KR100617730B1 - System and method for handover to minimize service delay due to ping pong effect in a mobile communication system - Google Patents

Abstract

The present invention relates to a method for recognizing whether a mobile subscriber station maintains connection information at a serving base station in a mobile communication system including a serving base station providing a service to a mobile subscriber station and a target base station adjacent to the serving base station. The method may include receiving a handover request message from the serving base station, the handover request message including a resource maintenance type field indicating whether to maintain the connection information established with the serving base station, and the connection information at the serving base station according to the value of the resource maintenance type field. It includes the process of recognizing that it maintains.

Ping pong phenomenon, carrier-to-interference noise ratio, target base station, serving base station, handover

Description

System and method for minimizing service delay due to ping-pong phenomenon in mobile communication system {SYSTEM AND METHOD FOR HANDOVER TO MINIMIZE SERVICE DELAY DUE TO PING PONG EFFECT IN A MOBILE COMMUNICATION SYSTEM}

1 is a diagram schematically showing the structure of a general IEEE 802.16e communication system.

2 is a signal flow diagram illustrating a handover process according to an MSS request in a typical IEEE 802.16e communication system.

3 is a signal flow diagram illustrating a handover process according to a base station request in a general IEEE 802.16e communication system.

4 is a signal flow diagram illustrating a network re-entry process according to handover of an MSS in a general IEEE 802.16e communication system.

5 is a flowchart illustrating a schematic operation of an MSS when a ping pong phenomenon occurs due to a handover in an IEEE 802.16e communication system according to an embodiment of the present invention.

6 is a flowchart illustrating an operation process of an MSS according to whether a ping-pong phenomenon occurs when a handover situation occurs in an IEEE 802.16e communication system according to an embodiment of the present invention.                 

7 is a diagram illustrating a relationship between CINR values of respective base stations for recognizing a ping pong phenomenon by an MSS in an IEEE 802.16e communication system according to an embodiment of the present invention.

8 is a flowchart illustrating an operation of an MSS when a ping-pong phenomenon occurs during a network re-entry procedure according to handover in an IEEE 802.16e communication system according to an embodiment of the present invention.

FIG. 9 is a diagram illustrating a relationship between CINR values of respective base stations for recognizing a ping-pong phenomenon occurring during a network reentry procedure according to handover in an IEEE 802.16e communication system according to an embodiment of the present invention.

10 is a flowchart illustrating a process in which an MSS recognizes whether a serving base station maintains connection information in an IEEE 802.16e communication system according to an embodiment of the present invention.

11 is a flowchart illustrating a handover operation of an MSS according to whether a serving base station maintains MSS connection information in an IEEE 802.16e communication system according to an embodiment of the present invention.

The present invention relates to a mobile communication system, and more particularly, to a handover system and method for minimizing service delay due to a ping pong phenomenon.

In the 4th Generation (hereinafter, referred to as '4G') communication system, users of services having various quality of service (hereinafter referred to as 'QoS') having a transmission rate of about 100 Mbps are used. Active research is underway to provide them. In particular, in 4G communication systems, broadband wireless such as a wireless local area network (hereinafter, referred to as a 'LAN') system and a wireless metropolitan area network (hereinafter, referred to as a 'MAN') system are used. Research is being actively conducted to support high-speed services in a form of guaranteeing mobility and quality of service (BoS) in a broadband wireless access (BWA) communication system. (Institute of Electrical and Electronics Engineers) 802.16a communication system and IEEE 802.16e communication system.

The IEEE 802.16a communication system and the IEEE 802.16e communication system are orthogonal frequency division multiplexing (OFDM) for supporting a broadband transmission network on a physical channel of the wireless MAN system. Or OFDM) orthogonal frequency division multiple access (OFDMA) scheme. The IEEE 802.16a communication system is a system currently considering only a single cell structure and a state in which a subscriber station (SS) (hereinafter referred to as SS) is fixed, that is, no consideration of mobility of the SS is considered. . In contrast, the IEEE 802.16e communication system is a system considering the mobility of the SS in the IEEE 802.16a communication system, and the SS having the mobility is called a mobile subscriber station (MSS). It will be called.

Next, the structure of the IEEE 802.16e communication system will be described with reference to FIG. 1.

1 is a diagram schematically illustrating a structure of a general IEEE 802.16e communication system.

Referring to FIG. 1, the IEEE 802.16e communication system has a multi-cell structure, that is, a base station (BS) 110 having a cell 100 and a cell 150 and managing the cell 100. And a base station 140 that manages the cell 150 and a plurality of MSSs 111, 113, 130, 151, and 153. In addition, signal transmission and reception between the base stations 110 and 140 and the MSSs 111, 113, 130, 151, and 153 is performed using the OFDM / OFDMA scheme. However, among the MSSs 111, 113, 130, 151, and 153, the MSS 130 is a boundary area of the cell 100 and the cell 150, that is, a handover. ) Exists in the realm. That is, when the MSS 130 moves to the cell 150 managed by the base station 140 while transmitting and receiving a signal with the base station 110, the serving BS is transferred from the base station 110. The base station 140 is changed.

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2 is a signal flow diagram illustrating a handover procedure according to an MSS request in a general IEEE 802.16e communication system.

Referring to FIG. 2, the serving base station 210 first transmits a mobile subscriber station neighbor base station advertisement (MOB_NBR-ADV: Mobile Neighbor Advertisement, hereinafter 'MOB_NBR-ADV') message to the MSS 200 ( Step 211). The MOB_NBR-ADV message structure is as shown in Table 1 below.

As shown in Table 1, the MOB_NBR-ADV message includes a plurality of IEs, that is, a management message type indicating a type of a message to be transmitted, an operator ID indicating a network identifier, and a configuration indicating a number of configuration changes. A change count, an N_NEIGHBORS indicating the number of neighbor base stations, a neighbor BS-ID indicating an identifier (ID) of the neighbor base stations, a physical frequency indicating a physical channel frequency of the neighbor base station, and the neighbor besides the information. Other neighbor information (TLV (Type / Length / Value) Encoded Neighbor Information) indicating other information related to the base station is included.

The MSS 200 may obtain information about neighbor base stations according to the reception of the MOB_NBR-ADV message, and the MSS 200 itself may be a carrier of pilot channel signals transmitted from the neighbor base stations and the serving base station 210. A mobile subscriber station scan request (MOB_SCN-REQ) to the serving base station 210 when it wants to scan Carrier to Interference and Noise Ratio (CINR). In step 213, a message " MOB_SCN-REQ " Here, the MOB_SCN-REQ message structure is shown in Table 2 below.

As shown in Table 2, the MOB_SCN-REQ message includes a plurality of IEs, that is, a Management Message Type indicating a type of a message to be transmitted, and a scan interval for scanning CINRs of pilot signals transmitted from the neighbor base stations. It includes a Scan Duration indicating and a Start Frame indicating a frame to start the scanning operation. The scan duration is configured in units of frames. In Table 2, the Management Message Type of the MOB_SCN-REQ message is not determined at present (Management Message Type = undefined). Since the time point at which the MSS 200 makes a scan request is not directly related to the CINR scanning operation of the pilot channel signal, a detailed description thereof will be omitted.

Meanwhile, the serving base station 210 receiving the MOB_SCN-REQ message includes the information to be scanned by the MSS 200, and the mobile subscriber station scan response (MOB_SCN-RSP: Mobile Scanning Interval Allocation Response) whose scanning interval is not 0. (Hereinafter referred to as MOB_SCN-RES) message is transmitted to the MSS 200 (step 215).

The MOB_SCN-RSP message structure is as shown in Table 3 below.

As shown in Table 3, the MOB_SCN-RSP message includes a Management Message Type indicating a plurality of IEs, that is, a type of a message to be transmitted, and a connection identifier (CID: connection ID) of the MSS transmitting the MOB_SCN-REQ message. It will be referred to as 'CID' hereinafter), the scan section, and the time point at which the scan operation starts. In Table 3, the Management Message Type to which the MOB_SCN_RSP message is to be transmitted is currently undetermined (Management Message Type = undefined), and the scan interval indicates an interval in which the MSS performs the pilot CINR scanning and has a value of 0. The case indicates that the scanning request of the MSS is denied.

Upon receiving the MOB_SCN_RSP message including the scanning information, the MSS 200 receives parameters included in the MOB_SCN_RSP message for neighboring base stations and the serving base station 210 obtained by receiving the MOB_NBR_ADV message, that is, a scan interval. In step 217, CINR scanning of the pilot channel signals is performed.

After the scanning of the CINRs of the pilot channel signals received from the neighbor base stations and the serving base station 210 is completed, if the MSS 200 determines that the serving base station to which the MSS 200 currently belongs is to be changed (step 219). In other words, if the MSS 200 determines that the current serving base station should be changed to a new base station different from the base station 210, the MSS 200 requests an MSS handover to the serving base station 210 (MOB_MSSHO-REQ: Mobile Subscriber Station HandOver Request, hereinafter referred to as MOB_MSSHO-REQ) message (step 221). Here, a new base station that is not the serving base station to which the MSS 200 currently belongs, that is, a base station in which the MSS 200 is likely to become a new serving base station by handover will be referred to as a 'target BS'. . In addition, the MOB_MSSHO-REQ message structure is shown in Table 4 below.                         

