KR100630105B1 - Propagation delay estimation apparatus and method in mobile communication system - Google Patents

Abstract

The present invention provides a method for estimating a reception path of a signal received through the multipath in a mobile communication system for receiving a transmission signal at a predetermined time interval through at least two or more multipaths, wherein the received signal is a correlation matrix. Decomposing the signal component and the noise component using the method, searching for an estimated value for each of the noise component and the signal component, and using the estimated value of the found noise component and the signal component. The process of estimating the path is made.

Channel estimation, propagation delay, rake receiver, channel impulse response, noise portion, signal portion

Description

Propagation delay estimation apparatus and method in mobile communication system {METHOD AND APPARATUS FOR PROPAGATION DELAY ESTIMATION IN MOBILE COMMUNICATION SYSTEM}             

1 is a diagram illustrating a channel estimation process using a general delay estimator.

2 is a diagram illustrating a channel estimation process using a delay estimator according to the present invention.

3 is a diagram illustrating a received signal divided into a signal region and a noise region by a delay estimator of the present invention.

4 is a view showing the signal strength of the weight proposed in the present invention.

5 shows the effect of channel estimation in accordance with the present invention and the conventional general scheme.

The present invention relates to a channel estimation apparatus and method for a mobile communication system, and more particularly, to this propagation delay estimation in the downlink.

As the mobile telecommunication system is rapidly developed and the amount of data serviced by the mobile telecommunication system is rapidly increased, a third generation mobile telecommunication system for transmitting data at higher speed has been developed. As the third generation mobile communication system, Europe uses a wideband code division multiple access (W-CDMA) scheme, which is asynchronous between base stations, and North America is synchronized between base stations. A code division multiple access-2000 (CDMA-2000) scheme is standardized to a wireless access standard, and the mobile communication system typically communicates with a plurality of user equipments (UEs) through one base station (Node B). It consists of a form. However, in the mobile communication system, distortion of a received signal is generated due to a fading phenomenon occurring on a wireless channel during high speed data transmission. Since the fading phenomenon reduces the amplitude of the received signal from several dB to several tens of dB, the received signal distorted by the fading phenomenon causes information error of the transmitted data transmitted from the transmitting side if the data is not compensated for during demodulation. It lowers the quality of mobile communication service. Therefore, in order to transmit high-speed data without deterioration of service quality in a mobile communication system, a fading phenomenon must be overcome, and various kinds of diversity schemes are used to overcome the fading phenomenon.

In general, a CDMA method employs a Rake receiver for diversity reception using delay spread of a channel signal. Receive diversity is applied to the rake receiver to receive a multi-path signal, and each finger of the rake receiver is assigned a signal path to perform demodulation. On the other hand, the rake receiver to which the diversity technique using the above-described delay spread is applied does not operate when the delay spread is smaller than the set value. In addition, a time diversity scheme using an interleaving scheme and a coding scheme is generally used in a Doppler spread channel. However, the time diversity scheme has a problem in that it is difficult to use the slow Doppler spreading channel.

As described above, in the mobile receiving environment in which the multipath fading channel is affected, signals are received by the mobile station at different time delays and sizes through a plurality of paths. It is necessary to combine the received signals in order to convert the signal received at the mobile terminal into a signal having a sufficient size with the different reception delay time and magnitude. In order to combine the received signals, an algorithm capable of estimating the delay time and the degree of attenuation of each path is required.

Figure 1 shows an algorithm that can estimate the delay time and the degree of attenuation of each path. Hereinafter, an algorithm for estimating a delay time and attenuation degree of each path will be described in detail with reference to FIG. 1. 1 includes a matching filter 100, a correlator 102, a square detector 104, an averager 106, and a detector 108. Hereinafter, the role performed by the matching filter 100 will be described and the operation performed by the remaining components will be described.

In a mobile communication system, a user's data symbols are spread in a spectrum, which is an effective spreading sequence including a spreading code and a scrambling code. The spread signal is transmitted through a radio channel through a filter in the form of a pulse. The baseband model of the transmission signal for one mobile terminal can be expressed as Equation 1 below.

