US20040082329A1 - Control device, handover control method and mobile communication system - Google Patents

Control device, handover control method and mobile communication system Download PDF

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Publication number
US20040082329A1
US20040082329A1 US10/690,524 US69052403A US2004082329A1 US 20040082329 A1 US20040082329 A1 US 20040082329A1 US 69052403 A US69052403 A US 69052403A US 2004082329 A1 US2004082329 A1 US 2004082329A1
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Prior art keywords
access interface
core network
access
information
control device
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US10/690,524
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English (en)
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Toshihiro Suzuki
Hiroshi Kawakami
Akihito Okura
Masami Yabusaki
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NTT Docomo Inc
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NTT Docomo Inc
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Assigned to NTT DOCOMO, INC. reassignment NTT DOCOMO, INC. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: KAWAKAMI, HIROSHI, OKURA, AKIHITO, SUZUKI, TOSHIHIRO, YABUSAKI, MASAMI
Publication of US20040082329A1 publication Critical patent/US20040082329A1/en
Priority to US11/858,677 priority Critical patent/US7684801B2/en
Abandoned legal-status Critical Current

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/24—Reselection being triggered by specific parameters
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L47/00—Traffic control in data switching networks
    • H04L47/10—Flow control; Congestion control
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/24—Reselection being triggered by specific parameters
    • H04W36/32—Reselection being triggered by specific parameters by location or mobility data, e.g. speed data
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/24—Reselection being triggered by specific parameters
    • H04W36/32—Reselection being triggered by specific parameters by location or mobility data, e.g. speed data
    • H04W36/326—Reselection being triggered by specific parameters by location or mobility data, e.g. speed data by proximity to another entity
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W84/00—Network topologies
    • H04W84/005—Moving wireless networks

Definitions

  • the present invention relates to control device, handover control method and mobile communication system, and more particularly, to handover control method by a mobile communication system constituted comprising a mobile host, or a moving network comprising a plurality of mobile hosts; a plurality of mutually connectable access interfaces each constituting an interface for the connection to a core network at the mobile host or moving network; and a control device for controlling a handover relating to the connection to the core network at the access interfaces, as well as to the mobile communication system and a control device that constitutes the mobile communication system.
  • the technology relating to a conventional multihoming moving network and host mainly involves addressing, routing, and so forth. More specifically, a routing protocol according to which it is verified whether or not a plurality of addresses have been assigned according to multihoming, and, if a plurality of addresses have been assigned, even when a certain interface is disconnected, the data destined for the address assigned to the interface can be transmitted to the mobile host and network, has been proposed.
  • the principal object of multihoming is load sharing and fault tolerant (for example, “Requirements for IPv6 Site-Multihoming Architectures” (see http://www.ietf.org/internet-drafts/draft-ietf-multi6-m ultihoming-requirements-07.txt)).
  • a mobile host and moving network that are multi-homed by means of a plurality of access interfaces exhibit the characteristic that the communication quality of a line connected to each access interface varies according to movement.
  • the present invention was conceived in view of resolving the above problems, an object thereof being to provide control device, handover control method, and mobile communication system, which use the merits of multihoming, and make it possible to avoid packet loss and implement a seamless handover by minimizing the handover latency when a handover is implemented by a moving network and host.
  • the control device is a control device, which constitutes a mobile communication system together with a mobile host, or a moving network comprising a plurality of mobile hosts, and a plurality of mutually connectable access interfaces each constituting an interface for the connection to a core network at the mobile host or moving network, and which serves to control a handover relating to the connection to the core network at the access interfaces, comprising: connection status acquiring means for acquiring information on the connection status to the core network at each access interface, from each access interface; handover predicting means for predicting a subsequent handover on the basis of the information on the connection status to the core network at each access interface; and changing means for dynamically changing the access interface adopted as the connection interface in accordance with predetermined logic when a predetermined condition is satisfied on the basis of the information on the connection status to the core network at each access interface or the prediction information for a subsequent handover.
  • the handover control method is a handover control method of a mobile communication system that is constituted comprising a mobile host, or a moving network comprising a plurality of mobile hosts; a plurality of mutually connectable access interfaces each constituting an interface for the connection to a core network at the mobile host or moving network; and a control device for controlling a handover relating to the connection to the core network at the access interfaces, wherein the control device dynamically changes the access interface adopted as the connection interface in accordance with predetermined logic when a predetermined condition is satisfied on the basis of the connection status to the core network at each access interface or the prediction information for a subsequent handover.