As shown in Table 4, the MOB_MSSHO-REQ message includes a management message type indicating a plurality of IEs, that is, a type of a transmitted message, and a scanning result of pilot channel signals of a MSS serving a base station and a plurality of neighbor base stations. In Table 4, N_Recommended indicates the number of neighbor base stations that have transmitted pilot channel signals having a predetermined CINR or more as a result of the MSS scanning the CINR of the pilot channel signal for each of the neighbor base stations. The number of neighbor base stations that the MSS recommends for handover. The MOB_MSSHO_REQ message also includes identifiers for each of the neighbor base stations indicated by N_Recommended, a CINR of the pilot channel signal for each of the neighbor base stations, a service level that the neighbor base stations are expected to provide to the MSS, In addition, an estimated HO time is indicated when the neighboring base station is selected as a target base station to start a handover.

When the serving base station 210 receives the MOB_MSSHO-REQ message transmitted by the MSS 200, the MSS 200 detects a list of target base stations to which the MSS 200 can handover from the N_Recommended information of the received MOB_MSSHO-REQ message. (Step 223). For convenience of description, the handoverable target base station list will be referred to as a handoverable target base station list. In FIG. 2, the first target base station 220 and the second target base station are included in the handover capable target base station list. Assume that 230 exists. Of course, the handover capable target base station list may include a plurality of target base stations. The serving base station 210 informs handover to target base stations belonging to the handover capable target base station list, that is, the first target base station 220 and the second target base station 230 (HO-PRE-NOTIFICATION, hereinafter 'HO'). -PRE-NOTIFICATION '(see step 225, step 227). The HO-PRE-NOTIFICATION message structure is shown in Table 5 below.

As shown in Table 5, the HO-PRE-NOTIFICATION message includes a global header commonly included in a plurality of IEs, that is, messages exchanged between base stations in a backbone network, and a first target base station as target base stations ( 220 or an Estimated Time to HO indicating an identifier (MSS ID) of the MSS 200 to handover to the second target base station 230 and the time when the MSS 200 is expected to start handover; The MSS 200 includes information such as required bandwidth, which is bandwidth information required for a target base station to be a new serving base station, and required QoS, which is service level information that the MSS 200 wants to receive. The bandwidth and service level required by the MSS 200 are the same as expected service level information recorded in the MOB_MSSHO_REQ message described in Table 4 above.

The structure of a general global header commonly included in messages exchanged between base stations in the same backbone network as the HO-PRE-NOTIFICATION message is shown in Table 6 below.

Field Size Notes  Message Type =? 8 bit  Sender BS-ID 48 bit  Base station unique identifier (Same number as broadcast on the DL-MAP message)  Target BS-ID 48 bit  Base station unique identifier (Same number as broadcast on the DL-MAP message)  Time stamp 32 bit  Number of multiseconds since midnight GMT (set to 0xffffffff to ignore)  Num records 16 bit  Number of MSS identity records

As shown in Table 6, the Global Header includes a plurality of IEs, that is, a Message Type indicating a type of a message to be transmitted, a Sender BS-ID indicating a transmission base station transmitting the transmitted message, and a message transmitted. Target BS-ID indicating a receiving base station to receive, and Num Records indicating the number of MSS to be the target of the record included in the transmitted message.

When the first target base station 220 and the second target base station 230 receive the HO-PRE-NOTIFICATION message from the serving base station 210, the handover notification response that is a response message to the HO-PRE-NOTIFICATION message (HO-PRE-NOTIFICATION-RESPONSE, hereinafter referred to as 'HO-PRE-NOTIFICATION-RESPONSE') A message is transmitted to the serving base station 210 (steps 229 and 231). The HO-PRE-NOTIFICATION-RESPONSE message structure is shown in Table 7 below.                         

As shown in Table 7, the HO-PRE-NOTIFICATION-RESPONSE message includes a global header and target base stations commonly included in a plurality of IEs, that is, messages exchanged between base stations in a backbone network as described in Table 6 above. The MSS ID of the MSS to be handed over to the UE, an acknowledgment (ACK / NACK) of whether the target base stations can perform the handover according to the MSS handover request, and the target base stations to the MSS Includes bandwidth and service level information that each of the target base stations can provide when handing over.

Meanwhile, the serving base station 210 that has received the HO-PRE-NOTIFICATION-RESPONSE message from the first target base station 220 and the second target base station 230 includes the first target base station 220 and the second target base station ( Analyzing the HO-PRE-NOTIFICATION-RESPONSE message received from 230, the MSS provides a target base station capable of optimally providing the bandwidth and service level required by the MSS 200 when the MSS 200 performs a handover. 200 selects the final target base station to be handed over. For example, the service level that the first target base station 220 may provide is lower than the service level required by the MSS 200, and the service level that the second target base station 230 may provide is the MSS. Assuming the same service level as requested by the 200, the serving base station 210 selects the second target base station 230 as the final target base station to be handed over by the MSS 200. Therefore, the serving base station 210 confirms a handover notification as a response message to the second target base station 230 (HO-CONFIRM, hereinafter 'HO-CONFIRM') as a response message to the HO-PRE-NOTIFICATION-RESPONSE message. In step 233, the message is transmitted. The HO-CONFIRM message structure is shown in Table 8 below.

As shown in Table 8, the HO-confirm message includes a global header commonly included in a plurality of IEs, that is, a message exchanged between base stations in the backbone network described in Table 6, and an MSS to handover to a selected target base station. And a bandwidth and service level information that can be provided from the target base station when the MSS hands over to the selected target base station.

In addition, the serving base station 210 transmits a message to the MSS 200 as a response message to the MOB_MSSHO-REQ message, a base station handover response (MOB_BSHO-RSP: BS HandOver Response, hereinafter referred to as 'MOB_BSHO-RSP') message. (Step 235). Here, the MOB_BSHO-RSP message includes information on a target base station to be handed over by the MSS 200, and the structure of the MOB_BSHO-RSP message is shown in Table 9 below.

As shown in Table 9, the MOB_BSHO-RSP message includes a plurality of IEs, that is, a Management Message Type indicating a type of a transmitted message, a time expected to start a handover procedure, and a target base station selected by a serving base station. Results are shown. In addition, N_Recommended of the MOB_BSHO-RSP message indicates the number of target base stations satisfying the bandwidth and service level requested by the MSS among target base stations on the handoff-capable target base station list. In the MOB_BSHO-RSP message, identifiers for each of the target base stations indicated by N_Recommended, and a service level each of the target base stations are expected to provide to the MSS are indicated. In FIG. 2, only one target base station information of the second target base station 230 is included in the MOB_BSHO-RSP message among the target base stations existing in the handover capable target base station list. If there are a plurality of target base stations in the list that can provide the bandwidth and service level required by the MSS 200, the MOB_BSHO-RSP message includes information on the plurality of target base stations.

Upon receiving the MOB_BSHO-RSP message, the MSS 200 analyzes N_Recommended information included in the MOB_BSHO-RSP message and selects a target base station to which the MSS 200 itself will hand over. The MSS 200 that selects the target base station to be handed over to the serving base station 210 is called a mobile subscriber station handover indication (MOB_HO_IND: Mobile Handover Indication, MOB_HO_IND), which is a response message to the MOB_BSHO-RSP message. In step 237, the message is transmitted. The MOB_HO-IND message structure is shown in Table 10 below.

As shown in Table 10, the MOB_HO_IND message indicates a plurality of IEs, that is, a Management Message Type indicating a type of a message to be transmitted, and whether the MSS has decided to handover or cancel the handover to a selected final target base station. HO_IND_type, if it is determined to handover, the identifier of the last target base station selected by the MSS, and HMAC Tuple for authenticating the MOB_HO-IND message. In HO_IND_type, if the MSS performs handover to the final target base station, HO_IND_type = 00, or if the handover is to be canceled, HO_IND_type = 01, or if the handover is to be rejected, MOB_HO- is set to HO_IND_type = 10. Send an IND message. Upon receiving the MOB_HO-IND message with the MOB_HO_IND = 10 set, the serving base station 210 rewrites the MOB_BSHO-RSP message to the MSS 200 after newly creating a handover capable target base station list.                         

After receiving the MOB_HO_IND message including the HO_IND_type = 00, the serving base station 210 recognizes that the MSS 200 will hand over to the target base station included in the MOB_HO_IND message, that is, the second target base station 230. When the MSS 200 releases connection information currently set up or when the MSS 200 receives a notification that the handover procedure is completely completed from the target base station, that is, the second target base station 230, which has been finally selected. The connection information which is set up with the MSS 200 is set in advance until the predetermined set time (step 239). As such, after transmitting the MOB_HO-IND message to the serving base station 210, the MSS 200 performs the remaining handover operation with the second target base station 230.

In FIG. 2, the handover process according to the MSS request in the conventional IEEE 802.16e communication system has been described. Next, the handover process according to the base station request in the general IEEE 802.16e communication system will be described with reference to FIG. 3. .

3 is a signal flow diagram illustrating a handover process according to a base station request in a general IEEE 802.16e communication system.

Prior to the description of FIG. 3, first, when a handover occurs according to a base station request, the load of the base station itself becomes excessive and load sharing for distributing the load of the base station itself to neighboring base stations is necessary. Or it is for responding to the change of the uplink state of the MSS. Referring to FIG. 3, the serving base station 310 first transmits a MOB_NBR-ADV message to the MSS 300 (step 311). Upon receiving the MOB_NBR-ADV message, information about neighboring base stations can be obtained.

On the other hand, when the serving base station 310 detects the need for handover of the MSS 300 managed by the serving base station 310 itself (step 313), the serving base station 310 transmits the HO-PRE-NOTIFICATION message to neighboring base stations. (Steps 315, 317). In this case, the HO-PRE-NOTIFICATION message includes information on the bandwidth and service level that the target base station to be the new serving base station of the MSS 300 should provide to the MSS 300. In FIG. 3, it is assumed that neighboring base stations of the serving base station 310 are two base stations of the first target base station 320 and the second target base station 330.

