JP2007201942A - Hands-off control method and radio communication terminal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hands-off control method and a radio communication terminal by which frequencies for performing hands-off between a communication terminal (At) and a packet controller (PCF) are reduced even when the AT moves near a boundary of a control area of the PCF, etc. and a stable hands-off destination is constantly secured. <P>SOLUTION: The radio communication terminal is equipped with: a storage part which stores information about candidate base stations which are candidates of a base station at a hands-off destination; an operation part which calculates reference for performing the hands-off to second candidate base stations based on the number of first candidate base stations which are the candidates base stations included in a first subnet to which base stations under execution of communication belong and the number of second candidate base stations which are the candidates base stations included in a second subnet to which the most numbers of candidates base stations belong other than the first subnet and a hands-off control part which performs control so as to perform the hands-off to the first candidate base stations in preference to the second candidate base stations based on the reference. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a handoff control method and a wireless communication terminal in a mobile communication system.

  In mobile communication networks using code division multiple access (CDMA), 1xEV-DO (1x evolution-data only) that realizes high-speed data communication is provided.

  In the mobile communication network 2 having the configuration shown in FIG. 12, a radio communication terminal (AT: Access Terminal) responds to changes in the reception strength of a pilot signal (hereinafter referred to as pilot strength) and the like as a communication partner base station ( A handoff is performed to switch AN (Access Network).

  Such handoff includes handoff between base stations (AN) under the same packet control device (PCF) (handoff between ANs) and handoff between base stations (AN) under different packet control devices (PCF). (PCF handoff).

  Specifically, as shown in FIG. 12, the inter-AN handoff means that the wireless communication terminal (AT) 10a is changed from the base station (AN) 21a under the same packet control device (PCF) 30a to the base station (AN) 22a. To handoff. Also, the inter-PCF handoff means that the radio communication terminal (AT) 10b performs a handoff from the base station (AN) 23a under the packet control device (PCF) 30a to the base station (AN) 21b under the packet control device (PCF) 30b. It is to be.

  Next, the sequence of the handoff between ANs and the handoff between PCFs will be described with reference to FIGS. Hereinafter, it is assumed that the wireless communication terminal is AT, the base station is AN, and the packet control device is PCF.

  FIG. 13 is a sequence diagram when the AT 10a performs handoff between ANs from the AN 21a under the same PCF 30a to the AN 22a.

  In step S310, the AT 10a is executing communication with the AN 21a. At this time, the AT 10a holds a plurality of ActiveSet ANs. Here, the AN of the Active Set is an AN (for example, AN 22a or AN 23a in FIG. 12) under the control of the PCF 30a that connects the AT 10a and the wireless session, and the pilot strength and the like in the AT 10a satisfy a predetermined value. In addition, the AN of the ActiveSet has a connection with the AT 10a in advance, and reserves resources so that the AT 10a can handoff to the AN at any time.

  In step S320, the AT 10a transmits a RouteUpdate message to the AN 22a having the strongest pilot strength among the ANs of the ActiveSet.

  In step S330, the AN 22a transmits a TrafficChannelAssignment message to the AT 10a and allocates a traffic channel.

  In step S340, the AT 10a transmits a Reverse Pilot signal, which is an uplink pilot signal, to the AN 22a.

  In step S350, the AN 22a transmits an RTCAck message indicating that the Reverse Pilot signal has been received from the AT 10a to the AT 10a.

  In step S360, the AT 10a transmits a Traffic Channel Complete message indicating the establishment of the Traffic Channel to the AN 22a.

  In step S370, the AT 10a switches the DRC Cover signal transmitted to the AN 21a to the AN 22a.

  FIG. 14 is a sequence diagram when the AT 10b performs handoff between PCFs from the AN 23a under the PCF 30a to the AN 21b under the PCF 30b.

  In step S405, the AT 10b is executing communication with the AN 23a. At this time, the AT 10b connects a connection with the AN 23a, and connects a wireless session with the PCF 30a.

