US9271283B2 - Method and user equipment for transmitting channel state information and method and base station for receiving channel state information - Google Patents

Method and user equipment for transmitting channel state information and method and base station for receiving channel state information Download PDF

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US9271283B2
US9271283B2 US14/405,369 US201314405369A US9271283B2 US 9271283 B2 US9271283 B2 US 9271283B2 US 201314405369 A US201314405369 A US 201314405369A US 9271283 B2 US9271283 B2 US 9271283B2
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csi
request field
triggered
cell
aperiodic
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US20150131568A1 (en
Inventor
Hyangsun You
Kijun KIM
Suckchel YANG
Jonghyun Park
Joonkui AHN
Dongyoun Seo
Illsoo Sohn
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LG Electronics Inc
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LG Electronics Inc
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    • H04W72/042—
    • 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
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/20—Control channels or signalling for resource management
    • H04W72/23—Control channels or signalling for resource management in the downlink direction of a wireless link, i.e. towards a terminal
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B17/00—Monitoring; Testing
    • H04B17/30—Monitoring; Testing of propagation channels
    • H04B17/309—Measuring or estimating channel quality parameters
    • H04B17/345—Interference values
    • 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
    • H04L5/0035—Resource allocation in a cooperative multipoint environment
    • 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
    • H04L5/0037—Inter-user or inter-terminal allocation
    • 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
    • H04L5/0053—Allocation of signaling, i.e. of overhead other than pilot signals
    • 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
    • H04L5/0053—Allocation of signaling, i.e. of overhead other than pilot signals
    • H04L5/0057—Physical resource allocation for CQI
    • 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
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
    • H04W4/70—Services for machine-to-machine communication [M2M] or machine type communication [MTC]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
    • H04W88/02—Terminal devices
    • 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
    • H04L5/0001—Arrangements for dividing the transmission path
    • H04L5/0003—Two-dimensional division
    • H04L5/0005—Time-frequency
    • H04L5/0007—Time-frequency the frequencies being orthogonal, e.g. OFDM(A), DMT
    • H04L5/001—Time-frequency the frequencies being orthogonal, e.g. OFDM(A), DMT the frequencies being arranged in component carriers

Definitions

  • the present invention relates to a wireless communication system and, more particularly, to a method and apparatus for transmitting or receiving channel state information.
  • M2M machine-to-machine
  • BS base station
  • a general wireless communication system performs data transmission/reception through one downlink (DL) band and through one uplink (UL) band corresponding to the DL band (in case of a frequency division duplex (FDD) mode), or divides a prescribed radio frame into a UL time unit and a DL time unit in the time domain and then performs data transmission/reception through the UL/DL time unit (in case of a time division duplex (TDD) mode).
  • a base station (BS) and a user equipment (UE) transmit and receive data and/or control information scheduled on a prescribed time unit basis, e.g. on a subframe basis.
  • the data is transmitted and received through a data region configured in a UL/DL subframe and the control information is transmitted and received through a control region configured in the UL/DL subframe.
  • various physical channels carrying radio signals are formed in the UL/DL subframe.
  • carrier aggregation technology serves to use a wider UL/DL bandwidth by aggregating a plurality of UL/DL frequency blocks in order to use a broader frequency band so that more signals relative to signals when a single carrier is used can be simultaneously processed.
  • a communication environment has evolved into increasing density of nodes accessible by a user at the periphery of the nodes.
  • a node refers to a fixed point capable of transmitting/receiving a radio signal to/from the UE through one or more antennas.
  • a communication system including high-density nodes may provide a better communication service to the UE through cooperation between the nodes.
  • Such a multi-node cooperative communication scheme in which a plurality of nodes performs communication with the UE using the same time-frequency resource has much better data throughput than a conventional communication scheme in which the nodes perform communication with the UE without any cooperation by operating as independent BSs.
  • a multi-node system may perform cooperative communication using a plurality of nodes, each node operating as a BS, an access point, an antenna, an antenna group, a radio remote head (RRH), or a radio remote unit (RRU).
  • a plurality of nodes does not directly participate in signal transmission or signal reception simultaneously, since the nodes are capable of performing signal transmission/reception while reducing mutual interference therebetween, overall communication system throughput can be raised.
  • the nodes are typically separated from each other by a predetermined interval or more in the multi-node system.
  • the nodes may be managed by one or more BSs or BS controllers for controlling the operation thereof or scheduling data transmission/reception therethrough.
  • Each node is connected to the BS or BS controller for managing the node through a cable or a dedicated line.
  • Such a multi-node system may be regarded as a type of MIMO system in that distributed nodes are capable of communicating with a single UE or multiple UEs by simultaneously transmitting/receiving different streams.
  • the multi-node system transmits signals using nodes distributed at various locations, a transmission region which should be covered by each antenna decreases in comparison with antennas included in the conventional centralized antenna system. Accordingly, compared with a conventional system implementing MIMO technology in the centralized antenna system, a transmit power needed when each antenna transmits a signal may be reduced in the multi-node system.
  • the transmission distance between an antenna and a UE is shortened, path loss is reduced and high-speed data transmission is achieved.
  • transmission capacity and power efficiency of a cellular system can be enhanced and communication performance having relatively uniform quality can be satisfied irrespective of the locations of UEs in a cell. Furthermore, in the multi-node system, since BS(s) or BS controller(s) connected to multiple nodes performs cooperative data transmission/reception, signal loss generated in a transmission process is reduced. In addition, when nodes distant from each other by a predetermined distance or more perform cooperative communication with the UE, correlation and interference between antennas are reduced. Hence, according to the multi-node cooperative communication scheme, a high signal to interference-plus-noise ratio (SINR) can be achieved.
  • SINR signal to interference-plus-noise ratio
  • the multi-node system Due to such advantages of the multi-node system, in the next-generation mobile communication system, the multi-node system has emerged as a new basis of cellular communication through combination with or by replacing conventional centralized antenna systems in order to reduce additional installation costs of a BS and maintenance costs of a backhaul network and simultaneously to expand service coverage and enhance channel capacity and SINR.
  • a new channel state reporting scheme is needed in consideration of a situation in which a plurality of carriers is used for communication for the UE and/or a situation in which a plurality of nodes coordinate to provide the UE with a communication service.
  • a method for transmitting channel state information (CSI) by a user equipment comprises: receiving downlink control information for a specific serving cell, the downlink control information including a CSI request field; and performing an aperiodic CSI report on a physical uplink shared channel (PUSCH) of the specific serving cell, wherein the aperiodic CSI report is triggered by the CSI request field.
  • the CSI request field may indicate whether or not the aperiodic CSI report is triggered for a set of CSI process(es) configured by a higher layer among CSI process(es) for the serving cell when the user equipment can be configured with one or more CSI processes per serving cell.
  • a method for receiving channel state information (CSI) by a base station comprises: transmitting downlink control information for a specific serving cell to a user equipment, the downlink control information including a CSI request field; and receiving an aperiodic CSI report on a physical uplink shared channel (PUSCH) of the specific serving cell, wherein the aperiodic CSI report is triggered by the CSI request field.
  • CSI channel state information
  • a user equipment for transmitting channel state information (CSI).
  • the user equipment comprises: a radio frequency (RF) unit and a processor configured to control the RF unit, wherein the processor is configured to control the RF unit to receive downlink control information for a specific serving cell, the downlink control information including a CSI request field; and is configured to control the RF unit to perform an aperiodic CSI report on a physical uplink shared channel (PUSCH) of the specific serving cell, and the aperiodic CSI report is triggered by the CSI request field.
  • RF radio frequency
  • PUSCH physical uplink shared channel
  • a base station for receiving channel state information (CSI).
  • the base station comprises: a radio frequency (RF) unit and a processor configured to control the RF unit, wherein the processor is configured to control the RF unit to transmit downlink control information for a specific serving cell to a user equipment, the downlink control information including a CSI request field; and is configured to control the RF unit to receive an aperiodic CSI report on a physical uplink shared channel (PUSCH) of the specific serving cell, and the aperiodic CSI report is triggered by the CSI request field.
  • PUSCH physical uplink shared channel
  • the CSI request field may consist of two bits.
  • the user equipment may be configured with a plurality of serving cells including the specific serving cell. If the user equipment is configured in a mode in which a plurality of CSI processes can be configured for at least one of the serving cells, the CSI request field may indicate whether or not the aperiodic CSI report is triggered for the set of CSI process(es).
  • each of the set of CSI process(es) is associated with a CSI reference resource for signal measurement and a interference measurement resource for interference measurement.
  • the user equipment may receive the CSI request field in a user equipment specific search space.
  • CSI channel state information
  • FIGS. 1( a ) and 1 ( b ) illustrate the structure of a radio frame used in a wireless communication system.
  • FIG. 2 illustrates the structure of a downlink (DL)/uplink (UL) slot in a wireless communication system.
  • FIGS. 3( a ) and 3 ( b ) illustrate a radio frame structure for transmission of a synchronization signal (SS).
  • SS synchronization signal
  • FIG. 4 illustrates a secondary synchronization signal (SSS) generation scheme.
  • FIG. 5 illustrates the structure of a DL subframe used in a wireless communication system.
  • FIG. 6 illustrates configuration of cell specific common reference signals (CRSs).
  • FIG. 7 illustrates the structure of a UL subframe used in a wireless communication system.
  • FIG. 7 illustrates channel state information reference signal (CSI-RS) configurations.
  • CSI-RS channel state information reference signal
  • FIG. 8 illustrates the structure of a UL subframe used in a wireless communication system.
  • FIGS. 9( a ) and 9 ( b ) are diagrams for explaining single-carrier communication and multi-carrier communication.
  • FIG. 10 illustrates the state of cells in a system supporting carrier aggregation.
  • FIGS. 11( a ), 11 ( b ), 11 ( c ), and 11 ( d ) illustrate links configurable according to carrier aggregation and a coordinated multi-point transmission/reception (CoMP) environment.
  • CoMP coordinated multi-point transmission/reception
  • FIG. 12 is a diagram for explaining an embodiment of the present invention.
  • FIG. 13 is a diagram for explaining another embodiment of the present invention.
  • FIG. 14 is a block diagram illustrating elements of a transmitting device 10 and a receiving device 20 for implementing the present invention.
  • 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
  • MC-FDMA multicarrier frequency division multiple access
  • CDMA may be embodied through radio technology such as universal terrestrial radio access (UTRA) or CDMA2000.
  • TDMA may be embodied through radio technology such as global system for mobile communications (GSM), general packet radio service (GPRS), or enhanced data rates for GSM evolution (EDGE).
  • GSM global system for mobile communications
  • GPRS general packet radio service
  • EDGE enhanced data rates for GSM evolution
  • OFDMA may be embodied through radio technology such as institute of electrical and electronics engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, or evolved UTRA (E-UTRA).
  • UTRA is a part of a universal mobile telecommunications system (UMTS).
  • 3rd generation partnership project (3GPP) long term evolution (LTE) is a part of evolved UMTS (E-UMTS) using E-UTRA.
  • 3GPP LTE employs OFDMA in DL and SC-FDMA in UL.
  • LTE-advanced (LTE-A) is an evolved version of 3GPP LTE. For convenience of description, it is assumed that the present invention is applied to 3GPP LTE/LTE-A.
  • a user equipment may be a fixed or mobile device.
  • the UE include various devices that transmit and receive user data and/or various kinds of control information to and from a base station (BS).
  • the UE may be referred to as a terminal equipment (TE), a mobile station (MS), a mobile terminal (MT), a user terminal (UT), a subscriber station (SS), a wireless device, a personal digital assistant (PDA), a wireless modem, a handheld device, etc.
  • a BS generally refers to a fixed station that performs communication with a UE and/or another BS, and exchanges various kinds of data and control information with the UE and another BS.
