JP2015223005A - Radio communication system and communication control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a processing load of a user device for recognizing a base station.SOLUTION: A radio communication system CS comprises: a first base station eNB which is identified by a first cell identifier PCI; a second base station PhNB which is identified by a second cell identifier PCI; and a user device UE which can execute radio communication with the respective base stations (eNB and PhNB). The user device UE detects first transmission timing on the basis of a first synchronization signal SS from the first base station eNB, and establishes a synchronization state with the first base station eNB. The first base station eNB notifies the user device UE of synchronization state information about a synchronization state with the second base station PhNB and frequency information about an identification signal frequency to be used by the second base station PhNB for transmitting an identification signal. For the identification signal frequency indicated by the frequency information, the user device UE executes specific processing of the second cell identifier PCI indicated by the identification signal on the basis of the synchronization state information.

Description

  The present invention relates to a wireless communication system and a communication control method.

  Various wireless communication systems complying with 3GPP (Third Generation Partnership Project) standards are used. In a wireless communication system that conforms to the LTE / SAE (Long Term Evolution / System Architecture Evolution) standard of the 3GPP standard, a user apparatus performs a cell search to establish synchronization with a macro base station and perform wireless communication. In the cell search described above, the user apparatus performs a correlation operation between the synchronization signal transmitted from the macro base station and the replica signal stored in the user apparatus, so that the transmission timing of the synchronization signal and the physical cell identifier (Physical (Cell Identity, PCI) is detected and the macro base station is recognized (identified).

JP 2009-188612 PR

  The above wireless communication system is a new base station (hereinafter referred to as 3.5 GHz band) that performs wireless communication using a frequency band (for example, 3.5 GHz band) different from the frequency band (for example, 2 GHz band) that the macro base station uses for wireless communication. , Referred to as a small base station). In the configuration in which the user apparatus performs cell search in both the frequency band used by the macro base station and the frequency band used by the small base station, the user device is compared with the configuration in which the cell search is performed only for one frequency band. The processing load such as correlation calculation executed by the apparatus is large, and consequently the power consumption of the user apparatus is large.

  In view of the above circumstances, an object of the present invention is to reduce a processing load for a user apparatus to recognize a base station in a wireless communication system including a plurality of base stations.

  The wireless communication system of the present invention can execute wireless communication in the first frequency band, can execute wireless communication in the second frequency band with the first base station identified by the first cell identifier, A plurality of base stations including a second base station identified by a second cell identifier; and a user apparatus capable of performing wireless communication with each of the plurality of base stations. The first base station includes a first transmission unit that transmits a first synchronization signal indicating the first cell identifier for identifying the first base station at a first transmission timing, and the second base station A second transmission unit configured to transmit an identification signal indicating the second cell identifier for identifying a second base station, wherein the user apparatus receives the first synchronization signal based on the first synchronization signal received from the first base station; A cell search unit that detects a transmission timing and executes a timing search process for establishing synchronization with the first base station is provided, and the first base station synchronizes the first base station and the second base station. An information notification unit for notifying the user apparatus of synchronization state information regarding a state and frequency information regarding an identification signal frequency used by the second base station for transmitting the identification signal in the second frequency band; The device The search unit executes, for the identification signal frequency indicated in the frequency information, a process for specifying the second cell identifier indicated in the identification signal based on the synchronization state information from the first base station. .

  In a preferred aspect of the present invention, the first base station and the second base station are capable of performing wireless communication in synchronization with each other, and the second transmission unit of the second base station is at a second transmission timing. The synchronization status information notified by the information notification unit of the first base station indicates whether or not the first base station and the second base station are synchronized, If the synchronization state information indicates that the first base station and the second base station are synchronized, the cell search unit of the user apparatus does not perform a timing search process for the second base station. Based on the first transmission timing, the second cell identifier specifying process indicated in the identification signal is executed.

  In a preferred aspect of the present invention, the first base station and the second base station are capable of performing wireless communication in synchronization with each other, and the second transmission unit of the second base station is at a second transmission timing. The synchronization status information notified by the information notification unit of the first base station indicates whether or not the first base station and the second base station are synchronized, When the synchronization state information indicates that the first base station and the second base station are in synchronization, the cell search unit of the user apparatus performs the second base over a predetermined period including the first transmission timing. The second transmission timing is specified by executing a timing search process for a station, and the second cell identifier specifying process indicated by the identification signal is executed based on the second transmission timing.

  In a preferred aspect of the present invention, the second transmission unit of the second base station further transmits a cell specific signal including the identification signal and different from the second synchronization signal, and the cell search unit of the user apparatus Performs the specifying process of the second cell identifier indicated in the identification signal included in the cell specific signal.

  In a preferred aspect of the present invention, the information communication unit of the first base station receives configuration information indicating a transmission timing of the cell specific signal and CP length information when the second base station performs radio communication. The cell search unit of the user apparatus transmits the user apparatus UE, and further uses the configuration information and the CP length information to specify the second cell identifier indicated in the identification signal included in the cell specific signal. Execute the process.

  In a preferred aspect of the present invention, the second transmission unit of the second base station uses the second transmission timing obtained by delaying the first transmission timing of the first base station by a time corresponding to a transmission offset value. The second synchronization signal including the identification signal is transmitted, and the synchronization state information notified by the information notification unit of the first base station is the transmission offset value with respect to the first transmission timing of the first base station. And the cell search unit of the user apparatus performs the identification without performing a timing search process for the second base station based on the first transmission timing and the transmission offset value indicated by the synchronization state information. The process of specifying the second cell identifier indicated by the signal is executed.

  The second transmission unit of the second base station includes the identification signal at the second transmission timing obtained by delaying the first transmission timing of the first base station by a time corresponding to a transmission offset value. The synchronization state information transmitted from the first base station and transmitted by the information notification unit of the first base station indicates the transmission offset value with respect to the first transmission timing of the first base station, and transmits the synchronization signal. The search unit executes the timing search process for the second base station over a predetermined period including a transmission timing delayed by a time corresponding to the transmission offset value indicated by the synchronization state information. The second transmission timing is specified, and the second cell identifier specifying process indicated in the identification signal is performed based on the second transmission timing. To.

  In a preferred aspect of the present invention, the second base station further includes a received power measuring unit that measures received power of a radio signal received from the first base station, and the received power measured by the received power measuring unit. And an offset value setting unit that sets a transmission offset value to a larger value, and the second transmission unit of the second base station corresponds to the first transmission timing of the first base station to the transmission offset value. At the second transmission timing advanced by time, the second synchronization signal including the identification signal is transmitted, and the synchronization status information notified by the information notification unit of the first base station includes the first base station and Indicates whether or not the second base station is synchronized, and the cell search unit of the user apparatus indicates that the synchronization state information indicates that the first base station and the second base station are synchronized If the second base Without executing the timing search process for, based on the first transmission timing, perform specific processing of the second cell identifiers indicated in the identification signal.

  In a preferred aspect of the present invention, the synchronization state information further includes an identifier list indicating a plurality of the second cell identifiers corresponding to a plurality of the second base stations, and the cell search unit of the user apparatus includes: The specifying process is executed only for the plurality of second base stations corresponding to the plurality of second cell identifiers indicated in the identifier list.