Each of the first target base station 320 and the second target base station 330 receives a HO-PRE-NOTIFICATION-RESPONSE message as a response message to the HO-PRE-NOTIFICATION message as the HO-PRE-NOTIFICATION message is received. The serving base station 310 transmits to steps 319 and 321. The HO-PRE-NOTIFICATION-RESPONSE message includes a response (ACK / NACK) indicating whether the target base stations can perform the handover requested by the serving base station 310 and the MSS 300 as described in Table 7 above. Contains bandwidth and service level information that can be provided.

When the serving base station 310 receives the HO-PRE-NOTIFICATION-RESPONSE message from each of the first target base station 320 and the second target base station 330, the serving base station 310 obtains the bandwidth and service level required by the MSS 300. Select target base stations that can be provided. For example, the service level that the first target base station 320 may provide is lower than the service level required by the MSS 300, and the service level that the second target base station 330 may provide is the MSS. Assuming that the service level is the same as the service level requested by the 300, the serving base station 310 selects the second target base station 330 as a target base station to which the MSS 300 can handover. The serving base station 310 that selects the second target base station 330 as the handoverable target base station includes a base station handover request (MOB_BSHO-REQ) including a list of the target base stations available for handover (MOB_BSHO-). REQ ') is transmitted to the MSS 300 (step 323). In this case, the target base station list capable of handover may include a plurality of target base stations. In addition, the MOB_BSHO-REQ message structure is shown in Table 11 below.

As shown in Table 11, the MOB_BSHO-REQ message includes a plurality of IEs, that is, a management message type indicating a message type to be transmitted, and information about target base stations selected by the serving base station 310. In Table 11, N_Recommended indicates the number of adjacent base stations selected by the serving base station as a target base station capable of handover, identifiers for each of the neighbor base stations indicated by N_Recommended, and bandwidth that the neighbor base stations can provide to the MSS. And information about service level.

Upon receiving the MOB_BSHO-REQ message, the MSS 300 detects that handover is requested by the serving base station 310, and refers to the N_Recommended information included in the MOB_BSHO-REQ message to perform a handover. Select the base station. At this time, if the MSS 300 itself wants to scan CINRs of pilot channel signals transmitted from the serving base station 310 and neighboring base stations before selecting the final target base station, the MOB_SCN-REQ message to the serving base station 310. In step 325. Since the time point at which the MSS 300 makes a scan request is not directly related to the CINR scanning operation of the pilot channel signal, a detailed description thereof will be omitted. Upon receiving the MOB_SCN-REQ message, the serving base station 310 transmits a MOB_SCN-RSP message including information to be scanned by the MSS 300 to the MSS 300 (step 327). Upon receiving the MOB_SCN-RSP message including the scanning information, the MSS 300 receives neighbor base stations obtained by receiving the MOB_NBR_ADV message, and target base stations and servings capable of handover obtained by receiving the MOB_BSHO-REQ message. The base station 310 performs CINR scanning of the pilot channel signals according to the parameters included in the MOB_SCN-RSP message, that is, the scan interval (step 329).

The MSS 300 selects a final target base station to be handed over, and then an MSS Handover Response (MOB_MSSHO-RSP) message, which is a response message to the MOB_BSHO-REQ message (hereinafter, referred to as a MOB_MSSHO-RSP) message. Transmits to the serving base station 310 (step 331). The MOB_MSSHO-RSP message structure is shown in Table 12 below.

Syntax Size Notes  MOB_MSSHO-RSP_Message_Format   Mnangement Message Type = 54 8 bits   Estimated HO time 8 bits   For (j = 0; J <N_Recommended; j ++) { N_Recommended can be derived form the known length of the message     Neighbor BS-ID 48 bits     BS S / (N + 1) 8 bits  } }

As shown in Table 12, the MOB_MSSHO-RSP message includes a plurality of IEs, that is, a management message type indicating a message type to be transmitted, a time expected to start a handover procedure, and information on target base stations selected by the MSS. It includes. In Table 12, N_Recommended indicates the number of neighbor base stations selected by the MSS as a target base station capable of handover, identifiers for each neighbor base station indicated by N_Recommended, and a service level that the MSS can be provided from the neighbor base stations. Contains information about

Meanwhile, the serving base station 310 transmits the HO-CONFIRM message as a response message to the HO-PRE-NOTIFICATION-RESPONSE message to the neighboring base station selected as the final target base station by the MSS 300 (step 333). . The MSS 300 selecting the final target base station transmits the MOB_HO_IND message with HO_IND_type = 00 set to the serving base station 310 (step 335). Upon receiving the MOB_HO_IND message with the HO_IND_type = 00 set, the serving base station 310 recognizes that the MSS 300 will handover to the last target base station included in the MOB_HO_IND message, and is currently set up with the MSS 300. The connection information with the MSS 300 is maintained for a preset time until release of the connection information or notification of the completion of the handover procedure from the second target base station 330. (Step 337). As such, after transmitting the MOB_HO_IND message to the serving base station 310, the MSS 300 performs the remaining handover operation with the second target base station 330.

In FIG. 3, a handover process according to a base station request in a general IEEE 802.16e communication system has been described. Next, network re-entry according to MSS handover in a general IEEE 802.16e communication system is described with reference to FIG. 3. The process will be described.

4 is a signal flow diagram illustrating a network re-entry process according to handover of an MSS in a general IEEE 802.16e communication system.

Referring to FIG. 4, first, as the MSS 400 switches to the final target base station 450, the MSS 400 acquires downlink synchronization with the final target base station 450 and then transmits the data from the final target base station 450. In step 411, a DL (DownLink) _MAP message is received. Here, the DL_MAP message is a message including parameters related to the downlink of the final target base station 450. In addition, the MSS 400 receives an UL (UpLink) _MAP message transmitted from the final target base station 450 (step 413). Here, the UL_MAP message is a message including parameters related to uplink of the final target base station 450, and the fast uplink ranging (MSS 400) of the MSS 400 to which the last target base station 450 performs the handover ( It includes a fast uplink ranging information element (FAST UL RANGING Information Element) allocated to support FAST UL RANGING. The reason why the final target base station 450 allocates the fast uplink ranging information element to the MSS 400 is to minimize the delay that may occur when the MSS 400 performs the handover. 400 may allow initial ranging with the final target base station 450 in a contention-free manner corresponding to the fast uplink ranging information element. Here, the fast uplink ranging information element included in the UL_MAP message is shown in Table 13 below.

Syntax Size Notes  Fast_UL_ranging_IE   MAC address 48 bits  MSS MAC address as provided on the RNG_REQ message on initial system entry.   UIUC 4 bits  UIUC = 15. A four-bit code used to define the type of uplink access and the burst type associated with that access.   OFDM Symbol offset 10 bits  The offset of the OFDM symbol in which the burst starts, the offset value is defined in units of OFDM symbols and is relevant to the Association Start Time field given in the UL_MAP message.   Subchannel offset 6 bits  The lowest index OFDMA subchannel used for carrying the burst, starting from subchannel 0.   No OFDMA Symbol 10 bits  The number of OFDM symbols that are used to carry the UL Burst.   No subchannels 6 bits  The number of OFDMA subchannels with subsequent indexes, used to carry the burst.   Reserved 4 bits

Fast_UL_ranging_IE () of Table 13 records a medium access control (MAC) address of an MSS to be provided with a ranging opportunity and a start offset value for the Fast_UL_ranging. UIUC (Uplink Interval Usage Code, hereinafter referred to as 'UIUC') for providing region information, and information about the offset, the number of symbols, the number of sub-channels, etc. of the ranging opportunity interval of the non-competitive scheme allocated to the MSS 400 Doing. The MAC address of the MSS 400 is a HO-PRE-NOTIFICATION message and a HO-PRE-NOTIFICATION-RESPONSE message exchanged between a serving base station and the final target base station in a backbone network during the handover process described with reference to FIGS. 2 and 3. And the final target base station 450 through messages such as a HO-CONFIRM message.

Upon receiving the UL_MAP message, the MSS 400 sends a ranging request (RNG_REQ: Ranging Request, hereinafter 'RNG_REQ') message to the final target base station 450 corresponding to the fast uplink ranging information element. After transmitting (step 415), the final target base station 450 receiving the RNG_REQ message sends a ranging response (RNG_RSP) to the MSS 400 including information for correcting the frequency, time, and transmission power for the ranging. Ranging Response (hereinafter, referred to as 'RNG_RSP')) is transmitted (step 417).

After completing the initial ranging, the MSS 400 and the final target base station 450 perform a re-authentication operation on the MSS 400 (MSS RE-AUTHENTICATION) (step 419). If the security context exchanged between the serving base station to which the MSS 400 previously belonged and the final target base station 450 is not changed when the re-authentication operation is performed, the final target base station 450 performs the security. Use context as it is. Here, the MSS information response (MSS_INFO-RSP: MSS-information-response, hereinafter referred to as MSS_INFO-RSP) message structure, which is a backbone network message providing security context information of the MSS 400, is described in the following table. As shown in 14.

In Table 14, the MSS_INFO-RSP message includes identifier information of an MSS registered in a serving base station, security context information such as security association information for each MSS, network service information for each MSS, and Capability information of MSS is included.

