CN113595607A - Hybrid precoding method and system based on reconfigurable holographic super surface - Google Patents

Hybrid precoding method and system based on reconfigurable holographic super surface Download PDF

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CN113595607A
CN113595607A CN202110954014.7A CN202110954014A CN113595607A CN 113595607 A CN113595607 A CN 113595607A CN 202110954014 A CN202110954014 A CN 202110954014A CN 113595607 A CN113595607 A CN 113595607A
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holographic
beam forming
matrix
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coding
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CN113595607B (en
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宋令阳
邸博雅
邓若琪
张雨童
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Peking University
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413—MIMO systems
    • H04B7/0456—Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
    • H04B7/046—Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting taking physical layer constraints into account
    • H04B7/0469—Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting taking physical layer constraints into account taking special antenna structures, e.g. cross polarized antennas into account
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
    • H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
    • H04B7/0617—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal for beam forming
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/08—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station
    • H04B7/0837—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station using pre-detection combining
    • H04B7/0842—Weighted combining
    • H04B7/086—Weighted combining using weights depending on external parameters, e.g. direction of arrival [DOA], predetermined weights or beamforming
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
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    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

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Abstract

The invention discloses a hybrid pre-coding method and a hybrid pre-coding system based on a reconfigurable holographic super surface. The method comprises the following steps: carrying out digital beam forming coding on the target sending signal according to the digital beam forming matrix; inputting a digital beam coding signal into a feed source of the reconfigurable holographic super-surface antenna, enabling a reference wave which is sent by the feed source and carries a target sending signal to enter a metamaterial radiation unit of the reconfigurable holographic super-surface antenna, carrying out holographic beam forming coding on the reference wave by the metamaterial radiation unit according to the holographic beam forming matrix, and sending the holographic beam coding signal to a user. The invention can solve the problems of high antenna manufacturing cost and large power loss in the mobile communication process and simultaneously improve the communication quality.

Description

Hybrid precoding method and system based on reconfigurable holographic super surface
The present application claims priority of chinese patent application entitled "a hybrid precoding method and system based on reconfigurable holographic super surface" filed by chinese patent office at 16/07/2021 under application number 202110807244.0, which is incorporated herein by reference in its entirety.
Technical Field
The invention relates to the field of wireless communication, in particular to a hybrid precoding method and a hybrid precoding system based on a reconfigurable holographic super surface.
Background
In order to implement ubiquitous intelligent information networks, the upcoming sixth generation (6G) wireless communication puts stringent requirements on antenna technology, such as capacity enhancement and precise beam steering. While the ability of both the widely used dish antennas and phased array antennas to achieve these goals has been met, they all have their own inherent drawbacks that have severely hampered their future development. In particular, dish antennas require heavy and expensive beam steering mechanisms, while phased arrays rely heavily on power amplifiers, consume large amounts of power, have complex phase shifting circuits, and numerous phase shifters, especially in the high frequency band. The existing antenna for realizing mobile communication has high manufacturing cost and large power loss, and in the communication process, the beam forming is coded independently, and the communication quality of the antenna needs to be improved.
Disclosure of Invention
Based on the above, the embodiments of the present invention provide a hybrid precoding method and system based on a reconfigurable holographic super surface, which can improve communication quality while solving the problems of high antenna manufacturing cost and large power loss in the mobile communication process.
In order to achieve the purpose, the invention provides the following scheme:
a hybrid precoding method based on a reconfigurable holographic super surface comprises the following steps:
acquiring a target sending signal;
carrying out digital beam forming coding on the target sending signal according to the digital beam forming matrix to obtain a digital beam coding signal;
inputting the digital beam coding signals into a feed source of the reconfigurable holographic super-surface antenna, enabling reference waves which are sent by the feed source and carry the target sending signals to enter a metamaterial radiation unit of the reconfigurable holographic super-surface antenna, and enabling the metamaterial radiation unit to perform holographic beam forming coding on the reference waves according to a holographic beam forming matrix to obtain holographic beam coding signals and sending the holographic beam coding signals to a user.
Optionally, the method for determining the digital beam forming matrix and the holographic beam forming matrix includes:
constructing a digital pre-coding function and a holographic beam forming function;
and taking the minimum mean square error between the signal received by the user and the target transmission signal as a target, and performing alternate iterative solution on the digital pre-coding function and the holographic beam forming function based on a holographic beam forming optimization algorithm to obtain a final digital beam forming matrix and a final holographic beam forming matrix.
