CN107135023B - Three-dimensional training codebook design method and beam alignment method for millimeter wave communication system - Google Patents
Three-dimensional training codebook design method and beam alignment method for millimeter wave communication system Download PDFInfo
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- H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
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Abstract
The invention disclosesA three-dimensional training codebook design method and a beam alignment method for a millimeter wave communication system are disclosed, wherein the three-dimensional training codebook design method comprises the following steps: 1. according to resolution and beam spaceEstablishing a three-dimensional training codebook tree structure with the depth of S and the degree of N; 2. will be provided withEqually divided into N rectangular regionsIs recorded as a set Having a set of beamsCorresponding to it; the root node of the tree structure isAnda combination of (1); 3. determining the b-th node C of the s-th layers,b,Cs,bIs composed ofAnd beam setA combination of (1); determining each node in 2 to S layers in turn4. Solving the beam forming vector contained in the corresponding beam set of each nodeA three-dimensional training codebook is obtained, where q is 1, …, N. The three-dimensional training codebook generated by the method can be used for realizing high-precision beam alignment and channel estimation, and can remarkably reduce the training overhead of the system.
Description
Technical Field
The invention belongs to the technical field of wireless communication, and particularly relates to a three-dimensional training codebook design method for a millimeter wave communication system with uniform planar array arrangement of receiving and transmitting end antennas.
Background
With the continuous development of wireless communication technology, high-speed data services and ubiquitous access demands are exhibiting an explosive increase. The next generation of 5G mobile communication technology will have higher and higher demands for capacity, energy consumption and bandwidth. Millimeter wave communication technology operating in the 30-300GHz relatively idle band is considered as one of the key technologies for next generation wireless local area networks and mobile communications due to the large amount of unauthorized bandwidth contained in the operating band, because direct spread spectrum bandwidth is simple and effective for increasing system capacity. Research has shown that millimeter wave communication can achieve peak transmission rates of 10 Gbps.
However, compared to the conventional microwave band, the millimeter wave transmission suffers from larger path loss, so the communication distance and coverage are very limited. The millimeter wave signal has extremely short wavelength, a large number of antennas can be packaged in a small size, and then a large-scale array antenna is combined with a digital-analog hybrid beam forming technology, and the array gain and the space division multiplexing gain provided by the millimeter wave signal can make up for partial attenuation of a system, so that the transmission rate and the transmission quality of the system are improved. In addition, in order to obtain the array gain better, it is necessary to perform beam alignment on the transmitting and receiving beams at the beginning of communication, and the high-precision beam alignment plays a key role in establishing a reliable millimeter wave communication link, obtaining required transmission data, and enlarging the communication coverage of the area. Accurate beam alignment can also be used for improving the channel estimation performance of the millimeter wave system by estimating relevant parameters including an arrival angle (AoA), a departure angle (AoD), path gain and the like.
In practical millimeter wave communication systems, there is a certain difficulty in achieving accurate beam alignment. First, the high frequency band in the millimeter wave band means that the channel may change rapidly in a short time, and beam alignment needs to be done in a very short channel coherence time, so an exhaustive beam search algorithm is not suitable here. Secondly, to fully utilize the array gain of a large antenna array, the training beam should be narrow enough, which will undoubtedly increase the complexity of beam alignment, and therefore it is necessary to provide an efficient beam codebook design method and a beam search algorithm. To reduce the training overhead of beam alignment, an effective approach is to use a tree search algorithm based on a hierarchical multiresolution training codebook. The layered training codebook generally consists of sub codebooks of different levels, wherein on a high level, the sub codebooks contain a small number of training beams with low resolution to cover a preset angle range; on a low level, the number of training beams included in the subcode book is increased, and the resolution is improved to a certain extent.
