CN109995413B - Relay-assisted environment backscattering communication method - Google Patents

Relay-assisted environment backscattering communication method Download PDF

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CN109995413B
CN109995413B CN201910370718.2A CN201910370718A CN109995413B CN 109995413 B CN109995413 B CN 109995413B CN 201910370718 A CN201910370718 A CN 201910370718A CN 109995413 B CN109995413 B CN 109995413B
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relay
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information
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CN109995413A (en
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张超
脱艳红
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Xian Jiaotong University
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/14—Relay systems
    • H04B7/15—Active relay systems
    • H04B7/155—Ground-based stations
    • H04B7/15507—Relay station based processing for cell extension or control of coverage area
    • 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
    • H04W40/22—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

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Abstract

The invention discloses a relay-assisted environment backscattering communication method, wherein a relay simultaneously assists a radio frequency transmitter and backscattering communication equipment to communicate with respective target receivers, the backscattering communication equipment modulates own information onto a signal of the radio frequency transmitter, the relay decodes the information in a serial interference elimination mode, forwards the decoded information to respective information receivers in a non-orthogonal multiple access mode, and optimizes the environment backscattering communication performance by optimizing a reflection coefficient of the environment backscattering communication equipment and a power distribution factor of the relay on the premise of ensuring the communication quality of a radio frequency communication link. Compared with the traditional decoding forwarding relay communication system, the relay-assisted environment backscattering communication method provided by the invention can obviously improve the communication performance of the system.

Description

Relay-assisted environment backscattering communication method
Technical Field
The invention belongs to the technical field of wireless communication, and particularly relates to a relay-assisted environment backscattering communication method.
Background
With the development of the internet of things, the power supply and communication problems of massive nodes are urgently needed to be solved, and obviously, the traditional wired power supply mode is not suitable any more; it is an approach to replace or charge batteries periodically, but this is inconvenient for sensor networks with thousands of nodes; the solar energy is utilized to supply power unstably, so that the stable operation of the system is influenced. Meanwhile, the traditional wireless communication technology needs to send radio frequency signals, and has the problems of high power consumption and high cost. The ambient backscattering (AmbientBackscatter) technique solves these problems to some extent.
The environmental backscattering technology is a novel radio frequency identification technology, and a backscattering device (backscattering device) can modulate information bits required to be transmitted by itself on radio frequency signals of the surrounding environment, such as WIFI signals, television tower signals, base station signals and the like, so as to realize communication with a receiver of the backscattering device. The environmental backscattering technology utilizes radio frequency signals existing in the environment as the only power source for communication, and the radio frequency signals are nearly ubiquitous today with the prosperous development of communication, so the technology can realize the communication between the devices at almost any place. In the process, the environment backscatter device does not need a special radio frequency transmitter, can avoid the trouble of frequently replacing a battery and charging, has low cost and low power consumption, has wide application prospect, can further promote the development of the mobile Internet of things, and is a green communication technology.
In an ambient backscatter communication system, when the communication distance between a backscatter device and its information receiver is long, the communication is interrupted, and in response to this problem, a relay-assisted ambient backscatter communication method has been proposed.
Disclosure of Invention
The technical problem to be solved by the present invention is to provide a relay-assisted ambient backscatter communication method for solving the problem that communication is interrupted when the communication distance between a backscatter radio frequency transmitter and a backscatter device and an associated information receiver is long, in view of the above-mentioned deficiencies in the prior art. Compared with the traditional decoding and forwarding relay communication technology, the method can remarkably improve the throughput of the whole communication system while ensuring the communication quality of the traditional radio frequency link.
The invention adopts the following technical scheme:
a relay-assisted environment backscattering communication method is characterized in that a relay-assisted environment backscattering communication network comprises a radio frequency transmitter, a relay, a radio frequency signal receiver, backscattering equipment and an information receiver thereof which are respectively represented by a node S, a node R, a node D, a node C and a node T; the relay simultaneously assists the radio frequency transmitter and the backscatter communication equipment to communicate with respective target receivers to complete channel estimation, and the backscatter communication equipment modulates information of the backscatter communication equipment to a signal of the radio frequency transmitter to complete signal transmission of a signal source; the relay decodes the information in a serial interference elimination mode and forwards the decoded information to respective information receivers in a non-orthogonal multiple access mode to complete relay forwarding; and on the premise of ensuring the communication quality of the radio frequency communication link, the performance of the environmental backscattering communication is optimized by optimizing the reflection coefficient of the environmental backscattering communication equipment and the power distribution factor of the relay.
