KR20140011593A - Method and apparatus transmitting control information in heterogeneous network - Google Patents

Abstract

A control information transmission method and an apparatus in a heterogeneous network is provided. The apparatus receives from a terminal, an event report including a cell identifier (ID) of a neighboring cell, when an event in which the intensity of a signal of a serving cell providing a service to the terminal becomes greater than the intensity of the neighboring cell by a certain offset or greater, is triggered. The apparatus also monitors, during a certain trigger time, the wireless connection status with the terminal, and transmits terminal context information to a target base station when the intensity of a signal received by the terminal is weaker than a certain reference value, and a measurement report is not transmitted from the terminal during a certain trigger time. According to the present invention, the RRC connection status can be maintained by successfully performing an RRC connection resetting process, the service can be well provided without disconnection, and disconnection of the service and battery consumption can be prevented. [Reference numerals] (AA) Terminal; (BB) Source base station; (CC) Target base station; (S400) Report an A3 event (Target cell ID); (S405) Wireless connection monitoring; (S406) Start an RLF; (S410) Terminal context information; (S415) Declare an RLF; (S420) Re-select a cell; (S425) Request an RRC connection reset; (S430) Reset RRC connection; (S435) Complete RRC connection reset

Description

METHOD AND APPARATUS TRANSMITTING CONTROL INFORMATION IN HETEROGENEOUS NETWORK}

The present invention relates to a wireless communication system, and more particularly, to a method and apparatus for transmitting control information in a heterogeneous network system.

In particular areas, such as hot spots inside the cell, there is a great demand for communication, and in certain areas such as cell edges or coverage holes, the reception sensitivity of radio waves may be reduced. Background of the Invention As wireless communication technology has developed, small cells in a macro cell, for example, a pico cell, have been used for the purpose of enabling communication in an area such as a hot spot, a cell boundary, A pico cell, a femtocell, a remote radio head (RRH), a relay, and a repeater are installed together. Such a network is called a heterogeneous network (HetNet). In a heterogeneous network environment, when compared with a femto cell and a pico cell, a macro cell is a large coverage cell, and a femto cell and a pico cell are small coverage cells.

A terminal connected to a heterogeneous network can perform communication with an arbitrary cell or perform a cell change according to a channel environment or a moving state. For example, a terminal may disconnect from a macro cell and connect to another macro cell or picocell due to deterioration of a channel state in a state of being connected to a macro cell. Or, as the terminal moves while connected to the macro cell, it can disconnect from the macro cell and connect to another macro cell or picocell.

When performing the handover from the macro cell to the pico cell, if the handover procedure fails, the UE tries to maintain the RRC connection by performing an RRC connection reestablishment procedure.

However, when signaling between the UE and the serving cell fails in the early stage of the need for handover and attempts to reset the RRC connection to the target cell to be handed over, the target cell may fail the RRC connection reconfiguration procedure because there is no context information of the corresponding UE. have. At this time, the UE transitions to the RRC idle state and then returns to the RRC connected state by performing an RRC connection establishment procedure. Therefore, there is a problem of disconnection of the service for a relatively long time, and the battery consumption increases due to more signaling.

An object of the present invention is to provide a method and apparatus for transmitting control information about a terminal between base stations.

Another object of the present invention is to provide a method and apparatus for transmitting control information for a terminal to perform an RRC connection reconfiguration procedure.

According to an aspect of the present invention, a method of transmitting control information by a base station in a heterogeneous network system triggers an event in which the signal strength of a neighboring cell becomes larger than a signal offset of a signal of a serving cell providing a service to a terminal. Receiving an event report including a cell ID of the neighbor cell from the terminal; Monitoring a wireless connection state with the terminal for a predetermined trigger time; And if the strength of the signal received by the terminal is weaker than a predetermined reference value and the measurement report is not transmitted from the terminal during the predetermined trigger time, transmitting terminal context information to a target base station.

According to another aspect of the present invention, if a base station transmitting control information in a heterogeneous network system triggers an event in which the signal strength of a neighbor cell becomes larger than a signal offset of a signal of a serving cell providing a service to a terminal, the event is triggered. A receiver configured to receive an event report including a cell ID of a neighbor cell from the terminal; A monitoring unit for monitoring a wireless connection state with the terminal for a predetermined trigger time; And a transmitter configured to transmit terminal context information to a target base station when the signal strength received by the terminal is weaker than a predetermined reference value and a measurement report is not transmitted from the terminal during the predetermined trigger time.

