US20160065335A1 - Apparatus and method for controlling inter-cell interference - Google Patents

Abstract

An apparatus and method for controlling inter-cell interference is disclosed. The user equipment for controlling inter-cell interference in a wireless communication system includes an interference level measuring module configured to measure interference levels of neighboring cells using at least one of information about the number of antennas among antennas deployed in the neighboring cells, information about indexes of the effective antennas, and information about reference signal of the neighboring cells, an interference restriction request determination module configured to compare the interference levels of the neighboring cells with a predetermined threshold and to determine whether or not UE requests an interference restriction to the neighboring cells, and a transmitter configured to transmit information about one or more neighboring cells, to which the interference restriction request will be transmitted, to a serving base station.

Description

TECHNICAL FIELD
• The present invention relates to a wireless communication system, and more particularly, to an apparatus and method for controlling inter-cell interference.
BACKGROUND ART
• A Distributed Antenna System (DAS) utilizes a plurality of distributed antennas connected to a single base station in a wired manner or through a dedicated line. The base station includes a plurality of antennas which is distributed and located in a cell for providing a service. The DAS is different from a Centralized Antenna System (CAS), in which a plurality of base station antennas is provided at the center of a cell, in that a plurality of antennas is distributed and located so as to be spaced apart from one another by a predetermined distance in a cell. The CAS is generally a cellular communication system such as a Wideband Code Division Multiple Access (WCDMA), High Speed Packet Access (HSPA), Long Term Evolution (LTE)/Long Term Evolution-Advanced (LTE-A) or 802.16 system, and utilizes various multiple antenna schemes, in which multiple antennas are mounted in a single base station in a cell-based structure, such as an Open Loop-Multi Input Multi Output (MIMO) scheme, a Closed Loop-MIMO scheme or a Multi-BS MIMO scheme.
• The DAS is different from a femto cell in that each distributed antenna unit does not directly manage an antenna region thereof, but the base station located at the center of the cell manages all distributed antenna regions located in the cell. In addition, the DAS is different from a multi-hop type relay system or an ad-hoc network, in which a base station and a Relay Node (RN) are wirelessly connected, in that the distributed antenna units are connected in the wired manner or through the dedicated line. In addition, the DAS is different from a repeater structure amplifying a signal and transmitting the amplified signal in that each distributed antenna can transmit different signals to User Equipments (UE) adjacent to the antenna according to a command of the base station.
• Such a DAS may be considered a MIMO system because the distributed antennas simultaneously transmit and receive different data streams so as to support a single UE or multiple UEs. From the viewpoint of the MIMO system, in the DAS, since the antennas are distributed at various positions in the cell, a transmission region of each antenna is reduced compared with the CAS, thereby reducing transmit power. In addition, the transmission distance between the antenna and the UE is reduced so as to reduce path loss and to increase data transfer rate. Therefore, it is possible to increase transmission capacity and power efficiency of a cellular system and to satisfy communication performance with relatively uniform quality regardless of the position of a user in the cell, as compared with the CAS. In addition, since the base station and the plurality of distributed antennas are connected in the wired manner or through the dedicated line, signal loss is low, con-elation and interference between antennas are reduced, and a Sipal-to-Interference plus Noise Ratio (SINR) is high.
• The DAS may be utilized in parallel with the existing: CAS or may replace the CAS so as to establish a new cellular communication standard, in order to reduce costs necessary for installing more base stations in a next-generation mobile communication system and costs necessary for maintaining a backhaul network, to enlarge service coverage and to improve SINR.
• However, until now, no research has been conducted into an apparatus and method for controlling inter-cell interference in a multi-cell environment, to which the DAS is applied.
DISCLOSURE OF INVENTIONTechnical Problem
• An object of the present invention devised to solve the problem lies on an user equipment for controlling inter-cell interference.
• Another object of the present invention devised to solve the problem lies on a base station for controlling inter-cell interference.
• Another object of the present invention devised to solve the problem lies on a method for controlling inter-cell interference by an user equipment.
• Another object of the present invention devised to solve the problem lies on a method for controlling inter-cell interference by a base station.
Solution to Problem
• The object of the present invention can be achieved by providing a user equipment for controlling inter-cell interference in a wireless communication system in which plurality of antennas is deployed in each cell, the user equipment including an interference level measuring module configured to measure interference levels of neighboring cells using at least one of information about the number of antennas information about indexes of the antennas, and information about reference signal of the neighboring cells, an interference restriction request determination module configured to compare the interference levels of the neighboring cells with a predetermined threshold and to determine whether or not the UE requests an interference restriction to the neighboring cells, and a transmitter configured to transmit information about one or more neighboring cells, to which the interference restriction request will be transmitted, to a serving base station.
• The user equipment may further include a receiver configured to receive the information about the number of antennas, the information about the indexes of the antennas, and the information about the reference signal of the neighboring cells from the serving base station. The at least one of information is about effective antennas, which cause interference to the user equipment, among antennas deployed in the neighboring cells.
• The user equipment may further include an effective antenna determination module configured to determine at least one of the number of effective antennas, which cause interference to the user equipment, among the antennas deployed in die neighboring cells and the indexes of the effective antennas.
• In another aspect of the present invention, provided herein is a base station for controlling inter-cell interference in a wireless communication system in which *plurality of antennas is deployed in each cell, the base station including: a receiver configured to receive a message for requesting interference restriction from one or more user equipments or respective serving base stations of one or more user equipments; and a processor configured to turn off previously defined effective antennas which cause interference to the one or more user equipments or specific beam pattern groups which cause interference to the one or more user equipments among beam antenna groups of the effective antennas or restrict the use thereof in a specific time and/or frequency domain.
• In another aspect of the present invention, provided herein is a method for controlling inter-cell interference by a user equipment in a wireless communication system in which a plurality of antennas is deployed in each cell, the method including; measuring interference levels of neighboring cells using at least one of information about the number of antennas, information about indexes of the antennas, and information about reference signal of the neighboring cells; comparing the interference levels of the neighboring cells with a predetermined threshold and determining whether or not the UE requests an interference restriction to the neighboring cells; and transmitting information about one or more neighboring cells, to which the interference restriction request will be transmitted, to a serving base station.
• The method may further include receiving the information about the number of antennas, the information about the indexes of the antennas, and the information about the reference signal al the neighboring cells from the serving base station. The at least one of information is about effective antennas, which cause interference to the user equipment, among antennas deployed in the neighboring cells.
• The method may further include determining at least one of the number of effective antennas, which cause interference to the user equipment, amona the antennas deployed in the neighboring cells and the indexes of the effective antennas.
• In another aspect of the present invention, provided herein is a method for controlling inter-cell interference by a base station in a wireless communication system in which a plurality of antennas is deployed in each cell, the method including: receiving a message for requesting interference restriction from one or more user equipments or respective serving base stations of one or more user equipments; and turning off previously defined effective antennas which cause interference to the one or more user equipments or specific beam pattern groups which cause interference to the one or more user equipments among beam antenna groups of the effective antennas or re restricting the use thereof in a specific time and/or frequency domain.
Advantageous Effects of Invention
• In the apparatus and method for controlling inter-cell interference of the present invention, it is possible to remarkably improve communication and throughput by reducing interference experienced by an user equipment located at a cell edge.
• In particular, according to the present invention, it is possible to remarkably improve communication performance in a system in which antennas are distributed, in each cell.
BRIEF DESCRIPTION OF DRAWINGS
• The accompanying drawings, which are included to provide a further understanding of the invention, illustrate embodiments of the invention and together with the description serve to explain the principle of the invention.
• In the drawings;
• FIG. 1 is a block diagram showing the configurations of a base station (eNB)105 and a User Equipment (UE)110 in a wireless communication system according to the present invention;
• FIG. 2 is a diagram explaining physical channels used in a 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) system which is an example of a mobile communication system, and a general signal transmission method using the physical channels;
• FIG. 3 is a diagram explaining a procedure of processing, a baseband signal representing a downlink physical channel by the eNB105, for downlink signal transmission;
• FIG. 4 is a diagram explaining the concept of a Distributed Antenna. System (DAS);
• FIG. 5 is a schematic block diagram showing the configuration of a UE500 for controlling inter-cell interference in a DAS of a multi-cell based environment;
• FIG. 6 is a block diagram showing the configuration of aprocessor540 of the UE500;
• FIG. 7 is a diagram explaining a method for controlling inter-cell interference in a multi-cell based DAS;
• FIG. 8 is a block diagram showing the configuration of an eNB according to the present invention;
• FIG. 9 is a block diagram showing the configuration of an eNB900 of a neighboring cell according to the present invention:
• FIGS. 10 and 11 are diagrams showing examples of a process of exciting information between eNBs;
• FIG. 12 is a diagram showing an example of a process of performing scheduling with respect to an interference restriction request and sharing scheduling information between eNBs, by an eNB2 which is a neighboring eNB.
• FIG. 13 is a diagram showing another example of a process of performing scheduling with respect to an interference restriction request and sharing scheduling information between eNBs, by an eNB2 which is a neighboring enB: and
• FIG. 14 is a diagram showing another example of a process of performing scheduling with respect to an interference restriction request and sharing scheduling information between eNBs, by an eNB2 which is a neighboring eNB.
BEST MODE FOR CARRYING OUT THE INVENTION
• Hereinafter, the preferred embodiments of the present invention will be described with reference to the accompanying drawings. It is to be understood that the detailed description which will be disclosed with reference to the accompanying drawings is intended to describe the exemplary embodiments of the present invention, and is not intended to describe a unique embodiment through which the present invention can be carried out. Hereinafter, the detailed description includes detailed matters to provide full understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention can be carried out without the detailed matters. For example, the following description will be made on the assumption that a mobile communication system is a 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTF) system, but the present invention is applicable to other mobile communication systems excluding the unique matters of the 3GPP LTE system.
• In some instances, well-known structures and devices are omitted in order to avoid obscuring the concepts of the present invention and the important functions of the structures and devices are shown in block diagram form. The same reference numbers will be used throughout the drawings to refer to the same or like parts. The “exemplary” embodiment of the specification does not mean that this embodiment is in any way preferable to other embodiments.
• In the following description, it is assumed that a terminal includes a mobile or fixed user end device such as a user equipment (UE), a mobile station (MS) and an
• Advanced Mobile Station (AMS), and a base station (BS includes a node of a network end communicating with a terminal, such as a Node-B, eNobe B, eNB, and an Access Point (AP).
• In a mobile communication system, a UE may receive information from an eNB in a downlink and transmit information in an uplink. The information transmitted or received by the UE includes data and a variety of control information, and a variety of physical channels is present according to the type and usage of information transmitted or received by the UE. In the present invention, the term “base station (BS)” may also be referred to as a cell or a sector in the regional sense.
• FIG. 1 is a block diagram showing the configurations of aeNB105 and a user Equipment (UE)1101n a wireless communication system according to the present invention.
• Although one eNB105 and oneUE110 are shown in order to simplify the configuration of thewireless communication system100, one or more base stations and/or one or more UEs may be included,
• Referring toFIG. 1, theeNB105 may include a transmission (Tx)data processor115, asymbol modulator120, atransmitter125, a transmission/reception antenna130, a processor ISO, amemory185, areceiver190, asymbol demodulator195, and a reception (Rx)data processor197. TheUE110 may include aTx data processor165, asymbol modulator170, atransmitter175, a transmission/reception antenna135, aprocessor155, amemory160, areceiver140, asymbol demodulator155, and anRx data processor150. Although oneantenna130 and oneantenna135 are respectively included in theeNB105 and theUE110, each of theeNB105 and theUE110 includes a plurality of antennas. Accordingly, theeNB105 and theUE110 according to the present invention support a Multiple Input Multiple Output (MIMO) system. TheeNB105 and theUE110 according to the present invention support both a Single User-MIMO (SU-MIMO) scheme and a Multi User-MIMO (MU--MIMO) scheme.
• In downlink, theTx data processor115 receives traffic data, formats and codes the received traffic data, interleaves and modulates the coded traffic data (or performs symbol mapping), and provides modulated symbols (“data symbols”). Thesymbol modulator120 receives and processes the data symbols and pilot symbols and provides a symbol stream.
• The symbol modulator multiplexes data and pilot signals and transmits the multiplexed data to thetransmitter125. At this time, the transmitted symbols may be data symbols, pilot symbols or zero signal values, in each symbol period, the pilot symbols may be consecutively transmitted. The pilot symbols may be Frequency Division Multiplexed (FDM), Orthogonal Frequency Division Multiplexed (OFDM). Time Division Multiplexed (TDM) or Code Division Multiplexed (CDM) symbols.
• Thetransmitter125 receives and converts the symbol stream into one or more analog signals, additionally adjusts (e.g., amplifies, filters, and frequency-up-converts) the analog signals, and generates a downlink signal suitable for transmission through a radio channel. Subsequently, the downlink signal is transmitted to the UE through theantenna130.
• In theUE110, theantenna135 receives the downlink signal from the eNB and provides the received signal to thereceiver140. Thereceiver140 adjusts (e.g., filters, amplifies, frequency-down-converts) the received signal and digitizes the adjusted signal so as to acquire samples. Thesymbol demodulator145 demodulates the received pilot symbols and provides the demodulated pilot symbols to theprocessor155, for channel estimation.
• Thesymbol demodulator145 receives downlink frequency response estimation values from theprocessor155, performs data demodulation with respect to the received data symbols, acquires data symbol estimation values (which are estimation values of the transmitted data symbols), and provides the data symbol estimation values to theRx data processor150. TheRx data processor150 demodulates (that is, symbol-demaps and deinterleaves) the data symbol estimation values, decodes the demodulated values, and restores transmitted traffic data.
• The processes performed by thesymbol demodulator145 and theRx data processor150 are complementary to the processes performed by thesymbol modulator120 and theTx data processor115 of theeNB105.
• In theUE110, in uplink, theTx data processor165 processes the traffic data and provides data symbols. Thesymbol modulator170 receives the data symbols, multiplexes the data symbols and pilot symbols, performs modulation with respect to the symbols and provides a symbol stream to thetransmitter175. Thetransmitter175 receives and processes the symbol stream, generates an uplink signal., and transmits the uplink signal to theeNB105 through theantenna135.
• TheeNB105 receives the uplink signal from theUE110 through theantenna130 andreceiver190 processes the received uplink signal and acquires samples. Subsequently, thesymbol demodulator195 processes the samples and provides pilot symbols received in the uplink and data symbol estimation values. TheRx data processor197 processes the data symbol estimation values and restores traffic data transmitted from theUE110.
• The respective processors of theUE110 and theeNB105 instruct (e.g., control, adjust, manages, etc.) the respective operations of theUE110 and theeNB105. Theprocessors155 and180 may be connected to thememories160 and185 for storing program codes and data. Thememories160 and1.85 may be respectively connected to theprocessors155 and180 so as to store operating systems, applications and general files.
• Each c)f theprocessors155 and180 may also be referred to as a controller, a microcontroller a microprocessor, a microcomputer, etc.
• Theprocessors155 and180 may be implemented by hardware, firmware, software, or a combination thereof. If a method for controlling inter-cell interference according to the embodiments of the present invention is implemented by hardware, Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs). Programmable Logk: Devices (PLDs), Field Programmable Gate Arrays (FPGAs), etc. may be included in theprocessors155 and180.
• If the method of controlling inter-cell interference according to the embodiments of the present invention is implemented by firmware o software, the firmware or software may be configured to include modules, procedures, functions, etc. for performing the functions or operations of the present invention. The firmware or software configured to perform the present invention may be included in theprocessors155 and180 or may be stored in thememories160 and185 so as to be driven by theprocessors155 and180.
• Layers of the radio interface piotocal between theUE110 and theeNB105 in the wireless communication system ;network) may be classified into a first layer (L1), second layer (L2) and a third layer (L3) based on the three low-level layers of the known Open System Interconnection (OSI) model of a communication system. A physical layer belongs to the first layer and provides an information transport service through a physical channel. A Radio Resource Control (RRC) layer belongs to the third layer and provides control radio resources between the1.lE and the network. TheUE110 and theeNB105 exchange RRC messages with each other through a wireless communication network and the RRC layer.
• In a 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) system, a signal processing procedure for transmittina an uplink signal and a downlink signal will now be described.
• FIG. 2 is a diagram explaining a procedure of processing baseband signal representing an uplink physical channel, for uplink signal transmission.
• In theUE110, ascrambling module210 may scramble a transmitted signal using a specific scrambling signal of theUE110, for uplink signal transmission. The scrambled signal may be supplied to amodulation mapper220 so as to be modulated into complex symbols using Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK) or 16 Quadrature Amplitude Modulation (QAM) according to the type of the transmitted signal and/or a channel state. Thereafter, the modulated complex symbols are processed by atransform precoder230 and the processed symbols are supplied to afesoutee element mapper240. Theresource element mapper240 may map the complex symbols to time-frequency resource elements to be used for actual transmission. The processed signal may be converted into a Radio Frequency (RF) signal through an SC-FDMA signal generator250 so as to be transmitted to the eNB through theantenna135.
• FIG. 3 is a diagram explaining a procedure of processing a baseband signal representing a downlink physical channel by theeNB105, for downlink signal transmission.
• In the 3GPP LTE system, theeNB105 may transmit one or more codewords in a downlink. Accordingly, one or more codewords may be processed through a scrambling module310 and a modulation mapper320 so as to obtain complex symbols, similar to the uplink ofFIG. 2. Thereafter, the complex symbols are mapped to a plurality of layers by a layer mapper330, and each layer is multiplied by a predetermined precoding matrix selected according to the channel state by a precoding module340 so as to be supplied to a resource element mapper350. The resource element mapper350 maps the precoded signals to resource elements and supplies the mapped signals to an OFDM signal generator360. The OFDIM signal generator360 processes the signals received from the resource element mapper350 and generates OFDM signals. The OFDIVI signals may be converted into RF signals so as to be transmitted to theUE110 through eachantenna130.
