KR102036344B1 - Method for transmitting data packet in handover procedure of a mobile communication system - Google Patents

Abstract

In this embodiment, in the method of transmitting a data packet in a handover procedure of a mobile communication system, a relay node selects a target node based on a measurement report received from a terminal, and determines to execute the handover to the target node. Doing; The flushing time, which is the time required for the relay node to transmit all data packets in the transmission queue to the terminal, is calculated, and the maximum that can maintain the connection between the relay node and the terminal from the time of determining the execution of the handover. Calculating an amount of data packets of the transmission queue that can be transmitted directly to the terminal based on the maximum delay time and the flushing time; Requesting the relay node to stop transmission of data packets to the relay node, and transmitting status information of the transmission queue including the calculated amount of data packets to the content server through the donor base station; step; And immediately after the relay node receives a handover request response message from the target node, directly transmitting a data packet of the transmission queue corresponding to the calculated amount of data packet to the terminal. Provides a data packet transmission method.

Description

METHODO FOR TRANSMITTING DATA PACKET IN HANDOVER PROCEDURE OF A MOBILE COMMUNICATION SYSTEM}

The present invention relates to a method of transmitting a data packet in a handover procedure of a mobile communication system, and more particularly, to a terminal directly transmitting a data packet stored in a transmission queue of a relay node in a handover procedure of a mobile communication system including a relay node. The present invention relates to a data packet transmission method capable of minimizing waste of radio resources due to data packet transmission.

Relay technology in a mobile communication system is a cooperative communication technology in which a relay node located between a base station and a user equipment relays bilateral communication, and is currently widely used. In the past, the relay technology merely performs amplify-and-forward function by amplifying and forwarding a communication signal, but currently decode-and-forward by decoding a communication signal or reconstructing and transmitting a communication signal. It performs various functions such as reconfiguration-and-forward.

Meanwhile, the mobile communication system provides a handover technology for automatically switching channels so that a user can seamlessly transmit and receive data even while moving. The handover procedure is started based on a value representative of channel quality, such as signal-to-noise ratio (SNR) of the base station signal. That is, when the terminal receives a signal of another base station stronger than the signal of the source base station, the handover procedure is started with the base station as the target base station.

This handover procedure includes an operation of forwarding data packets stored in the transmission queue of the source base station to the target base station. However, when the handover procedure of a mobile communication system including a relay node serving as a source base station is performed in the same manner, a waste of radio resources occurs in a data packet transmission process.

In order to solve this problem, the present embodiment transmits all or part of the data packets stored in the transmission queue of the relay node directly from the relay node to the terminal in the handover procedure of the mobile communication system including the relay node, It is intended to provide a data packet transmission method that can minimize waste.

According to an aspect of the present embodiment, in a method of transmitting a data packet in a handover procedure of a mobile communication system, a relay node selects a target node based on a measurement report received from a terminal, and performs the handover to the target node. Determining to execute; The flushing time, which is the time required for the relay node to transmit all data packets in the transmission queue to the terminal, is calculated, and the maximum that can maintain the connection between the relay node and the terminal from the time of determining the execution of the handover. Calculating an amount of data packets of the transmission queue that can be transmitted directly to the terminal based on the maximum delay time and the flushing time; Requesting the relay node to stop transmission of data packets to the relay node, and transmitting status information of the transmission queue including the calculated amount of data packets to the content server through the donor base station; step; And immediately after the relay node receives a handover request response message from the target node, directly transmitting a data packet of the transmission queue corresponding to the calculated amount of data packet to the terminal. Provides a data packet transmission method.

According to another aspect of the present embodiment, in a method of transmitting a data packet in a handover procedure of a mobile communication system, a relay node selects a target node based on a measurement report received from a terminal, and performs the handover to the target node. Determining to execute; The flushing time, which is the time required for the relay node to transmit all data packets in the transmission queue to the terminal, is calculated, and the maximum that can maintain the connection between the relay node and the terminal from the time of determining the execution of the handover. Calculating an amount of data packets of the transmission queue that can be transmitted directly to the terminal based on the maximum delay time and the flushing time; Requesting the relay node to stop transmission of data packets to the relay node, and transmitting status information of the transmission queue including the calculated amount of data packets to the content server through the donor base station; step; And immediately after the relay node transmits a handover request message to the target node, directly transmitting a data packet of the transmission queue corresponding to the calculated amount of data packet to the terminal. It provides a data packet transmission method.

