KR20030059569A - Method for transmitting/receiving signal in mobile communication system - Google Patents

Abstract

PURPOSE: A method for transmitting and receiving signals in a mobile communication system is provided to reduce a calculation quantity by retrieving an optimum preprocess filter coefficient from a predetermined filter group such as a DFT(Discrete Fourier Transform) matrix. CONSTITUTION: A random combination selected from a DFT matrix and a channel vector estimated from a receiving signal are combined, and an equivalent channel vector is generated. A maximum eigen-value of a matrix multiplication with respect to the equivalent channel vector is calculated. An eigen-vector corresponding to the maximum eigen-value and indexes with respect to the combination are transmitted to a transmission terminal. A preprocess filter coefficient value corresponding to the index and a weight value corresponding to the eigen-vector are applied to a transmission signal.

Description

Signal transmission and reception method in mobile communication system {Method for transmitting / receiving signal in mobile communication system}

The present invention relates to a mobile communication system, and more particularly, to a signal transmission and reception method in a mobile communication system having a plurality of antennas.

In general, in the mobile communication system, for the high data rate and high quality transmission and reception of multimedia packet data including voice and video, there is an increasing demand for an effective countermeasure against fading phenomenon occurring in a mobile wireless channel.

In order to actively cope with such fading phenomenon, various methods of appropriately using various types of diversity in time, frequency, and spatial domains have been studied.

In particular, in the uplink (reverse) link, the reception diversity gain can be increased by using a plurality of antennas provided in the base station, but in the downlink (forward) link, the number of antennas that can be installed in the terminal is limited due to the increased complexity of the hardware structure. Therefore, a single transmit antenna cannot obtain sufficient reception space diversity effect.

Therefore, in order to overcome this problem, a transmission diversity scheme using multiple transmission antennas has recently emerged to increase usable capacity and provide high quality service in the IMT-2000 downlink. Adaptation Arrays) and preprocessing filter systems.

In the TxAA system, the receiver detects a received signal by estimating a given multipath fading channel characteristic (h ₀ (t) to h _M-1 (t)), and receives a receive diversity gain based on the multipath fading channel characteristic. After calculating the weight to maximize, information about the weight is fed back to the transmitter.

Thus, the transmitter applies the feedback weight to the transmission signal.

That is, the TxAA system uses a closed loop transmission diversity scheme.

The preprocessing filter system selects coefficients of a preprocessing filter of a transmitting end that maximizes the reception diversity gain from a standardized filter group, and feeds back the filter coefficient information to a transmitter, or receives a signal-to-noise ratio (SNR). Calculate the coefficient values directly through the maximization process and feed back the coefficient information to the transmitter.

Thus, the transmitter predistorts the transmission signal using the coefficients of the fed back prefilter.

In other words, the preprocessing filter system uses a closed loop transmission diversity scheme.

In the transmitter of the transmit diversity system using the preprocessing filter, the same data is passed through the preprocessing filters for each antenna and then transmitted to the receiving end through M transmitting antennas, and the receiver is received with a single receiving antenna and then combined with the maximum ratio. Detect data through

That is, the receiver calculates coefficients of the preprocessing filter through the estimated channel and feeds back this information to the transmitter. Here, the preprocessing filter assumes a linear filter in the form of a finite impulse response filter having a complex coefficient value.

The coefficient of the pretreatment filter is obtained by the following two methods.

First, a method of obtaining coefficients of a preprocessing filter in a predetermined filter group.

Each row of a K × 1 Discrete Fourier Transform (DFT) or Hadamard matrix is used as a coefficient for the K-tap preprocessing filter, and the receiver searches for a combination that maximizes SNR. After obtaining the optimal preprocessing filter coefficient value (that is, a specific row of the matrix) for each transmitting antenna through the feedback, only the indices of the selected row is fed back to the transmitter.

The second method is to optimize according to a given channel environment without using standardized preprocessing filter coefficients such as DFT matrix or Hadamard matrix.

At this time, coefficient values of the preprocessing filter are determined as values maximizing the SNR by a given channel characteristic, and complicated calculations are required to calculate them, and a large amount of transmission data is required to feed them back to the transmitter.

In addition, the conventional TxAA system used in the 3rd generation IMT-2000 mobile communication system calculates and applies a single weight only to a given multipath channel for each antenna, so that the diversity gain is determined solely by the given channel characteristics. There is a limit to the increase in city gain.

On the other hand, as a method of increasing diversity using a preprocessing filter, a preprocessing filter derived from a normalized orthogonal matrix such as a DFT or Hadamard matrix in a frequency non-selective fading channel environment, and an equalizer at a receiver corresponding thereto are used. The open-loop transmit diversity method and the mathematical interpretation thereof have been proposed, but are limited in that only the case where the number of taps of the preprocessing filter is equal to the number of transmitting antennas is dealt with.

