KR20100079094A - A method of handover in mobile communications system - Google Patents

Abstract

PURPOSE: A handover method in a mobile communication system is provided to periodically transmit spatial/temporal information and channel state information from mobile nodes to an IS to enable a mobile node to predict a channel state with PoA(Point Of Attachment) at a location without additional scanning, thereby quickly performing handover of the mobile node. CONSTITUTION: A mobile node receives spatial and temporal information from mobile nodes between adjacent networks(S11). If handover trigger is generated, the mobile node transmits an adjacent network list request message and location/speed information of the mobile node to an IS(Information Server) for vertical handover(S12). The IS determines the order of networks suitable for the mobile node. The IS transmits information for selected networks to the mobile node(S13). The mobile node performs handover according to an adjacent network list(S14).

Description

Handover method in mobile communication system {A METHOD OF HANDOVER IN MOBILE COMMUNICATIONS SYSTEM}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile communication system, and more particularly, to a vertical handover technology that can seamlessly receive Internet services while moving in a heterogeneous wireless network environment in a mobile communication system.

The prior art is a technology for supporting handover in a heterogeneous network and includes a mobile node (ie, a terminal) having a heterogeneous air interface and an information server (IS) that stores and maintains information about the heterogeneous network. In the prior art, the mobile node requests the IS of information of the surrounding network to perform vertical handover, and the IS performs a response thereto. This prior art is described in IEEE 802.21 Media Independent Handover (MIH).

FIG. 1 is a signal flow diagram illustrating a vertical handover procedure based on IEEE 802.21.

As shown in FIG. 1, when a handover trigger occurs, the mobile node (IS) requests the IS (MIIS in FIG. 1) for information about available networks in its periphery (S1). . The IS delivers information about the surrounding network to the mobile node (S2). The mobile node scans all available networks for measuring channel conditions between neighboring networks based on the information received from the IS (ie, information about the neighboring networks) in step S2 (S3). The mobile node ranks networks using the network decision function based on the measured channel condition and predetermined handover decision policies, then selects the point of attachment (PoA) of the highest ranking network (e.g., For example, vertical handover is performed to the WLAN_PoA (1) selected in FIG. 1) (S4) and the selected network (that is, the WLAN_PoA (1) selected in FIG. 1) (S5). Here, the neighboring networks correspond to base stations of different networks. That is, for example, the peripheral networks correspond to HSDPA_PoA, WLAN_PoA (1), WLAN_PoA (2), and WiBro_PoA in FIG. PoA means a base station.

In the prior art, the mobile node performs scanning to measure the channel state of the neighboring network during vertical handover, which causes a long delay in the scanning process (for example, several hundred msec in the case of WLAN), and also uses As the number of possible networks increases, the scanning delay time is long, which in turn has a technical limitation that a handover delay occurs.

Accordingly, the present invention provides a method for reducing the channel scanning time, that is, the time for determining a channel state with an available network, in a conventional vertical handover technique. That is, the present invention proposes a technique for identifying channel state information without using a separate scanning process by using spatial / temporal locality, and proposes a database configuration technique for supporting such a process in an IS (server). As a result, a network list request and a network list response for vertical handover are performed between the mobile node and the IS.

In order to achieve the above object, a handover method in a mobile communication system according to the present invention,

Receiving, by the server, channel state information of a neighboring network for handover; And configuring and managing, by the server, a database for performing handover based on the received channel state information.

Preferably, the channel state information is

The terminal is transmitted from the terminal to the server through a neighbor PoA information message.

Preferably, the channel state information is

And the SNR of the neighbor network signal, the ID of the neighbor network, the virtual grid coordinates of the terminal, and the time at which the signal of the neighbor network is received.

Preferably, the server receives a message requesting information of the peripheral network to be handed over; Generating, by the server, a rank list of the neighboring networks to be handed over based on channel state information of the neighboring networks established in the database; And sending, by the server, a response message including information on the generated ranking list of the neighboring network to the terminal.

Preferably, the terminal further comprises the step of performing a handover with reference to the ranking list of the peripheral network.

Preferably, the request message is a neighbor ordering list request message, the response message is a method of performing a handover in a mobile communication system, characterized in that the message.

