KR20080080803A - Handoff Method and System in Mobile Communication System - Google Patents

Abstract

In a mobile communication system according to the present invention, the handover method includes performing a handover procedure when the mobile terminal moves from a source base station provided with a service to a target base station, and when the handover procedure is performed, the mobile terminal is configured to perform the handover procedure. A method of measuring channel quality indicator (CQI) information for adaptive modulation and coding (AMC) band-specific operation included in a target base station, and the mobile station of the target base station to be handed over And including the channel quality indicator information in the handover complete message.

Description

METHOD AND SYSTEM FOR HANDOVER IN MOBILE COMMUNICATION SYSTEM}

1 is a diagram illustrating an example of a structure of a next generation mobile communication system;

2 is a diagram illustrating a protocol structure of a next generation mobile communication system;

3 is a signal flow diagram illustrating a resource allocation to a mobile station by a target base station when the mobile station hands over to a target base station according to the first embodiment of the present invention;

4 is a method flowchart of a mobile terminal according to a first embodiment of the present invention;

5 is an operation flowchart of a source base station according to the first embodiment of the present invention;

6 is a flowchart illustrating a target base station according to the first embodiment of the present invention;

7 is a signal flow diagram illustrating a resource allocation to a mobile station by a target base station when the mobile station hands over to a target base station according to the second embodiment of the present invention;

8 is an operation flowchart of a mobile terminal according to a second embodiment of the present disclosure;

9 is an operation flowchart of a target base station according to a second embodiment of the present invention.

The present invention relates to a mobile communication system, and more particularly, to a handover method and system in a mobile communication system.

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

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

1 illustrates an example of a structure of a next generation (Evolved) UMTS mobile communication system.

Referring to FIG. 1, as illustrated, an Evolved UMTS Radio Access Network (hereinafter referred to as an “E-UTRAN”) 110 is an Evolved Node B (hereinafter referred to as “ENB” or “Node B”). 120, 122, 124, 126, and 128, and the upper node (anchor node) 130, 132 is simplified to a two-node structure. The user equipment 101 (hereinafter referred to as 'UE') 101 connects to the Internet Protocol network 114 by the E-UTRAN 110.

The ENBs 120 to 128 correspond to existing Node Bs of the UMTS system and are connected to the UE 101 by a radio channel. Unlike the existing Node B, the ENBs 120 to 128 play a more complex role. In LTE, all user traffic, including real-time services such as voice over IP (VoIP), is serviced through a shared channel. A device is needed, which is handled by the ENBs 120-128.

In addition, LTE is expected to use Orthogonal Frequency Division Multiplexing (OFDM) as a radio access technology in a 20 MHz bandwidth to achieve a transmission rate of up to 100 Mbps. In addition, an adaptive modulation & coding (AMC) scheme that determines a modulation scheme and a channel coding rate according to the channel state of the terminal will be applied.

Adaptive modulation and coding scheme band (AMC band) is a cell, that is, data to determine the modulation scheme and coding scheme of different data channels according to the channel state between the base station and the mobile terminal, thereby improving the use efficiency of the entire cell The transmission method. The AMC band scheme has a plurality of modulation schemes and a plurality of coding schemes, and modulates and codes a data channel signal by combining the modulation schemes and coding schemes. Typically, if each combination of the modulation schemes and coding schemes is called a modulation and coding scheme, a plurality of MCSs may be defined from level 1 to level N according to the number of MCSs. In other words, the AMC band scheme is to adaptively determine the level of the MCS according to a channel state between a mobile station and a base station that is currently wirelessly connected, thereby improving overall system efficiency. In the next generation mobile communication system, in order to increase the data transmission speed, AMC bands are allocated to sub-channels within a range of resources allowed for each mobile terminal by distinguishing between good and relatively poor channels in consideration of the state of each sub-channel. Use the method. When the AMC band scheme is applied as described above, a mobile terminal assigned a resource composed of good channels is modulated to have a higher capacity, thereby enabling high-speed data transmission. In the AMC band method, the mobile station measures channel quality indicator (CQI) information, collects channel information of a subchannel in operation, and uses a band composed of only subchannels having good status based on the channel quality indicator (CQI) information. The interference is less affected, and thus the mobile terminal to which the AMC band is applied can increase the coding rate and transmit at a relatively high transmission rate.

