WO2012044019A2 - Inter-cell interference coordination in a wireless communication system - Google Patents
Inter-cell interference coordination in a wireless communication system Download PDFInfo
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- WO2012044019A2 WO2012044019A2 PCT/KR2011/007058 KR2011007058W WO2012044019A2 WO 2012044019 A2 WO2012044019 A2 WO 2012044019A2 KR 2011007058 W KR2011007058 W KR 2011007058W WO 2012044019 A2 WO2012044019 A2 WO 2012044019A2
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- subframe
- base station
- cell
- subframes
- downlink
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Classifications
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J11/00—Orthogonal multiplex systems, e.g. using WALSH codes
- H04J11/0023—Interference mitigation or co-ordination
- H04J11/005—Interference mitigation or co-ordination of intercell interference
- H04J11/0053—Interference mitigation or co-ordination of intercell interference using co-ordinated multipoint transmission/reception
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
- H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
- H04B7/0682—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission using phase diversity (e.g. phase sweeping)
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/003—Arrangements for allocating sub-channels of the transmission path
- H04L5/0058—Allocation criteria
- H04L5/0073—Allocation arrangements that take into account other cell interferences
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/08—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station
- H04B7/0837—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the receiving station using pre-detection combining
- H04B7/084—Equal gain combining, only phase adjustments
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/0001—Systems modifying transmission characteristics according to link quality, e.g. power backoff
- H04L1/0023—Systems modifying transmission characteristics according to link quality, e.g. power backoff characterised by the signalling
- H04L1/0026—Transmission of channel quality indication
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/003—Arrangements for allocating sub-channels of the transmission path
- H04L5/0032—Distributed allocation, i.e. involving a plurality of allocating devices, each making partial allocation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W24/00—Supervisory, monitoring or testing arrangements
- H04W24/02—Arrangements for optimising operational condition
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
- H04W52/04—TPC
- H04W52/18—TPC being performed according to specific parameters
- H04W52/24—TPC being performed according to specific parameters using SIR [Signal to Interference Ratio] or other wireless path parameters
- H04W52/243—TPC being performed according to specific parameters using SIR [Signal to Interference Ratio] or other wireless path parameters taking into account interferences
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W16/00—Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
- H04W16/24—Cell structures
- H04W16/32—Hierarchical cell structures
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W24/00—Supervisory, monitoring or testing arrangements
- H04W24/10—Scheduling measurement reports ; Arrangements for measurement reports
Definitions
- the present invention relates to a wireless communication system, and more particularly, to a method and apparatus for coordinating and reducing inter-cell interference in a wireless communication system.
- FIG. 1 illustrates a heterogeneous network wireless communication system 100 including a macro base station eNBl and a micro base station eNB2.
- the term "heterogeneous network” refers to a network wherein a macro base station 110 and a micro base station 120 co-exist even when the same RAT (Radio Access Technology) is being used.
- RAT Radio Access Technology
- a macro base station 110 refers to a general base station of a wireless communication system having a broad coverage range (service provision area) and a high transmission power.
- the macro base station 110 may also be referred to as a macro cell.
- the micro base station 120 may also be referred to as a micro cell, a pico cell, a femto cell, a home eNB (HeNB) , a relay, and so on. More specifically, the micro base station 120 corresponds to a smaller version of the macro base station 110. Accordingly, the micro base station 120 may independently perform most of the functions of the macro base station.
- the micro base station 120 may correspond to an overlay base station, which may be installed in an area covered by the macro base station, or to a non-overlay base station, which may be installed in a shadow area that cannot be covered by the macro base station.
- the micro base station 120 has a narrower coverage range and a lower transmission power and may accommodate a smaller number of terminals.
- a terminal 130 may directly receive services from (or be served by) the macro base station 110 (hereinafter referred to as a macro-terminal) or may directly receive services from (or be served by) the micro base station 120 (hereinafter referred to as a micro-terminal ) .
- a terminal 130 present within the coverage area of the micro base station 120 may receive services from the macro base station 110.
- FIG. 1 shows a state in which the terminal 130 is connected to the micro base station 120.
- the micro base station may be categorized into two different types, the first type being a CSG (Closed Subscriber Group) micro base station, and the second type being an OA (Open Access) or OSC (Open Subscriber Group) micro base station. More specifically, the CSG micro base station may serve only specific terminals that are authorized, and the OSG micro base station may serve all types of terminals without any particular access limitations.
- CSG Cell Subscriber Group
- OSC Open Subscriber Group
- interference may occur due to a strong signal from the macro base station 110.
- the terminal served by the macro base station is adjacent to a micro base station, interference may occur in a signal received by the terminal from the macro base station due to a strong signal from the micro base station.
- Such interference may be referred to as inter-cell interference and the above- described example relates to inter-cell interference in downlink from a base station to a terminal.
- inter-cell interference may occur in uplink from a terminal to a base station.
- An object of the present invention devised to solve the problem lies in a method of transmitting and receiving a cooperative signal between cells in which interference occurs, in order to reduce inter-cell interference.
- the object of the present invention can be achieved by providing a method of transmitting channel state information (CSI) measurement resource information by a base station, including determining first and second subframe sets, in which CSI measurement will be performed, among a plurality of downlink subframes, transmitting information indicating the first and second subframe sets to a terminal, and receiving the CSI of each of the first and second subframe sets from the terminal.
- CSI channel state information
- a subframe belonging to the first subframe set and a subframe belonging to the second subframe set do not overlap, and some of the plurality of subframes do not belong to either of the first and second subframe sets.
- a method of performing channel state information (CSI) measurement by a terminal including receiving, from a base station, information indicating first and second subframe sets, in which the CSI measurement will be performed, among a plurality of downlink subframes, performing CSI measurement with respect to each of the first and second subframe sets, and transmitting the CSI to the base station.
- CSI channel state information
- a subframe belonging to the first subframe set and a subframe belonging to the second subframe set do not overlap, and some of the plurality of subframes do not belong to either of the first and second subframe sets.
- a base station for transmitting channel state information (CSI) measurement resource information, including a reception module configured to receive an uplink signal from a terminal, a transmission module configured to transmit a downlink signal to the terminal, and a processor configured to control the base station including the reception module and the transmission module.
- the processor is configured to determine first and second subframe sets, in which CSI measurement will be performed, among a plurality of downlink subframes, transmit information indicating the first and second subframe sets to the terminal through the transmission module, and receive the CSI of each of the first and second subframe sets from the terminal through the reception module.
- a subframe belonging to the first subframe set and a subframe belonging to the second subframe set do not overlap, and some of the plurality of subframes do not belong to either of the first and second subframe sets.
- a terminal for performing channel state information (CSI) measurement including a reception module configured to receive a downlink signal from a base station, a transmission module configured to transmit an uplink signal to the base station, and a processor configured to control the terminal including the reception module and the transmission module.
- the processor is configured to receive, from the base station, information indicating first and second subframe sets, in which the CSI measurement will be performed, among a plurality of downlink subframes through the reception module, perform the CSI measurement with respect to each of the first and second subframe sets, and transmit the CSI to the base station through the transmission module.
- a subframe belonging to the first subframe set and a subframe belonging to the second subframe set do not overlap, and some of the plurality of subframes do not belong to either of the first and second subframe sets.
- the base station may determine the first and second subframe sets using information indicating a subset of blank subframes of a neighbor cell.
- the first subframe set may include a subframe in which a probability of being set as a blank subframe by a neighbor cell is higher than that of the second subframe set .
- a method of setting measurement resources by a first base station including receiving information about setting of a blank subframe of a second base station among a plurality of subframes, and setting resources in which a terminal will perform measurement using the information about setting of the blank subframe of the second base station.
- the information about setting of the blank subframe of the second base station includes first and second bitmaps, the first bitmap indicates blank subframes and non-blank subframes, and the second bitmap indicates a subset of subframes indicated as the blank subframes by the first bitmap.
- a base station of a cell which is subject to interference which sets measurement resources, including a reception module configured to receive a signal from a base station of a cell which causes interference, a transmission module configured to transmit a signal to the base station of the cell which causes interference, and a processor configured to control the base station of the cell which is subject to interference, which includes the reception module and the transmission module.
- the processor is configured to receive information about setting of a blank subframe of the base station of the cell which causes interference among a plurality of subframes through the reception module, and set resources in which a terminal will perform measurement using the information about setting of the blank subframe of the base station of the cell which causes interference.
- the information about setting of the blank subframe of the base station of the cell which causes interference includes first and second bitmaps, the first bitmap indicates blank subframes and non-blank subframes, and the second bitmap indicates a subset of subframes indicated as the blank subframes by the first bitmap.
- Each of the blank subframes of the second base station indicated by the first bitmap may belong to any one of a first group or a second group, the first group may include subframes indicated by the second bitmap as belonging to a subset of blank subframes, and the second group may include subframes indicated by the second bitmap as not belonging to a subset of blank subframes .
- a probability of the second base station setting a subframe belonging to the first group to a blank subframe may be different from a probability of the second base station setting a subframe belonging to the second group to a blank subframe .
- the probability of the second base station setting the subframe belonging to the first group to the blank subframe may be higher than the probability of the second base station setting the subframe belonging to the second group to the blank subframe .
- the setting of the resources may be performed by the first base station using a subset of blank subframes of the second base station indicated by the second bitmap.
- a method of transmitting information indicating resources from a first base station to a second base station including determining a downlink subframe which cannot be used by the first base station due to inter-cell interference among a plurality of downlink subframes, and transmitting information indicating the determined downlink subframe to the second base station.
- the first base station may be a base station of a cell which is subject to interference and the second base station may be a base station of a cell which causes interference.
- a base station of a cell which is subject to interference which transmits information indicating resources, including a reception module configured to receive a signal from a base station of a cell which causes interference, a transmission module configured to transmit a signal to the base station of the call which causes interference, and a processor configured to control the base station of the cell which is subject to interference, which includes the reception module and the transmission module.
- the processor is configured to determine a downlink subframe which cannot be used by the base station of the cell which is subject to interference due to inter-cell interference among a plurality of downlink subframes, and transmit information indicating the determined downlink subframe to the base station of the cell which causes interference through the transmission module.
- the information indicating the determined downlink subframe may be configured in the form of a bitmap.
- the method may further include receiving, by the first base station, blank subframe setting information set by the second base station in consideration of the information indicating the determined downlink subframe.
- the downlink subframe which cannot be used by the first base station may be determined based on a downlink measurement result from a terminal served by the first base station.