While hierarchical searching can significantly reduce the training overhead of the system, its performance depends largely on the hierarchical training codebook used. There have been many studies on hierarchical codebook design methods, but these studies have focused mainly on Uniform Linear Array (ULA) structures, while very few studies have been made on Uniform Planar Array (UPA) structures. In order to realize variable-precision three-dimensional beam coverage and obtain larger beam forming gain, the invention provides a three-dimensional training codebook design method suitable for a millimeter wave communication system. In the present invention, the overshoot of the training beam pattern and the ripple of the main side lobe are properly constrained so that each training beam has a relatively flat amplitude response and a more desirable transition band. The three-dimensional training codebook designed by the invention can realize high-precision beam alignment and channel estimation in a millimeter wave communication system even under the condition of low signal-to-noise ratio.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the problems in the prior art, the invention discloses a three-dimensional training codebook design method for a millimeter wave communication system, wherein the three-dimensional training codebook generated by the method can be used for realizing high-precision beam alignment and channel estimation and can obviously reduce the training overhead of the system.
The technical scheme is as follows: the invention discloses a three-dimensional training codebook design method for a millimeter wave communication system, which comprises the following steps:
(1) establishing a three-dimensional training codebook tree structure with the depth of S and the degree of N according to the resolution rs and the range of the beam space B;
let resolution rs ═ ve×vaThe width of the beam space B in the e direction is WeA width in the a direction of WaI.e. B is We×WaThe degree of the tree structure N is Ne×NaThe depth S and the degree N satisfy the condition:
each node in layers 1 to S-1 in the three-dimensional training codebook tree structure is provided with N sub-nodes;
(2) taking beam space B in e direction by NeAliquoting, N in the a directionaEqually dividing, i.e. equally dividing B into N rectangular areasN=Ne×NaIs recorded as a setEach rectangular regionWith beamforming vectorsCorrespondingly, i is 1, …, and N, N beamforming vectors form a beam setNamely, it is
Root node C of three-dimensional training codebook tree structure1,1Is a set of rectangular regionsAnd beam setIn combination with (1)
(3) Determining the (b) th node C of the s layer of the three-dimensional training codebook tree structures,b,Cs,bIs a set of rectangular regionsAnd beam setIn combination with (1)
to pairIn the e direction by NeAliquoting, N in the a directionaEqually dividing to obtain N sub-rectangular areasEach sub-rectangular regionWith beamforming vectorsCorrespondingly, i is 1, …, and N, N beamforming vectors form a beam setNamely, it is
(4) Solving the beamforming vector contained in each node in the three-dimensional training codebook tree structureA three-dimensional training codebook is obtained, where q is 1, …, N.
Preferably, each node in the three-dimensional training codebook tree structure contains a beamforming vectorHaving constant but not identical amplitude response values in the main and side lobes, i.e.
Wherein psi ═ psie,ψa)=(sin(θe),sin(θa) Is a pitch angleθeAnd azimuth angle thetaaThe combination of the sine values of (a) and (b),for antenna array response vector a in horizontal directionh(2π/λdhsin(θe)cos(θa) Antenna array response vector a in the vertical directionv(2π/λdvsin(θa) The Kronecker product of (c),is a beamforming vectorThe amplitude response value of (a); wherein q is 1, …, N.
wherein epsilon is the ripple of the main and side lobes of the training beam and is a very small positive real number,respectively, main side lobe corresponding regions.
Preferably, forSampling discretization is carried out to obtain discrete wave beam main and side lobe corresponding areas And (4) a region.
To avoid overshoot after discrete sampling, constraint bars are introducedPieceSolving the beamforming vector in step (4)To solve the optimization problem:
wherein epsilon is the ripple of the main and side lobes of the training beam and is a small positive real number; esIs constant, the value decreases with increasing s;respectively, the main and side lobe corresponding areas of the discrete wave beam.
