CN104426820A - Method for channel estimation in LTE system - Google Patents

Abstract

The invention discloses a method for channel estimation in an LTE system, the method including the steps of: obtaining the code division relation between each of the odd sub-carriers and even sub-carriers of MU LS channel estimation and the ideal channel estimation of two users in accordance with the pilot frequency sequence orthogonal code division multiplexing relation between the two users; respectively obtaining the SU LS channel estimation of the first user and the SU LS channel estimation of the second user in accordance with the code division relation through channel separation; and sequentially filtering the SU LS channel estimation of the first user and the SU LS channel estimation of the second user to obtain the channel estimation of the first user and the channel estimation of the second user. The method is applicable to two-user multi-input multi-output of uplink in the LTE system, and can reduce the implementation complexity on the basis of ensuring the channel estimation performance.

Description

A kind of method of channel estimating in LTE system

Technical field

The application relates to communication technical field, more specifically, relates to the method for channel estimating in a kind of LTE system.

Background technology

Along with the growth of number of users and user's request, wireless communication system needs the transfer of data bearing explosive increase, and limited Radio Resource especially frequency spectrum resource becomes more and more nervous along with radio communication service and developing rapidly of broadband data service.In the face of this contradiction, operation commercial city wishes that system has higher message capacity, higher spectrum efficiency.Multiple-input, multiple-output (MIMO) technology, as the core technology of LTE communication system, becomes and realizes utilizing confined space resource to improve the inevitable choice of spectrum efficiency.

The MIMO technology of LTE is on multi-antenna array hardware foundation, under certain free space channel condition, adopt specific Space Time Coding, modulation and other signal processing technologies, make the multichannel input/output signal of isospace at the same time can keep the integration radio communication technology of respective transmission reliability as much as possible.

Wireless signal is in free space transmission process, and the spread spectrum become during delay spread, the channel of multipath effect, the angle spread, noise jamming etc. of space correlation all will cause signal distortion, bring many difficulties to Signal reception.Under MIMO scene, multiple signals are in free space superposed transmission, and receiver also needs to isolate influencing each other between the MIMO signal of each road, and recovering signal is to reach correct reception to greatest extent.For reduction is through mutual aliasing and through each road MIMO signal of channel distortions, in the LTE implementation framework determined, the channel estimating of receiver is just most important with channel equalization.

As the basis of channel equalization, the task of channel estimating is the time domain or the frequency-domain transmission characteristic that accurately identify channel, and channel estimating receives particularly important to the reduction of signal.Real-time LTE receiver, all except considering the performance of system algorithm, also will consider the complexity of process, the power consumption etc. of algorithm realization in real time.Therefore, channel estimating is applied to actual LTE communication system, needs comprehensive evaluation algorithm performance and algorithm complex.

LTE system is OFDM (OFDM) system, and on time synchronized basis, have employed Cyclic Prefix (CP) technology, and anti-multipath time delay and anti-fading ability by force, ensure basis for receiver side provides superperformance.LTE system uplink traffic transmission, all with CAZAC sequence pilot frequency signal, is convenient to receiver side and is used pilot-symbol aided channel estimation.In LTE channel estimating, common pilot-symbol aided channel estimation has least square (LS) and minimum mean square error criterion (MMSE) channel estimating, and the various amplification expansions that LS estimates and MMSE estimates.

LS channel estimating general principle be the difference receiving pilot tone and known pilot square reach minimum, i.e. H _lS=agrmin|Y-SH _lS|, wherein H _lSbe the LS channel estimation results on carrier wave, Y is the pilot value received, and S is known standard pilot value, and for LTE upward signal, can derive to obtain H _lS=Y*S ^*, S ^*the conjugate sequence of pilot tone S.LS algorithm can go out the channel transfer function value at pilot signal place by simple method of estimation, and easy to understand realizes, but the method does not consider noise effect, cannot the evaluated error brought of stress release treatment.Therefore, multi-user's multiple-input, multiple-output (MU-MIMO) scene of LTE system cannot be directly applied to.

MMSE channel estimation methods will carry out two-dimensional process at time-domain and frequency-domain in theory.After preliminary simplification, carrying out filtering at frequency domain can be expressed as H _mMSE=R _hH(R _hH+ σ ²(SS ^h) ^-1) ^-1h _lS, wherein H _mMSEmMSE channel estimation results, H _lSthe LS channel estimation results on carrier wave, R _hHchannel autocorrelation matrix, σ ²be additive white Gaussian noise (AWGN), S be known standard pilot value.MMSE algorithm has good channel estimating performance, but it is very complicated to calculate channel autocorrelation matrix in real time.

