CN113938891A - Reflecting surface assisted user node untrusted NOMA network secure communication method - Google Patents

Reflecting surface assisted user node untrusted NOMA network secure communication method Download PDF

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CN113938891A
CN113938891A CN202111199074.9A CN202111199074A CN113938891A CN 113938891 A CN113938891 A CN 113938891A CN 202111199074 A CN202111199074 A CN 202111199074A CN 113938891 A CN113938891 A CN 113938891A
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reflecting surface
base station
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noma
phase shift
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CN113938891B (en
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岳新伟
裴英杰
汪川
李学华
刘元玮
刘荣科
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Beijing Information Science and Technology University
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W24/00—Supervisory, monitoring or testing arrangements
    • H04W24/02—Arrangements for optimising operational condition
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W12/00—Security arrangements; Authentication; Protecting privacy or anonymity
    • H04W12/80—Arrangements enabling lawful interception [LI]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W24/00—Supervisory, monitoring or testing arrangements
    • H04W24/06—Testing, supervising or monitoring using simulated traffic
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W28/00—Network traffic management; Network resource management
    • H04W28/16—Central resource management; Negotiation of resources or communication parameters, e.g. negotiating bandwidth or QoS [Quality of Service]
    • H04W28/18—Negotiating wireless communication parameters
    • H04W28/22—Negotiating communication rate
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
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Abstract

The invention discloses a reflecting surface-assisted user node untrusted NOMA network secure communication method, which mainly aims at an internal eavesdropping scene, a base station sends superposed information to two non-orthogonal users through the assistance of an intelligent reflecting surface, and mutual eavesdropping risks exist between user nodes. Compared with an intelligent reflector-assisted orthogonal multiple access system and a reflector-assisted-free physical layer secure communication system, the invention has the advantages that the system security and the energy efficiency are obviously improved, and the application value is better.

Description

Reflecting surface assisted user node untrusted NOMA network secure communication method
Technical Field
The invention relates to the technical field of wireless communication, in particular to a method for improving the system security rate in an internal eavesdropping scene by introducing two optimization algorithms of a BCD (binary coded decimal) algorithm and an MM (millimeter-wave) algorithm, and more particularly relates to a NOMA (non-trusted machine access) network security communication method assisted by a reflecting surface for a user node.
Background
With the continuous development of the fifth generation mobile communication system (5G), the amount of data in the wireless communication service is rapidly increasing. In order to cope with the pressure of future large-scale data, new methods for expanding system capacity and improving energy efficiency are urgently sought. NOMA has received widespread attention in recent years due to its higher spectral efficiency. Generally, NOMA can allocate resource blocks to multiple users according to different signal powers, which can increase the spectrum efficiency gain, thereby reducing the outage probability of the communication system and improving the overall communication quality.
However, no matter the traditional OMA or emerging NOMA transmission mode is adopted, the wireless signal is inevitably exposed in the transparent and complex electromagnetic environment during transmission, and eavesdroppers existing in the communication process, such as external eavesdroppers for malicious interception and eavesdropping of user information or passive internal eavesdroppers as non-orthogonal users, can easily steal the wireless signal of the user, and further illegally acquire the user information. Therefore, it is very important to realize secure communication capable of ensuring stable and reliable communication service for users in a wireless communication network by using the characteristics of diversity, time-varying property and reciprocity of wireless channels, that is, ensuring the security of a NOMA communication network through a physical layer bottom layer is a key problem to be considered first.
In recent years, the smart reflective surface has received much attention as a new method of low power consumption and high energy efficiency. In particular, the intelligent reflective surface is a planar array comprising several independent reconfigurable passive reflective elements and is connected to a controller that can change the mode of operation. Unlike the traditional wireless communication mode which can only passively adapt to the surrounding channel state, each reflecting unit in the intelligent reflecting surface can reconstruct the wireless communication environment by adjusting the amplitude and the phase of the incident electromagnetic wave. Compared with the multi-antenna relay widely used at present, the intelligent reflecting surface with low power consumption is cleaner and cheaper. In addition, the power gain of the system can be conveniently improved by simply adding the number of reflection units.
Disclosure of Invention
The invention aims to provide a NOMA network security communication method for user node untrusted by reflecting surface assistance, which realizes the security and reliability transmission on limited communication resources by configuring an intelligent reflecting surface in a NOMA system and introducing two algorithms of BCD and MM, designs an efficient security communication transmission scheme and meets the actual use requirements.