Optionally, the digital precoding function specifically includes:
Figure BDA0003219693410000021
s.t.Tr(VHV)≤PT
where V represents a digital beamforming matrix, M is a holographic beamforming matrix, I is an identity matrix, σ2For the noise power at the receiving end of the user,
Figure BDA0003219693410000022
for an equivalent channel matrix, Tr represents the trace of the matrix, L represents the total number of users, VHThe conjugate transpose of V is represented,
Figure BDA0003219693410000031
to represent
Figure BDA0003219693410000032
By conjugate transposition of PTRepresenting the transmit power of the base station.
Optionally, the holographic beam forming function specifically includes:
Figure BDA0003219693410000033
s.t.0≤Mm,n≤1
where V represents a digital beamforming matrix, M is a holographic beamforming matrix, I is an identity matrix, σ2For the noise power at the receiving end of the user,
Figure BDA0003219693410000034
is an equivalent channel matrix, Mm,nThe element representing the mth row and nth column in the holographic beamforming matrix, Tr representing the trace of the matrix, L representing the total number of users,
Figure BDA0003219693410000035
to represent
Figure BDA0003219693410000036
The conjugate transpose of (c).
Optionally, the alternately and iteratively solving the digital precoding function and the holographic beamforming function based on a holographic beamforming optimization algorithm with the minimum mean square error between the signal received by the user and the target transmission signal as a target to obtain a final digital beamforming matrix and a final holographic beamforming matrix specifically includes:
under the current iteration times, acquiring a holographic beam forming matrix under the last iteration times;
substituting the holographic beam forming matrix under the last iteration number into the digital pre-coding function and solving to obtain a digital beam forming matrix under the current iteration number;
substituting the digital beam forming matrix under the current iteration times into the holographic beam forming function, and solving by adopting the holographic beam forming optimization algorithm to obtain the holographic beam forming matrix under the current iteration times;
calculating the mean square error between the signal received by the user under the current iteration number and the target transmission signal based on the digital beam forming matrix under the current iteration number and the holographic beam forming matrix under the current iteration number;
judging whether the mean square error under the current iteration times is smaller than a set threshold value or not;
if so, determining the digital beam forming matrix under the current iteration number as a final digital beam forming matrix, and determining the holographic beam forming matrix under the current iteration number as a final holographic beam forming matrix;
if not, the next iteration is carried out.
The invention also provides a hybrid pre-coding system based on the reconfigurable holographic super surface, which comprises the following components:
the sending signal acquisition module is used for acquiring a target sending signal;
the digital beam coding module is used for carrying out digital beam forming coding on the target sending signal according to the digital beam forming matrix to obtain a digital beam coding signal;
the holographic beam coding module is used for inputting the digital beam coding signals into a feed source of the reconfigurable holographic super-surface antenna, reference waves which are sent by the feed source and carry target sending signals enter a metamaterial radiation unit of the reconfigurable holographic super-surface antenna, the metamaterial radiation unit carries out holographic beam forming coding on the reference waves according to a holographic beam forming matrix to obtain holographic beam coding signals, and the holographic beam coding signals are sent to a user;
optionally, the hybrid precoding system based on the reconfigurable holographic super surface further includes:
a matrix determination module to determine the digital beamforming matrix and the holographic beamforming matrix; the matrix determination module specifically includes:
the function constructing unit is used for constructing a digital pre-coding function and a holographic beam forming function;
and the alternate solving unit is used for alternately and iteratively solving the digital pre-coding function and the holographic beam forming function based on a holographic beam forming optimization algorithm by taking the minimum mean square error between the signal received by the user and the target transmission signal as a target so as to obtain a final digital beam forming matrix and a final holographic beam forming matrix.
Optionally, the digital precoding function in the function constructing unit specifically includes:
Figure BDA0003219693410000051
s.t.Tr(VHV)≤PT
where V represents a digital beamforming matrix, M is a holographic beamforming matrix, I is an identity matrix, σ2For the noise power at the receiving end of the user,
Figure BDA0003219693410000052
for an equivalent channel matrix, Tr represents the trace of the matrix, L represents the total number of users, VHThe conjugate transpose of V is represented,
Figure BDA0003219693410000053
to represent
Figure BDA0003219693410000054
By conjugate transposition of PTRepresenting the transmit power of the base station.
Optionally, the holographic beam forming function in the function constructing unit specifically includes:
Figure BDA0003219693410000055
s.t.0≤Mm,n≤1
where V denotes a digital beamforming matrix, M is a holographic beamforming matrix, σ2For the noise power at the receiving end of the user,
Figure BDA0003219693410000056
is an equivalent channel matrix, Mm,nThe element representing the mth row and nth column in the holographic beamforming matrix, Tr representing the trace of the matrix, L representing the total number of users,
Figure BDA0003219693410000057
to represent
Figure BDA0003219693410000058
The conjugate transpose of (c).
