Rake receiver
A rake receiver includes impulse response measurement means and path allocation means for allocating paths to rake fingers in dependence on the output of the impulse response measurement means, wherein the path allocating means is configured to compare the magnitudes of pairs of peaks, represented in the output of the impulse response measurement means, and ignore the lesser member of a pair for the allocation of paths to rake fingers, if the magnitudes of the pair differ in a predetermined manner so as to exclude spurious paths, the pairs having peaks temporally separated by a period characteristic of the separation of main and side lobes of filters for producing the baseband pulse shape expected by the receiver are used for the allocation of the paths to the rake fingers.
1. A rake receiver comprising:
impulse response measurement means and path allocation means for allocating paths to rake fingers in dependence on the output of the impulse response measurement means,
wherein the path allocating means is configured to:
calculate temporal differences between delays output by the impulse response measurement means; and
if none of the temporal differences corresponds to a filter sampling period, supply a delay to each of the rake fingers, the supplied delays having the greatest magnitudes,
if one or more of the temporal differences correspond to the filter sampling period:
calculate a ratio adjusted by a reference value for each pair of delays having the corresponding temporal difference;
if the calculated ratio is lower than a threshold, remove the delay having the lower magnitude; and
supply a delay to each of the rake fingers, the supplied delays having the greatest magnitudes.
2. A rake receiver according to claim 1 , wherein the calculated ratio is within a predetermined range.
3. A rake receiver according to claim 2 , wherein the calculated ratio adjusted by the reference value is less than the threshold value.
4. A rake receiver according to claim 1 , wherein the reference value corresponds to a theoretical lobe ratio increased by an amount attributable to an uncertainty introduced by noise.
5. A rake receiver according to claim 4 , wherein said reference value comprises half the sum of the upper and lower bounds of a confidence interval in a probability density for the lobe ratio, the confidence interval being not less than 90%.
6. A rake receiver according to claim 5 , wherein said threshold value is half the width of said confidence interval.
7. A rake receiver according to claim 1 , wherein said ratio comprises:
M
p
1
M
p
2
-
R
<
I
where M p1 and M p2 are the magnitudes of the peaks of a pair, R is a reference ratio for a main lobe and a side lobe and I is a confidence factor.
8. A rake receiver according to claim 7 , wherein R is approximately 0.175, and I is approximately 0.065.
9. A mobile phone network receiver including a receiver according to claim 1 .
10. A rake receiver for receiving CDMA signals, the receiver comprising a baseband signal processor configured:
to implement a plurality of rake fingers,
to perform impulse response measurement, and
to perform path allocation for allocating paths to rake fingers in dependence on the result impulse response measurement,
wherein said path allocation comprises:
calculating temporal differences between delays output by the impulse response measurement means; and
if none of the temporal differences corresponds to a filter sampling period, supplying a delay to each of the rake fingers, the supplied delays having the greatest magnitudes,
if one or more of the temporal differences correspond to the filter sampling period:
calculating a ratio adjusted by a reference value for each pair of delays having the corresponding temporal difference;
if the calculated ratio is lower than a threshold, removing the delay having the lower magnitude; and
supplying a delay to each of the rake fingers, the supplied delays having the greatest magnitudes.
11. A rake receiver according to claim 10 , wherein ratio is within a predetermined range.
12. A rake receiver according to claim 11 , wherein the calculated ratio adjusted by the reference value is less than the threshold value.
13. A rake receiver according to claim 12 , wherein the reference value corresponds to a theoretical lobe ratio increased by an amount attributable to an uncertainty introduced by noise.
14. A rake receiver according to claim 13 , wherein said reference value comprises half the sum of the upper and lower bounds of a confidence interval in a probability density for the lobe ratio, the confidence interval being not less than 90%.
15. A rake receiver according to claim 14 , wherein said threshold value is half the width of said confidence interval.
16. A rake receiver according to claim 10 , wherein said ratio comprises:
M
p
1
M
p
2
-
R
<
I
where M p1 and M p2 are the magnitudes of the peaks of a pair, R is a reference ratio for a main lobe and a side lobe and I is a confidence factor.
17. A rake receiver according to claim 16 , wherein R is approximately 0.175, and I is approximately 0.065.
18. A mobile phone network receiver including a receiver according to claim 10 .