Preferably, the constraint condition is relaxed, and an optimization problem is solved by using a constraint concave-convex process iterative algorithm, wherein the steps are as follows:
(6.1) determining an iteration initial value f0The following constraint optimization problem is constructed:
whereinThe real part of the number in parentheses is taken,respectively representing discretized main and side lobe corresponding regions;
(6.2) iteratively solving the optimization problem in the step (6.1), checking whether the r value obtained by the iteration meets the convergence standard, and if so, obtaining the optimal solution f of the iterationnI.e. the final solutionIf not, according to the optimal solution f of the iterationnSolving the optimization problem in the step (6.1) again;
Preferably, the initial value f in step (6.1)0Determined by solving the following optimization problem:
the invention also discloses a beam alignment method, which comprises the following steps:
(8.1) parameter configuration and initialization: the receiving and transmitting end designs the three-dimensional training codebook according to any one of the three-dimensional training codebook design methods;
the designed three-dimensional training code book is designed to contain S training sub code booksRespectively corresponding to S training stages; the degree of the designed three-dimensional training codebook tree structure is N; beamforming vectorsThe subscript values in (1) are initialized as: s is 1, bf=1;
(8.2) the transmitting end continuously uses the low resolution training beam vector in the first layer sub-codebookTo transmit a training signal z, and repeat training M for each training beamsTo increase the received signal-to-noise ratio of the system;
(8.3) the receiving end receives the signal according to the correspondingSelecting the beamforming vector that yields the highest received energy, i.e.
Whereinp is the transmit power, h is the channel matrix, hHIs a conjugate transpose of h and,additive Gaussian noise;
the receiving end indexes the valueIs fed back to the transmitting end, whereby the transmitting end is based onAnd its corresponding rectangular areaPreliminarily determining the area of the departure angle AoD corresponding to the strongest wave beam;
(8.4) transmitting end according to index valueSelecting a set of beamforming vectors with higher resolution in a sub-codebook of a next layer of a three-dimensional codebookTo transmit training signals to further more accurately determine the area where the AoD is located;
And (8.5) repeating the steps (8.3) to (8.4) until the beamforming vector meeting the highest resolution requirement is found, wherein the rectangular domain corresponding to the beamforming vector is the area where the AoD is located.
Has the advantages that: the three-dimensional training codebook design method suitable for the millimeter wave communication system can be used for realizing high-precision beam alignment and channel estimation, and has the advantages that:
(1) the existing research mainly aims at a millimeter wave system with antennae arranged in an ULA mode, the UPA structure is fully considered, and the defects of the existing research are overcome. Under the UPA structure, more transmission antennas can be configured in a limited two-dimensional space, so that a wider geographical area can be detected and intercepted, three-dimensional beam coverage with variable precision is realized, and a larger beam forming gain is obtained.
(2) The invention processes the overshoot phenomenon which may occur on the non-sampling point in the training beam pattern, and properly restricts the ripple of the main and side lobes, so that each training beam has relatively flat amplitude response and ideal transition frequency band, which is beneficial to improving the beam alignment precision.
(3) The three-dimensional training codebook generated by the invention is suitable for a beam alignment algorithm based on a tree search algorithm, can obviously reduce the training overhead of the system, and can realize high-precision beam alignment and channel estimation performance in a millimeter wave communication system based on a UPA structure.
Drawings
FIG. 1 is a schematic diagram of a Uniform Planar Array (UPA) architecture;
FIG. 2 is a schematic structural diagram of a three-dimensional training codebook generated in the embodiment;
FIG. 3 is a schematic diagram of main side lobe amplitude fluctuation;
FIG. 4 is a diagram of 4 training beam vectors generated in an embodimentAn amplitude response map of (a);
FIG. 5 is a training beam diagram under two codebook design methods (BPSA, LSA);
fig. 6 is a detailed flowchart of the three-dimensional training codebook design method and a flowchart for beam training after codebook generation according to the present invention;
fig. 7 is a graph showing the variation trend of the average beam alignment error rate with the signal-to-noise ratio under two codebook design methods (BPSA, LSA).
Detailed Description
The invention is further elucidated with reference to the drawings and the detailed description.
As shown in fig. 1, the three-dimensional training codebook design method disclosed in the present invention is suitable for a millimeter wave system with antennas arranged in a uniform area array, taking a transmitting end as an example, N in the figureh、NvRespectively, the number of antennas in the horizontal direction and the vertical direction, so that the total number of transmitting antennas NT=NhNv,dhAnd dvThe distance between two adjacent antennas in the horizontal direction and the vertical direction is respectively.
The beam space B is a rectangular area, the e direction and the a direction are vertical to each other, and the width of B in the e direction is WeA width in the a direction of WaI.e. B is We×WaA rectangular area of (a).