When the re-authentication operation for the final target base station 450 and the MSS 400 is completed, the MSS 400 registers a registration request to the final target base station 450 (REG_REQ: REG_REQ). Message) (Step 421). The REG_REQ message includes registration information of the MSS 400. The final target base station 450 transmits a registration response (REG_RSP: REG_RSP) message, which is a response message to the REG_REQ, to the MSS 400 (step 423). Here, the final target base station 450 may detect the registration information of the MSS 400 included in the REG_REQ message received from the MSS 400 to recognize that the MSS 400 has handed over. . Accordingly, the final target base station 450 maps the connection configuration information at the previous serving base station of the MSS 400 and the connection configuration information at the final target base station 450, and actually at the final target base station 450. The REG_RSP message is transmitted to the MSS 400 by including a type length variable (TLV) value capable of resetting a service flow that can be provided. Here, the structure of the TLV including mapping information on the connection configuration at the serving base station and the final target base station 450 is shown in Table 15 below.

In Table 15, the TLV included in the REG_RSP message corresponds to a connection identifier (CID: Connection ID, hereinafter referred to as 'CID') used by a serving base station before the MSS 400 performs handover. CID information to be used by the final target base station 450 is provided. In addition, the TLV includes information about service parameters different from the previous case when the final target base station 450 provides a service different from the service flow provided by the serving base station before the handover.

The MSS 400 completes the network re-entry procedure with the final target base station 450, and performs normal communication service through the final target base station 450 (step 425).

As described above, when the CINR of the pilot signal of the serving base station is reduced to such an extent that communication with the current serving base station cannot be maintained in the IEEE 802.16e communication system, the serving base station differs from the serving base station according to the request of the MSS or the request of the base station. The MSS performs handover to the neighbor base station, that is, the final target base station. However, in the IEEE 802.16e communication system, while the MSS performs a network reentry operation with the final target base station, the CINR of the pilot signal transmitted from the final target base station is decreased, so that communication service through the final target base station becomes impossible. In this case, the MSS may switch the connection to the serving base station.

However, when the MSS undergoes the pingpong effect as described above during the handover with the final target base station, the MSS switches to the serving base station, and then resumes the communication service through the serving base station. You must perform a connection setup procedure, that is, a network reentry operation. Therefore, if the ping-pong phenomenon occurs frequently while the MSS performs the handover, the MSS also frequently performs the network re-entry operation, resulting in a long service delay. In addition, the frequent performance of the network re-entry operation has a problem that increases the signaling load (signalling load) to reduce the overall system performance.

Accordingly, an object of the present invention is to provide a handover system and method for preventing a ping pong phenomenon by recognizing a ping pong phenomenon in advance in a handover in a mobile communication system.

Another object of the present invention is to provide a handover system and method for minimizing communication service delay when a ping-pong phenomenon occurs in a mobile communication system.

The first method of the present invention for achieving the above objects; A mobile communication system comprising a serving base station providing a service to a mobile subscriber station and a target base station adjacent to the serving base station, wherein the mobile subscriber station recognizes whether to maintain connection information at the serving base station. Receiving a handover request message from the serving base station including a resource maintenance type field indicating whether to maintain the connection information established with the serving base station; maintaining the connection information at the serving base station according to the value of the resource maintenance type field; Includes the process of recognizing the presence

A second method of the present invention for achieving the above objects; In a broadband wireless access communication system including a serving base station providing a service to a mobile subscriber station and a target base station adjacent to the serving base station, the mobile subscriber station performs handover to the serving base station. Requesting, receiving, from a serving base station, a handover response message including a resource retention type field indicating whether connection information is set to be retained between the serving base station and the mobile subscriber station, and according to the value of the resource retention type field; And recognizing whether the serving base station holds the connection information.

The third method of the present invention for achieving the above objects; In a broadband wireless access communication system comprising a mobile subscriber station, a serving base station providing a service to the mobile subscriber station, and a target base station adjacent to the serving base station, the serving base station performs handover in the mobile station. Transmitting, to the subscriber station, a handover request message including a resource retention type field indicating whether connection information established between the serving base station and the mobile subscriber station is maintained; and receiving a handover indication message from the mobile subscriber station. And maintaining the connection information corresponding to the value of the resource maintenance type field.
A fourth method of the present invention for achieving the above objects; In a communication system in which a mobile subscriber station, a serving base station providing a service to the mobile subscriber station, and a target base station adjacent to the serving base station are present, a method for performing handover by the serving base station comprises: a hand from the mobile subscriber station; Receiving an over request message, transmitting a handover response message including a resource maintenance type field indicating whether to maintain the connection information set in the mobile subscriber station to the mobile subscriber station; And receiving the handover indication message from the server, and maintaining the connection information corresponding to the value of the resource maintenance type field.
The fifth method of the present invention for achieving the above objects; In a broadband wireless access communication system having a mobile subscriber station, a serving base station with which the mobile subscriber station communicates, and a plurality of adjacent base stations, a handover method for minimizing service delay due to a ping-pong phenomenon, Receiving and detecting a handover request including information on at least two candidate target base stations selectable from the serving base station as a final target base station which is any adjacent base station among the neighbor base stations, and each of the candidate target base stations; Measuring the carrier-to-interference noise ratios (CINRs) of the reference signal transmitted by the UE, comparing the measured CINR values with a predetermined first threshold value, and wherein the comparison results in a CINR value less than the first threshold value When transmitting a reference signal having a CINR value less than the first threshold value Removing the candidate target base station from the candidate target base stations, determining the final target base station among the candidate target base stations except for the first candidate target base station, and handing over to the serving base station to the final target base station; Including the notification process.
A sixth method of the present invention for achieving the above objects; In a broadband wireless access communication system having a mobile subscriber station, a serving base station through which the mobile subscriber station communicates, and a plurality of neighboring base stations, a handover method for minimizing service delay due to a ping-pong phenomenon, the serving base station includes: When the mobile subscriber station is notified that the mobile subscriber station is to be handed over to a target base station, which is a particular neighbor among the neighbor base stations, the mobile subscriber station deletes or retains the connection information of the mobile subscriber station for a preset time; Determining to switch to the serving base station when a ping-pong phenomenon is detected while performing a network re-entry procedure with the target base station, receiving a handover request or a handover response message from the serving base station, and each message On reception Correspondingly detecting and recognizing whether to maintain the connection information for the mobile subscriber station included in each of the messages; and if the serving base station maintains the connection information for the mobile subscriber station, only the initial ranging procedure Performing the step of resuming communication with the serving base station.

A first system of the present invention for achieving the above objects; In a broadband wireless access communication system having a mobile subscriber station, a serving base station through which the mobile subscriber station communicates, and a plurality of neighboring base stations, a handover system for minimizing service delay due to a ping-pong phenomenon, wherein the serving base station includes: If it is detected that the handover to the last target base station, which is any of the neighbor base stations, needs to be handed over to the serving base station, and selects the last target base station received from the serving base station in response to the handover request. Detects information about at least two candidate target base stations, measures carrier-to-interference noise ratios (CINRs) of reference signals transmitted from each of the candidate target base stations, and sets the measured CINR values in advance. 1 threshold value, and the comparison result If there is a CINR value of less than 1 threshold, the candidate candidate base station transmitting a reference signal having a CINR value of less than the first threshold value is excluded from the candidate target base stations, and the candidate except the first candidate target base station is excluded. A mobile subscriber station that determines the final target base station among the target base stations, and notifies the serving base station that the mobile terminal is to be handed over to the final target base station, and receives a handover request of the mobile subscriber station and correspondingly receives the handover request. And a serving base station transmitting information on at least two candidate target base stations that the terminal can select as the final target base station and being informed of the handover from the mobile subscriber station to the final target base station.

The second system of the present invention for achieving the above objects; In a broadband wireless access communication system having a mobile subscriber station, a serving base station with which the mobile subscriber station communicates, and a plurality of adjacent base stations, a handover system for minimizing service delay due to a ping-pong phenomenon, The serving base station receives and detects a handover request including information on at least two candidate target base stations that can be selected as a final target base station, which is one of the neighbor base stations, and transmits each of the candidate target base stations. Measuring carrier-to-interference noise ratios (CINRs) of the reference signal, and comparing the measured CINR values with a first threshold value that is preset, and if the CINR value is less than the first threshold value as a result of the comparison; A first candidate target for transmitting a reference signal having a CINR value below the threshold A mobile subscriber station which excludes a station from the candidate target base stations, determines the final target base station among the candidate target base stations excluding the first candidate target base station, and informs the serving base station that it will hand over to the final target base station. And a serving base station that requests handover of the mobile subscriber station and is informed of the final target base station information determined to handover from the mobile subscriber station accordingly.
A third system of the present invention for achieving the above objects; In a mobile communication system performing a handover, there is a mobile subscriber station and a serving base station, and the mobile subscriber station requests a handover to a serving base station and indicates a resource holding type indicating whether to hold preset connection information from the serving base station. Receiving a handover response message including a field and recognizing whether the serving base station maintains connection information corresponding to a value of a resource retention type field, and the serving base station receives a handover request message from the mobile subscriber station. Receive a handover response message including a resource maintenance type field indicating whether to maintain connection information of the mobile subscriber station, receive a handover instruction message from the mobile subscriber station, and Resource Retention Type Characterized in that in correspondence to the value of the de-holding connection information.
A fourth system of the present invention for achieving the above objects; In a mobile communication system performing a handover, a mobile subscriber station and a serving base station exist, and the mobile subscriber station includes a resource maintenance type field indicating whether the serving base station maintains connection information from the serving base station. Receiving a handover request message and recognizing whether the serving base station maintains connection information corresponding to the value of the resource maintenance type field, and the serving base station maintains connection information of the mobile subscriber station to the mobile subscriber station; Transmitting a handover request message including a resource maintenance type field indicating whether a message is generated, receiving a handover indication message from the mobile subscriber station, and maintaining connection information according to a value of the resource maintenance type field; do.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that in the following description, only parts necessary for understanding the operation according to the present invention will be described, and descriptions of other parts will be omitted so as not to distract from the gist of the present invention.