In addition, as in a mobile communication system supporting High Speed Downlink Packet Access (HSDPA) or Enhanced Uplink Dedicated Channel (E-DCH) services, the ENB 120 to 128 and the UE may be used in an LTE system. Hybrid ARQ (HARQ) is performed between 101. However, since the HARQ alone cannot satisfy the requirements of various Quality of Service (QoS), an outer ARQ may be performed in a higher layer, and the separate ARQ (hereinafter, 'outer-' ARQ ') may also be performed between the terminal 101 and the ENBs 120 to 128.

As described above, in many next-generation mobile communication systems including the LTE system, both HARQ and ARQ may be used as an error correction technique.

HARQ is a technique of increasing reception success rate by soft combining with retransmitted data without discarding previously received data. In more detail, the HARQ receiver determines whether there is an error in a received packet, and according to the presence of the error, a HARQ positive acknowledgment signal (hereinafter referred to as a HARQ ACK) signal or a HARQ negative acknowledgment. : Hereinafter referred to as 'HARQ NACK') transmits the signal to the transmitting side. Therefore, the transmitter performs retransmission of the HARQ packet or transmission of a new HARQ packet according to the HARQ ACK / NACK signal. And, the HARQ receiving side reduces the probability of error by soft combining the retransmitted packet with the previously received packet.

ARQ, on the other hand, checks the serial number of the received packet and requests retransmission for the unreceived packet, and does not soft combine the previously received packet with the retransmitted packet.

In particular, the LTE system is responsible for the ARQ operation in the protocol layer called RLC, HARQ operation in the MAC or physical layer.

2 illustrates a protocol structure of a next generation mobile communication system. 2 is a protocol structure of Long Term Evolution (LTE), which is currently under discussion in next generation mobile communication.

Referring to FIG. 2, the protocol structure may be set as a sender protocol structure or as a receiver protocol structure in response to a forward or reverse service. Accordingly, in the following description, the protocol structure of the transmitting side and the receiving side is not limited to one of a terminal and a base station. Here, an entity and a layer can be used interchangeably as a term referring to the same structure. In particular, an entity is a term that means that a layer can be composed of a plurality of blocks and that each block operates independently. On the other hand, a layer is the same as an entity, but it is a term that focuses on the role of the layer rather than the independent operation of each block. Thus, it is obvious that the entity and the hierarchy are referred to by the same terminology and thus there is no distinction.

In the LTE system, one packet data convergence protocol (service packet data convergence protocol, 205, 210, 215, 280, 285, 290, hereinafter referred to as PDCP) entity and radio link control (Radio Link Control, 220, 225, 230, 265, 270, 275, hereinafter referred to as "RLC" entity.

The PDCP is in charge of IP header compression / restore and the like, and the RLC configures a PDCP PDU (Packet Data Unit) to an appropriate size to perform an ARQ operation. Here, the packet data unit (PDU) refers to a packet output from a specific protocol entity, and the PDCP PDU refers to a packet output from the PDCP entity.

The MAC layers 235 and 260 are connected to several RLC entities configured in one terminal to multiplex multiple RLC PDUs output from the RLC entities into MAC PDUs, or demultiplex RLC PDUs from the MAC PDUs. Perform.

The HARQ layers 240 and 250 transmit and receive MAC PDUs through a predetermined HARQ operation, and the physical layers 245 and 250 channel-code and modulate higher layer data into OFDM symbols and transmit them on a wireless channel or transmit a wireless channel. The demodulation and channel decoding of the received OFDM symbol is carried out to the upper layer.

