A Dual-Intelligent Reflecting Surface-Assisted Relay Cooperative Communication System Based on Wireless Energy Transfer and Its Working Method

Abstract

The present invention relates to a dual-intelligent reflecting surface assisted relay cooperative communication system and a working method based on wireless energy transfer, belonging to the technical field of cooperative wireless communication. The system consists of a source node, a relay node, a destination node and two intelligent reflecting surfaces. IRS1 is deployed between the source node and the relay node, and IRS2 is deployed between the relay node and the destination node. The energy of the relay node needs to obtain energy from the RF signal sent by the source node to maintain power supply, and forward the source data to the destination node according to the decode-and-forward protocol. Compared with the existing methods of information relaying or energy harvesting in IRS-assisted relay systems or single-IRS-assisted SWIPT systems, the present invention can give full play to the advantages of IRS in the relay cooperative communication system to a greater extent, improve the collection efficiency of RF energy and the probability of successful end-to-end information transmission, greatly enhance the ergodic capacity of the system, and expand the communication coverage range.

Description

Technical Field

[0001] The present invention provides a dual-intelligent reflecting surface (IRS, Intelligent Reflecting Surface)-assisted relay cooperative communication system and a working method based on wireless energy transfer, belonging to the field of cooperative wireless communication technology. Background Art

[0002] At present, people's demand for wireless transmission continues to grow, and the number of deployed communication nodes globally is increasing day by day. While the network coverage and capacity are improved, a series of problems are also brought, such as severe co-channel interference, higher energy consumption, and maintenance costs. Although advanced technical means can cope with the explosive growth of wireless transmission requirements, such as MIMO (Massive Multiple Input Multiple Output), millimeter-wave communication, and even terahertz communication, the implementation of these technologies requires deploying more nodes and installing more antennas, which will inevitably greatly increase the hardware cost of the system and the complexity of signal processing. In an urban area, wireless signal propagation is extremely vulnerable to obstruction by obstacles. In a rich scattering environment, after the wireless signal undergoes direct transmission and multipath reflection, the multipath signals will superimpose at the receiving end and present a random fading effect, and the long-distance transmission of wireless signals will suffer severe path loss. Therefore, in a complex communication environment, the signal strength received at the receiving end is very weak and fluctuates, making it difficult to effectively guarantee the communication quality. As a new type of passive adjustable signal reflection element, the intelligent reflecting surface (IRS) can reconfigure the wireless transmission environment, making the signals arriving at the receiving end stronger after superposition, which helps to improve the communication quality and system capacity. The deployment of the IRS can optimize the wireless communication environment, effectively combat signal fading and interference, and it can be flexibly integrated into the existing wireless network without significantly modifying the physical layer standard, with a relatively low deployment cost, and is expected to play a key role in future wireless networks.

[0003] Cooperative relay transmission can effectively improve the robustness of communication and expand the network coverage by obtaining space-time diversity and multi-user diversity gains. Most traditional relay nodes are active devices that require an external power supply, and the supplied energy is very limited. Especially in energy-constrained networks, relay nodes are powered by batteries with limited capacity. Relay nodes need to consume their own energy to complete the data forwarding task, which is unfair to some relay nodes. Therefore, relay nodes tend to assist the source node in forwarding data without consuming their own energy. To achieve energy self-sufficiency, the academic community has proposed various energy harvesting strategies, including multiple energy sources such as solar energy, thermal energy, wind energy, and kinetic energy. Wireless energy harvesting based on electromagnetic waves has received more extensive attention because, compared with bursty and intermittent energy sources, the receiving end can specify the transmitting end to send exclusive energy signals to achieve on-demand energy harvesting. The energy harvesting process has better predictability and certainty and is easier to meet the communication quality requirements. SWIPT (Simultaneous Wireless Information and Power Transfer) technology can simultaneously transmit information and energy through RF (Radio Frequency) signals, simultaneously meeting the energy and data transmission requirements of energy-constrained devices, and significantly extending the network lifetime. Each communication node collects the energy of specific RF signals and stores the collected energy in a battery or supercapacitor to achieve the purpose of data acquisition and transmission, which helps to reduce carbon emissions, achieve low-power green communication, save system operation costs, and improve the reliability and sustainability of the communication system. Since the energy harvesting and information decoding circuit structures of relay nodes are usually separated, the EH (Energy Harvesting) and ID (Information Decoding) elements can use TS (Time Switching) and PS (Power Splitting) technologies to complete tasks in the time and power domains respectively. For the TS technology, a part of the time is allocated for energy harvesting, and the remaining time is used for information decoding; for the PS technology, the received signal is split into two parts by power at the receiving end, one part of the signal is used for energy harvesting, and the other part is used for information decoding.

[0004] In recent years, the auxiliary applications of IRS in cooperative wireless communication systems and SWIPT systems have attracted extensive attention. The deployment of IRS in traditional relay networks provides strong guarantee for the stability of communication links, helps to overcome adverse communication situations such as long distances or many obstacles blocking, expands the coverage of the system, and ensures the communication quality and efficiency of users. In the SWIPT system, the processing of RF signals by IRS can reduce the fading of energy signals in complex communication environments, enable energy receivers to collect more energy, and improve the efficiency of wireless energy transmission. Traditional models generally assume that there are line-of-sight links between the deployed IRS and other nodes in the system, and do not fully consider the negative impacts brought by the random position distribution of nodes and some potential obstacles. This assumption is not very reasonable in practice. In existing IRS-assisted cooperative communication systems, most relay nodes are powered by batteries with limited battery capacity. Once the energy supply cannot meet their communication requirements, it is difficult to ensure the reliable operation of the entire communication system, and even cause system paralysis. Therefore, in IRS-assisted cooperative relay communication, by introducing wireless energy transmission, the life cycle of relay nodes can be greatly extended, and the utility of IRS can be given full play. By optimizing the signal propagation environment, IRS can not only improve the quality and efficiency of information transmission, but also enhance the energy collection effect of receivers, and ensure the continuous energy supply of communication nodes. Considering the adverse impacts of obstacles, deep fading, path loss, etc. on the communication environment, the present invention realizes efficient data and energy transmission in energy-constrained networks, can meet the requirements of network green communication, enhanced node adaptability, expanded network coverage, etc., and guides the design and deployment of relay transmission systems based on IRS and SWIPT, which has important theoretical significance and application value. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention proposes a novel dual-IRS-assisted relay cooperative communication system and working method based on wireless energy transmission, and the energy supply of the relay all comes from the RF energy collected from the source node. Compared with the existing methods of information relaying or energy collection in IRS-assisted relay systems or single-IRS-assisted SWIPT systems, the present invention can give full play to the advantages of IRS in the relay cooperative communication system to a greater extent, improve the collection efficiency of RF energy and the probability of successful end-to-end information transmission, greatly enhance the ergodic capacity of the system, and expand the communication coverage.

