CN115499277A - High-resolution broadband airspace non-stationary channel parameter estimation method - Google Patents
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Abstract
The invention discloses a high-resolution broadband airspace non-stationary channel parameter estimation method, which can extract multipath information from channel measurement data and is divided into four steps, and the method specifically comprises the following steps: 1) Initializing parameters, wherein the initialized parameters comprise an arrival angle, a departure angle and time delay of multipath; 2) Refining the parameters, namely performing refined search on the initialization parameters based on the spherical wave model; 3) Multipath spatial domain occurrence and extinction identification, wherein the step is used for identifying the occurrence and extinction of multipath in an array domain; 4) And multipath screening, which is used for eliminating multipath estimation results with low signal-to-noise ratio. The algorithm provided by the invention adopts spherical wavefront, considers the antenna polarization, and introduces the generation and extinction of multipath in array dimension in the maximum likelihood estimation for the first time. Channel measurement data verification shows that the algorithm can extract more effective multipaths compared with the traditional algorithm. In addition, the algorithm supports parameter estimation of any array shape, and single polarization channel parameter estimation can be supported by simplifying estimation of multipath polarization components.
Description
Technical Field
The invention belongs to the field of large-scale MIMO wireless channel measurement and parameter estimation, and relates to a high-resolution broadband airspace non-stationary channel parameter estimation method.
Background
With the development of mobile communication technology, a plurality of novel application scenarios, such as millimeter wave, ultra-large scale MIMO, communication perception integration and the like, appear. The novel application scene brings new channel characteristics, the bandwidth of the millimeter wave frequency band channel is generally large, and the broadband characteristics are brought; the super-large-scale MIMO brings spherical wave characteristics due to the large array size; in order to obtain high-resolution time delay and angle information in a common-sense integrated application scene, a broadband ultra-large-scale MIMO array is required, so that the common-sense integrated application scene has broadband and spherical wave characteristics. In order to establish a channel model capable of accurately describing the new application scenarios, channel measurement corresponding to the scenarios needs to be carried out first, and then channel model parameters are extracted through a channel parameter estimation algorithm.
However, the new channel characteristics present challenges to conventional channel parameter estimation algorithms. Far-field assumptions and narrow-band assumptions commonly used in conventional channel parameter estimation algorithms will no longer apply in wideband super-large scale MIMO measurements. The specific reason is as follows: 1) Far-field plane waves are assumed to represent that electromagnetic waves that multipath departs from or arrives at the antenna array can be viewed as plane wave fronts. This assumption holds when the distance between the transmitting and receiving ends is greater than the rayleigh distance, however, as the number of antennas increases, the aperture of the antenna array increases, the distance between the transmitting and receiving ends may be less than the rayleigh distance of the array, at which time the plane wave assumption will no longer apply, requiring the use of a spherical wave front. In the spherical wave assumption, a scatterer is abstracted into a point, and the time delay and the angle of multipath leaving or arriving at the array need to be calculated according to the geometric relationship between the scatterer and the array; 2) Narrow band is assumed to be G/lambda < f c Where G represents the antenna aperture, λ represents the wavelength of the propagating signal, and f c Representing the center frequency and B the signal bandwidth.When the signal bandwidth is increased to the point that the narrow-band assumption is not satisfied, the time delay and the angle of the multipath are no longer independent parameters, and the estimation cannot be separated in the parameter estimation; 3) In addition, a large number of channel measurement results show that the ultra-large scale MIMO array has the multipath generation and extinction phenomenon in the space domain, which is also called as the non-stationary characteristic of the space domain.
Existing parameter estimation algorithms can be divided into three types: a spectrum estimation algorithm, a parameter subspace estimation algorithm, and a maximum likelihood estimation algorithm. Parameter estimation algorithms based on spectral estimation are generally low in complexity, but the resolution of the spectral estimation algorithms is also low. Signal parameter Estimation (ESPRIT) and multiple signal classification (MUSIC) based on rotational invariance techniques are two classical parameter estimation algorithms based on parameter subspace. However, both algorithms are based on plane wave assumption and cannot be applied to a super-large-scale MIMO scene. The Expectation Maximization (EM) algorithm is a classical maximum likelihood estimation algorithm, which has features of high resolution and high complexity. In order to reduce the complexity of the EM algorithm, a space-alternating generalized expectation-maximization (SAGE) algorithm is proposed, which reduces the search complexity by dividing the parameters into a plurality of subsets to be estimated separately. SAGE algorithms are widely used in measurement data processing due to their high resolution and acceptable complexity. However, despite the large number of measurements that have found spatial multipath fading in wideband super-large-scale MIMO, current SAGE algorithms still do not take such channel characteristics into account. The mismatch between the model and the measurement results may cause estimation errors, which may result in many pseudo paths being estimated by the algorithm, and may even result in the algorithm failing to converge. In order to make up for the defects of the existing channel parameter estimation algorithm, the invention provides a high-resolution channel parameter estimation algorithm based on maximum likelihood, and the algorithm considers spherical wavefront and broadband effect. In addition, the invention introduces a space domain nonstationary factor in the traditional spherical wave channel model, and can identify the occurrence and the extinction of the multipath in the space domain by estimating the space domain nonstationary factor of each multipath.
