CN111464477A - Low-complexity carrier synchronization method in OFDM power wireless private network - Google Patents
Low-complexity carrier synchronization method in OFDM power wireless private network Download PDFInfo
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Abstract
The invention discloses a low-complexity carrier synchronization method in an OFDM electric wireless private network, which is characterized by comprising the following steps of: 1) arranging a multi-antenna OFDM system, and reconstructing a received signal of the OFDM system; 2) and obtaining the CFO of the OFDM system by using a multi-shift invariance PM algorithm. The present invention reconstructs the received signal, utilizing shift invariance to estimate the Carrier Frequency Offset (CFO). The method provided by the invention can well realize CFO estimation without knowing constant modulus and statistical characteristics, and has better CFO estimation performance compared with the traditional PM algorithm and ESPRIT algorithm. The method provided by the invention does not need to carry out eigenvalue decomposition on the cross-correlation matrix and also does not need to carry out singular value decomposition on the received data, so the algorithm complexity is lower.
Description
Technical Field
The invention relates to a low-complexity carrier synchronization method in an OFDM electric power wireless private network system, belonging to the blind CFO estimation problem in the OFDM electric power wireless private network.
Background
The power wireless private network builds a 4G TD-L TE network in a 1.8GHz Frequency band, Orthogonal Frequency Division Multiplexing (OFDM) is one of the key technologies, an OFDM system is sensitive to Carrier Frequency Offset (CFO) generated by a channel, and the CFO causes serious reduction of system performance.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the blind CFO estimation problem in the OFDM power wireless private network is solved, and the estimation performance is improved.
In order to solve the problems proposed above, the present invention adopts the following scheme:
a low-complexity carrier synchronization method in an OFDM power wireless private network is characterized by comprising the following steps:
1) arranging a multi-antenna OFDM system, and reconstructing a received signal of the OFDM system;
2) and obtaining the CFO of the OFDM system by using a multi-shift invariance PM algorithm.
The invention achieves the following beneficial effects:
the invention provides a Multi-shift invariance propagation operator method (MI-PM) aiming at the problem of Carrier Frequency Offset (CFO) estimation of an OFDM power wireless private network system. The method provided by the invention can well realize CFO estimation without knowing constant modulus and statistical characteristics, and has better CFO estimation performance compared with the traditional PM algorithm and ESPRIT algorithm. The method provided by the invention does not need to carry out eigenvalue decomposition on the cross-correlation matrix and also does not need to carry out singular value decomposition on the received data, so the algorithm complexity is lower.
Drawings
FIG. 1 is a plot of CFO estimation performance versus conventional PM and ESPRIT algorithms for different signal-to-noise ratios;
FIG. 2 is a comparison graph of CFO estimation performance under different signal block numbers according to the method of the present invention under different SNR conditions;
FIG. 3 is a comparison graph of CFO estimation performance under different antenna numbers according to the method of the present invention under different SNR conditions;
FIG. 4 is a comparison graph of CFO estimation performance under different channel numbers according to the method of the present invention under different SNR conditions;
fig. 5 is a comparison graph of CFO estimation performance under different numbers of subcarriers by the method of the present invention under different snr conditions.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.
The symbols represent: used in the invention (·)TRepresentation matrix transposition, (.)HRepresenting the conjugate transpose of the matrix (.)*Representation matrix conjugation, (.)+Representing Mole-Penrose inverse (pseudo-inverse), | · |. Y phosphorFDenotes the norm, diag (v) denotes the diagonal matrix made up of the elements in v.
