CN105049100A - Multi-cell MIMO system double-layer pre-coding method - Google Patents

Abstract

The invention provides a multi-cell MIMO system double-layer pre-coding method. According to the method, users are divided into center users and edge users according to the interference type and interference degree affecting the users, and then double-layer pre-coding processing is performed on user interference by the combined technology of an interference alignment technology and a maximized signal-to-leakage-and-noise ratio technology, wherein the first layer of pre-coding adopts the interference alignment technology so as to eliminate inter-cell interference affecting the edge users, and the second layer of pre-coding adopts the maximized signal-to-leakage-and-noise ratio technology so as to suppress intra-cell interference affecting the users. The method is based on degree of spatial freedom and has no limit to the number of antennas.

Description

The double-deck method for precoding of a kind of multiple cell mimo system

Technical field

The present invention relates to multiple-input, multiple-output (MultipleInputMultipleOutput, MIMO) communication system, particularly the double-deck Precoding Design of multiple cell mimo system.

Background technology

In multiple cell mimo system, the interference type that user is subject to and annoyance level are not quite similar, and user may be subject to the interference with minizone in community simultaneously.The presence of intercell interference be subject near the user of center of housing estate is less, negligible, and the presence of intercell interference that the user being positioned at cell edge is subject to is larger, thus when base station end is carried out pretreated, distinguish central user and edge customer and respectively AF panel carried out to it, schemes existing a large amount of in this respect at present.

Wherein, a kind of scheme is the received power value by estimating user, predicts in community whether there is edge customer; If existed, then multi-cell coordination technology edge user is adopted to carry out AF panel; If there is no, then single area interference suppression technology is adopted.This method is without the need to the channel condition information (CSI) of all neighbor cell users, and it greatly reduces the exchange capacity of CSI between base station.A kind of scheme maximizes criterion than (SLNR) eliminate intra-cell interference based on believing in community that leakage is made an uproar, and obtain according to game theory principle the interference that certain precoding vector suppresses minizone.A kind of scheme utilizes the feedback information of community user to design two kinds of precoders at transmission end of base station: a kind of precoder designs ZF (ZF) precoder based on block diagonalization (BD) technology, another kind of precoder is the MMSE precoder based on Minimum Mean Square Error (MMSE) channel inversion technique, in order to suppress intra-cell interference; BD technology is then utilized to find the shaping vector of received beam, to eliminate the interference of minizone at user's receiving terminal.But the above number of antennas of these schemes to receiving terminal, transmitting terminal has strict restriction, and spatial degrees of freedom is not high.

Based on this, the present invention is directed to existing double-deck method for precoding spatial degrees of freedom this problem limited, propose a kind of will interference alignment techniques and maximize multiple cell mimo system bilayer method for precoding believe that leaking makes an uproar combines than technology, wherein adopt interference alignment suppression technology to carry out ground floor precoding to suppress presence of intercell interference, utilize to maximize and believe that leakage is made an uproar and carry out second layer precoding to suppress intra-cell interference than technology.

Summary of the invention

Goal of the invention: propose the double-deck method for precoding of a kind of multiple cell mimo system, for system interference process spatial degrees of freedom limitation problem, adopts interference alignment techniques and maximizes letter leakage and make an uproar than technology, to suppress interference.

For realizing object of the present invention, its feature comprises:

Double-deck method for precoding, ground floor adopts interference alignment techniques, and to suppress presence of intercell interference, the second layer adopts and maximizes letter leakage and to make an uproar ratio, to suppress intra-cell interference.

Technical scheme of the present invention:

System model as shown in Figure 1, supposes total C community, and total party B-subscriber in each community, the number of transmit antennas of base station end is M, and it is N that user side receives number of days.First obtain channel matrix, particularly, base station j is to user (k, i), after transmission source data message, user (k, i) estimates the CSI of every root antenna to self of each base station, then user (k, i) is by CSI feedback to base station, and base station obtains according to CSI wherein, in user (k, i) ShikGe community, obtain i-th user, represent the channel matrix of base station j to user (k, i), M and N is number of transmit antennas, reception antenna number respectively, i ∈ 1,2 ..., B}, k ∈ 1,2 ..., C}, j ∈ 1,2 ..., C}.Suppose that channel elapsed-time standards and frequency steadily decline, the separate and multiple Gaussian Profile of satisfied (0,1) of each element.

