Codebook design method

Abstract

The invention relates to a codebook design method, and belongs to the technical field of communication networks. A codebook design method is characterized in that a codebook with the rank being R forms a precoding matrix W according to the following mode: # imgabs0 # imgabs1 #, the dimension of the # imgabs2 # matrix W1 is 2N1N2 * 2L, N1 and N2 respectively represent the number of first-dimensional antenna ports and the number of second-dimensional antenna ports in each polarization direction, and the number of the first-dimensional antenna ports and the number of the second-dimensional antenna ports in each polarization direction are equal to the number of the first-dimensional antenna ports and the number of the second-dimensional antenna ports. And the matrix B comprises L column vectors, L is greater than or equal to 1, and the lth column vector of the matrix B is bl: # imgabs3 #. The codebook construction method provided by the invention is adaptive to a super-large-scale antenna array, and corresponding channels can be matched by selecting different codebooks no matter the communication terminal is in a far field or a near field.

Description

Technical Field

[0001] The invention relates to a codebook design method and belongs to the technical field of communication networks. Background Art

[0002] Massive Multiple-Input Multiple-Output (Massive MIMO) antenna systems have become a reality in 5G wireless communication networks, where base station equipment is equipped with 16 or 32 antennas. In order to obtain beamforming gain, the 3GPP standardization organization has designed a high-precision codebook for 5G's Massive MIMO antennas, where the precoding matrix W can be expressed as:

[0003]

[0004] Among them, W1 describes the long-term, broadband characteristics of the channel and contains a DFT beam group; W2 describes the short-term, sub-band characteristics of the channel, and 2N represents the number of antenna ports equipped by the base station. Since the base station is equipped with dual-polarized antennas, the number of antenna ports in each polarization direction is N, so the total number of dual-polarized antenna ports is 2N. The structure of W1 is:

[0005]

[0006] Where B=[b0,…,b L-1 ] is a matrix composed of L oversampled DFT vectors. The two diagonal blocks of W1 are for two polarization directions respectively. Here, it is assumed that the DFT beam groups of the two polarization directions are the same, that is, the same DFT beam is used for the two polarization directions. From its structure, the role of W1 is to determine a set of DFT beams, and the role of W2 is to linearly merge the DFT beams. The elements in W2 are complex numbers and are fed back in the form of amplitude and phase. Assuming that there are 2N transmitting antennas at the base station end, then each polarization direction contains N antennas, then there are a total of ON DFT beams in the beam set, where O is an integer greater than or equal to 1, indicating the oversampling multiple. Then the m+1th DFT beam can be expressed as:

[0007]

[0008] Matrix B is a matrix consisting of L beam vectors selected from ON DFT beams.

[0009] Looking forward to the 6G mobile communication system, the application of higher frequency bands such as millimeter waves and terahertz will further reduce the size of antennas, which means that the scale of array antennas is expected to expand further. In future 6G base stations, there may be 256 or even more antennas, namely extremely large-scale antenna arrays (ELAA), which will lead to a rapid expansion of the near-field area of ​​the array. In the near-field area, the propagation of electromagnetic waves no longer follows the assumption of far-field plane waves, but exhibits the characteristics of spherical waves. Therefore, the near-field characteristics have become a new issue worthy of attention in the study of 6G ELAA.

[0010] In the codebook design of the 5G communication system, it is assumed that the terminal device is in the far field area of ​​the radio waves radiated by the base station. The boundary between the so-called far field and near field is usually defined as the Rayleigh Distance, which is expressed as Where D represents the array aperture of the base station equipment, that is, the maximum size of the antenna array, and λ represents the wavelength. Usually, the location of the terminal device is far beyond the Rayleigh distance of the antenna array and is considered to be the far field, otherwise it is the near field.

[0011] Under far-field conditions, the propagation of electromagnetic signals follows a plane; wave assumptions, such as Figure 1 As shown, under the assumption of plane waves, the steering vector of the antenna array can be expressed as

[0012]

[0013] It can be seen that under the assumption of plane waves, the phase of the channel response presents a linear relationship between antennas. Therefore, the DFT vector in formula (2) can be used to characterize the channel steering quantity.

[0014] As the number of base station antennas increases, the Rayleigh distance can reach several hundred meters. At this time, we should consider Figure 2 For a spherical wave, the steering vector of the channel should be expressed as:

[0015]

[0016] Obviously, the phase of the channel response no longer presents a linear relationship between the antennas. Using DFT vectors to characterize the channel steering vector will inevitably cause serious performance loss. Summary of the invention

[0017] In order to solve the codebook design problem of overcoming the near-field effect under a very large-scale antenna array, a codebook design method is provided.

