Methods and apparatus for spectral filtering channel estimates

• US 7,173,991 B2
• Filed: 06/17/2002
• Issued: 02/06/2007
• Est. Priority Date: 06/17/2002
• Status: Expired due to Fees

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Scarpa, Carl G.
• Primary Examiner(s): Ghayour; Mohammed
• Assistant Examiner(s): Vlahos; Sophia
• Application Number:
  US10/172,984
• Publication Number:
  US 20030231725A1
• Time in Patent Office: 1,695 Days
• Field of Search: 375/142, 375/150, 375/232, 375/267, 375/343, 375/347, 375/349, 375/350, 375/346, 375/140, 375/141, 375/229, 375/230, 375/285, 375/341, 375/340, 370/290, 370/355, 370/437, 370/468, 370/330, 370/335, 370319-321, 370/479, 370/210, 455/65, 455/134, 455/231, 455/303, 455/52.1, 455/52.3, 455/67.1, 455/67.3, 455/67.6, 455/306, 455/506, 708/222, 708/300, 708/322
• US Class Current: 375/350
• CPC Class Codes: H04L 25/022 of frequency response

Abstract

Methods and apparatus for performing spectral filtering of channel estimates corresponding to a communications channel used to transmit a multi-tone signal are described. A channel estimate is examined to identify portions where significant multi-path interference is present. Real, as opposed to complex, low pass filters are used to perform spectral filtering on the channel estimate to produce a filtered channel estimate. Values corresponding to portions of the channel estimate determined to correspond to areas where significant multi-path interference is present are replaced with the original unfiltered channel estimate values to generate a selectively filtered channel estimate. By using unfiltered channel estimate values in areas of multi-path interference, the errors introduced in such areas by real filtering are avoided without the need to resort to complex filtering.

Claims

1. A method of processing an initial channel estimate including a plurality of initial channel estimate values, the initial channel estimate corresponding to a multi-tone communications channel, the method comprising:

filtering the initial channel estimate using a real filter to produce a filtered channel estimate including a set of filtered channel estimate values;

identifying regions of said initial channel estimate corresponding to multi-path interference;

performing a channel compensation operation using at least one initial channel estimate value corresponding to a channel estimate region where multi-path interference is identified and using at least one filtered channel estimate value in another channel estimate region;

wherein said communications channel is a communications channel through which an orthogonal frequency division multiplexed signal is transmitted;

wherein each of said initial communications channel estimate values corresponds to the frequency of a tone of said orthogonal frequency division multiplexed signal; and

wherein said step of identifying regions of said initial channel estimate corresponding to multi-path interference includes identifying regions where said multi-path interference is sufficient to cause said filtering to produce filtered channel estimate values which are less accurate than the unfiltered channel estimate values corresponding to the same regions.

9. A machine readable medium including machine executable instructions used to control a machine to perform the steps recited in claim 1.

2. A method of processing an initial channel estimate including a plurality of initial channel estimate values, the initial channel estimate corresponding to a multi-tone communications channel, the method comprising:

filtering the initial channel estimate using a real filter to produce a filtered channel estimate including a set of filtered channel estimate values;

identifying regions of said initial channel estimate corresponding to multi-path interference;

performing a channel compensation operation using at least one initial channel estimate value corresponding to a channel estimate region where multi-path interference is identified and using at least one filtered channel estimate value in another channel estimate region; and

wherein channel estimate regions of multi-path interference are regions where the channel estimate values are degraded by performing said filtering using a real filter.

3. A method of processing an initial channel estimate including a plurality of initial channel estimate values, the initial channel estimate corresponding to a multi-tone communications channel, the method comprising:

filtering the initial channel estimate using a real filter to produce a filtered channel estimate including a set of filtered channel estimate values;

identifying regions of said initial channel estimate corresponding to multi-path interference;

performing a channel compensation operation using at least one initial channel estimate value corresponding to a channel estimate region where multi-path interference is identified and using at least one filtered channel estimate value in another channel estimate region; and

replacing filtered channel estimate values in said filtered channel estimate corresponding to regions of multi-path interference with unfiltered channel estimate values corresponding to said regions of multi-path interference to thereby produce a selectively filtered channel estimate.

4. The method of claim 3, wherein said step of:

identifying regions of said initial channel estimate corresponding to multi-path interference includes;

generating channel state information values from said initial channel estimate values;

comparing each of said channel state information values to a threshold; and

determining that a region of said initial channel estimate corresponding to a compared channel state information value corresponds to a region of multi-path interference when said threshold value is not exceeded.

5. The method of claim 3, wherein said step of:

identifying regions of said initial channel estimate corresponding to multi-path interference includes;

generating channel state information values from said initial channel estimate values; and

comparing said channel state information values to a threshold.

6. The method of claim 3, wherein said step of performing a channel compensation operation using initial channel estimate values corresponding to channel estimate regions where multi-path interference is identified and using filtered channel estimate values in other channel estimate regions includes using said selectively filtered channel estimate.

7. The method of claim 6, wherein said real filter is a real low pass filter.

8. The method of claim 7,

wherein said communications channel is a communications channel through which an orthogonal frequency division multiplexed signal is transmitted;

and

wherein each of said initial communications channel estimate values corresponds to the frequency of a tone of said orthogonal frequency division multiplexed signal.

10. A multi-tone communications apparatus, comprising:

a real low pass filter circuit for performing a real low pass filtering operation on a set of initial channel estimate values to generate a filtered channel estimate including filtered channel estimate values;

a channel state confidence computation module for identifying at least one initial channel estimate value resulting from multi-path interference; and

a selective replacement module being coupled to said real low pass filter module to receive said filtered channel estimate and being coupled to said channel state confidence computation module, said selective replacement module generating a selectively filtered channel estimate by replacing at least one filtered channel estimate value with an identified initial channel estimate value.

11. The apparatus of claim 10, wherein channel state confidence computation module includes:

means for generating confidence state information values from said initial channel estimate values; and

a comparator for comparing said generated confidence state information values to a threshold value.

12. The apparatus of claim 11, wherein said threshold value is programmable, said channel state confidence computation module including an input for receiving said threshold value.

13. The apparatus of claim 11, further comprising:

a channel computation circuit coupled to said selective replacement module for performing a channel compensation operation as a function of the selectively filtered channel estimate generated by said selective replacement module.

14. The apparatus of claim 13, further comprising:

a channel estimate computation module coupled to said low pass filter and said channel state confidence computation module.

15. The apparatus of claim 14, wherein said channel estimate computation module is further coupled to said selective replacement module.

16. The apparatus of claim 15, wherein said channel state confidence computation module is coupled to said channel compensation module and provides weighting information to said channel compensation module used to weight different values included in said selectively filtered channel estimate as part of a channel compensation operation.

17. The apparatus of claim 15, wherein said channel estimate computation circuit computes a channel estimate for an orthogonal frequency division multiplied communications channel.

18. An apparatus for processing an initial channel estimate including a plurality of initial channel estimate values, the initial channel estimate corresponding to a multi-tone communications channel, the apparatus comprising:

means for filtering the initial channel estimate using a real filter to produce a filtered channel estimate including a set of filtered channel estimate values;

means for identifying at least one region of said initial channel estimate corresponding to multi-path interference;

means for performing a channel compensation operation using an initial channel estimate value corresponding to said at least one region of said initial channel estimate where multi-path interference is identified and using at least one filtered channel estimate value in another channel estimate region; and

means for replacing filtered channel estimate values in said filtered channel estimate corresponding to regions of multi-path interference with unfiltered channel estimate values corresponding to regions of multi-path interference to thereby produce a selectively filtered channel estimate.