- the downlink subframe which cannot be used by the first base station may be determined to be a subframe in which the strength of inter-cell interference from the second base station is higher than the strength of a signal from the first base station to the terminal served by the first base station by a predetermined threshold.
- FIG. 1 is a diagram showing a heterogeneous network wireless communication system
- FIG. 2 is diagram showing the structure of a downlink radio frame
- FIG. 3 is a diagram showing a resource grid in a downlink slot
- FIG. 4 is a diagram showing the structure of a downlink subframe
- FIG. 5 is a diagram showing the structure of an uplink subframe
- FIG. 6 is a diagram showing the configuration of a radio communication system having multiple antennas
- FIG. 7 is a diagram showing patterns of CRSs and DRSs defined in the existing 3GPP LTE system
- FIG. 8 is a diagram showing the structure of an uplink subframe including an SRS symbol
- FIG. 9 is a diagram showing an example of implementing transmission and reception functions of an FDD-mode relay node (RN) ;
- FIG. 10 is a diagram showing transmission to a UE from an RN and downlink transmission to the RN from a base station;
- FIG. 11 is a flowchart illustrating a method of transmitting inter-cell cooperative information from a cell which is subject to interference to a cell which causes interference according to an embodiment of the present invention
- FIG. 12 is a flowchart illustrating a method of transmitting and receiving cooperative information between cells in which interference occurs according to an embodiment of the present invention
- FIG. 13 is a diagram showing an example of setting a subframe group.
- FIG. 14 is a diagram showing a base station (eNB) device and a terminal device according to an exemplary embodiment of the present invention. [Best Mode]
- the following embodiments are proposed by combining constituent components and characteristics of the present invention according to a predetermined format.
- the individual constituent components or characteristics should be considered to be optional factors on the condition that there is no additional remark. If required, the individual constituent components or characteristics may not be combined with other components or characteristics. Also, some constituent components and/or characteristics may be combined to implement the embodiments of the present invention.
- the order of operations to be disclosed in the embodiments of the present invention may be changed to another. Some components or characteristics of any embodiment may also be included in other embodiments, or may be replaced with those of the other embodiments as necessary.
- the embodiments of the present invention are disclosed on the basis of a data communication relationship between a base station and a terminal.
- the base station is used as a terminal node of a network via which the base station can directly communicate with the terminal.
- Specific operations to be conducted by the base station in the present invention may also be conducted by an upper node of the base station as necessary.
- Base Station may be replaced with a fixed station, Node-B, eNode-B (eNB) , or an access point as necessary.
- the term “relay” may be replaced with a Relay Node (RN) or a Relay Station (RS) .
- the term “terminal” may also be replaced with a User Equipment (UE) , a Mobile Station (MS) , a Mobile Subscriber Station (MSS) or a Subscriber Station (SS) as necessary.
- UE User Equipment
- MS Mobile Station
- MSS Mobile Subscriber Station
- SS Subscriber Station
- Exemplary embodiments of the present invention are supported by standard documents disclosed for at least one of wireless access systems including an Institute of Electrical and Electronics Engineers (IEEE) 802 system, a 3 rd Generation Project Partnership (3GPP) system, a 3GPP Long Term Evolution (LTE) system, and a 3GPP2 system.
- IEEE Institute of Electrical and Electronics Engineers
- 3GPP 3 rd Generation Project Partnership
- LTE 3GPP Long Term Evolution
- 3GPP2 3 rd Generation Project 2
- All terminology used herein may be supported by at least one of the above- mentioned documents.
- the following embodiments of the present invention can be applied to a variety of wireless access technologies, for example, CDMA (Code Division Multiple Access) , FDMA (Frequency Division Multiple Access) , TDMA (Time Division Multiple Access) , OFDMA (Orthogonal Frequency Division Multiple Access) , SC-FDMA (Single Carrier Frequency Division Multiple Access), and the like.
- the CDMA may be embodied with wireless (or radio) technology such as UTRA (Universal Terrestrial Radio Access) or CDMA2000.
- the TDMA may be embodied with wireless (or radio) technology such as GSM (Global System for Mobile communications) /GPRS (General Packet Radio Service) /EDGE (Enhanced Data Rates for GSM Evolution) .
- GSM Global System for Mobile communications
- GPRS General Packet Radio Service
- EDGE Enhanced Data Rates for GSM Evolution
- the OFDMA may be embodied with wireless (or radio) technology such as Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX) , IEEE 802-20, and E-UTRA (Evolved UTRA).
- IEEE Institute of Electrical and Electronics Engineers
- Wi-Fi Wi-Fi
- WiMAX WiMAX
- IEEE 802-20 E-UTRA
- the UTRA is a part of the UMTS (Universal Mobile Telecommunications System) .
- the 3GPP (3rd Generation Partnership Project) LTE (long term evolution) is a part of the E-UMTS (Evolved UMTS) , which uses E-UTRA.
- the 3GPP LTE employs the OFDMA in downlink and employs the SC-FDMA in uplink.
- the LTE - Advanced (LTE-A) is an evolved version of the 3GPP LTE.
- WiMAX can be explained by an IEEE 802.16e (WirelessMA - OFDMA Reference System) and an advanced IEEE 802.16m (WirelessMAN-OFDMA Advanced System) .
- IEEE 802.16e WirelessMA - OFDMA Reference System
- advanced IEEE 802.16m WirelessMAN-OFDMA Advanced System
- 3GPP LTE and 3GPP LTE- A system 3GPP LTE- A system.
- technical features of the present invention are not limited thereto.
- Orthogonal Frequency Division Multiplexing (OFDM) radio packet communication system uplink/downlink data packet transmission is performed in subframe units.
- One subframe is defined as a predetermined time interval including a plurality of OFDM symbols.
- the 3GPP LTE standard supports a type 1 radio frame structure applicable to Frequency Division Duplex (FDD) and a type 2 radio frame structure applicable to Time Division Duplex (TDD) .
- FIG. 2(a) is a diagram showing the structure of the type 1 radio frame.
- a downlink radio frame includes 10 subframes, and one subframe includes two slots in time domain.
- a time required for transmitting one subframe is defined in a Transmission Time Interval (TTI) .
- TTI Transmission Time Interval
- one subframe may have a length of 1 ms and one slot may have a length of 0.5 ms .
- One slot may include a plurality of OFDM symbols in time domain and include a plurality of Resource Blocks (RBs) in frequency domain. Since the 3GPP LTE system uses OFDMA in downlink, the OFDM symbol indicates one symbol duration. The OFDM symbol may be called a SC-FDMA symbol or a symbol duration.
- a RB is a resource allocation unit and includes a plurality of contiguous subcarriers in one slot.
- the number of OFDM symbols included in one slot may be changed according to the configuration of a Cyclic Prefix (CP) .
- the CP includes an extended CP and a normal CP. For example, if the OFDM symbols are configured by the normal CP, the number of OFDM symbols included in one slot may be seven. If the OFDM symbols are configured by the extended CP, the length of one OFDM symbol is increased, the number of OFDM symbols included in one slot is less than that of the case of the normal CP. In case of the extended CP, for example, the number of OFDM symbols included in one slot may be six. If a channel state is instable, for example, if a User Equipment (UE) moves at a high speed, the extended CP may be used in order to further reduce interference between symbols.
- UE User Equipment
- one subframe includes 14 OFDM symbols.
- the first two or three OFDM symbols of each subframe may be allocated to a Physical Downlink Control Channel (PDCCH) and the remaining OFDM symbols may be allocated to a Physical Downlink Shared Channel (PDSCH) .
- PDCCH Physical Downlink Control Channel
- PDSCH Physical Downlink Shared Channel
- FIG. 2(b) is a diagram showing the structure of the type 2 radio frame .
- the type 2 radio frame includes two half frames, each of which includes five subframes, a downlink pilot time slot (DwPTS) , a guard period (GP) , and an uplink pilot time slot (UpPTS) .
- DwPTS downlink pilot time slot
- GP guard period
- UpPTS uplink pilot time slot
- One of these subframes includes two slots.
- the DwPTS is used for initial cell search, synchronization and channel estimation at a user equipment.
- the UpPTS is used for channel estimation and uplink transmission synchronization of the user equipment.
- the guard period is to remove interference occurring in an uplink due to multi-path delay of a downlink signal between the uplink and a downlink.
- one subframe includes two slots regardless of a type of the radio frame.
- the structure of the radio frame is only exemplary. Accordingly, the number of subframes included in the radio frame, the number of slots included in the subframe or the number of symbols included in the slot may be changed in various manners .
- FIG. 3 is a diagram showing a resource grid in a downlink slot.
- one downlink slot includes seven OFDM symbols in a time domain and one RB includes 12 subcarriers in a frequency domain in the figure, the present invention is not limited thereto.
- one slot includes 7 OFDM symbols.
- one slot includes 6 OFDM symbols.
- Each element on the resource grid is referred to as a resource element.
- One RB includes 12x7 resource elements.
- the number N DL of RBs included in the downlink slot is determined based on a downlink transmission bandwidth.
- the structure of the uplink slot may be equal to the structure of the downlink slot.
- FIG. 4 is a diagram showing the structure of a downlink subframe.
- a maximum of three OFDM symbols of a front portion of a first slot within one subframe corresponds to a control region to which a control channel is allocated.
- the remaining OFDM symbols correspond to a data region to which a Physical Downlink Shared Channel (PDSCH) is allocated.
- Examples of the downlink control channels used in the 3GPP LTE system include, for example, a Physical Control Format Indicator Channel (PCFICH) , a Physical Downlink Control Channel (PDCCH) , a Physical Hybrid automatic repeat request Indicator Channel (PHICH) , etc.
- PCFICH Physical Control Format Indicator Channel
- PDCH Physical Downlink Control Channel
- PHICH Physical Hybrid automatic repeat request Indicator Channel
- the PCFICH is transmitted at a first OFDM symbol of a subframe, and includes information about the number of OFDM symbols used to transmit the control channel in the subframe.
- the PHICH includes a HARQ ACK/NACK signal as a response of uplink transmission.
- the control information transmitted through the PDCCH is referred to as Downlink Control Information (DCI) .
- the DCI includes uplink or downlink scheduling information or an uplink transmit power control command for a certain UE group.
