KR20120077474A - Method for transmitting, passing and using information of downlink subframe pattern - Google Patents

Abstract

The present invention relates to a method and an apparatus for transmitting, transmitting, and using information about a downlink subframe pattern for coordinating inter-cell interference in a communication system. The present invention relates to transmitting information about a downlink subframe pattern according to the present invention. The method includes selecting a subframe pattern to be applied to downlink transmission on a pattern table consisting of an applicable subframe pattern and a pattern index corresponding to the subframe pattern, and transmitting a pattern index corresponding to the selected subframe pattern. Include.

Description

Transmission method, transmission method and method of using downlink subframe pattern information {METHOD FOR TRANSMITTING, PASSING AND USING INFORMATION OF DOWNLINK SUBFRAME PATTERN}

The present invention relates to a wireless communication system, and more particularly, to a method for controlling inter-cell interference and an apparatus using the same.

The 3rd Generation Partnership Project (3GPP) long term evolution (LTE), an enhancement of Universal Mobile Telecommunications System (UMTS), is introduced as 3GPP release 8. 3GPP LTE uses orthogonal frequency division multiple access (OFDMA) in downlink and single carrier-frequency division multiple access (SC-FDMA) in uplink. A multiple input multiple output (MIMO) with up to four antennas is employed. Recently, a discussion on 3GPP LTE-Advanced (LTE-A), an evolution of 3GPP LTE, is underway.

With the development of wireless communication technology, a heterogeneous network (hetero network) environment has emerged.

In the hetero network environment, a micro cell such as a femto cell and a pico cell is used together with a macro cell. A micro cell is a system that covers an area smaller than a radius of an existing mobile communication service when compared to a macro cell.

In such a communication system, a user terminal located in one cell may experience inter-cell interference in which signal interference is caused by a signal generated from another cell.

An object of the present invention is to provide a method for accurately transmitting information on a femto cell specific ABS pattern in a hetero network to a macro cell base station.

It is an object of the present invention to provide a method in which a macro cell base station can limit measurement of a terminal of a macro cell based on information on a femto cell specific ABS pattern in a hetero network.

An object of the present invention is to provide a method for coordinating inter-cell interference in a hetero network and facilitating network operation.

An aspect of the present invention is a method for transmitting information about a downlink subframe pattern for coordinating inter-cell interference in a communication system, comprising: a pattern table including an applicable subframe pattern and a pattern index corresponding to the subframe pattern A subframe pattern to be applied to downlink transmission is selected, and a pattern index corresponding to the selected subframe pattern is transmitted.

The subframe pattern constituting the pattern table may be defined by the number of low interference subframes per frame or the number of low interference subframes constituting the applicable downlink subframe pattern.

The pattern index corresponding to the selected subframe pattern may be transmitted on the PDSCH using SIB1 / SIB2 or on the PBCH using MIB.

After transmitting the pattern index corresponding to the selected subframe pattern, if the inter-cell interference persists, the pattern index may be retransmitted.

Another aspect of the present invention is a method for transmitting information about a downlink subframe pattern for coordinating inter-cell interference between a first cell and a second cell in a communication system, the method comprising: applying a downlink subframe pattern; Receiving a pattern index of the downlink subframe pattern from the one-cell base station, and transmitting information on the received downlink subframe pattern index to the second cell base station, wherein the pattern index may be applied by the first cell base station; The first cell base station and the second cell base station correspond to a subframe pattern selected by the first base station on a pattern table composed of subframe patterns.

In this case, when it is determined that the interference between cells exceeds a predetermined reference value, the interference message may be transmitted to the first cell.

The measurement of the communication environment with the second base station is performed based on the measurement limit received from the second cell base station, and the measurement limit received from the second cell base station is information on the downlink subframe pattern index of the second base station. Can be transmitted based on.

Another aspect of the present invention is a method of using information about a downlink subframe pattern for coordinating intercell interference in a communication system, the method comprising: from a base station of a cell applying the downlink subframe pattern for coordinating intercell interference; Downlink applied by a cell base station based on a pattern table configured to receive information on a downlink subframe pattern through a user equipment and to configure a downlink subframe pattern that can be applied by the base station of the cell. Recognizing the link subframe pattern, and transmits a measurement limit message for measuring the communication environment in the low interference subframe on the recognized downlink subframe pattern to the terminal affected by the interference from the cell.

According to the present invention, information on a femto cell specific ABS pattern can be accurately transmitted to a macro cell base station in a hetero network.

According to the present invention, based on the information on the femto-cell specific ABS pattern in the hetero network, the macro cell base station can limit the measurement of the terminal of the macro cell, so that accurate measurement of the communication environment can be made. Based on this, it is possible to smoothly perform an operation required for network operation such as downlink scheduling.

1 is a block diagram illustrating a wireless communication system.
2 is a block diagram illustrating functional division between an E-UTRAN and an EPC.
3 is a block diagram illustrating a radio protocol structure for a user plane.
4 is a block diagram illustrating a radio protocol architecture for a control plane.
5 is a diagram schematically illustrating a concept of a hetero network including a macro cell, a femto cell, and a pico cell.
6 is a conceptual diagram schematically illustrating a configuration of a femto cell.
7 is a schematic illustration of a network structure for operating an HNB using an HNB gateway.
8 is a diagram schematically illustrating that a user terminal is affected by interference between a macro cell and a femto cell in downlink.
9 is a diagram schematically illustrating an example of downlink subframe patterns of a macro cell and a femto cell.
10 is a diagram schematically illustrating a concept of uplink HARQ.
11 to 13 are exemplary views schematically illustrating various models of an ABS pattern of a femto cell.
14 is a flowchart schematically illustrating that information about an ABS pattern of a femto cell is transmitted to a macro cell using an ABS pattern table.
15 is a flowchart schematically illustrating a method of applying an ABS pattern by a femto cell base station.
16 is a block diagram schematically illustrating a configuration of a femto cell base station, a macro cell terminal, and a macro cell base station in a hetero network to which the present invention is applied.

The present invention relates to a communication system in which a micro cell exists in a macro cell and a micro cell, that is, a method for controlling inter-cell interference with respect to a hetero network (Inter Cell Interference Coordination (ICIC)).

By controlling downlink transmission of a cell that is an aggressor in inter-cell interference in units of time, the downlink of the aggregator cell base station is performed without performing a separate operation at a base station of a cell that is a Victim in inter-cell interference. The influence of interference due to link transmission can be reduced. According to the present invention, the Victim cell can effectively grasp the control pattern for downlink transmission of the aggregator cell. Therefore, it is possible to greatly reduce the influence of the user of the Big Team cell by the inter-cell interference.

Hereinafter, the contents related to the present invention will be described in detail with reference to exemplary drawings and embodiments, together with the contents of the present invention. It should be noted that, in adding reference numerals to the constituent elements of the drawings, the same constituent elements are denoted by the same reference symbols as possible even if they are shown in different drawings. In addition, in describing the embodiments of the present specification, when it is determined that the detailed description of the related well-known configuration or function may obscure the subject matter of the present specification, the detailed description thereof will be omitted.

In addition, in describing the components of the present specification, terms such as first, second, A, B, (a), and (b) may be used. These terms are intended to distinguish the constituent elements from other constituent elements, and the terms do not limit the nature, order or order of the constituent elements. If a component is described as being "connected", "coupled", or "connected" to another component, that component may be directly connected or connected to that other component, but there is another component between each component. It will be understood that may be "connected", "coupled" or "connected".

In addition, the present invention will be described with respect to a wireless communication network. The work performed in the wireless communication network may be performed in a process of controlling a network and transmitting data by a system (e.g., a base station) Work can be done at a terminal connected to the network.

1 is a block diagram illustrating a wireless communication system. This may be a network structure of 3GPP LTE / LTE-A. The E-UTRAN (Evolved-UMTS Terrestrial Radio Access Network) includes a base station 20 (BS) that provides a control plane and a user plane to a user equipment (UE) 10. do.

The terminal 10 may be fixed or mobile and may be called by other terms such as a mobile station (MS), a user terminal (UT), a subscriber station (SS), a mobile terminal (MT), and a wireless device. .

