KR20100089264A - Method and apparatus of reference signal transmisstion scheme in multi- antenna ofdm wireless telecommunication system - Google Patents

Abstract

PURPOSE: A reference signal transmitting method in a multiple antenna OFDM(Orthogonal Frequency Division Multiplexing) system and a device thereof are provided to perform data demodulation using channel information of a reference signal without information about precoding. CONSTITUTION: A control channel receiver(1105) receives a control channel signal. A control channel information processor(1107) extracts control channel information from the control channel signal. A channel estimator(1113) estimates a channel through a reference signal according to contents and existence of precoding information of the control channel information and rank information. A data channel receiver(1111) receives a data channel according to the estimated result and the precoding information.

Description

METHOD AND APPARATUS OF REFERENCE SIGNAL TRANSMISSTION SCHEME IN MULTI- ANTENNA OFDM WIRELESS TELECOMMUNICATION SYSTEM}

The present invention relates to a method and apparatus for transmitting a reference signal (RS) in an orthogonal frequency division multiplexing (OFDM) communication system using multiple antennas. The present invention relates to a method and a transmission / reception apparatus using a reference signal (RS) pattern having a rank dependence on the presence or absence of precoding.

The OFDM transmission method is a method of transmitting data using a multi-carrier, that is, a multi-carrier, in which a plurality of multi-carriers in which symbol strings are serially input in parallel and each of them are orthogonal to each other In other words, it is a type of multi-carrier modulation that modulates and transmits a plurality of sub-carrier channels.

Such a system using a multicarrier modulation scheme was first applied to military high frequency radios in the late 1950s, and the OFDM scheme of overlapping a plurality of orthogonal subcarriers began to develop in the 1970s, but the implementation of orthogonal modulation between multicarriers was implemented. Since this was a difficult problem, there was a limit to the actual system application. However, in 1971, Weinstein et al. Announced that modulation and demodulation using the OFDM scheme can be efficiently processed using a Discrete Fourier Transform (DFT). Also known is the use of guard intervals and the insertion of cyclic prefixes (CPs) into the guard intervals to further mitigate the adverse effects of the system on multipath and delay spread. Was reduced.

Thanks to these technological advances, the OFDM technology is used for digital audio broadcasting (DAB) and digital video broadcasting (DVB), wireless local area network (WLAN), and wireless asynchronous transmission mode (WATM). It is widely applied to digital transmission technology such as wireless asynchronous transfer mode. In other words, the OFDM method is not widely used due to hardware complexity, and recently, various digital signal processing techniques including fast Fourier transform (FFT) and inverse fast Fourier transform (IFFT) have been introduced. It is made possible by the development.

The OFDM scheme is similar to the conventional frequency division multiplexing (FDM) scheme, but has a characteristic of obtaining optimal transmission efficiency in high-speed data transmission by maintaining orthogonality among a plurality of tones. In addition, the OFDM scheme has good frequency usage efficiency and is strong in multi-path fading, so that an optimum transmission efficiency can be obtained in high-speed data transmission.

Another advantage of the OFDM scheme is that the frequency spectrum is superimposed so that it is efficient to use frequency, is strong in frequency selective fading, is strong in multipath fading, and inter-symbol interference (ISI) using guard intervals. It is possible to reduce the effects of symbol interference, to easily design an equalizer structure in hardware, and to be strong in impulsive noise, and thus it is being actively used in a communication system structure.

The factors that hinder high-speed, high-quality data services in wireless communication are largely due to the channel environment. In the wireless communication, the channel environment includes a Doppler according to power change, shadowing, movement of a terminal, and frequent speed change of a received signal caused by fading in addition to additive white Gaussian noise (AWGN). Doppler), interference with other users and multi-path signals are often changed. Therefore, in order to support high-speed and high-quality data services in wireless communication, it is necessary to effectively overcome the above-mentioned obstacles in the channel environment.

In the OFDM scheme, a modulated signal is located in a two-dimensional resource composed of time and frequency. The resources on the time axis are divided into different OFDM symbols and they are orthogonal to each other. The resources on the frequency axis are divided into different tones, which are also orthogonal to each other. That is, in the OFDM scheme, if a specific OFDM symbol is designated on the time axis and a specific tone is designated on the frequency axis, one minimum unit resource may be indicated, which is called a resource element (hereinafter, referred to as a RE). Different REs have orthogonality to each other even though they pass through a frequency selective channel, so that signals transmitted to different REs may be received at a receiving side without causing mutual interference.

