CN100502371C - A Channel Estimation Method in MIMO-OFDM System - Google Patents

Abstract

This invention relates to input cross frequency multiple system signal channel estimation method in wireless communication technique field, which comprises the following steps: according to the system to receive cross training sequence and to isolate multiple antenna into several parallel single antenna signal channel to get initial signal estimation; getting frequency OLS estimation on initial channel estimation for square limitation according to system signal zone length L. This invention method uses system characteristics to isolate multiple channel to get single antenna initial channel and then uses rough channel zone responding length to process non spectrum filter section to get rough bar LS frequency signal channel estimation with high accuracy.

Description

Channel estimation methods in a kind of multiple-input and multiple-output-ofdm system

Technical field

The present invention relates to the channel estimation methods in a kind of multiple-input and multiple-output-ofdm system, relate in particular to the processing method of robust least square (hereinafter to be referred as LS) channel estimating when having unloaded ripple in multiple-input and multiple-output-OFDM (hereinafter to be referred as MIMO-OFDM) system, belong to wireless communication technology field.

Background technology

Adopt MIMO-OFDM technology under the prerequisite that does not increase channel width and transmitting power, to significantly improve power system capacity.No matter be carry out data stream separation at receiving terminal, decoding when empty, data coherency detects or carry out precoding at transmitting terminal, it all is necessary that precise channels is estimated.Channel estimating in MIMO-ofdm system will be estimated the channel parameter between every pair of transmit receive antenna.Not only wait that the number of estimating parameter obviously increases a lot than a single aerial system this moment, and because received signal is the stack of each transmission antennas transmit signal, exist between all the other each antennas and disturb, can have a strong impact on performance for estimating channel and the further decoding performance that influences system, so channel estimating is a problem very crucial in MIMO-ofdm system.

In MIMO-ofdm system can by the design quadrature training sequence separate belong to different antennae to channel, the channel estimating in MIMO-ofdm system has just changed into the channel estimation problems in a single aerial system like this.The performance of mimo system is more more responsive to precision of channel estimation than a single aerial system, channel estimation errors can cause many antenna interference in MIMO-ofdm system in demodulating process, traditional a single aerial system channel estimation methods can not satisfy the performance requirement of mimo system, therefore needs the higher channel estimation methods of research precision.

Traditional single antenna ofdm system utilizes training sequence to carry out the LS channel estimating at frequency domain usually.Generally training sequence is designed to frequency domain and is ± 1 sequence in order to reduce computation complexity, when carrying out frequency domain LS channel estimating, can avoid matrix inversion operation like this, thereby can just can obtain frequency domain channel on corresponding each subcarrier by simple multiplying.Training sequence by the design quadrature in MIMO-ofdm system can be converted into the problem that mimo channel is estimated the problem that single antenna channel is estimated, still can use said method to obtain frequency domain channel and estimate.But such frequency domain LS precision of channel estimation generally is not enough for MIMO-ofdm system, thereby will cause the remarkable decline of systematic function.Frequency domain LS estimates not utilize the prior information of any channel, generally can know some prior informations of channel in the reality, such as rough channel time domain response length L, utilize this information to estimate that further carrying out filtering improves channel estimating performance to frequency domain LS.All subcarriers all are used for transmission signals when system, are called entire spectrum filtering in conjunction with the method for above-mentioned filtering.General ofdm system can vacate the direct current carrier wave usually and several high frequency subcarriers reduces problems such as direct current biasing and adjacent-channel interference, has same problem in MIMO-ofdm system, therefore has unloaded ripple equally.Call effective subcarrier removing unloaded ripple all subcarriers in addition.When there was unloaded ripple in system, the method that the length information that utilizes channel time domain to respond carries out filtering was called non-entire spectrum filtering.The estimation error variance difference of frequency domain channel estimated value on different subcarriers that adopts non-entire spectrum filtering to obtain, wherein the channel estimation error variance on the subcarrier of contiguous unloaded ripple is bigger.For the ofdm communication system based on the bag transmission, any one subcarrier causes error code because of evaluated error is excessive, all can seriously reduce systematic function.Therefore if want to improve the actual ofdm system performance that free carrier wave is arranged, must address the above problem.The performance of cyclic shift sign indicating number quadrature training sequence is best when frequency deviation and phase noise, so cyclic shift sign indicating number quadrature training sequence has better comprehensive performance.