In this embodiment, the millimeter wave communication system with the transmitting antennas arranged in a uniform area array is considered, where N ish=Nv32, the distance d between two adjacent antennash=dvλ is the wavelength of the millimeter wave signal, 3 λ/8. For simplicity, it is assumed that the receiving end is equipped with only a single antenna. It should be noted that, although the three-dimensional training codebook design at the transmitting end is taken as an example in this embodiment, this method is also applicable to codebook design at the receiving end.
A three-dimensional training codebook design method for a millimeter wave communication system comprises the following steps:
let resolution rs ═ ve×va(ii) a Pitch angle theta of the transmitted beameAzimuth angle thetaaAre respectively located in an angle rangeIn the embodiment, the beam space B can be defined as sin (θ) by the independent and uncorrelated variations of the pitch angle and the azimuth angle, which can be expressed by the variations of the two perpendicular directions e and ae)、sin(θa) The product of the corresponding ranges, i.e. B ═ sin (θ)e),sin(θe)]×[-sin(θa),sin(θa)]=[-0.64,0.64)]×[-0.64,0.64)]In (sin (theta))e),sin(θa) Plane is a rectangular field, i.e., We=2sin(θe),Wa=2sin(θa)。
Degree N-N of three-dimensional training codebook tree structuree×NaThe depth S and the degree N satisfy the condition: i.e. equally dividing the beam space B into NSAnd after the small rectangular areas, each small rectangular area is less than or equal to the resolution.
Each node in layers 1 to S-1 in the three-dimensional training codebook tree structure is provided with N sub-nodes;
step 2, carrying out N on the beam space B in the e directioneAliquoting, N in the a directionaEqually dividing, i.e. equally dividing B into N rectangular areasN=Ne×NaIs recorded as a setEach rectangular regionWith beamforming vectorsCorrespondingly, i is 1, …, and N, N beamforming vectors form a beam setNamely, it is
Root node C of three-dimensional training codebook tree structure1,1Is a set of rectangular regionsAnd beam setIn combination with (1)
Step 3, determining the b-th node C of the s-th layer of the three-dimensional training codebook tree structures,b,Cs,bIs a set of rectangular regionsAnd beam setIn combination with (1)
to pairIn the e direction by NeAliquoting, N in the a directionaEqually dividing to obtain N sub-rectangular areasEach sub-rectangular regionWith beamforming vectorsCorrespondingly, i is 1, …, and N, N beamforming vectors form a beam setNamely, it isAnd isCorresponding;
Step 4, solving the beam forming vector contained in each node in the three-dimensional training codebook tree structureA three-dimensional training codebook is obtained, where q is 1, …, N.
The tree structure of the three-dimensional training CodeBook (CodeBook) has S layers, each layer is a Sub-CodeBook (Sub-CodeBook) and corresponds to a training stage; the sub-code book at the s-th layer has Ns-1Nodes, each node comprising N code words (CodeWord), each node being assembled by beamsAnd its corresponding rectangular areaTo represent;and its corresponding rectangular areaIn combination with (1)Is a code word.
As shown in fig. 2, the three-dimensional training codebook generated in this embodiment has a quadtree structure, i.e., the degree N of the tree structure of the three-dimensional training codebook is equal to Ne×Na2 × 2. The training device consists of S sub code books corresponding to S training stages; subcode book for the s-th training phaseIn total, contains 4sA beamforming vector having the same main lobe width, and these vectors constitute 4s-1A set of beamsWherein the b-th setIncluding beamforming vectorsZi code bookThe number of the beam forming vectors in (1) is the sub-codebook of the previous layer4 times of the number of middle training beams. In the s-th training phase, the beam space is partitioned into 4s-1Rectangular fields of the same sizeWherein the b-th rectangular fieldAnd beam setAre related to, andsimultaneous beamforming vectorsAre respectively connected withOne-to-one correspondence is realized; in the next training phase, the rectangular fieldAnd equally divided into 4 smaller sub-regions, j ∈ { LL, LR, RL, RR }, i.e., the
Beamforming vectors designed to improve beam alignment performance for millimeter wave communicationsHave constant but not identical amplitude response values on the main and side lobes, respectively, i.e.:
wherein psi ═ psie,ψa)=(sin(θe),sin(θa) Is a pitch angle θeAnd azimuth angle thetaaThe combination of the sine values of (a) and (b),is an antenna array response vector a in the horizontal direction and the vertical directionh(2π/λdhsin(θe)cos(θa) A and av(2π/λdvsin(θa) Kronecker product of d)hAnd dvThe distance between two adjacent antennas in the horizontal direction and the vertical direction respectively, lambda is the wavelength of the millimeter wave signal,is a beam vectorThe amplitude response value of (a).