  In addition, the AT 10b acquires the AN information of the surrounding area at regular intervals from the broadcast information (SectorParameters message) notified from the AN 23a. The AT 10b decides to handoff to the AN 21b having the strongest pilot strength based on the acquired AN information.

  In step S410, the AT 10b transmits a Connection Close message to the AN 23a that is the PCF handoff source, and disconnects the connection with the AN 23a. Then, the AT 10b disconnects the wireless session with the PCF 30a.

  In step S420, the AT 10b transmits a UATIRequest message to the AN 21b that is the inter-PCF handoff destination.

  In step S430, the AN 21b transmits a UATISignature message, and is assigned a UATI (Unicast Access Terminal Identifier). Then, the AT 10b connects a wireless session with the PCF 30b.

  In steps S440 to S480, the AT 10b performs the same processing as the above-described inter-AN handoff step (steps S320 to S360 in FIG. 12) on the AN 21b.

  In step S490, the AT 10b starts transmitting a DRC Cover signal to the AN 21b.

The ActiveSet AN described above is effective only under the same PCF, and thus is released when the wireless session with the PCF 30a is disconnected. Therefore, immediately after the inter-PCF handoff, the AN of the ActiveSet is only the AN 21b.
3GPP2 C.S0024-A Version 1.0 cdma2000 High Rate Packet Data AirInterface Specification, March 2004 1.Overview 3GPP2 C.S0024-A Version 2.0 cdma2000 High Rate Packet Data AirInterface Specification, August 2005 8.7.6.1.2.3 Pilot Strength Measurement

  However, as described above, in the handoff between PCFs, it is necessary to switch the wireless session between the wireless communication terminal (AT) and the packet control device (PCF). The load becomes high.

  In addition, the inter-PCF handoff requires a more complicated handoff sequence than the inter-AN handoff. Therefore, an overhead occurs when the radio communication terminal (AT) performs handoff, and packet loss is likely to occur.

  Furthermore, immediately after the inter-PCF handoff, the ActiveSet AN is the only AN that is the inter-PCF handoff destination, so even if the communication state with the AN deteriorates, it is not possible to quickly handoff to another AN.

  Therefore, when the handoff between PCFs is frequently performed when the wireless communication terminal (AT) moves near the boundary of the control area of the packet control device (PCF), the mobile communication network network on the base station (AN) side. In some cases, the load on the network increases, packet loss occurs, and a stable handoff destination may not be secured.

  Therefore, the present invention has been made in view of such a situation, and even when the wireless communication terminal (AT) moves near the boundary of the control area of the packet control device (PCF), the inter-PCF handoff is performed. It is an object of the present invention to provide a handoff control method and a wireless communication terminal that can reduce the frequency of performing the communication and can always ensure a stable handoff destination.

  A first feature of the present invention is that a wireless communication terminal stores information of candidate base stations that are candidates for a handoff destination base station, and a base station that is executing communication with the wireless communication terminal belongs to The number of first candidate base stations that are the candidate base stations included in one subnet and the second candidate that is the candidate base station included in the second subnet to which the largest number of candidate base stations other than the first subnet belongs A calculation step in which the wireless communication terminal calculates a reference for handing off to the second candidate base station based on the number of base stations; and the wireless communication terminal determines the second candidate base station based on the reference The hand-off control method includes a hand-off control step of controlling to hand off to the first candidate base station with higher priority than the first candidate base station.

In the first aspect of the present invention, the base station has a plurality of sectors,
In the handoff control step, the wireless communication terminal may perform control so as to preferentially handoff to another sector of the first candidate base station having a sector that is performing communication.

In the first aspect of the present invention, the base station has a plurality of sectors,
In the handoff control step, the wireless communication terminal may perform control so as to preferentially handoff a sector having an identification number within a predetermined threshold range from an identification number of a sector that is performing communication.