The base station 20 refers to a fixed station communicating with the terminal 10, and may be referred to by other terms such as an evolved-NodeB (eNB), a base transceiver system (BTS), an access point, and the like.

One or more cells may exist in one base station 20. In this case, the cell should be interpreted as a comprehensive meaning indicating a partial area covered by the base station 11 and encompasses various coverage areas such as a mega cell, a macro cell, a micro cell, a pico cell, a femto cell, a relay, and the like.

An interface for transmitting user traffic or control traffic may be used between the base stations 20. The base stations 20 may be connected to each other through an X2 interface.

The base station 20 is connected to a Mobility Management Entity (MME) through an Evolved Packet Core (EPC), more specifically, S1-MME through an S1 interface, and a Serving GateWay (S-GW) through S1-U. The S1 interface supports a many-to-many-relation between the base station 20 and the MME / SAE gateway 30.

Hereinafter, downlink means communication from the base station 20 to the terminal 10, and uplink means communication from the terminal 10 to the base station 20. In downlink, the transmitter may be part of the base station 20 and the receiver may be part of the terminal 10. In addition, in uplink, the transmitter may be part of the terminal 10 and the receiver may be part of the base station 20.

2 is a block diagram illustrating a functional split between an E-UTRAN and an EPC. The hatched box represents the radio protocol layer and the white box represents the functional entity of the control plane. Describe the function of each functional entity.

The base station performs the following functions.

(1) Radio resource management such as radio bearer control, radio admission control, connection mobility control, and dynamic resource allocation to a terminal ; RRM) function. (2) Internet Protocol (IP) header compression and encryption of user data streams. (3) Routing of user plane data to S-GW. (4) Scheduling and sending of paging messages. (5) Scheduling and transmission of broadcast information. (6) Set up measurements and measurement reports for mobility and scheduling.

The MME performs the following functions.

(1) Non-Access Stratum (NAS) signaling. (2) NAS signaling security. (3) idle mode UE Reachability, (4) tracking area list management. (5) Roaming Functions (6) Authentication.

S-GW performs the following functions.

(1) mobility anchoring. (2) lawful interception.

P-GW (P-Gateway) performs the following functions.

(1) Terminal IP (Internet Protocol) allocation. (2) packet filtering.

3 is a block diagram illustrating a radio protocol architecture for a user plane. 4 is a block diagram illustrating a radio protocol structure for a control plane. The data plane is a protocol stack for user data transmission, and the control plane is a protocol stack for control signal transmission.

3 and 4, a physical layer (PHY) provides an information transfer service to a higher layer by using a physical channel. The physical layer is connected to the upper layer MAC (Medium Access Control) layer through a transport channel.

Data travels between the MAC and physical layers over the transport channel. Transport channels are classified according to how and with what characteristics data is transmitted over the air interface. 3GPP LTE / LTE-A includes the following transport channels.

The BCH (Broadcast Channel) has a fixed transmission format by standard, and is used to transmit some of Broadcast Control Channel (BCCH) system information such as a master information block (MIB).

A paging channel (PCH) is used to transmit paging information from a paging control channel (PCCH), which is a logical channel, and may use discontinuous reception (DRX) so that the UE can receive the PCH only in a predetermined time interval.

Downlink Shared Channel (DL-SCH) is a main transport channel used for downlink data transmission.

Multicast Channel (MCH) is used to support Multimedia Broadcast / Multicast Service (MBMS), and may use semi-static transmission format and scheduling.

The UL-SCH (Uplink Shared Channel) is a channel for transmitting uplink data and may be referred to as a channel corresponding to the DL-SCH.

Random Access Channel (RACH) is a transport channel used for random access, but does not carry a transport block.

Meanwhile, data moves between physical layers, that is, between physical layers of a transmitter and a receiver. In the physical layer, a physical control channel may be used.

The physical downlink control channel (PDCCH) informs the terminal of resource allocation of a paging channel (PCH) and downlink shared channel (DL-SCH) and hybrid automatic repeat request (HARQ) information related to the DL-SCH. The PDCCH may carry an uplink scheduling grant informing the UE of resource allocation of uplink transmission.

PDSCH (Physical Downlink Shared Channel) is the primary physical channel for unicast (unicast) transmission, can also be used for the transmission of paging information.

The Physical Control Format Indicator Channel (PCFICH) is a channel that provides information required for decoding the PDCCH, such as informing the UE of the number of OFDM symbols used for the PDCCHs, and is transmitted every subframe.

Physical Hybrid ARQ Indicator Channel (PHICH) carries an HARQ ACK / NAK signal for uplink transmission.

Physical Uplink Control Channel (PUCCH) carries uplink control information such as HARQ ACK / NAK, scheduling request, and CQI for downlink transmission.

The PUSCH (Physical Uplink Shared Channel) carries an UL-SCH (Uplink Shared Channel) and may be referred to as a channel corresponding to the PDSCH.

PBCH (Physical Broadcast Channel) transmits a part of information required for the terminal to access the network.

Physical Multicast Channel (PMCH) is used for Multicast-Broadcast Single Frequency Network (MBSFN) operation, and Physical Random Access Channel (PRACH) is used for random access.

Functions of the MAC layer include mapping between logical channels and transport channels and multiplexing / demultiplexing into transport blocks provided as physical channels on transport channels of MAC service data units (SDUs) belonging to the logical channels.

The MAC layer provides a service to a Radio Link Control (RLC) layer through a logical channel. The logical channel may be divided into a control channel for transmitting control region information and a traffic channel for delivering user region information.

Functions of the RLC layer include concatenation, segmentation, and reassembly of RLC SDUs.

In order to guarantee the various quality of service (QoS) required by the radio bearer (RB), the RLC layer uses a transparent mode (TM), an unacknowledged mode (UM), and an acknowledged mode. , Three modes of operation (AM). AM RLC provides error correction through Automatic Repeat reQuest (ARQ).

Functions of the Packet Data Convergence Protocol (PDCP) layer in the user plane include delivery of user data, header compression, and ciphering. Functions of the PDCP layer in the user plane include the transfer of control plane data and encryption / integrity protection.

The RRC (Radio Resource Control) layer is defined only in the control plane. The RRC layer is responsible for the control of logical channels, transport channels and physical channels in connection with the configuration, re-configuration and release of radio bearers.

The radio bearer (RB) refers to a logical path provided by the first layer (PHY layer) and the second layer (MAC layer, RLC layer, PDCP layer) for data transmission between the terminal and the network. The establishment of the RB means a process of defining characteristics of a radio protocol layer and a channel to provide a specific service, and setting each specific parameter and operation method.

The radio bearer RB may be divided into two types, a signaling RB (SRB) and a data RB (DRB). The SRB is used as a path for transmitting the RRC message in the control plane, and the DRB is used as a path for transmitting the user data in the user plane.

The non-access stratum (NAS) layer located above the RRC layer performs functions such as session management and mobility management.

On the other hand, the quality of each radio link changes rapidly and to some extent randomly within the cell of mobile radio communication, and this change must be considered in order to effectively operate the communication system.

A scheduler is one way to deal with this quality link change. The downlink scheduler generally includes a round-robin (RR) scheduler in which terminals alternately use shared resources without considering channel status, and a terminal having an absolute best downlink channel status is scheduled. -C / I scheduler (also known as maximum rate scheduler), a PF (Proportional-Fair) scheduler that allocates shared resources to the terminal with the highest radio link state but limits the long-term quality of service difference between terminals to a certain level or less. For example, the greedy filling scheduler is mainly used in non-orthogonal multiple access.

Unlike the downlink in which the power resources are concentrated in the base station, in the uplink, the power resources are divided among the terminals. In addition, the maximum uplink transmission power of a single terminal is generally significantly lower than the output of the base station. In this regard, uplink scheduling may be different from downlink scheduling, but the above-described scheduling principles for downlink may also be applied to uplink.

