JP5533308B2 - Relay device and synchronization maintaining method - Google Patents

Description

  The present invention relates to a relay device and a synchronization maintaining method, and more particularly to a relay device that establishes synchronization between a mobile communication device and a base station device, and a synchronization maintaining method using the relay device.

  The mobile communication network secures an area where mobile communication devices can communicate by arranging a plurality of base stations. Here, an area covered by one base station is referred to as a cell. The reception quality of the mobile communication device deteriorates at the cell boundary. This is because the mobile communication device located at the cell boundary is far from the base station and the reception quality becomes unstable. Therefore, in order to improve the reception quality of the mobile communication device at the cell boundary, in the 3GPP of the standardization organization, studies are underway to install a Relay Node (RN) under the base station. 3GPP is a standardization organization that is promoting standardization of LTE (Long Term Evolution), which is a next-generation mobile communication network. In LTE, a base station is generally referred to as an eNB (evolved Node-B), and a mobile communication device is generally referred to as a UE (User Equipment).

  In downlink communication in which data is transmitted from the eNB to the UE, the RN receives a signal from the eNB and transmits the signal to the UE. On the other hand, in uplink communication in which data is transmitted from the UE to the eNB, the RN receives a signal from the UE and transmits the signal to the eNB. By installing RN, the distance between UE and RN becomes shorter than the distance between UE and eNB. Here, the longer the communication distance, the greater the power used to transmit data. Since the distance between the UE and the RN is short, the UE and the RN can communicate using low power. The smaller the power used, the less interference that occurs in the cell. As a result, the reception quality at the UE improves and the system capacity increases. In addition, in order to perform communication between the UE and the eNB in this way, it is necessary to maintain stable synchronization.

  Patent Document 1 discloses a technique in which a mobile communication device that is out of synchronization shifts to a synchronization established state. Specifically, the mobile communication device and the base station in the synchronized state maintain the synchronized state using a timing adjustment command (TAC). The base station periodically transmits a TAC to the mobile communication device. Thereby, the synchronization state is maintained. Therefore, if the TAC is not transmitted from the base station to the mobile communication device, the synchronization state is canceled. In such a case, the mobile communication device transmits a preamble to the base station using a random access channel. The random access channel is a channel that can transmit a signal even when the synchronization state is not maintained. The base station that has received the preamble through the random access channel transmits a TAC (Timing Advance Command) as a response signal to the mobile communication device. Thus, the mobile communication device that has received the TAC can transition to the synchronized state.

JP 2009-164832 A

  However, Patent Document 1 does not disclose a synchronization establishment procedure when an RN is interposed between a mobile communication device and a base station. In general, synchronization between the RN and the eNB is maintained by receiving a CRS (Cell-specific Reference Signal). The CRS is set in a data area for transmitting user data transmitted from the base station to the RN. However, it is not assumed that the RN cannot receive CRS and cannot maintain synchronization. Therefore, when RN cannot receive CRS, the problem that synchronization with eNB cannot be established arises.

  The present invention has been made to solve such a problem. Even when the RN is arranged between the mobile communication device and the base station and the CRS cannot be received, the RN and the base station device are provided. It is an object to provide a relay device and a synchronization maintaining method that can maintain synchronization with each other.

  A relay apparatus according to a first aspect of the present invention is a relay apparatus arranged between a mobile communication apparatus and a base station apparatus, and is a reference set in a data area for transmitting user data from the base station apparatus A base station synchronization establishment unit that maintains synchronization with the base station device using a signal, and the base station synchronization establishment unit is configured to communicate with the base station device by not transmitting the reference signal from the base station device. When synchronization is canceled, synchronization with the base station apparatus is established using a synchronization establishment procedure used at the time of initial access from the relay apparatus to the neighboring base station apparatus.

  The synchronization maintaining method according to the second aspect of the present invention provides synchronization between the relay device and the base station device when a relay device is disposed between the mobile communication device and the base station device. Maintaining the synchronization with the base station apparatus using a reference signal set in a data area for transmitting user data from the base station apparatus, and from the base station apparatus When the synchronization with the base station apparatus is released due to the reference signal not being transmitted, the synchronization with the base station apparatus is performed using the synchronization establishment procedure used at the time of initial access from the relay apparatus to the neighboring base station apparatus. Establishing the step.