According to another aspect of the present invention, in a heterogeneous network system, a method of transmitting control information by a base station includes a signal strength of a signal received by a terminal from a serving cell is lower than a predetermined reference value, and a measurement report is transmitted from the terminal for a predetermined trigger time. If it is not transmitted to a source base station, receiving terminal context information from the source base station; Receiving a RRC connection re-establishment request message including a C-RNTI from the terminal; And if the terminal context information corresponds to the C-RNTI, transmitting an RRC connection reconfiguration message to the terminal.

According to another aspect of the present invention, a method for transmitting control information by a terminal in a heterogeneous network system includes an event in which the signal strength of a neighboring cell becomes larger than the signal strength of a serving cell providing a service to the terminal by a predetermined offset or more. If triggered, transmitting an event report including a cell identifier (ID) of the neighboring cell to a source base station; Transmitting a measurement report including a measurement result of performing measurement on the neighbor cell to the source base station; Declaring a radio connection failure with the serving cell and performing cell reselection; And transmitting a Radio Resource Control connection re-establishment request message including the C-RNTI to a target base station targeted for cell reselection.

According to the present invention, it is possible to successfully perform the RRC connection reset procedure to maintain the RRC connection state and provide a service relatively without interruption, and to prevent disconnection of the service and battery consumption.

1 schematically illustrates a concept of a heterogeneous network composed of a macro cell, a femtocell, and a picocell.
2 shows a distribution diagram of cells of various coverages in a heterogeneous network.
3 illustrates a wireless connection monitoring procedure and a handover procedure of a terminal to which the present invention is applied.
4 is a diagram illustrating an example of a UE performing an RRC connection reconfiguration procedure according to the present invention.
5 is a diagram illustrating an example of the strength of a signal received by a terminal according to the present invention.
6 is a block diagram illustrating a base station and a terminal for transmitting control information according to an embodiment of the present invention.

Hereinafter, the contents related to the present invention will be described in detail with reference to exemplary drawings and embodiments, together with the contents of the present invention. It should be noted that, in adding reference numerals to the constituent elements of the drawings, the same constituent elements are denoted by the same reference symbols as possible even if they are shown in different drawings. In addition, in describing the embodiments of the present specification, when it is determined that the detailed description of the related well-known configuration or function may obscure the subject matter of the present specification, the detailed description thereof will be omitted.

In describing the components of the present specification, terms such as first, second, A, B, (a), and (b) may be used. These terms are intended to distinguish the constituent elements from other constituent elements, and the terms do not limit the nature, order or order of the constituent elements. If a component is described as being "connected", "coupled", or "connected" to another component, that component may be directly connected or connected to that other component, but there is another component between each component. It will be understood that may be "connected", "coupled" or "connected".

On the other hand, the base station and the cell are not necessarily the same, and there may be a case where several cells are included in one base, and only one cell is included in one base. For the sake of convenience, the following describes that a terminal receives a service (or signal) from a base station or a cell, it also receives a service (or signal) from a cell (or serving cell) .

Simple cell segmentation of macro cells and micro cells makes it difficult to meet the growing demand for data services. Accordingly, a data service for small indoor and outdoor areas can be provided by using a pico cell, a femto cell, a relay, or the like. Although the use of small cells is not particularly limited, in general, picocells can be used in a communication shadow area, which is not covered only by macro cells, or in an area where data service demand is high, that is, hotspots. Femtocells are generally available in indoor offices or homes. In addition, the wireless relay can compensate for the coverage of the macrocell. By configuring a heterogeneous network (HetNet), not only the shadow areas of the data service can be eliminated, but also the data transmission speed can be increased.

1 schematically illustrates a concept of a heterogeneous network composed of a macro cell, a femtocell, and a picocell. For convenience of description, a heterogeneous network composed of macro cells, femtocells, and picocells is described, but the heterogeneous network may also include other types of cells. A femto cell is a low power wireless access point, which is a small base station for mobile communication used indoors such as a home or an office. The femtocell can be connected to the mobile communication core network using a home or office DSL or cable broadband.

Referring to FIG. 1, a macro base station 110, a femto base station 120, and a pico base station 130 are operated together in a heterogeneous network. The macro base station 110, the femto base station 120, and the pico base station 130 have unique cell coverage. The cell provided by the macro base station 110 is referred to as a macro cell 111 and the cell provided by the femto base station 120 is referred to as a femto cell 121 and the cell provided by the pico base station 130 is referred to as a pico cell 131. [

The femto base station 120 is a low power wireless access point, for example, a base station for a small mobile communication used in a room such as a home or an office. The femto base station 120 can access the mobile communication core network using a home or office DSL or cable broadband. The femto base station 120 is connected to a mobile communication network through a wired network such as the Internet. A terminal in a femtocell can access a mobile communication network or an Internet network through a femto base station. Although FIG. 1 illustrates a heterogeneous network composed of macro cells, femtocells, and picocells for convenience of description, the heterogeneous network may be configured to include relays or other types of cells.