The data packet transmission method in the handover procedure according to the present embodiment has the effect of minimizing the waste of radio resources by directly transmitting all or part of the data packets stored in the transmission queue to the terminal.

In addition, the data packet transmission method in the handover procedure according to the present embodiment, the relay node transmits the status information of the transmission queue to the content server through the donor base station, thereby minimizing the overhead of signal exchange required for the handover execution It is effective.

1 is a diagram schematically illustrating a configuration of a mobile communication system including a relay node.
2 is a diagram illustrating a handover procedure according to the prior art.
3 is a diagram illustrating a handover procedure according to an aspect of the present embodiment.
4 is a diagram illustrating a data packet transmission process in a handover procedure according to an embodiment of the present embodiment.
5 is a diagram illustrating a handover procedure according to another aspect of the present embodiment.

Hereinafter, some embodiments of the present invention will be described in detail through exemplary 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 elements as much as possible even though they are shown in different drawings. In describing 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 gist of the present invention, the detailed description thereof will be omitted.

In addition, in describing the component of this invention, terms, such as 1st, 2nd, A, B, (a), (b), can be used. These terms are only for distinguishing the components from other components, and the nature, order or order of the components are not limited by the terms. Throughout the specification, when a part is said to include, 'include' a certain component, which means that it may further include other components, except to exclude other components unless otherwise stated. . In addition, as described in the specification. The term 'module' refers to a unit that processes at least one function or operation, which may be implemented by hardware or software or a combination of hardware and software.

In the present embodiment, the mobile communication service is a service for providing voice, video, data, etc., and may be provided based on various mobile communication standards and mobile communication technologies. For example, the mobile communication service according to the present embodiment includes a wideband code division multiple access (WCDMA) mobile communication service and a CDMA2000 mobile communication service according to a 3G mobile communication standard, and a high speed downlink packet according to a 3.9G mobile communication standard. Access) may include a mobile communication service and a Long Term Evolution (LTE) mobile communication service, LTE Advanced (LTE-A) mobile communication service according to the 4G mobile communication standard, and a mobile communication service provided by 5G mobile communication. However, it should be noted that this is merely illustrative and does not limit the embodiments of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a diagram schematically illustrating a configuration of a mobile communication system including a relay node.

Referring to FIG. 1, a mobile communication system 100 including a relay node is a system for providing various mobile communication services such as a voice call and a data packet, and includes a content server 110, a base station 130, and a relay node. 150 and the terminal 170 may be included.

The content server 110 may be implemented as a database server that stores and manages a plurality of data packets in order to provide content providing services such as video and audio to the terminal 170.

The base station 130 refers to a fixed station used for communicating with a plurality of terminals, and may be expressed in various terms such as Node B, evolved Node B (eNB), Base Station (BS), or Access Point (AP). At least one cell, which is a mobile communication service providing area, may exist in one base station 130.

The relay node 150 refers to a fixed station or a mobile station used to relay communication between the base station 130 and the terminal 170, and is expressed in various terms such as a relay node (RN) or a relay station (RS). Can be. The relay node 150 is installed between the base station 130 and the terminal 170 to relay transmission and reception signals, thereby improving the data throughput of the base station 130 or expanding the cell area to cover the service shadow area. can do.

The relay node 150 may be operated in a full duplex manner in which transmission and reception bands are separated, or in a half duplex manner in which transmission and reception time intervals are separated.

The relay node 150 may be classified into a transparent relay node and a non-transparent relay node according to whether the terminal 170 may recognize the existence of the relay node 150. The transparent relay node refers to a case in which the terminal 170 can recognize whether the terminal 170 communicates with the network through the relay node 150, and the opaque relay node communicates with the network through the relay node 150 through the relay node 150. If it does not recognize whether or not.

In order to improve the data throughput, the transparent relay node amplifies and relays only the data channel to the terminal 170. The link between the transparent relay node and the terminal 170 is directly controlled by the base station 130, which is called a centralized control method.

