KR101610769B1 - Method of aggregate resource management for reference signal - Google Patents

Abstract

The present invention relates to a method for allocating a dedicated reference signal to a layer transmitted from a base station to a mobile station in a mobile communication system and estimating a channel according to an allocated transmission signal. Transmitting a dedicated reference signal pattern to the terminal through the signaling; determining whether to transmit a dedicated reference signal according to precoding applied to the terminal; And notifying the UE of the control information according to the allocated dedicated reference signal pattern. Accordingly, in the present invention, in order to improve the overall system capacity by properly allocating wasted resources or insufficient resources due to the fixed resource allocation to the reference signal based on the channel environment and other factors affecting the system, Time, frequency, and power resources.

Layer, reference signal, DMRS pattern, channel estimation

Description

[0001] METHOD OF AGGREGATE RESOURCE MANAGEMENT FOR REFERENCE SIGNAL [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to a method for allocating resources in a wireless mobile communication system, and more particularly, to a method and apparatus for allocating resources in a wireless mobile communication system, A MIMO transmission method for maintaining transparency for MU-MIMO in a wireless mobile communication system, a long term average signal-to-interference and noise ratio (SINR), an average channel quality, A method for adaptively allocating an appropriate amount of time, frequency, and power resources to a reference signal (pilot symbol) using a data rate, a modulation scheme, a code rate, .

The current mobile communication system has evolved into a high quality wireless packet data communication system for providing data service and multimedia service apart from providing initial voice oriented service. Various standardization organizations such as 3GPP, 3GPP2, and IEEE are conducting various mobile communication standards such as Long Term Evolution (LTE), Ultra Mobile Broadband (UMB), and 802.16m. Existing 3G mobile communication system is based on a multi-carrier multiple access scheme. In order to improve the transmission efficiency, a third-generation evolved mobile communication system employs a multiple-input multiple-output (MIMO) scheme and uses beam-forming, Adaptive Modulation and Coding (AMC) And a channel-responsive scheduling method.

The various techniques described above can control the amount of data to concentrate or transmit the transmission power transmitted from various antennas according to the channel state and the like. In addition, various techniques described above can improve transmission efficiency and improve capacity performance of a mobile communication system by selectively transmitting data to a user having a good channel state. Most of these technologies operate based on channel state information between an evolved Node B (eNB) and a user equipment (MS). Therefore, the BS or the MS must measure the channel state between the BS and the MS. At this time, a reference signal is used to establish a channel state between the BS and the MS.

A reference signal (pilot symbol) measures the state of a channel between a base station and a user through a channel strength, a distortion, an interference strength, a Gaussian noise, etc. in a wireless mobile communication system, is a signal used to help demodulate and decode data symbols. In a wireless mobile communication system employing a multiple access scheme using a multi-carrier, a difference occurs in channel estimation performance as a reference signal is located in several time symbols and subcarriers in time and frequency. In addition, the channel estimation performance is also affected by how much power is allocated to the reference signal. Accordingly, when radio resources such as more time, frequency, and power are allocated to the reference signal, the channel estimation performance is improved and the demodulation and decoding performance of the received data symbol is also improved.

Since the time, frequency and power resources are limited, the system throughput performance can be adjusted according to the channel state, data rate, modulation scheme, and coding rate. The optimal system throughput performance can be obtained only when properly allocated.

MIMO is a single-terminal MIMO (SU-MIMO) that transmits a single terminal to one terminal at the same time and frequency resource at the same time, a multi-terminal MIMO (MU- MIMO), a Cooperative Multi-Point (CoMP) scheme transmitted by a plurality of base stations to one or a plurality of UEs, and the type and amount of reference signal resources required for each technology may be different.

In the LTE (-A) standard, a MIMO technique can be implemented using multiple antennas. For this, an individual reference signal must be transmitted for each layer. The reference signal transmitted per layer is determined according to the rank of the data traffic channel signal transmitted by the base station. The base station adaptively determines the rank of the data traffic channel signal according to a given channel environment, the number of terminals to be served, and the scheduling result. Individual reference signals transmitted per layer enable channel estimation for each layer.

There are various channel estimation schemes using a reference signal. Examples of the channel estimation scheme include MMSE channel estimation, Discrete Fourier Transform (DFT) -based channel estimation, and LS (Least Square) channel estimation. The performance of the channel estimation techniques depends on the number and arrangement of reference signals arranged on time and frequency resources and is also influenced by the power allocated to the reference signals.

In general, when reference signals are appropriately distributed on time and frequency resources, improved channel estimation results can be obtained as the number of reference signals and the allocated power increase. In addition, since various techniques applied to improve the transmission efficiency of the 3G mobile communication system require channel information, improvement in channel estimation performance leads to improvement in performance of the techniques, And contributes to performance improvement.

However, time, frequency, and power resources are limited in mobile communication systems. Therefore, if more resources are allocated to the reference signal, the resources that can be allocated to the data traffic channel transmission are reduced, and the absolute amount of data to be transmitted can be reduced.

In this case, the performance of the techniques for improving the transmission efficiency of the system can be improved based on the channel estimation performance improvement, but the absolute amount of data to be transmitted is reduced, so the overall system capacity performance may be lowered. Therefore, a proper allocation between the resources for the reference signal and the resources for the signal for data traffic channel transmission is required to achieve optimal performance in terms of overall system capacity. In the wireless mobile communication system, the reference signal and the data traffic channel transmission, which can improve the overall system capacity according to various factors such as the average signal to interference and noise ratio, average channel quality, data transmission rate, modulation scheme and coding rate, The optimal value of the resource allocation for the signal for the signal is different.

Generally, in the third generation evolved radio mobile communication system standard, a reference signal is a common reference signal (Common Pilot Symbol), a dedicated reference signal (Dedicated Reference Signal, Dedicated Pilot Symbol ), And a channel state measurement reference signal (Channel State Information RS).

1) Common reference signal: In 3GPP LTE system, it is referred to as a cell-specific RS or a common RS, and is a reference signal transmitted to all terminals of a cell to which the corresponding base station belongs. A reference signal pattern that can be divided into antenna ports is defined so that channel estimation can be performed when transmission using multiple antennas is performed. The LTE system supports up to four antenna ports.

2) Dedicated reference signal: A reference signal transmitted separately from the common reference signal and transmitted only to a specific terminal designated by the base station. In 3GPP LTE system, it is also called UE-specific RS, DRS or Demodulation Reference Signal (DMRS), and is generally used to support a data traffic channel transmission using a non-codebook based precoding.

3) Channel state measurement reference signal: Each terminal determines a data rate, a coding rate, a modulation scheme, a MIMO scheme, and the like that can be supported by each terminal using a channel state measurement reference signal. The determined information is transmitted to the base station using the uplink, and the base station decides what type of transmission is to be performed to the corresponding terminal using the information.

In a third-generation evolved wireless mobile communication system (hereinafter referred to as LTE (-A)), a base station performs downlink transmission on a subframe (1 msec) basis. That is, the BS can perform downlink data traffic channel transmission to one or a plurality of UEs at the same time for each subframe. For example, if the base station performs transmission using the two layers to the terminal 1 and the terminal 2 in the time interval t _A , the base station performs transmission using the single layer to the terminal 3, the terminal 4, and the terminal 5 in the time interval t _B .

개의 layer를 갖게 된다.In addition, the system bandwidth to be transmitted by the base station can be divided and allocated to different terminals during one subframe. A system bandwidth, which is a frequency domain resource of a base station, can be allocated to terminals by being divided into a plurality of resource blocks (RBs). The RB is composed of 12 subcarriers and occupies a frequency interval of 180 kHz in total. The LTE (-A) base station can perform downlink transmission to a plurality of terminals using a plurality of RBs for each subframe, and can select different terminals to receive signals on the corresponding RBs in units of one RB. The number of layers of the transmission signal of the LTE (-A) base station is equal to the sum of the layers of the signals of each terminal transmitted using the same time and frequency resources. That is, when a base station transmits a transmission signal having L _i layers to N terminals using the same frequency and time resources,

Layer.

As described above, in order to support the multi-antenna transmission technique using multiple antennas in the third generation evolved wireless mobile communication system standard, channel estimation for each antenna port or layer must be possible. For this purpose, a reference signal that can be distinguished by antenna port or layer must be transmitted. On the receiving side, a channel for each antenna or layer can be estimated through a reference signal. Accordingly, when reference signals for different antenna ports are transmitted at the same time, various multiplexing methods are used to distinguish reference signals for respective antenna pods at the receiving end. Four representative multiplexing methods will be described with reference to Figures 1-4.

