Wave beam out-of-focus suppression method of near-field broadband uniform planar antenna array based on delayer

Abstract

The invention discloses a delayer-based beam out-of-focus suppression method for a near-field broadband uniform planar antenna array. The method comprises the following steps of S1, modeling a near-field uniform planar array; s2, providing a full-connection delayer auxiliary beam forming framework, and replacing phase shifter auxiliary beam forming in a traditional beam forming framework with a delayer; s3, optimizing the fully connected delayer auxiliary beam forming architecture to obtain a layered delayer beam forming architecture, and decoupling beam defocus into two parts which are respectively influenced by the transverse and longitudinal structures of the antenna array; and S4, proposing a delayer configuration scheme of beam forming based on a layered delayer beam forming framework under the constraint of an actual delayer. According to the method, beam defocus can be effectively suppressed, beam gain of an expected coverage position is ensured on different subcarrier frequencies, meanwhile, the proposed delayer configuration scheme can effectively reduce system hardware overhead, and the method adapts to delayer performance constraints in an actual system.

Description

Technical Field

[0001] The invention belongs to the technical field of wireless communications and relates to a method for suppressing beam defocus of a near-field broadband uniform planar antenna array based on a delay device. Background Art

[0002] Terahertz communication is considered to be an important technology in the next generation of communication systems because it can meet the increasing speed requirements of current communication systems. However, the increase in communication frequency and the continuous expansion of antenna array size may greatly increase the Rayleigh distance in future communication systems. Rayleigh distance is a commonly used boundary value to distinguish the radiation far field from the near field. Generally, the present invention considers that the range less than the Rayleigh distance is the radiation near field area, and the range greater than the Rayleigh distance is the radiation far field area. In traditional communication systems, the Rayleigh distance is often less than one meter, but with the continuous increase in antenna scale and communication frequency, the Rayleigh distance in future communication systems may reach tens or even hundreds of meters, which makes the near-field effect cannot be ignored in future communication systems, and near-field communication will also become an important scenario in future communications.

[0003] At the same time, another challenge that terahertz communication brings to the present invention is the more serious spatial broadband effect. In previous communication systems, the spatial broadband effect is usually manifested as a beam offset phenomenon, that is, only the beam at the center frequency can point to the expected position, and on any subcarrier that is not equal to the center frequency, the beam will show an offset relative to the expected position. In the near-field communication scenario, this effect may be further exacerbated. This is because in near-field communication, the electromagnetic wave model can no longer be approximated as a plane wave, and the near-field spherical wave model must be considered. However, the additional distance resolution introduced by the spherical wave model makes the spatial broadband effect not only manifested as an angle offset, but also further causes an offset in the distance domain, which makes the spatial broadband effect further manifested as beam defocusing, aggravating the impact on system performance. At present, there have been preliminary studies on the spatial broadband effect in the near field, but it is limited to linear arrays and only stays on the analysis of the spatial broadband effect, and no specific suppression method has been proposed.

[0004] A literature search of the prior art revealed that the research is limited to far-field communication scenarios and only focuses on scenarios where the transmitting end is equipped with a linear array. As a form of antenna that is more widely used in actual communications, uniform planar arrays have not yet been involved in existing work. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and integrate with the current new technology to provide a beam defocusing suppression method for a near-field broadband uniform planar antenna array based on a delay device.

[0006] The specific technical solution is:

[0007] The method for suppressing beam defocus of a near-field broadband uniform planar antenna array based on a delay device comprises the following steps:

[0008] S1. Modeling of near-field uniform planar arrays: beam defocusing effects caused by beamforming for broadband systems using traditional phase shifter-assisted beamforming architectures and their impact on system performance;

[0009] S2. A fully connected delayer-assisted beamforming architecture is proposed, which uses a delayer to replace the phase shifter in the traditional beamforming architecture to assist beamforming.

