CN114884788B - Frequency offset estimation method and frame synchronization method - Google Patents
Frequency offset estimation method and frame synchronization method 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
- H04L27/2656—Frame synchronisation, e.g. packet synchronisation, time division duplex [TDD] switching point detection or subframe synchronisation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2662—Symbol synchronisation
- H04L27/2663—Coarse synchronisation, e.g. by correlation
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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
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Abstract
The invention belongs to the technical field of communication systems, and particularly relates to a frequency offset estimation method and a frame synchronization method, which comprise the following steps: receiving a preamble signal; performing cross-correlation operation on frequency domain signals corresponding to two adjacent OFDM symbols to obtain a cross-correlation operation result; re-calculating the cross-correlation operation result to obtain a first complex signal; the frequency domain signal corresponding to each OFDM symbol is calculated as follows: for a frequency domain signal corresponding to a certain OFDM symbol, accumulating all first complex signals corresponding to k to obtain accumulated first complex signals; the phase of the accumulated first complex signal is obtained; judging by using threshold parameters according to the phase of the accumulated first complex signals corresponding to each frequency domain OFDM symbol so as to determine the inversion position of the preamble signal; and determining the number of the leading signal symbols according to the inversion position, and further realizing frame synchronization and frequency offset estimation when the sampling clock has larger deviation.
Description
Technical Field
The invention belongs to the technical field of communication systems, and particularly relates to a frequency offset estimation method and a frame synchronization method.
Background
OFDM (OrthogonalFrequencyDivisionMultiplexing) -orthogonal frequency division multiplexing is one of MCM Multi-carrier modulation, multi-carrier modulation. When the OFDM technology is used for communication, a leading signal is inserted before a data frame by a transmitting end before the signal is transmitted, and when a receiving end receives the data signal, the symbol timing and the frame timing are determined through auto-correlation or cross-correlation, so that the aim of correctly receiving the data signal is fulfilled. The preamble is composed of several identical OFDM symbols. The preamble signal is composed of a plurality of OFDM symbols SYNCP and at least 1 OFDM symbol SYNCM; wherein, SYNCP is CENELEC-A frequency band leading signal symbol in G3-PLC standard protocol, and SYNCP is multiplied by-1 to obtain SYNCM. The number of SYNCPs is generally 5 to 10, and the number of SYNCMs is generally 1 to 2.
Digital communication systems, particularly OFDM systems, are very sensitive to Zhong Caiyang frequency offset, and because the clock sampling frequency of the transmitter D/a converter and the clock sampling frequency of the receiver a/D converter are not synchronous, a certain clock sampling frequency offset exists between the transmitter and the receiver, which can cause inter-sub-channel interference (ICI), destroy orthogonality among sub-carriers, and greatly impair the receiving performance of the system, so clock sampling synchronization is one of the key technologies in OFDM systems.
With the widespread use of OFDM systems, cost control of transmitters and receivers is a primary concern. Under the demand of cost reduction, more and more communication modules adopt crystal oscillator modules with low cost, and along with the increase of service life and aging factors, the error of the crystal oscillator is larger and larger, so that a clock of a receiving and transmitting system has a large error, generally having a value of +/-300 ppm and seriously even reaching +/-600 ppm.
Typically, frequency offset estimation first requires determining a known synchronization signal, i.e., a preamble. The periodicity and repeatability of the preamble signal are utilized, and the phase deflection generated by the clock deviation is utilized to estimate the clock deviation. The initial position of the leading signal is found initially, i.e. coarse synchronization is performed, and then the end position of the leading signal is synchronized according to the phase reversal signal, so that the data signal is determined, and a complete communication signal is received. The frequency offset estimation method carries out clock offset estimation based on the segment of the preamble signal. If a very large clock deviation occurs, a large phase deviation is generated on the received signal along with the time, and it is difficult to determine the starting position of the preamble signal; because the phase changes sharply, the signals with repeated periods have serious distortion, the correlation drops greatly, even reverse, and erroneous judgment is caused, and at the moment, the ending position of the leading signal cannot be normally determined, so that the subsequent sampling clock estimation cannot be normally carried out.
