CN115118564B - 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, wherein 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 the 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 calculated phase difference between the adjacent sampling points to remove phase folding, and obtaining a corrected phase difference sequence; s04, calculating carrier frequency deviation output according to the corrected phase difference sequence. The invention has the advantages of simple implementation method, low complexity, small calculation amount, compatibility with various linear modulation modes, 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 deviation estimation method and apparatus.
Background
In cooperative communication, carrier frequency offset is mainly caused by doppler shift, and unequal transceiver oscillator frequencies. In non-cooperative communications, the receiver is difficult to know the accurate value of the carrier frequency of the transmitter, so the carrier frequency deviation after down-conversion is often very large and can even be compared with the signal bandwidth. The carrier frequency deviation can rotate the signal constellation point, so that carrier synchronization is needed for correct demodulation to make the carrier of the receiving end and the transmitting end have the same frequency, namely, the corresponding frequency deviation needs to be estimated and compensated, otherwise, the problems of performance degradation, demodulation loss increase and the like of the demodulator can be caused, and even correct information data cannot be demodulated.
If the modulation information is not affected, the down-converted received signal is a single frequency signal with the 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 training sequence is mainly used for removing the influence of the modulation information on the received signal. For non-cooperative communication, the pilot information or synchronization header is often unknown, and data assistance is not applicable, since it does not have a priori information. Therefore, in the demodulation process of the non-cooperative signal, only a non-data auxiliary method, such as square law method, cyclic accumulation method, etc., can be adopted to obtain the carrier frequency deviation of the signal, and a nonlinear transformation method is usually adopted to remove the modulation information.
In the prior art, the square law method correspondingly carries out M times on the signal according to the modulation order M of the signal, a frequency spectrum can generate discrete spectral lines at M times of carrier frequency, carrier frequency estimation can be completed by searching frequency points corresponding to the spectral lines, but the calculated amount is large, and the problem of noise power amplification after square or high power exists, so that the square law method is not applicable to high-order modulated signals. The cyclic accumulation method is to extract carrier frequency information by using cyclic moment and cyclic accumulation, and has high estimation accuracy, but has the problems of large calculation amount and high algorithm complexity for high-order modulation signals. For carrier frequency deviation estimation, the prior art usually adopts inter-symbol differential operation, but this type of method only uses the best sampling point of each data symbol to estimate, which must require the receiver to complete symbol synchronization before estimation, and has large calculation amount and high complexity.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: aiming at the technical problems existing in the prior art, the invention provides the carrier frequency deviation estimation method and the carrier frequency deviation estimation device which are simple in implementation method, low in complexity, small in calculation amount, capable of being compatible with various linear modulation patterns and wide in application range.
In order to solve the technical problems, the technical scheme provided by the invention is as follows:
a carrier frequency deviation estimation 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 the 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 calculated phase difference between the adjacent sampling points to remove phase folding, and obtaining a corrected phase difference sequence;
s04, calculating carrier frequency deviation output according to the corrected phase difference sequence.
Further, in the step S01, the instantaneous phase angle of the complex baseband sequence is calculated by using a cordic algorithm, and the calculation expression is as follows:
wherein,for instantaneous phase angle sequence, n represents time, Φ a (n) phase at time n of data symbol, im [ x (n)]Re [ x (n) is the imaginary part of the complex baseband sequence x (n)]Is the real part of the complex baseband sequence x (n), T s For the sampling interval time, Δf is the carrier frequency deviation, Φ N And (n) is the phase disturbance caused by the channel noise.
Further, in the step S02, the instantaneous phase difference between the adjacent sampling points is calculated specifically according to the following formula:
wherein,for the instantaneous phase angle at time n +.>Is the phase angle at time n-1, +.>T is the instantaneous phase difference sequence s For the sampling interval time, Δf is the carrier frequency deviation, Φ a (n) phase of data symbol at time n, Φ N And (n) is phase disturbance caused by channel noise at time n.
Further, in the step S03, the phase difference between the adjacent sampling points is specifically corrected according to the following formula:
wherein,for the phase angle sequence>For transient phase difference sequence, +.>For the corrected instantaneous phase difference sequence, n represents the time.
Further, the step S03 and the step S04 are followed by low-pass filtering the corrected phase difference sequence to obtain a filtered signal output.
Further, in the step S04, the carrier frequency deviation is calculated specifically according to the following formula:
wherein,low-pass filtering the corrected phase difference sequence to obtain a signal T s Is the sampling interval time.
