CN112104401B - NOMA-based bidirectional relay transmission system and method - Google Patents

NOMA-based bidirectional relay transmission system and method Download PDF

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CN112104401B
CN112104401B CN202011189360.2A CN202011189360A CN112104401B CN 112104401 B CN112104401 B CN 112104401B CN 202011189360 A CN202011189360 A CN 202011189360A CN 112104401 B CN112104401 B CN 112104401B
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terminal
base station
relay
signal
transmitted
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CN112104401A (en
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方朝曦
陆颖之
沈士根
周海平
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University of Shaoxing
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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
    • H04B7/15564—Relay station antennae loop interference reduction
    • H04B7/15585—Relay station antennae loop interference reduction by interference cancellation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
    • H04W52/04—TPC
    • H04W52/18—TPC being performed according to specific parameters
    • H04W52/24—TPC being performed according to specific parameters using SIR [Signal to Interference Ratio] or other wireless path parameters
    • H04W52/242—TPC being performed according to specific parameters using SIR [Signal to Interference Ratio] or other wireless path parameters taking into account path loss
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
    • H04W52/04—TPC
    • H04W52/18—TPC being performed according to specific parameters
    • H04W52/26—TPC being performed according to specific parameters using transmission rate or quality of service QoS [Quality of Service]
    • H04W52/267—TPC being performed according to specific parameters using transmission rate or quality of service QoS [Quality of Service] taking into account the information rate
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
    • H04W52/04—TPC
    • H04W52/38—TPC being performed in particular situations
    • H04W52/46—TPC being performed in particular situations in multi hop networks, e.g. wireless relay networks

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  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
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  • Mobile Radio Communication Systems (AREA)
  • Radio Relay Systems (AREA)

Abstract

The invention discloses a two-way relay transmission system and a method based on NOMA, wherein the system comprises a base station and a relay station; the method comprises the following steps: (1) in a first time slot, a first relay station receives a superposed signal of signals sent by a base station and a first terminal; (2) in the second time slot, the second relay station receives the superposed signal of the signals sent by the base station and the second terminal; (3) in the third time slot, the two relay stations respectively forward the received signals to the base station and the terminal; (4) in the third time slot, the base station demodulates the received signal to obtain the sending data symbol of each terminal according to the non-orthogonal multiple access principle; (5) in the third time slot, each terminal detects the received signal respectively to obtain the transmitted data symbol of the base station. The invention can solve the technical problem of system capacity reduction caused by excessive time slot resource occupation and unreasonable power distribution among relay stations.

Description

NOMA-based bidirectional relay transmission system and method
Technical Field
The invention belongs to the technical field of wireless communication, and particularly relates to a two-way relay transmission system and a two-way relay transmission method based on NOMA.
Background
In a wireless communication system, a base station and a terminal need to transmit information to each other, but when the base station and the terminal are far away, the transmission power of the terminal is greatly increased due to large propagation path loss, and the transmission error rate is significantly increased, thereby resulting in a low data transmission rate. Usually, a dedicated relay station is deployed between a base station and a terminal to amplify and forward signals, so that power consumption of the mobile terminal can be reduced, and system capacity can be improved.
In a two-way relay wireless communication TDD system comprising two terminals, a base station needs four time slots for completing one information transmission with the two terminals, in the first time slot and the second time slot, the base station receives and transmits information with the first terminal through a first relay station, and in the third time slot and the fourth time slot, the base station receives and transmits information with the second terminal through a second relay station.
The prior art has the following problems: the information transmission of each terminal independently occupies time slot resources, so that more time slot resources are occupied when the number of the terminals is increased, and the system capacity is reduced; on the other hand, the unreasonable power distribution coefficient between relay stations for amplifying and forwarding can increase the error rate of signals received by the base station and the terminal, and further reduce the system capacity.
