KR101976722B1 - Method and Apparatus for Synchronization Acquisition Between Small Cells - Google Patents

Abstract

A method for acquiring synchronization between small cells is disclosed. The method may comprise determining a target small cell for synchronization acquisition of a particular small cell of the small cells and attempting to obtain synchronization acquisition from the determined target small cell in the particular small cell . The step of determining a target small cell for synchronization acquisition of a specific small cell among the small cells may include referring to synchronization status information of the small cells excluding the specific small cell.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a synchronous acquisition method and apparatus for small cells,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to techniques related to small cells, and more particularly to techniques for acquiring synchronization between small cells.

In recent radio access networks, a small size cell such as a micro cell, a pico cell, and a femto cell has a relatively large size macro cell It is evolving into an interlocking form. A small cell is a low-power wireless access node that has a narrower service area than a general cell, and is similar to a DSL modem, allowing it to connect to a wired IP network in the home and to use wired and wireless communication freely to terminals such as mobile phones. In order to solve the problem that the efficiency is lowered as the number of users per base station decreases and the quality degradation and shaded area occur in the cell boundary region and the building, the size of the small cell is reduced according to Cooper's Law It is proposed to increase the traffic density by positioning the terminal close to the base station.

The use of small cells has the following advantages. First, the power consumption of the terminal is reduced. When the terminal and the base station are located close to each other, the power consumption is more efficient because the signal can be transmitted and received with very little power. Second, the advantages of Multiple-Input and Multiple Output (MIMO) are maximized. According to the trend of mobile traffic usage in recent years, most of the generated traffic is generated indoors, and it is expected that small cells will be installed mainly in indoor in the future. In this indoor environment, the multi-path of the wireless signal can be performed at various angles, so that the advantage of MIMO is maximized and the spectrum can be efficiently used. Third, there is an advantage that the installation cost and the maintenance cost are less than that of the existing base station.

Currently, studies for improving the performance of small cells are being actively conducted mainly by 3GPP (3rd Generation Partnership Project). As part of this research, several schemes have been proposed to match timing and frequency synchronization in small cells. As one of them, a synchronization method according to IEEE 1588 is known. This synchronization method synchronizes with a synchronous server on a wireless network. Although it provides sufficient precision in terms of frequency synchronization in operation of small cells, it has a low accuracy of timing synchronization and can not be used in small cells operating in TDD have. A Global Positioning System (GPS) synchronization scheme is also known in which a small cell receives a GPS signal and extracts timing synchronization and frequency synchronization. As another proposed synchronization scheme, there is a synchronization scheme based on NL (Network Listening). In this scheme, a small cell receives a synchronization signal from a synchronized base station (macro cell, etc.) and extracts timing synchronization and frequency synchronization. However, since the small cell is typically operated in an indoor environment, it may not be able to receive a GPS signal or a synchronization signal from an adjacent base station. Therefore, both the GPS synchronization method and the NL synchronization method are difficult to apply to small cells as a reliable synchronization method. Furthermore, in the case of the NL synchronization method, if the distance between the macro cell and the small cell is long, the time required for signal transmission between the macro cell and the small cell becomes long and deviation of the timing synchronization occurs accordingly. There is a problem.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and apparatus for acquiring synchronization by sharing synchronization information among small cells even in a room where GPS synchronization or NL synchronization is impossible.

The problems to be solved by the present invention are not limited to the above-mentioned problems, and other matters not mentioned can be clearly understood by those skilled in the art from the following description.

In one aspect, a method of managing a small cell synchronization state is provided. The method includes: preparing a database storing synchronous state information for small cells; receiving a neighbor cell list from a particular small cell, the neighbor cell list comprising at least one neighbor cell's ID Selecting at least one candidate cell among the at least one adjacent small cell with reference to the database, transmitting the ID of the selected at least one candidate cell to the specific small cell, Receiving a synchronization result report message from the synchronization result report message, and updating the database according to the synchronization result report message.

In one embodiment, preparing the database storing synchronization status information for the small cells includes storing synchronization status information for each of the small cells in the database, wherein each of the small cells The synchronization status information for the small cell includes a ID of the corresponding small cell, synchronization acquisition status information for the corresponding small cell, information on the number of hops for the corresponding small cell, and a list of synchronization cells for the corresponding small cell, Wherein the synchronization acquisition status information for the corresponding small cell indicates that the corresponding small cell has acquired synchronization or has not acquired synchronization, and the hop count information for the corresponding small cell indicates that the corresponding small cell has most recently acquired synchronization Represents the number of hops from the smallest cell in the forefront of the involved synchronous chain to the corresponding small cell, The synchronous cell list for the small cell includes an ID of at least one small cell included in the corresponding synchronous chain, excluding the corresponding small cell.

In one embodiment, the synchronization acquisition status information for the corresponding small cell may include information indicating that the small cell at the forefront of the corresponding synchronization chain has acquired synchronization from a reliable synchronization source, or information indicating that the small cell acquires synchronization And information indicating failure.

In one embodiment, the information indicating that the small cell at the forefront of the corresponding synchronization chain has obtained synchronization from a reliable synchronization source includes information identifying the reliable synchronization source.

In one embodiment, the step of selecting at least one candidate cell of the at least one neighboring small cell with reference to the database further comprises the step of selecting, using the respective IDs of the at least one neighboring small cell in the database, Based on the synchronization acquisition status information and the hop number information for each of the at least one neighboring small cells, the synchronization acquisition status information and the hop number information for each of the adjacent small cells, And selecting the at least one candidate cell among the small cells.

In one embodiment, the step of selecting the at least one candidate cell of the at least one neighboring small cell based on the synchronization acquisition state information and the number of hops information for each of the at least one neighboring small cells comprises: And selecting, as the at least one candidate cell, a neighboring small cell that is synchronized among the at least one neighboring small cell based on the synchronization acquisition state information for each of at least one neighboring small cell.

In one embodiment, the step of selecting the at least one candidate cell of the at least one neighboring small cell based on the synchronization acquisition state information and the number of hops information for each of the at least one neighboring small cells comprises: And acquiring, from the at least one neighboring small cell based on the synchronization acquisition state information and the hop count information for each of at least one neighboring small cell, a neighboring small cell having a number of hops less than a predetermined number, And selecting the cell as one candidate cell.

In one embodiment, the step of receiving a synchronization result report message from the specific small cell includes receiving an ID of a target small cell from which the specific small cell directly acquired synchronization from the specific small cell, The step of updating the database according to the result report message may include modifying the synchronization status information for the specific small cell to be the same as the synchronization status information for the target small cell, And modifying the cell list synchronous with the specific small cell so that the ID of the target small cell is included in the synchronous cell list for the specific small cell .

In one embodiment, the step of receiving a synchronization result report message from the specific small cell includes receiving a synchronization failure report message from the specific small cell, and updating the database according to the synchronization result report message Includes modifying the synchronization acquisition status information for the specific small cell so that the synchronization acquisition status information for the specific small cell indicates that the specific small cell failed to acquire synchronization.

In one embodiment, the step of updating the database according to the synchronization result reporting message comprises: if there is a small cell involved in a synchronous chain including the specific small cell, acquiring synchronization acquisition status information for the small cell involved, And modifying the synchronization acquisition state information for the involved small cell to indicate that the cell did not acquire synchronization.

In one embodiment, the method further comprises causing a message to be delivered to perform the resynchronization procedure to the involved small cell.

In another aspect, a method of acquiring synchronization in a small cell is provided. The method includes the steps of measuring signals from neighboring cells through network listening, generating a neighboring cell list based on the measured signals, the neighboring cell list comprising at least one neighboring cell And transmitting the neighbor cell list to a synchronization state management server, wherein the synchronization state management server stores synchronization state information for small cells, and the synchronization state information for the small cells is Wherein the synchronization status information for each of the small cells includes an ID of the corresponding small cell, synchronization acquisition status information for the corresponding small cell, and a hop for the corresponding small cell, Wherein the synchronization acquisition status information for the corresponding small cell indicates that the corresponding small cell has acquired synchronization And the hop count information for the corresponding small cell is determined based on the hop count from the smallest cell in the forefront of the synchronous chain in which the small cell is most recently acquired to acquire the synchronization, The method comprising the steps of: receiving at least one candidate cell ID from the synchronous state management server, the small cell identified by the at least one candidate cell ID having a number of hops And attempting to obtain synchronization acquisition from the small cell identified by the at least one candidate cell ID.

