Terahertz hybrid precoding method for liquid crystal response time delay

Abstract

The invention discloses a terahertz hybrid precoding method for liquid crystal response time delay. The method comprises the following steps: setting a multi-antenna array and a broadband channel based on a terahertz large-scale MIMO system of a liquid crystal phase shifter and terahertz channel characteristics; performing preliminary decoupling on the coupled digital precoding and analog precoding; constructing a function about the influence value of the phase shifter to obtain a final approximate optimal precoding matrix under the time delay response of the liquid crystal phase shifter; and calculating the communication performance of the phase shifter response time delay-oriented hybrid precoding method. According to multi-antenna array setting and beam coherence time, constraint conditions of maximum allowable phase shift delay are constructed, after the constraint conditions are optimized, coupled digital pre-coding and analog pre-coding are preliminarily decoupled through a communication rate maximization method, and then an approximate optimal pre-coding matrix and corresponding communication performance are obtained. The problem that terahertz hybrid precoding cannot be carried out for liquid crystal response time delay characteristics is solved.

Description

Technical Field

[0001] The present invention relates to the field of terahertz (THz) technology, and in particular to a terahertz hybrid precoding method for liquid crystal response delay. Background Art

[0002] As the amount of global communication data increases day by day, it is expected that the peak rate of wireless communication will reach the Tbps level in 2030. The 5G microwave millimeter wave frequency band can no longer support such a huge capacity rate demand, forcing the future 6G to evolve to a higher frequency band. Among them, THz spectrum resources are abundant, and it has the ability to carry large-scale data transmission. The application of terahertz communication technology can not only effectively alleviate the current problem of tight wireless communication spectrum resources, but also break through the capacity bottleneck of existing wireless communication systems and support future 6G vertical industry applications, such as autonomous driving, virtual reality, industrial automation and smart Internet of Things. However, THz path loss is large, the molecular absorption effect is significant, and the transmission power is low compared to traditional microwave millimeter waves, resulting in limited THz communication and perception distance. In order to meet the needs of THz long-distance communication and perception business scenarios, large-scale MIMO (multiple input multiple output) must be used to combat the problems of low THz transmission power and high path loss. Considering the needs of multi-user multi-radio connection, hybrid beamforming is generally used in large-scale terahertz MIMO arrays, so the phased array targeted by this application is a hybrid architecture. Compared with traditional terahertz devices (CMOS and vanadium dioxide), liquid crystal phased arrays have advantages such as high phase shift resolution, low processing cost, and short product cycle, so liquid crystal phased arrays are used for precoding. However, due to the interaction and viscosity between liquid crystal molecules in the liquid crystal phase shifter, the liquid crystal phase shifter has a certain response delay, resulting in a certain lag in precoding, reducing the spectrum efficiency.

[0003] At present, hybrid precoding methods targeting phase shifter characteristics are divided into three categories: (1) large-scale phased array hybrid precoding for infinite resolution phase shifters; (2) large-scale phased array hybrid precoding for finite resolution phase shifters; (3) large-scale phased array hybrid precoding for fixed resolution. The hybrid precoding method for infinite resolution phase shifters cannot be implemented through hardware; the hybrid precoding method for finite resolution considers the discrete phase and constant modulus constraints of the phase shifter, but does not consider the response delay of the liquid crystal phase shifter; the hybrid precoding method for fixed resolution phase shifters does not need to pay attention to the response delay of the liquid crystal phase shifter, but it is difficult to realize the integration of large-scale switching networks and liquid crystal phase shifters. In summary, under the premise that the response delay is not directly related to precoding, the three methods cannot be directly applied to the hybrid precoding of liquid crystal phased arrays. Therefore, it is urgent to propose new terahertz hybrid precoding methods targeting the response delay characteristics of liquid crystals. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention provides a terahertz hybrid precoding method for liquid crystal response delay.