A typical handover procedure in a mobile communication system as described above is a handover from a source ENB to a target ENB by a mobile terminal, and the target base station receives a handover complete message from the mobile terminal. Later, since the mobile station reports channel quality Governor information on the downlink from the base station, a coding / modulation scheme optimized for the mobile terminal at the initial scheduling after the handover procedure from the target base station And resource allocation was not possible.

After the handover procedure was completed, data transmission was performed between the target base station and the mobile terminal to some extent, and the CQI information was transmitted by determining the reference signal of the base station. In the related art, the target base station allocates a resource to a mobile terminal with a high resource (for example, a high coding rate of the mobile terminal) at the time of resource allocation immediately after the handover. Then, after the target base station receives the CQI information, resource allocation is performed based on the received CQI information.

As described above, in the prior art, since the target base station does not know the state of the mobile terminal immediately after the handover of the mobile terminal, optimized resource allocation cannot be made to the mobile terminal.

The present invention provides a handover method and system in a mobile communication system.

The present invention provides a method and system for performing a resource allocation for a mobile station during initial scheduling by allowing the mobile station to measure and transmit channel quality indicator information of the target base station in a mobile communication system.

In a mobile communication system according to the present invention, the handover method includes performing a handover procedure when the mobile terminal moves from a source base station provided with a service to a target base station, and when the handover procedure is performed, the mobile terminal is configured to perform the handover procedure. A method of measuring channel quality indicator (CQI) information for adaptive modulation and coding (AMC) band-specific operation included in a target base station, and the mobile station of the target base station to be handed over And including the channel quality indicator information in the handover complete message.

A mobile communication system supporting handover of a mobile terminal according to the present invention performs a handover procedure from a source base station to a target base station, and when performing the handover procedure, adaptive modulation and coding included in the target base station (Adaptive) Modulation Coding (AMC) Measures Channel Quality Indicator (CQI) information for each band operation, and transmits the measured channel quality indicator information of the target base station to the handover complete message after performing the handover procedure. And the target base station for allocating resources to the mobile terminal according to the channel quality indicator information received from the mobile terminal.

In the mobile communication system according to the present invention, a handover method includes a process of a mobile terminal measuring reference signal strength of neighboring base stations, and a candidate target base station among the neighboring base stations to be handed over from a source base station with which the mobile terminal is currently communicating. Generating channel quality indicator information of the mobile station; transmitting the mobile station including the generated channel quality indicator information in a measurement report message; and transmitting a target handover of the channel quality indicator information by the source base station; And transmitting the channel quality indicator information corresponding to the target base station to a context data message indicating information related to communication of the mobile terminal, and the target base station based on the channel quality indicator included in the context data message. Resource definition to allocate to mobile terminal A comprises the step of determining.

A mobile communication system supporting handover of a mobile terminal according to the present invention measures channel quality indicator information of candidate target base stations among neighbor base stations to be handed over from a source base station with which current communication is performed, and measures the measured channel quality indicator information. Among them, a mobile terminal including the channel quality indicator information corresponding to the target base station with handover included in the measurement report message, and transmitting the channel quality indicator information in the context data message indicating the information related to the communication of the mobile terminal. And the target base station for determining resource information to be allocated to the mobile terminal based on the channel quality indicator information included in the context data message.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that in the following description, only parts necessary for understanding the operation according to the present invention will be described, and descriptions of other parts will be omitted so as not to distract from the gist of the present invention.

Hereinafter, the embodiments of the present invention will be briefly described before explaining the present invention. According to the first embodiment of the present invention, when the signal strength measured by the mobile terminal is greater than or equal to a threshold value (Event 1a occurs), CQI information about the target ENB is included in the measurement report message and transmitted. In the example, when a mobile terminal performs a handover and then transmits a handover complete message to a target base station, the mobile communication system proposes a method and system for allocating a resource during handover by including and transmitting CQI information about the target base station. will be.