[0006] In order to ensure the successful transmission of the first-hop signal, the present invention deploys the first IRS between the source node and the relay node, which can not only increase the energy collected by the relay node, but also obtain cooperative diversity gain in the first hop, thereby improving the robustness of information transmission. The relay node uses TS or PS technology to obtain RF energy and decode the source data. If the relay node decodes the source data successfully, it forwards the data to the destination node. If the relay node fails to demodulate the source node data, the data cannot be forwarded. The second IRS is deployed between the relay node and the destination node to assist the relay node in forwarding data to the destination node in the second hop, improve the signal propagation environment of the second hop, and improve the signal transmission quality and efficiency of the second hop. Since the energy collected by the relay node is limited, the relay node only relies on all the energy collected in the first hop when forwarding data. Therefore, deploying IRS on the second hop can reduce the fading of the signal during transmission, improve the reliability of relay transmission, and help overcome the dilemma of limited energy of the relay node, thereby ensuring that the received signal strength of the destination node can meet the communication quality requirements.

[0007] The technical solution of the present invention is:

[0008] A dual intelligent reflector-assisted relay cooperative communication system based on wireless energy transmission, comprising a source node (S), a relay node (R), a destination node (D) and two intelligent reflector surfaces (IRS), wherein the source node, the relay node and the destination node are all equipped with an omnidirectional antenna and work in half-duplex mode;

[0009] The two intelligent reflection surfaces are IRS1 and IRS2. There are obstacles between IRS1 and IRS2. IRS1 is deployed between the source node and the relay node, and IRS2 is deployed between the relay node and the destination node to facilitate the transmission of IRS hop-by-hop auxiliary signals and energy collection of relay nodes. Each reflection unit of IRS is adjusted to achieve the best phase shift and ensure the maximum reflection amplitude, so as to optimize the signal propagation environment;

[0010] The source node and the destination node have a stable energy supply, for example, they can be connected to the power grid or powered by a large-capacity battery. The energy of the relay node is limited and it needs to obtain energy from the radio frequency (RF) signal sent by the source node to maintain power supply and forward the source data to the destination node according to the Decode and Forward (DF) protocol.

[0011] Preferably, the relay node has the functions of energy harvesting, information decoding, and information transmission at the same time; in the PS-based relay protocol, each time block contains T seconds and is divided into two stages with equal durations; among them, the first stage is used for simultaneous wireless information and power transfer (SWIPT) from the source node (S) to the relay node (R), and the second stage is used for data forwarding from the relay node (R) to the destination node (D).

[0012] The signal received in the first stage can be divided into two parts by the PS factor ρ, which are used for energy harvesting (EH) and information decoding (ID) of the relay node respectively; in the TS-based relay protocol, a time block is segmented by the TS factor α. First, the first αT seconds are used for energy harvesting (EH), and the remaining time is divided into two equal parts. Among them, the first (1 - α)T / 2 is used for information decoding (ID) of the relay node, and the second (1 - α)T / 2 is used for data transmitted from the relay node (R) to the destination node (D); only when the relay node (R) correctly decodes the source data can the data be transmitted to the destination, otherwise the data will not be forwarded within the allocated time.

[0013] Preferably, the channel coefficients from the source node S to the relay node R, from the source node S to IRS1, and from IRS1 to the relay node R are denoted as h SR h SI and h IR respectively, and the channel coefficients from the relay node R to the destination node D, from the relay node R to IRS2, and from IRS2 to the destination node D are denoted as g RD g RI and g ID respectively;

[0014] Assume that all links experience independent small-scale fading and large-scale fading. The small-scale fading follows the Rayleigh distribution, and the large-scale fading is mainly path loss; the channel coefficients of the first-hop link can be expressed as h SR = k SR l SR h SI = k SI l SI h IR = k IR l IR where p ∈ {SR, SI, IR} represents the large-scale fading coefficient, d p represents the distances of S→R, S→IRS1, and IRS1→R, and r represents the path loss exponent; similarly, the channel coefficients of the second-hop link can be expressed as g RD = k RD l RD g RI = k RI lRI , g ID = k ID l ID , where q ∈ {RD, RI, ID} represents the path loss of large-scale fading, and d q is the distance of R→D, R→IRS2, and IRS2→D; k SR , k RD , and are all circularly symmetric complex Gaussian random variables with zero mean and unit variance, used to represent small-scale fading coefficients;

[0015] The data transmission time is divided into equal-length time blocks, and the length of each time block is denoted as T; the small-scale fading of each channel remains unchanged in each time block, but varies independently in different time blocks, and the small-scale fades of different channels are independent of each other; during data transmission, the positions of the nodes are fixed, so the large-scale path loss is also unchanged in each time block.

[0016] Preferably, for the PS-based energy harvesting and relay transmission protocol, S simultaneously sends radio frequency (RF) signals to R and IRS1 in the first half of the time block, and IRS1 reflects the received incident signal to R after phase optimization processing; the signal received by R in the first hop is denoted as y R , which can be expressed as:

[0017]

[0018] where is the transmit power of the source node S; represents the reflection coefficient matrix of IRS1, θ 1i ∈[0, 2π) and η 1i ∈[0, 1] represent the phase and reflection amplitude gain of the i-th element of IRS1 respectively; s is the normalized signal, indicating that the average power of the signal is 1; is the additive Gaussian white noise, representing the noise power; is the composite channel coefficient of the first hop, which can be rewritten as where h Si represents the channel coefficient from S to the i-th reflection element of IRS1, h iR represents the channel coefficient from the i-th reflection element of IRS1 to R, θ SR , θ Si and θ iR respectively represent h SR , h Siand h iR phase; assuming that each reflection unit of IRS1 has the same reflection amplitude gain and optimal phase shift, so θ 1i = θ SR -(θ Si + θ iR ), η 1i = η, then the composite channel coefficient of the first hop can be denoted as h1, and for simplicity of expression, it can be given by the following formula:

[0019]

[0020] where λ1 = ηl SI l IR ,

[0021] According to mathematical derivation, the closed - form expression of the distribution function of h1 can be approximately calculated as:

[0022]

[0023] where γ represents the lower incomplete gamma function, and x, y represent the independent variables of the function; based on the PS relay protocol, where ρ part of the signal received by the relay node R is used for EH, this part can be expressed as:

[0024]

[0025] represents the part of the signal used for EH by the relay node;

[0026] The noise can be ignored, and the energy harvested by R in the first hop can be expressed as:

[0027]