  The second feature of the present invention is that a storage unit (Neighborlist storage unit 120) that stores information on a candidate base station that is a candidate for a handoff destination base station (e.g., Neighborlist), and a base station that is executing communication (e.g., AN 211) includes the number of first candidate base stations that are the candidate base stations included in a first subnet (eg, subnet S1), and a second subnet (to which the largest number of candidate base stations other than the first subnet belong). For example, a calculation unit (subnet ratio) that calculates a reference (for example, a subnet ratio) for handing off to the second candidate base station based on the number of second candidate base stations that are the candidate base stations included in the subnet S2) And the first candidate base in preference to the second candidate base station (for example, AN 221) based on the calculation unit 130) and the criterion. (E.g., AN212) is summarized in that a handoff control unit for controlling so as to handoff the wireless communication terminal having a (handoff control unit 140) and (AT100).

  In the second aspect of the present invention, the base station (for example, AN 211) has a plurality of sectors (for example, sector 211α to sector 211γ), and the handoff control unit includes a sector (for example, sector) that is executing communication. 211α) may be controlled to preferentially handoff to other sectors (eg, sector 211β, sector 211γ) of the first candidate base station (eg, AN 211).

In the second aspect of the present invention, the base station has a plurality of sectors,
The handoff control unit may control to handoff preferentially to a sector having an identification number within a predetermined threshold range from an identification number (for example, PN number) of a sector that is performing communication.

  As described above, according to the present invention, even when the wireless communication terminal (AT) moves near the boundary of the control area of the packet control device (PCF), the frequency of performing the handoff between PCFs is reduced. Therefore, it is possible to provide a handoff control method and a wireless communication terminal that can always ensure a stable handoff destination.

(Schematic configuration of mobile communication network)
FIG. 1 is a schematic configuration diagram of a mobile communication network 1 including a wireless communication terminal according to the present embodiment.

  The mobile communication network 1 is a mobile communication network that supports 1xEV-DO.

  A mobile communication network 1 includes a radio communication terminal (AT) 100, a base station (AN) 200, a packet control device (PCF) 300, a packet data switching node (PSDN) 400, a carrier, And an IP network 500.

  Hereinafter, it is assumed that the wireless communication terminal is AT, the base station is AN, the packet controller is PCF, and the packet / data exchange node is PSDN. The quantities of AT 100 (AT 101 to 102), AN 200 (AN 211 to 213, AN 221 to 223, AN 231 to 232), PCF 300 (PCF 310 to 330), and PSDN 400 included in the mobile communication network 1 are shown in FIG. It is not limited to quantity.

  The AT 100 performs data communication via the AN 200, the PCF 300, the PSDN 400, and the carrier IP network 500. The AT 100 connects a wireless session with the PCF 300, and performs data communication using the wireless session.

  Next, the subnets constituting the mobile communication network 1 will be specifically described.

  The subnet is a sub-network configured by one PCF 300 and the AN 200 under the PCF 300 in the mobile communication network 1, and indicates a control area of the PCF 300. The subnet is identified by a subnet address, and the ANs 200 belonging to the same subnet all have the same subnet address.

  Note that the same wireless session can be used in the same subnet. Therefore, in the handoff between the ANs 200 belonging to the same subnet (inter-AN handoff), it is not necessary to switch the wireless session. On the other hand, in handoff between ANs 200 belonging to different subnets (handoff between PCFs), switching of radio sessions is required.

  Specifically, as illustrated in FIG. 1, the subnet S <b> 1 includes a PCF 310 and ANs 211 to 213 under the PCF 310. Similarly, the subnet S2 includes a PCF 320 and ANs 221 to 223 under the PCF 320.

  Here, when the AT 101 performs handoff from the AN 211 to the AN 212 belonging to the subnet S1, an inter-AN handoff is performed. On the other hand, when the AT 102 hands off from the AN 211 belonging to the subnet S1 to the AN 221 belonging to the subnet S2, a handoff between PCFs is performed.

  In the mobile communication network 1, as shown in FIG. 2, the AN 211 belonging to the subnet S1 may have a plurality of sectors 211α to 211γ.

  Here, the sectors 211α to 211γ are one function of the AN 211 having directivity.

