DSpace Collection:
http://hdl.handle.net/2117/1256
2014-08-28T11:21:51ZA rate-splitting approach to fading channels with imperfect channel-state information
http://hdl.handle.net/2117/23656
Title: A rate-splitting approach to fading channels with imperfect channel-state information
Authors: Pastore, Adriano; Koch, Tobias; Rodríguez Fonollosa, Javier
Abstract: As shown by Médard, the capacity of fading channels with imperfect channel-state information can be lower-bounded by assuming a Gaussian channel input X with power P and by upper-bounding the conditional entropy h(X|Y,H) by the entropy of a Gaussian random variable with variance equal to the linear minimum mean-square error in estimating X from \(Y, H). We demonstrate that, using a rate-splitting approach, this lower bound can be sharpened: by expressing the Gaussian input X as the sum of two independent Gaussian variables X1 and X2 and by applying Médard's lower bound first to bound the mutual information between X1 and Y while treating X2 as noise, and by applying it a second time to the mutual information between X2 and Y while assuming X1 to be known, we obtain a capacity lower bound that is strictly larger than Médard's lower bound. We then generalize this approach to an arbitrary number L of layers, where X is expressed as the sum of L independent Gaussian random variables of respective variances Pl, l = 1, ¿ ,L summing up to P. Among all such rate-splitting bounds, we determine the supremum over power allocations Pl and total number of layers L. This supremum is achieved for L 8 and gives rise to an analytically expressible capacity lower bound. For Gaussian fading, this novel bound is shown to converge to the Gaussian-input mutual information as the signal-to-noise ratio (SNR) grows, provided that the variance of the channel estimation error H-H tends to zero as the SNR tends to infinity.2014-07-31T09:02:21ZNoncooperative day-ahead bidding strategies for demand-side expected cost minimization with real-time adjustments: a GNEP approach
http://hdl.handle.net/2117/23344
Title: Noncooperative day-ahead bidding strategies for demand-side expected cost minimization with real-time adjustments: a GNEP approach
Authors: Atzeni, Italo; García Ordoñez, Luis; Scutari, Gesualdo; Palomar, Daniel P.; Rodríguez Fonollosa, Javier
Abstract: The envisioned smart grid aims at improving the interaction between the supply-and the demand-side of the electricity network, creating unprecedented possibilities for optimizing the energy usage at different levels of the grid. In this paper, we propose a distributed demand-side management (DSM) method intended for smart grid users with load prediction capabilities, who possibly employ dispatchable energy generation and storage devices. These users participate in the day-ahead market and are interested in deriving the bidding, production, and storage strategies that jointly minimize their expected monetary expense. The resulting day-ahead grid optimization is formulated as a generalized Nash equilibrium problem (GNEP), which includes global constraints that couple the users' strategies. Building on the theory of variational inequalities, we study the main properties of the GNEP and devise a distributed, iterative algorithm converging to the variational solutions of the GNEP. Additionally, users can exploit the reduced uncertainty about their energy consumption and renewable generation at the time of dispatch. We thus present a complementary DSM procedure that allows them to perform some unilateral adjustments on their generation and storage strategies so as to reduce the impact of their real-time deviations with respect to the amount of energy negotiated in the day-ahead. Finally, numerical results in realistic scenarios are reported to corroborate the proposed DSM technique.2014-07-01T08:28:06ZFrequency-domain GLR detection of a second-order cyclostationary signal over fading channels
http://hdl.handle.net/2117/22790
Title: Frequency-domain GLR detection of a second-order cyclostationary signal over fading channels
Authors: Riba Sagarra, Jaume; Font Segura, Josep; Villares Piera, Nemesio J.; Vázquez Grau, Gregorio
