CN100385824C - An Adaptive Channel Estimation Method for MIMO-OFDM System - Google Patents

Abstract

The present invention discloses a channel estimation method for MIMO-OFDM systems, which comprises the transmission of data frame structures and channel estimation. Transmitted data is divided into training OFDM symbols and data transmission OFDM symbols, wherein the training symbols are composed of training pilot symbols and 0 symbols and are used for establishing the initial parameter of channel estimation, and the data transmission OFDM symbols are composed of reference pilot symbols and data symbols; an adaptive algorithm is adopted for the channel estimation. The method of the present invention has the advantage of high spectrum efficiency, and an algorithm of a receiver has the advantage of low calculating complexity.

Description

An Adaptive Channel Estimation Method for MIMO-OFDM System

Technical field:

The invention belongs to the field of wireless communication, and particularly relates to channel estimation in MIMO-OFDM system.

Background technique:

Future wireless communication systems require higher spectral efficiency to provide high-speed and reliable data transmission services. A Multiple Input Multiple Output (MIMO) wireless communication system can significantly improve the communication system capacity or communication reliability, and can also provide a compromise between the two. (See literature [L. Zheng, et al, "Diversity and Multiplexing: A Fundamental Tradeoff in Multiple-Antenna Channels, IEEE Trans. On Inform. Theory, vol.49, No.5, pp.1073-1096, May2003]). At the same time, the future mobile communication system should be a broadband system. The typical problem of broadband systems is multipath effect. In order to simplify the receiver design, OFDM modulation is considered as a competitive solution, and OFDM is used in MIMO systems, namely MIMO- The OFDM system can obtain the advantages of MIMO and OFDM technology at the same time, so it is considered to have a wide range of application prospects in future wireless communication applications. (See literature [D.Agrawal, et al., "Space-time coded OFDM for highdata-rate wireless communication over wideband channels," in IEEE Vehi.Tech.Conference, vol.3, pp.2232--2236, 1998.] and [Y.(G.) Li, et.al., "Transmit diversity for OFDM systems and its impact on high-rate data wireless networks,” IEEE J.Select.Areas Commun., vol.17, pp.1233-1243, July 1999.]

The frequency domain signal model of the MIMO-OFDM system is (as shown in Figure 1 and Figure 2):

$Y_i[\mathrm{no},k]=\underset{q=1}{\overset{m_T}{\mathrm{\Σ}}}{h}_{i,q}[\mathrm{no},k]S_q[\mathrm{no},k]+V_i[\mathrm{no},k]$ i=1, 2, ..., M _R , k = 0, 1, ..., N-1 (1)

Among them, S _q [n, k] is the signal sent by the qth transmitting antenna in the kth subcarrier in the nth OFDM symbol; N is a positive integer, indicating the number of OFDM subcarriers; let h _{i, q} [n, l] be The path fading coefficient of the lth multipath component between the qth transmit antenna and the ith receive antenna in the nth OFDM symbol: $h_{i,q}[\mathrm{no},k]=\underset{l=0}{\overset{L-1}{\mathrm{\&Sigma;}}}{h}_{i,q}[\mathrm{no},l]e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="C20041002186400182.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{2\mathrm{\&pi;kl}}{N}}$ is the channel frequency response where L is a positive integer representing the channel order; V _i [n, k] is zero-mean additive white Gaussian noise, satisfying

$\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; \{</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; no</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; k</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; ]</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; \}</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; V</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&delta;</span>}<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; i</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ]</span>\mathrm{<span\; class="notranslate">\; \&delta;</span>}<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; no</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; ]</span>\mathrm{<span\; class="notranslate">\; \&delta;</span>}<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; m</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Among them, δ[mn] takes the value of 1 when mn is 0, and is 0 in other cases. σ _V ² represents the noise variance.

In various MIMO-OFDM systems, the estimation and tracking of wideband MIMO time-frequency dual-selective fading channels is the premise and key to realize the optimal decoding of the receiver. The channel estimation technology of the traditional single-send-single-receive (SISO) OFDM system has achieved fruitful results (see Y. (G.) Li, "Pilot-Symbol-Aided Channel Estimation for OFDM in Wireless Systems", IEEE Trans On Vehicular Technology vol ..49, no.4, pp1207-1215, July 2000 and its references). Recently, the channel estimation of the MIMO-OFDM system has also attracted widespread attention. The main channel estimation methods for the MIMO-OFDM system currently proposed mainly include:

[1] Channel estimation scheme suitable for decision feedback or optimal training sequence under MMSE criterion (see literature Y. (G.) Li, "Simplified Channel Estimation for OFDM Systems with Multiple Transmit Antennas", IEEETrans.On Wireless Comm., vol.1, pp.67-75, Jan.2002),

[2] Time-domain interpolation method based on pilot symbols (see K.Lee and D.B.Williamos, "Pilot-Symbol-Assisted Channel Estimation for Space-Time Coded OFDM Systems," EURASIP Journal on Applied Signal Processing 2002: 5, 507- 516),

，et al.，“Blind ChannelIdentification and Equalization in OFDM-Based Multiantenna Systems”，IEEE Trans On SignalProcessing，vol.50，pp96-109，Jan 2002)[3] Blind channel estimation algorithm based on subspace and other methods (see literature H.

