LNTwww:About LNTwww

Welcome to the English version of LNTwww

»$\text{https://en.lntwww.de}$«  is an e-learning tutorial for Communications Engineering with nine didactic multimedia textbooks including exercises with solutions,  learning videos,  and interactive applets.  It is offered by the  »Institute for Communications Engineering«  of the  »Technical University of Munich«. 

⇒   It is freely accessible,  registration is not necessary and no system requirements are needed.

The German-language version   »$\text{https://www.lntwww.de}$«   ⇒   »$\rm L$erntutorial für $\rm N$achrichten$\rm T$echnik im $\rm w$orld $\rm w$ide $\rm w$eb«  was created between 2001 – 2021 by members of our Institute.  The toolbar entry  »Deutsch«  takes you to the German original.  In spring 2020 we started the English translation,  and in spring 2023 we finished.

• The current version from 2023 is based on the software  »MediaWiki«,  known by the encyclopaedia  »WIKIPEDIA«.   The following is a kind of  »user guide«  to our e–learning project.  Corresponding links to this file  »About LNTwww«  can be found at the bottom of each page between  »Privacy policy« and  »Disclaimer«.

• You can find more information on our e-learning project in the PDF document  »LNTwww - Praxisbericht zum E-Learning aus den Ingenieurwissenschaften«,  a German-language contribution by Günter Söder in the special issue  »So gelingt E-Learning«,  Reader zum Higher Education Summit 2019,  Munich:  Pearson Studium.

• We consider the present version as final;  an extension is currently not planned.  But of course we will continue to improve detected errors or inaccuracies promptly.  So if you notice any inadequacies regarding content,  presentation or handling,  then please send a detailed message by mail to  »LNTwww@ice.cit.tum.de«.

• On the  »Information«  page you will find notes about temporary restrictions  $($e.g. in case of unavailability due to service work$)$  and a list of bugs already detected by us,  but not yet fixed.   We wish  that in this list there are only few entries and only for a short time.

We would be pleased if we could arouse your interest in our e-learning offer.  We wish you a successful learning success.

$\text{Have fun and good luck!}$  

$\text{Gerhard Kramer}$,   $\text{Javier Garcia Gomez}$,  $\text{Tasnád Kernetzky}$,   $\text{Benedikt Leible}$,  $\text{Günter Söder}$

Munich,  in spring 2023          

Content

(A)   The didactic concept of LNTwww

At the beginning of the work on  $\rm LNTwww$  in 2001,  we gave ourselves the following ten rules.  These still apply today:

(1)   The teaching area  »Information and Communication Technology«  $\text{(I&K)}$  including associated basic subjects  $($Signal Representation,  Fourier and Laplace Transform,  Stochastic Signal Theory, etc.$)$  is presented in a didactically and multimedia prepared form.

(2)   Nine subject areas were selected,  each of which is covered by a self-contained book in the scope of a one-semester course with three semester hours per week to five semester hours per week.

(3)   The target group of our online offer are students of  $\text{I&K}$  technology,  especially of Communications Engineering,  as well as practicing engineers  $($Keywords:  »professional training«,  »lifelong learning«$)$.

(4)   In particular,  the interrelationships between different subfields of our extensive e-leatning offer should also be shown,  which is promoted by a nomenclature that is largely consistent in all books.

(5)   $\rm LNTwww$  offers two modes of learning:   Beginners should proceed sequentially  –   for advanced learners,  use it as a tutorial  $($work through exercises first,  jump to the theory part if deficits are identified$)$.

(6)   The theory is explained as in a traditional engineering textbook through texts,  graphics,  and mathematical derivations.  In addition,  each chapter includes at least one multimedia module.

(7)   $\rm LNTwww$  shall provide the user with multiple interaction options regarding the selection and presentation of theory chapters,  exercises,  learning videos as well as multimedia and calculation modules.

(8)   The methodology of hyperlinks typical of the  »world wide web«  is extensively used within the  $\rm LNTwww$  and externally.  This is also intended to show connections between different teaching areas.