The present invention relates to a target BS to which a mobile subscriber station (MSS) is to be handed over in a mobile communication system, in particular, an IEEE 802.16e communication system. This paper proposes a method for minimizing service delay by recognizing that a pingpong effect occurs during a base station) and a handover operation. That is, the present invention is to prevent the ping-pong phenomenon by recognizing the ping-pong phenomenon when the MSS cancels the handover to the target base station and switching to the serving base station while the MSS performs the handover operation with the target base station; Suggest. In addition, the serving base station maintains the connection information of the MSS according to the channel state and proposes a method for the MSS to quickly perform the connection setup according to the handover. Here, the IEEE 802.16e communication system includes orthogonal frequency division multiplexing (OFDM) and orthogonal frequency division multiple access (OFDMA). It is a broadband wireless access communication system using the method). Since the IEEE 802.16e communication system uses an OFDM / OFDMA scheme, high-speed data transmission is possible by transmitting a physical channel signal using a plurality of sub-carriers, and supports a multi-cell structure. Is a communication system that supports the mobility of MSS.

5 is a flowchart illustrating a schematic operation of an MSS when a ping pong phenomenon occurs due to handover in an IEEE 802.16e communication system according to an embodiment of the present invention.

Referring to FIG. 5, first, in step 502, the MSS requests a MSS handover request to a base station providing a service to the MSS, that is, a serving base station (MOB_MSSHO-REQ: MOB_MSSHO-REQ). A base station handover response (MOB_BSHO-RSP: Base Station HandOver ReSPonse, hereinafter 'MOB_BSHO-RSP') message, or a base station handover request from the serving base station MOB_BSHO-REQ: Receives Base Station HandOver REQuest (hereinafter referred to as MOB_BSHP-REQ) message, and responds to MSS Handover Response (MOB_MSSHO-RSP: Mobile Subscriber Station HandOver ReSPonse, hereinafter called MOB_MSSHO-RSP). In step 504, a message exchange procedure related to a series of handover requests and responses for transmitting a message is performed.
In step 504, the MSS recognizes handoverable final target base station candidate list information included in a series of handover request or response messages transmitted and received with the serving base station, and proceeds to step 506. In step 506, the MSS measures Carrier to Interference and Noise Ratio (CINR) for each of the handover final target base station candidates, and proceeds to step 508. In step 508, the MSS determines a handover indication type (MOB_HO-IND_type: HandOver InDication type, hereinafter referred to as 'HO_IND_type') according to whether or not a ping-pong phenomenon occurs, and proceeds to step 510. In step 510, the MSS transmits a MOB_HO-IND message including the determined type information to the serving base station.

In FIG. 5, the operation of the MSS when the ping-pong phenomenon occurs due to handover in the IEEE 802.16e communication system according to an embodiment of the present invention has been described. Next, an embodiment of the present invention will be described with reference to FIG. 6. In the IEEE 802.16e communication system according to the operation of the MSS according to whether the ping-pong phenomenon occurs when the handover situation will be described.

6 is a flowchart illustrating an operation process of an MSS according to whether a ping-pong phenomenon occurs when a handover situation occurs in an IEEE 802.16e communication system according to an embodiment of the present invention.

Referring to FIG. 6, when the MSS detects the occurrence of a situation in which the MSS needs to be handed over in step 602, i = 0, which is a counter initial value for neighboring base stations, and a handover cancel indicator (HO_cancel_flag: HandOver cancel flag; Hereinafter, 'HO_cancel_flag' will be set to '0' and the flow proceeds to step 604. That is, the MSS performs an initialization procedure for measuring the CINR value for each neighboring base station belonging to the final target base station candidate list capable of handover. Here, the HO_cancel_flag is a flag for notifying that a neighbor base station except a serving base station among the neighbor base stations belonging to the final target base station candidate list capable of handover is not selected as the final target base station. In step 604, the MSS determines for each of the base stations belonging to the final target base station candidate list that satisfies a predetermined condition among neighboring base stations arranged in good order in consideration of quality of services (QoS) and CINR. Determine if all CINR values are measured. If there is a base station that does not measure the CINR value as a result of the determination, i.e., i <N_Neighbors, the process proceeds to step 606.
In step 606, the MSS sets a ping-pong threshold value (hereinafter, referred to as 'CINR_BS') of the base stations that are arranged above the aligned final target base station candidates (hereinafter, referred to as 'CINR_BS') (hereinafter, 'PP_THRESHOLD'). Is referred to as). Here, PP_THRESHOLD is a value larger than a handover threshold value (hereinafter, referred to as 'HO_THRESHOLD'), which is a threshold value for determining that the MSS should handover from a serving base station to which the MSS previously belongs to a base station other than the serving base station. This value is set to set the MSS to handover to a reliable target base station, that is, to remove unnecessary handover due to the ping-pong phenomenon.

If the CINR_BS value is less than the PP_THRESHOLD, the MSS proceeds to step 608. In step 608, the MSS deletes the neighboring base station from the final target base station candidate list since the CINR_BS is less than the PP_THRESHOLD. In step 610, the MSS increases the value of i by 1 and repeats the process from step 604 for the next base station in the list. If the CINR value of the neighboring base station is greater than the PP_THRHESHOLD value in step 606, that is, if CINR_BS> PP_THRESHOLD, the process proceeds to step 612. In step 612, the MSS determines whether the base station is an adjacent base station or a serving base station. As a result of the determination, if the base station is a serving base station, the MSS sets the HO_cancel_flag to '1' and proceeds to step 610 to perform a subsequent process. Otherwise, if the base station is an adjacent base station, the process proceeds to step 616. In step 616, the MSS determines whether the HO_cancel_flag set so far is '1'. As a result of the determination, if the HO_cancel_flag is not '1', the process proceeds to step 618 and, if the HO_cancel_flag is '1', the process proceeds to step 620. In step 618, the MSS determines that the base station is the last target base station to be handed over to the base station. In step 622, the MSS sends a MOB_HO-IND (type = '00 ') message to the current serving base station to inform the handover to the determined final target base station. In step 620, the MSS resets the HO_cancel_flag to '0', determines the base station as the final target base station, and proceeds to step 622.

On the other hand, if the MSS has not detected a base station exceeding the PP_THRESHOLD value as a result of measuring the CINR value for each of the base stations included in the final target candidate list including the serving base station in step 606, steps 604 through 624. Proceed to In step 624, the MSS determines whether HO_cancel_flag is currently set to '1'. If the determination result is set to '1', the flow proceeds to step 626. In step 626, the MSS informs the serving base station of the handover cancellation by transmitting a HO_IND message including '01', that is, handover cancellation (HO_cancel) information, in the HO_IND_type field. If it is not '1' in step 624, the MSS proceeds to step 628 and the MSS notifies the handover rejection by transmitting a HO_IND message including '01', that is, a handover rejection (HO_reject) information, to the serving base station. do.

Since the MSS sorts the neighbor base stations belonging to the handover target base station candidate list from the base station having the optimal handover condition, the MSS selects one of the other neighbor base stations except the serving base station as the final target base station through the ping-pong recognition procedure. If so, the selected target base station corresponds to a base station having a better condition than other neighbor base stations which have not yet performed a ping pong or not procedure, and thus transmits a MOB_HO-IND message including a HO-Release option to the serving base station. It may be determined that handover to the neighbor base station selected as the target base station is to be performed.

Next, the relationship between CINR values of respective base stations for recognizing a ping-pong phenomenon by the MSS in the IEEE 802.16e communication system according to an embodiment of the present invention will be described with reference to FIG. 7.

FIG. 7 illustrates a relationship between CINR values for recognizing a ping pong phenomenon by an MSS in an IEEE 802.16e communication system according to an embodiment of the present invention.

Referring to FIG. 7, when the MSS first examines CINRs and thresholds necessary for recognizing a ping-pong phenomenon, PP_THRESHOLD 700 indicates a CINR value threshold suitable for receiving a normal communication service after handover, and HO_THRESHOLD. 750 denotes a CINR value threshold preset in the MSS to select a target base station capable of handover. On the other hand, 710 represents a CINR value of the serving base station, 720 represents a CINR value of the neighbor base station 1, 730 represents a CINR value of the neighbor base station 2. That is, the ping-pong phenomenon may occur when the CINR value measured by the MSS for any base station is lower than the PP_THRESHOLD and higher than the HO_THRESHOLD.

Then, the relationship between the CINR values for each base station illustrated in FIG. 7 will be described. The CINR 710 of the serving base station measured by the MSS at 702 hours is smaller than the HO_THRESHOLD 750, and the CINR 720 of neighboring base station 1 and the CINR 730 of the neighboring base station 2 are the serving base station CINR 710. Since the neighbor base station 1 and the neighbor base station 2 can be selected as a target base station capable of handover. However, the neighbor base station 1 and the neighbor base station 2 are not selected as the final target base station because the value of each CINR is smaller than PP_THRESHOLD. If the MSS ignores the PP_THRESHOLD and re-measures the CINR of the neighbor BS 2 while performing the handover to the neighbor BS 2, the likelihood that the MSS may fall below HO_THRESHOLD is increased, and the MSS performs handover to another BS again. It means that the ping-pong phenomenon to be performed is generated.

