Communication and navigation integrated method suitable for amplitude modulation broadcast

Abstract

The invention discloses a communication and navigation integrated method suitable for amplitude modulation broadcast, which adopts an MPPSK / AM composite modulation mode, designs a digital information format, fully utilizes the characteristics of medium wave signal composite modulation, and adopts a method based on cross-correlation and coherent demodulation to carry out distance measurement and communication. According to the invention, not only can high-speed and downward compatible digital communication be provided, but also a backup positioning means is provided for a GNSS denial environment, so that the resource utilization rate is greatly improved, and the hardware cost is greatly reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of communication positioning, and in particular relates to a communication and navigation integration method suitable for amplitude modulation broadcasting. Background Art

[0002] Digitalization has become an inevitable trend in the development of existing radio and television. The two mainstream digital broadcasting systems are: the Digital Audio Broadcasting (DAB) system proposed by the European Telecommunications Standards Institute and the High Definition Broadcasting (HDR) system proposed by the Federal Communications Commission of the United States. The DAB system adopts a multi-carrier transmission system based on coded orthogonal frequency division multiplexing to achieve full digitization of AM broadcasting in the LW / MW / SW frequency bands, which can effectively improve the frequency selective fading caused by the multipath effect and improve the signal quality. In addition to being widely used in Europe, the system has also been introduced to 30 countries and regions such as Australia, Singapore, and South Korea. However, the DAB system is completely incompatible with the existing AM / FM broadcasting system, and a new working frequency band needs to be divided, which limits the promotion of the DAB system. The HDR system uses in-band co-frequency technology, that is, using the carrier frequency sideband of the existing AM / FM broadcasting band to transmit digital signals, which can better be compatible with the existing analog broadcasting system and achieve a smooth transition from analog to digital. It has been rapidly promoted in the United States and other regions. However, the broadcasting system in some countries in the world (including China) is completely different from the frequency division in the US broadcasting system, which has greatly hindered the application of HDR in other regions. Since 2007, my country's Academy of Radio and Television has carried out research and experiments on China's digital audio broadcasting system, which was designated as an international standard by the International Telecommunication Union in 2018. However, there are still some shortcomings, such as incompatibility with medium wave AM broadcasting, the need to modify and upgrade transmitters, and design and develop new receivers.

[0003] In response to the above shortcomings, Multi-Position Phase Shift Keying (MPPSK) was proposed. MPPSK uses the phase of the carrier to carry digital signals and is compatible with traditional medium wave AM broadcasting. As long as the power spectrum of the digital signal is at least 50dB lower than the carrier within the 9kHz (carrier 4.5kHz) bandwidth, the simulcast of analog and digital information can be achieved. In the receiver, the signal is divided into two demodulation paths, one is the double-sideband amplitude modulation signal (DSB-AM) signal demodulation, which can still use traditional envelope detection; the other is MPPSK coherent demodulation to obtain digital broadcast information. The MPPSK / AM composite modulation scheme can achieve a smooth transition from analog broadcasting to digital broadcasting without changing the original broadcasting system, greatly improving the spectrum utilization of the medium wave broadcasting band.

[0004] On the other hand, with the development of electronic warfare, the global navigation system (GNSS) faces serious threats. In a complex electromagnetic environment, if a strong enemy conducts electromagnetic interference on our GNSS, serious malicious interference may even cause the satellite signal to fail completely, making it impossible for us to use GNSS to ensure the normal progress of various tasks. For example, the British government conducted a GNSS signal interference test with two low-cost jammers in 2008 and found that it could block all satellite navigation signals within 30 kilometers of the North Sea. In addition, the global satellite navigation system has its own shortcomings due to some of its own limitations. For example, satellites are located in space orbits and are easy to be discovered and destroyed; if users are in canyons, forests, cities, underground and other environments with severe obstruction, they may not receive satellite signals and thus cannot obtain location navigation information; therefore, it is of great significance to develop navigation and positioning technology in GNSS denial environments. According to statistics, there are more than 1,200 medium-wave transmitters in my country, which are characterized by many points, large numbers and wide coverage. How to use this rich resource is of great significance. At the same time, this also provides an effective means for positioning in GNSS behavior environments, that is, using medium-wave broadcasting to achieve communication and positioning. Summary of the invention

[0005] In order to overcome the shortcomings of the prior art, the present invention provides a communication and navigation integration method suitable for AM broadcasting, adopts the MPPSK / AM composite modulation mode, and designs a digital information format, making full use of the characteristics of medium wave signal composite modulation, and adopts a method based on cross-correlation and coherent demodulation for ranging and communication. The present invention can not only provide high-speed and backward compatible digital communication, but also provide a backup positioning means for GNSS denied environments, so that resource utilization is greatly improved and hardware costs are greatly reduced.

