KR102061196B1 - Method and apparatus of DRX reconfiguration coonsidering handover - Google Patents

Abstract

The present invention relates to a DRX reconfiguration method and apparatus in consideration of handover in a wireless communication system, and provides a DRX method in consideration of handover by a terminal in a wireless communication system. The method includes generating a measurement report message indicating initiation of a handover, transmitting the measurement report message to a base station, controlling a DRX operation of the terminal based on a preset DRX parameter, and from the base station Monitoring the transmitted physical downlink PDCCH subframes during an active time defined in the DRX operation, wherein the short duration DRX mode is continuously maintained or the DRX is initiated off. This can reduce the probability of handover failure.

Description

Method and apparatus for DRX reconfiguration considering handover {Method and apparatus of DRX reconfiguration coonsidering handover}

The present invention relates to a wireless communication system, and more particularly, to a DRX reconfiguration method and apparatus in consideration of handover in a wireless communication system.

In a wireless communication system, packet data traffic is often very bursty, such as a lot of transmission activity during a transitory period of time and no long transmissions or a sudden large amount of traffic. bursty) In terms of delay, in order to receive an uplink scheduling grant or downlink data transmission, it is preferable to observe downlink control signaling in every subframe and react immediately according to the change in traffic operation.

However, since the power consumption by the receiving circuit of the general terminal is also a non-negligible consumption, the operation of the continuous receiving circuit leads to an increase in the power consumption of the terminal. In order to reduce the power consumption of the terminal, LTE supports discontinuous reception (DRX). This concept corresponds to HSPA's Continuous Packet Connectivity (CPC) function.

On the other hand, handover (handover) or handoff (handoff) as the terminal moves away from the current communication service area (hereinafter referred to as the source cell (source cell)) to the adjacent communication service area (hereinafter referred to as the target cell (target cell)) When moving, it is a function that automatically tunes to a new traffic channel of an adjacent communication service area so that the call is continuously maintained. That is, a terminal communicating with a specific base station is linked to another neighboring base station (target base station) when the signal strength of the specific base station (hereinafter referred to as a source base station) is weakened. . If a handover is made, the problem of call disconnection occurring when moving to an adjacent cell can be solved.

However, when a handover occurs while the terminal uses the DRX mode, the DRX is designed to operate in a wake-up and sleep period, and thus, a handover command may not be received at a desired time point during the handover. In particular, when the DRX cycle is long, a sleep interval is long, and thus a delay may occur when the UE receives a handover command. This causes a problem of a handover failure.

An object of the present invention is to provide a method and apparatus for performing reconfiguration of DRX in a wireless communication system.

Another technical problem of the present invention is to provide a method and apparatus for a UE to perform reconfiguration of DRX when a handover occurs while using the DRX mode.

Another technical problem of the present invention is to provide a method and apparatus for continuously maintaining a short-term DRX mode when a UE generates a handover while using the DRX mode.

Another technical problem of the present invention is to provide a method and apparatus for turning off the DRX when a handover occurs while the terminal uses the DRX mode.

According to an aspect of the present invention, there is provided a terminal for performing a discontinuous reception (DRX) operation in consideration of handover in a wireless communication system. The terminal includes a HO processor for generating a measurement report message indicating the initiation of handover, a transmitter for transmitting the measurement report message to a base station, a DRX processor for controlling a DRX operation of the terminal based on a preset DRX parameter, and And a receiver configured to monitor a physical downlink PDCCH subframe transmitted from the base station for an active time defined in the DRX operation, wherein the DRX processor is configured to continuously maintain a short-term DRX mode or initiate a DRX off ( initiate).

According to another aspect of the present invention, there is provided a base station for controlling a DRX operation of a terminal considering a handover in a wireless communication system. The base station includes a receiver for receiving a measurement report message indicating the initiation of a handover from a terminal, a DRX processing unit for generating a short term DRX maintenance request message or a DRX off maintenance message based on a constantly received measurement report message, and the generated short term DRX And a transmitter for transmitting a maintenance request message or a DRX off maintenance message to the terminal.

According to still another aspect of the present invention, there is provided a DRX method considering handover by a terminal in a wireless communication system. The method includes generating a measurement report message indicating initiation of a handover, transmitting the measurement report message to a base station, controlling a DRX operation of the terminal based on a preset DRX parameter, and from the base station Monitoring the transmitted physical downlink PDCCH subframes during an active time defined in the DRX operation, wherein the short duration DRX mode is continuously maintained or the DRX is initiated off.

According to another aspect of the present invention, there is provided a method of controlling a DRX operation of a terminal in consideration of handover by a base station in a wireless communication system. The method may further include receiving a measurement report message indicating initiation of a handover from a terminal, generating a short term DRX maintenance request message or a DRX off maintenance message based on a constantly received measurement report message, and maintaining the generated short term DRX. And transmitting a request message or a DRX off maintenance message to the terminal.

According to the present invention, when a handover occurs while using the DRX mode, the UE may continuously maintain the short-term DRX mode or turn off the DRX and receive a handover command, thereby reducing the probability of a handover failure. In addition, the base station may explicitly instruct DRX reset, or the terminal may implicitly perform DRX reset.

1 shows a wireless communication system to which the present invention is applied.
2 shows a structure of a subframe to which the present invention is applied.
3 is an explanatory diagram for explaining a DRX operation to which the present invention is applied.
4 is an example of a handover operation for explaining the present invention.
5 is an example of a case where a handover failure occurs to explain the present invention.
6 shows an example of a DRX operation according to the present invention.
7 shows an example of a DRX operation during handover according to the present invention.
8 is a flowchart illustrating an operation of maintaining a short DRX cycle during handover according to an embodiment of the present invention.
9 shows a DRX short-term maintenance MAC CE to which the present invention is applied.
FIG. 10 is a flowchart illustrating a case in which a handover reception timer is operated as a timer for releasing continuous maintenance of a short-term DRX mode according to an embodiment of the present invention.
11 is a flowchart illustrating a case in which T310 is used as a timer for terminating short-term DRX mode maintenance according to an embodiment of the present invention.
12 is an example of a DRX mode change by an RRC reconfiguration message during continuous maintenance of a short-term DRX mode according to an embodiment of the present invention.
13 illustrates a DRX off operation during handover during a DRX operation according to an embodiment of the present invention.
14 is a flowchart illustrating a DRX off operation during handover according to an embodiment of the present invention.
15 illustrates a DRX off operation according to a DRX off request message according to an embodiment of the present invention.
16 is a flowchart illustrating an operation of turning off DRX during handover according to an embodiment of the present invention.
17 shows an example of a handover procedure to which a DRX operation is applied according to the present invention.
18 shows another example of a handover procedure to which a DRX operation is applied according to the present invention.
19 is a block diagram of a terminal and a base station for performing handover and DRX operations according to an embodiment of the present invention.

Hereinafter, some embodiments of the present invention will be described in detail with reference to the accompanying drawings. In adding reference numerals to the components of each drawing, it should be noted that the same reference numerals are assigned to the same components as much as possible even though they are shown in different drawings. In addition, in the following description of the embodiments of the present invention, when it is determined that the detailed description of the related well-known configuration or function may obscure the subject matter of the present specification, the detailed description thereof will be omitted.

In addition, the present specification describes a wireless communication network, the operation performed in the wireless communication network is performed in the process of controlling the network and transmitting data in the system (for example, the base station) that is in charge of the wireless communication network, or the corresponding wireless Work may be done at the terminal coupled to the network.

1 shows a wireless communication system to which the present invention is applied.

Referring to FIG. 1, the wireless communication system 10 is widely deployed to provide various communication services such as voice and packet data. The wireless communication system 10 includes at least one base station (BS) 11. Each base station 11 provides a communication service for specific cells 15a, 15b, and 15c. The cell can in turn be divided into a number of regions (called sectors). The base station 11 may be called in other terms such as an evolved-NodeB (eNB), a base transceiver system (BTS), an access point, an femto base station, a home nodeB, a relay, and the like. . A cell is meant to encompass all of the various coverage areas such as megacell, macrocell, microcell, picocell, femtocell, and the like.