In order to achieve the purpose, the invention provides the following technical scheme: a NOMA network security communication method for user node un-credible assisted by reflecting surface comprises the following steps:
the method comprises the following steps: establishing an intelligent reflector assisted user node untrusted NOMA (non-trusted access point) secure communication system model;
step two: setting parameter configuration of an intelligent reflector assisted user node untrusted NOMA (non-trusted access point) safety communication system model;
step three: in an internal eavesdropping scene, a far-end user is used as an eavesdropper to eavesdrop information of a near-end user, and a reachable security speed expression of the system is given;
step four: further abstracting the expression to be a non-convex function maximum solving problem;
step five: for the non-convex function, obtaining an optimization formula of a beam forming vector at the base station side by adopting mathematical derivation based on Rayleigh entropy;
step six: for the non-convex function, a BCD algorithm is adopted, and the reachable safety rate of the system is maximized by alternately optimizing the beam forming vector of the base station side and the phase shift matrix of the intelligent reflecting surface;
step seven: for the non-convex function, adopting an MM algorithm, and performing alternate optimization on a beam forming vector at the base station side and a phase shift matrix of an intelligent reflecting surface to maximize the reachable safety rate of the system;
step eight: comparing and analyzing the system reachable security rate given in the third step with the reachable security rates under different transmission modes and scenes;
step nine: under the condition that the achievable safe rate is not changed, the influence of the deployment of the intelligent reflection surface on the transmission power of the base station side is considered.
As a preferred embodiment of the present invention, the first step specifically includes:
the safety communication system comprises a base station, an intelligent reflecting surface and two non-orthogonal users (a near-end user n and a far-end user m), wherein the risk of mutual information eavesdropping exists between user nodes, namely the far-end user is used as an eavesdropper to eavesdrop the information of the near-end user, the base station sends the superposed information of the two users to the users under the assistance of the intelligent reflecting surface, meanwhile, the eavesdropper adopts a passive eavesdropping mode to eavesdrop legal information, a communication link between the base station and the users in the system is blocked by a building and cannot be directly communicated, and the communication can be completed only through the assistance of the reflecting surface.
As a preferred embodiment of the present invention, the second step specifically includes:
the base station is provided with M antennas, the intelligent reflecting surface comprises N reflecting units, and the complex channel coefficients from the base station to the reflecting surface and from the reflecting surface to the user are respectively GbrAnd
Figure BDA0003304224540000031
representing and modeling the channel as a rice fading channel, and the gain of a cascade channel from a base station to an intelligent reflecting surface and then to a user should meet the following conditions without loss of generality:
Figure BDA0003304224540000032
at this time, the received signals of the near-end user n and the far-end user m can be expressed as:
Figure BDA0003304224540000033
wherein the content of the first and second substances,
Figure BDA0003304224540000034
matrix, beta, representing the reflection characteristics of the intelligent reflecting surfacem∈(0,1]Denotes the reflection magnification factor, theta, of the m-th cell on the reflecting surfacemE [0,2 π) represents the phase shift of the mth reflecting element, xnAnd xmNormalized energy signals, a, representing the near-end and far-end users, respectivelynAnd amRepresenting power allocation factors of near-end and far-end users and satisfying relation am≥anAnd am+an＝1，PsRepresents the normalized transmit power at the base station, e £ £N×NIs a phase shift matrix of an intelligent reflecting surface, w is epsilonM×1Represents the beamforming vector on the base station side,
Figure BDA0003304224540000035
representing a user
Figure BDA0003304224540000036
White gaussian noise.
As a preferred embodiment of the present invention, step three specifically includes:
the safe speed expression is achieved by the system as follows:
Figure BDA0003304224540000041
wherein the content of the first and second substances,
Figure BDA0003304224540000042
indicating the transmit end signal-to-noise ratio.
