KR102514379B1 - Method and apparatus for handover in wireless communication system - Google Patents

Abstract

In the handover preparation step performed between the source base station and the target base station, when the terminal receives a prior random access command from the source base station to which the terminal is currently connected through L2 (Layer2) signaling, in the handover preparation step, the prior random access command According to the access command, a random access procedure with the target base station is performed.

Description

Handover method and apparatus in wireless communication system {METHOD AND APPARATUS FOR HANDOVER IN WIRELESS COMMUNICATION SYSTEM}

The present invention relates to a handover method and apparatus in a wireless communication system, and more particularly, to a handover method and apparatus capable of minimizing data interruption time that occurs when a terminal performs handover in a wireless communication system. it's about

In a wireless communication system such as LTE (Long Term Evolution), the handover procedure of a terminal performing handover from a source base station to a target base station includes a handover preparation step and a handover (Handover Execution) step.

In the handover preparation step, the source base station receives a handover call acceptance from the target base station, and then transmits a handover command message to the corresponding terminal. In the handover step, the terminal disconnects from the source base station, adjusts downlink synchronization for a communication connection with the target base station, receives system information from the target base station, and then performs a random access procedure. After completing the random access procedure with the target base station, the terminal transmits a handover complete message to the target base station through uplink resources allocated from the target base station through the random access procedure, and then transmits and receives data with the target base station.

In this handover procedure, the time from when the terminal disconnects from the source base station to when the handover complete message is transmitted to the target base station through uplink resources allocated from the target base station is the data interruption time. That is, the data interruption time that occurs during the handover performance phase of the terminal is mainly due to the random access procedure for the terminal to allocate uplink resources necessary for timing advance and transmission of the handover complete message to the target base station. .

Since the data interruption time that occurs when performing a general handover in such a 3GPP LTE system is the time when the terminal loses all connections with the source base station and the target base station, it negatively affects the service quality of the terminal running latency-sensitive applications. give.

An object to be solved by the present invention is to provide a handover method and apparatus capable of reducing data interruption time caused by a random access procedure with a target base station in the handover performing step.

According to one embodiment of the present invention, a method for performing handover in a terminal of a wireless communication system is provided. The handover method includes, in a handover preparation step performed between a source base station and a target base station to which the terminal is currently connected, receiving a pre-random access command from the source base station through L2 (Layer 2) signaling, and the handover preparation step. , performing a random access procedure with a target base station according to the prior random access command.

The advance random access command may include a cell identifier of the target base station and a random access channel configuration index indicating random access channel configuration information of the target base station.

One unused logical channel identifier among logical channel identifiers for the downlink common channel transmitted by the source base station may be used as the advance random access command.

The handover method further comprises receiving system information from the source base station, wherein random access channel configuration information of a plurality of cells in the wireless communication system is mapped to a plurality of random access configuration indices, respectively, and the system information is It may include mapping information between the plurality of random access channel configuration information and the plurality of random access configuration indexes.

The handover method may further include receiving system information including random access channel configuration information of a plurality of cells in the wireless communication system from the source base station.

The performing of the random access procedure includes temporarily stopping communication with the source base station, and transmitting a random access preamble corresponding to a predefined preamble index to the target base station for random access in the handover preparation step. After that, it may include immediately resuming communication with the source base station.

The performing of the random access procedure further includes receiving a random access response message from the target base station, and the random access response message is sent from the source base station in a handover performed between the terminal and the target base station. It may be received through a received handover command message.

In the handover preparation step, the source base station transmits a handover request message to the target base station, and the target base station accepting the handover of the terminal transmits the handover request acceptance message to the source base station, The handover request message includes the predefined preamble index, the handover request accept message includes the random access response message, and in the handover performing step, from a source base station receiving the handover request accept message. The method may further include receiving the handover command message.

The handover method includes receiving a handover command message from the source base station after the random access procedure, communicating with the source base station until a start time of uplink resources pre-allocated from the target base station through the random access procedure. After continuing, terminating the connection with the source base station, and transmitting a handover complete message to the target base station through the pre-allocated uplink resource.

According to another embodiment of the present invention, a method for performing handover in a terminal of a wireless communication system is provided. In the handover method, when the handover preparation step performed between the source base station and the target base station to which the terminal is currently connected is completed, the cell identifier and preamble index of the target base station and the random access channel of the target base station are received from the source base station. Receiving a handover command message including configuration information, temporarily suspending communication with the source base station, transmitting a random access preamble to the target base station based on the preamble index, and immediately resuming communication with the source base station and receiving a random access response message from the target base station through the source base station.

