Blind burst signal rapid capture and blind synchronization method

Abstract

The invention discloses a blind burst signal rapid capture and blind synchronization method, which belongs to the technical field of communication, and comprises the following steps that: firstly, a receiving end adopts a burst signal frame without a synchronization head, and generates an evaluation function S (y) by calculating an incoherent value of a signal and a local template by using a CSK modulation characteristic; the joint coarse estimation of the time offset t0 and the frequency offset f0 is realized by accumulating frequency domain correlation peak values in a multi-symbol period; a time-frequency two-dimensional grid search space is constructed, the time resolution T and the frequency resolution F of a grid are dynamically adjusted according to a step length decreasing strategy, a large step length is initially adopted to cover a fully uncertain range, and the step length is gradually reduced to complete capture; based on a judgment mechanism of an incoherent evaluation function S (y) and a dynamic threshold U0, judging the existence of a signal, and calculating a missed start probability Pmd and a virtual start probability Pfa; performing blind synchronization on burst signals; and the information is obtained through CRC decoding. According to the method, rapid and effective signal acquisition and synchronization can be realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of wireless communication, and particularly relates to a blind burst signal fast acquisition and blind synchronization method. BACKGROUND

[0002] In a digital communication system, due to the clock asynchronization between a sending end and a receiving end and the delay problem in a signal transmission process, the receiving end cannot sample at an optimal decision point of each symbol. In addition, the existence of a filter causes a part of the signal to be distorted, which reduces the signal-to-noise ratio of the sampling point data and also causes inter-symbol interference, increases the bit error rate of signal demodulation, and deteriorates the performance of the communication system. Therefore, realizing fast and effective signal acquisition and synchronization is the key to improving the performance of the communication system. SUMMARY

[0003] Therefore, the application aims to provide a blind burst signal fast acquisition and blind synchronization method, which can solve the above technical problems.

[0004] To achieve the above object, the application provides the following technical scheme. The application discloses a blind burst signal fast acquisition and blind synchronization method, which comprises the following steps. Step one: the receiving end uses a burst signal frame without a synchronization header, utilizes the CSK modulation characteristics, and generates an evaluation function S(y) by calculating the non-coherent value of the signal and a local template; Step two: the joint coarse estimation of a time offset t0 and a frequency offset f0 is realized by accumulating the frequency domain correlation peak values in a plurality of symbol periods; the calculation of the frequency domain correlation peak values comprises the following steps: the received signal is divided into a plurality of data blocks of M symbol periods, the frequency domain correlation is independently performed on each data block, and the amplitude square peak value is extracted; the energy of the M peak values is accumulated as the output of the evaluation function; Step three: a time-frequency two-dimensional grid search space is constructed, the time resolution T and the frequency resolution F of the grid are dynamically adjusted according to a step decrement strategy, a large step is initially used to cover the whole uncertain range, and the step is gradually reduced to complete the acquisition; Step four: based on the judgment mechanism of the non-coherent evaluation function S(y) and a dynamic threshold U0, the existence of the signal is judged, and the miss detection probability Pmd and the false alarm probability Pfa are calculated; Step five: blind synchronization of the burst signal; Step six: information is obtained through CRC decoding.

[0005] Further, the expression of the evaluation function S(y) is specifically as follows: wherein y represents a received baseband signal, c represents a local template, and y represents a non-coherent value. τ: the locally generated CSK reference chip sequence, tau is the chip phase offset to be searched; Delta f is the frequency offset to be compensated; k is an index variable, representing the current accumulated symbol period number, yk is the baseband sampling data block of the received signal in the kth symbol period; M is the number of accumulated symbol periods; FFT(·) and IFFT(·) are fast Fourier transform and its inverse transform; and * is a complex conjugate operation.

[0006] Further, step two is specifically: In the accumulated evaluation function, the time delay corresponding to the global maximum value is found And the frequency offset The coarse estimation values of the time offset t0 and the frequency offset f0 are: , .

[0007] Further, in step four, for the evaluation function S(y), a high value is taken when H1 is true, and a low value is taken when H0 is true; Missed start probability: Pmd=P(S(y)<U0|H1); False start probability: Pfa=P(S(y)≥U0|H0).

[0008] Further, step five specifically includes the following steps: Coarse chip synchronization: coarse chip synchronization, which reduces the time error on the chip synchronization to within a single CSK symbol; Symbol synchronization: based on the overmodulation sequence, the CSK symbol synchronization is completed, and the chip synchronization time error is further reduced; Fine frequency offset synchronization: fine frequency offset estimation to suppress the remaining frequency offset error; Code-aided chip fine synchronization: combined with the LDPC error correction coding check node reliability measure to realize chip fine synchronization.

