Apparatus, and associated method, for filtering a receive signal by adaptive operation of an input noise whitening filter
View Patent ↗Apparatus, and an associated method, for the receive part of a receiving station, such as a mobile station or other transceiver of a cellular communication system. Selection is made of filter characteristics to be exhibited by an adaptive, input noise whitening filter. A noise estimator estimates a noise component of a noise sequence. An autocorrelation estimator estimates the noise-component autocorrelation. A determination is made as to whether the autocorrelation exceeds a threshold. If so, filter characteristics are selected to cause the input noise whitening filter to operate to inject whitening noise into the received sequence.
1. A receiver having improved interference suppression comprising:
a first receiver filter; and
an input noise whitening filter adapted to selectively add whitening to a received signal coupled from said first receiver filter comprising:
an autocorrelation estimator adapted to accept a noise estimate signal derived from said received signal, calculate a first autocorrelation function from said accepted noise estimate signal, and determine an autocorrelation function from an absolute value of said first autocorrelation function,
a filter characteristic selector adapted to receive said autocorrelation estimate, compare said autocorrelation estimate to a threshold value, and select a non-unitary, white noise additive, filter characteristic when said autocorrelation estimate is above said threshold value and select a unitary filter characteristic when said autocorrelation estimate is below said threshold value, and
a selectable filter, responsive to said filter characteristic selector to recover an output signal having informational content from said received signal as modified by said selected filter characteristic.
2. The receiver of claim 1 wherein said first receiver filter further includes a wide passband.
3. The receiver of claim 1 wherein said input noise whitening filter further comprises a linear prediction error filter, LPF.
4. The receiver of claim 3 wherein said filter characteristics further comprise LPF filter coefficients.
5. The receiver of claim 4 wherein said LPF filter coefficients are unitary when said autocorrelation estimate is below said threshold value.
6. The receiver of claim 1 wherein said received signal further comprises a received sequence.
7. The receiver of claim 6 wherein said noise estimate signal further comprises said received sequence, a channel impulse response estimation, and a known training response.
8. A method of improving interference suppression in a receiver, comprising:
filtering a received signal; and
selectively adding whitening to said filtered received signal by:
deriving a noise estimate signal from said filtered received signal,
calculating a first autocorrelation function from said noise estimate signal, determining an autocorrelation function from an absolute value of said first autocorrelation function,
comparing said autocorrelation estimate to a threshold value,
selecting a non-unitary, white noise additive, filter characteristic when said autocorrelation estimate is above said threshold value and selecting a unitary filter characteristic when said autocorrelation estimate is below said threshold value, and
recovering an output signal having informational content from said filtered received signal as modified by a selectable filter employing said selected filter characteristic.
9. The method of claim 8 further comprising filtering said received signal with a wide passband filter.
10. The method of claim 8 wherein said recovering an output signal further comprises modifying said filtered received signal with a linear prediction error filter, LPF.
11. The method of claim 8 wherein said filter characteristics further comprise LPF filter coefficients.
12. The method of claim 11 further comprises setting said LPF filter coefficients to unitary values when said autocorrelation estimate is below said threshold value.
13. The method of claim 8 wherein said filtering a received signal further comprises filtering a received sequence.
14. The method of claim 8 further comprises calculating said noise estimate signal further from said received sequence, a channel impulse response estimation, and a known training sequence response.
15. The method of claim 14 wherein said channel impulse response estimator is estimated over a known training sequence.
16. The method of claim 15 wherein said noise estimate signal is estimated by subtracting a remodulated training sequence from said filtered received signal.