CN101297510A

CN101297510A - Channel estimation method in multiple-input multiple-output orthogonal frequency division multiplexing system and training signal creation method for channel estimation

Info

Publication number: CN101297510A
Application number: CNA2005800519008A
Authority: CN
Inventors: 李炫�; 崔源喆; 全炯九
Original assignee: Electronics and Telecommunications Research Institute ETRI
Current assignee: Electronics and Telecommunications Research Institute ETRI
Priority date: 2005-08-19
Filing date: 2005-12-02
Publication date: 2008-10-29

Abstract

The present invention provides a method for generating a training signal using a pulse train coded with an orthogonal code and a channel estimation method for decoding with an orthogonal code in a MIMO-OFDM system. A channel estimation method using orthogonal code decoding in a MIMO-OFDM system includes the steps of: creating a plurality of orthogonal codes depending on the number of receiving antennas; using the orthogonal codes to decode signals received through each receiving antenna; The received signal decoded by the orthogonal code is averaged for each OFDM symbol to estimate the channel response.

Description

Channel estimation method in multiple-input multiple-output orthogonal frequency division multiplexing system and training signal creation method for channel estimation

技术领域 technical field

本发明涉及多输入多输出正交频分多路复用(MIMO-OFDM)系统中的信道估计方法和用于信道估计的训练信号生成方法。更具体地说，本发明的目的是在MIMO-OFDM系统中使用利用正交码(例如，沃尔什(Walsh)码)编码的脉冲列的训练信号生成方法、和利用正交码解码的信道估计方法，其中，通过在发送端生成和发送利用正交码编码的脉冲列作为训练信号，并且在接收端利用正交码解码接收的信号然后对解码信号求平均而简单和准确地进行信道估计。The present invention relates to a channel estimation method and a training signal generation method for channel estimation in a Multiple Input Multiple Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) system. More specifically, the object of the present invention is to use a training signal generation method of a pulse train encoded with an orthogonal code (for example, Walsh code) and a channel decoded with an orthogonal code in a MIMO-OFDM system. Estimation method in which channel estimation is simply and accurately performed by generating and transmitting a pulse train encoded with an orthogonal code at a transmitting end as a training signal, and decoding a received signal with an orthogonal code at a receiving end and then averaging the decoded signals .

背景技术 Background technique

MIMO技术指的是通过从安排在发送端和接收线端上的多个天线的每一个发送分立数据，无需增加任何带宽就可以提高传送速率的技术。The MIMO technology refers to a technology that can increase a transmission rate without increasing any bandwidth by transmitting discrete data from each of a plurality of antennas arranged on a transmission side and a reception line side.

众所周知，OFDM是将数据分配给多个正交载波和发送它们的频率多路复用方案。换句话说，OFDM指的是尽管一部分发送频带是重叠的，但通过给定载波之间的正交条件，可以在接收器上分离每个载波的频率多路通信方案。As we all know, OFDM is a frequency multiplexing scheme that allocates data to multiple orthogonal carriers and transmits them. In other words, OFDM refers to a frequency multiplexing communication scheme in which each carrier can be separated at a receiver by giving an orthogonal condition between carriers although a part of transmission frequency bands overlap.

因此，MIMO-OFDM技术是汇集了MIMO技术和IFDM技术，和基于当每个天线发送不同数据时，理论信道容量与发送天线数量和接收天线数量当中的较小数量成正比的事实的技术。也就是说，由于要发送的数据量与天线数量成正比，因此MIMO-OFDM技术的特征在于，无需任何附加带宽就可以提高单位时间的数据传送速率。Therefore, MIMO-OFDM technology is a technology that brings together MIMO technology and IFDM technology, and is based on the fact that when each antenna transmits different data, a theoretical channel capacity is proportional to the smaller number of the number of transmission antennas and the number of reception antennas. That is, since the amount of data to be transmitted is proportional to the number of antennas, the MIMO-OFDM technology is characterized in that the data transfer rate per unit time can be increased without any additional bandwidth.

图1是例示应用了Nt个发送天线和Nr个接收天线的传统MIMO-OFDM系统的配置的图形。FIG. 1 is a diagram illustrating a configuration of a conventional MIMO-OFDM system to which Nt transmission antennas and Nr reception antennas are applied.