[0005] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0006] A terahertz hybrid precoding method for liquid crystal response delay comprises the following steps:

[0007] S1. Terahertz massive MIMO system and terahertz channel characteristics based on liquid crystal phase shifters, setting up multi-antenna arrays and broadband channels;

[0008] S2. Determine the beam coherence time, construct the constraint condition of the maximum allowable phase shift delay according to the beam coherence time and the multi-antenna array set in step S1, and after optimizing the constraint condition, construct the ideal model of the communication rate of the subcarrier by the communication rate maximization method to preliminarily decouple the coupled digital precoding and analog precoding;

[0009] S3, constructing a function of the influence value of the phase shifter according to the digital precoding and analog precoding preliminarily decoupled in step S2, and obtaining a final approximate optimal precoding matrix under the delay response of the liquid crystal phase shifter according to the function of the influence value of the phase shifter;

[0010] S4. Based on the broadband channel set in step S1 and the approximate optimal precoding matrix under the final liquid crystal phase shifter delay response in step S3, the communication performance of the hybrid precoding method oriented to the phase shifter response delay is calculated.

[0011] Furthermore, step S1 includes the following steps:

[0012] S11. A terahertz massive MIMO system based on liquid crystal phase shifters uses partially connected architecture hybrid precoding for beamforming. Each RF chain signal transmits the signal to a liquid crystal phased array subarray through a horn antenna, and beamforming of the air interface signal is performed through the phase shifter matrix of each subarray to achieve multi-user hybrid precoding, so as to set up a multi-antenna array.

[0013] S12. Based on the terahertz channel characteristics, broadband channel settings are performed for different subcarriers in the signal propagation process of the terahertz massive MIMO system.

[0014] Furthermore, in step S1, a broadband channel is set, which is expressed as:

[0015]

[0016] Where: H[k] is the channel of the kth subcarrier, γ is the normalization factor, m is the ray cluster number, N clis the total number of ray clusters, n is the ray bar number in the ray cluster, N ray is the total number of rays in the ray cluster, g m,n,k is the path gain of the kth subcarrier of the nth ray in the mth cluster, β m,n,k is the delayed component of the kth subcarrier of the nth ray in the mth cluster, is the normalized departure angle array response vector of the k-th subcarrier of the n-th ray in the m-th cluster, is the normalized arrival angle array response vector of the k-th subcarrier of the n-th ray in the m-th cluster.

[0017] Further, in step S2, the ideal model of the communication rate of the subcarrier is expressed as:

[0018]

[0019] Where: R[k] is the communication rate of the kth subcarrier, F BB [k] is the digital precoding matrix of the kth subcarrier, F BB [k] H is the matrix F BB [k] is the transpose, σ is the noise power, P is the average signal power in the channel, F RF is the simulated precoding matrix, H[k] is the channel of the kth subcarrier.

[0020] Furthermore, in step S3, a function of the influence value of the phase shifter is constructed, including the following steps:

[0021] A1. Construct the first variable matrix, the second variable matrix, the third variable matrix, the fourth variable matrix and the fifth variable matrix, expressed as:

[0022] Q[k]=F BB [k]F BB [k] H ,

[0023]

[0024] D m [k]=Q[k] -1 m,m -Q[k] -1 m,\m C m [k] -1 Q[k] -1 \m,m ,

[0025]

[0026] Where: Q[k] is the first variable matrix, F BB[k] is the digital precoding matrix of the kth subcarrier, F BB [k] H is the matrix F BB The transpose of [k], C m [k] is the second variable matrix, m is the mth column of the matrix, m,\m is the mth column of the matrix excluding the mth row, σ is the noise power, P is the average signal power in the channel, F RF To simulate the precoding matrix, For D m [k] is the third variable matrix, G m [k] is the fourth variable matrix, H em,n [k] is the fifth variable matrix;

[0027] A2. Construct a function of the influence value of the phase shifter according to the first variable matrix, the second variable matrix, the third variable matrix, the fourth variable matrix and the fifth variable matrix, which is expressed as:

[0028]

[0029] Where: R[k] is the communication rate of the kth subcarrier.