=

는 칩구간을 의미한다. 상기 송신 신호는 L개의 경로를 갖는 다중 경로 채널을 통해 이동통신 시스템의 수신부로 전달된다. 하기 〈수학식 2〉는 채널의 임펄스 응답으로서

은 각 경로의 지연 시간을 의미하며,

는 크기와 위상을 나타내는 복소값이다.S (t) is a transmission signal, and p (t) is a root-raised cosine pulse having a roll-off factor of 0.22. In addition, the T means the length of the symbol interval,

=

Means chip segment. The transmission signal is transmitted to a receiver of a mobile communication system through a multipath channel having L paths. Equation 2 is an impulse response of a channel.

Means the delay time of each path,

Is a complex value representing magnitude and phase.

The transmission signal passing through the wireless channel is added to the white Gaussian noise n (t) to receive a reception signal of the form as shown in Equation 3 below.

After the filtering is performed in the matching filter having the same impulse response as the matching filter used in the transmitting end, the final output is expressed by Equation 4 below.

로서 필터를 통과한 잡음과 다른 사용자 간섭신호를 의미한다. 일반적인 이동통신 시스템과 마찬가지로 수신단은 미리 알려진 데이터 심볼이 연속적으로 송출되고 파일럿 채널(Pilt Channel)이 존재한다고 가정한다. 또한 하나의 이동단말에 대한 서로 다른 데이터 채널들은 모두 상기 파일럿 채널에 직교하므로, 상기 데이터 채널에 대한 신호는 상기 〈수학식 3〉의 잡음항n(t)에 포함시킬 수 있다. 상기 파일럿 채널로 전송되는 파일럿 심볼을 A라 하면, 상기 〈수학식 1〉은 하기 〈수학식 5〉와 같이 나타낼 수 있다.R_p (t) is an autocorrelation function of p (t), and n '(t) is

This refers to noise passing through the filter and other user interference signals. As in a general mobile communication system, a receiver assumes that a known data symbol is continuously transmitted and a pilot channel exists. In addition, since all different data channels for one mobile terminal are orthogonal to the pilot channel, the signal for the data channel can be included in the noise term n (t) of Equation (3). If A is a pilot symbol transmitted on the pilot channel, Equation 1 may be expressed as Equation 5 below.

라 하면 상기 z(t)는 하기 〈수학식 6〉으로, 상기

는 하기 〈수학식 7〉로 나타낼 수 있다.The matching filter for the pilot channel is called z (t) and the output of the pure signal excluding the noise term

If z (t) is represented by the following equation (6),

Can be represented by Equation 7 below.

는 상기 효과적인 확산 시퀀스를 벡터 형태로 나타낸 것이며, 칩 단위로 샘플링된 효과적인 채널 임펄스 응답인 h는 하기 〈수학식 8〉과 같이 나타낼 수 있다.remind

Denotes the effective spreading sequence in the form of a vector, and h, which is an effective channel impulse response sampled in units of chips, may be represented by Equation 8 below.

라 하면, j번째 블록은 하기 〈수학식 9〉와 같이 나타낼 수 있다. Hereinafter, the operation in the correlator 102 will be described. The correlator 102 cannot use an infinitely long signal sequence as in Equation 8, and obtains a channel response using only a part of the effective spreading sequence. When estimating the W samples of the channel impulse response using the correlator having length N, the received signals are grouped into (N + W-1) chip unit blocks. The starting position index of the chip unit block

In this case, the j-th block may be represented by Equation 9 below.

D _j has a matrix in which the effective spreading sequence is shifted as shown in Equation 10 below.

를 이용하여 간단한 행렬 곱셈의 형태로 나타낼 수 있다.Assuming that the channel impulse response does not change during the (N + W-1) chip period in Equation (9), the operation of the correlator is a W (N + W-1) matrix as shown in Equation (11).

Can be expressed in the form of simple matrix multiplication.

는 벡터 d의

위치에서부터 길이 N만큼의 길이를 취한 서브시퀀스(subsequence)이다. 이 경우, 상기 상관기의 출력인 채널 추정값인

는 수신 신호의 벡터

에

를 곱한 형태로서 하기 〈수학식 12〉와 같이 나타낼 수 있다.remind

Of the vector d

It is a subsequence taking the length N from the position. In this case, the channel estimate that is the output of the correlator

Vector of receive signal

on

It can be expressed as <Equation 12> as a multiplied form.

