CN115118564A - Carrier frequency deviation estimation method and device - Google Patents
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Abstract
The invention discloses a carrier frequency deviation estimation method and a device, and the method comprises the following steps: s01, inputting a sampling sequence received by a digital intermediate frequency receiver, obtaining a complex baseband sequence after down-conversion, and calculating a phase angle of each sampling point in the complex baseband sequence; s02, calculating phase differences between adjacent sampling points according to the calculated phase angles; s03, correcting according to the phase difference between the adjacent sampling points obtained through calculation to remove phase folding, and obtaining a corrected phase difference sequence; and S04, calculating carrier frequency deviation output according to the corrected phase difference sequence. The invention has the advantages of simple realization method, low complexity, small calculation amount, compatibility with various linear modulation patterns, wide application range and the like.
Description
Technical Field
The present invention relates to the field of non-cooperative communication technologies, and in particular, to a carrier frequency offset estimation method and apparatus.
Background
In cooperative communication, carrier frequency deviation is mainly caused by doppler shift and unequal transceiver oscillator frequencies. In non-cooperative communication, because it is difficult for a receiver to know an accurate value of carrier frequency of a transmitter, carrier frequency deviation after down-conversion is often very large and even can be compared with signal bandwidth. The carrier frequency deviation can rotate the signal constellation point, so that carrier synchronization is required for correct demodulation to enable the carrier at the receiving end to have the same frequency as that at the sending end, namely, the corresponding frequency deviation needs to be estimated and compensated, otherwise, the problems of performance reduction of a demodulator, large demodulation loss and the like can be caused, and even correct information data can not be demodulated.
If there is no modulation information, the down-converted received signal is a single frequency signal with a frequency equal to the carrier frequency offset. If the modulation information can be removed from the received signal, a frequency estimation method of a single frequency signal in noise can be used to estimate the carrier frequency offset. In fact, in the data-aided method of the training sequence in the prior art, the main role of the training sequence is to remove the influence of the modulation information on the received signal. For non-cooperative communication, the data-aided approach is not applicable since no a priori information is available, and the pilot information or synchronization header is often unknown. Therefore, in the demodulation process of the non-cooperative signal, only a non-data aided method, generally a method of non-linear transformation, such as a square law method, a cyclic accumulation method, etc., can be used to remove the modulation information in order to obtain the carrier frequency deviation of the signal.
In the prior art, the square law method is to perform M power on a signal correspondingly according to the modulation order M of the signal, discrete spectral lines appear in a frequency spectrum at M times of a carrier frequency, and carrier frequency estimation can be completed by searching frequency points corresponding to the spectral lines, but the calculation amount is large, and the problem of noise power amplification after square or high power exists, so that the square law method is not suitable for high-order modulation signals. The cyclic accumulation method is to extract carrier frequency information by using cyclic moment and cyclic accumulation, has high estimation precision, but has the problems of large calculation amount and high algorithm complexity for high-order modulation signals. For carrier frequency offset estimation, the prior art usually adopts differential operation between symbols, but this kind of method only uses the optimal sampling point of each data symbol for estimation, and must require the receiver to complete symbol synchronization before estimation, and the amount of calculation is large and the complexity is high.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: aiming at the technical problems in the prior art, the invention provides the carrier frequency deviation estimation method and the carrier frequency deviation estimation device which have the advantages of simple implementation method, low complexity, small calculation amount, compatibility with various linear modulation patterns and wide application range.
In order to solve the technical problems, the technical scheme provided by the invention is as follows:
a carrier frequency offset estimation method, comprising the steps of:
s01, inputting a sampling sequence received by a digital intermediate frequency receiver, obtaining a complex baseband sequence after down-conversion, and calculating a phase angle of each sampling point in the complex baseband sequence;
s02, calculating phase differences between adjacent sampling points according to the calculated phase angles;
s03, correcting according to the phase difference between the adjacent sampling points obtained through calculation to remove phase folding, and obtaining a corrected phase difference sequence;
and S04, calculating carrier frequency deviation output according to the corrected phase difference sequence.
Further, in step S01, a cordic algorithm is used to calculate the instantaneous phase angle of the complex baseband sequence, and the calculation expression is:
wherein,
for instantaneous phase angle sequences, n denotes the time of day, phi a (n) phase at time n of data symbol, Im [ x (n)]Is the imaginary part of the complex base band sequence x (n), Re [ x (n)]Is the real part, T, of the complex baseband sequence x (n) s For the sampling interval time, Δ f is the carrier frequency deviation, Φ N And (n) is phase disturbance caused by channel noise.
