CN114465865B - Frequency offset estimation method for pilot frequency segmentation and recombination - Google Patents
Frequency offset estimation method for pilot frequency segmentation and recombination Download PDFInfo
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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
- H04L27/2657—Carrier synchronisation
- H04L27/266—Fine or fractional frequency offset determination and 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
- H04L27/2602—Signal structure
- H04L27/261—Details of reference signals
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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
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- 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 frequency offset estimation method for pilot frequency segmentation and recombination, which mainly solves the problem that the existing carrier frequency offset estimation technology cannot consider pilot frequency overhead, estimation precision and operation complexity in a communication system with overhigh information transmission rate. The implementation scheme is as follows: sampling points are extracted and recombined at equal intervals on a local pilot frequency and a received pilot frequency sequence at a receiving end, so that a plurality of pairs of local recombined pilot frequencies and received recombined pilot frequency sequences are obtained; calculating the average periodic chart of a plurality of de-modulated sequences, searching the peak value of the average periodic chart to obtain the rough estimated position of the frequency offset; and fine tuning the rough estimation position by utilizing the peak value of the average periodic chart and the left and right adjacent amplitude values thereof to obtain an accurate frequency offset position, and calculating according to the frequency offset position to obtain an accurate carrier frequency offset estimation value. The method can achieve higher estimation precision with lower pilot frequency expenditure and lower operation complexity, and is suitable for spaceflight measurement and control and satellite communication.
Description
Technical Field
The invention belongs to the technical field of wireless communication, and particularly relates to a frequency offset estimation method which can be used for carrier synchronization in a high-speed transmission frequency hopping burst digital communication system.
Background
Compared with the traditional communication mode, the frequency hopping burst communication technology is widely applied to the field of modern military communication due to the characteristics of good confidentiality, interception resistance, interference resistance and the like, but in actual communication, the relative motion of two communication parties can cause Doppler frequency offset, so that frequency deviation exists between a carrier wave in a received signal and a carrier wave at a transmitting end, and the communication quality is reduced, therefore, how to realize effective carrier synchronization by utilizing a pilot sequence with small overhead is a hotspot and a difficulty in research of the field of communication under the condition of high-speed transmission, and is important for guaranteeing the reliability of military communication.
In the existing traditional carrier synchronization algorithm, the frequency domain data auxiliary algorithm is commonly applied to short burst communication with the advantages of low complexity and low signal to noise ratio threshold, the estimation algorithm utilizes a section of known pilot sequence to estimate and compensate carrier frequency offset based on a frequency domain periodic graph function, such as an R & A frequency offset estimation algorithm proposed by Calvo P M, sevillano J F, velez I and Irizar A in Enhanced Implementation of Blind Carrier Frequency Estimators for QPSK Satellite Receivers at Low SNR (IEEE Transaction on Consumer Electronics,2005,51 (7): 442-448), the pilot sequence is segmented first and then estimated, the complexity is low, the implementation is easy, but the estimation accuracy is low and the error is larger when the pilot overhead is fixed. In order to make up the defect of the algorithm, liu Peng proposes an RPA frequency offset estimation algorithm in paper 'research and implementation of efficient carrier synchronization technology of short burst SOQPSK system', the basic principle is that after pilot frequency sequences are subjected to frequency offset rotation for a plurality of times, carrier frequency offset is calculated through an average periodic chart of a frequency domain, and estimation and compensation of the frequency offset are realized. In addition, the above algorithm cannot guarantee good performance under the conditions of small pilot overhead and too high baseband signal transmission rate.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a frequency offset estimation method for pilot frequency segmentation recombination, so as to reduce the operation complexity and improve the estimation precision under the conditions of small pilot frequency overhead and overhigh data transmission rate.
