KR20060013886A - Method of handover in broadband wireless access system - Google Patents

Abstract

The present invention relates to a broadband wireless access system (MS) having a mobile subscriber station (MSS) and at least one base station (BS), whereby the mobile station performs scanning on neighboring base stations and as a result Storing information; receiving information regarding at least one base station capable of becoming a handover target base station from a first base station; and using the scanning result, the second base station among the at least one base station. A method of performing a handover comprising the steps of: selecting a; transmitting information about the result of the selection to the first base station; and connecting to the second base station. Reduce latency, manage radio resources more efficiently, and It is not to the effect that can be handed over to more efficiently.

Broadband Wireless Access System, Handover

Description

Handover Method Applied to Broadband Wireless Access System {Method of Handover in Broadband Wireless Access System}

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an explanatory diagram of a handover operation in a data plane in a broadband wireless access system.

2 is a diagram illustrating an embodiment of handover operation in a control plane in a broadband wireless access system.

3 is a flow diagram of an embodiment of a cell selection process of a mobile station.

4 is a flowchart illustrating an embodiment of a neighbor base station information broadcasting and scanning procedure according to the prior art.

5 is an embodiment flow diagram illustrating a handover procedure initiated by a base station, in accordance with the prior art.

6 is an embodiment flow diagram illustrating a handover procedure initiated by a base station, in accordance with the present invention.

The present invention relates to a method for performing a handover applied to a broadband wireless access system, and more particularly, to perform neighbor base station scanning at an early stage and to use the handover base station. And to perform a handover by selecting.

1 is a diagram illustrating an embodiment of handover operation in a data plane in a broadband wireless access system.

As shown in FIG. 1, in the data plane, the broadband wireless access system includes a mobile subscriber station (MSS) 11, a base station (BS) 12, and a data backbone network (BS). It consists of (13).

2 is a diagram illustrating an embodiment of handover operation in a control plane in a broadband wireless access system.

As shown in Fig. 2, in the control plane, the broadband wireless access system includes a mobile subscriber station (MSS) 21, a base station (BS) 22, and an authentication management server (ASA). astion Service Authorization) (23).

1 and 2, a common physical layer (PHY) and a medium access control layer (MAC) are defined between a base station and a mobile station.

The preprocessing process for handover according to the prior art consists of Network Topology Advertisement, MSS Scanning of Neighbor BS, and Association Procedure of the mobile station.

In the network topology advertisement, a service providing base station informs terminals of information related to neighboring base stations through broadcasting. Meanwhile, the neighbor base station scanning procedure is a process in which a mobile station measures the quality of a signal transmitted from neighbor base stations based on the neighbor base station information. In addition, the association procedures (Association Procedures) is a process for preparing the initial terminal power value, the time difference value for synchronization with the selected neighbor base station.

The preprocessing process for the handover will now be described in more detail.

First, a base station broadcasts information related to network configuration information to all mobile stations in a cell using a MAC message through a network topology advertisement procedure. The mobile station that has received the information related to the network configuration information as described above scans the neighbor base station to perform the handover. The mobile station requests a scanning period for scanning the neighboring base station from the base station, and the base station allocates the scanning period to the mobile station in response. In addition, the base station may allocate a scanning period directly to the mobile station without requesting the mobile station. The search period for scanning neighbor base stations and the offset for starting the search are allocated in units of mode frames.

Association procedures are processes in which a mobile station normally joins a cell by ranging with a base station. The ranging process means a process in which the mobile station acquires basic information for communication from the base station. When the mobile station scans the neighboring base station and selects the target base station for handover, the mobile station joins the target base station. To this end, the mobile station transmits the ranging request message to the target base station, and the target base station transmits the ranging response message to the mobile station to set the power offset value and the timing offset value of the terminal to appropriate values.

The initial ranging operation of sending the ranging request message is for the mobile station to perform network entry. When the target base station becomes a new service providing base station through the handover, the new service providing base station stores information about the mobile station that has been associated with its cell and transmits it to the conventional service providing base station.

The mobile station that has undergone the handover preprocessing as described above performs a handover procedure. The prior art handover procedure includes cell selection, handover cancellation, termination with the serving base station, and handover rejection.

