CN104852876A - Wireless aviation burst communication system - Google Patents

Abstract

The invention discloses a wireless aviation burst communication system, which comprises a burst frame construction module, a receiving digital front-end processing module, a burst detector, a carrier and phase parameter extraction and recovery module, and a timing parameter extraction and recovery module, wherein the burst frame construction module is used for constructing a burst frame, and the burst frame is composed of an AGC training sequence, two identical repeated CAZAC training sequences, and a data block; the receiving digital front-end processing module is used for acquiring an initial demodulation signal with frequency offset, phase offset and timing errors; the burst detector is used for adopting the repeated CAZAC training sequences for carrying out matched filter on the initial demodulation signal, acquiring a burst sign and outputting two related peak values and related peak sidelobe values; the carrier and phase parameter extraction and recovery module is used for estimating carrier and phase parameters and completing recovery; and the timing parameter extraction and recovery module completes timing recovery. The burst frame detection probability can be effectively improved, and complexity of burst communication carrier, phase and timing recovery is reduced.

Description

A kind of aviation wireless burst communication system

Technical field

The invention belongs to wireless communication technology field, is a kind of implementation method relating to aviation wireless communication burst input, timing and carrier synchronization parameter Estimation.

Background technology

Burst communication system is wireless communication system information launched with the short period, because signal open-assembly time in transmitting procedure is shorter, effectively reduces the probability that signal of communication is scouted, intercepted and captured, thus improves the antijamming capability of communication system.The feature of burst communication determines and is difficult to realize carrier synchronization and Timing Synchronization by feedback control loop in this type systematic, burst communication receiving terminal will demodulate information first must carry out burst signal detection, detect and carry out timing, carrier parameter estimation and recovery again after signal arrives, complete the operations such as demodulating and decoding afterwards, recover originating data.

Burst communication system adopts usually based on data-aided burst signal detection method, mainly contains following several method: 1, frequency domain detection method.Received signal strength is transformed to frequency domain, calculates the characteristic spectrum range value of auxiliary data, then compare with the thresholding of setting, be greater than thresholding and be judged to signal arrival.This method has how many sampling point to participate in calculating the FFT that will calculate how many points, and operand is larger, and decision threshold can change along with signal level.2, power detection method.Calculate the power of Received signal strength and compare adjudicate with the thresholding of setting.It is insensitive that the advantage of this method is that thresholding is arranged carrier wave frequency deviation, but thresholding is also relevant with signal amplitude, and the dynamic range of signal is limited.3, matching matrix.This method is responsive to carrier wave frequency deviation, needs dynamic decision, the bad setting of thresholding.

Summary of the invention

The object of the invention is to solve the deficiencies in the prior art, propose a kind of aviation wireless burst communication system, utilize two multiple CAZAC training sequence as training sequence, carry out burst by a kind of bimodal detection scheme newly to detect, program amplitude to received signal and signal to noise ratio insensitive, two correlation peaks can be utilized simultaneously to carry out carrier wave, phase place and timing parameters and to estimate.The method can improve the detection probability of burst frame effectively, reduces the complexity of burst communication carrier wave, phase place and Timed Recovery simultaneously.

Summary of the invention of the present invention is achieved through the following technical solutions:

A kind of aviation wireless burst communication system, comprises the burst frame being positioned at transmitting terminal and builds module, is positioned at the reception digital front-end processing module of receiving terminal, burst detector, carrier wave, phase parameter extraction and recovers module and timing parameters extraction and recover module;

Described burst frame builds module and is used for encoding to information source and burst frame structure, and by sign map and front-end processing, completes the burst transmissions to information; Described burst frame is made up of AGC training sequence, two identical multiple CAZAC training sequences, data blocks, and the spacing of two multiple CAZAC training sequences are D symbol, and D is positive integer;

Described reception digital front-end processing module is used for carrying out initial down-conversion and filtering to the ADC input signal carrying out bandpass sampling, obtains the initial demodulation signal with frequency deviation, skew and timing error; And initial demodulation signal feeding buffer is carried out buffer memory;

Described burst detector carries out matched filtering for adopting multiple CAZAC training sequence to initial demodulation signal, if former and later two correlation peaks exceed thresholding, provides burst and indicates and export two correlation peaks and relevant peaks side lobe levels;

Described carrier wave, phase parameter extract and recover module and be used for utilizing two relevant peaks and relevant peaks side lobe levels to carry out carrier error parameter, phase error parameter Estimation, and complete carrier wave, phase recovery according to the burst original position in a buffer that burst mark is determined to initial demodulation signal;

Described timing parameters extracts and recovers module and is used for utilizing two relevant peaks and relevant peaks side lobe levels to carry out timing error parameter estimation, to the data completion timing recovery completing carrier wave, phase recovery, and delivers to subsequent decoding module recovery information.

