IPC분류정보
국가/구분 |
United States(US) Patent
등록
|
국제특허분류(IPC7판) |
|
출원번호 |
US-0040870
(2005-01-20)
|
등록번호 |
US-7394789
(2008-07-01)
|
우선권정보 |
JP-2004-228863(2004-08-05) |
발명자
/ 주소 |
- Sakawa,Kozo
- Tateno,Masayoshi
- Higuma,Isao
|
출원인 / 주소 |
- Hitachi Communication Technologies, Inc.
|
대리인 / 주소 |
Townsend and Townsend and Crew LLP
|
인용정보 |
피인용 횟수 :
9 인용 특허 :
18 |
초록
▼
When an access terminal is handed off, requested-data-rate information based on a data rate control signal from each access terminal, average throughput of each access terminal before handoff, and a handoff request count are obtained from a base transceiver subsystem. A throughput after handoff of e
When an access terminal is handed off, requested-data-rate information based on a data rate control signal from each access terminal, average throughput of each access terminal before handoff, and a handoff request count are obtained from a base transceiver subsystem. A throughput after handoff of each access terminal is estimated from a ratio of the data rate information of each access terminal to the number of connected access terminals, and an estimated throughput ratio representing the degree of change from the average throughput of each access terminal before handoff to the estimated throughput is calculated. If the estimated throughput ratio is lower than or equal to a given value, the corresponding access terminal is not handed off. If the estimated throughput ratio is higher than the given value, the access terminal having the highest estimated throughput among access terminals requesting handoff is handed off.
대표청구항
▼
What is claimed is: 1. A handoff control method for use in a radio communication system which includes a base station controller, a base transceiver subsystem, and a plurality of access terminals and performs handoff control by which an access terminal is switched from one base transceiver subsyste
What is claimed is: 1. A handoff control method for use in a radio communication system which includes a base station controller, a base transceiver subsystem, and a plurality of access terminals and performs handoff control by which an access terminal is switched from one base transceiver subsystem to another base transceiver subsystem, the handoff control method, when one or more access terminals are moving from a first base transceiver subsystem to a second base transceiver subsystem during communication and when communication in the second base transceiver subsystem becomes possible, for each of the one or more access terminals, comprising: a step of obtaining information indicating a requested data rate included in a data rate control signal to the base transceiver subsystems; a step of obtaining, at a time prior to calculating an estimated throughput, an average throughput, a handoff request count to the second base transceiver subsystem, and the number of access terminals connected to the second base transceiver subsystem; a step of calculating the estimated throughput for each access terminal that requests handoff the calculating being based on said each access terminal having been handed off to the second base transceiver system, the calculating further being based on the information indicating a request data rate and the number of access terminals connected to the second base station subsystem, and calculating an estimated throughput ratio which represents a degree of change from the average throughput to the estimated throughput; and a step of preventing handoff of an access terminal if the estimated throughput ratio is lower than or equal to a given threshold, and executing handoff to the second base station subsystem of an access terminal having the highest throughput ratio among the one or more access terminals if the highest estimated throughput ratio is greater than the given threshold, wherein the throughput ratio of each access terminal is estimated by the following expressions: description="In-line Formulae" end="lead"Te(i)=DRC(i)/k description="In-line Formulae" end="tail" description="In-line Formulae" end="lead"TIR(i)=(Te(i)-T(i))/ T(i)description="In-line Formulae" end="tail" where i is an identification number of an access terminal, k is the number of access terminals connected in the second base transceiver subsystem, DRC(i) is the data rate information of access terminal AT(i), Te(i) is an estimated throughput, T(i) is the current average throughput, and TIR(i) is an estimated throughput ratio. 2. A handoff control method according to claim 1, wherein, if a plurality of access terminals requests handoff, one access terminal is handed off in accordance with the estimated throughput ratio, and then it is repeatedly judged whether to hand off the other access terminals requesting handoff in accordance with a throughput ratio estimated in the radio environment at the handoff destination with the access terminal added by handoff being taken into account. 