CN105471806B - Interference avoidance and secure transmission method based on signal alignment for use in collaborative device-to-device (D2D) system - Google Patents

Abstract

The invention discloses an interference avoidance and secure transmission method based on signal alignment for use in a collaborative device-to-device (D2D) system. The method comprises the following steps that: a base station (SB), a user D<1>, a user D<2> and a cellular user (CU) transmit signal constellation points out after signal constellation rotation firstly during information transmission; and every collaborative transmission between a D2D subsystem and a cellular subsystem consists of two stages, wherein at a first stage, the BS, the CU and the user D<2> transmit respective signals to the user D<1> respectively; and at a second stage, the user D<1> forwards a composite signal consisting of the signal transmitted by the BS and the signal transmitted by the CU to realize bilateral information transmission between the CU and the BS, and meanwhile, the user D<1> transmits a signal needing to be transmitted of the user D<1> to the user D<2>. Through adoption of the method, the security of the collaborative D2D system can be enhanced effectively, and the symbol error rate of the collaborative D2D system is lowered.

Description

Avoided and safe transmission method based on the interference of signal alignment in collaborative D2D systems

Technical field

The invention belongs to wireless communication technology field, is related in a kind of collaborative D2D systems based on the interference of signal alignment Avoid and safe transmission method.

Background technology

With continuing to bring out for the new applications such as mobile multimedia, social networkies, car networking, terminal direct connection (Device- One of to-Device, D2D) technology arises at the historic moment, and be considered as the key technology of next generation cellular network.Supporting D2D In the cellular system of communication, the shared identical frequency spectrum of transmission link between the straight-through link of equipment room and phone user, therefore, such as What realizes that effective interference management is most important for the performance for lifting D2D communications.Existing interference management scheme is mainly adopted Power Control, resource allocation and signal processing technology come eliminate or weaken interference impact；And by setting up coordination mechanism, can be with Further alleviate interfering between cellular link and D2D links and lift system performance.Here it is collaborative D2D transmission Basic thought.In the transmission mode, the transmitter of D2D systems serves as the via node of cellular link, and auxiliary cellular system is complete Into end-to-end information transfer, spectrum opportunities are obtained with this.A kind of network is proposed as the materialization of this thought, Zhao et al. The coordination strategy of coding auxiliary, it is tactful that Ma et al. proposes a kind of cooperation D2D based on supercomposed coding, in the strategy, D2D The machine of penetrating takes the mode of supercomposed coding to send its data and phone user's data simultaneously.The weak point of two kinds of strategies exists In：The spectrum efficiency for being limited to double jump characteristic and the node half-duplex constraint of relay transmission, D2D transmission and cellular transmission is all difficult to Lifted.In order to overcome this defect, Yiyang Pei et al. to propose a kind of cooperation transmitted in both directions strategy of high spectrum effect, the strategy Allow to be set up between a pair of D2D equipment and be bi-directionally connected, while one of D2D user realizes phone user and Ji as relaying Bidirectional information transmission between standing.

Although above-mentioned cooperation transmitted in both directions strategy has higher spectrum efficiency, it still suffers from the problem of two aspects. First, the signal that any terminal is received all includes itself desired signal and is sent to the signal of other users, therefore system is Interference-limited, this can cause serious error floor, so as to the error sign ratio for causing system cannot be with the rising of signal to noise ratio Decline.Second, in actual applications, any user all requirements with data confidentiality, the data of phone user need to use D2D Family maintains secrecy to ensure the privacy of its information transfer, and the data of D2D user are also required to keep privacy to phone user, however, In above-mentioned cooperation transmitted in both directions strategy, any node is able to access that (receive) data for coming from other any terminals, Which results in the problem of Information Security.According to investigation, there is presently no related work and solve in collaborative D2D communication systems Above-mentioned two problems.

The content of the invention

It is an object of the invention to overcome the shortcoming of above-mentioned prior art, there is provided be based in a kind of collaborative D2D systems The interference of signal alignment is avoided and safe transmission method, and the method can effectively improve the safety of collaborative D2D systems, drop The error sign ratio of low collaborative D2D systems.

