Partially matched filtering signal acquisition method based on discrete group pilot structure

Abstract

The present invention discloses a partial matched filtering signal capture method based on a discrete group pilot structure, which mainly solves the problem of low frequency domain capture accuracy in the prior art. The implementation scheme is: 1) inserting a local group pilot sequence into an encoded information sequence, modulating it and sending it into a channel for transmission; 2) the receiving end stores the received signal in a delay register: 3) grouping the signal in the delay register and extracting the received group pilot sequence, using a segmented matched filter to perform correlation operations on the local pilot group sequence and the received pilot group sequence, performing FFT transformation on the related output value and taking the modulus value, recording the maximum value therein, and delaying the received signal by one sampling signal; 4) looping 3) comparing the recorded maximum value sequence with the set threshold to determine the capture result, and calculating the timing deviation estimate and the frequency deviation estimate when the capture is successful. The present invention reduces the sampling rate, improves the frequency domain capture accuracy, and can be used in high-speed transmission burst digital communication systems.

Description

Technical Field

[0001] The invention belongs to the technical field of wireless communication, and in particular relates to a signal capture method which can be used in a high-speed transmission burst digital communication system. Background Art

[0002] The synchronous capture of signals has always been an indispensable part of the communication system. The performance of the communication system depends to a certain extent on the speed and accuracy of the system's synchronization of the received signal. Without accurate synchronization, the received signal cannot be processed. Synchronization includes signal capture and tracking. Capture is used to make a rough estimate of the code phase and carrier Doppler, paving the way for fine estimation of the code phase and carrier Doppler in the subsequent tracking process. Therefore, the capture process is the premise and basis for accurate synchronization.

[0003] Among the existing acquisition algorithms, the synchronous acquisition algorithm combined with the fast Fourier transform FFT is widely used in short burst communication because of its fast search speed and short acquisition time. This type of acquisition algorithm uses a known pilot sequence to estimate and compensate for the timing error and carrier frequency deviation based on time domain correlation and FFT. For example, Povey GJR, and Grant PM proposed a PMF-FFT synchronous acquisition algorithm based on partial matching filter and fast Fourier transform in "Simplified matched filter receiver designs for spread spectrum communications applications [J]. Electronics & Communication Engineering Journal, 1993, 5 (2): 59-64." The basic principle is to group the received pilot and the local pilot according to the same length and then perform cross-correlation, and then perform FFT transformation and modulus value on the cross-correlation result to select the peak value. When the peak value exceeds the capture threshold, the capture is successful, and the corresponding Doppler frequency deviation and code phase are obtained at the same time. Although this method is easy to implement with low complexity, it requires a higher number of FFT transform points to ensure spectral resolution when the pilot overhead is small and the signal transmission rate is too high, that is, the grouping is large, which results in each group length being too short, greatly reducing the anti-interference ability and failing to ensure good estimation accuracy. If a certain group length needs to be maintained in order to resist interference, the number of groups will decrease accordingly, resulting in fewer FFT points and lower frequency resolution. Summary of the invention

[0004] The purpose of the present invention is to address the deficiencies of the above-mentioned prior art and propose a partial matched filtering signal capture method based on a discrete group pilot structure to improve the frequency domain capture accuracy when the pilot overhead is small and the data transmission rate is too high.

[0005] The technical idea of ​​the present invention is to reduce the sampling rate when the receiving end performs FFT and improve the frequency domain capture accuracy by discretely inserting the pilot sequence of the group into the information sequence of the group. The implementation scheme includes the following:

[0006] (1) The transmitter sends a baseband sampling signal:

[0007] At the transmitting end, a local pilot sequence u' is selected and grouped to obtain a local grouped pilot sequence u = [u1u2…u i …u N ], where u i is the i-th group local group pilot sequence, i = 1, 2, ..., N, N u' is the total length of the local pilot sequence, l0 is the length of each group of pilot sequences;

[0008] Insert the local group pilot sequence u into the encoded information sequence d to form a transmission sequence a = [u1 d1u2 d2…u i d i …u N d N ], where d i is the i-th group of information sequence;

