WO2012060656A2 - Method for transmitting channel measurement information and device therefor - Google Patents

Abstract

The present invention relates to a wireless communication system. More specifically, the present invention relates to a method for feeding back downlink measurement information and a device therefor, wherein the method comprises the steps of: measuring a signal of a macro base station according to each serving cell, and generating a plurality of first signal measurement values; measuring signals of pico base stations, and generating second signal measurement values; and providing said second measurement values to said macro base station if predetermined conditions are satisfied, wherein said predetermined conditions include a condition that the sum of said second signal measurement values and bias values is larger than at least one of the plurality of said first signal measurement values, and each of said bias values is independently given to every serving cell relative to a plurality of serving cells that constitute the macro base station.

Description

Method for transmitting channel measurement information and apparatus therefor

The present invention relates to a wireless communication system, and more particularly, to a method for transmitting channel measurement information and an apparatus therefor.

Wireless communication systems are widely deployed to provide various kinds of communication services such as voice and data. In general, a wireless communication system is a multiple access system capable of supporting communication with multiple users by sharing available system resources (bandwidth, transmission power, etc.). Examples of multiple access systems include code division multiple access (CDMA) systems, frequency division multiple access (FDMA) systems, time division multiple access (TDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, and single carrier frequency (SC-FDMA). division multiple access) system.

An object of the present invention is to provide a method and an apparatus therefor for efficiently transmitting channel measurement information in a wireless communication system. Another object of the present invention is to provide a method and an apparatus therefor for efficiently transmitting channel measurement information in a multicarrier situation.

Technical problems to be achieved in the present invention are not limited to the above technical problems, and other technical problems that are not mentioned will be clearly understood by those skilled in the art from the following description.

According to an aspect of the present invention, in a wireless communication system including a macro base station and a pico base station, a communication device feeds downlink measurement information, the method comprising: measuring a plurality of first signals by measuring a signal of the macro base station for each serving cell Generating a value; Measuring a signal of the pico base station to generate a second signal measurement value; And if the predetermined condition is satisfied, providing the second measurement value to the macro base station, wherein the predetermined condition is that the sum of the second signal measurement value and the bias value is the plurality of first signal measurement values. And a bias value is greater than at least one of the above, wherein the bias value is independently given to each serving cell for a plurality of serving cells constituting the macro base station.

In another aspect of the present invention, a communication apparatus configured to feedback downlink measurement information in a wireless communication system including a macro base station and a pico base station, comprising: a radio frequency (RF) unit; And a processor, wherein the processor measures a signal of the macro base station for each serving cell to generate a plurality of first signal measurement values, and measures a signal of the pico base station to generate a second signal measurement value. And if the condition is met, provide the second measurement value to the macro base station, wherein the predetermined condition is that a sum of the second signal measurement value and a bias value is greater than at least one of the plurality of first signal measurement values. The bias value is provided with a communication device is provided independently for each serving cell for a plurality of serving cells constituting a macro base station.

Preferably, the bias value for each serving cell is calculated using the bias value and the offset value of the reference serving cell.

Preferably, the bias value for each serving cell is calculated using a ratio of the number of ABS (Almost Blank Subframe) of the reference serving cell and the number of ABS of the serving cell for a predetermined time interval.

Preferably, the bias value for each serving cell is calculated using a ratio of the number of orthogonal frequency division symbols (OFDM) for physical downlink control channel (PDCCH) transmission of the reference serving cell and the number of OFDM symbols for PDCCH transmission of the corresponding serving cell.

Preferably, the bias value for each serving cell is calculated using a ratio of the maximum transmit power of the reference serving cell and the maximum transmit power of the corresponding serving cell.

According to the present invention, channel measurement information can be efficiently transmitted in a wireless communication system. More specifically, channel measurement information can be efficiently transmitted in a multicarrier situation.

Effects obtained in the present invention are not limited to the above-mentioned effects, and other effects not mentioned above may be clearly understood by those skilled in the art from the following description. will be.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included as part of the detailed description in order to provide a thorough understanding of the present invention, provide examples of the present invention and together with the description, describe the technical idea of the present invention.

1 illustrates physical channels used in a 3GPP LTE system, which is an example of a wireless communication system, and a general signal transmission method using the same.

2 illustrates a structure of a radio frame.

3 illustrates a resource grid of a downlink slot.

4 shows a structure of a downlink frame.

5 illustrates a structure of an uplink subframe.

6 illustrates a Carrier Aggregation (CA) system.

7 illustrates a heterogeneous network comprising a macro cell and a micro cell.

8 illustrates a situation in which inter-cell interference occurs in a heterogeneous network.

9 illustrates a method for canceling intercell interference in a heterogeneous network.

10 illustrates a conventional feedback process for canceling inter-cell interference.

11 illustrates a problem expected when applying a conventional feedback process for intercell interference in a multicarrier situation.

12 illustrates a process of performing feedback according to an embodiment of the present invention.

13 shows an application example according to an embodiment of the present invention.

14 illustrates a base station and a terminal that can be applied to an embodiment of the present invention.

The following techniques include code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA), and the like. It can be used in various radio access systems. CDMA may be implemented with a radio technology such as Universal Terrestrial Radio Access (UTRA) or CDMA2000. TDMA may be implemented with wireless technologies such as Global System for Mobile communications (GSM) / General Packet Radio Service (GPRS) / Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may be implemented in a wireless technology such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, Evolved UTRA (E-UTRA). UTRA is part of the Universal Mobile Telecommunications System (UMTS). 3rd Generation Partnership Project (3GPP) long term evolution (LTE) employs OFDMA in downlink and SC-FDMA in uplink as part of Evolved UMTS (E-UMTS) using E-UTRA. LTE-A (Advanced) is an evolution of 3GPP LTE.

For clarity, the following description focuses on 3GPP LTE / LTE-A, but the technical spirit of the present invention is not limited thereto. In addition, specific terms used in the following description are provided to help the understanding of the present invention, and the use of such specific terms may be changed to other forms without departing from the technical spirit of the present invention.

FIG. 1 is a diagram for explaining physical channels used in a 3GPP LTE system and a general signal transmission method using the same.