The opaque relay node relays both the control channel and the data channel to the terminal 170 in order to expand the cell area of the base station 130. The link between the opaque relay node and the terminal 170 is directly controlled by the opaque relay node 130, which is called a distributed control scheme.

The terminal 170 refers to a device having a wireless communication function, such as a smart phone and a notebook computer, and may be expressed in various terms such as a user equipment (UE) and a mobile equipment (ME).

The content server 110 and the base station 130 may be connected to each other by an IP-based wired network. The network element between the content server 110 and the base station 130 includes a system architecture evolution access gateway, which performs gateway functions for interconnection, routing and forwarding of data packets, and mobility of the terminal 170. It consists of a Mobility Management Entity (MME) that performs management and authentication, non-access stratum (NAS) signaling control, and the like.

The base station 130 and the relay node 150 may be connected by a wireless backhaul link to communicate in both directions.

The base station 130 and the terminal 170, or the relay node 150 and the terminal 170 may be connected by a wireless access link (access link) to communicate in both directions.

Downlink means a communication channel from the base station 130 to the relay node 150, or from the base station 130 to the terminal 170, the uplink (uplink) from the relay node 150 to the base station 130 Or means a communication channel from the terminal 170 to the base station 130.

When there is a request for data transmission from the terminal 170, the mobile communication system 100 transmits the corresponding data packet from the content server 110 to the base station 130 through a wired network and the base station 130 through a wireless backhaul down link. From the relay node 150 to the relay node 150, through the wireless access downlink from the relay node 150 to the terminal 170, each can be sequentially transmitted to provide a data service.

Hereinafter, the present embodiment will be described on the assumption of a mobile communication system including an opaque relay node. However, it should be noted that this is for convenience of description only and does not limit the present embodiment.

2 is a view schematically showing a handover procedure according to the prior art.

Referring to FIG. 2, in step 1, the terminal transmits a measurement report message to a relay node (hereinafter, referred to as a serving relay node) currently connected.

The measurement report includes: (1) Reference Signal Receive Power (RSRP) and Received Signal Strength Indicator (RSSI) for measuring the signal strength of the serving cell and the neighboring cell or the signal strength relative to the total received power. , RLM (Radio Resource Monitoring) measurement such as Reference Signal Received Quality (RSRQ), and (2) RLM that can evaluate radio link failure by measuring link quality with serving cell (Radio Link Monitoring) A concept that includes measurements.

The terminal transmits the measurement report message to the serving relay node periodically or periodically when the RSRP or RSRQ value of the neighboring cell is greater than or equal to a predetermined threshold. At this time, the serving relay node may determine the measurement report message received from the terminal as an initial message for triggering handover.

In step 2, the serving relay node determines to perform a handover of the terminal based on the measurement report message received from the terminal and Radio Resource Management (RRM) information, and selects a target node. Here, the target node may be a base station (or relay node) of a neighbor cell that transmits a signal stronger than the serving relay node to the terminal (that is, has a better channel quality than the serving relay node).

In step 3, the serving relay node transmits a handover request message to the target node through the donor base station. The handover request message includes information necessary for the target node to prepare for handover. For example, the handover request message may include context data such as a bearer to be set by the target node, a target cell ID, a terminal X2 signaling context reference at the relay node, a terminal S1 EPC signaling context reference, and an RRC context including the C-RNTI of the terminal. It may include.

In step 4, the target node receives the handover request message and determines whether to accept the handover request in consideration of the available radio resource status of the target node. That is, when the target node has a radio resource for connection with the terminal, the target node may accept the handover request.

If the target node accepts the handover request from the terminal, in step 5, the target node transmits a handover request acknowledgment message to the serving relay node through the donor base station. The handover request response message may include a portion of the handover command information to be transmitted to the terminal, for example, parameters such as a new C-RNTI and a dedicated RACH preamble in the form of a transparent container.

In step 6, the serving relay node transmits the status information of the transmission queue including the number of all data packets stored in the current transmission queue to the donor base station in response to a request of the donor base station.

In step 7, the donor base station transmits the status information of the transmission queue received from the serving relay node to the content server.