, et al., "Blind Channel Identification and Equalization in OFDM-Based Multiantenna Systems", IEEE Trans On Signal Processing, vol.50, pp96-109, Jan 2002)

The above methods are applicable to different occasions respectively, but each has some significant disadvantages. Method [1] has optimized performance, but it requires a large amount of calculation, requires strong receiver processing capability, and is expensive, so it is difficult to apply to practical wireless communication systems. The method based on training sequences requires frequent transmission of training sequences in fast fading applications. This leads to a great loss of spectral efficiency. The typical problem of the method [2] is that due to the limitation of the Nyquist sampling rate on the pilot symbol interval, the spectral efficiency loss is relatively large in the case of fast fading, and the spectral efficiency loss is proportional to the number of transmitting antennas. The typical problem of the method [3] is that the computational complexity is very large, and there will be problems such as phase ambiguity, and the practical value is not high.

Contents of the invention

The purpose of the present invention is to provide a method for channel estimation of MIMO-OFDM system, which has higher spectral efficiency and its receiver algorithm has lower computational complexity.

For the convenience of explanation, the following terms are defined:

Training pilot symbol: a symbol known at both the sending and receiving ends, transmitted by the specific subcarrier of the first OFDM symbol (i.e. training OFDM symbol) of the data frame, and its function is to make the channel estimation module of the receiver estimate using the least squares ( LS) method to estimate the initial value of the channel.

Reference pilot symbol: A symbol known to both the transmitting and receiving ends, transmitted by a specific subcarrier of the OFDM symbol (that is, the data transmission OFDM symbol) after the first OFDM symbol of the data frame, used to generate the adaptive channel tracking algorithm The input signal vector of .

Main multipath component selection (STC): From the channel time-domain impulse response estimation with a large order (consisting of more estimated values of multipath fading coefficients), according to the principle of reducing the estimation error, select less of them. The path fading coefficient is used as the estimation result of the channel time domain impulse response, and its purpose is to reduce the multipath fading coefficient, reduce the number of parameters and reduce the estimation error. See Y.(G.) Li, Simplified Channel Estimation for OFDM Systems With MultipleTransmit Antennas, IEEE Trans.On Wirel.Comm.Vol.1, pp.67-75, Jan.2002 and its references for its implementation method.

Channel impulse response truncation: From the channel time-domain impulse response estimation with a larger order (composed of more estimated values of multipath fading coefficients), according to the principle of shortening the length of the channel impulse response, from the multipath with the shortest delay Starting from fading coefficients, a specific number of multipath fading coefficients with short delays are extracted as channel impulse response estimates.

Least Mean Square Algorithm (LMS Algorithm): A typical adaptive algorithm based on the minimum mean square error criterion (MMSE). For its implementation, please refer to the literature Simon Haykin Adaptive Filter Theory, Third edition, Prentice Hall1998.

Iterative Least Squares Algorithm (RLS Algorithm): A typical adaptive algorithm based on the Least Squares Criterion (LS), its implementation can refer to the literature Simon Haykin Adaptive Filter Theory, Third edition, Prentice Hall 1998.

QR-RLS algorithm: an implementation method of RLS algorithm, its implementation can refer to the literature Simon Haykin AdaptiveFilter Theory, Third edition, Prentice Hall 1998.

A kind of new adaptive MIMO-OFDM channel estimation method of the present invention is characterized in that it comprises sending end step and receiving end step:

The sending step is carried out according to step 1 and step 2:

Step 1: Introduce training pilot symbols and reference pilot symbols to form a data frame structure

For any transmitting antenna, transmit data in a frame-by-frame manner, each frame contains N _t (N _t is a positive integer) OFDM symbols; the first OFDM symbol in the frame is a training OFDM symbol (n=0, n represents the OFDM symbol sequence number) ; N _t −1 OFDM symbols after the intra-frame training OFDM symbols are OFDM symbols for data transmission (n=1, 2, . . . , N _t −1). (as shown in Figure 3); insert training pilot symbols and insert reference pilot symbols according to the following method:

Insert training pilot symbol: in the training OFDM symbol, for the qth (where q=1, 2, ..., M _T , M _T represents the number of transmitting antennas, which is a positive integer) transmitting antenna, the first one transmits the training pilot The subcarrier number of the symbol is q-1, and a training pilot symbol is inserted every D _f0 subcarriers thereafter; for the transmitting antenna, at the non-training pilot symbol subcarrier, the transmission amplitude is 0 symbols of 0; (such as Figure 4).

N为OFDM子载波数；Insert reference pilot symbols: In any data transmission OFDM symbol, all transmit antennas use the same subcarrier to transmit reference pilot symbols; for any transmit antenna, the subcarrier sequence number of the first reference pilot symbol is k ₀ (0 ≤k ₀ <D _f1 , D _f1 is a positive integer), and then a reference pilot symbol is inserted every D _f1 subcarriers; for any transmitting antenna, at the non-reference pilot symbol subcarrier, transmit the space-time coding output data symbol. The sequence number of the subcarrier transmitting the reference pilot symbol is k _p , p=0, 1, ..., P-1,

N is the number of OFDM subcarriers;

Step 2: Send according to the frame structure formed in step 1.