A physical channel is a channel of a physical layer that transmits modulation symbols that modulate one or more encoded bit streams. In Orthogonal Frequency Division Multiple Access (OFDMA) systems, a plurality of physical channels are configured and transmitted according to the purpose of the information string to be transmitted or the receiver. The transmitter and the receiver must promise in advance which RE to arrange and transmit one physical channel. The rule is called mapping (hereinafter, referred to as mapping).

1 is a diagram for explaining a subframe structure in a long term evolution (LTE) system.

One resource block ("RB") 101 is composed of 12 tones arranged on the frequency axis and 14 OFDM symbols 114 arranged on the time axis. RB 1 101 represents a first RB, and FIG. 1 shows a bandwidth consisting of K RBs up to RB K 102. The 14 OFDM symbols on the time axis constitute one subframe 113 and become the basic unit of resource allocation on the time axis. One subframe 113 has a length of 1 ms and consists of two slots 112.

The reference signal (hereinafter referred to as "RS") is a signal promised to the base station transmitting to the terminal so that the terminal can make a channel estimation. The RS0 121, RS1 122, RS2 123, and RS3 124 Denote RSs transmitted from antenna ports 0, 1, 2, and 3, respectively. If the number of antenna ports is 1 or more, this means using a multi-antenna. If only one transmit antenna port is used, only RS0 121 is used for data transmission, RS1 122 is not used for transmission, and RS2 123 and RS3 124 are used for data or control signal symbol transmission. Also, if two transmit antenna ports are defined, RS0 121 and RS1 122 are used for data transmission, and RS2 102 and RS3 103 are used for data or control signal symbol transmission.

The absolute position of the RE where the RS is placed on the frequency axis is set differently for each cell, but the relative spacing between the RSs remains constant. That is, the RS of the same antenna port maintains a 6RE interval, and the interval between RS0 121 and RS1 122 maintains a 3RE interval between the RS2 123 and the RS3 124. The reason why the absolute position of the RS is set differently for each cell is to avoid collision between cells of the RS.

The control channel signal is located at the head of one subframe on the time axis. In FIG. 1, 111 illustrates an area where a control channel signal can be located. The control channel signal may be transmitted over L OFDM symbols located at the head of the subframe. L may have a value of 1,2 or 3 (111, 115). If the amount of control channel is small enough to transmit a control channel signal with one OFDM symbol, only the first 1 OFDM symbol is used for the control channel signal transmission (L = 1) and the remaining 13 OFDM symbols are used for the data channel signal transmission. do. When the control channel signal consumes 2 OFDM symbols, only the first 2 OFDM symbols are used for control channel signal transmission (L = 2), and the remaining 12 OFDM symbols are used for data channel signal transmission. When the amount of control channel signals is large enough to use all 3 OFDM symbols, the first 3 OFDM symbols are used for control channel signal transmission (L = 3) and the remaining 11 OFDM symbols are used for data channel signal transmission.

The reason for placing the control channel signal at the head of the subframe is to determine whether to perform the data channel reception operation by first receiving the control channel signal and recognizing whether the data channel signal transmitted to the terminal is transmitted. Therefore, if there is no data channel signal transmitted to the self, it is not necessary to receive the data channel signal, thus saving the power consumed in the data channel signal receiving operation.

The downlink control channel defined in the LTE system includes a Physical Control Format Indicator Channel (PCFICH), a Physical Hybrid ARQ Indicator Channel (PHICH), and a Packet Data Control Channel (PDCCH).