The random access response message received through the source base station indicates allocation information of uplink resources allocated by the target base station, a cell identifier of the target base station added by the source base station, and a communication end point with the source base station. time information, and the handover method includes terminating a connection with the source base station based on the time information, and transmitting a handover completion message to the target base station through the pre-allocated uplink resource. do.

In the handover preparation step, the source base station transmits a handover request message to the target base station, and the target base station accepting the handover of the terminal transmits the handover request acceptance message to the source base station, The handover request acceptance message may include a cell identifier and preamble index of the target base station, and random access channel configuration information of the target base station.

The stopping may include stopping communication with the source base station in a transmission period of a random access preamble according to random access channel configuration information of the target base station.

According to another embodiment of the present invention, an apparatus for handover of a terminal in a wireless communication system is provided. The handover device includes a processor and a transceiver. For handover to the target base station, the processor temporarily suspends the connection with the source base station currently connected to the terminal, transmits a random access preamble to the target base station, immediately resumes communication with the source base station, and the target base station After continuing communication with the source base station until the start time of the allocated uplink resources, the connection with the source base station is terminated, and handover completion is notified to the target base station through the allocated uplink resources. And the transceiver is connected to the processor to transmit and receive radio signals with the source base station and the target base station.

The processor is predefined for random access in the handover preparation step according to a prior random access command received through L2 (Layer2) signaling from the source base station in the handover preparation step performed between the source base station and the target base station. A random access preamble corresponding to the specified preamble index is transmitted to the target base station, and the prior random access command may include a cell identifier of the target base station and a random access channel configuration index indicating random access channel configuration information of the target base station. there is.

Random access channel configuration information of a plurality of cells in the wireless communication system is mapped to a plurality of random access configuration indices, respectively, and mapping information between the plurality of random access channel configuration information and the plurality of random access configuration indices is provided through system information. It may be received from the source base station.

The processor receives a random access response message including uplink resource allocation information from the target base station through the transceiver, and the random access response message is transmitted from the source base station in a step of performing a handover between the terminal and the target base station. It may be received through a handover command received from the base station.

One unused logical channel identifier among logical channel identifiers for the downlink common channel transmitted by the source base station may be used as the advance random access command.

After the handover preparation step performed between the source base station and the target base station is completed, the processor transmits the random access preamble to the target base station in the step of performing handover between the terminal and the target base station, and transmits the random access preamble from the target base station. A random access response message including allocation information of the uplink resource may be received through the source base station.

The random access response message by the source base station further includes a cell identifier of the target base station and time information indicating an end point of communication with the source base station, and the processor terminates the connection with the source base station based on the time information. and transmit the handover completion.

According to an embodiment of the present invention, the data interruption time in the handover execution step can be reduced, and the data interruption time occurring through performing random access in the handover preparation step can also be greatly reduced compared to the existing invention.

1 is a diagram illustrating a handover procedure in an existing LTE system.
2 is a diagram illustrating a handover method according to the first embodiment of the present invention.
3 is a diagram illustrating a DL-SCH header and an LCID index defined in the existing 3GPP standard.
4 is a diagram showing an example of a pre-random access command (pre-RACH Command) according to an embodiment of the present invention.
5 is a diagram illustrating an example of a MAC CE of a pre-RACH Command according to an embodiment of the present invention.
6 is a flowchart illustrating an operation of a terminal in the handover preparation step described in FIG. 2 .
7 is a flowchart illustrating an operation of a terminal in the step of performing handover described in FIG. 2 .
8 is a diagram explaining a handover method according to a second embodiment of the present invention.
9 is a flowchart illustrating an operation of a terminal in the handover performance step described in FIG. 8 .
10 is a diagram illustrating a handover device of a terminal according to an embodiment of the present invention.

Hereinafter, with reference to the accompanying drawings, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. And in order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, and similar reference numerals are attached to similar parts throughout the specification.

Throughout the specification and claims, when a certain component is said to "include", it means that it may further include other components without excluding other components unless otherwise stated.