如图1所示，首先将用户数据b[1，k]施加于MIMO-OFDM系统中的MIMO编码和码元映射单元11，其中，数据被编码和映射成码元。然后，通过快速付里叶逆变换器(IFFT)单元12正交变频和发送映射数据。包括在IFFT单元12中的IFFT 121到IFFT 123的每一个同时并行处理来自MIMO编码和码元映射单元11的输出，因此，将它们的数量设置成相信应于来自MIMO编码和码元映射单元11的输出的数量。As shown in Fig. 1, user data b[1,k] is firstly applied to the MIMO encoding and symbol mapping unit 11 in the MIMO-OFDM system, where the data is encoded and mapped into symbols. Then, the map data is quadrature-converted and transmitted by an inverse fast Fourier transformer (IFFT) unit 12 . Each of the IFFT 121 to IFFT 123 included in the IFFT unit 12 simultaneously processes in parallel the output from the MIMO encoding and symbol mapping unit 11, and therefore, their number is set to be believed to correspond to the output from the MIMO encoding and symbol mapping unit 11. The number of outputs.

与IFFT单元12连接的是用于向无线电环境发送来自IFFT 12的发送信号的由多个发送天线组成的发送天线单元13。Connected to the IFFT unit 12 is a transmission antenna unit 13 composed of a plurality of transmission antennas for transmitting the transmission signal from the IFFT 12 to the radio environment.

另一方面，通过多个发送天线13向无线电环境发送的发送信号被混合，并且随后在接收端通过接收天线单元14的每个接收天线接收。On the other hand, the transmission signals transmitted to the radio environment via the plurality of transmission antennas 13 are mixed and then received by each reception antenna of the reception antenna unit 14 at the reception end.

与接收天线单元14连接的是对通过Nr个接收天线接收的每个信号进行FFT(快速付里叶变换)的FFT单元15。FFT单元15的输出可以通过下式表示：Connected to the receiving antenna unit 14 is an FFT unit 15 that performs FFT (Fast Fourier Transform) on each signal received through the Nr receiving antennas. The output of the FFT unit 15 can be expressed by the following formula:

${Y Y}_{j j} [[l l,, k k]] = = {Σ Σ}_{i i = = 11}^{{N N}_{i i}} {H h}_{ij ij} [[l l,, k k]] {X x}_{i i} [[l l,, k k]] + + {Ω Ω}_{j j} [[l l,, k k]],, j j = = 1,2 1,2,, . . . . . . {N N}_{R R} - - - - - - Eq Eq . . ((11))$

其中，H_ij[l，k]表示在第1码元间隔上，对于第k子信道，第i发送天线与第j接收天线之间的多路信道的频率响应，和Ω_j[i，j]表示平均值是0和方差是σ²Ω的加性白高斯噪声(AWGN)的FFT输出。Among them, H _ij [l, k] represents the frequency response of the multi-channel channel between the i-th transmit antenna and the j-th receive antenna for the k-th sub-channel on the first symbol interval, and Ω _j [i, j ] represents the FFT output of additive white Gaussian noise (AWGN) with mean 0 and variance σ ² Ω.

发送信号相互混合、通过各自接收天线14接收的信号由FFT单元15变换成相应时域信号。为了上述目的，接收端需要与发送端天线数量一样多的FFT 151到153。The transmitted signals are mixed with each other and the signals received by the respective receiving antennas 14 are transformed by the FFT unit 15 into corresponding time-domain signals. For the above purpose, the receiving end needs as many FFTs 151 to 153 as the number of antennas at the transmitting end.

来自FFT 151到153每一个的信号是从通过接收天线接收的混合信号变换的时域信号，因此，需要检测块从它们中分离出每一个，其中，MIMO解码和码元去映射单元16被用作检测块。The signals from each of the FFTs 151 to 153 are time-domain signals transformed from the mixed signals received through the receiving antennas, therefore, a detection block is required to separate each of them, wherein the MIMO decoding and symbol demapping unit 16 is used as a detection block.

作为用在MIMO-OFDM系统中的检测算法，存在有最小均方误差法(MMSE)、垂直贝尔实验室分层时空法(VBLAST)、迫零法(ZF)、最大似然法(ML)等。这些检测算法的性能主要依赖于天线之间的子信道的信道估计器17的精确度。并且，与信道估计器17连接的是通过检测算法附加配备的码元映射单元18。As the detection algorithm used in the MIMO-OFDM system, there are minimum mean square error method (MMSE), vertical Bell Labs layered space-time method (VBLAST), zero forcing method (ZF), maximum likelihood method (ML), etc. . The performance of these detection algorithms mainly depends on the accuracy of the channel estimator 17 for the sub-channels between the antennas. Also, connected to the channel estimator 17 is a symbol mapping unit 18 additionally equipped with a detection algorithm.