In another aspect, a synchronization state management server that supports synchronization acquisition between small cells is provided. The synchronous state management server includes a database for storing synchronous state information for small cells, a communication unit configured to receive a neighbor cell list from a specific small cell, the neighbor cell list including IDs of at least one adjacent small cell, And a control unit configured to select at least one candidate cell among the at least one adjacent small cell with reference to the database and to transmit the ID of the selected at least one candidate cell to the specific small cell through the communication unit, Is further configured to receive a synchronization result report message from the specific small cell, and the control unit may be further configured to update the database according to the synchronization result report message.

In one embodiment, the database stores synchronization status information for each of the small cells, and the synchronization status information for each of the small cells includes ID of the corresponding small cell, synchronization acquisition status information , Hop count information for the corresponding small cell, and a list of synchronous cells for the small cell, and the synchronization acquisition status information for the corresponding small cell indicates that the corresponding small cell acquires synchronization or does not acquire synchronization The number of hops for the corresponding small cell indicates the number of hops from the smallest cell at the forefront of the synchronous chain involved in acquiring the most recent synchronization of the corresponding small cell to the corresponding small cell, Wherein the synchronous chain cell list for the corresponding small cell is included in the corresponding synchronous chain excluding the corresponding small cell Lt; RTI ID = 0.0 > ID < / RTI >

In one embodiment, the synchronization acquisition status information for the corresponding small cell may include information indicating that the small cell at the forefront of the corresponding synchronization chain has acquired synchronization from a reliable synchronization source, or information indicating that the small cell acquires synchronization And information indicating failure.

In one embodiment, the information indicating that the small cell at the forefront of the corresponding synchronization chain has obtained synchronization from a reliable synchronization source includes information identifying the reliable synchronization source.

In one embodiment, the control unit searches the database for the synchronization acquisition status information and the hop count information for each of the at least one neighboring small cell using each ID of the at least one neighboring small cell, And to select the at least one candidate cell of the at least one neighboring small cell based on the synchronization acquisition state information and the hop count information for each of at least one adjacent small cell.

In one embodiment, the control unit may be configured to perform, based on the synchronization acquisition state information for each of the at least one neighboring small cells, neighboring small cells that have been synchronized among the at least one neighboring small cells, As shown in FIG.

In one embodiment, the control unit determines whether synchronization is obtained among the at least one neighboring small cell based on the synchronization acquisition state information and the hop count information for each of the at least one neighboring small cells, And to select an adjacent small cell having the number of hops as the at least one candidate cell.

In one embodiment, the communication unit is further configured to receive an ID of a target small cell in which the specific small cell directly acquires synchronization from the specific small cell, and the control unit sets synchronization state information on the specific small cell Modifies the number of hops for the specific small cell so that the number of hops for the specific small cell is increased by 1, modifies the hop count information for the specific small cell, To modify the list of cells that are synchronized for the particular small cell so that the ID of the target small cell is included in the list.

In one embodiment, the communication unit is further configured to receive a synchronization failure report message from the specific small cell, and the control unit determines that the synchronization acquisition status information for the specific small cell does not cause the specific small cell to acquire synchronization And to modify the synchronization acquisition status information for the particular small cell to indicate that the synchronization has been established.

In one embodiment, the control unit may be configured to, if there is a small cell involved in a synchronous chain that includes the particular small cell, synchronize acquisition status information for the small cell involved to indicate that the small cell involved did not acquire synchronization And to modify the synchronization acquisition status information for the involved small cell.

In one embodiment, the control unit is further configured to cause a message to be transmitted to perform the resynchronization procedure to the small cell involved.

In another aspect, a method of acquiring synchronization between small cells is provided. The method may comprise determining a target small cell for synchronization acquisition of a particular small cell of the small cells and attempting to obtain synchronization acquisition from the determined target small cell in the particular small cell .

In one embodiment, the step of determining a target small cell for synchronization acquisition of a specific small cell among the small cells includes referring to synchronization status information of the small cells excluding the specific small cell.

In another aspect, a method of acquiring synchronization in a small cell is provided. The method includes the steps of measuring signals from neighboring cells through network listening, identifying adjacent small cells based on the measured signals, determining a synchronous state information request message Receiving synchronous state information from each of the adjacent small cells, selecting at least one candidate small cell of the neighboring small cells based on the synchronous state information, and transmitting the at least one candidate small cell And attempting to obtain synchronization acquisition from the cell.

In one embodiment, the synchronization state information from each of the neighboring small cells includes synchronization acquisition state information for the corresponding neighboring small cell and information about the number of hops for the neighboring small cell, The synchronization acquisition status information for the adjacent small cell indicates that the corresponding neighboring small cell has acquired synchronization or has not acquired synchronization, and the hop count information for the neighboring small cell indicates that the neighboring small cell is most recently synchronized Represents the number of hops from the smallest cell at the forefront of the involved sync chain to the corresponding adjacent small cell.

In one embodiment, the synchronization acquisition status information for the corresponding small cell may include information indicating that the small cell at the forefront of the corresponding synchronization chain has acquired synchronization from a reliable synchronization source, or information indicating that the small cell acquires synchronization And information indicating failure.

In one embodiment, the information indicating that the small cell at the forefront of the corresponding synchronization chain has obtained synchronization from a reliable synchronization source includes information identifying the reliable synchronization source.

In one embodiment, the step of selecting at least one candidate small cell among the neighboring small cells based on the synchronization state information comprises: determining whether the neighboring small cells are adjacent to each other, based on the synchronization acquisition state information and the hop number information for each of the adjacent small cells, And selecting the at least one candidate small cell among the small cells.

In one embodiment, the step of selecting at least one candidate small cell of the neighboring small cells based on the synchronization state information comprises: selecting, from among the adjacent small cells, Selecting the obtained adjacent small cells as the at least one candidate small cell.

In one embodiment, the step of selecting at least one candidate small cell among the neighboring small cells based on the synchronization state information comprises: determining whether the neighboring small cells are adjacent to each other, based on the synchronization acquisition state information and the hop number information for each of the adjacent small cells, And selecting a neighboring small cell having the number of hops less than the predetermined number of the small cells to be synchronized, as the at least one candidate small cell.

In one embodiment, the method further comprises managing synchronization status information for the small cell in the small cell, wherein the synchronization status information for the small cell includes synchronization acquisition status information for the small cell And the hop count information for the small cell, the synchronization acquisition status information for the small cell indicates that the small cell has acquired synchronization or has not acquired synchronization, and the hop count information for the small cell is Represents the number of hops from the smallest cell to the smallest cell at the forefront of the synchronous chain involved in obtaining the most recent synchronization of the small cell.

In one embodiment, the method further comprises modifying the synchronization state information for the small cell when the small cell succeeds in acquiring synchronization from the at least one candidate small cell, Wherein the modifying the synchronization state information comprises modifying the synchronization state information for the small cell to be the same as the synchronization state information for the at least one candidate small cell, And modifying the hop count information for the small cell.

In one embodiment, the method further comprises transmitting a synchronization success report message to the at least one candidate small cell if the small cell succeeds in acquiring synchronization from the at least one candidate small cell.

In one embodiment, the method further comprises: managing a post cell list for the small cell in the small cell, wherein the cell list includes an ID of a small cell that is synchronized from the small cell Wherein if the small cell fails to acquire synchronization from the at least one candidate small cell, the synchronization acquisition status information for the small cell indicates that the small cell failed to acquire synchronization, Modifying the synchronization acquisition status information, and transmitting a synchronization failure report message to the small cell identified by the ID included in the cell list thereafter.

In another aspect, a method is provided that is performed to support acquisition of synchronization in a small cell. The method includes: managing synchronization status information for the small cell and a cell list thereafter, the synchronization status information for the small cell includes synchronization acquisition status information for the small cell and hop count information for the small cell Wherein the synchronization acquisition status information for the small cell indicates that the small cell has acquired synchronization or has not acquired synchronization, and the hop count information for the small cell indicates that the small cell has most recently acquired synchronization The number of hops from the smallest cell to the smallest cell at the forefront of the involved synchronous chain, and the subsequent cell list includes the ID of the small cell that has obtained synchronization from the small cell, Receiving a status information request message, receiving, in response to receiving the synchronization status information request message, The method comprising: transmitting the synchronization status information to the neighboring cells; receiving a synchronization success report message from the neighboring cell, the synchronization success report message including an ID of the neighboring cell; And including the ID of the neighboring cell in the subsequent cell list in response to the request.