Optionally, the alternating solving unit specifically includes:
the matrix acquisition subunit is used for acquiring the holographic beam forming matrix under the previous iteration number under the current iteration number;
the first solving subunit is used for substituting the holographic beam forming matrix under the last iteration number into the digital precoding function and solving to obtain a digital beam forming matrix under the current iteration number;
the second solving subunit is used for substituting the digital beam forming matrix under the current iteration number into the holographic beam forming function and adopting the holographic beam forming optimization algorithm to solve to obtain the holographic beam forming matrix under the current iteration number;
the mean square error calculation subunit is used for calculating the mean square error between the signal received by the user under the current iteration number and the target transmission signal based on the digital beam forming matrix under the current iteration number and the holographic beam forming matrix under the current iteration number;
the threshold judging subunit is used for judging whether the mean square error under the current iteration times is smaller than a set threshold;
the optimal matrix determining subunit is used for determining the digital beam forming matrix under the current iteration number as a final digital beam forming matrix and determining the holographic beam forming matrix under the current iteration number as a final holographic beam forming matrix if the mean square error under the current iteration number is smaller than a set threshold; and if the mean square error under the current iteration times is not less than the set threshold, performing the next iteration.
Compared with the prior art, the invention has the beneficial effects that:
the embodiment of the invention provides a hybrid pre-coding method and a hybrid pre-coding system based on a reconfigurable holographic super surface, when a base station communicates with a user, digital beam forming coding is carried out on a target sending signal to be sent by the base station according to a digital beam forming matrix, the digital beam coding signal is input into a feed source of a reconfigurable holographic super surface antenna, a reference wave which is sent by the feed source and carries the target sending signal enters a metamaterial radiation unit of the reconfigurable holographic super surface antenna, the metamaterial radiation unit carries out holographic beam forming coding on the reference wave according to the holographic beam forming matrix, and the holographic beam coding signal is sent to the user. The invention adopts the reconfigurable holographic super-surface antenna to realize holographic beam forming coding, solves the problems of large volume, high power consumption and high hardware cost of the existing antenna (such as a phased array antenna) with beam forming capability, adopts the digital beam forming matrix and the holographic beam forming matrix to carry out beam forming hybrid coding, and improves the communication quality compared with a single coding mode. Therefore, the invention can solve the problems of high antenna manufacturing cost and large power loss in the mobile communication process and simultaneously improve the communication quality.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
FIG. 1 is a flow chart of a hybrid precoding method based on a reconfigurable holographic super surface according to an embodiment of the present invention;
fig. 2 is a flowchart of a digital beam forming matrix and a method for determining the holographic beam forming matrix according to an embodiment of the present invention;
FIG. 3 is a schematic structural diagram of a reconfigurable holographic super-surface antenna provided by an embodiment of the invention;
fig. 4 is a schematic structural diagram of a metamaterial radiation unit provided in an embodiment of the present invention;
fig. 5 is a schematic structural diagram of a complementary capacitance-inductance resonant ring according to an embodiment of the present invention;
FIG. 6 is a schematic diagram of a reconfigurable holographic super surface antenna provided by embodiments of the present invention;
fig. 7 is a flowchart of an MMSE hybrid precoding joint optimization algorithm provided in an embodiment of the present invention;
FIG. 8 is a block diagram of a hybrid pre-coding system based on a reconfigurable holographic super surface according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
The dish antenna and the phased array antenna have the defects of high cost, large power loss and the like, and in order to meet the data requirement of mobile equipment with exponential growth in a 6G wireless system in the future, a more economic and efficient antenna technology is needed. Among the existing antenna technologies, the holographic antenna is a small-sized, low-power-consumption planar antenna, and is receiving increasing attention due to its multi-beam control capability with low manufacturing cost and low hardware cost. Specifically, the holographic antenna uses a metal patch to construct a holographic pattern on the surface, and records the interference between a reference wave and a target wave according to the interference principle. The radiation characteristics of the reference wave can then be varied by means of the holographic pattern to produce the desired radiation direction.
However, as mobile devices have increased explosively, conventional holographic antennas have presented significant challenges because once the holographic pattern is established, the radiation pattern of the conventional holographic antenna is fixed and thus cannot meet the requirements of mobile communications. Due to the controllability of metamaterials, emerging Reconfigurable Holographic Surface (RHS) technology shows great potential in the aspect of improving the defects of traditional holographic antennas. The RHS is an ultra-light thin plane antenna, and a plurality of metamaterial radiating elements are embedded on the surface of the antenna. In particular, the RHS is excited by the reference wave generated by the antenna feed in the form of a surface wave, making it possible to manufacture an RHS based on Printed Circuit Board (PCB) technology with a compact structure. According to the hologram pattern, each radiation element can generate a desired radiation direction by electrically controlling the radiation amplitude of the reference wave. Therefore, compared with the traditional dish antenna and the traditional phased array antenna, the RHS can realize dynamic beam forming without a heavy mechanical movement device and a complex phase shift circuit, can greatly save the manufacturing cost and the power loss of the antenna, and is very convenient to install due to a light and thin structure.
