CN100459446C - An estimation and search method for channel path of multi-path fading channel - Google Patents

Abstract

The related search method employs Teager-Kaiser energy operator to process the preliminary channel impulse response signal output by Steiner channel estimator and remove random distribution effect of path phase shift, then uses response signal to calculate power and estimate noise power for setting threshold, and extracting impulse response signal from every user window while setting inhibited noise into zero. This invention holds the effective multipath information, and removes pseudo path and noise.

Description

A kind of channel path estimation and search method of multidiameter fading channel

Technical field

The present invention relates to the channel path estimation and search method of the multidiameter fading channel of third generation TDS-CDMA mobile communication system (being called for short the TD-SCDMA system).

Background technology

The transmission of signal is subjected to the influence that multipath fading, noise and multiple access disturb usually in the TD-SCDMA system, particularly in high chromatic dispersion that is subjected to noise pollution and multipath channel, more and more being difficult to synchronously of received signal keeps, the orthogonality of user characteristics sign indicating number decreases, and the accurate estimation of channel is difficulty more and more.

Multipath signal has and the remarkable different feature of noise, the Energy distribution of multipath signal concentrate on usually signal space more among a small circle in, and noise spectrum is uniformly distributed in the bigger scope usually.Simultaneously, in slow fading channel, it is faster that multipath signal amplitude and bit comparison mutually postpone variation, and be more vulnerable to The noise.Usually, complicated wireless transmission channel can be by the finite impulse response simulation of a sparse length, and wherein, the channel characteristics parameter comprises multiple transmission decline and time-delay.As in the wireless channel environment of typical city, the multipath number is generally 2～6.Parameterized channel model can reduce channel matrix and signal subspace dimension greatly, improves the performance of estimator and equalizer.Therefore, channel estimating and transmission path search accurately is significant.

In prior art Steiner channel estimator, channel estimating adopts the basic training sequences sign indicating number (abbreviating the midamble sign indicating number as) of cyclic shift as training sequence, and the different terminals user uses different displacements to distinguish.Characteristics according to cyclic shift, the training sequence that transfer pair receives in the time of can utilizing the fast discrete Fourier calculates its frequency response, make comparisons with the frequency response of the reference of this locality then, output after the comparison through the fast discrete inverse-Fourier transform, is obtained preliminary channel impulse response estimation.This method provide a kind of fast, the channel estimation methods of low-cost.But the output signal of this method is subjected to the The noise of amplifying in interchannel noise and the processing procedure usually, causes the receiving terminal error rate to rise, and demodulation performance descends.

At present, the improved method of channel estimating in the prior art is normally directly carried out back level threshold processing to the Steiner channel estimating.Wherein a kind of method is to choose thresholding according to the certain proportion of most powerful path power, and another kind of method is that the certain multiple according to the noise power of estimating is provided with thresholding.Then, extract channel impulse response according to the hard thresholding of choosing.Patent ZL01130907.5 has adopted the iterative channel estimation approach, promptly after received signal is through matched filtering, multipath signal search and despreading unwinding, the multipath signal that separates is carried out first order channel estimating and removes interference.Then, the multipath signal that the first order is removed after the interference carries out partial matched filtering and despreading unwinding, carries out second level channel estimating again.The shortcoming of the method is need carry out multi-stage channel to estimate, has not only increased the complexity of information processing but also strengthened estimation time delay.

Summary of the invention

Searching method of the present invention is realized the raising that channel estimating, route searching obtain probability from the approach that reduces noise.What is called is obtained probability and is meant 3GPP multidiameter fading channel model according to emulation, the multipath number of the actual correct channel impulse response estimation of extracting on the counting statistics meaning and the ratio of the multipath number that should receive.Teager-Kaiser operator (abbreviating the TK operator as) has been used to extract the sound characteristic parameter to improve speech recognition as a robust nonlinear filter that suppresses the noise extraction signal characteristic.Because to the impulse insensitive for noise, it also is applied in image border identification with in strengthening.Usually can the local level and smooth and high pass characteristic of Teager-Kaiser operator can be applied to channel estimating and route searching by the characteristics of the finite impulse response of sparse length simulation according to the wireless transmission channel parameter model.Utilize the Teager-Kaiser operator by the random noise in the output of low-complexity nonlinear energy process inhibition Steiner estimator, and accurately extract multipath signal wherein, thereby reach the purpose that improves channel path estimating searching precision, the performance that makes the back level unite detection is improved.

