CN113938367B - SC-FDE system frequency offset estimation method using phase difference successive approximation - Google Patents
SC-FDE system frequency offset estimation method using phase difference successive approximation Download PDFInfo
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- CN113938367B CN113938367B CN202111158115.XA CN202111158115A CN113938367B CN 113938367 B CN113938367 B CN 113938367B CN 202111158115 A CN202111158115 A CN 202111158115A CN 113938367 B CN113938367 B CN 113938367B
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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
- H04L27/2659—Coarse or integer 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
- H04L27/2647—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
- H04L27/2689—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation
- H04L27/2692—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation with preamble design, i.e. with negotiation of the synchronisation sequence with transmitter or sequence linked to the algorithm used at the receiver
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Abstract
The invention discloses a frequency offset estimation method of an SC-FDE system by utilizing phase difference successive approximation, and relates to the technical field of broadband wireless communication. The method comprises the following steps: first for the received signal S 0 Coarse frequency offset estimation is carried out on the preamble training sequence of the carrier frequency offset estimation valueThen for the acquired received signal S 0 Carrying out primary frequency offset correction to obtain a signal S 1 The method comprises the steps of carrying out a first treatment on the surface of the For two UW sequences inside the Nth symbol, the phase difference is used to calculate the frequency offsetThe UW sequence formed by combining the Nth symbol and the N-1 th symbol is utilized to sequentially carry out correlation operation on the former N-2 combined UW sequences to obtain the phase difference between the sequences, and N-2 frequency offset arrays are calculated according to the phase differenceWherein i is more than or equal to 1 and less than or equal to N-2; and finally, obtaining a proper frequency offset value for frequency offset estimation through comparison. The method effectively improves the estimation accuracy of the carrier frequency offset.
Description
Technical Field
The invention relates to the technical field of broadband wireless communication.
Background
With the improvement of the scientific and technical level, the technology in the communication field is rapidly developed, and the fourth generation mobile communication taking the OFDM as a key technology has already entered people's life. With the development of wireless communication technology, some new technical problems are also beginning to occur. For example, the blocking of the signal by objects such as buildings and walls on the propagation path can generate reflection, diffraction and scattering phenomena, which can cause the received signal to be a superposition of different delay signals of multiple paths, i.e. the channel has multipath fading, which can seriously affect the propagation of the signal.
To address these problems, research has resulted in the SC-FDE approach. SC-FDE is a very effective method of combating multipath effects in broadband wireless communications. In SC-FDE systems, carrier frequency deviations may occur at the transceiver end, which is mainly due to the limited stability between the receiver crystal and the transmitter crystal, and other reasons are due to the doppler effect under moving conditions. After the signal is transformed into the frequency domain by FFT, the carrier frequency offset is equivalent to adding the inter-carrier interference ICI, and after the signal is transformed into the time domain by IFFT, the received signal still has constellation point offset, which affects symbol judgment and causes the increase of error rate, so the carrier frequency offset needs to be estimated and tracked.
The prior proposal for solving the problem is to only adopt a preamble sequence to carry out frequency offset estimation, the error of the estimation algorithm is larger, and the estimation algorithm is particularly obvious under the condition of longer frame length and when encountering a fast time-varying multipath channel.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a frequency offset estimation method of an SC-FDE system by utilizing phase difference successive approximation, which is realized by the following technical scheme:
the method comprises the steps of setting two identical leader sequences at the head of a signal for carrier coarse synchronization, wherein the head and the tail of each symbol have two identical UW sequences, the UW sequences in each symbol are consistent, and using the phase difference of the UW sequences between the symbols to perform accurate carrier frequency estimation, and the method comprises the following steps:
step 1: by means of the received signal S 0 Coarse frequency offset estimation is carried out on the preamble training sequence of the carrier frequency offset estimation value
Step 2: for the received signal S 0 Carrying out primary frequency offset correction to obtain a signal S 1 ；
Step 3: for signal S 1 The N-th symbol of the sequence calculates the frequency offset by using the phase difference of two UW sequences inside the N-th symbol
Step 4: the UW sequences adjacent to the head and tail between adjacent symbols are combined,generating N-1 combined sequences, using UW sequences formed by combining the N-th symbol and the N-1 th symbol, sequentially carrying out correlation operation on the N-2 previous combined UW sequences to obtain phase differences among the sequences, and calculating N-2 frequency offset arrays according to the phase differencesWherein i is more than or equal to 1 and less than or equal to N-2;
step 5: array is arranged intoThe value of>Subtracting the obtained difference Deltaf s (i) Arranged according to the number sequence of the symbols and according to the sequence from the big number to the small number and the maximum frequency error f calculated theoretically Δmax (i) Comparing;
step 6: in the process of comparing in turn, when the frequency error f at the maximum is obtained Δmax (i) When the difference value is within the range, stopping comparing, and correcting the current symbol frequency offset by taking the frequency offset value in the corresponding frequency offset array; if all the differences are compared to be larger than the maximum frequency error, the calculated in the step 3 is takenAnd correcting the current symbol frequency offset.
