CN115695124B - UQPSK coherent demodulation method and system - Google Patents
UQPSK coherent demodulation method and system Download PDFInfo
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Abstract
The invention provides a method and a system for coherent demodulation of UQPSK, which belong to the technical field of digital communication and comprise the following steps: acquiring an unbalanced quadriphase shift keying signal of an optimal sampling point and performing square processing; calculating each jump phase of the unbalanced four-phase shift keying signal after square processing, and determining the minimum jump phase type interval; clustering jump phases of the squared unbalanced four-phase shift keying signal according to the minimum jump phase type interval to obtain jump phase types; jump phase compensation is carried out on the square processed unbalanced four-phase shift keying signals in each jump phase class; and sequentially carrying out frequency offset compensation and phase offset compensation on the unbalanced quadrature phase shift keying signal subjected to the hopping phase compensation. The invention can quickly and accurately estimate the frequency deviation and the phase deviation, achieves the purposes of frequency deviation compensation and phase deviation compensation, and realizes the demodulation and carrier recovery functions with the power ratio in a larger range of-35dB to 35dB.
Description
Technical Field
The invention belongs to the technical field of digital communication, and particularly relates to a method and a system for coherent demodulation of UQPSK.
Background
With the continuous development of digital communication technology, unbalanced Quadrature Phase Shift Keying (UQPSK) derived from Phase Shift Keying (PSK) is widely used in the field of data link systems of unmanned aerial vehicles and satellite digital communication. The UQPSK modulation is characterized in that an in-phase branch (I path) and a quadrature branch (Q path) of a signal can use different powers or different symbol rates for data transmission. In practical applications, the two I/Q paths of the UQPSK signal usually have the same symbol rate and different powers. The UQPSK modulation allows the UQPSK constellation to vary between QPSK and BPSK by adjusting the I/Q power ratio (IGain), i.e., the UQPSK constellation gradually approaches QPSK as the I/Q power ratio approaches 0 dB. The UQPSK constellation gradually trends towards BPSK when the I/Q power ratio is greater than 35dB or less than-35 dB. The phase discontinuity and uncertain phase change of the UQPSK enable the signal to have strong confidentiality, but also increase the difficulty of demodulating the signal by a receiver. Furthermore, the fast changing channel characteristics cause the UQPSK signal to generate frequency offset and phase jitter during transmission, resulting in poor communication quality. Therefore, research on the coherent demodulation technology of the UQPSK signal is carried out, and the method has certain significance on the application of the UQPSK modulation in digital communication.
Currently, there is less research on coherent demodulation of the UQPSK signal, and the existing UQPSK coherent demodulation method includes a phase-locked loop and a quadratic spectrum. Simon M K. Transporting performance of unbalanced QPSK modulators Part I phase Costas loop with passive arm filters [ j ] (IEEE Transactions on Communications, 1978, 26 (8): 1147-1156) uses a Costas loop based phase locked loop correlation to perform carrier synchronization. An improved digital UQPSK carrier synchronization method (the university of Beijing university of science and technology 2020, 40 (5): 537-542) adopts a decision feedback loop to carry out carrier synchronization, both can realize carrier recovery, but the demodulation performance depends on the design of a loop filter, the engineering practice is complex, and the range of the I/Q power ratio capable of being demodulated is small. In radar/communication reconnaissance, a demodulation method based on a quadratic spectrum is adopted in phase coding signal analysis processing technology research (national defense science and technology university, 2007), the complexity is low, and the realization is simple, but due to the fact that the UQPSK signal has the characteristics of discontinuous phase and uncertain phase change, when the I/Q power ratio approaches to 0dB, the frequency offset cannot be correctly estimated through the method based on the quadratic spectrum, and carrier recovery cannot be achieved.
Disclosure of Invention
One of the objectives of the present invention is to provide a UQPSK coherent demodulation method, which can quickly and accurately estimate frequency offset and phase offset, achieve the purpose of frequency offset compensation and phase offset compensation, and implement demodulation and carrier recovery functions with I/Q power ratios in a large range of-35db to 35db.
The second objective of the present invention is to provide a UQPSK coherent demodulation system.
Can be used in UQPSK demodulation system with timing of receiving end and non-synchronous carrier to
In order to achieve one of the purposes, the invention adopts the following technical scheme:
a UQPSK coherent demodulation method, the UQPSK coherent demodulation method comprising:
s1, acquiring an Unbalanced Quadrature Phase Shift Keying (UQPSK) signal of an optimal sampling point and squaring the signal;
s2, calculating each jump phase of the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal after square processing to determine the minimum jump phase type interval;
s3, clustering each jump phase of the unbalanced quadrature phase shift keying UQPSK signal after square processing to obtain each jump phase class;
s4, according to the minimum jump phase type interval, carrying out jump phase compensation on the square processed Unbalanced Quadrature Phase Shift Keying (UQPSK) signals in each jump phase type;
and S5, sequentially carrying out frequency offset compensation and phase offset compensation on the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal subjected to hopping phase compensation.
Further, the specific implementation process of step S2 includes:
step S21, performing arc tangent calculation on the square processed unbalanced quadrature phase shift keying UQPSK signal to determine the phase of the square processed unbalanced quadrature phase shift keying UQPSK signal;
and S22, carrying out differential processing on the phase of the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal subjected to square processing to obtain each jump phase.