- the PDCCH may include resource allocation and transmission format of a Downlink Shared Channel (DL-SCH) , resource allocation information of an Uplink Shared Channel (UL-SCH) , paging information of a Paging Channel (PCH) , system information on the DL-SCH, resource allocation of an higher layer control message such as a Random Access Response (RAR) transmitted on the PDSCH, a set of transmit power control commands for an individual UEs in a certain UE group, transmit power control information, activation of Voice over IP (VoIP), etc.
- a plurality of PDCCHs may be transmitted within the control region.
- the UE may monitor the plurality of PDCCHs.
- the PDCCHs are transmitted on an aggregation of one or several consecutive control channel elements (CCEs) .
- CCEs control channel elements
- the CCE is a logical allocation unit used to provide the PDCCHs at a coding rate based on the state of a radio channel.
- the CCE corresponds to a plurality of resource element groups.
- the format of the PDCCH and the number of available bits are determined based on a correlation between the number of CCEs and the coding rate provided by the CCEs.
- the base station determines a PDCCH format according to a DCI to be transmitted to the UE, and attaches a Cyclic Redundancy Check (CRC) to control information.
- the CRC is masked with a Radio Network Temporary Identifier (RNTI) according to an owner or usage of the PDCCH.
- RNTI Radio Network Temporary Identifier
- a cell- RNTI (C-RNTI) of the UE may be masked to the CRC.
- C-RNTI cell- RNTI
- a paging indicator identifier (P-RNTI) may be masked to the CRC.
- P-RNTI paging indicator identifier
- SIB system information block
- SI- RNTI system information RNTI
- RA- RNTI random access-RNTI
- FIG. 5 is a diagram showing the structure of an uplink frame.
- the uplink subframe may be divided into a control region and a data region in a frequency domain.
- a Physical Uplink Control Channel (PUCCH) including uplink control information is allocated to the control region.
- a Physical uplink Shared Channel (PUSCH) including user data is allocated to the data region.
- PUCCH Physical Uplink Control Channel
- PUSCH Physical uplink Shared Channel
- the PUCCH for one UE is allocated to a RB pair in a subframe. RBs belonging to the RB pair occupy different subcarriers with respect to two slots. Thus, the RB pair allocated to the PUCCH is "frequency-hopped" at a slot boundary.
- FIG. 6 is a diagram showing the configuration of a radio communication system having multiple antennas.
- the transfer rate may be theoretically increased by a product of a maximum transfer rate R 0 upon using a single antenna and a rate increase ratio Rj . .
- the transmitted information may be expressed as follows.
- the transmitted information Sj 1 , S2 ? may have different transmit powers. If the respective transmit p p ... p
- the transmitted information with adjusted powers may be expressed as follows.
- S may be expressed using a diagonal matrix P of the transmit powers as follows.
- Xl > X2 » ' ' ' ' XN T are configured by applying a weight matrix ⁇ W ⁇ to the information vector S with the adjusted transmit powers.
- the weight matrix serves to appropriately distribute the transmitted information to each antenna according to a transport channel state, etc.
- X1 » X2 » ' ' ' » XJV r may be expressed by using the vector X as follows.
- Equation 5 ⁇ ⁇ w lz ⁇ - *>W T
- V denotes a weight between an ⁇ -th transmission antenna and j-th information.
- W is also called a precoding matrix.
- the channels may be distinguished according to transmission/reception antenna indexes.
- a channel from the transmission antenna j to the reception antenna i is denoted by hi j .
- hi j it is noted that the indexes of the reception antennas precede the indexes of the transmission antennas in view of the order of indexes.
- FIG. 6(b) is a diagram showing channels from the N T transmission antennas to the reception antenna i.
- the channels may be combined and expressed in the form of a vector and a matrix.
- the channels from the N T transmission antennas to the reception antenna i may be expressed as follows.
- AWGN Additive White Gaussian Noise
- N R added to the N T transmission antennas may be expressed as follows.
- the received signals may be expressed as follows.
- the number of rows and columns of the channel matrix H indicating the channel state is determined by the number of transmission and reception antennas.
- the number of rows of the channel matrix H is equal to the number N R of reception antennas and the number of columns thereof is equal to the number N T of transmission antennas. That is, the channel matrix H is an N R XN t matrix.
- the rank, of the matrix is defined by the smaller of the number of rows or columns, which is independent from each other. Accordingly, the rank of the matrix is not greater than the number of rows or columns.
- the rank the channel matrix H is restricted as follows. Equation 11
- the rank When the matrix is subjected to Eigen value decomposition, the rank may be defined by the number of Eigen values excluding 0. Similarly, when the matrix is subjected to singular value decomposition, the rank may be defined by the number of singular values excluding 0. Accordingly, the physical meaning of the rank in the channel matrix may be a maximum number of different transmittable information in a given channel.
- Reference Signal RS
- a signal may be distorted during transmission.
- distortion of the received signal should be corrected using channel information.
- a method of transmitting a signal, of which both the transmission side and the reception side are aware, and detecting channel information using a distortion degree when the signal is received through a channel is mainly used.
- the above signal is referred to as a pilot signal or a reference signal (RS) .
- each transmission antenna has an individual RS .
- a downlink RS includes a Common RS (CRS) shared among all UEs in a cell and a Dedicated RS (DRS) for only a specific-UE. It is possible to provide information for channel estimation and demodulation using such RSs.
- CRS Common RS
- DRS Dedicated RS
- the reception side estimates the channel state from the CRS and feeds back an indicator associated with channel quality, such as a Channel Quality Indicator (CQI) , a Precoding Matrix Index (PMI) and/or a Rank Indicator (RI) , to the transmission side (eNodeB) .
- CQI Channel Quality Indicator
- PMI Precoding Matrix Index
- RI Rank Indicator
- the CRS may be also called a cell -specific RS .
- an RS associated with the feedback of Channel State Information (CSI) such as CQI/PMI/RI may be separately defined as a CSI-RS.
- the DRS may be transmitted through REs if data demodulation on a PDSCH is necessary.
- the UE may receive the presence/absence of the DRS from a higher layer and receive information indicating that the DRS is valid only when the PDSCH is mapped.
- the DRS may be also called a UE- specific RS or a Demodulation RS (DMRS) .
- DMRS Demodulation RS
- FIG. 7 is a diagram showing a pattern of CRSs
- the downlink RB pair as a mapping unit of the RSs may be expressed in units of one subframe on a time domain x 12 subcarriers on a frequency domain. That is, on the time axis, one RB pair has a length of 14 OFDM symbols in case of the normal CP (FIG. 7 (a) ) and has a length of 12 OFDM symbols in case of the extended CP (FIG. 7(b)).
- FIG. 7 shows the locations of the RSs on the RB pair in the system in which the eNodeB supports four transmission antennas.
- Resource Elements (REs) denoted by “0”, u l" , "2" and w 3" indicate the locations of the CRSs of the antenna port indexes 0, 1, 2 and 3, respectively.
- the RE denoted by "D” indicates the location of the DRS .
- the CRS is used to estimate the channel of a physical antenna and is distributed over the entire band as an RS which is able to be commonly received by all UEs located within a cell.
- the CRS may be used for CSI acquisition and data demodulation.
- the CRS is defined in various formats according to the antenna configuration of the transmission side (eNodeB) .
- the 3GPP LTE (e.g., Release-8) system supports various antenna configurations, and a downlink signal transmission side (eNodeB) has three antenna configurations such as a single antenna, two transmission antennas and four transmission antennas. If the eNodeB performs single- antenna transmission, RSs for a single antenna port are arranged. If the eNodeB performs two-antenna transmission, RSs for two antenna ports are arranged using a Time Division Multiplexing (TDM) and/or Frequency Division Multiplexing (FDM) scheme.
- TDM Time Division Multiplexing
- FDM Frequency Division Multiplexing
- the RSs for the two antenna ports are arranged in different time resources and/or different frequency resources so as to be distinguished from each other.
- RSs for four antenna ports are arranged using the TDM/FDM scheme.
- the channel information estimated by the downlink signal reception side (UE) through the CRSs may be used to demodulate data transmitted using a transmission scheme such as single antenna transmission, transmit diversity, closed-loop spatial multiplexing, open-loop spatial multiplexing, or Multi-User MIMO (MU-MIMO) .
- a transmission scheme such as single antenna transmission, transmit diversity, closed-loop spatial multiplexing, open-loop spatial multiplexing, or Multi-User MIMO (MU-MIMO) .
- MU-MIMO Multi-User MIMO
- Equation 12 The rule of mapping the CRSs to the RBs is defined by Equation 12.
- Equation 12 k denotes a subcarrider index, 1 denotes a symbol index, and p denotes an antenna port index. denotes the number of OFDM symbols of one downlink slot,
- n s denotes the number of RBs allocated to the downlink
- the location of the RS in the frequency domain depends on a value V sh i ft . Since the value Vghif depends on the cell ID, the location of the RS has a frequency shift value which varies according to the cell .
- the locations of the CRSs in the frequency domain may be shifted so as to be changed according to the cells.
- the RSs are located at an interval of three subcarriers, the RSs are arranged on 3k-th subcarriers in one cell and arranged on (3k+l) -th subcarriers in the other cell.
- the RSs are arranged at an interval of 6 REs (that is, interval of 6 subcarriers) in the frequency domain and are separated from REs, on which RSs allocated to another antenna port are arranged, by 3 REs in the frequency domain.
- power boosting is applied to the CRSs.
- the power boosting indicates that the RSs are transmitted using higher power by bringing (stealing) the powers of the REs except for the REs allocated for the RSs among the REs of one OFDM symbol .
- the time interval is differently defined according to the CP length.
- the RSs are located on symbol indexes 0 and 4 of the slot in case of the normal CP and are located on symbol indexes 0 and 3 of the slot in case of the extended CP. Only RSs for a maximum of two antenna ports are defined in one OFDM symbol .
- the RSs for the antenna ports 0 and 1 are located on the symbol indexes 0 and 4 (the symbol indexes 0 and 3 in case of the extended CP) of the slot and the RSs for the antenna ports 2 and 3 are located on the symbol index 1 of the slot .
- the frequency locations of the RSs for the antenna ports 2 and 3 in the frequency domain are exchanged with each other in a second slot .
- a system e.g., an LTE-A system having the extended antenna configuration may be designed.
- the extended antenna configuration may have, for example, eight transmission antennas .
- UEs which operate in the existing antenna configuration needs to be supported, that is, backward compatibility needs to be supported. Accordingly, it is necessary to support a RS pattern according to the existing antenna configuration and to design a new RS pattern for an additional antenna configuration. If CRSs for the new antenna ports are added to the system having the existing antenna configuration, RS overhead is rapidly increased and thus data transfer rate is reduced.