In yet another aspect, an apparatus for acquiring synchronization in a small cell is provided. The apparatus includes a communication unit and a control unit, wherein the control unit measures signals from neighboring cells through network listening, identifies adjacent small cells based on the measured signals, Wherein the communication unit is configured to receive synchronization status information from each of the adjacent small cells, and the control unit is configured to transmit the synchronization status information to each of the adjacent small cells based on the synchronization status information, Selecting at least one candidate small cell, and attempting to obtain synchronization acquisition from the at least one candidate small cell.

In one embodiment, the synchronization status information from each of the adjacent small cells includes synchronization acquisition status information for the corresponding neighboring small cell and information about the hop number for the neighboring small cell, Indicates that the corresponding neighboring small cell has acquired synchronization or has not acquired synchronization, and the hop count information for the neighboring small cell indicates that the neighboring small cell has most recently acquired synchronization Represents the number of hops from the smallest cell at the forefront of the synchronized chain involved to the corresponding adjacent small cell.

In one embodiment, the synchronization acquisition status information for the corresponding small cell may include information indicating that the small cell at the forefront of the corresponding synchronization chain has acquired synchronization from a reliable synchronization source, or information indicating that the small cell acquires synchronization And information indicating failure.

In one embodiment, the information indicating that the small cell at the forefront of the corresponding synchronization chain has obtained synchronization from a reliable synchronization source includes information identifying the reliable synchronization source.

In one embodiment, the control unit is further configured to select the at least one candidate small cell of the adjacent small cells based on the synchronization acquisition state information and the hop count information for each of the adjacent small cells.

In one embodiment, the control unit is further configured to select, as the at least one candidate small cell, a neighboring small cell that has been synchronized among the neighboring small cells based on the synchronization acquisition state information for each of the adjacent small cells .

In one embodiment, the control unit may be configured to determine, based on the synchronization acquisition state information and the hop count information for each of the adjacent small cells, a neighboring small cell whose synchronization is obtained among the neighboring small cells and has a smaller number of hops than the predetermined number As the at least one candidate small cell.

In one embodiment, the apparatus further comprises a storage unit for storing synchronization status information for the small cell, and the synchronization status information for the small cell includes synchronization acquisition status information for the small cell, Wherein the synchronization acquisition status information for the small cell indicates that the small cell has acquired synchronization or has not acquired synchronization, and the hop count information for the small cell indicates that the small cell Represents the number of hops from the smallest cell to the smallest cell at the forefront of the involved synchronization chain in obtaining the most recent synchronization.

In one embodiment, the control unit may be configured to synchronize the synchronization status information for the small cell with the synchronization status information for the at least one candidate small cell when the small cell succeeds in acquiring synchronization from the at least one candidate small cell. And modifying the hop count information for the small cell so that the number of hops for the small cell is increased by one.

In one embodiment, the control is further configured to transmit a synchronization success report message to the at least one candidate small cell if the small cell succeeds in acquiring synchronization from the at least one candidate small cell.

In one embodiment, the storage further stores a subsequent cell list for the small cell, wherein the cell list further includes an ID of a small cell that is synchronized from the small cell, Correcting the synchronization acquisition status information for the small cell so that the synchronization acquisition status information for the small cell fails to acquire synchronization from the at least one candidate small cell, And to send a synchronization failure report message to the small cell identified by the ID included in the cell list thereafter.

In yet another aspect, an apparatus is provided for supporting synchronization acquisition in a small cell. The apparatus comprises: a storage unit for storing synchronization status information for the small cell and a cell list thereafter; the synchronization status information for the small cell includes synchronization acquisition status information for the small cell and hop count information for the small cell Wherein the synchronization acquisition status information for the small cell indicates that the small cell has acquired synchronization or has not acquired synchronization and the hop count information for the small cell indicates that the small cell is most recently synchronized Wherein the cell list indicates the number of hops from the smallest cell to the smallest cell at the forefront of the synchronized chain involved in acquiring, wherein the cell list includes an ID of a small cell that is synchronized from the small cell, In response to receiving the synchronization status information request message from the mobile station, the synchronization status information for the small cell to the neighboring cell And a control unit configured to include the ID of the neighbor cell in the subsequent cell list in response to receiving a synchronization success report message from the neighbor cell, wherein the synchronization success report message includes the ID of the neighbor cell. .

According to the embodiments of the present invention, there is a technical effect that the synchronous coverage of a small cell can be extended by synchronizing a small cell even in a room where GPS synchronization or NL synchronization is impossible.

1 is a diagram illustrating a network configuration diagram for explaining a method of acquiring synchronization between small cells according to a server management method.
2 is a block diagram of a synchronization state management server according to an embodiment of the present invention.
3 is a diagram illustrating an embodiment of a data table in which synchronization status information for small cells is stored.
4 is a diagram illustrating an embodiment of a synchronization chain in which small cells acquire synchronization.
5 is a diagram illustrating a data table for explaining a process of selecting a candidate cell by a control unit of the synchronization state management server.
6 is a diagram illustrating an example of a result of modifying the data table of FIG. 5 in response to receiving a synchronization success report message from a small cell at a controller of the synchronization state management server.
7 is a diagram illustrating an example of a result of modifying the data table of FIG. 5 in response to receiving a synchronization failure report message from a small cell at a controller of the synchronization state management server.
Figure 8 is a block diagram of a small cell.
9 is a diagram illustrating a message flow diagram for illustrating an embodiment of a procedure for acquiring synchronization from a neighboring small cell in a small cell according to a server management method.
10 is a diagram illustrating a network configuration diagram for explaining a method of acquiring synchronization between small cells according to a dispersion management method.
FIG. 11 is a block diagram of a small cell of FIG. 10 according to an embodiment of the present invention.
12A is a diagram showing an embodiment of a data table in which synchronization status information for a small cell is stored.
12B is a diagram showing an embodiment of a data table in which a cell list for a small cell is stored later.
13 is a diagram illustrating an embodiment of a synchronous chain in which small cells acquire synchronization.
FIGS. 14A to 14C are diagrams showing data states of synchronization status information received from adjacent small cells in order to select a candidate small cell in a small cell. FIG.
15 is a flowchart illustrating an example of a procedure for acquiring synchronization from a neighboring small cell in a small cell according to a distributed management scheme;
Figure 16 is a flow diagram illustrating one embodiment of a procedure performed to support synchronization acquisition in a small cell according to a distributed management scheme.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of attaining them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. To fully disclose the scope of the invention to a person skilled in the art, and the invention is only defined by the scope of the claims.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. For example, an element expressed in singular < Desc / Clms Page number 5 > terms should be understood to include a plurality of elements unless the context clearly dictates a singular value. In addition, in the specification of the present invention, it is to be understood that terms such as "include" or "have" are intended to specify the presence of stated features, integers, steps, operations, components, The use of the term does not exclude the presence or addition of one or more other features, numbers, steps, operations, elements, parts or combinations thereof. Further, in the embodiments described herein, 'module' or 'sub-unit' may mean at least one function or a functional part performing an operation.

In addition, all terms used herein, including technical or scientific terms, unless otherwise defined, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries should be construed as meaning consistent with meaning in the context of the related art and may be interpreted in an ideal or overly formal sense unless explicitly defined in the specification of the present invention It does not.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, well-known functions or constructions will not be described in detail if they obscure the subject matter of the present invention.

According to the embodiments disclosed herein, synchronization can be obtained between small cells even in a room where GPS synchronization or NL synchronization is not possible. If any small cell placed indoors fails to perform, for example, GPS synchronization or NL synchronization, a target small cell for synchronization acquisition of the small cell is determined, and the small cell attempts to acquire synchronization from the determined target small cell can do. Here, in order to determine the target small cell, the synchronization status information of the small cells excluding the small cell can be referred to. Synchronization between small cells can be achieved by a server management method or a distributed management method.

1 is a diagram illustrating a network configuration diagram for explaining a method of acquiring synchronization between small cells according to a server management method.

