CN112272073A - Hidden beam forming design method for ideal WCSI hidden communication - Google Patents

Abstract

The invention provides a hidden beam forming design method aiming at ideal WCSI hidden communication, and considers a universal unicast beam forming network. For the ideal WCSI (Willie's channel state information) case, this problem is addressed under ideal concealment constraints, and a concealed beamformer was developed by using semi-positive definite relaxation and bisection. Zero-forcing beamformer designs with single iteration processing are also presented.

Description

Hidden beam forming design method for ideal WCSI hidden communication

Technical Field

The invention relates to a hidden beam forming design method aiming at ideal WCSI hidden communication.

Background

Due to the nature of wireless communications and their broadcasts, they are vulnerable to malicious security attacks. By using encryption and key exchange techniques, traditional security methods focus primarily on preventing the transmitted wireless signal form from being decoded by unintended users [1], but not hiding them. For many wireless scenarios, such as law enforcement and military communications, the transmitted signal should not be detected in order to perform stealth missions. Thus, the paradigm of covert communications, also known as Low Probability of Detection (LPD) communications, is intended to hide the transmission state and protect the privacy or privacy of the user.

In a typical secret communication scenario, a sender (Alice) wishes to send information to a secret recipient (Bob), but is not detected by an eavesdropper (Willie). Here Willie may or may not be the legitimate recipient, but the purpose is to detect whether propagation from Alice to Bob has occurred based on the observed results. Mathematically, Willie's ultimate goal is to distinguish between two hypotheses by using a particular decision rule

Or also

Wherein

Denotes a null hypothesis, i.e. Alice does not send a private data stream to Bob, but

Represents another assumption, namely that Alice faces Bob [2]]The private data stream is sent. In general, the assumed prior probability

And

each equal to 1/2, assuming equality. Thus, Willie's detection error probability is defined as [2]：

Indicating that Alice sent information to Bob,

indicating another situation. For a given ε ∈ [0, 1]]If the probability xi of the detection error is not less than 1-epsilon, namely xi is more than or equal to 1-epsilon, secret communication can be realized. Here, epsilon is a predetermined value for specifying a secret communication constraint condition.

Practical secret communications have been studied by studying spread spectrum techniques for decades [3]However, the information theory limit of implicit communication has been recently developed [4]-[6]. In [ 4]]The realizability of Square Root Law (SRL) is established to enable implicit communication over an Additive White Gaussian Noise (AWGN) channel. In the use of n-channel, Alice can send to Bob at most

A bit. In addition, SRL results have been validated in Discrete Memoryless Channels (DMC) [ 5]]，[6]Two-hop system [7]Multiple access channels [8 ]]And broadcast channel [9 ]]. In short, these results indicate that despite the noiseless transmission, the average number of concealed bits used per channel asymptotically approaches zero,

fortunately, other work [10]-[22]It is disclosed that Alice can achieve a positive concealment rate when Willie is not certain of its noise statistics, transmitting in at least n channels under secret transmission conditions

Bit-general [10 ]]-[13]. Based on the proposed rate control and power control strategies, the authors are [16 ]]The feasibility of secret transmission in amplifying and forwarding one-way relay networks is verified. In case of limited channel usage, at [18 ]]The study of delay intolerant covert communication shows that random transmit power can enhance covert communication. In addition, in [20 ]]The impact of a finite block length (i.e., a finite n) on covert communications was investigated. By using Full Duplex (FD) receivers, [20 ] under fading channels]A check was made for covert communication in which the FD receiver would generate artificial noise to confuse Willie. In [21 ]]The optimality of the gaussian signal was studied by using Kullback-leibler (kl) divergence as the hiding metric. By expressing the LPD communication as the fastest detection problem, [22 ]]The hidden throughput maximization problem was investigated by the authors in (1) using three different detection methods, Shewhart, cumulative sum (CUSUM) and Shiryaev-Roberts (SR) tests. Alice can also use 14 in n channels with the help of a friendly and unknowingly jammer]，[15]To make

The individual masked bits are communicated to Bob. By suppressing Willie's detection by generating artifacts, Alice can reliably and privately transmit information to Bob [17]. Most of the work currently available [4]-[9]，[14]-[18]，[20]-[22]Perfect Channel State Information (CSI) of all users is used to study the secret transmission, and in this work this strong assumption is relaxed by using multiple antennas, while still guaranteeing switched transmission. In [19 ]]In (1), a single-input single-output (SISO) covert communication scheme is considered, and then an accurate expression of the optimal threshold of the wowden detector is derived. The authors then analyzed the achievable rate with outage constraints under imperfect CSI.

Reference documents:

[1]M.Bloch and J.Barros,Physical-Layer Security:From Information Theory to Security Engineering,U.K.:Cambridge Univ.,2011.

[2]E.L.Lehmann and J.P.Romano,Testing Statistical Hypotheses,Springer New York, 2005.

[3]M.K.Simon,J.K.Omura,R.A.Scholtz,and B.K.Levitt,Spread Spectrum Communications Handbook,New York,NY,USA:McGraw-Hill,Apr.1994.

[4]B.A.Bash,D.Goeckel,and D.Towsley,“Limits of reliable communication with low probability of detection on AWGN channels,”IEEE J.Sel.Areas Commun.,vol.31,no. 9,pp.1921–1930,2013.

[5]M.R.Bloch,“Covert communication over noisy channels:A resolvability perspective,”IEEE Trans.Inf.Theory,vol.62,no.5,pp.2334–2354,2016.

[6]L.Wang,W.Wornell,and L.Zheng,“Fundamental limits of communication with low probability of detection,”IEEE Trans.Inf.Theory,vol.62,no.6,pp.3493–3503,Jun. 2016.

[7]H.Wu,X.Liao,Y.Dang,Y.Shen,and X.Jiang,“Limits of covert communication on two-hop AWGN channels,”in Int.Conf.Netw.Netw.Appl.,pp.42–47,Oct.2017.

[8]K.S.K.Arumugam and M.R.Bloch,“Covert communication over a k-user multiple access channel,”IEEE Trans.Inf.Theory,vol.65,no.11,pp.7020–7044,Nov. 2019.

[9]V.Y.F.Tan and S.Lee,“Time-division is optimal for covert communication over some broadcast channels,”IEEE Trans.Inf.Forensics

Security,vol.14,no.5,pp.1377–1389,2019.

[10]S.Lee,R.J.Baxley,M.A.Weitnauer,and B.Walkenhorst,“Achieving undetectable communication,”IEEE J.Sel.Topics Signal Process.,vol.9,no.7,pp. 1195–1205,2015.

