JP5803566B2 - Wireless communication system, mobile station, base station, and communication control method - Google Patents

Description

  The present invention relates to a radio communication system, a mobile station, a base station, and a communication control method.

  In recent years, studies on technologies related to a network system in which base stations having different cell ranges are mixed (hereinafter referred to as “heterogeneous network”) are in progress. In this heterogeneous network, it is desirable to synchronize signals between base stations in order to reduce interference between cells.

  As a method of synchronizing signals between base stations, a synchronization method using GPS (Global Positioning System), a synchronization method using IEEE 1588 which is a standard protocol for synchronizing devices, and a synchronization method using network listening It has been known.

3GPP TS36.922 6.4.1.2 Synchronization requirement

  However, the above-described conventional method has the following problems. For example, in a synchronization method using GPS, when a base station is installed in an indoor environment where it is difficult to receive radio waves from GPS satellites, the signals can be synchronized between the base stations using GPS signals. It becomes difficult.

  In addition, in the synchronization method using IEEE 1588 or network listening, it is necessary to implement functions of communication devices that execute IEEE 1588 or network listening for all base stations to be synchronized, which increases the manufacturing and development costs of the base station. .

  The disclosed technology has been made in view of the above, and a radio communication system, a mobile station, and a mobile station that can easily realize signal synchronization between base stations regardless of the environment in which the base stations are installed. It is an object to provide a base station and a communication control method.

  In the wireless communication system disclosed in the present application, a mobile station transmits first and second reference signals transmitted from a first base station and a second base station at predetermined timings and used for synchronization with each base station. Receive. The mobile station includes a first receiving unit and a first transmitting unit. The first receiving unit receives predetermined identification information from the first base station. The first transmission unit transmits a signal corresponding to the predetermined identification information to the first base station at a timing corresponding to a reception timing of the second reference signal transmitted from the second base station. To do. The first base station includes a second receiving unit and a second transmitting unit. The second receiving unit receives a signal corresponding to the predetermined identification information transmitted from the mobile station. The second transmission unit transmits the first reference signal to the mobile station at a timing corresponding to a reception timing of a signal corresponding to the predetermined identification information. The mobile station receives the first reference signal synchronized with the timing of the second reference signal.

  According to one aspect of the wireless communication system disclosed in the present application, it is possible to easily realize signal synchronization between base stations regardless of the environment in which the base stations are installed.

FIG. 1 is a diagram illustrating a configuration example of a wireless communication system according to the present embodiment. FIG. 2 is a block diagram illustrating the configuration of the eNB according to the present embodiment. FIG. 3 is a diagram illustrating a specific example of processing by the eNB sequence number transmission instruction unit. FIG. 4 is a diagram illustrating a hardware configuration example of the eNB illustrated in FIG. FIG. 5 is a block diagram illustrating the configuration of the UE according to the present embodiment. FIG. 6 is a diagram illustrating an example of the downlink information storage unit. FIG. 7 is a diagram illustrating another example of the downlink information storage unit. FIG. 8 is a diagram illustrating a hardware configuration example of the UE illustrated in FIG. FIG. 9 is a sequence diagram illustrating the flow of pre-processing by the radio communication system according to the present embodiment before the femto base station performs synchronization processing between base stations. FIG. 10 is a sequence diagram illustrating the flow of the inter-base station synchronization processing by the wireless communication system according to the present embodiment.

  Hereinafter, a wireless communication system, a mobile station, a base station, and a communication control method disclosed in the present application will be described in detail with reference to the drawings.

  FIG. 1 is a diagram illustrating a configuration example of a wireless communication system according to the present embodiment. As illustrated in FIG. 1, the wireless communication system according to the present embodiment includes base stations (eNB: Evolved UTRAN NodeB) 10 a to 10 n and a mobile station (UE: User Equipment) 20.

  eNB10a-10n is a communication apparatus which accommodates the cells 1-3 which are the radio | wireless communication area | region which has predetermined | prescribed area, and provides a radio link with respect to UE20 located in the cell which an own station accommodates. Here, the femto base station 10a among the eNBs 10a to 10n is illustratively narrower in cell range than the base station 10b. Also, another base station 10b that overlaps or is adjacent to a cell under the femto base station 10a may be referred to as a macro base station 10b. Hereinafter, the eNBs 10a to 10n may be referred to as the eNB 10 unless particularly distinguished.

  The UE 20 is a movable wireless communication device, for example, a mobile phone terminal. UE20 communicates with other UE etc. via eNB10 which has accommodated the cell in which it is located. For example, when the UE 20 is located in the cell 1 accommodated by the femto base station 10a, a radio link is set between the UE 20 and the femto base station 10a, and communicates with other UEs and the like through the set radio link. I do.

  Further, the UE 20 receives reference signals transmitted from the femto base station 10a and the macro base station 10b at predetermined timings and used for downlink synchronization with each base station. Hereinafter, a reference signal used for downlink synchronization between the UE 20 and the femto base station 10a is referred to as a first reference signal, and a reference signal used for downlink synchronization between the UE 20 and the macro base station 10b is referred to as a second reference signal. .