Summary of the invention

The objective of the invention is to propose the channel estimation methods in a kind of multiple-input and multiple-output-ofdm system, at practical MIMO-ofdm system that free carrier wave is arranged, solve channel estimating big problem of estimation error variance on the subcarrier of contiguous unloaded ripple when having unloaded ripple.

Channel estimation methods in multiple-input and multiple-output-ofdm system that the present invention proposes comprises following each step:

(1) according to the quadrature training sequence that receives in multiple-input and multiple-output-ofdm system, multi-antenna channel is separated into a plurality of parallel single antenna channel, the initial channel estimation of the single antenna channel after obtaining separately is designated as j transmitting antenna to the initial channel estimation between i the reception antenna

(2) according to channel time domain response length information L in the system, respectively above-mentioned initial channel estimation is carried out the non-entire spectrum filtering of square restriction, obtain frequency domain least square channel estimating, be designated as H ^Fine

Above-mentioned channel estimation methods wherein is separated into multi-antenna channel the method for a plurality of parallel single antenna channel, may further comprise the steps:

(1) receive the radiofrequency signal that sends in multiple-input and multiple-output-ofdm system, carry out down-frequency conversion, and periodic sampling, the base-band digital received signal obtained;

(2) from the received signal of each reception antenna of receiver, intercepting is used for the data of the quadrature training sequence of channel estimating, adopts the frequency domain least square method to obtain unsegregated domain channel response H _All

(3) according to above-mentioned quadrature training sequence, with above-mentioned unsegregated domain channel response H _AllBe separated into a plurality of parallel single antenna channel, the initial channel estimation of each single antenna channel after obtaining separating

Above-mentioned channel estimation methods, wherein according to channel time domain response length information L, the method to initial channel estimation is carried out the non-entire spectrum filtering of square restriction may further comprise the steps:

(1) estimates from frequency domain initial

In the corresponding element of all effective subcarriers in intercepting and the system, constitute the frequency domain initial estimate vector of effective subcarrier, be designated as H _Cut

(2) from standard fast fourier transform matrix F, intercept and the corresponding row of above-mentioned all effective subcarriers, and be listed as, constitute a part fast fourier transform matrix F with the corresponding preceding L of channel time domain response length L _p

(3) utilize square non-entire spectrum filtering method of restriction, to the frequency domain initial estimate vector H of above-mentioned effective subcarrier _CutCarry out filtering, the frequency domain channel that obtains on effective subcarrier is estimated

(4) above-mentioned

In with the corresponding position of unloaded ripple on insert 0, obtain frequency domain least square method channel estimating H ^Fine

Channel estimation methods in multiple-input and multiple-output-ofdm system that the present invention proposes, for the MIMO-ofdm system that utilizes quadrature training sequence, utilize the orthogonal property of training sequence that multi-antenna channel is separated into a plurality of parallel single antenna channel, the initial channel estimation of the single antenna channel that obtains separating earlier.Utilize rough channel time domain response length information L that the initial channel estimation of the single antenna channel separated is carried out the non-entire spectrum filtering of square restriction again, obtain the higher robust LS frequency domain channel of precision and estimate.If length of field was L when channel was true _Real, require channel time domain length L 〉=L among the present invention _Real, and L approaches L more _RealPerformance is good more.The inventive method has the following advantages:

(1) the present invention only needs rough channel time domain response length information, only requires L 〉=L _RealGet final product, be convenient in the reality realize;

(2) the present invention has reduced the dimension of matrix by non-entire spectrum filtering, thereby has reduced computation complexity;

(3) the present invention has solved the big problem of estimation error variance on the contiguous unloaded marble carrier wave of non-entire spectrum filtering effectively by adopting the diagonal square restriction that loaded simple realization;

(4) diagonal loading coefficient α can obtain by prior search among the present invention, can search out the diagonal loading coefficient corresponding to different channels time-domain response length L in practice in advance, reduces amount of calculation.

Description of drawings

Fig. 1 is the FB(flow block) of an embodiment of the inventive method.

Fig. 2 is an embodiment of the inventive method, receives in MIMO-ofdm system at 44, adopts the structure chart of the training sequence of cyclic shift sign indicating number quadrature.

