KR20150106807A - Method and apparatus for communicating in mobile communication networks - Google Patents

Abstract

Provided are a communication method and a communication device through an ultra-small cell in a mobile communication network. A terminal monitors a discovery signal transmitted from a ultra-small cell base station through an operation frequency of an upper base station located around the ultra-small cell base station, directly accesses the ultra-small cell base station when the discovery signal is detected, and performs data communications with the ultra-small cell base station without HARQ operation. Information related to an ultra-small cell which is required to communicate with neighboring ultra-small cell base stations is provided to the terminal from an existing base station.

Description

Field of the Invention [0001] The present invention relates to a method and apparatus for communicating in a mobile communication network,

The present invention relates to a method and apparatus for performing communications over very small cells in a multi-layered, hierarchical high-dense deployed mobile communication network.

The mobile communication system has been developed for the purpose of providing communication while ensuring the mobility of the user. The mobile communication system has come to the stage where it can provide high-speed data communication service as well as voice communication owing to the remarkable development of the technology. One of the next generation mobile communication systems, LTE-A (Long Term Evolution-Advanced), is a fourth generation communication standard developed by the 3rd Generation Partnership Project (3GPP). LTE-A includes a technique for implementing high-speed packet-based communication with a higher transmission rate.

With the development of LTE system, mobile communication system is developing rapidly. However, users are demanding more stable and high-level communication conditions, and the necessity of network capacity increase due to the development of multimedia contents is constantly being raised.

The standardization work of the fourth generation communication which ensures a stable and high transmission rate to the user has a discussion on a small cell technology in which a plurality of cells having a small service radius are arranged in order to increase the maximum transmission speed of the user . In addition, an extremely small-sized cell having a smaller service radius (for example, 5 m or less) than a small cell (for example, 5 m to several hundreds of meters) a multi-layer structure is proposed. Such a multi-layered mobile communication network is expected to provide users with improved transmission speeds and to provide efficient traffic control (i.e., offloading).

Because microcells are super-dense in the form of overlapping macrocells or small cells, they require innovative mobility support technologies. On the other hand, the extremely small service radius provides a very good channel environment (i.e. extremely low pathloss) and negligible uplink time difference, thus simplifying existing similar technologies or providing room for improvement in order to pursue high performance to provide. In addition, since the micro cells are arranged in a multi-layer structure in the form of a macro-small-micro cell overlapping with existing macro cells or small cells, interworking between the micro cells and existing cells (macro cells or small cells) This is very important. In particular, intelligent interworking with existing cells is required for efficient mobility support and traffic distribution control.

The present invention relates to a method and apparatus for effectively operating micro cells in a multi-layered ultra high density mobile communication environment.

The present invention relates to a method and apparatus for providing communication services through micro-cells in a mobile communication network.

The present invention relates to a method and an apparatus for allowing a terminal to easily dispose of an ultra-small cell in the vicinity.

The present invention relates to a method and apparatus for a terminal to set parameters that are applied to communication with a micro-cell.

The present invention is directed to a method and apparatus for changing and changing parameters for error correction techniques.

The present invention is directed to a method and apparatus for changing and switching parameters for serving cell and neighbor cell measurements.

A method according to a preferred embodiment of the present invention comprises: A method for communicating a terminal in a mobile communication network, the method comprising: monitoring a discovery signal transmitted from the microcell base station through an operating frequency of an upper base station located in the vicinity of the microcell base station; And performing data communication with the micro cell base station without performing a Hybrid Automatic Retransmission Request (HARQ) operation.

A method according to another embodiment of the present invention is a communication method of a base station in a mobile communication network, the method comprising: determining to further set a micro cell for a serving terminal; Requesting discovery signal information for the micro-cells of the cell, and transmitting the micro-cell-related information on neighboring micro-cells to the UEs based on the information received from the small cell base station.

An apparatus according to an exemplary embodiment of the present invention is a terminal apparatus for performing communication in a mobile communication network. The apparatus monitors a discovery signal transmitted from the micro-cell base station through an operating frequency of an upper- And a controller for directly accessing the microcell base station when the discovery signal is detected and controlling the transceiver to perform data communication with the microcell base station without HARQ operation.

According to another aspect of the present invention, there is provided a base station apparatus for performing communication in a mobile communication network, the apparatus comprising: a control unit for deciding to additionally set a small cell for a serving terminal; And a transceiver for requesting discovery signal information for at least one microcell and for transmitting the microcell related information about neighboring microcells to the terminals in the cell based on information received from the small cell base station .

Wherein the discovery signal information includes at least one of information specifying each micro cell, information specifying a frequency and a time resource in which a discovery signal is transmitted from each micro cell, and a signal pattern of the discovery signal, The related information includes information for specifying each micro cell, information for specifying a transmission resource to which the discovery signal from each micro cell is transmitted, operating frequency and physical cell identifier (PCI) range of each micro cell, Information on a first threshold value for determining access or non-accessibility, a second threshold value for determining whether to maintain a connection of the corresponding micro cell, information on a transmission resource used for direct access to the micro cell, direct access window information, Access back-off information, and information on the TA of the corresponding micro-cell.

A method according to an embodiment of the present invention comprises: A method of communicating a terminal in a mobile communication network, the method comprising: receiving measurement related information from a network; performing measurements on signals of a serving cell and at least one neighboring cell based on the measurement related information; Determining whether to perform a measurement result report according to a measurement result, determining whether the measurement result falls within a predetermined range, and, when the measurement result falls within the range, Reporting to the network a first information unit set to a predetermined value and a second information unit indicating a measurement result if the measurement result does not fall within the range; do.

A method according to an embodiment of the present invention comprises: A method for communicating a base station in a mobile communication network, the method comprising: transmitting measurement related information to a terminal; receiving a measurement message from a terminal, Wherein the message includes a first information unit indicating the measurement result when the measurement result belongs to the range, and when the measurement result does not belong to the range, a predetermined value And a second information unit indicating the measurement result.

An apparatus according to an embodiment of the present invention includes: A terminal apparatus for performing communication in a mobile communication network, comprising: a transceiver for receiving measurement-related information from a network; and means for performing measurements on signals of a serving cell and at least one neighboring cell based on the measurement- Determining whether to perform a measurement result report according to the measurement result, determining whether the measurement result falls within a predetermined range, and, when the measurement result falls within the range, And transmits the first information unit set to a predetermined value and the second information unit indicating the measurement result to the network through the transceiver when the measurement result does not fall within the range, And a control unit for reporting.

An apparatus according to an embodiment of the present invention includes: A base station apparatus for performing communication in a mobile communication network, the base station apparatus comprising: measurement-related information transmission means for transmitting measurement-related information to a terminal; a message indicating a measurement result of signals of the serving cell and the at least one neighboring cell from the terminal, And a control unit for analyzing the message, wherein the message includes a first information unit indicating the measurement result when the measurement result falls within the range, The first information unit set to a predetermined value and the second information unit indicating the measurement result.

1 is a diagram for explaining a network structure of a multi-layered mobile communication environment.
2 is a flowchart illustrating a procedure for performing data communication through a micro-cell according to an embodiment of the present invention.
3 is a message flow diagram illustrating an overall procedure for communication in a micro-cell according to an embodiment of the present invention.
4 is a flowchart illustrating an operation of a terminal for communication in a micro-cell according to an embodiment of the present invention.
FIG. 5 illustrates transmission resources of an ultra small cell discovery signal according to an embodiment of the present invention.
6 is a message flow diagram illustrating a procedure for receiving a discovery signal of a micro-cell according to an embodiment of the present invention.
7 is a message flow diagram illustrating a direct access procedure for a micro-cell according to an embodiment of the present invention.
8 is a block diagram for explaining a direct access operation when connecting a small cell or an ultra small cell
9 shows a timing diagram of a direct access operation in accordance with an embodiment of the present invention.
10 is a message flow diagram illustrating a procedure for setting an error correction technique for a micro-cell according to an embodiment of the present invention.
11 is a flowchart illustrating an operation of switching an error correction technique according to an embodiment of the present invention.
12 is a flowchart illustrating an operation of selecting a measurement report method according to an embodiment of the present invention.
13 is a block diagram illustrating a structure of a terminal according to an embodiment of the present invention.
14 is a block diagram illustrating a structure of a base station according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. The following terms are defined in consideration of the functions of the present invention, and these may be changed according to the intention of the user, the operator, or the like. Therefore, the definition should be based on the contents throughout this specification.

1 shows a network structure of a multi-layered mobile communication environment. As shown in the figure, in the multi-layered mobile communication environment, the macro cell 135, the small cell 125, and the micro cells 100 coexist and the terminal connects to any one of the cells 100, 105, Transmit or receive.

Referring to FIG. 1, the macro cell base station 130 covers the macro cell 135, which is a very large service area, and is mainly useful for servicing terminals moving at high speed. The small cell 125 has a smaller service area than the macro cell 135 and the small cell base station 105 can be connected to a wired backhaul 115 for flexible interworking with the macro cell base station 130 . The wired backhaul 115 is used to exchange control signaling for interworking between the base stations and is used to transfer the data of the terminals connected to the small cell 125 to the small cell 125 according to the user plane protocol structure It is possible.

