KR20040098768A - Data transmission method for mimo radio communication system - Google Patents

Abstract

In the data transmission method for a multiple input / output mobile communication system according to the present invention, when the number of channel codes for identifying terminals is smaller than the number of terminals, one or more terminals may share the channel codes according to channel conditions. When the channel code is limited, the channel code can be shared between the terminals for each transmit antenna, thereby increasing the throughput of data that can be transmitted through each channel code.

Description

Signal transmission method in multi-input wireless communication system {DATA TRANSMISSION METHOD FOR MIMO RADIO COMMUNICATION SYSTEM}

The present invention relates to a MULTIPLE-INPUT MULTIPLE-OUTPUT (MIMO) wireless communication system, and more particularly to a signal transmission method that can efficiently use resources in a multiple input-output wireless communication system.

With the rapid growth of mobile communication technology and the demand for various multimedia services in a wireless environment, a large capacity of transmission data and a high speed of data transmission are progressing. Accordingly, for many studies to efficiently use the limited frequency resources to effectively provide a variety of multimedia services, multiple input and output (MIMO) signal processing technology for transmitting and receiving data using a plurality of antennas in a mobile communication environment New data transmission schemes are actively discussed.

Transmission techniques using antenna signal processing techniques can be largely divided into open-loop and closed-loop. The open-loop scheme enables code re-use and antenna diversity to be implemented together so that the mobile station does not need to feed back channel information to the base station. Meanwhile, in the closed-loop method, the weight information w used for the multiple antennas is obtained by using the channel information measured and fed back at the receiving end, and the respective weights are applied to each antenna to transmit a signal.

Multi-Stream Beamforming (MSB) MIMO system is one of closed-loop MIMO system of Frequency Division Duplex (FDD).

1 is a block diagram of a conventional MSB MIMO system. The transmitter examines the magnitude of each eigen value through eigenvalue separation of a channel matrix estimated by a receiver, and then uses a high level of 64QAM or 16QAM for a channel space having a large eigen value. Use high order modulation and use low order modulation, such as BPSK or QPSK, for channel spaces with relatively small eigenvalues, and maintain the independence of symbols sent to different streams. To ensure that the eigenvectors of the channel matrix are multiplied by each symbol, they are transmitted. In other words, instead of using the same modulation scheme for all symbols transmitted in each transmission stream, the receiver receives a channel status of the transmitter / receiver from the terminal to determine the modulation scheme to be used for each stream according to the channel situation. The same algorithm can be used to know the modulation scheme used by each antenna when receiving.) In addition, the symbols transmitted differently in each stream are multiplied by the eigenvectors obtained by the eigenvalue separation of the channel matrix. By using the transmission, the correlation in the channel space is maximized, and the independence between the transmission streams is maintained. In addition, the eigenvalues obtained through the eigenvalue separation of the channel matrix do not transmit a symbol at all for a small channel space below a certain value, thereby preliminarily excluding a possibility that a symbol transmitted from a transmitting antenna causes an error at a receiving end. Even if you do this, you can assign symbols to the streams with good channel conditions to use a high modulation scheme. Transmission antennas Consists of two receiving antennas. A mobile communication channel matrix that passes through different transmission signals through two transmission antennas before being received by a receiver When the receiver estimates the channel matrix, the eigenvalues and eigenvector values separated by the eigenvalue separation at the receiver are fed back to the transmitter or have a pre-and-committed modulation scheme assignment table by comparing the eigenvalues. May return an index corresponding to the modulation scheme to be used for each stream.

The receiver generally estimates the signal vector generated by beamforming each symbol at the transmitter by the well-known zero-forcing or MMSE method, and conjugates the signal vectors to the weight vectors multiplied by each symbol at the transmitter. Multiply the values to detect each symbol. In addition, it modulates according to the modulation scheme corresponding to the symbol transmitted from each transmitting antenna, and finally multiplexes to find out the bits transmitted from the transmitter and reconstructs the bit streams transmitted from the transmitter.

In the conventional MSB MIMO system, a method of forming a beam in each symbol may be summarized by Equation 1 below.

<Equation 1>

=

here Is a weight vector for beamforming each symbol. from Up to the data symbol, Can be referred to as a signal vector after beamforming in which beamforming is performed on each symbol. Each symbol , ..., Is a symbol composed of independent bit streams from independent M coding blocks.

The symbols transmitted from each transmit antenna are not modulated by the same modulation scheme, but are modulated by a modulation scheme determined for each channel situation by receiving channel state information of each antenna from the terminal. Therefore, the weight vector to be multiplied by each symbol at Equation 1 is obtained as follows.

A mobile communication channel matrix that passes through different transmission signals through two transmission antennas before being received by a receiver At the receiving end Matrix with two receive antennas Becomes an N * M matrix. When each antenna of the transmitter transmits a pilot symbol or a separate pilot channel known to the transmitter / receiver in advance, the receiver matrix Each component of can be estimated.