[0009] The beneficial effects of the present application are: The traditional matched filter needs to accurately synchronize the carrier phase, while the present scheme eliminates the phase dependence through non-coherent accumulation (modulo square), is suitable for blind acquisition scenarios, converts the time domain correlation into frequency domain complex conjugate multiplication by using the convolution theorem of Fourier transform, reduces the operation time, and can realize fast acquisition. At the same time, the traditional method adopts fixed step search, and the present scheme can take into account the search speed and accuracy through the step decreasing strategy of the time-frequency grid.

[0010] Through the technical scheme of the present application, the receiving end uses only the burst signal frame containing information load to perform burst signal acquisition, the CSK demodulation converts the time domain correlation operation into frequency domain multiplication, the correlation peak value is accumulated to complete the burst signal fast acquisition and blind synchronization, the signal acquisition-demodulation detection-correction integrated design of the synchronization header and the coded message data is realized, and the inter-symbol interference caused by time delay spread can be offset Additional advantages, objects, and features of the application will be apparent to those skilled in the art upon examination of the following detailed description, and it is intended that any such advantages, objects, and features of the present application be within the scope of the claimed application. The objectives and other advantages of the application will be realized and attained by the apparatus particularly pointed out in the written description and claims hereof as well as the appended drawings. BRIEF DESCRIPTION OF DRAWINGS

[0011] In order to make the objectives, technical solutions and beneficial effects of the present application clearer, the present application provides the following drawings for description: Figure 1 Flow chart of the method of the present application; DETAILED DESCRIPTION As shown in the drawings, Figure 1 The disclosed blind burst signal fast acquisition and blind synchronization method comprises the following steps: Step one: the receiving end uses a burst signal frame without a synchronization header to perform burst signal acquisition using a burst signal frame containing only information load, uses the CSK modulation characteristics to convert the time domain correlation operation into a frequency domain complex conjugate multiplication operation, and generates an evaluation function S(y) by calculating the non-coherent value of the signal and the local template; the receiving end uses a buffer with a length of 2Nq chips, Nq being the number of chips of the maximum expected time offset, the buffer containing the expected frame, the size being related to the uncertainty of symbol synchronization under low signal-to-noise ratio; Step two: the joint coarse estimation of the time offset t0 and the frequency offset f0 is realized by accumulating the frequency domain correlation peak values in a multi-symbol period; the calculation of the frequency domain correlation peak value comprises: the received signal is divided into M data blocks of symbol periods, each block containing N chips, the frequency domain correlation is independently performed on each data block, and the amplitude square peak value is extracted, and the energy of the M peak values is accumulated as the output of the evaluation function.

[0012] Step three: a time-frequency two-dimensional grid search space is constructed, the time resolution T and the frequency resolution F of the grid are dynamically adjusted according to the step-down strategy, a large step is used initially to cover the full uncertainty range, the step of 1 / 2 chip is the large step, and then the step is gradually reduced to a fine step to complete the acquisition; the traditional method uses a fixed step search, and the step-down strategy of the time-frequency grid, such as gradually refining from 1 / 2 chip to 1 / 8 chip, can take into account the search speed and accuracy.

[0013] Step four: based on the judgment mechanism of the non-coherent evaluation function S(y) and the dynamic threshold U0, the signal existence is judged, and the miss detection probability Pmd and the false alarm probability Pfa are calculated; Step five: blind synchronization of the burst signal; Step six: information is obtained through CRC decoding.

[0014] In this embodiment, the accumulation of the frequency domain correlation peak value is realized through the following steps: 1) The received signal is divided into M consecutive data blocks y1, y2, …, yM with symbol period length Tsym, each block containing N chips; 2) The frequency domain correlation operation is independently performed on each data block yk , and the amplitude square peak value is extracted ; 3) The peak values of M symbol periods are accumulated to obtain the final evaluation function , which is used for signal existence decision.

[0015] The expression of the evaluation function S(y) is as follows: Wherein, y: the received baseband signal (complex form, containing time offset t0 and frequency offset f0), c τ : the locally generated CSK reference chip sequence, τ is the chip phase offset to be searched; Δf is the frequency offset to be compensated; k is an index variable, representing the symbol period sequence number currently accumulated, yk is the baseband sampling data block of the received signal in the kth symbol period; M is the number of accumulated symbol periods (used to improve the detection probability under low signal-to-noise ratio); FFT(·) and IFFT(·): fast Fourier transform and its inverse transform; ∗: complex conjugate operation.

[0016] The real-time performance is significantly improved by converting the time domain correlation into frequency domain multiplication; In a low signal-to-noise ratio, the correlation peak in a single symbol period may be overwhelmed by noise. By accumulating the energy of M symbol periods, the signal-to-noise ratio is improved.