Searching method of the present invention adopts the Teager-Kaiser energy operator that the preliminary channel impulse response signal of Steiner channel estimator output is handled, the conjugation item of its Teager-Kaiser energy operator operation result has been eliminated the influence that path phase shift random distribution is brought, difference Xiang Ze has kept signal preferably, utilize channel impulse response calculated signals power and the estimating noise power of handling through the Teager-Kaiser operator again and thresholding is set, extract the channel impulse response of each user's window then respectively by thresholding, the noise that is suppressed has been extracted multipath signal so more exactly by zero setting.The pseudo-footpath that searching method of the present invention can significantly be distinguished effective multipath signal and noise and caused keeps effective multipath information wherein, has removed pseudo-footpath and noise.

Description of drawings

Fig. 1 is a TD-SCDMA system burst structural representation

Fig. 2 is a prior art signal processing flow schematic diagram of getting thresholding behind the Steiner estimator estimation channel impulse response again

Fig. 3 is a searching method signal processing flow schematic diagram of the present invention

Fig. 4 adopts searching method of the present invention and adopts the channel path of prior art threshold processing method to estimate to obtain the probability comparison diagram

Fig. 5 is the ZF ZF combined detection performance comparison diagram that adopts searching method of the present invention and adopt prior art threshold processing method

Below in conjunction with drawings and Examples searching method of the present invention is further described.

Fig. 1 is a TD-SCDMA system burst structural representation.As shown in Figure 1, the information of user terminal and base station communication is placed on the data symbol block both sides, and 144 chips of middle midamble sign indicating number are directly delivered to sending module as training sequence without steps such as coding and spread spectrums.In same sub-district, all users adopt identical basic midamble sign indicating number, but different users adopts different midamble displacements.In different sub-districts, adopt different basic midamble sign indicating numbers, selection principle is that the cross correlation between them is very little, hypothesis is ignored under synchronous fully situation usually.

Fig. 2 is a prior art signal processing flow schematic diagram of getting thresholding behind the Steiner estimator estimation channel impulse response again.As seen from the figure, local midamble sign indicating number and reception midamble sign indicating number are imported the Steiner estimator respectively, after the Steiner estimator is handled, obtain preliminary channel impulse response signal, estimate through power calculation and noise power again, choose thresholding then and extract channel impulse response according to thresholding.

Fig. 3 is a searching method schematic flow sheet of the present invention.As can be seen from Figure 3, compared with prior art, after the Steiner channel estimator is estimated output, adopt the Teager-Kaiser energy operator that the preliminary channel impulse response signal that the Steiner channel estimator obtains is handled.Because the Teager-Kaiser operator is as a robust nonlinear filter that suppresses the noise extraction signal characteristic, the conjugation item of Teager-Kaiser energy operator operation result has been eliminated the influence that path phase shift random distribution is brought, difference Xiang Ze has kept effective multipath signal preferably, has reduced noise and has removed random phase.The mould value of calculating Teager-Kaiser energy operator operation result promptly obtains preliminary channel impulse response performance number after treatment, the noise power of Gu Jiing will be more more accurate than prior art on this basis, then, thresholding and press thresholding and extract channel impulse response is set.Obviously, because having adopted the Teager-Kaiser energy operator that the Steiner channel estimator is estimated to export preliminary channel impulse response estimation handles, effectively suppressed the random noise in the output of Steiner estimator, and extracted multipath signal wherein accurately, thereby improved channel path estimating searching precision, the performance of follow-up joint-detection is improved.

Operational analysis:

Suppose that continuous time, each bar footpath of Steiner channel estimating can be expressed as desirable trigonometric function:

$h\left(t\right)=\underset{l=1}{\overset{L}{\mathrm{\Σ}}}{\mathrm{\α}}_l\mathrm{\Λ}(t-{\mathrm{\τ}}_l,T_c)e^{j{\mathrm{\θ}}_l}---\left(1\right)$

Wherein:

Be one and have length 2T _c, be the trigonometric function at center with the zero point.Here α _l, θ _l, τ _lBe respectively amplitude, phase place and the delay in l bar footpath.

