KR20100085817A - Method for synchronizing cells in multi-cell environment - Google Patents

Abstract

PURPOSE: A method for synchronizing cells in a multi-cell environment is provided to improve communication performance of a terminal by accurately synchronizing the multi cell base stations which perform cooperative MIMO method. CONSTITUTION: Transmission delay for a cooperative base station is measured(S220), and the measured transmission delay is transferred to a serving base station(S230). If the serving base station transfers the transmission delay to the cooperative base station, the data for cooperative MIMO in which transmission location is controller is received from the cooperative base station based on the transmission delay(S240,S250). The cooperative base station adjusts the transmission location of the data for the cooperative MIMO. The transmission delay is transferred to the serving base station only if the transmission delay is larger than a certain length.

Description

Method for Synchronizing Cells in Multi-cell Environment

The present invention relates to wireless communication, and more particularly, to a method for synchronizing between cells in a multi-cell environment.

Recently, multiple input multiple output (MIMO) technology has been in the spotlight as one of the technologies used in next generation mobile communication and wireless transmission systems. Multiple input / output (MIMO) technology is a method of increasing the spectral efficiency by using a plurality of antennas in order to increase the low spectral efficiency, which was a problem of the previous single input single output (SISO) method.

Multiple input / output (MIMO) technology can be classified into spatial multiplexing and spatial diversity according to whether identical data is transmitted.

Spatial multiplexing is a method of simultaneously transmitting different data through multiple transmit / receive antennas. That is, the transmitting side transmits different data through each transmitting antenna, and the receiving side performs appropriate interference cancellation and signal processing on the received signal to acquire the transmitted data, so that the data rate is proportional to the number of transmitting antennas. It is a technique to improve.

Spatial Diversity is a method of obtaining transmit diversity by transmitting the same data through multiple transmit antennas. That is, the space diversity scheme is a kind of space-time channel coding technique.

In such a spatial diversity scheme, transmission diversity gain can be greatly improved by transmitting the same data from several transmission antennas. However, the spatial diversity technique is not a method for improving the data rate, but is intended to improve the reliability of data transmission by improving the diversity gain.

In addition, multiple input / output (MIMO) technology may be classified into an open loop method and a closed loop method according to whether information on a channel is fed back from a receiver to a transmitter. Among these, closed-loop multiple input / output (MIMO) technology improves the data rate by using channel information fed back from the receiver. For example, in a wireless communication system using a closed loop MIMO technology, the base station on the transmitting side receives feedback of the transmission channel information from the terminal on the receiving side and transmits data using the base station.

Meanwhile, a coordinated multi-point transmission (CoMP) method has been developed to reduce inter-cell interference in a multi-cell environment. By using a coordinated multi-point transmission (CoMP) method, a terminal may be jointly supported by a multi-cell base station.

In addition, each base station can simultaneously support one or more terminals using the same frequency resource (Frequency Resource) to improve the performance of the system. In a multi-cell environment, the CoMP method may be used to improve communication performance of a terminal located at a cell edge.

Such a coordinated multipoint transmission (CoMP) method includes a collaborative MIMO type joint processing method through data sharing, a worst companion and a best companion. Like a companion, there is a coordinated scheduling / beamforming scheme for reducing inter-cell interference.

Among these, in order to smoothly perform a collaborative MIMO method such as joint processing, synchronization between multiple cells that perform this should be properly performed. However, a method for accurately synchronizing multiple cell base stations performing a collaborative MIMO method such as joint processing has not yet been established.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for accurately synchronizing multiple cell base stations performing a collaborative MIMO method in a multi-cell environment. will be.

Another object of the present invention is to provide a method for further improving communication performance of a terminal located at a cell edge by accurately synchronizing multiple cell base stations performing a collaborative MIMO method in a multi-cell environment with each other. will be.