First embodiment:

The first embodiment of the present invention measures the signal strengths of the serving base station and the target base station measured by the mobile terminal, and if the signal strength of the target base station is greater than or equal to a certain intensity (Event 1a occurrence), measuring and reporting the CQI information of the target base station When the transmission is included in the Measurement Report message, a source ENB delivers the CQI information to a target ENB, so that a target BS performs an initial resource allocation based on the CQI information. do.

3 is a signal flow diagram in which the target base station 315 allocates resources to the mobile terminal 305 when the mobile terminal 305 hands over to the target base station 315 according to the first embodiment of the present invention.

In step 320, the mobile terminal 305 measures the reference signal strength of the source base station 310 and the target base station 315. In step 320, the mobile terminal 305 checks whether the received signal strength exceeds a predetermined threshold (checks whether event 1a is triggered) so that the source base station 310 determines whether the mobile terminal 305 is handed over. can do.

In addition, the mobile terminal measuring the signal strength in step 320 can determine a candidate target base station to be handed over by checking the signal strength exceeding a threshold value among the received signal strengths. At this time, there may be a plurality of candidate target base stations. Accordingly, the mobile terminal 305 measures and generates CQI information for each AMC band by measuring the AMC band for the candidate target base station in step 325. In step 330, the mobile terminal 305 transmits the generated CQI information of the candidate target base station and the measured received signal strength information to the source base station 310 by including it in a measurement report message.

In step 335, the source base station 310 determines whether to perform a handover based on the received signal strength measurement values included in the measurement report message received in step 330, and if the handover is determined in step 335, step 340 The source base station 310 in the context data (Context data) indicating the information related to the communication of the mobile terminal 305 including the CQI information of the corresponding target base station 315 handover is determined from the received CQI information of the candidate target base stations The message is sent to the target base station 315. The context data message is a handover related message for requesting handover from the source base station 310 to the target base station 315. In this case, the context data message may include an identifier (ID) of the mobile terminal 305 and capability information of the mobile terminal 305 such as band information supported by the mobile terminal 305.

In step 345, the target base station 315 determines system information, which is a resource allocation parameter, and resource to be allocated, based on the CQI information of the context data message received in step 340.

In operation 350, the target base station 315 transmits a context confirm message including the resource allocation information determined in operation 345 to the source base station 310. In this case, the resource allocation information included in the context confirmation message may include AMC information, a system information block (SIB), an access parameter, and the like.

In step 355, the source base station 310 transmits the resource allocation information received from the target base station 315 to the mobile terminal 305 through a handover command message, and in step 360 the mobile terminal 305 Perform the handover procedure.

4 is a method flowchart of a mobile terminal 305 according to the first embodiment of the present invention.

In step 405, the mobile terminal 305 measures the reference signal strength from the base stations, and if the measured reference signal strength is greater than or equal to a predetermined strength, the mobile terminal 305 generates the CQI information of the candidate target base station in step 410. Measure the signal strength.

In operation 415, the mobile terminal 305 transmits a measurement report message including the measured CQI information of the candidate target base station to the source base station 310.

After transmitting the measurement report message including the CQI information of the candidate target base station in step 415, the mobile terminal 305 receives a handover command message from the source base station 310 in step 420, the source base station (step 425) In step 310, the serving base station is changed to the target base station 315, and the handover procedure after the change is performed. On the other hand, if the handover command message is not received in step 420, the mobile terminal 305 proceeds to step 405 to measure the reference signal strength of the base stations again.

5 is a flowchart illustrating the operation of the source base station 310 according to the first embodiment of the present invention.

In step 505, the source base station 310 receives the measurement report message received from the mobile terminal 305, and determines in step 510 whether handover is necessary according to the signal strength information included in the received measurement report message. In this case, in step 510, if there is a signal strength that is greater than or equal to a predetermined threshold value among the received signal strengths, the source base station 310 determines that a handover is necessary, and determines the target base station 315.

