CN114143791B - Transmission method of Cell-free system based on RSMA - Google Patents

Abstract

The invention discloses a transmission scheme of a Cell-free system based on RSMA, which consists of M access points, K legal users and an eavesdropper. An eavesdropper eavesdrops on the signal sent to the legitimate user throughout the data transmission process. And the common message serves a dual purpose, as a desired message at the legitimate user and as artificial noise at the eavesdropper, without consuming additional transmission power. The physical layer security and rate of the system are maximized by jointly optimizing the beamforming vector and rate assignment, and then solving the optimization problem using a continuous convex approximation method.

Description

Transmission method of Cell-free system based on RSMA

Technical Field

The invention belongs to the field of wireless communication, and particularly relates to a transmission method of a Cell-free system based on RSMA.

Background

Rate-division multiple access (Rate-SPLITTING MULTIPLE ACCESS, RSMA) is a more versatile, powerful multiple access approach for downlink multi-antenna systems that can meet the high throughput, qoS heterogeneity and huge connection requirements of future multi-antenna wireless networks. Rate-division multiple access is suitable for various network loads (underload and overload conditions) and user deployments (with different channel strengths, channel directions) compared to non-orthogonal multiple access. Recently, a Cell-free massive MIMO network has been receiving increasing attention, the wireless network is composed of a large number of Access Points (APs) randomly distributed in a network area, and the APs jointly serve a large number of users. In a Cell-free massive MIMO system, all APs may be interconnected by a Central Processing Unit (CPU) to perform beamforming transmission tasks. Cell-free massive MIMO networks can provide more diversity gain, better coverage and energy efficiency than traditional massive MIMO networks. Therefore, the Cell-free system based on the rate division multiple access is studied, and the future communication system can be better dealt with.

Disclosure of Invention

In order to improve the coverage of wireless communication, the invention discloses a transmission method of a Cell-free system based on RSMA, in particular to a physical layer security and rate maximization method in the Cell-free system based on rate division multiple access, which jointly optimizes beam forming vectors and rate distribution.

The embodiment of the invention provides the following technical scheme:

a method for physical layer security and rate maximization in a Cell-free system based on rate division multiple access, the method comprising:

step A, a Cell-free system model based on rate division multiple access is established, and received signals at legal users and eavesdroppers Eve are solved;

step B, respectively solving a transmission rate expression corresponding to the decoding public stream and the private stream at the legal user U _k and the eavesdropper and a physical layer security rate expression which can be realized by the kth user;

and step C, initializing an optimization variable in the iterative algorithm.

And D, substituting the value of the optimized variable in the nth iteration into a convex problem obtained by using a continuous convex approximation method, solving an optimal value by using a Newton steepest descent gradient method, and updating the value of the (n+1) th optimized variable by using the obtained optimal value of the optimized variable.

And E, defining the condition for ending the iterative optimization.

The step A specifically comprises the following steps:

A1, a Cell-free system model based on rate division multiple access is established, and the system model consists of M Access Points (AP), K legal users (U _k) and a passive eavesdropper. Where each AP is equipped with N antennas, both legitimate users and eavesdroppers are single antennas. The AP is connected to a CPU through a perfect backhaul network, which provides an error-free and higher capacity connection.

A2, at each AP, messages for U _k are split into public and private parts according to the rate splitting principle. All common parts are then combined together and encoded into a common stream s _c,s_c for decoding by all users. The private parts are each encoded as a private stream s _k,s_k, which is decoded only by the corresponding user. Stream s= [ s _c,s₁,...,s_K]^T ] is linear precoded using precoder p= [ P _c,p₁,...,p_K. The transmit signal at the mth AP is:

A3, the received signals at the legal user U _k and the eavesdropper are respectively: And Wherein/>Representing the wireless channel matrix between the mth access point and the kth legal user U _k, respectively,/>, between the mth access point and the eavesdropperAnd/>Additive white gaussian noise at the legitimate user U _k and the eavesdropper, respectively.