Disclosure of Invention
In view of the above defects or improvement needs in the prior art, the present invention provides a system and method for NOMA-based bidirectional relay transmission, which aims to solve the technical problems of system capacity reduction caused by excessive system timeslot resource occupation and unreasonable power allocation among relays.
To achieve the above object, according to one aspect of the present invention, there is provided a NOMA-based bidirectional relay transmission system, comprising a base station and a relay station;
the base station is used for communicating with a plurality of terminals through corresponding relay stations, wherein data are sent to the relay stations in a time division multiplexing mode, terminal data forwarded by the relay stations are received simultaneously by adopting a non-orthogonal multiple access technology, and data of each terminal are obtained through demodulation;
the relay station is used for receiving and forwarding communication data between the base station and a terminal far away from the base station, receiving data sent by the base station and the terminal at the same time and forwarding the data to the base station and the terminal at the same time.
According to another aspect of the present invention, a NOMA-based bidirectional relay transmission method is provided, which specifically includes the following steps:
(1) in the first time slot, the first relay station R1Receiving the signal sent by the base stationNumber and first terminal U1Superimposed signal y of the transmitted signalsR，1；
(2) In the second time slot, the second relay station R2Receiving signals sent by the base station and the second terminal U2Superimposed signal y of the transmitted signalsR，2；
(3) In the third time slot, the first relay station R1The received signal yR，1Amplifying to obtain an amplified signal xR，1Simultaneously sending to the base station and the first terminal U1(ii) a Second relay station R2The received signal yR，2Amplifying to obtain an amplified signal xR，2Simultaneously transmitting to the base station and the second terminal U2；
(4) In the third time slot, the base station receives all the relay stations R simultaneouslykTransmitted signal xR，kTo obtain a received superposed signal yBDetecting it according to the non-orthogonal multiple access principle to demodulate each terminal UkIs transmitted with data symbols sU，kWherein k is 1, 2;
(5) in the third time slot, each terminal UkRespectively receive corresponding relay stations RkTransmitted signal xR，kTo obtain a received signal yU，kRespectively detected to obtain the transmitted data symbols s of the base stationB，k。
Preferably, each relay station R in step (1) and step (2)kReceived superimposed signal yR，kThe method specifically comprises the following steps:
yR，k＝hBR，kxB，k+hUR，kxU，k+nR，k
wherein h isBR，kIndicating base station and relay station RkFading factor of the channel between, hUR，kPresentation terminal UkAnd relay station RkFading factor of the channel between, nR，kRepresents a relay station RkWhite Gaussian noise, xB，kFor signals transmitted by base stations, particularly
Figure BDA0002752294320000021
(PBIs the transmission power of the base station, sB，kIs sent to the terminal U by the base stationkData symbol of) xU，kIs terminal UkTransmitted signals, particularly
Figure BDA0002752294320000031
Figure BDA0002752294320000032
(PkIs terminal UkOf the transmission power of sU，kIs terminal UkData symbols transmitted to the base station).
Preferably, the superposed signal y received by the base station in step (4)BFor simultaneous reception of signals from two relays, e.g. in
Figure BDA0002752294320000033
Wherein n isBRepresenting gaussian white noise of the base station.
Preferably, the relay station R in step (3)kAmplified signal xR，kIs concretely provided with
xR，k＝θkyR，k
Wherein theta iskRepresents a relay station RkThe amplification factor of (2) is specifically:
Figure BDA0002752294320000034
σ2representing the power of Gaussian white noise, alphakRepresents a relay station RkPower distribution coefficient of (P)RRepresenting the total power of the two relay stations.
