US20160262091A1 - Base station, user terminal and radio communication method - Google Patents

Base station, user terminal and radio communication method Download PDF

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Publication number
US20160262091A1
US20160262091A1 US15/024,916 US201415024916A US2016262091A1 US 20160262091 A1 US20160262091 A1 US 20160262091A1 US 201415024916 A US201415024916 A US 201415024916A US 2016262091 A1 US2016262091 A1 US 2016262091A1
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Prior art keywords
discovery
small cell
user terminal
base station
measurement
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US15/024,916
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English (en)
Inventor
Hiroki Harada
Kazuaki Takeda
Satoshi Nagata
Hiroyuki Ishii
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NTT Docomo Inc
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NTT Docomo Inc
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Assigned to NTT DOCOMO, INC. reassignment NTT DOCOMO, INC. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: HARADA, HIROKI, ISHII, HIROYUKI, NAGATA, SATOSHI, TAKEDA, KAZUAKI
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W48/00—Access restriction; Network selection; Access point selection
    • H04W48/16—Discovering, processing access restriction or access information
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J11/00—Orthogonal multiplex systems, e.g. using WALSH codes
    • H04J11/0069—Cell search, i.e. determining cell identity [cell-ID]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J11/00—Orthogonal multiplex systems, e.g. using WALSH codes
    • H04J11/0069—Cell search, i.e. determining cell identity [cell-ID]
    • H04J11/0073—Acquisition of primary synchronisation channel, e.g. detection of cell-ID within cell-ID group
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J11/00—Orthogonal multiplex systems, e.g. using WALSH codes
    • H04J11/0069—Cell search, i.e. determining cell identity [cell-ID]
    • H04J11/0083—Multi-mode cell search, i.e. where several modes or systems can be used, e.g. backwards compatible, dual mode or flexible systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W24/00—Supervisory, monitoring or testing arrangements
    • H04W24/10—Scheduling measurement reports ; Arrangements for measurement reports
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W48/00—Access restriction; Network selection; Access point selection
    • H04W48/08—Access restriction or access information delivery, e.g. discovery data delivery
    • H04W48/12—Access restriction or access information delivery, e.g. discovery data delivery using downlink control channel
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W16/00—Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
    • H04W16/24—Cell structures
    • H04W16/32—Hierarchical cell structures

Definitions

  • the present invention relates to a base station, a user terminal and a radio communication method in a next-generation mobile communication system.
  • LTE Long term evolution
  • OFDMA Orthogonal Frequency Division Multiple Access
  • SC-FDMA Single Carrier Frequency Division Multiple Access
  • LTE-advanced LTE-advanced
  • LTE enhancement LTE enhancement
  • a HetNet Heterogeneous Network
  • small cells for example, pico cells, femto cells and so on
  • small cells for example, pico cells, femto cells and so on
  • a study is in progress to use carriers of different frequency bands between the macro cell (macro base station) and the small cells (small base stations), in addition to the same frequency band.
  • Non-Patent Literature 1 3GPP TS 36.300 “Evolved UTRA and Evolved UTRAN Overall Description”
  • Non-Patent Literature 2 3GPP TR 36.814 “E-UTRA Further Advancements for E-UTRA Physical Layer Aspects”
  • small cells may be placed within the macro cell.
  • a novel small cell discovery mechanism small cell discovery is under study for introduction, to provide a method of allowing user terminals to efficiently discover and connect with the small cells.
  • the present invention has been made in view of the above, and it is therefore an object of the present invention to provide a base station, a user terminal and a radio communication method that enable adequate radio communication even when discovery signals for existing user terminals and small cell discovery/measurement signals coexist.
  • the base station of the present invention provides a base station that forms a macro cell having a coverage area to include a small cell, and that communicates with a user terminal that can connect with the small cell, and this base station has a commanding section that commands, with respect to a predetermined frequency, one or both of a first discovery process to use a synchronization signal transmitted from the small cell, and a second discovery process to use a discovery/measurement signal transmitted from the small cell, to the user terminal, and a transmitting section that, when the commanding section commands the second discovery process, transmits information about the parameters of the discovery/measurement signal to the user terminal.
  • FIG. 1 is a conceptual diagram of a HetNet
  • FIG. 2 is a diagram to explain example DS transmission timings in small cell discovery
  • FIG. 3 is a diagram to explain an overview of small cell discovery and legacy cell search
  • FIG. 4 is a diagram to explain a method of controlling small cell discovery and legacy cell search according to the present embodiment
  • FIG. 5 is a diagram to explain the small cell discovery operation in a user terminal in idle mode, according to the present embodiment
  • FIG. 6 is a schematic diagram to show an example of a radio communication system according to the present embodiment.