[0009] The transmission sequence a is modulated to obtain the baseband sampling signal s, which is then sent into the Gaussian white noise channel for transmission;

[0010] (2) The receiving end receives the signal sent by the transmitting end and stores the received signal r into the delay register;

[0011] (3) Divide the signal in the delay register into N groups, and then extract the received group pilot sequence p = [p1 p2 ... p i …p N ], where p i is the pilot sequence of the i-th group of received packets;

[0012] (4) Use the local group pilot sequence u and the received group pilot sequence p for synchronous acquisition:

[0013] (4a) The local group pilot sequence u is stored in N segment matched filters PMF as the coefficients of the FIR filter, and the received group pilot sequence p is passed through the filter to obtain N related output values;

[0014] (4b) After performing N-point FFT transformation on the N related output values ​​and taking the modulus value, the FFT transformation result Z of the N related output values ​​is obtained: Z = [Z1 Z2 ... Z i …Z N ], record the maximum value Z in Z maxand the position k of the maximum value in Z max ;

[0015] (4c) The delay register performs the received signal r The time delay, where f s is the baseband signal sampling rate; repeat steps (3) to (4b) until the delay register works at a frequency equal to l0 / 3, and set the maximum value Z among the Z recorded when the delay register works at a frequency of h max Denoted as Z' h , get all the maximum value data sequences h=0,1,…,l0 / 3;

[0016] (4d) Set a capture threshold Z0 according to the channel conditions and take the maximum value Z' in Z' n Compare with:

[0017] If Z' n >Z0, the capture is successful and execute (4e);

[0018] Otherwise, it is considered as capture failure;

[0019] (4e) According to Z' n The corresponding delay register works n times, and the estimated value of timing deviation is calculated Using the corresponding k max Calculate the frequency offset estimate

[0020]

[0021]

[0022] in, To receive the packet pilot p i The sampling rate, Q is the oversampling factor, f s is the sampling rate of the baseband signal, l is the length of each group of pilot signals plus the information sequence, and N is the number of FFT transformation points.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] In view of the situation that the sampling rate of the baseband signal is too high in the high-speed transmission mode, the present invention can make the equivalent sampling rate of the adjacent group pilot sequence smaller by inserting the pilot group into the data frame, and the required number of FFT operation points is reduced compared with the existing PMF-FFT algorithm. It not only reduces the calculation complexity and the number of pilot groups, but also increases the group pilot length, improves the ability to resist noise, and can obtain better estimation accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic diagram of an existing burst communication system to which the present invention is applied;

[0026] Figure 2 It is a flow chart for realizing the present invention;

[0027] Figure 3 The frame structure used in the present invention and the frame structure used in the prior art are schematic diagrams. DETAILED DESCRIPTION

[0028] The embodiments and effects of the present invention are further described below in conjunction with the accompanying drawings.

[0029] Reference Figure 1 In the existing burst communication system, the pilot sequence and the encoded information sequence are first framed at the transmitting end, and then the framed sequence is modulated and sent into the channel for transmission; at the receiving end, the signal is first synchronized with the timing and carrier, and then the synchronized signal is demodulated and decoded to restore the transmitted information sequence.

[0030] In a burst communication system, if timing synchronization is not performed, the correct signal cannot be received. At the same time, due to the existence of Doppler frequency offset, a large carrier frequency deviation will be generated on the basis of the original signal. If no measures are taken, the received signal at this time will not be enough to restore the original signal, making the communication quality of the system lower. This example solves the problem of timing synchronization and carrier synchronization of signals at the receiving end in a burst communication system, and proposes a partially matched filter signal capture method based on a discrete packet pilot structure.

[0031] Reference Figure 2 , the implementation steps of this example are as follows:

[0032] Step 1: The transmitter sends a baseband sampling signal s.

[0033] (1.1) Select the local pilot sequence u' at the transmitting end:

[0034] u'=[u'(0)u'(1)…u'(n)…u'(N u' -1)]

[0035]

[0036] Where u'(n) represents the nth bit in the local pilot sequence u', n = 0, 1, ..., N u' -1,N u' is the length of the local pilot sequence u', μ∈{1,2,…,N u' -1} and N u' are relatively prime, and q is an arbitrary integer. In this embodiment, μ=1, q=0.