Abstract: Cyclostationary processes exhibit a form of frequency diversity. Based on that, we show that a digital waveform with symbol period T can be asymptotically represented as a rank-1 frequency-domain vector process which exhibits uncorrelation at different frequencies inside the Nyquist spectral support of 1/T. By resorting to the fast Fourier transform (FFT), this formulation obviates the need of estimating a cumbersome covariance matrix to characterize the likelihood function. We then derive the generalized likelihood ratio test (GLRT) for the detection of a cyclostationary signal in unknown white noise without the need of a assuming a synchronized receiver. This provides a sound theoretical basis for the exploitation of the cyclostationary feature and highlights an explicit link with classical square timing recovery schemes, which appear implicitly in the core of the GLRT. Moreover, to avoid the well-known sensitivity of cyclostationary-based detection schemes to frequency-selective fading channels, a parametric channel model based on a lower bound on the coherence bandwidth is adopted and incorporated into the GLRT. By exploiting the rank-1 structure of small spectral covariance matrices, the obtained detector outperforms the classical spectral correlation magnitude detector.2014-04-30T12:40:12ZRadio context awareness and applications
http://hdl.handle.net/2117/21937
Title: Radio context awareness and applications
Authors: Reggiani, Luca; Fiorina, Jocelyn; Gezici, Sinan; Morosi, Simone; Nájar Martón, Montserrat
Abstract: The context refers to “any information that can be used to characterize the situation of an entity, where an entity can be a person, place, or physical object.” Radio context awareness is defined as the ability of detecting and estimating a system state or parameter, either globally or concerning one of its components, in a radio system for enhancing performance at the physical, network, or application layers. In this paper, we review the fundamentals of context awareness and the recent advances in the main radio techniques that increase the context awareness and smartness, posing challenges and renewed opportunities to added-value applications in the context of the next generation of wireless networks.2014-03-07T14:41:47ZA non-data-aided SNR estimation technique for multilevel modulations exploiting signal cyclostationarity
http://hdl.handle.net/2117/21450
Title: A non-data-aided SNR estimation technique for multilevel modulations exploiting signal cyclostationarity
Authors: Riba Sagarra, Jaume; Villares Piera, Nemesio J.; Vázquez Grau, Gregorio
Abstract: Signal-to-noise ratio (SNR) estimators of linear
modulation schemes usually operate at one sample per symbol at
the matched filter output. In this paper we propose a new method
for estimating the SNR in the complex additive white Gaussian
noise (AWGN) channel that operates directly on the oversampled
cyclostationary signal at the matched filter input. Exploiting
cyclostationarity proves to be advantageous due to the fact that a
signal-free Euclidean noise subspace can be identified such that
only second order moments of the received waveform need to be
computed. The proposed method is nondata-aided (NDA), as well
as constellation and phase independent, and only requires prior
timing synchronization to fully exploit the cyclostationarity property.
The estimator can also be applied to nonconstant modulus
constellations without requiring any tuning, which is a feature not
found in existing approaches. Implementation aspects and simpler
suboptimal solutions are also provided.2014-02-04T14:32:34ZSpectrum sensing using correlated receiving multiple antennas in cognitive radios
http://hdl.handle.net/2117/21049
Title: Spectrum sensing using correlated receiving multiple antennas in cognitive radios
Authors: Sedighi, Saeid; Taherpour, Abbas; Sala Álvarez, José
Abstract: Spectrum sensing is a key component for enabling the cognitive radio paradigm. In this paper, we propose a novel totally-blind spectrum sensing technique for cognitive radio device equipped with multiple antennas, namely the Space Frequency Cross Product Sensing (SFCPS) algorithm. Existing correlation-based spectrum sensing techniques rely on the assumption that the received signals are correlated and their performance becomes poor when the signal correlation is low. By appropriately combining the received signals from multiple antennas, the proposed method creates new signals that are fully correlated and on which a sensing method is developed. SFCPS performs better than existing correlation-based techniques and with a lower computational complexity for small number of observed samples.2013-12-18T15:39:20ZArray gain in the DMT framework for MIMO channels
http://hdl.handle.net/2117/17178
Title: Array gain in the DMT framework for MIMO channels
Authors: García Ordoñez, Luis; Palomar, D.P.; Rodríguez Fonollosa, Javier
Abstract: Following the seminal work by Zheng and Tse on