  • FIG. 7 is a diagram to explain an overall structure of a radio base station according to the present embodiment.
  • FIG. 8 is a diagram to explain a functional structure of a macro base station according to the present embodiment.
  • FIG. 9 is a diagram to explain a functional structure of a small base station according to the present embodiment.
  • FIG. 10 is a diagram to explain an overall structure of a user terminal according to the present embodiment.
  • FIG. 11 is a diagram to explain a functional structure of a user terminal according to the present embodiment.
  • FIG. 1 is a conceptual diagram of a HetNet that is anticipated in Rel. 12 and later versions.
  • a HetNet refers to a radio communication system in which macro cells and small cells are arranged to overlap each other geographically at least in part.
  • a HetNet is comprised of a radio base station that forms a macro cell (hereinafter referred to as a “macro base station”), radio base stations that form small cells (hereinafter referred to as “small base stations”), and a user terminal that communicates with the macro base station and the small base stations.
  • macro base station radio base station that forms a macro cell
  • small base stations radio base stations that form small cells
  • the distribution of users and traffic are not fixed, but change over time or between locations. Consequently, when many small cells are placed within a macro cell, the small cells may be arranged in such a manner that their density and environment vary (sparse and dense) between locations. For example, in train stations, shopping malls and so on where many user terminals gather, it may be possible to increase the density to place small cells (dense small cells). By placing small cells densely and in a localized manner (in clusters) in places where the traffic is heavy, it is possible to achieve an off-loading effect between the cells.
  • small cell discovery a study is in progress to introduce a novel small cell discovery mechanism (small cell discovery) to provide a method of allowing user terminals to efficiently discover and connect with the small cells.
  • small cell discovery a study is in progress to carry out small cell discovery/measurements by using new small cell discovery/measurement signals (also referred to as “discovery signals (DSs)”), instead of using conventional cell discovery signals (synchronization signals (PSS/SSS)) and measurement signals (cell-specific reference signals (CRS)).
  • DSs new small cell discovery/measurement signals
  • PSS/SSS synchronization signals
  • CRS cell-specific reference signals
  • a discovery/measurement signal from a small cell in a long cycle, and, based on the receiving state (RSRP, RSRQ, etc.) reported from a user terminal having detected that DS, control the connection of the user terminals with the small cell.
  • DSs are transmitted from a plurality of small cells simultaneously, in predetermined durations in a long cycle (synchronous transmission) (see FIG. 2 ).
  • a user terminal to support Rel. 12 can use the existing mechanism (existing legacy cell search to use cell discovery signals (P55/585) and measurement signals (CRSs)) and also use the new mechanism (small cell discovery to use DSs).
  • existing mechanism existing legacy cell search to use cell discovery signals (P55/585) and measurement signals (CRSs)
  • CRSs measurement signals
  • small cell discovery to use DSs small cell discovery to use DSs
  • a user terminal to support Rel. 12 implements only the small cell discovery mechanism using DSs (hereinafter also referred to as “small cell discovery”).
  • the small cell discovery mechanism to use DSs has to be a mechanism to support operation in all existing LTE scenarios (macro cell discovery, user terminals in idle mode, user terminals in high speed motion, etc.). Consequently, similar to the PSS/SSS/CRS, DSs need to be transmitted repeatedly, in a short cycle, and therefore the interference between small cells and the overhead increase.
  • a user terminal not only use the small cell discovery mechanism to use DSs, but also use existing cell discovery signals (PSS/SSS) and measurement signals (CRSs). That is, there are cases where, depending on the situation of the subject terminal, a user terminal carries out DS-based measurements as supplementary measurements, in addition to measurements based on existing cell discovery signals (PSS/SSS) and measurement signals (CRSs), or carry out DS-based measurements alone.
  • PSS/SSS existing cell discovery signals
  • CRSs measurement signals
  • the problem is how to control the conditions for transmitting measurement reports in response to the legacy cell search measurement result and the DS-based small cell discovery measurement result (the contents to transmit, whether or not to transmit (event trigger), etc.).
  • a user terminal to support Rel. 12 carries out both legacy cell search (cell discovery using the PSS/SSS and RSRP/RSRQ measurements using CRSs) and small cell discovery (cell discovery and RSRP/RSRQ measurements using DSs) all the time, there is a possibility that the load in the user terminal increases.
  • the present inventors have come up with the idea of controlling the operation of a user terminal adequately, by controlling small cell discovery to use DSs. For example, the present inventors have arrived at commanding small cell discovery using DSs and/or legacy cell search from the base station to which the user terminal is connected, and also reporting information about DS parameters to the user terminal when small cell discovery is executed.
