Adaptive infinite impulse response (IIR)-based code detection for symbol-level equalizer
Code detection to assist a symbol-level equalizer in a receiver is described. In an embodiment, code detection uses adaptive Infinite Impulse Response (IIR) filtering to determine spreading code usage information and active code channels in a received signal. The spreading code usage information indicates if a spreading code associated with a code channel is among spreading codes used in the received signal. In another embodiment, the spreading code usage information is determined based on a forgetting factor associated with the filtering of a symbol power associated with the code channel.
1. A receiver, comprising:
a chip-level equalizer configured to receive samples of a received signal and to generate a first symbol estimate from the received samples;
a code detector configured to apply adaptive Infinite Impulse Response (IIR) filtering on a symbol power using a forgetting factor to compute a symbol power estimate and determine spreading code usage information based on a comparison of the forgetting factor and the symbol power estimate to respective thresholds, wherein the symbol power is determined using the first symbol estimate; and
a symbol-level equalizer configured to generate a second symbol estimate based on the first symbol estimate and the spreading code usage information.
2. The receiver of claim 1 , wherein the chip-level equalizer is configured to:
channel and noise equalize the received samples to generate equalized samples;
descramble the equalized samples using a descrambling code to generate descrambled samples; and
despread the descrambled samples to generate the first symbol estimate.
3. The receiver of claim 2 , wherein the descrambling code corresponds to a base station transmitting the received signal.
4. The receiver of claim 1 , wherein the received signal comprises one or more data symbols spread by respective spreading codes selected from a plurality of spreading codes.
5. The receiver of claim 4 , wherein the plurality of spreading codes are associated with a respective plurality of code channels, and wherein the symbol power is associated with a code channel of the respective plurality of code channels.
6. The receiver of claim 5 , wherein the spreading code usage information indicates if a spreading code associated with the code channel is among the respective spreading codes used to spread the one or more data symbols.
7. The receiver of claim 5 , wherein the code detector is further configured to:
compute an error based on the symbol power estimate and the symbol power; and
compute a next forgetting factor for the code channel based at least in part on the forgetting factor and the error.
8. A method, comprising:
receiving samples of a received signal;
generating a first symbol estimate from the received samples;
applying adaptive Infinite Impulse Response (IIR) filtering on a symbol power using a forgetting factor to compute a symbol power estimate, wherein the symbol power is determined using the first symbol estimate;
determining spreading code usage information based on a comparison of the forgetting factor and the symbol power estimate to respective thresholds; and
generating a second symbol estimate based on the first symbol estimate and the spreading code usage information.
9. The method of claim 8 , further comprising:
channel and noise equalizing the received samples to generate equalized samples;
descrambling the equalized samples using a descrambling code to generate descrambled samples; and
despreading the descrambled samples to generate the first symbol estimate.
10. The method of claim 8 , wherein the received signal comprises one or more data symbols spread by respective spreading codes selected from a plurality of spreading codes.
11. The method of claim 10 , wherein the plurality of spreading codes are associated with a respective plurality of code channels, and wherein the symbol power is associated with a code channel of the respective plurality of code channels.
12. The method of claim 11 , wherein the spreading code usage information indicates if a spreading code associated with the code channel is among the respective spreading codes used to spread the one or more data symbols.
13. The method of claim 11 , further comprising:
computing an error based on the symbol power estimate and the symbol power; and
computing a next forgetting factor for the code channel based at least in part on the forgetting factor and the error.
14. A receiver, comprising:
a chip-level equalizer configured to receive samples of a received signal and to generate a first symbol estimate from the received samples, wherein the received signal comprises one or more data symbols spread by respective spreading, codes; and
a code detector configured to apply adaptive Infinite Impulse Response (IIR) filtering on a symbol power using a forgetting factor to compute a symbol power estimate and determine spreading code usage information based on a comparison of the forgetting factor and the symbol power estimate to respective thresholds,
wherein the symbol power is determined using the first symbol estimate and is associated with a code channel of a respective plurality of code channels.
15. The receiver of claim 14 , wherein the chip-level equalizer is configured to:
channel and noise equalize the received samples to generate equalized samples;
descramble the equalized samples using a descrambling code to generate descrambled samples; and
despread the descrambled samples to generate the first symbol estimate.
16. The receiver of claim 15 , wherein the descrambling code corresponds to a base station transmitting the received signal.
17. The receiver of claim 14 , wherein the spreading code usage information indicates if a spreading code associated with the code channel is among the respective spreading codes used to spread the one or more data symbols.
18. The receiver of claim 14 , wherein the code detector is further configured to:
compute an error based on the symbol power estimate and the symbol power; and
compute a next forgetting factor for the code channel based at least in part on the forgetting factor and the error.
19. The receiver of claim 18 , wherein the error is equal to a difference between the symbol power estimate and the symbol power.
20. The receiver of claim 18 , wherein the code detector is further configured to compute the next forgetting factor for the code channel based on a predetermined step size.