JP6179589B2 - Mobile communication system, mobile station, base station, and cell detection method - Google Patents

Description

  The present invention relates to a mobile communication system, a mobile station, a base station, and a cell detection method.

  Conventionally, various devices have been devised to increase the transmission capacity in mobile communication systems (hereinafter sometimes referred to as “system capacity”). For example, 3GPP LTE (3rd Generation Partnership Project Radio Access Network Long Term Evolution) discusses a technique for increasing system capacity by utilizing “small cells” in addition to “macro cells”. Here, the “cell” is defined based on the “communication area” and “channel frequency” of one base station. The “communication area” may be the entire area where radio waves transmitted from the base station reach (hereinafter sometimes referred to as “range area”), or a divided area in which the range area is divided (so-called sector) ). The “channel frequency” is a unit of frequency used by the base station for communication, and is defined based on the center frequency and the bandwidth. The channel frequency is a part of the “operating band” assigned to the entire system. The “macro cell” is a cell of a base station that can transmit with high transmission power, that is, a base station with a large range area. A “small cell” is a cell of a base station that transmits with low transmission power, that is, a base station with a small range area.

  In 3GPP LTE, as a configuration of a mobile communication system, for example, a first configuration in which a plurality of small cells are included in a macro cell, a second configuration in which a plurality of small cells are arranged regardless of the macro cell, and the like are being studied. . In particular, the first configuration is mainly studied. In addition, when the mobile communication system adopts the first configuration, a technique in which a mobile station connects to a macro cell and a small cell at the same time has been studied.

  By the way, in order for the mobile station to start communication with the base station, the mobile station performs a process of detecting a connection target cell. Conventionally, a mobile station specifies a macro cell using a synchronization signal (PSS: Primary Synchronization Signal, SSS) transmitted in a macro cell in which the mobile station is located. The identification of the macro cell is possible because the synchronization signal has a one-to-one correspondence with PCI (Physical Cell Identification) which is an identification (ID) of the macro cell. Specifically, three types of code sequences are prepared for PSS, and 168 types of code sequences are prepared for SSS. Therefore, 504 PCIs can be represented by a combination of PSS and SSS. Then, the mobile station can perform efficient cell detection by first specifying the received PSS, then specifying the received SSS, and specifying the PCI from the combination of the specified PSS and SSS.

  However, when many small cells are introduced in addition to the macro cell in the mobile communication system, first, if the number of PCI is limited, the PCI will be insufficient. On the other hand, if the number of PCIs is increased, the number of cell detection targets increases, which increases the burden on the mobile station for cell detection. Since there is a need to extend the time during which the mobile station can operate with a single charge, it is desirable to reduce the load of cell detection processing and reduce the power consumption of the mobile station.

  In LTE, proposals have been made for the purpose of improving the efficiency of small cell detection.

  For example, in the first proposal, the macro cell base station notifies the mobile station of information (carrier frequency, cell ID, location information, etc.) on a small cell located in the vicinity as a white list, and the mobile station receives The small cell is detected using the white list. In the second proposal, the mobile station first notifies the macro cell base station of information on small cells in the vicinity of the mobile station, thereby optimizing the timing at which the macro cell base station issues a measurement instruction to the mobile station. ing. In the third proposal, a small cell detection signal (DS) is newly introduced to speed up cell detection by the mobile station and reduce power consumption of the mobile station.

3GPP TSG-RAN WG2 Meeting, R2-114951, “Discussion on enhancement of small cell discovery,” October 2011 3GPP TSG-RAN2 meeting, R2-115228, “Discussion on small cell discovery for HetNet mobility,” October 2011 3GPP TSG RAN WG1 Meeting, R1-120398, “Enhanced Cell Identification for Additional Carrier Type,” February 2012

  However, as the number of small cells in the macro cell increases, the number of small cells in the vicinity of the mobile station also increases. With the conventional small cell detection method, it is difficult to reduce the load of small cell detection by the mobile station. Further, it is difficult to uniquely identify a small cell simply by introducing a new small cell detection signal, and it is difficult to reduce the load of small cell detection.

  The disclosed technique has been made in view of the above, and an object thereof is to provide a mobile communication system, a mobile station, a base station, and a cell detection method that efficiently detect a connection target cell.

  In one aspect, the mobile communication system, mobile station, base station, and cell detection method disclosed in the present application include a base station and a mobile station corresponding to each of a plurality of cells. The cells are distributed to a plurality of first groups to which different types of synchronization signals are assigned. The base station includes the synchronization signal assigned to the first group to which the station belongs, and uses transmission resources defined by time and frequency corresponding to the synchronization signal and different for each first group. A transmission unit for transmitting a frame for notifying cell identification information is provided. The mobile station detects a synchronization signal from a received frame, and identifies the transmission resource in the received frame corresponding to the synchronization signal detected by the detection unit, and identifies the identified resource in the received frame A cell specifying unit that acquires the identification information from a transmission resource and specifies the cell.

  According to one aspect of the mobile communication system, the mobile station, the base station, and the cell detection method disclosed in the present application, it is possible to efficiently detect a connection target cell.

FIG. 1 is a diagram illustrating an example of a mobile communication system according to the first embodiment. FIG. 2 is a diagram for explaining cell group assignment in the first embodiment. FIG. 3 is a diagram illustrating an example of a base station corresponding to the small cell according to the first embodiment. FIG. 4 is a diagram for explaining the mapping of the PSS and the SSS by the small cell base station apparatus according to the first embodiment. FIG. 5 is a diagram for explaining a frame transmitted from each cell group according to the first embodiment. FIG. 6 is a diagram illustrating an example of a base station corresponding to the macro cell according to the first embodiment. FIG. 7 is a diagram illustrating an example of the mobile station according to the first embodiment. FIG. 8 is a sequence diagram illustrating an example of a processing operation of the mobile communication system according to the first embodiment. FIG. 9 is a diagram illustrating a modified example of grouping of cell groups. FIG. 10 is a diagram for explaining a frame transmitted from each cell group according to the second embodiment. FIG. 11 is a diagram for explaining a frame transmitted from each cell group according to the third embodiment. FIG. 12 is a diagram illustrating a hardware configuration example of a base station corresponding to a macro cell. FIG. 13 is a diagram illustrating a hardware configuration example of a base station corresponding to a small cell. FIG. 14 is a diagram illustrating a hardware configuration example of a mobile station.

  Hereinafter, embodiments of a mobile communication system, a mobile station, a base station, and a cell detection method disclosed in the present application will be described in detail with reference to the drawings. The mobile communication system, mobile station, base station, and cell detection method disclosed in the present application are not limited by the following embodiments. Moreover, the same code | symbol is attached | subjected to the structure which has the same function in embodiment, and the overlapping description is abbreviate | omitted. In the following description, an LTE system or an LTE-Advanced system that is an advanced form of the LTE system may be described as an example, but the present invention is not limited to this.

[Outline of mobile communication system]
FIG. 1 is a diagram illustrating an example of a mobile communication system according to the first embodiment. In FIG. 1, the mobile communication system 1 includes a base station 10, a plurality of base stations 20, and a mobile station 30. In FIG. 1, the macro cell C10 is defined by the range area of the base station 10 and the first channel frequency. In FIG. 1, two clusters CL41 and CL42 are shown as an example. Each of the clusters CL41 and CL42 includes a plurality of small cells C20. Each small cell C20 is defined by the range of one base station 20 and the second channel frequency. In FIG. 1, as an example, a case where the clusters CL41 and CL42 and the macro cell C10 overlap is shown. Further, the first channel frequency and the second channel frequency may be the same or different. In addition, the numbers of base stations 10, base stations 20, and mobile stations 30 shown in FIG. 1 are merely examples, and the present invention is not limited to this. That is, the mobile communication system 1 may include a plurality of macro cells C10 and clusters CL40 that overlap each macro cell C10. Hereinafter, the cluster CL41 and the cluster CL42 may be collectively referred to as a cluster CL40 unless they are particularly distinguished. This cluster CL40 is an example of a “second group”.