  • the BS may be referred to as an advanced base station (ABS), a node-B (NB), an evolved node-B (eNB), a base transceiver system (BTS), an access point (AP), a processing server (PS), etc.
  • ABS advanced base station
  • NB node-B
  • eNB evolved node-B
  • BTS base transceiver system
  • AP access point
  • PS processing server
  • eNB evolved node-B
  • AP access point
  • PS processing server
  • a node refers to a fixed point capable of transmitting/receiving a radio signal through communication with a UE.
  • Various types of eNBs may be used as nodes irrespective of the terms thereof.
  • a BS, a node B (NB), an e-node B (eNB), a pico-cell eNB (PeNB), a home eNB (HeNB), a relay, a repeater, etc. may be a node.
  • the node may not be an eNB.
  • the node may be a radio remote head (RRH) or a radio remote unit (RRU).
  • RRH radio remote head
  • RRU radio remote unit
  • the RRH or RRU generally has a lower power level than a power level of an eNB. Since the RRH or RRU (hereinafter, RRH/RRU) is generally connected to the eNB through a dedicated line such as an optical cable, cooperative communication between RRH/RRU and the eNB can be smoothly performed in comparison with cooperative communication between eNBs connected by a radio line.
  • At least one antenna is installed per node.
  • the antenna may mean a physical antenna or mean an antenna port, a virtual antenna, or an antenna group.
  • a node may be referred to as a point.
  • the same cell identity (ID) or different cell IDs may be used to transmit/receive signals to/from a plurality of nodes.
  • each of the nodes operates as a partial antenna group of one cell.
  • the multi-node system may be regarded as a multi-cell (e.g. a macro-cell/femto-cell/pico-cell) system.
  • a network formed by the multiple cells is referred to as a multi-tier network.
  • a cell ID of an RRH/RRU may be the same as or different from a cell ID of an eNB. When the RRH/RRU and the eNB use different cell IDs, both the RRH/RRU and the eNB operate as independent eNBs.
  • one or more eNBs or eNB controllers connected to multiple nodes may control the nodes such that signals are simultaneously transmitted to or received from a UE through some or all nodes. While there is a difference between multi-node systems according to the nature of each node and implementation form of each node, multi-node systems are discriminated from single node systems (e.g. a centralized antenna system (CAS), conventional MIMO systems, conventional relay systems, conventional repeater systems, etc.) since a plurality of nodes provides communication services to a UE in a predetermined time-frequency resource.
  • CAS centralized antenna system
  • a node refers to an antenna group spaced apart from another node by a predetermined distance or more, in general.
  • embodiments of the present invention which will be described below, may even be applied to a case in which a node refers to an arbitrary antenna group irrespective of node interval.
  • the embodiments of the preset invention are applicable on the assumption that the eNB controls a node composed of an H-pole antenna and a node composed of a V-pole antenna.
  • a communication scheme through which signals are transmitted/received via a plurality of transmit (Tx)/receive (Rx) nodes, signals are transmitted/received via at least one node selected from a plurality of Tx/Rx nodes, or a node transmitting a DL signal is discriminated from a node transmitting a UL signal is called multi-eNB MIMO or coordinated multi-point transmission/reception (CoMP).
  • Coordinated transmission schemes from among CoMP communication schemes may be broadly categorized into joint processing (JP) and scheduling coordination. The former may be divided into joint transmission (JT)/joint reception (JR) and dynamic point selection (DPS) and the latter may be divided into coordinated scheduling (CS) and coordinated beamforming (CB).
  • DPS may be called dynamic cell selection (DCS).
  • DCS dynamic cell selection
  • JP Joint Processing
  • JT refers to a communication scheme by which a plurality of nodes transmits the same stream to a UE
  • JR refers to a communication scheme by which a plurality of nodes receive the same stream from the UE.
  • the UE/eNB combine signals received from the plurality of nodes to restore the stream.
  • signal transmission reliability can be improved according to transmit diversity since the same stream is transmitted to/from a plurality of nodes.
  • DPS refers to a communication scheme by which a signal is transmitted/received through a node selected from a plurality of nodes according to a specific rule.
  • signal transmission reliability can be improved because a node having a good channel state between the node and the UE is selected as a communication node.
  • a cell refers to a prescribed geographical area to which one or more nodes provide a communication service. Accordingly, in the present invention, communicating with a specific cell may mean communicating with an eNB or a node which provides a communication service to the specific cell.
  • a DL/UL signal of a specific cell refers to a DL/UL signal from/to an eNB or a node which provides a communication service to the specific cell.
  • a node providing UL/DL communication services to a UE is called a serving node and a cell to which UL/DL communication services are provided by the serving node is especially called a serving cell.
  • channel status/quality of a specific cell refers to channel status/quality of a channel or communication link formed between an eNB or node which provides a communication service to the specific cell and a UE.
  • An interfering cell refers to a cell interfering with a specific cell. Namely, if a signal of a neighboring cell interferes with a signal of a specific cell, the neighboring cell becomes an interfering cell with respect to the specific cell and the specific cell becomes a victim cell with respect to the neighboring cell. If neighboring cells interfere with each other or unilaterally, such interference is referred to as inter-cell interference (ICI).
  • ICI inter-cell interference
  • the UE may measure DL channel state received from a specific node using cell-specific reference signal(s) (CRS(s)) transmitted on a CRS resource and/or channel state information reference signal(s) (CSI-RS(s)) transmitted on a CSI-RS resource, allocated by antenna port(s) of the specific node to the specific node.
  • CRS cell-specific reference signal
  • CSI-RS channel state information reference signal
  • a 3GPP LTE/LTE-A system uses the concept of a cell in order to manage radio resources and a cell associated with the radio resources is distinguished from a cell of a geographic region. The cell associated with the radio resources will be described later with reference to FIGS. 9 and 10 .
  • the term “cell” means a cell associated with the radio resource unless particularly mentioned as a cell of a geographical area.
  • serving cell refers to a cell configured for a UE as the radio resources unless specified otherwise.
  • “cell” in cell specific reference signal (CRS), “cell” in cell identity, and “cell” in physical layer cell identity may be cells of a geographical region rather than cells associated with the radio resources.
  • CRS cell specific reference signal
  • the “serving cell” may be understood as a serving cell associated with the geographical region rather than a serving cell associated with the radio resources.
  • the “cell” may be understood as a cell associated with the geographical region rather than a cell associated with the radio resources.
  • 3GPP LTE/LTE-A standards define DL physical channels corresponding to resource elements carrying information derived from a higher layer and DL physical signals corresponding to resource elements which are used by a physical layer but which do not carry information derived from the higher layer.
  • a physical downlink shared channel (PDSCH), a physical broadcast channel (PBCH), a physical multicast channel (PMCH), a physical control format indicator channel (PCFICH), a physical downlink control channel (PDCCH), and a physical hybrid ARQ indicator channel (PHICH) are defined as the DL physical channels, and a reference signal and a synchronization signal are defined as the DL physical signals.
  • a reference signal also called a pilot, refers to a special waveform of a predefined signal known to both an eNB and a UE.
  • a cell-specific RS CRS
  • a UE-specific RS CRS
  • PRS positioning RS
  • CSI-RS channel state information RS
  • the 3GPP LTE/LTE-A standards define UL physical channels corresponding to resource elements carrying information derived from the higher layer and UL physical signals corresponding to resource elements which are used by a physical layer but which do not carry information derived from the higher layer.
  • a physical uplink shared channel PUSCH
  • a physical uplink control channel PUCCH
  • a physical random access channel PRACH
  • DM RS demodulation reference signal
  • SRS sounding reference signal
  • a physical downlink control channel (PDCCH), a physical control format indicator channel (PCFICH), a physical hybrid automatic retransmit request indicator channel (PHICH), and a physical downlink shared channel (PDSCH) refer to a set of time-frequency resources or resource elements (REs) carrying downlink control information (DCI), a set of time-frequency resources or REs carrying a control format indicator (CFI), a set of time-frequency resources or REs carrying downlink acknowledgement (ACK)/negative ACK (NACK), and a set of time-frequency resources or REs carrying downlink data, respectively.
  • DCI downlink control information
  • CFI control format indicator
  • ACK downlink acknowledgement
  • NACK negative ACK
  • a physical uplink control channel (PUCCH), a physical uplink shared channel (PUSCH) and a physical random access channel (PRACH) refer to a set of time-frequency resources or REs carrying uplink control information (UCI), a set of time-frequency resources or REs carrying uplink data and a set of time-frequency resources or REs carrying random access signals, respectively.
  • PUCCH physical uplink control channel
  • PUSCH physical uplink shared channel
  • PRACH physical random access channel
  • a time-frequency resource or RE that is assigned to or belongs to PDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH is referred to as PDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH RE or PDCCH/PCFICH/PHICH/PDSCH/PUCCH/PUSCH/PRACH time-frequency resource, respectively.
  • PUCCH/PUSCH/PRACH transmission of a UE is conceptually identical to UCI/uplink data/random access signal transmission on PUSCH/PUCCH/PRACH, respectively.
  • PDCCH/PCFICH/PHICH/PDSCH transmission of an eNB is conceptually identical to downlink data/DCI transmission on PDCCH/PCFICH/PHICH/PDSCH, respectively.
  • a CRS port, a UE-RS port, and a CSI-RS port refers to an antenna port configured to transmit a CRS, an antenna port configured to transmit a UE-RS, and an antenna port configured to transmit a CSI-RS, respectively.
  • Antenna ports configured to transmit CRSs may be distinguished from each other by the locations of REs occupied by the CRSs according to CRS ports
  • antenna ports configured to transmit UE-RSs may be distinguished from each other by the locations of REs occupied by the UE-RSs according to UE-RS ports
  • antenna ports configured to transmit CSI-RSs may be distinguished from each other by the locations of REs occupied by the CSI-RSs according to CSI-RS ports. Therefore, the terms CRS/UE-RS/CSI-RS ports may also be used to indicate patterns of REs occupied by the CRSs/UE-RSs/CSI-RSs in a predetermined resource region.
  • FIGS. 1( a ) and 1 ( b ) illustrate the structure of a radio frame used in a wireless communication system.
  • FIG. 1( a ) illustrates an exemplary structure of a radio frame which can be used in frequency division multiplexing (FDD) in 3GPP LTE/LTE-A
  • FIG. 1( b ) illustrates an exemplary structure of a radio frame which can be used in time division multiplexing (TDD) in 3GPP LTE/LTE-A
  • the frame structure of FIG. 1( a ) is referred to as frame structure type 1 (FS1)
  • the frame structure of FIG. 1( b ) is referred to as frame structure type 2 (FS2).
  • a 3GPP LTE/LTE-A radio frame is 10 ms (307,200T s ) in duration.
  • the radio frame is divided into 10 subframes of equal size.
  • Subframe numbers may be assigned to the 10 subframes within one radio frame, respectively.
  • Each subframe is 1 ms long and is further divided into two slots. 20 slots are sequentially numbered from 0 to 19 in one radio frame. Duration of each slot is 0.5 ms.
  • a time interval in which one subframe is transmitted is defined as a transmission time interval (TTI).
  • Time resources may be distinguished by a radio frame number (or radio frame index), a subframe number (or subframe index), a slot number (or slot index), and the like.
  • a radio frame may have different configurations according to duplex modes.
  • FDD mode for example, since DL transmission and UL transmission are discriminated according to frequency, a radio frame for a specific frequency band operating on a carrier frequency includes either DL subframes or UL subframes.
  • TDD mode since DL transmission and UL transmission are discriminated according to time, a radio frame for a specific frequency band operating on a carrier frequency includes both DL subframes and UL subframes.
  • Table 1 shows an exemplary UL-DL configuration within a radio frame in TDD mode.
  • D denotes a DL subframe
  • U denotes a UL subframe
  • S denotes a special subframe.
  • the special subframe includes three fields, i.e. downlink pilot time slot (DwPTS), guard period (GP), and uplink pilot time slot (UpPTS).
