所发送的测距码的各个脉 冲与第其一个脉冲的标称延迟和所述本地时钟值，估算该调频广播接收机接收到所述测距码的第一个脉冲的估算时钟值以及所述调频广播接收机与调频广播发射机之间的相对频差。
调频广播接收机A1生成与发射机A0信号c(t)波形相同的本地测距码CL(n)。将CL(n)与D(n)进行滑动相关运算。根据测距码的相关性，当D(n)和CL(n)相位对齐时，此时相关结果最大，即得到一个相关峰。假设在任一给定时间段Tsel内，所述滑动相关运算获得了M个相关峰，第m个相关峰是这一时间段内第m测距码所对应的相关峰，假设第m个相关峰对应的本地时钟值为λm。取其中M乘以rate(一个给定的百分比)个最大的相关峰进行下述估值运算：
待估计的值为：
(1)第一个相关峰对应的脉冲的起始到达本地时刻的最优估值θ；
(2)发射机A0和接收机A1(此处以接收机A1为例)时钟的频差系数k。
已知：
任意第m个脉冲相对于第1个脉冲的标称延迟为tm(t1＝0)，有
T＝[t1，t2，...tm.....，tM]T
其中[]T表示矩阵转置。
现有观测值：
M个脉冲到达时间(本地时钟值)Ф＝[λ1，λ2，λ3，..λm....，λM]T，假设各脉冲到达时间测量噪声为ζ＝[υ1，υ2，υ3，..υm...，υM]T。
观测方程：
第m个相关峰对应的本地时钟值为λm，即第m观测方程可表示为：
λm＝(k+1)tm+θ+υm
或
λm-tm＝ktm+θ+υm
其中k是待求的发射和接收时钟的频差系数；θ是待求的第一个相关峰对应的脉冲的起始到达本地时刻的最优估值，υm是第m个脉冲到达时间测量噪声
矩阵表示：上述观测方程可以表示矩阵形式。
令X＝[k，θ]T
则上述问题可表述为：
Ф-T＝Γ*X+ζ
其中
Figure PCTCN2016085079-appb-000005
即
Figure PCTCN2016085079-appb-000006
用最小二乘求解，有：
X＝(ΓTΓ)-1ΓT(Ф-T)
X＝[k，θ]T中的最优估值θ和频差系数k即为所求值。其中，θ为所求测距码到达时刻，频差系数k为与自身时钟调频广播发射机A0的相对频差。
需要解释的是，获取λm的技术在通信中是成熟技术，一般取相关峰最大的那个采样点以及超前滞后的相邻采样点(一共三个采样点)进行计算。
时间差计算单元42，用于根据所述远端位置信息、本地位置信息、远端时间信息和估算时间信息，计算得出所述调频广播接收机时钟与调频广播发射机时钟之间的时间差；
接收机A1的时间差计算单元42根据其本地位置信息和发射机A0的远端位置信息，得出接收机A1与发射机A0之间的距离S，且调频广播信号在空气中传输速度接近光速，从而求得信号自发射机A0到接收机A1的传播时间；从而接收机根据远端时间信息、估计时间信息(即上述测距码到达时刻θ)和传输时间，计算得出接收机A1与发射机A0时钟之间的时间差。
同步单元43，用于根据所述时间差和相对频差，同步该调频广播接收机本地时钟的时刻和频率。
接收机A1的同步单元43通常在数字电路上用数字秒计数器维护本地时间，该数字电路有一个工作时钟，该工作时钟的频率存在波动，但是频率标称值是已知的(频率标称值设为Fdef)，接收机A1默认启动时，接收机A1认为当数字秒计数器每增加Fdef时认为时间过了一秒，即秒溢出一次。当检测到接收机A1与发射机A0存在时间差时，将秒计时器的值(即接收机A1的时刻)相应的减少时间差乘以频率标称值；当检测到相对频差(即频差系 数k)时，将该数字电路的工作时钟实际频率调整为Fdef/(1+K)。