The types of picocell are "picocell for coverage hole" (hereinafter referred to as "coverage hole picocell") and "picocell for hot spot" (hereinafter referred to as hotspot picocell).

The Coverage Hole Pico cell is used when a terminal can not transmit / receive data through a macro cell and a terminal transmits / receives data via a pico cell instead of a macro cell. A hotspot picocell is a device in which a terminal transmits and receives data through a picocell in place of a macrocell in order to reduce the load of the macrocell, although the terminal can transmit and receive data through the macrocell. Hot spots may also refer to areas where the population is flooded or residential, or where demand traffic is high. Generally, a hot spot region may occur irrespective of an electro-magnetic field. In this case, the pico-cell may be divided into two types, i.e., an intra-frequency pico cell and an inter-frequency pico cell. .

An intra-frequency picocell refers to a picocell that uses the same frequency band as a macrocell. By reusing the same frequency resources in spatially separated areas, the same radio resources as the macro cells can be secured within the pico cell coverage. A picocell for most coverage holes corresponds to an intra-frequency picocell.

An inter-frequency picocell is a picocell that uses a different frequency band from a macrocell. When the signal of the macro cell received in the hot spot region is strong, the performance degradation due to the interference problem between the pico cell and the macro cell may occur. And can be used when a hot spot exists at a position close to the center of the macro cell.

In general, the UE performs measurements to determine whether neighbor cells exist or not. At this time, the neighboring cells existing in the intra-frequency transmit signals through the same frequency band as the current serving cell. Therefore, it is possible to measure neighbor cells at the same time while transmitting and receiving with the serving cell. However, since neighboring cells existing in the inter-frequency transmit signals through a frequency band different from that of the serving cell, the UE temporarily suspends transmission / reception with the serving cell, retunes the RF chain, A signal for a frequency band identified as having a possibility of being present. Here, an RF chain refers to a portion of an antenna in which a filter and a power amplifier are combined. Therefore, measurements on neighboring cells in inter-frequency are limited in terms of time.

After the terminal performs the measurement, the measurement result is reported to the base station. This is referred to as a measurement report, which includes periodic reporting and event-triggered reporting. In the event-triggered reporting, the triggering of the event to be reported includes an A1 event (when the measurement result of the serving cell is larger than a predetermined threshold), an A2 event (when the measurement result of the serving cell is smaller than a predetermined threshold ), A3 event (when the measurement result of the neighboring cell is larger than the measurement result of the serving cell by a predetermined offset), A4 event (when the measurement result of the neighboring cell is larger than the predetermined threshold), A5 event (When the measurement result of the neighboring cell is larger than the predetermined threshold) or B2 (when the result is smaller than the measurement result of the neighboring cell by a predetermined offset), and in case of inter-RAT mobility Event (when the measurement result of the serving cell is smaller than the measurement result of the neighboring cell by a predetermined threshold value).

The measurement report may be performed through a measurement report message. The measurement report message may include reference signal received power (RSRP), reference signal received quality (RSRQ) values, physical cell ID (PCI), and cell global ID (CGI). do.

2 shows a distribution diagram of cells of various coverages in a heterogeneous network.

Referring to FIG. 2, macro cells and small cells are distributed in horizontal and vertical planes in meters, and the degree of distribution may be expressed by the number of macro cells and small cells. One hexagon represents a macro cell, and three hexagons (ie, macro cells) are collectively called a site. Many small cells are densified in each macro cell. The small cell may be located at the boundary of multiple macro cells. For example, for each cell size, the diameter of one site may be about 600m, the diameter of the macro cell may be about 300m, and the diameter of the small cell may be about 20-30m.

Now, a method apparatus for transmitting control information in a heterogeneous network system according to the present invention will be described.

3 illustrates a wireless connection monitoring procedure and a handover procedure of a terminal to which the present invention is applied.

Referring to FIG. 3, the radio link monitoring 300 is a procedure for determining a signal state of whether there is a problem in signal strength between a terminal and a current serving base station. The handover process 350 is a procedure in which a UE performs handover to a neighboring cell having a better signal state by comparing a signal strength of a serving cell and a signal strength of neighboring cells.

In the wireless connection monitoring 300 procedure, a radio link failure (RLF) timer T310 is started when radio problem detection (305) occurs (310) and when the terminal receives a handover command (378) It is reset (315). For example, if the channel quality information (CQI) is less than the predetermined threshold Qout, the radio problem is detected (305).