The receiving step is carried out according to the following phase 1 and phase 2:

Phase 1: Estimate the channel at the training OFDM symbol of each frame to obtain the initial parameters used for adaptive channel tracking during data transmission in this frame, and follow the three steps of A, B and C in sequence:

Step A: use the least squares (ie LS) estimation to obtain the estimated value of the frequency response of all training pilot symbol subcarriers of the current channel:

其中0≤l≤N-1)。其中i＝1，2，…，M_R，M_R为接收天线数。Step B: For the result of step A, use the frequency domain->time domain transformation to estimate the channel impulse response between all transmitting antennas and all receiving antennas (record the channel impulse response, from the qth transmitting antenna to the ith in the nth OFDM symbol The estimation of the multipath fading coefficient of the lth multipath component between receiving antennas is

where 0≤l≤N-1). Wherein, i=1, 2, ..., M _R , where M _R is the number of receiving antennas.

Step C: Obtain the delay time of the main multipath component of the channel and extract the fading coefficient of the main multipath component:

中选择(

为正整数)条主多径，存储其延迟时间(以采样周期为单位)为l_i，q，k和相应路径的衰落系数

其中 $k=\mathrm{1,2},\&CenterDot;\&CenterDot;\&CenterDot;,\stackrel{\&LeftRightArrow;}{L}.$ Using the calculation results in step B, using the channel impulse response direct truncation method or the main multipath component selection (STC) method, for the channel between any transmitting antenna q to any receiving antenna i, from its channel multipath fading coefficient

choose from (

is a positive integer) main multipath, store its delay time (in sampling period) as l _{i, q, k} and the fading coefficient of the corresponding path

in $k=\mathrm{1,2},\&Center\; Dot;\&Center\; Dot;\&CenterDot;,\stackrel{\&LeftRightArrow;}{L}.$

Phase 2: Adaptive channel tracking during data transmission:

For the nth (n=1, 2, ..., N _t -1) data transmission OFDM symbol in the frame, for any receiving antenna i, use the following channel estimation method (repeat the following steps A, B and C):

Step A: Set the initial value of the adaptive channel tracking algorithm:

Set the initial value of the adaptive channel estimation as the final value of the channel estimation of the n-1th OFDM symbol:

n=1, 2, ..., N _t -1 (3)

表示第n个OFDM符号内，经过p次迭代后，所有发射天线至接收天线i之间信道的估计结果，

表示第n个OFDM符号中，经过P次迭代后，所有发射天线至接收天线i之间信道估计的最终的结果，

表示第n个OFDM符号中，经过P次迭代后，第q个发射天线至接收天线i之间信道估计的最终的结果，其中in:

Indicates the channel estimation results between all transmit antennas and receive antenna i after p iterations in the nth OFDM symbol,

Indicates the final result of channel estimation between all transmit antennas and receive antenna i after P iterations in the nth OFDM symbol,

Indicates the final result of channel estimation between the qth transmit antenna and the receive antenna i after P iterations in the nth OFDM symbol, where

Step B: Adaptive channel tracking:

Any reference pilot symbol subcarrier corresponds to one iteration of the adaptive algorithm, for any p (0≤p≤P-1, P is the number of reference pilot symbols):

The reference signal of the adaptive algorithm is Y _i [n, k _p ] (the received signal at the pth reference pilot subcarrier of the i receiving antenna during the nth OFDM symbol), where k _p is the transmission of the pth reference pilot The subcarrier sequence number of the frequency symbol;

The input signal vector _wp [n] of the adaptive algorithm is:

${\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="w"\; filenames="C20041002186400171.png,C20041002186400182.png"\; state="\{\{state\}\}">w</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; p</span>}}^{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="w"\; filenames="C20041002186400182.png"\; state="\{\{state\}\}">w</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; p</span>}}^{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; ,</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; w</span>}}_{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; p</span>}}^{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; ]</span>}^{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

表示第n个数据传输OFDM内第q发射天线的第p个参考导频符号的值，接收端已知该值；in

Indicates the value of the p-th reference pilot symbol of the q-th transmit antenna in the n-th data transmission OFDM, which is known at the receiving end;

在当前数据传输OFDM符号内，迭代共进行P次(P为每个OFDM符号中参考导频符号的个数)，得到

作为本OFDM符号内的时域信道估计的结果，即

Adaptive channel estimation: It can be adjusted by typical adaptive algorithms (including any one of LMS algorithm, RLS algorithm and QR-RLS algorithm)

In the current data transmission OFDM symbol, the iteration is performed for a total of P times (P is the number of reference pilot symbols in each OFDM symbol), and we get

As a result of the time-domain channel estimation within this OFDM symbol, that is

得到所有发射天线至接收天线i间的信道各主要多径分量的估计。记第q发射天线至第i接收天线间主多径分量的估计值为

使用傅立叶变换(或者FFT)后得到第n个OFDM符号期间第q发射天线至第i接收天线间信道第k子载波频域信道估计。Step C: Utilize the result of adaptive channel estimation in step B to estimate the frequency responses of all channel subcarriers according to the combination order of (4) and (5), split

Estimates of each main multipath component of the channel between all transmitting antennas and receiving antenna i are obtained. Note that the estimated value of the main multipath component between the qth transmitting antenna and the ith receiving antenna is

After Fourier transform (or FFT) is used, the frequency-domain channel estimation of the kth subcarrier of the channel between the qth transmitting antenna and the ith receiving antenna during the nth OFDM symbol period is obtained.