在本实施例中，调频广播接收机的信号接收模块10接收与标准时间同步的调频广播发射机广播的信号中的无线数据广播信号，然后解调模块20提取无线数据广播信号中的时间同步信号以及本地时间获取模块30获取该调频广播接收机的本地时间信息和本地位置信息，最后同步模块40根据本地位置信息、时间同步信号和本地时间信息，同步该调频广播接收机本地时钟的时刻和频率，从而将无线数据广播信号寄生在传统的FM调频信号的空置资源中，由于FM频段的数据广播具有传播距离远、绕射和传输能力强的特点，从而本发明通过FM调频广播实现伪卫星系统或类似伪卫星系统中时钟的同步，即通过调频广播发射机将标准时间通过FM频段的数据广播发送至对应的调频广播接收机以完成接收机时钟的同步，解决了伪卫星系统或类似伪卫星系统的时钟同步过于依赖卫星导航的技术问题。
进一步地，在本发明调频广播接收机第一实施例的基础上，提出调频广播接收机的第二实施例，在第二实施例中，所述本地时间获取模块30包括；
脉冲生成单元31，用于生成与所述调频广播发射机所发送的测距码的脉冲信号波形相同的本地测距码；
时钟值获取单元32，用于获取所述本地测距码的脉冲波形与所述调频广播发射机所发送的测距码的脉冲波形相位对齐时的本地时钟值；
调频广播接收机A1的脉冲生成单元31生成与发射机A0信号c(t)波形相同的本地测距码CL(n)。时钟值获取单元32将CL(n)与D(n)进行滑动相关运算。根据测距码的相关性，当D(n)和CL(n)相位对齐时，此时相关结果最大，即得到一个相关峰，记录每个相关峰产生时的本地时钟值(即当前的时刻)。
所述估算单元41，还用于根据所述调频广播发射机所发送的测距码的各个脉冲与其第一个脉冲的标称延迟和所述本地时钟值，估算该调频广播接收机接收到所述测距码的第一个脉冲的估算时钟值以及所述调频广播接收机与调频广播发射机之间的相对频差。
调频广播接收机A1生成与发射机A0信号c(t)波形相同的本地测距码CL(n)。将CL(n)与D(n)进行滑动相关运算。估算单元41根据测距码的相关性， 当D(n)和CL(n)相位对齐时，此时相关结果最大，即得到一个相关峰。假设在任一给定时间段Tsel内，所述滑动相关运算获得了M个相关峰，第m个相关峰是这一时间段内第m测距码所对应的相关峰，假设第m个相关峰对应的本地时钟值为λm。取其中M乘以rate(一个给定的百分比)个最大的相关峰进行下述估值运算：
待估计的值为：
(1)第一个相关峰对应的脉冲的起始到达本地时刻的最优估值θ；
(2)发射机A0和接收机A1(此处以接收机A1为例)时钟的频差系数k。
已知：
任意第m个脉冲相对于第1个脉冲的标称延迟为tm(t1＝0)，有
T＝[t1，t2，...tm.....，tM]T
其中[]T表示矩阵转置。
现有观测值：
M个脉冲到达时间(本地时钟值)Ф＝[λ1，λ2，λ3，..λm....，λM]T，假设各脉冲到达时间测量噪声为ζ＝[υ1，υ2，υ3，..υm...，υM]T。
观测方程：
第m个相关峰对应的本地时钟值为λm，即第m观测方程可表示为：
λm＝(k+1)tm+θ+υm
或
λm-tm＝ktm+θ+υm
其中k是待求的发射和接收时钟的频差系数；θ是待求的第一个相关峰对应的脉冲的起始到达本地时刻的最优估值，υm是第m个脉冲到达时间测量噪声
矩阵表示：上述观测方程可以表示矩阵形式。
令X＝[k，θ]T
则上述问题可表述为：
Ф-T＝Γ*X+ζ
其中
Figure PCTCN2016085079-appb-000007
即
Figure PCTCN2016085079-appb-000008
用最小二乘求解，有：
X＝(ΓTΓ)-1ΓT(Ф-T)
X＝[k，θ]T中的最优估值θ和频差系数k即为所求值。其中，θ为所求测距码到达时刻，频差系数k为与自身时钟调频广播发射机A0的相对频差。需要解释的是，获取λm的技术在通信中是成熟技术，一般取相关峰最大的那个采样点以及超前滞后的相邻采样点(一共三个采样点)进行计算。
已有的导航技术中(例如GPS导航、北斗导航等)，带宽一般达到2Mhz以上，且测距码是连续的，通过码相位跟踪就可以达到亚米级的码相位分辨率，而在本发明中测距码不是连续的，相邻的测距码之间存储有数据块，D(t)信号的带宽只有几百KHz(带宽窄)，通常采用1Msps的采样时钟去采样，此时时钟的分辨率只有1us，这样的同步误差显然太大了。