Throughout the specification, a terminal includes a mobile terminal (MT), a mobile station (MS), an advanced mobile station (AMS), and a high reliability mobile station (HR-MS). , subscriber station (SS), portable subscriber station (PSS), access terminal (AT), user equipment (UE), etc., and may refer to MT, MS, AMS , HR-MS, SS, PSS, AT, UE, etc. may include all or some functions.

In addition, a base station (BS) includes an advanced base station (ABS), a high reliability base station (HR-BS), a node B, and an evolved node B (eNodeB). ), access point (AP), radio access station (RAS), base transceiver station (BTS), mobile multihop relay (MMR)-BS, relay station serving as a base station , RS), a relay node (RN) serving as a base station, an advanced relay station (ARS) serving as a base station, and a high reliability relay station (HR- RS), small base stations (femto BS, home node B (HNB), home eNodeB (HeNB), pico BS, metro BS, micro BS) etc.], etc., and may include all or some functions of ABS, NodeB, eNodeB, AP, RAS, BTS, MMR-BS, RS, RN, ARS, HR-RS, small base station, etc. .

Now, a handover method and apparatus in a wireless communication system according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a diagram illustrating a handover procedure in an existing LTE system.

Referring to FIG. 1 , the terminal 100 transmits a neighbor cell measurement report message to the source base station 200 (S102). The neighbor cell measurement report message includes measurement values of neighbor cells measured by the UE.

The source base station 200 determines the handover of the terminal based on the measurement value of the neighboring cell measured by the terminal (S104).

When the source base station 200 determines handover for the UE, it performs a handover preparation step. In the handover preparation step, the source base station transmits a handover request (HO REQ) message from the target base station 300 (S106). The target base station 300 accepts the handover of the terminal 100 (S108) and transmits a handover request acceptance (HO-REQ ACK) message to the source base station 200 (S110). When the source base station 200 receives the handover request acceptance (HO-REQ ACK) message from the target base station 300, it transmits a handover command message to the terminal 100 (S112).

When the handover preparation step is completed in this way, a handover execution step proceeds.

In the handover performance step, the terminal 100 disconnects from the source base station 200 and is detached from the source base station 200 (S114). Next, the terminal 100 performs downlink synchronization for communication connection with the target base station 300, receives system information from the target base station 300, and then performs a random access procedure. For the random access procedure, the terminal 100 transmits a random access preamble to the target base station 300 (S116). The target base station 300 transmits a random access response (RAR) message to the terminal 100 (S118). The RAR message may include timing advance (TA) information for the terminal 100 to synchronize uplink, and uplink resource allocation information through which the terminal 100 may transmit a handover confirmation message. The terminal 100 adjusts uplink synchronization based on the received RAR message and completes a random access procedure with the target base station 300 . Next, the terminal 100 transmits a handover confirmation message to the target base station 300 through the uplink resources allocated from the target base station 300 (S120), and then exchanges data with the target base station 300. send and receive

In this handover procedure, after the terminal 100 disconnects from the source base station 200, it transmits a handover confirmation message to the target base station 300 through uplink resources allocated from the target base station 300. Until, data interruption time occurs. This data downtime negatively affects the quality of service of latency-sensitive applications. An embodiment of the present invention proposes a handover method capable of minimizing data interruption time.

2 is a diagram illustrating a handover method according to the first embodiment of the present invention.

Referring to FIG. 2 , the terminal 100 transmits a neighbor cell measurement report message to the source base station 200 (S202). The neighbor cell measurement report message includes measurement values of neighbor cells measured by the UE. In addition, cell IDs (physCellId) of neighboring cells measured by the terminal are sequentially arranged and included in the information element of the neighboring cell measurement report (Measurement Report) message.

The source base station 200 performs a handover decision of the terminal 100 based on the measurement value of the neighboring cell in the neighboring cell measurement report message (S204).

When the source base station 200 determines handover for the terminal 100, it transmits a pre-random access command (pre-RACH Command) instructing the terminal 100 to transmit a random access preamble to the target base station 300. (S206). In addition, the source base station 200 transmits a handover request (HO REQ) message from the target base station 300 (S208). The handover request (HO REQ) message may include a preamble index for fast handover based on prior random access. The source base station 200 selects one preamble index for fast handover based on prior random access and transmits it to the terminal 100 in advance through a system information block or RRC signaling. When the source base station 200 determines handover for the terminal 100 in step S204, the preamble index for fast handover based on prior random access allocated to the terminal 100 is sent to the handover request (HO REQ) message. It can be transmitted to the target base station 300 through.