Further, in step S3, the specific process of clustering includes:
s31, randomly selecting 3 jump phases from the jump phases to serve as 3 initial clustering centers respectively;
step S32, calculating the distance from each residual jump phase to the 3 initial clustering centers respectively to determine the minimum distance from each jump phase to the 3 initial clustering centers respectively;
s33, distributing each residual jump phase to a cluster where an initial cluster center corresponding to the minimum distance is located to obtain 3 new clusters;
step S34, calculating the mean value of each jump phase of each new cluster and the absolute value of the difference value between each jump phase and the corresponding mean value in each new cluster to determine the minimum absolute value corresponding to each of the 3 new clusters and the jump phase corresponding to each of the 3 minimum absolute values;
step S35, respectively taking the jump phases corresponding to the 3 minimum absolute values as cluster centers of corresponding new clusters, judging whether the cluster centers of the 3 new clusters are the same as the corresponding initial cluster centers, if so, outputting the 3 new clusters and the corresponding cluster centers, and ending; if not, adjusting 3 initial clustering centers, and returning to the step S32.
Further, in step S4, the implementation process of the jump phase compensation includes:
s41, selecting a first cluster corresponding to the maximum cluster center and a second cluster corresponding to the minimum cluster center from the cluster centers corresponding to the 3 new clusters;
step S42, subtracting the absolute value of the minimum jump phase type interval from all jump phases in the first cluster respectively;
and S43, adding the absolute values of the minimum jump phase type intervals to all jump phases in the second clustering respectively.
Further, in the step S5, the specific implementation process of the frequency offset compensation includes:
step S511, fast Fourier transform is carried out on the unbalanced quadrature phase shift keying UQPSK signal after jump phase compensation, so as to determine the position corresponding to the maximum peak value in the spectral line of the unbalanced quadrature phase shift keying UQPSK signal and the amplitude corresponding to the frequency point of one frequency interval before and after the maximum peak value;
step S512, calculating a correction factor according to the amplitude corresponding to the frequency point of one frequency interval before and after the maximum peak value;
step S513, after correcting the position corresponding to the maximum peak value by using the correction factor, dividing the position by the number of points of FFT (fast Fourier transform) which is 2 times that of the maximum peak value to obtain a frequency compensation value of the unbalanced quadrature phase shift keying UQPSK signal;
and step S514, performing frequency offset compensation on the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal subjected to hopping phase compensation by using the frequency compensation value.
Further, in the step S5, the implementation process of the phase offset compensation includes:
step S521, calculating a Q-path mean value and an I-path mean value of the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal after frequency offset compensation;
step S522, performing arc tangent processing on the mean value of the Q path and the mean value of the I path of the unbalanced quadrature phase shift keying UQPSK signal after frequency offset compensation, and removing an initial phase to obtain a phase compensation value;
step S523, performing phase offset compensation on the unbalanced quadrature phase shift keying UQPSK signal after the frequency offset compensation by using the phase compensation value.
In order to achieve the second purpose, the invention adopts the following technical scheme:
a UQPSK coherent demodulation system, the UQPSK coherent demodulation system comprising:
the acquisition module is used for acquiring an Unbalanced Quadrature Phase Shift Keying (UQPSK) signal of an optimal sampling point and performing square processing;
the calculating module is used for calculating each jump phase of the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal after the square processing so as to determine the minimum jump phase type interval;
the clustering module is used for clustering each jump phase of the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal after the square processing to obtain each jump phase class;
a first compensation module, configured to perform jump phase compensation on the squared Unbalanced Quadrature Phase Shift Keying (UQPSK) signal in each jump phase class according to the minimum jump phase class interval;
and the second compensation module is used for sequentially carrying out frequency offset compensation and phase offset compensation on the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal subjected to hopping phase compensation.
Further, the calculation module comprises:
the first arc tangent processing submodule is used for carrying out arc tangent calculation on the square-processed unbalanced quadrature phase shift keying UQPSK signal so as to determine the phase of the square-processed unbalanced quadrature phase shift keying UQPSK signal;
and the differential processing submodule is used for carrying out differential processing on the phase of the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal after square processing to obtain each jump phase.
Further, the clustering module comprises:
the initial clustering center selecting submodule is used for randomly selecting 3 jump phases from each jump phase to be respectively used as 3 initial clustering centers;
the first calculation submodule is used for calculating the distance from each residual jump phase to the 3 initial clustering centers respectively so as to determine the minimum distance from each jump phase to the 3 initial clustering centers respectively;
the distribution submodule is used for distributing each residual jump phase to the cluster where the initial cluster center corresponding to the minimum distance is located to obtain 3 new clusters;
the second calculation submodule is used for calculating the mean value of each hopping phase of each new cluster and the absolute value of the difference value between each hopping phase in each new cluster and the corresponding mean value so as to determine the minimum absolute value corresponding to each of the 3 new clusters and the hopping phase corresponding to each of the 3 minimum absolute values;
the judging submodule is used for respectively taking the jump phases corresponding to the 3 minimum absolute values as the clustering centers of the corresponding new clusters, judging whether the clustering centers of the 3 new clusters are the same as the corresponding initial clustering centers or not, if so, outputting the 3 new clusters and the corresponding clustering centers, and ending; if not, adjusting 3 initial clustering centers and transmitting to the first computing submodule.