  In FIG. 1, the cluster CL40 has a plurality of small cells C20. A different PCI is assigned to each macro cell C10.

  The small cell C20 included in the same cluster is divided into three cell groups. Here, the small cells C20 belonging to each cell group are selected to have a large distance. By increasing the distance between the small cells C20, it is possible to reduce the influence of interference between the small cells C20 belonging to the same cell group. For example, as shown in FIG. 1, in CL40, there are three cell groups: a small cell C20 cell group indicated by a solid color, a small cell C20 cell group indicated by diagonal lines, and a small cell C20 cell group indicated by dots. Divided into groups.

  Each cell group is assigned a different PSS. The small cell C20 included in each cell group has a PSS assigned to the cell group to which it belongs. Also, one SSS of 168 types is assigned to the three cell groups. That is, each small cell C20 is assigned a PCI that is a cell ID represented by a combination of PSS and SSS assigned to the cell group to which each small cell C20 belongs.

  FIG. 2 is a diagram for explaining cell group assignment in the first embodiment. As shown in FIG. 2, in this embodiment, both the clusters CL41 and CL42 are divided into three cell groups. A different PSS is assigned to each cell group of each cluster CL40. For example, in this embodiment, “0” is assigned as PSS to group 1 of the cell group. In addition, “1” is assigned as PSS to group 2 of the cell group. Also, “2” is assigned as PSS to group 3 of the cell group. And between cluster CL41 and cluster CL42, the same PSS is assigned to the group of the same number.

  Each base station 20 is assigned identification information that can be uniquely identified. The identification information that can uniquely identify each base station 20 can also uniquely identify the small cell 20 </ b> C corresponding to each base station 20. That is, the identification information that can uniquely identify each base station 20 can be said to be identification information that can uniquely identify the small cell C20. As identification information of the small cell C20, ECGI (E-UTRAN Cell Global Identifier) or the like can be used. In this embodiment, the ECGI has a size of 52 bits and is too large to identify the small cell C20. Therefore, a part of the EGCI (Truncated ECGI: T-ECGI) is included in the small cell C20 as identification information of the small cell C20. Assigned.

  Here, the base station 20 of the small cell C20 transmits a synchronization signal or the like specific to the cell ID assigned to the own station. This synchronization signal includes PSS and SSS. At this time, the base station 20 transmits T-ECGI information using a subframe corresponding to the PSS in the frame for transmitting the synchronization signal.

  The mobile station 30 detects the PSS of the small cell C20 from the synchronization signal transmitted by the base station 20, and establishes slot timing synchronization with a period of 5 ms. Further, the mobile station 30 detects a PSS sequence in the detected PSS.

  The mobile station 30 acquires the position of the subframe in which the T-ECGI is stored from the detected PSS. Thereafter, the mobile station 30 acquires T-ECGI from the designated subframe. The mobile station 30 can uniquely identify the small cell C20 that has transmitted the synchronization signal by acquiring the EGCI. Then, the mobile station 30 transmits information on the small cell C20 specified by EGCI to the base station 10.

  Moreover, the mobile station 30 detects PCI by detecting SSS. Then, the mobile station 30 establishes synchronization of frame timing with a period of 10 ms and detects a CP (Cyclic Prefix) length.

  The base station 10 determines the small cell C20 to which the mobile station 30 is connected using the received power notified from the mobile station 30 and the information on the small cell specified by EGCI.

  By realizing the small cell detection method using T-ECGI described above, it is possible to make the determination of connection target cells more efficient.

[Configuration Example of Base Station 20]
FIG. 3 is a diagram illustrating an example of a base station corresponding to the small cell according to the first embodiment. In FIG. 3, the base station 20 includes a control unit 21 and a radio unit 22. The control unit 21 includes a packet generation unit 201, a MAC (Media Access Control) control unit 202, a MAC scheduling unit 203, an encoding unit 204, a modulation unit 205, a multiplexing unit 206, and an IFFT (Inverse Fast Fourier Transform) unit 207. . The control unit 21 includes a radio resource control unit 208, an FFT (Fast Fourier Transform) unit 209, a demodulation unit 210, a decoding unit 211, and a separation unit 212. The radio unit 22 includes a transmission radio unit 221 and a reception radio unit 222.

  The packet generator 201 receives transmission data addressed to the mobile station 30, that is, user data, and generates a transmission packet using the received user data. Then, the packet generation unit 201 outputs the generated transmission packet to the MAC scheduling unit 203.

  The MAC control unit 202 allocates resources used for communication between the mobile station 30 and the mobile station 30 based on channel quality information (CQI: Channel Quality Indicator) reported from the mobile station 30. This resource is defined by, for example, time and frequency. Then, the MAC control unit 202 outputs the individual control information including information on the allocated resources (hereinafter sometimes referred to as “allocated resources”) to the MAC scheduling unit 203 and the multiplexing unit 206.

  The MAC scheduling unit 203 outputs the packet addressed to the mobile station 30 received from the packet generation unit 201 to the encoding unit 204 at a timing corresponding to the time allocated to the mobile station 30 by the MAC control unit 202. Note that the MAC scheduling unit 203 may divide the packet into data units having a predetermined data size and output the data units to the encoding unit 204.

  Encoding section 204 performs an encoding process on the packet received from MAC scheduling section 203 and outputs the encoded packet to modulation section 205.

  Modulation section 205 modulates the encoded packet received from encoding section 204 and outputs the modulated packet to multiplexing section 206.

  The multiplexing unit 206 multiplexes the input signal by mapping it to a predetermined resource, and outputs the multiplexed signal to the IFFT unit 207.

  Specifically, the multiplexing unit 206 receives the individual control information from the MAC control unit 202 and maps it to a resource area allocated to a downlink control channel (for example, PDCCH: Physical Downlink Control Channel).

  The multiplexing unit 206 receives the packet from the modulation unit 205 and maps it to the downlink allocated resource indicated by the individual control information.

  Further, the multiplexing unit 206 receives a common reference signal (CRS) common in the cluster CL40, for example. Then, the multiplexing unit 206 maps the common reference signal to a predetermined resource. In addition to CRS, multiplexing section 206 receives CSI-RS (Channel State Information-Reference Signal) which is a reference signal for channel quality measurement. Then, the multiplexing unit 206 maps the CSI-RS to a predetermined resource.

  Further, the multiplexing unit 206 receives information on the PSS and SSS assigned to the own station. Then, the multiplexing unit 206 maps the PSS and SSS to a plurality of predetermined locations of predetermined resources.

  FIG. 4 is a diagram for explaining the mapping of the PSS and the SSS by the small cell base station apparatus according to the first embodiment. A frame 500 in FIG. 4 represents time resources in the horizontal direction and frequency resources in the vertical direction.

  Frame 500 includes a subframe for transmitting a PBCH (Physical Broadcast CHannel) synchronization signal. PBCH is a broadcast information resource transmitted by the base station 20. The multiplexing unit 206 transmits a synchronization signal including PSS and SSS using the frame 500.