Fig. 1 is a flowchart of a hybrid precoding method based on a reconfigurable holographic super surface according to an embodiment of the present invention. Referring to fig. 1, the hybrid precoding method based on the reconfigurable holographic super surface provided by the embodiment includes:
step 101: and acquiring a target sending signal.
Step 102: and carrying out digital beam forming coding on the target sending signal according to the digital beam forming matrix to obtain a digital beam coding signal.
Step 103: inputting the digital beam coding signals into a feed source of the reconfigurable holographic super-surface antenna, enabling reference waves which are sent by the feed source and carry the target sending signals to enter a metamaterial radiation unit of the reconfigurable holographic super-surface antenna, and enabling the metamaterial radiation unit to perform holographic beam forming coding on the reference waves according to a holographic beam forming matrix to obtain holographic beam coding signals and sending the holographic beam coding signals to a user.
Fig. 2 is a flowchart of a digital beamforming matrix and a method for determining the holographic beamforming matrix according to an embodiment of the present invention. Referring to fig. 2, the determination method of the digital beamforming matrix and the holographic beamforming matrix is as follows:
step 201: and constructing a digital pre-coding function and a holographic beam forming function.
The digital precoding function is specifically:
Figure BDA0003219693410000091
s.t.Tr(VHV)≤PT
where V represents a digital beamforming matrix, M is a holographic beamforming matrix, I is an identity matrix, σ2For the noise power at the receiving end of the user,
Figure BDA0003219693410000092
for an equivalent channel matrix, Tr represents the trace of the matrix, L represents the total number of users, VHThe conjugate transpose of V is represented,
Figure BDA0003219693410000101
to represent
Figure BDA0003219693410000102
By conjugate transposition of PTRepresenting the transmit power of the base station.
The holographic beam forming function is specifically:
Figure BDA0003219693410000103
s.t.0≤Mm,n≤1
where V represents a digital beamforming matrix, M is a holographic beamforming matrix, I is an identity matrix, σ2For the noise power at the receiving end of the user,
Figure BDA0003219693410000104
is an equivalent channel matrix, Mm,nRepresenting the elements of the mth row and nth column in the holographic beamforming matrix, M ═ Mm,nTr denotes the trace of the matrix, L denotes the total number of users,
Figure BDA0003219693410000105
to represent
Figure BDA0003219693410000106
The conjugate transpose of (c).
Step 202: and taking the minimum mean square error between the signal received by the user and the target transmission signal as a target, and performing alternate iterative solution on the digital pre-coding function and the holographic beam forming function based on a holographic beam forming optimization algorithm to obtain a final digital beam forming matrix and a final holographic beam forming matrix. The method specifically comprises the following steps:
1) and under the current iteration times, acquiring the holographic beam forming matrix under the last iteration time.
2) And substituting the holographic beam forming matrix under the last iteration number into the digital pre-coding function and solving to obtain the digital beam forming matrix under the current iteration number.
3) And substituting the digital beam forming matrix under the current iteration number into the holographic beam forming function, and solving by adopting the holographic beam forming optimization algorithm to obtain the holographic beam forming matrix under the current iteration number.
4) And calculating the mean square error between the signal received by the user under the current iteration number and the target transmission signal based on the digital beam forming matrix under the current iteration number and the holographic beam forming matrix under the current iteration number.
5) Judging whether the mean square error under the current iteration times is smaller than a set threshold value or not; if so, determining the digital beam forming matrix under the current iteration number as a final digital beam forming matrix, and determining the holographic beam forming matrix under the current iteration number as a final holographic beam forming matrix; if not, the next iteration is carried out.
As shown in fig. 3, the reconfigurable holographic super-surface antenna in this embodiment includes a feed source 1, a parallel plate waveguide 2, and a metamaterial radiation unit array 3, where the metamaterial radiation unit array 3 includes a plurality of metamaterial radiation units arranged in an array. As shown in fig. 4, the metamaterial radiating unit includes a microstrip line 4, a dielectric layer 5 and a metal ground 6, and the microstrip line 4 is a microstrip line embedded with a complementary capacitive-inductive resonant ring. As shown in fig. 5, the complementary capacitance-inductance resonant ring includes a metal patch 7 and a varactor diode 8. The principle of the reconfigurable holographic super-surface antenna is shown in fig. 6, wherein a feed source 1 emits electromagnetic waves, the electromagnetic waves are transmitted on a parallel plate waveguide in the form of surface waves a, in the transmission process, a metamaterial radiation unit is controlled by a variable capacitance diode 8, and the radiation amplitude of the electromagnetic waves transmitted to the metamaterial radiation unit can be adjusted by adjusting the voltage of the variable capacitance diode 8 applied to each metamaterial radiation unit, so that the bias voltage applied to the variable capacitance diode 8 in the metamaterial radiation unit is adjusted to a target value, and the amplitude value of the electromagnetic waves radiated on the metamaterial radiation unit is a target amplitude value.