Although there are various scheduling schemes, the scheduling algorithm or the scheduling strategy itself is generally a matter of (base station) implementation, so other standards, including 3GPP, do not specifically standardize it. However, almost all service providers attempt to effectively use radio resources in a cell while maintaining an appropriate quality of service (QoS) between users in base station construction and wireless communication system operation. Therefore, a terminal having a relatively advantageous channel condition by using a channel change between terminals while guaranteeing the same average user throughput for all terminals or a certain minimum user throughput for at least all terminals. Scheduling is the overall goal of most schedulers.

As such, there may be a significant gain in system capacity if the state of the channel is taken into account for scheduling. Scheduling according to channels is used in HSPA / HSUPA or LTE. In case of LTE, not only the channel change in the time domain but also the channel change in the frequency domain can be considered.

In order to schedule according to the channel state in the downlink, the terminal may transmit a channel-status report based on the measurement to the base station. The channel status report may include instantaneous channel quality in the time and / or frequency domain. In case of spatial multiplexing, information necessary for antenna processing may also be included in the channel status report.

The channel state report is a report regarding transmission settings and / or parameters determined by the terminal to be suitable for use when transmitting the DL-SCH to the corresponding terminal. The UE determines transmission configuration and / or parameters based on the downlink instantaneous channel state. The channel status report may be configured according to a setting, and may include one or more of the following indicators.

Rank indicator (RI) is an indicator transmitted only when the terminal supports spatial multiplexing, and provides information on the rank of the channel, that is, the number of layers desired to be used for downlink transmission to the terminal. do.

Precoder Matrix Indicator (PMI) is an indicator reported only when the UE is in a closed-loop spatial multiplexing mode and provides information on a precoder matrix that is desired to be used for downlink transmission. In this case, the reported precoder matrix is determined based on the number of layers reported through the rank indicator.

Channel-Quality Indicator (CQI) indicates a modulation scheme and coding rate that are desired to be used for downlink transmission.

The base station does not have to follow the manner in which these indicators recommand. For example, for the precoder, when the base station follows the channel status report, it is only necessary to confirm that the precoder setting indicated by the precoder matrix indicator is used for downlink transmission. If the base station does not follow the channel status report, information about the precoder used should be explicitly included in the downlink scheduling assignment.

In the case of LTE, the channel status report may be periodic or aperiodic. In the aperiodic case, when there is an explicit request from the base station, a channel status report is sent to the base station. The base station or the network may request a channel status report by including a flag for requesting a channel status report in an uplink scheduling grant or the like.

In the case of periodic channel status report, the channel status report is transmitted from the terminal to the base station at a predetermined period. The above-mentioned different information, for example, rank indicator, precoder matrix indicator, channel quality indicator, etc., need not all be reported in the same period or the same number of times. In general, the periodic channel status report may be delivered to the base station through the PUCCH physical channel.

Channel-based scheduling is generally used for downlink transmission, but channel-based scheduling may also be used for uplink transmission. In the case of scheduling according to channel state in uplink, a sounding reference signal (SRS) transmitted from each terminal may be generally used for estimating channel quality at the base station.

As such, what is basically needed at the transmitting side is an estimate that reflects the channel state at the moment of transmission. That is, in order to schedule considering the instantaneous channel state, the instantaneous channel state information is required. However, the network must also know the state of communication within the cell for other purposes.

The terminal continuously or at a specific time point measures the communication quality of a serving cell currently providing a service and the communication quality of a neighbor cell around the serving cell. The terminal transmits the communication quality of the measured cells to the base station according to the base station's request, the terminal's own needs, or according to predetermined rules or instructions, and the base station sends a handover command to the terminal based on the measured value reported by the terminal. You can also get off.

Meanwhile, in a heterogeneous network in which heterogeneous cells exist in the same space, coordination between different cells constituting the hetero network needs to be considered along with scheduling for the terminal.

Hereinafter, a heterogeneous network will be described.

Simple cell division of macro and micro cells is difficult to meet the growing demand for data services. Accordingly, data services for indoor and outdoor small areas can be operated using micro cells such as pico cells and femto cells. Although the use of micro cells is not particularly limited, pico cells can generally be used in communication shadow areas that are not covered only by macro cells, or in areas with high data service requirements, so-called hot zones. Femtocells can generally be used in indoor offices or at home.

The configuration of a hetero network not only eliminates the shadow area of the data service but also increases the data transfer rate.

5 is a diagram schematically illustrating a concept of a hetero network including a macro cell, a femto cell, and a pico cell. Although FIG. 5 illustrates a hetero network including a macro cell, a femto cell, and a pico cell for convenience of description, the hetero network may include a relay or another type of cell.

Referring to FIG. 5, a macro cell 510, a femto cell 520, and a pico cell 530 are operated together in a hetero network. The macro cell 510, the femto cell 520, and the pico cell 530 each have their own cell coverages 510, 520, and 530.

A femto cell is a low power wireless access point, which is a small base station for mobile communication used indoors such as a home or an office. A femto cell can access a mobile communication core network using DSL or cable broadband in a home or office.

6 is a conceptual diagram schematically illustrating a configuration of a femto cell.

Referring to FIG. 6, a femtocell base station 620 in a home 610 or office is connected to a mobile communication network 640 via a high speed internet 630. The terminal 650 in the femto cell may access the mobile communication network or the high speed internet through the femto cell base station 620.

On the other hand, the femto cells may be supported with a self-organization (Self-Organization) function. Required. Self-organization functions are classified into a self-configuration function, a self-optimization function, and a self-monitoring function.

Self-configuration is a feature that allows a wireless base station to be installed on its own based on an initial installation profile without going through a cell planning step.

Self-Optimization is a function that identifies neighboring base stations, obtains information, optimizes the neighboring base station list, and optimizes coverage and communication capacity according to subscriber and traffic changes.

Self-Monitoring is a function to control service performance not to be degraded through collected information.

Plug and play functionality is required to support self-configuration in femtocells. This includes obtaining an IP address, setting RF / Radio parameters and / or network parameters, installing software, recognizing and / or authenticating base stations, and security procedures such as authentication / authorization can also be performed without the help of an operator.

For user convenience, continuity for voice / data services may be ensured between the macro cell and the femto cell. In addition, the femtocell may distinguish registered users from unregistered users and allow access only to registered users. Cells that allow access only to registered users are called Closed Subscriber Groups (hereinafter referred to as "CSGs"), and access to normal users is also referred to as open access. It is also possible to mix these two methods.

A base station providing a CSG service is called a home node b (HNB) or a home enode b (henb) in 3GPP. Hereinafter, in the present specification, both HNB and HeNB are collectively referred to as HNB. The HNB basically aims to provide specialized services only to members belonging to the CSG. However, the service may be provided to other users besides the CSG according to the operation mode setting of the HNB.

7 is a schematic illustration of a network structure for operating an HNB using an HNB gateway (GW).

The HNBs are connected to the EPC or directly to the EPC via the HNB GW. Here, the HNB GW looks like a normal base station to the MME. The HNB GW also looks like the MME to the HNB. Therefore, the HNB and the HNB GW are connected to the S1 interface, and the HNB GW and the EPC are also connected to the S1 interface. In addition, when the HNB and the EPC are directly connected, they are connected to the S1 interface. The function of the HNB is mostly the same as that of a general base station.

In general, the HNB has a lower wireless transmission power than the BS owned by the mobile network operator. Therefore, the coverage provided by the HNB is generally smaller than the service area provided by the BS. Due to this characteristic, a cell provided by an HNB may be classified as a femto cell in comparison with a macro cell provided by a BS from a service area perspective.

In terms of providing a service, when the HNB provides a service only to the CSG group, a cell provided by the HNB is referred to as a CSG cell.

HNB does not always need to allow access to the CSG terminal. In addition, depending on the configuration of the HNB, it is possible to allow the connection of the terminal other than the CSG member. Which UE is allowed to access depends on the configuration setting of the HNB, where the configuration setting refers to the setting of the operation mode of the HNB. The operation mode of the HNB is classified into three types according to which UE provides a service.

1) Closed access mode: A mode in which services are provided only to specific CSG members. The HNB provides a CSG cell.

2) Open access mode: A mode in which a service is provided without a specific CSG member such as a general BS. The HNB provides a generic cell that is not a CSG cell.

