Hierarchical codebook design method based on cascaded channels

Abstract

The application belongs to the technical field of 6G communication, and particularly relates to a hierarchical codebook design method based on a cascaded channel. The application defines a cascaded channel direction by combining an incident direction and a reflection direction, and one cascaded channel direction may correspond to multiple groups of incident-reflection directions; the cascaded channel direction defined in this way realizes a hierarchical codebook; the hierarchical codebook can be used for beam search in a single-user static scene, and can also be used in an analog beamforming scene of an active array to solve hierarchical codebook design based on a constant modulus constraint; unlike a traditional hierarchical codebook design which needs to know the array size in advance, the hierarchical codebook proposed in the application can be applied to any size of array. The application has more universality and application flexibility, and effectively solves the problem of too long beam search time of an intelligent reflecting surface. The codebook can be used on any size of array, and when the number of arrays increases, the codebook can be directly used without changing the codebook, and the larger the array, the better the performance of the codebook.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of 6G communication, and particularly relates to a hierarchical codebook design method under a constant modulus constraint scene on an intelligent reflecting surface. BACKGROUND

[0002] With the proposal of millimeter wave and terahertz, the scale of the array becomes larger and larger. This is mainly due to two reasons: on the one hand, due to the serious attenuation of high-frequency signals, it is necessary to increase the array scale to provide sufficient beamforming gain; on the other hand, due to the short wavelength of millimeter waves, more antennas can be integrated in the same space range. Especially since the proposal of intelligent reflecting surface, the cost of the antenna array is getting lower and lower, which makes the scale of the antenna array larger and larger. The intelligent reflecting surface is a new type of passive array device proposed in 6G. Since it has no radio frequency link, its manufacturing cost is lower; and since the intelligent reflecting surface is mainly used in the millimeter wave frequency band, the size of the antenna is smaller due to the shorter wavelength, and more antennas can be integrated in a limited range. Since the intelligent reflecting surface has no radio frequency link, it can provide less gain than the relay device under the same array size, which often requires a larger array to provide sufficient reflected power. In summary, due to the low cost and application needs, the array size of the intelligent reflecting surface is generally very large, that is, the number of antennas on the intelligent reflecting surface is often very large. However, a super large scale array will form a pencil wave with very narrow beam width. The pencil wave has the characteristics of large beamforming gain but small direction coverage range. The smaller coverage range leads to a longer time delay in the beam alignment process to search for the accurate beam. In practical applications, we want to retain the advantages of large pencil wave gain and avoid the defect of long search time. At the same time, since the intelligent reflecting surface serves a cascaded channel, not a single-hop channel like a traditional array. Therefore, the beam search work on the intelligent reflecting surface needs to consider both the incident channel direction and the reflected channel direction, which also brings certain difficulties to the beam search work. SUMMARY

[0003] The purpose of the application is to provide a hierarchical codebook design method on a linear array based on a cascaded channel, to solve the problem of hierarchical codebook design under the condition of constant modulus constraint.

[0004] The hierarchical codebook design method based on a cascaded channel provided by the application defines the combination of the incident direction and the reflected direction as a cascaded channel direction, and one cascaded channel direction may correspond to multiple groups of incident-reflected directions; based on the defined cascaded channel direction, a hierarchical codebook is realized. The hierarchical codebook can be used for beam search work in a single-user static scene, and can also be used in an analog beamforming scene of an active array, thereby solving the hierarchical codebook design based on constant modulus constraint.

[0005] The application provides a hierarchical codebook design method based on a cascade channel, and the specific steps are as follows:

[0006] (I) According to the application requirement and the number of array elements, the number of layers to be divided is determined; let the number of array elements be Q, the number of layers be S, and 2 S ≤Q be met.

[0007] (II) Assuming that the i-th code word of the S-th layer codebook is

[0008] For a passive beamforming scene, the following is met:

[0009]

[0010] For an analog beamforming scene, the following is met:

[0011]

[0012] Wherein, n is the index of the array element, n=1, 2, …, Q, s is the index of the codebook, s=1, 2, …, S, j represents an imaginary number, and k is the wave number, which can be determined through , wherein λ is the wavelength of the signal carrier, d is the array element spacing, and on a traditional active array, is generally set to On an intelligent reflecting surface, is set to

[0013] The hierarchical codebook designed in the application divides the direction range in the form of a binary tree; the first layer of code words divides the direction range to be searched in half, the second layer divides in four, and so on until the direction range width that cannot be divided by the resolution of the array is reached; see the figure. Figure 1

[0014] The purpose of codebook search on an active array is to traverse all values of sinθ, that is, (-1, 1), wherein θ is the elevation direction of the array; the purpose of codebook search on a passive array (intelligent reflecting surface) is to traverse all values of sinθ i +sinθ r , that is, (-2, 2), wherein θ i and θ r are the incident direction and the reflection direction of the intelligent reflecting surface respectively.

