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«.

• 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 good 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

A central role in our didactic concept play »exercises«. We believe that the sensible use of »LNTwww« by a user with previous knowledge should be that he first work on the exercises relating to his actual learning area and only jump to the corresponding theory section when required.

You can find the  »exercise overview«  for all books  $($approx.  $640$  exercises, approx.  $3100$  subtasks)  on the home page via the link  »Exercises«.  All exercises are structured in the same way:

• Each exercise consists of the »exercise description« and 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 Task«   ⇒   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«$)$.

1. If you were able to solve all exercises of a chapter without any problems,  we believe that you are familiar with the content of the entire chapter. 
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 first book can be accessed via the link  »Signal Representation: Exercises«. 

• From there,  we move on to the individual exercises,  e.g. 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 »Arithmetic Task« with two real-valued computational queries   ⇒   subtask  (4).

• However,  most of our exercises are not that easy.  Although MediaWiki also calls an arithmetic task  »quiz«,  answering them is usually much more difficult than in the numerous quiz shows on TV.   Because: 

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

• We recommend:  First print the exercise   ⇒   »printable version«  and solve the exercise  offline  before checking  online.

(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! moment". 

• 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

Due to the fact,  that our e–learning project LNTwww was first conceived in German and the wish for an English version came much later,  in the English version the assignment between  »Formula signs«   and  »Designation«  is not quite easy.   What do for example

1.   $f_{\rm T}$,
2.   $s_{\rm TP}(t)$, 
3.   $e$,
4.   $E$?

Here the link  »Glossary«  on the home page below can help with the following alphabetically ordered entries:

  »Formula sign«   ⇒   »German name«   ⇒   »English name«

The file is self-explanatory. A few explanations are given under the last menu item  »Some remarks to the Glossary«.

$\text{Example 6:}$  In this file you will find the following entries:

  $f_{\rm T}$   ⇒   Trägerfrequenz   ⇒   carrier frequency

  $s_{\rm TP}(t)$   ⇒   äquivalentes Tiefpass–Sendesignal   ⇒   equivalent low-pass transmitted signal

  $e= 2.718281828456$...   ⇒   Eulersche Zahl   ⇒   Eulerian number

  $ E$   ⇒   $(1)$ Schwellenwert,  $(2)$ Energie   ⇒   $(1)$ threshold value,  $(2)$ energy

From the context,  the decision for  $(1)$  or  $(2)$  should be easy.

(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?")  Günter Söder began 2001 planning the German-language project  »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 his own teaching materials as well as those of his 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$)$.

Just a few dates about progress of the German-language LNTwww project,  eleven years after the planned completion :

• First of all our own platform had to be developed by students  $($Marin Winkler,  Yven Winter$)$.  The authoring system  »LNTwww«  was based on the http server  »Apache«,  the database  »MySQL«,  the script language  »Perl«  and  »Shock Wave Flash«  $\rm (SWF)$  as a basis for multimedia applications   ⇒   version  »LNTwww.v1«  $($2003$)$.

• Work of the following years was online adaptation of the manuscripts,  input into the database with the rather complicated LNTwww syntax,  creation of the graphs as well as conception and realization of multimedia elements.  After completion of all nine textbooks the desired final state was reached   ⇒   version  »LNTwww.v2«  $($2016$)$.

• At the same time,  it became known that  »SWF«  would not longer be supported by relevant manufacturers.  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 based on  »MediaWiki«   ⇒   version  »LNTwww.v3«  $($2021$)$.

Finally,  a few sentences about the English LNTwww version. 

• At the beginning of the Corona pandemic and the associated lockdowns,  the call for  »e-learning«  also became louder and louder at the universities,  even from professors who had previously rather rejected this form of teaching. 

• Suddenly,  funds were also made available,  to provide as many e-learning courses as possible in as short a time as possible.  Our chair  »Gerhard Kramer«  therefore already submitted a corresponding application for working student funds in spring 2020,  which was approved within a few weeks.

• In June 2020 we started the English translation with support of the  »DEEPL«  program  $($free version$)$  and finished it in April 2023.  From the LNT staff were involved:  »Javier Garcia Gomez, Tasnád Kernetzky, Benedikt Leible and Günter Söder«.  Of the students involved,  »Noah Nagi«  and  »Jiwoo Hwang«  deserve special mention.

(J)   Acknowledgement

The Institute for Communications Engineering would like to thank the many people involved in the creation of  $\rm LNTwww$:

• The persons responsible for the German and/or English LNTwww projects:

$\text{Günter Söder}$,   $\text{Klaus Eichin}$,   $\text{Tasnád Kernetzky}$,   $\text{Javier Garcia Gomez}$,    $\text{Benedikt Leible}$.

• The  $($former$)$  LNT/LÜT colleagues,  who contributed as co–authors or experts or supervised student work:

$\text{Ronald Böhnke}$,   $\text{Joschi Brauchle}$,   $\text{Bernhard Göbel}$,   $\text{Norbert Hanik}$,   $\text{Thomas Hindelang}$,   $\text{Gianluigi Liva}$,  
$\text{Tobias Lutz}$,   $\text{Michael Mecking}$,   $\text{Markus Stinner}$,   $\text{Thomas Stockhammer}$,   $\text{Johannes Zangl}$,   $\text{Georg Zeitler}$.

• The more than  »50 students«,  who have worked on subareas,  designed learning videos and applets or implemented the porting to the MediaWiki version within the framework of Engineering practice,  diploma,  bachelor and master theses or within the framework of a working student activity.

• The  »Department of Electrical and Computer Engineering«  and the  »Technical University of Munich«  for funding working students in the years since 2016 within the framework of the  »MoliTUM«  resp.  »EXIni«  programs.

$\text{Gerhard Kramer}$