Downlink control channels defined in the LTE system include PCFICH (Physical Control Format Indicator Channel), PHICH (Physical Hybrid ARQ Indicator Channel), PDCCH (Packet Data Control Channel). PCFICH is a physical channel for transmitting CCFI (Control Channel Format Indicator) information. CCFI is information consisting of 2 bits to inform L. Since the CCFI must be received first to know and receive the number of symbols allocated to the control channel, the PCFICH is a channel to be first received in a subframe by all terminals except when a fixed downlink resource is allocated. PHICH is a physical channel for transmitting downlink ACK / NACK signal. A terminal receiving the PHICHs 121, 123, and 125 is a terminal that is performing data transmission on uplink. Therefore, the number of PHICHs is proportional to the number of terminals that are performing data transmission in uplink. The PDCCH 115 is a physical channel for transmitting data channel assignment information or power control information. The PDCCH may set a channel coding rate differently according to a channel state of a receiving terminal. Since PDCCH uses Quadrature Phase Shift Keying (QPSK) as a modulation method, it is necessary to change the amount of resources used by one PDCCH to change the channel coding rate. A high channel coding rate is applied to a terminal having a good channel state to reduce the amount of resources used. On the other hand, even if the amount of resources used is increased to the terminal in a bad channel state, the reception is possible by applying a high channel coding rate.

2 is a diagram illustrating a data transmission process in an LTE system.

Referring to FIG. 2, the transmitted data may be transmitted in one or more codewords when using multiple antennas, and each codeword in case of using multiple codewords. Is scrambled by the scrambler 203 and modulated via the modulator 205.

The modulated multiple codeword data is mapped by the layer mapper 207 to the multiple layers used and precoded by the precoder 209 according to the transmitted technique. do.

Precoding means preprocessing work used for multiple antenna transmission. The precoded data is mapped to the downlink frame by the resource element mapper 211 to the actual OFDM symbol, modulated into an OFDM signal through the operation of the signal generator 213, and transmitted through the antenna, respectively.

The information of the control channel included in the PDCCH includes information on a transmission method currently used for receiving by the UE, which is called a transmission mod.

3 is a diagram illustrating a transmission method used in an LTE system.

Among the transmission methods used in the LTE system, when the multi-antenna transmission uses common reference signals (CRS, common RS), as shown by reference numeral 301, precoding is applied to the data, but precoding is applied to the reference signal RS. Since it does not use (precoding) (303), the information is included in the precoding currently used in the transmission mode, and precoding (for each layer transmitted to multiple antennas as shown by reference numerals 301 and 303). After precoding is applied, a reference signal RS is added and transmitted. When the information about the precoding is not known, the terminal estimates the channel through the reference signal RS, and thus the channel state of the reference signal RS and the channel state of the precoded data are different. Can't demodulate data

Another transmission mode is a method of using precoding as a method used for transmission in beam-forming. As shown by reference numerals 305 and 307, a method of multiplexing a reference signal before applying precoding to a transmitted layer and using precoding thereafter.

In the method of using precoding, the terminal can demodulate the currently transmitted data without notifying the terminal of the precoding information used in the current transmission mode. However, the current LTE system supports this transmission mode only for beam-forming transmission using one antenna.

The reference signal can be classified into two types according to the purpose. The first is a reference signal used for channel estimation and the second is a reference signal for demodulating received data. The reference signal for data demodulation may be further divided into a common reference signal commonly used for all users in one cell and a dedicated reference signal transmitted only to resources allocated to a specific user. The dedicated reference signal is transmitted only in time and frequency resources allocated to one user, and the common reference signal is transmitted over all transmission bands. In the current LTE system, the common reference signal is used to simultaneously use the channel estimation and the reference signal for data demodulation, and in the case of using the beam-forming described above, the dedicated reference signal is transmitted to the allocated resource. . In the case of using a dedicated reference signal, the system uses the reference signal only for a specific resource, thereby minimizing the overhead of the reference signal for unused data demodulation, and beam-forming. When precoding is applied to the data as described above, the same precoding is applied to the reference signal so that transmission is possible without affecting other terminals. In addition, since precoding information can be known by estimating a channel of a reference signal without providing information on precoding, an optimal precoding can be used. However, since the reference signal to which precoding is applied is not transmitted in the entire band, it cannot be used for channel estimation, and it is difficult to effectively schedule in a broadband system using frequency selective gain.

In view of the above-described problems, an object of the present invention is to rank when multi-antenna transmission is performed using a reference signal RS to which precoding is applied and a reference signal RS to which precoding is not applied. The present invention provides a method and apparatus for transmitting and receiving a reference signal instructing application of precoding according to a rank.