  • PSS/SSS existing cell discovery signals
  • CRSs measurement signals
  • the frequency which the macro cell employs (F 1 ) and the frequency which the small cells employ (F 2 ) may be the same frequency (intra-frequency), or may be different frequencies (inter-frequency).
  • a case will be described below with a first example where a user terminal carries out small cell discovery in a predetermined frequency based on commands from the network (for example, base station).
  • the network for example, base station
  • FIG. 4 shows a system comprised of small base stations that form small cells, macro base stations that form macro cells which include small cells in their coverage areas, and user terminals that can communicate with the small base stations and the macro base stations. Also, FIG. 4 shows a case where the frequency which the macro cells employ and the frequency which the small cells employ are the same frequency (F 1 ), and a case where the frequency which the macro cells employ (F 1 ) and the frequency which the small cells employ (F 2 ) are different frequencies.
  • a base station (for example, a macro base station) commands whether or not to carry out small cell discovery in a predetermined frequency (for example, F 2 ) to a user terminal UE # 1 that is connected with that base station (connected UE).
  • the macro base station may also send commands regarding legacy cell search using synchronization signals (SSs) and reference signals (CRSs) transmitted from the small cells, with respect to a predetermined frequency (for example, F 2 ).
  • SSs synchronization signals
  • CRSs reference signals
  • FIG. 4 shows a case where a command for small cell discovery using DSs in F 2 is given to user terminal # 1 , and a command for small cell discovery and legacy cell search in F 2 is given to a user terminal # 2 . Also, in F 1 , it is also possible to employ a structure in which a user terminal # 3 to which no small cell discovery is commanded in F 1 or a user terminal # 4 in idle mode execute legacy cell search.
  • the macro base station can send the small cell discovery command by using higher layer signaling (for example, RRC signaling).
  • higher layer signaling for example, RRC signaling.
  • information as to whether or not to execute small cell discovery using DSs, per frequency is included in the information element (MeasObjectEUTRA (hereinafter also referred to as “MeasObject”)) that defines the measurement object, and reported to a user terminal.
  • MeasObjectEUTRA hereinafter also referred to as “MeasObject”
  • the macro base station When small cell discovery is executed, the macro base station reports information about the parameters of the discovery/measurement signals (DSs) (for example, transmission timings) to the user terminal. At this time, the macro base station specifies DS timings synchronous with the macro cell (the macro cell's system frame number (SFN), subframe number, transmission cycle). If small cells are synchronous with the macro cell, the user terminal can carry out small cell discovery and so on adequately based on the synchronization information of the macro cell.
  • DSs discovery/measurement signals
  • the base station may report, as information about DS parameters, parameters (assist information) such as the transmission power, the number of antenna ports, the DS frequency, the bandwidth, the signal configuration and so on, in addition to DS transmission timings, to the user terminals.
  • parameters assist information
  • the base station may report, as information about DS parameters, parameters (assist information) such as the transmission power, the number of antenna ports, the DS frequency, the bandwidth, the signal configuration and so on, in addition to DS transmission timings, to the user terminals.
  • the user terminal can adequately learn DS arrival timings and so on and execute DS discovery/measurements efficiently.
  • the assist information may be included in the information element “MeasObject,” which defines the measurement object, or may be commanded as “DiscoveryRS-Config,” which defines the configuration of the DS signal.
  • the NW for example, the macro base station
  • the NW includes, in MeasObject, a small cell discovery command (DiscoveryConfig), and DS timings (DiscoverySubframePatternConfig) such as the system frame number (SFN), subframe numbers and so on, and reports this to the user terminal.
  • DiscoveryConfig small cell discovery command
  • DS timings DS timings
  • the base station can command, separately, whether or not the user terminal should carry out legacy cell search in a specified frequency, and whether or not to the user terminal should carry out small cell search (option 1).
  • four patterns of operations namely (1) carrying out neither legacy cell search nor small cell discovery, (2) carrying out legacy cell search alone, (3) carrying out small cell discovery alone, and (4) carrying out both legacy cell search and small cell discovery, can be specified with two bits. Note that this two-bit information does not necessarily have to be stipulated in the small cell discovery command (DiscoveryConfig) field. It is equally possible to stipulate one bit in the small cell discovery command (DiscoveryConfig) field and one bit in the legacy cell search command (LegacyConfig) field (total two bits).
  • the base station commands whether or not the user terminal should carry out small cell search in a specified frequency (option 2).