在检测算法中，如果在估计信道系数中卷入估计误差，就不能正确地从接收信号中分离出每个发送天线的发送信号。其结果是，来自其它发送天线的信号以噪声的形式保留在其中，导致MIMO-OFDM系统的性能降低。因此，为了提高MIMO-OFDM系统的性能，需要一种能够精确估计尤其在多路衰落环境下的信道的技术。In the detection algorithm, if an estimation error is involved in estimating the channel coefficient, the transmission signal of each transmission antenna cannot be correctly separated from the reception signal. As a result, signals from other transmit antennas remain in it in the form of noise, resulting in degraded performance of the MIMO-OFDM system. Therefore, in order to improve the performance of the MIMO-OFDM system, a technology capable of accurately estimating the channel especially in the environment of multipath fading is needed.

估计这样的信道的现有技术之一是基于利用脉冲信道响应的延迟分布的MMSE技术的信道估计方法。这种方法通过考虑时域中信道响应的长度有效地消除了AWGN成分。但是，这样的方法将求解复杂的逆矩阵，随着信道响应的长度越来越长和发送天线数量和接收天线数量不断增加，使计算量急剧增大。One of the existing techniques for estimating such a channel is a channel estimation method based on the MMSE technique using the delay profile of the impulse channel response. This approach effectively eliminates the AWGN component by considering the length of the channel response in the time domain. However, such a method will solve a complex inverse matrix, and as the length of the channel response becomes longer and the number of transmitting antennas and the number of receiving antennas continue to increase, the amount of calculation will increase dramatically.

为了降低成为基于如上所述的MMSE技术的信道估计方法的一个问题的计算复杂性，人们提出了不利用逆矩阵，而是借助于信道的延迟分布估计信道的技术。也就是说，这种技术以这样的方式估计信道，即，每个天线发送在时域中存在不同时间延迟的训练信号，以便使信道响应在接收端上不相互混合。In order to reduce the computational complexity which is a problem of the channel estimation method based on the MMSE technique as described above, a technique of estimating the channel by means of the delay distribution of the channel instead of the inverse matrix has been proposed. That is, this technique estimates channels in such a way that each antenna transmits training signals with different time delays in the time domain so that channel responses are not mixed with each other on the receiving end.

这种技术与MMSE信道估计方法相比较简单，但仍然存在复杂的结构。而且，该技术存在前信道估计值的精确度严重影响当前信道估计的精确度的反馈结构。由于这样的反馈结构，难以将该技术应用于低SNR(信噪比)或信道迅速变化的环境下的系统。This technique is simpler than the MMSE channel estimation method, but still has a complex structure. Moreover, this technique has a feedback structure in which the accuracy of the previous channel estimate seriously affects the accuracy of the current channel estimate. Due to such a feedback structure, it is difficult to apply this technique to systems in environments with low SNR (Signal to Noise Ratio) or rapidly changing channels.

发明内容 Contents of the invention

技术问题technical problem

因此，本发明的一个目的是提供生成和发送借助于正交码(沃尔什码)编码的脉冲列作为用于接收端的信道估计的训练信号、MIMO-OFDM系统中利用借助于正交码编码的脉冲列的训练信号生成方法。Therefore, an object of the present invention is to provide generation and transmission by means of an orthogonal code (Walsh code) coded pulse train as a training signal for channel estimation at the receiving end, in a MIMO-OFDM system utilizing A training signal generation method for pulse trains.

本发明的另一个目的是提供能够通过借助于正交码解码接收信号，然后对解码信号求平均简单和准确地进行信道估计、MIMO-OFDM系统中利用正交码解码的信道估计方法。Another object of the present invention is to provide a channel estimation method using orthogonal code decoding in a MIMO-OFDM system capable of performing simple and accurate channel estimation by decoding received signals by means of orthogonal codes and then averaging the decoded signals.

本发明的其它目的和优点可以通过如下的描述来理解，也可以通过本发明的实施例更清楚地明白。并且，可以容易地看出，本发明的目的和优点可以通过规定在权利要求书中的途径及其组合实现。Other purposes and advantages of the present invention can be understood through the following description, and can also be more clearly understood through the embodiments of the present invention. And, it can be easily seen that the objects and advantages of the present invention can be achieved by means specified in the claims and combinations thereof.

技术解决方案technical solution

按照本发明的一个方面，提供了多输入多输出正交频分多路复用(MIMO-OFDM)系统中将借助于正交码编码的脉冲列用于接收端的信道估计的训练信号生成方法，该方法包括如下步骤：根据发送天线的数量创建多个正交码；和针对每个发送天线，生成由借助于正交码编码的脉冲列组成的训练信号。According to one aspect of the present invention, there is provided a training signal generation method for channel estimation at a receiving end by using a pulse train coded by an orthogonal code in a multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system, The method comprises the steps of: creating a plurality of orthogonal codes depending on the number of transmitting antennas; and generating, for each transmitting antenna, a training signal consisting of pulse trains encoded by means of the orthogonal codes.

