KR20090105429A - Method for transmitting index of code set in wireless communication system - Google Patents

Abstract

PURPOSE: A code-set index transmission method in a wireless communication system is provided to improve the performance of the entire system and improve the reliability of the communication by selecting the code set. CONSTITUTION: A code-set index transmission method in a wireless telecommunications system is as follows. An equivalence channel matrix about each code-set is included in a code book(S110, S120). The code set in which an interference component is a minimum is selected by using the equivalence channel matrix(S130). An index of the selected code-set is transmitted(S140). The code-set is the transmission format of a data symbol.

Description

TECHNICAL FOR TRANSMITTING INDEX OF CODE SET IN WIRELESS COMMUNICATION SYSTEM}

The present invention relates to a wireless communication system, and more particularly, to a method of transmitting a codeset index in a wireless communication system.

The next generation multimedia wireless communication system, which is being actively researched recently, requires a system capable of processing and transmitting various information such as video, wireless data, etc., out of an initial voice-oriented service. The purpose of a wireless communication system is to enable a large number of users to communicate reliably regardless of location and mobility. However, the wireless channel may include path loss, noise, intersymbol interference due to multipath, or Doppler effect due to mobility of UE. There is a non-ideal characteristic of. Various techniques have been developed to overcome the non-ideal characteristics of the wireless channel and to improve the reliability of the wireless communication.

Multiple Input Multiple Output Antennas (MIMO) technology improves the transmission and reception efficiency of data using multiple transmission antennas and multiple reception antennas. MIMO technology can be divided into spatial multiplexing and spatial diversity. According to the spatial multiplexing technique, by transmitting different data at the same time, high speed data is transmitted without increasing the bandwidth of the system. According to the spatial diversity scheme, the reliability of data is increased by obtaining diversity by transmitting the same data through multiple transmit antennas.

The MIMO system can be decomposed into a plurality of independent channels according to the number of transmit antennas and the number of receive antennas. Each independent channel may be referred to as a spatial layer or a stream.

The characteristics of the MIMO technique can be combined and applied. Space-Time Coding, such as space-frequency block code (SFBC) and space-time block code (STBC), is a MIMO technique that combines spatial diversity and spatial multiplexing. And STC). SFBC is a technique that efficiently applies selectivity in the spatial domain and frequency domain to secure both diversity gain and multi-user scheduling gain in the corresponding dimension. STBC is a technique for applying selectivity in the space domain and the time domain.

1 shows an example of a data transmission method using STC. The data transmission method of FIG. 1 applies a well-known Alamouti code.

Referring to FIG. 1, data transmitted through two transmit antennas is in the form of data symbols s ₁ and s ₂ . The transmitter transmits a first data symbol s ₁ through a first transmit antenna 11 and a second data symbol s ₂ through a second transmit antenna 12 during a first time slot 1. do. Further, the second time slot (time slot 2) for the first transmit data symbols -s ₂ ^* through the transmit antenna 11, and transmits the second transmission antenna 12, the data symbols s ₁ through ^*. Here, ( ^* ) ^* is a complex conjugate.

The first received symbol r ₁ received by the receiver during the first time slot and the second received symbol r ₂ received during the second time slot may be expressed by the following equation.

Where h ₁ is the first channel response from the first transmit antenna 11 to the receive antenna 13, and h ₂ is the second channel response from the second transmit antenna 12 to the receive antenna 13. and, n ₁ is the noise (noise) of the first channels, n ₂ is the noise of the second channel.

Equation 1 is modified to form an equivalent channel matrix for the first data symbol s ₁ and the second data symbol s ₂ .

Consider the following equation for the equivalent channel matrix H.

Where ^H is a Hermitian matrix. In the first channel response h ₁ and the second channel response h ₂ , the smaller the rate of change during successive time slots, the closer the non-diagonal element of the H ^H H matrix is to zero. That is, the greater the quasi static characteristic of the channel, the greater the orthogonality of the equivalent channel. If the orthogonality of the equivalent channel increases, the channel for the first data symbol s ₁ and the channel for the second data symbol s ₂ may be completely decoupling. That is, the greater the orthogonality of the equivalent channel, the lower the complexity of the calculation process for the receiver to estimate the transmission symbol, it is possible to obtain full transmit diversity (full transmit diversity).

As described above, when data is transmitted through two transmission antennas, an orthogonality of equivalent channels can be increased by a transmission format using an Alamouti code. However, when transmitting data through three or more transmitting antennas, various transmission formats using STC are possible. According to the transmission antenna, subcarrier, or time slot used for data transmission, the data transmission format using STC can be various. When data is transmitted through three or more transmission antennas, each of a plurality of transmission formats may be represented by a matrix, and the matrix may be referred to as a code set. In addition, a plurality of code sets may be referred to as a code book. For smooth communication between the transmitter and the receiver, the transmitter and the receiver may hold information about a codebook and a codeset included in the codebook.

