KR20090101760A - A method for transmitting a data by collaborating of a plurality of base station in a multi-cell environments and a method for receiving using the same - Google Patents

Abstract

PURPOSE: A method of transmitting data by joining many base stations in the multi-cell environment and a data receiving method thereof are provided to perform the scheduling for cooperative transmission by the specific base station without a separate apparatus. CONSTITUTION: A method of transmitting data in the multi-cell environment is composed of the steps of receiving a pilot signal from a first base station(11) and a second base station(14), transmitting at least one downlink channel quality information of the first and second base stations based on the pilot signal, and receiving the data from the first base station and the second base station according to the cooperative MIMO scheduling determined in the first base station by the channel quality information.

Description

A method for transmitting a data by collaborating of a multiple of base station in a multi-cell environments and a method for receiving using the same}

The present invention relates to a multi-cell environment, and more particularly, to a method for transmitting data in cooperation with a plurality of base stations in a multi-cell environment, and a method for receiving data using the same.

In a multi-cell environment, the user at the edge of a cell exhibits poor reception performance in intercell interference. One way to reduce the effects of inter-cell interference in a multi-cell environment is to use resource reuse.

In the resource reuse scheme, a base station divides a system band by a reuse factor N , and allocates data of each user to the divided band and transmits the data. For example, when a base station (BS) is located at the center of each cell, and the reuse factor N = 1 in the frequency reuse scheme, all cells transmit data using the same frequency band. When the reuse factor N = 3, each base station can reduce interference by dividing the entire system band into three bands and avoiding the use of frequency resources such as neighboring cells.

The combination of the two methods described above may allow the entire frequency band to be used within the cell and different frequency resources around the cell reference value. In this case, additional reuse methods may be applied to maximize cell throughput.

In a cellular system, a system where N = 1 is common for system-wide efficiency, in which case it has the highest cell transmission yield, but because all cells use the same band of resources, there is a significant deterioration in reception performance when users are located at the cell baseline. Will suffer.

In addition, the use of the reuse factor N as a large value in a cellular system has the advantage that the frequency (or time) reuse technique can reduce neighbor cell interference by using different resources between adjacent cells. As N increases, the performance gain decreases in terms of transmission yield or spectral efficiency of the entire cell. This is because the system bandwidth is limited, and when N increases, not only the amount of resources available for each cell is reduced, but also the resources may be insufficient or wasted because the required transmission amount of users varies from cell to cell.

Accordingly, the resource reuse scheme described above has a limitation in that the user at the edge of a cell in a multi-cell environment has a limitation in compensating reception performance characteristics vulnerable to inter-cell interference.

This document provides a method for transmitting data in cooperation with a plurality of base stations in a multi-cell environment and a method for receiving data using the same in the background art described above.

In one embodiment of the present invention, a method for receiving data in a multi-cell environment includes receiving pilot signals from a first base station and a second base station, wherein the first base station and the second base station are based on the pilot signals. Transmitting downlink channel quality information for the at least one of the first base station and the second base station and collaborative MIMO scheduling determined based on the channel quality information at the first base station. Receiving data from the second base station.

The second base station may receive cooperative MIMO scheduling information from the first base station. In this case, the cooperative MIMO scheduling information may include one or more of MIMO execution time information, MIMO technique information, and region information.

The second base station may schedule based on the cooperative MIMO scheduling information and transmit a result to the first base station.

The area information may include one of a specific frequency band index, a scheduling area bitmap, and an area index previously promised between base stations.

Meanwhile, when an area is determined for each base station for cooperative MIMO scheduling, the area information may be transmitted as base station information.

In another embodiment of the present invention, a method in which a plurality of base stations cooperate to transmit data in a multi-cell environment includes receiving downlink channel quality information for the first base station and the second base station from a terminal at a first base station. Performing cooperative MIMO scheduling based on the channel quality information at the first base station; transmitting cooperative MIMO scheduling information determined according to the cooperative MIMO scheduling to the second base station; Receiving a result of scheduling based on the cooperative MIMO scheduling information from a base station and transmitting data in cooperation with the first base station and the second base station to the terminal.

The cooperative MIMO scheduling information may include one or more of MIMO execution time information, MIMO technique information, and region information.

The area information may include one of a specific frequency band index, a scheduling area bitmap, and an area index previously promised between base stations.

When a scheduling area is determined according to which base station collaborates with MIMO scheduling, the area information may be transmitted as base station information.

The data transmission method includes: rescheduling a scheduling result received from a plurality of base stations including the second base station; And transmitting each of the base stations including the second base station to the rescheduling result.