Preferably, the base station in step (4) detects the received signal y according to the non-orthogonal multiple access principleBTo demodulate each terminal UkIs transmitted with data symbols sU，kThe specific process is as follows:
the base station receives the signal y fromBThe removing base station sends to the first relay station R1And a second relay station R2Then receiving the interference signal back to obtain the signal sent by the terminal
Figure BDA0002752294320000035
Comprises the following steps:
Figure BDA0002752294320000036
wherein
Figure BDA0002752294320000037
Signals transmitted by base station to terminal
Figure BDA0002752294320000038
Detecting, and connecting the second terminal U2Is transmitted with data symbols sU，2The interference signal is regarded as the first terminal U is obtained by demodulation1Is transmitted with data symbols sU，1Then the demodulation is carried out to obtain a first terminal U1Is transmitted with data symbols sU，1Slave signal
Figure BDA0002752294320000039
Removing the second terminal U, and demodulating to obtain the second terminal U2Is transmitted with data symbols sU，2。
Preferably, each relay station RkPower distribution coefficient alpha ofkDistributing coefficients for optimal power
Figure BDA0002752294320000041
The system capacity is maximum;
each relay station RkOptimum power distribution coefficient of
Figure BDA0002752294320000042
The setting is as follows:
total capacity of system
Figure BDA0002752294320000043
Comprises the following steps:
Figure BDA0002752294320000044
wherein
Figure BDA0002752294320000045
Represents each terminal UkThe uplink capacity to the base station is specifically:
Figure BDA0002752294320000046
wherein
Figure BDA0002752294320000047
Figure BDA0002752294320000048
Representing base station to each terminal UkThe downlink capacity of (a) is specifically:
Figure BDA0002752294320000049
total capacity of system
Figure BDA00027522943200000410
At high signal-to-noise ratio the approximation is:
Figure BDA00027522943200000411
where ρ isk＝Pk/σ2，ρR＝PR/σ2，ρB＝PB/σ2；C00.5772. denotes the euler constant; gBR，k＝E(|hBR，k|2) And GUR，k＝E(|hUR，k|2) Represents an average gain of a corresponding channel, and E () represents expectation; mu.sk＝αkρR/(αkρR+ρk)，μ4＝α2ρR/(ρB+ρR)，c1＝α2ρ2GUR，2/α1ρ1GUR，1；
Average total capacity of the system
Figure BDA00027522943200000412
At maximum, the optimal power distribution coefficient
Figure BDA00027522943200000413
And
Figure BDA00027522943200000414
comprises the following steps:
Figure BDA0002752294320000051
Figure BDA0002752294320000052
preferably, each terminal U in step (5)kReceived signal yU，kIn particular to
yU，k＝hUR，kxR，k+nU，k
Wherein n isU，kPresentation terminal UkWhite gaussian noise.
Preferably, each terminal U in step (5)kSeparately detecting the received signals yU，kTo obtain a transmitted data symbol s of the base stationB，kThe specific process is as follows:
terminal UkFirst from the received signal yU，kThe medium removing terminal sends to the relay station RkThen receives the interference signal back to obtain the interference signal sent to the terminal U by the base stationkThe signals of (a) are:
Figure BDA0002752294320000053
terminal UkAccording to
Figure BDA0002752294320000054
Measuring transmitted data symbols s to a base stationB，k。
According to another aspect of the present invention, a terminal for NOMA-based bidirectional relay transmission is provided, which is characterized in that the terminal comprises a signal analysis module, wherein the signal analysis module is configured to remove interference signals from received base station data forwarded by a relay station and demodulate the base station data to obtain data sent by the base station.
In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:
(1) the invention provides a NOMA-based bidirectional relay transmission system, which combines a time division duplex mode and NOMA technology in a multilink bidirectional transmission relay system comprising a base station and a relay station to integrally optimize data transmission efficiency.
(2) The NOMA-based bidirectional relay transmission method provided by the invention utilizes three time slots to finish the sending and receiving of primary information between the base station and the two terminals and the data detection, reduces the occupation of one time slot, reduces the occupation of system time slot resources and improves the system capacity compared with the prior art. The method for setting the optimal power distribution coefficient between the two relay stations can reasonably distribute power between the two relay stations, so that the performance of signals received by the base station and the terminal is optimal, and the system capacity is improved.