는 잡음항과 신호항으로 구성된 수신 신호에서 잡음 항을 제외한 표현이다. 따라서, 상기 상관기(102)의 출력

는 상관되지 않은 잡음 항을 포함하여

와 같이 표현된다. 상기 잡음항을 포함한

를 채널 스냅샷(Channel Snapshot)이라 한다. 또한 상기 N이 충분한 값을 가진다면

는 (W×W)의 단위 행렬로 근사화됨으로서 상기

는 상기

의 추정 값이 된다.remind

Is the expression excluding the noise term from the received signal consisting of the noise term and the signal term. Thus, the output of the correlator 102

Including the uncorrelated noise term

It is expressed as Including the noise term

This is called a channel snapshot. Also, if N has a sufficient value

Is approximated by a unit matrix of (W × W)

Above

Is an estimated value of.

Hereinafter, operations performed by the square detector 104 and the averager 106 will be described. In general, a method of finding a peak position from a power delay profile (PDP) of a channel impulse response is used to estimate a delay time of a signal received at the correlator 102. The PDP of the channel is obtained by averaging the power of each sample of M consecutive channel snapshots as shown in Equation 13 and Equation 14 below.

Equation 13 represents a process performed by the square detector 104, and Equation 14 represents a process performed by the averager 106. The signal output from the averager 106 is input to the detector 108. The detector 108 detects only a signal that exceeds a set value in the input signal.

In general, the energy of the signal is mostly concentrated around the line of sight (LOS) component on the time base. In particular, in the case of indoor reception having a relatively short length of delay spread, it is necessary to accurately separate paths received at a small size from paths adjacent to each other such as a fat finger. However, it is not easy to isolate path delays that are received consecutively within a relatively small or short period of less than one chip. In addition, the conventional rake receiver is divided into a search part for estimating propagation delay using a correlator and a detection part for separating delays of about 1/2 chip. Small propagation delay is detected in the search part, or even in the detection part, there is a disadvantage that the paths are considered as one path when signals are adjacent to each other. Thus, ways to overcome the above disadvantages are discussed.

Accordingly, an object of the present invention is to propose an apparatus and method for accurately estimating a received signal along a path from a received signal received through a multipath.

Another object of the present invention is to propose an apparatus and method for accurately estimating a received signal along a path to prevent a small received signal from being absorbed by a large received signal and recognized as one receiving path.

Another object of the present invention is to propose an apparatus and method for recovering a signal transmitted from a transmitter without error by accurately estimating a received signal along a path.

In the mobile communication system for receiving a transmission signal at a predetermined time interval through at least two or more multi-path in order to achieve the above object of the present invention, in the method for estimating the receiving path of the signal received through the multi-path, Decomposing the received signal into a signal component and a noise component using a correlation matrix, searching for an estimated value for each of the noise component and the signal component, and searching for the detected noise component and the signal component Estimating the path of the received signal using the estimated value.

An apparatus for estimating a reception path of a signal received through the multipath in a mobile communication system for receiving one transmission signal at a predetermined time interval through at least two or more multipaths in order to achieve the objects of the present invention, A signal / noise detector for decomposing the received signal into signal and noise components using a correlation matrix, a noise detector for calculating an estimate using the searched noise components, and calculating an estimate using the searched signal components And a detector for estimating the path of the received signal using the calculated estimates.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. In addition, in describing the present invention, when it is determined that the detailed description of the related known functions or configurations may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

2 is a diagram illustrating a process of recovering a transmission signal by estimating a delayed signal according to the present invention. 2 illustrates a matched filter 200, correlator 202, detector 204, signal / noise detector 206, noise detector 208, signal detector 210, multiplier 212, and detector 214. It consists of.

The operation performed by the matching filter 200 and the correlator 202 is the same as the operation performed by the matching filter 100 and the correlator 102 illustrated in FIG. 1. Hereinafter, an operation performed by the searcher 204 will be described. The searcher 204 obtains a correlation matrix for spatial decomposition of a signal and noise, defines an autocorrelation matrix of continuous channel snapshots output from the correlator 200 as R, and defines the autocorrelation function by an eigenvalue. When analyzed, it can be expressed as an eigenvector and an eigenvalue, as shown in Equation 15 below.