Compared with the prior art, the invention has the remarkable advantages that:
1. compared with a method for carrying out coarse frequency offset estimation by using a preamble sequence, the method utilizes the phase difference of UW between symbols to carry out accurate frequency offset estimation, and improves the frequency offset estimation precision better.
2. Under the condition of long frame length, the robust frequency offset estimation precision can still be maintained.
3. Removing the frequency deviation f greater than the maximum Δmax (i) The final frequency offset estimation accuracy is not deteriorated by abrupt frequency offset or other conditions.
The present invention will be described in further detail with reference to the accompanying drawings.
Drawings
FIG. 1 is a schematic diagram of a data processing flow of the present invention.
Fig. 2 is a schematic diagram of a communication signal frame structure in the present invention.
FIG. 3 is a schematic diagram showing the implementation of step 6 in the present invention.
Detailed Description
The invention is further described below with reference to the accompanying drawings, but the scope of the invention is not limited by the embodiments. The method for estimating the frequency offset of the SC-FDE system by utilizing the successive approximation of the phase difference is described with reference to FIG. 1.
As shown in fig. 1, the present invention comprises the following specific steps:
step 1: by means of the received signal S 0 Coarse frequency offset estimation is carried out on the preamble training sequence of the carrier frequency offset estimation value
Preferably, wherein the signal S is received 0 Can be described as:
a (t) represents a modulated signal, f 0 Representing the carrier frequency.
Step 2: for the received signal S 0 Carrying out primary frequency offset correction to obtain a signal S 1 ；
Preferably, the corrected signal S 1 Can be specifically described as follows:
where af represents the hypothetical actual carrier frequency offset,representing the estimated carrier frequency offset.
Step 3: for signal S 1 The N-th symbol of the sequence calculates the frequency offset by using the phase difference of two UW sequences inside the N-th symbol
Preferably, the method for calculating the phase difference between two UW sequences in the symbol is a correlation method, which can be specifically described as:
where Δφ represents the phase difference of two UW sequences, L is the length of the UW sequence, and x (N) represents the UW sequence in the N-th symbol.
Step 4: combining UW sequences adjacent to the head and tail of adjacent symbols to generate N-1 combined sequences, sequentially performing correlation operation on the N-2 combined UW sequences to obtain a phase difference between the sequences by using the UW sequences formed by combining the N-th symbol and the N-1-th symbol, and calculating N-2 frequency offset arrays according to the phase differenceWherein i is more than or equal to 1 and less than or equal to N-2;
preferably, the method for calculating the phase difference of two combined UW sequences between symbols is a correlation method, which can be specifically described as:
wherein the method comprises the steps ofThe phase difference of two UW sequences is represented, 2L is the length of the combined UW sequence, y (N) represents the UW sequence formed by combining the N-th symbol with the N-1 th symbol, and z (N) represents the first N-2 combined UW sequences.
Step 5: array is arranged intoThe value of>Subtracting the obtained difference Deltaf s (i) Arranged according to the number sequence of the symbols and according to the sequence from the big number to the small number and the maximum frequency error f calculated theoretically Δmax (i) Comparing;
preferably, the maximum frequency error can be specifically described as:
wherein f Δmax (i) Represents the maximum frequency error, D i Representing signal delay, T s Representing the sampling period.
Step 6: in the process of comparing in turn, when the frequency error f at the maximum is obtained Δmax (i) When the difference value is within the range, stopping comparing, and correcting the current symbol frequency offset by taking the frequency offset value in the corresponding frequency offset array; if all the differences are compared to be larger than the maximum frequency error, the calculated in the step 3 is takenAnd correcting the current symbol frequency offset.