[0030] Furthermore, in step S3, an approximate optimal precoding matrix under the final liquid crystal phase shifter delay response is obtained according to a function of the influence value of the phase shifter. The specific process is: according to the function of the influence value of the phase shifter, the contribution of the phase shifters connected to different RF chains is isolated to locally optimize the digital precoding and analog precoding, and after optimizing a column of phase shifters, the digital precoding matrix is ​​updated to obtain the approximate optimal precoding matrix under the final liquid crystal phase shifter delay response.

[0031] Further, in step S4, the communication performance of the hybrid precoding method oriented to the phase shifter response delay is calculated, which is expressed as:

[0032]

[0033] Where: R is the communication performance advantage value of the hybrid precoding method, k is the subcarrier number, K is the total number of subcarriers, I is the unit matrix, σ is the noise power, P is the average signal power in the channel, H[k] is the channel of the kth subcarrier, F RF is the simulated precoding matrix, F BB [k] is the digital precoding matrix of the kth subcarrier, is the matrix F BB The transpose of [k].

[0034] The present invention has the following beneficial effects:

[0035] The present invention constructs the constraint conditions of the maximum allowable phase shift delay according to the multi-antenna array setting and the beam coherence time. After optimizing the constraint conditions, the coupled digital precoding and analog precoding are preliminarily decoupled through the communication rate maximization method, so as to obtain the approximately optimal precoding matrix and the corresponding communication performance, thereby solving the problem that terahertz hybrid precoding cannot be performed for the liquid crystal response delay characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A schematic diagram of a terahertz hybrid precoding method for liquid crystal response delay;

[0037] Figure 2 A schematic diagram showing the comparison of simulation results of a terahertz hybrid precoding method for liquid crystal response delay under different signal-to-noise ratios;

[0038] Figure 3 Schematic diagram of the comparison of simulation results of a terahertz hybrid precoding method for liquid crystal response delay under different bandwidths. DETAILED DESCRIPTION

[0039] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0040] like Figure 1 As shown, a terahertz hybrid precoding method for liquid crystal response delay includes steps S1-S4, which are as follows:

[0041] S1. Terahertz massive MIMO system and terahertz channel characteristics based on liquid crystal phase shifters, setting up multi-antenna arrays and broadband channels.

[0042] In an optional embodiment of the present invention, step S1 includes the following steps:

[0043] S11. The terahertz massive MIMO system based on liquid crystal phase shifters adopts partially connected architecture hybrid precoding for beamforming. Each RF chain signal transmits the signal to the liquid crystal phased array sub-array through the horn antenna, and the beamforming of the air interface signal is performed through the phase shifter matrix of each sub-array to realize multi-user hybrid precoding to set up a multi-antenna array.

[0044] The present invention transmits each RF chain signal to a liquid crystal phased array subarray through a horn antenna: the liquid crystal phased array is set as a planar array, with a total of M liquid crystal units, including multiple subarrays, the number of which is N t, each sub-array is composed of multiple liquid crystal units; the liquid crystal phased array is different from MEMS devices and semiconductor devices. It realizes the deflection of the light beam by controlling the voltage distribution on the liquid crystal phase shifter array. Therefore, part of the connection structure of the liquid crystal phased array is connected in the form of non-feeder to realize fast signal transmission and phase control; the present invention sets the number of RF chains With the number of horn antennas M t , each RF chain signal is transmitted to each sub-array of the liquid crystal phased array through the corresponding horn antenna.

[0045] The present invention realizes multi-user hybrid precoding by performing beamforming of air interface signals through each subarray phase shifter matrix: the present invention performs beamforming of air interface signals by adjusting the phase value of each subarray phase shifter matrix; the present invention performs hybrid precoding according to channel state information (CSI) of different users, digital precoding is used to suppress interference between users, and analog precoding is performed through each subarray phase shifter matrix.

[0046] S12. Based on the terahertz channel characteristics, broadband channel settings are performed for different subcarriers in the signal propagation process of the terahertz massive MIMO system.