When the transmitter transmits data using a codeset included in the codebook, the receiver may select the codeset and transmit the index of the selected codeset to the transmitter. In this case, it is preferable that the receiver transmits the codeset index having the best performance in consideration of the channel environment. The greater the orthogonality of the equivalent channel, the lower the complexity of the calculation process by which the receiver estimates the transmitted symbols, so it is more efficient to select the codeset with the largest orthogonality of the equivalent channel. However, since the channel environment may change over time, there is a need for a method of adaptively selecting a codeset having the largest orthogonality of equivalent channels and transmitting the selected codeset.

An object of the present invention is to provide a method of transmitting a codeset index from a codebook including a plurality of codesets in a wireless communication system.

In one aspect, a method is provided for transmitting a codeset index from a codebook comprising a plurality of codesets in a wireless communication system. The method includes obtaining an equivalent channel matrix for each codeset included in the codebook, selecting a codeset having a minimum interference component using the equivalent channel matrix, and transmitting an index of the selected codeset. It includes.

The smaller the sum of the interference components, the greater the orthogonality of the equivalent channel and the higher the degree of decoupling of the channel. The greater the orthogonality of the equivalent channel, the lower the complexity of the calculation process by which the receiver estimates the transmitted symbols. Therefore, if a codeset having the smallest sum of interference components is selected, it is possible to improve communication reliability and to improve performance of the entire system. In addition, since the complexity of the codeset selection process is low and the amount of information transmitted from the receiver is small, the implementation is easy.

The following techniques can be used in various wireless communication systems. Wireless communication systems are widely deployed to provide various communication services such as voice and packet data. This technique can be used for downlink or uplink. In general, downlink means communication from a base station (BS) to a mobile station (MS), and uplink means communication from a terminal to a base station. A base station generally refers to a fixed station for communicating with a terminal, and may be referred to in other terms such as node-B, base transceiver system (BTS), and access point. The terminal may be fixed or mobile and may be called in other terms such as user equipment (UE), user terminal (UT), subscriber station (SS), wireless device (wireless device), and the like.

The wireless communication system may be an Orthogonal Frequency Division Multiplexing (OFDM) / Orthogonal Frequency Division Multiple Access (OFDMA) based system. OFDM uses multiple orthogonal subcarriers. OFDM uses orthogonality between inverse fast Fourier Transform (IFFT) and fast Fourier Transform (FFT). At the transmitter, data is sent by performing an IFFT. The receiver performs FFT on the received signal to recover the original data. The transmitter uses an IFFT to combine multiple subcarriers, and the receiver uses a corresponding FFT to separate multiple subcarriers. OFDMA is a technique for providing multiplexing of multiple users by combining OFDM with frequency division multiple access (FDMA), time division multiple access (TDMA), or code division multiple access (CDMA).

2 is a block diagram illustrating a transmitter having multiple antennas.

Referring to FIG. 2, the transmitter 100 includes a scheduler 110, a channel encoder 120, a mapper 130, a MIMO preprocessor 140, an OFDM modulator 150, and Nt (Nt> 1) transmit antennas. (190-1, ..., 190-Nt). The transmitter 100 may be part of a base station in downlink.

The scheduler 110 schedules a data transmission format using multiple transmit antennas. The scheduler 110 may schedule the transmission format using the received codeset index, or may schedule the transmission format without using the received codeset index.

The channel encoder 120 encodes the data according to a predetermined coding scheme to form coded data. The mapper 130 maps the coded data into symbols representing positions on signal constellations. This is called a data symbol. The modulation scheme in the mapper 130 is not limited and may be m-Phase Shift Keying (m-PSK) or m-Quadrature Amplitude Modulation (m-QAM).

The MIMO preprocessor 140 processes the input data symbols by the MIMO scheme according to the transmission antennas 190-1, ..., 190-Nt. For example, according to a data transmission format using a multiple transmission antenna determined by the scheduler 110, space-time coding (STC) may be performed on transmission data.

The OFDM modulator 150 performs OFDM modulation on the input symbol and outputs an OFDM symbol. The OFDM modulator 150 may perform an inverse fast fourier transform (IFFT) on the input symbol, and may further insert a cyclic prefix (CP) after performing the IFFT. The OFDM symbol is transmitted through each transmit antenna 190-1,..., 190 -Nt.

3 is a block diagram illustrating a receiver.

Referring to FIG. 3, the receiver 200 includes an OFDM demodulator 210, a channel estimator 220, a MIMO postprocessor 230, a demapper 240, a channel decoder 250, a controller 260, and an Nr (Nr). > 1) receive antennas 290-1, ..., 290-Nr. The receiver 200 may be part of the terminal in downlink.