If the RLF timer T310 expires without being reset, an RLF may occur (320).

When the RLF occurs, the RLF timer T311 operates (325). The T311 starts operation when the UE sends an RRC connection reset request message to the base station after the RLF occurs and stops the operation when the UE transmits an RRC connection reset complete message to the UE. If the UE does not succeed in resetting the RRC connection for T311 time, the UE transitions to the RRC idle state.

On the other hand, the handover procedure 350 is composed of one step (state 1, 360), two steps (State 2, 370) and three steps (State 3, 390).

The first step 360 is before the event entry condition 365 and the second step 370 is after the event entry condition 365. Step 3 390 is after the handover command 378 is received. Here, the event entering condition (365) may be that the A3 event is triggered, it means a time when the signal of the target cell is larger than the signal of the current serving cell by a predetermined offset (for example, A3 offset) or more. . That is, since the signal strength of the target cell is larger than the current serving cell by the offset, it may be the first time point that it is determined that handover is necessary.

If the event entry condition 365 is satisfied, the terminal may perform measurement and finally determine whether to handover.

Event A3 is triggered to perform a measurement for a predetermined time (TTT, 372), trigger a measurement report (374) to proceed with the handover preparation time (376), and receive a handover command (378). In step 397, after the handover execution time 395 proceeds, the handover is completed (397).

If the UE succeeds in receiving the handover command 378, the RLF timer T310 is reset (315).

However, a problem may occur in the wireless connection during the TTT 372 to become a wireless problem detection 305. In this case, the UE may fail to receive a handover command 378 through PDCCH (Physical Downlink Control CHannel).

If the UE fails to receive the handover command 378, the RLF timer T310 continues to run. The RLF is generated 320 when the RLF timer T310 expires.

At this time, even though the terminal fails to receive the handover command (378), the terminal does not know whether it actually failed to receive the handover command, the RLF timer T310 is expired to generate the RLF (320) It is inevitable that the reception of the handover command has failed.

Alternatively, if a bad link condition is detected because the CQI is smaller than a predetermined threshold Qout (380), the UE requests a scheduling request (SR) requested to transmit a measurement report message. A problem may occur in a PDCCH order or an uplink grant. Therefore, the measurement report transmitted by the terminal may not be quickly and accurately transmitted to the base station, and it is difficult to determine that the terminal has properly received the handover command transmitted by the base station.

After the bad connection condition 380 is detected, if the bad connection 382 state in which the CQI is smaller than Qin continues, and the reception of the handover command 378 fails, the handover fails (382). However, the UE cannot know at that time whether the reception of the handover command 378 has failed, and it can be seen that the handover has failed at the time 320 when the T310 timer expires and the RLF occurs.

In this way, if the UE fails to handover due to the RLF, the RRC connection with the source cell is disconnected, so the RRC connection reestablishment is attempted. Here, the RRC connection reconfiguration procedure is used for resuming the existing connection when the UE in the RRC connected state is disconnected from the current source cell (or the RRC connection) (or when the RLF is generated).

The original terminal transmits the context information of the terminal to the target base station through the handover request message in the handover procedure.

An example of the context information of the terminal is shown in the following table.

Information element / group name Presence range Information element types and references UE Context Information One MME UE S1AP ID M INTEGER (0..2 ³² -1) > UE Security Capabilities M > AS Security Information M > UE Aggregate Maximum Bit Rate M Subscriber Profile ID for RAT / Frequency priority O

Here, UE context information is UE context information, MME UE S1AP ID is S1 Application Protocol ID of UE assigned to MME, and UE Security Capabilities are encryption and integrity protection of UE. Algorithms supported for protection, AS security information is a security key value used for the security of the terminal and the AS (Access Stratum), and the UE aggregate maximum bit rate is a guaranteed bit rate bearer applied to the terminal. The uplink and downlink maximum bit rate of the bearer is not, and the Subscriber profile ID for RAT / Frequency priority is a subscriber profile ID for RAT / Frequency priority. Presence indicates whether the presence of the element is mandatory or optional, M means mandatory, O means optional. An information element type is a type of the information element and a reference means that the type of the information element is defined elsewhere. The MME UE S1AP ID is one of integers between 0 and 2 ³² -1.

However, when the measurement report transmitted by the terminal is not successfully delivered to the source base station, the target cell may not have the UE context information. As such, when the UE intends to perform RRC connection reconfiguration to the cell, the target cell that does not have the context information of the UE is called an unprepared cell.

