CN105812043A - Pre-coding method based on channel covariance feedback - Google Patents

Abstract

The embodiment of the invention discloses a pre-coding method based on channel covariance feedback. The method comprises a transmitter, an information receiver and an energy receiver. The transmitter sends data. The information receiver and the energy receiver receive data at the same time. The design criteria provided by the invention is that pre-coding is designed to enabling the system information transmission rate to be maximized under the condition of satisfying energy demands according to the energy demands and signal statistic information of a system. The transmitter firstly obtains the channel covariance and the Signal to Noise Ratio information from a transmitting end to the two receivers through measurement; a dual function is constructed by importing two auxiliary parameters; a pre-coding solving problem is converted into an equivalent dual problem; and the optimum pre-coding is solved by using a high-dimensional steepest descent cyclic iterative method specific to the dual problem. Compared with an isotropic transmission scheme, the method has the advantages that the system transmission rate is higher when the system energy demands are given and the information-energy reachable domain is wider than the former.

Description

A kind of method for precoding based on channel covariancc feedback

Technical field

The present invention relates to wireless communication technology field, particularly relate to the method for precoding of a kind of wireless messages and energy joint transmission system.

Background technology

Energy collection technology can provide energy, the life cycle of extension device node for radio sensing network or cellular mobile network, thus receives extensive concern in recent years.On the other hand, information transmission problem is always up key and the study hotspot of communication system.Therefore, two kinds of technology combine, and create the new technique of wireless messages and energy joint transmission.

" 2011 year International Electrical with Electronic Engineering Association's theory of information seminar " (" ShannonmeetsTesla:wirelessinformationandpowertransfer; " IEEEInternationalSymposiumonInformationTheory (ISIT), Austin, Texas, U.S.A, 2011,2363-2367) have studied how in the problem of communication system joint transmission information Yu energy.Based on transmitting terminal can obtain ideal communication channel information it is assumed that this article devises the circuit system of reality, it is provided that the concrete derivation of system achievable rate energy domain." International Electrical with Electronic Engineering Association's radio communication journal " (" Simultaneouswirelessinfromationandpowertransferunderdiff erentCSIacquisitionschemes; " IEEETransactionsonWirelessCommunications, 2015,14 (4): 1911-1926) have studied the information of the multi-aerial radio communication system of three nodes and energy joint transmission problem, this system includes a sending node and two receiving nodes, respectively in order to obtain information and energy.This article have studied transmitting terminal for channel information (channelstateinformation, CSI) the three kinds of situations obtained: known portions CSI when known portions CSI, FDMA multiplexing when the unknown, TDMA multiplexing, energy and message interrupts probability to these case studies respectively, gives the energy transmission period of optimum and the ratio of channel estimating/feedback period.

Current existing research needs instant channel condition information mostly, no matter is desirable or imperfect information.If channel is rapid fading change, then frequently measures and feedback channel information inevitably will bring very big burden to system backhaul link.

Summary of the invention

Embodiment of the present invention technical problem to be solved is in that, it is provided that a kind of method for precoding based on channel covariancc feedback.Channel statistical information channel transceiver covariance matrix and signal to noise ratio can be used, it is possible to significant reduction systematic survey and feedback overhead.

In order to solve above-mentioned technical problem, embodiments provide a kind of method for precoding based on channel covariancc feedback, comprise the following steps:

S1: the signal to noise ratio obtaining the transmitting terminal information channel to intelligence receiver and the covariance information of energy channels of energy receiver, information channel respectively is measured in base station within the setting time；

S2: initialize iteration index, two auxiliary parameters, step-size in search, calculates pre-coding matrix and dual function numerical value as initial value according to subalgorithm；

S3: update said two auxiliary parameter；

S4: according to said two auxiliary parameter, adopts described subalgorithm to calculate new pre-coding matrix and dual function numerical value；

S5: according to determining that criterion decides whether to terminate, when being unsatisfactory for described decision criterion, increases described iteration index, and repeats step S3 until terminating, and output precoding matrix.