[0037] (1.2) Divide the local pilot sequence u' into N groups of equal length to obtain the local group pilot sequence u = [u1 u2 ... u i …u N ]:

[0038] u i =[u'((i-1)*N u' / N+1),u'((i-1)*N u' / N+2),…,u'(i*N u' / N)]

[0039] where u i is the i-th group local group pilot sequence, i = 1, 2, ..., N, is the number of groups, N u' is the total length of the local pilot sequence, l0 is the length of each group of pilot sequences, and * is the multiplication symbol;

[0040] (1.3) The sender encodes the binary information sequence and divides it into N groups of equal length, obtaining the grouped information sequence d = [d1 d2…d i …d N ]:

[0041] d i =[d((i-1)*N d / N+1),d((i-1)*N d / N+2),…,d(i*N d / N)];

[0042] Among them, d i is the i-th group of information sequence, N d is the total length of the encoded information sequence d.

[0043] (1.4) The transmitter sends the i-th group of local group pilot u i Placed in the coded i-th information sequence d i Before, the sending sequence is a=[u1 d1 u2 d2…u i d i …u N d N ];

[0044] (1.5) The transmission sequence a is modulated to obtain the baseband sampling signal s, which is then sent into the Gaussian white noise channel for transmission.

[0045] Step 2: The receiving end processes the received signal to obtain a received packet pilot sequence p.

[0046] (2.1) The receiving end receives the signal sent by the sending end, and the received signal r is expressed as:

[0047] r=[r(0)r(1)…r(m)…r(N r -1)]

[0048]

[0049] Where r(m) represents the mth sample point in the received signal r, m = 0, 1, ..., N r -1, Δf is the carrier frequency deviation, f s is the baseband signal sampling rate, N r is the length of the received signal r, N r =(N u' +N d )*Q, Q is the oversampling multiple, s(m) represents the baseband sampling signal, w(m) represents the complex Gaussian random noise with zero mean and variance N0 / 2, N0 is the unilateral power spectral density of the noise, and j is a complex unit;

[0050] (2.2) The receiving end stores the received signal r into the delay register;

[0051] (2.3) Divide the signals in the delay register into N groups, each group length l = (N u' +N d ) / N, extract the first Q·N of each group u' / N sampling signals, and obtain the oversampled receiving packet pilot sequence p'=[p'1p'2…p' i …p' N ], where p' i is the pilot sequence of the i-th group of oversampled received packets, expressed as follows:

[0052] p' i =[r((i-1)*N r / N)r((i-1)*N r / N+1)…r(((i-1)*N r +Q*N u' ) / N)]

[0053] Among them, N r is the length of the received signal r, N r =(N u' +N d )*Q, Q is the oversampling multiple, N u' is the total length of the local pilot sequence u';

[0054] (2.3) For p' i From the first sampling signal, a sampling signal is taken every (Q-1) points to obtain the pilot sequence p of the i-th group of received packets. i Finally, the received packet pilot sequence p = [p1 p2…p i…p N ], 1≤i≤N.

[0055] Step 3: Use the received packet pilot sequence p = [p1 p2 ... p i …p N ] and local group pilot sequence u=[u1u2…u i …u N ] for synchronous capture.

[0056] (3.1) The pilot sequence p of the i-th group of received packets is i and the i-th group local group pilot sequence u i Multiply by the conjugate transpose of to get N related values ​​z:

[0057] z=[z1 z2…z i …z N ]

[0058] z i =p i u i *

[0059] where z i represents the i-th correlation value, u i * is u i The conjugate transpose of ;

[0060] (3.2) After performing N-point FFT transformation on the N related output values ​​and taking the modulus value, the FFT transformation result Z of the N related output values ​​is obtained:

[0061] Z=|FFT(z,N)|

[0062] Wherein, z is all relevant values, and N is the number of FFT transformation points;