To reach above-mentioned purpose, the interference in collaborative D2D systems of the present invention based on signal alignment is avoided and pacified Full transmission method, collaborative D2D systems include base station BS, user D₁, user D₂And phone user CU, base station BS and honeycomb use Family CU constitutes cellular subsystems, user D₁With user D₂D2D subsystems are constituted, is assisted between D2D subsystems and cellular subsystems Make, user D₁Bidirectional data interaction is completed as via node assistant base station BS and phone user CU, cellular subsystems allow to use Family D₁And user D₂Communicated using Cellular Networks frequency spectrum, specifically included：

Base station BS, user D₁, user D₂And phone user CU is in information transfer, first by signal constellation point through signal Retransmit away after constellation rotation；

Each cooperation transmission between D2D subsystems and cellular subsystems is made up of two stages, wherein, in the first rank Section, base station BS, phone user CU, user D₂Respective signal is sent respectively to user D₁；In second stage, user D₁Forwarding by The composite signal that the signal that the signal and phone user CU that base station BS sends sends is combined into, realizes phone user CU and base station BS Between bidirectional information transmission, meanwhile, user D₁The signal transmission for sending itself will be needed to user D₂。

Base station BS, phone user CU, user D₁And user D₂Constellation rotation angle meet condition be：

Work as x₀To take from the symbol of original constellation collection χ, postrotational symbol x=e^jθx₀, anglec of rotation θ satisfaction：

Wherein, i ≠ k,AndThe respectively real part and imaginary part of symbol x, xⁱAnd x^kRespectively postrotational constellation Any two constellation point in set；

For base station BS and phone user CU, the constellation rotation angle that phone user CU and base station BS are usedAndIt is full Foot：

Wherein,AndMinimum squared distance respectively at base station BS and phone user CU between constellation point,x_BWithRespectively base station BS Jing Any two signal constellation point after signal constellation (in digital modulation) rotation, x_CWithRespectively after the rotation of phone user CU Jing signal constellation (in digital modulation)s Any two signal constellation point, h_B1And h_C1Respectively link BS → D₁Channel coefficients and link CU → D₁Channel coefficients；

User D₁With user D₂The constellation rotation angle for usingAndMeet：

Wherein,AndRespectively user D₁With user D₂Minimum squared distance between place's constellation point, WithRespectively user D₁After the rotation of Jing signal constellation (in digital modulation)s Any two signal constellation point,WithRespectively user D₂Any two signal constellation (in digital modulation) after the rotation of Jing signal constellation (in digital modulation)s Point, h₁₂For link D₁→D₂Channel coefficients.

In the first phase, base station BS sending signalPhone user's CU sending signalsAnd user D₂Sending signalTo user D₁In, wherein, x_B、x_C、Respectively For base station BS, phone user CU and user D₂Multiple constellation point after the rotation of Jing signal constellation (in digital modulation)s, P is base station BS, phone user CU And user D₂Transmission power；h_B1For base station BS and user D₁Between channel coefficients, h_C1For phone user CU and user D₁It Between channel coefficients, h₁₂For user D₁With user D₂Between channel coefficients；∠h_B1、∠h_C1And ∠ h₁₂Respectively h_B1Phase place, h_C1Phase place and h₁₂Phase place, then user D₁The signal for receivingFor：

Wherein,For user D in the first stage₁The channel additive noise at place,For user D₁ExtractVoid Portion and using maximum-likelihood criterion estimate value, then further according toAnd formula (1) determinesSo as to obtain user D₂'s Information.

In second stage, user D₁The signal of transmissionExpression formula be：

Wherein,For user D₁It is sent to user D₂Data, α and β be the power normalization factor,Then user D₂The signal for receivingExpression formula For

Wherein, h₁₂For the channel coefficients between user D1 and user D2,For user D in second stage₂The channel at place adds Property noise；

User D₂To the signal for receivingMatched filtering is carried out, the imaginary part of filtered signal is then extracted, further according to The imaginary part of filtered signal obtains decision statistics

Wherein,Due toFor user D₂Send in the first stage Signal, user D₂Deduct from formula (8)Itself interference is eliminated, maximum-likelihood criterion inspection is then recycled SurveyRecover signal

In second stage, the reception signal of base station BSExpression formula be：

Base station BS is used firstIt is multiplied by reception signalThe real part for extracting acquired results obtains decision statisticsWherein,

Wherein,Base station BS fromIn deductSelf-interference is eliminated, and obtains signalWherein,

Base station BS completes right according to formula (12) using maximum-likelihood criterionDetection, determine honeycomb further according to formula (1) Multiple constellation point x after the rotation of user CU Jing signal constellation (in digital modulation)s_C, so as to obtain the information of phone user CU.

