A method to allow delayed transmission in SWIPT two-way transmission relay system based on TS strategy

Abstract

The present invention discloses a delayed transmission method in a SWIPT two-way transmission relay system based on a TS strategy. The signal-energy simultaneous transmission (SWIPT) two-way transmission relay system includes two active source nodes and a passive relay node. The relay node has the ability to collect radio frequency energy and adopts a time segmentation (TS) strategy. The entire communication channel is a quasi-static Rayleigh attenuation channel. The SWIPT two-way transmission relay system adopts a delayed relay (TDR) strategy, which means that the receiving node and the sending node are not required to perform strict time synchronization. Through theoretical derivation, the functional relationship between the actual maximum throughput and the energy collection time coefficient is obtained. An optimization problem is established with the optimal actual maximum throughput as the goal, and an optimization algorithm is used to obtain the optimal energy collection time coefficient and the optimal actual maximum throughput.

Description

Technical Field

[0001] The invention belongs to the technical field of wireless communications, and in particular relates to a method for allowing delayed transmission in a SWIPT bidirectional transmission relay system based on a TS strategy. Background Art

[0002] Radio frequency signals not only carry the information to be transmitted, but also have energy. In wireless communication systems, if energy can be transmitted while using radio frequency signals to transmit information, the service life of the wireless network system can be greatly extended. The technology of simultaneously transmitting radio frequency signal information and energy is called information-energy simultaneous transmission technology, also known as SWIPT (Simultaneous Wireless Information and Power Transfer) technology. The research on this technology is of great significance to the development of wireless transmission networks.

[0003] The key to the simultaneous transmission of information and energy lies in the design of the receiver. The receiving strategies of existing receivers mainly include time division (TS), power division (PS) and the combination of TS and PS.

[0004] SWIPT technology can effectively improve the spectrum utilization rate of the network, reduce latency, and reduce power consumption. Therefore, many scholars consider applying SWIPT technology to relay communication systems. In the process of one-way relay transmission, the distance of network transmission can be increased, but it requires more time resources as a cost. The two-way relay transmission method can solve this drawback well. Most of the research on maximum throughput in the existing SWIPT two-way transmission system tends to be idealized. The present invention discloses a method for allowing delayed transmission in a SWIPT two-way transmission relay system based on the TS strategy, in which the passive relay adopts the TS receiving strategy. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention discloses a method for allowing delayed transmission in a SWIPT two-way transmission relay system based on a TS strategy. The present invention considers a SWIPT two-way transmission relay system based on a time segmentation (TS) strategy, wherein two source nodes are active and a relay node is passive. The structural block diagram is shown in Figure 1 Given in.

[0006] like Figure 1As shown in the figure, two active source nodes transmit information to each other, but the two source nodes cannot communicate directly. The signal must pass through the passive relay node in the middle, which has the ability to collect RF energy, to reach the other source node. Therefore, during the entire communication process, the relay node not only needs to forward the information sent by the source nodes on both sides, but also needs to obtain energy from the RF signal emitted by one of the source nodes to ensure the normal operation of the entire communication system. The entire communication system adopts a time-delayed relay (TDR) strategy. The TDR strategy means that the receiving node and the transmitting node are not required to be strictly time synchronized, that is, the sending rate and the receiving rate are not required to be equal. For the two channels on both sides of the relay node that are connected to the two source nodes respectively, only the channel conditions on one side need to be considered under the TDR strategy. As long as the channel gain on one side meets the communication requirements, information transmission on one side can be performed without considering the channel conditions on the other side. For example, if the channel conditions of the uplink (the link where two source nodes send information to the relay node) meet the communication conditions, the sender will send information to the relay node; if the downlink (the link where the relay node forwards information to the two source nodes) does not meet the communication conditions, the relay node will not forward the received information, but will continue to receive the information sent by the sender. After the downlink meets the communication conditions, the relay node will forward the received information to the receiver in sequence. Therefore, the traversal capacity can be achieved by the transmission rate being equal to the traversal capacity rate, and the traversal capacity of the receiving end is calculated according to the respective channel gains, thereby determining the actual maximum throughput.

