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Search Results: 1 - 10 of 6063 matches for " Stefano Tomasin "
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Efficient Bidirectional DFE for Doubly Selective Wireless Channels
Tomasin Stefano
EURASIP Journal on Advances in Signal Processing , 2006,
Abstract: The bidirectional decision feedback equalizer (DFE) performs two equalizations, one on the received signal and one on its time-reversed version. In this paper, we apply the bidirectional DFE to wireless transmissions on rapidly time-varying dispersive channels and we propose an efficient implementation obtained by implementing the feedforward filter in the frequency domain. The feedback filter is adapted to the channel variations within one block and we propose a simplified design of the feedback filter coefficients based on a polynomial model of channel variations. Simulations performed on time-varying channels show that the proposed structure significantly outperforms existing architectures.
Secret Message Transmission by HARQ with Multiple Encoding
Stefano Tomasin,Nicola Laurenti
Computer Science , 2014,
Abstract: Secure transmission between two agents, Alice and Bob, over block fading channels can be achieved similarly to conventional hybrid automatic repeat request (HARQ) by letting Alice transmit multiple blocks, each containing an encoded version of the secret message, until Bob informs Alice about successful decoding by a public error-free return channel. In existing literature each block is a differently punctured version of a single codeword generated with a Wyner code that uses a common randomness for all blocks. In this paper instead we propose a more general approach where multiple codewords are generated from independent randomnesses. The class of channels for which decodability and secrecy is ensured is characterized, with derivations for the existence of secret codes. We show in particular that the classes are not a trivial subset (or superset) of those of existing schemes, thus highlighting the novelty of the proposed solution. The result is further confirmed by deriving the average achievable secrecy throughput, thus taking into account both decoding and secrecy outage.
A Comparison of Scheduling Strategies for MIMO Broadcast Channel with Limited Feedback on OFDM Systems
Ermanna Conte,Stefano Tomasin,Nevio Benvenuto
EURASIP Journal on Wireless Communications and Networking , 2010, DOI: 10.1155/2010/968703
Abstract: We consider a multiuser downlink transmission from a base station with multiple antennas (MIMO) to mobile terminals (users) with a single antenna, using orthogonal frequency division multiplexing (OFDM). Channel conditions are reported by a feedback from users with limited rate, and the base station schedules transmissions and beamforms signals to users. We show that an important set of schedulers using a general utility function can be reduced to a scheduler maximizing the weighted sum rate of the system. For this case we then focus on scheduling methods with many users and OFDM subcarriers. Various scheduling strategies are compared in terms of achieved throughput and computational complexity and a good tradeoff is identified in greedy and semiorthogonal user selection algorithms. In the greedy selection algorithm, users are selected one by one as long as the throughput increases, while in the semiorthogonal approach users are selected based on the channel correlation. An extension of these approaches from a flat-fading channel to OFDM is considered and simplifications that may be useful for a large number of subcarriers are presented. Results are reported for a typical cellular transmission of the long-term evolution (LTE) of 3GPP.
A Comparison of Scheduling Strategies for MIMO Broadcast Channel with Limited Feedback on OFDM Systems
Conte Ermanna,Tomasin Stefano,Benvenuto Nevio
EURASIP Journal on Wireless Communications and Networking , 2010,
Abstract: We consider a multiuser downlink transmission from a base station with multiple antennas (MIMO) to mobile terminals (users) with a single antenna, using orthogonal frequency division multiplexing (OFDM). Channel conditions are reported by a feedback from users with limited rate, and the base station schedules transmissions and beamforms signals to users. We show that an important set of schedulers using a general utility function can be reduced to a scheduler maximizing the weighted sum rate of the system. For this case we then focus on scheduling methods with many users and OFDM subcarriers. Various scheduling strategies are compared in terms of achieved throughput and computational complexity and a good tradeoff is identified in greedy and semiorthogonal user selection algorithms. In the greedy selection algorithm, users are selected one by one as long as the throughput increases, while in the semiorthogonal approach users are selected based on the channel correlation. An extension of these approaches from a flat-fading channel to OFDM is considered and simplifications that may be useful for a large number of subcarriers are presented. Results are reported for a typical cellular transmission of the long-term evolution (LTE) of 3GPP.
Achievable Secrecy Rates over MIMOME Gaussian Channels with GMM Signals in Low-Noise Regime
Francesco Renna,Nicola Laurenti,Stefano Tomasin
Mathematics , 2014,
Abstract: We consider a wiretap multiple-input multiple-output multiple-eavesdropper (MIMOME) channel, where agent Alice aims at transmitting a secret message to agent Bob, while leaking no information on it to an eavesdropper agent Eve. We assume that Alice has more antennas than both Bob and Eve, and that she has only statistical knowledge of the channel towards Eve. We focus on the low-noise regime, and assess the secrecy rates that are achievable when the secret message determines the distribution of a multivariate Gaussian mixture model (GMM) from which a realization is generated and transmitted over the channel. In particular, we show that if Eve has fewer antennas than Bob, secret transmission is always possible at low-noise. Moreover, we show that in the low-noise limit the secrecy capacity of our scheme coincides with its unconstrained capacity, by providing a class of covariance matrices that allow to attain such limit without the need of wiretap coding.