[0017] In this embodiment, step two is specifically: In the accumulated evaluation function, find the time delay and frequency offset corresponding to the global maximum value, and the coarse estimation value of the time offset t0 and the frequency offset f0 is: , .

[0018] In this embodiment, in step four, the evaluation function S(y) takes a high value when H1 is true, and takes a low value when H0 is true; Missed alarm probability: Pmd=P(S(y)<U0|H1); When the signal actually exists (H1 is true), the probability that the detection algorithm fails to correctly determine the existence of the signal; For example, the burst signal has reached the receiving end, but the system does not trigger the capture process, resulting in data loss. When the threshold is too high, the probability increases.

[0019] False alarm probability: Pfa = P(S(y) ≥ U0 | H0). The probability that the detection algorithm falsely detects a signal when there is no signal (H0 is true, only noise). For example: noise is falsely detected as valid signal, triggering subsequent invalid demodulation or synchronization operations. The probability increases when the threshold is too low.

[0020] In this embodiment, step five specifically includes the following steps: Chip coarse synchronization: coarse chip synchronization, reducing the time error on chip synchronization to within a single CSK symbol; Symbol synchronization: based on the overmodulation sequence, complete the CSK symbol synchronization, while further reducing the time error of chip synchronization; Fine frequency offset synchronization: fine frequency offset estimation to suppress the remaining frequency offset error; Code-aided chip fine synchronization: combined with the LDPC error correction coding check node reliability measure to achieve chip fine synchronization.

[0021] Through the different steps of the above blind synchronization process, from the initial coarse time / frequency estimation (t1, f1) to the final correct time / frequency estimation (t4, f3), the estimation value is infinitely close to the actual value.

[0022] Finally, it should be pointed out that the above preferred embodiments are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present application.

Claims

1. A method for fast acquisition of blind burst signals and blind synchronization, characterized in that, The method comprises the following steps: Step one: the receiving end adopts a burst signal frame without a synchronization header, uses the CSK modulation characteristics, and generates an evaluation function S(y) by calculating the non-coherent value of the signal and the local template; Step two: the joint coarse estimation of the time offset t0 and the frequency offset f0 is realized by accumulating the frequency domain correlation peak value in multiple symbol periods; The calculation of the frequency domain correlation peak value comprises: dividing the received signal into M symbol period data blocks, independently performing frequency domain correlation on each data block, extracting the amplitude square peak value, and accumulating the energy of the M peak values as the evaluation function output; Step three: a time-frequency two-dimensional grid search space is constructed, the time resolution T and the frequency resolution F of the grid are dynamically adjusted according to the step decrement strategy, the initial large step is used to cover the whole uncertainty range, and the step is gradually reduced to complete the acquisition; Step four: based on the judgment mechanism of the non-coherent evaluation function S(y) and the dynamic threshold U0, the signal existence is judged, and the miss detection probability Pmd and the false alarm probability Pfa are calculated; Step five: burst signal blind synchronization; Step six: information is obtained through CRC decoding.

2. The method of blind burst signal fast acquisition and blind synchronization as claimed in claim 1, wherein, The expression of the evaluation function S(y) is specifically: where y: received baseband signal, c τ : locally generated CSK reference chip sequence, τ: chip phase offset to be searched; Δf: frequency offset to be compensated; k: index variable, representing the current accumulated symbol period number, yk: baseband sampling data block of the received signal in the kth symbol period; M: accumulated symbol period number; FFT(·) and IFFT(·): fast Fourier transform and its inverse transform; ∗: complex conjugate operation.

3. A method for fast acquisition of blind burst signals and blind synchronization according to claim 2, characterized in that, Step two is specifically: In the accumulated evaluation function, find the global maximum value corresponding to the time delay and frequency offset , the coarse estimate of the time offset t0and the frequency offset f0is: , .

4. The method of blind burst signal fast acquisition and blind synchronization of claim 3, wherein, In step four, the evaluation function S(y) takes a high value when H1 is true, and takes a low value when H0 is true; Miss detection probability: Pmd=P(S(y)<U0|H1); False alarm probability: Pfa=P(S(y)≥U0|H0).

5. A method for fast acquisition of blind burst signals and blind synchronization according to claim 4, characterized in that, Step five specifically comprises the following steps: Chip coarse synchronization: coarse chip synchronization, which reduces the time error on the chip synchronization to within a single CSK symbol; Symbol synchronization: based on the overmodulation sequence, the CSK symbol synchronization is completed, and the chip synchronization time error is further reduced; Fine frequency offset synchronization: fine frequency offset estimation is performed to suppress the remaining frequency offset error; Code-aided chip fine synchronization: combined with the LDPC error correction coding check node reliability measure, chip fine synchronization is realized.

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