Further, the first compensation module comprises:
the selecting submodule is used for selecting a first cluster corresponding to the maximum cluster center and a second cluster corresponding to the minimum cluster center from the cluster centers corresponding to the 3 new clusters;
a first compensation submodule for subtracting absolute values of the minimum transition phase class intervals from all transition phases in the first cluster, respectively;
a second compensation submodule, configured to add all the hopping phases in the second aggregation to an absolute value of the minimum hopping phase class interval.
Further, the second compensation module comprises:
the fast Fourier transform submodule is used for carrying out fast Fourier transform on the unbalanced quadrature phase shift keying UQPSK signal after jump phase compensation so as to determine the position corresponding to the maximum peak value in the spectral line of the unbalanced quadrature phase shift keying UQPSK signal and the amplitude corresponding to the frequency point of one frequency interval before and after the maximum peak value;
the second calculation submodule is used for calculating a correction factor according to the amplitude corresponding to the frequency point of one frequency interval before and after the maximum peak value;
the correction submodule is used for correcting the position corresponding to the maximum peak value by adopting the correction factor and then dividing the position by 2 times of the number of points of FFT (fast Fourier transform) to obtain a frequency compensation value of the unbalanced quadrature phase shift keying UQPSK signal;
and the frequency offset compensation submodule is used for carrying out frequency offset compensation on the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal subjected to hopping phase compensation by adopting the frequency compensation value.
Further, the second compensation module further comprises:
the third calculation submodule is used for calculating the mean value of the Q path and the mean value of the I path of the unbalanced quadrature phase shift keying UQPSK signal after frequency offset compensation;
the second arc tangent processing submodule is used for carrying out arc tangent processing on the mean value of the Q path and the mean value of the I path of the unbalanced quadrature phase shift keying UQPSK signal after frequency offset compensation and removing an initial phase to obtain a phase compensation value;
and the phase offset compensation submodule is used for performing phase offset compensation on the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal after frequency offset compensation by adopting the phase compensation value.
In conclusion, the technical scheme of the invention has the beneficial effects that:
for the estimation of the frequency offset, the invention considers the characteristics of discontinuous phase and uncertain phase change of the UQPSK signal; according to the invention, based on the phase jump condition, a phase difference cluster compensation mode is adopted, frequency deviation and phase deviation are more accurately estimated, demodulation of the I/Q power ratio in a larger range of-35dB to 35dB can be realized, and the square phase difference of the UQPSK signal is clustered, so that the original phase jump type is reduced by half, the algorithm complexity is further reduced, the interval of the minimum jump phase type is doubled, and the misjudgment probability between adjacent constellation points in a judgment stage is further reduced; the invention estimates the phase offset through the compensated non-frequency offset constellation characteristic and the UQPSK constellation characteristic, realizes the rapid phase rotation of the non-frequency offset constellation, and obtains the UQPSK demodulation symmetrical constellation.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
FIG. 1 is a schematic flow chart of a UQPSK coherent demodulation method of the present invention;
FIG. 2 is a state transition diagram of a phase jump of a UQPSK signal;
FIG. 3 is a diagram illustrating a UQPSK signal and a phase jump of its square;
FIG. 4 is a diagram of the squared time domain of a UQPSK signal before and after phase jump compensation;
FIG. 5 is a schematic diagram of UQPSK constellation comparison before and after demodulation;
FIG. 6 is a schematic diagram illustrating a comparison of demodulation measurement constellations when IGain is 1 dB;
fig. 7 is a diagram showing the EVM variation of the demodulation error vector rms.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
This embodiment provides a UQPSK coherent demodulation method, and referring to fig. 1, the UQPSK coherent demodulation method includes:
s1, acquiring an Unbalanced Quadrature Phase Shift Keying (UQPSK) signal of an optimal sampling point and performing square processing.
The Unbalanced Quadrature Phase Shift Keying (UQPSK) signal after setting is as follows:
wherein the content of the first and second substances,s(n) The signal is an Unbalanced Quadrature Phase Shift Keying (UQPSK) signal after timing;jis an imaginary number;ncounting the sampling interval;Nis the total number of code elements;Tis a symbol interval;θ(n) Phase information for the received signal; z (n) is Gaussian complex noise.
The Unbalanced Quadrature Phase Shift Keying (UQPSK) signal after being decimated by the optimal sampling point can be expressed as:
wherein the content of the first and second substances,
for the second sampled by the optimum sampling pointkUnbalanced Quadrature Phase Shift Keying (UQPSK) signals corresponding to the code elements;ϕ(k) For the second sampled by the optimum sampling pointkUnbalanced four-phase shift key corresponding to each code elementControlling the modulation phase of the UQPSK signal;kis a code element;f Δ andφ Δ respectively representing the frequency offset and the phase offset to be estimated;Tis the symbol interval.
For the I/Q power ratio IGain isaUQPSK modulation of dB, orderβ=10 a/20 ，aIs the I/Q power ratio, thenϕ(k) Comprises the following steps:
from equation (2), the phase of the UQPSK signal is:
wherein the content of the first and second substances,
for the second sampled by the optimum sampling pointkThe phase of the unbalanced quadrature phase shift keyed UQPSK signal corresponds to one symbol.
And S2, calculating each jump phase of the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal after square processing to determine the minimum jump phase type interval.