1 is a diagram showing reference signals arranged by a time division multiplexing method according to the related art.

Referring to FIG. 1, the reference signals for different antenna ports are arranged so as not to overlap with different time symbols in time as shown in FIG. 1 through a time division multiplexing reference signal allocation method. In a data traffic channel transmitted to one antenna port, a subcarrier position for a reference signal of another antenna port is left empty without transmitting data.

위치에 전송된다. 이때 안테나 포트 #0에 전송되는 데이터 심볼은 다른 안테나 포트를 위한 기준 신호 위치인

를 위해 비워두고 전송된다. 따라서, 수신단이 각각의 안테나 포트 별 기준 신호 위치를 알고 있다면 각 안테나 포트 별로 데이터 트래픽이 겪게 되는 채널을 추정할 수 있다.For example, referring to FIG. 1 for the antenna port # 0, the reference signal for the antenna port # 0 is

Lt; / RTI > Here, the data symbol transmitted to the antenna port # 0 is a reference signal position for another antenna port

Lt; / RTI > Therefore, if the receiver knows the reference signal position for each antenna port, it can estimate the channel experienced by the data traffic for each antenna port.

In FIG. 1, the unit of the frequency domain corresponds to one subcarrier, and the unit of the time domain corresponds to one OFDM symbol. 1 can implement reference signals for four individual antenna ports, and the base station can perform MIMO transmission for up to four layers using the reference signals.

2 is a diagram illustrating reference signals arranged in a frequency / time division multiplexing method according to the related art.

Referring to FIG. 2, reference signals for different antenna ports are arranged so as not to overlap time symbols and subcarriers in time and frequency, as shown in FIG. 2, through the frequency / time division multiplexing reference signal arranging method. In a data traffic channel transmitted to one antenna port, a subcarrier position for a reference signal of another antenna port is left empty without transmitting data.

위치에 전송된다. 이때 안테나 포트 #0에 전송되는 데이터 심볼 은 다른 안테나 포트를 위한 기준 신호 위치인

는 비워두고 전송된다. 따라서, 수신단에서는 각각의 안테나 포트 별 기준 신호 위치를 알고 있다면 각 안테나 포트 별로 데이터 트래픽 채널이 겪게 되는 채널을 추정할 수 있다.For example, referring to FIG. 2 for the antenna port # 0, the reference signal for the antenna port # 0 is

Lt; / RTI > Here, the data symbol transmitted to the antenna port # 0 is a reference signal position for another antenna port

Is left empty. Therefore, if the receiver knows the reference signal position for each antenna port, it can estimate the channel experienced by the data traffic channel for each antenna port.

A reference signal for four individual antenna ports can be implemented through the reference signal arrangement of FIG. The base station can then perform MIMO transmission on up to four layers.

3 is a diagram illustrating a reference signal arrangement according to a conventional code division multiplexing method.

Referring to FIG. 3, reference signals for different antennas are superimposed on subcarriers and OFDM symbols having the same frequency and time in the code division multiplexing reference signal arrangement method, as shown in FIG. Each reference signal is classified by using an orthogonal code or a semi-orthogonal code such as a Walsh code. In the code division multiplexing reference signal allocation method, the reference signal for each port is distinguished through orthogonal codes such as Walsh codes within the adjacent time interval and frequency interval.

As an example, it is assumed that the reference signal for two antenna ports is code-division multiplexed by two Walsh codes having a length of 2 within the same time interval as shown in FIG. In this case, in the case of DMRS 0, Walsh code 0 of length 2 is used, and the first two symbols of the Walsh code are transmitted in two adjacent time intervals, which are the same frequency interval, Division multiplexing of the reference signal.

The code division multiplexing reference signal allocation method is advantageous in channel estimation because the reference signal allocation density can be increased. However, since different reference signals are distinguished through code division, if the orthogonality between codes is damaged due to a channel, interference may occur and the channel estimation performance may be degraded.

The reference signal constellation of FIG. 3 may implement a reference signal for two individual antenna ports. The base station can then perform MIMO transmission on up to two layers.

FIG. 4 is a diagram showing reference signals arranged according to a frequency / code / time division multiplexing method according to the related art.

Referring to FIG. 4, reference signals for different antennas are multiplexed and arranged in frequency, time, and code regions as shown in FIG. 4 through a frequency / code / time division multiplexing reference signaling method. In Fig for example 4 DMRS 0, using the Walsh code _{0 (f A, t A)} , (f B, t B), (f C, t A), (f D, t B), (f E, t _A ), (f _F , t _B ) and the sub-carrier. And DMRS 3 uses the Walsh code _{2 (f A, t B)} , (f B, t A), (f C, t B), (f D, t A), (f E, t B), (f _F , t _A ) and the sub-carrier.

The four multiplexing methods enable channel estimation for one or more layers or antennas when a base station performs MIMO transmission using the same frequency and time resources. The base station may use open loop diversity for one or more UEs using the reference signal multiplexing method, SU-MIMO (Single User MIMO) for supporting multiple layer transmissions for one UE, And MU-MIMO (Multiple User MIMO) that supports transmission of a plurality of layers.

In the case of a transmission scheme using a plurality of antennas such as MU-MIMO, SU-MIMO, and open loop diversity, a data traffic channel signal to be transmitted is precoded and transmitted. The precoding is a process of encoding a transmission signal in advance by a transmitter in order to obtain effects such as spatial multiplexing and transmit diversity. In order for the UE to receive the data traffic channel signal of the base station on which precoding has been performed as described above, the UE needs to know what precoding is applied to the data traffic channel signal.

There are two methods for determining precoding applied to a data traffic channel signal of a base station by a terminal. First, a base station transmits a precoded data traffic channel signal, and transmits control information to which precoding is not applied together with a corresponding data traffic channel signal to notify which precoding will be applied. Second, a base station transmits a reference signal to which a precoding is applied to a terminal, without precisely notifying the terminal of precoding applied to the data traffic channel signal.

Generally, since a reference signal to which precoding is applied is optimized for a specific UE, a reference signal used for the above-mentioned purpose is called a demodulation reference signal (DMRS). The same precoding as the data traffic channel signal transmitted precoding is applied to the DMRS. Therefore, in case of MIMO transmission in which a plurality of layers are implemented, a separate DMRS pattern for performing individual channel estimation for each layer should be allocated.

In the LTE system, a base station can perform transmission for two layers. The two layers may be allocated to one UE and implemented as SU-MIMO, or may be allocated to two different UEs and implemented as MU-MIMO. In the LTE system, a base station allocates a separate DMRS pattern to each layer in allocating two layers.

A method of allocating a separate DMRS pattern to each layer is a method of indirectly notifying a base station of which DMRS pattern is allocated to a terminal to which a downlink data traffic channel is to be transmitted. The BS reports two transport block size information to the UE to which data is to be transmitted. The UE knows which transport block is transmitted by the BS through the received two transport block size information and which DMRS is used to estimate the corresponding transport block. The transport block size information may be valid or invalid according to the determination of the BS. If the information about the transport block size is valid, it indicates the amount of information to be transmitted, but it is used for other purposes if it is invalid. More specifically, if only the first of the two transport block size information is valid, the UE knows that it performs the transmission corresponding to the first transport block size using the first individual DMRS pattern. Also, if only the second of the two transport block size information is valid, the UE knows that it performs transmission corresponding to the second transport block size using the second individual DMRS pattern. If both transport block size information are valid, the UE knows that it will perform the transmission corresponding to the first and second transport block sizes using the first and second individual DMRS patterns.

In the LTE-A system, when a base station performs SU-MIMO or MU-MIMO transmission, the number or rank of layers of a transmission signal depends on the number of receiving terminals selected by the scheduler of the base station, . For example, when a signal transmitted by a base station implements two layers, the base station allocates DMRS 0 and DMRS 1 of FIG. 3 to one or two terminals receiving each layer. As another example, when a signal transmitted from a base station implements four layers, the base station allocates DMRS 0, DMRS 1, DMRS 2, and DMRS 3 of FIG. 4 to a maximum of four terminals receiving each layer.

In the above two examples, the BS transmits two control information to the UE in allocating the DMRS resources. The two types of control information are information on how many layers of the BS transmission are transmitted and the portion allocated to the MS in the DMRS pattern used by the BS. That is, when a base station can transmit data in two layers or four layers, when a base station transmits MIMO to one or a plurality of terminals using the same time and frequency resources, it is determined whether the transmission is for two layers, the control information indicating the transmission acknowledgment to the layer and the DMRS index information should be transmitted. The reason for notifying the transmission of several layers is that the DMRS index information alone can not determine how the DMRS allocated to each terminal is transmitted. For example, in the case of performing transmission for two layers, when the DMRS pattern of FIG. 3 is used and transmission is performed for four layers, or when the DMRS pattern of FIG. 4 is used, , The UE can not know which DMRS pattern is based on the DMRS 0. Then, the UE can not perform channel estimation as a result.

