JP2014143606A - Radio communication system, radio communication method, radio base station, and user equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress reduction in reception accuracy by appropriately notifying user equipment of information required for reception processing even when downlink signals are transmitted to the user equipment from a plurality of transmission points.SOLUTION: A radio communication system comprises: a plurality of radio base stations; and user equipment capable of performing coordinated multi-point transmission with the plurality of radio base stations. The radio base station comprises: a generation unit for generating synchronization related information in relation to time synchronization and frequency synchronization for a downlink signal; a multiplexing unit for multiplexing a preamble signal having a signal series included in the synchronization related information into a downlink signal; and a transmission unit for transmitting the downlink signal to the user equipment. The user equipment comprises: a holding unit for holding the synchronization related information generated by the generation unit; a reception unit for receiving the downlink signal into which the preamble signal is multiplexed; and a synchronization processing unit for performing synchronization processing on the downlink signal by using the synchronization related information hold by the holding unit and the signal series in the preamble signal.

Description

  The present invention relates to a radio communication system, a radio communication method, a radio base station, and a user terminal applicable to a cellular system or the like.

  In a UMTS (Universal Mobile Telecommunications System) network, HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access) are adopted for the purpose of improving frequency utilization efficiency and data rate. A feature of a system based on CDMA (Wideband-Code Division Multiple Access) is maximally extracted. With respect to this UMTS network, LTE (Long Term Evolution) has been studied for the purpose of further high data rate and low delay (Non-patent Document 1).

  The third generation system can realize a transmission rate of about 2 Mbps at the maximum on the downlink using a fixed band of 5 MHz in general. On the other hand, in the LTE system, a transmission rate of about 300 Mbps at the maximum in the downlink and about 75 Mbps in the uplink can be realized using a variable band of 1.4 MHz to 20 MHz. In addition, in the UMTS network, a successor system of LTE is also being studied for the purpose of further increasing the bandwidth and speed (for example, LTE Advanced (LTE-A)). The system band of the LTE-A system includes at least one component carrier (CC: Component Carrier) having the system band of the LTE system as a unit. Collecting a plurality of component carriers (cells) in this way to increase the bandwidth is called carrier aggregation (CA).

  Incidentally, inter-cell orthogonalization is one promising technique for further improving system performance over the LTE system. For example, in the LTE-A system, orthogonalization within a cell is realized by orthogonal multi-access for both the uplink and the downlink. That is, in the downlink, orthogonalization is performed between user terminals UE (User Equipment) in the frequency domain. On the other hand, between cells, as in W-CDMA, interference randomization by one-cell frequency repetition is fundamental.

  Therefore, in 3GPP (3rd Generation Partnership Project), a coordinated multi-point transmission / reception (CoMP) technique is being studied as a technique for realizing inter-cell orthogonalization. In this CoMP transmission / reception, a plurality of cells perform transmission / reception signal processing in cooperation with one or a plurality of user terminals UE. For example, in the downlink, simultaneous transmission of multiple cells to which precoding is applied, cooperative scheduling / beamforming, and the like are being studied. Application of these CoMP transmission / reception techniques is expected to improve the throughput characteristics of the user terminal UE located particularly at the cell edge.

3GPP, TR25.912 (V7.1.0), "Feasibility study for Evolved UTRA and UTRAN", Sept. 2006

  LTE Rel. Up to 10, the user terminal UE has only to perform reception processing (synchronization processing) assuming that a downlink signal is transmitted from a single radio base station. However, LTE Rel. 11, a transmission mode is assumed in which downlink signals are transmitted from a plurality of transmission points to the user terminal UE with the introduction of the above-described CoMP technology or the like.

  When downlink signals are transmitted from a plurality of transmission points (radio base stations), the characteristics (reception timing, frequency offset, etc.) of each downlink signal depend on the positional relationship between the user terminal UE and each transmission point, etc. May be different. In such a case, when the user terminal UE performs the synchronization process assuming that the downlink signal is transmitted from a single radio base station as in the conventional case, the time synchronization of the downlink signal, the frequency synchronization, etc. May not be acquired, and reception accuracy may be reduced.

  For this reason, when downlink signals are transmitted from a plurality of transmission points to the user terminal UE, the reception timing and frequency offset of the downlink signals transmitted from each transmission point on the user terminal UE side are considered. It is necessary to perform synchronous processing. However, for example, in a situation where the user terminal UE moves, a situation is assumed in which synchronization processing of each downlink signal is repeated. As a result, there exists a problem that the load accompanying the synchronization process in the user terminal UE increases.

  The present invention has been made in view of such a point, and even when a downlink signal is transmitted from a plurality of transmission points to a user terminal, a radio communication system capable of reducing a load associated with synchronization processing in the user terminal An object of the present invention is to provide a radio communication method, a radio base station, and a user terminal.

  The radio communication system of the present invention is a radio communication system comprising a plurality of radio base stations and a user terminal capable of cooperative multipoint transmission with the plurality of radio base stations, wherein the radio base station is a downlink. A generator that generates synchronization-related information related to signal time synchronization and frequency synchronization, a multiplexing unit that multiplexes a preamble signal having a signal sequence included in the synchronization-related information into a downlink signal, and the preamble signal are multiplexed. A transmission unit that transmits the downlink signal to the user terminal, and the user terminal includes a holding unit that holds the synchronization-related information generated by the generation unit, and a downlink in which the preamble signal is multiplexed. The receiver uses a receiving unit that receives a link signal, the synchronization-related information held in the holding unit, and the signal sequence included in the preamble signal. And having a synchronization processing unit for performing processing for synchronizing click signal.

  ADVANTAGE OF THE INVENTION According to this invention, even when it is a case where a downlink signal is transmitted from a some transmission point with respect to a user terminal, the load accompanying the synchronization process in a user terminal can be reduced.

It is a figure for demonstrating cooperation multipoint transmission. It is a figure explaining the reception power and reception timing of the downlink signal transmitted from each transmission point in cooperative multipoint transmission. It is a figure which shows an example of the mapping pattern of CRS transmitted from each transmission point using a normal sub-frame. It is an example of the table which shows the parameter information corresponding to the identifier of parameter information. It is a figure when a downlink signal is transmitted from a some transmission point, and a figure explaining an example of each parameter information. It is a figure explaining a heterogeneous network structure. It is a figure explaining operation | movement of the user terminal based on the synchronous relevant information prescribed | regulated with the radio | wireless communication method which concerns on this Embodiment. It is explanatory drawing of an example of the signal sequence which changed the time multiplexing position contained in a synchronous relevant information. It is explanatory drawing of an example of the signal series which changed the frequency multiplexing position contained in a synchronous relevant information. It is a figure explaining operation | movement of the user terminal UE based on the synchronous relevant information prescribed | regulated with the radio | wireless communication method which concerns on this Embodiment. It is explanatory drawing of the wireless base station which belongs to a co-location group. It is a figure which shows an example of the table which manages the index of a co-location group. Cells 1 to 5 corresponding to component carriers # 1 to # 5 to be carrier-aggregated are shown. It is a figure for demonstrating the system configuration | structure of a radio | wireless communications system. It is a figure for demonstrating the whole structure of a wireless base station. It is a figure for demonstrating the whole structure of a user terminal. It is a block diagram which shows the structure of the baseband signal processing part in the radio base station shown in FIG. It is a block diagram which shows the structure of the baseband signal processing part in the user terminal shown in FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  First, downlink multi-point (CoMP) transmission will be described with reference to FIG. Downlink CoMP transmission includes Coordinated Scheduling / Coordinated Beamforming (CS / CB) and Joint processing. CS / CB is a method of transmitting a shared data channel (PDSCH) only from one transmission / reception point (or radio base station, cell) to one user terminal UE, as shown in FIG. Radio resources are allocated in the frequency / space region in consideration of interference from transmission / reception points and interference with other transmission / reception points.

  On the other hand, Joint processing is a method in which precoding is applied and a shared data channel is simultaneously transmitted from a plurality of transmission / reception points. As shown in FIG. 1B, shared data is transmitted from a plurality of transmission / reception points to one user terminal UE. There are joint transmission (JT) for transmitting a channel and dynamic point selection (DPS) for instantaneously selecting one transmission / reception point and transmitting a shared data channel as shown in FIG. 1C. There is also a transmission form called Dynamic Point Blanking (DPB) that stops data transmission in a certain area with respect to a transmission / reception point that causes interference.

  CoMP transmission is applied in order to improve the throughput of the user terminal UE existing at the cell edge. For this reason, CoMP transmission is controlled to be applied when the user terminal UE exists at the cell edge. In this case, in the radio base station, quality information (for example, RSRP (Reference Signal Received Power)), RSRQ (Reference Signal Received Quality), or SINR (Signal Interference plus Noise Ratio) from the user terminal UE When the difference is obtained and the difference is equal to or smaller than the threshold, that is, when the quality difference between the cells is small, it is determined that the user terminal UE exists at the cell edge, and CoMP transmission is applied.