  Here, the inter-base station synchronization method by the wireless communication system of the present embodiment will be described. First, the femto base station 10a transmits a predetermined sequence number among RACH (Random Access Channel) sequence numbers, which are physical control channels common to the UE, to the UE 20 as identification information for synchronization between base stations.

  And UE20 which received the sequence number (henceforth "eNB sequence number") used as the identification information for the synchronization between base stations stores an eNB sequence number in a memory | storage part.

  Then, the femto base station 10a transmits the RACH-P transmission request signal for requesting transmission of a RACH preamble (hereinafter abbreviated as “RACH-P”) signal used for uplink synchronization to the UE 20 including the eNB sequence number.

  And UE20 receives the RACH-P transmission request signal containing an eNB sequence number. Then, the UE 20 transmits a RACH-P signal corresponding to the eNB sequence number to the femto base station 10a at a timing corresponding to the reception timing of the second reference signal transmitted from the macro base station 10b.

  Then, the femto base station 10a that has received the RACH-P signal corresponding to the eNB sequence number transmits a first reference signal to the UE 20 at a timing according to the reception timing of the RACH-P signal. Thereby, UE20 can receive the 1st reference signal synchronized with the timing of the 2nd reference signal from macro base station 10b from femto base station 10a.

  Thus, in the radio communication system of the present embodiment, the femto base station 10a notifies the UE 20 of a part of the RACH sequence number as the eNB sequence number, and the UE 20 transmits the RACH-P signal corresponding to the eNB sequence number. It returns to the femto base station 10a. Then, the femto base station 10a that has received the RACH-P signal corresponding to the eNB sequence number transmits a first reference signal to the UE 20 at a timing according to the reception timing of the RACH-P signal. For this reason, the radio | wireless communications system of a present Example can implement | achieve the synchronization between base stations, without using GPS, IEEE1588, and network listening. That is, the radio communication system of the present embodiment can easily realize signal synchronization between base stations regardless of the environment in which the base stations are installed.

  Next, the configuration of the eNB according to the present embodiment will be described. FIG. 2 is a block diagram illustrating a configuration of the eNB 10 according to the present embodiment. As illustrated in FIG. 2, the eNB 10 includes an upper layer protocol processing unit 11, a downlink signal processing unit 12, a downlink baseband processing unit 13, a radio transmission unit 14, a duplexer (DUX: DUpleXer) unit 15, and an antenna 16. . The eNB 10 includes a radio reception unit 17, an uplink baseband processing unit 18, an uplink signal processing unit 19, and a scheduler unit 110.

  The upper layer protocol processing unit 11 performs various processes such as protocol termination on the received data input from the uplink signal processing unit 19. In addition, when transmitting data to the outside such as the UE 20, the upper layer protocol processing unit 11 generates transmission data and outputs the generated transmission data to the downlink baseband processing unit 13.

  The downlink signal processing unit 12 performs downlink layer 2 processing such as retransmission, concealment, and rate control on the transmission data input from the higher layer protocol processing unit 11. The downlink baseband processing unit 13 performs baseband processing such as channel coding, modulation, and radio resource mapping on the transmission data input from the downlink signal processing unit 12. The radio transmission unit 14 performs radio processing such as D (Digital) / A (Analog) conversion, up-conversion to a radio frequency band, and power amplification on transmission data input from the downlink baseband processing unit 13. .

  The duplexer unit 15 transmits the signal input from the wireless transmission unit 14 to the UE 20 via the antenna 16. Further, the duplexer unit 15 outputs a signal received from the antenna 16 to the wireless reception unit 17. The antenna 16 is an antenna that receives a signal transmitted from the UE 20 and transmits a signal to the outside.

  The radio reception unit 17 performs radio processing such as A / D conversion, down-conversion to a baseband frequency band, and power amplification on the signal input from the duplexer unit 15. The uplink baseband processing unit 18 performs baseband processing such as decoding, demodulation, and radio resource demapping on the reception data input from the radio reception unit 17. The uplink signal processing unit 19 performs uplink layer 2 processing such as retransmission request signal generation and deciphering on the reception data input from the uplink baseband processing unit 18.

  The scheduler unit 110 controls uplink synchronization between the eNB 10 and the UE 20 and synchronization between the eNBs 10. The scheduler unit 110 includes a reference signal transmission instruction unit 111, an eNB sequence number storage unit 112, an eNB sequence number transmission instruction unit 113, a RACH-P signal transmission request unit 114, a RACH-P signal reception timing detection unit 115, and a transmission timing correction unit. 116.