[0007] like Figure 1 As shown in the SWIPT bidirectional transmission relay model based on TS strategy, there are two active source nodes U1 and U2 and one energy-constrained relay node. h represents the source node U1 and the relay node The channel gain between the source node U2 and the relay node P1 represents the transmission power of source node U1, and P2 represents the transmission power of source node U2.

[0008] This model satisfies the following conditions: (1) The entire communication channel is a quasi-static Rayleigh fading channel. The channel gain probability density function between Source node U2 and relay node The channel gain probability density function between Among them, λ h and λ g are the means of the exponential random variables of the two channel gains respectively; accordingly, the probability distribution functions of the two channel gains are and (2) The relay node selects the amplification-forward (AF) strategy; (3) The power consumed by the relay node for signal processing is ignored. This neglect is reasonable when the transmission distance is large enough and the collected energy is the main source of consumption; (4) An energy storage device with unlimited capacity is set in the relay node; (5) The relationship between the channel gain between the two source nodes and the relay node is known (for example, a detection signal is sent to the relay by the two source nodes at the same time), so the relay node can determine which source node to obtain energy from to make the energy collection efficiency and communication efficiency higher. For the purpose of describing this patent, the relay node collects energy from the source node U1.

[0009] Figure 2 is the internal structure of the relay node based on the TS strategy, n A It represents the noise generated by the antenna when receiving the signal, n A is a circularly symmetric complex Gaussian random variable, that is Indicates n A (t) obeys a complex Gaussian distribution with a mean of 0 and a variance of n B represents the noise introduced during information processing, and definition The energy collection efficiency factor is denoted as η.

[0010] n d represents the noise generated by the antenna and the conversion module from the source node, and

[0011] The time distribution relationship between the relay node collecting energy and transmitting information is as follows: Figure 3 As shown in the figure, T represents a complete time block, α represents the energy collection time coefficient of the relay node within the time block T, α∈[0,1], that is, the relay node needs to spend αT time to obtain the required energy for forwarding information. When the collected energy is sufficient to forward the received information, the relay node uses (1-α)T / 2 time to receive the information sent by the two source nodes, and then uses (1-α)T / 2 time to forward the received information to the source node at the other end, thereby completing the communication.

[0012] Source node U1 to relay node Transmit information, then relay node The communication process forwarded to the source node U2 is called link L1; similarly, the communication process from the source node U2 to the relay node Transmit information, then relay node The communication process forwarded to the source node U1 is called link L2.

[0013] Through theoretical derivation, we can get the ergodic capacity C1 of the receiving end of link L1 as

[0014]

[0015] In the formula, is the signal-to-noise ratio probability density function of link L1, and its expression is

[0016]

[0017] In the formula,

[0018] The ergodic capacity C2 of the receiving end of link L2 is

[0019]

[0020] In the formula, is the signal-to-noise ratio probability density function of link L2, and its expression is

[0021]

[0022] In the formula,

[0023] The expression for the actual maximum throughput is

[0024]

[0025] The optimization problem P is established with the goal of optimizing the actual maximum throughput:

[0026]

[0027] In λ h , g ,η,P1,P2, and When the parameters are given, an optimization algorithm, such as the golden section method, is used to obtain the optimal energy collection time coefficient and the optimal actual maximum throughput. The optimal actual maximum throughput is denoted as τ*; the energy collection time coefficient corresponding to the optimal actual maximum throughput is defined as the optimal energy collection time coefficient, denoted as α*. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0029] Figure 1It is a SWIPT two-way transmission relay system model based on TS strategy provided by the present invention;

[0030] Figure 2 It is the internal structure of the relay node based on the TS strategy provided by the present invention;

[0031] Figure 3 It is the time allocation relationship between the relay node collecting energy and transmitting information based on the TS strategy provided by the present invention;

[0032] Figure 4 is the relationship between the actual maximum throughput τ and the energy collection time coefficient α; DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] The main purpose of the present invention is to propose a delayed transmission method in a SWIPT bidirectional transmission relay system based on TS strategy, so that the system can obtain the optimal actual maximum throughput. The two source nodes are active, the relay node is passive, and the structural block diagram is shown in Figure 1 Among them, the passive relay adopts the TS receiving strategy.