3) Hybrid access mode: A mode that can provide a CSG service to a specific CSG member and provide a service to a non-CSG member like a normal cell, and is recognized as a CSG cell by a CSG member UE. The CSG member UE is recognized as a normal cell. Such a cell is called a hybrid cell.

When a femto cell is in an open access mode in a hetero network in which a femto cell is operated together with a macro cell, a user may access a desired cell among a macro cell and a femto cell to use a data service.

If the femto cell is in, for example, a closed mode, the end user using the macro cell will not be able to use the femto cell even if the macro cell is interfering with the femto cell transmitting a strong signal.

In addition, as shown in FIG. 7, the base stations BS of the macro cell are connected to each other through an X2 interface. The X2 interface not only supports seamless and lossless handovers between base stations, but also balances network load and supports management of radio resources. Accordingly, the X2 interface plays a large role in inter-cell interference coordination (ICIC) between base stations of a macro cell to be described later.

In contrast, there is no X2 interface between the base station of the macro cell and the base station of the femto cell. Accordingly, between the base station of the macro cell and the base station of the femto cell, dynamic signaling is not performed as between the BSs of the macro cell.

Unlike the femto cell, in the pico cell, there is an X2 interface between the base station of the pico cell and the base station of the macro cell. Accordingly, dynamic signaling is performed between the base station of the pico cell and the base station of the macro cell, and even if the SON function is not supported in the pico cell, the pico cell can detect information of an adjacent macro cell. In addition, unlike a femto cell, a pico cell is not operated in a closed subscriber group (CSG), and when a user is located within a cell range of the pico cell, the pico cell may be connected to the pico cell without limitation. In other words, unlike the interference between the macro cell and the femto cell in the hetero network, the interference between the macro cell and the defendant cell may be dynamically adjusted through the X2 interface. Therefore, in the present specification, unless otherwise stated, the interference between the macro cell and the femto cell will be described.

8 is a diagram schematically illustrating that a user terminal is affected by interference between a macro cell and a femto cell in downlink.

Referring to FIG. 8, the user terminal 950 may access the femto cell 930 and use the femto cell. However, if the femto cell 930 is in the CSG mode and the user terminal 960 near the HNB is not a registered user terminal of the CSG, the user terminal 960 cannot connect to the femto cell with strong signal strength, and the femto cell Compared to the signal strength of, the only way to access the macro cell is weak signal strength. Thus, in this case the user terminal 960 may be affected by interference from the femto cell.

For Inter-Cell Interference between a macro cell and a femto cell, a Victim cell that is more affected by the interference or needs to be more protected from the interference is a macro cell. On the other hand, an aggressor cell that affects or is less affected by the Victim cell by the interference is a femto cell. In general, the interference of the weak signal of the macro cell is greater than the strong signal output from the base station of the nearby femto cell, because there are much more users of the macro cell than the user of the femto cell.

Inter-Cell Interfernce Coordination (ICIC) is a method of reducing inter-cell interference.

In general, inter-cell interference coordination is a method for supporting a reliable communication to a user when a user belonging to a Victim cell is near an aggregator cell. In order to coordinate inter-cell interference, for example, a scheduler may be imposed on the use of certain time and / or frequency resources. It may also impose a constraint on the scheduler how much power to use for a particular time and / or frequency resource. In order to coordinate interference between adjacent cells, a downlink subframe pattern of cells may be configured.

Hereinafter, a configuration of a subframe pattern for reducing intercell interference in a communication system will be described.

As described above, since there is no X2 interface between the base station of the macro cell and the base station of the femto cell, the downlink subframe pattern of the macro cell and the femto cell is either static or semi-static. good. Herein, the pattern of subframes refers to an arrangement of subframes repeated at regular periods. In this case, the pattern of the subframe may be composed of various subframes. For example, the pattern of the subframe may be configured by repeating an arrangement of low interference subframes that generate less interference between cells, such as a normal subframe and an almost blank subframe (ABS), at regular intervals, as described below. have.

Downlink in LTE has a subframe pattern of 40 ms (milliseconds) in a frequency division duplex (FDD) scheme. In the 40 ms subframe, there is a subframe that the base station must transmit in downlink. For example, an uplink HARQ, a PBCH, a PSS / SSS, a MIB, a paging message, and an SIB-1 should be transmitted by a base station as accurately as possible with downlink.

9 is a diagram schematically illustrating an example of downlink subframe patterns of a macro cell and a femto cell. As shown in FIG. 9, the HARQ ACK / NACK signal transmission of the base station is performed in 8 ms units, and the retransmission of the terminal is also performed in 8 ms units. Therefore, up to four HARQ ACK / NACK signals may be transmitted in a 40 ms subframe configuration and retransmission of uplink data may be performed accordingly.

As described above, the base station must deliver uplink HARQ, PBCH, PSS / SSS, MIB, paging message, SIB-1, etc. as accurately as possible downlink for system operation.

Physical Broadcast Channel (PBCH) is a physical channel that conveys basic system information that allows other channels to be configured and operated in a cell. PBCH is transmitted in a broadcast manner. In order for the system to operate successfully, coverage capable of receiving broadcast channels over which the PBCH is transmitted is important. In addition, the PBCH should be able to receive even if the system band is not known in advance, have a low system overhead, and have a high reception reliability at the cell boundary.

Primary Synchronization Signal (PSS) and Secondary Synchronization Signal (SSS) are signals transmitted in downlink to help cell search. When the PSS is detected, the physical layer cell ID and slot synchronization can be obtained. When the SSS is detected, the length of the cyclic prefix (CP), the physical layer cell group ID, and frame synchronization can be obtained. When the user terminal acquires the frame synchronization and the physical layer cell ID, the user terminal may know what a corresponding cell specific reference signal is and start channel estimation.

System Information Block (SIB) constitutes system information, each containing a set of functionally-related parameters. Among the SIBs, the MIB (Master Information Block) is delivered on the PBCH and consists of a limited number of the most frequently transmitted parameters necessary for initial access to the cell. The MIB includes information on downlink cell bandwidth, information on PHICH configuration of a cell, and a system frame number (SFN) of a system. SIB (System Information Block) -1 of the SIB mainly includes information related to whether the user terminal is located in the cell. In addition, SIB-1 has information on scheduling on the time domain of the remaining SIBs.

The paging message is used to establish a network initiated connection. In the idle state, the terminal monitors the paging channel to detect an incoming call and obtain system information. In the idle state, the user terminal is only required to receive a paging message at a normal paging occassion. Therefore, in order to increase the reliability of reception, the paging message for notifying the change of the system information is a change of the Broadcast Control Channel (BCCH), which is a logical channel for transmitting system information from the network to all user terminals in the cell. It is sent repeatedly during the period.

Uplink HARQ and control information such as PBCH, PSS / SSS, MIB, SIB-1, paging message, etc. are transmitted according to a certain rule.

For example, an uplink HARQ ACK / NACK signal is transmitted at 8 ms intervals, that is, at 8 subframe intervals.

10 is a diagram schematically illustrating a concept of uplink HARQ.

Referring to FIG. 10, the base station (BS) transmits an UL grant to the user equipment (UE) on the PDCCH. The uplink grant is a message for distribution of uplink transmission resources. The user terminal receiving the uplink grant from the base station transmits data to the base station on the PUSCH after the fourth subframe based on the subframe in which the base station transmits the uplink grant. After transmitting the uplink grant, the base station transmits ACK (ACKnowledgement) / NACK (Not-ACKnowledgement) information indicating whether data is normally received after eight subframes, that is, after 8 ms. The uplink HARQ ACK / NACK signal is transmitted on the PHICH. In the 40ms downlink subframe configuration, 4 HARQ ACK / NACK signals can be transmitted. Even if the base station does not succeed in decoding the data received from the user terminal, it is possible to retransmit data by transmitting a NACK signal to the user terminal up to the maximum number of retransmissions set through the Radio Resource Control (RRC) layer.

PBCH (Physical Broadcast Channel) is transmitted in the middle resource block (RB) of subframe 0, PSS (Primary Synchronization Signal) and SSS (Secondary Synchronization Signal) is the center resource of subframe 0 and 5 Transmitted in blocks (RBs).