The micro-cell 100 provides a smaller service area than the small cell 125 and can provide high-speed data service to a terminal moving at a very low speed or not moving. The micro cell base station 100 may interwork with an upper cell such as the macro cell base station 130 or the small cell base station 120 to service a terminal connected to the micro cell 100. [ The macro cell base station 100 or the small cell base station 120 can be arranged in a compact manner within a macro cell 135 or a small cell 125, And wired backhaul may be inefficient. Accordingly, the micro-cell base station 100 can interwork with the small cell base station 120 or the macro-cell base station 130 using a wireless backhaul 110. [

For convenience of explanation, the cells are classified into a type 0 cell (macro cell), a type 1 cell (small cell), and a type 2 cell (micro cell). The Type 0 cell refers to a macro cell in a general cellular environment, and the Type 1 cell is a small cell that covers an area much smaller than a macro cell. Type 2 cells are very small cells that cover much smaller areas than small cells and are arranged to maximize cell splitting gain to cope with the explosive increase in data demand. Within a given area, a plurality of micro-cells may be arranged, and the area covered by one micro-cell may be significantly smaller than the area covered by a typical cellular cell. For example, when a macro cell covers an area of several hundreds of meters in radius, and a small cell covers an area of several tens of meters in radius, the micro cell can cover an area having a radius of m.

Several conditions must be met in order for the micro cell to operate efficiently. First, in order to increase the density of numerous micro cells, the deployment cost of the micro cells must be sufficiently low. In other words, without the operator having to establish a precise cell plan, the micro cell must be able to be deployed without connecting the wired backbone. For this, the micro-cell is directly connected to an anchor node in a higher level, instead of being directly connected to the existing cellular network, and the anchor node can be connected to a cellular network and a wired backbone. The anchor node connected to the micro-cell may be, for example, a small cell base station or a macro cell base station. That is, the micro cell is wirelessly connected to the small cell base station, and the small cell base station can be connected to the macro cell base station and the core network and the wired backbone. In other implementations, the microcell can be connected to the macrocell base station and the wireless backbone.

Since the radio wave arrival region of the microcell is extremely narrow, the period of time in which the terminal stays in the area of the microcell can be relatively short. Therefore, in order to maximize the use of the resources of the micro-cell in a given period, the micro-cell base station should quickly recognize that the mobile station has entered the area of the micro-cell, and promptly start data communication of the mobile station in the micro-cell. In order for the terminal to use the transmission resources of the micro-cells as much as possible within a given time, it is desirable for the terminal to determine itself and resume communication immediately.

In order to satisfy the precondition for the efficient operation of the micro-cell as described above, the terminal must quickly discovery the micro-cell without consuming another battery, and start transmitting / receiving data quickly in the found micro-cell.

2 is a flowchart illustrating a procedure for performing data communication through a micro-cell according to an embodiment of the present invention.

2, the UE 200 performs the following three processes 210, 215, and 220 in order to be connected to the micro-cell base station 205 and receive data communication services. Although the miniature cell base station 205 is illustrated as being directly connected to the terminal 200, the miniature cell base station 205 may be connected to the terminal 200 through a small cell base station (not shown) The base station 205 may be wirelessly connected to the small cell base station and the small cell base station may be connected to the macro cell base station by wire.

In step 210, the terminal 200 determines whether a connectable microcell base station 205 exists in the vicinity, and discovers the microcell base station 205. The terminal may periodically tune the transceiver to a non-serving frequency to search for a cell other than its serving frequency, i.e., a cell of a non-serving frequency, Frequency signal. Information on the non-serving frequency that can detect the presence of the micro cell base station can be provided to the terminal 200 from the macro cell base station or the small cell base station serving as the serving base station.

In step 215, the UE 200 detects a procedure for creating a small cell of the UE 206 as a serving cell of the UE, for example, uplink synchronization And reports that it has successfully connected to the microcell base station 205. At this time, the terminal 200 does not receive an explicit instruction from the macro cell base station or the small cell base station and attempts direct access to the miniature cell base station 205 when the connectable miniature cell base station 205 is found. In order to perform the direct access, the terminal 200 performs four-step Random Access (RA) such as preamble transmission, response reception, request message transmission, and contention resolution message reception in a general cell Instead, a layer 2 (L2) control message for direct access is directly transmitted to the microcell base station 205 by using a transmission resource satisfying a predetermined condition.

After the direct access is successfully performed, in step 220, the UE performs data transmission / reception in the ultra-small cell (220). Performs ARQ (Automatic Retransmission Request) and HARQ (Hybrid ARQ) operations for error correction in data communication in a macro cell or a small cell. Usually ARQ is performed in the RLC (Radio Link Control) layer, and HARQ is performed in the MAC (Media Access Control) layer. On the other hand, since a very small cell has a very small service radius, it can be assumed that it normally has a very good communication environment. Therefore, it is not necessary to perform an ARQ or HARQ operation for error correction in a very small cell. Therefore, in a communication in a very small cell, a UE can adjust parameters for ARQ and HARQ operations to exclude or simplify an error correcting operation.

3 is a flowchart illustrating an operation of a terminal for communication in a micro-cell according to an embodiment of the present invention. Here, the macro cell base station 305 manages the frequency f1, the small cell base station 310 that operates the frequency f2 in the macro cell covered by the macro cell base station 305, and the micro cell base station 315 that operates the frequency f3 ) And the micro cell BS 2 (320) exist.

Referring to FIG. 3, the MS 300 may communicate with the MS 300 or MS 320 through a small cell BS 310. In the case of communicating with the micro cell base station 315 or 320 through the micro cell base station 310, in step 325 and step 330, the mobile station 300 performs an operation for adding a small cell according to the setting of the macro cell base station 305 . That is, in step 325, the terminal 300 provides measurement information (signal measurement values) of neighboring small cells to the macro cell base station 305, and the macro cell base station 305 transmits the measurement information And transmits the setting information of the small cell base station 310 of the small cell to which the addition is determined to the terminal 300. [ In operation 330, the terminal 300 performs a random access and a cell activation trigger operation to connect to the small cell base station 310 based on the setting information.

In step 335, the macro cell base station 305 determines to add the micro cell to the terminal 300. The macro cell base station 305 may count the signal strengths of the macro cell base station 305 and the small cell base station 310 sufficiently to service the terminal 300 based on the measurement information reported from the terminal 300 Determines to add the micro cell to the terminal 300 in the case where the terminal 300 determines that the terminal 300 is adjacent to the area where the microcell base station is located based on the location information of the terminal 300, To the micro-cell. In another embodiment, the MS 300 may determine to perform the micro-cell addition when the signal strength of the serving cell (macro cell or small cell) satisfies a predetermined condition without the control of the macro cell base station 305. [

In operation 340, the UE 300 performs an ultra-small cell discovery to find neighboring micro-cells. As an example, the terminal 300 may monitor the discovery signals transmitted from the neighboring microcell base stations 315 and 320, and may detect the microcell based on the detected discovery signal. A more detailed description of the miniature cell discovery will be described later.

In step 345, the MS 300 finds a very small cell of the MS 320, and in step 350, the MS 300 attempts to directly access the MS 320 of the MS 300. The small cell base station 2 320 notifies the small cell base station 310 which is the current serving base station of the terminal 300 that the terminal 300 directly attempts to access the small cell base station 310, Lt; / RTI > When the current serving BS of the MS 300 is the macro cell BS 305, the macro cell BS 305 can identify the MS 300 in response to a request from the MS2 320.

The downlink data for the terminal 300 is transmitted from the small cell base station 310 to the small cell base station 2 320 in step 360 and the small cell base station 2 320 transmits the downlink data to the terminal 300 do. The uplink data of the MS 300 is received by the MSB 320 in step 365 and the MS 320 receives the uplink data from the MS 300. In step 365, To the small cell base station (310).

In step 370, the UE detects an out-of-service area of the UE 320, and in step 375, transmits an indicator for indicating the UE to the UE serving as a serving BS. In one embodiment, the indicator may be defined as an L2 message. After the small cell base station 310 detects the small cell detachment of the terminal 300, the terminal 300 receives the data service from the small cell base station 310 in step 380.

In the above signal flow, the case where the small cell base station 310 is the serving base station of the terminal 300 before the entry of the micro cell is described. However, when the macro cell base station 305 is the serving base station of the terminal 300, The macro cell base station 305 may interwork with the small cell base station 2 320 to serve the terminal 300. [

As described above, in the case of a small cell base station and a small cell connected with a macro cell base station and a wired backbone, and a mobile communication system in which a small cell base station and a mini-cell base station connected with a wireless backbone and a very small cell exist, In order to perform communication, the small cell related information required for communication with the micro cell is received from the small cell base station or the macro cell base station, and the micro cell can be discovered and accessed to perform communication.

In one embodiment, the micro-cell related information may include at least one of the following information.

- Discovery signal information: information for specifying a cell to which a discovery signal is transmitted, information for specifying a transmission resource (frequency / time resource) to which the discovery signal is transmitted

- Smallest cell information: the operating frequency of the micro cell and the physical cell identification (PCI) range of the micro cell. Here, the PCI range means an identifier range of cells allowed to be set by the terminal as a secondary serving cell.

- Thresholds: a threshold value (hereinafter referred to as TH1) of a discovery signal for determining whether or not to access the micro cell, and a threshold value (hereinafter referred to as TH2) of a pilot signal for determining whether to maintain connection of the micro cell. Here, the discovery signal is a signal used for finding a micro-cell, and can be transmitted through the operating frequency of the micro-cell or the operating frequency of other cells in the vicinity. Also, the pilot signal is a signal that can be detected while connecting to the micro-cell, and is transmitted through the operating frequency of the micro-cell.