Disclosure of Invention
The invention aims to provide a frame synchronization method for solving the problem that frame synchronization cannot be realized due to incapability of accurately determining the number of leading signal symbols in the prior art, and a frequency offset estimation method for solving the problem that sampling frequency offset cannot be accurately determined due to incapability of accurately determining the number of leading signal symbols in the prior art.
In order to solve the technical problems, the technical scheme and the corresponding beneficial effects of the technical scheme provided by the invention are as follows:
the invention provides a frame synchronization method, which is characterized by comprising the following steps:
s1, receiving a preamble signal;
s2, converting each time domain OFDM symbol in the preamble signal into a frequency domain to obtain a frequency domain signal corresponding to each OFDM symbolN is the total number of subcarriers in the frequency domain signal corresponding to one OFDM symbol;
s3, carrying out cross-correlation operation on frequency domain signals corresponding to two adjacent OFDM symbols according to the following formula to obtain a cross-correlation operation result:
wherein S is l (k) A kth subcarrier signal which is a frequency domain signal corresponding to the ith OFDM symbol, S l+1 (k) A kth subcarrier signal which is a frequency domain signal corresponding to the (1+1) th OFDM symbol, R l (k) For the real part of the cross-correlation result, I l (k) Z (k, l) is the cross correlation operation result, l is the receiving sequence number of OFDM symbol, l is more than or equal to 1, k is the index value of subcarrier signal,
s4, processing the cross-correlation operation result obtained in the step S3 according to the following formula to obtain a first complex signal Z 1 (k,l)：Z 1 (k,l)＝R l (k)+i*I l (k)/k；
S5, carrying out the following calculation on the frequency domain signal corresponding to each OFDM symbol: for the frequency domain signal corresponding to the first OFDM symbol, accumulating all the first complex signals Z corresponding to k 1 (k, l) obtaining the accumulated first complex signal C 1 (l) The method comprises the steps of carrying out a first treatment on the surface of the Find the accumulated first complex signal C 1 (l) Phase phi (l);
s6, according to the accumulated first complex signals C corresponding to the OFDM symbols of each frequency domain 1 (l) Is determined as follows:
if l satisfies the following formula, determining that the position corresponding to l is the inversion position:
|φ(l)+φ(l-1)+…+φ(l-x)-φ(l-x-1)-φ(l-x-2)-…-φ(l-2x-1)|＞ThrPhase
wherein ThrPhase is a threshold parameter, L-j > L > x, and x is more than or equal to 0 and less than or equal to 4;
s7, determining the number of the leading signal symbols according to the determined inversion position, and further realizing frame synchronization.
The beneficial effects of the technical scheme are as follows:
under the condition that the clock deviation is serious, namely the error is +/-300 ppm and even +/-600 ppm, the frame synchronization method is used for determining the inversion position in the preamble signal through cross-correlation calculation, subcarrier phase proportional change elimination calculation, noise elimination calculation and threshold parameter judgment calculation, further determining the number of preamble signal symbols, realizing frame synchronization and ensuring the receiving and transmitting of normal data signals.
Further, in order to eliminate the influence of noise and frequency offset to accurately determine the inversion position, the determination of l corresponding to the inversion position in step S6 also satisfies the following condition:
|φ(l-1)|+|φ(l-2)|+…+|φ(l-2x-1)|＜Thr1
or (b)
Phi (l-1) phi (l-2) phi + … +|phi (l-2 x-1) phi > Thr1 and phi (l) phi < Thr2
Wherein Thr1 and Thr2 are threshold parameters.
Further, for accurate and fast calculation, x=1.
Further, thrphase=2, thr1=2.4, thr2=1.2.