[0018] Based on the original codebook design, the present invention adapts to both far - field and near - field conditions by enhancing the construction method of W1 in the original codebook. The specific technical solution is as follows:

[0019] A codebook design method, characterized in that a codebook with rank R forms a precoding matrix W in the following manner:

[0020]

[0021] Wherein, The dimension of matrix W1 is 2N1N2×2L, where N1 and N2 respectively represent the number of antenna ports in the first dimension and the number of antenna ports in the second dimension for each polarization direction; matrix B contains L column vectors, where L≥1, and the l - th column vector of matrix B is b l :

[0022]

[0023] Where v m,β and u n,β are column vectors of N1×1 and N2×1 respectively:

[0024]

[0025] represents the Kronecker product, and b l is a column vector of N1N2×1. O≥1 is an integer, 0≤γ1≤1, 0≤γ2≤1, and O, γ1, γ2, N1, N2 are configuration parameters sent from the base station to the terminal device; 0≤β≤1, 0≤m<ON1 is an integer, 0≤n<ON2 is an integer, and β, m, and n are parameters reported from the terminal device to the base station. Matrix W2 is a complex matrix with dimension 2L×R, where the modulus of each element in matrix W2 is less than or equal to 1, and the phase is greater than or equal to 0 and less than 2π. e is the natural exponent, j is the unit imaginary number, which are conventional mathematical expressions; βk is a parameter for constructing the beamforming vector and requires terminal feedback.

[0026] Based on the above - mentioned technical solution, the present application makes the following improvements and enhancements to the above - mentioned technical solution:

[0027] Further, the parameter β is quantized into K values within the value range, K>1, and the terminal device reports an integer from 0 to K - 1 to indicate the quantized β value.

[0028] Further, the parameter β is uniformly quantized into K values within the range of 0 to 1, that is

[0029] Further, the parameter β is non - uniformly quantized into K values within the range of 0 to 1, that is

[0030] Furthermore, each element of W2 is a complex number, which is fed back to the base station in the form of amplitude and phase.

[0031] The above-mentioned codebook construction method introduces a product term related to the parameter β on the basis of the original codebook W1, so that the codebook is applicable to both far-field conditions, that is, β=0, and near-field conditions, that is, β>0. After the terminal device determines whether it is in the far field or near field according to the downlink channel, it can freely switch between the near field and the far field by reporting the β value to the base station. The present invention is adapted to ultra-large-scale antenna arrays. Regardless of whether the communication terminal is in the far field or the near field, different codebooks can be selected to match the corresponding channels. It can be seen that the codebook has super strong scene adaptability. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a schematic diagram of a plane wave;

[0033] Figure 2 Schematic diagram of spherical wave;

[0034] Figure 3 is a schematic diagram of spherical wave distance;

[0035] Figure 4 Schematic diagram of a two-dimensional antenna array. DETAILED DESCRIPTION

[0036] The following embodiments, in conjunction with the accompanying drawings, are only intended to illustrate the technical solutions described in the claims and are not intended to limit the protection scope of the claims.

[0037] The present invention mainly solves the codebook design problem of overcoming the near-field effect under a very large-scale antenna array.

[0038] Assume that the location coordinates of the communication terminal are (x u , z u ). In each polarization direction, the base station is equipped with N transmitting antennas, and the coordinates of the antennas are (0,0), (d,0), ... ((N-1)d,0), such as Figure 3 As shown, d represents the distance between the base station antennas. The distance r from the communication terminal to the nth antenna of the base station n It can be expressed as:

[0039]

[0040] R n Perform Taylor expansion, ignoring higher-order terms above 2, and we have:

[0041]

[0042] For the first term of formula (6) It has nothing to do with the coordinates of the base station antenna, that is, it is the same for all receiving antennas of the base station, so it can be ignored. is the sine value of the angle θ between the line connecting the receiving antenna 0 of the communication terminal and the base station and the normal line, that is, The third term of formula (6) can be further written as:

[0043]

[0044] Substitute Equation 6 and Equation 7 into the near-field steering vector Equation 4. The nth element in the steering vector Equation 4 is:

[0045] set up Then formula (8) becomes:

[0046]

[0047] Other, So:

[0048]

[0049] Among them, β is a quantity related to the distance from the communication terminal to the base station, and It is related to the antenna spacing of the base station and is a semi-static quantity. In the codebook design, the value of γ can be sent by the base station to the communication terminal.

[0050] The value of β is 0 to 1. When β=0, formula (9) degenerates into the traditional DFT codebook form, that is, the codebook under the far field condition. The value of β is 0 to 1, which can adapt to the far field and the near field of different distances.

[0051] It should be noted that since the value of β is a real number between 0 and 1, the terminal device cannot report the real value of β to the base station. The present invention proposes to quantize β into a finite number of values, that is, quantize it into K values. The terminal device can report an integer value between 0 and K-1 to indicate one of the K quantized values.