[0010] S3, optimizing the fully connected delayer-assisted beamforming architecture to obtain a layered delayer beamforming architecture, decoupling the beam defocusing into two parts affected by the lateral and longitudinal structures of the antenna array respectively;

[0011] S4. Based on the layered delayer beamforming architecture under actual delayer constraints, a beamforming delayer configuration scheme is proposed.

[0012] Furthermore, step S1 specifically includes:

[0013] In the near-field downlink broadband transmission scenario, the transmitter is equipped with a uniform planar antenna array and uses orthogonal frequency division multiplexing technology to serve a single-antenna user. The total bandwidth of the system is B, and there are P subcarriers in total. Therefore, the frequency f of the pth subcarrier is p for:

[0014]

[0015] Among them, f c is the system center frequency;

[0016] The antenna array contains a total of N y ×N z antenna elements, where N y With N z represent the number of columns and rows of the antenna array respectively, and the antenna element spacing d is set to half a wavelength, that is, where λ c is the wavelength corresponding to the center frequency;

[0017] Polar coordinates are used to represent the positions of antenna array elements and users. The user position is expressed as Where r is the distance from the user to the center of the antenna element, θ and are the elevation angle and azimuth angle from the user to the antenna center respectively; the near-field spherical wave channel model h between the user and the antenna array on the pth subcarrier p for

[0018]

[0019] Among them, α p is the path loss suffered by the p-th subcarrier, is the beam steering vector between the base station and the user location, and the specific formula is:

[0020]

[0021] In the formula, is the wave number at the pth subcarrier, For users to (n y ,n z ) is the distance between antenna elements, j represents an imaginary unit;

[0022] Based on the Taylor expansion and the fact that the user's distance r from the antenna array is much larger than the antenna spacing d, It is expressed as:

[0023]

[0024] Beamforming is performed using the beam steering vector corresponding to the center frequency to The beam gain obtained by the pth subcarrier for:

[0025]

[0026] Among them, k c Represents the wave number at the center frequency. When the subcarrier frequency is equal to the center frequency, the optimal beam gain is obtained, that is,

[0027] Furthermore, step S2 specifically includes:

[0028] Connect to (n y ,n z ) antenna elements is denoted by The resulting delay is recorded as The frequency response produced at the pth subcarrier frequency It is expressed as:

[0029]

[0030] Therefore, using the delay-assisted beamforming architecture, the system obtains a beam gain of for:

[0031]

[0032] Among them, The delay setting is:

[0033]

[0034] Here, c represents the speed of light.

[0035] Furthermore, step S3 specifically includes:

[0036] Substituting equation (4) into equation (5), the beam gain expression is simplified to:

[0037]

[0038] in,

[0039] In the layered delay beamforming architecture, the first layer of the network consists of N y elements, the second layer network contains N z elements, and the nth y The elements are recorded as Its delay is recorded as The nth z The elements are recorded as Its delay is recorded as The beam gain obtained by the layered delay beamforming architecture at the target position at the pth subcarrier frequency is for:

[0040]

[0041] In order to ensure the optimal beam gain at the expected coverage location, the delays of the two layers of delay devices are set separately:

[0042]

[0043] in, and Respectively represent the set delays of the first layer network and the second layer network.

[0044] Furthermore, step S4 specifically includes:

[0045] Set the maximum delay value that the first group of delay devices can provide to be τ max,1 , the maximum delay value that the second group of delay devices can provide is τ max,2 , the delay resolution provided by all delay devices is recorded as χ, then the delay value sets of the two groups of delay devices are

[0046] Any delay in the delay value set is recorded as as well as Then the beam gain obtained by the system at the target position at the pth subcarrier frequency under the actual delay is for:

[0047]

[0048] in, Where n and m are arbitrary integers. and The closer it is to 0, the greater the beam gain obtained;

[0049] Considering the maximum delay range of the delay device, the value ranges of n and m are expressed as:

[0050]

[0051] Under hardware constraints, and The best value of and

[0052]

[0053]

[0054] According to one aspect of the present invention, there is provided a storage medium, wherein instructions are stored in the storage medium. When a computer reads the instructions, the computer executes any one of the above-mentioned methods for suppressing beam defocus of a near-field broadband uniform planar antenna array based on a delay device.