  According to the present invention, even when an RN is arranged between a mobile communication device and a base station and CRS cannot be received, a relay device and a synchronization that can maintain synchronization between the RN and the base station device A maintenance method can be provided.

1 is a configuration diagram of a relay device according to a first embodiment; 1 is a configuration diagram of a relay device according to a first embodiment; 1 is a configuration diagram of a mobile communication network according to a first embodiment. FIG. 3 is a synchronization establishment sequence according to the first embodiment. 3 is a sequence showing a RACH procedure according to the first embodiment. It is a figure which shows the allocation range of C-RNTI and preamble concerning Embodiment 1. FIG. FIG. 6 is a diagram for explaining occurrence of loss of synchronization according to the first embodiment. FIG. 3 is a diagram for explaining a synchronization maintaining method according to the first exemplary embodiment; 4 is a synchronization re-establishment sequence according to the first embodiment.

(Embodiment 1)
Embodiments of the present invention will be described below with reference to the drawings. A configuration example of the relay device 30 according to the first exemplary embodiment of the present invention will be described with reference to FIG. The relay device 30 includes a base station synchronization establishment unit 31. The relay device 30 is disposed between the mobile communication device 10 and the base station device 20.

  The mobile communication device 10 is a mobile phone terminal, PHS (Personal Handy-phone System), PDA (Personal Digital Assistant), or the like, and is a terminal having a communication function.

  The base station device 20 is arranged between a core network (not shown) and the mobile communication device 10 and communicates with the mobile communication device 10 via radio. In addition, when communicating with the mobile communication device 10 via the relay device 30, the base station device 20 communicates with the relay device 30 wirelessly or by wire.

  The base station synchronization establishment unit 31 maintains synchronization with the base station apparatus 20 using a reference signal set in a data area in which user data is transmitted from the base station apparatus 20. Base station apparatus 20 transmits data to relay apparatus 30 using a data area for transmitting control information and a data area for transmitting user data. The reference signal used to maintain synchronization between the relay device 30 and the base station device 20 is set in a data area for transmitting user data.

  Here, when the reference signal is not transmitted, the base station synchronization establishment unit 31 cannot maintain the synchronization with the base station apparatus 20, and the synchronization state is canceled. When the reference signal is not transmitted, for example, the user data may not be transmitted because there is no user data to be transmitted from the base station apparatus 20 to the relay apparatus 30. In this case, the reference signal set in the data area for transmitting user data is not transmitted. In such a case, the base station synchronization establishment unit 31 establishes synchronization with the base station device 20 using a synchronization establishment procedure used at the time of initial access to the neighboring base station devices.

  As described above, when the relay device 30 according to FIG. 1 is used, the reference signal is not transmitted from the base station device 20, and the synchronization between the relay device 30 and the base station device 20 cannot be maintained. In the above, the synchronization between the relay device 30 and the base station device 20 can be established by using the synchronization establishment procedure used at the time of initial access to the neighboring base station devices.

  Then, the detailed structural example of the relay apparatus 30 concerning Embodiment 1 of this invention is demonstrated using FIG. The relay device 30 includes a base station synchronization establishment unit 31, a mobile communication device synchronization establishment unit 32, and a control unit 33.

  The base station synchronization establishment unit 31 establishes synchronization with the base station apparatus 20 in the UE mode that operates when establishing synchronization with the base station apparatus 20. The synchronization between the base station synchronization establishment unit 31 and the base station apparatus 20 uses a synchronization establishment procedure used at the time of initial access from the mobile communication apparatus 10 to the neighboring base station apparatus when the relay apparatus 30 is not provided. The initial access time is, for example, access from the mobile communication device 10 to the neighboring base station device after the mobile communication device 10 is powered on. As another example, the time of initial access includes the first access to the handover destination base station apparatus when the mobile communication apparatus 10 is handed over. Handover refers to moving to an area covered by a base station different from the base station covering the area where the current position is located when the mobile communication device 10 moves.

  The mobile communication device synchronization establishment unit 32 establishes synchronization with the mobile communication device 10 in the RN mode that operates when establishing synchronization with the mobile communication device 10. The synchronization between the mobile communication device synchronization establishment unit 32 and the mobile communication device 10 is similar to the synchronization between the base station synchronization establishment unit 31 and the base station device 20 from the mobile communication device 10 to the neighboring base station devices. The synchronization establishment procedure used at the time of initial access is used.