As shown in FIG. 1, the small cells 111-116 may be used for indoor / outdoor (indoor / outdoor), such as home, enterprise, urban, (GSM) network, a 2G wireless communication network such as a Code Division Multiple Access (CDMA) network, a wideband code division multiple access (WCDMA) network, or the like, for one or more terminals (not shown) A mobile Internet network such as a WiBro (Wireless Broadband Internet) network and a WiMax (Worldwide Interoperability for Microwave Access) network, and the like, such as an Internet access network, an LTE (Long Term Evolution) network and a wireless Internet platform for interoperability Lt; / RTI > The small cells 111-116 may attempt to obtain synchronization from the synchronization source 120 or from adjacent small cells. In embodiments of the present invention, the small cells 111-116 may function as a synchronization source and perform the function of providing synchronization information to adjacent small cells. Although FIG. 1 shows that six small cells are arranged, it is to be understood that more or fewer small cells may be arranged. The small cells 111-116 are low power wireless connection base stations and are small base stations with an operating range of at least 10m to several hundreds of meters. The small cells 111-116 may be classified into femtocells, pico cells, metro cells, and microcell microcells depending on the use range and usage, . Also, since LTE refers to a small cell as a normal HeNB (Home eNB), small cells 111-116 should be understood as a concept including an HeNB. The synchronization source 120 includes at least one of a Global Navigation Satellite System (GNSS) 122, a synchronized base station (macro cell) 124, and an IEEE 1588 master server 126 based on a Precision Time Protocol (PTP) However, it should be appreciated that the types of synchronization sources are not limited to these. The satellite positioning system 122 may include any one of a GPS (Global Positioning System), a GLONASS (Global Navigation Satellite System), and a GALILEO (European Satellite Navigation System). Generally, most of the small cells 111-116 except the small cells 111-116 are likely to fail to acquire the synchronization from the synchronization source 120 because of the environmental characteristics of the small cells distributed in the building. In this case, each of the small cells 111-116 may receive information on the candidate cell for synchronization acquisition from the synchronization state management server 130 and attempt to acquire synchronization from the candidate cell. The synchronization state management server 130 stores and manages synchronization state information for each of the small cells 111-116 in the database. The synchronization state management server 130 determines candidate cells for synchronization acquisition based on synchronization state information for each of the small cells 111-116. The small cells 111-116 may be connected to each other by a wired network such as the Internet. The small cells 111-1116 and the synchronization state management server 130 may be connected to each other by a wired network such as the Internet. In the context of the LTE network, the HeNBs, which are small cells, are managed by HeMS (Home eNB Management Server), which functions to determine and direct settings for operation of small cells based on information reported by small cells, It is possible to implement the synchronous state management server 130 as a part of the HeMS.

2 is a block diagram of a synchronization state management server according to an embodiment of the present invention.

As shown in FIG. 2, the synchronization state management server 130 may include a database 220. The database 220 stores synchronization status information for each of the small cells 111-116. In one embodiment, synchronization status information for each of the small cells 111-116 may be managed as a data table. The synchronization status information for each of the small cells 111-116 includes ID of the corresponding small cell, synchronization acquisition status information for the small cell, hop count information for the corresponding small cell, Cell list. The synchronization acquisition status information for the small cell indicates that the small cell has acquired synchronization or has not acquired synchronization. In one embodiment, the synchronization acquisition status information for the small cell is information indicating that the small cell at the forefront of the involved synchronization chain in acquiring the most recent synchronization of the small cell has acquired synchronization from a reliable synchronization source Or information indicating that the small cell did not acquire synchronization. In one embodiment, the information indicating that the small cell at the forefront of the synchronization chain has obtained synchronization from a reliable synchronization source includes information identifying the synchronization source that is reliable. The hop count information for the small cell represents the number of hops from the smallest cell to the smallest cell in the most upstream of the synchronous chain involved in obtaining the most recent synchronization of the small cell. The synchronous chain cell list for the small cell includes an ID of at least one small cell included in the synchronous chain excluding the small cell.

3 is a diagram illustrating an embodiment of a data table in which synchronization status information for small cells is stored.

The embodiment of the data table 300 shown is configured on the assumption that the small cells 111-116 have acquired synchronization according to the synchronization chain shown in Fig. That is, the embodiment of the data table 300 shown shows that the small cell 111 has obtained synchronization from a satellite positioning system (GNSS) 122, which is one of the synchronization sources included in the synchronization source 120, The small cell 113 is a small cell 111, the small cell 114 is a small cell 113, the small cell 115 is a small cell 113, The small cell 116 is configured in a state in which it is assumed that synchronization is obtained from the small cell 115. It is also assumed that the IDs of the small cells 111-116 are '00', '01', '02', '03', '04', and '05', respectively. First, in the case of the small cell 111, the data of the cell ID field is 00. The data in the synchronization source field is 1 because the small cell 111 acquired synchronization directly from the satellite positioning system 122, which is a reliable synchronization source with guaranteed quality. 01 ", which represents the satellite positioning system 122 as data of the synchronization source field, may be stored. The data in the number of hops field is zero because the small cell 111 has acquired synchronization directly from the satellite positioning system 122. [ The synchronous chain cell list is empty. In the case of the small cell 112, the data of the cell ID field is 01. The data in the synchronization source field is 1 because the small cell 112 has acquired synchronization from the small cell 111 directly synchronized with the satellite positioning system 122, which is a reliable synchronization source with guaranteed quality. The data in the hop count field is 1 because the small cell 112 has acquired synchronization from the small cell 111. [ 00 in the small cell 111 is stored in the synchronous chain cell list field. In the case of the small cell 113, the data of the cell ID field is 02. The data in the synchronization source field is 1 because the small cell 113 has acquired synchronization from the small cell 111 directly acquired from the satellite positioning system 122, which is a reliable synchronization source with guaranteed quality. The data in the hop count field is 1 since the small cell 113 acquires synchronization from the small cell 111. [ 00 in the small cell 111 is stored in the synchronous chain cell list field. In the case of the small cell 114, the data of the cell ID field is 03. The data in the sync source field is 1. The data in the hop count field is 2 because the small cell 114 has acquired synchronization from the small cell 111 and the small cell 113. [ The ID 00 of the small cell 111 and the ID 02 of the small cell 113 are stored in the synchronous chain cell list field. In the case of the small cell 115, the data of the cell ID field is 04. The data in the sync source field is 1. The data in the hop count field is 2 because the small cell 115 has acquired synchronization from the small cell 111 and the small cell 113. [ The ID 00 of the small cell 111 and the ID 02 of the small cell 113 are stored in the synchronous chain cell list field. In the case of the small cell 116, the data of the cell ID field is 05. The data in the sync source field is 1. The data in the hop count field is 3 since the small cell 115 acquired synchronization along a synchronous chain composed of the small cell 111, the small cell 113 and the small cell 115. [ The ID 00 of the small cell 111, the ID 02 of the small cell 113, and the ID 04 of the small cell 115 are stored in the synchronous chain cell list field.

The database 220 may be a flash memory type, a hard disk type, a MultiMedia Card (MMC), a card type memory (for example, SD (Secure Digital) card or XD (Random Access Memory), SRAM (Static Random Access Memory), ROM (Read Only Memory), EEPROM (Electrically Erasable Programmable Read Only Memory), PROM Capacity memory of magnetic memory, magnetic memory, magnetic disk, or optical disk, but those skilled in the art will recognize that the embodiment of the database 220 is not limited thereto.

Referring again to FIG. 2, the synchronization state management server 130 may further include a communication unit 230. The communication unit 230 may be configured to receive a neighbor cell list from the small cells 111-116. Wherein the neighboring cell list may include an ID of at least one neighboring small cell. The communication unit 230 may be further configured to receive a synchronization result report message from the small cells 111-116. The synchronization result report message may be a synchronization success report message or a synchronization failure report message. The synchronization success report message may include the ID of the target small cell in which the small cells 111-116 directly acquire the synchronization. The communication unit 230 may be configured to implement a communication protocol that enables the synchronization state management server 130 to transmit and receive packets to and from the small cells 111-116 through a wired network such as the Internet. In this case, the communication protocol may be implemented with appropriate hardware and / or firmware. In one embodiment, the communication protocol may include a Transmission Control Protocol / Internet Protocol (TCP / IP) protocol and / or a User Datagram Protocol (UDP) protocol.