Optimize channel matrix: calculate former the F norm often arranged, selects the maximum D of F norm (M > D>=N) row and forms new matrix

The process that method is concrete is:

1. according to estimating the channel matrix obtained, calculate base station j ∈ 1,2 ..., in C}, every transmit antennas is to the F norm of the channel fading coefficient of all reception antennas of user (k, i):

Wherein represent channel matrix d arranges, || || _fthe F norm of representing matrix.

2. two S set are defined again _j=1,2 ..., M} and s _j(being initialized as empty set), respectively the transmitting antenna set of initialization base station k and the transmitting antenna set selected.The channel matrix relatively calculated respectively arranges the size of F norm, requires that the target antenna found must meet formula:

When selecting target antenna s, just from S _jmiddle removal s, adds s to s simultaneously _jin, until have selected D transmit antennas, the transmitting antenna set this moment selected is s _j=1,2 ..., D} is base station j initialization transmitting antenna S set _j=1,2 ..., a subset of M}.

3. the base station of C community forms an antenna set after carrying out day line options know set after, the channel matrix of each base station j to user can be determined it represents that line options set on the same day is s _jshi little Qu j is to the channel matrix of user (k, i).

4. suppose that base station k is the pre-coding matrix that user (k, i) sets and is i ∈ 1,2 ..., B}, k ∈ 1,2 ..., C}, n are the communication data numbers that base station sends, n=D/2; S _{(k, i)}for the former communication data of n × 1 dimension, then the signal that user (k, i) receives is:

Wherein, in equation, Section 1 represents the desired signal that user (k, i) receives, and Section 2 represents intra-cell interference signal, and Section 3 represents inter-cell interference signals, Section 4 N _{(k, i)}represent the additive white Gaussian noise meeting (0,1).

Divide user, the presence of intercell interference degree be generally subject to distance or the user of base station according to user divides simultaneously.Setpoint distance door threshold, when the close together of user and base station, the interference that other base station is caused this community user, thinks noise, user-center user now; When the distance of user and base station is greater than threshold, the adjacent base station signal that user receives and this cell signal very nearly the same, user is now edge customer.Or the interference power door threshold that a user is critical is set, when the interference power that user is subject to is less than threshold, user-center user, on the contrary be edge customer.Finally carry out AF panel.

Ground floor precoding adopts interference alignment techniques process presence of intercell interference.Interference alignment techniques suppresses the basic thought of interference to be: Received signal strength spatialization is divided into desired signal and the separate subspace of unwanted signal two, by the preliminary treatment of base station end, the interference signal of the machine of spontaneous emission is in the future limited in unwanted signal subspace, receiving terminal, by the process of simple ZF criterion, just can suppress interference completely; Receiver then obtains useful signal in desired signal subspace, and the impact of the signal that can not be interfered.

Concrete ground floor precoding process is as follows:

Suppose channel matrix and pre-coding matrix all full ranks.System model as shown in Figure 2, in order to easy, simplify system model, suppose C=5, and a user is only served in each base station in each community.Now, writing a Chinese character in simplified form channel matrix is T _ji, it represents the CSI of base station j to user i.