- Direct access related information: direct access transmission resource information, direct access window information, direct access backoff information

- TA (Timing Advance) information: difference between downlink timing and uplink timing of a micro cell. The UE establishes the uplink frame timing at a time point preceding the TA in the downlink frame timing of the miniature cell.

In order to minimize the battery consumption for the discovery operation of the terminal, the microcell base station may set the operating frequency of the small cell (for example, f2) or the operating frequency of the macrocell (for example, (E. G., F1). ≪ / RTI > In other words, the microcell base station uses the operating frequency of the small cell or the macro cell at which it is located for the transmission of the discovery signal. The device / cell that transmits the discovery signal and the device / cell that owns (or controls or controls) the resource to which the discovery signal is transmitted may be different. The terminal recognizes the actual operating frequency of the micro-cell and the frequency at which the micro-cell discovery signal is transmitted through the micro-cell related information. The micro-cell discovery signal is transmitted at the frequency at which the UE is tuned (i.e., the serving frequency of the UE), so that the UE can detect whether the UE is in the vicinity by searching for the current serving frequency without additional battery consumption.

4 is a flowchart illustrating an operation of a terminal for communication in a micro-cell according to an embodiment of the present invention.

Referring to FIG. 4, in step 400, the UE receives information about neighboring micro cells from a macro cell or a small cell, and micro cell related information necessary for performing communication in the micro cells. The micro cell related information may include information related to the macro cell or all the micro cells existing in the small cell.

In step 405, the terminal searches for discovery signals of the micro-cells through the discovery transmission resource based on the micro-cell related information. As described above, the discovery signal of the micro-cell is transmitted at the operating frequency of a small cell or a macro cell that covers a wider area than an operating frequency of the micro-cell. Accordingly, the terminal can receive the discovery signal of the ultra-small cell without separately monitoring the operating frequency of the ultra-small cell. In step 407, the MS detects a discovery signal of at least one micro-cell and determines whether the strength of the discovery signal is greater than TH 1. The TH 1 may be obtained from the micro-cell-related information of the process 400, or may be preset.

If the strength of the discovery signal is not greater than TH 1 or if the discovery signal continues to stay above TH 1 for a predetermined time, the terminal may continue to monitor neighboring micro cells in step 405. If the UE does not find a suitable small cell for a predetermined time, it can report that the connection with the small cell is not possible to the serving base station and terminate the miniature cell discovery operation.

If the strength of the discovery signal is greater than TH1 or if the intensity of the discovery signal continues to be greater than TH1 for a predetermined period of time, in step 410, the terminal transmits the discovery signal to the transceiver at the operating frequency of the micro- . The operating frequency of the micro-cell may be obtained from the micro-cell related information of the process 400. If a plurality of micro-cells having a signal strength greater than TH 1 are detected, the UE selects one of the micro-cells providing the largest signal strength among the plurality of cells, or considering one of the micro- You can choose.

In step 415, the UE performs downlink synchronization with the micro-cell. The downlink synchronization includes an operation in which a terminal receives a synchronization signal of the microcell and acquires a frame timing of the microcell, and the terminal having established the downlink synchronization can correctly receive the downlink signal of the microcell do. The downlink synchronization may be performed, for example, according to the operation defined in the standard TS 36.213.

In step 420, the UE determines the uplink transmission timing in consideration of the downlink reception timing. For example, the uplink transmission timing can be calculated by acquiring from the micro-cell related information at the downlink reception timing or applying a predetermined TA. That is, the UE can determine the uplink transmission timing by applying a pre-signaled TA to the downlink reception timing of the micro-cell from the serving base station through an RRC (Radio Resource Control) control message. TA is for correcting the propagation delay. In the case of a very small cell, the propagation delay is negligible, so that it can be provided in advance through the micro cell related information. Determining that the uplink transmission timing is the same as establishing uplink synchronization. In other words, the UE establishes uplink synchronization using the indicated TA through the micro-cell related information. If the TA is not indicated through the micro cell related information, the terminal assumes TA to be 0. In other words, the uplink transmission timing is considered to coincide with the downlink reception timing. Or the UL frame boundary is determined to coincide with the DL frame boundary.

In step 425, the UE monitors a scheduling channel of a very small cell. The scheduling channel is also referred to as a physical downlink control channel (PDCCH), and carries downlink grant information (DL grant), which is downlink allocation information (DL Assignment) or uplink scheduling information, which is downlink scheduling information. The structure of the PDCCH and the downlink / downlink scheduling information are as defined in Specification 36.211 or Specification 36.212. The microcell base station transmits downlink allocation information or uplink grant information for a specific UE through the scheduling channel. At this time, at least a part of downlink allocation information or uplink grant information is scrambled or masked with a specific identifier. The terminal performs a CRC (Cyclic Redundancy Check) operation in a predetermined manner based on a specific identifier for the received scheduling information, Or the scheduling information transmitted to the mobile station.

Scheduling information for UEs accessing the micro cells is scrambled or masked with a Radio Network Temporary Identifier (RNTI), for example a DA (Direct Access) -RNTI, which is a predefined identifier. That is, downlink allocation information or uplink grant information of the micro-cells is addressed by the DA-RNTI.

In step 430, the UE attempts to receive UL grant indicated by the DA-RNTI. Specifically, the UE performs a CRC operation using a DA-RNTI defined in advance for uplink grant information received through a scheduling channel of a very small cell. If the CRC operation is successful, the UE determines that the UL grant information allocated to the UE has been successfully received. The DA-RNTI is a public identifier used in the micro-cells, and the UEs in the micro-cells can transmit uplink data according to uplink grant information, which is scheduling information designated by the DA-RNTI. Upon receiving the UL grant information addressed to the DA-RNTI, in step 435, the UE transmits control information for reporting that the UE accesses the UL cell through the UL transmission resource allocated by the UL grant information do. The control information is conveyed to a micro cell base station via a Media Access Control Packet Data Unit (MAC PDU) as an example.

The MAC PDU includes a MAC Control Element (CE), which is MAC control information including a C-RNTI, which is a unique identifier of the UE. The control information used to report to the micro-cell that a new terminal accesses the micro-cell is hereinafter referred to as DA MAC CE. The DA MAC CE may include at least one of the following information.

- C-RNTI of a terminal used in a macro cell or a small cell. The UE performs data transmission / reception in a very small cell using the C-RNTI in the future.

- Information specifying the cell in which the terminal is currently establishing a connection (ie, the serving cell of the terminal). For example, the PCI and center frequency information of the serving cell. Or information that specifies the serving cell (i.e., cell that owns the discovery signal transmission resource) from which the terminal received the discovery signal.

- DA Header information specifying MAC CE. For example, a Logical Channel Identification (LCID) included in the MAC CE is coded with a value indicating that the MAC CE is a DA MAC CE.

When the MAC PDU including the DA MAC CE has successfully arrived at the microcell base station, the microcell base station recognizes the access of the MS and transmits UL grant information or DL allocation information addressed to the C-RNTI of the MS to the MS , And notifies the terminal that the access has been successfully completed. Accordingly, after transmitting the DA MAC CE according to the uplink grant information addressed to the DA-RNTI, the UE determines whether uplink grant information or downlink allocation information addressed to its C-RNTI is received for a predetermined period in step 440 Monitoring. The predetermined period is referred to as a direct access window and can be indicated by direct access window information included in the micro cell related information of the process 400. If the scheduling information addressed to the C-RNTI is received before the direct access window is terminated, the terminal proceeds to step 445. [

On the other hand, if the scheduling information addressed to the C-RNTI is not received until the direct access window expires, the terminal determines that the transmission of the DA MAC CE fails (that is, the direct access has failed) Resume the CE transfer procedure. The failure of the direct access means that the collision between the DA MAC CEs occurs when the other UEs use the scheduling information indicated by the DA-RNTI, or when the DA MAC CE transmitted by the UE has not been successfully received by the micro- Can happen.

Although not shown, the scheduling information addressed to the C-RNTI from the microcell base station despite the fact that the DA MAC CE is transmitted and the scheduling information addressed to the C-RNTI is monitored for a predetermined number of n times during the direct access window The UE can abandon the access to the micro cell and perform the discovery signal search to find a new micro cell. When searching for a new microcell, the microcell can be excluded from access even if the microcell that previously failed to access provides a signal strength that exceeds the threshold. This is because, if an access attempt fails because many terminals attempt to connect to the microcell, the access may fail even if the signal strength of the microcell is still good.

In step 445, the UE stops monitoring the DA-RNTI and starts data communication in the ultra-small cell in step 450. That is, the UE receives downlink data or transmits uplink data according to downlink allocation information or uplink grant information addressed to the C-RNTI. A terminal that succeeds in accessing a micro cell can connect only a part of bearers of a plurality of bearers set in the UE to a micro cell. In a mobile communication system such as LTE and LTE-A, a packet stream requiring a predetermined QoS (Quality of Service) can be served through one bearer. For example, within a terminal, Voice over Internet Protocol (VoIP) is serviced through bearer x while FTP (File Transfer Protocol) is serviced via bearer y. When a plurality of bearers are set in the UE, the UE may serve only some indicated bearers among the set bearers in the micro cell according to the instructions of the network (or macro cell or small cell base station) Can be serviced in small cells.

