Forward link inter-generation soft handoff between 2G and 3G CDMA systems

• US 6,804,519 B1
• Filed: 03/27/2003
• Issued: 10/12/2004
• Est. Priority Date: 12/02/1998
• Status: Expired due to Term

• Current Assignee: Intel Deutschland GmbH (Intel Corporation)
• Original Assignee: Infineon Technologies North America Corporation (Infineon Technologies AG)
• Inventors: Czaja, Stanislaw, Anderson, Kraig
• Primary Examiner(s): Trost, William
• Assistant Examiner(s): ZEWDU, MELESS NMN
• Application Number:
  US10/402,041
• Time in Patent Office: 565 Days
• Field of Search: 455/422.1, 455/424, 455/425, 455/436, 455/437, 455/442, 455/443, 455/448, 455/452.2, 455/444, 455/464, 455/550.1, 370/320, 370/331, 370/332, 370/335, 370/342, 370/365, 370/441
• US Class Current: 455/442
• CPC Class Codes: H04W 36/14 Reselecting a network or an air interface
• CPC Class Codes: H04W 36/18 for allowing seamless reselection, e.g. soft reselection
• CPC Class Codes: H04W 36/30 by measured or perceived connection quality data

Abstract

In a CDMA cellular radiotelephone system, a soft handoff (SHO) is performed when a mobile station communicates with a new inter-generation base station, without interrupting communications with the old base station. Currently, a SHO can only be used between CDMA channels having identical frequency assignments and within the same system generation (i.e., 2G⇄2G, or 3G⇄3G, where 2G is a second generation system, and 3G is a third generation system). The proposed IS-2000 standard for a 2G⇄3G handoff is a hard handoff or “Break-Before-Make” procedure, which greatly reduces the quality of service (QOS). The present invention allows for SHO between second and third generation CDMA systems (2G⇄3G and 3G⇄2G), by modifying the proposed messaging structure. This provides a smooth service transition when a mobile station travels from one service area (i.e., 2G), to another service area (i.e., 3G), using the SHO or “Make-Before-Break” approach.

Claims

1. A CDMA cellular radiotelephone system, comprising:

a first base station;

a second base station;

a base station controller; and

a mobile station,

wherein the mobile station is operable to;

receive from the first base station a first data signal that is modulated according to a first modulation scheme;

receive from the second base station a second data signal that is modulated according to a second modulation scheme, the second modulation scheme being different from the first modulation scheme;

receive from the base station controller modulation information identifying the modulation scheme used by the second system; and

perform a soft handoff between the first and second base stations by;

using the received modulation information to select a soft handoff procedure from a plurality of soft handoff procedures including a first procedure and a second procedure; and

if the first procedure is selected;

demodulating and decoding the first data signal while independently demodulating and decoding the second data signal; and

dropping the first data signal upon determining that the second data signal is stronger than the first data signal;

if the second procedure is selected;

demodulating the first data signal while independently demodulating the second data signal;

combining the first and second data signals and decoding the two signals together; and

dropping the first data signal upon determining that the second data signal is stronger than the first data signal.

2. The system of claim 1, wherein:

the first base station is an IS-95 CDMA base station and the second base station is an IS-2000 CDMA base station.

3. The system of claim 1, wherein:

the first and second modulation schemes differ in that they have different spreading rates.

4. The system of claim 1, wherein:

each modulation scheme has a spreading rate, a data rate and a coding rate; and

the received modulation information identifies the spreading, data, and coding rates of the second modulation scheme.

5. The system of claim 4, wherein using the received modulation information to select a handoff procedure includes:

using the received modulation information to determine whether the first and second modulation schemes have the same spreading, data, and coding rates.

6. The system of claim 5, wherein:

the first procedure is selected if the first and second modulation schemes have the same data rates but different spreading and coding rates.

7. The system of claim 5, wherein:

the second procedure is selected if the first and second modulation schemes have the same data and coding rates, but different spreading rates.

8. The system of claim 1, wherein determining that the second data signal is stronger than the first data signal includes:

determining that the strength of the first data signal has dropped below a threshold energy value.

9. The system of claim 8, wherein:

the received modulation information specifies the threshold energy value.

10. The system of claim 1, wherein determining that the second data signal is stronger than the first data signal includes:

determining that the number of good frames that have been decoded from the second data signal meets a threshold number of frames.

11. The system of claim 10, wherein:

the received modulation information specifies the threshold frame number of frames.

12. A mobile cellular radiotelephone station, comprising:

means for receiving from a first base station a first data signal that is modulated according to a first modulation scheme;

means for receiving from a second base station a second data signal that is modulated according to a second modulation scheme, the second modulation scheme being different from the first modulation scheme;

means for receiving from a base station controller modulation information identifying the modulation scheme used by the second system; and

means for perform a soft handoff between the first and second base stations by;

using the received modulation information to select a soft handoff procedure from a plurality of soft handoff procedures including a first procedure and a second procedure; and

if the first procedure is selected;

demodulating and decoding the first data signal while independently demodulating and decoding the second data signal; and

dropping the first data signal upon determining that the second data signal is stronger than the first data signal;

if the second procedure is selected;

demodulating the first data signal while independently demodulating the second data signal;

combining the first and second data signals and decoding the two signals together; and

dropping the first data signal upon determining that the second data signal is stronger than the first data signal.

13. The mobile station of claim 12, wherein:

the first base station is an IS-95 CDMA base station and the second base station is an IS-2000 CDMA base station.

14. The mobile station of claim 12, wherein:

the first and second modulation schemes differ in that they have different spreading rates.

15. The mobile station of claim 12, wherein:

each modulation scheme has a spreading rate, a data rate and a coding rate; and

the received modulation information identifies the spreading, data, and coding rates of the second modulation scheme.

16. The mobile station of claim 15, wherein using the received modulation information to select a handoff procedure includes:

using the received modulation information to determine whether the first and second modulation schemes have the same spreading, data, and coding rates.

17. The mobile station of claim 16, wherein:

the first procedure is selected if the first and second modulation schemes have the same data rates but different spreading and coding rates.

18. The mobile station of claim 16, wherein:

the second procedure is selected if the first and second modulation schemes have the same data and coding rates, but different spreading rates.

19. The mobile station of claim 12, wherein determining that the second data signal is stronger than the first data signal includes:

determining that the strength of the first data signal has dropped below a threshold energy value.

20. The mobile station of claim 19, wherein:

the received modulation information specifies the threshold energy value.

21. The mobile station of claim 12, wherein determining that the second data signal is stronger than the first data signal includes:

determining that the number of good frames that have been decoded from the second data signal meets a threshold number of frames.

22. The mobile station of claim 21, wherein:

the received modulation information specifies the threshold frame number of frames.