Disclosure of Invention
The invention provides a high-resolution broadband airspace non-stationary channel parameter estimation method, which considers the birth and extinction of multipath in an airspace, spherical wave front, large bandwidth and antenna polarization.
The specific technical scheme of the invention is as follows:
and S1, introducing a broadband airspace non-stationary channel model.
And S2, introducing a continuous interference elimination method.
And S3, giving a specific process for initializing parameters of the channel parameter estimation algorithm.
And S4, providing a detailed process for parameter refinement of the channel parameter estimation algorithm.
And S5, providing a specific flow of airspace multipath generation and extinction identification of a channel parameter estimation algorithm.
And S6, providing a specific process of multipath screening of the channel parameter estimation algorithm.
Specifically, step S1 specifically includes the following steps:
step S101, assume that there is M at receiving end of antenna array r Root antenna, transmitting end having M t And for each antenna, the transmission functions of the ith multipath at the mth antenna at the receiving end and the nth antenna at the transmitting end under the assumption of the narrowband plane wave are as follows:
wherein
Represents M f A transmission frequency point [] T Which represents the operation of transposition by means of a transposition operation,<·>represents an inner product operation, P Rx And P Tx Respectively representing the polarization of the receiving and transmitting end antennas,
indicating the l-th multipath at the receiving end P Rx Polarization and transmitting terminal P Tx PolarizationComplex gain of omega Rx,l And Ω Tx,l Respectively representing the angle-of-arrival and angle-of-departure of the ith multipath,
and
respectively indicating that the m-th antenna of the receiving end is at P R× Polarized complex gain and transmitting end n antenna at P Tx Complex gain of polarization. Under the narrow-band assumption, the influence of the frequency points on the antenna gain is ignored, and only the antenna gain at the central frequency point is considered. r is Rx,m And r Tx,n Respectively representing the position vectors, tau, of the mth antenna at the receiving end and the nth antenna at the transmitting end l Indicating the delay of the ith multipath.
Step S102, under the broadband ultra-large scale MIMO array, the assumption of narrow-band plane waves is not applicable any more, at the moment, the assumption of spherical waves is needed, the relation between antenna gain and frequency points needs to be considered, and at the moment, the ith multipath is in the fth multipath k The transmission function of each frequency point is:
wherein omega Rx,m,l Represents the arrival angle, omega, of the mth multipath antenna at the receiving end Tx,n,l Indicating the departure angle of the nth multipath at the transmitting end,
indicating that the mth antenna of the receiving end is at the kth frequency point and omega Rx,m,l The complex gain of the direction is given by,
indicating that the nth antenna of the sending end is at the kth frequency point and omega Tx,n,l Complex gain in direction, τ m,n,l And the time delay of the ith multipath from the mth antenna of the receiving end to the nth antenna of the transmitting end is shown.
The broadband spherical wave model in step S103 and step S102 may be rewritten into a matrix form, specifically as follows:
wherein the content of the first and second substances,
parameter set representing the number of multipaths forming, d T×,l Represents the distance from the first hop cluster to the reference antenna at the transmitting end, d Rx,l Represents the distance theta from the l-th last hop cluster to the reference antenna at the receiving end Tx,l And theta Rx,l Respectively representing the pitch departure angle and the pitch arrival angle of the ith multipath, phi Tx,l And phi Rx,l An azimuth departure angle and an azimuth arrival angle respectively representing the l-th multipath,. Alpha.indicating multiplication of corresponding elements of the matrix,. Phi., l time delay matrix representing the l-th multipath, A l A complex amplitude matrix representing the ith multipath.
Step S104, the broadband spherical wave model does not consider the generation and the extinction of the multipath in the array domain, and the array generation and extinction coefficient zeta is introduced Rx And ζ Tx And obtaining a broadband spatial domain non-stationary channel transmission function:
therein, ζ Rx,l And ζ Tx,l Respectively representing the birth and death coefficients of the l-th multipath at the receiving end and the transmitting end. Zeta Rx,l The mth element is marked as ζ Rx,m,l Representing the life and extinction coefficients of the mth multi-path antenna at the receiving end, the value range is 0 and 1, and zeta is Rx,m,l =0 denotes that the mth antenna of the l-th multipath disappears at the receiving end, ζ Rx,m,l And =1 indicates that the mth multipath survives at the m-th antenna of the receiving end. Zeta Tx,n,l The coefficient of the nth antenna of the sending end of the ith multipath is represented, the value range is {0,1}, and the specific meaning is zeta Rx,m,l As such, the explanation is not repeated here.