The constellation rotation criterion also meets：As k ≠ l, then have,

Wherein, any two original constellation point that base station BS is adoptedPhone user CU is adopted Any two original constellation pointX=e^jθu；

If base station BS, phone user UC adopt identical modulation system, i.e. χ_BS=χ_CU=χ, then formula (15) be converted to：

If u^(k)-u^(l)For real number, obtained by formula (15)：

|h_B1|cosθ_BS=| h_C1|cosθ_CU (16)

With can maximum cellular link least square Euclidean distance as object solving formula (16), obtain：

Wherein,AndMinimum squared distance respectively at base station BS and phone user CU between constellation point,x_BWithRespectively base station BS Jing Any two signal constellation point after signal constellation (in digital modulation) rotation, x_CWithRespectively after the rotation of phone user CU Jing signal constellation (in digital modulation)s Any two signal constellation point, h_B1And h_C1Respectively link BS → D₁With link CU → D₁Channel coefficients.

The invention has the advantages that：

Interference in collaborative D2D systems of the present invention based on signal alignment is avoided with safe transmission method in data During transmission, base station BS, user D₁, user D₂And phone user CU first rotates signal constellation point through signal constellation (in digital modulation) After retransmit away, so as to effectively improve the safety of information transfer, while user D₁With user D₂D2D subsystems are constituted, Cooperated between D2D subsystems and cellular subsystems so that in any one receiving terminal, the one of echo signal alignment receiving terminal Dimensional signal space, another dimensional signal space of interference signal alignment receiving terminal, so as to avoid interference, improving reduces collaborative D2D The error sign ratio of system.Meanwhile, interference signal is the in-phase stacking of two unknown disturbances signals, and decoding performance is deteriorated, from And improve the safety of collaborative D2D systems.It should be noted that the present invention need not depend on the interference management mechanism of complexity, Also the encryption/decryption technique of higher level protocol suite need not be used, need to only utilizes the Design of Signal of physical layer just can realize doing simultaneously That what is disturbed avoids and security of system lifting, facilitates implementation, in being highly suitable to be applied for collaborative D2D systems.

Description of the drawings

Fig. 1 is the system model schematic diagram of the present invention；

Fig. 2 is in D in emulation experiment₁Error sign ratio curve synoptic diagram during place's detection CU signals；

Fig. 3 is CU → D in emulation experiment₁The error sign ratio curve synoptic diagram of → BS transmission links；

Fig. 4 be emulation experiment in BS at detection D₁Error sign ratio curve synoptic diagram during signal；

Fig. 5 is D in emulation experiment₁→D₂The error sign ratio curve synoptic diagram of transmission link.

Specific embodiment

The present invention is described in further detail below in conjunction with the accompanying drawings：

With reference to Fig. 1, the interference in collaborative D2D systems of the present invention based on signal alignment is avoided and safe transmission side Method, collaborative D2D systems include base station BS, user D₁, user D₂And phone user CU, base station BS and phone user CU compositions Cellular subsystems, user D₁With user D₂D2D subsystems are constituted, is cooperated between D2D subsystems and cellular subsystems, user D₁Bidirectional data interaction is completed as via node assistant base station BS and phone user CU, cellular subsystems allow user D₁And use Family D₂Communicated using Cellular Networks frequency spectrum, specifically included：

Base station BS, user D₁, user D₂And phone user CU is in information transfer, first by signal constellation point through signal Retransmit away after constellation rotation；

Each cooperation transmission between D2D subsystems and cellular subsystems is made up of two stages, wherein, in the first rank Section, base station BS, phone user CU, user D₂Respective signal is sent respectively to user D₁；In second stage, user D₁Forwarding by The composite signal that the signal that the signal and phone user CU that base station BS sends sends is combined into, realizes phone user CU and base station BS Between bidirectional information transmission, meanwhile, user D₁The signal transmission for sending itself will be needed to user D₂。

Base station BS, phone user CU, user D₁And user D₂Constellation rotation angle meet condition be：

Work as x₀To take from the symbol of original constellation collection χ, postrotational symbol x=e^jθx₀, anglec of rotation θ satisfaction：

Wherein, i ≠ k,AndThe respectively real part and imaginary part of symbol x, xⁱAnd x^kRespectively postrotational constellation Any two constellation point in set；