According to an embodiment of the present invention, the pre-random access command (pre-RACH Command) uses a pre-random access command medium access control (MAC) control element (CE) that is an L2 signaling message.

3 is a diagram showing a DL-SCH header and an LCID index defined in the existing 3GPP standard, and FIG. 4 is a diagram showing an example of a pre-RACH command according to an embodiment of the present invention. 5 is a diagram illustrating an example of a MAC CE of a pre-RACH Command according to an embodiment of the present invention.

3 and 4, the pre-random access command (pre-RACH Command) is L2 signaling, and the downlink shared channel (DL-SCH) transmitted from the source base station 200 One of Logical Channel Identifiers (LCIDs) composed of 5 bits for each channel is used.

Referring to FIG. 3, the R/R/E/LCID type subheader includes four fields corresponding to R, R, E, and LCID. R is set to 0 as an unused (Reserved) bit. In addition, E is an extension field and includes a flag bit indicating whether an additional field exists in the MAC header. When E is set to 1, it indicates that another subheader of R/R/E/LCID type exists. The LCID is a logical channel identifier field and indicates whether a corresponding logical channel or MAC CE exists. For example, when the LCID is set to 11011, it indicates that a MAC CE for indicating activation/deactivation exists.

Referring to FIG. 3, in the current 3GPP standard TS 36.321 V12.5.0, there are 24 LCIDs for reserved DL-SCHs. One of LCIDs for 24 unused DL-SCHs is used as a pre-random access command (pre-RACH Command). For example, as shown in FIG. 4, LCID “11001” may be used as a MAC CE for a pre-RACH Command.

Referring to FIG. 5, the MAC CE of the pre-RACH Command is 1 octet (8 bits), and includes a 4-bit target cell index (targetCellIndex) and a 4-bit RACH (Random Access Channel) configuration index (rachConfigIndex). ) is composed of The target cell index (targetCellIndex) is a cell of sequentially arranged neighbor cells included in the last neighbor cell measurement report message among neighbor cell measurement report messages transmitted from the terminal 100 to the source base station 200. IDs (physCellId) are mapped with the target cell index (targetCellIndex). For example, the cell ID (physCellId) of the first neighboring cell is mapped to "0000" of the target cell index (targetCellIndex), and the cell ID (physCellId) of the second neighboring cell is mapped to "0000" of the target cell index (targetCellIndex). 0001". At this time, the target cell index (targetCellIndex) “1111” is when the source base station 200 does not know the RACH configuration information of the corresponding neighboring cell, the terminal 100 receives the system information block from the target base station 300, and the target base station 300 ) is used to instruct the random access preamble to be transmitted. A transport channel, RACH, is mapped to a physical channel, Physical Random Access Channel (PRACH). RACH configuration information may refer to PRACH configuration information.

Since the RACH configuration parameter values of base stations actually constructed within the same operator/system are mainly used, the RACH configuration information of cells configured by mutually adjacent base stations is limited to a predetermined number (eg, 15) of types. , and maps RACH configuration information of neighboring cells with a 4-bit RACH configuration index (rachConfigIndex). In this case, the terminal 100 knows in advance the RACH configuration information within a predetermined number (eg, 15), or the system information block broadcasted by the source base station 200 contains a predetermined number (eg, 15) of RACH configuration information. RACH configuration information of neighboring cells may be known through a system information block broadcasted by the source base station 200.

The pre-random access command (pre-RACH Command) is an indicator for performing a pre-random access to the corresponding terminal 100, and the source base station 200 transmits the pre-random access command (pre-RACH Command) to the corresponding terminal 100. The timing of the transmission is determined by considering the L2 signaling transmission time and the processing time of the UE based on the RACH transmission interval information [RACH slot] of the RACH configuration information of the target base station 300.

Upon receiving the pre-RACH Command, the terminal 100 checks the cell ID (targetPhysCellId) of the target base station through the target cell index (targetCellIndex) of the MAC CE of the pre-RACH Command. And, RACH transmission period information of the target base station 300 may be obtained through the RACH configuration index (rachConfigIndex).