It should be noted that the implementation of the scheme of the present invention is based on using the method proposed by the present invention on the insertion of pilot symbols and the processing algorithm at the receiving end, and adopts the method of a typical MIMO-OFDM system based on pilot symbol-assisted channel estimation accomplish.

Basic principle of design of the present invention:

1) For different transmit antennas, different subcarriers are used to transmit training pilot signals at the training OFDM symbols, and the MIMO channel can be converted into multiple independent and mutually orthogonal SISO channels, so the simple LS method is used to estimate the The channel response between all antenna pairs of ;

2) All multipath components of a multipath channel experience different fading and noise interference, so eliminating multipath components with low SNR can effectively improve the accuracy of channel estimation.

3) The traditional channel estimator based on training is only suitable for the occasions where the time-varying speed of the channel is low, and the channel estimation method with the help of distributed training pilot symbols and reference pilot symbols can effectively track the time-varying channel.

4) The optimal channel estimator often needs the statistical characteristics of the channel as prior information, which often requires training time overhead in practical applications, and adaptive channel estimation can avoid this requirement. In addition, the adaptive channel estimation also avoids the performance deterioration problem of the optimal channel estimation when the channel statistical characteristics change.

5) The adaptive algorithm needs a certain number of reference signals to converge, and the channel response changes continuously between consecutive OFDM symbols, so the channel estimation result of the previous OFDM symbol is used as the initial value of the adaptive estimation of the current OFDM symbol The required number of reference data can be reduced, so that deterioration of spectral efficiency can be avoided.

The innovation of the present invention is:

1) The transmitted data consists of two parts, and the channel estimation is also divided into two stages: the transmitted data is divided into training OFDM symbols and data transmission OFDM symbols (as shown in Figure 3). The training OFDM symbols are composed of training pilot symbols and 0 symbols, which are used to establish initial parameters for channel estimation; the data transmission OFDM symbols are composed of reference pilot symbols and data symbols. The difference between the reference pilot symbol and the traditional pilot symbol in the present invention is that its function is used to generate the input signal of the adaptive channel estimation algorithm to adaptively track the time-varying broadband channel (note: not for the sum interpolation method combined to estimate the channel frequency response). Another significant advantage about reference pilot symbols is that reference pilot symbols of different transmit antennas occupy the same subcarrier, so the frequency overhead caused by reference pilot symbols has nothing to do with the number of transmit antennas, and no special design is required. The insertion patterns of training pilot symbols and reference pilot symbols are shown in FIG. 4 .

2) The channel estimation algorithm adopts an adaptive algorithm: the adaptive algorithm has the function of dynamically tracking channel parameters as the channel changes, and has the characteristics of no need for channel statistical characteristics and a small amount of calculation.

The present invention has the following advantages:

1) Channel estimation uses training OFDM symbols as the initial value of channel estimation to speed up the convergence speed of the adaptive channel estimation algorithm;

2) During data transmission OFDM symbols, all transmitting antennas use the same subcarrier to transmit reference pilot symbols; and its function is to generate the input signal and reference signal of the adaptive algorithm instead of interpolation, with high spectrum utilization;

3) Adaptive algorithm is used to track the channel without channel statistical characteristics;

4) Channel tracking is performed in the time domain;

5) The method of the present invention can adopt the main multipath component selection technology to reduce the error of the initial value of channel estimation, and can reduce the number of channel parameters to be tracked, thereby reducing the amount of computation and improving the estimation accuracy.

Description of drawings

Figure 1 is a typical MIMO-OFDM system transmission block diagram

为第n个OFDM符号期间第q发射天线第

采样时刻传送的时域信号；n表示一帧内OFDM符号的序号(n为整数，0 ≤n＜N_T)，k表示OFDM子载波序号(k为整数，0 ≤k＜N，N表示OFDM子载波总数)，

表示采样时刻(

为整数， $-N_g\&le;\tilde{m}<N,$ 其中N_g表示OFDM循环前缀采样点数)。其中的帧形成模块完成插入训练符号和导频符号的功能，本发明中，帧形成模块需插入特殊的训练导频符号和参考导频符号。Wherein S _q [n, k] is the signal transmitted by the kth subcarrier of the qth transmit antenna during the nth OFDM symbol period;

is the qth transmit antenna during the nth OFDM symbol

The time-domain signal transmitted at the sampling moment; n represents the sequence number of OFDM symbols in a frame (n is an integer, 0 ≤ n< _NT ), k represents the sequence number of OFDM subcarriers (k is an integer, 0 ≤ k<N, N represents OFDM total number of subcarriers),

Indicates the sampling time (

is an integer, $-N_g\&le;\tilde{m}<N,$ Where N _g represents the number of OFDM cyclic prefix sampling points). The frame forming module therein completes the function of inserting training symbols and pilot symbols. In the present invention, the frame forming module needs to insert special training pilot symbols and reference pilot symbols.