  The PBCH is transmitted using 6 RBs in the frequency direction around the center frequency. Resource block 510 represents one subframe for transmitting PBCH.

  The multiplexing unit 206 maps the PBCH to the position represented by the region 530 of the resource block 510. Further, the multiplexing unit 206 maps the common reference signal and the reference signal to the position represented by the region 540 of the resource block 510.

  Further, the multiplexing unit 206 maps the PSS to the column 521 of the resource block 510 and maps the SSS to the column 522. Here, conventionally, PPS and SSS are mapped only to column 521 and column 522. On the other hand, in this embodiment, the multiplexing unit 206 maps the PSS to the column 523 and the column 525 as well. The multiplexing unit 206 also maps the SSS to the columns 524 and 526.

  Multiplexer 206 improves the signal density of PSS and SSS in the subframe by allocating resources at three positions in the time direction in the subframe transmitting the PBCH to PSS and SSS. Thus, by increasing the density of PSS and SSS in the subframe, the multiplexing unit 206 can improve the detection accuracy of the mobile station 30 for PSS and SSS.

  Conventionally, the mobile station 30 has averaged the received PSS and SSS to improve detection accuracy because the signal strength of the PSS and SSS is weak. Therefore, the mobile station cannot complete the detection of PSS and SSS until it receives a predetermined number of PSS and SSS. In contrast, in this embodiment, since the signal strength of PSS and SSS in one frame is increased, the mobile station can detect PSS and SSS without averaging, and can perform synchronization supplementation and PCI detection at high speed. Can be done.

  Further, the multiplexing unit 206 stores the position of the subframe in one frame corresponding to the PSS of the own station. The multiplexing unit 206 stores T-ECGI information in a subframe at a position corresponding to the PSS of the local station.

  FIG. 5 is a diagram for explaining a frame transmitted from each cell group according to the first embodiment. The frame 541 is a frame transmitted from the cell group of PSS = 0 in the cluster CL41. The frame 542 is a frame transmitted from the cell group of PSS = 1 in the cluster CL41. The frame 543 is a frame transmitted from the PSS = 2 cell group of the cluster CL41. Furthermore, the frame 551 is a frame transmitted from the cell group of PSS = 0 of the cluster CL42. A frame 552 is a frame transmitted from the cell group of PSS = 1 in the cluster CL42. The frame 553 is a frame transmitted from the cell group of PSS = 2 in the cluster CL42.

  As shown in FIG. 5, the positions of the subframes storing T-ECGI in each of the frames 541 to 543 are arranged so as not to overlap in the time direction. In the frame 541, T-ECGI information is stored in the subframe 544 next to the subframe in which the PSS and SSS are transmitted. In the frame 542, T-ECGI information is stored in a subframe 545 that is two frames after the subframe in which the PSS and SSS are transmitted. In the frame 543, T-ECGI information is stored in a subframe 546 that is three times after the subframe in which the PSS and SSS are transmitted. Further, subframe transmission is muted at a timing when a subframe storing T-ECGI information is transmitted from another group.

  The positions of the subframes 544 to 546 are determined so that they are not output at the same timing, and do not overlap in time. In addition, at the timing when the subframes 544 to 546 are transmitted, the frames of other groups are muted. Therefore, it is possible to reduce interference due to subframes storing T-ECGI information between cell groups, and the mobile station 30 can reliably acquire T-ECGI information.

  Returning to FIG. 2, the description will be continued. The radio resource control unit 208 is connected to a backbone network. The radio resource control unit 208 acquires a reference timing for transmitting a subframe including PBCH, PSS, and SSS from the backbone network. This reference timing is a timing based on the operation of the base station 10 of the macro cell C10.

  Radio resource control section 208 then outputs timing for transmitting subframes including PBCH, PSS, and SSS to each section within the dashed-dotted line frame in FIG. 2 adjust the timing so that subframes including PBCH, PSS, and SSS are transmitted at the timing designated by the radio resource control unit 208.

  For example, the case of FIG. 5 will be described. The radio resource control unit 208 of each small cell C20 belonging to the cluster CL41 obtains a reference timing from the backbone network and obtains a subframe transmission timing 547. Then, the radio resource control unit 208 of the base station 20 belonging to the cluster CL41 starts transmission of subframes including PBCH, PSS, and SSS at the transmission timing 547.

  Further, the radio resource control unit 208 of each base station 20 belonging to the cluster CL42 obtains a reference timing from the backbone network, and obtains a subframe transmission timing 547. Further, the radio resource control unit 208 of each base station 20 belonging to the cluster CL42 adds a predetermined time T to the transmission timing to obtain the transmission timing 554. T is such that the transmission timing of the subframe storing the T-ECGI information by the base station 20 of the cluster CL42 does not overlap the transmission timing of the subframe storing the T-ECGI information by the base station 20 of the cluster CL41. It is time to do. Then, the radio resource control unit 208 of each base station 20 belonging to the cluster CL42 starts transmission of subframes including PBCH, PSS, and SSS at the transmission timing 554.

  In this way, by shifting the time for transmitting subframes storing T-ECGI information for each cluster CL40, interference between subframes storing T-ECGI information between clusters CL40 can be reduced. it can. Thereby, the mobile station 30 can acquire the information of T-ECGI reliably.

  The IFFT unit 207 performs an inverse fast Fourier transform process on the multiplexed signal received from the multiplexing unit 206 to form an OFDM (Orthogonal Frequency Division Multiplexing) signal, and outputs the formed OFDM signal to the transmission radio unit 221. To do. The IFFT unit 207 may perform a process of adding a CP (Cyclic Prefix) for each symbol. Here, the packet generation unit 201, the MAC scheduling unit 203, the encoding unit 204, the modulation unit 205, the multiplexing unit 206, and the IFFT unit 207 function as a transmission signal forming unit.

  The transmission radio unit 221 performs predetermined transmission radio processing on the OFDM signal received from the IFFT unit 207, that is, digital-analog conversion, up-conversion, and the like to form a radio signal, and transmits the formed radio signal via the antenna. .

  Reception radio section 222 performs predetermined reception radio processing, that is, down-conversion, analog-digital conversion, etc., on the received signal received via the antenna, and outputs the received signal after reception radio processing to FFT section 209.

  FFT section 209 performs fast Fourier transform processing on the received signal received from reception radio section 222 and outputs the received signal after fast Fourier transform processing to demodulation section 210.

  Demodulation section 210 demodulates the received signal received from FFT section 209 and outputs the demodulated received signal to decoding section 211.

  Decoding section 211 decodes the reception signal received from demodulation section 210 and outputs the decoded reception signal to separation section 212.

  The separation unit 212 extracts control information and reception data from the reception signal received from the decoding unit 211, outputs the extracted control information to the MAC control unit 202, and outputs the extracted reception data to the upper layer function unit. Here, the control information output to the MAC control unit 202 includes, for example, CQI measured based on the reference signal by the mobile station 30 that has received the reference signal transmitted from the base station 20. The MAC control unit 202 performs resource allocation for the mobile station 30 based on the CQI.

[Configuration Example of Base Station 10]
FIG. 6 is a diagram illustrating an example of a base station corresponding to the macro cell according to the first embodiment. In FIG. 6, the base station 10 includes a control unit 11 and a radio unit 12. The control unit 11 includes a packet generation unit 101, a MAC control unit 102, a MAC scheduling unit 103, an encoding unit 104, a modulation unit 105, a multiplexing unit 106, and an IFFT unit 107. The control unit 11 includes a radio resource control unit 108, an FFT unit 109, a demodulation unit 110, a decoding unit 111, and a separation unit 112. The radio unit 12 includes a transmission radio unit 121 and a reception radio unit 122.