Embodiment

Channel estimation methods in multiple-input and multiple-output-ofdm system that the present invention proposes, at first according to the quadrature training sequence that receives in multiple-input and multiple-output-ofdm system, multi-antenna channel is separated into a plurality of parallel single antenna channel, the initial channel estimation of the single antenna channel after obtaining separately is designated as j transmitting antenna to the initial channel estimation between i the reception antenna

According to channel time domain response length information L, wherein L 〉=L in the system _Real, respectively above-mentioned initial channel estimation is carried out the non-entire spectrum filtering of square restriction, obtain frequency domain least square channel estimating, be designated as H ^Fine

In the said method, the method that multi-antenna channel is separated into a plurality of parallel single antenna channel is: at first receive the radiofrequency signal that sends in multiple-input and multiple-output-ofdm system, carry out down-frequency conversion, and periodic sampling, the base-band digital received signal obtained; From the received signal of each reception antenna of receiver, intercepting is used for the data of the quadrature training sequence of channel estimating, adopts the frequency domain least square method to obtain unsegregated domain channel response H _AllAccording to above-mentioned quadrature training sequence, with above-mentioned unsegregated domain channel response H _AllBe separated into a plurality of parallel single antenna channel, the initial channel estimation of each single antenna channel after obtaining separating

In the said method, according to channel time domain response length information L, the method for initial channel estimation being carried out the non-entire spectrum filtering of square restriction is: estimate from frequency domain initial

In the corresponding element of all effective subcarriers in intercepting and the system, constitute the frequency domain initial estimate vector of effective subcarrier, be designated as H _CutFrom standard fast fourier transform matrix F, intercept and the corresponding row of above-mentioned all effective subcarriers, and be listed as, constitute a part fast fourier transform matrix F with the corresponding preceding L of channel time domain response length L _pUtilize square non-entire spectrum filtering method of restriction, to the frequency domain initial estimate vector H of above-mentioned effective subcarrier _CutCarry out filtering, the frequency domain channel that obtains on the higher effective subcarrier of precision is estimated

Can utilize following diagonal loading technique to realize,

$H_{\mathrm{cut}}^{\mathrm{fine}}=F_p{(F_p^H{F}_p+\mathrm{\αI})}^{-1}{F}_p^H\·H_{\mathrm{cut}},$

In the following formula, α is the diagonal loading coefficient, and L is relevant with channel time domain response length, and its optimal value can be according to the known rough prior information of channel circumstance is obtained by search in advance; Above-mentioned

In with the corresponding position of unloaded ripple on insert 0, obtain frequency domain least square method channel estimating H ^Fine

Introduce the embodiment of the inventive method below in conjunction with Fig. 1, cyclic shift is counted between the Q representative group among Fig. 1, and cyclic shift is counted in the P representative group:

MIMO of the present invention-ofdm system robust LS channel estimation methods at first will separate and belong to the right channel of different transmit receive antennas.At 4 the 4 cyclic shift sign indicating number quadrature training sequences of receiving shown in Figure 1, at first from the training sequence that each reception antenna receives, take out the long code that is used for channel estimating, adopt frequency domain LS to estimate to obtain all transmitting antennas superpose and channel response.

If s _tThe elementary cell of expression long code, H _bBe the channel frequency domain response corresponding to a long code elementary cell, N is a noise, receives data so and can be expressed as Y=H _bs _t+ N.

Can be expressed as corresponding to a long code elementary cell of all transmitting antenna stacks with channel response ${\hat{H}}_b={\mathrm{Ys}}_t^{-1}.$

In real system, because the value of each element of long code only may be ± 1 (s _tIn the value of each element can only be ± 1, and it is diagonal matrix, therefore $s_t^{-1}=s_t$ ), following formula can be write as: ${\hat{H}}_b={\mathrm{Ys}}_t.$

Utilize the sign indicating number orthogonal property and the cyclic shift characteristic of training sequence that multi-antenna channel is separated into a plurality of parallel single antenna channel below respectively.The training sequence of sign indicating number orthohormbic structure can be expressed as:

$S_t=C\⊗s_t,$

Wherein, C indication code orthogonal matrix, and CC ^H=I,

Expression Kronecker is long-pending, S _tRepresent whole sign indicating number quadrature training sequence.By S _tOn the estimated whole long code training sequence that goes out with channel response H _AllFor:

$H_{\mathrm{all}}=C\⊗{\hat{H}}_b.$

The training sequence of sign indicating number quadrature separately not during on the same group channel response method as follows:

$H_{\mathrm{decoupling}}=H_{\mathrm{all}}{C}^H=(C\⊗{\hat{H}}_b)C^H=\left({\mathrm{CC}}^H\right)\⊗{\hat{H}}_b=I\⊗{\hat{H}}_b,$

Wherein, H _DecouplingThe expression component from after channel, be time quadrature, the channel that belongs to has so not on the same group just separated.