In LTE system application, conventional MMSE channel estimating is the method more simplified: H _mMSE=WH _lS, W is the filter designed in advance according to awgn channel parameter, namely carries out linear MMSE filtering to LS channel estimation results, and the method can be claimed to be the LMMSE channel estimation methods simplified.The LMMSE channel estimation methods simplified is comparatively simple owing to realizing, the LS channel estimating of Performance Ratio LS channel estimating and time domain denoising is all more superior, the most common in the application of LTE real system, be for single user (SU), all blanket channel estimation methods of multi-user-multiple-input and multiple-output (MU-MIMO).But under MU-MIMO scene, because the number of users that same running time-frequency resource carries is double, LMMSE channel estimation process time and resource also need double, the real-time of influential system and power consumption.

Summary of the invention

The embodiment of the present invention proposes the method for channel estimating in a kind of LTE system, can be applied in multi-user's multiple-input, multiple-output of LTE system, the basis of guarantee channel estimating performance reduces the complexity of realization.

The technical scheme of the embodiment of the present invention is as follows:

A method for channel estimating in LTE system, described method comprises:

According to the pilot frequency sequence Orthogonal Frequency Division Multiplexing relation of two users, the code of the strange subcarrier and even subcarrier and two users' perfect channel estimation that obtain multi-user least square MU LS channel estimating divides relation;

Pass through channel separation by a described code point relation, obtain the single user least square SU LS channel estimating of first user and the SU LS channel estimating of the second user respectively;

Successively filtering process is carried out to the SU LS channel estimating of first user and the SU LS channel estimating of the second user, obtain the channel estimating of first user and the channel estimating of the second user.

The described pilot frequency sequence Orthogonal Frequency Division Multiplexing relation according to two users, a code point relation for the strange subcarrier and even subcarrier and two users' perfect channel estimation that obtain MU LS channel estimating comprises:

The pilot frequency sequence of single user carries out to the multi-user's multiple-input, multiple-output MU-MIMO reference signal received the MU LS channel estimating that LS channel estimating obtains two users;

Form according to the pilot frequency sequence Orthogonal Frequency Division Multiplexing relation of two users and the MU LS channel estimating of two users, obtain described code point relation.

The SU LS channel estimating of described the SU LS channel estimating and the second user that obtain first user respectively comprises:

Divide relation by the strange subcarrier of MU LS channel estimating and the code of even subcarrier and two users' perfect channel estimation, obtain corresponding strange subcarrier MU LS channel estimating expression formula and corresponding even subcarrier MU LS channel estimating expression formula;

The SU LS channel estimating obtaining first user is added by described strange subcarrier MU LS channel estimating expression formula and described even subcarrier MU LS channel estimating expression formula;

The SU LS channel estimating of acquisition second user is subtracted each other by described strange subcarrier MU LS channel estimating expression formula and described even subcarrier MU LS channel estimating expression formula.

Described filtering process comprises linear MMSE criterion LMMSE filtering.

As can be seen from technique scheme, in embodiments of the present invention, according to the pilot frequency sequence Orthogonal Frequency Division Multiplexing relation of two users, the code of the strange subcarrier and even subcarrier and two users' perfect channel estimation that obtain MU LS channel estimating divides relation; Pass through channel separation by a described code point relation, obtain the SU LS channel estimating of first user and the SU LS channel estimating of the second user respectively; Successively filtering process is carried out to the SU LS channel estimating of first user and the SU LS channel estimating of the second user, obtain the channel estimating of first user and the channel estimating of the second user.Because SU LS channel estimation length is half of the prior art after channel separation, therefore just reduce the complexity of realization.But performance is but suitable with prior art.

Accompanying drawing explanation

Fig. 1 is the method flow schematic diagram of channel estimating in LTE system;

Fig. 2 is simulation performance schematic diagram under SCME model;

Fig. 3 is simulation performance schematic diagram in UMiNLOS environment.

Embodiment

Express clearly clear for making the object, technical solutions and advantages of the present invention, below in conjunction with drawings and the specific embodiments, the present invention is further described in more detail.