  The number of sectors 211α to 211γ is not limited to the number shown in FIG. Further, the AN 212 may have a plurality of sectors 212α to 212γ, similarly to the AN 211. Similarly, the AN 221 belonging to the subnet S2 may have a plurality of sectors 221α to 221γ.

  In such a configuration, handoff between sectors 211α to 211γ (inter-sector handoff) may be performed. Specifically, as shown in FIG. 2, the inter-sector handoff is that the AT 101 hands off from the sector 211α of the same AN 211 to the sector 211γ. Note that the AT 101 may perform a handoff (an inter-AN handoff) from the sector 211α of the AN 211 to the sector 212α of the AN 212.

  The AT 101 may perform a handoff (inter-PCF handoff) from the sector 211α of the AN 211 belonging to the subnet S1 to the sector 221α of the AN 221 belonging to the subnet S2.

  Hereinafter, in the present embodiment, it is assumed that the wireless communication terminal (AT) 100 performs communication with a sector included in the base station (AN) 200. That is, the wireless communication terminal (AT) 100 is handed off by switching the sector that performs communication.

(Function block configuration of wireless communication terminal)
With reference to FIG. 3, a functional block configuration of a radio communication terminal (AT) 100 configuring the mobile communication network 1 will be described.

  Hereinafter, portions related to the present invention will be mainly described. Therefore, it should be noted that the AT 100 may include a functional block (such as a power supply unit) that is essential for realizing the function as the device and that is not illustrated or omitted.

  As shown in FIG. 3, the AT 100 includes a transmission / reception unit 110, a neighbor list storage unit 120, a subnet ratio calculation unit 130, and a handoff control unit 140.

  The transmission / reception unit 110 receives the Sectorparameters message at a predetermined cycle.

  The Neighborlist storage unit 120 stores information on candidate base stations that are candidates for the handoff destination base station. Specifically, the Neighborlist storage unit 120 stores the Neighborlist included in the Sectorparameters message received by the transmission / reception unit 110 at a predetermined period.

  As shown in FIG. 4, the Neighborlist is a “sector ID” that identifies a candidate sector of a handoff destination, a “PN number” that identifies a pseudo noise (PN) code, and a “subnet mask”. ”. The logical product of the sector ID and the subnet mask is the subnet address. The subnet address identifies the subnet, and all sectors belonging to the same subnet have the same subnet address.

  Hereinafter, “subnet X” indicates a subnet (first subnet) to which a sector in communication with the AT 100 belongs. “Subnet Y” indicates a subnet (second subnet) other than subnet X and having the largest number of sectors stored in the Neighborlist storage unit 120.

  The subnet ratio calculation unit 130 calculates the number of sectors (first candidate base stations) included in the subnet X in the Neighborlist. Specifically, the subnet ratio calculation unit 130 calculates the number of sectors (first candidate base stations) having the same subnet address as the sector in communication with the AT 100 in the Neighborlist.

  Similarly, the subnet ratio calculation unit 130 calculates the number of sectors (second candidate base stations) included in the subnet Y in the Neighborlist.

  Based on the above calculation result, the subnet ratio calculation unit 130 calculates a subnet ratio that is a reference for handing off to a sector included in the subnet Y (handoff between PCFs).

  Specifically, the subnet ratio is calculated based on the ratio between the number of sectors belonging to the subnet X and the number of sectors belonging to the subnet Y among the sectors existing in the Neighborlist.

For example, the subnet ratio may be a ratio of the number of sectors belonging to subnet X to the total number of sectors belonging to subnet X and subnet Y, as shown in the following equation.

  For example, when the sector in communication with the AT 100 is “sector 211α”, “subnet S1” is subnet X and “subnet S2” is subnet Y.

  Based on the subnet ratio, the handoff control unit 140 controls the handoff of the AT 100 so as to preferentially handoff the sector belonging to the subnet X over the sector belonging to the subnet Y.