The terminal which is powered on again or enters a new cell while the power is turned off performs an initial cell search operation such as synchronizing with the base station in step S101. To this end, the UE receives a Primary Synchronization Channel (P-SCH) and a Secondary Synchronization Channel (S-SCH) from the base station, synchronizes with the base station, and obtains information such as a cell ID. Thereafter, the terminal may receive a physical broadcast channel from the base station to obtain broadcast information in a cell. Meanwhile, the terminal may check a downlink channel state by receiving a downlink reference signal (DL RS) in an initial cell search step.

After completing the initial cell search, the UE receives a physical downlink control channel (PDSCH) according to the physical downlink control channel (PDCCH) and the physical downlink control channel information in step S102. System information can be obtained.

Thereafter, the terminal may perform a random access procedure such as steps S103 to S106 to complete the access to the base station. To this end, the UE transmits a preamble through a physical random access channel (PRACH) (S103), a response message to the preamble through a physical downlink control channel and a corresponding physical downlink shared channel. Can be received (S104). In case of contention-based random access, contention resolution procedures such as transmission of an additional physical random access channel (S105) and reception of a physical downlink control channel and a corresponding physical downlink shared channel (S106) may be performed. .

After performing the above-described procedure, the UE performs a physical downlink control channel / physical downlink shared channel reception (S107) and a physical uplink shared channel (PUSCH) / as a general uplink / downlink signal transmission procedure. The physical uplink control channel (PUCCH) transmission (S108) may be performed. The control information transmitted from the terminal to the base station is collectively referred to as uplink control information (UCI). UCI includes Hybrid Automatic Repeat and reQuest Acknowledgment / Negative-ACK (HARQ ACK / NACK), Scheduling Request (SR), Channel Quality Indicator (CQI), Precoding Matrix Indicator (PMI), Rank Indication (RI), and the like. In the present specification, HARQ ACK / NACK is simply referred to as HARQ-ACK or ACK / NACK (A / N). HARQ-ACK includes at least one of positive ACK (simply ACK), negative ACK (NACK), DTX, and NACK / DTX. UCI is generally transmitted through PUCCH, but may be transmitted through PUSCH when control information and traffic data should be transmitted at the same time. In addition, the UCI may be aperiodically transmitted through the PUSCH by the request / instruction of the network.

2 illustrates the structure of a radio frame. In a cellular OFDM wireless packet communication system, uplink / downlink data packet transmission is performed in subframe units, and one subframe is defined as a predetermined time interval including a plurality of OFDM symbols. The 3GPP LTE standard supports a type 1 radio frame structure applicable to frequency division duplex (FDD) and a type 2 radio frame structure applicable to time division duplex (TDD).

2 (a) illustrates the structure of a type 1 radio frame. The downlink radio frame consists of 10 subframes, and one subframe consists of two slots in the time domain. The time taken for one subframe to be transmitted is called a transmission time interval (TTI). For example, one subframe may have a length of 1 ms, and one slot may have a length of 0.5 ms. One slot includes a plurality of OFDM symbols in the time domain and a plurality of resource blocks (RBs) in the frequency domain. In the 3GPP LTE system, since OFDMA is used in downlink, an OFDM symbol represents one symbol period. An OFDM symbol may also be referred to as an SC-FDMA symbol or symbol period. A resource block (RB) as a resource allocation unit may include a plurality of consecutive subcarriers in one slot.

The number of OFDM symbols included in one slot may vary depending on the configuration of a cyclic prefix (CP). CPs include extended CPs and normal CPs. For example, when an OFDM symbol is configured by a standard CP, the number of OFDM symbols included in one slot may be seven. When the OFDM symbol is configured by the extended CP, since the length of one OFDM symbol is increased, the number of OFDM symbols included in one slot is smaller than that of the standard CP. In the case of an extended CP, for example, the number of OFDM symbols included in one slot may be six. If the channel state is unstable, such as when the terminal moves at a high speed, an extended CP may be used to further reduce intersymbol interference.

When a standard CP is used, since one slot includes 7 OFDM symbols, one subframe includes 14 OFDM symbols. In this case, the first up to three OFDM symbols of each subframe may be allocated to a physical downlink control channel (PDCCH), and the remaining OFDM symbols may be allocated to a physical downlink shared channel (PDSCH).

2 (b) illustrates the structure of a type 2 radio frame. Type 2 radio frames consist of two half frames, each of which has five subframes, a downlink pilot time slot (DwPTS), a guard period (GP), and an uplink pilot time slot (UpPTS). One subframe consists of two slots. DwPTS is used for initial cell search, synchronization or channel estimation at the terminal. UpPTS is used for channel estimation at the base station and synchronization of uplink transmission of the terminal. The guard period is a period for removing interference generated in the uplink due to the multipath delay of the downlink signal between the uplink and the downlink.

The structure of the radio frame is only an example, and the number of subframes included in the radio frame or the number of slots included in the subframe and the number of symbols included in the slot may be variously changed.

3 illustrates a resource grid of a downlink slot.

Referring to FIG. 3, the downlink slot includes a plurality of OFDM symbols in the time domain. One downlink slot may include 7 (6) OFDM symbols, and the resource block may include 12 subcarriers in the frequency domain. Each element on the resource grid is referred to as a resource element (RE). One RB contains 12x7 (6) REs. The number of RBs included in the downlink slot NRB depends on the downlink transmission band. The structure of an uplink slot is the same as that of a downlink slot, but an OFDM symbol is replaced with an SC-FDMA symbol.

4 illustrates a structure of a downlink subframe.

Referring to FIG. 4, up to three (4) OFDM symbols located at the front of the first slot of a subframe correspond to a control region to which a control channel is allocated. The remaining OFDM symbols correspond to data regions to which the Physical Downlink Shared CHance (PDSCH) is allocated. Examples of a downlink control channel used in LTE include a Physical Control Format Indicator Channel (PCFICH), a Physical Downlink Control Channel (PDCCH), a Physical Hybrid ARQ Indicator Channel (PHICH), and the like. The PCFICH is transmitted in the first OFDM symbol of a subframe and carries information about the number of OFDM symbols used for transmission of a control channel within the subframe. The PHICH carries a HARQ ACK / NACK (Hybrid Automatic Repeat request acknowledgment / negative-acknowledgment) signal in response to uplink transmission.