Drawings
Fig. 1 is a schematic diagram of a wireless communication system of two user dual-relay stations of the present invention;
fig. 2 is a flow chart of the method of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
As shown in fig. 1, for a conventional Time Division Duplex (TDD) mode, in a multi-link bidirectional transmission relay system including a base station and a relay station, a Time Division Duplex (TDD) mode and a Non-Orthogonal Multiple Access (NOMA) technology are combined, so that data transmission efficiency is integrally optimized, and system capacity is improved.
The invention provides a NOMA-based bidirectional relay transmission system, which comprises a base station and a relay station;
the base station is used for communicating with a plurality of terminals through corresponding relay stations, wherein time division multiplexing is adopted for sending data to the relay stations, a non-orthogonal multiple access technology is adopted for simultaneously receiving terminal data forwarded by the relay stations, and the data of each terminal are obtained through demodulation;
the relay station is used for receiving and forwarding communication data between the base station and a terminal far away from the base station, receiving data sent by the base station and the terminal at the same time and forwarding the data to the base station and the terminal at the same time;
in general, the distance between relay stations is long, and communication between relay stations is impossible and only communication with a base station and terminals in the vicinity of each relay station is possible.
The invention provides a NOMA-based terminal for bidirectional relay transmission, which is used for communicating with a base station through a corresponding relay station; the terminal comprises a signal analysis module, wherein the signal analysis module is used for demodulating the received base station data forwarded by the relay station after removing the interference signal to obtain the data sent by the base station.
As shown in fig. 2, the present invention provides a NOMA-based bidirectional relay transmission method, which specifically includes the following steps:
(1) in the first time slot, the first relay station R1Receiving signals sent by a base station and a first terminal U1Superimposed signal y of the transmitted signalsR，1；
The received superimposed signal yR，1The method specifically comprises the following steps:
yR，1＝hBR，1xB，1+hUR，1xU，1+nR，1
wherein h isBR，1Indicating a base station and a first relay station R1Fading factor of the channel between, hUR，1Represents the first terminal U1With the first relay station R1Fading factor of the channel between, nR，1Denotes a first relay station R1White Gaussian noise, xB，1For signals transmitted by base stations, particularly
Figure BDA0002752294320000071
(PBIs the transmission power of the base station, sB，1Is sent to a first terminal U by a base station1Data symbol of) xU，1Is a first terminal U1Transmitted signals, particularly
Figure BDA0002752294320000072
(P1Is a first terminal U1Of the transmission power of sU，1Is a first terminal U1Data symbols transmitted to the base station);
(2) in the second time slot, the second relay station R2 receives the signal transmitted by the base station and the second terminal U2Superimposed signal y of the transmitted signalsR，2；
The received superimposed signal yR，2The method specifically comprises the following steps:
yR，2＝hBR，2xB，2+hUR，2xU，2+nR，2
wherein h isBR，2Indicating a base station and a second relay station R2Fading factor of the channel between, hUR，2Represents the second terminal U2With a second relay station R2Fading factor of the channel between, nR，2Represents the secondRelay station R2White Gaussian noise, xB，2For signals transmitted by base stations, particularly
Figure BDA0002752294320000073
(sB，2Is sent to the second terminal U by the base station2Data symbol of) xU，2Is a second terminal U2Transmitted signals, particularly
Figure BDA0002752294320000074
Figure BDA0002752294320000075
(P2Is a second terminal U2Of the transmission power of sU，2Is a second terminal U2Data symbols transmitted to the base station);