Next, at 704, the MSS measures the serving base station CINR 710 value and the neighboring base station 1 CINR 720 value, and is measured to be larger than HO_THRESHOLD, and the neighboring base station 2 is measured to be smaller than HO_THRESHOLD. Can be. In 704, since there is no base station corresponding to the CINR value measured larger than PP_THRESHOLD, the final target base station does not exist.

Next, at 706, the MSS measured CINR values in the order of the CINR 720 value of neighboring base station 1, the serving base station CINR 710 value, and the size of the CINR 730 value of neighboring base station 2, all of which are larger than HO_THRESHOLD. It can be seen that. In this case, since there is no base station corresponding to the CINR value measured larger than PP_THRESHOLD as in step 704, the final target base station does not exist.

Next, at 708, the MSS is larger than PP_THRESHOLD as a result of measuring the CINR 720 value of neighboring base station 1, and is smaller than PP_THRESHOLD as a result of measuring CINR 730 and serving base station CINR 710 of the neighbor BS 2. You can see the greater than. Accordingly, the MSS may select the neighbor base station 1 as the final target base station to be handed over.

Next, with reference to FIG. 8, the operation of the MSS will be described when the ping-pong phenomenon occurs during the network re-entry procedure according to the handover in the IEEE 802.16e communication system according to the present invention.

8 is a flowchart illustrating an operation of an MSS when a ping-pong phenomenon occurs during the network re-entry procedure according to handover in the IEEE 802.16e communication system according to an embodiment of the present invention.

Referring to FIG. 8, first, in step 802, the MSS proceeds to step 804 while performing a network re-entry procedure with the final target base station through a series of procedures related to the handover of FIGS. 2 to 3. In step 804, the MSS measures the CINR value of the last target base station and proceeds to step 806. In step 806, the MSS compares the measured CINR value of the last target base station, that is, CINR_BS and PP_THRESHOLD. If the CINR_BS is greater than the PP_THRESHOLD as a result of the comparison, the network reentry procedure with the last target base station, which has been performed in step 802, is continuously performed. However, if the CINR_BS is smaller than the PP_THRESHOLD in step 806, the process proceeds to step 808. Since CINR_BS is smaller than PP_THRESHOLD in step 808, the MSS recognizes that a ping-pong phenomenon may occur and performs the corresponding procedure of FIG. 6.

Next, the relationship between CINR values for checking whether a ping-pong phenomenon occurs while performing the network re-entry procedure will be described with reference to FIG. 9.

FIG. 9 is a diagram illustrating a relationship between CINR values of base stations for recognizing a ping-pong phenomenon occurring during a network reentry procedure according to handover in an IEEE 802.16e communication system according to an embodiment of the present invention.

Referring to FIG. 9, first, the final target base station CINR 920 value measured by the MSS at 902 is greater than PP_THRESHOLD, and the serving base station CINR 910 value is smaller than HO_THRESHOLD. Thus, the MSS performs handover with the final target base station. In 904 to 906, the MSS measures the CINR 920 value of the last target base station, which is larger than PP_THRESHOLD, and the CINR 910 value of the serving base station is greater than HO_THRESHOLD. Thus, the MSS performs handover with the final target base station. In 908, when the MSS measures CINR values of the serving base station and the final target base station, both values are smaller than PP_THRESHOLD and larger than HO_THRESHOLD. Accordingly, the MSS recognizes that it is impossible to perform handover with the final target base station and perform a ping pong phenomenon that requires handover to another base station.

Next, in the IEEE 802.16e communication system according to an embodiment of the present invention, the MSS according to the resource connection information maintenance or deletion information included in the MOB_BSHO-REQ message or the MOB_BSHO-RSP message transmitted from the serving base station. The operation process to be performed will be described.

10 is a flowchart illustrating a process in which an MSS recognizes whether a serving base station maintains connection information in an IEEE 802.16e communication system according to an embodiment of the present invention.

Referring to FIG. 10, in step 1002, the MSS receives a MOB_BSHO-REQ or MOB_BSHO-RSP message from a serving base station and proceeds to step 1004. Here, as described in the prior art, the serving BS MOB_HO_IND message ( "HO_IND_Type = 00") is received and then, deletes the connection information with the MSS, or a handover procedure completion from the final target BS by the MSS transmits The connection information may be maintained for a predetermined time until notified. If the serving base station deletes the connection information with the MSS, when the MSS undergoes a ping-pong phenomenon during the network reentry procedure with the final target base station and switches to the serving base station, the information on the MSS Since it does not have the serving base station and the MSS is performed from the initial communication initial procedure. Therefore, if the MSS knows whether the serving base station has deleted the connection information for itself or maintains a predetermined time, it is possible to reduce the overhead due to the ping-pong phenomenon by performing a procedure for each case.

Therefore, in the present invention, whether the serving base station receiving the MOB_HO-IND ("HO_IND_type = 00") message from the MSS as described above deletes the connection information of the MSS or maintains the connection information for a predetermined time. The method of minimizing the delay that may occur in the reconnection establishment with the serving base station by informing the base station will be described with reference to Tables 16 and 17.

Tables 16 and 17 shown below are structures of modified handover messages proposed in the present invention. The modified handover messages maintain or delete resource connection information for the MSS in the MOB_BSHO-RSP and MOB_BSHO-REQ messages transmitted by the serving base station among the handover messages exchanged between the MSS and the serving base station during the existing handover procedure. The information about (Resource_Remain_Type, hereinafter referred to as 'Resource_Remain_Type') and resource retention time ('Resource_Retain_Time', hereinafter referred to as 'Resource_Retain_Time') is added.

As shown in Table 16, the MOB_BSHO-RSP message newly proposed by the present invention has a structure in which a Resource_Remain_Type field and a Resource_Retain_Time field are newly added to an existing MOB_BSHO-RSP message. The Resource_Remain_Type field provides information on whether the serving base station deletes or maintains connection information for the MSS. If the value of the Resource_Remain_Type field of Table 16 is '0', the serving base station will delete the connection information for the MSS. If the value of the Resource_Remain_Type field is '1', the serving base station will maintain the connection information for the MSS for the Resource_Retain_Time. . The information on the predetermined time is stored in a frame unit in the Resource_Retain_Time field. For example, is the MSS MSS is Resource_Remain_Type = 1, and has received the MOB_BSHO-RSP message is set to Resource_Retain_Time = 10, the serving BS MOB_HO-IND ( "HO_IND_type = 00 ") after ten frames after receiving the message, Maintain connection information without deleting it. If the MSS receives a MOB_BSHO-RSP message with Resource_Remain_Type = 1 and Resource_Retain_Time = 0, the MSS does not delete the connection information for the MSS during a pre-negotiated time during the registration procedure with the serving base station. Be aware that you will keep it. Although the unit of the Resource_Retain_Time field is specified as a frame unit, the frame unit may have the same meaning as the time unit. For example, one frame unit can be converted into a 20 ms time unit.

On the other hand, when the serving base station needs to change the connection information holding time of the MSS negotiated in advance during the registration procedure with the MSS, for example, the serving base station has insufficient buffer capacity, When it is difficult to maintain the connection information for the preset time or when the buffer status of the serving base station becomes better than when performing the previous registration procedure, the connection information of the MSS to be handed over can be maintained longer than the preset time. The Resource_Retain_Time value of the MOB_BSHO-RSP message or MOB_BSHO-REQ message may be set to any value other than zero.

Table 17 below shows the MOB_BSHO-REQ message structure newly proposed in the present invention.                     

As shown in Table 17, the MOB_BSHO-REQ message is the same as the MOB_BSHO-RSP message, the Resource_Remain_Type field indicating whether to delete or maintain the connection information in the existing MOB_BSHO-REQ message for a predetermined time It is a structure in which a Resource_Retain_Time field is added to indicate the predetermined time when maintaining. The serving base station sets the Resource_Retain_Time field value to '0' as the MOB_BSHO-RSP message, if the previously negotiated time is applied as it is during the registration procedure with the MSS, and the serving base station arbitrarily maintains the connection information. If you decide to set it to any value other than '0'.                     

On the other hand, when the serving base station maintains the connection information of the MSS that performed the handover, in addition to performing the handover due to the ping-pong phenomenon, the MSS performs the handover procedure with the serving base station when the MSS performs a drop situation. Can also be useful when discovering a drop recovery target target base station and performing a communication service with the drop recovery target target base station. That is, if the MSS knows that the serving base station maintains the connection information with the MSS, the MS notifies the drop recovery target target base station that the MSS can receive the MSS own connection information from the serving base station through the backbone network. By doing so, the drop recovery procedure can be performed quickly.

Therefore, in step 1004, the MSS proceeds to the next step according to whether the value recorded in the Resource_Remain_Type field included in the MOB_BSHO-REQ or MOB_BSHO-RSP message transmitted by the serving base station. If '0' is recorded in the Resource_Remain_Type field, the process proceeds to step 1006. In step 1006, the MSS recognizes that the serving base station deletes the connection information of the MSS. If '1' is recorded in the Resource_Remain_Type field in step 1004, the process proceeds to step 1008. In step 1008, the MSS checks whether '0' is recorded in the Resource_Retain_Time field included in the MOB_BSHO-REQ or MOB_BSHO-RSP message, and proceeds to step 1010 when '0' is recorded in the Resource_Retain_Time field. In step 1010, the MSS recognizes that the serving base station will maintain its connection information for a predetermined time while performing the registration procedure with the serving base station. On the other hand, in step 1008, if any value other than '0' is recorded in the Resource_Retain_Time field, the MSS proceeds to step 1012. In step 1012, the MSS recognizes that the serving base station will maintain its connection information for the time recorded in the Resource_Retain_Time field. Accordingly, when the serving base station hands over to the serving base station while communicating with another target base station while the serving base station maintains the connection information of the MSS, only the ranging procedure is performed during the network re-entry procedure. Communication can be resumed.