The invention discloses a low-complexity carrier synchronization method in an OFDM power wireless private network, which comprises the following steps:
1) the method for reconstructing the OFDM system comprises the following steps of arranging a multi-antenna OFDM system and reconstructing a received signal of the OFDM system:
11) the OFDM uplink system comprises a receiver, wherein the receiver is provided with 1 transmitting antenna and I receiving antennas, the number of subcarriers is N, and the cyclic prefix uses L sampling intervals, so that the number of samples of each OFDM system is N + L which is larger than the maximum propagation delay;
12) the transmission array defining the kth block is s (k) ═ s1(k),s2(k),K,sP(k)]TWherein s isp(k) For the kth data block transmitted on the P subcarrier, P parallel data are modulated on P subcarriers, that is, the number of channels of the system is P, P is less than N, the remaining N-P subcarriers are virtual carriers, and the multicarrier modulation signal is filled by a Cyclic Prefix (CP) before being transmitted into a multipath fading channel;
removing the cyclic prefix CP, the output signal of the k block of the ith antenna is
xi(k)=EFPdiag(hi)s(k)ej2πΔf(k-1)(N+L)(1)
Wherein j represents an imaginary number symbol,represents a set of complex numbers, Δ f is CFO; e is a natural index;
intermediate variablesIs a CFO matrix, an intermediate variable Representing the first P columns of the inverse Fourier transform, the frequency domain channel vector for the ith receive antenna is hi=[Hi(1),Hi(2),K,Hi(P)]T(ii) a The frequency response defined as the nth subcarrier is Hi(n) corresponding to the ith antenna, the multi-antenna frequency domain channel matrix H is:
13) assuming that K block channel parameters are constants, defining a source matrix Xi=[xi(1)xi(2)Lxi(K)]Is defined as
Xi=Adiag(hi)BT=ADi(H)BT,i=1,2,...,I (3)
Where the matrix B ═ diag {1, e ═ dj2πΔf(N+L),K,ej2πΔf(K-1)(N+L)},Di() Represents the ith row of the extraction matrixConstructing a diagonal matrix; a ═ EFP∈CN×PIs a Vandermonde matrix, a data model of the received signal taking into account the presence of noiseIs written as
Wherein WiIs the noise received by the ith array element;
the signal in equation (3) can also be expressed as a trilinear model
Wherein xn,k,iRepresenting X in the matrix equation (3)iThe (n, k) th element of (a)n,pRepresents the (n, p) th element of the matrix A, bk,pRepresents the (k, p) th element, h, of the matrix Bi,pRepresents the (i, p) th element of the frequency domain channel matrix H, and the rest is the same; n, K, I are the number of subcarriers, the number of blocks of the source and the number of antennas, respectively;
output signal X of ith antennai=ADi(H)BTI may be regarded as a slice of the trilinear model along the antenna direction, and a reconstructed matrix Y is obtained by matrix reconstruction according to the symmetry of the trilinear modeln:
Yn=HDn(A)BT,n=1,2,...,N (6)
Wherein Y isnN1, 2.., N, which may be considered as the reconstruction of equation (3);
Wherein L is the number of fast beats.
2) And obtaining the CFO of the OFDM system by using a multi-shift invariance PM algorithm.
The multi-shift invariance PM algorithm provided by the invention is a popularization of the PM algorithm, is used for DOA estimation, and utilizes the MI-PM algorithm to estimate CFO.
From equation (6), the following matrix is constructed
Y=AEBT(9)
Wherein
Matrix arrayWherein, I, N and P are the number of antennas, the number of subcarriers and the number of channels used by the system respectively, and the matrix AEThe block-shaped materials are divided into blocks,represents a complex set of a plurality of
Wherein the matrix oneIs a full rank matrix, matrix twoThus in matrix one A1And the matrix two A2There is one linear transformation operator to satisfy
A2=PcA1(12)
Order to
Wherein P iscIs a matrix of propagation operators, IPIs an identity matrix of P × P, and the propagation operator P is obtained by minimizing the cost function in the presence of noisecIs estimated value of
Wherein Jcsm() To relate toOf a convex function of the second order, matrixIs a received signalFirst P columns of, matrixIs a received signalThe remaining columns;
From the equations (12) and (13), the following relational expression is obtained
Thus, it is possible to provide
According to equation (16), a relationship matrix P is defined1And relation matrix bip2Is composed of
Thus, the relationship matrix P1And relation matrix bip2There exists the following relation
Defining the matrix Ψ:
so equation (19) is expressed as
P2=P1Ψ(21)
Then
Wherein the matrix Ψ and the rotation matrix Φ have the same Eigenvalue, and the matrix Ψ is subjected to Eigenvalue Decomposition (EVD) to obtain the Eigenvalue Decomposition
Where tr (.) is defined as the sum of the main diagonal elements of the matrix,an estimate of the rotation matrix Φ, an estimate of the CFOEstimated by equation (23).
The carrier synchronization method of the invention is analyzed and simulated, and the analysis process comprises the following steps:
(1) and (3) complexity analysis: the multi-shift invariance algorithm (MI-PM algorithm) does not need to carry out characteristic decomposition on the cross-correlation matrix and singular value decomposition on the received data, so the complexity is low, and the main calculation complexity of the MI-PM algorithm is O (KI)2N2+P3) Where O (-) represents the computational complexity.
