CN113347727B - Base station and wireless information and energy cooperative transmission system - Google Patents

Base station and wireless information and energy cooperative transmission system Download PDF

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CN113347727B
CN113347727B CN202110501001.4A CN202110501001A CN113347727B CN 113347727 B CN113347727 B CN 113347727B CN 202110501001 A CN202110501001 A CN 202110501001A CN 113347727 B CN113347727 B CN 113347727B
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energy
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reflecting surface
base station
information
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CN113347727A (en
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程亚军
彭薇
江涛
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Huazhong University of Science and Technology
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Huazhong University of Science and Technology
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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
    • H04B7/04013—Intelligent reflective surfaces
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/50—Allocation or scheduling criteria for wireless resources
    • H04W72/54—Allocation or scheduling criteria for wireless resources based on quality criteria
    • H04W72/543—Allocation or scheduling criteria for wireless resources based on quality criteria based on requested quality, e.g. QoS
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J50/00—Circuit arrangements or systems for wireless supply or distribution of electric power
    • H02J50/20—Circuit arrangements or systems for wireless supply or distribution of electric power using microwaves or radio frequency waves
    • 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
    • H04B7/0426—Power distribution
    • 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
    • H04B7/14—Relay systems
    • H04B7/145—Passive relay systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/04—Wireless resource allocation
    • H04W72/044—Wireless resource allocation based on the type of the allocated resource
    • H04W72/0446—Resources in time domain, e.g. slots or frames
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/04—Wireless resource allocation
    • H04W72/044—Wireless resource allocation based on the type of the allocated resource
    • H04W72/0473—Wireless resource allocation based on the type of the allocated resource the resource being transmission power
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/50—Allocation or scheduling criteria for wireless resources
    • H04W72/54—Allocation or scheduling criteria for wireless resources based on quality criteria
    • H04W72/542—Allocation or scheduling criteria for wireless resources based on quality criteria using measured or perceived quality

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  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Quality & Reliability (AREA)
  • Power Engineering (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

The invention discloses a base station and a wireless information and energy cooperative transmission system, and belongs to the field of wireless communication. The method comprises the following steps: determining a time factor tau and a power factor rho according to the real-time service quality requirement of a user side, taking tau T as a first stage, taking (1-tau) T as a second stage, and taking P astIs divided into PtAnd (1-. rho) Pt(ii) a In a first phase, a beam w is transmitted by energyEEnergy ρ PtTo the intelligent reflecting surface for energy transmission, while transmitting w via the information beamIEnergy (1-rho) PtTransmitting the signal to a user terminal for signal transmission; in the second stage, the beam w is transmitted by informationuAll energy is delivered to the user side. The invention combines time switching and power distribution, the time switching realizes the state switching of the intelligent reflecting surface, and plays a key role in the energy absorption of the intelligent reflecting surface and the energy efficiency of a system; the power distribution ensures the real-time service quality of the user terminal, improves the energy collection of the intelligent reflecting surface in the energy absorption stage, and has great influence on the energy absorption of the intelligent reflecting surface, the service quality of the user terminal and the energy efficiency of the system.

Description

Base station and wireless information and energy cooperative transmission system
Technical Field
The invention belongs to the field of wireless communication, and particularly relates to a base station and a wireless information and energy cooperative transmission system.
Background
To realize an energy-efficient communication system, a passive transmission mode based on a low-energy-consumption and low-cost intelligent reflecting surface is considered to be one of the most potential and revolutionary technologies. The conventional information and energy cooperative transmission system has the problems of limited system capacity, low system energy efficiency and the like, and is assisted by introducing an intelligent reflecting surface. Patent CN112332548A, "a wireless energy transmission method and system", applies an intelligent reflection surface to the field of energy transmission, and proposes the design of energy beam and an energy transmission mechanism of first absorption and then reflection, so as to realize efficient energy transmission. However, the patent is only suitable for energy transmission, does not consider information transmission, and has relatively limited application fields and scenes.