- LTE-A Advanced
- separate RSs CSI-RSs
- the DRS (or the UE-specific RS) is used to demodulate data.
- a precoding weight used for a specific UE upon multi-antenna transmission is also used in an RS without change so as to estimate an equivalent channel, in which a transfer channel and the precoding weight transmitted from each transmission antenna are combined, when the UE receives the RSs.
- the existing 3GPP LTE system (e.g., Release-8) supports four-transmission antenna transmission as a maximum and the DRS for Rank 1 beamforming is defined.
- the DRS for Rank 1 beamforming is also denoted by the RS for the antenna port index 5.
- the rule of the DRS mapped on the RBs is defined by Equations 13 and 14. Equation 13 is for the normal CP and Equation 14 is for the extended CP.
- Equations 13 and 14 k denotes a subcarrider index, 1 denotes a symbol index, and p denotes an antenna port N RB
- sc denotes the resource block size in the frequency domain and is expressed by the number of subcarriers.
- FRB denotes a physical resource block number.
- ⁇ denotes the bandwidth of the RB of the PDSCH
- n s denotes a slot index
- 1D denotes a cell ID.
- mod indicates a modulo operation.
- the location of the RS in the frequency domain depends on a value V sh i ft - Since the value V sh i f depends on the cell ID, the location of the RS has a frequency shift value which varies according to the cell.
- DRS-based data demodulation is considered. That is, separately from the DRS (antenna port index 5) for Rank 1 beamforming defined in the existing 3GPP LTE (e.g., Release-8) system, DRSs for two or more layers may be defined in order to support data transmission through the added antenna.
- CoMP Cooperative Multi-Point
- CoMP transmission/reception technology may be referred to as co-MIMO, collaborative MIMO or network MIMO
- the CoMP technology can increase the performance of the UE located on a cell edge and increase average sector throughput .
- ICI Inter-Cell Interference
- a method of enabling the UE located on the cell edge to have appropriate throughput and performance using a simple passive method such as Fractional Frequency Reuse (FFR) through the UE-specific power control in the environment restricted by interference is applied.
- FFR Fractional Frequency Reuse
- the ICI is reduced or the UE reuses the ICI as a desired signal.
- a CoMP transmission scheme may be applied.
- the CoMP scheme applicable to the downlink may be largely classified into a Joint Processing (JP) scheme and a Coordinated Scheduling/Beamforming (CS/CB) scheme.
- JP Joint Processing
- CS/CB Coordinated Scheduling/Beamforming
- each point (eNodeB) of a CoMP unit may use data.
- the CoMP unit refers to a set of eNodeBs used in the CoMP scheme.
- the JP scheme may be classified into a joint transmission scheme and a dynamic cell selection scheme.
- the joint transmission scheme refers to a scheme for transmitting a PDSCH from a plurality of points (a part or the whole of the CoMP unit) . That is, data transmitted to a single UE may be simultaneously transmitted from a plurality of transmission points. According to the joint transmission scheme, it is possible to coherently or non- coherently improve the quality of the received signals and to actively eliminate interference with another UE .
- the dynamic cell selection scheme refers to a scheme for transmitting a PDSCH from one point (of the CoMP unit) . That is, data transmitted to a single UE at a specific time is transmitted from one point and the other points in the cooperative unit at that time do not transmit data to the UE.
- the point for transmitting the data to the UE may be dynamically selected.
- the CoMP units may cooperatively perform beamforming of data transmission to a single UE. Although only a serving cell transmits the data, user scheduling/beamforming may be determined by the coordination of the cells of the CoMP unit.
- coordinated multi-point reception refers to reception of a signal transmitted by coordination of a plurality of geographically separated points.
- the CoMP scheme applicable to the uplink may be classified into Joint Reception (JR) and Coordinated Scheduling/Beamforming (CS/CB) .
- the JR scheme indicates that a plurality of reception points receives a signal transmitted through a PUSCH
- the CS/CB scheme indicates that only one point receives a PUSCH
- user scheduling/beamforming is determined by the coordination of the cells of the CoMP unit.
- SRS Sounding RS
- An SRS is used for enabling an eNodeB to measure channel quality so as to perform frequency-selective scheduling on the uplink and is not associated with uplink data and/or control information transmission.
- the present invention is not limited thereto and the SRS may be used for improved power control or supporting of various start-up functions of UEs which are not recently scheduled.
- the start-up functions may include, for example, initial Modulation and Coding Scheme (MCS) , initial power control for data transmission, timing advance, and frequency-semi-selective scheduling (scheduling for selectively allocating frequency resources in a first slot of a subframe and pseudo-randomly hopping to another frequency in a second slot) .
- MCS Modulation and Coding Scheme
- the SRS may be used for downlink channel quality measurement on the assumption that the radio channel is reciprocal between the uplink and downlink. This assumption is particularly valid in a Time Division Duplex (TDD) system in which the same frequency band is shared between the uplink and the downlink and is divided in the time domain.
- TDD Time Division Duplex
- the subframe through which the SRS is transmitted by a certain UE within the cell is indicated by cell -specific broadcast signaling. -bit cell-specific
- “srsSubframeConfiguration” parameter indicates 15 possible configurations of the subframe through which the SRS can be transmitted within each radio frame. By such configurations, it is possible to provide adjustment flexibility of SRS overhead according to a network arrangement scenario. The remaining one (sixteenth) configuration of the parameters indicates the switch-off of the SRS transmission within the cell and is suitable for a serving cell for serving high-rate UEs .
- the SRS is always transmitted on a last SC-FDMA symbol of the configured subframe. Accordingly, the SRS and a Demodulation RS (DMRS) are located on different SC-FDMA symbols. PUSCH data transmission is not allowed on the SC-FDMA symbol specified for SRS transmission and thus sounding overhead does not approximately exceed 7% even when it is highest (that is, even when SRS transmission symbols are present in all subframes) .
- DMRS Demodulation RS
- Each SRS symbol is generated by the basic sequence (random sequence or Zadoff-Ch (ZC) -based sequence set) with respect to a given time unit and frequency band, and all UEs within the cell use the same basic sequence.
- the SRS transmission of the plurality of UEs within the cell in the same time unit and the same frequency band is orthogonally distinguished by different cyclic shifts of the base sequence allocated to the plurality of UEs.
- the SRS sequences of different cells can be distinguished by allocating different basic sequences to respective cells, but the orthogonality between the different basic sequences is not guaranteed.
- Relay Node (RN) Relay Node
- a RN may be considered for, for example, enlargement of high data rate coverage, improvement of group mobility, temporary network deployment, improvement of cell edge throughput and/or provision of network coverage to a new area.
- a RN forwards data transmitted or received between the eNodeB and the UE, two different links (backhaul link and access link) are applied to the respective carrier frequency bands having different attributes.
- the eNodeB may include a donor cell .
- the RN is wirelessly connected to a radio access network through the donor cell.
- the backhaul link between the eNodeB and the RN may be represented by a backhaul downlink if downlink frequency bands or downlink subframe resources are used, and may be represented by a backhaul uplink if uplink frequency bands or uplink subframe resources are used.
- the frequency band is resource allocated in a Frequency Division Duplex (FDD) mode and the subframe is resource allocated in a Time Division Duplex (TDD) mode.
- the access link between the RN and the UE(s) may be represented by an access downlink if downlink frequency bands or downlink subframe resources are used, and may be represented by an access uplink if uplink frequency bands or uplink subframe resources are used.
- the eNodeB must have functions such as uplink reception and downlink transmission and the UE must have functions such as uplink transmission and downlink reception.
- the RN must have all functions such as backhaul uplink transmission to the eNodeB, access uplink reception from the UE, the backhaul downlink reception from the eNodeB and access downlink transmission to the UE.
- FIG. 9 is a diagram showing an example of implementing transmission and reception functions of a FDD- mode RN.
- the reception function of the RN will now be conceptually described.
- a downlink signal received from the eNodeB is forwarded to a Fast Fourier Transform (FFT) module 912 through a duplexer 911 and is subjected to an OFDMA baseband reception process 913.
- An uplink signal received from the UE is forwarded to a FFT module 922 through a duplexer 921 and is subjected to a Discrete Fourier Transform- spread-OFDMA (DFT-s-OFDMA) baseband reception process 923.
- FFT Fast Fourier Transform
- DFT-s-OFDMA Discrete Fourier Transform- spread-OFDMA
- the process of receiving the downlink signal from the eNodeB and the process of receiving the uplink signal from the UE may be simultaneously performed.
- the transmission function of the RN will now be described.
- the uplink signal transmitted to the eNodeB is transmitted through a DFT-s-OFDMA baseband transmission process 933, an Inverse FFT (IFFT) module 932 and a duplexer 931.
- the downlink signal transmitted to the UE is transmitted through an OFDM baseband transmission process 943, an IFFT module 942 and a duplexer 941.
- the process of transmitting the uplink signal to the eNodeB and the process of transmitting the downlink signal to the UE may be simultaneously performed.
- duplexers shown as functioning in one direction may be implemented by one bidirectional duplexer.
- the duplexer 911 and the duplexer 931 may be implemented by one bidirectional duplexer and the duplexer 921 and the duplexer 941 may be implemented by one bidirectional duplexer.
- the bidirectional duplexer may branch into the IFFT module associated with the transmission and reception on a specific carrier frequency band and the baseband process module line.
- the case where the backhaul link operates in the same frequency band as the access link is referred to as "in-band” and the case where the backhaul link and the access link operate in different frequency bands is referred to as "out-band” .
- in-band the case where the backhaul link operates in the same frequency band as the access link
- out-band the case where the backhaul link and the access link operate in different frequency bands.
- a UE which operates according to the existing LTE system e.g., Release-8) , hereinafter, referred to as a legacy UE, must be able to be connected to the donor cell.
- the RN may be classified into a transparent RN or a non-transparent RN depending on whether or not the UE recognizes the RN.
- transparent indicates that the UE cannot recognize whether communication with the network is performed through the RN and the term "non- transparent” indicates that the UE recognizes whether communication with the network is performed through the RN.
- the RN may be classified into a RN configured as a part of the donor cell or a RN for controlling the cell.
- the RN configured as the part of the donor cell may- have a RN ID, but does not have its cell identity.
- RRM Radio Resource Management
- the RN is configured as the part of the donor cell
- such an RN can support a legacy UE.