在第二实施例中，通过估算单元41综合使用多个相关峰估算出第一个相关峰对应的脉冲的起始到达本地时刻的最优估值θ，以及发射机A0和接收机A1(此处以接收机A1为例)时钟的频差系数k，从而对接收机A1的本地时钟时刻和频率进行调整，以与发射机A0同步，实现了在频率比较低的采样时钟和窄带信号的情况下取得了高精度的时间同步，参照图6，图6给出了使用48个脉冲，脉冲使用率rate分别为0.6，0.8，1时最优估值θ均方误差，经测量同步的精度通常可以达到10纳秒量级，其中，图6中的横坐标Eb/N0为接收到的无线电信号的每比特数据的能量与噪声功率密度的比，是本领域中表示接收到的无线电信号质量的通用方法；图6的纵坐标RMSE为θ的估计值与真实值之间的方均根误差，单位为纳秒，是本领域中表示估值质量的通用方法。
进一步地，在本发明调频广播接收机第二施例的基础上，提出调频广播接收机的第三实施例，在第三实施例中，所述时间差计算单元42还用于：
根据所述远端位置信息和本地位置信息，计算得出信号自所述调频广播发射机到调频广播接收机的传播时间；
设发射机A0的远端位置信息为Ptx＝[xtx，ytx，ztx]，接收机A1的本地位置信息为Prx＝[xrx，yrx，zrx]，时间差计算单元42计算信号自发射机A0到接收机A1的传播时间Tprop＝|Ptx-Prx|/C，其中C为光速。
根据所述远端时间信息、估计时间信息和传输时间，计算得出所述调频广播接收机时钟与调频广播发射机时钟之间的时间差。
远端时间信息包括在预设时间内(如Tsel内)第一个脉冲对应的发射机A0时间为θtx，接收机接收到第一个脉冲对应的本地时间为θrx＝θ，发射机A0与接收机A1时钟的时间差TE＝θtx+Tprop-θrx。
在本实施例中，通过时间差计算单元42根据接收机的本地位置信息和发射机的远端位置信息计算得出信号在发射机和接收机之间的传播时间，再根据发射机的远端时间信息、接收机的估计时间信息和传输时间，计算得出接收机时钟与发射机时钟之间的时间差，以一种简单的计算方式获得接收机时钟与发射机时钟之间的时间差。
进一步地，在本发明调频广播接收机第三施例的基础上，提出调频广播接收机的第四实施例，在第四实施例中，所述同步单元43还用于：
根据所述相对频差和所述调频广播接收机的频率标称值，调整所述调频广播接收机时钟的频率；
根据所述时间差和所述调频广播接收机的频率标称值，调整所述调频广播接收机时钟的时刻。
在本实施例中，调频广播接收机通常在数字电路上用数字秒计数器来维护本地时间，该数字电路有一个工作时钟，其频率存在波动，但是频率标称值(单位：MHz)是已知的，设定该频率标称值为Fdef。接收机A1默认启动时，若接收机A1的数字秒计时器每增加Fdef则时间过了一秒，即秒溢出一次。当检测到发射机A0与接收机A1存在时间差TE时，则将秒计数器的值相应的减少{TE*Fdef}(需要四舍五入，也可能是负值)。当检测到频差系数k时，说明该数字电路的一个工作时钟实际频率为Fdef/(1+k)，因此调频广播接收机A1应调整秒溢出机制，变为当数字秒计数器达到频率标称值增加了Fdef/(1+K)(需要四舍五入)时认为时间过了一秒。
以上仅为本发明的优选实施例，并非因此限制本发明的专利范围，凡是利用本发明说明书及附图内容所作的等效结构或等效流程变换，或直接或间接运用在其他相关的技术领域，均同理包括在本发明的专利保护范围内。

Claims (16)

  1. 一种基于数字调频广播的时钟同步方法，其特征在于，所述基于数字调频广播的时钟同步方法包括：
    调频广播接收机接收与标准时间同步的调频广播发射机所广播的无线数据广播信号；
    所述调频广播接收机解调出所述无线数据广播信号中时间同步信号；
    所述调频广播接收机获取其接收到所述时间同步信号的本地时间信息；
    所述调频广播接收机根据自身的本地位置信息、所述时间同步信号和本地时间信息，同步该调频广播接收机本地时钟的时刻和频率。