The UE 12 may be fixed or mobile and may have a mobile station (MS), a mobile terminal (MS), a mobile terminal (MT), a user terminal (UT), a subscriber station (SS), a wireless device, or a PDA. (personal digital assistant), wireless modem (wireless modem), a handheld device (handheld device) may be called other terms.

Hereinafter, downlink refers to a transmission link from the base station 11 to the terminal 12, and uplink refers to a transmission link from the terminal 12 to the base station 11. it means. In downlink, the transmitter may be part of the base station 11 and the receiver may be part of the terminal 12. In uplink, the transmitter may be part of the terminal 12 and the receiver may be part of the base station 11. There is no limitation on the multiple access scheme applied to the wireless communication system. Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier-FDMA (SC-FDMA), OFDM-FDMA, OFDM-TDMA For example, various multiple access schemes such as OFDM-CDMA may be used. The uplink transmission and the downlink transmission may use a time division duplex (TDD) scheme that is transmitted using different times, or may use a frequency division duplex (FDD) scheme that is transmitted using different frequencies.

2 shows a structure of a subframe to which the present invention is applied.

Referring to FIG. 2, one radio frame includes 10 subframes, and one subframe includes two consecutive slots. The preceding 1, 2, 3 or 4 OFDM symbols of the first slot in the subframe are the control channel region to which the PDCCH is mapped, and the remaining OFDM symbols are the physical downlink shared channel (PDSCH). This is the data channel region to be mapped. The control channel region may be called a control region, and the data channel region may be called a data region. In addition to the PDCCH, a control channel such as PCFICH and PHICH may be allocated to the control channel region.

The terminal uses the cell-radio network temporary identifier (C-RNTI), transmission power control (TPC) -PUCCH-RNTI, TPC-PUSCH-RNTI, and semi persistent scheduling (SPS) -RNTI, Monitoring can be performed. Monitoring of the PDCCH can be controlled by the DRX operation, the parameters related to the DRX is transmitted by the base station to the terminal by the RRC message. In addition to the RNTIs, the UE should always receive system information (RN) -RNTI, p (paging) -RNTI, etc. regardless of the DRX operation configured by the RRC message. Here, the remaining PDCCHs except the PDCCH scrambled with C-RNTI are always received through a common search space of the main serving cell.

If the terminal has a DRX parameter configured in the RRC connected state, the terminal performs discontinuous monitoring on the PDCCH based on the DRX operation. On the other hand, if the DRX parameter is not configured, the UE monitors the continuous PDCCH. Discontinuous PDCCH monitoring may mean that the UE monitors the PDCCH only in a specific subframe, and continuous PDCCH monitoring may mean that the UE monitors the PDCCH in all subframes. On the other hand, if PDCCH monitoring is required in a DRX independent operation such as a random access procedure, the UE monitors the PDCCH according to the requirements of the corresponding operation.

In other words, DRX allows a UE to stop monitoring a packet data control channel (PDCCH) for a period of time (ie, a sleep period or an inactive time). The UE repeats a wake up or active and sleep or non-active or inactive period in the DRX mode. Wake up (or activity) means monitoring the packet data control channel (PDCCH). Sleep (or inactivity) means stopping monitoring the Packet Data Control Channel (PDCCH).

The DRX may be configured by radio resource control / media access control (RRC / MAC). Related DRX parameters may include a long DRX cycle, a DRX Inactivity Timer, and a DRX Retransmission Timer. Also optionally, the DRX includes a short DRX cycle and a DRX Short Cycle Timer (drxShortCycleTimer). The long term DRX cycle provides a longer sleep period for the terminal than the short term DRX cycle.

3 is an explanatory diagram for explaining a DRX operation to which the present invention is applied.

Referring to FIG. 3, the DRX operation is repeated in units of DRX cycles 300, and the DRX cycle 300 is a periodic repetition of a DRX opportunity (DRX opportunity 310) and a duration (On Duration 305). Is defined. One cycle of DRX cycle 300 includes a duration 305 and a DRX opportunity (310). The DRX cycle 300 includes, for example, a long DRX cycle applied in a range between 10 subframes and 2560 subframes, and in another example, a short DRX cycle applied in a range of 2 subframes to 640 subframes. DRX cycle). At this time, the short term DRX cycle is applied only while the DRX short cycle timer (drxShortCycleTimer) is operating, and the long term DRX cycle is applied outside the DRX short cycle timer. Here, in the DRX short cycle timer, one short DRX cycle becomes a basic unit. At this time, the length of the short-term DRX cycle timer may be 1 to 16, for example. When the terminal is operating in the short-term DRX cycle may be referred to as a short-term DRX mode, when the terminal is operating in the long-term DRX cycle.

The RRC layer manages several timers to control the DRX operation. Timers controlling the DRX operation include a duration timer (onDurationTimer), a DRX inactivity timer (DRxInactivity Timer), a DRX retransmission timer (drxRetransmission Timer).

The duration timer is started by the start of the DRX cycle. In other words, the start of the duration timer coincides with the start of the DRX cycle. The duration timer increases by 1 for every PDCCH subframe. The duration timer expires when the duration timer value becomes equal to a preset expiration value. The duration timer is valid until the duration timer value is equal to the expiration value.

The DRX inactivity timer may be defined as the number of consecutive PDCCH subframes from the time point of successfully decoding the PDCCH for uplink or downlink user data transmission. Since continuous data reception may occur, it is time for the UE to continuously monitor the PDCCH. The DRX Inactivity Timer is started or restarted when the UE successfully decodes the PDCCH for HARQ initial transmission in the PDCCH subframe.

The DRX retransmission timer is a timer that operates based on the maximum number of consecutive numbers of PDCCH subframes for which downlink retransmission is expected by the terminal soon. The DRX retransmission timer is a timer that is started when the retransmission data is not received even though the HARQ RTT timer has expired. The terminal may monitor the reception of data retransmitted in the HARQ process while the DRX retransmission timer is in progress. The setting of the DRX retransmission timer is defined by the MAC-MainConfig message of the RRC layer.

The time that the duration timer, the DRX inactivity timer, or the DRX retransmission timer is in progress is called an active time. Alternatively, the activity time may mean all sections in which the terminal is awake. Non-active time during the DRX cycle may be referred to as non-active time. The active time may be called a wake up interval, and the inactive time may be called a sleep interval. The UE monitors the PDCCH for the PDCCH subframe during the active time. Here, the PDCCH subframe means a subframe including the PDCCH. For example, in TDD configuration, downlink subframes and downlink pilot time slot (DwPTS) subframes correspond to PDCCH subframes. A timer unit of a DRX timer, such as a duration timer, a DRX inactivity timer, or a DRX retransmission timer, is a PDCCH subframe (psf). That is, DRX timers are counted based on the number of PDCCH subframes.

Other parameters to control DRX operation include long DRX cycle (longDRX-Cycle) and DRX start offset (drxStartOffset), and the base station optionally sets DRX short cycle timer (drxShortCycleTimer) and short DRX-cycle (shortDRX-Cycle). Can be. In addition, a HARQ round trip time (RTT) timer is defined for each downlink HARQ process.

The DRX start offset is a value that defines the subframe where the DRX cycle 300 begins. The DRX short cycle timer is a timer that defines the number of consecutive subframes that a UE must follow in a short DRX cycle. The HARQ RTT timer is a timer that defines the minimum number of subframes before the interval in which downlink HARQ retransmission is expected by the UE.

Meanwhile, the DRX configuration information may be received by being included in a MAC-MainConfig message, which is an RRC message used to specify a main configuration of a MAC layer for a signaling radio bearer (SRB) and a data radio bearer (DRB). DRX configuration information may be configured, for example, as shown in the table below.