(3) in the third time slot, the first relay station R1The received signal yR，1Amplifying to obtain an amplified signal xR，1Simultaneously sending to the base station and the first terminal U1(ii) a Second relay station R2The received signal yR，2Amplifying to obtain an amplified signal xR，2Simultaneously transmitting to the base station and the second terminal U2；
The relay station RkAmplified signal xR，kIs concretely provided with
xR，k＝θkyR，k
Where k is 1, 2, thetakRepresents a relay station RkThe amplification factor of (2) is specifically:
Figure BDA0002752294320000081
σ2representing the power of Gaussian white noise, alphakRepresents a relay station RkPower distribution coefficient of (P)RRepresenting the total power of the two relay stations;
wherein the parameter alphakInfluence the total capacity of the system, when alpha is1And alpha2For optimum powerDistribution coefficient
Figure BDA0002752294320000082
And
Figure BDA0002752294320000083
the system capacity can be maximized;
the relay station RkOptimum power distribution coefficient of
Figure BDA0002752294320000084
And
Figure BDA0002752294320000085
set as follows:
terminal UkThe uplink capacity to the base station is:
Figure BDA0002752294320000086
wherein
Figure BDA0002752294320000087
Base station to terminal UkThe downlink capacity of (c) is:
Figure BDA0002752294320000088
obtaining the total system capacity according to the uplink capacity and the downlink capacity
Figure BDA0002752294320000089
Comprises the following steps:
Figure BDA00027522943200000810
total capacity of system
Figure BDA00027522943200000811
At high signal-to-noise ratio can be approximated as:
Figure BDA00027522943200000812
Figure BDA0002752294320000091
where ρ isk＝Pk/σ2，ρR＝PR/σ2，ρB＝PB/σ2；C00.5772. denotes the euler constant; gBR，k＝E(|hBR，k|2) And GUR，k＝E(|hUR，k|2) Represents an average gain of a corresponding channel, and E () represents expectation; mu.sk＝αkρR/(αkρR+ρk)，μ4＝α2ρR/(ρB+ρR)，c1＝α2ρ2GUR，2/α1ρ1GUR，1。
Average total capacity of the system
Figure BDA0002752294320000092
At maximum, the optimal power distribution coefficient
Figure BDA0002752294320000093
And
Figure BDA0002752294320000094
comprises the following steps:
Figure BDA0002752294320000095
Figure BDA0002752294320000096
(4) in the first placeThree time slots, the base station receives the first relay station R simultaneously1And a second relay station R2Transmitted signal xR，kTo obtain a received signal yBDetects it according to the NOMA principle to demodulate the terminal UkIs transmitted with data symbols sU，k；
Signal y received by the base stationBFor the base station to receive the signals forwarded by the relay station from the two terminals simultaneously in the same time slot, the signals include information of the two terminals, specifically
Figure BDA0002752294320000097
Wherein n isBWhite gaussian noise representing a base station;
the base station detects the received signal y according to the NOMA principleBTo demodulate out the terminal UkIs transmitted with data symbols sU，kThe specific process is as follows:
the base station receives the signal y fromBThe removing base station sends to the first relay station R1And a second relay station R2Then receiving the interference signal back to obtain the signal sent by the terminal
Figure BDA0002752294320000098
Comprises the following steps:
Figure BDA0002752294320000101
wherein
Figure BDA0002752294320000102
Signals transmitted by base station to terminal
Figure BDA0002752294320000103
Detecting, and connecting the second terminal U2Is transmitted with data symbols sU，2The interference signal is regarded as the first terminal U is obtained by demodulation1Is transmitted with data symbols sU，1Then the demodulation is carried out to obtain a first terminal U1Is transmitted with data symbols sU，1Slave signal
Figure BDA0002752294320000104
Removing the second terminal U, and demodulating to obtain the second terminal U2Is transmitted with data symbols sU，2；
(5) In the third time slot, each terminal UkRespectively receive corresponding relay stations RkTransmitted signal xR，kTo obtain a received signal yU，kRespectively detected to obtain the transmitted data symbols s of the base stationB，k；