[11]D.Goeckel,B.Bash,S.Guha,and D.Towsley,“Covert communications when the warden does not know the background noise power,”IEEE Commun.Lett.,vol.20,no.2,pp. 236–239,Feb.2016.

[12]P.H.Che,M.Bakshi,C.Chan,and S.Jaggi,“Reliable deniable communication with channel uncertainty,”in Proc.IEEE Inf.Theory

Workshop,pp.30–34,2014.

[13]B.He,S.Yan,X.Zhou,and V.K.N.Lau,“On covert communication with noise uncertainty,”IEEE Commun.Lett.,vol.21,no.4,pp.941–944,Apr.2017.

[14]T.V.Sobers,B.A.Bash,D.Goeckel,S.Guha,and D.Towsley,“Covert communication with the help of an uninformed jammer achieves positive rate,”in Proc. Asilomar Conf.Signals,Syst.,Comput.,pp.625–629,Nov.2015.

[15]T.V.Sobers,B.A.Bash,S.Guha,D.Towsley,and D.Goeckel,“Covert

communication in the presence of an uninformed jammer,”IEEE Trans.

Wireless Commun.,vol.16,no.9,pp.6193–6206,Sep.2017.

[16]J.Hu,S.Yan,X.Zhou,F.Shu,J.Li,and J.Wang,“Covert communication achieved by a greedy relay in wireless networks,”IEEE

Trans.Wireless Commun.,vol.17,no.7,pp.4766–4779,Jul.2018.

[17]R.Soltani,D.Goeckel,D.Towsley,B.A.Bash,and S.Guha,“Covert wireless communication with artificial noise generation,”IEEE Trans.Wireless Commun.,vol.17,no. 11,pp.7252–7267,Nov.2018.

[18]S.Yan,B.He,X.Zhou,Y.Cong,and A.L.Swindlehurst,“Delay-intolerant covert communications with either fixed or random transmit power,”IEEE Trans.Inf.Forensics Security,vol.14,no.1,pp.129–140,

Jan.2019.

[19]K.Shahzad,X.Zhou,and S.Yan,“Covert communication in fading channels under channel uncertainty,”in Proc.IEEE VTC Spring,pp.1–5,Jun.2017.

[20]K.Shahzad,X.Zhou,S.Yan,J.Hu,F.Shu,and J.Li,“Achieving covert wireless communications using a full-duplex receiver,”

IEEE Trans.Wireless Commun.,vol.17,no.12,pp.8517–8530,2018.

[21]S.Yan,Y.Cong,S.V.Hanly,and X.Zhou,“Gaussian signalling for covert communications,”IEEE Trans.Wireless Commun.,vol.18,no.7,pp.3542–3553,2019.

[22]K.Huang,H.Wang,D.Towsley,and H.V.Poor,“LPD communication:A sequential change-point detection perspective,”IEEE Trans.Commun.,vol.68,no.4,pp. 2474–2490,2020.

disclosure of Invention

The purpose of the invention is as follows: in order to solve the technical problems existing in the background technology, the invention provides a hidden beam forming design method aiming at the ideal WCSI hidden communication, which comprises the following steps:

step 1, establishing a covert communication environment;

step 2, under the condition of ideal WCSI (Willie channel state information), carrying out hidden beam forming design;

the step 1 comprises the following steps: alice denotes a base station, Carol denotes a regular user, Willie denotes an eavesdropper, Bob denotes a hidden user, and Alice always sends a data stream x to Carol_cAnd is incorporated in

Case private data stream x_bIs sent to Bob, where

Denotes a null hypothesis, i.e. Alice does not send a private data stream to Bob, but

Representing another assumption that Alice sends a private data stream to Bob. Meanwhile, Willie is observing the communication environment as an eavesdropper and tries to identify whether Alice is transmitting to Bob; alice can use the transmission to Carol as a cover to enable secret communication.

In the step 1, Alice is set to be provided with N antennae, and Carol, Bob and Willie all have only one antenna; order to

In particular, the amount of the solvent to be used,

representing a signal x_cThe power of (a) is determined,

representing a signal x_bOf the power of (c). Use of

Events indicating that Alice really sent information to Bob, uses

An event indicating that Alice does not send information to Bob.

In step 1, from Willie's perspective, Alice's transmission signal x is as follows:

wherein w_c,0And w_c,1Respectively represent x_cUnder the assumption that

And assume that

Of a transmit beamformer vector, w_bDenotes x_bBy P, the transmit beamformer vector of_totalRepresenting the maximum transmit power of Alice, the beamformer vector satisfies: in that

In case, | w_c,0||²≤P_totalAnd in

In case, | w_c,1||²+||w_b||²≤P_total；

For Carol, it receives a signal y_cComprises the following steps:

wherein

Is the channel coefficient from Alice to Carol,

is the noise received by Carol, where

Represents an N-dimensional complex vector, and represents a complex vector,

signal noise z representing Carol_cObeying a mean of 0 and a variance of

Complex gaussian distribution of (a);

for Bob, it receives the signal y_bComprises the following steps:

wherein

Is the channel gain from Alice to Bob,

is the noise received by Carol and is,

signal noise z representing Bob_bObeying a mean of 0 and a variance of

Complex gaussian fraction ofAnd (3) cloth.

In step 1, Willie receives signal y_wWriting into:

wherein

Are the channel coefficients from Alice to Willie,

is the noise received by Willie and is,

signal noise z representing Willie_wObeying a mean of 0 and a variance of

Complex gaussian distribution.

In step 1, Carol is set in accordance with (3)

And

at an instantaneous rate of R_c,0(w_c,0) And R_c,1(w_c,1,w_b) Written as:

wherein

Signal noise z representing Carol_cThe noise variance of (2).

Based on (4), Bob is set at

At an instantaneous rate of R_b(w_c,1,w_b) Given by:

let p be₀(y_w) And p₁(y_w) Are respectively shown in

And

lower Willie received signal likelihood function, based on (5), p₀(y_w) And p₁(y_w) Respectively as follows:

wherein

Wherein

Signal noise z representing Carol_wOf the noise variance, λ₀And λ₁Representing the auxiliary variable.