In step 8, the content server transmits all data packets accumulated in the transmission queue to the target node based on the status information of the transmission queue received from the donor base station.

In step 9, the serving relay node transmits a handover command to the terminal. The handover command is delivered through an RRC connection reconfiguration message.

In step 10, the UE performs synchronization for connection with the target node in response to the handover command, and accesses the target node through a random access channel (RACH). If the terminal successfully accesses the target node, in step 11, the terminal transmits a Handover Complete message to the target node, and the handover procedure is completed.

The transmission method of the data packet in the handover procedure according to the prior art is as follows.

(1) A data packet stored in a transmission queue of a serving relay node is a data packet transmitted from a content server using a wireless backhaul link through a donor base station.

(2) When the handover of the terminal is determined and the serving relay node receives the handover request response message from the target node (that is, the target base station or the target relay node), the serving relay node transmits the state of the transmission queue to the donor base station. Send the information. The donor base station transmits the status information of the transmission queue received from the serving relay node back to the content server.

(3) The content server transmits all data packets accumulated in the transmission queue to the target node based on the state information of the transmission queue received from the donor base station.

However, there are some problems in the data packet transmission method in the handover procedure according to the prior art.

First, radio resources (ie, wireless backhaul links) consumed while data packets are transmitted to the serving relay node are wasted.

Second, in order for the content server to transmit the data packet accumulated in the transmission queue to the target node, it is necessary to receive the status information of the transmission queue of the serving relay node from the donor base station, thereby increasing the overhead of signal exchange.

Embodiment of the present invention is derived to solve such a problem,

First, the serving relay node directly transmits the data packet of the transmission queue to the terminal, thereby minimizing waste of radio resources and preventing inefficiency of transmitting the already queued data packet back to the target node.

Second, if it is determined that the handover is performed, the serving relay node transmits the status information of the transmission queue to the donor base station without any request, thereby minimizing the overhead of signal exchange for transmitting the data packet of the transmission queue to the target node. Can be. In addition, the donor base station can determine in advance the data packet to be transmitted to the target node can increase the efficiency of the transmission.

Hereinafter, a method of transmitting a data packet in a handover procedure according to the present embodiment will be described in detail with reference to the accompanying drawings.

3 is a diagram illustrating a handover procedure according to an aspect of the present embodiment.

Referring to FIG. 3, in step 1, the terminal transmits a measurement report message to a relay node (hereinafter, referred to as a serving relay node) currently connected.

In step 2, the serving relay node determines to perform a handover of the terminal based on the measurement report message received from the terminal and Radio Resource Management (RRM) information, and selects a target node. Here, the target node may be a base station (or relay node) of a neighbor cell that transmits a signal stronger than the serving relay node to the terminal (that is, has a better channel quality than the serving relay node).

In step 3, the serving relay node generates the state information of the transmission queue including the number of all data packets currently stored in the transmission queue, the number of data packets that can be directly transmitted to the terminal before executing the handover. The specific contents and creation process are as follows.

Set maximum handover delay time

)을 설정한다. 최대 핸드오버 지연시간(

)이란 단말이 서빙 릴레이 노드에서 타겟 노드로의 핸드오버를 실행하지 않고 서빙 릴레이 노드와의 연결을 유지할 수 있는 최대 허용시간을 말한다.The serving relay node will use the maximum handover latency (

). Maximum Handover Latency (

) Means the maximum time allowed for the terminal to maintain connection with the serving relay node without executing handover from the serving relay node to the target node.

)은 단말로 전송될 데이터 패킷의 중요도에 따라 다양하게 가변될 수 있다. 여기서, 데이터 패킷의 중요도는, 예컨대 H.264/AVC(Advanced Video Coding) 표준에 따른 멀티미디어 데이터 패킷의 경우, NAL(Network Abstraction Layer) 헤더의 Priority 필드 등을 기초로 식별될 수 있다.Maximum Handover Latency (

) May vary depending on the importance of the data packet to be transmitted to the terminal. In this case, the importance of the data packet may be identified based on, for example, a priority field of a network abstraction layer (NAL) header in the case of a multimedia data packet according to the H.264 / Advanced Video Coding (AVC) standard.