  • the mobile communication system is a mobile communication system that is constituted comprising a mobile host, or a moving network comprising a plurality of mobile hosts; a plurality of mutually connectable access interfaces each constituting an interface for the connection to a core network at the mobile host or moving network; and a control device for controlling a handover relating to the connection to the core network at the access interfaces, wherein the control device comprises: connection status acquiring means for acquiring information on the connection status to the core network at each access interface, from each access interface; handover predicting means for predicting a subsequent handover on the basis of the information on the connection status to the core network at each access interface; and changing means for dynamically changing the access interface adopted as the connection interface in accordance with predetermined logic when a predetermined condition is satisfied on the basis of the information on the connection status to the core network at each access interface or the prediction information for a subsequent handover.
  • changing means of the control device should continue the transmission and receipt of data with respect to an appropriate access interface capable of maintaining a predetermined communication quality, and maintain the connection to the core network with respect to an access interface other than the appropriate access interface while causing the access interface to enter a closed state in which the transmission and receipt of data is disabled.
  • the access interface change processing is switched locally without propagation to the entire network or informing the origin of the transmission as per an ordinary handover procedure, and hence the switching time can be shortened.
  • An access interface other than the appropriate access interface is afforded a closed state in which the transmission and receipt of data is disabled without disconnecting the connection to the core network.
  • changing means of the control device upon dynamically changing the access interface, continue the transmission and receipt of data, when a mobile host is -connected to the appropriate access interface which is capable of maintaining a predetermined communication quality and when the access interface connected to the mobile host is connected to the appropriate access interface.
  • changing means of the control device desirably continue communications by establishing a connection between the mobile host and the appropriate access interface or a connection between the access interface connected to the mobile host and the appropriate access interface.
  • the transmission and receipt of data in which a predetermined communication quality is maintained can be implemented by continuing the transmission and receipt of data via the appropriate access interface.
  • the transmission and receipt of data in which a predetermined communication quality is maintained can be implemented by continuing transmission by establishing a connection between the mobile host and the appropriate access interface or a connection between the access interface connected to the mobile host and the appropriate access interface, when the mobile host is not connected to the appropriate access interface and the access interface connected to the mobile host is not connected to the appropriate access interface.
  • control device desirably further comprises downlink control means that perform control so that downlink data from the core network is transmitted via an access router that is connected to the appropriate access interface, among the access routers in the core network. Therefore, the transmission and receipt of data in which a predetermined communication quality is maintained, can be implemented by performing controlling so that downlink data from the core network is also transmitted and received via the appropriate access interface.
  • a condition according to which a predicted value for the field strength between the access interface and the core network which is predicted on the basis of subsequent movement prediction should be less than a predetermined threshold value can also be adopted as the predetermined condition.
  • a logic that involves selecting an access interface that corresponds with a maximum-value field strength from among the field strengths between each access interface and the core network can be adopted as the predetermined logic used when the access interface is dynamically changed by the control device.
  • a logic that involves selecting an access interface that corresponds with a predicted value for the maximum-value field strength from among predicted values for the field strengths between each access interface and the core network, which are predicted on the basis of subsequent movement prediction can be adopted as the above predetermined logic.
  • the control device is characterized in that the connection status acquiring means are constituted comprising: locational relationship tracking means for tracking the locational relationship of all the access interfaces connected to the mobile hosts and the moving network; and information receiving means for receiving information on the connection status between each access interface and the core network, and switching information that includes identification information for identifying the previous access router and the destination access router at the time switching occurs, as well as switching end time information, the information being reported by each access interface; and wherein the handover predicting means are constituted comprising: velocity tracking means for tracking at least velocity information pertaining to the mobile hosts and the moving network in accordance with a predetermined tracking logic, on the basis of the locational relationship of each access interface thus tracked and the connection status information and switching information thus received; and predicting means for predicting subsequent movement and changes in the field strength based on the tracked information.
  • the connection status acquiring means are constituted comprising: locational relationship tracking means for tracking the locational relationship of all the access interfaces connected to the mobile hosts and the moving network; and information receiving means for receiving information on the connection status between
  • the handover control method is characterized in that the control device tracks the locational relationship of all the access interfaces connected to the mobile hosts and the moving network; the control device receives information on the connection status between each access interface and the core network, and switching information that includes identification information for identifying the previous access router and the destination access router at the switching time, as well as switching end time information, this information being reported by each access interface; the control device tracks at least velocity information pertaining to the mobile hosts and moving network in accordance with a predetermined tracking logic; and the control device predicts subsequent movement and changes in the field strength, on the basis of the tracked information.