[0006] The technical solution adopted by the present invention to solve the technical problem is as follows:

[0007] Step 1: The single-frame navigation information includes a frame synchronization header, base station parameters, communication data, and a reserved bit. The navigation information is encoded in M-ary system as s=[s(1), ..., s(l), ..., s(L)], where s(l) has M values;

[0008] Step 2: Perform MPPSK modulation on the navigation information s, and its expression is:

[0009]

[0010] Among them, a l (t) represents the MPPSK modulation signal, 0≤θ≤π, w c Indicates the carrier frequency; N indicates that the carrier duration is N carrier cycles, K indicates that the carrier modulation period lasts K carrier cycles, T = 2π / w cIndicates the carrier period;

[0011] Step 3: Send the navigation digital signal to the broadcast transmitter for amplitude modulation. The composite modulated signal is expressed as:

[0012] y(t)=A(1+k m (t)m(t))a l (t) (2)

[0013] Step 4: Sample the received signal and perform zero-phase filtering to obtain the composite modulated signal sent by the corresponding base station, which is divided into two paths for processing;

[0014] Step 5: In the first path, the received signal is envelope detected to extract the audio signal and obtain the audio information, which is expressed as A(1+k m (n△f)m(n△f)), where △f is the sampling frequency, n represents the nth sampling point, m(n△f) represents the sampled audio signal, k m (n△f) represents the modulation parameter corresponding to the nth sampling point;

[0015] Step 6: The received signal in the second path is divided by the audio signal to remove the interference of the analog signal on the digital signal, which is expressed as The length is N 1 ;

[0016] Step 7: Perform coherent accumulation on the signal to improve the signal-to-noise ratio of the digital signal;

[0017] Step 8: Construct a second-order Costas loop and recover the carrier signal, expressed as d(n);

[0018] Step 9: Use the least squares method to determine the phase of the recovered carrier and recover the carrier signal It is expressed as:

[0019]

[0020] Step 10: Perform coherent demodulation;

[0021] Step 11: Calculate the difference between the original frame synchronization signal and the original carrier signal as the sample signal; calculate the difference between the recovered carrier signal and the received signal as the signal of the estimated transmission time; the sample signal and the difference signal are respectively expressed as:

[0022]

[0023] e(n)=y sync (n)-sin(w c n△f) (5)

[0024] Among them, y sync(t) represents the signal after the frame synchronization information is modulated by MPPSK, and its length is N 2 ;

[0025] Step 12: Calculate the autocorrelation function R of the reference signal ee The cross-correlation function of the reference signal and the difference signal And its corresponding power spectrum G ee and It is expressed as:

[0026]

[0027] Among them, e(n+m) * represents the conjugate transpose of the difference e(n) signal after sliding m sampling points, and FFT(.) represents Fourier transform;

[0028] Step 13: Calculate R ee and The cross-correlation function R and its corresponding power spectrum G are expressed as:

[0029]

[0030] G(n)=FFT(R(i)) (9)

[0031] Among them, i represents the sampling point corresponding to the delay;

[0032] Step 14: Weight the power spectrum G and calculate its inverse Fourier transform, which is expressed as:

[0033]

[0034] in, is the weighting factor, IFFT(.) means inverse Fourier transform;

[0035] Step 15: R ss Perform peak detection and estimation, expressed as:

[0036]

[0037] That is, the rough transmission time estimate between the sample signal and the received signal;

[0038] Step 16: Right of and sync (n) Interpolate and save as difference signal and sync-r (n), where △f′ is the upsampling frequency, and sync-r The length of (n) is N 1′ and N 2 ′; The interpolation formula is expressed as:

[0039]

[0040] Step 17: Slide y sync-r (n) Take the minimum value of the difference and estimate the precise value of the communication and navigation information frame sending time, which is expressed as:

[0041]

[0042] in, represents the number of sampling points corresponding to the estimated optimal delay, Indicates the number of sampling points corresponding to the sliding delay;

[0043] Step 18: Calculate the time value corresponding to the frame transmission time of the communication navigation information in the receiver and its corresponding pseudo-range, expressed as:

[0044]

[0045]

[0046] Among them, t 0 is the time when the communication and navigation information frame is sent, t 1 is the sampling start time, t error is the time correction parameter;

[0047] Preferably, the base station parameters include hardware delay, working status, clock correction, and sending time information t 0 .