- examples of such an RN include various types of relays such as smart repeaters, decode-and-forward relays, L2 (second layer) relays and Type-2 relays.
- the RN controls one or several cells, unique physical layer cell identities are provided to the cells controlled by the RN, and the same RRM mechanism may be used. From the viewpoint of the UE, there is no difference between access to the cell controlled by the RN and access to the cell controlled by a general eNodeB.
- the cell controlled by such an RN may support a legacy UE .
- examples of such an RN include self-backhauling relays, L3 (third layer) relays, Type-1 relays and Type-la relays.
- the Type-1 relay is an in-band relay for controlling a plurality of cells, which appears to be different from the donor cell, from the viewpoint of the UE .
- the plurality of cells has respective physical cell IDs (defined in the LTE Release-8) and the RN may transmit its synchronization channel, RSs, etc.
- the UE may directly receive scheduling information and HARQ feedback from the RN and transmit its control channel (Scheduling Request (SR) , CQI, ACK/NACK, etc.) to the RN.
- SR Service Request
- a legacy UE (a UE which operates according to the LTE Release- 8 system) regards the Type-1 relay as a legacy eNodeB (an eNodeB which operates according to the LTE Release-8 system) . That is, the Type- 1 relay has backward compatibility.
- the UEs which operates according to the LTE-A system regard the Type-1 relay as an eNodeB different from the legacy eNodeB, thereby achieving performance improvement .
- the Type-la relay has the same characteristics as the above-described Type-1 relay except that it operates as an out-band relay.
- the Type-la relay may be configured so as to minimize or eliminate an influence of the operation thereof on an LI (first layer) operation.
- the Type-2 relay is an in-band relay and does not have a separate physical cell ID. Thus, a new cell is not established.
- the Type-2 relay is transparent to the legacy UE and the legacy UE does not recognize the presence of the Type-2 relay.
- the Type-2 relay can transmit a PDSCH, but does not transmit at least a CRS and a PDCCH.
- resource partitioning In order to enable the RN to operate as the in-band relay, some resources in a time-frequency space must be reserved for the backhaul link so as not to be used for the access link. This is called resource partitioning.
- the backhaul downlink and the access downlink may be multiplexed on one carrier frequency using a Time Division Multiplexing (TDM) scheme (that is, only one of the backhaul downlink or the access downlink is activated in a specific time) .
- TDM Time Division Multiplexing
- the backhaul uplink and the access uplink may be multiplexed on one carrier frequency using the TDM scheme (that is, only one of the backhaul uplink or the access uplink is activated in a specific time) .
- the multiplexing of the backhaul link using a FDD scheme indicates that backhaul downlink transmission is performed in a downlink frequency band and the backhaul uplink transmission is performed in an uplink frequency band.
- the multiplexing of the backhaul link using the TDD scheme indicates that the backhaul downlink transmission is performed in a downlink subframe of the eNodeB and the RN and the backhaul uplink transmission is performed in an uplink subframe of the eNodeB and the RN.
- the in-band relay for example, if the backhaul downlink reception from the eNodeB and the access downlink transmission to the UE are simultaneously performed in a predetermined frequency band, the signal transmitted from the transmitter of the RN may be received by the receiver of the RN and thus signal interference or RF jamming may occur in the RF front end of the RN. Similarly, if the access uplink reception from the UE and the backhaul uplink transmission to the eNodeB are simultaneously performed in a predetermined frequency band, signal interference may occur in the RF front end of the RN.
- the RN operates so as not to transmit a signal to the UE while a signal is received from the donor cell. That is, a gap may be generated in the transmission from the RN to the UE and any transmission from the RN to the UE (including the legacy UE) may not be performed. Such a gap may be set by configuring a Multicast Broadcast Single Frequency Network (MBSFN) subframe (see FIG. 10) .
- MMSFN Multicast Broadcast Single Frequency Network
- a first subframe 1010 is a general subframe, in which a downlink (that is, access downlink) control signal and data is transmitted from the RN to the UE
- a second subframe 1020 is an MBSFN subframe, in which a control signal is transmitted from the RN to the UE in a control region 1021 of the downlink subframe, but any signal is not transmitted from the RN to the UE in the remaining region 1022 of the downlink subframe.
- the PDCCH is transmitted from the RN to the UE in the control region 1021 of the second subframe, it is possible to provide backward compatibility to the legacy UE served by the RN. While any signal is not transmitted from the RN to the UE in the remaining region 1022 of the second subframe, the RN may receive the signal transmitted from the eNodeB. Accordingly, the resource partitioning disables the in-band RN to simultaneously perform the access downlink transmission and the backhaul downlink reception.
- the second subframe 1022 using the MBSFN subframe will now be described in detail.
- the MBSFN subframe is essentially used for a Multimedia Broadcast and Multicast Service (MBMS) which simultaneously transmits the same signal in the same cell.
- MBMS Multimedia Broadcast and Multicast Service
- the control region 1021 of the second subframe may be a RN non-hearing interval .
- the RN non-hearing interval refers to an interval in which the RN does not receive a backhaul downlink signal and transmits an access downlink signal. This interval may be set to 1, 2 or 3 OFDM lengths as described above.
- the RN performs the access downlink transmission to the UE in the RN non- hearing interval 1021 and performs the backhaul downlink reception from the eNodeB in the remaining region 1022. At this time, since the RN cannot simultaneously perform the transmission and reception in the same frequency band, it takes a certain length of time to switch the RN from the transmission mode to the reception mode.
- a guard time to switch the RN from the transmission mode to the reception mode in a first portion of the backhaul downlink reception region 1022.
- a guard time to switch the RN from the reception mode to the transmission mode may be set.
- the length of the guard time may be set to values of the time domain, for example, values of k (k ⁇ l) time samples Ts or one or more OFDM symbol lengths.
- the guard time of a last portion of the subframes may not be defined or set.
- Such a guard time may be defined only in the frequency domain set for the transmission of the backhaul downlink subframe, in order to maintain backward compatibility (the legacy UE cannot be supported if the guard time is set in the access downlink interval) .
- the RN can receive a PDCCH and a PDSCH from the eNodeB in the backhaul downlink reception interval 1022 except for the guard time.
- PDCCH and the PDSCH are physical channels dedicated for RN and thus may be represented by a R-PDCCH (Relay-PDCCH) and a R-PDSCH (Relay-PDSCH) .
- interference may occur in a terminal served by one base station due to a strong downlink signal from another base station. If inter-cell interference occurs, it is possible to reduce inter-cell interference using a method of transmitting an inter-cell cooperative signal between the two base stations. In the following various embodiments of the present invention, it is assumed that a signal may be smoothly transmitted and received between two base stations in which interference occurs.
- a wired/wireless link e.g., a backhaul link or Un interface
- good transmission conditions such as a good transmission bandwidth or time delay.
- time synchronization between two base stations is performed within an allowable error range (e.g., if a downlink subframe boundary between two base stations in which interference occurs is aligned)
- an offset of a subframe boundary between the two base stations is clearly recognized.
- the eNBl 110 is a macro base station which provides services over a wide area with high transmit power and the eNB2 120 is a micro base station (e.g., a pico base station) which provides services over a narrow area with low transmit power.
- the terminal 130 which is located at a cell edge of the eNB2 120 and is served by the eNB2 120 receives strong interference from the eNBl 110, it may be difficult to perform efficient communication without appropriate inter-cell cooperation.
- a probability of inter-cell interference occurring is high.
- a predetermined coordination (bias) value may be added to power received from the micro base station and may not be added to power received from the macro base station so as to compute and compare the received powers of the downlink signals from the macro and micro base stations.
- the terminal may set a base station which provides highest downlink receive power as a serving base station. Then, more terminals may be connected to the micro base station.
- the micro base station may be set as the serving base station, and the terminal connected to the micro base station may experience strong interference from the macro base station. In this case, it may be difficult for terminals located at the edge of the micro base station to perform correct operations due to strong interference from the macro base station if inter-cell cooperation is not provided.
- inter-cell interference when inter-cell interference is present, in order to perform efficient operation, appropriate cooperation should be performed between two base stations in which inter-cell interference occurs, and a signal enabling such cooperative operation may be transmitted and received through a link between the two base stations.
- the macro base station may control an inter-cell cooperative operation and the micro base station may perform an appropriate operation according to a cooperative signal indicated by the macro base station.
- inter-cell interference occurs in other situations (e.g., the case where inter-cell interference occurs between a CSG HeNB and an OSG macro base station, the case where a micro base station causes interference and a macro base station is subject to interference, the case where inter-cell interference occurs between micro base stations or macro base stations, etc.).
- a cell which causes interference is referred to as an eNBl and a cell which is subject to interference is referred to as an eNB2.
- the eNBl is a macro base station and the eNB2 is a micro base station.
- the present invention is not limited thereto and the principle of the present invention is applicable to various forms of inter- cell interference.
- a method of silencing operation which reduces the transmission power of eNBl (including power reduction to zero transmission power) to mitigate inter-cell interference to a terminal connected to the eNB2 in a specific resource region (that is, this method may be represented by a method of transmitting a null signal or a silencing method) is applicable.
- a cell which causes interference may configure a specific subframe by an MBSFN subframe . In a downlink subframe configured by the MBSFN subframe, a signal is transmitted only in a control region and a signal is not transmitted in a data region.
- a cell which causes interference may configure a specific subframe by an Almost Blank Subframe (ABS) or ABS-with MBSFN.
- ABS refers to a subframe in which only a CRS is transmitted in a control region and data region of a downlink subframe and the other control information and data are not transmitted.
- a downlink channel and downlink signal such as a PBCH, PSS or SSS may be transmitted.
- the ABS-with-MBSFN refers to a subframe in which even the CRS of the data region is not transmitted unlike the above-described ABS.
- the specific resource region in which silencing is performed may be represented by time resources and/or frequency resources.
- a time resource location in which silencing is performed may be determined by a combination of at least one of an overall time domain, a specific subframe, a specific slot and a specific OFDM symbol unit.
- a frequency resource location in which silencing is performed may be determined by a combination of at least one of an overall frequency band, a specific carrier (in case of carrier aggregation in which a plurality of carriers is used) , a specific resource block and a specific subcarrier unit.
- the resource region in which silencing is performed is clearly specified.
- the present invention proposes an inter-cell cooperative signal transmission/reception method for blanking downlink transmissions in the cell eNBl which causes interference in a specific resource region (that is, silencing) , in order to smoothly operate the terminal (UE) of the cell eNB2 which is subject to interference.