In addition, the master information block (MIB) of the SIB is transmitted to the resource blocks (RBs) of the subframe 0, and the SIB (System Information Block) -1 is transmitted to the subframe 5 of the even-numbered frame.

In paging message transmission, the paging message may be divided into three types according to the number of transmission of the paging message per 40ms subframe, that is, the transmission pattern of the paging message. Type 1 with paging message sent to subframe 9, Type 2 with paging message sent with subframes 4 and 9, and Type 3 with paging message sent with subframes 1, 4, 5 and 9. There is this. The transmission of the paging message has a cell specific period, and each cell transmits the paging message according to any one of types 1 to 3 in any one of 32 frames, 64 frames, 128 frames, and 256 frames. For example, a cell having a period of 32 frames and transmitting a paging message according to type 1 transmits a paging message in 9 subframes every frame during 32 frames.

For example, when a macro cell and a femto cell use the same resource, if the downlink transmission of cells is completely synchronized, subframes in which important information is transmitted for system operation are affected by interference. Therefore, when different types of cells transmit downlink, sub-transmissions of information required for system operation, for example, the above-described information such as uplink HARQ and PBCH, PSS / SSS, MIB, SIB-1, paging message, etc. In order to best exclude frames affected by interference, a constant offset may be placed between the subframe pattern of the macro cell and the femto cell.

In addition, among the subframes transmitted in the downlink of the macro cell for a subframe in which important information for system operation such as HARQ ACK / NACK signal, PBCH, PSS / SSS, MIB, SIB-1, paging message, etc. is transmitted, It may be considered to limit the subframe of the corresponding femto cell to a subframe capable of minimizing interference to the macro cell. As described above, in general, the effect of the interference of weak signals of the macro cell is greater than that of the strong strength signal output from the nearby femto cell base station, and the femto cell has more users than the users of the femto cell. It is desirable to reduce the interference received by the macro cell as much as possible by adjusting the subframe setting transmitted in the downlink of the cell.

Almost blank subframe (ABS) may be used as a low interference subframe capable of minimizing interference on a corresponding subframe. ABS is a subframe that transmits data that can not be sent as much as possible. In addition, in general, an ABS subframe may include an MBSFN subframe.

As described above, the uplink HARQ ACK / NACK signal and the PBCH, PSS / SSS, SIB-1, MIB, Paging message for system operation is preferably transmitted in the normal subframe. However, among the control information, since the PBCH, PSS / SSS and MIB is transmitted to the resource blocks in the middle of the subframe, it is robustly protected (robostic). Therefore, the PBCH, PSS / SSS and MIB may be transmitted to the ABS. On the other hand, HARQ ACK / NACK signal, SIB-1, Paging message is transmitted in the normal subframe.

The normal subframe in which the HARQ ACK / NACK signal, the SIB-1, and the paging message are transmitted needs to be minimized by avoiding transmission at the same time in the macro cell and the femto cell.

As such, a femto cell corresponding to a subframe of a macro cell in which a predetermined offset is provided between subframes transmitted in downlink of the macro cell and subframes transmitted in the downlink of the femtocell and information required for system operation is transmitted. The subframe of may be configured of ABS. Through this, it is possible to protect the subframe transmitting information to be protected among the subframes transmitted in the downlink of the macro cell from interference by the femto cell.

The downlink subframe pattern of the macro cell may also be limited corresponding to the downlink subframe pattern of the femto cell. Therefore, the subframe pattern of the macro cell together with the downlink subframe pattern of the femto cell may be statically or semi-statically operated. That is, according to the downlink subframe pattern of the femto cell, the macro cell is a PBCH, PSS / SSS, SIB- for uplink HARQ ACK / NACK signal and system operation in a subframe where interference may be less generated in the downlink subframe. 1, MIB, paging message and the like can be sent.

In order to adjust inter-cell interference using the subframe pattern, the pattern of the ABS constituting the subframe pattern is important. Hereinafter, a pattern of a subframe in which ABS is disposed to adjust inter-cell interference is called an ABS pattern (Almost Blank Subframe Pattern).

11 to 13 schematically illustrate various models of an ABS pattern of a femto cell.

As shown in FIG. 11, an ABS pattern that may be used for downlink transmission of a femto cell may be considered to be a case where all femto cells use the same ABS pattern P1 up to femto cells belonging to a neighboring macro cell. As shown in FIG. 12, only femto cells belonging to the same macro cell may use the same ABS pattern. In this case, femto cells belonging to macro cell 1 may use ABS pattern P1, and femto cells belonging to macro cell 2 may use ABS pattern P2. In addition, as shown in FIG. 13, a case where a specific ABS pattern is used for each femto cell may be considered.

If all femto cells use the same ABS pattern as shown in FIG. 11, the macro cell needs to inform the femto cell about which ABS pattern should be used, and the femto cell has an apparatus for receiving downlink transmissions from the macro cell. Should be. In the case of FIG. 12, there is a problem similar to that of FIG. 11. In the case of a femto cell 1270 located at a boundary of a neighboring macro cell, it may be a question of which macro cell to use an ABS pattern.

Thus, the case of FIG. 13 using femto cell specific ABS pattern may be the most desirable model of hetero network.

Meanwhile, when interference occurs between a femto cell and a macro cell, the femto cell may adjust inter-cell interference by transmitting data using an ABS pattern. At this time, it is necessary to inform the macro cell base station of the ABS pattern applied by the femto cell base station. For example, when a femtocell base station applies an ABS pattern, subframes that cause interference with subframes transmitted from the macrocells received by the macrocell terminal and subframes that do not generate interference or generate little interference Will exist. The subframe of the macro cell corresponding to the ABS of the ABS pattern used by the femto cell is a subframe in which no interference occurs or less interference occurs. At this time, even though the necessary information is transmitted well on a subframe in which interference does not occur or less interference occurs, when the measurement on the channel state is performed on a subframe in which interference occurs, the reliability of the measurement is deteriorated. The received macro cell base station may incorrectly recognize the channel state. Therefore, when all femto cells in a macro cell use the same ABS pattern, but the femto cell-specific ABS pattern is femto cell specific, the femto cell-specific ABS pattern is not defined between the macro cell and the femto cell without the X2 interface. The way you tell the macro cell can be a problem.

Hereinafter, a method of informing the macro cell of the ABS pattern used by the femto cell will be described.

<ABS pattern notification by bitmap transmission>

The femto cell base station (HNB: Home NodeB / Home eNodeB) transmits the ABS pattern to the macro cell UE (MUE) in the form of a bitmap, and the received macro cell terminal transmits the ABS pattern to the macro cell base station (MeNB). : Macro cell eNodeB). The macro cell terminal is a terminal in which the serving cell is a macro cell.

The ABS pattern transmitted in the form of a bitmap may be transmitted from the femto cell base station in SIB1 or SIB2. When transmitted in SIB1 or SIB2, an ABS pattern in the form of a bitmap may be transmitted on a PDSCH.

In addition, the ABS pattern in the form of a bitmap may be transmitted in a master information block (MIB). When transmitted to the MIB, an ABS pattern in the form of a bitmap may be transmitted on the PBCH. As described above, the PBCH can be received even if the system band is not known in advance, has a low system overhead, and has high reception reliability at the cell boundary. Therefore, when transmitting the ABS pattern to the MIB than when transmitting the SIB1 / SIB2, it is easy to receive the ABS pattern information of the femto cell in the macro cell terminal.

As shown in Table 1, the MIB (Master Information Block) has a 10-bit spare space.

--ASN1START


MasterInformationBlock :: = SEQUENCE {
dl-Bandwidth ENUMERATED {
n6, n15, n25, n50, n75, n100},
pitch-Config PHICH-Config,
systemFrameNumbber BIT STRING (SIZE (8)),
spare BIT STRING (SIZE (10))
}


--ASN1STOP

When the ABS pattern of the femto cell is transmitted to the MIB, it can be transmitted using the spare space of the MIB. Since important system information is transmitted to the MIB, the ABS pattern transmission of the femtocell using the spare space of the MIB may be used only when interference occurs and the femtocell applies the ABS pattern.