In step 450, a new error correction technique, which is not an error correction technique used in a macro cell or a small cell, can be used when a UE transmits and receives data of a predetermined bearer through a micro-cell. For convenience of explanation, an error correction technique used in a macro cell or a small cell is called an error correction technique 1, and an error correction technique used in a micro cell is called an error correction technique 2. In a very small cell, a UE can decide whether to convert an error correction technique of a specific bearer into an error correction technique 2 in an error correction technique 1 without any instruction from a macro cell base station or a small cell base station. As described above, since the UE can have a very good communication environment in the micro-cell, the error correction technique 2 used in the micro-cell can restrict the number of transmissions by one, for example.

In step 455, the UE determines whether the signal strength of the pilot signal transmitted from the ultra-small cell is lower than a predetermined threshold value TH 2 while transmitting and receiving data in the ultra-small cell. The threshold value TH 2 is predetermined as an example, or a value that can be obtained from the microcell-related information of the process 400, and is used to determine whether or not to continue the connection with the currently connected microcell. In other words, the terminal can quickly and quickly determine the return from the microcell to the previous serving cell without control of the network (or base station).

If the signal strength of the pilot signal is not lower than TH 2, the terminal continues to transmit and receive data in the ultra-small cell. On the other hand, if the signal strength of the pilot signal is lower than TH 2, or if the signal intensity of the pilot signal continues to be lower than TH 2 for a predetermined time, communication with the microcell is stopped in step 460, The operation of the transceiver with respect to the operating frequency of the transceiver is stopped.

In step 465, the UE transmits a MAC PDU containing a MAC CE for reporting the connection disconnection to the previous serving cell, that is, the macro cell or the small cell, to the base station of the previous serving cell. In step 470, the MS restarts data communication with the macro cell or the small cell, which is the previous serving cell. In a macro cell or a small cell, the UE performs data transmission / reception using the error correction technique 1.

As described above, the terminal considers the signal strength of the discovery signal transmitted at an operating frequency other than the operating frequency of the micro-cell, in order to determine whether to start direct access in the micro-cell. In order to determine whether to continue transmitting and receiving data in a very small cell (or whether to maintain a connection with the small cell or whether to keep the small cell in a secondary serving cell (SCell)), Consider the signal strength of the pilot channel transmitted at the operating frequency of the cell.

FIG. 5 illustrates transmission resources of an ultra small cell discovery signal according to an embodiment of the present invention.

Referring to FIG. 5, the discovery signal of the micro-cells may be transmitted in a predetermined resource unit 500 on a two-dimensional resource area having a frequency and a time. The terminal receives a discovery signal periodically transmitted by the micro-cells, and can identify the micro-cells in the vicinity. The transmission resource information (frequency and time specifying pattern) of the discovery signal is provided from a macro cell or a small cell. The UE can recognize the transmission resource of the discovery signal from the micro cell related information provided from the macro cell or the small cell serving as the serving cell.

The discovery signal of the micro-cell may be transmitted in a different frequency band than the operating frequency band of the micro-cell. In one embodiment, in order to minimize battery consumption of a terminal, a discovery signal may be transmitted through a frequency / time resource of a macrocell or a small cell in which the microcell is located. For convenience of explanation, the cell having the frequency / time resource to which the discovery signal is transmitted is referred to as a discovery signal resource cell. The terminal transmits and receives data in a discovery signal resource cell and receives a discovery signal transmitted from the micro-cell through a predetermined frequency / time resource of the discovery signal resource cell. A very small cell base station transmitting a discovery signal transmits a discovery signal with a signal strength enough for the terminal located in its service area to receive the discovery signal. Therefore, when the terminal receives the discovery signal, it can determine that the terminal has entered the area of the micro cell that transmits the discovery signal.

6 is a message flow diagram illustrating a procedure for receiving a discovery signal of a micro-cell according to an embodiment of the present invention. Here, the macro cell base station 605 operates the frequency f1, the small cell base station 610 that operates the frequency f2 within the macro cell covered by the macro cell base station 605, and the micro cell base station 615 that operates the frequency f3 And the micro cell base station 2 (620) exist.

Referring to FIG. 6, in step 625, the macro cell BS 605 determines to add a micro cell to the MS 600, and in step 630, the macro cell BS 605 transmits a message to the neighboring small cell BS 610 And requests discovery signal information for surrounding micro-cells 615 and 620. In step 635, the small cell base station 610 transmits the discovery signal information on the neighboring micro cells 615 and 620 to the macro cell base station 605. If the macro cell base station 605 is directly connected to the neighboring micro cells instead of the small cell base station 610, the steps 630 and 635 may be omitted.

In general, a very large number of very small cell base stations may be arranged in the network, and therefore it may be difficult for the communication carrier to grasp information on all the miniature cell base stations. Also, without the consent or management of the operator, the user can purchase the equipment of the ultra-small cell base station and install it in the necessary position. The micro cell base station can detect surrounding base stations, i.e. macro cell base stations or small cell base stations, at installation, and can report its operation information by connecting the macro cell base station or the small cell base station to the wireless backhaul. At this time, the micro cell base station can be allocated a transmission resource for a discovery signal from an upper network entity or the existing base station, and the communication resource is determined from the operation resources of the existing base station. The discovery signal information for the micro cell base station is generated by the micro cell base station or the existing base station based on the allocated transmission resource. The existing base station recognizes the existence of the micro cell base station and manages the micro cell related information including the discovery signal information. A terminal that wants to connect to a micro cell base station can acquire discovery signal information of the micro cell base station from a neighboring existing base station that manages the micro cell base station through a wireless backhaul, that is, a macro cell base station or a small cell base station.

In step 640, the macro cell base station 605 transmits the micro cell related information including the discovery signal information or the discovery signal information to the terminal 600. The discovery signal information includes a center frequency of a frequency band in which the discovery signals of the micro-cells 615 and 620 are transmitted, frequency and time information of the discovery signal, and the like. In the illustrated example, the discovery signal transmission cell is the micro cell 615, 620 and the discovery signal source cell is the small cell 610. Therefore, the discovery signal information includes information indicating the center frequency of the discovery signal transmission cells 615 and 620 (for example, E-UTRAN Absolute Radio Frequency Channel Number (EARFCN)), information specifying the discovery signal resource cell, (E.g., information on the frequency and time of the resource to which the discovery signal is transmitted), and information specifying the discovery signal (e.g., a discovery signal pattern).

In the illustrated example, the center frequency of the discovery signal transmission cell (i.e., the microcells of the microcell base stations 615 and 620) is f3 and the discovery signaling cell is a small cell controlled by the small cell base station 610. If the discovery signal resource cell is set to Scell of the terminal 600, the terminal 600 receiving the operation frequency f2 of the small cell does not need to receive signals of other frequencies in order to receive the discovery signal, Can be minimized. In one embodiment, the information specifying the discovery signal resource cell may be a SCell index.

In step 645, the terminal receives the discovery signal transmitted from the surrounding micro-cells 615 and 620 through the f2 (or f1) operating frequency of the neighboring cell using the discovery signal information. As another example, the discovery signal may be transmitted over an operating frequency f3 that provides data service in the micro-cells 615, In this case, the UE can periodically tune the transceiver from the operating frequency f2 of the serving cell to the operating frequency f3 of the micro cells to monitor the discovery signal of the frequency f3.

In step 650, the terminal detects a connectable microcell by sensing a discovery signal transmitted on frequency f2. In other words, a discovery signal having a signal intensity higher than TH 1 is detected on the frequency f2. If a plurality of discovery signals having a signal strength higher than TH 1 are detected, the terminal can determine to access the ultra-small cell transmitting the discovery signal having the highest signal strength. In another embodiment, when a plurality of discovery signals having a signal strength higher than TH 1 are detected, the terminal accesses a microcell that transmits a discovery signal having a signal strength exceeding a predetermined threshold value (for example, TH 3) .

In one embodiment, the discovery signal may comprise a sequence commonly assigned to all micro cells. As another example, the discovery signal may contain identification information that can individually identify the micro cells.

In step 655, the terminal adjusts the transceiver so that it can receive the operating frequency f3 of the discovery signal transmission cell (e. G., The micro-cell 2 620) that transmits the discovery signal (or drives a new transceiver for the frequency f3 ) Discovery signal transmission cell and a downlink synchronization procedure. After establishing the downlink synchronization with the micro cell 2 620, the UE performs direct access to the micro cell 2 620 in step 660.

7 is a message flow diagram illustrating a direct access procedure for a micro-cell according to an embodiment of the present invention. Here, a direct access procedure using a DA-RNTI is described.

Referring to FIG. 7, in step 710, the MS 700 performs downlink synchronization with the MS base station 705 and determines the uplink transmission timing in consideration of the downlink reception timing. After that, the terminal 700 proceeds the direct access procedure.

In step 715, the UE 700 attempts to receive the scheduling information addressed to the DA-RNTI in the PDCCH transmitted by the microcell base station 705. In step 720, the UE 700 receives the scheduling information indicated by the DA-RNTI, and transmits the DA MAC CE addressed to the C-RNTI of the UE on the uplink resource indicated by the scheduling information in step 725. The DA MAC CE is received and transmitted in the MAC PDU. Depending on the size of the MAC PDU, the MAC PDU may further include a BSR (Buffer Status Report) or simple data. The BSR indicates the amount of transmittable uplink data stored in the bearer to be connected to the MS 700 by the BSR.