[0035] like Figure 1As shown in the figure, two active source nodes transmit information to each other, but the two source nodes cannot communicate directly. The signal must pass through the passive relay node in the middle, which has the ability to collect RF energy, to reach the other source node. Therefore, during the entire communication process, the relay node not only needs to forward the information sent by the source nodes on both sides, but also needs to obtain energy from the RF signal emitted by one of the source nodes to ensure the normal operation of the entire communication system. The entire communication system adopts a time-delayed relay (TDR) strategy. The TDR strategy means that the receiving node and the transmitting node are not required to be strictly time synchronized, that is, the sending rate and the receiving rate are not required to be equal. For the two channels on both sides of the relay node that are connected to the two source nodes respectively, only the channel conditions on one side need to be considered under the TDR strategy. As long as the channel gain on one side meets the communication requirements, information transmission on one side can be performed without considering the channel conditions on the other side. For example, if the channel conditions of the uplink (the link where two source nodes send information to the relay node) meet the communication conditions, the sender will send information to the relay node; if the downlink (the link where the relay node forwards information to the two source nodes) does not meet the communication conditions, the relay node will not forward the received information, but will continue to receive the information sent by the sender. After the downlink meets the communication conditions, the relay node will forward the received information to the receiver in sequence. Therefore, the traversal capacity can be achieved by the transmission rate being equal to the traversal capacity rate, and the traversal capacity of the receiving end is calculated according to the respective channel gains, thereby determining the actual maximum throughput.

[0036] like Figure 1 As shown in the SWIPT bidirectional transmission relay model based on TS strategy, there are two active source nodes U1 and U2 and one energy-constrained relay node. h represents the source node U1 and the relay node The channel gain between the source node U2 and the relay node P1 represents the transmission power of source node U1, and P2 represents the transmission power of source node U2.

[0037] This model satisfies the following conditions: (1) The entire communication channel is a quasi-static Rayleigh fading channel. The channel gain probability density function between Source node U2 and relay node The channel gain probability density function between Among them, λ h and λ g are the means of the exponential random variables of the two channel gains respectively; accordingly, the probability distribution functions of the two channel gains are and (2) The relay node selects the amplification-forward (AF) strategy; (3) The power consumed by the relay node for signal processing is ignored. This neglect is reasonable when the transmission distance is large enough and the collected energy is the main source of consumption; (4) An energy storage device with unlimited capacity is set in the relay node; (5) The relationship between the channel gain between the two source nodes and the relay node is known (for example, a detection signal is sent to the relay by the two source nodes at the same time), so the relay node can determine which source node to obtain energy from to make the energy collection efficiency and communication efficiency higher. For the purpose of describing this patent, the relay node collects energy from the source node U1.

[0038] Figure 2 is the internal structure of the relay node based on the TS strategy, n A It represents the noise generated by the antenna when receiving the signal, n A is a circularly symmetric complex Gaussian random variable, that is Indicates n A (t) obeys a complex Gaussian distribution with a mean of 0 and a variance of y r，i (t) represents the signal sent by the source node and assigned to the information processing module, where the subscript i=1 or 2 represents the source node number, i.e., y r1 (t) represents the signal sent by the source node U1 and then distributed to the information processing module, y r2 (t) indicates the signal sent by the receiving source node U2 and then distributed to the information processing module. B represents the noise introduced during information processing, and definition y r (t) indicates the signal received by the relay node from the two source nodes and processed by the baseband signal. r，i (t) represents the signal amplified and forwarded by the relay node, where the subscript i=1 or 2 represents the source node number, i.e., s r1 (t) represents the signal from the source node U1 amplified by the relay node and forwarded to the source node U2, s r2 (t) represents a signal obtained by amplifying the signal from the source node U2 at the relay node and forwarding it to the source node U1.

