CN111988803A - TS strategy-based delay-limited transmission method in SWIPT bidirectional transmission relay system - Google Patents

TS strategy-based delay-limited transmission method in SWIPT bidirectional transmission relay system Download PDF

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CN111988803A
CN111988803A CN202010882194.8A CN202010882194A CN111988803A CN 111988803 A CN111988803 A CN 111988803A CN 202010882194 A CN202010882194 A CN 202010882194A CN 111988803 A CN111988803 A CN 111988803A
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relay node
relay
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李建雄
张宏宇
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Tianjin Polytechnic University
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W24/00—Supervisory, monitoring or testing arrangements
    • H04W24/02—Arrangements for optimising operational condition
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W40/00—Communication routing or communication path finding
    • H04W40/02—Communication route or path selection, e.g. power-based or shortest path routing
    • H04W40/04—Communication route or path selection, e.g. power-based or shortest path routing based on wireless node resources
    • H04W40/10—Communication route or path selection, e.g. power-based or shortest path routing based on wireless node resources based on available power or energy
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W40/00—Communication routing or communication path finding
    • H04W40/02—Communication route or path selection, e.g. power-based or shortest path routing
    • H04W40/22—Communication route or path selection, e.g. power-based or shortest path routing using selective relaying for reaching a BTS [Base Transceiver Station] or an access point
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W56/00—Synchronisation arrangements
    • H04W56/001—Synchronization between nodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

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Abstract

The invention discloses a method for limiting delay transmission in an SWIPT bidirectional transmission relay system based on a TS strategy. A simultaneous transfer of information and energy (SWIPT) bidirectional transmission relay system comprises two active source nodes and a passive relay node. The relay node has radio frequency energy harvesting capability and employs a Time Slicing (TS) strategy. The entire communication channel is a quasi-static rayleigh fading channel. The SWIPT bidirectional transmission relay system adopts a Limited Delay Relay (LDR) strategy, wherein the LDR strategy means that strict time synchronization must be ensured at a receiving end node and a sending end node, and if the channel gain of a single channel cannot meet the communication condition, the communication of the whole communication system is interrupted. And obtaining a functional relation between the actual maximum throughput and the energy collection time coefficient through theoretical derivation. And establishing an optimization problem by taking the optimum of the actual maximum throughput as a target, and obtaining an optimum energy collecting time coefficient and an optimum actual maximum throughput by adopting an optimization algorithm.

Description

TS strategy-based delay-limited transmission method in SWIPT bidirectional transmission relay system
Technical Field
The invention belongs to the technical field of wireless communication, and particularly relates to a method for limiting delay transmission in an SWIPT (switched wire power protocol packet) bidirectional transmission relay system based on a TS (transport stream protocol) strategy.
Background
The radio frequency signal not only carries the information to be transmitted, but also has its own energy. In a wireless communication system, if energy can be transmitted while information is transmitted using radio frequency signals, the service life of the wireless network system can be greatly extended. The technology of simultaneous transmission of radio frequency signal Information and energy is called as a signal energy simultaneous transmission technology, also called as a swipt (simplex Wireless Information and Power transfer) technology, and research on the technology has great significance for the development of Wireless transmission networks.
The key of the simultaneous transmission of information and energy lies in the design of a receiver, the receiving strategy of the existing receiver mainly adopts several modes of time division (TS), power division (PS), TS and PS combination and the like.
The SWIPT technology can effectively improve the frequency spectrum utilization rate of the network, reduce delay and reduce power consumption, so that a lot of students consider applying the SWIPT technology to a relay communication system. In the process of one-way relay transmission, the distance of network transmission can be increased, but more time resources are consumed as cost, and the disadvantage can be well solved by a two-way relay transmission mode. The invention discloses a method for limiting delay transmission in an SWIPT bidirectional transmission relay system based on a TS strategy, wherein a TS receiving strategy is adopted by passive relay.
Disclosure of Invention
Aiming at the defects of the prior art, the invention discloses a method for limiting delay transmission in an SWIPT bidirectional transmission relay system based on a TS strategy. The invention considers a SWIPT bidirectional transmission relay system based on a time division (TS) strategy, wherein two source nodes are active, a relay node is passive, and a structural block diagram is given in figure 1.