(9)   In order to prevent a user from getting lost in his learning environment and using  $\rm LNTwww$  only for  »surfing«,  a purposeful path must be recognizable for him at all times despite certain freedoms.

(10)  For reasons of sustainability of learning success,  there are possibilities for printing the texts and graphics,  ignoring the fact that today's students generation often devalues this as a  »relapse into the analog age«.

(B)   Content and scope of LNTwww

$\rm LNTwww$  is a virtual course totaling  $\text{36}$  semester hours per week 

• with  $\text{23}$  semester hours per week  (quasi) lectures   ⇒   $\text{23L}$

• and  $\text{13}$  semester hours per week exercises   ⇒   $\text{13E}$. 

It is organized in book form.  Each book contains a one-semester course.  For example,  in the case of the third book,  it is indicated that the book  »Theory of Stochastic Signals«  corresponds to a face-to-face–course with three semester hours per week of  »lecture«  and two semester hours per week of  »exercises«   ⇒   $\text{3L +2E}$.

Textbooks:

1. Signal Representation   ⇒   »Impressum«,
2. Linear and Time Invariant Systems   ⇒  »Impressum«,
3. Theory of Stochastic Signals   ⇒  »Impressum«,
4. Information Theory   ⇒  »Impressum«,
5. Modulation Methods   ⇒  »Impressum«,
6. Digital Signal Transmission   ⇒  »Impressum«,
7. Mobile Communications   ⇒  »Impressum«,
8. Channel Coding   ⇒  »Impressum«,
9. Examples of Communication Systems   ⇒  »Impressum«.

• The theory pages of all books result in the print version in approx.  $1500$  pages  $($DIN A4$)$  and contain on average one and a half graphics per page. 

• In addition,  LNTwww provides via the link  »Biographies & Bibliography«  a subject-specific bibliography with approx.  $400$  entries, 
  plus links to the WIKIPEDIA biographies of important scientists.

(C)   Design and structure of LNTwww

One can reach the nine reference books and »Biographies & Bibliography«  through the link  »Book Overview«.  From this interface one can reach the individual books.  

• Each book is divided into several  »main chapters«, 

• each main chapter into several  »chapters«,  and

• each chapter includes several  »sections«.

$\text{Example 1:}$  We consider the book  »Signal Representation«.  This contains five  »main chapters«.

• By clicking on the first main chapter  »Basic Terms of Communications Engineering«,  one can get to three  »chapters«.  Each chapter corresponds to a MediaWiki file.

• The exemplary chapter  »Principles of Communication«  contains ten  »sections»  or  »pages».

• The last two pages are almost the same in all chapters,  namely  »Exercises for the chapter«  and  »References«.

(D)   Content overviews for LNTwww

A brief overview of all books is available on the selection interface  »Book Overview«.

• More information is provided by the  »first page«  of each book.

• The respective main chapter content can be found in the first subchapter on the first page of each.

$\text{Example 2:}$  The first page  $($title page$)$  of the book  »Signal Representation«  provides the following information:

1. A brief summary of the entire book;
2. scope of learning offer:  $2{\rm L} + 1{\rm E}$   ⇒   lecture with two semester hours per week and one additionalhour exercise. 
3. five main chapters,  19 chapters,  127 sections,  58 exercises;
4. links to the five main chapters of the book;
5. links to the associated exercises,  learning videos,  and interactive applets in the book  »Signal Representation«;
6. Bibliography for the book;
7. The imprint to the book  $($Authors,  other contributors,  materials as a starting point of the book,  referencces$)$.

The content of the first main chapter  »Principles of Communication« can be found on the first page  »# OVERVIEW OF THE FIRST MAIN CHAPTER #« .

(E)   LNTwww exercises

You can find the  »exercise overview«  for all books  $($approx.  $640$  exercises, approx.  $3100$  subtasks)  on the home page via the link  »Exercises«.  Please note:

• Each exercise consists of several  »subtasks«.   An exercise is only solved correctly if all subtasks are correct.