The present invention has been proposed to enable fast vertical handover by improving handover delay due to scanning process in various networks of the prior art. In particular, in the present invention, the IS has only static information about a neighboring network, whereas in the present invention, a mobile node which needs to perform a handover by several mobile nodes periodically sending channel status information to the IS together with spatial and temporal information. Based on this, it is possible to predict the channel state with PoA at any position without any additional scanning process. In addition, the IS information can be used to dynamically set the range in which the signals of each PoA are affected.

The present invention is applied to a mobile communication network system to which the handover technology is applied. However, the technical idea of the present invention is not limited thereto, and may be applied to other communication systems and methods.

As the inventive concept allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

Terms including ordinal numbers such as first and second may be used to describe various components, but the components are not limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as the second component, and similarly, the second component may also be referred to as the first component. The term and / or includes any item of a plurality of related listed items or a plurality of related listed yields.

When an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, but other elements may be present in between. On the other hand, when a component is said to be "directly connected" or "directly connected" to another component, it should be understood that there is no other component in between.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "have" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described on the specification, and one or more other features. It is to be understood that the present disclosure does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art, and, unless expressly defined in this application, are construed in ideal or excessively formal meanings. It doesn't work.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The description will be omitted.

The basic concept of the present invention is that, in the conventional vertical handover technology, the spatial / temporal locality is separately used to reduce the time (ie, the channel scanning time) for identifying the channel state with the available network. It consists of the technology to identify channel status information without scanning process, database configuration technology to support such process in IS, network list request for vertical handover, and network list response.

The present invention is to perform a fast vertical handover process of the present invention, to build a spatial and temporal information of the neighboring network for performing the handover proposed by the present invention as a database, to perform a fast handover based on this That is, 1) a mobile node (or a plurality of mobile nodes) periodically sends channel state information with a neighbor network to an information server (IS) through a neighbor PoA information message; 2) the IS builds and manages a database for performing handover based on the information received from the mobile node; 3) the mobile node sends a neighbor ordering list request message to the IS for ranking handover information for vertical handover; 4) the IS calculates (generates) a list of neighbor networks (ranked list of neighbor networks to be handed over) for handover of the mobile node; 5) the IS sends the generated list to the mobile node via a neighbor ordering list response message; 6) The mobile node refers to the list and performs handover based on the ranking of the neighboring network.

2 is a block diagram of a virtual grid-based network structure according to an embodiment of the present invention. FIG. 2 is a schematic diagram of a network structure, which is composed of an IS (server), a mobile node, base stations (i.e., a Node B connected to an HSDPA backbone network, and a RAS connected to a WiBro backbone network). In particular, in the present invention, in order to construct data on spatial coordinates when the mobile node is handed over, the network structure is configured in a virtual grid. Hereinafter, the structure of the network of the present invention will be described with reference to FIG.

The service provider configures and manages a grid virtual grid environment for efficient network management. In a virtual grid environment, one grid has a unit length d and the available networks (eg WLAN, WiBro, HSDPA, etc.) can be represented as a collection of these grids. Each grid can be represented by A (1,1), A (1,2), A (2,1), A (2,2), etc. with the lower left corner as the origin.

3 is a diagram illustrating a structure of a database constructed by an IS server according to one embodiment of the present invention.

Hereinafter, with reference to FIG. 3, the structure of the IS-created (built) database, that is, the IS_DB will be described. Point of attachment identification ( PoA_ID ) is the primary key of the IS_DB. Accordingly, the IS_DB is managed by PoA_IDs , that is, by networks (base stations), as shown in FIG. PoA is a term commonly used in MIH as defined in MIH. That is, in case of WLAN, an access point (AP), in case of WiBro, a radio access station (RAS), and in case of HSDPA, Node B corresponds to PoA. In each PoA_ID, there is an A_S (Area Set) which is a set of areas to which a PoA signal arrives. A_S is configured based on the location information in a message periodically sent by the mobile nodes to the IS. This part is described in the IS_DB update process. It consists of time (t) when mobile nodes measure channel state with PoA_ID , location ( x, y ) of mobile node when channel state is measured, and channel state information (Signal-to-noise ratio: SNR). . The above information is sorted according to the measurement time of the channel state for each PoA_ID , and used to predict the channel state with the surrounding PoA at an arbitrary position.

