Method and apparatus for mobile-initiated, CDMA-dispatch soft handoff

• US 6,788,941 B2
• Filed: 12/20/2001
• Issued: 09/07/2004
• Est. Priority Date: 12/20/2001
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Wilson, Timothy J., Chinitz, Leigh M., Needham, Michael L.
• Primary Examiner(s): Gelin, Jean Alland
• Application Number:
  US10/027,041
• Publication Number:
  US 20030119513A1
• Time in Patent Office: 992 Days
• Field of Search: 455/436, 455/437, 455/438, 455/439, 455/442, 455/445, 455/518, 455/519, 370/331, 370/332, 370/335, 370/342, 370/441, 370/320, 370/322
• US Class Current: 455/442
• CPC Class Codes: H04W 36/18 for allowing seamless reselection, e.g. soft reselection
• CPC Class Codes: H04W 4/08 User group management

Abstract

To address the need for an apparatus and method for CDMA-dispatch soft handoff, the present invention enables mobile-initiated soft handoff for dispatch calls. A mobile station (120) in a dispatch call establishes an individual inbound link (137) with the serving base site (111). When the mobile station determines that a handoff with an adjacent site (112) is needed, the mobile station uses its individual inbound link to request a soft handoff with the adjacent base site. After notifying the adjacent base site, the serving base site then transmits the handoff information to the mobile station to enable the mobile station to begin a soft handoff with the adjacent site.

Claims

1. A method for a base site to facilitate mobile-initiated, CDMA-dispatch soft handoff comprising the steps of:

establishing, by the base site, a first outbound link for a dispatch call;

transmitting, by the base site, the dispatch call via the first outbound link;

establishing, by the base site, an inbound link with a mobile station (MS) for the dispatch call;

receiving, by the base site from the MS via the inbound link, a request to begin a soft handoff with an adjacent base site;

notifying the adjacent base site of the soft handoff request of the MS;

receiving, by the base site in response to the request to begin a soft handoff from the MS, an indication of a second outbound link at the adjacent site enabling the soft handoff; and

indicating, by the base site, to the MS the identity of the second outbound link.

2. The method of claim 1 wherein the inbound link comprises a low-rate inbound link used to communicate at least one of forward power control information and reverse power information.

3. The method of claim 1 wherein the first outbound link and the second outbound link each comprises a full-rate CDMA outbound traffic channel.

4. The method of claim 1 wherein the step of indicating comprises the step of signaling in-band on the first outbound link the identity of the second outbound link.

5. The method of claim 1 wherein the step of indicating comprises the step of signaling via a paging channel the identity of the second outbound link.

6. The method of claim 5 wherein the step of signaling via a paging channel comprises the step of transmitting a broadcast page to convey the identity of the second outbound link.

7. The method of claim 1 further comprising the step of indicating the identity of the first MS with the identity of the second outbound link.

8. The method of claim 1 further comprising the step of indicating the identity of the adjacent base site with the identity of the second outbound link.

9. The method of claim 8 wherein the step of indicating the identity of the adjacent base site with the identity of the second outbound link comprises transmitting to the MS a pseudorandom noise scrambling code offset of the adjacent base site.

10. The method of claim 1 wherein the step of indicating to the MS the identity of the second outbound link comprises transmitting to the MS a CDMA code used for the second outbound link.

11. A method for a mobile station (MS) to initiate a CDMA-dispatch soft handoff comprising the steps of:

receiving a dispatch call via a first outbound link with a base site;

establishing an inbound link with the base site for the dispatch call;

transmitting via the inbound link a request to begin a soft handoff with an adjacent bass site; and

receiving, from the base site in response to the request to begin a soft handoff, an indication of the identity of a second outbound link at the adjacent site with which to begin the soft handoff.

12. The method of claim 11 further comprising the step of beginning the soft handoff by simultaneously receiving the dispatch call via the first outbound link and the second outbound link.

13. The method of claim 12 further comprising the step of transmitting a request to establish an inbound link with the adjacent base site for the dispatch call.

14. The method of claim 11 wherein the step of receiving the indication comprises the step of receiving in-band signaling on the first outbound link that conveys the identity of the second outbound link.

15. The method of claim 11 wherein the step of receiving the indication comprises the step of receiving a broadcast page that conveys the identity of the second outbound link.

16. The method of claim 11 wherein the request comprises a signal strength report.

17. A base site comprising:

a transmitter;

a receiver; and

a controller, coupled to the transmitter and the receiver, adapted to establish a first outbound link for a dispatch call, adapted to instruct the transmitter to transmit the dispatch call via the first outbound link, adapted to establish an inbound link with a mobile station (MS) for the dispatch call, adapted to receive using the receiver a request to begin a soft handoff with an adjacent base she from the MS via the inbound link, adapted to notify the adjacent base site of the soft handoff request of the MS, adapted to receive, in response to the request to begin a soft handoff from the MS, an indication of a second outbound link at the adjacent site enabling the soft handoff, and adapted to instruct the transmitter to transmit to the MS an indication of the identity of the second outbound link.

18. The base site of claim 17 wherein the inbound link comprises a low-rate inbound link used for communicate at least one of forward power control information and reverse power information.

19. The base site of claim 17 wherein the first outbound link and the second outbound link each comprises a full-rate CDMA outbound traffic channel.

20. The base site of claim 17 wherein the controller instructs the transmitter to transmit signaling in-band on the first outbound link to convey the identity of the second outbound link.

21. The base site of claim 17 wherein the controller instructs the transmitter to transmit a broadcast page via the paging channel to convey the identity of the second outbound link.

22. A mobile station (MS) comprising:

a transmitter;

a receiver; and

a processor, coupled to the transmitter and the receiver, adapted to instruct the receiver to receive a dispatch call via a first outbound link with a base site, adapted to establish an inbound link with the base site for the dispatch call, adapted to instruct the transmitter to transmit via the inbound link a request to begin a soft handoff with an adjacent base site, and adapted to receive, from the base site using the receiver and in response to the request to begin a soft handoff, an indication of the identity of a second outbound link at the adjacent site with which to begin the soft handoff.

23. The MS of claim 22 wherein the processor is further adapted to instruct the receiver to begin the soft handoff by simultaneously receiving the dispatch call via the first outbound link and the second outbound link.

24. The MS of claim 22 wherein the processor is further adapted to instruct the transmitter to transmit a request to establish an inbound link with the adjacent base site for the dispatch call.