KR20080026470A - Method and apparatus for handover in mobile telecommunication system - Google Patents

Abstract

A handover method and apparatus in a mobile communication system are provided to allow a terminal to transmit a status report to a source ENB(Evolved Node B) immediately before handover occurs, and not retransmit RLC PDU(Packet Data Unit)s, which have not received a positive acknowledgement signal yet, thereby minimizing a data amount from the source ENB to a target ENB. A measurement controller(1205) controls measurement of the size of a reception signal of neighbor cells. A radio resource controller(1210) generates a measurement result received from the measurement controller(1205) as a message and transmits the same to a base station of a source cell. Before performing handover to a target cell, a radio link controller(1220) receives a status report command from the radio resource controller(1210), generates a status report message, and transmits it to the base station of the source cell. The measurement controller(1205) determines whether the measurement result report satisfies handover conditions previously agreed with the base station of the source cell. The radio resource controller transmits the status report command to the radio link controller(1220) according to determination of the measurement controller(1205).

Description

METHOD AND APPARATUS FOR HANDOVER IN MOBILE TELECOMMUNICATION SYSTEM}

1 is a diagram illustrating an example of a next-generation mobile communication system architecture

2 is a diagram illustrating a protocol stack of a next generation mobile communication system.

3 illustrates an example of an RLC operation;

4 is a diagram illustrating data transfer during handover.

5 illustrates in more detail data transfer during handover.

6 is a diagram showing the overall operation according to the first embodiment of the present invention.

7 is a view for explaining the operation of the base station according to the first embodiment of the present invention;

8 is a view for explaining the operation of the terminal according to the first embodiment of the present invention;

9 is a diagram showing the overall operation according to the second embodiment of the present invention.

10 is a diagram illustrating an operation of a base station according to a second embodiment of the present invention.

11 is a diagram illustrating a terminal operation according to a second embodiment of the present invention.

12 illustrates a terminal device according to first and second embodiments of the present invention.

13 is a diagram illustrating a conventional transmission resource allocation process.

14 is a diagram showing the overall operation according to the third embodiment of the present invention.

15A is a diagram illustrating a format of a conventional buffer status report.

15B is a diagram illustrating an example of a format of a buffer status report according to the third embodiment of the present invention.

16 is a diagram illustrating a terminal operation according to a third embodiment of the present invention.

17 is a diagram illustrating an operation of a base station according to a third embodiment of the present invention.

18 illustrates a terminal device according to a third embodiment of the present invention.

The present invention relates to a mobile communication system, and more particularly, to a method and apparatus for minimizing data transfer between base stations when a handover occurs.

UMTS (Universal Mobile Telecommunication Service) system is based on the European mobile communication system Global System for Mobile Communications (GSM) and General Packet Radio Services (GPRS), and Wideband Code Division Multiple Access, CDMA) is a third generation asynchronous mobile communication system.

The 3rd Generation Partnership Project (3GPP), which is in charge of UMTS standardization, is discussing Long Term Evolution (LTE) as the next generation mobile communication system of the UMTS system. LTE is a technology that implements high-speed packet-based communication with a transmission rate of up to 100 Mbps, aiming for commercialization in 2010. To this end, various schemes are discussed. For example, a scheme of reducing the number of nodes located on a communication path by simplifying a network structure, or approaching wireless protocols as close as possible to a wireless channel are under discussion.

1 illustrates an example of a next generation mobile communication system structure. Here, the system structure based on the UMTS system is shown.

Referring to FIG. 1, as illustrated, next-generation radio access networks (hereinafter referred to as E-RANs) 110 and 112 may be referred to as next-generation base stations (Evolved Node B, ENB or Node B) 120 , 122, 124, 126, and 128, and the upper node (anchor node) 130, 132 is simplified to a two-node structure. The user equipment (hereinafter referred to as UE) 101 is connected to the Internet Protocol (hereinafter referred to as IP) network by the E-RANs 110 and 112.

The ENBs 120 to 128 correspond to existing Node Bs of the UMTS system and are connected to the UE 101 by a radio channel. Unlike the existing Node B, the ENBs 120 to 128 play a more complex role. In LTE, all user traffic, including real-time services such as Voice over IP (VoIP) over the Internet protocol, is serviced through a shared channel, which requires a device that collects and schedules UE information. 120 to 128 are in charge. One ENB typically controls a number of cells.

In order to realize a transmission rate of up to 100 Mbps, LTE is expected to use orthogonal frequency division multiplexing (OFDM) as a radio access technology in a 20 MHz bandwidth. In addition, an adaptive modulation & coding (AMC) scheme for determining a modulation scheme and a channel coding rate according to the channel state of the terminal will be applied.

Meanwhile, many next generation mobile communication systems including LTE use HARQ (Hybrid Automatic Retransmission Request) as an error correction technique. HARQ is a technique of increasing reception success rate by soft combining with retransmitted data without discarding previously received data. In more detail, the HARQ receiver determines whether there is an error in a received packet, and then transmits a HARQ positive acknowledgment (HARQ ACK) signal or a HARQ negative acknowledgment (HARQ NACK) signal. Send to the sender. The transmitter performs retransmission of the HARQ packet or transmission of a new HARQ packet according to the HARQ ACK / NACK signal. The HARQ receiver soft-combines the retransmitted packet with the previously received packet to reduce the probability of error occurrence.

2 illustrates a protocol stack of an LTE system.