  In a preferred aspect of the present invention, the user apparatus includes a terminal transmission unit that transmits a terminal detection signal indicating a terminal identifier for identifying the user apparatus, and the second transmission unit of the second base station includes the terminal The identification signal having a signal format common to the detection signal is transmitted.

  In a preferred aspect of the present invention, the second transmission unit of the second base station indicates an arrangement of the identification signal in each of a plurality of subframes, and the identification is performed according to an identification signal pattern for identifying the second base station. Send a signal.

  The communication control method of the present invention can execute wireless communication in the first frequency band, can execute wireless communication in the second frequency band with the first base station identified by the first cell identifier, A communication control method for a wireless communication system, comprising: a plurality of base stations including a second base station identified by a second cell identifier; and a user apparatus capable of performing wireless communication with each of the plurality of base stations. The first base station transmits a first synchronization signal indicating the first cell identifier for identifying the first base station at a first transmission timing, and the second base station transmits the second synchronization signal. Transmitting an identification signal indicating the second cell identifier for identifying a base station, and detecting the first transmission timing based on the first synchronization signal received from the first base station in the user apparatus, Said Performing a timing search process for establishing synchronization with a base station; in the first base station, synchronization state information regarding a synchronization state between the first base station and the second base station; and the second frequency band The frequency information on the identification signal frequency used for transmission of the identification signal by the second base station is notified to the user apparatus, and the user apparatus is configured to respond to the identification signal frequency indicated by the frequency information. The second cell identifier included in the identification signal is specified using the synchronization state information from the first base station.

  According to the present invention, the user apparatus performs the process of specifying the second cell identifier indicated in the second synchronization signal transmitted by the second base station, based on the frequency information and synchronization state information notified from the first base station. Run. Since the timing search process for the small base station PhNB is omitted, the processing load for the user apparatus UE to recognize the small base station PhNB is reduced.

1 is a block diagram showing a wireless communication system according to a first embodiment. It is a figure which shows the example of the cell which a base station forms around. It is a figure which shows the format of a radio | wireless frame. It is a figure which shows the local identifier and group identifier which are contained in a physical cell identifier. It is a flowchart which shows roughly the flow of the synchronization establishment and cell recognition (cell search) using a synchronization signal. It is an operation | movement flow which shows an example of the specific process of the physical cell identifier of 1st Embodiment. It is a figure which shows an example of transmission of the radio signal by the macro base station and small base station of 1st Embodiment. It is a block diagram which shows the structure of the user apparatus of 1st Embodiment. It is a block diagram which shows the structure of the macro base station of 1st Embodiment. It is a block diagram which shows the structure of the small base station of 1st Embodiment. It is a figure which shows an example of transmission of the radio signal by the macro base station and small base station of 2nd Embodiment. It is explanatory drawing of the specific process of the physical cell identifier of the small base station of 2nd Embodiment. It is a block diagram which shows the radio | wireless communications system which concerns on 3rd Embodiment. It is a block diagram which shows the structure of the small base station of 3rd Embodiment. It is a block diagram which shows the radio | wireless communications system which concerns on 7th Embodiment. It is explanatory drawing of the reference signal in 7th Embodiment. It is a block diagram which shows the radio | wireless communications system which concerns on 8th Embodiment. It is a block diagram which shows the structure of the user apparatus of 8th Embodiment. It is explanatory drawing of the terminal detection signal which the some user apparatus of 8th Embodiment transmits. It is explanatory drawing of the identification signal which the small base station of 8th Embodiment transmits. It is explanatory drawing of arrangement | positioning of CSI-RS in one resource block of 9th Embodiment. It is a figure which shows the specific example of the hopping pattern of 9th Embodiment. It is a figure which shows the modification of a hopping pattern. It is explanatory drawing of the modification in which a new version user apparatus and an old version user apparatus are mixed.

1. First Embodiment 1 (1). Overview of Radio Communication System FIG. 1 is a block diagram showing a radio communication system CS according to the first embodiment of the present invention. The radio communication system CS includes a macro base station eNB, a small base station PhNB, and a user apparatus UE as elements. The radio communication system CS may include elements (not shown) other than those described above, for example, an exchange, a serving gateway, a PDN gateway, and the like. The network NW includes elements other than the user apparatus UE among the elements included in the radio communication system CS.

  Each element in the radio communication system CS performs communication in accordance with a predetermined access technology (Access Technology), for example, LTE / SAE (Long Term Evolution / System Architecture Evolution) standard included in 3GPP (Third Generation Partnership Project) standard. According to the terms defined in the 3GPP standard, the user equipment UE is User Equipment, the macro base station eNB is evolved Node B, the switching center is a Mobile Management Entity, the serving gateway is a Serving Gateway, and the PDN gateway is Packet Data Network Gateway. The small base station PhNB is a new base station that performs wireless communication in a frequency band different from that of the macro base station eNB (details will be described later).

  The user apparatus UE can wirelessly communicate with the macro base station eNB and the small base station PhNB. Each base station (eNB, PhNB) is identified by a unique physical cell identifier PCI. As will be described later, each base station (eNB, PhNB) may be identified by a unique identification signal. A method of radio communication between the user apparatus UE and each base station (eNB, PhNB) is arbitrary. For example, OFDMA (Orthogonal Frequency Division Multiple Access) may be employed in the downlink, and SC-FDMA (Single-Carrier Frequency Division Multiple Access) may be employed in the uplink. It is also possible to adopt a configuration in which the wireless communication method used by the macro base station eNB and the wireless communication method used by the small base station PhNB are different.

  The macro base station eNB and the small base station PhNB are connected to each other by a wired interface such as an optical fiber capable of transmitting a clock signal. The macro base station eNB and the small base station PhNB can be synchronized with each other according to a clock signal. The clock signal may be generated in one of the base stations (preferably, in the macro base station eNB) and transmitted to the other base station, or may be arranged separately from each base station (not shown) It may be generated by the clock generator and transmitted to each base station.

  In addition, each of the macro base station eNB and the small base station PhNB is connected to the core network. The core network is a packet communication network having an exchange, a serving gateway, a PDN gateway, and the like. The small base station PhNB may be connected to the core network via the macro base station eNB instead of being directly connected to the core network.

  FIG. 2 shows an example of a cell C formed around each base station (eNB, PhNB). The macro base station eNB forms a macro cell C1 around it, and the small base station PhNB forms a small cell C2 around it. In each cell C, the antenna of each base station is schematically shown. For convenience of drawing, the plane in which the macro cell C1 is shown and the plane in which the small cell C2 are shown are drawn separately, but in reality, the macro cell C1 and the small cell C2 are superimposed on the same plane (the ground surface or the like). Can be done. Cell C is a range in which radio waves from each base station effectively reach the user apparatus UE. Therefore, the user apparatus UE can perform radio communication with the base station corresponding to the cell C in which the user apparatus UE is located.

  The small base station PhNB is smaller than the macro base station eNB and has a small radio transmission capability (average transmission power, maximum transmission power, etc.). Further, the frequency band (second frequency band, for example, 3.5 GHz band) used by the small base station PhNB for wireless communication is higher than the frequency band (first frequency band, for example, 2 GHz band) used by the macro base station eNB for wireless communication. High frequency and large propagation loss. Therefore, the small cell C2 has a smaller area than the macro cell C1.