After the intelligent Reflecting surface is introduced, the energy supply problem exists, and the energy autonomy of the intelligent Reflecting surface is proposed by 'Wireless Power Integrated 1 reagent Reflecting surface for Enhancing Wireless Communications'. But it only pursues the maximization of system throughput and does not consider the real-time service quality of the user terminal. Under the mechanism, a user may not obtain information within a certain time period, and all energy is used for energy supply of the intelligent reflecting surface.
Disclosure of Invention
Aiming at the defects and improvement requirements of the prior art, the invention provides a base station and a wireless information and energy cooperative transmission system, aiming at realizing energy autonomy of an intelligent reflecting surface by combining time and power distribution, improving the energy efficiency of the system, having stronger practicability and being applicable to the fields of wireless sensor networks, industrial Internet of things and the like.
To achieve the above object, according to a first aspect of the present invention, there is provided a base station comprising:
a processor, configured to determine a time factor τ and a power factor ρ according to a user-side real-time quality of service requirement, where τ is greater than 0 and less than 1, ρ is greater than 0 and less than 1, τ T is used as a first stage, T (1- τ) is used as a second stage, and the transmission power P of the base station is used astIs divided into PtAnd (1-. rho) PtT represents a period of information transmission from the base station to the user terminal;
an antenna array for passing the energy beam vector w in the first stageEEnergy ρ PtTransmitted to the intelligent reflecting surface for energy transmission, and simultaneously the residual energy (1-rho) PtFor signal transmission by means of an information beam vector wITransmitting the information to the user terminal; in the second stage, all energy is used for information transmission, and under the auxiliary channel of the intelligent reflecting surface, the beam vector w is passeduGeneral informationThe information is delivered to the user side.
Preferably, the processor determines the time factor τ and the power factor ρ under the following constraint conditions with the aim of maximizing the system energy efficiency;
the constraint conditions include: (1) the information beam transmission vector and the energy transmission beam vector of the first stage of the base station are optimal; (2) the second stage optimizes the information transmission beam vector of the base station and the phase of the intelligent reflecting surface; (3) the signal-to-noise ratio of the user side at each stage meets the required threshold; (4) the intelligent reflecting surface in the first stage absorbs energy to meet the energy consumption in the second stage.
Has the advantages that: according to the invention, the signal-to-noise ratio of the user side is used as the real-time service quality index of the user side, and the time factor tau and the power factor rho are determined by adopting the mode, so that the energy efficiency of the system can be maximized, the real-time service quality requirement of the user side can be met, the energy supply of the intelligent reflecting surface is realized, and the energy autonomy of the intelligent reflecting surface is realized.
Preferably, the system energy efficiency EE calculation formula is as follows:
Figure GDA0003513132970000031
Figure GDA0003513132970000032
Figure GDA0003513132970000033
wherein R is1(ρ, wI) represents the reachable rate of the first-stage user terminal, R2(wuPhi) indicates the achievable rate of the second-stage ue, PeRepresenting the energy consumption of a single antenna of the base station, M representing the number of antennas in the antenna array, gamma1(ρ，wI) Representing the signal-to-noise ratio, gamma, of the first stage user terminal2(wuPhi) represents the signal-to-noise ratio of the second-stage user terminal, B represents the information bandwidth,
Figure GDA0003513132970000034
indicating that the object in parentheses is expected and phi indicates the smart reflector phase.
Preferably, the optimal information beam and energy beam vectors
Figure GDA0003513132970000035
And
Figure GDA0003513132970000036
the calculation formula is as follows:
Figure GDA0003513132970000037
Figure GDA0003513132970000038
Figure GDA0003513132970000039
Figure GDA00035131329700000310
wherein, γ1(ρ，wI) Representing the signal-to-noise ratio of the first stage subscriber terminal, Er(τ，ρ，wE，wI) Representing the energy absorbed by the intelligent reflecting surface in the first stage, sigma2Representing the noise of the user terminal, g representing the channel between the base station and the user terminal, H representing the channel between the base station and the intelligent reflecting surface,
Figure GDA00035131329700000311
indicating that objects within the curly brackets are expected.