Referring to FIG. 2, PDCP (Packet Data Convergence Protocol) 205, 240 is responsible for operations such as IP header compression / restore, and radio link control (hereinafter referred to as RLC) 210, 235 An ARQ operation is performed by reconfiguring a PDCP PDU (Packet Data Unit, hereinafter, a packet output from a specific protocol entity, referred to as a PDU of the protocol) to an appropriate size. As shown in FIG. 2, PDCPs 205 and 240 are located at the UE and the anchor node and RLC 235 is located at the UE and ENB.

The MAC layers 215 and 230 are connected to several RLC entities configured in one terminal, and multiplex RLC PDUs to MAC PDUs and demultiplex RLC PDUs from MAC PDUs.

The physical layers 220 and 225 channel-code and modulate higher layer data, make the OFDM symbols and transmit them to the wireless channel, or demodulate and channel decode the OFDM symbols received through the wireless channel and transmit them to the upper layer.

Most HARQ operations, such as channel decoding of received packets, soft combining with previously received packets, and taking CRC operations, are performed at the physical layer, and the MAC layer controls them.

3 illustrates an example of an RLC operation.

As described above, the RLC layers 210 and 235 ensure reliable data transmission and reception through the ARQ process. Referring to FIG. 3, the transmission buffer 305 of the transmitting RLC layer stores the PDCP PDUs 310 before transmitting to the receiving RLC layer. The PDCP PDU 310 is reconfigured to an appropriate size in the framing block 315 and is then transmitted to the receiving RLC layer with a serial number incremented by one, and receives an acknowledgment (ACK) from the receiving RLC layer. Until it is buffered in the retransmission buffer 320.

The receiving RLC layer stores the received RLC PDUs in the receiving buffer 330 and checks the serial number to recognize the serial number of the lost RLC PDU during transmission, and the transmitting RLC layer is lost to the transmitting RLC layer during the transmission. Request retransmission for the generated RLC PDU.

In FIG. 3, for example, RLC PDUs [7] to RLC PDUs [10] are transmitted at an arbitrary time point, and only RLC PDUs [7] and RLC PDUs [9] are received and stored in the reception buffer 330. The receiving RLC layer transmits a status report 340 containing information indicating that the RLC PDU [7] and the RLC PDU [9] received well and the RLC PDU [8] did not receive at any point in time. The RLC layer on the side is stored in the retransmission buffer 320, the RLC PDU [8] requested for retransmission is retransmitted, and the well-transmitted RLC PDU [7] and RLC PDU [9] are discarded. .

4 illustrates a data transfer process during handover.

When the UE handovers to a cell of an ENB different from the current cell (hereinafter referred to as handover between ENBs), since the RLC is reconfigured in the target cell, the source cell delivers packets that have not been transmitted until the corresponding time point to the target cell. Data 430 transferred from the RLC entity of the source ENB 420 to the RLC entity of the target ENB 425 during an inter-ENB handover includes PDCP PDUs that have not yet been transmitted and PDCP PDUs that have already been transmitted but not positively acknowledged. .

When any PDCP PDU is transmitted distributed among n RLC PDUs, the PDCP PDU is considered positive only if all of the n RLC PDUs are positively recognized.

The RLC of the target ENB 425 transmits PDCP PDUs that have not been transmitted yet and PDCP PDUs that have already been transmitted but not positively acknowledged to the UE, thereby preventing packet loss that may occur during handover between ENBs. However, transmission lines used for data transmission between ENBs generally have low transmission speeds, so it is desirable to minimize data transmission between the ENBs.

An object of the present invention is to provide a method and apparatus for minimizing data transfer from a source ENB to a target ENB when a terminal is handed over to a cell belonging to another ENB.

According to an embodiment of the present invention, in a method for handover of a terminal from a source cell to a target cell in a mobile communication system, the terminal transmits a measurement result report on received signal sizes of neighboring cells to a base station of the source cell. And transmitting, by the terminal, a status report including a serial number of a packet data unit that has been successfully received and a serial number of a packet data unit that has not been successfully received to the base station of the source cell. And receiving a handover command from the base station of the source cell and performing a handover.

In addition, according to an embodiment of the present invention, in a mobile station, a terminal device handing over from a source cell to a target cell, the measurement control unit for controlling the measurement of the received signal size of the neighboring cells, and the measurement result received from the measurement control unit And a radio resource controller for generating a message to a base station of the source cell and receiving a status report command from the radio resource controller and generating a status report message before handing over to the target cell. It characterized in that it comprises a radio link control unit for transmitting.

Hereinafter, with reference to the accompanying drawings will be described in detail the operating principle of the preferred embodiment of the present invention. In the following description of the present invention, detailed descriptions of well-known functions or configurations will be omitted if it is determined that the detailed description of the present invention may unnecessarily obscure the subject matter of the present invention. Terms to be described later are terms defined in consideration of functions in the present invention, and may be changed according to intentions or customs of users or operators. Therefore, the definition should be made based on the contents throughout the specification.

In the present invention, when the UE handovers to a cell belonging to another ENB, data transmission from the ENB (hereinafter referred to as a source ENB) of the cell to which the UE belongs to the ENB (hereinafter referred to as a target ENB) of the target cell to be handed over by the UE. A method and apparatus for minimizing are presented.

In the following description of the present invention, the LTE system evolved from the UMTS system is used as an example, but the present invention can be applied to all mobile communication systems to which base station scheduling is applied.