In step 1, Willie wants to minimize the detection error probability ξ by applying the optimal detector, setting:

ξ＝1-V_T(p₀,p₁), (9)

wherein V_T(p₀,p₁) Is p₀(y_w) And p₁(y_w) The general variation between them, the Pincker inequality is adopted (reference [23 ]]T.m.cover and j.a.thomas, Elements of Information Theory, New York: Wiley, 2006)), gave:

wherein D (p)₀||p₁) Represents from p₀(y_w) To p₁(y_w) KL (Kullback-Leibler) divergence (relative entropy) of D (p)₁||p₀) Is from p₁(y_w) To p₀(y_w) KL divergence of (1);

D(p₀||p₁) And D (p)₁||p₀) Respectively as follows:

to achieve covert communication with a given ξ, i.e., ξ ≧ 1- ε, the KL divergence of the likelihood function should satisfy one of the following constraints:

the step 2 comprises the following steps: the ideal WCSI case refers to: willie is a legitimate user and wants to get Bob's personal information, in which case Alice knows channel h_wAnd uses it to help Bob avoid wilE, monitoring;

problem (15) is established:

s.t.R_c,1(w_c,1,w_b)＝R_c,0(w_c,0), (15b)

D(p₀||p₁)＝0, (15c)

||w_b||²+||w_c,1||²≤P_total (15d)

to solve the problem (15), two beam former design methods are proposed, namely a blind beam former design and a ZF (zero forcing) beam former design, which are respectively as follows:

the hidden beamformer design is as follows:

defining auxiliary variables

And

and introducing an auxiliary variable r_bQuestion (15) is restated as the equivalent of question (16):

||w_b||²+||w_c,1||²≤P_total (16e)

applying SDR (semi-positive relaxation) technology (ref [24] z.luo, w.ma, a.m.so, y.ye, and s.zhang,

“Semidefinite relaxation of quadratic optimization problems,”IEEE Signal Process.

mag., vol.27, No.3, pp.20-34,2010.) to relax the problem (16), the following conditions were used:

ignoring the constraint of rank 1, a relaxed form of the problem (16), namely the problem (18), is obtained:

Tr(W_c,1)+Tr(W_b)≤P_total, (18e)

W_c,1≥0,W_b≥0 (18f)

order:

the following results were obtained:

function(s)

s.t.φ(W_b)≥r_bθ(W_c,1) (20)

r_bIs concave when being more than or equal to 0;

an algorithm 1 is established, wherein the algorithm 1 comprises the following steps:

step a1, selecting ζ>0 (end parameter), lower speed limit

And upper speed limit

Make Bob's optimal speed

Is located at

Performing the following steps;

step a2, initialization

Step a3, when

If yes, executing the step a4 to the step a 5;

step a4, setting

Step a5, if the problem (18) is feasible, get the solution W_bAnd W_c,1And is provided with

Otherwise, set up

Step a6, when

Ending the circulation;

step a7, outputting

Outputting optimal solution by Algorithm 1

And

reconstruction of the beamformer W from the solution given by Algorithm 1_c,1And W_bIf, if

And is

Then

Also given is an optimal solution to the problem (15), the Singular Value Decomposition (SVD) is used to obtain the optimal beamformer W_c,1And W_bI.e. by

And

if it is not

Or

Use of a Gaussian randomization procedure for problem (15) (reference [24]]Z.luo, w.ma, a.m.so, y.ye, and s.zhang, "semimidefinite repetition of quadrature optimization schemes," IEEE Signal process.mag., vol.27, No.3, pp.20-34, 2010 ") to obtain a rank 1 solution;

the ZF (zero forcing) beamformer is designed as follows: the problem (16) is recalculated to the following problem (21):

||w_b||²+||w_c,1||²≤P_total. (21g)

to solve the problem (21), under the constraints of (21d), (21e) and (21f), by minimizing the transmission power | | w_c,1||²To optimize the beam former w_c,1(ii) a The total transmission power constraint (21g) comprises w_bAnd w_c,1In order to maximize the objective function (21a),it is desirable to design a beamformer w with minimum transmit power_c,1(ii) a ZF beamformer w_c,1The design problem is expressed as:

s.t.(21d),(21e),(21f),

by relaxing

To W_c,1Not less than 0, the problem (22) is restated as:

W_c,1≥0, (23e)

is provided with

Is the optimal solution to the problem (23) if

Then

Is the optimal solution of the problem (15), the optimal beamformer w is obtained by singular value decomposition_c,1I.e. by

Otherwise, if

Using a Gaussian randomization procedure (ref 24)]Z.luo, w.ma, a.m.so, y.ye, and s.zhang, "semimidefinite repetition of quadrature optimization schemes," IEEE Signal process. mag., vol.27, No.3, pp.20-34,2010 ") to obtain a rank 1 solution to the problem (22);

by using

Beam shaper for representing problem (23), use of

To represent

The problem (21) is expressed as:

s.t.||w_b||²+P_c≤P_total (24b)

(21b),(21c),

the method is equivalent to the following steps:

(21b),(21c),(24b)

and (3) optimizing and solving by using a standard convex optimization solver (such as CVX) (reference [25] M.Grant and S.Boyd, "CVX: Matlab software for divided consistent programming, version 2.1," http:// cvxr.com/CVX, Mar.2014.), and finally obtaining the ZF beam shaper of the problem (21).

Has the advantages that: while Willie's CSI (channel state information) is ideal for Alice, the present invention not only proposes a blind beamforming design, but to reduce computational complexity, the present invention proposes a low complexity zero-forcing (ZF) beamformer design with a single iterative process that provides a promising compromise between complexity and performance. Such results can be used as a theoretical basis for evaluating the concealment performance of the beamformer. The simulation results of the present invention further reveal a tradeoff between Willie's reconnaissance performance and Bob's concealment rate.

Drawings

The foregoing and/or other advantages of the invention will become further apparent from the following detailed description of the invention when taken in conjunction with the accompanying drawings.

Fig. 1 is a schematic diagram of a secret communication scenario.

FIG. 2 is the instantaneous rate R of Bob under the hidden beamformer design and ZF (zero forcing) beamformer design proposed by the present invention_b(bits/sec/hz) maximum transmit power P with Alice_total(dBW) variation graph.

FIG. 3 is the instantaneous rate R of the proposed buried beamformer design of the present invention and the proposed ZF beamformer design at Bob_bAccording to different ratios

Graph of the variation.

FIG. 4 is the instantaneous rate R of Bob_bAnd the number of antennas N is shown in the relationship diagram under the design of the hidden beam former and the design of the ZF beam former.

FIG. 5 is a graphical illustration of a cumulative density function.

FIG. 6 is a graph of the epsilon value versus the instantaneous rate R of Bob_bAnd a relationship diagram of the detection error probability.