Preferably, the optimal information beam vector
Figure GDA0003513132970000041
And optimum phase phi*The calculation formula is as follows：
Figure GDA0003513132970000042
Figure GDA0003513132970000043
h(Φ)＝zΦH
Wherein, γ2(wuPhi) represents the signal-to-noise ratio of the second stage user terminal, H (phi) represents the equivalent auxiliary channel under the assistance of the intelligent reflecting surface, z represents the channel between the intelligent reflecting surface and the user terminal, phi represents the phase of the intelligent reflecting surface, and H represents the channel between the base station and the intelligent reflecting surface.
Preferably, the energy collected by the intelligent reflecting surface in the first stage meets the energy consumption of the second stage, namely
Er(τ，ρ，wE，wI)≥Pirs(τ，N)
Pirs(τ，N)＝(1-τ)NPu
Wherein, Er (tau, rho, w)E，wI) Representing the energy collected in the first stage of the intelligent reflecting surface, Pirs(tau, N) represents the energy consumed by the second stage of the intelligent reflecting surface, N represents the number of units of the intelligent reflecting surface, PuRepresenting the energy consumption of the intelligent reflector unit.
To achieve the above object, according to a second aspect of the present invention, there is provided a wireless information and energy cooperative transmission system, comprising the base station according to the first aspect, an intelligent reflective surface, and a plurality of user terminals;
the base station adopts separated beam forming to transmit information and energy at the same time;
the intelligent reflecting surface alternately performs energy absorption and information auxiliary transmission.
Generally, by the above technical solution conceived by the present invention, the following beneficial effects can be obtained:
(1) the invention provides a base station, in timeA power factor rho is additionally introduced on the basis of the factor tau, a combined mechanism of time switching and power distribution is adopted, the time switching mechanism is mainly used for state switching of the intelligent reflecting surface, the power distribution ensures real-time service quality of a user side, meanwhile, energy collection of the intelligent reflecting surface in an energy absorption stage is improved, and great influence is brought to energy absorption of the intelligent reflecting surface, real-time service quality of the user side and system energy efficiency. The first-stage system simultaneously performs energy transmission and signal transmission, realizes complete passivity of the intelligent reflecting surface, and simultaneously ensures the real-time service quality of users. Wherein the base station passes the beam vector wEEnergy ρ PtTransmitted to the intelligent reflecting surface for energy transmission, and simultaneously the residual energy (1-rho) PtFor information transmission, the base station transmits information to the user terminal through the information beam vector wI. In the second stage, all energy is used for information transmission, and the base station transmits the beam vector wuAnd transmitting the signal to the user terminal. The appropriate time factor and power factor have key effects on energy absorption of the intelligent reflecting surface and system energy efficiency, and the two are optimized in a combined mode, so that not only is the energy autonomy of the intelligent reflecting surface realized, and the intelligent reflecting surface gets rid of the constraint of an external power supply, but also the real-time service quality of a user side can be ensured, the effective communication of the user is guaranteed, and the energy and information cooperative transmission with high energy efficiency is realized.
(2) The invention provides a wireless information and energy cooperative transmission system.A base station end adopts separated beam forming to simultaneously transmit information and energy, and an intelligent reflecting surface alternately performs energy absorption and information auxiliary transmission, so that the intelligent reflecting surface is charged and simultaneously performs information transmission. The system energy efficiency is improved, the system deployment is simplified, the practicability is high, and the method can be applied to the fields of wireless sensor networks, industrial Internet of things and the like.
