text:
Another clarification today in just how bad the NCAA wants to screw USC. Prison screw.
The NCAA has clarified that it will currently allow other teams to contact USC juniors and seniors in attempts to recruit them away from the Trojans. Furthermore, it will allow the other teams to waive the typical transfer year of ineligibility so the players can get on the field THIS SEASON! That means Oregon could call Mitch Mustain today and offer him Masoli's quarterback position with promise of immediate play. Don't you think that would be enticing? What about CJ Gable and Marc Tyler? I wouldn't be surprised if Gable wants to use his last year of eligibility to prove he's NFL worthy, or if Tyler finally wants the chance to get the major playing time he wasn't able to earn at USC.


text:
This building is listed under the Planning (Listed Buildings and Conservation Areas) Act 1990 as amended for its special architectural or historic interest.
Name: CHURCH OF ST STEPHEN
List entry Number: 1136676
The building may lie within the boundary of more than one authority.
National Park: PEAK DISTRICT
Grade: II
Date first listed: 14-Apr-1967
Date of most recent amendment: Not applicable to this List entry.
The contents of this record have been generated from a legacy data system.
Legacy System: LBS
This list entry does not comprise part of an Asset Grouping. Asset Groupings are not part of the official record but are added later for information.
Legacy Record - This information may be included in the List Entry Details.
SJ 97 SE MACCLESFIELD FOREST C.P.5/99 Church of St Stephen
(Forest Chapel).14.4.67GV IIChurch: Origins dated 1673 but nave and chancel completely rebuilt
1831. Coursed squared buff-pink sandstone rubble, sandstone
dressings. Kerridge stone-slate roof and stone ridge. Nave and
chancel in one range of 5 bays. Semi-circular headed window reveals
have T-shaped tracery and lattice leaded windows. Porch on south side
of nave is gabled and entrance has a rusticated cambered head, the
keystone having the date of rebuilding, and the original stone reading
SS 1673 above. Low 3-stage west tower with saddleback roof of heavy
flags has west door under a plain lintel and single light bell
openings with stone louvres in top stage.
Interior: Very simple with no division between nave and chancel.
Some Victorian glass in east window.
Listing NGR: SJ9743272141
National Grid Reference: SJ 97432 72141
The above map is for quick reference purposes only and may not be to scale. For a copy of the full scale map, please see the attached PDF - 1136676.pdf - The pdf will be generated from our live systems and may take a few minutes to download depending on how busy our servers are. We apologise for this delay.
This copy shows the entry on 03-Aug-2015 at 01:33:23.

subset: commoncrawl


text:
Registered Massage Therapists
by Stephanie Perreault-Bittner / Wednesday, 01 April 2015 / Published in
- Full Time
- Edmonton, Calgary
Posted 4 months ago
Website EvelineCharles
|Registered Massage Therapist
|Calgary, Edmonton, Kelowna
|Closing date
|When position is filled.
EvelineCharles Salons & Spas is among the largest and most distinctive personal care destinations in Canada. We offer only the finest in haircare, esthetics, massage services and products.Join the incredible team of compassionate massage practitioners providing massage and spa body services in our elegant spas. Qualified applicants are licensed, devoted to excellence in guest care, are passionate for the profession, and have a nurturing soul.EvelineCharles provides specialized training in our signature treatments, client service procedures and retail products and customer education. Our performance based pay system provides stability and focuses on individual growth in all aspects of your career as well as providing an excellent benefits package.
Must be a trained massage practitioner
Must have 2200 hours OR 1200 hours while currently enrolled in education to complete the remaining hours.
|Why Work For EvelineCharles?
|EvelineCharles is constantly setting standards for innovative salon and spa services and products. We are continually recognized for our business achievements and successes.Global Salon Business Awards, Global Salon Entrepreneur of the Year Award
Cool Companies Magazine, Cool Company Award
Consumer Choice for Salon and Spa Award
Profit Magazine, Top 100 Women Entrepreneurs recognition
Junior Achievement Alberta Business Hall of Fame, First Female Inductee
Consumer's Choice Awards, Business Woman of the Year Award
Alberta Venture Magazine, Marketer of the Year Award
Spa Management, International Day Spa of the Year Award
Salon Today, Top 200 Fastest Growing Salons in Canada and USA Award
Alberta Venture, Fastest Growing Companies in Alberta AwardHealth and dental benefits
Competitive hourly wages
A Beauty Plan! Great product and service discounts.
Continuous education and a fulfilling career path.
Fast paced environment with growth and new venture implementations
Committed support team
|Permanent Full Time
|Next Steps
|If you are interested in applying for this opportunity, please send your resume with cover letter stating your salary expectations. Email applications to : email@example.com ; fax: Attention: Careers to 780 425-0763.
To apply for this job email your details to firstname.lastname@example.com


text:
Boys basketball player of the week: Tyler Pate, Port Aransas
CORPUS CHRISTI - Tyler Pate
Port Aransas
The 6-foot-2 junior had a huge week, averaging 36 points per game in Port Aransas' three contests. He scored 40 points in a win over Taft and 38 in a win over Austwell-Tivoli. Pate scored 30 in Tuesday night's loss to Orange Grove. So far this season, Pate is averaging 27.4 points per game and has made 14 3-pointers in nine games. Here's a little info behind the person with all the stats:
Q: If you could only eat one thing everyday for the rest of your life, what would it be?
A: Fried chicken
Q: What is your favorite sports movie?
A: Hoosiers
Q: What is your favorite subject in school?
A: History
Q: One word people use to describe you is ...
A: Competitive
Q: To get pumped up before a big game you listen to ...
A: Tech N9ne
Q: Who is the person who inspires you the most?
A: Coach K and my basketball coach
Q: If you were given the opportunity to meet one famous person (dead or alive) it would be ...
A: Brandon Jennings
Q: Would you rather be rich and ugly or handsome and poor?
A: Handsome and poor
Q: My favorite sports memory has been ...
A: My first playoff game in my freshman year
Q: After high school I want to....
A: Play college basketball
Q: One thing people don't know about me is ...
A: I love to cook
Q: If I could invite any three people dead or alive to dinner, I'd invite...
A: Pat Riley, Michael Jordan, Jesus
Q: My favorite sports teams to root for are...
A: Duke, Phoenix Suns, Los Angeles Angels, Texas
Q: Which cartoon super hero would you be if you could be one and why?
A: Superman, because he's strong and he can fly.
Q: If you could change one physical thing about you what would you change?
A: My height. I wish I could be 6-foot-6.
Q: Are you superstitious and if so, what is one of your superstitions?
A: I eat the same breakfast in the morning on game day: French Toast. Before games, I eat Fried Elvis Presleys (peanut butter and banana sandwiches).
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text:
Session overview by Robert Kieft
This session is the inaugural meeting of a new interdisciplinary MLA discussion group formed by librarians within the Association for the
discussion of matters of mutual interest with scholars. The advent of technological tools that perform some familiar tasks of literary
research and offer new opportunities for gathering, working with, and publishing texts, images, and data challenge the ability of libraries
and IT organizations to support faculty and student work and require complex collaborations on campus and often with scholars, librarians,
and technologists at other institutions. Panelists will present current work, and the group will discuss agenda for its future and how
it can promote the creation and curation of scholarly collections and archives, publications, research data, and teaching and study tools
through professional associations and on their own campuses.
