JP2016058784A - Base station and user device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique in which an appropriate RACH-less handover control is achieved.SOLUTION: A user device of the present invention comprises: a transmission/reception section which communicates with a base station through a cell; and a handover control section which stops a TA (Timing Advance) timer in response to a handover instruction from the base station, and starts handover to a target cell. When the handover instruction is a RACH-less handover instruction, the handover control section executes RACH-less handover to the target cell by transmitting a scheduling request to the target cell regardless of an operation state of the TA timer.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a wireless communication system.

  In an LTE (Long Term Evolution) system, handover control is always performed in order to cause a user device (User Equipment: UE) in an RRC (Radio Resource Control) connected state to perform communication in an optimal cell. That is, by measurement control by the base station (evolved NodeB: eNB), the user apparatus measures the communication state with the neighboring cells, and detects a cell with better communication quality than the connected cell, the event is sent to the base station. Notice. When the notification is received, the base station transmits a handover instruction for transitioning to the cell to the user apparatus, and the user apparatus tries to connect to the transition destination cell specified by the handover instruction.

  FIG. 1 is a sequence diagram illustrating handover control in the LTE system. As shown in FIG. 1, the user apparatus (UE) measures the communication state of neighboring cells under measurement control by the connected base station (S-eNB), and sends the measurement result (Measurement report) to the base station ( S-eNB). When a cell having better communication quality than the connected cell is detected, the base station (S-eNB) transmits a handover request (HO request) to the target base station (T-eNB) of the detected cell. To do. Upon receiving a delivery confirmation (HO request ACK) for the handover request from the target base station (T-eNB), the base station (S-eNB) transmits a handover instruction to the user apparatus (UE) and at the same time the user apparatus (UE ) To the target base station (T-eNB).

  When receiving the handover instruction, the user apparatus (UE) executes a random access (RA) procedure in order to connect to the target base station (T-eNB) specified in the handover instruction. When the connection with the target base station (T-eNB) is completed, the user apparatus transmits an RRC connection reconfiguration complete to the target base station (T-eNB). When receiving the message, the target base station (T-eNB) transmits a Path switch request to the core node (CN) in order to notify that the connection destination of the user apparatus (UE) has been changed. Thereafter, the core node changes the transmission destination of the packet addressed to the user apparatus (UE) from the source base station (S-eNB) to the target base station (T-eNB).

3GPP TS36.300 V12.2.0 (2014-06) 3GPP TS36.213 V12.2.0 (2014-06)

  In the current LTE specification, it is stipulated that the user equipment always performs the RA procedure in order to establish uplink synchronization at the time of handover. For this reason, an instantaneous interruption accompanying the RA procedure occurs at the time of handover. On the other hand, there is actually a case (such as handover between the same frequencies) where establishment of uplink synchronization by such an RA procedure is not required, and in this case, an instantaneous interruption of communication due to an unnecessary RA procedure occurs.

  Therefore, in a case where such an RA procedure is unnecessary, the RA procedure is omitted, and a RACH (Random Access Channel) that executes a handover without performing the RA procedure in order to avoid a decrease in throughput due to a momentary interruption at the time of handover. -Less handover control is under consideration.

  However, the current LTE specification stipulates that when a handover procedure is started, the user apparatus stops a timing advance (TA) timer by a MAC (Medium Access Control) reset. For this reason, the user apparatus cannot perform transmission other than PRACH (Physical Random Access Channel), and cannot perform RACH-less handover without performing the RA procedure.

  Further, during normal handover, it is specified that the user apparatus continues to transmit PRACH while gradually increasing transmission power (power ramping) until the RA procedure is completed. However, such a power ramping is not defined for the scheduling request transmitted to the target cell in the RACH-less handover, and the uplink transmission timing matches, but the scheduling request is received due to power shortage. May happen. In this case, retransmission of scheduling requests is exceeded, and the user apparatus may eventually execute the RA procedure.

  In view of the above-described problems, an object of the present invention is to provide a technique for realizing appropriate RACH-less handover control.