FIG. 7 Bob instantaneous Rate R_bAnd detecting error v of error probability and CSI (channel state information)_wSchematic diagram of the relationship of (1).

FIG. 8 is the instantaneous rate R of Bob_bThe relationship with the number of antennas N is shown schematically.

Detailed Description

In the invention, the following representation method is adopted: the lower case and upper case letters in bold represent vectors and matrices, respectively. Re (-) and Im (-) denote the real and imaginary parts of their argument, respectively. With mean μ and variance σ²By using a complex-valued circularly symmetric Gaussian distribution

To indicate.

The scenario considered by the present invention is shown in fig. 1, where Alice (base station) always sends a data stream x to Carol (regular user)_cAnd is incorporated in

Case private data stream x_bIs sent to Bob, where

Denotes a null hypothesis, i.e., Alice does not send a private data stream to Bob, but

Representing another assumption that Alice sends a private data stream to Bob. Meanwhile, Willie is observing the communication environment as an eavesdropper and tries to identify whether Alice is transmitting to Bob; alice can use the transmission to Carol as a cover to enable covert communications. Alice is assumed to be equipped with N antennas, while Carol, Bob and Willie all have only one antenna. For the sake of simplicity, order

In particular, the amount of the solvent to be used,

representing a signal x_cThe power of (a) is determined,

representing a signal x_bOf the power of (c). . Recall thatIn one aspect, Willie's goal is to determine which hypothesis(s) to use by using a particular decision rule: (a)

Or

) Is correct. For convenience, use is made of

An event that indicates that Alice does (does not) send information to Bob.

One, signal model and implicit constraint:

from Willie's perspective, Alice's transmission signal is as follows:

for Carol, the received signal is:

for Bob, the received signal is:

the signal received by Willie can be written as:

according to (3), the instantaneous rates for Carol are set to be expressed as

And

r of_c,0(w_c,0) And R_c,1(w_c,1,w_b) Written as:

based on (4), set R_b(w_c,1,w_b) Is assumed to be

The instantaneous rate of Bob, below, is given by:

since Willie needs to be based on the signal y it receives_wTo distinguish these two hypotheses, further describe y_wThe probability of (c).

Let p be₀(y_w) And p₁(y_w) Are respectively shown in

And

the likelihood function of Willie's received signal. Based on (5), p₀(y_w) And p₁(y_w) Respectively as follows:

willie wants to minimize the detection error probability ξ by applying the best detector.

To incorporate ξ into the problem formulation, the conditions of the likelihood function are next specified so that implicit communication can be achieved using a given ε. First, setting:

ξ＝1-V_T(p₀,p₁), (9)

the method adopts a Pincker inequality to obtain:

D(p₀||p₁) And D (p)₁||p₀) Respectively as follows:

the KL (Kullback-Leibler) divergence (relative entropy) of the likelihood function should satisfy one of the following constraints:

D(p₀||p₁)≤2ε², (12a)

D(p₁||p₀)≤2ε². (12b)

second, CSI availability

It is assumed that Alice can accurately estimate the CSI of Bob and Carol. In most cases, such CSI may be learned at the receiving end and the transmitting end through training and feedback. However, WCSI may not always be accessible to Alice due to the potentially limited cooperation between Alice and Willie. Therefore, the following two cases are considered:

(1) scenario 1. ideal WCSI: consider a situation that is often found in practiceNow, in the scenario where Willie is a legitimate user, wants to get Bob's personal information, in this case Alice knows channel h_wAnd uses it to help Bob avoid Willie's listening.

(2) Scenario 2. non-ideal WCSI: in this case, Alice is unaware of the channel to Willie, i.e., Alice is on Alice-to-Willie channel h_wAn estimation is made and there is an error in the estimation. The undesirable WCSI is modeled as:

wherein h is_wIs the channel gain from Alice to Willie,

represents the estimated CSI vector between Alice and Willie, and Δ h_wRepresenting the corresponding CSI error vector. In addition, the CSI error vector Δ h_wIs characterized by an elliptical area, namely:

wherein is defined as_wIs the error vector Δ h_wThe set of ranges of (a) is,

controlling the axis of the ellipsoid, v_w>0 determines the volume of the ellipsoid.

Three, ideal WCSI proposal of concealed transmission

Consider the ideal WCSI (Willie channel state information) scheme (scenario 1) and maximize Bob's concealment rate by optimizing Alice's beamformer. In particular, maximizing Bob's achievable rate R was investigated_bIn order to solve the problem of the target joint beam forming design, the constraint conditions of completely concealed transmission are satisfied, the constraint of Carol QoS and Alice total transmission power is satisfied, and the mathematical expression is as follows:

s.t.R_c,1(w_c,1,w_b)＝R_c,0(w_c,0), (15b)

D(p₀||p₁)＝0, (15c)

||w_b||²+||w_c,1||²≤P_total (15d)

constraint D (p)₀||p₁)＝0

And D (p)₁||p₀) 0 is equivalent for a perfect blind transmission case. To solve the non-convex problem (15), two beamformer design methods are proposed, namely the blind beamformer design and the ZF (zero forcing) beamformer design.

3.1 design of hidden beamformer

To simplify the derivation, auxiliary variables are defined

And

and introducing an auxiliary variable r_bQuestion (15) is restated in the equivalent form:

||w_b||²+||w_c,1||²≤P_total (16e)

applying SDR (semi-positive relaxation) technique to relax the problem (16), the following conditions were used:

ignoring the constraint of rank 1, a relaxed form of the problem (16) is obtained:

Tr(W_c,1)+Tr(W_b)≤P_total, (18e)

W_c,1≥0,W_b≥0 (18f)

note that for any determined r_b≧ 0, the problem (18) is a convex-half positive definite program (SDP). Thus, the problem (18) is pseudo-convex, at any given r_bNext, by checking its feasibility, its optimal solution can be found.

Then, the maximization problem (18b) can be proved againstr_bIs concave. More specifically, let:

the following results were obtained.

Introduction 1: function(s)

s.t.φ(W_b)≥r_bθ(W_c,1) (20)

r_bWhen the shape is more than or equal to 0, the shape is concave.