The phase of the UQPSK signal is differentiated to obtain a phase difference, i.e. a jump phase, where the jump phase can be expressed as:
wherein the content of the first and second substances,
for the second sampled by the optimum sampling pointk+ 1 symbol and the second symbolkJump phase between Unbalanced Quadrature Phase Shift Keying (UQPSK) signals corresponding to the code elements;
is a firstk+1 symbol and the secondkThe modulation phase difference between the Unbalanced Quadrature Phase Shift Keying (UQPSK) signals corresponding to each symbol.
According to UQPSK constellation characteristics, 16 types of transition states of phase jump are obtained, 6 types of jump phases are obtained, and the phase angle of the first quadrant is set as
The transition state of the phase jump of the UQPSK signal is shown in fig. 2. The jump phase can be further expressed as:
wherein, P is the transition state of phase jump; p is hl Is from the first tohJumping to the second constellation point position in quadrantlThe position of the constellation point within the quadrant,h(ii) =1,2,3 and 4,l(ii) =1,2,3 and 4,handlboth represent quadrants. The minimum jump phase species interval is then
。
After square processing the UQPSK signal, the signal can be expressed as:
wherein, the first and the second end of the pipe are connected with each other,
is the second after square processingkThe non-balanced quadrature phase shift keying (UQPSK) signals corresponding to each code element.
After square processing of the UQPSK signal, the phase at this time is differentiated to obtain a jump phase, which is expressed as:
wherein the content of the first and second substances,
is the first after square processingk+1 symbol and the secondkJump phase between Unbalanced Quadrature Phase Shift Keying (UQPSK) signals corresponding to the code elements; p is hl Is from the first tohConstellation point position jump to the second in quadrantlThe position of the constellation point within the quadrant,h(ii) =1,2,3 and 4,l=1,2,3 and 4,handlboth represent quadrants. At this time, the hopping phase kinds are reduced to 3, and the minimum hopping phase kind interval becomes
。
To sum up, the specific implementation process of this step includes:
step S21, performing arc tangent calculation on the square-processed unbalanced quadrature phase shift keying UQPSK signal to determine the phase of the square-processed unbalanced quadrature phase shift keying UQPSK signal;
and S22, carrying out differential processing on the phase of the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal subjected to square processing to obtain each jump phase.
And S3, clustering all jump phases of the unbalanced quadrature phase shift keying UQPSK signal after square processing to obtain all jump phase classes.
This example adoptsKMean value clustering algorithm, which is to process the phase difference (i.e. jump phase) of UQPSK signal after square processing
And (6) clustering. Hopping phase sets
Through which is passedKObtaining 3 subsets after mean clustering to form 3 classes, wherein the 3 classes are centered on
。C 1 To a jump state
Lower jump phase class center;C 2 to a jump state
Lower jump phase class center;C 3 to a jump state
Lower jump phase class center. The specific process of clustering comprises the following steps:
s31, randomly selecting 3 jump phases from the jump phases to serve as 3 initial clustering centers respectively;
step S32, calculating the distance from each residual jump phase to the 3 initial clustering centers respectively to determine the minimum distance from each jump phase to the 3 initial clustering centers respectively;
s33, distributing each residual jump phase to the cluster where the initial cluster center corresponding to the minimum distance is located to obtain 3 new clusters;
step S34, calculating the mean value of each jump phase of each new cluster and the absolute value of the difference value between each jump phase and the corresponding mean value in each new cluster to determine the minimum absolute value corresponding to each of the 3 new clusters and the jump phase corresponding to each of the 3 minimum absolute values;
the minimum absolute value in this embodiment refers to the minimum value among the absolute values of the differences between each jump phase and the corresponding mean value in the corresponding new cluster.
Step S35, respectively taking the jump phases corresponding to the 3 minimum absolute values as cluster centers of corresponding new clusters, judging whether the cluster centers of the 3 new clusters are the same as the corresponding initial cluster centers, if so, outputting the 3 new clusters and the corresponding cluster centers, and ending; if not, adjusting 3 initial clustering centers, and returning to the step S32.
And S4, according to the minimum jump phase type interval, carrying out jump phase compensation on the square-processed Unbalanced Quadrature Phase Shift Keying (UQPSK) signals in each jump phase type.
Compensating the jump phase after clusteringC 1 Each jump phase in the subset of jump phases in the cluster (i.e. the second cluster) is added (compensated) to the absolute value of the minimum jump phase class interval, i.e. 4 arctan: (β) Is located atC 3 The jump phase subset in the cluster (i.e. the first cluster) has the absolute value of each jump phase minus (compensating) the minimum jump phase class intervalC 2 The phase of each jump in the cluster is not changed. The specific process of jump phase compensation comprises the following steps:
s41, selecting a first cluster corresponding to the maximum cluster center and a second cluster corresponding to the minimum cluster center from the cluster centers corresponding to the 3 new clusters;
in this embodiment, 3 cluster centers (i.e., 3 hopping phases) are sequenced, a new cluster corresponding to a largest cluster center (i.e., a hopping phase) of the 3 cluster centers (i.e., 3 hopping phases) is used as a first cluster, and a new cluster corresponding to a smallest cluster center (i.e., a hopping phase) is used as a second cluster.
Step S42, subtracting the absolute value of the minimum jump phase type interval from all jump phases in the first cluster respectively;
and S43, adding the absolute values of the minimum jump phase type intervals to all jump phases in the second clustering respectively.