  In order to solve the above problems, according to one aspect of the present invention, a transmission / reception unit that communicates with a base station via a cell, a TA (Timing Advance) timer in response to a handover instruction from the base station, and a target cell And a handover control unit that initiates a handover to the mobile device, and when the handover instruction is a RACH-less handover instruction, the handover control unit targets a scheduling request regardless of an operating state of the TA timer. The present invention relates to a user apparatus that performs RACH-less handover to the target cell by transmitting to the cell.

  Another aspect of the present invention is a transmission / reception unit that communicates with a base station via a cell, and a handover control unit that transmits a scheduling request to a target cell by power ramping control in response to a RACH-less handover instruction from the base station. It is related with the user apparatus which has.

  According to still another aspect of the present invention, a communication control unit that controls radio communication with a user apparatus and a RACH-less handover instruction that specifies transmission power of a scheduling request transmitted to a target cell are notified to the user apparatus. The present invention relates to a base station having a handover control unit.

  According to the present invention, appropriate RACH-less handover control can be realized.

FIG. 1 is a sequence diagram illustrating handover control in the LTE system. FIG. 2 is a schematic diagram illustrating a wireless communication system according to an embodiment of the present invention. FIG. 3 is a block diagram showing the configuration of the user apparatus according to the first embodiment of the present invention. FIG. 4 is a flowchart showing a RACH-less handover process in the user apparatus according to the first embodiment of the present invention. FIG. 5 is a block diagram illustrating a configuration of a user apparatus according to the second embodiment of the present invention. FIG. 6 is a diagram illustrating retransmission timing of an exemplary scheduling request according to the second embodiment of the present invention. FIG. 7 is a diagram showing retransmission timings of another example scheduling request according to the second embodiment of the present invention. FIG. 8 is a flowchart showing scheduling request retransmission processing in the user apparatus according to the second embodiment of the present invention. FIG. 9 is a block diagram illustrating a configuration of a base station according to the second embodiment of the present invention. FIG. 10 is a flowchart showing a transmission power notification process in the base station according to the second embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  In an embodiment to be described later, a base station and a user apparatus that perform a RACH-less handover that realizes a handover without executing an RA procedure are disclosed.

  To summarize the first embodiment of the present invention, when the received handover instruction is a RACH-less handover instruction, the user equipment makes a scheduling request to the target cell regardless of the operating state of the TA timer that is stopped when the normal handover is activated. To perform RACH-less handover. If the TA timer is stopped, transmissions other than the PRACH cannot be performed. However, in the case of a RACH-less handover instruction, the user apparatus transmits a scheduling request to the target cell regardless of the operating state of the TA timer. According to the present embodiment, the RACH-less handover can be activated by enabling the scheduling request to be transmitted even when the TA timer is stopped when the RACH-less handover is activated.

  In outline of the second embodiment of the present invention, transmission power of a scheduling request transmitted from a user apparatus to a target cell is controlled. In one embodiment, when retransmitting the scheduling request, the user apparatus retransmits the scheduling request under power ramping control. In another embodiment, the base station determines the transmission power of a scheduling request suitable for transmission by the user equipment based on the acquired power headroom (PHR) or transmission power control (TPC) command, and the user equipment Transmits a scheduling request with the transmission power. According to the present embodiment, it is possible to appropriately control the transmission power of the scheduling request in the RACH-less handover.

  First, a radio communication system according to an embodiment of the present invention will be described with reference to FIG. FIG. 2 is a schematic diagram illustrating a wireless communication system according to an embodiment of the present invention.

  As illustrated in FIG. 2, the wireless communication system 10 includes base stations 101, 102 or 301, 302 (hereinafter collectively referred to as base stations 100, 300) and user devices 200 or 400. For convenience of explanation, in the first embodiment described later, the base station 100 and the user apparatus 200 are used, and in the second embodiment, the base station 300 and the user apparatus 400 are used. In one embodiment, the wireless communication system 10 is an LTE system or an LTE-Advanced system. In the illustrated embodiment, only two base stations 101, 102 or 301, 302 are shown, but in general, a large number of base stations are arranged to cover the service area of the wireless communication system 10.