On the other hand, when a femtocell transmits an ABS pattern, interference occurs and the ABS pattern is used. Therefore, it may be difficult for the macro cell terminal under interference to correctly receive the ABS pattern of the femto cell delivered in the form of a bitmap.

<ABS pattern notification using ABS pattern table>

A method of configuring a table by defining an ABS pattern that can be used by the femto cell and configuring an index indicating the ABS pattern on the table can be used by the femto cell base station to transmit the index to the macro cell terminal. Even in the case of an interfering macro cell terminal, the ABS pattern index transmitted in a simple data format can be easily received.

14 is a flowchart schematically illustrating that information about an ABS pattern of a femto cell is transmitted to a macro cell using an ABS pattern table.

First, the ABS pattern table is already transmitted to the femto cell base station (HNB) and the macro cell base station (MeNB) (S1410). The ABS pattern table may include an ABS pattern table used by the macro cell base station in the femto cell base station, or may be delivered to the femto cell base station and the macro cell base station by separate signaling or user input.

In order to configure an ABS pattern table with a predetermined number of ABS patterns, an ABS pattern that can be used by a femto cell may be defined in advance.

There are various ways to define the ABS pattern. For example, the ABS pattern is limited by a subframe blank rate per downlink subframe pattern of the femto cell, a subframe blank rate per downlink frame of the femto cell, and a limitation of the number of ABSs that can be continuously arranged. can do.

When the ABS pattern is defined through the subframe blank ratio per downlink subframe pattern of the femtocell, the number n of ABSs included in one period of the downlink subframe pattern of the femtocell is determined, and In one cycle, the ABS pattern table may be configured of ABS patterns having the number n of ABS. Also, the number of ABSs that can be included in one period of the downlink subframe pattern of the femtocell (n) is determined, and the ABS patterns having ABSs less than the number (n) of the ABS in one period of the subframe pattern are ABS. You can also configure a pattern table. Also, the number of ABSs to be included in one period of the downlink subframe pattern of the femtocell (n) is determined, and the ABS is ABS patterns having more ABS than the number (n) of the ABS during one period of the subframe pattern. You can also configure a pattern table. In addition, a range of the number of ABS that can be included in one period of the downlink subframe pattern of the femto cell may be determined, and an ABS pattern table may be configured with ABS patterns having the number of ABS within this range.

When the ABS pattern is defined through the subframe blank ratio per downlink frame of the femtocell, the number of ABSs included per downlink frame of the femtocell (n) is determined, and the number of ABSs (n) during one frame is determined. The branches may form an ABS pattern table with ABS patterns. Further, the number n of ABSs that can be included per downlink frame of the femto cell may be determined, and the ABS pattern table may be configured with ABS patterns having less ABS than the number n of the ABS for one frame. In addition, the number n of ABSs to be included per downlink frame of the femto cell may be determined, and the ABS pattern table may be configured with ABS patterns having more ABS than the number n of the ABS in one frame. In addition, a range of the number of ABS that can be included per downlink frame of the femto cell may be determined, and an ABS pattern table may be configured with ABS patterns having the number of ABS within this range.

An ABS pattern table may be configured with ABS patterns that satisfy this limitation, while limiting the number of ABS that may be continuously disposed in the downlink subframe pattern of the femtocell.

As such, the ABS patterns constituting the ABS pattern table may be defined in various ways. In this case, the above-described methods for defining the ABS pattern may be applied in duplicate.

Here, examples of limitations on the femtocell's ABS pattern include the ratio of subframe spacing per downlink subframe pattern of the femto cell, the ratio of subframe spacing per downlink frame of the femto cell, and the limitation on the number of ABSs that can be continuously arranged. Although described, the present invention is not limited thereto, and it should be noted that the present invention can be applied to various limitations on ABS patterns that can be applied to construct an ABS pattern table with predetermined ABS patterns.

In the case where N ABS patterns are obtained by defining the ABS pattern according to a criterion for defining the ABS pattern that can be used by the femto cell, the ABS pattern table may be represented by K bits satisfying Equation 1.

Table 2 schematically shows an example of an ABS pattern table.

Femto Cell ABS Pattern ABS Pattern index ABS pattern # 0 0 ABS pattern # 1 One ABS pattern # 2 2 ABS pattern # 3 3 ABS pattern # 4 4 ABS pattern # 5 5 ABS pattern # 6 6 ABS pattern # 7 7

Table 2 shows an example in which there are eight ABS patterns that can be used by a femto cell, that is, three bits.

When the ABS pattern index indicating the ABS pattern of the femto cell is transmitted through the MIB, the 10-bit spare space existing in the MIB is transmitted, so that each index constituting the ABS pattern table can be represented within 10 bits. In order to do this, the number of ABS patterns that a femto cell can use must be limited.

Meanwhile, the ABS pattern corresponding to the ABS pattern index may have at least one subset ABS pattern. The subset ABS pattern may be referred to as an ABS pattern determined based on an ABS pattern corresponding to the ABS pattern index. For example, the subset ABS pattern may be a subframe pattern configured by changing a part of a normal subframe to ABS without changing the ABS arrangement of the ABS pattern corresponding to the ABS pattern index. The femto cell may use a subset ABS pattern of the ABS pattern corresponding to the ABS pattern index for downlink transmission. Therefore, for the ABS patterns, the ABS pattern table is configured with less information amount by using the overlapping ABS arrangement as the basic ABS pattern and using the ABS pattern in which the ABS is added to the basic ABS pattern as the subset ABS pattern of the basic ABS pattern. You may.

In addition, the number of ABS patterns may vary depending on whether the transmission scheme of the femto cell and the macro cell is TDD (Frequency Division Duplexing) or FDD (Frequency Division Duplexing).

The femto cell selects an ABS pattern to be used for inter-cell interference coordination among the ABS patterns on the ABS pattern table (S1420). The femto cell may select an ABS pattern in advance to adjust when interference occurs. In addition, the femto cell detects that the macro cell terminal is being interfered with by the femto cell, and may select an ABS pattern to adjust this. The femto cell may detect that the terminal of the macro cell is being interfered with by the femto cell in various ways. For example, by receiving an interference message such as an interference stress message from the macro cell terminal, it may be detected that the macro cell terminal is currently being interfered with by the femto cell.

The femto cell transmits the selected ABS pattern index to the macro cell terminal (S1430). The femto cell may transmit the ABS pattern index to the macro cell terminal which is affected by the interference from the femto cell. In addition, the femto cell may transmit an index of an ABS pattern to a macro cell terminal in advance when interference occurs.

The index of the transmitted ABS pattern is an index mapped on the ABS pattern table for the ABS pattern selected for use in inter-cell interference coordination.

The femto cell base station may transmit the ABS pattern index to SIB1 or SIB2. When the femto cell base station transmits the ABS pattern index to SIB1 or SIB2, the ABS pattern index may be transmitted on the PDSCH. In this case, the ABS pattern index may be included in paging information and transmitted.

In addition, the femto cell base station may transmit the ABS pattern index to the MIB. When the femto cell base station transmits the ABS pattern index to the MIB, the ABS pattern index may be transmitted on the PBCH. The PBCH can be received even if the system band is not known in advance, has a low system overhead, and has high reception reliability at the cell boundary. Accordingly, when the ABS pattern index is transmitted to the MIB rather than the SIB1 / SIB2, it is easy for the macro cell terminal to receive the ABS pattern information of the femto cell.

In the case of transmitting the ABS pattern index to the femtocell MIB, since the 10-bit reserved space existing in the MIB is transmitted, the ABS pattern index should be expressed within 10 bits. In addition, since important system information and the like are transmitted to the MIB, the ABS pattern index may be transmitted using the spare space of the MIB only when the femto cell needs to adjust inter-cell interference by applying the ABS pattern.

The macro cell terminal receives the ABS pattern index from the femto cell base station, and transmits information about the ABS pattern to the macro cell base station (S1440).