Robert Kieft, College Librarian, Occidental College (firstname.lastname@example.com)
Heather Bowlby
"Digitizing Julia Margaret Cameron's Illustrations to Tennyson's Idylls of the King, and Other Poems (1874-75): A Case Study"
As a digital humanities intern at the Networked Infrastructure for Nineteenth-Century Electronic Scholarship (NINES) group based at the University of Virginia, I am currently working to create a digital edition of Julia Margaret Cameron's photographically illustrated edition of Alfred Tennyson's Idylls of the King, entitled Illustrations to Tennyson's Idylls of the King, and Other Poems (1874-75). In this presentation, I discuss the challenges that I have encountered in the process of developing this interdisciplinary project and address the implications of these issues for integrating editorial work with the practice of creating a sustainable digital resource.
Cameron's illustrated version of Tennyson's Idylls of the King is well-known in the field of book history, but a complete scholarly edition is not available. I began my project one year ago with the goal of creating a digital edition of this important work that would be suitable for scholarly use in many academic fields, particularly English literature, art, art history, history, book history, and women's studies. I plan to reproduce the physical object as much as possible in an electronic format while maintaining the appropriate scholarly framework.
While I have made progress under the sponsorship of NINES, I have not yet been able to accomplish my objective of creating a widely-accessible, digital scholarly edition of Cameron's illustrated Idylls. Having access to digital humanities resources at the University of Virginia has enabled me to consider the structural design of my project and the editorial procedures that might best represent it in a digital environment. However, the considerable assistance I have received has not enabled me to solve other problems I have experienced in developing my project. As I have discovered, many factors are involved in successfully launching a digital resource. Some of these considerations include locating the necessary technical support, determining the specific function of the resource within different scholarly contexts, securing an enduring online space to house the resource, and collaborating with librarians and other professionals in related fields to fit the resource within pre-existing institutional frameworks.
These issues are often more difficult for graduate students like myself to address effectively. In addition to having limited opportunities for ongoing institutional support, graduate students developing digital resources also must consider how best to position their projects within the broader research they perform to earn their degrees. My experience creating my digital edition of Cameron's illustrated Idylls is representative of these widespread issues in many ways, and in this presentation, I propose it as a case study of the problems facing graduate students involved in similar digital projects.
Heather Bowlby, Doctoral Candidate, Department of English, University of Virginia (email@example.com)
Marija Dalbello
Digital Archives and Digital Paleography in the Humanities Program
Creating a digital archive is an act of re-inscription of media and information, opening new space for interpretation of writing, reading, and structuring of text. At its core, this activity is central to the humanities program. In my panel presentation I will focus on the cultures of writing, collecting, and reading in the context of building digital archives - by outlining trends, exemplifying practice, and drawing curricular conclusions.
First, I will explore humanistic engagement with technologies of text represented by vernacular digital archives, i.e. the archives of primary sources created by scholars for scholars, and their central and growing importance as a form and, instrumentally, in teaching, and scholarship. Based on the characteristics of some 150 projects that were identified as influential in the fields of history, literature and languages through extensive searches of conference programs, professional associations' newsletters, syllabi, and published reviews from 1996 to date, I will give an overview of patterns, historical trends, typologies, and the archives' status in disciplinary discourses.
Secondly, I will address the work of "editing" for a digital archive based on first-hand experience with two exemplary collections of letters – Frautschi Letters Virtual Archive (http://csumc.wisc.edu/flva/let/FLVAlettershome.html) at the University of Wisconsin-Madison (2000), and Digitizing Immigrant Letters (http://ihrc.umn.edu/research/dil/index.html) at the Immigration History Research Center (University of Minnesota) (2010). I argue that "editing" letters for a digital archive can reveal complex relationships between text and image, and of the interstitial nature of writing in the transposition of chirographic to typographic forms, and in written forms rooted in oral performance of language. I will demonstrate how that affected the contextualization for digital archives of letters: their literary, historical and informational aspects.
In this presentation I link interpretive information studies to the pedagogy of digital humanities and argue for curricular centrality of the history of books, documents, records and information in that context.
Marija Dalbello, Associate Professor, School of Communication & Information, Rutgers University (firstname.lastname@example.com)
Amy Earhart
"19th-Century Concord Digital Archive Project"
As our cultural heritage is being digitized at an increasingly rapid rate we are experiencing greater access to materials, but are also confronted with new problems of use. Universities, libraries, and museums are digitizing their collections, but the metadata and search capacities of the materials continue to work in isolation, leaving numerous digital objects unused. It is crucial that those entities participating in the development of digital resources advance interoperable ways to interconnect collections. And, because the participants involved with humanities digital objects creation are often scholarly or non-profit organizations, the development of low-cost, open source solutions that are easily applied by the non-specialized user is imperative.
Earhart will discuss The 19th-Century Concord Digital Archive partnership as a possible model for interaction between scholars and library entities. This project leverages resources and skills to develop a model of interaction between academic, museum, library, and community partners, and to create multiple interfaces for browsing digital information about the town of Concord. The model will be useful to those searching to develop such a collaboration, particularly those small libraries and museums who might be able to harness volunteers, but not expensive technical support. In addition, the ability to search multiple sites that contain metadata and digital objects related to a subject matter, such as 19th-century Conord, as well as to display that material in new and innovative ways, such as GIS based maps, timelines, and exhibits, will encourage use of the material by both scholars and the public and produce greater cultural understanding of this historical and literary period.
Manuel M. Martin-Rodriguez
The Chicano/a Literature Intertextual Database: Toward a Literary History Beyond Borders
Manuel M.
Martín-Rodríguez, Professor of Literature, University of
California, Merced ( email@example.com )
Susanne Woods
Collaborative Development of Information Literacy and Advanced Undergraduate Research in the Liberal Arts Colleges
The Council of Independent Colleges (CIC) has collaborated over the last ten years with the Association of College and Research Libraries (ACRL) and other groups and institutions to help transform the college library and offer faculty and librarians practical assistance in confronting swift and dramatic changes in the research environment. A current CIC-ACRL collaboration, funded by a generous grant from The Andrew W. Mellon Foundation, seeks to help institutions develop campus-specific plans for information fluency in literature majors. The CIC experience suggests models for developing collaborations among faculty, librarians, and academic technologists in both general education programs and in the major.
In response, the CIC received Mellon funding for a series of workshops on "Transforming the College Library," offering teams from private liberal arts colleges the opportunity to learn from experts and each other how they might adapt to the new environment. The three-day workshops were offered at various locations between 2002 and 2008, and brought together librarians, academic technologists, and chief academic officers to work out practical plans from what had been competing cultures. The National Institute for Technology in Liberal Education (NITLE) was also involved in these earlier workshops, and toward the end both the United Negro College Fund and the Appalachian Colleges Association had become part of the project.
Susanne Woods,Council of Independent Colleges Senior Advisor; Provost and Professor of English Emerita, Wheaton College (MA) (firstname.lastname@example.com)
Susan Barnes Whyte, College Librarian, Linfield College;
ACRL Liaison to the CIC (email@example.com)
Panel organizer/convener: James R. Kelly, Humanities Bibliographer, W.E.B. Du Bois Library, University of Massachusetts Amherst (email@example.com)


text:
The Department of Intercollegiate Athletics and Physical Education is pleased to announce another fall and winter of the Columbia University Swim School. The Columbia University Swim School will be administered by the coaching staff of the Columbia University Women and Men's varsity swimming programs.