3. A handoff control method according to claim 1, wherein the throughput is estimated further in accordance with an availability in the service area. 4. A handoff control method according to claim 1, further comprising: a step in which the base station controller or the base transceiver subsystem of the second base transceiver subsystem to which handoff is requested sends a data with a lock bit set to UNLock to the access terminal if a decrease in throughput is estimated after the handoff; a step in which the access terminal receives the data with the lock bit set to UNLock, and sends a data rate control signal selecting the base transceiver subsystem of the first base transceiver subsystem to the base transceiver subsystems of the first base transceiver subsystem and the second base transceiver subsystem although C/I of the base transceiver subsystem of the second base transceiver subsystem to which handoff is requested is higher than C/I of the base transceiver subsystem of the first base transceiver subsystem where communication is in progress; a step in which the base station controller or the base transceiver subsystem of the first base transceiver subsystem sends a data with the lock bit set to Lock to the access terminal; and a step in which the base station controller or the base transceiver subsystem of the second base transceiver subsystem sends a data with the lock bit set to UNLock to the access terminal. 5. A base station controller in a radio communication system which includes the base station controller, a base transceiver subsystem, and a plurality of access terminals, and performs handoff control by which an access terminal is switched from one base transceiver subsystem to another base transceiver subsystem, when one or more access terminals moving from a first base transceiver subsystem where communication is in progress to a second base transceiver subsystem become ready to communicate in the second base transceiver subsystem, for each of the one or more access terminals, the base station controller comprising: a storage block for storing information related to the access terminal in the base transceiver subsystems and information related to handoff; throughput estimation block for estimating a throughput; a comparison/determination block for determining whether to execute or prevent handoff, in accordance with the result of the calculation made by the throughput estimation block; and a handoff control block for executing or preventing handoff, the throughput estimation block: receiving the average data rate before handoff of each access terminal from the first base transceiver subsystem and receiving a data rate control signal to the base transceiver subsystems, from the first base transceiver subsystem or the second base transceiver subsystem; obtaining information indicating a requested data rate corresponding to each access terminal, in accordance with the received data rate control signal; obtaining, at a time prior to calculating an estimated throughput, an average throughput, a handoff request count to the second base transceiver subsystem, and the number of access terminals connected to the second base transceiver subsystem; and calculating the estimated throughput for each access terminal that requests handoff the calculating being based on said each access terminal having been handed off to the second base transceiver system, the calculating further being based on the information indicating a request data rate and the number of access terminals connected to the second base station subsystem, and calculating an estimated throughput ratio, which represents a degree of change from the average throughput to the estimated throughput, the comparison/determination block comparing the estimated throughput ratio and a given threshold, the handoff control block preventing handoff of an access terminal if the estimated throughput ratio is lower than or equal to a given threshold, and executing handoff to the second base station subsystem of an access terminal having the highest throughput ratio among the one or more access terminals if the highest estimated throughput ratio is greater than the given threshold, wherein the throughput ratio of each access terminal is estimated by the following expressions: description="In-line Formulae" end="lead"Te(i)=DRC(i)/k description="In-line Formulae" end="tail" description="In-line Formulae" end="lead"TIR(i)=(Te(i)-T(i))/ T(i)description="In-line Formulae" end="tail" where i is an identification number of an access terminal, k is the number of access terminals connected in the second base transceiver subsystem, DRC(i) is the data rate information of access terminal AT(i), Te(i) is an estimated throughput, T(i) is the current average throughput, and TIR(i) is an estimated throughput ratio. 6. A base station controller according to claim 5, wherein, if a plurality of access terminals request handoff, one access terminal is handed off in accordance with the estimated throughput ratio, and then it is repeatedly judged whether to hand off the other access terminals requesting handoff in accordance with a throughput ratio estimated in the radio environment at the handoff destination with the access terminal added by handoff being taken into account. 7. A base station controller according to claim 5, wherein the throughput is estimated further in accordance with an availability in the service area. 8. A base station controller according to claim 5, wherein the base station controller or the base transceiver subsystem of the second base transceiver subsystem to which handoff is requested sends a data with a lock bit set to UNLock to the access terminal if a decrease in throughput is estimated after the handoff; the access terminal receives the data with the lock bit set to UNLock, and sends a data rate control signal selecting the base transceiver subsystem of the first base transceiver subsystem to the base transceiver subsystems of the first base transceiver subsystem and the second base transceiver subsystem although C/I of the base transceiver subsystem of the second base transceiver subsystem to which handoff is requested is higher than C/I of the base transceiver subsystem of the first base transceiver subsystem where communication is in progress; the base station controller or the base transceiver subsystem of the first base transceiver subsystem sends a data with the lock bit set to Lock to the access terminal; and the base station controller or the base transceiver subsystem of the second base transceiver subsystem sends a data with the lock bit set to UNLock to the access terminal. 