The signal received from the receiving antennas 290-1,..., 290 -Nr is subjected to fast Fourier transform (FFT) by the OFDM demodulator 210. Channel estimator 220 estimates the channel. The MIMO post processor 230 performs post processing corresponding to the MIMO preprocessor 140. The demapper 240 demaps the input symbol into encoded data, and the channel decoder 250 decodes the encoded data to restore the original data.

The controller 260 obtains an equivalent channel matrix for each codeset included in the codebook, and selects a codeset having a minimum interference component using the equivalent channel matrix. The index of the selected codeset is transmitted to the transmitter 100 (see FIG. 2).

Hereinafter, an example of a codebook including six code sets will be described. However, this is merely an example and does not limit the number of codesets included in the codebook and the shape of the codesets.

The codebook B may be B = { B ₁ , B ₂ , B ₃ , B ₄ , B ₅ , B ₆ }. Codesets B ₁ to B ₆ included in the codebook may be represented by the following equation.

Here, s ₁ to s ₈ are data symbols.

The rows and / or columns of the codeset may correspond to transmit antennas, subcarriers, time slots, and the like. For example, each row of the codeset may correspond to each transmit antenna, and each column may correspond to a time slot. As another example, each row may correspond to each transmit antenna, and each column may correspond to each subcarrier. However, this is merely an example, and a method of corresponding to a row and / or column of a codeset corresponding to a transmission antenna, a subcarrier, a time slot, or the like may vary.

4 shows an example of a data transmission method using the code set B ₁ . Here, each row of the codeset corresponds to each transmit antenna, columns 1 and 2 correspond to the first subcarrier, columns 3 and 4 correspond to the second subcarrier, and columns 1 and 3 correspond to the first time slot, columns 2 and 4 Is a data transmission method corresponding to the second time slot.

Referring to FIG. 4, during the first time slot, the transmitter transmits s ₁ , s ₅ through the first transmit antenna 21, transmits s ₂ , s ₇ through the second transmit antenna 22, and S ₃ and s ₆ are transmitted through the third transmission antenna 23, and s ₄ and s ₈ are transmitted through the fourth transmission antenna 24. In this case, s ₁ , s ₂ , s ₃ , and s ₄ are modulated with a first subcarrier, and s ₅ , s ₇ , s ₆ , and s ₈ are modulated with a second subcarrier. In addition, during the second time slot, -s ₂ ^* , -s ₇ ^* are transmitted through the first transmit antenna 21, s ₁ ^* , s ₅ ^* are transmitted through the second transmit antenna 22, -S ₄ ^* and -s ₈ ^* are transmitted through the third transmit antenna 23 and s ₃ ^* and s ₆ ^* are transmitted through the fourth transmit antenna 24. In this case, -s ₂ ^* , s ₁ ^* , -s ₄ ^* , and s ₃ ^* are modulated with the first subcarrier, and -s ₇ ^* , s ₅ ^* , -s ₈ ^* , and s ₆ ^* are modulated with the second subcarrier. do.

As shown in FIG. 4, the row index of the codeset may represent an antenna number, and columns 1 and 2 may be modulated with a first subcarrier, and columns 3 and 4 may be modulated with a second subcarrier. Also, columns 1 and 3 may be transmitted during the first time slot, and columns 2 and 4 may be transmitted during the second time slot. In this case, B ₁ , B _{2 group} the first transmit antenna 21 and the second transmit antenna 22 for a first diversity pair, and generate a second for the second diversity pair. The third transmit antenna 23 and the fourth transmit antenna 24 are grouped together. B ₃ and B _{4 group} the first transmit antenna 21 and the third transmit antenna 23 for the first diversity pair, and the second transmit antenna 22 and the fourth transmit for the second diversity pair. The antennas 24 are grouped together. Further, B ₅ , B _{6 group} the first transmit antenna 21 and the fourth transmit antenna 24 for the first diversity pair, and the second transmit antenna 22 and the second transmit antenna 22 for the second diversity pair. Three transmit antennas 23 are grouped together.

However, the problem is whether the code book B those containing B ₁ to B _6, by applying any of the code set B ₁ to B ₆ to transmit data. The receiver may select one code set of B ₁ to B ₆ and transmit the index of the selected codebook to the transmitter. In this case, for efficient communication, a method for selecting a codeset having a large orthogonality of channels is needed.

5 is a flowchart illustrating a codeset index transmission method according to an embodiment of the present invention.

Referring to FIG. 5, the receiver obtains an equivalent channel matrix H for each code set (S110). Equivalent channel matrices H ₁ to H ₆ are obtained from code sets B ₁ to B ₆ , respectively. Equivalent channel matrices H ₁ to H ₆ can be represented by the following equation.