The technical idea of the invention is that the local pilot frequency and the received pilot frequency are processed by a pilot frequency segmentation recombination method, so that the operation complexity is reduced; and fine adjustment is carried out on the frequency deviation rough estimation value obtained by the average periodogram method, so that the estimation precision is improved. The implementation scheme comprises the following steps:
(1) Selecting a local pilot frequency sequence u at a transmitting end, arranging the local pilot frequency sequence u in front of an encoded and modulated information sequence d through a multiplexing module to form a complex baseband signal s= [ u d ], and transmitting the complex baseband signal s= [ u d ] into a Gaussian white noise channel for transmission;
(2) The signal arrives at the receiving end to obtain a received signal r, the receiving end extracts a received pilot sequence p from the received signal r through a demultiplexing module, and performs segmentation and recombination operation on the local pilot u and the received pilot p:
(2a) Segmenting the received pilot frequency p, wherein each l bits are one segment, and extracting the first bit from each segment to form the received recombined pilot frequency p 1 And the local pilot frequency u is processed in the same way to obtain the local recombined pilot frequency u 1 ；
(2b) Extracting the second bit from each segment of the received pilot frequency p and the local pilot frequency u to form the received recombined pilot frequency p 2 And local recombined pilot u 2 And so on, obtaining the common l receiving recombined pilot frequency p i And local recombined pilot u i Where i=1, 2, …, l;
(3) Frequency offset estimation is carried out on the recombinant pilot frequency by using the method:
(3a) Local recombined pilot u i And receiving the recombined pilot p i Performing point-by-point conjugate multiplication to obtain l de-modulated sequences z i ；
(3b) For l de-modulation sequences z i Performing frequency offset rotation to obtain a frequency shift sequence c i ；
(3c) For the frequency shift sequences c i Fourier transforming and obtaining amplitude to obtain one periodic chart function P i Find the full period map function P i Average of (2) to obtain an average periodic chart
Wherein, the liquid crystal display device comprises a liquid crystal display device,mean periodic diagram +.>K data of (P) i (k) Representing a periodogram function P i K=0, 1, …, N fft -1，N fft Points are fast fourier transform points.
(3d) Searching an average periodogramTo obtain the peak position k m ；
(3e) Using average periodogram peaksAnd the average periodogram amplitude +.about adjacent positions thereof>Andfor peak position k m Fine tuning is performed to obtain an accurate frequency offset position k max ：
(3f) Using the exact frequency offset position k max Calculating to obtain accurate frequency offset estimation value
Wherein, the liquid crystal display device comprises a liquid crystal display device,to receive recombined pilot p i Sampling rate f of (f) s Sampling rate for baseband signal;
(4) Using accurate frequency offset estimatesCorrecting the received signal r by means of complex phase rotation to obtain a corrected signal r':
where r '(m) represents the m-th sample point in the correction signal r', m=0, 1, …, N-1, N is the length of the received signal r, and j represents the imaginary unit.
Compared with the prior art, the invention has the following advantages:
firstly, in a high-speed transmission mode, the sampling rate of a baseband signal is too high, the FFT point number of the conventional RPA algorithm is too high, and the complex and difficult to realize.
Secondly, under the condition of small pilot frequency overhead, the existing RPA algorithm is seriously affected by noise and has large operation error.
Description of the drawings:
fig. 1 is a schematic diagram of a conventional frequency hopping burst system;
FIG. 2 is a flow chart of an implementation method of the present invention;
FIG. 3 is a normalized root mean square error comparison graph of frequency offset estimation for the system of FIG. 1 using the present invention and the existing RPA algorithm, respectively;
FIG. 4 is a graph comparing the frequency offset estimation of the system of FIG. 1 with the prior RPA algorithm and the bit error performance of the system without frequency offset.
The specific embodiment is as follows:
embodiments and effects of the present invention are further described below with reference to the accompanying drawings.
Referring to fig. 1, the application scenario of the present embodiment is a high-speed transmission frequency hopping burst communication system, which includes a transmitting end and a receiving end, and the channel model adopts an additive white gaussian noise channel. The basic working principle of the system is as follows:
at the transmitting end, the binary information sequence is RS-encoded, then the encoded signal is shaped and offset to be SOQPSK modulated, and the local pilot frequency sequence is arranged in front of the encoded and modulated information sequence through multiplexing, so that a complex baseband signal is obtained and transmitted to a channel for transmission.
At the receiving end, frequency offset estimation is carried out by utilizing the local pilot frequency and the received pilot frequency sequence, the signal is compensated by utilizing the estimation value, the compensation signal is demodulated to obtain a hard decision demodulation signal, and finally, the sent binary information sequence can be recovered through decoding of an RS decoder.
Referring to fig. 2, the present invention performs frequency offset estimation based on the system of fig. 1, and the implementation steps include the following:
step 1, a transmitting end selects a local pilot frequency sequence u, and the local pilot frequency sequence u is placed in front of an encoded and modulated information sequence d to form a complex baseband signal s, and the complex baseband signal s is transmitted into a Gaussian white noise channel for transmission.