The invention provides a frequency offset estimation method which is characterized by comprising the following steps:
s1, receiving a preamble signal;
s2, converting each time domain OFDM symbol in the preamble signal into a frequency domain to obtain a frequency domain signal corresponding to each OFDM symbolN is one OFDM symbolThe total number of subcarriers in the corresponding frequency domain signal;
s3, carrying out cross-correlation operation on frequency domain signals corresponding to two adjacent OFDM symbols according to the following formula to obtain a cross-correlation operation result:
wherein S is l (k) A kth subcarrier signal which is a frequency domain signal corresponding to the ith OFDM symbol, S l+1 (k) A kth subcarrier signal which is a frequency domain signal corresponding to the (1+1) th OFDM symbol, R l (k) For the real part of the cross-correlation result, I l (k) Z (k, l) is the cross-correlation operation result, l is the receiving sequence number of OFDM symbol, l is not less than 1, k is the index value of subcarrier signal,
s4, processing the cross-correlation operation result obtained in the step S3 according to the following formula to obtain a first complex signal Z 1 (k,l)：Z 1 (k,l)＝R l (k)+i*I l (k)/k；
S5, carrying out the following calculation on the frequency domain signal corresponding to each OFDM symbol: for the frequency domain signal corresponding to the first OFDM symbol, accumulating all the first complex signals Z corresponding to k 1 (k, l) obtaining the accumulated first complex signal C 1 (l) Find the first complex signal C after accumulating 1 (l) Phase phi (l);
s6, according to the accumulated first complex signals C corresponding to the OFDM symbols of each frequency domain 1 (l) Is determined as follows:
if l satisfies the following formula, determining that the position corresponding to l is the inversion position,
|φ(l)+φ(l-1)+…+φ(l-x)-φ(l-x-1)-φ(l-x-2)-…-φ(l-2x-1)|＞ThrPhase
wherein ThrPhase is a threshold parameter, L-j > L > x, x is more than or equal to 0 and less than or equal to 4;
s7, determining the number L of leading signal symbols according to the determined inversion position;
s8, calculating sampling frequency offset according to the determined preamble signal symbol number L.
The beneficial effects of the technical scheme are as follows:
under the condition that the error appears in the clock under the ultra-large clock deviation is +/-300 ppm, serious and even +/-600 ppm, the reverse position is determined through the cross-correlation calculation, the elimination calculation of the proportional change of the subcarrier phase, the noise elimination calculation and the threshold parameter judgment calculation, the number of leading signal symbols is further determined, the frequency offset compensation is realized, the normal data signal is received and transmitted, the frequency offset estimation is not needed to be carried out after the frame synchronization, the operation efficiency is greatly improved, and the receiving time is shortened.
Further, in order to eliminate the influence of noise and frequency offset to accurately determine the inversion position, the following formula is also satisfied when determining the inversion position in step S6:
|φ(l-1)|+|φ(l-2)|+…+|φ(l-2x-1)|＜Thr1
or (b)
Phi (l-1) phi (l-2) phi + … +|phi (l-2 x-1) phi > Thr1 and phi (l) phi < Thr2
Wherein Thr1 and Thr2 are threshold parameters.
Further, the calculation method of the sampling frequency offset in step S8 is as follows:
s801, calculating the cross-correlation operation result obtained in the step S3 according to the following formula to obtain a second complex signal Z 2 (k,l)：Z 2 (k,l)＝R l (k)*k*k+i*I l (k)*k；
S802, carrying out the following calculation on the frequency domain signal corresponding to each OFDM symbol: for the frequency domain signal corresponding to the first OFDM symbol, accumulating all the second complex signals Z corresponding to k 2 (k, l) obtaining an accumulated second complex signal C 2 (l)；
S803, accumulating the accumulated second complex signal C according to the determined preamble signal symbol number L by using the following formula 2 (l) To obtain a relevant parameter C;
wherein j is the integer number of OFDM symbols SYNCP in one period;
s804, calculating sampling frequency deviation delta f according to the related parameter C, wherein the calculation formula of the sampling frequency deviation delta f is as follows:
Δf＝F s *I(C)/(R(C)*2π)
wherein F is s Is the sampling frequency of the signal, I (C) is the imaginary part of the correlation parameter C, and R (C) is the real part of the correlation parameter C.
