Throughput optimization method in SWIPT relay system with direct link based on TS strategy

Abstract

The present invention discloses a throughput optimization method in a SWIPT relay system including a direct link based on a TS strategy. The signal-to-energy simultaneous transmission (SWIPT) relay system including a direct link includes a source node, a relay node and a destination node. The source node and the destination node are active; the relay node is passive, but has a radio frequency energy collection capability, and adopts a time segmentation (TS) strategy. All channels are quasi-static block fading channels. The destination node uses a maximum ratio combining method to combine signals from a direct link (a link between a source node and a destination node) and a relay forwarding link, respectively, as the final signal of the destination node. The entire communication system adopts a transmission mode with limited delay. Through theoretical derivation, the functional relationship between throughput and energy collection time coefficient is obtained. An optimization problem is established with the optimal throughput as the goal, and an optimization algorithm is used to obtain the optimal energy collection time coefficient and the optimal throughput.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless communications, and in particular relates to a throughput optimization method in a SWIPT relay system including a direct link based on a TS strategy. Background Art

[0002] With the rapid development of the information age, the scale of wireless networks continues to expand, and the number of nodes in the network has increased dramatically. In traditional networks, the energy of nodes is provided by batteries with limited capacity. This energy supply method determines the limited service life of nodes. At the same time, with more and more nodes, frequent battery replacement will consume a lot of manpower and material resources. However, the emergence and development of Simultaneous Wireless Information and Power Transfer (SWIPT) technology provides a new idea for solving this problem. SWIPT technology can collect energy for passive nodes in communication networks through radio frequency signals, and can also use radio frequency signals to transmit information. This technology avoids the drawbacks of traditional energy supply methods and greatly extends the service life of network nodes. Therefore, the application of SWIPT technology in wireless communication networks has attracted much attention.

[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 of the network, reduce latency, and reduce power consumption. Therefore, many scholars consider applying SWIPT technology to relay communication systems.

[0005] With the rapid development of SWIPT technology, many researchers consider using SWIPT technology in relay systems. For single-input single-output relay systems, the operation strategy of relays is the focus of current research. After adding relays to the communication system, path attenuation can be effectively reduced, and the transmission distance and system performance of the system can be improved. In current research, most scholars ignore direct link transmission and only consider the transmission of relay links, which will cause a waste of resources, affect the communication efficiency of the system, and limit the improvement of system performance. Therefore, the present invention discloses a throughput optimization method in a SWIPT relay system including a direct link based on a TS strategy. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention discloses a method for optimizing throughput in a SWIPT relay system including a direct link based on a TS strategy. Figure 1As shown in FIG. 1 , the SWIPT relay system model including a direct link includes a source node S, a relay node R and a destination node D. The link that transmits information from the source node S to the destination node D is called a direct link (DL). The link that sends information from the source node S to the destination node D through the relay node R is called a relay forwarding link (RL). The source node S and the destination node D are active, that is, these two nodes have no energy restrictions and both have fixed energy supplies; while the relay node R has no energy supply equipment and needs to obtain energy from the radio frequency signal of the source node S. The relay node uses the collected energy to forward the information from the source node S to the destination node D. The relay node adopts the TS receiving strategy. The relay node works in the decoding and forwarding (DF) mode. Only when the signal-to-noise ratio of the signal received by the relay node is greater than or equal to the threshold, the relay node will decode correctly, otherwise an interruption will occur and the relay node will not forward the information to the destination node. The relay node stores the collected energy to maintain the basic operation of the relay system, including the energy consumed by the circuit itself and the energy required for decoding. After successful decoding, the energy collected by the relay node is completely used to relay and forward information. The destination node uses the maximum ratio combining (MRC) method to combine the signals from the direct link (DL) and the relay link (RL) as the final signal of the destination node.