Step S105, the actually measured channel transfer function Y (f) is:
wherein, theta l ＝{Γ l ,ζ Rx,l ,ζ Tx,l Denotes a parameter set constituting the L-th multipath in the wideband spatial domain non-stationary channel model, L denotes the number of multipaths, n (f) denotes a noise vector,
representing the power of the noise.
The interference of high-power multipath to low-power multipath can be effectively reduced by the continuous interference cancellation method, the interference cancellation method is adopted in the invention, and the flow of the method is elaborated in step S2:
step S201: spatial domain non-stationary channel model and estimated ith multi-path parameter set
Reconstructing the channel transfer function H (f; theta) of the first multipath l )。
Step S202: method for estimating transmission function Y of l-th multipath based on continuous interference cancellation method l (f)：
Steps S3-S6 mainly describe the detailed flow of the algorithm, the algorithm is divided into four steps of parameter initialization, parameter refinement, multipath birth and death identification and multipath screening, and step S3 describes the parameter initialization step in detail.
Step S301: in the parameter initialization step, the parameter estimation is based on a narrowband plane wave channel model, so some frequency points near the center frequency need to be selected from broadband measurement data first to ensure that the extracted channel measurement data meets the narrowband assumption. Let the extracted frequency point be f narr Then the first multi-path delay initialization nodeThe fruit is:
step S302: the initialization result of the l-th multipath angle of arrival is:
wherein | represents the Frobenius norm, C Rx,l,init The method represents a receiving end guide vector in the parameter initialization process, wherein the guide vector is obtained by calculation based on the assumption of narrow-band plane waves, and the specific calculation method comprises the following steps:
in addition to this, the present invention is,
representing three-dimensional matrices
For a matrix slice of dimension 1, where the (m, n) th element in matrix X is:
step S303: the initialization result of the ith multipath departure angle is:
wherein the content of the first and second substances,
g is in f k The frequency point calculation method comprises the following steps:
wherein [ ·] * Representing a conjugate operation.
And
indicates the receiving end P Rx Polarization at f k Guide vector and sending terminal P corresponding to frequency point Tx Polarization at f k And (4) pilot vectors corresponding to the frequency points. In the course of the initialization of the parameters,
and
are used separately
And
instead, and the antenna gain at the center frequency is employed in calculating the steering vector. Matrix D at f k The frequency point calculation method comprises the following steps:
wherein the content of the first and second substances,
representing the kronecker product. C Rx/Tx,k,l Indicating the l-th multipath at f k Guide vector of receiving end/transmitting end antenna array at frequency point in parameter initialization process C Rx,k,l And C Tx,k,l Respectively with C Rx,l,init And C Tx,l,init Instead, and using the centre frequency when calculating the steering vectorAnd (4) antenna gain.
Step S4 is used for parameter refinement, wherein the parameter estimation in the parameter refinement step is based on spherical wave assumption, and the detailed steps are as follows:
step S401: the first multipath arrival angle refinement method comprises the following steps:
here the guide vector C Rx,l Based on the spherical wave model calculation, and the antenna gain at the center frequency is adopted in calculating the steering vector.
Step S402: the first multipath departure angle refinement method comprises the following steps:
wherein, the first and the second end of the pipe are connected with each other,
based on the estimation
Calculated by spherical wave model, and a steering vector C Tx,l The antenna gain at the center frequency is also used in the calculation based on the spherical wave model, and the calculation of the steering vector.
Step S403: the time delay refining method comprises the following steps:
wherein, the first and the second end of the pipe are connected with each other,
based on the estimation
The method is obtained by calculation by adopting a spherical wave model,
based on the estimation
And calculating by using a spherical wave model. In addition, in order to improve the delay resolution, all frequency points of the broadband signal need to be considered in the delay refinement process, so that the guide vector of each frequency point needs to be calculated independently. Because the arrival angle, the departure angle and the time delay are preliminarily estimated in the parameter initialization process, the parameter search range in the parameter refinement step can be greatly reduced, and the complexity of the algorithm is reduced.
Step S404: first multipath amplitude alpha l The estimation method comprises the following steps:
step S5 is used to estimate the birth and death coefficients of the multipaths in the array domain, and iteratively estimate the result of the previous parameter estimation until the estimation result of the ith multipath converges, and the specific steps are as follows:
step S501: estimating the extinction coefficient zeta of the mth multi-path at the receiving end Rx,m,l
Wherein the content of the first and second substances,
Y m,:,l (f) Representing the three-dimensional matrix Y (f) for a 1 st dimension of the matrix slice.
