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

• US 7,085,691 B2
• Filed: 07/09/2001
• Issued: 08/01/2006
• Est. Priority Date: 11/04/1999
• Status: Expired due to Fees

• Current Assignee: Verticalband Limited
• Original Assignee: Verticalband Limited
• Inventors: Schwartz, Stuart, Riess, Eilon, Sabel, Les, Turner, Laurence
• Primary Examiner(s): Rodriguez, Paul L.
• Assistant Examiner(s): Thangavelu, Kandasamy
• Application Number:
  US09/899,852
• Publication Number:
  US 20020037062A1
• Time in Patent Office: 1,849 Days
• Field of Search: 703/2, 375/346, 375/341, 375/227, 375/347, 375/220, 375/216, 375/261, 375/343, 375/355, 375/222, 375/224, 375/229, 375/148, 375/314, 370/347, 370/465, 370/335, 370/524, 370/203, 714/776
• US Class Current: 703/2
• 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 for use in a communication system for transmitting symbols of a high order constellation, comprising:

identifying reliable symbols from a sequence of captured data samples recovered from a communication channel;

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

estimating a gain of the communication channel based on the estimated constellation size.

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

P₁^{^q}=sign(q) (P₁^{^max}/(√

M−

1)) (2|q|−

1), where

P₁^{^max} represents the estimated constellation size,

M represents an order of the constellation, and

q is an index provided along an axis of the constellation.

3. The channel gain estimation method of claim 1, further comprising estimating constellation points P_1J^{^q} within a general constellation according to:

P_1J^{^q}=sign(q_j) (P_1J^{^max}/(√

M_J−

1)) (2|q_J|−

1), where

P_1J^{^max} represents the estimated constellation size along a J^th axis,

M_J represents an order of the constellation along the J^th axis, and

q_j is an index provided along the J^th axis of the constellation.

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 set of constellation points P₂^{^q} according to:

P₂^{^q}=P₁^{^q}+(|q|−

1)·

e₁^{^}, where

e₁^{^}=(1/s)Σ

_q(1/(2|q|−

1)Σ

<sub>n ∈

sq</sub>(P₁^{^q}−

y_n^q)

P₁^{^q}=sign(q) (P₁^{^max}/(√

M−

1)) (2|q|−

1)

P₁^{^max} represents the estimated value of the magnitude of the maximum constellation point,

M represents an order of the constellation,

s is a number of detected reliable symbols,

sq is a set of reliable symbols that are associated with the constellation point q,

{_n⁹} are the set of sample values which are reliable symbols that are associated with the q^th estimated constellation point . . . and

q is an index provided along an axis of the constellation.

6. A reliable symbol identification method for use in a communication system for transmitting symbols of a high order constellation comprising:

calculating a reliability factor of a candidate sample from constellation points nearest to each of a plurality of other samples in proximity to the candidate sample, wherein the candidate sample and the plurality of other samples represent a data signal recovered from a communication channel,

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:

R_n=Σ

<sub>i=−

K1,i≠

0</sub>^K2(|P<sub>n−

i</sub>|c_i, where

P<sub>n−

i</sub> is the value of a constellation point nearest to the sample y<sub>n−

i</sub> which is in proximity to the candidate sample y_n,

K1, K2 are numbers of samples adjacent to the candidate sample, and

c_i, is a coefficient representing any prior knowledge of intersymbol interference effects.

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

R_n=Σ

<sub>i=K1,i≠

0</sub>^K2√

(P<sub>1n−

i</sub>²+P<sub>2n−

i</sub>²)·

C_i, where

P<sub>1n−

i</sub> and P<sub>2n−

i</sub> respectively represent first and second dimensional values of a constellation point nearest to y<sub>n−

i</sub> which is in proximity to the candidate sample y_n,

K1, K2 are numbers of samples adjacent to the candidate sample, and

c_i is a coefficient representing any prior knowledge of intersymbol interference effects.

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.

13. A method of identifying reliable symbols for use in a communication system for transmitting symbols of a high order constellation, comprising:

for a candidate sample y_n recovered from a communication channel;

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−

i</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.

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, representing any prior knowledge of intersymbol interference effects.

15. The method of claim 13, the predetermined limit is (K1+K2) d_min where d_min 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.

17. A method of identifying reliable symbols for use in a communication system for transmitting symbols of a high order constellation, comprising:

for a candidate sample recovered from a communication channel;

determining whether any of a plurality of constellation points is within a predetermined threshold, where each of the plurality of constellation points is associated with samples neighboring the candidate sample also recovered from a communication channel,

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