• In the standard of a mobile communication system, in order to secure high data capacity required in current and future communication protocols, it is necessary to support MIMO transmission even in a Distributed Antenna System (DAS). That is, it is necessary to perform transmission ofrank 2 or more for each UE in the same frequency domain and to support MU-MIMO transmission simultaneously supporting several Us, in a downlink or uplink. Such SU-MIMO communication and MU-MIMO communication are necessarily considered in the IEEE 802 and 3GPP LTE which are the standardization organizations and are actually treated in standards such as IEEE 802.16 and 3GPP LTE Releases 8 and 9. However, since current communication protocols are only designed in consideration of a Centralized Antenna System (CAS) applying evolved technology such as the MIMO technology to the DAS is difficult. Accordingly, there is a need for a communication protocol supporting the DAS, for development of the communication system.
• FIG. 4 is a diagram explaining the concept of the DAS.
• Referring toFIG. 4, the DAS may be variously implemented according to the number and positions of antennas in each cell, in each cell of the DAS, the antennas may be distributed so as to be separated from one another by a predetermined distance or a group of several antennas may be present at each position. In the DAS, if the coverage of the antennas overlap each other, transmission ofrank 2 or more is possible, regardless of the distribution form of the antennas. This is a difference between the currently implemented DAS and a DAS to be implemented in the future. In a DAS including a total of eight antennas, three UEs are pre-sent and the coverage of each antenna includes parts of neighboring antennas. In this case, theUE1 may receive signals ofantennas1,2,5 and6, but the signals ofantennas3,4,7 and8 are small enough to be ignored due to path loss. Similarly, theUE2 may ignore all signals except the signals of the antennas6 and7 and theUE3 may dominantly receive only the signal of theantenna3.
• As shown inFIG. 4, in the DAS, no problem occurs when performing Multi User-MIMO (MU-MIMO) communication with UEs near the cell edge. For example, in the DAS, theantennas1,2,5 and6 may communicate with theUE1, theantenna3 may communicate with the UE3, and the antenna7 may communicate with theUE2. The DAS may be managed such thatantennas4 and8 are used for transmission toUE2 orUE3 or are turned off.
• In the DAS, during Single User-MIMO (SU-MIMO) and MU-MIMO communication the number of data streams (layers) of each UE may vary, and an antenna or an antenna group may be allocated to each UE. That is, the DAS may support a specific antenna or antenna group with respect to each UE, and the number of antennas (antenna groups) may frequently change.
• Transmission using the cooperative MIMO scheme in the existing CAS is proposed in order to reduce inter-cell interference in a multi-cell environment. If the cooperative MIMO system is used, the UE commonly may receive data from multiple eNBs, addition, each eNB may simultaneously support one or more UEs using the same frequency resources hi order to improve system performance. In addition, the eNB may perform a Space Division Multiple Access (SDMA) method based on information on the channel state between the eNB and the UE.
• In the cooperative MIMO system, a serving eNB and one or more cooperative eNBs are connected to a scheduler through a backbone network. The schedulex may operate by receiving the information on the channel state between each UE and each co-operative eNB which is measured by each base station through the backbone network. For example, the scheduler schedules information for the cooperative MIMO operation with respect to the serving eNB and one or more cooperative eNBs. That is, the scheduler directly indicates the cooperative MIMO operation to each eNB.
• The DAS refers to a system in which a single eNB manages antennas distributed at various position in a cell, unlike a CAS in which antennas of an eNB are centralized on the center of a cell. That is, the DAS is a system in which the antennas of the eNB are distributed in the cell, in such a DAS, UEs may select different effective antennas in the cell and receive data from the eN through the selected effective antennas, in each DAS, since beams are formed by different effective antennas in each cell, the beams formed by the different effective antennas are influenced by interference of a neighboring cell, unlike the CAS.
• The existing CAS can improve communication performance of UE located at a cell edge using a Coordinate Multi Point (CoMP) scheme in a multi-cell environment. In such a CoMP scheme, there are a cooperative MIMO-based Joint Processing (IP) scheme through data sharing and a Coordinate Scheduling/Coordinated Beamforming (CS/CB) scheme for reducing inter-cell interference, such as a worst companion scheme or a best companion scheme.
• The worst companion scheme is an interference elimination scheme enabling a UE to report a PMI having highest interference to one or more neighboring cells for performing the CoMP operation so as to enable the cells to utilize PMls other than the high interference PMI. The best companion scheme is a scheme for enabling a UE to report a PMI with lowest interference to one or more neighboring cells so as to enable the cells to utilize the PMI such that inter-cell interference is reduced. The UE which performs the CoMP operation can improve the communication performance of the UE located at the cell edge by using another adequate. CoMP scheme according to situations (e.g., an intra eNB and an inter eNB). However, the PMI report for the best/worst worst companion increases uplink feedback overhead. If the number of neighboring cells that cause interference is increased or a plurality of PMIs is transmitted for more accurate scheduling. In addition, excessive backhaul delay and overhead may be caused due to the increase in the exchange amount of a restricted/recommended PMI and associated information with the eNB.
• Such problems may occur in the CoMP scheme of the DAS as well as the CAS. Accordingly, an interference restriction (e.g., silencing) method for reducing feedback overhead of a UE is proposed. A beam coordination scheme refers to a scheme for enabling a UE report a restricted or recommended PMI to a serving eNB and transmitting a desirable signal with low interference from the neighboring cells to the UE. In contrast, the silencing scheme, which is an interference restriction scheme, enables a UP., which experiences interference, to restrict power to a predetermined value or less with respect to effective antennas of neighboring cells or beam patterns (e.g. PMIs) used by the neighboring cells or to request the use restriction of the effective antennas so as not to transmit any signal (data and reference signal). The feedback information of the UE may not include information such as PMI, but may include information having a size of 1 bit, which is capable of turning on/off silencing.
• In the present invention, the concept of the “effective antenna” for a specific UE needs to be defined. The effective antenna of the serving eNB for the specific UE refers to an antenna for dominantly transmitting a signal to the specific UE, and an effective antenna of a neighboring eNB for a cell) refers to an antenna which has influence on the specific UE. In the present specification, a cell to which the DAS applied may be referred to as a “DAS cell”.
• In order to apply the best/worst companion scheme or silencing scheme based on the PMI or on/off information to the DAS, the UE may require information on neighboring cells. However, in case of cell-specific silencing:, the information on the neighboring cells may not be required and this will be described later.
• In the existing CAS, since the neighboring cells operate using a fixed antenna configuration, the UE in the serving cell feeds back a PMI based on the fixed antenna configuration using the best/worst companion scheme. In the existing CAS, one or more neighboring cells in a set which performs the CoMP operation include the same number of antennas and a UE knows the antenna configuration information or the serving cell informs the UE of antenna configuration information of one or more neighboring cells in the COMP set such that the UE can know the antenna configuration information. Unlike the CAS, in the DAS, since the antenna configuration of each cell varies and thus an effective antenna configuration varies, a problem occurs when the UE measures and feeds back interference of neighboring cells. That is, the UE may require information on the number of effective antennas of the neighboring cells, the indexes of the effective antennas, and the pilot patterns of the neighboring cells. The UE may transmit indication information ;e.g.,1-bit on/off information) for the PMI or silencing of the neighboring cells which have influence on the UE to the serving eNB (cell) or the neighboring eNB (cell) based on such information.
• In the DAS of a single-cell environment, in order to determine effective antennas for theUE110, the following methods may be used. Thereceiver190 of theeNB105 receives uplink data, a pilot signal, a sounding channel, a feedback channel, an Acknowledgement/Negative Acknowledgement (ACK/NACK), etc. from theUE105 through theantenna130. Then, theprocessor180 may measure an uplink signal and determine the number and/or the indexes of effective downlink transmission antennas for the UE in the downlink. In contrast, thereceiver140 of theUE110 may receive a downlink signal through theantenna135, and theprocessor155 may measure the channel state of the received downlink signal and determine the number and/or the indexes of effective downlink transmission antennas. Thetransmitter175 may transmit information on the number and/or the indexes of effective antennas to theeNB105 through theantenna135. TheeNB105 may appropriately change the fed-back number and/or the indexes of effective downlink transmission antennas according to network load and the like.
• Hereinafter, a method of enabling a UE to control inter-cell interference in a multicell DAS will be described.
• FIG. 5 is a schematic block diagram showing the configuration of aUE500 for controlling inter-cell interference in a DAS of a multi-cell based environment, andFIG. 6 is a block diagram showing the detailed configuration of aprocessor540 of theUE500.
• Referring to FIG,5, theUE500 may include a receiver510, asymbol demodulator520, anRx data processor530, aprocessor540, amemory550, aTx data processor560, asymbol modulator570, atransmitter580 and anantenna590.
• The receiver510 may receive information on the number of antennas for one or more neighboring cells, information on the indexes of the antennas, and information on a reference signal of each neighboring cell from a serving eNB through theantenna590, in this case, the received information on the antennas may he effective antennas.
• Thesymbol demodulator520 performs data demodulation with respect to data symbols corresponding to the information received by the receiver510, and acquires and supplies data symbol estimation values to theRx data processor530.
• Referring toFIG. 6, theprocessor540 may include an interferencelevel measuring module541, an interference restriction request determination module542, and an effectiveantenna determination module543.