  Reception radio section 122 performs predetermined reception radio processing, that is, down-conversion, analog-digital conversion, etc., on the received signal received via the antenna, and outputs the received signal after reception radio processing to FFT section 109.

  FFT section 109 performs a fast Fourier transform process on the received signal received from reception radio section 122 and outputs the received signal after the fast Fourier transform process to demodulation section 110.

  Demodulation section 110 demodulates the reception signal received from FFT section 109 and outputs the demodulated reception signal to decoding section 111.

  Decoding section 111 decodes the received signal received from demodulation section 110 and outputs the received signal after decoding to separation section 112.

  The separation unit 112 extracts control information and reception data from the reception signal received from the decoding unit 111, outputs the extracted control information to the radio resource control unit 108 and the MAC control unit 102, and extracts the extracted reception data of the upper layer. Output to the functional part. Here, the control information output to the radio resource control unit 108 may include information on the received power (RSRP: Reference Signal Received Power) of the common reference signal and T-EGCI information. Specifically, the control information output to the radio resource control unit 108 may first include information related to the received power of the common reference signal at the mobile station 30. Secondly, the control information output to the radio resource control unit 108 may include information about the received power for the common reference signal notified from the mobile station 30 to the mobile station 30. On the other hand, the control information output to the MAC control unit 102 may include information on the received power measured by the mobile station 30 for the common reference signal transmitted by the local station. That is, the control information output to the MAC control unit 102 may include channel quality information (CQI) reported from the mobile station 30, for example.

  The radio resource control unit 108 forms radio resource control information (that is, RRC (Radio Resource Control) control information) based on the control information received from the demultiplexing unit 112, and sends the formed radio resource control information to the packet generation unit 101. Output.

  Specifically, the radio resource control unit 108 receives information about received power and T-ECGI information about the common reference signal measured by the mobile station 30. And the radio | wireless resource control part 108 specifies the small cell C20 used as the connection destination of the mobile station 30 which transmitted received power using the information of T-ECGI. Next, the radio resource control unit 108 includes the information of the specified small cell C20 in the radio resource control information and outputs the information to the packet generation unit 101.

  The packet generation unit 101 receives transmission data addressed to the mobile station 30, that is, user data, and radio resource control information addressed to the mobile station 30 from the radio resource control unit 108, and uses the received user data and radio resource control information. Generate a transmission packet. Then, the packet generation unit 101 outputs the generated transmission packet to the MAC scheduling unit 103.

  The MAC control unit 102 allocates resources used for communication between the mobile station 30 and the mobile station 30 based on channel quality information (CQI) reported from the mobile station 30. This resource is defined by, for example, time and frequency. Then, the MAC control unit 102 outputs the individual control information including information on the allocated resource to the MAC scheduling unit 103 and the multiplexing unit 106.

  The MAC scheduling unit 103 outputs the packet addressed to the mobile station 30 received from the packet generation unit 101 to the encoding unit 104 at a timing corresponding to the time allocated to the mobile station 30 by the MAC control unit 102. Note that the MAC scheduling unit 103 may divide the packet into data units having a predetermined data size and output the data units to the encoding unit 104.

  Encoding section 104 performs an encoding process on the packet received from MAC scheduling section 103 and outputs the encoded packet to modulation section 105.

  Modulation section 105 modulates the encoded packet received from encoding section 104 and outputs the modulated packet to multiplexing section 106.

  The multiplexing unit 106 maps and multiplexes the input signal to a predetermined resource, and outputs the multiplexed signal to the IFFT unit 107.

  Specifically, the multiplexing unit 106 receives the individual control information from the MAC control unit 102 and maps it to a resource region assigned to a downlink control channel (for example, PDCCH: Physical Downlink Control Channel).

  Multiplexer 106 receives the packet from modulator 105 and maps it to the downlink allocated resource indicated by the individual control information.

  The multiplexing unit 106 receives a common reference signal (CRS) and a synchronization signal that are common to the macro cell C10. Then, the multiplexing unit 106 maps the common reference signal and the synchronization signal to predetermined resources.

  The IFFT unit 107 performs an inverse fast Fourier transform process on the multiplexed signal received from the multiplexing unit 106 to form an OFDM (Orthogonal Frequency Division Multiplexing) signal, and outputs the formed OFDM signal to the transmission radio unit 121. To do. The IFFT unit 107 may perform a process of adding a CP (Cyclic Prefix) for each symbol. Here, the packet generation unit 101, the MAC scheduling unit 103, the encoding unit 104, the modulation unit 105, the multiplexing unit 106, and the IFFT unit 107 function as a transmission signal forming unit.

  The transmission radio unit 121 performs predetermined transmission radio processing on the OFDM signal received from the IFFT unit 107, that is, digital-analog conversion, up-conversion, and the like to form a radio signal, and transmits the formed radio signal via the antenna. .

[Configuration Example of Mobile Station 30]
FIG. 7 is a diagram illustrating an example of the mobile station according to the first embodiment. In FIG. 7, the mobile station 30 includes a control unit 31 and a radio unit 32. The control unit 31 includes an FFT unit 301, a control channel demodulation unit 302, a channel state (CS) measurement unit 303, a small cell identification information detection unit 304, a cell search unit 305, a demodulation unit 306, a decoding unit 307, and a control. An information processing unit 308 is included. The control unit 31 includes a data processing unit 309, a multiplexing unit 310, a symbol mapping unit 311, a multiplexing unit 312, an FFT unit 313, a frequency mapping unit 314, and an IFFT unit 315. The radio unit 32 includes a reception radio unit 321 and a transmission radio unit 322.

  The reception radio unit 321 performs predetermined reception radio processing, that is, down-conversion, analog-digital conversion, and the like on the reception signal received via the antenna. Then, reception radio section 321 outputs the reception signal after the reception radio processing to FFT section 301 and cell search section 305.

  The cell search unit 305 identifies the PCI corresponding to the synchronization signal based on the synchronization signal included in the reception signal after the reception radio processing. That is, the cell search unit 305 detects the PSS and SSS of the small cell C20 where the local station is located. Then, the cell search unit 305 notifies the small cell identification information detection unit 304 of the detected PSS information. Further, the cell search unit 305 identifies the PCI of the small cell C20 from the detected PSS and SSS. Then, the cell search unit 305 outputs the specified PCI to the control information processing unit 308. Note that the number of specified cell PCIs may be one or plural.

  The small cell identification information detection unit 304 stores the position of the subframe in which the T-ECGI information is stored and the PSS value in association with each other. The small cell identification information detection unit 304 specifies the position of the subframe in which the T-ECGI information corresponding to the PSS information received from the cell search unit 305 is stored. Then, the small cell identification information detection unit 304 acquires T-ECGI information from the subframe in which the T-ECGI information in the frame received from the FFT unit 301 is stored. Then, the small cell identification information detection unit 304 outputs the acquired T-EGCI information to the control information processing unit 308.

  The FFT unit 301 performs fast Fourier transform processing on the received signal after reception radio processing, and the received signal after the fast Fourier transform processing is subjected to control channel demodulation unit 302, channel state measurement unit 303, small cell identification information detection unit. 304 and the demodulator 306.

  Control channel demodulation section 302 receives a radio network temporary identifier (RNTI) from control information processing section 308, and a portion corresponding to the search space of the PDCCH region indicated by RNTI in the received signal received from FFT section 301 Then, the control information addressed to the own station is searched. Control channel demodulation section 302 then outputs the resource allocation information to demodulation section 306 and decoding section 307 when resource allocation information addressed to itself is found.

