Method and apparatus for performing mobile assisted hard handoff between communication systems

• US 6,304,755 B1
• Filed: 05/10/1999
• Issued: 10/16/2001
• Est. Priority Date: 01/15/1997
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Tiedemann, Edward G. Jr., Wheatley, Charles E. III, Chen, Tao
• Primary Examiner(s): Trost, William
• Assistant Examiner(s): SOBUTKA, PHILIP
• Application Number:
  US09/307,878
• Time in Patent Office: 890 Days
• Field of Search: 455/437, 455/438, 455/426, 455/510, 455/524, 455/525, 455/422, 455/436, 455/552, 370/331, 370/332, 370/328, 375/130
• US Class Current: 455/437
• CPC Class Codes: H04W 36/0061 of neighbour cell information
• CPC Class Codes: H04W 36/0066 of control information between different types of networks in order to establish a new radio link in the target network
• CPC Class Codes: H04W 36/0079 in case of hand-off failure or rejection
• CPC Class Codes: H04W 36/0094 Definition of hand-off measurement parameters
• CPC Class Codes: H04W 36/14 Reselecting a network or an air interface
• CPC Class Codes: H04W 36/30 by measured or perceived connection quality data
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A method and apparatus for performing inter-system hard handoff between communication systems or inter-frequency hard handoff within a CDMA communication system is disclosed. The purpose of this invention is to reduce the probability of dropped calls during inter-system hard handoff. In the event that a hard handoff attempt is unsuccessful, the mobile station will return to the original system with information which the communication system of the present invention uses to assist in the performance of future handoff attempts. Alternatively, with no handoff attempt made, the mobile station monitors the destination system then returns to the original system with information used to assist in subsequent handoff attempts. The information returned from monitoring a CDMA system consists of results of a search for one or more pilots given at offsets in a specific list provided to the mobile station by the base station or a set of offsets based upon a predetermined search algorithm.

Claims

1. In a wireless communication system wherein a mobile station is moving from the coverage area of an origination system operating at a first frequency into the coverage area of a destination system operating at a second frequency, a method for providing handoff from said origination system to said destination system, the method comprising:

predicting at least one PN offset associated with the destination system;

transmitting, at the first frequency, from said origination system to said mobile station a set of search parameter data associated with the at least one PN offset;

determining at said mobile station the availability of said destination system in accordance with said set of search parameter data;

transmitting from said mobile station to said origination system a message indicative of the received strength of signals associated with the at least one PN offset measured at the mobile station;

generating at said origination system a set of acquisition parameters in accordance with said message from said mobile station; and

attempting at said mobile station to acquire said destination system in accordance with said set of acquisition parameters.

2. The method of claim 1, wherein said generating further comprises electing at said origination system a new set of at least one PN offset associated with the destination system.

3. The method of claim 1, wherein said attempting further comprises electing at said mobile station a new set of at least one PN offset associated with the destination system.

4. A method of providing handoff of a mobile station from an origination system operating at a first frequency to a destination system operating at a second frequency, comprising:

receiving from the origination system at least one PN offset associated with the destination system and a minimum total received pilot value;

tuning, at the mobile station, to the second frequency;

determining a pilot energy associated with the at least one PN offset received at the mobile station;

comparing the determined pilot energy with the minimum total received pilot value; and

sending, from the mobile station to the origination system, a message based on said comparing.

5. The method of claim 4 wherein said message comprises said determined pilot energy.

6. The method of claim 4 wherein said receiving further comprises receiving from the origination system a set of additional parameters comprising instructions to the mobile station following a failed hard handoff attempt.

7. The method of claim 6 wherein said sending is based on said instructions.

8. The method of claim 4 further comprising performing a search at the second frequency based on said comparing.

9. The method of claim 8 wherein said performing a search is based on said instructions.

10. A method of providing handoff of a mobile station from an origination system operating at a first frequency to a destination system operating at a second frequency, comprising:

receiving from the origination system at least one PN offset associated with the destination system and a received power threshold;

tuning, at the mobile station, to the second frequency;

determining a pilot energy associated with the at least one PN offset received at the mobile station;

measuring in-band energy received by the mobile station at the second frequency;

comparing the measured in-band energy with the received power threshold; and

sending, from the mobile station to the origination system, a message based on said comparing.