• The interferencelevel measuring module541 may measure the interference level of each neighboring cell using at least one of the information on the number of effective antennas which cause interference to theUE500, among antennas distributed in each neighboring cell, the information on the indexes of the effective antennas, and the information on the reference signal of each neighboring cell. The interferencelevel measuring module541 may use the information on the effective antennas of each neighboring cell, the information on the indexes of the effective antennas, and the information on the reference signal of each neighboring cell, all of which are received by the receiver510, or may directly measure the interference level so as to obtain the information on the effective antennas of each neighboring cell, the information on the indexes of the effective antennas, and the information on the reference signal of each neighboring cell. The interferencelevel measuring module541 requires the antenna configuration information of the neighboring cells in order to more accurately measure the interference levels of one or more neighboring cells in the multi-cell DAS. The antenna configuration information may include at least one of the information on the number of effective antennas, the information on the indexes of the effective antennas, and the information on the reference signal of each neighboring cell. Hereinafter, the antenna configuration information will he described in brief.
• 1. Number of Effective Antennas in each Neighboring Cell
• In the DAS, the UP,500 which performs the CoMP operation requires information on the number of effective antennas of each neighboring cell, which cause interference to theUE500. That is, the interferencelevel measuring module541 of theUE500 may measure interference of neighboring cells based on at least one of the received information on the effective antennas of each neighboring cell, the received information on the indexes of the effective antennas, and the received information on the reference signal of each reference signal, or the interferencelevel measuring module541 may measure interference of neighboring cells based on reference signals of the neighboring cells.
• The interference restriction request determination module542 compares the interference level of each neighboring cell with a predetermined threshold, and determines whether or not theUE500 requests an interference restriction to each neighboring cell. Thetransmitter580 may transmit an interference restriction request indication (or silencing indication) information to the serving eNB through theantenna590.
• FIG. 7 is a diagram explaining a method for controlling inter-cell interference in a multi-cell based DAS.
• As shown inFIG. 7, it is assumed that three DAS cells each having four distributed antennas are present. The receiver510 of theUE500 belonging to the cell A (serving cell) may receive a desirable signal from anantenna group710 including distributedantennas1 and4 (Tx1 and. Tx4) of the cell A through theantenna590. In this case, if theprocessor540 of theUE500 selects a best PMI from two transmission antennas based codebooks, thetransmitter580 transmits the best PMI to the serving cell.
• In addition theUE500 may receive strong interference from the effective antenna group720 (antennas2 and4) including two distributed antennas of the cell B. In addition, theUE500 receives strong interference from the effective antenna group (antennas1,3, and4) including three distributed antennas of the cell C.
• In order to enable the interferencelevel measuring module541 to accurately measure the interference levels of the neighboring cells (that is, the cell B and the cell C) and to enable theUE500 to report more accurate interference restriction indication (that is, silencing indication) information, theUE500 needs to receive the number of effective antennas, which cause interference to the UE, from each cell. That is the interferencelevel measuring module541 of theUE500 may measure an interference degree (or an interference level) using the signal received from theeffective antenna group720 including two distributed antennas of the cell B. Similarly, the interferencelevel measuring module541 may measure an interference degree using the signal received from theeffective antenna group730 including three distributed antennas of the cell C. Accordingly, if the UE SIX) knows the information on the number of effective antennas of each of the cell B and the cell C, it is possible to more accurately and efficiently measure the interference levels of the neighboring cells. Therefore, it is possible to perform the COMP operation with respect to theUE500 located at the cell edge and to reduce and control interference from one or more neighboring cells to which the DAS is applied.
• (2) Indexes of Effective Antennas
• In order to enable the interferencelevel measuring module541 of theUE500 to efficiently measure the interference levels of the neighboring cells (e.g., the cell B and the cell C), the information on the indexes of the effective antennas are required in addition to the information on the number of effective antennas of the neighboring cells. The antenna ports (distributed antennas) of each cell may transmit respective reference signals in different time and frequency domains (including TDM scheme, an FDM scheme, and a CDM scheme). Accordingly, it is difficult for the interferencelevel measuring module541 to accurately measure interference only using information indicating how many distributed antennas configure the effective antenna group, which is received from the neighboring cells. Accordingly, in addition to the number of effective antennas, theUE500 may receive information on the substantial indexes of the antennas such that the interferencelevel measuring module541 may accurately measure the interference level corresponding to the number of distributed antennas.
• For example, as shown inFIG. 7, it is assumed that three DAS cells each having four distributed antennas are present. TheUE500 receives strong interference from theeffective antenna group720 includingantennas2 and4 among the four distributed antennas of the neighboring cell B and receives strong interference from theeffective antenna group730 includingantennas1,3 and4 among the four distributed antennas of the cell C. The interferencelevel measuring module541 may more accurately measure neighboring cell interference, if the information on the indexes of theeffective antenna groups720 and730 of the neighboring cells are known.
• (3) Information on Reference Signal of Neighboring Cells, for Interference Measurement
• If the interferencelevel measuring module541 measures the interference levels of the neighboring cells using the information on the reference signal of the neighboring cells, it is possible to more accurately measure the interference levels. TheUE500 may implicitly know the reference signal of the neighboring cells defined in advance according to a cell identifier or the eNB may directly and explicitly inform theUE500 of the reference signal of the neighboring cells. The interferencelevel measuring module541 of theUE500 may accurately measure the intensity of the interference by measuring the time and frequency domains, in which the reference signals of the neighboring cells are transmitted, based on at least one of the information on the her of effective antennas, information on the indexes of the effective antennas, and information on the reference signal of the neighboring cells, and theUE500 can accurately obtain information on a PMI which causes interference. Through such a process, theUE500 can efficiently perform the CS/CB scheme or the SP scheme between the cells in the multi-cell environment to which the DAS is applied.
• The interference restriction request determination module542 may compare the interference levels of the neighboring cells measured by the interferencelevel measuring module541 with the predetermined threshold and determine whether or not the interference restriction request is transmitted to the neighboring cells. The interference restriction request determination module542 may determine whether or not the information on the interference restriction (that is, silencing) request is transmitted to the serving eNB, based on the predetermined threshold (e.g., channel quality and interference level). The interference restriction request determination module542 may transmit the interference restriction (that is, silencing) request to the serving eNB if the measured interference values of the neighboring cells exceed the predetermined threshold.
• Thetransmitter580 may transmit the information on one or more neighboring cells, to which the interference restriction request will be transmitted, to the serving eNB. Therefore. It is possible to reduce or eliminate inter-cell inteference while minimizing uplink feedback overhead.
• UE-specific silencing for DAS
• (1) eNB-Centric Indication Method
• FIG. 8 is a block diagram showing the configuration of an eNB according to the present invention.
• Referring toFIG. 8, theeNB800 may include aTx data processor810, asymbol modulator820, atransmitter830, aprocessor840, amemory850, areceiver860, asymbol demodulator870, anRx data processor880 and anantenna890.
• If cells of the DAS cooperatively operate (CoMP), thetransmitter830 of theeNB800 may transmit antenna configuration information (effective antenna number information and effective antenna index information) of one or mare neighboring cells to theUP500 through theantenna890. That is, an eNB-central indication method of enabling the eN B800 (that is, the serving eNB S00) of the serving cell A to indicate the antenna configuration information to theUE500 may be employed. TheeNB800 of the serving cell A directly indicates one or more of the information on the number of effective antennas of the neighboring cells, the information on the effective antenna indexes and the information on reference signal of the neighboring cells to theUE500. The servingeNB800 may indicate the antenna configuration information to theUE500 through higher layer signaling or L1/L2 control signaling. The interferencelevel measuring module541 of theUE500 may accurately and efficiently measure the interference of the neighboring cells based on the antenna configuration information received from theeNB800 of the serving cell A. The interference restriction request determination module542 may determine to request silencing of the neighboring cells if the measured interference value exceeds a specific threshold. In this case, thetransmitter580 of theUE500 may transmit only information about the interference restriction request (that is, silencing indication) having a size of l bit to the servingeNB800. Additionally, thetransmitter580 of theUE500 may feed hack the cell IDs of the neighboring cells or the cell ID indexes to the servingeNB800. If the serving cell A and theUE500 share the information about the neighboring cells and the silencing indication information feedback order of the neighboring cells is previously set, the servingeNB800 may identify with which neighboring cell the silencing indication information is associated using only the silencing indication information, without any need for the cell IDs or the cell ID indexes.
• For example, it is predefined in advance that the DAS is configured as shown inFIG. 7 and theUE500 feeds back the silencing indication information to the cell B and the cell C in turn. If theUE500 requests silencing only to the cell B, thetransmitter580 of theUE500 may transmit feedback (cell B: silencing on, cell C: silencing off) having a size of 2 bits (“10”) to the servingeNB800 or the neighboring cell B. Since the cells can share the information about the effective antennas, it is possible to perform silencing of the effective antennas only using silencing on information. That is, the cell B may turn off the distributedantennas2 and4 (530) which cause interference to theUE500.
• (2) UE-Centric Indication Method