  The communication path state measuring unit 303 measures the received power of the common reference signal included in the received signal received from the FFT unit 301 and outputs the measured received power value of the common reference signal to the control information processing unit 308. That is, the communication path state measurement unit 303 measures the reception power of the common reference signal transmitted in the macro cell C10 or the small cell C20 where the local station is located.

  The control information processing unit 308 extracts the RNTI transmitted from the base station 10 from the reception data output from the decoding unit 307, and outputs the extracted RNTI to the control channel demodulation unit 302.

  The control information processing unit 308 receives the reception power value of the common reference signal corresponding to the T-ECGI received from the small cell identification information detection unit 304 from the communication path state measurement unit 303. Then, control information processing section 308 outputs the received power value of the received common reference signal to multiplexing section 310. As a result, the control information processing unit 308 transmits the T-ECGI information and the received power value of the common reference signal to the base station 10. When there are a plurality of T-ECGI information and a plurality of received power values of the common reference signal, the control information processing unit 308 sets the maximum value and the maximum value among the received power values of the plurality of common reference signals. The corresponding T-ECGI may be transmitted to the base station 10. Also, the control information processing unit 308 outputs the T-ECGI received from the small cell identification information detection unit 304 and the received power value of the common reference signal received from the channel state measurement unit 303 to the multiplexing unit 310.

  The data processing unit 309 outputs the user data to the multiplexing unit 310.

  The multiplexing unit 310 forms a multiplexed signal by mapping user data received from the data processing unit 309 and various types of information received from the control information processing unit 308 to predetermined resources, and outputs the formed multiplexed signal to the symbol mapping unit 311. .

  Symbol mapping section 311 maps the multiplexed signal received from multiplexing section 310 to a symbol, and outputs the obtained modulated signal to multiplexing section 312.

  Multiplexing section 312 multiplexes the modulation signal received from symbol mapping section 311 and the pilot signal, and outputs the multiplexed signal to FFT section 313.

  The FFT unit 313 performs fast Fourier transform processing on the multiplexed signal received from the multiplexing unit 312 and outputs the multiplexed signal after the fast Fourier transform processing to the frequency mapping unit 314.

  The frequency mapping unit 314 maps the multiplexed signal received from the FFT unit 313 to a predetermined frequency, and outputs the obtained transmission signal to the IFFT unit 315.

  The IFFT unit 315 performs an inverse fast Fourier transform process on the transmission signal received from the frequency mapping unit 314 to form an OFDM signal, and outputs the formed OFDM signal to the transmission radio unit 322.

  The transmission radio unit 322 performs predetermined transmission radio processing on the OFDM signal received from the IFFT unit 315, that is, digital / analog conversion, up-conversion, and the like to form a radio signal, and transmits the formed radio signal via the antenna. .

[Operation of mobile communication system]
The processing operation of the mobile communication system 1 having the above configuration will be described. FIG. 8 is a sequence diagram illustrating an example of a processing operation of the mobile communication system according to the first embodiment.

  The multiplexing unit 206 of the base station 20 maps the PSS and the SSS to a plurality of resources in the time direction within the subframe for notifying the PBCH (Step S1). In the present embodiment, the multiplexing unit 206 allocates three time direction resources in one subframe to each of the PSS and the SSS. Thereby, the base station 20 improves the signal density of PSS and SSS.

  Further, the multiplexing unit 206 of the base station 20 stores the T-ECGI information in a subframe at a predetermined position corresponding to the PSS of the own station (step S2). The multiplexing unit 206 maps the PBCH, the reference signal, etc. to the same subframe.

  Then, the base station 20 transmits a frame including a subframe in which PSS, SSS, PBCH, and the like are mapped, and a subframe in which T-ECGI information is stored, to the mobile station 30 (step S3).

  The mobile station 30 detects the PSS of the small cell C20 in which the mobile station is located (step S4). That is, the mobile station 30 uses the cell search unit 305 to specify the PSS corresponding to the synchronization signal based on the synchronization signal included in the reception signal after the reception radio processing. Note that the number of specified PSSs may be one or plural. The cell search unit 305 also specifies SSS.

  Then, the small cell identification information detection unit 304 of the mobile station 30 acquires T-ECGI information from the subframe located at the position corresponding to the PSS detected by the cell search unit 305 (step S5).

  Furthermore, the mobile station 30 measures the received power of the small cell C20 corresponding to the acquired T-ECGI (step S6). That is, the communication path state measurement unit 303 of the mobile station 30 measures the received power of the common reference signal transmitted from the base station 20 having the acquired T-ECGI.

  The mobile station 30 transmits information indicating the received power of the measured common reference signal and T-ECGI information corresponding to the received power to the base station 10 (step S7). Here, when there are a plurality of small cells C20 to be measured, the control information processing unit 308 in the mobile station 30 receives the reception power and T-ECGI of the common reference signal for all the small cells C20 to be measured. May be notified to the base station 10 in a state of being associated with each other. In addition, the control information processing unit 308 may notify the base station 10 of T-ECGI information corresponding to the small cell C20 having the largest received power of the common reference signal.

  The base station 10 acquires information indicating the received power and T-ECGI information corresponding to the received power from the mobile station 30. Then, the base station 10 determines a connection target cell by the radio resource control unit 108 (step S8). For example, when only one T-ECGI is notified from the mobile station 30, the radio resource control unit 108 sets the base station 20 having the T-ECGI as a connection target, and sets the small cell C20 of the base station 20 The cell to be connected. Further, when a plurality of T-ECGIs are notified from the mobile station 30, the radio resource control unit 108 corresponds to the T-ECGI having the highest received power of the common reference signal among the plurality of T-ECGIs. A base station 20 is a connection target, and a small cell C20 corresponding to the base station 20 is a connection target cell.

  The base station 10 notifies the mobile station 30 of information on the small cell C20 determined as the connection target cell (step S9). Thereafter, the mobile station 30 connects to the notified small cell C20 and performs communication.

  As described above, the mobile communication system according to the present embodiment transmits a synchronization signal by increasing the signal density, and further stores a signal for uniquely identifying a small cell in a subframe at a position corresponding to the synchronization signal. To send. Accordingly, the mobile station can improve the detection accuracy for detecting the synchronization signal, and can perform synchronization supplement at high speed. Furthermore, by using a signal that uniquely identifies a small cell, the mobile station can uniquely identify the peripheral small cell at the stage of synchronization, and can detect the peripheral small cell at high speed and with low power consumption. Can do.

  Also, in the mobile communication system according to the present embodiment, the small cell identification information is stored and transmitted in subframes at different positions in time for each cell group assigned according to the type of synchronization signal. Further, at a timing when a base station belonging to a certain cell group transmits small cell identification information, base stations of other cell groups perform frame transmission muting. Also, the timing for transmitting subframes in which small cell identification information is stored is shifted between clusters. Thereby, inter-cell interference in reception of small cell identification information is reduced in the mobile station, and the mobile station can reliably receive small cell identification information.

(Modification)
In the above, PSS is used as information for determining a subframe in which T-ECGI is stored. However, this information may be other information as long as it is information for identifying a group of small cells C20.

  For example, a case will be described where the clusters CL41 and CL42 in FIG. 1 are divided into M cell groups. Here, the cell group is divided more finely while using three types of PSS. Therefore, first, the clusters CL41 and CL42 are divided into M / 3 PCI groups.