Based on the basic thought of interference alignment techniques, the aligned condition that must meet is:

Mobile subscriber MS ₁place, span (T ₁₂v ₂)=span (T ₁₃v ₃)=span (T ₁₄v ₄)=span (T ₁₅v ₅) (4)

Mobile subscriber MS ₂place, span (T ₂₁v ₁)=span (T ₂₃v ₃)=span (T ₂₄v ₄)=span (T ₂₅v ₅) (5)

Mobile subscriber MS ₃place, span (Τ ₃₁v ₁)=span (T ₃₂v ₂)=span (T ₃₄v ₄)=span (T ₃₅v ₅) (6)

Mobile subscriber MS ₄place, span (T ₄₁v ₁)=span (T ₄₂v ₂)=span (T ₄₃v ₃)=span (T ₄₅v ₅) (7)

Mobile subscriber MS ₅place, span (T ₅₁v ₁)=span (T ₅₂v ₂)=span (T ₅₃v ₃)=span (T ₅₄v ₄) (8)

Wherein, the column vector of span (X) representing matrix X the space of opening, V ₁, V ₂, V ₃, V ₄, V ₅represent the pre-coding matrix that base station 1,2,3,4,5 is arranged for respective user respectively.Above-mentioned equation is simplified respectively and obtains:

T ₁₂V ₂＝T ₁₃V ₃＝T ₁₄V ₄＝T ₁₅V ₅(9)

T ₂₁V ₁＝T ₂₃V ₃＝T ₂₄V ₄＝T ₂₅V ₅(10)

T ₃₁V ₁＝T ₃₂V ₂＝T ₃₄V ₄＝T ₃₅V ₅(11)

T ₄₁V ₁＝T ₄₂V ₂＝T ₄₃V ₃＝T ₄₅V ₅(12)

T ₅₁V ₁＝T ₅₂V ₂＝T ₅₃V ₃＝T ₅₄V ₄(13)

Introduce matrix G ₁, make equation span (V ₁)=span (G ₁v ₁) set up, use V ₁represent V ₂, V ₃, V ₄, V ₅, obtain equation:

$V_2=T_{32}^{-1}{T}_{31}{V}_1=T_{42}^{-1}{T}_{41}{V}_1=T_{52}^{-1}{T}_{51}{V}_1---\left(14\right)$

$V_3=T_{23}^{-1}{T}_{21}{V}_1=T_{43}^{-1}{T}_{41}{V}_1=T_{53}^{-1}{T}_{51}{V}_1---\left(15\right)$

$V_4=T_{24}^{-1}{T}_{21}{V}_1=T_{34}^{-1}{T}_{31}{V}_1=T_{54}^{-1}{T}_{51}{V}_1---\left(16\right)$

$V_5=T_{25}^{-1}{T}_{21}{V}_1=T_{35}^{-1}{T}_{31}{V}_1=T_{45}^{-1}{T}_{41}{V}_1---\left(17\right)$

Solve suppose g ₁, g ₂, g ₃, g ₄..., g _dmatrix G ₁characteristic vector, then V ₁any D/2 characteristic vector can be expressed as, have:

V ₁＝[g ₁,g ₂,g ₃,g ₄,...,g _D/2](18)

In like manner V can be obtained ₂, V ₃, V ₄, V ₅.Interference signal has been limited in unexpected letter subspace, in receiving terminal design AF panel matrix W _{(k, i)}∈ C ^{n × n}, unwanted signal is fallen in the kernel of desired signal subspace, thus eliminates presence of intercell interference completely.

W _(k,i)＝null[(T _miV _m) ^H,(T _niV _n) ^H](19)

Wherein, the kernel of null [X] representing matrix row, then by after ground floor precoding, the Received signal strength of user (k, i) is:

Second layer precoding adopts the interference maximizing and believe and leak and make an uproar than in process community.Although conventional Optimality Criteria maximizes Signal to Interference plus Noise Ratio, but SLNR technology has lower complexity, simultaneously leak to make an uproar with the letter maximizing each user and carry out precoding than for criterion, this technology does not only have spatial degrees of freedom---the restriction of number of antennas and users multiplexing number, the closed solutions close to optimal solution can also be obtained, effectively eliminate intra-cell interference.