As shown in fig. 1, two active source nodes transmit information to each other, but the two source nodes cannot communicate directly with each other, and the signal must pass through an intermediate passive relay node with radio frequency energy harvesting capability to reach the other source node. Therefore, the relay node not only needs to forward the information sent by the source nodes on both sides in the whole communication process, but also needs to acquire energy from the radio frequency signal transmitted by one of the source nodes to ensure the normal operation of the whole communication system. The whole communication system adopts a Limited Delay Relay (LDR) strategy. The LDR strategy means that strict time synchronization must be ensured between the receiving end node and the transmitting end node, that is, the receiving rate is always equal to the transmitting rate, and if the channel gain of a single channel cannot satisfy the communication condition, the communication of the whole communication system is interrupted.
As shown in FIG. 1, in the SWIPT bidirectional transmission relay model based on the TS strategy, two active source nodes U are included1、U2And an energy-limited relay node
Figure BSA0000217970410000021
h represents a source node U1And relay node
Figure BSA0000217970410000026
G denotes the source node U2And relay node
Figure BSA0000217970410000027
Channel gain between, P1Represents the source node U1Transmit power of P2Represents the source node U2The transmit power of.
This model satisfies the following conditions: (1) the entire communication channel is a quasi-static rayleigh fading channel. Source node U1And relay node
Figure BSA0000217970410000022
Has a channel gain probability density function of
Figure BSA0000217970410000023
Source node U2And relay node
Figure BSA0000217970410000024
Has a channel gain probability density function of
Figure BSA0000217970410000025
Wherein λ ishAnd λgRespectively is the average value of the exponential random variables of the two channel gains; (2) the relay node selects an amplifying-forwarding (AF) strategy; (3) neglecting the power consumed by the relay node for signal processing when transmittingThis is reasonable when the distance is large enough and the energy collected is the main source of consumption; (4) an energy storage device with infinite capacity is arranged in the relay node; (5) the magnitude relationship of the channel gains between the two source nodes and the relay node is known (for example, two source nodes simultaneously send a detection signal to the relay), so that the relay node can determine from which source node the energy is obtained, and the energy collection efficiency and the communication efficiency can be higher. To express this patent, the relay node is slave to the source node U1And collecting energy.
FIG. 2 shows the internal structure of a relay node based on TS strategy, nARepresenting the noise generated by the antenna when receiving a signal, nAIs a circularly symmetric complex Gaussian random variable, i.e.
Figure BSA0000217970410000031
Represents nA(t) obeys a complex Gaussian distribution with a mean of 0 and a variance of
Figure BSA0000217970410000032
nBRepresenting noise introduced during information processing, and having
Figure BSA0000217970410000033
Definition of
Figure BSA0000217970410000034
The energy collection efficiency factor is denoted as η.
ndRepresenting noise generated by the antenna and the conversion module from the source node, and having
Figure BSA0000217970410000035
The time distribution relationship between the energy collection and the information transmission of the relay node is shown in fig. 3, T represents a complete time block, α represents an energy collection time coefficient of the relay node within the time block T, α ∈ [0, 1], that is, the relay node needs to spend α T time for obtaining energy required for forwarding information, when the collected energy is enough to forward the received information, the relay node receives information sent by two source nodes by using (1- α) T/2 time, and then forwards the received information to the source node at the other end by using (1- α) T/2 time, thereby completing communication.
Source node U1To relay node
Figure BSA0000217970410000038
Transmitting information to the relay node
Figure BSA0000217970410000039
Forward to source node U2Is called link L1(ii) a Similarly, source node U2To relay node
Figure BSA00002179704100000310
Transmitting information to the relay node
Figure BSA0000217970410000036
Forward to source node U1Is called link L2. Link L1Is denoted as pout1Link L2Is denoted as pout2。
Defining a signal-to-noise ratio threshold gamma0Minimum signal-to-noise ratio for meeting communication conditions without interruption. Signal to noise ratio at the channel is equal to gamma0Information transfer rate under the conditions, denoted R0. Obtained by the Shannon theorem
Figure BSA0000217970410000037
When the signal-to-noise ratio of the communication system is larger than the signal-to-noise ratio threshold value gamma0When the time is long, the sending information rate of the two source nodes and the forwarding information rate of the relay node are both R0＝log2(1+γ0) In this case, more time can be used to transmit information in the entire time block T, so that the communication efficiency of the entire communication system can be made higher.