  The reference signal transmission instructing unit 111 instructs the downlink baseband processing unit 13 to transmit a reference signal used for downlink synchronization between the eNB 10 and the UE 20 at a predetermined timing. For example, when the eNB 10 is the femto base station 10a, the reference signal transmission instruction unit 111 instructs the downlink baseband processing unit 13 to transmit the first reference signal used for synchronization with the femto base station 10a. To do. Further, when the eNB 10 is the macro base station 10b, the reference signal transmission instruction unit 111 instructs the downlink baseband processing unit 13 to transmit the second reference signal used for synchronization with the macro base station 10b. To do. Note that the transmission timing at which the reference signal transmission instruction unit 111 transmits the reference signal is corrected by a transmission timing correction unit 116 described later.

  The eNB sequence number storage unit 112 stores an eNB sequence number that is identification information for synchronization between base stations.

  The eNB sequence number transmission instructing unit 113 instructs the upper layer protocol processing unit 11 to transmit an eNB sequence number serving as identification information for synchronization between base stations. Here, the process by the eNB sequence number transmission instruction unit 113 will be specifically described.

  FIG. 3 is a diagram illustrating a specific example of processing by the eNB sequence number transmission instruction unit 113. The eNB sequence number transmission instructing unit 113 secures a part of the sequence numbers of the RACH-P signal used for uplink synchronization between the eNB 10 and the UE 20 as an eNB sequence number, and the secured eNB sequence number as an eNB sequence The number is stored in the number storage unit 112. In the example of FIG. 3, the eNB sequence number transmission instruction unit 113 assigns two sequence numbers (# 62 and # 63) among the 64 sequence numbers (# 0 to # 63) of the RACH-P signal to the eNB sequence number. And the secured eNB sequence number is stored in the eNB sequence number storage unit 112.

  Then, the eNB sequence number transmission instructing unit 113 uses the eNB sequence number stored in the eNB sequence number storage unit 112 for the broadcast information that broadcasts the cell-specific parameter to the UE 20 located in the cell under the eNB 10. Multiplex. In the example of FIG. 3, the eNB sequence number transmission instruction unit 113 multiplexes eNB sequence numbers # 62 and # 63 with the broadcast information. Then, the eNB sequence number transmission instruction unit 113 instructs the upper layer protocol processing unit 11 to transmit broadcast information including the eNB sequence number to the UE 20.

  Returning to FIG. 2, the RACH-P signal transmission request unit 114 performs downlink baseband processing so as to transmit a Sync req signal that is a signal requesting the UE 20 to transmit a RACH-P signal corresponding to a specific sequence number. The unit 13 is instructed. The RACH-P signal transmission request unit 114 transmits a Sync req signal including a sequence number other than the eNB sequence number stored in the eNB sequence number storage unit 112 in the RACH-P signal when uplink synchronization timing arrives. The downlink baseband processing unit 13 is instructed to do so. On the other hand, the RACH-P signal transmission request unit 114 receives a Sync req signal including the eNB sequence number stored in the eNB sequence number storage unit 112 in the RACH-P signal when the timing of synchronization between base stations arrives. The downlink baseband processing unit 13 is instructed to transmit.

  Note that the synchronization timing between the base stations is assumed to be a periodic timing, a power-on timing of the eNB 10, a timing of transition from a state where the UE 20 does not exist in a cell under the eNB 10 to a state where the UE 20 exists, etc. The Further, when the eNB 10 is a femto base station, the synchronization timing between the base stations may be a timing at which the eNB 10 recovers from the sleep mode.

  The RACH-P signal reception timing detection unit 115 detects the reception timing of the RACH-P signal transmitted from the UE 20 according to the Sync req signal. Specifically, the RACH-P signal reception timing detection unit 115 receives the RACH-P signal transmitted from the UE 20. The RACH-P signal reception timing detection unit 115 is an example of a second reception unit. Then, RACH-P signal reception timing detection section 115 detects the reception timing of the RACH-P signal by executing a correlation operation between the received RACH-P signal and a known signal pattern.

  The RACH-P signal reception timing detection unit 115 notifies the reception timing of the detected RACH-P signal to the transmission timing correction unit 116 together with the sequence number of the received RACH-P signal.

  The transmission timing correction unit 116 corrects the reference signal transmission timing by the reference signal transmission instruction unit 111. The transmission timing correction unit 116 and the reference signal transmission instruction unit 111 are an example of a second transmission unit. Specifically, transmission timing correction section 116 receives the RACH-P signal reception timing and RACH-P signal sequence number from RACH-P signal reception timing detection section 115. Then, the transmission timing correction unit 116 determines whether or not the sequence number of the RACH-P signal matches the eNB sequence number stored in the eNB sequence number storage unit 112.

  When the sequence number of the RACH-P signal matches the eNB sequence number stored in the eNB sequence number storage unit 112, the transmission timing correction unit 116 determines the reference signal based on the reception timing of the RACH-P signal. Correct the transmission timing. For example, the transmission timing correction unit 116 requests the reference signal transmission instructing unit 111 to transmit the reference signal earlier in time by the propagation delay between the reception timing of the RACH-P signal and the known signal pattern. Correct the signal transmission timing.