The synchronous state management server 130 may further include a control unit 210. The control unit 210 may be configured to transmit information required for the cell search by the small cells 111-116 to the small cells 111-116 through the communication unit 230. [ This information allows the small cells 111-116 to perform cell search efficiently as information on the cell search range. In response to receiving the neighbor cell list from the small cells 111-116, the control unit 210 refers to the database 220 to determine at least one of the adjacent small cells identified by the IDs included in the neighbor cell list And transmit the ID of the selected candidate cell to the corresponding small cell through the communication unit 230. [ The control unit 210 searches the database 220 for the synchronization acquisition state information and the hop count information for each of the adjacent small cells using the respective IDs of the adjacent small cells and acquires the synchronization acquisition state information And / or < / RTI > the number of hops. In one embodiment, the control unit 210 may be further configured to select, as candidate cells, adjacent small cells that have been synchronized among adjacent small cells based on the synchronization acquisition state information for each of the adjacent small cells. The neighboring small cells for which synchronization has been obtained are cells directly or indirectly referred to as reliable synchronization sources such as the satellite positioning system 122, the synchronized base station 124 and the IEEE 1588 master server 126, It is possible to prevent the occurrence of a synchronization error due to the link being broken on the synchronization chain at the time of synchronization, or the formation of a synchronization chain of the closed loop without an absolute synchronization reference. In another embodiment, the controller 210 acquires synchronization among the adjacent small cells based on the synchronization acquisition state information and the hop count information for each of the adjacent small cells, and transmits the adjacent small cells having a smaller number of hops than the selected number to the candidate cells As shown in FIG. When the synchronization is propagated several times on the synchronous chain, the synchronization error of each small cell accumulates and the synchronization error gradually becomes larger. By selecting an adjacent small cell having a smaller number of hops than the predetermined number as the candidate cell, It is possible to prevent the synchronization error from increasing.

5 is a diagram illustrating a data table for explaining a process of selecting a candidate cell by a control unit of the synchronization state management server.

When the control unit 210 receives a list of neighbor cells including 02, 03, and 04, which are small cell IDs, from the small cell 116, the control unit 210 refers to the data table 500, The small cell 113, the small cell 114, and the small cell 115, which are identified by the synchronization status information. According to the search result, the small cell 113 has acquired synchronization from a reliable synchronization source whose quality is ensured, and the number of hops therefor is one. The small cell 114 can see that the data in the synchronization source field for the small cell 114 is 0, which means that the synchronization is lost or the synchronization is not obtained. The small cell 115 has acquired synchronization from a reliable synchronization source whose quality is ensured, and the number of hops therefor is two. If the predetermined number of the thresholds for the number of hops is set to 2, the controller 210 excludes the small cells 114 that have not acquired synchronization, The small cell 113 having a small number of cells is selected as a candidate cell. The control unit 210 may be configured to transmit the ID of the selected candidate cell, that is, 02, to the small cell 116 through the communication unit 230. [

Referring again to FIG. 2, the controller 210 may be further configured to update the data table 500 stored in the database 220 in response to receiving the synchronization result report message from the small cells 111-116. The synchronization result report message may be a synchronization success report message, and the synchronization success report message may include an ID of a target small cell whose synchronization has been directly acquired by the small cell. The controller 210 modifies the synchronization state information for the small cell 111-116 that transmitted the synchronization success report message to be the same as the synchronization state information for the target small cell identified by the ID included in the synchronization message, The hop count information for the small cells 111-116 is modified so that the number of hops for the small cells 111-116 is increased by one and the ID of the target small cell is added to the synchronous chain cell list for the small cells 111-116 Lt; RTI ID = 0.0 > 111-116 < / RTI > For example, if the small cell 116 receives ID 02 from the control unit 210 and successfully acquires synchronization from the small cell 113, the small cell 116 is synchronized with ID 02 The control unit 210 of the synchronous state management server 130 transmits synchronization status information for the small cell 116 to the small cell 113 identified by the ID 02, And increments the number of hops for the small cell 116 by one and adds ID 02 to the list of synchronous cells for the small cell 116. [ Also, since the small cell 116 has acquired synchronization from the small cell 113, the data of the synchronization source field for the small cell 116 is modified from 0 to 1. The result of modifying the synchronization status information for the small cell 116 is illustrated in the data table of FIG.

In response to receiving the synchronization failure report message from the small cell 111-116, the control unit 210 transmits the synchronization acquisition status information for the small cell to the small cell so as to indicate that the small cell failed to acquire synchronization Lt; / RTI > may be further configured to modify the synchronization acquisition status information for the mobile station. The control unit 210 determines whether or not the small cell involved in the synchronous chain including the small cell containing the ID of the small cell failed to acquire the synchronization in the synchronous chain cell list, Cell '), < / RTI > it is further possible to modify the synchronous acquisition state information for the small cell involved to indicate that the small cell in which the synchronous acquisition state information for the involved small cell is involved has failed to acquire synchronization. For example, when the synchronization status management server 130 receives the synchronization failure report message from the small cell 113 identified by the ID 02 in the state where the data table of FIG. 5 is maintained, the controller 210 controls the small cell 113, 0 is written in the synchronous source field for the small cells 114 and 115, and 0 is written in the synchronous source fields for the small cells 114 and 115 that contain the ID 02 in the synchronous chain cell list. The control unit 210 may further be configured to cause a message to notify the failed small cell that the synchronization has failed (sync fail message) or a message to perform the resynchronization procedure to be delivered directly or indirectly.

The controller 210 described above may be implemented as application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices At least one of programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, and microprocessors Based hardware platform. The control unit 210 may also be implemented as a firmware / software module executable on the hardware platform described above. In this case, the software module may be implemented by a software application written in an appropriate program language.

Figure 8 is a block diagram of a small cell.

As shown, the small cells 111-116 may include a control unit 810, a communication unit 820, and a storage unit 830. The small cells 111-116 may be configured to acquire synchronization from a synchronization source 120 wherein the control unit 810 of the small cells 111-116 may be configured to receive the satellite positioning system It is possible to obtain synchronization by receiving a 1-PPS (1 pulse per second) signal from the base station 122 and extracting the timing of the received 1-PPS signal and matching the boundary of the LTE downlink frame at this time.

The small cells 111-116 may further be configured to acquire synchronization from adjacent small cells where the control unit 810 of the small cells 111-116 uses a network listening function to communicate with the communication unit 820 ≪ / RTI > may be configured to receive information about neighboring cells by receiving and measuring signals from neighboring cells. If the small cells 111-116 are configured to communicate in the WCDMA manner, the signal from the neighboring cell may be Received Signal Code Power (RSCP). When the small cells 111-116 are configured to communicate in the LTE scheme, the signal from the neighboring cell may be Reference Signal Received Power (RSRP). The control unit 810 can be further configured to generate a neighboring cell list based on the information about the acquired neighboring cells. The neighbor cell list may include an ID of at least one neighboring small cell whose RSCP or RSRP is equal to or greater than a predetermined value. The control unit 810 transmits the neighbor cell list to the synchronization state management server 130 via the communication unit 820 and transmits at least one candidate cell ID from the synchronization state management server 130 via the communication unit 820 Lt; / RTI > In one embodiment, the small cell identified by at least one candidate cell ID received from the synchronization state management server 130 may be a small cell from which synchronization is obtained. In another embodiment, the small cell identified by at least one candidate cell ID received from the synchronization state management server 130 may be a small cell having a smaller number of hops than a predetermined number of acquires of synchronization.

The control unit 810 may be further configured to attempt to obtain synchronization acquisition from the small cell identified by the at least one candidate cell ID. The control unit 810 receives a downlink signal from a small cell (target small cell) identified by the candidate cell ID, detects a synchronization signal, and then transmits a downlink frame boundary to a target cell To match the downlink timing. When the small cells 111-116 are configured to communicate in the LTE scheme, the synchronization signal may be a synchronization signal defined in the 3GPP TS 36.211 standard as one of the downlink physical channels of the LTE system. In this way, the small cells 111-116 can align the timing of the small cell at the 1-PPS timing. The control unit 810 of the small cell 111-116 may transmit the synchronization result report message to the synchronization state management server 130 through the communication unit 820. [ The synchronization result report message may include a synchronization success report message or a synchronization failure report message. The synchronization success report message may include the ID of the target small cell.