In step 727, the UE 700 determines whether the scheduling information indicated by the C-RNTI is received. If the scheduling information is not received for a predetermined period of time or at a predetermined timing, the terminal 700 determines that the direct access has failed and proceeds to step 730. The failure of the direct access may occur when a collision has occurred using the scheduling information of the process 720 or when the MAC CE of the process 725 transmitted by the UE has not been successfully received by the microcell base station 705.

In step 730, the UE 700 acquires the scheduling information indicated by the DA-RNTI, and transmits the DA MAC CE addressed to its C-RNTI through the UL resource indicated by the scheduling information in step 735 to the UL sub- And transmits it to the base station 705 again. In step 740, the UE receives the scheduling information indicated by the C-RNTI, and performs data transmission and / or reception with the MC base station 705 in step 745. Specifically, the UE transmits BSR and / or UL packet data through the UL resource indicated by the scheduling information in step 740, or transmits downlink packet data through the DL resource indicated by the scheduling information in step 740 .

8 is a flowchart illustrating a direct access operation of a terminal according to an embodiment of the present invention. Here, a direct access procedure for connecting to a small cell or a small cell is shown. The access to the small cell is determined by the control of the network, and the terminal knows which cell is to be set to Scell according to the explicit instruction of the base station, and performs an access operation to the cell. On the other hand, access to the micro-cell is directly determined by the terminal based on the information provided by the base station

Referring to FIG. 8, in step 800, the UE determines to start access to a small cell or a small cell. In one embodiment, if the UE receives an indication from the currently connected base station to set a cell other than the current serving cell to Scell, or if it finds a cell with a signal strength greater than or equal to a threshold value, It can be judged.

In step 805, the UE performs downlink synchronization with the cell. In step 810, the UE determines whether the cell to be accessed is a small cell (type 1 cell) or a small cell (type 2 cell). Specifically, when the UE receives detailed information on the cell from the BS and receives an explicit indication to set the cell to SCell, the UE determines that the cell is a small cell, that is, a type 1 cell. On the other hand, if the terminal finds the cell based on the information provided from the base station and decides to access the cell by itself, the terminal determines that the cell is a very small cell, that is, a type 2 cell. In the case of the Type 1 cell, the base station provides the UE with control information for identifying the Type 1 cell through the RRC control message and information necessary for performing random access in the Type 1 cell. In the case of a Type 2 cell, the base station transmits at least one threshold value defining the minimum information on the Type 2 cell, for example, the operating frequency information of the Type 2 cell, the identifier range, and the access start condition for the Type 2 cell to provide.

If the cell to be accessed as a Scell is a type 1 cell, that is, a small cell, in step 815, the UE transmits a preamble in frequency / time resources of the small cell to perform random access, and in step 820, (RAR) is received. If a valid random access response has been received, the UE transmits an RRC message to the small cell base station in step 825. The RRC message reports to the small cell base station that the UE successfully configured the SCell and is transmitted to the base station through the uplink resource indicated by the RAR.

As an example, the UE transmits a preamble and monitors whether a RAR addressed to a predetermined RA-RNTI is received from the base station for a predetermined RAR window after 2ms. The length of the RAR window may be set through a System Information Block (SIB) broadcast from the base station. The RA-RNTI is an identifier of a UE used for random access, and is determined according to the transmission position on the time-frequency of the preamble transmitted by the UE. During the RAR window, the UE monitors whether the scheduling information addressed to the RA-RNTI is received on the PDCCH. If the scheduling information addressed to the RA-RNTI is detected, the UE receives the RAR according to the scheduling information. The RAR includes at least one of TA information for uplink time synchronization, uplink scheduling information for transmitting a Layer 3 message, and information about a temporary C-RNTI.

In step 830, the UE performs data communication with the small cell base station by applying the error correction technique 1 defined for the macro cell or the small cell.

If the cell to be accessed as a Scell is a type 2 cell, i.e., a micro cell, in step 835, the UE monitors the PDCCH, which is a scheduling channel transmitted by the micro-cell, and transmits scheduling information, in particular UL grant information Is received. When the uplink grant information addressed to the DA-RNTI is received, in step 845, the UE generates a DA MAC CE for reporting that the UE accesses the microcell using the transmission resource indicated by the UL grant information, Transmits the BSR to the cellular base station, and monitors the PDCCH during the direct access window. Upon receipt of the DA MAC CE, the UL base station allocates uplink / downlink transmission resources to the UE using the C-RNTI of the UE accommodated in the DA MAC CE. Then, the DA MAC CE is transmitted to the small cell base station (and the macro cell base station) to report to the small cell base station (and the macro cell base station) that the terminal is connected to the micro cell.

In step 850, the UE checks whether the scheduling information addressed to the C-RNTI during the direct access window, i.e., the downlink allocation information or the UL grant information, is received on the PDCCH of the micro cell. When the scheduling information addressed to the C-RNTI is received, the UE performs data communication with the MSB using the uplink and downlink transmission resources indicated by the scheduling information in step 855. That is, the small cell base station or the macro cell base station transmits the downlink data related to the terminal to the microcell base station in response to the report of the microcell base station, and the downlink data is transmitted from the microcell to the terminal. At this time, the UE can transmit and receive data by applying the error correction technique 2 defined for the micro cell.

If the scheduling command addressed to the C-RNTI from the micro-cell during the direct access window is not received in step 850, the UE proceeds to step 860. In step 860, the UE determines whether a predetermined access right ), And then proceeds to step 835. In another embodiment, the UE may retry uplink transmission using the DA-RNTI after backoff. That is, if the UE fails to receive the scheduling command addressed to the C-RNTI during back-off, the process returns to step 845 and transmits the DA MAC CE again according to the scheduling information addressed to the DA-RNTI received in step 840. The DA MAC CE contains the C-RNTI of the UE as described above and can be addressed to the DA-RNTI.

 The back-off is for preventing continuous collision. For example, if two or more UEs transmit a DA MAC CE using the same DA-RNTI resource, the base station fails to receive the DA MAC CE due to the collision. If the two or more UEs attempt to receive a DA-RNTI at the same time after the direct access window expires, the same collision may occur again. Therefore, the terminals failing direct access will calculate the direct access backoff and wait for the direct access backoff and retry the transmission of the DA MAC CE.

In one embodiment, the length of the direct access backoff can be determined by Equation (1) below.

Where f1 is a function that selects one integer with the same probability between two integers. MAX_BO is a value that can be notified from the BS to the MS. For example, MAX_BO is indicated by the direct access backoff information included in the micro cell related information. As another embodiment, MAX_BO can be determined as Equation (2) using C-RNTI of the terminal and a predetermined integer.

Where X may be indicated by direct access backoff information conveyed from the base station.

The terminal may use the initial transmission output indicated by the base station in determining the transmission power of the uplink signal to be transmitted to the microcell for direct access. Each time an access fails, the transmission output of the DA MAC CE for direct access is ramped, or increased, by the unit value indicated by the base station. The initial value of the transmission power and the unit value for the increase of the transmission power can be transmitted from the base station to the mobile station through the micro cell related information.

As another embodiment, instead of using the transmission resource allocated to the DA-RNTI in order to transmit the DA MAC CE for direct access, a pre-allocated transmission resource (hereinafter referred to as a DA transmission resource) may be used. The information on the DA transmission resource may be included in the micro cell related information, for example, and the UE may transmit the DA MAC CE related information through the transmission resource indicated by the DA transmission resource information in the micro cell- Can be transmitted.

9 shows a timing diagram of a direct access operation in accordance with an embodiment of the present invention.

Referring to FIG. 9, in a subframe [n] 905, a UE transmits a DA MAC CE 910 for requesting direct access to a microcell. Then, the subframe [n] becomes the reference time point at which to start the direct access window. In another embodiment, the time point at which the UE receives the uplink grant information addressed to the DA-RNTI and the transmission resource of the micro-cell is allocated may be a reference point for determining the start of the direct access window.

The terminal computes the direct access window offset according to Equation (3) below to determine the starting point of the direct access window.

Here, the offset_seed and offset_minimum can be transferred from the BS to the MS through the direct access window information included in the micro cell related information, and the C-RNTI is the ID of the MS allocated in the serving cell.

If the DA window offset is determined to be o, the UE starts the access window directly to the subframe [n + o] 915 which has elapsed by o in the subframe [n] as the reference time point. During the direct access window, the UE monitors whether the scheduling information addressed to the C-RNTI, i.e., DL allocation information or UL grant information, is received from the micro-cell, and the scheduling information If not, the terminal considers that the transmission of the DA MAC CE is unsuccessful. K that determines the size of the direct access window may be included in the micro cell related information as an example and be provided from the base station to the terminal. If the micro-cell related information does not include the size of the direct access window, the terminal can set k to a predetermined value, for example, 1.

The terminal waits for a direct access backoff 925 from the end time 920 of the direct access window (925) and retransmits the DA MAC CE to the microcell. B, which determines the length of the direct access backoff, can be indicated by the direct access backoff information included in the micro cell related information, or can be predetermined. That is, when the UE receives the uplink grant information addressed to the DA-RNTI in the direct access window, it transmits the DA MAC CE using the allocated uplink transmission resource, or transmits the DA MAC CE to the UE arriving for the first time after the direct access back- DA MAC CE is transmitted using transmission resources.