[0047] Step S12 includes the following steps:

[0048] S121, set the transmission signal, expressed as:

[0049] x[k]=F RF F BB [k]s[k]

[0050] Where: x[k] is the transmitted signal of the kth subcarrier, s[k] is the original signal transmitted by the kth subcarrier, and its size is N s ×1, the original transmitted signal satisfies E[s[k]]=0, and E[s[k]s H [k]]=I Ns , E[s[k]] is the expected value of s[k], I Ns N s dimensional unit vector, the total power of the analog precoder and the digital precoder is calculated according to Normalized, P t is the transmission power of each data stream. The present invention assumes that the transmission power of all subcarriers is equal. s is the dimension of the transmitted signal.

[0051] S122. Based on the terahertz channel characteristics and the transmission signal set in step S121, broadband channel setting is performed on different subcarriers in the terahertz massive MIMO system signal propagation process.

[0052] Based on the set transmission signal, the transmission signal x[k] is transmitted on the channel H[k] before being received. Based on the terahertz channel characteristics, that is, the sparsity of the terahertz signal, the present invention sets a broadband channel, which is expressed as:

[0053]

[0054] Where: H[k] is the channel of the kth subcarrier, γ is the normalization factor, N t is the number of transmitting antennas, N r is the number of receiving antennas, m is the number of ray clusters, N cl is the total number of ray clusters, n is the ray bar number in the ray cluster, N ray is the total number of rays in the ray cluster, g m,n,k is the path gain of the kth subcarrier of the nth ray in the mth cluster, β m,n,k is the delayed component of the kth subcarrier of the nth ray in the mth cluster, is the normalized departure angle array response vector of the k-th subcarrier of the n-th ray in the m-th cluster, is the normalized arrival angle array response vector of the k-th subcarrier of the n-th ray in the m-th cluster.

[0055] The array response vectors are expressed as:

[0056]

[0057] Where: j is the imaginary unit, is the normalized departure angle of the kth subcarrier of the nth ray in the mth cluster, is the normalized angle of arrival of the k-th subcarrier of the n-th ray in the m-th cluster.

[0058] S2. Determine the beam coherence time, and construct the constraint condition of the maximum allowable phase shift delay according to the beam coherence time and the multi-antenna array set in step S1. After optimizing the constraint condition, construct the ideal model of the communication rate of the subcarrier through the communication rate maximization method to preliminarily decouple the coupled digital precoding and analog precoding.

[0059] In an optional embodiment of the present invention, the present invention determines the beam coherence time T B (θ). During the beam coherence time T B Within (θ), the beam can maintain a high signal-to-noise ratio to support communication without changing the phase; when the beam coherence time is exceeded, the phase needs to be readjusted for shaping.

[0060] The present invention constructs the constraint condition of the maximum allowable phase shift delay according to the beam coherence time pair and the multi-antenna array set. The specific process is: the multi-antenna array and the beam coherence time pair set by the present invention, it can be known that the maximum allowable phase shift delay Δ is related to the beam coherence time T B (θ) There is a constraint relationship Δ <T B (θ); In addition, the time complexity of the channel estimation and beamforming algorithms must be considered in the phase update process. The time complexity of the algorithm is constant, so the algorithm time consumption is considered as a constant T under the premise of the same computing resources. A , the maximum allowable phase shift delay Δ and beam coherence time T B The (θ) constraint is further expressed as Δ≤T B (θ)-T A There is a nonlinear mapping relationship between the maximum allowable phase shift delay Δ and the phase shift range [α, β]. The present invention obtains the maximum phase shift range [α min ,β max ] to complete the constraint condition of constructing the maximum allowable phase shift delay.

[0061] The present invention optimizes the constraint conditions of the maximum allowable phase shift delay through the constraints of the liquid crystal phased array to obtain the optimized constraint conditions. The constraints of the liquid crystal phased array include the constant modulus constraint of the liquid crystal phase shifter, the limited bit constraint of the liquid crystal phase shifter, and the limited phase shift range constraint of the liquid crystal phase shifter.