  Next, the small cell C20 included in the created PCI group is divided into three cell groups. As a result, M cell groups can be created for each of the clusters CL41 and CL42.

  For example, FIG. 9 is a diagram illustrating a modification example of grouping of cell groups. FIG. 9 shows a case where 6 (M = 6) cell groups are generated for each of the clusters CL41 and CL42.

  First, as shown in FIG. 9, each cluster is divided into 2 (= M / 3) PIC groups (in the figure, represented as “PCIg”). A value connected with PCIg and an equal sign in FIG. 9 indicates a group number. In the following, each PCI group is called by a numbered name. Then, the small cell C20 included in each PCI group is set to have the same SSS. Thereby, the cluster CL41 has two groups, PCI group 1 and PCI group 2. The cluster CL42 has two groups, a PCI group 3 and a PCI group 4.

  Further, each PCI group is divided by PSS. That is, the PCI group is divided into three groups: a group of small cells C20 with a PSS of 0, a group of small cells C20 with a PSS of 1, and a group of small cells C20 with a PSS of 2.

  By dividing in this way, each cluster CL40 has six cell groups.

  Furthermore, in this modification, cell groups are divided using the fact that there are three types of PSS, but other methods may be used for dividing cell groups. For example, the cell group can be divided using PCI configured by PSS and SSS. In that case, for example, a cell group can be created using six appropriate PCIs. Thus, the use of PCI can improve the degree of freedom in creating a cell group. Then, when PCI is used for cell group division, the mobile station 30 detects PSS and SSS, thereby obtaining PCI, and from the obtained PCI, subframe information in which T-ECGI is stored is obtained. get.

  As described above, the mobile communication system according to the present modification can reduce the number of small cells belonging to each cell group by increasing the number of cell groups included in the cluster. The cell distance can be increased. That is, it is possible to reduce inter-cell interference in reception of small cell identification information within the same cell group in the mobile station, and the mobile station can more reliably acquire small cell identification information.

  In the present embodiment, ECGI or T-ECGI is used as small cell identification information. However, other forms of identification information may be used. In addition to the identification information, other information can also be transmitted.

  As another modification, the multiplexing unit 206 transmits a frame after encrypting the frame by applying scrambling based on the PCI value when transmitting a frame storing PSS, SSS, and ECGI information. May be. Specifically, the multiplexing unit 206 applies different scrambling for each cell group as scrambling based on the PCI value.

  In this way, by applying different scrambling for each cell group, it is possible to randomize interference to other cells having different cell groups.

  Next, Example 2 will be described. The mobile communication system according to the present embodiment is different from the first embodiment in that inter-cell interference is reduced by notifying T-ECGI using different frequencies that do not overlap for each cell group.

  The mobile communication system according to the present embodiment is shown in FIG. Further, the base station 20, the base station 10, and the mobile station 30 according to the present embodiment are represented by the block diagrams of FIGS. 3, 6, and 7, respectively. Hereinafter, a T-ECGI storage method in the base station 20 will be mainly described.

  The multiplexing unit 206 receives information on the PSS and SSS assigned to the own station. Then, the multiplexing unit 206 maps the PSS and SSS to a plurality of predetermined locations of predetermined resources.

  Furthermore, the multiplexing unit 206 stores the next subframe of the subframe including the synchronization signal as a subframe for storing T-ECGI. Further, the multiplexing unit 206 stores a frequency band for storing T-ECGI in a subframe corresponding to the PSS of the local station. Then, multiplexing section 206 stores T-ECGI information in the frequency band corresponding to the PSS of the local station in the subframe next to the subframe including the synchronization signal.

  FIG. 10 is a diagram for explaining a frame transmitted from each cell group according to the second embodiment. The horizontal direction in FIG. 10 represents the time direction, and the vertical direction represents the frequency direction. The frame 601 is a frame transmitted from the cell group of PSS = 0 in the cluster CL41. The frame 602 is a frame transmitted from the cell group of PSS = 1 in the cluster CL41. A frame 603 is a frame transmitted from the cell group of PSS = 2 in the cluster CL41. Further, the frame 611 is a frame transmitted from the PSS = 0 cell group of the cluster CL42. The frame 612 is a frame transmitted from the cell group of PSS = 1 in the cluster CL42. The frame 613 is a frame transmitted from the PSS = 2 cell group of the cluster CL42.

  As shown in FIG. 10, the sub-frames storing the T-ECGI in each of the frames 601 to 603 are arranged so that the frequency bands for transmitting the T-ECGI of each cell group do not overlap.

  Specifically, in any of the frames 601 to 603, T-ECGI is stored in the subframe next to the subframe in which the PSS and SSS are transmitted. In frame 601, T-ECGI information is transmitted using the highest frequency band 604 among the three sub-frame frequency bands. In the frame 602, T-ECGI information is transmitted using an intermediate frequency band 605 out of the three sub-frame frequency bands. In the frame 603, T-ECGI information is transmitted using the lowest frequency band 606 among the frequency bands of the subframe divided into three. Further, subframe transmission is muted in a frequency band used by other cell groups to transmit T-ECGI information.

  Thus, the frequency bands 604 to 606 are determined so that the frequencies do not overlap and do not overlap in the frequency direction. Further, in a frame transmitted by a certain cell group, a frequency band in which other cell groups in a subframe transmitting T-ECGI transmit T-ECGI information is muted. Therefore, interference between cell groups in transmission of T-ECGI information between cell groups can be reduced, and the mobile station 30 can reliably acquire T-ECGI information.

  Radio resource control section 208 outputs timing for transmitting subframes including PBCH, PSS, and SSS to each section within the dashed-dotted frame in FIG. 2 adjust the timing so that subframes including PBCH, PSS, and SSS are transmitted at the timing designated by the radio resource control unit 208.

  For example, the case of FIG. 10 will be described. The radio resource control unit 208 of each small cell C20 belonging to the cluster CL41 obtains a reference timing from the backbone network and obtains a subframe transmission timing 607. Then, the radio resource control unit 208 of each base station 20 belonging to the cluster CL41 starts transmission of subframes including PBCH, PSS, and SSS at the transmission timing 607.

  Also, the radio resource control unit 208 of each base station 20 belonging to the cluster CL42 obtains a reference timing from the backbone network, and obtains a subframe transmission timing 607. Further, the radio resource control unit 208 of each base station 20 belonging to the cluster CL42 adds a predetermined time T 'to the transmission timing to obtain the transmission timing 614. T ′ is such that the transmission timing of the subframe storing the T-ECGI information by the base station 20 of the cluster CL42 does not overlap the transmission timing of the subframe storing the T-ECGI information by the base station 20 of the cluster CL41. It is time to make it. Then, the radio resource control unit 208 of each base station 20 belonging to the cluster CL41 starts transmission of subframes including PBCH, PSS, and SSS at the transmission timing 614.

  In this way, by shifting the time for transmitting subframes storing T-ECGI information for each cluster CL40, interference between subframes storing T-ECGI information between clusters CL40 can be reduced. it can. Thereby, the mobile station 30 can acquire the information of T-ECGI reliably.

  As described above, in the mobile communication system according to the present embodiment, the frequency bands for transmitting the base station identification information are different between different cell groups in the same cluster. Thereby, the inter-cell interference in the reception of the identification information of the base station by the mobile station can be reduced. Therefore, by changing the frequency band for transmitting the base station identification information between the cell groups, the mobile station can reliably acquire the base station identification information.