A method of allocating an individual DMRS pattern for transmitting a DMRS in an LTE system is a method of notifying a transport block size of each layer using a Physical Downlink Control Channel (PDCCH) that transfers control information to a mobile station from a base station. When there is valid information among the received transport block sizes, the UE performs channel estimation using individual DMRS patterns that are fixedly allocated to a layer to which the corresponding transport block is transmitted. If only one of the transport block size information received by the UE is valid, the UE knows that one layer has been allocated to the UE and that an individual DMRS pattern has been allocated to the layer. On the other hand, if both transport block size information are valid, the UE finds that both layers are allocated to itself.

As described above, the DMRS pattern in the LTE system is fixedly allocated to each of the two layers. As described above, a method of fixedly allocating a specific individual DMRS pattern to a specific layer may be appropriate in the case of implementing a small number of layers as in the LTE system, but when the base station performs transmission using a larger number of layers It does not allow flexible allocation of DMRS resources.

The DMRS pattern allocation method in the LTE system is a method of notifying each terminal, which receives each layer, of a fixed pattern allocated to two layers using a PDCCH. LTE-Advanced (LTE-Advanced), a more advanced wireless communication system, is designed to allow a base station to implement up to eight layers, and each terminal is designed to receive up to two layers .

When using the DMRS pattern allocation method in the LTE system as it is in the LTE-A system, the base station must transmit the transport block size for eight layers through the PDCCH. That is, the UE observes the transport block size information for the eight layers among the received PDCCH control information to determine whether the transport block size information is valid. As described above, the base station transmits transport block size information for all eight layers to the mobile station using the PDCCH.

When the transport block size information for all of the plurality of layers is transmitted to the UE using the PDCCH, excessive performance of the control information may be transmitted, thereby degrading overall performance of the system. Another problem with the DMRS pattern allocation method in the LTE system is that individual DMRS patterns are fixedly allocated to each layer. The DMRS pattern allocation method in the LTE system may cause system performance degradation by allocating certain radio resources to the DMRS in a state where the base station does not know how many layers are actually transmitted.

Another problem with the DMRS pattern allocation method in the LTE system is that the BS allocates the same radio resources regardless of the modulation scheme, the transmission rate, the coding rate, and the terminal movement speed of the downlink data traffic channel to be transmitted. In general, a terminal capable of supporting a high data rate can be received at a high signal-to-noise ratio (SNR) because it exists in a position relatively close to a base station. Also, even if the base station allocates a relatively small amount of radio resources to the DMRS transmission, the terminal can perform accurate channel estimation. That is, the radio resources to be allocated to the DMRS transmission by the base station in order to satisfy the proper channel estimation accuracy in the terminal vary depending on the data rate, modulation scheme, terminal movement rate, number of layers received by the terminal, . However, the DMRS pattern allocation method in the LTE system has a problem in that static radio resources are allocated to individual DMRS patterns required to perform channel estimation for one layer while ignoring these variables.

When the base station performs transmission of a plurality of layers to a plurality of UEs, the allocation of fixed radio resources to the individual DMRS patterns as described above can not guarantee sufficient channel estimation for some UEs, .

Since standards such as the current LTE (-A) allocate fixed resources to the reference symbols regardless of the MIMO scheme, the number of layers to be transmitted (rank of base station transmission signal), channel state, data rate, Is not achieved efficiently.

Therefore, an object of the present invention to solve the above problems is to dynamically allocate DMRS resources to one or a plurality of terminals while maintaining transparency of MU-MIMO in an LTE-A system. The present invention also aims to improve the overall system capacity performance by appropriately allocating the DMRS resources among one or a plurality of terminals based on the MIMO scheme, the channel environment, and other factors affecting the reception performance.

According to another aspect of the present invention, there is provided a resource allocation method including: transmitting at least one dedicated reference signal pattern set for preset channel estimation to a terminal through signaling; Determining whether to transmit a dedicated reference signal according to precoding to be transmitted to the UE, and notifying the UE of control information according to a dedicated reference signal pattern allocated to a layer transmitted to the UE when the dedicated reference signal is transmitted .

According to another aspect of the present invention, there is provided a channel estimation method comprising: determining whether a dedicated reference signal is transmitted using control information received from a base station; The method comprising the steps of: identifying a plurality of allocation indicators indicating the number of dedicated reference signal patterns allocated to the layer and the dedicated reference signal patterns assigned to the layer; and performing channel estimation according to the identified dedicated reference signal patterns and the plurality of allocation indicators .

According to the present invention, the LTE-A base station dynamically allocates a preset DMRS resource to a plurality of terminals, and a plurality of terminals, which are allocated a plurality of layers transmitted by the base station, respectively perform sufficient channel estimation. In addition, whether the LTE-A base station uses transmission for a plurality of layers using either the LTE scheme or the LTE-A scheme can be dynamically performed. In addition, according to the determination of the LTE-A base station, related control information is transmitted on the PDCCH to the mobile station, thereby notifying the mobile station whether the base station performs multi-layer transmission of the LTE scheme or the LTE-A scheme

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings and drawings. In the following description, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. The following terms are defined in consideration of the functions of the present invention, and these may be changed according to the intention of the user, the operator, or the like. Therefore, the definition should be based on the contents throughout this specification.

In describing the embodiments of the present invention in detail, OFDM-based wireless communication systems, particularly 3GPP EUTRA (or LTE) or Advanced E-UTRA (or LTE-A) , It is to be understood that the subject matter of the present invention is also applicable to other communication systems having similar technical background and channel form with slight modifications within the scope of the present invention without departing from the scope of the present invention, It will be possible at the judgment of the person having it. The LTE-A system can be implemented with various MIMO schemes mixed within the same system bandwidth. That is, a single-terminal MIMO (SU-MIMO) in which one base station transmits to one terminal simultaneously using the same time and frequency resources, a multi-terminal MIMO (MU- MIMO), a Cooperative Multi-Point (CoMP) scheme transmitted by a plurality of base stations to one or a plurality of terminals, and the like can be implemented within the same system bandwidth.

In implementing the MU-MIMO in the LTE-A system, there is a method of making the MU-MIMO transparent and a method of not having transparency. The transparency of the MU-MIMO indicates that the BS does not know whether the signal transmitted from the BS is a part of the MU-MIMO signal or the SU-MIMO signal in performing MU-MIMO on a plurality of MSs. If the terminal receiving the MU-MIMO signal does not know whether the signal transmitted from the base station is part of the MU-MIMO signal, the terminal does not need a separate reception structure or reception operation for the MU-MIMO. That is, the UE receiving the MU-MIMO signal restores the signal for the UE using the SU-MIMO receiver and the reception operation. As described above, the advantage of transparency of MU-MIMO is that it does not require a separate receiving structure and receiving operation considering MU-MIMO and realizes reception structure for receiving SU-MIMO and receiving operation only, It is relatively easy to implement.

In a case where a pattern of a dedicated reference signal (DMRS) is differently applied according to the rank of a signal transmitted from a base station and only one individual DMRS is allocated to one layer, the base station performs channel estimation It is necessary to inform the UE of the number of layers to which the signal transmitted by the base station is transmitted and the DMRS index. That is, the BS controls one or more DMRS indexes indicating how many layers are transmitted and which individual DMRSs are allocated to the UE so that the UE can perform channel estimation to recover the data traffic channel signal Information is notified to the terminal every subframe (1 msec) in the form of information.

If a DMRS pattern is used, which is determined according to how many transmission layers of the base station are transmitted, the UE calculates the number of individual DMRS allocated to itself and how many layers the BS performs transmission MIMO transmission or SU-MIMO transmission if the transmission of the corresponding base station is MU-MIMO transmission. That is, transparency of MU-MIMO is lost. For example, when the BS informs the MS that the BS transmission signal is a signal for four layers and assigns DMRS 0 and DMRS 1, the MS transmits a message indicating that the BS transmission is for four layers and that the DMRS 0, DMRS 1, DMRS 2, and DMRS 3, that is, only the DMRS 0 and the DMRS 1 are allocated, it can be determined that the signal transmitted to the UE is part of the MU-MIMO transmission.

