Method and apparatus for filtering post decision feedback equalization noise

A method for compensating for noise during decision feedback equalization, including the steps of:

• (a) performing decision feedback equalization on a noisy signal;
• and
• (b) while performing step (a), isolating noise components of the noisy signal, thereby generating isolated noise components, and filtering the isolated noise components to generate post-decision feedback equalization noise having a desired spectrum and power, wherien step (b) includes the steps of:
• filtering first isolated noise components of the noisy signal in a first filter having a first transfer function;
• and
• filtering second isolated noise components of the noisy signal in a second filter having a second transfer function, wherein e(z) are the first isolated noise components, e' (z) are the second isolated noise components, the first transfer function and the second transfer function have a combined transfer function of form zB' (z)/C'(z), and the first isolated noise components, the second isolated noise components, the combined transfer function satisfy a relation e'(z)=(zB'(z)/C(z))e(z), the first transfer function has form zB'(z)=b.sub.1 +b.sub.2 (z).sup.-1 + . . . + b.sub.n1 (z).sup.-(n1)+1, and the second transfer function has form C'(z)=c.sub.0 +c.sub.1 (z).sup.-1 +c.sub.2 (z).sup.-2 + . . . +C.sub.n2 (z).sup.-n2, where b.sub.1, b.sub.2, . . . , b.sub.n1, c.sub.1, c.sub.2, . . . , and c.sub.n2 are constant values.

A decision feedback equalization apparatus, including:

• decision feedback equalization means for performing decision feedback equalization on a noisy signal;
• and
• a noise filter means connected to the decision feedback means, including means for isolating noise components of the noisy signal thereby generating isolated noise components, and means for filtering the isolated noise components to generate post-decision feedback equalization noise having a desired spectrum and power, wherein the noise filter means includes:
• a first filter having a first transfer function, for filtering first isolated noise components of the noisy signal;
• and
• a second filter having a second transfer function for filtering second isolated noise components of the noisy signal, wherein e9z) are the first isolated noise components, e'(z) are the second isolated noise components, the first transfer function B(z) and the second transfer function C(z) have a combined transfer function of form B(z)/C(z) wherein B(z)=1+b.sub.1 (z).sup.-1 +b.sub.2 (z).sup.-2 + . . . + b.sub.n1 (z).sup.-n1 and C(z)=1+c.sub.1 (z).sup.-1 +c.sub.2 (z).sup.-2 + . . . + C.sub.n2 (z).sup.-n2 and the first isolated noise components, the second isolated noise components, and the combined transfer function satisfy e'(z)=(B(z)/C(z)e(z).

A decision feedback equalization apparatus, including:

• decision feedback equalization means for performing decision feedback equalization on a noisy signal;
• and
• a noise filter means connected to the decision feedback means, including means for isolating noise components of the noisy signal thereby generating isolated noise components, and means for filtering the isolated noise components to generate post-decision feedback equalization noise having a desired spectrum and power, wherien the noise filter means includes:
• a first filter having a first transfer function, for filtering first isolated noise components of the noisy signal;
• and
• a second filter having a second transfer function for filtering second isolated noise components of the noisy signal, whrein e(z) are the first isolated noise components, e'(z) are the second isolated noise components, the first transfer function and the second transfer function have a combined transfer function of form zB'(z)/C'(z), and the first isolated noise components, the second isolated noise components, the combined transfer function satisfy e'(z)=(ZB'(z)/C'(z))e(z), the first transfer function has form zB'(z)=b.sub.1 +b.sub.2 (z).sup.-1 + . . . +b.sub.n1 (z).sup.-(n1)+1, and the second transfer function has form C'(z)=c.sub.0 +C.sub.1 (z).sup.-1 +c.sub.2 (z).sup.-2 + . . . +C.sub.n2 (z).sup.-n2, where b.sub.1, b.sub.2, . . . , b.sub.n1, c.sub.1, c.sub.2, . . . , and Chd n2 are constant values.

An apparatus for performing decision feedback equalization on a receive filtered signal x(n) resulting from filtration of a transmitted signal in a feedforward filter, wherein the transmitted signal has resulted from transmission of an input signal through a transmission channel, said apparatus including:

• a subtraction circuit for receiving the receive filtered signal x(n) and subtracting a replica signal x'(n) therefrom to generate a signal y(n);
• noise filter means for generating a corrected signal y'(n) from the signal y(n), wherein the corrected signal y'(n) includes post-decision feedback equalization noise having a desired spectrum and power;
• a quantizer for receiving the corrected signal y'(n) and generating a second replica signal s"(n) in response to the corrected signal y'(n), wherein the second replica signal s"(n) is a replica of the input signal;
• and
• feedback filter means for receiving the second replica signal s"(n) and generating the replica signal x'(n) in response thereto, and providing replica signal x'(n) to the subtraction circuit.