  2. 如权利要求1所述的基于数字调频广播的时钟同步方法，其特征在于，所述时间同步信号包括测距码、所述调频广播发射机广播所述测距码的远端时间信息和所述调频广播发射机的远端位置信息，
    所述调频广播接收机根据所述时间同步信号、本地时间信息和本地位置信息，同步该调频广播接收机本地时钟的时刻和频率的步骤包括：
    调频广播接收机根据所述本地时间信息，估算该调频广播接收机接收到所述测距码的估算时间信息以及所述调频广播接收机与调频广播发射机之间的相对频差；
    调频广播接收机根据所述远端位置信息、本地位置信息、远端时间信息和估算时间信息，计算得出所述调频广播接收机时钟与调频广播发射机时钟之间的时间差；
    调频广播接收机根据所述时间差和相对频差，同步该调频广播接收机本地时钟的时刻和频率。
  3. 如权利要求2所述的基于数字调频广播的时钟同步方法，其特征在于，所述调频广播接收机获取其接收到所述时间同步信号的本地时间信息的步骤包括；
    所述调频广播接收机生成与所述调频广播发射机所发送的测距码的脉冲信号波形相同的本地测距码；
    所述调频广播接收机获取所述本地测距码的脉冲波形与所述调频广播发射机所发送的测距码的脉冲波形相位对齐时的本地时钟值；
    所述调频广播接收机根据所述本地时间信息，估算该调频广播接收机接收到所述测距码的估算时间信息以及所述调频广播接收机与调频广播发射机之间的相对频差的步骤包括：
    所述调频广播接收机根据所述调频广播发射机所发送的测距码的各个脉冲与第其一个脉冲的标称延迟和所述本地时钟值，估算该调频广播接收机接收到所述测距码的第一个脉冲的估算时钟值以及所述调频广播接收机与调频广播发射机之间的相对频差。
  4. 如权利要求3所述的基于数字调频广播的时钟同步方法，其特征在于，所述调频广播接收机根据所述远端位置信息、本地位置信息、远端时间信息和估算时间信息，计算得出所述调频广播接收机时钟与调频广播发射机时钟之间的时间差的步骤包括：
    所述调频广播接收机根据所述远端位置信息和本地位置信息，计算得出信号自所述调频广播发射机到调频广播接收机的传播时间；
    所述调频广播接收机根据所述远端时间信息、估计时间信息和传输时间，计算得出所述调频广播接收机时钟与调频广播发射机时钟之间的时间差。
  5. 如权利要求4所述的基于数字调频广播的时钟同步方法，其特征在于，所述调频广播接收机根据所述时间差和相对频差，调整自身时钟的时刻和频率的步骤包括：
    所述调频广播接收机根据所述相对频差和所述调频广播接收机的频率标称值，调整所述调频广播接收机时钟的频率；
    所述调频广播接收机根据所述时间差和所述调频广播接收机的频率标称值，调整所述调频广播接收机时钟的时刻。
  6. 如权利要求3所述的基于数字调频广播的时钟同步方法，其特征在于，所述调频广播接收机根据所述时间差和相对频差，调整自身时钟的时刻和频率的步骤包括：
    所述调频广播接收机根据所述相对频差和所述调频广播接收机的频率标称值，调整所述调频广播接收机时钟的频率；
    所述调频广播接收机根据所述时间差和所述调频广播接收机的频率标称值，调整所述调频广播接收机时钟的时刻。
  7. 如权利要求2所述的基于数字调频广播的时钟同步方法，其特征在于，所述调频广播接收机根据所述远端位置信息、本地位置信息、远端时间信息和估算时间信息，计算得出所述调频广播接收机时钟与调频广播发射机时钟之间的时间差的步骤包括：
    所述调频广播接收机根据所述远端位置信息和本地位置信息，计算得出信号自所述调频广播发射机到调频广播接收机的传播时间；
    所述调频广播接收机根据所述远端时间信息、估计时间信息和传输时间，计算得出所述调频广播接收机时钟与调频广播发射机时钟之间的时间差。
  8. 如权利要求2所述的基于数字调频广播的时钟同步方法，其特征在于，所述调频广播接收机根据所述时间差和相对频差，调整自身时钟的时刻和频率的步骤包括：