• In the above description, the eNB-centric indication method of enabling the servingeNB800 to transmit the antenna configuration information of the neighboring cells to theUE500 was described. In contrast the servingbase station800 may indicate only some of the antenna configuration information of the neighboring cells to theUE500 and theUE500 may directly measure and determine the remaining antenna configuration information. In such a UE-centric indication method, it is possible to accurately measure the effective antennas of the neighboring cells which substantially cause interference to the UE. In the UE-centric indication method, theUE500 determines the antenna configuration information of the neighboring cells which substantially cause interference to theUP500. In this method, the servingeNB800 may indicate the reference signal information of the neighboring cells of the antenna configuration information to theUP500. If the reference signal of the neighboring cells are predefined according to cell IDs, theprocessor540 of theUE500 may read and decode the IDs the neighboring cells and implicitly identify the reference signal of the neighboring cells.
• In the UE-centric indication method, thetransmitter580 of theUE500 may transmit antenna configuration information selected by direct measurement to the servingeNB800. In addition to the silencing indication information which is the feedback information of the UE in the eNB-centric indication method. Theprocessor540 of theUE1 may control the feedback of the effective antenna number information and the effective antenna index information except the reference signal of the neighboring cells of the antenna configuration information, and thetransmitter580 transmits only the effective antenna number information and the effective antenna index information the servingeNB800. The effectiveantenna determination module543 of theUE500 may measure and determine the number of effective antennas which cause most significant interference to theUE500 and the antenna indexes based on the reference signal of the neighboring cells. The effectiveantenna determination module543 of theUE500 may use a predetermined threshold in order to determine the number of effective antennas and the antenna indexes. In order to reduce feedback, the number of effective antennas which may be selected by theUE500 for the purpose of interference restriction may be defined in advance. In this case, the antenna indexes alone may be fed back to the servingeNB800. Alternatively, the UE1 (510) may feed back only the silencing indication information, and the antenna configuration information may he used only in the measurement. If theUE1510 feeds back only the silencing indication information, the effectiveantenna determination module543 determines the predefined number of effective antennas and the effective antenna indexes, and thetransmitter580 may feed back the information on the predetermined number of effective antennas and/or the effective antenna indexes to the servingeNB800. Then, the servingeNB800 may request that the neighboring cells perform interference restriction (that is, silencing) in specific subband subframes of those antennas.
• Cell-Specific Silencing for DAS
• It is assumed that theUE500 which performs the CMP operation is located at the cell edge where a sufficient channel state from the serving cell A is not guaranteed or severe interference from one or more neighboring cells is received. TheUE500 located at the cell edge moves at a low speed and receives data atRank 1. In case of theUE500 which perlin-ms the CoMP operation and is located at the cell edge, the method based on the feedback information of the UE increases uplink feedback overhead and backhaul overhead.
• Accordingly, a method based on a beam pattern (e.g., PMTI which is predefined upon cell deployment may be employed. Upon initial cell deployment, effective antennas including specific antennas of cells and the beams (e.g., PMIs) of the effective antennas having a specific directivity are predefined. In general, the beam pattern ofRank 1 has more explicit directivity than the beam of a higher rank. The cells may share the information about the effective antennas which cause interference among neighboring cells and the beam patterns having the specific directivity of the effective antennas. Accordingly. If a specific cell (e.g., a cell A) which performs the CoMP operation receives the request for the restriction of the effective antennas or the effective antenna beam patterns from another specific cell (e.g., a cell B), it is possible to reduce interference of another specific neighboring cell (e.g., the cell B) by restricting the effective antennas which cause interference to the specific neighboring cell or the group of the effective antenna beams having directivity to the specific cell.
• That is, while the existing method is a UE-specific beam restriction method enabling neighboring cells to restrict/recommend or silence a specific PMI which causes interference to the UE, this method is a cell-specific silencing method of enabling the neighboring cells to restrict predefined effective antennas having directivity to the UE or a beam pattern group (e.g., a RMI set) of effective antennas. Upon cell deployment, the beam pattern group having directivity between cells may include a uniform number of beam patterns or a non-uniform number of beam patterns, for a specific purpose. That is, thetransmitter580 of theUE500 which receives interference from the neighboring cells may transmit silencing indication information to the servingeNB800. By the transmission of the silencing indication information, the neighboring cells restrict specific PM is (beam pattern groups) of the effective antenna group having directivity to the serving cell (e.g., SDM), silence a specific subband (e.g., FDM), or silence a specific time resource region (e.g., TDM), thereby reducing interference on theUE500.
• The interference restriction of the neighboring cells may be performed by a specific PMI set of a specific effective antenna group or may be performed with respect to the time and frequency resource region of the specific effective antenna group. Thetransmitter830 of the servingeNB800 may transmit the above-described antenna configuration information to theUE500, and theUE500 may perform feedback without the antenna configuration information of the servingeNB800. In the cell-specific silencing method according to the present invention, the UE feeds back the silencing indication information without receiving the antenna configuration information.
• It is assumed that the number of cells which perform the CoMP operation in the DAS is three. Description will be given with reference toFIG. 7. TheUE500 belongs to the cell A. The effective antennas including theantennas2 and4 (Tx2 and Tx4) of the cell B and theantennas1,3 and4 (Tx1, Tx3 and Tx4) of the cell C substantially cause interference to the cell A. Beam pattern groups W1, W2 and W3 and W6, W7 and W8 having directivity to the cell A of the beam patterns ofRank 1 of the effective antennas, which are predefined upon cell deployment, are present.
• If theUE500 which belongs to the cell A but is located at the cell edge receives a severe interference signal from the cells B and C, thetransmitter580 of theUE500 or thetransmitter830 of theeNB800 of the serving cell A may feed back the interference restriction request (that is, silencing request) for the effective antennas, which substantially cause interference to the cell A, to the cells B and C. That is, thetransmitter580 of theUE500 may transmit information requesting restriction of the use of the effective antennas including theantennas2 and4 (Tx2 and Tx4) and theantennas1,3 and4 (Tx1, Tx3 and Tx4) to the servingeNB800 or the cells B and C. Alternatively, thetransmitter830 of theeNB800 of the serving cell A may transmit information requesting restriction of the use of the effective antennas to the cells B and C.
• FIG. 9 is a Nock diagram showing the configuration of aneNB900 of a neighboring cell according to the present invention.
• Referring toFIG. 9, similar to the servingeNB800 shown inFIG. 8, theeNB900 may include aTx data processor910, asymbol modulator920, atransmitter930, aprocessor940, amemory950, areceiver960, asymbol demodulator970, anRx data processor980 and anantenna990. TheeNB900 of the neighboring cell may correspond to the. eNB of the B or the cell B shown inFIG. 7.
• Thereceiver960 receives the interference restriction request (or the silencing request) from theUE500 or the servingeNB800 of theUE500 through theantenna990.
• Theprocessor940 may control transmission of a signal with power equal to or less than a predetermined level in a specific subband or time resource region used by theUE500 through the effective antennas which cause interference to theUE500 of the cell A, or disable transmission of a signal such as data or a reference signal. If thereceiver960 of the neighboring eNB90( )receives the restriction request information of the beam pattern group having directivity to the cell A among the effective antennas of the cell to which the neighboringeNB900 belongs, theprocessor940 enables the restriction of the use of the beam pattern groups W1, W2 and W3 and W6, W7 and W8 of the effective antennas. Theprocessor940 may control the restriction of the specific beam pattern groups or the silencing of the specific effective antennas in specific subframes or subbands. The interference restriction in the specific subframes or subbands may be requested by the servingeNB800 or may be determined by the neighboringeNB900.
• Hereinafter, a feedback information transmission method and a triggering method in the cell-specific silencing method will be described.
• TheUE500 may request cell-specific silencing when a specific condition is satisfied. When the channel state measured by the interferencelevel measuring module541 is not satisfied, the interference restriction request determination module542 may determine that cell-specific beam avoidance needs to be requested. The determination of the channel state of the interferencelevel measuring module541 may depend on whether or not the measurement is performed with respect to neighboring cells.
• The case where the interferencelevel measuring module541 does not perform measurement with respect to the neighboring cells will be described first. If communication based on single cell is performed in a state in which the interferencelevel measuring module541 does not performs measurement with respect to the neighboring cells, the interference restriction request determination module542 may determine whether or not a cell-specific interference restriction (or silencing) request is performed, by the channel state such as Channel Quality Information (CQI) and the comparison between the noise and interference level from the remaining cells except the serving cell and a threshold. In this case, thetransmitter580 of theUP500 may transmit the interference restriction request for the neighboring cells to theeNB800 of the serving cell A in the form of a message having a predetermined bit size (e.g., 1 bit). Thetransmitter580 of theUP500 transmits the interference restriction request message to the servingeNB800 in the form of a Physical Uplink Control Channel (PUCCH), a Physical Uplink Shared Channel (PUSCH); or a Radio Resource Control (RRC), thereby performing a cell-specific interference restriction request (silencing request). When thereceiver860 of theeNB800 receives the cell-specific interference restriction request from theUE500, theprocessor840 may control the cell-specific interference restriction request to be transmitted to the neighboringeNB900.