Wherein, the initialization of described step S2 includes arranging iteration index k=0；Auxiliary parameter λ >=0 and μ >=0；Step-size in search t meets 0 < t < 1.

Wherein, described subalgorithm includes step:

S201: loop initialization index i=0；Step-size in search 0 < s < 1, randomly chooses a complex matrix as initial pre-coding matrix, is designated as W⁽⁰⁾；

S202: calculate the direction of search D (W under current iteration according to following formula⁽ⁱ⁾),

$D\left(W^{\left(i\right)}\right)=E\{W^{\left(i\right)}{H}_D^H{H}_D/{\mathrm{\&sigma;}}_D^2{(I_{N_T}+{\left(W^{\left(i\right)}\right)}^H{W}^{\left(i\right)}{H}_D^H{H}_D/{\mathrm{\&sigma;}}_D^2)}^{-1}\}-W^{\left(i\right)}A$

$A={\mathrm{uI}}_{N_T}-\mathrm{\&lambda;}Tr\left({\mathrm{\&theta;}}_{RE}\right){\mathrm{\&theta;}}_{TE}$

Wherein,Be dimension it is N_TUnit matrix, N_TBeing transmission antenna number, Τ r (x) is matrix trace function；E (x) represents random matrix H_DAsk expectation, θ_RE、θ_TETo be transmitting terminal respectively receive to the channel of energy receiver, channel sends covariance matrix；H_DIt is the transmitting terminal channel matrix to intelligence receiver, for multiple N_D×N_TMatrix, be defined as:

$H_D={\mathrm{\&theta;}}_{R,D}^{1/2}{H}_{\mathrm{\&omega;},D}{\mathrm{\&theta;}}_{T,D}^{1/2},$

In above formula, H_{ω, D}Be a dimension it is N_D×N_TMultiple gaussian random matrix, each element statistical iteration, and obey average zero, variance 1 multiple Gauss distribution, N_DIt is the number of antennas of intelligence receiver,It it is the noise power of information channel；

S203: update pre-coding matrix W⁽ⁱ⁺¹⁾:=W⁽ⁱ⁾+sD(W⁽ⁱ⁾),

S204: if | L (W⁽ⁱ⁺¹⁾,λ,u)-L(W⁽ⁱ⁾, λ, u) | < ξ, ξ are pre-determined threshold, and algorithm terminates, and export L (W⁽ⁱ⁺¹⁾, λ, u) and W⁽ⁱ⁺¹⁾；Otherwise increase loop index, return step S202, function L (W, λ, u) for Lagrangian, be defined as:

$\begin{array}{c}L(W,\mathrm{\&lambda;},u)=E\{\log \det \&lsqb;I_{N_D}+H_D{W}^H{\mathrm{WH}}_D^H/{\mathrm{\&sigma;}}_D^2\&rsqb;\}\\ +\mathrm{\&lambda;}\&lsqb;Tr\left(W^H{\mathrm{W\&theta;}}_{TE}\right)Tr\left({\mathrm{\&theta;}}_{RE}\right)-{\mathrm{\&epsiv;}}_{ng}\&rsqb;-u\&lsqb;Tr\left(W^{H}W\right)-P_T\&rsqb;\end{array}$

Wherein P_TFor transmit power.

Wherein, described step S3 renewal said two auxiliary parameter updates according to the following formula:

Wherein t is step-size in search.

Wherein, described step S4 dual function is

Wherein, described decision criterion is by judging the difference of the dual function numerical value of twice iteration acquirement | g (λ^(k+1),u^(k+1))-g(λ^(k),u^(k)) | whether meet and set thresholding.

Implement the embodiment of the present invention, have the advantages that the present invention passes through to feed back based on channel covariancc and system signal noise ratio, a kind of method for precoding is provided for information and energy joint transmission system, the method can while meeting system capacity needs, effective lifting system information transmissions speed, comparing non-precoded method isotropism transmission method, when meeting identical energy requirement, the rate of information throughput that the method obtains is higher；Its information-energy is also broader up to territory.The present invention also has the advantage that feedback quantity is little, overhead is little.