[0015] The hierarchical codebook designed in the application can be used for beam search in a single-user static scene, see the figure, and the specific steps are as follows: Figure 2

[0016] First, according to the array size in actual use, the required signal quality of communication, and the requirement of initial access delay, the number of layers S of the hierarchical codebook to be required is determined; use b to mark the index of the optimal code word; initially, set b=1. ​​

[0017] Then the beam search is performed using the code words with indices 2b-1 and 2b in the first layer, and the optimal code word is selected, and b is updated to the index of the new optimal code word, and the beam search in the first layer is completed.

[0018] The beam search in the second layer does not need to search all the code words in the second layer, but only needs to search within the coverage of the code words in the first layer, that is, only the code words with indices 2b-1 and 2b need to be searched, and after the search is completed, the index b of the optimal code word is updated again, and so on until the last layer.

[0019] The hierarchical codebook scheme provided by the application can be used for passive beamforming and can also be used for analog beamforming.

[0020] The hierarchical codebook scheme provided by the application can be used under different array sizes.

[0021] The hierarchical codebook scheme provided by the application can freely select the width of the final required codebook, and even on a super large array, a codebook with fewer layers can be used.

[0022] For a scene in which it is not determined how many antennas / reflection units are used, a preset number of search layers can be used by using the codebook. S If the preset number of layers is too large to cause the condition 2 s When 2

[0023] The hierarchical codebook provided by the application adopts a binary tree form codebook, and users can easily design other forms of hierarchical codebooks according to the same principle, for example, a ternary tree form, which is also regarded as the achievement of the application.

[0024] The application can be used in passive array scenes such as intelligent reflecting surfaces, and can also be used in active array scenes such as base stations and users, and the application can solve the antenna phase shift configuration problem in the above-mentioned scenes, and solve the problem of slow convergence of optimization algorithms in the case of a large number of arrays.

[0025] The traditional hierarchical codebook design for intelligent reflecting surfaces distinguishes between the incident direction and the reflection direction, and searches the incident and reflection directions using hierarchical codebooks on the two variables, while the application provides a hierarchical codebook design based on cascaded channel directions, which can search the incident and reflection directions at the same time.

[0026] In order to realize the wide beam in the high layer of the hierarchical codebook, the traditional algorithm mostly uses the beam synthesis method to realize, while the wide beam in the application is directly formed, and does not need to perform beam synthesis.

[0027] The codebook can be used on an array of any size, and when the array size increases, the codebook can be directly used without changing, and the larger the array, the better the performance of the codebook.

[0028] The wide beam technology in the hierarchical codebook can form a wide beam with all antennas of the array, and for the intelligent reflecting surface scene, all antennas participate in reflection, which means that the array can provide greater beamforming gain, which reasonably utilizes the advantage of the large number of intelligent reflecting surface antennas and to some extent avoids the disadvantage of the intelligent reflecting surface without radio frequency link.

[0029] The more the number of antennas, the closer the wide beam formed by the technology of using all antennas to form a wide beam to the ideal wide beam, that is, the beam is more flat inside, the beam edge is sharp cut-off, and the beam side lobe is smaller. Such technology applied to hierarchical codebook design can significantly reduce the mismatch rate when using hierarchical codebook to search for a beam.

[0030] Advantages of the present application:

[0031] (1) The present application realizes the hierarchical codebook design in the passive beamforming scene such as intelligent reflecting surface, effectively solving the problem of long beam search time of intelligent reflecting surface;

[0032] (2) The present application unifies analog beamforming and passive beamforming, which is more convenient for designing a unified beam search scheme;

[0033] (3) In the present application, the hierarchical codebook can be designed without knowing the array size in advance, which is easier to determine a unified beam search standard in a system;

[0034] (4) In the present application, the widths of the wide beams in the same layer of hierarchical codebook are different, so that when searching for users in different directions, the mismatch rate of the hierarchical codebook is the same, which ensures the robustness of the algorithm. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 is a schematic diagram of a hierarchical codebook.