  • DwPTS is a time slot reserved for DL transmission
  • UpPTS is a time slot reserved for UL transmission.
  • Table 2 shows an example of the special subframe configuration.
  • FIG. 2 illustrates the structure of a DL/UL slot structure in a wireless communication system.
  • FIG. 2 illustrates the structure of a resource grid of a 3GPP LTE/LTE-A system.
  • One resource grid is defined per antenna port.
  • a slot includes a plurality of orthogonal frequency division multiplexing (OFDM) symbols in the time domain and includes a plurality of resource blocks (RBs) in the frequency domain.
  • the OFDM symbol may refer to one symbol duration.
  • a signal transmitted in each slot may be expressed by a resource grid including N DL/UL RB *N RB sc subcarriers and N DL/UL symb OFDM symbols.
  • N DL RB denotes the number of RBs in a DL slot
  • N UL RB denotes the number of RBs in a UL slot.
  • N DL RB and N UL RB depend on a DL transmission bandwidth and a UL transmission bandwidth, respectively.
  • N DL symb denotes the number of OFDM symbols in a DL slot
  • N UL symb denotes the number of OFDM symbols in a UL slot
  • N RB sc denotes the number of subcarriers configuring one RB.
  • An OFDM symbol may be referred to as an OFDM symbol, a single carrier frequency division multiplexing (SC-FDM) symbol, etc. according to multiple access schemes.
  • the number of OFDM symbols included in one slot may be varied according to channel bandwidths and CP lengths. For example, in a normal cyclic prefix (CP) case, one slot includes 7 OFDM symbols. In an extended CP case, one slot includes 6 OFDM symbols. Although one slot of a subframe including 7 OFDM symbols is shown in FIG. 2 for convenience of description, embodiments of the present invention are similarly applicable to subframes having a different number of OFDM symbols. Referring to FIG. 2 , each OFDM symbol includes N DL/UL RB *N RB sc subcarriers in the frequency domain.
  • the of the subcarrier may be divided into a data subcarrier for data transmission, a reference signal (RS) subcarrier for RS transmission, and a null subcarrier for a guard band and a DC component.
  • the null subcarrier for the DC component is unused and is mapped to a carrier frequency f 0 in a process of generating an OFDM signal or in a frequency up-conversion process.
  • the carrier frequency is also called a center frequency f c .
  • One RB is defined as N DL/UL symb (e.g. 7) consecutive OFDM symbols in the time domain and as N RB sc (e.g. 12) consecutive subcarriers in the frequency domain.
  • N DL/UL symb e.g. 7
  • N RB sc e.g. 12
  • a resource composed of one OFDM symbol and one subcarrier is referred to a resource element (RE) or tone.
  • one RB includes N DL/UL symb *N RB sc REs.
  • Each RE within a resource grid may be uniquely defined by an index pair (k, l) within one slot.
  • k is an index ranging from 0 to N DL/UL RB *N RB sc ⁇ 1 in the frequency domain
  • l is an index ranging from 0 to N DL/UL symb ⁇ 1 in the time domain.
  • one RB is mapped to one physical resource block (PRB) and one virtual resource block (VRB).
  • a PRB is defined as N DL symb (e.g. 7) consecutive OFDM or SC-FDM symbols in the time domain and N RB sc (e.g. 12) consecutive subcarriers in the frequency domain.
  • N DL symb e.g. 7
  • N RB sc e.g. 12
  • one PRB is configured with N DL/UL symb *N RB sc REs.
  • PRB physical resource block
  • Two RBs configuring a PRB pair have the same PRB number (or the same PRB index).
  • FIGS. 3( a ) and 3 ( b ) illustrate a radio frame structure for transmission of a synchronization signal (SS).
  • FIGS. 3( a ) and 3 ( b ) illustrate a radio frame structure for transmission of an SS and a PBCH in frequency division duplex (FDD), wherein FIG. 3( a ) illustrates transmission locations of an SS and a PBCH in a radio frame configured as a normal cyclic prefix (CP) and FIG. 3( b ) illustrates transmission locations of an SS and a PBCH in a radio frame configured as an extended CP.
  • FDD frequency division duplex
  • the UE performs an initial cell search procedure of acquiring time and frequency synchronization with the cell and detecting a physical cell identity of the cell.
  • the UE may establish synchronization with the eNB by receiving synchronization signals, e.g. a primary synchronization signal (PSS) and a secondary synchronization signal (SSS), from the eNB and obtain information such as a cell identity (ID).
  • PSS primary synchronization signal
  • SSS secondary synchronization signal
  • An SS will be described in more detail with reference to FIGS. 3( a ) and 3 ( b ).
  • An SS is categorized into a PSS and an SSS.
  • the PSS is used to acquire time-domain synchronization such as OFDM symbol synchronization or slot synchronization and/or frequency-domain synchronization and the SSS is used to acquire frame synchronization, a cell group ID, and/or CP configuration of a cell (i.e. information as to whether a normal CP is used or an extended CP is used).
  • each of a PSS and an SSS is transmitted on two OFDM symbols of every radio frame.
  • SSs are transmitted in the first slot of subframe 0 and the first slot of subframe 5, in consideration of a global system for mobile communication (GSM) frame length of 4.6 ms for facilitation of inter-radio access technology (inter-RAT) measurement.
  • GSM global system for mobile communication
  • inter-RAT inter-radio access technology
  • a PSS is transmitted on the last OFDM symbol of the first slot of subframe 0 and on the last OFDM symbol of the first slot of subframe 5
  • an SSS is transmitted on the second to last OFDM symbol of the first slot of subframe 0 and on the second to last OFDM symbol of the first slot of subframe 5.
  • a boundary of a corresponding radio frame may be detected through the SSS.
  • the PSS is transmitted on the last OFDM symbol of a corresponding slot and the SSS is transmitted on an OFDM symbol immediately before an OFDM symbol on which the PSS is transmitted.
  • a transmit diversity scheme of an SS uses only a single antenna port and standards therefor are not separately defined. That is, a single antenna port transmission scheme or a transmission scheme transparent to a UE (e.g. precoding vector switching (PVS), time switched transmit diversity (TSTD), or cyclic delay diversity (CDD)) may be used for transmit diversity of an SS.
  • PVS precoding vector switching
  • TSTD time switched transmit diversity
  • CDD cyclic delay diversity
  • An SS may represent a total of 504 unique physical layer cell IDs by a combination of 3 PSSs and 168 SSSs.
  • the physical layer cell IDs are divided into 168 physical layer cell ID groups each including three unique IDs so that each physical layer cell ID is a part of only one physical layer cell ID group.
  • a UE may be aware of one of three unique physical layer IDs by detecting the PSS and may be aware of one of 168 physical layer cell IDs associated with the physical layer ID by detecting the SSS.
  • a length-63 Zadoff-Chu (ZC) sequence is defined in the frequency domain and is used as the PSS.
  • the ZC sequence may be defined by the following equation.
  • conjugate symmetry indicates the relationship of the following Equation.
  • a sequence d(n) used for a PSS is generated from a frequency-domain ZC sequence as follows.
  • Equation 3 the Zadoff-Chu root sequence index u is given by the following table.
  • a UE may discern that a corresponding subframe is one of subframe 0 and subframe 5 because the PSS is transmitted every 5 ms but the UE cannot discern whether the subframe is subframe 0 or subframe 5. Accordingly, the UE cannot recognize the boundary of a radio frame only by the PSS. That is, frame synchronization cannot be acquired only by the PSS.
  • the UE detects the boundary of a radio frame by detecting an SSS which is transmitted twice in one radio frame with different sequences.
  • FIG. 4 illustrates an SSS generation scheme. Specifically, FIG. 4 illustrates a relationship of mapping of two sequences in the logical domain to sequences in a physical domain.
  • a sequence used for the SSS is an interleaved concatenation of two length-31 m-sequences and the concatenated sequence is scrambled by a scrambling sequence given by a PSS.
  • an m-sequence is a type of a pseudo noise (PN) sequence.
  • PN pseudo noise
  • a PSS-based scrambling code may be obtained by cyclically shifting an m-sequence generated from a polynomial of x 5 +x 3 +1 and 6 sequences are generated by cyclic shift of the m-sequence according to an index of a PSS.
  • S2 is scrambled by an S1-based scrambling code.
  • the S1-based scrambling code may be obtained by cyclically shifting an m-sequence generated from a polynomial of x 5 +x 4 +x 2+ x 1 +1 and 8 sequences are generated by cyclic shift of the m-sequence according to an index of S1.
  • the SSS code is swapped every 5 ms, whereas the PSS-based scrambling code is not swapped.
  • an SSS of subframe 0 carries a cell group ID by a combination of (S1, S2)
  • an SSS of subframe 5 carries a sequence swapped as (S2, S1).
  • a boundary of a radio frame of 10 ms can be discerned.
  • the used SSS code is generated from a polynomial of x 5 +x 2 +1 and a total of 31 codes may be generated by different cyclic shifts of an m-sequence of length-31.
  • a combination of two length-31 m-sequences for defining the SSS is different in subframe 0 and subframe 5 and a total of 168 cell group IDs are expressed by a combination of the two length-31 m-sequences.
  • the m-sequences used as sequences of the SSS have a robust property in a frequency selective environment.
  • the m-sequences can be transformed by high-speed m-sequence transform using fast Hadamard transform, if the m-sequences are used as the SSS, the amount of calculation necessary for a UE to interpret the SSS can be reduced. Since the SSS is configured by two short codes, the amount of calculation of the UE can be reduced.
  • a sequence d(0), . . . , d(61) used for the SSS is an interleaved concatenation of two length-31 binary sequences.
  • the concatenated sequence is scrambled by a sequence given by the PSS.
  • a combination of two length-31 sequences for defining the PSS becomes different in subframe 0 and subframe 5 according to the following.
  • Equation 4 0 ⁇ n ⁇ 30.
  • the indices m 0 and m 1 are derived from the physical-layer cell-identity group N (1) ID according to the following.
  • Equation 5 The output of Equation 5 is listed in Table 4 following Equation 11.
  • the two sequences s (m0) 0 (n) and s (m1) 1 (n) are defined as two different cyclic shifts of the m-sequence s(n).
  • s 0 (m 0 ) ( n ) s (( n+m 0 )mod 31)
  • s 1 (m 1 ) ( n ) s (( n+m 1 )mod 31) [Equation 6]
  • the two scrambling sequences c 0 (n) and c 1 (n) depend on the PSS and are defined by two different cyclic shifts of the m-sequence c(n) according to the following equation.
  • c 0 ( n ) c (( n+N ID (2) )mod 31)
  • c 1 ( n ) c (( n+N ID (2) +3)mod 31) [Equation 8]
  • the scrambling sequences z (m0) 1 (n) and z (m1) 1 (n) are defined by a cyclic shift of the m-sequence z(n) according to the following equation.
  • z 1 (m 0 ) ( n ) z (( n +( m 0 mod 8))mod 31)
  • z 1 (m 1 ) ( n ) z (( n +( m 1 mod 8))mod 31) [Equation 10]
  • x ( ⁇ + 5) ( x ( ⁇ + 4)+ x ( ⁇ + 2)+ x ( ⁇ + 1)+ x ( ⁇ ))mod 2,0 ⁇ i ⁇ 25 [Equation 11]
  • a UE which has demodulated a DL signal by performing a cell search procedure using an SSS and determined time and frequency parameters necessary for transmitting a UL signal at an accurate time, can communicate with an eNB only after acquiring system information necessary for system configuration of the UE from the eNB.
  • the system information is configured by a master information block (MIB) and system information blocks (SIBs).
  • MIB master information block
  • SIBs system information blocks
  • Each SIB includes a set of functionally associated parameters and is categorized into an MIB, SIB Type 1 (SIB1), SIB Type 2 (SIB2), and SIB3 to SIB8 according to included parameters.