- a specific resource region that is, silencing
- UE terminal
- the range of the present invention is not limited thereto and the principle of the present invention is applicable to an operation for performing silencing in specific frequency resources between the cell eNBl which causes interference and the cell eNB2 which is subject to interference.
- FIG. 11 is a flowchart illustrating an operation
- the eNB2 may determine a subframe in which a silencing operation of the eNBl is required and inform the eNBl of the subframe .
- the present embodiment relates to a method of enabling the cell eNB2 which is subject to interference to transmit the index of a downlink subframe with strong interference to the cell eNBl which causes interference in the form of load indication information.
- the eNB2 may- determine a downlink subframe in which the eNBl needs to perform silencing (that is, a subframe set to be set to a blank subframe (ABS) ) and transmit information indicating the determined downlink subframe to the eNBl.
- the eNBl may determine a subframe in which silencing will be performed (that is, a subframe which will be set to an ABS) and inform the eNB2 of the subframe .
- the eNB2 may- receive, from the terminal (UE) , information about downlink measurement from each base station to the terminal.
- the information about downlink measurement may include channel state information (CSI) , radio resource management (RRM) measurement information, radio link monitoring (RLM) measurement information, etc.
- CSI channel state information
- RRM radio resource management
- RLM radio link monitoring
- the eNB2 may check the strength of a signal from each base station to the terminal, channel quality, link state, etc.
- the eNB2 may determine the number/indices of subframes for requesting the eNBl to perform silencing based on the information received in step S1110.
- the eNB2 may determine the locations and/or number of specific subframes in which the eNBl should perform silencing (that is, subframes in which the eNB2 may provide a service to the UE without strong interference from the eNBl) , based on the number and locations of UEs connected thereto and traffic load of the UEs.
- the eNB2 may determine in which UE a problem occurs in reception of a control channel and/or a data channel when the eNBl does not perform silencing.
- the eNB2 may determine a list of UEs in which a difference between the strength of a signal received by the UE from the eNBl and the strength of a signal from the eNB2 is greater than a predetermined threshold. Thus, the eNB2 may determine the number of subframes necessary to process all traffic for the determined UE on the assumption that interference is not caused by the eNBl. The eNB2 may determine in which subframe the eNBl performs silencing (that is, a subframe index) .
- the eNB2 may send information about the subframe in which the silencing operation of the eNBl is requested to the eNBl. That is, the eNB2 may transmit information specifying preferred silent subframes in which the eNBl performs the silencing operation to the eNBl.
- the information specifying the subframes may be information implicitly indicating (estimating) the number of subframes, a subframe index, or the number/indices of subframes.
- the eNBl may perform the silencing operation in consideration of the silencing subframe information sent from the eNB2.
- the information specifying the information sent from the eNB2 to the eNBl that is, the subframe in which the silencing operation is requested, will be described in detail.
- the eNB2 may compute the preferred number of subframes in which the silencing operation of the eNBl is requested in constant duration (e.g., four radio frames (that is, 40 subframes) units and transmit the preferred number of subframes to the eNBl.
- constant duration e.g., four radio frames (that is, 40 subframes) units
- the eNBl may appropriately select subframes in which silencing will be performed within the duration, the operation of the eNBl is not restricted.
- the eNB2 may determine the indices (or locations) of the subframes in which the silencing operation of the eNBl is requested and transmit the indices of the subframes to the eNBl. Transmission of the indices of the subframes in which the silencing operation will be performed indicates that the eNBl is informed of the pattern of subframes in which silencing is desired to be performed.
- an inter-cell interference coordination operation that is, silencing
- silencing may be performed to be further compatible with the operation of the UE connected to the eNB2 , as compared to the case where only the number of subframes in which silencing will be performed within a predetermined duration is indicated.
- the pattern of a subframe in which silencing is performed with the period of 10 ms may be determined and the eNBl may be informed thereof, thereby improving the effect of inter-cell interference coordination for the SPS traffics.
- SPS semi-persistent scheduling
- the pattern of a subframe in which silencing is performed with the period of 8 ms may be determined and the eNBl may be informed thereof, thereby improving the effect of inter-cell interference coordination for the general HARQ processes.
- the pattern of the subframe in which silencing of the eNBl is requested may be represented in the form of an overload indicator (01) or a load indication for downlink.
- the existing 01 is defined for uplink in the 3GPP LTE and is information indicating that the cell which is subject to interference informs a neighbor cell which causes interference that a specific resource region is subject to strong interference from the neighbor cell in uplink.
- the present invention defines the 01 with respect to the downlink subframe and proposes a method of enabling the eNB2 to inform the eNBl of the indices of specific resources (e.g., specific subframes) in which an efficient service is impossible due to strong interference from the eNBl among resources (e.g., subframes) , in which the UE connected to the eNB2 should receive a downlink service, in the form of the 01.
- the eNB2 may inform the eNBl of information indicating specific resources which cannot be used by the eNB2 (that is, specific resources which are not available as resources protected from inter-cell interference) due to presence of strong interference from the eNBl among downlink resources.
- the eNBl may control designation of a blank subframe of the eNBl in consideration of the 01 information from the eNB2.
- the . specific resource region may be determined by a combination of time resources and/or frequency resources.
- the 01 may be sent from the eNB2 to the eNBl in the form of a bitmap per RB.
- the cell eNBl which causes interference may determine an operation which will be performed in downlink resources (S1210) and transmit information about the operation to the cell eNB2 which is subject to interference (S1220) . More specifically, the eNBl may determine information indicating in which downlink resources silencing will be performed and transmit the information to the eNB2.
- the operation for enabling the eNBl to transmit information about the resources in which silencing will be performed to the eNB2 may be transmitted as a response to information about silencing request resources received by the eNBl from the eNB2.
- the information about silenced resources preferred by eNB2 may be transmitted from the eNB2 before step S1210, which corresponds to the result of performing the operations of S1110 to S1130 of FIG. 11 by the eNB2.
- the eNBl may specify resources in which the eNBl may perform silencing and inform cells which are subject to interference of neighbors of the resources in which the eNBl may perform silencing. That is, in FIG. 12, a step of receiving, by the eNBl, the silencing resource information from the eNB2 is not performed before step S1210 and only step S1210 may be performed.
- the cell which receives the information about the resources in which the eNBl will perform silencing may schedule downlink transmission to terminals connected thereto in specific resources in which interference from the eNBl is not present (or is low) based on the information or operate in a manner of indicating resources (subframes) in which downlink measurement will be performed in consideration of presence/absence of interference (or severity of interference) (step S1230) .
- the eNB2 indicates subframes in which downlink measurement will be performed to the terminals connected thereto will be described subsequent to the description of the present embodiment.
- silencing may be performed in predetermined time-frequency resource units.
- the eNBl may inform the eNB2 of the indices of the subframes in which silencing will be performed. For example, the eNBl may transmit a downlink low interference indicator (LII) to the eNB2 with respect to each subframe .
- LII downlink low interference indicator
- Setting LII to 1 with respect to a certain subframe indicates that the eNBl performs the silencing operation in the subframe so as to secure low inter-cell interference.
- Setting LII to 0 with respect to a certain subframe indicates that the eNBl may not secure low inter-cell interference in the subframe.
- This scheme can be efficient when the eNBl can accurately predict traffic load. That is, if information indicating in which downlink subframe the silencing operation will be performed is provided in advance, the eNBl performs the silencing operation according to the provided information so as to prevent the eNB2 from being subject to interference. Accordingly, it is possible to accurately control interference according to a predetermined agreement between the cells eNBl and eNB2 in which interference occurs .
- the above-described scheme may inefficiently use resources when the eNBl may not accurately predict traffic load thereof. For example, in the case where the eNBl informs the eNB2 that silencing will be performed in some subframes in advance, even when the traffic load of the eNBl is reduced more than expected and thus silencing may be performed in more subframes than the number of subframes reported in advance, the eNB2 is unaware of information about the operation of the eNBl in the subframes other than the subframes reported to the eNB2 that silencing will be performed.
- the eNBl may not perform the silencing operation in the subframes other than the subframe reported in advance . Accordingly, resource use efficiency may be deteriorated.
- the eNBl may inform the eNB2 of newly determined silencing subframes based on the changed traffic load, time delay may occur due to transmission and application of the new information. Accordingly, this scheme may not be immediately (or dynamically) used according to traffic load changes.
- FIG. 13 is a diagram showing an example of configuring a subframe group according to silencing priority.
- the eNBl may configure the subframe group and inform the eNB2 of subframe group setting (corresponding to S1220 of FIG. 12) , and the eNB2 may perform downlink scheduling or indicate resources in which downlink measurement of the terminal will be performed based on the subframe group setting information (corresponding to S1230 of FIG. 12) .
- a subframe group 0 includes a set of subframe (s) in which silencing is necessarily performed
- a subframe group 1 includes a set of subframe (s)
- subframe groups 2 to N may be similarly determined according to silencing priority. That is, as the index of the subframe group is decreased (approaches 0) , a probability of the eNBl performing silencing is increased. As the index of the subframe group is increased (approaches N) , a probability of the eNBl not performing silencing is increased.
- the eNBl may perform silencing with a probability close to 1 in the subframe group 0 and perform downlink transmission with a probability close to 1 in the subframe group N.
- the subframe groups 1 to N-l may be soft cooperative silencing subframes in which the eNBl stochastically performs silencing. As the index of the subframe group is increased, a probability of silencing being performed is decreased.
- the eNBl may preferentially perform silencing in all subframes of the subframe group 0 and may perform silencing in the subframes of the subframe group 1 if additional silencing becomes possible due to traffic load changes, etc.
- a determination as to whether or not the silencing operation of the eNBl is performed in the subframe groups 2 to N may be made in a similar manner.
- the eNB2 may use the subframe group information in downlink scheduling of the terminals connected thereto. For example, the eNB2 may preferentially select subframes belonging to the subframe group 0 and perform downlink scheduling with respect to terminals which require silencing of the eNBl due to strong interference from the eNBl (e.g., terminals located at the cell edge). Additionally, with respect to terminals which additionally require silencing of the eNBl, subframes belonging to the subframe group 1 may be selected so as to perform downlink scheduling. In a similar manner, subframes belonging to the subframe groups 2 to N are sequentially selected such that the eNB2 may perform downlink scheduling with respect to the terminals connected thereto. That is, subframes which may be scheduled to the terminals which require silencing of the eNBl by the eNB2 may be selected in ascending order of the indices of the subframe groups .