In order to achieve the above object, the present invention provides a method for synchronizing multiple cells to perform a cooperative multiple input and output method, the method comprising the steps of measuring a transmission delay for the cooperative base station; Delivering the measured transmission delay to a serving base station; And when the serving base station transmits the transmission delay to the cooperative base station, receiving data for cooperative multi-input / output of which a transmission position is adjusted based on the transmission delay from the cooperative base station. Provides a synchronization method between cells.

Preferably, the coordination base station to adjust the transmission position of the data for the cooperative multiple input and output, the guard zone on the time domain is set in the radio resource (resource) used for the cooperative multiple input and output (guard zone) By adjusting). More preferably, a guard band is set on a frequency domain in a radio resource used for the cooperative multiple input / output.

In this case, the transmission delay measurement may be made using at least one of a reference signal (RS) or a synchronization channel (SCH) of each base station.

In addition, the measured transmission delay may be represented by a difference value based on the transmission delay of the serving base station. In addition, the measured transmission delay may be represented by a relative value of a cyclic prefix (CP) of the serving base station. Meanwhile, the measured transmission delay may be transmitted to the serving base station only when the transmission delay is larger than a predetermined length.

Meanwhile, the measured transmission delay may transmit the transmission delay to the serving base station through a physical uplink control channel (PUCCH) or a physical uplink shared channel (PUSCH).

On the other hand, the present invention, a method for synchronizing multiple cells for performing a cooperative multiple input and output method, comprising the steps of measuring the transmission delay for the cooperative base station by the terminal and the synchronization of the base station; Transmitting, by the terminal, the measured transmission delay to a corresponding cooperative base station; And adjusting, by the cooperative base station, a transmission position of data for cooperative multiple input / output based on the transmission delay.

According to the inter-cell synchronization method in a multi-cell environment according to the present invention, multi-cell base stations performing a collaborative MIMO method in a multi-cell environment can be accurately synchronized with each other.

In addition, according to the cell-to-cell synchronization method according to the present invention, by accurately synchronizing the multi-cell base station performing the collaborative MIMO method in a multi-cell environment with each other, the terminal of the terminal located at the cell edge The communication performance can be further improved.

Hereinafter, with reference to the accompanying drawings an embodiment according to the present invention will be described in detail. Like numbers refer to like elements throughout.

In the present embodiment, a description will be given of data transmission / reception relations between a base station and a terminal. Here, the base station operates as a terminal node of a network that directly communicates with the terminal. Some of the operations and processes described as being performed at the base station may be performed at higher nodes of the base station in some cases.

In addition, in the present embodiment, the term base station may be used interchangeably with a fixed station, a node B, an eNode B (eNB), an access point, and the like. In addition, the term "terminal" may be used interchangeably with a user equipment (UE), a mobile station (MS), a mobile subscriber station (MSS), or the like.

A wireless communication system that performs a cooperative multiple input / output method such as joint processing includes a base station (hereinafter referred to as a 'serving base station') and a cooperative multiple input / output (Collaborative MIMO) of a serving cell to which a terminal belongs. A base station (hereinafter referred to as a `` cooperative base station '') of a neighboring cell to perform and a backing network may be configured as a serving base station and a scheduler connected to a cooperating base station through a backbone network. FIG. 1 illustrates a configuration of a cooperative multiple input / output communication system that performs such a cooperative multiple input / output.

1 is a schematic structural diagram schematically illustrating a configuration of a multi-cell communication system for performing a cooperative multiple input / output method. As shown in FIG. 1, the serving base station 110 and the cooperative base stations 112 and 114 are connected to the scheduler 130 through the backbone network 120.

Here, the scheduler 130 may operate by receiving feedback about the channel state between the terminal 140 and the base stations 110, 112, and 114 through the backbone network 120. For example, scheduler 130 schedules for performing collaborative MIMO operations for serving base station 110 and one or more collaborative base stations 112 and 114, and cooperative multiple input / output to each base station 110, 112, 114. Deliver instructions for performing the operation.