  Next, Example 3 will be described. The mobile communication system according to the present embodiment reduces inter-cell interference by differentiating the frequency band for transmitting T-ECGI for each cluster and further reporting T-ECGI using different frequencies that do not overlap for each cell group. doing.

  The mobile communication system according to the present embodiment is shown in FIG. Further, the base station 20, the base station 10, and the mobile station 30 according to the present embodiment are represented by the block diagrams of FIGS. 3, 6, and 7, respectively. Hereinafter, a T-ECGI storage method in the base station 20 will be mainly described.

  The multiplexing unit 206 receives information on the PSS and SSS assigned to the own station. Then, the multiplexing unit 206 maps the PSS and SSS to a plurality of predetermined locations of predetermined resources.

  Further, multiplexing section 206 stores the next subframe of the subframe including the synchronization signal as a subframe for storing T-ECGI. Further, the multiplexing unit 206 stores a frequency band used for T-ECGI transmission corresponding to the cluster CL41 or CL42 to which the own station belongs. Here, the frequency band used for T-ECGI transmission corresponding to the cluster CL41 or CL42 is a frequency band that is different for each cluster and does not overlap each other. Further, the multiplexing unit 206 stores a frequency band of T-ECGI transmission according to the PSS of the local station in the frequency band assigned to the cluster to which the local station belongs.

  Then, the multiplexing unit 206 stores T-ECGI information in the frequency band of T-ECGI transmission corresponding to the PSS of the local station in the frequency band assigned to the cluster to which the local station belongs.

  FIG. 11 is a diagram for explaining a frame transmitted from each cell group according to the third embodiment. The horizontal direction in FIG. 11 represents resources in the time direction, and the vertical direction represents resources in the frequency direction. A frame 701 is a frame transmitted from the cell group of PSS = 0 in the cluster CL41. A frame 702 is a frame transmitted from the cell group of PSS = 1 in the cluster CL41. The frame 703 is a frame transmitted from the PSS = 2 cell group of the cluster CL41. Further, the frame 711 is a frame transmitted from the cell group of PSS = 0 in the cluster CL42. The frame 712 is a frame transmitted from the cell group of PSS = 1 in the cluster CL42. The frame 713 is a frame transmitted from the cell group of PSS = 2 of the cluster CL42.

  As shown in FIG. 11, the sub-frames storing T-ECGI in each of frames 701 to 703 and 711 to 713 are arranged so that the frequency bands for transmitting T-ECGI of each cell group do not overlap.

  Specifically, in any of the frames 701 to 703 and 711 to 713, the T-ECGI is stored in the subframe next to the subframe that transmitted the PSS and SSS. In a frame transmitted by the base station 20 belonging to the cluster CL41, the upper half frequency band in the subframe is allocated as a band for transmitting T-ECGI. In the frame transmitted by the base station 20 belonging to the cluster CL41, the upper half frequency band in the subframe is allocated as a band for transmitting the T-ECGI. Then, the base station 20 belonging to a certain cluster CL40 mutes a frequency band used for the base station 20 belonging to another cluster CL40 to transmit T-ECGI.

  For example, in the frame 701 transmitted by the base station 20 belonging to the cluster CL41, the frequency band 705 assigned to the cluster CL42 is muted. In the frame 711 transmitted by the base station 20 belonging to the cluster CL42, the frequency band 715 assigned to the cluster CL41 is muted.

  In frame 701, T-ECGI information is transmitted using the highest frequency band 704 among the upper half frequency band of the subframe divided into three. In frame 702, T-ECGI information is transmitted using an intermediate frequency band obtained by dividing the upper half frequency band of the subframe into three. In frame 703, T-ECGI information is transmitted using the lowest frequency band of the upper half of the subframe divided into three. Further, in frames 701 to 703, subframe transmission in a frequency band used by another cell group to transmit T-ECGI information is muted.

  Also, in the frame 711, T-ECGI information is transmitted using the highest frequency band 714 out of the lower half frequency band of the subframe. In frame 712, T-ECGI information is transmitted using an intermediate frequency band obtained by dividing the lower half frequency band of the subframe into three. In the frame 713, T-ECGI information is transmitted using the lowest frequency band obtained by dividing the lower half frequency band of the subframe into three. Further, in frames 711 to 713, sub-frame transmission in the frequency band used by other cell groups to transmit T-ECGI information is muted.

  Thus, the frequency bands for transmitting the T-ECGI are set so as not to overlap between the clusters CL41 and CL42, and the frequency bands for transmitting the T-ECGI for each cell group do not overlap in the cluster CL40. It is decided so. Further, in a frame transmitted by a certain cell group, a frequency band in which another cell group belonging to the same cluster CL40 transmits T-ECGI information and a frequency at which the base station 20 of another cluster CL40 transmits T-ECGI information. The band is muted. Therefore, it is possible to reduce interference in transmission of T-ECGI information between the clusters CL40 and between cell groups, and the mobile station 30 can reliably acquire T-ECGI information.

  Radio resource control section 208 outputs timing for transmitting subframes including PBCH, PSS, and SSS to each section within the dashed-dotted frame in FIG. 2 adjust the timing so that subframes including PBCH, PSS, and SSS are transmitted at the timing designated by the radio resource control unit 208.

  For example, the case of FIG. 11 will be described. The radio resource control unit 208 of each small cell C20 belonging to the cluster CL41 obtains a reference timing from the backbone network and obtains a subframe transmission timing 706. Then, the radio resource control unit 208 of each base station 20 belonging to the cluster CL41 starts transmission of subframes including PBCH, PSS, and SSS at the transmission timing 706. Further, the radio resource control unit 208 of each base station 20 belonging to the cluster CL42 starts transmission of subframes including PBCH, PSS, and SSS at the transmission timing 706.

  Thus, in the present embodiment, the base stations 20 of different clusters CL40 can transmit subframes storing T-ECGI information at the same transmission timing 706.

  As described above, according to the mobile communication system according to the present embodiment, the subframe storing the base station identification information is the same even when the subframes storing the base station identification information are transmitted in the same cluster. Interference between each other can be reduced. Thereby, the mobile station can acquire the identification information of a base station reliably.

  In addition, since the base station identification information is transmitted at the same timing, the mobile station can identify the base station to be communicated at a time even when there are a plurality of clusters, and more quickly The station can be specified.

(Hardware configuration)
The base station 10, the base station 20, and the mobile station 30 in each embodiment can be realized by the following hardware configuration, for example.

  FIG. 12 is a diagram illustrating a hardware configuration example of a base station corresponding to a macro cell. As illustrated in FIG. 12, a base station 800 corresponding to the macro cell C10 includes an RF (Radio Frequency) circuit 801, a processor 802, a memory 803, and a network IF (Inter Face) 804. Examples of the processor 802 include a central processing unit (CPU), a digital signal processor (DSP), and a field programmable gate array (FPGA). Examples of the memory 803 include a random access memory (RAM) such as an SDRAM (Synchronous Dynamic Random Access Memory), a read only memory (ROM), and a flash memory.

  The various processing functions performed in the base station 10 corresponding to the macro cell C10 of each embodiment may be realized by executing programs stored in various memories such as a nonvolatile storage medium by a processor included in the amplification device. Good. That is, a program corresponding to each process executed by the control unit 11 may be recorded in the memory 803 and each program may be executed by the processor 802.

  Here, although base station 800 has been described as an integral device, the present invention is not limited to this. For example, base station 800 may be configured by two separate devices, a wireless device and a control device. In this case, for example, the RF circuit 801 is disposed in the wireless device, and the processor 802, the memory 803, and the network IF 804 are disposed in the control device.