Columbia Varsity Swim School Summer Session (CVSS):
Try Outs: Tuesday September 9 and Thursday September 11 - New Swimmers Only
|Session 1
Sep. 16 - Dec 18
(Off Thanksgiving week)
|Ages 12 and under
|cost: $450
Tuesdays & Thursdays
6:00pm - 7:00pm
11:00am - 12:00pm
|Session 2
Jan 20- May 14
(No practice March 16 -20)
|Ages 12 and under
|cost: $450
Tuesday & Thursdays
6:00pm - 7:00pm
11:00am - 12:00pm
All practices will be organized and administered by members of the Men's and Women's coaching staffs.
- Make checks payable to "Columbia University"
- Participation is up to the discretion of the family. We recommend attending all weekly sessions for maximum skill development. Fees will not be prorated due to other sports, classes, etc.
-Once checks are deposited, there will be no refunds
- Competitive meets are not a focus of this program. Skill development is the focus and meet participation is at the discretion of the coaches.
Important Information for Returning Participants: If you are a returning participant, we must receive registration forms and a check by September 15th. At that time, we will open registration to new participants and we WILL NOT BE ABLE to guarantee a space for the fall. Emails will not save your space in the program.
**practices subject to cancelation/change due to building closure, university swim meets, or other university obligations.
For information about the current session, please contact Gustavo Leal email@example.com or Jim Bolster email@example.com
Click Here for Registration Form


text:
CorpCast Episode 6: A Brief Introduction to the Delaware Rapid Arbitration Act
Alternate Dispute Resolution
Paths to Dispute Resolution
Polsinelli Podcasts - What Employers Need to Know about Mediation and Arbitration
Polsinelli Podcasts - Protecting Policy Holders From Arbitration Bias
Blecker: GM Recalls Show Need for Harsher Penalties for "Red Collar" Criminals
Polsinelli Podcasts - Jury or Bench Trial? A Business Litigation Survival Guide
Polsinelli Podcast - Business Litigation Survival Guide
Two-Pronged Approach to Defending Lawsuits – Interview with Dominic Picca, Member, Mintz Levin
Patent Mediation – Interview with John Delehanty, Member, Mintz Levin
Bill on Bankruptcy: Junk Debt Interest Rates at 30-Year Low
Legal Fallout of an Armstrong Confession
Lance's Lawyer: Armstrong Didn't Betray Me
Lance's Lawyer: Armstrong Didn't Betray Me: Video
Lawyer: Madoff May Be One of My Clients' Better Investments
In this issue: New Maritime Law Awaited; Increased Private Sector Involvement in Dubai Water and Electricity Sector; Pro Bono initiative: Women's Rights and the Convention on the Elimination of All Forms of Discrimination...more
The first thing that strikes the reader of the essays is the richness of the carefully selected
topics and areas covered by the authors. Its richness is reflected in a number of ways: the
authors elaborate on various globally...more
Information on prevalence of anti-Muslim bias and strategies to minimize this bias in court presented by two experienced trial consultants. ...more
How to identify authoritarian jurors. What the literature says that can aid you in selecting or de-selecting these jurors based on the facts of your case. ...more
Should attorneys decry racial profiling by police officers and yet use it in jury selection? A British philosopher inquires and experienced trial consultants offer their thoughts. ...more
Obstacles to and benefits of maintaining racial diversity on juries for better decision-making. ...more
Find an Alternative Dispute Resolution (ADR) Author »
Your first step to building a free, personalized, morning email brief covering pertinent authors and topics on JD Supra:
Sign up to create your digest using LinkedIn*
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Copyright ©


text:
FinancialThe finances of the church, whether they are the finances of a congregation, synod or the churchwide organization, are an important and necessary function of its mission. Through responsibly organized and managed financial resources, we are able to support and carry on the work of the church as we serve and love our neighbor, and do God's work of restoring and reconciling communities in Jesus Christ's name throughout the world.
On the financial web pages, you will find information about the finances of the ELCA and resources helpful to treasurers, bookkeepers and leaders, including but not limited to:
- the churchwide organization's year-end report for the prior fiscal year;
- the most recent quarterly financial reports;
- the budget proposal as presented to the most recent Churchwide Assembly;
- resources for congregational treasurers and bookkeepers;
- various forms and procedures for synod treasurers and bookkeepers;
- mileage rate reimbursement information;
- an expense report form.


text:
|Viewing 1-1 of 1 Record(s)
|Title: Walking on the moon: Life on earth has not been the same since the day these unforgettable words crackled over the airwaves: "Houston, Tranquility Base here. The Eagle has landed." Forty years later, the men who made the Apollo 11 mission a success tell t
|Authors: Vine,Katy
|Source: Texas Monthly, 2009, 37 :7 ,pg 106- 113
|Subjects: United States National Aeronautics and Space Administration Space vehicles - Landing - Moon
|Additional Information: ID: 1884; RP: NOT IN FILE
|Ref ID: 81687
|Viewing 1-1 of 1 Record(s)
Return to the Index to Texas Magazines and Documents Homepage


text:
Posts Tagged «HDTVs»
Will LG's wallpaper-thin OLED TV catch on? May 28, 2015 at 1:44 pm
LG recently unveiled a concept television design that, if produced, would be the thinnest ever. The 55-inch OLED display is barely 1mm wide — about the width of a DVD.
Report: New Apple TV, SDK to appear at WWDC March 20, 2015 at 4:12 pm
Apple has been spinning its wheels with the Apple TV for years now, but recent reports claim that Cupertino is finally willing to show off what it's been working on.
Roku takes aim at TV market with new Roku TV August 19, 2014 at 12:01 pm
Not content with producing the best media streaming box on the market, Roku has now set its sights on the television market by releasing an HDTV with all of the Roku's streaming capabilities built in.
New OLED tech could make smartphone screens cheaper and more power-efficient November 11, 2013 at 9:07 am
Companies like Samsung and LG have been increasingly relying on OLED display technologies for smartphones, digital cameras, and even TVs. A new type of OLED panel could make screens more energy efficient and cheaper at the same time.
Apple iTV expected to launch this year, featuring finger-worn iRing remote control April 3, 2013 at 2:00 pm
As Apple looks to sneak its way into other markets — or in the case of the iWatch, create them — its long-rumored attempt at a television always seems to find its way to the forefront of the conversation. On cue, one analyst detailed very specific components of what Apple's iTV will have — most notably, an iPad-sized second screen on which to watch media, and a ring you wear on your finger that acts as a remote control.
Samsung's upgradable TV: DOA, unless the company reinvents itself July 27, 2012 at 11:09 am
Samsung has started shipping the first televisions equipped with its new Smart Evolution technology, but moving to an upgradable model of business will only work if the company rethinks its own priorities.
IKEA announces furniture with integrated TV, speakers, and Blu-ray April 17, 2012 at 7:08 am
If you long for those balmy days when TVs looked like pieces of furniture, good news: This fall, IKEA will release Uppleva, a range of home entertainment systems that integrate a flat-screen full HD TV, 2.1 sound, and a Blu-ray player.
Bye bye, Best Buy? January 6, 2012 at 1:15 pm
I admit it: I shop at online retailers all the time — but I still felt my heart sink into my kneecaps when I read some chilling statistics about Best Buy teetering on the edge of solvency.
OLED TVs are hot at CES, but are nothing more than a technological pipe dream January 4, 2012 at 10:45 am
OLEDs would be awesome — if we could get them built in large panels.