  The base stations 100 and 300 provide one or more cells and wirelessly communicate with the user apparatuses 200 and 400 via the cells. In the illustrated embodiment, base stations 101 and 301 provide cells C11 and C12 and are currently connected to user equipments 200 and 400 via cell C11. On the other hand, the base stations 102 and 302 provide the cell C21 and are arranged adjacent to the base stations 101 and 301. The user apparatuses 200 and 400 measure the communication state of the neighboring cells C12 and C21 during connection with the cell C11, and report the measurement results to the base stations 101 and 301 (measurement control). When a cell having better communication quality than the connected cell C11 is detected, the base stations 101 and 301 notify the user equipment 200 and 400 of a handover instruction with the cell as a transition destination. In the following embodiments, the handover between the cells C11, C12, and C21 can correspond to the RACH-less handover that can be handed over without executing the RA procedure. The base stations 101 and 301 and the base stations 102 and 302 are connected to each other and can communicate with each other via the X2 interface.

  The base stations 100 and 300 typically include a communication circuit for wirelessly communicating with the user apparatuses 200 and 400, a communication interface for communicating with a core network (not shown) and other base stations, a core network and a user. It is configured by hardware resources such as a processor, a memory, and various circuits for controlling wireless communication with the devices 200 and 400. Each function and process of the base stations 100 and 300 to be described later may be realized by a processor or a communication circuit processing or executing data or a program stored in the memory. However, the base stations 100 and 300 are not limited to the hardware configuration described above, and may have any other appropriate hardware configuration.

  The user apparatuses 200 and 400 are located in any of the cells provided by the base stations 100 and 300, and wirelessly communicate with the base stations 100 and 300 via the cells. In the following embodiment, as illustrated, the user equipments 200 and 400 are performing RACH-less handover from the source cells of the base stations 101 and 301 to the target cells of the base stations 102 and 302. However, the present invention is not limited to this, and may be applied to RACH-less handover from the source cell to the target cell in the base stations 101 and 301, for example.

  The user devices 200 and 400 are any appropriate information processing devices having a wireless communication function such as a smartphone, a mobile phone, a tablet, and a wearable terminal. Use various communication services provided by. User devices 200 and 400 include a CPU (Central Processing Unit) such as a processor, a memory device such as a RAM (Random Access Memory) and a flash memory, and a wireless communication circuit for transmitting and receiving wireless signals to and from the base stations 100 and 300. Etc. For example, each function and process of the user devices 200 and 400 to be described later is performed by a CPU processing or executing data or a program stored in a memory device, or by a wireless communication circuit transmitting or receiving a wireless signal. It may be realized. However, the user devices 200 and 400 are not limited to the hardware configuration described above, and may be configured by a circuit or the like that realizes one or more of the processes described below.

  Next, a TA timer control process according to the first embodiment of the present invention will be described with reference to FIGS. In the first embodiment to be described later, when it is notified that the TA timer is not stopped in the received handover instruction, the user apparatus 200 does not stop the TA timer that is stopped at the time of normal handover activation, and does not stop the RACH- Execute less handover.

  FIG. 3 is a block diagram showing the configuration of the user apparatus according to the first embodiment of the present invention. As illustrated in FIG. 3, the user apparatus 200 includes a transmission / reception unit 210 and a handover control unit 220.

  The transmission / reception unit 210 communicates with the base stations 101 and 102 via the cell. Specifically, the transmission / reception unit 210 transmits / receives various radio channels such as an uplink / downlink control channel and an uplink / downlink data channel to / from the base stations 101 and 102.

  In response to the handover instruction from the base station 101, the handover control unit 220 stops the TA timer and activates the handover to the target cell. In the present embodiment, when the handover instruction is a RACH-less handover instruction, the handover control unit 220 transmits a scheduling request to the target cell regardless of the operating state of the TA timer, thereby performing a RACH-less handover to the target cell. Execute.

  That is, the handover control unit 220 stops the TA timer at the time of normal handover activation, and transmission other than PRACH is disabled. On the other hand, when the received handover instruction is a RACH-less handover instruction, the handover control unit 220 transmits a scheduling request to the target cell regardless of whether the TA timer is activated or stopped, that is, regardless of the operating state of the TA timer. Then, RACH-less handover is activated. According to the present embodiment, even if the MAC reset is executed as in the case of normal handover activation and the TA timer is stopped accordingly, if the handover instruction is a RACH-less handover instruction, the handover control unit 220 Exceptionally, it is possible to transmit a scheduling request, and RACH-less handover to the target cell can be activated.