Preferably, described buffer adopts circular buffer, and buffer depth is greater than 1 bursty data and always counts.

Preferably, described burst detector two correlation peaks are carried out thresholding relatively before, first energy normalizing is carried out to the data of the highest two the correlation peak place data segments of matching degree.

Preferably, the number of the relevant peaks side lobe levels of described burst detector output is each two of the left and right of relevant peaks.

Preferably, described carrier wave, phase parameter extract and recover module by first corresponding correlation peak during the thresholding of mistake burst detector and second correlation peak are carried out difference, obtain carrier error parameter; By using phase value corresponding to first relevant peaks as initial phase value, then obtain digital NCO phase value with this initial phase value and carrier error parameter; With digital NCO phase value, carrier phase recovery is carried out to data in buffer.

Preferably, described timing parameters extracts and recovers module and obtains timing error parameter by following formula:

Wherein M is that FFT counts, and k is over-sampling rate, and q is for specifying frequency, and N is sequence hangover.

Preferably, described timing parameters extracts and recovers module and adopts cubic interpolation device to carry out resampling, and described cubic interpolation device is shown below:

$\left\{\begin{array}{c}{C}_{-2}=\frac{1}{6}{\mathrm{\τ}}^3-\frac{1}{6}\mathrm{\τ}\\ C_{-1}=-\frac{1}{2}{\mathrm{\τ}}^3+\frac{1}{2}{\mathrm{\τ}}^2+\mathrm{\τ}\\ C_0=\frac{1}{2}{\mathrm{\τ}}^3-{\mathrm{\τ}}^2-\frac{1}{2}\mathrm{\τ}+1\\ C_1=-\frac{1}{6}{\mathrm{\τ}}^3+\frac{1}{2}{\mathrm{\τ}}^2-\frac{1}{3}\mathrm{\τ}\end{array}\right..$

Preferably, aviation wireless burst communication system, by changing the space D of former and later two identical multiple CAZAC training sequences, realizes carrying out rapid adjustment to spectrum estimation scope and precision.

The present invention has following several technical essential:

1, transmitting terminal is using two multiple CAZAC training sequence as synchronizing sequence, completes burst frame and builds.Burst signal detection false alarm probability is reduced by two CAZAC Sequence Detection;

2, to through first down-conversion and filtered data, what adopt matched filter to complete to multiple CAZAC sequence is real-time relevant, is completed the detection of burst due in by a kind of burst detector of the novel pair of training sequence based on energy normalizing;

3, according to the burst due in that burst detector obtains, obtain that matched filter obtains with correlation peak R that is two multiple CAZAC training sequence ₁and R (0) ₂(0); And extract former and later two correlations R of correlation peak ₁(-2), R ₁(-1), R ₁(1), R ₁and R (2) ₂(-2), R ₂(-1), R ₂(1), R ₂(2); Adopt correlation and side lobe levels thereof to complete carrier wave, phase place and timing parameters to extract, reduce burst communication system carrier timing parameter extraction difficulty.

Beneficial effect of the present invention is:

1, adopt CAZAC sequence as training sequence, its good autocorrelation performance ensure that burst detects and net synchronization capability; Have employed a kind of burst detection scheme newly, improve traditional mode using fixed threshold as detection threshold, adopt the ratio of relevant peaks modulus value and performance number as detected value, the program has signal strength signal intensity and the insensitive characteristic of SNR;

3, adopt two CAZAC sequence as training sequence, directly can obtain carrier wave and phase information by former and later two correlation peaks, and extract according to the left and right secondary lobe completion timing control information of correlation peak, realize simple;

3, realize excellent performance, this programme detection perform is excellent, and parameter Estimation is simple, is applicable to burst communication system.Adopt the OQPSK burst communication system detected based on this burst communication signals to survey error performance as shown in Figure 9, Figure 10, visible employing the inventive method excellent performance, has good error performance.