  The control unit 33 switches between the UE mode and the RN mode according to the opposite device that establishes synchronization. When establishing synchronization with the base station apparatus 20, the control unit 33 sets the relay apparatus 30 to the UE mode and operates it. In addition, when establishing synchronization with the mobile communication device 10, the control unit 33 sets the relay device 30 to the RN mode to operate.

  As described above, by using the relay device 30 according to FIG. 2, even when the relay device 30 is arranged between the mobile communication device 10 and the base station device 20, the mobile communication device 10 and the base station device. Synchronization with 20 can be established. That is, the relay device 30 establishes synchronization with the mobile communication device 10 and the base station device 20, respectively. Further, when establishing synchronization with the mobile communication device 10 and the base station device 20, the relay device 30 uses a synchronization establishment procedure used during initial access from the mobile communication device 10 to the base station device 20. Thus, the mobile communication device 10 and the base station device 20 can establish synchronization via the relay device 30.

  Next, a configuration example of the mobile communication network according to the first exemplary embodiment of the present invention will be described using FIG. A configuration example of a mobile communication network will be described using an access network in LTE. The mobile communication network includes UEs 11 to 14, RN 35, and eNB 21. The UEs 11 to 14 are mobile communication devices that can communicate with an LTE access network. The eNB 21 is a base station device used for an LTE access network. The RN 35 corresponds to the relay device 30 in FIG. UE11 thru | or 13 communicates with eNB21 via RN35. UE11 thru | or 13 are located in the boundary of the cell which eNB21 covers. Therefore, UE11 thru | or 13 communicates with eNB21 via RN35. The UE 14 directly communicates with the eNB 21 without going through the RN 35.

  UE11 thru | or 13 establishes a synchronization with RN35. Moreover, UE14 establishes a synchronization with eNB21. The RN 35 establishes synchronization with the UEs 11 to 13 and establishes synchronization with the eNB 21. Here, the space between the UEs 11 to 13 and the RN 35 is referred to as an access link, and the space between the RN 35 and the eNB 21 is referred to as a backhaul link.

  Next, a synchronization establishment sequence according to the first embodiment of the present invention will be described with reference to FIG. FIG. 4 shows a synchronization establishment sequence when the power of the RN 35 is turned on. First, the RN 35 operates in the UE mode when the power is turned on and started (S11). Here, the UE mode and the RN mode will be described.

  The UE mode is a mode set in the RN 35 when the RN 35 communicates with the eNB 21. The RN 35 operates as a UE with respect to the eNB 21 when operating in the UE mode. The RN mode is a mode set in the RN 35 when the RN 35 communicates with the UEs 11 to 13. The RN 35 operates as an eNB for the UEs 11 to 13 when operating in the RN mode.

  Returning to FIG. 4, the RN 35 communicates with the eNB 21 according to the RACH procedure with the eNB 21 (S12). When the RACH procedure is completed, synchronization between the RN 35 and the eNB 21 is established (S13). Here, the RACH procedure will be described with reference to FIG.

  First, the RN 35 selects one from a plurality of preambles prepared in advance in a storage unit (not shown) included in the RN 35. The RN 35 transmits a RACH preamble message including the selected preamble to the eNB 21 (S21).

  Next, when receiving the RACH preamble message, the eNB 21 transmits a RACH response message to the RN 35 (S22). The RACH response message includes a preamble received by the eNB 21, timing information indicating the timing at which the RN 35 transmits the message, and an identifier (C-RNTI) for identifying the RN 35 in the subsequent RACH procedure.

  Next, when the RN 35 receives the RACH response message, the RN 35 transmits a terminal identification message to the eNB 21 (S23). The terminal identification message includes a terminal identifier that the RN 35 has to identify the RN 35.

  The RN 35 transmits the selected preamble using the RACH preamble message. In this case, the eNB 21 may receive the same preamble at the same time from an RN different from the UE or the RN 35. In this case, since a preamble collision occurs, the eNB 21 cannot determine the RN or UE that transmitted the preamble. In such a case, the RN 35 executes the preamble transmission procedure again after the random time has elapsed.

  The eNB 21 identifies the RN 35 using the received terminal identification message. If the identification is completed normally, a conflict resolution message is transmitted to the RN 35 (S24).

