KR20150111154A - Method and Apparatus of controlling a remote radio head in a wireless communication system - Google Patents

Abstract

According to an embodiment of the present invention, a method for controlling a remote radio head (RRH) having multiple antenna ports includes the steps of: transmitting a first reference signal through a first port among the antenna ports; transmitting a second reference signal through a second port among the antenna ports; receiving a measurement value of a terminal regarding at least one among the first and second reference signals; and transmitting the same downlink sub-frame, which is transmitted through one among the first and second ports, to another port based on the value of the terminal received in the previous step.

Description

[0001] The present invention relates to a method and apparatus for controlling a remote radio head (RRH) in a wireless communication system,

The present invention relates to a method and apparatus for controlling the operation of an RRH (Remote Radio Head) having a plurality of antenna ports in a wireless communication system.

Due to the widespread use of portable devices such as smart phones, the amount of wireless data has increased dramatically, which has led to the need to upgrade the mobile communication network, which has been optimized mainly for voice services, around data services. In the process of reconfiguring the wireless network, an additional base station (base station) is required, which requires a great deal of resources. The remote radio head (RRH) is one of the ways to provide data high-speed wireless data services while minimizing the cost of upgrading the communication network. By installing the RRH instead of adding a base station, the shadow area can be eliminated.

For example, an RRH may be used to provide mobile communication services within a shielded building. Although RRH may have a single antenna port, it is common for recent RRHs to have multiple antenna ports. Each antenna port of the RRH may be configured to cover different floors, for example, in a 2-port RRH, the first port may be configured to cover the higher layer and the second port to cover the lower layer.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide an RRH control method capable of acquiring synchronization with a changed antenna port without disconnection of communication even when the terminal is located in coverage of an antenna port of an RRH connected to the terminal, And to provide such a device.

The technical problem of the present invention is not limited to this, and other technical problems can be deduced from the embodiments of the present invention.

A method of controlling a remote radio head (RRH) having a plurality of antenna ports in a wireless communication system according to an embodiment of the present invention includes receiving a first reference signal through a first one of the plurality of antenna ports, ; Transmitting a second reference signal through a second one of the plurality of antenna ports; Receiving a measured value of a terminal for at least one of the first reference signal and the second reference signal; And transmitting the downlink subframe transmitted through one of the first port and the second port equally to another port according to the measurement value of the received terminal.

Preferably, the first reference signal and the second reference signal may be cell-specific signals having the same sequence and mapped to different physical resources.

The step of transmitting the downlink sub-frame may further include copying the downlink sub-frame transmitted through the one port and inputting the downlink sub-frame to the other port, It is possible to transmit the downlink subframe in parallel.

When the measured value of the second reference signal is less than the threshold value or the measured value of the second reference signal is not received, the one port is determined to be the first port and the other port is determined to be the second Lt; / RTI > port.

When the measured value of the second reference signal is less than the threshold value or the measured value of the second reference signal is not received, the one port is determined to be the first port and the other port is determined to be the second Lt; / RTI > port.

In addition, SFBC (Space Frequency Block Coding) for providing diversity for transmission of the first port to the MS is set in the second port, and transmitting the downlink sub-frame is performed in the second port, It can cancel the diversity due to the SFBC setting and transmit the downlink subframe.

The transmitting the downlink subframe may include: obtaining downlink data SFBC coded according to the SFBC setting of the second port; Performing SFBC coding on the SFBC coded downlink data again before erasing the diversity before inputting the SFBC coded downlink data to the second port; And inputting the downlink data in which the diversity is canceled to the second port.

The step of transmitting the downlink sub-frame may further comprise the steps of: if the measurement value of the second reference signal is less than the threshold value or the measured value of the second reference signal is not received, To the input terminal of the switch SW2.

The transmitting of the downlink Surf frame may further include: selecting either the first reference signal or the second reference signal based on the received measurement value; And transmitting the selected reference signal simultaneously through the first port and the second port.

In addition, the measurement value may include at least one of a channel quality indicator (CQI), a rank indicator (RI), and a reference signal received power (RSRP).

The method of claim 1, further comprising determining whether the terminal can switch synchronization from any one port to the other, wherein the step of transmitting the downlink sub- If it is determined that the synchronization can not be switched, the DL subframe transmitted through one port can be transmitted to the other port equally.

There is provided a computer-readable recording medium storing a program for executing the above-described method according to another embodiment of the present invention.

In an apparatus for controlling a remote radio head (RRH) having a plurality of antenna ports in a wireless communication system according to another exemplary embodiment of the present invention, a first reference signal a transmission module for transmitting a second reference signal through a second one of the plurality of antenna ports; A receiving module for receiving a measured value of a terminal for at least one of the first reference signal and the second reference signal; And a controller for controlling the transmitting module to transmit the downlink subframe transmitted through any one of the first port and the second port equally to another port according to the measured value of the received terminal, .

A method of controlling a remote radio head (RRH) having a plurality of antenna ports in a wireless communication system according to another exemplary embodiment of the present invention includes receiving an RRH having a plurality of antenna ports through a Multi-Input-Multi-Output ) Mode or a transmission diversity mode; Setting the RRH to a Transmission Copy mode when a rate of call drop of terminals connected through the RRH exceeds a threshold value; And copying downlink subframes input to any one of the plurality of antenna ports and inputting the copied downlink subframe to another port.

Preferably, a first port and a second port of the plurality of antenna ports correspond to a first coverage, a third port and a fourth port correspond to a second coverage, and the downlink sub-frame is copied and input May copy the first downlink sub-frame of the first port and input it to the third port, and copy the second downlink sub-frame of the second port to the fourth port.