Step S502: estimation ofCalculating the extinction coefficient zeta of the nth antenna of the ith multipath at the transmitting end Tx,n,l
Wherein, the first and the second end of the pipe are connected with each other,
Y :,n,l (f) Matrix slice representing three-dimensional matrix Y (f) for 2 nd dimension
Step S503: the first multipath parameter iteration estimation, the first estimated multipath parameter set is recorded as
The parameter set estimated in the ith iteration is recorded as
The parameter iteration of the step is updated in sequence according to the arrival angle, the departure angle, the time delay, the complex amplitude, the receiving end array extinction coefficient and the sending end array extinction coefficient until the final parameter is converged. The method comprises the following specific steps:
wherein, the first and the second end of the pipe are connected with each other,
the method is characterized in that a cost function obtained by calculation based on a broadband airspace non-stationary spherical wave model is represented, and the calculation method comprises the following steps:
because the number of multipaths obtained by actual channel measurement is an unknown parameter, a larger number of multipaths is generally set in the channel parameter estimation algorithm to ensure that all multipath information can be extracted. However, among the estimated multipaths, there are some multipath estimation results that are pseudo-spectra generated by algorithm errors. Therefore, it is necessary to remove the unreliable multipath estimation results to ensure the reliability of the channel parameter estimation results. Step S6 is multipath screening, unreliable multipath estimation results can be deleted in the step, and the specific steps are as follows:
step S601: in the algorithm, one multipath parameter is estimated at a time
The likelihood function is calculated, then the difference between the multi-path likelihood function and the previous multi-path likelihood function is calculated, gamma is added on the basis of the calculated difference as a punishment item of overfitting, if the calculated total likelihood function difference is more than 0, the multi-path is regarded as the overfitting result, the multi-path estimation result is deleted, and the time delay point is skipped in the next search. Where γ is taken to be 2, multipath estimation results corresponding to signal-to-noise ratios below 0dB will be eliminated. The method for calculating the difference between the two multipath likelihood values comprises the following steps:
step S602: and deleting the multipath estimation result of which the number of visible antennas at the transmitting and receiving ends is less than half of the total number of the arrays.
Advantageous effects
The invention provides a high-resolution broadband airspace non-stationary channel parameter estimation algorithm which can simultaneously consider broadband characteristics, spherical wave characteristics, multi-path generation and extinction in airspace and antenna polarization and can be simplified to different application scenes through flexible configuration. In addition, the algorithm effectively reduces the complexity of the algorithm through parameter initialization and refined estimation steps; and deleting unreliable multipath estimation results through a multipath screening step, and ensuring the reliability of the multipath estimation results of the algorithm.
In order to verify the accuracy of the algorithm, the parameter extraction is carried out on the indoor office scene channel measurement result based on the algorithm provided by the invention. The channel measurement includes a line-of-sight (LOS) location point and a non-LOS (NLOS) location point. The measurement data is processed by using the traditional spherical wave SAGE algorithm and the broadband airspace non-stationary parameter estimation algorithm provided by the invention, and the result shows that the algorithm provided by the invention can estimate more effective multipath information.
Drawings
FIG. 1 is a flow chart of a high resolution wideband spatial domain non-stationary channel parameter estimation algorithm proposed by the present invention;
FIG. 2-1 is a time delay-azimuth angle of arrival power spectrum measured at a LOS location point in the present invention;
FIG. 2-2 is a power spectrum of the delay-azimuth arrival angle estimated by the LOS location based on the spherical wave SAGE algorithm in the present invention;
FIGS. 2-3 are power spectra of delay-azimuth arrival angle estimated by LOS location points based on the algorithm of the present invention;
FIG. 3-1 is a time delay-azimuth arrival angle power spectrum measured at an NLOS location point in the present invention;
FIG. 3-2 is a power spectrum of the delay-azimuth arrival angle estimated by the NLOS location point based on the SAGE algorithm of the present invention;
fig. 3-3 are delay-azimuth arrival angle power spectra estimated by NLOS location points based on the algorithm of the present invention.
Detailed Description
In order to better understand the purpose, structure and function of the present invention, the following describes the high resolution wideband spatial domain non-stationary channel parameter estimation algorithm in detail with reference to the accompanying drawings.
The specific technical scheme of the invention is as follows:
and S1, introducing a broadband airspace non-stationary channel model.
And S2, introducing a continuous interference elimination method.
And S3, giving a specific initialization flow of the channel parameter estimation algorithm parameters.
And S4, providing a detailed process for parameter refinement of the channel parameter estimation algorithm.
And S5, providing a specific flow of airspace multipath generation and extinction identification of a channel parameter estimation algorithm.
And S6, providing a specific process of multipath screening of a channel parameter estimation algorithm.
Specifically, step S1 specifically includes the following steps:
step S101, assume that there is M at receiving end of antenna array r Root antenna, transmitting end having M t And for each antenna, the transmission functions of the ith multipath at the mth antenna at the receiving end and the nth antenna at the transmitting end under the assumption of the narrowband plane wave are as follows:
wherein
Represents M f A transmission frequency point [ ·] T Which represents the operation of transposition by means of a transposition operation,<·>representing inner product operation, P Rx And P Tx Respectively representing the polarization of the antennas at the receiving end and the transmitting end,
indicating that the l-th multipath is at the receiving end P Rx Polarization and transmitting terminal P Tx Complex gain of polarization, omega Rx,l And Ω Tx,l Respectively representing the angle-of-arrival and angle-of-departure of the ith multipath,
and
respectively indicating that the m-th antenna of the receiving end is at P Rx Polarized complex gain and transmitting end n antenna at P Tx Complex gain of polarization. Under the narrow-band assumption, the influence of the frequency points on the antenna gain is ignored, and only the antenna gain at the central frequency point is considered. r is Rx,m And r Tx,n Respectively representing the position vectors of the mth antenna of the receiving end and the nth antenna of the transmitting end, tau l Indicating the delay of the ith multipath.