As a preferred embodiment of the present invention, the step four specifically includes:
the design method can be further abstracted into a non-convex function maximum solving problem S based on formula (2)1：
Figure BDA0003304224540000043
Wherein, C1And C2For the constraint condition, that is, the maximum solving problem, except for satisfying the requirement of the phase shift matrix theta of the intelligent reflecting surface, the power of the beam forming vector w at the base station side must not exceed the total transmission power P of the base stations。
As a preferred embodiment of the present invention, step five specifically includes:
for S1Adopting mathematical derivation based on Rayleigh entropy to obtain an optimization formula of a beam forming vector at the base station side; the beamforming vector w should be as parallel as possible to the receive channel of the legitimate user n
Figure BDA0003304224540000044
And as orthogonal as possible to the eavesdropping channel of the eavesdropping user m
Figure BDA0003304224540000048
So as to enhance the reliability of a legal channel and reduce the eavesdropping capability of the user m;
when the phase shift matrix at the intelligent reflective surface is fixed, the optimization formula of the beamforming vector can be written as:
Figure BDA0003304224540000045
wherein the content of the first and second substances,
Figure BDA0003304224540000046
IMis an identity matrix of dimension M,
Figure BDA0003304224540000047
is a relevant parameter of additive white gaussian noise.
As a preferred embodiment of the present invention, step six specifically includes:
when the beam forming vector of the base station side is fixedTime varying, phase shift matrix theta has elements { theta }i}i≠kThe BCD optimization formula of (a) can be written as:
Figure BDA0003304224540000051
wherein the content of the first and second substances,
Figure BDA0003304224540000052
Figure BDA0003304224540000053
Figure BDA0003304224540000054
is a channel matrix GbrThe (c) th row of (a),
Figure BDA0003304224540000055
the main implementation steps of the BCD algorithm can be summarized in the following table:
Figure BDA0003304224540000056
as a preferred embodiment of the present invention, step seven specifically includes:
unlike the BCD algorithm in which each phase shift unit θ iskRegarding the phase shift matrix as an optimization block, in the MM algorithm, the whole phase shift matrix Θ is considered as an optimization block, so that all phase shift units are processed in parallel in one optimization iteration process;
the optimization problem for the objective function can be rewritten as:
Figure BDA0003304224540000061
wherein the content of the first and second substances,
Figure BDA0003304224540000062
the lower bound function g (v) can be expressed as:
Figure BDA0003304224540000063
wherein the content of the first and second substances,
Figure BDA0003304224540000064
is the value of v in the t-th iteration of the MM algorithm,
Figure BDA0003304224540000065
represents an objective function in
Figure BDA0003304224540000066
A lower bound value at the point;
the optimization problem of the phase shift matrix Θ in each iteration can be transformed into:
Figure BDA0003304224540000067
wherein the content of the first and second substances,
Figure BDA0003304224540000068
therefore, when the beamforming vector w at the base station is fixed, the optimal solution equation for the phase shift matrix Θ is:
Figure BDA0003304224540000069
when the phase shift matrix at the intelligent reflecting surface is fixed, the optimization formula of the beam forming vector is shown in formula (4);
the main implementation steps of the MM algorithm are shown in the following table:
Figure BDA0003304224540000071
as a preferred embodiment of the present invention, step eight specifically includes:
comparing the system achievable safety rate given in the above steps with the achievable safety rate in different transmission modes (such as OMA transmission) and different transmission scenes (such as scenes without deploying intelligent reflecting surfaces); the difference between the NOMA safe communication rate assisted by the intelligent reflecting surface and the safe rate under other transmission modes and transmission scenes is compared by changing the transmitting power of the system, the number of transmitting antennas of the base station and the number of reflecting units of the reflecting surface of the intelligent reflecting surface.
As a preferred embodiment of the present invention, the step nine specifically includes:
under the condition that the system safety rate is not changed, aiming at the NOMA transmission scene, comparing the difference of the base station transmitting power through whether an intelligent reflecting surface is deployed or not; in addition, BCD and MM algorithms are introduced to optimize the NOMA network assisted by the intelligent reflecting surface, and the obvious difference of the two algorithms in the aspect of lightening the load capacity of the transmitting power of the base station can be observed.
Compared with the prior art, the invention has the following beneficial effects:
according to the invention, the beam forming vector at the base station and the dependent unit matrix at the intelligent reflecting surface are optimized by introducing BCD and MM algorithms in the NOMA physical layer safety communication system based on the intelligent reflecting surface to maximize the average safety rate of the system, effectively reduce the transmission power under the condition of ensuring that the safety rate of the system is not changed, and reduce the transmission burden of the base station. The method achieves the purpose of further improving the safety of the NOMA communication network, and has the characteristics of easy operation, low cost and low power consumption.