  • SIB includes most frequency transmitted parameters which are essential for initial access of the UE to a network of the eNB.
  • SIB1 includes parameters needed to determine if a specific cell is suitable for cell selection, as well as information about time-domain scheduling of the other SIBs.
  • the UE may receive the MIB through a broadcast channel (e.g. a PBCH).
  • the MIB includes DL bandwidth (BW), PHICH configuration, and a system frame number SFN. Accordingly, the UE can be explicitly aware of information about the DL BW, SFN, and PHICH configuration by receiving the PBCH. Meanwhile, information which can be implicitly recognized by the UE through reception of the PBCH is the number of transmit antenna ports of the eNB. Information about the number of transmit antennas of the eNB is implicitly signaled by masking (e.g. XOR operation) a sequence corresponding to the number of transmit antennas to a 16-bit cyclic redundancy check (CRC) used for error detection of the PBCH.
  • masking e.g. XOR operation
  • CRC cyclic redundancy check
  • the PBCH is mapped to four subframes during 40 ms.
  • the time of 40 ms is blind detected and explicit signaling about 40 ms is not separately present.
  • the PBCH is transmitted on OFDM symbols 0 to 3 of slot 1 in subframe 0 (the second slot of subframe 0) of a radio frame.
  • a PSS/SSS and a PBCH are transmitted only in a total of 6 RBs, i.e. a total of 72 subcarriers, irrespective of actual system BW, wherein 3 RBs are in the left and the other 3 RBs are in the right centering on a DC subcarrier on corresponding OFDM symbols. Therefore, the UE is configured to detect or decode the SS and the PBCH irrespective of DL BW configured for the UE.
  • a UE which has accessed a network of an eNB may acquire more detailed system information by receiving a PDCCH and a PDSCH according to information carried on the PDCCH.
  • the UE which has performed the above-described procedure may perform reception of a PDCCH/PDSCH and transmission of a PUSCH/PUCCH as a normal UL/DL signal transmission procedure.
  • FIG. 5 illustrates the structure of a DL subframe used in a wireless communication system.
  • a DL subframe is divided into a control region and a data region in the time domain.
  • a maximum of 3 (or 4) OFDM symbols located in a front part of a first slot of a subframe corresponds to the control region.
  • a resource region for PDCCH transmission in a DL subframe is referred to as a PDCCH region.
  • OFDM symbols other than the OFDM symbol(s) used in the control region correspond to the data region to which a physical downlink shared channel (PDSCH) is allocated.
  • PDSCH physical downlink shared channel
  • a resource region available for PDSCH transmission in the DL subframe is referred to as a PDSCH region.
  • Examples of a DL control channel used in 3GPP LTE include a physical control format indicator channel (PCFICH), a physical downlink control channel (PDCCH), a physical hybrid ARQ indicator channel (PHICH), etc.
  • the PCFICH is transmitted in the first OFDM symbol of a subframe and carries information about the number of OFDM symbols available for transmission of a control channel within a subframe.
  • the PHICH carries a HARQ (Hybrid Automatic Repeat Request) ACK/NACK (acknowledgment/negative-acknowledgment) signal as a response to UL transmission.
  • HARQ Hybrid Automatic Repeat Request
  • the control information transmitted through the PDCCH will be referred to as downlink control information (DCI).
  • the DCI includes resource allocation information for a UE or UE group and other control information.
  • Transmit format and resource allocation information of a downlink shared channel (DL-SCH) are referred to as DL scheduling information or DL grant.
  • Transmit format and resource allocation information of an uplink shared channel (UL-SCH) are referred to as UL scheduling information or UL grant.
  • the size and usage of the DCI carried by one PDCCH are varied depending on DCI formats.
  • the size of the DCI may be varied depending on a coding rate.
  • formats 0 and 4 for UL and formats 1, 1A, 1B, 1C, 1D, 2, 2A, 2B, 3 and 3A for DL are defined.
  • Combination selected from control information such as a hopping flag, RB allocation, modulation coding scheme (MCS), redundancy version (RV), new data indicator (NDI), transmit power control (TPC), cyclic shift, cyclic shift demodulation reference signal (DM RS), UL index, channel quality information (CQI) request, DL assignment index, HARQ process number, transmitted precoding matrix indicator (TPMI), precoding matrix indicator (PMI) information is transmitted to the UE as the DCI.
  • Table 5 illustrates an example of the DCI format.
  • a plurality of PDCCHs may be transmitted within a control region.
  • a UE may monitor the plurality of PDCCHs.
  • An eNB determines a DCI format depending on the DCI to be transmitted to the UE, and attaches cyclic redundancy check (CRC) to the DCI.
  • the CRC is masked (or scrambled) with an identifier (for example, a radio network temporary identifier (RNTI)) depending on usage of the PDCCH or owner of the PDCCH.
  • RNTI radio network temporary identifier
  • the CRC may be masked with an identifier (for example, cell-RNTI (C-RNTI)) of the corresponding UE.
  • C-RNTI cell-RNTI
  • the CRC may be masked with a paging identifier (for example, paging-RNTI (P-RNTI)). If the PDCCH is for system information (in more detail, system information block (SIB)), the CRC may be masked with system information RNTI (SI-RNTI). If the PDCCH is for a random access response, the CRC may be masked with a random access RNTI (RA-RNTI). For example, CRC masking (or scrambling) includes XOR operation of CRC and RNTI at the bit level.
  • SIB system information block
  • SI-RNTI system information RNTI
  • RA-RNTI random access RNTI
  • the PDCCH is transmitted on an aggregation of one or a plurality of continuous control channel elements (CCEs).
  • the CCE is a logic allocation unit used to provide a coding rate based on the status of a radio channel to the PDCCH.
  • the CCE corresponds to a plurality of resource element groups (REGs). For example, one CCE corresponds to nine resource element groups (REGs), and one REG corresponds to four REs.
  • Four QPSK symbols are mapped to each REG.
  • a resource element (RE) occupied by the reference signal (RS) is not included in the REG. Accordingly, the number of REGs within given OFDM symbols is varied depending on the presence of the RS.
  • the REGs are also used for other downlink control channels (that is, PDFICH and PHICH).
  • the number of DCI formats and DCI bits is determined in accordance with the number of CCEs. CCEs are numbered and used consecutively.
  • the PDCCH having a format that includes n CCEs may only start on a CCE having a CCE number corresponding to a multiple of n.
  • the number of CCEs used for transmission of a specific PDCCH is determined by the eNB in accordance with channel status. For example, one CCE may be required for a PDCCH for a UE (for example, adjacent to eNB) having a good downlink channel.
  • a power level of the PDCCH may be adjusted to correspond to a channel status.
  • a set of CCEs on which a PDCCH can be located for each UE is defined.
  • a CCE set in which the UE can detect a PDCCH thereof is referred to as a PDCCH search space or simply as a search space (SS).
  • An individual resource on which the PDCCH can be transmitted in the SS is called a PDCCH candidate.
  • a set of PDCCH candidates that the UE is to monitor is defined as the SS.
  • SSs for respective PDCCH formats may have different sizes and a dedicated SS and a common SS are defined.
  • the dedicated SS is a UE-specific SS and is configured for each individual UE.
  • the common SS is configured for a plurality of UEs.
  • the following table shows aggregation levels for defining SSs.
  • Y k ( A ⁇ Y k-1 )mod D [Equation 12]
  • SI-RNTI, C-RNTI, P-RNTI, RA-RNTI, etc. may be used as an RNTI for n RNTI .
  • m′ m.
  • the carrier indicator field value is the same as a serving cell index (ServCellIndex) of a corresponding serving cell.
  • CIF carrier indicator field
  • the CIF is included in DCI and, in carrier aggregation, the CIF is used to indicate for which cell the DCI carries scheduling information.
  • An eNB may inform the UE of whether the DCI received by the UE may include the CIF through a higher layer signal. That is, the UE may be configured with the CIF by a higher layer. Carrier aggregation is described in more detail with reference to FIGS. 9( a ), 9 ( b ), and FIG. 10 .
  • the eNB transmits an actual PDCCH (DCI) on a PDCCH candidate in a search space and the UE monitors the search space to detect the PDCCH (DCI).
  • DCI actual PDCCH
  • monitoring implies attempting to decode each PDCCH in the corresponding SS according to all monitored DCI formats.
  • the UE may detect a PDCCH thereof by monitoring a plurality of PDCCHs. Basically, the UE does not know the location at which a PDCCH thereof is transmitted. Therefore, the UE attempts to decode all PDCCHs of the corresponding DCI format for each subframe until a PDCCH having an ID thereof is detected and this process is referred to as blind detection (or blind decoding (BD)).
  • blind detection or blind decoding (BD)
  • a specific PDCCH is CRC-masked with a radio network temporary identity (RNTI) ‘A’ and information about data transmitted using a radio resource ‘B’ (e.g. frequency location) and using transport format information ‘C’ (e.g. transmission block size, modulation scheme, coding information, etc.) is transmitted in a specific DL subframe.
  • RNTI radio network temporary identity
  • C transport format information
  • the UE monitors the PDCCH using RNTI information thereof.
  • the UE having the RNTI ‘A’ receives the PDCCH and receives the PDSCH indicated by ‘B’ and ‘C’ through information of the received PDCCH.
  • a DCI format which can be used for the UE differs according to a transmission mode (TM) configured for the UE.
  • TM transmission mode
  • the UE is semi-statically configured by higher layers so as to receive PDSCH data transmission, which was signaled through a PDCCH, according to one of transmission modes 1 to 9.
  • Table 7 illustrates a transmission mode for configuring multi-antenna technology and a DCI format where the UE performs blind decoding in accordance with the corresponding transmission mode.
  • Transmission modes 1 to 9 are listed in Table 7 but transmission modes other than the transmission modes listed in Table 7 may be defined.
  • Table 7 illustrates a relation between PDSCH and PDCCH configured by C-RNTI.
  • the UE configured to decode the PDCCH with CRC scrambled in C-RNTI by an upper layer decodes the PDCCH and also decodes the corresponding PDSCH in accordance with each combination defined in Table 7. For example, if the UE is configured in transmission mode 1 by upper layer signaling, the UE acquires either DCI of DCI format 1A or DCI of DCI format 1 by respectively decoding the PDCCH through the DCI format 1A and 1.
  • RSs may be categorized into RSs for demodulation and RSs for channel measurement.
  • CRSs defined in the 3GPP LTE system can be used for both demodulation and channel measurement.
  • a dedicated RS (DRS) is known only to a specific UE and the CRS is known to all UEs.
  • DRS dedicated RS
  • the cell-specific RS may be considered a sort of the common RS.
  • demodulation since demodulation is a part of a decoding process, the term demodulation in embodiments of the present invention is used interchangeably with decoding.
  • FIG. 6 illustrates configuration of cell specific reference signals (CRSs). Especially, FIG. 6 illustrates configuration of CRSs for a 3GPP LTE system supporting a maximum of four antennas.
  • CRSs cell specific reference signals
  • the CRSs are transmitted in all DL subframes in a cell supporting PDSCH transmission and are transmitted through all antenna ports configured at an eNB.
  • a UE may measure CSI using the CRSs and demodulate a signal received on a PDSCH in a subframe including the CRSs. That is, the eNB transmits the CRSs at predetermined locations in each RB of all RBs and the UE performs channel estimation based on the CRSs and detects the PDSCH.
  • the UE may measure a signal received on a CRS RE and detect a PDSCH signal from an RE to which the PDSCH is mapped using the measured signal and using the ratio of reception energy per CRS RE to reception energy per PDSCH mapped RE.
  • the UE may measure a signal received on a CRS RE and detect a PDSCH signal from an RE to which the PDSCH is mapped using the measured signal and using the ratio of reception energy per CRS RE to reception energy per PDSCH mapped RE.