1 (2). Radio Frame and Physical Cell Identifier FIG. 3 is a diagram illustrating a format of a radio frame F transmitted by each of the macro base station eNB and the small base station PhNB. Various radio signals (control signal, user signal, etc.) are mounted on the radio frame F and transmitted from the base stations (eNB, PhNB). One radio frame F includes 10 subframes SF. Since the time length of each subframe SF is 1 millisecond, the time length of one radio frame F is 10 milliseconds. Each subframe SF has any subframe number from # 0 to # 9 that is repeatedly given in the order of transmission. The synchronization signal SS indicating the physical cell identifier PCI is transmitted in the first and sixth subframes SF (SF # 0 and SF # 5) in the radio frame F. Therefore, the synchronization signal SS is transmitted at a period of 5 subframes (ie every 5 milliseconds).

  The physical cell identifier PCI indicated in the synchronization signal SS is set for each base station (for each cell) and is used for various processes such as synchronization establishment, cell recognition, channel estimation, data scrambling, and the like (3GPP TS 36.211 V10. 1.0 (2011-03), Chapter 6.11, Synchronization signals). The synchronization signal SS includes a PSS (Primary Synchronization Signal) indicating a local identifier of the cell and an SSS (Secondary Synchronization Signal) indicating a group identifier of the cell. That is, the synchronization signal SS has a function as an identification signal.

  FIG. 4 is a diagram showing local identifiers and group identifiers included in the physical cell identifier PCI. There are 168 types of group identifiers and three types of local identifiers. Since there are three types of local identifiers for each group identifier, there are 504 types (= 168 × 3) of physical cell identifiers PCI.

1 (3). Synchronization establishment and cell recognition (cell search)
1 (3) -1. FIG. 5 is a flowchart schematically showing the flow of synchronization establishment and cell recognition (cell search) using synchronization signals SS (PSS and SSS). is there. The cell search includes a first stage process and a second stage process. In the first stage, the user apparatus UE performs a correlation operation between the radio signal received from the base station (for example, the macro base station eNB) and the PSS replica signal stored in the user apparatus UE, and the radio signal PSS transmission timing (subframe timing) and local identifier included in the. Note that the process of detecting the transmission timing (subframe timing) of the PSS may be referred to as “timing search process”.

  In the second stage, the user apparatus UE performs a correlation operation between the SSS included in the received radio signal and the SSS replica signal stored in the user apparatus UE based on the transmission timing detected in the first stage. To detect the SSS transmission timing (frame timing) and group identifier included in the radio signal. By the processing executed in the first stage and the second stage, the local identifier and group identifier indicated by the synchronization signal SS in the received radio signal are identified. As a result, the user apparatus UE recognizes the physical cell identifier PCI of the base station (eNB, PhNB) that transmits the synchronization signal SS.

  In the first stage, since the user apparatus UE does not recognize where the synchronization signal SS is located in the received radio signal, the user apparatus UE performs correlation calculation over the entire received radio signal. On the other hand, in the second stage, since the user apparatus can recognize the position of the synchronization signal SS (and thus SSS) in the received radio signal based on the transmission timing detected in the first stage, the user apparatus UE receives the received radio signal. The correlation calculation is executed only for the portion corresponding to SSS. Therefore, the arithmetic processing load of the first stage is significantly higher than the arithmetic processing load of the second stage.

1 (3) -2. Cell search of small base station using transmission timing of macro base station With reference to FIG. 6 and FIG. 7, the identification process of the physical cell identifier PCI of the small base station PhNB in this embodiment will be described. FIG. 6 is an operation flow illustrating an example of the physical cell identifier PCI specifying process. FIG. 7 is a diagram illustrating an example of radio signal transmission by the macro base station eNB and the small base station PhNB that are synchronized with each other.

  As described above, the macro base station eNB and the small base station PhNB of the first embodiment are synchronized with each other. That is, as shown in FIG. 7, there is no difference between the transmission timing at which the macro base station eNB transmits the synchronization signal SS and the transmission timing at which the small base station PhNB transmits the synchronization signal SS (or above) The difference between the transmission timings is significantly smaller than the time length of the radio signal unit (resource element or the like).

  The macro base station eNB periodically transmits a synchronization signal SS indicating a physical cell identifier PCI for identifying the macro base station eNB at a transmission timing as shown in FIGS. 3 and 7 (S10). Based on the synchronization signal SS received from the macro base station eNB, the user apparatus UE performs cell detection (processing for specifying a physical cell identifier PCI indicating the macro base station eNB) and synchronization establishment with the macro base station eNB. (S20). More specifically, as described above, based on the PSS included in the synchronization signal SS from the macro base station eNB, the user apparatus UE detects the transmission timing and local identifier of the PSS (first stage). Then, based on the SSS included in the synchronization signal SS from the macro base station eNB, the user apparatus UE detects the transmission timing and group identifier of the SSS, and specifies the transmission timing of the synchronization signal SS and the physical cell identifier PCI. Then, the user apparatus UE establishes a wireless connection with the macro base station eNB (S30).

  The macro base station eNB sends, to the user apparatus UE, synchronization state information regarding the synchronization state with the small base station PhNB located in the vicinity thereof and frequency information regarding the identification signal frequency used by the small base station PhNB for transmission of the synchronization signal SS. Notify (S40). In the first embodiment, since the macro base station eNB and the small base station PhNB are synchronized, the above synchronization state information indicates that the macro base station eNB and the small base station PhNB are synchronized. . The user apparatus UE stores the received synchronization state information and frequency information.

  The small base station PhNB periodically transmits a synchronization signal SS indicating a physical cell identifier PCI for identifying the small base station PhNB at a transmission timing as shown in FIG. 7 (S50). The user apparatus UE performs cell detection (processing for specifying a physical cell identifier PCI indicating the small base station PhNB) based on the synchronization signal SS received from the small base station PhNB (S60). The above cell detection is performed using the synchronization state information and frequency information notified in step S40. More specifically, when the synchronization status information indicates that “the macro base station eNB and the small base station PhNB are synchronized”, the user apparatus UE does not perform the timing search process for the small base station PhNB. Based on the transmission timing of the synchronization signal SS from the macro base station eNB, the local identifier and group identifier detection processing is executed for the identification signal frequency of the small base station PhNB indicated in the frequency information. Then, the user apparatus UE establishes a wireless connection with the small base station PhNB (S70).

  In the cell detection in step S60, the user apparatus UE does not need to search for the position (transmission timing) of the synchronization signal SS included in the radio signal from the small base station PhNB. In other words, the user apparatus UE can omit the first stage of cell search. As described above, since the macro base station eNB and the small base station PhNB are synchronized and the transmission timing of the synchronization signal SS of both is common, the user apparatus UE acquires the macro acquired in step S20. This is because the cell detection (correlation calculation with the replica signal) can be executed by regarding the transmission timing of the synchronization signal SS of the base station eNB as the transmission timing of the synchronization signal SS of the small base station PhNB.