In order to achieve the above object, a reference signal transmission method using multiple antennas of a base station according to an embodiment of the present invention includes the steps of calculating a rank suitable for a terminal and the calculated rank value. Determining the number of reference antenna ports (M) for determining whether to apply the precoding, determining whether the number of reference antenna ports (M) is larger than the number of reference antenna ports (M), and, as a result of the determination, the rank value is greater than the number of reference antenna ports (M). In a large case, the method includes transmitting a signal by applying precoding to only the data channel signal among the data channel signal and the reference signal.

As a result of the determination, when the rank value is smaller than the reference antenna port number M, the method may further include transmitting a signal by applying precoding to both the data channel signal and the reference signal.

In accordance with a preferred embodiment of the present invention, a method for receiving a reference signal using multiple antennas of a terminal for receiving the object includes receiving control channel information and checking whether precoding information (PMI) exists in the control channel information. And a step of estimating a channel using the reference signal and demodulating the data using the precoding information and the estimated channel value when the precoding information PMI is present as a result of the checking.

As a result of the checking, when the precoding information does not exist, estimating a channel, restoring the precoding information through an estimated channel value, and demodulating a data channel using the information obtained through the channel estimation. It characterized in that it further comprises a process.

In the reference signal transmission apparatus using the multiple antenna of the base station according to an embodiment of the present invention for achieving the above object, the rank value and precoding information depending on whether the rank value is larger than the number of antenna ports (M) A selector for selectively providing (PMI) a first transmission mode processor for transmitting without applying precoding to a reference signal if the rank value is greater than the number of reference antenna ports (M) and the rank value of the reference antenna port If less than the number (M) includes a second transmission mode processor for transmitting without applying precoding to the reference signal.

In the reference signal receiving apparatus using multiple antennas according to an embodiment of the present invention for achieving the above object, a control channel receiver for receiving a control channel signal control channel for extracting control channel information from the control channel signal An information processor; a channel estimator for estimating a channel through a reference signal according to the content and presence of precoding information and rank information of the control channel information; and a data channel receiver for receiving a data channel according to the channel estimation result and precoding information. Include.

When the effect obtained by the typical thing of the invention disclosed below is demonstrated briefly, it is as follows. According to the present invention, when transmitting a reference signal (RS) to which precoding is applied, the UE can demodulate data using channel information of the reference signal (RS) without precoding information and predetermine. When transmitting a reference signal RS to which no coding is applied, the terminal may demodulate data using information on precoding of data received on a control channel.

In the LTE system using up to 4 multi-antennas, the latter is used, but when the multi-antenna of the LTE system is extended to 8, the overhead of the reference signal (RS) is greatly increased when the existing method is applied in the same way. The data channel is less efficient. In this case, when the precoded reference signal RS is used, an optimized reference signal RS overhead may be applied according to a rank used, and a different pattern may be applied according to the rank. By applying this, 8 multi-antenna transmission efficiency can be optimized.

Hereinafter, with reference to the accompanying drawings will be described in detail the operating principle of the embodiment of the present invention. In the following description of the present invention, detailed descriptions of well-known functions or configurations will be omitted if it is determined that the detailed description of the present invention may unnecessarily obscure the subject matter of the present invention. Terms to be described below are terms defined in consideration of functions in the present invention, which may vary according to intention or custom of a user or an operator. Therefore, the definition should be made based on the contents throughout the specification. In the following description, the LTE system is described as an example, but the present invention can be applied to other wireless communication systems to which base station scheduling is applied without any addition or subtraction.

First, a transmission mode according to an embodiment of the present invention will be described.

The information of the control channel included in the PDCCH includes information on a transmission method currently used for receiving by the UE, which is called a transmission mod.

A transmission mode according to an embodiment of the present invention includes the following two types. First, there is a method of not applying precoding to a reference signal, and second, a method of applying precoding to a reference signal.

According to an embodiment of the present invention, a method of determining a transmission mode calculates a rank value and a reference antenna port number (hereinafter, referred to as "M") of a base station for determining whether to apply precoding, and rank ) And the reference antenna port number (M), and determines the transmission mode according to the comparison result.

That is, when the rank value is larger than M, the signal is transmitted by applying precoding only to the data channel signal among the data channel signal and the reference signal.

If the precoding information (PM!) Is not known, the UE estimates the channel through the reference signal (RS), so that the channel state of the reference signal (RS) is different from that of the precoded data. Can't demodulate Accordingly, in this case, when the current rank value is smaller than the M value, the base station transmits rank information (RI) and precoding information (PMI) to the terminal through the control channel (PDCCH).