However, the problem of applying different DMRS patterns according to rank of signals transmitted by the base station and assigning only one individual DMRS pattern to one layer is that when performing MU-MIMO for a plurality of terminals at the same time, The DMRS resource can not be allocated. Channel estimation performed to recover a transmission signal distorted by a wireless communication channel requires different channel estimation accuracy depending on a wireless channel environment, a data rate, a modulation / demodulation scheme, a coding rate, and the like of the corresponding transmission signal.

For example, relatively high data rates operating at relatively high signal-to-noise ratios require relatively fewer DMRS resources than at low data rates operating at relatively low signal-to-noise ratios. Also, when the UE moves at a low speed, since the time change of the wireless channel is not large, a relatively small amount of DMRS resources are required compared with the case where the UE moves at high speed. For example, in FIG. 4, DMRS transmission for four layers can be performed, but 25% of the entire DMRS resources are unconditionally channel-estimated for each layer without considering the data rate and radio channel environment for each layer .

In order to perform dynamic DMRS resource allocation on a terminal-by-terminal basis while maintaining the transparency of the MU-MIMO mentioned above, the base station sets a plurality of aggregate DMRS patterns and then allocates resources of the corresponding set DMRS patterns to a plurality of exclusive Lt; / RTI > pattern. A plurality of exclusive DMRS patterns in the aggregated DMRS pattern are dynamically allocated to one or a plurality of terminals so that the corresponding terminals or terminals can perform effective channel estimation. Here, there are the following two resources allocated to transmit the DMRS.

1) Resource element: In 3GPP LTE (-A), each subcarrier of an OFDM (A) symbol is referred to as a resource element (RE) as a time and frequency resource capable of transmitting one modulated signal . The DMRS is also allocated a resource element that is a time and frequency resource.

2) Transmission power: Since the transmission power used for transmitting signals in the wireless mobile communication system is limited, when transmitting one OFDM (A) symbol, the maximum transmission power that can be used for each subcarrier is appropriately allocated, .

FIG. 5 is a diagram illustrating a set DMRS pattern for a DMRS resource allocation method according to an embodiment of the present invention. Referring to FIG.

The aggregated DMRS pattern shown in FIG. 5 uses a total of 24 REs and is made up of eight individual DMRS patterns. The eight individual DMRSs are multiplexed on frequency, time, and code, and enable channel estimation for up to eight layers.

FIG. 6 is another diagram illustrating a set DMRS pattern for a DMRS resource allocation method according to an embodiment of the present invention. Referring to FIG.

The aggregated DMRS pattern illustrated in FIG. 6 uses a total of 12 REs and is composed of four individual DMRS patterns. The four individual DMRSs are multiplexed on frequency, time and code and allow channel estimation for up to four layers.

FIG. 7 is another diagram illustrating a set DMRS pattern for a DMRS resource allocation method according to an embodiment of the present invention. Referring to FIG.

The aggregated DMRS pattern shown in FIG. 7 uses a total of 12 REs and is composed of two individual DMRS patterns. The two separate DMRSs are multiplexed on frequency, time, and code, enabling channel estimation for up to two layers.

In the present invention, the base station selects one of a plurality of applicable sets of DMRS patterns as shown in FIG. 5, FIG. 6, and FIG. And the selected DMRS pattern selection is performed in the network optimization step. The network optimization means setting related parameters such that a base station can be efficiently operated in consideration of a radio channel environment of a region managed by the base station and the number of terminals requesting a service, -static. The selected set DMRS pattern is individually selected for each base station, and information on the selected set DMRS pattern is notified using upper signaling when the UE enters the service area of the corresponding base station.

The selection of the aggregated DMRS pattern can be performed in consideration of the radio channel environment of the base station and the number of terminals requesting the service. For example, in the case of a base station installed in an area in which a wireless channel environment can communicate with a plurality of layers and a plurality of terminals simultaneously request services on the average, a set DMRS pattern as shown in FIG. 5 . On the other hand, in the case of a base station installed in an area where a wireless channel environment is not easy to communicate with a plurality of layers and a small number of terminals simultaneously request services, a set DMRS pattern Can be selected. The aggregate DMRS pattern of FIG. 5 can support transmission for more layers. The aggregated DMRS pattern of FIG. 7 has a relatively large amount of radio resources that can be allocated to the data traffic channel signal transmission.

FIG. 8 shows an example in which a set DMRS pattern is applied to different frequency bands within a whole system bandwidth according to an embodiment of the present invention.

Referring to FIG. 8, the set reference signal pattern can be determined for each base station. As shown in FIG. 8, different sets of DMRS patterns can be applied to different frequency bands within one base station. For example, in a frequency interval A within a bandwidth in which one base station transmits data in FIG. 8, an aggregate DMRS pattern capable of performing transmission for eight layers as shown in FIG. 5 is applied. In another frequency B, a combined DMRS pattern capable of performing transmission for two layers as shown in FIG. 7 can be applied. In addition, the set DMRS pattern determination for each frequency interval is not performed dynamically as in the case of the set DMRS pattern determination for each base station, and is notified using the upper signaling to the UE after being set in the network optimization step.

As shown in FIG. 8, the system frequency of a base station is divided into a plurality of subbands to assign an aggregate DMRS pattern to each subband differently, and a method of assigning different aggregate DMRS patterns to terminals receiving signals from the corresponding base station Do. When allocating a different aggregate DMRS pattern for each UE, the Node B notifies the UE of using a specific aggregate DMRS pattern in a specific subband using upper signaling. Therefore, different terminals receiving services from the same base station can be set to different aggregate DMRS patterns even in the same subband. Here, the method of setting the aggregate DMRS pattern is as follows.

Method 1: The same aggregate DMRS pattern is commonly set in the base station system band, and it is notified to all terminals in common.

Method 2: A method of dividing a base station system band into a plurality of subbands, separately setting an aggregate DMRS pattern for each subband, and notifying all the terminals in common.

Method 3: An aggregate DMRS pattern is set for each terminal and the method is reported for each terminal. In this case, a specific terminal may use the same aggregate DMRS pattern in the system band, but different terminals may have different aggregate DMRS patterns.

Method 4: A method of collecting DMRS patterns by subband by terminal and notifying each terminal. In this case, when a specific terminal uses an aggregate DMRS pattern set for each subband in the system band, the DMRS patterns may be set differently for each terminal.

When the aggregated DMRS pattern is determined at the base station and notified to the UEs receiving the data traffic channel transmission from the corresponding base station, each UE receives at least one individual DMRS pattern constituting a combined DMRS pattern to receive channel data, . Here, the individual DMRS patterns can be illustrated as shown in FIG.

9 is a diagram illustrating an individual DMRS pattern according to an embodiment of the present invention.

The difference between the prior art and the present invention is that when a set DMRS pattern is preset and an individual DMRS pattern is allocated to the terminal, the DMRS pattern is allocated only without notifying the terminal of the number of layers of signals transmitted by the base station . That is, only the individual DMRS pattern is allocated to the UE, and it can not be determined whether the received signal is a part of a signal transmitted to the MU-MIMO. This is because the same set of DMRS patterns are used irrespective of how many layers the transmission signal of the base station is transmitted. However, in the prior art, the reference signal pattern is changed according to the number of layers of the signal transmitted by the base station, so that the terminal must recognize in advance how many layers the transmission signal of the base station is transmitted.

In the present invention, a method of notifying the base station of which individual DMRS pattern is allocated to the terminal is to make an individual DMRS pattern allocation table promised between the base station and the terminal in advance. The individual DMRS pattern allocation table must be created for every selectable DMRS pattern of the base station. For example, a separate DMRS pattern allocation table for FIG. 9 can be created as shown in Table 1.

Individual reference signal pattern indicator ( Frequency, time) code 0 _{(F A, T A),} (F C, T B), (F E, T A), (F G, T B),
_{(F I, T A),} (F K, T B) Walsh code 0 One _{(F A, T A),} (F C, T B), (F E, T A), (F G, T B),
_{(F I, T A),} (F K, T B) Walsh code 1 2 _{(F B, T A),} (F D, T B), (F F, T A), (F H, T B),
(F _J , T _A ), (F _L , T _B ) Walsh code 0 3 _{(F B, T A),} (F D, T B), (F F, T A), (F H, T B),
(F _J , T _A ), (F _L , T _B ) Walsh code 1 4 _{(F A, T B),} (F C, T A), (F E, T B), (F G, T A),
_{(F I, T B),} (F K, T A) Walsh code 0 5 _{(F A, T B),} (F C, T A), (F E, T B), (F G, T A),
_{(F I, T B),} (F K, T A) Walsh code 1 6 _{(F B, T B),} (F D, T A), (F F, T B), (F H, T A),
_{(F J, T B),} (F L, T A) Walsh code 0 7 _{(F B, T B),} (F D, T A), (F F, T B), (F H, T A),
_{(F J, T B),} (F L, T A) Walsh code 1

Each individual DMRS pattern indicator in Table 1 indicates a set DMRS pattern using a specific frequency, time, and code in FIG. For example, if the value of the individual DMRS pattern indicator is 0, it means the individual pattern 0 in FIG.

