Invention content
For the deficiency of existing method, the present invention propose it is a kind of assisted based on uplink traffic channel information it is extensive
The Downlink channel estimation method of MIMO communication system.
Include the following steps for realizing technical solution of the invention:
Step 1:Base station uses a uniform linear array with N root antennas, and mobile subscriber uses single antenna.It is mobile
User's pilot signal transmitted after base station receives signal, goes out uplink channel using classical Least Square Method, is denoted as
Step 2:Base station pilot signal transmitted matrix X within T moment, the then signal that mobile subscriber receives are y=Φ
(β)w+n。
Step 3:Iterations counting variable l=1 is set, the precision vector of w is initializedIn each element be
1, initializationPrecision vectorIn each element be 1, initialize noise precisionInitialize β simultaneously
For full neutral element.
Step 4:α is updated,γ and τ.
Step 5:Update β.
Step 6:Judge whether iteration count variable l reaches whether the upper limit L or γ restrain, if be all unsatisfactory for, iteration
Counting variable l=l+1, and return to step 4.
Step 7:Thresholding η is set, and chooses the effective angle set omega of downlink channel using the thresholding.
Step 8:Using effective angle set omega, final downlink channel is estimated.
Beneficial effects of the present invention:
Uplink traffic channel information is fused in Downlink channel estimation by the present invention, using uplink channel under
The joint sparse characteristic of Downlink channels so that the corresponding available observation sample quantity of rarefaction representation optimization problem improves
One times.Compared with the conventional method, the present invention can significantly improve the performance of channel estimation
Specific implementation mode
The invention will be further described in the following with reference to the drawings and specific embodiments.
As shown in Figure 1, the method for the present invention includes following steps:
(1) base station uses a uniform linear array with N root antennas, and mobile subscriber uses single antenna.It is mobile to use
Family pilot signal transmitted after base station receives signal, goes out uplink channel using classical Least Square Method, is denoted asAnd it is expressed as the form of sparse signal recovery:Wherein:
The referred to as calculation matrix of uplink,
Expression is evenly dividingN number of mesh point, i.e.,
dn, n=1,2 ..., N, the spacing of expression the n-th array element and the 1st array element,Indicate uplink electrical magnetic wave
Wavelength,
In element βiIndicate θiOn angular deviation,
It is channel in calculation matrixOn rarefaction representation vector,
E is that the mean value of a N-dimensional is 0, and precision isWhite Gaussian noise vector.
(2) base station pilot signal transmitted matrix X within T moment, the then signal that mobile subscriber receives are y=Φ (β) w
+ n, wherein
Φ (β)=XA (β) is known as the calculation matrix of downlink,
A (β)=[a (θ1+β1),a(θ2+β2),...,a(θN+βN)],
λ indicates the wavelength of downlink electromagnetic wave,
W is rarefaction representation vector of the channel on calculation matrix Φ (β),
N is that the mean value of T dimensions is 0, the white Gaussian noise vector that precision is α.
(3) iterations counting variable l=1 is set, the precision vector of w is initializedIn each element be 1, just
BeginningizationPrecision vectorIn each element be 1, initialize noise precisionIt is complete zero to initialize β simultaneously
Element.
(4) α is updated,γ and τ, i.e.,:
Wherein:
The mark of tr () representing matrix, | | | |22 norms of representing matrix, []iiI-th of representing matrix is diagonal
Line element, ()HExpression conjugate transposition, a=b=0.0001,
μ (α, γ, β)=α Σ (α, γ, β) ΦH(β) y, Σ (alpha, gamma, β)=(α ΦH(β)Φ(β)+diag(γ))-1
⊙ indicates Hadamard products,
Diag () indicates diagonal operation matrix, Ξ (alpha, gamma, β)=μ (alpha, gamma, β) μH(alpha, gamma, β)+Σ (alpha, gamma, β),
(5) β is updated, i.e.,:
Wherein
Sign () expressions take sign operation,
Re () expressions take real part operation,
ci1=-α (χii+|μi|2),
μiIndicate i-th of element of μ (alpha, gamma, β), χjiIndicate Σ (α, γ, β)
(j, i) a element,
(·)*Indicate conjugate operation, a'(θi+βi) indicate a (θi+βi) about βiDerivative,
It indicatesI-th of element,It indicates
(j, i) a element,It indicatesAbout βiDerivative.
(6) judge whether iteration count variable l reaches upper limit L (such as L=100) or whether γ restrains (i.e. when secondary update
As a result whether equal with last time update result), if be all unsatisfactory for, iteration count variable l=l+1, and return to (4).
(7) thresholding is setWhereinIndicate the maximum element of i-th of value in μ (alpha, gamma, β), and
Using the thresholding choose downlink channel effective angle set omega=i | (μi)2>=η, i=1,2 ..., N }.
(8) effective angle set omega is utilized, estimates final downlink channel:Wherein
(·)ΩIndicate by the corresponding Column vector groups of set omega in matrix at submatrix,The generalized inverse of representing matrix.
The effect of the present invention is described further with reference to emulation experiment.
In order to assess the performance of this method, it is assumed that base station uses a homogenous linear battle array with N=150 root antennas
The working frequency of row, downlink is 1980MHz, and the working frequency of downlink is 2170MHz, and wireless channel is by 3GPP
Spatial channel model (SCM) model randomly generates, and each element of base station pilot signal transmitted matrix X obeys zero
The independent Gaussian of mean value unit variance is distributed, and ambient noise is assumed to be white Gaussian noise.
Experiment condition
It uses the present invention in signal-to-noise ratio for 0dB, 200 estimations is carried out to channel when pilot tone moment T is changed by 30 to 100,
Simulation result is as shown in Figure 2.
Experimental analysis
Figure it is seen that the present invention can accurately estimate out the downlink channel of extensive MIMO communication system,
NMSE performances are substantially better than conventional method.
The series of detailed descriptions listed above only for the present invention feasible embodiment specifically
Bright, they are all without departing from equivalent implementations made by technical spirit of the present invention not to limit the scope of the invention
Or change should all be included in the protection scope of the present invention.