And (3) proving that: will function g (r)_b) Rewrite to the following compact form:

s.t.a(W)≥xb(W), (41b)

wherein W ═ W_b,W_c,1],a(W):＝φ(W_b),b(W):＝θ(W_c,1),x≥0。

Next, the concavity of the function f (x) at x ≧ 0 will be examined by the following definition. First, for 0 ≦ θ ≦ 1 and x₁,x₂Not less than 0, including:

s.t.a(W)≥(θx₁+(1-θ)x₂)b(W), (42c)

then, there is θ f (x)₁) And (1-theta) f (x)₂) As follows:

s.t.a(W)≥x₁b(W), (44b)

s.t.a(W)≥x₂b(W) (44b)

is provided with

Comprises the following steps:

s.t.0≤x₁≤c(W), (45b)

0≤x₂≤c(W) (45c)

wherein x is₁,x₂≥0。

When 0. ltoreq. theta.ltoreq.1, x shown in (42c)₁And x₂Is larger than the feasible region in (45). Comprises the following steps:

θf(x₁)+(1-θ)f(x₂)≤f(θx₁+(1-θ)x₂), (47)

indicates that f (x) is concave in x, in other words, the function (18) is at r_bIs concave in the middle.

Therefore, first, the problem (18) is converted into a series of r_bThe convex sub-problem of more than or equal to 0 can be optimized and solved by a standard convex optimization solver (such as CVX). Next, a binary search method is used to find the proposed hidden beamformer W_bAnd W_c,1. The detailed information of the binary search method is summarized as algorithm 1 in Table 1, which outputs the optimal solution

And

finally, the beamformer W is reconstructed from the solution given by Algorithm 1_c,1And W_b. The design method of the beam former based on SDR (semi-positive definite relaxation) needs to solve a series of problemsColumn feasibility sub-problem. The computational complexity of this approach is high, which requires further development of an alternative approach with lower computational complexity.

3.2 design of proposed zero forcing beamformer

In this section, a ZF (zero forcing) beamformer design with iterative processing is proposed that enables an ideal trade-off between complexity and performance. In particular by designing w_bSo that

And

to eliminate

And

the interference signal of (2). At the same time, by design w_c,1So that

To eliminate interference signals

Mathematically, applying the ZF beamformer design principle, the problem (16) is recalculated as:

||w_b||²+||w_c,1||²≤P_total. (21g)

to solve the design problem (21) of the joint ZF beamformer, first under the constraints of (21d), (21e) and (21f), by minimizing the transmission power | | | w_c,1||²To optimize the beam former w_c,1. This is because the objective function (21a) does not depend on w_c,1But increases with the power of the beamformer. The total transmission power constraint (21g) comprises w_bAnd w_c,1. Therefore, in order to maximize the objective function (21a), it is necessary to design the beamformer w with the minimum transmit power_c,1. Thus, the ZF beamformer w_c,1The design problem is expressed as:

s.t.(21d),(21e),(21f),

this is also non-convex. To solve the non-convex problem, the problem (22) is relaxed to convex form by applying SDR (semi-positive relaxation), specifically by relaxing

To W_c,1Not less than 0, the problem (22) is restated as:

W_c,1≥0, (23e)

this is a convex SDP (semi positive plan). Is provided with

Is the optimal solution to the problem (23). Due to the fact that the material is loose,

may not equal 1. Therefore, if

Then

Is the optimal solution of the problem (15), the optimal beamformer w is obtained by singular value decomposition_c,1I.e. by

Otherwise, if

A gaussian randomization process is employed to obtain a high quality rank 1 solution to the problem (22).

Next, consider w_bThe design of (3). Let

A beamformer representing the problem (23). Let

To represent

The transmission power of (1). The problem (21) is expressed as:

s.t.||w_b||²+P_c≤P_total (24b)

(21b),(21c),

the method is equivalent to the following steps:

(21b),(21c),(24b)

the solution problem (25) is optimized with a standard convex optimization solver (e.g., CVX). Thus, the ZF transmit beamformer of problem (21) is finally obtained.

Robust concealment transmission scheme for non-ideal WCSI

In practice, the CSI obtained usually is corrupted by some estimation errors (ref 5)]，[6]). It is therefore further proposed to propose a robust beamforming design for the optimization problem (15) in non-ideal WCSI scenarios. In this case, it is difficult to achieve perfect secret transmission, i.e., D (p)₀||p₁) 0. Therefore, the use of the covert constraint D (p) according to (12)₀||p₁)≤2ε²And D (p)₁||p₀)≤2ε²(reference [ 4]]-[6]，[21]). In addition, based on the developed robust beamformer, Willie's best case is further investigated, in which case Willie can reach the desired detection error probability.

4.1D(p₀||p₁)≤2ε²In the case of

In the case of imperfect WCSI, the goal is to design w jointly under the QoS, privacy and total power constraints of Carol_c,1And w_bTo realize R_b(w_c,1,w_b) And (4) maximizing. Mathematically, the robust rate maximization problem is expressed as the following problem (26):

s.t.R_c,1(w_c,1,w_b)＝R_c,0(w_c,0), (26b)

D(p₀||p₁)≤2ε², (26c)

||w_b||²+||w_c,1||²≤P_total, (26d)

the problem (26) is not convex and it is therefore difficult to directly obtain an optimal solution. To solve this problem, first, a function is used

At x>The property at 0 reconstructs the covert constraint (26 d). More specifically, the covert constraint

Equivalently converting into:

in the formula

And

is the equation

Two roots of (2). Thus, the constraint (26c) is equivalently re-expressed as:

here, because

Δ h in constraint (26e)_wThere are infinite options that make the problem (26) non-convex and tricky. To overcome this challenge, a method of relaxation and constraint is proposed. Specifically, in the relaxation step, the non-convex robust design problem is converted into a convex SDP (semi-positive definite programming) problem; in the constraint step, an infinite number of complex constraints are converted into a finite number of Linear Matrix Inequalities (LMIs).

For mathematical convenience, define

And auxiliary variables

And

equivalently re-expressed by defining a reduce constraint (28) as:

in applying SDR to W_c,1And W_bThen, the problem (26) relaxes as follows:

Tr(W_c,1)+Tr(W_b)≤P_total, (30d)

W_c,1≥0,W_b≥0, (30e)

(29a),(29b)

in the formula

Is the relaxation variable. The SDR (semi-definite relaxation) problem (30) is pseudo-convex because the objective function and constraints are at W_c,1And W_bIs linear. Due to the fact that

The problem (30) involves an infinite number of constraints and is therefore still computationally difficult. Next, an infinite number of constraints are reconstructed into a set of LMIs using an S-process, which is a processable approximation. The S-lemma is used to reconstruct an infinite number of constraints into a set of LMIs (Linear matrix inequalities), which is a processable approximation. Therein introduction (S-introduction reference [26 ]]D.W.K.Ng,E.S.Lo,and R.Schober,“Robust beamforming for secure communication in systems with wireless information and power transfer, "IEEE Trans. Wireless Commun., vol.13, No.8, pp.4599-4615,2014"), and set function f_m(x),m∈{1,2},

Is defined as:

wherein

Is a complex Hermitian matrix of which,

relation of implication and cul

If and only if there is a variable η ≧ 0, such that:

wherein

Represents an N x 1-dimensional complex vector,

representing a real number.