Further, for accurate and fast calculation, x=1.
Further, thrphase=2, thr1=2.4, thr2=1.2.
Drawings
Fig. 1 is a schematic diagram of a data structure of a preamble of the present invention;
fig. 2 is a flow chart of the present invention for implementing frequency offset estimation and frame synchronization.
Detailed Description
The invention will be further described with reference to the drawings and examples.
Frame synchronization method embodiment:
the present embodiment is described with reference to a high-speed carrier power line communication system, in which the preamble signal designed in the high-speed carrier power line communication protocol has good correlation, can be used for frame timing synchronization, and is known to the receiving end. In general, as shown in fig. 1, the preamble format is a periodic sequence of 13 OFDM symbols, 10.5 SYNCPs and 2.5 SYNCMs, and syncp= -SYNCM, wherein the first 0.5 SYNCPs of the preamble are the second half of SYNCPs and the last 0.5 SYNCMs are the first half of SYNCMs. It can be seen that a periodic splice interrupt occurs at symbol SYNCP10 and symbol SYNCM11, and instead a phase inverted signal is used to splice, i.e., syncp= -SYNCM. The synchronization of the receiving end is realized by utilizing the periodicity and the inversion characteristics of the preamble signal, and the frequency offset estimation is obtained by utilizing the periodicity characteristics of the transmitting end, however, under the condition that a very large clock offset occurs, the receiving signal generates a large phase offset along with the time, and the starting position of the preamble signal is difficult to determine. Meanwhile, due to the fact that the phase changes sharply, the signals with repeated periods are severely distorted, the correlation is greatly reduced, even the signals are reversed, misjudgment is caused, the ending position of the leading signal cannot be normally determined at the moment, and the follow-up sampling clock estimation cannot be normally carried out.
The flow of the embodiment of the frame synchronization method of the invention is shown in fig. 2, and the specific steps comprise the following steps:
s1, determining a starting position of a preamble signal and an ending mark of the preamble signal, wherein the starting mark and the ending mark are defined in advance in a communication system, the phases of a front symbol and a rear symbol are reversed, and a last symbol and a front symbol are set to be in an inverse relation. The start position of the preamble signal as in FIG. 1, i.e., the start point of SYNCP 1; according to the periodicity of the preamble signal, let the periodicity be N, preamble signal S l (N), n=0, …, N-1, 1.ltoreq.l.ltoreq.12; a preamble signal is received.
S2, one OFDM symbol S in the preamble signal l (n) conversion to frequency domain data, a preamble S l (N) converting in the frequency domain into N frequency domain subcarrier signals, wherein the kth subcarrier signal of the frequency domain signal corresponding to the OFDM symbol is denoted as S l (k) K is the frequency domain subcarrier sequence number, l is the reception sequence number of the OFDM symbol,n is the total number of subcarriers in the frequency domain signal corresponding to one OFDM symbol, S l (k) Is a complex value.
The time domain sampling number of each OFDM symbol is N, and the frequency domain sampling number is converted into a frequency domain value of N points after FFT, and corresponds to the frequency domain information of N subcarriers. In high-speed carrier power line communication, the real number is transmitted and received in the real number domain, and the real number FFT conversion is central conjugate symmetrical in the frequency domain, namely only half of information is available, so that the method is generally adopted
S3, S of frequency domain signal corresponding to the first OFDM symbol l (k) S of frequency domain signal corresponding to the (1+1) th OFDM symbol l+1 (k) Performing cross-correlation processing on each corresponding k value in the table, and obtaining a cross-correlation operation result Z (k, l) =R by using a formula (1) l (k)+i*I l (k) I.e. R l (k) As the real part of the cross-correlation result Z (k, l), I l (k) Is the imaginary part of the cross-correlation result Z (k, l).