[0039] The time distribution relationship between the relay node collecting energy and transmitting information is as follows: Figure 3As shown in the figure, T represents a complete time block, α represents the energy collection time coefficient of the relay node within the time block T, α∈[0,1], that is, the relay node needs to spend αT time to obtain the energy required for forwarding information. When the collected energy is enough to forward the received information, the relay node uses (1-α)T / 2 time to receive the information sent by the two source nodes, and then uses (1-α)T / 2 time to forward the received information to the source node at the other end, thereby completing the communication. Therefore, the communication process of the TS-based TDR strategy (TS-TDR for short) can be divided into three stages: the relay node obtains energy stage; the relay node receives information stage (information uplink stage); the relay node forwards information stage (information downlink stage).

[0040] For the convenience of the following formula derivation and introduction, the source node U1 sends Transmit information, then relay node The communication process forwarded to the source node U2 is called link L1; similarly, the communication process from the source node U2 to the relay node Transmit information, then relay node The communication process forwarded to the source node U1 is called link L2.

[0041] According to the above introduction, the actual maximum throughput expression under the TS-TDR strategy can be expressed as

[0042]

[0043] In the formula, C1 and C2 represent the traversal capacity of links L1 and L2 respectively. The product of the sum of the traversal capacity of these two links and the time coefficient (1-α) / 2 of the forwarding information is the actual maximum throughput τ of the entire communication system under the TS-TDR strategy. In order to derive the relationship between the actual maximum throughput and the energy collection time coefficient α, it is necessary to express the traversal capacity with the energy collection time coefficient α.

[0044] Link L i (where the subscript i=1 or 2 represents the link number) is the ergodic capacity C of the receiving end i It can be expressed as

[0045]

[0046] In the formula, is the expectation that depends on the random channel gains h and g, Indicates link L i The signal-to-noise ratio of the signal received by the receiving source node, Indicates link L i The signal-to-noise ratio probability density function. According to the definition of the probability density function, we can get

[0047]

[0048] In the formula, Indicates link L i The signal-to-noise ratio probability distribution function.

[0049] In order to explore the relationship between the actual maximum throughput and the energy collection time coefficient α, the analysis of the entire communication system will be introduced in turn according to the three stages of the communication process.

[0050] (1) Relay node energy acquisition stage

[0051] The relay node can obtain the channel state information (CSI) of the two channels by receiving the detection signals sent by the two source nodes, and the relay node can determine which channel condition is better, so as to obtain energy using the channel with better channel condition. In this embodiment, the relay node always obtains energy from the source node U1.

[0052] In link L1, after the relay node receives the signal sent by the source node U1, the signal y is assigned to the information processing module r1 (t) can be expressed as

[0053]

[0054] In the formula, x1(t) represents the signal sent from the source node U1, and E[|x1(t)| 2 ]=1, where E[·] represents the expected value and |·| represents the modulus value. The noise generated by the relay node receiving antenna n A，1 (t) is a circularly symmetric complex Gaussian random variable, that is Indicates n A，1 (t) obeys a complex Gaussian distribution with a mean of 0 and a variance of σ A，1 2 The energy collected by the relay node is E h It can be expressed as

[0055] E h =ηαTP1|h| 2 (5)

[0056] Where η is the energy collection efficiency factor, η∈[0,1]. The energy required by the relay node to complete the forwarding of information E c It can be expressed as

[0057]

[0058] Where P RIn order to obtain the actual maximum throughput in the entire time block T, the energy collection time coefficient α must be reduced to the minimum under the premise of maintaining communication. Then this critical point is when all the energy collected by the relay node is used to relay and forward information in the entire time block T, that is,

[0059] E h =E c (7)

[0060] Substituting equations (5) and (6) into equation (7), we can get the amplification and forwarding power P R The relationship with the energy collection time coefficient α is:

[0061]

[0062] (2) Relay node receiving information stage (information uplink stage)