Hereinafter, the switching between the error correction technique 1 for data communication in a macro cell or a small cell and the error correction technique 2 for data communication in an ultra small cell will be described.

The small cell and the small cell can be connected to the wireless backhaul. In order for the small cell to provide the HARQ feedback for the uplink transmission of the small cell, the backhaul delay must be shorter than the HARQ RTT (Round Trip Time) There is a high possibility that the condition is not satisfied. Also, since the ultra-small cell has a high possibility that an obstacle does not exist between the UE and the base station and the channel quality is very good due to a small path loss, the utility of the HARQ in the ultra small cell may not be high. In consideration of this, the UE applies an error correction technique 2 using only ARQ without using HARQ in a very small cell. That is, in a very small cell, HARQ retransmission is excluded and an ARQ requests an immediate retransmission in case of an error, thereby preventing a transmission delay and preventing an unnecessary terminal operation.

Table 1 below compares error correction technique 1 and error correction technique 2.

Error Correction Techniques 1 Error Correction Technique 2 HARQ use. MAC Device Control unused ARQ use. The RLC device controls use. The RLC device controls When an unreceived packet is found Request retransmission after waiting for t-Reordering Immediate resend request Request retransmission The interval between retransmission requests is at least t-StatusProhibit There is no restriction on the interval between retransmission requests. Status Report At the time when the status report is triggered, the retransmission request information for all packets whose order has been reordered and are not received is stored Only retransmission request information for non-retransmission packets for which retransmission is not requested before a predetermined period, among packets that are not in a retention state at the time when the status report is triggered,

Error Correction Technique 1 is a technique in which HARQ and ARQ are driven together, and a retransmission request on an ARQ operation is performed after waiting until it is confirmed that an unreceived packet is not in the HARQ operation. To prevent too frequent retransmission requests, a timer called t-StatusProhibit is started when a status report for a retransmission request is sent, and the status report is no longer transmitted while the timer is running.

Error correction technique 2 is a technique that only ARQ is driven. In Error Correction Technique 2, the terminal triggers transmission of a status report as soon as an unreceived packet is found. To do this, the values of the t-Reordering timer and the t-StatusProhibit timer are set to zero. In order to prevent an unnecessary retransmission request, during a predetermined period (t-StatusProhibit) after a retransmission is once requested for an unreceived packet, the terminal can no longer receive a retransmission request for the unreceived packet even if the status report is triggered by another unreceived packet Do not request retransmission. That is, the status report triggered by the other non-received packet does not include the retransmission request information for the non-received packet.

10 is a message flow diagram illustrating a procedure for setting an error correction technique for a micro-cell according to an embodiment of the present invention.

Referring to FIG. 10, in step 1015, the UE 1000 performs downlink synchronization with a micro-cell and triggers the error correction technique 2 for data communication with the micro-cell in step 1020. FIG. Error Correction Technique 2 refers to a technique in which ARQ operations performed in the RLC layer and HARQ operations performed in the MAC layer are adjusted and controlled according to the environment of a micro cell. In step 1025, the UE resets the parameters of the RLC layer managing the ARQ operation. That is, T_reordering = 0 and t-StatusProhibit = 0 (or a very small value). Here, T_reordering is a timer that triggers transmission of the RLC status report, which is ARQ feedback information, and t-StatusProhibit is a timer for preventing frequent transmission of ARQ feedback information. The ARQ-related parameters set as described above allow the ARQ retransmission to be requested immediately when an ARQ error occurs. Also, the UE resets parameters related to the HARQ operation. That is, maxHARQ-Tx = 1 is set. maxHARQ-Tx means the maximum allowed number of retransmissions of HARQ, and when set to 1, HARQ retransmission is not performed.

In step 1030, the UE performs direct access to the micro cell base station, and performs error-free data communication in steps 1035 to 1045 by applying the error correction technique 2. The UE receives packets through a DL shared channel (DL-SCH) and does not request HARQ retransmission even if it fails to receive a packet as in step 1040.

In step 1050, the UE detects the occurrence of an ARQ error and triggers an RLC status report. Since T_reordering is set to 0, in step 1055, the UE transmits an RLC status report to the microcell base station as soon as the RLC status report is triggered. The microcell base station transmits the RLC status report to the small cell base station or the macro cell base station, which is an upper base station.

In step 1060, the UE detects that the UE has deviated from the service area of the UE based on the pilot signal transmitted from the UE. Then, in step 1065, the terminal terminates the connection with the micro cell and switches to the error correction technique 1. Switching from Error Correction Technique 1 to Error Correction Technique 2, or switching to Error Correction Technique 1 from Error Correction Technique 2, changes the ARQ parameters such as t-Reordering timer and t-StatusProhibit timer and HARQ parameters such as maxHARQ-Tx . When the UE starts data transmission / reception in a very small cell or when a UE that has performed data transmission / reception in a very small cell restarts data transmission / reception in a cell other than a very small cell, the UE changes its HARQ parameters .

11 is a flowchart illustrating an operation of switching an error correction technique according to an embodiment of the present invention.

Referring to FIG. 11, in step 1100, the UE acquires RLC configuration information (RLC-config) and MAC configuration information including parameters of an ARQ and HARQ scheme from a base station. RLC setting information includes T_reordering and t-StatusProhibit for ARQ operation, and MAC setting information includes maxHARQ-Tx for HARQ setting information. The base station may be a macro or a small cell base station.

In step 1105, the UE detects that it is necessary to transmit the uplink data and decides to start transmission of the uplink data. In step 1110, the UE determines whether the serving cell for transmitting uplink data is a small cell (type 1 cell) or a small cell (type 2 cell). If the serving cell is a small cell, in step 1115, the UE applies the obtained configuration information to perform ARQ and HARQ operations. Specifically, the UE transmits uplink data according to ARQ and HARQ operations. On the other hand, if the serving cell is not a small cell, in step 1120, the UE performs uplink transmission using the setup information set for the microcell instead of the setup information received from the base station. That is, the UE does not apply the HARQ retransmission to the uplink data. When an unreceived packet is detected in the ARQ operation, the UE immediately requests retransmission, and the interval t-StatusProhibit between retransmission requests is set to zero.

However, the ultra small cell base station can always be configured to use the error correction technique 2 in transmitting the downlink data to the mobile station.

In a mobile communication system, a serving cell or a neighboring cell measurement of a terminal is a core part in radio resource management and mobility management.

The UE can measure a reference signal received power (RSRP) or a reference signal received quality (RSRQ) of a specific frequency according to an instruction from the base station. The former represents the strength of the reference signal and the latter represents the quality of the reference signal taking into account the relative strength of the interference signal and the reference signal.

According to the LTE standard, the RSRQ reported by the UE is -19.5 dB to -3 dB. The lower limit of the RSRQ range is determined based on the receiver performance of a conventional terminal. For example, it is assumed that the UE fails to perform normal communication in a cell whose RSRQ is -19.5 dB or less. The receiver performance of the terminal is steadily developing and even when the cell size is much lower than the lower limit value at the time when the miniaturized cell is commercialized, the reception operation of the terminal can be possible.

In the embodiment of the present invention described later, the RSRQ measurement report limited to the above range (hereinafter referred to as the first range) is extended to a wider range.

The first range is the RSRQ range defined above. For example, the first range is defined as 34 code points, and each code point has the same meaning as in Table 2 below. Hereinafter, the RSRQ measurement result indicating a value within the first range is referred to as a first RSRQ code point.

Reported value Measured quantity value Unit RSRQ_00 RSRQ <-19.5 dB RSRQ_01 -19.5? RSRQ <-19 dB RSRQ_02 -19? RSRQ <-18.5 dB RSRQ_32 -4? RSRQ <-3.5 dB RSRQ_33 -3.5? RSRQ <-3 dB RSRQ_34 -3 ≤ RSRQ dB

The second range is defined such that it does not overlap the first range and is represented by y code points representing a range lower than the lower limit value of the first range and z code points representing a range higher than the upper limit value of the first range. Table 3 below shows an example of the second range. The result of the RSRQ measurement indicating a value within the second range is hereinafter referred to as a second RSRQ code point.

Reported value Measured quantity value Unit RSRQ_35 RSRQ <-n dB RSRQ_36 -n? RSRQ <- (n-1) .5 dB RSRQ_ (34 + y) -20? RSRQ <-19.5 dB RSRQ_ (34 + y + 1) -3? RSRQ <-2.5 dB RSRQ_ (34 + y + 2) -2.5? RSRQ <-2 dB RSRQ (34 + y + z) m? RSRQ dB

If the measured RSRQ is in the first range, the UE receives and reports a first RSRQ code point corresponding to the measured RSRQ to an existing information element (IE) rsrqResult.

If the measured RSRQ belongs to the second range, the UE receives and reports a second RSRQ code point corresponding to the measured RSRQ to a new information unit rsrqResult-new. The UE does not know whether the base station reporting the RSRQ measurement result can understand the second RSRQ code point, so that the rsrqResult containing the first RSRQ code point set to a predetermined value is reported together with the rsrqResult-new. The predetermined value is determined as follows. That is, if the RSRQ measurement result is higher than the upper limit of the first range (i.e., if the RSRQ measurement result exceeds -3 dB), the first RSRQ code point is set to RSRQ_34. If the RSRQ measurement result is lower than the first range lower limit (i.e., if the RSRQ measurement result is less than -19.5 dB), the first RSRQ code point is set to RSRQ_00.