Drawings
Fig. 1 is a schematic diagram of a wireless information and energy cooperative transmission mechanism according to an embodiment of the present invention;
fig. 2 is a schematic diagram of split beamforming based on time switching and power allocation according to an embodiment of the present invention;
fig. 3 is a diagram illustrating the impact of ue quality of service (snr) requirements on the optimal time factor and power factor of the proposed method for joint time handover and power allocation optimization according to an embodiment of the present invention;
fig. 4 is a graph comparing energy efficiency of systems provided by embodiments of the present invention, including the combined time and power allocation scheme proposed by the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Furthermore, the technical features mentioned in the embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.
As shown in fig. 1, a base station performs information and energy transmission simultaneously, and firstly, the base station respectively realizes the energy transmission of the intelligent reflecting surface and the information transmission of communication users through a split beam forming design; the intelligent reflecting surface is used for auxiliary transmission of information and is divided into an energy absorption stage and a wireless information auxiliary transmission stage. The energy absorption stage only absorbs energy, the intelligent reflection surface does not process incident signals of the base station in the information auxiliary stage, and the channel state between the base station and a user is adjusted by changing the reflection coefficient of the intelligent reflection surface, so that auxiliary communication is realized; the energy consumed in the process of auxiliary information transmission of the intelligent reflecting surface is provided by the energy absorbed in the energy absorption stage, and an additional power supply is not needed. The introduction of the intelligent reflecting surface can effectively improve the transmission rate, and the simultaneous transmission mechanism of energy and information can ensure the real-time service quality of a user terminal and realize the energy autonomy of the intelligent reflecting surface; beamforming and phase adjustment can improve the transmission efficiency of energy and information, thereby improving the energy efficiency of the system.
A base station:
first phase τ T:
(1) transmitting power P of base station endtIs divided into PtAnd (1-. rho) Pt；
(2) Transmitting beams by energyVector WEEnergy ρ PtTo the intelligent reflective surface while simultaneously transferring energy (1-P) P via information beam transfer vector wItAnd carrying out signal transmission with the user terminal.
Second stage (1-. tau.) T: transmitting a beam vector w by informationuAnd transmitting all the energy to the user terminal.
Wherein rho represents the power ratio of energy transmission at the base station end, and rho is more than 0 and less than 1; tau represents a time factor, 0 < tau < 1; t represents the period of information transmission from the base station to the user terminal.
The intelligent reflecting surface:
first phase τ T: in an absorbing state, absorbing energy ErEfficient collection and storage.
Second stage (1-. tau.) T: and in a total reflection state, the self reflection coefficient is changed through phase adjustment to adjust the channel state between the base station and the user so as to assist information transmission.
The quality of service of the first-stage ue is less than or equal to the quality of service of the second-stage ue, specifically, γ1(ρ，wI)≤γ2(wuPhi), wherein, gamma1(ρ，wI) For the first phase user side SNR, gamma2(wuPhi) is the second stage ue snr.
Preferably, the base station is adapted to switch states and functions of the intelligent reflecting surface, and in the first stage, it transmits a signal:
Figure GDA0003513132970000071
wherein, PtIs the transmitting power of the base station end, rho is more than 0 and less than 1, w is the power ratio of the base station for energy transmissionEAnd wIBeam vectors, x, for the base station side for energy and information transmission, respectivelyEAnd xIRespectively, an energy carrying signal and an information transmission signal. In the second stage, the energy used by the base station for information transmission is represented as: x1＝PtwuxuWherein w isuTransmitting beam vector, x, for the base station side information at this stageuTo transmitAnd (6) outputting the signal. The intelligent reflecting surface is switched to auxiliary information transmission, and the real-time phase matrix is phi.
Preferably, the first-stage base station side optimal information beam and energy beam vector
Figure GDA0003513132970000081
And
Figure GDA0003513132970000082
respectively as follows:
Figure GDA0003513132970000083
and
Figure GDA0003513132970000084
second-stage base station terminal optimal information beam vector
Figure GDA0003513132970000085
And intelligent optimal phase adjustment phi of reflecting surface*Comprises the following steps:
Figure GDA0003513132970000086
wherein the content of the first and second substances,
Figure GDA0003513132970000087
and
Figure GDA0003513132970000088
for the first and second phase signal-to-noise ratio, sigma, of the user terminal2Is the user side noise;
Figure GDA0003513132970000089
Figure GDA00035131329700000810
in the first stage, the energy absorbed by the intelligent reflecting surface is H (phi), z is a channel between the intelligent reflecting surface and a user, g is a channel between the base station and the user, H is a channel between the base station and the intelligent reflecting surface,
Figure GDA00035131329700000811
means to take the expectation for "·".