On the basis of the above research results, a method of improving diversity using a preprocessing filter that does not limit the number of taps and a MAP equalizer at the receiver is proposed. However, this method uses a DFT or Hadamard matrix to determine the preprocessing filter coefficients. As a result of searching and finding, there is also a limitation in considering only the frequency non-selective fading channel environment, which does not satisfy the condition for maximizing the reception diversity gain.

In addition, methods for optimizing according to a given channel environment without using standardized preprocessing filter coefficients such as a DFT matrix or a Hadamard matrix have been proposed. Therefore, coefficient values of a preprocessing filter in a MISO system are determined at a receiving end. It is calculated to satisfy only signal to interference and maximization of noise ratio. At this time, the coefficient values of the preprocessing filter are directly determined by given channel characteristics, and the amount of transmission data for feeding back these coefficient values to the transmitter is greatly increased.

In addition, the simultaneous optimization of the coefficient values of the pre-processing and post-distortion filters in the MIMO (Multi-Input Multi-Output) system is proposed to satisfy the maximum signal-to-interference and noise ratio at the receiver. A large amount of computation is required to obtain the coefficient values of the filters, and in particular, the simultaneous optimization process has a problem that the information of the pre / post distortion filter must be continuously transmitted on the uplink and the downlink.

Accordingly, the present invention has been made in view of the above-mentioned problems of the prior art, and provides a signal transmission / reception method in a mobile communication system to obtain a diversity gain, which is an advantage of a TxAA system, and an increase effect of a received SNR of a preprocessing filter. It is to provide.

In addition, the present invention is to provide a method for transmitting and receiving a signal in a mobile communication system that is suitable to reduce the amount of feedback information.

According to an aspect of the present invention for achieving the above object, a signal transmission and reception method in a mobile communication system comprises the steps of: generating an equivalent channel vector combining a channel vector estimated from any combination selected from a DFT matrix and a received signal; Calculating a maximum eigenvalue of a matrix product for the equivalent channel vector; Transmitting eigenvectors corresponding to the maximum eigenvalues and indices for the combination to a transmitting end; And applying a preprocessing filter coefficient value corresponding to the index and a weight corresponding to the eigenvector to the transmission signal.

Preferably, an equivalent channel vector is generated by the combination and the convolution operation of the channel vector. In this case, the equivalent channel vector is generated for K preprocessing filter coefficients and for each path.

1 is a block diagram illustrating a signal transmission / reception system according to the present invention.

* Description of the symbols for the main parts of the drawings *

101: multiplier

102: pretreatment filter

103: weight application unit

104: transmit antenna

105: receiving antenna

106: diffusion part

107: maximum ratio combiner

108: judge

Hereinafter, a configuration and an operation according to an exemplary embodiment of the present invention will be described with reference to the accompanying drawings.

1 is a diagram illustrating a transmission / reception system for transmission diversity according to the present invention.

Referring to FIG. 1, the proposed system includes a multiplier 101 for multiplying an input bitstream d (t) with a signature signal s (t), a preprocessing filter 102 for predistorting the result of this product, and A weighting unit 103 for applying a weight to the distorted signal, a transmitter comprising a transmission antenna 104 for transmitting the signal to which the weight is applied, a receiving antenna 105 for receiving the transmitted signal, and A despreader 106 for detecting a received signal, a maximum ratio combiner 107 for combining the detected signals of the detected paths with a maximum ratio, and a determiner 108 for determining the sign value of the combined signal; It comprises a receiver configured.

The operation description according to the above configuration is as follows.

In the transmitter, the same data is pre-distorted by the pre-processing filter 102 for each antenna, and the pre-distorted signal is weighted for each antenna by the weight applying unit 103, and the signal to which the weight is applied is M pieces. It is transmitted to the receiver via the transmit antenna.

In the receiver, the despreader 106 detects a signal received through a single receiving antenna for each path, combines the detected signals for each path at a maximum ratio by the maximum ratio combiner 107, and combines the combined signals. The determiner 108 determines the sign bit from the signal.

The coefficient value and antenna weight of the preprocessing filter used in the transmitter of the proposed system are determined and fed back to the receiver by the following method. That is, the receiver calculates the coefficients of the preprocessing filter through the estimated channel vector and feeds back this information. Here, the preprocessing filter assumes a linear filter in the form of a finite impulse response filter having a complex coefficient value.