  • At least velocity information pertaining to the mobile host and moving network is tracked in accordance with a predetermined tracking logic, on the basis of the locational relationship of each access interface thus tracked and of the reported information on the connection status between each access interface and the core network, and switching information that includes identification information for identifying the previous access router and the destination access router at the time switching occurs, as well as switching end time information, and subsequent movement and changes in the field strength are predicted based on the tracked information. For this reason, handover prediction information of favorable accuracy can be obtained, and it is possible to implement a, seamless handover more reliably.
  • velocity tracking means of the control device desirably tracks a value obtained by dividing the distance x by the switching time difference t, as the velocity pertaining to the mobile host and moving network, based on a switching time difference t and a distance x between the access interfaces for the adjacent switchings. In this case, the velocity of the mobile host and moving network can be tracked with favorable accuracy.
  • velocity tracking means of the control device desirably tracks, based on a plurality of combinations of the switching time difference t and the distance x between the access interfaces for the adjacent switchings, a direction which links the two access interfaces and where the first-switched access interface lies foremost as the direction of movement, and a value obtained by dividing the distance x by the switching time difference t as the velocity, with respect to each combination; and finds the vector sum of the velocity vectors for each combination and tracks the direction of movement and velocity of the mobile host and moving network by means of the vector sum thus obtained.
  • the direction of movement and velocity pertaining to the mobile host and moving network can be tracked with favorable accuracy.
  • FIG. 1 is a constitutional view of the mobile communication system of the first embodiment.
  • FIG. 2 is a function block constitutional view of the MMF of the first embodiment.
  • FIG. 3A is a pre-handover state diagram which serves to illustrate the logic of a seamless handover using multihoming, of a multihoming moving network.
  • FIG. 3B is a state diagram of the state at the start of a handover which serves to illustrate the logic of a seamless handover using multihoming, of the multihoming moving network.
  • FIG. 3C is a state diagram after handover completion which serves to illustrate the logic of a seamless handover using multihoming, of the multihoming moving network.
  • FIG. 4A shows the state before the MMF issues a switching instruction in the mode in which the MH is not aware of switching.
  • FIG. 4B shows the state after the MMF issues a switching instruction in the mode in which the MH is not aware of switching.
  • FIG. 5 is a flowchart showing the MMF control operation of the example in FIGS. 4A and 4B.
  • FIG. 6A shows the state before the MMF issues a switching instruction in the mode in which the MH is aware of switching.
  • FIG. 6B shows the state after the MMF issues a switching instruction in the mode in which the MH is aware of switching.
  • FIG. 7 is a flowchart showing the MMF control operation of the example in FIGS. 6A and 6B.
  • FIG. 8 shows the initial state of the mobile communication system of the second embodiment.
  • FIG. 9 is a function block constitutional view of the MMF of the second embodiment.
  • FIG. 10 is a flowchart showing the velocity tracking processing on the basis of information based on a single AI combination.
  • FIG. 11 shows the state immediately after the NAI is switched to the new AR.
  • FIG. 12 shows the state immediately after the OAI is switched to the new AR.
  • FIG. 13 is a diagram which serves to illustrate the processing in which a vector sum is calculated.
  • FIG. 14 is a flowchart showing the velocity and the direction of movement tracking processing on the basis of information based on a plurality of AI combinations.
  • FIG. 1 is a constitutional view of a mobile communication system of a first embodiment.
  • a mobile communication system 1 is constituted by a core network 10 , which is constituted comprising a plurality of access routers (referred to as “AR” hereinafter) 11 , 12 ; and a moving network (referred to as “MN” hereinafter) 20 , which is constituted comprising a plurality of access interfaces (referred to as “AI” hereinafter) 21 , 22 , a plurality of mobile hosts (referred to as “MH” hereinafter) 31 , 32 , and a control device (referred to as “MMF” hereinafter) 50 , that is provided with a function for governing mobile management and switching instructions (MMF: Mobility Management Function).
