Giulio Colavolpe - Academia.edu (original) (raw)

Papers by Giulio Colavolpe

2022 56th Asilomar Conference on Signals, Systems, and Computers

The paper summarizes the recent investigation on feasibility of adapting state-of-the-art coheren... more The paper summarizes the recent investigation on feasibility of adapting state-of-the-art coherent fiber-optics (FO) systems for Free Space Optical (FSO) scenarios. This investigation is critically dependent on the intertwined aspects of architecture, as well as device and propagation impairments (including the channel) appearing in the aforementioned systems. Towards this, the work identified the key system differences between the two systems. Particularly, the FSO channel model was investigated, impact of atmospheric turbulence on FSO was discussed and a channel series was generated. Subsequently, relevant FO techniques including coherent detection, wavelength division multiplexing and Time-Frequency packing (TFP) were reviewed. Another departure from FSO works was the emphasis on coherent reception; receiver architectures and diversity schemes were first investigated. The former strived to make fair comparison amongst the receivers considering the diverse nature of perturbation added, while the latter indicated gain in performance through increase of diversity order (2-4 dB gain). An immediate conclusion is a suggestion on adaptation of wavelength diversity when coherent receivers. The investigation also evaluated the capacity and outage of fast and slow fading channels with parameters motivated by the channel modelling work. The shaping gain was evaluated and an LDPC code design example was provided for FSO downlinks. Finally, TFP enabled a remarkable performance gain when applied to coherent detection schemes, but only marginal with direct detection. The paper concludes by pointing to the next steps that build on this investigation and the need to corroborate with measurements.

2019 26th International Conference on Telecommunications (ICT)

This paper compares the spectral efficiency of some of the most popular multicarrier schemes prop... more This paper compares the spectral efficiency of some of the most popular multicarrier schemes proposed for the fifth generation (5G) of cellular systems, such as orthogonal frequency-division multiplexing (OFDM), filterbank multicarrier (FBMC), generalized frequency-division multiplexing (GFDM), and universal filtered multicarrier (UFMC). First, we propose a unified signal model valid for many multicarrier schemes. Second, we employ the mismatched detection theory, together with the unified signal model, to obtain closed-form achievable lower bounds on the channel capacity, conditioned on the multipath channel realization. Third, we numerically compare the achievable spectral efficiency (ASE) of OFDM, FBMC, GFDM and UFMC, in different multipath channel scenarios. Our analysis proves that the best (ASE-optimal) multicarrier scheme depends on the channel model and on the signal-to-noise ratio (SNR).

Consorzio Nazionale Interuniversitario per le Telecomunicazioni, 2019

2020 IEEE 3rd 5G World Forum (5GWF), 2020

The evolution of 5G into beyond 5G and 6G networks aims at responding to the increasing need of o... more The evolution of 5G into beyond 5G and 6G networks aims at responding to the increasing need of our society of ubiquitous and continuous connectivity services in all areas of our life: from education to finance, from politics to health, from entertainment to environment protection. The next generation network communication infrastructure is called to support this increasing demand of connectivity by enforcing: energy- and costefficiency to guarantee environmental and economical sustainability; scalability, flexibility, and adaptability to ensure support to the heterogeneity of the service characteristics and constraints, as well as the variety of equipment; reliability and dependability to fulfil its role of critical infrastructure able to provide global connectivity no matter the social, political, or environmental situation. In this framework, non-terrestrial networks (NTN) are recognized to play a crucial role. It is in fact generally understood that the terrestrial network alone cannot provide the flexibility, scalability, adaptability, and coverage required to meet the above requirements, and the integration of the NTN component is a key enabler. In this framework, 3GPP has started to address the inclusion of technology enablers in the NR standard to support NTN. However, to fully exploit the potential of the NT component in an integrated terrestrial and NT architecture, several research and innovation challenges shall be addressed. In this paper, we first discuss the current development of NTN in 5G and then we present the vision of the role of NTN in B5G and 6G networks and we elaborate the corresponding research challenges.

2016 IEEE Global Communications Conference (GLOBECOM), 2016

The need for increased data rates has led towards the development of advanced broadband satellite... more The need for increased data rates has led towards the development of advanced broadband satellite systems able to achieve higher capacity for providing Internet and backbone services in remote areas. Aside of the more conventional geostationary orbit (GEO), Medium Earth Orbit (MEO) satellite constellations are envisaged due to their advantages in terms of shorter link path and low latency; MEO satellite constellations are currently operating at Ka-band and are already showing signs of spectrum saturation in high demand areas in their coverage. In search of additional spectrum, in this paper, we employ the Q-band by investigating the performance of a multi-satellite MEO constellation network in terms of system capacity considering sophisticated propagation and physical layer tools. In particular, within the proposed Q-band solution, a higher throughput can be achieved with respect to a corresponding Ka-band system, by reaching up to 100% gain in terms of system capacity in a clear sky conditions.