In the case of performing joint processing between the multi-cell base stations, smooth joint processing is possible only when the signals transmitted from the multi-cell base station are synchronized with each other. Through this accurate synchronization, the terminal can effectively demodulate (demodulation) the signal transmitted from the multi-cell base station.

For synchronization between such multi-cell base stations, the multi-cell base station performing joint processing transmits data for joint processing to a physical resource block (PRB) at the same location in advance, thereby performing synchronization. It may be.

However, even if the data shared in the same physical resource block (PRB) is transmitted in advance after synchronization in advance between the multi-cell base stations, since the propagation delay of each cell base station is different on the receiving terminal side, the multi-cell There is a situation that the signals of the base station are not synchronized with each other. Therefore, a need exists for a method that can more accurately synchronize a multi-cell base station with each other.

The present invention proposes a method for accurately synchronizing multiple cell base stations performing a collaborative multiple input / output (Collaborative MIMO) method in a wireless communication system in a multi-cell environment. That is, according to the present invention, multi-cell base stations performing a collaborative MIMO method such as joint processing transmit data to the same physical resource block (PRB), and corresponding physical resource block (PRB). By setting a guard zone that changes according to the transmission delay value of a corresponding cell before and after), we propose a method for performing accurate synchronization between multi-cell base stations.

Hereinafter, a method for synchronizing between cells in a multi-cell environment according to the present invention will be described in detail with reference to FIG. 2. 2 is a flowchart illustrating an inter-cell synchronization method in a multi-cell environment according to the present invention.

Here, the serving base station 110 and the cooperative base stations 112 and 114 performing the cooperative multiple input / output method may use a physical resource block (PRB) having a guard zone Δt as shown in FIG. Sending data.

3 illustrates an example of a configuration of a radio resource used in the inter-cell synchronization method in a multi-cell environment according to the present invention. At this time, the guard zone is set before and after the corresponding Physical Resource Block (PRB) as shown in FIG.

First, the terminal 140 synchronizes with the serving base station 110 of the serving cell to which the terminal belongs (S210).

Subsequently, the transmission delay of the cooperative base stations 112 and 114 of the neighboring cell performing collaborative MIMO is measured based on it (S220). In this case, the terminal 140 may measure a transmission delay through a reference signal (RS) or a synchronous channel (SCH) from each cell base station.

The transmission delay information of the cooperative base stations 112 and 114 measured as described above is transmitted to the serving base station 110 by the terminal 140 (S230). Here, the transmission delay of the cooperative base stations 112 and 114 measured by the terminal 140 may be represented by a value corresponding to the difference based on the transmission delay of the serving base station 110. In addition, the difference value may be represented by a predetermined unit value (for example, 1 μs, 0.1 μs, or the like).

On the other hand, the difference value may be divided into unit intervals, and the value within the interval may be represented by a method of redefining. For example, the difference value may be divided into 5 μs unit intervals, and may be configured by bits representing the corresponding intervals and bits representing the values within the intervals.

In addition, the transmission delay measured by the terminal 140 may be represented by a relative value of a cyclic prefix (CP) that the serving base station 110 has. For example, the transmission delay of the cooperative base station (112,114) is measured and displayed in the 1/4 unit or 1/8 unit, or 1/16 unit or 1/32 unit of the CP that the serving base station 110 has, The serving base station 110 may be fed back. In this case, the transmission delay measured by the relative value of the cyclic prefix (CP) may be displayed and fed back as a different number of bits according to the unit and range of the relative value.

Thereafter, the serving base station 110 transmits the received transmission delay to the corresponding cooperative base station 112 and 114, respectively (S240). Based on the transmission delay information received as described above, the cooperative base stations 112 and 114 perform an operation for synchronization between cells.

Thereafter, each of the cooperative base stations 112 and 114 is shifted by its transmission delay (for example, Δt1) measured and fed back by the terminal 140, as shown in FIG. 3 (b). (I.e., Δt-Δt1) configures a Physical Resource Block (PRB) to transmit data (S250).