  • the eNB since the eNB should transmit the CRSs in all RBs, unnecessary RS overhead occurs.
  • a UE-specific RS (hereinafter, UE-RS) and a CSI-RS are further defined in addition to a CRS.
  • the UE-RS is used for demodulation and the CSI-RS is used to derive CSI.
  • the UE-RS is one type of a DRS.
  • the UE-RS is configured to be transmitted only in RB(s) to which the PDSCH is mapped in a subframe in which the PDSCH is scheduled, unlike the CRS which is configured to be transmitted in every subframe regardless of whether the PDSCH is present.
  • the CSI-RS is a DL RS introduced for channel measurement.
  • a plurality of CSI-RS configurations is defined for CSI-RS transmission.
  • CSI-RS sequence r l,n s (m) is mapped to complex modulation symbols a k,l (p) used as RSs on antenna port p according to the following equation.
  • a k,l (p) w l′′ ⁇ r l,n s ( m ′) [Equation 14]
  • Equation 14 w l′′ , k, l are given by the following equation.
  • k k ′ + 12 ⁇ ⁇ m + ⁇ - 0 for ⁇ ⁇ p ⁇ ⁇ 15 , 16 ⁇ , normal ⁇ ⁇ cyclic ⁇ ⁇ prefix - 6 for ⁇ ⁇ p ⁇ ⁇ 17 , 18 ⁇ , normal ⁇ ⁇ cyclic ⁇ ⁇ prefix - 1 for ⁇ ⁇ p ⁇ ⁇ 19 , 20 ⁇ , normal ⁇ ⁇ cyclic ⁇ ⁇ prefix - 7 for ⁇ ⁇ p ⁇ ⁇ 21 , 22 ⁇ , normal ⁇ ⁇ cyclic ⁇ ⁇ prefix - 0 for ⁇ ⁇ p ⁇ ⁇ 15 , 16 ⁇ , extended ⁇ ⁇ cyclic ⁇ ⁇ prefix - 3 for ⁇ ⁇ p ⁇ ⁇ 17 , 18 ⁇ , extended ⁇ ⁇ cyclic ⁇ ⁇ prefix - 6 for ⁇ ⁇ p ⁇ ⁇ 19 , 20
  • FIG. 7 illustrates CSI-RS configurations. Particularly, FIG. 7( a ) illustrates 20 CSI-RS configurations 0 to 19 available for CSI-RS transmission through two CSI-RS ports among the CSI-RS configurations of Table 8, FIG. 7( b ) illustrates 10 available CSI-RS configurations 0 to 9 through four CSI-RS ports among the CSI-RS configurations of Table 8, and FIG. 7( c ) illustrates 5 available CSI-RS configurations 0 to 4 through 8 CSI-RS ports among the CSI-RS configurations of Table 8.
  • the CSI-RS ports refer to antenna ports configured for CSI-RS transmission. For example, referring to Equation 15, antenna ports 15 to 22 correspond to the CSI-RS ports. Since CSI-RS configuration differs according to the number of CSI-RS ports, if the numbers of antenna ports configured for CSI-RS transmission differ, the same CSI-RS configuration number may correspond to different CSI-RS configurations.
  • a CSI-RS is configured to be transmitted at a prescribed period corresponding to a plurality of subframes. Accordingly, CSI-RS configurations vary not only with the locations of REs occupied by CSI-RSs in an RB pair according to Table 8 or Table 9 but also with subframes in which CSI-RSs are configured. That is, if subframes for CSI-RS transmission differ even when CSI-RS configuration numbers are the same in Table 8 or Table 9, CSI-RS configurations also differ.
  • T CSI-RS transmission periods
  • ⁇ CSI-RS start subframes
  • CSI-RS configurations CSI-RS configurations
  • the CSI-RS configuration of the latter will be referred to as a CSI-RS resource configuration.
  • an eNB may inform the UE of information about the number of antenna ports used for transmission of CSI-RSs, a CSI-RS pattern, CSI-RS subframe configuration I CSI-RS , UE assumption on reference PDSCH transmitted power for CSI feedback P c , a zero-power CSI-RS configuration list, a zero-power CSI-RS subframe configuration, etc.
  • CSI-RS subframe configuration I CSI-RS is information for specifying subframe configuration periodicity T CSI-RS and subframe offset ⁇ CSI-RS regarding occurrence of the CSI-RSs.
  • the following table shows CSI-RS subframe configuration I CSI-RS according to T CSI-RS and ⁇ CSI-RS .
  • CSI-RS CSI-RS subframe CSI-RS- periodicity T CSI-RS offset ⁇ CSI-RS SubframeConfig I CSI-RS (subframes) (subframes) 0-4 5 I CSI-RS 5-14 10 I CSI-RS ⁇ 5 15-34 20 I CSI-RS ⁇ 15 35-74 40 I CSI-RS ⁇ 35 75-154 80 I CSI-RS ⁇ 75
  • P c is the ratio of PDSCH EPRE to CSI-RS EPRE, assumed by the UE when the UE derives CSI for CSI feedback.
  • EPRE indicates energy per RE.
  • CSI-RS EPRE indicates energy per RE occupied by the CSI-RS and PDSCH EPRE denotes energy per RE occupied by a PDSCH.
  • the zero-power CSI-RS configuration list denotes CSI-RS pattern(s) in which the UE should assume zero transmission power. For example, since the eNB will transmit signals at zero transmission power on REs included in CSI-RS configurations indicated as zero transmission power in the zero power CSI-RS configuration list, the UE may assume signals received on the corresponding REs as interference or decode DL signals except for the signals received on the corresponding REs.
  • the zero power CSI-RS configuration list may be a 16-bit bitmap corresponding one by one to 16 CSI-RS patterns for four antenna ports.
  • the most significant bit corresponding to a CSI-RS configuration of the lowest CSI-RS configuration number (also called a CSI-RS configuration index) and subsequent bits correspond to CSI-RS patterns in an ascending order.
  • the UE assumes zero transmission power with respect to REs of a CSI-RS pattern corresponding to bit(s) set to ‘1’ in the 16-bit zero power CSI-RS bitmap configured by a higher layer.
  • a CSI-RS pattern in which the UE assumes zero transmission power will be referred to as a zero power CSI-RS pattern.
  • a zero power CSI-RS subframe configuration is information for specifying subframes including the zero power CSI-RS pattern.
  • a subframe in which the zero power CSI-RS occurs may be configured for the UE using I CSI-RS according to Table 10.
  • the UE may assume that subframes satisfying Equation 16 include the zero power CSI-RS pattern.
  • I CSI-RS may be separately configured with respect to a CSI-RA pattern in which the UE should assume non-zero transmission power and a zero power CSI-RS pattern in which the UE should assume zero transmission power, on REs.
  • the UE configured for a transmission mode may perform channel measurement using a CSI-RS and demodulate or decode a PDSCH using a UE-RS.
  • FIG. 8 illustrates the structure of a UL subframe used in a wireless communication system.
  • a UL subframe may be divided into a data region and a control region in the frequency domain.
  • One or several PUCCHs may be allocated to the control region to deliver UCI.
  • One or several PUSCHs may be allocated to the data region of the UE subframe to carry user data.
  • subcarriers distant from a direct current (DC) subcarrier are used as the control region.
  • subcarriers located at both ends of a UL transmission BW are allocated to transmit UCI.
  • a DC subcarrier is a component unused for signal transmission and is mapped to a carrier frequency f 0 in a frequency up-conversion process.
  • a PUCCH for one UE is allocated to an RB pair belonging to resources operating on one carrier frequency and RBs belonging to the RB pair occupy different subcarriers in two slots.
  • the PUCCH allocated in this way is expressed by frequency hopping of the RB pair allocated to the PUCCH over a slot boundary. If frequency hopping is not applied, the RB pair occupies the same subcarriers.
  • the PUCCH may be used to transmit the following control information.
  • SR Scheduling request
  • OOK on-off keying
  • HARQ-ACK is a response to a PDCCH and/or a response to a DL data packet (e.g. a codeword) on a PDSCH.
  • HARQ-ACK indicates whether the PDCCH or PDSCH has been successfully received.
  • 1-bit HARQ-ACK is transmitted in response to a single DL codeword and 2-bit HARQ-ACK is transmitted in response to two DL codewords.
  • a HARQ-ACK response includes a positive ACK (simply, ACK), negative ACK (NACK), discontinuous transmission (DTX), or NACK/DRX.
  • HARQ-ACK is used interchangeably with HARQ ACK/NACK and ACK/NACK.
  • CSI Channel state information
  • CSI is feedback information for a DL channel.
  • CSI may include channel quality information (CQI), a precoding matrix indicator (PMI), a precoding type indicator, and/or a rank indicator (RI).
  • CQI channel quality information
  • PMI precoding matrix indicator
  • RI rank indicator
  • MIMO-related feedback information includes the RI and the PMI.
  • the RI indicates the number of streams or the number of layers that the UE can receive through the same time-frequency resource.
  • the PMI is a value reflecting a space characteristic of a channel, indicating an index of a preferred precoding matrix for DL signal transmission based on a metric such as an SINR.
  • the CQI is a value of channel strength, indicating a received SINR that can be obtained by the UE generally when the eNB uses the PMI.
  • FIGS. 9( a ) and 9 ( b ) are diagrams for explaining single-carrier communication and multi-carrier communication. Specially, FIG. 9( a ) illustrates a subframe structure of a single carrier and FIG. 9( b ) illustrates a subframe structure of multiple carriers.
  • a general wireless communication system transmits/receives data through one downlink (DL) band and through one uplink (UL) band corresponding to the DL band (in the case of frequency division duplex (FDD) mode), or divides a prescribed radio frame into a UL time unit and a DL time unit in the time domain and transmits/receives data through the UL/DL time unit (in the case of time division duplex (TDD) mode).
  • FDD frequency division duplex
  • TDD time division duplex
  • a carrier aggregation is different from an orthogonal frequency division multiplexing (OFDM) system in that DL or UL communication is performed using a plurality of carrier frequencies, whereas the OFDM system carries a base frequency band divided into a plurality of orthogonal subcarriers on a single carrier frequency to perform DL or UL communication.
  • OFDM orthogonal frequency division multiplexing
  • each of carriers aggregated by carrier aggregation will be referred to as a component carrier (CC).
  • CC component carrier
  • three 20 MHz CCs in each of UL and DL are aggregated to support a BW of 60 MHz.
  • the CCs may be contiguous or non-contiguous in the frequency domain.
  • FIG. 9( b ) illustrates that a BW of UL CC and a BW of DL CC are the same and are symmetrical, a BW of each component carrier may be defined independently.
  • asymmetric carrier aggregation where the number of UL CCs is different from the number of DL CCs may be configured.
  • a DL/UL CC for a specific UE may be referred to as a serving UL/DL CC configured at the specific UE.
  • the 3GPP LTE-A system uses a concept of cell to manage radio resources.
  • the “cell” associated with the radio resources is defined by combination of DL resources and UL resources, that is, combination of DL CC and UL CC.
  • the cell may be configured by DL resources only, or may be configured by DL resources and UL resources.
  • linkage between a carrier frequency of the DL resources (or DL CC) and a carrier frequency of the UL resources (or UL CC) may be indicated by system information.
  • SIB2 system information block type 2
  • the carrier frequency means a center frequency of each cell or CC.
  • a cell operating on a primary frequency may be referred to as a primary cell (Pcell) or PCC
  • a cell operating on a secondary frequency may be referred to as a secondary cell (Scell) or SCC.
  • the carrier corresponding to the Pcell on DL will be referred to as a DL primary CC (DL PCC)
  • the carrier corresponding to the Pcell on UL will be referred to as a UL primary CC (UL PCC).
  • a Scell means a cell that may be configured after completion of radio resource control (RRC) connection establishment and used to provide additional radio resources.