Upon receiving the pre-RACH command, the terminal 100 temporarily suspends communication with the source base station 200 and transmits PSS (Primary Synchronization Signals) and SSS (Secondary Synchronization Signals) from the target base station 300. After receiving, a random access preamble is transmitted to the target base station 300 using a preamble index for quick handover based on a predefined random access (S210). The random access preamble is transmitted through L2 signaling. That is, steps S206 and S210 in FIG. 2 may be performed through L2 signaling, and the remaining steps may be performed through L3 signaling.

After transmitting the random access preamble to the target base station 300, the terminal 100 immediately resumes communication with the source base station 200. In general, as described with reference to FIG. 1 , terminal 100 transmits a random access preamble and then receives an RAR message from target base station 300 . According to an embodiment of the present invention, the terminal 100 resumes communication with the source base station 200 without receiving the RAR message after transmitting the random access preamble.

Upon receiving the random access preamble from the terminal 100, the target base station 300 accepts the handover of the terminal 100 (S212), and sends a handover request acceptance (HO-REQ ACK) message to the source base station 200. It is transmitted through the interface (X2) between the terminals (S214). At this time, the RAR message may be included in the handover request acceptance (HO-REQ ACK) message. That is, the handover request acceptance (HO-REQ ACK) message includes TA information obtained by the target base station 300 by calculating uplink timing synchronization of the corresponding terminal 100, and also includes the handover request Information on a pre-allocated uplink resource pre-allocated for transmission of a Handover Confirm message and a new Cell Radio Network Temporary Identifier (C-RNTI) may be included.

Upon receiving the handover request acceptance (HO-REQ ACK) message from the target base station 300, the source base station 200 includes the RAR message in the handover command message and transmits it to the terminal 100 (S216) . That is, the handover command message may include TA information, pre-allocated uplink resource information, and C-RNTI.

After receiving the handover command message from the source base station 200, the terminal 100 continues communication with the source base station 200 until the start time of the uplink resource pre-allocated by the target base station 300, The connection with the source base station 200 is terminated at an appropriate time considering the start time of the pre-allocated uplink resource, and the base station is separated from the source base station 200 (S218).

Thereafter, the terminal 100 receives the PSS and SSS from the target base station 300 and transmits a handover confirmation message to the target base station 300 through the pre-allocated uplink resources (S220). At this time, the terminal 100 may transmit a handover confirmation message to the target base station 300 and simultaneously receive data from the target base station 300 .

Upon receiving the Handover Confirm message, the target base station 300 transmits and receives uplink and downlink data packets with the corresponding terminal 100 (S222).

As such, according to the handover procedure according to the embodiment of the present invention, the terminal 100 can know the RACH configuration information of the target base station 300 in advance even without receiving the system information block from the target base station 300 . In addition, in the handover preparation step, the source base station 200 commands the terminal 100 to perform random access to the target base station through L2 signaling, so that the random access procedure for handover of the terminal is a handover preparation step. is performed in At this time, the terminal 100 that has transmitted the random access preamble to the target base station 300 immediately resumes communication with the source base station 200 without receiving an RAR message from the target base station 300, thereby reducing data interruption time.

If the target base station 300 did not accept the handover for the terminal 100 in step S214 of transmitting a handover request acceptance (HO-REQ ACK) message to the source base station 200, or the target base station 300 ) does not allow uplink synchronization in advance through a preliminary random access procedure, the target base station 300 indicates this fact in a handover request acceptance (HO-REQ ACK) message and transmits it to the source base station 200, , The source base station 200 also indicates and transmits this fact in a handover command message to the corresponding terminal 100. In this case, the terminal 100 performs handover through the existing handover procedure described in FIG. 1 instead of the handover procedure according to the embodiment of the present invention.

6 is a flowchart illustrating an operation of a terminal in the handover preparation step described in FIG. 2 .

Referring to FIG. 6 , when the terminal 100 receives a pre-random access command (pre-RACH Command) from the source base station 200 (S602), the terminal 100 receives a target cell index (targetCellIndex) from the pre-random access command (pre-RACH Command). ) and a RACH configuration index (rachConfigIndex).

If the target cell index (targetCellIndex) is one of values from 0000 to 1110, the terminal 100 waits until an appropriate frame to transmit the random access preamble according to the PRACH resource configuration of the target base station 300 is reached.

