Method and system for frequency scan using an adaptive measurement interval

1. A method of determining a power value at a user device for subsequent use in cell selection or cell re-selection, the method comprising:

determining a first power value at a carrier frequency in respect of a first measurement time interval by determining at least one of a first and second metric for each of at least one channel hypotheses, each channel hypothesis having a hypothetical occupied portion and a hypothetical guard band portion, a first metric based on a power measurement and at least one additional power measurement of the hypothetical occupied portion and a second metric based on a difference between the power measurement and the at least one additional power measurement of the hypothetical occupied portion and a power measurement and at least one additional power measurement of the hypothetical guard band portion;

determining whether or not the first power value meets at least one criterion;

when the first power value does not meet the at least one criterion, determining at least one additional power value at the carrier frequency in respect of a second measurement time interval;

selecting at least one power value from a set of power values that have been determined, the set including the at least one additional power value, wherein selecting the at least one power value includes at least determining a maximum power value from the set of power values that have been determined;

determining the power value for the calculation of an RSSI metric for use in cell selection or cell re-selection based on the selected at least one power value.

2. The method of claim 1 wherein selecting at least one power value comprises:

if there is a power value of the at least one additional power value that satisfies the at least one criterion, selecting at least that power value, in which case the power value for use in cell selection or cell re-selection is set to the power value of the at least one additional power value that satisfies the at least one criterion.

3. The method of claim 1 wherein selecting the at least one power value further comprises:

generating a subset of the set of power values by selecting for inclusion in the subset the maximum power value and any power values of the set of power values that are within a specified range of the maximum power value of the set of power values.

4. The method of claim 3 wherein determining the power value for use in cell selection and cell re-selection comprises determining an average power value from the subset of the set of power values.

5. The method of claim 1 wherein determining at least one additional power value comprises determining at least one additional power value until either one of:

a current additional power value meets the at least one criterion; or

a maximum number of repetitions of determining at least one additional power value have been performed.

6. The method of claim 1 wherein determining a power value is performed for each of one or more of a plurality of candidate carrier frequencies.

7. The method of claim 6 wherein determining a power value is performed for each of one or more channel hypothesis associated with at least one of the plurality of candidate carrier frequencies.

8. The method of claim 1 wherein selecting the at least one channel hypothesis for further processing comprises:

arranging the metrics determined for the plurality of channel hypotheses according to order of magnitude and selecting N f metrics, where N f ≧1, each associated with a channel hypothesis based on the largest magnitude metrics; and

selecting at least one of the N f channel hypotheses for further processing based on a largest magnitude metric.

9. The method of claim 1 wherein determining a first power value in respect of a first measurement time interval comprises:

determining the first power value in respect of a first measurement time interval for each of at least one channel hypothesis.

10. The method of claim 9 wherein determining at least one additional power value comprises determining at least one additional power value until either one of:

a current metric meets the at least one criterion; or

a maximum number of repetitions of determining the metric have been performed.

11. The method of claim 1 , wherein determining a first power value in respect of a first measurement time interval comprises:

for each of a plurality of candidate carrier frequencies:

determining a first metric in respect of a power measurement of a first measurement time interval; and

determining a second metric in respect of the power measurement of the first measurement time interval.

12. The method of claim 11 , further comprising:

for the plurality of candidate carrier frequencies:

arranging the second metrics, each associated with a respective candidate carrier frequency, in order of magnitude and selecting N S , where N S ≧1, largest second metrics; and

wherein determining whether or not the first power value meets at least one criterion comprises:

for each of the N S candidate carrier frequencies associated with the second metrics, determining whether a first metric associated with the same candidate carrier frequency meets at least one criterion.

13. The method of claim 12 , wherein determining whether the first metric meets at least one criterion comprises:

for each of the N s candidate carrier frequencies:

when the first metric does not meet the at least one criterion;

determining at least one additional power measurement; and

wherein selecting at least one power value from a set of power values that have been determined comprises:

recalculating the first and second metrics based upon the power measurement of the first measured time interval and the at least one additional power measurement.

14. The method of claim 13 , wherein determining the power value for use in cell selection or cell re-selection based on the selected at least one power value comprises:

re-arranging all of the second metrics, including original and re-calculated metrics, in order of magnitude and selecting the N S , where N S ≧1, largest second metrics;

for each of the N S candidate carrier frequencies associated with the second metrics, determining whether a first metric associated with the same candidate carrier frequency meets at least one criterion.

15. The method of claim 14 further comprising:

arranging the candidate carrier frequencies associated with the at least N s second metrics in order of magnitude and selecting N f metrics, where N f ≧1, based on the largest magnitude second metrics; and

selecting at least one of the N f candidate carrier frequencies for further processing.

16. The method of claim 11 wherein determining the first and second metrics is performed for a plurality of channel hypotheses associated with at least one of the plurality of candidate carrier frequencies.

17. The method of claim 13 wherein re-calculating the first and second metrics comprises:

re-calculating the first and second metrics based upon a power value based upon a maximum power value determined from a set of power measurements including the power measurement value of a first measurement time interval and the at least one additional power measurement.

18. A wireless device comprising:

a processor;

an adaptive measurement interval function configured to:

determine a first power value at a carrier frequency in respect of a first measurement time interval by determining at least one of a first and second metric for each of at least one channel hypotheses, each channel hypothesis having a hypothetical occupied portion and a hypothetical guard band portion, a first metric based on a power measurement and at least one additional power measurement of the hypothetical occupied portion and a second metric based on a difference between the power measurement and the at least one additional power measurement of the hypothetical occupied portion and a power measurement and at least one additional power measurement of the hypothetical guard band portion;

determine whether or not the first power value meets at least one criterion;

when the first power value does not meet the at least one criterion, determine at least one additional power value at the carrier frequency in respect of a second measurement time interval;

select at least one power value from a set of power values that have been determined, the set including the at least one additional power value, wherein selecting the at least one power value includes at least determining a maximum power value from the set of power values that have been determined;

determine a power value for the calculation of an RSSI metric for use in cell selection or cell re-selection based on the selected at least one power value.