The terminal UkReceived signal yU，kThe method specifically comprises the following steps:
yU，k＝hUR，kxR，k+nU，k
wherein n isU，kPresentation terminal UkWhite gaussian noise of (1);
each terminal UkSeparately detecting the received signals yU，kTo obtain a transmitted data symbol s of the base stationB，kThe specific process is as follows:
terminal UkFirst from the received signal yU，kThe medium removing terminal sends to the relay station RkThen, receiving the returned interference signal, and obtaining the signal sent by the base station to the terminal is:
Figure BDA0002752294320000105
terminal UkAccording to
Figure BDA0002752294320000106
Detecting and obtaining the transmitted data symbol s of the base stationB，k。
In the steps of the invention, three time slots are used for completing the data sending and receiving between the base station and the terminal and the data detection, compared with the prior art which needs four time slots to complete the whole process, the invention reduces the occupied time slot number and improves the system capacity.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (10)

1. A NOMA-based bidirectional relay transmission method is characterized by comprising the following steps:
(1) in the first time slot, the first relay station R1Receiving signals sent by a base station and a first terminal U1Superimposed signal y of the transmitted signalsR，1；
(2) In the second time slot, the second relay station R2Receiving signals sent by the base station and the second terminal U2Superimposed signal y of the transmitted signalsR，2；
(3) In the third time slot, the first relay station R1The received signal yR，1Amplifying to obtain an amplified signal xR，1Simultaneously sending to the base station and the first terminal U1(ii) a Second relay station R2The received signal yR，2Amplifying to obtain an amplified signal xR，2Simultaneously transmitting to the base station and the second terminal U2；
(4) In the third time slot, the base station receives all the relay stations R simultaneouslykTransmitted signal xR，kTo obtain a received superposed signal yBDetecting it according to the non-orthogonal multiple access principle to demodulate each terminal UkIs transmitted with data symbols sU，kWherein k is 1, 2;
(5) in the third time slot, each terminal UkRespectively receive corresponding relay stations RkTransmitted signal xR，kTo obtain a received signal yU，kRespectively detected to obtain the transmitted data symbols s of the base stationB，k。
2. NOMA-based bidirectional relay transmission method according to claim 1Wherein each of the relay stations R in the step (1) and the step (2)kReceived superimposed signal yR，kThe method specifically comprises the following steps:
yR，k＝hBR，kxB，k+hUR，kxU，k+nR，k
wherein h isBR，kIndicating base station and relay station RkFading factor of the channel between, hUR，kPresentation terminal UkAnd relay station RkFading factor of the channel between, nR，kRepresents a relay station RkWhite Gaussian noise, xB，kFor signals transmitted by base stations, particularly
Figure FDA0002988578210000011
PBIs the transmission power of the base station, SB，kIs sent to the terminal U by the base stationkData symbol of (2), xU，kIs terminal UkTransmitted signals, particularly
Figure FDA0002988578210000012
PkIs terminal UkOf the transmission power of sU，kIs terminal UkData symbols transmitted to the base station.
3. The NOMA-based two-way relay transmission method of claim 2, wherein the superimposed signal y received by said base stationBFor simultaneous reception of signals from two relays, e.g. in
Figure FDA0002988578210000021
Wherein n isBWhite Gaussian noise, x, representing the base stationR，kRepresents a relay station RkAnd (3) amplifying the received signal, wherein k is 1 and 2.
4. A NOMA-based bi-directional relay transmission method as claimed in claim 3, characterized in thatThe relay station RkAmplified signal xR，kIs concretely provided with
xR，k＝θkyR，k
Wherein theta iskRepresents a relay station RkThe amplification factor of (2) is specifically:
Figure FDA0002988578210000022
σ2representing the power of Gaussian white noise, alphakRepresents a relay station RkPower distribution coefficient of (P)RRepresenting the total power of the two relay stations.