• For each exercise there is a detailed  "sample solution",  sometimes with the indication of several ways to the goal.

• The exercise types used are:

1. "Single Choice"   ⇒   only one of the  $n$  given answers is correct;
        ⇒   Marks of alternative answers:  ${\huge\circ}$
2. "Multiple Choice"   ⇒   of the  $n$  given answers, between zero and  $n$  answers can be correct;
        ⇒   Marks of alternative answers:  $\square$
3. "Arithmetic exercise"   ⇒   numerical value query,  possibly with sign;
       small deviations  $($usually  $\pm 3\%)$  are allowed when checking real-valued results.

• We distinguish between  »exercises«  $($e.g.  "Exercise 1.1"$)$  and  »additional exercises«  (e.g.  $($e.g.  "Exercise 1.1Z"$)$.

1. If you were able to solve all exercises of a chapter without any problems,  we believe that you are familiar with the entirechapter content. 
2. If you have solved one exercise incorrectly,  you should also work on the following,  usually somewhat easier additional exercise.

$\text{Example 3:}$  The  $58$  exercises/additional exercises of the book  "Signal Representation"  can be accessed via the link  »Signal Representation: Exercises«. 

• From there,  we move on to the individual exercises,  for example,  to  »Exercise 1.1: Music Signals«.  This relatively simple exercise consists of

1.   one „Single Choice”   ⇒   subtask  (1),
2.   two „Multiple Choice”   ⇒   subtasks  (2),  (3),  and
3.   one computational task with two real-valued computational queries   ⇒   Subtask  (4).

• But there are also much more difficult exercises in  $\rm LNTwww$.  Although MediaWiki also calls arithmetic exercises  "quizzes",  answering them is usually much more difficult than than on the numerous quiz shows on TV.   Because: 

There are no predetermined answers in an arithmetic exercise,  and moreover: 
Integrals often have to be solved beforehand,  such as in  »Exercise 4.4: Two-dimensional Gaussian probabilty density function«.

• We recommend:  Print the exercise first   ⇒   »$\text{printable version}$«  and solve the exercise  offline  before checking  online
       ⇒   Note:  In the  "printable version":  For links,  the target addresses are always given in brackets.

(F)   LNTwww learning videos

You can access approximately  $30$  learning videos via the link  »Videos«  on the start page.  The realization of a learning video required the following individual steps: 

Writing the script and texts   ⇒   Creating a set of slides with only slight differences between successive slides   ⇒   Voicing texts and audio editing   ⇒;   Combining texts and images into a coherent video stream.

1. Clicking on this link brings up a; list of all learning videos,  grouped by textbook.  Some videos appear for multiple books.
2. After selecting the desired learning video,  a wiki description page appears with a short content description and user interface.
3. From here you can start the video in  »mp4«  and  »ogv«  format.  The browser will search for the appropriate format.
4. The videos can be played by many browsers  $($Firefox, Chrome, Safari, ...$)$  as well as smartphones and tablets.
5. The bottom link provides all available learning videos in alphabetical order.

Note:   All learning videos are with German language.  English translations are not planned.

$\text{Example 4:}$  We'll take a look at   »Analog and digital signals«  as an example.  This provides a two-part video in mp4 and ogv format.

• Each video part can be started by single click and paused by another click.

• The playback speed of the videos can be changed:
  • Firefox offers a submenu after right-clicking on the video.
  • For Google Chrome you can install e.g. the plugin  »Video Speed Controller«.

(G)   LNTwww applets

Applets have a similar function as laboratories in mathematical-scientific courses:  Supplementing lecture/exercise with independent work by the student on the topic covered. 

You can access the provided interactive applets via the link of the same name on the home page.  It should be noted:

1. Clicking on the link  »Applets«  a list of all applets appears,  grouped by reference books. 
2. We distinguish between the newer  $\text{HTML 5/JavaScript}$  applets  $($in the respective lists above$)$  and the older  $\text{SWF}$  applets  $($below$)$. 
3. The SWF applets unfortunately do not work on smartphones and tablets.
4. After selecting an HTML 5/JS applet  a wiki description page appears with introductory theory section,  exercises to be solved and sample solutions. 
5. At the beginning and end of this wiki description page there are links to the actual applet in German resp. English Language.