The anglec of rotation for meeting formula (1) is clearly not unique, therefore, each node need be in all rotations for meeting formula (1) Optimal angle value is selected in gyration, specifically, for base station BS and phone user CU, phone user CU and base station BS are used Constellation rotation angleAndMeet：

Wherein,AndMinimum squared distance respectively at base station BS and phone user CU between constellation point,x_BWithRespectively base station BS Jing Any two signal constellation point after signal constellation (in digital modulation) rotation, x_CWithRespectively after the rotation of phone user CU Jing signal constellation (in digital modulation)s Any two signal constellation point, h_B1And h_C1Respectively link BS → D₁Channel coefficients and link CU → D₁Channel coefficients；

User D₁With user D₂The constellation rotation angle for usingAndMeet：

Wherein,AndRespectively user D₁With user D₂Minimum squared distance between place's constellation point, WithRespectively user D₁After the rotation of Jing signal constellation (in digital modulation)s Any two signal constellation point,WithRespectively user D₂Any two signal constellation (in digital modulation) after the rotation of Jing signal constellation (in digital modulation)s Point, h₁₂For link D₁→D₂Channel coefficients.

In the first phase, base station BS sending signalPhone user's CU sending signalsAnd user D₂Sending signalTo user D₁In, wherein, x_B、x_C、Respectively For base station BS, phone user CU and user D₂Multiple constellation point after the rotation of Jing signal constellation (in digital modulation)s, P is base station BS, phone user CU And user D₂Transmission power；h_B1For base station BS and user D₁Between channel coefficients, h_C1For phone user CU and user D₁It Between channel coefficients, h₁₂For user D₁With user D₂Between channel coefficients；∠h_B1、∠h_C1And ∠ h₁₂Respectively h_B1Phase place, h_C1Phase place and h₁₂Phase place, then user D₁The signal for receivingFor：

Wherein,For user D in the first stage₁The channel additive noise at place,For user D₁ExtractVoid Portion and using maximum-likelihood criterion estimate value, then further according toAnd formula (1) determinesSo as to obtain user D₂'s Information.

Due to mutual mistrust each other between D2D subsystems and cellular subsystems, therefore for cellular subsystems, user D₁It is counted as a listener-in, user D₁Specifically, can be used according to the information of formula (4) decoding base station BS and phone user CU Family D₁ExtractReal part obtain：

According to formula (5), user D₁Estimated using joint maximum likelihood detection algorithmWithYet withWithIn user D₁Place is aligned in same direction, therefore increased user D₁Decoding base station BS and phone user CU The difficulty of data, so as to improve the safety of data transfer between base station BS and phone user CU.

In second stage, user D₁The signal of transmissionExpression formula be：

Wherein,For user D₁It is sent to user D₂Data, α and β be the power normalization factor,Then user D₂The signal for receivingExpression formula For

Wherein, h₁₂For the channel coefficients between user D1 and user D2,For user D in second stage₂The channel at place adds Property noise；

User D₂To the signal for receivingMatched filtering is carried out, the imaginary part of filtered signal is then extracted, further according to The imaginary part of filtered signal obtains decision statistics

Wherein,Due toFor user D₂Send in the first stage Signal, user D₂Deduct from formula (8)Itself interference is eliminated, maximum-likelihood criterion inspection is then recycled SurveyRecover signal

User D₂The potential listener-in of cellular subsystems is counted as, the data of base station BS and phone user CU can be stolen, In order to realize eavesdropping, user D₂The following decision statistics of construction：

By formula (9) as can be seen that the signal alignment of base station BS and phone user CU is in same direction, therefore increased user D₂The difficulty of joint decoding is carried out to this two paths of data, so as to enhance the safety of information transfer.

In second stage, the reception signal of base station BSExpression formula be：

Base station BS is used firstIt is multiplied by reception signalThe real part for extracting acquired results obtains decision statisticsWherein,

Wherein,Base station BS fromIn deductSelf-interference is eliminated, and obtains signalWherein,

Base station BS completes right according to formula (12) using maximum-likelihood criterionDetection, determine honeycomb further according to formula (1) Multiple constellation point x after the rotation of user CU Jing signal constellation (in digital modulation)s_C, so as to obtain the information of phone user CU.

