Soft hand-off in cellular mobile communications networks

• US 6,658,252 B2
• Filed: 01/11/2002
• Issued: 12/02/2003
• Est. Priority Date: 05/14/1998
• Status: Active Grant

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Mohebbi, Behzad
• Primary Examiner(s): Nguyen, Lee
• Assistant Examiner(s): Milord, Marceau
• Application Number:
  US10/043,492
• Publication Number:
  US 20020058512A1
• Time in Patent Office: 690 Days
• Field of Search: 455/437, 455/426, 455/436, 455/439, 455/442, 455/440, 455/441, 455/447, 370/331, 370/332, 370/347
• US Class Current: 455/437
• CPC Class Codes: H04B 7/022 Site diversity; Macro-diversity using two or more spaced independent antennas H04B7/04
• CPC Class Codes: H04W 36/18 for allowing seamless reselection, e.g. soft reselection
• CPC Class Codes: H04W 36/32 by location or mobility data, e.g. speed data
• CPC Class Codes: H04W 52/40 during macro-diversity or soft handoff

Abstract

In a cellular mobile communications network a mobile station is capable of receiving a downlink signal from each of a plurality of base stations and transmitting an uplink signal to the plurality of the base stations through a wireless channel. The mobile station produces a measure of signal quality of the downlink signals from the plurality of base stations to the mobile station and selects a base station from which the downlink signal shows a preferred signal quality. The mobile station transmits an uplink signal indicating the selected base station among the plurality of base stations for subsequent communications with the mobile station. Each base station processes the uplink signal to identify the selected base station from among the plurality of base stations.

Claims

1. A mobile station capable of receiving a downlink signal from each of a plurality of base stations and transmitting an uplink signal to the plurality of base stations through a wireless channel, the plurality of base stations in a soft hand-off mode with the mobile station, said mobile station comprising:

a selection processing means for producing a measure of a signal quality of the downlink signals from each of the plurality of base stations in said soft hand-off mode with the mobile station, and selecting a base station from which the downlink signal shows a preferred signal quality; and

,

a transmission means for transmitting the uplink signal indicating the selected base station among the plurality of base stations for subsequent communication with the mobile station,

wherein said mobile station receiving the next downlink signal and maintaining the soft handoff mode with the plurality of base stations and, while in said soft handoff mode, periodically re-selecting a base station from which the downlink signal shows the best signal quality and transmitting the uplink signal including the identification of the selected base station, among the plurality of base stations in said soft hand-off mode.

2. The mobile station as claimed in claim 1, wherein said transmission means transmits she uplink signal including an identification of the selected base station among the plurality of base stations in the soft hand-off mode.

3. The mobile station as claimed in claim 1, wherein the signal quality of the downlink signals from each of the plurality of base stations is represented by signal strengths of the received downlink signals.

4. A mobile station capable of receiving a downlink signal from each of a plurality of base stations and transmitting an uplink signal to the plurality of base stations through a wireless channel, the plurality of base stations in a soft hand-off mode with the mobile station, said mobile station comprising:

a selection processing unit for producing a measure of a signal quality of the downlink signals from each of the plurality of base stations in said soft hand-off mode with the mobile station, and selecting a base station from which the downlink signal shows the best signal quality; and

a transmitter unit for transmitting the uplink signal indicating the selected base station, among the plurality of base stations in said soft hand-off mode, for subsequent communication with the mobile station,

wherein said mobile station receiving the next downlink signal from one or more of the plurality of base stations and maintaining the soil handoff mode with the plurality of base stations and, while in said soft handoff mode, periodically re-selecting a base station from which the downlink signal shows the best signal quality and transmitting the uplink signal including the identification of the selected base station, among the plurality of base stations in said soft hand-off mode.

5. The mobile station as claimed in claim 4, wherein the transmitter unit transmits the uplink signal including an identification of a single selected base station among the plurality of base stations in the soft hand-off mode.

6. The mobile station as claimed in claim 4, wherein the signal quality of the downlink signals from each of the plurality of base stations is represented by signal strengths of the received downlink signals.

7. A mobile station capable of receiving a downlink signal from each of a plurality of base stations and transmitting an uplink signal to the plurality of base stations through a wireless channel, the plurality of base stations in a soft handoff mode with the mobile station, said mobile station comprising:

a processor which produces a measure of a signal quality of the downlink signals from the plurality of base stations in said soft handoff mode, and selects a base station from which the downlink signal shows a preferred signal quality; and

a transmitter which transmits the uplink signal including an identification of the selected base station, from among the plurality of base stations in said soft handoff mode, for subsequent communication of a next downlink signal with the mobile station,

wherein said selected base station transmits the next downlink signal to said mobile station, said mobile station receiving the next downlink signal and maintaining the soft handoff mode with the plurality of base stations and said mobile station, while in said soft handoff mode, periodically re-selecting a base station from which the downlink signal shows the best signal quality and transmitting the uplink signal including the identification of the selected base station, among the plurality of base stations in said soil hand-off mode.

8. The mobile station as claimed in claim 7, wherein the signal quality of the downlink signals from each of the plurality of base stations is represented by signal strengths of the received downlink signals.