On the other hand, if the rank value is less than M as a result of the determination, the signal is transmitted by applying precoding to both the data channel signal and the reference signal. In this case, the base station transmits only rank information (RI) to the terminal through the control channel.

The LTE system is designed to transmit up to four antennas. Accordingly, the reference signal transmitted by each antenna is configured to enable channel estimation and demodulation of data transmitted to each antenna. In this structure, an additional reference signal is needed to extend the configuration to enable eight antenna transmissions in the current LTE system. However, if the additional reference signal is added to a system optimized for four-antenna transmission, data transmission efficiency is reduced.

However, even if the antenna is extended to eight antennas, the existing LTE terminal must be able to receive additionally, when using a common reference signal additionally brings down the performance of the entire system band. Accordingly, it is advantageous to configure a dedicated reference signal such that only a terminal capable of receiving eight antennas can be received in terms of overhead of the reference signal. However, in the case of the dedicated reference signal, a flexible reference signal can be configured according to a rank transmitted, and the amount of overhead used varies according to the rank. Therefore, the best performance can be achieved when the pattern that is optimal for the current rank is used.

As shown by reference numerals 309 and 311, it is advantageous to use a precoding reference signal when the rank is low and a reference signal to which precoding is not applied when the rank is high.

4 and 5 are diagrams for describing a dedicated reference signal according to an embodiment of the present invention.

4 illustrates an example of a reference signal to which precoding is not applied. Reference numerals 403, 405, 407, and 409 denote subframes including common reference signals for four antennas used in an LTE system. Meanwhile, in order to apply a dedicated reference signal to which precoding is not applied, an example in which a rank is 4 or more is illustrated in the present invention. That is, reference numerals 411, 413, 415, and 417 are subframes to which reference signals are applied to four additional transmission antennas when the ranks are 5, 6, 7, and 8.

On the other hand, FIG. 5 shows a dedicated reference signal to which precoding is applied when the rank is 4 or less. Reference numerals 501, 503, 505, and 507 are examples of dedicated reference signals used when ranks 1, 2, 3, and 4 are applied, respectively.

Embodiments of the present invention will be described using the dedicated reference signals of FIGS. 4 and 5, and embodiments of the present invention can be applied to patterns other than FIGS. 4 and 5. Accordingly, in the present invention, a method of using a precoding-only reference signal and a reference signal to which precoding is not applied according to a rank without effectively causing the above-mentioned problem, a method of transmitting and receiving accordingly, and We propose a transceiver structure. Hereinafter, specific embodiments of the structure proposed by the present invention will be described.

First embodiment

The first embodiment is a method of dynamically changing a precoding-only reference signal and a non-precoding-only reference signal to which precoding is not applied.

When the terminal uses multiple antennas, the terminal informs the terminal of the corresponding information through the PDCCH of the control channel. The information informed by the PDCCH is different depending on the transmission mode, and various modes configure different PDCCHs so that the UE can obtain information for location and demodulation of the transmitted data which is the base station using the received information.

In general, when transmitting using multiple antennas, the LTE system informs the number of ranks of data to be transmitted and precoding information for demodulation of a receiving UE.

According to an embodiment of the present invention, when one of the transmission modes is used, the system transmits using a precoding-only reference signal when the number of ranks of the transmitted signal is smaller than M. FIG. On the other hand, if it is larger than M, it indicates that transmission is performed using a non-precoding reference signal to which precoding is not applied.

In order to cope with a dynamically changing rank, the base station indicates a precoding index and the number of ranks above M according to the reference rank value in the PDCCH information. Only rank is reported.

As the reference M value, a value set by the system may be used. Alternatively, the changed value may be used for higher signaling. In the present invention, the information of precoding is defined as a precoding matrix indicator (PMI) and the information of rank is defined as a rank indicator (RI). Table 1 below is for explaining control channel information applied in the first embodiment of the present invention.

The current transmission rank Information in the control channel RI PMI 1-M 1-M PMI indicator M-8 M-8 NA

As disclosed in Table 1, the control channel information includes rank information (RI) and precoding information (PMI) when the current rank value is smaller than the M value. In addition, when the current rank value is larger than the M value, only the rank information RI is included.