    所述调频广播接收机根据所述相对频差和所述调频广播接收机的频率标称值，调整所述调频广播接收机时钟的频率；
    所述调频广播接收机根据所述时间差和所述调频广播接收机的频率标称值，调整所述调频广播接收机时钟的时刻。
  9. 一种调频广播接收机，其特征在于，所述调频广播接收机包括：
    信号接收模块，用于接收与标准时间同步的调频广播发射机所广播的无线数据广播信号；
    解调模块，用于解调出所述无线数据广播信号中时间同步信号；
    本地时间获取模块，用于获取所述调频广播接收机接收到所述时间同步信号的本地时间信息；
    同步模块，用于根据自身的本地位置信息、所述时间同步信号和本地时间信息，同步该调频广播接收机本地时钟的时刻和频率。
  10. 如权利要求9所述的调频广播接收机，其特征在于，所述时间同步信号包括测距码、所述调频广播发射机广播所述测距码的远端时间信息和所述调频广播发射机的远端位置信息，
    所述同步模块包括：
    估算单元，用于根据所述本地时间信息，估算该调频广播接收机接收到所述测距码的估算时间信息以及所述调频广播接收机与调频广播发射机之间的相对频差；
    时间差计算单元，用于根据所述远端位置信息、本地位置信息、远端时间信息和估算时间信息，计算得出所述调频广播接收机时钟与调频广播发射机时钟之间的时间差；
    同步单元，用于根据所述时间差和相对频差，同步该调频广播接收机本地时钟的时刻和频率。
  11. 如权利要求10所述的调频广播接收机，其特征在于，所述本地时间获取模块包括；
    脉冲生成单元，用于生成与所述调频广播发射机所发送的测距码的脉冲信号波形相同的本地测距码；
    时钟值获取单元，用于获取所述本地测距码的脉冲波形与所述调频广播发射机所发送的测距码的脉冲波形相位对齐时的本地时钟值；
    所述估算单元，还用于根据所述调频广播发射机所发送的测距码的各个脉冲与其第一个脉冲的标称延迟和所述本地时钟值，估算该调频广播接收机接收到所述测距码的第一个脉冲的估算时钟值以及所述调频广播接收机与调频广播发射机之间的相对频差。
  12. 如权利要求11所述的调频广播接收机，其特征在于，所述时间差计算单元还用于：
    根据所述远端位置信息和本地位置信息，计算得出信号自所述调频广播发射机到调频广播接收机的传播时间；
    根据所述远端时间信息、估计时间信息和传输时间，计算得出所述调频 广播接收机时钟与调频广播发射机时钟之间的时间差。
  13. 如权利要求12所述的调频广播接收机，其特征在于，所述同步单元还用于：
    根据所述相对频差和所述调频广播接收机的频率标称值，调整所述调频广播接收机时钟的频率；
    根据所述时间差和所述调频广播接收机的频率标称值，调整所述调频广播接收机时钟的时刻。
  14. 如权利要求11所述的调频广播接收机，其特征在于，所述同步单元还用于：
    根据所述相对频差和所述调频广播接收机的频率标称值，调整所述调频广播接收机时钟的频率；
    根据所述时间差和所述调频广播接收机的频率标称值，调整所述调频广播接收机时钟的时刻。
  15. 如权利要求10所述的调频广播接收机，其特征在于，所述时间差计算单元还用于：
    根据所述远端位置信息和本地位置信息，计算得出信号自所述调频广播发射机到调频广播接收机的传播时间；
    根据所述远端时间信息、估计时间信息和传输时间，计算得出所述调频广播接收机时钟与调频广播发射机时钟之间的时间差。
  16. 如权利要求10所述的调频广播接收机，其特征在于，所述同步单元还用于：
    根据所述相对频差和所述调频广播接收机的频率标称值，调整所述调频广播接收机时钟的频率；
    根据所述时间差和所述调频广播接收机的频率标称值，调整所述调频广播接收机时钟的时刻。
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