1 (4). Configuration 1 (4) of each element-1. Configuration of User Device FIG. 8 is a block diagram illustrating a configuration of the user device UE according to the first embodiment. The user apparatus UE includes a radio communication unit 110, a storage unit 120, and a control unit 130. Illustrations of an output device that outputs audio, video, and the like and an input device that receives an instruction from the user are omitted for the sake of convenience. The wireless communication unit 110 is an element for performing wireless communication with the macro base station eNB and the small base station PhNB, a transmission / reception antenna, a receiving circuit that receives a radio signal (radio wave) and converts it into an electrical signal, and a control A transmission circuit that converts electric signals such as signals and user signals into radio signals (radio waves) and transmits the signals. The storage unit 120 stores information related to communication control, in particular, the transmission timing of the synchronization signal SS of the base station (eNB, PhNB) that has established synchronization, and the above-described synchronization state information and frequency information. The control unit 130 includes a cell search unit 132 in addition to transmitting and receiving user signals and control signals. The cell search unit 132 performs the above-described plurality of cell searches, that is, the normal two-stage cell search (FIG. 5) and the cell search of the small base station PhNB using the transmission timing of the macro base station eNB (FIG. 6 and the like). To do. The control unit 130 and each element in the control unit 130 are configured by a CPU (Central Processing Unit) (not shown) in the user apparatus UE executing a computer program stored in the storage unit 120 and functioning according to the computer program. It is a functional block that is realized.

1 (4) -2. Configuration of Macro Base Station FIG. 9 is a block diagram illustrating a configuration of the macro base station eNB according to the first embodiment. The macro base station eNB includes a radio communication unit 210, a network communication unit 220, a storage unit 230, and a control unit 240. The radio communication unit 210 is an element for executing radio communication with the user apparatus UE, and has the same configuration as the radio communication unit 110 of the user apparatus UE. The network communication unit 220 is an element for performing communication with other nodes (small base station PhNB, switching office, etc.) in the network NW, and transmits / receives signals to / from other nodes. The storage unit 230 stores information related to communication control. The control unit 240 includes a transmission unit 242 and an information notification unit 244 in addition to executing transmission / reception of user signals and control signals. The transmission unit 242 transmits the synchronization signal SS indicating the physical cell identifier PCI for identifying the macro base station eNB via the wireless communication unit 210. The information notification unit 244 notifies the user apparatus of the above-described synchronization state information and frequency information via the wireless communication unit 210. The control unit 240 and each element in the control unit 240 are functions realized by a CPU (not shown) in the macro base station eNB executing a computer program stored in the storage unit 230 and functioning according to the computer program. It is a block.

1 (4) -3. Configuration of Small Base Station FIG. 10 is a block diagram illustrating a configuration of the small base station PhNB according to the first embodiment. The small base station PhNB includes a wireless communication unit 310, a network communication unit 320, a storage unit 330, and a control unit 340. The radio communication unit 310 is an element for executing radio communication with the user apparatus UE, and has the same configuration as the radio communication unit 210 of the macro base station eNB. The network communication unit 320 is an element for executing communication with other nodes (such as the macro base station eNB) in the network NW, and transmits and receives signals to and from other nodes. The storage unit 330 stores information related to communication control. The control unit 340 includes a transmission unit 342 in addition to transmitting and receiving user signals and control signals. The transmission unit 342 transmits a synchronization signal SS indicating the physical cell identifier PCI for identifying the small base station PhNB via the wireless communication unit 310. The control unit 340 and each element in the control unit 340 are functions realized by a CPU (not shown) in the small base station PhNB executing a computer program stored in the storage unit 330 and functioning according to the computer program. It is a block.

1 (5). Advantages of the present embodiment According to the configuration of the present embodiment described above, the user apparatus UE does not execute the timing search process for the small base station PhNB, based on the transmission timing of the synchronization signal SS of the macro base station eNB. The physical cell identifier PCI specified in the synchronization signal SS transmitted by the small base station PhNB can be executed. As a result, since the timing search process for the small base station PhNB is omitted, the processing load for the user apparatus UE to recognize the small base station PhNB is reduced.

2. Second Embodiment A second embodiment of the present invention will be described below. In each embodiment illustrated below, about the element which an effect | action and a function are equivalent to 1st Embodiment, the code | symbol referred by the above description is diverted and each description is abbreviate | omitted suitably.

  In the first embodiment, the macro base station eNB and the small base station PhNB synchronize with each other and simultaneously transmit the synchronization signal SS. In the second embodiment, as illustrated in FIG. 11, the transmission timing of the synchronization signal SS of the macro base station eNB is transmitted at a transmission timing that is transmitted for a time corresponding to the transmission offset value OV. 342) transmits the synchronization signal SS.

  Hereinafter, with reference to FIG. 12, the identification process of the physical cell identifier PCI of the small base station PhNB in the present embodiment will be described. Cell detection and synchronization establishment (from step S12 to step S32) regarding the macro base station eNB performed by the user apparatus UE are the same as step S10 to step S30 of the first embodiment, and thus description thereof is omitted.

  The macro base station eNB sends, to the user apparatus UE, synchronization state information regarding the synchronization state with the small base station PhNB located in the vicinity thereof and frequency information regarding the identification signal frequency used by the small base station PhNB for transmission of the synchronization signal SS. Notify (S42). In the second embodiment, there is a time difference corresponding to the transmission offset value OV between the transmission timing of the macro base station eNB and the transmission timing of the small base station PhNB. The transmission offset value OV with respect to the transmission timing is shown. The user apparatus UE stores the received synchronization state information and frequency information.

  The small base station PhNB periodically transmits a synchronization signal SS indicating a physical cell identifier PCI for identifying the small base station PhNB at a transmission timing as shown in FIG. 11 (S52). The user apparatus UE performs cell detection (processing for specifying a physical cell identifier PCI indicating the small base station PhNB) based on the synchronization signal SS received from the small base station PhNB (S62). The above cell detection is performed using the synchronization state information (transmission offset value OV) and frequency information notified in step S42. More specifically, the user apparatus UE performs frequency search based on the transmission timing of the synchronization signal SS from the macro base station eNB and the transmission offset value OV without executing the timing search process for the small base station PhNB. A local identifier and group identifier detection process is executed for the identification signal frequency of the small base station PhNB shown. Then, the user apparatus UE establishes a wireless connection with the small base station PhNB (S72).

In the cell detection of step S62, the user apparatus UE does not need to search for the position (transmission timing) of the synchronization signal SS included in the radio signal from the small base station PhNB. In other words, the user apparatus UE can omit the first stage of cell search. As described above, since there is a time difference corresponding to the transmission offset value OV between the transmission timing of the macro base station eNB and the transmission timing of the small base station PhNB, the user apparatus UE acquires in step S22. This is because the transmission timing of the synchronization signal SS of the small base station PhNB can be acquired by adding the transmission offset value OV to the transmission timing of the synchronization signal SS of the macro base station eNB.
According to the above configuration, the same technical effects as those of the first embodiment are achieved.

3. Third Embodiment A third embodiment of the present invention will be described below. In the first embodiment, the macro base station eNB and the small base station PhNB are connected and synchronized with each other by an interface (such as an optical fiber) that can transmit a clock signal. In the third embodiment, the small base station PhNB receives the synchronization signal SS from the macro base station eNB and synchronizes with the macro base station eNB.