Specifically, the channels between the base station and the intelligent reflector, and between the intelligent reflector and the user are Rician channels, that is, the channels are Rician channels
Figure GDA00035131329700000812
And
Figure GDA00035131329700000813
wherein, K1And K2Is Rician factor, betasrAnd betaruIn order to obtain a large-scale fading coefficient,
Figure GDA00035131329700000814
and
Figure GDA00035131329700000815
in order to be a direct path of light,
Figure GDA00035131329700000816
and
Figure GDA00035131329700000817
obeying a Rayleign distribution; base station to user channel
Figure GDA00035131329700000818
Wherein, betaruIn order to obtain a large-scale fading coefficient,
Figure GDA00035131329700000819
obeying a Rayleigh distribution.
Firstly, calculating energy beam vectors of a base station end in each stage: the optimal beam vector of the first stage information transmission adopts maximum ratio transmission
Figure GDA0003513132970000091
Maximum signal-to-noise ratio of corresponding user terminal
Figure GDA0003513132970000092
Figure GDA0003513132970000093
Optimal beamforming vector
Figure GDA0003513132970000094
v1Is HHThe maximum energy absorbed by the corresponding intelligent reflecting surface is as follows:
Figure GDA0003513132970000095
m and N are respectively the number of base station antennas and the number of intelligent reflector units; the second stage base station beam adopts the joint maximum ratio transmission vector as the optimal beam vector, and is expressed as
Figure GDA0003513132970000096
Maximum signal-to-noise ratio of corresponding user terminal
Figure GDA0003513132970000097
The optimal phase matrix of the intelligent reflecting surface is
Figure GDA0003513132970000098
Maximum signal-to-noise ratio of corresponding user terminal
Figure GDA0003513132970000099
Preferably, the optimal time factor τ and power factor ρ are determined prior to wireless information and energy transfer with the goal of maximizing system energy efficiency. In the time T, the intelligent reflecting surface is in an energy absorption stage, the stage rho is the proportion of the energy transmission power of the base station, and the residual energy is used for information transmission; and in the time of (1-tau) T, the intelligent reflecting surface is in an information auxiliary transmission state, all energy of the base station end is used for information transmission, and T is the period length.
Using the beamforming and phase adjustment scheme described above (
Figure GDA00035131329700000910
And phi*) And designing a joint wireless information and energy transmission mechanism based on time switching and power allocation.Specifically, the mechanism of joint wireless information and energy transmission based on time switching and power allocation as shown in fig. 2 includes two phases: within T period time, in the first stage T time, the base station divides the emission power into rho P by the power factor rhotAnd (1-. rho) PtAnd respectively carrying out energy and information transmission. At this stage, the intelligent reflecting surface is in an absorption state and absorbs energy
Figure GDA00035131329700000911
Effective collection and storage, energy required for self phase adjustment of the next stage, and user terminal signal-to-noise ratio of
Figure GDA0003513132970000101
In the second stage of time (1-tau) T, the intelligent reflecting surface is in the information auxiliary transmission state, the energy used by the base station end is used for information transmission, and the signal-to-noise ratio of the user end is
Figure GDA0003513132970000102
On the premise of ensuring the real-time service quality of a user side, the energy autonomy of an intelligent reflecting surface is realized, and an optimal time factor and a power factor are designed from the perspective of maximizing energy efficiency by combining a time switching mechanism and a power distribution mechanism.