The following describes the update process of IS_DB.

The mobile node periodically transmits ( T ) channel state information with the surrounding network to the IS. Here, the information sent by the mobile node to the IS is used to shorten the scanning time at the time of handover by the mobile node. That is, the information sent by the mobile node to the IS is information about spatiality and temporality. That is, the mobile node at the specific time t, the channel state information (e.g., SNR) of the peripheral network (base station) (e.g., PoA_ID_1 parameter, which may correspond to WLAN_PoA (1), for example). It measures and transmits its spatial or local information (i.e., virtual grid coordinate values) (x, y in FIG. 3) to the IS. Accordingly, the specific time t corresponds to time information, and the virtual grid coordinate value corresponds to space or area information.

The message sent by the mobile node to the IS includes information corresponding to spatiality and locality, that is, parameters corresponding to PoA_ID , t, x, y, and SNR. In other words, the mobile node sends the SNR value with PoA_ID to the IS together with the spatial and temporal information when (t), where ( x, y ) were measured. The IS receiving this information calculates which grid the location of the mobile node belongs to, and adds this grid to the A_S field if the calculated grid does not belong to A_S . For example, assuming that A_S = {A (1,1), A (2,1)} for a PoA in the network structure of FIG. 2, the mobile node in the A (1,2) grid is this PoA. If we send the SNR value for, that is, region A (1,2) assumes that the PoA signal arrives, A_S = {A (1,1), A (2,1), A (1,2) } To update. Finally, (t, x, y, SNR ) records are inserted into the DB, and the update process is completed.

FIG. 5 is a schematic signal flow diagram illustrating a process of performing a handover based on spatial and temporal information according to an embodiment of the present invention.

Hereinafter, the network determination process in the IS will be described with reference to FIG. 5.

As described above, the IS receives spatial and temporal information periodically measured by the mobile node between neighboring networks from the mobile node, and the IS configures the database IS_DB based on the information (S11).

)를, 이동 노드의 현재 위치

와 네트워크의 단위 길이(d), 반경(R)을 이용하여 구한다. 이 후, IS_DB에 저장돼 있는 각 PoA_ID의 A_S와 앞에서 구한

와 겹치는 부분이 없는 PoA_ID는, 이동 노드의 핸드오버를 위한 후보 네트워크에서 제외시킨다.The mobile node having a handover trigger sends a neighbor ordering list response message for vertical handover to the IS including its location and speed information (S12). The IS receiving the request message determines the rank of networks suitable for the mobile node through the algorithm of FIG. . Then, information about the networks selected in the determined order is transmitted to the mobile node through a neighbor message (Neighbor ordering list response) (S13). On the other hand, determining the rank of the network suitable for the mobile node, for example through the algorithm of FIG. Hereinafter, the operation of the algorithm of FIG. 4 will be described in more detail. The IS determines the expected radius R of the mobile node based on the speed of the mobile node. That is, a fast mobile node considers a vertical handover target for a wider range, and a slow mobile node considers a vertical handover target only for a narrow range. And the grid that belongs to the radius of the

), The current position of the mobile node

And the unit length (d) and radius (R) of the network. After that, A_S of each PoA_ID stored in IS_DB and

PoA_ID having no overlapping part is excluded from the candidate network for handover of the mobile node.

와 채널상태정보를 보낸 위치

와의 거리에 따라 IS 데이터베이스에 있는 레코드를 오름차순으로 정렬하게 된다 (즉, 공간적 지역성을 활용). 그런 다음 정렬된 레코드에 대해서 첫번째 레코드에 가장 높은 가중치를 그리고 마지막 레코드에 가장 낮은 가중치를 부여하여 평균 SNR을 계산하게 된다. 단, 여기서 모든 가중치의 합은 1이 되도록 한다. 계산된 평균 SNR은 해당 PoA에 대한 예상 SNR 값이 되고 이 값과 미리 저장된 사용자의 프로파일의 다른 정보를 사용하여 각 네트워크 또는 PoA에 대해서 네트워크 점수를 계산한다. 이렇게 산출된 점수들을 가지고 PoA_ID 들을 내림차순 정렬 후, 이를 네트워크 리스트 요청 메시지에 대한 응답 메시지를 통해 이동 노드에게 전송한다.In addition, since the channel state information measured a long time ago is not related to the current channel state, only the channel state information within W time from the current time is used using the time window W (that is, using temporal locality). In addition, the channel position measured near the current position will have a higher correlation, so the current position