In connection with the above description, the actual maximum throughput τ under TS-based LDR policy (TS-LDR for short) can be expressed as
τ＝(1-pout)R0(1-α)
In the formula, poutIs the outage probability of the entire communication system.
Because the two channels are independent of each other, the interruption probability p of the whole communication system under the TS-LDR strategyoutCan be expressed as
pout＝pout1+pout2-pout1·pout2
The expression for obtaining the actual maximum throughput tau through theoretical derivation is
τ＝(1-pout1-pout2+pout1·pout2)(1-α)log2(1+γ0)
In the formula (I), the compound is shown in the specification,
Figure BSA0000217970410000041
Figure BSA0000217970410000042
in the formula (I), the compound is shown in the specification,
Figure BSA0000217970410000043
Figure BSA0000217970410000044
establishing an optimization problem P by taking the optimum of the actual maximum throughput as a target:
Figure BSA0000217970410000045
at λh、λg、γ0、η、P1、P2、
Figure BSA0000217970410000046
And
Figure BSA0000217970410000047
under the condition of given parameters, an optimization algorithm, such as a golden section method, is adopted to obtain an optimal energy collecting time coefficient and an optimal actual maximum throughput. Recording the optimal actual maximum throughput as tau; and defining the collection energy time coefficient corresponding to the optimal actual maximum throughput as the optimal collection energy time coefficient, and marking the optimal collection energy time coefficient as alpha.
Description of the drawings:
in order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
Fig. 1 is a model of a SWIPT bidirectional transmission relay system based on a TS strategy provided by the invention;
fig. 2 is an internal structure of a relay node based on a TS policy provided by the present invention;
fig. 3 is a time distribution relationship between the collected energy and the transmitted information of the relay node based on the TS policy provided by the present invention;
FIG. 4 is a graph of the actual maximum throughput τ versus the energy-collected time coefficient α;
the specific implementation mode is as follows:
the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention aims to provide a method for limiting delay transmission in an SWIPT bidirectional transmission relay system based on a TS strategy, so that the system obtains the optimal actual maximum throughput. The two source nodes are active, the relay node is passive, and the structural block diagram is given in fig. 1. Wherein, the passive relay adopts a TS receiving strategy.
As shown in fig. 1, two active source nodes transmit information to each other, but the two source nodes cannot communicate directly with each other, and the signal must pass through an intermediate passive relay node with radio frequency energy harvesting capability to reach the other source node. Therefore, the relay node not only needs to forward the information sent by the source nodes on both sides in the whole communication process, but also needs to acquire energy from the radio frequency signal transmitted by one of the source nodes to ensure the normal operation of the whole communication system. The whole communication system adopts a Limited Delay Relay (LDR) strategy. The LDR strategy means that strict time synchronization must be ensured between the receiving end node and the transmitting end node, that is, the receiving rate is always equal to the transmitting rate, and if the channel gain of a single channel cannot satisfy the communication condition, the communication of the whole communication system is interrupted.
As shown in FIG. 1, in the model of the SWIPT bidirectional transmission relay system based on the TS strategy, two active source nodes U are included1、U2And an energy-limited relay node
Figure BSA0000217970410000069
h represents a source node U1And relay node
Figure BSA00002179704100000611
G denotes the source node U2And relay node
Figure BSA00002179704100000610
Channel gain between, P1Represents the source node U1Transmit power of P2Represents the source node U2The transmit power of.
This model satisfies the following conditions: (1) the entire communication channel is a quasi-static rayleigh fading channel. Source node U1And relay node
Figure BSA0000217970410000061
Has a channel gain probability density function of
Figure BSA0000217970410000062
Source node U2And relay node
Figure BSA0000217970410000063
Has a channel gain probability density function of
Figure BSA0000217970410000064
Wherein λ ishAnd λgRespectively is the average value of the exponential random variables of the two channel gains; (2) the relay node selects an amplifying-forwarding (AF) strategy; (3) neglecting the power consumed by the relay node for signal processing, which 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 infinite capacity is arranged in the relay node; (5) the magnitude relationship of the channel gains between the two source nodes and the relay node is known (for example, two source nodes simultaneously send a detection signal to the relay), so that the relay node can determine from which source node the energy is obtained, and the energy collection efficiency and the communication efficiency can be higher. To express this patent, the relay node is slave to the source node U1And collecting energy.