按照本发明的另一个方面，提供了MIMO-OFDM系统中利用正交码解码的信道估计方法，该方法包括如下步骤：创建视接收天线的数量而定的多个正交码；利用正交码解码通过每个接收天线接收的信号；和通过将借助于正交码解码的接收信号对每个OFDM码元求平均来估计信道响应。According to another aspect of the present invention, a channel estimation method using orthogonal code decoding in a MIMO-OFDM system is provided, the method comprising the steps of: creating a plurality of orthogonal codes depending on the number of receiving antennas; using the orthogonal code decoding the signal received through each receiving antenna; and estimating the channel response by averaging the received signal decoded by means of the orthogonal code for each OFDM symbol.

有利效果beneficial effect

本发明的有利之处在于，通过在像无线电信道那样存在严重噪声的环境下，利用沃尔什码的正交性为天线之间的信道估计指定训练信号，以少量计算更精确地估计无线电信道，可以提高接收信号的质量。The present invention is advantageous in that the radio channel can be estimated more accurately with a small amount of computation by utilizing the orthogonality of Walsh codes to assign training signals for channel estimation between antennas in environments with severe noise like radio channels , can improve the quality of the received signal.

另外，本发明还存在通过将沃尔什解码过程和零填充用于接收天线端的信道估计，可以显著降低噪声方差的益处。In addition, the present invention has the benefit that the noise variance can be significantly reduced by using the Walsh decoding process and zero padding for channel estimation at the receive antenna end.

附图描述Description of drawings

通过结合附图对本发明的优选实施例进行如下描述，本发明的上面和其它目的和特征将更加显而易见，在附图中：The above and other objects and features of the present invention will be more apparent by describing preferred embodiments of the present invention in conjunction with the accompanying drawings, in which:

图1是例示传统MIMO-OFDM系统的配置的图形；FIG. 1 is a diagram illustrating a configuration of a conventional MIMO-OFDM system;

图2是描述按照本发明实施例的MIMO-OFDM系统中利用沃尔什编码脉冲列的训练信号生成方法和利用沃尔什解码的信道估计方法的视图；和2 is a view describing a training signal generation method utilizing Walsh coded pulse trains and a channel estimation method utilizing Walsh decoding in a MIMO-OFDM system according to an embodiment of the present invention; and

图3是描述按照本发明实施例的MIMO-OFDM系统中的沃尔什编码训练信号和天线接收信号的视图。FIG. 3 is a view describing a Walsh coded training signal and an antenna reception signal in a MIMO-OFDM system according to an embodiment of the present invention.

具体实施方式 Detailed ways

通过结合附图进行如下详细描述，本发明的上述目的、特征、和优点将更加显而易见，因此，本领域的普通技术人员可以容易地想像本发明的附属物。并且，在如下的描述中，将不详细描述那些众所周知的现有技术，因为它们有可能使本发明埋没在不必要的细节之中。在下文中，将参照附图详细给出本发明的优选实施例。The above objects, features, and advantages of the present invention will be more apparent through the following detailed description in conjunction with the accompanying drawings, so those skilled in the art can easily imagine the appendages of the present invention. Also, in the following description, well-known prior arts will not be described in detail since they might obscure the present invention in unnecessary detail. Hereinafter, preferred embodiments of the present invention will be given in detail with reference to the accompanying drawings.

首先，在详细描述本发明之前，简单说明传统OFDM技术。First, before describing the present invention in detail, a conventional OFDM technique is briefly explained.

为了防止OFDM中的码元间干扰(ISI)，其中配备了比信道响应的长度长的循环前缀(CP)。考虑到信道的最大响应长度，CP的长度大约是整个OFDM码元长度的1/4。因此，在时域中，在一个OFDM码元的长度内可能存在4次信道响应。In order to prevent inter-symbol interference (ISI) in OFDM, a cyclic prefix (CP) longer than the length of the channel response is provided therein. Considering the maximum response length of the channel, the length of CP is about 1/4 of the whole OFDM symbol length. Therefore, in the time domain, there may be 4 channel responses within the length of one OFDM symbol.

本发明提供了发送利用沃尔什码编码的训练信号，以便MIMO-OFDM系统可以使用如上所述的信道的时间响应特性，和可以在接收端作出准确信息估计的方法。The present invention provides a method of transmitting a training signal coded with a Walsh code so that the MIMO-OFDM system can use the time response characteristics of the channel as described above and can make accurate information estimation at the receiving end.