Step S102, under the broadband ultra-large scale MIMO array, the assumption of narrow-band plane waves is not applicable any more, at the moment, the assumption of spherical waves is needed, the relation between antenna gain and frequency points needs to be considered, and at the moment, the ith multipath is in the fth multipath k The transmission function of each frequency point is:
wherein omega Rx,m,l Represents the arrival angle, omega, of the mth multipath antenna at the receiving end Tx,n,l Indicating the departure angle of the nth antenna of the ith multipath at the transmitting end,
indicating that the mth antenna of the receiving end is at the kth frequency point and omega Rx,m,l The complex gain of the direction is given by,
indicating that the nth antenna of the sending end is at the kth frequency point and omega Tx,n,l Complex gain of direction, τ m,n,l And the time delay of the ith multipath from the mth antenna of the receiving end to the nth antenna of the transmitting end is shown.
The broadband spherical wave model in step S103 and step S102 may be rewritten into a matrix form, specifically as follows:
wherein the content of the first and second substances,
representing the set of parameters constituting the ith multipath, d Tx,l Represents the distance from the first hop cluster to the reference antenna at the transmitting end, d Rx,l Represents the distance theta from the l-th last hop cluster to the reference antenna at the receiving end Tx,l And theta Rx,l Respectively representing the elevation departure angle and elevation arrival angle, phi, of the ith multipath Tx,l And phi Rx,l An azimuth departure angle and an azimuth arrival angle respectively representing the l-th multipath,. Phi. l Time delay matrix representing the l-th multipath, A l A complex amplitude matrix representing the ith multipath.
Step S104, the broadband spherical wave model does not consider the generation and the extinction of the multipath in the array domain, and the array generation and extinction coefficient zeta is introduced Rx And ζ Tx And obtaining a broadband airspace non-stationary channel transmission function:
therein, ζ Rx,l And ζ Tx,l Respectively representing the birth and death coefficients of the l-th multipath at the receiving end and the transmitting end. ζ represents a unit Rx,l M-th element of (D) is marked as ζ Rx,m,l Representing the life and extinction coefficients of the mth multi-path antenna at the receiving end, the value range is 0 and 1, and zeta is Rx,m,l =0 denotes that the mth antenna of the l-th multipath disappears at the receiving end, ζ Rx,m,l And =1 indicates that the mth multipath survives at the m-th antenna of the receiving end. Zeta Tx,n,l Is shown asThe value range of the life and extinction coefficients of the n th antenna of the l multi-paths at the transmitting end is {0,1}, and the specific meaning is zeta Rx,m,l As such, the explanation is not repeated here.
Step S105, the channel transfer function Y (f) obtained by actual measurement is:
wherein, theta l ＝{Γ l ,ζ Rx,l ,ζ Tx,l Denotes a parameter set constituting the L-th multipath in the wideband spatial domain non-stationary channel model, L denotes the number of multipaths, n (f) denotes a noise vector,
representing the power of the noise.
The interference cancellation method is adopted in the invention, and the step S2 will explain the flow of the method in detail:
step S201: spatial domain non-stationary channel model and estimated ith multi-path parameter set
Reconstructing channel transfer function H (f; theta) of the ith multipath l )。
Step S202: method for estimating transmission function Y of l-th multipath based on continuous interference cancellation method l (f)：
Steps S3-S6 mainly describe the detailed flow of the algorithm, which is divided into four steps of parameter initialization, parameter refinement, multipath birth and death identification and multipath screening, and step S3 describes the parameter initialization step in detail.
Step S301: in the parameter initialization step, the parameter estimation is based on the narrowband plane wave channel model, so that the wideband is required to be firstly startedSome frequency points near the central frequency are selected from the measured data to ensure that the extracted channel measured data meets the narrow-band assumption. Let the extracted frequency point be f narr Then, the result of the initialization of the ith multipath delay is:
step S302: the initialization result of the l-th multipath angle of arrival is:
wherein | represents the Frobenius norm, C Rx,l,init The method represents a receiving end guide vector in the parameter initialization process, wherein the guide vector is obtained by calculation based on the assumption of narrow-band plane waves, and the specific calculation method comprises the following steps:
in addition to this, the present invention is,
representing three-dimensional matrices
For a matrix slice of dimension 1, where the (m, n) th element in matrix X is:
step S303: the initialization result of the ith multipath departure angle is:
wherein, the first and the second end of the pipe are connected with each other,
g is in f k The frequency point calculation method comprises the following steps:
wherein [ ·] * Representing a conjugate operation.