$\text{Example 5:}$  The didactic importance of applets shall be proved by  »Eye Pattern and Worst-Case Error Probability«:

• The  »eye diagram«  is a proven transmission engineering tool,  to capture the influence of  »line dispersion«   ⇒   »intersysmbol interference«  on the quality characteristic  »error probability«  of a digital transmission system.  

• Such applets serve the clarification of more difficult facts,  in this example  »the step-by-step construction of the eye diagram from the symbol sequence«.  The program offers a lot of setting possibilities.  However, not every setting brings the user a relevant learning success and even fewer lead to a so-called "aha effect". 

• This is why we guide the user specifically through the program on the basis of the experiment.  He has to solve various tasks:  Predict and evaluate results,  Optimize parameters,  etc.

• A top 10% student has of course the possibility,  to set himself tasks going beyond the execution of experiments with the help of the applet and thus to penetrate very deeply into the presented subject matter.

In addition to these  $\approx\hspace{-0.1cm} 30$  HTML 5/JS based applets  we still offer some of our  $\approx\hspace{-0.1cm}50$  older German-language applets,  which are based on  »Shock Wave Flash«  $\rm (SWF)$.  These were programmed for  »Adobe Flash«. 

1. Since the Flashplayer browser plugin is no longer supported for security reasons,  these applets must be opened with the  »projector version«.
2. You do not need to install the projector version and it will not be integrated into your browser.  So there are no security concerns in this regard.
3. On the corresponding wiki pages you can find the projector version of the flash player and of course the applet itself.

(H)   Glossary

Aufgrund der Tatsache,  dass unser e–Learning–Projekt LNTwww zunächst in deutscher Sprache konzipiert wurde und der Wunsch nach einer englischen Version erst sehr viel später kam,  ist in der englischen Version die Zuordnung zwischen  »Bezeichnung«   und  »Formelzeichen«   nicht ganz einfach.  Hier einige Beispiele:

1. Trägerfrequenz  $f_{\rm T}$,
2. $s_{\rm TP}(t)$   ⇒   äquivalentes Tiefpass–Sendesignal   ⇒   equivalent low-pass transmitted signal
   

All texts for LNTww can be found as PDF under the link   Zum Download-Verzeichnis

! Noch überarbeiten !

(I)    History of LNTwww

At the  »Institute for Communications Engineering«  $\rm (LNT)$  of the  »Technical University of Munich«  $\rm (TUM)$  two  teaching software packages  $\text{(LNTsim, LNTwin)}$  were realized by  »Günter Söder« from 1984 to 1996, which were used in our practical courses.  Several other universities have also acquired and used these programs.

At the beginning of the first Internet euphoria,  there were inquiries from students whether we could also provide such simulation and demonstration programs online.  After careful consideration  ("Is the expected big effort worth it?")  he began 2001 planning the German-language  »www.LNTwww.de«.  Co-responsible was his colleague  »Klaus Eichin«.  The project was to be completed by 2011 at the latest,  since both would be retiring this year.

The content was derived from her own teaching materials as well as those of her colleague  »Norbert Hanik«  $($Associate Professor of Line Transmission Technology$)$.  Other lecture material was also taken into account,  which was produced at the Institute of Communications Engineering under the last four chair holders:

• Professor »Hans Marko«  $($Head of the LNT from 1962 to 1993$)$,
• Professor »Joachim Hagenauer«  $($Head of the LNT from 1993 to 2006$)$,
• Professor »Ralf Kötter»  $($Head of the LNT from 2007 to 2009$)$,  and
• Professor »Gerhard Kramer«  $($Head of the LNT since 2010$)$.

Before we could start to implement our ideas, several dedicated and IT-savvy students had to develop the platform "LNTwww" as part of their final theses.  The authoring system was based on the http server "Apache", the database "MySQL" and the script language "Perl".  All entered entities  (texts and text fragments, equations, diagrams, hyperlinks, multimedia elements, etc.)  were stored in the database, which was huge for the time, along with various display features for color coding of definitions, examples, etc.