  Note that the transmission timing correction unit 116, when the sequence number of the RACH-P signal does not match the eNB sequence number stored in the eNB sequence number storage unit 112, is based on the reception timing of the RACH-P signal. The amount of transmission timing correction is calculated. Then, the transmission timing correction unit 116 returns the calculated uplink transmission timing correction amount in the RACH response signal to the UE 20. The UE 20 that has received the RACH response signal corrects the uplink timing using the correction amount of the uplink transmission timing.

  Note that the eNB 10 illustrated in FIG. 2 is physically realized by the hardware configuration illustrated in FIG. 4, for example. FIG. 4 is a diagram illustrating a hardware configuration example of the eNB 10 illustrated in FIG. As illustrated in FIG. 4, the eNB 10 includes a host processing processor 101, a baseband processing processor 102, a storage device 103, a baseband processing circuit 104, a wireless processing circuit 105, and an antenna 106. The storage device 103 is, for example, an SDRAM (Synchronous Dynamic Random Access Memory), a ROM (Read Only Memory), a flash memory, or the like. The baseband processing circuit 104 and the wireless processing circuit 105 are LSI (Large Scale Integration) or the like. The antenna 106 is connected to the wireless processing circuit 105. The upper layer protocol processing unit 11 of the eNB 10 is realized by the upper processing processor 101, for example. Further, the downlink signal processing unit 12, the uplink signal processing unit 19, and the scheduler unit 110 are realized by the baseband processing processor 102. Also, the downlink baseband processing unit 13 and the uplink baseband processing unit 18 are realized by the baseband processing circuit 104, for example. Further, the wireless transmission unit 14, the wireless reception unit 17, and the duplexer unit 15 are realized by the wireless processing circuit 105. The antenna 16 is realized by the antenna 106.

  Next, the configuration of the UE according to the present embodiment will be described. FIG. 5 is a block diagram illustrating a configuration of the UE 20 according to the present embodiment. As illustrated in FIG. 5, the UE 20 includes an upper layer protocol processing unit 21, an uplink signal processing unit 22, an uplink baseband processing unit 23, a radio transmission unit 24, a duplexer unit 25, and an antenna 26. In addition, the UE 20 includes a radio reception unit 27, a downlink baseband processing unit 28, a downlink signal processing unit 29, and a scheduler unit 210.

  The upper layer protocol processing unit 21 performs various processes such as protocol termination on the received data input from the downlink signal processing unit 29. Further, when transmitting data to the outside such as the eNB 10, the upper layer protocol processing unit 21 generates transmission data and outputs the generated transmission data to the uplink signal processing unit 22.

  The uplink signal processing unit 22 performs uplink layer 2 processing such as retransmission, concealment, and rate control on the transmission data input from the higher layer protocol processing unit 21. The uplink baseband processing unit 23 performs baseband processing such as channel coding, modulation, and radio resource mapping on the transmission data input from the uplink signal processing unit 22. The radio transmission unit 24 performs radio processing such as D / A conversion, up-conversion to a radio frequency band, and power amplification on the transmission data input from the uplink baseband processing unit 23.

  The duplexer unit 25 transmits the signal input from the wireless transmission unit 24 to the eNB 10 via the antenna 26. Further, the duplexer unit 25 outputs a signal received from the antenna 26 to the wireless reception unit 27. The antenna 26 is an antenna that receives a signal transmitted from the eNB 10 and transmits a signal to the outside.

  The radio reception unit 27 performs radio processing such as A / D conversion, down-conversion to a baseband frequency band, and power amplification on the signal input from the duplexer unit 25. The downlink baseband processing unit 28 performs baseband processing such as decoding, demodulation, and radio resource demapping on the reception data input from the radio reception unit 27. The downlink signal processing unit 29 performs downlink layer 2 processing such as retransmission request signal generation and deciphering on the reception data input from the downlink baseband processing unit 28.

  The scheduler unit 210 controls uplink synchronization between the eNB 10 and the UE 20 and synchronization between the eNBs 10. The scheduler unit 210 includes a received power measurement unit 211, a reference signal reception timing detection unit 212, and a downlink information storage unit 213. Further, scheduler section 210 includes eNB sequence number storage section 214, eNB sequence number reception section 215, RACH-P signal transmission timing determination section 216, and RACH-P signal transmission instruction section 217.

  The reception power measurement unit 211 measures the reception power of the reference signal from the eNB 10 received through the radio reception unit 27, the downlink baseband processing unit 28, and the like. The received power measurement unit 211 stores the measured received power of the reference signal in the downlink information storage unit 213 for each eNB 10.

  The reference signal reception timing detection unit 212 detects the reception timing of the reference signal from the eNB 10 received through the radio reception unit 27, the downlink baseband processing unit 28, and the like. Specifically, the reference signal reception timing detection unit 212 detects the reception timing of the reference signal by executing a correlation calculation between the received reference signal and a known signal pattern. The reference signal reception timing detection unit 212 stores the detected reception timing of the reference signal in the downlink information storage unit 213 for each eNB 10.