  The environment to which CoMP transmission / reception is applied includes, for example, a configuration including a plurality of remote radio equipment (RRE: Remote Radio Equipment) connected to a radio base station (radio base station eNB) by an optical fiber (RRE configuration) Based control) and a configuration of a radio base station (radio base station eNB) (autonomous distributed control based on an independent base station configuration).

  When CoMP is applied, downlink signals (downlink control signals, downlink data signals, synchronization signals, reference signals, etc.) are transmitted to the user terminal UE from a plurality of transmission points or specific transmission points. The user terminal UE that has received the downlink signal may, for example, use a reference signal (cell specific reference signal (CRS), user specific demodulation reference signal (DM-RS), channel state measurement). Reception processing is performed using a reference signal (CSI-RS: Channel State Information Reference Signal, etc.). Examples of reception processing performed by the user terminal UE include signal processing such as channel estimation, synchronization processing, demodulation processing, and feedback information (CSI) generation processing.

  However, when downlink signals are transmitted from a plurality of geographically different transmission points to the user terminal UE, reception signal levels, reception timings, and the like of the downlink signals transmitted from the respective transmission points may be different ( (See FIGS. 2A and 2B). The user terminal UE cannot grasp from which transmission point each received downlink signal (for example, a reference signal assigned to a different antenna port (AP)) is transmitted. For this reason, when performing channel estimation, a demodulation process, etc. using all the reference signals which the user terminal UE received, there exists a possibility that reception accuracy may fall.

  Therefore, when the reception process is performed using the reference signal transmitted from each transmission point, the user terminal UE considers the geographical position of each transmission point (propagation characteristics of the downlink signal transmitted from each transmission point). It is desirable to perform reception processing. Therefore, the case where the long-term propagation path characteristics are the same between different antenna ports (APs) is assumed to be “Quasi co-location” (the same pseudo-geographical relationship), and between each downlink signal, the Quasi co It has been studied that each user terminal UE performs different reception processing depending on whether or not it is -location.

  Here, long-term propagation path characteristics refer to delay spread, Doppler spread, Doppler shift, average gain, average delay, etc. A quasi co-location is assumed if some or all of them are the same. Note that “Quasi co-location” corresponds to a geographically identical case, but is not necessarily limited to a physical proximity.

  For example, when transmission is performed from an AP that is geographically distant (not Quasi co-location), the user terminal UE recognizes that transmission is performed from an AP that is geographically distant, and then the Quasi co A reception process different from that assumed when -location is assumed can be performed. Specifically, reception processing (for example, signal processing such as channel estimation, synchronization processing, demodulation processing, and feedback information (CSI) generation processing) is performed independently for each geographically separated AP.

  As an example, a CRS is transmitted from an AP that is determined to be geographically identical (Quasi co-location), and CSI is transmitted from AP # 15 and AP # 16 that are determined to be geographically separated (not Quasi co-location). -Assume a case where an RS is transmitted (see FIG. 2A). In this case, the user terminal UE performs reception processing using CRS as in the conventional case. On the other hand, for CSI-RS, the user terminal UE performs independent channel estimation for AP # 15 and AP # 16, and then generates and feeds back channel quality information.

  In addition, in the user terminal UE, as targets for assuming whether or not the quasi co-location is between different APs, for example, PSS (Primary synchronization signals) / SSS (Secondary synchronization signals), CRS, DM-RS (for PDSCH) ), DM-RS (for ePDCCH), CSI-RS, and the like.

  Thus, LTE Rel. 11, it is important to perform reception processing on the user terminal UE side in consideration of a correspondence relationship (Quasi co-location relationship) between downlink signals.

  Further, when downlink signals are transmitted from a plurality of transmission points to the user terminal UE by CoMP or the like, the user terminal UE considers a control signal transmitted from each transmission point, a mapping pattern of reference signals, and the like. It is desirable to specify (rate matching) the resource (RE) to which the PDSCH is allocated. For example, when transmitting to the user terminal UE from a plurality of transmission points (TP1 and TP2) (for example, JT CoMP), the user terminal UE uses PDCCH (Physical Downlink Control Channel), CRS, and CSI-RS in TP1 and TP2. It is preferable to perform rate matching in consideration of a mapping pattern and the like.

  For example, it is assumed that the user terminal UE applies CoMP (for example, JT CoMP) using TP1 and TP2 in a wireless system configured to be connectable to a plurality of transmission points (TP1 to TP3). In this case, the user terminal UE performs rate matching in consideration of mapping patterns such as control signals and reference signals respectively transmitted from TP1 and TP2 (see FIG. 3). 3A to 3C show examples of mapping patterns in the normal subframes TP1 to TP3, and FIG. 3D corresponds to a mapping pattern that takes into account signals transmitted from TP1 and TP2.

  When JT CoMP is applied to TP1 and TP2, as shown in FIG. 3D, among radio resources after a predetermined symbol to which a downlink control channel is allocated, PDSCH (Physical Downlink Shared) Channel) is mapped. The user terminal UE can improve reception processing accuracy by performing reception processing in consideration of the pattern of FIG. 3D. In FIG. 3, only CRS is shown as a reference signal. However, when CSI-RS is mapped, rate matching is performed in consideration of CSI-RS.

  Further, FIG. 3 shows a normal subframe in which CRS is mapped across the entire frequency band, but as a subframe configuration, an MBSFN (Multicast-Broadcast service Single Frequency Network) subframe or a new carrier type (NCT) : New Carrier Type) is also being studied.

  MBSFN is a scheme in which a plurality of radio base stations constituting the MBSFN can perform RF (Radio frequency) synthesis of signals transmitted from each radio base station by the user terminal UE by simultaneously transmitting the same signal. The MBSFN subframe is a subframe in which a portion other than the control channel is a blank period (blank period) and no CRS is assigned to the PDSCH region. A subframe of a new carrier type (also referred to as “Extension carrier type”) is a subframe that does not have an existing PDCCH from the top of the subframe to a predetermined OFDM symbol (maximum 3 OFDM symbols), and to which no CRS is assigned. .

  For example, when TP1 is a normal subframe and TP2 is an MBSFN subframe (or NCT), there is no CRS pattern in the PDSCH region of TP2. For this reason, the rate matching pattern of TP1 + TP2 is equal to the mapping pattern of TP1. That is, the user terminal UE can perform rate matching considering only the mapping pattern of RE for PDSCH of TP1 using normal subframes.

  As described above, in the user terminal UE, by performing rate matching in consideration of the mapping pattern and subframe configuration of PDCCH, CRS, and CSI-RS transmitted from a plurality of transmission points, PDSCH resources of the serving cell and the neighboring cell Can be specified and received. That is, LTE Rel. 11, it is important for the user terminal UE to perform rate matching in consideration of mapping patterns such as PDCCH, CRS, CSI-RS, and subframe configuration.

  Therefore, a method for appropriately notifying the user terminal UE of information (Quasi co-location relationship, PDSCH resource mapping information, etc.) for the user terminal UE to appropriately perform reception processing is required.

  For example, parameter information (PDSCH RE Mapping and Quasi) in which PDSCH resource mapping information (PDSCH RE mapping Parameter) and Quasi-co-location information (Quasi-co-location Configuration Parameter) are defined for each component carrier (CC). Preparation of a predetermined number (for example, 4 sets) of -co-location Configuration) and notifying the user terminal UE is being studied.

  Specifically, on the radio base station (network) side, in consideration of transmission points and communication environments around the user terminal UE, parameter information including PDSCH resource mapping information and Quasi co-location information (hereinafter, “ A predetermined number (for example, four types) is defined. And the said some parameter information is notified to the user terminal UE by upper layer signaling (for example, RRC signaling). Further, it is considered that an instruction for allowing the user terminal UE to select specific parameter information from the four types of parameter information # 1 to # 4 is included in the downlink control information (DCI) and dynamically notified to the user terminal UE. (See FIG. 4).

  That is, parameter information # 1 to # 4 (PDSCH RE Mapping and Quasi-co-location Configuration # 1- # 4) shown in FIG. 4 is notified to the user terminal UE by higher layer signaling and corresponds to each parameter information. Bit information (“00”, “01”, “10” or “11”) is included in downlink control information (DCI) and notified to the user terminal UE.

  Here, an example of parameter information including PDSCH resource mapping information and Quasi co-location information will be described with reference to FIG. FIG. 5A shows a case where one transmission / reception point is instantaneously selected from a plurality of transmission / reception points (here, three of TP1, TP2, and TP3) and DPS CoMP for transmitting a shared data channel is applied. The network dynamically selects one transmission point (radio base station) and transmits a data signal to the user terminal UE.

  For example, in DPS CoMP shown in FIG. 5A, in subframe # 1, a data signal is transmitted from transmission point TP1 to user terminal UE, and in subframe # 2, a data signal is transmitted from transmission point TP2 to user terminal UE. In subframe # 3, a data signal can be transmitted from transmission point TP3 to user terminal UE.