  Note that when the TA command is received even once after the execution of the RACH-less handover, the handover control unit 220 may stop the exceptional transmission control of the scheduling request described above. That is, when the TA command is received, the target base station 102 has confirmed the uplink transmission of the user apparatus 200.

  In one embodiment, the RACH-less handover instruction may include MobilityControlInfo for notifying the TA timer not to stop. When the RACH-less handover instruction including the non-stop notification of the TA timer is received, the handover control unit 220 performs a scheduling request to the target cell for the RACH-less handover without stopping the TA timer with the execution of the MAC reset. Send. In this embodiment, the RACH-less handover instruction explicitly instructs non-stop of the TA timer, thereby avoiding the stop of the TA timer that disables transmission other than the PRACH, and the scheduling request for the RACH-less handover. Enables sending.

  In this case, the handover control unit 220 confirms the information element in the received RACH-less handover instruction, and detects the non-stop notification of the TA timer without stopping the TA timer with the execution of the MAC reset. Continue timing and activate RACH-less handover. On the other hand, if the TA element non-stop notification is not detected in the information element, the handover control unit 220 executes the MAC reset and stops the TA timer. However, the handover control unit 220 stops the TA timer regardless of the operation state of the TA timer. A RACH-less handover is initiated by sending a scheduling request. Further, the Mobility ControlInfo may specify a dedicated RACH resource. Accordingly, when the RACH-less handover fails due to excessive retransmission of the scheduling request to the target cell, the handover control unit 220 can execute the RA procedure using the designated dedicated RACH resource, and the RA procedure can be performed at an early stage. Can be completed.

  In one embodiment, when the RACH-less handover instruction notifies the TA timer not being stopped, the handover control unit 220 may restart the TA timer and execute the RACH-less handover to the target cell. When the RACH-less handover instruction is notified just before the TA timer expires, the TA timer expires before the RACH-less handover is completed, and the handover control unit 220 can transmit a scheduling request during the activation of the RACH-less handover. There is a possibility of disappearing. In this embodiment, in order to avoid such a situation, the handover control unit 220 may restart the TA timer and start the RACH-less handover to the target cell.

  For example, the handover control unit 220 responds that the TA command is included in the received RACH-less handover instruction, or that the TA command MAC CE (Control Element) is multiplexed in response to the RACH-less handover instruction. The TA timer may be restarted.

  FIG. 4 is a flowchart showing a RACH-less handover process in the user apparatus according to the first embodiment of the present invention.

  As shown in FIG. 4, in step S <b> 101, the handover control unit 220 receives a RACH-less handover instruction from the base station 101.

  In step S102, the handover control unit 220 determines whether the received RACH-less handover instruction includes a notification that the TA timer is not stopped. For example, the handover control unit 220 may check the mobility control info of the received RACH-less handover instruction and detect whether the information element includes a non-stop notification of the TA timer.

  If there is a notification of non-stop of the TA timer (S102: YES), the handover control unit 220 executes RACH-less handover in step S103 without stopping the TA timer with execution of the MAC reset.

  On the other hand, when there is no notification of non-stop of the TA timer (S102: NO), the handover control unit 220 executes MAC reset to stop the TA timer in step S104, but the target cell is not related to the stop of the TA timer. RACH-less handover is performed by sending a scheduling request to

  Next, a scheduling request transmission power control process according to the second embodiment of the present invention will be described with reference to FIGS. In a second embodiment to be described later, the transmission power of a scheduling request for RACH-less handover is controlled. A case where the user apparatus 400 applies power ramping to the retransmission of the scheduling request will be described with reference to FIGS. 5 to 8. With reference to FIGS. 9 to 10, the base station 300 supplies the appropriate transmission power of the scheduling request to the user. A case of notifying the device 400 will be described.