And
indicates the receiving end P Rx Polarization at f k Guide vector and sending terminal P corresponding to frequency point Tx Polarization at f k And (5) pilot vectors corresponding to the frequency points. In the course of the initialization of the parameters,
and
respectively using
And
instead, and the antenna gain at the center frequency is employed in calculating the steering vector. Matrix D at f k The frequency point calculation method comprises the following steps:
wherein the content of the first and second substances,
representing the kronecker product. C Rx/Tx,k,l Indicating the l-th multipath at f k Receiver/transmitter antenna at frequency pointGuide vectors of line arrays, in parameter initialization process C Rx,k,l And C Tx,k,l Respectively with C Rx,l,init And C Tx,l,init Instead, and the antenna gain at the center frequency is employed in calculating the steering vector.
Step S4 is used for parameter refinement, wherein the parameter estimation in the parameter refinement step is based on spherical wave assumption, and the detailed steps are as follows:
step S401: the first multipath arrival angle refinement method comprises the following steps:
here the guide vector C Rx,l Based on the spherical wave model calculation, and the antenna gain at the center frequency is adopted in calculating the steering vector.
Step S402: the first multi-path departure angle refinement method comprises the following steps:
wherein the content of the first and second substances,
based on the estimation
Calculated by using a spherical wave model, and a guide vector C Tx,l The antenna gain at the center frequency is also used in the calculation based on the spherical wave model, and the calculation of the steering vector.
Step S403: the time delay refining method comprises the following steps:
wherein the content of the first and second substances,
based on the estimation
The method is obtained by calculation by adopting a spherical wave model,
based on the estimation
And calculating by using a spherical wave model. In addition, in order to improve the delay resolution, all frequency points of the broadband signal need to be considered in the delay refinement process, so that the steering vector of each frequency point needs to be calculated independently. As the arrival angle, the departure angle and the time delay are preliminarily estimated in the parameter initialization process, the parameter search range in the parameter refinement step can be greatly reduced, and the complexity of the algorithm is reduced.
Step S404: first multipath amplitude alpha l The estimation method comprises the following steps:
step S5 is used to estimate the birth and death coefficients of the multipaths in the array domain, and iteratively estimate the result of the previous parameter estimation until the estimation result of the ith multipath converges, and the specific steps are as follows:
step S501: estimating the extinction coefficient zeta of the mth multi-path at the receiving end Rx,m,l
Wherein the content of the first and second substances,
Y m,:,l (f) Representing the three-dimensional matrix Y (f) for a 1 st dimension of the matrix slice.
Step S502: estimating the extinction coefficient zeta of the nth antenna of the first multipath at the transmitting end Tx,n,l
Wherein the content of the first and second substances,
Y :,n,l (f) Matrix slice representing three-dimensional matrix Y (f) for 2 nd dimension
Step S503: the first multipath parameter iteration estimation, the first estimated multipath parameter set is recorded as
The parameter set estimated in the ith iteration is recorded as
The parameter iteration of the step is updated in sequence according to the arrival angle, the departure angle, the time delay, the complex amplitude, the receiving end array extinction coefficient and the sending end array extinction coefficient until the final parameter is converged. The method comprises the following specific steps:
wherein the content of the first and second substances,
the method is characterized in that a cost function obtained by calculation based on a broadband airspace non-stationary spherical wave model is represented, and the calculation method comprises the following steps:
because the number of multipaths obtained by actual channel measurement is an unknown parameter, a larger number of multipaths is generally set in the channel parameter estimation algorithm to ensure that all multipath information can be extracted. However, among the estimated multipaths, there are some multipath estimation results that are pseudo-spectra generated by algorithm errors. Therefore, it is necessary to remove the unreliable multipath estimation results to ensure the reliability of the channel parameter estimation results. Step S6 is multipath screening, unreliable multipath estimation results can be deleted in the step, and the specific steps are as follows:
step S601: in the algorithm, one multipath parameter is estimated at a time
The likelihood function is calculated, then the difference between the multi-path likelihood function and the previous multi-path likelihood function is calculated, gamma is added on the basis of the calculated difference as a punishment item of overfitting, if the calculated total likelihood function difference is more than 0, the multi-path is regarded as the overfitting result, the multi-path estimation result is deleted, and the time delay point is skipped in the next search. Here gamma isWith a value of 2, multipath estimation results corresponding to signal-to-noise ratios below 0dB will be cancelled. The method for calculating the difference between the two multipath likelihood values comprises the following steps:
step S602: and deleting the multipath estimation result of which the number of visible antennas at the transmitting and receiving ends is less than half of the total number of the arrays.
And (3) comparing the difference between the delay-azimuth arrival angle joint power spectrum estimated by the two algorithms and the measurement result, and fig. 2 shows the comparison between the delay-azimuth arrival angle joint power spectrum measured by the LOS position point and the estimation result of the two algorithms. Fig. 3 shows the comparison of the delay-azimuth arrival angle joint power spectrum obtained by NLOS position point measurement and the estimation results of the two algorithms. The estimation results of the two algorithms are compared to find that the estimation result of the algorithm parameters provided by the invention is closer to the measurement result, which shows that the algorithm performance provided by the invention is better.