[0007] All nodes use half-duplex working mode. h represents the channel gain between the source node and the relay node, g represents the channel gain between the relay node and the destination node, and f represents the channel gain between the source node and the destination node. d1 represents the distance between the source node and the relay node, d2 represents the distance between the relay node and the destination node, and d represents the distance between the source node and the destination node.

[0008] All channels are quasi-static block fading channels, and they are frequency non-selective fading. In a communication time block T, the channel gain remains constant, and the channel gain changes between different time blocks. These random channel gains are independent and obey the Rayleigh distribution. |f| 2 、|h| 2 and |g| 2 are all random variables, subject to exponential distribution, and their expectations are E[|f| 2 ]=E[|h| 2 ]=E[|g| 2 ]=1, where E[·] means taking the expectation, and |·| means taking the modulus value. Random variable |f| 2 The probability density function is f f (z) = e -z , the probability distribution function is F f (z)=P(|f| 2 <z)=1-e -z; Random variable |h| 2 The probability density function is f h (x) = e -x , the probability distribution function is F h (x) = P(|h| 2 <x)=1-e -x ; Random variable |g| 2 The probability density function is f g (y) = e -y , the probability distribution function is F g (y)=P(|g| 2 <y)=1-e -y During the communication process, the most important energy loss is the path loss, and the loss coefficient is set to m.

[0009] Figure 2 is the SWIPT relay system model based on TS strategy, x s is the normalized signal emitted by the source node, that is, E[|x s (t)| 2 ]=1, the average transmission power is P s .n r represents the noise generated by the antenna of the relay node when receiving the signal, n r is a circularly symmetric complex Gaussian random variable, that is Indicates n r (t) obeys a complex Gaussian distribution with a mean of 0 and a variance of EH stands for Energy Harvesting Module. r (t) represents the signal received by the relay node, x r (t) represents the signal forwarded by the relay node, and its power is P r .n d It represents the noise generated by the antenna when the destination node receives the signal, and y d (t) represents the signal received by the destination node. In addition, the energy collection efficiency factor is denoted as η.

[0010] The time allocation relationship between the relay node collecting energy and transmitting information based on the TS strategy is as follows: Figure 3 As shown in the figure, T represents a complete time block, α represents the time coefficient of the relay node collecting energy within the time block T, α∈[0,1]; the relay node uses the time αT 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 source node; at the same time, the source node also sends the same information to the destination node; then the relay node uses (1-α)T / 2 time to forward the received information to the destination node, thus completing the communication.

[0011] The entire communication system adopts a delay-limited transmission mode, in which the receiver decodes the received information in units of a time block, and the system throughput performance is measured by the interruption probability. The information transmission rate of the source node is fixed to R0, so the signal-to-noise ratio threshold is set

[0012] Through theoretical derivation, the interruption probability of the direct link is for

[0013]

[0014] In the formula,

[0015] The outage probability between the source node and the relay node for

[0016]

[0017] In the formula,

[0018] The destination node uses the maximum ratio combining method to combine the signals from the direct link and the relay forwarding link, and the final signal of the destination node is still not correctly decoded. This is the probability of outage in this case. for

[0019]

[0020] In the formula,

[0021] Finally, from the perspective of the destination node, the probability of communication interruption P out , that is, the probability that the destination node cannot decode correctly is

[0022]

[0023] The throughput of the SWIPT relay system with direct link based on TS strategy is

[0024]

[0025] The optimization problem P is established with the goal of optimal throughput:

[0026]

[0027] st 0≤α≤1

[0028] In P s , R0, η, d1, d2, d, m, 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 throughput. The optimal throughput is denoted as τ*; the energy collection time coefficient corresponding to the optimal throughput is defined as the optimal energy collection time coefficient, denoted as α*. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] 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.

[0030] Figure 1 The present invention provides a direct link SWIPT relay system model;

[0031] Figure 2 It is a SWIPT relay system model based on TS strategy provided by the present invention;

[0032] 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;

[0033] Figure 4 is the relationship between the throughput τ and the energy collection time coefficient α; DETAILED DESCRIPTION

[0034] 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.