Thus, by using the S-theorem, constraints (29a) and (29b) are recast into a limited number of LMIs, respectively:

thus, a conservative approximation of the problem (30) is obtained as follows:

s.t.(30b),(30c),(30d),(30e),(33a),(33b)

when in use

Fixed, the problem (34) is a convex SDP (semi-positive definite programming) that is effectively solved by an off-the-shelf convex solver (ref [25]]M.Grant and S.Boyd, "CVX: Matlab software for differentiated summary programming, version 2.1," http:// cvxr.com/CVX, Mar.2014 "). The proposed dichotomy can therefore effectively solve the problem (34), which is summarized in algorithm 2. The algorithm 2 comprises the following steps:

step b1, selecting ζ>0 (end parameter), lower speed limit

And upper speed limit

To optimize Bob's speed

Is located at

Performing the following steps;

step b2, initialization

Step b3, when

Executing the step b4 to the step b 5;

step b4, setting

Step b5, if the problem (34) is feasible, get the solution W_bAnd W_c,1And is provided with

Otherwise, set up

Step b6, when

Ending the circulation;

step b7, outputting the optimal solution

Also, if

And is

An optimal solution to the problem (15) is given and the optimal beamformer w is obtained by singular value decomposition_c,1And w_bI.e. by

And

however, if

Or

A Gaussian randomization procedure (seeExamination paper [24]Z.luo, w.ma, a.m.so, y.ye, and s.zhang, "semimidefinite repetition of quadrature optimization schemes," IEEE Signal process.mag., vol.27, No.3, pp.20-34, 2010 ") to obtain a high quality rank 1 solution to problem (15).

4.2D(p₁||p₀)≤2ε²In the case of

In this subsection, constraint D (p) is considered₁||p₀)≤2ε²The corresponding robust concealment rate maximization problem is expressed as:

s.t.R_c,1(w_c,1,w_b)＝R_c,0(w_c,0), (35b)

D(p₁||p₀)≤2ε², (35c)

||w_b||²+||w_c,1||²≤P_total, (35d)

here, the

Except for the covert constraint, it can be seen that problem (35) is similar to problem (26). Hidden constraint condition

Equivalently, to:

is an equation

Two roots of (2).

The relaxation and restraint methods are applied to solve the problem (35). For the sake of brevity, detailed derivations are omitted. It is noted that although these methods are similar, the achievable concealment rates are different under the two concealment constraints.

4.3 Ideal detection Properties of Willie

To evaluate the design of the above robust beamformer, Willie's optimal decision threshold, and the corresponding false alarm probability and missed detection probability, were further investigated. Consider the ideal case of Willie, the beamformer w known to Willie_b、 w_c,0And w_c,1This is the worst case for Bob.

According to the Neyman-Pearson criterion (reference [2]), the best criterion to minimize Willie's detection error is the likelihood ratio test (reference [2]), i.e.:

wherein

And

respectively corresponding to the hypothesis

And

is determined in two-way. Further (37) is equivalently re-expressed as:

in the formula (I), the compound is shown in the specification,

representing the optimal detection threshold of Willie. Here, [ lambda ] is given in (8)₀And λ₁Dependent on the beamformer vector w_b、w_c,0、w_c,1。

According to (8), in

And

y of_w|²Cumulative Density Function (CDFs)

And

respectively as follows:

therefore, based on the optimal detection threshold φ^*False alarm

And probability of missed detection

As follows:

thus, the desired detection performance of Willie can be measured in terms of φ^*，

And

to characterize. These results can be used as a theoretical basis for evaluating the concealment performance of a robust beamformer design. The detection properties of Willie will be discussed further in the next section.

Five, numerical results

In this section, numerical results are presented and discussed to evaluate the performance of the proposed blind beamformer design, ZF (zero forcing) beamformer design, and robust beamformer design methods for blind communications.

In the simulation, the number of antennas at Alice is set to 5, i.e., N is 5, and the noise variance of three users is normalized to 1, i.e., N is 1

Alice to P_totalTotal transmit power of 10dBW and | | w_c,0||²1 dBW. Furthermore, it is assumed that all channels experience rayleigh flat fading, i.e.

5.1 evaluation of scene 1

The method proposed in scenario 1, i.e. Alice using the perfect WCSI (Willie's channel state information), is evaluated first.

FIG. 2 is the concealment rate R of Bob under the proposed concealment beamformer design and ZF beamformer design_b(bits/sec/hz) total transmit power P with Alice_total(dBW) variation graph. Drawing (A)2 depicts the concealment rate R of Bob under the proposed concealment beamformer design and the proposed ZF beamformer design_bRelative to the total transmission power P_totalThe value of the change. It can be seen that with the transmission power P of Alice_totalIncrease of (b), the concealment rate R of Bob_bIs also increasing, and the R of the proposed buried beamforming design is increasing_bR than ZF beamformer design_bIs high. In addition, by comparing Carol | | | w_c,0||²In that

Transmitting power of two different wave beam formers_c,0||²Observed transmit power | | w_c,0||²The lower Bob's concealment rate R_bThe higher. This is because when the transmission power | | | w_c,0||²At lower times, Bob may be allocated more power.

Fig. 3 shows the proposed buried beamformer design and ZF beamformer design versus different ratios

Concealment rate R for lower Bob_bIn which P is_total10W. In this figure, the equivalent ratio is observed

Fixed, ZF beamformer designed R_bR lower than the hidden beamformer design_bThis is consistent with fig. 2. In addition, with

Increase in the ratio, Bob's concealment rate R_bAnd decreases. At the same time, the rate gap between the blind beamformer design and the ZF beamformer design is also reduced.

In fig. 4, the concealment rate R of Bob for the proposed concealment beamformer design and ZF beamformer design is plotted_bA graph of the number of antennas N of Alice, where P_total10W. Observe thatBob's concealment rate R as the number of antennas N increases_bAt the increase, the rate gap from ZF beamformer design also increases. This is because with more antennas, more spatial multiplexing gain can be utilized.