  FIG. 13 is a diagram illustrating a hardware configuration example of a base station corresponding to a small cell. As illustrated in FIG. 13, the base station 810 corresponding to the small cell C20 includes an RF circuit 811, a processor 812, a memory 813, and a network IF 814. Examples of the processor 812 include a CPU, DSP, FPGA, and the like. Further, examples of the memory 813 include RAM such as SDRAM, ROM, flash memory, and the like.

  Various processing functions performed in the base station 20 corresponding to the small cell C20 of each embodiment are realized by executing programs stored in various memories such as a nonvolatile storage medium by a processor included in the amplification device. Also good. That is, a program corresponding to each process executed by the control unit 21 may be recorded in the memory 813 and each program may be executed by the processor 812.

  Here, the base station 810 has been described as an integrated device, but the present invention is not limited to this. For example, the base station 810 may be configured by two separate devices, a wireless device and a control device. In this case, for example, the RF circuit 811 is disposed in the wireless device, and the processor 812, the memory 813, and the network IF 814 are disposed in the control device.

  FIG. 14 is a diagram illustrating a hardware configuration example of a mobile station. As illustrated in FIG. 14, the mobile station 820 includes an RF circuit 821, a processor 822, a memory 823, a display unit 824, a speaker 825, a microphone 826, and an operation unit 827.

  Examples of the processor 822 include a CPU, a DSP, and an FPGA. Further, examples of the memory 823 include RAM such as SDRAM, ROM, flash memory, and the like.

  Various processing functions performed in the mobile station 30 of each embodiment may be realized by executing a program stored in various memories such as a nonvolatile storage medium by a processor included in the amplification device. That is, a program corresponding to each process executed by the control unit 31 may be recorded in the memory 823, and each program may be executed by the processor 822. Each process executed by the control unit 31 may be shared and executed by a plurality of processors such as a baseband CPU and an application CPU. The wireless unit 32 is realized by the RF circuit 821.

DESCRIPTION OF SYMBOLS 1 Mobile communication system 10 Base station 11 Control part 12 Radio part 20 Base station 21 Control part 22 Radio part 30 Mobile station 31 Control part 32 Radio part 101 Packet generation part 102 MAC control part 103 MAC scheduling part 104 Encoding part 105 Modulation part 106 Multiplexer 107 IFFT Unit 108 Radio Resource Control Unit 109 FFT Unit 110 Demodulation Unit 111 Decoding Unit 112 Separation Unit 201 Packet Generation Unit 202 MAC Control Unit 203 MAC Scheduling Unit 204 Coding Unit 205 Modulation Unit 206 Multiplexing Unit 207 IFFT Unit 208 Radio Resource control unit 209 FFT unit 210 Demodulation unit 211 Decoding unit 212 Separation unit 301 FFT unit 302 Control channel demodulation unit 303 Channel state measurement unit 304 Small cell identification information detection unit 305 Cell search unit 306 Demodulation Unit 307 decoding unit 308 control information processing unit 309 data processing unit 310 multiplexing unit 311 symbol mapping unit 312 multiplexing unit 313 FFT unit 314 frequency mapping unit 315 IFFT unit 321 reception radio unit 322 transmission radio unit

Claims (11)

A communication system having a base station and a mobile station corresponding to each of a plurality of cells,
The cells are allocated to a plurality of first groups to which different types of synchronization signals are assigned,
The base station
Including the synchronization signal assigned to the first group to which the local station belongs, corresponding to the synchronization signal, and different for each first group, and transmitting the cell identification information using transmission resources defined by time and frequency. A transmission unit for transmitting a notification frame;
The mobile station
A detection unit for detecting a synchronization signal from the received frame;
A cell identification unit that identifies the transmission resource in the received frame corresponding to the synchronization signal detected by the detection unit, acquires the identification information from the identified transmission resource in the reception frame, and identifies the cell And a mobile communication system.   The base station further includes a synchronization signal arrangement unit that arranges a plurality of the synchronization signals assigned to the first group to which the base station belongs in one synchronization subframe. Mobile communication system.   2. The mobile communication system according to claim 1, wherein the transmission unit transmits the identification information using the transmission resources whose transmission timing does not overlap for each of the first groups in the frame.   2. The mobile communication system according to claim 1, wherein the transmission unit transmits the identification information using the transmission resource in which frequency bands do not overlap for each of the first groups in the frame.   The mobile communication system according to claim 1, wherein the transmission unit sets the transmission resource used by a base station belonging to a first group other than the first group of the own station in the frame as a non-transmission area. .   The mobile communication system according to claim 1, wherein the transmitting unit applies different scrambling for each of the first groups in transmitting the identification information. The first group is divided into a plurality of second groups,
2. The transmission unit according to claim 1, wherein the transmission unit varies the transmission timing of the frame for each second group, and varies the transmission resource for transmitting the identification information between the second groups. Mobile communication system. A base station corresponding to each of a plurality of cells,
The cells are allocated to a plurality of groups to which different types of synchronization signals are assigned,
A frame including the synchronization signal assigned to the group to which the local station belongs is transmitted, and transmission resources defined by time and frequency are different for each group corresponding to the synchronization signal in the frame. A base station comprising a transmitter for transmitting identification information of the local station to the mobile station. Each of a plurality of cells allocated to a plurality of first groups to which different types of synchronization signals are allocated, each of which includes the synchronization signal allocated to the first group, and corresponds to the first synchronization signal. A detection unit that detects a synchronization signal from a received frame received from a base station that transmits a frame that notifies the identification information of the cell using transmission resources that are different for each group and is defined by time and frequency,
A cell identification unit that identifies the transmission resource in the received frame corresponding to the synchronization signal detected by the detection unit, acquires the identification information from the identified transmission resource in the reception frame, and identifies the cell A mobile station characterized by comprising: A cell detection method in a communication system having a base station and a mobile station corresponding to each of a plurality of cells,
The cells are allocated to a plurality of first groups to which different types of synchronization signals are assigned,
The base station
Wherein said synchronization signals allocated to the first group which the own station belongs, and, in response to the synchronization signal different for each said first group, of the cell using the transmission resources defined by time and frequency Send a frame to notify the identification information,
The mobile station
Detect sync signal from received frame,
Identifying the transmission resource in the received frame corresponding to the detected synchronization signal;
The cell detection method characterized by acquiring the identification information from the specified transmission resource in the received frame and specifying the cell. A communication system having a first base station corresponding to a first cell, a second base station corresponding to each of a plurality of second cells having a communication area included in the first cell, and a mobile station,
The second cells are allocated to a plurality of first groups to which different types of synchronization signals are assigned,
The second base station is
A frame including the synchronization signal assigned to the first group to which the own station belongs is transmitted, and transmission resources defined by time and frequency corresponding to the synchronization signal and different for each first group are used. And a transmission unit for transmitting a frame for notifying the identification information of the second cell,
The mobile station
A detection unit for detecting a synchronization signal from the received frame;
A cell that identifies the transmission resource in the received frame corresponding to the synchronization signal detected by the detection unit, acquires the identification information from the identified transmission resource in the received frame, and identifies the second cell A specific part,
A measurement unit for measuring the received power of the signal transmitted from the second cell identified by the cell identification unit;
A notification unit that notifies the first base station of the received power measured by the measurement unit and the identification information of the second cell;
The first base station is
A mobile communication system, comprising: a determination unit that determines the second cell to which the mobile station is connected based on the received power notified from the mobile station and the identification information of the second cell.

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