Accompanying drawing explanation

Fig. 1 is the schematic flow sheet of a kind of aviation wireless burst communication of the present invention system;

Fig. 2 is the structural representation of burst frame in the present invention;

Fig. 3 is the structural representation of burst detector in the present invention;

The Output rusults of burst detector when Fig. 4 is varying input signal amplitude in embodiment;

The Output rusults of burst detector when Fig. 5 is different SNR in embodiment;

Fig. 6 is the detection perform schematic diagram of burst detector in the present invention;

Fig. 7 is carrier wave in the present invention, phase parameter extracts and recover the carrier phase recovery performance schematic diagram of module;

Fig. 8 is that in the present invention, timing parameters extracts and recovers the timing parameters estimated performance schematic diagram of module;

Fig. 9 is that under awgn channel, the present invention surveys error performance schematic diagram;

Figure 10 is invention actual measurement error performance schematic diagram under Rician channel.

Embodiment

Below in conjunction with drawings and Examples, the present invention is described in further detail.

As shown in Figure 1, the difference of the present invention's a kind of aviation wireless burst communication system and continuous communiction system be that burst frame builds, burst signal detection, timing subcarriers parameter Estimation and recovery.The present invention mainly comprises the burst frame being positioned at transmitting terminal and builds module, is positioned at the reception digital front-end processing module of receiving terminal, burst detector, carrier wave, phase parameter extraction and recovers module and timing parameters extraction and recover module.By encoding to information source and burst frame structure, and by sign map and front-end processing, complete the burst transmissions to information; Initial down-conversion and filtering are carried out to the ADC input signal carrying out bandpass sampling, obtains the initial demodulation signal with frequency deviation, skew and timing error; Buffer memory is carried out to initial demodulation signal, and carries out matched filtering with multiple CAZAC training sequence, adopt burst detector to complete burst and detect, provide burst and indicate and obtain two correlation peaks and relevant peaks side lobe levels; Utilize relevant peaks and side lobe levels thereof to carry out parameter Estimation, obtain carrier wave, phase place and timing parameters; Determine burst original position in the buffer by burst mark, complete carrier wave, phase place and Timed Recovery, carry out adjudicating to demodulation result, and deliver to subsequent decoding module and can recover information.

Below modules is elaborated.

(1) burst frame builds

With reference to Fig. 2, give burst frame structure of the present invention.As described in Figure, burst frame of the present invention is made up of AGC training sequence, the multiple CAZAC training sequence of two identical 32 symbols, data block.Wherein AGC training sequence is used for burst transmissions power stability, can determine this sequence length according to real system; Two multiple CAZAC training sequence is used for burst arrival and detects and carrier wave/phase place/timing parameters extraction, and the spacing of two multiple CAZAC training sequences is D symbol, and D value will affect carrier estimation scope, can according to system requirements flexible design; Data block is for filling business information.This burst frame builds link and builds module corresponding to the burst in Fig. 1.

(2) digital front-end processing module is received

For carrying out digital front-end process to the received signal, primarily of Digital Down Convert, filtering etc., final output 4 times of over-sampling matched filterings export.This Output rusults also exists carrier wave/phase residual error needs calibration, and also there is timing error needs to recover.

Owing to adopting burst frame structure as described in Figure 2, only receive second CAZAC complex sequences and could judge that bursty data arrives, therefore need to cushion bursty data.In the present invention, bursty data buffer adopts circular buffer, and buffer depth is always counted slightly larger than 1 bursty data, and before ensureing continuing process in the completed, current burst frame data are uncovered.

(3) burst detector

As described in Figure 3, the data wherein entering burst detector are 2 times of character rate over-sampling data after digital front-end process to the burst detector adopted in the present invention.(because burst detector only needs 2 times of over-samplings, and digital front-end output is 4 times of over-sampling rates, and the information therefore entering burst detector is data after 4 times of over-sampling rate data dot interlaces extract.)