DRX-Config :: = CHOICE {
release NULL,
setup SEQUENCE {
onDurationTimer ENUMERATED {
psf1, psf2, psf3, psf4, psf5, psf6,
psf8, psf10, psf20, psf30, psf40,
psf50, psf60, psf80, psf100, psf200},
drx-InactivityTimer ENUMERATED {
psf1, psf2, psf3, psf4, psf5, psf6,
psf8, psf10, psf20, psf30, psf40,
psf50, psf60, psf80, psf100,
psf200, psf300, psf500, psf750,
psf1280, psf1920, psf2560, psf0-v1020,
spare9, spare8, spare7, spare6,
spare5, spare4, spare3, spare2,
spare1},
drx-RetransmissionTimer ENUMERATED {
psf1, psf2, psf4, psf6, psf8, psf16,
psf24, psf33},
longDRX-CycleStartOffset CHOICE {
sf10 INTEGER (0..9),
sf20 INTEGER (0..19),
sf32 INTEGER (0..31),
sf40 INTEGER (0..39),
sf64 INTEGER (0..63),
sf80 INTEGER (0..79),
sf128 INTEGER (0..127),
sf160 INTEGER (0..159),
sf256 INTEGER (0..255),
sf320 INTEGER (0..319),
sf512 INTEGER (0..511),
sf640 INTEGER (0..639),
sf1024 INTEGER (0..1023),
sf1280 INTEGER (0..1279),
sf2048 INTEGER (0..2047),
sf2560 INTEGER (0..2559)
},
shortDRX SEQUENCE {
shortDRX-Cycle ENUMERATED {
sf2, sf5, sf8, sf10, sf16, sf20,
sf32, sf40, sf64, sf80, sf128, sf160,
sf256, sf320, sf512, sf640},
drxShortCycleTimer INTEGER (1..16)
} OPTIONAL-Need OR
}
}

Referring to Table 1, the DRX configuration information includes an onDurationTimer field defining a value of a duration timer, a drx-InactivityTimer field indicating a value of a DRX inactivity timer, and a drx-RetransmissionTimer field indicating a value of a DRX retransmission timer. do. In addition, the DRX configuration information includes a longDRX-CycleStartOffset field indicating a length of a long DRX cycle and a starting subframe, and a shortDRX field regarding a short DRX that may be configured as optional. The shortDRX field specifically includes a shortDRX-Cycle subfield indicating the length of a short DRX cycle and a drxShortCycleTimer subfield indicating a value of a short term DRX cycle timer in which the UE is continuous.

The onDurationTimer field may be set to any one of {psf1, psf2, psf3, ... psf200}. psf means a PDCCH subframe, and the number after psf indicates the number of PDCCH subframes. That is, psf represents the expiration value of the timer as the number of PDCCH subframes. For example, if the onDurationTimer field = psf1, the duration timer expires after progressing up to one PDCCH subframe cumulatively including the subframe in which the DRX cycle is started. Or if the onDurationTimer field = psf4, the duration timer expires after progressing up to four PDCCH subframes cumulatively from the start of the DRX cycle. The drx-InactivityTimer field may be set to any one of {psf1, psf2, psf3, ... psf2560}. For example, if the drx-InactivityTimer field = psf3, the DRX Inactivity Timer progresses up to three PDCCH subframes cumulatively including the subframe at the time when it is driven and then expires. The drx-RetransmissionTimer field may be set to any one of {psf1, psf2, psf4, ... psf33}. For example, if the drx-RetransmissionTimer field = psf4, the DRX retransmission timer expires after progressing up to four PDCCH subframes including the subframe at the time when it is driven.

The longDRX-CycleStartOffset field may be set to any one of values of {sf10, sf20, sf32, sf40, ... sf2560} as the length of a long DRX cycle, and the subframe where the long DRX cycle starts is the length of the long DRX cycle. The value may be set to any one of {INTEGER (0..9), INTEGER (0..19), INTEGER (0..31), ... INTEGER (0..2559)}. For example, if the longDRX-CycleStartOffset field = sf20, INTEGER (0..19), one long DRX cycle includes 20 subframes, and the long DRX cycle includes any subframe of subframe indexes 0 to 19. This long term DRX cycle start subframe may be selected. The shortDRX-Cycle subfield constituting the shortDRX field may be set to any one of {sf2, sf5, sf8, ... sf640}. For example, if the shortDRX-Cycle subfield = sf5, one short DRX cycle includes 5 subframes. In addition, the drxShortCycleTimer subfield constituting the shortDRX field may indicate any one of integers 1 to 16. For example, if the drxShortCycleTimer subfield = 3, the short DRX cycle has gone through three times and then expires.

When a handover occurs while the terminal uses the DRX mode, the DRX is designed to operate by dividing the active time and the inactive time, so that a handover command may not be received at the desired time point during the handover. In particular, in the long DRX cycle state, a long inactivity time may cause a delay in receiving a handover command from the terminal, which causes a problem of a handover failure.

In addition, recently, small cells, such as hot cells, cell boundaries, and coverage holes, can be used to enable communication in areas such as small cells. For example, heterogeneous networks (HetNet) systems in which pico cells, femto cells, micro cells, and the like are installed are considered. In a heterogeneous network environment, a macro cell is a large coverage cell, and a small cell such as a femto cell and a pico cell is a small coverage cell. Small cells generally have greater attenuation of signals with distance than macro cells. Therefore, when the UE connected to the small cell leaves the small cell according to the movement, a handover failure may occur due to the rapid attenuation of the radio signal before receiving the handover command, and the UE may be in the DRX mode (especially, the long-term DRX mode). The probability of handover failure can be further increased when in operation.

4 is an example of a handover operation for explaining the present invention.

Referring to FIG. 4, the source base station configures a measurement to be performed by the terminal by transmitting an RRC connection reconfiguration message to the terminal (S400). This may be referred to as measurement control, and the RRC connection reconfiguration message includes measurement configuration information for setting a measurement to be performed by the terminal.

The terminal reports the result of the measurement based on the measurement configuration information to the source base station using a measurement report message (S405). The terminal measures RSRP (Reference Signal Received Power) or RSRQ (Reference Signal Received Quality) based on the measurement configuration information, and includes a measured RSRP or RSRQ value when RSRP or RSRQ of a neighbor cell is above a certain threshold. Report to the base station. Where RSRP represents the average received power of resource elements carrying a cell-specific reference signal within a specific frequency bandwidth, and RSRQ represents the quality of the received reference signal. ). RSRP and RSRQ are used in the handover procedure in the RRC connection (RRC_connection) mode. In addition, RSRP may be used for a cell selection or cell recelection procedure in an RRC idle (RRC_idle) mode.

The source base station determines whether to perform the handover based on the measurement report message (S410). In this case, the time from the handover determination to the time when the handover command (handover command) is sent to the terminal handover preparation phase (handover preparation phase) (S410 handover determination from the time of transmitting the handover command from the base station in S430 or in S4325 Until the base station receives the handover request confirmation message). If it is appropriate not to perform the handover, the following procedure (S410 or less) can be omitted.

If it is determined to perform the handover, the source base station requests the handover to the target base station through the handover request message (S415).

The target base station determines whether to approve the handover based on the handover request message (S420). That is, the target base station performs admission control on whether to approve handover. Even if the source base station decides to perform the handover, the handover is performed only after approval of the target base station.

The target base station transmits a handover request acknowledgment message to the source base station (S425). This informs the source base station whether the target base station has approved the handover. The handover request confirmation message may be referred to as handover approval information or handover request ACK when the handover is approved. On the other hand, the handover request confirmation message may be referred to as handover rejection information or handover request NACK when handover is rejected.

When it is determined to perform the handover, that is, when the handover request ACK message is received, the source base station sends a handover command message to the terminal to command the handover (S430). After the terminal receives the handover command message, the actual handover process is performed. From this time, the handover execution phase (handover execution phase) (S430 from the time when the terminal receives the handover command from the handover in S435) Up to the point at which the target base station receives the confirmation message).

Subsequently, the terminal initiates a procedure for performing the remaining handover from the source base station to the target base station (S435). In more detail, the terminal performs a handover process after the RACH operation in the target base station and transmits a handover confirm message to the target base station.