[0048] Preferably, in step 2, the parameters N, K and θ are set to ensure that the power spectrum of the navigation information is 50 dB lower than the carrier frequency, to ensure that the digital signal does not interfere with the analog signal, and to ensure that the navigation information is not lost after passing through the transmitter with filtering characteristics.

[0049] The beneficial effects of the present invention are as follows:

[0050] 1. The present invention uses MPPSK modulation to add digital signals to the original analog signals, so that the digital signals and analog signals are broadcast using the same frequency band and hardware resources.

[0051] 2. The present invention is backward compatible and can directly use the existing AM broadcasting system, such as the division of frequency resources, the infrastructure of AM broadcasting transmitters, the broadcasting format of DSB-AM transmission, the AM radio receiving format, etc. A simple modification of the broadcasting base station can realize the transmission of the original audio information and communication navigation information in the same frequency band resources, which greatly improves the frequency band utilization and greatly saves investment.

[0052] 3. The present invention designs a digital signal frame format and a processing method thereof, which can complete the ranging function while realizing analog audio communication and digital communication, and can further realize positioning, greatly improving the utilization rate of hardware resources and completing the integration of communication and ranging functions. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 This is a schematic diagram of the communication and navigation message structure according to an embodiment of the present invention;

[0054] Figure 2 In the figure, (a) is a composite modulated signal waveform diagram according to an embodiment of the present invention, and (b) is a composite modulated signal power spectrum diagram according to an embodiment of the present invention;

[0055] Figure 3 This is a principle block diagram of a receiver according to an embodiment of the present invention;

[0056] Figure 4 The waveform diagram of the audio signal of the embodiment of the present invention (SNR=30dB);

[0057] Figure 5 Schematic diagram of MPPSK signal after coherent accumulation according to an embodiment of the present invention, (a) is the waveform of MPPSK signal after 30 coherent accumulations, (b) is a partial enlarged diagram;

[0058] Figure 6 This is a schematic diagram of a second-order Costas ring according to an embodiment of the present invention;

[0059] Figure 7 This is a schematic diagram of a locally recovered carrier waveform according to an embodiment of the present invention;

[0060] Figure 8 A schematic diagram of a detection and decision waveform according to an embodiment of the present invention;

[0061] Fig. 9 This is a peak waveform diagram related to an embodiment of the present invention;

[0062] Fig.10 This is a waveform matching diagram of an embodiment of the present invention;

[0063] Fig.11 This is a diagram of the time estimation error under different SNRs in an embodiment of the present invention. DETAILED DESCRIPTION

[0064] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0065] In order to achieve positioning in a GNSS-denied environment, the present invention proposes a solution for communication and positioning using medium wave broadcasting, which is compatible with the digital audio broadcasting system, fully utilizes the potential of medium wave resources, and provides a positioning backup method in a complex environment. The present invention adopts the MPPSK / AM composite modulation method, and designs a digital information format, making full use of the characteristics of medium wave signal composite modulation, and adopts a method based on cross-correlation and coherent demodulation for ranging and communication.

[0066] The technical problem to be solved by the present invention is to provide a communication and positioning method based on MPPSK / AM composite modulation. The method adopts MPPSK / AM composite modulation at the transmitting end. In order to meet the requirements of ranging, the digital information format of the transmitting end is also defined. The above modulation method and information format can meet the requirements of communication and ranging at the same time.

[0067] The communication and positioning integrated method based on MPPSK / AM composite modulation provided by the present invention includes the following steps in the sending end processing:

[0068] Step 1: Single frame navigation information includes frame synchronization header, base station parameters (hardware delay, working status, clock correction, transmission time information t 0 etc.), communication data, reserved bits, and the navigation information is encoded in M-ary system as s=[s(1), ..., s(L)], where s(l) has M values ​​among 1, 2, ..., M.

[0069] Step 2: Perform MPPSK modulation on the navigation information s, and its expression is:

[0070]

[0071] Where, 0≤θ≤π, carrier period T=2π / w c , N means the carrier duration is N carrier cycles, K means the carrier modulation period lasts K carrier cycles. The parameters N, K and θ are set to ensure that the power spectrum of the navigation information is 50 dB below the carrier frequency, to ensure that the digital signal does not interfere with the analog signal, and to ensure that the navigation information is not seriously lost after passing through the transmitter with filtering characteristics.

[0072] Step 3: Send the navigation digital signal to the broadcast transmitter for amplitude modulation. The composite modulated signal can be expressed as:

[0073] y(t)=A(1+k m (t)m(t))a l (t) (2)

[0074] The receiving end synchronization process includes the following steps:

[0075] Step 4: Sample the received signal and perform zero-phase filtering to obtain the composite modulated signal sent by the corresponding base station, which is divided into two paths for processing.