  • the Scell may form a set of serving cells for the UE together with the Pcell in accordance with capabilities of the UE.
  • RRC radio resource control
  • DL secondary CC DL secondary CC
  • UL SCC UL secondary CC
  • the eNB may activate all or some of the serving cells configured in the UE or deactivate some of the serving cells for communication with the UE.
  • the eNB may change the activated/deactivated cell, and may change the number of cells which is/are activated or deactivated. If the eNB allocates available cells to the UE cell-specifically or UE-specifically, at least one of the allocated cells is not deactivated unless cell allocation to the UE is fully reconfigured or unless the UE performs handover.
  • Pcell a cell which is not deactivated unless CC allocation to the UE is fully reconfigured
  • Scell a cell which may be activated/deactivated freely by the eNB
  • the Pcell and the Scell may be discriminated from each other on the basis of the control information.
  • specific control information may be set to be transmitted and received through a specific cell only.
  • This specific cell may be referred to as the Pcell, and the other cell(s) may be referred to as Scell(s).
  • FIG. 10 illustrates the state of cells in a system supporting carrier aggregation.
  • a configured cell refers to a cell in which carrier aggregation is performed for a UE based on measurement report from another eNB or UE among cells of an eNB and is configured per UE.
  • the cell configured for the UE may be a serving cell in terms of the UE.
  • resources for ACK/NACK transmission for PDSCH transmission are reserved in advance.
  • An activated cell refers to a cell configured to be actually used for PDSCH/PUSCH transmission among cells configured for the UE and CSI reporting and SRS transmission for PDSCH/PUSCH transmission are performed in the activated cell.
  • a deactivated cell refers to a cell configured not to be used for PDSCH/PUSCH transmission by the command of an eNB or the operation of a timer and, if a cell is deactivated, CSI reporting and SRS transmission are also stopped in the cell.
  • each of a transmitter and a receiver performs beamforming based on the channel information, i.e. CSI, to obtain a multiplexing gain of MIMO antennas.
  • CSI channel information
  • time and frequency resources which can be used by the UE are controlled by then eNB.
  • the eNB commands the UE to feed back DL CSI by allocating a PUCCH or a PUSCH to the UE in order to obtain the DL CSI.
  • a CSI report is periodically or aperiodically configured.
  • a periodic CSI report is transmitted by the UE on the PUCCH except for a special case (e.g. when the UE is not configured for simultaneous PUSCH and PUCCH transmission and when a PUCCH transmission timing collides with a subframe with PUSCH allocation).
  • the RI is typically fed back to the UE from the eNB at a cycle longer than that of a PMI and CQI.
  • an aperiodic CSI report is transmitted on the PUSCH.
  • the aperiodic CSI report is triggered by a CSI request field included in the DCI (e.g.
  • the UE which has decoded the UL DCI format or a random access response grant for a specific serving cell (hereinafter, serving cell c) in subframe n, performs aperiodic CSI reporting using the PUSCH in subframe n+k in serving cell c when the CSI request field is set to trigger the CSI report and when the CSI request field is not reserved.
  • a UE for which a TDD UL/DL configuration is 6 detects a UL DCI format for serving cell c in subframe 9
  • the UE performs aperiodic CSI reporting triggered by a CSI request field in the detected UL DCI format on the PUSCH of serving cell c in subframe 9+5, i.e. in subframe 4 of a radio frame following a radio frame including subframe 9 in which the UL DCI format is detected.
  • the CSI request field is 1 bit or 2 bits in length. If the CSI request field is 1 bit, the CSI request field set to ‘1’ triggers the aperiodic CSI report for serving cell c. If the CSI request field is 2 bits, the aperiodic CSI report corresponding to the following table is triggered. That is, the following table shows the CSI request field with the UL DCI format.
  • CoMP technology involves a plurality of nodes. If CoMP technology is introduced to the LTE/LTE-A system, a new transmission mode may be defined in association with CoMP technology.
  • a UE configured in a CoMP mode When the UE is configured in a mode in which one or more CSI-RS resource configurations can be configured, that is, when the UE is configured in a CoMP mode, the UE may receive a higher layer signal including information about one or more CSI-RS resource configurations. If carrier aggregation (hereinafter, CA) as well as CoMP is configured for the UE, one or more CSI-RS resource configurations per serving cell can be used.
  • CA carrier aggregation
  • the UE has transmitted/received signals to/from one node in a specific serving cell.
  • the conventional LTE/LTE-A system since only one radio link is present in one serving cell, only one CSI could be calculated by the UE with respect to one serving cell.
  • DL channel states may differ per node or per combination of nodes. Since CSI-RS resource configurations may differ according to a node or combination of nodes, CSI is associated with a CSI-RS resource. In addition, channel states may vary with an interference environment between nodes participating in CoMP.
  • a channel state per node or per combination of nodes may be measured by the UE and, since CSI may be present in each interference environment, a maximum number of CSIs which can be calculated per serving cell of the UE may be an integer greater than one.
  • a maximum number of CSIs which can be calculated per serving cell of the UE may be an integer greater than one.
  • which CSI should be reported by the UE and how the UE should reports the CSI may be configured by higher layers.
  • a plurality of CSIs as well as one CSI can be calculated by the UE. Accordingly, when a CoMP mode is configured for the UE, a CSI report for one or more CSIs per serving cell of the UE may be configured for periodic or aperiodic CSI reporting.
  • the CSI is associated with a CSI-RS resource used for channel measurement and a resource used for interference measurement (hereinafter, an interference measurement (IM) resource).
  • IM interference measurement
  • association of a CSI-RS resource for signal measurement and an IM resource for interference measurement will be referred to as a CSI process. That is, the CSI process may be associated with a CSI-RS resource and a IM resource (IMR).
  • an eNB to which a UE is connected or an eNB for managing a node of a cell in which the UE is located (hereinafter, a serving eNB) transmit no signals on an IMR.
  • the IMR may be configured for the UE by the same scheme as in a zero-power CSI-RS.
  • the eNB may inform the UE of REs used by the UE for interference measurement using the 16-bit bitmap indicating the above-described zero power CSI-RS pattern and using the CSI-RS subframe configuration.
  • the UE measures interference on the IMR and calculates CSI under the assumption that the measured interference is interference on a CSI reference resource which is reference for CSI measurement. More specifically, the UE may perform channel measurement based on a CSI-RS or a CRS, perform interference measurement based on the IMR, and derive the CSI based on channel measurement and interference measurement.
  • a CSI reported by the UE may correspond to a CSI process.
  • Each CSI process may have an independent CSI feedback configuration.
  • the independent feedback configuration refers to a feedback mode, a feedback period, a feedback offset, etc.
  • the feedback offset corresponds to a start subframe with feedback among subframes in a radio frame.
  • the feedback mode is differently defined according to whether CQI included in feedback CSI among an RI, CQI, a PMI, and a TPMI is CQI for a wideband, CQI for a subband, or CQI for a subband selected by the UE, whether the CSI includes the PMI, and whether the CSI includes a single PMI or a plurality of PMIs.
  • FIGS. 11( a ), 11 ( b ), 11 ( c ), and 11 ( d ) illustrate links configurable according to carrier aggregation and a CoMP environment.
  • f1, f2, f3, and f4 correspond to carrier frequencies in which a cell operates when eNB 1 and/or eNB 2 communicate with a UE.
  • an eNB transmits a 1-bit CSI request field to the UE through DCI format 0 or 4 (hereinafter, DCI format 0/4).
  • DCI format 0/4 As illustrated in FIG. 11( b ), if the UE has multiple serving cells in a CA environment, the eNB transmits a 2-bit CSI request field according to Table 12 to the UE through DCI format 0/4.
  • the CSI request field of DCI format 0/4 may be interpreted as one bit and, if the UE has multiple serving cells in the CA environment, the CSI request field of DCI format 0/4 may be interpreted as 2 bits. That is, if a CoMP mode is not configured, the aperiodic CSI report may be triggered using the 1-bit or 2-bit CSI request field according to whether CA is configured as described above.
  • a plurality of CSIs per serving cell i.e. a plurality of CSI processes, may be configured as described previously.
  • a transmission mode in which one or plural CSIs can be configurable for serving cell c i.e. a CoMP mode
  • a method for triggering the aperiodic CSI report is problematic.
  • the UE has a single cell, i.e. if only one serving cell is configured for the UE, and if multiple CSIs for CoMP are configured in the cell, or although not shown, if the UE has a single cell and multiple CSIs for CoMP, i.e. multiple CSI processes, are configured for the cell, it is necessary to determine how to use the CSI request field and how to interpret the CSI request field.
  • the UE has multiple serving cells in the CA environment and if multiple CSIs for CoMP, i.e. multiple processes, are configured for some or all serving cells, it is necessary to determine how to use the CSI request field and how to interpret the CSI request field.
  • a CA+CoMP environment an environment in which the UE has multiple serving cells in the CA environment and multiple CSIs for CoMP, i.e. multiple CSI processes are configured for some or all serving cells.
  • the UE is considered to be in the CA+CoMP environment.
  • a serving cell used for both CoMP and CA in the CA+CoMP environment is referred to as a CoMP cell and a cell used only for CA and not used for CoMP is referred to as a non-CoMP cell.
  • methods for configuring and interpreting the CSI request field in the CA+CoMP environment will be proposed.
  • embodiments of the present invention will be described by way of example when CA+CoMP is configured, the embodiments of the present invention are identically applicable when only CoMP is configured without configuring CA. That is, the embodiments of the present invention may be applied to a UE configured in a CoMP mode.
  • Embodiment A of the present invention proposes a CSI request field in a CA+CoMP environment.
  • the CSI request field may consist of two or more bits.
  • the present invention proposes that CSI request(s) for all or some of the following be used in the CSI request field.
  • aperiodic CSI is reported by a PUSCH of serving cell c as described in association with Table 11 and Table 12.
  • Aperiodic CSI report is triggered for the first CSI-RS (or CSI-RS resource+IM resource) set for a serving cell configured by higher layers”
  • Aperiodic CSI report is triggered for the first CSI-RS (or CSI-RS resource+IM resource) set for a set of serving cells configured by higher layers”
  • “Aperiodic CSI report is triggered for a set of CSI processes for serving cell c” means that some or all CSI process(es) configured by higher layers (e.g. RRC) are reported among CSI process(es) of serving cell c. If a UE is configured in a CoMP mode, one or more CSI processes may be configured for serving cell c.
  • the UE Upon receiving the CSI request field set to a value corresponding to “Aperiodic CSI report is triggered for a set of CSI processes for serving cell c”, the UE performs an aperiodic CSI reporting about a set of CSI process(es) configured by higher layers (e.g. RRC) among the CSI process(es) configured for serving cell c.
  • Aperiodic CSI report is triggered for a set of CSI processes for a set of serving cells configured by higher layers means that some or all CSI process(es) configured by the higher layers are reported among all CSI processes of a set of serving cells configured by the higher layers (e.g. RRC).
  • CSI(s) which are configured by the higher layers and triggered by the CSI request field set to indicate one of the above descriptions so as to be fed back, may differ according to serving cell c to which a PUSCH carrying the aperiodic CSI report is allocated.
  • the present invention proposes Table 13 and Table 14 as examples of values which can be set in the CSI request field in the CA+CoMP environment.
  • a UE in the CA+CoMP environment may transmit the aperiodic CSI report triggered by the CSI request field on a PUSCH of the specific serving cell in subframe n+k according to Table 13 or Table 14.
  • Table 13 for example, when the UE receives the CSI request field set to ‘00’ in the CA+CoMP environment, the UE performs no aperiodic CSI reporting on the PUSCH of the specific serving cell.
  • the aperiodic CSI report is triggered for a set of CSI process(es) configured by the higher layers among CSI process(es) of the specific serving cell and the UE performs an aperiodic CSI report for a set of CSI process(es) on the PUSCH of the specific serving cell.
