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. Apparatus for a receive circuit that receives a receive sequence having noise, said apparatus comprising:
a noise estimator adapted to receive the receive sequence and to determine an estimated value of the noise present in the receive sequence, said estimated value determined by subtracting a remodulated training sequence from the received sequence;
a noise autocorrelation estimator adapted to receive said estimated value, calculate a first autocorrelation function based upon said estimated value, and determine an absolute value of said first autocorrelation function as an autocorrelation estimate; and
a filter characteristic selector adapted to receive said autocorrelation estimate from said autocorrelation estimator, to compare said autocorrelation estimate to a threshold autocorrelation value, and to select a filter characteristic for a filter in response to the comparison, wherein said filter characteristic selector is adapted to select a unitary-filter characteristic in which whitening noise is not added upon a determination that said autocorrelation estimate is below said threshold autocorrelation value and adapted to select one non-unitary filter characteristic in which whitening noise is added upon a determination that said autocorrelation estimate is above said threshold autocorrelation value.
2. The apparatus of claim 1 wherein said noise estimator is further configured to determine a channel impulse response of a channel upon which the receive sequence is communicated, and wherein estimation of the noise component utilizes the channel impulse response.
3. The apparatus of claim 1 wherein said filter is adapted to receive a representation of the receive sequence and an indication of the filter characteristic selected by said filter characteristic selector, said filter configured to filter the receive sequence in conformity with the filter characteristic selected by said filter characteristic selector.
4. The apparatus of claim 3 wherein said filter comprises a linear prediction error filter.
5. The apparatus of claim 4 wherein the linear prediction error filter comprises a multi-tap filter.
6. The apparatus of claim 4 wherein the linear prediction error filter forming said filter is defined by filter coefficients and wherein the filter characteristic selected by said filter characteristic selector is determinative of the filter coefficients.
7. The apparatus of claim 4 wherein said filter comprises an INWF, adaptive Input Noise Whitening Filter.
8. A method for operating upon a receive sequence received at a receiving station, the received sequence having noise, said method comprising the operations of:
estimating an estimated value of noise present in the receive sequence by subtracting a remodulated training sequence from the received signal;
receiving the estimated value of the noise present in the receive sequence;
calculating a first autocorrelation function based upon the estimated value;
determining an absolute value of the first autocorrelation function as the autocorrelation estimate;
comparing the autocorrelation estimate to a threshold autocorrelation value; and,
selecting a filter characteristic for a filter in response to the comparison, a unitary-filter characteristic in which whitening noise is not added being selected upon a determination that the autocorrelation estimate is below the threshold value and a non-unitary filter characteristic in which whitening noise is added being selected upon a determination that the auto correlation estimate is above the threshold value.
9. Apparatus for a receive circuit that receives a receive sequence x(n) having noise, said apparatus comprising:
a noise sample estimator configured to receive a timing offset, to receive a channel impulse response “CIR” of a channel upon which the receive sequence is communicated, and to receive a known training sequence “TS”, from which CIR and TS a remodulated training sequence is generated, the remodulated training sequence being subtracted from the receive sequence to determine an estimated value of the noise present in the receive sequence;
a noise autocorrelation estimator adapted to: receive the estimated value of the noise present in the receive sequence, calculate a first autocorrelation function based upon the estimated value, and determine an absolute value of the first autocorrelation function as the autocorrelation estimate;
a filter-characteristic selector adapted to: receive from the estimator the autocorrelation estimate, to compare the autocorrelation estimate to a threshold autocorrelation value, and to select a filter characteristic in response to the comparison, wherein the filter-characteristic selector is adapted to select a unitary-filter characteristic from which whitening noise is not added upon a determination that the autocorrelation estimate is below the threshold value and adapted to select one non-unitary filter characteristic from which whitening noise is added upon a determination that the autocorrelation estimate is above the threshold value; and
a linear prediction error filter adapted to receive a representation of the receive sequence and an indication of the filter characteristic selected by said filter-characteristic selector, said filter configured to filter the receive sequence in conformity with the filter characteristic selected by said filter characteristic selector.
10. A method for operating upon a receive sequence received at a receiving station, the received sequence having noise, said method comprising the operations of:
estimating an estimated value of noise present in the receive sequence utilizing a known training sequence comprising the steps of:
receiving a timing offset,
receiving a channel impulse response “CIR” of a channel upon which the receive sequence is communicated,
receiving a known training sequence “TS”,
generating a remodulated training sequence from the CIR and TS, and
subtracting the remodulated training sequence from the receive sequence to determine an estimated value of the noise present in the receive sequence;
receiving the estimated value of the noise present in the receive sequence;
calculating a first autocorrelation function based upon the estimated value;
determining an absolute value of the first autocorrelation function as the autocorrelation estimate;
comparing the autocorrelation estimate to a threshold autocorrelation value; and,
selecting a filter characteristic in response to the comparison, a unitary-filter characteristic being selected from which whitening noise is not added upon a determination that the autocorrelation estimate is below the threshold value and a non-unitary filter characteristic from which whitening noise is added being selected upon a determination that the auto correlation estimate is above the threshold value; and
receiving a representation of the receive sequence and an indication of the selected filter characteristic and filtering the receive sequence in conformity with the selected filter characteristic by way of a linear prediction error filter.