The jump phase of the square of the compensated UQPSK signal can be expressed as:
wherein, the first and the second end of the pipe are connected with each other,
for the first time after jump phase compensationk+1 symbol and the secondkNon-equilibrium of symbol correspondencesThe hopping phase between the quadrature phase shift keyed UQPSK signals.
After jump phase compensation, the square of the UQPSK signal can be converted into:
wherein the content of the first and second substances,
after phase compensation for jumpkThe square of an Unbalanced Quadrature Phase Shift Keying (UQPSK) signal corresponding to each code element;
to square the initial phase (i.e. initial modulation phase) of the processed unbalanced quadrature phase shift keyed (qpsk) UQPSK signal,
. As can be seen from the comparison between equation (7) and equation (10), the square of the UQPSK signal becomes the frequency of
A single frequency signal of (a). When N point single frequency signal
When the signal is exactly an integral multiple of the period signal, the signal can be directly coupled
Performing Fast Fourier Transform (FFT), and obtaining the frequency corresponding to the peak position of the spectral line
. But the number of data points collected is generally set randomly, so
Often, the signal is not an integral multiple of the period, if the estimation is directly performed by FFTCounting the frequency, an estimation error due to spectral leakage may occur.
And S5, sequentially carrying out frequency offset compensation and phase offset compensation on the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal subjected to jump phase compensation.
To improve the accuracy of the frequency offset estimation, the
After the FFT, further refinement is performed by a correction factor. Is provided with
After FFT, a sequence is obtained
：
Wherein the content of the first and second substances,
the second corresponding to the square of the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal after jump phase compensation after Fourier transformationiAn FFT transform sequence point;isequence points are transformed by FFT;N FFT for the total number of FFT-transformed sequence points,N FFT =N-1. Then find out
Position corresponding to maximum value
The position of the fine estimate is obtained by correcting as follows
：
Wherein, real: (δ) Taking intermediate variablesδThe real part value of (a).
The estimated frequency offset (i.e., frequency offset value) is:
after estimating the frequency deviation, the pair
Performing frequency offset compensation, then equation (10) is converted into:
wherein the content of the first and second substances,
for the frequency offset compensated secondkThe square of an Unbalanced Quadrature Phase Shift Keying (UQPSK) signal corresponding to each code element;
is the first after square processingkThe initial phase (i.e., initial modulation phase) of the Unbalanced Quadrature Phase Shift Keyed (UQPSK) signal corresponds to one symbol.
In summary, the specific implementation process of the frequency offset compensation in this embodiment includes:
step S511, fast Fourier transform is carried out on the unbalanced quadrature phase shift keying UQPSK signal after jump phase compensation, so as to determine the position corresponding to the maximum peak value in the spectral line of the unbalanced quadrature phase shift keying UQPSK signal and the amplitude corresponding to the frequency point of one frequency interval before and after the maximum peak value;
step S512, calculating a correction factor according to the amplitude corresponding to the frequency point of one frequency interval before and after the maximum peak value;
step S513, after correcting the position corresponding to the maximum peak value by using the correction factor, dividing the position by the number of points of FFT (fast Fourier transform) which is 2 times that of the maximum peak value to obtain a frequency compensation value of the unbalanced quadrature phase shift keying UQPSK signal;
and step S514, performing frequency offset compensation on the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal subjected to hopping phase compensation by using the frequency compensation value.
Phase deviation of the present embodiment
The (i.e., phase compensation value) can be calculated as follows:
wherein the content of the first and second substances,
and
respectively after frequency offset compensationkThe imaginary part (namely Q path) and the real part (namely I path) of the square of the unbalanced quadrature phase shift keying UQPSK signal corresponding to each symbol;
is the first after square processingkThe initial phase (i.e. initial modulation phase) of the unbalanced quadrature phase shift keyed UQPSK signal corresponding to one symbol,
determining according to the symmetry characteristics of UQPSK constellation
Positive and negative of (2).
And carrying out frequency offset and phase offset compensation on the UQPSK signal after the receiving timing to obtain a demodulated measurement signal. Thus, carrier recovery of the UQPSK signal at the receiving end is completed.
In this embodiment, the specific implementation process of the phase offset compensation includes:
step S521, calculating a Q-path mean value and an I-path mean value of the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal after frequency offset compensation;
step S522, performing arc tangent processing on the mean value of the Q path and the mean value of the I path of the unbalanced quadrature phase shift keying UQPSK signal after frequency offset compensation, and removing an initial phase to obtain a phase compensation value;
step S523, performing phase offset compensation on the unbalanced quadrature phase shift keying UQPSK signal after the frequency offset compensation by using the phase compensation value.
By calculating the root mean square value of the error vector between the measured signal and the reference signalEVMTo measure the effectiveness of demodulation.EVMThe calculation method is as follows:
wherein, the first and the second end of the pipe are connected with each other,
is the reference signal best sample point data,
is the optimal sample point data for demodulating the measurement signal,xandyrepresenting the real and imaginary parts of the data, respectively.
The following describes the technical effects of the present embodiment in detail with reference to practical engineering tests:
1. test conditions and contents:
the signal transmitter transmits a UQPSK signal with a specific I/Q power ratio, and the receiver demodulates the received signal by using the UQPSK coherent demodulation method of this embodiment after radio frequency front end processing.