[0063] The principle is the same as that of equation (4). In link L2, after the relay node receives the signal sent by the source node U2, the signal y assigned to the information processing module is r2 (t) can be expressed as

[0064]

[0065] In the formula, x2(t) represents the signal sent by the source node U2, and E[|x2(t)| 2 ]=1,n A，2 (t) is a circularly symmetric complex Gaussian random variable generated by the receiving antenna of the relay node, and has According to equations (4) and (9), the relay node receives the signals sent by the two source nodes and the signal y after baseband signal processing is r (t) can be expressed as

[0066]

[0067] Where n A (t) is the total noise generated by the receiving antenna of the relay node, n B (t) represents the noise generated when the relay node processes the received signal, and

[0068] (3) Relay node forwarding information stage (information downlink stage)

[0069] Link L1 and link L2 are analyzed separately and then integrated.

[0070] ① Link L1

[0071] In link L1, the relay node amplifies the signal sent by the source node U1 and forwards the signal s to the source node U2. r1 (t) can be expressed as

[0072]

[0073] In the formula,

[0074] The signal y received by source node U2 d1 (t) is

[0075] y d1 (t) = gs r1 (t)+n d (t) (12)

[0076] Where n d is the noise generated by the antenna and conversion module of the source node, and

[0077] Substituting equations (10) and (11) into equation (12) in turn, we can obtain the overall expression of the signal received by the source node U2:

[0078]

[0079] In the formula,

[0080] Due to the self-interference cancellation, the x2(t) term in equation (13) is eliminated. After the elimination, the expression of the signal received by the source node U2 is:

[0081]

[0082] The signal-to-noise ratio of the signal received by the source node U2 on link L1 can be obtained by equation (14) and the signal-to-noise ratio formula: The expression is

[0083]

[0084] According to the definition of probability distribution function, the definition of signal-to-noise ratio probability distribution function of link L1 is:

[0085]

[0086] Substituting equation (15) into equation (16) and using equation (8), we can obtain the signal-to-noise ratio probability distribution function of link L1:

[0087]

[0088] In the formula,

[0089] Because in formula (17) |g| 2 The positive and negative coefficients of are not determined, and need to be calculated according to a1|h| 4 and b1γ|h| 2 The size relationship of is classified and discussed, and we can get

[0090]

[0091] In formula (18), when |h| 2 When <b1γ / a1, the square term on the left side of the inequality (|g| 2 ) must be greater than zero, while the numerator on the right side of the inequality (c1γ|h| 2 +d1γ) is greater than zero. According to the boundary value of the piecewise function, the denominator (a1|h| 4 -b1γ|h| 2 ) is less than zero, then the right side of the inequality must be less than zero, so the inequality always holds, and its probability is 1.

[0092] Since the channel condition is a quasi-static Rayleigh fading channel, the source node U1 and the relay node The channel gain probability density function between

[0093]

[0094] Source node U2 and relay node The channel gain probability density function between

[0095]

[0096] In the formula, λ h , g are the means of the exponential random variables of the two channel gains. Correspondingly, the probability distribution functions of the two channel gains are

[0097] F h (z)=p(|h| 2 < z) = 1-exp(-z / λ h ) (twenty one)

[0098] F g (z)=p(|g| 2 < z) = 1-exp(-z / λ g ) (twenty two)

[0099] Substituting equations (19) to (22) into the piecewise function of equation (18), we can obtain The integral expression of the independent variable z is

[0100]

[0101] right Taking the partial derivative of γ, we get the signal-to-noise ratio probability density function of link L1 Its expression is

[0102]

[0103] Substituting equation (24) into equation (2) for calculating the ergodic capacity, we can obtain the ergodic capacity C1 of the receiving end of link L1, which is

[0104]

[0105] ②Link L2

[0106] The analysis process of link L2 is basically the same as that of link L1. In link L2, the relay node amplifies the signal from source node U2 and forwards the signal s to source node U1. r2 (t) can be expressed as

[0107]

[0108] The signal y received by the source node U1 d2 (t) is

[0109] y d2 (t) = hs r2 (t)+n d (t) (27)

[0110] Substituting equations (10) and (26) into equation (27) in turn, due to the elimination of self-interference, the signal y received by the source node U1 is d2 (t) is

[0111]

[0112] Then, the signal-to-noise ratio of the signal received by the source node U1 of link L2 is for

[0113]

[0114] The signal-to-noise ratio probability distribution function of link L2 is:

[0115]

[0116] In the formula,

[0117] In formula (30), |h| 4 The positive and negative coefficients of are not determined, and need to be calculated according to a2|g| 2 The relationship between the magnitude of and b2γ can be classified and discussed.