Wherein S is l (k) A kth subcarrier signal which is a frequency domain signal corresponding to the ith OFDM symbol, S l+1 (k) K is a subcarrier signal of the frequency domain signal corresponding to the (i+1) th OFDM symbol, k is a subcarrier signal index value,
s4, utilizing R l (k) And I l (k) And generates a new first complex signal Z based on formulas (2) and (3) 1 (k, l) and a second complex signal Z 2 (k,l)。
Z 1 (k,l)＝R l (k)+i*I l (k)/k (2)
Z 2 (k,l)＝R l (k)*k*k+i*I l (k)*k (3)
When no noise exists, the frequency offset value can be calculated according to one subcarrier; when noise exists, the same frequency offset is used, the corresponding phase information of different subcarriers is different in change, and the subcarrier phase information is changed in proportion with the increase of the k value, so that the frequency offset is calculated by using a plurality of subcarriers as much as possible. And processing each subcarrier and accumulating to obtain data influenced only by the frequency offset information. In order to eliminate the problem that the corresponding phase information of different subcarriers is different under the same frequency offset, the influence of the factor is eliminated by using the formula (2) and the formula (3) for compensation, and the influence only by the frequency offset factor is remained.
S5, for a certain l, accumulating all first complex signals Z corresponding to k 1 (k, l) obtaining the accumulated first complex signal C based on equation (4) 1 (k, l) and further obtaining the accumulated first complex signal C 1 The phase phi (l) of (k, l).
Wherein, the value range of L is not less than 1 and not more than L-1, and in the embodiment, the value range of L is not less than 1 and not more than 11.
For a certain l, accumulating all second complex signals Z corresponding to k 2 (k, l) obtaining an accumulated second complex signal C based on equation (5) 2 (l) The method comprises the following steps:
after eliminating factors related to phase change among subcarriers, the noise influence is eliminated by adding up for multiple times through the formula (4), and the useful information is overlapped to increase the signal to noise ratio.
S6, the preamble signal symbol comprises L periodic signals at most, and the preamble signal symbol in the embodiment comprises 12 complete periods at most. l is incremented from 1 and the calculations of steps S2 to S6 are repeated. The accumulated first complex signal C 1 The phase phi (l) of (k, l) and the accumulated first complex signal C 2 (l) The value range of l is more than or equal to 1, and l is less than or equal to N-1. Here, the OFDM symbol when l=1 is the first OFDM symbol obtained after the initial synchronization, and is not the first OFDM symbol from which the preamble symbol period starts, and the subsequent OFDM symbols are also ordered in the order obtained after the initial synchronization. Since the number of preamble symbols in the high-speed carrier power line communication system is 12, which is the transmitting end. But to the receiving end, it is blind since the sampling instant does not know at all from which point of which symbol it starts. The starting position is obtained after the initial synchronization, but it is not known what OFDM symbol is. Most desirably from the firstInitially, only the last one is possible. It is also necessary to find the inversion position according to the method of the present invention, and then perform the final synchronization of the preamble, i.e. obtain the synchronization of the current signal frame.
S7, determining the inversion position of the leading signal symbol according to the phase phi (l), namely, determining the position of the inversion position at the front-back phase abrupt change, wherein the inversion position is influenced by noise and frequency deviation, so that a plurality of front-back continuous phases are needed to participate in calculation. Let l start at 4 in this embodiment, i.e., x=4, and the determination is made according to the following equation:
|φ(l)+φ(l-1)-φ(l-2)-φ(l-3)|＞ThrPhase (6)
if equation (6) is satisfied, the determination is again made according to either of the following two equations:
|φ(l-1)|+|φ(l-2)|+|φ(l-3)|＜Thr1 (7)
phi (l-1) phi (l-2) phi (l-3) phi > Thr1 and phi (l) phi < Thr2 (8)
If equation (7) or (8) is satisfied, determining the inversion position, where the number of preamble symbols is l=l+j, where j is the integer number of SYNCM in the preamble, in this embodiment l=l+2; otherwise, increment l, let l=l+1, proceed with the judgment of steps S2 to S7. ThrPhase, thr1 and Thr2 in the formula are threshold parameters, thrphase=2, thr1=2.4, thr2=1.2. Step S7 is repeated for not more than L-j times, in this embodiment L-2, i.e. 10 times, otherwise, the synchronization is considered to be impossible, and no frame signal is sent. S8, determining the number of the preamble signal symbols further realizes frame synchronization, wherein the timing synchronization generally comprises frame synchronization and symbol timing synchronization in the OFDM system, and the frame symbol format in the high-speed carrier power line communication system based on OFDM modulation is fixed, so that the frame synchronization is equivalent to the symbol timing synchronization.