As described above, in the inter-ENB handover, the source ENB delivers PDCP PDUs that have not been transmitted yet and PDCP PDUs transmitted but not positively acknowledged to the target ENB. In this case, the PDCP PDU that has not been transmitted is inevitable, but the PDCP PDU transmitted but not positively recognized does not need to be delivered if a positive acknowledgment signal is received from the UE before the handover is executed.

5 shows a structure of data delivered in handover.

Referring to FIG. 5, when a source ENB receives a positive acknowledgment signal for up to RLC PDU [Y-1] 510 at a certain point in time, the source ENB may receive a serial number lower than that of the RLC PDU [Y-1]. Branch removes the RLC PDUs 505 from the retransmission buffer.

The source ENB then transmits RLC PDU [Y] through RLC PDU [Y + 5] following normal RLC operation. If the handover is performed in a state in which a positive acknowledgment signal for the PDUs is not received, the RLC PDU [Y] 515 and the RLC PDU [are highly likely to be successfully received by the terminal because the source ENB has already completed transmission. Y + 1] 520, RLC PDU [Y + 2] 525, RLC PDU [Y + 3] 530, RLC PDU [Y + 4] (535), RLC PDU [Y + 5] (540 PDCP PDU [x] 545, PDCP PDU [x + 1] 550, and PDCP PDU [x + 2] 555 corresponding to the Ns) should be delivered to the target ENB. If the RLC PDUs have been successfully transmitted and receive a positive acknowledgment signal that the source ENB has successfully received from the UE to the RLC PDU [Y + 5] just before the handover is executed, the PDCP PDUs will be delivered to the target ENB. no need.

In the present invention, as mentioned above, RLC PDUs that have already been transmitted but have not yet received a positive acknowledgment signal are likely to have been successfully transmitted, so that the UE sends a status report to the source ENB immediately before the handover occurs. do. This minimizes the amount of data passed from the source ENB to the target ENB.

6 shows the operation of the system according to the first embodiment of the present invention.

Referring to FIG. 6, the terminal 605 measures a common pilot channel of a neighbor cell through a predetermined method. If the measurement result satisfies a predetermined criterion, the measurement result report 650 is transmitted to the source ENB 610.

The measurement result report may include, for example, information that the quality of a specific cell is better than the quality of the current cell. When the source ENB 610 receives the 'best cell change' from the terminal 605 in this manner, Handover to the optimal cell may be determined.

Conventionally, if a handover is determined, the target ENB 615 performs a handover preparation process, and after the preparation for handover is completed, the source ENB 610 transmits a message instructing the handover to the terminal 605. It was. However, in the present invention, when the handover is determined, the source ENB 610 further transmits a message 655 to the terminal 605 indicating that the handover is imminent.

Control messages related to handover are typically processed through a control layer called Radio Resource Control (hereinafter referred to as RRC), and the RRC 365 of the source ENB 610 is referred to as 'HOover preparation'. The RRC message 665 is transmitted to the RRC 625 of the terminal 605. The handover preparation message may include transmission resource information for the UE to transmit the RLC status report.

The RRC 625 of the terminal 605 receiving the message instructs the RLC entities 620 configured at the corresponding time point to 'create and transmit an RLC status report since the HO is imminent' (660). For convenience, the command is called a 'status report command'.

After receiving the status report command, the RLC entities 620 generate a status report, which is reception status information up to a corresponding time point, according to a predetermined method, and transmit the status report to the source ENB 610 (670). If a transmission resource for transmitting a status report is allocated through the handover preparation message, the terminal transmits a status report using the allocated transmission resource. In the status report, for example, serial numbers of RLC PDUs received up to this point in time and serial numbers of RLC PDUs determined not to be received are stored. The RLC PDUs determined to have not been received are RLC PDUs having a missing serial number when the received RLC PDUs are arranged in a reception buffer according to a serial number.

When the RLC entities 630 of the source ENB 610 receive a status report, they discard the RLC PDUs reported by the RLC entities 620 of the terminal 605 in the retransmission buffer. And all related RLC PDUs discard the received PDCP PDUs, i.e., the positively recognized PDCP PDUs, in the retransmission buffer. In operation 675, the RLC PDUs reported as not received by the RLC entity 625 of the UE 605 are retransmitted to the UE. If one PDCP PDU is composed of several RLC PDUs and only one of the RLC PDUs is not received and all others are received, the RLC PDU in the target cell is retransmitted in the source cell. There is no need to resend them. On the other hand, if the RLC PDU is not retransmitted in the source cell, since all RLC PDUs constituting the PDCP PDU must be retransmitted in the target cell, retransmission in the source cell is more efficient in terms of radio resource efficiency.

Meanwhile, as described above, the source ENB 610 performs a handover preparation process with the target ENB 615 separately from the processes 660, 670, 675 (665). The preparation process is a process of immediately resuming communication in a new cell when the UE is handed over to a new cell. For example, the preparation process may include a process of setting RLC entities and MAC entities.

When the preparation process for the handover with the target ENB 615 is completed, the source ENB 610 transmits a 'handover command' to the terminal 605 to allow the terminal 605 to handover to the target cell (680). The source ENB 610 then delivers 685 'PDCP PDUs not yet positively recognized' to the target ENB 615.

According to the first embodiment of the present invention described above, in step 670, since the source ENB 610 receives the status report from the terminal 605 and discards the successfully transmitted RLC PDUs and PDCP PDUs, in step 685 The number of PDCP PDUs delivered to the target ENB 615 may be minimized.