Figure 2 is a block diagram of a typical MIMO-OFDM receiver

表示第n个OFDM符号期间第i根接收天线第

时刻接收到的采样信号，Y_i[n，k]为接收机第n个OFDM符号期间第i接收天线第k子载波分离出来用于空时解码的解码器输入信号；其中i为正整数，1≤i≤M_R，M_R为接收天线数；其中的信道估计模块使用从接收信号中提取的导频符号估计MIMO信道频率响应。in

Indicates that during the nth OFDM symbol period, the i-th receiving antenna

The sampled signal received at any time, Y _i [n, k] is the decoder input signal separated from the kth subcarrier of the i-th receiving antenna during the n-th OFDM symbol of the receiver for space-time decoding; where i is a positive integer, 1≤i≤M _R , _MR is the number of receiving antennas; the channel estimation module uses the pilot symbols extracted from the received signal to estimate the MIMO channel frequency response.

Fig. 3 is the data transmission frame structure of the present invention

There are N _t OFDM symbols in each frame, wherein the first (n=0) OFDM symbol is a training OFDM symbol, and the following N _t -1 OFDM symbols are data transmission OFDM symbols (n=1, 2, ... , N _t -1).

Figure 4 is the pattern of training pilot symbols and reference pilot symbols designed in this scheme

表示训练导频符号，

表示参考导频符号，

表示数据符号，

表示0符号。The figure shows the composition patterns of the training pilot symbols and reference pilot symbols of the transmitting antenna q (where q=1, 2, ..., M _T , M _T is the number of transmitting antennas); the first column in the figure represents the training OFDM symbol, and the remaining N _t -1 columns represent OFDM symbols for data transmission; n represents the sequence number of OFDM symbols, 0≤n≤N _t -1), k represents the sequence number of subcarriers, 0≤k≤N-1, N _t is each The number of frame OFDM symbols; D _f0 is the subcarrier spacing of two adjacent training pilot symbols in any transmitting antenna in the training OFDM symbol; D _f1 is the subcarrier spacing of two adjacent reference pilot symbols in the data transmission OFDM symbol of any transmitting antenna ;

Denotes training pilot symbols,

Indicates the reference pilot symbol,

represents the data symbol,

Represents the 0 symbol.

Fig. 5 is a schematic diagram of the channel adaptive tracking scheme of the present invention

According to the type of the current OFDM symbol, when the first OFDM symbol in the frame is the training OFDM symbol, use the least squares (LS) algorithm to estimate the current channel response and select the main multipath component, which is the first one processed by the receiver stage; when the current OFDM symbol is an OFDM symbol for data transmission, enter the second stage of channel estimation at the receiving end, that is, use an adaptive channel tracking algorithm to track the channel.

Fig. 6 is a system performance simulation example using channel estimation of the scheme of the present invention

The figure shows a bit error rate (BER) computer target performance curve of a special case of the scheme of the present invention, wherein SNR represents the signal-to-noise ratio, esti represents the result estimated using the method of the present invention, and ideal represents the result of ideal channel estimation. The adaptive algorithm adopts the LMS algorithm. The figure shows the bit error rate performance of the system under parameter selection in the following specific embodiments. The dotted line is the ideal channel estimation performance, and the solid line is the performance of the scheme in this paper.

Detailed ways

The implementation steps of this patent under a specific MIMO-OFDM configuration are given below. The parameters in this example do not affect the generality of the invention.

Originating processing steps:

Step A: Introduce training pilot symbols and reference pilot symbols to form a data frame structure

For each transmitting antenna, the data transmission is transmitted in a frame-by-frame manner; the first OFDM symbol in each frame is a training OFDM symbol; the subsequent OFDM symbols are data transmission OFDM symbols; the number of OFDM symbols contained in each frame is N _t =40.

The training pilot symbols are located in the training OFDM symbols, and different transmitting antennas use different subcarriers to transmit the training pilot symbols. (As shown in Figure 4). The subcarrier allocated to the pth training pilot symbol of the qth transmit antenna is

${\stackrel{\&OverBar;}{k}}_{q,p}=q-1+\mathrm{<figure-callout\; id="0"\; label="p\; D.\; f"\; filenames="C20041002186400171.png"\; state="\{\{state\}\}">p</figure-callout>}{\mathrm{D.}}_f{0}_{},$ $p=\mathrm{0,1},\&Center\; Dot;\&CenterDot;\&Center\; Dot;,\stackrel{\&OverBar;}{P}-1,$ q=1, 2, ..., M _T

为训练OFDM符号处单个发射天线发射的训练导频符号个数；in

The number of training pilot symbols transmitted by a single transmit antenna at the training OFDM symbol;

Where q is the serial number of the transmitting antenna, 1≤q≤M _T , in this example, the number of transmitting antennas M _T =2 is selected, and the number of OFDM modulation carriers is N=1024; 0 symbol,

In any data transmission OFDM symbol, all transmit antennas use the same subcarrier to transmit reference pilot symbols. The sequence numbers of the subcarriers used to transmit the reference pilot symbols are:

k _p = pD _f1 + k ₀ , p = 0, 1, . . . , P-1

其中本例中选择D_f1＝16，k₀＝0 。在其它子载波处传送空时网格编码的编码结果。The total number of reference subcarriers is

In this example, D _f1 =16 and k ₀ =0 are selected. The coding results of space-time trellis coding are transmitted at other subcarriers.