Control information transmitted through the PDCCH is referred to as downlink control information (DCI). The DCI format is defined as format 0 for uplink, formats 1, 1A, 1B, 1C, 1D, 2, 2A, 3, 3A, and so on for downlink. The DCI format includes a hopping flag, RB assignment, modulation coding scheme (MCS), redundancy version (RV), new data indicator (NDI), transmit power control (TPC), and cyclic shift DM RS, depending on the application. Information including a reference signal (CQI), a channel quality information (CQI) request, a HARQ process number, a transmitted precoding matrix indicator (TPMI), and a precoding matrix indicator (PMI) confirmation are optionally included.

The PDCCH includes a transmission format and resource allocation information of a downlink shared channel (DL-SCH), a transmission format and resource allocation information of an uplink shared channel (UL-SCH), a paging channel, Resource allocation information of upper-layer control messages such as paging information on PCH), system information on DL-SCH, random access response transmitted on PDSCH, Tx power control command set for individual terminals in terminal group, Tx power control command , The activation instruction information of the Voice over IP (VoIP). A plurality of PDCCHs may be transmitted in the control region. The terminal may monitor the plurality of PDCCHs. The PDCCH is transmitted on an aggregation of one or a plurality of consecutive control channel elements (CCEs). CCE is a logical allocation unit used to provide a PDCCH with a coding rate based on radio channel conditions. The CCE corresponds to a plurality of resource element groups (REGs). The format of the PDCCH and the number of PDCCH bits are determined according to the number of CCEs. The base station determines the PDCCH format according to the DCI to be transmitted to the terminal, and adds a cyclic redundancy check (CRC) to the control information. The CRC is masked with an identifier (eg, a radio network temporary identifier (RNTI)) according to the owner or purpose of use of the PDCCH. For example, when the PDCCH is for a specific terminal, an identifier (eg, cell-RNTI (C-RNTI)) of the corresponding terminal may be masked on the CRC. If the PDCCH is for a paging message, a paging identifier (eg, paging-RNTI (P-RNTI)) may be masked to the CRC. When the PDCCH is for system information (more specifically, a system information block (SIC)), a system information RNTI (SI-RNTI) may be masked to the CRC. If the PDCCH is for a random access response, a random access-RNTI (RA-RNTI) may be masked to the CRC.

5 illustrates a structure of an uplink subframe used in LTE.

Referring to FIG. 5, an uplink subframe includes a plurality of slots (eg, two). The slot may include different numbers of SC-FDMA symbols according to the CP length. The uplink subframe is divided into a data region and a control region in the frequency domain. The data area includes a PUSCH and is used to transmit a data signal such as voice. The control region includes a PUCCH and is used to transmit uplink control information (UCI). The PUCCH includes RB pairs located at both ends of the data region on the frequency axis and hops to a slot boundary.

PUCCH may be used to transmit the following control information.

SR (Scheduling Request): Information used for requesting an uplink UL-SCH resource. It is transmitted using OOK (On-Off Keying) method.

HARQ ACK / NACK: This is a response signal for a downlink data packet on a PDSCH. Indicates whether the downlink data packet was successfully received. One bit of ACK / NACK is transmitted in response to a single downlink codeword (CodeWord, CW), and two bits of ACK / NACK are transmitted in response to two downlink codewords.

Channel Quality Indicator (CQI): Feedback information for the downlink channel. Multiple input multiple output (MIMO) related feedback information includes a rank indicator (RI), a precoding matrix indicator (PMI), a precoding type indicator (PTI), and the like. 20 bits are used per subframe.

The amount of control information (UCI) that a UE can transmit in a subframe depends on the number of SC-FDMA available for control information transmission. SC-FDMA available for transmission of control information means the remaining SC-FDMA symbol except for the SC-FDMA symbol for transmitting the reference signal in the subframe, and in the case of the subframe in which the Sounding Reference Signal (SRS) is set, the last of the subframe SC-FDMA symbols are also excluded. The reference signal is used for coherent detection of the PUCCH. PUCCH supports seven formats according to the transmitted information.

Table 1 shows a mapping relationship between PUCCH format and UCI in LTE.

Table 1

PUCCH format	Uplink Control Information (UCI)
Format 1	Scheduling Request (SR) (Unmodulated Waveform)
Format 1a	1-bit HARQ ACK / NACK (with or without SR)
Format 1b	2-bit HARQ ACK / NACK (with or without SR)
Format 2	CQI (20 coded bits)
Format 2	CQI and 1- or 2-bit HARQ ACK / NACK (20 bit) (Extended CP only)
Format 2a	CQI and 1-Bit HARQ ACK / NACK (20 + 1 Coded Bits)
Format 2b	CQI and 2-bit HARQ ACK / NACK (20 + 2 coded bits)

6 illustrates a Carrier Aggregation (CA) communication system. The LTE-A system uses a carrier aggregation or bandwidth aggregation technique that combines a plurality of uplink / downlink frequency bandwidths for a wider frequency bandwidth and uses a larger uplink / downlink bandwidth. Each small frequency bandwidth is transmitted using a component carrier (CC). The component carrier may be understood as the carrier frequency (or center carrier, center frequency) for the corresponding frequency block.

Each of the CCs may be adjacent or non-adjacent to each other in the frequency domain. The bandwidth of the CC may be limited to the bandwidth of the existing system for backward compatibility with the existing system. For example, the existing 3GPP LTE system supports {1.4, 3, 5, 10, 15, 20} MHz bandwidth, LTE_A can support a bandwidth greater than 20MHz using only the bandwidths supported by LTE. . The bandwidth of each CC can be determined independently. It is also possible to merge asymmetric carriers in which the number of UL CCs and the number of DL CCs differ. The DL CC / UL CC link may be fixed in the system or configured semi-statically. For example, as shown in FIG. 6 (a), when there are four DL CCs and two UL CCs, DL-UL linkages can be configured to correspond to DL CC: UL CC = 2: 1. Similarly, as shown in FIG. 6 (b), DL-UL linkage can be configured to correspond to DL CC: UL CC = 1: 2 when two DL CCs are four UL CCs. Unlike illustrated, symmetric carrier merging is possible, where the number of DL CCs and the number of UL CCs are the same. In this case, a DL-UL linkage configuration of DL CC: UL CC = 1: 1 is also possible.