  FIG. 13 is a block diagram showing a radio communication system CS according to the third embodiment. The small base station PhNB receives the synchronization signal SS from the macro base station eNB, detects the transmission timing, and synchronizes with the macro base station eNB. However, in the third embodiment, unlike the first embodiment, the synchronization timing is delayed only by the time required for the radio signal transmitted from the macro base station eNB to reach the small base station PhNB and be processed. . Therefore, the small base station PhNB of the third embodiment advances the transmission timing of the synchronization signal SS according to the distance from the macro base station eNB.

  FIG. 14 is a block diagram illustrating a configuration of the small base station PhNB according to the third embodiment. The control unit 340 of the small base station PhNB further includes a synchronization detection unit 344, a received power measurement unit 346, and an offset value setting unit 348. The synchronization detection unit 344 detects the transmission timing of the synchronization signal SS from the macro base station eNB and supplies it to the transmission unit 342 in the same manner as the cell search unit 132 of the user apparatus UE of the above-described embodiment. The reception power measurement unit 346 measures reception power of a radio signal (reference signal) from the macro base station eNB received via the radio communication unit 310. The offset value setting unit 348 sets the transmission offset value OV to be larger as the reception power measured by the reception power measurement unit 346 is smaller, and supplies the transmission offset value OV to the transmission unit 342. The transmission unit 342 is configured to advance the transmission timing of the macro base station eNB supplied from the synchronization detection unit 344 by a transmission timing that is advanced by a time corresponding to the transmission offset value OV supplied from the offset value setting unit 348. A PhNB synchronization signal SS is transmitted.

  As can be understood from the above, the small base station PhNB of the third embodiment increases the transmission timing earlier (advances earlier) as the reception power of the radio signal from the macro base station eNB is smaller. Transmission of the synchronization signal SS) is executed. Since the radio signal is attenuated as it propagates in space, the small reception power of the radio signal from the macro base station eNB in the small base station PhNB means that the distance from the macro base station eNB to the small base station PhNB is large. To do. Therefore, according to the above small base station PhNB, the transmission timing is corrected (advanced) according to the distance from the macro base station eNB. As a result, the difference between the transmission timing of the macro base station eNB and the transmission timing of the small base station PhNB is reduced.

4). Fourth Embodiment A fourth embodiment of the present invention will be described below. In the first embodiment, the transmission timing at which the macro base station eNB transmits the synchronization signal SS and the transmission timing at which the small base station PhNB transmits the synchronization signal SS are synchronized with each other (FIG. 7). Since 168 types of SSSs are not orthogonal to each other, they interfere with each other when a plurality of SSSs are transmitted at the same transmission timing. Therefore, when performing the cell search (FIG. 6) of the small base station PhNB using the transmission timing of the macro base station eNB described in the first embodiment, depending on the radio environment or the like, the group identifier (and thus the physical cell identifier PCI) ) May not be identified with sufficient accuracy.

  Therefore, the small base station PhNB (transmission unit 342) of the fourth embodiment transmits a cell specific signal including a signal (identification signal) indicating the physical cell identifier PCI corresponding to the small base station PhNB. The cell specific signal is a signal different from the synchronization signal SS, for example, a reference signal other than the synchronization signal SS. Examples of reference signals include CRS (Cell Specific Reference Signal), CSI-RS (CSI Reference Signal), PRS (Positioning Reference Signal), and MBSFN-RS (MBSFN Reference Signal). The details of the above reference signals are described in, for example, 3GPP TS 36.211 V10.1.0 (2011-03), Chapter 6.10, Reference signals. For example, since CRS has 6 patterns of frequency shift, there is less interference due to collision compared to SSS. In addition, since symbols are spread over the entire system bandwidth in the CRS, more correlation energy can be acquired in the correlation calculation. Note that any signal indicating the physical cell identifier PCI corresponding to the small base station PhNB may be adopted as the cell specific signal.

  The user apparatus UE (cell search unit 132) specifies the physical cell identifier PCI of the small base station PhNB indicated in the identification signal included in the cell specific signal in the cell detection (step S60 in FIG. 6). The position (transmission timing) of the cell specific signal is determined as a relative position (transmission timing) with respect to the synchronization signal SS of the small base station PhNB. Further, as described above, the macro base station eNB and the small base station PhNB are synchronized, and the transmission timing of the synchronization signal SS of both is common. Therefore, the user apparatus UE (cell search unit 132) regards the transmission timing of the synchronization signal SS of the macro base station eNB acquired in step S20 as the transmission timing of the synchronization signal SS of the small base station PhNB, and Cell detection can be performed on the signal. Note that the user apparatus UE (cell search unit 132) may perform cell detection on a combination of the synchronization signal SS and the cell specific signal or a combination of a plurality of cell specific signals.

  According to the configuration of the present embodiment, since the cell detection of the small base station PhNB can be performed using a cell specific signal different from the synchronization signal SS, the group identifier (physical cell identifier PCI) is used using only the SSSs that interfere with each other. It is possible to specify the group identifier (physical cell identifier PCI) with higher accuracy compared to the configuration for specifying.

5. Fifth Embodiment A fifth embodiment of the present invention will be described below. The fifth embodiment relates to details of cell search of the small base station PhNB using a reference signal (CSI-RS). The macro base station eNB (information notification unit 244) of the fifth embodiment, in addition to the above-described synchronization state information and frequency information, information related to the configuration of the CSI-RS transmitted by the small base station PhNB (reference signal configuration information, CSI) -RS Configuration) and the CP length (cyclic prefix length) in wireless communication by the small base station PhNB are transmitted to the user apparatus UE.

  CSI-RS is a reference signal sequence generated using various parameters including physical cell identifier PCI. The radio resources (time and frequency) for transmitting the CSI-RS are not fixed and are determined independently of the physical cell identifier PCI (3GPP TS 36.211 V10.1.0 (2011-03), Chapter 6.11.1, Cell-specific reference signals). The reference signal configuration information described above indicates a radio resource in which CSI-RS is transmitted.

  The CP length is the time length of the cyclic prefix. The cyclic prefix is a guard interval that is inserted before an effective symbol in order to avoid the influence of a delayed wave during wireless communication using OFDM. The CP length is either “normal” or “extended”. The position of the SSS on the radio frame F (position with respect to the PSS) is determined according to the CP length (not shown in FIGS. 3 and 7).

  With reference to FIG. 6 again, the cell search of the small base station PhNB of this embodiment will be described. The establishment of wireless connection (steps S10 to S30) between the user apparatus UE and the macro base station eNB is the same as that in the above-described embodiment, and thus the description thereof is omitted. As described above, the macro base station eNB (information notification unit 244) notifies the user apparatus UE of synchronization state information, frequency information, reference signal configuration information, and CP length information (S40). The frequency information of the present embodiment indicates the frequency used for transmission of the synchronization signal SS and the frequency used for transmission of the CSI-RS as identification signal frequencies.