2. And (3) analyzing a test result:
as can be seen from fig. 3, after the square processing is performed on the UQPSK signal, the hopping phase class is reduced, and the minimum hopping phase class interval is doubled.
As can be seen from fig. 4, after the cluster compensation jump phase, the square of the UQPSK signal becomes a single frequency signal.
As can be seen from fig. 5, with the method of this embodiment, frequency offset compensation and phase offset compensation are performed on the timed signal, so that constellation convergence rotates to the UQPSK quadriphase symmetric baseband constellation.
Fig. 6 is a schematic diagram illustrating comparison between the performance of the present embodiment and that of the square spectrum-based UQPSK signal demodulation method in the same test environment. Fig. 6 shows demodulation constellations corresponding to the two demodulation methods when the I/Q power ratio IGain is 1 dB. FIG. 7 shows the demodulated EVM values corresponding to the two demodulation methods within the range of I/Q power ratio IGain of-35dB to 35dB. As can be seen from fig. 6 and fig. 7, compared with the UQPSK coherent demodulation method based on the quadratic spectrum, the UQPSK coherent demodulation method of the present embodiment has a better demodulation effect, and when the I/Q power ratio IGain approaches 0, the method is invalid and the demodulation is erroneous.
For the estimation of the frequency offset (frequency compensation value), the present embodiment considers the characteristics of phase discontinuity and uncertain phase change of the UQPSK signal; the embodiment starts from the phase jump condition, adopts a phase difference clustering compensation mode, ensures the accuracy of frequency deviation and phase deviation, realizes the demodulation of the I/Q power ratio in a larger range of-35dB to 35dB, and clusters the square phase difference of the UQPSK signal, thereby not only reducing the original phase jump variety by half, further reducing the algorithm complexity, but also doubling the minimum jump phase variety interval and reducing the false judgment probability between adjacent constellation points in the judgment stage; in this embodiment, the phase offset is estimated through the compensated non-frequency-offset constellation characteristic and the UQPSK constellation characteristic, so that the fast phase rotation of the non-frequency-offset constellation is realized, and the UQPSK demodulation symmetric constellation is obtained.
This embodiment can be implemented by using the UQPSK coherent demodulation system given in the following embodiment:
another embodiment provides a UQPSK coherent demodulation system, including:
the acquisition module is used for acquiring an Unbalanced Quadrature Phase Shift Keying (UQPSK) signal of an optimal sampling point and performing square processing;
the calculating module is used for calculating each jump phase of the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal after the square processing so as to determine the minimum jump phase type interval;
the clustering module is used for clustering each jump phase of the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal after the square processing to obtain each jump phase class;
a first compensation module, configured to perform jump phase compensation on the squared Unbalanced Quadrature Phase Shift Keying (UQPSK) signal located in each jump phase class according to the minimum jump phase class interval;
and the second compensation module is used for sequentially carrying out frequency offset compensation and phase offset compensation on the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal subjected to hopping phase compensation.
Further, the calculation module comprises:
the first arc tangent processing submodule is used for carrying out arc tangent calculation on the square-processed unbalanced quadrature phase shift keying UQPSK signal so as to determine the phase of the square-processed unbalanced quadrature phase shift keying UQPSK signal;
and the differential processing submodule is used for carrying out differential processing on the phase of the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal subjected to square processing to obtain each jump phase.
Further, the clustering module comprises:
the initial clustering center selecting submodule is used for randomly selecting 3 jump phases from each jump phase to be respectively used as 3 initial clustering centers;
the first calculation submodule is used for calculating the distance from each residual jump phase to the 3 initial clustering centers respectively so as to determine the minimum distance from each jump phase to the 3 initial clustering centers respectively;
the distribution submodule is used for distributing each residual jump phase to the cluster where the initial cluster center corresponding to the minimum distance is located to obtain 3 new clusters;
the second calculation submodule is used for calculating the mean value of each hopping phase of each new cluster and the absolute value of the difference value between each hopping phase in each new cluster and the corresponding mean value so as to determine the minimum absolute value corresponding to each of the 3 new clusters and the hopping phase corresponding to each of the 3 minimum absolute values;
a judging submodule, configured to use the jump phases corresponding to the 3 minimum absolute values as cluster centers of respective corresponding new clusters, and judge whether the cluster centers of the 3 new clusters are the same as the corresponding initial cluster centers, if so, output the 3 new clusters and the corresponding cluster centers, and end; if not, adjusting 3 initial clustering centers and transmitting to the first computing submodule.
Further, the first compensation module comprises:
the selecting submodule is used for selecting a first cluster corresponding to the maximum cluster center and a second cluster corresponding to the minimum cluster center from the cluster centers corresponding to the 3 new clusters;
a first compensation submodule for subtracting absolute values of the minimum transition phase class intervals from all transition phases in the first cluster, respectively;
a second compensation submodule, configured to add all the hopping phases in the second aggregation to an absolute value of the minimum hopping phase class interval.
Further, the second compensation module comprises:
the fast Fourier transform submodule is used for carrying out fast Fourier transform on the unbalanced quadrature phase shift keying UQPSK signal after jump phase compensation so as to determine the position corresponding to the maximum peak value in the spectral line of the unbalanced quadrature phase shift keying UQPSK signal and the amplitude corresponding to the frequency point of one frequency interval before and after the maximum peak value;
the third calculation submodule is used for calculating a correction factor according to the amplitude corresponding to the frequency point of one frequency interval before and after the maximum peak value;
the correction submodule is used for correcting the position corresponding to the maximum peak value by adopting the correction factor and then dividing the position by 2 times of the number of points of FFT (fast Fourier transform) to obtain a frequency compensation value of the unbalanced quadrature phase shift keying UQPSK signal;
and the frequency offset compensation submodule is used for carrying out frequency offset compensation on the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal subjected to hopping phase compensation by adopting the frequency compensation value.