换句话说，由于考虑到最大响应长度，在一个OFDM码元中可以容纳4个脉冲，本发明可以发送4个沃尔什编码脉冲列；并且，当4个天线发送各自相应沃尔什编码脉冲列时，允许4×4个MIMO-OFDM信道估计信道响应。In other words, due to consideration of the maximum response length, 4 pulses can be accommodated in one OFDM symbol, and the present invention can transmit 4 Walsh coded pulse trains; and, when 4 antennas transmit respective corresponding Walsh coded pulses When in columns, 4×4 MIMO-OFDM channels are allowed to estimate the channel response.

图2是描述按照本发明实施例的MIMO-OFDM系统中利用沃尔什编码脉冲列的训练信号生成方法和使用沃尔什解码的信道估计方法的视图。图3是描述按照本发明实施例的MIMO-OFDM系统中的沃尔什编码训练信号和天线接收信号的视图。2 is a view describing a training signal generation method using Walsh coded pulse trains and a channel estimation method using Walsh decoding in a MIMO-OFDM system according to an embodiment of the present invention. FIG. 3 is a view describing a Walsh coded training signal and an antenna reception signal in a MIMO-OFDM system according to an embodiment of the present invention.

将本发明应用于下面参照图2描述本发明信道估计方法的概念的MIMO-OFDM系统。The present invention is applied to a MIMO-OFDM system in which the concept of the channel estimation method of the present invention is described below with reference to FIG. 2 .

在发送端，首先在框21中通过沃尔什编码生成训练信号，然后在框22中进行IFFT变换。通过发送天线发送IFFT变换信号。然后，在接收端，在框23中接收信号被沃尔什解码和零填充，然后在框24中进行FFT变换。这样，估计各自发送天线与接收天线之间的信道。At the sending end, the training signal is first generated by Walsh encoding in block 21, and then IFFT is performed in block 22. The IFFT transformed signal is transmitted through the transmitting antenna. Then, at the receiving end, the received signal is Walsh-decoded and zero-filled in block 23 and then FFT-transformed in block 24 . In this way, the channels between the respective transmit and receive antennas are estimated.

首先，下面将对在发送端实现的使用沃尔什编码脉冲列的训练信号生成方法加以描述。First, a method of generating a training signal using a Walsh coded pulse train implemented at the transmitting end will be described below.

在发送端，根据发送天线的数量生成多个沃尔什码，以便创建由利用沃尔什码编码的脉冲列组成的训练信号。At the transmitting end, a plurality of Walsh codes are generated according to the number of transmitting antennas in order to create a training signal consisting of pulse trains encoded with Walsh codes.

如果发送天线和接收天线的数量分别是4个，所使用的沃尔什码的阶也是4，这可以通过下面的Eq.(2)给出。此时，在发送天线和接收天线的数量分别大于4个的情况下，如果使用了2个OFDM码元和使用了更高阶的沃尔什码，则可以扩展到8。If the number of transmit antennas and receive antennas is 4 respectively, the order of the Walsh code used is also 4, which can be given by Eq. (2) below. At this time, when the number of transmitting antennas and receiving antennas is greater than 4, it can be extended to 8 if 2 OFDM symbols and higher order Walsh codes are used.

$(\begin{matrix} {W W}_{11} [[11]],, & {W W}_{11} [[22]],, & {W W}_{11} [[33]],, & {W W}_{11} [[44]] \\ {W W}_{22} [[11]],, & {W W}_{22} [[22]],, & {W W}_{22} [[33]],, & {W W}_{22} [[44]] \\ {W W}_{33} [[11]],, & {W W}_{33} [[22]],, & {W W}_{33} [[33]],, & {W W}_{33} [[44]] \\ {W W}_{44} [[11]],, & {W W}_{44} [[22]],, & {W W}_{44} [[33]],, & {W W}_{44} [[44]] \end{matrix}) = = (\begin{matrix} 11,, & 11,, & 11,, & 11 \\ 11,, & - - 11,, & 11,, & - - 11 \\ 11,, & 11,, & - - 11,, & - - 11 \\ 11,, & - - 11,, & - - 11,, & 11 \end{matrix}) - - - - - - Eq Eq . . ((22))$

并且，在上面描述的Eq.(2)中的沃尔什码具有相互正交性；因此，获得如下方程。Also, the Walsh codes in Eq. (2) described above have mutual orthogonality; therefore, the following equation is obtained.

如果发送天线的数量是4，则沃尔什编码训练信号如图3所示。也就是说，以这样的方式从发送天线31发送训练信号，即，如上面Eq.(2)所示的沃尔什码出现在时域中最大响应时间间隔(L个样本)上。If the number of transmit antennas is 4, the Walsh coded training signal is shown in FIG. 3 . That is, the training signal is transmitted from the transmission antenna 31 in such a manner that the Walsh code as shown in Eq. (2) above appears over the maximum response time interval (L samples) in the time domain.

