The book "Digital Communications الإتصالات الرقمية", written by Salem Iseed, illustrates the subjects of digital communications in a simple method.
Although the first communication system which is the telegraph was demonstrated by Samuel Morse at 1837, this system is considered to be digital. This system was using four types which are dots, dashes, letter spaces and word spaces. Despite that, inventing the telegraph did not lead to the modern (present-day) digital communication systems. In reality, Pulse Code Modulation (PCM) proposed by Alec Reeves at 1937 leaded to the modern digital communication systems.
Analog communications are the communications that deal with analog signals (signals for which their values vary continuously with time, like voice signal). So in this case, a high-frequency carrier is modulated according to the analog signal that we want to transmit.
While digital communications are the communications that deal with digital signals (signals for which their values are represented at any time instant by specific symbols, for example in binary system are represented by only 0 and 1 at any time instant). So in this case, a high-frequency carrier is modulated according to 1 and 0.
To transmit an analog signal, such as voice- or image-signal, by digital means, we have to convert this analog signal to digital one. This process is usually referred to as Analog-to-Digital Conversion (ADC).
The most important techniques that are used to convert an analog signal to digital one are Pulse Code Modulation (PCM) and Delta Modulation (DM).
Although digital communications are more complicated than analog ones, the digital communications are characterized by the following advantages:
Thus, digital communications have many advantages. But the large amount of conversions from analog to digital forms make them to require large transmission bandwidth.
Analog-to-Digital Conversion, Analog Pulse Modulation, Line Codes, Pulse Shaping and Optimum Receiver, Digital Modulation and finally Muliplexing.
This book of digital communications contains solved examples which cover roughly all the subjects included in this book.
Every chapter in this book contains questions similar to that written in Alshaamel examinations for 2-year colleges.
Contents of the entire book are written in the page of Contents.
The book is arranged according to the international standard method of writting the books.
Quotations from the book are shown only in the Arabic-language page: مقتبسات من كتاب الاتصالات الرقمية