Specifically, the channel estimation specifically includes:
a radio frequency transmitter S first transmits a pilot sequence to a relay node R in a communication network, the relay node RR estimation of direct link channel information h using pilot signals(S,R)And a backscatter link channel h(S,C)·h(C,R)Simultaneously, the relay node R sends a pilot frequency sequence to a radio frequency signal receiver D and an information receiver T of the backscattering equipment, and the radio frequency signal receiver D estimates channel information h(R,D)Information receiver T of a backscatter device estimates channel information h(R,T)。
Specifically, the information source signal transmission specifically includes:
the radio frequency transmitter S sends a radio frequency signal carrying data information to the relay R, the backscattering equipment C receives the radio frequency signal, the backscattering equipment C modulates the information required to be sent to the received radio frequency signal and backscatters the information out, the signals from the radio frequency transmitter S and the backscattering equipment C are simultaneously received at the relay node R and decode the two paths of signals, the information of the backscattering equipment C is attached to the radio frequency signal sent by the radio frequency transmitter S, and the relay simultaneously decodes the signal S of the radio frequency transmitter and the signal C of the backscattering equipment by utilizing a serial interference elimination technology.
Further, the signal y received by the relay node RrComprises the following steps:
Figure BDA0002049846450000031
wherein, PsRepresenting the transmission power of the radio frequency transmitter, α representing the path loss coefficient, s representing the information signal transmitted by the radio frequency transmitter, and E { | s |21, c represents the information signal sent by the backscatter device, η represents the backscatter coefficient of the backscatter device, nrIt is indicative of the thermal noise that is,
Figure BDA0002049846450000032
d(A,B)and h(A,B)Respectively, the distance between device A and device B and the small scale fading, where A, B ∈ { S, D, R, C, T }, h0Representing the channel coefficient, h, of the backscatter link0＝h(S,C)h(C,R)。
Further, the relay node R is connectedReceived Signal-to-interference-and-noise ratio (SINR) gamma for decoding a signal ssrComprises the following steps:
Figure BDA0002049846450000033
after the relay node R correctly decodes the signal s and eliminates the influence thereof, the signal-to-noise ratio gamma of the signal c is obtainedcrComprises the following steps:
Figure BDA0002049846450000034
specifically, the relay forwarding specifically includes:
the relay node R transfers the information s of the transmitting frequency transmitter to a radio frequency information receiver D, simultaneously the relay node R transfers the information c of the backscattering equipment to an information receiver T of the backscattering equipment, and the information is transferred in a non-orthogonal multiple access mode to respectively transfer the decoded signals
Figure BDA0002049846450000047
And
Figure BDA0002049846450000048
for the node D and the node T, the relay node R uses the energy of the relay node R to forward information, and the transmission power is PrThe power division factors are β respectivelysAnd βc，βs+β c1, in power distribution, the radio frequency transmitter communicates signals
Figure BDA0002049846450000049
Has higher priority than the backscatter communication signal
Figure BDA00020498464500000410
Is set to βs＞βcAt the information receiver of the backscatter device, serial interference cancellation is employed to obtain information of interest to itself.
Further, the transmission signal x of the relay node R is:
Figure BDA0002049846450000041
signal y received at node D or node Td(or t)Comprises the following steps:
Figure BDA0002049846450000042
wherein n isdRepresenting the noise at the node D, and,
Figure BDA0002049846450000043
ntwhich represents the noise of the node T,
Figure BDA0002049846450000044
node D only needs to decode signal s, node T needs to decode signal s first and then signal c, and SINR gamma corresponding to signal s at node D or node Tsd(or st)Comprises the following steps:
Figure BDA0002049846450000045
for the node T, after the signal s is successfully decoded, the snr corresponding to the signal c concerned by the node T itself is:
Figure BDA0002049846450000046
further, for the radio frequency communication link, the interrupting comprises: the relay node R cannot correctly decode the signal s; the probability of interruption of the radio frequency communication link, the interruption occurring at node D after the relay node R can correctly decode the signal s
Figure BDA0002049846450000051
The expression is as follows:
Figure BDA0002049846450000052
wherein the content of the first and second substances,
Figure BDA0002049846450000053
Figure BDA0002049846450000054
representing the mean of the channel powers of node A and node B, A, B ∈ { S, R, C, D, T }, E1(. cndot.) represents an exponential integration function.