The step B specifically comprises the following steps:

And B1, based on the received signal obtained in the step A, at a receiving end, each legal user firstly takes all private streams as noise to decode the public streams, and the signal-to-interference-and-noise ratio of the decoded public streams at U _k, K E { 1.. To ensure that the common message can be decoded at all legitimate users, the achievable rate of decoding the common message accordingly should be: r _c＝min{R_c,1,R_c,2,...,R_c,K, where R _c,k＝log₂(1+γ_c,k), K e { 1.. K is the achievable rate of decoding the common stream at U _k.

B2, then delete the common stream from the received signal with SIC at U _k, and decode s _k at its corresponding private stream s _k.U_k with the signal-to-interference-and-noise ratio: the corresponding achievable rates for decoding the private stream at U _k are: r _k＝log₂(1+γ_k).

B3, using the public message as a dual purpose, as a desired message at the legitimate user and as artificial noise at the eavesdropper. In order for the public message to be considered as artificial noise satisfying at the eavesdropper, the condition should be satisfied: c _c,e≤R_c, wherein C _c,e represents the rate at which the eavesdropper decodes the common message. It is assumed that an eavesdropper can eavesdrop on all users' private messages.

And B4, decoding the public stream and the private stream at the eavesdropper, wherein the received signal-to-interference-and-noise ratios are respectively as follows: And/> The corresponding achievable rates for decoding the public stream and the private stream at the eavesdropper are respectively: c _c,e＝log₂(1+γ_c,e) and C _k,e＝log₂(1+γ_k,e).

B5, the physical layer security rate achievable by the kth user isWherein,Indicating that the public message transmitted to U _k can achieve a safe rate, v _k indicates the proportion of the kth user's public message that can achieve a safe rate. /(I)The private message transmitted to U _k may be indicative of a secure rate.

The step C specifically comprises the following steps:

C1, setting the iteration number n=1, first using maximum ratio transmission and singular value decomposition to precoder Initializing precoder/>, for private stream s _k Initializing toWherein/>Lambda is more than or equal to 0 and less than or equal to 1. Precoder/>, for common stream s _c Initializing toWhere p _c＝(1-λ)P_t,u_c is the eigenvector corresponding to the largest left singular value of the channel matrix h= [ g _1k,g_2k,...,g_MK ], which is calculated from U _c =u (: 1), where h=usv ^H.

C2, the auxiliary variable alpha ^[1],ρ^[1],/>β^[1],/>Respectively initialize to,/>

The step D specifically comprises the following steps:

And D1, updating an optimization variable by utilizing a convex optimization problem obtained by a continuous convex approximation algorithm. Wherein the objective function of the convex optimization problem is r, which represents the system physical layer security and rate. Constraints on the convex optimization problem include user private rate constraints, public message is treated as artificial noise public rate constraints, and total power constraints at the AP.

D2, user private rate constraints are specifically expressed as Ω^[n](p_k,g_m,k,β_k)≤ρ_k,Ω^[n](p_k,h_m,β_k,e)≥ρ_k,e,1+ρ_k-Γ^[n](α_k)≤0,Wherein,

D3, the common rate constraint for treating common messages as artificial noise is specifically expressed asΩ^[n](p_c,g_m,k,β_c,k)≥ρ_c,k,Ω^[n](p_c,h_m,β_c,e)≤ρ_c,e,/>1+Ρ _c,e-Γ^[n](α_c,e) is less than or equal to 0. Wherein,

D4, solving the convex optimization problem by utilizing the newton steepest descent gradient method, wherein the iteration process is η (m) = (t (m), P (m), α (m), α _c(m),ρ(m),ρ_c(m),β(m),β_c (m)),|Eta (m+1) -eta (m) | ² < delta, where mu=0.39, delta=10 ^-3,/>To obtain optimal values of objective function and optimization variable for eta (m) gradient r^*,P^*,α^*,α_c ^*,ρ^*,ρ_c ^*,β^*,β_c ^*.