From fig. 2, 3, 4 it is observed that the concealment rate of the proposed concealment beamformer design is always higher than the proposed ZF beamformer design. However, the computational complexity of ZF beamformer designs is significantly lower than that of blind beamformer designs. Specifically, table one shows a comparison of the computation times for the blind beamformer design and the ZF beamformer design, all simulations of both methods were performed using MATLAB2016b, 2.30GHz, 2.29GHz dual CPUs, and 128GB RAM. Table one shows that the computation time for the blind beamformer and ZF beamformer designs increases with the number of antennas N. More importantly, the computation time of the ZF beamformer is less than 1/10 for the blind beamformer design time.

TABLE 1

5.2 evaluation of scene 2

A robust beamformer design under scenario 2, i.e., Alice in the case of imperfect WCSI, is evaluated below.

In FIG. 5, the masking threshold 2 ε²0.02, CSI error v_w0.005. FIG. 5 shows D (p)₀||p₁) The Cumulative Density Function (CDF) of (1), wherein the relative entropy requirement is D (p)₀||p₁)≤0.02，||w_c,0||²＝8dBW，v_w0.005. From these results, it is observed that CDF in KL divergence of the non-robust design cannot guarantee requirements, and the robust beamforming design satisfies KL divergence constraint, i.e., satisfies Willie's error detection probability requirement, thereby achieving the objective.

The left and right panels in FIG. 5 show the obtained D (p), respectively₀||p₁) And D (p)₁||p₀) Empirical CDF of, for robust and non-robust settingsMeter, in which the threshold value of concealment is 2 epsilon²0.02, i.e. D (p)₀||p₁) Less than or equal to 0.02 and D (p)₁||p₀) Less than or equal to 0.02, and the CSI error parameter is v_w0.005. Here, the non-robust design refers to a concealed design with perfect WCSI proposed under the same conditions. As can be seen from the left and right diagrams in FIG. 5, the proposed robust design satisfies the concealment constraint, namely D (p)₀||p₁) Less than or equal to 0.02 and D (p)₁||p₀) Less than or equal to 0.02. On the other hand, non-robust designs cannot satisfy the concealment constraint, where the result D (p)₀||p₁) 45% of the total amount of the particles exceeds a concealment threshold 2 epsilon²0.02 and result D (p)₁||p₀) Approximately 50% exceeds the concealment threshold. The left and right diagrams in fig. 5 verify the necessity and effectiveness of the proposed robust design.

The left diagram of fig. 6 depicts the CSI error v_wConcealment rate R in case of two KL divergences of 0.005_bA relation graph with epsilon value, wherein

Shown in case D (p)₀||p₁) False alarm probability of down

Shown in case D (p)₁||p₀) False alarm probability of down

Other symbol definitions are similar. The simulation result is consistent with the theoretical analysis, when epsilon becomes larger, the hidden constraint condition is relaxed, and R is caused_bBecomes larger. CSI error v in FIG. 6_w0.005. In fig. 7, ∈ is 0.1. The right graph of fig. 6 plots the false alarm probability

And probability of missed detection

Relation to the value of ε, where the error of CSI v_w0.005. Observe the false alarm probability under any one of the covert constraints

And probability of missed detection

Both decrease with increasing epsilon, wherein

Is always less than

This means that Willie's detection performance will be better when the transition constraints are looser.

Furthermore, the right diagram of fig. 6 also verifies the effectiveness of the proposed robust beamformer design in covert communications, i.e.

Thus, from fig. 6, a compromise between Willie's detection performance and Bob's concealment rate is revealed, and the desired compromise can be achieved by an appropriate robust beamformer design.

CSI error v in FIG. 8_w＝0.005。

The left diagram of FIG. 7 depicts two covert constraints D (p)₀||p₁)≤2ε²And D (p)₁||p₀)≤2ε²Hidden Rate R of_bAnd the CSI error v_wThe relationship (2) of (c). It is observed that with v_wIncrease of (2), concealment rate R of two concealment constraints_bDecreasing, the rate gap increases. In the right diagram of FIG. 7, two covert constraints D (p)₀||p₁)≤2ε²And D (p)₁||p₀)≤2ε²In case of false alarm probability

And probability of missed detection

And CSI error v_wThe relationship (2) of (c). The false alarm probability under two concealed constraint conditions is observed

And probability of missed detection

Are all following v_wIs increased by an increase in which

Is always less than

In addition, FIG. 7 shows at the concealment rate R_bOn the other hand, the error v is increased_wWhich may result in a poor beamformer design. However, such a beamformer may confuse Willie detection, which is also beneficial to Bob. Therefore, this trade-off should also be noted in the design of the beamformer.

Finally, FIG. 8 shows the two concealment constraints D (p)₀||p₁)≤2ε²And D (p)₁||p₀)≤2ε²Hidden Rate R of_bRelation with the number of antennas N, wherein w_c,0||²1dBW,. epsilon. 0.1 and v_w0.005. It can be seen from fig. 8 that the higher the number N of antennas, the higher the concealment rate R is achieved_bThe higher this is, similar to the situation in fig. 4. From FIGS. 6 to 8, it is observed that the hidden constraint condition D (p)₀||p₁)≤2ε²Is higher than with the blind constraint D (p)₁||p₀)≤2ε²The rate of (c). This is because D (p)₀||p₁)≤2ε²Ratio D (p)₁||p₀)≤2ε²More strictly, this conclusion is (ref [21 ]]) Was also verified.

The present invention derives Willie's optimal detection threshold and corresponding detection error probability based on reliable beamformer vectors. Such results can be used as a theoretical basis for evaluating the concealment performance of the beamformer. The simulation results of the present invention further reveal a tradeoff between Willie's detection performance and Bob's privacy ratio.

Claims (8)

1. A hidden beam forming design method aiming at ideal WCSI hidden communication is characterized by comprising the following steps:

step 1, establishing a covert communication environment;

and 2, under the condition of ideal WCSI, carrying out hidden beam forming design.

2. The method of claim 1, wherein step 1 comprises: alice denotes a base station, Carol denotes a regular user, Willie denotes an eavesdropper, Bob denotes a hidden user, and Alice always sends a data stream x to Carol_cAnd is incorporated in

Case private data stream x_bIs sent to Bob, where

Denotes a null hypothesis, i.e. Alice does not send a private data stream to Bob, but

Represents another assumption that Alice sends a private data stream to Bob; meanwhile, Willie is observing the communication environment as an eavesdropper and tries to identify whether Alice is transmitting to Bob; alice can use the transmission to Carol as a cover to enable secret communication.

