Handover method, and a cellular radio system

• US 6,198,928 B1
• Filed: 03/02/1998
• Issued: 03/06/2001
• Est. Priority Date: 08/31/1995
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Nokia Telecommunications Oy (Nokia Corporation)
• Inventors: Keurulainen, Jere, Häkkinen, Hannu, Hämäläinen, Seppo
• Primary Examiner(s): Bost, Dwayne
• Assistant Examiner(s): Trinh, Sonny
• Application Number:
  US09/043,012
• Time in Patent Office: 1,100 Days
• Field of Search: 455/436, 455/437, 455/442, 455/59, 455/86, 455/315, 455/522, 370/331, 375/200
• US Class Current: 455/436
• CPC Class Codes: H04W 36/36 by user or terminal equipment

Abstract

A cellular radio system and a handover method in a cellular radio system is provided. The cellular radio system includes a subscriber terminal and a base station. In the system, the subscriber terminal maintains and continuously updates an active set of base stations. One or several base stations belonging to the active set has a connection or connection set-up facilities to the subscriber terminal. The subscriber terminal controls the downlink transmission of one or several base stations of the active set by switching the transmission of the base station on or off. This method provides a fast soft handover similar to a hard handover.

Claims

1. A handover method in a cellular radio system including a subscriber terminal and a plurality of base stations, the method comprising:

maintaining and continuously updating, by the subscriber terminal, an active set of the base stations, at least one of the base stations belonging to the active set having a respective connection to the subscriber terminal; and

deciding, by the subscriber terminal, to switch on or off a respective downlink transmission of the at least one base station of the active set.

2. A method according to claim 1, wherein the subscriber terminal transmits a command signal ordering the at least one base station of the active set to switch on the respective downlink transmission.

3. A method according to claim 1, wherein the subscriber terminal transmits a command signal ordering the at least one base station of the active set to switch off the respective downlink transmission.

4. A method according to claim 1, wherein the subscriber terminal decides to switch on or off the respective downlink transmission of the at least one base station of the active set by controlling signaling and a traffic channel in such a way that the at least one base station of the active set loses the respective connection to the subscriber terminal, whereupon the at least one base station of the active set switches off the respective downlink transmission.

5. A method according to claim 1, wherein the at least one base station of the active set switches off the respective connection with the subscriber terminal after a predetermined delay.

6. A method according to claim 1, wherein the at least one base station of the active set switches off the respective connection with the subscriber terminal by reducing transmit power within a predetermined period of time.

7. A method according to claim 2, wherein the subscriber terminal transmits a command signal separately for each base station.

8. A method according to claim 2, wherein the command signal is common to all base stations of the active set.

9. A method according to claim 2, wherein the subscriber terminal transmits a command signal at regular intervals.

10. A method according to claim 9, wherein a transmission of traffic channels takes place at regular intervals in a form of frames and the subscriber terminal transmits the command signal at intervals of a frame.

11. A method according to claim 2, wherein when the command signal intended for the at least one base station of the active set is divided in fragments received by different base stations, the command signal intended for the at least one base station is assembled in a base station controller or in some part of the network from said fragments, and the command signal formed in this manner is signaled back to the at least one base station.

26. A method according to claim 3, wherein the at least one base station of the active set switches off the respective connection with the subscriber terminal after a predetermined delay.

27. A method according to claim 4, wherein the at least one base station of the active set switches off the respective connection with the subscriber terminal after a predetermined delay.

28. A method according to claim 3 wherein the at least one base station of the active set switches off the respective connection with the subscriber terminal by reducing transmit power within a predetermined period of time.

29. A method according to claim 4 wherein the at least one base station of the active set switches off the respective connection with the subscriber terminal by reducing transmit power within a predetermined period of time.

30. A method according to claim 3, wherein the subscriber terminal transmits a command signal separately for each base station.