[0062] The present invention calculates the maximum communication rate to construct an ideal model of the communication rate of the subcarrier through the communication rate maximization method, and the expression for calculating the maximum communication rate is:

[0063]

[0064]

[0065] [F RF ] i,g ∈F,

[0066] [F RF ] i,g ∈[α max,i,g ,β max,i,g ],

[0067]

[0068] Where: R[k] is the communication rate of the kth subcarrier, H[k] is the kth subcarrier channel, F BB [k] is the digital precoding matrix of the kth subcarrier, F RF To simulate the precoding matrix, [F RF ] i,gis the element in the i-th row and g-th column of the simulated precoding matrix, N t is the number of transmitting antennas, F is the limited bit position, α min,i,g and β max,i,g are respectively the minimum and maximum values ​​of the maximum phase shift range of the phase shifter in the i-th row and g-th column.

[0069] After optimizing the constraint conditions, the present invention constructs an ideal model of the communication rate of the subcarrier through the communication rate maximization method to preliminarily decouple the coupled digital precoding and analog precoding. The specific process is as follows:

[0070] According to the properties of matrix operations, the present invention further expresses the communication rate R[k] of each subcarrier as:

[0071]

[0072] Furthermore, when F BB When [k] is a square matrix, F BB [k]F BB [k] H is a full rank matrix, F BB [k]F BB [k] H Reversible, number of RF chains At this time, the communication rate R[k] is further expressed as:

[0073]

[0074] Furthermore, when F BB When [k] is a high matrix, F BB [k]F BB [k] H is a non-full rank matrix, F BB [k]F BB [k] H Irreversible, number of RF chains The present invention decouples the optimization process of digital precoding and analog precoding, approximates the expression of communication rate, and converts F BB [k]F BB [k] H Adding a very small diagonal matrix with equal elements, we can ensure that F BB [k]F BB [k] H It is reversible, and the communication rate of the subcarrier is determined as the ideal model of the communication rate of the subcarrier, which is expressed as:

[0075]

[0076] Where: R[k] is the communication rate of the kth subcarrier, F BB[k] is the digital precoding matrix of the kth subcarrier, F BB [k] H is the matrix F BB [k] is the transpose, σ is the noise power, P is the average signal power in the channel, F RF is the simulated precoding matrix, H[k] is the channel of the kth subcarrier.

[0077] S3. According to the digital precoding and analog precoding initially decoupled in step S2, a function of the influence value of the phase shifter is constructed, and the approximate optimal precoding matrix under the final liquid crystal phase shifter delay response is obtained according to the function of the influence value of the phase shifter.

[0078] In an optional embodiment of the present invention, the present invention constructs a function of the influence value of the phase shifter, comprising the following steps:

[0079] A1. Construct the first variable matrix, the second variable matrix, the third variable matrix, the fourth variable matrix and the fifth variable matrix, expressed as:

[0080] Q[k]=F BB [k]F BB [k] H ,

[0081]

[0082] D m [k]=Q[k] -1 m,m -Q[k] -1 m,\m C m [k] -1 Q[k] -1 \m,m ,

[0083]

[0084] Where: Q[k] is the first variable matrix, F BB [k] is the digital precoding matrix of the kth subcarrier, F BB [k] H is the matrix F BB The transpose of [k], C m [k] is the second variable matrix, m is the mth column of the matrix, m,\m is the mth column of the matrix excluding the mth row, σ is the noise power, P is the average signal power in the channel, F RF To simulate the precoding matrix, For D m [k] is the third variable matrix, G m [k] is the fourth variable matrix, H em,n[k] is the fifth variable matrix.

[0085] A2. Construct a function of the influence value of the phase shifter according to the first variable matrix, the second variable matrix, the third variable matrix, the fourth variable matrix and the fifth variable matrix, which is expressed as:

[0086]

[0087] Where: R[k] is the communication rate of the kth subcarrier.

[0088] Step A2 includes the following steps:

[0089] A21. Isolate the phase shifters outside the mth column, and move the element corresponding to the mth column and the mth row of the matrix corresponding to the latter term in the ideal model of the communication rate of the subcarrier to the first column and the first row, and obtain the first expression, which is expressed as:

[0090]

[0091] Where: m,\m is the mth column of the matrix excluding the mth row.