(1.1) selecting a local pilot sequence u at a transmitting end:
where u (N) represents the nth bit in the local pilot u, n=0, 1, …, N u -1，N u For the length of the local pilot u, μ∈ {1,2, …, N u -1 and with N u Mutually, q is any integer. In this example, μ=1, q=0;
(1.2) the transmitting end encodes and modulates the binary information sequence to obtain an encoded and modulated information sequence d:
d＝[d(0),d(1),…,d(N-1)]
wherein N is the length of the encoded and modulated information sequence d;
(1.3) the transmitting end puts the local pilot frequency u in front of the coded and modulated information sequence d to form a complex baseband signal s= [ u d ], and transmits the complex baseband signal s= [ u d ] into a Gaussian white noise channel for transmission;
and 2, after receiving the received signal r, the receiving end extracts the received pilot frequency p from the received signal r, and performs segmentation and recombination operation on the local pilot frequency u and the received pilot frequency p.
(2.1) the receiving end receives the complex baseband signal r:
wherein r (m) represents the m-th sample point in the received signal r, m=0, 1, …, N-1, Δf is carrier frequency offset, f s For the sampling rate of the baseband signal, N is the length of the received signal r, w (m) represents the mean value of zero and the variance of N 0 Complex gaussian random noise of/2, N 0 The single-side power spectrum density of noise is represented by j, which is a complex unit;
(2.2) the receiving end extracts the received pilot sequence p from the received signal r.
(2.3) segmenting the received pilot sequence p, each l bits being one segment, extracting the first bit from each segment to form the received re-assembled pilot p 1 The local pilot frequency u is processed in the same way to obtain the local recombined pilot frequency u 1 . In this example, take l=5;
(2.4) extracting the second bit from each segment of the received pilot frequency p and the local pilot frequency u respectively to form the received recombined pilot frequency p 2 And local recombined pilot u 2 And so on, obtaining the common l receiving recombined pilot frequency p i And local recombined pilot u i ：
Where i=1, 2, …, l, p ((j-1) l+i-1) represents the i-1 th bit of the j-th segment in the received pilot p, u ((j-1) l+i-1) represents the i-1 th bit of the j-th segment in the local pilot u,
step 3, utilizing the received recombined pilot frequency p i And local recombined pilot u i And performing frequency offset estimation.
(3.1) local re-combining Pilot u i And receiving the recombined pilot p i Performing point-by-point conjugate multiplication to obtain l de-modulated sequences z i ：
z i (n)＝p i (n)u i * (n)
Wherein z is i (n) represents the de-modulation sequence z i N-th bit of p i (n) represents the local re-allocated pilot p i N-th bit of (u) i * (n) represents local re-allocated pilot u i Is the conjugate of the nth bit of (c),
(3.2) for l de-modulation sequences z i Frequency offset rotation is carried out to obtain a frequency shift sequence c i ：
Wherein c i (n) represents a frequency shift sequence c i Is selected from the group consisting of the n-th bit,for the spectral resolution of the fast fourier transform, N fft For fast Fourier transform points, < >>To receive recombined pilot p i Is a sampling rate of (a);
(3.3) for the l frequency-shifted sequences c, respectively i Fourier transforming and obtaining amplitude to obtain one periodic chart function P i ：P i (k)＝|FFT(c i ,N fft ) I, find the full part periodic chart function P i Average of (2) to obtain an average periodic chart
Wherein, the liquid crystal display device comprises a liquid crystal display device,mean periodic diagram +.>K data of (P) i (k) Representing a periodogram function P i K=0, 1, …, N fft -1；
(3.4) searching for an average periodogramTo obtain the peak position k m ；
(3.5) Using the average periodogram peak valueAnd the average periodogram amplitude +.about adjacent positions thereof>Andfor peak position k m Fine tuning is performed to obtain an accurate frequency offset position k max ：
(3.6) utilizing the precise frequency offset position k max Calculating to obtain accurate frequency offset estimation value
Wherein the method comprises the steps ofTo receive recombined pilot p i Is used for the sampling rate of (a).
Step 4, correcting the received signal r:
using accurate frequency offset estimatesCorrecting the received signal r by means of complex phase rotation to obtain a corrected signal r':
where r '(m) represents the m-th sample point in the correction signal r', m=0, 1, …, N-1, N is the length of the received signal r.