In practical application, one specific implementation process of the hybrid precoding method based on the reconfigurable holographic super surface is as follows:
considering a base station (transmitting device) of a reconfigurable holographic super surface (RHS) antenna with L feed sources to communicate with L users, the positions of the L mobile users relative to the transmitting device are the directions of the transmission beams required by the transmitting device. The RHS is assumed to be composed of M × N metamaterial radiation elements, and the radiation amplitude of each radiation element is [0, 1%]The transmission channel between each radiating element of the RHS and each user
Figure BDA0003219693410000111
The total channel matrix between the base station and each user l is represented by HlExpressed in dimensions of 1 × MN; suppose that the signal sent by the base station to the user is s, where s is an L-dimensional column vector and s islRepresenting the signal sent to user/. The base station firstly carries out digital beam forming coding on a signal (target sending signal) sent to a user according to a digital beam forming matrix, then the coded signal (the digital beam coding signal) is input into a feed source of the RHS, and the feed source sends out a holographic beam forming (namely, a metamaterial radiation unit on the M-th row and the n-th column according to an element M in the holographic beam forming matrix) of a reference wave carrying the target sending signal and passing through the RHSm,nRadiating reference wave energy into the free space to form a beam with a fixed direction), and then transmitting the reference wave energy to each user, the received signal of each user can be expressed as:
Figure BDA0003219693410000121
wherein, ylFor signals received by the l-th user, WlIs the fixed received signal demodulation matrix for the ith user,
Figure BDA0003219693410000122
is the conjugate transpose of the fixed demodulation matrix of the received signal for the L-th user, V is the digital beamforming matrix of size K x L, V is the fixed demodulation matrix of the L-th userlIs the l column of V corresponding to the l user, M is a group element
Figure BDA0003219693410000123
Forming a matrix of size MN × K, KsIs the propagation vector of the reference wave propagating on the surface of the RHS,
Figure BDA0003219693410000124
is the distance vector, z, from the kth feed to the (m, n) th radiation elementlFor Gaussian white noise in the channel, the conjugate transpose of the equivalent channel matrix of the l-th user is abbreviated as
Figure BDA0003219693410000125
Vl′Column l's representing Vl′Representing the signal sent to user i'.
To minimize the Mean square Error value of the signal received by each user and the signal transmitted by the base station, the Minimum Mean Squared Error (MMSE) problem can be modeled as:
Figure BDA0003219693410000126
Figure BDA0003219693410000127
y is a signal vector received by all users, is an L-dimensional column vector, and the second term is a base station transmitting total power limiting condition.
The digital beam forming and holographic beam forming joint optimization design algorithm is described as follows:
(1) constructing a digital precoding function:
for a fixed holographic beamforming matrix, the MMSE problem can be written as follows:
Figure BDA0003219693410000131
s.t.Tr(VHV)≤PT
where V represents a digital beamforming matrix, M is a holographic beamforming matrix, I is an identity matrix, σ2For the noise power at the receiving end of each user,
Figure BDA0003219693410000132
is an equivalent channel matrix with dimension L multiplied by MN between RHS and users, Tr represents the trace of the matrix, L represents the total number of users, PTRepresents the transmit power of the base station; the superscript H denotes a conjugate transpose, e.g. VHThe conjugate transpose of V is represented,
Figure BDA0003219693410000133
to represent
Figure BDA0003219693410000134
The conjugate transpose of (1);
Figure BDA0003219693410000135
h in (a) denotes a channel matrix.
Then V that minimizes the objective function is:
Figure BDA0003219693410000136
(2) holographic beamforming function construction:
for a fixed digital beamforming matrix, the MMSE problem can be written as follows:
Figure BDA0003219693410000137
s.t.0≤Mm,n≤1
since M is a real number, the above problem can be solved by a linear programming method.
(3) And iteratively optimizing the digital pre-coding function and the digital pre-coding function by using a computer to obtain a digital beam forming matrix and the holographic beam forming matrix.