[0035] The main purpose of the present invention is to propose a throughput optimization method in a SWIPT relay system including a direct link based on a TS strategy, so that the system can obtain the optimal throughput. The source node and the destination node are active, the relay node is passive, and the structural block diagram is in Figure 1 Among them, the passive relay adopts the TS receiving strategy.

[0036] Figure 1It is a direct link SWIPT relay system model, which includes a source node S, a relay node R and a destination node D. The link that transmits information from the source node S to the destination node D is called a direct link (DL). The link that sends information from the source node S to the destination node D through the relay node R is called a relay forwarding link (RL). The source node S and the destination node D are active, that is, these two nodes have no energy restrictions and they both have a fixed energy supply; while the relay node R has no energy supply equipment and needs to obtain energy from the radio frequency signal of the source node S. The relay node uses the collected energy to forward the information from the source node S to the destination node D. The relay node adopts the TS receiving strategy. The relay node works in the decode-and-forward (DF) mode. Only when the signal-to-noise ratio of the signal received by the relay node is greater than or equal to the threshold, the relay node will decode correctly, otherwise an interruption will occur and the relay node will not forward the information to the destination node. The relay node stores the collected energy to maintain the basic operation of the relay system, including the energy consumed by the circuit itself and the energy required for decoding. After successful decoding, the energy collected by the relay node is completely used to relay the information.

[0037] In the actual communication process, when the channel condition is good, the path loss will be very small, and the direct link can accurately send information; when the channel condition is poor, the path loss is large, and when the energy of the relay node is sufficient, the relay node can accurately forward the information to the destination node; when the channel condition is very poor, it will cause the situation that both the direct link transmission and the relay forwarding link transmission cannot accurately transmit information to the destination node, but the destination node will perform maximum ratio combining (MRC) on the signals on the two links and may be able to correctly decode them.

[0038] In this patent, the source node sends information to the destination node through both the relay forwarding link and the direct link. The destination node uses the maximum ratio combining (MRC) method to combine the signals from the direct link and the relay forwarding link as the final signal of the destination node, thereby enabling the system to achieve higher throughput and improve the communication performance of the system.

[0039] All nodes use half-duplex working mode. h represents the channel gain between the source node and the relay node, g represents the channel gain between the relay node and the destination node, and f represents the channel gain between the source node and the destination node. d1 represents the distance between the source node and the relay node, d2 represents the distance between the relay node and the destination node, and d represents the distance between the source node and the destination node.

[0040] All channels are quasi-static block fading channels with frequency non-selective fading. In a communication time block T, the channel gain remains constant. Between different time blocks, the channel gain will change. These random channel gains are independent of each other and obey the Rayleigh distribution. |f| 2 、|h| 2 and |g| 2 are all random variables, subject to exponential distribution, and their expectations are E[|f| 2 ]=E[|h| 2 ]=E[|g| 2 ]=1, where E[·] means taking the expectation, and |·| means taking the modulus value. Random variable |f| 2 The probability density function of

[0041] f f (z) = e -z (1)

[0042] Random variable |f| 2 The probability distribution function of

[0043] F f (z)=P(|f| 2 <z)=1-e -z (2)

[0044] Random variable |h| 2 The probability density function of

[0045] f h (x) = e -x (3)

[0046] Random variable |h| 2 The probability distribution function of

[0047] F h (x) = P(|h| 2 <x)=1-e -x (4)

[0048] Random variable |g| 2 The probability density function of

[0049] f g (y) = e -y (5)

[0050] Random variable |g| 2 The probability distribution function of

[0051] F g (y)=P(|g| 2 <y)=1-e -y (6)

[0052] During the communication process, the most important energy loss is path loss, and the loss coefficient is set to m.