  • MMF mobility Management Function
  • the MH 31 is connected to an AR (AR 11 in the example in FIG. 1) on the side of the core network 10 via either line 41 of the AI 21 or line 42 of the AI 22 (line 41 in the example in FIG. 1), and thus transmits and receives data.
  • AR AR 11 in the example in FIG. 1
  • line 41 of the AI 21 or line 42 of the AI 22 line 41 in the example in FIG. 1
  • the MN 20 moves from left to right in FIG. 1.
  • the AI 22 which lies foremost in the direction of movement is called an NAI (New Access Interface)
  • the AI 21 that lies rearward in the direction of, movement is called an OAI (Old Access Interface).
  • FIG. 2 is a function block constitutional view of the MMF 50 of the first embodiment.
  • the MMF 50 is constituted comprising a connection status acquisition section 51 , which acquires information from each AI on the connection status of each AI to the core network 10 ; a handover prediction section 52 , which predicts a subsequent handover on the basis of the connection status information for each AI thus acquired; a change section 53 for dynamically changing the AI adopted as the connection interface in accordance with predetermined logic when a predetermined condition is satisfied on the basis of the connection status information for each AI or prediction information on a subsequent handover; and a downlink control unit 54 that performs control so that an MH is allowed to transmit downlink data from the core network 10 via an AR, of the AR 11 , 12 on the side of the core network 10 , which is connected to an AI (referred to as “FAI” (Fine AI) hereinafter) that is capable of maintaining a predetermined communication quality.
  • FAI human AI
  • FIGS. 3 A- 3 C show the logic for a handover using multihoming, of the MN 20 has the multihoming function.
  • the two AI 21 , 22 are connected to the same AR 11 , and data packets are transmitted and received between the MN 20 and the core network 10 via the lines 41 , 42 of the AI 21 , 22 respectively.
  • the NAI 22 which is frontward in the direction of movement, transitionally enters a mode in which same is connected to the new AR 12 , as shown in FIG. 3B.
  • the line 41 on the side of the OAI 21 is disconnected in keeping with movement.
  • the MMF 50 implements close processing (that is, processing to disable the transmission and receipt of data although the line 41 is not disconnected) so that all the transmission data P 1 and P 2 is transmitted by using the line 42 to which the NAI 22 is connected. Further, after the handover has ended, the line 41 on the side of the OAI 21 can then be connected to the new AR 12 as shown in FIG. 3C, and hence a data transfer using two lines as per the initial state in FIG. 3A is feasible.
  • Switching processing is thus switched locally without propagation to the entire network or informing the origin of the transmission as per an ordinary handover procedure. Hence, packet loss and a handover latency caused by a disconnection of the line on the side of the OAI and by performing non-local switching processing can be avoided, whereby a seamless handover can be implemented.
  • FIGS. 4A and 4B are state transition diagrams for the mode in which the MH is not aware of switching
  • FIG. 5 is a flowchart showing the MMF control operation for the example of FIGS. 4A and 4B.
  • each AI 21 , 22 reports the connection status to the core network 10 , to the MMF 50 at fixed intervals.
  • the MMF 50 receives information on the connection status between each AI and the core network 10 from each AI (S 01 ), and, on the basis of this connection status information, judges whether the line quality of one AI is poor or not in light of a predetermined condition (S 02 ).
  • the predetermined condition may be that the field strength between the AI and core network 10 should be less than a predetermined threshold value, and may be that a predicted value for the field strength between the AI and the core network 10 that is predicted on the basis of subsequent movement prediction should be less than a predetermined threshold value.
  • the OAI 21 which has thus received the switching instruction, causes the line 41 to enter a closed state so that data is not transmitted or received, without disconnecting the connection on the line 41 to the core network 10 , and establishes a connection to the NAI 22 . Further, also in the case of the core network 10 , which has thus received a switching instruction, the AR 11 connected to the OAI 21 causes the line 41 to enter a closed state so that data is not transmitted or received, while still maintaining the connection on the line 41 to the OAI 21 .
  • a portion of the data transmitted from the MN 20 to the core network 10 can be transmitted to the core network 10 via the side of the NAI 22 access line 42 by passing via the connecting link between the OAI 21 and the NAI 22 , without the MH 31 , 32 in the MN 20 being aware of this operation. That is, as shown in FIG. 4B, the transmission data P 1 transmitted by the MH 31 to the core network 10 is transmitted to the core network 10 via the side of the NAI 22 access line 42 together with the transmission data P 2 transmitted by the MH 32 to the core network 10 .