  FIG. 5B shows an example of parameter information (Configuration). Parameter information # 1, # 2, and # 3 (Configuration # 1, # 2, and # 3) are parameters of TP1, TP2, and TP3, respectively. It corresponds. Also, these parameter information # 1 to # 3 are notified to the user terminal UE via higher layer signaling (for example, RRC signaling).

  In FIG. 5, the CRS pattern includes the number of CRS antenna ports and the shift amount. Thereby, the mapping pattern of CRS can be specified. The MBSFN configuration (MBSFN config) corresponds to the MBSFN configuration, and the presence or absence of a CRS pattern in the PDSCH region can be determined from the MBSFN configuration. The non-zero power CSI-RS (NZP CSI-RS) is a reference signal that can be used for estimating a desired signal, and the CSI-RS pattern (NZP CSI-RS pattern) is notified to the user terminal UE. -Quasi co-location relationship between RS and DM-RS can be determined. Zero power CSI-RS (ZP CSI-RS) is a reference signal that can be used for interference signal estimation, and PDSCH is not multiplexed. By notifying the user terminal UE of the zero power CSI-RS pattern (ZP CSI-RS pattern), rate matching can be performed appropriately. The PDSCH starting symbol is a parameter indicating a head symbol in which the PDSCH is arranged. Thereby, the user terminal UE can specify the leading symbol of the PDSCH of the adjacent cell. Note that the parameter information in FIG. 5 is an example, and the present invention is not limited to this.

  The identifier indicating each piece of parameter information (PDSCH RE Mapping and Quasi-co-location Configuration) shown in FIG. 5B may be called PQI (PDSCH RE Mapping and Quasi-co-location Indicator). The PQI is included in downlink control information (DCI) and notified to the user terminal UE. For example, as described above, when data is transmitted from TP1 to the user terminal UE in the subframe # 1, the downlink control information is notified so that the parameter information # 1 is applied to the user terminal UE. For example, when the relationship between the parameter information and the PQI is shown in FIG. 4, the PQI set in the DCI is “00”.

  Also, it has been studied to newly provide “DCI format 2D” as downlink control information (DCI) for configuring PQI. Note that the DCI format 2D is also being studied as a DCI format used in the CoMP transmission mode (TM10). Furthermore, it has been studied to set four sets of parameter information for each CC by using the DCI format 2D.

  In the user terminal UE, by determining the PQI set in the DCI format 2D as described above, time synchronization and frequency synchronization of downlink signals transmitted from a plurality of transmission points are ensured, and transmission is performed from which transmission point. It is possible to grasp what is being done. For example, in the user terminal UE, while ensuring the frequency synchronization of the downlink signal (identifying the frequency offset) from the CRS pattern shown in FIG. 5B, the CSI-RS pattern (non-zero power CSI-RS pattern, zero power CSI-RS pattern) ) To ensure time synchronization of downlink signals. Moreover, since CRS is linked | related with cell ID, cell ID can be specified from a CRS pattern, and the transmission point used as a transmission source can be specified by this cell ID.

  By the way, as a radio network configuration to which LTE-A is applied, as shown in FIG. 6, a heterogeneous network configuration in which a large number of small cells S are arranged on the area of the macro cell M has been studied (see FIG. 6). . For example, in a heterogeneous network, a small cell S using a frequency (for example, 3.5 GHz) different from the macro cell M is overlaid on the area of the macro cell M using an existing frequency (for example, 2 GHz or 800 MHz). LTE Rel. 12, the density of such small cells S is being further increased (SCE: Small Cell Enhancement). For example, it is considered to arrange several hundred small cells S for a single macro cell M.

  As illustrated in FIG. 6, in a network in which the small cells S are densely arranged on the area of the macro cell M, it is assumed that CoMP transmission is performed between the small cells S for the user terminal UE. In this case, the user terminal UE can stably realize high throughput by using a plurality of small cells S seamlessly. In order to realize such CoMP transmission between the small cells S, the user terminal UE secures time synchronization and frequency synchronization with these small cells S, and specifies the small cell S as a transmission source. It is necessary to do.

  As described above, the user terminal UE secures time synchronization and frequency synchronization of downlink signals transmitted from a plurality of transmission points by determining the PQI set in the DCI format 2D, and Can be identified. However, when the small cells S are densely arranged, it is assumed that transmission points (for example, the small cells S) frequently switch as the user terminal UE moves. Under such circumstances, when synchronization with a transmission point is ensured based on the DCI format 2D, the load accompanying the PDCCH decoding process in the user terminal UE increases.

  In the network configuration in which the small cells S are densely arranged on the area of the macro cell M, the inventor can secure time synchronization and frequency synchronization with the transmission point by a simpler method. The present invention has been conceived by paying attention to reducing the load associated with the decoding process and improving the throughput characteristics. That is, in the present invention, information related to time synchronization and frequency synchronization with a radio base station serving as a transmission point (hereinafter referred to as “synchronization related information”), instead of synchronization processing using PDCCH including DCI format 2D. ) Is transmitted from the radio base station to the user terminal UE, and the synchronization process is executed in the user terminal UE based on the synchronization related information.

  In general, the synchronization process is the "acquisition" process, which is the process until the synchronization state is established at the beginning of communication, and the synchronization state is not lost due to modulation or noise after the synchronization is established. This includes “synchronized tracking (tracking) processing” that is a process that continues to be monitored. In this specification, “synchronization” refers to one or both of “synchronization acquisition” and “synchronization tracking”, unless otherwise specified, and “synchronization processing” refers to “synchronization acquisition processing”. ”And“ synchronous tracking process ”.

  According to a first aspect of the present invention, a radio base station generates synchronization related information related to time synchronization and frequency synchronization of a downlink signal, and downlinks a preamble signal having a signal sequence included in the synchronization related information. The signal is multiplexed and transmitted to the user terminal. On the other hand, in the user terminal UE, the synchronization related information generated in the radio base station is held, the downlink signal in which the preamble signal is multiplexed is received, and the held synchronization related information and the signal included in the preamble signal are received The downlink signal is synchronized using the sequence.

  In this case, the synchronization-related information generated in the radio base station may be configured by, for example, identification information (for example, a cell ID) of the radio base station serving as a transmission point and a signal sequence associated with the identification information. it can. In this case, for example, in the user terminal UE, it is possible to obtain time synchronization and frequency synchronization from the corresponding signal sequence included in the downlink signal by grasping the identification information and signal sequence of the radio base station before the synchronization processing. And a radio base station associated with this signal sequence can be specified. As a result, even when the transmission point is frequently switched in accordance with the movement of the user terminal UE, it is possible to avoid a situation in which the PDCCH decoding process is repeated, and thus it is possible to reduce the load associated with the synchronization process in the user terminal UE. It becomes.

  Examples of the signal sequence included in the synchronization-related information include LTE Rel. CRS, CSI-RS, and PSS / SSS. 11 and a signal sequence obtained by extending these reference signals and synchronization signals can be used. In addition, LTE Rel. 11 or other reference signals (for example, DM-RS) or signal sequences obtained by extending the reference signals can be used. The signal sequence may be composed of a PN (Pseudo-random) sequence, or may be composed of a Gold sequence or a Zadoff-Chu sequence.

  In addition, as a signal sequence included in the synchronization-related information, a Cell-specific reference signal transmitted from the small cell can be used in order to find a small cell suitable for user data transmission in the user terminal UE. Hereinafter, this reference signal is referred to as “DISCOVERY SIGNAL”. DISCOVERY SIGNAL may also be called PDCH (Physical Discovery Channel), BS (Beacon Signal), or DPS (Discovery Pilot Signal), for example.

Note that a signal having the following characteristics can be used for DISCOVERY SIGNAL. DISCOVERY SIGNAL may be configured by any of the signals (a) to (d) shown below, or may be configured by arbitrarily combining the signals (a) to (d).
(A) LTE Rel. The synchronization signals (PSS, SSS) defined by 8 can be used.
(B) LTE Rel. A signal multiplexed at different positions in the time / frequency direction using the same sequence as the synchronization signal defined in FIG. 8 can be used. For example, a signal obtained by multiplexing PSS and SSS in different slots can be used.
(C) The newly defined DISCOVERY SIGNAL is used to select a small cell. For example, LTE Rel. As compared with the synchronization signals (PSS, SSS) defined in FIG.
(D) LTE Rel. The existing reference signals (CSI-RS, CRS, DM-RS, PRS, SRS) defined in 10 can be used. Alternatively, a part of an existing reference signal (for example, a signal that transmits 1-port CRS at a cycle of 5 msec) may be used.

  The synchronization related information can be notified to the user terminal UE by higher layer signaling (for example, RRC signaling), for example. The user terminal UE can hold the notified synchronization related information. In addition, the user terminal UE and the plurality of radio base stations can hold the information before the synchronization acquisition process. In addition, when notifying by higher layer signaling, it is not necessary to hold | maintain before a synchronous acquisition process in the user terminal UE and several radio base stations. In this case, since the synchronization related information can be updated to Semi-Static, only the necessary synchronization related information according to the location of the user terminal UE can be notified to the user terminal UE.