In this manner, the present invention changes the guard zone of the cooperative base station based on the transmission delay of the cooperative base station measured by the terminal, thereby preventing the timing of the signal from being shifted by the transmission delay of the cooperative base station. And multiple cell base stations can be synchronized with each other.

In the above, all the transmission delay information of the cooperative base station measured by the terminal is transmitted to the serving base station, but it is not necessarily configured as such. That is, as shown in Figure 4, it is also possible to configure the terminal to transmit the transmission delay information of the cooperative base station directly to each corresponding cooperative base station. 4 is a diagram illustrating another configuration example of a method for synchronizing between cells in a multi-cell environment according to the present invention.

In addition, in the above embodiment, the synchronization is performed by feeding back the transmission delay to all the cooperative base stations performing the Collaborative MIMO method and adjusting the transmission position of the data according to the received transmission delay. The present invention is not necessarily limited thereto.

That is, instead of feeding back a transmission delay for the entire cooperative base station performing the Collaborative MIMO method, the transmission delay may be fed back only to a specific cooperative base station. For example, the transmission delay may be fed back to the serving cell only when the transmission delay measured by the UE is greater than the CP (cyclic prefix) of the serving cell. In this case, the terminal may feedback the transmission delay only to the cooperative base station corresponding to a predetermined criterion, thereby reducing the amount of uplink data transmission for performing synchronization.

Meanwhile, in the above, a guard zone is set in the time domain to perform accurate synchronization between the multi-cell base stations. However, the present invention is a collaborative MIMO with a guard zone. The guard band may be set on both sides of the radio frequency used in the method.

FIG. 5 shows an example in which a guard band of a frequency domain is set together with a guard zone of a time domain in a radio resource used in a collaborative MIMO method. to be. FIG. 5 illustrates that a guard band in a frequency domain is set together with a guard zone in a time domain according to the present invention in a radio resource used in a collaborative MIMO method. It is a figure which shows an example.

As such, by setting a guard band in a radio frequency region used in a collaborative MIMO method, inter-subcarrier interference is reduced in an orthogonal frequency division modulation (OFDM) symbol. Can be. Through this, interference between the radio frequency domain for unicast and the radio frequency domain for a collaborative MIMO method may be reduced.

Hereinafter, as an embodiment of the present invention, a specific method of applying the present invention to a Long Term Evolution (LTE) system will be described with reference to FIG. 6. FIG. 6 is a diagram illustrating an example of setting a guard band in a frequency domain together with a guard zone in a time domain according to the present invention in a radio resource used in a Long Term Evolution (LTE) system. to be.

In the LTE system, downlink transmission is divided into a physical downlink control channel (PDCCH) region consisting of 1 to 3 symbols and a physical downlink shared channel (PDSCH) region consisting of 11 to 13 symbols. In order to apply the present invention to such an LTE system, as shown in FIG. 6, the present invention may be applied to a PDSCH region except for a PDCCH region (1 to 3 symbols). That is, the guard zone of the present invention is applied based on the PDSCH region except for the PDCCH region.

In more detail, the PDCCH region may be allocated from 1 symbol to 3 symbols. Accordingly, multiple cells performing collaborative MIMO may be performing downlink transmission using different PDCCH regions.

That is, when multiple cells perform downlink transmission using the same PDCCH region, each cell may apply the present invention from the time point when the PDCCH region ends. However, when downlink transmission is performed using different PDCCH regions, the same criteria for applying the present invention between multiple cells is required.

As an example, the present invention can be applied by assuming that the maximum symbol is 3 symbols regardless of the PDCCH region of the multiple cells, and is regarded as the PDSCH region from the fourth symbol. Alternatively, the present invention may be applied by determining a PDCCH region based on a cell using the most symbols among PDCCH regions of multiple cells performing collaborative MIMO and then setting the PDSCH region thereafter. . In this case, in the case of a cell using an area smaller than the number of symbols as the PDCCH, the remaining part may not be used or may be used for other data.