  The small base station PhNB periodically transmits a synchronization signal SS indicating the physical cell identifier PCI for identifying the small base station PhNB and the above-described CSI-RS (S50). The user apparatus UE performs cell detection based on the synchronization signal SS and CSI-RS received from the small base station PhNB (S60). The above cell detection is performed using synchronization state information, frequency information, reference signal configuration information, and CP length information. More specifically, when the synchronization status information indicates that “the macro base station eNB and the small base station PhNB are synchronized”, the user apparatus UE does not perform the timing search process for the small base station PhNB. Based on the transmission timing of the synchronization signal SS from the macro base station eNB and the reference signal configuration information, the local identifier, group identifier, and CSI-RS of the identification signal frequency of the small base station PhNB indicated in the frequency information Perform detection processing. Then, the user apparatus UE establishes a wireless connection with the small base station PhNB (S70). The above operation can also be applied to the configuration of the second embodiment in which the transmission timing of the small base station PhNB is offset. The above configuration can also be applied to arbitrary signals (other reference signals, small cell discovery signals (Discovery Signals), etc.) that can be used for cell identification.

  Since the user apparatus UE is notified of the reference signal configuration information from the macro base station eNB, the user apparatus UE recognizes the radio resource to which the CSI-RS is transmitted. Therefore, in the cell detection of step S60, the user apparatus UE performs CSI-RS detection processing (correlation calculation between the CSI-RS transmitted from the small base station PhNB and the replica signal stored in the user apparatus UE). Can be executed. Further, since the user equipment UE is notified of the CP length information from the macro base station eNB, the user apparatus UE recognizes the position on the radio frame F of SSS (position with respect to PSS). Therefore, in the cell detection in step S60, the user apparatus UE does not need to specify whether the SSS position (transmission timing) corresponds to the “normal” CP length or the “extended” CP length.

  According to the above configuration, the same technical effects as those of the first embodiment are achieved. Furthermore, since the cell detection of the small base station PhNB is performed using the reference signal (CSI-RS), the cell can be identified with higher accuracy than the configuration in which the cell detection is performed using only the SSSs that interfere with each other. It becomes possible to do. Moreover, even if the small base station PhNB has a plurality of transmission points and each transmission point is identified by a reference signal (CSI-RS), according to the above configuration, not only the small base station PhNB but each It is also possible to identify the transmission point.

6). Sixth Embodiment A sixth embodiment of the present invention will be described below. Synchronization between the macro base station eNB and the small base station PhNB is not always exact. It may be assumed that the synchronization accuracy between the macro base station eNB and the small base station PhNB is low. In such a case, even if the above-described synchronization state information indicates that “the macro base station eNB and the small base station PhNB are synchronized” as in the first embodiment, actually, the macro base station eNB There is a possibility that the transmission timing of the synchronization signal SS from the base station is different from the transmission timing of the synchronization signal SS from the small base station PhNB.

  Therefore, the user apparatus UE (cell search unit 132) performs a detection process based on the transmission timing of the synchronization signal SS from the macro base station eNB instead of the first stage (timing search process) of the cell search for the small base station PhNB. (Tracking process) is executed. More specifically, in the cell detection (step S60 in FIG. 6) for the small base station PhNB, the user apparatus UE indicates that the synchronization state information is “the macro base station eNB and the small base station PhNB are synchronized”. Indicates a timing search process over a predetermined period including the transmission timing of the synchronization signal SS from the macro base station eNB (for example, 5 microseconds centering on the above transmission timing) (that is, limiting the period) Then, after specifying the transmission timing of the small base station PhNB, the above-described cell detection is performed.

  The above situation is the same in the second embodiment in which the transmission timing of the small base station PhNB is offset. That is, when the accuracy of synchronization between the macro base station eNB and the small base station PhNB is low, the transmission timing (calculation in which the transmission timing of the macro base station eNB is delayed by the time corresponding to the transmission offset value OV indicated by the synchronization state information) There is a possibility that the transmission timing of the small base station PhNB) and the actual transmission timing of the synchronization signal SS from the small base station PhNB are shifted.

  Therefore, the user apparatus UE performs transmission by delaying the transmission timing of the synchronization signal SS from the macro base station eNB by a time corresponding to the transmission offset value OV in the cell detection (step S62 in FIG. 12) for the small base station PhNB. Perform timing search processing over a predetermined period (for example, 5 microseconds centered on the above transmission timing) including timing (that is, calculation transmission timing of the small base station PhNB) (that is, limit the period) The cell detection is performed after the transmission timing of the small base station PhNB is specified.

  According to the above configuration, even if the synchronization accuracy between the macro base station eNB and the small base station PhNB is low, the same technical effect as that of the above-described embodiment is achieved.

7). Seventh Embodiment A seventh embodiment of the present invention will be described below. In the seventh embodiment, as illustrated in FIG. 15, a case is assumed in which a plurality of small base stations PhNB exist under the macro base station eNB. The plurality of small base stations PhNB are synchronized with the connected macro base station eNB.

  As illustrated in FIG. 16, the multiple small base stations PhNB transmit a common reference signal (for example, CSI-RS) at the same transmission timing. The above reference signals are synchronization reference signals used by the user apparatus UE to establish synchronization with the small base station PhNB. Further, as illustrated in FIG. 16, each of the plurality of small base stations PhNB transmits reference signals (for example, CSI-RS) having different transmission timings or sequences. The above reference signals are identification reference signals used for the user apparatus UE to identify the small base station PhNB.

  In addition, considering that the macro base station eNB and the small base station PhNB are synchronized, only the macro base station eNB may transmit the above reference signal for synchronization. In this case, the small base station PhNB only needs to transmit an identification reference signal indicating itself.

  According to the above configuration, synchronization with a plurality of small base stations PhNB can be simultaneously detected by using a common synchronization reference signal. Furthermore, since each small base station PhNB transmits a different identification reference signal, the user apparatus UE can identify each small base station PhNB.

8). Eighth Embodiment An eighth embodiment of the present invention will be described below. In the eighth embodiment, as illustrated in FIG. 17, in the radio communication system CS, the user apparatuses UE directly perform radio communication. FIG. 18 is a block diagram illustrating a configuration of a user apparatus UE according to the eighth embodiment. The control unit 130 of the user apparatus UE further includes a terminal transmission unit 134 that transmits a terminal detection signal indicating a terminal identifier for identifying the user apparatus.

  FIG. 19 is an explanatory diagram of terminal detection signals transmitted by a plurality of user apparatuses UE. Each user apparatus UE (terminal transmission unit 134) transmits a terminal detection signal in the resource block RB allocated to the user apparatus UE. In FIG. 19, the hatching of the resource block RB corresponds to each different user apparatus UE. In the eighth embodiment, the terminal detection signal is an uplink signal transmitted using SC-FDMA. Reduction of the peak-to-average power ratio (PAPR) is realized by transmitting a signal from the user apparatus UE on a single carrier.

  FIG. 20 is an explanatory diagram of an identification signal transmitted by the small base station PhNB. The small base station PhNB (transmission unit 342) transmits an identification signal having a signal format common to the terminal detection signal transmitted by the user apparatus UE, in the plurality of resource blocks RB. “Common signal format” means that the signal length, the number of selectable signal sequences, the modulation / demodulation method used at the time of signal transmission / reception, and the like are common.

  In FIG. 20, the type of hatching of the resource block RB differs depending on the small base station PhNB that is the transmission source. As can be understood from FIG. 20, a plurality of resource blocks RB may be transmitted on one time axis or on one frequency axis. According to the above configuration, the diversity effect in the time domain or the frequency domain by the plurality of resource blocks RB is realized.