  When the received conflict resolution message includes the terminal identifier of the RN 35, the RN 35 determines that synchronization has been established with the eNB 21 and performs data transmission / reception (S25). When the received conflict resolution message does not include the terminal identifier of the RN 35, the RN 35 performs the RACH procedure again.

  As described above, the synchronization between the RN 35 and the eNB 21 can be established by executing the RACH procedure of FIG.

  Returning to FIG. 4, the RN 35 operates in the RN mode after establishing synchronization with the eNB 21 (S14). Next, the RN 35 searches for UEs located in the area formed by the RN 35, and generates a list of searched UEs (S15). UE located in the area which RN35 comprises is UE11 thru | or 13 located in the cell boundary of eNB21.

  Subsequently, the RN 35 executes the RACH procedure with the searched UEs 11 to 13 (S16). The RACH procedure executed between the UEs 11 to 13 and the RN 35 is the same as the RACH procedure described in FIG. However, the RN 35 operates in the RN mode. For this reason, the RN 35 receives the RACH preamble message transmitted from the UEs 11 to 13 and transmits the RACH response message. That is, the RN 35 operates as the eNB in FIG. UE11 thru | or 13 operate | moves as RN in FIG. The RACH procedure is executed between the RN 35 and the UEs 11 to 13, thereby establishing synchronization between the RN 35 and the UEs 11 to 13 (S17).

  RN35 adjusts the timing which transmits data from UE11 thru | or 13 to RN35 according to the timing which transmits data from RN35 to eNB21, and establishes the synchronization between UE11 thru | or 13 and RN35. The frequency used when transmitting data from the UEs 11 to 13 to the RN 35 is the same as the frequency used when transmitting data from the RN 35 to the eNB 21. Therefore, when the timing for transmitting data from the UEs 11 to 13 to the RN 35 coincides with the timing for transmitting data from the RN 35 to the eNB 21, the respective signals interfere with each other. Therefore, when establishing synchronization with the UEs 11 to 13, the RN 35 adjusts and synchronizes so that the timing of transmitting data from the RN 35 to the eNB 21 is different from the timing of transmitting data from the UE 11 to 13 to the RN 35. Establish. Specifically, the control unit 33 transmits the timing information to the UEs 11 to 13 to the mobile communication device synchronization establishment unit 32 according to the timing information for transmitting the data acquired by the base station synchronization establishment unit 31. To control.

  Next, the RN 35 transmits the C-RNTI list assigned to the UEs 11 to 13 to the eNB 21 (S18). The eNB 21 can recognize the UEs 11 to 13 located under the RN 35 by receiving the C-RNTI list from the RN 35. Thereby, the synchronization between UE11 thru | or 13 and eNB21 is established (S19).

  Data synchronization between UE11 thru | or 13 and eNB21 is attained by establishing the synchronization between UE11 thru | or 13 and eNB21 (S20). In this case, the RN 35 relays data transmitted from the UEs 11 to 13 and the eNB 21 and transmits data to the eNB 21 and the UEs 11 to 13. The eNB 21 can transmit data to the UEs 11 to 13 located under the RN 35 by acquiring the C-RNTI list from the RN 35.

  Here, the preambles used in the access link, the backhaul link, and the C-RNTI may be used by selecting values in different ranges. For example, as shown in FIG. 6, C-RNTI used for access link is a value in the range of X to Y. The preamble used for the access link is a value in the range of Z to W. The other 0-X and Y-65535 are C-RNTI for the backhaul link, and 0-Z and W-63 are the preamble for the backhaul link.

  Thus, by distinguishing the preamble and C-RNTI used in the access link from the preamble and C-RNTI used in the backhaul link, even when the preamble is erroneously transmitted from the UEs 11 to 13 to the eNB 21, The eNB 21 determines that the preamble has been transmitted in error, and does not execute the procedure for establishing synchronization with the UEs 11 to 13. Thereby, it is possible to prevent the reception quality of the UEs 11 to 13 from deteriorating due to the UEs 11 to 13 located at the cell boundary establishing direct synchronization with the eNB 21.

  As described above, by arranging the RN according to the first embodiment of the present invention, the RN can switch the operation according to the opposite device that establishes synchronization. Accordingly, synchronization can be established between the RN and the UE, and between the RN and the eNB. Therefore, since synchronization between the UE and the eNB can be established, data can be transmitted and received between the UE and the eNB.