[0076] First route:

[0077] Step 5: Perform envelope detection on the received signal to extract the audio signal and obtain the audio information, which is expressed as A(1+k m (n△f)m(n△f)), where △f is the sampling frequency.

[0078] Second route:

[0079] Step 6: Divide the received signal by the audio signal to remove the interference of the analog signal on the digital signal, which is expressed as The length is N 1 ;

[0080] Step 7: Perform coherent accumulation on the signal to improve the signal-to-noise ratio of the digital signal.

[0081] Step 8: Construct a second-order Costas loop and recover the carrier signal, expressed as d(n);

[0082] Step 9: Use the least squares method to determine the phase of the recovered carrier and recover the carrier signal It is expressed as:

[0083]

[0084] Step 10: Perform coherent demodulation.

[0085] Step 11: Calculate the difference between the original frame synchronization signal and the original carrier signal as the sample signal; calculate the difference between the recovered carrier signal and the received signal as the signal of the estimated transmission time. The sample signal and the difference signal are respectively expressed as:

[0086]

[0087] e(n)=y sync (n)-sin(w c n△f) (5)

[0088] Among them, y sync (t) represents the signal after the frame synchronization information is modulated by MPPSK, and its length is N 2 .

[0089] Step 12: Calculate the autocorrelation function R of the reference signal ee The cross-correlation function of the reference signal and the difference signal And its corresponding power spectrum G ee and It is expressed as:

[0090]

[0091] Step 13: Calculate R ee and The cross-correlation function R and its corresponding power spectrum G are expressed as:

[0092]

[0093] G(n)=FFT(R(i)) (9)

[0094] Step 14: Weight the power spectrum G and calculate its inverse Fourier transform, which is expressed as:

[0095]

[0096]

[0097] in, is the weighting factor.

[0098] Step 15: R ss Perform peak detection and estimation, expressed as:

[0099]

[0100] It is the rough estimate of the transmission time between the sample signal and the received signal.

[0101] Step 16: Right of and sync (n) Interpolate and save as difference signal and sync-r (n), where △f′ is the upsampling frequency, and sync-r The length of (n) is N 1 ′ and N 2 ′. The interpolation formula is expressed as:

[0102]

[0103] Step 17: Slide y sync-r (n) Take the minimum value of the difference and estimate the precise value of the communication and navigation information frame sending time, which is expressed as:

[0104]

[0105] in,

[0106] Step 18: Calculate the time value corresponding to the frame transmission time of the communication navigation information in the receiver and its corresponding pseudo-range, expressed as:

[0107]

[0108] Among them, t 0 is the time when the communication and navigation information frame is sent, t 1 is the sampling start time, t error It is the time correction parameter.

[0109] Example:

[0110] MPPSK / AM composite modulation transmitter system:

[0111] (1) According to Figure 1 The digital information frame structure shown generates a 200-bit binary code, wherein the frame synchronization code is known by both the transmitting and receiving ends.

[0112] (2) Using MPPSK modulation with N=128, M=64, K=1 and θ=π as shown in equation (1), followed by amplitude modulation, the waveform is as follows Figure 2 (a) is shown. The spectrum of the MPPSK signal is shown in Figure 2 As shown in (b), the power spectrum of the digital signal is 50dB lower than the carrier, which meets the management requirements of the radio spectrum for medium wave AM broadcasting and will not interfere with the demodulation of the analog signal.

[0113] Communication and navigation receiver;

[0114] According to the background technology, the communication and navigation integration method proposed by the present invention first demodulates the audio signal, then demodulates the digital information and performs ranging processing. The principle block diagram of the entire receiver system is as follows: Figure 3 shown.

[0115] (1) The received signal is filtered and envelope detected to obtain an audio signal with a signal-to-noise ratio of 30 dB. Figure 4 shown.

[0116] (2) Remove the analog signal and perform coherent accumulation, the number of accumulation times is 30, such as Figure 5 shown.

[0117] (3) Construct Figure 6 The Costas loop shown in FIG. 1 and the formula (3) are used to recover the local carrier, as shown in FIG. Figure 7 shown.

[0118] (4) According to Figure 3 According to the principle shown in the figure, the signal can be coherently demodulated to obtain digital bit information, where the detection decision waveform is as follows: Figure 8 shown.

[0119] (5) The difference signal is obtained according to equations (4) and (5), and generalized cross-correlation processing is performed according to equations (5) to (12). The correlation peak diagram is shown in the figure below: Fig. 9 shown.