D5, let iteration number n=n+1, update objective function and optimization variable in nth iteration based on the optimal value of objective function and optimization variable obtained in step D4, r ^[n]＝r^*,P^[n]＝P^*,α^[n]＝α^*,ρ^[n]＝ρ^*,β^[n]＝β^*,/>

The step E specifically comprises the following steps:

E1, setting convergence accuracy epsilon=10 ^-3, and repeating the step D when |r ^[n]-r^[n-1] | < epsilon is not established.

E2, when the condition |r ^[n]-r^[n-1] | < ε is satisfied, jump out of the loop, output an optimal value r ^*＝r^[n],P^*＝P^[n],α^*＝α^[n],ρ^*＝ρ^[n],/>β^*＝β^[n],/>

Compared with the prior art, the technical scheme has the following advantages:

The invention discloses a physical layer security and rate maximization method in a Cell-free system based on RSMA. This scheme considers the use of public messages for dual purposes, as desired messages at legitimate users, as artificial noise at eavesdroppers, without consuming additional transmission power. The rate division multiple access method can flexibly cope with the change of the number of users in wireless communication. Consider the use of a Cell-free system to improve the coverage of a wireless network.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

Fig. 1 is a flow chart of a transmission method of a RSMA-based Cell-free system according to an embodiment of the present invention.

Detailed Description

As described in the background section, how to improve the physical layer security in wireless communication, improve the communication quality and reliability of users, and realize secure transmission of data is a problem to be solved by those skilled in the art.

The core idea of the invention is to provide a transmission method of a Cell-free system based on RSMA, in particular to a physical layer security and rate maximization method in the Cell-free system based on rate division multiple access, so as to improve the security of data transmission. By using a method of continuous convex approximation, the physical layer security and rate of the system is maximized by jointly optimizing the beamforming vector and rate allocation.

Referring to fig. 1, the implementation of the present invention provides a physical layer security and rate maximization method in a Cell-free system based on rate division multiple access, the method comprising:

And step A, a Cell-free system model based on rate division multiple access is established, and received signals at legal users and eavesdroppers Eve are solved.

And step B, respectively solving transmission rate expressions corresponding to the decoded public stream and the decoded private stream at the legal user U _k and the eavesdropper and physical layer security rate expressions which can be realized by the kth user.

And step C, initializing an optimization variable in the iterative algorithm.

And D, substituting the value of the optimized variable in the nth iteration into a convex problem obtained by using a continuous convex approximation method, solving an optimal value by using a Newton steepest descent gradient method, and updating the value of the (n+1) th optimized variable by using the obtained optimal value of the optimized variable.

And E, defining the condition for ending the iterative optimization.

The step A specifically comprises the following steps:

A1, a Cell-free system model based on rate division multiple access is established, and the system model consists of M Access Points (AP), K legal users (U _k) and a passive eavesdropper. Where each AP is equipped with N antennas, both legitimate users and eavesdroppers are single antennas. The AP is connected to a CPU through a perfect backhaul network, which provides an error-free and higher capacity connection.

A2, at each AP, messages for U _k are split into public and private parts according to the rate splitting principle. All common parts are then combined together and encoded into a common stream s _c,s_c for decoding by all users. The private parts are each encoded as a private stream s _k,s_k, which is decoded only by the corresponding user. Stream s= [ s _c,s₁,...,s_K]^T ] is linear precoded using precoder p= [ P _c,p₁,...,p_K. The transmit signal at the mth AP is:

A3, the received signals at the legal user U _k and the eavesdropper are respectively: And Wherein/>Representing the wireless channel matrix between the mth access point and the kth legal user U _k, respectively,/>, between the mth access point and the eavesdropperAnd/>Additive white gaussian noise at the legitimate user U _k and the eavesdropper, respectively.

The step B specifically comprises the following steps:

And B1, based on the received signal obtained in the step A, at a receiving end, each legal user firstly takes all private streams as noise to decode the public streams, and the signal-to-interference-and-noise ratio of the decoded public streams at U _k, K E { 1.. To ensure that the common message can be decoded at all legitimate users, the achievable rate of decoding the common message accordingly should be: r _c＝min{R_c,1,R_c,2,...,R_c,K, where R _c,k＝log₂(1+γ_c,k), K e { 1.. K is the achievable rate of decoding the common stream at U _k.