If the ripple epsilon of the main and side lobes of the training beam is strictly limited to 0, it is difficult to successfully design the three-dimensional codebook, and to avoid this infeasibility and ensure high-precision beam alignment performance, as shown in fig. 3, the main and side lobes of the beam pattern may be allowed to have small amplitude fluctuation, and the amplitude response value of the main lobe should be as large as possible under the condition that the value of the ripple epsilon is fixed, so the design of the training beam can be expressed as the following optimization problem:
where epsilon is a very small positive real number,are respectively a main area and a side lobe corresponding area,is a rectangular areaIn the interior of said container body,is composed ofAnd (3) outside. Due to the fact thatContinuous and countless, so the corresponding area of the main and side lobes of the wave beam must be sampled or discretized; and because the number of sampling points is limited, overshoot phenomenon possibly exists in an area which is not sampled, and in order to avoid the overshoot phenomenon after discrete sampling, a constraint condition of | | | f | | < E | is introduceds,EsThe value of (c) is reduced along with the increase of s, i | · | | is 2 norms of the vector, namely the optimization problem is as follows:
the present embodiment employs the following finite scattering channel model:
where L is the total number of channels, αlIs the complex gain of the ith path, β is the average path loss,is an antenna array response vector, and ab(b ∈ { h, v }) has the following form: is the Kronecker product operator.
With beamforming vectors in a training codeword in a three-dimensional training codebookFor example, the code word is in a discrete beam regionHas a large amplitude response value, and is in other regionsThe amplitude response of the training beam is extremely small, the design problem of the training beam is a non-convex optimization problem, and the solution is difficult. By relaxing the partially non-convex constraint, the non-convex optimization problem can be transformed into a convex optimization problem and solved using a constrained concave-convex process (CCCP) iterative algorithm. If fnThe optimal solution f of the next iteration is shown if the optimal solution obtained by the nth iteration is representedn+1This can be obtained by solving the following problem:
whereinThe real part of the number in parentheses is taken,respectively representing discretized main and side lobe corresponding regions.
Since initialization has a large influence on the convergence performance of the CCCP algorithm, to obtain a good initial value, the following optimization problem can be solved:
this problem is a second order cone programming problem (SOCP) that can be solved by the CVX toolkit in the MATLAB simulation platform.
Obtaining good initial value f0Then, the three-dimensional training beam design method based on the CCCP algorithm specifically comprises the following steps:
(6.1) constructing and solving the following constraint optimization problem:
whereinThe real part of the number in parentheses is taken,respectively representing discretized main and side lobe corresponding regions;
(6.2) iteratively solving the optimization problem in the step (6.1), checking whether the r value obtained by the iteration meets the convergence standard, and if so, obtaining the optimal solution f of the iterationnI.e. the final solution f*(ii) a If not, according to the optimal solution f of the iterationnSolving the optimization problem in the step (6.1) again;
(6.3) outputting the final solution f*And obtaining the required three-dimensional training beam.
FIG. 4 shows 4 training codewords generated by the design method of the present invention, taking the first layer of sub-codebook in the three-dimensional codebook as an exampleThe amplitude response map of (a). It can be seen that the beam patterns of these several codewords have relatively flat amplitude responses and ideal transition bands, and no overshoot occurs at the unsampled points. Fig. 5 also compares the present invention with a Least Squares (LS) based beam design method, where BPSA represents the three-dimensional codebook design algorithm proposed by the present invention and LSA represents the least squares beam design algorithm. It can be seen from the figure that the side lobes of the training beams generated by the LS method have relatively large fluctuation, and in addition, the width of the transition band is also large, which further embodies the superiority of the three-dimensional training codebook design method provided by the present invention.