If it is determined in step 510 that the handover is necessary, in step 515, the source base station 310 determines that the corresponding handover is determined from among the CQI information of the candidate target base stations included in the measurement report message received in step 505. Generate handover related information including CQI information of the base station 315 and transmit a context data message including the handover related information to the target base station 315. In this case, the handover related information may be ID of the mobile terminal and capability information of the mobile terminal. The context data message is a message indicating information related to communication of the mobile terminal 305.

In step 520, the source base station 310 checks whether a context confirmation message is received from the target base station 315, and if the check result context confirmation message is received in step 520, allocates the resources included in the context confirmation message in step 525. A handover command message including the information is transmitted to the mobile terminal 305.

6 is a method flowchart of a target base station 315 according to the first embodiment of the present invention.

In step 605, the target base station 315 receives, from the source base station 310, a context data message indicating information related to communication of the mobile terminal 305 including CQI information of the target base station 315 and handover related information.

In step 610, the target base station 315 generates a message including system information (SI) and a handover parameter based on the CQI information of the target base station 315 received in step 605, In step 615, the context confirmation message including the generated handover parameter is transmitted to the source base station 310.

Second embodiment:

According to the second embodiment of the present invention, after the mobile terminal performs the handover, when the handover complete message is transmitted to the target base station, the mobile station includes the CQI information for the target base station and transmits the information, and the target base station completes the handover of the mobile terminal. A method of performing resource allocation based on the CQI information will be described after receiving a message. In the second embodiment, the target base station may inform the source base station of the format information about the CQI information to be included in the handover complete message in advance in the handover procedure. That is, in the second embodiment of the present invention, since the target base station 715 does not know how the mobile terminal 705 transmits the CQI information to the target base station 715, the CQI information may be previously used through a handover procedure or another method. You can promise in advance how you will send it.

7 is a signal flow diagram in which the target base station 710 allocates resources to the mobile terminal when the mobile terminal 705 hands over to the target base station 715 according to the second embodiment of the present invention.

In step 720, the mobile terminal 705 measures the received signal strength and reports the received signal strength in step 725 to the source base station 710 by including it in the measurement report message. In step 730, the source base station 710 determines a handover according to the received signal strength and performs a handover procedure. After the handover procedure is completed, the mobile terminal 705 typically transmits a handover complete message to the target base station 715 indicating that the handover is completed.

In step 735 according to the second embodiment of the present invention, the mobile terminal 705 measures and generates CQI information for each AMC band for the target base station 715 immediately before transmitting the handover complete message, and measures the CQI measured in step 740. The information is included in the handover complete message and transmitted to the target base station 715.

In step 740, the target base station 715 receiving the handover complete message performs resource allocation to the mobile terminal 705 based on the received CQI information immediately after the handover in step 745. In this case, the target base station 715 may inform the CQI format information to be included in the handover complete message during the handover procedure operation 730.

8 is a flowchart illustrating an operation of a mobile terminal 705 according to a second embodiment of the present invention.

In step 805, the mobile terminal 705 measures signal strength and transmits the measured signal strength to the source base station 710 by including the measured signal strength in a measurement report message. In step 815, the mobile terminal 705 performs the handover procedure after transmitting the measurement report message, and in step 820, before generating the handover complete message after the handover procedure, for generating CQI information for the target base station 715. Measure signal strength.

After measuring the CQI information for the target base station 715, the mobile terminal 705 transmits the measured CQI information to the target base station 715 by including the measured CQI information in the handover complete message in step 825.

Operation of the source base station 710 according to the second embodiment of the present invention is the same as the conventional method will be omitted.

9 is a flowchart illustrating an operation of the target base station 715 according to the second embodiment of the present invention. In step 905, the target base station 715 performs a handover procedure by the handover request. In this case, the mobile station 705 may inform mode information for the CQI report of the target base station 715 to be transmitted in the handover complete message.

Thereafter, when the target base station 715 receives the handover complete message including the CQI information of the target base station 715 from the mobile terminal 705 in step 910, the mobile terminal 705 based on the received CQI information in step 915. Determine the appropriate coding / modulation method and allocate resources.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but it will be apparent to those skilled in the art that various modifications are possible without departing from the scope of the present invention.