  • the aperiodic CSI report may include CSI(s) about the CSI process(es).
  • the aperiodic CSI report is triggered for a set of CSI process(es) among all CSI process(es) for a set of serving cell(s) configured by the higher layers.
  • the aperiodic CSI report is triggered for a set of CSI process(es) among all CSI process(es) for another set of serving cell(s) configured by the higher layers.
  • CSI request bits may be formed by the same number of bit(s) as bits of a conventional CSI request field even in the CoMP environment.
  • an eNB may use two or more bits for the CSI request field. Therefore, the CSI request field in the CA+CoMP environment and/or the CoMP environment may be configured in many ways. For example, the CSI request field may be configured according to any one of the following schemes.
  • one of the bits of the CSI request field may be used for CoMP/CA indication.
  • the bit indicates whether the other bit(s) of the CSI request field are interpreted as the CSI request field for the CoMP environment or as the CSI request field for the CA environment. Accordingly, upon interpreting the CSI request field of received DCI format 0/4, the UE determines, through one specific bit of the CSI request field, whether the other bit(s) of the CSI request field are interpreted as the CSI request field for CoMP or the CSI request field for CA.
  • the UE may determine for which serving cell the aperiodic CSI report is triggered, based on the other bit(s) of the CSI request field by the scheme described with reference to Table 11 and Table 12.
  • the UE may determine for which CSI processes the aperiodic CSI report is triggered, based on the other bit(s) of the CSI request field by the scheme described in Embodiment A of the present invention.
  • partial value(s) of the CSI request field may be fixed to indicate a specific aperiodic CSI report and the other value(s) of the CSI request field may be used to indicate a set of CSI(s), i.e. a set of CSI process(es), configured by the higher layers (e.g. RRC).
  • the set of CSI(s) may be composed of combination of CSI of each non-CoMP cell and multiple CSIs of each CoMP cell.
  • the other values of the CSI request field may indicate a set of CSI(s) configured by the higher layers.
  • the value of the CSI request field is 000, this may indicate that no aperiodic CSI report is triggered, if the value of the CSI request field is 001, this may indicate that the aperiodic CSI report is triggered for a cell used for aperiodic CSI PUSCH transmission, and the other value(s) of the CSI request field may indicate that a set of CSI(s) configured by the higher layers (e.g. RRC) is triggered.
  • the CSI request field may be set according to any one of descriptions proposed in Embodiment A of the present invention.
  • the CSI request field for CoMP may be provided according to Embodiment A of the present invention.
  • the CSI request field used in CA may be provided according to a description associated with Table 11 and Table 12. For instance, if the CSI request field for CA consists of one bit, the CSI request field set to ‘1’ triggers the aperiodic CSI report for serving cell c. If the CSI request field used in CA consists of two bits, the aperiodic CSI report corresponding to the values of Table 12 is triggered.
  • Embodiment C of the present invention proposes that serving cells in the CoMP+CA environment be divided into multiple groups and RRC configuration for a CSI set be independently performed in each group.
  • Embodiment C of the present invention proposes that RRC configuration for a CSI set be independently performed in each serving cell in the CoMP+CA environment. That is, in Embodiment C of the present invention, serving cells transmitting aperiodic CSI PUSCHs in the CoMP+CA environment, i.e. serving cells to which PUSCHs carrying aperiodic CSIs are allocated may be divided into multiple groups and set(s) of CSIs which can be triggered by the CSI request field, i.e. CSI set(s), may be independently configured per serving cell group.
  • the same CSI request field value may trigger different CSI sets according to a serving cell group including a serving cell to which a PUSCH carrying the aperiodic CSI report triggered by the CSI request field is mapped.
  • CSI set(s) which can be triggered by the CSI request field may be independently configured per serving cell.
  • the CSI request field of each cell or cell group includes values indicating the aperiodic CSI report for CSI sets configured by RRC.
  • sets of serving cells configured by RRC in conventional CA are the same for all serving cells irrespective of which serving cell transmits the aperiodic CSI PUSCH, that is, which serving cell is a cell to which the PUSCH carrying the aperiodic CSI report is mapped.
  • CSI sets configured by RRC for the CSI request field are the same when the aperiodic CSI PUSCH is triggered for serving cells belonging to the same group but are not always the same for serving cell(s) belonging to different groups when the aperiodic CSI PUSCH is triggered for serving cell(s) belonging to different groups.
  • CSI set(s) for the CSI request field are independently configured with respect to each serving cell, it cannot be interpreted that the CSI field always triggers report on the same CSI set when serving cells carrying the aperiodic CSI PUSCH are different although the values of the CSI request field are the same in a situation in which serving cells are different.
  • two RRC configured CSI sets may be ⁇ CSI 1, CSI 1+CSI 2 ⁇ for the case in which the aperiodic CSI PUSCH is triggered for group 1, i.e. for the case in which aperiodic CSI reporting is performed on a PUSCH of a serving cell belonging to group 1, and two RRC configured CSI sets for the case the aperiodic CSI PUSCH is triggered for group 2 may be ⁇ CSI 1+CSI 3, CSI 1+CSI 2+CSI 3 ⁇ .
  • a CSI set indicated by the CSI request field may be interpreted as one of ⁇ CSI 1, CSI 1+CSI 2 ⁇ and, if the aperiodic CSI PUSCH is triggered for cell 3 or cell 4, a CSI set indicated by the CSI request field may be interpreted as one of ⁇ CSI 1+CSI 3, CSI 1+CSI 2+CSI 3 ⁇ .
  • a CoMP configured UE may interpret the CSI request field according to Embodiment A of the present invention.
  • Embodiment D of the present invention proposes that, if the aperiodic CSI PUSCH is triggered for a CoMP cell, i.e. if aperiodic CSI reporting should be performed on a PUSCH of the CoMP cell, the CSI request field is interpreted as the CSI request field for CoMP and, if the aperiodic CSI PUSCH is triggered for a non-CoMP cell, the CSI request field be interpreted as the CSI request field for CA.
  • Embodiment D of the present invention for example, if the aperiodic CSI PUSCH is triggered for cell f1 in FIG. 11( d ), i.e.
  • the UE interprets the CSI request field as the CSI request field for CoMP but, if the aperiodic CSI PUSCH is triggered for cells f2, f3, and f4, the UE interprets the CSI request field as the CSI request field for CA.
  • FIG. 12 is a diagram for explaining an embodiment of the present invention.
  • Embodiment D of the present invention proposes that, if the aperiodic CSI PUSCH is triggered for a CoMP cell, the CSI request field be interpreted as the CSI request field for CoMP in the CoMP cell and, if the aperiodic CSI PUSCH is triggered for a non ⁇ CoMP cell, the CSI request field be interpreted as the CSI request field for CA.
  • the CSI request field be interpreted as the CSI request field for CA.
  • the present invention proposes that, if the aperiodic CSI PUSCH is triggered for cell f1, the CSI request field be interpreted as the CSI request field for CoMP by considering only a CoMP environment of cell f1, if the aperiodic CSI PUSCH is triggered for cell f2, the CSI request field should be interpreted as the CSI request field for CoMP by considering only a CoMP environment of cell f2, and if the aperiodic CSI PUSCH is triggered for cell f3, the CSI request field should be interpreted as the CSI request field for CA.
  • the CSI request field for CoMP may be provided according to Embodiment A of the present invention.
  • the CSI request field for CA may be given according to a description associated with Table 11 and Table 12.
  • Embodiment E of the present invention proposes that the CSI request field in the CA+CoMP environment be properly used according to a CoMP environment or a CA environment and whether the CSI request field will be interpreted as the CSI request field for CoMP or the CSI request field for CA differ according to the location of a subframe.
  • the UE may interpret the CSI request as the CSI request field for CoMP and, if the subframe in which the CSI request is transmitted is an even-numbered (or odd-numbered) subframe, the UE may interpret the CSI request as the CSI request field for CA.
  • the UE may interpret the CSI request as the CSI request field for CoMP and, if the CSI request is transmitted in subframes 5 to 9 (or subframes 0 to 4), the UE may interpret the CSI request as the CSI request field for CA.
  • the CSI request field for CoMP may be given according to Embodiment A of the present invention.
  • the CSI request field for CA may be given according to a description associated with Table 11 and Table 12.
  • Embodiment F of the present invention proposes that the CSI request field in the CA+CoMP environment be properly used according to a CoMP environment or a CA environment and the UE be informed of whether the CSI request field is interpreted as the CSI request field for CoMP or the CSI request field for CA using another field in DCI format 0/4.
  • DCI format 0 is used for scheduling of a PUSCH in one UL cell
  • DCI format 4 is used for scheduling the PUSCH in one UL cell for a multi-antenna port transmission mode.
  • Table 15 and Table 16 shows DCI which can be transmitted by DCI format 0 and DCI format 4, respectively.
  • Frequency hopping flag (FH) 1 Hopping resource allocation N UL — hop (N UL — hop ) Resource block assignment ⁇ log 2 (N RB UL (N RB UL + 1)/2) ⁇ ⁇ N UL — hop (RA)
  • New data indicator (NDI) 1 TPC command for scheduled 2 PUSCH (TPC) Cyclic shift for DM RS and 3 OCC index (DM RS CS) CSI request (CSI request) 1 or 2 SRS request (SRS) 0 or 1 Resource allocation type 0 or 1 (RAT)
  • Carrier indicator 1 or 3 Resource block assignment (RA) max ⁇ ( ⁇ log 2 ⁇ ( N RB UL ⁇ ( N RB UL + 1 ) / 2 ) ⁇ , ⁇ log 2 ⁇ ( ( ⁇ N RB UL / P + 1 ⁇ 4 ) ) ⁇ ) TPC command for scheduled PUSCH 2 (TPC) Cyclic shift for DM RS and OCC index 3 (DM RS CS) CSI request (CSI request) 1 or 2 SRS request (SRS) 2 Resource allocation type (RAT) 1 Modulation and coding scheme and 5 redundancy version for transport block 1 (MCS & RV 1) New data indicator for transport block 1 1 (NDI1) Modulation and coding scheme and 5 redundancy version for transport block 2 (MCS & RV 2) New data indicator for transport block 2 1 (NDI2) Precoding information and number of 3 or 6 layers (Precoding information)
  • a bit of any one of the following fields may be used to indicate whether the CSI request field is interpreted as the CSI request field for CoMP or the CSI request field for CA.
  • a bit of “Cyclic shift for DM RS and OCC index” field among fields in DCI format 0/4 may be used to indicate whether the CSI request field is interpreted as the CSI request field for CoMP or the CSI request field for CA.
  • the eNB transmits the CSI request to the UE and simultaneously informs the UE of whether the CSI request field is interpreted as the CSI request field for CoMP or the CSI request field for CA using one bit of “Cyclic shift for DM RS and OCC index” field. If the aperiodic CSI report is requested through the CSI request field in the CoMP+CA environment, the UE determines whether the CSI request field is interpreted as the CSI request field for CoMP or the CSI request field for CA using one determined bit of “Cyclic shift for DM RS and OCC index” field in DCI including the CSI request field.
  • the UE may interpret the CSI request field as the CSI request field for CoMP and, if the value of “Cyclic shift for DM RS and OCC index” field is one of the other four values, the UE may interpret the CSI request field as the CSI request field for CA.
  • the UE may interpret the CSI request field as the CSI request field for CoMP and if “Cyclic shift for DM RS and OCC index” field has one of values ⁇ 100, 101, 110, and 111 ⁇ , the UE may interpret the CSI request field as the CSI request field for CA.
  • a bit of “Resource block assignment and hopping resource allocation” field of DCI format 0 and/or a bit of “Resource block assignment” field of DCI format 4 may be used as a bit for indicating whether the CSI request field is interpreted as the CSI request field for CoMP or the CSI request field for CA.