  The preamble signal transmitted from the radio base station has the signal sequence described above. This preamble signal is multiplexed with a downlink signal (more specifically, user data for the user terminal UE) and transmitted to the user terminal UE. In the user terminal UE, synchronization processing is performed based on the signal sequence included in the preamble signal multiplexed on the downlink signal and the synchronization related information held.

  The operation when the synchronization related information is defined in this way will be described with reference to FIG. FIG. 7 is a diagram for explaining the operation of the user terminal UE based on synchronization-related information defined by the radio communication method according to the present embodiment. FIG. 7 shows a case where different signal sequences (sequence 1 to sequence 3) are assigned to the three radio base stations eNB1 to eNB3 that are transmission points.

  Here, it is assumed that the user terminal UE holds synchronization-related information including identification information (cell ID) of these radio base stations eNB1 to eNB3 and a signal sequence associated with this identification information. Here, in this synchronization related information, CRS is defined as the signal sequence of the radio base station eNB1, CSI-RS is defined as the signal sequence of the radio base station eNB2, and DM-RS is defined as the signal sequence of the radio base station eNB3. It shall be stipulated.

  When receiving the downlink signal, the user terminal UE performs a cross-correlation process on the signal sequence included in the preamble signal multiplexed on the downlink signal and the signal sequence defined in the synchronization related information. Specifically, the user terminal UE calculates a correlation between a signal sequence replica held in association with each signal sequence and a downlink signal (preamble signal). For example, when a downlink signal including a signal sequence (CRS) is transmitted from the radio base station eNB1, it is possible to detect a peak for the signal sequence by performing cross-correlation processing (see FIG. 7). Thereby, in the user terminal UE, it can grasp | ascertain that the transmission point used as the transmission source of a downlink signal is the wireless base station eNB1. At the same time, since the user terminal UE knows in advance that the signal sequence is CRS, time synchronization and frequency synchronization can be secured from the CRS.

  In the above description, a case has been described in which the synchronization-related information is configured by identification information of a radio base station serving as a transmission point and a signal sequence associated with this identification information. However, the configuration of the synchronization related information is not limited to this, and can be changed as appropriate. For example, it is possible to include multiple positions of signal sequences included in the synchronization-related information. In this case, in the user terminal UE, time synchronization is performed from the signal sequence included in the downlink signal and the multiplexed position by grasping the identification information of the radio base station, the signal sequence and the multiplexed position thereof before the synchronization process. In addition, it is possible to ensure the frequency synchronization and specify the radio base station associated with this signal sequence.

  As the multiplexing position included in the synchronization related information, for example, the time at which the position where the signal sequence is multiplexed among the radio resources (resource element (RE)) constituting each subframe is temporally different. Multiple positions can be used. In this case, the time-multiplexed position of the signal sequence is used as the configuration information of the synchronization related information.

  FIG. 8 is an explanatory diagram of an example of a signal sequence in which the time multiplexing position included in the synchronization related information is changed. FIG. 8 shows a signal sequence multiplexed at a time multiplexing position included in the synchronization related information. In FIG. 8, the vertical axis and the horizontal axis indicate frequency and time, respectively, and three consecutive subframes 1 to 3 in the downlink are illustrated. In FIG. 8, the signal sequence constituting the preamble signal is indicated as “P”, and the transmission data for the user terminal UE is indicated as “DATA”. Note that the time-multiplexed positions of the signal sequences shown in FIGS. 8A to 8C are examples, and are not limited to this.

  FIG. 8A shows a case where a signal sequence is multiplexed on a radio resource arranged at the head of each subframe. Thus, when a signal sequence is multiplexed at the head part of a subframe, the buffering load of the received signal in the user terminal UE can be reduced. In addition, since a new carrier type (NCT) subframe does not have an existing PDCCH region, a PDCCH region in a general subframe may be used.

  FIG. 8B shows a case where a signal sequence is multiplexed on radio resources arranged at the head and tail of each subframe. In other words, the signal sequence is multiplexed before and after the transmission data of each subframe. As described above, when the signal sequence is multiplexed on the head portion and the tail portion of the subframe, the accuracy of frequency synchronization can be improved. That is, frequency synchronization is generally obtained by comparing the phases of two estimation target signals (reference signals) that are temporally separated. In this case, when two signals to be estimated are multiplexed on continuous radio resources, it is assumed that the difference is insufficient and the estimation accuracy deteriorates, as shown in FIG. 8B. By multiplexing the signal sequence in the part and the tail part, it is possible to estimate based on two estimation target signals that are temporally separated, and the accuracy of frequency synchronization can be improved.

  FIG. 8C shows a case where a signal sequence is spread and multiplexed in transmission data. Note that a signal sequence spreading method for transmission data can be determined in advance. When the signal sequence is spread and multiplexed in the transmission data in this way, it is possible to obtain a time diversity gain because the signal sequence can be transmitted to the user terminal UE while shifting the time within the subframe. .

  As described above, the synchronization-related information is divided into identification information (for example, cell ID) of the radio base station serving as a transmission point, a signal sequence associated with the identification information, and a position where the signal sequence is multiplexed (time multiplexed position). When configured, it is possible to give meaning to the multiplexed position of the signal sequence itself. Thereby, even if the signal sequences are the same, they can be handled as different signal sequences by changing the time multiplexing position.

  In the example illustrated in FIG. 7, in the synchronization-related information held in the user terminal UE, the CRS arranged at the head portion of each subframe is defined as the signal sequence of the radio base station eNB1, and the signal of the radio base station eNB2 A case is assumed in which CRSs arranged at the head and tail of each subframe are defined as sequences, and CRSs spread in transmission data are defined as signal sequences of the radio base station eNB3.

  When receiving the downlink signal, the user terminal UE performs cross-correlation processing on three types of signal sequences (CRSs arranged at different time multiplexed positions) defined in the synchronization-related information. Specifically, the user terminal UE calculates the correlation between the signal sequence replica held in association with each signal sequence and the downlink signal. For example, when a downlink signal including a signal sequence (CRS arranged at the head portion of each subframe) is transmitted from the radio base station eNB1, it is possible to detect a peak for the signal sequence by performing cross-correlation processing. (See FIG. 7). Thereby, in the user terminal UE, it can grasp | ascertain that the transmission point used as the transmission source of a downlink signal is the wireless base station eNB1. At the same time, since the user terminal UE knows in advance that the signal sequence is CRS, time synchronization and frequency synchronization can be secured from this CRS.

  Note that a preamble signal including such a signal sequence can be switched for each subframe. For example, a subframe 1 transmits a preamble signal in which a signal sequence is multiplexed at the beginning of the subframe, a subframe 2 multiplexes a preamble signal in which the signal sequence is multiplexed at the beginning and tail of the subframe, and a subframe 3 has a signal sequence. Can be transmitted in the transmission data and transmitted. In this case, since synchronization processing can be performed between different transmission points every 1 millisecond, it is possible to switch transmission points at high speed when CoMP DPS is applied.

  In addition, switching a preamble signal including such a signal sequence periodically (for example, every 5 milliseconds) or transmitting a preamble signal in response to a transmission request (trigger) from the user terminal UE is an overhead. It is preferable from the viewpoint. In the former, unnecessary synchronization processing can be suppressed, for example, by associating or associating the cycle of switching the signal sequence included in the preamble signal with the switching cycle of the transmission point of CoMP, and the load associated with the synchronization processing in the user terminal UE Can be reduced.

  Furthermore, as a multiplexing position included in the synchronization-related information, a frequency multiplexing position in which the position where the signal sequence is multiplexed is different among the radio resources (resource elements (RE)) constituting each subframe is used. be able to. In this case, the frequency multiplex position of the signal sequence is used as the configuration information of the synchronization related information.

  FIG. 9 is an explanatory diagram of an example of a signal sequence in which the frequency multiplexing position included in the synchronization-related information is changed. In FIG. 9, the vertical axis and the horizontal axis indicate frequency and time, respectively. Specifically, 20 MHz is shown as a frequency band constituting the transmission band, and a single subframe in the downlink is shown. Further, in FIG. 9, the signal series constituting the preamble signal is indicated as “P”. Note that the frequency multiplexing positions of the signal sequences shown in FIGS. 9A to 9C are examples, and are not limited thereto.

  FIG. 9A shows a case where the signal sequence is multiplexed in the highest frequency band among the radio resources arranged at the head of the subframe. Similarly, FIG. 9B shows a case where a signal sequence is multiplexed in a frequency band arranged near the center of the transmission frequency among the radio resources arranged at the head of the subframe. FIG. 9C shows a case where the signal sequence is multiplexed in the lowest frequency band among the radio resources arranged at the head of the subframe.