On the other hand, based on the PDCCH region of the serving cell, the present invention may be applied by forcibly adjusting and setting the PDCCH regions of neighboring cells performing collaborative MIMO. Alternatively, a predetermined PDCCH region (for example, PDCCH region = 1 at the time of performing joint processing) may be determined between multiple cells performing joint processing, and the present invention may be applied based on this.

Hereinafter, various methods that can be used to transmit transmission delay information of a cooperative base station performing a collaborative MIMO method from a terminal to a serving base station in the present invention will be described.

As described above, in order to perform the inter-cell synchronization method in the multi-cell environment of the present invention, a precoding matrix index (PMI) and a channel of a neighbor cell that performs a collaborative MIMO method. In addition to existing information such as channel quality information (CQI), transmission delay information should be transmitted to the serving base station.

Accordingly, in the present invention, a different physical uplink control channel (PUCCH) format may be used for transmission of transmission delay information. For example, the terminal measures the transmission delay is mapped in order from _{a 0, a 1, a 2} , ... a A-1 of a _0-bit channel quality of the transmission delay value of the cooperative base station (channel quality bit) sequence It can be mapped.

In addition, a mapping order of transmission delays may include, in advance, transmitting cell ID information of a cell base station performing a collaborative MIMO method, and transmitting corresponding transmission delay information to an interference degree ( can be transmitted in the order of interference level). On the other hand, the order of the cell ID may be set in advance, and the transmission delay information may be transmitted in the order of the preset cell ID. The measured transmission delays of adjacent cells may be transmitted in a small order or in a large order.

Meanwhile, when the UE feeds back the transmission delay in the predetermined order, it may be fed back using a differential encoding scheme. That is, based on the first transmission delay, the next transmission delay can be encoded and transmitted only for the amount of change from the first transmission delay. In this way, the number of bits transmitted can be reduced.

In addition, when the transmission delay of the cooperative base station performing the collaborative multiple input / output (Collaborative MIMO) method is transmitted, a precoding matrix index (PMI) and a wideband CQI (unicast) are used for unicast in the existing UE. It is also possible to transmit using the timing for transmitting the Quality Information.

In the present invention, the information that can be fed back from the terminal may include not only a transmission delay but also a PMI set, a cell ID, a CQI set, and the like. As such, when the information fed back from the terminal increases, the present invention may increase the number of transmissions for the feedback or use an extended format that may include more information.

For example, the first transmission timing may be configured to transmit only transmission delays for a predetermined number of cooperative base stations, and transmit transmission delays for the remaining cooperative base stations at a next transmission timing. In addition, in the case of transmitting other information as well as the transmission delay, a transmission delay is transmitted at the first transmission timing, a PMI set is transmitted at the next transmission timing, and a cell ID at the next transmission timing. , CQI set, etc. may be transmitted.

Meanwhile, in the present invention, when there is much feedback information for a cooperative base station, the feedback information may be transmitted through a physical uplink shared channel (PUSCH). In this case, the PUSCH (Physical Uplink Shared Channel) for transmitting the feedback information may be used in a manner of being allocated periodically or in a manner of being allocated aperiodically.

In the case of periodic allocation, the terminal may be notified of a predetermined period by using a flag such as a CQI report flag at the beginning of the collaborative MIMO method. On the other hand, when a non-periodic assignment is performed, the base station uses a flag to flag a PUSCH (Physical Uplink Shared Channel) at a point in time when feedback from the corresponding UE is required. Can be assigned. In this case, the feedback information may be multiplexed with the data information, or only the corresponding feedback information may be transmitted.

The feedback information transmitted from the terminal through the physical uplink shared channel (PUSCH) includes a PMI set, a cell ID, a CQI set, as well as transmission delay information for the cooperative base station measured by the terminal. The method of transmitting such information may include the above-described Physical Uplink Control Channel (PUCCH). You can use the same method as in.