  • the eNB transmits the CSI request to the UE and simultaneously informs the UE of whether the CSI request field is interpreted as the CSI request field for CoMP or the CSI request field for CA using one bit of “Resource block assignment and hopping resource allocation/Resource block assignment” field.
  • the UE determines whether the CSI request field is interpreted as the CSI request field for CoMP or the CSI request field for CA using one determined bit of “Resource block assignment and hopping resource allocation field/Resource block assignment” field in DCI including the CSI request field.
  • a bit of “Resource allocation type” field may be used as a bit for indicating whether the CSI request field is interpreted as the CSI request field for CoMP or the CSI request field for CA.
  • the eNB transmits the CSI request to the UE and simultaneously informs the UE of whether the CSI request field is interpreted as the CSI request field for CoMP or the CSI request field for CA using the bit of “Resource allocation type” field.
  • the UE determines whether the CSI request field is interpreted as the CSI request field for CoMP or the CSI request field for CA using the bit of “Resource allocation type” field in the DCI including CSI request field. If the bit of “Resource allocation type” field is used to indicate whether the CSI request field is interpreted as the DCI request field for CoMP or the DCI request field for CA, a resource allocation type of a PUSCH may be a prescheduled default mode or an RRC configured mode. Alternatively, a resource allocation type used in previous PUSCH transmission may be used as the resource allocation type of the PUSCH carrying the aperiodic CSI report triggered by the CSI request field.
  • Embodiment F of the present invention proposes that bit(s) of another field in DCI format 0/4 be used in order to determine whether a 2-bit CSI request field is interpreted as the CSI request field for CoMP of a specific cell or the CSI request field for CA when one or more cells performing CoMP are present as illustrated in FIG. 12 .
  • Embodiment F of the present invention proposes that whether the CSI request field is interpreted as the CSI request field for CoMP of the specific cell or the CSI request field for CA be determined using “Cyclic shift for DM RS and OCC index” field.
  • the UE determines whether the CSI request field is interpreted as the CSI request field for CoMP of the specific cell or the CSI request field for CA according to values of “Cyclic shift for DM RS and OCC index” field of 3 bits.
  • 8 values 000 to 111 of “Cyclic shift for DM RS and OCC index” field are divided into 3 sets. If the actual value of “Cyclic shift for DM RS and OCC index” field is one of value(s) belonging to the first set, the UE may interpret the CSI request field as the CSI request field considering only the CoMP environment of cell f1, if the actual value of “Cyclic shift for DM RS and OCC index” field is one of value(s) belonging to the second set, the UE may interpret the CSI request field as the CSI request field considering only the CoMP environment of cell f2, that is, as the CSI request field for CoMP, and if the actual value of “Cyclic shift for DM RS and OCC index” field is one of value(s) belonging to the third set, the UE may interpret the CSI request field as the CSI request field considering only the CA environment, that is, as the CSI
  • Embodiment F of the present invention may be limitedly applied only to the case in which the CSI request field does not indicate no CSI report and/or aperiodic CSI report on a cell carrying the aperiodic CSI PUSCH.
  • Embodiment G of the present invention proposes UE operation when aperiodic CSI feedback for CSI not included in a specific cell, i.e. an aperiodic CSI report, is requested to be transmitted through a PUSCH of serving cell c.
  • CSI feedback for a set of CoMP CSIs for serving cell a i.e. CSI feedback for a set of CSI process(es) for serving cell a is requested to be transmitted through the PUSCH of serving cell c
  • the case in which feedback cannot be performed may occur because CSI for all or some of the set of CoMP CSIs for serving cell a are not valid.
  • the UE may not perform CSI feedback for all of the requested set of CoMP CSIs or may not perform feedback for only some invalid CSI(s).
  • the UE may perform aperiodic CSI reporting (e.g.
  • aperiodic CSI corresponding to ‘01’ of Table 11) of serving cell a based on a transmission mode in which CoMP is not performed, i.e. transmission mode 9.
  • the UE may feed back all CoMP CSIs of serving cell a irrespective of whether CoMP CSIs are valid.
  • the UE may also feed back specific CSI configured by higher layers. Alternatively, the UE may feed back prerequested CSI for serving cell a.
  • FIG. 13 is a diagram for explaining another embodiment of the present invention.
  • Serving cell c may support UL CoMP using UL carriers of multiple TPs and a DL carrier linked with a UL carrier of TP B which is one of TPs participating in UL CoMP of serving cell c may not be configured for the UE.
  • the UE may receive, through serving cell c or serving cell a, a PUSCH grant, which is a UL grant, indicating that a PUSCH carrying an aperiodic CSI report should be transmitted through serving cell c.
  • the UE may transmit the PUSCH to TP B by designating TP B.
  • the UE since the UE is requested to perform aperiodic CSI reporting so as to transmit CSI of a cell to which the PUSCH is allocated, since the UE transmits the PUSCH to TP B, the UE transmits a CSI report for a DL carrier linked with a UL carrier of serving cell c of TP B to TP B.
  • the UE does not use the DL carrier of TP B in serving cell c, the UE does not need to feed back CSI about the DL carrier.
  • the UE may disregard the CSI request and may not perform feedback at all. That is, in this case, the aperiodic CSI report corresponding to the CSI request may be dropped.
  • the UE may perform CSI reporting on a DL carrier of serving cell c of TP A, which is a TP transmitting a PUSCH grant, among DL carriers of serving cell c.
  • FIG. 14 is a block diagram illustrating elements of a transmitting device 10 and a receiving device 20 for implementing the present invention.
  • the transmitting device 10 and the receiving device 20 respectively include Radio Frequency (RF) units 13 and 23 capable of transmitting and receiving radio signals carrying information, data, signals, and/or messages, memories 12 and 22 for storing information related to communication in a wireless communication system, and processors 11 and 21 operationally connected to elements such as the RF units 13 and 23 and the memories 12 and 22 to control the elements and configured to control the memories 12 and 22 and/or the RF units 13 and 23 so that a corresponding device may perform at least one of the above-described embodiments of the present invention.
  • RF Radio Frequency
  • the memories 12 and 22 may store programs for processing and controlling the processors 11 and 21 and may temporarily store input/output information.
  • the memories 12 and 22 may be used as buffers.
  • the processors 11 and 21 generally control the overall operation of various modules in the transmitting device and the receiving device. Especially, the processors 11 and 21 may perform various control functions to implement the present invention.
  • the processors 11 and 21 may be referred to as controllers, microcontrollers, microprocessors, or microcomputers.
  • the processors 11 and 21 may be implemented by hardware, firmware, software, or a combination thereof. In a hardware configuration, application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), or field programmable gate arrays (FPGAs) may be included in the processors 11 and 21 .
  • ASICs application specific integrated circuits
  • DSPs digital signal processors
  • DSPDs digital signal processing devices
  • PLDs programmable logic devices
  • FPGAs field programmable gate arrays
  • firmware or software may be configured to include modules, procedures, functions, etc. performing the functions or operations of the present invention.
  • Firmware or software configured to perform the present invention may be included in the processors 11 and 21 or stored in the memories 12 and 22 so as to be driven by the processors 11 and 21 .
  • the processor 11 of the transmitting device 10 performs predetermined coding and modulation for a signal and/or data scheduled to be transmitted to the outside by the processor 11 or a scheduler connected with the processor 11 , and then transfers the coded and modulated data to the RF unit 13 .
  • the processor 11 converts a data stream to be transmitted into K layers through demultiplexing, channel coding, scrambling, and modulation.
  • the coded data stream is also referred to as a codeword and is equivalent to a transport block which is a data block provided by a MAC layer.
  • One transport block (TB) is coded into one codeword and each codeword is transmitted to the receiving device in the form of one or more layers.
  • the RF unit 13 may include an oscillator.
  • the RF unit 13 may include N t (where N t is a positive integer) transmit antennas.
  • a signal processing process of the receiving device 20 is the reverse of the signal processing process of the transmitting device 10 .
  • the RF unit 23 of the receiving device 20 receives radio signals transmitted by the transmitting device 10 .
  • the RF unit 23 may include N r (where N r is a positive integer) receive antennas and frequency down-converts each signal received through receive antennas into a baseband signal.
  • the processor 21 decodes and demodulates the radio signals received through the receive antennas and restores data that the transmitting device 10 intended to transmit.
  • the RF units 13 and 23 include one or more antennas.
  • An antenna performs a function for transmitting signals processed by the RF units 13 and 23 to the exterior or receiving radio signals from the exterior to transfer the radio signals to the RF units 13 and 23 .
  • the antenna may also be called an antenna port.
  • Each antenna may correspond to one physical antenna or may be configured by a combination of more than one physical antenna element.
  • the signal transmitted from each antenna cannot be further deconstructed by the receiving device 20 .
  • An RS transmitted through a corresponding antenna defines an antenna from the view point of the receiving device 20 and enables the receiving device 20 to derive channel estimation for the antenna, irrespective of whether the channel represents a single radio channel from one physical antenna or a composite channel from a plurality of physical antenna elements including the antenna.
  • an antenna is defined such that a channel carrying a symbol of the antenna can be obtained from a channel carrying another symbol of the same antenna.
  • An RF unit supporting a MIMO function of transmitting and receiving data using a plurality of antennas may be connected to two or more antennas.
  • a UE operates as the transmitting device 10 in UL and as the receiving device 20 in DL.
  • an eNB operates as the receiving device 20 in UL and as the transmitting device 10 in DL.
  • a processor, an RF unit, and a memory included in the UE will be referred to as a UE processor, a UE RF unit, and a UE memory, respectively, and a processor, an RF unit, and a memory included in the eNB will be referred to as an eNB processor, an eNB RF unit, and an eNB memory, respectively.
  • the eNB processor may generate a higher layer signal, a PDCCH, and/or a PDSCH and control the eNB RF unit to transmit the generated higher layer signal, the PDCCH, and/or the PDSCH.
  • the eNB processor may set a CSI request field in DCI for UL transmission in a specific cell according to any one of the embodiments of the present invention.
  • the CSI request field of the DCI may be set according to any one of the embodiments of the present invention.
  • the eNB processor may control the eNB RF unit to transmit the DCI on a PUCCH.
  • the UE processor controls the UE RF unit to receive the higher layer signal, the PDCCH, and/or the PDSCH.
  • the UE processor may receive the DCI for a specific cell on the PDCCH. If the DCI includes the CSI request field and a CoMP mode is configured for the UE by the higher layer signal, i.e. if the UE is capable of being configured by one or more CSI processes per serving cell, the UE processor determines the CSI request field according to any one of the embodiments of the present invention.
  • the UE processor may control the UE RF unit to transmit an aperiodic CSI report for a set of CSI process(es) configured by the higher layers (e.g. RRC) among CSI process(es) configured for the specific serving cell. If a subframe in which the DCI is received is subframe n, the UE processor controls the RF unit to transmit the aperiodic CSI report on a PUSCH to the specific serving cell in subframe n+k.
  • the higher layers e.g. RRC
  • k may be 4 and, for TDD, k may be given by Table 11.
  • the PUSCH is allocated to the specific cell according to the DCI. Embodiment of the present invention can be applied even when a serving cell to which a PDCCH carrying the DCI is allocated is different from the specific serving cell used for transmission of the aperiodic CSI report.
  • the embodiments of the present invention are applicable to a BS, a UE, or other devices in a wireless communication system.

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EP2863679A1 (en) 2015-04-22
WO2013187739A1 (ko) 2013-12-19
US9877315B2 (en) 2018-01-23
KR20130141382A (ko) 2013-12-26
JP6235576B2 (ja) 2017-11-22
US20160150509A1 (en) 2016-05-26
US20150131568A1 (en) 2015-05-14
EP2863679A4 (en) 2016-03-09
JP2015519855A (ja) 2015-07-09
CN104365136B (zh) 2019-03-26
CN104365136A (zh) 2015-02-18
KR101443650B1 (ko) 2014-09-23

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