Next, a data transmission method according to the first embodiment of the present invention will be described. 6 is a view for explaining a data transmission method according to a first embodiment of the present invention.

First, in step 603, the base station determines whether to transmit current transmission data to multiple antennas. Next, the base station determines a transmission mode by determining a suitable transmission method from among multiple antenna transmission methods in step 605. Next, the base station obtains a rank (rank) suitable for the current terminal in step 607 and checks whether the value is greater than M.

As a result of checking in step 607, if the rank value is greater than M, the base station determines a PMI suitable for transmission in step 609. Then, the base station maps the transmission data to the corresponding subframe in step 611. Then, after precoding is performed according to the PMI determined in step 613, the reference signal is mapped to the corresponding subframe in step 615.

That is, in steps 609 to 615, when the rank value is larger than M, precoding is not performed on the reference signal.

On the other hand, if it is determined in step 607 that the rank (rank) is less than M, the base station determines the PMI suitable for transmission in step 617. Thereafter, the base station maps transmission data to the corresponding subframe in step 619 and maps the reference signal to the corresponding subframe in step 621. Then, the precoding is generated according to the PMI determined in step 623. That is, steps 617 to 623 perform precoding on both the reference signal and the data signal when the rank value is smaller than M. FIG.

Subsequently, after performing precoding according to a rank as described above, the base station transmits a frame including the above-described subframes in step 625.

Next, a method of receiving a downlink frame transmitted according to the method described with reference to FIG. 6 will be described. 7 is a view for explaining a data receiving method according to a first embodiment of the present invention.

The terminal receives the control channel in step 703 and checks the transmission mode in step 705.

In addition, the terminal receives the transmission mode in step 707 to receive the contents and information of the rank (rank) and PMI information.

As described above, the control channel information includes rank information (RI) and precoding information (PMI) when the rank value is smaller than the M value, and rank information when the rank value is larger than the M value. (RI) only. For this reason, the terminal checks whether the precoding information (PMI) exists in the control channel information in step 709.

In this case, when the precoding information PMI exists in step 709, the UE estimates a channel using the reference signal in step 711, and uses the precoding information PMI and the estimated channel value in step 713. Demodulate the data channel. That is, in steps 711 to 713, the data channel is demodulated using the precoding matrix of the precoding information (PMI).

In this case, if the precoding information PMI does not exist in step 709, the UE estimates a channel in step 715 and restores the precoding information PMI through the channel value estimated in step 717. Then, the terminal demodulates the data channel using the information obtained through channel estimation in step 719. That is, in steps 715 to 719, the data channel is demodulated using the precoding matrix when demodulating the data channel according to the precoding information (PMI).

After demodulation of the data channel is completed through the above-described process, the terminal completes reception of the current frame in step 721.

Second embodiment

The second embodiment is a method of transmitting a dedicated reference signal to which precoding is applied and a dedicated reference signal to which precoding is not applied in different transmission modes.

Since the transmission mode of the terminal is notified to the terminal as a higher signal of the system, the terminal cannot dynamically change the transmission mode according to the channel state, and when the transmission mode using a dedicated reference signal to which precoding is applied is used. In case of using a transmission mode in which the UE can transmit only a rank of M or less and uses a dedicated reference signal without precoding, the UE can receive only when the rank is M or more. Do.

In this case, the M value may be set by the system or may be determined through signal exchange between the terminal and the base station.

Next, a data transmission method according to a second embodiment of the present invention will be described. 8 is a diagram for describing a data transmission method according to a second embodiment of the present invention.

Referring to FIG. 8, the base station first determines whether to transmit current transmission data to multiple antennas in step 803.

Then, the base station determines whether the value is greater than M by obtaining a rank (rank) suitable for the current terminal in step 805.

As a result of checking in step 805, when the rank value is greater than M, the base station sets the transmission mode to transmission mode A, which is a mode in which precoding is not applied to the dedicated reference signal in step 807. Then, the base station determines a PMI suitable for transmission in step 809, and maps the transmission data to the corresponding subframe in step 811. Next, the base station performs precoding only on data according to the PMI determined in step 813. Next, the base station maps the reference signal to the corresponding subframe in step 815.