  • two patterns of operations namely (1) not carrying out small cell discovery (carrying out legacy cell search alone) and (2) carrying out small cell discovery, can be specified with one bit.
  • the base station wants the user terminal to carry out small cell discovery alone, it is only necessary to send a report to the user terminal, in advance, to the effect that legacy cell search is to be skipped when above “(2) carrying out small cell discovery” is reported.
  • the base station commands whether or not the user terminal should carry out small cell search in a specified frequency, and commands to carry out small cell discovery alone, without performing legacy cell search, if the frequency is not the user terminal's connecting frequency (option 3).
  • two patterns of operations namely (1) not carrying out small cell discovery (carrying out legacy cell search alone) and (2) carrying out small cell discovery, can be indicated with one bit.
  • the user terminal compares the specified frequency and the frequency of the communicating state, and, if the frequencies do not match, the user terminal carries out small cell discovery using DS signals, and does not execute legacy cell search.
  • a user terminal when executing small cell discovery, can carry out efficient small cell discovery by using assist information such as DS timings.
  • the NW may include a small cell discovery command (DiscoveryConfig) in MeasObject, and report this to the user terminal, and, meanwhile, include assist information such as the transmission power, the number of antenna ports, the DS frequency, the bandwidth, the signal configuration and so on in the information element (DiscoveryRS-Config) that defines the discovery reference signal configuration, and report this to the user terminal.
  • DiscoveryConfig small cell discovery command
  • the NW may include a small cell discovery command (DiscoveryConfig) in MeasObject, and report this to the user terminal, and, meanwhile, include assist information such as the transmission power, the number of antenna ports, the DS frequency, the bandwidth, the signal configuration and so on in the information element (DiscoveryRS-Config) that defines the discovery reference signal configuration, and report this to the user terminal.
  • DiscoveryRS-Config information element that defines the discovery reference signal configuration
  • the user terminal executes small cell discovery using DSs, in the specified frequency. Otherwise, the user terminal executes legacy cell search alone.
  • the user terminal can perform small cell discovery in the specified timing with reference to the synchronization with the connecting cell (for example, the macro cell or other small cells).
  • the interference between the cells for example, interference between the CRSs, interference due to PSS/SSS collisions, etc.
  • the interference between the cells have an impact, and therefore small cell discovery becomes time-consuming when legacy cell search is used.
  • small cell discovery by commanding small cell discovery to use DSs in a predetermined frequency and/or legacy cell search from a base station to user terminals, it is possible to control small cell discovery adequately, depending on each user terminal's condition of connection.
  • both small cell discovery to use DSs and legacy cell search are commanded from a base station to user terminals, so that the user terminals (for example, user terminal # 2 in FIG. 4 ) becomes capable of discovering/measuring small cells by way of legacy cell search even during the DS transmission cycle.
  • the user terminals for example, user terminal # 2 in FIG. 4
  • the DS for small cell discovery may be configured freely in the network, without stipulating the transmitting subframes with the specifications on a fixed basis.
  • the DS transmission cycle is not a multiple of 10 or 5
  • the locations of subframes in the radio frame that transmits the DS change on a per cycle basis. This may give a threat that existing synchronization signals (PSS/SSS), cell-specific reference signals (CRS), broadcast signals (PBCH), system information (SIB), paging information(Paging) and so on collide with the DSs.
  • a configuration is employed here in which, when there is a possibility that DS resources might collide with the PSS/SSS/CRS/PBCH, SIB, paging and so on, legacy cell search alone is carried out, without performing small cell discovery (DS transmission).
  • the user terminal can operate on the assumption that there is no DS in resources where the PSS/SSS/CRS/PBCH, SIB, paging and so on are allocated. Meanwhile, small cell discovery is performed on the assumption that the resource elements to use for DSs are not used in PDSCH transmission.
  • the NW base station
  • the resources system frame number, subframe number or the combination of these
  • the user terminal when the NW (base station) commands small cell discovery by using MeasObject and so on, the resources (system frame number, subframe number or the combination of these) that are not subject to small cell discovery are indicated to the user terminal.
  • the user terminal can execute legacy cell search alone, without executing small cell discovery in the resources specified by the base station.
  • the small cell discovery frequency, timing and so on are reported to user terminals in idle mode, by using broadcast information from the macro cell (see FIG. 5 ).
  • the base station additionally specifies the discovery frequency (DiscoveryFrequency), the discovery subframe pattern configuration (DiscoverySubframePatternConfig) and so on in the system information block (SIB-X), and reports this to user terminals.