Accompanying drawing explanation

Fig. 1 is the implementing procedure figure of the method for precoding of the present invention；

Fig. 2 is the subalgorithm flow chart that method for precoding of the present invention relates to；

In Fig. 3 method under three node 2 × 2MIMO system situation with isotropism transmission method performance comparison figure.

Detailed description of the invention

For making the object, technical solutions and advantages of the present invention clearly, below in conjunction with accompanying drawing, the present invention is described in further detail.

With reference to the implementing procedure figure shown in Fig. 1.

A kind of method for precoding based on channel covariancc feedback of the embodiment of the present invention, by three nodes: a sending node, an energy acceptance node and an information receiving node, they are equipped with 2 antennas.

Adopting classical correlation of indices model that channel covariance matrices is modeled, (i, element j) is ρ to the type matrix position^|i-j|, wherein constant ρ is the index of correlation；Correlation matrix θ is set_R,E、θ_T,E、θ_R,D、θ_T,DThe index of correlation respectively 0.4,0.8,0.3 and 0.5.Additionally, also define the signal to noise ratio that signal to noise ratio is information channel of system, namelyHere PT is transmitting terminal transmit power,It is information channel noise power, emulation is arrangedBeing 1, system signal noise ratio is set to 5 decibels, therefore PT=3.16；The transformation efficiency η of energy receiver is set to 1.

In general, the operation of transmitting terminal is segmented into two stages: training stage and data transmission phase.In the training stage, transmitting terminal is launched pilot signal, energy and intelligence receiver and is measured respective channel matrix, calculates transmitting-receiving covariance matrix, feeds back to transmitting terminal；It addition, intelligence receiver also wants the signal to noise ratio of feedback information channel.Sending data phase, first transmitting terminal calculates optimum pre-coding matrix W according to the channel information of feedback, then user data is multiplied by pre-coding matrix W and sends.

Concrete operations comprise the steps:

S1: base station obtains information channel and the signal to noise ratio of the covariance information of energy channels, information channel respectively by the measurement of a period of time, and information channel and energy channels refer to the transmitting terminal channel to intelligence receiver and energy receiver respectively here.

S2: initialize iteration index, auxiliary parameter, step-size in search；Pre-coding matrix and dual function numerical value is calculated as initial value according to a subalgorithm.

Wherein concretely comprise the following steps:

Iteration index k=0 is set；Auxiliary parameter λ >=0 and u >=0；Step-size in search t meets 0 < t < 1.

The dual function that this step is mentioned is defined as:

The subalgorithm mentioned in this step, as in figure 2 it is shown, include:

S201: loop initialization index i=0；Step-size in search 0 < s < 1, randomly chooses a complex matrix as initial pre-coding matrix, is designated as W⁽⁰⁾。

S202: calculate the direction of search D (W under current iteration according to following formula⁽ⁱ⁾),

$\begin{array}{c}D\left(W^{\left(i\right)}\right)=E\{W^{\left(i\right)}{H}_D^H{H}_D/{\mathrm{\&sigma;}}_D^2{(I_{N_T}+{\left(W^{\left(i\right)}\right)}^T{W}^{\left(i\right)}{H}_D^H{H}_D/{\mathrm{\&sigma;}}_D^2)}^{-1}\}-W^{\left(i\right)}A\\ =E\left\{W^{\left(i\right)}{H}_D^H{H}_D{(I_2+{\left(W^{\left(i\right)}\right)}^T{W}^{\left(i\right)}{H}_D^H{H}_D)}^{-1}\right\}-W^{\left(i\right)}A\end{array}$

$A={\mathrm{uI}}_{N_T}-\mathrm{\&lambda;}Tr\left({\mathrm{\&theta;}}_{RE}\right){\mathrm{\&theta;}}_{TE}={\mathrm{uI}}_2-2\mathrm{\&lambda;}\left[\begin{array}{cc}1& 0.8\\ 0.8& 1\end{array}\right]$