How Nvidia's 3D Vision works with Skyrim, Battlefield 3, and others December 5, 2011 at 9:00 am
Thinking about taking the plunge into stereoscopic 3D this holiday season? Matthew Murray did some extensive testing — and whole lot of gaming — with Nvidia's 3D Vision 2 so you'll know what to expect.


text:
A multilevel optical receiver can comprise a plurality of comparators that generally correspond with the number of levels in a multilevel data stream. Each comparator can be individually controlled and fed a decision threshold in order to decode a multilevel signal. The multilevel optical receiver can generate a statistical characterization of the received symbols in the form of a marginal cumulative distribution function (CDF) or probability density function (pdf). This characterization can be used to produce a set of ε-support estimates from which conditional pdfs are derived for each of the transmission symbols. These conditional pdfs may then be used to determine decision thresholds for decoding the received signal. The conditional pdfs may further be used to continuously estimate the fidelity or error rate of the received signal without the transmission of a testing sequence. The ε-supports may further be used to automatically control the gain on the receiver.
1. A desymbolizer for receiving and decoding a multilevel communication signal, comprising:
an analog-to-digital converter for receiving and decoding the multilevel communication signal and comprising a plurality of comparators;
a signal integrity unit coupled to the analog-to-digital converter, comprising a microcontroller for controlling a threshold voltage of each comparator located in the analog-to-digital converter, the microcontroller calculating at least one of a cumulative distribution function and a probability density function derived from the multilevel signal and associated with the threshold voltage of each comparator, and a digital-to-analog controller coupled to inputs of the comparators of the analog-to-digital converter.
2. The desymbolizer of
3. The desymbolizer of
a plurality of comparators for receiving the multilevel signal; and
a decoder coupled to the outputs of the comparators.
4. The desymbolizer of
5. The desymbolizer of
6. The desymbolizer of
7. A desymbolizer for receiving and decoding a multilevel communication signal, comprising:
an analog-to-digital converter for receiving and decoding the multilevel communication signal;
a signal integrity unit coupled to the analog-to-digital converter for calculating and controlling one or more threshold voltages supplied to the analog-to-digital converter, for calculating at least one of a cumulative distribution function and a probability density function derived from the multilevel signal and associated with the one or more threshold voltages; and
a signal conditioning filter that equalizes and optimally filters the multilevel communication signal prior to the analog-to-digital converter, where the signal integrity unit selects an operating point of the signal conditioning filter based upon the determination of the fidelity of the multilevel signal.
8. The desymbolizer of
9. The desymbolizer of
10. The desymbolizer of
11. The desymbolizer of
a plurality of comparators for receiving the multilevel signal; and
a decoder coupled to the outputs of the comparators.
12. The desymbolizer of
13. The desymbolizer of
14. The desymbolizer of
15. The desymbolizer of
16. The desymbolizer of
17. A method for determining threshold voltages of comparators in a multilevel signal receiver system, comprising the steps of:
evaluating voltage levels of a multilevel signal at predetermined time intervals;
estimating a probability density function based on the voltage levels;
determining one or more statistical centers positioned on local minima that are present in the probability density function; and
adjusting one or more threshold voltage levels based on the one or more statistical centers.
18. The method of
19. The method of
This application is a continuation of and claims priority to application Ser. No. 10/108,598 filed Mar. 28, 2002, entitled "Method and System for Decoding Multilevel Signals." The entire contents of which are hereby incorporated by reference.
The present invention relates to optical fiber communication systems and increasing the throughput of data transmission over an optical fiber communication system through the use of multilevel modulation. Specifically, the present invention relates to a method and system for demodulating multilevel signals.
The use of multilevel signals in an optical network architecture increases channel data throughput rates without requiring replacement of the existing optical fiber in a link (i.e., the optical fiber plant). While multilevel signals can offer this advantage of increased channel data throughput rates to an optical network architecture, conventional hardware and software used to decode the multilevel signal often cannot achieve this advantage because of difficulties in establishing thresholds by receivers for a multilevel signal. These thresholds are needed by the receiver to decode the multilevel signal into the one or more symbols that make up the multilevel signal.
The difficulties in establishing the thresholds are associated with reliably characterizing the noise that is present within a multilevel signal. Further, conventional hardware and software do not address multilevel signals comprising greater than two-level data streams. That is, the conventional art only provides methods for automatically controlling the threshold or decision points for traditional two-level data streams.
The voltage detection thresholds or decision points of multilevel receivers are usually centered in a statistical center of each of the troughs of a graphical representation of a marginal probability density function (pdf) that corresponds to the "eyes" of an "eye diagram" for a multilevel signal in order to minimize the number of decoding errors. Since the troughs or "eyes" of a pdf are usually not uniformly distributed in voltage, a simple conventional direct analog-to-digital conversion (ADC) at a minimum number of bits is not adequate for decoding a multilevel signal.
Conventional receivers for decoding two-level multilevel signals frequently assume additive noise with parametric noise distributions such as a Gaussian distribution. Conventional receivers for decoding two-level multilevel signals also usually assume simple linear dependencies on the transmitted two-level multilevel signal.
However, the noise in optical channels of a multilevel signal may have distributions that are non-Gaussian. Further, the distortion of multilevel signals may be nonlinear in nature resulting in asymmetric or multi-modal pdfs for the received signal.
In addition to the problems associated with estimating noise distributions in a multilevel signal, another problem exists in the conventional art with respect to reliably determining the fidelity of a received multilevel signal without the explicit transmission of a "testing" data sequence that is already known to the receiver. Conventional performance monitors can generally be categorized into one of two sets.
The first set are those that use a secondary threshold (or sampling phase) to approximately determine how often a received symbol is near to the primary threshold (or sampling phase) used for decoding. When the detected sample from this second threshold differs from the primary sample, a pseudo-error is said to have occurred. The link is then characterized with the pseudo-error rate. This class of approaches, however, neglects the fact that under optimal filtering, the primary and secondary samples will be heavily statistically correlated, and thus, misrepresents the link performance.
The second set of performance monitors of the conventional art are those that rely on acquiring statistics from an error correction module. Specifically, forward error correction coding is used at the transmitter to allow the receiver to correct a small number of errors. If the true number of errors incurred during transmission is sufficiently small, then the receiver can correct all of the errors and report the rate at which errors occur. This class of performance monitors, however, suffers two significant drawbacks.
First, these methods require the use of an error correction code so that errors can be detected. The second drawback is that transmission errors must occur in order to acquire statistics regarding their frequency of occurrence. By the very nature of the high quality of the link, these errors will rarely occur, and thus, the performance monitor requires a significant amount of time to reliably report the error rate.
In view of the foregoing, there exists a need in the art for a multilevel signal receiver that does not assume a particular noise distribution in a received multilevel signal. That is, a need exists in the art for a multilevel signal receiver that employs robust estimates of noise distributions in order to process complex signal distortions that may be present in a multilevel signal while maintaining high performance for classic Gaussian noise distributions that may also be present in a multilevel signal. Aspects include the need in the art for (1) a method and system for automatically selecting the decision thresholds for a multilevel signal receiver on an adaptive basis, (2) a multilevel signal receiver that can process multi-modal conditional probability density functions, and (3) a method and system for decoding multilevel signals that can provide a reliable fidelity measure of the received signal without the transmission of explicit error testing sequences known to the receiver. In other words, a need exists in the art for a complete statistical characterization of link noise to reliably establish decision thresholds and infer error rates without suffering from the aforementioned drawbacks of the conventional art.