5. A NOMA-based bidirectional relay transmission method as claimed in claim 4, wherein the base station detects the received signal y based on the non-orthogonal multiple access principleBTo demodulate each terminal UkIs transmitted with data symbols sU，kThe specific process is as follows:
the base station receives the signal y fromBThe removing base station sends to the first relay station R1And a second relay station R2Then receiving the interference signal back to obtain the signal sent by the terminal
Figure FDA0002988578210000023
Comprises the following steps:
Figure FDA0002988578210000024
wherein
Figure FDA0002988578210000025
Signals transmitted by base station to terminal
Figure FDA0002988578210000026
Detection ofConnecting the second terminal U2Is transmitted with data symbols sU，2The interference signal is regarded as the first terminal U is obtained by demodulation1Is transmitted with data symbols sU，1Then the demodulation is carried out to obtain a first terminal U1Is transmitted with data symbols sU，1Slave signal
Figure FDA0002988578210000027
Removing the second terminal U, and demodulating to obtain the second terminal U2Is transmitted with data symbols sU，2。
6. A NOMA-based bi-directional relay transmission method as claimed in claim 4, wherein each relay station RkPower distribution coefficient alpha ofkDistributing coefficients for optimal power
Figure FDA0002988578210000031
For, system capacity is maximum;
each relay station RkOptimum power distribution coefficient of
Figure FDA0002988578210000032
The setting is as follows:
total capacity of system
Figure FDA0002988578210000033
Comprises the following steps:
Figure FDA0002988578210000034
wherein
Figure FDA0002988578210000035
Represents each terminal UkThe uplink capacity to the base station is specifically:
Figure FDA0002988578210000036
wherein
Figure FDA0002988578210000037
Figure FDA0002988578210000038
Representing base station to each terminal UkThe downlink capacity of (a) is specifically:
Figure FDA0002988578210000039
total capacity of system
Figure FDA00029885782100000310
At high signal-to-noise ratio the approximation is:
Figure FDA00029885782100000311
where ρ isk＝Pk/σ2，ρR＝PR/σ2，ρB＝PB/σ2；C00.5772. denotes the euler constant; gBR，k＝E(|hBR，k|2) And GUR，k＝E(|hUR，k|2) Represents an average gain of a corresponding channel, and E () represents expectation; pik＝αkρR/(αkρR+ρk)，π4＝α2ρR/(ρB+ρR)，c1＝α2ρ2GUR，2/α1ρ1GUR，1；
Average total capacity of the system
Figure FDA00029885782100000312
At maximum, optimal power allocationCoefficient of performance
Figure FDA00029885782100000313
And
Figure FDA00029885782100000314
comprises the following steps:
Figure FDA00029885782100000315
Figure FDA00029885782100000316
7. the NOMA-based bidirectional relay transmission method of claim 2, wherein each terminal UkReceived signal yU，kIn particular to
yU，k＝hUR，kxR，k+nU，k
Wherein n isU，kPresentation terminal UkWhite gaussian noise.
8. The NOMA-based bidirectional relay transmission method of claim 7 wherein each terminal UkSeparately detecting the received signals yU，kTo obtain a transmitted data symbol s of the base stationB，kThe specific process is as follows:
terminal UkFirst from the received signal yU，kThe medium removing terminal sends to the relay station RkThen receives the interference signal back to obtain the interference signal sent to the terminal U by the base stationkThe signals of (a) are:
Figure FDA0002988578210000041
terminal UkAccording to
Figure FDA0002988578210000042
Detecting and obtaining the transmitted data symbol s of the base stationB，k。
9. A NOMA-based bidirectional relay transmission system, characterized in that a NOMA-based bidirectional relay transmission method according to any of claims 1 to 8 is applied.
10. A NOMA-based two-way relay transmission system as claimed in claim 9 comprising a base station and a relay station;
the base station is used for communicating with a plurality of terminals through corresponding relay stations, wherein data are sent to the relay stations in a time division multiplexing mode, terminal data forwarded by the relay stations are received simultaneously by adopting a non-orthogonal multiple access technology, and data of each terminal are obtained through demodulation;
the relay station is used for receiving and forwarding communication data between the base station and a terminal far away from the base station, receiving data sent by the base station and the terminal at the same time and forwarding the data to the base station and the terminal at the same time.
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