7 illustrates an operation of a source ENB for executing handover according to the first embodiment of the present invention.

When receiving the measurement report from the terminal in step 705, the source ENB proceeds to step 710 to determine whether to perform a handover based on the measurement result reported by the terminal and the surrounding cell conditions.

For example, when the UE reports that the cell having the best measurement quality has been changed, the source ENB prepares to handover the UE to the cell having the best measurement quality.

If the source ENB decides not to execute the handover in step 710, the process proceeds to step 715, and waits until a new measurement report arrives.

In step 720, the source ENB transmits a 'handover preparation' command to the terminal, and in step 725, the source ENB executes a handover preparation process with the target ENB. The source ENB may pre-allocate a transmission resource that the terminal can use for transmitting a status report through the handover preparation command.

When the handover preparation process with the target ENB is completed by receiving a signal that the handover preparation is completed from the target ENB, the source ENB proceeds to step 735 and transmits a handover command to the terminal. PDCP PDUs that have not been sent and PDCP PDUs that have already been sent but not positively recognized.

8 illustrates an operation of a terminal that receives a 'handover ready' signal in a handover process according to the first embodiment of the present invention.

When receiving a 'handover ready' signal from the source ENB in step 805, in step 810 the RRC of the terminal delivers a command 'status report command' to the RLC entities configured at the time. Since the 'status report command' is impending handover, it is a command to configure and send a status report to the source ENB.

In step 820, the RLC entities receiving the status report command from the RRC generate a status report containing the RLC PDU reception status at the corresponding time and transmit the status report to the source ENB. At this time, if there is a transmission resource allocated in the handover preparation command, the terminal transmits a status report using the transmission resource.

Next, a handover method according to a second embodiment of the present invention will be described.

In the second embodiment of the present invention, a terminal proposes a method for transmitting a status report by recognizing that the handover will be executed soon.

9 shows the operation of the entire system according to the second embodiment of the present invention.

Referring to FIG. 9, the terminal 905 measures signal strength of a common pilot channel of a neighbor cell through a predetermined method. If the measurement result satisfies a predetermined criterion, the measurement result report 950 is transmitted to the source ENB 910.

The measurement is generally performed for mobility support of the terminal, and the base station may instruct the terminal of various types of measurement and measurement result reporting methods according to the type of mobility support. For example, when a cell quality of a neighboring cell exceeds a predetermined threshold value, a measurement result may be reported. When a cell quality of a neighboring cell has a better channel quality than a current cell, a command to report a measurement result is performed. You may.

In the second embodiment of the present invention, among the various types of measurement result reports, the UE and the network recognize in advance which measurement result report is likely to cause handover. The measurement report that is likely to cause the handover may be defined for each operator according to the operator's policy or network operation plan. In general, reporting measurement results such as optimal cell changes is more likely to cause handovers.

After the RRC 925 of the terminal transmits a measurement result report, if the measurement result report is a measurement result report that is likely to cause a handover, the RLC entities configured at the corresponding time point 'HO is imminent, so the RLC status report Create and command to send (960). Transmitting the measurement result report from the RRC entry means transmitting the measurement result to a lower layer.

The source ENB 910 informs the terminal 905 of the measurement result report as a measurement result report that needs to deliver a status report command to the RLC entities after reporting the measurement result, that is, a handover is likely to occur. You can inform. Alternatively, the type of measurement result report to which the status report command should be delivered may be determined in advance. The most representative example of a measurement result report that is likely to cause handover is an optimal cell change report.

The RLC entities 920 of the terminal receiving the status report command generate a status report which is reception status information up to a corresponding time point and transmit the status report to the source ENB 910 (970). In the status report, for example, serial numbers of RLC PDUs received up to this point in time and serial numbers of RLC PDUs determined not to be received are stored. The RLC PDUs, which are determined to have not been received, refer to RLC PDUs having serial numbers corresponding to empty holes on the serial numbers when the received RLC PDUs are arranged in the receiving buffer according to the serial numbers.

When the RLC entities 930 of the source ENB receive the status report, the RLC PDUs reported as received by the RLC entities 920 of the UE and all related RLC PDUs discard the received PDCP PDUs in the buffer. In operation 975, the RLC entity 920 of the terminal performs retransmission for the RLC PDUs reported as not received.

Meanwhile, the source ENB 910 performs a handover preparation process with the target ENB 915 separately from the processes 960, 970 and 975 (965). The preparation process is a preparation process for immediately resuming communication in a new cell when the UE 905 is handed over to a new cell. For example, the preparation process may include a process of setting RLC entities and MAC entities.

When the handover preparation process with the target ENB 915 is completed, the source ENB 910 transmits a 'handover command' to allow the terminal 905 to handover to the target cell (980).

Source ENB 910 delivers 'PDCP PDUs not yet positively recognized' to target ENB 915 (985).

The sequence of messages transmitted by the terminal in FIG. 9 is merely an example of describing a front-rear relationship of the operation of the terminal, and a sequence of messages different from that of FIG. 9 may be used. For example, transmission of a measurement result that is likely to cause handover 950 and transmission of a status report that is derived from generation of the measurement result that is likely to cause handover 970 may actually proceed at the same point in time. As described above, the RRC entity delivers a measurement result report that is likely to cause handover to a lower layer, and then instructs the RLC entities to generate and send a status report. In this case, the measurement result report is stored in the transmission buffer of the second layer until the transmission resource is allocated from the scheduler. Since the allocation of transmission resources from the scheduler is a process of transmitting a predefined signal through a random access channel or the like and receiving a response thereto, the measurement result report is stored in the transmission buffer of the second layer for several msec. It can reach several tens of msec. On the other hand, since the time required for the RLC entities to generate the status report is very short, it is highly likely that the measurement result report and the status report are actually transmitted together.