此时，发送天线i利用沃尔什码。并且，从发送天线i发送的W_i[m]训练信号可以通过使用如下的单位脉冲函数表示成时域中的离散信号：At this time, Walsh codes are used for the transmission antenna i. Also, the W _i [m] training signal transmitted from transmit antenna i can be represented as a discrete signal in the time domain by using the unit impulse function as follows:

is_i(n)＝W_i[1]δ[n]+W_i[2]δ[n-L]+W_i[3]δ[n-2L]+W_i[4]δ[n-3L] Eq.(4)其中，is_i(n)表示从天线i发送的时间训练信号的第n样本；n具有0≤n≤N-1的关系，N是总子信道数和是2的指数次方的值；δ[n]代表只有当n＝0时单位脉冲函数才具有1；和L(＝N/4)表示OFDM信号的最大响应长度。频域中的沃尔什编码训练信号TS_i(n)可以通过执行如下的FFT获得：is _i (n)＝W _i [1]δ[n]+W _i [2]δ[nL]+W _i [3]δ[n-2L]+W _i [4]δ[n-3L] Eq .(4) Among them, is _i (n) represents the nth sample of the time training signal sent from antenna i; n has a relationship of 0≤n≤N-1, N is the total number of sub-channels and is the exponential power of 2 δ[n] represents that the unit pulse function has 1 only when n=0; and L(=N/4) represents the maximum response length of the OFDM signal. The Walsh coded training signal TS _i (n) in the frequency domain can be obtained by performing the FFT as follows:

TS_i(n)＝FFT[ts_i(n)] Eq.(5)TS _i (n)=FFT[ts _i (n)] Eq.(5)

其中，FFT[]指示快速付里叶运算。Among them, FFT[] indicates fast Fourier operation.

现在，详细描述在接收端使用沃尔什解码的信道估计方法。与发送端一样，接收端也应该生成视接收天线的数量而定的多个沃尔什码。在下文中，对与发送端一样，发送天线和接收天线的数量都是4，并使用沃尔什码的例子给予描述。Now, the channel estimation method using Walsh decoding at the receiving end will be described in detail. Like the transmitter, the receiver should also generate a number of Walsh codes depending on the number of receive antennas. Hereinafter, a description will be given of an example in which the number of transmitting antennas and the number of receiving antennas are both 4 as in the transmitting end, and Walsh codes are used.

如图3所示，在本发明的MIMO-OFDM系统中，当从每个发送天线31发送ts_i(n)信号时，通过每个发送天线31发送的信号是重叠的，并且通过每个相应接收天线32接收。As shown in Figure 3, in the MIMO-OFDM system of the present invention, when ts _i (n) signals are transmitted from each transmitting antenna 31, the signals transmitted by each transmitting antenna 31 are overlapped, and through each corresponding The receiving antenna 32 receives.

这个重叠信号(接收信号)包含每个天线的信道响应。也就是说，通过接收天线j接收的信号是通过使来自每个发送天线的沃尔什编码训练信号都经过该信道重叠的信号。接收信号可以通过下式表示：This superimposed signal (received signal) contains the channel response of each antenna. That is, the signal received by the receiving antenna j is a signal that is overlapped by passing the Walsh coded training signal from each transmitting antenna through this channel. The received signal can be represented by the following formula:

${r r}_{i i} [[n no]] = = {Σ Σ}_{j j = = 11}^{44} {ts ts}_{j j} [[n no]] * * {h h}_{ij ij} [[n no]]$

$= = {Σ Σ}_{j j = = 11}^{44} (({W W}_{j j} [[11]] {h h}_{ij ij} [[n no]] + + {W W}_{j j} [[22]] {h h}_{ij ij} [[n no - - L L]] + + {W W}_{j j} [[33]] {h h}_{ij ij} [[n no - - 22 L L]] + + {W W}_{j j} [[44]] {h h}_{ij ij} [[n no - - 33 L L]])) - - - - - - Eq Eq . . ((66))$

其中，*表示卷积算符，和h_ij[n]示出发送天线j与接收天线i之间的信道的时间响应。考虑因果系统，这可以通过下式给出：where * denotes a convolution operator, and h _ij [n] shows the time response of the channel between transmit antenna j and receive antenna i. Considering a causal system, this can be given by:

如果n＜0或L-1＜n，则h_ij[n]＝0 Eq.(7)If n<0 or L-1<n, then h _ij [n]=0 Eq.(7)

从上面Eq.(6)和Eq.(7)中导出的重叠信号经历分离各自相应天线之间的信道响应的沃尔什解码过程。此时，通过使用如上面Eq.(3)所述的沃尔什码的正交性，可以非常简单地在时域中执行沃尔什解码过程。The overlapping signals derived from Eq. (6) and Eq. (7) above undergo a Walsh decoding process that separates the channel responses between the respective antennas. At this time, the Walsh decoding process can be performed in the time domain very simply by using the orthogonality of Walsh codes as described in Eq. (3) above.