The macro cell terminal receives the ABS pattern index from the femto base station to SIB1 / SIB2 or MIB. The macro cell terminal may transmit the received ABS pattern index to the macro cell base station as it is. In addition, the macro cell terminal may read out the ABS pattern index from the received information on the SIB1 / SIB2 or MIB and transmit ABS pattern information corresponding to the ABS pattern index to the macro cell base station. In order to transmit ABS pattern information corresponding to the received ABS pattern index to the macro cell base station, the macro cell terminal may store the ABS pattern table used by the femto cell base station and / or information thereof as necessary. In this case, the macro cell terminal may configure the ABS pattern information to be transmitted to the macro cell base station based on the received ABS pattern index, the stored ABS pattern table and / or information thereof. In this case, the ABS pattern table used by the femto cell base station and / or information thereof may be stored in the macro cell terminal in advance, or may be transferred from the macro cell base station through higher layer signaling such as RRC.

When the macro cell terminal receives the ABS pattern index from the femto cell base station, the macro cell terminal may transmit it to the macro cell base station as separate information. In addition, the macro cell terminal may include ABS pattern index information (such as ABS pattern index or ABS pattern information) in a general measurement report and transmit the same to the macro cell base station.

The macro cell base station recognizes the femto cell specific ABS pattern through the ABS pattern index information transmitted from the macro cell terminal (S1450). The ABS pattern table used by the femto cell base station and / or information thereof may be stored in the macro cell base station in advance when configuring the hetero network including the femto cell. In addition, the ABS pattern table used by the femto cell base station and / or information about it may be delivered to the macro cell additionally by separate signaling or by a network manager / user. Therefore, the macro cell base station can recognize which ABS pattern the femto cell uses, based on the information on the ABS pattern index received from the macro cell terminal.

The macro cell base station transmits a measurement restriction according to the femto cell specific ABS pattern to the macro cell terminal (S1460).

As described above, the macro cell base station may report a result of a measurement (hereinafter, referred to as 'measurement') related to channel state or communication quality performed by the macro cell terminal by various needs including downlink scheduling. When the femtocell base station applies the ABS pattern, there are subframes that cause interference and subframes that do not generate interference or generate less interference for subframes transmitted from the macro cell received by the macro cell terminal. . The subframe of the macro cell corresponding to the ABS of the ABS pattern used by the femto cell is a subframe in which no interference occurs or less interference occurs. At this time, even though the necessary information is transmitted well on a subframe in which interference does not occur or less interference occurs, when the measurement on the channel state is performed on a subframe in which interference occurs, the reliability of the measurement is deteriorated. The received macro cell base station may incorrectly recognize the channel state.

Therefore, the macro cell base station may limit the measurement to the macro cell terminal to perform the measurement according to the ABS pattern, that is, on a subframe corresponding to the ABS of the ABS pattern used by the femto cell. If there is no restriction on the measurement, there is a fear that the result according to the existing measurement method will be continued without reflecting the channel condition to which the interference adjustment is applied.

The macro cell base station may transmit a measurement limit to the macro cell terminal through higher layer signaling such as RRC signaling.

The macro cell terminal reports the measurement result reflecting the measurement limitation to the macro cell base station (S1470). The macro cell base station may perform an operation required for network operation such as downlink scheduling based on the measurement report received from the macro cell terminal.

15 is a flowchart schematically illustrating a method of applying an ABS pattern by a femto cell base station.

The femto cell selects an ABS pattern to be used for inter-cell interference coordination on the ABS pattern table (S1510). The femto cell may select an ABS pattern in advance to adjust when interference occurs. In addition, the femto cell detects that the macro cell terminal is being interfered with by the femto cell, and may select an ABS pattern to adjust this. The femto cell may detect that the terminal of the macro cell is being interfered with by the femto cell in various ways. For example, by receiving an interference message such as an interference stress message from the macro cell terminal, it may be detected that the macro cell terminal is currently being interfered with by the femto cell.

The femto cell transmits the ABS pattern index of the selected ABS pattern (S1520). As described above, the femto cell base station may transmit the ABS pattern index to SIB1 or SIB2, or may transmit to the MIB.

The femto cell base station determines whether an interference message is received from the macro cell terminal (S1530).

The macro cell terminal receiving the ABS pattern index from the femto cell may transmit the ABS pattern index information to the macro cell base station. The macro cell base station may recognize the ABS pattern of the femto cell through the received ABS pattern index and transmit a measurement limit to the macro cell terminal. At this time, if the macro cell base station incorrectly recognizes the ABS pattern used by the femto cell, even if the macro cell terminal measures according to the measurement limit transmitted by the macro cell base station, the measurement can be performed on the subframe in which interference occurs. . Accordingly, the measurement result of the macro cell terminal may indicate that the interference between cells is greatly affected. In this case, the macro cell terminal may transmit an interference message such as an interference stress message to the femto cell base station.

Upon receiving the interference message from the macro cell terminal, the femto cell base station can know that information about the ABS pattern has not been delivered to the macro cell base station or that the ABS pattern, which is the macro cell base station, has been incorrectly recognized.

When the femto cell base station receives the interference message from the macro cell terminal, it transmits the ABS pattern index again (S1520). At this time, the macro cell terminal receives the ABS pattern index from the femto cell base station again, and transmits the ABS pattern index information to the macro cell base station. The macro cell base station modifies and transmits a measurement limit for the macro cell terminal based on the received ABS pattern index information.

The ABS pattern index transmission of the femto cell base station may be repeated until no interference message is received from the macro cell terminal.

If no interference message is received, the current ABS pattern is maintained. The femto cell base station may continue to maintain the current ABS pattern, or may maintain the current ABS pattern for a predetermined time. When the ABS pattern is maintained for a predetermined time, a surf frame pattern that returns after a predetermined time has elapsed may be set in advance. Whether to maintain the ABS pattern or return to a specific subframe pattern after a predetermined time has elapsed may be determined in advance by setting.

If there is a change in channel state or the like as time passes, the femtocell base station may receive an interference message from the macro cell terminal (S1540). Even when the inter-cell interference is adjusted by the applied ABS pattern or the applied ABS pattern, the macro cell terminal may again receive the interference by the femto cell over time. In this case, the macro cell terminal may transmit an interference message such as an interference stress message to the femto cell base station.

When the interference message is received from the macro cell terminal, the femto cell base station may select the ABS pattern again (S1510). If the ABS pattern is currently applied, the femtocell base station may select a new ABS pattern on the ABS pattern table instead of the ABS pattern currently applied. If the state returns to the specific subframe pattern, the femtocell base station may select the ABS pattern to be applied on the ABS pattern table.

The femtocell base station may transmit the ABS pattern index for the selected ABS pattern to the macro cell terminal (S1520).

Here, although the femtocell base station transmits the ABS pattern index and applies the ABS pattern, the present invention has been described as receiving an interference message from the macro cell terminal. However, the present invention is not limited thereto. If it is determined that the influence of the interference exceeds a predetermined reference value based on the terminal's own measurement, the interference message may be transmitted to the femtocell base station at any time. In contrast, the femtocell base station may perform steps S1520 or less when the ABS pattern is selected, and steps S1510 or less when the ABS pattern is not selected.

16 is a block diagram schematically illustrating a configuration of a femto cell base station, a macro cell terminal, and a macro cell base station in a hetero network to which the present invention is applied.

The hetero network includes a femto cell base station 1610 and a macro cell base station 1630. The macro cell terminal 1620 is a terminal (UE) in which the macro cell is a serving cell.

The femto cell base station 1610 includes a transceiver 1640, a controller 1650, and a storage 1660.

The femtocell base station 1610 may transmit and receive information necessary for network operation of the femtocell through the transceiver 1640.

The storage unit 1660 may store information necessary for femto cell network operation. When the femto cell base station 1610 delivers the ABS pattern to be applied to the macro cell base station 1630 using the ABS pattern table, the storage unit 1660 may store an ABS pattern table configured with a limited ABS pattern.

The controller 1650 may be connected to the storage 1660 and the transceiver 1640 to control the storage 1660 and the transceiver 1640. The controller 1650 may select an ABS pattern to be applied to adjust interference occurring between the macro cell on the ABS pattern table stored in the storage 1660. The controller 1650 may transmit the ABS pattern index corresponding to the ABS pattern selected on the ABS pattern table to the macro cell terminal 1620 through the transceiver 1640. In addition, when the control unit 1650 receives the interference message from the macro cell terminal 1620 through the transceiver 1640, the controller 1650 may retransmit the selected ABS pattern index to the macro cell terminal through the transceiver 1640.