As described above, according to the second embodiment of the present invention, by receiving a status report in step 970, the recently successfully received RLC PDUs and PDCP PDUs are discarded, so the number of PDCP PDUs delivered in step 985 is minimized. do.

10 illustrates an operation of a source ENB for executing handover according to the second embodiment of the present invention.

When receiving the measurement report from the terminal in step 1005, the source ENB proceeds to step 1010 to determine whether to perform a handover based on the measurement result reported by the terminal and the surrounding cell conditions.

For example, when the UE reports that the cell having the best measurement quality has been changed, the source ENB prepares to handover the UE to the cell having the best measurement quality.

If it is determined in step 1010 not to execute the handover, the source ENB proceeds to step 1015 and waits for a new measurement report to arrive. If it is determined to execute the handover, the source ENB proceeds to step 1020.

In step 1020, the source ENB performs a handover preparation process with the target ENB.

When the handover preparation process with the target ENB is completed by receiving a signal that the handover preparation is completed from the target ENB, the source ENB proceeds to step 1035 and transmits a handover command to the terminal. PDCP PDUs that have not been sent and PDCP PDUs that have already been sent but not positively recognized.

11 illustrates the operation of the terminal in the handover process according to the second embodiment of the present invention.

In step 1105, the UE measures the channel quality of the neighbor cell, and if the measurement result generation condition set in advance by the base station is satisfied, the terminal makes a measurement result report.

In step 1110, the UE checks whether the measurement result report is a measurement result report that is likely to cause a handover, and transmits the measurement result report to a base station (source ENB). That is, if the optimal cell change report is defined as a measurement result report that is likely to cause a handover, the terminal checks whether the measurement result report generated in step 1105 is the optimal cell change report and transmits the measurement result report to the source ENB. . The RRC transmission of the measurement result report to the base station means the same as delivering the measurement result report to a lower layer. Thereafter, the measurement result report is transmitted to the base station through a predetermined lower layer operation.

If the UE determines that the measurement result report transmitted in step 1110 is not likely to cause a handover, the UE proceeds to step 1115 and waits until a new measurement result report occurs, and reports a measurement result with a high possibility of handover. If it is determined that the process proceeds to step 1120.

In step 1120, the RRC of the UE delivers a command called 'status report command' to the RLC entities configured at the corresponding time. Since the 'status report command' is impending handover, it is a command to configure and send a status report to the source ENB.

The RLC entities that receive the status report command from the RRC make a status report containing the RLC PDU reception status at that time and transmit it to the base station in step 1125. The status report is transmitted to the base station through a predetermined process. At this time, the status report and the measurement result report that are likely to cause handover may be simultaneously transmitted through the same transmission resource.

12 illustrates a structure of a terminal device according to an embodiment of the present invention.

12, a terminal according to an embodiment of the present invention includes a measurement control unit 1205, an RRC 1210, an RLC 1220, and a MAC / PHY 1225.

The measurement control unit 1205 controls the measurement process of the received signal strength of the terminal and, if the measurement result report condition is satisfied, transmits the measurement result to be received in the measurement result report to the RRC 1210.

Particularly, in the second embodiment of the present invention, when the measurement control unit 1205 recognizes a type of 'reporting of the measurement result that is likely to cause a handover' and 'reports a measurement result that is likely to cause a handover' occurs, The RRC 1210 is notified of this.

When the measurement result is reported from the measurement control unit 1205, the RRC 1210 forms an RRC message called a measurement result report and transmits the result to the base station. In addition, when the measurement control unit 1205 notifies that a 'report of a measurement result that is likely to cause a handover' has occurred, the RRC 1210 generates a status report to the RLC entities of the RLC layer 1220 configured at that time. Command to send. Alternatively, upon receiving the handover preparation message from the RRC of the base station, the RRC 1210 instructs the RLC layer 1220 RLC entities configured at the corresponding time to generate and transmit a status report.

The RLC layer 1220 is a set of RLC entities that are responsible for reliable transmission and reception of higher layer data or RRC messages, and the MAC / PHY 1225 is a device that is responsible for the transmission and reception of RLC PDUs.

In a third embodiment of the present invention, a method and apparatus for transmitting a buffer status report for retransmission to a scheduler by a terminal after transmitting a measurement result report that is likely to cause handover are proposed.

13 illustrates a conventional buffer status report and transmission resource allocation process.

Referring to FIG. 13, in a mobile communication system including a terminal 1305 and an ENB 1310, the terminal 1305 starts a buffer status reporting procedure when certain conditions are met. The constant condition is referred to as a buffer status reporting procedure triggering condition. The most representative example of the buffer status reporting procedure triggering is the periodic method. That is, the terminal 1305 transmits a buffer status report and triggers the buffer status report again after a predetermined time passes.