31. A method according to claim 3, wherein when the command signal intended for the at least one base station of the active set is divided in fragments received by different base stations, the command signal intended for the at least one base station is assembled in a base station controller or in some part of the network from said fragments, and the command signal formed in this manner is signaled back to the at least one base station.

12. A cellular radio system comprising:

a subscriber terminal; and

a plurality of base stations, the subscriber terminal maintaining and continuously updating an active set of the base stations, at least one of the base stations belonging to the active set and having a connection to the subscriber terminal, wherein

the subscriber terminal comprises;

means for deciding to switch on or off a downlink transmission of at least one base station of the active set.

13. A cellular radio system according to claim 12, wherein the subscriber terminal comprises means for forming and transmitting a command signal ordering the at least one base station of the active set to switch on a transmission.

14. A cellular radio system according to claim 12, wherein the subscriber terminal comprises means for forming and transmitting a command signal ordering the at least one base station of the active set to switch off a transmission.

15. A cellular radio system according to claim 12, wherein the means for deciding to switch on or off downlink transmission of at least one base station of the active set is arranged to control signaling and traffic channels of the subscriber terminal in such a way that the at least one base station of the active set loses the connection to the subscriber terminal, and at least one of the base stations comprises means for switching off a respective downlink transmission when the at least one of the base station loses a respective connection to the subscriber terminal.

16. A cellular radio system according to claim 12, wherein the base stations, each comprise means for switching off a respective transmission after a predetermined delay.

17. A cellular radio system according to claim 12, wherein the base stations, each comprise means for switching off a respective transmission by reducing transmit power within a predetermined period of time.

18. A cellular radio system according to claim 13, wherein the subscriber terminal comprises means for transmitting a command signal separately for each of the base stations.

19. A cellular radio system according to claim 13, wherein the subscriber terminal comprises means for transmitting a command signal that is common to all of the base stations of the active set.

20. A cellular radio system according to claim 12, wherein the subscriber terminal comprises means for transmitting a command signal at regular intervals.

21. A cellular radio system according to claim 20, wherein transmission of traffic channels takes place at regular intervals in a form of frames and the subscriber terminal comprises means for transmitting a command signal at intervals of a frame.

32. A cellular radio system according to claim 14, wherein the base stations, each comprise means for switching off a respective transmission after a predetermined delay.

33. A cellular radio system according to claim 15, wherein the base stations, each comprise means for switching off a respective transmission after a predetermined delay.

34. A cellular radio system according to claim 14, wherein the base stations, each comprise means for switching off a respective transmission by reducing transmit power within a predetermined period of time.

35. A cellular radio system according to claim 15, wherein the base stations, each comprise means for switching off a respective transmission by reducing transmit power within a predetermined period of time.

36. A cellular radio system according to claim 14, wherein the subscriber terminal comprises means for transmitting a command signal separately for each of the base stations.

37. A cellular radio system according to claim 14, wherein the subscriber terminal comprises means for transmitting a command signal that is common to all of the base stations of the active set.

22. A subscriber terminal for a cellular radio system, wherein the subscriber terminal comprises:

means for maintaining and continually updating an active set of base stations; and

means for deciding to switch on or off a respective downlink of at least one of the base stations of the active set.

23. The subscriber terminal according to claim 22, wherein said means for deciding to switch on or off a a respective downlink of at least one of the base stations of the active set comprises means for transmitting a command signal to order the at least one base station of the active set to switch on the respective downlink transmission.

24. The subscriber terminal according to claim 22, wherein said means for deciding to switch on or off a a respective downlink of at least one of the base stations of the active set comprises means for transmitting a command signal to order the at least one base station of the active set to switch off the respective downlink transmission.

25. The subscriber terminal according to claim 22, wherein said means for deciding to switch on or off a a respective downlink of at least one of the base stations of the active set comprises means for controlling signaling and a traffic channel such that the at least one base station of the active set loses a respective connection to the subscriber terminal and the at least one base station of the active set switches off the respective downlink transmission.