Further, for a scattering communication link, at the node R or the T, the SINR of the received signal s is required to be greater than the decoding threshold γsThen continue to decode the signal c, define
Figure BDA0002049846450000055
RcRepresenting the transmission rate of the node C, the outage probability of the scattered communication link is:
Figure BDA0002049846450000056
Figure BDA0002049846450000057
Figure BDA0002049846450000058
Figure BDA0002049846450000059
Figure BDA00020498464500000510
Figure BDA00020498464500000511
wherein k represents an integer not less than zero, (α, x) represents an incomplete gamma function, ψ (z) represents a prosci function, (z) is a gamma function, Re (z) > 0;
Figure BDA0002049846450000061
representing the meryer G function.
Furthermore, the communication quality of the radio frequency communication link is ensured
Figure BDA0002049846450000062
Optimizing the reflection coefficient and the power distribution factor of the relay, and establishing an optimization model as follows:
Figure BDA0002049846450000063
Figure BDA0002049846450000064
0≤η≤1
βc+βs＝1
0≤βc≤βs≤1
Ps≥0,Pr≥0
compared with the prior art, the invention has at least the following beneficial effects:
according to the relay-assisted environment backscattering communication method provided by the invention, the relay can simultaneously transmit the information of the frequency transmitter and the environment backscattering equipment, the problem that the environment backscattering equipment and the information receiver thereof can only communicate within a short distance range is solved, and from a simulation result, compared with a traditional relay communication system, the relay-assisted environment backscattering communication method provided by the invention can be seen, and the communication performance of the system can be obviously improved.
In a further development of the invention, the channel estimation stage is that the radio frequency transmitter S first transmits a pilot sequence to a relay node R in the communication network, which relay node R estimates the direct link channel information h using the pilot signal(S,R)And a backscatter link channel h(S,C)·h(C,R)Simultaneously, the relay node R sends a pilot frequency sequence to a radio frequency signal receiver D and an information receiver T of the backscattering equipment, and the radio frequency signal receiver D estimates channel information h(R,D)Information receiver T of a backscatter device for estimating a channelInformation h(R,T)All the devices with receiving function can obtain necessary channel information, which is convenient for decoding process of signal.
Further, in the source signal transmission stage, the rf transmitter S sends an rf signal carrying data information to the relay R, and the backscatter device C can receive the rf signal, modulate the information to be sent by the backscatter device C onto the received rf signal and backscatter it, and receive the signals from the rf transmitter S and the backscatter device C at the relay node R simultaneously, and decode the two signals, considering the complexity of the decoding algorithm and the characteristics of the environmental backscatter communication itself-the information signal C of the backscatter device C is attached to the rf signal S sent by the rf transmitter S.
Further, in the relay forwarding stage, while the relay node R forwards the information s of the transmission frequency transmitter to the radio frequency information receiver D, the relay node R can also forward the information c of the backscatter device to the information receiver T of the backscatter device, and the forwarding adopts a non-orthogonal multiple access manner to forward the decoded signals respectively
Figure BDA0002049846450000072
And
Figure BDA0002049846450000073
for the node D and the node T, the relay node R uses the energy of the relay node R to forward information, and the transmission power is PrThe power division factors are β respectivelysAnd βc，βs+βcWhen power is distributed, the signal is set in consideration of protection of communication quality of the original radio frequency communication link
Figure BDA0002049846450000074
Is higher priority than the signal
Figure BDA0002049846450000075
Priority ofTherefore, in the present invention, the power ratio of the relay for relaying the transmitter signal is greater than the power ratio for relaying the backscatter device signal, i.e., βs＞βc. At the information receiver of the backscatter device, serial interference cancellation is employed to obtain information of interest to itself.
Further, since the node C transmits information by using the rf signal of the node S, the communication quality of the rf communication link should be ensured first
Figure BDA0002049846450000071
Under the premise, the invention enables the scattering communication link to have the best interrupted communication performance by optimizing the reflection coefficient and the power distribution factor of the relay.