In the multi-cell environment disclosed in this document, a plurality of base stations cooperate to transmit data, and thus the terminal may receive data from the plurality of base stations.

In addition, in a multi-cell environment disclosed in this document, data transmission and reception of a certain performance or more may be performed to a terminal located at a cell edge through a method in which multiple base stations cooperate to transmit data.

In addition, scheduling for multiple cooperative transmissions may be performed by a specific base station without having a separate device.

In addition, signaling for cooperative transmission is possible between a base station performing scheduling for cooperative transmission and a base station performing data transmission together with the base station.

1 is a diagram illustrating a structure of a plurality of transmitters for transmitting data and a receiver for receiving data according to a collaborative MIMO scheme in a multi-cell environment according to an embodiment of the present invention.

2 is a flowchart illustrating a method of transmitting and receiving data using a collaborative MIMO scheme in a multi-cell environment according to an embodiment of the present invention.

3 is a diagram for explaining an example of a method of performing a collaborative MIMO technique according to an embodiment of the present invention.

4 illustrates an example of a method of performing a collaborative MIMO technique in accordance with an embodiment of the present invention.

FIG. 5 illustrates an example of a method for transmitting schedulable area information from a master base station to a slave base station when performing a collaborative MIMO scheme according to an embodiment of the present invention. FIG.

FIG. 6 illustrates an example of a method for transmitting schedulable region information from a master base station to a slave base station when performing a collaborative MIMO scheme according to an embodiment of the present invention; FIG.

Recently, the demand for wireless communication services is rapidly increasing due to the generalization of information communication services, the appearance of various multimedia services, and the emergence of high quality services. To cope with this actively, there is a demand for a technology capable of increasing the capacity of a communication system and increasing the reliability of data transmission.

In order to increase the communication capacity in a wireless communication environment, a method of finding new available frequency bands and increasing the efficiency of a given resource can be considered. Of these, the latter method is equipped with multiple antennas in the transceiver to obtain additional spatial area for resource utilization to obtain diversity gain, or to increase transmission capacity by transmitting data in parallel through each antenna. Multiple Input Multiple Output Antenna (MIMO) has recently been actively developed with great attention.

Hereinafter, various embodiments will be described a specific method for applying MIMO as a method for providing a higher quality service to the user at the edge of the cell from the effect of inter-cell interference.

In a similar way to the enhanced reception by single-user MIMO or multi-user MIMO through the base station's multi-antenna, diversity, single-user MIMO or multiplexing is achieved by receiving signals for the same channel from base stations located in multiple adjacent cells. User MIMO can be implemented. In particular, the terminal located at the edge of the cell susceptible to interference from the neighboring cell may reversely use this situation to receive a signal for the same channel from neighboring base stations, thereby implementing diversity, single-user MIMO, or multi-user MIMO. There will be. Hereinafter, a method for transmitting by applying a MIMO technique in a plurality of base stations is called a cooperative MIMO technique.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a diagram illustrating a structure of a plurality of transmitters for transmitting data and a receiver for receiving data according to a cooperative MIMO scheme in a multi-cell environment according to an embodiment of the present invention.

As shown in FIG. 1, a communication system of a multi-cell environment in which a collaborative MIMO scheme according to the present embodiment can be applied includes a terminal MS 10 and an uplink signal transmitted from the terminal MS 10. And a plurality of base stations including a serving base station BS1 11 and a neighbor base station BS2 14 corresponding to a neighboring cell of the serving base station BS1 11.

According to the present embodiment, cooperative MIMO scheduling may be performed at a scheduler or controller of a specific base station. For example, in the case of the serving base station, the channel information may be received from the terminal as an uplink signal, thereby reflecting the current channel state, and if the collaborative MIMO scheduling is performed at the serving base station, the scheduling gain may be increased.

That is, according to the present embodiment, the serving base station BS1 11 of a specific terminal may play a leading role in collaborative MIMO scheduling for the terminal. In the following description, a base station that plays a leading role in cooperative MIMO scheduling for a specific terminal is referred to as a master base station (Master BS), and a base station that performs cooperative MIMO with the master base station is a slave base station (Slave BS). It is called. As described above, the master base station may be a serving base station of a specific terminal that receives data by collaborative MIMO.

In the following description, it is assumed that there is only one slave base station, but it will be obvious that cooperative MIMO may be performed together with multiple slave base stations.