[0028] where ζ ∈ (0,1) represents the energy conversion efficiency, and the signal used for ID at the relay node R can be expressed as:

[0029]

[0030] where is the noise introduced when the signal is converted from the RF band to the baseband; the signal - to - noise ratio at the relay node R can be expressed as:

[0031]

[0032] represents the power of the antenna noise, represents the power of the conversion noise generated when the band signal is converted to the baseband signal;

[0033] If the relay node R correctly decodes the source data in the first hop, it will forward the data to D using all the collected energy in the second hop; to simplify the performance analysis of the second-hop transmission, a finite number of energy levels are defined to approximate the actual transmit power of the relay node R; μ represents the maximum achievable transmit power of the relay node, and M+1 energy levels are defined, i.e., L0 = 0, ..., L M = μ; where M is a non-zero integer, and the larger M is, the higher the approximation degree between the discrete energy levels and the continuous energy values; given the actual available power P R of the relay node R, then the approximate transmit power level of R can be denoted as If the actual power P R satisfies L i < P R < L i+1 , i ∈ {0, 1,..., M - 1}, then the transmit power of R can be approximated as this energy level, and Δ is the interval between any two adjacent energy levels However, when the energy collected by R is equal to or greater than the battery capacity, the approximate transmit power of R is denoted as For the PS protocol, the actual transmit power of R is denoted as Expressed as:

[0034]

[0035] In the second half of a time block, the relay node R forwards the decoded data to the destination node D and IRS2, and IRS2 reflects the received incident signal to D; then the signal received by D can be given by the following formula:

[0036]

[0037] where represents the reflection coefficient matrix of IRS2, θ 2i ∈ [0, 2π) and η 2i ∈ [0, 1] represent the phase shift and reflection amplitude gain of the i-th reflection element at IRS2, respectively; represents the additive Gaussian white noise at the destination node D, and the noise introduced by the RF baseband signal conversion is represents the composite channel coefficient of the second hop; similar to the first hop, each reflection unit of IRS2 can achieve the maximum reflection amplitude gain and select the optimal phase shift, and the composite channel coefficient of the second hop is denoted as g2 and can be expressed as:

[0038]

[0039] where \(g\) Ri and \(g\) iD are the channel coefficients from the \(i\)-th reflection unit of \(R\) to the \(i\)-th reflection unit of IRS2 and from the \(i\)-th reflection unit of IRS2 to \(D\), respectively; The derivation of the distribution function of \(g_2\) is similar to that of \(h_1\) and can be expressed as:

[0040]

[0041] where \(\lambda_2=\eta l\) RI \(l\) ID ,

[0042] Then, based on the PS protocol, the signal-to-noise ratio at the destination node \(D\) can be expressed as:

[0043]

[0044] For the PS-based energy harvesting and relay transmission protocol, when the signal is successfully transmitted from the source node \(S\) to the destination node \(D\), this event is defined as If an outage occurs during the transmission on the first hop, this event is denoted as If an outage occurs during the transmission on the second hop, this event is denoted as Event means that the signal is successfully transmitted to the destination node within the system without an outage occurring on any hop;

[0045] According to the relationship between the success probability and outage probability of signal transmission, the success probability of the system can be expressed as:

[0046]

[0047] \(Pr\{\}\) represents the probability of an event;

[0048] When the instantaneous signal-to-noise ratio of the system is lower than the predetermined threshold , the signal transmission will experience an outage; then the outage probability of the first hop is expressed as:

[0049]

[0050] where \(V\) represents the data transmission rate; After formula derivation, \(Pr\{B\) ps \} can be expressed as:

[0051]

[0052] where

[0053] Similarly, the outage probability of the second hop can be derived as:

[0054]

[0055] where

[0056] the relay's transmit power is related to the first-hop channel coefficient; for the PS-based protocol, the actual continuous transmit power of relay node R is denoted as its approximate discrete transmit power is denoted as When time Δ is the interval between any two adjacent energy levels the probability of this situation occurring can be calculated as:

[0057]

[0058] When time is approximated as the maximum energy level, the probability of this situation occurring can be calculated as:

[0059]

[0060] After discretizing the transmit power of R, the second-hop outage probability can be approximated as:

[0061]

[0062] where is an indicator random variable (1(i≠M) in Equation (19) is this indicator random variable), which equals 1 when the condition is satisfied and 0 otherwise; substituting and Pr{C ps} into the success probability can be obtained;

[0063] The end-to-end achievable rate and ergodic capacity of the communication system are denoted as R ps and can be expressed as Using Jensen's inequality, the upper bound of the ergodic capacity is derived as where and represent and the upper bounds of; using Holder's inequality, we can obtain the expectation of is:

[0064]

[0065] G SR denotes |hSR Channel power gain of Indicates the channel power gain of B1;

[0066] Through mathematical derivation, The result of

[0067]

[0068] Where Similarly, Can be calculated as

[0069]

[0070] Where

[0071] Preferably, for the TS-based energy harvesting and relay transmission protocol, in the first-hop signal transmission, the signal received by the relay node R is the same as the signal received under the PS protocol, denoted by y R ; Different from the PS protocol, the TS protocol allocates the first α part within a time block to EH, and the energy collected by the relay node R during this part of the time is denoted as E ts , expressed as Then, (1-α) / 2 part of the time will be used for ID at the relay node R, and this part of the signal can be expressed as

[0072]

[0073] Then the signal-to-noise ratio of the relay node is:

[0074]

[0075] Adopt Indicates the actual transmit power of R, which can be given by the following formula:

[0076]

[0077] The composite channel coefficient g2 of the second hop is the same as that under the PS protocol, then the signal received by the relay node D can be denoted as Expressed as

[0078]

[0079] Correspondingly, the signal-to-noise ratio at the destination node D can be expressed as:

[0080]

[0081] For the TS-based protocol, define the successful data transmission from S to D as event The interruption of the signal on the first hop is an event The interruption of the signal on the second hop is denoted as an event Then the success probability of the system when adopting the TS relay protocol can be written as

[0082]

[0083] Different from the PS-based protocol, the signal-to-noise ratio threshold of the TS-based protocol is Then the outage probability of the first hop of the system can be expressed as:

[0084]

[0085] Where Similarly, the outage probability of the second hop can be expressed as:

[0086]

[0087] Where

[0088] In the TS-based protocol, the actual transmission power of R is denoted as The approximate discrete transmission power of R is denoted as

[0089] When At this time The probability of this situation occurring can be calculated as:

[0090]

[0091] When At this time The approximation of is The probability of this situation occurring can be calculated as:

[0092]

[0093] After discretizing the transmission power of R, the outage probability of the second hop can be approximated as:

[0094]

[0095] Substitute and Pr{C tss} into The success probability can be obtained;

[0096] Similar to the PS-based protocol, the end-to-end achievable rate of the TS-based protocol is defined as It can be given by Given The upper bound of is denoted as Expressed as After mathematical derivation; The upper bound of

[0097]

[0098] is: Similarly, The calculation result of

[0099]

[0100] is:

[0101] For the parts not elaborated in the present invention, reference can be made to the prior art.