In addition, the first downlink subframe and the second downlink subframe may be set to be spatial-multiplexed with each other or may be set to have mutual transmit diversity gain.

In an apparatus for controlling a remote radio head (RRH) having a plurality of antenna ports in a wireless communication system according to another embodiment of the present invention, an RRH having the plurality of antenna ports is called a Multi-Input-Multi-Output Mode or a transmission diversity mode, and when the ratio of call drops of terminals connected through the RRH in the MIMO mode or the transmit diversity mode exceeds a threshold value, the RRH is set to A processor for setting a transmission copy mode; And a transmission module for copying downlink subframes input to any one of the plurality of antenna ports under the control of the processor and inputting the copied subframe to the other port.

According to the embodiment of the present invention, the RRH control mode suitable for the in-building can be set to reduce the investment cost of the in-building, and the terminal can acquire the synchronization for the antenna port changed without communication disconnection. Further, Input Multi Output can be used to expand the coverage area.

The effects of the present invention are not limited thereto and other effects can be deduced from the embodiments of the present invention.

1 is a diagram schematically illustrating an E-UMTS network structure as an example of a mobile communication system.
2 is a diagram showing a structure of a downlink sub-frame.
FIG. 3 is a diagram illustrating an in-building environment to which an RRH control method and apparatus according to the present invention can be applied.
4 is a diagram showing a CRS pattern when there are two antenna ports of the RRH.
FIG. 5 is a diagram illustrating an in-building environment to which the RRH control method and apparatus according to the present invention is applied.
6 is a diagram illustrating a base station and an RRH according to an embodiment of the present invention.
7 is a diagram illustrating a base station and an RRH according to another embodiment of the present invention.
8 is a diagram illustrating a method of inputting the same data to the first port and the second port of the RRH according to an embodiment of the present invention.
9 is a flowchart illustrating an RRH control method according to an embodiment of the present invention.
10 is a flowchart illustrating an RRH control method according to another embodiment of the present invention.
11 is a diagram illustrating a base station, an RRH, and a UE according to another embodiment of the present invention.
12 is a diagram illustrating a downlink subframe according to an embodiment of the present invention.
13 is a diagram illustrating an RRH according to an embodiment of the present invention.
14 is a diagram illustrating an RRH according to another embodiment of the present invention.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following detailed description, together with the accompanying drawings, is intended to illustrate exemplary embodiments of the invention and is not intended to represent the only embodiments in which the invention may be practiced. The following detailed description includes specific details in order to provide a thorough understanding of the present invention. However, those skilled in the art will appreciate that the present invention may be practiced without these specific details. For example, the following detailed description assumes that a mobile communication system is a 3GPP LTE and an LTE-A system. However, other than specific aspects of 3GPP LTE and LTE-A, Applicable.

In some instances, well-known structures and devices may be omitted or may be shown in block diagram form, centering on the core functionality of each structure and device, to avoid obscuring the concepts of the present invention. In the following description, the same components are denoted by the same reference numerals throughout the specification.

In the following description, it is assumed that the UE collectively refers to a mobile stationary or stationary user equipment such as a UE (User Equipment), an MS (Mobile Station), an AMS (Advanced Mobile Station), and an M2M (Machine To Machine) It is also assumed that the base station collectively refers to any node at a network end that communicates with a terminal such as a Node B, an eNode B, a base station, and an access point (AP). In this specification, a base station can be used as a concept including a cell, a sector, and the like.

In a mobile communication system, a user equipment can receive information through a downlink from a base station, and the terminal can also transmit information through an uplink. The information transmitted or received by the terminal includes data and various control information, and various physical channels exist depending on the type of information transmitted or received by the terminal.

The following description is to be understood as illustrative and non-limiting, such as code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access And can be used in various wireless access systems. CDMA may be implemented in radio technology such as Universal Terrestrial Radio Access (UTRA) or CDMA2000. The TDMA may be implemented in a wireless technology such as Global System for Mobile communications (GSM) / General Packet Radio Service (GPRS) / Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may be implemented in wireless technologies such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, and Evolved UTRA (E-UTRA). UTRA is part of the Universal Mobile Telecommunications System (UMTS). 3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution) is part of E-UMTS (Evolved UMTS) using E-UTRA, adopts OFDMA in downlink and SC-FDMA in uplink. LTE-A (Advanced) is an evolved version of 3GPP LTE.

For clarity of description, 3GPP LTE / LTE-A is mainly described, but the technical idea of the present invention is not limited thereto. In addition, the specific terms used in the following description are provided to aid understanding of the present invention, and the use of such specific terms may be changed into other forms without departing from the technical idea of the present invention.

1 is a diagram schematically illustrating an E-UMTS network structure as an example of a mobile communication system. The Evolved Universal Mobile Telecommunications System (E-UMTS) system evolved from the existing UMTS (Universal Mobile Telecommunications System). In general, E-UMTS may be referred to as an LTE (Long Term Evolution) system.

The E-UMTS includes an access gateway (AG) located at the end of a user equipment (UE), a base station (eNode B, eNB) and a network (E-UTRAN) and connected to an external network. The base station may simultaneously transmit multiple data streams for broadcast services, multicast services, and / or unicast services. Although not shown in FIG. 1, RRH may be used to extend the coverage of the base station. The RRH may be implemented as part of a base station or as a separate device from a base station.

