Methods for managing alignment and latency in interference suppression
An interference cancelling receiver combines data from multiple paths after aligning to transmitter timing, and uses either an equalizer or a Rake receiver to compute symbol estimates. Interference estimates are generated from the symbol estimates, and multiple interference estimates are combined after re-aligning the interference estimates to receiver timing. At least two segments of symbol estimates are computed for each segment of interference cancelled data. Various techniques may be employed for controlling the latency and sequencing of these operations, and the subsystems within the canceller may use different processing clock speeds.
1. A chipset for receiving a signal, the chipset comprising:
a front end configured to receive a signal;
an analog-to-digital converter configured to sample the signal at a sample rate that is greater than or equal to a chipping rate to produce sample-rate data;
a downsampler configured to convert sample-rate data to a chipping rate to create chip-level data;
a symbol estimator configured to operate on chip-level data to create symbol-level data;
a post-processor configured to operate on symbol-level data to produce modified symbol-level data;
a respreader configured to apply a spreading code to the modified symbol-level data to create chip-level data indicative of a plurality of chip-level interference estimates; and
an interpolator configured to interpolate the chip-level data to create sample-level data indicative of a plurality of sample-level interference estimates.
2. The chipset of claim 1 , wherein the symbol estimator is configured to operate at a different clock speed than the analog-to-digital converter.
3. The chipset of claim 1 , wherein the symbol estimator uses a Fast Hadamard Transform.
4. The chipset of claim 1 , wherein the post-processor is further configured to exclude symbol-level data having a received strength less than a threshold strength derived from a noise floor.
5. The chipset of claim 1 , wherein the post-processor is further configured to weight symbol-level data based on a measure of merit.
6. The chipset of claim 1 , further comprising an interference removal module configured to subtract sample-level data indicative of sample-level interference estimates from sample-rate data to obtain an interference cancelled signal.
7. A method, comprising:
receiving a signal with a front end of a receiver;
sampling the signal, with an analog-to-digital converter, at a sample rate that is greater than or equal to a chipping rate to produce sample-rate data;
downsampling the sample-rate data to a chipping rate to create chip-level data;
estimating symbol-level data based on the chip-level data;
operating on the symbol-level data to produce modified symbol-level data;
applying a spreading code to the modified symbol-level data to create chip-level data indicative of a plurality of chip-level interference estimates; and
interpolating the chip-level data to create sample-level data indicative of a plurality of sample-level interference estimates.
8. The method of claim 7 , wherein said sampling the signal operates at a different clock speed than said estimating.
9. The method of claim 7 , wherein said operating comprises creating the symbol-level data based on a Fast Hadamard Transform.
10. The method of claim 7 , further comprising excluding symbol-level data having a received strength less than a threshold strength derived from a noise floor.
11. The method of claim 7 , further comprising weighting symbol-level data based on a measure of merit.
12. The method of claim 7 , further comprising subtracting sample-level data indicative of sample-level interference estimates from sample-rate data to obtain an interference cancelled signal.
13. A non-transitory computer readable storage medium, comprising a plurality of instructions, that in response to being executed, result in a receiver:
sampling a signal at a sample rate that is greater than or equal to a chipping rate to produce sample-rate data;
downsampling the sample-rate data to a chipping rate to create chip-level data;
estimating symbol-level data based on the chip-level data;
operating on the symbol-level data to produce modified symbol-level data;
applying a spreading code to the modified symbol-level data to create chip-level data indicative of a plurality of chip-level interference estimates; and
interpolating the chip-level data to create sample-level data indicative of a plurality of sample-level interference estimates.
14. The non-transitory computer readable storage medium of claim 13 , wherein the plurality of instructions further result in the receiver sampling the signal at a different clock speed than the receiver estimates the symbol-level data.
15. The non-transitory computer readable storage medium of claim 13 , wherein the plurality of instructions further result in the receiver creating the symbol-level data based on a Fast Hadamard Transform.
16. The non-transitory computer readable storage medium of claim 13 , wherein the plurality of instructions further result in the receiver excluding symbol-level data having a received strength less than a threshold strength derived from a noise floor.
17. The non-transitory computer readable storage medium of claim 13 , wherein the plurality of instructions further result in the receiver weighting symbol-level data based on a measure of merit.
18. The non-transitory computer readable storage medium of claim 13 , wherein the plurality of instructions further result in the receiver subtracting sample-level data indicative of sample-level interference estimates from sample-rate data to obtain an interference cancelled signal.