3 is a flowchart illustrating an exemplary cell selection process of a mobile station. Cell selection operation enters a base station capable of receiving a signal having a strength greater than the signal to interference noise ratio (SINR) transmitted by the base station of the current cell before the terminal enters a new cell. To change the cell means.

Handover may be initiated by a base station or initiated by a mobile station. When the base station requests a handover, the base station first transmits a handover request message to the mobile station. On the other hand, when the mobile station requests handover, the mobile station first transmits to the base station.

When the mobile station transmits a handover request message, the mobile station measures the signal to interference noise ratio (SINR) of the signal received from the neighboring base station, and according to the result, the candidate base station that can be the target base station during handover. Send a Candidate BS to a serving base station. When the serving base station receives a handover request message from the mobile station, or when handing over a specific mobile station, the serving base station allows handover of the mobile station after receiving confirmation of whether the neighboring base station can handover the specific mobile station. do.

After the mobile station or base station sends a handover request message to perform the handover, the mobile station may cancel the handover (Handover cancellation).

On the other hand, when the handover is successfully completed, the mobile station transmits to the conventional serving base station that the handover was successfully performed. The conventional serving base station terminates all connections that have been allocated for data transmission for the handed over mobile station.

When a handover is requested by the base station, the mobile station may reject the handover requested by the base station. When the base station receives the handover rejection message from the mobile station, it newly configures information about the handover target base station and transmits it to the mobile station.

4 is a flowchart illustrating a neighbor base station information broadcasting and scanning procedure according to the prior art. As shown in FIG. 4, the serving base station 42 broadcasts information on the neighbor base stations 43 and 44 to all mobile stations in the cell (S411). Table 1 below shows an example of an adjacent base station advertisement message broadcast to a mobile station in a cell.

Syntax Size Notes MOB-NBR-ADV_Message_Format () {   Management Message Type = 49 8 bits   Operator ID 24 bits Unique ID assigned operator   N_NEIGHBORS 8 bits   For (j = 0; j <N_NEIGHBORS; j ++) {     Neighbor BS-ID 48 bits     Physical Frequency 32 bits     Configuration Change Count 8 bits Incremented each time information for the associated neighbor BS has changed     Hysteresis threshold 8 bits     MAHO report period 8 bits     TVL Encoded Neighbor information Variable TVL specific    }   }

The mobile station 41 receiving the information on the neighbor base stations 43 and 44 transmits a message to the service providing base station 42 requesting the scanning time allocation to scan the neighbor base stations 43 and 44 (S412). ). Table 2 below shows an example of a message for the scanning time allocation request.

Syntax Size Notes MOB-SCN-REQ_Message_Format () {   Management Message Type = 50 8 bits   Scan Duration 12 bits Units are frames   Reserved 4 bits   }

The service providing base station 42 allocates a scanning time and transmits information on this to the mobile station 41 (S413). The scanning time allocation information of the service providing base station 42 may perform scanning for several frames, and includes information on whether to start scanning after several frames. Table 3 below shows an example of a message for transmitting the scanning time allocation information.

Syntax Size Notes MOB-SCN-RSP_Message_Format () {   Management Message Type = 50 8 bits   Scan Duration 12 bits Units are frames   Start frame 4 bits   }

As shown in FIG. 4, the mobile station 41 having received the information on the scanning time allocation from the serving base station 42 starts scanning for the neighbor base stations 43 and 44 after the M frame (S414), The neighbor base stations 43 and 44 are scanned during the N frame period (S415).

While the mobile station performs scanning on the neighboring base stations 43 and 44, the service providing base station 42 stops transmitting data to the mobile station 41, and resumes data transmission after the scanning interval expires.

5 is an embodiment flow diagram illustrating a handover procedure initiated by a base station, according to the prior art. As shown in FIG. 5, when a network problem occurs such as when the service base station 52 is overloaded or needs to adjust radio resources, it is determined to transmit a handover request to the mobile station 51 (S511).

The service providing base station 52 may include an identifier of the mobile station 53 and 54 which is to perform handover to the target base stations 53 and 54 which may be a handover target, a communication capability, Information on the required bandwidth and the quality of service is transmitted (S512, S513). Such information may be transmitted through a HO-pre-notification message.