On the other hand, when it is confirmed in step 805 that the rank value is smaller than M, the base station sets the transmission mode B, which is a mode in which precoding is applied to the dedicated reference signal, in step 817. Then, the base station determines a PMI suitable for transmission in step 819. Subsequently, the base station maps transmission data to the corresponding subframe in step 821 and maps the reference signal to the corresponding subframe in step 823.

Subsequently, the base station may precode the data and the reference signal according to the PMI determined in operation 825.

Subsequently, after performing precoding according to a transmission mode according to a rank as described above, the base station transmits a frame including the above-described subframes in step 827.

Next, a method of receiving a downlink frame transmitted according to the method described with reference to FIG. 8 will be described. 9 is a view for explaining a data receiving method according to a second embodiment of the present invention.

The terminal receives a control channel in step 903 and receives a transmission mode in step 905. Then, the terminal checks whether the transmission mode is A in step 907.

In step 907, if the transmission mode is A, the UE receives rank and precoding information (PMI) in step 909 and estimates a channel using a reference signal in step 911. Then, the terminal demodulates data using PMI and channel estimation in step 913.

On the other hand, if the transmission mode is B as a result of checking in step 907, since there is no precoding information (PMI), the terminal estimates the channel in step 915, and the precoding information (PMI) through the estimated channel in step 917 Restore Then, the terminal demodulates the data channel using the information obtained through channel estimation in step 919.

After demodulation of the data channel is completed through the above-described process, the terminal completes reception of the current frame in step 921.

Third embodiment

The third embodiment is a case where a dedicated reference signal to which precoding is applied is defined differently according to rank. In the first and second embodiments, the dedicated reference signal transmitted from one antenna regardless of rank has the same pattern and overhead, and one pattern may be disposed orthogonally in a resource. However, the rank value is determined by the terminal according to the channel state, and channel estimation capability of the same performance is not necessary according to the channel state. Therefore, different patterns or patterns having overheads can be defined according to ranks. In the first and second embodiments, one pattern of a dedicated reference signal is required, whereas in the third embodiment, M patterns are required. I need a pattern.

Fourth embodiment

Criteria for determining whether the system applies precoding to a dedicated reference signal are based on a case where a precoding-only reference signal is used when the number of layers to be transmitted is M, and a precoding is applied. The reference signal having the least overhead among the signals is used. The least overhead is when performance is optimal.

Next, a base station and a terminal according to an embodiment of the present invention will be described.

10 is a diagram illustrating a base station transmitter structure according to an embodiment of the present invention.

The transmitter of the base station according to the embodiment of the present invention includes a selector 1005, a control channel processor (PDCCH) 1007, a first transmission mode processor (Tx Process 1) 1009, and a second transmission mode processor (Tx Process2) ( 1031, mux 1027, and transfer processor 1029.

The selector 1005 selects the rank information and the precoding information PMI according to whether the rank value is greater than the M value, and inputs the rank information and the precoding information PMI to the first or second transfer mode processor 1009.

That is, the base station determines the transmission of each information by using the selector 1005 because the precoding information (PMI) and rank (RANK) information transmitted according to the transmission mode is different.

The control channel processor 1007 configures the PDCCH control signal based on the information determined according to whether the rank value of the selector 1005 is greater than the M value and selects a transmission method according to the configuration.

The first transfer mode processor 1009 includes a data channel processor 1011 for generating a data channel signal, a reference signal processor 1013 for generating a reference signal, a mux 1015 for multiplexing the data channel signal and a reference signal, and multiplexing. A precoder 1017 that applies a precoding matrix to the data channel signal and the reference signal.

The second transfer mode processor 1031 includes a data channel processor 1019 for generating a data channel signal, a reference signal processor 1021 for generating a reference signal, a precoder 1023 for applying precoding metrics to the data channel signal, and The mux 1025 multiplexes the data channel signal and the reference signal to which the precoding matrix is applied.

That is, when the base station uses a dedicated reference signal to which precoding is applied, the base station multiplexes the transmission data channel signal and the reference signal through the first transmission mode processor 1009 and passes through a precoder 1017. To print.

On the other hand, when the base station uses a dedicated reference signal to which precoding is not applied, the base station passes the transmission data channel signal through the second transmission mode processor 1031 to the precoder 1023 and then the reference signal. Output multiplexed.

Although the above-described first and second transfer mode processors 1009 and 1031 are illustrated as different modules, they may be configured as one module.