In this case, each of the base stations performing the cooperative MIMO may include controllers 12 and 15 for cooperative MIMO control. Within each base station, the controllers 12 and 15 for cooperative MIMO control may be implemented in addition to the existing base station configuration, or may be implemented by adding new functions to the existing scheduler or controller. Of course it will.

According to the present embodiment, the transmission method including the MIMO technique applied to the terminal 10 receiving data through the collaborative MIMO may be to follow the determination of the master base station (11). In this case, for this cooperative MIMO, scheduling is cooperatively performed between two base stations, and cooperative MIMO coding according to this scheduling may be cooperatively applied or identically applied to each controller.

In this case, the controller 12 of the master base station may receive channel information about each base station that performs cooperative MIMO together from the terminal and use the same for cooperative MIMO scheduling. For example, the channel information may include channel quality information (CQI), precoding matrix information, rank information, and the like.

In addition, in determining the coding scheme, modulation scheme, and MIMO scheme for the terminal in the controller of the master base station, data is appropriately adapted to the channel situation for each base station by using channel information of each base station performing cooperative MIMO together. Can be configured. The channel information may be used to determine an optimal scheduling region for the channel state of the corresponding terminal and to transmit and receive data for the terminal within this region.

For this operation, the master base station 11, particularly the controller 12 of the master base station, informs the slave base station 14 of the cooperative MIMO scheduling information after performing scheduling for the cooperative MIMO operation between the two base stations. The slave base station 14, in particular, the controller 15 of the slave base station schedules based on this cooperative MIMO scheduling information and notifies the master base station 11 of the scheduling result.

In this case, the cooperative MIMO scheduling information transmitted from the master base station 11 to the slave base station 14 may include MIMO scheme information for performing cooperative MIMO such as a precoding matrix index, scheduleable region information, and the like. In this case, the schedulable region information may be transmitted in the form of one of a frequency band index and a region index previously scheduled between each base station.

In the controller 12 of the master base station, the base stations located in a plurality of adjacent cells cooperatively transmit signals to the terminal, particularly, the terminal located at the edge of the cell, but apply various MIMO techniques to transmit the signals more effectively. By configuring the data for and can be delivered to each base station. Various MIMO techniques known in the art may be applied in the same or similar manner to the MIMO coding according to the cooperative MIMO technique.

The controller 15 of the slave base station performs scheduling based on the cooperative MIMO scheduling information transmitted from the master base station. For example, the controller 15 of the slave base station may determine the scheduling area within the scheduleable area through the area information determined by the master base station. Then, the scheduling result information thus determined is informed to the master base station 11 again.

In the MIMO coding unit 13 of the master base station and the MIMO coding unit 16 of the slave base station, the cooperative MIMO scheduling information and scheduling result information determined by the controllers of the master base station 11 and the slave base station 14 described above can be obtained. MIMO coding is performed as a basis. And, the MIMO coded data will be transmitted to the corresponding terminal.

The present invention relates to a method for applying a collaborative MIMO method in order for a terminal of a cellular system to be provided with a good quality of service when it is located in a cell boundary region in a multi-cell environment and is being interfered with by an adjacent cell. According to the embodiment, there is an advantage that resources for collaborative MIMO can be allocated, especially without a scheduler above the base station.

2 is a flowchart illustrating a method of transmitting and receiving data using a collaborative MIMO scheme in a multi-cell environment according to an embodiment of the present invention.

In the following description, it is assumed that a first base station performs a function of a master base station as a serving base station of a terminal, and a second base station transmits data to the terminal through a cooperative MIMO scheme together with the first base station. In this case as well, although the slave base station is illustrated as having only the second base station, it will be understood that the cooperative MIMO can be performed with the plurality of slave base stations as described above. At this time, the operation between the master base station and each slave base station may be performed in the same or similar to the operation of the first base station and the second base station in FIG.

According to the method for transmitting / receiving data according to the cooperative MIMO scheme in the multi-cell environment according to the present embodiment, first, in step S20, the first base station and the second base station transmit pilot signals that can be received by the terminal. The terminal may receive a pilot from these base stations to measure the channel state for each base station.

The terminal transmits the measured channel information to the first base station which is the serving base station in step S21. In this case, the channel information transmitted may include channel quality information, precoding matrix information, rank information, and the like. In addition, according to the present embodiment, in transmitting channel information to the first base station, the terminal may transmit channel information measured for each base station, that is, channel information for the first base station and channel information for the second base station. have. For example, in the case of the channel quality information, the channel quality information CQI_BS1 for the first base station and the channel quality information CQI_BS2 for the second base station may be transmitted.