And channel status information sent

By sorting the records in the IS database in ascending order (that is, using spatial locality). Then, the average SNR is calculated by assigning the highest weight to the first record and the lowest weight to the last record. However, the sum of all weights is 1 here. The calculated average SNR is an expected SNR value for the corresponding PoA, and the network score is calculated for each network or PoA using this value and other information of the user's profile stored in advance. After sorting the PoA_IDs in descending order with the scores calculated in this way, they are transmitted to the mobile node through a response message to the network list request message.

The mobile node performs the handover based on the neighbor network list to perform the handover received from the IS in step S13 (S14). In this case, the mobile node does not need to scan a neighboring network in order to find a network of a target to be handed over in the related art. For example, with reference to the list received from the IS, the mobile node may perform a handover by selecting the highest ranking network (ie WLAN_PoA (1)) in the list.

However, if the mobile node fails to perform the handover to WLAN_PoA (1), the handover may be performed to the next-order network (ie, WiBro_PoA) without the need for another network scanning procedure.

As described above, the present invention can solve the problem of a handover delay caused by the mobile node scanning the neighboring network to perform the conventional handover. That is, by performing the database IS_DB structure of FIG. 3, the algorithm of FIG. 4, and the handover procedure of FIG. 5, the problem of time delay in the conventional handover can be solved.

The present invention can be used in products such as small devices that can move in heterogeneous network environments that require vertical handover technology and can use Internet applications, or in vehicle network environments that must continue to maintain Internet connectivity while moving quickly and continuously.

The method according to the invention described thus far can be implemented in software, hardware, or a combination thereof. For example, the method according to the present invention may be stored in a storage medium (eg, mobile terminal internal memory, flash memory, hard disk, etc.) and may be stored in a processor (eg, mobile terminal internal microprocessor). It may be implemented as codes or instructions in a software program that can be executed by.

In the above, the present invention has been described with reference to the embodiments shown in the drawings, but this is merely exemplary, and those skilled in the art may realize various modifications and other equivalent embodiments therefrom. I will understand. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

FIG. 1 is a signal flow diagram illustrating a vertical handover procedure based on IEEE 802.21.

2 is a block diagram of a virtual grid-based network structure according to an embodiment of the present invention.

3 is a diagram illustrating a structure of a database constructed by an IS server according to one embodiment of the present invention.

4 is an example of an embodiment of the present invention, an algorithm for estimating channel state of neighboring networks and selecting a network to be a handover target.

FIG. 5 is a schematic signal flow diagram illustrating a process of performing a handover based on spatial and temporal information according to an embodiment of the present invention.

Claims (6)

Receiving, by the server, channel state information of a neighboring network for handover; And configuring and managing, by the server, a database for performing a handover based on the received channel state information. The channel state information of claim 1, wherein: A method for performing handover in a mobile communication system, characterized in that transmitted from the terminal to the server through a neighbor PoA information message. The channel state information of claim 1, wherein: And a SNR of the neighbor network signal, an ID of the neighbor network, a virtual grid coordinate of the terminal, and a time at which the signal of the neighbor network is received. The method of claim 1, Receiving, by the server, a message requesting information of the peripheral network to be handed over; Generating, by the server, a rank list of the neighboring networks to be handed over based on channel state information of the neighboring networks established in the database; And sending, by the server, a response message including information on the generated ranking list of the neighboring network to the terminal. The method of claim 4, wherein And performing a handover by the terminal by referring to a rank list of the neighboring network. The method of claim 4, wherein The request message is a neighbor ordering list request message, And the response message is a neighbor ordering list response message.

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