FIG. 2 shows the internal structure of a relay node based on TS strategy, nARepresenting the noise generated by the antenna when receiving a signal, nAIs a circularly symmetric complex Gaussian random variable, i.e.
Figure BSA0000217970410000065
Represents nA(t) obeys a complex Gaussian distribution with a mean of 0 and a variance of
Figure BSA0000217970410000066
yr，i(t) represents a signal assigned to the information processing module after receiving a signal from the source node, where a subscript i ═ 1 or 2 represents a source node serial number, that is, yr1(t) denotes a receiving source node U1Signals, y, assigned to information-processing modules after the signals are emittedr2(t) denotes a receiving source node U2Send outAfter the signal of (2), the signal is distributed to the information processing module. n isBRepresenting noise introduced during information processing, and having
Figure BSA0000217970410000067
Definition of
Figure BSA0000217970410000068
yrAnd (t) represents a signal which is obtained by receiving the signals sent by the two source nodes and processing the baseband signal by the relay node. sr，i(t) denotes the signal amplified and forwarded by the relay node, where the subscript i ═ 1 or 2 denotes the source node number, i.e., sr1(t) represents the Relay node amplifying from the Source node U1And to the source node U2The forwarded signal, sr2(t) represents the Relay node amplifying from the Source node U2And to the source node U1The forwarded signal.
The time distribution relationship between the energy collection and the information transmission of the relay node is shown in fig. 3, T represents a complete time block, α represents an energy collection time coefficient of the relay node within the time block T, α ∈ [0, 1], that is, the relay node needs to spend α T time for obtaining energy required for forwarding information, when the collected energy is enough to forward the received information, the relay node receives information sent by two source nodes by using (1- α) T/2 time, and then forwards the received information to the source node at the other end by using (1- α) T/2 time, thereby completing communication. Therefore, the communication process of TS-based LDR policy (TS-LDR for short) can be divided into three stages: a relay node acquires energy; a relay node receives information (information uplink phase); and a relay node information forwarding stage (information downlink stage).
For convenience in derivation and introduction of the following formula, the source node U1To relay node
Figure BSA0000217970410000071
Transmitting information to the relay node
Figure BSA0000217970410000072
Forward to source node U2Is called link L1(ii) a Similarly, source node U2To relay node
Figure BSA0000217970410000073
Transmitting information to the relay node
Figure BSA0000217970410000074
Forward to source node U1Is called link L2。
In the actual communication process, the whole process of information transmission is doped with some interference factors, such as interference signals and noise, and if these interference factors are too large, the receiving end cannot correctly decode the effective part of the signal. According to the LDR strategy, when the two channels formed by the two source nodes and the relay node have different conditions, if one of the channels is insufficient to complete the information transmission task, the entire communication system is completely interrupted. The criterion for judging whether the system is interrupted is signal-to-noise ratio (SNR), namely when the actual signal transmission SNR is smaller than the SNR threshold, the whole system is judged to be insufficient to complete the task of transmitting information, namely communication interruption.
According to the above description, the link L1Probability of interruption pout1And a link L2Probability of interruption pout2Can be respectively expressed as
Figure BSA0000217970410000083
Figure BSA0000217970410000086
In the formula (I), the compound is shown in the specification,
Figure BSA0000217970410000084
represents a link L1The signal-to-noise ratio of the received signal at the receiving end,
Figure BSA0000217970410000085
represents a link L2Signal-to-noise ratio, gamma, of the received signal at the receiving end0Representing a signal-to-noise threshold, i.e. a signal-to-noise threshold gamma0Minimum signal-to-noise ratio for meeting communication conditions without interruption. Signal to noise ratio at the channel is equal to gamma0Information transfer rate under the conditions, denoted R0. Obtained by the Shannon theorem
Figure BSA0000217970410000081
Because the two channels are independent of each other, the interruption probability p of the whole communication system under the TS-LDR strategyoutCan be expressed as
pout＝pout1+pout2-pout1·pout2 (3)
When the signal-to-noise ratio of the communication system is larger than the signal-to-noise ratio threshold value gamma0When the time is long, the sending information rate of the two source nodes and the forwarding information rate of the relay node are both R0＝log2(1+γ0) In this case, more time can be used to transmit information in the entire time block T, so that the communication efficiency of the entire communication system can be made higher. In connection with the above description, the actual maximum throughput under the TS-LDR strategy can be expressed as τ
Figure BSA0000217970410000082
Wherein molecule (2 (1-p)out)R0T) is the total amount of information transmitted by the communication system under the whole T time block, T is the effective information transmission time of the whole communication system, and T is (1-alpha) T/2 under the TS-LDR strategy.