In this case, as shown in FIG. 2, all of the channel quality information of the plurality of base stations may be transmitted to the first base station, which is a serving base station, but the channel quality information of each base station may be directly transmitted to the corresponding base station.

The first base station performs scheduling for the terminal based on the channel information received from the terminal. At this time, according to the present embodiment, scheduling is performed according to the cooperative MIMO scheme together with the second base station in step S22. In performing cooperative MIMO scheduling in this step, it may be preferable that the first base station uses channel information received in the previous step S20.

After the cooperative MIMO scheduling in the first base station, the cooperative MIMO scheduling information is transmitted to the second base station in step S23. In this step, MIMO scheme information and schedulable region information may be transmitted as collaborative MIMO scheduling information. In addition, time information (Col-MIMO start / end) for performing cooperative MIMO may be transmitted. The first base station may transmit channel quality information CQI_BS2 for the second base station received from the terminal to the second base station. If cooperative MIMO is performed with a plurality of slave base stations, channel quality information CQI_BS # for each slave base station may be transmitted from the first base station to the corresponding slave base station.

The MIMO technique information may include information indicating what MIMO technique is applied for collaborative MIMO, and may include control information required when the MIMO technique is applied. Of course, when performing cooperative MIMO, a fixed MIMO scheme may be used and only necessary control information may be transmitted. For example, when the precoding technique is applied as the MIMO technique, the precoding matrix index information may correspond to this.

In addition, the schedulable region information may be transmitted in the form of one of a specific frequency band index, a scheduling region bitmap, and an region index previously reserved between each base station. Meanwhile, the cooperative MIMO scheduling information may include information on coding scheme and modulation scheme as well as MIMO scheme information and schedulable region information. In step S23, information about a coding scheme and a modulation scheme determined based on channel information about a second base station received from the terminal by the first base station may be transmitted. Alternatively, a method transmitted separately from the cooperative MIMO scheduling information may be considered.

The second base station may perform scheduling in step S24 based on the received cooperative MIMO scheduling information. In this case, scheduling is performed based on the cooperative MIMO scheduling information received in step S23. That is, scheduling for MIMO coding is performed based on MIMO scheme information, and scheduled in a possible scheduling region determined by the first base station based on region information. When the scheduling is determined in the second base station as described above, the scheduling result may be transmitted back to the first base station in step S25.

The first base station and the second base station perform MIMO coding on the data transmitted from each base station in steps S26 and S27 according to the cooperative MIMO scheduling information and the scheduling result information determined by the second base station. Then, the MIMO coded data is transmitted to the terminal in step S28.

Meanwhile, prior to steps S26 and S27, the first base station may perform rescheduling by collecting scheduling result information transmitted from each slave base station including the second base station. In this case, rescheduling result information is transmitted to each slave base station, and MIMO coding may be performed in steps S26 and S27 according to the rescheduling result.

MIMO coding in each base station described above may be performed through various techniques. For example, block coding techniques using various space-time codes (STCs), spatial multiplexing (SM) techniques, cyclic delay diversity (CDD) techniques, precoding techniques Antenna selection (AS), antenna hopping (AH), beamforming (BF), and the like. Among the above-listed techniques, the various MIMO techniques described above will be described in more detail below.

Spatial multiplexing can increase the data rate by dividing the input signal into several parallel signals and transmitting them simultaneously. If the sequence of information bits corresponding to the input signal is defined as s1, s2, s3, s4, it can be represented as Table 1 below.

Coding determinant # of ANT (One) 2 (2) 3 (3) 4

A block coding technique using a space-time code is a technique of simultaneously obtaining diversity and coding gain by applying coding to a space axis and a time axis corresponding to an antenna. In addition, when a sequence of information bits is defined as s1, s2, s3, and s4, various space-time codes may be represented as shown in Table 2 below.

Space-time code rank # of ANT (One) One 2 (2) 2 2 (3) One 4 (4) One 4 (5) 2 4

In Table 2, the rank represents the number of transmission streams transmitted in one block coding and may be referred to as a spatial multiplexing rate. In addition, it is shown that different space-time codes are required according to the structure of the antenna, for example, the number of antennas (# of ANT). In each determinant of Table 2, a row may represent an antenna and a column may represent a time slot.

Meanwhile, the space-time coding scheme of Table 2 may be extended to implement not only a space-time coding scheme but also a space-frequency coding scheme, a space-time-frequency coding scheme, and the like. For example, when extended to a space-frequency coding scheme, a column in each determinant of Table 2 may represent a subcarrier.