• Next, the case where the interferencelevel measuring module541 performs measurement with respect to the neighboring cells will be described. After the interferencelevel measuring module541 performs measurement with respect to the neighboring cells B and C, the interference restriction request determination module542 determines whether or not the interference restriction (or silencing) request is transmitted to the neighboring cells B and C, by the channel state of the serving cell A and the comparison between the interference levels of the neighboring cells13 and C which perform the CoMP operation and the threshold. In a state in which the50 acquires the antenna configuration information, the interferencelevel measuring module541 may more accurately measure the interference of the effective antennas. In a state in which the antenna configuration information is not acquired, after the interference values from all the antennas of the neighboring cells are roughly calculated, the interference restriction request determination module542 may determine whether or not the interference restriction (or silencing) request is performed based on the roughly calculated interference levels. In this case, after the interferencelevel measuring module541 of theUP500 perform measurement, thetransmitter580 may determine whether Or not the measured information is transmitted through theantenna590.
• The case where thetransmitter580 transmits the fileasttired information to the servingeNB800 after the interferencelevel measuring module541 performs measurement will he described. The interferencelevel measuring module541 may perform measurement in the form of Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), etc. with respect to the neighboring cells and thetransmitter580 may transmit the RSRP or RSRQ and the cell is of the neighboring cells to the servingeNB800 through theantenna590. When thereceiver860 of the servingeNB800 receives the measured information of the neighboring cells, the servingeNB800 may check the neighboring cell ID information, the interference level, etc.
• The interference restriction request determination module542 may determine whether or not the cell-specific interference (or silencing) request is performed by the comparison between the interference levels of the neighboring cells measured by the interferencelevel measuring module541 and the threshold. The interference restriction request determination module542 may determine that one or more neighboring cells which cause most significant interference need to be requested to perform interference restriction (or silencing). If the interference restriction request determination module542 determines to perform the interference restriction request with respect to one or more neighboring cells, the interference restriction request determination module542 may determine to perform the interference restriction request with respect to predefined N neighboring cells or may determine to perform the interference restriction request with respect to neighboring cells baying the interference levels exceeding the threshold.
• Similarly, thetransmitter580 of theUE500 may transmit the interference restriction request for the neighboring cells to theeNB800 of the serving cell A in the form of a message having a predetermined length in bits (e.g., 1 bit). Thetransmitter580 of theUE500 transmits the interference restriction request message to the servingeNB800 in the form of a Physical Uplink Control Channel (PUCCH), a Physical Uplink Shatrd Channel (PUSCH) or a Radio Resource Control (RRC), thereby performing cell-specific interference restriction request (silencing request). Thetransmitter580 of theUE500 may transmit the interference restriction request in descending order of interference levels of the neighboring cells regardless of the cell IDs or the cell ID indexes together with the cell ID indexes of the neighboring cells to he restricted or may transmit only the cell ID indexes.
• When thereceiver860 of the servingeN800 receives the information measured by the interferencelevel measuring module541 from theUE500, theprocessor840 may classify the measured information of the neighboring cells in order of interference levels. The classified information may be shared between theUE500 and the servingeNB800 without separate signaling. The processor84( )may determine the neighboring cells, to which the interference restriction request will be transmitted, without the cell ID indexes based on the classification information, and thetransmitter830 may transmit the interference restriction request signal for specific effective antennas and the beam pattern group to the determined neighboring cells.
• The case where theUE500 does not transmit the measured information to the servingeNB800 after the interference restriction request determination module542 performs measurement will be described, in this case, thetransmitter580 of theUE500 may transmit the interference restriction request message and the cell IDs and the cell ID indexes of the neighboring cells, the interference of which will be restricted, or transmit only the cell IDs and the cell ID indexes to the servingeNB800. Alternatively, if the servingeNB800 and theUE500 share the information about the neighboring cells and the order of interference restriction request indications (or silencing request indications) of the neighboring cells are defined in advance, theprocessor840 may identify with which neighboring cell the interference restriction request indication (silencing indication) information is associated, using only the interference restriction request indication (or the silencing request indication) without the cell IDs or the cell ID indexes. Theprocessor840 controls the transmission of the interference levels of the neighboring cells in addition to the interference restriction request indication, and thetransmitter830 may transmit the interference level information of the neighboring cells in addition to the interference restriction request indication information. The interference restriction request determination module542 may determine whether or not the interference restriction request is performed with respect to the neighboring cells, by comparison between the threshold and the measured value. By this process, thetransmitter580 of theLTE500 may transmit the interference restriction request (or silencing request) signal to one or more neighboring cells.
• Thereceiver860 of the servingeNB800 may receive the interference restriction request signal from theUE500 and then transmit the signal requesting restriction of the use of the specific effective antennas and the specific beam pattern groups to the neighboring cells. Alternatively, after the interference restriction request determination module542 determines whether or not the interference restriction request is performed by comparison with the threshold, thetransmitter580 of theCE500 may transmit the interference restriction (or silencing) request signal of nonspecific neighboring cells to the servingeNB800. In this case, thetransmitter580 of theUE500 may transmit one restriction request message to the servingeNB800 regardless of the cell IDs, and theprocessor840 of the servingeNB800 may control the request for the restriction of the use of one or more effective antennas and the beam pattern groups having directivity to the serving cell to the neighboring cells geographically located close to the serving cell.
• The cell-specific interference restriction (or silencing) request may be arbitrarily triggered by the servingeNB800. In communication based on a single cell, thereceiver860 of theeNB800 periodically or non-periodically receives single cell based channel information from theUE500. Theprocessor840 of the servingeNB800 may determine that the interference restriction request is arbitrarily transmitted to the neighboring cells by the comparison between the channel information received from the UE and the predefined threshold. Alternatively, if thereceiver860 of the servingeNB800 receives the measured information from theUE500, theprocessor840 of the servingeNB800 may restrict the effective antennas and the beam pattern group having directivity to its cell, with respect to a neighboring cell which causes most significant interference, a predetermined number of neighboring cells with sting interference, or neighboring cells with interference exceeding the threshold.
• Hereinafter, a method of exchanging information between eNBs (or cells) will be described.
• Thetransmitter580 of theUE500 transmits the cell-specific interference restriction (or silencing) request or the serving eNB8t)0 arbitrarily transmits cell-specific interference restriction (or silencing) request, the servingeNB800 may transmit or receive associated information such as information about the neighboring cells, the effective antennas and the beam pattern group restriction and the interference level. In this way, it is possible to efficiently perform cell-specific interference restriction (or silencing) request between the cells.
• Theprocessor840 of the servingeNB800 enables a message requesting restriction of the effective antennas and the beam pattern groups having directivity to its cell to the neighboring cells. Thereceiver960 of the neighboringeNB900 receives the interference restriction request messages from several cells, and theprocessor940 controls the restriction of the effective antennas and the beam patterns based on the interference restriction request messages. However, if the neighboring eNB receives the interference restriction requests from several cells, theprocessor940 needs to solve a ranking problem associated with a determination as to which effective antenna or beam pattern restricted.
• In order to solve this problem, thereceiver860 of the servingeNB800 may receive information about the interference levels generated by the neighboring cells, etc. in addition to the interference restriction request message. Theprocessor940 may determine which effective antenna or beam pattern is restricted using the interference restriction request message received by thereceiver860 and the interference level information of the neighboring cells.
• FIGS. 10 and 11 are diagrams showing examples of a process of exchanging information between eNBs.
• As described above, the eNBs may exchange associated information such as the restriction request for the effective antennas and the beam pattern groups and the interference level measurement information, and scheduling information. In a multi-cell environment using the DAS, it is assumed that aneNB A1010 belonging to the cell A,eNB B1020 belonging to the cell B, and aneNB C1030 belonging to the cell C are present.
• TheeNB A1010 may transmit a signal requesting restriction of the use of the specific effective antennas and specific beam pattern groups, which cause interference to the cell A, to which the eNB A belongs, to the eNB B andC1020 and1030, which are neighboring eN Bs, and theeNB C1030 may transmit a signal for requesting the restriction of the use of the specific effective antennas and specific beam pattern groups, which cause interference to the cell C, to the eNBs A and IWO and1020 which are the neighboring eNBs. TheeNB B1020 may transmit a response “yes” or “no” for the interference restriction request to theeNB A1010 and theeNB C1030, theeNB A1010 transmits a response “yes” or “no” for the interference restriction request to theeNB C1030, and theeNB C1030 may transmit a response “yes” or “no” for the interference restriction request to theeNB A1010. Alternatively, as shown inFIG. 11, theeNB B1020 may transmit a signal indicating that the use of the specific effective antennas and specific beam pattern groups which cause interference to the cell A is restricted in a J-th subframe or subband to theeNB A1010, and transmit a signal indicating that the use of the specific effective antennas and specific beam pattern groups which cause interference to the cell C is restricted in a K-th subframe or subband to theeNB C1030. TheeNB C1030 may transmit a signal indicating that the use of the specific effective antennas and specific beam pattern groups which cause interference to the cell A is restricted in an L-th subframe or subband to theeNB A1010, and transmit a signal indicating that the use of the specific effective antennas and specific beam pattern groups which cause interference to the cell A is restricted in an M-th subframe or subband to theeN B C1030.