Consider from the angle of information transmission safety, it will be assumed that base station BS is for user D₁With user D₂Between number According to being a listener-in for exchange, in order to realize eavesdropping, base station BS is usedIt is multiplied by reception signalThen imaginary part is extracted To obtain following decision statistics：

According to formula (13), base station BS completes rightWithJoint maximum likelihood detection, yet with user D₁With with Family D₂Signal be aligned in same direction in formula (13), therefore its detection performance will be excessively poor, so as to ensureThe safety of transmission.

Due to link CU → D₁→ BS and link BS → D₁The symmetry of → CU, the signal detection that phone user CU is completed The signal detection process that process is completed with the above-mentioned base station BS for being given is identical.

The constellation rotation criterion also meets：As k ≠ l, then have,

Wherein, any two original constellation point that base station BS is adoptedPhone user CU is adopted Any two original constellation pointX=e^jθu；

Restrictive condition given by formula (14) destroys aligned signal, i.e.,With) between one-to-one relationship, its effect is：Even if system Average signal-to-noise ratio SNR tends to infinite so that user D₁Or user D₂Aligned signal can be inerrably decoded, also cannot be uniquely DetermineWithWhy it is worth respectively, so that user D₁Or user D₂Error floor occurs when being eavesdropped With high detection error probability.

But formula (14) is given to strengthen the safety constellation rotation angle condition to be met, but the formula (14) clear and definite criterion is not provided, in order to solve this problem, if base station BS and phone user CU adopt identical modulation methods Formula, i.e. χ_BS=χ_CU=χ, then formula (14) be converted to：

If u^(k)-u^(l)For real number, obtained by formula (15)：

|h_B1|cosθ_BS=| h_C1|cosθ_CU (16)

With can maximum cellular link least square Euclidean distance as object solving formula (16), obtain：

Wherein,AndMinimum squared distance respectively at base station BS and phone user CU between constellation point,x_BWithRespectively base station BS Jing Any two signal constellation point after signal constellation (in digital modulation) rotation, x_CWithRespectively after the rotation of phone user CU Jing signal constellation (in digital modulation)s Any two signal constellation point, h_B1And h_C1Respectively link BS → D₁With link CU → D₁Channel coefficients.

Emulation experiment

In order to verify the performance of method proposed by the invention, following Computer Simulation is We conducted：

In simulations, it will be assumed that all nodes are all distributed in two dimensional surface, without loss of generality, if base station BS and honeycomb are used Family CU is located at (0,0) and (1,1) respectively；User D₁The random distribution in the first quartile of 1 × 1 rectangular coordinate system, for any One given user D₁Position coordinateses, limit another D2D user D₂With user D₁The distance between be less than L, wherein, L Value be much smaller than the distance between BS and CU, in simulations we set L=0.3, and channel coefficients obey multiple Gauss random distribution Model, i.e.,：IfWherein, d_ijFor the distance between node i and j, η=3 refer to for path loss Number, unless stated otherwise, each node adopts QPSK as modulation system in following emulation, in order to enter with existing method Row contrast, it is considered to supercomposed coding method and cooperation bidirectional transmission method.It is pointed out that supercomposed coding method is a kind of unidirectional Transmission plan, and cooperate bidirectional transmission method and institute's extracting method of the present invention are all transmitted in both directions schemes, therefore, in order to carry out public affairs Flat contrast, it will be assumed that each node uses the modulation system of 16QAM in supercomposed coding method.

With reference to Fig. 2, Fig. 2 is given in D₁Error sign ratio (Symbol Error during place detection phone user CU Probability, SEP) simulation result, as shown in Figure 2, during using two kinds of pedestal methods, error sign ratio can be with the liter of signal to noise ratio It is high and decline, therefore both pedestal methods all cannot effectively protect the data privacy of cellular subsystems, and adopt this Bright, error sign ratio curve will appear from obvious error floor, so as to meet the transmission security requirement of cellular subsystems.

With reference to Fig. 3, two kinds of pedestal methods all have the error sign ratio of obvious error floor, i.e. system will not be with signal to noise ratio Rising and decline.This is by caused by the interference-limited characteristic of both strategies；But the present invention can be avoided fully Disturb, therefore the SEP of system rapidly declines the rising with SNR.