Space-Time Trellis Code (STTC) is a diversity and coding scheme for multiple antenna systems under a fading channel. In the space-time trellis coding scheme, a space-time diversity gain can be obtained by transmitting a coded signal through multiple antennas, and a coding gain can be obtained without increasing an additional bandwidth in the conventional scheme.

The STTC encoding process of the transmitter is performed as follows. When an information bit is input, a symbol is allocated to each of multiple antennas according to constellations so that diversity gain and coding gain are maximized according to a given trellis degree, and the allocated symbols are simultaneously transmitted through each antenna. The symbols transmitted through each transmit antenna undergo independent fading, thereby obtaining diversity gain.

Space-Frequency Trellis Code (SFTC) is a method of encoding in the frequency domain when the space-time trellis coding scheme is applied to an orthogonal frequency division multiplexing (OFDM) scheme. There is a difference in that it can be basically performed in the same manner as the space-time trellis coding technique described above.

The cyclic delay diversity scheme is a technique in which a frequency diversity gain is obtained at a receiving end by transmitting all signals with different delays or different sizes when transmitting an OFDM signal in a system having multiple transmit antennas.

According to the cyclic delay diversity scheme, OFDM symbols are separately transmitted to each antenna through a serial-to-parallel converter and a multi-antenna encoder, and then a Cyclic Prefix (CP) is attached to the receiver to prevent interference between channels. Is sent. At this time, the data sequence transmitted to the first antenna is transmitted to the receiving end as it is, but the data sequence transmitted to the next antenna is transmitted with a cyclic delay by a predetermined bit compared to the antenna of the previous sequence.

Meanwhile, if the cyclic delay diversity scheme is implemented in the frequency domain, the cyclic delay may be expressed as a product of a phase sequence. Each data sequence in the frequency domain may be multiplied by a predetermined phase sequence set differently for each antenna, and then may be transmitted to a receiver by performing fast inverse Fourier transform (IFFT), which is called a phase shift diversity technique. It may be.

According to the phase shift diversity scheme, a flat fading channel can be changed into a frequency selective channel and a frequency diversity gain or a frequency scheduling gain can be obtained through the channel code. In the phase shift diversity scheme, when a phase sequence is generated using a large value of a cyclic delay, the frequency selectivity is shortened, and thus frequency selectivity is increased, and thus, the channel code can obtain a frequency diversity gain. It is mainly used in open-loop systems.

In addition, since a cycle of frequency selectivity is long when a small cyclic delay is used, a closed-loop system may use this to obtain a frequency scheduling gain by allocating a resource to a region having the best channel. In the phase shift diversity scheme, when a phase sequence is generated using a small value of a cyclic delay, a constant subcarrier region of a flat fading channel has a large channel size, and another subcarrier region has a small channel size. In this case, in an orthogonal frequency division multiple access (OFDMA) system that accommodates a large number of users, the signal-to-noise ratio can be increased by transmitting a signal through a subcarrier with a larger channel size for each user.

On the other hand, the precoding scheme described above includes a codebook based precoding scheme used when the feedback information is finite in a closed loop system, and a method of quantizing and feeding back channel information. The codebook-based precoding is a method of obtaining a signal-to-noise ratio (SNR) gain by feeding back an index of a precoding matrix known to the transmitter / receiver to the transmitter.

On the other hand, for example, if you want to use two antennas in the intersection , If the precoding matrix constructed as described above is used to cross at a specific time, a result of using the antenna of the signal transmitted from each base station can be obtained.

Cooperative MIMO coding is performed on the information bits according to the various MIMO coding schemes described above, and the resulting streams are branched and transmitted to corresponding base stations participating in the cooperative MIMO scheme. In addition, according to the present embodiment, MIMO coding of each base station is performed according to the above-described various MIMO coding schemes for the input stream. After that, it may be transmitted to the terminal through each antenna.

Any of the various MIMO coding techniques described above may be used for collaborative MIMO coding and MIMO coding of each base station. If possible, it may be possible to apply various MIMO coding techniques together. For example, each base station receiving the cooperative MIMO coding signal may be transmitted to the terminal by applying precoding using an antenna and a cyclic delay diversity. In this case, in performing the secondary MIMO coding, it may be preferable that the MIMO technique is selected in such a way that a higher diversity effect and an interference cancellation effect can be obtained.

Meanwhile, when performing cooperative MIMO coding and delivering a cooperative MIMO coded signal to each base station, all of the same MIMO coded signals may be delivered to each base station. In addition, a partial or separate combination of the MIMO coded signals may be transmitted to each base station so as to be distributedly transmitted from the plurality of base stations. Hereinafter, examples of configuring a signal to be transmitted from each base station to the terminal by using a partial or separated combination of MIMO coded signals will be described.