[0102] The beneficial effects of the present invention are as follows:

[0103] 1. The present invention proposes a relay transmission system based on dual IRS and wireless energy harvesting communication. The first IRS can assist the relay node in collecting more energy to ensure the successful demodulation of the source node's data, and the second IRS can assist the relay node in forwarding data to the destination node, which helps to overcome the dilemma of limited energy of the relay node and ensures the successful demodulation of data at the destination node.

[0104] 2. The present invention introduces three benchmark systems for comparison with the system of the present invention, namely, a single-relay system, an IRS1-relay system, and a relay-IRS2 system. Through comparison, it can be seen that the dual IRS system can significantly improve the communication environment, enhance the energy harvesting and data forwarding effects of the relay node. Compared with the three benchmark systems, the success probability and ergodic capacity of the present invention are the best.

[0105] 3. The present invention discretizes the transmission power of the relay node by setting a finite number of energy levels, decouples the energy harvesting and data forwarding operations of the relay node, and reduces the complexity of system performance analysis. Based on the discrete energy state of the relay node and according to the statistical characteristics of channel fading, the closed-form expressions of the success probability and ergodic capacity of the dual IRS-assisted energy transmission relay communication system of the present invention are derived. Through extensive experimental verification, the theoretical results and simulation results are highly consistent, which can prove the accuracy of the theoretical analysis. The theoretical results provide guiding significance for IRS-based wireless energy harvesting communication.

[0106] 4. The present invention reveals the influence of key parameters such as the transmission power of the source node and the deployment positions of each node on the system communication success probability and ergodic capacity. Through the relationship between the system communication success probability and the deployment positions of each node, it is found that compared with the three benchmark systems, the system of the present invention can greatly save the system transmission power, and when the IRS of each hop of the system of the present invention is located in the middle of two nodes in the horizontal direction, the communication effect is better. This also provides a reference for the node deployment of the IRS-assisted relay communication system. BRIEF DESCRIPTION OF THE DRAWINGS

[0107] The accompanying drawings forming a part of this application are used to provide a further understanding of this application. The schematic embodiments of this application and their descriptions are used to explain this application and do not constitute an improper limitation to this application.

[0108] Figure 1 It is a system model diagram; the solid line represents the transmission of the first hop, and the dashed line represents the transmission of the second hop.

[0109] Figure 2 It is a schematic diagram of energy harvesting and signal transmission based on the PS protocol within a time block.

[0110] Figure 3 It is a schematic diagram of energy harvesting and signal transmission based on the TS protocol within a time block.

[0111] Figure 4 It is the relationship between the system success probability and the PS factor.

[0112] Figure 5 It is the relationship between the system success probability and the TS factor.

[0113] Figure 6 It is the relationship between the system maximum success probability and the source node transmission power.

[0114] Figure 7 It is the relationship between the system maximum success probability and the deployment location of IRS1.

[0115] Figure 8 It is the relationship between the system maximum success probability and the deployment location of IRS2.

[0116] Figure 9 It is the relationship between the system maximum success probability and the deployment location of the relay node.

[0117] Figure 10 It is the relationship between the system ergodic rate and the PS factor.

[0118] Figure 11 It is the relationship between the system ergodic rate and the TS factor.

[0119] Figure 12 It is the relationship between the system maximum ergodic rate and the source node transmission power. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0120] In order to enable those skilled in the art of this technology to better understand the technical solutions in this specification, the following combines the accompanying drawings in the embodiments of this specification to clearly and completely describe the technical solutions in the embodiments of this invention, but not limited to this. For those not elaborated in this invention, they are all in accordance with the conventional technologies in the art.

[0121] Embodiment 1

[0122] A dual-intelligent reflecting surface-assisted relay cooperative communication system based on wireless energy transfer, as Figure 1 shown, consists of a source node (S), a relay node (R), a destination node (D) and two intelligent reflecting surfaces (IRS). The source node, relay node, and destination node are all equipped with an omnidirectional antenna and operate in a half-duplex mode. The number of reflecting elements in IRS1 and IRS2 are N1 and N2 respectively. Due to the presence of obstacles blocking and severe path loss between the source node S and the destination node D, or the influence of deep signal fading, there is no direct link between them. Data needs to be forwarded to D through the relay node. Considering potential obstacle blocking in the complex communication environment, there is also no direct link between the two IRSs, and only the first reflection of the same signal by the IRS is considered, ignoring multiple reflections;

[0123] The two intelligent reflecting surfaces are IRS1 and IRS2 respectively. There is an obstacle between IRS1 and IRS2. IRS1 is deployed between the source node and the relay node, and IRS2 is deployed between the relay node and the destination node to facilitate the hop-by-hop assistance of signal transmission and energy harvesting of the relay node. Each reflecting element of the IRS is adjusted to achieve the optimal phase shift and ensure the maximum reflection amplitude to optimize the signal propagation environment;

[0124] The source node and the destination node have stable energy supplies. For example, they can be connected to the power grid or powered by large-capacity batteries. The energy of the relay node is limited and it needs to obtain energy from the radio frequency (RF) signal sent by the source node to maintain power supply, and forward the source data to the destination node according to the decode and forward (DF) protocol.

[0125] The relay node has the functions of energy harvesting, information decoding, and information transmission at the same time. In the relay protocol based on PS, each time block contains T seconds and is divided into two equal-duration phases. Among them, the first phase is for simultaneous wireless information and power transfer (SWIPT) from the source node (S) to the relay node (R), and the second phase is for data forwarding from the relay node (R) to the destination node (D);

[0126] The signal received in the first stage can be divided into two parts by the PS factor ρ, which are used for energy harvesting (EH) and information decoding (ID) of the relay node respectively; in the relay protocol based on TS, a time block is segmented by the TS factor α. First, the first αT seconds are used for energy harvesting (EH), and the remaining time is divided into two equal parts. The first (1 - α)T / 2 is used for information decoding (ID) of the relay node, and the second (1 - α)T / 2 is used for the data transmitted from the relay node (R) to the destination node (D); only when the relay node (R) correctly decodes the source data can the data be transmitted to the destination, otherwise the data will not be forwarded within the allocated time.