The handover procedure described by way of example in FIG. 4 may be performed simultaneously with the DRX mode operation described by way of example in FIG. 3. If the terminal does not receive the handover command within a certain time, the signal from the source base station is gradually weakened, which may cause RLF (Radio Link Failure) operation, etc., which may result in a handover failure. That is, the UE may not receive a handover command due to an RLF during the handover preparation phase or a bad link state due to poor channel quality in the handover process, and a handover failure may occur. May occur.

5 is an example of a case where a handover failure occurs to explain the present invention.

Referring to FIG. 5, in view of the radio link monitor process (A), when CQI <Qout, the T310 timer for the RLF is started, and when the T310 expires, the wireless connection fails ( RLF: radio link failure occurs. In terms of the handover process (B), the UE measures the RSRP or RSRQ according to a measurement configuration to measure the RSRP or RSRQ of a neighboring cell above a certain threshold. If is measured, the process proceeds to an event entering condition. In this case, the terminal does not immediately transmit a measurement report message for handover to the base station, but transmits the measurement report message to the terminal after hold for a time to trigger (TTT) period. That is, the measurement report is triggered only when the RSRQ or RSRQ of the neighbor cell is kept above a certain limit during the TTT period after the event occurs. The terminal then receives a handover command through a handover preparation step and performs a handover execution. Therefore, the terminal does not receive a handover command in the handover procedure (B) until the time when T310 expires in the radio connection monitoring procedure (A), that is, RLF, or T310 expires in the radio connection monitoring procedure (A). If the handover command is transmitted in the handover procedure (B) before but the terminal is in a bad link condition that is difficult for the terminal to receive the handover command, the terminal does not receive the handover command and thus the handover failure (handover failure) ) May occur. That is, if a bad link condition detection is detected during the TTT period in the handover procedure B, and then the bad link CQI <Qin is continuously maintained, the terminal cannot receive the handover command. Can be.

In particular, when the UE handovers between the small cell and the macro cell, the time for receiving the handover command may be relatively small due to the rapid decay of signal strength. Therefore, in order to reduce the handover failure situation due to the UE failing to receive the handover command, the UE should be able to receive the handover command as soon as possible. However, when the UE uses DRX, the base station schedules a handover command in consideration of the DRX cycle. In a section configured as a long-term DRX, a handover command may be transmitted to the terminal after the corresponding period.

As described above, such a problem is more likely to occur when the terminal uses the DRX mode. Because the terminal is designed to operate in the DRX mode divided into the active time and inactive time, when the terminal is operating in the inactive time, especially in the long DRX cycle state because of the long inactivity time delay, This is because the UE does not receive the handover command until the time T310 expires, or the UE may enter a bad connection state where the handover command is transmitted before the time T310 expires but it is difficult to receive the handover command. Therefore, DRX reconfiguration considering handover is required to solve this problem.

6 shows an example of a DRX operation according to the present invention. 6 shows a case in which the long-term DRX cycle is 20ms, the duration is 2ms, the short-term DRX cycle is 10ms, and the DRX short-cycle timer is 3. In FIG. 6, one square represents one subframe.

Referring to FIG. 6, an arrow 600 represents an operation of receiving a scheduled PDCCH to a terminal. The UE monitors the PDCCH transmitted in a corresponding subframe in a duration 620. In fact, even if there is no scheduling data (scheduling data) for the terminal, the terminal checks the PDCCH in the duration (620).

If there is a PDCCH for the UE in the duration 620, the UE operates by changing the DRX type from the long-term DRX cycle to the short-term DRX cycle after the DRX inactivity timer ends, after the DRX retransmission timer ends, or after the MAC contention resolution timer ends.

7 shows an example of a DRX operation during handover according to the present invention. In case (a), the UE does not receive a handover command in an RLF (T310 expired) or a bad radio connection state during operation in a long DRX cycle. In case (b), the UE triggers the DRX mode in a short DRX cycle after transmitting a measurement report message indicating the initiation of handover, or the base station transmits a signal of at least 1 bit to shorten the DRX mode. The following example shows triggering on a DRX cycle. (b) shows an example in which the at least 1 bit signal is a DRX Command MAC CE signal.

Referring to FIG. 7, in the case of (a), when the DRX short cycle timer expires, the terminal changes to a long term DRX cycle after the short DRX cycle period. At this time, when the terminal receives a handover command 700 during a long DRX cycle, the terminal 310 expires prior to receiving the handover command 700, thereby causing RLF (Radio Link Failure, 730-1). In some cases, the handover command 700 may not be received due to a bad radio link 730-2. In this case, a handover failure may occur.

On the other hand, in (b), a short DRX cycle period is triggered after the UE transmits the measurement report 750 message indicating the initiation of handover, or the UE has a signal including at least 1 bit of information, for example, a DRX command MAC CE 760. ), The short-term DRX cycle period is triggered, and the terminal maintains the short-term DRX cycle period, for example, until receiving a handover command 770 or for a specific time. Therefore, in this case, the time at which the handover command 770 can be received may be earlier than in the case of (A), and the terminal handovers before the RLF 730-1 occurs or the bad wireless connection 730-2. The likelihood of receiving command 770 increases significantly. In other words, it is possible to minimize the time when the terminal receives the handover command as much as possible to minimize the occurrence of the RLF (730-1) or bad radio connection (730-2). In particular, in the case of a mobile terminal moving at a high speed, the likelihood of occurrence of an RLF 730-1 or a bad wireless connection 730-2 may be significantly reduced.

In the case of (b), the terminal and the base station may operate as follows to transmit the signal including the information of the at least 1 bit from the base station to the terminal so that the terminal operates in the short-term DRX mode.

8 is a flowchart illustrating an operation of maintaining a short DRX cycle during handover according to an embodiment of the present invention.

Referring to FIG. 8, the terminal transmits a measurement report message to the base station (S800). The measurement report message is a message indicating the initiation of handover. When the RSRP or RSRQ value of the neighbor cell is greater than or equal to a threshold, the terminal transmits the measurement report message to the base station. In this case, the base station may determine the measurement report message as an initial message that triggers the handover process.

Even during the handover process, the UE may rapidly weaken the reception power from the serving cell due to the movement. Therefore, it is required to perform a quick handover procedure. On the other hand, the UE may continuously maintain the DRX state during the handover process. That is, the terminal may be operated with a periodicity divided into an on duration or an active time and a non-active time and an inactive time, and thus, when the terminal is operated in a long DRX cycle. An over command may be received with a significant delay, etc. In this case, the RLF or the bad connection state may be lost due to the weakening of the received signal from the serving cell due to the movement of the terminal and the delay due to the long inactive period of the long DRX cycle. Persisting, and eventually failing to receive a handover command, a handover failure may occur.

Therefore, the base station transmits a short DRX keep request message to the terminal after receiving the measurement report message (S820). Here, the short-term DRX maintenance request message is a message including at least 1 bit of information, and is a message that the UE requests to continuously maintain the short-term DRX mode (not to enter the long-term DRX mode). Here, maintaining the short-term DRX mode continuously means that the length of the DRX short-cycle timer is not limited to, e.g., n cycles, but the length of the DRX short-cycle timer is not limited to, or is not limited to, the DRX short-cycle timer. It means to keep. However, for a certain period of time, for example, when a specific timer expires or the UE receives a handover command, the short-term DRX mode may be released.

Alternatively, in consideration of the approximate time for receiving the handover command 770 of the terminal, the DRX short cycle timer may be designated as a specific value to maintain the DRX terminal cycle.

As an example, the short-term DRX maintenance request message is 1 bit, and a value of 1 may indicate that the terminal maintains a short-term DRX mode, and 0 may indicate that the terminal enters the long-term DRX mode. Accordingly, the terminal may maintain the short-term DRX mode based on a value of 1 bit, which is a short-term DRX maintenance request message, or may enter the long-term DRX mode after a certain period of time passes. Of course, what 0 and 1 indicate may change.