)은 미리 설정된 시스템 파라미터일 수 있다.Or the maximum handover delay (

) May be a preset system parameter.

Flushing time output

The serving relay node calculates the time required for emptying all data packets stored in the transmission queue (hereinafter, flushing time). Here, the flushing time may be calculated by the calculation of Equation 1 below.

는 플러싱 시간,

은 서빙 릴레이 노드의 전송 큐에 저장된 데이터의 총량,

은 프레임(frame)당 단말로 전송되는 데이터의 평균량,

는 프레임의 지속시간(duration)을 의미한다.here,

Is the flushing time,

Is the total amount of data stored in the transmission queue of the serving relay node,

Is the average amount of data transmitted to the terminal per frame,

Denotes a duration of a frame.

Calculation of Transmission Capacity of Serving Relay Node

)을 최대 핸드오버 지연시간(

)과 비교하여, 핸드오버 실행 전에 단말로 직접 전송할 수 있는 데이터의 양(이하, 전송 가능량)을 산출한다.Next, the serving relay node has a flushing time (

) To the maximum handover latency (

) To calculate the amount of data that can be transmitted directly to the terminal (hereinafter, the amount of transmission) before handover execution.

)이 최대 핸드오버 지연시간(

) 이하인 경우, 전송 가능량은 서빙 릴레이 노드의 전송 큐에 저장된 데이터의 총량이 된다. 즉, 서빙 릴레이 노드는 플러싱 시간 동안 전송 큐에 저장된 모든 데이터 패킷을 단말로 직접 전송할 수 있다.As a result of the comparison, the flushing time (

) Is the maximum handover latency (

), The transmittable amount is the total amount of data stored in the transmission queue of the serving relay node. That is, the serving relay node may directly transmit all data packets stored in the transmission queue to the terminal during the flushing time.

)을 초과하는 경우, 전송 가능량은 하기 수학식 2의 계산에 의해 산출될 수 있다.On the contrary, as a result of the comparison, the flushing time is the maximum handover delay time (

), The transmittable amount may be calculated by the calculation of Equation 2 below.

는 전송 가능량,

은 최대 핸드오버 지연시간,

는 프레임의 지속시간(duration),

은 프레임(frame)당 단말로 전송되는 데이터의 평균량을 의미한다.here,

Is the transmittable amount,

Is the maximum handover delay,

Is the duration of the frame,

The average amount of data transmitted to the terminal per frame (frame).

In step 4, the serving relay node transmits a data packet stop request message including status information of a transmission queue to a donor base station. Here, the data packet transmission stop request message refers to a message requesting to stop transmitting the data packet addressed to the terminal to the serving relay node.

In step 5, the donor base station stops transmitting the data packet to the serving relay node through the backhaul link in response to the data packet stop request message.

As the donor base station stops transmitting data packets to the serving relay node, generation of late data packets is prevented. Here, the rate data packet is a data packet transmitted to the serving relay node after the handover decision, and means a data packet that cannot be transmitted to the terminal but must be transmitted to the target node. In this way, waste of wireless backhaul link resources consumed when transmitting data packets from the donor base station to the serving relay node are prevented.

In step 6, the donor base station transmits the status information of the transmission queue included in the data packet stop request message to the content server.

In step 7, the content server transmits the remaining data packets to the target node except for the data packet to be directly transmitted to the terminal by the serving relay node based on the status information of the transmission queue received from the donor base station.

In step 8, the serving relay node transmits a handover request message to the target node through the donor base station. The handover request message includes information necessary for the target node to prepare for handover.

In step 9, the target node determines whether to accept the handover request based on the available radio resource status in response to the handover request message. That is, when the target node has a radio resource for connection with the terminal, the target node may accept the handover request.

When the target node accepts the handover request of the terminal, in step 10, the target node transmits a handover request acknowledgment message to the serving relay node through the donor base station.

)에 해당하는 개수의 데이터 패킷을 전송 큐로부터 단말로 직접 전송할 수 있다. In step 11, the serving relay node immediately after receiving the handover request response message, calculates the amount of transmissions calculated in step 3

The number of data packets corresponding to) may be directly transmitted from the transmission queue to the terminal.