  As described above, the synchronization-related information is divided into the identification information (for example, cell ID) of the radio base station serving as the transmission point, the signal sequence associated with this identification information, and the position where the signal sequence is multiplexed (frequency multiplexed position). When configured, it is possible to give meaning to the multiplexed position of the signal sequence itself. Thereby, even if the signal sequence is the same, it can be handled as a different signal sequence by changing the frequency multiplexing position.

  In the example illustrated in FIG. 7, the synchronization-related information held in the user terminal UE defines a CRS arranged at the highest frequency position of the transmission frequency as the signal sequence of the radio base station eNB1, and the radio base station eNB2 Assume that a CRS arranged near the center of the transmission frequency is defined as the signal sequence, and a CRS arranged at the lowest frequency position of the transmission frequency is defined as the signal sequence of the radio base station eNB3.

  When the downlink signal is received, the user terminal UE performs cross-correlation processing on three types of signal sequences (CRSs arranged at different frequency multiplexing positions) defined in the synchronization related information. Specifically, the user terminal UE calculates the correlation between the signal sequence replica held in association with each signal sequence and the downlink signal. For example, when a downlink signal including a signal sequence (CRS arranged at the highest frequency position of the transmission frequency) is transmitted from the radio base station eNB1, it is possible to detect a peak for the signal sequence by performing cross-correlation processing (See FIG. 7). Thereby, in the user terminal UE, it can grasp | ascertain that the transmission point used as the transmission source of a downlink signal is the wireless base station eNB1. At the same time, since the user terminal UE knows in advance that the signal sequence is CRS, time synchronization and frequency synchronization can be secured from this CRS.

  Here, a case is described in which the frequency level in the transmission band is changed as the frequency position (frequency multiplexing position) where the signal series is multiplexed. However, the frequency multiplexing position of the signal sequence is not limited to this. For example, the frequency multiplexing position of the signal sequence may be changed. For example, it may be distributed and arranged (Distribute arrangement), may be arranged locally (Localize arrangement), or may be arranged over the entire transmission band (Full band arrangement). Furthermore, the above-described signal sequence time-multiplexed position and frequency-multiplexed position may be used in combination.

  In addition to the above-described information (for example, radio base station identification information, signal sequence, etc.), the configuration of synchronization-related information can also include a demodulation reference signal sequence for a received signal associated with the signal sequence. In this case, since the user terminal UE can grasp the reference signal sequence for demodulating the received signal based on the signal sequence constituting the preamble signal, it can easily demodulate the received signal without requiring any special processing. It becomes possible.

  In the above description, the synchronization-related information includes identification information (for example, a cell ID) of a radio base station serving as a transmission point and a signal sequence associated with this identification information. The case of assigning a series is described. However, the configuration of the synchronization related information is not limited to this, and can be changed as appropriate. For example, it is good also as a structure which assigns a signal sequence uniquely to the user terminal UE.

  In this case, the synchronization-related information can be composed of, for example, a signal sequence unique to the user terminal UE and a demodulation reference signal sequence for a received signal associated with this signal sequence. The reference signal sequence for demodulating the received signal is unique to the user terminal UE, similarly to the signal sequence. In this case, for example, in the user terminal UE, the signal sequence unique to the user terminal UE and the demodulation reference signal sequence of the received signal are grasped before the synchronization process, and are included in the downlink signal. It is possible to ensure time synchronization and frequency synchronization from the signal sequence and to appropriately demodulate the received signal associated with this signal sequence.

  Note that the signal sequence included in the synchronization-related information can be configured in the same manner as in the above-described example (that is, an example in which a signal sequence is uniquely assigned to a transmission point). Also, the multiplexing position (time multiplexing position, frequency multiplexing position) of the signal sequence can be configured in the same manner as in the above-described example. Furthermore, the notification of the synchronization related information can also be notified to the user terminal UE using, for example, higher layer signaling (for example, RRC signaling).

  The operation when the synchronization related information is defined in this way will be described with reference to FIG. FIG. 10 is a diagram for explaining the operation of the user terminal UE based on synchronization-related information defined by the radio communication method according to the present embodiment. FIG. 10 shows a case where a specific signal sequence (sequence 1) is assigned to the user terminal UE.

  Here, it is assumed that the user terminal UE holds synchronization-related information including a signal sequence unique to the user terminal UE and a reference signal sequence for demodulation of a received signal associated with the signal sequence. In this synchronization related information, CRS is defined as a signal sequence unique to the user terminal UE, and DM-RS is defined as a demodulation reference signal sequence for a received signal associated with this CRS.

  When the downlink signal is received, the user terminal UE performs a cross-correlation process on a unique signal sequence (CRS) defined in the synchronization related information. Specifically, the user terminal UE calculates the correlation between the signal sequence replica held in association with the specific signal sequence and the downlink signal. In this case, in the user terminal UE, as shown in FIG. 10, peak detection can be performed at the timing when the unique signal sequence is received. As a result, the user terminal UE cannot grasp the transmission point that is the transmission source of the downlink signal, but appropriately grasps the demodulation reference signal sequence (DM-RS) of the received signal in advance. The received signal can be demodulated, and time synchronization and frequency synchronization can be ensured.

  The second aspect of the present invention transmits synchronization related information indicating whether or not a plurality of radio base stations are synchronized to the user terminal UE, and based on this synchronization related information, the user terminal UE The necessity of synchronization processing with the radio base station is determined, and when the radio base station that is the transmission point is not synchronized, the synchronization processing of the downlink signal transmitted from the radio base station is performed .

  In the network configuration in which the small cells S are densely arranged on the area of the macro cell M, the macro cell M and the small cell S connected by the backhaul link using the X2 interface or the like is generally connected to the user terminal UE. The transmission timing of transmission data is synchronized. On the other hand, cells other than between the cells synchronized in this way are generally not synchronized. Such synchronization-related information regarding synchronization / asynchronization between cells can be grasped in advance on the network (wireless base station) side.

  In the second aspect of the present invention, such synchronization-related information regarding synchronization / asynchronization between cells is transmitted to the user terminal UE, which is used as a material for determining the necessity of synchronization processing in the user terminal UE. The user terminal UE determines the necessity of synchronization processing with the radio base station serving as a transmission point based on the content of the synchronization-related information, and synchronizes the downlink signal transmitted from the radio base station serving as the transmission point. Process. As a result, the synchronization process can be performed only when necessary with the radio base station serving as a transmission point, so the synchronization process between the synchronized radio base stations can be omitted, and the synchronization process in the user terminal UE Can be reduced.

  Note that in the second aspect, the synchronization-related information related to synchronization / asynchronization is not limited to the case where synchronization is substantially ensured by wired connection as described above. For example, based on factors such as delay spread, Doppler spread, Doppler shift, average gain, average delay, etc., quasi co-location (hereinafter, Whether it is simply “co-location” or not may be determined based on whether it is synchronous or asynchronous. That is, the case where it is a co-location can be recognized as synchronized, while the case where it is not a co-location can be recognized as not synchronized.

  In this case, as synchronization-related information, for example, a group of cells (for example, small cells) that are co-location (hereinafter referred to as “co-location group”) is grasped in advance, and this co-location group is used as the user terminal. The UE can be notified. In the user terminal UE, the necessity of the synchronization process for the downlink signal is determined based on the relationship notified in the co-location group and the relationship with the radio base station serving as the transmission point. In this case, when a radio base station belonging to the same co-location group as the currently communicating radio base station becomes a transmission point, synchronization processing for a downlink signal from the radio base station can be omitted. , The load associated with the synchronization process can be reduced.

  FIG. 11 is an explanatory diagram of radio base stations belonging to the co-location group. FIG. 11 shows two co-location groups A and B and radio base stations belonging to these co-location groups. The radio base stations eNB1 to eNB4 belong to the co-location group A, and the radio base stations eNB5 to eNB8 belong to the co-location group B. Further, in FIG. 11, the movement path of the user terminal UE is indicated by an arrow A.

  In the example illustrated in FIG. 11, for example, the user terminal UE performs radio communication with the radio base stations eNB1, eNB2, and eNB3 belonging to the co-location group A and then belongs to the co-location group B. Wireless communication is performed between the eNB 5 and the eNB 6. Since the radio base stations eNB1, eNB2, and eNB3 are synchronized with each other, and that fact (that is, belonging to the same co-location group) is notified as synchronization related information, in the user terminal UE, the radio base station After ensuring synchronization with the station eNB1, there is no need to perform synchronization processing between the radio base stations eNB2 and eNB3.

  On the other hand, the radio base station eNB5 belonging to the co-location group B is not synchronized with the radio base station eNB3, and that fact (that is, belonging to a different co-location group) is notified as synchronization related information. In the user terminal UE, it is necessary to perform a synchronization process with the radio base station eNB5. In addition, since the radio base stations eNB5 and eNB6 are synchronized with each other and the fact is notified as synchronization-related information, the user terminal UE secures synchronization with the radio base station eNB5, and then the radio base station eNB6 There is no need to synchronize with the.