Consider the influence of random noise, the frequency response of the Steiner channel estimating of continuous time can be represented by the formula:

$H\left(\mathrm{\ω}\right)=\underset{l=1}{\overset{L}{\mathrm{\Σ}}}{\mathrm{\α}}_l{e}^{-j({\mathrm{\ω\τ}}_l-{\mathrm{\θ}}_l)}+N\left(\mathrm{\ω}\right)---\left(3\right)$

Wherein: first is the frequency response sum in L bar footpath, and second is the frequency response of random noise n (t).

And the Steiner channel estimating (1) of continuous time can be represented by the formula after handling through the Teager-Kaiser operator:

${\mathrm{\Ψ}}_c\left[h\left(t\right)\right]=h\left(t\right)h^{*}\left(t\right)-\frac{1}{2}[h(t-1)h^{*}(t+1)+h(t+1)h^{*}(t-1)]$

$\frac{1}{T_c^2}[{\left(\underset{l=1}{\overset{L}{\mathrm{\Σ}}}{\mathrm{\α}}_l\mathrm{sgn}(t-{\mathrm{\τ}}_i)\mathrm{\Π}(t-{\mathrm{\τ}}_l,T_c)\cos {\mathrm{\θ}}_l\right)}^2+{\left(\underset{l=1}{\overset{L}{\mathrm{\Σ}}}{\mathrm{\α}}_l\mathrm{sgn}(t-{\mathrm{\τ}}_l)\mathrm{\Π}(t-{\mathrm{\τ}}_l,T_c)\sin {\mathrm{\θ}}_l\right)}^2]$

$+\frac{1}{{2T}_c}[h^{*}\left(t\right)\left(\underset{l=0}{\overset{L}{\mathrm{\Σ}}}{\mathrm{\α}}_l\mathrm{\δ}(t-{\mathrm{\τ}}_l)e^{{\mathrm{j\θ}}_l}\right)+h\left(t\right)\left(\underset{l=0}{\overset{L}{\mathrm{\Σ}}}{\mathrm{\α}}_l\mathrm{\δ}(t-{\mathrm{\τ}}_l)e^{-j{\mathrm{\θ}}_l}\right)]---\left(4\right)$

Here:

Be one and have length 2T _c, be the rectangular function at center with the zero point, sgn (t) is-symbol function, h ^*(t) expression is got conjugation to h (t).

From the contrast of formula (3) and (4) as can be seen, after the processing of preliminary channel impulse response estimation through the Teager-Kaiser operator of Steiner channel estimating output, the local smoothness properties that it is apparent that the Teager-Kaiser operator has suppressed noise item wherein, and high-pass filtering has simultaneously kept effective multipath signal item well.

In the TD-SCDMA system,, obtain 128 channel estimating training chips from 144 16 chips that may be subjected to intersymbol interference of training chips to remove front end.Behind 128 point discrete Fourier conversion and discrete inverse-Fourier transform, obtain 128 discrete time Steiner channel impulse response estimation.Because community user is counted kcell=8, then the length of each user's window is 16, after handling through the Teager-Kaiser operator, can be represented by the formula:

t _k，m＝Ψ _d[h _k，m]，m＝1…，16 (6)

Here h _{K, m}Be m channel impulse response in k user's window.

Because the Teager-Kaiser operator is an energy operator, the mould value of calculating formula (6) is preliminary channel impulse response performance number after treatment:

p _k，m＝‖t _k，m‖，m＝1，…，16 (7)

Choose first thresholding according to the power maximum:

λ ₁＝k ₁max(p _k，m) (8)

Wherein: proportionality coefficient k ₁Can be according to actual conditions value in 0.3～0.5.

To be multipath signal greater than the judgement of this thresholding, be considered as noise, calculate the noise variance σ that estimates then less than all performance numbers of this thresholding ²Promptly get noise power.

Choose second thresholding according to the multiple of noise power again:

λ ₂＝k ₂σ ² (9)

Wherein: multiple k ₂Can in 3～8, round numerical value according to actual conditions.