는 대각 성분이 R의 고유 값(

)으로 구성된 대각 행렬이다. k번째 고유값에 해당하는 신호 벡터의 전력을

라 하면

는 하기 〈수학식 16〉과 같이 나타낼 수 있다.As such, the signal / noise detector 206 detects signal components and noise components through the eigenvectors and eigenvalues output from the searcher 204. 3 shows the eigenvectors and eigenvalues in the signal region and the noise region. In FIG. 3, the matrix U is a unitary matrix in which each column is an eigenvector of the matrix R.

Is the eigenvalue of R

Is a diagonal matrix of the power of the signal vector corresponding to the kth eigenvalue

If

Can be expressed as in Equation 16 below.

와 나머지 고유벡터들로 구성된

을 분리하면, 상기 행렬 U는 [

] 으로 나타낼 수 있다. 상기 행렬 U는 신호 영역과 잡음 영역으로 구분되며, 상기 신호영역은

으로 나타낼 수 있으며, 상기 잡음영역은

으로 나타낼 수 있다.Assuming that the signal component L is known, the region can be divided into a signal region and a noise region as described above. The matrix U has the largest eigenvector as a column

And the remaining eigenvectors

If we separate, the matrix U is [

] The matrix U is divided into a signal region and a noise region, and the signal region is

The noise region is

It can be represented as

를 칩단위로 샘플링한 값을 원소로 가지는 길이 W인 자기 상관 벡터

는 하기 〈수학식 17〉과 같이 나타낼 수 있다.p (t) delayed by τ is an autocorrelation function

Autocorrelation vector of length W with elements as the sample of

Can be expressed as in Equation 17 below.

의 잡음 부분 공간에 대한 투영(projection) 형태가 된다. 상기 잡음 부분의 추정값

을 구하기 위해 연속된 M개의 채널 스냅샷의 자기 상관 행렬을 시평균함으로서 구할 수 있다. 하기 〈수학식 18〉은 상기 잡음 부분의 추정값

을 구하기 위해 시평균하는 과정을 나타내고 있다.Multiple signal classification (MUSIC) spectrum is a signal vector

Is a projection of the noise subspace of. Estimate of the noise portion

It can be found by time-averaging the autocorrelation matrix of successive M channel snapshots. Equation 18 is an estimated value of the noise portion.

The time-averaging process is shown to find.

를 이용하여 구한다. 상기 고유값은

의 크기에 따라 정렬하고, 상기 정렬된

를

으로 나누면 상기 MUSIC는 하기 〈수학식 19〉와 같이 나타낼 수 있으며, 상기 잡음 검출기(208)에서 수행되는 잡음 성분의 추정값을 탐색하는 동작을 보여준다.Eigenvalue analysis is performed using the time mean value obtained in Equation (18). The eigenvalue analysis

Obtain using The eigenvalue is

Sorted according to the size of the

To

Dividing by, the MUSIC can be expressed as in Equation 19, and shows an operation of searching for an estimated value of a noise component performed by the noise detector 208.

은 서로 직교하므로 상기 MUSIC 스펙트럼이 최대치를 형성하는 τ가 채널의 경로 지연시간이다. 이하 상기 신호 검출기(210)에서 수행되는 성분의 추정값을 탐색하는 동작에 대해 알아본다. 상기 신호/잡음 검출기(206)의 출력 신호는 상기 신호 검출기(210)로 전달된다. 일반적으로 잡음 부분 공간의 추정 고유벡터를 순수한 신호 영역에 대해 투영을 취하면, 상기 투영 결과는 평균이 0인 가우시안이며, 이에 대한 행렬은 하기 〈수학식 20〉과 〈수학식 21〉과 같다.g (tau) and noise domain eigenvectors

Are orthogonal to each other, and τ, where the MUSIC spectrum forms a maximum, is the path delay time of the channel. Hereinafter, an operation of searching for an estimated value of the component performed by the signal detector 210 will be described. The output signal of the signal / noise detector 206 is transmitted to the signal detector 210. In general, when the estimated eigenvectors of the noise subspace are projected onto a pure signal region, the projection result is a Gaussian having an average of 0, and the matrixes thereof are as shown in Equations 20 and 21.