Fig. 4 illustrates the detection user D at base station BS₁Data when SEP simulation results.Supercomposed coding method and cooperation Bidirectional transmission method cannot all realize gratifying security performance, but in the present invention, SEP will be remained at higher than 10^-1 The order of magnitude, even if SEP also will not decline when the average signal-to-noise ratio of system tends to infinite, it means that, base station BS cannot be obtained User D must be related to₁Any useful information, therefore D₁→D₂The safety of transmission link has obtained effective guarantee.

With reference to Fig. 5, the SEP of the bidirectional transmission method that cooperates will not improve with the rising of SNR, and supercomposed coding method is in middle height Significant performance gain is obtained in that during signal to noise ratio, this is because supercomposed coding method allows D2D receivers to translate in the first stage The signal of code phone user CU, the D2D user D so at the end of second stage₂Just can first by the signal of phone user CU Eliminate, then further decoding its data, so as to weaken the impact of phone user's interference；Compared with the present invention, supercomposed coding side Method still embodies obvious performance inferior position, and this is the user D due in supercomposed coding method₂Decoding in the first stage has May make a mistake, so as to cause second stage at the end of user D₂Interference eliminate it is unsuccessful.With supercomposed coding method and association Make bidirectional transmission method different, by the present invention in that with signal alignment technology to reach the purpose for avoiding interference completely, so that The present invention has superior performance relative to prior art.

Claims (3)

1. the interference in a kind of collaborative D2D systems based on signal alignment is avoided and safe transmission method, it is characterised in that cooperation Formula D2D system includes base station BS, user D₁, user D₂And phone user CU, base station BS and phone user CU composition honeycomb subsystems System, user D₁With user D₂D2D subsystems are constituted, is cooperated between D2D subsystems and cellular subsystems, user D₁As in Bidirectional data interaction is completed after node assistant base station BS and phone user CU, cellular subsystems allow user D₁And user D₂Use Cellular Networks frequency spectrum is communicated, and is specifically included：

Base station BS, user D₁, user D₂And phone user CU is in information transfer, first by signal constellation point through signal constellation (in digital modulation) Retransmit away after rotation；

Each cooperation transmission between D2D subsystems and cellular subsystems is made up of two stages, wherein, in the first stage, base Stand BS, phone user CU, user D₂Respective signal is sent respectively to user D₁；In second stage, user D₁Forwarding is by base station BS The composite signal that the signal that the signal of transmission and phone user CU send is combined into, realizes between phone user CU and base station BS Bidirectional information is transmitted, meanwhile, user D₁The signal transmission for sending itself will be needed to user D₂；

Base station BS, phone user CU, user D₁And user D₂Constellation rotation angle meet condition be：

Work as x₀To take from original constellation collectionSymbol, postrotational symbol x=e^jθx₀, anglec of rotation θ satisfaction：

Wherein, i ≠ k,AndThe respectively real part and imaginary part of symbol x, xⁱAnd x^kRespectively postrotational constellation set Middle any two constellation point；

For base station BS and phone user CU, the constellation rotation angle that phone user CU and base station BS are usedAndMeet：

$({\mathrm{\&theta;}}_{CU}^{*},{\mathrm{\&theta;}}_{BS}^{*})=\underset{\left|h_{B1}\right|{\mathrm{cos\&theta;}}_{BS}=\left|h_{C1}\right|{\mathrm{cos\&theta;}}_{CU}}{\arg \max }\min \{d_{\min ,B}^2,d_{\min ,C}^2\}---\left(2\right)$

Wherein,AndMinimum squared distance respectively at base station BS and phone user CU between constellation point,x_BWithRespectively base station BS Jing Any two signal constellation point after signal constellation (in digital modulation) rotation, x_CWithRespectively after the rotation of phone user CU Jing signal constellation (in digital modulation)s Any two signal constellation point, h_B1And h_C1Respectively link BS → D₁Channel coefficients and link CU → D₁Channel coefficients；

User D₁With user D₂The constellation rotation angle for usingAndMeet：

$({\mathrm{\&theta;}}_{D_1}^{*},{\mathrm{\&theta;}}_{D_2}^{*})\underset{{\mathrm{cos\&theta;}}_{D_1}=\sqrt{P}\mathrm{\&beta;}\left|h_{12}\right|{\mathrm{cos\&theta;}}_{D_2}}{\arg \max }\min \{d_{\min ,D_1}^2,d_{\min ,D_2}^2\}---\left(3\right)$

