About LNTwww

From 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"  $\rm (LNT)$  of the  "Technical University of Munich"  $\rm (TUM)$. 

⇒   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.  The interim status in September 2022 is:

  • Seven textbooks are completed  (Tutorial & Exercises):
  1.   "Signal Representation",
  2.   "Linear and Time-Invariant Systems",  
  3.   "Theory of Stochastic Signals",  
  4.   "Information Theory" 
  5.   "Modulation Methods",
  6.   "Digital Signal Transmission",
  7.   "Mobile Communications".
  • The last two textbooks are in progress.  They are scheduled for completion in the first quarter of 2023:
  1.   "Channel Coding",
  2.   "Examples of Communication Systems".

$\rm LNTwww$  is based on the management software  "MediaWiki",  known by the encyclopedia#  "WIKIPEDIA".  In the following you can find a kind of  "User Manual"  about our e-learning tutorial.  Corresponding links to the file  "About LNTwww"  are provided at the bottom of each page between  "Privacy policy"  and  " Disclaimers".

Since we have only translated part of the German version so far,  there are still some limitations regarding the already finished books.  You can find this via the link  "$\text{Information}$".  If you notice any deficiencies regarding content,  presentation or handling,  please send us a detailed report by e-mail to  "LNTwww (at) LNT.ei.tum.de".

$\text{Have fun and good luck!}$   We would be pleased if we could arouse your interest in our  $\rm LNTwww$.  We wish you a good learning success.

Munich, September 2022           $\text{Gerhard Kramer}$,   $\text{Javier Garcia Gomez}$ $\text{Tasnád Kernetzky}$,   $\text{Benedikt Leible}$$\text{Günter Söder}$


(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 as a tutorial  $($work through tasks first,  jump to theory if deficits are identified$)$.

(6)   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  $\text{36 sh/w}$  (semester hours per week) 

  • with  $\text{23 sh/w}$  (quasi-)lectures
  • and  $\text{13 sh/w}$  exercises. 

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 this book corresponds to a face-to-face–course with three semester hours per week of LECTURE and two semester hours per week of EXERCISES.

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

  • 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  $\text{main chapters}$, 
  • each main chapter into several  $\rm chapters$,  and
  • each chapter includes several  $\rm sections$.

$\text{Example 1:}$  We consider the book  "Signal Representation".  This contains five  "main chapters", including  "Basic Terms of Communications Engineering".

  • By clicking on the first main chapter,  one can get to three  "chapters"  including the first chapter  "Principles of Communication"
    Such a chapter corresponds to a saved MediaWiki–file.
  • The exemplary chapter  "Principles of Communication"  contains ten  "sections".  The last two sections 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 sub–chapter on the first page of each.

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

  • A brief summary;
  • Scope of learning:  Lecture with two semester hours per week  $\rm (2\ sh/w)$  and additional  $\rm 1 sh/w$  exercise.  Five main chapters.  Nineteen chapters;
  • Links to the five main chapters;
  • Links to the assignments, learning videos, and interactive applets in the book  "Signal Representation";
  • Recommended reading for the book;
  • Other notes about the book  (Authors, Other contributors, Materials as a starting point of the book, List of sources).

The content of the first main chapter „Time-variant transmission channels” can be found on the 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 also 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;
         ⇒   alternative answers– mark:  ${\huge\circ}$
  2. "Multiple Choice"   ⇒   of the  $n$  given answers, between zero and  $n$  answers can be correct;
         ⇒   alternative answers– mark:  $\square$
  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.  "Exercise 1.1Z").
  • If you were able to solve all exercises of a chapter without any problems,  we believe that you are familiar with the chapter content.  If you have solved one exercise incorrectly,  you should also work on the following,  usually somewhat easier additional exercise.

$\text{Example 3:}$  The  $93$  exercises/additional exercises of the book  "Theory of Stochastic Signals"  can be accessed via the link  "Theory of Stochastic Signals: Exercises"

  • From there you can proceed to the individual exercises,  for example  Exercise 1.1: "A Special Dice Game".  This relatively simple exercise consists of a  "Multiple Choice"  and an  "Arithmetic Exercise".  You can see that the  "solution"  is described very detailed and even includes a short video.
  • 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 with  "Jauch".   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 PDF".
  • 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, cutting and audio editing   –   Combining texts and images into a coherent video stream.

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

$\text{Example 4:}$  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

You can access the provided interactive applets via the link  "Applets"  on the start page.

  • If you click on it,  a  "list"  of all applets appears,  grouped by textbook.  We distinguish between the newer  $\text{HTML 5/JavaScript}$ applets  (in the respective lists above)  and the older  $\text{SWF}$ applets  (below).  Unfortunately, the latter do not work on smartphones and tablets.
  • After selecting an  $\text{HTML 5/JS}$  applet,  a wiki description page appears with a description of the content,  an often longer theory section,  and then the execution of the experiment with sample solutions.  At the beginning and end of this page there are links to the actual HTML5 applet in German and English.

$\text{Example 5:}$  The didactic significance of the applets is to be demonstrated by means of   "Eye Pattern and Worst-Case Error Probability".   The eye diagram is a proven tool of transmission technology to capture the influence of line dispersion on the quality characteristic  "error probability".  It is used to clarify more difficult issues,  in the example of 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".  Therefore,  we guide the user specifically through the program on the basis of the experimental procedure.  He has to solve different tasks:  Predict and evaluate results, optimize parameters, etc.

Applets have a similar function as practical courses in mathematical-scientific courses:  Supplementing lecture/exercise with independent work by the student on the topic covered.  A "top 10%" student has of course the possibility to use the applet to set himself tasks that go beyond the execution of the experiment and thus penetrate very deeply into the presented subject matter.

In addition to these  $30$  or so HTML 5/JS applets, we also offer some of our  $50$  SWF  (Shock Wave Flash)  applets.  These were programmed for "Adobe Flash".  Since the Flashplayer Browser Plugin is no longer supported for security reasons, these applets have to be opened with the "Projector Version".

You do not have to install the projector version and it will not be integrated into your browser.  So there are no security concerns in that regard, as long as you trust our  $\rm LNTwww$.   On the corresponding wiki pages you can find the projector version of the flash player and of course the applet itself.

(H)   The download area of LNTwww

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 from 1984 to 1996, which were used in our practical courses.  Several other universities have also used these programs in teaching.

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?")  Günter Söder  started planning "LNTww.v1"   (2001).  Co-responsible was  Klaus Eichin, who was already very active in the 1970s in "computer-assisted teaching" - that was the name of "e-learning" at that time.  The project was to be completed by 2011 at the latest.

The content was based on the teaching materials of Klaus Eichin and Günter Söder as well as  Norbert Hanik  (Professorship "Conducted Transmission Technology"). Other lecture material, which was produced at the Institute of Communications Engineering under the last four chair holders, was also taken into account:

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 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;