  That is, in the movement route illustrated in FIG. 11, the user terminal UE may perform synchronization processing with one radio base station belonging to the co-location group. Then, after ensuring the synchronization, there is no need to perform the synchronization process unless moving across the co-location group. As a result, the number of synchronization processes can be reduced, and the load associated with the synchronization process can be reduced.

  Note that this co-location group can be signaled by adding an index (identifier) corresponding to the co-location group when configuring CSI-RS, for example. FIG. 11 illustrates information signaled to the user terminal UE in association with the respective radio base stations eNB1 to eNB8. Here, for convenience of explanation, not the index corresponding to the co-location group but the type of the co-location group is shown.

  Regarding the radio base station eNB1, the user terminal UE is signaled with the number “13” as CSI-RS configuration, and with the co-location group A to which the radio base station eNB1 belongs. Similarly, regarding the radio base stations eNB2, eNB3, and eNB4, numbers “1”, “7”, and “8” are signaled as CSI-RS configuration, respectively, and the co-location group to which these radio base stations eNB belong A is signaled.

  On the other hand, regarding the radio base station eNB5, the number “16” is signaled to the user terminal UE as CSI-RS configuration, and the co-location group B to which the radio base station eNB1 belongs is signaled. Similarly, regarding the radio base stations eNB6, eNB7, and eNB8, numbers “10”, “5”, and “4” are signaled as CSI-RS configuration, respectively, and co-location groups to which these radio base stations eNB belong B is signaled.

  The user terminal UE can determine whether synchronization processing is necessary based on the content signaled in addition to such CSI-RS configuration. In this case, since the index of the co-location group is notified in addition to the existing CSI-RS configuration, the necessity of synchronization processing is transmitted to the user terminal UE without requiring a significant change. be able to.

  Here, a case is described in which the index of the co-location group is added to the CSI-RS configuration on the assumption that the synchronization processing in the user terminal UE is performed using CSI-RS. However, the signaling target to which the co-location group index is added is not limited to CSI-RS configuration, and can be changed as appropriate.

  FIG. 12 is a diagram illustrating an example of a table for managing an index of a co-location group. In the table shown in FIG. 12, contents belonging to three co-location groups A to C (indexes 1 to 3) and contents not belonging to any co-location group A to C are defined ( Index 0). In this case, the indexes 0 to 4 are represented by 2 bits. For example, index 0 is represented by “00”, and index 1 is represented by “01”. Similarly, the index 2 is represented by “10”, and the index 3 is represented by “11”.

  In the example illustrated in FIG. 11, bit information “01” is added in the CSI-RS configuration corresponding to the radio base stations eNB1 to eNB4 belonging to the co-location group A. On the other hand, in the CSI-RS configuration corresponding to the radio base stations eNB5 to eNB8 belonging to the co-location group B, bit information “10” is added.

  Further, when the radio base station does not belong to any co-location group, bit information “00” is added in the CSI-RS configuration. Since it is signaled when it does not belong to any co-location group, the user terminal UE can clearly grasp that synchronization processing is necessary for the corresponding radio base station. .

  Further, as the synchronization related information, information related to co-location with the reference radio base station (hereinafter referred to as “co-location information”) can be notified to the user terminal UE. Note that, as a reference radio base station, for example, a radio base station with which the user terminal UE is currently communicating, a radio base station that manages a macro cell (macro base station), or the like can be designated. By notifying such co-location information, the user terminal UE needs to perform synchronization processing with a radio base station that is a transmission point based on the co-location information between the user base UE and the reference radio base station. It is possible to determine whether or not.

  As the co-location information, for example, information indicating whether or not the co-location with the reference radio base station can be notified to the user terminal UE. In this case, the necessity of synchronization processing with the radio base station serving as a transmission point is clearly determined according to information indicating whether or not it is a co-location with the reference radio base station. It becomes possible to do.

  Further, as the co-location information, for example, information indicating how much time difference is present from the co-location state with the reference radio base station can be notified to the user terminal UE. . In this case, synchronization with the radio base station serving as a transmission point is performed according to information indicating how much time difference exists from the co-location state with the reference radio base station. It becomes possible to clearly determine whether processing is necessary.

  The temporal difference can be expressed by a plurality of bit information. For example, when four types of synchronization states are indicated, they can be represented by 2-bit bit information. For example, “00” indicates that it is not co-location (that is, that it is asynchronous) with a reference radio base station, and it indicates that it is not completely synchronized but is synchronized with high accuracy. 01 ". Similarly, “10” indicates that synchronization with a reference radio base station is performed with a lower accuracy than the synchronization state indicated by “01”, and the synchronization indicated by “10”. “11” can be used to indicate that synchronization is performed in a state where the accuracy is further lowered than the state.

  The synchronization state indicated by these bit information “01”, “10” and “11” can be designated as a numerical value. These numerical values may be predetermined numerical values or may be designated from the radio base station. In particular, in the latter case, a numerical value (time) indicating the synchronization state can be appropriately designated, so that synchronization can be flexibly ensured while changing the synchronization accuracy.

  By the way, when carrier aggregation (CA) is applied at the time of data transmission, the user terminal UE has to perform synchronization processing for each cell (radio base station) corresponding to the component carrier (CC). In this case, the radio communication method according to the second aspect can be applied to a CC to be CA. That is, synchronization related information indicating whether or not the radio base stations corresponding to each CC are synchronized is transmitted to the user terminal UE, and between the radio base stations in the user terminal UE based on the synchronization related information The necessity of the synchronization process is determined, and when a specific radio base station is not synchronized, the downlink signal transmitted from the radio base station can be synchronized.

  FIG. 13 shows cells 1 to 5 corresponding to CC # 1 to CC # 5 to be CA. Here, it is assumed that the cell 1 is a primary cell (PCell) and the cells 2 to 5 are secondary cells (SCell). In signaling related to existing co-location (hereinafter referred to as “co-location signaling”), for example, PDSCH allocated to CC # 3 is associated with CC # 3 number “7” as CSI-RS configuration. Is signaled. That is, existing co-location signaling is performed within a single CC.

  On the other hand, when applying the radio communication method in the second aspect, by notifying the user terminal UE of synchronization related information indicating whether or not the radio base stations corresponding to each CC is synchronized, In the user terminal UE, it is possible to determine the necessity of synchronization processing with the radio base station corresponding to each CC, and the number of downlink signal synchronization processing can be reduced. As a result, even when CA is applied at the time of data transmission to the user terminal UE, it is possible to reduce the load associated with the synchronization process in the user terminal UE.

  As a method for notifying the user terminal UE of synchronization-related information indicating whether or not radio base stations corresponding to each CC are synchronized, for example, the above-described co-location group for each radio base station corresponding to the CC A corresponding index can be added and signaled. For example, as shown in FIG. 13, the fact that the radio base stations corresponding to CC # 1 to CC # 3 (cell 1 to cell 3) belong to co-location group A, CC # 4, CC # 5 (cell 4, The user terminal UE can be notified that the radio base station corresponding to the cell 5) belongs to the co-location group B. In this case, it is possible to avoid a situation where the synchronization process is performed for each CC in the user terminal UE, and it is possible to reduce a load associated with the synchronization process in the user terminal UE.

  Further, as a method of notifying the user terminal UE of synchronization-related information indicating whether or not radio base stations corresponding to each CC are synchronized, co-location signaling can be performed across CCs to be CA. For example, the PDSCH assigned to CC # 2 is signaled as being associated with CC # 1 number “5” as CSI-RS configuration. By performing co-location signaling in this way, the user terminal UE can grasp that the radio base station corresponding to CC # 2 is synchronized with the radio base station corresponding to CC # 1, and CC # The synchronization process with the radio base station corresponding to 2 can be omitted.

  Further, as a method of notifying the user terminal UE of synchronization-related information indicating whether or not the radio base stations corresponding to each CC are synchronized, co-location with the radio base station corresponding to the reference CC Information can also be notified to the user terminal UE. As described above, the co-location information includes information indicating whether or not the co-location with the radio base station corresponding to the reference CC or the reference radio base station. , Information indicating how much time difference is present from the co-location state can be notified.

  Note that, as the radio base station corresponding to the reference CC, for example, a radio base station corresponding to the primary cell can be selected. When all the secondary cells are co-location with the primary cell, the user terminal UE performs a synchronization process only once with the radio base station managing the primary cell, and the radio base stations corresponding to all CCs Synchronization can be established. Note that the radio base station corresponding to the reference CC is not limited to the radio base station corresponding to the primary cell, and can be changed as appropriate.

(Configuration of wireless communication system)
FIG. 14 is a schematic configuration diagram of a radio communication system according to the present embodiment. Note that the radio communication system illustrated in FIG. 14 is a system including, for example, an LTE system or SUPER 3G. In this radio communication system, carrier aggregation in which a plurality of basic frequency blocks (component carriers) with the system bandwidth of the LTE system as one unit is integrated is applied. Further, this radio communication system may be called IMT-Advanced, or may be called 4G, FRA (Future Radio Access).