  The downlink information storage unit 213 stores information related to the downlink for each eNB 10. An example of the downlink information storage unit 213 is shown in FIG. The downlink information storage unit 213 illustrated in FIG. 6 includes items such as a physical cell ID, reception power, and reception timing as information regarding the downlink.

  The physical cell ID is information for identifying the eNB 10, and here indicates an identifier of a cell accommodated by the eNB 10. The received power indicates the received power of the reference signal from the eNB 10. The reception timing represents the reception timing of the reference signal from the eNB 10 and includes a frame number, a subframe number, an OFDM (Orthogonal Frequency Division Multiplexing) symbol number, and a sampling number. The frame number indicates a frame number including a reference signal among a plurality of frames transmitted from the eNB 10. The subframe number indicates the number of a subframe including a reference signal among a plurality of subframes included in one frame. The OFDM symbol number indicates the number of an OFDM symbol including a reference signal among a plurality of OFM symbols included in one subframe. The sampling number indicates the number of a sample including a reference signal among a plurality of samples included in one OFDEM symbol.

  For example, the received power measuring unit 211 measures the received power “X” of the reference signal from the eNB 10 identified by the physical cell ID “11”, and stores the measured received power in the corresponding downlink power storage unit 213. The reference signal reception timing detection unit 212 detects the reference signal reception timings “A”, “B”, “C”, and “D” from the eNB 10 identified by the physical cell ID “11” and supports Stored at the reception timing.

  6 shows an example in which the downlink information storage unit 213 includes the reception timing of the reference signal from each eNB. However, the relative difference between the eNB that accommodates a certain cell and another eNB is used to receive the reference signal. It may be included as timing. Another example of the downlink information storage unit 213 is shown in FIG. The downlink information storage unit 213 illustrated in FIG. 7 includes items such as a physical cell ID, reception power, and reception timing as information regarding the downlink. The physical cell ID and the received power shown in FIG. 7 are the same as those in FIG. Also, the eNB 10 identified by the physical cell ID “11” in FIG. 7 is assumed to accommodate a serving cell for the UE 20.

  The reception timing represents the reception timing of the reference signal from the eNB 10 and includes a frame number, a subframe number, an OFDM symbol number, and a sampling number. The frame number indicates the difference between the frame number including the reference signal and the frame number corresponding to the eNB 10 having the physical cell ID “11”. The subframe number indicates a difference between the number of the subframe including the reference signal and the number of the subframe corresponding to the eNB 10 having the physical cell ID “11”. The OFDM symbol number indicates a difference between the number of the OFDM symbol including the reference signal and the number of the OFDM symbol corresponding to the eNB 10 having the physical cell ID “11”. The sampling number indicates the difference between the number of the sample including the reference signal and the number of the sample corresponding to the eNB 10 having the physical cell ID “11”.

  Returning to FIG. 5, the eNB sequence number storage unit 214 stores an eNB sequence number that is identification information for synchronization between base stations.

  The eNB sequence number receiving unit 215 receives the eNB sequence number from the eNB 10 and stores it in the eNB sequence number storage unit 214. The eNB sequence number receiving unit 215 is an example of a first receiving unit. Specifically, the eNB sequence number reception unit 215 monitors the reception data from the eNB 10 input to the upper layer protocol processing unit 21 and detects broadcast information from the reception data. Then, the eNB sequence number receiving unit 215 receives the eNB sequence number and stores it in the eNB sequence number storage unit 214 by separating the eNB sequence number from the detected broadcast information.

  The RACH-P signal transmission timing determination unit 216 determines the transmission timing of the RACH-P signal. Specifically, the RACH-P signal transmission timing determination unit 216 determines whether or not the sequence number included in the Sync req signal received from the eNB 10 matches the eNB sequence number stored in the eNB sequence number storage unit 214. To do.

  Then, the RACH-P signal transmission timing determination unit 216 performs the following process when the sequence number included in the Sync req signal matches the eNB sequence number. That is, the RACH-P signal transmission timing determination unit 216 refers to the downlink information storage unit 213 and searches for the eNB 10 having the highest received power among the eNBs 10 other than the eNB 10 that accommodates the cell in which the UE 20 is located. Then, RACH-P signal transmission timing determining section 216 determines the reception timing of the reference signal corresponding to the cell of eNB 10 having the highest received power as the RACH-P signal transmission timing.

  On the other hand, when the sequence number included in the Sync req signal does not match the eNB sequence number, that is, when the sequence number included in the Sync req signal is a sequence number for uplink synchronization, RACH-P signal transmission timing determination section 216 The following processing is performed. That is, the RACH-P signal transmission timing determination unit 216 refers to the downlink information storage unit 213 to determine the reception timing of the reference signal corresponding to the cell where the UE 20 is located as the RACH-P signal transmission timing.