  • discovery frequency DiscoveryFrequency
  • discovery subframe pattern configuration DiscoverySubframePatternConfig
  • SIB-X system information block
  • the transmission control for measurement reports in response to measurement results acquired in legacy cell search and in small cell discovery for example, the receiving state (RSRP/RSRQ, etc.) in user terminals will be described.
  • the user terminal When a user terminal carries out legacy cell search and small cell discovery separately, the cell ID/RSRP/RSRQ corresponding to a predetermined cell acquired by the legacy cell search, and the cell identifier/RSRP/RSRQ corresponding to the predetermined cell acquired by the small cell discovery, are given.
  • the user terminal can report the measurement results to the base station (NW), as measurement reports, by using one of following methods 1 to 3.
  • the user terminal transmits both the result acquired from legacy cell search and the result acquired from small cell discovery to the base station as measurement reports.
  • the base station can acquire more information regarding the receiving states of the user terminal and the small cell base stations.
  • the user terminal may transmit the result acquired from legacy cell search and the result acquired from small cell discovery at the same timing or at different timings.
  • the user terminal transmits the information that is discovered in each cell, and, as for the receiving states, the result of small cell discovery is prioritized and transmitted to the base station as a measurement report. That is, when there is a cell identifier (for example, a cell ID) that is discovered in legacy cell search, this cell identifier is added to the result of small ell discovery and reported.
  • the cell identifiers for example, cell IDs
  • Method 2 is particularly effective when small cell discovery shows higher accuracy of discovery/measurements than legacy cell search.
  • the user terminal Given the result acquired from legacy cell search and the result acquired from small cell discovery, the user terminal transmits the result of legacy cell search on an as-is basis, and, as for the result of small cell discovery, only the cell identifiers (for example, cell IDs) that were not discovered in legacy cell search are transmitted.
  • the result of legacy cell search alone with respect to the receiving state information, it is possible to reduce the increase of report size.
  • Method 3 is particularly effective when, as has been heretofore, the result of legacy cell search is used as a base and the result of small cell discovery is transmitted as supplementary information.
  • the user terminal when the user terminal transmits the result acquired from legacy cell search and/or the result acquired from small cell discovery as a measurement report, the user terminal can employ the method of sending reports periodically or the method of sending reports when a predetermined condition (event trigger) is fulfilled.
  • the following event trigger can be configured:
  • Event A1-ds as a result of small cell discovery, the serving cell (Serving) exceeds the threshold
  • Event A3-ds as a result of small cell discovery, the difference between a neighboring cell (Neighbor) and the PCell exceeds the offset
  • Event A4-ds as a result of small cell discovery, a neighboring cell (Neighbor) exceeds the threshold
  • Event A5-ds as a result of small cell discovery, the PCell falls below threshold 1 and a neighboring cell (Neighbor) exceeds a threshold 2
  • Event A6-ds as a result of small cell discovery, the difference between a neighboring cell (Neighbor) and the SCell exceeds the offset
  • each event trigger or specify the threshold, separately, for every frequency of the measurement object (MeasObject).
  • the serving cell refers to the connecting cell, and the threshold to use in the PCell frequency in the above events A1 and A2 and the threshold to use in the SCell frequency can be specified separately.
  • events A3, A5, A6 and so on cases might occur where the legacy cell search measurement result and the result acquired in small cell discovery are compared.
  • legacy cell search and small cell discovery both take place between a neighboring cell and the PCell/SCell.
  • the user terminal may compare each result directly, or compare these by adding an offset to one result (for example, the result of small cell discovery) based on received quality and so on.
  • Information about the offset can be reported from the base station to the user terminal.
  • FIG. 6 is a schematic configuration diagram of a radio communication system according to the present embodiment.
  • a radio communication system 1 includes a macro base station 11 that forms a macro cell C 1 , and small base stations 12 a and 12 b that form small cells C 2 , which are placed within the macro cell C 1 and which are narrower than the macro cell C 1 .
  • User terminals 20 are structured to be capable of carrying out radio communication with at least one of the macro base station 11 and the small base stations 12 a and 12 b (hereinafter collectively referred to as “small base stations 12 ”).
  • small base stations 12 the number of macro base stations 11 and small base stations 12 is by no means limited to the number illustrated in FIG. 6 .
  • the macro cell C 1 and the small cells C 2 may use the same frequency band or may use different frequency bands.
  • the macro base station 11 and each small base station 12 are connected with each other via an inter-base station interface (for example, optical fiber, X2 interface, etc.).
  • the macro base station 11 and the small base stations 12 are each connected with a higher station apparatus 30 , and are connected with a core network 40 via the higher station apparatus 30 .