In this embodiment, the inversion position is determined by the following equations (6) to (8), in which 4 OFDM symbols are selected to determine the inversion position. As other embodiments, 6 OFDM symbols may also be selected to determine the inversion position, in other possible embodiments, x=6, and equations (6), (7) and (8) may also be as follows:
|φ(l)+φ(l-1)+φ(l-2)-φ(l-3)-φ(l-4)-φ(l-5)|＞ThrPhase (9)
|φ(l-1)|+|φ(l-2)|+|φ(l-3)|+|φ(l-4)|+|φ(l-5)|＜Thr1 (10)
phi (l-1) phi (l-2) phi++ phi (l-3) phi (l-4) phi++ phi (l-5) phi > Thr1 and phi (l) phi < Thr2 (11)
Of course, other numbers can be selected, and the general formula is as follows:
|φ(l)+φ(l-1)+…+φ(l-x)-φ(l-x-1)-φ(l-x-2)-…-φ(l-2x-1)|＞ThrPhase (12)
|φ(l-1)|+|φ(l-2)|+…+|φ(l-2x-1)|＜Thr1 (13)
or (b)
Phi (l-1) phi (l-2) phi + … + phi (l-2 x-1) phi > Thr1 and phi (l) phi < Thr2 (14)
Wherein L-j > L > x, and 0.ltoreq.x.ltoreq.4.
Frequency offset estimation method embodiment:
the embodiment of the frequency offset estimation method of the present invention is still described by taking a high-speed carrier power line communication system as an example, and the flow is shown in fig. 2, and the process of the method includes:
the preamble symbol number is calculated by the same method as in steps S1 to S7 in the above-described frame synchronization method embodiment. Then, according to the number of the leading signal symbols, calculating the sampling frequency offset, wherein the specific calculating method of the sampling frequency offset comprises the following steps:
s8, accumulating the accumulated second complex signal C according to the determined preamble signal symbol number L by using the following formula 2 (l) To obtain a relevant parameter C;
in the present embodiment, the number of preamble symbols is 12, i.e., l=12, j=2, and the accumulated second complex signal C is accumulated using the following equation (17) 2 (l) And (4) the related parameter C, and further, based on the related parameter C, using a formula (16) to calculate the magnitude of the sampling frequency offset delta f.
S9, calculating sampling frequency deviation delta f according to the related parameter C, wherein the calculation formula of the sampling frequency deviation delta f is as follows:
Δf＝F s *I(C)/(R(C)*2π) (17)
wherein F is s Is the sampling frequency of the signal, I (C) is the imaginary part of the correlation parameter C, and R (C) is the real part of the correlation parameter C.
In summary, the invention has the following characteristics:
1) The frequency offset estimation method provided by the invention can realize the frequency offset estimation value under the condition of the ultra-large clock offset.
2) The frame synchronization method provided by the invention can realize frame synchronization under the condition of ultra-large clock deviation.
3) The invention can simultaneously carry out large frequency offset estimation and frame synchronization without frame synchronization and then frequency offset estimation, thereby greatly improving the operation efficiency and shortening the time for receiving signals.
4) Under the condition of overlarge clock deviation, the method provided by the invention realizes frame synchronization and frequency offset compensation, and ensures the receiving and transmitting of normal data signals.