Further, in step S02, the instantaneous phase difference between adjacent sampling points is specifically calculated according to the following formula:
wherein,
is the instantaneous phase angle at time n,
is the phase angle at the time n-1,
for a sequence of instantaneous phase differences, T s For the sampling interval time, Δ f is the carrier frequency deviation, Φ a (n) is the phase at time n of the data symbol, phi N And (n) is phase disturbance caused by channel noise at the time n.
Further, in step S03, the phase difference between the adjacent sampling points is corrected specifically according to the following formula:
wherein,
is a sequence of phase angles and is,
in order to be a sequence of instantaneous phase differences,
for the corrected instantaneous phase difference sequence, n represents the time of day.
Further, after the step S03 and before the step S04, low-pass filtering is performed on the corrected phase difference sequence to obtain a filtered signal output.
Further, in step S04, the carrier frequency offset is specifically calculated according to the following formula:
wherein,
low-pass filtered signal, T, for said corrected phase difference sequence s Is the sampling interval time.
A carrier frequency offset estimation apparatus comprising:
the phase angle calculation module is used for inputting a sampling sequence received by the digital intermediate frequency receiver, obtaining a complex baseband sequence after down-conversion, and calculating the phase angle of each sampling point in the complex baseband sequence;
the phase difference calculation module is used for calculating the phase difference between adjacent sampling points according to each phase angle obtained by calculation;
the phase folding removal module is used for correcting according to the phase difference between the adjacent sampling points obtained through calculation so as to remove phase folding and obtain a corrected phase difference sequence;
and the frequency deviation calculation module is used for calculating carrier frequency deviation output according to the corrected phase difference sequence.
Further, a low-pass filtering module is connected between the phase folding removal module and the frequency deviation calculation module, and is used for performing low-pass filtering on the corrected phase difference sequence to obtain a filtered signal output.
A computer device comprising a processor and a memory for storing a computer program, the processor being adapted to execute the computer program to perform the method as described above.
A computer-readable storage medium having stored thereon a computer program which, when executed, implements the method as described above.
Compared with the prior art, the invention has the advantages that:
1. the carrier frequency deviation estimation method and the carrier frequency deviation estimation device do not need to remove modulation information in signals, carry out carrier frequency deviation estimation on baseband signals directly, have low complexity and small calculated amount, have an estimation process irrelevant to modulation orders, can be compatible with various linear modulation modes such as FSK/MSK/MPSK/DMPSK/MAPSK/MQAM and the like, simultaneously estimate by utilizing all sampling data sequences without paying attention to sampling position deviation, realize carrier frequency deviation estimation before symbol synchronization and have a very large adaptive carrier frequency deviation range.
2. The carrier frequency deviation estimation method and the carrier frequency deviation estimation device can be suitable for non-cooperative communication and high-order modulation signals, the non-cooperative communication does not need to be identified in a modulation mode in advance, the high-order modulation signals do not need to be subjected to high-order nonlinear calculation, the problem of noise power amplification does not exist, the complexity is not increased, and the realization complexity and the calculation amount can be greatly reduced.
3. The carrier frequency deviation estimation method and the device realize carrier frequency deviation estimation by combining differential operation of adjacent sampling points, can remove modulation information by the differential operation, do not need to remove the modulation information by utilizing prior information such as training sequences and the like or by nonlinear transformation like the traditional estimation method, further combine a narrow-band low-pass filter, can filter out phase difference distortion values at jump positions of adjacent symbols, do not need prior information such as the training sequences and the like or remove the modulation information by nonlinear transformation, can quickly and efficiently realize accurate carrier frequency deviation estimation, have low complexity and are easy to realize engineering.
Drawings
Fig. 1 is a schematic flow chart of a carrier frequency offset estimation method according to this embodiment.
Fig. 2 is a schematic structural diagram of the carrier frequency offset estimation device of the present embodiment.
Fig. 3 is a schematic flow chart of the carrier frequency offset estimation implemented in the embodiment of the present invention.
Detailed Description
The invention is further described below with reference to the drawings and specific preferred embodiments of the description, without thereby limiting the scope of protection of the invention.