There is one or more cells in one base station. The cell may be set to one of the bandwidths of 1.25, 2.5, 5, 10, 15, 20 MHz and the like. Different cells may be set up to provide different bandwidths. The base station controls data transmission / reception for a plurality of terminals. The base station transmits downlink scheduling information for downlink (DL) data, and transmits the downlink scheduling information to the corresponding terminal in a time / frequency region, a coding, a data size, a Hybrid Automatic Repeat reQuest (HARQ) Information. Also, the base station transmits uplink scheduling information to the corresponding uplink (UL) data, and transmits the uplink scheduling information to the corresponding terminal in a time / frequency region, coding, data size, hybrid automatic retransmission request related information, (Transmisson Power Control, TPC).

2 is a diagram showing a structure of a downlink sub-frame. In a subframe, a maximum of three OFDM symbols in the first part of the first slot corresponds to a control area to which a control channel is allocated. The remaining OFDM symbols correspond to a data area to which a Physical Downlink Shared Chanel (PDSCH) is allocated.

The downlink control channels used in the 3GPP LTE system include, for example, a physical control format indicator channel (PCFICH), a physical downlink control channel (PDCCH), a physical HARQ indicator channel (Physical Hybrid Automatic Repeat Request Indicator Channel (PHICH)). The PCFICH includes information on the number of OFDM symbols transmitted in the first OFDM symbol of the subframe and used for control channel transmission in the subframe. The PHICH includes an HARQ ACK / NACK signal as a response to the uplink transmission.

The control information transmitted through the PDCCH is referred to as downlink control information (DCI). The DCI includes uplink or downlink scheduling information or includes an uplink transmission power control command for an arbitrary terminal group. The PDCCH includes a resource allocation and transmission format of a downlink shared channel (DL-SCH), resource allocation information of an uplink shared channel (UL-SCH), paging information of a paging channel (PCH), system information on a DL- A set of transmission power control commands for individual terminals in an arbitrary terminal group, transmission power control information, activation of VoIP (Voice over IP), resource allocation of upper layer control messages such as random access response And the like.

FIG. 3 is a diagram illustrating an in-building environment to which an RRH control method and apparatus according to the present invention can be applied. 3 shows a case where one RRH 10 is connected to the base station 20 and FIG. 3 (b) shows a case where two RRHs 40 and 50 are connected to the base station 60 Respectively. Each of the RRHs 10, 40, and 50 has two antenna ports, and the antennas installed in the buildings are connected to the antenna ports of the RRHs 10, 40, and 50 to provide mobile communication services in the building. The number of RRHs and the number of antenna ports of each RRH in the illustrated embodiment may be changed according to the embodiment.

3A, the antennas embedded in the high-level portion 110 are connected to the first port of the RRH 10, and the antennas embedded in the low-level portion 120 are connected to the second port of the RRH 10 . At this time, the synchronization of the first port and the second port may be different from each other, and the synchronization for each port can be obtained through the transmitted reference signal.

The downlink reference signal includes a cell-specific reference signal (CRS), a demodulation regenerance signal (DMRS), a channel state information reference signal (CSI-RS), and the like. The downlink reference signal is different in the transmission frequency and the position mapped in the downlink subframe according to its type.

The UE-specific reference signal, DMRS, is used for data demodulation and the CRS is used for both channel information acquisition and data demodulation. This CRS is a cell-specific reference signal, and the base station transmits a CRS every sub-frame over a wide band. In a cell-specific CRS, reference signals for up to four antenna ports are transmitted according to the number of transmission antennas of a base station. For example, if there are two antenna ports of the RRH, the CRS for the antenna ports 0 and 1 is transmitted, and if there are four antennas, the CRS for the antenna ports 0 to 3 are respectively transmitted.

4 is a diagram showing a CRS pattern when there are two antenna ports of the RRH. As shown in FIG. 4, CRS (R0, R1) for two antenna ports are allocated so that time-frequency resources are not overlapped in 1RB (resouce block).

The CSI-RS is characterized in that the existing CRS is designed for the purpose of channel measurement, unlike that used for data demodulation in addition to the purpose of measurement such as channel measurement, handover, and the like. Of course, the CSI-RS can also be used for measurement purposes such as handover. Unlike the CRS, the CSI-RS is not transmitted every subframe since it is transmitted only for the purpose of obtaining information on the channel state. Therefore, in order to reduce the overhead due to the CSI-RS transmission, the BS intermittently transmits the CSI-RS on the time axis and a DM-RS dedicated to the scheduled UE in the corresponding time- send. That is, the DM-RS of a specific terminal is transmitted only in a time-frequency domain in which the terminal can receive the scheduled domain, i.e., data.

In order for the UE to measure the reference signal, it is necessary for the UE to know the time-frequency position, the reference signal sequence, the reference signal frequency shift, and the like of the reference signal for each antenna port of the cell to which the UE belongs. The UE feeds back channel information such as CQI, PMI, and Rank of each band to the base station using the received reference signal, and the base station performs a scheduling operation using the feedback channel information.

Referring back to FIG. 3 (a), when the synchronization between the first port and the second port is different, the reference signal transmitted from the first port and the reference signal transmitted from the second port are set to be different from each other . If the terminal 30 is located in the high-level section 110, it can transmit / receive data to / from the base station 20 by acquiring synchronization with the first port through the reference signal transmitted from the first port. When the terminal moves to the lower layer 120, the terminal 30 acquires synchronization again with respect to the second port through the reference signal transmitted from the second port, and transmits the synchronization signal to the base station 20, And data can be transmitted and received. The handover procedure is different from the handover procedure because the serving base station 20 or the RRH 10 is not changed.

On the other hand, some terminals synchronized only with the first port of the RRH 10 can not acquire synchronization with the second port even when they are moving. The terminal 30 determines that the second port does not exist at the time of acquiring the synchronization for the first port and because the terminal 30 does not detect the reference signal of the second port even when it is located in the coverage 120 of the second port And does not acquire synchronization with the second port. The handover in the strict sense is not triggered when moving from the first port to the second port. As a result, the terminal 30 may have a problem that the communication is disconnected in the coverage of the second port.

