CN113949612A - Burst signal capturing method and system in helicopter and satellite communication - Google Patents
Burst signal capturing method and system in helicopter and satellite communication Download PDFInfo
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- CN113949612A CN113949612A CN202110976346.5A CN202110976346A CN113949612A CN 113949612 A CN113949612 A CN 113949612A CN 202110976346 A CN202110976346 A CN 202110976346A CN 113949612 A CN113949612 A CN 113949612A
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2656—Frame synchronisation, e.g. packet synchronisation, time division duplex [TDD] switching point detection or subframe synchronisation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2662—Symbol synchronisation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2689—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation
- H04L27/2692—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation with preamble design, i.e. with negotiation of the synchronisation sequence with transmitter or sequence linked to the algorithm used at the receiver
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
- H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
- H04L27/38—Demodulator circuits; Receiver circuits
- H04L27/3845—Demodulator circuits; Receiver circuits using non - coherent demodulation, i.e. not using a phase synchronous carrier
- H04L27/3854—Demodulator circuits; Receiver circuits using non - coherent demodulation, i.e. not using a phase synchronous carrier using a non - coherent carrier, including systems with baseband correction for phase or frequency offset
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
- Y02D30/00—Reducing energy consumption in communication networks
- Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks
Abstract
The invention discloses a method and a system for capturing burst signals in communication between a helicopter and a satellite, and belongs to the technical field of satellite communication. The method comprises the following steps: shift registers, frequency rate of change estimation and compensation, FFT transformation, and acquisition decisions. The invention carries out frequency change rate estimation based on pilot frequency assistance by symbol sliding based on pilot frequency symbols which are dispersedly inserted, carries out change rate compensation by utilizing an estimated value, then calculates the peak value and the average value of a frequency spectrum by utilizing FFT (fast Fourier transform) conversion, and judges the capture. The problem of burst signal capture under the conditions of high Doppler dynamic, low link signal-to-noise ratio and rotor shielding is solved, and the method has a certain application prospect in helicopter satellite communication.
Description
Technical Field
The invention relates to a method and a system for capturing burst signals in communication between a helicopter and a satellite, and belongs to the technical field of satellite communication.
Background
The airborne terminal in the helicopter satellite communication communicates with the ground gateway station or other terminals through the satellite, and information transmission can be carried out in a wider area due to the fact that relay forwarding is not needed by the ground relay station, and the application field is very wide. However, limited by platform space, only an antenna with a small caliber (e.g. below 0.5 m) can be installed on the helicopter, the terminal communication capability is weak, especially in VHF/UHF band, and the communication rate can only reach several Kbps generally. For a helicopter with high maneuvering characteristics, along with the violent change of the flight attitude, the communication signal of the helicopter has larger Doppler dynamic, and the demodulation difficulty of the low carrier rate signal is improved. Meanwhile, in the flight process of the helicopter, a communication link can be influenced by the shielding of the rotor wing, so that the periodic power attenuation of a received signal is caused.
Helicopter satellite communication generally adopts a burst communication mode, and for burst signal demodulation, burst acquisition is generally the basis of subsequent other parameter estimation and synchronization. Since a plurality of channel parameters (such as frequency offset, frequency change rate, burst start position, etc.) are in an unknown state, in order to reduce the acquisition difficulty, burst acquisition is generally completed by using a known preamble head through time domain correlation or frequency domain FFT. The time domain correlation acquisition method has low implementation complexity, but has limited adaptability to frequency offset. The conventional frequency domain acquisition algorithm is insensitive to frequency offset, but under high Doppler dynamic condition, the frequency change rate can cause the signal frequency spectrum to have platform effect, and the acquisition performance is rapidly deteriorated.
Disclosure of Invention
The technical problem solved by the invention is as follows: the method and the system for capturing the frequency domain in the helicopter satellite communication overcome the defects of the existing frequency domain capturing method, provide a frequency domain capturing method and a frequency domain capturing system combining frequency change rate estimation, and solve the problem of capturing the burst signal with low signal-to-noise ratio under high Doppler dynamic conditions in the helicopter satellite communication.
The technical solution of the invention is as follows:
a burst signal capturing method in helicopter and satellite communication comprises the following steps:
1) the receiver receives the AD sampling signal, obtains a modulation symbol of the burst signal after symbol synchronization processing, and carries out shift register processing on the modulation symbol by using a shift register;
2) after receiving a new modulation symbol, performing frequency change rate estimation and compensation once to obtain a pilot frequency symbol after frequency change rate compensation;
3) performing FFT according to the pilot frequency symbol after frequency change rate compensation obtained in the step 2) to obtain an FFT result so as to obtain a ratio of a frequency spectrum peak value to an average value;
4) and (4) performing acquisition judgment, finishing acquisition work if judging that the burst signal is acquired, and returning to the step 2) otherwise.