The target base stations 53 and 54 transmit information to the service providing base station 52 about whether the corresponding service can be accommodated and whether the required service quality can be supported (S514 and S515). Such information may be transmitted through a pre-notification-response message.

The service providing base station 52 selects a base station capable of supporting the highest level of service among the target base stations 53 and 54, and informs the selected base station that it is selected as the handover target base station (S516). This may be transmitted through a handover confirmation message (HO-confirm).

The base station may be selected in plural, and in this case, the base station is informed that the base station is selected as the handover target base station (S518). The base station selected as the handover destination base station reserves a radio resource for providing a service to the mobile station.

The service providing base station 52 transmits a message requesting the mobile station to perform a handover together with the information on the selected base stations (S517). This may be transmitted through a handover request message (MOB-BSHO-REQ).

The mobile station 51 informs the service providing base station to hand over to the handover target base station according to the handover request message (S519). This may be transmitted through a handover notification message (MOB_HO_IND), and may not inform which base station to perform the handover. When the base station receives the handover notification message MOB_HO_IND, the base station may delete the mobile station related information stored in the base station.                         

The mobile station 51 performs scanning on neighboring base stations 53 and 54 recommended by the service providing base station 52 to measure channel quality for each base station (S520). The mobile station acquires information that there is allocated resource for the mobile station through ranging (S521, S522), and performs a procedure for accessing the handover target base station 54 (S523, S524).

After performing the handover, the mobile station 51 and the new service providing base station 54 complete the initial network entry procedure (S525). On the other hand, the conventional service providing base station 52 informs the fact that the handover is canceled with respect to the base station 53 where the handover has not occurred (S526). This may be transmitted through a handover cancellation message (HO-withdraw).

The handover method according to the prior art has the following problems.

First, the mobile station transmits the handover confirmation message (HO-confirm) to all base stations that may be candidates for the target base station, rather than transmitting a handover confirmation message (HO-confirm) only to the target base station to perform the actual handover. send. Therefore, all base stations that can be candidates for a handover target base station must reserve radio resources for handover, and thus there is a problem in that the radio resources cannot be efficiently used.

Second, since the mobile station scans the neighboring base station after receiving the handover request from the base station, there is a problem that a time delay occurs from the time when the handover request is performed from the base station until the actual handover is completed.

Third, when the service providing base station recommends several base stations for handover to the mobile station, when the actual mobile station completes the handover, it is determined whether the mobile station has handed over to which of the recommended base stations. The serving base station is unknown. Therefore, when a conventional service providing base station attempts to transmit a handover cancellation message (HO-withdraw) to a target base station on which handover is not performed, there is a problem in which it is not known which base station to transmit.

An object of the present invention is to provide a handover method that can reduce latency and allocate radio resources more efficiently in a broadband wireless access system.

The present invention for achieving the above object is, in the Broadband Wireless Access System having a mobile subscriber station (MSS) and at least one base station (BS), the mobile station is a first A method for performing a handover from a base station to a second base station, the method comprising: performing a scanning of a neighboring base station by the mobile station and storing a result thereof; and at least one handover target base station from the first base station. Receiving information about base stations, using the scanning result to select the second base station among the at least one base station, and transmitting information about the selection result to the first base station; And providing a handover method comprising the step of accessing the second base station. The.

In addition, the present invention relates to a mobile station in a broadband wireless access system (MSS) having a mobile subscriber station (MSS) and at least one base station (BS), the mobile station from the first base station to the second base station. A method for performing a handover, wherein the first base station selects at least one base station that can be a handover target base station of the mobile station by using information about neighboring base stations, and selects the selected base station information. Transmitting to the mobile station, receiving information regarding the selected base station from the mobile station to the second base station, and transmitting a message to the second base station indicating that the mobile station will be handed over. The purpose is to provide a method of implementation.

The above objects, features and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

6 is an embodiment flow diagram illustrating a handover procedure initiated by a base station, in accordance with the present invention.

The mobile subscriber station (MSS) 61 periodically scans the neighbor base stations 63 and 64 to measure channel quality for the neighbor base stations and reports the results to the serving base station 62. (S612-S613). If there is a network problem such as when the service providing base station 62 is overloaded or needs to adjust radio resources, it is determined to transmit a handover request to the mobile station 61 (S614).