In order to solve this problem, a scheme of using two RRHs 40 and 50 as shown in FIG. 3 (b) can be considered. The first port of the RRH 40 is connected to the antenna of the upper layer 410 and the first port of the RRH 50 is connected to the antenna of the lower layer 510. The second port of the RRH 40 and the second port of the RRH 50 are terminated and are not connected to the antenna.

Each of the RRHs 40 and 50 operates in a SIMO (Single Input Multi Output) mode. That is, the second port is terminated and only the first port is activated, so that it operates in the SIMO mode. Also, the first ports of the RRHs 40 and 50 are synchronous and transmit the same signal. That is, the terminal 70 recognizes that the first port of the RRH 40 and the first port of the RRH 50 are the same antenna port. Therefore, even if the terminal 70 moves from the high-level portion 410 to the low-level portion 510, there is no problem that the communication is disconnected.

However, by using only one of the two ports of the RRH, the use efficiency of the RRH is lowered. There is a problem in that the investment cost is higher than when both ports are used.

FIG. 5 is a diagram illustrating an in-building environment to which the RRH control method and apparatus according to the present invention is applied. FIG. 5 is a diagram illustrating a case where an RRH control method and apparatus according to the present invention is applied to solve the above problems. The RRH control method is performed by improving a digital unit corresponding to software of a base station, Or by updating the firmware.

Comparing FIG. 5 with FIG. 3A, although one RRH 10 is provided in FIG. 3A, the synchronization of the first port and the second port of the RRH 10 is different from each other, And the second port can output different signals, respectively. In Fig. 5, one RRH is provided, but the first port and the second port of the RRH have the same synchronization and output the same signal. In other words, one signal identical to the entire building is transmitted in the RRH as shown in FIG. 3 (b), but unlike FIG. 3 (b), only one RRH is used in FIG.

As shown in FIG. 5, the first port and the second port have the same synchronization, which means that the reference signal transmitted through the first port and the reference signal transmitted through the second port have the same physical resource mapping. That is, as shown in FIG. 5, the reference signal R0 transmitted from the first port is transmitted equally to the second port. Therefore, it can be understood that the second port enlarges the coverage of the first port.

In the following embodiments, the meaning that the first port and the second port output the same signal is not necessarily limited to outputting the same signal to all the terminals. For example, FIG. 12 illustrates a downlink sub-frame transmitted from a first port (port # 0) and a second port (port # 1). The data shaded is the data of the first terminal, and the data displayed in black is the data of the second terminal. The first port and the second port of the RRH output the same signals for the first terminal but output different signals for the second terminal. Accordingly, the first terminal receives the same signal at the first port and the second terminal, while the second terminal receives the different signal at the first port and the second port, and the second terminal operates as MIMO, City gain can be obtained.

On the contrary, when the entire downlink subframe of the first port is copied and transmitted to the second port, it can be understood that the first port and the second port output the same signal to all the terminals.

In the embodiments of the present invention, it is defined as a transmission copy mode (Tx copy mode) that signals of the first port and the second port of the RRH are output equally to each terminal or all terminals. Hereinafter, exemplary embodiments of the transmission replication mode will be described.

6 is a diagram illustrating a base station and an RRH according to an embodiment of the present invention. The illustration of the general components is omitted in order to prevent the problem of the description in FIG. 6 from being blurred.

Referring to FIG. 6, a base station inputs IQ data corresponding to a downlink sub-frame for each RRH port. The RRH converts the IQ data received from the base station into an RF signal and outputs it to each port. The base station of FIG. 6 transmits an IQ Copy Control Block (hereinafter referred to as 'IQ CCB') to operate in a transmission replication mode. The IQ CCB may be implemented with a new hardware configuration, but may be implemented with a software configuration added to the program code that controls the base station. When the IQ CCB is implemented in a software configuration, the actual execution of the IQ CCB is handled by a processor (not shown) and a transmitting module (not shown) of the base station.

IQ CCB does not operate in MIMO, SIMO, Tx diversity mode, but only in transmit replication mode. In the IQ CCB mode, the IQ data of the first port is copied and input to the second port, or conversely, the IQ data of the second port is copied and input to the first port.

Therefore, the same IQ data are simultaneously and parallelly input to the first port and the second port. The RRH outputs IQ data input to the first port and the second port, respectively, as RF signals. The output RF signal of the first port and the RF signal of the second port are equal to each other. According to the present embodiment, since the operation of the RRH in the transmission / duplication mode is the same as that of the MIMO, SIMO, and Tx diversity modes, it is not necessary to modify the RRH hardware or software.

7 is a diagram illustrating a base station and an RRH according to another embodiment of the present invention. The description overlapping with the above-described embodiment is omitted.

The RRH in Fig. 7 includes a switch. If it is not in the transmit replication mode, the switch shorts node A-B and shorts node C-D. In transmit cloning mode, the switch opens node A-B and shorts nodes A-C-D, or opens node C-D and shorts node C-A-B. In other words, the switch inputs the IQ data of the first port to the second port or inputs the IQ data of the second port to the first port.

The base station controls the switch through a 2-bit signal. That is, a state in which the IQ data of the first port is input to the second port in the transmission replication mode, a state in which the IQ data (complex transmission symbol) of the second port is input to the second port in the transmission replication mode, State The switch is controlled through a 2-bit signal representing three states.