B2, then delete the common stream from the received signal with SIC at U _k, and decode s _k at its corresponding private stream s _k.U_k with the signal-to-interference-and-noise ratio: the corresponding achievable rates for decoding the private stream at U _k are: r _k＝log₂(1+γ_k).

B3, using the public message as a dual purpose, as a desired message at the legitimate user and as artificial noise at the eavesdropper. In order for the public message to be considered as artificial noise satisfying at the eavesdropper, the condition should be satisfied: c _c,e≤R_c, wherein C _c,e represents the rate at which the eavesdropper decodes the common message. It is assumed that an eavesdropper can eavesdrop on all users' private messages.

And B4, decoding the public stream and the private stream at the eavesdropper, wherein the received signal-to-interference-and-noise ratios are respectively as follows: And/> The corresponding achievable rates for decoding the public stream and the private stream at the eavesdropper are respectively: c _c,e＝log₂(1+γ_c,e) and C _k,e＝log₂(1+γ_k,e).

B5, the physical layer security rate achievable by the kth user isWherein,Indicating that the public message transmitted to U _k can achieve a safe rate, v _k indicates the proportion of the kth user's public message that can achieve a safe rate. /(I)The private message transmitted to U _k may be indicative of a secure rate.

The step C specifically comprises the following steps:

C1, setting the iteration number n=1, first using maximum ratio transmission and singular value decomposition to precoder Initializing precoder/>, for private stream s _k Initializing toWherein/>Lambda is more than or equal to 0 and less than or equal to 1. Precoder/>, for common stream s _c Initializing toWhere p _c＝(1-λ)P_t,u_c is the eigenvector corresponding to the largest left singular value of the channel matrix h= [ g _1k,g_2k,...,g_MK ], which is calculated from U _c =u (: 1), where h=usv ^H.

C2, the auxiliary variable alpha ^[1],ρ^[1],/>β^[1],/>Respectively initialize to,/>

The step D specifically comprises the following steps:

And D1, updating an optimization variable by utilizing a convex optimization problem obtained by a continuous convex approximation algorithm. Wherein the objective function of the convex optimization problem is r, which represents the system physical layer security and rate. Constraints on the convex optimization problem include user private rate constraints, public message is treated as artificial noise public rate constraints, and total power constraints at the AP.

D2, user private rate constraints are specifically expressed as Ω^[n](p_k,g_m,k,β_k)≤ρ_k,Ω^[n](p_k,h_m,β_k,e)≥ρ_k,e,1+ρ_k-Γ^[n](α_k)≤0,/>Wherein,

D3, the common rate constraint for treating common messages as artificial noise is specifically expressed asΩ^[n](p_c,h_m,β_c,e)≤ρ_c,e，/>1+Ρ _c,e-Γ^[n](α_c,e) is less than or equal to 0. Wherein,

D4, solving the convex optimization problem by utilizing the newton steepest descent gradient method, wherein the iteration process is η (m) = (t (m), P (m), α (m), α _c(m),ρ(m),ρ_c(m),β(m),β_c (m)),|Eta (m+1) -eta (m) | ² < delta, where mu=0.39, delta=10 ^-3,/>To an optimal value r ^*,P^*,α^*,/>, for the η (m) gradient, to obtain the objective function and the optimization variablesρ^*,/>β^*,/>

D5, let iteration number n=n+1, update objective function and optimization variable in nth iteration based on the optimal value of objective function and optimization variable obtained in step D4, r ^[n]＝r^*,P^[n]＝P^*,α^[n]＝α^*,ρ^[n]＝ρ^*,β^[n]＝β^*,/>

The step E specifically comprises the following steps:

E1, setting convergence accuracy epsilon=10 ^-3, and repeating the step D when |r ^[n]-r^[n-1] | < epsilon is not established.