[0053] Figure 2 is the SWIPT relay system model based on TS strategy, x s is the normalized signal emitted by the source node, that is, E[|x s (t)| 2 ]=1, the average transmission power is P s .n r represents the noise generated by the antenna of the relay node when receiving the signal, n r is a circularly symmetric complex Gaussian random variable, that is Indicates n r (t) obeys a complex Gaussian distribution with a mean of 0 and a variance of EH stands for Energy Harvesting Module. r (t) represents the signal received by the relay node, x r (t) represents the signal forwarded by the relay node, and its power is P r .n d It represents the noise generated by the antenna when the destination node receives the signal, and y d (t) represents the signal received by the destination node.

[0054] The time allocation relationship between the relay node collecting energy and transmitting information based on the TS strategy is as follows: Figure 3 As shown in the figure, T represents a complete time block, α represents the time coefficient of the relay node collecting energy within the time block T, α∈[0,1]; the relay node uses the time αT 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 source node; at the same time, the source node also sends the same information to the destination node; then the relay node uses (1-α)T / 2 time to forward the received information to the destination node, thus completing the communication.

[0055] The entire communication system adopts a delay-limited transmission mode, in which the receiver decodes the received information in units of a time block, and the system throughput performance is measured by the interruption probability. The information transmission rate of the source node is fixed to R0, so the signal-to-noise ratio threshold is set

[0056] In order to explore the relationship between throughput and energy collection time coefficient α, they will be introduced separately according to link characteristics.

[0057] (1) Direct Link (DL)

[0058] In the DL transmission link, since there is no forwarding by relay nodes, there is no energy collection problem involved. The signal received by the destination node can be expressed as

[0059]

[0060] The signal-to-noise ratio of the destination node for

[0061]

[0062] Probability of direct link outage for

[0063]

[0064] Substituting equation (8) into equation (9) and using equation (2), we can get the outage probability of the direct link: for

[0065]

[0066] In the formula,

[0067] (2) Relay Link (RL)

[0068] The signal y received by the relay node r It can be expressed as

[0069]

[0070] In the first αT time, the relay node uses all the received RF signals for energy reception. Therefore, the energy collected by the relay is

[0071]

[0072] Where η is the energy collection efficiency factor, η∈[0,1].

[0073] In the first (1-α)T / 2 time, the relay node uses all received RF signals for information reception. Then the signal-to-noise ratio at the relay node is for

[0074]

[0075] if If the relay node cannot accurately decode the information from the source node, it will cause an interruption and the relay node will not forward the information. The energy collected by the relay node will be stored at the relay node to maintain the basic operation of the relay node, meet the energy required for decoding and circuit consumption, etc.

[0076] The outage probability between the source node and the relay node for

[0077]

[0078] Substituting equation (13) into equation (14) and using equation (4), we can get the interruption probability for

[0079]

[0080] In the formula,

[0081] if The relay node will successfully decode the information from the source node, and then the relay node uses all the collected energy E r , to forward the decoded information to the destination node. The transmission power of the relay node can be expressed as

[0082]

[0083] It can be seen from equation (16) that the transmission power of the relay node will be affected by the energy collection time coefficient α. In the second (1-α)T / 2 time, the relay node forwards the decoded information. The signal y received by the destination node d It can be expressed as

[0084]

[0085] The signal-to-noise ratio of the destination node for

[0086]

[0087] The probability of interruption between the relay node and the destination node for

[0088]

[0089] In the formula,

[0090] Using equations (3) to (6), we can get

[0091]

[0092] In the relay link (RL), the relay node and the destination node are used to determine whether an interruption has occurred. If an interruption occurs at any one of them, the entire transmission will be interrupted and the transmission will fail. Therefore, the interruption probability of the relay link (RL) is for

[0093]

[0094] According to the definition of throughput, if we do not consider direct links and only rely on relay forwarding links for communication, the throughput of the system is

[0095]

[0096] (3) Relay-forwarding link combined with direct link (RL-DL)