According to another embodiment, the switch control signal may indicate ON / OFF of the transmission duplication mode by 1-bit. In this case, the IQ data of the first port is always input to the second port in the transmission replication mode.

On the other hand, a repeater may be included in the RF output terminal of the RRH in place of the switch at the IQ data input terminal of the RRH, and the repeater can be controlled in a manner similar to the above-described switch.

8 is a diagram illustrating a method of inputting the same data to the first port and the second port of the RRH according to an embodiment of the present invention. For transmit diversity mode in multi-antenna transmission, SFBC (Spatial Frequency Block Coding) or SFBC / FSTD (Frequency Shift Transmit Diversity) combining is used. SFBC is used for transmit diversity for two antenna ports, and SFBC / FSTD is used for transmit diversity for four antenna ports. Hereinafter, the case of two antenna ports will be described, but those skilled in the art can understand the operation of the present invention in the case of four antenna ports from the following description.

Referring to FIG. 8 (a), when SFBC is coded, the symbols Si and Si + 1 are mapped as they are in the first port, but in the second port, the order is reversed in the frequency domain. - ^* Si + 1 and ^* Si.

FIG. 8 (b) shows a method of SFBC coding the SFBC coded symbol again to obtain the symbol before the first SFBC coding. In an environment in which the transmission diversity mode is set in advance, a scheme for performing SFBC coding again may be considered as a method for switching to the transmission replication mode, as shown in Fig. 8 (b).

For example, when SFBC (Space Frequency Block Coding) for providing diversity for transmission of the first port is set to the second port, the base station cancels the diversity by the SFBC setting in the second port, Frame. More specifically, the base station obtains SFBC coded symbols according to the SFBC setting of the second port. The base station again SFBC-codes the SFBC coded downlink data before inputting the SFBC coded transmission symbols to the second port of the RRH, thereby canceling the diversity. The base station inputs the original symbol whose diversity is canceled to the second port of the RRH. Through this, the same symbols can be simultaneously input to the first port and the second port of the RRH in parallel.

On the other hand, the SFBC unit may be placed in the RRH, and the second SFBC coding may be performed by the RRH. At this time, the base station can output to the RRH a control signal for turning on / off the SFBC unit of the RRH.

9 is a flowchart illustrating an RRH control method according to an embodiment of the present invention. The RRH control method is performed in the RRH control device, and the RRH control device can be included in the base station or the RRH. The description overlapping with the above embodiments is omitted.

Referring to FIG. 9, the base station first controls the RRH to transmit a first reference signal through a first port, and transmits a second reference signal through a second port (910). Here, the reference signal may be the CRS described above. The first reference signal and the second reference signal may be generated to have the same sequence.

는 수학식 1에 따라서 생성될 수 있다.Sequence of CRS

Can be generated according to Equation (1).

는 프레임에서 슬롯 넘버를 의미하고,

은 해당 슬롯에서 OFDM 심볼 넘버를 의미하고,

는 의사-랜덤 시퀀스(pseudo-random sequence)를 의미한다. 한편, 하나의 프레임은 10개의 서브프레임을 갖고, 하나의 서브프레임은 2개의 슬롯을 포함할 수 있다.here,

Denotes a slot number in a frame,

Denotes an OFDM symbol number in the corresponding slot,

Quot; means a pseudo-random sequence. On the other hand, one frame may have ten subframes, and one subframe may include two slots.

Since the pseudo-random sequence is generated based on the cell ID and the first port and the second port are connected to the same base station cell, the first CRS and the second CRS transmitted from the first port and the second port are in the same sequence . The physical resource areas to which the first CRS and the second CRS are mapped are different from each other, and a description thereof will be described with reference to FIG.

The base station receives the measurement value of the terminal for transmission of the first reference signal and the second reference signal through the RRH (915). For example, the base station receives the channel status report of the terminal. The measured value of the received terminal may include at least one of a Channel Quality Indicator (CQI), a Rank Indicator (RI), a Precoding Matrix Indicator (PMI), and a Reference Signal Received Power (RSRP). If the terminal receives both the first reference signal and the second reference signal, the terminal transmits both the measurement value for the first reference signal and the measurement value for the second reference signal. On the other hand, if only one reference signal is received, the UE does not know the existence of the other reference signal, so the measurement value for the other reference signal is not reported.

The base station determines whether the measured value of the received reference signal satisfies a threshold value (920). For example, when the RI indicates 2 layers, the RI threshold value for operating in the MIMO / Tx diversity mode is satisfied. In the case of representing the RI 1 layer, it operates only in either the SIMO mode or the Tx copy mode. If the base station considers the CQI and / or the RSRP, the RI may indicate 2 layers, but if the CQI / RSRP for any one antenna port is less than the predetermined threshold, the MIMO / Tx diversity mode may be replaced by the SIMO mode or the Tx copy mode . In other words, if the CQI / RSRP is less than the predetermined threshold, it is determined that it can not operate in the MIMO / Tx diversity mode.

The base station sets a MIMO / Tx diversity mode (935) if it is determined that the measurement value satisfies the threshold for the MIMO / Tx diversity mode operation. For example, in FIG. 13, the base station can set the MIMO / Tx diversity mode for downlink transmission to the UE 3. FIG. That is, if the UE transmitting the measured value of the reference signal is UE 3, the Node B controls the RRH to transmit in the MIMO / Tx diversity mode to the UE 3. However, the MIMO / Tx diversity mode is set for the UE 3, and the MIMO / Tx diversity mode is not set for the UE 1 or the UE 2.