When the terminal 100 receives an appropriate frame to transmit the random access preamble according to the PRACH resource configuration of the target base station 300 (S606), the terminal 100 temporarily suspends communication with the source base station 200 (S610), and the target base station 300 Synchronizes with the target base station 300 by receiving the PSS and SSS of (S612), and transmits a random access preamble to the target base station 300 using a preamble index for handover based on a predefined random access (S612). S614). Here, an appropriate frame for transmitting the random access preamble may be determined in consideration of the processing time of the terminal 100 before the start time of the transmission period of the random access preamble according to the PRACH resource configuration arrives.

After transmitting the random access preamble, the terminal 100 immediately resumes communication with the source base station 200 (S616).

Meanwhile, when the target cell index (targetCellIndex) is 1111 (S604), the terminal 100 receives a system information block from the target base station 300 (S608). As described above, the case where the target cell index (targetCellIndex) is 1111 is used when the source base station 200 does not know the RACH configuration information of the target base station. Accordingly, the terminal 100 additionally performs a process of receiving a system information block from the target base station 300 to obtain RACH configuration information of the target base station 300 . Next, the terminal 100 temporarily suspends communication with the source base station 200 (S610), receives the PSS and SSS of the target base station 300, synchronizes with the target base station 300 (S612), and predefines A random access preamble is transmitted to the target base station 300 using the preamble index for fast handover based on the pre-random access (S614). Then, communication with the source base station 200 is resumed immediately (S616).

7 is a flowchart illustrating an operation of a terminal in the step of performing handover described in FIG. 2 .

Referring to FIG. 7, when the terminal 100 receives a handover command message from the source base station 200 (S702), before the start time of the pre-allocated uplink resources, the terminal 100 appropriately takes into account the processing time of the terminal. Wait until frame.

When an appropriate frame arrives before the start of the pre-allocated uplink resources (S704), the terminal 100 disconnects from the source base station 200 and is separated from the source base station 200 (step S706).

Next, the terminal 100 receives PSS and SSS from the target base station 300 and synchronizes with the target base station 300 (S708).

Then, the terminal 100 transmits a handover confirmation message to the target base station 300 through the uplink resources pre-allocated by the target base station 300 (S710).

The terminal 100 resumes communication with the target base station 300 (S712).

Through this procedure, in the handover step, after the terminal 100 disconnects from the source base station 200, it does not perform a random access procedure to the target base station 300, so data in the handover step Downtime can be reduced. In addition, the terminal 100 transmits only the random access preamble even in the handover preparation stage and resumes communication with the source base station 200, thereby reducing overall data interruption time due to handover.

8 is a diagram explaining a handover method according to a second embodiment of the present invention.

Referring to FIG. 8 , steps S802 to S810 , that is, after the source base station 200 determines the handover of the terminal 100 and the handover preparation step, are similar to those described in FIG. 1 . However, when the target base station 300 determines to accept handover for the terminal 100 (S808), it transmits a handover request acceptance (HO-REQ ACK) message to the source base station 200 (S810). Unlike the HO-REQ ACK message, a preamble index for contention-free random access and RACH configuration information, which is system information of the target base station 300, are included and transmitted. .

Upon receiving the HO-REQ ACK message from the target base station 300, the source base station 200 transmits a handover command message to the terminal 100 (S812). The handover command message may include a target cell ID (targetPhysCellId), a preamble index, and RACH configuration information that is system information of the target base station.

Upon receiving the handover command message, the terminal 100 temporarily suspends communication with the source base station 200, receives PSS and SSS from the target base station 300, and synchronizes with the target base station 300. .

Next, the terminal 100 transmits a random access preamble to the target base station through L2 signaling based on the preamble index (S814).

The terminal 100 immediately resumes communication with the source base station 200 after transmitting the random access preamble to the target base station 300 .

After receiving the random access preamble from the terminal 100, the target base station 300 decodes the random access preamble, calculates TA information for uplink synchronization, and the terminal 100 sends a handover confirmation message. Uplink resources are allocated for transmission.

The target base station 300 transmits an RAR message including TA information, uplink resource allocation information, and C-RNTI to the source base station 200 to the source base station 200 through the X2 interface (S816), and the terminal 100 Request forwarding to

Upon receiving the RAR message from the target base station 300, the source base station 200 includes the target cell ID (targetPhysCellId) in the information included in the corresponding RAR message and time information indicating the point in time at which communication with the source base station 200 is terminated (detach). An indirect RAR (Indirect-RAR, I-RAR) message to which is added is transmitted to the terminal 100 through L2 signaling (S818). In FIG. 8 , steps S812 and S818 may be performed through L2 signaling, and the remaining steps may be performed through L3 signaling. At this time, in the case of time information indicating the point of time when communication with the source base station 200 of the corresponding terminal 100 is terminated, the source base station 200 considers uplink resource allocation information and processing delay time of the corresponding terminal 100. and set its value.

