Linear filter equalizer
An apparatus ( 100 ) and a method ( 400 ) suitable for use in a communication device by equalizing an input signal received to mitigate multipath distortion effects present in the input signal in the communication device are provided. A first filter ( 102 ) samples the input signal ( 104 ) and generates a first filter output ( 106 ) based upon the sampled input signal and a filter coefficient array ( 108 ). An error signal ( 112 ) is then generated based upon a difference between the first filter output ( 106 ) and a desired signal ( 114 ), and the filter coefficient array ( 108 ) is updated based upon a product of the error signal ( 112 ) and an adaptation constant ( 118 ). A second filter ( 126 ) samples a delayed input signal ( 124 ) and generates a second filter output ( 128 ) based upon the sampled delayed input signal and the filter coefficient array ( 108 ).
1 . A linear filter equalizer comprising:
a first filter configured to receive an input signal, the first filter further configured to generate a first filter output based upon a plurality of sampled input signals weighted by a filter coefficient array;
an error signal generator coupled to the first filter, the error signal generator configured to generate an error signal based upon the first filter output and a desired signal;
a filter coefficient generator coupled to the error signal generator, the filter coefficient generator configured to generate the filter coefficient array based upon the error signal and an adaptation constant;
a delay generator configured to add a delay time to the input signal to generate a delayed input signal; and
a second filter coupled to the filter coefficient generator and to the delay generator, the second filter configured to generate a second filter output based upon a plurality of sampled delayed input signals weighted by the filter coefficient array.
2 . The linear filter equalizer of claim 1 , wherein the error signal based upon the first filter output and the desired signal includes an error signal generated based upon a difference between the first filter output and the desired signal.
3 . The linear filter equalizer of claim 1 , wherein the filter coefficient array generated is further based upon at least one of the input signal and a previous filter coefficient array.
4 . The linear filter equalizer of claim 1 , wherein the adaptation constant is varied based upon a rate of change of the input signal.
5 . The linear filter equalizer of claim 1 , wherein the delay time is varied based upon a rate of change of the input signal.
6 . The linear filter equalizer of claim 1 , wherein at least one of the first filter and the second filter is a tapped delay line comprising a plurality of delay elements.
7 . The linear filter equalizer of claim 6 , wherein the filter coefficient array has a plurality of array elements corresponding to the plurality of delay elements.
8 . The linear filter equalizer of claim 1 , wherein:
the first filter is a tapped delay line comprising a plurality of first filter delay elements.
the second filter is a tapped delay line comprising a plurality of second filter delay elements, the plurality of second filter delay elements equal in numbers as the plurality of first filter delay elements, and
the filter coefficient array has a plurality of array elements corresponding to the plurality of the first filter delay elements and to the plurality of second filter delay elements.
9 . The linear filter equalizer of claim 8 , wherein the plurality of array elements corresponding to the plurality of the first filter delay elements also corresponds to the plurality of the second filter delay elements.
10 . A wireless communication device having a linear filter equalizer comprising:
a first filter configured to accept an input signal, the first filter further configured to generate a first filter output based upon a plurality of sampled input signals weighted by a filter coefficient array;
an error signal generator coupled to the first filter, the error signal generator configured to generate an error signal based upon the first filter output and a desired signal;
a filter coefficient generator coupled to the error signal generator, the filter coefficient generator configured to generate the filter coefficient array based upon the error signal and an adaptation constant;
a delay generator configured to add a delay time to the input signal to generate a delayed input signal; and
a second filter coupled to the filter coefficient generator and to the delay generator, the second filter configured to generate a second filter output based upon a plurality of sampled delayed input signals weighted by the filter coefficient array.
11 . The wireless communication device of claim 10 , wherein the error signal based upon the first filter output and the desired signal includes an error signal generated based upon a difference between the first filter output and the desired signal.
12 . The wireless communication device of claim 10 , wherein the filter coefficient array generated is further based upon at least one of the input signal and a previous filter coefficient array.
13 . The wireless communication device of claim 10 , wherein the adaptation constant is varied based upon a rate of change of the input signal.
14 . The wireless communication device of claim 10 , wherein the delay time is varied based upon a rate of change of the input signal.
15 . The wireless communication device of claim 10 , wherein at least one of the first filter and the second filter is a tapped delay line comprising a plurality of delay elements.
16 . The wireless communication device of claim 10 , wherein the filter coefficient array has a plurality of array elements corresponding to the plurality of delay elements.
17 . The wireless communication device of claim 10 , wherein:
the first filter is a tapped delay line comprising a plurality of first filter delay elements.
the second filter is a tapped delay line comprising a plurality of second filter delay elements, the plurality of second filter delay elements equal in numbers as the plurality of first filter delay elements, and
the filter coefficient array has a plurality of array elements corresponding to the plurality of the first filter delay elements and to the plurality of second filter delay elements.
18 . The wireless communication device of claim 17 , wherein the plurality of array elements corresponding to the plurality of the first filter delay elements also corresponds to the plurality of the second filter delay elements.
19 . A method in a linear filter equalizer for equalizing an input signal, the method comprising:
receiving the input signal;
sampling the input signal;
generating a first output based upon the sampled input signal and a filter coefficient array;
generating an error signal based upon the first output and a desired signal;
updating the filter coefficient array based upon the error signal and an adaptation constant;
delaying the input signal by a delay time;
sampling the delayed input signal; and
generating a second output based upon the sampled delayed input signal and the updated filter coefficient array.
20 . The method of claim 19 , wherein generating an error signal based upon the first output and a desired signal includes generating an error signal based upon a difference between the first filter output and the desired signal.
21 . The method of claim 19 , wherein updating the filter coefficient array based upon the error signal and the adaptation constant includes updating the filter coefficient array based upon a product of the error signal and an adaptation constant.
22 . The method of claim 19 , further comprising:
evaluating a rate of change of the input signal; and
varying the adaptation constant based upon the rate of change of the input signal.
23 . The method of claim 19 , further comprising:
evaluating a rate of change of the input signal; and
varying the delay time based upon the rate of change of the input signal.
24 . The method of claim 19 , wherein generating a first output includes using a tapped delay line.
25 . The method of claim 19 , wherein generating a second output includes using a tapped delay line.