Drawings
FIG. 1 is a diagram of a NOMA network-based secure communication system model with reflector-assisted user nodes according to the present invention;
FIG. 2 is a graph comparing the average safe rate performance of BCD and MM algorithms applied in NOMA/OMA transmission mode and transmission scenario with intelligent reflecting surface/no intelligent reflecting surface;
FIG. 3 is a graphical illustration of the effect of different numbers of base station antennas on the average security rate performance of a smart reflector assisted NOMA communication network incorporating the BCD algorithm when the number of reflector elements changes;
FIG. 4 is a graphical illustration of the effect of changes in base station transmit power on the average safe rate performance of an intelligent reflector assisted NOMA communication network incorporating the BCD algorithm as the kappa factor in the Rice channel model changes;
FIG. 5 is a graph comparing the average safe rate performance change for a single antenna base station and a multiple antenna base station when the base station transmit power changes;
FIG. 6 is a graph comparing the effect of changes in the number of intelligent reflector units on the transmit power of base stations in an intelligent reflector assisted NOMA network incorporating the BCD/MM algorithm and a non-intelligent reflector assisted NOMA network when the average safe rate of the system is constant;
FIG. 7 is a flow chart of a design method of a physical layer safety communication system based on an intelligent reflection surface auxiliary NOMA network.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1-7, the present invention provides a technical solution:
the invention aims to realize safe and reliable transmission on limited communication resources by configuring an intelligent reflecting surface in a NOMA system and introducing two algorithms of BCD and MM, and designs an efficient safe communication transmission scheme.
A NOMA network security communication method for user node un-credible assisted by reflecting surface comprises the following steps:
the method comprises the following steps: establishing an intelligent reflector assisted user node untrusted NOMA (non-trusted access point) secure communication system model;
step two: setting parameter configuration of an intelligent reflector assisted user node untrusted NOMA (non-trusted access point) safety communication system model;
step three: in an internal eavesdropping scene, a far-end user is used as an eavesdropper to eavesdrop information of a near-end user, and a reachable security speed expression of the system is given;
step four: further abstracting the expression to be a non-convex function maximum solving problem;
step five: for the non-convex function, obtaining an optimization formula of a beam forming vector at the base station side by adopting mathematical derivation based on Rayleigh entropy;
step six: for the non-convex function, a BCD algorithm is adopted, and the reachable safety rate of the system is maximized by alternately optimizing the beam forming vector of the base station side and the phase shift matrix of the intelligent reflecting surface;
step seven: for the non-convex function, adopting an MM algorithm, and performing alternate optimization on a beam forming vector at the base station side and a phase shift matrix of an intelligent reflecting surface to maximize the reachable safety rate of the system;
step eight: comparing and analyzing the system reachable security rate given in the third step with the reachable security rates under different transmission modes and scenes;
step nine: under the condition that the achievable safe rate is not changed, the influence of the deployment of the intelligent reflection surface on the transmission power of the base station side is considered.
The first step specifically comprises the following steps: the secure communication system comprises a base station, an intelligent reflecting surface and two non-orthogonal users (a near-end user n and a far-end user m), wherein risks of mutual information eavesdropping exist between user nodes, namely the far-end user is used as an eavesdropper to eavesdrop the information of the near-end user. The base station sends the superposed information of two users to the users under the assistance of the intelligent reflecting surface, meanwhile, an eavesdropper adopts a passive eavesdropping mode to steal legal information, a communication link between the base station and the users in the system is blocked by a building and cannot be directly communicated, and the communication can be finished only through the assistance of the reflecting surface.
The second step specifically comprises: the base station is provided with M antennas, the intelligent reflecting surface comprises N reflecting units, and the base station is connected with the base stationThe complex channel coefficients of the reflecting surface and the reflecting surface to the user are respectively GbrAnd
Figure BDA0003304224540000101
representing and modeling the channel as a rice fading channel, and the gain of a cascade channel from a base station to an intelligent reflecting surface and then to a user should meet the following conditions without loss of generality:
Figure BDA0003304224540000102
at this time, the received signals of the near-end user n and the far-end user m can be expressed as:
Figure BDA0003304224540000103
wherein the content of the first and second substances,
Figure BDA0003304224540000104
matrix, beta, representing the reflection characteristics of the intelligent reflecting surfacem∈(0,1]Denotes the reflection magnification factor, theta, of the m-th cell on the reflecting surfacemE [0,2 π) represents the phase shift of the mth reflecting element, xnAnd xmNormalized energy signals, a, representing the near-end and far-end users, respectivelynAnd amRepresenting power allocation factors of near-end and far-end users and satisfying relation am≥anAnd am+an＝1，PsRepresents the normalized transmit power at the base station, e £ £N×NIs a phase shift matrix of an intelligent reflecting surface, w is epsilonM×1Represents the beamforming vector on the base station side,
Figure BDA0003304224540000108
representing a user
Figure BDA0003304224540000105
White gaussian noise.
