Digital communications M - Z

Knowledge and understanding the most important elements regarding digital communications

Capture and understanding the basic elements to analyze digital transmission techniques, and the procedures for achieving the main parameters characterizing a digital and analog communication system.
Improving capabilities to analyze both vector spaces to represent signals, and techniques for analog-to-digital conversion.

Applying knowledge and understanding of the state-of-art technologies of digital communications systems, also targeted to the practical application in non-usual contexts

Skills development for analysis of reference systems of analog and digital communications systems, also aimed at the individuation of the main system parameters (signal-to-noise ratio, bit error rate, bandwidth, energy consumption, circuit complexity). The target is to allow the student to use this knowledge also for future systems, although different from the ones studied in this course.

Making judgements of the main topics of this course

Outgrowth of a sufficient level of making judgements in discovering the main peculiarities of analog and digital communications systems and of the available tools not only for the design of simple systems like the ones studied during the course, but also of more complex systems, like satellite communications, 5G e 6G, which require further maturation of what studied during the course.

Communication skills finalized to heterogeneous interlocutors

Outgrowth of an effective and high-level communications skill for topics regarding analog and digital transmission, modulation systems and transmission devices.

Learning skills of the evolutions of the topics studied during the course, independently

Outgrowth of skills for autonomous training regarding scientific evolution and specific digital communications technologies to deepen new transmission technologies for cables, fiber and wireless, also with reference to techniques applied to ADSL, LTE, 4G, 5G and 6G.

The course includes 58 hours of lessons (frontal teaching, exercises and laboratory).

In the case lectures will be partially or fully realized remotely by a video-communications platform, what declared above could undergo some changes, in order to achieve the objectives targeted in this Syllabus.

Convolution

Bandwidth of a base-band and passband signal

Power spectrum and autocorrelation function

Periodical signals

Probability theory, random variables and random processes

Probability density function of random variables

Time-invariant linear systems, filters and distortions

Sampling of a signal and interpolation from a sequence

The course is organized in the following six Elementary Teaching Units (ETU):

1. Introduction

Course organization, the history of TLC (*). Recall of signal theory. General description of a communication system, analog and digital sources, classification of signals and services, transducers. Performance parameters: bit-rate, SNR, MOS, BER, SER. Types of messages and audio frequencies. Hearing and pain threshold, hearing loss (*). Communication channels: ideal, perfect, linear and permanent, linear and non-permanent. Channel bandwidth. Equalization. Non-linear channels: harmonic distortion and intermodulation noise, effects and solutions. Noisy channels. AWGN noise and interference. The radio channel and electromagnetic waves. Attenuation in free space and Friis' formula. Effects of the medium and atmospheric phenomena on propagation (*). The multipath phenomenon. Noisy quadripoles: equivalent noise bandwidth, temperature and noise figure. Resistive quadrupoles (*). Friis formula for cascaded quadrupoles. Antenna and system temperature. Exercises.

2. Digital transmission of voice signals

Voice signal characteristics. A/D conversion: sampling, uniform and non-uniform quantization. Quantization SNR. PCM coding, A and μ compression law. Transmission of PCM signals on noisy channels (*). Linear prediction vocoder. ITU-T and ETSI voice compression standards. Exercises.

3. Source coding and channel coding

Information theory: Information measurement and entropy. Examples of discrete sources. Source coding: properties of codes, length of a code, coding efficiency, block coding (*), Gray, Shannon-Fano, Huffman codes. Exercises.

Channel coding: Block codes. Code rate. Coding/decoding delay. Linear and systematic code. Spectral efficiency. Repeating and parity code. Interleaver (*).

4. Baseband digital transmission

The digital transmitter. Binary and M-ary line coding. Spectrum of a line code. Clock recovery. Binary and M-ary PAM systems. Intersymbol interference (ISI) and Nyquist criterion. Eye diagram. Shannon Hartley theorem on channel capacity.

Digital receiver. Structure of a digital receiver. Maximum likelihood decider. Calculation of bit and symbol error probability in binary and M-ary baseband receivers.

5. Introduction to passband modulations

DSB, SSB, AM and VSB amplitude modulation and demodulation. FM and PM angular modulation (*). Phase and frequency offset. Comparison of modulation techniques: power, bandwidth, SNR, complexity. Frequency division multiplexing (FDM) and time division multiplexing (TDM).

6. Digital modulations

ASK, PSK, FSK binary modulations. Performance comparison: power, bandwidth, BER, complexity. Multidimensional M-ary modulations (*): M-PSK, QAM, M-FSK. DMT and OFDM transmission systems.

(*) Topic belonging only to the complete program

[1] Leon W. Couch, Fondamenti di Telecomunicazioni, Prentice Hall
[2] Alessandro Falaschi, Trasmissione dei Segnali e Sistemi di Telecomunicazione, Web edition, Versione 2.0, 2023.
[3] K. Sam, Shanmugam “Digital and Analog Communication Systems”, John Wiley & Sons.
[4] Teacher's notes

The course does not require mandatory attendance, but it is strongly recommended to pass the exam. The laboratory is mandatory with a minimum attendance of 70%.

Type of assessment 1:

- Ongoing test of 2 exercises in 90 minutes on the first 3 parts of the program – valid for 1 year

- Thesis (groups of ¾ people, due by May) – valid for 1 year

- Oral test of 2 questions on a reduced program – without topics with (*)

Type of assessment 2:

- Ongoing test of 1 exercise in 45 minutes on the first 2 parts of the program – valid for 1 year

- Project (groups of ¾ people, due by May) – valid for 1 year

- Oral test of 2 questions on a reduced program – without topics with (*)

Type of assessment 3:

- Ongoing test not passed or not completed

- Thesis or project (groups of ¾ people, due by May) – valid for 1 year

- Oral test of 3 questions on a complete program + 1 exercise on the first 3 parts of the program (thesis)

The ongoing test is passed with at least the 50% of correct execution. For the first two types of tests, those who do not pass the oral exam must retake only this one, registering for the subsequent sessions.