When the relationship between the individual DMRS pattern indicators and the individual DMRS patterns is established as shown in Table 1, the base station can notify the individual DMRS patterns to be allocated to the terminals to receive the transmission signals. One of the individual DMRS pattern notification methods is to notify whether the individual DMRS pattern indicated by the reference signal pattern indicator is allocated to the terminal using one bit for each DMRS pattern indicator in a bitmap manner.

In the case of allocating the individual DMRS pattern indicators 0, 1, and 2 to a specific UE in FIG. 9 and Table 1, the BS uses a PDCCH (Physical Downlink Control Channel) of LTE (-A) 'Of the bitmap information. The i-th bit in the 8-bit bitmap information indicates that the individual DMRS pattern indicated by the i-th individual DMRS pattern indicator is assigned to the corresponding terminal when the value is 1.

Another method of notifying the individual DMRS patterns is to notify the UE of a starting point and an ending point in the allocation table when the allocation table as shown in Table 1 is determined. For example, when the individual DMRS patterns 0, 1, and 2 are assigned to a specific UE in Table 1, the BS determines '000' (interpreted as an indicator 0) and '010' Quot; 000010 " to the corresponding terminal using the PDCCH. The notification of the start and end points to the terminal and notification of the individual DMRS pattern to the terminal is advantageous in that it requires a relatively small number of bits as compared with the method of notifying the terminal of bitmap information as described above. There are operational limitations in that a DMRS pattern indicator can not be allocated consecutively when all DMRS pattern indicators are allocated.

Another method of notifying an individual DMRS pattern is to notify the starting point and the number of individual DMRS patterns in the corresponding allocation table when the allocation table as shown in Table 1 is determined. For example, if the individual DMRS patterns 0, 1, 2, and 3 are assigned to a specific UE in Table 1, the BS determines '000' (interpreted as indicator 0), which means the starting point, and '100' 000100 ", which is a combination of " 000100 " As described above, the notification of the start point and the number of individual DMRS patterns to the UE is advantageous in that relatively few bits are required compared with the scheme of notifying the bit map information as described above. However, a plurality of DMRS pattern indicators are allocated There is an operational limitation that it is inevitable to assign a continuous DMRS pattern indicator.

A method of notifying the UE of a start point and an ending point in an individual DMRS pattern allocation table among the methods of notifying the individual DMRS patterns and a method of notifying the starting point and the number of individual reference signal patterns may be performed depending on how the individual DMRS pattern allocation table is set It can have different effects. In the above-mentioned two methods, when four individual DMRS patterns are assigned to one UE in order to perform channel estimation for a plurality of layers in Table 1, the BS allocates four consecutive DMRS patterns as illustrated in Table 1 .

As described above, four individual DMRS patterns allocated to one terminal are allocated to individual DMRS patterns classified into CDM regardless of whether individual DMRS patterns are allocated to other terminals. For example, if you want to assign an individual DMRS pattern indicator 0,1,2,3 to a specific terminal from Table 1 that the terminal (F _A, T _A), (F _C, T _B), (F _E, T _{A), (F G, T B),} (F I, T a), (F K, T B) and _{(F B, T a),} (F D, T B), (F F, T a), (F Four separate DMRS patterns are assigned to Walsh code 0 and Walsh code 1 in time and frequency units of _H , T _B , F _J , T _A , and F _L and T _B , respectively.

As shown in FIG. 5, in a situation where eight individual DMRSs can be allocated, the BS can allocate fewer than eight individual DMRS patterns to one terminal. For example, the BS allocates the individual DMRS patterns 0 and 1 and the individual DMRS patterns 2 and 3 using the same time and frequency resources and the Walsh codes to one terminal in Table 1. Then, the base station does not use the remaining four individual DMRS patterns, or can assign it to other terminals. In this case, the UE uses the individual DMRS patterns to be CDM due to the individual DMRS pattern allocation table configuration order shown in Table 1 above. The use of individual DMRS patterns that are distinguished using CDM, even though there are other individual DMRS patterns, can lead to performance degradation in CDM that must maintain orthogonality.

In FIG. 5, the individual DMRS pattern 0 and the individual DMRS pattern 1 are CDM on the time axis. In this case, the orthogonality of the Walsh code for CDM of the individual DMRS pattern 0 and the individual DMRS pattern 1 when the terminal moves at a high speed is no longer guaranteed And the channel estimation performance may deteriorate.

As described above, when a plurality of individual DMRS patterns are assigned to one UE, the BS allocates individual DMRS patterns that are not CDMs as much as possible. When the bitmap scheme is used in allocating the individual DMRS patterns to the UE, the BS can freely assign the DMRS patterns to the UEs in the individual DMRS pattern allocation table. Therefore, the BS can allocate a separate DMRS pattern that is not CDM as much as possible to one UE. However, since the method of notifying the start point and the end point and the method of notifying the starting point and the number of individual DMRS patterns allocate consecutive individual DMRS pattern indicators in the individual DMRS pattern allocation tables, Different results can be obtained.

A method of notifying the individual DMRS patterns assigned to the same terminal as much as possible by using the method of notifying the start point and the end point of the individual DMRS pattern allocation method and the method of allocating the starting point and the number of individual DMRS patterns, As shown in Table 2.

Individual reference signal pattern indicator ( Frequency, time) code 0 _{(F A, T A),} (F C, T B), (F E, T A), (F G, T B),
_{(F I, T A),} (F K, T B) Walsh code 0 One _{(F A, T B),} (F C, T A), (F E, T B), (F G, T A),
_{(F I, T B),} (F K, T A) Walsh code 0 2 _{(F B, T A),} (F D, T B), (F F, T A), (F H, T B),
(F _J , T _A ), (F _L , T _B ) Walsh code 0 3 _{(F B, T B),} (F D, T A), (F F, T B), (F H, T A),
_{(F J, T B),} (F L, T A) Walsh code 0 4 _{(F A, T A),} (F C, T B), (F E, T A), (F G, T B),
_{(F I, T A),} (F K, T B) Walsh code 1 5 _{(F A, T B),} (F C, T A), (F E, T B), (F G, T A),
_{(F I, T B),} (F K, T A) Walsh code 1 6 _{(F B, T A),} (F D, T B), (F F, T A), (F H, T B),
(F _J , T _A ), (F _L , T _B ) Walsh code 1 7 _{(F B, T B),} (F D, T A), (F F, T B), (F H, T A),
_{(F J, T B),} (F L, T A) Walsh code 1

In the case of the individual DMRS pattern allocation table 2 in Table 2, when a terminal is allocated a plurality of individual DMRS patterns, the corresponding DMRS patterns may be included in the individual DMRS pattern indicators 0, 1, 2 and 3, or the individual DMRS pattern indicators 4, 5, 7, there is a characteristic of not being CDM between individual DMRS patterns of one terminal.

For example, the BS allocates individual DMRS patterns corresponding to the individual DMRS pattern indicators 0, 1, 2 and 3 to one terminal in the individual DMRS pattern allocation table of Table 2, and assigns the individual DMRS pattern indicators 4, 5, 6, and 7, respectively. Here, the individual DMRS patterns allocated by the first UE are not divided into CDMs therebetween. Also, the individual DMRS patterns allocated by the second terminal are also not divided into CDMs therebetween. The individual DMRS patterns separated by the CDM exist only between the individual DMRS patterns used by different terminals. That is, the individual DMRS patterns corresponding to the individual DMRS pattern indicator 0 allocated to the first UE and the individual DMRS patterns corresponding to the individual DMRS pattern indicator 4 allocated to the second UE are classified into CDMs.

In this example, the individual DMRS patterns allocated to the other terminals are distinguished from each other by the CDM, which is advantageous in performance compared with the case where the individual DMRS patterns allocated to the same terminal are classified into CDMs. The reason for this is that, when MU-MIMO transmission is performed to a plurality of terminals, signals transmitted to different terminals undergo different beamforming, so that signals of respective terminals are individually spatially isolated It is because. In a situation where signals of different terminals are spatially separated, the influence of one terminal on other terminals is relatively small, so that even if orthogonality is not guaranteed between individual DMRS patterns classified by the CDM, the performance deterioration thereof is relatively small have.