[0120] (6) According to equations (13) and (14), interpolation and sliding matching are performed respectively to obtain the estimated value of the start time of the navigation information frame. The waveform matching is as follows: Fig.10 shown.

[0121] (7) According to equations (15) and (16), the accurate estimated value of the communication navigation information frame reception time and distance information are obtained. Fig.11 Estimation error plots for different signal-to-noise ratios are given.

Claims

1. A communication and navigation integration method suitable for AM broadcasting, characterized in that: The steps include: Step 1: The single-frame navigation information includes a frame synchronization header, base station parameters, communication data, and a reserved bit. The navigation information is encoded in M-ary system as s=[s(1), ..., s(l), ..., s(L)], where s(l) has M values; Step 2: Perform MPPSK modulation on the navigation information s, and its expression is: Among them, a l (t) represents the MPPSK modulation signal, 0≤θ≤π, w c Indicates the carrier frequency; N indicates that the carrier duration is N carrier cycles, K indicates that the carrier modulation period lasts K carrier cycles, T = 2π / w c Indicates the carrier period; Step 3: Send the navigation digital signal to the broadcast transmitter for amplitude modulation. The composite modulated signal is expressed as: y(t)=A(1+k m (t)m(t))a l (t) (2) Step 4: Sample the received signal and perform zero-phase filtering to obtain the composite modulated signal sent by the corresponding base station, which is divided into two paths for processing; Step 5: In the first path, the received signal is envelope detected to extract the audio signal and obtain the audio information, which is expressed as A(1+k m (n△f)m(n△f)), where △f is the sampling frequency, n represents the nth sampling point, m(n△f) represents the sampled audio signal, k m (n△f) represents the modulation parameter corresponding to the nth sampling point; Step 6: The received signal in the second path is divided by the audio signal to remove the interference of the analog signal on the digital signal, which is expressed as The length is N1; Step 7: Perform coherent accumulation on the signal to improve the signal-to-noise ratio of the digital signal; Step 8: Construct a second-order Costas loop and recover the carrier signal, expressed as d(n); Step 9: Use the least squares method to determine the phase of the recovered carrier and recover the carrier signal It is expressed as: Step 10: Perform coherent demodulation; Step 11: Calculate the difference between the original frame synchronization signal and the original carrier signal as the sample signal; calculate the difference between the recovered carrier signal and the received signal as the signal of the estimated transmission time; the sample signal and the difference signal are respectively expressed as: e(n)=y sync (n)-that(w c n△f) (5) Among them, y sync (t) represents the signal after the frame synchronization information is modulated by MPPSK, and its length is N2; Step 12: Calculate the autocorrelation function R of the reference signal ee The cross-correlation function of the reference signal and the difference signal And its corresponding power spectrum G ee and It is expressed as: Among them, e(n+m) * represents the conjugate transpose of the difference e(n) signal after sliding m sampling points, and FFT(.) represents Fourier transform; Step 13: Calculate R ee and The cross-correlation function R and its corresponding power spectrum G are expressed as: G(n)=FFT(R(i)) (9) Among them, i represents the sampling point corresponding to the delay; Step 14: Weight the power spectrum G and calculate its inverse Fourier transform, which is expressed as: in, is the weighting factor, IFFT(.) means inverse Fourier transform; Step 15: R ss Perform peak detection and estimation, expressed as: That is, the rough transmission time estimate between the sample signal and the received signal; Step 16: Right of and sync (n) Interpolate and save as difference signal and sync-r (n), where △f′ is the upsampling frequency, and sync-r The lengths of (n) are N1′ and N2′ respectively; the interpolation formula is expressed as: Step 17: Slide y sync-r (n) Take the minimum value of the difference and estimate the precise value of the communication and navigation information frame sending time, which is expressed as: Among them, 0≤n≤N1-1, represents the number of sampling points corresponding to the estimated optimal delay, Indicates the number of sampling points corresponding to the sliding delay; Step 18: Calculate the time value corresponding to the frame transmission time of the communication navigation information in the receiver and its corresponding pseudo-range, expressed as: Among them, t0 is the time when the communication navigation information frame is sent, t1 is the sampling start time, and t error It is the time correction parameter.

2. The communication and navigation integration method suitable for AM broadcasting according to claim 1, characterized in that: The base station parameters include hardware delay, working status, clock correction, and sending time information t0.

3. The communication and navigation integration method suitable for AM broadcasting according to claim 2, characterized in that: In step 2, the parameters N, K and θ are set to ensure that the power spectrum of the navigation information is 50 dB lower than the carrier frequency, to ensure that the digital signal does not interfere with the analog signal, and to ensure that the navigation information is not lost after passing through the transmitter with filtering characteristics.

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