The controller 810 described above can be implemented as a part or as a part of a SON (Self Organizing Network) function for detecting surrounding cells in a small cell and automatically setting a wireless operating environment. The controller 810 may be implemented as a hardware platform based on at least one of an application specific integrated circuit, a digital signal processor, a digital signal processing device, a programmable logic device, a field programmable gate array, a processor, a controller, a microcontroller, have. The control unit 810 may also be implemented as a firmware / software module executable on the hardware platform described above. In this case, the software module may be implemented by a software application written in a suitable programming language.

WCDMA, LTE / LTE-A, WiFi, WiBro, and WiMax, which enable small cells 111-116 to communicate wirelessly with one or more terminals within its coverage. And / or firmware that implements a variety of RAT (Radio Access Technology) In one embodiment, the communication unit 820 may be implemented to comply with a wireless communication interface specification such as LTE-Ue. The communication unit 820 may be configured to implement a communication protocol that supports small cells 111-116 to transmit and receive packets to the synchronization state management server 130 via a wired network such as the Internet. In this case, the communication protocol may be implemented with appropriate hardware and / or firmware. In one embodiment, the communication protocol may comprise a TCP / IP protocol and / or a UDP protocol.

The storage 830 may be used to store one or more software / firmware modules that implement the functions of the controller 810. The storage unit 830 may be a flash memory type, a hard disk type, a multimedia card, a card type memory (for example, an SD card or an XD card), a RAM, an SRAM, a ROM, an EEPROM, a PROM, Optical disk. However, those skilled in the art will appreciate that the embodiment of the storage unit 830 is not limited thereto.

9 is a diagram illustrating a message flow diagram for illustrating an embodiment of a procedure for acquiring synchronization from a neighboring small cell in a small cell according to a server management method.

Referring to FIG. 9, the procedure begins with measuring the signals from neighboring cells using the network listening function in the small cells 111-116 and generating a neighbor cell list based on the measurements (S905). The neighbor cell list may include the ID of at least one adjacent small cell. In step S910, the small cell 111-116 transmits the neighbor cell list to the synchronization state management server 130. [ In step S915, the synchronization state management server 130 refers to the database 120 and selects at least one candidate cell among at least one adjacent small cell identified by the IDs included in the neighbor cell list. As described above, the synchronization state management server 130 stores synchronization state information for each of the small cells 111-116. The synchronization state information for each of the small cells 111-116 includes the ID of the small cell, the synchronization acquisition state information for the small cell, the hop count information for the small cell, and the synchronization chain cell list for the small cell . The synchronization acquisition status information for the small cell indicates that the small cell has acquired synchronization or has not acquired synchronization, and the hop number information for the small cell indicates that the small cell is involved in acquiring the most recent synchronization The number of hops from a small cell at the forefront of the synchronous chain to the corresponding small cell and the synchronous chain cell list for the small cell indicates the ID of at least one small cell included in the synchronous chain excluding the small cell . The synchronization state management server 130 searches the database 120 for synchronization acquisition state information and hop count information for each of at least one adjacent small cell using each ID of at least one adjacent small cell, The at least one candidate cell of at least one adjacent small cell can be selected. In one embodiment, the synchronization state management server 130 may select, as at least one candidate cell, adjacent small cells that have been synchronized among at least one neighboring small cell. In another embodiment, the synchronization state management server 130 can select a neighboring small cell having at least one neighboring small cell whose synchronization is acquired and has a smaller number of hops than the predetermined number, as at least one candidate cell. In step S920, the ID of the selected at least one candidate cell is transmitted to the small cell 111-116.

In step S925, the small cell identified by the ID of the candidate cell received from the synchronization state management server 130 in the small cell 111-116 is set as a target small cell, and an attempt is made to acquire synchronization therefrom. After the synchronization acquisition attempt, the small cell 111-116 transmits a synchronization result report message to the synchronization state management server 130 in step S930. In step S935, the synchronization status management server 130 checks whether the synchronization result report message includes the ID of the target small cell or the synchronization failure report message. If the synchronization result report message includes the synchronization success report message Message and updates the database 120 in accordance with the synchronization success report message. As described above, the update of the database 120 modifies the synchronization status information for the small cells 111-116 to be the same as the synchronization status information for the target small cell, and updates the hop count for the small cells 111-116 1 in the small cell 111-116 so that the ID of the target small cell is included in the synchronous cell list for the small cell 111-116 Lt; RTI ID = 0.0 > cell list < / RTI > If the synchronization result report message is the synchronization failure report message, the synchronization status management server 130 updates the database 120 according to the synchronization failure report message. The update of the database 120 may be performed such that the synchronization acquisition status information for the small cells 111-116 is synchronized to the small cells 111-116 to indicate that the small cells 111-116 failed to acquire synchronization If there is a small cell involved in a synchronous chain including a small cell, that is, a small cell 111-116, including the ID of the small cell 111-116 in the synchronous chain cell list, May be accomplished by modifying the synchronization acquisition state information for the small cell involved to indicate that the small cell in which the synchronization acquisition state information for that cell is acquired did not acquire the synchronization. At this stage, it is possible to cause a message to notify that the synchronization has failed (sync fail message) or a message to perform the resynchronization procedure to be transmitted to the small cell involved.

10 is a diagram illustrating a network configuration diagram for explaining a method of acquiring synchronization between small cells according to a dispersion management method.

10 is similar to the embodiment shown in FIG. 1, but the embodiment shown in FIG. 10 is different from the embodiment shown in FIG. 1 in that in the embodiment of FIG. 10, The synchronous state information is managed by each small cell instead of managing the synchronous state information. In the case of the embodiment of FIG. 10, the small cells 1011-1016 can also try to obtain synchronization from the synchronization source 1020 or from adjacent small cells. The small cells 1011-1016 may function as a synchronization source and perform the function of providing synchronization information to adjacent small cells. Although it is shown in Fig. 10 that six small cells are arranged, it is to be understood that more or fewer small cells may be arranged. 1, synchronization source 1020 may include at least one of a satellite positioning system (GNSS) 1022, a synchronized base station 1024, and an IEEE 1588 master server 126 based on PTP, It is to be appreciated that the type of < / RTI > The satellite positioning system 1022 may include any of GPS, GLONASS, GALILEO, and the like. Generally, most of the small cells 1011 to 1016 are likely to fail to acquire synchronization from the synchronous source 1020, except for a part of the small cells 1011 to 1016 because of the environmental characteristics of the small cells distributed in the building. In this case, each of the small cells 1011 to 1016 requiring synchronization acquisition requests and receives a synchronous state information request message from each of the adjacent small cells, and based on these synchronous state information, generates at least one candidate small cell And attempt to acquire synchronization from the selected at least one candidate small cell. The small cells 1011-1016 are connected to each other by a wired network such as the Internet to exchange information with each other through a backhaul interface. In the case of small cells 1011-1016 communicating in the LTE scheme, information can be exchanged with each other through the X2 interface.

FIG. 11 is a block diagram of a small cell of FIG. 10 according to an embodiment of the present invention.

As shown in FIG. 11, the small cells 1011-1016 may include a control unit 1110, a storage unit 1120, and a communication unit 1130. The storage unit 1120 stores synchronization state information for the small cells 1011-1016 and a cell list thereafter. Synchronization status information includes synchronization acquisition status information for small cells 1011-1016 and hop count information for small cells 1011-1016. The synchronization acquisition status information for the small cells 1011-1016 indicates that the small cells 1011-1016 have acquired synchronization or have not acquired synchronization. The hop count information for the small cells 1011-1016 can be used to determine the number of small cells 1011-1016 from the smallest cell at the forefront of the synchronizing chain involved in the most recent synchronization acquisition of the small cells 1011-1016 And the number of hops. The cell list then contains the ID of the small cell that has obtained synchronization from the small cells 1011-1016.

12A and 12B are views each showing an embodiment of a data table in which synchronization status information for a small cell is stored and a data table in which a cell list for a small cell is stored.