First, the receiver selects the coefficient values of the preprocessing filter capable of performing any combination of the rows of the DFT matrix, and then the receiver multiplies the matrix for the new equivalent channel by combining the combination and the channel vector estimated from the downlink pilot channel, V ^H. Calculate the maximum eigenvalue of V.

By repeating the above process, we find the combination of DFT matrix rows that produce the largest maximum eigenvalue, and feed back only the indexes of these rows to the transmitter, and the transmitter uses the rows of corresponding indexes of the same DFT matrix as coefficient values of M preprocessing filters. .

In addition, the eigenvector corresponding to the maximum eigenvalue of V ^H V when the selected preprocessing filters are used is fed back as a weight vector of the transmitting antenna.

Therefore, the information to be fed back in the proposed system requires only the row index of the DFT matrix for the M preprocessing filters and the M antenna weight information.

In detail, assuming that the multipath channel parameter of the downlink from the transmitter (base station) to the receiver (terminal) is estimated, the multipath fading channel h _m (t) received from the mth transmit antenna to the receiver is It is represented as 1. However, it is assumed that all channels are composed of L paths that can be decomposed into Tc intervals, which are chip intervals of a user signature code.

here, Is the i th multipath component between the m th transmit antenna and the receive antenna. The preprocessing filter of the m th transmission antenna having K taps Is expressed as in Equation 2 below.

here, Is the k th filter coefficient of the m th transmit antenna predistortion filter, ' It is expressed as', and it is a normalized factor.

New equivalent channels in the whole system are preprocessed filters With, channel It may be expressed as a convolution result of, and is represented by Equation 3 below.

Equation (3) above, preprocessing filter coefficients And channel vector Suppose that the equivalent channel of the entire system of convolutiond L + K-1 tap lengths, the signal r (t) transmitted through M transmit antennas in the proposed system and received at the receiver is represented by Equation 4 below.

here, Is the weight of the m th transmit antenna, Is a transmission symbol at bit interval T, s (t) is the user's signature code at chip interval Tc, Is Additive White Gaussian Noise (AWGN). In addition, it is assumed that the channel characteristic is kept constant for one bit interval of data, and the transmission delay of the i-th path signal received from the transmission antennas is the same.

Assuming a perfect estimate of the transmission delay, the output after despreading at the despread section 106 (commonly known as the rake finger) of the i-th path of the receiver Is expressed as in Equation 5 below.

(i = 0, ..., L + K-2)

here, ' 'to be.

The result of combining the outputs of these L + K-1 despreaders 106 at the maximum ratio is shown in Equation 6 below.

here, Is 0 and the variance is Is a Gaussian random variable.

At this time, the SNR of the output of the despreader 106 Using SNR of the maximum ratio combiner 107 output using Is expressed as Equation 7 below.

In Equation 7 Silver noise component Is the dispersion of. therefore, Once we determine the optimal weight vector to maximize. The SNR of also has the following maximum values, resulting in the maximum eigenvalues of the matrix V ^H V It can be seen that it is proportional to.

The superscript H is a mission operator.

In Equation 7, the vector w having the size of M × 1 represents a weight expressed as '[w ₀ , w ₁ , ..., w _M-1 ] ^T ', and the weights for each transmitting antenna are expressed as one vector. will be. here, ' Assume that it is normalized to '.

In addition, a new equivalent channel matrix V of M × (L + K-1) size obtained as a result of the convolution of the preprocessing filter coefficients and the channel vector may be expressed by the following Equation (8).

The vector w maximizing the SNR of Equation 8 is the maximum eigenvalue of the V ^H V matrix. Corresponding eigenvectors, these M eigenvector values are transmitted to the transmitter and used as weights for each transmit antenna.

In addition, the maximum eigenvalue Find the combination of DFT matrix rows to generate. Since the index of these rows is sent from the receiver to the transmitter, the transmitter uses M, the rows of this index, as the preprocessing filter coefficient value.

As described above, the present invention can not only reduce the calculation amount but also feedback only the index of the corresponding row of the DFT matrix by retrieving an optimal preprocessing filter coefficient from a predetermined filter group, such as a DFT matrix, to drastically reduce the feedback information. have.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

Claims (3)

Generating an equivalent channel vector combining any combination selected from the DFT matrix and the channel vector estimated from the received signal; Calculating a maximum eigenvalue of a matrix product for the equivalent channel vector; Transmitting eigenvectors corresponding to the maximum eigenvalues and indices for the combination to a transmitting end; And applying a preprocessing filter coefficient value corresponding to the index and a weight corresponding to the eigenvector to a transmission signal. The method of claim 1, wherein an equivalent channel vector is generated by the combination and a convolution operation of the channel vector. The method of claim 2, wherein the equivalent channel vector is generated for each of K preprocessing filter coefficients and each path.