In order to explore the relation between the actual maximum throughput and the collected energy time coefficient alpha, the analysis of the whole communication system is sequentially introduced according to three stages of the communication process.
(1) Energy obtaining phase of relay node
The relay node can obtain Channel State Information (CSI) of the two channels by receiving detection signals sent by the two source nodes, and the relay node can relay the CSIThe node can determine which channel condition is better and thereby use the channel with the better channel condition to obtain energy. In this embodiment, the relay node is always slave to the source node U1Energy is acquired.
At link L1In, the relay node receives the source node U1Signals y distributed to information processing modules after the signals are emittedr1(t) can be represented as
Figure BSA0000217970410000091
In the formula, x1(t) represents a slave source node U1Transmitted signal and has E [ | x1(t)|2]1, wherein E [ ·]Expressing the expectation, |, expressing the modulus value. Noise n generated by relay node receiving antennaA，1(t) is a circularly symmetric complex Gaussian random variable, i.e.
Figure BSA0000217970410000092
Represents nA，1(t) obeys a complex Gaussian distribution with a mean of 0 and a variance of σA，1 2. Energy E collected by the relay nodehCan be expressed as
Eh＝ηαTP1|h|2 (6)
Where eta is an energy collection efficiency factor, eta is an element of [0, 1]]. Energy E required by relay node to finish information forwardingcCan be expressed as
Figure BSA0000217970410000093
In the formula, PRRepresenting the amplified forwarding power required by the relay node to forward information to both source nodes. In order to obtain the actual maximum throughput in the whole time block T, the time coefficient α of the collected energy must be reduced to the minimum value under the premise that the communication can be maintained, and then the critical point, that is, all the collected energy of the relay node is used for relaying and forwarding information in the whole time block T
Eh＝Ec (8)
By substituting formula (6) and formula (7) into formula (8), amplified forward power P can be obtainedRThe relation with the time coefficient alpha of the collected energy is
Figure BSA0000217970410000094
(2) The stage of receiving information by relay node (information uplink stage)
In the same principle as the formula (5), in the link L2In, the relay node receives the source node U2Signals y distributed to information processing modules after the signals are emittedr2(t) can be represented as
Figure BSA0000217970410000095
In the formula, x2(t) represents a source node U2Transmitted signal and has E [ | x2(t)|2]＝1，nA，2(t) is a circularly symmetric complex Gaussian random variable generated by the receiving antenna of the relay node and has
Figure BSA0000217970410000101
As can be seen from equations (5) and (10), the relay node receives the signals transmitted by the two source nodes and performs baseband signal processing on the received signalsr(t) can be represented as
Figure BSA0000217970410000102
In the formula, nA(t) is the total noise generated by the receive antennas of the relay node,
Figure BSA0000217970410000103
Figure BSA0000217970410000104
nB(t) indicates the signal received by the relay node pairNoise generated during signal processing, and
Figure BSA0000217970410000105
(3) relay node information forwarding stage (information downlink stage)
Will link L1And link L2The analysis is carried out separately and finally the integration is carried out.