为了更便于沃尔什解码，将接收信号r_i[n]划分成4个间隔，因此，可以按如下表示成2维排列信号：In order to facilitate Walsh decoding, the received signal r _i [n] is divided into 4 intervals, therefore, it can be expressed as a 2-dimensional array signal as follows:

${r r}_{i i} [[11]] [[n no]] = = {r r}_{i i} [[n no]],,$

$= = {Σ Σ}_{j j = = 11}^{44} {W W}_{j j} [[11]] {h h}_{ij ij} [[n no]],, 00 \leq \leq n no \leq \leq L L - - 11 - - - - - - Eq Eq . . ((88))$

${r r}_{i i} [[22]] [[n no]] = = {r r}_{i i} [[n no + + L L]],,$

$= = {Σ Σ}_{j j = = 11}^{44} {W W}_{j j} [[22]] {h h}_{ij ij} [[n no]],, 00 \leq \leq n no \leq \leq L L - - 11 - - - - - - Eq Eq . . ((99))$

${r r}_{i i} [[33]] [[n no]] = = {r r}_{i i} [[n no + + 22 L L]],,$

$= = {Σ Σ}_{j j = = 11}^{44} {W W}_{j j} [[33]] {h h}_{ij ij} [[n no]],, 00 \leq \leq n no \leq \leq L L - - 11 - - - - - - Eq Eq . . ((1010))$

${r r}_{i i} [[44]] [[n no]] = = {r r}_{i i} [[n no + + 33 L L]],,$

$= = {Σ Σ}_{j j = = 11}^{44} {W W}_{j j} [[44]] {h h}_{ij ij} [[n no]],, 00 \leq \leq n no \leq \leq L L - - 11 - - - - - - Eq Eq . . ((1111))$

时域中多种多样天线的重叠信道响应可以通过下面作为沃尔什解码过程的Eq.(12)分离。换句话说，将通过每个接收天线接收的信号乘以相应沃尔什码进行沃尔什解码。然后，通过将沃尔什解码接收信号对每个OFDM码元求平均估计信道响应。The overlapping channel responses of various antennas in the time domain can be separated by Eq. (12) below as a Walsh decoding process. In other words, Walsh decoding is performed by multiplying the signal received through each receiving antenna by the corresponding Walsh code. The channel response is then estimated by averaging the Walsh decoded received signal for each OFDM symbol.

${\overset{~ ~}{h h}}_{ij ij} [[n no]] = = \frac{11}{44} {Σ Σ}_{m m = = 11}^{44} {r r}_{i i} [[m m]] [[n no]] {W W}_{j j} [[m m]]$

$= = \frac{11}{44} {Σ Σ}_{m m = = 11}^{44} (({Σ Σ}_{i i = = 11}^{44} {W W}_{i i} [[m m]] {h h}_{ij ij} [[n no]])) {W W}_{j j} [[m m]]$

$= = {Σ Σ}_{i i = = 11}^{44} ((\frac{11}{44} {Σ Σ}_{m m = = 11}^{44} {W W}_{i i} [[m m]] {W W}_{j j} [[m m]])) {h h}_{ij ij} [[n no]] - - - - - - Eq Eq . . ((1212))$

通过使用如Eq.(3)所述的沃尔什码的正交性，可以沃尔什解码通过上面Eq.(12)估计的信道响应：By using the orthogonality of Walsh codes as described in Eq.(3), the channel response estimated by Eq.(12) above can be Walsh decoded:

如果l＝j，则 ${\tilde{h}}_{ij} [n] = h_{ij} [n] - - - Eq . (13)$ If l=j, then ${\tilde{h}}_{ij} [no] = h_{ij} [no] - - - Eq . (13)$

在分离了各自相应信道之间的信道响应之后，将零填充进去，以考虑信道的延迟分布。也就是说，对接在每个OFDM码元保护间隔的数据之后的部分进行零填充。更具体地说，通过在h_ij[n]之后填充(N-L)个零，然后进行FFT，可以导出信道的频率响应。After separating the channel responses between respective corresponding channels, zeros are padded in to account for the delay distribution of the channels. That is to say, zero padding is performed on the part following the data of the guard interval of each OFDM symbol. More specifically, by padding _hij [n] with (NL) zeros followed by FFT, the frequency response of the channel can be derived.