In conclusion, the high-resolution broadband airspace non-stationary channel parameter estimation algorithm provided by the invention can provide multipath information from the channel measurement result, and the performance is better than that of the traditional spherical wave SAGE algorithm. The multipath parameters extracted by the algorithm can be used for channel modeling or channel characteristic analysis, and have important significance for establishing an accurate channel model.
It will be understood that the present invention is described in terms of actual channel measurement data and that various changes, modifications, and equivalents may be made to these features and embodiments without departing from the invention, as will be apparent to those skilled in the art. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.
Claims (7)
1. A high-resolution broadband airspace non-stationary channel parameter estimation method is characterized by comprising the following steps:
constructing a broadband spatial domain non-stationary channel model;
estimating the transmission function of the l multipath;
initializing channel parameters, wherein the initialized channel parameters comprise an arrival angle, a departure angle and time delay of multipath;
refining the channel parameters, wherein the step of refining the initialized channel parameters is carried out on the basis of a spherical wave model;
multipath spatial domain occurrence and extinction identification, wherein the step is used for identifying the occurrence and extinction of multipath in an array domain;
and multipath screening, which is used for eliminating multipath estimation results with low signal-to-noise ratio.
2. The method for estimating the parameters of the high-resolution wideband spatial domain non-stationary channel according to claim 1, wherein the specific steps for constructing the wideband spatial domain non-stationary channel model comprise:
suppose that there is M at the receiving end of an antenna array r Root antenna, transmitting end having M t For each antenna, the transmission functions of the mth antenna at the receiving end and the nth antenna at the transmitting end of the ith multipath under the assumption of narrowband plane waves are as follows:
wherein
Represents M f A transmission frequency point [ ·] T Which represents the operation of transposition of the image,<·>representing inner product operation, P Rx And P Tx Respectively representing the polarization of the receiving and transmitting end antennas,
indicating that the l-th multipath is at the receiving end P Rx Polarization and transmitting terminal P Tx Complex gain of polarization, omega Rx,l And Ω Tx,l Respectively representing the arrival angle and departure angle of the ith multipath,
and
respectively indicates that the m-th antenna at the receiving end is at P Rx Polarized complex gain and transmitting end n antenna at P Tx A complex gain of polarization; r is Rx,m And r Tx,n Respectively representing the position vectors of the mth antenna of the receiving end and the nth antenna of the transmitting end, tau l The time delay of the ith multipath is represented;
the l multipath being at f k The transmission function of each frequency point is:
wherein omega Rx,m,l Represents the arrival angle, omega, of the mth multipath antenna at the receiving end Tx,n,l Indicating the departure angle of the nth antenna of the ith multipath at the transmitting end,
indicates that the mth antenna of the receiving end is at the kth frequency point and omega Rx,m,l The complex gain of the direction is given by,
indicating that the nth antenna of the sending end is at the kth frequency point and omega Tx,n,l Complex gain of direction, τ m,n,l Representing the time delay of the l multipath from the m th antenna of the receiving end to the n th antenna of the transmitting end;
rewriting the broadband spherical wave model into a matrix form, specifically as follows:
wherein the content of the first and second substances,
representing the set of parameters constituting the ith multipath, d Tx,l Represents the distance from the first hop cluster to the reference antenna at the transmitting end, d Rx,l Represents the distance theta from the l-th last-hop cluster to the reference antenna of the receiving end Tx,l And theta Rx,l Respectively representing the elevation departure angle and elevation arrival angle, phi, of the ith multipath Tx,l And phi Rx,l An azimuth departure angle and an azimuth arrival angle respectively representing the l-th multipath,. Phi. l Time delay matrix representing the l-th multipath, A l A complex amplitude matrix representing the l-th multipath;
broadband spherical wave model introduced array extinction coefficient zeta Rx And ζ Tx And obtaining a broadband airspace non-stationary channel transmission function:
wherein, theta l ＝{Γ l ,ζ Rx,l ,ζ Tx,l And represents the parameter set of the I < th > multipath formed in the wideband spatial domain non-stationary channel model. Zeta Rx,l And ζ Tx,l Respectively representing the life and extinction coefficients of the first multipath at a receiving end and a transmitting end; zeta Rx,l The mth element is marked as ζ Rx,m,l Showing the extinction coefficient, zeta, of the mth antenna of the mth multipath at the receiving end Rx,m,l =0 denotes that the mth antenna of the l-th multipath disappears at the receiving end, ζ Rx,m,l =1 represents that the mth antenna of the l multipath survives at the receiving end; ζ represents a unit Tx,n,l And the birth and death coefficients of the ith multipath at the nth antenna of the transmitting end are shown.