When the buffer status reporting procedure is triggered, the terminal 1305 first transmits a predetermined signal, called a scheduling request, to the ENB 1310. The scheduling request is a signal for requesting the ENB 1310 to allocate a transmission resource for transmitting a buffer status report. The scheduling request may be transmitted through a predetermined physical channel that is periodically set. For convenience of description, the predetermined physical channel that is periodically set to transmit the scheduling request is called an access slot. When the buffer status reporting procedure is triggered in step 1315, the terminal 1305 transmits a predetermined scheduling request through an access slot of the closest time point in step 1320.

When the ENB 1310 receives the scheduling request, the ENB 1310 allocates a transmission resource so that the terminal 1305 can transmit a buffer status report in step 1330, and the terminal 1305 reports the buffer status using the transmission resource in step 1335. Send it.

In step 1340, the ENB 1310 allocates a transmission resource to the terminal 1305 in consideration of the amount of data stored in the terminal 1305, which is information stored in the buffer status report, the priority of the data, and the like. In operation 1345, 1305 transmits data using the transmission resource.

The conventional buffer status reporting method works well in general data transmission, but is not suitable for data transmission that needs to be transmitted as quickly as possible.

Therefore, the third embodiment of the present invention proposes a buffer status report and a transmission resource allocation process to be applied when transmitting a measurement result report that is likely to cause a handover.

14 shows the overall operation of the mobile communication system according to the third embodiment of the present invention.

Referring to FIG. 14, in the mobile communication system including the terminal 1405 and the base station 1410, when a measurement result report having a high probability of causing a handover occurs in step 1415, the terminal 1405 may trigger a buffer status report procedure. This is deemed satisfied and the buffer status reporting procedure is started in step 1420. For convenience of explanation, the reporting of the measurement result that is likely to cause handover is referred to as 'type 1 measurement result report'.

When the Type 1 measurement result report occurs, the type 1 measurement result report is transmitted as quickly as possible by immediately starting the buffer status report procedure without waiting for a timer to expire.

If the buffer status reporting procedure is triggered, the terminal 1405 transmits a predetermined scheduling request through an access slot of the closest time point in step 1430.

When the ENB 1410 receives the scheduling request, the ENB 1410 allocates a transmission resource so that the UE 1405 transmits a buffer status report in step 1435, and the UE 1405 uses the transmission resource in step 1440 using the ENB 1410. Send a buffer status report. When the type 1 measurement result report occurs, the terminal 1405 determines that the handover is imminent, and the following information is included in the buffer status report generated when the handover is imminent.

■ The size of the type 1 measurement result report or the size of data stored in the buffer of the radio bearer or group of radio bearers to which the type 1 measurement result report belongs.

The sum of the sizes of the forward status reports of the RLC entities configured at that time.

The total number of RLC PDUs to be retransmitted in the backward direction from the RLC entities configured at that time.

According to the third embodiment of the present invention, if a type 1 measurement result report that is likely to cause a handover occurs, the terminal instructs the RLC entities configured at the corresponding time to generate a forward status report, and the created forward direction. Status reports are stored in the transmission buffer of the radio bearer. The second item refers to the size of the status reports generated as soon as the handover time.

In LTE, the size of an RLC PDU is variable depending on the channel situation. For example, a small RLC PDU is transmitted when the channel condition is bad, and a large RLC PDU is transmitted when the channel condition is good. When the UE performs handover, the channel situation is poor and the size of the RLC PDU is likely to be small. Therefore, an IP packet having a size of up to 1500 bytes is likely to be divided into several RLC PDUs. .

When the handover is performed, the terminal reconfigures the RLC entity and resumes RLC PDU transmission in a new cell using the reconfigured RLC entity. At this time, all IP packets that are not successfully transmitted at all in the previous cell are retransmitted in the new cell. For example, when any IP packet is transmitted divided into n RLC PDUs, if any one of the n RLC PDUs does not succeed, the entire IP packet is retransmitted in the target cell. As described above, some transmission failures lead to retransmission of the entire IP packet. When handover is imminent, completing retransmission of RLC PDUs requiring retransmission is advantageous in terms of efficient use of transmission resources.

Therefore, in the third embodiment of the present invention, the information on the RLC PDUs that need to be retransmitted is included in the buffer status report generated when the handover is imminent, and a transmission resource is allocated so that a scheduler can complete retransmission of the RLC PDUs to the UE. Assign it. The RLC PDUs requiring retransmission mean RLC PDUs that have been requested to be retransmitted to an RLC receiver or lower layer of an ENB but have not yet been retransmitted. The third item is the sum of the sizes of the RLC PDUs requiring retransmission.

Upon receiving the buffer status report, the ENB 1410 allocates a transmission resource so that the UE 1405 reports a measurement result and transmits a forward status report and a reverse RLC PDU requiring retransmission in step 1445, and the UE 1405 1450. In the step, using the transmission resources, the measurement result report, the forward status report, and transmits the reverse RLC PDUs that require retransmission.

15A and 15B illustrate a structure of a buffer status report. In FIG. 15A, a structure of a general buffer status report is illustrated, and FIG. 15B illustrates a structure of a buffer status report transmitted by a terminal impending handover.

Referring to FIG. 15A, a buffer status report is composed of a plurality of buffer status elements 1555, and one buffer status element indicates a buffer status of one radio bearer or a group of radio bearers.

