Estimating link qualities in multi-carrier systems

1. A method for estimating qualities of links between a transmitter and a receiver on respective carrier frequencies in a multi-carrier wireless communication system from measurements made during a scanning interval in which pilot signals may be transmitted from the transmitter to the receiver in a plurality of carrier-time bins, each carrier-time bin corresponding to a respective carrier frequency of the multi-carrier system and a respective time slot within the scanning interval, the method comprising:

during the scanning interval, making test measurements in less than all of the carrier-time bins, each test measurement comprising transmitting a respective signal from the transmitter to the receiver in a respective carrier time bin and measuring a strength of the corresponding signal received by the receiver; and

using the test measurements to determine:

a value indicative of a predicted quality of a link between the transmitter and the receiver in a carrier-time bin of the scanning interval in which no test measurement is made during the scanning interval; and

a value indicative of a predicted quality of a link between the transmitter and the receiver over a period of time within or equal to the scanning interval on a carrier frequency for which no test measurement is made in at least one carrier-time bin during said period of time.

2. The method of claim 1 , further comprising:

prior to the scanning interval, making a plurality of preliminary measurements, said preliminary measurements being indicative of at least one of:

a variation with time in a quality of a link between the transmitter and the receiver on at least one of said carrier frequencies in the multi-carrier wireless communication system; and

a correlation between the quality of a link between the transmitter and the receiver on one of said carrier frequencies in the multi-carrier system and a quality of a link between the transmitter and the receiver on at least one different one of said carrier frequencies in the multi-carrier system.

3. The method of claim 1 , wherein said making of said test measurements comprises:

making a first plurality of said test measurements in a first period of the scanning interval, the first plurality of test measurements comprising a respective test measurement on each of the plurality of carrier frequencies.

4. The method of claim 3 , wherein each of the first plurality of test measurements is made in a different respective time slot.

5. The method of claim 3 , wherein said using of the test measurements comprises determining a respective value indicative of a predicted quality of a link between the transmitter and the receiver in each carrier-time bin of the first period of scanning interval in which no test measurement is made from all of the first plurality of measurements.

6. The method of claim 3 , wherein said using of the test measurements comprises determining a respective value indicative of a predicted quality of a link between the transmitter and the receiver in each carrier-time bin of the first period of the scanning interval in which no test measurement is made by multiplying a result of a respective one of the first plurality of test measurements by a respective multiplication factor.

7. The method of claim 6 , wherein the respective multiplication factor is determined from preliminary measurements.

8. The method of claim 3 , wherein said making of said test measurements comprises:

making a second plurality of said test measurements in a second period of the scanning interval, the second plurality of test measurements comprising a respective test measurement on each of the plurality of carrier frequencies.

9. The method of claim 8 , wherein each of the second plurality of test measurements is made in a different respective time slot.

10. The method of claim 8 , wherein said using of the test measurements comprises determining a respective value indicative of a predicted quality of a link between the transmitter and the receiver in each carrier-time bin of the second period of the scanning interval in which no test measurement is made from all of the second plurality of measurements.

11. The method of claim 8 , wherein the second period of the scanning interval is immediately after the first period of the scanning interval.

12. The method of claim 8 , wherein the second period of the scanning interval begins a time interval after the end of the first period of the scanning interval.

13. The method of claim 12 , further comprising determining the delay time interval.

14. The method of claim 12 , wherein said making of said test measurements comprises:

making a third plurality of said test measurements in a third period of the scanning interval, the third period being between the first and second periods.

15. The method of claim 14 , wherein each of the third plurality of test measurements is made in a different respective time slot on the same carrier frequency.

16. The method of claim 14 , wherein said using of the test measurements comprises determining a respective value indicative of a predicted quality of a link between the transmitter and the receiver in each carrier-time bin of the third period of scanning interval in which no test measurement is made from a measurement made in another carrier-time bin of the third time period and at least one test measurement made during the first time period.