  • FIGS. 6A and 6B are the state transition diagrams of the mode in which the MH is aware of switching
  • FIG. 7 is a flowchart showing the MMF control operation of the example in FIGS. 6A and 6B.
  • each AI 21 , 22 reports the connection status to the core network 10 , to the MMF 50 periodically.
  • the MMF 50 receives information on the connection status between each AI and the core network 10 from each AI (S 11 ), and, on the basis of this connection status information, it is judged whether the line quality of one AI is poor or not in light of predetermined conditions (S 12 ).
  • the predetermined condition may be that the field strength between the AI and core network 10 should be less than a predetermined threshold value, and may be that a predicted value for the field strength between the AI and the core network 10 that is predicted on the basis of subsequent movement prediction should be less than a predetermined threshold value.
  • the OAI 21 which has thus received the switching instruction, causes the line 41 to enter a closed state so that data is not transmitted or received, without disconnecting the connection on the line 41 to the core network 10 . Further, also in the case of the core network 10 , which has thus received a switching instruction, the AR 11 connected to the OAI 21 causes the line 41 to enter a closed state so that data is not transmitted or received, while still maintaining the connection on the line 41 to the OAI 21 . In addition, the MH 31 establishes a connection to the NAI 22 instead of the OAI 21 .
  • the transmission data P 1 transmitted by the MH 31 to the core network 10 can be transmitted to the core network 10 via the side of the NAI 22 access line 42 by way of the connecting link between the MH 31 and the NAI 22 , as per FIG. 6B.
  • an AI corresponding with the maximum-value field strength may be selected from among the field strengths between each AI and the core network 10 , for example.
  • an AI that corresponds with the predicted value for the maximum-value field strength may be selected from among predicted values for the field strengths between each AI and the core network 10 Which are predicted on the basis of subsequent movement prediction.
  • FIG. 8 is a constitutional view of the initial state of a mobile communication system lS of the second embodiment.
  • a mobile communication system lS is constituted by the core network 10 , which is constituted comprising a plurality of AR 11 , 12 ; and the MN 20 , which is constituted comprising a plurality of AI 21 , 22 , the MH 31 , and a control device (MMF) 50 that is provided with a function for governing mobile management and switching instructions (MMF: Mobility Management Function).
  • MMF Mobility Management Function
  • the MN 20 moves from left to right in FIG. 8.
  • the AI 22 that lies foremost in the direction of movement is called an NAI (New Access Interface)
  • the AI 21 that lies rearward in the direction of movement is called an OAI (Old Access Interface).
  • the MN 20 is therefore a moving network in which the two AI 21 , 22 are multihomed.
  • FIG. 9 is a function block constitutional view of the MMF 50 of the second embodiment.
  • the connection status acquisition section 51 is constituted comprising a locational relationship tracking section 51 A that tracks the locational relationship of all the AI, an information receiver section 51 B that receives information on the connection status of each AI to the core network 10 , and switching information that includes identification information for, identifying the switching origin AR when switching occurs and the switching destination AR, as well as switching end time information, the information being reported by each AI.
  • the handover prediction section 52 is constituted comprising a velocity tracking section 52 A for tracking at least velocity information pertaining to the MN 20 in accordance with a tracking logic (described later), on the basis of the locational relationship of each AI thus tracked and the connection status information and switching information thus received, and a prediction section 52 B for predicting subsequent movement and changes in the field strength from the tracked information.
  • the velocity tracking section 52 A pre-stores information on the distance x between the two AI 21 , 22 , and, upon recognizing, on the basis of the switching information from each AI, that adjacent switching is with respect to the same AR, the velocity tracking section 52 A tracks, given a switching time difference t for the adjacent switching and a distance x between the two AI, a value obtained by dividing the distance x by the switching time difference t as the velocity pertaining to the MN 20 .
  • Velocity tracking processing which is based on switching information from a single AI combination (that is, the two AI 21 , 22 ) executed by the MMF, 50 , will be described hereinbelow on the basis of the flowchart of FIG. 10 and the state diagrams of FIGS. 8, 11, and 12 .
  • the mobile communication system is in the initial state of FIG. 8, and the AI 21 , 22 report the connection status to the core network 10 , to the MMF 50 periodically.
  • the MMF 50 receives information on the connection status between each AI and the core network 10 from each AI (S 21 ), and, on the basis of this connection status information, judges whether the line quality of one AI is poor or not in light of predetermined conditions (S 22 ).