[0092] A22. According to the block matrix determinant calculation formula, the first expression in step A21 is converted into a second expression, which is expressed as:

[0093]

[0094] A23. Split the obtained expression and regard it as related to the vector F RF,m H A function is used to convert the second expression in step A22 into a third expression, which is expressed as:

[0095]

[0096] A24、Optimize the expression with F RF,m H The expression form of the irrelevant terms is used to convert the third expression in step A23 into a fourth expression, which is expressed as:

[0097]

[0098] A25. Consider the expression as the effect of the mth and nth phase shifters F RF,m,n H The function of the first variable matrix, the second variable matrix, the third variable matrix, the fourth variable matrix and the fifth variable matrix are substituted into the fourth expression in step A24 to construct a function about the influence value of the phase shifter.

[0099] The present invention obtains an approximate optimal precoding matrix under the final liquid crystal phase shifter delay response according to a function of the influence value of the phase shifter. The specific process is: according to the function of the influence value of the phase shifter, the contribution of the phase shifters connected to different radio frequency chains is isolated to locally optimize the digital precoding and analog precoding, and after optimizing a column of phase shifters, the digital precoding matrix is ​​updated to obtain the approximate optimal precoding matrix under the final liquid crystal phase shifter delay response.

[0100] The present invention isolates the contribution of phase shifters connected to different RF chains according to a function of the influence value of the phase shifter to locally optimize digital precoding and analog precoding. The specific process is as follows: the present invention uses the mth and nth phase shifters in the analog phase shift matrix as independent variables for the function of the influence value of the phase shifter, and converts the communication rate of the subcarrier into a complex function of the mth and nth phase shifters, which is expressed as: R[k]=f(F RF，m,n H ). Then, the present invention obtains the optimal phase of the mth and nth phase shifters by finding the extreme value of the complex function, so as to locally optimize the digital precoding and the analog precoding.

[0101] The present invention updates the digital precoding matrix after optimizing a column of phase shifters to obtain the approximate optimal precoding matrix under the final liquid crystal phase shifter delay response. The specific process is as follows: the present invention solves the optimal phase of the phase shifters other than the nth phase shifter in the mth column through iterative optimization; the optimal phase of the mth and nth phase shifters is obtained under the premise of fixing other phase shifters, and at this time, the other phase shifters are not the optimal phases, and multiple rounds of iterations are required to solve the optimal phases of other phase shifters in the mth column to approach the actual optimal phase; after solving the optimal phases of the mth and nth phase shifters, the present invention isolates the contribution of the n0th phase shifter in the mth column and fixes other phase shifters. At this time, the communication rate of the subcarrier is converted into a complex function about the mth and n0th phase shifters, which is expressed as: The present invention obtains an approximate optimal solution for the phase of all phase shifters in the mth column through iterative optimization; then the present invention optimizes the digital precoding matrix according to the iterative optimization result; the present invention optimizes the digital precoding matrix according to the variable D m [k] Definition: D m [k]=Q[k] -1 m,m -Q[k] -1 m,\m C m [k] -1 Q[k] -1 \m,m , digital precoding matrix F BB [k] H With the simulated precoding matrix F RF Hcoupling; the present invention solves the optimal solution of the phase of all phase shifters in the mth column and optimizes the digital precoding matrix; when the present invention solves the phase shifter in the m0th column except the phase shifter in the mth column, the expression of the communication rate obtained can be regarded as After solving the optimal phase of the phase shifter in the m0th column, the digital precoding matrix is ​​optimized, and so on. Column phase shifter and update the digital precoding matrix After times, the approximate optimal precoding matrix under the delay response of the liquid crystal phase shifter is finally obtained.

[0102] S4. Based on the broadband channel set in step S1 and the approximate optimal precoding matrix under the final liquid crystal phase shifter delay response in step S3, the communication performance of the hybrid precoding method oriented to the phase shifter response delay is calculated.