- Subframe (s) in which a probability of performing silencing in the eNBl is high are set to a first subframe group and subframe (s) in which a probability of not performing silencing in the eNBl is high may be set to a second subframe group .
- the eNBl may inform the eNB2 of such subframe group setting and then the eNB2 may determine in which subframe the eNBl performs silencing (that is, whether interference of the eNBl is high or low) . Accordingly, the eNB2 may not perform downlink scheduling with respect to the terminals connected to the eNB2 in subframes in which the interference of the eNBl is high, thereby coordinating interference.
- the first subframe group (subframes in which the eNBl will perform silencing) may correspond to the subframe groups 0 to N-l in the example of FIG. 13 and the second subframe group (subframes in which a probability of not performing silencing in the eNBl is high) may correspond to the subframe group N in the example of FIG. 13.
- the eNBl may transmit a downlink high interference indicator (HII) to the eNB2. That is, a subframe in which the HII is set to 1 corresponds to the second subframe group (e.g., the subframe group N of FIG. 13) and indicates that a probability of the eNBl causing high inter-cell interference in the subframe is high. Alternatively, a subframe in which the HII is set to 0 corresponds to the first subframe group (e.g., the subframe group 0 to N-l of FIG.
- HII downlink high interference indicator
- the LII and the HII may be selectively or complementarily applied.
- the number of subframes in which a probability of (necessarily) performing silencing in the eNBl is high is generally small.
- a subframe in which a probability of not performing silencing in the eNBl is high (that is, the eNBl will perform downlink transmission) may be specified.
- a subframe in which interference of the eNBl is low (that is, which is used by the eNB2 for downlink scheduling) and a subframe in which interference of the eNBl is high (that is, which is not used by the eNB2 for downlink scheduling) may be clearly determined.
- the two cells in which interference occurs may operate without limitation.
- the subframes corresponding to the subframe group indices 1 to N-l do not belong to the subframes with highest interference and do not belong to the subframes with lowest interference.
- the subframe group may be set using an opposing method. That is, the index of the subframe group may be increased as the silencing priority is increased. Even in this case, as described above, a subframe in which a probability of the cell which causes interference performing silencing is high may be indicated to neighbor cells using the LII and/or HII.
- the present invention proposes a method of sending subframe group setting information. More specifically, the cell (eNBl) which causes interference may inform the cell (eNB2) which is subject to interference of subframe group setting information, and the cell (eNB2) which is subject to interference may send the information to the terminals served by the cell (eNB2) .
- Such information may be transmitted and received between the cells, in which interference occurs, through an X2 interface (or a backhaul link) , and information indicating which subframe belongs to which subframe group may be expressed in a bitmap manner.
- an X2 interface or a backhaul link
- information indicating which subframe belongs to which subframe group may be expressed in a bitmap manner.
- a heterogeneous network of a macro cell and a pico cell and a heterogeneous network of a macro cell and a femto cell may be considered.
- An enhanced inter-cell interference coordination (elCIC) scheme has been discussed as a method for solving a problem in that the strength of inter-cell interference is greater than the strength of a signal of a serving cell.
- elCIC scheme a method of setting a specific subframe to an ABS by a cell which causes interference so as to reduce interference with another cell may be considered.
- the cell which causes interference may transmit information (that is, ABS information) about the subframe which is set to the ABS to the cell which is subject to interference.
- the terminal of the cell which is subject to interference performs measurement of a downlink channel in the subframe which is set to the ABS in the cell which causes interference, thereby reducing the influence of interference.
- the cell which causes interference may transmit information about ABS setting to the cell which is subject to interference through an X2 interface and the eNB of the cell which is subject to interference may signal information about measurement which will be performed by the terminal on a per subframe basis to the terminal .
- the eNB of the cell which causes interference may signal two bitmaps to the eNB of the cell which is subject to interference through the X2 interface .
- Each bitmap may include 40 bits and express the attribute of each subframe in units of 40 subframes .
- one bitmap represents information indicating a subframe which is currently set to the ABS although being differently set in the future (or information indicating a subframe which is not currently set to the ABS and may not be set to the ABS in the future) .
- Another bitmap represents a subframe in which a possibility of changing ABS setting is low.
- the first bitmap may correspond to a bitmap in which the ABS subframe is set to "1" and the other subframes are set to "0" .
- a second bitmap may correspond to a bitmap indicating a subframe in which a probability of being set to an ABS is high in the first bitmap (that is, a subframe which is necessarily set to an ABS in the second bitmap may correspond to a subset of subframes which are set to an ABS in the first bitmap) .
- the first bitmap corresponds to information indicating subframes in which silencing priority of the cell (eNBl) which causes interference is relatively low (that is, silencing is performed but silencing probability is relatively low) and the second bitmap corresponds to information indicating subframes in which silencing priority of the cell (eNBl) which causes interference is relatively high (that is, a probability of silencing being performed is high) .
- a subframe which does not correspond to the ABS in the first bitmap may correspond to a subframe in which a probability of interference occurring is high.
- the eNB of the cell which is subject to interference may select subframes in which the terminal should perform measurement based on the information about the subframe pattern received through the X2 interface and transmit the information about a subframe set, in which the terminal will perform measurement, to a terminal which requires measurement restriction among terminals within the cell.
- the reason why measurement restriction is necessary is because an accurate measurement result cannot be obtained when the terminal performs measurement using the same method in both a subframe with high interference (e.g., a subframe which is not set to an ABS in the cell which causes interference) and a subframe with low interference (e.g., a subframe in which a probability of being set to an ABS is high in the cell which causes interference) and thus downlink measurement should be performed using different methods according to presence/absence of interference (or severity of interference) . Then, it is possible to accurately measure an actual channel state .
- the eNB of the cell which is subject to interference may transmit the information about the subframe set to be measured to the terminal through RRC signaling.
- RRM radio resource management
- RL radio link monitoring
- RRM measurement may include reference signal received power (RSRP) , reference signal received quality (RSRQ) , a received signal strength indicator (RSSI) , etc.
- RLM measurement may include measurement for detection of radio link failure (RLF) such as downlink control signal reception impossibility or received signal quality deterioration.
- RRM/RLM measurement may perform RRM/RLM measurement using a reference signal (e.g., a CRS, etc.) transmitted in the subframe.
- a reference signal e.g., a CRS, etc.
- the ' remaining two subframe patterns transmitted to the terminal through RRC signaling are associated with channel state information (CSI) measurement.
- the terminal which receives the subframe patterns associated with CSI measurement may perform CSI measurement (RI, PMI , CQI measurement/computation) using a reference signal (e.g., a CSI-RS, etc.) transmitted in the subframe.
- a reference signal e.g., a CSI-RS, etc.
- the two subframe patterns associated with CSI measurement may include a pattern indicating a subframe with high interference (e.g., a subframe in which the cell which causes interference does not perform silencing) and a pattern indicating a subframe with low interference (e.g., a subframe in which a probability of the cell which causes interference performing silencing is high) .
- Each subframe pattern is signaled with a period of 40 ms and information indicating one subframe pattern has a size of 40 bits.
- the length of one subframe is 1 ms and a subframe pattern of units of 40 subframes may be indicated by 40 bits.
- signaling overhead of a total of 120 bits (40 bitsx3) occurs.
- Each subframe pattern which is signaled from the cell, which is subject to interference, to the terminal is shown in Table 1.
- RRM/RL RRM/RLM subset RRM/RLM measurement 40 bits measurement subframe
- the subframe patterns associated with CSI measurement may be classified into CSI_Subsetl, CSI_Subset2 and a Complementary subset.
- CSI_Subsetl is information indicating a subframe with low interference and has a size of 40 bits.
- CSI_Subset2 is information indicating a subframe with high interference and has a size of 40 bits.
- CSI_Subsetl and CSI_Subset2 may be set so as not to overlap. Although the case in which CSI_Subsetl indicates a subframe with low interference and CSI_Subset2 indicates a subframe with high interference is described, the subframes indicated by CSI_Subsetl and CSI_Subset2 may have different interference characteristics
- the complementary subset includes subframes which do not belong to both CSI_Subsetl and CSI_Subset2.
- the complementary subset Since the complementary subset is determined from CSI_Subsetl and CSI_Subset2, the complementary subset does not need to be signaled. In a subframe which is determined to belong to the complementary subset, the terminal does not perform measurement and the base station does not require a measurement result. That is, a certain subframe belongs to any one of CSI_Subsetl, CSI_Subset2 or Complementary subset Setting of CSI_Subsetl, CSI_Subset2 or the complementary subset may be determined based on information (ABS information) associated with a silenced subframe which is received by the cell, which is subject to interference, from the cell which causes interference through the X2 interface.
- ABS information information associated with a silenced subframe which is received by the cell, which is subject to interference, from the cell which causes interference through the X2 interface.
- the ABS information may include a first bitmap (indicating a subframe which is set to an ABS and a subframe which is not set to an ABS) and a second bitmap (indicating a subframe in which a probability of being set to an ABS is high among ABS subframes) .
- RRM/RLM_Subset is information indicating a subframe in which the terminal will perform RRM/RLM measurement and has a size of 40 bits. Since RRM/RLM measurement is for signal strength measurement, RLF detection, etc., RRM/RLM_Subset for accurate measurement may include subframes with low interference from the cell which causes interference (subframes in which low interference is guaranteed) .
- the present invention proposes a method of reducing the number of bits necessary to signal subframe patterns through a combination of the above-described subframe patterns.
- CSI_Subsetl and RRM/RLM_Subset may be regarded as subframes having similar properties, because they are set to ABSs by the cell which causes interference and are subframes in which dominant interference is barely present.
- RRM/RLM measurement is compared with CSI measurement, a portion necessary for RRM/RLM measurement (a portion to be measured) is relatively longer than a portion necessary for CSI measurement and an RRM/RLM measurement interval (interval between a measurement operation and a next measurement operation) is relatively longer than a CSI measurement interval. Accordingly, RRM/RLM_Subset may be included in CSI_Subsetl.
- one subframe may be represented by four states, that is, (1) a state in which the subframe belongs to both CSI_Subsetl and RRM/RLM_Subset , (2) a state in which the subframe belongs to CSI_Subsetl, (3) a state in which the subframe belongs to the CSI_Subset2, and (4) a state in which the subframe does not belong to any one of (1) to (3) .
- Such four states may be represented by subframe measurement types.
- the present invention proposes a method of dividing subframes into four states in consideration of subframe properties and signaling information about each subframe measurement type using 2 bits. This is shown in Tables 2 and 3.