In embodiments of the present invention, according to the orthogonal property of the pilot tone adjacent sub-carrier of two users, multi-user's least square (MU LS) channel estimating of two users is separated; After being separated, single user least square (SU LS) channel estimation length of user is half of the prior art, because this reducing the complexity of realization, the basis of guarantee channel estimating performance reduces the complexity of realization.

See the method flow schematic diagram that accompanying drawing 1 is channel estimating in LTE system, specifically comprise the following steps:

For LTE uplink service MU-MIMO channel estimating, the MU number of users of LTE uplink service MU-MIMO is the scene of 2.

101, according to the pilot frequency sequence Orthogonal Frequency Division Multiplexing relation of two users, the code of the strange subcarrier and even subcarrier and two users' perfect channel estimation that obtain MU LS channel estimating divides relation.

A () determines the MU LS channel estimation value of user.

First, MU-MIMO two users wireless signal superposes when free space transmission, and through additive white Gaussian noise (AWGN) channel, the pilot signal Y that receiving terminal receives can be expressed as follows:

Y(k,l)＝H ₀(k,l)S ₀(k,l)+H ₁(k,l)S ₁(k,l)+N(k,l) （1）

K represents carrier wave, l conventional letter number.H() function stand ideally subscriber channel response, S() function stand user pilot frequency sequence.Subscript 0 represents first user, and subscript 1 represents the second user.

The pilot frequency sequence of single user carries out to the MU-MIMO reference signal received the MU LS channel estimating that MU LS channel estimating obtains two users.MU LS channel estimating not only comprises perfect channel estimation and the noise of this user, also comprises the perfect channel estimation of another user.Therefore, the MULS channel estimating of two users can be obtained by the pilot frequency sequence of single user.

${\tilde{H}}_0(k,l)=Y(k,l){S^{*}}_0(k,l)=H_0(k,l)+H_1(k,l)S_1(k,l){S^{*}}_0(k,l)+N(k,l){S^{*}}_0(k,l)---\left(2\right)$

The product of the MU-MIMO reference signal received and the pilot frequency sequence conjugation of two users equals the MULS channel estimating of user.

Wherein, N(k, l) represent white noise.The MU LS channel estimation value of user obtain under the impact of white noise.

B the strange carrier wave of () MU LS channel estimating and the code of even subcarrier and two users' perfect channel estimation divide relation.

The pilot tone of LTE reverse link traffic channel is CAZAC sequence, and according to LTE protocol, 2 MU user's pilot frequency sequences exist following relation: wherein S ₁(k, l), S ₀(k, l) is the second user, the pilot tone of first user at symbol k carrier wave l place respectively; Delta_n _csfor the integer of [1,11], it is two users' cyclic shift difference.After considering 2 user's pilot superimposition of MU, mutual minimum interference, is set to delta_n _cs=12/2, now

S ₁(k,l)＝S ₀(k,l)e ^jπk（3）

K=0,1 ... K-1, K are the length of pilot frequency sequence.

Utilize user's pilot frequency sequence S of first user in (3) ₀the local reference sequences S of (k, l) and the second user ₁the relation of (k, l) existing odd even subcarrier, i.e. the pilot frequency sequence Orthogonal Frequency Division Multiplexing relation of two users: S ₀(2m, l)=S ₁(2m, l), S ₀(2m+1, l)=-S ₁(2m+1, l), k=2m.

The odd even subcarrier of MU LS sequence of can deriving and the code point relation of two users' perfect channel estimation as follows:

Even subcarrier MU LS channel estimating

$\tilde{H}(2m,l)=H_0(2m,l)+H_1(2m,l)S_0(2m,l){S^{*}}_0(2m,l)+N(2m,l){S^{*}}_0(2m,l)$ （4）

$=H_0(2m,l)+H_1(2m,l)+N(2m,l){S^{*}}_0(2m,l)$

Strange subcarrier MU LS channel estimating

$\tilde{H}(2m+1,l)=H_0(2m+1,l)-H_1(2m+1,l)S_0(2m+1,l){S^{*}}_0(2m+1,l)+N(2m+1,l){S^{*}}_0(2m+1,l)$ （5）

$=H_0(2m+1,l)-H_1(2m+1,l)+N(2m+1,l){S^{*}}_0(2m+1,l)$

102, pass through channel separation by a code point relation for strange subcarrier MU LS channel estimating and even subcarrier MU LS channel estimating, obtain the SU LS channel estimating of first user and the SU LS channel estimating of the second user respectively.

(4) be strange subcarrier MU LS channel estimating, (5) are even subcarrier MU LS channel estimating.The perfect channel estimation of MU LS channel odd even subcarrier and two users forms code division multiplexing relation.

