| 1. |
- Colavolpe, Giulio, et al.
(author)
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Multiuser Detection in Multibeam Satellite Systems: Theoretical Analysis and Practical Schemes
- 2016
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In: IEEE Transactions on Communications. - 0090-6778 .- 1558-0857. ; 65:2, s. 945-955
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Journal article (peer-reviewed)abstract
- We consider the rates achievable by a user in a multibeam satellite system for unicast applications, and propose alternatives to the conventional single-user symbol-by-symbol detection applied at user terminals. Single-user detection is known to suffer from strong degradation when the terminal is located near the edge of the coverage area of a beam, and when aggressive frequency reuse is adopted. For this reason, we consider multiuser detection, and take into account the strongest interfering signal. We also analyze two additional transmissionstrategies requiring modifications at medium access control layer. We describe an information-theoretic framework to compare the different strategies by computing the information rate of the user in the reference beam. Furthermore, we analyze the performance of coded schemes that could approach the information-theoreticlimits.We show that classical codes from the DVB-S2(X) standard are not suitable when multiuser detection is adopted, and we propose two ways to improve the performance, based on the redesign of the code and of the bit mapping.
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| 2. |
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| 3. |
- Graell i Amat, Alexandre, 1976, et al.
(author)
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Proving Threshold Saturation for Nonbinary SC-LDPC Codes on the Binary Erasure Channel
- 2014
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In: 31st General Assembly and Scientific Symposium of the International Union of Radio Science, URSI GASS 2014; Beijing; China; 16 August 2014 through 23 August 2014. - 9781467352253 ; , s. Art. no. 6929239-
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Conference paper (peer-reviewed)abstract
- We analyze nonbinary spatially-coupled low-density parity-check (SC-LDPC) codes built on the general linear group for transmission over the binary erasure channel. We prove threshold saturation of the belief propagation decoding to the potential threshold, by generalizing the proof technique based on potential functions recently introduced by Yedla et al.. The existence of the potential function is also discussed for a vector sparse system in the general case, and some existence conditions are developed. We finally give density evolution and simulation results for several nonbinary SC-LDPC code ensembles.
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| 4. |
- Messai, Malek, et al.
(author)
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Binary CPMs With Improved Spectral Efficiency
- 2016
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In: IEEE Communications Letters. - 1558-2558 .- 1089-7798. ; 20:1, s. 85-88
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Journal article (peer-reviewed)abstract
- We design new continuous phase modulation (CPM) formats, which are based on the combination of a proper precoder with binary input and a ternary CPM. The proposed precoder constrains the signal phase evolution in order to increase the minimum Euclidean distance, and to limit the bandwidth expansion due to the use of a ternary CPM. The resulting schemes are highly spectrally efficient and outperform classical binary and quaternary formats in terms of coded and uncoded performance.
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| 5. |
- Modenini, Andrea, et al.
(author)
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On the Use of Multiple Satellites to Improve the Spectral Efficiency of Broadcast Transmissions
- 2015
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In: IEEE Transactions on Broadcasting. - 0018-9316. ; 61:4, s. 590-602
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Journal article (peer-reviewed)abstract
- We consider the use of multiple co-located satellites to improve the spectral efficiency of broadcast transmissions. In particular, we assume that two satellites transmit on overlapping geographical coverage areas, with overlapping frequencies. We first describe the theoretical framework based on network information theory and, in particular, on the theory for multiple access channels. The application to different scenarios will be then considered, including the bandlimited additive white Gaussian noise channel with average power constraint and different models for the nonlinear satellite channel. The comparison with the adoption of frequency division multiplexing and with the Alamouti space-time block coding is also provided. The main conclusion is that a strategy based on overlapped signals is the most convenient in the case of no power unbalance, although it requires the adoption of a multiuser detection strategy at the receiver.
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| 6. |
- Piemontese, Amina, et al.
(author)
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A New Analytical Model of Phase Noise in Communication Systems
- 2022
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In: IEEE Wireless Communications and Networking Conference, WCNC. - 1525-3511. ; 2022-April, s. 926-931
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Conference paper (peer-reviewed)abstract
- We consider the phase noise affecting communication systems, where local oscillators are employed to obtain a reference signal for frequency and phase synchronizations. We try to fill the gap between measurements and analytical models, in case of free-running and phase-locked oscillators. In particular, we propose a closed form expression for the power spectral density of the phase noise described by few parameters that are explicitly linked to the oscillator measurements. We also propose an analytical model for the oscillator power spectral density.
