Introduction to digital communications.
Optimum receiver for signal with random phase in AWGN channels.
Carrier and symbol synchronization.
Communications through band limited channels.
Equalization techniques.
Digital communication of waveforms with memory.
Propagation through channels affected by multipath.
Fading.
OFDM modulation.
R. Steele: Mobile radio communications. Pentech Press, London, 1992.
D. Parsons: The mobile radio propagation channel. Pentech Press, London, 1992.
E. Damosso, R. Stola: Radiopropagazione. Sola superiore G. Reiss Romoli, 1992.
G. M. Vitetta: Fondamenti di trasmissione numerica con applicazioni alle radiocomunicazioni; Parte II. Pitagora Editrice, 2008.
Learning Objectives
Skills acquired by the student: evaluation of the behavior of digital communication systems in operating conditions; designing such systems.
Prerequisites
Topics of Analog Signal Theory and Communication Systems
Teaching Methods
Classroom lectures
Further information
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Type of Assessment
Oral examination.
Course program
Introduction to Digital Communications - Model of a communication system; description of the main subsystems; definition of the performance parameters.
Transmission through band-limited channels - The problem of Inter-Symbol Interference. The eye diagram, the Nyquist criterion. Technical limitation of intersymbol interference. Main methodologies for channel equalization: Zero-Forcing equalization, MMSE equalization. Equalizers: T and T/2 equalizers, zero-forcing and MMSE adaptive equalizers, decision-feedback equalizer.
Synchronization recovery of carrier and symbol - Influence of synchronization errors on the performance of a digital communication system. The circuits of synchronism within a receiver for digital modulations. MAP and ML criteria for parameter estimation: joint recovery of carrier and timing synchronizations, decision-directed and non-directed decision recovery of carrier synchronization, decision-directed and non-directed decision recovery of timing synchronization. Circuits for the carrier synchronization: Phase Locked Loop; Costas Loop, Square Law Loop, Decision-Feedback Circuit. Circuits for the timing synchronization: Early-Late Gate Synchronizer.
Waveform transmission through Gaussian channels with incoherent demodulation – Optimum demodulation criterion. Physical implementation of the optimum demodulator. Applications to digital modulation schemes: performance of incoherent demodulation of an M-ary FSK scheme.
Differential Techniques: DPSK and DQPSK, differential modulators, coherent and incoherent demodulators, performance.
Transmission of waveforms with memory - Main properties. The MLSE decision criterion; application of the Viterbi algorithm for the MLSE demodulation. Full and partial response CPM. Coded modulation for band-limited channels (TCM): trellis representation, set partitioning method and rules of Ungerboeck, demodulation using the Viterbi algorithm, performance.
Characterization of the propagation on multi-paths, time-varying transmission channels. General characteristics of the mobile radio channels. Analysis of small-scale approximation for a finite number of paths. Dispersion in frequency and time. Bello’ functions of the channel. Statistical characterization: Rayleigh and Rice channels. Autocorrelation functions of the functions of Bello in the case of WSSUS channel; power delay profile and correlation function in frequency; Doppler spectrum and the correlation function in time; band and time of coherence; scattering function. Flat channel in frequency (non-selective); flat channel in time (slowly varying); flat channel in frequency and time.
Effects of multipath fading on digital modulations and countermeasures. Evaluation of the performance of binary PSK and FSK modulations in the presence of flat frequency and time fading. Diversity transmissions and performance evaluation of diversity techniques for binary modulations; Maximal Ratio Combiner.
Fundamentals of OFDM transmission; implementation of OFDM modulation and demodulation using DFT; implementation of OFDM modulation for transmissions in mobile radio channels: use of the guard and COFDM. Differential encoding. Analysis of the effects of the errors of frequency and phase.