As shown in fig. 1 and 2, the carrier frequency offset estimation method of the present embodiment includes the steps of:
s01, inputting a sampling sequence received by a digital intermediate frequency receiver, obtaining a complex baseband sequence after down-conversion, and calculating a phase angle of each sampling point in the complex baseband sequence;
s02, calculating phase differences between adjacent sampling points according to the calculated phase angles;
s03, correcting according to the phase difference between the adjacent sampling points obtained through calculation to remove phase folding, and obtaining a corrected phase difference sequence;
and S04, calculating carrier frequency deviation output according to the corrected phase difference sequence.
Considering that the sampling frequency in the digital intermediate frequency receiver is far greater than the symbol rate, the embodiment implements carrier frequency deviation estimation by combining the differential operation of adjacent sampling points on the basis that the used sampling frequency is far greater than the symbol rate, and since most of the adjacent sampling points are in the same data symbol, the modulation information of the adjacent sampling points can be considered to be the same, the modulation information can be removed by the differential operation without using prior information such as training sequences or removing the modulation information by nonlinear transformation as in the conventional method. And because all the sampled data sequences are used for estimation, rather than only the optimal sampling point of each data symbol as in the traditional estimation mode, the estimation does not need to pay attention to the sampling position deviation, and the estimation of the carrier frequency deviation is not influenced even if the symbol synchronization is not finished by signals, the estimation of the carrier frequency deviation can be realized before the symbol synchronization, the carrier synchronization is finished, so that the selection of a receiver symbol synchronization algorithm is wider, and the realization complexity is greatly reduced.
For the digital intermediate frequency receiver, the sampling sequence r (n) of the received signal is subjected to digital down-conversion to obtain a complex baseband signal sequence x (n), which can be expressed as:
where A is the signal amplitude, a (mTs) is the transmitted data symbol, g [ (n-m) T s ]For shaping the filtered impulse response, M is the shaping filter order, T s For the sampling interval, Δ f is the carrier frequency deviation, θ is the initial phase of the carrier, N (nT) s ) The signal is sampled for noise.
In step S01 of this embodiment, a cordic algorithm is specifically adopted to calculate the phase of each sample point in the complex baseband signal sequence x (n) according to the following formula, so as to obtain an instantaneous phase sequence
Wherein, Im [ x (n)]Is the imaginary part of the complex base band sequence x (n), Re [ x (n)]Is the real part, Φ, of the complex baseband sequence x (n) a (n) is the phase at time n of the data symbol, related only to the transmitted data symbol and the shaping filter, phi N And (n) is phase disturbance caused by channel noise.
The amplitude and phase angle of the complex baseband signal sequence x (n) satisfy the relation:
wherein a (n) is the amplitude value of the complex baseband signal sequence x (n),
is the phase angle of the complex baseband signal sequence x (n).
Calculating instantaneous phase sequence as described above
Thereafter, step S02 of the present embodiment further calculates the instantaneous phase sequence
In every two adjacent miningPhase difference between the samples. The frequency is the first difference of the instantaneous phase sequence, i.e.:
wherein,
is the instantaneous phase angle at time n,
is the phase angle at the time instant n-1,
is the nth instantaneous phase difference.
Calculating the phase difference between two adjacent sampling points of the complex baseband signal sequence x (n)
The specific expression of (A) is as follows:
since the phase of x (n) is calculated modulo 2 pi, there is a phase fold that needs to be corrected for the instantaneous phase difference of adjacent samples. In step S03, the present embodiment corrects the phase difference between adjacent sampling points according to the following formula:
wherein,
is a corrected instantaneous phase difference sequence.
In this embodiment, after step S03 and before step S04, the method further includes performing low-pass filtering on the corrected phase difference sequence to obtain a filtered signal output.
Sampling frequency f in digital intermediate frequency receiver s Will be much larger than the data symbol rate R s I.e. the sampling interval time Ts is much smaller than the width of the transmitted data symbol, the phases of two adjacent sampling points of the transmitted signal can be considered equal except near the transition point of the transmitted data symbol, i.e.:
Φ a (n)≈Φ a (n-1) (7)
and [ phi ] because the transmitted data symbols are random a (n)-Φ a (n-1)]Has a mean value of zero, [ phi ] N (n) is the phase perturbation due to channel noise, thus [ phi ] N (n)-Φ N (n-1)]Should also be zero. Calculated by equation (5)
Passing through a narrow band (the passband bandwidth is much less than the symbol rate R s ) After the low-pass filtering, the phase distortion value near the data symbol jumping point and the phase disturbance caused by channel noise can be sent, namely the last two terms ([ phi ] of the right side of the equation (5) are filtered a (n)-Φ a (n-1 and. PHINn-1). Then to the corrected instantaneous phase difference sequence
After narrow-band low-pass filtering, the following components are obtained:
for the corrected instantaneous phase difference sequence
After narrow-band low-pass filtering, phase disturbance caused by data symbols and noise can be filtered out to obtain filtered signals
The passband of the low-pass filter is much smaller than the symbol rate R of the signal s Start of stop bandFrequency is also less than R s 。
In step S04 of this embodiment, the carrier frequency deviation is calculated according to the following formula specifically based on the relationship between the frequency and the phase:
wherein,
low-pass filtered signal, T, for the corrected phase difference sequence s Is the sampling period.