(2) And (3) error analysis: i.e. the estimation error is analyzed. Suppose thatWhereinIs an error estimation matrix, thenBy pairsTo obtain an estimate of the matrix Ψ
Has a k-th characteristic value ofβ thereinpThe eigenvalues of the matrix Ψ are represented,epis a unit vector whose p-th element is 1 and the remaining elements are 0. Using a first order approximation, the variance of the CFO estimation error is
Wherein, E2]E { } denotes the desired value, φ p2 pi Δ f, Re { } denotes the real part of the complex number.
The method reconstructs the received signal and utilizes the multiple shift invariance to estimate the CFO, so that the method has higher CFO estimation performance than the traditional PM algorithm and ESPRIT algorithm.
And (3) simulation results:
the CFO estimation performance is evaluated by 1000 Monte Carlo simulations, and a noisy signal model is expressed asWherein WnTo receive noise, the Signal-to-noise ratio (SNR) can be defined as
In all simulations, let us say that the OFDM system in the simulation has N-32 subcarriers, P-20, and the sampling interval of CP is 8, and the channel model is Lm=4(Lm< L), where Δ ω ═ 2 π Δ f is taken to be 0.4 ω, where ω ═ 2 π/N is the subcarrier spacing, dB represents one unit of the magnitude of the signal-to-noise ratio.
The performance of the CFO estimate was quantitatively evaluated using Mean Square Error (MSE), defined as follows
WhereinIs the CFO estimate for the mth Monte Carlo simulation, M is the Monte Carlo simulation times, Δ f is the exact value of CFO.
Fig. 1 is a comparison graph of CFO estimation performance of the method of the present invention and the conventional PM algorithm and ESPRIT algorithm under different snr conditions, where the simulation parameters are total carrier number N of 32, antenna number I of 4, signal block number K of 100 and channel number P of 20 for transmitting data.
It is apparent from fig. 1 that the CFO estimation performance of the MI-PM algorithm is superior to the conventional PM algorithm and the ESPRIT algorithm.
Fig. 2 is a comparison graph of CFO estimation performance under different signal-to-noise ratios, where N is 36, P is 20, and I is 7.
It can be seen from fig. 2 that the CFO estimation performance of the MI-PM algorithm is significantly improved as the number of signal blocks K increases.
Fig. 3 is a comparison graph of CFO estimation performance under different antenna numbers and under different snr conditions, where N is 36, P is 20, and K is 100.
As is apparent from FIG. 3, the CFO estimation performance of the MI-PM algorithm improves significantly as I increases.
Fig. 4 is a comparison graph of CFO estimation performance under different channel numbers under different snr conditions, where N is 32, I is 4, and K is 100.
As is apparent from fig. 4, the CFO estimation performance of the MI-PM algorithm significantly degrades as P increases.
Fig. 5 is a comparison graph of CFO estimation performance under different carrier numbers under different snr conditions, where the parameter is set to K-100, I-4, and P-5N/8.
It is apparent from fig. 5 that the CFO estimation performance of the MI-PM algorithm significantly degrades as N increases.
The above embodiments are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modifications made on the basis of the technical scheme according to the technical idea of the present invention fall within the protection scope of the present invention.
Claims (6)
1. A low-complexity carrier synchronization method in an OFDM power wireless private network is characterized by comprising the following steps:
1) arranging a multi-antenna OFDM system, and reconstructing a received signal of the OFDM system;
2) and obtaining the CFO of the OFDM system by using a multi-shift invariance PM algorithm.
