Physical Layer Performance of Multi-User Detection in Broadband Multi-Beam Systems based on DVB-S2

vIn this paper we investigate the physical layer performance that can be obtained in a DVB-S2-based broadband system when high frequency reuse is applied and Multi-User Detection (MUD) is adopted at the receiver side to cope with the presence of interference. By calculating the Bit Error Rate (BER) which results from the application of MUD in various cases, the sensitivity of the algorithm to the signals' parameters is first assessed. Then, we show that by jointly detecting/decoding the useful signal and the interferers the peak data rate of the users affected by strong co-channel interference can be significantly increased

LTE Adaptation for Mobile Broadband Satellite Networks

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A Unitary Approach to Information and Estimation Theory in Digital Communication Systems

This thesis presents the outcomes of a Ph.D. course in telecommunications engineering. It is focused on the optimization of the physical layer of digital communication systems and it provides innovations for both multi- and single-carrier systems. For the former type we have first addressed the problem of the capacity in presence of several nuisances. Moreover, we have extended the concept of Single Frequency Network to the satellite scenario, and then we have introduced a novel concept in subcarrier data mapping, resulting in a very low PAPR of the OFDM signal. For single carrier systems we have proposed a method to optimize constellation design in presence of a strong distortion, such as the non linear distortion provided by satellites' on board high power amplifier, then we developed a method to calculate the bit/symbol error rate related to a given constellation, achieving an improved accuracy with respect to the traditional Union Bound with no additional complexity. Finally we have designed a low complexity SNR estimator, which saves one-half of multiplication with respect to the ML estimator, and it has similar estimation accuracy.Questa tesi presenta i risultati ottenuti durante un dottorato di ricerca in ingegneria delle telecomunicazioni. Oggetto di studio è stato il livello fisico dei sistemi di trasmissione numerica, e sono state proposte innovazioni per i sistemi multi-portante e a portante singola. Nel primo caso è stata valutata la capacità di un sistema affetto da varie non idealità. In seguito l'idea di Single Frequency Network è stata estesa dall'ambito terrestre a quello satellitare, ed infine è stata presentata una nuova tecnica per effettuare il mapping da bit a simboli, che ha permesso di raggiungere fattori di cresta particolarmente bassi per il segnale OFDM. Per i sistemi a portante singola, è stato proposto un metodo per ottimizare il progetto delle costellazioni in presenza di una forte distorsione, quale ad esempio la distorsione non lineare dovuta agli amplificatori di potenza a bordo dei satelliti. In seguito è stato sviluppato un metodo per calcolare la probabilità d'errore per bit e per simbolo riferita ad una data costellazione. Tale metodo ha la stessa complessità dello Union Bound ma risulta essere più accurato. Infine si è progettato uno stimatore di rapporto segnale-rumore, che permette il risparmio di metà delle moltiplicazioni rispetto al tradizionale stimatore a massima verosimiglianza, ma che mantiene prestazioni di stima comparabili

On the Constrained Capacity of OFDM in Rayleigh Fading Channels

In this paper, the instantaneous capacity of Orthogonal Frequency-Division Multiplexing (OFDM) in frequencyselective Rayleigh fading is evaluated, based on constrained capacity arguments, to account for the signal constellations used on the sub-carriers, and on a form of the Central Limit Theorem suitable for correlated random variables. If the number of subcarriers is large, the overall capacity is shown to be Gaussiandistributed, and its mean and variance are derived, as well as their dependence on the selected constellation, the signalto- noise ratio and the channel parameters. The results show the separation between constrained and unconstrained capacity, and indicate the usefulness of adaptive modulation in exploiting all the signal-to-noise ratio range. Furthermore, the statistical characterization of the instantaneous capacity is instrumental in defining the outage capacity for OFDM systems

Robust SC-FDMA subcarrier mapping for non-linear channels

Multicarrier modulations have several advantages, allowing them to be adopted in a large number of communication systems; one of their drawbacks is that they are particularly affected by non-linear distortion, typical of power-constrained systems. Among several multicarrier communication systems, the single-carrier frequency division multiple access (SC-FDMA) is gaining an increasing interest in the satellite area due to its usage in the DVB-NGH, and the research efforts in DVB-TM-RCS2 and DVB-TM-S2. In this paper we consider the application of single-carrier frequency division multiple access (SC-FDMA) to satellite communications, by investigating the effect of different mapping schemes in terms of both in-band distortion and out-of-band spectral regrowth when a non-linear amplifier is present in the transmit equipment. The outcomes of this analysis demonstrate that a mapping based on Minimum Shift Keying (MSK) outperforms the conventional QPSK mapping in terms of resilience to non-linear distortion

Coarse Beamforming Techniques for Multi-Beam Satellite Networks

Coarse beamforming is a space processing scheme which allows for efficient use of the available spectral resources on the feeder link of a multi-beam broadband satellite system. In this framework, spectral occupancy of the multiplexed antenna signals that must be exchanged between the satellite and the gateway is a critical issue, up to the point that a costly multiple gateway infrastructure could be required to restrain bandwidth usage. Alternatively, a hybrid on board/on ground processing ar- chitecture is desirable, where the effect of space processing allows to project feed signals on a subspace, thus reducing the required feeder link bandwidth. This foresees a fixed processing scheme on board the satellite, which we refer to as Coarse Beamforming, yielding an overall system which relies on reasonable payload complexity, together with on ground processing flexibility. We explore two Coarse Beamforming techniques for the return link of a multi beam satellite system, and we evaluate the effect of compression in terms of reconstructed signal degradation. We show how, without significant distortion, bandwidth occupancy can be considerably reduced

A robust interference mitigation technique for BFSK Fast Frequency Hopped signals

This paper presents an improvement to the Frequency Shift Keying - Fast Frequency Hopping demodulator, which provides increased resilience to interference with a very slight complexity increase. The additional robustness against jamming is achieved by jointly observing the FSK demodulator branches. This allows the proposed demodulator to distinguish the jammer from the signal more accurately. This demodulator is particularly robust for the case of high J/S (Jammer to Signal Ratio), while for the case of low J/S its performance is in line with state-of-the-art receivers