  Specifically, when the subnet ratio is equal to or greater than the threshold value R, the handoff control unit 140 obtains a predetermined value Psub from Ec / Io (hereinafter, Ec / Io) that is the signal strength of a pilot channel of a sector that does not belong to the subnet X. Subtract. That is, the handoff control unit 140 makes the Ec / Io of the sector belonging to the subnet X relatively stronger than the Ec / Io of the sector not belonging to the subnet X.

  That is, since handoff is performed for the sector with the strongest Ec / Io, the handoff control unit 140 gives priority to the sector belonging to the subnet X by relatively strengthening the Ec / Io of the sector belonging to the subnet X. Therefore, the handoff of the AT 100 is controlled so that the handoff is performed (ie, the inter-AN handoff is preferentially performed).

  Further, the handoff control unit 140 may control the handoff of the AT 100 so as to preferentially hand off to another sector belonging to the same AN 200 as the sector that is performing communication. In this case, for example, the handoff control unit 140 adds the predetermined value Ploc to Ec / Io of the sector having the same latitude / longitude information as the sector. It is assumed that the latitude / longitude information of a plurality of sectors included in the AN 200 is set equal.

  Further, the handoff control unit 140 may control the handoff of the AT 100 so as to preferentially handoff to a sector having a PN number within a predetermined threshold range from the PN number of the sector that is performing communication. In such a case, for example, the handoff control unit 140 adds a predetermined value Ppn to Ec / Io of a sector having a PN number within a predetermined threshold range from the PN number of the sector that is executing communication. When the threshold value is “1”, the handoff control unit 140 adds a predetermined value Ppn to the Ec / Io of the sector having the PN numbers before and after the sector in execution of communication.

  The subnet ratio threshold R described above is preferably less than 50%. The predetermined values Psub, Ploc, and Ppn for adjusting Ec / Io are preferably in a relationship of Psub> Ploc> Ppn.

(Operation of wireless communication terminal included in mobile communication network)
The operation of the radio communication terminal (AT) 100 included in the mobile communication network 1 described above will be described with reference to FIGS.

  FIG. 5 is a flowchart showing an operation in which the AT 100 prioritizes inter-AN handoff over inter-PCF handoff. Note that the AT 100 is in communication with the sector 211α belonging to the subnet S1. That is, the subnet S1 corresponds to the subnet X described above.

  In step S110, the AT 100 receives the SectorParameters message from the sector 211α that is performing communication at a predetermined cycle.

  In step S120, the AT 100 stores the NeighborList included in the SectorParameters message.

In step S130, the AT 100 calculates the subnet ratio as described above. (Refer to the subnet ratio calculation unit 130)
In step S140, the AT 100 determines whether or not the subnet ratio calculated in step S130 is less than a threshold value R (for example, R = 30 (%)). When the subnet ratio is less than the threshold value R (Yes in step S140), this operation ends. If the subnet ratio is equal to or greater than the threshold value R (No in step S140), the operation proceeds to step S150.

  In step S150, the AT 100 subtracts a predetermined value from Ec / Io of a sector that does not belong to the subnet X in the NeighborList. That is, the predetermined value Psub is subtracted from Ec / Io of a sector (eg, sector 221α) that does not belong to the subnet S1 to which the sector 211α belongs.

  In step S160, the AT 100 may add a predetermined value Ploc to Ec / Io of sectors having the same latitude and longitude information as the sector 211α (for example, sectors 211β and 211γ) in the NeighborList.

  In step S170, the AT 100 may add a predetermined value Ppn to Ec / Io of sectors having PN numbers before and after the sector 211α (for example, sector 211β in FIG. 4) in the NeighborList.

  Next, the operation in which the AT 100 performs the inter-PCF handoff when the subnet ratio is less than the threshold value R (for example, R = 30 (%)) (Yes in step S140 in FIG. 5) will be described.

  FIG. 6 is a flowchart showing an operation when the AT 100 performs the inter-PCF handoff.

  In step S210, for example, the AT 100 performs an inter-PCF handoff from the sector 211α of the subnet S1 to the sector 221α of the subnet S2.

  In step S220, the sector 221α becomes a sector that is currently performing communication with the AT 100 by the handoff between PCFs in step S210, so the subnet S2 to which the sector 221α belongs becomes the new subnet X.