[0097] The destination node uses the maximum ratio combining method to combine the signals from the direct link and the relay forwarding link as the final signal of the destination node. It is the sum of the signal-to-noise ratio of the direct link and the relay forwarding link, and its expression is

[0098]

[0099] The corresponding outage probability for

[0100]

[0101] In the formula,

[0102] Using equations (1) to (6), we can get

[0103]

[0104] Finally, from the perspective of the destination node, the probability of communication interruption P out , that is, the probability that the destination node cannot decode correctly is

[0105]

[0106] Substituting equation (10), equation (15) and equation (25) into equation (26), we obtain

[0107]

[0108] According to the definition of throughput, the system throughput τ is obtained as

[0109]

[0110] The optimization problem P is established with the goal of optimal throughput:

[0111]

[0112] In P s , R0, η, d1, d2, d, m, 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 throughput. The optimal throughput is denoted as τ*; the energy collection time coefficient corresponding to the optimal throughput is defined as the optimal energy collection time coefficient, denoted as α*.

[0113] When the golden section method is used to solve the optimization problem P of formula (29), the optimal energy collection time coefficient α* and the optimal throughput τ* are obtained. The steps are as follows:

[0114] Step 1: Given the initialization interval [a, b] and precision e of α;

[0115] Step 2: Solve the golden section points of the interval a1 = a + (1-0.618) (ba), a2 = a + 0.618 × (ba);

[0116] Step 3: Solve the throughputs τ(a1) and τ(a2) corresponding to a1 and a2 respectively; if the throughput τ(a1) < τ(a2), jump to step 4, otherwise jump to step 5;

[0117] Step 4: If a2-a1<e, stop iteration, output the optimal solution α*=a2, and output the optimal throughput τ*=τ(a2); otherwise, let a=a1, a1=a2, a2=a+0.618×(ba), and jump to step 3;

[0118] Step 5: If a2-a1<e, stop iteration, output the optimal solution α*=a2, and output the optimal throughput τ*=τ(a2); otherwise, let b=a2, a2=a1, a1=a+(1-0.618)(ba), and jump to step 3.

[0119] The technical solution provided by the present invention is further described below in conjunction with specific experimental simulations.

[0120] The present invention simulates and verifies the throughput optimization method in a SWIPT relay system including a direct link based on the TS strategy, and uses the following parameter settings: s =1, R0=2, eta=1, d1=0.45, d2=2.55, d=d1+d2=3, m=2.7,

[0121] See also Figure 4 , since both contain relay link transmission, the throughput of the relay forwarding link (RL) and the relay forwarding link combined with the direct link (RL-DL) first increases and then decreases as α increases. They both have the optimal energy collection time coefficient α *, at which point their throughputs both reach their optimal values. Through numerical calculations, we find that the optimal point of the RL-DL link is (0.27, 0.4791) and the optimal point of the RL link is (0.33, 0.4133). * As α increases, the throughput also increases. * As it continues to increase, the throughput decreases. Figure 4 It can be seen that when α approaches 0: (1) For RL links, the throughput is almost 0, because at this time the time the relay node uses to collect energy is almost 0, and the relay node cannot obtain the energy required to forward information, so an interruption occurs at the relay node, causing the throughput to drop to almost 0; (2) For RL-DL links, due to the existence of DL links, its throughput is a finite value greater than 0. When α approaches 1: In terms of time allocation, there is almost no time allocated to the source node for sending information, resulting in the destination node's throughput being almost 0. From Figure 4 It can be seen that no matter how large the energy collection time coefficient is, the throughput of the RL-DL link is always greater than the throughput of the RL link, and the optimal throughput is improved by 15.9%.

[0122] In summary, the present invention discloses a throughput optimization method in a SWIPT relay system including a direct link based on a TS strategy, so that the system obtains an optimal throughput.