Wherein, transmission antenna number N_TIt is 2, soTo be dimension be 2 unit matrix；Τ r (x) is matrix trace function；E (x) represents random matrix H_DAsk expectation；θ_R,E、θ_T,ETo be transmitting terminal respectively receive to the channel of energy receiver, channel sends covariance matrix；H_DIt is the transmitting terminal channel matrix to intelligence receiver, is called information channel, be the matrix of multiple 2 × 2,

$\begin{array}{c}{H}_D={\mathrm{\&theta;}}_{R,D}^{1/2}{H}_{\mathrm{\&omega;},D}{\mathrm{\&theta;}}_{T,D}^{1/2}\\ ={\left[\begin{array}{cc}1& 0.3\\ 0.3& 1\end{array}\right]}^{\mathrm{1/2}}{H}_{\mathrm{\&omega;},D}{\left[\begin{array}{cc}1& 0.5\\ 0.5& 1\end{array}\right]}^{\mathrm{1/2}}\end{array}$

In above formula, H_ω,DIt is the multiple gaussian random matrix of 2 × 2, each element statistical iteration, and obey the multiple Gauss distribution of average zero, variance 1.

Finally, it is necessary to explanation, D (W is being calculated⁽ⁱ⁾) time, first produce some H_ω,DSample, then by each sample together with given data W⁽ⁱ⁾, u, λ etc. substitute into D (W⁽ⁱ⁾) expression formula, calculate be averaging.

S203: update pre-coding matrix: W⁽ⁱ⁺¹⁾:=W⁽ⁱ⁾+sD(W⁽ⁱ⁾)

S204: if | L (W⁽ⁱ⁺¹⁾,λ,u)-L(W⁽ⁱ⁾, λ, u) | < ξ, ξ are pre-determined threshold, and algorithm terminates, and export W⁽ⁱ⁺¹⁾With g (λ, u) ≈ L (W⁽ⁱ⁺¹⁾,λ,u)；Otherwise increase loop index, return step S202.Here function L (W, λ, u) for Lagrangian, be defined as:

$\begin{array}{c}L(W,\mathrm{\&lambda;},u)=E\{\log \det \&lsqb;I_{N_D}+H_D{W}^H{\mathrm{WH}}_D^H/{\mathrm{\&sigma;}}_D^2\&rsqb;\}\\ +\mathrm{\&lambda;}\&lsqb;Tr\left(W^H{\mathrm{W\&theta;}}_{TE}\right)Tr\left({\mathrm{\&theta;}}_{RE}\right)-{\mathrm{\&epsiv;}}_{ng}\&rsqb;-u\&lsqb;Tr\left(W^{H}W\right)-P_T\&rsqb;\\ =E\{\log \det \&lsqb;I_{N_D}+H_D{W}^H{\mathrm{WH}}_D^H\&rsqb;\}\\ +\mathrm{\&lambda;}\&lsqb;2Tr\left(W^{H}W\left[\begin{array}{cc}1& 0.8\\ 0.8& 1\end{array}\right]\right)-{\mathrm{\&epsiv;}}_{ng}\&rsqb;-u\&lsqb;Tr\left(W^{H}W\right)-3.16\&rsqb;\end{array}$

Above formula ε_ngIt it is given energy requirement.It is to be appreciated that calculating L (W⁽ⁱ⁺¹⁾, λ, time u), is also first produced some H by Matlab_ω,DSample, then together with given data W⁽ⁱ⁺¹⁾U, λ etc. substitute into above formula and are averaging, thus substituting desired computing.