In summary, in the method for relay-assisted environmental backscatter communication provided by the present invention, a relay can simultaneously relay information of a transmitting frequency transmitter and an environmental backscatter device, and a problem that the environmental backscatter device and an information receiver thereof can only communicate within a short distance is solved. From the simulation result, compared with the traditional relay communication system, the relay-assisted environment scattering communication method provided by the invention can obviously improve the communication performance of the system.
The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.
Drawings
FIG. 1 is a diagram of a model of the overall system of the present invention;
FIG. 2 is a graph of the probability of interruption as a function of reflection coefficient;
FIG. 3 is a graph of outage probability as a function of distance from a backscatter device to a relay node;
fig. 4 is a graph of system throughput as a function of distance from a backscatter device to a relay node and a comparison of system throughput of the present invention with a conventional decode-and-forward relay communication system.
Detailed Description
The invention provides a relay-assisted environment backscattering communication method, wherein a relay simultaneously assists a radio frequency transmitter and backscattering communication equipment to communicate with respective target receivers, the backscattering communication equipment modulates own information onto a signal of the radio frequency transmitter, the relay decodes the information in a serial interference elimination mode, forwards the decoded information to respective information receivers in a non-orthogonal multiple access mode, and optimizes the environment backscattering communication performance by optimizing a reflection coefficient of the environment backscattering communication equipment and a power distribution factor of the relay on the premise of ensuring the communication quality of a radio frequency communication link. Compared with the traditional decoding forwarding relay communication system, the relay-assisted environment backscattering communication method provided by the invention can obviously improve the communication performance of the system.
Firstly, a relay-assisted environment backscatter communication network is set to comprise a radio frequency transmitter, a relay, a radio frequency signal receiver, backscatter equipment and an information receiver thereof, which are respectively represented by a node S, a node R, a node D, a node C and a node T. h is(A,B)Is a small scale fading between device A and device B, d(A,B)Is the distance between device a and device B, (a, B) ∈ { S, R, D, C, T }, S being the information of the radio frequency transmitter and C being the information of the backscatter device.
Referring to fig. 1, a method for relay-assisted ambient backscatter communication according to the present invention includes the following steps:
s1, channel estimation;
the radio frequency transmitter S first transmits a pilot sequence to a relay node R in the communication network, where the relay node R can estimate the direct link channel information h using the pilot signal(S,R)And a backscatter link channel h(S,C)·h(C,R)Meanwhile, the relay node R also sends a pilot frequency sequence to the radio frequency signal receiver D and the information receiver T of the backscattering equipment, and the radio frequency signal receiver D can estimate the channel information h(R,D)The information receiver T of the backscatter device is able to estimate the channel information h(R,T)。
S2, source signal transmission stage;
the radio frequency transmitter S sends a radio frequency signal carrying data information to the relay R, the backscattering equipment C receives the radio frequency signal, the backscattering equipment C modulates the information required to be sent to the received radio frequency signal and backscatters the information out, two paths of signals from the radio frequency transmitter and the backscattering equipment are received at the relay node R simultaneously, the two paths of signals are decoded, the complexity of a decoding algorithm and the characteristics of environment backscattering communication are considered, the information of the backscattering equipment is attached to the radio frequency signal sent by the radio frequency transmitter, and therefore in the invention, the relay simultaneously decodes the signal S of the radio frequency transmitter and the signal C of the backscattering equipment by utilizing a serial interference elimination technology.
Signal y received by relay node RrComprises the following steps:
Figure BDA0002049846450000091
wherein, PsRepresenting the transmission power of the radio frequency transmitter, α representing the path loss factor, s representing the information signal transmitted by the radio frequency transmitter, and E { | s |21, c represents the information signal sent by the backscatter device, η represents the backscatter coefficient of the backscatter device, nrIt is indicative of the thermal noise that is,
Figure BDA0002049846450000092
d(A,B)and h(A,B)Respectively, the distance between device A and device B and the small scale fading, where A, B ∈ { S, D, R, C, T }; h0Representing the channel coefficient, h, of the backscatter link0＝h(S,C)h(C,R)。
Signal-to-interference-and-noise ratio (SINR) gamma received by relay node R for decoding signal ssrComprises the following steps:
Figure BDA0002049846450000101
after the relay node R correctly decodes the signal s and eliminates the influence thereof, the signal-to-noise ratio gamma of the signal c is obtainedcrComprises the following steps:
Figure BDA0002049846450000102
s3, relay forwarding stage;
the relay node R transfers information s of a transmitting frequency transmitter to a radio frequency information receiver D, simultaneously the relay node R transfers information c of a backscattering device to an information receiver T of the backscattering device, in order to ensure the communication quality of a radio frequency link, the transfer adopts a non-orthogonal multiple access mode, during power distribution, the protection of two-way communication quality of original radio frequency communication is considered, more power is always used for transferring the information of the radio frequency transmitter, a general receiver is adopted for decoding the information at the radio frequency receiver, and serial interference elimination is adopted at the information receiver of the backscattering device to obtain the information concerned by the relay node R.