E2, when the condition |r ^[n]-r^[n-1] | < ε is satisfied, jump out of the loop, output an optimal value r ^*＝r^[n],P^*＝P^[n],α^*＝α^[n],ρ^*＝ρ^[n],/>β^*＝β^[n],/>

Compared with the prior art, the technical scheme has the following advantages:

The present invention considers a transmission scheme of an RSMA-based Cell-free system in which a common message is used as a desired message at a legitimate user and as artificial noise at an eavesdropper without consuming additional transmission power. Under the constraints of common information as noise constraint, total power constraint of a transmitting end and the like, physical layer security and rate of a user are maximized through joint optimization of active beam forming vector and rate distribution.

The invention discloses a physical layer security and rate maximization method in a Cell-free system based on RSMA. The method considers the introduction of the rate division multiple access technology into the Cell-free system for the first time to improve the coverage of wireless signals, and proposes a method for jointly optimizing the active beam forming vector and the rate distribution under the constraint that a common message is used as noise constraint, the total power constraint of a transmitting end and the like.

The invention provides a Cell-free system based on RSMA, which considers the problem of physical layer safety and rate maximization in the system, sequentially solves a series of convex problems by using a continuous convex approximation method, and carries out iterative optimization on an optimization variable so as to obtain an optimal solution of the optimization variable, thereby maximizing the physical layer safety and rate in the system.

In the present description, each part is described in a progressive manner, and each part is mainly described as different from other parts, and identical and similar parts between the parts are mutually referred.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (1)

1. The transmission method of the Cell-free system based on RSMA is characterized by comprising the following steps:

Step A, a Cell-free system model based on a rate division multiple access technology RSMA is established, and received signals at legal users and eavesdroppers Eve are solved;

step B, respectively solving a transmission rate expression corresponding to the decoding public stream and the private stream at the legal user U _k and the eavesdropper and a physical layer security rate expression which can be realized by the kth user;

step C, initializing an optimization variable in an iterative algorithm;

Substituting the value of the optimized variable in the nth iteration into a convex problem obtained by using a continuous convex approximation method, solving an optimal value by using a Newton steepest descent gradient method, and updating the value of the (n+1) th optimized variable by using the obtained optimal value of the optimized variable;

Step E, defining the condition for ending the iterative optimization;

The step A specifically comprises the following steps:

A1, establishing a Cell-free system model based on rate division multiple access, wherein the system model consists of M Access Points (APs), K legal users U _k and a passive eavesdropper, each AP is provided with N antennas, the legal users and the eavesdropper are single antennas, and the APs are connected to a CPU through a perfect backhaul network, so that an error-free and higher-capacity connection is provided;

a2, at each AP, the message for U _k is split into public and private parts according to the rate splitting principle, then all public parts are combined together and encoded into a public stream s _c,s_c to be decoded by all users, the private parts are each encoded into a private stream s _k,s_k to be decoded by only the corresponding users, the stream s= [ s _c,s₁,...,s_K]^T ] is linearly precoded using a precoder p= [ P _c,p₁,...,p_K ], and the transmitted signal at the mth AP is:

A3, the received signals at the legal user U _k and the eavesdropper are respectively: And/> Wherein/>Representing the wireless channel matrix between the mth access point and the kth legal user U _k, respectively,/>, between the mth access point and the eavesdropperAnd/>Additive white gaussian noise at legal user U _k and eavesdropper, respectively;

The step B specifically comprises the following steps:

And B1, based on the received signal obtained in the step A, at a receiving end, each legal user firstly takes all private streams as noise to decode the public streams, and the signal-to-interference-and-noise ratio of the decoded public streams at U _k, K E { 1.. To ensure that the common message can be decoded at all legitimate users, the achievable rate of decoding the common message accordingly should be: r _c＝min{R_c,1,R_c,2,...,R_c,K }, where R _c,k＝log₂(1+γ_c,k), K e {1,., K } is the achievable rate of decoding the common stream at U _k;