The present invention solves the aforementioned problems by providing a system and method for decoding multilevel signals. More specifically, the present invention is generally drawn to a method and system for selecting an optimal set of decision thresholds that can be used by an optical receiver in order to decode a multilevel optical signal. In one exemplary embodiment, the multilevel optical receiver can comprise a plurality of comparators that generally correspond with the number of levels in a multilevel data stream. Each comparator can be individually controlled and fed a decision threshold in order to decode a particular channel from a multilevel signal.
Unlike conventional optical receivers, the present invention can automatically control the thresholds or decision points for comparators of multilevel optical receivers that process multilevel data streams, where the noise corrupting the received signal is not necessarily Gaussian, signal independent, nor time-invariant. In other words, multilevel data streams can be distorted by noise where the noise follows a non-Gaussian probability distribution whose parameters depend on the transmitted signal values and vary with time. However, the present invention can still effectively process multilevel signals that have Gaussian, time-invariance, or signal-independence characteristics.
According to one aspect of the present invention, a multilevel optical receiver can comprise a plurality of voltage comparators, a decoder, a latch, an analog low-pass filter coupled to the latch, and a low-speed high resolution analog-to-digital converter coupled to the low-pass filter. With such structure, the multilevel optical receiver can generate an estimate of a cumulative distribution function (CDF) based on the received multilevel data signal.
The CDF can completely characterize the received multilevel data signal. From the CDF, the optical receiver can further generate an equivalent marginal probability density function (pdf) which is used to determine a near-optimal set of decision thresholds. A marginal pdf can be defined as an "overall" pdf characterizing the received signal when random symbols are transmitted. A marginal pdf can comprise one or more conditional pdfs. A conditional pdf is the pdf for an individual symbol of a multilevel signal, i.e. the pdf of the received signal conditioned on a particular symbol being transmitted.
Instead of using the calculated pdf to determine an optimal set of thresholds, the CDF function itself in one exemplary embodiment can be used to determine the decision thresholds as it conveys the same information as the pdf but in a less intuitive form. In either case, the invention can assist with centering the voltage detection thresholds for each of the plurality of comparators. In the pdf exemplary embodiment, the invention can center the voltage detection thresholds at the troughs or local minima of the pdf (or equivalently at the points of inflection of the CDF) which correspond to near-optimal decision thresholds for the received signal. In this way, the probability of error in the detection of the individual symbols that make-up multilevel signal can be minimized.
The centering of voltage detection thresholds based upon the calculated pdfs can involve several different steps. In one exemplary embodiment, a first step can comprise calculating an initial set of ε-support estimates corresponding to ranges of received voltages of significant probability for receiving a particular symbol. Next, the ε-support regions are combined until there is a 1-to-1 correspondence between the transmitted symbol levels and the ε-support regions. Possible threshold candidates can then be determined by establishing the threshold between the ε-support regions.
According to another aspect of the present invention, a multilevel optical receiver can comprise a plurality of voltage comparators, an analog low-pass filter, and a low-speed high resolution analog-to-digital converter coupled to the low-pass filter. According to this exemplary aspect, a latch that can be coupled to the low-pass filter has been removed. The removal of this latch can change the region of the signal that is being characterized. Specifically, latching the comparator output focuses the CDF/pdf characterization to the portion of the signal synchronized with the system clock and decision output. By removing the latch, the statistical characterization applies to the entire received signal and not just that portion which is used for the decision output.
For an alternative exemplary embodiment of the present invention, the CDF and pdf can be generated in a digital fashion (rather than the analog fashion described above) by using a track-and-hold circuit or a sample-and-hold circuit. The track-and-hold circuit or the sample-and-hold circuit can sample an input multilevel data signal and accumulate the samples over time. These samples can then be digitally processed to provide either a marginal pdf or CDF. As before, the CDF or pdf may then be used to determine the decision threshold voltages.
According to another alternative exemplary embodiment of the present invention, a high-resolution analog-to-digital converter (ADC) can measure the voltage of the received multilevel signal. The digitized multilevel signal can be provided to a digital signal processor (DSP) which computes the pdf and decision thresholds. The DSP can then use the computed thresholds to decode subsequent symbols digitized from the multilevel signal.
Those skilled in the art will recognize that different hardware or software or both can be substituted for the exemplary embodiments described herein without departing from the scope and spirit of the present invention. Specifically, as long as the hardware or software (or both) performs the functions described herein, then those skilled in the art will appreciate that the present invention would be embodied in such alternative hardware or software or both.
A further aspect of the invention can include calculating the fidelity of a multilevel signal based upon an estimated marginal pdf. Specifically, the marginal pdf can be used to estimate a set of conditional pdfs (one for each candidate symbol of a multilevel signal). These conditional pdfs can then be used to estimate the probability of error for each symbol and hence the system as a whole. This aspect of the invention allows for error performance to be measured without explicit error tests that require testing sequences (known to the receiver) to be transmitted.
The present invention can select a near-optimal set of decision thresholds that can be used by an optical receiver in order to decode a multilevel optical signal. The multilevel optical receiver can comprise a plurality of comparators that generally correspond with the number of levels in a multilevel data stream. Each comparator can be individually controlled and fed a decision threshold in order to decode a particular symbol from a multilevel signal. Alternatively, a high-resolution analog-to-digital converter (ADC) can measure the voltage of the received multilevel signal. The digitized multilevel signal can be provided to a digital signal processor (DSP) which computes the pdf and decision thresholds. The DSP can then use the computed thresholds to decode subsequent digitized symbols from the multilevel signal.
The present invention typically does not require the assumption of Gaussianity, time-invariance, signal-independence, or binary signaling. Contrary to the conventional art, the invention is designed to perform well when these assumptions do not hold. However, the present invention can also perform well if the assumptions do hold or are valid.
A CDF can completely characterize the received multilevel signal data. From the CDF, the optical receiver can further generate an equivalent marginal probability density function (pdf) which is used to determine an optimal set of decision thresholds. A marginal pdf can be defined as an "overall" pdf characterizing the received signal when the symbol transmitted is unknown. A marginal pdf can comprise one or more conditional pdfs. A conditional pdf is the pdf for an individual symbol of a multilevel signal, i.e. the pdf of the received signal conditioned on a particular symbol being transmitted.
The determining of voltage detection thresholds based upon the calculated pdfs can involve several different steps. In one exemplary embodiment, a first step can comprise calculating an initial set of ε-support estimates that comprise ranges of received voltages. Next, the ε-support regions are combined until there is a 1-to-1 correspondence between the transmitted symbol levels and the ε-support regions. Possible threshold candidates can then be determined by establishing the threshold between the ε-support regions.
Referring now to the drawings, in which like numerals represent like elements throughout the several Figures, aspects of the present invention and the illustrative operating environment will be described.