  • the higher station apparatus 30 may be, for example, an access gateway apparatus, a radio network controller (RNC), a mobility management entity (MME) and so on, but is by no means limited to these.
  • RNC radio network controller
  • MME mobility management entity
  • the macro base station 11 is a radio base station having a relatively wide coverage, and may be referred to as an “eNodeB (eNB),” a “radio base station,” a “transmission point” and so on.
  • the small base stations 12 are radio base stations that have local coverages, and may be referred to as “RRHs (Remote Radio Heads),” “pico base stations,” “femto base stations,” “HeNBs (Home eNodeBs),” “transmission points,” “eNodeBs (eNBs)” and so on.
  • the user terminals 20 are terminals to support various communication schemes such as LTE and LTE-A, and may not only be mobile communication terminals, but may also be stationary communication terminals as well.
  • OFDMA Orthogonal Frequency Division Multiple Access
  • SC-FDMA Single-Carrier Frequency Division Multiple Access
  • a downlink shared channel (PDSCH: Physical Downlink Shared Channel), which is used by each user terminal 20 on a shared basis, a downlink control channel (PDCCH (Physical Downlink Control Channel), an EPDCCH (Enhanced Physical Downlink Control Channel), a PCFICH, a PHICH, a broadcast channel (PBCH) and so on are used as downlink communication channels.
  • PDSCH Physical Downlink Shared Channel
  • PDCCH Physical Downlink Control Channel
  • EPDCCH Enhanced Physical Downlink Control Channel
  • PCFICH Physical Downlink Control Channel
  • PCFICH Physical Downlink Control Channel
  • PHICH Physical Downlink Control Channel
  • PBCH broadcast channel
  • DCI Downlink control information
  • an uplink shared channel (PUSCH: Physical Uplink Shared Channel) that is used by each user terminal 20 on a shared basis
  • an uplink control channel (PDCCH: Physical Uplink Control Channel) and so on are used.
  • User data and higher layer control information are communicated by the PUSCH.
  • downlink radio quality information CQI; Channel Quality Indicator
  • ACK/NACK delivery acknowledgement information
  • the macro base station 11 and the small base stations 12 will be hereinafter collectively referred to as “radio base station 10 ,” unless specified otherwise.
  • FIG. 7 is a diagram to show an overall structure of a radio base station 10 according to the present embodiment.
  • the radio base station 10 has a plurality of transmitting/receiving antennas 101 for MIMO communication, amplifying sections 102 , transmitting/receiving sections 103 , a baseband signal processing section 104 , a call processing section 105 and an interface section 106 .
  • User data to be transmitted from the radio base station 10 to a user terminal 20 on the downlink is input from the higher station apparatus 30 , into the baseband signal processing section 104 , via the interface section 106 .
  • a PDCP layer process division and coupling of user data, RLC (Radio Link Control) layer transmission processes such as an RLC retransmission control transmission process, MAC (Medium Access Control) retransmission control, including, for example, an HARQ transmission process, scheduling, transport format selection, channel coding, an inverse fast Fourier transform (IFFT) process and a pre-coding process are performed, and the result is forwarded to each transmitting/receiving section 103 .
  • RLC Radio Link Control
  • MAC Medium Access Control
  • HARQ transmission process scheduling, transport format selection, channel coding, an inverse fast Fourier transform (IFFT) process and a pre-coding process
  • IFFT inverse fast Fourier transform
  • pre-coding a pre-coding
  • Each transmitting/receiving section 103 converts the downlink signals, which are pre-coded and output from the baseband signal processing section 104 on a per antenna basis, into a radio frequency band.
  • the amplifying sections 102 amplify the radio frequency signals having been subjected to frequency conversion, and transmit the signals through the transmitting/receiving antennas 101 .
  • radio frequency signals that are received in the transmitting/receiving antennas 101 are each amplified in the amplifying sections 102 , converted into baseband signals through frequency conversion in each transmitting/receiving section 103 , and input into the baseband signal processing section 104 .
  • the user data that is included in the input uplink signals is subjected to an FFT process, an IDFT process, error correction decoding, a MAC retransmission control receiving process and RLC layer and PDCP layer receiving processes, and the result is forwarded to the higher station apparatus 30 via the interface section 106 .
  • the call processing section 105 performs call processing such as setting up and releasing communication channels, manages the state of the radio base stations 10 and manages the radio resources.
  • the interface section 106 transmits and receives signals to and from neighboring radio base stations (backhaul signaling) via an inter-base station interface (for example, optical fiber, X2 interface, etc.). For example, data is transmitted and received between the macro base station 11 and the small base stations 12 via the interface section 106 . Alternatively, the interface section 106 transmits and receives signals to and from the higher station apparatus 30 via a predetermined interface.