If the target cell of the handover is an unprepared cell, since the unprepared cell does not have UE context information, the RRC connection reconfiguration fails. If the RRC connection reset fails, the terminal transitions to the RRC idle state and then transitions to the RRC connected state through the RRC connection establishment procedure.

The RRC connection establishment procedure is a procedure for the RRC idle state terminal to perform the RRC connection with the base station. For example, when the terminal sends an RRC connection request to the base station (or EUTRAN), the base station (or EUTRAN) sends the RRC connection configuration to the terminal, the terminal sends the completion of the RRC connection configuration to the base station (or EUTRAN).

In this way, after the transition to the RRC idle state, the service received by the UE will not be interrupted or smoothed for a time taken until the RRC connection establishment procedure is successful.

On the other hand, there may also be a case where the measurement report of FIG. 3 is successfully delivered to the base station. In this case, the target cell is not ready because it can receive a UE context.

4 is a diagram illustrating an example of a UE performing an RRC connection reconfiguration procedure according to the present invention. As an example, the serving base station may be a base station of a pico cell and the target base station may be a base station of a macro cell.

Referring to FIG. 4, when an A3 event occurs (or an A3 event is triggered), the terminal transmits an A3 event report to the serving base station (S400). A3 event triggering may be an example of the event entry condition of FIG. 3, and an A3 event may occur when a signal strength of a target cell is greater than a signal strength of a current serving cell by a predetermined offset (for example, A3 offset). . This corresponds to the A3 event report 366 of FIG. 3. The A3 event report may include the target cell ID (ie, ID of the macro cell). The serving base station may determine a target base station to transmit the terminal context information based on the ID of the target cell.

After receiving the A3 event report, the source base station monitors the radio connection state with the terminal for a TTT time (S405). An operation similar to the radio connection monitoring operation performed by the terminal is performed at the base station.

For example, the base station monitors whether the PDCCH reception is successful during the TTT time from the time when the A3 event report is received from the terminal, and reaches the current terminal when the reception failure of the PDCCH is 10% or more (in another embodiment, 3% or more). It is determined that there is a problem in the signal strength of the wireless connection.

In the wireless communication system, the RLF may be defined based on the PDCCH reception success rate. The UE may detect a radio connection problem based on an error rate of 10% PDCCH in order to determine whether the RLF, and may define a Qout value by converting the CQI value (for example, SNR). Similarly, Qin can be defined as a CQI value based on a 3% error rate.

For example, the base station is a PDCCH requesting ACK / NACK (acknowledgement / non-acknowledgement) transmitted by the corresponding UE in the nth subframe to determine whether the PDCCH reception has failed, that is, C-RNTI (Cell-Radio Network Temporary) It is possible to check whether ACK / NACK for the PDCCH scrambled ID is received in the n + kth subframe. If ACK / NACK for the corresponding UE is not received in the n + kth subframe, this means that the PDCCH reception has failed in the UE. Here, the k value may be 4 in the case of frequency division duplex (FDD), and may be determined differently in downlink and uplink subframe configurations based on a TDD setting currently operating in the case of time division duplex (TDD). For example, in the case of TDD, the k value may be a value of 4 to 11. In addition, the k value may be defined in relation to a HARQ RTT (Hybrid Automatic Repeat request Round Trip Time) value. For example, it may be defined as half of the HARQ RTT value.

If it is determined that there is a problem with the signal strength of the wireless connection, and the base station does not receive the measurement report after both the TTT time and the predetermined offset value have elapsed after receiving the A3 event report, the base station may have a problem with the wireless connection. Therefore, it is determined that the measurement report has not been received, and it is determined that the handover has failed. The offset value is defined as a retransmission time point that the terminal can transmit last in consideration of the maximum number of HARQ retransmissions and the HARQ RTT value that can be transmitted through the uplink, which is a connection from the terminal to the base station.

On the other hand, when the PDCCH scrambled with the C-RNTI more than a predetermined number of times during the TTT time is determined, if it is determined that there is no problem in the signal strength of the wireless connection or the base station receives the measurement report message from the terminal, the RRC connection resetting procedure Perform a handover procedure.

Alternatively, when the PDCCH transmission is not performed for a predetermined number of times during the TTT time (for example, when the PDCCH transmission for the UE, ie, the PDCCH transmission that scrambled the C-RNTI is not performed), or the PDCCH generated during the entire TTT time. The monitoring result may be ignored when PDCCH transmission of less than n% of transmission opportunities (that is, when too small data transmission and reception occurs). This is because the base station can be regarded as a state in which there is no data transmission / reception with respect to a terminal that does not generate PDCCH scrambled C-RNTI, and thus may determine that it is not necessary to perform an RRC connection reconfiguration procedure as soon as possible. In other words, a user who does not receive a current data service even when the wireless communication service is disconnected while the RRC connection is reestablished through the RRC connection establishment after the RRC connection reset failure after the handover failure, which is a problem considered in the present invention, There is no dissatisfaction with the quality of service since no wireless communication service is used.