The exemplary optical network architecture 100 further comprises an optical waveguide 130 that can include one or more spans of optical fiber. The optical waveguide 130 couples the light source 120 to an optical detector 140. The optical detector 140 can be coupled to a receiver 150 that is responsible for decoding the multilevel signal into one or more channels of digital data output. The receiver 150 takes a single multilevel digital signal comprising 2n levels at the same symbol rate and converts the multilevel signal into a set of n high-speed digital binary inputs or channels. The receiver 150 typically comprises all circuitry required to operate a corresponding optical detector 140 and to amplify the detected signal. Further details of the receiver 150 will be discussed below with respect to
Referring now to
The optional signal conditioning filter 215 can comprise one or more programmable analog signal processing modules such as equalizers and filters. The signal conditioning filter 215 is also coupled to and controlled by the SIU 220. The SIU 220 can determine the decision or voltage thresholds that are used to decode the multilevel signal. Further details of various exemplary embodiments of the SIU 220 will be discussed below with respect to
A clock recovery unit 225 can be coupled to the output of the amplifier 210 or an optional signal conditional filter 215. The clock recovery unit 225 can generate a timing signal that is used to operate an optional holding circuit 230 and an analog-to-digital converter (ADC) 235. The holding circuit 230 is not required for each of the exemplary embodiments. The holding circuit 230 can comprise one of a track-and-hold circuit or a sample-and-hold circuit as known to those skilled in the art. The holding circuit 230 is coupled to the output of the signal conditioning filter 215.
Coupled to the output of the optional holding circuit 230 is the ADC 235 which decodes the multilevel signal. The ADC 235 can convert a 2n-level signal into n binary data streams. Further details of various exemplary embodiments of the ADC 235 will be discussed below with respect to
Background on Multilevel Signals
A multilevel signal allows for more than one bit to be transmitted per clock cycle, thereby improving the spectral efficiency of the transmitted signal. For multilevel optical transmission, some characteristic (i.e., signal property) of a transmitted pulse (such as amplitude, phase, frequency, etc.) is modulated over 2n levels in order to encode n bits into the single pulse, thereby improving the spectral efficiency of the transmitted pulse. Multilevel modulation can increase aggregate channel throughput by combining n OOK data streams (each with bit rate, B, in bits/s) into one 2n-level signal (with a symbol rate, B, in symbols/s) for an aggregate throughput (in bits/s) that is n times greater than B. The aggregate data rate of the 16-level signal shown in
As a specific example, the assumption may be made that the 16-level signal in
Exemplary Portion of a Simulated Received Multilevel Signal
Referring now to
Exemplary Eye-diagram for Received Multilevel Signal
Referring now to
Eye diagram 365 illustrates the difficulty in determining the thresholds for multilevel data streams. From this simulation, it is apparent that the noise is signal dependent. Specifically, larger signal levels usually have a larger associated noise variance as is evidenced by the thickening of the eye-lids towards the top of the eye-diagram 365. It is desired to have voltage detection thresholds centered in the statistical center of each of the 15 "eyes" 370. Furthermore, the eyes 370 are no longer uniformly distributed in voltage because the transmitter (with prior knowledge of the signal dependent noise variance) spaces the transmitted levels in a nonuniform manner in order to minimize the susceptibility to the noise and hence minimize the probability of error.
Because the transmitted levels are not uniformly spaced, a simple conventional direct ADC 235 at the minimum number of bits (log2(16)=4 in this case) is not adequate. Hypothetically, the received voltage signal could be digitized at a higher resolution (additional bits) and signal processing applied to determine the correct level. Unfortunately, at the targeted symbol rates of many optical systems (i.e. OC-192 at 10 Gb/s), this would require order-of-magnitude speed improvements of readily available ADC and signal processing technologies.
Exemplary Embodiments for Analog-to-digital Converters (ADCs) and Signal Integrity Units (SIUs)
Referring now to
The comparator 425 used in the EDC should ideally be identical to and in the same environment as the first comparators 405. This will allow for the SIU to accurately determine threshold settings of the ADC with a one-to-one voltage correspondence. Assuming that the ADC 235 is in the form of an integrated circuit (IC), the first comparators 405 and the second comparator 425 should be realized with the same basic circuitry and located in the same region of the IC to provide good thermal matching. In other words, the first comparators 405 and the second comparator 425 in this exemplary embodiment are manufactured on or within the same integrated circuit in order to improve thermal matching.
The output of the second optional latch 430 is fed into a filter 435 that is part of the signal integrity unit 220. The output of the second optional latch 430 is called Event Detection (ED). After low-pass filtering by the LPF 435, the DC component remains and is termed the event monitor voltage vem and is an analog probability estimate for the controlled reference voltage vrv exceeding the received signal vin where vrv is generated by the digital-to-analog converters 415. Further details of the analog probability estimate vem and the controlled reference voltage vrv will be discussed below.
The output of the second optional latch 430 can be fed to a second analog-to-digital converter 440 that is part of the signal integrity unit 220. Opposite to first ADC 235, the second ADC 440 may be characterized as a low-speed high-resolution ADC that measures the averaged event-detector output representing the CDF value. Specifically, the reference voltage vrv is swept over a range of voltage levels while the second ADC 440 samples the voltage vem from the filter 435 to produce an estimate of the CDF.
More specifically, pseudo-code to construct the CDF could comprise one or more of the following steps: Step 1: Set the reference voltage vrv to the minimum value of interest, i.e. lowest possible received voltage. This could be referred to as the start of the sweep. Step 2: Measure the averaged event-detector output voltage vem and take that value as the CDF value for the set reference voltage. Step 3: Increment the reference voltage. Step 4: If the reference voltage is above the maximum value of interest, a "sweep" has been completed and then the reference voltage is reset and the process returns to Step 1. Otherwise, the process of "sweeping" continues and returns to Step 2. It is noted that a single point of the CDF (step 2) is obtained for each value of the reference voltage.
Therefore, the SIU 220 sets vrv to a fixed value and then measures the averaged ED output. The SIU 220 then sets vrv to a different fixed value and measures another point of the CDF. This process is completed until the CDF curve is formed.
The second ADC 440 feeds its output to a microcontroller 445. Microcontroller 445 processes the cumulative distribution function (CDF) to determine threshold voltage values for the first comparators 405. Further details of the microcontroller's processing of the CDF will be discussed below with respect to
Through the use of the second optional latch 430 in
Although the data rate of the received signal can be very high (e.g. on the order of tens of gigabits per second), receiver 150 of the present invention does need not sample the signal at this high rate to analyze the signal. The receiver 150 avoids this impediment by using the simple high-speed second comparator 425 that indicates whether a controlled reference voltage exceeds the received signal at the clocked sample time. The resulting binary signal can then be averaged in time with the analog low-pass filter 435 to estimate the probability that the reference voltage exceeds the received signal. This probability estimate is a slowly-varying (ideally a constant) function and can thus be sampled with a high-resolution low-speed ADC 440.
Referring now to
Referring now to
Referring now to
Exemplary Cumulative Distribution Function of Simulated Received Multilevel Signal
Referring now to
Generating this probability estimate over a range of reference voltages produces CDF 605 that can completely characterize the received signal. In particular, the estimated noise distribution (and hence threshold selection method) is free from restrictive assumptions such as Gaussianity and symmetry that, while commonly used, can be detrimental in some circumstances when dealing with multilevel data. But it is noted that the present invention can also function when Gaussian and symmetry conditions hold.
Exemplary Probability Density Function (pdf) Derived from the CDF
Referring now to
Referring now to both
Alternate Exemplary Embodiment for ADC and SIU of
Referring now to
In this exemplary embodiment, the CDF 605 and pdf 615 can be measured in a digital fashion (rather than the analog fashion described above) by using a holding circuit 705. The holding circuit 705 can comprise a track-and-hold circuit or a sample-and-hold circuit. The track-and-hold circuit or the sample-and-hold circuit of holding circuit 705 can sample an input multilevel data signal and accumulate the samples over time. These samples can then be digitally processed to provide either a marginal pdf 605 or CDF 615. As before, the CDF 605 or marginal pdf 615 may then be used by the microcontroller 445 to determine the optimal decision threshold voltages for the comparators 405.