Optionally, the method for performing the capture determination in step 4) specifically includes:
and 3) judging whether the ratio in the step 3) is larger than a threshold, if so, judging that the burst signal is captured, otherwise, jumping to the step 2).
Optionally, the obtaining the pilot symbol after the frequency change rate compensation in step 2) specifically includes:
and extracting a pilot frequency symbol from the shift register according to a burst signal frame format, and performing frequency change rate estimation and compensation to obtain the pilot frequency symbol after frequency change rate compensation.
Optionally, the determination principle of the threshold in step 4) is determined by simulation according to the required capture probability and mis-capture probability index.
A burst signal capturing system in helicopter satellite communication for implementing the above burst signal capturing method in helicopter and satellite communication, comprising: the device comprises a shift register, a frequency change rate estimation and compensation module, an FFT (fast Fourier transform) module and a capture judgment module;
a shift register: receiving a modulation symbol of a burst signal obtained after symbol synchronization processing, and carrying out shift register processing on the modulation symbol;
frequency rate of change estimation and compensation module: for sampling points in the shift register, extracting pilot symbols according to a burst signal frame format, and performing frequency change rate estimation and compensation to obtain the pilot symbols after frequency change rate compensation;
an FFT transform and acquisition decision module: and performing FFT (fast Fourier transform) on the pilot symbols after frequency change rate compensation, then calculating the ratio of the peak value and the mean value of the frequency spectrum, and performing acquisition judgment.
The frequency change rate estimation and compensation module performs frequency change rate estimation and compensation once every time the shift register receives a new symbol.
The FFT transform and acquisition decision module performs an FFT transform and acquisition decision each time the shift register receives a new symbol.
The FFT conversion and acquisition judgment module carries out acquisition judgment, and specifically comprises the following steps:
and when the ratio is larger than a set threshold, the burst signal is considered to be captured.
The burst signal adopts a distributed pilot frequency frame structure, and the burst frame length is LFIs divided into N sections, each section is LDEach segment comprising 1 pilot symbol and (L)D-1) data symbols. L isDIs in the range of 10 to 100.
Compared with the prior art, the invention has the advantages that:
1) the method simultaneously carries out Doppler change rate estimation and frequency domain burst capture, and eliminates the influence of the Doppler change rate on the capture performance;
2) in the method, both Doppler change rate estimation and frequency domain burst capture adopt a data-aided method, so that the performance under the condition of low signal-to-noise ratio is ensured.
Drawings
FIG. 1 is a schematic view of rotor shielding in helicopter satellite communications;
FIG. 2 is a schematic diagram of signal fading due to rotor occlusion;
fig. 3 is a diagram illustrating a structure of a distributed pilot frame;
FIG. 4 is a block diagram of the present invention;
FIG. 5 is a schematic diagram of a shift register;
FIG. 6 is a schematic diagram illustrating the influence of the frequency change rate on the signal spectrum according to the frequency domain acquisition method of the present invention.
Detailed Description
The invention discloses a burst signal capturing method in helicopter and satellite communication, which comprises the following steps:
1) the receiver receives the AD sampling signal, obtains a modulation symbol of the burst signal after symbol synchronization processing, and carries out shift register processing on the modulation symbol by using a shift register;
2) after receiving a new modulation symbol, performing frequency change rate estimation and compensation once to obtain a pilot frequency symbol after frequency change rate compensation;
3) performing FFT according to the pilot frequency symbol after frequency change rate compensation obtained in the step 2) to obtain an FFT result so as to obtain a ratio of a frequency spectrum peak value to an average value;
4) and (4) performing acquisition judgment, finishing acquisition work if judging that the burst signal is acquired, and returning to the step 2) otherwise.
The method for performing capture judgment in step 4) specifically comprises the following steps:
and judging whether the ratio in the step 3) is larger than a threshold, if so, judging that the burst signal is captured, otherwise, jumping to the step 2) to continue capturing.
The step 2) of obtaining the pilot symbols after frequency change rate compensation specifically includes:
extracting a pilot frequency symbol from a shift register according to a burst signal frame format, and performing frequency change rate estimation and compensation to obtain the pilot frequency symbol after frequency change rate compensation;
and 4) determining the threshold by simulation according to the required capture probability and mis-capture probability indexes.