IEEE Transactions on Aerospace and Electronic Systems, 2017

In this paper, the performance of a reference Medium Earth Orbit (MEO) satellite constellation sy... more In this paper, the performance of a reference Medium Earth Orbit (MEO) satellite constellation system operating at Ka-band and employing single links to ground is compared with next generation advanced systems in higher RF or optical bands employing multiple diversity links. The fill rate of existing MEO constellations offering broadband and trunking services in Ka-band is growing fast rendering the search for additional spectrum of vital importance. Therefore, this paper reports on the results of a system study investigating the option of using Q/V band, or even optical wavelengths, instead of Ka-band, to deliver substantially higher system capacity. The system study takes a holistic approach covering from atmospheric channel impairments to waveform optimization and system analysis for realistic assumptions. After proposing a sophisticated channel model to generate spatio-temporal time series of atmospheric attenuation, an optimization of the performance at physical layer is performed to derive the inputs necessary to the system analysis. Five different advanced high frequency RF and optical systems are compared in terms of outage capacity and availability for various locations of single ground stations, multiple ground stations (site diversity) and from multiple satellites (orbital diversity). For maximizing the realism of the comparison, similar on board satellite resources (mass, power) are assumed for all scenarios.

2016 8th Advanced Satellite Multimedia Systems Conference and the 14th Signal Processing for Space Communications Workshop (ASMS/SPSC), 2016

We investigate the problem of increasing the spectral efficiency of current high rate telemetry s... more We investigate the problem of increasing the spectral efficiency of current high rate telemetry systems in two different scenarios, which exploit one and two channels, respectively. We will analyze several techniques aimed at improving different stages of the transceiver scheme. We will optimize the transmission parameters and apply advanced receiver architectures, able to take into account part of the channel memory and of the interchannel interference. We will propose a new signal predistortion algorithm, which has very good performance in both considered scenarios, and we will show that, by combining the presented techniques, significant gains are possible over the current configuration. The whole analysis is aimed at providing information theoretical bounds to the achievable transmission rates.

Algorithms and Implementations, 2016

Motivation and Background Historically, the evolution of wireless cellular systems has been fuele... more Motivation and Background Historically, the evolution of wireless cellular systems has been fueled by the need for increased throughput. Indeed, the need for larger data-rates has been the main driver of the path that has led us from 2G systems 1 to 4G systems, with data-rates evolving from tens of kbit/s up to the current state-of-the-art tens of Mbit/s. Focusing on the physical (PHY) layer, and in particular on the adopted modulation schemes, the transition has been from 1 Indeed analog 1G cellular systems had no data transmission capability; they just offered voice services.

39th European Conference and Exhibition on Optical Communication (ECOC 2013), 2013

We investigate the time-frequency packing technique on long-haul optical links in order to increa... more We investigate the time-frequency packing technique on long-haul optical links in order to increase the spectral efficiency. This solution is compared to high-order formats at equal bit or baud rate, demonstrating that higher spectral efficiency can be more effectively reached.

Journal of Lightwave Technology, 2010

We analyze the orthogonal frequency division multiplexing (OFDM) technique in long-haul next gene... more We analyze the orthogonal frequency division multiplexing (OFDM) technique in long-haul next generation optical communication links and compare it with the well-established single-carrier (SC) data transmission using high-level modulation formats and coherent detection. The analysis of the two alternative solutions is carried out in the 100 Gbps scenario, which is commonly considered to be the next upgrade of existing optical links, with special emphasis on quaternary phase-shift keying (QPSK) modulations. The comparison between OFDM and SC takes into account the main linear and nonlinear impairments of the optical channel, e.g., group velocity dispersion (GVD), polarization mode dispersion (PMD), self-phase modulation (SPM), cross-phase modulation (XPM), and four-wave mixing (FWM), as well as the phase noise due to transmit and receive lasers, their relative frequency offset, other synchronization aspects, the overall complexity, the power and spectral efficiency, and the technological constraints.

Journal of Lightwave Technology, 2008

This paper analyzes optical transmission systems based on high-order modulations such as phase-sh... more This paper analyzes optical transmission systems based on high-order modulations such as phase-shift keying signals and quadrature amplitude modulations. When the channel is affected by group velocity dispersion (GVD), polarization mode dispersion (PMD), and phase uncertainties due to the laser phase noise, the optimal receiver processing based on maximum-likelihood sequence detection and its practical implementation through a Viterbi processor is described without a specific constraint on the receiver front end. The implementation issues are then faced, showing that at least a couple of widely known front ends, with proper modifications, can be used to extract the required sufficient statistics from the received signal. The aspects related to the receiver adaptivity, the complexity reduction of the Viterbi processor, and the possibility of employing polarization diversity at the transmitter end are also discussed. It is demonstrated that, as long as a sufficient number of Viterbi processor trellis states is employed, GVD and PMD entail no performance degradation with respect to the case of no channel distortions (the back-to-back case).