In one embodiment, even if the RSRQ measurement result falls within the second range, the measurement report message may be transmitted to a base station of another system other than the LTE base station, for example, a Universal Mobile Telecommunication Systems (UMTS) base station or a Global System for Mobile communications , The UE reports only the rsrqResult set to the first RSRQ code point (i.e., RSRQ_00 or RSRQ_34) set to a predetermined value, and does not report the second RSRQ code point.

The first RSRQ code point and the second RSRQ code point are stored in one report message. The rsrqResult storing the first RSRQ code point and the rsrqResult-new storing the second RSRQ code point are separated into different IEs , And can be stored in a space that is not adjacent to each other. This is to allow only the first RSRQ code point to be understood and the second RSRQ code point to be able to efficiently process the message if the base station does not understand it.

12 is a flowchart illustrating an operation of selecting a measurement report method according to an embodiment of the present invention.

Referring to FIG. 12, in step 1205, the UE receives a measurement instruction from the network through an RRC control message. The RRC control message includes information for specifying a frequency to perform RSRQ measurement or a radio access technology (RAT), information for indicating an event of a situation where a measurement result is to be reported, information related to a measurement cycle, At least one of the information required for the user. The RAT may be, for example, UMTS Terrestrial Radio Access (UTRA), Enhanced UTRA (E-UTRA), or the like. The event to report the measurement result may be, for example, reporting the measurement result when the measurement result of the serving cell is less than or equal to a predetermined reference value for a predetermined period or periodically reporting the measurement result have. As an example of the measurement period, if the base station sets DRX (Discontinuous Reception) to the UE, the UE can perform the measurement at least once every DRX cycle. With respect to the processing of the measurement result, for example, a value obtained by filtering the most recent measurement result and the previous measurement result by assigning different weights is the final measurement result, and the filtering coefficient related to the weight is calculated by the RRC control Message. &Lt; / RTI &gt;

In step 1210, the UE measures the RSRQ of the serving cell (s) and the neighboring cell (s) at predetermined intervals based on the measurement related information stored in the RRC control message, applies filtering to the measured value, The 3-layer filtered measurement result is called a 3-layer filtered measurement (L3 filtered measurement) and is referred to as a 3-layer measurement result.

In step 1215, the UE determines whether the updated measurement result value triggers the measurement result report. If the measurement result value satisfies a predetermined condition, it can be determined that the measurement result report is triggered. For example, a measurement result report may be triggered when a 3-layer measurement result of at least one neighboring cell is maintained for a predetermined period of time above a predetermined reference value above a 3-layer measurement result of the serving cell. Or a measurement result report may be triggered at a predefined period.

If it is not necessary to report the measurement result, proceed to step 1210 to continue the measurement. On the other hand, if it is necessary to report the measurement result, the process proceeds to step 1220.

In step 1220, the UE checks whether the measurement result falls within a first range, and if it is within a first range (i.e., between -19.5 dB and -3 dB), the UE proceeds to step 1230. If the measurement result does not fall within a first range I.e., less than -19.5 dB or greater than -3 dB, proceed to step 1225.

In step 1230, the UE stores the first RSRQ code point corresponding to the measurement result value belonging to the first range in the rsrqResult, stores the rsrqResult in a predetermined control message, and reports the received rsrqResult to the BS. And returns to step 1210 to continue the measurement.

In step 1225, the UE checks whether the measurement result report is performed in the LTE network or whether the UE has established an RRC connection with the LTE base station or whether the primary cell (PCell) of the UE is an E-UTRA cell. The process proceeds to 1240; otherwise, the process proceeds to 1235.

Proceeding from step 1225 to step 1235 means that the UE performs measurement on E-UTRA in another RAT such as UMTS or GSM and reports the result to the UMTS or GSM network. The UMTS base station controller or the GSM base station The controller can not understand the second range of RSRQ measurements. Accordingly, the UE generates an rsrqResult containing a first RSRQ code point set to a predetermined value, and reports the received control message to the UMTS or GSM base station controller in the rsrqResult. And returns to step 1210 to continue the measurement.

In step 1240, the UE generates rsrqResult containing the first RSRQ code point set to a predetermined value and rsrqResult-New containing the second RSRQ code point corresponding to the measurement result value.

In step 1245, the UE receives rsrqResult and rsrqResult-New in a control message and reports it to the BS. rsrqResult and rsrqResult-New may be stored in the control message such that they are separated from each other by different IEs. Then, the UE returns to step 1210 to continue the measurement.

13 is a block diagram illustrating a structure of a terminal according to an embodiment of the present invention.

13, the upper layer processor 1310 corresponds to the RLC layer, the multiplexer / demultiplexer 1305 corresponds to the MAC layer, the control message processor 1315 corresponds to the RRC layer, and the transceiver 1300 ) Corresponds to the physical layer. The above elements 1300, 1305, 1310, and 1315 operate as a transceiver that performs communication with the base station under the control of the controller 1320.

The multiplexing and demultiplexing apparatus 1305 transmits and receives data to and from the upper layer processing unit 1310 and transmits and receives control messages through the control message processing unit 1315. Upon transmission of a control message or data, the multiplexer / demultiplexer 1305 multiplexes the data and / or control message to be transmitted under the control of the controller 1320, and then transmits the data through the transceiver 1300. On the other hand, upon receipt of a control message or data, the multiplexer / demultiplexer 1305 demultiplexes the signal received from the transceiver 1300 into data and / or control messages under the control of the controller 1320, Or the control message to the upper layer processing unit 1310 or the control message processing unit 1315. [

The control unit 1320 controls the transceiver 1300 and the multiplexer / demultiplexer 1305 according to at least one of the above-described embodiments to connect to the macro / small cell or the micro cell, The data communication is performed by applying the error correction technique 1 or 2 according to whether the serving cell transmitting the cell or the downlink data is a macro / small cell or a small cell. The control unit may also perform the control of the measurement control and the measurement result report as described in Fig.

14 is a block diagram illustrating a structure of a base station according to an embodiment of the present invention.

14, a plurality of upper layer processing units 1425 and 1430 correspond to an RLC layer, a multiplexing and demultiplexing unit 1420 corresponds to a MAC layer, a control message processing unit 1435 corresponds to an RRC layer , And the transceiver 1405 corresponds to the physical layer. The components 1405, 1420, 1425, 1430, and 1435 operate as a transceiver that performs communication with the terminal under the control of the controller 1410.

The transceiver 1405 transmits data and control signals on the downlink carrier and receives data and control signals on the uplink carrier. When a plurality of carriers are set in the base station, the transceiver 1405 can perform data transmission / reception and control signal transmission / reception through the plurality of carriers.

The multiplexing and demultiplexing apparatus 1420 multiplexes the data and / or control messages generated by the upper layer processing units 1425 and 1430 and the control message processing unit 1435 or demultiplexes the signals received from the transceiver 1405 And / or control messages to appropriate upper layer processing units 1425 and 1430, control message processing unit 1435, or control unit 1410.

The plurality of upper layer processing units 1425 and 1430 may be configured for each terminal and each service and may process data generated in user services such as FTP and VoIP and transmit the processed data to the multiplexing and demultiplexing unit 1420, Demultiplexer 1420 and transfers the processed data to a higher layer service application. The scheduler 1415 allocates transmission resources to the mobile station at an appropriate time in consideration of at least one of the buffer state of the mobile station, the channel state, and the active time of the mobile station, and notifies the transceiver 1405 of the signal Or send a signal to the terminal.

The controller 1410 controls the transceiver 1405 and the multiplexer / demultiplexer 14320 according to at least one of the above-described embodiments to connect to the terminal, provide necessary information, and perform communication with the terminal. The control unit 1410 can also control the base station operation corresponding to the operation of the terminal described with reference to FIG. Specifically, the control unit sends the measurement-related information to the UEs in the RRC control message, receives a control message including at least one of rsrqResult and rsrqResult-New from the UE, and transmits the control message to the UE in accordance with at least one of rsrqResult and rsrqResult- And acquires the measurement result value transmitted by the terminal.

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. Therefore, the scope of the present invention should not be limited by the illustrated embodiments, but should be determined by the scope of the appended claims and equivalents thereof.