That is, the cell base station may transmit cell ID information for performing a collaborative MIMO method in advance, and transmit corresponding transmission delay information in the order of interference level. The order of the cell ID may be set in advance, and the transmission delay information may be transmitted in the order of the preset cell ID. In addition, the measured transmission delay of the cooperative base station may be transmitted in a small order, or the transmission delay may be transmitted in a large order, or may be fed back using a differential encoding scheme.

As described above, according to the inter-cell synchronization method in a multi-cell environment according to the present invention, multi-cell base stations, particularly joint processing, performing a collaborative MIMO method in a multi-cell environment It is possible to accurately synchronize the multi-cell base station to perform each other, thereby improving the communication performance of the terminal located at the cell edge.

Various embodiments have been described to illustrate the original idea associated with the various aspects of the invention. However, one or more specific features in one particular embodiment may apply to one or more other embodiments. Some components or steps described in each embodiment and its associated drawings may be modified and may include, delete, move, or include additional components and / or steps.

The various spirits and characteristics described herein may be embodied in various forms within the features of the present invention, and the above-described embodiments are not limited by the above-described detailed description, unless explicitly stated. It should be interpreted broadly within the scope defined by the scope. Therefore, all changes and modifications falling within the scope or the equivalent thereof are included in the appended claims.

1 is a schematic structural diagram schematically illustrating a configuration of a multi-cell communication system for performing a cooperative multiple input / output method.

 2 is a flowchart illustrating an inter-cell synchronization method in a multi-cell environment according to the present invention.

3 illustrates an example of a configuration of a radio resource used in the inter-cell synchronization method in a multi-cell environment according to the present invention.

4 is a diagram illustrating another configuration example of a method for synchronizing between cells in a multi-cell environment according to the present invention.

FIG. 5 is a diagram illustrating an example of setting a guard band in a frequency domain together with a guard zone in a time domain in a radio resource used in a collaborative MIMO method. .

FIG. 6 is a diagram illustrating an example of setting a guard band in a frequency domain together with a guard zone in a time domain according to the present invention in a radio resource used in a Long Term Evolution (LTE) system. .

Claims (9)

A method for synchronizing multiple cells performing a cooperative multiple input / output method, Measuring a transmission delay for the cooperating base station; Delivering the measured transmission delay to a serving base station; And And when the serving base station transmits the transmission delay to the cooperative base station, receiving data for cooperative multi-input / output with a transmission position adjusted based on the transmission delay from the cooperative base station. How to sync between. The method of claim 1, The coordination base station adjusts a transmission position of data for the cooperative multiple input / output by adjusting a guard zone in a time domain set in a radio resource used for the cooperative multiple input / output. Method for synchronizing between cells in a multi-cell environment, characterized in that. The method of claim 2, The radio resource used for the cooperative multiple input and output, the guard band (guard band) is set in the frequency domain, characterized in that the inter-cell synchronization in a multi-cell environment. The method of claim 1, The transmission delay measurement for the cooperative base station is performed using at least one of a reference signal (RS) or a synchronization channel (SCH) of each base station. The method of claim 1, The transmission delay measurement result for the cooperative base station is expressed as a difference value based on the transmission delay of the serving base station. The method of claim 1, The transmission delay measurement result for the cooperative base station is represented by a relative value of the cyclic prefix (CP) of the serving base station, characterized in that the inter-cell synchronization in a multi-cell environment. The method of claim 1, The transmitting of the measured transmission delay to the serving base station may include transmitting to the serving base station only when the transmission delay is greater than a predetermined length. The method of claim 1, In the transmitting of the measured transmission delay to the serving base station, the transmission delay is transmitted to the serving base station through a physical uplink control channel (PUCCH) or a physical uplink shared channel (PUSCH). How to sync between cells. 3. The method of claim 2, The protected area is applied to a physical downlink shared channel (PDSCH) area except for a physical downlink control channel (PDCCH) area.

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