B2, then delete the common stream from the received signal with SIC at U _k, and decode s _k at its corresponding private stream s _k,U_k with the signal-to-interference-and-noise ratio: The corresponding achievable rates for decoding the private stream at U _k are: r _k＝log₂(1+γ_k);

B3, using the public message as a dual purpose, as a desired message at the legitimate user and as an artificial noise at the eavesdropper, in order for the public message to be considered as an artificial noise satisfying at the eavesdropper, the condition should be satisfied: c _c,e≤R_c, wherein C _c,e represents the rate at which the eavesdropper decodes the public message, assuming that the eavesdropper can eavesdrop on all users' private messages;

And B4, decoding the public stream and the private stream at the eavesdropper, wherein the received signal-to-interference-and-noise ratios are respectively as follows: And The corresponding achievable rates for decoding the public stream and the private stream at the eavesdropper are respectively: c _c,e＝log₂(1+γ_c,e) and C _k,e＝log₂(1+γ_k,e);

b5, the physical layer security rate achievable by the kth user is Wherein/>Indicating that the public message transmitted to U _k can realize the safe rate, v _k indicates the proportion of the public message of the kth user to realize the safe rate,/>Indicating that the private message transmitted to U _k may achieve a secure rate;

The step C specifically comprises the following steps:

C1, setting the iteration number n=1, first using maximum ratio transmission and singular value decomposition to precoder Initializing precoder/>, for private stream s _k Initialized to/>Wherein/>Precoder/>, for common stream s _c Initialized to/>Where p _c＝(1-λ)P_t,u_c is the eigenvector corresponding to the largest left singular value of the channel matrix h= [ g _1k,g_2k,...,g_MK ], which is calculated from uc=u (: 1), where h=usv ^H;

C2, auxiliary variables Respectively initialize to,/>

The step D specifically comprises the following steps:

D1, updating an optimization variable by utilizing a convex optimization problem obtained by a continuous convex approximation algorithm, wherein an objective function of the convex optimization problem is r, r represents the security and the speed of a physical layer of a system, constraint conditions of the convex optimization problem comprise private speed constraint of a user, public information is regarded as public speed constraint of artificial noise, and total power constraint at an AP (access point);

D2, user private rate constraints are specifically expressed as Ω^[n](p_k,g_m,k,β_k)≤ρ_k,Ω^[n](p_k,h_m,β_k,e)≥ρ_k,e,1+ρ_k-Γ^[n](α_k)≤0,Wherein,

D3, the common rate constraint for treating common messages as artificial noise is specifically expressed asΩ^[n](p_c,g_m,k,β_c,k)≥ρ_c,k,Ω^[n](p_c,h_m,β_c,e)≤ρ_c,e,/>1+Ρ _c,e-Γ^[n](α_c,e) is less than or equal to 0; wherein,

D4, solving the convex optimization problem by utilizing the newton steepest descent gradient method, wherein the iteration process is η (m) = (t (m), P (m), α (m), α _c(m),ρ(m),ρ_c(m),β(m),β_c (m)),|Eta (m+1) -eta (m) | ² < delta, where mu=0.39, delta=10 ^-3,/>To obtain optimal values of objective function and optimization variable for eta (m) gradient r^*,P^*,α^*,α_c ^*,ρ^*,ρ_c ^*,β^*,/>

D5, let iteration number n=n+1, update objective function and optimization variable in nth iteration based on the optimal value of objective function and optimization variable obtained in step D4, r ^[n]＝r^*,P^[n]＝P^*,α^[n]＝α^*,ρ^[n]＝ρ^*,β^[n]＝β^*,/>

The step E specifically comprises the following steps:

e1, setting convergence accuracy epsilon=10 ^-3, and repeating the step D when |r ^[n]-r^[n-1] | < epsilon is not satisfied;

E2, when the condition |r ^[n]-r^[n-1] | < ε is satisfied, jump out of the loop, output an optimal value r ^*＝r^[n],P^*＝P^[n],α^*＝α^[n], ρ^*＝ρ^[n],/>β^*＝β^[n],/>