If it is determined that the measurement value does not satisfy the threshold for the MIMO / Tx diversity mode operation, the base station determines whether the terminal that transmitted the measurement value for the reference signal can perform synchronization switching between the RRH antenna ports 925). As described above, in some terminals, even if the synchronization between the RRH antenna ports is different, communication can be performed at any port, but communication may be disconnected at some other terminals. Since it depends on the type of the terminal, the operator can determine whether or not the terminal is of the type in which the communication is disconnected through the information on the terminal, for example, the model name and the identification information.

Referring to FIG. 13, UE 1 is located in the coverage 1320 of the first port. It is assumed that UE 1 can not detect the second reference signal transmitted from the second port but transmits only the measured value for the first reference signal. The base station determines whether the UE 1 is capable of switching between the synchronization of the first port and the synchronization of the second port. Similarly, the base station can determine whether the UE 2 is capable of switching between the synchronization of the first port and the synchronization of the second port.

If the base station determines that the terminal is capable of switching the synchronization, the SIMO mode is set (940). For example, in FIG. 13, if it is determined that UE 1 is a terminal capable of switching synchronization, the base station sets the SIMO mode for UE 1. When the SIMO mode is set, downlink data for UE 1 is transmitted at the first port but downlink data for UE 1 is not transmitted at the second port. That is, the second port is terminated for UE 1. If UE 1 moves to coverage 1310 of the second port, UE 1 acquires synchronization for the second port. Thereafter, downlink data for UE 1 is not transmitted at the first port but downlink data for UE 1 is transmitted at the second port. If the UE 1 is located in the area where the coverage 1320 of the first port and the coverage 1310 of the second port are overlapped, the base station can set the MIMO or Tx diversity mode for the UE 1.

Returning to FIG. 9, if it is determined that the UE can not switch the synchronization between the RRH antenna ports, the base station sets the Tx Copy mode (930). For example, if it is determined in FIG. 13 that the UE 2 can not switch the synchronization between the RRH antenna ports, the base station sets the Tx Copy mode for the UE 2. The downlink data for the UE 2 transmitted through the second port is transmitted through the first port. In other words, the first port and the second port of the RRH simultaneously transmit the downlink data of the same UE 2 in parallel. Therefore, UE 2 can not differentiate between the second port and the first port of RRH, and even if UE 2 moves to coverage 1320 of the first port, it does not need to acquire synchronization again with respect to the first port. Operations of the base station and the RRH in the Tx copy mode are described with reference to FIGS. 5 to 8 described above.

In the above description, MIMO, Tx diversity, SIMO, and Tx copy mode are set for each terminal, but the present invention is not limited thereto. For example, if priority is given to the operation of MIMO, Tx diversity, SIMO, and Tx copy mode, and if any terminal requires operation of Tx copy mode, Tx Copy mode may be set for all terminals.

10 is a flowchart illustrating a method of controlling an RRH according to another embodiment of the present invention. The description of the foregoing embodiments can be referred to in order to understand the present embodiment.

Referring to FIG. 10, the base station sets RRH to MIMO or Tx diversity mode (1010). A plurality of RRHs can be connected to the base station, and the base station monitors each RRH.

Through the monitoring, the base station determines whether the rate of a call drop of a specific RRH exceeds a threshold value (1015). The threshold for the call drop rate of the RRH may be preset in the base station. If there are terminals in the specific RRH that can not be synchronized between the antenna ports of the RRH, the call drop rate of the specific RRH can be measured to be higher than the call drop rate of the other RRHs. The mobile communication system operator can preset a threshold value of the call drop rate for the RRH to the base station in order to detect the RRH.

If the call drop rate of a particular RRH exceeds the threshold, the base station sets a particular RRH to Tx copy mode (1020). When the Tx copy mode is set, the base station copies the downlink subframe input to a predetermined port of the RRH and inputs the copied subframe to another port (1025).

For convenience of description, the case where the antenna port of the RRH is two has been exemplified, but the present invention is not limited thereto. For example, the RRH may have four or eight antenna ports. For example, FIG. 14 shows an RRH with four antenna ports (# 0, # 1, # 2, # 3). In this embodiment, the first port (# 0) and the second port (# 1) have the first coverage 1410, and the third port (# 2) It is assumed that port # 3 has a second coverage 1420.

The first port (# 0) and the second port (# 1) sharing the same first coverage 1410 operate in spatial multiplexing based MIMO within the first coverage 1410, And may be set to have diversity. Likewise, the third port (# 2) and the fourth port (# 3) may also be configured to operate with MIMO or have transmit diversity.

When the Tx copy mode is set, the base station copies the first downlink subframe of the first port of the RRH and inputs it to the third port, and copies the second downlink subframe of the second port to the fourth port . At this time, the first downlink subframe and the second downlink subframe may be set to be spatial-multiplexed with each other or may be set to have mutual transmit diversity gain.

Therefore, in the case where the number of antenna ports of the RRH is four or more, a MIMO or Tx diversity operation can be performed in the first coverage 1410 or the second coverage 1420, even if the Tx copy mode is set. It will be understood by those skilled in the art that SIMO operation is also possible since MIMO or Tx diversity operation is possible.

11 is a diagram illustrating a base station, an RRH, and a UE according to another embodiment of the present invention. The description of the above embodiments can be applied to the base station, the RRH and the terminal in Fig.

15, a base station 1410 includes a receiver 1411, a transmitter 1412, a processor 1413, and a memory 1414. [ The base station 1410 is coupled to an RRH 1415 having a plurality of antenna ports. The receiver 1411 can receive various signals, data and information on the uplink from the terminal. The transmitter 1412 can transmit various signals, data, and information on the downlink to the terminal. The processor 1413 may control the operation of the entire base station 1410. The processor 1413 of the base station 1410 further functions to process information received by the base station 1410 and information to be transmitted to the outside and the memory 1414 stores the processed information and the like for a predetermined time And may be replaced by a component such as a buffer (not shown).