9. A mobile station capable of receiving a downlink signal from each of a plurality of base stations and transmitting an uplink signal to the plurality of base stations through a wireless channel, the plurality of base stations in a soft hand-off mode with the mobile station, said mobile station comprising:

a processor which produces a measure of signal quality of the downlink signals from the plurality of base stations in said soft hand-off mode, and selects a base station from which the downlink signal shows the best signal quality; and

a transmitter which transmits the uplink signal including an identification of the selected base station, among the plurality of base stations in said soft hand-off mode, for subsequent communication with the mobile station,

wherein said mobile station, while in said soft handoff mode, periodically re-selecting a base station from which the downlink signal shows the best signal quality and transmitting the uplink signal including the identification of the selected base station, among the plurality of base stations in said soft hand-off mode.

10. The mobile station as claimed in claim 9, wherein the signal quality of the downlink signals from each of the plurality of base stations is represented by signal strengths of the received downlink signals.

11. A mobile station capable of receiving a downlink signal from each of a plurality of base stations and transmitting an uplink signal to each of the plurality of base stations through a wireless channel, the plurality of base stations in a soft hand-off mode with the mobile station, said mobile station comprising:

a processor which produces a measure of signal strengths of the downlink signals received from the plurality of base stations, and selects a base station from which a received downlink signal shows the highest signal strength; and

a transmitter which transmits the uplink signal including an identification of the selected base station, among the plurality of base stations, for subsequent communication with the mobile station,

wherein said mobile station, while in said soft handoff mode, periodically re-selecting a base station from which the downlink signal shows the highest signal strength and transmitting the uplink signal including the identification of the selected base station, among the plurality of base stations in said soft hand-off mode.

12. A mobile station capable of receiving a downlink signal from each of a plurality of base stations and transmitting an uplink signal to the plurality of the base stations through a wireless channel, comprising:

a processor which establishes a soft hand-off operation with one or mare base stations, periodically produces a measure of a signal quality of the downlink signals from each of the base stations in said soft band-off mode, selects a base station from which the downlink signal shows a preferred signal quality, and controls transmission of the uplink signal to include an identification of the selected base station, among the base stations in said soft hand-off operation, for subsequent communication of a next downlink signal with the mobile station,

wherein while in said soft handoff mode, periodically re-selecting a base station from which the downlink signal shows the best signal quality and transmitting the uplink signal including the identification of the selected base station among the plurality of base stations in said soft hand-off mode.

13. The mobile station as claimed in claim 12, wherein the signal quality of the downlink signals from each of the base stations is represented by signal strengths of the received downlink signals.

14. A mobile station capable of receiving a downlink signal from each of a plurality of base stations and transmitting an uplink signal to the plurality of base stations through a wireless channel, the plurality of base stations in a soft handoff mode wit the mobile station, said mobile station comprising:

a processor which establishes a soft hand-off operation with one or more base stations, periodically produces a measure of signal strengths of the downlink signals from each of the base stations in said soft hand-off operation, selects a base station front which the downlink signal shows the highest signal strength, and controls transmission of the uplink signal to include an identification of the selected base station among the base stations for subsequent communication with the mobile station, wherein said mobile station receiving the next downlink signal and maintaining the soft handoff operation with the base stations,

wherein while in said soft handoff mode, periodically re-selecting a base station from which the downlink signal shows the best signal quality and transmitting the uplink signal including the identification of the selected base station, among the plurality of base stations in said soft hand-off mode.

15. A mobile station of a cellular mobile communications network capable of receiving a downlink signal from each base station of a plurality of base stations and transmitting an uplink signal to the plurality of base stations, the mobile station transmitting and receiving radio frames having a predetermined length, said mobile station comprising:

a transmitter which transmits the uplink signal to each base station of the plurality of base stations involved in a soft hand-off mode with said mobile station;

a receiver that receives the downlink signal from each base station of a plurality of base stations; and

a controller for providing an identification to each base station involved in a soft hand-off mode with the mobile station,

wherein while in said soft handoff mode, periodically re-selecting a base station from which the downlink signal shows the best signal quality and transmitting the uplink signal including the identification of the selected base station, among the plurality of base stations in said soft hand-off mode.

16. The mobile station of claim 15, further comprising:

a message generator which generates an identification message which includes the identification of each base station provided by the controller, wherein said identification message is transmitted in the uplink signal.

17. The mobile station of claim 16, wherein the identification message is transmitted in a control channel of the uplink signal to said each base station of the plurality of base stations involved in the soft hand-off mode.

18. A mobile station of a cellular mobile communications network capable of receiving a downlink signal from each base station of a plurality of base stations and transmitting an uplink signal to the plurality of base stations, the plurality of base stations involved in a soft hand-off mode, the mobile station transmitting and receiving radio frames having a predetermined length, said mobile station comprising:

a controller for providing an identification to each base station involved in the soft hand-off mode with the mobile station,

wherein while in said soft handoff mode, periodically re-selecting a base station from which the downlink signal shows the best signal quality and transmitting the uplink signal including the identification of the selected base station, among the plurality of base stations in sad soft hand-off mode.

19. The mobile station of claim 18, further comprising:

a message generator which generates an identification message which includes the identification of each base station provided by the controller, said identification message transmitted in the uplink signal.

20. The mobile station of claim 19, wherein the identification message is transmitted in a control channel of the uplink signal to said each base station of the plurality of base stations involved in the soft hand-off mode.