A burst signal capturing system in helicopter satellite communication for implementing the above burst signal capturing method in helicopter and satellite communication, comprising: the device comprises a shift register, a frequency change rate estimation and compensation module, an FFT (fast Fourier transform) module and a capture judgment module;
a shift register: receiving a modulation symbol of a burst signal obtained after symbol synchronization processing, and carrying out shift register processing on the modulation symbol; in order to provide data for other processing modules, a shift memory is arranged according to the length of a burst signal frame, and the sampling points after symbol synchronization are subjected to shift register symbol by symbol.
Frequency rate of change estimation and compensation module: for sampling points in the shift register, extracting pilot symbols according to a burst signal frame format, and performing frequency change rate estimation and compensation to obtain the pilot symbols after frequency change rate compensation;
an FFT transform and acquisition decision module: and performing FFT (fast Fourier transform) on the pilot symbols after frequency change rate compensation, then calculating the ratio of the peak value and the mean value of the frequency spectrum, and performing acquisition judgment.
The frequency change rate estimation and compensation module performs frequency change rate estimation and compensation once every time the shift register receives a new symbol.
The FFT transform and acquisition decision module performs an FFT transform and acquisition decision each time the shift register receives a new symbol.
The FFT conversion and acquisition judgment module carries out acquisition judgment, and specifically comprises the following steps:
and when the ratio is larger than a set threshold, the burst signal is considered to be captured. At this time, a complete burst frame is buffered in the shift register.
The burst signal adopts a distributed pilot frequency frame structure, and the burst frame length is LFIs divided into N sections, each section is LDEach segment comprising 1 pilot symbol and (L)D-1) data symbols. L isDGenerally, the value of (A) is in the range of 10 to 100.
The invention will now be further described with reference to the accompanying drawings.
The receiving and transmitting antenna of the helicopter can be generally only installed below the rotor of the helicopter, and the installation schematic diagram is shown in figure 1. When receiving and transmitting the satellite communication signals, the helicopter satellite communication antenna can be shielded by a rotor wing of the helicopter, and in the flying process of the helicopter, the rotor wing periodically shields an antenna surface, so that airborne received signals are attenuated according to a certain period, as shown in fig. 2.
To assist in receiver signal demodulation, pilot symbols are typically inserted into the physical layer frame structure to assist in signal detection and synchronization. During the period of helicopter rotor shielding, due to the extremely low signal-to-noise ratio (Es/No can be as low as-10 dB or less), in order to enable the receiving end to normally perform burst signal capture and carrier synchronization, a distributed pilot frame structure is adopted (as shown in FIG. 3).
Under the condition that the helicopter rotor is shielded, the demodulation processing flow of the receiving end is as shown in fig. 4, and mainly comprises the following steps: symbol synchronization, burst signal detection, frequency offset and frequency change rate estimation, phase offset estimation and soft demapping. The details are as follows.
(1) Symbol synchronization: receiving an AD sampling signal to obtain an optimal sampling point of a modulation symbol;
(2) and (3) capturing a burst signal: when a new symbol is received, frequency change rate estimation and compensation are executed once, FFT conversion is carried out on the pilot frequency symbol after frequency change rate compensation, then the ratio of the peak value and the average value of the frequency spectrum is calculated, when the ratio is larger than a set threshold, a burst signal is captured, and the whole burst signal is output;
(3) carrier synchronization and soft demapping: and for the positioned burst signal, carrying out carrier frequency offset estimation and compensation by adopting a data-assisted or non-data-assisted method, then carrying out de-mapping processing according to the adopted modulation mode, and outputting soft de-mapping information.
The symbol synchronization, the carrier synchronization and the soft demapping may be processed by many existing methods, and this patent is not described in detail. Only burst acquisition is described in detail below.
The burst frame format includes data symbols and pilot symbols, one pilot symbol is inserted every several data symbols, and the burst frame structure is as shown in fig. 4. Specifically, the burst frame length is LFIs divided into N sections, each section is LDComprising 1 pilot symbol sum (L)D-1) data symbols. The equivalent baseband signal after symbol synchronization can be expressed as
Where s (modulated signal sent by n originating terminal, T)sIs a symbol period, fdIs the carrier frequency offset, alpha is the rate of change of frequency,
to initiate phase bias, w (n is a complex Gaussian random variable with mean of0, variance is
Assume that the scattered pilot symbol is p (N) N ═ 0,1, …, N-1. Shift register depth L for data cacheFThe buffered complex signal data is g (n) n ═ 0,1, …, LF-1). The shift register is cyclically shifted to the left as shown in fig. 5 every time 1 symbol r (n) is received.