(ii) Link L1
At link L1In, the relay node amplifies the receiving source node U1The sent signal is sent to the source node U2The retransmitted signal sr1(t) can be represented as
Figure BSA0000217970410000106
In the formula (I), the compound is shown in the specification,
Figure BSA0000217970410000107
source node U2Received signal yd1(t) is
yd1(t)＝gsr1(t)+nd(t) (13)
In the formula, ndIs noise generated by the antenna from the source node and the conversion module, and has
Figure BSA0000217970410000108
By substituting formula (11) and formula (12) in the formula (13) in this order, the source node U can be obtained2The overall expression of the received signal is
Figure BSA0000217970410000109
Figure BSA0000217970410000111
In the formula (I), the compound is shown in the specification,
Figure BSA0000217970410000112
x in equation (14) due to self-interference cancellation2Item (t) is eliminated, source node U after elimination2The received signal is expressed as
Figure BSA0000217970410000113
The link L can be obtained from the formula (15) and the SNR formula1Source node U of2Signal to noise ratio of received signal
Figure BSA0000217970410000114
Is expressed as
Figure BSA0000217970410000115
In order to obtain the relation between the actual maximum throughput τ and the energy-collecting time coefficient α, p in the formula (3) needs to be expressedoutThe link L is obtained by substituting equation (16) for equation (1) and using equation (9) as the energy collection time coefficient α1Probability of interruption pout1Is composed of
Figure BSA0000217970410000116
In the formula, for convenience of representation, simplification is made as follows:
Figure BSA0000217970410000117
Figure BSA0000217970410000118
because | g tintin formula (17)2The positive and negative of the coefficient (a) are not determined, and need to be according to a1|h|4And b1|h|2The size relationship of (2) is discussed in classification, so that
Figure BSA0000217970410000121
In formula (18), when | h tint2＜b1/a1Time, the left square term (| g |) of the inequality2) Must be greater than zero, and the right side of the inequality is the molecule (c)1|h|2+d1) Greater than zero, the denominator (a) is known from the boundary value of the piecewise function1|h|4-b1|h|2) If it is smaller than zero, the right side of the inequality is smaller than zero, so the inequality is always true, so its probability is 1.
The source node U is a quasi-static Rayleigh fading channel1And relay node
Figure BSA0000217970410000126
Has a channel gain probability density function of
Figure BSA0000217970410000122
Source node U2And relay node
Figure BSA0000217970410000123
Has a channel gain probability density function of
Figure BSA0000217970410000124
In the formula, λh、λgRespectively, the mean of the exponential random variables of the two channel gains. Accordingly, the probability distribution functions of the gains of the two channels are respectively
Fh(z)＝p(|h|2＜z)＝1-exp(-z/λh) (21)
Fg(z)＝p(|g|2＜z)＝1-exp(-z/λg) (22)
Substitution of formulae (19) to (22) for a segmentation function of formula (18)In this case, p can be obtainedout1The integral expression for the independent variable z is
Figure BSA0000217970410000125
Figure BSA0000217970410000131
Link L2
Link L2Analysis process and link L1Is substantially the same in the link L2In, the relay node amplifies the signal from the source node U2And to the source node U1The retransmitted signal sr2(t) can be represented as
Figure BSA0000217970410000132
Source node U1Received signal yd2(t) is
yd2(t)＝hsr2(t)+nd(t) (25)
By substituting equation (11) and equation (24) in the equation (25) in this order, the source node U is eliminated from the interference1Received signal yd2(t) is
Figure BSA0000217970410000133
Then, the link L2Source node U of1Signal to noise ratio of received signal
Figure BSA0000217970410000134
Is composed of
Figure BSA0000217970410000135
Similarly, formula (27) is substituted for formula (2) and utilizedEquation (9), available Link L2Probability of interruption pout2Is composed of
Figure BSA0000217970410000136
In the formula (I), the compound is shown in the specification,
Figure BSA0000217970410000141
(ii) in formula (28) | h +4The positive and negative of the coefficient (a) are not determined, and need to be according to a2|g|2And b2The size relationship of (2) is discussed in classification, so that
Figure BSA0000217970410000142
In formula (29), when | g tint2＜b2/a2The left side of the inequality is a 4 th power term (| h! non-woven phosphor4) Must be greater than zero, and the right side of the inequality is the molecule (c)2|g|2+d2) Greater than zero, the denominator (a) is known from the boundary value of the piecewise function2|g|2-b2) If it is smaller than zero, the right side of the inequality is smaller than zero, so the inequality is always true, so its probability is 1.
