CN112702093A - Channel estimation method in FDD downlink multi-user large-scale MIMO system - Google Patents
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Abstract
The invention provides a channel estimation method in an FDD downlink multi-user large-scale MIMO system, which comprises the following steps: s1, designing training sequences and processing received signals aiming at a plurality of users; s2, carrying out corresponding angle estimation according to the received signal; s3, constructing a channel guide vector through an angle estimation value; and S4, reconstructing the state information of the downlink channel according to the constructed channel guide vector. The channel estimation method based on a small amount of uniform training sequences can simultaneously estimate the channel state information by a plurality of users, effectively reduce the pilot frequency overhead and lay a foundation for realizing higher system throughput.
Description
Technical Field
The invention relates to the technical field of wireless communication, in particular to a channel estimation method in an FDD downlink multi-user large-scale MIMO system.
Background
In a large-scale multiple-input multiple-output (MIMO) system, by utilizing a large-scale antenna array of a Base Station (BS), the system can obtain extremely high spatial resolution and spatial division multiplexing gain, can provide services for a plurality of users simultaneously under the condition of not being seriously interfered, and greatly improves the spectral efficiency and the transmission rate of the system. But these good performances all depend on the availability of Channel State Information (CSI), so how to acquire the complete CSI in a real system is crucial to the system performance.
For a Frequency Division Duplex (FDD) massive MIMO system, a large amount of pilot overhead is required to acquire complete downlink CSI. This is because in an actual large-scale MIMO system, the number of training times and the feedback overhead are in direct proportion to the number of BS antennas, and the resources for acquiring complete CSI by using a conventional linear channel estimation method (such as least square algorithm (LS) and Linear Minimum Mean Square Error (LMMSE) algorithm) need to transmit training sequences with the same number as that of base station antennas, so that in an FDD downlink channel estimation method developed in recent years, different training sequences are almost designed for channel information of different users to acquire CSI, and thus, for a multi-user system, more time and resources are consumed, which is impractical.
In view of the above technical problems, it is desirable to improve.
Disclosure of Invention
The invention aims to provide a channel estimation method in an FDD downlink multi-user large-scale MIMO system aiming at the defects of the prior art.
In order to achieve the purpose, the invention adopts the following technical scheme:
the channel estimation method in the FDD downlink multi-user large-scale MIMO system comprises the following steps:
s1, designing training sequences and processing received signals aiming at a plurality of users;
s2, carrying out corresponding angle estimation according to the received signal;
s3, constructing a channel guide vector through an angle estimation value;
and S4, reconstructing the state information of the downlink channel according to the constructed channel guide vector.
Further, in step S1, the training sequence is designed by multiple users and the received signal is processed by K independent single-antenna users, a base station, and M antennas are equipped at the base station.
Furthermore, M antennas provided at the base station are arranged in a planar array, and M is equal to MhMvWherein each row has MhA root antenna, each column having MvFor a root antenna, the channel from the base station to the receiving end for the K (K ═ 1,2,3, …, K) th user is specifically represented as:
wherein: pkRepresenting the number of propagation paths between the base station and the receiving end of the kth user; gk,lThe channel complex gain of the l path representing the k user; α (θ, φ) represents a steering vector of the channel; alpha (theta)k,l,φk,l) A steering vector representing a channel of the ith path of the kth user; thetak,lAnd phik,lRespectively representing the elevation and azimuth of the ith path of the kth user.
Further, the steering vector α (θ, φ) of the channel is expressed as:
wherein: d represents the distance between antenna elements, and if d is lambda/2, lambda is the carrier wavelength; alpha is alphav(theta) includes information on the longitudinal angle of the planar array, alphah(θ, φ) contains lateral angle information of the planar array.
Further, the designing of the training sequence in step S1 specifically includes:
suppose that the base station transmits S signals to all K usersNThe matrix is an M × N matrix, and is specifically expressed as:
wherein: fnA discrete Fourier DFT matrix representing n dimensions; 0nA zero matrix of n dimensions; 0(M-7n)×nThe matrix is a zero matrix with (M-7N) multiplied by N dimensions, wherein N is equal to N when N is 4N, and N is the total number of samples.