  In step S230, the AT 100 recalculates the subnet ratio based on the above calculation formula. Here, since the inter-PCF handoff is performed when the subnet ratio becomes less than the threshold value R, the subnet ratio obtained by recalculation immediately after the handoff is approximately 100% -R%.

(Handoff control based on subnet ratio)
The handoff control based on the subnet ratio will be described with reference to FIGS.

  First, with reference to FIGS. 7 to 8, the change in subnet ratio and handoff control accompanying movement of the AT 100 will be described. In the following description, the threshold value R is 30%.

  FIG. 7 is a diagram illustrating the moving direction of the ATs 101 to 104.

  As shown in FIG. 7, the AT 101 moves through the points P11 to P13 and moves in the handoff direction (A). Here, the point P11 is the starting point when the AT 101 moves in the handoff direction (A), the point P12 is the boundary point of the control area between the subnet S1 and the subnet S2, and the point P13 is the point where the AT 101 performs handoff between PCFs. is there.

  FIG. 8 is a diagram showing a change in the subnet ratio accompanying the movement of the ATs 101 to 104 shown in FIG. Here, as shown in the above formula, the subnet ratio is the ratio of the number of sectors belonging to subnet X to the total number of sectors belonging to subnet X and subnet Y. Note that the points P11 to P13 in FIG. 7 correspond to the points P11 to P13 in FIG.

  As shown in FIG. 8, the subnet ratio (ratio of subnet X) at the point P11 is 100%. At this time, subnet X is subnet S1, and subnet Y is subnet S2. At point P11, the AT 101 performs an inter-AN handoff within the subnet S1.

  The subnet ratio at the points P11 to P12 continues to decrease. Also at points P11 to P12, the AT 101 performs an inter-AN handoff within the subnet S1.

  The subnet ratio at the point P12 is 50%. Even at the point P12, the AT 101 performs an inter-AN handoff in the subnet S1, but when the present invention is not applied, the AT 101 generally performs an inter-PCF handoff in the vicinity of the point P12.

  The subnet ratio at the points P12 to P13 continues to decrease further. At points P12 to P13, the AT 101 moves in the control area of the subnet S2. However, since the Ec / Io adjustment is performed according to the present invention, the AT 101 performs an inter-AN handoff within the subnet S1.

  The subnet ratio at the point P13 is 30%. Since the subnet ratio is less than the threshold value R (30%), the AT 101 performs the inter-PCF handoff at the point P13. Then, since subnet S2 is subnet X and subnet S1 is subnet Y, the subnet ratio immediately after handoff is about 70% (about 100% -30%).

  The subnet ratio at the point P13˜ continues to increase. At point P13 ~, the AT 101 performs an inter-AN handoff within the subnet S2.

  Similarly, handoff control based on the subnet ratio is performed for the AT 102 moving in the handoff direction (B), the AT 103 moving in the handoff direction (C), and the AT 104 moving in the handoff direction (D).

  Second, the frequency of inter-PCF handoff will be described with reference to FIGS.

  FIG. 9 is a diagram illustrating the moving direction of the AT 105.

  As shown in FIG. 9, the AT 105 moves in the handoff direction (E) near the boundary of the control area between the subnet S1 and the subnet S2. Here, the points P21 to P25 are boundary points of the control area between the subnet S1 and the subnet S2, and the point P21a is a point where the AT 105 performs handoff between PCFs in the present invention.

  FIG. 10 is a diagram showing the timing of handoff in the conventional example, and is a diagram briefly showing the movement of the AT 105 shown in FIG. Note that the points P21 to P25 and P21a in FIG. 9 correspond to the points P21 to P25 and P21a in FIG.

  Here, at “control area boundary” in FIG. 10, the ratio of the number of sectors belonging to subnet X to the total number of sectors belonging to subnet X and subnet Y is approximately 50%. In the conventional example to which the present invention is not applied, the inter-PCF handoff is performed every time the control areas of the subnet S1 and the subnet S2 are crossed. Therefore, the inter-PCF handoff is performed five times at the points P21 to P25.