And (3) on the basis of the functions constructed in the steps (1) and (2), the MMSE hybrid precoding joint optimization algorithm is designed, and the problem of maximizing the total data rate of the users is solved in an iterative manner. In particular, in maintaining the holographic beamforming matrix { M }m,nIn the case of fixation, can pass V*The calculation formula of (a) obtains the digital beamforming matrix V. Then using holographic beam forming optimization algorithm to pair { Mm,nAnd (6) optimizing. The optimized digital beamformer and holographic beamformer are used as initial solutions. In each subsequent iteration, the two sub-problems are solved alternately. Until the value difference of the mean square error value between two adjacent iterations is less than a predefined threshold, the iteration is completed, and a digital beam forming matrix V is obtained*And holographic beamforming matrix
Figure BDA0003219693410000141
The specific process is shown in fig. 7.
The hybrid precoding method based on the reconfigurable holographic super surface of the embodiment has the following advantages:
1. thereby traditional dish antenna rotates through bulky mechanical device control antenna and realizes that beam control is complicated not only structure and later maintenance cost are high, compares in this mode, and the RHS size is little, makes to use PCB technique to make its compact structure and frivolous, and manufacturing cost greatly reduced easily direct mount on emitter, adopts the mode of electric control can reach fine dynamic multi-beam control effect, therefore the RHS is applicable to multi-user mobile communication very much.
And 2, the RHS has low power consumption and low hardware cost. Although the phased array antenna also controls the beam direction by using electricity, the phased array relies on a large number of phase shifters to control the phase of electromagnetic waves in each antenna, and a large number of power amplifiers are also required, so that the phased array antenna requires a complicated phase shifting circuit, and has large power loss and high hardware cost. Compared with the prior art, the RHS does not need a phase shifter and a complex phase shifting circuit, and can control the difference of the electromagnetic wave energy radiated by each radiating unit by using the switch state of the diode, namely, the beam control can be completed in an amplitude modulation mode, so that the RHS is used for assisting multi-user communication, the power consumption is low, the hardware cost is low, and the RHS has great advantages compared with a phased array antenna.
3. And the digital beam forming matrix and the holographic beam forming matrix are adopted for carrying out beam forming hybrid coding, so that compared with a single coding mode, the communication quality is improved.
4. The bit error rate of the system can be reduced by using MMSE as a precoding target, so that the signals received by a receiver are as close to the data transmitted by the transmitting end as possible, and the communication quality is further improved.
The invention also provides a hybrid pre-coding system based on the reconfigurable holographic super surface, and FIG. 8 is a structural diagram of the hybrid pre-coding system based on the reconfigurable holographic super surface provided by the embodiment of the invention.
Referring to fig. 8, the system comprises:
a transmission signal acquiring module 801, configured to acquire a target transmission signal.
The digital beam coding module 802 is configured to perform digital beam forming coding on the target transmission signal according to the digital beam forming matrix to obtain a digital beam coding signal.
The holographic beam coding module 803 is configured to input the digital beam coding signal into a feed source of the reconfigurable holographic super-surface antenna, where a reference wave sent by the feed source and carrying the target sending signal enters a metamaterial radiation unit of the reconfigurable holographic super-surface antenna, and the metamaterial radiation unit performs holographic beam forming coding on the reference wave according to a holographic beam forming matrix to obtain a holographic beam coding signal, and sends the holographic beam coding signal to a user.
As an optional implementation, the system further includes:
a matrix determination module 804 for determining the digital beamforming matrix and the holographic beamforming matrix; the matrix determining module 804 specifically includes:
and the function construction unit is used for constructing a digital pre-coding function and a holographic beam forming function.
And the alternate solving unit is used for alternately and iteratively solving the digital pre-coding function and the holographic beam forming function based on a holographic beam forming optimization algorithm by taking the minimum mean square error between the signal received by the user and the target transmission signal as a target so as to obtain a final digital beam forming matrix and a final holographic beam forming matrix.
As an optional implementation manner, the digital precoding function in the function constructing unit specifically includes:
Figure BDA0003219693410000161
s.t.Tr(VHV)≤PT
where V represents a digital beamforming matrix, M is a holographic beamforming matrix, I is an identity matrix, σ2For users to connectThe noise power at the receiving end is set,
Figure BDA0003219693410000162
for an equivalent channel matrix, Tr represents the trace of the matrix, L represents the total number of users, VHThe conjugate transpose of V is represented,
Figure BDA0003219693410000163
to represent
Figure BDA0003219693410000164
By conjugate transposition of PTRepresenting the transmit power of the base station.
As an optional implementation manner, the holographic beamforming function in the function constructing unit specifically includes:
Figure BDA0003219693410000165
s.t.0≤Mm,n≤1
where V denotes a digital beamforming matrix, M is a holographic beamforming matrix, σ2For the noise power at the receiving end of the user,
Figure BDA0003219693410000166
is an equivalent channel matrix, Mm,nThe element representing the mth row and nth column in the holographic beamforming matrix, Tr representing the trace of the matrix, L representing the total number of users,
Figure BDA0003219693410000167
to represent
Figure BDA0003219693410000168
The conjugate transpose of (c).