  • an inter-base station interface for example, optical fiber, X2 interface, etc.
  • data is transmitted and received between the macro base station 11 and the small base stations 12 via the interface section 106 .
  • the interface section 106 transmits and receives signals to and from the higher station apparatus 30 via a predetermined interface.
  • FIG. 8 is a diagram to show a functional structure of a macro base station 11 according to the present embodiment. Note that the following functional structure is formed with the baseband signal processing section 104 provided in the macro base station 11 and so on.
  • the macro base station 11 has a scheduler (control section) 301 , a DS parameter determining section 302 , a small cell discovery commanding section 303 , a DL signal generating section 304 , a measurement report acquiring section 305 and so on.
  • the scheduler 301 allocates (schedules) the radio resources for DL signals to transmit to the user terminal 20 and the radio resources for UL signals to be transmitted from the user terminal 20 . For example, with respect to the user terminal 20 , when small cell discovery is performed, the scheduler 301 commands the DL signal generating section 304 to generate information about DS parameters (assist information such as transmission timings).
  • the scheduler 301 can execute control so that, as has been shown with the above first embodiment, a small cell discovery command (DiscoveryConfig), and DS timings (DiscoverySubframePatternConfig) such as the system frame number (SFN) and subframe numbers and so on can be included in MeasObject (above-described method 1 of the first embodiment).
  • DiscoveryConfig small cell discovery command
  • DiscoverySubframePatternConfig DS timings
  • SFN system frame number
  • subframe numbers and so on can be included in MeasObject (above-described method 1 of the first embodiment).
  • the scheduler 301 can execute control so that, while a small cell discovery command (DiscoveryConfig) is included in MeasObject and transmitted to the user terminal, assist information such as the transmission power, the number of antenna ports, the DS frequency, the bandwidth, the signal configuration and so on are also included in the information element (DiscoveryRS-Config) that defines the discovery reference signal configuration (above-described method 2 of the first embodiment).
  • DiscoveryConfig small cell discovery command
  • assist information such as the transmission power, the number of antenna ports, the DS frequency, the bandwidth, the signal configuration and so on are also included in the information element (DiscoveryRS-Config) that defines the discovery reference signal configuration (above-described method 2 of the first embodiment).
  • the small cell discovery commanding section 303 controls commands for small cell discovery using DSs for user terminals.
  • the small cell discovery commanding section 303 commands a user terminal (Connected UE) that is connected to the macro base station 11 as to whether or not to perform small cell discovery in a predetermined frequency (for example, F 2 ).
  • the small cell discovery commanding section 303 also sends a command for legacy cell search using synchronization signals (SSs) and reference signals (CRSs) transmitted from the small cells, with respect to the predetermined frequency(for example, F 2 ).
  • SSs synchronization signals
  • CRSs reference signals
  • the DS parameter determining section 302 determines information about DS parameters.
  • the information about DS parameters includes parameters (assist information) such as DS transmission timings, the transmission power, the number of antenna ports, the DS frequency, the bandwidth, the signal configuration and so on.
  • the information that is determined in the DS parameter determining section 302 is output to the scheduler 301 and the DL signal generating section 304 .
  • the DL signal generating section 304 generates DL signals based on commands from the scheduler 301 and the DS parameter determining section 302 .
  • the signals generated in the DL signal generating section 305 are transmitted to the user terminal 20 via the transmitting/receiving section 103 .
  • the measurement report acquiring section 305 acquires measurement reports sent from the user terminal.
  • the measurement report acquiring section 305 acquires at least part of the result acquired from legacy cell search in the user terminal and the result acquired from small cell discovery using DSs, each as a measurement report. Then, the measurement report acquiring section 305 controls the connection of the user terminal with the small cells based on the measurement reports.
  • FIG. 9 is a diagram to show a functional structure of a small base station 12 according to the present embodiment. Note that the following functional structure is comprised of the baseband signal processing section 104 provided in the small base station 12 and so on.
  • the small base station 12 has a UL signal detection section 311 , a scheduler 312 , a DL signal generating section 313 and so on.
  • the UL signal detection section 311 detects UL signals that are transmitted from the user terminal.
  • the UL signal detection section 311 can also receive measurement reports sent from the user terminal.
  • the scheduler 312 allocates (schedules) the radio resources for DL signals to transmit to the user terminal 20 . Also, the scheduler 312 controls the transmission of discovery/measurement signals (DSs).
  • DSs discovery/measurement signals
  • the DL signal generating section 313 generates DL signals based on commands from the scheduler 312 .