The three-dimensional training codebook generated by the invention can be used for realizing beam alignment based on a tree search algorithm, detecting the strongest beam of a single-path millimeter wave channel, and estimating related parameters of a millimeter wave communication channel, such as an angle of departure (AoD) and an angle of arrival (AoA), and specifically comprises the following steps:
(8.1) parameter configuration and initialization: the transceiving end designs a three-dimensional training codebook according to the method of any one of claims 1 to 7;
setting S layer of the three-dimensional training codebook tree structure, namely S training subcodebooksRespectively corresponding to S training stages; the degree of the designed three-dimensional training codebook tree structure is N; beamforming vectorsThe subscript values in (1) are initialized as: s is 1, bf=1;
(8.2) the transmitting end continuously uses the low resolution training beam vector in the first layer sub-codebookTo transmit a training signal z, and repeat training M for each training beamsTo increase the received signal-to-noise ratio of the system;
(8.3) the receiving end receives the signal according to the correspondingSelecting the beamforming vector that yields the highest received energy, i.e.
Whereinp is the transmit power, h is the channel matrix, hHIs a conjugate transpose of h and,additive Gaussian noise;
the receiving end indexes the value q*Is fed back to the transmitting end, whereby the transmitting end is based onAnd its corresponding rectangular areaPreliminarily determining the area of the departure angle AoD corresponding to the strongest wave beam;
(8.4) transmitting end according to index value q*Selecting a set of beamforming vectors with higher resolution in a sub-codebook of a layer below the three-dimensional codebookTo transmit training signals to further more accurately determine the area where the AoD is located;
wherein b isf+1=bf*N-N+q*;
For the quad-tree structure in this embodiment, bfThe updating of (1) follows the following principle:
a) if q is*LL, then bf+1=4bf-3;
b) If q is*If it is LR, then bf+1=4bf-2;
c) If q is*RL, then bf+1=4bf-1;
d) If q is*RR, then bf+1=4bf;
And (8.5) repeating the steps (8.3) to (8.4) until the beamforming vector meeting the highest resolution requirement is found, wherein the rectangular domain corresponding to the beamforming vector is the area where the AoD is located.
Fig. 6 shows a specific flow of the three-dimensional training codebook design method (BPSA) proposed by the present invention, and besides, fig. 6 also shows a specific process for beam training after codebook generation. As shown in fig. 7, this figure shows the variation trend of the average beam alignment error probability (BAER) with the signal-to-noise ratio (SNR) generated by the beam training using the codebooks generated by the LS method and the method of the present invention when the path gain of the millimeter wave communication channel is fixed to 1. It can be seen from the figure that the performance of the codebook generated by the method of the present invention is obviously superior to that of the LSA codebook, and more accurate beam alignment and channel estimation performance can be realized. As the SNR increases, BAER corresponding to two codebooks decreases, but the error probability corresponding to the BPSA codebook decays significantly, while the error probability corresponding to the LSA codebook decays slowly.
Claims (2)
1. A three-dimensional training codebook design method for a millimeter wave communication system is characterized by comprising the following steps:
(1) according to resolution rs and beam spaceEstablishing a three-dimensional training codebook tree structure with the depth of S and the degree of N;
let resolution rs ═ ve×vaSpace of wave beamThe e direction and the a direction are two vertical directions;width in e direction is WeA width in the a direction of WaI.e. byIs We×WaThe degree of the tree structure N is Ne×NaThe depth S and the degree N satisfy the condition:and is
Each node in layers 1 to S-1 in the three-dimensional training codebook tree structure is provided with N sub-nodes;
(2) space beamIn the e direction by NeAliquoting, N in the a directionaIs divided equally, i.e. aboutEqually divided into N rectangular regionsN=Ne×NaIs recorded as a setEach rectangular regionWith beamforming vectorsCorrespondingly, i is 1, …, and N, N beamforming vectors form a beam setNamely, it is
Root node C of three-dimensional training codebook tree structure1,1Is a set of rectangular regionsAnd beam setIn combination with (1)
(3) Determining the (b) th node C of the s layer of the three-dimensional training codebook tree structures,b,Cs,bIs a set of rectangular regionsAnd beam setIn combination with (1)
to pairIn the c direction by NeAliquoting, N in the a directionaEqually dividing to obtain N sub-rectangular areasEach sub-rectangular regionWith beamforming vectorsCorrespondingly, i is 1, …, and N, N beamforming vectors form a beam setNamely, it is
(4) Solving the beamforming vector contained in each node in the three-dimensional training codebook tree structureObtaining a three-dimensional training codebook, wherein q is 1, …, N; a beamforming vector contained by each node in the three-dimensional training codebook tree structureHaving constant but not identical amplitude response values in the main and side lobes, i.e.