)에 해당하는 개수의 데이터 패킷을 전송 큐로부터 단말로 직접 전송할 수 있다.Specifically, the serving relay node may sequentially transmit (ie, in a first-in first-out (FIFO) manner) according to the queued order.

The number of data packets corresponding to) may be directly transmitted from the transmission queue to the terminal.

)에 해당하는 개수의 데이터 패킷을 전송 큐로부터 단말로 직접 전송할 수 있다. 여기서, 데이터 패킷의 중요도는, 예컨대 H.264/AVC(Advanced Video Coding) 표준에 따른 멀티미디어 데이터 패킷의 경우, NAL(Network Abstraction Layer) 헤더의 Priority 필드 등을 기초로 식별될 수 있다.Alternatively, the serving relay node may selectively transmit the amount according to the importance of the queued data packet.

The number of data packets corresponding to) may be directly transmitted from the transmission queue to the terminal. In this case, the importance of the data packet may be identified based on, for example, a priority field of a network abstraction layer (NAL) header in the case of a multimedia data packet according to the H.264 / Advanced Video Coding (AVC) standard.

According to one aspect of the present embodiment, in order to prevent deterioration of the channel state of the terminal, the serving relay node may temporarily increase the transmission power while transmitting the data packet directly to the terminal.

)에 따른 데이터 패킷을 전송 큐로부터 단말로 모두 전송하는 시점이, 단말의 핸드오버 실행(Handover Execution) 시점이 될 수 있다.The serving relay node can transmit

The time point at which all data packets are transmitted from the transmission queue to the terminal may be a handover execution time point of the terminal.

In step 12, the serving relay node transmits a handover command to the terminal. The handover command is delivered through an RRC connection reconfiguration message.

In step 13, the UE that receives the RRC connection reconfiguration message performs synchronization for connection with the target node and accesses the target node through a random access channel (RACH). If the terminal successfully accesses the target node, in step 14, the terminal transmits a handover complete message to the target node, and the handover procedure is completed.

A method of transmitting data packets in the handover procedure according to the present embodiment described above is as follows.

(1) A data packet stored in a transmission queue of a serving relay node is a data packet transmitted from a content server using a wireless backhaul link through a donor base station.

(2) When the handover execution of the terminal is determined, the serving relay node generates state information of the transmission queue. The terminal transmits a data packet stop request message including status information of the transmission queue to the donor base station.

(3) The donor base station transmits the status information of the transmission queue included in the data packet stop request message to the content server.

(4) The content server transmits the remaining data packets to the target node except for the data packet to be directly transmitted by the serving relay node to the terminal based on the received state information of the transmission queue.

(5) The serving relay node transmits all or part of the data packets stored in the transmission queue to the terminal before handover based on the status information of the transmission queue, in particular, the amount of transmission possible.

As described above, according to the data packet transmission method in the handover procedure according to the present embodiment, two problems of the related art described above with reference to FIG. 2 may be solved.

First, since the serving relay node directly transmits all or part of the data packets stored in the transmission queue, it is possible to minimize the waste of radio resources generated during the data packet transmission process.

Second, even if the serving relay node transmits the status information of the transmission queue to the donor base station without a separate request, the overhead of signal exchange for transmitting the data packet of the transmission queue to the target node can be minimized.

4 is a diagram illustrating a data packet transmission process in a handover procedure according to an embodiment of the present embodiment.

Referring to FIG. 4, in step S410, the serving relay node determines to perform handover of the terminal based on the measurement report message and the radio resource management (RRM) information received from the terminal, and selects the target node. Select.

In step S420, the serving relay node sets a maximum handover delay time, which is a maximum allowable time for the terminal to maintain a connection with the serving relay node without executing handover from the serving relay node to the target node.

In step S430, the serving relay node calculates a time (hereinafter, referred to as a flushing time) required to empty all data packets stored in the transmission queue. Here, the specific method of calculating the flushing time is as described above with reference to FIG. 3.

In step S440, the serving relay node compares the flushing time with the maximum handover delay time to calculate the amount of data (hereinafter, the amount of transmission) that the serving relay node can directly transmit to the terminal before executing the handover.