[0118]

[0119] In formula (31), when |g| 2 <b2γ / a2, the fourth-order term on the left side of the inequality (|h| 4 ) must be greater than zero, while the numerator on the right side of the inequality (c2γ|g| 2 +d2γ) is greater than zero. According to the boundary value of the piecewise function, the denominator (a2|g| 2 -b2γ) is less than zero, then the right side of the inequality must be less than zero, so the inequality always holds, and its probability is 1.

[0120] Substituting equations (19) to (22) into the piecewise function of equation (31), we can obtain The integral expression of the independent variable z is

[0121]

[0122] right Taking the partial derivative of γ, we can calculate the signal-to-noise ratio probability density function of link L2: Its expression is

[0123]

[0124] In the formula,

[0125] Substituting equation (33) into equation (2) for calculating the ergodic capacity, we can obtain the ergodic capacity C2 of the receiving end of link L2, which is

[0126]

[0127] After deriving the functional expressions of the ergodic capacities C1 and C2 of the link L1 and link L2 under the TS-TDR strategy with respect to the energy collection time coefficient α, substituting them into equation (1), we can obtain the expression of the actual maximum throughput τ with respect to the energy collection time coefficient α.

[0128] The optimization problem P is established with the goal of optimizing the actual maximum throughput:

[0129]

[0130] In λ h , g ,η,P1,P2, and When the parameters are given, an optimization algorithm, such as the golden section method, is used to obtain the optimal energy collection time coefficient and the optimal actual maximum throughput. The optimal actual maximum throughput is denoted as τ*; the energy collection time coefficient corresponding to the optimal actual maximum throughput is defined as the optimal energy collection time coefficient, denoted as α*.

[0131] When the golden section method is used to solve the optimization problem P of formula (35), the optimal energy collection time coefficient α* and the optimal actual maximum throughput τ* are obtained. The steps are:

[0132] Step 1: Given the initialization interval [a, b] and precision e of α;

[0133] Step 2: Solve the golden section points of the interval a1 = a + (1-0.618) (ba), a2 = a + 0.618 × (ba);

[0134] Step 3: Solve the actual maximum throughputs τ(a1) and τ(a2) corresponding to a1 and a2 respectively; if the actual maximum throughput τ(a1) < τ(a2), jump to step 4, otherwise jump to step 5;

[0135] Step 4: If a2-a1<e, stop iteration, output the optimal solution α*=a2, and output the optimal actual maximum throughput τ*=τ(a2); otherwise, let a=a1, a1=a2, a2=a+0.618×(ba), and jump to step 3;

[0136] Step 5: If a2-a1<e, stop iteration, output the optimal solution α*=a2, and output the optimal actual maximum throughput τ*=τ(a2); otherwise, let b=a2, a2=a1, a1=a+(1-0.618)(ba), and jump to step 3.

[0137] The technical solution provided by the present invention is further described below in conjunction with specific experimental simulations.

[0138] The present invention simulates and verifies the delayed transmission method in the SWIPT two-way transmission relay system based on the TS strategy, and uses the following parameter settings: energy collection efficiency factor η = 1, two source node transmission power P1 = P2 = 1, channel gain index random variables h and g mean λ h and λ g Set to 1 respectively, the noise power generated by the relay node when receiving information and the noise power generated when the source node receives information Both are set to 0.01.