Step B: send according to the frame structure of step A;

Channel estimation is performed at the receiving end; it is performed in two stages: phase 1 and phase 2:

Phase 1: Estimate the channel at the training OFDM symbol of each frame to obtain the initial parameters used for adaptive channel tracking during data transmission in this frame, and follow the three steps of A, B and C in sequence:

Step A: use the least squares (ie LS) estimation to obtain the estimated value of the frequency response of all training pilot symbol subcarriers of the current channel:

i＝1，2，…，M_R，q＝1，2，…，M_T， $p=\mathrm{0,1},\&CenterDot;\&CenterDot;\&CenterDot;,\stackrel{\&OverBar;}{P}-1,$ n＝0

i=1, 2, ..., M _R , q = 1, 2, ..., M _T , $p=\mathrm{0,1},\&Center\; Dot;\&Center\; Dot;\&CenterDot;,\stackrel{\&OverBar;}{P}-1,$ n=0

为发射天线q至接收天线i处第子载波处的频率响应的估计，

为第n个OFDM符号内第i接收天线第

子载波接收信号；

为第q发射天线在第

个子载波传送的已知的训练信号；其中i为接收天线序号，1≤i≤M_R，本例中选择M_R＝2。in

is the position from the transmitting antenna q to the receiving antenna i An estimate of the frequency response at the subcarriers,

is the i-th receive antenna in the n-th OFDM symbol

The subcarrier receives the signal;

is the qth transmitting antenna at the

The known training signal transmitted by subcarriers; where i is the serial number of the receiving antenna, _1≤i≤MR , and M _R =2 is selected in this example.

Step B: Estimate the channel impulse response from all transmit antennas to all receive antennas using frequency domain -> time domain transform:

i＝1，2，…，M_R，q＝1，2，…，M_T，n＝0

i=1, 2, ..., M _R , q = 1, 2, ..., M _T , n = 0

in:

为帧内第n个OFDM符号处，第q发射天线至第i接收天线间信道脉冲响应的估计，

为相应的帧内第n个OFDM符号处，第q发射天线至第i接收天线间信道第l条路径多径系数的估计；

is the estimate of the channel impulse response between the qth transmit antenna and the ith receive antenna at the nth OFDM symbol in the frame,

is the estimation of the multipath coefficient of the lth path of the channel between the qth transmit antenna and the ith receive antenna at the nth OFDM symbol in the corresponding frame;

为由每根发射天线

个训练导频按照步骤A估计的频域信道(在第n个OFDM符号期间的第q发射天线至第i接收天线频域信道系数)。W_q为与第q发射天线相关的

维变换矩阵，其第u行第v列元素为：

for each transmit antenna

The frequency-domain channel estimated by the training pilots according to step A (frequency-domain channel coefficients from the qth transmit antenna to the i-th receive antenna during the nth OFDM symbol period). W _q is associated with the qth transmit antenna

Dimensional transformation matrix, the elements of row u and column v are:

${<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; W</span>}}_{\mathrm{<span\; class="notranslate">\; q</span>}}<span\; class="notranslate">\; ]</span>}_{\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; v</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{\frac{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="j"\; filenames="C20041002186400182.png"\; state="\{\{state\}\}">j</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; q</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{<span\; class="notranslate">\; \&Integral;</span>\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; v</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}$

Where q is the serial number of the transmitting antenna, 1≤q≤M _T , $u=\mathrm{1,2},\&CenterDot;\&Center\; Dot;\&Center\; Dot;,\stackrel{\&OverBar;}{P},$ v=1, 2, . . . , N.

(其中0≤l≤N-1)中选择选择

较大的

条主多径，记录其延迟时间(以采样周期为单位)为

(第q发射天线至第i接收天线之间)，相应路径的衰落系数

本例中主多径分量选择 $\stackrel{\&LeftRightArrow;}{L}=6.$ Step C: Obtain the delay time of the main multipath component of the channel and extract the fading coefficient of the main multipath component. Using the calculation results in step B, according to the main multipath component selection (STC) method, for any transmission antenna q to any reception antenna i Single send single receive (SISO) channel, from its channel multipath fading coefficient

(where 0≤l≤N-1) choose to choose

larger

main multipath, record its delay time (in the unit of sampling period) as

(between the qth transmit antenna and the i-th receive antenna), the fading coefficient of the corresponding path

In this example, the main multipath component selection $\stackrel{\&LeftRightArrow;}{L}=6.$

Phase 2: Adaptive channel tracking during data transmission:

When receiving data and transmitting OFDM symbols (n=1, 2, ..., N _T -1), for any receiving antenna i, the channel estimation method is as follows (all receiving antennas need to repeat the following three steps of A, B and C step):

Step A: Set the initial value of the adaptive channel tracking algorithm:

The channel estimation results between all transmitting antennas and receiving antenna i (should be stored in the memory of the receiving end during actual operation) are recorded as the following vectors:

为第n个OFDM符号中，第q发射天线至第i接收天线之间SISO信道主多径衰落系数的估计值组成的向量。当接收机处理，第1个数据传输OFDM符号时(n＝1)，

由阶段1的步骤C得到；其它的数据传输OFDM符号中(n＝2，3，…，N_t-1)，  (7)式的值由对第n-1个OFDM符号期间信道自适应追踪的结果得到。此时，设置信道估计初值为上一个OFDM符号信道估计的终值：in

is a vector composed of estimated values of the main multipath fading coefficients of the SISO channel between the qth transmit antenna and the ith receive antenna in the nth OFDM symbol. When the receiver processes the first data transmission OFDM symbol (n=1),