Additional Eye Diagram and Corresponding Digitally Processed Histogram
Referring now to
Ideally samples would occur at times centered temporally in the high-speed data stream's eyes. This would require critical timing requirements and therefore not be expected to be cost effective. Instead, the voltage samples can be easily made at random times thereby allowing for the elimination of all critical timing circuitry. The result of random signal voltage sample times is similar to the ideal sampling case due to the smaller probability of sampling during a signal transition. While not dominant, samples do occur during a signal transition which results in a data "floor" in the histogram, which can be removed during subsequent signal processing.
Random sampling for this application means random to the high-speed data rate. This can be achieved by using a periodic sample rate, which is not harmonically related to the high-speed data rate. The actual average sample rate of the random voltage samples is dictated by the threshold update speed desired. If the communication channel is expected to vary quickly with time, the sample rate must be correspondingly high. As an example, assuming that the channel varies with a 10 ms characteristic time and 1000 samples forms the histogram; average conversion speed only need be 100,000 samples per second.
To produce the histogram 810 of
Method For Decoding a Multilevel Signal
Referring now to
The method 900 starts with step 905 in which a multilevel signal is received by the first comparator 405 of a multilevel receiver 150. In step 907, the received multilevel signal is continuously sampled. Step 907 basically describes an approach where the multilevel signal is continuously observed in order to decode the received data. In other words, step 907 may describe a loop where the multilevel signal is continuously sampled while the remaining steps of
Next in routine 910, a cumulative distribution function (CDF) based upon previous symbols in the multilevel signal is calculated by the microcontroller 445 of the signal integrity unit 220. Further details of routine 910 will be discussed below with respect to
Next, in optional routine 915, a marginal probability density function (pdf) is calculated by the microcontroller 445 based upon the CDF calculated in routine 910. As noted above, a marginal pdf can be defined as an "overall" pdf that results from random symbols being received. A marginal pdf can comprise one or more conditional pdfs. A conditional pdf is a pdf associated or corresponding to an individual symbol of a multilevel signal. Routine 915 is optional since decision thresholds can be calculated from the CDF alone. Further details of routine 915 will be discussed below with respect to
In routine 920, one or more decision thresholds based on at least one of the CDF and pdf can be determined. As mentioned previously, since the calculation of the pdf is optional, decision thresholds can be determined from a calculated CDF alone. The microcontroller 445 is usually responsible for performing routine 920. Further details of routine 920 will be discussed below with respect to
In step 925, the microcontroller 445 associates a threshold voltage level with each determined decision threshold calculated in routine 920. The microcontroller 445 forwards these voltage levels to the one or more first comparators 405 of the first analog-to-digital converter (ADC) 235.
Next, in step 930, each first comparator 405 compares the received multilevel signal with the one or more threshold voltages supplied by the microcontroller 445. In step 935, the decoder 410 of the first ADC 235 decodes the multilevel signal into one or more data streams based upon the comparisons.
In routine 940, the microcontroller estimates the fidelity of the received multilevel signal. Further details of routine 940 will be discussed below with respect to
In step 945, the operation of the programmable analog signal processors located in the signal conditioning filter 215 can be adjusted by the microcontroller 445 of the signal integrity unit 220 based upon the calculated fidelity in routine 940. For example, the weighting coefficients of a programmable delay line equalization filter could be adjusted to minimize the estimated probability of error inferred from this fidelity measure. Similarly, a controllable delay on the clock timing may be adjusted to maximize the fidelity measure.
Next in step 950, the gain of the entire system can be adjusted based on the range of received signal values inferred from the pdf as is discussed later.
Exemplary Embodiment of Sub-Method for Calculating Cumulative Distribution Function (CDF)
Referring now to
To understand why this occurs, consider the reference vrv held at a constant voltage. The output of the second comparator 425 is a binary value equal to one if vin≦vrv and equal to 0 otherwise. This output can thus be written as the indicator function 1 (vin≦vrv). The low-pass filter 435 (labeled LPF) then averages this function over time, i.e. it approximates the fraction of the time that vin is less than vrv, or in other words, it approximates the probability P(vin≦vrv). More precisely,
Next in step 1010, the microcontroller 445 measures the resulting probability estimate in order to generate the CDF 605 illustrated in
Exemplary Embodiment of Sub-Method for Calculating a Probability Density Function
Referring now to
Unless a very large number of samples are used for each of the CDF points, there will be a considerable amount of statistical noise in the resulting pdf. Thus, step 1215 smoothes the histogram h(vrv) (not shown) by filtering the histogram along the reference voltage. Specifically, h(vrv) is convolved with a boxcar function to filter the histogram along vrv to produce the smoothed pdf g(vrv). This operation is motivated by regularity assumptions on the underlying noise distribution. Furthermore, the application of the differentiation (step 1205) and convolution to the CDF can be combined into one step, i.e.
In step 1220, the histogram g(vrv) (not shown) can be smoothed along the time domain. Specifically, the histogram is smoothed along the time domain because should the pdfs vary slowly with time (if at all), by smoothing in time, more samples are being used (in an iterative framework) to estimate the probabilities without having to acquire many samples to generate each probability estimate. In essence, measurements of vem are being recycled to estimate the pdf. To be more precise, first consider the pdf evaluated for a particular voltage v, i.e. consider the pdf on a pointwise basis. For each iteration n, a pdf value gn(v) (i.e. the pdf smoothed along voltage) is measured providing a noisy measurement of the true pdf value pn(v) at time n, i.e. the observation model is
The reader may wonder why using Eq. (5) is preferable to simply using more samples to generate each gn(v). Although both approaches can be used to provide an estimate with high statistical significance, the brute force method of simply using more samples requires an associated larger amount of time to acquire those samples. The state-space approach in Eq. (2.4) recycles information so that the time required to generate each gn(v) can be considerably reduced. Eqs. (2) and (5) provide a smoothed (in both voltage and time) pdf 615 from the CDF provided through vem. The smoothing (in either voltage or time) steps 1215 and 1220 are optional and may not be required if adequate statistical significance can be achieved in a reasonable amount of time. After generating and optionally smoothing the pdf 615, the process then returns to routine 920 of
Exemplary Embodiment of Sub-Method for Calculating Decision Thresholds
Referring now to
The manner in which the pdf's structure is exploited will be through the use of what this detailed description refers to as "ε-supports". The support of a function ƒ(x) is mathematically defined to be the set {x|ƒ(x)>0}, i.e. where the function is strictly positive. This is generalized to define the ε-support of a pdf as
In practice, the conditional pdf's are usually unknown. However, an estimate {circumflex over (p)}(y) of the marginal pdf can be obtained from the low-pass filtered event-detector output. Because the modes of the pdf are well separated (as in
Note that one skilled in the art will understand that a variety of functions can be used in place of Eq. (11) and still yield the desired result. All that is required is that the chosen function conveys a notion of the distance between sets. It should also be noted that step 1315 above has the additional benefit that if the data exhibits multiple eye-lids or multiple-rails for a single transmitted symbol, then the merging will associate the multiple eye-lids according to their underlying common transmitted symbol. Specifically, link characteristics such as nonlinearities and intersymbol interference result in signal distortions that manifest themselves as multi-modal conditional pdf's (or equivalently multiple eye-lids when the data is viewed as an eye-diagram). The multiple modes result in extra, but closely spaced, regions in Ŝε. The merging in step 1315 combines these multiple modes according to the underlying transmitted symbol.