10 illustrates a process of recognizing whether the MSS maintains connection information with a serving base station in the IEEE 802.16e communication system according to an embodiment of the present invention. Next, referring to FIG. The handover operation of the MSS according to whether the serving base station maintains the connection information of the MSS in the IEEE 802.16e communication system will be described.

11 is a flowchart illustrating a handover operation of an MSS according to whether a serving base station maintains MSS connection information in an IEEE 802.16e communication system according to an embodiment of the present invention.

Referring to FIG. 11, in step 1102, the MSS proceeds to step 1104 while performing a network re-entry procedure with the final target base station. In step 1104, the MSS determines if the CINR value of the last target base station is smaller than PP_THRESHOLD, that is, a ping-pong phenomenon may occur. If it is determined that the ping-pong phenomenon does not occur, the process returns to step 1102 to continuously perform the network re-entry procedure, and if it is recognized that the ping-pong phenomenon will occur, proceeds to step 1106. In step 1106, the MSS determines to switch to a serving base station, that is, perform handover, and proceeds to step 1108. In step 1108, the MSS determines whether the serving base station maintains its connection information. Here, the MSS may determine whether to maintain the connection information based on information (Resource_Remain_Type) obtained through the MOB_BSHO-RSP message or the MOB_BSHO-REQ message received from the serving base station. If the serving base station maintains the connection information of the MSS as a result of the determination, step 1110 is performed. In step 1110, the MSS acquires synchronization with the serving base station and proceeds to step 1112. After completing the synchronization with the serving base station in step 1112, the MSS includes a basic connection identifier (Basic CID), which is used when communicating with the serving base station, in an RNG_REQ message for initial ranging. In step 1114, the controller transmits to the serving base station. In step 1114, the MSS receives an RNG_RSP message corresponding to the RNG_REQ message transmission from the serving base station and proceeds to step 1116. In step 1116, the MSS may resume communication with the serving base station by omitting procedures related to basic capacity negotiation, authentication, and registration using the connection information maintained by the serving base station.

On the other hand, if the serving base station deletes the connection information of the MSS in step 1108, it proceeds to step 1118. In step 1118, the MSS acquires synchronization with the serving base station and proceeds to step 1120. In step 1120, the MSS transmits an RNG-REQ message to a serving base station to perform an initial ranging procedure and proceeds to step 1122. Here, the RNG-REQ message transmitted by the MSS is set to CID = 0x0000 as in the general initial ranging procedure. In step 1122, the MSS receives an RNG_RSP message from the serving base station and proceeds to step 1124. In step 1124, the MSS performs an existing network reentry procedure, that is, basic capacity negotiation, authentication, and registration related procedures with the serving base station, and proceeds to step 1126. After completing the network re-entry procedure in step 1126, the MSS resumes communication with the serving base station.

Then, the encoding structure of the RNG_REQ message for the Basic CID included in the RNG-REQ message is shown in Table 18 below.

As shown in Table 18, the RNG_REQ message encoding for the Basic CID includes a Type indicating that the type of TLV (Type Length Value) set in the RNG_REQ message is a Basic CID, a Length indicating a length (2 bytes) of the Basic CID. And a Value indicating what the Basic CID means. The basic CID is basic CID information used when the MSS communicates with the serving base station. It should be noted that the value of the type field is a temporary value of 6 and may be modified in the future.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined not only by the scope of the following claims, but also by the equivalents of the claims.

As described above, in the IEEE 802.16e communication system, which is a broadband wireless access communication system using the OFDM / OFDMA scheme, the MSS may generate frequent handover between a serving base station and a plurality of target base stations, that is, a ping-pong phenomenon may occur. You can recognize the situation in advance. That is, PP_THRESHOLD is set to prevent handover to a base station having a CINR value lower than the PP_THRESHOLD. Accordingly, the MSS has an advantage of maximally preventing a situation in which the ping pong phenomenon may occur. In addition, by allowing the base stations to flexibly maintain or delete the connection information of the MSS in the channel state, when the base station performs a handover with the last target base station holding the connection information, by performing a network reentry procedure that performs only initial ranging. It has the advantage of being able to resume communication services quickly.

Claims (50)