• In the case where the use of the effective antennas and the beam pattern group in restricted over the entire band or the entire radio frame with respect to a specific cell, UEs within the specific cell suffer from considerable performance deterioration. Accordingly, it is possible to efficiently use transmission resources by the efficient time and frequency resource allocation between the eINBs and scheduling of the transmission information. That is, the eN Bs share scheduling for applying the restriction for the specific cell to a specific subframe or subframe such that the effective antennas which cause interference and the beam patterns can be efficiently used in subframe or subband units.
• The scheduling information may be shared among theeNBs1010,1020 and1030 through an X2 interface as L1/L2 control information or L3 RRC connection control information. The method of sharing scheduling information amonize the eNBs will be briefly described.
• FIG. 12 is a diagram showing an example of a process of performing scheduling with respect to an interference restriction request and sharing scheduling information between eNBs, by aneNB2 which is a neighboring eNB.
• Referring toFIG. 12,eNB1 and aneNB3 receive signals for requesting the restriction of the use of specific effective antennas and specific beam pattern groups from aUE1 and aUE2, respectively. Then, the eNB and theeNB3 may transmit signals for requesting the restriction of the use of the specific effective antennas and the specific beam pattern groups in preferred subframes and/or subbands to theeNB2 which is the neighboring eNB, respectively. At this time, the eNB1 and the eNB3 may further transmit associated it/formation including the interference level information of the neighboring eNB, etc. to theeNB2 which is the neighboring eNB, respectively. The processor of theeNB2 performs scheduling based on interference restriction request information received from theeNB1 and theeNB3. The processor of theeNB2 performs scheduling using the associated information if the associated informational is received from theeNB1 and theeNB3. After the processor of theeNB2 performs scheduling, for example, the transmitter of theeNB2 may transmit a response signal ‘yes’ indicating that the interference is restricted in response to the interference restriction request to the eNB1, but may transmit a response signal “no” in response to the interference restriction request to theeNB3, if theeNB2 rejects the interference restriction request of theeNB3, a proposal based on a second best plan may be transmitted. That is, theeNB2 may transmit a response signal indicating that the effective antennas and the beam pattern groups will not be used in the subframes or subbands other than the specific subframes or subbands requested by theeNB3.11421FIG. 13 is a diagram showing another example of a process of performing scheduling with respect to an interference restriction request and sharing scheduling information between eNBs aneNB2 which is a neighboring enB.
• Referring toFIG. 13,eNB1 and aneNB3 receive signals requesting restriction of the use of specific effective antennas and specific beam pattern groups from aUE1 and aUE2, respectively. That is, the1 and theUE3 may perform scheduling and transmit the signals requesting restriction of the use of the specific effective antenna, and the specific beam pattern groups in specific subframes or subbands to theeNB1 and theeNB3, respectively. Then, unlikeFIG. 12, the processor of theeNB1 and the processor of theeNB3 perform scheduling based on the interference restriction request received from theUE1 and theUE3, respectively. The processor of theeNB1 and the processor of theeNB3 collect the scheduling information received from several UEs (e.g., theUE1 in case of theeNB1 and theUE3 in case of the eNB3) belonging to the respective cells and then perform scheduling for restricting the use of the effective antennas and the beam pattern groups in consideration of the collected scheduling information, associated information, and traffic of the neighboring cell, etc. After performing scheduling, theeNB1 and theeNB3 may further include associated information including the interference level information of the neighboring eNB in addition to feedback information and transmit the associated information.
• Thereafter, the processor of theeNB2 may efficiently perform scheduling based on the received information. The processor of the.eNB2 performs scheduling based on the feedback information received by the receiver. After performing scheduling, for example, the transmitter of theeNB2 may transmit a response signal “yes” indicating that the interference is restricted in response to the interference restriction request to theeNB1, but may transmit a response signal “no” in response to the interference restriction request to theeNB3. If theeNB2 rejects the interference restriction request of theeNB3, a proposal based on a second best plan may be transmitted. That is, theeNB2 may transmit a response signal indicating that the effective antennas and the beam pattern groups will not be used in the subframes subbands other than the specific subframes or subbands requested by theeNB3.
• FIG. 14 is a diagram showing another example of a process of performing scheduling with respect to an interference restriction request and sharing scheduling information between eNBs, by aneNB2 which is a neighboring eNB.
• Referring toFIG. 14, aUE1 and aUE3 may perform scheduling and transmit the signals requesting restriction of the use of the specific effective antennas and the specific beam pattern groups in specific subframes or subbands to an eNB l and aneNB3, respectively. Thereafter, theeNB1 which is the serving eNB of the UE and theeNB3 which is the serving eNB of theUE3 may transmit feedback information (information scheduled to restrict the use of the specific effective antennas and the specific beam pattern groups in the specific subframes subbands) received from theUE1 and theUE3 to theeNB2 which is the neighboring eNB without processing, respectively. The processor of theeNB2 may efficiently perform scheduling based on the interference restriction request received from the eNB l and theeNB3. After performing scheduling, for example, the transmitter of theeNB2 may transmit a response signal “yes” indicating that the interference is restricted in response to the interference restriction request to theeNB1, but may transmit a response signal “no” in response to the interference restriction request to theeNB3. If theeNB2 rejects the interference restriction request of theeNB3, a proposal based on a second best plan may be transmitted. That is, the.eNB2 may transmit a response signal indicating that the effective antennas and the beam pattern groups will not be used in the subframes or subbands other than the specific subframes or subbands requested by theeNB3.
• In the above description, interference restriction (or silencing) for restricting the effective antennas beam pattern groups of the neighboring cells having specific directivity to the serving cell was described. However, the inter-cell interference restriction method according to the present invention is applicable to the JP method among multiple cells. If multiple cells independently transmit data without sharing the data, effective antennas and beam patterns having directivity to a serving cell cause interference. However, in the JP method of enhancing the signal by sharing data among multiple cells, effective antennas and beam patterns having directivity to a serving cell may be the best PMI groups. Accordingly, an interference restriction (or silencing) technology restricting the effective antennas and the beam pattern groups of the neighboring cells is applicable to the JP technology of enhancing the signal of a UE located at a cell edge by sharing data among multiple cells.
• In the present invention, theUE500 feeds back N (N≧1)-bit interference restriction/ indication information in a state in which interference is caused by neighboring cells so as to request the interference restriction for silencing) to N neighboring cells. In the above-described invention, the UE transmits 1-bit interference restriction indication information to each of the neighboring cells which cause interference. In theUE500 subjected to interference caused by the neighboring cells, addition to the method of requesting the restriction of the use of the effective antennas, the interferencelevel measuring module541 may measure the interference of each of the antennas of the neighboring cells, the interference restriction request determination module542 may determine an antenna subjected to great interference and the index of the antenna, thetransmitter580 may transmit a signal requesting interference restriction (or silencing) including the index information of the antenna to the servingeNB800.
• That is, the interference restriction request determination module542 determines a predefined number of antenna indexes and may determine that an antenna index having interference exceeding a specific threshold is fed back. This method is applicable to the above-described UE-specific silencing method and cell-specific silencing method.
• In order to completely eliminate the interference of the neighboring cells, in addition to the method of restricting the transmission of certain signals of the neighboring cells and the method of lowering the transmit power of the effective antennas to be equal to or less than a predetermined level by the neighboring eNns in response to the silencing request, theprocessor540 of theUE500 may determine the transmit power of the effective antennas of the neighboring cells and feed back the transmit power. This value may be represented by quantized N (N≧1) bits. The determination of the transmit power of the antennas of the neighboring cells by theUE500 is applicable to a method of directly determining the indexes of the antennas of the neighboring cells which cause interference by the interference restriction request determination module542 and feeding back the indexes by thetransmitter580, in addition to the indication of the effective antenna group. This method is applicable to the above-described UE-specific silencing method and cell-specific silencing method.
• The aforementioned methods are applicable to CAS as well as DAS.
• The detailed description of the exemplary embodiments of the present invention has been given to enable those skilled in the art to implement and practice the invention. Although the invention has been described with reference to the exemplary embodiments, those skilled in the art will appreciate that various modifications and variations can be made in the present invention without departing fixing the spirit or scope of the invention described in the appended claims. For example, those skilled in the art may use each construction described in the above embodiments in combination with each other. Accordingly, the invention should not be limited to the specific embodiments described herein, but should be accorded the broadest scope consistent with the principles and novel features disclosed herein.
Mode for the Invention
• Various embodiments have been described in the best mode for carrying out the invention.
• It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departig, from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.
INDUSTRIAL APPLICABILITY
• Apparatus and method for controlling inter-cell interference a wireless communication system in which a plurality of antennas is deployed in each cell are applied to communication standards such as 3GPP LTE, LTE-A, IEEE 802.16 and like that.