Upon receiving the I-RAR message from the source base station 200, the terminal 100 initiates communication with the source base station 200 in a subframe corresponding to time information on the end of communication with the source base station 200. When finished, it is separated from the source base station 200 (S820).

Thereafter, the terminal 100 receives PSS and SSS from the target base station 300, synchronizes with the target base station 300, and completes handover to the target base station 300 through pre-allocated uplink resources (Handover Confirm) The message is transmitted (S822). At this time, the terminal 100 may transmit a handover confirmation message to the target base station 300 and simultaneously receive data from the target base station 300 .

Upon receiving the handover confirmation message, the target base station 300 transmits and receives uplink and downlink data packets with the corresponding terminal 100 (S824).

According to the handover procedure described in FIG. 8, the source base station 200 includes some system information such as RACH configuration information of the target base station 300 in the handover command message transmitted to the terminal 100. There is a difference from the handover procedure. Through this, when the terminal 100 performs handover to the target base station 300, it is not necessary to receive the system information broadcasted by the target base station 300, so the data interruption time due to reception of the system information broadcasted by the target base station 300 can reduce In addition, when random access of the terminal 100 to the target base station 300 is performed in the handover step, the target base station 300 does not directly transmit the RAR message to the terminal 100, but the source base station 200 through the X2 interface. , and the source base station 200 forwards it to the terminal 100, which is different from the existing handover procedure. Through this, the terminal 100 does not continuously interrupt the connection with the source base station 200 in order to receive the RAR message from the target base station 300, and resumes communication with the source base station 200 immediately after transmitting the random access preamble. Therefore, it is possible to reduce data interruption time due to handover.

9 is a flowchart illustrating an operation of a terminal in the handover performance step described in FIG. 8 .

Referring to FIG. 9 , when the terminal 100 receives a handover command from the source base station 200 (S902), the terminal 100 transmits a random access preamble according to the PRACH resource configuration of the target base station 300 to an appropriate frame. waiting.

When the terminal 100 receives an appropriate frame to transmit a random access preamble according to the PRACH resource configuration of the target base station 300 (S904), the terminal 100 temporarily suspends communication with the source base station 200 (S906), and the target base station 300 The PSS and SSS of are synchronized with the target base station 300 (S908), and a random access preamble is transmitted to the target base station 300 using the preamble index included in the handover command (S910). .

After transmitting the random access preamble, the terminal 100 immediately resumes communication with the source base station 200 (S912).

When the terminal 100 receives the I-RAR message from the source base station 200 (S914), it waits until an appropriate frame considering the processing time of the terminal before the start time of the pre-allocated uplink resource.

When an appropriate frame arrives before the start of the pre-allocated uplink resources (S916), the terminal 100 disconnects from the source base station 200 and is separated from the source base station 200 (step S918).

Next, the terminal 100 receives PSS and SSS from the target base station 300 and synchronizes with the target base station 300 (S920).

After that, the terminal 100 transmits a handover confirmation message to the target base station 300 through the uplink resources pre-allocated by the target base station 300 (S922).

The terminal 100 resumes communication with the target base station 300 (S924).

Through this procedure, a random access procedure is performed in the handover execution step, but the time at which the terminal 100 receives system information of the target base station 300, which occurs in the existing random access procedure, RACH transmission of the target base station 300 Since the waiting time for the interval and the waiting time for receiving the RAR message from the target base station 300 are eliminated, the data interruption time in the handover performance step can be reduced.

10 is a diagram illustrating a handover device of a terminal according to an embodiment of the present invention.

Referring to FIG. 10 , a handover device 1000 of a terminal 100 includes a processor 1010, a transceiver 1020, and a memory 1030.

The processor 1010 may operate to implement the handover procedure, method, and functions of the terminal 100 described based on FIGS. 2 to 9 .

The transceiver 1020 is connected to the processor 1010 to transmit and receive radio signals.

