Equalization with DC-offset compensation

• US 6,449,320 B1
• Filed: 07/02/1999
• Issued: 09/10/2002
• Est. Priority Date: 07/02/1999
• Status: Expired due to Term

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Lindoff, Bengt
• Primary Examiner(s): TSE, YOUNG TOI
• Application Number:
  US09/347,230
• Time in Patent Office: 1,166 Days
• Field of Search: 375/231, 375/232, 375/262, 375/265, 375/316, 375/317, 375/319, 375/340, 375/341, 375/346, 375/348, 375/350, 714/792, 714/794, 714/795, 714/796, 455/296
• US Class Current: 375/319
• CPC Class Codes: H04L 25/0212 of impulse response
• CPC Class Codes: H04L 25/023 with extension to other symbols
• CPC Class Codes: H04L 25/025 using least-mean-square [LMS] method
• CPC Class Codes: H04L 25/061 providing hard decisions only; arrangements for tracking or suppressing unwanted low frequency components, e.g. removal of dc offset removal of dc offset in coupling arrangements H04L25/029, H04L25/0296

Abstract

A radio signal that has been received from a channel is equalized by estimating the channel, generating an initial estimate of a DC-offset that has been introduced into the radio signal, and estimating a variance of the initial estimate of the DC-offset. The channel estimate, the initial estimate of the DC-offset and the estimated variance are then used to determine a most likely symbol represented by the radio signal. The initial estimate of the DC-offset that has been introduced into the radio signal may be determined from a training sequence portion of the received signal and a reference training sequence signal. For example, a least squares technique may be used to generate the DC-offset as well as the channel estimate and the variance of the initial estimate of the DC-offset. In an equalizer section, the DC-offset and variance values are taken into consideration when the most likely symbol represented by the radio signal is decided.

Claims

1. A method of equalizing a radio signal that has been received from a channel, comprising the steps of:

estimating the channel;

generating an initial estimate of a DC-offset that has been introduced into the radio signal;

estimating a variance of the initial estimate of the DC-offset; and

using the channel estimate, the initial estimate of the DC-offset and the estimated variance to determine a most likely symbol represented by the radio signal.

2. The method of claim 1, wherein the step of generating the initial estimate of the DC-offset that has been introduced into the radio signal comprises the step of using a training sequence portion of the received signal and a reference training sequence signal to generate the initial estimate of the DC-offset that has been introduced into the radio signal.

3. The method of claim 1, wherein the steps of estimating the channel, generating the initial estimate of the DC-offset and estimating the variance of the initial estimate of the DC-offset are performed by using a Least Squares technique to determine the channel estimate, the initial estimate of the DC-offset and the variance of the initial estimate of the DC-offset from a training sequence portion of the received signal and a reference training sequence signal.

4. The method of claim 1, wherein the step of using the channel estimate, the initial estimate of the DC-offset and the estimated variance to determine the most likely symbol represented by the radio signal comprises the steps of:

determining a plurality of possible DC-offset values based on a model of DC-offset variation;

for each possible transition from a state i to a state j in a decoding trellis, determining a plurality of first metric values in correspondence with the plurality of possible DC-offset values;

determining which one of the plurality of possible DC-offset values corresponds to a best one of the plurality of first metric values, and selecting said one of the plurality of possible DC-offset values as an optimal DC-offset value;

using the optimal DC-offset value to determine an accumulated metric associated with the transition from state i to state j;

finding a lowest accumulated metric associated with a best path through the decoding trellis to state j; and

determining the most likely symbol represented by the radio signal based on the lowest accumulated metric associated with the best path through the decoding trellis to state j.

5. The method of claim 1, wherein the step of using the channel estimate, the initial estimate of the DC-offset and the estimated variance to determine the most likely symbol represented by the radio signal comprises the steps of:

determining a plurality of possible DC-offset values based on a model of DC-offset variation; and

using a delayed decision feedback sequence estimation technique to determine the most likely symbol represented by the radio signal, wherein the delayed decision feedback sequence estimation technique determines a metric that is based, in part, on the plurality of possible DC-offset values.

6. An equalizer for equalizing a radio signal that has been received from a channel, comprising:

a channel estimator;

means for generating an initial estimate of a DC-offset that has been introduced into the radio signal;

means for estimating a variance of the initial estimate of the DC-offset; and

means for using the channel estimate, the initial estimate of the DC-offset and the estimated variance to determine a most likely symbol represented by the radio signal.

7. The equalizer of claim 6, wherein the means for generating the initial estimate of the DC-offset that has been introduced into the radio signal comprises means for using a training sequence portion of the received signal and a reference training sequence signal to generate the initial estimate of the DC-offset that has been introduced into the radio signal.

8. The equalizer of claim 6, wherein the channel estimator, the means for generating the initial estimate of the DC-offset and the means for estimating the variance of the initial estimate of the DC-offset are performed by a unit that uses a Least Squares technique to determine the channel estimate, the initial estimate of the DC-offset and the variance of the initial estimate of the DC-offset from a training sequence portion of the received signal and a reference training sequence signal.

9. The equalizer of claim 6, wherein the means for using the channel estimate, the initial estimate of the DC-offset and the estimated variance to determine the most likely symbol represented by the radio signal comprises:

means for determining a plurality of possible DC-offset values based on a model of DC-offset variation;

means for determining, for each possible transition from a state i to a state j in a decoding trellis, a plurality of first metric values in correspondence with the plurality of possible DC-offset values;

means for determining which one of the plurality of possible DC-offset values corresponds to a best one of the plurality of first metric values, and selecting said one of the plurality of possible DC-offset values as an optimal DC-offset value;

means for using the optimal DC-offset value to determine an accumulated metric associated with the transition from state i to state j;

means for finding a lowest accumulated metric associated with a best path through the decoding trellis to state j; and

means for determining the most likely symbol represented by the radio signal based on the lowest accumulated metric associated with the best path through the decoding trellis to state j.

10. The equalizer of claim 6, wherein the means for using the channel estimate, the initial estimate of the DC-offset and the estimated variance to determine the most likely symbol represented by the radio signal comprises:

means for determining a plurality of possible DC-offset values based on a model of DC-offset variation;

a delayed decision feedback sequence estimator that determines the most likely symbol represented by the radio signal, wherein the delayed decision feedback sequence estimator determines a metric that is based, in part, on the plurality of possible DC-offset values.