According to letter leak make an uproar than definition (useful energy of user than upper its leak to the energy plus noise of other user in community and value), the leakage of user (k, i) to the energy of other user in community is:

$\left|\right|W_{(k,i)}^{*}\underset{\stackrel{m=1}{m\≠i}}{\overset{B}{\Σ}}{W}_{(k,m)}^H{T}_k^{(k,m)}{V}_{(k,m)}|{|}^2---\left(21\right)$

Therefore the SLNR of user (k, i) is:

${\mathrm{SLNR}}_{(k,i)}=\frac{\left|\right|W_{(k,i)}^{*}{W}_{(k,i)}^H{T}_k^{(k,i)}{V}_{(k,i)}|{|}^2}{\left|\right|W_{(k,i)}^{*}\underset{\stackrel{m=1}{m\≠i}}{\overset{B}{\Σ}}{W}_{(k,m)}^H{T}_k^{(k,m)}{V}_{(k,m)}|{|}^2+{\mathrm{\ζ}}_{(k,i)}}---\left(22\right)$

Wherein represent the second layer pre-coding matrix that user (k, i) designs, represent the noise that user is subject to.

Base station is user (k, i) when designing precoding vector, solves power constraint exactly and (for simplicity, power constraint is designed to single user power constraint P _{(k, i)}) under the max problem of SLNR, it is so-called that to maximize that interference leaks than coding be that interference that useful signal is formed other user compared to it is large as far as possible, to make the interference of overall system little as much as possible.That is:

Generally all suppose in practical application that power constraint is base station power constraint, irrigation technique can be adopted to solve the power of user according to the SNR of user.According to generalized Rayleigh quaotient problem, can know that optimal solution is pencil of matrix generalized eigenvector corresponding to eigenvalue of maximum, therefore user (k, i) second layer precoding vector is:

$W_{(k,i)}^{*}={\mathrm{\φ}}_{max}\frac{\left|\right|W_{(k,i)}^H{T}_k^{(k,i)}{V}_{(k,i)}|{|}^2}{\left|\right|\underset{\stackrel{m=1}{m\≠1}}{\overset{B}{\Σ}}{W}_{(k,m)}^H{T}_k^{(k,m)}{V}_{(k,m)}|{|}^2+\frac{{\mathrm{\ζ}}_{(k,i)}}{P_{(k,i)}}I}---\left(24\right)$

Then after double-deck precoding, gained transmitting terminal pre-coding matrix is:

Accompanying drawing explanation

Fig. 1 multiple cell MIMO communication system model;

Fig. 2 disturbs alignment model;

The double-deck precoding flow process of Fig. 3 multiple cell mimo system.

Embodiment

Be described below in detail embodiments of the invention, the example of described embodiment is shown in the drawings, and wherein same or similar label represents same or similar element or has element that is identical or similar functions from start to finish.Being exemplary below by the embodiment be described with reference to the drawings, only for explaining the present invention, and can not limitation of the present invention being interpreted as.

In describing the invention, it will be appreciated that, term " longitudinal direction ", " transverse direction ", " on ", D score, "front", "rear", "left", "right", " vertically ", " level ", " top ", " end " " interior ", the orientation of the instruction such as " outward " or position relationship be based on orientation shown in the drawings or position relationship, only the present invention for convenience of description and simplified characterization, instead of indicate or imply that the device of indication or element must have specific orientation, with specific azimuth configuration and operation, therefore can not be interpreted as limitation of the present invention.

In describing the invention, unless otherwise prescribed and limit, it should be noted that, term " installation ", " being connected ", " connection " should be interpreted broadly, such as, can be mechanical connection or electrical connection, also can be the connection of two element internals, can be directly be connected, also indirectly can be connected by intermediary, for the ordinary skill in the art, the concrete meaning of above-mentioned term can be understood as the case may be.

The double-deck method for precoding flow process of multiple cell mimo system is as shown in Figure 3, specific as follows:

Step 10, starts;

Step 20, first base station is to after user's transmission source data message, and user estimates the CSI of every root antenna to oneself of each base station, then user by CSI feedback to base station, base station obtains according to CSI and obtains channel condition information (what suppose acquisition is desirable), thus obtains channel matrix;

Step 30, adopts the method based on maximum norm to be optimized it, to obtain the relatively good channel matrix of performance for the channel matrix obtained;

Step 40, the power obtained according to user and door threshold or estimate its distance to base station, judge that user belongs to central user or edge customer;

Step 50, adopts interference alignment techniques to carry out ground floor suppression, to eliminate the presence of intercell interference that edge customer is subject to user's interference;

Step 60, adopts and maximizes letter and leak to make an uproar and carry out second layer suppression than technology to the interference that user is subject to, to eliminate the intra-cell interference that user is subject to;

Step 70, judges that whether the AF panel situation of user is up to standard;

Step 80, does not have up to standard, jumps to step 30, carries out iteration to reach target, otherwise then terminates.