Claims (14)

What is claimed is:

1. A method of performing inter-cell interference coordination by a first eNodeB (eNB) in a wireless communication system, the method comprising:

transmitting a message comprising first information, second information and third information to a second eNB, the first information indicating a level of interference experienced by the first eNB, the second information related to silenced subframes in which transmission in the first eNB is restricted, and the third information indicating a number of specific antennas from among a plurality of antennas of the first eNB,

wherein a downlink transmission or an uplink reception for a user equipment (UE) served by the second eNB is scheduled based on at least the first information, the second information and the third information.

2. The method ofclaim 1, wherein the message further comprises fourth information related to interference caused by the first eNB.

3. The method ofclaim 1, wherein the message is transmitted via X2 interface signaling.

4. A non-transitory computer readable medium recorded thereon a program for executing the method ofclaim 1.

5. An eNodeB (eNB) performing inter-cell interference coordination in a wireless communication system, the eNB comprising:

a X2 interface module configured to transmit a message comprising first information, second information and third information to another eNB, the first information indicating a level of interference experienced by the eNB, the second information related to silenced subframes in which transmission in the eNB is restricted, and the third information indicating a number of specific antennas from among a plurality of antennas of the eNB,

wherein a downlink transmission or an uplink reception for a user equipment (UE) served by the another eNB is scheduled based on at least the first information, the second information and the third information.

6. The eNB ofclaim 5, wherein the message further comprises fourth information related to interference caused by the eNB.

7. The eNB ofclaim 5, wherein the message is transmitted via X2 interface signaling.

8. A method of performing inter-cell interference coordination by a second eNodeB (eNB) in a wireless communication system, the method comprising:

receiving a message comprising first information, second information and third information from a first eNB, the first information indicating a level of interference experienced by the first eNB, the second information related to silenced subframes in which transmission in the first eNB is restricted, and the third information indicating a number of specific antennas from among a plurality of antennas of the first eNB; and

scheduling a downlink transmission or an uplink reception for a user equipment (UE) served by the second eNB based on at least the first information, the second information and the third information.

9. The method ofclaim 8, wherein the message further comprises fourth information related to interference caused by the first eNB.

10. The method ofclaim 8, wherein the message is received via X2 interface signaling.

11. A non-transitory computer readable medium recorded thereon a program for executing the method ofclaim 8.

12. An eNodeB (eNB) performing inter-cell interference coordination in a wireless communication system, the eNB comprising:

a X2 interface module configured to receive a message comprising first information, second information and third information from another eNB, the first information indicating a level of interference experienced by the another eNB, the second information related to silenced subframes in which transmission in the another eNB is restricted, and the third information indicating a number of specific antennas from among a plurality of antennas of the another eNB; and

a processor configured to schedule a downlink transmission or an uplink reception for a user equipment (UE) served by the eNB based on at least the first information, the second information and the third information.

13. The eNB ofclaim 12, wherein the message further comprises fourth information related to interference caused by the another eNB.

14. The eNB ofclaim 12, wherein the message is received via X2 interface signaling.

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