[0063] (3.3) Record the maximum value Z in Z max and the position k of the maximum value in Z max ;

[0064] (3.4) The delay register performs the received signal r The time delay, where f s is the baseband signal sampling rate; repeat steps (2.3) to (3.3) until the delay register works at a frequency equal to l0 / 3, and set the maximum value Z among the Z recorded each time max Denoted as Z' h , get all the maximum value data sequence Z':

[0065]

[0066] Where, h = 0, 1, ..., l0 / 3 is the number of times the delay register works;

[0067] (3.5) Set a capture threshold Z0 according to the channel conditions and take out the maximum value Z' in Z' n In comparison, if Z' n >Z0, the capture is successful and (3.6) is executed; otherwise, the capture is considered to have failed;

[0068] (3.6) According to Z' n The corresponding delay register works n times, and the estimated value of timing deviation is calculated Using the corresponding k max Calculate the frequency offset estimate Complete synchronous capture;

[0069]

[0070]

[0071] in, To receive the packet pilot p i The sampling rate, Q is the oversampling factor, f s is the sampling rate of the baseband signal, l is the length of each group of pilot signals plus the information sequence, and N is the number of FFT transformation points.

[0072] The effect of the present invention can be further illustrated by the calculation results of the frequency domain capture accuracy that can be achieved by using the PMF-FFT method for the existing frame structure and the frame structure of the present invention:

[0073] 1. System parameters:

[0074] One of the application scenarios of the present invention is that the channel coding is turbo code, the modulation mode is QPSK, the pilot is a Chu sequence with a length of 1560 bits, the data length is 11240 bits, and the number of packets is 10. The additional carrier frequency deviation Δf of the channel is 6000Hz, the number of oversampling points Q is 4, and the baseband signal sampling rate f s =51.2Mbps.

[0075] The existing frame structure is as follows Figure 3 As shown in a, the pilot signal is placed before the data signal as a whole, and the interval length between adjacent pilot sequences is l0.

[0076] The frame structure of the present invention is as follows Figure 3 As shown in FIG. 2 , the pilot signal and the data signal are divided into 10 groups, and the grouped pilot signals are inserted before the grouped data signals, and the interval length between adjacent pilot sequences is l.

[0077] 2. Calculate the spectral resolution corresponding to the two frame structures

[0078] The spectrum resolution corresponding to the existing frame structure is:

[0079] The spectrum resolution corresponding to the frame structure of the present invention is:

[0080] By comparing the spectrum resolutions of the two frame structures, it can be seen that the spectrum resolution corresponding to the frame structure of the present invention is improved by 8.21 times compared with the spectrum resolution corresponding to the existing frame structure, which can achieve better capture accuracy and greatly improve system performance.

Claims

1. A partially matched filtering signal acquisition method based on a discrete group pilot structure, characterized in that: include: (1) The transmitter sends a baseband sampling signal: At the transmitting end, a local pilot sequence u' is selected and grouped to obtain a local grouped pilot sequence u = [u1 u2 ... u i …u N ], where u i is the i-th group local group pilot sequence, i = 1, 2, ..., N, N u' is the total length of the local pilot sequence, l0 is the length of each group of pilot sequences; Insert the local group pilot sequence u into the encoded information sequence d to form a transmission sequence a = [u1 d1 u2d2…u i d i …u N d N ], where d i is the i-th group of information sequence; The transmission sequence a is modulated to obtain the baseband sampling signal s, which is then sent into the Gaussian white noise channel for transmission; (2) The receiving end receives the signal sent by the transmitting end and stores the received signal r into the delay register; (3) Divide the signal in the delay register into N groups, and then extract the received group pilot sequence p = [p1 p2 ... p i …p N ], where p i is the pilot sequence of the i-th group of received packets; (4) Use the local group pilot sequence u and the received group pilot sequence p for synchronous acquisition: (4a) The local group pilot sequence u is stored in N segment matched filters PMF as the coefficients of the FIR filter, and the received group pilot sequence p is passed through the filter to obtain N related output values; (4b) After performing N-point FFT transformation on the N related output values ​​and taking the modulus value, the FFT transformation result Z of the N related output values ​​is obtained: Z = [Z1 Z2 ... Z i …Z N ], record the maximum value Z in Z max and the position k of the maximum value in Z max ; (4c) The delay register performs the received signal r The time delay, where f s is the baseband signal sampling rate; repeat steps (3) to (4b) until the delay register works at a frequency equal to l0 / 3, and set the maximum value Z among the Z recorded when the delay register works at a frequency of h max Denoted as Z' h , get all the maximum value data sequences h=0,1,…,l0 / 3; (4d) Set a capture threshold Z0 according to the channel conditions and take the maximum value Z' in Z' n Compare with: If Z' n >Z0, the capture is successful and execute (4e); Otherwise, it is considered as capture failure; (4e) According to Z' n The corresponding delay register works n times, and the estimated value of timing deviation is calculated Using the corresponding k max Calculate the frequency offset estimate in, To receive the packet pilot p i The sampling rate, Q is the oversampling factor, f s is the baseband signal sampling rate, l is the length of each group of pilot signals plus the information sequence, and N is the number of FFT transformation points.