  FIG. 5 is a block diagram illustrating a configuration of a user apparatus according to the second embodiment of the present invention. As illustrated in FIG. 5, the user apparatus 400 includes a transmission / reception unit 410 and a handover control unit 420.

  The transmission / reception unit 410 communicates with the base stations 301 and 302 via the cell. Specifically, the transmission / reception unit 410 transmits / receives various radio channels such as an uplink / downlink control channel and an uplink / downlink data channel to / from the base stations 301 and 302.

  In response to the RACH-less handover instruction from the base station 301, the handover control unit 420 transmits a scheduling request to the target cell by power ramping control. Specifically, the handover control unit 420 implements the RACH-less handover, in the case where the allocation permission such as the uplink grant cannot be received when transmitting the scheduling request to the designated target cell. Each time a request is retransmitted, the transmission power is gradually increased (power ramping control). This means that if the target base station 302 cannot receive a scheduling request due to insufficient transmission power, the target base station 302 can receive the scheduling request more reliably by retransmitting the scheduling request with higher transmission power. It is for making.

  Here, the transmission power increase amount α (ramping step) and the initial transmission power pi in each ramping up may be notified by the RACH-less handover instruction from the source base station 301.

  In one embodiment, when the handover control unit 420 receives the allocation permission for the transmitted scheduling request, the handover control unit 420 may perform subsequent uplink transmission according to the transmission power of the scheduling request corresponding to the allocation permission. For example, when the uplink grant can be received for the scheduling request transmitted at the xth time under power ramping control, the handover control unit 420 transmits the transmission power pi + (x−1) of the scheduling request transmitted at the xth time. ) Α may be used for uplink transmission such as transmission of a subsequent PUSCH (Physical Uplink Shared Channel). This makes it possible for the target cell to appropriately receive subsequent uplink transmissions.

  Here, typically, when the initial transmission of the scheduling request to the target cell does not reach the target base station 302 due to lack of transmission power at the time of handover, the scheduling request is the next in which resources for the scheduling request are set. It is possible to retransmit at the timing. However, when such a scheduling request transmission interval is set to 20 ms or the like, the delay reduction effect by RACH-less handover may be limited. This is because the RA procedure is normally expected to be completed in about several tens of milliseconds. For this reason, in one embodiment, when retransmitting the scheduling request, the handover control unit 420 may retransmit the scheduling request under power ramping control with a transmission interval shorter than the transmission interval set in the scheduling request. . For example, although the transmission interval set in the scheduling request is normally set to 20 ms or the like, the retransmission timing of the scheduling request by the RACH-less handover may be set to 1 to 2 ms or the like in order to reduce the delay. Good.

  FIG. 6 is a diagram illustrating retransmission timing of an exemplary scheduling request according to the second embodiment of the present invention. As shown in FIG. 6, the transmission interval for retransmitting the scheduling request at the time of RACH-less handover may be set shorter than the transmission interval of the scheduling request set in the normal handover with the RA procedure.

  In Example 1 of FIG. 6, when retransmitting the scheduling request, the handover control unit 420 transmits the scheduling request to the target base station 302 under power ramping control with a short transmission interval until an uplink grant for the scheduling request is received. The retransmission may be continued.

  In Example 2 of FIG. 6, when retransmitting the scheduling request, the handover control unit 420 continues after each transmission timing of the scheduling request set in the normal handover with the RA procedure until an uplink grant for the scheduling request is received. The retransmission of the scheduling request may be continued a predetermined number of times under power ramping control. After the scheduling request is retransmitted at a short transmission interval a predetermined number of times, the handover control unit 420 retransmits the scheduling request at the transmission timing set in the normal handover involving the RA procedure.

  FIG. 7 is a diagram showing retransmission timings of another example scheduling request according to the second embodiment of the present invention. As illustrated in FIG. 7, the handover control unit 420 may return to the transmission interval set in the scheduling request when the RACH-less handover to the target cell is not completed within a predetermined period. That is, when resending the scheduling request, the handover control unit 420 resends the scheduling request to the target base station 302 under power ramping control with a short transmission interval within a predetermined period until an uplink transmission for the scheduling request is received. However, after the elapse of the period, retransmission may be continued at the transmission timing of the scheduling request set in the normal handover involving the RA procedure. This is to avoid a decrease in resource utilization efficiency when resources for scheduling requests with short transmission intervals are set for each user apparatus. For example, the handover control unit 420 starts a timer at the start of transmission of a scheduling request in RACH-less handover, continues retransmission of the scheduling request at a short transmission interval until the timer expires, and when the timer expires, You may make it return to a transmission interval.