Transmission module 1412 transmits a first reference signal through a first one of a plurality of antenna ports of RRH 1415 and transmits a second reference signal through a second port. The receiving module 1411 also receives the measured values of the terminal 1420 for at least one of the first reference signal and the second reference signal.

The processor 1413 transmits the downlink subframe transmitted through one of the first port and the second port of the RRH to the other port in accordance with the measured value of the received terminal 1420 Module 1412. < / RTI >

If the measured value of the second reference signal is less than the threshold value or the measured value of the second reference signal is not received, the processor 1413 determines which one port is the first port and the other port is the second Can be determined as a port.

In an embodiment in which Space Frequency Block Coding (SFBC) for providing diversity for transmission of the first port is set to the second port, the processor 1413 sets diversity according to the SFBC setting in the second port And transmit the downlink sub-frame. For example, the processor 1413 obtains the SFBC-coded downlink data according to the SFBC setting of the second port, and before the SFBC-coded downlink data is input to the second port, the processor 1413 performs the SFBC- To cancel the diversity, and to input the downlink data whose diversity is canceled to the second port.

In another embodiment, the processor 1413 may be configured such that the input of the second port of the RRH is coupled to the input of the first port when the measured value of the second reference signal is below the threshold or when the measured value of the second reference signal is not received .

The processor 1413 can control to select either the first reference signal or the second reference signal based on the received measurement value and simultaneously transmit the selected reference signal through the first port and the second port.

The processor 1413 determines whether or not the terminal can switch synchronization from any port to the other port and if it is determined that the terminal can not switch the synchronization, The same subframe may be transmitted to the other port.

In another embodiment, the processor 1413 sets the RRH with multiple antenna ports to a Multi-Input-Multi-Output (MIMO) mode or a Transmission Diversity (MIMO) mode, If the rate of call drop of the terminals connected through the RRH in the city mode exceeds the threshold value, the RRH can be set to the transmission copy mode. At this time, the transmission module 1412 can copy the downlink subframe input to any one of the plurality of antenna ports of the RRH under the control of the processor 1413, and input the copied downlink subframe to the other port.

Further, in the embodiment where there are four or more antenna ports, the transmission module 1412 copies the first downlink sub-frame of the first port and inputs it to the third port, under the control of the processor 1413, The second downlink subframe of the second downlink subframe may be copied and input to the fourth port.

15, a terminal 1420 may include a receiver 1421, a transmitter 1422, a processor 1423, a memory 1424 and a plurality of antennas 1425. [ The receiver 1421 can receive various signals, data, and information on the downlink from the base station. The transmitter 1422 can transmit various signals on the uplink to the base station, data, and control information including TPC commands. The processor 1423 can control the operation of the entire terminal 1420.

The specific configurations of the base station and the terminal as described above may be implemented such that the elements described in the various embodiments of the present invention described above are applied independently or two or more embodiments are applied at the same time and the duplicated description is omitted for the sake of clarity .

The description of the base station 1410 and the RRH 1415 in the description of FIG. 11 may be applied to a repeater device as a downlink transmission entity or an uplink receiving entity. The present invention can be similarly applied to a repeater device as a downlink receiving entity or an uplink transmission entity.

The above-described embodiments of the present invention can be implemented by various means. For example, embodiments of the present invention may be implemented by hardware, firmware, software, or a combination thereof.

In the case of hardware implementation, the method according to embodiments of the present invention may be implemented in one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs) , FPGAs (Field Programmable Gate Arrays), processors, controllers, microcontrollers, microprocessors, and the like.

In the case of an implementation by firmware or software, the method according to embodiments of the present invention may be implemented in the form of a module, a procedure or a function for performing the functions or operations described above. The software code can be stored in a memory unit and driven by the processor. The memory unit may be located inside or outside the processor, and may exchange data with the processor by various well-known means.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The foregoing description of the preferred embodiments of the invention disclosed herein has been presented to enable any person skilled in the art to make and use the present invention. While the present invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. For example, those skilled in the art can utilize each of the configurations described in the above-described embodiments in a manner of mutually combining them. Accordingly, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the above description should not be construed in a limiting sense in all respects and should be considered illustrative. The scope of the present invention should be determined by rational interpretation of the appended claims, and all changes within the scope of equivalents of the present invention are included in the scope of the present invention. In addition, claims that do not have an explicit citation in the claims may be combined to form an embodiment or be included in a new claim by amendment after the filing.

Claims (27)