In the relay forwarding stage, relays respectively forward decoded signals in a non-orthogonal multiple access mode
Figure BDA0002049846450000106
And
Figure BDA0002049846450000107
to node D and node T. In this scenario, the relay node R uses its own energy to forward information, and the transmission power is PrThe power division factors are β respectivelysAnd βc，βs+βc＝1。
β is set because the communication priority of the radio frequency transmitter is higher than the priority of the backscatter communications≥βcIf the transmission signal x of the relay node R is:
Figure BDA0002049846450000103
signal y received at node D (or node T)d(or t)Comprises the following steps:
Figure BDA0002049846450000104
wherein n isdRepresenting nodesThe noise of D is a noise that is,
Figure BDA0002049846450000105
ntwhich represents the noise of the node T,
Figure BDA0002049846450000111
because of the priority, node D only needs to decode signal s, and node T needs to decode signal s first and then signal c, and accordingly, the SINR γ corresponding to signal s at node D (or node T)sd(or st)Comprises the following steps:
Figure BDA0002049846450000112
for the node T, after successfully decoding the signal s, the signal-to-noise ratio (SNR) corresponding to the signal c concerned by the node T itself is:
Figure BDA0002049846450000113
for a radio frequency communication link (S- > R- > D), there are two possibilities for an interruption to occur:
one is that the relay node R cannot decode the signal s correctly;
the second case is when an interruption occurs at node D after the relay node R can decode the signal s correctly.
So for a radio frequency communication link, the probability of interruption
Figure BDA0002049846450000114
The expression is as follows:
Figure BDA0002049846450000115
wherein the content of the first and second substances,
Figure BDA0002049846450000116
Figure BDA0002049846450000117
representing the mean of the channel powers of node A and node B, A, B ∈ { S, R, C, D, T }; E1(. cndot.) represents an exponential integration function.
For a scattered communication link (S->C->R->D) Similarly to the rf communication link, the interruption of the communication includes two situations. Different from the above, since the relay node R and the node T both need to perform SIC detection, at the node R (or T), the SINR of the received signal s is greater than the decoding threshold γsThe decoding of signal c can continue. Definition of
Figure BDA0002049846450000118
Wherein R iscRepresenting the transmission rate of node C. Therefore, from the viewpoint of correct decoding, the probability of interruption of the scattering communication link can be obtained as follows:
Figure BDA0002049846450000121
Figure BDA0002049846450000122
Figure BDA0002049846450000123
Figure BDA0002049846450000124
Figure BDA0002049846450000125
Figure BDA0002049846450000126
wherein k represents an integer not less than zero, (α, x) represents an incomplete gamma function, ψ (z) represents a prosci function, (z) is a gamma function, Re (z) > 0;
Figure BDA0002049846450000127
representing the meryer G function.
Since the node C transmits information by using the radio frequency signal of the node S, the communication quality of the radio frequency communication link should be ensured firstly
Figure BDA00020498464500001210
On the premise, the scattering communication link can have better communication performance by optimizing the reflection coefficient and the power distribution factor of the relay, and an optimization model is established as follows:
Figure BDA0002049846450000128
Figure BDA0002049846450000129
0≤η≤1
βc+βs＝1
0≤βc≤βs≤1
Ps≥0,Pr≥0
in order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, 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 some, but not all, embodiments of the present invention. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. 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.