2. The method according to claim 1, characterized in that The local pilot sequence u' in step (1) is expressed as follows: u'=[u'(0)u'(1)…u'(n)…u'(N u' -1)] Where u'(n) represents the nth bit in the local pilot sequence u', n = 0, 1, ..., N u' -1, N u' is the length of the local pilot u', μ∈{1,2,…,N u' -1} and N u' Coprime, q is any integer.

3. The method according to claim 1, characterized in that The i-th group of local group pilot sequences u in step (1) i and the i-th information sequence d i , which are as follows: u i =[u'((i-1)*N u' / N+1),u'((i-1)*N u' / N+2),…,u'(i*N u' / N)]; d i =[d((i-1)*N d / N+1),d((i-1)*N d / N+2),…,d(i*N d / N)]; Among them, 1≤i≤N, N is the number of groups, N u' is the total length of the local pilot sequence u', N d is the total length of the encoded information sequence d.

4. The method according to claim 1, characterized in that The received signal r in step (2) is expressed as follows: r=[r(0)r(1)…r(m)…r(N r -1)] Where r(m) represents the mth sample point in the received signal r, m = 0, 1, ..., N r -1, Δf is the carrier frequency deviation, f s is the baseband signal sampling rate, N r is the length of the received signal r, N r =(N u' +N d )*Q, s(m) represents the baseband sampling signal, w(m) represents the complex Gaussian random noise with zero mean and variance N0 / 2, N0 is the unilateral power spectral density of the noise, and j is a complex unit.

5. The method according to claim 1, characterized in that In step (3), the received group pilot sequence p is extracted from each group of received signals, which is implemented as follows: (3a) Extract the first Q·N of each group from the received signal r divided into N groups u' / N sampling signals, and obtain the oversampled receiving packet pilot sequence p'=[p'1p'2…p' i …p' N ], where p' i is the pilot sequence of the i-th group of oversampled received packets, expressed as follows: p' i =[r((i-1)*N r / N)r((i-1)*N r / N+1)…r(((i-1)*N r +Q*N u' ) / N)] Among them, N r is the length of the received signal r, N r =(N u' +N d )*Q, Q is the oversampling multiple, N u' is the total length of the local pilot sequence u'; (3b) For p' i From the first sampling signal, a sampling signal is taken every (Q-1) points to obtain the pilot sequence p of the i-th group of received packets. i Finally, the received packet pilot sequence p = [p1 p2…p i …p N ], 1≤i≤N.

6. The method according to claim 1, characterized in that In step (4a), N relevant output values ​​are obtained, which are expressed as follows: z=[z1 z2…z i …With N ] where z i =p i u i * represents the i-th correlation value, u i * is u i The conjugate transpose of , i = 1, 2, …, N.

7. The method according to claim 1, characterized in that The step (4b) performs N-point FFT transformation on the N related output values ​​and takes the modulus value, and the formula is as follows: Z=|FFT(z,N)|, where z is all relevant values ​​and N is the number of FFT transformation points.

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