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| 7. |
- Piemontese, Amina, et al.
(author)
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A New Discrete-Time Model for Channels Impaired by Phase Noise
- 2021
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In: 2021 IEEE Global Communications Conference, GLOBECOM 2021 - Proceedings.
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Conference paper (peer-reviewed)abstract
- We propose a novel discrete-time model for the phase noise signal, in case of free-running and phase-locked oscillators. In particular, we show how the PN can be described by an autoregressive process. The strength of the proposed model is that it can be easily expressed in terms of measurement parameters of practical oscillators. We then analyse the most common discrete-time phase noise channel model with reference to the measurement parameters and to the system bandwidth. The derived analytical models for the discrete-time phase noise signal can be used for the design of estimation/detection algorithms, for performance evaluation, or simply for fast simulations.
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| 8. |
- Piemontese, Amina, 1980, et al.
(author)
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Discrete-Time Models and Performance of Phase Noise Channels
- 2024
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In: IEEE Open Journal of the Communications Society. - 2644-125X. ; 5, s. 2211-2225
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Journal article (peer-reviewed)abstract
- This paper deals with the phase noise affecting communication systems, where local oscillators are employed to obtain reference signals for carrier and timing synchronizations. The most common discrete-time phase noise channel model is analyzed, with the aim to fill the gap between measurements and analytical models. In particular, the power loss and the intersymbol interference due to the presence of phase noise is evaluated with reference to the measurements parameters and to the system bandwidth. Moreover, the impact on the communication systems’ performance of the phase noise originating from the oscillator non-idealities is considered, in case of free-running and phase-locked oscillators. The proposed analysis allows to extrapolate useful information about the performance of practical systems by investigating the power spectral density of the oscillator phase noise. An expression for the variance of the residual phase error after tracking, which depends on the main parameters of practical oscillators, is derived, and used to study the dependence of the performance on the symbol rate.
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| 9. |
- Piemontese, Amina, et al.
(author)
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Frequency Packing and Multiuser Detection for CPMs: How to Improve the Spectral Efficiency of DVB-RCS2 Systems
- 2013
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In: IEEE Wireless Communications Letters. - 2162-2345 .- 2162-2337. ; 2:1, s. 74-77
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Journal article (peer-reviewed)abstract
- We consider a frequency division multiplexed systemwhere each user adopts a continuous phase modulation (CPM)and multiuser detection is employed at the receiver side. Thespectral efficiency (SE) is used as a performance measure tocompare, from an information-theoretic point of view, differentmodulation formats. More precisely, we consider the newCPM formats recently included in the DVB-RCS2 standard.We describe a framework for computing the information rate(IR) and the SE of such systems, and use it for optimizing thechannel spacing between adjacent users and the CPM phaseresponse. Our analysis reveals that modulation formats adoptedin the DVB-RCS2 standard are suboptimal in terms of SE, whileif we allow multiuser detection excellent performance can beachieved by using simple binary formats and highly frequencypacked signals. Furthermore, we consider practical schemes,where CPMs are serially concatenated with an outer code, and alow-complexity multiuser receiver is employed, showing that thetheoretical limits predicted by the IR analysis can be approached.
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| 10. |
- Piemontese, Amina, 1980, et al.
(author)
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MDS-Coded Distributed Caching for Low Delay Wireless Content Delivery
- 2019
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In: IEEE Transactions on Communications. - 0090-6778 .- 1558-0857. ; 67:2, s. 1600-1612
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Journal article (peer-reviewed)abstract
- We investigate the use of maximum distance separable (MDS) codes to cache popular content to reduce the download delay of wireless content delivery. In particular, we consider a cellular system, where popular files are cached in a distributed fashion in a limited number of the mobile devices using an MDS code and can be downloaded from them using device-to-device (D2D) communication. The base station controls the D2D communication and assists the requests that cannot be fully satisfied by the distributed caching (DC) network by providing the missing data. We consider a network model, where the cell is divided into clusters, where D2D links can be activated. We derive an analytical expression for the delay incurred in downloading content from the wireless network assuming that devices roam in and out of clusters according to a Poisson random process. Our analysis allows to identify the parameters of the wireless network that mostly affect the performance and to compare different caching strategies in terms of delay. We show that DC using MDS codes can dramatically reduce the download delay with respect to the scenario where content is always downloaded from the base station and to the case of uncoded DC.
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