As another example, the short-term DRX maintenance request message may be implemented using an existing MAC CE, such as a DRX Command Medium Access Control Control Element (MAC CE), or through a new MAC CE. Or it may be implemented through an RRC (Radio Resource Control) message.

Hereinafter, as an example of a short-term DRX maintenance request message, an RRC connection reconfiguration message including a DRX command MAC CE, a new MAC CE, a DRX short keeping MAC CE, and DRX configuration information will be described. Start the operation.

1. Based on DRX command MAC CE

The DRX command is responsible for stopping or starting a DRX related timer. When the base station receives the measurement report message indicating the start of the handover in S800, the base station may be able to maintain the short-term DRX by transmitting a DRX command MAC CE to the terminal. For example, the terminal configured with the short-term DRX may start or restart the DRX short-cycle cycle timer and use the short-term DRX cycle when the DRX command MAC CE is received after transmitting a measurement report message indicating the initiation of the handover. . The above example may be implemented as follows.

If the DRX Inactivity Timer expires or the DRX Command MAC CE is received in the current subframe:
If short-term DRX cycles are configured:
Start or restart the DRX short cycle timer;
-Use short dRX cycles.
-Otherwise:
Use long-term DRX cycles.

Table 2 is configured to start or restart the DRX short cycle timer when the terminal receives the DRX command MAC CE, and use the short DRX cycle. In addition, when the terminal receives the DRX command MAC CE after transmitting a measurement report message indicating the initiation of handover in S800, the terminal may recognize the DRX command MAC CE to receive the handover command. At this time, the terminal may continuously maintain the short-term DRX mode. However, the UE may use a timer for releasing the short-term DRX mode, or may release the short-term DRX mode when receiving an RRC connection reconfiguration message including a handover command or DRX configuration information. Alternatively, when the RLF occurs because the T310 for the RLF expires, the UE may release the short-term DRX mode.

2.Based on DRX short keeping MAC CE

In addition to the DRX command MAC CE, a new MAC CE may be used to continuously maintain the short-term DRX mode. This is called DRX short-term maintenance MAC CE, and DRX short-term maintenance MAC CE is used to continuously maintain short-term DRX. The MAC CE may be identified whether or not the DRX short-term maintenance MAC CE is based on a Logical Channel IDentifier (LCID) included in a subheader constituting a MAC header. In this case, the LCID identifying the DRX short-term maintenance MAC CE may be configured as follows, for example.

Index LCID values 00000 CCCH 00001-01010 Identity of the logical channel 01011-11010 Reserved 11011 Activation / Deactivation 11100 UE Contention Resolution Identity 11101 Timing Advance Command 11110 DRX Command X DRX short keeping 11111 Padding

Referring to Table 3, X is an index indicating DRX short term maintenance, and may be assigned at least one of reserved values 01011 to 11010 among LCID indexes of the subheader. For example, as shown in Table 4, when the LCID value is 11010, it may indicate that the corresponding MAC CE is a DRX short-term maintenance MAC CE.

Index LCID values 00000 CCCH 00001-01010 Identity of the logical channel 01011-11001 Reserved 11010 DRX short keeping 11011 Activation / Deactivation 11100 UE Contention Resolution Identity 11101 Timing Advance Command 11110 DRX Command 11111 Padding

Of course, if the index is reorganized due to the addition of DRX short-term maintenance, a value other than the reserved value may be assigned to X. Here, when the DRX short-term maintenance MAC CE simply instructs the terminal to maintain the short-term DRX mode, it may not configure a separate MAC CE format. However, if it is desired to add a parameter for the short-term DRX mode to the DRX short-term maintenance MAC CE, the MAC CE may be configured as follows.

9 shows a DRX short-term maintenance MAC CE to which the present invention is applied.

Referring to FIG. 9, the DRX short-term maintenance MAC CE 90 may be configured as 8 bits, and may be divided into a short DRX cycle (SC) 900 and a short DRX timer 950 (ST). The SC 900 and the ST 950 may be configured with 4 bits, respectively. That is, the SC 900 and the ST 950 have values of the indexes 0 to 15, respectively.

In the case of the SC, each index may indicate the number of subframes (sf: subframes) constituting a short DRX cycle. For example, index 0 = sf2, 1 = sf5, 2 = sf8, 3 = sf10, 4 = sf16, 5 = sf20, 6 = sf32, 7 = sf40, 8 = sf64, 9 = sf80, 10 = sf128, 11 = sf160, 12 = sf256, 13 = sf320, 14 = sf512, and 15 = sf640.

In the case of ST, each index can represent the number of repetitions of a short DRX cycle. For example, 0 = drxShortCycleTimer 1, 1 = drxShortCycleTimer 2,... , 15 = drxShortCycleTimer 16.

3. Based on DRX reconfiguration message

In order to maintain short-term DRX, an RRC reconfiguration message including DRX configuration information may be used. The RRC reconfiguration message may include short term DRX related information to reconfigure short term DRX as follows.

shortDRX SEQUENCE {
shortDRX-Cycle ENUMERATED {
sf2, sf5, sf8, sf10, sf16, sf20,
sf32, sf40, sf64, sf80, sf128, sf160,
sf256, sf320, sf512, sf640},
drxShortCycleTimer INTEGER (0.1..16)
} OPTIONAL-Need OR

Table 5 shows the DRX parameters in the RRC connection reconfiguration message. Referring to Table 5, the DRX short cycle timer (drxShortCycleTimer) is a value corresponding to the number of times to repeat the short DRX cycle, for example, an infinite number of short-term DRX iterations may be performed by adding a value of zero. have. Or in this case, an operation of DRX off to be described later may be performed. As another example, the DRX short cycle timer may be set to a specific value from 1 to 16 so that the short term DRX is maintained only for a predetermined period.

Referring to FIG. 8 again, the terminal maintains a short-term DRX mode based on the short-term DRX maintenance request message (S840). At this time, the terminal continuously maintains the short-term DRX mode. Therefore, in this case, the terminal enters the long-term DRX interval, thereby reducing the possibility that the terminal cannot receive the handover command in time or within a predetermined time. This can significantly reduce the possibility of handover failure. However, the terminal may operate a timer for the short-term DRX mode, or may release the short-term DRX mode when the terminal receives the handover command.

Thereafter, the base station may transmit a handover command to the terminal. The handover command is a message instructing the terminal to perform a handover. Since the terminal is operating in the short-term DRX mode based on the short-term DRX maintenance request message, it is more likely to receive a handover command before the RLF or the bad connection state is maintained as compared with the case in the long-term DRX mode. The terminal receiving the handover command may handover to the target eNB, and at this time, the DRX configuration may be set again at the target base station after the handover.

On the other hand, when the terminal maintains the short-term DRX mode until receiving the handover command, if the base station decides not to transmit the handover command or if the base station transmits a handover command but the terminal does not receive Short-term DRX mode may continue to be maintained. Therefore, if the base station decides not to send a handover command, there is a need to terminate the short-term DRX mode by sending a specific signal, or to set the short-term DRX mode to be maintained for a certain period of time rather than until the handover command is received. do. That is, when the short-term DRX mode is maintained unnecessarily, it may cause battery consumption of the terminal. Therefore, the terminal or the base station should release the short-term DRX mode or switch to the long-term DRX mode at an appropriate time.

There are various embodiments that may release the short term DRX mode. For example, the terminal may maintain the short-term DRX mode only for a certain period of time, and may operate a timer for terminating the short-term DRX mode after that period. As another example, even if the short-term DRX mode is configured to be maintained for a certain period, the terminal may terminate the short-term DRX mode by receiving a specific signal from the base station.

FIG. 10 is a flowchart illustrating a case in which a handover reception timer is operated as a timer for continually maintaining the short term DRX mode according to an embodiment of the present invention.

Referring to FIG. 10, operations of S1000 and S1020 are the same as operations of S800 and S820 of FIG. 8.