The memory 1030 stores instructions to be executed by the processor 1010 or loads and temporarily stores instructions from a storage device (not shown). The processor 1010 may execute instructions stored or loaded in the memory 1030 . Also, the memory 1030 may store information related to the operation of the processor 1010 .

The processor 1010 and the memory 1030 are connected to each other through a bus (not shown), and an input/output interface (not shown) may also be connected to the bus. At this time, the transceiver 1020 is connected to the input/output interface, and peripheral devices such as an input device, a display, a speaker, and a storage device may be connected.

Embodiments of the present invention are not implemented only through the devices and / or methods described above, and may be implemented through a program that realizes functions corresponding to the configuration of the embodiments of the present invention or a recording medium in which the program is recorded, Such an implementation can be easily implemented by an expert in the technical field to which the present invention belongs based on the description of the above-described embodiment.

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 concept of the present invention defined in the following claims are also included in the scope of the present invention. that fall within the scope of the right.

Claims (20)

As a method of handover in a terminal of a wireless communication system,
When handover is determined by the source base station to which the terminal is currently connected, receiving a preliminary random access command from the source base station through L2 (Layer2) signaling in a handover preparation step performed between the source base station and the target base station ,
In the handover preparation step, transmitting a random access preamble to the target base station using a preamble index predefined according to the random access command, and
In the handover performing step performed between the terminal and the target base station after the handover preparation step is completed, a handover command message including the random access response is received from the source base station that has received the random access response from the target base station. and performing handover to the target base station.
A handover method comprising a. In paragraph 1,
The pre-random access command includes a cell identifier of the target base station and a random access channel configuration index indicating random access channel configuration information of the target base station. In paragraph 2,
A handover method in which one unused logical channel identifier among logical channel identifiers for a downlink common channel transmitted from the source base station is used as the pre-random access command. In paragraph 2,
Receiving system information from the source base station
Including more,
Random access channel configuration information of a plurality of cells in the wireless communication system is mapped to a plurality of random access configuration indices, respectively;
The system information includes mapping information between the plurality of random access channel configuration information and the plurality of random access configuration indexes. In paragraph 2,
Receiving system information including random access channel configuration information of a plurality of cells in the wireless communication system from the source base station
A handover method further comprising. In paragraph 1,
The sending step is
temporarily stopping communication with the source base station; and
and immediately resuming communication with the source base station after transmitting a random access preamble corresponding to the preamble index to the target base station. delete In paragraph 1,
In the handover preparation step, the source base station transmits a handover request message to the target base station, and the target base station accepting the handover of the terminal transmits the handover request acceptance message to the source base station.
Including more,
The handover request message includes the predefined preamble index, and the handover request accept message includes the random access response message. In paragraph 6,
After receiving the handover command message, continuing communication with the source base station until a start time of uplink resources pre-allocated from the target base station, and then terminating the connection with the source base station; and
Transmitting a handover complete message to the target base station through the pre-allocated uplink resource
A handover method further comprising. delete delete delete delete As a handover device of a terminal in a wireless communication system,
When the handover is determined by the source base station to which the terminal is currently connected, in the handover preparation step performed between the source base station and the target base station, the terminal responds to a predefined preamble index according to a random access command received from the source base station. transmits a random access preamble to the target base station, and in a handover performing step performed between the terminal and the target base station after the handover preparation step is completed, from the source base station receiving a random access response from the target base station A processor receiving a handover command message including the random access response and performing handover to the target base station; and
A transceiver connected to the processor to transmit and receive radio signals with the source base station and the target base station
A handover device comprising a. In paragraph 14,
The pre-random access command includes a cell identifier of the target base station and a random access channel configuration index indicating random access channel configuration information of the target base station. In clause 15,
Random access channel configuration information of a plurality of cells in the wireless communication system is mapped to a plurality of random access configuration indices, respectively;
wherein the mapping information between the plurality of random access channel configuration information and the plurality of random access configuration indexes is received from the source base station through system information. In paragraph 14,
The random access response includes allocation information of uplink resources by the target base station,
The processor temporarily suspends the connection with the source base station, transmits a random access preamble to the target base station, immediately resumes communication with the source base station, and until the start time of uplink resources allocated from the target base station, the source base station A handover device that continues to communicate with In paragraph 14,
A handover device in which one unused logical channel identifier among logical channel identifiers for a downlink common channel transmitted from the source base station is used as the pre-random access command. delete delete

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