  FIG. 8 is a flowchart showing scheduling request retransmission processing in the user apparatus according to the second embodiment of the present invention.

  As shown in FIG. 8, in step S <b> 201, the handover control unit 420 receives a RACH-less handover instruction from the source base station 301. The RACH-less handover instruction may include, for example, a transmission power increase amount α (ramping step) and initial transmission power pi in each ramping up together with the target cell.

  In step S202, the handover control unit 420 transmits a scheduling request to the target cell. For example, when the initial transmission power pi is specified in the RACH-less handover instruction, the handover control unit 420 may transmit a scheduling request with the transmission power pi.

  In step S203, the handover control unit 420 determines whether the allocation permission (uplink grant) for the scheduling request transmitted in step S202 has been received. When the allocation permission has been received (S203: YES), the handover control unit 420 determines that the RACH-less handover for the target cell has been completed, and starts subsequent uplink transmission such as PUSCH transmission in step S204. .

  On the other hand, when the allocation permission cannot be received (S203: NO), the handover control unit 420 retransmits the scheduling request by increasing the transmission power under the power ramping control. For example, when the ramping step α is specified in the RACH-less handover instruction, the handover control unit 420 retransmits the scheduling request with the transmission power pi + α that has been ramped up. For example, when it is specified that retransmission of a scheduling request is performed with a transmission interval (such as 1 to 2 ms) shorter than a transmission interval (such as 20 ms) of a scheduling request set at the time of handover involving an RA procedure, handover control is performed. Unit 420 repeats steps S202, 203, and 205 at the short transmission interval.

  Thereafter, the handover control unit 420 continues resending the scheduling request while gradually increasing the transmission power under the power ramping control until the allocation permission for the scheduling request can be received.

  FIG. 9 is a block diagram illustrating a configuration of a base station according to the second embodiment of the present invention. In the embodiments shown in FIGS. 5 to 9, the user apparatus continues resending the scheduling request under power ramping control. However, in this embodiment, the base station 300 uses the appropriate transmission power in the RACH-less handover instruction. The user apparatus 400 transmits a scheduling request to the target cell with the notified transmission power.

  As illustrated in FIG. 9, the base station 300 includes a communication control unit 310 and a handover control unit 320.

  The communication control unit 310 controls wireless communication with the user device 400. Specifically, the communication control unit 310 transmits / receives various control signals and data signals to / from the user apparatus 400 via the cell.

  The handover control unit 320 notifies the user apparatus 400 of a RACH-less handover instruction that specifies the transmission power of the scheduling request transmitted to the target cell. Specifically, the source base station 301 causes the user apparatus 400 to measure a communication state with a neighboring cell, and measures a cell identifier (Physical Cell Identifier: PCI) indicating a measurement target neighboring cell and detected communication quality. Report the result (Measurement Report) (Measurement Control). When a neighboring cell with better communication quality than the connected cell is detected, the handover control unit 320 determines whether the detected neighboring cell is a cell that can be RACH-less handover, and the detected cell is RACH−. In the case of a cell capable of less handover, the user apparatus 400 is caused to execute RACH-less handover to the cell by specifying the transmission power of the scheduling request to the target cell. For example, the RACH-less handover capable cell may include at least one of a neighboring cell having the same frequency as that of the source cell and a cell of the same base station 301 as the source cell.

  In one embodiment, the handover control unit 320 may determine transmission power based on a cumulative value of a power headroom report (PHR) and a transmission power control (TPC) command acquired from the user apparatus 400. Here, the PHR is an index indicating the remaining transmission power in the user apparatus 400, and the TPC command is a transmission power value applied to communication with the source base station 301.