In addition, even if the system overall bandwidth is composed of N CCs, the frequency band that a specific UE can monitor / receive may be limited to M (<N) CCs. Various parameters for carrier aggregation may be set in a cell-specific, UE group-specific or UE-specific manner. Meanwhile, the control information may be set to be transmitted and received only through a specific CC. A specific CC may be referred to as a primary CC (PCC) and the remaining CC may be referred to as a secondary CC (SCC).

LTE-A uses the concept of a cell to manage radio resources. A cell is defined as a combination of downlink resources and uplink resources, and uplink resources are not required. Accordingly, the cell may be configured with only downlink resources or with downlink resources and uplink resources. If carrier aggregation is supported, the linkage between the carrier frequency (or DL CC) of the downlink resource and the carrier frequency (or UL CC) of the uplink resource may be indicated by system information. A cell operating on the primary frequency (or PCC) may be referred to as a primary cell (PCell), and a cell operating on the secondary frequency (or SCC) may be referred to as a secondary cell (SCell). The PCell is used by the terminal to perform an initial connection establishment process or to perform a connection re-establishment process. PCell may refer to a cell indicated in the handover process. The SCell is configurable after a Radio Resource Control (RRC) connection is established and can be used to provide additional radio resources. PCell and SCell may be collectively referred to as a serving cell. Therefore, in the case of the UE that is in the RRC_CONNECTED state, but carrier aggregation is not configured or does not support carrier aggregation, there is only one serving cell configured only with the PCell. On the other hand, in the case of the UE in the RRC_CONNECTED state and the carrier aggregation is configured, one or more serving cells exist, and the entire serving cell includes the PCell and the entire SCell. For carrier aggregation, after the initial security activation process is initiated, the network may configure one or more SCells for the UE supporting carrier aggregation in addition to the PCell initially configured in the connection establishment process.

7 illustrates a heterogeneous network comprising a macro cell and a micro cell. In next-generation communication standards including 3GPP LTE-A, heterogeneous networks in which microcells with low power transmission power overlap within existing macro cell coverage are discussed.

Referring to FIG. 7, a macro cell may overlap one or more micro cells. The service of the macro cell is provided by the macro base station (Macro eNodeB, MeNB). In the present specification, the macro cell and the macro base station may be used interchangeably. The terminal connected to the macro cell may be referred to as a macro UE. The macro terminal receives a downlink signal from the macro base station and transmits an uplink signal to the macro base station.

Micro cells are also referred to as femto cells, pico cells. The service of the micro cell is provided by a pico base station (Pico eNodeB), a home base station (Home eNodeB, HeNB), a relay node (Relay Node, RN) and the like. For convenience, a pico base station (Pico eNodeB), a home base station (Home eNodeB, HeNB), and a relay node (Relay Node, RN) are collectively referred to as a home base station (HeNB). In the present specification, the micro cell and the home base station may be used interchangeably. The terminal connected to the micro cell may be referred to as a micro terminal or a home terminal. The home terminal receives a downlink signal from the home base station and transmits an uplink signal to the home base station.

Micro cells may be divided into OA (open access) cells and CSG (closed subscriber group) cells according to accessibility. The OA cell refers to a micro cell that can receive a service at any time when the terminal is required without additional access restriction. On the other hand, the CSG cell refers to a micro cell in which only a specific authorized terminal can receive a service.

In heterogeneous networks, inter-cell interference is more problematic because macro and micro cells overlap. As shown in FIG. 7, when the macro terminal is at the boundary between the macro cell and the micro cell, the downlink signal of the home base station acts as an interference to the macro terminal. Similarly, the downlink signal of the macro base station may act as interference to the home terminal in the micro cell. In addition, the uplink signal of the macro terminal may act as an interference to the home base station. Similarly, the uplink signal of the home terminal may act as an interference to the macro base station.

8 illustrates a situation in which inter-cell interference occurs in a heterogeneous network in more detail. Dotted lines indicate communication links and dotted lines indicate interference in the figures. Referring to FIG. 8, (a) the macro terminal not connected to the CSG cell may be interfered by the home base station, (b) the macro terminal may cause interference with the home base station, and (c) the CSG terminal May be interfered by other CSG home base stations. The illustrated interference situation is an example, and various interference situations may occur according to a network and a terminal configuration.

As described above, in the case of the macro-pico heterogeneous network, the macro cell may cause strong interference to the terminal of the pico cell, particularly the pico cell at the boundary of the pico cell. Accordingly, a method of resolving uplink and downlink interference on data and L1 / L2 control signals, synchronization signals, and reference signals is required. Inter-Cell Interference Cancellation (ICIC) schemes can be addressed in the time, frequency and / or spatial domains.

9 illustrates a method for canceling intercell interference in a heterogeneous network. For convenience, it is assumed that an object to be protected from intercell interference is a pico terminal. In this case, the network node causing interference becomes a macro cell (or macro base station).

Referring to FIG. 9, a macro cell causing intercell interference may configure an ABS (or ABSF) (Almost Blank Subframe) in a radio frame. ABS represents a subframe (Subframe, SubF) is set so that the normal DL signal is not transmitted except for a specific DL signal. Specific DL signals include, but are not limited to, for example, a cell-specific reference signal (CRS) or a cell-common reference signal (CRS). The ABS may be repeated to have a constant pattern within one or more radio frames. The figure illustrates a case where ABS is set in subframe # 2 / # 6. The macro cell informs the pico cell of the ABS configuration through the backhaul, and the pico cell may schedule the pico terminal using the ABS configuration. For example, the pico terminal may be scheduled only during the ABS period. In this case, channel state information (CSI) measurement of the pico terminal may be performed only in the ABS.