[0055] According to another aspect of the present invention, there is provided an electronic device, comprising a processor and the above-mentioned storage medium, wherein the processor executes instructions in the storage medium.

[0056] Compared with the prior art, the present invention has the following beneficial effects:

[0057] 1. This invention is the first to model and study the near-field broadband planar array communication system, and systematically analyzes the performance of the spatial broadband effect in this system, namely, the beam defocusing effect.

[0058] 2. The present invention studies for the first time how to suppress the beam defocusing effect in a near-field broadband planar array by using delay-assisted beamforming, and reduces the required number of delays by flexibly designing the delay network structure.

[0059] 3. The present invention considers for the first time a beam defocusing suppression method under the hardware limitation of the delay device, and proposes a delay device network configuration method under the hardware limitation by analyzing the beam gain expression of the expected target position. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0061] Figure 1 A near-field broadband planar array communication system model involved in the present invention;

[0062] Figure 2 It is a schematic diagram of the suppression effect of the method of the present invention on beam defocusing in the elevation angle domain;

[0063] Figure 3 It is a schematic diagram of the suppression effect of the method of the present invention on beam defocusing in the rotation angle domain;

[0064] Figure 4 It is a schematic diagram of the suppression effect of the method of the present invention on beam defocusing in the distance domain;

[0065] Figure 5 Schematic diagram of the number of delay devices required in the embodiment of the present invention. DETAILED DESCRIPTION

[0066] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0067] Step 1. The present invention considers a near-field downlink broadband transmission scenario. The transmitter is equipped with a uniform planar antenna array (UPA) and uses orthogonal frequency division multiplexing (OFDM) to serve a single-antenna user. The total system bandwidth is B and there are P subcarriers. Therefore, the frequency of the pth subcarrier is:

[0068]

[0069] where f c is the system center frequency. The antenna array contains a total of N y ×N z antenna elements, where N y With N z Represent the number of columns and rows of the antenna array respectively. The antenna element spacing d is set to half a wavelength, that is, where λ c is the wavelength corresponding to the center frequency. Polar coordinates are used to represent the positions of antenna array elements and users. The user position is expressed as Where r is the distance from the user to the center of the antenna element, θ and are the elevation angle and azimuth angle from the user to the antenna center, respectively.

[0070] In view of the fact that electromagnetic waves suffer from severe path loss in millimeter wave and terahertz systems, only line-of-sight paths are considered in the present invention. Therefore, the near-field spherical wave channel model between the user and the antenna array on the pth subcarrier can be expressed as:

[0071]

[0072] Among them, α p is the path loss suffered by the p-th subcarrier, is the beam steering vector between the base station and the user location, which can be expressed as:

[0073]

[0074] In the formula, is the wave number at the pth subcarrier, For users to (n y ,n z ) antenna elements. Considering the Taylor expansion And usually, the user's distance r from the antenna array is much larger than the antenna spacing d, so It is expressed as:

[0075]

[0076] In a conventional narrowband communication system, the present invention generally uses the beam steering vector corresponding to the expected coverage position as the beam forming vector for beam forming. The beam steering vector of a single frequency point can be provided by a beam forming network based on a phase shifter. However, in a broadband system, the frequencies of different subcarriers are different, so the corresponding beam steering vectors are also different. If the beam steering vector corresponding to the center frequency is used for beam forming, then at the expected coverage position, i.e., the user location, The beam gain obtained by the pth subcarrier for:

[0077]

[0078] It can be seen from the formula that the optimal beam gain can be obtained only when the subcarrier frequency is equal to the center frequency, that is, Using the steering vector of the center frequency for beamforming on any other subcarrier frequency will result in performance loss. At the same time, it can be found that when using the steering vector corresponding to the center frequency for beamforming on other subcarrier frequencies, not only the expected coverage position, but no position in space can obtain the ideal beam gain. The present invention names this phenomenon as the beam defocusing effect. It can be seen that the beam defocusing effect will seriously affect the beamforming performance of the broadband system, because the transmit beam cannot be focused on the user position, which will cause serious energy leakage.