Further, the processing of the received signal in step S1 specifically includes:
after the noise is mixed, the received signal of the kth (K ═ 1,2, 3., K) ue is represented as:
wherein: ρ is the signal-to-noise ratio, zkThe noise mixed in the k user is assumed to be Gaussian noise which obeys zero mean and unit variance;
for transmitting signalsPerforming an inverse DFT transform, the actual received signal at the kth user is represented as:
wherein, ykRepresenting the received signal.
Further, the step S2 specifically includes:
s21, setting a codebook, and enabling a transverse vector alpha in a channel guide vector alpha (theta, phi)hCos θ sin φ and longitudinal vector α in (θ, φ)vSin theta in (theta) is respectively regarded as two integers in the interval (-1, 1); two M codebooks are respectively created in the (-1,1) interval, and M is equal to M/2;
s22, the received signal of i (i ═ 1,2, …, P) path at k-th user is yk(i) The noise of the ith path of the kth user is derived and is expressed as:
wherein,andrepresenting the value of the set angle codebook in each traversal;representing the value after traversing the set angle codebook each time;
s23, combining a preset codebook, setting the code words as follows:
combining set code wordsTraverse a predetermined codebook from yk,r(i) Selecting the code word with the maximum projection power, and expressing as:
in a code wordAndreconstructing the steering vector of the channel by using the estimated value of the angle information for the estimated value of the angle information in the steering vector of the channel in the ith path of the kth user
S24, traversing the angle codebook by combining a preset codebook, and selecting and obtaining an estimation value of angle information, thereby estimating the ith path gain of the kth user, wherein the estimation is represented as:
further, the step S3 is specifically:
incorporating angle information estimatesBy α in the channel steering vector α (θ, φ)v(theta) and alphah(theta, phi) form to construct steering matrix transverse vectorAnd a longitudinal vectorThe product of the two tensorsConstructing channel steering vectors
Further, the step S4 is specifically: steering vector based on reconstructed channelAnd channel complex gain estimatesAnd reconstructing the channel matrix to recover the downlink channel information.
Compared with the prior art, the channel estimation method based on a small amount of uniform training sequences can simultaneously estimate the channel state information by a plurality of users, effectively reduce the pilot frequency overhead and lay a foundation for realizing higher system throughput.
Drawings
Fig. 1 is a flowchart of a channel estimation method in an FDD downlink multi-user massive MIMO system according to a first embodiment;
fig. 2 is a simulation diagram of a channel estimation method in an FDD downlink multi-user massive MIMO system according to a first embodiment.
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention. It is to be noted that the features in the following embodiments and examples may be combined with each other without conflict.
Example one
The present embodiment provides a channel estimation method in an FDD downlink multi-user massive MIMO system, as shown in fig. 1, including:
s1, designing training sequences and processing received signals aiming at a plurality of users;
s2, carrying out corresponding angle estimation according to the received signal;
s3, constructing a channel guide vector through an angle estimation value;
and S4, reconstructing the state information of the downlink channel according to the constructed channel guide vector.
In the channel estimation method in the FDD downlink multi-user large-scale MIMO system of the present embodiment, a channel estimation method based on a small number of uniform training sequences is used for a downlink multi-user large-scale MIMO system, and is improved in view of the shortcomings of the existing channel estimation method.
The specific application case is as follows:
suppose that there are 1 cell, 1 base station, and the number of antennas of the base station is 128, the sampling number N is 32, N is 8, and m is 64. Number of paths P for radio signals from base station to each userkEach user receive antenna is 1 ═ 6. Number of antennas M per row of planar array antenna h16, number of antennas per column M v8, carrier wavelength λ 3 × 108/1.5×109The array element spacing d is lambda/2, and the elevation angle theta and the azimuth angle phi contained in the steering vector in the channel matrix are obedient intervals (-900,900)]Uniformly distributed therein.
In step S1, training sequences are designed for a plurality of users and received signals are processed.
The 128 antennas provided at the base station are arranged in a Planar Array (UPA Uniform-Planar-Array) and M is 16 × 8, where each row has 16 antennas and each column has 8 antennas. The channel from the base station to the receiving end of the kth user is specifically represented as:
wherein: pkThe number of propagation paths, g, between the base station and the receiving end of the kth userk,lThe channel complex gain of the i-th path representing the k-th user is assumed to follow a complex gaussian distribution of zero mean, unity variance. Alpha (theta)k,l,φk,l) Steering vector, theta, of channel representing the ith path of the kth userk,lAnd phik,lThe l-th bars representing the k-th users respectivelyElevation and azimuth of the path.