[0139] See also Figure 4, when α*=0.2, the optimal actual maximum throughput τ*=3.7513. According to the simulation graph, it can be concluded that when α is too small or too large, the actual maximum throughput is less than the optimal actual maximum throughput.

[0140] In summary, the present invention discloses a method for allowing delayed transmission in a SWIPT bidirectional transmission relay system based on a TS strategy, so that the system obtains the optimal actual maximum throughput.

[0141] The above content is a further detailed description of the present invention in combination with a specific preferred embodiment. It cannot be determined that the specific embodiments of the present invention are limited to this. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as belonging to the scope of patent protection of the present invention determined by the submitted claims.

Claims

1. A method for allowing delayed transmission in a SWIPT two-way transmission relay system based on TS strategy, characterized in that: include: The SWIPT bidirectional transmission relay system consists of two active source nodes U1 and U2 and a passive relay node. The relay node has the ability to collect radio frequency energy and adopts the time segmentation (TS) strategy. Two source nodes cannot communicate directly, and the signal must pass through the intermediate relay node to reach the other source node. The channel gain between the source node U2 and the relay node is h. The channel gain between them is g; the transmission power of source node U1 is P1, and the transmission power of source node U2 is P2; The SWIPT two-way transmission relay system adopts the time-delayed relay (TDR) strategy. The TDR strategy does not require the receiving node to be strictly synchronized with the sending node, that is, the sending rate and the receiving rate are not required to be equal. For the two channels on both sides of the relay node that are connected to the two source nodes, only the channel conditions on one side need to be considered under the TDR strategy. As long as the channel gain on one side meets the communication requirements, information transmission on one side can be carried out without considering the channel conditions on the other side. Therefore, the traversal capacity can be achieved by making the transmission rate equal to the traversal capacity rate, and the traversal capacity of the receiving end is calculated according to the respective channel gains, thereby determining the actual maximum throughput. The SWIPT two-way transmission relay system meets the following conditions: (1) The entire communication channel is a quasi-static Rayleigh fading channel: the source node U1 and the relay node The channel gain probability density function between Source node U2 and relay node The channel gain probability density function between Among them, λ h and λ g are the means of the exponential random variables of the two channel gains respectively; accordingly, the probability distribution functions of the two channel gains are and (2) The relay node selects the amplify-and-forward (AF) strategy; (3) The power consumed by the relay node for signal processing is ignored; (4) An energy storage device with infinite capacity is set up in the relay node; (5) The relationship between the channel gains of the two source nodes and the relay node is known, and the relay node collects energy from the source node U1; In the internal structure of the relay node, n A It represents the noise generated by the antenna when receiving the signal, n A is a circularly symmetric complex Gaussian random variable, that is Indicates n A (t) obeys a complex Gaussian distribution with a mean of 0 and a variance of n B represents the noise introduced during information processing, and definition The energy collection efficiency factor is denoted as η; n d represents the noise generated by the antenna and the conversion module from the source node, and α represents the energy collection time coefficient of the relay node within the time block T, α∈[0,1], that is, the relay node needs to spend αT time to obtain the required energy for forwarding information. When the collected energy is enough to forward the received information, the relay node uses (1-α)T / 2 time to receive the information sent by the two source nodes, and then uses (1-α)T / 2 time to forward the received information to the source node at the other end, thereby completing the communication; Source node U1 to relay node Transmit information, then relay node The communication process forwarded to the source node U2 is called link L1; similarly, the communication process from the source node U2 to the relay node Transmit information, then relay node The communication process forwarded to the source node U1 is called link L2; The ergodic capacity C1 of the receiving end of link L1 is In the formula, is the signal-to-noise ratio probability density function of link L1, and its expression is In the formula, The ergodic capacity C2 of the receiving end of link L2 is In the formula, is the signal-to-noise ratio probability density function of link L2, and its expression is In the formula, The expression for the actual maximum throughput is The optimization problem P is established with the goal of optimizing the actual maximum throughput: In λ h , g ,η,P1,P2, and When the parameters are given, the optimization algorithm is used to obtain the optimal energy collection time coefficient and the optimal actual maximum throughput.

Images