는 크로넥커 델타 함수(Kronecker delta function)이며, 상기 Q는 하기 〈수학식 22〉와 같다.Of Equation 20 above

Is a Kronecker delta function, and Q is represented by Equation 22 below.

는 신호영역 좌표이고,

는 새로운 가중치 신호세기이며,

는 고유값으로서, 상기

는 하기 〈수학식 23〉과 같이 나타낸다.Σ ² in Equation 22 is the variance of noise, L is the number of signal components, k is greater than or equal to 1, less than or equal to L,

Is the signal domain coordinate,

Is the new weight signal strength,

Is an eigenvalue,

Is represented by the following <Equation 23>.

는 도 4에서 도시하고 있다. 하기 〈수학식 24〉는 상기 Q에 대한 예를 보이고 있다.Regarding Equation 23 above

4 is shown in FIG. Equation 24 below shows an example for the above Q.

를 잡음 부분 공간의 추정값에 대해 투영시킨 결과를 e라 가정하면, 상기 벡터 e는

로 나타낼 수 있으며, 가우시안 랜덤 벡터의 특성을 가진다. 이와 같은 성질로 인해 하기 〈수학식 25〉와 같이 PDF(Probability Density Function)을 가진다.remind

Let e be the result of projecting the estimated value of the noise subspace to e, then the vector e

It can be expressed as a Gaussian random vector. Due to such a property, it has a PDF (Probability Density Function) as shown in Equation 25 below.

이므로 상기 〈수학식 20〉과 비교하면 하기 〈수학식 26〉과 같이 나타낼 수 있다.K is a covariance matrix of e,

Therefore, when compared with Equation 20, Equation 26 may be represented.

의 스칼라곱 형태를 가지게 된다.상기 도 2에서 보이고 있는 본 발명에 따른 알고리즘에 의하면 상기 지연 추정은

가 최대값을 형성하는 위치에서 지연 값

를 구하는 과정과 동일하다. 상기 벡터 E에 대한 로그 라이클리우드(log-likelihood) 함수는 하기 〈수학식 27〉과 같다.As shown in Equation 26, K is a unit matrix of W × W.

According to the algorithm of the present invention shown in FIG. 2, the delay estimation is

The delay at the position where

Is the same process as The log-likelihood function for the vector E is expressed by Equation 27 below.

Maximization of the log-likelihood function of Equation 27 can be obtained by dividing both sides of Equation 27 by M. Equation 28 is a result of dividing both sides of Equation 27 by M.

By maximizing the resultant value obtained by Equation 28, the log-likelihood function to be obtained in the present invention can be maximized. In this case, if M converges to infinity, the first term of Equation 28 becomes 0, and if averaged for a sufficiently long interval, the log-likelihood function can be expressed as an equation expressed as Equation 29 below. have.

In Equation 29, since Q is an unknown value, an estimate is used. Equation 30 below shows an estimate of Q.

는 신호 부분 공간의 추정값이며, 잡음부분에 대한 분산의 추정치는 하기 〈수학식 31〉가 같이 구할 수 있다.remind

Is an estimate of the signal subspace, and Equation 31 can be obtained as shown in Equation 31 below.

If Equation 31 is defined as a log-likelihood function using an algorithm according to the present invention, Equation 31 may be expressed as Equation 32, which is performed by the multiplier 212.

가 곱해진 형태이다. 상기

가 경로 지연에 대한 함수이므로

의 분자항과 분모항은 모두

의 함수이다. 본원 발명에서 제안하는 알고리즘에서 상기 log-likelihood 함수를 최대로 만들기 위해 상기 분모항과 분자항을 모두 이용한다. 즉, 잡음 영역뿐만 아니라 신호영역도 동시에 이용한다. 상기 도 4에서 도시하고 있는 바와 같이 상기 〈수학식 22〉의 Q 행렬에 포함된 새로운 가중치 신호 전력인

는 신호대잡음(SNR)인

가 1에 가까운 작은 값이 될수록 오히려 큰 값을 갖는다. 따라서, 분자항의 이용은 SNR이 낮아 잡음과 섞여 구분하기 힘들었던 작은 피크값을 갖는 신호들의 크기를 증가시켜 주는 역할을 수행한다.Equation (32) is a molecular term of the MUSIC spectrum of Equation (19).