A case where cooperative MIMO coding is performed by a space-time block coding technique using a space-time code of Table 1 (1), Table 2 (1), or Table 2 (2) will be described. For example, when collaborative MIMO is performed by using two base stations, data to be transmitted to each base station can be transmitted to each base station by (1 row: 2 rows) or (1, 2 rows: 1,2) of the space-time code in (1) of Table 2. Line).

A case in which cooperative MIMO coding is performed using a space-time block coding technique using the space-time code of Table 1 (3), Table 2 (3), Table 2 (4), or Table 2 (5) do. For example, when collaborative MIMO is performed using two base stations, each row may be separated and combined in various ways and transmitted to the base station. In this case, the separated criteria may be a channel state and scheduling of an antenna transmitted from each base station.

For example, if two base stations are used, (row 1: row 2, 3, 4), (row 2: row 1, 3, 4), (row 3: row 1, 2, 4), (row 4 : 1, 2, 3), (1, 2: 3, 4), (1, 3: 2, 4), (1, 4: 2, 3). In addition, all combinations where one row branches to different base stations, such as (1,2,3 rows, 2,3,4 rows), (1,2,3,4 rows 1,2,3,4 rows) This is possible.

The rows divided into two groups are transmitted to each base station. Each base station may apply another MIMO coding according to the present embodiment in order to transmit data for each row. That is, in addition to the cooperative MIMO scheme, an additional gain may be obtained by applying another MIMO scheme such as a cyclic delay diversity scheme or a block coding scheme such as an Alamouti-based coding scheme. This will apply equally or similarly to three or more base stations.

Meanwhile, the base station may perform spatial beamforming on the signal to be transmitted. That is, each base station can multiply and transmit the weight so as to determine the channel state with the terminal to form a beam directed to the terminal. In this case, spatial nulling may be performed to other users, so that spatial beamforming may be applied to cooperative MIMO transmission. In addition, when performing spatial beamforming using the antenna of each base station as described above, the terminal may transmit feedback information for beamforming to generate the beamforming weight in the base station.

3 is a diagram for explaining an example of a method of performing a collaborative MIMO scheme according to an embodiment of the present invention in a MIMO system using OFDM.

A case in which a cooperative MIMO scheme is applied to data transmitted to the terminal 30 through two base stations, a base station BS1 31 as a master base station and a base station BS2 35 as a slave base station, will be described.

In FIG. 3, it is assumed that s ₁ is transmitted to the master base station 31 and s ₂ is transmitted to the slave base station 35. That is, it can be described as a case where the base stations performing cooperative MIMO together transmit different data streams.

The controller 32 of the master base station performs cooperative MIMO scheduling based on uplink channel information received from the terminal 30. Then, the scheduling information is transferred to the slave base station 35 that performs the cooperative MIMO, and accordingly, the controller 36 of the slave base station performs scheduling for the terminal 30. The slave base station then transfers the scheduling result information back to the master base station 31.

As a result, scheduling information is exchanged between the master base station 31 and the slave base station 35, and thus data to which the cooperative MIMO scheme by the two base stations is applied may be transmitted to the terminal 30.

More specifically, referring to FIG. 3, a weight is determined by a precoding matrix with MIMO coding in each base station as a MIMO scheme for cooperative MIMO in the master base station 31. To A cyclic delay diversity (CDD) scheme that can take diversity gain by also transmitting a signal to which a predetermined delay value 33. 37 is applied may be applied.

In this case, the MIMO scheme information among the cooperative MIMO scheduling information transmitted from the master base station 31 to the slave base station 35 is the slave base station 35 for the precoding matrix index and cyclic delay diversity applied by the slave base station 35. We can send the delay value applied in

At each base station Considering only the delay of, the signal received at the terminal can be represented by Equation 1.

In Equation 1, h _{BSk _ rt} means a channel formed between the t th transmit antenna of the base station BS_k performing cooperative MIMO and the r th antenna of the terminal. In Equation 1, h _{BSk _ rt} denotes a channel formed between the r th antenna of the terminal and the t th transmission antenna of the base station BS_k performing cooperative MIMO. And, Denotes a predetermined delay value applied to apply the cyclic delay diversity scheme as shown in FIG.

As described above, the cyclic delay diversity scheme is applied and then OFDM modulated to the IFFT modules 34 and 38 for each transmit antenna and transmitted through the antenna.