If transmit as s (t), if through awgn channel, Received signal strength is through down-conversion and local carrier quadrature downconvert, and after low pass filter, the Received signal strength obtained is:

$r\left(t\right)=s\left(t\right)e^{j(\mathrm{\Δwt}+{\mathrm{\θ}}_0)}+n\left(t\right)$

In formula, Δ w is frequency deviation, θ ₀for carrier wave initial phase difference, n (t) is multiple Gaussian noise.Have after above formula is sampled

$r\left(k\right)=s\left(k\right)e^{j(\mathrm{\Δwk}{T}_s+{\mathrm{\θ}}_0)}+n\left(k\right)$

R (k) carries out related operation with multiple CAZAC training sequence to the received signal, will produce two relevant peaks when Received signal strength mates with training sequence.

First relevant peaks is

$\begin{array}{c}R\left(k\right)=\underset{m=0}{\overset{L-1}{\mathrm{\Σ}}}r(m+k)c_L^{*}\left(k\right)\\ =R_{\mathrm{cs}}\left(k\right)\frac{e^{\mathrm{j\ΔwT}}-e^{\mathrm{j\Δw}(L+1)T}}{1-e^{\mathrm{j\ΔwT}}}{e}^{\mathrm{j\θ}}+v_1\end{array}$

Second relevant peaks is

$\begin{array}{c}R(k+D)=\underset{m=0}{\overset{L-1}{\mathrm{\Σ}}}x(m+k+D)c_L^{*}\left(k\right)\\ =R_{\mathrm{cs}}(k+D)e^{\mathrm{j\ΔwDT}}\frac{e^{\mathrm{j\ΔwT}}-e^{\mathrm{j\Δw}(L+1)T}}{1-e^{\mathrm{j\ΔwT}}}{e}^{\mathrm{j\θ}}+v_2\end{array}$

Wherein, D is spacing between two training sequences, R _csk () is training sequence and the correlation function receiving data, only have to receive when data are mated with training sequence just to there will be peak value.

Burst frame structure as described in Figure 2, adopt two multiple CAZAC training sequences, wherein two training sequences are identical.Convolution two correlation peaks can obtain

$R(k+D)R^{*}\left(k\right)=R_{\mathrm{cs}}(k+D)R_{\mathrm{cs}}^{*}\left(k\right)e^{\mathrm{j\ΔwDT}}+V$

When only having former and later two training sequences all to mate in above formula, can be just a very large real number, V be noise item.When receiving data and mating with training, be correlated with and be equivalent to matched filtering, in order to eliminate frequency deviation phase effect, delivery has:

$\left|R_0\right|\≈\underset{m=0}{\overset{L-1}{\mathrm{\Σ}}}\left|r(m+k)\right|$

$\left|R_D\right|\≈\underset{m=0}{\overset{L-1}{\mathrm{\Σ}}}\left|r(m+k+D)\right|$

At this moment have

|R(k+D)R ^*(k)|≈|R ₀||R _D|

Above formula becomes positive correlation with signal energy, in order to avoid fixed threshold to amplitude and noise more responsive, can be normalized according to the energy higher value of two the highest reception data segments of matching degree.Burst detector through energy normalizing exports and can be write as following formula

$d\left(k\right)=\frac{\left|R(k+D)R^{*}\left(k\right)\right|}{\max \{P(k+D),P\left(k\right)\}}\≈\frac{\left|R_0\right|\left|R_D\right|}{\max \{P\left(k\right),P(k+D)\}}$

When above formula crosses thresholding, then think that burst arrives, and produce relevant peaks mark, at this moment record the correlation peak of correlation R (k) as Received signal strength and first CAZAC sequence, R (k+D) is as the correlation peak of Received signal strength and second CAZAC sequence.Meanwhile, each 2 relevant peaks side lobe levels by the original position of burst in relevant peaks mark determination buffer and about exporting correlation peak and relevant peaks.

With reference to burst detector structure described in Fig. 3, carried out Computer Simulation to the input signal of signal to noise ratio identical under different amplitude, simulation result as shown in Figure 4; Carried out Computer Simulation to the signal of input amplitude identical under different signal to noise ratio, simulation result as shown in the figure.From the simulation result of Fig. 4 and figure, this burst detect and to input signal amplitude size and signal to noise ratio size insensitive.Fig. 6 gives the detection perform of detector, and this detector known has very low detection threshold and excellent detection perform.