Obtained by step C of stage 1; in other data transmission OFDM symbols (n=2, 3, ..., N _t -1), the value of (7) formula is obtained by channel adaptive tracking during the n-1th OFDM symbol The result is obtained. At this point, set the initial value of the channel estimation to the final value of the channel estimation of the last OFDM symbol:

表示第n个OFDM符号内第i接收天线经过p次迭代后的估计结果，

为相应的第n个OFDM符号自适应估计最终的结果，即自适应算法迭代P次后的结果。in

Indicates the estimation result of the i-th receiving antenna in the n-th OFDM symbol after p iterations,

The final result is adaptively estimated for the corresponding nth OFDM symbol, that is, the result after the adaptive algorithm iterates P times.

Step B: Adaptive channel tracking:

Here, the LMS algorithm is used to realize the adaptive tracking of the channel.

For any p (p = 0, 1, ..., P-1) (i.e., within any data transmission OFDM symbol, for all reference pilot symbol subcarriers):

The LMS algorithm reference signal is Y _i [n, k _p ] (the received signal at the pth reference pilot subcarrier of the ith receiving antenna during the nth OFDM symbol period), and the input signal vector of the adaptive algorithm is determined by the known reference The pilot signal is obtained by combining the position of the reference pilot subcarrier and the delay time of the main multipath component. The generation method is:

The input signal vector _wp [n] of the LMS algorithm at the pth iteration is constructed as:

${\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="w"\; filenames="C20041002186400171.png,C20041002186400182.png"\; state="\{\{state\}\}">w</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; p</span>}}^{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="w"\; filenames="C20041002186400182.png"\; state="\{\{state\}\}">w</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; p</span>}}^{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; ,</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; w</span>}}_{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; p</span>}}^{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; ]</span>}^{\mathrm{<span\; class="notranslate">\; T</span>}}$

表示第n个数据传输OFDM内第q发射天线的第p个参考导频符号的值，接收端已知该值；

由阶段1的步骤C选择。在当前数据传输OFDM符号内，迭代共P＝64次，得到

作为本OFDM符号内的时域信道估计的结果。in

Indicates the value of the p-th reference pilot symbol of the q-th transmit antenna in the n-th data transmission OFDM, which is known at the receiving end;

Selected by Step C of Phase 1. In the current data transmission OFDM symbol, a total of P = 64 iterations, get

As a result of time-domain channel estimation within this OFDM symbol.

The method of realizing the channel tracking of the LMS algorithm is as follows:

For all p=0, 1, ..., P-1, iterative calculation:

$\mathrm{<span\; class="notranslate">\; e</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}^{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; ]</span>{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; ]</span>$

${\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; =</span>{\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; h</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&mu;</span>}{\mathrm{<span\; class="notranslate">\; w</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}^{<span\; class="notranslate">\; *</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; ]</span>\mathrm{<span\; class="notranslate">\; e</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; ]</span>$

Among them: μ is the step size factor, the basis for selection is to make the algorithm converge and have a small estimation error. In this example, the step size factor of the LMS algorithm is taken as μ = 0.02.

Step C: Estimate the frequency response of all channel subcarriers using the result of adaptive channel estimation in step B

拆分得到所有发射天线至接收天线i间的信道各主要多径分量的估计为

其中

为该主多径延迟时间的估计值(以采样周期为单位)， $\stackrel{\&LeftRightArrow;}{l}=\mathrm{1,2},\&CenterDot;\&CenterDot;\&CenterDot;,\stackrel{\&LeftRightArrow;}{L}.$ 则经傅立叶变换后得到第n个OFDM符号期间第q发射天线至第i接收天线间信道第k子载波频域信道估计为：Depend on

Split to obtain the estimation of each main multipath component of the channel between all transmitting antennas and receiving antenna i as

in

is the estimated value of the main multipath delay time (in sampling period), $\stackrel{\&LeftRightArrow;}{l}=\mathrm{1,2},\&Center\; Dot;\&Center\; Dot;\&CenterDot;,\stackrel{\&LeftRightArrow;}{L}.$ Then after Fourier transform, the frequency domain channel estimation of the kth subcarrier of the channel between the qth transmit antenna and the ith receive antenna during the nth OFDM symbol period is obtained for:

Where k represents the serial number of the subcarrier (the value range is 0≤k<N-1). In this example, the spectral efficiency loss is $\mathrm{\&xi;}=\frac{N+({\mathrm{D.}}_i-1)P}{{\mathrm{D.}}_{i}N},$ That is 8.6%. Fig. 6 has provided and used the bit error rate (BER) computer target performance curve of a special example of the scheme of the present invention, and simulation result shows, when higher SNR, SNR loss is about 1dB in the present embodiment.

