Reliable symbols as a means of improving the performance of information transmission systems

• US 20020037062A1
• Filed: 07/09/2001
• Published: 03/28/2002
• Est. Priority Date: 11/04/1999
• Status: Active Grant

• Current Assignee: Verticalband Limited
• Original Assignee: Verticalband Limited
• Inventors: Riess, Eilon, Schwartz, Stuart, Sabel, Les, Turner, Laurence
• Granted Patent: US 7,085,691 B2
• Time in Patent Office: Days
• US Class Current: 375/348
• CPC Class Codes: H04L 2025/0349 as a feedback filter
• CPC Class Codes: H04L 2025/03694 Stop and go
• CPC Class Codes: H04L 25/0238 using blind estimation
• CPC Class Codes: H04L 25/03057 with a recursive structure H04L25/03031 takes precedence
• CPC Class Codes: H04L 25/067 providing soft decisions, i.e. decisions together with an estimate of reliability H04L25/068 and H04L25/069 take precedence; sequence estimation techniques H04L25/03178

Abstract

All practical communication channels impose some type of corruption on received data through inter-symbol interference (ISI). ISI corruption is particularly acute in high-order constellation transmission. Although ISI effects of high-order constellation transmission are very large on average, some symbols may be received that suffer relatively low levels of ISI. These symbols are “reliable symbols” and can be used to provide blind estimation of the ISI coefficients. Once the ISI effects of a channel are known, all captured signals may be corrected.

Claims

1. A channel gain estimation method, comprising:

identifying reliable symbols from a sequence of captured data samples,

estimating a constellation size from a set of maximally-sized reliable symbols.

2. The channel gain estimation method of claim 1, further comprising estimating constellation points {circumflex over (P)}^q within a square constellation with uniformly separated points according to:

3. The channel gain estimation method of claim 1, further comprising estimating constellation points {circumflex over (P)}₁^q, within a general constellation according to:

4. The channel gain estimation method of claim 1, further comprising revising the estimate of the constellation size based on additional reliable symbols.

5. The channel gain estimation method of claim 4, wherein the revising comprises estimating a second s et of constellation points {circumflex over (P)}hd 2^q according to:

{circumflex over (P)}₂^q={circumflex over (P)}₁^q+(2|q|−

1)·

ê

₁, where

6. A reliable symbol identification method comprising:

calculating a reliability factor of a candidate sample from constellation points nearest to each of a plurality of samples in proximity to the candidate sample,

if the reliability factor is less than a predetermined limit, designating the candidate sample as a reliable symbol.

7. The method of claim 6, wherein the reliability factor R_n of the candidate sample is given by:

8. The method of claim 6, wherein the reliability of a two-dimensional candidate sample y_n is given by:

9. The method of claim 6, further comprising, for any samples having similar reliability factors, prioritizing the samples based on the samples'"'"' values.

10. The method of claim 6, further comprising, for any sample having a reliability factor that is less than the predetermined limit, comparing the sample'"'"'s value against a second threshold and, if the value exceeds the threshold, disqualifying the sample as a reliable symbol.

11. The method of claim 6 further comprising, for any samples having similar reliability factors, prioritizing the samples based on values of constellation points nearest to the samples.

12. The method of claim 6 further comprising, for any sample having a reliability factor that is less than the predetermined limit, comparing a value of a constellation point nearest to the sample to a second threshold and, if the value exceeds the threshold, disqualifying the sample as a reliable symbol.

14. The method of claim 13, wherein the adding adds a scaled value of the constellation point to the reliability factor, the value scaled in accordance with a predetermined coefficient c_i.

15. The method of claim 13, the predetermined limit is (K₁+K₂)d_min where dmin is half a distance between two constellation points that are closest together in a governing constellation.

16. The method of claim 13, wherein the predetermined limit is the product of K₁ +K₂ and half the width of an annular constellation ring associated with the candidate symbol.

18. The method of claim 17, wherein the neighboring samples occur in a first window adjacent to the candidate sample on one side of the candidate sample.

19. The method of claim 17, wherein the neighboring samples occur in a pair of windows that are adjacent to, and on either side of the candidate sample.

13. A method of identifying reliable symbols, comprising, for a candidate sample y_n:

iteratively, for i=−

·

K₁ to K₂, i≠

0;

adding to a reliability factor a value derived from a constellation point nearest to a sample y<sub>n−

1</sub>,

if the reliability factor exceeds a predetermined limit, disqualifying the candidate sample as a reliable symbol, and

otherwise, incrementing i and, if i=0, re-incrementing i for a subsequent iteration;

thereafter, unless the candidate symbol has been disqualified, designating the candidate sample as a reliable symbol.

17. A method of identifying reliable symbols, comprising, for a candidate sample,

determining whether any of a plurality of constellation points each associated with sample neighboring the candidate sample is within a predetermined threshold,

if none of the constellation points exceed the threshold, designating the candidate sample as a reliable symbol.