As described above, according to the present invention, during handover, the channel quality indicator information of the downlink of the target base station is transmitted during the handover operation through the measurement report message for the handover or after the handover operation through the handover completion message. As a result, the target base station immediately applies a modulation and coding scheme optimized to the mobile terminal during initial scheduling, thereby improving system efficiency.

Claims (12)

In the handover method in a mobile communication system, Performing a handover procedure when the mobile station moves from a source base station provided with a service to a target base station; When the handover procedure is performed, the mobile station measures channel quality indicator (CQI) information for adaptive modulation and coding (AMC) band-specific operation included in the target base station; and, And transmitting, by the mobile terminal, channel quality indicator information of the target base station to be handed over in a handover complete message. According to claim 1, The target base station further comprises the step of allocating resources to the mobile terminal based on the channel quality indicator information. According to claim 1, And reporting, by the target base station, format information of channel quality indicator information to be transmitted by the mobile terminal during the handover procedure. In a mobile communication system supporting handover of a mobile terminal, A channel quality indicator for performing a handover procedure from a source base station to a target base station and performing adaptive modulation and coding (AMC) band-specific operation included in the target base station when performing the handover procedure. A mobile terminal for measuring CQI) information and including the measured channel quality indicator information of the target base station in a handover complete message after performing the handover procedure; And a target base station for allocating resources to the mobile terminal according to channel quality indicator information received from the mobile terminal. The method of claim 4, wherein The target base station further comprises the format information of the channel quality indicator information to be transmitted by the mobile terminal during the handover procedure handover system in a mobile communication system. In the handover method in a mobile communication system, Measuring, by the mobile terminal, reference signal strengths of neighboring base stations; Generating channel quality indicator information of candidate target base stations of the neighbor base stations to be handed over by a source base station with which the mobile terminal is currently communicating; Transmitting, by the mobile terminal, the generated channel quality indicator information in a measurement report message; Transmitting, by the source base station, the channel quality indicator information corresponding to the target base station from which the handover is determined, from the channel quality indicator information to the target base station by including it in a context data message indicating information related to communication of the mobile terminal; And determining, by the target base station, resource information to be allocated to the mobile terminal based on the channel quality indicator included in the context data message. The method of claim 6, The target base station including the determined resource allocation information in a context confirmation message and transmitting to the source base station; The source base station further comprises the step of transmitting the resource allocation information included in the context confirmation message in the handover command message to the mobile terminal further handover method in a mobile communication system. The method of claim 6, The determining of the resource information to be allocated to the mobile terminal by the target base station, Storing a context of a radio access network of a mobile terminal included in the context data message; Determining system information based on the channel quality indicator information; And determining an adaptive modulation and coding method according to the determined system information. In a mobile communication system supporting handover of a mobile terminal, A mobile terminal for measuring channel quality indicator information of candidate target base stations among neighboring base stations to be handed over by a source base station currently communicating with and transmitting the measured channel quality indicator information in a measurement report message; The source base station transmitting channel quality indicator information corresponding to the target base station for which handover is determined among the channel quality indicator information in a context data message indicating information related to communication of the mobile terminal and transmitting the information to the target base station; And the target base station for determining resource information to be allocated to the mobile terminal based on channel quality indicator information included in the context data message. The method of claim 9, And the target base station transmits the determined resource allocation information to the source base station by including the determined resource allocation information in a context confirmation message. The method of claim 10, The source base station further comprises transmitting the resource allocation information included in the context confirmation message in the handover command message to the mobile terminal. The method of claim 9, The target base station, Storing a context of a radio access network of the mobile terminal, determining system information based on the channel quality indicator information, and determining an adaptive modulation and coding method according to the determined system information to the mobile terminal. Handover system in a mobile communication system comprising determining resource information to allocate.

Images