As described above, the time domain mux 1027 multiplexes the output data channel signal and the reference signal in time. The transmission processing device 1035 then transmits the multiplexed signals.

Next, a terminal receiver structure according to an embodiment of the present invention will be described. 11 is a view for explaining the structure of a terminal receiver according to an embodiment of the present invention.

A receiver of a terminal according to an embodiment of the present invention includes a reception processor (Rx Process) 1101, a time domain mux 1103, a control channel (PDCCH) receiver 1105, and control channel information (Rank, PMI). A processor 1107, a reference signal (RS) receiver 1109, a data channel (PDSCH) receiver 1111, and a channel estimator 1113.

The reception processor 1101 converts the received signal into a baseband signal and outputs it. Then, the time domain mux 1103 separates the baseband signal into a reference signal, a control channel signal, and a data channel signal on the time domain.

The control channel receiver 1105 receives the separated control channel signal PDCCH, and the control channel information processor 1107 extracts precoding information (PMI) and rank information from the control channel signal.

The reference signal receiver 1109 receives a reference signal from the time domain mux 1103.

The channel estimator 1113 estimates a channel using a reference signal according to the content and presence of extracted precoding information (PMI) and rank information. That is, if there is no precoding information PMI, the channel estimator 1113 estimates a channel and provides the precoding information PMI to the data channel receiver 1111.

Meanwhile, if there is precoding information (PMI), the channel estimator 1113 estimates a channel through the precoding information by using the received information, and through this, the data channel (PDSCH) receiver 1111 receives a data channel signal. (PDSCH) is received.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

1 is a view for explaining a subframe structure in a Long Term Evolution (LTE) system.

2 is a view for explaining a data transmission process in the LTE system.

3 is a view for explaining a transmission method used in the LTE system.

4 and 5 are diagrams for explaining a dedicated reference signal according to an embodiment of the present invention.

6 is a view for explaining a data transmission method according to a first embodiment of the present invention.

7 is a view for explaining a data receiving method according to a first embodiment of the present invention.

8 is a view for explaining a data transmission method according to a second embodiment of the present invention.

9 is a view for explaining a data receiving method according to a second embodiment of the present invention.

10 is a diagram illustrating a base station transmitter structure according to an embodiment of the present invention.

11 is a view for explaining the structure of a terminal receiver according to an embodiment of the present invention.

Claims (6)

In the reference signal transmission method using multiple antennas of a base station, Calculating a rank suitable for the terminal; Determining whether the calculated rank value is greater than a reference antenna port number M; As a result of the determination, when the rank value is larger than the number of the reference antenna ports (M), the step of transmitting a signal by applying precoding only to the data channel signal of the data channel signal and the reference signal multiplexing of the base station Reference signal transmission method using an antenna. The method of claim 1, As a result of the determination, when the rank value is smaller than the reference antenna port number M, the method may further include transmitting a signal by applying precoding to both the data channel signal and the reference signal. Reference signal transmission method used. In the reference signal receiving method using multiple antennas of the terminal, Receiving control channel information to determine whether precoding information (PMI) exists in the control channel information; As a result of the checking, when the precoding information (PMI) is present, estimating a channel using a reference signal, and demodulating data using the precoding information and the estimated channel value. Reference signal receiving method using multiple antennas of the terminal. The method of claim 3, As a result of the check, if the precoding information does not exist, Estimating a channel and restoring the precoding information through the estimated channel value; And demodulating a data channel by using the information obtained through the channel estimation. In the reference signal transmission apparatus using multiple antennas of a base station, A selector for selectively providing a rank value and precoding information (PMI) according to whether the rank value is greater than the reference antenna port number (M); A first transmission mode processor for transmitting the reference signal without applying precoding to the reference signal when the rank value is larger than the reference antenna port number (M); And And a second transmission mode processor for transmitting a signal without applying precoding to a reference signal when the rank value is smaller than the number of the reference antenna ports (M). . In the reference signal receiving apparatus using multiple antennas, A control channel receiver for receiving a control channel signal; A control channel information processor for extracting control channel information from the control channel signal; A channel estimator estimating a channel through a reference signal according to the content and presence of precoding information and rank information of the control channel information; And And a data channel receiver configured to receive a data channel according to the channel estimation result and the precoding information.

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