Communication system using multiple wireless resources during a soft handoff

• US 7,894,817 B2
• Filed: 07/03/2007
• Issued: 02/22/2011
• Est. Priority Date: 08/31/2006
• Status: Expired due to Fees

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Takada, May, Katayama, Rintaro, Mazawa, Shiro, Takahashi, Yosuke
• Primary Examiner(s): Cumming; William D
• Application Number:
  US11/822,228
• Publication Number:
  US 20080057970A1
• Time in Patent Office: 1,330 Days
• Field of Search: 455/166.2, 455/446, 455/447, 455/450, 370/209, 370/252, 370/331, 370/335, 375/130
• US Class Current: 455/446
• CPC Class Codes: H04W 36/18 for allowing seamless reselection, e.g. soft reselection
• CPC Class Codes: H04W 36/28 involving a plurality of connections, e.g. multi-call or multi-bearer connections

Abstract

In a wireless communications system operating according to CDMA or the like, when one terminal simultaneously performs communication using multiple wireless resources (e.g., multiple carriers), there was a problem that when it was attempted to guarantee network mobility by the same soft handoff system as in the case where communication was performed using only one wireless resource, efficiency suffered from the viewpoint of network forwarding load, processing load and wireless resource occupancy time. Soft handoff termination is judged and soft handoff is forcibly terminated according to whether or not the data rate obtained for all resources on the network side satisfies a requested rate, based on a reception state notification from a terminal concerning wireless resources. By performing this processing, the soft handoff period is shortened, sufficient received strength in the terminal is maintained and terminal mobility is guaranteed, while at the same time network forwarding load, terminal processing load and wireless resource occupancy time are suppressed to the absolute minimum.

Claims

1. A wireless communications system comprising multiple base stations connected to a network, communication with a terminal being performed using multiple carriers, and a soft handoff of said terminal being performed among said multiple base stations, wherein when said terminal is in a soft handoff state between said first and second base stations, said first base station and second base station receive communication quality information about said multiple carriers from said terminal, wherein a termination message of a network side soft handoff which instructs termination of soft handoff of at least a second carrier to be determined based on the received communication quality information about at least a first carrier, is notified to said terminal from said first or second base station.

2. The wireless communications system according to claim 1, having a control node connected between said multiple base stations and a communication network, wherein said communication quality information is information about a data rate obtained by any of the base stations in each carrier, and wherein when a data rate for all the carriers of this terminal obtained from said first or second base station exceeds a predetermined request rate, said control node makes a judgment to terminate soft handoff for said second or first base station and for all carriers.

3. The wireless communications system according to claim 2, wherein said predetermined request rate is a QoS rate of this terminal or a best effort guarantee rate determined by each base station.

4. The wireless communications system according to claim 1, having a control node connected between said multiple base stations and said a communication network, wherein when said first base station has received a terminal side soft handoff termination message for said first carrier from said terminal, said control node makes a judgment to terminate soft handoff also for said second carrier.

5. The wireless communications system according to claim 1, wherein said communication quality information is information about a data rate obtained by any of the base stations in each carrier, wherein when the base station is the base station which is the origin of the handoff, said first base station forwards communication data to a terminal received from the network to said second base station, and wherein when a data rate for all the carriers of the terminal concerned obtained from said first or second base station exceeds a predetermined request rate, a judgment to terminate soft handoff of said second or first base station for all the carriers is made.

6. The wireless communications system according to claim 5, wherein said predetermined request rate is a QoS rate of said terminal or a best effort guarantee rate determined by each base station.

7. The wireless communications system according to claim 1, wherein when the base station is the base station which is the origin of the handoff, said first base station forwards communication data addressed to the terminal received from the network to said second base station, and wherein when said first base station receives a terminal side soft handoff termination message which notifies termination of soft handoff for said first carrier from said terminal, a judgment to terminate soft handoff also for said second carrier is made.

8. The wireless communications system according to claim 1, wherein after notifying said termination message of a network side soft handoff for said first or second base station to said terminal, a request which adds said first or second base station from this terminal to an Active Set is refused according to predetermined conditions.

9. The wireless communications system according to claim 1, wherein, in a pilot received power determining method for soft handoff start in this terminal, there is a first threshold which is a soft handoff start condition in the first carrier, a second threshold which is a condition starting soft handoff in the second carrier while there is already soft handoff in the first carrier, and a third threshold which is a condition starting soft handoff in the third carrier while there is already soft handoff in the first carrier and second carrier, the magnitudes of said thresholds being set in the order:

first threshold<

second threshold<

third threshold.

10. The wireless communications system according to claim 9, wherein the values of the threshold 1, threshold 2, and threshold 3 can be changed, and there is a message interface which connects the values from this base station to this terminal.

11. The wireless communications system according to claims 9, wherein the values of the threshold 1, threshold 2, and threshold 3 are distinguished by whether this terminal is communicating by a QoS call, or communicating by a best effort call, and different values are set accordingly.

12. The wireless communications system according to claim 1, wherein, in a pilot received power determining method for soft handoff start in this terminal, there is a first threshold which is a soft handoff start condition in the first carrier, a second threshold which is a condition starting soft handoff in the second carrier, and a third threshold which is a condition starting soft handoff in the third carrier, a magnitude relation between these thresholds being set based on the frequency characteristic of a band to which each carrier belongs, the number of connectors belonging to the area used and their communication throughput, and the QoS preference in the area used.