  • the predetermined conditions may be that the field strength between the AI and core network 10 should be less than a predetermined threshold value, and may be that a predicted value for the field strength between the AI and the core network 10 predicted on the basis of subsequent movement prediction, should be less than a predetermined threshold value.
  • the NAI 22 and core network 10 which have thus received the switching instruction, switch the connection destination of the NAI 22 to the new AR 12 , and hence the AR 12 and NAI 22 are connected by the line 42 . Further, location information on the new AR 12 and information about the time (switching time) t1 when switching to the AR 12 has completed, are transmitted to the MMF 50 .
  • the MMF 50 receives the location information on the, new AR 12 and the information about the switching time t1 from the NAI 22 , and cumulatively stores them (S 24 ) Because, at this time, only one AI 22 is switched, S 25 yields a negative judgment, and processing returns to S 21 , whereupon the processing of step S 21 and subsequent steps are executed once again.
  • the MMF 50 transmits a switching instruction for the OAI 21 and the core network 10 to switch the connection destination of the OAI 21 from the current AR 11 to the new AR.
  • the OAI 21 and core network 10 which have thus received the switching instruction, switch the connection destination of the OAI 21 to the new AR 12 , and hence the AR 12 and OAI 21 are connected by the line 41 . Further, location information on the new AR 12 and information about the time (switching time) t2 when switching to the AR 12 has completed, is transmitted to the MMF 50 .
  • the MMF 50 receives the location information on the new AR 12 and the information about the switching time t2 from the OAI 21 , and cumulatively stores them (S 24 ) Because, at this time, the location information on the new AR and the information about the switching time have been received from both of the two AI, S 25 yields an affirmative judgment, and processing proceeds to S 26 .
  • the velocity tracking section 52 A recognizes that the switching between the two AI 22 , 21 is the switching between the same AR, by the fact that the location information on the new AR 12 of the NAI 22 corresponds to the location information on the new AR 12 of the OAI 21 .
  • the velocity tracking section 52 A obtains a value by dividing the pre-prepared distance x between the AI 21 , 22 by the switching time difference t (where t is equivalent to (t2-t1)) for the two switching events, and tracks the value as the velocity pertaining to the MN 20 .
  • the velocity tracking section 52 A is able to track the direction of movement in which the NAI 22 locates forward side and the OAI 21 locates backward side, as the direction of movement of the MN 20 .
  • the prediction section 52 B is able to predict the subsequent movement of the MN 20 and change in the field strength on the basis of the velocity and the direction of movement of the MN 20 .
  • MN velocity tracking was described in the above description on the basis of the switching information from one combination of AIs (that is, the two AI 21 , 22 ), the velocity and the direction of movement of the MN can be tracked as detailed below, on the basis of switching information from plural combinations of AIs (that is, three or more AI), by applying the above-described technology to practical use.
  • the processing of FIG. 14 is executed by the MMF 50 .
  • the velocity tracking section 52 A executes the above-described velocity tracking processing in FIG. 10, for each of a plurality of combinations of the AIs.
  • two velocity vectors v1, v2 are obtained as shown in FIG. 13 on the basis of the switching information from two combinations of AIs.
  • the direction of each velocity vector is equivalent to the tracked direction of movement
  • the size of each velocity vector is equivalent to a value for the tracked velocity.
  • the velocity tracking section 52 A calculates a vector sum in S 33 , and, in S 34 , tracks the direction of movement and the velocity of the MN on the basis of the vector obtained.
  • a synthesized vector V is obtained by calculating the vector sum of the two velocity vectors v1, v2, and the direction of movement of the MN can be tracked on the basis of the direction of the synthesized vector V, and the velocity of the MN can be tracked on the basis of the size of this synthesized vector V.
  • the prediction section 52 B is able to predict the subsequent movement and change in the field strength of the MN 20 on the basis of the velocity and direction of movement of the tracked MN 20 .
  • the velocity and direction of movement of the MN 20 can also be tracked on the basis of either the switching information from one combination of AIs (two AIs) or switching information from a plurality of combinations of AIs (three or more AIs), and the subsequent movement and change in the field strength is predicted on the basis of the tracked information. For this reason, handover prediction information of favorable accuracy can be obtained, and it is possible to implement a seamless handover more reliably.
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US7684801B2 (en) 2010-03-23
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