When the interfered UE is configured to perform measurement for Radio Link Management (RLM) / RRM (Radio Resource Management) only in a limited subframe (eg, ABS), it prevents unnecessary RLF (Radio Link Failure) and RSRQ The measurement results of (Reference Signal Received Quality) / RSRP (Reference Signal Received Power) can be accurate. 3GPP RAN (Radio Access Network) 2 requires defining new signaling indicating which subframe should be measured. For example, bitmap signaling having the same period as backhaul signaling (eg, 1 means “terminal can measure” in the corresponding subframe, and 0 means “terminal should not measure” in the corresponding subframe). Can be applied). The restriction pattern can be constructed independently from the backhaul bit-pattern.

10 illustrates a conventional feedback process for canceling inter-cell interference. This example illustrates a conventional feedback process for cell range expansion (CRE). CRE refers to a method in which the coverage of a specific cell is expanded by adding a bias to a signal measurement value of a specific cell when the terminal measures the signal of each cell. The coverage of a specific cell is virtually extended by the CRE, so that the base station of the specific cell may be preferred at the time of cell selection or handover. In FIG. 10, it is assumed that a terminal is in a state of being serviced by a macro cell (macro base station) and that pico cell # 1 (pico base station # 1) and pico cell # 2 (pico base station # 2) are overlaid in the macro cell.

Referring to FIG. 10, the terminal receives bias information from the macro base station (S1002). The bias information may be used in a CRE process (eg, feedback information generation, feedback triggering, etc.). The bias information indicates a bias value for the PCell of the macro base station and may be given independently for each pico base station. The bias information may be given by broadcast information and higher layer (RRC layer) signaling. The bias information may be given cell-specific, terminal-group specific, terminal-specific. Although not shown, the terminal may receive information about the pico base station from the macro base station. Information about the pico base station may include, but is not limited to, pico base station identification information, frequency configuration information of the pico base station. The bias information and the information about the pico base station may be signaled together or separately signaled.

Thereafter, the terminal measures downlink signals of the macro base station, the pico base station # 1, the pico base station # 2 (S1004). Downlink signal measurement is performed based on a reference signal (RS). The reference signal includes a cell-specific reference signal (CRS). The downlink signal measurement result can be obtained in various forms. For example, Signal to Noise Ratio (SNR), Signal to Interference and Noise Ratio (SINR), Carrier to Interference Ratio (CIR), Carrier to Interference and Noise Ratio (CINR), Reference Signal Received Power (RSRP), RSRQ (RSRQ) Reference Signal Received Quality) or a value related thereto.

Thereafter, the terminal compares the measured value of the pico base station signal with the measured value of the macro base station signal in consideration of the bias (S1006). Assuming that the signal measurement value is RSRP, the UE can compare [RSRP _{Pico # 1} + Bias # 1] and [RSRP _Macro ] and compare [RSRP _{Pico # 2} + Bias # 2] and [RSRP _Macro ]. have. RSRP _{Pico #} X represents the RSRP for the signal of Pico Base Station # X, and Bias # X represents the bias value given for Pico Base Station #X for the PCell of the macro base station. When the measurement / comparison of the pico base station signal is performed in units of cells (ie, component carriers), RSRP _{pico #} X may be replaced with RSRP _{pico #} X _{and cell # i} . Cell #i represents the cell (ie, component carrier) index of the pico base station. The RSRP macro represents the RSRP for the PCell of the macro base station. [RSRP _{Pico #} X + Bias # X] has an effect of relatively increasing the coverage of Pico Base Station #X compared to the PCell coverage of the Macro Base Station.

Thereafter, the terminal transmits the feedback information to the macro base station (S1008). The feedback information can be obtained when [RSRP _{Pico #} X + Bias # X]> (or ≥) [RSRP _Macro ] is satisfied or [RSRP _{Pico #} X + Bias #X]> (or ≥) [RSRP _Macro ] It can be sent if it is satisfied during the period. That is, the frequency / number of feedback transmissions for the pico base station can be adjusted by the bias value. The feedback information may include information indicating a pico base station that satisfies [RSRP _{pico #} X + bias # X]> (or ≥) [RSRP _macro ], or signal measurement information related to the pico base station. For example, if [RSRP _{Pico #} X + Bias # X]> (or ≥) [RSRP _Macro ] is satisfied, the feedback information is an identifier of Pico Base Station #X, [RSRP _{Pico #} X] and [RSRP _{Pico #} X]. It may include at least one of + bias # X]. The macro base station may share feedback information from the terminal with the pico base station using a backhaul link. Although step S1008 describes a case in which the feedback information includes only information about the pico base station, this is an example. In this example, the pico base station related information in the feedback information may be replaced with or included with the macro base station related information.

Thereafter, the terminal and the macro / pico base station may perform various operations in consideration of the feedback information (S1010). For example, the terminal and the macro / pico base station may perform handover, cell- (re) selection process, etc. using the feedback information. For example, the UE may perform a cell- (re) selection process by selecting a pico cell (pico base station) having the largest value of [RSRP _{pico #} X + bias # X]. When the feedback information includes [RSRP _{Pico #} X], the macro base station may convert [RSRP _{Pico #} X] to [RSRP _{Pico #} X + Bias # X] and then perform a handover process. When the feedback information includes [RSRP _{Pico #} X + Bias # X], the macro base station may perform a handover process using the feedback information as it is.

The above-described process mainly describes the case where the UE belongs to the macro cell (that is, the macro terminal), but this is an example for canceling the inter-cell interference in a similar manner even when the UE belongs to the pico cell (ie, the pico terminal). The feedback process can be performed. The bias value may be added to the measured value of the macro cell signal or the measured value of the pico cell signal according to the cell priority.