A carrier frequency offset estimation device 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 the calculated phase angles;
the phase folding removing module is used for correcting according to the calculated phase difference between the adjacent sampling points 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 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.
A computer device comprising a processor and a memory for storing a computer program, the processor being for executing the computer program to perform a method as described above.
A computer readable storage medium storing a computer program which when executed performs a method as described above.
Compared with the prior art, the invention has the advantages that:
1. the carrier frequency deviation estimation method and device of the invention do not need to remove modulation information in signals, directly carry out carrier frequency deviation estimation on baseband signals, have low complexity and small calculated amount, the estimation process is irrelevant to modulation orders, can be compatible with various linear modulation modes such as FSK/MSK/MPSK/DMPSK/MAPSK/MQAM and the like, simultaneously utilize all sampling data sequences to estimate, do not need to pay attention to sampling position deviation, can realize carrier frequency deviation estimation before symbol synchronization, and has 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, do not need to identify a modulation mode in advance for the non-cooperative communication, do not need to conduct high-order nonlinear calculation for the high-order modulation signals, cannot have the problem of noise power amplification, cannot increase complexity, and can greatly reduce the implementation complexity and the calculation amount.
3. According to the carrier frequency deviation estimation method and device, carrier frequency deviation estimation is achieved through combining differential operation of adjacent sampling points, modulation information can be removed through differential operation, prior information such as training sequences and the like or modulation information is removed through nonlinear transformation in a traditional estimation method is not needed, a narrow-band low-pass filter is further combined, phase difference distortion values at adjacent symbol jump positions can be filtered, prior information such as training sequences and the like or modulation information is removed through nonlinear transformation, accurate carrier frequency deviation estimation can be achieved rapidly and efficiently, complexity is low, and engineering implementation is easy.
Drawings
Fig. 1 is a schematic flow chart of an implementation of the carrier frequency deviation estimation method of the present embodiment.
Fig. 2 is a schematic diagram of the carrier frequency deviation estimating device according to the present embodiment.
Fig. 3 is a flow chart illustrating the implementation of carrier frequency offset estimation in a specific application embodiment of the present invention.
Detailed Description
The invention is further described below in connection with the drawings and the specific preferred embodiments, but the scope of protection of the invention is not limited thereby.
As shown in fig. 1 and 2, the carrier frequency deviation 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 the 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 calculated phase difference between the adjacent sampling points to remove phase folding, and obtaining a corrected phase difference sequence;
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 realizes carrier frequency deviation estimation by combining differential operation of adjacent sampling points on the basis that the sampling frequency is far greater than the symbol rate, and because most of the conditions of the adjacent sampling points which are subjected to differential 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, and the prior information such as a training sequence and the like is not needed to be utilized or the modulation information is removed by nonlinear conversion as in the traditional method. And because all sampled data sequences are utilized for estimation, rather than only using the optimal sampling point of each data symbol as in the traditional estimation mode, sampling position deviation does not need to be concerned, and the signal does not influence the estimation of carrier frequency deviation even if symbol synchronization is not completed, so that the estimation of carrier frequency deviation can be realized before symbol synchronization and carrier synchronization is completed, thereby leading the selection of a receiver symbol synchronization algorithm to be wider and greatly reducing the realization complexity.
For a digital intermediate frequency receiver, a sampling sequence r (n) of a received signal is subjected to digital down-conversion to obtain a complex baseband signal sequence x (n), which can be expressed as:
wherein A is signal amplitude, a (mTs) is transmitted data symbol, g [ (n-m) T s ]For shaping the filter impulse response, M is the shaping filter order, T s For the sampling interval time, Δf is the carrier frequency deviation, θ is the carrier initial phase,N(nT s ) Is a noise sampled signal.
In step S01 of this embodiment, the cordic algorithm is specifically adopted to calculate the phase of each sampling point in the complex baseband signal sequence x (n) according to the following method, so as to obtain an instantaneous phase sequence
Wherein Im [ x (n)]Re [ x (n) is the imaginary part of the complex baseband sequence x (n)]Is the real part of the complex baseband sequence x (n), Φ a (n) the phase of the data symbol at time n, which is related only to the transmitted data symbol and the shaping filter, Φ N And (n) is the phase disturbance caused by the channel noise.