The third step specifically comprises: the safe speed expression is achieved by the system as follows:
Figure BDA0003304224540000106
wherein the content of the first and second substances,
Figure BDA0003304224540000107
indicating the transmit end signal-to-noise ratio.
The fourth step specifically comprises: the design method can be further abstracted into a non-convex function maximum solving problem S based on formula (2)1：
Figure BDA0003304224540000111
Wherein, C1And C2For the constraint condition, that is, the maximum solving problem, except for satisfying the requirement of the phase shift matrix theta of the intelligent reflecting surface, the power of the beam forming vector w at the base station side must not exceed the total transmission power P of the base stations。
The fifth step specifically comprises: for S1And adopting an optimization formula for obtaining the beam forming vector at the base station side by adopting Rayleigh entropy-based mathematical derivation. In this design, the beamforming vector w should be as parallel as possible to the receiving channel of the legitimate user n
Figure BDA0003304224540000112
And as orthogonal as possible to the eavesdropping channel of the eavesdropping user m
Figure BDA0003304224540000113
So as to enhance the reliability of the legal channel and reduce the eavesdropping capability of the user m.
In this design, when the phase shift matrix at the intelligent reflective surface is fixed, the optimization formula of the beamforming vector can be written as:
Figure BDA0003304224540000114
wherein the content of the first and second substances,
Figure BDA0003304224540000115
IMis an identity matrix of dimension M,
Figure BDA0003304224540000116
is a relevant parameter of additive white gaussian noise.
The sixth step specifically comprises: when the beamforming vector on the base station side is fixed, the element { theta in the phase shift matrix theta is fixedi}i≠kThe BCD optimization formula of (a) can be written as:
Figure BDA0003304224540000117
wherein the content of the first and second substances,
Figure BDA0003304224540000118
Figure BDA0003304224540000121
Figure BDA0003304224540000122
is a channel matrix GbrThe (c) th row of (a),
Figure BDA0003304224540000123
the main implementation steps of the BCD algorithm can be summarized in the following table:
Figure BDA0003304224540000124
TABLE 1 BCD Algorithm steps
The seventh step specifically comprises: unlike the BCD algorithm in which each phase shift unit θ iskConsidering as an optimization block, in the MM algorithm, the entire phase shift matrix Θ is considered as an optimization block, thereby enabling all phase shift units to be processed in parallel during one optimization iteration.
The optimization problem for the objective function can be rewritten as:
Figure BDA0003304224540000125
wherein the content of the first and second substances,
Figure BDA0003304224540000131
the lower bound function g (v) can be expressed as:
Figure BDA0003304224540000132
wherein the content of the first and second substances,
Figure BDA0003304224540000133
is the value of v in the t-th iteration of the MM algorithm.
Figure BDA0003304224540000134
Represents an objective function in
Figure BDA0003304224540000135
Lower bound value at point.
The optimization problem of the phase shift matrix Θ in each iteration can be transformed into:
Figure BDA0003304224540000136
wherein the content of the first and second substances,
Figure BDA0003304224540000137
therefore, when the beamforming vector w at the base station is fixed, the optimal solution equation for the phase shift matrix Θ is:
Figure BDA0003304224540000138
and when the phase shift matrix at the intelligent reflecting surface is fixed, the optimization formula of the beam forming vector is shown in formula (4).
The main implementation steps of the MM algorithm are shown in the following table:
Figure BDA0003304224540000139
Figure BDA0003304224540000141
TABLE 2 MM algorithm steps
The eighth step specifically comprises:
the system achievable security rate given in the above steps is compared with the achievable security rate in different transmission modes (such as OMA transmission) and different transmission scenarios (such as scenarios without deploying intelligent reflective surfaces). The difference between the NOMA safe communication rate assisted by the intelligent reflecting surface and the safe rate under other transmission modes and transmission scenes is compared by changing the transmitting power of the system, the number of transmitting antennas of the base station and the number of reflecting units of the reflecting surface of the intelligent reflecting surface.