The above-described conventional CRE feedback process considers only the PCell of the macro base station. That is, the coverage increase effect of the pico base station is effective only for the PCell of the macro base station, and for this, a bias value for the CRE is also given only for the PCell. Only the PCell is considered in the CRE process because the RLF (Radio Link Failure) determination and the handover process are performed based on the PCell, so that the feedback process of the neighbor cell (base station) signal is performed based only on the PCell signal of the macro base station. For this reason, even if the macro base station supports multicarrier, feedback information for canceling inter-cell interference is not provided for the SCC (that is, the SCell), thereby reducing flexibility in resource usage. In addition, despite the different signal strength, load, etc. for each CC, the coverage of each CC is determined based on the PCC (ie, PCell), which is inflexible for supporting various communication scenarios. For example, in a multicarrier situation, a PCell / SCell reconfiguration within one base station may be restricted when two or more base stations divide a PCell and a SCell for one terminal.

11 illustrates a problem expected when applying a conventional feedback process for intercell interference in a multicarrier situation. For convenience, it is assumed that one pico cell is overlaid on the macro cell, and both the macro cell and the pico cell use the same frequency band (ie, f1 and f2). This example has been described in terms of pico terminals.

In FIG. 11, an ABS (almost blank subframe) is a sub-blank of an area of the remaining PDSCH except for important information (eg, PCFICH, PDCCH, PSCH, SSCH, PBCH, SIB1, Paging) during one subframe for interference control. Frame. In this example, it is assumed that ABS is configured in the radio frame of the macro cell, but this may be configured as an example in the radio frame of the pico cell. The ABS may have various patterns during one or multiple radio frames. The pico terminal located at the pico cell boundary may remove the influence of the interference from the macro base station by receiving the scheduling in the pico subframe corresponding to the ABS at f2. However, since control information such as CRS and PDCCH exist in the ABS, the pico terminal is interrupted due to the control information signal of the macro base station even when scheduled in the pico subframe corresponding to the ABS. For this reason, the pico terminal may not be able to smoothly perform PDCCH decoding of the pico cell downlink. To overcome this problem, cross scheduling may be used.

In detail, since component carriers of a macro cell may set different PDCCH lengths and PDSCH loads, as shown in FIG. 11, a short PDCCH is allocated to f2 (or the same number of OFDM symbols are actually transmitted. By allocating a small load or ABS by reducing the number of PDCCHs, it is possible to reduce the influence of interference on the pico cell PCell (f2) containing important information of the pico cell.

In this case, the pico terminal and / or pico base station may arbitrarily increase the coverage of the pico cell by adding a bias to a signal measurement value (eg, RSRP / RSRQ) for the pico PCell. Signal measurement for the pico PCell f2 may be performed in a pico subframe corresponding to the ABS. Data throughput of the macro cell, which is lost in ABS, can be obtained from the pico cell, and the throughput of the entire cell can be improved through the offload effect of the macro cell.

However, as described above, in the feedback based on the existing CRE, the pico terminal measures and reports RSRP / RSRQ based on only one component carrier (ie, PCell, f2). However, according to the conventional method, when there is a pico terminal having a PCellCellCell interference f1 severely, there is no contrast between the signal of f2 and the neighbor cell signal and accordingly feedback, the corresponding pico terminal f2 can have a good channel situation There is a constraint on PCell change to. That is, in order to handover to f2 the terminal holding f1 as a PCell, it is necessary to report RSRP / RSRQ in consideration of the signal / coverage of the neighbor cell for each component carrier.

Accordingly, the present invention proposes a method of independently using a bias value for each CC (ie, cell, serving cell) in downlink channel measurement (eg, RSRP / RSRQ measurement) in a heterogeneous network. According to the present invention, by independently assigning a bias value to each component carrier, it is possible to easily control PCell change or to increase resource flexibility by maintaining cell coverage differently for each component carrier.

12 illustrates a process of performing feedback according to an embodiment of the present invention.

Referring to FIG. 12, the terminal receives bias information from the macro base station (S1202). The bias information may be used in a CRE process (eg, feedback information generation, feedback triggering, etc.). The bias information indicates a bias value for the PCC (ie, PCell) and / or SCC (ie, SCell) of the macro base station, and may be given independently for each pico base station. Each CC-specific bias value may be explicitly given by broadcast information, higher layer (RRC layer) signaling, and L1 signaling (eg, PDCCH). The bias information may be given cell-specific, terminal-group specific, terminal-specific, preferably terminal-specific.

Alternatively, the bias value of the other CC may be calculated implicitly from the bias value of the reference CC. The reference CC may be a PCC (PCell) or a CC initially receiving an explicit bias value from the base station. As a method of calculating the implicit value implicitly, the following method may be considered.

1. The bias value and the constant offset value of the reference CC can be determined by +/-. The offset value may be signaled from the base station to the terminal through higher layer (eg, RRC) signaling. The bias value of the reference CC and the bias offset value for the corresponding CC may be signaled together or separately. Alternatively, the offset step size may be determined in advance, and only the increase or decrease may be signaled.

2. The bias value may be calculated according to the number of ABS set for N (N≥1) radio frames per CC (or during one cycle of an ABS configuration). For example, the bias value of each CC may be determined according to a ratio of the ABS number of the reference CC and the ABS number of the CC, or may be set according to an inverse relationship. As another example, the bias value may be calculated by considering only the number of ABS for a given period in each CC without considering the ratio of the number of ABS. For example, the mapping relationship between the ABS number and the bias value accordingly can be determined in advance, and the bias value can be automatically calculated according to the ABS number. The number of ABS and the bias value may be proportional.

3. If the number of OFDM symbols for the PDCCH transmission (or simply referred to as the number of PDCCH symbols) is configured in RRC, the bias value of each CC is the number of PDCCHM symbols of the reference CC and the number of PDCCH symbols of the CC. It can be determined according to the ratio. For example, a bias value may be set to be small for a CC having a large number of PDCCH symbols. As another example, the bias value may be calculated by considering only the number of PDCCH symbols for a given period in each CC without considering the ratio of the number of PDCCH symbols. For example, the mapping relationship between the number of PDCCH symbols and the corresponding bias value may be determined in advance, and the bias value may be automatically calculated according to the number of PDCCH symbols. The number of PDCCH symbols and the bias value may be inversely proportional.