Simulation experiment and effect analysis
Simulation parameters:
transmission power P of radio frequency transmitters10dBm, relay transmission power Pr0dBm, distance between communication equipments is d(S,R)＝10m，d(S,C)＝12m，d(R,D)＝10m，d(C,R)＝5m，d(C,T)The corresponding small-scale fading is subject to rayleigh fading, and | | h(A,B)||2The average of (a, B) ∈ { S, D, C, R } is 1, the backscatter device reflection coefficient η is 0.6, the path loss factor α is 3, and the radio frequency transmitter data rate Rs1bit/s/Hz, backscatter device data rate Rc1bit/s/Hz, noise power
Figure BDA0002049846450000131
The interrupt probability performance curve of the system provided by the invention is simulated according to the parameters, and the throughput is compared with the traditional relay wireless communication system.
Referring to fig. 2, the relationship between the reflection coefficient and the outage probability of the system is shown. Different colors in the graph represent the outage probability curves for different power distribution coefficients. As can be seen from the figure, as the reflection coefficient increases, the probability of interruption of the radio frequency communication link increases, and the probability of interruption of the scattering communication link decreases and then remains almost constant. This is because the reflection coefficient increases, so that the interference of the scattering link to the radio frequency signal increases, resulting in an increase in the probability of interruption of the radio frequency communication link, while for the scattering communication link, the probability of interruption decreases as its useful signal increases. When the reflection coefficient is increased to a certain value, the decoding of the radio frequency signal is influenced, so that the interruption probability of the scattered communication is not obviously reduced.
It can be seen from the figure that the interruption probability of the radio frequency communication link decreases with the increase of the distance from the node S to the node R, because the power of the scattered signal received by the relay node R from the node C decreases as the distance from the node S to the node R increases, and the interruption performance decreases for the radio frequency signal as the interference received decreases.
Referring to fig. 4, the relation between the transmission power of the rf transmitter and the system throughput is shown when the data transmission rate of the node S and the data transmission rate of the node C are both 2 bits/S/Hz. It can be seen from the figure that the throughput of the radio frequency communication link and the scattering communication link increases as the transmit power of the radio frequency transmitter increases. Meanwhile, compared with the traditional decoding and forwarding relay system, the relay-assisted environment backscatter communication system provided by the invention has higher throughput, and the influence of the improvement on the original relay communication system is very small.
The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.

Claims (7)

1. A relay-assisted environment backscatter communication method is characterized in that a relay-assisted environment backscatter communication network is set to comprise a radio frequency transmitter, a relay, a radio frequency signal receiver, backscatter equipment and an information receiver thereof, which are respectively represented by a node S, a node R, a node D, a node C and a node T; the relay simultaneously assists the radio frequency transmitter and the backscatter communication equipment to communicate with respective target receivers to complete channel estimation, and the backscatter communication equipment modulates information of the backscatter communication equipment to a signal of the radio frequency transmitter to complete signal transmission of a signal source; the relay decodes the information in a serial interference elimination mode and forwards the decoded information to respective information receivers in a non-orthogonal multiple access mode to complete relay forwarding; on the premise of ensuring the communication quality of the radio frequency communication link, the performance of the environmental backscattering communication is optimized by optimizing the reflection coefficient of the environmental backscattering communication equipment and the power distribution factor of the relay; the information source signal transmission specifically comprises:
the radio frequency transmitter S sends a radio frequency signal carrying data information to the relay R, the backscattering equipment C receives the radio frequency signal, the backscattering equipment C modulates the information required to be sent to the received radio frequency signal and backscatters the information out, the signals from the radio frequency transmitter S and the backscattering equipment C are simultaneously received at the relay node R and decode the two paths of signals, the information of the backscattering equipment C is attached to the radio frequency signal sent by the radio frequency transmitter S, the relay simultaneously decodes the signal S of the radio frequency transmitter and the signal C of the backscattering equipment by utilizing a serial interference elimination technology, and the signal y received by the relay node RrComprises the following steps:
Figure FDA0002469424380000011
wherein, PsRepresenting the transmission power of the radio frequency transmitter, α representing the path loss coefficient, s representing the information signal transmitted by the radio frequency transmitter, and E { | s |21, c represents the information signal sent by the backscatter device, η represents the backscatter coefficient of the backscatter device, nrIt is indicative of the thermal noise that is,
Figure FDA0002469424380000012
d(A,B)and h(A,B)Respectively, the distance between device A and device B and the small scale fading, where A, B ∈ { S, D, R, C, T }, h0Representing the channel coefficient, h, of the backscatter link0＝h(S,C)h(C,R)；
The relay forwarding specifically includes:
the relay node R transfers the information s of the transmitting frequency transmitter to the radio frequency information receiver D, and simultaneously the relay node R transfers the information c of the backscattering equipment to the backscattering equipmentThe information receiver T of the scattering equipment respectively forwards the decoded signals in a non-orthogonal multiple access mode
Figure FDA0002469424380000021
And
Figure FDA0002469424380000022
for the node D and the node T, the relay node R uses the energy of the relay node R to forward information, and the transmission power is PrThe power division factors are β respectivelysAnd βc，βs+βc1, in power distribution, the radio frequency transmitter communicates signals
Figure FDA0002469424380000023
Has higher priority than the backscatter communication signal
Figure FDA0002469424380000024
Is set to βs＞βcAt the information receiver of the backscatter device, serial interference cancellation is employed to obtain information of interest to itself.