  The radio communication system 1 shown in FIG. 14 includes a radio base station 11 that forms a macro cell C1, and radio base stations 12a and 12b that are arranged in the macro cell C1 and form a small cell C2 that is narrower than the macro cell C1. . Moreover, the user terminal 20 is arrange | positioned at the macrocell C1 and each small cell C2. The user terminal 20 is configured to be capable of wireless communication with both the wireless base station 11 and the wireless base station 12.

  Communication between the user terminal 20 and the radio base station 11 is performed using a carrier having a relatively low frequency band (for example, 2 GHz) and a wide bandwidth (referred to as an existing carrier or a legacy carrier). On the other hand, between the user terminal 20 and the radio base station 12, a carrier having a relatively high frequency band (for example, 3.5 GHz) and a narrow bandwidth may be used. The same carrier may be used. The wireless base station 11 and each wireless base station 12 are wired or wirelessly connected.

  The radio base station 11 and each radio base station 12 are connected to the upper station apparatus 30 and connected to the core network 40 via the upper station apparatus 30. The upper station device 30 includes, for example, an access gateway device, a radio network controller (RNC), a mobility management entity (MME), and the like, but is not limited thereto. Further, each radio base station 12 may be connected to a higher station apparatus via the radio base station 11.

  The radio base station 11 is a radio base station having a relatively wide coverage, and may be referred to as an eNodeB, a radio base station apparatus, a transmission point, or the like. The radio base station 12 is a radio base station having local coverage, and may be called a pico base station, a femto base station, a Home eNodeB, an RRH (Remote Radio Head), a micro base station, a transmission point, or the like. Good. Hereinafter, when the radio base stations 11 and 12 are not distinguished, they are collectively referred to as a radio base station 10. Each user terminal 20 is a terminal that supports various communication schemes such as LTE and LTE-A, and may include not only mobile communication terminals but also fixed communication terminals.

  In a radio communication system, OFDMA (Orthogonal Frequency Division Multiple Access) is applied to the downlink and SC-FDMA (Single Carrier Frequency Division Multiple Access) is applied to the uplink as radio access schemes. OFDMA is a multi-carrier transmission scheme that performs communication by dividing a frequency band into a plurality of narrow frequency bands (subcarriers) and mapping data to each subcarrier. SC-FDMA is a single-carrier transmission scheme that reduces interference between terminals by dividing the system bandwidth into bands composed of one or continuous resource blocks for each terminal, and a plurality of terminals using different bands. is there.

  Here, communication channels used in the wireless communication system shown in FIG. 14 will be described. The downlink communication channel has PDSCH shared by each user terminal 20 and downlink L1 / L2 control channels (PDCCH, PCFICH, PHICH, extended PDCCH). User data and higher control information are transmitted by the PDSCH. PDSCH and PUSCH scheduling information and the like are transmitted by the PDCCH. The number of OFDM symbols used for PDCCH is transmitted by PCFICH (Physical Control Format Indicator Channel). HARQ ACK / NACK for PUSCH is transmitted by PHICH (Physical Hybrid-ARQ Indicator Channel). Also, PDSCH and PUSCH scheduling information and the like may be transmitted by an extended PDCCH (also called Enhanced Physical Downlink Control Channel, ePDCCH, E-PDCCH, FDM type PDCCH, etc.). This enhanced PDCCH (enhanced downlink control channel) is frequency-division multiplexed with PDSCH (downlink shared data channel), and is used to compensate for the lack of PDCCH capacity.

  The uplink communication channel includes a PUSCH (Physical Uplink Shared Channel) as an uplink data channel shared by each user terminal 20 and a PUCCH (Physical Uplink Control Channel) that is an uplink control channel. User data and higher control information are transmitted by this PUSCH. Also, downlink radio quality information (CQI: Channel Quality Indicator), ACK / NACK, and the like are transmitted by PUCCH.

  FIG. 15 is an overall configuration diagram of the radio base station 10 (including the radio base stations 11 and 12) according to the present embodiment. The radio base station 10 includes a plurality of transmission / reception antennas 101 for MIMO transmission, an amplifier unit 102, a transmission / reception unit 103, a baseband signal processing unit 104, a call processing unit 105, and a transmission path interface 106. Yes.

  User data transmitted from the radio base station 10 to the user terminal 20 via the downlink is input from the higher station apparatus 30 to the baseband signal processing unit 104 via the transmission path interface 106.

  The baseband signal processing unit 104 performs PDCP layer processing, user data division / combination, RLC layer transmission processing such as RLC (Radio Link Control) retransmission control transmission processing, MAC (Medium Access Control) retransmission control, for example, HARQ transmission processing, scheduling, transmission format selection, channel coding, inverse fast Fourier transform (IFFT) processing, and precoding processing are performed and transferred to each transceiver 203. The downlink control channel signal is also subjected to transmission processing such as channel coding and inverse fast Fourier transform, and is transferred to each transceiver 103.

  Moreover, the baseband signal processing part 104 notifies the control information for communication in the said cell with respect to the user terminal 20 with an alerting | reporting channel. The information for communication in the cell includes, for example, the system bandwidth in the uplink or the downlink.

  Each transmission / reception unit 103 converts the baseband signal output by precoding for each antenna from the baseband signal processing unit 104 to a radio frequency band. The amplifier unit 102 amplifies the frequency-converted radio frequency signal and transmits the amplified signal using the transmitting / receiving antenna 101. The transmission / reception unit 103 functions as a transmission unit that transmits a downlink signal multiplexed with a preamble signal to the user terminal 20.

  On the other hand, for data transmitted from the user terminal 20 to the radio base station 10 via the uplink, radio frequency signals received by the respective transmission / reception antennas 101 are amplified by the amplifier units 102 and frequency-converted by the respective transmission / reception units 103. It is converted into a baseband signal and input to the baseband signal processing unit 104.

  The baseband signal processing unit 104 performs FFT processing, IDFT processing, error correction decoding, MAC retransmission control reception processing, RLC layer, and PDCP layer reception processing on user data included in the input baseband signal. The data is transferred to the higher station apparatus 30 via the transmission path interface 106. The call processing unit 105 performs call processing such as communication channel setting and release, status management of the radio base station 10, and radio resource management.

  FIG. 16 is an overall configuration diagram of the user terminal 20 according to the present embodiment. The user terminal 20 includes a plurality of transmission / reception antennas 201 for MIMO transmission, an amplifier unit 202, a transmission / reception unit (reception unit) 203, a baseband signal processing unit 204, and an application unit 205.

  For downlink data, radio frequency signals received by a plurality of transmission / reception antennas 201 are respectively amplified by an amplifier unit 202, frequency-converted by a transmission / reception unit 203, and converted into a baseband signal. The baseband signal is subjected to FFT processing, error correction decoding, retransmission control reception processing, and the like by the baseband signal processing unit 204. Among the downlink data, downlink user data is transferred to the application unit 205. The application unit 205 performs processing related to layers higher than the physical layer and the MAC layer. Also, broadcast information in the downlink data is also transferred to the application unit 205.

  On the other hand, uplink user data is input from the application unit 205 to the baseband signal processing unit 204. The baseband signal processing unit 204 performs retransmission control (H-ARQ (Hybrid ARQ)) transmission processing, channel coding, precoding, DFT processing, IFFT processing, and the like, and forwards them to each transmission / reception unit 203. The transmission / reception unit 203 converts the baseband signal output from the baseband signal processing unit 204 into a radio frequency band. Thereafter, the amplifier unit 202 amplifies the frequency-converted radio frequency signal and transmits the amplified signal using the transmission / reception antenna 201.

  The transmission / reception unit 203 functions as a reception unit that receives a downlink signal multiplexed with a preamble signal.

  FIG. 17 is a block diagram showing a configuration of baseband signal processing section 104 in the radio base station shown in FIG. The baseband signal processing unit 104 mainly includes a layer 1 processing unit 1041, a MAC processing unit 1042, an RLC processing unit 1043, a synchronization related information generating unit 1044, and a multiplexing unit 1045.

  The layer 1 processing unit 1041 mainly performs processing related to the physical layer. For example, the layer 1 processing unit 1041 performs channel decoding, Discrete Fourier Transform (DFT), frequency demapping, and inverse fast Fourier transform (IFFT) on a signal received on the uplink. Processing such as data demodulation. Further, the layer 1 processing unit 1041 performs processing such as channel coding, data modulation, frequency mapping, and inverse fast Fourier transform (IFFT) on a signal transmitted on the downlink.

  The MAC processing unit 1042 performs processing such as retransmission control at the MAC layer for a signal received in the uplink, scheduling for the uplink / downlink, selection of a PUSCH / PDSCH transmission format, selection of a PUSCH / PDSCH resource block, and the like. .

  The RLC processing unit 1043 performs packet division, packet combination, retransmission control in the RLC layer, etc. on packets received on the uplink / packets transmitted on the downlink.