As shown in Table 2, a method of limiting the plurality of individual DMRS patterns allocated to one UE to CDM is as follows. First, the base station appropriately arranges individual DMRS patterns connected to individual DMRS pattern indicators, and allocates one Walsh code to each of the continuous DMRS pattern indicators. The base station then assigns the next Walsh code to the next consecutive individual DMRS pattern indicator. Therefore, Walsh code 0 is assigned to individual DMRS pattern indicators 0 through 3 as shown in Table 2, and Walsh code 1 is assigned to individual DMRS pattern indicators 4 through 7, which can no longer use Walsh code 0 .

The set DMRS pattern of FIG. 6 is a subpattern of the set DMRS pattern of FIG. 5, and the set DMRS pattern of FIG. The set of 6 is a subpattern of the DMRS pattern. The set DMRS pattern is a subpattern of another set DMRS pattern, and the corresponding set DMRS pattern is a part of another set DMRS pattern in a given time frequency resource.

As in the case of FIGS. 5, 6 and 7, a set DMRS pattern capable of supporting a small number of rank among different sets of DMRS patterns that can be used in the same system is a subpattern of a set DMRS pattern , It can have high flexibility in implementing MU-MIMO within the system bandwidth transmitted by one base station.

10 is a diagram illustrating a base station MIMO transmission for one or a plurality of terminals in different frequency intervals within one system bandwidth according to an embodiment of the present invention. When the DMRS pattern is set to the DMRS pattern shown in FIG. 9, the UE is informed from the base station by using upper signaling for the set DMRS patterns used in different frequency intervals within the system bandwidth. Then, in the frequency interval A of FIG. 10, the base station transmits SU-MIMO to the SS # 1. On the other hand, in the frequency interval B, the BS performs MU-MIMO transmission for the UE 1 and the UE 4.

In FIG. 10, the terminal 1 receives the SU-MIMO signal from the base station in the frequency sections A, B, On the other hand, the terminal 4 receives the MU-MIMO signal from the base station in the frequency sections C, D, and E. In FIG. 9, the number of layers transmitted in the frequency sections A and B is L ₁ due to the transmission of the terminal 1 and the terminal 4. And the number of layers transmitted in the frequency domain C is L ₁ + L ₄ . 5, 6, and 7, a set DMRS pattern that can support a small number of rank among different sets of DMRS patterns that can be used in the same system can be used in a set DMRS pattern In the case of subpattern, another MIMO transmission can be implemented in different frequency intervals as shown in FIG.

As shown in FIG. 10, when performing a different type of MIMO transmission within a frequency interval received by a UE, it is a problem that the BS allocates a specific DMRS pattern to the UE. More specifically, the UE 1 receives the SU-MIMO signal in the frequency domain A and B, but receives a part of the MU-MIMO signal in the frequency domain C. As described above, the base station can use another MIMO scheme within a reception frequency interval of one UE, and each frequency interval can be set to use different sets of DMRS patterns as shown in FIG. However, it is a problem to allocate DMRS resources to a terminal receiving a downlink traffic channel in a plurality of frequency bands based on a certain set DMRS pattern.

The method proposed in the present invention allocates DMRS resources based on a set DMRS pattern of a specific frequency interval promised between a base station and a UE among a plurality of frequency intervals allocated to the UE. Another method is to allocate a DMRS resource based on a set DMRS pattern used in a frequency interval of the lowest frequency band among a plurality of frequency intervals allocated to the UE. Another method is to allocate based on the set DMRS pattern used in the frequency interval of the highest frequency band among a plurality of frequency intervals allocated to the UE. In addition to the above two methods, it is possible to promise a reference point between the base station and the terminal by various methods.

In the case of a UE receiving a plurality of frequency intervals using different sets of DMRS patterns as described above, individual DMRS patterns are allocated based on a set DMRS pattern of a specific frequency interval. Also, when a DMRS resource is allocated based on a set DMRS pattern of a specific frequency interval, the UE can use the same individual DMRS pattern in another frequency interval. Also, when the base station allocates the DMRS resource based on the set DMRS pattern of a specific frequency interval, it determines that the same DMRS resource is allocated to the UE in another frequency interval received by the corresponding UE.

For example, the following situation is assumed. In FIG. 9, the base station sets the set DMRS pattern of FIG. 7 in the frequency domain A and B and sets the set DMRS pattern of FIG. 6 in the frequency domain C, As shown in FIG. In this case, when the BS allocates the individual DMRS pattern 0 of FIG. 7 to the MS based on the frequency interval A, the UEs are allocated the same individual DMRS pattern 0 in the frequency interval B, and in the frequency interval C, The DMRS pattern 0 and the individual DMRS pattern 2 are allocated. If the DMRS pattern is allocated as described above, the UE can receive the same DMRS resources at the same frequency and time position within the frequency band that the UE receives, even if the number of allocated frequency segments, the set DMRS patterns of the frequency segments, have.

If the same DMRS resource can be allocated to the UE even if different sets of DMRS patterns are used in a plurality of frequency intervals as described above, But it is possible only when the base station sets up the frequency-based collective DMRS pattern and informs the UE in advance.

For example, when a DMRS pattern is set for each rank of signals transmitted by a base station, and the rank of the signal transmitted by the base station is notified to the mobile station dynamically, which is not a subpattern relation, the MU- It can not be implemented. Or a rank of a signal transmitted from the base station to the mobile station or when transmission of different ranks is performed in a plurality of frequency bands transmitted to the mobile station, the base station determines whether the rank information is transmitted to the mobile station based on a certain frequency interval I can not judge. Also, even if the rank information is notified to the UE based on a specific frequency interval, the allocation of the same DMRS resource can not be guaranteed within a plurality of frequency intervals that one UE receives, unless the DMRS patterns are subpattern-related. Therefore, the downlink data transmission should be performed as shown in FIG.

11 is a diagram illustrating a base station MIMO transmission for one or a plurality of terminals in different frequency intervals within a system bandwidth according to another embodiment of the present invention.

11 and FIG. 10, it can be seen that the MIMO scheme is not changed in a plurality of frequency intervals in which one terminal receives a base station signal in the case of FIG. That is, the terminal 1 receives a transmission signal from the base station in the frequency sections A, B, and C, and is transmitted to the MU-MIMO together with the signal of the terminal 4 in three frequency bands.

As shown in FIG. 11, the BS may restrict transmission of radio resources, and consequently may have poor performance as compared with the case where a free MIMO scheme can be used for each frequency interval as shown in FIG. 10 .

The above-mentioned individual DMRS pattern allocation method allocates one individual DMRS pattern for one layer. That is, each individual DMRS pattern is allocated to each layer and used to estimate the radio channel of the layer. The assignment of one DMRS pattern to one layer as described above is indispensable when transmission is performed for as many layers as the maximum number of layers supported by the set DMRS pattern. On the other hand, if the transmission signal of the base station is transmitted to a layer smaller than the maximum number of layers supported by the set DMRS pattern, or if one individual DMRS pattern is assigned to one layer, some of the available individual DMRS patterns may not be used have.

As described above, the problem that the available individual DMRS patterns to be transmitted for a layer smaller than the maximum number of layers supported by the set DMRS pattern is not used can be solved by allocating a plurality of individual DMRS patterns per one layer. One method of allocating a plurality of individual DMRS call patterns per layer is to notify multiple allocation indicator information while allocating individual DMRS patterns to each terminal.

For example, when a BS performs transmission using two layers to a specific UE and allocates two separate DMRS patterns for channel estimation for each layer, the BS allocates four individual DMRS patterns and sets '1' And transmits the multiple allocation indicator information together with other control information to the terminal. When a base station performs transmission using two layers to a specific UE and allocates one individual DMRS pattern for channel estimation for each layer, the BS assigns two individual DMRS patterns and transmits a plurality And transmits allocation indicator information together with other control information to the terminal.

The allocation of a plurality of individual DMRS patterns to the one layer may allow a more accurate channel estimation as the transmission power, frequency and time resources of a relatively large number of base stations are allocated for channel estimation for one layer in the UE do.

The method of allocating a plurality of individual DMRS patterns for the one layer includes a method of notifying the bit map notification method, a starting point and an end point, control information necessary for a method of notifying a poetic point and a number of individual DMRS pattern numbers, And notifies the terminal of the allocation indicator information. The plurality of allocation indicator information is one bit, and the information is information indicating that one or two individual DMRS patterns are allocated to each layer. The plurality of allocation indicator information may allocate three or more individual DMRS patterns using more than one bit. For example, if the multiple allocation indicator information is 2 bits, the BS may allocate one, two, three, or four individual DMRS patterns to the UEs per layer.

12 is a diagram illustrating the multiple allocation indicator according to an embodiment of the present invention.