By substituting equations (19) to (22) into the piecewise function of equation (29), p can be obtainedout2The integral expression for the independent variable z is
Figure BSA0000217970410000143
To this end, two links L1And L2Probability of interruption pout1And pout2After all are calculated, the actual maximum throughput τ can be calculated using equations (3) and (4), which are expressed as
τ＝(1-pout1-pout2+pout1·pout2)(1-α)log2(1+γ0) (31)
Establishing an optimization problem P by taking the optimum of the actual maximum throughput as a target:
Figure BSA0000217970410000144
at λh、λg、γ0、η、P1、P2、
Figure BSA0000217970410000145
To know
Figure BSA0000217970410000146
Under the condition of given parameters, an optimization algorithm, such as a golden section method, is adopted to obtain an optimal energy collecting time coefficient and an optimal actual maximum throughput. Recording the optimal actual maximum throughput as tau; and defining the collection energy time coefficient corresponding to the optimal actual maximum throughput as the optimal collection energy time coefficient, and marking the optimal collection energy time coefficient as alpha.
When the optimization problem P of the formula (32) is solved by adopting a golden section method, the optimal energy collection time coefficient alpha and the optimal actual maximum throughput tau are obtained, and the steps are as follows:
step 1: setting a value interval [ a, b ] and precision e of the initialization alpha;
step 2: solving section golden section point a1 ═ a + (1-0.618) (b-a), a2 ═ a +0.618 × (b-a);
and 3, step 3: solving actual maximum throughputs tau (a1) and tau (a2) corresponding to a1 and a2 respectively; jumping to the 4 th step if the actual maximum throughput tau (a1) < tau (a2), otherwise jumping to the 5 th step;
and 4, step 4: if a2-a1 < e, stopping iteration, outputting an optimal solution alpha-a 2 and an optimal actual maximum throughput tau (a 2); otherwise, let a be 1, a1 be a2, a2 be a +0.618 × (b-a), and jump to step 3;
and 5, step 5: if a2-a1 < e, stopping iteration, outputting an optimal solution alpha-a 2 and an optimal actual maximum throughput tau (a 2); otherwise, let b be a2, a2 be a1, a1 be a + (1-0.618) (b-a), and jump to step 3.
The technical scheme provided by the invention is further explained by combining specific experimental simulation.
The invention carries out simulation verification on the method for limiting delay transmission in the SWIPT bidirectional transmission relay system based on the TS strategy, and the use parameters are set as follows: the energy collection efficiency factor eta is 1, and the transmitting power P of the two source nodes1＝P 21, mean value λ of random variables h and g of channel gain indexhAnd λgRespectively set to 1, noise power generated when the relay node receives information
Figure BSA0000217970410000151
And noise power generated when the source node receives information
Figure BSA0000217970410000152
Are all set to 0.01, the signal-to-noise ratio threshold gamma0Set to 7.
Referring to fig. 4, when α is 0.32, the optimum practical maximum throughput τ is 1.0415. From the simulation plot, it can be concluded that the actual maximum throughput is smaller when α is smaller or larger. When the α is smaller, the energy collected by the relay node is less than the energy required for forwarding the currently received information, and the information is forwarded without sufficient forwarding power, so that the signal-to-noise ratio of the signal forwarded to the receiving end is reduced, the interruption probability is increased, and the actual maximum throughput is smaller; when α is large, although the energy collected by the relay node increases, the time for receiving the signal becomes short, resulting in a small actual maximum throughput.
In summary, the invention discloses a method for limiting delay transmission in a SWIPT bidirectional transmission relay system based on a TS strategy, so that the system obtains the optimal actual maximum throughput.
