Method and device in a communication network

1. A method of estimating a quality of a signal, the method in a first device comprising:

measuring a signal transmitted from a second device to a third device;

determining a value of a metric from an autocorrelation function of the measured signal by calculating a magnitude of the autocorrelation function and adjusting or zeroing a central tap in an output of the step of calculating; and

determining an estimate of the quality of the signal from the determined metric.

2. The method as claimed in claim 1 , wherein the step of measuring comprises measuring the signal in the time domain, and the step of determining a value of a metric comprises determining the autocorrelation function of the time domain signal and noise.

3. The method as claimed in claim 1 , wherein the step of determining a value of a metric comprises determining the autocorrelation function comprises: normalizing the measured signal to give a sequence r; taking the fast Fourier transform of this sequence to give f; determining the squared magnitude of each sample in f; and taking the inverse fast Fourier transform of the sequence resulting from the step of determining the squared magnitude to give an autocorrelation sequence a.

4. The method as claimed in claim 1 , wherein the step of determining a value of a metric from an autocorrelation function of the measured signal comprises calculating the squared magnitude of the autocorrelation function.

5. The method as claimed in claim 1 , wherein the step of determining a value of a metric further comprises adjusting or zeroing the tap adjacent the central tap in the output of the step of calculating.

6. The method as claimed in claim 1 , wherein the step of determining a value of a metric comprises: identifying the tap with the largest magnitude in the taps remaining in the output of the step of calculating; and setting the metric to the value of the magnitude of the identified tap.

7. The method as claimed in claim 4 , wherein the step of determining a value of a metric comprises adjusting or zeroing the central tap in the output of the step of calculating, and wherein the step of determining a value of a metric further comprises: identifying the tap with the largest squared magnitude in the taps remaining in the output of the step of calculating; and setting the metric to the value of the squared magnitude of the identified tap.

8. The method as claimed in claim 6 , wherein the step of determining a value of a metric further comprises: adjusting the value of the metric based on the distance of the identified tap from the central tap.

9. The method as claimed in claim 6 wherein the step of determining a value of a metric further comprises: adjusting the value of the metric based on a function of a peak to average power ratio of the measured signal.

10. The method as claimed in claim 9 , wherein the step of adjusting the value of the metric based on a function of a peak to average power ratio of the measured signal comprises: in the event that the peak to average power ratio of the measured signal is below a threshold value, adjusting the value of the metric to a minimum value.

11. The method as claimed in claim 1 , wherein the step of determining an estimate of the quality of the signal from the determined metric comprises comparing the determined metric to a look-up table.

12. The method as claimed in claim 1 , wherein the step of determining an estimate of the quality of the signal from the determined metric comprises using a curve-fitting technique to match the determined metric to a predetermined relationship between values for the metric and the quality of the signal.

13. The method as claimed in claim 1 , wherein the step of measuring comprises measuring a Zadoff-Chu reference signal transmitted from the second device to the third device.

14. The method as claimed in claim 13 , wherein the step of measuring a Zadoff-Chu reference signal comprises estimating the position of the Zadoff-Chu reference signal in time.

15. The method as claimed in claim 13 , wherein the step of measuring comprises measuring a portion of the Zadoff-Chu reference signal.

16. The method as claimed in claim 1 , further comprising the step of using a scheduler to ensure that no signals will be transmitted to the first device from other devices associated therewith that might interfere with the execution of the step of measuring.

17. The method as claimed in claim 1 , wherein the quality of the signal is a signal to noise ratio.

18. The method as claimed in claim 1 , wherein the first device is a femtocell base station, the second device is a mobile device and the third device is a macrocell base station or another femtocell base station, and wherein the mobile device is associated with the macrocell base station or said another femtocell base station.

19. A network element for use in a communication network, the network element comprising a first device configured to:

measure a signal transmitted from a second device to a third device;

determine a value of a metric from an autocorrelation function of the measured signal by calculating a magnitude of the autocorrelation function and adjusting or zeroing a central tap in an output of the step of calculating; and

determine an estimate of the quality of the signal from the determined metric.

20. The network element as claimed in claim 19 , wherein the network element comprises a femtocell base station.

21. A method of estimating a quality of a signal, the method in a first device comprising:

measuring a signal transmitted from a second device to third device;

determining a value of metric from an autocorrelation function of the measured signal which includes calculating the magnitude of the autocorrelation function and adjusting or zeroing a central tap in an output resulting from the calculating; and

determining an estimate of the quality of the signal from the determined metric.

22. A method of estimating a quality of a signal, the method in a first device comprising:

measuring a signal transmitted from a second device to a third device;

determining a value of a metric from an autocorrelation function of the measured signal by calculating a squared magnitude of the autocorrelation function such that the calculating includes adjusting or zeroing a central tap in an output generated by the calculating; and

determining an estimate of the quality of the signal from the determined metric.