[0127] Embodiment 2

[0128] A dual-intelligent reflecting surface-assisted relay cooperative communication system based on wireless energy transfer is as described in Embodiment 1, except that, as Figure 1 , the channel coefficients from the source node S to the relay node R, from the source node S to IRS1, and from IRS1 to the relay node R are denoted as h SR , h SI and h IR respectively, and the channel coefficients from the relay node R to the destination node D, from the relay node R to IRS2, and from IRS2 to the destination node D are denoted as g RD , g RI and g ID ;

[0129] Assume that all links experience independent small-scale fading and large-scale fading. The small-scale fading follows the Rayleigh distribution, and the large-scale fading is mainly path loss; the channel coefficients of the first-hop link can be expressed as h SR =k SR l SR , h SI =k SI l SI , h IR =k IR l IR , where represents the large-scale fading coefficient, d p represents the distances of S→R, S→IRS1, and IRS1→R, and r represents the path loss exponent; similarly, the channel coefficients of the second-hop link can be expressed as g RD =k RD l RD , g RI =k RI l RI , g ID =k ID l ID , and is used to represent the path loss of the large-scale fading, d qare the distances of R→D, R→IRS2, and IRS2→D; k SR , k RD , and are all circularly symmetric complex Gaussian random variables with zero mean and unit variance, used to represent small-scale fading coefficients;

[0130] The data transmission time is divided into equal-length time blocks, and the length of each time block is denoted as T; the small-scale fading of each channel remains unchanged in each time block but varies independently in different time blocks, and the small-scale fading of different channels is independent of each other; during the data transmission process, the positions of the nodes are fixed, so the large-scale path loss is also unchanged in each time block.

[0131] The implementation of the present invention involves two energy harvesting methods for relay nodes, namely the power splitting (PS)-based and time switching (TS)-based energy harvesting relay transmission protocols, as Figure 2 and Figure 3 shown. The energy harvesting and data transmission situations of the system of the present invention under the two methods are as in Embodiment 3 and Embodiment 4:

[0132] Embodiment 3

[0133] A working method of a dual-intelligent reflecting surface-assisted relay cooperative communication system based on wireless energy transfer. For the PS-based energy harvesting and relay transmission protocol, S simultaneously sends radio frequency (RF) signals to R and IRS1 in the first half of the time block, and IRS1 reflects the received incident signal to R after phase optimization processing; the signal received by R in the first hop is denoted as y R , which can be expressed as:

[0134]

[0135] where is the transmit power of the source node S; represents the reflection coefficient matrix of IRS1, θ 1i ∈[0, 2π) and η 1i ∈[0, 1] represent the phase and reflection amplitude gain of the i-th element of IRS1 respectively; s is the normalized signal, indicating that the average power of the signal is 1; is the additive Gaussian white noise, representing the noise power; is the composite channel coefficient of the first hop and can be rewritten as where h Si represents the channel coefficient from S to the i-th reflection element of IRS1, h iRDenote the channel coefficient from the \(i\)-th reflecting element of IRS1 to R as \(\theta\). SR , \(\theta\) Si and \(\theta\) iR respectively represent the phases of \(h\) SR , \(h\) Si and \(h\) iR ; assume that each reflecting unit of IRS1 has the same reflection amplitude gain and optimal phase shift, so \(\theta\) 1i = \(\theta\) SR - (\(\theta\) Si + \(\theta\) iR ), \(\eta\) 1i = \(\eta\), Then the composite channel coefficient of the first hop can be denoted as \(h_1\), and for simplicity of expression, it can be given by the following formula:

[0136]

[0137] where \(\lambda_1=\eta l\) SI l IR ,

[0138] According to mathematical derivation, the closed - form expression of the distribution function of \(h_1\) can be approximately calculated as:

[0139]

[0140] where \(\gamma\) represents the lower incomplete gamma function, and \(x,y\) represent the independent variables of the function; based on the PS relay protocol, where \(\rho\) part of the signal received by the relay node R is used for EH, this part can be expressed as:

[0141]

[0142] represents the part of the signal used for EH by the relay node;

[0143] The noise can be ignored, and the energy harvested by R in the first hop can be expressed as:

[0144]

[0145] where \(\zeta\in(0,1)\) represents the energy conversion efficiency, and the signal used for ID at the relay node R can be expressed as:

[0146]

[0147] where is the noise introduced when the signal is converted from the RF band to the baseband; the signal - to - noise ratio at the relay node R can be expressed as:

[0148]

[0149] represents the power of the antenna noise, represents the power of the conversion noise generated when converting the band signal to the baseband signal;

[0150] If the relay node R correctly decodes the source data in the first hop, it will forward the data to D using all the collected energy in the second hop; to simplify the performance analysis of the second-hop transmission, a finite number of energy levels are defined to approximate the actual transmit power of the relay node R; μ represents the maximum achievable transmit power of the relay node, and M + 1 energy levels are defined, namely L M = μ; where M is a non-zero integer, and the larger M is, the higher the approximation degree between the discrete energy levels and the continuous energy values; given the actual available power P R of the relay node R, then the approximate transmit power level of R can be denoted as If the actual power P R satisfies L i < P R < L i+1 , i ∈ {0, 1,..., M - 1}, then the transmit power of R can be approximated as this energy level, and Δ is the interval between any two adjacent energy levels However, when the energy collected by R is equal to or greater than the battery capacity, the approximate transmit power of R is denoted as For the PS protocol, the actual transmit power of R is denoted as which is expressed as:

[0151]

[0152] In the second half of a time block, the relay node R forwards the decoded data to the destination node D and IRS2, and IRS2 reflects the received incident signal to D; then the signal received by D can be given by the following formula:

[0153]

[0154] where represents the reflection coefficient matrix of IRS2, and θ 2i ∈ [0, 2π) and η 2i ∈ [0, 1] represent the phase shift and reflection amplitude gain of the i-th reflection element at IRS2, respectively; represents the additive Gaussian white noise at the destination node D, and the noise introduced by the RF baseband signal conversion is Denote the composite channel coefficient of the second hop; similar to the first hop, each reflection unit of IRS2 can achieve the maximum reflection amplitude gain and select the optimal phase shift. The composite channel coefficient of the second hop is denoted as g2 and can be expressed as:

[0155]

[0156] where g Ri and g iD are the channel coefficients from R to the i-th reflection unit of IRS2 and from the i-th reflection unit of IRS2 to D, respectively; the derivation of the distribution function of g2 is similar to that of h1 and can be expressed as:

[0157]

[0158] where λ2 = ηl RI l ID ,

[0159] Then, based on the PS protocol, the signal-to-noise ratio at the destination node D can be expressed as:

[0160]

[0161] For the PS-based energy harvesting and relaying transmission protocol, when the signal is successfully transmitted from the source node S to the destination node D, this event is defined as If the signal is interrupted during the first-hop transmission, this event is denoted as If the signal is interrupted during the second-hop transmission, this event is denoted as Event means that the signal is successfully transmitted to the destination node within the system without signal interruption in any hop;

