Echo canceller having an adaptive filter with a dynamically adjustable step size
The present invention is directed to an echo canceller adapted for use in a communication system that includes a hybrid circuit. The echo canceller comprises an adaptive digital filter that generates an estimated echo signal {circumflex over (z)}[k] in response to: (i) a sampled input data sequence x[k] and (ii) an error signal sequence e[k] indicative of the difference between a near end signal sequence y[k] and the estimated echo signal {circumflex over (z)}[k]. The adaptive digital filter computes filter coefficients based upon the error signal sequence e[k] using a stochastic quadratic descent estimator, such as for example a least mean square (LMS) estimator, that employs a dynamically adjustable step size vector μ [k]. The adaptive digital filter computes the dynamically adjustable step size vector μ [k] of the form μ _ [ k + 1 ] = μ _ [ k ] + α ϕ _ [ k ] · x _ [ k ] e [ k ] | μ min μ max , where φ [k+1]= φ [k]•( 1 − μ [k]• x 2 [k])+e[k])+e[k] x [k] and α is a scalar. In an open loop embodiment, the dynamically adjustable step size vector μ [k] equals to μ [k]=μ[k] 1 , that is, all elements of the vector take the same value collapsing to the particular case of a scalar. The step size is computed using an expression of the form μ[k+1]=μ[k]+ξ[k], where ξ[k] is an empirically derived set of values.
1. An echo canceller adapted for use in a communication system that includes a hybrid circuit, said echo canceller comprising:
an adaptive digital filter that generates an estimated echo signal {circumflex over (z)}[k] in response to (i) a sampled input data sequence x[k] and (ii) an error signal sequence e[k] indicative of the difference between a near end signal sequence y[k] and the estimated echo signal {circumflex over (z)}[k], wherein said adaptive digital filter computes filter coefficients based upon said error signal sequence e[k] using a stochastic quadratic descent estimator that employs a dynamically adjustable step size vector μ [k] and said adaptive digital filter comprises means for computing said dynamically adjustable step size vector μ [k] of the form
μ
_
[
k
+
1
]
=
μ
_
[
k
]
+
α
ϕ
_
[
k
]
·
x
_
[
k
]
e
[
k
]
|
μ
min
μ
max
,
where φ [k+1]= φ [k]•( 1 − μ [k]• x 2 [k])+e[k] x [k] and α is a scalar.
2. The echo canceller of claim 1 , wherein said stochastic quadratic descent estimator comprises a least mean square (LMS) estimator that includes said dynamically adjustable step size.
3. An integrated circuit that includes an echo canceller adapted for use in a communication system that includes a hybrid circuit that provides a return signal, said echo canceller comprising:
an adaptive digital filter that generates an estimated echo signal {circumflex over (z)}[k] in response to (i) a sampled input data sequence x[k] and (ii) an error signal sequence e[k] indicative of the difference between a near end signal sequence y[k] and the estimated echo signal {circumflex over (z)}[k], wherein said adaptive digital filter computes filter coefficients based upon said error signal sequence e[k] using a stochastic quadratic descent estimator that employs a dynamically adjustable step size vector μ [k] and said adaptive digital filter comprises means for computing said dynamically adjustable step size vector μ [k] of the form
μ
_
[
k
+
1
]
=
μ
_
[
k
]
+
α
ϕ
_
[
k
]
·
x
_
[
k
]
e
[
k
]
|
μ
min
μ
max
,
where φ [k+1]= φ [k]•( 1 − μ [k]• x 2 [k])+e[k] x [k] and α is a scalar.
4. The integrated circuit of claim 3 , wherein said stochastic quadratic descent estimator comprises a least mean square (LMS) estimator that includes said dynamically adjustable step size.
5. A digital signal processor that includes executable program instructions to provide an echo canceller adapted for use in a communication system which includes a hybrid circuit that provides a return signal, said echo canceller comprising:
an adaptive digital filter that generates an estimated echo signal {circumflex over (z)}[k] in response to (i) a sampled input data sequence x[k] and (ii) an error signal sequence e[k] indicative of the difference between a near end signal sequence y[k] and the estimated echo signal {circumflex over (z)}[k], wherein said adaptive digital filter computes filter coefficients based upon said error signal sequence e[k] using a stochastic quadratic descent estimator that employs a dynamically adjustable step size vector μ [k] and said adaptive digital filter comprises means for computing said dynamically adjustable step size vector μ [k] of the form
μ
_
[
k
+
1
]
=
μ
_
[
k
]
+
α
ϕ
_
[
k
]
·
x
_
[
k
]
e
[
k
]
|
μ
min
μ
max
,
where φ [k+1]= φ [k]•( 1 − μ [k]• x 2 [k])+e[k] x [k] and α is a scalar.