Here, h ₁ to h ₈ are channel responses between the transmitting antenna and the terminal estimated by the receiver.

The receiver calculates a Hermitian matrix (H ^H) gopin the multiplication matrix (H ^H H) of obtaining, the Hermitian matrix and the equivalent channel matrix of the equivalent channel matrix (H) for each of the code set (S120).

For example, gopin multiplication matrix ^(H ₁ H H ₁₎ of the Hermitian matrix ^(H ₁ H) and equivalent channel matrix (H ₁₎ for the code set B ₁ it can be expressed as the following mathematical expression.

Here, α ₁ to α ₄ are intersymbol interference. However, since the actual channel environment changes between the first time slot and the second time slot, the values h ₁ to h ₈ may vary. In this case, H ₁ ^H H ₁ can be expressed as the following equation.

Here, the non-diagonal elements α ₁ to α ₄ , β ₁ to β ₄ , and γ ₁ to γ ₄ all correspond to an interference component.

In this manner, each multiplication matrix H ₁ ^H H ₁ to H ₆ ^H H ₆ is obtained for each code set B ₁ to B ₆ .

The receiver selects a codeset in which the sum of interference components is the minimum (S130).

The receiver obtains a sum of interference components obtained by adding interference components for every H ₁ ^H H ₁ to H ₆ ^H H ₆ obtained for each code set. For example, the sum Sum ₁ in the interference component of the multiplication matrix ^(H ₁ H H ₁₎ for the code set B ₁ can be expressed as the following mathematical expression.

In this manner, Sum ₁ to Sum ₆ , which are the sum of interference components, are obtained for each code set B ₁ to B ₆ . The receiver then compares Sum ₁ to Sum ₆ , which is the sum of the interference components, to find the sum of the interference components having the minimum value. Then, the code set corresponding to the sum of the minimum interference components is selected. For example, if Sum ₄ has the minimum value, select codeset B ₄ .

The smaller the sum of the interference components, the greater the orthogonality of the equivalent channel and the higher the degree of decoupling of the channel. The greater the orthogonality of the equivalent channel, the lower the complexity of the calculation process by which the receiver estimates the transmitted symbols. Therefore, if a codeset having the smallest sum of interference components is selected, it is possible to improve communication reliability and to improve performance of the entire system.

The receiver transmits the selected codeset index to the transmitter (S140). The transmitter may receive the codeset index and apply the selected codeset to transmit data. This is because the receiver can reduce the amount of transmission information by notifying only the index of the selected code set. For example, if there are six selectable codesets, the number of bits in the codeset index is at least 3 bits.

This codeset selection method is easy to implement because it improves the reliability of communication, improves the performance of the entire system, has low computational complexity, and reduces the amount of information transmitted from the receiver.

All of the above functions may be performed by a processor such as a microprocessor, a controller, a microcontroller, an application specific integrated circuit (ASIC), or the like according to software or program code coded to perform the function. The design, development and implementation of the code will be apparent to those skilled in the art based on the description of the present invention.

Although the present invention has been described above with reference to the embodiments, it will be apparent to those skilled in the art that the present invention may be modified and changed in various ways without departing from the spirit and scope of the present invention. I can understand. Therefore, the present invention is not limited to the above-described embodiment, and the present invention will include all embodiments within the scope of the following claims.

1 shows an example of a data transmission method using STC.

2 is a block diagram illustrating a transmitter having multiple antennas.

3 is a block diagram illustrating a receiver.

4 shows an example of a data transmission method using the code set B ₁ .

5 is a flowchart illustrating a codeset index transmission method according to an embodiment of the present invention.

Claims (6)

In the method for transmitting a codeset index from a codebook comprising a plurality of codesets, Obtaining an equivalent channel matrix for each codeset included in the codebook; Selecting a codeset having a minimum interference component using the equivalent channel matrix; And And transmitting the index of the selected codeset. The method of claim 1, wherein the code set is a transmission format of a space-time coded data symbol. The method of claim 1, wherein the interference component is obtained from a multiplication matrix that is a product of a Hermitian matrix of the equivalent channel matrix and the equivalent channel matrix. 4. The method of claim 3, wherein the interference component is a non-diagonal element of the multiplication matrix. The method according to claim 1, wherein the codebook B is B = { B ₁ , B ₂ , B ₃ , B ₄ , B ₅ , B ₆ }, and the code sets B ₁ to B ₆ are

Codeset index transmission method characterized in that. Here, s ₁ to s ₈ are data symbols. 6. The method of claim 5, wherein each row of the codeset corresponds to a respective antenna, columns 1 and 2 correspond to a first subcarrier, columns 3 and 4 correspond to a second subcarrier, and columns 1 and 3 Wherein the columns correspond to the first time slot, and columns 2 and 4 correspond to the second time slot.

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