Embodiments of the illustrated data tables 1220 and 1240 store synchronous state information for the small cell 1014 and the following cell list respectively and the small cells 1011-1016 are stored according to the synchronous chain shown in Figure 13 It is composed on the assumption that it acquires motivation. That is, embodiments of the illustrated data tables 1220 and 1240 may be used to obtain synchronization from a satellite positioning system (GNSS) 1022, where the small cell 1011 is one of the synchronization sources included in the synchronization source 1020 The small cell 1012 from the small cell 1011, the small cell 1013 from the small cell 1011, the small cell 1014 from the small cell 1012, the small cell 1015 from the small cell 1014 , And the small cell 1016 is configured in a state in which it is assumed that the small cell 1015 has acquired synchronization. It is also assumed that the IDs of the small cells 1011-1016 are '00', '01', '02', '03', '04', and '05', respectively. First, the data in the synchronization source field is a small cell 1011 obtained by directly acquiring synchronization from the satellite positioning system 1022, which is a reliable synchronization source in which the small cell 1014 is guaranteed in quality, and a small cell 1012). 01 " indicating the satellite positioning system 1022 as data of the synchronization source field, for example, 01 may be stored. The data in the number of hops field is 2 since the small cell 1014 has acquired synchronization through the small cell 1011 and the small cell 1012. Since the small cell 1015 and the small cell 1016 acquire synchronization through the small cell 1014, the ID cell of the small cell 1015 and the small cell 1016 are included in the subsequent cell list for the small cell 1014. [ 05 "

The storage unit 1120 may be used to store one or more software / firmware modules that implement the functions of the controller 1110. The storage unit 1120 may also be used to temporarily store synchronization status information received from adjacent small cells. The storage unit 1120 may be a flash memory type, a hard disk type, a multimedia card, a card type memory (e.g., an SD card or an XD card), a RAM, SRAM, ROM, EEPROM, PROM, Or an optical disk. However, those skilled in the art will recognize that the embodiment of the storage unit 1120 is not limited thereto.

11, the control unit 1110 may be configured to allow the small cells 1011-1016 to acquire synchronization from the synchronization source 1020, in which case the control unit 1110 of the small cells 1011-1016, Receives the 1-PPS signal from the satellite positioning system 1022 using, for example, a built-in GNSS receiver, extracts the timing of the received 1-PPS signal, and synchronizes the boundary of the LTE downlink frame at this point can do.

The small cells 1011-1016 may be further configured to acquire synchronization from adjacent small cells. In this case, the control unit 1110 of the small cells 1011-1016 may communicate with the neighboring small cells through the communication unit 1130 May be configured to measure signals from the cells and to identify adjacent small cells based on the measured signals. When the small cells 1011-1016 are configured to communicate in the WCDMA manner, the signal from the neighboring cell may be RSCP. If the small cells 1011-1016 are configured to communicate in the LTE scheme, the signal from the neighboring cell may be RSRP. The control unit 1110 may be configured to transmit a synchronization status information request message to each of the adjacent small cells through the communication unit 1130 and receive synchronization status information therefrom. The controller 1110 may be further configured to select at least one candidate small cell of adjacent small cells based on the synchronization status information. The control unit 1110 may be configured to select at least one candidate small cell of adjacent small cells based on the synchronization acquisition state information and / or the hop count information for each of the adjacent small cells. In one embodiment, the controller 1110 may select the adjacent small cells that have been synchronized among the adjacent small cells as at least one candidate small cell. The neighboring small cells for which synchronization has been obtained are cells that directly or indirectly refer to a reliable synchronization source, such as the satellite positioning system 1022, the synchronized base station 1024, and the IEEE 1588 master server 1026, It is possible to prevent the formation of a synchronous chain of a closed loop in which a link on the synchronous chain is disconnected at the time of synchronization and a synchronization error occurs or there is no absolute synchronization reference. In another embodiment, the control unit 1110 may select adjacent small cells with at least one candidate small cell having a smaller number of hops than the predetermined number, and the synchronization is obtained among the adjacent small cells. When the synchronization is propagated several times on the synchronous chain, the synchronization error of each small cell accumulates and the synchronization error gradually becomes larger. By selecting an adjacent small cell having a smaller number of hops than the predetermined number as the candidate cell, It is possible to prevent the synchronization error from increasing.

FIGS. 14A to 14C are diagrams showing data states of synchronization status information received from adjacent small cells in order to select a candidate small cell in a small cell. FIG.

The synchronization status information indicated by the data tables in FIGS. 14A to 14C indicates that the small cells 1011 to 1016 acquire synchronization according to the synchronization chain shown in FIG. 13, but that only the small cell 1013 has lost synchronization Which is obtained by the small cell 1014 above. When the control unit 1110 of the small cell 1014 identifies the small cell 1011, the small cell 1012 and the small cell 1013 as adjacent small cells, the small cell 1011, the small cell 1012, Cell 1013 and receives synchronization status information. 14A to 14C show a data table showing synchronization status information received from the small cell 1011, a data table indicating synchronization status information received from the small cell 1012, and synchronization status information received from the small cell 1013 The data tables shown are indicated by reference numerals 1420, 1440 and 1460, respectively. In the case of the synchronization state information received from the small cell 1011, since the small cell 1011 acquires synchronization directly from the satellite positioning system 1022, which is a reliable synchronization source ensured in quality, the data indicating the synchronization source is 1 The data indicating the number of hops is zero. In the case of the synchronization state information received from the small cell 1012, since the small cell 1012 acquires the synchronization through the small cell 1011 which has acquired the synchronization directly from the reliable synchronization source whose quality is assured, The data is 1 and the data indicating the number of hops is 1. In the case of the synchronization state information received from the small cell 1013, since the small cell 1013 has lost synchronization, the data indicating the synchronization source is 0, and in this case, the data indicating the number of hops has no meaning. The control unit 1110 refers to the synchronization status information received from the small cell 1011, the small cell 1012 and the small cell 1013 to output at least one of the small cell 1011, the small cell 1012, and the small cell 1013 One candidate small cell is selected. Referring to FIGS. 4A to 4C, the small cell 1013 is excluded from the selection of the candidate small cell because it is in a state where synchronization is lost or synchronization is not obtained. The small cell 1011 is obtained from a reliable synchronization source whose quality is assured, the number of hops to it is 0, and the small cell 1012 is also a cell whose synchronization is obtained from a reliable synchronization source, In this case, if the predetermined number of thresholds for the number of hops is set to 2, the controller 1110 can select the small cell 1011 and the small cell 1012 as candidate small cells. In one embodiment, the control unit 1110 may select a small cell 1011 and a small cell 1012 having a smaller number of hops from among the small cell 1012 as candidate small cells.

Referring again to FIG. 11, the controller 1110 may be configured to make the selected candidate small cell into a target small cell and to make an attempt to acquire synchronization therefrom. The control unit 1110 receives the downlink signal from the target small cell, detects the synchronization signal, and matches the boundary of the downlink frame with the downlink timing of the target small cell. When the small cells 1011-1016 are configured to communicate in the LTE scheme, the synchronization signal may be a synchronization signal defined in the 3GPP TS 36.211 standard as one of the downlink physical channels of the LTE system. In this way, the small cells 1011-1016 can align the timing of the small cell at the 1-PPS timing. The control unit 1110 may be configured to modify the synchronization status information for the small cells 1011-1016 when the synchronization acquisition is successful by attempting synchronization acquisition from the target small cell. Modification of the synchronization status information for the small cells 1011-1016 modifies the synchronization status information for the small cells 1011-1016 to be the same as the synchronization status information for the target small cell, By modifying the hop count information for the small cells 1011-1016 so that the number of hops for the small cells 1011-1016 is increased by one. The control unit 1110 may also be configured to transmit a synchronization success report message to the target small cell through the communication unit 1130 when the synchronization acquisition from the target small cell is successful. The synchronization success report message may include the ID of the small cell 1011-1016.

On the other hand, when the synchronization acquisition from the target small cell fails, the controller 1110 determines that the synchronization acquisition status information for the small cells 1011-1016 is smaller than the small cells 1011-1016 0.0 > 1011-1016). ≪ / RTI > For example, in the case of the synchronous state information for the small cell 1014 illustrated in FIG. 12A, the data in the synchronous source field is modified to zero. Also, in this case, the controller 1110 transmits a message indicating that synchronization has failed to the small cells identified by the ID included in the cell list (sync fail message) or a message to perform the resynchronization procedure through the communication unit 1130 directly Or indirectly. As an example of a subsequent cell list for the small cell 1014 illustrated in FIG. 12B, a message (sync fail message) indicating that the synchronization has failed to the small cells 1015, 1016 identified by IDs 04 and 05, A message is sent to perform the procedure.