  Specifically, when the source base station 301 transmits a handover request to the target base station 302, the source base station 301 reports to the target base station 302 the accumulated values of the PHR and TPC commands obtained from the user apparatus 400 at that time. The target base station 302 calculates transmission power suitable for transmission of the scheduling request to the target cell based on the received PHR and the accumulated value of the TPC command, and notifies the user apparatus 400 via the source base station 301. The source base station 301 may notify the user apparatus 400 of the calculated transmission power as the initial transmission power. When receiving the RACH-less handover instruction specifying the initial transmission power, the user apparatus 400 transmits a scheduling request to the target cell with the specified initial transmission power. When the above-described power ramping control is applied, the user apparatus 400 may retransmit the scheduling request by the power ramping control using the ramping step notified together with the initial transmission power.

  In addition, about the user apparatus 400 shown in FIG. 5 and the base station 300 shown in FIG. 9, in order to report the present power headroom to the base station 300 at an early stage, The apparatus 400 may report a PHR when receiving a handover instruction.

  FIG. 10 is a flowchart showing a transmission power notification process in the base station according to the second embodiment of the present invention.

  As illustrated in FIG. 10, in step S <b> 301, the target base station 302 acquires the accumulated values of the PHR and TPC commands of the user apparatus 400 from the source base station 301.

  In step S302, the target base station 302 determines the transmission power of the scheduling request by the user apparatus 400 at the time of RACH-less handover based on the acquired cumulative value of the PHR and the TPC command.

  In step S <b> 303, the source base station 301 notifies the user apparatus 400 of a RACH-less handover instruction that specifies the transmission power notified by the target base station 302. For example, the designated transmission power may be used as the initial transmission power under power ramping control.

  The first and second embodiments described above can be used in combination. That is, according to the first embodiment, when RACH-less handover to the target cell is instructed, the user equipments 200 and 400 transmit a scheduling request to the target cell regardless of the operating state of the TA timer, and When the uplink grant is not received, retransmission of the scheduling request may be continued under power ramping control.

  As mentioned above, although the Example of this invention was explained in full detail, this invention is not limited to the specific embodiment mentioned above, In the range of the summary of this invention described in the claim, various deformation | transformation・ Change is possible.

10 Wireless communication system 100, 101, 102, 300, 301, 302 Base station 200, 400 User equipment

Claims (10)

A transceiver that communicates with a base station via a cell;
In response to a handover instruction from the base station, a TA (Timing Advance) timer is stopped, and a handover control unit that starts a handover to a target cell;
A user device comprising:
When the handover instruction is a RACH (Random Access Channel) -less handover instruction, the handover control unit transmits a scheduling request to the target cell regardless of the operating state of the TA timer, thereby A user apparatus that performs RACH-less handover.   The user apparatus according to claim 1, wherein the RACH-less handover instruction includes MobilityControlInfo that notifies non-stop of the TA timer.   The user equipment according to claim 2, wherein the Mobility Control Info specifies a dedicated RACH resource.   4. When the RACH-less handover instruction notifies that the TA timer is not stopped, the handover control unit restarts the TA timer and executes a RACH-less handover to the target cell. 5. The user device according to any one of claims. A transceiver that communicates with a base station via a cell;
In response to the RACH-less handover instruction from the base station, a handover control unit that transmits a scheduling request to the target cell by power ramping control;
A user device.   The user equipment according to claim 5, wherein the handover control unit, when receiving an allocation permission for the transmitted scheduling request, executes subsequent uplink transmission with a transmission power of a scheduling request corresponding to the allocation permission.   The user apparatus according to claim 5 or 6, wherein the handover control unit transmits the scheduling request at a transmission interval shorter than a transmission interval set in the scheduling request when retransmitting the scheduling request.   The user apparatus according to claim 7, wherein the handover control unit returns to the transmission interval set in the scheduling request when the RACH-less handover to the target cell is not completed within a predetermined period. A communication control unit for controlling wireless communication with the user device;
A handover control unit for notifying the user apparatus of a RACH-less handover instruction specifying transmission power of a scheduling request transmitted to a target cell;
Base station with   The base station according to claim 9, wherein the handover control unit determines the transmission power based on a cumulative value of a power headroom report (PHR) and a transmission power control (TPC) command acquired from the user apparatus.

Images