Method and apparatus for signal quality estimation
A receiver ( 13 ) of user equipment, UE, ( 10 ) of a Universal Mobile Telecommunications System, UMTS, network receives a digitally encoded radio signal over a downlink ( 11 ) from a base station ( 12 ). A Digital Signal Processor, DSP, ( 14 ) of the UE ( 10 ) estimates BER of data bits of power control commands received in the signal during an out of synchronisation procedure. More specifically, the DSP ( 14 ) samples the amplitude with which the data bits are received and determines a ratio of functions of one or more moments of the sampled amplitudes. The DSP ( 14 ) then compares the determined ratio to one or more values of BER for different ratios in a look-up table to estimate BER.
1. An apparatus for estimating signal quality, the apparatus comprising:
a receiver for sampling magnitudes with which symbols of a signal are received; and
a processor for determining a ratio F 1 /F 2 , where F 1 is a function of a first moment M i of order i of the sampled magnitudes, F 2 is a function of a second moment M j of order j of the sampled magnitudes, i≠j, and F 1 and F 2 are non-identical, and for estimating signal quality of the signal from the determined ratio, wherein the processor is configured to vary at least one of the orders i,j of the first and second moments according to at least one of: a degree of asymmetry of a distribution of the sampled magnitudes; and the estimated signal quality.
2. The apparatus of claim 1 , wherein F 1 [M i ]=M i k/i and F 2 [M j ]=M j k/j and k is any real number.
3. The apparatus of claim 1 , wherein M i is computed as an expectation value of an ith power of the signal and M j , is computed as an expectation value of a jth power of the signal.
4. The apparatus of claim 1 , wherein at least one of F 1 and F 2 includes a normalization factor.
5. The apparatus of claim 1 , wherein the ratio F 1 [M i ]/F 2 [M j ] comprises a ratio between the moment M i and the moment M j .
6. The apparatus of claim 5 , wherein the moments M i and M j are both even order moments.
7. The apparatus of claim 5 , wherein the moments M i and M j are both odd order moments.
8. The apparatus of claim 6 , wherein M i comprises a second order moment and M j comprises a fourth order moment.
9. The apparatus of claim 1 , wherein the processor is configured to estimate signal quality by deriving a value for a signal quality parameter from the ratio.
10. The apparatus of claim 1 , further comprising a look-up table of signal quality parameter values for different ratios, wherein the processor is configured to derive the signal quality parameter value by comparing the derived ratio to the one or more of the ratios in the look-up table.
11. The apparatus of claim 10 , wherein the processor is configured to interpolate between signal quality parameter values in the look-up table to derive the signal quality parameter value.
12. The apparatus of claim 10 , wherein the signal quality parameter values in the look-up table are spaced logarithmically.
13. The apparatus of claim 9 , wherein the signal quality parameter is one of: bit error rate; signal to noise ratio; block error rate; and packet error rate.
14. The apparatus of claim 1 , wherein the receiver is configured to sample the magnitudes of all the symbols of a stream of symbols in the signal.
15. The apparatus of claim 1 , wherein the receiver is configured to sample the magnitudes of symbols received during a period of time.
16. The apparatus of claim 15 , wherein the processor is configured to vary the period of time according to the estimated signal quality.
17. The apparatus of claim 1 , wherein the symbols are bits.
18. The apparatus of claim 1 , wherein the magnitude is amplitude.
19. A method of estimating signal quality, the method comprising:
sampling magnitudes at which symbols of a signal are received;
determining a ratio F 1 /F 2 , where F 1 is a function of a first moment M i of order i of the sampled magnitudes, F 2 is a function of a second moment M j of order j of the sampled magnitudes, i≠j, and F 1 and F 2 are non-identical;
varying at least one of the orders i,j of the first and second moments according to at least one of: a degree of asymmetry of a distribution of the sampled magnitudes and the estimated signal quality; and
estimating signal quality of the signal from the determined ratio.
20. The method of claim 19 , wherein F 1 [M 1 ]=M i k/i and F 2 [M j ]=M j k/j and k is any real number.
21. The method of claim 19 , wherein M i is computed as the expectation value of the ith power of the signal and M j is computed as the expectation value of the jth power of the signal.
22. The method of claim 19 , wherein at least one of F 1 and F 2 includes a normalisation factor.
23. The method of claim 19 , wherein the ratio F 1 [M 1 ]/F 2 [M j ] comprises a ratio between the first moment M i and the second moment M j .
24. The method of claim 23 , wherein the moments are both even order moments.
25. The method of claim 23 , wherein the moments are both odd order moments.
26. The method of claim 24 , wherein the first moment is a second order moment and the second moment is a fourth order moment.
27. The method of claim 19 , comprising estimating signal quality by deriving a value for a signal quality parameter from the ratio.
28. The method of claim 19 , comprising deriving the signal quality parameter value by comparing the derived ratio to one or more ratios in a look-up table of signal quality parameter values for different ratios.
29. The method of claim 28 , wherein the comparison includes interpolating between signal quality parameter values in the look-up table to derive the signal quality parameter value.
30. The method of claim 28 , wherein the signal quality parameter values in the look-up table are spaced logarithmically.
31. The method of claim 27 , wherein the signal quality parameter is one of: bit error rate; signal to noise ratio; block error rate; and packet error rate.
32. The method of claim 19 , comprising sampling the magnitude of all the symbols of a stream of symbols in the signal.
33. The method of claim 19 , comprising sampling the magnitude of symbols received during a period of time.
34. The method of claim 33 , comprising varying the period of time according to the estimated signal quality.
35. The method of claim 19 , wherein the symbols are bits.
36. The method of claim 19 , wherein the magnitude is amplitude.
37. A non-transitory computer readable storage medium comprising instructions configured to cause a processor to implement a method that includes:
sampling magnitudes at which symbols of a signal are received;
determining a ratio F 1 /F 2 , where F 1 is a function of a first moment M i of order i of the sampled magnitudes, F 2 is a function of a second moment M j of order j of the sampled magnitudes, i≠j, and F 1 and F 2 are non-identical;
varying at least one of the orders i,j of the first and second moments according to at least one of: a degree of asymmetry of a distribution of the sampled magnitudes and the estimated signal quality; and
estimating signal quality of the signal from the determined ratio.