A Multi-Service Oriented Multiple-Access Scheme For Next-Generation Mobile Networks
Nassar Ksairi,Stefano Tomasin,Mérouane Debbah
Mathematics , 2015,
Abstract: One of the key requirements for future-generation cellular networks is their ability to handle densely connected devices with different quality of service (QoS) requirements. In this article, we consider an integrated network for handheld and machine-to-machine (M2M) devices, which yields easier deployment, economies of scale, reduced latency for handheld-M2M communications and better service integration. The proposed solution, denoted multi-service oriented multiple access (MOMA), is based on a) hierarchical spreading of the data signal and b) a mix of multiuser and single user detection scheme at the receiver. The spreading of MOMA is able to provide various interference pattern, while on the other hand the flexible receiver structure allows to focus the receiver complexity where effectively needed. Practical implementations of the MOMA principle are next provided for orthogonal frequency division multiplexing (OFDM) transmission schemes along with a discussion of the associated receiver structure. Finally, it is shown that MOMA is fully compatible with the case where the base station is equipped with a large number of antennas. Indeed, in such a massive-multiple-input-multiple-output (MIMO) scenario, users' channels undergo the so-called channel hardening effect which allows for a simpler receiver structure.
Parallel BCC with One Common and Two Confidential Messages and Imperfect CSIT
Ahmed Benfarah,Stefano Tomasin,Nicola Laurenti
Mathematics , 2014,
Abstract: We consider a broadcast communication system over parallel sub-channels where the transmitter sends three messages: a common message to two users, and two confidential messages to each user which need to be kept secret from the other user. We assume partial channel state information at the transmitter (CSIT), stemming from noisy channel estimation. The first contribution of this paper is the characterization of the secrecy capacity region boundary as the solution of weighted sum-rate problems, with suitable weights. Partial CSIT is addressed by adding a margin to the estimated channel gains. The second paper contribution is the solution of this problem in an almost closed-form, where only two single real parameters must be optimized, e.g., through dichotomic searches. On the one hand, the considered problem generalizes existing literature where only two out of the three messages are transmitted. On the other hand, the solution finds also practical applications into the resource allocation of orthogonal frequency division multiplexing (OFDM) systems with both secrecy and fairness constraints.
Distributed Power Loss Minimization in Residential Micro Grids: a Communications Perspective
Riccardo Bonetto,Stefano Tomasin,Michele Rossi
Computer Science , 2013,
Abstract: The constantly increasing number of power generation devices based on renewables is calling for a transition from the centralized control of electrical distribution grids to a distributed control scenario. In this context, distributed generators (DGs) are exploited to achieve other objectives beyond supporting loads, such as the minimization of the power losses along the distribution lines. The aim of this work is that of designing a full-fledged system that extends existing state of the art algorithms for the distributed minimization of power losses. We take into account practical aspects such as the design of a communication and coordination protocol that is resilient to link failures and manages channel access, message delivery and DG coordination. Thus, we analyze the performance of the resulting optimization and communication scheme in terms of power loss reduction, reduction of aggregate power demand, convergence rate and resilience to communication link failures. After that, we discuss the results of a thorough simulation campaign, obtained using topologies generated through a statistical approach that has been validated in previous research, by also assessing the performance deviation with respect to localized schemes, where the DGs are operated independently. Our results reveal that the convergence and stability performance of the selected algorithms vary greatly. However, configurations exist for which convergence is possible within five to ten communication steps and, when just 30% of the nodes are DGs, the aggregate power demand is roughly halved. Also, some of the considered approaches are quite robust against link failures as they still provide gains with respect to the localized solutions for failure rates as high as 50%.
LLR Compression for BICM Systems Using Large Constellations
Stefano Rosati,Stefano Tomasin,Matteo Butussi,Bixio Rimoldi
Mathematics , 2012,
Abstract: Digital video broadcasting (DVB-C2) and other modern communication standards increase diversity by means of a symbol-level interleaver that spans over several codewords. De-interleaving at the receiver requires a large memory, which has a significant impact on the implementation cost. In this paper, we propose a technique that reduces the de-interleaver memory size. By quantizing log-likelihood ratios with bit-specific quantizers and compressing the quantized output, we can significantly reduce the memory size with a negligible increase in computational complexity. Both the quantizer and compressor are designed via a GMI-based maximization procedure. For a typical DVB-C2 scenario, numerical results show that the proposed solution enables a memory saving up to 30%.
On the Achievable Error Region of Physical Layer Authentication Techniques over Rayleigh Fading Channels
Augusto Ferrante,Nicola Laurenti,Chiara Masiero,Michele Pavon,Stefano Tomasin
Computer Science , 2013,
Abstract: For a physical layer message authentication procedure based on the comparison of channel estimates obtained from the received messages, we focus on an outer bound on the type I/II error probability region. Channel estimates are modelled as multivariate Gaussian vectors, and we assume that the attacker has only some side information on the channel estimate, which he does not know directly. We derive the attacking strategy that provides the tightest bound on the error region, given the statistics of the side information. This turns out to be a zero mean, circularly symmetric Gaussian density whose correlation matrices may be obtained by solving a constrained optimization problem. We propose an iterative algorithm for its solution: Starting from the closed form solution of a relaxed problem, we obtain, by projection, an initial feasible solution; then, by an iterative procedure, we look for the fixed point solution of the problem. Numerical results show that for cases of interest the iterative approach converges, and perturbation analysis shows that the found solution is a local minimum.
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