  • the DL signal generating section 313 generates synchronization signals (PSS/SSS), reference signals (CRS), measurement/discovery signal (DSs), control signals, data signals and so on.
  • the signals generated in the DL signal generating section 313 are transmitted to the user terminal 20 via the transmitting/receiving section 103 .
  • FIG. 10 is a diagram to show an overall structure of a user terminal 20 according to the present embodiment.
  • the user terminal 20 has a plurality of transmitting/receiving antennas 201 for MIMO communication, amplifying sections 202 , transmitting/receiving sections (receiving sections) 203 , a baseband signal processing section 204 and an application section 205 .
  • radio frequency signals that are received in a plurality of transmitting/receiving antennas 201 are each amplified in the amplifying sections 202 , and subjected to frequency conversion and converted into the baseband signal in the transmitting/receiving section 203 .
  • This baseband signal is subjected to an FFT process, error correction decoding, a retransmission control receiving process and so on in the baseband signal processing section 204 .
  • downlink user data is forwarded to the application section 205 .
  • the application section 205 performs procedures related to higher layers above the physical layer and the MAC layer. Furthermore, the broadcast information in the downlink data is also forwarded to the application section 205 .
  • uplink user data is input from the application section 205 into the baseband signal processing section 204 .
  • the baseband signal processing section 204 performs a retransmission control (HARQ (Hybrid ARQ)) transmission process, channel coding, pre-coding, a DFT process, an IFFT process and so on, and the result is forwarded to each transmitting/receiving sections 203 .
  • Baseband signals that are output from the baseband signal processing section 204 are converted into a radio frequency band in the transmitting/receiving sections 203 .
  • the amplifying sections 202 amplify the radio frequency signals having been subjected to frequency conversion, and transmit the result from the transmitting/receiving antennas 201 .
  • FIG. 11 is a diagram to show a principle functional structure of the baseband signal processing section 204 provided in the user terminal 20 .
  • the baseband signal processing section 204 provided in the user terminal 20 at least has a cell discovery/measurement section 401 , a measurement report transmission control section 402 and a UL signal generating section 403 .
  • the cell discovery/measurement section 401 performs legacy cell search using synchronization signals (PSS/SSS) and reference signals (CRSs) transmitted from the small base station 12 , and small cell discovery using discovery/measurement signals (DSs). Also, the cell discovery/measurement section 401 receives information related to commands for legacy cell search and/or small cell discovery, from the macro base station 11 , via RRC signaling (the above first embodiment). Also, the cell discovery/measurement section 401 , when carrying out small cell discovery, discovers the DSs based on the DS parameter-related information (assist information) that is reported from the macro base station 11 .
  • PSS/SSS synchronization signals
  • CRSs reference signals
  • DSs discovery/measurement signals
  • the cell discovery/measurement section 401 receives information related to commands for legacy cell search and/or small cell discovery, from the macro base station 11 , via RRC signaling (the above first embodiment). Also, the cell discovery/measurement section 401 , when carrying out small cell discovery, discovers
  • the cell discovery/measurement section 401 can perform legacy cell search on the assumption that there are no DSs in resources where the PSS/SSS/CRS/PBCH, SIB, paging and so on are allocated. In the meantime, the cell discovery/measurement section 401 performs small cell discovery on the assumption that the resource elements used for DSs are not used for PDSCH transmission (the above second embodiment). Also, when the user terminal 20 is in idle mode, the cell discovery/measurement section 401 performs small cell discovery based on broadcast signals transmitted from the macro base station 11 (the above third embodiment).
  • the measurement report transmission control section 402 controls the transmission of the result of the legacy cell search that was carried out in the cell discovery/measurement section 401 and the result of the small cell discovery, as measurement reports.
  • the measurement report transmission control section 402 acquires the cell ID/RSRP/RSRQ corresponding to a predetermined cell, acquired by legacy cell search, and the cell identifier/RSRP/RSRQ corresponding to the predetermined cell, acquired by small cell discovery.
  • the measurement report transmission control section 402 executes control so that the measurement results are reported to the base station (NW) as measurement reports by using one of above-described methods 1 to 3 of the fourth embodiment.
  • the measurement report transmission control section 402 controls the transmission of measurement reports based on predetermined conditions (event triggers) that are configured separately for the result acquired in legacy cell search and the result acquired in small cell discovery (the above fourth embodiment).
  • the UL signal generating section 403 generates measurement reports and so on based on commands from the measurement report transmission control section 402 . Furthermore, the UL signal generating section 403 also generates uplink control signals such as delivery acknowledgement signals, and uplink data signals.

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CN105580411B (zh) 2020-05-15
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