  The RACH-P signal transmission timing determination unit 216 notifies the RACH-P signal transmission instruction unit 217 of the determined RACH-P signal transmission timing and the sequence number included in the Sync req signal.

  The RACH-P signal transmission instruction unit 217 receives the RACH-P signal transmission timing from the RACH-P signal transmission timing determination unit 216 and the sequence number included in the Sync req signal from the RACH-P signal transmission timing determination unit 216. Accept. Then, the RACH-P signal transmission instructing unit 217 instructs the uplink baseband processing unit 23 to transmit the RACH-P signal corresponding to the sequence number included in the Sync req signal to the eNB 10 at the received transmission timing. Instruct. The RACH-P signal transmission timing determination unit 216 and the RACH-P signal transmission instruction unit 217 are examples of the first transmission unit.

  Note that the UE 20 illustrated in FIG. 5 is physically realized by, for example, the hardware configuration illustrated in FIG. FIG. 8 is a diagram illustrating a hardware configuration example of the UE 20 illustrated in FIG. As illustrated in FIG. 8, the UE 20 includes a processor 201, a storage device 202, a baseband processing circuit 203, a wireless processing circuit 204, and an antenna 205. The storage device 202 is, for example, an SDRAM, a ROM, a flash memory, or the like. The antenna 205 is connected to the wireless processing circuit 204. The upper layer protocol processing unit 21, the uplink signal processing unit 22, the downlink signal processing unit 29, and the scheduler unit 210 of the UE 20 are realized by the processor 201, for example. Further, the uplink baseband processing unit 23 and the downlink baseband processing unit 28 are realized by the baseband processing circuit 203, for example. The wireless transmission unit 24, the wireless reception unit 27, and the duplexer unit 25 are realized by the wireless processing circuit 204. The antenna 26 is realized by the antenna 205.

  Next, the flow of processing by the wireless communication system according to the present embodiment will be described with reference to FIGS. 9 and 10. Here, a flow of processing in which the femto base station 10a illustrated in FIG. 1 performs signal synchronization with the macro base station 10b will be described.

  FIG. 9 is a sequence diagram showing the flow of pre-processing by the radio communication system according to the present embodiment before the femto base station 10a performs synchronization processing between base stations. As illustrated in FIG. 9, the femto base station 10a transmits a first reference signal to the UE 20 at a predetermined timing (step S101). Then, the UE 20 that has received the first reference signal performs downlink synchronization based on the reception timing of the first reference signal.

  Subsequently, the femto base station 10 a secures some of the sequence numbers of the RACH-P signal as eNB sequence numbers, and stores the secured eNB sequence numbers in the eNB sequence number storage unit 112. Then, the femto base station 10a multiplexes the eNB sequence number with the broadcast information for broadcasting the cell-specific parameter to the UE 20 located in the cell of the femto base station 10a. Then, the femto base station 10a transmits broadcast information including the eNB sequence number to the UE 20 (step S102).

  Subsequently, the UE 20 that has received the broadcast information receives the eNB sequence number by separating the eNB sequence number from the broadcast information (step S103) and stores the eNB sequence number in the eNB sequence number storage unit 214 (step S104).

  FIG. 10 is a sequence diagram illustrating the flow of the inter-base station synchronization processing by the wireless communication system according to the present embodiment. Here, the flow of processing until the femto base station 10a performs signal synchronization with the macro base station 10b after the processing shown in FIG. 9 will be described.

  As illustrated in FIG. 10, the femto base station 10a and the macro base station 10b transmit the first reference signal and the second reference signal to the UE 20 at predetermined timings (steps S201 and S202). Then, the UE 20 that has received the first reference signal and the second reference signal measures the received power of each reference signal, and stores the measured received power of the reference signal in the downlink information storage unit 213 for each eNB. Then, the UE 20 detects the reception timing of each reference signal, and stores the detected reception timing of the reference signal in the link information storage unit 213 for each eNB.

  Subsequently, when the timing of uplink synchronization arrives, the femto base station 10a transmits a Sync req signal including a sequence number other than the eNB sequence number stored in the eNB sequence number storage unit 112 in the RACH-P signal to the UE 20 Send to. On the other hand, the femto base station 10a transmits a Sync req signal including the eNB sequence number stored in the eNB sequence number storage unit 112 to the UE 20 when the timing of synchronization between the base stations arrives (step S203). ).

  Subsequently, the UE 20 that has received the Sync req signal determines whether or not the sequence number included in the Sync req signal matches the eNB sequence number stored in the eNB sequence number storage unit 214 (Step S204). When the sequence number included in the Sync req signal does not match the eNB sequence number (No at Step S204), the UE 20 performs the following processing. That is, the UE 20 refers to the downlink information storage unit 213 and determines the timing of the reference signal corresponding to the cell of the femto base station 10a as the RACH-P signal transmission timing (step S205). Then, UE20 advances a process to step S208.