The service providing base station 61 may identify an identifier, a connection parameter, a capability, and a request of a mobile station to perform a handover to target base stations 63 and 64, which may be handover purposes. Information on the required bandwidth and quality of service is transmitted (S615 and S616). Such information may be transmitted through a HO-pre-notification.

The target base stations (63, 64) transmits information on whether it can accommodate the service and whether it can support all of the required quality of service to the service providing base station 62 (S617, S618). Such information may be transmitted through a pre-notification-response message.

The service providing base station 62 transmits a message requesting to perform a handover to the mobile station together with the information on the selected base stations 63 and 64 (S619). This may be transmitted through the handover request message (MOB-BSHO-REQ), and the information transmitted through the handover request message includes information about the ID of the recommended target base stations 63 and 64 and the degree of service provision. .

The mobile station 61 informs the service providing base station 62 to handover to the specific handover destination base station 64 according to the handover request message (S620). This may be transmitted through a handover notification message (MOB_HO_IND). At this time, the mobile station 61 selects the specific target base station 64 to be handed over based on the results of the neighbor base station scanning procedures S611 to S613. When the service providing base station 62 receives the handover notification message MOB_HO_IND, the mobile station related information stored in the service providing base station 62 may be deleted.

The service providing base station 62 informs the specific handover destination base station 64 selected by the mobile station 61 that the mobile station 61 will handover (S621). This may be transmitted through a handover confirmation message (HO-confirm). The base station 64 selected as the handover destination base station reserves a radio resource for providing a service to the mobile station 61.

The mobile station 61 obtains information that a resource for the mobile station has already been allocated through a fast ranging process (Fast Ranging_IE) for the handover target base station 64 (S622). The mobile station accesses the handover destination base station 64 through the ranging request (S623) and the ranging response (S624).

The handover destination base station 64 connected to the mobile station informs the conventional service providing base station 61 that the mobile station has handed over to the handover destination base station 64 (S625). This may be transmitted through a handover complete message (HO-complete).

Upon receiving the information that the mobile station has handed over to the handover destination base station 64, the conventional service providing base station 62 releases the connection and resources for the mobile station 61 and deletes the information on the mobile station (S626). . As the mobile station completes the initial network entry procedure, the handover process is terminated (S627).

The present invention can reduce unnecessary time delay in handover, operate radio resources more efficiently, and do not send a handover cancel message, thereby performing handover more efficiently.

Claims (9)

In a Broadband Wireless Access System having a mobile subscriber station (MSS) and at least one base station (BS), the mobile station performs handover from the first base station to the second base station. In the method, The mobile station performing scanning on a neighbor base station and storing the result; Receiving information about at least one base station that may be a handover destination base station from the first base station; Selecting the second base station from the at least one base station using the scanning result; And Transmitting information regarding the selection result to the first base station; Accessing the second base station Handover performed method comprising a. The method of claim 1, And the scanning is performed at regular intervals. The method of claim 1, The information on at least one base station which may be the handover destination base station includes a base station identifier and information on a service level that can be provided. The method of claim 1, The selecting of the second base station may include selecting a base station having the best channel quality as a result of the scanning, from among at least one base station likely to be the handover target base station. In a Broadband Wireless Access System having a mobile subscriber station (MSS) and at least one base station (BS), the mobile station performs handover from the first base station to the second base station. In the method, Selecting, by the first base station, at least one base station that can be a handover destination base station of the mobile station using information about neighboring base stations; Transmitting the selected base station information to the mobile station; Receiving information about the base station selected as the second base station from the mobile station; And Sending a message to the second base station indicating that the mobile station will be handed over Handover performed method comprising a. The method of claim 5, Selecting the at least one base station, Transmitting, by the first base station, information about a mobile station that requires handover to the neighbor base stations to a neighbor base station; And Receiving information about a degree of service that can be supported for the mobile station from neighboring base stations; How to perform a handover comprising a. The method of claim 6, The information on the degree of service includes an identifier of the mobile station, a connection parameter, communication capability, required bandwidth and quality of service. The method of claim 5, The information on at least one base station which may be the handover destination base station includes a base station identifier and information on a service level that can be provided. The method of claim 5, Disconnecting the mobile station.

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