Determine total thresholding then:

$\mathrm{\λ}=\left\{\begin{array}{cc}{\mathrm{\λ}}_1& \mathrm{if}{\mathrm{\λ}}_1>{\mathrm{\λ}}_2\\ {\mathrm{\λ}}_2& \mathrm{if}{\mathrm{\λ}}_1\≤{\mathrm{\λ}}_2\end{array}\right.---\left(10\right)$

From the Steiner channel impulse response estimation, extract useful multipath signal according to thresholding.

L-G simulation test

Be the actual effect of checking searching method of the present invention, l-G simulation test the TD-SCDMA down link.

The l-G simulation test condition: it is that 8, modulation system are the multipath channel models casel that QPSK, spreading factor SF=16, channel model adopt the 3GPP suggestion that community user is counted kcell=8, activated code channel number, this model has two different paths, and wherein the second path is respectively 10dB and 2928ns with respect to the decline and the delay in article one path.

In the l-G simulation test, at first calculate from 10000 o'clock actual search to the path, compare with desirable multipath number then, obtain the probability that obtains on the statistical significance.

Fig. 4 adopts searching method of the present invention and adopts the channel path of threshold processing method in the prior art to estimate to obtain the probability comparison diagram.Wherein abscissa is signal to noise ratio E _b/ N ₀, ordinate is the probability that obtains of effective multipath signal.Searching method of the present invention is adopted in curve (1) expression, and curve (2) expression adopts the Steiner estimator of prior art to estimate the method for getting thresholding again behind the channel impulse response.By curve (1), curve (2) more as can be known, in signal to noise ratio is-10 to 6dB scope, adopt searching method of the present invention to improve channel path and estimate to obtain probability about 10%, it is equivalent to about 10dB, significantly suppressed noise, the bigger accuracy rate that improves multipath signal search after the channel impulse response estimation.

Fig. 5 is the ZF ZF combined detection performance comparison diagram that adopts this method and adopt conventional threshold processing method.Wherein abscissa is signal to noise ratio E _b/ N ₀, ordinate is the average original error rate that joint detection receiver receives judgement.Searching method of the present invention is adopted in curve (1) expression, and curve (2) expression adopts the Steiner estimator of prior art to estimate the method for getting thresholding again behind the channel impulse response.。More as can be known, in signal to noise ratio is 0 to 20dB scope, adopt the average original error rate of searching method of the present invention all low by curve (1), curve (2), significantly improved combined detection performance than art methods.

Searching method of the present invention also can have other various embodiments; under the situation of spirit that does not deviate from searching method of the present invention and essence thereof; those skilled in the art work as can make various corresponding changes or distortion according to searching method of the present invention, but these corresponding changes or distortion all belong to the claim protection range of searching method of the present invention.

Claims (4)

1, the channel path estimation and search method of the multidiameter fading channel of a kind of TD-SCDMA system adopts the Steiner channel estimator to obtain preliminary channel impulse response signal, it is characterized in that: according to formula

${\mathrm{\Ψ}}_c\left[h\left(t\right)\right]=h\left(t\right)h^{*}\left(t\right)-\frac{1}{2}[h(t-1)h^{*}(t+1)+h(t+1)h^{*}(t-1)]$

$\frac{1}{T_c^2}[{\left(\underset{l=1}{\overset{L}{\mathrm{\Σ}}}{\mathrm{\α}}_l\mathrm{sgn}(t-{\mathrm{\τ}}_l)\mathrm{\Π}(t-{\mathrm{\τ}}_l,T_c)\cos {\mathrm{\θ}}_l\right)}^2+{\left(\underset{l=1}{\overset{L}{\mathrm{\Σ}}}{\mathrm{\α}}_l\mathrm{sgn}(t-{\mathrm{\τ}}_l)\mathrm{\Π}(t-{\mathrm{\τ}}_l,T_c)\sin {\mathrm{\θ}}_l\right)}^2]$