In the embodiment, by adopting a differential operation method of adjacent sampling points, modulation information in signals does not need to be removed, carrier frequency offset estimation is directly performed on baseband signals, and a narrow-band low-pass filter is further combined to filter out a phase difference distortion value at a jump position of adjacent symbols, so that accurate carrier frequency offset estimation can be quickly and efficiently realized.
The adaptive carrier frequency deviation range is an important index for estimating the carrier frequency deviation, and the sampling frequency f of the invention is s Much larger than the symbol rate R s And the difference operation between adjacent sampling points is adopted, and the carrier frequency offset range is ((-f) s /4,f s 4) greater than the symbol rate R of the signal s In a non-cooperative communication scene, the method can be used for directly carrying out carrier frequency offset estimation on the signal without pretreatment such as carrier frequency rough estimation and the like.
In a specific application embodiment, as shown in fig. 3, a detailed procedure for implementing carrier frequency offset estimation includes:
step 1: the amplitude and phase angle of the complex baseband sequence x (n) are calculated using cordic algorithm.
Wherein a (n) is the amplitude value of x (n),
is the phase angle of x (n).
Step 2: calculating the instantaneous phase difference of adjacent sampling points:
and step 3: removing phase folding, and correcting the instantaneous phase difference of adjacent sampling points:
and 4, step 4: for corrected instantaneous phase difference sequence
Narrow-band low-pass filtering is carried out to filter out phase disturbance caused by data symbols and noise to obtain filtered signals
The passband of the low-pass filter is much smaller than the symbol rate R of the signal s The starting frequency of the stop band is less than R s 。
And 5: according to frequency and phase relationship, according to filtered
Calculating a frequency value to obtain a carrier frequency deviation:
as shown in fig. 2, the carrier frequency offset estimation device of the present embodiment includes:
the phase angle calculation module is used for inputting a sampling sequence received by the digital intermediate frequency receiver, obtaining a complex baseband sequence after down-conversion, and calculating the phase angle of each sampling point in the complex baseband sequence;
the phase difference calculation module is used for calculating the phase difference between adjacent sampling points according to each phase angle obtained by calculation;
the phase folding removal module is used for correcting according to the phase difference between the adjacent sampling points obtained through calculation so as to remove phase folding and obtain a corrected phase difference sequence;
and the frequency deviation calculation module is used for calculating the carrier frequency deviation output according to the corrected phase difference sequence.
In this embodiment, a low-pass filtering module is further connected between the phase folding removal module and the frequency deviation calculation module, so as to perform low-pass filtering on the corrected phase difference sequence, and obtain a filtered signal output.
As shown in fig. 2, the phase angle calculation module includes a down-conversion circuit composed of two multipliers and a phase angle calculation circuit, the down-conversion circuit inputs a sampling sequence r (n), outputs two paths of intersecting signals i (n) and q (n) through down-conversion, and calculates the phase angle of a complex baseband sequence x (n) by the phase angle calculation circuit according to a cordic algorithm; the phase difference calculation module samples a differential circuit and calculates an instantaneous phase difference sequence according to a formula (4)
Outputting the filtered signal after correction and low-pass filtering
And calculating the final frequency deviation delta f and outputting the final frequency deviation delta f through a frequency deviation calculation module according to the formula (8).
The carrier frequency offset estimation apparatus of the present embodiment corresponds to the carrier frequency offset estimation method one by one, and is not described herein again.
The present embodiment also provides a computer device comprising a processor and a memory, the memory being configured to store a computer program, the processor being configured to execute the computer program to perform the method as described above.
The present embodiment is a computer-readable storage medium storing a computer program, which when executed implements the method described above.