This channel matrix The receiver performs Eigen-Decomposition with Equation 2. In this system, the channel matrix is assumed because the number of antennas of the antenna array of the transmitting end is larger than that of the antenna array of the receiving end. Since is not a square matrix, the eigenvalue decomposition of the channel matrix itself cannot be performed. Perform eigenvalue decomposition of.

<Equation 2>

=>

Where H is Hermitian Is a matrix Eigenval terminals Denotes eigenvectors.

Since each eigenvector generally maintains orthogonality with each other, when a transmitter wants to transmit a symbol at a time according to the number of antennas of a transmitter, a signal may be multiplied by an independent weight vector.

When the transmitter transmits signals by beamforming each symbol as shown in <Equation 1>, the receiver performs signal processing as follows. Since each symbol is multiplied by an independent weight vector, the signal is generally transmitted using the well-known zero-forcing or MMSE method. After estimating, multiply each symbol by the weight vector and the weight vector, and the signal received by the transmitter can be represented by Equation 3 below.

<Equation 3>

here Represents AWGN.

Signal vector transmitted by multiplying each symbol by weight vector using zero-forcing To estimate the signal vector Say Can be expressed as in Equation 4.

<Equation 4>

=

Signal vector transmitted by multiplying each symbol by weight vector using MMSE To estimate the signal vector Say Can be expressed as in Equation 5 below.

<Equation 5>

=

here Is the signal-to-interference noise ratio, Denotes an identity matrix. Signal vector transmitted by multiplying each symbol by weight vector using zero-forcing or MMSE method Is a signal vector After estimating, multiply each symbol by the transmitter and reconstruct the conjugate value of the weight vector. Multiply by the symbols sent by the transmitter from Estimate to from Can be estimated as

<Equation 6>

=

...

=

Estimated after from To find the bits before assigning them to each symbol by demodulating according to the modulation scheme used, and to find out the bit stream transmitted from the transmitter through the consonant multiplexing which finds the bits of the symbol transmitted from each antenna.

In addition to multiplying each symbol by the eigenvectors of the channel matrix estimated by the receiver when transmitting different symbols from the transmitted antennas, the eigenvalues of the channel matrix obtained through the eigenvalue separation at the receiver to consider channel conditions of each antenna together. The comparison is made to select the channel coding and modulation method of symbols to be transmitted by each antenna. In order to obtain Joule weight vectors by multiplying the symbols to be transmitted independently from each transmitting antenna, the eigenvalue separation of the channel matrix estimated by the receiver must be performed, and since the eigenvalue separation can be obtained together, eigenvalue values and eigenvectors can be obtained. There is nothing to be done. That is, since the same modulation scheme is not used for all symbols transmitted from each transmitting antenna, the modulation scheme to be used for each stream is determined according to the channel situation by receiving feedback from each channel space situation. from Different modulation schemes are used by comparing the eigenvalues of the channel matrix. That is, a high modulation scheme is assigned to a stream allocated to a channel space having a high eigen value through separation of channel eigenvalues, and a low modulation scheme is assigned to an antenna allocated to a channel space having a relatively small eigen value. Of course, after determining the channel coding scheme and modulation scheme of the symbol to be transmitted to each stream, beamforming is independently performed on each symbol using the eigenvectors of the channel matrix obtained at the receiver as the weight vector. In this case, a method of determining a modulation and coding scheme (MCS) to be allocated to each antenna is as follows.

In order to determine the modulation scheme to be allocated to each stream with the eigenvalues obtained through the eigenvalue separation carried out as in Equation 2, the relative ratio of each eigenvalue ( Is determined.

Through this relative ratio, if the smallest eigenval value is below a certain threshold, the symbol is not transmitted in the channel space that is created by the corresponding eigenvector. For the channel space with the largest eigenvalue, use high MCS. For intermediate values, compare the relative values to use the intermediate MCS. In addition, after confirming this selection in advance through experiments through various channel conditions, when multiple terminals are serviced simultaneously in a required mapping system, the terminals are distinguished by using a channelization code. Streams transmitted by one terminal at the same time can be distinguished by the orthogonal characteristics of the eigenvectors, and the distinction between the terminals is divided into channelization codes.

FIG. 2 is a table for explaining a method of allocating radio resources when several terminals are serviced simultaneously and a channel code is smaller than the number of terminals in a conventional MIMO system. 3 is an example in which the number of terminals is 8 and the number of channel codes is 4, only terminals 1, 3, 7, 7, and 8 are assigned with a channel code and communicate with each other. In spite of the availability of available resources, the terminal 6 does not receive a channel code and thus cannot communicate.

As shown in FIG. 2, in the conventional MIMO system, when the number of channelization codes is smaller than the number of UEs, resources are not allocated due to lack of channel codes even though there is room for resources that can be used within limited channel resources. .

In addition, if the channel link quality between the base station and the terminal is not all good, that is, if the transmission and reception channel link is some good and some bad, the stream assigned to the bad link uses a low MCS (modulation and coding scheme) or transmit at all It can not be used enough, such as not doing.