The effect of the invention can be further illustrated by the following simulations:
1. simulation parameters:
the invention uses MATLAB R2019a simulation software in simulation, the length of each data frame of the frequency hopping system in simulation is N=10000, the channel code is RS code, and the parameters are as follows: the code length n=15, the information symbol length k=13, the minimum code distance d=3, and the number of bits included in each symbol m=5. The modulation mode adopts SOQPSK, and the pilot frequency is a Chu sequence with 1500 bits long. Channel-attached carrier frequency offset Δf=200 Hz, baseband signal sampling rate f s ＝30Msps。
2. The simulation content:
simulation 1, the frequency offset estimation is carried out on the system of fig. 1 by adopting the method and the existing RPA algorithm respectively, and the normalized root mean square error curve is shown in fig. 3.
As can be seen from fig. 3, under the same pilot frequency length, the root mean square error of the estimation method of the present invention is smaller, the estimation is more accurate, the requirement on the signal-to-noise ratio threshold is lower, and the performance is obviously better than that of the existing RPA algorithm. In addition, the RPA algorithm performs 16 times of frequency offset rotation on pilot frequency and then performs 4096-point fast Fourier transform, so that the operation amount is 16 times of 4096-point FFT, and the invention only performs 2048-point FFT on 5 segments of recombined pilot frequency sequences, so that the operation amount is only 5 times of 2048-point FFT, and the complexity is obviously reduced compared with the RPA algorithm. In conclusion, the invention can estimate the carrier frequency offset with lower complexity and higher estimation precision when the pilot frequency spending is fixed.
Simulation 2, the invention is adopted to carry out frequency offset estimation on the system of fig. 1 by adopting the conventional RPA algorithm under the condition of frequency offset delta f=200 Hz, and bit error performance pairs of the system under the condition of no frequency offset are shown in fig. 4.
As can be seen from FIG. 4, the frequency offset estimation method of the present invention has a bit error rate of 10 in the system -5 When the system is in level, compared with the system performance under the condition of no frequency offset, the loss is less than 2.5dB, and compared with the existing RPA algorithm, the signal-to-noise ratio gain of 7dB can be obtained, and the transmission reliability of the system is greatly improved.
The invention has the following reasons for great improvement of system performance:
first, the baseband sampling rate of the high-speed transmission system is too high, at this time, the spectrum resolution of the RPA algorithm is too low, so that correct estimation cannot be performed, and the sampling rate can be reduced only by sampling the pilot frequency at equal intervals, but this operation can cause too short pilot frequency sequence and serious performance loss. The method of the invention fully utilizes the whole pilot frequency, thereby obtaining better estimation performance under the condition of certain pilot frequency overhead.
Secondly, the SOQPSK modulation mode in the frequency hopping burst system is very sensitive to frequency offset, and the tiny frequency deviation can cause larger performance loss.
Claims (7)
1. The frequency offset estimation method for pilot frequency segmentation and recombination comprises the following steps:
(1) Selecting a local pilot frequency sequence u at a transmitting end, arranging the local pilot frequency sequence u in front of an encoded and modulated information sequence d through a multiplexing module to form a complex baseband signal s= [ u d ], and transmitting the complex baseband signal s= [ u d ] into a Gaussian white noise channel for transmission;
(2) The signal arrives at the receiving end to obtain a received signal r, the receiving end extracts a received pilot sequence p from the received signal r through a demultiplexing module, and performs segmentation and recombination operation on the local pilot u and the received pilot p:
(2a) The received pilot p is segmented, one for each l bits,extracting the first bit from each segment to form the received re-composed pilot p 1 And the local pilot frequency u is processed in the same way to obtain the local recombined pilot frequency u 1 ；
(2b) Extracting the second bit from each segment of the received pilot frequency p and the local pilot frequency u to form the received recombined pilot frequency p 2 And local recombined pilot u 2 And so on, obtaining the common l receiving recombined pilot frequency p i And local recombined pilot u i Where i=1, 2, …, l;
(3) Frequency offset estimation is carried out on the recombinant pilot frequency by using the method:
(3a) Local recombined pilot u i And receiving the recombined pilot p i Performing point-by-point conjugate multiplication to obtain l de-modulated sequences z i ；
(3b) For l de-modulation sequences z i Performing frequency offset rotation to obtain a frequency shift sequence c i ；
(3c) For the frequency shift sequences c i Fourier transforming and obtaining amplitude to obtain one periodic chart function P i Find the full period map function P i Average of (2) to obtain an average periodic chart
Wherein, the liquid crystal display device comprises a liquid crystal display device,mean periodic diagram +.>K data of (P) i (k) Representing a periodogram function P i K=0, 1, …, N fft -1，N fft The points are fast Fourier transform points;
(3d) Searching an average periodogramTo obtain the peak position k m ；
(3e) Using average periodogram peaksAnd the average periodogram amplitude +.about adjacent positions thereof>Andfor peak position k m Fine tuning is performed to obtain an accurate frequency offset position k max ：
(3f) Using the exact frequency offset position k max Calculating to obtain accurate frequency offset estimation value
Wherein, the liquid crystal display device comprises a liquid crystal display device,to receive recombined pilot p i Sampling rate f of (f) s Sampling rate for baseband signal;
(4) Using accurate frequency offset estimatesCorrecting the received signal r by means of complex phase rotation to obtain a corrected signal r':
where r '(m) represents the m-th sample point in the correction signal r', m=0, 1, …, N-1, N is the length of the received signal r, and j represents the imaginary unit.