[0123] 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 optimizing throughput in a SWIPT relay system including a direct link based on a TS strategy, characterized in that: include: The signal-to-sense simultaneous transmission (SWIPT) relay system including a direct link includes a source node S, a relay node R and a destination node D; The link from source node S to destination node D is called direct link (DL); the link from source node S to destination node D through relay node R is called relay link (RL); source node S and destination node D are active, that is, these two nodes have no energy constraints and they both have fixed energy supply; The relay node R does not have a device to provide energy, so it needs to obtain energy from the RF signal of the source node S. The relay node uses the collected energy to forward the information from the source node S to the destination node D. The relay node adopts the time segmentation (TS) receiving strategy. The relay node works in the decoding and forwarding (DF) mode. Only when the signal-to-noise ratio of the signal received by the relay node is greater than or equal to the threshold, the relay node will decode correctly. Otherwise, an interruption will occur and the relay node will not forward the information to the destination node. The relay node will store the collected energy. After successful decoding, the energy collected by the relay node is completely used to relay the forwarding information. The destination node uses the maximum ratio combining (MRC) method to combine the signals from the direct link (DL) and the relay forwarding link (RL) as the final signal of the destination node. All nodes adopt half-duplex working mode; h represents the channel gain between the source node and the relay node, g represents the channel gain between the relay node and the destination node, and f represents the channel gain between the source node and the destination node; d1 represents the distance between the source node and the relay node, d2 represents the distance between the relay node and the destination node, and d represents the distance between the source node and the destination node; All channels are quasi-static block fading channels with frequency non-selective fading. In a communication time block T, the channel gain remains constant. Between different time blocks, the channel gain will change. These random channel gains are independent and obey the Rayleigh distribution. |f| 2 、|h| 2 and |g| 2 are all random variables, subject to exponential distribution, and their expectations are E[|f| 2 ]=E[|h| 2 ]=E[|g| 2 ]=1, where E[·] means taking the expectation, |·| means taking the modulus value; random variable |f| 2 The probability density function is f f (z) = e -z , the probability distribution function is F f (z)=P(|f| 2 <z)=1-e -z ; Random variable |h| 2 The probability density function is f h (x) = e -x , the probability distribution function is F h (x) = P(|h| 2 <x)=1-e -x ; Random variable |g| 2 The probability density function is f g (y) = e -y , the probability distribution function is F g (y)=P(|g| 2 <y)=1-e -y ; Set the path loss coefficient to m; The average power of the normalized signal transmitted by the source node is P s ;n r represents the noise generated by the antenna of the relay node when receiving the signal, n r is a circularly symmetric complex Gaussian random variable, that is Indicates n r (t) obeys a complex Gaussian distribution with a mean of 0 and a variance of n d It represents the noise generated by the antenna when the destination node receives the signal, and The energy collection efficiency factor is denoted as η; 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]; the relay node uses 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 source node; at the same time, the source node also sends the same information to the destination node; The relay node then uses (1-α)T / 2 time to forward the received information to the destination node, thus completing the communication; The entire communication system adopts a delay-limited transmission mode, in which the receiver decodes the received information in units of a time block, and the system throughput performance is measured by the interruption probability; the information transmission rate of the source node is fixed to R0, so the signal-to-noise ratio threshold is set The outage probability of the direct link is denoted by The outage probability between the source node and the relay node is denoted as The destination node uses the maximum ratio combining method to combine the signals from the direct link and the relay forwarding link, and the final signal of the destination node is still not correctly decoded. The probability of interruption in this case is recorded as From the perspective of the destination node, the probability of communication interruption P out , that is, the probability that the destination node cannot decode correctly is The throughput of the SWIPT relay system with direct link based on TS strategy is In the formula, The optimization problem P is established with the goal of optimal throughput: In P s , R0, η, d1, d2, d, m, and When the parameters are given, the optimization algorithm is used to obtain the optimal energy collection time coefficient and the optimal throughput.

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