  The synchronization related information generation unit 1044 constitutes a generation unit, and generates synchronization related information related to time synchronization and frequency synchronization of downlink signals. For example, the synchronization-related information generation unit 1044 generates synchronization-related information including identification information (for example, a cell ID) of a radio base station serving as a transmission point and a signal sequence associated with the identification information (first aspect) ). In addition to the identification information of the radio base station and the signal sequence associated with the identification information, the synchronization-related information generation unit 1044 includes a multiplexed position of the signal sequence and a reference signal sequence for demodulation of the received signal associated with the signal sequence. Synchronization-related information is generated (first aspect). Furthermore, the synchronization related information generation unit 1044 generates synchronization related information related to synchronization / asynchronization between cells (second aspect). The synchronization related information generated by the synchronization related information generation unit 1044 is notified to the user terminal 20 through, for example, higher layer signaling (for example, RRC signaling or notification).

  The multiplexing unit 1045 multiplexes the preamble signal having the signal sequence included in the synchronization related information on the downlink signal based on the synchronization related information generated by the synchronization related information generation unit 1044. Multiplexer 1045 multiplexes the signal sequence included in the synchronization-related information with the radio resource to which the downlink signal is assigned according to the content defined in the synchronization-related information. For example, the multiplexing unit 1045 multiplexes the preamble signal at a time multiplexing position or a frequency multiplexing position defined in the synchronization related information (first aspect). The downlink signal on which the preamble signal is multiplexed by the multiplexing unit 1045 is output to the transmission / reception unit 203 via the layer 1 processing unit 1041, and is transmitted to the user terminal 20 on the downlink.

  18 is a block diagram showing a configuration of the baseband signal processing unit 204 in the user terminal 20 shown in FIG. The baseband signal processing unit 204 mainly includes a layer 1 processing unit 2041, a MAC processing unit 2042, an RLC processing unit 2043, a synchronization related information holding unit 2044, and a synchronization processing unit 2045.

  The layer 1 processing unit 2041 mainly performs processing related to the physical layer. For example, the layer 1 processing unit 2041 performs processing such as channel decoding, discrete Fourier transform (DFT), frequency demapping, inverse fast Fourier transform (IFFT), and data demodulation on a signal received on the downlink. Further, the layer 1 processing unit 2041 performs processing such as channel coding, data modulation, frequency mapping, and inverse fast Fourier transform (IFFT) on a signal transmitted on the uplink.

  The MAC processing unit 2042 performs retransmission control (HARQ) at the MAC layer for a signal received on the downlink, analysis of downlink scheduling information (specification of PDSCH transmission format, identification of PDSCH resource block), and the like. In addition, the MAC processing unit 2042 performs processing such as MAC retransmission control for signals transmitted on the uplink, analysis of uplink scheduling information (specification of PUSCH transmission format, specification of PUSCH resource block), and the like.

  The RLC processing unit 2043 performs packet division, packet combination, retransmission control in the RLC layer, etc. on packets received on the downlink / packets transmitted on the uplink.

  The synchronization related information holding unit 2044 constitutes a holding unit, and holds the synchronization related information generated by the synchronization related information generation unit 1044 of the radio base station 10. For example, the synchronization related information holding unit 2044 holds synchronization related information notified by higher layer signaling (for example, RRC signaling). For example, the synchronization related information holding unit 2044 holds synchronization related information including identification information (for example, a cell ID) of a radio base station serving as a transmission point and a signal sequence associated with the identification information (first aspect) ). In addition to the identification information of the radio base station and the signal sequence associated with this identification information, the synchronization-related information holding unit 2044 includes a multiplexed position of the signal sequence and a reference signal sequence for demodulation of the received signal associated with the signal sequence. Holds synchronization-related information (first aspect). When synchronization related information is determined in advance in the user terminal 20 and the plurality of radio base stations 10, the synchronization related information holding unit 2044 holds the synchronization related information.

  Further, the synchronization related information holding unit 2044 can hold synchronization related information related to synchronization / asynchronization between cells generated in the synchronization related information holding unit 2044 (second aspect). For example, the synchronization related information holding unit 2044 holds information regarding the co-location group as the synchronization related information. In particular, information regarding the co-location group managed by the table shown in FIG. 12 may be held. The synchronization related information holding unit 2044 holds co-location information as the synchronization related information.

  The synchronization processing unit 2045 performs downlink signal synchronization processing using the synchronization related information held by the synchronization related information holding unit 2044 and the signal sequence included in the preamble signal received from the radio base station 10. For example, the synchronization processing unit 2045 performs downlink signal synchronization processing based on the correlation calculation result between the signal sequence of the synchronization related information held in the synchronization related information holding unit 2044 and the signal sequence of the preamble signal ( First aspect). In addition, the synchronization processing unit 2045 determines whether synchronization processing is necessary based on the synchronization related information held by the synchronization related information holding unit 2044. Then, when synchronization processing is necessary, synchronization processing is performed with a radio base station that is a downlink signal transmission source (second aspect).

  Although the present invention has been described in detail using the above-described embodiments, it is obvious to those skilled in the art that the present invention is not limited to the embodiments described in this specification. The present invention can be implemented as modified and changed modes without departing from the spirit and scope of the present invention defined by the description of the scope of claims. For example, the above-described plurality of aspects can be applied in appropriate combination. Therefore, the description of the present specification is for illustrative purposes and does not have any limiting meaning to the present invention.

DESCRIPTION OF SYMBOLS 1 Wireless communication system 10 Wireless base station 20 User terminal 30 Host station apparatus 40 Core network 201 Transmission / reception antenna 202 Amplifier part 203 Transmission / reception part 204 Baseband signal processing part 205 Application part 101 Transmission / reception antenna 102 Amplifier part 103 Transmission / reception part 104 Baseband signal processing Unit 105 Call processing unit 106 Transmission path interface 1041, 2041 Layer 1 processing unit 1042, 2042 MAC processing unit 1043, 2043 RLC processing unit 1044 Synchronization related information generation unit 1045 Multiplexing unit 2044 Synchronization related information holding unit 2045 Synchronization processing unit

Claims (9)

A radio communication system comprising a plurality of radio base stations and a user terminal capable of cooperative multipoint transmission with the plurality of radio base stations,
The radio base station includes a generation unit that generates synchronization related information related to time synchronization and frequency synchronization of a downlink signal, and a multiplexing unit that multiplexes a preamble signal having a signal sequence included in the synchronization related information on the downlink signal And a transmission unit that transmits a downlink signal multiplexed with the preamble signal to the user terminal,
The user terminal includes a holding unit that holds the synchronization-related information generated by the generation unit, a receiving unit that receives a downlink signal in which the preamble signal is multiplexed, and the synchronization-related held by the holding unit A wireless communication system, comprising: a synchronization processing unit that performs synchronization processing of a downlink signal using information and the signal sequence included in the preamble signal.   The radio communication system according to claim 1, wherein the synchronization related information includes identification information for identifying the radio base station, and the signal sequence is associated with identification information of the radio base station.   The radio communication system according to claim 2, wherein the synchronization related information includes a time-multiplexed position and / or a frequency-multiplexed position of the signal sequence for a radio resource.   The synchronization-related information includes the signal sequence unique to the user terminal and a reference signal sequence for demodulating a received signal in the user terminal, which is associated with the signal sequence. Wireless communication system.   The synchronization processing unit performs synchronization processing of a downlink signal based on a calculation result of a correlation between the signal sequence of the synchronization related information held in the holding unit and the signal sequence of the preamble signal. The wireless communication system according to claim 1.   The radio communication system according to claim 1, wherein the radio base station transmits the synchronization-related information generated by the generation unit to the user terminal using higher layer signaling. A wireless communication method comprising: a plurality of radio base stations; and a user terminal capable of cooperative multipoint transmission with the plurality of radio base stations,
In the radio base station, generating synchronization-related information related to time synchronization and frequency synchronization of a downlink signal, and multiplexing a preamble signal having a signal sequence included in the synchronization-related information to a downlink signal; Transmitting a downlink signal multiplexed with the preamble signal to the user terminal; holding the synchronization related information generated at the radio base station at the user terminal; and multiplexing the preamble signal And a step of receiving a downlink signal, and a step of performing a downlink signal synchronization process using the held synchronization-related information and the signal sequence included in the preamble signal. Communication method. A radio base station in a radio communication system comprising a plurality of radio base stations and a user terminal capable of cooperative multipoint transmission with the plurality of radio base stations,
A generating unit that generates synchronization-related information related to time synchronization and frequency synchronization of a downlink signal, a multiplexing unit that multiplexes a preamble signal having a signal sequence included in the synchronization-related information into a downlink signal, and the preamble signal And a transmitter that transmits the multiplexed downlink signal to the user terminal. A user terminal capable of cooperative multipoint transmission with a plurality of radio base stations,
A downlink signal generated by the radio base station and holding a synchronization related information related to time synchronization and frequency synchronization of a downlink signal, and a preamble signal having a signal sequence included in the synchronization related information is multiplexed And a synchronization processing unit that performs synchronization processing of a downlink signal using the synchronization-related information held in the holding unit and the signal sequence included in the preamble signal. User terminal.

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