2. The method of claim 1, wherein the local pilot sequence u selected at the transmitting end in (1) is represented as follows:
where u (N) represents the nth bit in the local pilot u, n=0, 1, …, N u -1，N u For the length of the local pilot u, μ∈ {1,2, …, N u -1 and with N u Mutually, q is any integer.
3. The method according to claim 1, characterized in that the coded and modulated information sequence d in (1) is represented as follows:
d＝[d(0),d(1),…,d(N-1)]
where N is the length of the encoded and modulated information sequence d.
4. The method according to claim 1, wherein l in (2 b) receives the recombined pilot p i And local recombined pilot u i The respective expressions are as follows:
wherein p ((j-1) l +)i-1) represents the i-1 th bit of the j-th segment in the received pilot p, u ((j-1) l + i-1) represents the i-1 th bit of the j-th segment in the local pilot u,N u is the length of the local pilot u.
5. The method according to claim 1, wherein the l de-modulated sequences z obtained in (3 a) i The expression is as follows:
z i (n)＝p i (n)u i * (n)
wherein z is i (n) represents the de-modulation sequence z i N-th bit of p i (n) represents the local re-allocated pilot p i N-th bit of (u) i * (n) represents local re-allocated pilot u i Is the conjugate of the nth bit of (c),N u is the length of the local pilot u.
6. The method according to claim 1, wherein the l frequency shift sequences c obtained in (3 b) i The expression is as follows:
wherein c i (n) represents a frequency shift sequence c i Is selected from the group consisting of the n-th bit,for the spectral resolution of the fast fourier transform, N fft For fast Fourier transform points, < >>For local reassembly pilot u i Sampling rate f of (f) s Is based onWith a signal sampling rate.
7. The method according to claim 1, wherein the one periodic graph function P obtained in (3 c) i The expression is as follows:
P i (k)＝|FFT(c i ,N fft )|
wherein P is i (k) Representing a periodogram function P i K=0, 1, …, N fft -1，N fft Points are fast fourier transform points.
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| CN102624419B (en) * | 2012-04-23 | 2013-12-25 | 西安电子科技大学 | Carrier synchronization method of burst direct sequence spread spectrum system |
| KR20140029833A (en) * | 2012-08-30 | 2014-03-11 | 한국전자통신연구원 | Apparatus and method for receiving data in communication system |
| CN103281280B (en) * | 2013-05-15 | 2016-03-02 | 西安电子科技大学 | Based on the carrier synchronization method of rotation average period map and demodulation Soft Inform ation |
| US9825794B2 (en) * | 2013-06-25 | 2017-11-21 | Thuy Duong NGUYEN | Weak signal detection in double transmission |
| CN103916357B (en) * | 2014-04-29 | 2017-04-19 | 西安电子科技大学 | SOQPSK carrier synchronization method based on pilot frequency and coding joint aiding |
| CN110149289B (en) * | 2019-06-11 | 2021-05-18 | 西安电子科技大学 | Frame structure design method for large frequency offset download wave frequency offset estimation |
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| CN110278169A (en) * | 2018-11-26 | 2019-09-24 | 周口师范学院 | A kind of time domain frequency excursion algorithm |
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