In this module, mainly contain following feature:

Because former and later two multiple CAZAC training sequences have good autocorrelation performance, effectively detection probability can be improved; According to the burst detector that two multiple CAZAC training sequences build, effectively false alarm probability can be reduced by the positional information between two CAZAC.

By the method for energy normalized, reduce the susceptibility of burst detector to signal amplitude and signal to noise ratio, fixed threshold can be adopted under difference inputs amplitude and signal to noise ratio.

(4) carrier wave, phase parameter extract and recover

Consider that the amounts of frequency offset of signal in a burst changes very little, therefore can think that difference that frequency deviation causes be slope is frequency spectrum, initial value is the straight line of first relevant peaks phase place.Thus, by the carrier error value estimating to obtain and phase value then with this phase value for initial value obtains digital NCO phase value, carrier phase recovery is carried out to data in buffer area.

First correlation peak and second correlation peak of correspondence of prescribing a time limit moving into one's husband's household upon marriage in burst detector carry out difference, can obtain

$R(k+D)R^{*}\left(k\right)=R_{\mathrm{cs}}(k+D)R_{\mathrm{cs}}^{*}\left(k\right)e^{\mathrm{j\ΔwDT}}+V$

Because two training sequences adopt identical multiple CAZAC training sequence, thus move into one's husband's household upon marriage in limited time, in above formula for real number, ignore noise item, so just can extract carrier error estimated value

Due to arg{R in above formula (k+D) R ^*(k) } span be (-π, π], thus the estimable relative frequency deviation scope of this algorithm is

Phase estimation can extract phase value corresponding to first relevant peaks, and as initial phase value, this phase estimation value is as follows:

Carrier phase recovery numeral NCO phase place generate as shown in the formula:

According in the phase recovery of NCO shown in above formula data buffer zone for data, carrier wave and phase recovery can be completed.As shown in Figure 7, this carrier phase recovery scheme known can directly utilize burst detection relevant peaks to carry out parameter extraction to carrier phase recovery Computer Simulation performance, realizes simple, excellent performance.

In this module, mainly contain following feature:

1, carry out fitting a straight line by the phase value of former and later two identical multiple CAZAC sequences, carry out carrier wave and phase recovery.

2, by changing former and later two identical multiple CAZAC sequence space D, rapid adjustment can be carried out to spectrum estimation scope and precision;

(5) timing parameters extracts and recovers

The modulus value of CAZAC complex correlation value has sharp-pointed correlation properties, and utilize the frequency domain time delay theorem of DFT algorithm known, timing offset will be presented as the phase error of correlation peak DFT, and Timing error estimate obtains by following formula.

Wherein M is that FFT counts, and k is over-sampling rate, and q is for specifying frequency, and N is sequence hangover.In the present invention, M value is 4, q value is 1, adopt 25 correlation analyses of trailing, wherein 5 correlations are the relevant peaks side lobe levels of correlation peak and each 2 of front and back thereof, and in conjunction with former and later two relevant peaks, common root carries out Timing error estimate according to 10 correlations.

Timed Recovery adopts cubic interpolation device to carry out resampling, and cubic interpolation device is shown below.

$\left\{\begin{array}{c}{C}_{-2}=\frac{1}{6}{\mathrm{\τ}}^3-\frac{1}{6}\mathrm{\τ}\\ C_{-1}=-\frac{1}{2}{\mathrm{\τ}}^3+\frac{1}{2}{\mathrm{\τ}}^2+\mathrm{\τ}\\ C_0=\frac{1}{2}{\mathrm{\τ}}^3-{\mathrm{\τ}}^2-\frac{1}{2}\mathrm{\τ}+1\\ C_1=-\frac{1}{6}{\mathrm{\τ}}^3+\frac{1}{2}{\mathrm{\τ}}^2-\frac{1}{3}\mathrm{\τ}\end{array}\right.$

As described in Figure 8, the timing synchronization algorithm as seen from the figure based on CAZAC correlation is insensitive to system frequency deviation for Timed Recovery Computer Simulation performance, can carry out reliable timing synchronisation information estimation under hostile transmission environment.

In this module, main feature is:

Correspond to the principle of frequency domain phase shift based on time domain time shift, carry out parameter Estimation by 10 correlations after former and later two relevant peaks and neighbouring brachymemma thereof, and adopt cubic interpolation device to carry out the recovery of resampling completion timing

Be understandable that, for those of ordinary skills, can be equal to according to technical scheme of the present invention and inventive concept thereof and replace or change, and all these change or replace the protection range that all should belong to the claim appended by the present invention.