Claims (9)
1. A method of frame synchronization comprising the steps of:
s1, receiving a preamble signal;
s2, converting each time domain OFDM symbol in the preamble signal into a frequency domain to obtain a frequency domain signal S corresponding to each OFDM symbol l (k)，N is the total number of subcarriers in the frequency domain signal corresponding to one OFDM symbol;
s3, carrying out cross-correlation operation on frequency domain signals corresponding to two adjacent OFDM symbols according to the following formula to obtain a cross-correlation operation result:
wherein S is l (k) A kth subcarrier signal which is a frequency domain signal corresponding to the ith OFDM symbol, S l+1 (k) A kth subcarrier signal which is a frequency domain signal corresponding to the (1+1) th OFDM symbol, R l (k) For the real part of the cross-correlation result, I l (k) Z (k, l) is the cross-correlation operation result, l is the receiving sequence number of OFDM symbol, l is not less than 1, k is the index value of subcarrier signal,
s4, processing the cross-correlation operation result obtained in the step S3 according to the following formula to obtain a first complex signal Z 1 (k,l)：Z 1 (k,l)＝R l (k)+i*I l (k)/k；
S5, carrying out the following calculation on the frequency domain signal corresponding to each OFDM symbol: for the frequency domain signal corresponding to the first OFDM symbol, accumulating all the first complex signals Z corresponding to k 1 (k, l) obtaining the accumulated first complex signal C 1 (l) Find the first complex signal C after accumulating 1 (l) Phase phi (l);
s6, according to the accumulated first complex signals C corresponding to the frequency domain signals corresponding to the OFDM symbols 1 (l) Is determined as follows:
if l satisfies the following formula, determining that the position corresponding to l is the inversion position:
|φ(l)+φ(l-1)+…+φ(l-x)-φ(l-x-1)-φ(l-x-2)-…-φ(l-2x-1)|＞ThrPhase
wherein ThrPhase is a threshold parameter, L-j > L > x, and x is more than or equal to 0 and less than or equal to 4;
s7, determining the number of the leading signal symbols according to the determined inversion position, and further realizing frame synchronization.
2. The frame synchronization method according to claim 1, wherein the determination in step S6 that l corresponding to the inversion position further satisfies the following condition:
|φ(l-1)|+|φ(l-2)|+…+|φ(l-2x-1)|＜Thr1
or (b)
Phi (l-1) phi (l-2) phi + … +|phi (l-2 x-1) phi > Thr1 and phi (l) phi < Thr2
Wherein Thr1 and Thr2 are threshold parameters.
3. The frame synchronization method according to claim 1 or 2, wherein x = 1.
4. The frame synchronization method according to claim 2, wherein thrphase=2, thr1=2.4, and thr2=1.2.
5. The frequency offset estimation method is characterized by comprising the following steps of:
s1, receiving a preamble signal;
s2, converting each time domain OFDM symbol in the preamble signal into a frequency domain to obtain a frequency domain signal S corresponding to each OFDM symbol l (k) K=0, …, N-1, N is the total number of subcarriers in the frequency domain signal corresponding to one OFDM symbol;
s3, carrying out cross-correlation operation on frequency domain signals corresponding to two adjacent OFDM symbols according to the following formula to obtain a cross-correlation operation result:
wherein S is l (k) A kth subcarrier signal which is a frequency domain signal corresponding to the ith OFDM symbol, S l+1 (k) A kth subcarrier signal which is a frequency domain signal corresponding to the (1+1) th OFDM symbol, R l (k) For the real part of the cross-correlation result, I l (k) Z (k, l) is the cross-correlation operation result, l is the receiving sequence number of OFDM symbol, l is not less than 1, k is the index value of subcarrier signal,
s4, processing the cross-correlation operation result obtained in the step S3 according to the following formula to obtain a first complex signal Z 1 (k,l)：Z 1 (k,l)＝R l (k)+i*I l (k)/k；
S5, carrying out the following calculation on the frequency domain signal corresponding to each OFDM symbol: for the frequency domain signal corresponding to the first OFDM symbol, accumulating all the first complex signals Z corresponding to k 1 (k, l) obtaining the accumulated first complex signal C 1 (l) Find the first complex signal C after accumulating 1 (l) Phase phi (l);
s6, according to the accumulated first complex signals C corresponding to the frequency domain signals corresponding to the OFDM symbols 1 (l) Is determined as follows:
if l satisfies the following formula, determining that the position corresponding to l is the inversion position,
|φ(l)+φ(l-1)+…+φ(l-x)-φ(l-x-1)-φ(l-x-2)-…-φ(l-2x-1)|＞ThrPhase
wherein ThrPhase is a threshold parameter, L-j > L > x, x is more than or equal to 0 and less than or equal to 4;
s7, determining the number L of leading signal symbols according to the determined inversion position;
s8, calculating sampling frequency offset according to the determined preamble signal symbol number L.