  Subsequently, a synchronization procedure between the UE and the eNB when the synchronization between the RN and the eNB is canceled (out of synchronization) will be described. First, a situation in which loss of synchronization occurs between the RN and the eNB will be described with reference to FIG. FIG. 7 illustrates a frame configuration of data transmitted from the eNB 21 to the RN 35. Data transmitted from the eNB 21 to the RN 35 includes a PDCCH that transmits control information and a PDSCH that transmits user data such as video information. An RS (Reference signal) including information necessary for data demodulation is mapped to the PDCCH. The RS also includes information necessary for maintaining synchronous detection.

  However, in the backhaul link between the RN 35 and the eNB 21, the RN 35 has restrictions on radio frames and subframes that can be transmitted and received in order to prevent self-interference. Self-interference is an event in which a transmission signal and a reception signal by RN cause interference. Communication is performed between the RN 35 and the eNB 21 and between the RN 35 and the UEs 11 to 13 using the same frequency. Therefore, the transmission signal and reception signal in the RN may cause interference. In particular, in 3GPP Rel-10, when a multi-media broadcast over a single frequency network (MBSFN) is assigned to all subframes, synchronization may not be maintained between the RN and the eNB.

  The RN 35 cannot receive the PDCCH due to the above-described restrictions. Therefore, the RN 35 enables synchronous detection of the R-PDCCH, R-PDSCH, and PDSCH by receiving a CRS (Cell Specific Reference Signal) mapped to the R-PDCCH region of the PDSCH. By receiving a TAC transmitted on the R-PDSCH in a state where synchronous detection is possible, synchronization between the RN 35 and the eNB 21 can be maintained.

  The RN 35 needs to receive the CRS mapped to the PDSCH in order to maintain the backhaul link synchronization. However, the PDSCH may not be assigned to the RN 35 because user data for the UEs 11 to 13 is not generated from the eNB 21. In such a case, the RN 35 cannot receive the CRS. Therefore, the RN 35 cannot perform synchronous detection and cannot receive TAC. As a result, the synchronization of the backhaul link cannot be maintained.

  Next, synchronization maintenance using TAC will be described with reference to FIG. The eNB 21 transmits a TAC to the RN 35. Further, the RN 35 transmits a TAC to the UEs 11 to 13. The RN 35 and the UEs 11 to 13 that have received the TAC start or restart tAT (time Alignment Timer). tAT expires after a predetermined time. The RN 35 and the UEs 11 to 13 determine that synchronization is maintained when the valid period is before the tAT timer expires. That is, when the tAT timer expires, the RN 35 and the UEs 11 to 13 determine that they are out of synchronization. Therefore, the eNB 21 and the RN 35 prevent the timer from expiring by periodically transmitting TAC and restarting tAT.

  Next, a resynchronization procedure when a loss of synchronization occurs will be described with reference to FIG. First, synchronization is established between the UEs 11 to 13 and the eNB 21 (S31), synchronization is maintained between the UEs 11 to 13 and the RN 35, and synchronization is also maintained between the RN 35 and the eNB 21. (S32 and S33). Next, loss of synchronization occurs between the RN 35 and the eNB 21 due to the factors described in FIG. 7 (S34).

  Next, when a loss of synchronization occurs between the RN 35 and the eNB 21, the RN 35 stops transmission of TAC to the UEs 11 to 13 (S35). Thereby, the RN 35 causes loss of synchronization between the UEs 11 to 13 and the RN 35 (S36). Here, the reason why the synchronization loss occurs between the UEs 11 to 13 and the RN 35 when the synchronization failure occurs between the RN 35 and the eNB 21 will be described.

  If a loss of synchronization occurs between the RN 35 and the eNB 21, if the RN 35 reestablishes the synchronization between the RN 35 and the eNB 21 without releasing the synchronization between the UEs 11 to 13 and the RN 35, the loss of synchronization occurs. The data transmission timing from the RN 35 to the eNB 21 before the occurrence of the error and the data transmission timing from the RN 35 to the eNB 21 after reestablishing synchronization are changed.