Referring to FIG. 12, the base station performs MU-MIMO to three UEs. Terminal 1 receives signals in two layers, terminal 2 receives two signals, and terminal 3 receives signals in one layer. For the channel estimation in the UEs, the BS allocates four, two, and two individual DMRS patterns to the UEs 1, 2, and 3, respectively.

The BS transmits allocation control information to each MS based on the individual DMRS pattern allocation method. More specifically, the base station performs channel estimation for the two layers in the four individual DMRS patterns in the case of the UE 1, and sets the multiple allocation indicator to '1' to notify the UE 1 of the allocation. Also, in the case of the terminal 3, since channel estimation is performed for one layer in two separate DMRS patterns, the base station sets the multiple allocation indicator to '1' and notifies the terminal 3 of the allocation. In the case of the terminal 2, since channel estimation is performed on two layers in two separate DMRS patterns, the base station sets the multiple allocation indicator to '0' and notifies the terminal 2 of the channel allocation. Accordingly, each UE is informed of a plurality of allocation indicators, so that it can know how many individual DMRS patterns are assigned to the layers it receives. Also, when a plurality of individual DMRS patterns are allocated for channel estimation of one layer, the UE determines that the corresponding DMRS patterns are transmitted with precoding equal to the data traffic channel signal transmitted to the corresponding layer.

In FIG. 12, each UE is notified from the BS of the number of layers to be subjected to channel estimation using the individual DMRS pattern allocated thereto and the corresponding DMRS pattern, and in addition, the signal received by the terminal is used as the MU- I do not know whether it is a part or not. For this reason, the individual pattern DMRS pattern allocation method can maintain transparency with respect to MU-MIMO.

FIG. 13 is a diagram illustrating a process of assigning an individual DMRS pattern included in a set DMRS pattern to a UE in a BS according to an embodiment of the present invention.

Referring to FIG. 13, in step 1200, the BS determines an aggregated DMRS pattern. The set DMRS pattern determined here may be set to be applied to all the system bandwidths transmitted by the base station as described above, or may be set to different DMRS patterns for different frequency ranges as shown in FIG. 8 by dividing the system bandwidth. The set aggregated DMRS pattern is informed to the UE by upper signaling.

Next, in step 1210, the BS determines, based on whether a set DMRS pattern is supported for a maximum number of layers, transmission to a UE, a certain modulation coding scheme (MCS) , What precoding to apply, and so on. In step 1210, the BS performs step 1220 of determining whether the DMRS transmission is required according to what precoding is applied. If it is determined in step 1210 that non-code based precoding is to be performed, the Node B informs the UE of a precoding applied to each layer to be transmitted to the UE, it decides to transmit the DMRS which takes precoding.

However, if it is determined in step 1220 that it is not necessary to use the DMRS, the BS transmits a Common Reference Signal (CRS) and a Physical Downlink Shared Channel (PDSCH) signal in step 1230. If it is determined in step 1220 that transmission using the DMRS is to be performed, the BS determines an individual DMRS pattern indicator to be allocated to each layer to be transmitted to one or a plurality of terminals in step 1240. In step 1250, the BS determines control information for notifying an individual DMRS pattern indicator to be allocated to each UE. In step 1260, the BS determines whether there is a UE allocated a plurality of individual DMRS patterns per layer among the UEs.

If it is determined in step 1260 that one individual DMRS pattern is allocated to each layer, the BS sets the multiple allocation indicator to '0' in step 1270. On the other hand, if it is determined in step 1260 that there is a layer to which one or more individual DMRS patterns are allocated, the BS sets '1' for the multiple allocation indicator of the UE receiving the layer in step 1280. And the multiple allocation indicator of the remaining terminals is set to '0'. The control information for the multiple allocation indicator and the individual DMRS pattern indicator determined in steps 1270 and 1280 is notified to each UE in step 1290 using a Physical Downlink Control Channel (PDCCH). In step 1295, the base station transmits the PDSCH and the individual DMRS pattern (s) transmitted in the same layer for each UE in step 1299 by applying predetermined precoding.

FIG. 14 is a diagram illustrating a process of assigning an individual DMRS pattern included in the aggregated DMRS pattern according to an embodiment of the present invention and performing channel estimation using the allocated DMRS pattern.

Referring to FIG. 14, in step 1300, the UE performs PDCCH detection, which may be transmitted to a UE in a given frequency band and time interval. In step 1300, the UE detects the PDCCH and demodulates and decodes the detected PDCCH. In step 1310, the UE determines whether the PDCCH is for itself or is valid.

If it is determined in step 1310 that the PDCCH is not a PDCCH for itself or is not a valid PDCCH, the MS performs the PDCCH detection mode again in step 1300. [ On the other hand, if it is determined in step 1310 that a valid PDCCH for the UE has been received, the UE determines in step 1320 whether the corresponding PDCCH is a PDCCH notifying scheduling for downlink transmission of the BS. If it is determined that the PDCCH is not a scheduling for downlink transmission in step 1320 and the PDCCH grants uplink transmission, the UE performs a control information related operation in step 1330 and returns to the PDCCH detection mode in step 1300. [

However, if it is determined in step 1320 that the PDCCH is a PDCCH notifying scheduling for downlink transmission, the UE receives control information for receiving the PDSCH as in step 1340. In step 1340, the control information received by the terminal from the base station includes whether or not the terminal receives the reception using the DMRS. Accordingly, if it is determined in step 1350 that the UE is transmitting using the DMRS, if it is determined that the UE does not transmit using the DMRS, the UE performs channel estimation using the CRS in step 1360.

On the other hand, if it is determined that the transmission is performed using the DMRS, the UE is notified of the individual DMRS patterns allocated to the UE through the control information stored in the PDCCH in step 1370. In step 1380, the terminal checks individual DMRS patterns and multiple allocation indicator values.

If the multiple allocation indicator value is '0' instead of '1' in step 1380, the terminal determines that one individual DMRS pattern is allocated to each layer in step 1390, Channel estimation is performed. However, if the multiple allocation indicator value is '1' in step 1380, the terminal performs channel estimation using a plurality of individual DMRS patterns allocated to one layer in step 1395.

In the present invention, the plurality of allocation indicator is control information for indicating how many individual DMRS patterns are allocated to one layer using one or a plurality of bits. In particular, when the number of layers of the signal to be transmitted by the base station is less than the number of individual DMRS patterns of the aggregated DMRS pattern, the multiple allocation indicator may allocate additional DMRS patterns to the specific layer to more accurately perform channel estimation for the layer . If the aggregated DMRS pattern is greater than the number of layers of signals to be transmitted by the base station, the remaining individual DMRS patterns can be used to perform additional data traffic channel signals in addition to more accurate channel estimation. In other words, when transmission is performed using two layers for a specific UE, and four individual DMRS patterns are allocated, the frequency, time, and frequency allocated to two individual DMRS patterns other than the two individual DMRS patterns required for channel estimation, And transmits data traffic channel signals using code resources. For example, when the individual DMRS pattern indicators 0, 1, 2, and 3 are assigned to the UEs receiving signals in two layers in Table 2, the radio resources indicated by the individual DMRS pattern indicators 2 and 3 transmit a data traffic channel signal .

Additional control information is required to notify the UE that the data traffic channel signal is transmitted using the additional DMRS pattern. The control information informs how many of the radio resources allocated to the individual DMRS patterns allocated to the UE are allocated the actual individual DMRS pattern and the data traffic channel signal is transmitted to the remaining ones.

In addition, another method of allocating one or more individual DMRS patterns to one layer is to notify the number of layers of the signal received by the terminal. That is, the base station informs the UE of how many layers to perform channel estimation using the information on the individual DMRS pattern indicator to be allocated to a part of the control information transmitted on the PDCCH and the allocated individual DMRS patterns. The amount of control information transmitted in addition to the method of allocating the individual DMRS pattern to the UE is determined according to the maximum number of layers that can be supported by the corresponding set DMRS pattern. That is, when the maximum number of layers that can be supported by the set DMRS pattern is N, the BS must transmit log ₂ N bits to the MS. The information on the number of layers transmitted to the UE is the number of layers allocated to a specific UE, not the layer number of the signal transmitted by the BS. Therefore, the terminal only receives information on the number of signal layers for itself, and does not know how many layers the base station transmits. Therefore, transparency of MU-MIMO is maintained.