Claims (24)

A communication method of a terminal in a mobile communication network,
The method comprising the steps of: monitoring a discovery signal transmitted from the microcell base station through an operating frequency of an upper-
Directly accessing the microcell base station when the discovery signal is detected;
And performing data communication with the microcell base station without performing a Hybrid Automatic Retransmission Request (HARQ) operation. The method as claimed in claim 1, further comprising the step of receiving the micro-cell related information necessary for communication with neighboring micro-cell base stations from the host base station,
The micro-cell related information includes:
Information specifying each micro cell, information specifying a transmission resource to which a discovery signal from each micro cell is transmitted, and an operating frequency and a physical cell identification (PCI) range of each micro cell, Information on a first threshold value for determining access or non-accessibility, a second threshold value for determining whether or not a connection of the corresponding micro-cell is maintained, information on a transmission resource used for direct access to the corresponding micro-cell, window information, direct access backoff information, and TA (Timing Advance) information of the corresponding micro-cell. The method according to claim 1,
Further comprising the step of acquiring downlink synchronization from the microcell base station when the discovery signal is detected. The method as claimed in claim 1,
Monitoring whether scheduling information addressed to a first identifier, which is predetermined for direct access, is received through a downlink control channel of the microcell base station;
When the scheduling information addressed to the first identifier is received, control information for direct access including a second identifier uniquely allocated to the UE according to the scheduling information addressed to the first identifier is transmitted to the microcell base station Transmitting,
Monitoring whether the scheduling information addressed to the second identifier is received through the control channel;
And if the scheduling information addressed to the second identifier is received, determining to perform data communication with the micro-cell base station according to the scheduling information addressed to the second identifier. 5. The method according to claim 4,
A second identifier used in a cell of an upper-layer base station of the micro-cell base station, information for specifying a serving cell for which the terminal is currently establishing a connection, and header information for specifying the control information . 6. The method of claim 5,
If the scheduling information addressed to the second identifier is not received during a direct access window provided by the upper base station, wait for a direct access backoff provided by the upper base station, And transmitting the control information to the microcell base station. The method of claim 1, wherein the step of performing the data communication comprises:
Acquiring first setting information of ARQ and HARQ operations from the higher-level base station;
Determining whether a serving cell to transmit the uplink data is a small cell if transmission of uplink data is requested;
Transmitting the uplink data to the serving cell base station using the first configuration information if the serving cell to transmit the uplink data is not a small cell,
And transmitting the uplink data to the base station of the micro cell according to second setting information set by the terminal for the micro cell if the serving cell to transmit the uplink data is a micro cell,
Wherein the second setting information comprises:
T_reordering = 0, which is a reference timer for triggering transmission of a retransmission request of the ARQ operation, t-StatusProhibit = 0, which is a timer for limiting the interval between retransmission requests of the ARQ operation, and maxHARQ-Tx Lt; RTI ID = 0.0 &gt; = 1. &Lt; / RTI &gt; A communication method of a base station in a mobile communication network,
Further comprising the steps of: determining to further set a micro cell for a serving terminal;
Requesting a neighboring small cell base station for discovery signal information for at least one micro cell in the vicinity;
And transmitting the micro-cell-related information on neighboring micro-cells to the terminals in the cell based on information received from the small cell base station,
The discovery signal information includes:
Information specifying at least one of the micro-cells, information specifying frequency and time resources in which the discovery signal is transmitted from each micro-cell, and a signal pattern of the discovery signal,
The micro-cell related information includes:
Information for specifying each micro cell, information for specifying a transmission resource to which a discovery signal from each micro cell is transmitted, an operating frequency and a physical cell identifier (PCI) range of each micro cell, and whether to access the micro cell Information on a first threshold and a second threshold for determining whether or not to keep a connection of the microcell, information on a transmission resource used for direct access to the microcell, direct access window information, direct access backoff information And information on the TA of the corresponding micro-cell. 1. A terminal apparatus for performing communication in a mobile communication network,
A transceiver for monitoring a discovery signal transmitted from the microcell base station through an operating frequency of an upper base station located in the vicinity of the microcell base station;
And a controller for directly accessing the microcell base station when the discovery signal is sensed and controlling the transceiver to perform data communication with the microcell base station without performing a Hybrid Automatic Retransmission Request (HARQ) operation. . The apparatus of claim 9, wherein the transceiver comprises:
Cell-related information necessary for communication with surrounding ultra-small cell base stations from the high-order base station,
The micro-cell related information includes:
Information for specifying each micro cell, information for specifying a transmission resource to which a discovery signal from each micro cell is transmitted, an operating frequency and a physical cell identifier (PCI) range of each micro cell, and whether to access the micro cell Information on a first threshold and a second threshold for determining whether or not to keep a connection of the microcell, information on a transmission resource used for direct access to the microcell, direct access window information, direct access backoff information , And information on the TA of the corresponding micro-cell. 10. The apparatus according to claim 9,
And acquires downlink synchronization from the microcell base station when the discovery signal is detected. The apparatus of claim 9, wherein the transceiver comprises:
The method comprising: monitoring whether scheduling information addressed to a first identifier predetermined for direct access is received through a downlink control channel of the microcell base station; and if scheduling information addressed to the first identifier is received, The control information for direct access including a second identifier uniquely assigned to the UE is transmitted to the micro-cell BS according to the scheduling information addressed to the UE, and the scheduling information addressed to the second identifier Lt; RTI ID = 0.0 &gt;
Wherein the control unit determines to perform data communication with the micro cell base station according to the scheduling information addressed to the second identifier when the scheduling information addressed to the second identifier is received. 13. The method according to claim 12,
A second identifier used in a cell of an upper-layer base station of the micro-cell base station, information for specifying a serving cell for which the terminal is currently establishing a connection, and header information for specifying the control information . 14. The apparatus of claim 13, wherein the transceiver comprises:
If the scheduling information addressed to the second identifier is not received during a direct access window provided by the upper base station, wait for a direct access backoff provided by the upper base station, And transmits the control information to the microcell base station. 10. The apparatus according to claim 9,
Acquires first configuration information of ARQ and HARQ operations from the upper base station, and determines whether a serving cell to transmit the uplink data is a very small cell if transmission of uplink data is requested, Controlling the transceiver to transmit the uplink data to the base station of the serving cell using the first setting information if the cell is not a cell and if the serving cell to transmit the uplink data is a small cell, Controls the transmitting / receiving device to transmit the uplink data to the base station of the micro-cell according to second setting information set by itself,
Wherein the second setting information comprises:
T_reordering = 0, which is a reference timer for triggering transmission of a retransmission request of the ARQ operation, t-StatusProhibit = 0, which is a timer for limiting the interval between retransmission requests of the ARQ operation, and maxHARQ-Tx Lt; RTI ID = 0.0 &gt; = 1. &Lt; / RTI &gt; A base station apparatus for performing communication in a mobile communication network,
A control unit for deciding to additionally set a micro cell for a serving terminal,
And requests discovery signal information of at least one micro cell in the vicinity from the small cell base station to the surrounding small cell base station and transmits the micro cell related information about the surrounding micro cells to the terminals in the cell based on the information received from the small cell base station And a transmitting /
The discovery signal information includes:
Information specifying at least one of the micro-cells, information specifying frequency and time resources in which the discovery signal is transmitted from each micro-cell, and a signal pattern of the discovery signal,
The micro-cell related information includes:
Information for specifying each micro cell, information for specifying a transmission resource to which a discovery signal from each micro cell is transmitted, an operating frequency and a physical cell identifier (PCI) range of each micro cell, and whether to access the micro cell Information on a first threshold and a second threshold for determining whether or not to keep a connection of the microcell, information on a transmission resource used for direct access to the microcell, direct access window information, direct access backoff information , And information on a TA of the corresponding micro-cell. A communication method of a terminal in a mobile communication network,
Receiving measurement related information from a network;
Performing measurements on signals of the serving cell and the at least one neighboring cell based on the measurement-related information;
Determining whether to perform a measurement result report according to the measurement result,
Determining whether the measurement result falls within a predetermined range;
Reporting a first information unit indicating the measurement result to the network when the measurement result falls within the range;
And reporting the first information unit set to a predetermined value and the second information unit indicating the measurement result to the network when the measurement result does not fall within the range. 18. The apparatus of claim 17, wherein the first information unit, which is set to a predetermined value, and the second information unit that represents the measurement result,
Wherein the measurement result is not within the range and is delivered to the network if the network supports a radio access technology (RAT) capable of understanding the second information unit. 18. The method of claim 17,
And reporting the first information unit set to a predetermined value to the network if the measurement result does not fall within the range and the network does not support a radio access technology (RAT) capable of understanding the second information unit Further comprising the steps of: A communication method of a base station in a mobile communication network,
Transmitting measurement related information to a terminal;
And receiving a message indicating a measurement result of signals of the serving cell and the at least one neighboring cell from the terminal based on the measurement related information,
Wherein the message includes a first information unit indicating the measurement result when the measurement result falls within the range, and when the measurement result does not fall within the range, the first information unit and the second information unit, And a second information unit indicating the measurement result. 1. A terminal apparatus for performing communication in a mobile communication network,
A transceiver for receiving measurement related information from a network,
A measurement of the signals of the serving cell and the at least one neighboring cell is performed based on the measurement-related information, and a determination is made as to whether to perform the measurement result report according to the measurement result. If the measurement result falls within a predetermined range And reporting a first information unit indicating the measurement result to the network through the transceiver when the measurement result falls within the range and if the measurement result does not fall within the range, And a control unit reporting the first information unit and the second information unit indicating the measurement result to the network through the transceiver. 22. The apparatus of claim 21,
Wherein when the measurement result does not belong to the range and the network supports a radio access technology (RAT) capable of understanding the second information unit, the first information unit set to the predetermined value and the measurement result And reporting the second information unit indicating the second information unit to the network. 22. The apparatus of claim 21,
And reporting the first information unit set to a predetermined value to the network if the measurement result does not fall within the range and the network does not support a radio access technology (RAT) capable of understanding the second information unit . A base station apparatus for performing communication in a mobile communication network,
A transceiver for transmitting measurement related information to a terminal and receiving a message indicating a measurement result of signals of the serving cell and at least one neighboring cell from the terminal based on the measurement related information;
And a control unit for interpreting the message,
Wherein the message includes a first information unit indicating the measurement result when the measurement result falls within the range, and when the measurement result does not fall within the range, the first information unit and the second information unit, And a second information unit indicating the measurement result.

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