Wherein,AndRespectively user D₁With user D₂Minimum squared distance between place's constellation point, WithRespectively user D₁After the rotation of Jing signal constellation (in digital modulation)s Any two signal constellation point,WithRespectively user D₂Any two signal constellation (in digital modulation) after the rotation of Jing signal constellation (in digital modulation)s Point, h₁₂For link D₁→D₂Channel coefficients；

In the first phase, base station BS sending signalPhone user's CU sending signalsAnd user D₂Sending signalTo user D₁In, wherein, x_B、x_C、Respectively For base station BS, phone user CU and user D₂Multiple constellation point after the rotation of Jing signal constellation (in digital modulation)s, P is base station BS, phone user CU And user D₂Transmission power；h_B1For base station BS and user D₁Between channel coefficients, h_C1For phone user CU and user D₁It Between channel coefficients, h₁₂For user D₁With user D₂Between channel coefficients；∠h_B1、∠h_C1And ∠ h₁₂Respectively h_B1Phase place, h_C1Phase place and h₁₂Phase place, then user D₁The signal for receivingFor：

Wherein,For user D in the first stage₁The channel additive noise at place,For user D₁ExtractImaginary part and profit With maximum-likelihood criterion estimate value, then further according toAnd formula (1) determinesSo as to obtain user D₂Information；

In second stage, user D₁The signal of transmissionExpression formula be：

Wherein,For user D₁It is sent to user D₂Data, α and β be the power normalization factor,Then user D₂The signal for receivingExpression formula be

$y_{D_2}^{\left(2\right)}=h_{12}{x}_{D_1}^{\left(trans\right)}+w_{D_2}^{\left(2\right)}---\left(7\right)$

Wherein, h₁₂For the channel coefficients between user D1 and user D2,For user D in second stage₂The channel additivity at place is made an uproar Sound；

User D₂To the signal for receivingMatched filtering is carried out, the imaginary part of filtered signal is then extracted, further according to filtering The imaginary part of signal afterwards obtains decision statistics

Wherein,Due toFor user D₂The letter for sending in the first stage Number, user D₂Deduct from formula (8)Itself interference is eliminated, maximum-likelihood criterion detection is then recycledRecover signal

2. the interference in collaborative D2D systems according to claim 1 based on signal alignment is avoided and safe transmission method, Characterized in that,

In second stage, the reception signal of base station BSExpression formula be：

$y_{BS}^{\left(2\right)}=h_{B1}{x}_{D_1}^{\left(trans\right)}+w_{BS}^{\left(2\right)}---\left(10\right)$

Base station BS is used firstIt is multiplied by reception signalThe real part for extracting acquired results obtains decision statistics Wherein,

Wherein,Base station BS fromIn deductSelf-interference is eliminated, and obtains signalWherein,

Base station BS completes right according to formula (12) using maximum-likelihood criterionDetection, determine phone user further according to formula (1) Multiple constellation point x after the rotation of CU Jing signal constellation (in digital modulation)s_C, so as to obtain the information of phone user CU.

3. the interference in collaborative D2D systems according to claim 2 based on signal alignment is avoided and safe transmission method, Characterized in that, the constellation rotation criterion also meets：As k ≠ l, then have,

Wherein, any two original constellation point that base station BS is adoptedIt is any that phone user CU is adopted Two original constellation pointsx=e^jθu；

If base station BS, phone user UC adopt identical modulation system, i.e.,Then formula (14) is converted to：

If u^(k)-u^(l)For real number, obtained by formula (15)：

|h_B1|cosθ_BS=| h_C1|cosθ_CU (16)

With can maximum cellular link least square Euclidean distance as object solving formula (16), obtain：

$({\mathrm{\&theta;}}_{CU}^{*},{\mathrm{\&theta;}}_{BS}^{*})=\underset{\left|h_{B1}\right|{\mathrm{cos\&theta;}}_{BS}=\left|h_{C1}\right|{\mathrm{cos\&theta;}}_{CU}}{\arg \max }\min \{d_{\min ,B}^2,d_{\min ,C}^2\}---\left(17\right)$

Wherein,AndMinimum squared distance respectively at base station BS and phone user CU between constellation point,x_BWithRespectively base station BS Jing Any two signal constellation point after signal constellation (in digital modulation) rotation, x_CWithRespectively after the rotation of phone user CU Jing signal constellation (in digital modulation)s Any two signal constellation point, h_B1And h_C1Respectively link BS → D₁With link CU → D₁Channel coefficients.