Preferably, the selection of the power factor is constrained by the quality of service requirement of the receiving end (using the signal-to-noise ratio as a reference index),
Figure GDA0003513132970000103
but also the energy absorbed by the intelligent reflecting surface in the first stage; the time factor is selected to satisfy the requirement that the energy collected by the intelligent reflecting surface in the first stage provides the energy consumption of the second stage, namely
Figure GDA0003513132970000104
Wherein, PuThe choice of time factor also has a significant impact on the overall speed of the system for the energy consumption of the intelligent reflector unit.
Energy efficiency of the system
Figure GDA0003513132970000105
By time factor τ, power factor ρ, and signal beam vectors wI and wuCo-determining, wherein PtFor base station side transmission power, PeAnd the energy consumption of a single antenna at the base station end is M, and the number of the antennas at the base station end is M. Wherein the content of the first and second substances,
Figure GDA0003513132970000106
for the rate reachable at the ue in the first phase,
Figure GDA0003513132970000107
the reachable rate is the second stage ue.
Preferably, the maximized system energy efficiency is expressed as:
Figure GDA0003513132970000108
the constraint conditions are as follows:
Figure GDA0003513132970000109
Figure GDA00035131329700001010
Figure GDA00035131329700001011
tau is more than 0 and less than 1, and rho is more than 0 and less than 1. Maximum system energy efficiency is achieved at a minimum time factor, i.e.
Figure GDA00035131329700001012
The time factor takes a minimum value at the maximum power factor. The optimal system energy efficiency for the joint time and power allocation is:
Figure GDA0003513132970000111
fig. 3 shows an embodiment of the optimal time and power allocation scheme of the proposed scheme under different snr requirements of the ue. As can be seen from fig. 3, the higher the snr requirement of the ue, the power factor of the base station will gradually decrease in the first phase, because more energy will be used for information transmission to meet the qos requirement of the ue; secondly, increasing the transmission power and the size of the base station side antenna can reduce the power allocation factor to some extent.
Based on the time switch mechanism, the change of the snr of the ue has less impact on its time factor, and is closely related to the transmit power of the bs and the antenna size thereof. Specifically, the larger the antenna size is, the larger the transmission power is, the smaller the time factor thereof is, because the large-scale antenna and transmission power can improve the instantaneous energy transmission efficiency between the base station and the intelligent reflecting surface in the first stage, and the improvement of the efficiency reduces the time consumption of the system on energy transmission to a certain extent, thereby allocating more sufficient time for information transmission. The joint optimization distribution of time switching and power splitting can realize the self-sufficiency of the energy of intelligent reflection on the premise of ensuring information communication, and improve the reachable rate of the system.
Fig. 4 shows a comparison of system energy efficiency under the information and energy transmission mechanism combined based on time switching and power allocation proposed by the embodiment with the system energy efficiency of the conventional transmission scheme (the conventional scheme comprises an externally-powered intelligent reflecting surface auxiliary system and an intelligent-free reflecting surface system). As can be seen from fig. 4, increasing the scale of the intelligent reflective surface can improve the system energy efficiency within a certain range, but as the intelligent reflective surface continues to increase, the energy efficiency continues to decrease instead. According to the time and power combined optimization mechanism provided by the scheme, even when the intelligent reflecting surface is in a small scale, the system energy efficiency is lower, even smaller than that of a system without the assistance of the intelligent reflecting surface, and extra path loss is brought by the introduction of the intelligent reflecting surface. Fortunately, this phenomenon can be effectively compensated by increasing the scale of the intelligent reflective surface, and as the scale of the intelligent reflective surface increases, the system energy efficiency continues to increase and is better than the other two conventional schemes. Particularly, the technical scheme provided by the invention can realize self-sufficiency of energy of the intelligent reflecting surface, does not need an additional external power supply, simplifies the deployment, saves the system cost, and avoids the maintenance and replacement of a power supply device.