((4)+(5))/2, can obtain

$\frac{\tilde{H}(2m,l)+\tilde{H}(2m+1,l)}{2}=\frac{H_0(2m,l)+N(2m,l){S^{*}}_0(2m,l)+H_0(2m+1,l)+N(2m+1,l){S^{*}}_0(2m+1,l)}{2}---\left(6\right)$

((4)-(5))/2, can obtain:

$\frac{\tilde{H}(2m,l)+\tilde{H}(2m+1,l)}{2}=\frac{H_1(2m,l)+N(2m,l){S^{*}}_0(2m,l)+H_1(2m+1,l)-N(2m+1,l){S^{*}}_0(2m+1,l)}{2}---\left(7\right)$

Because the coherence bandwidth of general LTE system is greater than 30kHz, the channel variation of adjacent sub-carrier is very little, can be similar to and think constant, that is:

H(2m,l)＝H(2m+1,l) （8）

Known according to formula (8):

H ₀(2m,l)＝H ₀(2m+1,l) （9）

H ₁(2m,l)＝H ₁(2m+1,l) （10）

Following result can be solved in conjunction with (6) and (9):

$H_0(2m,l)=H_0(2m+1,l)=\frac{{\tilde{H}}_0(2m,l)+{\tilde{H}}_0(2m+1,l)}{2}-\frac{N(2m,l){S^{*}}_0(2m,l)+N(2m+1,l){S^{*}}_0(2m+1,l)}{2}$

（11）

Following result can be solved in conjunction with (7) and (10):

$H_1(2m,l)=H_1(2m+1,l)=\frac{{\tilde{H}}_0(2m,l)-{\tilde{H}}_0(2m+1,l)}{2}-\frac{N(2m,l){S^{*}}_0(2m,l)-N(2m+1,l){S^{*}}_0(2m+1,l)}{2}$

（12）

The SU LS channel estimating comprising perfect channel estimation and white noise of first user and the second user in up MU-MIMO two users can be obtained according to (11) and (12), be respectively:

${\tilde{H}}_{0\mathrm{LS}}(2m,l)={\tilde{H}}_{0\mathrm{LS}}(2m+1,l)=\frac{{\tilde{H}}_0(2m,l)+{\tilde{H}}_0(2m+1,l)}{2}$ （13）

$=H_0(2m,l)+\frac{N(2m,l){S^{*}}_0(2m,l)+N(2m+1,l){S^{*}}_0(2m+1,l)}{2}$

${\tilde{H}}_{1\mathrm{LS}}(2m,l)={\tilde{H}}_{1\mathrm{LS}}(2m+1,l)=\frac{{\tilde{H}}_0(2m,l)+{\tilde{H}}_0(2m+1,l)}{2}$ （14）

$=H_1(2m,l)+\frac{N(2m,l){S^{*}}_0(2m,l)-N(2m+1,l){S^{*}}_0(2m+1,l)}{2}$

Through the channel separation of (13) and (14), two users SU LS channel estimation results separately can be obtained.SU LS channel estimation results perfect channel estimation containing respective user and noise item.

The SU LS channel estimating that can obtain first user is specially the SU LS channel estimating of the second user is specially wherein m=0,1 ... K/2-1.

103, successively filtering process is carried out to the SU LS channel estimating of first user and the SU LS channel estimating of the second user, obtain the channel estimating of first user and the channel estimating of the second user.

Respectively to the SU LS channel estimating of two users i=0,1 does filtering process of the prior art, such as linear minimum mean-squared error (LMMSE) filtering, and the tap number ratio of the filter coefficient of generation is used for filtering MULS channel estimating few half, and the number of bank of filters is constant.Which reduce implementation complexity, known by following emulation, systematic function is suitable with former algorithm.

In technical solution of the present invention, not only comprise noise in MU LS channel estimating, also comprise two user's perfect channel estimation compositions.The SU LS channel estimating of each user then only comprises perfect channel estimation and the noise of this user, eliminate the interference of another user, estimate to obtain MULS channel estimating to the LS of two users MU-MIMO Received signal strength by single user, channel separation is carried out to MU LS channel estimating and obtains each user SU LS channel estimating, thus obtain close to desirable channel estimating after filtering process.

The technique effect of labor technical solution of the present invention below.