  On the other hand, FIG. 11 is a diagram illustrating the timing of handoff according to the present invention, and is a diagram illustrating a change in the subnet ratio accompanying the movement of the AT 105 illustrated in FIG. Note that the points P21 to P25 and P21a in FIG. 9 correspond to the points P21 to P25 and P21a in FIG.

  As shown in FIG. 11, the subnet ratio (the ratio of subnet X) at the point P21 is approximately 50%. In the present invention, at the point P21, the AT 105 performs an inter-AN handoff within the subnet S1.

  When the AT 105 further moves and the subnet ratio becomes 30% (point P21a), the subnet ratio becomes less than the threshold value R (30%), so the AT 105 performs the inter-PCF handoff at the point P21a. Here, the subnet S2 is changed to the subnet X and the subnet S1 is changed to the subnet Y, and the subnet ratio by recalculation immediately after the handoff is about 70% (about 100% -30%).

  At points P22 to P25, since the subnet ratio is equal to or greater than the threshold value R (30%), inter-AN handoff is performed, and inter-PCF handoff is not performed.

(Action / Effect)
According to the mobile communication network 1 according to the present embodiment, the number of sectors (first candidate base stations) included in the subnet X (first subnet) and the sectors (second candidates) included in the subnet Y (second subnet). Handoff to sectors included in subnet Y (handoff between PCFs) to preferentially handoff to sectors included in subnet X based on the subnet ratio (reference) calculated based on the number of base stations) Can be performed less frequently.

  Moreover, since it is possible to appropriately determine whether to perform handoff between ANs or handoff between PCFs based on the subnet ratio (reference), a stable handoff destination can be secured.

  According to the mobile communication network 1 according to the present embodiment, the frequency of performing handoff (inter-PCF handoff) to a sector included in the subnet Y can be reduced, so that the mobile communication network on the AN 200 (base station) side The load can be reduced.

  According to the mobile communication network 1 according to the present embodiment, the frequency of performing handoff (inter-PCF handoff) to a sector included in the subnet Y can be reduced, and therefore overhead when the AT 100 (wireless communication terminal) performs handoff. And the occurrence of packet loss can be prevented.

  According to the mobile communication network 1 according to the present embodiment, the frequency of performing handoff (inter-AN handoff) to a sector included in the subnet X is high, so that a plurality of ActiveSet sectors are held immediately after the handoff. Therefore, a stable handoff destination can be secured.

  According to the mobile communication network 1 according to the present embodiment, the handoff to the sector under the same AN (base station) as the sector that is performing communication is frequently performed, so that the handoff is performed at high speed. be able to.

(Other embodiments)
As described above, the contents of the present invention have been disclosed through one embodiment of the present invention. However, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments will be apparent to those skilled in the art.

  For example, in the above-described embodiment of the present invention, the subnet ratio calculation formula is the ratio of the number of sectors belonging to subnet X to the total number of sectors belonging to subnet X and subnet Y, and the PCF when the subnet ratio is less than the threshold value. The inter-PCF handoff may be performed when the inter-PCF handoff is described.

  Further, the subnet ratio calculation formula may be the ratio of the number of sectors belonging to subnet Y to the number of sectors belonging to subnet X and subnet Y. When the subnet ratio is greater than (or greater than or equal to) the threshold, PCF An interim handoff may be performed.

  Further, the subnet ratio may be obtained by obtaining AN 200 as a handoff candidate from Neighborlist and calculating the subnet ratio based on the number of AN 200.

  Further, although the AT 100 performs communication with the sector, the AT 100 may perform communication directly with the AN 200. Further, handoff may be performed by switching the AN 200 that performs communication.

  Note that the wireless communication terminal AT may be not only a mobile phone but also a wireless card.

  Further, the above-described subnet ratio calculation unit 130 and handoff control unit 140 can also be provided as programs executable on a computer.