Simultaneously with step S405 or before and after S405, the radio side monitoring of the terminal side on the RRC connection state between the terminal and the current serving cell is started (S406). When the RLF timer T310 expires, the UE knows or detects a handover failure. In FIG. 3, it is a time point 320 when the RLF timer T310 expires.

If the source base station determines that the handover fails based on the operation of the wireless connection monitoring (S405), the source base station transmits the terminal context information to the target base station using the X2 interface (S410). The terminal context information may be information used by the terminal in the source base station. The terminal context information may be transferred from the source base station to the target base station through a UE context deliver message. The UE context transfer message may include both a C-RNTI value and UE context information.

The UE context information may include at least one of the MME UE S1AP ID, UE Security Capabilities, AS security information, and UE aggregate maximum bit rate Subscriber profile ID for RAT / Frequency priority of Table 1.

Subsequently, the terminal declares the RLF (S415). At this time, if the UE performs the radio connection monitoring by itself and the radio state does not recover until the RLF timer T310 expires (for example, if the CQI does not become larger than Qin), the UE confirms that there is a problem with the radio connection and performs the RRC connection reset procedure. do.

The terminal performs a cell reselection procedure (S420). For example, the UE may perform cell reselection to the target cell that the UE attempts to handover but fails due to an RLF.

Subsequently, the terminal transmits an RRC connection reestablishment request to the target base station in order to maintain the RRC connection state (ie, a state of receiving a service) (S425). For example, the terminal transmits an RRC connection reconfiguration request message to the target base station. The RRC connection reset request message may include a C-RNTI value.

Since the target cell has the terminal context information, it is not a ready cell.

The target base station determines whether there is terminal context information corresponding to the C-RNTI value based on the C-RNTI value included in the RRC connection reconfiguration request message. If the UE context information corresponding to the C-RNTI value exists, the target base station determines that the RRC connection reset is possible, and transmits an RRC connection reset message to the UE (S430).

Subsequently to step S430, the terminal transmits an RRC connection reset complete message to the target base station (S435).

5 is a diagram illustrating an example of the strength of a signal received by a terminal according to the present invention.

Referring to FIG. 5, when a terminal performs an RRC connection reconfiguration procedure from a source base station to a target base station, it indicates signal strength according to a moving distance of the terminal.

Although the serving base station is in the pico cell region and the target base station is in the macro cell region, an example will be described, but the scope of the present invention is not limited thereto.

As the terminal moves away from the source base station 500 in the pico cell region, the signal strength decreases drastically. On the other hand, when the terminal approaches the target base station 505 in the macro cell region, the signal strength gradually increases.

If the UE which fails in the handover due to the RLF generation because the target cell is not ready cell fails the RRC connection resetting procedure, since the UE transitions to the RRC idle mode and needs to start again from the RRC connection setup procedure, There is a disconnection of the service, and since the signal strength of the pico cell, which is the source cell, decreases drastically, it may have a very fatal effect on the terminal.

According to the present invention, even if the handover from the pico cell to the macro cell fails due to the RLF, since the target base station already has the context information of the terminal (that is, the target cell is not ready cell), the RRC connection reconfiguration procedure is performed. Since there is no context information, the data may be performed without fail to receive a service from the target base station.

On the other hand, when the source cell is a macro cell and the target cell is also a macro cell, the signal strength of the source cell is relatively not decreased so that the probability of failing to transmit a measurement report or a handover command message is relatively low. Therefore, it is less likely that the target cell becomes an unread cell.

6 is a block diagram illustrating a base station and a terminal for transmitting control information according to an embodiment of the present invention.

Referring to FIG. 6, the terminal 600 includes a receiver 610, a transmitter 620, and a controller 630.

The transmitter 620 includes a cell identifier (ID) of the neighboring cell when an event is generated in which the signal strength of the neighboring cell becomes larger than the signal strength of the serving cell providing the service to the terminal 600 by a predetermined offset or more. The event report is transmitted to the base station 650. In this case, the base station 650 may be a source base station. For example, an A3 event may be triggered, and an A3 event may occur when a signal strength of the target cell is greater than a signal strength of the current serving cell by a predetermined offset (for example, A3 offset). The serving base station may determine the target base station to which the terminal context information is to be transmitted based on the target cell ID (ie, macro cell ID) included in the A3 event report.