[0036] Figure 2 is a flowchart of an algorithm for searching a beam by applying a hierarchical codebook. DETAILED DESCRIPTION

[0037] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Although the description of the present invention is presented in conjunction with preferred embodiments, this does not mean that the features of the invention are limited to these embodiments. On the contrary, the purpose of describing the invention in conjunction with embodiments is to cover other options or modifications that may be derived based on the claims of the present invention. To provide a deep understanding of the invention, many specific details will be included in the following description. The invention may also be implemented without using these details. Furthermore, to avoid confusion or obscuring the focus of the invention, some specific details will be omitted in the description. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0038] It should be noted that in this specification, similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0039] as follows Figure 2 As shown, the first step is to determine how many layers the codebook needs. If the number of array elements is known, it is best to set the total number of layers S to satisfy 2. S ≤Q. The specific number of layers depends on the actual situation. More layers result in a narrower beam and greater beamforming gain, but also a longer search time. Choose the appropriate number of layers in the codebook based on the specific application's requirements for search time and beamforming gain. If the number of array elements is unknown, uncertain, or inconsistent, simply select the number of codebook layers based on the search time requirements.

[0040] After determining the number of layers, first use the codewords from the first layer of the codebook, that is... and The phase-shifting scheme in the array is configured, and then the optimal codeword is determined based on the received signal power at the receiver. This completes the first-level search. In the second-level search, it is not necessary to configure the array one by one using the four codewords in the second level; instead, only the sub-codeword corresponding to the codeword ultimately selected in the first level needs to be chosen. For example, the result of the first-level codeword search is using... If the received power is increased, then the second-level search only needs to compare... and The corresponding receiving power level; conversely, if the result of the first layer is using... If the received power can be increased, then the second layer only needs to compare... and The corresponding received power level. In short, in each search layer, we only need to compare two codewords that result in a higher received power.

[0041] While the present invention has been illustrated and described with reference to certain preferred embodiments, those skilled in the art should understand that the above description is a further detailed explanation of the invention in conjunction with specific embodiments, and should not be construed as limiting the specific implementation of the invention to these descriptions. Various changes in form and detail can be made by those skilled in the art, including several simple deductions or substitutions, without departing from the spirit and scope of the invention.

Claims

1. A hierarchical codebook design method based on cascaded channels, characterized in that, The incident and reflection directions are combined to define a cascaded channel direction, where one cascaded channel direction may correspond to multiple sets of incident-reflection directions. Based on this defined cascaded channel direction, a hierarchical codebook is implemented. This hierarchical codebook is used for beam search in single-user static scenarios or for simulated beamforming scenarios of active arrays to solve the hierarchical codebook design based on constant mode constraints. The specific steps are as follows: (a) Determine the number of layers required based on application needs and the number of array elements; let the number of array elements be Q and the number of layers be S, satisfying 2 S ≤Q; (ii) Assume the i-th codeword of the S-th layer codebook is For passive beamforming scenarios, we have: For simulated beamforming scenarios, we have: Where n is the subscript of the array element, n = 1, 2, ..., Q; s is the layer index of the codebook, s = 1, 2, ..., S; j represents the imaginary number; and k is the wave number. To determine, where λ is the wavelength of the signal carrier and d is the element spacing, set as on the active array. Set on the intelligent reflective surface The hierarchical codebook divides the directional range into binary tree form; the first layer codeword divides the directional range to be searched into two equal parts, the second layer divides it into four equal parts, and so on, until the directional range width that the array resolution cannot distinguish is reached.

2. The hierarchical codebook design method according to claim 1, characterized in that: Searching the codebook on the active array involves iterating through all values ​​of sinθ, i.e. (-1, 1), where θ is the elevation angle of the array. Searching the codebook on a passive array, i.e., an intelligent reflective surface, requires traversing sinθ. i +sinθ r All possible values ​​of θ, i.e. (-2, 2), where θ i and θ r These represent the incident direction and the reflection direction of the intelligent reflective surface, respectively.

3. The hierarchical codebook design method according to claim 1, characterized in that, The hierarchical codebook designed is used for beam search in a single-user static scene. The specific steps are as follows: First, based on the actual array size, the required signal quality for communication, and the initial access delay requirements, determine the required number of layers S in the hierarchical codebook; use b to mark the subscript of the optimal codeword; initially set b = 1; Then, the codewords with indices 2b-1 and 2b in the first layer are used to perform beam search, and the optimal codeword is selected. b is then updated to the indices of the new optimal codeword, thus completing the beam search of the first layer. The beam search for the second layer does not require searching all the second layer codewords. It only searches within the coverage area of ​​the first layer codewords, that is, only searching codewords with indices 2b-1 and 2b. After the search is completed, the indices b of the optimal codeword are updated again, and so on until the last layer.

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