The characteristic of cyclic shift is separated the channel response on the different antennae in same group in time domain in utilizing on the same group again.Only consider a group below.Expression formula according to received signal:

y _1，2(n)＝s(n)⊙h ₁(n)+s((n-N _cs) _N)⊙h ₂(n)+v(n)

＝s(n)⊙(h ₁(n)+h ₂((n-N _cs) _N))+v(n)，

Wherein, s ((n-N _Cs) _N) represent s (n) cyclic shift N _CsLater sequence, N be ofdm system FFT/IFFT count h ₁(n) and h ₂(n) represent in this group time domain channel response between first and second transmitting antenna and the reception antenna respectively, ⊙ represents circular convolution.

Work as N _CsDuring 〉=L, h ₁(n) and h ₂(n) be quadrature in time domain, can separate.With H _DecouplingTransform to time domain, separate h in time domain ₁(n) and h ₂(n), more respectively to h ₁(n) and h ₂(n) do the FFT conversion and can obtain channel frequency domain response on each antenna

Thereby MIMO-OFDM channel just is separated into a plurality of single antenna channel, and the initial channel estimation of each single antenna channel is

Each carries out following processing respectively to the channel after separating.Getting frequency domain initial estimates

In form a vector corresponding to the element of all effective subcarriers, be designated as H _CutGet in the standard FFT matrix F corresponding to the row of effective subcarrier and preceding L row and obtain part FFT matrix, be designated as F corresponding to channel time domain response length L _pTo H _CutCarry out non-entire spectrum filtering, and introduce square restriction and obtain the higher robust LS frequency domain channel of precision and estimate, can realize a square restriction, reduce estimation error variance on the contiguous unloaded marble carrier wave, thereby obtain by the diagonal loading technique:

$H_{\mathrm{cut}}^{\mathrm{fine}}=F_p{(F_p^H{F}_p+\mathrm{\αI})}^{-1}{F}_p^H\·H_{\mathrm{cut}},$

Wherein, α is the diagonal loading coefficient, can obtain optimum α value, channel time domain response length L difference, then F by search _pThereby the value of difference α is also different.

In insert 0 on the position corresponding to unloaded ripple, estimate H thereby obtain robust LS frequency domain channel ^Fine

Claims (2)

1. A method for channel estimation in MIMO-OFDM system, characterized in that the method comprises the following steps: (1) According to the orthogonal training sequence received in the MIMO-OFDM system, the multi-antenna channel is separated into multiple parallel single-antenna channels, and the initial channel estimation of the separated single-antenna channel is obtained , denote the initial channel estimate between the jth transmit antenna and the ith receive antenna as

(2) According to the channel time-domain response length information L in the system, perform square-limited non-full-spectrum filtering on the above-mentioned initial channel estimates respectively, and obtain the frequency-domain least squares channel estimate, denoted as H ^fine , the specific process includes the following steps: (a) Initial estimation from the frequency domain

Intercept the elements corresponding to all effective subcarriers in the system to form the frequency domain initial estimation vector of effective subcarriers, denoted as H _cut ; (b) Intercepting the rows corresponding to all the above-mentioned effective subcarriers from the standard FFT matrix F, and the first L columns corresponding to the channel time-domain response length L, to form a partial FFT matrix _Fp ; (c) Use the square-limited non-full spectrum filtering method to filter the frequency-domain initial estimation vector H _cut of the effective subcarriers above to obtain the frequency-domain channel estimation on the effective subcarriers

(d) in the above

0 is inserted in the position corresponding to the empty carrier to obtain the frequency domain least square method channel estimation H ^fine . 2. The channel estimation method according to claim 1, wherein said method of separating a multi-antenna channel into multiple parallel single-antenna channels comprises the following steps: (1) Receive the radio frequency signal sent in the MIMO-OFDM system, perform down-conversion, and periodically sample to obtain the baseband digital receiving signal; (2) From the received signal of each receiving antenna of the receiver, intercept the data of the orthogonal training sequence used for channel estimation, and obtain the unseparated frequency domain channel response _Hall by using the frequency domain least squares method; (3) According to the above-mentioned orthogonal training sequence, the above-mentioned unseparated frequency-domain channel response _Hall is separated into multiple parallel single-antenna channels, and the initial channel estimation of each separated single-antenna channel is obtained

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