A plurality of radio bearers may be configured in one terminal, and a transmission buffer exists for each radio bearer. Since reporting buffer status by radio bearer may increase the amount of buffer status reporting excessively, in order to reduce the amount of buffer status reporting, radio bearers having similar quality of service or priorities are grouped into one radio bearer group. You can also report Therefore, in a system for reporting buffer status for each radio bearer, the buffer status element indicates the buffer status of one radio bearer, and in a system for reporting buffer status for each radio bearer group, the buffer status element is the sum of the buffer status of one radio bearer group. Indicates. Since the radio bearer and the radio bearer group are the same in terms of the unit in which the buffer status is reported, the following description uses the radio bearer and the radio bearer group interchangeably.

The buffer status element consists of an identifier 1505 of a radio bearer group and buffer size information 1510 indicating the amount of data stored in a buffer of the radio bearer group. If a plurality of radio bearer groups are configured in any terminal, one buffer status report includes several buffer status elements. In a general case, the UE configures and transmits a buffer status report by including buffer states of all radio bearer groups in which data to be transmitted at that time is stored.

Unlike the general buffer status report, the buffer status report that is imminent in handover is transmitted by including only the type 1 measurement result report, status report, and information on reverse RLC PDUs to be retransmitted.

In general, the radio bearer group is set according to the priority, for example, the radio bearer group may be defined as shown in Table 1 below.

RB group id RBs of the group RB group 0 high priority control signaling: RB 1 RB group 1 low priority control signaling: RB 2 RB group 2 user plane RB whose priority is in the range of x ~ y: RB 3, RB 4 RB group 3 user plane RB whose prioiry is in the range of w to z: RB 5, RB 6, RB 7

As described above, when the RB groups are configured according to the priority of the RB, the status report or the priority of the reverse RLC PDUs to be retransmitted is the same as the priority of the corresponding RB, so the status reports or retransmissions of the RBs belonging to different RB groups The RLC PDUs to be stored are stored in the buffer status element of the corresponding RB group. As described above, the status report or RLC PDUs to be retransmitted are more important than the general RLC PDUs, but there is no way to express them in the normal buffer status report, and the scheduler of the base station does not reflect these matters in the scheduling.

Therefore, in the third embodiment of the present invention, in order to solve such a problem, the status report and the priority of the RLC PDU to be retransmitted have a predetermined priority, not a priority of the corresponding RB, at least during handover. To do that. For example, by setting the priority of the status report and the retransmission RLC PDU to the highest priority, not the priority of the corresponding RB, the status report and the retransmission RLC PDU are considered first in the scheduling process.

Referring to FIG. 5B, a buffer status report occurring in a situation where handover is imminent includes, for example, a buffer status element 1560 for reporting a type 1 measurement result and a buffer status element 1565 for the status report and retransmission RLC PDU. ) Is stored. In the buffer status element 1560 for reporting a type 1 measurement result, a radio bearer group identifier 1535 of the radio bearer to which the type 1 measurement result report belongs and a buffer status 1540 of the radio bearer group are stored, and a status report and In the buffer status element 1560 for the retransmission RLC PDU, an identifier 1545 of the radio bearer group corresponding to the priority to be applied to the RLC PDU to be retransmitted, status reports generated in all RBs, and all RBs are stored. The buffer state 1550 corresponding to the sum of the RLC PDUs to be retransmitted is stored.

16 illustrates a terminal operation according to the third embodiment of the present invention.

Referring to FIG. 16, in step 1605, the UE recognizes a priority to be applied to a status report and a priority to be applied to a retransmission PDU. The information may be signaled to the terminal during call setup. The two priorities may be the same, but a higher priority may be applied to either.

When the UE completes the call setup process, the UE transmits and receives the RLC PDU according to a predetermined procedure and measures the quality of neighbor cells. If the type 1 measurement result report is triggered in step 1610 while performing the neighbor cell measurement process, the terminal proceeds to step 1615 and immediately starts the buffer status report procedure. In other words, the scheduling request is sent through the nearest future access slot.

In step 1620, the UE configures a buffer status report according to a predetermined method. That is, for each radio bearer group, the amount of data stored in the radio bearer group is checked, and the information is stored in a separate buffer state element. In step 1625, the UE checks whether a status report is stored in the radio bearer group buffer, and if so, proceeds to step 1630, and if not, proceeds to step 1640.

If the status reports are stored in arbitrary radio bearer group buffers, the terminal configures a buffer status element by considering the priority to be applied to the status report recognized in step 1630 as the priority of the status reports in step 1630. . In other words, a buffer status element corresponding to the priority to be applied to the status report is created, and the sum of the status report sizes is stored in the buffer size information of the buffer status element. If a buffer status element corresponding to the priority to be applied to the status report already exists, the sum of the status report sizes is added to the existing buffer size information.

If the size of the status report is already included in the buffer status elements of the radio bearer group to which the status report belongs, the size of the status report is duplicated in the buffer status report by subtracting the size of the status report from the corresponding buffer status elements. Prevent it.

In step 1640, the UE checks whether there is a PDU to be retransmitted, and if there exists, proceeds to step 1645, and if not, proceeds to step 1655.

If the RLC PDUs to be retransmitted are stored in arbitrary radio bearer group buffers, the UE regards the priority to be applied to the RLC PDU to be retransmitted recognized in step 1605 as the priority of the RLC PDUs to be retransmitted in step 1645. Configure the buffer status element. In other words, a buffer status element corresponding to a priority to be applied to the RLC PDU to be retransmitted is created, and the sum of the sizes of the RLC PDUs to be retransmitted is stored in the buffer size information of the buffer status element. If a buffer status element corresponding to the priority to be applied to the RLC PDU to be retransmitted already exists, the sum of the RLC PUD sizes to be retransmitted is added to the existing buffer size information. If the size of the RLC PDUs to be retransmitted is already included in the corresponding buffer status elements, the size of the RLC PDUs to be retransmitted is included in the buffer status report by subtracting the sizes of the RLC PDUs to be retransmitted from the other buffer status elements. Prevent it.