[0052] In the codebook design, the value of β can be quantized into K values, and the quantization methods include:

[0053] 1) Uniform quantization, that is, in the interval 0 to 1 according to the interval Uniformly quantized into K values, namely:

[0054] In this way, β can be replaced by the value closest to β among the K values. The terminal indicates the quantized value of β by feeding back integers 0, 1, 2, ..., K-1, for example: K-1 indicates β = 1, K-2 indicates

[0055] 2) Non-uniform quantization, that is, quantizing β in the interval 0 to 1 as follows: In this way, β can be replaced by the value closest to β among the K values.

[0056] 0,1,2,…,K-1 indicates the quantized value of β, for example: K-1 indicates β=1, K-2 indicates Through this quantification method, the reporting of parameter β can be greatly simplified.

[0057] Based on formula (9), the codebook design method for ultra-large-scale arrays is given:

[0058] The codebook of rank R constructs the precoding matrix W as follows:

[0059]

[0060] The structure of W1 is:

[0061]

[0062] Where B=[b0,…,b L-1 ],b l is a vector determined by the parameters m and β, that is: b l =v m,β ,

[0063]

[0064] Among them, m=0,1,…,ON-1,0≤β≤1.

[0065] The communication terminal determines L vectors v by selecting L (m, β) pairs m,β To form B, and further to form W1. Furthermore, the parameter β is quantized into K values, and the terminal device indicates β by reporting the index k of the K quantized values ​​to the base station, that is, the terminal device feeds back the position index of L vectors (that is, the selected m and k) to the base station to indicate W1. The dimension of the matrix W2 is 2L×R, where each element of W2 is a complex number, which is fed back to the base station in the form of amplitude and phase.

[0066] Furthermore, when the array deployed at the base station is a two-dimensional array, a two-dimensional vector can be constructed. Assume that each polarization direction of the two-dimensional array has N1 columns and N2 rows of antennas, such as Figure 4 As shown, the total number of antennas is 2N1N2. Then for each polarization direction, the dimension of the vector is N1N2×1, and a two-dimensional vector is constructed by performing the Kronecker product of the first-dimensional vector and the second-dimensional vector.

[0067] In the case of a two-dimensional array, the codebook of rank R forms the precoding matrix W as follows:

[0068]

[0069] The structure of W1 is:

[0070]

[0071] Where B=[b0,…,b L-1 ],b l is a vector determined by the parameters m, n and β,

[0072] Right now:

[0073]

[0074] See also Figure 4 , Schematic diagram of two-dimensional antenna array,

[0075]

[0076] Note that the first dimension of the vector v m,β and the vector u of the second dimension n,β The selected β is the same. Furthermore, the parameter β is quantized into K values, and the terminal device indicates β by reporting the index k of the K quantized values ​​to the base station, that is, the terminal device feeds back the position index of L vectors (that is, the selected m, n and k) to the base station to indicate W1; β and k have no specific meaning, they are the parameters that constitute the beamforming vector and need to be fed back by the terminal. The dimension of the matrix W2 is 2L×R, where each element of W2 is a complex number, that is:

[0077]

[0078] Among them, p l,r is a real number, 0≤p l,r ≤1, 1≤l≤2L,1≤r≤R. The terminal feeds back W2 to the base station in the form of amplitude and phase; e is the natural exponent, and j is the unit imaginary number;.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A codebook design method, characterized in that: The codebook of rank R constructs the precoding matrix W as follows: in, The dimension of matrix W1 is 2N1N2×2L, where N1 and N2 represent the number of antenna ports in the first dimension and the number of antenna ports in the second dimension in each polarization direction, respectively; the matrix B contains L column vectors, where L≥1, and the lth column vector of matrix B is b l : where v m,β and u n,β They are N1×1 and N2×1 column vectors respectively: denotes the Kronecker product, b l is a column vector of N1N2×1; O≥1 is an integer, 0≤γ1≤1, 0≤γ2≤1, O, γ1, γ2, N1, N2 are configuration parameters sent by the base station to the terminal device; 0≤β≤1, 0≤m<ON1 is an integer, 0≤n<ON2 is an integer, β, m, and n are parameters reported by the terminal device to the base station; the matrix W2 is a complex matrix of dimension 2L×R, where the modulus of each element in the matrix W2 is less than or equal to 1, and the phase is greater than or equal to 0 and less than 2π.

2. The codebook design method according to claim 1, characterized in that: The parameter β is quantized into K values ​​within a value range, K>1, and the terminal device reports an integer from 0 to K-1 to indicate the quantized β value.

3. The codebook design method according to claim 1 or 2, characterized in that: The parameter β is uniformly quantized into K values ​​in the interval of 0 to 1, that is, 4. The codebook design method according to claim 1 or 2, characterized in that: The parameter β is non-uniformly quantized into K values ​​in the interval of 0 to 1, that is, 5. The codebook design method according to claim 1, characterized in that: Each element of W2 is a complex number, and is fed back to the base station in the form of amplitude and phase.

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