The actually measured channel transfer function Y (f) is:
where L represents the number of multipaths, n (f) represents the noise vector,
representing the power of the noise.
3. The method as claimed in claim 1, wherein the step of estimating the transfer function of the ith multipath comprises:
multipath estimation is carried out based on a continuous interference elimination method, and for the 1 st multipath transmission function, the transmission function Y (f) obtained by measurement is directly used for estimation; after estimating the first multipath parameter set, reconstructing to obtain the transmission function of the 1 st multipath, subtracting the transmission function of the first multipath from Y (f), then continuing the estimation of the next multipath, repeating the above operations until all L multipath are estimated; estimating the transmission function Y of the l-th multipath based on the method l (f) Is composed of
4. The method as claimed in claim 1, wherein the step of initializing the channel parameters comprises:
selecting frequency point f near central frequency from broadband measurement data narr The result of the initialization of the ith multipath delay is:
the initialization result of the l-th multipath angle of arrival is:
wherein | represents the Frobenius norm, C Rx,l,init The method comprises the following steps of representing a receiving end guide vector in a parameter initialization process, wherein the guide vector is obtained by calculation based on the assumption of narrow-band plane waves, and the specific calculation method comprises the following steps:
in addition to this, the present invention is,
representing three-dimensional matrices
For a matrix slice of dimension 1, where the (m, n) th element in matrix X is:
the initialization result of the ith multipath departure angle is:
wherein the content of the first and second substances,
g is in f k The frequency point calculation method comprises the following steps:
wherein [ ·] * Represents a conjugate operation;
and
indicates the receiving end P Rx Polarization at f k Guide vector and sending terminal P corresponding to frequency point Tx Polarization at f k A guide vector corresponding to the frequency point; in the course of the initialization of the parameters,
and
are used separately
And
instead, and the antenna gain at the center frequency is used in calculating the steering vector; matrix D at f k The frequency point calculation method comprises the following steps:
wherein the content of the first and second substances,
represents the kronecker product; c Rx/Tx,k,l Indicating the l-th multipath at f k Guide vector of receiving end/transmitting end antenna array at frequency point in parameter initialization process C Rx,k,l And C Tx,k,l Respectively with C Rx,l,init And C Tx,l,init Instead, and the antenna gain at the center frequency is employed in calculating the steering vector.
5. The method as claimed in claim 1, wherein the step of refining parameters comprises:
the first multipath arrival angle refinement method comprises the following steps:
guide vector C Rx,l Calculating based on a spherical wave model, and adopting antenna gain at the central frequency when calculating the guide vector;
the first multipath departure angle refinement method comprises the following steps:
wherein the content of the first and second substances,
based on the estimation
Calculated by using a spherical wave model, and a guide vector C Tx,l Calculating based on a spherical wave model, and adopting antenna gain at the central frequency when calculating the guide vector;
the time delay refining method comprises the following steps:
wherein the content of the first and second substances,
based on the estimation
The method is obtained by calculation by adopting a spherical wave model,
based on the estimation
Calculating by adopting a spherical wave model; the steering vector of each frequency point needs to be calculated independently;
first multipath amplitude alpha l The estimation method of (2):
6. the method as claimed in claim 1, wherein the specific steps of the multipath space domain occurrence and extinction identification include:
estimating the extinction coefficient zeta of the mth multi-path at the receiving end Rx，m，l
Wherein the content of the first and second substances,
Y m,:,l (f) A matrix slice representing the three-dimensional matrix Y (f) for the 1 st dimension;
estimating the extinction coefficient zeta of the nth antenna of the first multipath at the transmitting end Tx,n,l
Wherein, the first and the second end of the pipe are connected with each other,
Y :,n,l (f) A matrix slice representing the three-dimensional matrix Y (f) for the 2 nd dimension;
iterative estimation of the l-th multipath parameter, and recording the first estimated l-th multipath parameter set as
The parameter set estimated in the ith iteration is recorded as
The parameter iteration is updated in sequence according to the arrival angle, the departure angle, the time delay, the complex amplitude, the receiving end array extinction coefficient and the sending end array extinction coefficient until the final parameters are converged; the method comprises the following specific steps:
wherein the content of the first and second substances,
the method is characterized in that a cost function obtained by calculation based on a broadband airspace non-stationary spherical wave model is represented, and the calculation method comprises the following steps:
7. the method as claimed in claim 1, wherein the multipath screening comprises the following steps:
each time estimating a multipath parameter
Calculating the likelihood function, then calculating the difference between the multi-path likelihood function and the previous multi-path likelihood function, adding gamma on the basis of the calculated difference as a punishment item of overfitting, if the calculated total likelihood function difference is more than 0, regarding the multi-path as the overfitting result, deleting the multi-path estimation result, and skipping the time delay point in the next search; the calculation method of the difference value of the two multipath likelihood values comprises the following steps:
and deleting the multipath estimation result of which the number of visible antennas at the transmitting and receiving ends is less than half of the total number of the arrays.
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