The invention also provides a wireless information and energy transmission system, comprising: the system comprises a base station, an intelligent reflecting surface and a controller for controlling the base station and the intelligent reflecting surface to execute the wireless information and energy transmission method according to the embodiment. The related technical solutions are not described herein again.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (2)

1. A base station, characterized in that the base station comprises:
a processor for determining a time factor tau and a power factor rho, 0 according to a user terminal real-time service quality requirement<τ<1，0<ρ<1, taking T as a first stage and (1-T) T as a second stage, and taking the emission power P of the base stationtIs divided into PtAnd (1-. rho) PtT represents a period of information transmission from the base station to the user terminal;
an antenna array for passing the energy beam vector w in the first stageEEnergy ρ PtTransmitted to the intelligent reflecting surface for energy transmission, and simultaneously the residual energy (1-rho) PtFor signal transmission by means of an information beam vector wITransmitting the information to the user terminal; in the second stage, all energy is used for information transmission, and under the auxiliary channel of the intelligent reflecting surface, the beam vector w is passeduTransmitting the information to the user terminal;
the processor determines a time factor tau and a power factor rho under the following constraint condition with the aim of maximizing the system energy efficiency;
the constraint conditions include: (1) the information beam transmission vector and the energy transmission beam vector of the first stage of the base station are optimal; (2) the second stage optimizes the information transmission beam vector of the base station and the phase of the intelligent reflecting surface; (3) the signal-to-noise ratio of the user side at each stage meets the required threshold; (4) the first stage intelligent reflecting surface absorbs energy to meet the energy consumption of the second stage;
the energy efficiency EE calculation formula of the system is as follows:
Figure FDA0003513132960000011
Figure FDA0003513132960000012
Figure FDA0003513132960000013
wherein R is1(ρ,wI) Represents the reachable rate of the first-stage user terminal, R2(wuPhi) indicates the achievable rate of the second-stage ue, PeRepresenting the energy consumption of a single antenna of the base station, M representing the number of antennas in the antenna array, gamma1(ρ,wI) Representing the signal-to-noise ratio, gamma, of the first stage user terminal2(wuPhi) represents the signal-to-noise ratio of the second-stage user terminal, B represents the information bandwidth,
Figure FDA0003513132960000021
indicating that the object in the curly brackets is expected, and phi indicates the phase of the intelligent reflecting surface;
optimal information beam and energy beam vectors
Figure FDA0003513132960000022
And
Figure FDA0003513132960000023
the calculation formula is as follows:
Figure FDA0003513132960000024
Figure FDA0003513132960000025
Figure FDA0003513132960000026
Figure FDA0003513132960000027
wherein E isr(τ,ρ,wE,wI) Representing the energy absorbed by the intelligent reflecting surface in the first stage, sigma2Representing the noise of a user terminal, g representing a channel between a base station and the user terminal, and H representing a channel between the base station and an intelligent reflecting surface;
optimal information beam vector
Figure FDA0003513132960000028
And optimum phase phi*The calculation formula is as follows:
Figure FDA0003513132960000029
Figure FDA00035131329600000210
h(Φ)＝zΦH
h (phi) represents an equivalent auxiliary channel under the assistance of the intelligent reflecting surface, z represents a channel between the intelligent reflecting surface and a user side, and H represents a channel between a base station and the intelligent reflecting surface;
the energy collected by the intelligent reflecting surface in the first stage meets the energy consumption of the second stage, namely
Er(τ,ρ,wE,wI)≥Pirs(τ,N)
Pirs(τ,N)＝(1-τ)NPu
Wherein, Pirs(tau, N) represents the energy consumed by the second stage of the intelligent reflecting surface, N represents the number of units of the intelligent reflecting surface, PuPresentation intelligenceEnergy consumption of the reflective surface unit.
2. A wireless information and energy cooperative transmission system, comprising the base station of claim 1, an intelligent reflective surface and a plurality of clients;
the base station adopts separated beam forming to transmit information and energy at the same time;
the intelligent reflecting surface alternately performs energy absorption and information auxiliary transmission.
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