The amplitude and phase angle of the complex baseband signal sequence x (n) satisfy the relation:
where 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 the instantaneous phase sequence according to the aboveAfter that, step S02 of the present embodiment further calculates the instantaneous phase sequence +.>Every two adjacent sampling points. The frequency is the first difference of the instantaneous phase sequence, namely:
wherein,for the instantaneous phase angle at time n +.>Is the phase angle at time n-1, +.>Is the nth instantaneous phase difference.
Then the phase difference between two adjacent sampling points of the complex baseband signal sequence x (n) is calculatedThe specific expression of (2) is:
since the phase of x (n) is calculated as modulo 2pi, there is a phase folding that corrects the instantaneous phase difference of neighboring sampling points. In step S03 of this embodiment, the phase difference between adjacent sampling points is specifically corrected according to the following formula:
wherein,is the corrected instantaneous phase difference sequence.
In this embodiment, after step S03 and before step S04, low-pass filtering is performed on the corrected phase difference sequence to obtain a filtered signal output.
Sampling frequency f in digital intermediate frequency receiver s Will be much greater than the data symbol rate R s I.e. the sampling interval time Ts is much smaller than the width of the transmitted data symbolsThe phases of two adjacent sampling points of the transmission signal except for the vicinity of the transmission data symbol hopping point can be considered to be equal, namely:
Φ a (n)≈Φ a (n-1) (7)
and because the transmitted data symbols have randomness, [ phi ] a (n)-Φ a (n-1)]Is zero in average value phi N (n) is the phase disturbance caused by channel noise, thus [ phi ] N (n)-Φ N (n-1)]Should also be zero. Calculated by equation (5)Through narrow band (passband bandwidth is much smaller than symbol rate R s ) Can transmit phase distortion values near the data symbol trip point and phase disturbance caused by channel noise, namely the two last two items ([ phi ] of the right side of the equation of the filtering formula (5) a (n)-Φ a (n-1 and Φnn-1). Then +.>The narrow band low pass filtering is followed by:
for corrected instantaneous phase difference sequenceAfter narrow-band low-pass filtering, phase disturbance caused by data symbols and noise can be filtered out to obtain a filtered signal +.>The passband of the low pass filter is much smaller than the symbol rate R of the signal s The stop band initial frequency is also smaller than R s 。
In step S04 of this embodiment, according to the relationship between frequency and phase, the carrier frequency deviation is calculated according to the following formula:
wherein,low-pass filtering the corrected phase difference sequence to obtain a signal T s Is the sampling period.
According to the method, the differential operation method of adjacent sampling points is adopted, modulation information in signals is not required to be removed, carrier frequency offset estimation is directly carried out on baseband signals, phase difference distortion values at adjacent symbol jumping positions are further filtered through a narrow-band low-pass filter, accurate carrier frequency offset estimation can be quickly and efficiently achieved, the complexity is low, the calculated amount is small, engineering implementation is easy, the estimation process is irrelevant to modulation orders, various linear modulation modes such as FSK/MSK/MPSK/DMPSK/MAPSK/MQAM can be compatible, symbol synchronization is not required to be completed first, and carrier frequency offset estimation can be completed before symbol synchronization.
The adaptive carrier frequency offset range is an important index for carrier frequency offset estimation, and the invention adopts the sampling frequency f s Much greater than the symbol rate R s And is the differential operation between adjacent sampling points, the adaptive 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 signals without preprocessing such as carrier frequency coarse estimation and the like.
In a specific application embodiment, as shown in fig. 3, a detailed flow for implementing carrier frequency deviation estimation is as follows:
step 1: the amplitude and phase angle of the complex baseband sequence x (n) are calculated using the 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:
step 3: removing phase folding, and correcting the instantaneous phase difference of adjacent sampling points:
step 4: for corrected instantaneous phase difference sequenceCarrying out narrow-band low-pass filtering to remove phase disturbance caused by data symbol and noise to obtain filtered signal +.>The passband of the low pass filter is much smaller than the symbol rate R of the signal s The stop band initial frequency is also smaller than R s 。
Step 5: according to the relation between frequency and phase, according to the filteringCalculating carrier frequency deviation of the frequency value:
as shown in fig. 2, the carrier frequency deviation estimating 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 the calculated phase angles;
the phase folding removing module is used for correcting according to the calculated phase difference between the adjacent sampling points 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.