[0162] According to the relationship between the successful transmission probability and the interruption probability of the signal, the successful probability of the system can be expressed as:

[0163]

[0164] Pr{} represents the probability of an event;

[0165] When the instantaneous signal-to-noise ratio of the system is lower than the predetermined threshold , the signal transmission will be interrupted; then the interruption probability of the first hop is expressed as:

[0166]

[0167] where V represents the data transmission rate; after formula derivation, Pr{B ps} can be expressed as:

[0168]

[0169] where

[0170] Similarly, the outage probability of the second hop can be derived as:

[0171]

[0172] where

[0173] The transmit power of the relay is related to the channel coefficient of the first hop; for the PS-based protocol, the actual continuous transmit power of the relay node R is denoted as Its approximate discrete transmit power is denoted as When is true,[[]] Δ is the interval between any two adjacent energy levels The probability of this situation occurring can be calculated as:

[0174]

[0175] When is true,[[]] will be approximated as the maximum energy level, The occurrence probability of this situation can be calculated as:

[0176]

[0177] After discretizing the transmit power of R, the outage probability of the second hop can be approximated as:

[0178]

[0179] where is an indicator random variable (1(i≠M) in Equation (19) is exactly this indicator random variable), which is equal to 1 when the condition is satisfied and 0 otherwise; substituting and Pr{C ps} into the success probability can be obtained;

[0180] The end-to-end achievable rate and the ergodic capacity of the communication system are respectively denoted as R ps and can be expressed as Using Jensen's inequality, the upper bound of the ergodic capacity is derived as where and respectively represent and The upper bound; Using the Hölder inequality, we can obtain The expectation of

[0181]

[0182] G SR denotes the channel power gain of |h SR |; G B1 denotes the channel power gain of B1;

[0183] After mathematical derivation, The result of

[0184]

[0185] where Similarly, can be calculated as

[0186]

[0187] where

[0188] Embodiment 4

[0189] A working method of a dual-intelligent reflecting surface-assisted relay cooperative communication system based on wireless energy transfer. For the TS-based energy harvesting and relay transmission protocol, in the first-hop signal transmission, the signal received by the relay node R is the same as the signal received under the PS protocol, denoted by y R ; Different from the PS protocol, the TS protocol allocates the first α part of a time block to EH, and the energy collected by the relay node R during this part of the time is denoted as E ts , expressed as Then, (1 - α) / 2 part of the time will be used for ID at the relay node R, and this part of the signal can be expressed as

[0190]

[0191] Then the signal-to-noise ratio of the relay node is:

[0192]

[0193] Adopting denotes the actual transmission power of R, which can be given by the following formula:

[0194]

[0195] The composite channel coefficient g2 of the second hop is the same as that under the PS protocol, then the signal received by the relay node D can be denoted as Expressed as

[0196]

[0197] Correspondingly, the signal-to-noise ratio at the destination node D can be expressed as:

[0198]

[0199] For the TS-based protocol, define the successful data transmission from S to D as event The interruption of the signal on the first hop is event The interruption of the signal on the second hop is denoted as event Then the success probability of the system when adopting the TS relay protocol can be written as

[0200]

[0201] Different from the PS-based protocol, the signal-to-noise ratio threshold of the TS-based protocol is Then the outage probability of the first hop of the system can be expressed as:

[0202]

[0203] Where Similarly, the outage probability of the second hop can be expressed as:

[0204]

[0205] Where

[0206] In the TS-based protocol, the actual transmission power of R is denoted as The approximate discrete transmission power of R is denoted as

[0207] When At this time, The probability of this situation occurring can be calculated as:

[0208]

[0209] When At this time, The approximate value of is The probability of this situation occurring can be calculated as:

[0210]

[0211] After discretizing the transmission power of R, the outage probability of the second hop can be approximated as:

[0212]

[0213] Substitute and Pr{Ctss Substitute to obtain the success probability;

[0214] Similar to the PS - based protocol, the end - to - end achievable rate based on the TS protocol is defined as It can be given by and the upper bound of is denoted as expressed as After mathematical derivation; the upper bound of

[0215]

[0216] where Similarly, the calculation result of

[0217]

[0218] where

[0219] Based on the derivations of the above two different energy - harvesting methods (Example 3 and Example 4), the present invention respectively derives the end - to - end communication success probability of the system and the closed - form expressions of the ergodic capacity, providing a theoretical basis for the optimal design of the system. The present invention also introduces a single - relay system, an IRS1 - relay system, and a relay - IRS2 system for comparative analysis. In the simulation, unless otherwise specified, the system parameters are set as follows: N1 = 40, N2 = 40, r = 2.5, V = 0.5 bits / s / Hz, P s = 45 dBm, σ n 2 = 0.001 W, μ = 1 J, M = 100, and the coordinates of different nodes are set as S = [0,0], IRS1 = [5,10], R = [10,0], IRS2 = [15,10], D = [20,0]. Under the reasonable setting of these parameters, first, the variation trends of the system communication success probability and the system ergodic capacity with respect to the PS factor ρ and the TS factor α can be obtained. It should be additionally noted that in Figure 4 and Figure 5 the system transmission rate is set to V = 0.3 bits / s / Hz. In Figure 4 as ρ increases, the relay can harvest more energy in the first hop, so the signal can be transmitted with higher power in the second hop, and the communication success probability of the system increases accordingly. However, when ρ is large enough, the difficulty for the relay to correctly decode the source data increases, so the communication success probability of the system becomes lower. Figure 5It shows the relationship between the communication success probability of the system and the TS factor α. As α increases, due to the contradiction between the energy harvesting time and the signal transmission time at the relay node, the curves of the four systems first increase and then decrease. It can be seen that there is an optimal ρ or α that maximizes the system communication success probability.

[0220] In the subsequent simulations, based on the optimal ρ or α, the relationship between the maximum success probability of the system proposed in the present invention and the three benchmark systems and some key parameters is obtained. Figure 6 It shows the relationship between the system success probability and the source node transmission power P S of. As P S increases, after reaching a certain threshold, the maximum system success probability of the proposed system rapidly increases to 1, while the increase rates of the IRS1 + relay system, the relay + IRS2 system, and the single-relay system are slower.

[0221] Figure 7 It reveals the relationship between the communication success probability of the system and the deployment location of IRS1. When studying the influence of the location of IRS1 on each system, the location of IRS2 is fixed. We set the projection points of IRS1 and IRS2 on the S-D line segment as D1 and D2 respectively, and use d1 and d2 to represent the distances from S to D1 and D2 respectively. The relay + IRS2 system and the single-relay system are both independent of d1, while the maximum success probabilities of the system of the present invention and the IRS1 + relay system first increase and then decrease as d1 increases, and the system maximum success probability reaches the peak when the projection point of IRS1 on the S-D line is at the midpoint of the S-R line.

