## Learning objectives

The goals of the course, in terms of knowledge and comprehension, are the following:

- to give the students an overview of the main communication systems, with particular attention to digital communications.

The ability to use the knowledge and comprehension skills outlined above can be summarized as follows:

- to understand the operational principles of a communication system from its architecture

- to understand the trade-offs of a communication system.

- to numerically simulate a communication system.

## Prerequisites

Basic knowledge of probability theory is welcome, although the concepts will be reviewed in the course.

## Course unit content

Introduction to communication systems. The ISO-OSI model. Characterization of the wireless propagation medium. Satellite communications. Numerical simulations of communication systems. Foundations of information theory. Foundations of coding theory. Contention access methods (with fixed resource assignment and with random access). Cellular networks. Wireless communications.

## Full programme

LECTURE 1

Course introduction.

LECTURE 2

Decibel. Properties of decibels. Logarithmic scales. Loss and gain.

LECTURE 3

Cable loss. Wave. Wavelength. Free-space loss. The effective area of antennas. Fading.

LECTURE 4

Exercise.

Fading. Rayleigh statistics.

Margins in communications. Outage events. Outage probability.

Satellite communications. Satellite orbits.

LECTURE 5

Satellite communications. Satellite orbits. Satellite bands. Principal problems and solutions of satellite communications.

ISO-OSI model. Physical layer, data-link, network, transport, session, presentation, and application layers.

LECTURE 6

The MATLAB programming language. Comments. variables, matrices, conditions, cycles, vectorization, and functions.

LECTURE 7

MATLAB: instruction "end". Logical indexing. Random numbers. Struct and cell variables. Plots.

Virtual circuit. TCP/IP model.

LECTURE 8

MATLAB: computation of the Fourier transform of a sampled signal.

Anonymous functions.

The minimum and maximum frequency of a discrete-time representation of an analog signal.

fftshift command.

Example: signal modulation and the aliasing problem.

LECTURE 9

MATLAB: summary.

Solution of theoretical exercises 1-8.

LECTURE 10

MATLAB: the sampling of analog signals. Discrete-time and frequency choice.

Analysis of a sinusoidal signal. The problem of periodic repetition.

Frequency analysis of signals.

LECTURE 11

Solution of theoretical exercises 9-12.

Coding. Error detection and correction. Code rate.

Repetition codes. Probability of undetected word.

LECTURE 12

MATLAB: generation of signals AM, DSB, SSB.

LECTURE 13

MATLAB: AWGN noise generation. Relationship between noise power and its power spectral density.

Noise equivalent bandwidth.

LECTURE 14

MATLAB: Estimation of the signal-to-noise ratio (SNR). The problem of signal distortion in SNR evaluation.

SNR of a DSB transmission. Simulation of a DSB modulation through bandpass or lowpass signals.

LECTURE 15

Hard and soft coding.

Digital constellations. Multilevel digital modulations. Quadrature phase shift keying (QPSK), quadrature amplitude modulation (QAM). A first comparison between multilevel constellations.

Information theory.

Definition of information. Entropy. Mutual information. Average mutual information and channel capacity.

LECTURE 16

MATLAB: exercise on superheterodyne detection.

LECTURE 17

Shannon theorem: proof through Hartley's law.

Channel capacity with constraints.

Information rate. Impact of coding on the information rate.

Exercise on mutual information.

LECTURE 18

On the exploitation of correlations to improve expectations: control variates.

Medium access control (MAC). Static and dynamic resource allocation.

Frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA).

Direct-sequence spectrum (DSS): transmitter.

LECTURE 19

MATLAB: detection of a single pulse through the matched filter.

Convolution with conv.m.

SNR with a matched filter or a generic filter.

LECTURE 20

Dynamic allocation of resources.

The problem of collision. Throughput.

Aloha. Performance.

Slotted-aloha.

Carrier-sense multiple access (CSMA).

CSMA with collision detection (CSMA-CD).

Probability of successful transmission.

LECTURE 21

Ethernet. ethernet devices.

Manchester encoding.

Ethernet packet: minimum size.

Backoff strategy. Channel efficiency: average waiting time.

Ethernet cables: twisted-pair cable, optical fiber.

Optical fibers: advantages.

Single-mode and multi-mode optical fibers.

Wireless networks: problems.

Frequency hop spread spectrum (FHSS). Fast FHSS.

The hidden and the exposed terminal problem.

Carrier-sense multiple access collision avoidance (CSMA-CA).

LECTURE 22

Multiple-input-multiple-output (MIMO): basic idea.

Cellular networks.

Frequency reuse. Cell clusters.

Handover.

Cell sizing. Signal-to-interference noise.

Channel model in cellular networks. The multipath problem.

Orthogonal frequency division multiplexing (OFDM).

Solution of theoretical exercises 13-17.

LECTURE 23

MATLAB: Generation and detection of PAM signals. Error probability.

LECTURE 24

Solution of theoretical exercises 18-27.

## Bibliography

- A. B. Carlson e P. B. Crilly, Communication Systems: an Introduction to Signals and Noise in Electrical Communication, Mcgraw Hill Higher Education, 5th edition, 2010. ISBN-13: 978-0071263320.

- A. S. Tannenbaum e D. Wetherall, Reti di calcolatori, Pearson, 6th edition, 2021, ISBN: 9788891915313.

## Teaching methods

During the lectures, various topics related to performance analysis of communication systems, as detailed in the program, will be covered. Both slides and blackboard will be used. Some exercises will be solved during class. The slides of the course will be provided on the Elly platform.

Some lectures will use the software MATLAB to simulate communication systems.

## Assessment methods and criteria

The regular exam, made during official exam sessions, is written plus a project in the language MATLAB. The written part is based on exercises and open-ended questions. If not explicitly indicated, all questions have the same weight.

The project consists of a simulation of a communication system. The project is evaluated in terms of clarity, completeness, correctness, and plagiarism.

The final grade for the exam on communication systems is calculated as a weighted average based on the scheme 0.25*(grade part 1, analog) + 0.25*(grade part 1, digital) + 0.25*(grade part 2, written part) + 0.25*(grade part 2, project).

The exams will adhere to the University norms in effect at the time of the exam.

More details are in the introduction slides of the module.

## Other information

The teaching and support material will be provided in part by the teacher.