9. A base transceiver subsystem in a radio communication system which includes a base station controller, the base transceiver subsystem, and a plurality of access terminals, and performs handoff control by which an access terminal is switched from one base transceiver subsystem to another base transceiver subsystem, when one or more access terminals moving from a first base transceiver subsystem where communication is in progress to a second base transceiver subsystem become ready for communication in the second base transceiver subsystem, the base transceiver subsystem comprising: a storage block for storing information related to the access terminals in the base transceiver subsystems and information related to handoff; a throughput estimation block for estimating an throughput; a comparison/determination block for determining whether to execute or prevent handoff, in accordance with the result of calculation made by the throughput estimation block; a handoff control block for executing or preventing handoff; and a throughput calculation block for calculating an average throughput of each access terminal, the throughput estimation block: obtaining data rate information representing a requested data rate corresponding to each access terminal, in accordance with the data rate control signal for providing requested-data-rate information for the base transceiver subsystems; obtaining, at a time prior to calculating an estimated throughput, an average throughput of each access terminal before handoff, from the throughput calculation block, a handoff request count to the second base transceiver subsystem, and the number of access terminals connected in the second base transceiver subsystem, from the storage block; and calculating the estimated throughput for each access terminal that requests handoff the calculating being based on said each access terminal having been handed off to the second base transceiver subsystem, the calculating further being based on the information indicating a request data rate and the number of access terminals connected to the second base station subsystem, and calculating an estimated throughput ratio, which represents a degree of change from the average throughput to the estimated throughput, the comparison/determination block comparing the estimated throughput ratio with a given threshold, the handoff control block preventing handoff of an access terminal if the estimated throughput ratio is lower than or equal to a given threshold, and executing handoff to the second base station subsystem of an access terminal having the highest throughput ratio among the one or more access terminals if the highest estimated throughput ratio is greater than the given threshold, wherein the throughput ratio of each access terminal is estimated by the following expressions: description="In-line Formulae" end="lead"Te(i)=DRC(i)/k description="In-line Formulae" end="tail" description="In-line Formulae" end="lead"TIR(i)=(Te(i)-T(i))/ T(i)description="In-line Formulae" end="tail" where i is an identification number of an access terminal, k is the number of access terminals connected in the second base transceiver subsystem, DRC(i) is the data rate information of access terminal AT(i), Te(i) is an estimated throughput, T(i) is the current average throughput, and TIR(i) is an estimated throughput ratio. 10. A base transceiver subsystem according to claim 9, wherein, if a plurality of access terminals request handoff, one access terminal is handed off in accordance with the estimated throughput ratio, and then it is repeatedly judged whether to hand off the other access terminals requesting handoff in accordance with a throughput ratio estimated in the radio environment at the handoff destination with the access terminal added by handoff being taken into account. 11. A base transceiver subsystem according to claim 9, wherein the throughput is estimated further in accordance with an availability in the service area. 12. A base transceiver subsystem according to claim 9, wherein the base station controller or the base transceiver subsystem of the second base transceiver subsystem to which handoff is requested sends a data with a lock bit set to UNLock to the access terminal if a decrease in throughput is estimated after the handoff; the access terminal receives the data with the lock bit set to UNLock, and sends a data rate control signal selecting the base transceiver subsystem of the first base transceiver subsystem to the base transceiver subsystems of the first base transceiver subsystem and the second base transceiver subsystem although C/I of the base transceiver subsystem of the second base transceiver subsystem to which handoff is requested is higher than C/I of the base transceiver subsystem of the first base transceiver subsystem where communication is in progress; the base station controller or the base transceiver subsystem of the first base transceiver subsystem sends a data with the lock bit set to Lock to the access terminal; and the base station controller or the base transceiver subsystem of the second base transceiver subsystem sends a data with the lock bit set to UNLock to the access terminal.
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