As an optional implementation manner, the alternating solution unit specifically includes:
and the matrix acquisition subunit is used for acquiring the holographic beam forming matrix under the previous iteration number under the current iteration number.
And the first solving subunit is used for substituting the holographic beam forming matrix under the last iteration number into the digital precoding function and solving to obtain the digital beam forming matrix under the current iteration number.
And the second solving subunit is used for substituting the digital beam forming matrix under the current iteration number into the holographic beam forming function, and adopting the holographic beam forming optimization algorithm to solve to obtain the holographic beam forming matrix under the current iteration number.
And the mean square error calculation subunit is used for calculating the mean square error between the signal received by the user under the current iteration number and the target transmission signal based on the digital beam forming matrix under the current iteration number and the holographic beam forming matrix under the current iteration number.
And the threshold judgment subunit is used for judging whether the mean square error under the current iteration number is smaller than a set threshold.
The optimal matrix determining subunit is used for determining the digital beam forming matrix under the current iteration number as a final digital beam forming matrix and determining the holographic beam forming matrix under the current iteration number as a final holographic beam forming matrix if the mean square error under the current iteration number is smaller than a set threshold; and if the mean square error under the current iteration times is not less than the set threshold, performing the next iteration.
The hybrid pre-coding system based on the reconfigurable holographic super-surface solves the problems of large volume, high power consumption and high hardware cost of the conventional antenna (such as a phased array antenna) with beam forming capability; and the MMSE mixed precoding is realized based on the RHS, so that the minimum mean square error of the data received by the receiver and the data sent by the receiver can be minimized, and the communication quality is improved.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.

Claims (10)

1. A hybrid precoding method based on a reconfigurable holographic super surface is characterized by comprising the following steps:
acquiring a target sending signal;
carrying out digital beam forming coding on the target sending signal according to the digital beam forming matrix to obtain a digital beam coding signal;
inputting the digital beam coding signals into a feed source of the reconfigurable holographic super-surface antenna, enabling reference waves which are sent by the feed source and carry the target sending signals to enter a metamaterial radiation unit of the reconfigurable holographic super-surface antenna, and enabling the metamaterial radiation unit to perform holographic beam forming coding on the reference waves according to a holographic beam forming matrix to obtain holographic beam coding signals and sending the holographic beam coding signals to a user.
2. The hybrid precoding method of claim 1, wherein the digital beamforming matrix and the holographic beamforming matrix are determined by:
constructing a digital pre-coding function and a holographic beam forming function;
and taking the minimum mean square error between the signal received by the user and the target transmission signal as a target, and performing alternate iterative solution on the digital pre-coding function and the holographic beam forming function based on a holographic beam forming optimization algorithm to obtain a final digital beam forming matrix and a final holographic beam forming matrix.
3. The hybrid precoding method based on the reconfigurable holographic super surface as claimed in claim 2, wherein the digital precoding function is specifically:
Figure FDA0003219693400000011
s.t.Tr(VHV)≤PT
where V represents a digital beamforming matrix, M is a holographic beamforming matrix, I is an identity matrix, σ2For the noise power at the receiving end of the user,
Figure FDA0003219693400000021
for an equivalent channel matrix, Tr represents the trace of the matrix, L represents the total number of users, VHThe conjugate transpose of V is represented,
Figure FDA0003219693400000022
to represent
Figure FDA0003219693400000023
By conjugate transposition of PTRepresenting the transmit power of the base station.
4. The hybrid precoding method of claim 2, wherein the holographic beamforming function is specifically:
Figure FDA0003219693400000024
s.t.0≤Mm,n≤1
where V represents a digital beamforming matrix, M is a holographic beamforming matrix, I is an identity matrix, σ2For the noise power at the receiving end of the user,
Figure FDA0003219693400000025
is an equivalent channel matrix, Mm,nDenotes an element of an m-th row and an n-th column in the hologram beam forming matrix, and Tr denotesThe trace of the matrix, L represents the total number of users,
Figure FDA0003219693400000026
to represent
Figure FDA0003219693400000027
The conjugate transpose of (c).
