Learning in the information age is becoming vaguely connected to the traditional principles of teaching solely via lectures and studying via reading and doing homeworks. In engineering, it is the era in which ITU and other standardization bodies opened access to many of their documents and there are several interesting open source and open hardware projects to help learning through practice. Books continue to play an important role and can surely benefit from available standards and projects. Hence, this book suggests several practical applications for which open source tools and low cost hardware are key ingredients.

Current communication systems heavily rely on digital signal processing (DSP) and this fact also motivated the effort to present both. This way, the book can benefit from using the same nomenclature for both DSP and communications. But there is a well-known exploration versus exploitation tradeoff when defining the contents of a book, especially given that DSP and digital communications are such broad areas. In fact, when I teach them, I feel like the guide of a tourism group with seven days to visit Europe and low budget. This book is the result of my belief that, in spite of being impossible to visit all nice places, it is realistic that the readers can learn the basics of two important subjects for their careers and have fun along the process, especially by using resources of many interesting open projects!

Because there are so many good and comprehensive textbooks in these subjects, I took the alternative route of leaving out topics that are often part of classical courses (Signals and Systems, DSP or Digital Communications) in favor of including topics that I observe being used in current practice. The choices were biased by my experience in research and development projects with companies such as Ericsson and Brasilsat, which substantially influenced my teaching. Also, while writing I often recalled a character from the book "Hard Life" by Charles Dickens: a professor who demands his students to know "facts". I then tried to get inspired and concentrate on concepts that are being required in modern areas such as software defined radios. Based on previous versions of this manuscript, I could happily notice young engineers perform tasks such as generating waveforms with Octave and Matlab, interpreting results of a spectrum analyzer and saving them as big-endian files for processing in Java. The result of the tradeoff is that this book may better fit self-taught readers than the ones preparing for exams.

This is a book that benefits from free and open source. Hence, it is fair that all software is available at software download page. Even the figures can be reproduced by the reader with the provided source code and Matlab.

Both Mathwork's Matlab (R2011a) and Octave (version 3.6.4) -- which is used by many people as an open source version of Matlab -- are capable of running most of the code. Matlab's object-oriented programming (OOP) was deemphasized in favor of traditional functions that are compliant with Octave. Another intention is to motivate the reader to understand and develop his/her own software, not to use a library or GUI. Some recent developments make easier the life of a Matlab's user but hide important details from someone who is at the learning stage. The text not only avoids OOP but also specific Matlab toolboxes, such as Communication's. Scripts that run only on Matlab or Octave are organized in specific directories. For example, generating the book figures requires Matlab. Another organizational aspect is that, because URLs significantly change over time, instead of listing them in this printed copy, all references identified by url, such as [urlFMitu] (a unique identifier following the prefix url), are organized (and kept updated) at urls page.

I have adopted self publishing and targeted print on demand. Therefore, I had to perform several tasks that are typically taken care by a specialized publisher. It was not possible to have a professional proofreader reviewing the text yet and, therefore, I apologize for the grammar errors.

  - GNU Radio with GNU Radio Companion (GRC)

  - GNU Octave

  - Packages ("toolboxes") for GNU Octave, in octave.sourceforge.net (the default instalation of Octave does not include packages)

  - Audacity

  - Python

  - Playrec