The transmitter 620 transmits a measurement report including a measurement result of measuring the neighbor cell to the source base station 650. If it is determined that there is a problem in the signal strength of the wireless connection, and the source base station 650 does not receive the measurement report after both the TTT time and the predetermined offset value elapse after receiving the A3 event report, the source base station ( 650 may determine that the measurement report has not been received due to a problem with the wireless connection, and may determine that the handover has failed.

The control unit 630 performs radio connection monitoring on the RRC connection state with the serving cell simultaneously with or after the monitoring of the serving base station 650, and a handover command message until the predetermined RLF timer T310 expires. If a situation that is determined to be a wireless connection failure occurs, such as when the reception is not received, the wireless connection failure with the serving cell is declared and cell reselection is performed. That is, if the mobile station monitors the radio connection by itself and does not recover the radio state until the RLF timer T310 expires (for example, if the CQI does not become larger than Qin), the UE confirms that there is a problem with the radio connection and performs the RRC connection reset procedure. And cell reselection procedure. For example, the UE may perform cell reselection to the target cell that the UE attempts to handover but fails due to an RLF.

The transmitter 620 transmits an RRC connection re-establishment request message including the C-RNTI to a target base station targeted for cell reselection.

When the target cell has the terminal context information and is not a ready cell, that is, when the terminal context information corresponds to the C-RNTI, the receiver 610 may reset the RRC connection. Receive from base station.

The controller 630 performs an RRC connection reset based on the RRC connection reset message.

After completing the RRC connection reset, the transmitter 620 transmits an RRC connection reset complete message to the target base station.

The base station may be the source base station 650 or the target base station 880 in the RRC connection reconfiguration procedure.

The source base station 650 includes a receiver 660, a monitor 670, and a transmitter 675.

The receiver 660 includes a cell identifier (ID) of the neighboring cell when an event is generated in which the signal strength of the neighboring cell becomes larger than the signal strength of the serving cell providing the service to the terminal 600 by a predetermined offset or more. An event report is received from the terminal 600.

The monitoring unit 670 monitors a wireless connection state with the terminal for a predetermined trigger time. For example, after receiving the A3 event report, the monitoring unit 670 monitors the wireless connection state with the terminal 600. An operation similar to the radio connection monitoring operation performed by the terminal is performed at the base station. As another example, the base station monitors whether the PDCCH reception is successful during the TTT time from the time when the A3 event report is received from the terminal to reach the current terminal when the reception failure of the PDCCH is 10% or more (in another embodiment, 3% or more). It is determined that there is a problem in the signal strength of the wireless connection. If it is determined that there is a problem in the signal strength of the wireless connection, and the source base station 650 does not receive the measurement report after both the TTT time and the predetermined offset value elapse after receiving the A3 event report, the source base station ( 650 may determine that the measurement report has not been received due to a problem with the wireless connection, and may determine that the handover has failed.

The transmitter 675 transmits the terminal context information to the target base station 680 when the strength of the signal received by the terminal is weaker than a predetermined reference value and the measurement report is not transmitted from the terminal during the predetermined trigger time. do. At this time, the X2 interface may be used. The terminal context information may be information used by the terminal in the source base station. The terminal context information may be transferred from a source base station to a target base station through a terminal context transfer message. The UE context transfer message may include both a C-RNTI value and UE context information.

The monitoring unit 670 monitors whether the UE has received a physical downlink control channel scrambled with a Cell-Radio Network Temporary Identifier of the serving cell. can do.

The transmitter 675 may transmit a cell-wireless network temporary identifier of the serving cell together with the terminal context information to the target base station 680.

The transmitter 675 transmits the terminal context information to the target base station 680 when the first measurement report transmitted by the terminal is not transmitted from the terminal during the predetermined trigger time.

Meanwhile, in the RRC connection reconfiguration procedure, the target base station 680 includes a transmitter 690 and a receiver 695.

The receiving unit 695 may determine the context of the terminal from the source base station 650 if the strength of the signal received from the serving cell is lower than a predetermined reference value and the measurement report is not transmitted from the terminal to the source base station for a predetermined trigger time. ) Receive the information.

The receiver 695 receives an RRC connection re-establishment request message including the C-RNTI from the terminal 600. The RRC connection reset request message may include a C-RNTI value.