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 comprises a down-conversion circuit formed by 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 the phase angle calculation circuit calculates the phase angle of a complex baseband sequence x (n) according to a cordic algorithm; the phase difference calculation module samples the differential circuit and calculates to obtain an instantaneous phase difference sequence according to the formula (4)Output, output the filtered signal after correction and low-pass filtering module>And then the final frequency deviation delta f is calculated according to the formula (8) through a frequency deviation calculation module.
The carrier frequency deviation estimation device in this embodiment corresponds to the carrier frequency deviation estimation method in a one-to-one manner, and will not be described in detail here.
The present embodiment also provides a computer device comprising a processor and a memory, the memory being for storing a computer program, the processor being for executing the computer program to perform a method as described above.
The present embodiment is a computer-readable storage medium storing a computer program that when executed implements the method described above.
The invention can rapidly and efficiently realize carrier frequency offset estimation of baseband signals, has very wide modulation patterns, can be compatible with various linear modulation patterns such as FSK/MSK/MPSK/DMPSK/MAPSK/MQAM and the like, does not need to change the realization structure, parameter configuration and realize independence of modulation orders, does not need to recognize a modulation mode 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 complexity, and can greatly reduce the realization complexity and the calculated amount.
The foregoing is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. While the invention has been described with reference to preferred embodiments, it is not intended to be limiting. Therefore, any simple modification, equivalent variation and modification of the above embodiments according to the technical substance of the present invention shall fall within the scope of the technical solution of the present invention.
Claims (8)
1. 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 the 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 calculated phase difference between the adjacent sampling points to remove phase folding, and obtaining a corrected phase difference sequence;
s04, calculating carrier frequency deviation output according to the corrected phase difference sequence, and specifically calculating carrier frequency deviation according to the following formula:
wherein,low-pass filtering the corrected phase difference sequence to obtain a signal, ">Is the sampling interval time;
in the step S01, a cordic algorithm is adopted to calculate an instantaneous phase angle of the complex baseband sequence, and the calculation expression is as follows:
；
wherein,for a sequence of instantaneous phase angles, n denotes the moment, +.>Phase at time n of the data symbol, +.>For complex baseband sequences->Imaginary part of->For complex baseband sequences->Real part of->For sampling interval time, +.>For carrier frequency deviation, < >>Is the phase disturbance caused by channel noise.
2. The carrier frequency deviation estimation method according to claim 1, wherein in the step S02, the instantaneous phase difference between adjacent sampling points is calculated according to the following formula:
wherein,for the instantaneous phase angle at time n +.>Is the phase angle at time n-1, +.>For transient phase difference sequence, +.>For sampling interval time, +.>For carrier frequency deviation, < >>Phase at time n of the data symbol, +.>Is the phase disturbance caused by the channel noise at time n.
3. The carrier frequency deviation estimation method according to claim 1, wherein in the step S03, the phase difference between the adjacent sampling points is corrected according to the following formula:
wherein,for instantaneous phase angle sequence, +.>For transient phase difference sequence, +.>For the corrected instantaneous phase difference sequence, n represents the time.
4. A carrier frequency deviation estimation method according to any one of claims 1 to 3, wherein after step S03 and before step S04, the method further comprises performing narrow-band low-pass filtering on the corrected phase difference sequence to obtain a filtered signal output.
5. A carrier frequency deviation estimating 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 the calculated phase angles;
the phase folding removing module is used for correcting according to the calculated phase difference between the adjacent sampling points so as to remove phase folding and obtain a corrected phase difference sequence;
the frequency deviation calculating module is used for calculating carrier frequency deviation output according to the corrected phase difference sequence, and specifically calculating carrier frequency deviation according to the following formula:
wherein,low-pass filtering the corrected phase difference sequence to obtain a signal, ">Is the sampling interval time;
the phase angle calculation module calculates the instantaneous phase angle of the complex baseband sequence by adopting a cordic algorithm, and the calculation expression is as follows:
；
wherein,for a sequence of instantaneous phase angles, n denotes the moment, +.>Phase at time n of the data symbol, +.>For complex baseband sequences->Imaginary part of->For complex baseband sequences->Real part of->For sampling interval time, +.>For carrier frequency deviation, < >>Is the phase disturbance caused by channel noise.
6. The carrier frequency deviation estimation device according to claim 5, wherein 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.
7. A computer device comprising a processor and a memory for storing a computer program, characterized in that the processor is adapted to execute the computer program to perform the method according to any of claims 1-4.
8. A computer readable storage medium storing a computer program, characterized in that the computer program, when executed, implements the method according to any one of claims 1-4.
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