Synchronising a receiver to a signal having known structure

1. Apparatus for locating a specific point in a received signal of cyclical nature, the apparatus comprising a correlator arranged to correlate the received signal with a code that is potentially present in the received signal, a multiplier arranged to multiply the correlation result with a time-offset, complex-conjugated version of itself and a filter arranged to low pass filter the multiplication result to produce a signal suited to analysis for determination of said point;

wherein the time-offset used by the multiplier is adjustable; and

wherein the filter is an IIR filter and includes a loop of adjustable length.

2. Apparatus according to claim 1 , further comprising an assessor arranged to assess the filtering result to determine said point.

3. Apparatus according to claim 2 , wherein the assessor is arranged to seek a peak in the filtering result indicative of the presence of the code in the received signal.

4. Apparatus according to claim 2 , wherein the assessor is arranged to monitor changes in a peak located in the filtering result in order to locate said point.

5. Apparatus according to claim 4 , wherein the assessor is arranged to detect a drop in the height of the monitored peak to locate said point.

6. Apparatus according to claim 4 , wherein the assessor is arranged to detect a sequence of drops in the height of the monitored peak to locate said point.

7. Apparatus according to claim 1 , further comprising a suppressor arranged to suppress a DC component in the multiplication result prior to its use by the filter.

8. Apparatus according to claim 1 , further comprising a phase calculator arranged to assess the phase of the multiplication result as the basis of determining an error present in a frequency down-conversion process that is used to produce the received signal.

9. A UWB receiver comprising the apparatus of claim 1 .

10. A method of locating a specific point in a received signal of cyclical nature, the method comprising correlating, using a correlator, the received signal with a code that is potentially present in the received signal, multiplying, using a multiplier, the correlation result with a time-offset, complex-conjugated version of itself and filtering, using a low-pass filter, the multiplication result to produce a signal suited to analysis for determination of said point;

wherein the time-offset used in the multiplication step is adjustable; and

wherein the filtering step is HR filtering with a loop of adjustable length.

11. A method according to claim 10 , further comprising the step of analysing the filtering results to determine said point.

12. A method according to claim 11 , wherein the step of analysing the filtering result comprises seeking a peak in the filtering result indicative of the presence of the code in the received signal.

13. A method according to claim 11 , wherein the step of analysing the filtering result comprises monitoring changes in a peak located in the filtering result in order to locate said point.

14. A method according to claim 13 , wherein the step of monitoring changes in a peak comprises detecting a drop in the height of the monitored peak to locate said point.

15. A method according to claim 13 , wherein the step of monitoring changes in a peak comprises detecting a sequence of drops in the height of the monitored peak to locate said point.

16. A method according to claim 10 , further comprising suppressing a DC component in the multiplication result prior to its use in the filtering step.

17. A method according to claim 10 , further comprising assessing the phase of the multiplication result as the basis of determining an error present in a frequency down-conversion process that is used to produce the received signal.