2. The low complexity carrier synchronization method in the OFDM power wireless private network according to claim 1, wherein: in step 1), the method comprises the following steps:
11) the OFDM uplink system comprises a receiver, wherein the receiver is provided with 1 transmitting antenna and I receiving antennas, the number of subcarriers is N, and the cyclic prefix uses L sampling intervals, so that the number of samples of each OFDM system is N + L which is larger than the maximum propagation delay;
12) the transmission array defining the kth block is s (k) ═ s1(k),s2(k),K,sP(k)]TWherein s isp(k) For the kth data block transmitted on the P subcarrier, P parallel data are modulated on P subcarriers, namely the number of channels of the system is P, P is less than N, the remaining N-P subcarriers are virtual carriers, and the multicarrier modulation signal is filled by a cyclic prefix before being transmitted into a multipath fading channel;
removing the cyclic prefix CP, the output signal of the k block of the ith antenna is
xi(k)=EFPdiag(hi)s(k)ej2πΔf(k-1)(N+L)(1)
Wherein j represents an imaginary number symbol,represents a set of complex numbers, Δ f is CFO; e is a natural index;
intermediate variablesIs a CFO matrix, an intermediate variable Representing the first P columns of the inverse Fourier transform, the frequency domain channel vector for the ith receive antenna is hi=[Hi(1),Hi(2),K,Hi(P)]T(ii) a The frequency response defined as the nth subcarrier is Hi(n) corresponding to the ith antenna, the multi-antenna frequency domain channel matrix H is:
13) assuming that K block channel parameters are constants, defining a source matrix Xi=[xi(1) xi(2)…xi(K)]Is defined as
Xi=Adiag(hi)BT=ADi(H)BT,i=1,2,...,I (3)
Where the matrix B ═ diag {1, e ═ dj2πΔf(N+L),K,ej2πΔf(K-1)(N+L)},Di() Representing the ith row of the extraction matrix and constructing a diagonal matrix by using the ith row; a ═ EFP∈CN×PIs a Vandermonde matrix, a data model of the received signal taking into account the presence of noiseIs written as
Wherein WiIs the noise received by the ith array element;
output signal X of ith antennai=ADi(H)BTI is regarded as a slice of the trilinear model along the antenna direction, and a reconstructed matrix Y is obtained after matrix reconstruction according to the symmetry of the trilinear modeln:
Yn=HDn(A)BT,n=1,2,...,N (6)
Wherein Y isnN1, 2, as a reconstruction of equation (3);
Wherein L is the number of fast beats.
3. The low complexity carrier synchronization method in the OFDM power wireless private network according to claim 1, wherein: the signal in equation (3) is either expressed as a trilinear model
Wherein xn,k,iRepresenting X in the matrix equation (3)iThe (n, k) th element of (a)n,pRepresents the (n, p) th element of the matrix A, bk,pRepresents the (k, p) th element, h, of the matrix Bi,pRepresents the (i, p) th element of the frequency domain channel matrix H,the rest is the same; n, K, I are the number of subcarriers, the number of blocks of the source and the number of antennas, respectively.
4. The method for synchronizing low complexity carriers in an OFDM power wireless private network according to claim 3, wherein the number of subcarriers N is 32, the number of antennas I is 4, the number of signal blocks K is 100, and the number of system channels P for transmitting data P is 20.
5. The low complexity carrier synchronization method in the OFDM power wireless private network according to claim 1, wherein: in the step 2), the method specifically comprises the following steps:
from equation (6), the matrix Y is constructed
WhereinIs a rotation matrix; the CFO is estimated using the MI-PM algorithm according to the multiple shift invariant property of equation (8), and the matrix Y is expressed as
Y=AEBT(9)
Wherein
Matrix arrayWherein, I, N and P are the number of antennas, the number of subcarriers and the number of channels used by the system respectively, and the matrix AEThe block-shaped materials are divided into blocks,represents a complex set of a plurality of
Wherein the matrix oneIs a full rank matrix, matrix twoThus in matrix one A1And the matrix two A2There is one linear transformation operator to satisfy
A2=PcA1(12)
Order to
Wherein P iscIs a matrix of propagation operators, IPIs an identity matrix of P × P, and the propagation operator P is obtained by minimizing the cost function in the presence of noisecIs estimated value of
Wherein Jcsm() To relate toOf a convex function of the second order, matrixIs a received signalFirst P columns of, matrixIs a received signalThe remaining columns;
From the equations (12) and (13), the following relational expression is obtained
Thus, it is possible to provide
According to equation (16), a relationship matrix P is defined1And relation matrix bip2Is composed of
Thus, the relationship matrix P1And relation matrix bip2There exists the following relation
Defining the matrix Ψ:
so equation (19) is expressed as
P2=P1Ψ (21)
Then
Ψ=P1 +P2(22)
Wherein the matrix Ψ and the rotation matrix Φ have the same eigenvalue, and the matrix Ψ is subjected to eigenvalue decomposition to obtain
6. The low complexity carrier synchronization method in the OFDM power wireless private network according to claim 1, wherein: the performance of the CFO estimation is quantitatively evaluated using the mean square error MSE, defined as follows:
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