[0103] In an optional embodiment of the present invention, the present invention calculates the communication performance of the hybrid precoding method for phase shifter response delay, which is expressed as:

[0104]

[0105] Where: R is the communication performance advantage value of the hybrid precoding method, k is the subcarrier number, K is the total number of subcarriers, I is the unit matrix, σ is the noise power, P is the average signal power in the channel, H[k] is the channel of the kth subcarrier, F RF is the simulated precoding matrix, F BB [k] is the digital precoding matrix of the kth subcarrier, is the matrix F BB The transpose of [k].

[0106] In order to verify the performance advantages of the proposed hybrid precoding method for phase shifter response delay under different signal-to-noise ratios and different broadband channels, the present invention calculates the digital precoding matrix F under different signal-to-noise ratios based on the approximate optimal precoding matrix under the final liquid crystal phase shifter delay response under different signal-to-noise ratios. BB [k] and simulated precoding matrix F RF , in order to calculate the communication performance of the hybrid precoding method for phase shifter response delay under different signal-to-noise ratios. In order to verify the performance advantage of the proposed liquid crystal response delay in broadband scenarios, the present invention calculates the digital precoding matrix F under different broadband channels based on the set broadband channel and the final liquid crystal phase shifter delay response. BB [k] and simulated precoding matrix F RF , in order to calculate the communication performance of the hybrid precoding method for phase shifter response delay under different wideband channels.

[0107] The simulation results of the present invention are as follows Figure 2 and Figure 3 shown. Figure 2 The comparison of spectrum efficiency between the all-digital scheme and the traditional hybrid precoding scheme and the scheme proposed in the present invention under different signal-to-noise ratios is shown. Since the all-digital scheme does not need to consider the limitations of the limited resolution and response delay of the phase shifter, the performance is optimal and is the upper limit of the performance; the traditional hybrid precoding scheme does not consider the impact of the liquid crystal response delay, and only optimizes the priority resolution problem, with the lowest spectrum efficiency; the precoding scheme proposed in the present invention considers the dual impact of the liquid crystal response delay and limited resolution, and is closer to the performance of the all-digital scheme. Figure 3 The spectral efficiency comparison of the three schemes under different bandwidths (wideband channels) is shown. Compared with the traditional precoding scheme, the scheme proposed in the present invention has obvious performance gains under different bandwidths, and the spectral efficiency is less affected by the bandwidth. In summary, the present invention constructs the constraint conditions of the maximum allowable phase shift delay according to the multi-antenna array setting and the beam coherence time, and after optimizing the constraint conditions, the coupled digital precoding and analog precoding are preliminarily decoupled through the communication rate maximization method, and then the approximate optimal precoding matrix and the corresponding communication performance are obtained, which solves the problem that terahertz hybrid precoding cannot be performed for the liquid crystal response delay characteristics.

[0108] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0109] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0110] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0111] The present invention uses specific embodiments to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

[0112] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific variations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed by the present invention, and these variations and combinations are still within the protection scope of the present invention.

Claims

1. A terahertz hybrid precoding method for liquid crystal response delay, characterized in that: The following steps are involved: S1. Terahertz massive MIMO system and terahertz channel characteristics based on liquid crystal phase shifters, setting up multi-antenna arrays and broadband channels; S2. Determine the beam coherence time, construct the constraint condition of the maximum allowable phase shift delay according to the beam coherence time and the multi-antenna array set in step S1, and after optimizing the constraint condition, construct the ideal model of the communication rate of the subcarrier by the communication rate maximization method to preliminarily decouple the coupled digital precoding and analog precoding; S3, constructing a function of the influence value of the phase shifter according to the digital precoding and analog precoding preliminarily decoupled in step S2, and obtaining a final approximate optimal precoding matrix under the delay response of the liquid crystal phase shifter according to the function of the influence value of the phase shifter; S4. Based on the broadband channel set in step S1 and the approximate optimal precoding matrix under the final liquid crystal phase shifter delay response in step S3, the communication performance of the hybrid precoding method oriented to the phase shifter response delay is calculated.