[0079] Step 2. It can be seen from the derivation in step 1 that the traditional beamforming network based on phase shifters can only provide frequency-independent phase shifts, that is, it can only generate a beam steering vector corresponding to a special frequency value to serve all subcarrier frequencies, resulting in performance loss. Therefore, for broadband systems, frequency-dependent phase shifts are required at the transmitting antenna to serve different subcarriers. Considering that the delay device can provide frequency-dependent phase shifts, in the present invention, the present invention considers replacing the phase shifter in the traditional beamforming network with a delay device to suppress beam defocusing in the near-field broadband UPA system. Connect to the (nth) y ,n z ) antenna elements is denoted by The resulting delay is recorded as The frequency response generated at the pth subcarrier frequency is It can be expressed as:

[0080]

[0081] Therefore, using the delay-assisted beamforming architecture, the system obtains a beam gain of for:

[0082]

[0083] It can be seen from the formula that by reasonably setting the delay value of each delay device, the beam defocusing effect can be perfectly suppressed. The delay setting is:

[0084]

[0085] The beam defocusing effect can be completely overcome. The present invention names this beamforming architecture as a fully connected TTD-assisted beamforming architecture. This architecture uses the frequency-dependent characteristics of the delay in the frequency domain, so that on each subcarrier, the present invention can ensure That is, the optimal beam gain is achieved, thereby completely suppressing the beam defocusing effect.

[0086] Step 3: Although the fully connected TTD-assisted beamforming architecture proposed in step 2 can completely suppress beam defocusing, it requires the introduction of a total of N y N z Delay. Considering that the number of antennas in a very large-scale antenna array tends to be thousands, this architecture will introduce large hardware costs and energy overhead. Therefore, the present invention considers reducing the number of required TTDs by designing the structure of the TTD network. By substituting the approximation in equation (3) into equation (4), the beam gain expression can be simplified to:

[0087]

[0089] in,

[0090] Therefore, it can be found that the beam gain in the near-field broadband UPA system can be decoupled into the product of two terms related to the element distribution in the y-axis and z-axis directions of the antenna array. At the same time, it can be seen from formula (8) that there are N terms related to the antenna distribution in the y-axis direction. y There are N different values, and there are N items related to the antenna distribution in the z-axis direction. z Different values ​​are taken, and they do not affect each other. In view of this property, the present invention proposes a layered TTD auxiliary beamforming architecture. The first layer TTD network includes N y TTD elements to alleviate the need for N in the y-axis direction y The second layer TTD network contains N z TTD elements to alleviate the need for N in the z-axis direction z Different phase shifts. y The TTD elements are recorded as Its delay is recorded as Similarly, the nth z The TTD elements are recorded as Its delay is recorded as The hierarchical TTD-assisted beamforming architecture is adopted, and the beam gain obtained by the system at the target position at the pth subcarrier frequency is for:

[0091]

[0092] Therefore, in order to ensure the optimal beam gain at the expected coverage position, the delays of the two layers of delay devices can be set as follows:

[0093]

[0094] By setting the delay value of the delayer in this way, the proposed hierarchical TTD-assisted beamforming architecture can effectively suppress the beam defocusing effect in the near-field broadband UPA.

