Method for utilizing negative T—COMP to improve handoff reliability

• US 6,233,455 B1
• Filed: 05/03/1999
• Issued: 05/15/2001
• Est. Priority Date: 05/03/1999
• Status: Active Grant

• Current Assignee: Hanger Solutions, LLC (IP Investments Group LLC)
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Chheda, Ashvin, Jalali, Ahmad, Ramakrishna, Deepa
• Primary Examiner(s): VO, NGUYEN THANH
• Application Number:
  US09/304,144
• Time in Patent Office: 743 Days
• Field of Search: 455/436, 455/437, 455/442, 455/525, 370/331
• US Class Current: 455/437
• CPC Class Codes: H04W 36/18 for allowing seamless reselection, e.g. soft reselection

Abstract

A pre-determined negative constant is utilized in soft handoff mode to permit a new pilot signal to be added to an wireless phone'"'"'s active set. The negative constant is combined with the weakest pilot signal in the active set and then compared to the new pilot signal strength which allows the new pilot to trigger a Pilot Strength Measurement Message (PSMM) even when the new pilot signal is weaker than all active set pilot signals. The negative constant provides a soft handoff while maintaining or reducing drop rate probabilities and frame error rates. After initially triggering a PSMM, the next instance the new pilot may ordinarily cause a PSMM to be triggered is when the new pilot signal exceeds the strongest active set pilot signal. Triggering a PSMM when exceeding the strongest active set signal may increase the probability of dropped signals. To reduce the probability of dropped signals, a negative constant is utilized during soft handoff to add a new pilot to an active set. This step would also decrease the probability that the new pilot will overpower a weaker active set pilot signal.

Claims

1. A method for improving soft handoff reliability, comprising:

combining a pre-determined negative constant with a signal strength of a weakest pilot signal within an active set of pilot signals to obtain a result lower than the signal strength of the weakest pilot signal;

comparing the result with a signal strength for a new pilot signal not part of the active set;

if the result is less than or equal to the signal strength of the new pilot signal, initiating a message for adding the new pilot signal to the active set.

2. The method of claim 1, further comprising:

receiving a request for entry of the new pilot signal into the active set;

determining individual signal strengths of all pilot signals in the active set;

determining individual signal strengths of all pilot signals in a candidate set of pilot signals, wherein the candidate set includes the new pilot signal; and

ranking the signal strengths from weakest to strongest in both the active and candidate sets.

3. The method of claim 1, further comprising:

determining a first constant by subtracting the signal strength of the weakest pilot signal within the active set from a signal strength of a strongest pilot signal within the active set;

subtracting the signal strength for the new pilot signal from the signal strength of the strongest pilot signal within the active set to obtain an outcome;

comparing the first constant to an absolute value of the outcome; and

adding the new pilot signal to the active set if the absolute value of the outcome is less than or equal to the first constant.

4. The method of claim 1, wherein the step of combining the pre-determined negative constant with a signal strength of a weakest pilot signal within an active set of pilot signals to obtain a result lower than the signal strength of the weakest pilot signal further comprises:

detecting the new pilot signal, wherein the new pilot signal is not included in the active set and is increasing in strength.

5. The method of claim 4, further comprising:

determining a factor by subtracting the signal strength of the new pilot signal from a signal strength of a strongest pilot signal in the active set; and

comparing the factor to a second pre-determined constant.

6. The method of claim 5, further comprising:

if the factor is less than or equal to the second constant, adding the new pilot signal to the active set.

7. The method of claim 1, further comprising:

in determining whether to drop the weakest pilot signal from the active set,

computing a difference between the signal strength of the weakest pilot signal and a signal strength of a strongest pilot signal within the active set;

comparing an absolute value of the difference to a predefined amount;

responsive to determining that the absolute value of the difference exceeds the predefined amount, dropping the weakest pilot signal from the active set and recalculating parameters for the active set of pilot signals;

determining whether any parameters for the active set of pilot signals have changed;

if any parameter for the active set of pilot signals has changed, sending a message with all parameter changes to all pilot sectors having a pilot signal in the active set; and

if no parameter for the active set of pilot signals has changed, acknowledging a message requesting addition of the new pilot signal to the active set in order to prevent further requests.

8. The method in claim 1, wherein the step of initiating a message for adding the new pilot signal to the active set further comprises:

requesting entry of the new pilot signal into the active set;

sending a first message to all pilot sectors having a pilot signal in the active set to add the new pilot;

adding the new pilot to the active set; and

receiving a second message acknowledging the first message.

9. An apparatus for improving soft handoff reliability, comprising:

means for combining a pre-determined negative constant with a signal strength of a weakest pilot signal within an active set of pilot signals to obtain a result lower than the signal strength of the weakest pilot signal;

means for comparing the result with a signal strength of a new pilot signal not part of the active set;

means, responsive to the result being less than or equal to the signal strength of the new pilot signal, for initiating a message for adding the new pilot signal to the active set.

10. The apparatus of claim 9, further comprising:

means for receiving a request for entry of the new pilot signal into the active set;

means for determining individual signal strengths of all pilot signals in the active set;

means for determining individual signal strengths of all pilot signals in a candidate set of pilot signals, wherein the candidate set includes the new pilot signal; and

means for ranking the signal strengths from weakest to strongest in both the active and candidate sets.

11. The apparatus of claim 9, further comprising:

means for determining a first constant by subtracting the signal strength of the weakest pilot signal within the active set from a signal strength of a strongest pilot signal within the active set;

means for subtracting the signal strength of the new pilot signal from the signal strength of the strongest pilot signal within the active set to obtain an outcome;

means for comparing the first constant to an absolute value of the outcome; and

means for adding the new pilot signal to the active set if the absolute value of the outcome is less than or equal to the first constant.