3. The method of claim 2, wherein in step 1, Alice is configured with N antennas, and Carol, Bob and Willie have only one antenna; order to

Representing a signal x_cThe power of (a) is determined,

representing a signal x_bThe power of (d); use of

Events indicating that Alice really sent information to Bob, uses

An event indicating that Alice does not send information to Bob.

4. The method of claim 3, wherein in step 1, from Willie's perspective, Alice's transmission signal x is as follows:

wherein w_c,0And w_c,1Respectively represent x_cUnder the assumption that

And assume that

Of a transmit beamformer vector, w_bDenotes x_bBy P, the transmit beamformer vector of_totalRepresenting the maximum transmit power of Alice, the beamformer vector satisfies: in that

In case, | w_c,0||²≤P_totalAnd in

In case, | w_c,1||²+||w_b||²≤P_total；

For Carol, it receives a signal y_cComprises the following steps:

wherein

Is the channel coefficient from Alice to Carol,

is the noise received by Carol, where

Represents an N-dimensional complex vector, and represents a complex vector,

signal noise z representing Carol_cObeying a mean of 0 and a variance of

Complex gaussian distribution of (a);

for Bob, it receives the signal y_bComprises the following steps:

wherein

Is the channel gain from Alice to Bob,

is the noise received by Carol and is,

signal noise z representing Bob_bObeying a mean of 0 and a variance of

Complex gaussian distribution.

5. The method of claim 4, wherein in step 1, Willie receives signal y_wWriting into:

wherein

Are the channel coefficients from Alice to Willie,

is the noise received by Willie and is,

signal noise z representing Willie_wObeying a mean of 0 and a variance of

Complex gaussian distribution.

6. The method according to claim 5, wherein in step 1, Carol is set according to (3) in

And

at an instantaneous rate of R_c,0(w_c,0) And R_c,1(w_c,1,w_b) Written as:

wherein

Signal noise z representing Carol_cThe noise variance of (2);

based on (4), Bob is set at

At an instantaneous rate of R_b(w_c,1,w_b) Given by:

let p be₀(y_w) And p₁(y_w) Are respectively shown in

And

lower Willie received signal likelihood function, based on (5), p₀(y_w) And p₁(y_w) Respectively as follows:

wherein

Wherein

Signal noise z representing Carol_wOf the noise variance, λ₀And λ₁Representing the auxiliary variable.

7. The method of claim 6, wherein in step 1, Willie wishes to minimize the probability of detection error ξ by applying an optimal detector, setting:

ξ＝1-V_T(p₀,p₁), (9)

wherein V_T(p₀,p₁) Is p₀(y_w) And p₁(y_w) The total change between them is obtained by using the Pincker inequality:

wherein D (p)₀||p₁) Represents from p₀(y_w) To p₁(y_w) KL of (a) D (p)₁||p₀) Is from p₁(y_w) To p₀(y_w) KL divergence of (1);

D(p₀||p₁) And D (p)₁||p₀) Respectively as follows:

to achieve covert communication with a given ξ, i.e., ξ ≧ 1- ε, the KL divergence of the likelihood function should satisfy one of the following constraints:

8. the method of claim 7, wherein step 2 comprises: the ideal WCSI case refers to: willie is a legitimate user and wants to get Bob's personal information, in which case Alice knows channel h_wAnd uses it to help Bob avoid Willie's interception;

problem (15) is established:

s.t.R_c,1(w_c,1,w_b)＝R_c,0(w_c,0), (15b)

D(p₀||p₁)＝0, (15c)

||w_b||²+||w_c,1||²≤P_total (15d)

to solve the problem (15), two beam former design methods are proposed, namely a hidden beam former design and a ZF zero forcing beam former design, which are respectively as follows:

the hidden beamformer design is as follows:

defining auxiliary variables

And

and introducing an auxiliary variable r_bQuestion (15) is restated as the equivalent of question (16):

||w_b||²+||w_c,1||²≤P_total (16e)

applying SDR semi-positive relaxation technique to relax the problem (16), the following conditions were used:

ignoring the constraint of rank 1, a relaxed form of the problem (16), namely the problem (18), is obtained:

Tr(W_c,1)+Tr(W_b)≤P_total, (18e)

W_c,1≥0,W_b≥0 (18f)

order:

the following results were obtained:

function(s)

s.t.φ(W_b)≥r_bθ(W_c,1) (20)

r_bIs concave when being more than or equal to 0;

an algorithm 1 is established, wherein the algorithm 1 comprises the following steps:

step a1, selecting ζ>0 (end parameter), lower speed limit

And upper speed limit

Make Bob's optimal speed

Is located at

Performing the following steps;

step a2, initialization

Step a3, when

If yes, executing the step a4 to the step a 5;

step a4, setting

Step a5, if the problem (18) is feasible, get the solution W_bAnd W_c,1And is provided with

Otherwise, set up

Step a6, when

Ending the circulation;

step a7, outputting

Outputting optimal solution by Algorithm 1

And

reconstruction of the beamformer W from the solution given by Algorithm 1_c,1And W_bIf, if

And is

Then

Also given is an optimal solution to the problem (15), the Singular Value Decomposition (SVD) is used to obtain the optimal beamformer W_c,1And W_bI.e. by

And

if it is not

Or

A gaussian randomization procedure is employed to obtain a rank 1 solution for problem (15);

the ZF zero-forcing beamformer is designed as follows: the problem (16) is recalculated to the following problem (21):

||w_b||²+||w_c,1||²≤P_total (21g)

to solve the problem (21), under the constraints of (21d), (21e) and (21f), by minimizing the transmission power | | w_c,1||²To optimize the beam former w_c,1(ii) a The total transmission power constraint (21g) comprises w_bAnd w_c,1In order to maximize the objective function (21a), it is necessary to design the beamformer w with the minimum transmit power_c,1(ii) a ZF beamformer w_c,1The design problem is expressed as:

s.t.(21d),(21e),(21f),

by relaxing

To W_c,1Not less than 0, the problem (22) is restated as:

W_c,1≥0, (23e)

is provided with

Is the optimal solution to the problem (23) if

Then

Is the optimal solution of the problem (15), the optimal beamformer w is obtained by singular value decomposition_c,1I.e. by

Otherwise, if

Obtaining a rank 1 solution to the problem (22) using a gaussian randomization process;

by using

Beam shaper for representing problem (23), use of

To represent

The problem (21) is expressed as:

s.t.||w_b||²+P_c≤P_total (24b)

(21b),(21c),

the method is equivalent to the following steps:

(21b),(21c),(24b)

and (5) optimizing and solving by using a standard convex optimization solver to finally obtain the ZF beam former of the problem (21).

Images