The training sequence is specifically designed as follows:
for all K users, the basis for selecting training sequences at the base station is as follows: it should be satisfied that the number of sampling times of the horizontal angle information and the vertical angle information in the channel steering vector of the ith path of the kth user satisfies the ratio of the number of rows and the number of columns of the planar array antenna.
Suppose that the base station transmits S signals to all K usersNA matrix of 128 × 32 dimensions, which is specifically expressed as:
wherein: fnIs an 8-dimensional Discrete Fourier Transform (DFT) matrix, 0nZero matrix of 8 dimensions, 0(M-7n)×nThe matrix is a zero matrix with 72 × 8 dimensions, N is equal to N, and N is the total number of samples.
The processing of the received signal is specifically:
after mixing noise, the received signal of the kth ue is represented as:
wherein: ρ is the signal-to-noise ratio, zkThe noise mixed in at the kth user is assumed to be gaussian noise subject to zero mean, unit variance.
For transmitting signalsPerforming an inverse DFT transform, the actual received signal at the kth user is represented as:
wherein, ykRepresenting the received signal.
In step S2, a corresponding angle estimation is performed based on the received signal.
A codebook is created in advance for an angle and all codebooks are traversed next.
S21, setting a codebook, and enabling a transverse vector alpha in a channel guide vector alpha (theta, phi)hCos θ sin φ and longitudinal vector α in (θ, φ)vSin θ in (θ) is considered as two integers in the interval (-1,1), respectively. Two codebooks of 64 copies are created in the (-1,1) interval, respectively.
S22, the received signal of i (i ═ 1,2,3,4,5,6) paths at the k-th user is yk(i) The noise of the l path derived from the k user is expressed as follows:
wherein:andrepresenting the value of the set angle codebook for each traversal,and representing the value after traversing the set angle codebook each time.
S23, combining a preset codebook, setting the code words as follows:
binding settingsCode word ofTraverse a predetermined codebook from yk,r(i) Selecting the code word with the maximum projection power, wherein the specific calculation formula is as follows:
then in the code wordAndnamely the estimated value of the angle information in the channel guide vector in the ith path of the kth user, and the guide vector of the channel can be reconstructed by using the obtained estimated value of the angle information
S24, traversing the angle codebook by combining a preset codebook, and selecting and obtaining an estimation value of angle information, thereby estimating the ith path gain of the kth user, wherein the specific calculation formula is as follows:
in step S3, a channel steering vector is constructed from the angle estimates.
Incorporating angle information estimatesBy α in the channel steering vector α (θ, φ)v(θ) And alphah(theta, phi) form to construct steering matrix transverse vectorAnd a longitudinal vectorThe product of the two tensorsChannel steering vectors can be constructed
In step S4, the downlink channel state information is reconstructed from the constructed channel steering vector.
Steering vector based on reconstructed channelAnd channel complex gain estimatesAnd reconstructing the channel matrix to recover the downlink channel information.
In this embodiment, in order to analyze the performance of the proposed channel estimation method based on angle estimation in the FDD large-scale antenna system, the system throughput is defined as: c ═ log (1+ ρ | | | h)Hf||2) And f is precoding.
As shown in fig. 2, it is a simulation diagram of system throughput under the above exemplary conditions, where "ideal transition state" is a system throughput curve using real channel for precoding, and the method proposed in this embodiment uses reconstructed channel for precoding. As can be seen from fig. 2, the precoding performed by the channel estimation value obtained by the method provided by the present embodiment is smaller than about 1 bit in throughput difference of the system compared with the precoding performed by the real channel under the same condition, and the signal-to-noise ratio has little influence on the method provided by the present invention, so that the method has good system performance.
Compared with the prior art, in order to better save training overhead, the embodiment can be deduced by combining with the PRONY equation after theoretical derivation, and for a large-scale antenna system, for an array antenna, channels of the array antenna are in a form meeting the PRONY equation. Based on this, it is considered that in a multi-user scenario, different users can transmit the same training sequence to perform training simultaneously, and complete channel state information is acquired by combining an angle estimation method, so that pilot frequency overhead and time consumption are reduced. The channel estimation method based on a small amount of uniform training sequences can simultaneously estimate the channel state information by a plurality of users, effectively reduce the pilot frequency overhead and lay the foundation for realizing higher system throughput.
The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.