As a result of the comparison in step S440, when the flushing time is less than or equal to the maximum handover delay time (YES), the amount of transmission is the total amount of data stored in the transmission queue of the serving relay node, and the process proceeds to step S450.

In step S450, the serving relay node may directly transmit all data packets stored in the transmission queue to the terminal during the flushing time.

On the contrary, when the flushing time exceeds the maximum handover delay time as a result of the comparison in step S440, the amount of transmission is determined by the maximum handover delay time, the duration of the frame, and the average amount of data transmitted to the terminal per frame. Can be calculated using. Here, the specific method for calculating the transmittable amount is as described above with reference to FIG. 3, and the flow proceeds to step S460.

In step S460, the serving relay node transmits the status information of the transmission queue including the amount of transmissions calculated in step S440 to the content server through the donor base station. The content server transmits the remaining data packets of the transmission queue to the target node, except for the data packets transmitted directly by the serving relay node to the terminal, based on the state information of the transmission queue received from the donor base station.

In step S470, the serving relay node may directly transmit a data packet corresponding to the amount of transmission calculated in step S440 from the transmission queue to the terminal for the maximum handover delay time. In this case, the data packets directly transmitted from the transmission queue to the terminal may be selectively selected sequentially according to the queued order (ie, in a first-in first-out (FIFO) manner) or according to the importance of the data packets.

According to one aspect of the present embodiment, in order to prevent deterioration of the channel state of the terminal, the serving relay node may temporarily increase the transmission power while transmitting the data packet directly to the terminal.

In addition, the time point at which the serving relay node transmits all of the available amounts of transmission to the terminal may be the handover execution time point of the terminal.

5 is a diagram illustrating a handover procedure according to another aspect of the present embodiment.

The handover procedure of FIG. 5 differs from the handover procedure of FIG. 3 at a time point at which a relay node transmits a data packet of a transmission queue to a terminal. Hereinafter, descriptions overlapping with those of FIG. 3 will be omitted or briefly described.

Referring to FIG. 5, in step 1, the terminal transmits a measurement report message to a relay node (hereinafter, referred to as a serving relay node) currently connected.

In step 2, the serving relay node determines to perform a handover of the terminal based on the measurement report message and the radio resource management information received from the terminal, and selects a target node.

In step 3, the serving relay node sets a maximum handover delay time and calculates a time (hereinafter, referred to as a flushing time) required to empty all data packets stored in the transmission queue. The serving relay node calculates the amount of transmission available to the terminal based on a comparison result between the maximum handover delay time and the flushing time. Each specific generation and calculation method is as described above with reference to FIG.

Through this process, the serving relay node generates state information of the transmission queue including the number of data packets that can be directly transmitted to the terminal before executing the handover.

In step 4, the serving relay node transmits a data packet stop request message including status information of a transmission queue to a donor base station.

In step 5, the donor base station stops transmitting the data packet to the serving relay node through the backhaul link in response to the data packet stop request message.

In step 6, the donor base station transmits the status information of the transmission queue included in the data packet stop request message to the content server.

In step 7, the content server transmits the remaining data packets to the target node except for the data packet to be directly transmitted to the terminal by the serving relay node based on the status information of the transmission queue received from the donor base station.

In step 8, the serving relay node transmits a handover request message to the target node through the donor base station.

In step 9, the serving relay node may directly transmit the number of data packets corresponding to the amount of transmission calculated in step 3 from the transmission queue to the terminal immediately after transmitting the handover request message.

)에 해당하는 개수의 데이터 패킷을 전송 큐로부터 단말로 직접 전송할 수 있다.Specifically, the serving relay node may sequentially transmit (ie, in a first-in first-out (FIFO) manner) according to the queued order.

The number of data packets corresponding to) may be directly transmitted from the transmission queue to the terminal.

)에 해당하는 개수의 데이터 패킷을 전송 큐로부터 단말로 직접 전송할 수 있다. 여기서, 데이터 패킷의 중요도는, 예컨대 H.264/AVC(Advanced Video Coding) 표준에 따른 멀티미디어 데이터 패킷의 경우, NAL(Network Abstraction Layer) 헤더의 Priority 필드 등을 기초로 식별될 수 있다.Alternatively, the serving relay node may selectively transmit the amount according to the importance of the queued data packet.