6. The method for estimating frequency offset according to claim 5, wherein the method for calculating the sampling frequency offset in step S8 is as follows:
s801, calculating the cross-correlation operation result obtained in the step S3 according to the following formula to obtain a second complex signal Z 2 (k,l)：Z 2 (k,l)＝R l (k)*k*k+i*I l (k)*k；
S802, carrying out the following calculation on the frequency domain signal corresponding to each OFDM symbol: for the frequency domain signal corresponding to the first OFDM symbol, accumulating all the second complex signals Z corresponding to k 2 (k, l) obtaining an accumulated second complex signal C 2 (l)；
S803, accumulating the accumulated values according to the determined preamble signal symbol number L by using the following formulaA second complex signal C 2 (l) To obtain a relevant parameter C;
wherein j is the integer number of OFDM symbols SYNCP in one period;
s804, calculating sampling frequency deviation delta f according to the related parameter C, wherein the calculation formula of the sampling frequency deviation delta f is as follows:
Δf＝F s *I(C)/(R(C)*2π)
wherein F is s Is the sampling frequency of the signal, I (C) is the imaginary part of the correlation parameter C, and R (C) is the real part of the correlation parameter C.
7. The method according to claim 5 or 6, wherein the following formula is also satisfied when determining the inversion position in step S6:
|φ(l-1)|+|φ(l-2)|+…+|φ(l-2x-1)|＜Thr1
or (b)
Phi (l-1) phi (l-2) phi + … +|phi (l-2 x-1) phi > Thr1 and phi (l) phi < Thr2
Wherein Thr1 and Thr2 are threshold parameters.
8. The method of frequency offset estimation according to claim 7, wherein x = 1.
9. The method of frequency offset estimation according to claim 7, wherein thrphase=2, thr1=2.4, thr2=1.2.
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| CN104767705A (en) * | 2015-03-19 | 2015-07-08 | 深圳市力合微电子股份有限公司 | Frame synchronizing method and device for power-line carrier communication system based on OFDM modulation |
| US9538537B1 (en) * | 2015-08-11 | 2017-01-03 | Phasorlab, Inc. | Blind carrier synchronization method for OFDM wireless communication systems |
| CN110224968A (en) * | 2019-07-16 | 2019-09-10 | 深圳智微电子科技有限公司 | Frame timing synchronized method and device in a kind of ofdm communication system |
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| CN102263767A (en) * | 2011-08-30 | 2011-11-30 | 北京北方烽火科技有限公司 | Frame synchronization and frequency offset estimation method and device used for wireless communication |
| CN104767705A (en) * | 2015-03-19 | 2015-07-08 | 深圳市力合微电子股份有限公司 | Frame synchronizing method and device for power-line carrier communication system based on OFDM modulation |
| US9538537B1 (en) * | 2015-08-11 | 2017-01-03 | Phasorlab, Inc. | Blind carrier synchronization method for OFDM wireless communication systems |
| CN110224968A (en) * | 2019-07-16 | 2019-09-10 | 深圳智微电子科技有限公司 | Frame timing synchronized method and device in a kind of ofdm communication system |
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