The DMRS allocation method of the present invention is a method for allocating a DMRS resource to one or a plurality of terminals when a base station performs transmission for a maximum of eight layers in an LTE-A system. The base station in which the LTE-A system is implemented can basically perform both the transmission defined in the LTE-A standard and the transmission defined in the LTE standard. As described above, a base station capable of performing both transmission in the LTE standard and the LTE-A standard can use the LTE or LTE-A scheme when performing transmission for a plurality of layers using specific time and frequency resources. When the LTE-A base station uses the LTE scheme, as described in the related art, transmission of a plurality of layers is performed by transmitting information on two transport block sizes to the mobile station. When the LTE-A base station uses the LTE-A scheme, as described in the present invention, transmission of a plurality of layers is performed by allocating individual DMRS patterns within the set DMRS pattern to one or a plurality of terminals.

The LTE-A base station can dynamically use transmission for a plurality of layers using either the LTE scheme or the LTE-A scheme. In addition, according to the determination of the LTE-A base station, related control information is transmitted on the PDCCH to the terminal, thereby informing the terminal whether the corresponding base station performs multiple layer transmission of the LTE scheme or the LTE-A scheme.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. It will be apparent to those skilled in the art that other modifications based on the technical idea of the present invention are possible in addition to the embodiments disclosed herein.

1 is a diagram showing reference signals arranged by a time division multiplexing method according to the related art.

2 is a diagram illustrating reference signals arranged in a frequency / time division multiplexing method according to the related art.

3 is a diagram illustrating a reference signal arrangement according to a conventional code division multiplexing method.

FIG. 4 is a diagram showing reference signals arranged according to a frequency / code / time division multiplexing method according to the related art.

FIG. 5 is a diagram illustrating a set DMRS pattern for a DMRS resource allocation method according to an embodiment of the present invention. Referring to FIG.

[0001] The present invention relates to a method of allocating a DMRS resource, and more particularly, to a method of allocating a DMRS resource, Other drawings.

FIG. 8 shows an example in which a set DMRS pattern is applied to different frequency bands within a whole system bandwidth according to an embodiment of the present invention.

9 is a diagram illustrating an individual DMRS pattern according to an embodiment of the present invention.

10 is a diagram illustrating a base station MIMO transmission for one or a plurality of terminals in different frequency intervals within one system bandwidth according to an embodiment of the present invention.

11 is a diagram illustrating a base station MIMO transmission for one or a plurality of terminals in different frequency intervals within a system bandwidth according to another embodiment of the present invention.

12 is a diagram illustrating the multiple allocation indicator according to an embodiment of the present invention.

FIG. 13 is a diagram illustrating a process of assigning an individual DMRS pattern included in a set DMRS pattern to a UE in a BS according to an embodiment of the present invention.

FIG. 14 is a diagram illustrating a process of assigning an individual DMRS pattern included in the aggregated DMRS pattern according to an embodiment of the present invention and performing channel estimation using the allocated DMRS pattern.

Claims (22)

A method for allocating resources to a reference signal of a base station capable of performing multiple layer transmission in a mobile communication system, Transmitting at least one dedicated reference signal pattern preset for the layer-by-layer channel estimation to a terminal through higher signaling; Determining whether a dedicated reference signal is transmitted according to precoding applied to the UE, And notifying, when transmitting the dedicated reference signal, control information on a dedicated reference signal pattern allocated to a layer transmitted to the terminal, to the terminal. The method of claim 1, wherein the step of notifying the terminal Determining a number of dedicated reference signal patterns to be allocated to the layer; Setting a plurality of allocation indicator values according to the number of the identified dedicated reference signal patterns; Further comprising the step of notifying, by the control information, information on the set multiple allocation indicator value and the dedicated reference signal pattern. The method of claim 2, wherein the step of notifying the terminal Determining a dedicated reference signal pattern and control information to be allocated to each layer to be transmitted to at least one terminal when transmitting the dedicated reference signal; Further comprising the step of determining whether there is a terminal to which at least two dedicated reference signal patterns are allocated in one layer of the at least one terminal. A channel estimation method using a dedicated reference signal in a mobile station configuring a mobile communication system, Determining whether a dedicated reference signal is transmitted through the control information received from the base station, Determining a plurality of allocation indicator values indicating the number of dedicated reference signal patterns allocated to the layer and the dedicated reference signal patterns assigned to the layers, if the transmission is performed using the dedicated reference signal; And performing channel estimation according to the determined dedicated reference signal pattern and the plurality of allocation indications. 5. The method of claim 4, wherein the performing the channel estimation comprises: And performing channel estimation using a dedicated reference signal pattern allocated to one layer according to the multiple allocation indicator. 5. The method of claim 4, wherein the performing the channel estimation comprises: And performing channel estimation using at least two dedicated reference signal patterns allocated to one layer according to the multiple allocation indicator. 5. The apparatus of claim 4, wherein the plurality of allocation indicators 0 or 1, If the value of the multiple allocation indicator is 0, it indicates that one dedicated reference signal pattern is allocated to one layer, and that the value of the multiple allocation indicator is 1, that information indicating that at least two dedicated reference signal patterns are allocated to one layer Channel estimation method. 5. The method of claim 4, Further comprising the step of informing that a plurality of dedicated reference signal patterns are allocated by notifying a plurality of layers of the traffic channel in addition to the plurality of allocation indicators while allocating the individual reference signal patterns. 5. The method of claim 4, Further comprising the step of the base station allocating a different aggregate reference signal pattern to a plurality of subbands and notifying the terminal of the aggregated reference signal pattern with higher signaling. 5. The method of claim 4, Further comprising the step of the base station allocating a different aggregate reference signal pattern to a plurality of subbands for each mobile station and informing each mobile station of the aggregated reference signal pattern by higher signaling. 5. The method of claim 4, Wherein the base station further includes the step of implementing a dedicated dedicated reference signal pattern allocation table for allocating a dedicated reference signal resource so that a Walsh code resource is maximally used for a dedicated dedicated reference signal pattern to which Walsh code resources are connected. A base station capable of transmitting a plurality of layers in a mobile communication system, A transmitting and receiving unit for transmitting and receiving signals to and from the terminal; And And at least one dedicated reference signal pattern preset for the layer-by-layer channel estimation to be transmitted to the terminal through higher signaling, Determines whether to transmit a dedicated reference signal according to precoding applied to the UE, And a control unit for controlling the terminal to transmit control information related to a dedicated reference signal pattern allocated to a layer transmitted to the terminal when transmitting the dedicated reference signal. 13. The apparatus according to claim 12, The number of dedicated reference signal patterns allocated to the layer is checked, A plurality of allocation indicator values are set according to the number of the dedicated reference signal patterns, Wherein the control information includes information on the set allocation indicator value and the dedicated reference signal pattern included in the control information. 14. The apparatus of claim 13, Determining a dedicated reference signal pattern and control information to be allocated to each layer to be transmitted to at least one terminal when transmitting the dedicated reference signal, Wherein the base station determines whether a terminal having at least two dedicated reference signal patterns is present in one layer of the at least one terminal. In a terminal constituting a mobile communication system, A transmission / reception unit for transmitting / receiving signals to / from a base station; And Determines whether or not the transmission is performed using the dedicated reference signal through the control information received from the base station, A plurality of allocation indicator values indicating a number of dedicated reference signal patterns assigned to the layer and a number of dedicated reference signal patterns allocated to the layers, And a controller for performing channel estimation according to the determined dedicated reference signal pattern and a plurality of allocation indications. 16. The apparatus of claim 15, And performs channel estimation using one dedicated reference signal pattern allocated to one layer according to the multiple allocation indicator. 16. The apparatus of claim 15, And performs channel estimation using at least two dedicated reference signal patterns allocated to one layer according to the multiple allocation indicator. 16. The apparatus of claim 15, wherein the plurality of allocation indicators are divided into 0 or 1, If the value of the multiple allocation indicator is 0, it indicates that one dedicated reference signal pattern is allocated to one layer, and that the value of the multiple allocation indicator is 1, that information indicating that at least two dedicated reference signal patterns are allocated to one layer .  16. The apparatus of claim 15, And notifies a plurality of layers of the traffic channel in addition to the plurality of allocation directors while allocating the individual reference signal patterns, and notifies that a plurality of dedicated reference signal patterns are allocated. 16. The apparatus of claim 15, Wherein the base station allocates a different aggregate reference signal pattern to a plurality of subbands and notifies the terminal of the aggregated reference signal pattern by higher signaling. 16. The apparatus of claim 15, Wherein the base station assigns a different aggregate reference signal pattern to a plurality of subbands for each terminal and notifies each terminal of the aggregated reference signal pattern by upper signaling. 16. The method of claim 15, Wherein the base station implements an individual dedicated reference signal pattern allocation table for allocating a dedicated reference signal resource so that the Walsh code resource is maximally used for a dedicated dedicated reference signal pattern to which Walsh code resources are connected.

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