In step 1655, the terminal transmits the configured buffer status report.

17 illustrates an operation of a base station according to the third embodiment of the present invention.

Referring to FIG. 17, when receiving a type 1 measurement result report in step 1705, the base station determines whether to hand over in step 1710. The base station proceeds to step 1720 if it is determined to execute the handover, and proceeds to step 1715 if it is determined that the handover is not necessary to operate according to the prior art.

In step 1720, the base station performs a handover preparation process with the target base station.

When receiving the buffer status report in step 1725, the base station proceeds to step 1730 and allocates transmission resources to the terminal based on the buffer status report. At this time, the base station allocates sufficient transmission resources so that the terminal can transmit both the status report and the retransmission RLC PDU.

18 illustrates a terminal device according to a third embodiment of the present invention.

Referring to FIG. 18, the terminal according to the third embodiment of the present invention includes a measurement controller 1805, an RRC 1810, an RLC 1820, a MAC / PHY 1825, and a buffer status report controller 1830. .

The measurement controller 1805 controls the measurement process of the received signal strength of the terminal, and transmits the measurement result to be received in the measurement result report to the RRC 1810 when the measurement result report condition is satisfied. In particular, in the third embodiment of the present invention, the measurement control unit 1805 recognizes the type of 'reporting of the measurement result that is likely to cause a handover', and if the 'reporting of the measurement result that is likely to cause a handover' occurs, Notify the RRC 1810.

When the measurement result is reported from the measurement control unit 1805, the RRC 1810 makes an RRC message called a measurement result report and transmits the result to the base station. Also, when the measurement control unit 1805 notifies that a 'report of a measurement result that is likely to cause a handover' has occurred, the RRC 1810 generates a status report to the RLC entities of the RLC layer 1820 configured at that time. Command to send. The buffer status report controller 1830 notifies that the handover is imminent.

The RLC layer 1820 is a set of RLC entities that are responsible for the reliable transmission and reception of higher layer data or RRC messages, and the MAC / PHY 1825 is a device that is responsible for the transmission and reception of RLC PDUs.

The buffer status report control unit 1835 monitors the status of the transmission buffers of the radio bearers and monitors whether the buffer status report triggering condition is satisfied. When the buffer status reporting triggering condition is satisfied, the buffer status reporting procedure is started.

Upon receiving notification from the RRC layer that the handover is imminent, the buffer status report control unit 1835 immediately reports that the buffer status reporting triggering condition is satisfied and starts the buffer status reporting procedure.

The buffer status report control unit 1835 checks the status reports stored in the transmission buffers of the radio bearers and the size of the RLC PDUs to be retransmitted, and configures buffer status elements for the status reports and the RLC PDUs to be retransmitted. A buffer status report containing the configured buffer status elements is transmitted to the MAC / PHY 1825.

The MAC / PHY 1825 sends a buffer status report to the base station.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

In the present invention operating as described in detail above, the effects obtained by the representative ones of the disclosed inventions will be briefly described as follows.

According to the present invention, the UE transmits a STATUS REPORT to the source ENB immediately before the handover occurs, thereby not retransmitting the RLC PDUs that have been successfully transmitted but have not yet received a positive acknowledgment signal. Therefore, the amount of data transferred from the source ENB to the target ENB can be minimized.

Claims (7)

In the mobile communication system in the terminal handover from the source cell to the target cell, Transmitting, by the terminal, a measurement result report on received signal sizes of neighbor cells to a base station of the source cell; Transmitting, by the terminal, a status report including a serial number of a packet data unit that has been successfully received and a serial number of a packet data unit that has not been successfully received, to the base station of the source cell; And receiving, by the terminal, a handover command from a base station of the source cell and performing a handover. The method of claim 1, After the terminal transmits the measurement result report, receiving a handover preparation request from a base station of the source cell; The terminal receives the handover preparation request and transmits the status report. The method of claim 1, After the terminal transmits the measurement result report, it is determined whether the measurement result report satisfies a handover condition previously agreed with the base station of the source cell, and the status report when the handover condition is satisfied Handover method, characterized in that for transmitting. A terminal device for handover from a source cell to a target cell in a mobile communication system, A measurement control unit controlling measurement of the received signal magnitude of neighboring cells; A radio resource controller which generates a measurement result received from the measurement controller as a message and transmits the message to a base station of the source cell; And a radio link controller for receiving a status report command from the radio resource controller and generating a status report message to the base station of the source cell before handing over to the target cell. The method of claim 4, wherein The measurement controller determines whether the measurement result report satisfies a handover condition previously agreed with the base station of the source cell, and transmits the determination result to the radio resource controller. And the radio resource controller transmits the status report command to the radio link controller according to the determination of the measurement controller. The method of claim 4, wherein The radio resource control unit, And after receiving the handover preparation request from the base station of the source cell, transmitting the status report command to the radio link controller. The method of claim 4, wherein And the status report message comprises a serial number of a packet data unit that has been successfully received and a serial number of a packet data unit that has not been successfully received.

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