According to the present embodiment, as can be seen from checking the received signal of Equation 1, if the pilot structures for channel estimation are placed in (s ₁ , s ₂ ) as (1, 0) and (0, 1) s ₁ And it is possible to easily obtain the equivalent channel generated when transmitting s ₂ it is possible to perform signal recovery in the terminal more easily. In addition, since the pilot structure used in the case of applying the existing MIMO scheme, that is, in the case of applying the MIMO scheme in one base station can be applied as it is, there is an advantage that it is easy to implement the cooperative MIMO.

FIG. 4 is a diagram for explaining another example of a method of performing a collaborative MIMO scheme according to an embodiment of the present invention in a MIMO system using OFDM.

In another method, when each base station transmits a signal on which cooperative MIMO coding is performed, a role of each base station may be separated as shown in FIG. 4. For example, FIG. 4 shows that the cyclic delay diversity scheme is extended by a base station unit, and the base stations cooperate with each other in transmitting the cyclic delay diversity scheme for one symbol.

Even in this case, the case where the cooperative MIMO scheme is applied to the data transmitted to the terminal 40 through two base stations, that is, the base station BS1 41 as the master base station and the base station BS2 45 as the slave base station, will be described.

In FIG. 4, it is assumed that the same data stream s is transmitted to the master base station 41 and the slave base station 45. That is, it can be described as a case in which base stations that perform cooperative MIMO together transmit the same data stream but differently apply the MIMO technique to each base station.

That is, x _{BS1_0} (i) to x _{BSn _0} (i) representing the input signals of each of the base stations BS_1 51 to BS_n 52 are identically configured and transmitted to the master base station 41 and the slave base station 45, respectively. do. In addition, the weight of the precoding matrix is determined in each base station, and the cyclic delay diversity scheme is extended and transmitted in units of base stations as described above.

In order to apply the cyclic delay diversity scheme to each base station unit, the master base station 41 The predetermined delay value 43 is applied to the terminal, and the slave base station 45 transmits the delay value to the terminal without applying the delay value. Therefore, the signal received by the cooperative MIMO scheme in the terminal side can be received with a cyclic delay applied to each signal for the Alamouti code by the cooperative MIMO coding.

In addition to the cyclic delay diversity scheme, each base station can apply various MIMO schemes. In this case, the symbols are rearranged so that the symbols transmitted through the antennas of the base stations are identical at any moment through a predetermined coding scheme or a precoding matrix. can do.

As a result, the terminal may not only obtain a path diversity gain, but also may have an advantageous effect on channel estimation. In addition, as shown in FIG. 4, each base station applies closed-loop MIMO using cyclic delay diversity (CDD) and a precoding matrix with MIMO coding, but uses the same precoding matrix used by each base station. In this case, the feedback overhead may be reduced when transmitting feedback information compared to the case of independently transmitting a precoding matrix index (PMI) that should be used for each base station.

For example, the first base station performs space-time code coding on s ₁ and -s ₂ ^* , and the second base station performs space-time code coding on s ₂ and s ₁ ^* . At this time, the coding result of the first base station And the coding result of the second base station Create the same as each other.

In this way, even if the same data is not transmitted from each base station, it may be reconfigured to the same form through precoding at each base station, and a cyclic delay diversity gain between the base stations may be obtained. Meanwhile, each base station may determine the weight and order of the antennas actually transmitted using the precoding matrix, and apply the coding according to the channel situation of each base station.

FIG. 5 illustrates an example of a method for transmitting schedulable region information from a master base station to a slave base station when performing a collaborative MIMO scheme according to an embodiment of the present invention.

According to the method for transmitting schedulable region information described in the present embodiment, a scheduling region may be designated for each base station according to a case where each base station becomes a master base station. The slave base station may know a scheduling area capable of performing cooperative MIMO with the master base station by receiving information on the master base station.

In FIG. 5, when a base station of cell A is a master base station and wants to transmit data to a terminal through a cooperative MIMO scheme with a base station of cell B and a base station of cell C, cell B and cell performing cooperative MIMO in cell A base station. An index (eg, a cell Am index) for the base station of cell A may be transmitted as region information that can be scheduled to the base station of C. Then, the cell B base station schedules in the cooperative MIMO region of Cell Ba corresponding to the cooperative MIMO scheduling region corresponding to the cell Am index, or within the cooperative MIMO scheduling region. Scheduling in the cooperative MIMO region of the corresponding Cell Ca or the region and transmitting the result to the base station of the cell A.