- 2-bit information ndicating each subframe measurement type may be configured s shown in Table 3.
- the complementary subset includes subframes which do not belong to either CSI_Subsetl or CSI_Subset2 and do not belong to the RRM/RLM_Subset .
- each subframe measurement type is expressed by 2 bits, only 80 bits are required to express subframe patterns signaled in units of 40 ms .
- the terminal may be aware of each subframe measurement type through bitmap information having a size of 80 bits, which is signaled from the base station, and may perform measurement according to type. For example, if information indicating the measurement type of a certain subframe has a value of "00" , the terminal may perform RRM/RLM measurement in the subframe while performing CSI measurement (e.g., computation/generation of an RI , a PMI and a CQI on the assumption that interference from the cell which causes interference is low) corresponding to CSI_Subsetl in the subframe.
- CSI measurement e.g., computation/generation of an RI , a PMI and a CQI on the assumption that interference from the cell which causes interference is low
- Mapping of the combination of measurement subsets, the state and the bit value of Tables 2 and 3 is merely- exemplary and the scope of the present invention includes various modified examples in which subframe measurement types are distinguishably defined and are sent through a bitmap having a reduced bit size using information having a predetermined bit size. For example, if CSI_Subs " et2 and RRM/RLM_Subset have similar channel and interference properties, these subsets may be combined and represented by one state of the subset measurement type. Alternatively, in Tables 2 and 3, states 0, 1, 2 and 3 may be mapped to complementary subset, CSI_Subset2, CSI_Subsetl and CSI_Subsetl & RRM/RLM_Subset , respectively. Alternatively, states 0, 1, 2 and 3 may be mapped to bit values "11", "10", "01” and "00", respectively.
- information about the RRM/RLM_Subset of information indicating the subframe measurement type may be separately signaled.
- the subframe measurement type may be signaled.
- subframe setting that is, measurement type
- subframe setting that is, measurement type
- Information indicating the subframe measurement type in the above-described examples corresponds to information indicating presence/absence of interference (or severity of interference) from the cell (eNBl) which causes interference in each subframe and thus may be used as information indicating a degree of interference from the cell which causes interference in each subframe in the above-described various embodiments.
- a method of informing, by a base station, a terminal of CSI measurement resource setting information is as follows.
- the base station may determine first and second subframe sets (or CSI_Subsetl and CSI_Subset2) in which CSI measurement will be performed among a plurality of downlink subframes and transmit information indicating the first and second subframe sets to the terminal, and the terminal may receive information indicating the first and second subframe sets and determine in which subframe CSI measurement is performed.
- the terminal may perform CSI measurement with respect to each of the first and second subframe sets and transmit the result to the base station, and the base station may receive the CSI measurement result.
- the subframe belonging to the first subframe set CSI_Subsetl and the subframe belonging to the second subframe set CSI_Subset2 may not overlap. As described above, a subframe which does not belong to either of the first and second subframe sets may be present among the plurality of subframes. If such a base station belongs to a cell which is subject to interference, the first and second subframe sets CSI_Subsetl and CSI_Subset2 may be determined as follows .
- setting information of a subframe in which the cell (eNBl) which causes interference performs silencing may be sent from the cell (eNBl) which causes interference to the cell (eNB2) which is subject to interference.
- Such ABS setting information may include a first bitmap indicating a blank subframe and a non-blank subframe and a second bitmap indicating a subset of blank subframes.
- the first and second subframe sets CSI_Subsetl and CSI_Subset2 may be determined based on blank subframe setting information.
- the subframe belonging to the first subframe set may correspond to the subset of blank subframes indicated by the second bitmap
- the subframe belonging to the second subframe set may correspond to the non-blank subframe indicated by the first bitmap
- the subframe which does not belong to either of the first and second subframe sets may correspond the blank subframe indicated by the first bitmap
- a base station is described as a downlink transmission subject and a terminal is described as an uplink transmission subject in the description of the various embodiments of the present invention
- the scope of the present invention is not limited thereto. That is, the principle of the present invention described through the various embodiments of the present invention is equally applicable to a relay device functioning as a downlink transmission subject for transmitting a signal to a terminal or functioning as an uplink reception subject for receiving a signal from a terminal or a relay device functioning as an uplink transmission subject for transmitting a signal to a base station or a downlink reception subject for receiving a signal from a base station.
- FIG. 14 is a diagram showing a base station (eNB) device and a terminal device according to an exemplary embodiment of the present invention.
- eNB base station
- the eNB device 1410 may include a reception module 1411, a transmission module 1412, a processor 1413, a memory 1414, and a plurality of antennas 1415.
- the plurality of antennas 1415 supports MIMO transmission and reception.
- the reception module 1411 may receive signals, data, and information from an external device.
- the transmission module 1412 may transmit signals, data, and information to an external device.
- the processor 1413 may control the overall operation of the eNB device 1410.
- the eNB device 1410 may be configured to transmit CSI measurement resource information.
- the processor 1413 of the eNB device may be configured to determine first and second subframe sets in which CSI measurement will be performed among a plurality of downlink subframes .
- the processor 1413 may be configured to transmit information indicating the first and second subframe sets to the terminal 1420 through the transmission module 1412.
- the processor 1413 may be configured to receive CSI for the first and second subframe sets from the terminal 1420 through the reception module 1411.
- the subframe belonging to the first subframe set and the subframe belonging to the second subframe set may not overlap. Some of the plurality of subframes may not belong to either of the first and second subframe sets.
- the eNB device 1410 may be configured to transmit load indication information if it belongs to a cell which is subject to interference.
- the processor 1413 of the eNB device 1410 may be configured to determine a downlink subframe which is required to be set to a blank subframe by a base station of a cell which causes interference among the plurality of downlink subframes.
- the processor 1413 may be configured to transmit information indicating the determined downlink subframe to the base station of the cell which causes interference through the transmission module 1412.
- the eNB device 1410 may be configured to transmit blank subframe setting information if it belongs to a cell which causes interference.
- the processor 1413 of the eNB device 1410 may be configured to transmit the blank subframe setting information to the base station of a cell which is subject to interference.
- Such blank subframe setting information includes first and second bitmaps, the first bitmap includes information indicating a blank subframe and a non-blank subframe, and a second bitmap includes information indicating a subset of blank subframes.
- the processor 1413 of the eNB device 1410 performs a function for processing information received by the eNB device 1410 and information to be transmitted to an external device.
- the memory 1414 may store the processed information for a predetermined time and may be replaced with another component such as a buffer (not shown) .
- the terminal device 1420 may include a reception module 1421, a transmission module 1422, a processor 1423, a memory 1424 and a plurality of antennas 1425.
- the plurality of antennas 1425 supports IMO transmission and reception.
- the reception module 1421 may receive signals, data, and information from an eNB.
- the transmission module 1422 may transmit signals, data, and information to an eNB.
- the processor 1423 may control the overall operation of the terminal device 1420.
- the terminal device 1420 may be configured to perform CSI measurement.
- the processor 1423 of the terminal device 1420 may be configured to receive information indicating first and second subframe sets in which CSI measurement will be performed among a plurality of downlink subframes from the eNB 1410 through the reception module 1421.
- the processor 1423 may be configured to perform CSI measurement with respect to each of the first and second subframe sets.
- the processor 1423 may be configured to transmit CSI to the eNB 1410 through the transmission module 1422.
- the subframe belonging to the first subframe set and the subframe belonging to the second subframe set may not overlap. Some of the plurality of subframes may not belong to either of the first and second subframe sets.
- the processor 1423 of the terminal device 1420 performs a function for processing information received by the terminal device 1420 and information to be transmitted to an external device.
- the memory 1424 may store the processed information for a predetermined time and may be replaced with another component such as a buffer (not shown) .
- a description of the eNB device 1410 of FIG. 14 may be identically applied to a relay device functioning as a downlink transmission subject or an uplink reception subject, and a description of the terminal device 1420 of FIG. 14 may be identically applied to a relay device functioning as a downlink reception subject or an uplink transmission subject.
- the present invention can be implemented with application specific integrated circuits (ASICs) , Digital signal processors (DSPs) , digital signal processing devices (DSPDs) , programmable logic devices (PLDs) , field programmable gate arrays (FPGAs) , a processor, a controller, a microcontroller, a microprocessor, etc.
- ASICs application specific integrated circuits
- DSPs Digital signal processors
- DSPDs digital signal processing devices
- PLDs programmable logic devices
- FPGAs field programmable gate arrays
- the present invention can be implemented in the form of a variety of formats, for example, modules, procedures, functions, etc.
- the software codes may be stored in a memory unit so that it can be driven by a processor.
- the memory unit is located inside or outside of the processor, so that it can communicate with the aforementioned processor via a variety of well-known parts.
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Abstract
Description
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Priority Applications (6)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US13/822,909 US9742546B2 (en) | 2010-09-28 | 2011-09-26 | Inter-cell interference coordination in a wireless communication system |
EP11829525.2A EP2622763B1 (en) | 2010-09-28 | 2011-09-26 | Inter-cell interference coordination in a wireless communication system |
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EP3537748A4 (en) * | 2016-11-01 | 2020-08-19 | Cloudminds (Beijing) Technologies Co., Ltd. | Resource allocation method, allocation system, computer program product, and communications device |
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WO2012044019A3 (en) | 2012-06-07 |
KR101901927B1 (en) | 2018-09-27 |
AU2011308232B2 (en) | 2014-08-28 |
TW201215184A (en) | 2012-04-01 |
CN103125087A (en) | 2013-05-29 |
TW201431393A (en) | 2014-08-01 |
KR20120032414A (en) | 2012-04-05 |
AU2011308232A1 (en) | 2013-04-04 |
US9742546B2 (en) | 2017-08-22 |
US9876625B2 (en) | 2018-01-23 |
TWI523547B (en) | 2016-02-21 |
CA2812070A1 (en) | 2012-04-05 |
CA2812070C (en) | 2016-12-06 |
US20150092717A1 (en) | 2015-04-02 |
CN106209293B (en) | 2018-08-07 |
US20130223258A1 (en) | 2013-08-29 |
CN106209293A (en) | 2016-12-07 |
CN103125087B (en) | 2016-08-17 |
EP2622763A2 (en) | 2013-08-07 |
EP2622763B1 (en) | 2018-07-11 |
EP2622763A4 (en) | 2016-08-17 |
TWI479908B (en) | 2015-04-01 |
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