5. The hybrid precoding method based on the reconfigurable holographic super surface of claim 2, wherein the alternating iterative solution of the digital precoding function and the holographic beamforming function based on a holographic beamforming optimization algorithm with a minimum mean square error between a signal received by a user and a target transmission signal as a target to obtain a final digital beamforming matrix and a final holographic beamforming matrix specifically comprises:
under the current iteration times, acquiring a holographic beam forming matrix under the last iteration times;
substituting the holographic beam forming matrix under the last iteration number into the digital pre-coding function and solving to obtain a digital beam forming matrix under the current iteration number;
substituting the digital beam forming matrix under the current iteration times into the holographic beam forming function, and solving by adopting the holographic beam forming optimization algorithm to obtain the holographic beam forming matrix under the current iteration times;
calculating the mean square error between the signal received by the user under the current iteration number and the target transmission signal based on the digital beam forming matrix under the current iteration number and the holographic beam forming matrix under the current iteration number;
judging whether the mean square error under the current iteration times is smaller than a set threshold value or not;
if so, determining the digital beam forming matrix under the current iteration number as a final digital beam forming matrix, and determining the holographic beam forming matrix under the current iteration number as a final holographic beam forming matrix;
if not, the next iteration is carried out.
6. A hybrid precoding system based on a reconfigurable holographic super surface, comprising:
the sending signal acquisition module is used for acquiring a target sending signal;
the digital beam coding module is used for carrying out digital beam forming coding on the target sending signal according to the digital beam forming matrix to obtain a digital beam coding signal;
and the holographic beam coding module is used for inputting the digital beam coding signals into a feed source of the reconfigurable holographic super-surface antenna, reference waves which are sent by the feed source and carry the target sending signals enter a metamaterial radiation unit of the reconfigurable holographic super-surface antenna, and the metamaterial radiation unit carries out holographic beam forming coding on the reference waves according to a holographic beam forming matrix to obtain holographic beam coding signals and sends the holographic beam coding signals to a user.
7. The hybrid precoding system of claim 6, further comprising:
a matrix determination module to determine the digital beamforming matrix and the holographic beamforming matrix; the matrix determination module specifically includes:
the function constructing unit is used for constructing a digital pre-coding function and a holographic beam forming function;
and the alternate solving unit is used for alternately and iteratively solving the digital pre-coding function and the holographic beam forming function based on a holographic beam forming optimization algorithm by taking the minimum mean square error between the signal received by the user and the target transmission signal as a target so as to obtain a final digital beam forming matrix and a final holographic beam forming matrix.
8. The hybrid precoding system of claim 7, wherein the digital precoding function in the function constructing unit is specifically:
Figure FDA0003219693400000041
s.t.Tr(VHV)≤PT
where V represents a digital beamforming matrix, M is a holographic beamforming matrix, I is an identity matrix, σ2For the noise power at the receiving end of the user,
Figure FDA0003219693400000042
for an equivalent channel matrix, Tr represents the trace of the matrix, L represents the total number of users, VHThe conjugate transpose of V is represented,
Figure FDA0003219693400000043
to represent
Figure FDA0003219693400000044
By conjugate transposition of PTRepresenting the transmit power of the base station.
9. The hybrid precoding system of claim 7, wherein the holographic beamforming function in the function constructing unit is specifically:
Figure FDA0003219693400000045
s.t.0≤Mm,n≤1
where V denotes a digital beamforming matrix, M is a holographic beamforming matrix, σ2For the noise power at the receiving end of the user,
Figure FDA0003219693400000046
is an equivalent channel matrix, Mm,nRepresenting holographic beamforming momentsThe element in the mth row and nth column of the array, Tr represents the trace of the matrix, L represents the total number of users,
Figure FDA0003219693400000047
to represent
Figure FDA0003219693400000051
The conjugate transpose of (c).
10. The hybrid precoding system of claim 7, wherein the alternating solving unit specifically comprises:
the matrix acquisition subunit is used for acquiring the holographic beam forming matrix under the previous iteration number under the current iteration number;
the first solving subunit is used for substituting the holographic beam forming matrix under the last iteration number into the digital precoding function and solving to obtain a digital beam forming matrix under the current iteration number;
the second solving subunit is used for substituting the digital beam forming matrix under the current iteration number into the holographic beam forming function and adopting the holographic beam forming optimization algorithm to solve to obtain the holographic beam forming matrix under the current iteration number;
the mean square error calculation subunit is used for calculating the mean square error between the signal received by the user under the current iteration number and the target transmission signal based on the digital beam forming matrix under the current iteration number and the holographic beam forming matrix under the current iteration number;
the threshold judging subunit is used for judging whether the mean square error under the current iteration times is smaller than a set threshold;
the optimal matrix determining subunit is used for determining the digital beam forming matrix under the current iteration number as a final digital beam forming matrix and determining the holographic beam forming matrix under the current iteration number as a final holographic beam forming matrix if the mean square error under the current iteration number is smaller than a set threshold; and if the mean square error under the current iteration times is not less than the set threshold, performing the next iteration.
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