The number of data packets corresponding to) may be directly transmitted from the transmission queue to the terminal. In this case, the importance of the data packet may be identified based on, for example, a priority field of a network abstraction layer (NAL) header in the case of a multimedia data packet according to the H.264 / Advanced Video Coding (AVC) standard.

According to one aspect of the present embodiment, in order to prevent deterioration of the channel state of the terminal, the serving relay node may temporarily increase the transmission power while transmitting the data packet directly to the terminal.

The time point at which the serving relay node transmits all data packets corresponding to the amount of transmission possible from the transmission queue to the terminal may be a handover execution time of the terminal.

In step 10, the target node determines whether to accept the handover request based on the available radio resource status in response to the handover request message. That is, when the target node has a radio resource for connection with the terminal, the target node may accept the handover request.

When the target node accepts the handover request of the terminal, in step 11, the target node transmits a handover request acknowledgment message to the serving relay node through the donor base station.

In step 12, the serving relay node transmits a handover command to the terminal. The handover command is delivered through an RRC connection reconfiguration message.

In step 13, the UE that receives the RRC connection reconfiguration message performs synchronization for connection with the target node and accesses the target node through a random access channel (RACH). If the terminal successfully accesses the target node, in step 14, the terminal transmits a handover complete message to the target node, and the handover procedure is completed.

As described above, in FIGS. 2 to 5, a plurality of processes are sequentially performed, but this is merely illustrative of the technical idea of the present embodiment. In other words, a person of ordinary skill in the art to which the present embodiment belongs may perform the order described in FIGS. 2 to 5 or perform some of the plurality of processes in parallel without departing from the essential characteristics of the present embodiment. Since it will be applicable to various modifications and changes to be carried out as an example, Figures 2 to 5 are not limited to the time series order.

Meanwhile, the processes illustrated in FIGS. 2 to 5 may be embodied as computer readable codes on a computer readable recording medium. The computer-readable recording medium includes all kinds of recording devices in which data that can be read by a computer system is stored. That is, the computer-readable recording medium may be a magnetic storage medium (for example, ROM, floppy disk, hard disk, etc.), an optical reading medium (for example, CD-ROM, DVD, etc.) and a carrier wave (for example, the Internet Storage medium). The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion.

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

110: content server 130: base station
150: relay node 170: terminal

Claims (9)

In the data packet transmission method performed at the relay node for handover,
Determining to perform a handover to a target node based on the measurement report received from the terminal;
Calculating a flushing time, which is a time required to transmit all data packets of a transmission queue to the terminal, and a maximum delay time, which is a maximum time that can maintain a connection with the terminal from when the execution of the handover is determined; Calculating an amount of data packets that can be transmitted directly to the terminal based on a flushing time; And
And transmitting a data packet corresponding to the calculated amount of the data packet to the terminal, among all data packets in the transmission queue, in the handover procedure. The method of claim 1,
The state of the transmission queue including the calculated amount of data packets so that the remaining data packets of all data packets of the transmission queue except the data packets corresponding to the calculated amount of data packets are transmitted from a content server to the terminal. And transmitting information to the content server through a donor base station. The method of claim 1,
The target node,
A method of transmitting a data packet in a handover procedure, which is a base station or a relay node of a neighboring cell, which is different from a serving cell to which the terminal belongs. The method of claim 1,
The flushing time is,
And calculating the total amount of data packets in the transmission queue, an average amount of data packets transmitted to the terminal per frame, and a duration of the frame. The method of claim 1,
The data packet corresponding to the calculated amount of data packet,
A method of transmitting a data packet in a handover procedure, which is selected according to a first-in first-out (FIFO) scheme. The method of claim 1,
The data packet corresponding to the calculated amount of data packet,
A method of transmitting a data packet in a handover procedure, which is selected according to the importance of the data packet. The method of claim 1,
The transmitting step,
And transmitting a data packet corresponding to the calculated amount of data packet to the terminal to increase transmission power to prevent deterioration of the channel state of the terminal. delete delete

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