The present invention was devised to solve the above problems, and an object of the present invention is to provide a multi-input / output wireless communication system that can efficiently utilize radio resources by sharing multiple channel codes when the number of terminals is greater than the number of channel codes. It is to provide a signal transmission method of.

1 is a block diagram showing the configuration of a conventional multi-input and output system;

2 is a table for explaining a method for allocating radio resources when multiple terminals are serviced simultaneously and a channel code is smaller than the number of terminals in a conventional multiple input / output communication system.

3 is a block diagram showing the configuration of a multi-input / output system according to the present invention; And

4 is a table for explaining a method for allocating radio resources when multiple terminals are serviced simultaneously and have fewer channel codes than the number of terminals in a multiple input / output communication system according to the present invention.

In the data transmission method of the multi-input and output mobile communication system according to the present invention to achieve the above object, when the number of channel codes for identifying the terminal is less than the number of the terminal receiving the service to one or more terminals according to the channel situation Assign the same channel code.

According to the present invention, when there are several terminals in an existing system and distinguishing terminals through channel codes, the present invention uses the channel codes shared among the terminals. In this case, it is necessary to distinguish the terminal sharing the code, which allows channel code sharing only when the cross-correlation value of the weight vectors multiplied by the data streams of the terminals is smaller than a predetermined threshold value. Data streams are distinguished between terminals with a certain interference from other terminals.

The MSB MIMO system according to the present invention assumes a MIMO system having M transmit antennas, and is applied to a system in which streams using the same channel code, such as PARC and MSB, are separately coded and CRCs are respectively attached.

Hereinafter, a signal transmission method in a multiple input / output wireless communication system according to a preferred embodiment of the present invention will be described with reference to the accompanying drawings.

As shown in Figure 3, the MSB MIMO system according to the present invention is the same as the configuration of the existing closed loop MSB MIMO system except that a control block considering a multi-user is added.

4 is a table for explaining a method of allocating radio resources when several terminals are simultaneously serviced and the channel code is smaller than the number of terminals in the MSB MIMO system according to the present invention.

4 shows an example in which the number of terminals is eight and the number of channel codes is four. Only terminals 1, 3, 7, 7, and 8 are assigned with a channel code, and the remaining terminals 2, 4, and 5 are communicating. In spite of the availability of available resources, the terminal 6 does not receive a channel code and thus cannot communicate.

Streams of the terminals indicated by channel codes C1, C2, C3, and C4 may be clearly distinguished from each other. That is, stream 1, stream 2, stream 3 of terminal 1, and stream 1 of the terminal 2, stream 1 of the terminal 3, stream 2, stream 1 of the terminal 3, and stream 2 of the terminal 6 use different channel codes, so that they do not interfere with each other. It is distinguished. However, since stream 1, stream 2, stream 3 of terminal 1 and stream 1 of terminal 4 use the same channel code, different discrimination methods are required. Due to the characteristics of the MSB, stream 1, stream 2, and stream 3 of the terminal 1, which are data streams of the same terminal, can be distinguished from each other due to characteristics of eigenvectors having orthogonal characteristics, but in the case of stream 1 of terminal 4 Since there is no orthogonality between the eigenvectors and the eigenvectors used in stream 1, stream 2, and stream 3 of the terminal 1, in order to share channel codes between different terminals, the weights are multiplied by the data transmitted by sharing the same channel code. The correlation value between vectors should be below a certain threshold. This is expressed as in Equation 7 below.

<Equation 7>

here Denotes a weight vector multiplied by the i th stream of the k th terminal. Is a symbol configured from an independent bit stream derived from an i-th independent coding block of a k-th terminal. Can be referred to as a signal vector after beamforming in which beamforming is performed on each symbol. That is, the weight vector set of the terminal 1 And terminal 4 Since there is no orthogonality between them, the correlation between ( ) Allows channel code sharing only if the thresholds are below a certain threshold.

If the above technique is generalized and expressed, the requirement of weight set of multiple terminals to allow channel code sharing can be written as in Equation 8.

<Equation 8>

Where k and l are terminal numbers, and i and j are indexes of eigenvectors for each terminal.

It is well known that the use of multiple antennas at the transmitting and receiving end can increase the data transmission speed and improve the communication quality. In the signal transmission method in the multi-input and output system according to the present invention, when there are many users and the channel code is limited, the channel code is shared between the terminals for each transmitting antenna, thereby increasing the throughput of data that can be transmitted through each channel code. Increasing effect can be obtained.

Claims (2)

In a closed-loop multi-input / output mobile communication system, when the number of channel codes for identifying terminals is smaller than the number of terminals receiving services, the same channel code is allocated to one or more terminals according to channel conditions. Data transmission method for mobile communication system. The method of claim 1, wherein the same channel code is allocated to the users only when the correlation value of the weight set among the users sharing the channel code is equal to or less than a predetermined threshold value.