12. The apparatus of claim 9, wherein the means for combining the pre-defined negative constant with a signal strength of a weakest pilot signal within an active set of pilot signals to obtain a result lower than the signal strength of the weakest pilot signal further comprising:

means for detecting the new pilot signal, wherein the new pilot signal is not included in the active set and is increasing in strength.

13. The apparatus of claim 12, further comprising:

means for determining a factor by subtracting the signal strength of the new pilot signal from a signal strength of a strongest pilot signal in the active set; and

means for comparing the factor to a second pre-determined constant.

14. The apparatus of claim 13, further comprising:

means for adding the new pilot signal to the active set if the factor is less than or equal to the second constant.

15. The apparatus of claim 9, further comprising:

means employed in determining whether to drop the weakest pilot signal from the active set, including;

means for computing a difference between the signal strength of the weakest pilot signal and a signal strength of a strongest pilot signal within the active set;

means for comparing an absolute value of the difference to a predefined amount;

means, responsive to determining that the absolute value of the difference exceeds the predefined amount, for dropping the weakest pilot signal from the active set and recalculating parameters for the active set of pilot signals;

means for determining whether any parameters for the active set of pilot signals have changed;

means, responsive to any parameter for the active set of pilot signals having changed, for sending a message with all parameter changes to all pilot sectors having a pilot signal in the active set; and

means, responsive to no parameter for the active set of pilot signals having changes, for acknowledging a message requesting addition of the new pilot signal to the active set in order to prevent further requests.

16. The apparatus in claim 9, wherein means for initiating a message for adding the new pilot signal to the active set further comprises:

means for requesting entry of the new pilot signal into the active set;

means for sending a first message to all pilot sectors having a pilot signal in the active set to add the new pilot;

means for adding the new pilot to the active set; and

means for receiving a second message acknowledging the first message.

17. A program of instructions for a telecommunications device within an instruction bearing medium for improving soft handoff reliability, comprising:

instructions within the instruction bearing medium for combining a pre-determined negative constant with a signal strength of a weakest pilot signal within an active set of pilot signals to obtain a result lower than the signal strength of the weakest pilot signal;

instructions within the instruction bearing medium for comparing the result with a signal strength of a new pilot signal not part of the active set;

instructions within the instruction bearing medium for initiating a message for adding the new pilot signal to the active set if the result is less than or equal to the new pilot signal strength.

18. The program of instructions of claim 17, further comprising:

instructions within the instruction bearing medium for receiving a request for entry of the new pilot signal into the active set;

instructions within the instruction bearing medium for determining individual signal strengths of all pilot signals in the active set;

instructions within the instruction bearing medium for determining individual signal strengths of all pilot signals in a candidate set of pilot signals, wherein the candidate set includes the new pilot signal; and

instructions within the instruction bearing medium for ranking the signal strengths from weakest to strongest in both the active and candidate sets.

19. The program of instructions of claim 17, further comprising:

instructions within the instruction bearing medium for determining a first constant by subtracting the signal strength of the weakest pilot signal within the active set from a signal strength of a strongest pilot signal within the active set;

instructions within the instruction bearing medium for subtracting the signal strength of the new pilot signal from the signal strength of the strongest pilot signal within the active set to obtain an outcome;

instructions within the instruction bearing medium for comparing a first constant to an absolute value of the outcome; and

instructions within the instruction bearing medium for adding the new pilot signal to the active set if the absolute value of the outcome is less than or equal to the first constant.

20. The program of instructions of claim 17, wherein instructions for combining the pre-determined negative constant with a signal strength of a weakest pilot signal within an active set of pilot signals to obtain a result lower than the signal strength of the weakest pilot signal further comprises:

instructions within the instruction bearing medium for detecting the new pilot signal, wherein the new pilot signal is not included in the active set and is increasing in strength.

21. The program of instructions of claim 20, further comprising:

instructions within the instruction bearing medium for determining a factor by subtracting the signal strength of the new pilot signal from a signal strength of a strongest pilot signal in the active set; and

instructions within the instruction bearing medium for comparing the factor to a second pre-determined constant.

22. The program of instructions of claim 21, further comprising:

instructions within the instruction bearing medium for adding the new pilot signal to the active set if the factor is less than or equal to the second constant.

23. The program of instructions of claim 17, further comprising:

instructions within the instruction bearing medium for determining whether to drop the weakest pilot signal from the active set by;

computing a difference between the signal strength of the weakest pilot signal and a signal strength of a strongest pilot signal within the active set;

comparing an absolute value of the difference to a predefined amount;

responsive to determining that the absolute value of the difference exceeds the predefined amount, dropping the weakest pilot signal from the active set and recalculating parameters for the active set of pilot signals;

determining whether any parameters for the active set of pilot signals have changed;

sending a message with all parameter changes to all pilot sectors having a pilot signal in the active set if any parameter for the active set of pilot signals has changed; and

acknowledging a message requesting addition of the new pilot signal to the active set in order to prevent further requests if no parameter for the active set of pilot signals has changed.

24. The program of instructions of claim 17, wherein the instructions for adding the new pilot signal to the active set further comprise:

instructions within the instruction bearing medium for requesting entry of the new pilot signal into the active set;

instructions within the instruction bearing medium for sending a first message to all pilot sectors having a pilot signal in the active set to add the new pilot;

instructions within the instruction bearing medium for adding the new pilot to the active set; and

instructions within the instruction bearing medium for receiving a second message acknowledging the first message.