[0222] Figure 8 It represents the relationship between the communication success probability of the system and the deployment location of IRS2. With the location of IRS1 fixed, the IRS1 + relay system and the single-relay system are independent of d2. Then, as d2 increases, the maximum communication success probabilities of the system of the present invention and the relay + IRS2 system first increase and then decrease, and reach the peak when d2 is at the midpoint of the R-D line segment, with the best communication effect.

[0223] Figure 9 It shows the relationship between the communication success probability of the system and the deployment location of the relay node R, d RDenote the distance from S to R. Placing R at an appropriate position can effectively improve the success probability. When R is close to S, the success probabilities of the system of the present invention and the Relay + IRS2 system are relatively high. This is because when the relay is performing energy harvesting and signal decoding and forwarding, it can adjust ρ and α to balance the success probabilities of the two hops to maximize the total success probability. And IRS2 plays a crucial role in the data forwarding of the second hop, which can effectively help the system combat signal fading during the transmission process. Therefore, the Relay + IRS2 system has stronger anti-interference ability than the single-relay system. When R is close to D, the success probabilities of the system of the present invention and the IRS1 + Relay system increase. This is because IRS1 improves the signal propagation environment of the first hop, reduces the probability of the first-hop signal transmission interruption, and can harvest more energy to help R perform data forwarding in the second hop. Therefore, the success probability of the system is higher.

[0224] From Figure 10 and Figure 11 simulations, it can be seen that there is an optimal ρ or α that can maximize the system's ergodic rate. Similarly, in Figure 12 simulations, we use the optimal ρ and α to obtain the relationship between the maximum ergodic capacity of the system proposed in the present invention and the three benchmark systems and the transmit power of the source node. It can be seen that both the maximum communication success probability and the ergodic capacity of the system of the present invention are much better than the benchmark systems. As P S increases, the ergodic capacities of all systems increase steadily, and the increment of the ergodic capacity of the system of the present invention is significantly higher than that of the benchmark systems. By comparing the Relay + IRS2 system and the IRS1 + Relay system, after P S grows by more than 45 dBm, the role played by IRS2 in the second-hop transmission of the system can more effectively help the system improve the ergodic capacity.

[0225] In addition, through the comparison of two different relay transmission protocols, it can be seen that under the same conditions, the performance gains of the system based on the PS protocol are always higher than those based on the TS protocol. This also provides guiding significance for wireless energy harvesting communication based on IRS.

[0226] The above is the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art in this technical field, without departing from the principle described in the present invention, several improvements and refinements can still be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A working method of a dual-intelligent reflecting surface-assisted relay cooperative communication system based on wireless energy transfer, characterized in that The relay node simultaneously has the functions of energy harvesting, information decoding, and information transmission; in the PS-based relay protocol, each time block contains T seconds and is divided into two stages of equal duration; among them, the first stage is for wireless energy transfer from the source node to the relay node, and the second stage is for data forwarding from the relay node to the destination node; the signal received in the first stage is divided into two parts by the PS factor ρ, which are respectively used for energy harvesting and information decoding of the relay node; In the TS-based relay protocol, a time block is segmented by the TS factor α. First, the first αT seconds are used for energy harvesting, and the remaining time is divided into two equal parts. Among them, the first (1 - α)T / 2 is used for information decoding of the relay node, and the second (1 - α)T / 2 is for data transmitted from the relay node to the destination; only when the relay node correctly decodes the source data can it transmit the data to the destination, otherwise it will not forward the data within the allocated time; The channel coefficients from the source node S to the relay node R, from the source node S to IRS1, and from IRS1 to the relay node R are denoted as h SR , h SI and h IR , respectively. The channel coefficients from the relay node R to the destination node D, from the relay node R to IRS2, and from IRS2 to the destination node D are denoted as g RD , g RI and g ID ; Assume that all links experience independent small-scale fading and large-scale fading. The small-scale fading follows a Rayleigh distribution, and the large-scale fading is path loss. The channel coefficients of the first-hop link are denoted as h SR = k SR l SR , h SI = k SI l SI , h IR = k IR l IR , where represents the large-scale fading coefficient, d p represents the distances of S→R, S→IRS1, and IRS1→R, and r represents the path loss exponent. Similarly, the channel coefficients of the second-hop link are denoted as g RD = k RD l RD , g RI = k RI l RI , g ID = k ID l ID . Using to represent the path loss of the large-scale fading, d q is the distance of R→D, R→IRS2, and IRS2→D; and are both circularly symmetric complex Gaussian random variables with zero mean and unit variance, used to represent the small-scale fading coefficients; The data transmission time is divided into time blocks of equal length, and the length of each time block is denoted as T; the small-scale fading of each channel remains unchanged within each time block but varies independently in different time blocks, and the small-scale fades of different channels are independent of each other; during the data transmission process, the positions of the nodes are fixed, so the large-scale path loss is also unchanged within each time block.