  On the other hand, when the sequence number included in the Sync req signal matches the eNB sequence number (Yes at Step S204), the UE 20 performs the following processing. That is, the UE 20 searches the eNB 10 with the highest received power among the eNBs 10 other than the femto base station 10a with reference to the downlink information storage unit 213 (step S206). Here, it is assumed that the eNB 10 having the largest received power is the macro base station 10b. And UE20 determines the reception timing of the reference signal corresponding to the cell of macro base station 10b with the largest reception power as a transmission timing of a RACH-P signal (step S207).

  Then, the UE 20 transmits the RACH-P signal corresponding to the sequence number included in the Sync req signal to the femto base station 10a at the transmission timing determined in Step S205 or S207 (Step S208).

  Subsequently, the femto base station 10a receives the RACH-P signal transmitted from the UE 20 (step S209), and detects the reception timing of the received RACH-P signal (step S210). Then, the femto base station 10a determines whether or not the sequence number of the received RACH-P signal matches the eNB sequence number stored in the eNB sequence number storage unit 112 (step S211).

  If the sequence number of the received RACH-P signal does not match the eNB sequence number (No at step S211), the femto base station 10a determines the uplink transmission timing based on the RACH-P signal reception timing. A correction amount is calculated (step S212). Then, the femto base station 10a includes the calculated uplink transmission timing correction amount in the RACH response signal and returns it to the UE 20 (step S213). Then, the UE 20 that has received the RACH response signal corrects the uplink transmission timing (step S214).

  On the other hand, when the sequence number of the received RACH-P signal matches the eNB sequence number (Yes in step S211), the femto base station 10a transmits the first reference signal based on the reception timing of the RACH-P signal. The timing is corrected (step S215). As a result, the transmission timing of the first reference signal transmitted from the femto base station 10a is synchronized with the transmission timing of the second reference signal transmitted from the macro base station 10b (steps S216 and S217).

  As described above, in the radio communication system of the present embodiment, the femto base station 10a notifies the UE 20 of a part of the RACH sequence number as the eNB sequence number, and the UE 20 corresponds to the RACH-P corresponding to the eNB sequence number. A signal is returned to the femto base station 10a. Then, the femto base station 10a that has received the RACH-P signal transmits a first reference signal to the UE 20 at a timing according to the reception timing of the RACH-P signal. For this reason, the radio | wireless communications system of a present Example can implement | achieve the synchronization between base stations, without using GPS, IEEE1588, and network listening. That is, the radio communication system of the present embodiment can easily realize signal synchronization between base stations regardless of the environment in which the base stations are installed.

  Moreover, in the radio | wireless communications system of a present Example, UE20 is RACH- corresponding to eNB sequence number at the timing according to the reception timing of the reference signal transmitted from eNB10b with the largest received power among several other eNBs. A P signal is transmitted to the eNB 10a. For this reason, the radio | wireless communications system of a present Example can synchronize the transmission timing of the signal in the femto base station 10a with respect to the macro base station 10b with high possibility of causing inter-cell interference with the femto base station 10a.

  By the way, in the said Example, UE20 transmits RACH-P signal corresponding to an eNB sequence number to eNB10a at the timing according to the reception timing of the reference signal transmitted from eNB with the largest received power among several other eNB10b. An example of sending to is shown. However, the timing for transmitting the RACH-P signal is not limited to this. For example, the UE 20 transmits the RACH-P signal corresponding to the eNB sequence number to the eNB 10a at a timing corresponding to the reception timing of the reference signal transmitted from the eNB having the largest signal-to-noise ratio among the plurality of other eNBs 10b. You can also

10a femto base station 10b macro base station 11 upper layer protocol processing unit 12 downlink signal processing unit 13 downlink baseband processing unit 14 wireless transmission unit 15 duplexer unit 16 antenna 17 wireless reception unit 18 uplink baseband processing unit 19 uplink Signal processing unit 21 Upper layer protocol processing unit 22 Uplink signal processing unit 23 Uplink baseband processing unit 24 Wireless transmission unit 25 Duplexer unit 26 Antenna 27 Radio reception unit 28 Downlink baseband processing unit 29 Downlink signal processing unit 101 Upper layer Processing processor 102 Baseband processing processor 103 Storage device 104 Baseband processing circuit 105 Radio processing circuit 106 Antenna 110 Scheduler unit 111 Reference signal transmission instruction unit 112 eNB sequence number storage unit 113 NB sequence number transmission instruction unit 114 RACH-P signal transmission request unit 115 RACH-P signal reception timing detection unit 116 transmission timing correction unit 201 processor 202 storage device 203 baseband processing circuit 204 wireless processing circuit 205 antenna 210 scheduler unit 211 received power Measurement unit 212 Reference signal reception timing detection unit 213 Downlink information storage unit 214 eNB sequence number storage unit 215 eNB sequence number reception unit 216 RACH-P signal transmission timing determination unit 217 RACH-P signal transmission instruction unit