$+\frac{1}{{2T}_c}[h^{*}\left(t\right)\left(\underset{l=0}{\overset{L}{\mathrm{\Σ}}}{\mathrm{\α}}_l\mathrm{\δ}(t-{\mathrm{\τ}}_l)e^{j{\mathrm{\θ}}_l}\right)+h\left(t\right)\left(\underset{l=0}{\overset{L}{\mathrm{\Σ}}}{\mathrm{\α}}_l\mathrm{\δ}(t-{\mathrm{\τ}}_l)e^{-{\mathrm{j\θ}}_l}\right)]$

And formula

Utilize the Teager-Kaiser energy operator that the preliminary channel impulse response signal of Steiner channel estimator output is handled, again according to formula p _{K, m}=|| t _{K, m}||, m=1 ..., 16, formula λ ₁=k ₁Max (p _{K, m}), formula λ ₂=k ₂σ ²And formula $\mathrm{\λ}=\left\{\begin{array}{cc}{\mathrm{\λ}}_1& \mathrm{if}{\mathrm{\λ}}_1>{\mathrm{\λ}}_2\\ {\mathrm{\λ}}_2& \mathrm{if}{\mathrm{\λ}}_1\≤{\mathrm{\λ}}_2\end{array}\right.$ Channel impulse response calculated signals power and the estimating noise power that utilization is handled through the Teager-Kaiser operator also is provided with total thresholding, extracts the channel impulse response of each user's window then respectively by total thresholding; Wherein: formula

${\mathrm{\Ψ}}_c\left[h\left(t\right)\right]=h\left(t\right)h^{*}\left(t\right)-\frac{1}{2}[h(t-1)h^{*}(t+1)+h(t+1)h^{*}(t-1)]$

$\frac{1}{T_c^2}[{\left(\underset{l=1}{\overset{L}{\mathrm{\Σ}}}{\mathrm{\α}}_l\mathrm{sgn}(t-{\mathrm{\τ}}_l)\mathrm{\Π}(t-{\mathrm{\τ}}_l,T_c)\cos {\mathrm{\θ}}_l\right)}^2+{\left(\underset{l=1}{\overset{L}{\mathrm{\Σ}}}{\mathrm{\α}}_l\mathrm{sgn}(t-{\mathrm{\τ}}_l)\mathrm{\Π}(t-{\mathrm{\τ}}_l,T_c)\sin {\mathrm{\θ}}_l\right)}^2]$

$+\frac{1}{{2T}_c}[h^{*}\left(t\right)\left(\underset{l=0}{\overset{L}{\mathrm{\Σ}}}{\mathrm{\α}}_l\mathrm{\δ}(t-{\mathrm{\τ}}_l)e^{j{\mathrm{\θ}}_l}\right)+h\left(t\right)\left(\underset{l=0}{\overset{L}{\mathrm{\Σ}}}{\mathrm{\α}}_l\mathrm{\δ}(t-{\mathrm{\τ}}_l)e^{-{\mathrm{j\θ}}_l}\right)]$

Be the expression formula of the frequency response of the Steiner channel estimating of continuous time after handling through the Teager-Kaiser operator; Formula

Be one and have length 2T _c, be the rectangular function at center with the zero point, sgn (t) is-symbol function, h ^*(t) expression is got conjugation to h (t); In above-mentioned formula, L represents multipath number, T _cThe expression processing cycle, a _l, θ _lAnd τ _l, represent amplitude, phase place and the delay in l bar footpath respectively, t _{K, m}M the channel impulse response of expression in k user's window that the Teager-Kaiser operator is handled, p _{K, m}Be preliminary channel impulse response performance number after treatment, λ ₁Be first thresholding, k ₁Be first thresholding proportionality coefficient, σ ²Be noise variance, λ ₂Be second thresholding, k ₂Be second thresholding proportionality coefficient, λ is total thresholding.

2, according to the described searching method of claim 1, it is characterized in that: the mould value of calculating Teager-Kaiser energy operator operation result promptly obtains preliminary channel impulse response performance number after treatment.

3, according to the described searching method of claim 1, it is characterized in that: first thresholding λ ₁For the 0.3-0.5 of maximum power value doubly, i.e. k ₁Value 0.3-0.5.

4, according to the described searching method of claim 1, it is characterized in that: second thresholding λ ₂For the 3-8 of noise power doubly, i.e. k ₂Value 3-8.

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