While the invention has been described in further detail with reference to specific preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (1)

1. A method for limiting delay transmission in an SWIPT bidirectional transmission relay system based on a TS strategy is characterized by comprising the following steps:
the bidirectional transmission relay system for simultaneous transfer of information and energy (SWIPT) comprises two active source nodes U1、U2And a passive relay node
Figure FSA0000217970400000011
The relay node has radio frequency energy collection capability and adopts a time division (TS) strategy; two source nodes can not be directly communicated, and a signal can reach another source node only through an intermediate relay node; source node U1And relay node
Figure FSA0000217970400000012
The channel gain between is h, the source node U2And relay node
Figure FSA0000217970400000013
The channel gain in between is g; source node U1Has a transmission power of P1Source node U2Has a transmission power of P2；
The SWIPT bidirectional transmission relay system adopts a Limited Delay Relay (LDR) strategy, wherein the LDR strategy means that strict time synchronization must be ensured at a receiving end node and a sending end node, namely the receiving rate is always equal to the sending rate, and if the channel gain of a single channel cannot meet the communication condition, the communication of the whole communication system is interrupted;
the SWIPT bidirectional transmission relay system meets the following conditions: (1) the whole communication channel is a quasi-static Rayleigh fading channel; source node U1And relay node
Figure FSA0000217970400000014
Has a channel gain probability density function of
Figure FSA0000217970400000015
Source node U2And relay node
Figure FSA0000217970400000016
Has a channel gain probability density function of
Figure FSA0000217970400000017
Wherein λ ishAnd λgRespectively is the average value of the exponential random variables of the two channel gains; (2) the relay node selects an amplifying-forwarding (AF) strategy; (3) neglecting the power consumed by the relay node for signal processing, which 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 infinite capacity is arranged in the relay node; (5) the magnitude relation of the channel gains between the two source nodes and the relay node is known (for example, two source nodes send a detection signal to the relay at the same time), so that the relay node can judge from which source node the energy is obtained, and the energy collection efficiency and the communication efficiency can be higher; to express this patent, the relay node is slave to the source node U1Collecting energy;
in the internal structure of the relay node, nARepresenting the noise generated by the antenna when receiving a signal, nAIs a circularly symmetric complex Gaussian random variable, i.e.
Figure FSA0000217970400000021
Represents nA(t) obeys a complex Gaussian distribution with a mean of 0 and a variance of
Figure FSA0000217970400000022
nBRepresenting noise introduced during information processing, and having
Figure FSA0000217970400000023
Definition of
Figure FSA0000217970400000024
Recording the energy collection efficiency factor as eta;
ndrepresenting noise generated by the antenna and the conversion module from the source node, and having
Figure FSA0000217970400000025
Alpha represents the time coefficient of energy collected by the relay node in the time block T, and belongs to [0, 1], namely the relay node needs to spend the time of alpha T as the energy required by information forwarding, when the collected energy is enough to forward the received information, the relay node receives the information sent by the two source nodes by using (1-alpha) T/2 time, and then respectively forwards the received information to the source node at the other end by using (1-alpha) T/2 time, thereby completing communication;
source node U1To relay node
Figure FSA0000217970400000026
Transmitting information to the relay node
Figure FSA0000217970400000027
Forward to source node U2Is called link L1(ii) a Similarly, source node U2To relay node
Figure FSA0000217970400000028
Transmitting information to the relay node
Figure FSA0000217970400000029
Forward to source node U1Is called link L2(ii) a Link L1Is denoted as pout 1Link L2Is denoted as pout 2；
Defining a signal-to-noise ratio threshold gamma0Minimum signal-to-noise ratio for meeting communication conditions without interruption; signal to noise ratio at the channel is equal to gamma0Information transfer rate under the conditions, denoted R0(ii) a Obtained by the Shannon theorem
Figure FSA00002179704000000210
When the signal-to-noise ratio of the communication system is larger than the signal-to-noise ratio threshold value gamma0When the time is long, the sending information rate of the two source nodes and the forwarding information rate of the relay node are both R0＝log2(1+γ0) In this case, more time can be used to transmit information in the entire time block T, so that the communication efficiency of the entire communication system can be made higher;
the expression of the actual maximum throughput tau under the LDR strategy based on TS is
τ＝(1-pout 1-pout 2+pout 1·pout 2)(1-α)log2(1+γ0)
In the formula (I), the compound is shown in the specification,
Figure FSA0000217970400000031
Figure FSA0000217970400000032
in the formula (I), the compound is shown in the specification,
Figure FSA0000217970400000033
Figure FSA0000217970400000034
establishing an optimization problem P by taking the optimum of the actual maximum throughput as a target:
Figure FSA0000217970400000035
s.t. 0≤α≤1
at λh、λg、γ0、η、P1、P2、
Figure FSA0000217970400000036
And
Figure FSA0000217970400000037
under the condition of given parameters, an optimal energy collecting time coefficient and an optimal actual maximum throughput are obtained by adopting an optimization algorithm.
CN202010882194.8A 2020-08-28 2020-08-28 TS strategy-based delay-limited transmission method in SWIPT bidirectional transmission relay system Pending CN111988803A (en)

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