In this description, the present invention describes with reference to specific embodiment.But, still can make various amendment and conversion obviously and not deviate from the spirit and scope of the present invention.Therefore, specification and accompanying drawing are regarded in an illustrative, rather than a restrictive.

Claims (5)

1. the double-deck method for precoding of multiple cell mimo system, is characterized in that, comprising:

S1, obtains channel matrix, then optimizes channel matrix;

S2, divides central user and edge customer according to the annoyance level that user is subject to distance or the user of base station;

S3, ground floor is encoded---interference alignment techniques, the presence of intercell interference be subject to suppress edge customer;

S4, the second layer is encoded---and maximize letter leakage and make an uproar than technology, suppress the intra-cell interference that user is subject to.

2. the double-deck method for precoding of a kind of multiple cell mimo system according to claim 1, is characterized in that, in described S1, the acquisition of channel matrix and optimization comprise:

S1-1, the acquisition of channel matrix, base station is to after user's transmission source data message, and user estimates the CSI of every root antenna to self of each base station, then by the CSI feedback estimated to base station, base station obtains according to CSI be the channel matrix of base station j to user (k, i), (k, i) represents the jth user in kGe community;

S1-2, the optimization of channel matrix, calculates former the F norm often arranged, selects the maximum D of F norm and arranges to carry out data communication, to form new matrix represent the channel matrix of base station j to user (k, i).

3. the double-deck method for precoding of a kind of multiple cell mimo system according to claim 1, it is characterized in that, in described S2, the division of user comprises:

A critical power door threshold P is set _th, the interfering signal power that user is subject to is greater than P _thtime, show that this user is for edge customer; Otherwise, then user centered by.

4. the double-deck method for precoding of a kind of multiple cell mimo system according to claim 1, is characterized in that, in described S3, ground floor precoding interference alignment techniques comprises:

Channel matrix and pre-coding matrix all full ranks, V _{(k, i)}represent ground floor pre-coding matrix; For ease of illustrating, suppose community number C=5, and a user is only served in each base station in each community; Now, writing a Chinese character in simplified form channel matrix is T _ji, T _jirepresent the channel condition information of base station j to user i;

Based on the basic thought of interference alignment techniques, the aligned condition that must meet is:

Mobile subscriber MS ₁place, span (T ₁₂v ₂)=span (T ₁₃v ₃)=span (T ₁₄v ₄)=span (T ₁₅v ₅),

Mobile subscriber MS ₂place, span (T ₂₁v ₁)=span (T ₂₃v ₃)=span (T ₂₄v ₄)=span (T ₂₅v ₅),

Mobile subscriber MS ₃place, span (Τ ₃₁v ₁)=span (T ₃₂v ₂)=span (T ₃₄v ₄)=span (T ₃₅v ₅),

Mobile subscriber MS ₄place, span (T ₄₁v ₁)=span (T ₄₂v ₂)=span (T ₄₃v ₃)=span (T ₄₅v ₅),

Mobile subscriber MS ₅place, span (T ₅₁v ₁)=span (T ₅₂v ₂)=span (T ₅₃v ₃)=span (T ₅₄v ₄),

Wherein, the column vector of span (X) representing matrix X the space of opening, V ₁, V ₂, V ₃, V ₄, V ₅represent the pre-coding matrix that base station 1,2,3,4,5 is arranged for respective user respectively; Simplify above-mentioned formula, obtain:

T ₁₂V ₂＝T ₁₃V ₃＝T ₁₄V ₄＝T ₁₅V ₅，

Introduce matrix G ₁, make equation span (V ₁)=span (G ₁v ₁) set up, simultaneous is by V ₁the V represented ₂, V ₃, V ₄, V ₅equation, obtain:

$G_1=T_{52}^{-1}{T}_{51}{T}_{12}^{-1}{T}_{13}{T}_{23}^{-1}{T}_{24}{T}_{34}^{-1}{T}_{35}{T}_{45}^{-1}{T}_{41},$

Suppose g ₁, g ₂, g ₃, g ₄..., g _dmatrix G ₁characteristic vector, then V ₁be expressed as any D/2 characteristic vector, have:

V ₁＝[g ₁,g ₂,g ₃,g ₄,...,g _D/2]，

In like manner V can be obtained ₂, V ₃, V ₄, V ₅;

In receiving terminal design AF panel matrix W _{(k, i)}, unwanted signal is limited in the kernel of desired signal subspace, thus eliminates presence of intercell interference completely,

W _(k,i)＝null[(T _miV _m) ^H,(T _niV _n) ^H]。

5. the double-deck method for precoding of a kind of multiple cell mimo system according to claim 1, is characterized in that, in described S4, second layer precoding maximizes letter leakage and makes an uproar and to comprise than technology:

The leakage of user (k, i) to the energy of other user in community is:

$\left|\right|W_{(k,i)}^{*}\underset{\begin{array}{c}m=1\\ m\≠i\end{array}}{\overset{B}{\Σ}}{W}_{(k,m)}^H{T}_k^{(k,m)}{V}_{(k,m)}|{|}^2,$

Therefore the SLNR of user (k, i) is:

${\mathrm{SLNR}}_{(k,i)}=\frac{\left|\right|W_{(k,i)}^{*}{W}_{(k,i)}^H{T}_k^{(k,i)}{V}_{(k,i)}|{|}^2}{\left|\right|W_{(k,i)}^{*}\underset{\begin{array}{c}m=1\\ m\≠i\end{array}}{\overset{B}{\Σ}}{W}_{(k,m)}^H{T}_k^{(k,m)}{V}_{(k,m)}|{|}^2+{\mathrm{\ζ}}_{(k,i)}},$

Wherein, represent the second layer pre-coding matrix that user (k, i) designs, represent the noise that user is subject to;

Maximize letter leakage to make an uproar ratio, also namely solve following equation:

$\begin{array}{c}\underset{W_{(k,i)}^{*}}{\max }{\mathrm{SLNR}}_{(k,i)}\\ s.t.\left|\right|W_{(k,i)}^{*}|{|}^2=P_{(k,i)}\end{array},$

According to broad sense Rayleigh entropy problem, optimal solution is the generalized eigenvector that the eigenvalue of maximum of following pencil of matrix is corresponding:

$\[\left|\right|W_{(k,i)}^H{T}_k^{(k,i)}{V}_{(k,i)}|{|}^2,|\left|\underset{\begin{array}{c}m=1\\ m\≠i\end{array}}{\overset{B}{\Σ}}{W}_{(k,m)}^H{T}_k^{(k,m)}{V}_{(k,m)}\right|{|}^2+\frac{{\mathrm{\ζ}}_{(k,i)}}{P_{(k,i)}}I\],$

Therefore user (k, i) second layer precoding vector is:

$W_{(k,i)}^{*}={\mathrm{\φ}}_{max}\frac{\left|\right|W_{(k,i)}^H{T}_k^{(k,i)}{V}_{(k,i)}|{|}^2}{\left|\right|\underset{\begin{array}{c}m=1\\ m\≠i\end{array}}{\overset{B}{\Σ}}{W}_{(k,m)}^H{T}_k^{(k,m)}{V}_{(k,m)}|{|}^2+\frac{{\mathrm{\ζ}}_{(k,i)}}{P_{(k,i)}}I},$

Then after double-deck precoding, gained transmitting terminal pre-coding matrix is:

$V_{(k,i)}^{*}=W_{(k,i)}^{*}{V}_{(k,i)}.$