4. If the UE knows the maximum TX (Transmit) power of each CC, the bias value of each CC may be determined according to the ratio of the maximum power of the reference CC and the maximum power of the CC. As another example, the bias value may be calculated by individually considering the maximum TX power of each CC without considering the ratio of the maximum TX power. For example, a mapping relationship between TX maximum power and a corresponding bias value may be determined in advance, and a bias value may be automatically calculated according to the TX maximum power. The TX maximum power and bias values can be inversely proportional.

5. The bias value of the target CC can be determined according to the number of adjacent pico cells or the interference level (eg, SIR, SINR, CINR, etc.). For example, a bias value may be set to be small when the number of adjacent pico cells has a large interference level, and a bias value may be set to be large when the number of adjacent pico cells is small.

In addition, although not shown, the terminal may receive information about the pico base station from the macro base station. Information about the pico base station may include, but is not limited to, pico base station identification information, frequency configuration information of the pico base station. The bias information and the information about the pico base station may be signaled together or separately signaled.

Thereafter, the UE measures downlink signals of the macro base station, pico base station # 1, and pico base station # 2 (S1204). Downlink signal measurement is performed based on the reference signal. The downlink signal measurement result can be obtained in various forms. For example, SNR, SINR, CIR, CINR, RSRP, RSRQ or a value related thereto may be indicated.

Thereafter, the terminal compares the measured value of the pico base station signal with the measured value of the macro base station signal in consideration of the bias (S1206). Assuming that the signal measurement value is RSRP, the terminal compares the [RSRP _{Pico # 1} + bias # 1 _cell # _k ] and [RSRP _{macro, cell # k} ], and [RSRP _{Pico # 2} + bias # 2 _{cell # k} ] and [RSRP _{macro, cell #k} ] can be compared. RSRP _{Pico #} X represents RSRP for the signal of Pico Base Station #X. The bias #X _{cell #k} represents a bias value given for pico base station #X for _{cell #k} of the macro base station. When the signal of the pico base station is performed in units of cells (ie, component carriers), RSRP _{pico #} X may be replaced with RSRP _{pico #} X _{and cell # i} . Cell #i represents the cell (ie, component carrier) index of the pico base station. RSRP _{macro, cell #k} represents the RSRP for the cell #i signal of the macro base station.

Thereafter, the terminal transmits the feedback information to the macro base station (S1208). Feedback information is available when [RSRP _{Pico #} X + Bias # X _{Cell # k} ]> (or ≥) [RSRP _{Macro, Cell # k} ] is satisfied or [RSRP _{Pico #} X + Bias # X _{Cell # k} ]> ( Or ≥) [RSRP _{macro, cell #k} ] may be transmitted if it is satisfied for a predetermined period. That is, the frequency / number of feedback transmissions for the pico base station can be adjusted by the bias value. The feedback information includes information indicating a pico base station satisfying [RSRP _{pico #} X + bias # X _{cell # k} ]> (or ≥) [RSRP _{macro, cell # k} ], or signal measurement information related to the pico base station. can do. For example, if [RSRP _{Pico #} X + Bias # X _{Cell # k} ]> (or ≥) [RSRP _{Macro, Cell # k} ] is satisfied, the feedback information may be an identifier of Pico Base Station #X, [RSRP _{Pico #} X]. And [RSRP _{Pico #} X + Bias # X _{Cell # k} ]. When the signal of the pico base station is performed in units of cells (ie, component carriers), the feedback process may also be performed in units of cells of the pico base station. The macro base station may share feedback information from the terminal with the pico base station using a backhaul link. Step S1208 describes a case in which the feedback information includes only information about the pico base station. However, this is an example. In this example, the pico base station related information in the feedback information may be replaced with or included with the macro base station related information.

Thereafter, the terminal and the macro / pico base station may perform various operations in consideration of the feedback information (S1210). For example, the terminal and the macro / pico base station may perform PCell / SCell reconfiguration, handover, cell- (re) selection process, etc. using the feedback information. Specifically, the terminal may select a pico cell (Pico base station) having the largest value of [RSRP _{pico #X} + bias #X _{cell #k} ] to perform a corresponding operation. When the feedback information includes [RSRP _{pico #} X], the macro base station may convert [RSRP _{pico #} X] to [RSRP _{pico #} X + bias # X _{cell # k} ] and then perform a corresponding operation. When the feedback information includes [RSRP _{Pico #} X + Bias # X _{Cell # k} ], the macro base station may perform the operation by using the feedback information as it is.

The above-described process mainly describes the case where the UE belongs to the macro cell (that is, the macro terminal). However, this is an example and the CRE may be performed in a similar manner even when the UE belongs to the pico cell (ie, the pico terminal). have. The bias value may be added to the measured value of the macro cell signal or the measured value of the pico cell signal according to the cell priority.

The feedback method according to the embodiment of the present invention has the following advantages.

1. The pico base station or the macro base station may use the RSRP / RSRQ value of each component carrier received from the terminal for switching between the PCell and the SCell of each terminal to maximize the cell throughput.

2. The macro / pico base station may assign different bias values to component carriers to allow the terminal to control unnecessary or unintended reporting.

3. In terms of cell range extension, the macro terminal can easily make a handover procedure to a pico cell by increasing only a cell boundary of a component carrier having low interference effects. Through this, first of all, the total cell throughput can be increased by increasing the number of terminals belonging to the PCell of the pico cell.

4. Due to RF frequency characteristics, it may have a different cell range for each component carrier caused by different propagation distances. If it is necessary to keep the cell coverage of each component carrier the same for the purpose different from the third, it is possible to maintain the same cell range by assigning different bias values to each component carrier. This problem may be exacerbated in a non-contiguous carrier aggregation situation.

Thus, according to an embodiment of the present invention, it is possible to use carrier resources more flexibly and efficiently in a multicarrier situation.

13 shows an application example according to an embodiment of the present invention. For convenience, it is assumed that the macro CC2 is configured as the PCell and the macro CC1 is configured as the SCell for the specific macro terminal. In this case, according to an embodiment of the present invention, the macro terminal may compare and report the RSRP of the pico cell and the RSRP of the macro SCell. Therefore, the macro terminal / macro base station can compare the RSRP of the macro CC1 and pico CC1 & 2. If a large bias value is given to the pico CC2, the macro terminal will perform a feedback report, and may configure the pico CC2 as a SCell to the macro terminal in cooperation with the base stations. That is, for one terminal, the load balance for the SCell can be achieved by configuring the PCell as the macro CC2 and the SCell as the pico CC2. This can improve overall cell throughput.