Claims (9)

In a wireless communication system in which a mobile station receives first and second reference signals transmitted from a first base station and a second base station at predetermined timings and used for synchronization with each base station,
The mobile station
The first base station receives from the first base station a part of a plurality of sequence numbers included in a physical control channel used for uplink synchronization between the first base station and the mobile station A receiver,
A first transmission unit configured to transmit a signal corresponding to the partial sequence number to the first base station at a timing corresponding to a reception timing of the second reference signal transmitted from the second base station; And comprising
The first base station is
A sequence number transmitter for transmitting the partial sequence number to the mobile station;
A second receiver for receiving a signal corresponding to the partial sequence number transmitted from the mobile station;
A second transmitter that transmits the first reference signal to the mobile station at a timing corresponding to a reception timing of a signal corresponding to the partial sequence number ;
The wireless communication system, wherein the mobile station receives the first reference signal synchronized with the timing of the second reference signal. The radio communication system according to claim 1, wherein the signal corresponding to the partial sequence number is a random access signal. The first transmission unit is configured to transmit the second reference transmitted from the second base station having the highest reception power among the plurality of second base stations having reception power lower than that of the first base station. The radio communication system according to claim 1 or 2, wherein a signal corresponding to the partial sequence number is transmitted to the first base station at a timing according to a signal reception timing. The first transmission unit is transmitted from the second base station having the largest signal-to-noise ratio among the plurality of second base stations having a smaller signal-to-noise ratio than the first base station. The wireless communication according to claim 1 or 2, wherein a signal corresponding to the partial sequence number is transmitted to the first base station at a timing according to a reception timing of a second reference signal. system. In the mobile station that receives the first and second reference signals transmitted from the first base station and the second base station respectively at predetermined timings and used for synchronization with the base station,
A receiving unit that receives, from the first base station, a part of a plurality of sequence numbers included in a physical control channel used for uplink synchronization between the first base station and the mobile station When,
A transmitter for transmitting a signal corresponding to the partial sequence number to the first base station at a timing corresponding to a reception timing of the second reference signal transmitted from the second base station; With
A mobile station which receives the first reference signal transmitted from the first base station based on a signal corresponding to the partial sequence number and synchronized with the timing of the second reference signal . The first of the wireless communication system in which the mobile station receives the first and second reference signals transmitted from the first base station and the second base station at predetermined timings and used for synchronization with each base station. In the base station
A transmitter that transmits a part of a plurality of sequence numbers included in a physical control channel used for uplink synchronization between the first base station and the mobile station to the mobile station ;
A receiving unit that receives a signal corresponding to the partial sequence number transmitted at a timing corresponding to a reception timing of the second reference signal from the second base station in the mobile station;
A processor that corrects the predetermined timing for transmitting the first reference signal so that the first reference signal is transmitted to the mobile station at a timing according to the reception timing of the signal;
A first base station comprising: In the communication control method in which the mobile station receives the first and second reference signals transmitted from the first base station and the second base station, respectively, at a predetermined timing and used for synchronization with each base station.
The mobile station
Receiving from the first base station a part of a plurality of sequence numbers included in a physical control channel used for uplink synchronization between the first base station and the mobile station ;
Transmitting a signal corresponding to the partial sequence number to the first base station at a timing according to a reception timing of the second reference signal transmitted from the second base station;
The first base station is
Transmitting the partial sequence number to the mobile station;
Receiving a signal corresponding to the partial sequence number transmitted from the mobile station;
Transmitting the first reference signal to the mobile station at a timing corresponding to a reception timing of a signal corresponding to the partial sequence number ;
The mobile station
Receiving the first reference signal synchronized with the timing of the second reference signal. A communication control method comprising: A communication control method by a mobile station that receives first and second reference signals transmitted from a first base station and a second base station at predetermined timings and used for synchronization with the base station,
Receiving from the first base station a part of a plurality of sequence numbers included in a physical control channel used for uplink synchronization between the first base station and the mobile station ;
Transmitting a signal corresponding to the partial sequence number to the first base station at a timing according to a reception timing of the second reference signal transmitted from the second base station;
Receiving the first reference signal transmitted from the first base station based on a signal corresponding to the partial sequence number and synchronized with the timing of the second reference signal. Communication control method. The first of the wireless communication system in which the mobile station receives the first and second reference signals transmitted from the first base station and the second base station at predetermined timings and used for synchronization with each base station. A communication control method by a base station of
A part of a plurality of sequence numbers included in a physical control channel used for uplink synchronization between the first base station and the mobile station is transmitted to the mobile station;
The mobile station receives a signal corresponding to the partial sequence number transmitted at a timing corresponding to the reception timing of the second reference signal from the second base station,
Correcting the predetermined timing for transmitting the first reference signal so that the first reference signal is transmitted to the mobile station at a timing according to the reception timing of the signal. Communication control method.

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