17. The method of claim 12 , comprising making no test measurements between the first and second periods.

18. The method of claim 8 , wherein said making of said test measurements comprises:

making a fourth plurality of said test measurements in a fourth period of the scanning interval, the fourth period being after the second period.

19. The method of claim 18 , wherein each of the fourth plurality of test measurements is made in a different respective time slot on the same carrier frequency.

20. The method of claim 1 , wherein the receiver comprises a mobile receiver traveling at a speed v(t), the method further comprising:

measuring a first speed v 0 of the mobile receiver at a first time t o ;

performing a plurality of measurements of received signal strength at the mobile receiver versus time on at least one carrier frequency in a first time period following said first time;

determining from the first plurality of measurements a first value of a parameter indicative of a rate of variation of a received signal strength with time at the mobile receiver resulting from time-dependent fading between the transmitter and the receiver;

measuring a second speed v n of the mobile receiver at a second, later time t n ; and

determining a second value of said parameter, indicative of a second rate of said variation corresponding to speed v n , from the said first value and the first and second speeds.

21. The method of claim 20 , further comprising using said second value to determine at least one of said values indicative of a predicted quality of a link.

22. The method of claim 20 , wherein said performing of said plurality of measurements is performed before the scanning interval.

23. The method of claim 20 , further comprising determining a measurement time interval according to the first speed, wherein said performing a plurality of measurements comprises performing a respective measurement of received signal strength at each of a series of times, adjacent said times being separated by the measurement time interval.

24. The method of claim 20 , wherein said second time falls within the scanning interval.

25. The method of claim 20 , wherein said parameter indicative of a rate of variation of a received signal strength with time is an exponential time decay rate parameter u.

26. The method of claim 25 , wherein said first value is u 0 , said second value is u n , and u n =u 0 (v n /v 0 ).

27. A method of determining a value of a parameter indicative of a rate of variation of a received signal strength with time at a mobile receiver, traveling at a speed v(t), as a result of time-dependent fading between a transmitter and the mobile receiver, the method comprising:

measuring a first speed v 0 of the mobile receiver at a first time t o ;

performing a plurality of measurements of received signal strength at the mobile receiver versus time in a first time period following said first time;

determining from the first plurality of measurements a first value of a parameter indicative of a first rate of said variation of received signal strength with time;

measuring a speed v n of the mobile receiver at a later time t n ; and

determining a second value of said parameter, indicative of a second rate of said variation corresponding to speed v n , from the first said value and the first and second speeds.

28. The method of claim 27 , further comprising determining a measurement time interval according to the first speed, wherein said performing of said plurality of measurements comprises performing a respective measurement of received signal strength at each of a series of times, adjacent said times being separated by the measurement time interval.

29. The method of claim 28 , wherein said parameter indicative of a rate of variation of a received signal strength with time comprises an exponential time decay rate parameter u.

30. The method of claim 29 , wherein said first value is u 0 , said second value is u n , and u n =u 0 ·(v n /v 0 ).

31. A computer readable medium having stored thereon instructions arranged, when executed, to implement a method for estimating qualities of links between transmitter and receiver on respective carrier frequencies in a multi-carrier wireless communication system from measurements made during a scanning interval in which pilot signals may be transmitted from the transmitter to the receiver in a plurality of carrier-time bins, each carrier-time bin corresponding to a respective carrier frequency of the multi-carrier system and a respective time slot within the scanning interval, the method comprising:

during the scanning interval, making test measurements in less than all of the carrier-time bins, each test measurement comprising transmitting a respective signal from the transmitter to the receiver in a respective carrier time bin and measuring a strength of the corresponding signal received by the receiver; and

using the test measurements to determine:

a value indicative of a predicted quality of a link between the transmitter and the receiver in a carrier-time bin of the scanning interval in which no test measurement is made during the scanning interval; and

a value indicative of a predicted quality of a link between the transmitter and the receiver over a period of time within or equal to the scanning interval on a carrier frequency for which no test measurement is made in at least one carrier-time bin during said period of time.