在上面的过程中，为了例示信道估计，省略了噪声项。在考虑噪声项的情况下，1/4项处在上面Eq.(12)的沃尔什解码过程中，噪声方差降低为1/4。In the above procedure, the noise term is omitted in order to illustrate the channel estimation. In the case of considering the noise term, the 1/4 term is in the Walsh decoding process of Eq. (12) above, and the noise variance is reduced to 1/4.

因此，按照本发明的无线电信道估计装置和方法在其实现得到简化的同时，提高了信道估计的精确度。Therefore, the radio channel estimation apparatus and method according to the present invention improves the accuracy of channel estimation while its implementation is simplified.

虽然参照某些优选实施例已经对本发明进行了描述，但对于本领域的普通技术人员来说，显而易见，可以不偏离如所附权利要求书限定的本发明范围地作出各种各样的改变和修改。Although the invention has been described with reference to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the appended claims. Revise.

Claims

1. a kind of training signal generation method that uses the pulse train that utilizes orthogonal code coding to be used for the channel estimation of receiving end in MIMOOFDM system, the method comprises the steps:

Create multiple orthogonal codes according to the number of transmit antennas; and

For each transmit antenna, a training signal consisting of a pulse train encoded with an orthogonal code is generated.

2. The method according to claim 1, wherein, if the numbers of transmitting antennas and receiving antennas are 4 respectively, the orthogonal code creation step creates Walsh codes as the orthogonal codes as follows:

(\begin{matrix} {W W}_{11} [[11]],, & {W W}_{11} [[22]],, & {W W}_{11} [[33]],, & {W W}_{11} [[44]] \\ {W W}_{22} [[11]],, & {W W}_{22} [[22]],, & {W W}_{22} [[33]],, & {W W}_{22} [[44]] \\ {W W}_{33} [[11]],, & {W W}_{33} [[22]],, & {W W}_{33} [[33]],, & {W W}_{33} [[44]] \\ {W W}_{44} [[11]],, & {W W}_{44} [[22]],, & {W W}_{44} [[33]],, & {W W}_{44} [[44]] \end{matrix}) = = (\begin{matrix} 11,, & 11,, & 11,, & 11 \\ 11,, & - - 11,, & 11,, & - - 11 \\ 11,, & 11,, & - - 11,, & - - 11 \\ 11,, & - - 11,, & - - 11,, & 11 \end{matrix}) . .

3. The method according to claim 2, wherein the training signal generating step utilizes the following equation to generate a training signal for each transmit antenna:

ts _i (n)=W _i [1]δ[n]+W _i [2]δ[nL]+W _i [3]δ[n-2L]+W _i [4]δ[n-3L],

Among them, ts _i (n) represents the nth sample of the time-domain training signal sent from antenna i; n has a relationship of 0≤n≤N-1, and N is the total number of sub-channels; δ[n] represents only when n= The unit pulse function has 1 when 0; and L represents the maximum response length of the OFDM signal.

4. A channel estimation method using orthogonal code decoding in an MIMO system, the method comprising the steps of:

Create multiple orthogonal codes depending on the number of receive antennas;

decoding signals received through each receive antenna using an orthogonal code; and

The channel response is estimated by averaging the received signal decoded with the orthogonal code for each OFDM symbol.

5. The method of claim 4, further comprising the steps of:

Perform zero padding and fast Fourier transform on the part following the data of each OFDM symbol guard interval.

6. The method according to claim 4, wherein if the numbers of transmitting antennas and receiving antennas are 4 respectively, the orthogonal code creating step creates Walsh codes as the orthogonal codes using the equation set forth in claim 2.

7. The method according to claim 6, wherein, if the number of receiving antennas is 4, the channel estimation step utilizes the following equation to estimate the channel response:

{\overset{~ ~}{h h}}_{ij ij} [[n no]] = = \frac{11}{44} {Σ Σ}_{m m = = 11}^{44} {r r}_{i i} [[m m]] [[n no]] {W W}_{j j} [[m m]]

= = \frac{11}{44} {Σ Σ}_{m m = = 11}^{44} (({Σ Σ}_{i i = = 11}^{44} {W W}_{i i} [[m m]] {h h}_{ij ij} [[n no]])) {W W}_{j j} [[m m]]

= = {Σ Σ}_{i i = = 11}^{44} ((\frac{11}{44} {Σ Σ}_{m m = = 11}^{44} {W W}_{i i} [[m m]] {W W}_{j j} [[m m]])) {h h}_{ij ij} [[n no]] . .