The invention can quickly and efficiently realize the carrier frequency offset estimation of the baseband signal, has very wide modulation modes, can be compatible with various linear modulation modes such as FSK/MSK/MPSK/DMPSK/MAPSK/MQAM and the like, does not need to change the realization structure and parameter configuration, is independent of the modulation order, does not need to carry out modulation mode identification in advance if being applied to non-cooperative communication, does not need to carry out high-order nonlinear calculation when being applied to high-order modulation signals, does not have the problem of noise power amplification, does not increase the complexity, and can greatly reduce the realization complexity and the calculated amount.
The foregoing is considered as illustrative of the preferred embodiments of the invention and is not to be construed as limiting the invention in any way. Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention shall fall within the protection scope of the technical solution of the present invention, unless the technical essence of the present invention departs from the content of the technical solution of the present invention.
Claims (10)
1. A carrier frequency offset estimation method, characterized by comprising the steps of:
s01, inputting a sampling sequence received by a digital intermediate frequency receiver, obtaining a complex baseband sequence after down-conversion, and calculating a phase angle of each sampling point in the complex baseband sequence;
s02, calculating phase differences between adjacent sampling points according to the calculated phase angles;
s03, correcting according to the phase difference between the adjacent sampling points obtained through calculation to remove phase folding, and obtaining a corrected phase difference sequence;
and S04, calculating carrier frequency deviation output according to the corrected phase difference sequence.
2. The method for estimating carrier frequency offset according to claim 1, wherein in step S01, a cordic algorithm is used to calculate the instantaneous phase angle of the complex baseband sequence, and the calculation expression is:
wherein,
for instantaneous phase angle sequences, n denotes the time of day, phi a (n) phase at time n of data symbol, Im [ x (n)]Is the imaginary part of the complex baseband sequence x (n), Re [ x (n)]Is the real part, T, of the complex baseband sequence x (n) s For the sampling interval time, Δ f is the carrier frequency deviation, Φ N And (n) is phase disturbance caused by channel noise.
3. The carrier frequency offset estimation method according to claim 1, wherein in step S02, the instantaneous phase difference of adjacent sample points is calculated according to the following formula:
wherein,
is the instantaneous phase angle at time n,
is the phase angle at the time n-1,
for a sequence of instantaneous phase differences, T s For the sampling interval, Δ f is the carrier frequency deviation, Φ a (n) is the phase at time n of the data symbol, phi N And (n) is phase disturbance caused by channel noise at the time n.
4. The carrier frequency offset estimation method according to claim 1, wherein in step S03, the phase difference between the adjacent sample points is corrected specifically according to the following formula:
wherein,
is a sequence of instantaneous phase angles and,
in order to be a sequence of instantaneous phase differences,
for the corrected instantaneous phase difference sequence, n represents the time of day.
5. The method for estimating carrier frequency offset according to any of claims 1-4, further comprising after step S03 and before step S04, performing narrow-band low-pass filtering on the corrected phase difference sequence to obtain a filtered signal output.
6. The method for estimating carrier frequency offset according to claim 5, wherein in step S04, the carrier frequency offset is calculated specifically according to the following formula:
wherein,
low-pass filtered signal, T, for said corrected phase difference sequence s Is the sampling interval time.
7. A carrier frequency offset estimation apparatus, comprising:
the phase angle calculation module is used for inputting a sampling sequence received by the digital intermediate frequency receiver, obtaining a complex baseband sequence after down-conversion, and calculating the phase angle of each sampling point in the complex baseband sequence;
the phase difference calculation module is used for calculating the phase difference between adjacent sampling points according to each phase angle obtained through calculation;
the phase folding removal module is used for correcting according to the phase difference between the adjacent sampling points obtained through calculation so as to remove phase folding and obtain a corrected phase difference sequence;
and the frequency deviation calculation module is used for calculating carrier frequency deviation output according to the corrected phase difference sequence.
8. The carrier frequency offset estimation device according to claim 7, wherein a low-pass filtering module is further connected between the phase folding removal module and the frequency offset calculation module, and is configured to perform low-pass filtering on the corrected phase difference sequence to obtain a filtered signal output.
9. A computer device comprising a processor and a memory for storing a computer program, wherein the processor is configured to execute the computer program to perform the method of any one of claims 1 to 6.
10. A computer-readable storage medium storing a computer program, wherein the computer program when executed implements the method of any one of claims 1 to 6.
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