The specific processing steps for capturing the burst signal are as follows:
step 1: after each 1 new symbol is received, data-assisted demodulation is performed:
z(n)＝g((n-1)LD)*conj(p(n)),n＝0,1,…,N-1 (2)
step 2: conjugate difference is carried out on the pilot frequency at an interval of M:
x(n)＝z((n+M))*conj(z(n)),n＝0,1,…,N-M-1 (3)
step 3: after x (n is complemented by 0, obtaining
step 4: carry out N2The FFT of the points yields x (k) (k ═ 0,1, …, N2-1), and searching to obtain a position γ where a spectrum peak is located, thereby obtaining a normalized frequency change rate estimation value:
step 5: frequency rate of change compensation for z (n):
step 6: after y (n) is complemented by 0 to obtain
step 7: carry out N3The FFT of the points yields y (k) (k ═ 0,1, …, N3-1), then calculating the spectral peak and mean, resulting in a decision:
step 8: for a set capture threshold J'thIf J 'is not less than J'thIf so, the burst signal is considered to be captured; otherwise, jumping to step 1 to continue capturing.
Under the condition of the carrier rate of 8ksps, the capturing method provided by the patent is simulated, and as shown in fig. 6, when the frequency change rates are 0Hz/s and 2000Hz/s respectively, the peak characteristics of the frequency spectrum are basically consistent. Simulation results show that the capturing method can adapt to larger Doppler dynamics.
Although the present invention has been described with reference to the preferred embodiments, it is not intended to limit the present invention, and those skilled in the art can make variations and modifications of the present invention without departing from the spirit and scope of the present invention by using the methods and technical contents disclosed above.
Those skilled in the art will appreciate that those matters not described in detail in the present specification are well known in the art.
Claims (9)
1. A burst signal capturing method in helicopter and satellite communication is characterized by comprising the following steps:
1) the receiver receives the AD sampling signal, obtains a modulation symbol of the burst signal after symbol synchronization processing, and carries out shift register processing on the modulation symbol by using a shift register;
2) after receiving a new modulation symbol, performing frequency change rate estimation and compensation once to obtain a pilot frequency symbol after frequency change rate compensation;
3) performing FFT according to the pilot frequency symbol after frequency change rate compensation obtained in the step 2) to obtain an FFT result so as to obtain a ratio of a frequency spectrum peak value to an average value;
4) and (4) performing acquisition judgment, finishing acquisition work if judging that the burst signal is acquired, and returning to the step 2) otherwise.
2. The method according to claim 1, wherein the method for performing acquisition decision in step 4) is specifically:
and 3) judging whether the ratio in the step 3) is larger than a threshold, if so, judging that the burst signal is captured, otherwise, jumping to the step 2).
3. The method according to claim 2, wherein the step 2) of obtaining the frequency change rate compensated pilot symbols specifically comprises:
and extracting a pilot frequency symbol from the shift register according to a burst signal frame format, and performing frequency change rate estimation and compensation to obtain the pilot frequency symbol after frequency change rate compensation.
4. A method for capturing burst signals in helicopter and satellite communication according to claim 3, wherein the determination principle of said threshold in step 4) is determined by simulation according to the required capture probability and mis-capture probability indexes.
5. A burst signal acquisition system in helicopter satellite communication for implementing a burst signal acquisition method in helicopter-to-satellite communication according to any one of claims 1 to 4, comprising: the device comprises a shift register, a frequency change rate estimation and compensation module, an FFT (fast Fourier transform) module and a capture judgment module;
a shift register: receiving a modulation symbol of a burst signal obtained after symbol synchronization processing, and carrying out shift register processing on the modulation symbol;
frequency rate of change estimation and compensation module: for sampling points in the shift register, extracting pilot symbols according to a burst signal frame format, and performing frequency change rate estimation and compensation to obtain the pilot symbols after frequency change rate compensation;
an FFT transform and acquisition decision module: and performing FFT (fast Fourier transform) on the pilot symbols after frequency change rate compensation, then calculating the ratio of the peak value and the mean value of the frequency spectrum, and performing acquisition judgment.
6. A system for acquiring burst signals in helicopter satellite communications according to claim 5 and wherein said frequency change rate estimation and compensation module performs frequency change rate estimation and compensation each time a new symbol is received by said shift register.
7. The system of claim 6, wherein the FFT transform and acquisition decision module performs an FFT transform and acquisition decision each time a new symbol is received by the shift register.
8. The system for acquiring burst signals in helicopter satellite communication according to claim 7, wherein the FFT transformation and acquisition decision module makes an acquisition decision, specifically:
and when the ratio is larger than a set threshold, the burst signal is considered to be captured.
9. The system of claim 8, wherein the system further comprises: the burst signal adopts a distributed pilot frequency frame structure, and the burst frame length is LFIs divided into N sections, each section is LDEach segment comprising 1 pilot symbol and (L)D-1) data symbols. L isDIs in the range of 10 to 100.
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