Further, the second compensation module further comprises:
the fourth calculation submodule is used for calculating the mean value of the Q path and the mean value of the I path of the unbalanced quadrature phase shift keying UQPSK signal after frequency offset compensation;
the second arc tangent processing submodule is used for carrying out arc tangent processing on the mean value of the Q path and the mean value of the I path of the unbalanced quadrature phase shift keying UQPSK signal after frequency offset compensation and removing an initial phase to obtain a phase compensation value;
and the phase offset compensation submodule is used for performing phase offset compensation on the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal after frequency offset compensation by adopting the phase compensation value.
The principles and formulas of the above embodiments are applicable and are not described in detail herein.
It should be noted that the technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, however, as long as there is no contradiction between the combinations of the technical features, the scope of the present description should be considered. The above examples only express several embodiments of the present application, and the description thereof is more specific and detailed, but not to be construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (10)
1. A UQPSK coherent demodulation method is characterized in that the UQPSK coherent demodulation method comprises the following steps:
s1, acquiring an Unbalanced Quadrature Phase Shift Keying (UQPSK) signal of an optimal sampling point and performing square processing;
s2, calculating each jump phase of the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal after square processing to determine the minimum jump phase type interval;
the specific implementation process of the step S2 comprises the following steps:
step S21, performing arc tangent calculation on the square-processed unbalanced quadrature phase shift keying UQPSK signal to determine the phase of the square-processed unbalanced quadrature phase shift keying UQPSK signal;
step S22, carrying out differential processing on the phase of the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal after square processing to obtain each jump phase;
s3, clustering each jump phase of the unbalanced quadrature phase shift keying UQPSK signal after square processing to obtain each jump phase class;
s4, according to the minimum jump phase type interval, carrying out jump phase compensation on the square processed Unbalanced Quadrature Phase Shift Keying (UQPSK) signals in each jump phase type;
and S5, sequentially carrying out frequency offset compensation and phase offset compensation on the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal subjected to jump phase compensation.
2. The UQPSK coherent demodulation method according to claim 1, wherein in the step S3, the clustering process includes:
s31, randomly selecting 3 jump phases from the jump phases to serve as 3 initial clustering centers respectively;
step S32, calculating the distance from each residual jump phase to the 3 initial clustering centers respectively to determine the minimum distance from each jump phase to the 3 initial clustering centers respectively;
s33, distributing each residual jump phase to a cluster where an initial cluster center corresponding to the minimum distance is located to obtain 3 new clusters;
step S34, calculating the mean value of each jump phase of each new cluster and the absolute value of the difference value between each jump phase in each new cluster and the corresponding mean value to determine the minimum absolute value corresponding to each of the 3 new clusters and the jump phase corresponding to each of the 3 minimum absolute values;
step S35, respectively taking the jump phases corresponding to the 3 minimum absolute values as cluster centers of corresponding new clusters, judging whether the cluster centers of the 3 new clusters are the same as the corresponding initial cluster centers, if so, outputting the 3 new clusters and the corresponding cluster centers, and ending; if not, adjusting 3 initial clustering centers, and returning to the step S32.
3. The UQPSK coherent demodulation method according to claim 2, wherein in the step S4, the hopping phase compensation process includes:
s41, selecting a first cluster corresponding to the maximum cluster center and a second cluster corresponding to the minimum cluster center from the cluster centers corresponding to the 3 new clusters;
step S42, subtracting the absolute value of the minimum jump phase type interval from all jump phases in the first cluster respectively;
and S43, adding the absolute values of the minimum jump phase type intervals to all jump phases in the second clustering respectively.
4. The UQPSK coherent demodulation method according to claim 3, wherein in said step S5, said frequency offset compensation includes:
step S511, fast Fourier transform is carried out on the unbalanced quadrature phase shift keying UQPSK signal after jump phase compensation, so as to determine the position corresponding to the maximum peak value in the spectral line of the unbalanced quadrature phase shift keying UQPSK signal and the amplitude corresponding to the frequency point of one frequency interval before and after the maximum peak value;
step S512, calculating a correction factor according to the amplitude corresponding to the frequency point of one frequency interval before and after the maximum peak value;
step S513, after correcting the position corresponding to the maximum peak value by using the correction factor, dividing the position by 2 times of the number of points of FFT to obtain a frequency compensation value of the unbalanced quadrature phase shift keying UQPSK signal;
and step S514, performing frequency offset compensation on the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal subjected to hopping phase compensation by using the frequency compensation value.
5. The UQPSK coherent demodulation method according to claim 4, wherein in the step S5, the implementation of the phase offset compensation comprises:
step S521, calculating a Q-way average value and an I-way average value of the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal after frequency offset compensation;
step S522, performing arc tangent processing on the mean value of the Q path and the mean value of the I path of the unbalanced quadrature phase shift keying UQPSK signal after frequency offset compensation, and removing an initial phase to obtain a phase compensation value;
step S523, performing phase offset compensation on the unbalanced quadrature phase shift keying UQPSK signal after the frequency offset compensation by using the phase compensation value.