S3: update two auxiliary parameters；

λ^(k+1)=max (0, λ^(k)+tΔλ^(k)),

u^(k+1)=max (0, u^(k)+tΔu^(k)),

S4: according to two auxiliary parameters, adopts the subalgorithm identical with step S2 to calculate new pre-coding matrix and dual function；

S5: by judging the difference of the dual function numerical value of twice iteration acquirement, namely | g (λ^(k+1),u^(k+1))-g(λ^(k),u^(k)) | whether less than certain pre-determined threshold, decide whether to terminate algorithm.If being unsatisfactory for criterion, increasing iteration index, forwarding step S3 to；Otherwise algorithm terminates, output precoding matrix.

Including three nodes in the communication system that the method for the present invention is corresponding: a sending node, an information receiving node and an energy acceptance node, three nodes are equipped with many antennas, are N respectively_T、N_RDAnd N_RE.User data x needs to be multiplied by a pre-coding matrix W before transmitting, is then broadcasted.So, the reception signal expression of information and energy receiver is write as:

y_D=H_DWx+n_D

y_E=H_EWx+n_E

Wherein, H_DIt is N_D×N_TThe complex matrix of dimension, represents that transmitting terminal is to the channel of intelligence receiver, might as well be referred to as information channel；H_EIt is N_E×N_TThe complex matrix of dimension, represents that transmitting terminal is to the channel of energy receiver, might as well be referred to as energy channels；n_DIt is N_DThe column vector of dimension, is the noise vector of information channel, independent between element, each element obedience zero-mean,The multiple Gauss distribution of variance；n_EIt is N_EThe column vector of dimension, is the noise vector of information channel, independent between element, each element obedience zero-mean,The multiple Gauss distribution of variance.

After above-mentioned steps is finished, at given energy requirement ε_ngWith under system signal noise ratio, optimum precoding W just obtains.W is substituted into expression formulaCan in the hope of system information transmissions speed now.

Being can be derived from by energy acceptance signal expression, the energy that system obtained in the unit interval is

ε_ng=η Tr (W^HWθ_TE)Tr(θ_RE)

Wherein, constant η is energy conversion efficiency, and Τ r (x) represents Matrix Calculating mark, θ_TEAnd θ_REIt is transmission and the reception covariance matrix of energy channels respectively.

Namely the present invention designs precoding W, is meeting energy requirement ε_ngWhen, maximize rate of information throughput R.

The operation of transmitting terminal is segmented into two stages: training stage and data transmission phase.In the training stage, transmitting terminal is launched pilot signal, energy and intelligence receiver and is measured respective channel matrix, calculates transmitting-receiving covariance matrix, feeds back to transmitting terminal；It addition, intelligence receiver also wants the signal to noise ratio of feedback information channel.The transmitting terminal signal to noise ratio according to the transmitting-receiving covariance matrix of the information received and energy channels, information channel, calculates optimum pre-coding matrix W.Then system enters and sends data phase: user data is multiplied by pre-coding matrix W and sends by transmitting terminal.

As seen from Figure 3, under given energy requirement, relatively isotropism transmission plan is higher for the rate of information throughput that the inventive method obtains；It addition, this method is also broader up to information rate territory.

Above disclosed it is only one preferred embodiment of the present invention, certainly can not limit the interest field of the present invention, the equivalent variations therefore made according to the claims in the present invention with this, still belong to the scope that the present invention contains.

Claims (6)

1. the method for precoding based on channel covariancc feedback, it is characterised in that comprise the following steps:

S1: the signal to noise ratio obtaining the transmitting terminal information channel to intelligence receiver and the covariance information of energy channels of energy receiver, information channel respectively is measured in base station within the setting time；

S2: initialize iteration index, two auxiliary parameters, step-size in search, calculates pre-coding matrix and dual function numerical value as initial value according to subalgorithm；

S3: update said two auxiliary parameter；

S4: according to said two auxiliary parameter, adopts described subalgorithm to calculate new pre-coding matrix and dual function numerical value；

S5: according to determining that criterion decides whether to terminate, when being unsatisfactory for described decision criterion, increases described iteration index, and repeats step S3 until terminating, and output precoding matrix.