2. The method according to claim 1, wherein the channel estimation is specifically:
the radio frequency transmitter S first transmits a pilot sequence to a relay node R in the communication network, which estimates direct link channel information h using the pilot signal(S,R)And a backscatter link channel h(S,C)·h(C,R)Simultaneously, the relay node R sends a pilot frequency sequence to a radio frequency signal receiver D and an information receiver T of the backscattering equipment, and the radio frequency signal receiver D estimates channel information h(R,D)Information receiver T of a backscatter device estimates channel information h(R,T)。
3. Method according to claim 1, characterized in that the signal to interference plus noise ratio (SINR) γ for the decoded signal s received by the relay node RsrComprises the following steps:
Figure FDA0002469424380000025
after the relay node R correctly decodes the signal s and eliminates the influence thereof, the signal-to-noise ratio gamma of the signal c is obtainedcrComprises the following steps:
Figure FDA0002469424380000026
4. the method according to claim 1, wherein the transmission signal x of the relay node R is:
Figure FDA0002469424380000027
signal y received at node D or node Td(or t)Comprises the following steps:
Figure FDA0002469424380000028
wherein n isdRepresenting the noise at the node D, and,
Figure FDA0002469424380000029
ntwhich represents the noise of the node T,
Figure FDA00024694243800000210
node D only needs to decode signal s, node T needs to decode signal s first and then signal c, and SINR gamma corresponding to signal s at node D or node Tsd(or st)Comprises the following steps:
Figure FDA0002469424380000031
for the node T, after the signal s is successfully decoded, the snr corresponding to the signal c concerned by the node T itself is:
Figure FDA0002469424380000032
5. the method of claim 1, wherein the occurrence of the interruption to the radio frequency communication link comprises: the relay node R cannot correctly decode the signal s; the probability of interruption of the radio frequency communication link, the interruption occurring at node D after the relay node R can correctly decode the signal s
Figure FDA0002469424380000033
The expression is as follows:
Figure FDA0002469424380000034
wherein the content of the first and second substances,
Figure FDA0002469424380000035
Figure FDA0002469424380000036
representing the mean of the channel powers of node A and node B, A, B ∈ { S, R, C, D, T }, E1(. cndot.) represents an exponential integration function.
6. Method according to claim 1, characterized in that for a scattered communication link, at node R or T, the SINR for signal s that needs to be received is greater than the decoding threshold γsThen continue to decode the signal c, define
Figure FDA0002469424380000037
RcRepresenting the transmission rate of the node C, the outage probability of the scattered communication link is:
Figure FDA0002469424380000038
Figure FDA0002469424380000039
Figure FDA00024694243800000310
Figure FDA0002469424380000041
Figure FDA0002469424380000042
Figure FDA0002469424380000043
wherein k represents an integer not less than zero, (α, x) represents an incomplete gamma function, ψ (z) represents a prosci function, (z) is a gamma function, Re (z) > 0;
Figure FDA0002469424380000044
representing the meryer G function.
7. Method according to claim 1, characterized in that the communication quality of the radio frequency communication link is guaranteed
Figure FDA0002469424380000045
Optimizing the reflection coefficient and the power distribution factor of the relay, and establishing an optimization model as follows:
Figure FDA0002469424380000046
Figure FDA0002469424380000047
0≤η≤1
βc+βs＝1
0≤βc≤βs≤1
Ps≥0,Pr≥0。
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