The ninth step specifically comprises: under the condition that the system safety rate is not changed, aiming at the NOMA transmission scene, the difference of the base station transmitting power is compared through whether an intelligent reflecting surface is deployed or not. In addition, BCD and MM algorithms are introduced to optimize the NOMA network assisted by the intelligent reflecting surface, and the obvious difference of the two algorithms in the aspect of lightening the load capacity of the transmitting power of the base station can be observed.
The invention provides a physical layer security communication system based on an intelligent reflecting surface auxiliary NOMA network.
The average safety rate performance of the physical layer safety communication system based on the intelligent reflecting surface auxiliary NOMA network is verified through simulation. Without loss of generality, a pair of non-orthogonal users exists in the system, which are marked as a near-end legal user n and a wiretap user m, and the corresponding power of the non-orthogonal users is recordedThe factors are respectively set as an0.2 and am0.9, additive white gaussian noise parameter at user n and user m
Figure BDA0003304224540000142
Further improved, as shown in fig. 2: 1) the average security rate in NOMA networks is generally better than in traditional OMA; 2) the safety performance of the communication network can be obviously improved by deploying the intelligent reflecting surface in the system; 3) although the alternative optimization strategy is adopted, the performance of the BCD algorithm in the scene of optimizing the small-scale intelligent reflecting surface is stronger than that of the MM algorithm. The main causes of the above phenomenon are as follows: 1) NOMA has a higher spectral efficiency than OMA due to the effect of receiving non-orthogonal transmissions. Furthermore, when there are multiple legitimate users in the system, NOMA can provide service for all legitimate users simultaneously during the whole transmission period, which can significantly improve the security performance of the network; 2) the intelligent reflecting surface can reconfigure the wireless channel environment by adjusting the amplitude and the phase of the incident electromagnetic wave, thereby improving the capacity and the reliability of the system. In particular, the passive beam former of the intelligent reflecting surface can strengthen signals, weaken interference and reduce the eavesdropping capability of an eavesdropper; 3) because a global optimal solution is obtained for all blocks, BCD is more suitable for optimizing small-scale intelligent reflector parameters. In contrast, since the MM algorithm can optimize all phase shifting elements in one iteration, the convergence speed of the MM algorithm will be much faster than the BCD when the number of reflecting elements in the intelligent reflecting surface becomes large. That is, the MM algorithm is better suited for optimizing large intelligent reflective surfaces.
In a further improvement, as shown in fig. 3: the relation between the average security rate of the system and the number of reflecting units when different algorithms are used and the number of base station antennas changes is studied. It can be seen that the average security rate monotonically increases as N or M increases. This is because the addition of the number of reflection units and transmission antennas provides more spatial freedom for the design of the passive beamformer of the intelligent reflection plane or BS, which further improves the security passive gain of the communication system. Based on the foregoing discussion, BCD has more advantages in small-scale intelligent reflector scenes, and thus the BCD algorithm is more efficiently executed when applied to small-scale intelligent reflector systems.
Further improved, as shown in fig. 4: an increase in the value of the rice factor k will bring a significant benefit to the safety of the system. The intuitive explanation behind this phenomenon is that a large value of κ means that some scattering components in the network are significantly stronger than others. Thus, the transmission process will no longer follow rayleigh fading (k-40 dB), but rather corresponds to leis fading, which contains a strong LOS component. Considering that there is a strong propagation path in the LOS environment, the signal does not suffer any LOSs due to reflection, diffraction and scattering, i.e. the interference rejection of the received signal is enhanced, and the security and confidentiality of the system are improved.
Further improved, as shown in fig. 5: a multi-antenna base station makes the communication system more secure than if a single antenna were deployed. The reason is similar to fig. 3, i.e. more antennas will bring higher design freedom of the transmitting end and more possibility for the base station to generate optimal beam forming.
Further improved, as shown in fig. 6: as the number of reflective elements grows, the base station power consumed by the intelligent reflective surface assisted NOMA transmission is much less than in a scenario not equipped with an intelligent reflective surface. That is, by deploying the intelligent reflecting surface and loading a proper optimization algorithm, the transmission burden at the base station can be significantly reduced, and the average security rate of the system is ensured to be kept unchanged. The basic reason for this phenomenon is that the intelligent reflective surface enhances the signal strength of the legitimate user by passive beam forming to solve the problems of short transmission distance and low signal-to-noise ratio caused by the weakening of the transmission power of the base station, thereby alleviating the transmission power pressure of the base station.
Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. A NOMA network security communication method for user node un-credible assisted by a reflecting surface is characterized in that: the method comprises the following steps:
the method comprises the following steps: establishing an intelligent reflector assisted user node untrusted NOMA (non-trusted access point) secure communication system model;
step two: setting parameter configuration of an intelligent reflector assisted user node untrusted NOMA (non-trusted access point) safety communication system model;
step three: in an internal eavesdropping scene, a far-end user is used as an eavesdropper to eavesdrop information of a near-end user, and a reachable security speed expression of the system is given;
step four: further abstracting the expression to be a non-convex function maximum solving problem;
step five: for the non-convex function, obtaining an optimization formula of a beam forming vector at the base station side by adopting mathematical derivation based on Rayleigh entropy;
step six: for the non-convex function, a BCD algorithm is adopted, and the reachable safety rate of the system is maximized by alternately optimizing the beam forming vector of the base station side and the phase shift matrix of the intelligent reflecting surface;
step seven: for the non-convex function, adopting an MM algorithm, and performing alternate optimization on a beam forming vector at the base station side and a phase shift matrix of an intelligent reflecting surface to maximize the reachable safety rate of the system;
step eight: comparing and analyzing the system reachable security rate given in the third step with the reachable security rates under different transmission modes and scenes;
step nine: under the condition that the achievable safe rate is not changed, the influence of the deployment of the intelligent reflection surface on the transmission power of the base station side is considered.
2. A reflectron-assisted user node untrusted NOMA network secure communication method according to claim 1, characterized in that: the first step specifically comprises the following steps:
the safety communication system comprises a base station, an intelligent reflecting surface and two non-orthogonal users (a near-end user n and a far-end user m), wherein the risk of mutual information eavesdropping exists between user nodes, namely the far-end user is used as an eavesdropper to eavesdrop the information of the near-end user, the base station sends the superposed information of the two users to the users under the assistance of the intelligent reflecting surface, meanwhile, the eavesdropper adopts a passive eavesdropping mode to eavesdrop legal information, a communication link between the base station and the users in the system is blocked by a building and cannot be directly communicated, and the communication can be completed only through the assistance of the reflecting surface.
3. A reflectron-assisted user node untrusted NOMA network secure communication method according to claim 1, characterized in that: the second step specifically comprises:
the base station is provided with M antennas, the intelligent reflecting surface comprises N reflecting units, and the complex channel coefficients from the base station to the reflecting surface and from the reflecting surface to the user are respectively GbrAnd
Figure FDA0003304224530000021
representing and modeling the channel as a rice fading channel, and the gain of a cascade channel from a base station to an intelligent reflecting surface and then to a user should meet the following conditions without loss of generality:
Figure FDA0003304224530000022
at this time, the received signals of the near-end user n and the far-end user m can be expressed as:
Figure FDA0003304224530000023
wherein the content of the first and second substances,
Figure FDA0003304224530000024
matrix, beta, representing the reflection characteristics of the intelligent reflecting surfacem∈(0,1]Denotes the reflection magnification factor, theta, of the m-th cell on the reflecting surfacemE [0,2 π) represents the mth reflectionPhase shift of the cell, xnAnd xmNormalized energy signals, a, representing the near-end and far-end users, respectivelynAnd amRepresenting power allocation factors of near-end and far-end users and satisfying relation am≥anAnd am+an＝1，PsRepresents the normalized transmit power at the base station,
Figure FDA0003304224530000025
is a phase shift matrix of the intelligent reflecting surface,
Figure FDA0003304224530000026
represents the beamforming vector on the base station side,
Figure FDA0003304224530000027
representing a user
Figure FDA0003304224530000028
White gaussian noise.
4. A reflectron-assisted user node untrusted NOMA network secure communication method according to claim 1, characterized in that: the third step specifically comprises:
the safe speed expression is achieved by the system as follows:
Figure FDA0003304224530000029
wherein the content of the first and second substances,
Figure FDA00033042245300000210
indicating the transmit end signal-to-noise ratio.