A method of controlling a remote radio head (RRH) having a plurality of antenna ports in a wireless communication system,
Transmitting a first reference signal through a first one of the plurality of antenna ports;
Transmitting a second reference signal through a second one of the plurality of antenna ports;
Receiving a measured value of a terminal for at least one of the first reference signal and the second reference signal; And
And transmitting the downlink subframe transmitted through any one of the first port and the second port equally to another port according to the measured value of the received terminal. The method according to claim 1,
Wherein the first reference signal and the second reference signal are cell-specific signals having the same sequence, but mapped to different physical resources. The method of claim 1, wherein the step of transmitting the downlink sub-
And transmitting the downlink subframe through the first port and the second port simultaneously by copying the downlink subframe transmitted through the one port and inputting the copied downlink subframe to the other port, Way. The method according to claim 1,
If the measured value of the second reference signal is less than a threshold value or the measured value of the second reference signal is not received, the one port is determined to be the first port and the other port is determined to be the second port / RTI > The method according to claim 1,
A Space Frequency Block Coding (SFBC) for providing diversity for transmission of the first port to the UE is set in the second port,
Wherein the step of transmitting the downlink sub-frame discards the diversity due to the SFBC setting in the second port and transmits the downlink sub-frame. 6. The method of claim 5, wherein the transmitting the downlink sub-
Obtaining SFBC coded downlink data according to the SFBC setting of the second port;
Performing SFBC coding on the SFBC coded downlink data again before erasing the diversity before inputting the SFBC coded downlink data to the second port; And
And inputting the downlink data with the diversity canceled to the second port. The method of claim 1, wherein the step of transmitting the downlink sub-
Switching the input of the second port to be connected to the input of the first port when the measured value of the second reference signal is below the threshold or when the measured value of the second reference signal is not received . The method of claim 1, wherein the step of transmitting the downlink sur-
Selecting either the first reference signal or the second reference signal based on the received measurement value; And
And simultaneously transmitting the selected reference signal through the first port and the second port. 2. The method of claim 1,
A Channel Quality Indicator (CQI), a Rank Indicator (RI), and a Reference Signal Received Power (RSRP). The method according to claim 1,
Further comprising the step of determining whether or not the terminal can switch synchronization from any one port to the other port,
Wherein the step of transmitting the downlink sub-frame equally transmits a downlink sub-frame transmitted through a port to another port when the terminal determines that the terminal can not switch the synchronization. An apparatus for controlling a remote radio head (RRH) having a plurality of antenna ports in a wireless communication system,
A transmission module that transmits a first reference signal through a first port of the plurality of antenna ports and transmits a second reference signal through a second port of the plurality of antenna ports;
A receiving module for receiving a measured value of a terminal for at least one of the first reference signal and the second reference signal; And
A processor for controlling the transmitting module to transmit the downlink subframe transmitted through any one of the first port and the second port equally to another port according to a measured value of the received terminal, Comprising: 12. The method of claim 11,
Wherein the first reference signal and the second reference signal are cell-specific signals having the same sequence, but mapped to different physical resources. 12. The apparatus of claim 11,
And transmitting the downlink subframe through the first port and the second port simultaneously by copying the downlink subframe transmitted through the one port and inputting the copied downlink subframe to the other port, Device. 12. The apparatus of claim 11,
Wherein if the measured value of the second reference signal is less than a threshold value or the measured value of the second reference signal is not received, the one port is determined as the first port and the other port is determined as the second port Determining the device. 12. The method of claim 11,
A Space Frequency Block Coding (SFBC) for providing diversity for transmission of the first port to the UE is set in the second port,
Wherein the processor deletes diversity due to the SFBC setting in the second port and transmits the downlink sub-frame. 16. The apparatus of claim 15,
Coded downlink data according to the SFBC setting of the second port and SFBC-coded downlink data again before SFBC-coded downlink data is input to the second port, And erases the downlink data and the downlink data from which the diversity is canceled, to the second port. 12. The apparatus of claim 11,
And switches the input of the second port to be connected to the input of the first port when the measured value of the second reference signal is below the threshold or when the measured value of the second reference signal is not received. 12. The apparatus of claim 11,
And selects one of the first reference signal and the second reference signal based on the received measurement value and controls the selected reference signal to be simultaneously transmitted through the first port and the second port. 12. The method of claim 11,
(Channel Quality Indicator), a Rank Indicator (RI), and a Reference Signal Received Power (RSRP). 12. The apparatus of claim 11,
The method comprising the steps of: determining whether or not the terminal can switch synchronization from any one of the ports to the other port; and if it is determined that the terminal can not switch the synchronization, And transmits the downlink subframe to the other one of the ports equally. A method of controlling a remote radio head (RRH) having a plurality of antenna ports in a wireless communication system,
Setting an RRH having the plurality of antenna ports to a multi-input-multi-output (MIMO) mode or a transmission diversity mode;
Setting the RRH to a Transmission Copy mode when a rate of call drop of terminals connected through the RRH exceeds a threshold value; And
And copying downlink subframes input to any one of the plurality of antenna ports and inputting the copied downlink subframe to another port. 22. The method of claim 21,
Wherein a first port and a second port of the plurality of antenna ports correspond to a first coverage, a third port and a fourth port correspond to a second coverage,
The step of copying and inputting the downlink sub-
Copying the first downlink sub-frame of the first port to the third port, and copying the second downlink sub-frame of the second port to the fourth port. The method of claim 22, wherein
Wherein the first downlink subframe and the second downlink subframe are set to be spatial-multiplexed with each other or mutually have a transmit diversity gain. An apparatus for controlling a remote radio head (RRH) having a plurality of antenna ports in a wireless communication system,
Wherein the RRH having the plurality of antenna ports is set to a MIMO (Multi-Input-Multi-Output) mode or a Transmit Diversity (MIMO) mode, A processor for setting the RRH in a Transmission Copy mode if a rate of call drop of the RRH exceeds a threshold; And
And a transmitting module for copying downlink subframes input to any one of the plurality of antenna ports under the control of the processor and inputting the copied subframe to the other port. 25. The method of claim 24,
Wherein a first port and a second port of the plurality of antenna ports correspond to a first coverage, a third port and a fourth port correspond to a second coverage,
Wherein the transmitting module copies the first downlink subframe of the first port and inputs the first downlink subframe to the third port according to the control of the processor and copies the second downlink subframe of the second port, Input to the port, device. The method of claim 24, wherein
Wherein the first downlink subframe and the second downlink subframe are set to be spatial-multiplexed with each other or set to have a mutual transmit diversity gain. A computer-readable recording medium storing a program for executing the method according to any one of claims 1 to 10.

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