• We decided to use Shock Wave Flash (SWF) as the technical basis for the multimedia applications.  The decision was easy, because this tool was acknowledged to be the best at that time.

• The upcoming work in the following years was the adaptation of the manuscripts to online operation, the input into the database with the rather complicated LNTww syntax, the creation of the diagrams as well as the conception and realization of multimedia elements.

But only in 2016 - after fifteen years and five years after the planned completion - the desired final state of "LNTwww.v2" was reached.  At the same time, it became known that the base "SWF" of our multimedia applications would not be supported by relevant manufacturers in the future.

This fact and the criticism heard from some users about the meanwhile too staid design  (our authoring system was on the level of 2003)  were decisive for a new start with "LNTww.v3", based on MediaWiki (known by WIKIPEDIA).

• The conversion to "LNTww.v3" took more than four labor-intensive years.  For mathematical and scientific content, porting to another e-learning base  (like here from "LNTwww" to "MediaWiki")  is only possible manually due to many special characters, italics, superscripts and subscripts.
• The conversion of the learning videos  (from "swf" to "mp4" or "ogv")  could be largely automated.  In contrast, the conversion of the interactive applets  (from "swf" to "HTML5/JS")  required reprogramming, in which many of our students were involved, as in previous years.

After some control and correction iterations, our e-learning service  $\text{https://www.LNTwww.de}$  will now finally be released in March 2021, almost exactly twenty years after the first planning and ten years after the planned completion. 

In terms of content, this third version differs not only insignificantly from the second, but the multimedia elements in particular have been significantly improved.  We assume that "MediaWiki" will remain the quasi-standard for Internet applications for several years.  Then this effort would have been worthwhile.

(J)   Acknowledgement

Günter Söder, who is still responsible for  $\rm LNTwww$, would like to thank the many people involved in the creation of  $\rm LNTwww$, also on behalf of the Institute of Communications Engineering at the TU Munich and its director Gerhard Kramer,

• first of all to the two co-responsible persons  Dr. Klaus Eichin  (until 2011, besides planning also co–author) and  Tasnád Kernetzky (since 2016, responsible for the system configuration and administration as well as the conversion to MediaWiki, HTML5/JS, MP4);

• to  Martin Winkler  and  Yven Winter,  who laid the technical foundations with their diploma theses in the early 2000s; the latter was still a volunteer system administrator until 2016;

• to Prof.  Norbert Hanik (professorship "line-bound transmission technology" – co–author of several books and eager propagator of our learning opportunities in his lectures)  and  to his PhD students  Dr. Bernhard Göbel,  Tasnád Kernetzky  and  Benedikt Leible;

• to former LNT colleagues Dr. Ronald Böhnke,  Dr. Joschi Brauchle,  Dr. Thomas Hindelang,  Prof. Gianluigi Liva,  Dr. Tobias Lutz,  Dr. Michael Mecking,  Dr. Markus Stinner,  Dr. Thomas Stockhammer,  Dr. Johannes Zangl  and  Dr. Georg Zeitler, who contributed as co–authors or experts or supervised student work;

• to all colleagues of the LNT, who actively supported us in many often tedious and nerve-racking tasks:  Doris Dorn (entered countless texts and equations in the complicated LNTwww syntax), Manfred Jürgens, Martin Kontny, Winfried Kretzinger, Robert Schetterer and Christin Wizemann;

• to many  students involved in LNTwww – behind this link are almost fifty students who, between 2001 and 2021, have independently worked on subareas, designed learning videos and interactive applets elements or implemented the porting to the MediaWiki version within the framework of engineering practice, admission, diploma, bachelor and master theses or within the framework of a working student activity;

• to the  Department of Electrical and Computer Engineering  and the  Technical University of Munich  for funding working students within the framework of the  "MoliTUM"  and  "EXIni"  funding programs, respectively, in the years since 2016.