Claims (9)
- A channel estimation method in an FDD downlink multi-user large-scale MIMO system is characterized by comprising the following steps:s1, designing training sequences and processing received signals aiming at a plurality of users;s2, carrying out corresponding angle estimation according to the received signal;s3, constructing a channel guide vector through an angle estimation value;and S4, reconstructing the state information of the downlink channel according to the constructed channel guide vector.
- 2. The method of claim 1, wherein in step S1, the training sequences are designed for multiple users and the received signals include K independent single-antenna users, a base station, and M antennas equipped at the base station.
- 3. FDD downlink multiuser macro according to claim 2The channel estimation method in the scale MIMO system is characterized in that M antennas equipped at the base station adopt a planar array arrangement mode, and M is MhMvWherein each row has MhA root antenna, each column having MvFor a root antenna, the channel from the base station to the receiving end for the K (K ═ 1,2,3, …, K) th user is specifically represented as:wherein: pkRepresenting the number of propagation paths between the base station and the receiving end of the kth user; gk,lThe channel complex gain of the l path representing the k user; α (θ, φ) represents a steering vector of the channel; alpha (theta)k,l,φk,l) A steering vector representing a channel of the ith path of the kth user; thetak,lAnd phik,lRespectively representing the elevation and azimuth of the ith path of the kth user.
- 4. The method of claim 3, wherein the steering vector α (θ, φ) of the channel is expressed as:wherein: d represents the distance between antenna elements, and if d is lambda/2, lambda is the carrier wavelength; alpha is alphav(theta) includes information on the longitudinal angle of the planar array, alphah(theta, phi) transverse to an array comprising planesAnd (4) direction angle information.
- 5. The channel estimation method in an FDD downlink multiuser massive MIMO system according to claim 4, wherein the designing of the training sequence in the step S1 is specifically:suppose that the base station transmits S signals to all K usersNThe matrix is an M × N matrix, and is specifically expressed as:wherein: fnA discrete Fourier DFT matrix representing n dimensions; 0nA zero matrix of n dimensions; 0(M-7n)×nThe matrix is a zero matrix with (M-7N) multiplied by N dimensions, wherein N is equal to N when N is 4N, and N is the total number of samples.
- 6. The channel estimation method in an FDD downlink multiuser massive MIMO system according to claim 5, wherein the processing of the received signal in the step S1 is specifically:after the noise is mixed, the received signal of the kth (K ═ 1,2, 3., K) ue is represented as:wherein: ρ is the signal-to-noise ratio, zkThe noise mixed in the k user is assumed to be Gaussian noise which obeys zero mean and unit variance;for transmitting signalsPerforming an inverse DFT transform, the actual received signal at the kth user is represented as:wherein, ykRepresenting the received signal.
- 7. The channel estimation method in an FDD downlink multiuser massive MIMO system according to claim 6, wherein the step S2 specifically comprises:s21, setting a codebook, and enabling a transverse vector alpha in a channel guide vector alpha (theta, phi)hCos θ sin φ and longitudinal vector α in (θ, φ)vSin theta in (theta) is respectively regarded as two integers in the interval (-1, 1); two M codebooks are respectively created in the (-1,1) interval, and M is equal to M/2;s22, the received signal of i (i ═ 1,2, …, P) path at k-th user is yk(i) The noise of the ith path of the kth user is derived and is expressed as:wherein,andrepresenting the value of the set angle codebook in each traversal;representing the value after traversing the set angle codebook each time;s23, combining a preset codebook, setting the code words as follows:combining set code wordsTraverse a predetermined codebook from yk,r(i) Selecting the code word with the maximum projection power, and expressing as:in a code wordAndreconstructing the steering vector of the channel by using the estimated value of the angle information for the estimated value of the angle information in the steering vector of the channel in the ith path of the kth userS24, traversing the angle codebook by combining a preset codebook, and selecting and obtaining an estimation value of angle information, thereby estimating the ith path gain of the kth user, wherein the estimation is represented as:
- 8. the channel estimation method in an FDD downlink multiuser massive MIMO system according to claim 7, wherein the step S3 specifically comprises:
- 9. The channel estimation method in an FDD downlink multiuser massive MIMO system according to claim 8, wherein the step S4 specifically comprises: steering vector based on reconstructed channelAnd channel complex gain estimatesAnd reconstructing the channel matrix to recover the downlink channel information.
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