At the same time, when the UE belonging to the cell C performs cooperative MIMO scheduling with the cell B, the base station of the cell C transmits an index (for example, a cell Cm index) for the base station of the cell C to the cell B. Scheduling in the Cell Bc region corresponding to the cooperative MIMO scheduling region corresponding to the cell Cm index or in the region, and notifying the result. In this case, the Cell B-a region and the Cell B-c region may be preferably set so as not to overlap each other.

The area index (cell A-m, cell B-m etc) used at this time can reduce the amount of data transmitted to the backbone network if previously defined between each base station. Of course, if the base station transmits the range of the optimal channel state of the corresponding terminal to the slave base station in addition to the predefined area, the slave base station may also consider a method of scheduling within the area and sending the result. In this case, a method for notifying the channel information between the slave base station and the corresponding terminal may also be considered.

In addition, since the slave base station can coexist with other master base stations that want to schedule in this area, it is desirable to schedule these areas effectively. To this end, QoS (Quality of Service) information of the corresponding UE may be required.

FIG. 6 illustrates another example of a method for transmitting schedulable region information from a master base station to a slave base station when performing a collaborative MIMO scheme according to an embodiment of the present invention.

Although the scheduling region for the cooperative MIMO for each base station may be set to a contiguous resource region as shown in FIG. 5, the resource region distributed in the entire resource region or the cooperative MIMO region as shown in FIG. 6. May be set to. And, the scheduling area for the cooperative MIMO may be set and signaled based on the actual resource area, but is set based on the virtual resource area and information on this is already shared between the base stations and the area by signaling the virtual resource area. Information exchange may also take place.

FIG. 6 differs only from a method of determining a scheduling area for cooperative MIMO for each base station compared to FIG. 5, and is different from the embodiment of FIG. 5 in the method of exchanging area information between base stations performing cooperative MIMO. It may be performed in the same or similar way.

Meanwhile, in FIG. 5 and FIG. 6, the collaborative MIMO scheduling region allocated for each base station may be set as an area which can be changed at predetermined intervals in consideration of a multi-cell communication environment, or may be set as a fixed area. In the case of being configured as a changeable area, efficient scheduling is possible in consideration of a communication environment, and signaling between base stations may increase. In addition, if the fixed area is set, signaling between base stations can be reduced, but the scheduling gain is relatively low. Even in this case, however, if a method of selecting an optimal region within the region is used, a supplement to a certain level may be possible.

It is obvious that the claims may be combined to form an embodiment by combining claims that do not have an explicit citation relationship in the claims or as new claims by post-application correction.

Claims (11)

In the method for receiving data in a multi-cell environment, Receiving a pilot signal from a first base station and a second base station; Transmitting downlink channel quality information for the first base station and the second base station based on the pilot signal to at least one of the first base station and the second base station; And Receiving data from the first base station and the second base station according to cooperative MIMO scheduling determined by the first base station based on the channel quality information; Comprising a data reception method. The method of claim 1, And the second base station receives cooperative MIMO scheduling information from the first base station. The method of claim 2, The collaborative MIMO scheduling information includes one or more of MIMO execution time information, MIMO technique information, and region information. The method of claim 3, wherein And scheduling at the second base station based on the cooperative MIMO scheduling information and transmitting the result to the first base station. The method of claim 3, wherein And the area information comprises one of a specific frequency band index, a scheduling area bitmap, and an area index previously reserved between respective base stations. The method of claim 3, wherein If the area is determined for each base station for cooperative MIMO scheduling, the area information is characterized in that the base station information, data reception method. In the multi-cell environment in which a plurality of base stations cooperate to transmit data, Receiving downlink channel quality information for the first base station and the second base station from a terminal in a first base station; Performing collaborative MIMO scheduling based on the channel quality information at the first base station; Transmitting cooperative MIMO scheduling information determined to the cooperative MIMO scheduling to the second base station; Receiving a scheduling result from the second base station based on the cooperative MIMO scheduling information; And Transmitting data by the first base station and the second base station to cooperate with the terminal; Comprising a data transmission method. The method of claim 7, wherein The collaborative MIMO scheduling information includes one or more of MIMO execution time information, MIMO technique information, and region information. The method of claim 8, And the area information comprises one of a specific frequency band index, a scheduling area bitmap, and an area index previously reserved between base stations. The method of claim 8, And if the scheduling area is determined according to which base station collaborates on MIMO scheduling, the area information is base station information. The method of claim 7, wherein The data transmission method includes: rescheduling a scheduling result received from a plurality of base stations including the second base station; And transmitting the rescheduling result to each base station including the second base station.