The controller 1110 may further be configured to transmit synchronization status information for the corresponding small cell 1011-1016 to the neighboring cell through the communication unit 1130 in response to receiving the synchronization status information request message from the neighbor cell. In response to receiving a synchronization success report message from the neighboring cell through the communication unit 1130, the control unit 1110 is further configured to add the ID included in the message to the subsequent cell list for the corresponding small cell 1011-1016 .

The controller 1110 described above can be implemented as a part or as a part of a SON (Self Organizing Network) function for detecting surrounding cells in a small cell and automatically setting a wireless operating environment. The controller 1110 may be implemented as a hardware platform based on at least one of an application specific integrated circuit, a digital signal processor, a digital signal processing device, a programmable logic device, a field programmable gate array, a processor, a controller, a microcontroller and a microprocessor have. The controller 1110 may also be implemented as a firmware / software module executable on the hardware platform described above. In this case, the software module may be implemented by a software application written in a suitable programming language.

The communication unit 1130 may be any of GSM, CDMA, WCDMA, LTE / LTE-A, WiFi, WiBro, and WiMax And / or firmware that implements a variety of RAT (Radio Access Technology) In one embodiment, the communication unit 1130 may be implemented to comply with a wireless communication interface specification such as LTE-Ue. The communication unit 1130 may be configured to implement a communication protocol that enables the small cells 1011 to 1016 to transmit and receive packets to other small cells through a wired network such as the Internet. In this case, the communication protocol may be implemented with appropriate hardware and / or firmware. In one embodiment, the communication protocol may comprise a TCP / IP protocol and / or a UDP protocol.

15 is a flowchart illustrating an example of a procedure for acquiring synchronization from a neighboring small cell in a small cell according to a distributed management scheme;

Referring to FIG. 15, the procedure begins with measuring the signals from neighboring cells using the network listening function in the small cells 1011-1016 and generating a neighboring cell list based on the measurements (S1505). The neighbor cell list may include the ID of at least one adjacent small cell. In step S1510, the synchronous state information request message is transmitted to each of the neighboring smalls identified by the IDs included in the neighbor cell list. In step S1515, synchronization status information is received from each of the adjacent small cells. The synchronization status information received from each of the adjacent small cells may include synchronization acquisition status information and hop count information for the adjacent small cells. The synchronization acquisition status information for the neighboring small cell indicates that the neighboring small cell has acquired synchronization or can not acquire the synchronization. The hop count information for the neighboring small cell indicates the number of hops from the smallest cell at the forefront of the neighboring small cell to the neighboring small cell involved in acquiring the most recent synchronization. In step S1520, at least one candidate small cell among adjacent small cells is selected based on the received synchronization state information. At least one candidate small cell may be selected based on the synchronization acquisition state information and the hop count information for each of the adjacent small cells. In one embodiment, adjacent small cells that have been synchronized among adjacent small cells can be selected as at least one candidate small cell. In another embodiment, the adjacent small cells can be selected as at least one candidate small cell whose synchronization is obtained and has a smaller number of hops than the predetermined number.

In step S1525, the selected candidate small cell is set as a target small cell and an attempt is made to acquire synchronization therefrom. In step S1530, it is determined whether or not the synchronization acquisition is successful by attempting synchronization acquisition from the target small cell. If it is determined in step S1530 that the synchronization acquisition is successful, the synchronization state information for the small cells 1011-1016 is modified in step S1535. As described above, the correction of the synchronization status information for the small cells 1011-1016 is performed by modifying the synchronization status information for the small cells 1011-1016 to be the same as the synchronization status information for the target small cell, 1011 - 1016 may be modified by modifying the hop count information for the small cells 1011 - 1016 so that the number of hops for the small cells 1011 - 1016 is increased by one. In step S1540, the communication unit 1130 transmits a synchronization success report message to the target small cell. The synchronization success report message may include the ID of the small cell 1011-1016.

On the other hand, if it is determined in step S1530 that the synchronization acquisition fails, the synchronization acquisition status information for the small cells 1011-1016 is modified in step S1545. In this case, the synchronization acquisition state information for the small cells 1011-1016 is modified so that the small cells 1011-1016 can not acquire the synchronization. In step S1550, a message indicating that synchronization has failed to the small cells identified by the IDs included in the subsequent cell list for the small cells 1011-1016 or a message to perform the resynchronization procedure And the process returns to step S1505.

 Figure 16 is a flow diagram illustrating one embodiment of a procedure performed to support synchronization acquisition in a small cell according to a distributed management scheme.

Referring to Fig. 16, this procedure starts from synchronous state information for small cells 1011-1016 and then managing the cell list (S1605). In the present disclosure, 'managing synchronous state information and subsequent cell list' means storing synchronous state information and a cell list thereafter in the storage unit 1120, or storing it in a changeable state. Synchronization status information for the small cells 1011-1016 includes synchronization acquisition status information for the small cells 1011-1016 and hop number information for the small cells 1011-1016. The synchronization acquisition status information for the small cells 1011-1016 indicates that the small cells 1011-1016 have acquired synchronization or have not acquired synchronization. The hop count information for the small cells 1011-1016 is transmitted from the smallest cell at the forefront of the synchronous chain involved in acquiring the most recent synchronization of the small cells 1011-1016 to the corresponding small cells 1011-1016 . The cell list then contains the ID of the small cell that has obtained synchronization from the small cells 1011-1016. In step S1610, it is determined whether a synchronization status information request message is received. If it is determined in step S1610 that the synchronous state information request message is received, in step S1615, the small cells 1011 to 1016 are searched for in the peripheral small cells identified by the ID included in the synchronous state information request message And transmits synchronization status information for the mobile station. If it is determined in step S1610 that the synchronous state information request message is not received, the process returns to step S1610. In step S1620, it is determined whether a synchronization success report message is received from the neighboring cell identified by the ID. If it is determined in step S1620 that a synchronization success report message has been received from the neighboring cell identified by the ID, in step S1625, the neighboring cell for the small cell (1011-1016) And the process returns to step S1610. On the other hand, if it is determined in step S1620 that the synchronization success report message is not received from the neighboring cell identified by the ID, the process returns to step S1620.

While the foregoing has described various embodiments in which a small cell acquires synchronization from a neighboring small cell, such embodiments may be performed when the small cell fails to acquire a direct synchronization from a reliable synchronization source, It should be understood. Also, since the radio environment of a small cell varies with time, the above-described embodiment for acquiring synchronization may be periodically repeated to reflect this.

In the embodiments disclosed herein, the arrangement of the components shown may vary depending on the environment or requirements in which the invention is implemented. For example, some components may be omitted or some components may be integrated into one. In addition, the arrangement order and connection of some components may be changed.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention. Accordingly, the technical scope of the present invention should be determined only by the appended claims.

111-116: Small Cell
120, 1020: synchronous source
122, 1022: Satellite positioning system
124, 1024: Synchronized base station
126, 1026: IEEE 1588 master server
130: Synchronization state management server
210, 810, 1110:
220: Database
230, 820, and 1130:
830 and 1120:
1011-1016: Small Cell

Claims (2)

A method for acquiring synchronization between small cells,
Determining a target small cell for synchronization acquisition of a specific small cell among the small cells, and
And attempting to acquire synchronization from the determined target small cell in the specific small cell,
Wherein the step of determining a target small cell for synchronization acquisition of a specific small cell among the small cells includes referring to synchronization status information for each of the small cells excluding the specific small cell,
The synchronization status information for each of the small cells includes an ID of the corresponding small cell, synchronization acquisition status information for the corresponding small cell, information on the number of hops for the corresponding small cell, Cell list,
The synchronization acquisition status information for the corresponding small cell indicates that the corresponding small cell has acquired synchronization or failed to acquire synchronization,
The hop count information for the corresponding small cell indicates the number of hops from the smallest cell in the forefront of the synchronous chain involved in acquiring the most recent synchronization of the small cell to the corresponding small cell,
Wherein the synchronous chain cell list for the corresponding small cell includes an ID of at least one small cell included in the corresponding synchronous chain except for the corresponding small cell. delete

Images