The terminal continuously maintains the short-term DRX mode on the basis of the short-term DRX maintenance request message (S1040). However, the terminal may release the continuous maintenance of the short-term DRX mode. To this end, in addition to the method of setting the short-term DRX cycle timer value to a specific value based on a MAC CE or RRC message, the UE may operate a handover reception timer. Here, the handover reception timer may be started when receiving the short term DRX maintenance request message after transmitting the measurement report message for initiating the handover, or may be started when the maintenance of the short term DRX is determined. And may receive an expired handover command. Of course, even in this case, even if the handover command is received, it does not expire immediately, and it is natural that the handover reception timer may continue. The handover reception timer value may be set to a predetermined time by the terminal or the base station in consideration of the time during the handover preparation phase. For example, when the minimum value of the time taken during the handover preparation step is 30 ms, the terminal or the base station may set the handover reception timer to a value larger than 30 ms.

When the handover reception timer expires without receiving the handover command, the terminal reports that the handover command reception failure has been terminated by the terminal to maintain the short-term DRX mode (S1060). That is, in this case, the terminal no longer maintains the short-term DRX mode and may use the short-term DRX or the long-term DRX mode.

In addition, the terminal may use T310 to maintain the short-term DRX mode for a certain period of time.

11 is a flowchart illustrating a case in which T310 is used as a timer for terminating short-term DRX mode maintenance according to an embodiment of the present invention.

Referring to FIG. 11, operations of S1100 to S1120 are the same as those of S800 and S820 of FIG. 8.

The terminal continuously maintains the short-term DRX mode on the basis of the short-term DRX maintenance request message (S1040). At this time, the terminal may release the continuous maintenance of the short-term DRX mode. In this case, the UE may release the short-term DRX mode on the basis of T310 which is used to determine the RLF situation (S1060). That is, since the UE may determine that an RLF has occurred when T310 expires, it is no longer necessary to maintain the short-term DRX mode for receiving a handover command, and the terminal may use the short-term DRX or long-term DRX mode.

In addition, the terminal may release the short-term DRX maintenance by receiving a specific signal from the base station during the continuous maintenance of the short-term DRX mode. For example, when the UE receives an RRC connection reconfiguration message including the DRX configuration information during short-term DRX maintenance, the UE may operate as follows.

12 is an example of a DRX mode change by an RRC reconfiguration message during continuous maintenance of a short-term DRX mode according to an embodiment of the present invention.

Referring to FIG. 12, operations of S1200 to S1240 are the same as operations of S800 to S840 of FIG. 8.

The terminal receives an RRC connection reconfiguration message including the DRX configuration information from the base station during the continuous maintenance of the short-term DRX mode (S1250). In this case, the terminal changes the DRX related configuration based on the RRC connection reconfiguration message. As a result, the short-term DRX maintenance may be released (S1260).

On the other hand, even if the DRX mode is changed from the long-term DRX mode to the short-term DRX mode, there is still a possibility of handover failure due to the DRX operation, although less time than in the long-term DRX mode, because there is an inactivity time. do. Accordingly, the UE and the base station may turn off the DRX mode during the handover process. That is, the terminal may continuously maintain a wake-up state for monitoring the PDCCH.

13 illustrates a DRX off operation during handover during a DRX operation according to an embodiment of the present invention.

Referring to FIG. 13, the terminal transmits a measurement report (Measurement Repor, 1300) message to the base station. The measurement report message is a message indicating the initiation of handover. When the UE performs a measurement for handover and the RSRP or RSRQ of a neighbor cell is greater than or equal to a threshold, the measurement report is measured. 1300) to the base station. In this case, the terminal may turn off the DRX operation to receive the handover command 1340 from the base station. In the DRX off section 1320, the battery consumption of the UE may be larger than that of the short-term DRX mode. However, since the handover command 1340 may be always received, the probability of a handover failure may be reduced.

If the handover is normally made to the target base station after receiving the handover command 1340, the DRX configuration before the handover is unnecessary, and the terminal will follow the DRX configuration at the target base station after the handover. .

14 is a flowchart illustrating a DRX off operation during handover according to an embodiment of the present invention. This is a flowchart of DRX operation of a terminal and a base station according to the scenario of FIG. 13.

Referring to FIG. 14, the terminal transmits a measurement report message to the base station (S1400). The measurement report message is a message indicating the initiation of handover, and when the RSRQ or RSRQ value of the neighbor cell is greater than or equal to a certain threshold, the terminal transmits the measurement report message to the base station. In this case, the base station may determine the measurement report message as an initial message that triggers the handover process.

Even during the handover process, the UE may rapidly weaken the reception power from the serving cell due to the movement. Therefore, it is required to perform a quick handover procedure. On the other hand, the UE may continuously maintain the DRX state during the handover process. That is, the terminal may be operated with periodicity divided into on duration and inactivity intervals. Therefore, when the terminal is operating in the inactive period, a handover command or the like may be received with a significant delay. In this case, due to the weakening of the received signal from the serving cell due to the movement of the terminal and the delay due to the inactive period of the DRX cycle, the RLF or the bad connection state is maintained, and thus, the handover command is not received and thus the handover fails. failure may occur.

Therefore, the terminal may turn off the DRX operation after transmitting the measurement report message (S1420).

Thereafter, the terminal receives a handover (HO) command from the base station (S1440). In this case, since the terminal is in the DRX off state, it can be regarded as substantially operating in the activity section at all times, and can receive a handover command without a delay time.

After receiving the handover command, the terminal hands over to the target base station (S1460).

 Meanwhile, as shown in FIG. 14, after the UE reports the measurement triggering the handover process, the UE and the BS may operate the DRX off when receiving a specific signal including at least 1 bit of information instead of unconditionally operating the DRX off. have. If the specific signal is a DRX off request message, it may be represented as follows.

15 illustrates a DRX off operation according to a DRX off request message according to an embodiment of the present invention.

Referring to FIG. 15, unlike FIG. 13, in FIG. 15, the UE does not operate as a DRX off unconditionally after a measurement report for initiating handover progress, and then DRX off after receiving a DRX off request message 1500. That's the way. The DRX off request message may be implemented using an existing MAC CE such as a DRX command MAC CE or a new MAC CE such as a DRX stop MAC CE. Or it may be implemented through an RRC message. For example, when the DRX off request message is a DRX command MAC CE, the UE and the base station may operate as DRX off from the time when the DRX command MAC CE is received, and the time point when the base station transmits the DRX command MAC CE to the base station. May be determined by the base station in consideration of the transmission time of the handover command 1550.

In order to transmit the DRX off request message 1500 including the above information and at least 1 bit from the base station to the terminal so that the terminal operates in DRX off, the terminal and the base station may operate as follows.

16 is a flowchart illustrating an operation of turning off DRX during handover according to an embodiment of the present invention.

Referring to FIG. 16, the terminal transmits a measurement report message to the base station (S1600). If the RSRQ or RSRQ value of the neighbor cell is more than a certain threshold, the terminal transmits the measurement report message to the base station. In this case, the base station may determine the measurement report message as an initial message that triggers the handover process.

Even during the handover process, the UE may rapidly weaken the reception power from the serving cell due to the movement. Therefore, it is required to perform a quick handover procedure. On the other hand, the UE may continuously maintain the DRX state during the handover process. That is, the terminal may be operated with periodicity divided into an active time (or a duration) and an inactive (non-active) period. Therefore, when the terminal is operating in the inactive section (operating in the inactive section of the patent long-term DRX mode), a handover command or the like may be received with a significant delay. In this case, due to the weakening of the received signal from the serving cell due to the movement of the terminal and the delay due to the inactivity interval, the RLF or the bad connection state is maintained, and thus, a handover failure is not received because the handover command is not received. May occur.

Therefore, the base station transmits a DRX off request message to the terminal after receiving the measurement report message (S1620). Here, the DRX off request message is a message including at least 1 bit of information, so that the terminal maintains DRX off (ie, always active) for a certain period of time, for example, until a specific timer expires or until the terminal receives a handover command. Message). The DRX off request message may be implemented using an existing MAC CE, such as a DRX Command Medium Access Control Control Element (MAC CE), or through a new MAC CE. Or it may be implemented through an RRC (Radio Resource Control) message.