In order to assess technical solution of the present invention, adopt the conventional SU LS channel estimating of difference group number different rank linear filter to MU-MIMO two users to carry out MMSE filtering, having carried out the emulation under two kinds of channel scenario.The performance of Simulation Evaluation technical solution of the present invention, under SCME model terminal translational speed 3Km/h scene, simulation performance curve as shown in Figure 2, and under UMiNLOS environment moving velocity of terminal 30Km/h scene simulation performance curve is as shown in Figure 3.

The signal to noise ratio (snr) of emulation is transmitter side SNR, and 2 users in MIMO are not necessarily identical through the reception SNR of simulated channel.Technical scheme in 12*6new method described in figure and the present invention, employ 12 groups of filters, each filter tap number is 6.Old method and conventional MU channel estimation methods (every user LS carries out MMSE filtering after estimating).

As can be seen from accompanying drawing 2, SCME model terminal speed 3Km/h scene, in identical filter complexity situation, the channel estimation methods link performance that the present invention proposes is better than conventional algorithm, and (solid line represents technical scheme of the present invention, the existing technical scheme of represented by dotted arrows), namely, under identical SNR, Block Error Rate (BLER) is less.Compared with the conventional algorithm that technical solution of the present invention and filter complexity double, performance is close.

As can be seen from accompanying drawing 3, UMiNLOS model terminal speed 30Km/h scene, the technical scheme performance of the low complexity of channel estimation methods 12*6 of the present invention and conventional method 12*12 and 24*24MMSE filtering performance are more or less the same, the most about 1dB.Wherein, solid line represents technical scheme of the present invention, the existing technical scheme of represented by dotted arrows.

Channel estimation methods in the present invention significantly simplify the computation complexity of LTE uplink service 2 user MIMO LS channel estimating, and it is follow-up according to 12*6MMSE OCC filtering method or 12*6Real LowPassInterpolation filtering, its filtering treating capacity is 1/2 of 12*12MMSE filtering, is 1/4 of 24*24MMSE filtering.Show that the channel estimation methods that the present invention proposes ensure that receptivity by accompanying drawing 2 and accompanying drawing 3 simulation analysis, one between computation complexity and performance new balance.

The above, be only preferred embodiment of the present invention, be not intended to limit protection scope of the present invention.Within the spirit and principles in the present invention all, any amendment done, equivalent replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (4)

1. the method for channel estimating in LTE system, it is characterized in that, described method comprises:

According to the pilot frequency sequence Orthogonal Frequency Division Multiplexing relation of two users, the code of the strange subcarrier and even subcarrier and two users' perfect channel estimation that obtain multi-user least square MU LS channel estimating divides relation;

Pass through channel separation by a described code point relation, obtain the single user least square SU LS channel estimating of first user and the SU LS channel estimating of the second user respectively;

Successively filtering process is carried out to the SU LS channel estimating of first user and the SU LS channel estimating of the second user, obtain the channel estimating of first user and the channel estimating of the second user.

2. the method for channel estimating in LTE system according to claim 1, it is characterized in that, the described pilot frequency sequence Orthogonal Frequency Division Multiplexing relation according to two users, a code point relation for the strange subcarrier and even subcarrier and two users' perfect channel estimation that obtain MU LS channel estimating comprises:

The pilot frequency sequence of single user carries out to the multi-user's multiple-input, multiple-output MU-MIMO reference signal received the MU LS channel estimating that LS channel estimating obtains two users;

Form according to the pilot frequency sequence Orthogonal Frequency Division Multiplexing relation of two users and the MU LS channel estimating of two users, obtain described code point relation.

3. the method for channel estimating in LTE system according to claim 1, it is characterized in that, the SU LS channel estimating of described the SU LS channel estimating and the second user that obtain first user respectively comprises:

Divide relation by the strange subcarrier of MU LS channel estimating and the code of even subcarrier and two users' perfect channel estimation, obtain corresponding strange subcarrier MU LS channel estimating expression formula and corresponding even subcarrier MU LS channel estimating expression formula;

The SU LS channel estimating obtaining first user is added by described strange subcarrier MU LS channel estimating expression formula and described even subcarrier MU LS channel estimating expression formula;

The SU LS channel estimating of acquisition second user is subtracted each other by described strange subcarrier MU LS channel estimating expression formula and described even subcarrier MU LS channel estimating expression formula.

4. the method for channel estimating in LTE system according to claim 1, it is characterized in that, described filtering process comprises linear MMSE criterion LMMSE filtering.