Wherein psi ═ psie,ψa)=(sin(θe),sin(θa) Is a pitch angle θeAnd azimuth angle thetaaThe combination of the sine values of (a) and (b),for antenna array response vector a in horizontal directionh(2π/λdhsin(θe)cos(θa) Antenna array response vector a in the vertical directionv(2π/λdvsin(θa) The Kronecker product of (c),is a beamforming vectorThe amplitude response value of (a); wherein q is 1.., N; dnAnd dvThe distance between two adjacent antennas in the horizontal direction and the vertical direction is respectively;
for main and side lobe corresponding regionAndsampling discretization is carried out to obtain discrete wave beam main and side lobe corresponding areasAndan area;
wherein epsilon is the ripple of the main and side lobes of the training beam and is a small positive real number; esIs constant, the value decreases with increasing s;andrespectively corresponding areas of the main and side lobes of the discrete wave beam;
relaxing the constraint condition, and solving the optimization problem by adopting a constraint concave-convex process iterative algorithm, wherein the steps are as follows:
(6.1) determining an iteration initial value f0:
Initial value f0Determined by solving the following optimization problem:
the following constraint optimization problem is constructed:
wherein The real part of the number in parentheses is taken,respectively representing discretized main and side lobe corresponding regions;
(6.2) iteratively solving the optimization problem in the step (6.1), checking whether the r value obtained by the iteration meets the convergence standard, and if so, obtaining the optimal solution f of the iterationnI.e. the final solution f*(ii) a If not, according to the optimal solution f of the iterationnSolving the optimization problem in the step (6.1) again;
(6.3) outputting the final solution f*And obtaining the required three-dimensional training beam.
2. A method of beam alignment, comprising the steps of:
(8.1) parameter configuration and initialization: the transceiving end designs a three-dimensional training codebook according to the method in claim 1;
the designed three-dimensional training code book is designed to contain S training sub code booksRespectively corresponding to S training stages; the degree of the designed three-dimensional training codebook tree structure is N; beamforming vectorsThe subscript values in (1) are initialized as: s is 1, bf=1;
(8.2) the transmitting end continuously uses the low resolution training beam vector in the first layer sub-codebookTo transmit a training signal z, and repeat training M for each training beamsTo increase the received signal-to-noise ratio of the system;
(8.3) the receiving end receives the signal according to the correspondingSelecting the beamforming vector that yields the highest received energy, i.e.
Whereinp is the transmit power, h is the channel matrix, hHIs a conjugate transpose of h and,additive Gaussian noise;
the receiving end indexes the value q*Is fed back to the transmitting end, whereby the transmitting end is based onAnd its corresponding rectangular areaPreliminarily determining the area of the departure angle AoD corresponding to the strongest wave beam;
(8.4) transmitting end according to index value q*Selecting a set of beamforming vectors with higher resolution in a sub-codebook of a layer below the three-dimensional codebookTo transmit training signals to further more accurately determine the area where the AoD is located;
wherein b isf+1=bf*N-N+q*;
And (8.5) repeating the steps (8.3) to (8.4) until the beamforming vector meeting the highest resolution requirement is found, wherein the rectangular domain corresponding to the beamforming vector is the area where the AoD is located.
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