The identification signal transmitted by the small base station PhNB in the eighth embodiment is preferably transmitted using SC-FDMA. The above identification signal is preferably transmitted in a frequency band that can be received by the user apparatus UE. Therefore, when the uplink frequency and the downlink frequency are different in the small base station PhNB (that is, when FDD is adopted), the identification signal may be transmitted using SC-FDMA at the downlink frequency. In the above-described case where a plurality of resource blocks RB are transmitted on one frequency axis, a plurality of single carriers may be used for transmitting an identification signal. On the other hand, when the uplink frequency and the downlink frequency are common in the small base station PhNB (that is, when TDD is adopted), the identification signal may be transmitted at the common frequency.
Further, the identification signal may be transmitted using a dedicated radio resource. In the dedicated radio resource, it is preferable that transmission of signals other than the identification signal is stopped.

  According to the above configuration, the terminal detection signal for detecting the user apparatus UE and the identification signal for detecting the small base station PhNB have a common signal format. Therefore, the user apparatus UE can perform detection of the small base station PhNB and detection of other user apparatuses UE by a single mechanism.

9. Ninth Embodiment A ninth embodiment of the present invention will be described below. In the fifth embodiment, cell detection of the small base station PhNB is performed using a reference signal (CSI-RS). In the ninth embodiment, cell detection of the small base station PhNB is performed based on a hopping pattern (identification signal pattern) configured by a plurality of CSI-RSs.

  The small base station PhNB (transmission unit 342) of the ninth embodiment transmits a CSI-RS according to a hopping pattern unique to the small base station PhNB. The hopping pattern indicates the arrangement of CSI-RSs in each of the plurality of subframes SF. The user apparatus UE can identify the small base station PhNB based on the arrangement (hopping pattern) of the CSI-RS over a plurality of subframes SF.

  FIG. 21 is an explanatory diagram of arrangement of CSI-RSs in one resource block RB. A plurality of resource elements RE are included in the resource block RB. The CSI-RS is transmitted by one of resource elements RE (RE # 0 to RE # 19) numbered from 0 to 19 in FIG. 21 (a plurality of numbers may be selected). Note that there may be a resource block RB to which CSI-RS is not transmitted.

  FIG. 22 is a diagram illustrating a specific example of a hopping pattern. As illustrated, the small base station PhNB transmits CSI-RSs in the order (hopping pattern) of RE # 5-RE # 9-RE # 6-RE # 3-RE # 8. The user apparatus UE is notified of the hopping pattern used by each small base station PhNB from the macro base station eNB. Therefore, the user apparatus UE can identify the small base station PhNB by detecting the above hopping pattern.

  The repetition period of the hopping pattern may be set equal to the repetition period of the conventional CSI-RS (for example, 80 ms), or set to be equal to another period, for example, an integer multiple of the repetition period of the conventional CSI-RS. May be.

  In the ninth embodiment, similar to the seventh embodiment, a plurality of small base stations PhNB transmit a common synchronization CSI-RS, and each small base station PhNB transmits a different identification CSI-RS. May be.

  According to the above configuration, since more identification patterns are provided compared to the configuration in which the small base station PhNB is identified based only on the resource element RE to which the CSI-RS is transmitted, more small patterns are provided. A base station PhNB can be installed.

10. Modified example
The above embodiment can be variously modified. Specific modifications are exemplified below. Two or more aspects arbitrarily selected from the above embodiments and the following examples can be appropriately combined as long as they do not contradict each other.

10 (1). Modification 1
The radio communication system CS (network NW) of the above embodiment is a heterogeneous network including a macro base station eNB and a small base station PhNB, but only a single type of base station (for example, the macro base station eNB) is provided. A provided homogeneous network may be employed. In that case, one frequency band may be used.

10 (2). Modification 2
In the above embodiment, the macro base station eNB and the small base station PhNB are synchronized via an interface that can transmit a clock signal such as an optical fiber or a radio interface, but the macro base station eNB and the small base station PhNB are synchronized. The means for establishing is arbitrary. For example, the macro base station eNB and the small base station PhNB may establish synchronization based on the time indicated by the radio wave (GPS signal) transmitted from the GPS satellite.

10 (3). Modification 3
The macro base station eNB (information notification unit 244) notifies the user apparatus UE of an identifier list indicating physical cell identifiers PCI of a plurality of small base stations PhNB existing around the macro base station eNB in the synchronization state information. (Step S40, Step S42). The user apparatus UE (cell search unit 132) may perform cell detection (correlation calculation with a replica signal) only for the small base station PhNB corresponding to the physical cell identifier PCI indicated in the notified identifier list ( Step S60, Step S62). In the above case, since the number of cell identifiers PCI for performing cell detection is limited, the processing load of the user apparatus UE is further reduced.

10 (4). Modification 4
In the above embodiment, the small base station PhNB is identified by the physical cell identifier PCI, but the identifier for identifying the small base station PhNB is arbitrary. An identifier dedicated to identification of the small base station PhNB different from the physical cell identifier PCI may be adopted.

10 (5). Modification 5
There may be a plurality of small base stations PhNB under the control of one macro base station eNB. When there are a plurality of small base stations PhNB, the small base stations PhNB may transmit the synchronization signal SS in synchronization with each other, or may transmit the synchronization signal SS based on different transmission offset values OV. Also good. When a plurality of small base stations PhNB transmit the synchronization signal SS based on different transmission offset values OV, the macro base station eNB (information notification unit 244) notifies the user apparatus UE of each offset value OV as synchronization state information. To do.

10 (6). Modification 6
One reference signal configuration information (CSI-RS Configuration) may be set for a single small base station PhNB or a transmission point, or a plurality may be set. When a plurality of reference signal configuration information is set for a single small base station PhNB or a transmission point, the cell is specified with higher accuracy than when one reference signal configuration information is set. It becomes possible.

10 (7). Modification 7
In the sixth embodiment, the user apparatus UE performs a cell search (timing search process) using the synchronization signal SS. However, the user apparatus UE can execute a cell search (timing search process) using an arbitrary signal transmitted periodically. For example, the reference signals (CRS, CSI-RS, PRS, MBSFN-RS, etc.) described in the fourth embodiment can be used for cell search. In addition, the cell search may be performed using a combination of the synchronization signal SS and the above reference signals, or a combination of a plurality of reference signals.

10 (8). Modification 8
In the ninth embodiment, as shown in FIG. 23, a hopping pattern that hops not only the resource element RE in the subframe SF but also the resource block RB that transmits the CSI-RS may be employed. According to the above configuration, since more hopping patterns are provided, it is possible to install more small base stations PhNB.

10 (9). Modification 9
In the ninth embodiment, as shown in FIG. 24, a new version user apparatus UEN for identifying the small base station PhNB and the CSI-RS are transmitted using the CSI-RS hopping pattern (“for UEN” in FIG. 24). Both the old version user apparatus UEO that identifies the small base station PhNB based only on the resource element RE (for “UEO” in FIG. 24) may be mixed.

10 (10). Modification 10
The user apparatus UE is an arbitrary apparatus that can perform radio communication with the macro base station eNB and the small base station PhNB. The user apparatus UE may be, for example, a mobile phone terminal such as a feature phone or a smartphone, a desktop personal computer, a notebook personal computer, a UMPC (Ultra-Mobile Personal Computer), or a portable game machine. Other wireless terminals may be used.