This example is described from the viewpoint of a macro terminal, but this is an example and in the following description, the macro terminal may be replaced with a pico terminal.

14 illustrates a base station and a terminal that can be applied to an embodiment of the present invention. The base station includes a macro base station and a pico base station.

Referring to FIG. 14, a wireless communication system includes a base station (BS) 110 and a terminal (UE) 120. Base station 110 includes a processor 112, a memory 114, and a radio frequency (RF) unit 116. The processor 112 may be configured to implement the procedures and / or methods proposed in the present invention. The memory 114 is connected to the processor 112 and stores various information related to the operation of the processor 112. The RF unit 116 is connected with the processor 112 and transmits and / or receives a radio signal. The terminal 120 includes a processor 122, a memory 124, and an RF unit 126. The processor 122 may be configured to implement the procedures and / or methods proposed in the present invention. The memory 124 is connected with the processor 122 and stores various information related to the operation of the processor 122. The RF unit 126 is connected with the processor 122 and transmits and / or receives a radio signal. The base station 110 and / or the terminal 120 may have a single antenna or multiple antennas.

The embodiments described above are the components and features of the present invention are combined in a predetermined form. Each component or feature is to be considered optional unless stated otherwise. Each component or feature may be embodied in a form that is not combined with other components or features. It is also possible to combine some of the components and / or features to form an embodiment of the invention. The order of the operations described in the embodiments of the present invention may be changed. Some components or features of one embodiment may be included in another embodiment or may be replaced with corresponding components or features of another embodiment. It is obvious that the claims may be combined to form embodiments by combining claims that do not have an explicit citation in the claims or as new claims by post-application correction.

In this document, embodiments of the present invention have been mainly described based on data transmission / reception relations between a terminal and a base station. Certain operations described in this document as being performed by a base station may in some cases be performed by an upper node thereof. That is, it is obvious that various operations performed for communication with the terminal in a network including a plurality of network nodes including a base station may be performed by the base station or other network nodes other than the base station. A base station may be replaced by terms such as a fixed station, a Node B, an eNode B (eNB), an access point, and the like. In addition, the terminal may be replaced with terms such as a user equipment (UE), a mobile station (MS), a mobile subscriber station (MSS), and the like.

Embodiments according to the present invention may be implemented by various means, for example, hardware, firmware, software, or a combination thereof. In the case of a hardware implementation, an embodiment of the present invention may include one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), FPGAs ( field programmable gate arrays), processors, controllers, microcontrollers, microprocessors, and the like.

In the case of implementation by firmware or software, an embodiment of the present invention may be implemented in the form of a module, procedure, function, etc. that performs the functions or operations described above. The software code may be stored in a memory unit and driven by a processor. The memory unit may be located inside or outside the processor, and may exchange data with the processor by various known means.

It will be apparent to those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit of the invention. Accordingly, the above detailed description should not be construed as limiting in all aspects and should be considered as illustrative. The scope of the invention should be determined by reasonable interpretation of the appended claims, and all changes within the equivalent scope of the invention are included in the scope of the invention.

The present invention can be used in a wireless communication device such as a terminal, a relay, a base station, and the like.

Claims (10)

1. In the wireless communication system comprising a macro base station and a pico base station, a communication device for feeding back downlink measurement information,

   Measuring a signal of the macro base station for each serving cell to generate a plurality of first signal measurement values;

   Measuring a signal of the pico base station to generate a second signal measurement value; And

   If the predetermined condition is satisfied, providing the second measurement value to the macro base station,

   The predetermined condition includes a sum of the second signal measurement value and a bias value being greater than at least one of the plurality of first signal measurement values,

   The bias value is given independently for each serving cell for a plurality of serving cells constituting a macro base station.
2. The method of claim 1,

   The serving cell bias value is calculated using the bias value and the offset value of the reference serving cell.
3. The method of claim 1,

   The bias value for each serving cell is calculated using a ratio of the number of ABS (Almost Blank Subframe) of the reference serving cell and the number of ABS of the serving cell during a predetermined time interval.
4. The method of claim 1,

   A bias value for each serving cell is calculated by using a ratio of the number of orthogonal frequency division symbols (OFDM) for transmitting a physical downlink control channel (PDCCH) of a reference serving cell and the number of OFDM symbols for PDCCH transmission of a corresponding serving cell.
5. The method of claim 1,

   The bias value for each serving cell is calculated using a ratio of the maximum transmit power of the reference serving cell and the maximum transmit power of the corresponding serving cell.
6. A communication apparatus configured to feedback downlink measurement information in a wireless communication system including a macro base station and a pico base station,

   A radio frequency (RF) unit; And

   Includes a processor,

   The processor measures a signal of the macro base station for each serving cell to generate a plurality of first signal measurement values, measures a signal of the pico base station to generate a second signal measurement value, and when a predetermined condition is satisfied, the processor Provide a second measurement value to the macro base station,

   The predetermined condition includes a sum of the second signal measurement value and a bias value being greater than at least one of the plurality of first signal measurement values,

   And the bias value is independently given to each serving cell for a plurality of serving cells constituting a macro base station.
7. The method of claim 6,

   The serving cell bias value is calculated using the bias value and the offset value of the reference serving cell.
8. The method of claim 6,

   The bias value for each serving cell is calculated using a ratio of the number of ABS (Almost Blank Subframe) of the reference serving cell and the number of ABS of the serving cell during a predetermined time interval.
9. The method of claim 6,

   The bias value for each serving cell is a communication device using a ratio of the number of orthogonal frequency division symbols (OFDM) for transmitting a physical downlink control channel (PDCCH) of a reference serving cell and the number of OFDM symbols for PDCCH transmission of a corresponding serving cell.
10. The method of claim 6,

    The serving cell bias value is calculated using a ratio of the maximum transmit power of the reference serving cell and the maximum transmit power of the serving cell.

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