IEEE Photonics Technology Letters, 2006

Maximum likelihood sequence detection represents the most efficient technique in the electrical d... more Maximum likelihood sequence detection represents the most efficient technique in the electrical domain to combat fiber impairments such as polarization-mode dispersion and group-velocity dispersion. In order to successfully apply this technique, it is mandatory to estimate some key channel parameters needed by the Viterbi processor. We propose a simple and effective solution based on the least-mean-square algorithm to perform such an estimation.

Journal of Lightwave Technology, 2006

This paper thoroughly investigates the maximumlikelihood sequence detection (MLSD) receiver for t... more This paper thoroughly investigates the maximumlikelihood sequence detection (MLSD) receiver for the optical ON-OFF keying (OOK) channel in the presence of both polarization mode dispersion and group velocity dispersion (GVD). A reliable method is provided for computing the relevant performance for any possible value of the system parameters, with no constraint on the sampling rate. With one sample per bit time, a practically exact expression of the statistics of the received samples is found, and therefore the performance of a synchronous MLSD receiver is evaluated and compared with that of other electronic techniques such as combined feedforward and decision-feedback equalizers (FFE and DFE). It is also shown that the ultimate performance of electronic processing can be obtained by sampling the received signal at twice the bit rate. An approximate accurate closed-form expression of the receiver metrics is also identified, allowing for the implementation of a practically optimal MLSD receiver.

Journal of Lightwave Technology, 2011

One of the most severe impairments that affect coherent optical systems employing high-order modu... more One of the most severe impairments that affect coherent optical systems employing high-order modulation formats is phase noise due to transmit and receive lasers. This is especially detrimental in uncompensated links, where an ideal compensator for channel distortions and laser phase noise should first eliminate receive phase noise, then equalize channel distortions, and only later compensate for transmit phase noise. Unfortunately, the simultaneous presence of transmit and receive phase noise makes very difficult to discriminate between them, even in the presence of a pilot tone. Moreover, the picture is different for optical systems using single-carrier or orthogonal frequency division multiplexing, where transmit and receive phase noise components may have a different impact. All these aspects are analyzed and discussed in this paper. A novel digital coherence enhancement (DCE) technique, able to significantly reduce the phase noise of transmit or receive lasers by using an interferometric device plus a very simple electronic processing, is also described. The performance of this technique and the statistical properties of the residual phase noise are analytically derived and verified by simulations, showing a high increase of the maximum bit-rate-distance product. The practical implementation of DCE is finally discussed and some alternative implementation schemes are presented.

Journal of Lightwave Technology, 2009

This paper investigates optical coherent systems based on polarization multiplexing and high-orde... more This paper investigates optical coherent systems based on polarization multiplexing and high-order modulations such as phase-shift keying (PSK) signals and quadrature amplitude modulations (QAM). It is shown that a simple linear receiver processing is sufficient to perfectly demultiplex the two transmitted streams and to perfectly compensate for group velocity dispersion (GVD) and polarization mode dispersion (PMD). In addition, in the presence of a strong phase noise of the lasers at the transmitter and receiver, a symbol-by-symbol detector with decision feedback is able to considerably improve the receiver robustness with a limited complexity increase. We will also discuss the channel estimation and the receiver adaptivity to time-varying channel conditions as well as the problem of the frequency acquisition and tracking. Finally, a new two-dimensional (polarization/time) differential encoding rule is proposed to overcome a polarization-ambiguity problem. In the numerical results, the receiver performance will be assessed versus the receiver complexity.

We consider a joint radar estimation and communication system using orthogonal time frequency spa... more We consider a joint radar estimation and communication system using orthogonal time frequency space (OTFS) modulation. The scenario is motivated by vehicular applications where a vehicle equipped with a mono-static radar wishes to communicate data to its target receiver, while estimating parameters of interest related to this receiver. In a point-to-point communication setting over multi-path time-frequency selective channels, we study the joint radar and communication system from two perspectives, i.e., the radar estimation at the transmitter as well as the symbol detection at the receiver. For the radar estimation part, we derive an efficient approximated Maximum Likelihood algorithm and the corresponding Cram\'er- Rao lower bound for range and velocity estimation. Numerical examples demonstrate that multi-carrier digital formats such as OTFS can achieve as accurate radar estimation as state-of-the-art radar waveforms such as frequency-modulated continuous wave (FMCW). For the...

Applied Sciences

Impulsive noise is the main limiting factor for transmission over channels affected by electromag... more Impulsive noise is the main limiting factor for transmission over channels affected by electromagnetic interference. We study the estimation of (correlated) Gaussian signals in an impulsive noise scenario. In this work, we analyze some of the existing, as well as some novel estimation algorithms. Their performance is compared, for the first time, for different channel conditions, including the Markov–Middleton scenario, where the impulsive noise switches between different noise states. Following a modern approach in digital communications, the receiver design is based on a factor graph model and implements a message passing algorithm. The correlation among signal samples, as well as among noise states brings about a loopy factor graph, where an iterative message passing scheme should be employed. As is well known, approximate variational inference techniques are necessary in these cases. We propose and analyze different algorithms and provide a complete performance comparison among ...

Journal of Lightwave Technology, 2015

IFIP International Federation for Information Processing, 2005