2. the method for precoding based on channel covariancc feedback according to claim 1, it is characterised in that the initialization of described step S2 includes arranging iteration index k=0；Auxiliary parameter λ >=0 and μ >=0；Step-size in search t meets 0 < t < 1.

3. the method for precoding based on channel covariancc feedback according to claim 1, it is characterised in that described subalgorithm includes step:

S201: loop initialization index i=0；Step-size in search 0 < s < 1, randomly chooses a complex matrix as initial pre-coding matrix, is designated as W⁽⁰⁾；

S202: calculate the direction of search D (W under current iteration according to following formula⁽ⁱ⁾),

$D\left(W^{\left(i\right)}\right)=E\{W^{\left(i\right)}{H}_D^H{H}_D/{\mathrm{\&sigma;}}_D^2{(I_{N_T}+{\left(W^{\left(i\right)}\right)}^H{W}^{\left(i\right)}{H}_D^H{H}_D/{\mathrm{\&sigma;}}_D^2)}^{-1}\}-W^{\left(i\right)}A$

$A={\mathrm{uI}}_{N_T}-\mathrm{\&lambda;}Tr\left({\mathrm{\&theta;}}_{RE}\right){\mathrm{\&theta;}}_{TE}$

Wherein,Be dimension it is N_TUnit matrix, N_TBeing transmission antenna number, Τ r (x) is matrix trace function；E (x) represents random matrix H_DAsk expectation, θ_RE、θ_TETo be transmitting terminal respectively receive to the channel of energy receiver, channel sends covariance matrix；H_DIt is the transmitting terminal channel matrix to intelligence receiver, for multiple N_D×N_TMatrix, be defined as:

$H_D={\mathrm{\&theta;}}_{R,D}^{1/2}{H}_{\mathrm{\&omega;},D}{\mathrm{\&theta;}}_{T,D}^{1/2},$

In above formula, H_ω,DBe a dimension it is N_D×N_TMultiple gaussian random matrix, each element statistical iteration, and obey average zero, variance 1 multiple Gauss distribution, N_DIt is the number of antennas of intelligence receiver,It it is the noise power of information channel；

S203: update pre-coding matrix W⁽ⁱ⁺¹⁾:=W⁽ⁱ⁾+sD(W⁽ⁱ⁾),

S204: if | L (W⁽ⁱ⁺¹⁾,λ,u)-L(W⁽ⁱ⁾, λ, u) | < ξ, ξ are pre-determined threshold, and algorithm terminates, output L (W (ⁱ⁺¹⁾, λ, u) and W⁽ⁱ⁺¹⁾；Otherwise increase loop index, return step S202, function L (W, λ, u) for Lagrangian, be defined as:

$\begin{array}{c}L\left(W,\mathrm{\&lambda;},u\right)=E\left\{\log \det \&lsqb;I_{N_D}+H_D{W}^H{\mathrm{WH}}_D^H/{\mathrm{\&sigma;}}_D^2\&rsqb;\right\}\\ +\mathrm{\&lambda;}\&lsqb;Tr\left(W^H{\mathrm{W\&theta;}}_{TE}\right)Tr\left({\mathrm{\&theta;}}_{RE}\right)-{\mathrm{\&epsiv;}}_{ng}\&rsqb;-u\&lsqb;Tr\left(W^{H}W\right)-P_T\&rsqb;\end{array}$

Wherein P_TFor transmit power.

4. the method for precoding based on channel covariancc feedback according to claim 1, it is characterised in that described step S3 updates said two auxiliary parameter and updates according to the following formula:

Wherein t is step-size in search.

5. the method for precoding based on channel covariancc feedback according to claim 1, it is characterised in that described step S4 dual function is

6. the method for precoding based on channel covariancc feedback according to claim 1, it is characterised in that described decision criterion is by judging the difference of the dual function numerical value of twice iteration acquirement | g (λ^(k+1),u^(k+1))-g(λ^(k),u^(k)) | whether meet and set thresholding.