The macro cell terminal 1620 includes a transceiver 1643, a controller 1653, a storage 1663, and an interference detector 1670.

The macro cell terminal 1620 may transmit / receive necessary information with the femto cell base station 1610 and the macro cell base station 1630 through the transceiver 1643. The macro cell terminal 1620 may receive the ABS pattern index for the femto cell specific ABS pattern from the femto cell base station 1610 through the transceiver 1643. The macro cell terminal 1620 may receive a measurement restriction from the macro cell base station 1630 through the transceiver 1643.

The storage unit 1663 may store information necessary for the macro cell terminal 1620 to perform communication on a network. For example, when the macro cell terminal 1620 transmits ABS pattern information corresponding to the received ABS pattern index to the macro cell base station, the storage unit 1663 stores the ABS pattern table used by the femto cell base station and / or the related information. It may be storing information.

The controller 1653 may be connected to the interference detector 1670, the storage 1663, and the transceiver 1643 to control the interference detector 1670 and the transceiver 1643. The controller 1653 may transmit ABS pattern index information regarding the ABS pattern used in the femto cell to the macro cell base station 1630 through the transceiver 1643. In addition, the controller 1653 measures the downlink channel state of the macro cell and the like based on the measurement limit received from the macro cell base station 1630, and transmits the measured result to the macro cell base station 1630 through the transceiver 1643. Can be sent.

The interference detector 1670 may determine whether the interference by the femtocell is affected at the current location as a result of the measurement by the controller 1653. The interference detector 1670 may determine the degree of interference by the femto cell based on the channel state, data reception rate, and the like measured by the controller 1653. The interference detector 1670 may transmit an interference message such as an interference stress message to the femtocell base station 1610 through the transceiver 1643 when the influence of the interference by the femtocell is greater than or equal to a predetermined level. In addition, when the interference detector 1670 receives a message for transmitting an interference message from the macro cell base station 1630 to the femtocell base station 1610 through the transceiver 1643, the interference detector 1670 interferes with the transceiver 1643. The message may be sent to the femto cell base station 1610.

The macro cell base station 1630 includes a transceiver 1647, a controller 1657, and a storage 1667.

The macro cell base station 1630 may transmit and receive through the transceiver 1647. The macro cell base station 1630 may receive ABS pattern index information for the femto cell specific ABS pattern from the macro cell terminal 1620 through the transceiver 1647. The macro cell base station 1630 may receive a measurement result report regarding a channel state from the macro cell terminal 1620. In addition, the macro cell base station 1630 may transmit a measurement limit to the macro cell terminal 1620 through the transceiver 1647.

The storage unit 1667 may store information necessary for operating the macro cell network. The storage unit 1667 of the macro cell base station 1630 may store an ABS pattern table used by the femto cell base station 1610 and / or information thereof.

The controller 1657 may be connected to the storage 1667 and the transceiver 1647 to control the storage 1667 and the transceiver 1647. The controller 1625 may use the ABS used in the femtocell based on the femtocell-specific ABS pattern index information received from the macro cell terminal 1620 and the ABS pattern table stored in the storage unit 1667 and / or information thereof. Recognize patterns. The controller 1625 may transmit a measurement limit based on the recognition result of the femtocell specific ABS pattern to the macro cell terminal 1620 through the transceiver 1647. In addition, the controller 1625 may determine whether the macro cell terminal 1620 is greatly affected by the femtocell interference based on the measurement result report from the macro cell terminal 1620. When the influence of the interference exceeds a certain level, a message for transmitting the interference message to the femtocell base station 1610 may be transmitted to the macro cell terminal 1620 through the transceiver 1647.

In the above-described exemplary system, the methods are described on the basis of a flowchart as a series of steps or blocks, but the present invention is not limited to the order of the steps, and some steps may occur in different orders or simultaneously . In addition, those skilled in the art will appreciate that the steps shown in the flowcharts are not exclusive and that other steps may be included or one or more steps in the flowcharts may be deleted without affecting the scope of the present invention.

The above-described embodiments include examples of various aspects. While it is not possible to describe every possible combination for expressing various aspects, one of ordinary skill in the art will recognize that other combinations are possible. Accordingly, it is intended that the invention include all alternatives, modifications and variations that fall within the scope of the following claims.

Claims (13)

A method for transmitting information about a downlink subframe pattern for coordinating intercell interference in a communication system,
Selecting a subframe pattern to be applied to downlink transmission on a pattern table consisting of an applicable subframe pattern and a pattern index corresponding to the subframe pattern; And
And transmitting a pattern index corresponding to the selected subframe pattern. The method of claim 1, wherein the subframe pattern constituting the pattern table is defined by the number of low interference subframes per subframe pattern representing the number of low interference subframes constituting the applicable downlink subframe pattern. Downlink subframe pattern information transmission method characterized in that. The method of claim 2, wherein the number n of predetermined low interference subframes is determined, and subframe patterns having the n low interference subframes per downlink subframe pattern, and the low or less than n per downlink subframe pattern The pattern table is configured by subframe patterns of any one of subframe patterns having an interference subframe or subframe patterns having at least n low interference subframes per downlink subframe pattern. Subframe pattern information transmission method. 3. The method of claim 2, wherein the range of the number of predetermined low interference subframes is determined, and the pattern is divided into subframe patterns having low interference subframes within the range of the number of low interference subframes per downlink subframe pattern. A method for transmitting downlink subframe pattern information, comprising configuring a table. The method of claim 1, wherein the subframe pattern constituting the pattern table is defined by the number of low interference subframes per frame indicating the number of low interference subframes constituting the frame in the applicable downlink subframe pattern. Downlink subframe pattern information transmission method characterized in that. The method of claim 1, wherein the pattern index corresponding to the selected subframe pattern is transmitted on a physical downlink shared channel (PDSCH). The method of claim 1, wherein the pattern index corresponding to the selected subframe pattern is transmitted on a downlink broadcasting channel.  The method of claim 1, wherein a pattern index corresponding to the selected subframe pattern is transmitted on a master information block (MIB). The downlink method of claim 1, wherein after transmitting the pattern index corresponding to the selected subframe pattern, if the inter-cell interference continues, the pattern index corresponding to the selected subframe pattern is retransmitted. Method of transmitting link subframe pattern information. A method of transmitting information about a downlink subframe pattern for coordinating intercell interference between a first cell and a second cell in a communication system, the method comprising:
Receive a pattern index of the downlink subframe pattern from the first cell base station to which the downlink subframe pattern is applied; And
Transmitting the information on the received downlink subframe pattern index to the second cell base station,
The pattern index corresponds to a subframe pattern selected by the first base station on a pattern table composed of subframe patterns applicable to the first cell base station,
And the first cell base station and the second cell base station have information on the pattern table. The method of claim 10, wherein the inter-cell interference is determined based on the measured value of the communication environment with the second cell, and when it is determined that the inter-cell interference affects more than a predetermined reference value, A method for transmitting downlink subframe pattern information, comprising transmitting an interference message to one cell. The method of claim 10, further comprising: measuring a communication environment with the second base station based on a measurement limit received from the second cell base station;
The measurement limit received from the second cell base station, the method for transmitting downlink subframe pattern information, characterized in that the second base station is transmitted based on the information on the downlink subframe pattern index. A method of using information about a downlink subframe pattern for coordinating intercell interference in a communication system,
Receiving information on the downlink subframe pattern from a base station of a cell to which the downlink subframe pattern for coordinating intercell interference is received through a terminal;
Recognize a downlink subframe pattern applied by the base station of the cell based on the information on the downlink subframe and a pattern table including a downlink subframe pattern applicable by the base station of the cell; And
Coordinating inter-cell interference comprising transmitting a measurement restriction message for performing a measurement on a communication environment in a low interference subframe on the recognized downlink subframe pattern to a terminal affected by the interference from the cell Method for using downlink subframe pattern information for the.

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