2. The working method of the dual-intelligent reflecting surface assisted relay cooperative communication system based on wireless energy transfer according to claim 1, characterized in that For the PS-based energy harvesting and relaying transmission protocol, S simultaneously sends RF signals to both R and IRS1 in the first half of the time block. IRS1 reflects the received incident signals to R after phase optimization processing. The signal received by R in the first hop is denoted as y R , which is expressed as: wherein is the transmission power of the source node S; represents the reflection coefficient matrix of IRS1, θ 1i ∈[0, 2π) and η 1i ∈[0, 1] respectively represent the phase and reflection amplitude gain of the i-th element of IRS1; s is the normalized signal, indicating that the average power of the signal is 1; is the additive white Gaussian noise, indicating the noise power; is the composite channel coefficient of the first hop, rewritten as where h Si represents the channel coefficient from S to the i-th reflecting element of IRS1, h iR represents the channel coefficient from the i-th reflecting element of IRS1 to R, θ SR , θ Si and θ iR respectively represent the phases of h SR , h Si and h iR ; assuming that each reflecting unit of IRS1 has the same reflection amplitude gain and optimal phase shift, so then the composite channel coefficient of the first hop is denoted as h1, and for simplicity of expression, it is given by the following formula: where λ1 = ηl SI l IR , According to mathematical derivation, the closed-form expression of the distribution function of h1 is approximately calculated as: where γ represents the lower incomplete gamma function, and x, y represent the independent variables of the function; based on the PS relaying protocol, ρ part of the signal received by the relay node R is used for EH, and this part is expressed as: Indicates a partial signal for the relay node to perform EH; The noise is negligible, and the energy harvested by R in the first hop is expressed as: where ζ ∈ (0, 1) represents the energy conversion efficiency, and the signal for ID at the relay node R is expressed as: Among them is the noise introduced when the signal is converted from the RF band to the baseband; the signal-to-noise ratio at the relay node R is expressed as: represents the power of the antenna noise, represents the power of the conversion noise generated when converting a band signal into a baseband signal; If the relay node R correctly decodes the source data in the first hop, it will forward the data to D using all the collected energy in the second hop; to simplify the performance analysis of the second-hop transmission, a finite number of energy levels are defined to approximate the actual transmit power of the relay node R; μ represents the maximum achievable transmit power of the relay node, and M + 1 energy levels are defined, that is where M is a non-zero integer, and the larger M is, the higher the approximation degree between the discrete energy levels and the continuous energy values; given the actual available power P of the relay node R R , then the approximate transmit power level of R is denoted as If the actual power P R satisfies L i <P R <L i+1 , i ∈ {0, 1,..., M - 1}, then the transmit power of R is approximated as This energy level, Δ is the interval between any two adjacent energy levels When the energy collected by R is equal to or greater than the battery capacity, the approximate transmit power of R is denoted as For the PS protocol, the actual transmit power of R is denoted as Expressed as: In the second half of a time block, relay node R forwards the decoded data to destination node D and IRS2, and IRS2 reflects the received incident signals to D; then the signal received by D is given by the following equation: Among them represents the reflection coefficient matrix of IRS2, and θ 2i ∈[0, 2π) and η 2i ∈[0, 1] respectively represent the phase shift and reflection amplitude gain of the i-th reflection element at IRS2; represents the additive white Gaussian noise at the destination node D, and the noise introduced by the RF baseband signal conversion is represents the composite channel coefficient of the second hop; similar to the first hop, each reflection unit of IRS2 can achieve the maximum reflection amplitude gain and select the optimal phase shift. The composite channel coefficient of the second hop is denoted as g2 and is expressed as: where g Ri and g iD are the channel coefficients from the i-th reflecting unit of R to IRS2 and from the i-th reflecting unit of IRS2 to D, respectively; the derivation of the distribution function of g2 is similar to that of h1 and is expressed as: where λ2 = ηl RI l ID , Then, based on the PS protocol, the signal-to-noise ratio at the destination node D is expressed as: For the PS-based energy harvesting and relaying transmission protocol, when the signal is successfully transmitted from the source node S to the destination node D, this event is defined as If the signal is interrupted during the first-hop transmission, this event is denoted as If the signal is interrupted during the second-hop transmission, this event is denoted as Event occurrence means that the signal has been successfully transmitted to the destination node within the system without signal interruption in any hop; According to the relationship between the success probability and the outage probability of signal transmission, the success probability of the system is expressed as: Pr{} represents the probability of an event; When the instantaneous signal-to-noise ratio of the system is lower than a predetermined threshold the signal transmission will be interrupted; then the outage probability of the first hop is expressed as: Among them V represents the data transmission rate; through formula derivation, Pr{B ps} is expressed as: Among them Similarly, the outage probability of the second hop is derived as: Among them The transmission power of the relay is related to the channel coefficient of the first hop; for the PS-based protocol, the actual continuous transmission power of the relay node R is denoted as Its approximate discrete transmission power is denoted as When At this time Δ is the interval between any two adjacent energy levels The probability of this situation occurring is calculated as: When , is approximated as the maximum energy level, The occurrence probability of this case is calculated as: After discretizing the transmission power of R, the outage probability of the second hop is approximated as: where is an indicator random variable that equals 1 when the condition is satisfied and 0 otherwise; substituting and Pr{C ps} into yields the success probability. The end-to-end achievable rate and ergodic capacity of the communication system are denoted as \(R\) ps and denoted as Using Jensen's inequality, the upper bound of the ergodic capacity is derived as where and denote respectively and the upper bounds of; Using Hölder's inequality, we get The expectation of is: G SR represents |h SR | channel power gain; represents the channel power gain of B1; After mathematical derivation, The result is: Among them Calculated as Among them 3. The working method of the dual-intelligent reflecting surface-assisted relay cooperative communication system based on wireless energy transfer according to claim 2, wherein, For the TS-based energy harvesting and relaying transmission protocol, in the first-hop signal transmission, the signal received by the relay node R is the same as that received under the PS protocol, denoted by y R Different from the PS protocol, the TS protocol allocates the first α part within a time block to EH, and the energy harvested by the relay node R during this part of the time is denoted as E ts , expressed as Then, (1-α) / 2 part of the time will be used for ID at the relay node R, and this part of the signal is denoted as Then the signal-to-noise ratio of the relay node is: Adopt Indicates the actual transmit power of R, which is given by the following formula: If the composite channel coefficient g2 of the second hop is the same as that under the PS protocol, the signal received by relay node D is denoted as Expressed as Correspondingly, the signal-to-noise ratio at the destination node D is expressed as: For the TS-based protocol, the successful transmission of data from S to D is defined as an event The interruption of the signal on the first hop is an event The interruption of the signal on the second hop is denoted as an event Then the success probability of the system when adopting the TS relay protocol is written as The signal-to-noise ratio threshold based on the TS protocol is Then the outage probability of the first hop of the system is expressed as: Among them Similarly, the outage probability of the second hop is expressed as: Among them In the TS-based protocol, the actual transmission power of R is denoted as The approximate discrete transmission power of R is denoted as When , The probability of this situation occurring is calculated as: When , the approximation of The probability of this situation occurring is calculated as: After discretizing the transmission power of R, the outage probability of the second hop is approximated as: Substitute and Pr{C tss} into to obtain the success probability; The end-to-end implementation rate based on the TS protocol is defined as given by The upper bound of is denoted as expressed as After mathematical derivation; The upper bound of Among them The calculation result is: Among them 4. A dual-intelligent reflecting surface-assisted relay cooperative communication system based on wireless energy transfer, characterized in that, The working method described in any one of claims 1-3 is adopted for working, which consists of a source node, a relay node, a destination node, and two intelligent reflecting surfaces. The source node, the relay node, and the destination node are all equipped with an omnidirectional antenna and operate in a half-duplex mode; The two intelligent reflecting surfaces are IRS1 and IRS2 respectively. There is an obstacle between IRS1 and IRS2. IRS1 is deployed between the source node and the relay node, and IRS2 is deployed between the relay node and the destination node; The source node and the destination node have stable energy supplies. The energy of the relay node is limited and it needs to obtain energy from the radio frequency signal sent by the source node to maintain power supply, and forward the source data to the destination node according to the decode-and-forward protocol.

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