Hereinafter, as an example of the DRX off request message, the operation of the DRX command MAC CE, the DRX stop MAC CE which is a new MAC CE, and the DRX reconfiguration message, which is an RRC message, are started.

1. Based on DRX command MAC CE

When the terminal receives the DRX command MAC CE, that is, when the DRX command MAC CE is received after transmitting the DRX command MAC CE for initiating the handover process, the terminal may determine that the DRX off operation is required. This is to receive a handover command without delay. Accordingly, when the terminal receives the DRX command MAC CE, the terminal may perform a DRX off operation.

2.Based on DRX stop MAC CE

In addition to the DRX command MAC CE, a new MAC CE may be used for the UE to perform a DRX off operation. This is called DRX stop MAC CE, which is used to turn off short-term DRX. The MAC CE may be identified whether or not it is a DRX stop MAC CE based on a Logical Channel IDentifier (LCID) included in a subheader constituting a MAC header. The LCID identifying the DRX stop MAC CE may be configured as follows, for example.

Index LCID values 00000 CCCH 00001-01010 Identity of the logical channel 01011-11010 Reserved 11011 Activation / Deactivation 11100 UE Contention Resolution Identity 11101 Timing Advance Command 11110 DRX Command Y DRX stop 11111 Padding

Referring to Table 6, Y is an index indicating a DRX stop and may be assigned at least one of values reserved from 01011 to 11010 in the LCID index of the subheader. This is shown in Table 7 below.

Index LCID values 00000 CCCH 00001-01010 Identity of the logical channel 01011-11001 Reserved 11010 DRX stop 11011 Activation / Deactivation 11100 UE Contention Resolution Identity 11101 Timing Advance Command 11110 DRX Command 11111 Padding

Of course, when the index is reorganized due to the addition of the DRX stop, it is natural that the value Y may be assigned a value other than the current reservation value.

3. Based on DRX reconfiguration message

In order for the UE to perform a DRX off operation, an RRC connection reconfiguration (DRX reconfiguration) message including DRX configuration information may be used. The RRC reconfiguration message may include information related to DRX off so that the UE can perform DRX off.

Referring back to FIG. 16, the terminal performs a DRX off based on the DRX off request message (S1640). In this case, since the UE can continuously monitor the PDCCH, the possibility of handover failure can be significantly reduced.

The base station transmits a handover command to the terminal (S1660). The handover command is a message instructing the terminal to perform a handover. Since the terminal is operating in the DRX off, compared to the case of operating in the long-term or short-term DRX mode, the possibility of receiving a handover command before the RLF or bad connection state is maintained. The terminal receiving the handover command may handover to the target eNB, and at this time, the DRX configuration may be set again at the target base station after the handover.

On the other hand, when the terminal maintains the DRX off until the handover command is received, if the base station decides not to transmit the handover command or if the base station transmits the handover command but the terminal does not receive the DRX off continues Can be maintained. Therefore, in this case, if the base station decides not to send a handover command, it is necessary to send a specific signal to terminate the DRX off, or to set the DRX off to be maintained for a certain period of time, not until the handover command is received. exist. In other words, if the DRX off continues to be maintained unnecessarily, the terminal or the base station should release the DRX off or switch to the long-term or short-term DRX mode at an appropriate time since it may cause battery consumption of the terminal.

There are various embodiments that can release DRX off. For example, the terminal may maintain the DRX off only for a certain period of time, and may operate a timer for terminating the DRX off after that period. As another example, even when the DRX off is set to be maintained for a period of time, a specific signal may be transmitted to terminate the DRX off halfway. The timer or the specific signal may be a handover reception timer, an RRC connection reconfiguration message including T310 or DRX configuration information, as described with reference to FIGS. 10 to 12.

17 shows an example of a handover procedure to which a DRX operation is applied according to the present invention.

Referring to FIG. 17, the terminal transmits a measurement report message to the base station (S1700). The measurement report message is a message indicating the initiation of handover. When the UE performs a measurement for handover and the RSRQ or RSRQ value of the neighbor cell is greater than or equal to a threshold, the UE instructs to initiate handover. A measurement report message is generated and transmitted to the source base station.

The source base station determines to perform the handover based on the measurement report message (S1710).

The source base station transmits a short DRX keep request message to the terminal (S1720). Here, the short term DRX maintenance request message may include a DRX command MAC CE, a DRX short term maintenance MAC CE, or a DRX reconfiguration message as described in FIG. 8. Of course, omit S1720, and when the terminal generates the measurement report message indicating the start of the handover in S1700 and transmits to the source base station, as described above, the terminal may maintain the short-term DRX mode itself.

Although S1720 is shown after S1710 in FIG. 17, S1720 may be performed at any point between S1700 and S1770.

The UE keeps keeping the short-term DRX mode based on the short-term DRX maintenance request message in operation S1730. However, the UE may release the continuous maintenance of the short-term DRX mode in certain cases. As an example, the specific case may be until the handover command is received. In addition, the specific case may be when the handover reception timer or T310 expires or when the RRC connection reconfiguration message including the DRX configuration information is received as described with reference to FIGS. 10 to 12.

The source base station requests a handover to the target base station through a handover request message (S1740).

The target base station determines to approve the handover based on the handover request message (S1750). Even if the source base station decides to perform the handover, the handover is performed only after approval of the target base station.

When the target base station allows the handover, the target base station transmits a handover request ACK message to the source base station (S1760).

Based on the handover request ACK message, the source base station determines to perform the handover and transmits a handover command to the terminal (S1770).

Upon receiving the short term handover command, the terminal releases the continuous maintenance of the short term DRX mode (S1780). Subsequently, the terminal initiates a procedure for performing the remaining handover from the source base station to the target base station (S1790).

18 shows another example of a handover procedure to which a DRX operation is applied according to the present invention.

Referring to FIG. 18, the terminal transmits a measurement report message to the base station (S1800). The measurement report message is a message instructing the initiation of handover, and the UE instructs the initiation of handover when the RSRQ or the RSRQ value of the neighbor cell is greater than or equal to a threshold by performing a measurement for handover. A measurement report message is generated and sent to the source base station.

The source base station determines to perform the handover based on the measurement report message (S1810).

The source base station transmits a DRX Off request message to the terminal (S1820). Here, the DRX off request message may include an RRC connection reconfiguration message including a DRX command MAC CE, a DRX stop MAC CE, or DRX configuration information as described in FIG. 16. Of course, when omitting S1820 and the terminal generates a measurement report indicating the handover start in S1800 and transmits to the source base station, the terminal may perform DRX off by itself as described with reference to FIGS. 13 to 14. .

Although S1820 is shown after S1810 in FIG. 18, S1820 may be performed at any point between S1800 and S1870.

The terminal turns off DRX based on the DRX off request message (S1830). However, the UE may release the DRX off in a specific case. For example, the specific case may be when the terminal receives a handover command. In addition, the specific case may be when a handover reception timer or T310 expires or when an RRC connection reconfiguration message including DRX configuration information is received as described with reference to FIGS. 10 to 12.

The source base station requests a handover to the target base station through a handover request message (S1840).

The target base station may determine not to approve the handover based on the handover request message (S1850).

If the target base station determines not to approve the handover, it transmits a handover request NACK (NACK) message to the source base station (S1860).

When receiving the handover request NACK message, the base station may transmit an RRC connection reconfiguration message including the DRX configuration information to the terminal (S1870). Here, the base station transmitting the RRC connection reconfiguration message to the terminal is for releasing the DRX off state maintained in S1830 as described in FIG. 12. Of course, even if the base station does not transmit the RRC connection reconfiguration message, the terminal does not receive the RRC connection reconfiguration message, as described in Figures 10 to 11 when the handover reception timer or T310 expires, the terminal itself is the DRX off The state can be released as described above.