  As described above, the present invention naturally includes various embodiments that are not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

1 is an overall schematic configuration diagram of a mobile communication network according to an embodiment of the present invention. It is a block diagram of the subnet which concerns on embodiment of this invention. It is a functional block block diagram of the radio | wireless communication terminal which concerns on embodiment of this invention. It is a figure which shows Neighborlist which concerns on embodiment of this invention. It is a flowchart which shows operation | movement of the radio | wireless communication terminal which concerns on embodiment of this invention. It is a flowchart which shows operation | movement of the radio | wireless communication terminal which concerns on embodiment of this invention. It is a flowchart which shows the moving direction of the radio | wireless communication terminal which concerns on embodiment of this invention. It is a figure which shows the change of the subnet ratio accompanying the movement of the radio | wireless communication terminal which concerns on embodiment of this invention. It is a figure which shows the moving direction of the radio | wireless communication terminal which concerns on embodiment of this invention. It is a figure which shows the timing of the handoff in a prior art example. It is a figure which shows the timing of the handoff which concerns on embodiment of this invention. It is a whole schematic block diagram of the conventional mobile communication network. It is the handoff sequence between AN in the conventional mobile communication network. It is the handoff sequence between PCFs in the conventional mobile communication network.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Mobile communication network, 100 (101-105) ... AT, 110 ... Transmission / reception part, 120 ... Neighborlist memory | storage part, 130 ... Subnet ratio calculating part, 140 ... Handoff control part, 200 (211-213, 221-223, 231 to 232) ... AN, 211α to 211γ, 212α to 212γ ... sector, 300 (310 to 330) ... PCF, 400 ... PDSN, 500 ... carrier IP network, S1 to S3 ... subnet, C1, C2 ... cell, ST211α ~ 211γ, ST212α to 212γ ... sector, P11 to P13, P21 to P25, P21a ... point, 2 ... mobile communication network, 10a, 10b ... AT, 21a to 23a, 21b ... AN, 30a, 30b ... PCF, 40 ... PDSN , 50 ... Carrier IP network

Claims (6)

A storage step in which the wireless communication terminal stores information on candidate base stations that are candidates for a handoff destination base station;
The number of first candidate base stations that are the candidate base stations included in the first subnet to which the base station that is executing communication with the wireless communication terminal belongs, and the largest number of candidate base stations other than the first subnet belong Based on the number of second candidate base stations that are the candidate base stations included in the second subnet, a calculation step of calculating a reference for the wireless communication terminal to handoff to the second candidate base station;
A handoff control method comprising: a handoff control step of controlling the wireless communication terminal to handoff to the first candidate base station in preference to the second candidate base station based on the reference. The base station has a plurality of sectors,
The said handoff control process WHEREIN: The said radio | wireless communication terminal is controlled to preferentially hand off to the other sector of the said 1st candidate base station which has a sector in execution of communication. Handoff control method. The base station has a plurality of sectors,
2. The handoff control step, wherein the wireless communication terminal controls to handoff preferentially to a sector having an identification number within a predetermined threshold range from an identification number of a sector that is performing communication. 3. The handoff control method according to 2. A storage unit that stores information on candidate base stations that are candidates for a handoff destination base station;
Included in the number of first candidate base stations that are the candidate base stations included in the first subnet to which the base station performing communication belongs, and in the second subnet to which the largest number of candidate base stations other than the first subnet belong Based on the number of second candidate base stations that are the candidate base stations, a calculation unit that calculates a reference for handing off to the second candidate base station,
A wireless communication terminal comprising: a handoff control unit that controls to handoff to the first candidate base station in preference to the second candidate base station based on the reference. The base station has a plurality of sectors,
5. The wireless communication terminal according to claim 4, wherein the handoff control unit performs control so as to preferentially handoff to another sector of the first candidate base station having a sector that is performing communication. The base station has a plurality of sectors,
The wireless communication according to claim 4 or 5, wherein the handoff control unit controls to handoff preferentially a sector having an identification number within a predetermined threshold range from an identification number of a sector that is performing communication. Terminal.

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