  For example, before data loss occurs, while data is transmitted from the UEs 11 to 13 to the RN 35, data transmission from the RN 35 to the eNB 21 is stopped and data is transmitted from the eNB 21 to the RN 35. Suppose that data transmission from the RN 35 to the UEs 11 to 13 is stopped. However, after the synchronization is re-established, the timing at which data is transmitted from the UEs 11 to 13 to the RN 35 may coincide with the timing at which data is transmitted from the RN 35 to the eNB 21. In this case, the frequency used when data is transmitted from the UEs 11 to 13 to the RN 35 and the frequency used when data is transmitted from the RN 35 to the eNB 21 use the same frequency. Therefore, the RN 35 has a problem that the reception signal and the transmission signal interfere with each other.

  Therefore, when a loss of synchronization occurs between the RN 35 and the eNB 21, in order to adjust the data transmission timing between the UEs 11 to 13 and the RN 35 and the data transmission timing between the RN 35 and the eNB 21, Loss of synchronization is generated between the UEs 11 to 13 and the RN 35. Then, the RN 35 reestablishes synchronization with the eNB 21 and further reestablishes synchronization with the UEs 11 to 13. The synchronization establishment procedure from step S37 to step S43 is the same as that in FIG.

  As described above, by using the synchronization re-establishment procedure according to the first exemplary embodiment of the present invention, even when a loss of synchronization occurs between the RN and the eNB, the RN is synchronized with the eNB and the UE. By executing the procedure, the synchronization between the UE and the eNB can be recovered.

  Note that the present invention is not limited to the above-described embodiment, and can be changed as appropriate without departing from the spirit of the present invention.

10 mobile communication device 20 base station device 21 eNB
30 relay device 31 base station synchronization establishment unit 32 mobile communication device synchronization establishment unit 33 control unit 35 RN

Claims (8)

A relay device arranged between a mobile communication device and a base station device,
A base station synchronization establishment unit that maintains synchronization with the base station device using a reference signal set in a data region for transmitting user data from the base station device;
The base station synchronization establishment unit
When the synchronization with the base station device is canceled because the reference signal is not transmitted from the base station device, using the synchronization establishment procedure used during initial access from the relay device to the neighboring base station device, Establishing synchronization with the base station device ,
The synchronization with the base station apparatus is released by releasing the synchronization with the mobile communication apparatus, and the base station synchronization establishment unit establishes the synchronization with the base station apparatus using the synchronization establishment procedure. And a relay apparatus further comprising a mobile communication apparatus synchronization establishment unit that establishes synchronization with the mobile communication apparatus.   The synchronization establishment procedure means that the neighboring base station apparatus establishes synchronization with the relay apparatus by transmitting a response signal to the access signal transmitted from the relay apparatus using a collision-acceptable channel. Item 4. The relay device according to Item 1.   A different range between a preamble used when establishing synchronization with the mobile communication device and an identifier for identifying the mobile communication device, and an identifier for identifying the preamble and the own station used when synchronizing with the base station device The value of
The relay apparatus according to claim 1 or 2. The base station synchronization establishment unit
The relay device according to any one of claims 1 to 3, wherein an identifier of the mobile communication device whose synchronization is established by the mobile communication device synchronization establishment unit is transmitted to the base station device.   The relay device according to claim 3 or 4, wherein an access signal used for establishing synchronization between the mobile communication device and the relay device is used only between the mobile communication device and the relay device. A synchronization maintaining method for maintaining synchronization between the relay device and the base station device when a relay device is disposed between the mobile communication device and the base station device,
Maintaining synchronization with the base station device using a reference signal set in a data area for transmitting user data from the base station device;
When synchronization between the base station apparatus and the relay apparatus is canceled because the reference signal is not transmitted from the base station apparatus, a synchronization establishment procedure used at the time of initial access from the relay apparatus to the neighboring base station apparatus Using to establish synchronization between the base station device and the relay device;
After the synchronization between the relay device and the base station device is established, transmitting the identifier of the mobile communication device that is synchronized with the relay device to the base station device;
A synchronization maintaining method comprising: When the synchronization between the base station device and the relay device is released, releasing the synchronization between the mobile communication device and the relay device;
7. The method according to claim 6, further comprising: establishing synchronization between the mobile communication device and the relay device when synchronization between the relay device and the base station device is established using the synchronization establishment procedure. Synchronization maintenance method.   A different range between a preamble used in the step of establishing synchronization with the mobile communication device and an identifier for identifying the mobile communication device, and an identifier for identifying the preamble and the own station used in the step of synchronizing with the base station device The value of
The synchronization maintaining method according to claim 6 or 7.

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