When the terminal context information corresponds to the C-RNTI, the transmitter 690 transmits an RRC connection reconfiguration message to the terminal 600. That is, the transmitter 690 checks whether there is terminal context information corresponding to the C-RNTI value based on the C-RNTI value included in the RRC connection reconfiguration request message. If the UE context information corresponding to the C-RNTI value exists, the target base station determines that the RRC connection reset is possible, and transmits an RRC connection reset message to the UE.

The receiver 695 receives an RRC connection reset complete message from the terminal 600 when the terminal completes the RRC connection reset based on the RRC connection reset message.

In the above-described exemplary system, the methods are described on the basis of a flowchart as a series of steps or blocks, but the present invention is not limited to the order of the steps, and some steps may occur in different orders or simultaneously . It will also be understood by those skilled in the art that the steps shown in the flowchart are not exclusive and that other steps may be included or that one or more steps in the flowchart may be deleted without affecting the scope of the invention.

The above-described embodiments include examples of various aspects. While it is not possible to describe every possible combination for expressing various aspects, one of ordinary skill in the art will recognize that other combinations are possible. Accordingly, it is intended that the invention include all alternatives, modifications and variations that fall within the scope of the following claims.

Claims (13)

In a method for transmitting control information by a base station in a heterogeneous network system,
Receiving an event report including the cell identifier (ID) of the neighbor cell when the event that the signal strength of the neighbor cell becomes greater than a predetermined offset greater than the signal strength of the serving cell providing the service to the terminal is triggered step;
Monitoring a wireless connection state with the terminal for a predetermined trigger time; And
If the strength of the signal received by the terminal is less than a predetermined reference value and the measurement report is not transmitted from the terminal during the predetermined trigger time, the control information transmission method comprising transmitting the terminal context (context) information to a target base station . The method of claim 1,
Said monitoring.
And controlling whether the UE has received a physical downlink control channel scrambled with a Cell-Radio Network Temporary Identifier of the serving cell. Information transmission method. 3. The method of claim 2,
And transmitting the cell-wireless network temporary identifier of the serving cell together with the terminal context information to the target base station. The method of claim 1,
The measurement report is a control information transmission method, characterized in that the first measurement report transmitted from the terminal. In a base station for transmitting control information in a heterogeneous network system,
Receiving an event report including the cell identifier (ID) of the neighbor cell when the event that the signal strength of the neighbor cell becomes greater than a predetermined offset greater than the signal strength of the serving cell providing the service to the terminal is triggered Receiving unit;
A monitoring unit for monitoring a wireless connection state with the terminal for a predetermined trigger time;
And a transmitter configured to transmit terminal context information to a target base station when the signal received by the terminal is weaker than a predetermined reference value and a measurement report is not transmitted from the terminal during the predetermined trigger time. The method of claim 5, wherein
The monitoring unit,
A base station for monitoring whether the UE has received a physical downlink control channel scrambled with a Cell-Radio Network Temporary Identifier of the serving cell . The method according to claim 6,
Wherein the transmission unit comprises:
And a cell-wireless network temporary identifier of the serving cell along with the terminal context information to the target base station. The method of claim 5, wherein
Wherein the transmission unit comprises:
And the terminal context information is transmitted to the target base station if the first measurement report transmitted by the terminal is not transmitted from the terminal during the predetermined trigger time. In a method for transmitting control information by a base station in a heterogeneous network system,
Receiving terminal context information from the source base station if the strength of the signal received by the terminal from the serving cell is lower than a predetermined reference value and a measurement report is not transmitted from the terminal to the source base station for a predetermined trigger time;
Receiving a RRC connection re-establishment request message including a C-RNTI from the terminal; And
And if the terminal context information corresponds to the C-RNTI, transmitting an RRC connection reconfiguration message to the terminal. The method of claim 9,
And receiving the RRC connection resetting completion message from the terminal when the terminal completes the RRC connection resetting based on the RRC connection resetting message. In a method for transmitting control information by a terminal in a heterogeneous network system,
When an event is triggered in which the signal strength of a neighbor cell becomes larger than the signal strength of a signal of a serving cell providing a service to a terminal by a predetermined offset, transmitting an event report including a cell identifier (ID) of the neighbor cell to a source base station. step;
Transmitting a measurement report including a measurement result of performing measurement on the neighbor cell to the source base station;
Declaring a radio connection failure with the serving cell and performing cell reselection; And
And transmitting a Radio Resource Control connection re-establishment request message including a C-RNTI to a target base station targeted for cell reselection. 12. The method of claim 11,
If the terminal context information corresponds to the C-RNTI, receiving the RRC connection reestablishment message from the target base station. 13. The method of claim 12,
And after completing the RRC connection reset based on the RRC connection reset message, transmitting an RRC connection reset complete message to the target base station.

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