A mobile communication system comprising a serving base station providing a service to a mobile subscriber station and a target base station adjacent to the serving base station, the method of recognizing whether the mobile subscriber station maintains connection information at the serving base station, Receiving a handover request message from the serving base station, the handover request message including a resource maintenance type field indicating whether to maintain connection information established with the serving base station; And recognizing that the serving base station maintains the connection information according to the value of the resource maintenance type field. The method of claim 1, Transmitting a handover indication message including information for reporting handover performance to the serving base station; And releasing the connection with the serving base station. The method of claim 1, And the handover request message notifies resource holding time information when the resource holding type field indicates the connection information holding. The method of claim 3, And the resource holding time information includes a resource holding time indicating a time duration value in a handover request message. The method of claim 3, And wherein the resource holding time information includes a system holding time indicating a pre-negotiation time at registration performed between a serving base station and a mobile station. The method of claim 1, Determining reentry to the serving base station during handover to the target base station; Recognizing whether the mobile subscriber station maintains the connection information at the serving base station, further comprising resuming communication with the serving base station using the connection information when the serving base station requires connection information. Way. In a mobile communication system comprising a serving base station providing a service to a mobile subscriber station and a target base station adjacent to the serving base station, the mobile subscriber station performs a handover method, Requesting handover to the serving base station; Receiving, from a serving base station, a handover response message including a resource maintenance type field indicating whether connection information is set to be held between the serving base station and the mobile subscriber station; And performing the handover of the mobile subscriber station according to the value of the resource maintenance type field. The method of claim 7, wherein Transmitting a handover indication message including information indicating that handover is to be performed to the serving base station; And disconnecting the connection from the serving base station. The method of claim 7, wherein If the handover response message is a resource retention type field indicating the maintenance of connection information, the mobile subscriber station performs handover. The method of claim 9, The resource holding time information includes a resource holding time field indicating a time interval value in a handover response message. The method of claim 9, And the resource holding time information is a holding time indicating a pre-negotiated time when the registration procedure is performed between the serving base station and the mobile subscriber station. The method of claim 7, wherein Determining network reentry to the serving base station while performing a handover to the target base station; And if the serving base station maintains the connection information, resuming communication with the serving base station by using the connection information. A mobile communication system comprising a mobile subscriber station, a serving base station providing a service to the mobile subscriber station, and a target base station adjacent to the serving base station, wherein the serving base station performs handover. Transmitting, to the mobile subscriber station, a handover request message including a resource maintenance type field indicating whether connection information established between a serving base station and the mobile subscriber station is maintained; Receiving a handover instruction message from the mobile subscriber station; And maintaining the connection information corresponding to the value of the resource maintenance type field by the serving base station performing the handover by the serving base station. The method of claim 13, When the value of the resource maintenance type field indicates to maintain connection information, the connection base station maintains the connection information from the time point at which the handover indication message received from the mobile subscriber station is received. . The method of claim 14, The handover indication message includes a handover indication type (HO_IND_Type = 00) indicating disconnection from the serving base station. The method of claim 13, And determining whether to maintain the connection information in response to the reception of the handover indication message. The method of claim 13, And wherein the handover request message notifies resource retention time information when the resource maintenance type field indicates maintenance of the connection information. The method of claim 17, The resource holding time information includes a resource holding time field indicating a time interval value in the handover request message. The method of claim 17, And the resource holding time information includes a system holding time indicating a time negotiated beforehand when performing a registration procedure between the serving base station and the mobile subscriber station. The method of claim 15, If the serving base station maintains connection information of the mobile subscriber station while the mobile subscriber station performs a network reentry procedure, resuming communication with the mobile subscriber station using the connection information. Characterized in that the serving base station performs a handover. The method of claim 15, And deleting the connection information of the mobile subscriber station when the resource maintenance type field indicates the non-connection information maintenance. In a mobile communication system having a mobile subscriber station, a serving base station providing a service to the mobile subscriber station, and a target base station adjacent to the serving base station, the method for performing handover by the serving base station, Receiving a handover request message from the mobile subscriber station; Transmitting a handover response message including a resource maintenance type field indicating whether the mobile subscriber station maintains connection information set in the mobile subscriber station; Receiving a handover instruction message from the mobile subscriber station; And maintaining the connection information corresponding to the value of the resource maintenance type field. The method of claim 22, If the value of the resource maintenance type field indicates to maintain the connection information, the handover is performed by the serving base station, wherein the connection information is maintained from the time point at which the handover instruction message received from the mobile subscriber station is received. Way. The method of claim 23, wherein The handover indication message includes a handover indication type (HO_IND_Type = 00) indicating disconnection from the serving base station. The method of claim 23, wherein And determining whether to maintain the connection information in response to the reception of the handover indication message. The method of claim 22, And when the resource retention type field indicates maintenance of the connection information, notifying the resource retention time information using a handover response message. The method of claim 26, The resource holding time information includes a resource holding type field indicating a time interval value in a handover request message. The method of claim 26, The resource holding time information includes a system holding time indicating a time negotiated beforehand when performing a registration procedure between the serving base station and the mobile subscriber station. The method of claim 22, If the serving base station maintains connection information of the mobile subscriber station while the mobile subscriber station performs a network reentry procedure, resuming communication with the mobile subscriber station using the connection information. Handover method performed by the serving base station characterized in that. In a mobile communication system having a mobile subscriber station, a serving base station with which the mobile subscriber station communicates, and a plurality of neighbor base stations different from the serving base station, the handover method comprising: Requesting a handover to the serving base station when the serving base station detects that the handover should be handed over to a final target base station, which is one of the adjacent base stations; Detecting information on at least two candidate target base stations selectable as the final target base station received from the serving base station in response to the handover request; Measuring Carrier to Interference and Noise Ratio (CINR) of the reference signal transmitted from each of the candidate target base stations; Comparing the measured CINR values with a predetermined first threshold value, and transmitting a reference signal having a CINR value less than the first threshold value when a CINR value less than the first threshold value exists as a result of the comparison. 1) removing the candidate target base station from the candidate target base stations, And determining the final target base station among the candidate target base stations except for the first candidate target base station, and notifying the serving base station that the terminal is to be handed over to the final target base station. The method of claim 30, The detecting of the need to handover to the final target base station is to detect by handover to the final target base station when the CINR of the reference signal transmitted from the serving base station is less than a preset second threshold value. And the value is set to a value exceeding the second threshold. The method of claim 30, The determining of the final target base station may include determining, as the final target base station, a candidate target base station providing a service level or bandwidth required for the communication among candidate target base stations except for the first candidate target base station. The handover method. The method of claim 30, And notifying the serving base station not to perform the handover when all of the measured CINR values are less than the first threshold as a result of the comparison. The method of claim 30, Switching from the serving base station to the final target base station after notifying that the mobile station will be handed over to the final target base station; Performing network reentry with the last target base station after switching to the last target base station; And performing connection switching from the final target base station to the serving base station when the CINR value of the reference signal transmitted from the final target base station becomes less than the first threshold value during the network reentry operation. The handover method. In a mobile communication system having a mobile subscriber station, a serving base station through which the mobile subscriber station communicates, and a plurality of adjacent base stations, a handover method for minimizing service delay due to a ping-pong phenomenon, Receiving and detecting, from the serving base station, a handover request including information on at least two candidate target base stations that can be selected as a final target base station which is any neighbor among the neighbor base stations by the serving base station; Measuring carrier to interference noise ratios (CINRs) of a reference signal transmitted from each of the candidate target base stations; A first threshold value that compares the measured CINR values with a predetermined first threshold value and transmits a reference signal having a CINR value less than the first threshold value when a CINR value less than the first threshold value exists as a result of the comparison; Excluding a candidate target base station from the candidate target base stations; And determining the final target base station among the candidate target base stations except for the first candidate target base station, and notifying the serving base station that the handover is to be handed over to the final target base station. Handover method with minimal delay. 36. The method of claim 35 wherein The determining of the final target base station may include determining, as the final target base station, a candidate target base station providing a service level or bandwidth required for the communication among candidate target base stations except for the first candidate target base station. Handover method for minimizing service delay caused by the ping-pong phenomenon. 36. The method of claim 35 wherein The method may further include notifying the serving base station not to perform the handover when all of the measured CINR values are less than the first threshold value. Handover method. 36. The method of claim 35 wherein Switching from the serving base station to the final target base station after notifying that the mobile station will be handed over to the final target base station; Performing network reentry with the last target base station after switching to the last target base station; And performing connection switching from the final target base station to the serving base station when the CINR value of the reference signal transmitted from the final target base station becomes less than the first threshold value during the network reentry operation. Handover method for minimizing the service delay caused by the ping-pong phenomenon. In a mobile communication system having a mobile subscriber station, a serving base station through which the mobile subscriber station communicates, and a plurality of adjacent base stations, a handover method for minimizing service delay due to a ping-pong phenomenon, The serving base station deletes or retains the connection information of the mobile subscriber station for a preset time when the mobile subscriber station is informed that the mobile subscriber station is going to hand over to a target base station which is a particular neighbor among the neighbor base stations. Determining, by the mobile subscriber station, to switch to the serving base station if it recognizes that a ping-pong phenomenon occurs during the network reentry procedure with the target base station; Receiving a handover request or handover response message from the serving base station; Detecting whether or not to maintain connection information for the mobile subscriber station included in each of the messages corresponding to each message reception; Minimizing service delay due to the ping-pong phenomenon, when the serving base station maintains connection information for the mobile subscriber station, resuming communication with the serving base station by performing only an initial ranging procedure. Handover method. The method of claim 39, Resuming communication by the mobile subscriber station performing only initial ranging with the serving base station; Acquiring synchronization with the serving base station; Transmitting a ranging request message corresponding to an initial ranging procedure including a basic connection identifier used when communicating with the first base station, and receiving a ranging response message thereto; And resuming communication by using the connection information of the mobile subscriber station maintained by the serving base station. The method of claim 39, When the serving base station deletes the connection information of the mobile subscriber station, performing the existing network re-entry procedure to resume communication with the serving base station, minimizing service delay due to the ping-pong phenomenon. Handover method. The method of claim 39, If the mobile subscriber station recognizes that the serving base station maintains the connection information for itself, minimizing the service delay according to the ping-pong phenomenon, characterized in that it further comprises the step of detecting the preset connection information holding time information. Handover method. The method of claim 42, wherein And the serving base station recognizes that the connection information for the mobile subscriber station is maintained by the serving base station according to the connection information holding time information. In a mobile communication system having a mobile subscriber station, a serving base station through which the mobile subscriber station communicates, and a plurality of adjacent base stations, a handover system for minimizing service delay due to a ping-pong phenomenon, If the serving base station detects that the handover should be handed over to a final target base station which is any of the neighbor base stations, the handover is requested to the serving base station, and the final received from the serving base station in response to the handover request. Detects information on at least two candidate target base stations that can be selected as a target base station, measures carrier-to-interference noise ratios (CINRs) of reference signals transmitted by each of the candidate target base stations, and measures the measured CINR values in advance. The candidate candidate base station for comparing the first threshold value set and transmitting a reference signal having a CINR value less than the first threshold value when the comparison result indicates that the CINR value is less than the first threshold value; Excluded from target base stations, and among candidate target base stations except for the first candidate target base station. To determine the final target BS, and the serving base station and the mobile subscriber station to notify that the handover to the final target BS, Receives a handover request of the mobile subscriber station, correspondingly transmits information on at least two candidate target base stations that the mobile subscriber station can select as the final target base station, and transmits from the mobile subscriber station to the final target base station. And a serving base station that is notified that the handover is to be performed. The method of claim 44, In detecting that the mobile subscriber station should handover to the final target base station, when the CINR of the reference signal transmitted from the serving base station is less than a preset second threshold value, the mobile subscriber station detects handover to the final target base station. The first threshold value is set to a value exceeding the second threshold value, the handover system to minimize the service delay according to the ping-pong phenomenon. The method of claim 44, In determining, by the mobile subscriber station, the final target base station, a candidate target base station providing a service level or bandwidth required for the communication among the candidate target base stations except for the first candidate target base station is determined as the final target base station. Handover system to minimize the service delay according to the ping-pong phenomenon, characterized in that. The method of claim 44, And if the measured CINR values are less than the first threshold value, notifying the serving base station not to perform the handover, wherein the service delay according to the ping-pong phenomenon is minimized. In a mobile communication system having a mobile subscriber station, a serving base station through which the mobile subscriber station communicates, and a plurality of adjacent base stations, a handover system for minimizing service delay due to a ping-pong phenomenon, Receives and detects a handover request from the serving base station, wherein the serving base station includes information on at least two candidate target base stations that can be selected as a final target base station which is any neighbor among the neighbor base stations, and the candidate target base station. Measuring the carrier-to-interference noise ratios (CINRs) of the reference signals transmitted by each of the signals, comparing the measured CINR values with a predetermined first threshold value, and wherein the comparison results in a CINR value less than the first threshold value. In the case of the candidate target base stations except for the first candidate target base station for transmitting a reference signal having a CINR value less than the first threshold value from the candidate target base stations, the last target base station among the candidate target base stations except for the first candidate target base station Determine and inform the serving base station that it will hand over to the final target base station. And East subscriber station, And a serving base station requesting a handover of the mobile subscriber station and correspondingly informed of final target base station information determined to be handed over from the mobile subscriber station according to the present invention. Handover system. In a mobile communication system performing a handover, A mobile subscriber station, There is a serving base station, The mobile subscriber station requests a handover to a serving base station, receives a handover response message including a resource maintenance type field indicating whether to hold preset connection information from the serving base station, and the serving base station receives a resource maintenance type field. Whether or not to maintain the connection information corresponding to the value of, The serving base station receives a handover request message from the mobile subscriber station, transmits a handover response message including a resource maintenance type field indicating whether to maintain connection information of the mobile subscriber station to the mobile subscriber station, Receiving a handover indication message from the mobile subscriber station and retaining connection information corresponding to the value of the resource maintenance type field. In a mobile communication system performing a handover, A mobile subscriber station, There is a serving base station, The mobile subscriber station receives a handover request message including a resource maintenance type field indicating whether the serving base station maintains connection information from the serving base station, and the serving base station corresponding to the value of the resource maintenance type field. Whether or not to maintain this connection information, The serving base station transmits a handover request message including a resource maintenance type field indicating whether the mobile subscriber station maintains connection information of the mobile subscriber station, receives a handover instruction message from the mobile subscriber station. And maintaining the connection information corresponding to the value of the resource maintenance type field.

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