Upon receiving the DRX reconfiguration message, the terminal releases the DRX off (S1730). In this case, the UE may return to the long-term DRX mode or change the detailed DRX configuration according to the DRX configuration information included in the RRC connection reconfiguration message.

19 is a block diagram of a terminal and a base station for performing handover and DRX operations according to an embodiment of the present invention.

Referring to FIG. 19, the terminal 1900 includes a receiver 1905, a terminal processor 1910, and a transmitter 1920. The terminal processor 1910 further includes a DRX processor 1911 and a HO processor 1912.

The receiver 1905 receives a short-term DRX maintenance request message or a DRX off request message or a DRX reconfiguration message from the base station. Here, the short term DRX maintenance request message may include, for example, a DRX command MAC CE, a DRX short term maintenance MAC CE, or an RRC connection reconfiguration message as described in FIG. 8. The DRX off request message may include, for example, a DRX command MAC CE, a DRX stop MAC CE, and an RRC connection reconfiguration message as described in FIG. 16.

In addition, the receiver 1905 receives a handover command from the base station.

The DRX processor 1911 controls the DRX operation of the terminal based on a preset DRX parameter.

The DRX processing unit 1911 reconfigures DRX based on the DRX maintenance request message or the DRX off request message. In addition, the DRX processor 1911 manages an active time in a DRX cycle. The receiver 1905 monitors the physical downlink PDCCH subframe transmitted from the base station 1950 during the active time.

The DRX processor 1911 may continuously maintain the DRX mode in the short term DRX mode based on the received DRX maintenance request message. Alternatively, the DRX processor 1911 may turn off the DRX based on the DRX off request message.

In addition, when the HO processor 1912 generates or transmits a measurement report message indicating the initiation of handover to the transmitter 1920, the DRX processor 1911 continuously maintains the short-term DRX mode or DRX itself. OFF can be performed.

In addition, the DRX processing unit 1911 may release the continuous maintenance or the DRX off of the short-term DRX mode. For example, the DRX processor 1911 may release the short-term DRX mode or the continuous maintenance of the DRX off when the terminal 1900 receives a handover command from the base station. As another example, the DRX processing unit 1911 may release the short-term DRX mode continuous maintenance or DRX off when the handover reception timer or T310 expires, or receive an RRC connection reconfiguration message including the DRX configuration information from the base station. The short-term DRX mode may be kept in a continuous state or may be out of the DRX. The operation of continuously maintaining the short-term DRX mode or releasing the DRX off may include S1060 of FIG. 10, S1160 of FIG. 11, and S1250 and S1260 of FIG. 12.

The HO processor 1912 generates a measurement report message and transmits the measured report message to the transmitter 1920. The measurement report message is a message for instructing the initiation of handover. If the UE performs a measurement for handover and the RSRQ or RSRQ value of the neighbor cell is greater than or equal to a threshold, the UE instructs to initiate handover. The measurement report message is generated and transmitted to the transmission unit 1920.

In addition, the HO processor 1912 may perform a handover to the target base station based on the handover command received from the base station.

The transmitter 1920 transmits a measurement report message indicating the initiation of handover generated by the HO processor 1912 to the base station 1950.

The base station 1950 includes a transmitter 1955, a receiver 1960, and a base station processor 1970. The base station processor 1970 includes a DRX processor 1971 and a HO processor 1972.

The receiving unit 1960 receives a measurement report message indicating the initiation of handover from the terminal.

The DRX processing unit 1971 generates a short-term DRX maintenance request message or a DRX off request message based on the measurement report message and sends it to the transmission unit 1955. Here, the short term DRX maintenance request message may include, for example, a DRX command MAC CE, a DRX short term maintenance MAC CE, or a DRX reconfiguration message as described in FIG. 8. The DRX off request message may include, for example, a DRX command MAC CE, a DRX stop MAC CE, and a DRX reconfiguration message as described in FIG. 16.

In addition, the DRX processing unit 1971 may generate a DRX reconfiguration message and send it to the transmission unit 1955. Here, the DRX reconfiguration message may be used as a message for releasing short-term DRX maintenance or a message for releasing DRX off as described in FIG. 12.

The HO processor 1972 proceeds with the rest of the handover procedure based on the received measurement report message. For example, the HO processor 1922 determines to perform a handover after receiving a measurement report message, and transmits a handover request to the target base station. When the base station 1970 receives the handover request accept message from the target base station, the HO 1922 processor generates a handover command and transmits the handover command to the terminal 1900 through the transmitter 1955.

The transmitter 1955 transmits a short term DRX maintenance request message or a DRX off request message or a DRX reconfiguration message to the terminal 1900. In addition, the transmitter 1955 transmits a handover command to the terminal 1900. The short-term DRX maintenance request message or the DRX off request message may be transmitted to the terminal after the receiver receives the measurement report message and before the transmitter transmits the handover command to the terminal.

In the present invention described above, the terminal is a macrocell to a macrocell, a macrocell to a picocell, a picocell to a macrocell, a femtocell to a macrocell, a macrocell to a femtocell, a femtocell to a femtocell, and a picocell to a picocell As in the case of moving, it may be applied to the case where the terminal moves between the same cell or between different types of cells.

The above description is merely illustrative of the technical idea of the present invention, and those skilled in the art to which the present invention pertains may make various modifications and changes without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

Claims (16)

A terminal for performing a discontinuous reception (DRX) operation in consideration of handover in a wireless communication system,
A HO processor for generating a measurement report message indicating the initiation of a handover;
A transmitter for transmitting the measurement report message to a base station;
A DRX processor that controls a DRX operation of the terminal based on a preset DRX parameter; And
A receiver for monitoring the physical downlink PDCCH subframe transmitted from the base station for the active time defined in the DRX operation,
The DRX processing unit may initiate the continuous maintenance of the short-term DRX mode or the DRX off in the handover preparation step, and when the timer related to the handover reception timer or the radio connection failure expires during the handover preparation step, The terminal, characterized in that the continuous maintenance of the short DRX mode or to release the DRX off. The method of claim 1,
The DRX processing unit, characterized in that when the transmission unit transmits the measurement report message to the base station, the continuous maintenance of the short-term DRX mode or the DRX off. The method of claim 1,
Further comprising a receiving unit for receiving a short-term DRX maintenance request message or DRX off request message from the base station,
The DRX processing unit, characterized in that for continuing the maintenance of the short-term DRX mode or the DRX off based on the received short-term DRX maintenance request message or DRX off request message. The method of claim 3, wherein
The short term DRX maintenance request message is at least one of a DRX command medium access control (MAC) control element (CE), a DRX short term maintenance MAC CE, or an RRC connection reconfiguration message.
The DRX off request message is characterized in that at least one of DRX command MAC CE, DRX stop MAC CE, or DRX reconfiguration message. delete delete delete delete In the DRX method considering the handover by the terminal in a wireless communication system,
Generating a measurement report message indicating the initiation of a handover;
Transmitting the measurement report message to a base station;
Controlling a DRX operation of the terminal based on a preset DRX parameter; And
Monitoring a physical downlink PDCCH subframe transmitted from the base station for an active time defined in the DRX operation;
The terminal, during the handover preparation phase, initiates the continuous maintenance of the short-term DRX mode or DRX off, and when the handover reception timer or the timer related to the radio connection failure expires during the handover preparation phase, the short-term DRX mode, characterized in that the continuous maintenance of the DRX mode or to release the DRX off. The method of claim 9,
When the measurement report message is sent to a base station, continuing the short-term DRX mode or initiating the DRX off. The method of claim 9,
Receiving a short term DRX maintenance request message or a DRX off request message from the base station; And
And continuing the maintenance of the short term DRX mode or the DRX off based on the received short term DRX maintenance request message or DRX off request message. The method of claim 11,
The short term DRX maintenance request message is at least one of a DRX command MAC CE, a DRX short term maintenance MAC CE, or a DRC reconfiguration message.
The DRX off request message is at least one of a DRX command MAC CE, DRX stop MAC CE, or RRC connection reconfiguration message. delete delete delete delete

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