5. A reflectron-assisted user node untrusted NOMA network secure communication method according to claim 1, characterized in that: the fourth step specifically comprises:
can be further improvedThe design method is abstracted into a non-convex function maximum solving problem S based on a formula (2)1：
Figure FDA0003304224530000031
Wherein, C1And C2For the constraint condition, that is, the maximum solving problem, except for satisfying the requirement of the phase shift matrix theta of the intelligent reflecting surface, the power of the beam forming vector w at the base station side must not exceed the total transmission power P of the base stations。
6. A reflectron-assisted user node untrusted NOMA network secure communication method according to claim 1, characterized in that: the fifth step specifically comprises:
for S1Adopting mathematical derivation based on Rayleigh entropy to obtain an optimization formula of a beam forming vector at the base station side; the beamforming vector w should be as parallel as possible to the receive channel of the legitimate user n
Figure FDA0003304224530000032
And as orthogonal as possible to the eavesdropping channel of the eavesdropping user m
Figure FDA0003304224530000033
So as to enhance the reliability of a legal channel and reduce the eavesdropping capability of the user m;
when the phase shift matrix at the intelligent reflective surface is fixed, the optimization formula of the beamforming vector can be written as:
Figure FDA0003304224530000034
wherein the content of the first and second substances,
Figure FDA0003304224530000035
IMis an identity matrix of dimension M,
Figure FDA0003304224530000036
is a relevant parameter of additive white gaussian noise.
7. A reflectron-assisted user node untrusted NOMA network secure communication method according to claim 1, characterized in that: the sixth step specifically comprises:
when the beamforming vector on the base station side is fixed, the element { theta in the phase shift matrix theta is fixedi}i≠kThe BCD optimization formula of (a) can be written as:
Figure FDA0003304224530000041
wherein the content of the first and second substances,
Figure FDA0003304224530000042
Figure FDA0003304224530000043
Figure FDA0003304224530000044
Figure FDA0003304224530000045
is a channel matrix GbrThe (c) th row of (a),
Figure FDA0003304224530000046
the main implementation steps of the BCD algorithm can be summarized in the following table:
Figure FDA0003304224530000047
8. a reflectron-assisted user node untrusted NOMA network secure communication method according to claim 1, characterized in that: the seventh step specifically comprises:
unlike the BCD algorithm in which each phase shift unit θ iskRegarding the phase shift matrix as an optimization block, in the MM algorithm, the whole phase shift matrix Θ is considered as an optimization block, so that all phase shift units are processed in parallel in one optimization iteration process;
the optimization problem for the objective function can be rewritten as:
Figure FDA0003304224530000051
wherein the content of the first and second substances,
Figure FDA0003304224530000052
the lower bound function g (v) can be expressed as:
Figure FDA0003304224530000053
wherein the content of the first and second substances,
Figure FDA0003304224530000054
Figure FDA0003304224530000055
is the value of v in the t-th iteration of the MM algorithm,
Figure FDA0003304224530000056
represents an objective function in
Figure FDA0003304224530000057
A lower bound value at the point;
the optimization problem of the phase shift matrix Θ in each iteration can be transformed into:
Figure FDA0003304224530000058
wherein the content of the first and second substances,
Figure FDA0003304224530000059
therefore, when the beamforming vector w at the base station is fixed, the optimal solution equation for the phase shift matrix Θ is:
Figure FDA00033042245300000510
when the phase shift matrix at the intelligent reflecting surface is fixed, the optimization formula of the beam forming vector is shown in formula (4);
the main implementation steps of the MM algorithm are shown in the following table:
Figure FDA0003304224530000061
9. a reflectron-assisted user node untrusted NOMA network secure communication method according to claim 1, characterized in that: the eighth step specifically comprises:
comparing the system achievable safety rate given in the above steps with the achievable safety rate in different transmission modes (such as OMA transmission) and different transmission scenes (such as scenes without deploying intelligent reflecting surfaces); the difference between the NOMA safe communication rate assisted by the intelligent reflecting surface and the safe rate under other transmission modes and transmission scenes is compared by changing the transmitting power of the system, the number of transmitting antennas of the base station and the number of reflecting units of the reflecting surface of the intelligent reflecting surface.
10. A reflectron-assisted user node untrusted NOMA network secure communication method according to claim 1, characterized in that: the ninth step specifically comprises:
under the condition that the system safety rate is not changed, aiming at the NOMA transmission scene, comparing the difference of the base station transmitting power through whether an intelligent reflecting surface is deployed or not; in addition, BCD and MM algorithms are introduced to optimize the NOMA network assisted by the intelligent reflecting surface, and the obvious difference of the two algorithms in the aspect of lightening the load capacity of the transmitting power of the base station can be observed.
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