In step 1320, possible threshold candidates are determined based upon the combined remaining regions of the ε-supports. Specifically, having estimated N ε-supports (each associated with one of the possible signal levels An), the following describes how the thresholds are set between the regions. First, each of the conditional pdf's p(y|x=An) are modeled as a Gaussian (more to be said about the Gaussian modeling and application to non-Gaussian noise at the end of this subsection). In particular, for each transmitted signal level x=An(n∈{0, . . . , N−1}), the received symbol y is modeled with the conditional pdf
Referring back to
Using the Gaussian model and estimated parameters {circumflex over (μ)}n and {circumflex over (σ)}n the decision thresholds can now be proposed. The nature of noise in communications channels is that the noise perturbations are usually small rather than large. Not only is this the case for the Gaussian noise model, but for many other noise models as well. For this reason, in this and the following section, we consider only symbol errors associated with an adjacent level. These types of errors dominate the link performance characterization. Thus, it is sufficient to consider each pair of adjacent transmissions in a conventional on-off keying (OOK) context. In particular, the optimal threshold to differentiate levels An and An+1 is well approximated by
The statistical analysis of routine 920 will usually be continually performed; thereby adjusting the decision levels in real time to compensate for time varying distortion/noise of the received signal. After routine 1320, the process for the current iteration returns to step 925 of
Prior to moving onto the next subsection, the robustness of the Gaussian model is discussed. Like much of the conventional art, the conditional pdfs are modeled as Gaussian. However, because of the use of the ε-supports to estimate the parameters of the Gaussian pdfs, the method still performs well in situations where the data is not Gaussian distributed. Specifically, recall that the first step of the analysis is to compute N ε-support regions to characterize the region of significant probability for the conditional pdfs. Thus, if the s-supports are correctly associated with the conditional pdfs, then the thresholds will be established in the tails of the pdfs thus producing a low-probability of error. Fortunately, the method proposed in Eqs. (9)-(11), and the surrounding text, should easily and correctly determine the ε-supports because the modes of the pdfs will be well separated in realistic communications systems. Thus, even though a Gaussian model is used to establish the thresholds in this sub-section, the use of the ε-supports to determine the parameters still allow for non-Gaussian distributions (such as multi-modal distributions) to be handled as well.
Exemplary Embodiment of Sub-Method for Estimating Link Fidelity
Referring now to
This sub-method allows for error performance to be gauged without explicit data error tests that can only be performed in artificial settings where the transmitted values are known. Specifically, using the above statistical characterization of the received data, the performance of the link can be estimated using random data. Efforts in the conventional art usually estimate the error rate of the link by transmitting a testing sequence of data (already known to the receiver) which is detected by the receiver. The receiver of the conventional art then counts how many decoding errors were encountered.
The proposed method, in contrast, leverages the probabilistic modeling of the system to estimate link error rates without the transmission of a predetermined testing sequence. In particular, the error rate can be estimated while receiving random data during real-world operation by exploiting Eq. (22). Specifically, the overall link symbol error rate can be obtained by averaging the probability of symbol error conditioned on a given transmitted symbol yielding:
Referring now to
The validity of Eqs (22)-(26) is strongly dependent on the Gaussian model. If the noise is not Gaussian, then the Q-factor does not give the probability of error as stated. However, in the non-Gaussian case, the method still supplies an intuitive quantification of the fidelity of the received signal which is related to the probability of decoding error. Thus, while the numerical value provided by the fidelity measure may not exactly relate to detection error probability, it still characterizes the fidelity of the link, i.e. large numerical values indicate better signal fidelity.
Exemplary Embodiment of Sub-Method for Gain Control
Referring back to step 950, because the ε-support regions calculated in routine 920 represent all the voltage ranges where a candidate symbol is likely to be received, the ε-supports can be used to determine an appropriate gain normalization factor for the received signal. In particular, the largest and smallest voltages among all of the ε-support regions represents the largest and smallest voltage likely to be received for a symbol transmission. These extreme values can thus be used to provide appropriate gain to scale the received signal such that the entire voltage swing of the system is utilized.
Specifically, the automatic gain voltage Vagc can be taken as the reciprocal of the size of the convex hull of all of the ε-support regions, i.e.
Having given a detailed description of the embodiment illustrated by
Alternative Exemplary Embodiment of Method for Decoding Multilevel Signals of
The embodiment given by the use of
Alternative Exemplary Embodiment of Method for Decoding Multilevel Signals of
The embodiment given by the use of
Alternative Exemplary Embodiment of Method for Decoding Multilevel Signals of
Referring now to
Routine 915 starts with step 1105 in which the holding circuit 705 in combination with the ADC 220″ measure the voltage of the received multilevel signal. Specifically, microcontroller 445 can sample the received analog voltage of the multilevel signal by triggering the holding circuit 705 at some time random in relation to the received data stream. The holding circuit 705 will necessarily have a capture bandwidth commensurate with the high-speed data stream, but will only need to be able to sample at rate much lower than that of the high-speed data stream.
Next in step 1110, the microcontroller 445 would then trigger the second ADC 440 conversion and record the resulting voltage. In step 1115, the microcontroller 445 can collect the digitized measurements of the voltages and obtain the histogram 810 of measured voltages as illustrated in
The present invention uses a robust approach to setting the decision thresholds that assumes neither unimodality nor symmetry of the noise distributions but can also operate even if these assumptions hold. The invention exploits the estimated pdf and localized nature of the noise to detect regions of significant probability. Each of these regions should correspond to where a candidate symbol i should be declared in the decision process, i.e. each region determines the support of the conditional pdfs composing the observed marginal pdf. In cases where the number of regions exceeds the number of symbols (as may occur due to multi-modal noise distributions and estimation errors), the invention systematically merges regions based on prior knowledge that (i) redundant eyelids are spaced very close together (relative to the spacing between eye-lids associated with differing symbols) and (ii) the number of candidate symbols is a known system parameter.
Further, the voltage decision thresholds produced by the algorithm are used by the fifteen high-speed comparators, which are followed by combinational logic to properly decode the levels back to the encoded data streams. The fifteen comparators and combinational logic are closely related to a traditional flash ADC with the exception of optimal threshold control (as per present invention) and decoding methods more amenable to communication systems other than binary. The receiver 150 converts the 16-level input into properly decoded data streams.
As noted previously, it should be obvious to one skilled in the art that the simple circuits illustrated in
One skilled in the art can appreciate that the methods described here can be applied to other modulation schemes other than N-PAM. Examples of such modulation schemes are phase shift keying, frequency shift keying, and combinations methods such as quadrature amplitude modulation. The extension of the proposed method simply involves the appropriate change of the control variable in the CDF/pdf estimation. Because no restrictive form the noise distribution is assumed, the present invention will adapt to the different data distribution associated with other modulation schemes, which the conventional art cannot.
While it is contemplated that the present invention is very suitable for optical networking environments, it can be appreciated that the present invention could be easily employed in fields involving lower-speed communications. For example, lower-speed communication fields can include, but are not limited to, wireless applications, and applications utilizing modems such as telephone, digital subscriber lines (DSL), and analog or digital cable.
It should be understood that the foregoing relates only to illustrate the embodiments of the present invention, and that numerous changes may be made therein without departing from the scope and spirit of the invention as defined by the following claims.
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