Determination of active spreading codes and their powers
View Patent ↗The present invention relates to a method and a device for detecting active spreading codes for a signal in a communication system and estimating power of the active spreading codes. Further, the present invention ensures efficient interference cancellation. Multiple correlations are performed at a single level of a spreading code tree, the produced output samples are then observed at this level during a defined period, and a decision for the activity and power is met for all existing codes via extracting and processing information from these samples. At the correlation step, unitary fast Walsh Hadamard transformation is performed at practically the highest spreading factor in the system.
1. A device for detection of active spreading codes for a signal in a communication system and estimation of powers of the active spreading codes, wherein a received signal comprises a sequence of data symbols that are spread in the received signal and the spreading is defined by a spreading code and/or a spreading factor, wherein the device comprises:
correlation means for performing multiple correlations at a single level of a spreading code tree and producing output samples, said multiple correlations comprising:
performing first multiple correlations with all possible orthogonal codes at a level spreading factor=Lmax, where Lmax is the largest active spreading factor of the communication system; and
then performing multiple correlations with all possible orthogonal codes at a level spreading factor=Lmin, wherein Lmin is the lowest active spreading factor of the communication system; and
activity determination and power estimation means for observing said output samples produced at said Lmax and Lmin level, deciding on activity for all existing codes, and estimating powers of active spreading codes by extracting and processing information from said output samples.
2. The device according to claim 1 , wherein the correlation means are implemented by parallel correlators.
3. The device according to claim 1 , wherein the activity determination and power estimation means feature parallel implementation.
4. The device according to claim 1 , wherein the device represents a receiver in a communication system.
5. The device according to claim 1 , wherein the device represents an equalizer in a communication system.
6. The device according to claim 1 , wherein the device represents a Rake receiver in a communication system.
7. The device according to claim 1 , wherein the device represents a decision-directed adaptive equalizer.
8. The device according to claim 7 , wherein the decision-directed adaptive equalizer uses a training sequence.
9. The device according to claim 8 , wherein the training sequence is a pilot tone.
10. The device according to claim 7 , wherein the decision-directed adaptive equalizer is trained by the symbols of spreading codes detected by the activity determination and power estimation means.
11. The device according to claim 7 , wherein the device is a building block of an interference canceller.
12. Use of the device according to claim 7 to cancel interference in a communication system.
13. Use of the device as claimed in claim 12 , wherein the interference cancellation is a parallel interference cancellation.
14. Use of the device as claimed in claim 12 , wherein the interference cancellation is a serial interference cancellation.
15. A method of detecting active spreading codes for a signal in a communication system and estimation of powers of the active spreading codes, wherein a received signal comprises a sequence of data symbols that are spread in the received signal and the spreading is defined by a spreading code and/or a spreading factor, wherein the method comprises:
a first step of performing multiple correlations at a single level of a spreading code tree and producing output samples; and
a second step of observing said output samples produced at said single level, deciding on activity for all existing codes, and estimating powers of the active spreading codes via extracting and processing information from said output samples,
wherein said first and second step being first executed with all possible orthogonal codes at a level spreading factor=Lmax, where Lmax is the largest active spreading factor of the communications system and then with all possible orthogonal codes at a level spreading factor=Lmin, where Lmin is the lowest active spreading factor of the communication system.
16. The method according to claim 15 , wherein spreading codes of different users fall into different levels of said spreading code tree.
17. The method according to claim 15 , wherein said first step is implemented by fast Walsh Hadamard transformation (FWHT).
18. The method according to claim 15 , wherein said first step is performed at the highest spreading factor in use in the system.
19. The method according to claim 15 further comprising the step of observing said output samples during a defined period in the second step.
20. The method according to claim 15 further comprising the step of partitioning said output samples into groups of a predetermined number of elements in said second step.
21. The method according to claim 20 further comprising the step of performing activity determination and power estimation in said second step for each of said groups.
22. The method according to claim 21 further comprising the step of analyzing elements of groups of said output samples by partitioning the elements of a group in subgroups of various lengths comprising at least one element, wherein said spreading code tree is partitioned in sub trees, and wherein the activity determination and power estimation is performed by analyzing elements of the subgroups and codes of the sub trees of said spreading code tree and/or by amplitude hypothesis examination.
23. The method according to claim 22 comprising the step of using all levels of the sub trees of said spreading code tree for the activity determination and power estimation.
24. The method according to claim 22 comprising the step of using predetermined levels of sub trees of said spreading code tree for the activity determination and power estimation.
25. The method according to claim 22 comprising the step of performing the activity determination and power estimation serially.
26. The method according to claim 22 comprising the step of performing the activity determination and power estimation blockwise.
27. The method according to claim 22 , wherein the multiple correlations of the first step are performed in parallel.
28. A non-transitory computer program medium comprising code means for performing the steps of claim 15 when run on computer controlled device.