6. A UQPSK coherent demodulation system, comprising:
the acquisition module is used for acquiring the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal of the optimal sampling point and performing square processing;
the calculating module is used for calculating each jump phase of the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal after the square processing so as to determine the minimum jump phase type interval;
the calculation module comprises:
the first arc tangent processing submodule is used for carrying out arc tangent calculation on the unbalanced quadrature phase shift keying UQPSK signals after the square processing so as to determine the phase of the unbalanced quadrature phase shift keying UQPSK signals after the square processing;
the differential processing submodule is used for carrying out differential processing on the phase of the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal subjected to square processing to obtain each jump phase;
the clustering module is used for clustering each jump phase of the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal after the square processing to obtain each jump phase class;
a first compensation module, configured to perform jump phase compensation on the squared Unbalanced Quadrature Phase Shift Keying (UQPSK) signal located in each jump phase class according to the minimum jump phase class interval;
and the second compensation module is used for sequentially carrying out frequency offset compensation and phase offset compensation on the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal subjected to hopping phase compensation.
7. The UQPSK coherent demodulation system of claim 6, wherein the clustering module comprises:
the initial clustering center selection submodule is used for randomly selecting 3 hopping phases from each hopping phase to be respectively used as 3 initial clustering centers;
the first calculation submodule is used for calculating the distance from each residual jump phase to the 3 initial clustering centers respectively so as to determine the minimum distance from each jump phase to the 3 initial clustering centers respectively;
the distribution submodule is used for distributing each residual jump phase to the cluster where the initial cluster center corresponding to the minimum distance is located to obtain 3 new clusters;
the first calculation submodule is used for calculating the mean value of each hopping phase of each new cluster and the absolute value of the difference value between each hopping phase in each new cluster and the corresponding mean value so as to determine the minimum absolute value corresponding to each of the 3 new clusters and the hopping phase corresponding to each of the 3 minimum absolute values;
the judging submodule is used for respectively taking the jump phases corresponding to the 3 minimum absolute values as the clustering centers of the corresponding new clusters, judging whether the clustering centers of the 3 new clusters are the same as the corresponding initial clustering centers or not, if so, outputting the 3 new clusters and the corresponding clustering centers, and ending; if not, adjusting 3 initial clustering centers and transmitting to the first computing submodule.
8. The UQPSK coherent demodulation system of claim 7, wherein the first compensation module comprises:
the selecting submodule is used for selecting a first cluster corresponding to the maximum cluster center and a second cluster corresponding to the minimum cluster center from the cluster centers corresponding to the 3 new clusters;
a first compensation submodule, configured to subtract absolute values of the minimum jump phase class intervals from all jump phases in the first cluster, respectively;
a second compensation submodule, configured to add the absolute value of the minimum jump phase class interval to all jump phases in the second aggregation, respectively.
9. The UQPSK coherent demodulation system according to claim 8, wherein the second compensation module includes:
the fast Fourier transform submodule is used for carrying out fast Fourier transform on the unbalanced quadrature phase shift keying UQPSK signal after jump phase compensation so as to determine the position corresponding to the maximum peak value in the spectral line of the unbalanced quadrature phase shift keying UQPSK signal and the amplitude corresponding to the frequency point of one frequency interval before and after the maximum peak value;
the third calculation submodule is used for calculating a correction factor according to the amplitude corresponding to the frequency point of one frequency interval before and after the maximum peak value;
the correction submodule is used for correcting the position corresponding to the maximum peak value by adopting the correction factor and then dividing the position by 2 times of the number of points of FFT (fast Fourier transform) to obtain a frequency compensation value of the unbalanced quadrature phase shift keying UQPSK signal;
and the frequency offset compensation submodule is used for carrying out frequency offset compensation on the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal subjected to hopping phase compensation by adopting the frequency compensation value.
10. The UQPSK coherent demodulation system according to claim 9, wherein the second compensation module further includes:
the fourth calculation submodule is used for calculating the mean value of the Q path and the mean value of the I path of the unbalanced quadrature phase shift keying UQPSK signal after frequency offset compensation;
the second arc tangent processing submodule is used for carrying out arc tangent processing on the mean value of the Q path and the mean value of the I path of the unbalanced quadrature phase shift keying UQPSK signal after frequency offset compensation and removing an initial phase to obtain a phase compensation value;
and the phase offset compensation submodule is used for performing phase offset compensation on the Unbalanced Quadrature Phase Shift Keying (UQPSK) signal after frequency offset compensation by adopting the phase compensation value.
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| US5121071A (en) * | 1991-07-31 | 1992-06-09 | Loral Aerospace Corp. | Lock detector for unbalanced QPSK demodulators |
| US6385233B1 (en) * | 1999-03-16 | 2002-05-07 | Trw Inc. | Unbalanced quadrature waveform |
| EP1536579B1 (en) * | 2003-11-25 | 2006-07-19 | Alcatel | Modified DPSK optical transmission system |
| CN111935056A (en) * | 2020-08-17 | 2020-11-13 | 中天通信技术有限公司 | Signal demodulation method and related device |
| CN113225286B (en) * | 2021-04-22 | 2022-03-01 | 中国电子科技集团公司第五十四研究所 | UQPSK signal demodulating device |
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