As can be clearly seen from fig. 3, the parameter D accompanies the comparison process i The value is gradually increased, at the same time, f Δmax (i) The value of (2) is continuously shrinking, i.e. the error range is gradually shrinking. During the initial comparison, the estimateWill be greater than the corresponding f Δmax (1) And f Δmax (2). But will appear at f as the D value increases Δmax (i) Within the range ofThereby obtaining an accurate frequency offset estimation value.
Claims (7)
1. The SC-FDE system frequency offset estimation method using phase difference successive approximation is characterized in that: the signal header has two identical preamble sequences for coarse carrier synchronization, assuming N symbols in the signal, two identical UW sequences in the header and the tail of each symbol, the UW sequences in each symbol being identical, comprising:
step 1: by means of the received signal S 0 Coarse frequency offset estimation is carried out on the preamble training sequence of the carrier frequency offset estimation value
Step 2: for the received signal S 0 Carrying out primary frequency offset correction to obtain a signal S 1 ；
Step 3: for signal S 1 The N-th symbol of the sequence calculates the frequency offset by using the phase difference of two UW sequences inside the N-th symbol
Step 4: combining UW sequences adjacent to the head and tail of adjacent symbols to generate N-1 combined sequences, sequentially performing correlation operation on the N-2 combined UW sequences to obtain a phase difference between the sequences by using the UW sequences formed by combining the N-th symbol and the N-1-th symbol, and calculating N-2 frequency offset arrays according to the phase differenceWherein i is more than or equal to 1 and less than or equal to N-2;
step 5: array is arranged intoThe value of>Subtracting the obtained difference Deltaf s (i) Arranged according to the number sequence of the symbols and according to the sequence from the big number to the small number and the maximum frequency error f calculated theoretically △max (i) Comparing;
step 6: in the process of comparing in turn, when the frequency error f at the maximum is obtained △max (i) When the difference value is within the range, stopping comparing, and correcting the current symbol frequency offset by taking the frequency offset value in the corresponding frequency offset array; if all the differences are compared to be larger than the maximum frequency error, the calculated in the step 3 is takenAnd correcting the current symbol frequency offset.
2. The method for estimating frequency offset of SC-FDE system using successive approximation of phase difference as set forth in claim 1, wherein: the received signal S in the step 1 0 Comprising the following steps:
wherein a (t) represents a modulated signal, f 0 Representing the carrier frequency.
3. The method for estimating frequency offset of SC-FDE system using successive approximation of phase difference according to claim 1, wherein: the coarse frequency offset estimation method in step 1 is to perform correlation operation on two identical preamble sequences of a signal head to obtain a phase difference epsilon, and calculate a coarse frequency offset estimation value according to the phase difference epsilon
4. The method for estimating frequency offset of SC-FDE system using successive approximation of phase difference according to claim 1, wherein: the corrected signal S in the step 2 1 Comprising the following steps:
wherein f 0 Representing the carrier frequency, Δf representing the hypothetical real carrier frequencyThe rate offset is used to determine the rate,representing the estimated carrier frequency offset.
5. The method for estimating frequency offset of SC-FDE system using successive approximation of phase difference according to claim 1, wherein: the method for calculating the phase difference of the two UW sequences in the symbol in the step 3 is a correlation method, and comprises the following steps:
where Δφ represents the phase difference of two UW sequences, L is the length of the UW sequence, and x (N) represents the UW sequence in the N-th symbol.
6. The method for estimating frequency offset of SC-FDE system using successive approximation of phase difference as set forth in claim 1, wherein: the method for calculating the phase difference of the two combined UW sequences between the symbols in the step 4 is a correlation method, which comprises the following steps:
wherein the method comprises the steps ofThe phase difference of two UW sequences is represented, 2L is the length of the combined UW sequence, y (N) represents the UW sequence formed by combining the N-th symbol with the N-1 th symbol, and z (N) represents the first N-2 combined UW sequences.
7. The method for estimating frequency offset of SC-FDE system using successive approximation of phase difference according to claim 1, wherein: the maximum frequency error in step 5 includes:
wherein f △max (i) Represents the maximum frequency error, D i Representing signal delay, T s Representing a sampling period; parameter D as the comparison proceeds i Gradually increase with f △max (i) The value of (2) is continuously reduced, namely the error range is gradually reduced; the estimation accuracy is improved by successive comparisons.
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