11. The method of claim 10 wherein said message comprises said measured in-band energy.

12. The method of claim 10 wherein said receiving further comprises receiving from the origination system a set of additional parameters comprising instructions to the mobile station following a failed hard handoff attempt.

13. The method of claim 12 wherein said sending is based on said instructions.

14. The method of claim 10 further comprising performing a search at the second frequency based on said comparing.

15. The method of claim 14 wherein said performing a search is based on said instructions.

16. A method of providing handoff of a mobile station from an origination system operating at a first frequency to a destination system operating at a second frequency, comprising:

sending from the origination system to the mobile station at least one PN offset associated with the destination system and a minimum total received pilot value;

sending from the origination system to the mobile station a message directing the mobile station to perform a hard handoff to the destination system;

receiving at the origination system from the mobile station a message based on a total received pilot value measured by the mobile station at the second frequency; and

sending to the mobile station at least one adjusted PN offset having a different value than said at least one PN offset based on said message.

17. The method of claim 16 wherein said sending to the mobile station further comprises sending to the mobile station a set of additional parameters comprising instructions to the mobile station following a failed hard handoff attempt.

18. The method of claim 16 wherein said message further comprises measurements from a search performed at the second frequency.

19. A method of providing handoff of a mobile station from an origination system operating at a first frequency to a destination system operating at a second frequency, comprising:

sending from the origination system to the mobile station at least one PN offset associated with the destination system and a received power threshold;

sending from the origination system to the mobile station a message directing the mobile station to perform a hard handoff to the destination system;

receiving at the origination system from the mobile station a message based on a received power measured by the mobile station at the second frequency; and

sending to the mobile station at least one adjusted PN offset having a different value than said at least one PN offset based on said message.

20. The method of claim 19 wherein said sending to the mobile station further comprises sending to the mobile station a set of additional parameters comprising instructions to the mobile station following a failed hard handoff attempt.

21. The method of claim 19 wherein said message further comprises measurements from a search performed at the second frequency.

22. A mobile station apparatus comprising:

a receiver configured to tune to one of at least two system frequencies based on a frequency control signal; and

a control processor configured to generate the frequency control signal directing said receiver to tune to a first frequency associated with an origination system, to receive from the origination system at a first frequency at least one PN offset associated with a destination system and a minimum total received pilot value, to direct said receiver to tune to a second frequency associated with the destination system, to compare a pilot energy measured at the second frequency with the minimum total received pilot value to generate a comparison, to direct said receiver to tune back to the first frequency based on the comparison, and to generate a message for the origination system based on the comparison.

23. The mobile station apparatus of claim 22 wherein said message comprises the pilot energy measured at the second frequency.

24. The mobile station apparatus of claim 22 wherein said control processor is further configured to receive from the origination system a set of additional parameters comprising instructions to the mobile station following a failed hard handoff attempt.

25. The mobile station apparatus of claim 24 further comprising a searcher configured to perform a search at the second frequency based on commands from said control processor, and wherein said control processor directs said searcher to perform the search based on the instructions.

26. A mobile station apparatus comprising:

a receiver configured to tune to one of at least two system frequencies based on a frequency control signal; and

a control processor configured to generate the frequency control signal directing said receiver to tune to a first frequency associated with an origination system, to receive from the origination system at a first frequency at least one PN offset associated with a destination system and a received power threshold, to direct said receiver to tune to a second frequency associated with the destination system, to compare a received power measured at the second frequency with the received power threshold to generate a comparison, to direct said receiver to tune back to the first frequency based on the comparison, and to generate a message for the origination system based on the comparison.

27. The mobile station apparatus of claim 26 wherein said message comprises the received power measured at the second frequency.

28. The mobile station apparatus of claim 26 wherein said control processor is further configured to receive from the origination system a set of additional parameters comprising instructions to the mobile station following a failed hard handoff attempt.

29. The mobile station apparatus of claim 28 further comprising a searcher configured to perform a search at the second frequency based on commands from said control processor, and wherein said control processor directs said searcher to perform the search based on the instructions.