Is multiplied. remind

Is a function of the path delay

The numerator and denominator terms of both

Is a function of. In the algorithm proposed in the present invention, both the denominator term and the molecular term are used to maximize the log-likelihood function. That is, the signal area is used simultaneously as well as the noise area. As shown in FIG. 4, the new weighted signal power included in the Q matrix of Equation 22

Is the signal to noise (SNR)

The smaller the value is close to 1, the larger the value becomes. Therefore, the use of the molecular term increases the size of signals having small peak values that are difficult to distinguish from noise due to low SNR.

이다. 또한 상기에서 사용한 평균전력은 1. -20dB이며, 1000회 반복된 실험의 스펙트럼을 평균하여 나타낸 것이다. 상기 각 방식에서 채널의 PDP 및 행렬은 100개의 연속된 채널 스냅샷을 평균하여 계산하였다. 즉, M=100, 상관 행렬의 크기는 W×W= 5×5이며, N=256,

=0, 투영 그리드는

으로 선택하였다. 상기 도 4에서 보이고 있는 바와 같이 종래 일반적인 방식에서는 SNR이 낮은 두 번째 경로를 검출하지 못하고 있지만 본원 발명에 의한 방식에서는 2개의 경로에서 최대값을 형성함으로서 정확히 두개의 경로를 추정할 수 있게 된다.5 is a diagram showing the performance of the delay estimator according to the present invention and the delay estimator according to the conventional general method. The channel used in FIG. 5 is a fading channel having two paths, and each delay time is 0,

to be. In addition, the average power used in the above is 1. -20dB, it shows the average of the spectrum of 1000 repeated experiments. In each of these schemes, the PDP and matrix of the channel were calculated by averaging 100 consecutive channel snapshots. That is, M = 100, the magnitude of the correlation matrix is W × W = 5 × 5, N = 256,

= 0, the projection grid is

Selected. As shown in FIG. 4, although the second path having a low SNR is not detected in the conventional general method, exactly two paths can be estimated by forming a maximum value in the two paths in the method according to the present invention.

As described above, the present invention accurately estimates a received signal along a path from a received signal received through a multipath, thereby preventing a small received signal from being absorbed by a large received signal and being recognized as a single receive path. The signal transmitted from can be restored without error.

Claims (8)

In the mobile communication system for receiving a transmission signal at a predetermined time interval through at least two or more multi-path, in the method for estimating the receiving path of the signal received through the multi-path, Decomposing the received signal into signal components and noise components by applying eigenvalue analysis to the correlation matrix; Using a multiple signal classification (MUSIC) algorithm for the noise component, calculating a estimated value with a multiple signal classification (MUSIC) spectrum projecting an autocorrelation vector into a noise subspace, Calculating an estimated value for the signal component using the signal component as the following equation; And estimating a path of a received signal by applying a log-likelihood function to the estimated values of the MUSIC spectrum and the signal component.

Where σ ² is the variance of the noise, L is the number of signal components, k is greater than or equal to 1, less than or equal to L,

Is the signal domain coordinate,

Is the new weight signal strength,

Is eigenvalue. delete delete An apparatus for estimating a reception path of a signal received through the multipath in a mobile communication system for receiving one transmission signal at a predetermined time interval through at least two or more multipaths, A signal / noise detector that decomposes the received signal into signal and noise components by applying eigenvalue analysis to the correlation matrix; A noise detector using a multiple signal classification (MUSIC) algorithm for the noise component and calculating an estimated value with a multiple signal classification (MUSIC) spectrum projecting the autocorrelation vector into a noise subspace; A signal detector for calculating an estimated value for the signal component by using the signal component in the following equation; And a detector for applying a log-likelihood function to the MUSIC spectrum and the signal component estimate to estimate a path of a received signal.

Where σ ² is the variance of the noise, L is the number of signal components, k is greater than or equal to 1, less than or equal to L,

Is the signal domain coordinate,

Is the new weight signal strength,

Is eigenvalue. delete delete delete delete

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