Claims (8)

1. an aviation wireless burst communication system, comprise the burst frame being positioned at transmitting terminal and build module, be positioned at the reception digital front-end processing module of receiving terminal, burst detector, carrier wave, phase parameter extraction and recover module and timing parameters extraction and recover module, it is characterized in that:

Described burst frame builds module and is used for encoding to information source and burst frame structure, and by sign map and front-end processing, completes the burst transmissions to information; Described burst frame is made up of AGC training sequence, two identical multiple CAZAC training sequences, data blocks, and the spacing of two multiple CAZAC training sequences are D symbol, and D value is positive integer;

Described reception digital front-end processing module is used for carrying out initial down-conversion and filtering to the ADC input signal carrying out bandpass sampling, obtains the initial demodulation signal with frequency deviation, skew and timing error; And initial demodulation signal feeding buffer is carried out buffer memory;

Described burst detector carries out matched filtering for adopting multiple CAZAC training sequence to initial demodulation signal, if former and later two correlation peaks exceed thresholding, provides burst and indicates and export two correlation peaks and relevant peaks side lobe levels;

Described carrier wave, phase parameter extract and recover module and be used for utilizing two relevant peaks and relevant peaks side lobe levels to carry out carrier error parameter, phase error parameter Estimation, and complete carrier wave, phase recovery according to the burst original position in a buffer that burst mark is determined to initial demodulation signal;

Described timing parameters extracts and recovers module and is used for utilizing two relevant peaks and relevant peaks side lobe levels to carry out timing error parameter estimation, to the data completion timing recovery completing carrier wave, phase recovery, and delivers to subsequent decoding module recovery information.

2. a kind of aviation wireless burst communication system according to claim 1, it is characterized in that described buffer adopts circular buffer, buffer depth is greater than 1 bursty data block and always counts.

3. a kind of aviation wireless burst communication system according to claim 1, it is characterized in that described burst detector two correlation peaks are carried out thresholding relatively before, first energy normalizing is carried out to the data of the highest two the correlation peak place data segments of matching degree.

4. a kind of aviation wireless burst communication system according to claim 1, is characterized in that the number of the relevant peaks side lobe levels that described burst detector exports is each two of the left and right of relevant peaks.

5. a kind of aviation wireless burst communication system according to claim 1, it is characterized in that described carrier wave, phase parameter extract and recover module by first corresponding correlation peak during the thresholding of mistake burst detector and second correlation peak are carried out difference, obtain carrier error parameter; By using phase value corresponding to first relevant peaks as initial phase value, then obtain digital NCO phase value with this initial phase value and carrier error parameter; With digital NCO phase value, carrier phase recovery is carried out to data in buffer.

6. a kind of aviation wireless burst communication system according to claim 1, is characterized in that described timing parameters extracts and recovers module and obtains timing error parameter by following formula:

Wherein M is that FFT counts, and k is over-sampling rate, and q is for specifying frequency, and N is sequence hangover.

7. a kind of aviation wireless burst communication system according to claim 1, it is characterized in that described timing parameters extracts and recovers module and adopt cubic interpolation device to carry out resampling, described cubic interpolation device is shown below:

$\left\{\begin{array}{c}{C}_{-2}=\frac{1}{6}{\mathrm{\τ}}^3-\frac{1}{6}\text{\τ}\\ C_{-1}=-\frac{1}{2}{\mathrm{\τ}}^3+\frac{1}{2}{\mathrm{\τ}}^2+\mathrm{\τ}\\ C_0=\frac{1}{2}{\mathrm{\τ}}^3-{\mathrm{\τ}}^2-\frac{1}{2}\mathrm{\τ}+1\\ C_1=-\frac{1}{6}{\mathrm{\τ}}^3+\frac{1}{2}{\mathrm{\τ}}^2-\frac{1}{3}\mathrm{\τ}\end{array}\right..$

8. a kind of aviation wireless burst communication system according to claim 1, is characterized in that the space D by changing former and later two identical multiple CAZAC training sequences, realizing carrying out rapid adjustment to spectrum estimation scope and precision.