[0095] Step 4. In actual communication scenarios, some delay devices are subject to the constraints of limited delay range and delay resolution. This type of limited TTD can only provide a fixed delay value with limited resolution within a certain delay range. Therefore, the present invention further studies how the proposed layered TTD-assisted beamforming architecture performs TTD delay configuration under TTD constraints. Assume that the maximum delay value that the first group of delay devices can provide is τ max,1 , the maximum delay value that the first group of delay devices can provide is τ max,2 . Let the delay resolution that all TTDs can provide be denoted as χ, then the delay value sets that the two groups of TTDs can provide are Therefore, the configuration problem of layered TTD under the delay constraint is actually to select a delay value for each TTD in the available delay set so that the beam gain obtained at the final expected coverage position is the maximum. From the derivation in step 3, we can see that is the ideal configuration of each TTD in the proposed hierarchical TTD-assisted beamforming architecture. However, these ideal values ​​are not necessarily within the set of available delays of the TTD. The present invention denotes any delay within the set of available delays as as well as Then the beam gain obtained by the system at the target position at the pth subcarrier frequency under the actual delay is for:

[0096]

[0097] Obviously, due to the periodicity of the function, we can conclude that Where n and m are arbitrary integers. In this case, according to the monotonicity of the function, the present invention considers that when and The closer it is to 0, the greater the beam gain is. Considering the maximum delay range of the delay device, the value ranges of n and m can be expressed as:

[0098]

[0099] Under hardware constraints, and The best value of and It can be written as:

[0100]

[0101] By configuring the delay devices in the hierarchical TTD-assisted beamforming network of the present invention in this way, the proposed architecture can be extended to be used in delay-limited scenarios.

[0102] In summary, the present invention studies the problem of beam defocusing analysis and suppression in a near-field broadband planar antenna array system. The present invention proposes a delay-based beamforming architecture suitable for ideal hardware and hardware-constrained conditions to suppress beam defocusing.

[0103] The delay device assisted beamforming architecture proposed in the present invention has a suppressive effect on beam defocusing as shown in the attached figure. Figure 2-4 As shown, Figure 2-4 The antenna scale in the figure is N. y =256,N z =32. The system has a total of P = 64 subcarriers, and the system center frequency f c =30GHz, the total bandwidth is B=5GHz. It can be seen from the attached figure that if the traditional phase shifter-based beamforming structure is used for beamforming in the near-field broadband system, the system will suffer serious performance loss, especially in the distance domain and the rotation angle domain. The system can only obtain less than 10% of the optimal beam gain at the expected coverage position. The structure proposed in the present invention can effectively restore the beam loss caused by beam defocusing in the three domains, wherein more than 90% of the optimal beam gain can be restored in the three domains, which proves that the structure proposed in the present invention can be effectively applied to the beamforming of the near-field broadband planar antenna array system to overcome beam defocusing.

[0104] The number of delay devices required for the hierarchical delay device structure of the present invention is compared with the number of delay devices required for the fully connected delay device structure in the attached figure. Figure 5 As shown in the figure, the proposed layered delay structure can reduce the number of required delays from the multiplier level of the number of antenna rows and columns to the addition level compared to the fully connected delay. At the same time, the larger the antenna array, the more significant the effect of the proposed layered delay architecture on reducing the number of delays. This also reflects the importance and practical significance of the proposed architecture in ultra-large-scale antenna array systems.

[0105] The examples described in the present invention are merely descriptions of the preferred implementation modes of the present invention, and are not intended to limit the concept and scope of the present invention. Without departing from the design concept of the present invention, various modifications and improvements made to the technical solutions of the present invention by engineers and technicians in this field should all fall within the protection scope of the present invention.

Claims

1. A beam defocusing suppression method for a near-field broadband uniform planar antenna array based on a delay device, characterized in that: The steps include: S1. Modeling of near-field uniform planar arrays: beam defocusing effects caused by beamforming for broadband systems using traditional phase shifter-assisted beamforming architectures and their impact on system performance; S2. A fully connected delayer-assisted beamforming architecture is proposed, which uses a delayer to replace the phase shifter in the traditional beamforming architecture to assist beamforming. S3, optimizing the fully connected delayer-assisted beamforming architecture to obtain a layered delayer beamforming architecture, decoupling the beam defocusing into two parts affected by the lateral and longitudinal structures of the antenna array respectively; S4. Based on the layered delayer beamforming architecture under actual delayer constraints, a beamforming delayer configuration scheme is proposed.