Claims (1)

1. the adaptive channel estimation method of a MIMO-OFDM system is characterized in that it comprises make a start step and receiving end step:

The described step of making a start is carried out according to step 1 and step 2:

Step 1: introduce training frequency guide symbol and reference pilot symbols to form data frame structure

To any transmitting antenna, transmit data according to a minute frame mode, every frame comprises N _tIndividual OFDM symbol, N _tBe positive integer; First OFDM symbol is a training OFDM symbol in the frame, and n=0, n represent OFDM symbol sequence number; N behind the accent white silk OFDM symbol in the frame _t-1 OFDM symbol is a data transmission OFDM symbol, n=1, and 2 ..., N _t-1; Insert training frequency guide symbol and insert reference pilot symbols according to following method:

Insert training frequency guide symbol: in training OFDM symbol, for q transmitting antenna, q=1,2 ..., M _T, M _TThe expression number of transmit antennas, M _TBe positive integer, first subcarrier number that transmits training frequency guide symbol is q-1, thereafter every D _F0Individual subcarrier inserts a training frequency guide symbol; To q transmitting antenna, at non-training frequency guide symbol subcarrier place, the transmission amplitude is 00 symbol;

Insert reference pilot symbols: in any data transmission OFDM symbol, all transmitting antennas use identical subcarrier to transmit reference pilot symbols; To any transmitting antenna, the subcarrier sequence number that transmits the 1st reference pilot symbols is k ₀, 0≤k ₀＜D _F1, D _F1Be positive integer, thereafter every D _F1Individual subcarrier inserts a reference pilot symbols; To any transmitting antenna, at non-reference pilot symbols subcarrier place, transmit the data symbol of Space Time Coding output: the subcarrier sequence number that transmits reference pilot symbols is k _p, p=0,1 ..., P-1,

N is the OFDM sub-carrier number;

Step 2: the frame structure that forms according to step 1 sends.

Described receiving end step was carried out according to following stage 1 and stage 2:

Stage 1: estimate channel at the training OFDM symbol place of every frame, be used for the initial parameter that adaptive channel is followed the trail of during the transfer of data in this frame, carry out in turn according to A, B and three steps of C to obtain:

Steps A: the estimated value of obtaining the frequency response of all training frequency guide symbol subcarriers of current channel with least-squares estimation;

Step B: to the result of steps A, use frequency domain-＞spatial transform estimates that all transmitting antennas are to channel impulse response between all reception antennas, if in the channel impulse response, being estimated as of l bar multipath component multipath fading coefficient between q transmitting antenna to the i reception antenna in n OFDM symbol 0≤l≤N-1, i=1,2 ..., M _R, M _RBe the reception antenna number;

Step C: obtain channel master multipath component time of delay and extract main multipath component fading coefficients:

Utilize result of calculation among the step B, use direct truncation method of channel impulse response or main multipath component back-and-forth method, to the channel between the extremely any reception antenna i of any transmitting antenna q, from its channel multi-path fading coefficients

The middle selection

Bar master multipath,

Be positive integer, storage delay time l _{I, q, k}Fading coefficients with respective paths

$k=\mathrm{1,2},\&CenterDot;\&CenterDot;\&CenterDot;,\stackrel{\&infin;}{L};$

Stage 2: adaptive channel is followed the trail of during the transfer of data:

To n data transmission OFDM symbol in the frame, n=1,2 ..., N _t-1, wherein arbitrary reception antenna i, use following channel estimation methods:

Steps A: adaptive channel track algorithm initial value is set:

Adaptive channel is set estimates that initial value is the final value that n-1 OFDM symbol estimated:

n＝1，2，…，N _t-1 (1)

Wherein:

Represent in n the OFDM symbol that through after p iteration, all transmitting antennas are to the estimated result of channel between the reception antenna i,

Represent in n the OFDM symbol that through after P iteration, all transmitting antennas are to the final result of channel estimating between the reception antenna i,

Represent in n the OFDM symbol that through after P iteration, q transmitting antenna is to the final result of channel estimating between the reception antenna i, wherein

Step B: adaptive channel is followed the tracks of:

Arbitrarily the reference pilot symbols subcarrier is all corresponding to an iteration of adaptive algorithm, and to p arbitrarily, 0≤p≤P-1, P are the reference pilot symbols number, and the reference signal of adaptive algorithm is Y _i[n, k _p], the received signal at p reference pilot subcarrier of i reception antenna place during n OFDM symbol, k _pFor transmitting the subcarrier sequence number of p reference pilot symbols;

The input signal vector w of adaptive algorithm _p[n] is:

$w_p\left[n\right]=\left[w_{1.p}^T\right[n],w_{2.p}^T[n],...,w_{M_T.p}^T{\left[n\right]]}^T---\left(4\right)$

Wherein

The value of representing p reference pilot symbols of q transmitting antenna in n the data transmission OFDM, receiving terminal is known should to be worth;

Adaptive channel is estimated: adopt the adjustment of LMS algorithm or RLS algorithm or QR-RLS algorithm

In the current data transmission OFDM symbol, iteration is carried out P time altogether, and P is the number of reference pilot symbols in each OFDM symbol, obtains As the time domain channel results estimated in the OFDM symbol, promptly

Step C: utilize step B adaptive channel results estimated to estimate the order of all channel sub-carrier frequencies responses, split according to the combination of (2) and (3) formula

Obtain of the estimation of all transmitting antennas to each the main multipath component of channel between reception antenna i; The estimated value of remembering main multipath component between q transmitting antenna to the i reception antenna is

Use to obtain during n the OFDM symbol channel k sub-carrier frequency domain channel estimating between q transmitting antenna to the i reception antenna behind the Fourier transform,

All reception antennas are repeated above-mentioned steps A, B and C.

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