2. The terahertz hybrid precoding method for liquid crystal response delay according to claim 1, characterized in that: Step S1 includes the following steps: S11. A terahertz massive MIMO system based on liquid crystal phase shifters uses partially connected architecture hybrid precoding for beamforming. Each RF chain signal transmits the signal to a liquid crystal phased array subarray through a horn antenna, and beamforming of the air interface signal is performed through the phase shifter matrix of each subarray to achieve multi-user hybrid precoding, so as to set up a multi-antenna array. S12. Based on the terahertz channel characteristics, broadband channel settings are performed for different subcarriers in the signal propagation process of the terahertz massive MIMO system.

3. The terahertz hybrid precoding method for liquid crystal response delay according to claim 1, characterized in that: In step S1, a broadband channel is set, which is expressed as: Where: H[k] is the channel of the kth subcarrier, γ is the normalization factor, m is the ray cluster number, N cl is the total number of ray clusters, n is the ray bar number in the ray cluster, N ray is the total number of rays in the ray cluster, g m,n,k is the path gain of the kth subcarrier of the nth ray in the mth cluster, β m,n,k is the delayed component of the kth subcarrier of the nth ray in the mth cluster, is the normalized departure angle array response vector of the k-th subcarrier of the n-th ray in the m-th cluster, is the normalized arrival angle array response vector of the k-th subcarrier of the n-th ray in the m-th cluster.

4. The terahertz hybrid precoding method for liquid crystal response delay according to claim 1, characterized in that: In step S2, the ideal model of the communication rate of the subcarrier is expressed as: Where: R[k] is the communication rate of the kth subcarrier, F BB [k] is the digital precoding matrix of the kth subcarrier, F BB [k] H is the matrix F BB [k] is the transpose, σ is the noise power, P is the average signal power in the channel, F RF is the simulated precoding matrix, H[k] is the channel of the kth subcarrier.

5. The terahertz hybrid precoding method for liquid crystal response delay according to claim 1, characterized in that: In step S3, a function of the influence value of the phase shifter is constructed, including the following steps: A1. Construct the first variable matrix, the second variable matrix, the third variable matrix, the fourth variable matrix and the fifth variable matrix, expressed as: Q[k]=F BB [k]F BB [k] H , D m [k]=Q[k] -1 m,m -Q[k] -1 m,\m C m [k] -1 Q[k] -1 \m,m , Where: Q[k] is the first variable matrix, F BB [k] is the digital precoding matrix of the kth subcarrier, F BB [k] H is the matrix F BB The transpose of [k], C m [k] is the second variable matrix, m is the mth column of the matrix, m,\m is the mth column of the matrix excluding the mth row, σ is the noise power, P is the average signal power in the channel, F RF To simulate the precoding matrix, For D m [k] is the third variable matrix, G m [k] is the fourth variable matrix, H em,n [k] is the fifth variable matrix; A2. Construct a function of the influence value of the phase shifter according to the first variable matrix, the second variable matrix, the third variable matrix, the fourth variable matrix and the fifth variable matrix, which is expressed as: Where: R[k] is the communication rate of the kth subcarrier.

6. The terahertz hybrid precoding method for liquid crystal response delay according to claim 1, characterized in that: In step S3, the approximate optimal precoding matrix under the final liquid crystal phase shifter delay response is obtained according to the function of the influence value of the phase shifter. The specific process is: according to the function of the influence value of the phase shifter, the contribution of the phase shifters connected to different RF chains is isolated to locally optimize the digital precoding and analog precoding, and after optimizing a column of phase shifters, the digital precoding matrix is ​​updated to obtain the approximate optimal precoding matrix under the final liquid crystal phase shifter delay response.

7. The terahertz hybrid precoding method for liquid crystal response delay according to claim 1, characterized in that: In step S4, the communication performance of the hybrid precoding method oriented to the phase shifter response delay is calculated, which is expressed as: Where: R is the communication performance advantage value of the hybrid precoding method, k is the subcarrier number, K is the total number of subcarriers, I is the unit matrix, σ is the noise power, P is the average signal power in the channel, H[k] is the channel of the kth subcarrier, F RF is the simulated precoding matrix, F BB [k] is the digital precoding matrix of the kth subcarrier, is the matrix F BB The transpose of [k].

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