2. The method according to claim 1, characterized in that Step S1 specifically includes: In the near-field downlink broadband transmission scenario, the transmitter is equipped with a uniform planar antenna array and uses orthogonal frequency division multiplexing technology to serve a single-antenna user. The total bandwidth of the system is B, and there are P subcarriers in total. Therefore, the frequency f of the pth subcarrier is p for: Among them, f c is the system center frequency; The antenna array contains a total of N y ×N z antenna elements, where N y With N z represent the number of columns and rows of the antenna array respectively, and the antenna element spacing d is set to half a wavelength, that is, where λ c is the wavelength corresponding to the center frequency; Polar coordinates are used to represent the positions of antenna array elements and users. The user position is expressed as Where r is the distance from the user to the center of the antenna element, θ and are the elevation angle and azimuth angle from the user to the antenna center respectively; the near-field spherical wave channel model h between the user and the antenna array on the pth subcarrier p for Among them, α p is the path loss suffered by the p-th subcarrier, is the beam steering vector between the base station and the user location, and the specific formula is: In the formula, is the wave number at the pth subcarrier, For users to (n y ,n z ) is the distance between antenna elements, j represents an imaginary unit; Based on the Taylor expansion and the fact that the user's distance r from the antenna array is much larger than the antenna spacing d, It is expressed as: Beamforming is performed using the beam steering vector corresponding to the center frequency, at the user's location The beam gain obtained by the pth subcarrier for: Among them, k c represents the wave number at the center frequency; when the subcarrier frequency is equal to the center frequency, the optimal beam gain is obtained, that is, 3. The method according to claim 2, characterized in that Step S2 specifically includes: Connect to the (n y ,n z The delay time of each antenna element is denoted by The resulting delay is recorded as The frequency response produced at the pth subcarrier frequency It is expressed as: Therefore, using the delay-assisted beamforming architecture, the system obtains a beam gain of for: Among them, The delay setting is: Here, c represents the speed of light.

4. The method according to claim 3, characterized in that Step S3 specifically includes: Substituting equation (4) into equation (5), the beam gain expression is simplified to: in, In the layered delay beamforming architecture, the first layer of the network consists of N y elements, the second layer network contains N z elements, and the nth y The elements are recorded as Its delay is recorded as The nth z The elements are recorded as Its delay is recorded as The beam gain obtained by the layered delay beamforming architecture at the target position at the pth subcarrier frequency is for: In order to ensure the optimal beam gain at the expected coverage location, the delays of the two layers of delay devices are set separately: in, and Respectively represent the set delays of the first layer network and the second layer network.

5. The method according to claim 4, characterized in that Step S4 specifically includes: Set the maximum delay value that the first group of delay devices can provide to be τ max,1 , the maximum delay value that the second group of delay devices can provide is τ max,2 , the delay resolution provided by all delay devices is recorded as χ, then the delay value sets of the two groups of delay devices are Any delay in the delay value set is recorded as as well as Then the beam gain obtained by the system at the target position at the pth subcarrier frequency under the actual delay is for: in, Where n and m are arbitrary integers. and The closer it is to 0, the greater the beam gain obtained; Considering the maximum delay range of the delay device, the value ranges of n and m are expressed as: Under hardware constraints, and The best value of and for:

6. A storage medium, characterized in that: The storage medium stores instructions, and when a computer reads the instructions, the computer executes the effective prestress monitoring method under a component anchor based on the strain method as described in any one of claims 1 to 5.

7. An electronic device, characterized in that: The invention comprises a processor and the storage medium as claimed in claim 6, wherein the processor executes instructions in the storage medium.

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