Apparatus and method for noise enhancement reduction in an adaptive equalizer

1 . A method for noise enhancement reduction in an adaptive equalizer comprising a plurality of filter tap cells having respective coefficients and tap data values, the method comprising:

determining a step size based on a norm value of an i th parameter of an estimated channel response; and

updating the coefficient of the i th filter tap cell based on the step size, an error signal, and the tap data value of the i th filter tap cell; wherein the step size is a non-decreasing stepwise function of the norm value of the i th parameter of the estimated channel response.

2 . The method as claimed in claim 1 , wherein the channel response is estimated by the coefficients of tap filter cells, and the i th parameter of the estimated channel response is the coefficient of the i th tap filter cell.

3 . The method as claimed in claim 1 wherein the norm value of the i th parameter of the estimated channel response is referred to as the absolute value of the i th parameter.

4 . The method as claimed in claim 1 , wherein the determination step comprises:

determining a local maximum channel parameter having a local maximum norm value among the i th parameter of the estimated channel response and a plurality of parameters adjacent to the i th parameter; and determining the step size based on the local maximum channel parameter.

5 . The method as claimed in claim 1 , wherein the updating step comprises:

updating the coefficient of the i th tap filter cell based on the algorithm of the form:

c i ( n+ 1)= c i ( n )+ e ( n )· x i ( n )·μ[ h i ( n )]

where:

c i (n+1) is the coefficient of the i th tap filter cell at time n+1;

c i (n) is the coefficient of the i th tap filter cell at time n;

e(n) is the error signal at time n;

x i (n) is the tap data value of the i th tap filter cell at time n;

h i (n) is the i th channel parameter of the estimated channel response at time n; and

μ[|h i (n)|] denotes the step size, a non-decreasing stepwise function a norm value of the i th channel parameter |h i (n)|.

6 . The method as claimed in claim 1 , further comprising:

generating an output signal of the i th tap filter cell based on the corresponding coefficient and tap data value if a norm value of the corresponding coefficient is greater than a predetermined threshold, otherwise, setting output signal of the i th tap filter cell to be zero.

7 . The method as claimed in claim 1 , further comprising:

generating an output signal of the i th tap filter cell based on the corresponding coefficient and tap data value;

attenuating the output signal by multiplying the output signal with a preset factor if neither the corresponding coefficient nor the coefficient of the tap filter cell adjacent to the i th tap filter cell has its norm value greater than a predetermined threshold.

8 . The method as claimed in claim 7 , wherein the factor equals to ½ N where N is a positive integer.

9 . The method as claimed in claim 7 , wherein the factor equals to zero.

10 . An adaptive equalizer capable of achieving noise enhancement reduction, comprising:

a plurality of filter tap cells having respective coefficients and tap data values;

a coefficient adaptation unit for updating the coefficient of an i th filter tap cell based on the step size, an error signal, and the tap data value of the i th filter tap cell wherein the coefficient adaptation unit comprises a step size calculator for determining the step size based on a norm value of an i th parameter of an estimated channel response; wherein the step size is a non-decreasing stepwise function of a norm value of the i th parameter of the estimated channel response.

11 . The adaptive equalizer as claimed in claim 10 , wherein the channel response is estimated by the coefficients of tap filter cells, and the i th parameter of the estimated channel response is the coefficient of the i th tap filter cell.

12 . The adaptive equalizer as claimed in claim 10 , wherein the norm value of the i th parameter of the estimated channel response is referred to as the absolute value of the i th parameter.

13 . The adaptive equalizer as claimed in claim 10 , wherein:

the step size calculator determines a local maximum channel parameter having a local maximum norm value among the i th parameter and a plurality of parameters of the estimated channel response adjacent to the i th parameter, and calculates the step size based on the local maximum channel parameter.

14 . The adaptive equalizer as claimed in claim 10 , wherein:

the coefficient adaptation unit updates the i th coefficient based on the algorithm of the form:

c i ( n+ 1)= c i ( n )+ e ( n )· r ( n−i )·μ[h i ( n )]

where:

c i (n+1) is the i th coefficient of the equalizer at time n+1;

c i (n) is the i th coefficient of the equalizer at time n;

e(n) is the error signal at time n;

r(n-i) is the i th delayed version of the input signal at time n;

h i (n) is the i th channel parameter of the estimated channel response at time n; and

μ[h i (n)] denotes the step size, a non-decreasing stepwise function of the i th channel parameter h i (n).

15 . The adaptive equalizer as claimed in claim 10 , wherein:

the i th tap filter cell comprises a mask unit to set an output signal of the i th tap filter cell to be zero if a norm value of the corresponding coefficient is less than a predetermined threshold.

16 . The adaptive equalizer as claimed in claim 10 , wherein:

the i th tap filter cell comprises an attenuator to attenuate the output signal of the i th tap filter cell by multiplying the output signal with a preset factor if neither the corresponding coefficient nor the coefficient of the tap filter cell adjacent to the i th tap filter cell has its norm value greater than a predetermined threshold.

17 . The adaptive equalizer as claimed in claim 16 , wherein the factor equals to ½ N where N is a positive integer.

18 . The method as claimed in claim 16 , wherein the factor equals to zero.