10 (11). Modification 11
Each function executed by the CPU in each element (user apparatus UE, macro base station eNB, small base station PhNB) in the radio communication system CS may be executed by hardware instead of the CPU. For example, FPGA ( The program may be executed by a programmable logic device such as a field programmable gate array (DSP) or a digital signal processor (DSP).

UE …… User equipment 110 …… Radio communication unit 120 …… Storage unit 130 …… Control unit 132 …… Cell search unit eNB …… Macro base station 210 …… Radio communication unit 220 …… Network Communication unit 230 ... Storage unit 240 ... Control unit 242 ... Transmission unit 244 ... Information notification unit PhNB ... Small base station 310 ... Wireless communication unit 320 ... Network communication unit 330 ...... Storage unit, 340 ... Control unit, 342 ... Transmission unit, 344 ... Synchronization detection unit, 346 ... Received power measurement unit, 348 ... Offset value setting unit, C ... Cell, C1 ... Macro cell, C2: Small cell, CS: Wireless communication system, F: Wireless frame, NW ... Network, OV ... Transmission offset value, PCI ... Physical cell identifier, SF ... Subframe, SS ... synchronization signal.

Claims (10)

Wireless communication can be performed in the first frequency band, and wireless communication can be performed in the second frequency band with the first base station identified by the first cell identifier, and is identified by the second cell identifier. A plurality of base stations including a second base station;
A user apparatus capable of performing wireless communication with each of the plurality of base stations,
The first base station is
A first transmitter that transmits a first synchronization signal indicating the first cell identifier for identifying the first base station at a first transmission timing;
The second base station is
A second transmitter for transmitting an identification signal indicating the second cell identifier for identifying the second base station;
The user equipment is
A cell search unit for detecting the first transmission timing based on the first synchronization signal received from the first base station and executing a timing search process for establishing synchronization with the first base station;
The first base station is
Synchronization state information regarding the synchronization state between the first base station and the second base station, and frequency information regarding an identification signal frequency used by the second base station for transmitting the identification signal in the second frequency band, An information notification unit for notifying the user device;
The cell search unit of the user equipment is
A radio communication system that executes, for the identification signal frequency indicated in the frequency information, a process for specifying the second cell identifier indicated in the identification signal based on the synchronization state information from the first base station. The first base station and the second base station can perform wireless communication in synchronization with each other,
The second transmitter of the second base station transmits a second synchronization signal at a second transmission timing,
The synchronization status information notified by the information notification unit of the first base station indicates whether or not the first base station and the second base station are synchronized,
If the synchronization state information indicates that the first base station and the second base station are synchronized, the cell search unit of the user apparatus does not perform a timing search process for the second base station. The wireless communication system according to claim 1, wherein the second cell identifier specifying process indicated by the identification signal is executed based on the first transmission timing. The first base station and the second base station can perform wireless communication in synchronization with each other,
The second transmitter of the second base station transmits a second synchronization signal at a second transmission timing,
The synchronization status information notified by the information notification unit of the first base station indicates whether or not the first base station and the second base station are synchronized,
When the synchronization state information indicates that the first base station and the second base station are in synchronization, the cell search unit of the user apparatus performs the second base over a predetermined period including the first transmission timing. The wireless communication according to claim 1, wherein the second transmission timing is specified by executing a timing search process for a station, and the second cell identifier specifying process indicated by the identification signal is executed based on the second transmission timing. system. The second transmission unit of the second base station includes the identification signal at the second transmission timing obtained by delaying the first transmission timing of the first base station by a time corresponding to a transmission offset value. Send a sync signal,
The synchronization state information notified by the information notification unit of the first base station indicates the transmission offset value with respect to the first transmission timing of the first base station,
Based on the first transmission timing and the transmission offset value indicated by the synchronization state information, the cell search unit of the user apparatus does not perform a timing search process for the second base station, and outputs the identification signal. The radio | wireless communications system of Claim 1 which performs the specific process of the said 2nd cell identifier shown. The second transmission unit of the second base station includes the identification signal at the second transmission timing obtained by delaying the first transmission timing of the first base station by a time corresponding to a transmission offset value. Send a sync signal,
The synchronization state information notified by the information notification unit of the first base station indicates the transmission offset value with respect to the first transmission timing of the first base station,
The cell search unit of the user apparatus performs a timing search process for the second base station over a predetermined period including a transmission timing obtained by delaying the first transmission timing by a time corresponding to the transmission offset value indicated by the synchronization state information. 2. The wireless communication system according to claim 1, wherein the second transmission timing is specified by executing and the specifying process of the second cell identifier indicated in the identification signal is executed based on the second transmission timing. The second base station further includes:
A received power measuring unit that measures received power of a radio signal received from the first base station;
An offset value setting unit that sets a larger transmission offset value as the received power measured by the received power measurement unit is smaller;
The second transmission unit of the second base station includes the identification signal at the second transmission timing that is earlier than the first transmission timing of the first base station by a time corresponding to a transmission offset value. Send a sync signal,
The synchronization status information notified by the information notification unit of the first base station indicates whether or not the first base station and the second base station are synchronized,
If the synchronization state information indicates that the first base station and the second base station are synchronized, the cell search unit of the user apparatus does not perform a timing search process for the second base station. The wireless communication system according to claim 1, wherein the second cell identifier specifying process indicated by the identification signal is executed based on the first transmission timing. The synchronization state information further includes an identifier list indicating a plurality of the second cell identifiers corresponding to a plurality of the second base stations,
The cell search unit of the user apparatus executes the specifying process only for the plurality of second base stations corresponding to the plurality of second cell identifiers indicated in the identifier list. Any wireless communication system. The user equipment is
A terminal transmission unit for transmitting a terminal detection signal indicating a terminal identifier for identifying the user device;
The second transmitter of the second base station is
The wireless communication system according to claim 1, wherein the identification signal having a signal format common to the terminal detection signal is transmitted. The second transmitter of the second base station is
The radio communication system according to claim 1, wherein the identification signal is arranged in each of a plurality of subframes, and the identification signal is transmitted according to an identification signal pattern for identifying the second base station. Wireless communication can be performed in the first frequency band, and wireless communication can be performed in the second frequency band with the first base station identified by the first cell identifier, and is identified by the second cell identifier. A plurality of base stations including a second base station;
A communication control method for a wireless communication system comprising a user apparatus capable of performing wireless communication with each of the plurality of base stations,
In the first base station, transmitting a first synchronization signal indicating the first cell identifier for identifying the first base station at a first transmission timing;
Transmitting an identification signal indicating the second cell identifier for identifying the second base station in the second base station;
In the user apparatus, detecting the first transmission timing based on the first synchronization signal received from the first base station, and executing a timing search process for establishing synchronization with the first base station;
In the first base station, synchronization state information related to a synchronization state between the first base station and the second base station, and an identification signal used by the second base station for transmitting the identification signal in the second frequency band Notifying the user equipment of frequency information about the frequency;
In the user apparatus, for the identification signal frequency indicated in the frequency information, the second cell identifier included in the identification signal is specified using the synchronization state information from the first base station. And a communication control method.

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