the diversity and multiplexing tradeoff (DMT) of multiple-input
multiple-output (MIMO) channels, in this paper, we introduce
the array gain to investigate the fundamental relation between
transmission rate and reliability inMIMO systems. The array gain
gives information on the power offset that results from exploiting
channel state information at the transmitter or as a consequence
of the channel model. Hence, the diversity, multiplexing, and
array gain (DMA) analysis is able to cope with the limitations
of the original DMT and provide an operational meaning in the
sense that the DMA gains of a particular system can be directly
translated into a parameterized characterization of its associated
outage probability performance. In this paper, we derive the
best DMA gains achievable by any scheme employing isotropic
signaling in uncorrelated Rayleigh, semicorrelated Rayleigh, and
uncorrelated Rician block-fading MIMO channels. We use these
results to analyze the effect of important channel parameters on
the outage performance at different points of the DMT curve.2012-12-20T14:31:52ZDownlink coordinated radio resource management in cellular networks with partial CSI
http://hdl.handle.net/2117/16625
Title: Downlink coordinated radio resource management in cellular networks with partial CSI
Authors: Calvo Page, Eduard; Muñoz Medina, Olga; Vidal Manzano, José; Agustín de Dios, Adrián
Abstract: We explore decentralized coordination of sectored
cellular networks to adapt the usage of downlink resources to
the instantaneous network conditions. The transmission frame
consists of an orthogonal bandwidth usage phase, where sectors
perform FDMA and power control over an agreed frequency
chunk, and a shared bandwidth usage phase where each sector
performs FDMA over the full available bandwidth without power
control (interference is not controlled in this phase by any means).
Decentralized network utility maximization with global optimality
guarantee is enabled by fixing this structure of the transmission
frame, which does not cause significant network-wide losses. Thus,
the ability to better balance the resources gained from coordination
generates some slack that can be used to either i) provide
higher-quality access, ii) increase the number of active users, or
iii) reduce deployment and maintenance costs by operating larger
cells.2012-10-03T17:49:18ZAsymptotically optimum energy profile for successive interference cancellation in DS-CDMA under a power unbalance constraint
http://hdl.handle.net/2117/15654
Title: Asymptotically optimum energy profile for successive interference cancellation in DS-CDMA under a power unbalance constraint
Authors: Sala Álvarez, José; Rey Micolau, Francesc; Villares Piera, Nemesio J.
Abstract: A new Ordinary Differential Equation (ODE) governing the SNIR evolution of a Successive Interference Canceller (SIC) for DS-CDMA is derived when the number of users tends to infinity and all users share the same channel encoder. Using Variational Calculus, this ODE is applied to obtaining the energy profile that maximizes the average spectral efficiency when a constraint on the power unbalance (maximum power to minimum power ratio) of received users is enforced. The conditions for extremality of the optimum energy profile are established in terms of the common encoder's Packet Error Rate (PER) function.2012-03-22T19:25:00ZMultiantenna spectrum sensing exploiting spectral a priori information
http://hdl.handle.net/2117/14394
Title: Multiantenna spectrum sensing exploiting spectral a priori information
Authors: Vázquez Vilar, Gonzalo; López Valcarce, Roberto; Sala Álvarez, José
Abstract: Dynamic Spectrum Access (DSA) is receiving considerable interest as a means to improve spectral usage in licensed bands. In order to avoid interference to licensed users, spectrum sensing has emerged as an enabling technology for DSA. The requirements for spectrum sensors are stringent, as licensed user detection must be performed reliably at low signal-to-noise ratios (SNR). Sensing performance can be improved by exploiting signal features not present in the background noise. These approaches result in tradeoffs among performance and robustness to departures from the signal model. We consider second-order signal features and develop detectors exploiting spatial (by using multiple antennas) as well as temporal signal correlation, taking advantage of the fact that the power spectrum of the primary signal at each antenna can be known up to a complex scalar representing the unknown propagation channel. A low-SNR Generalized Likelihood Ratio approach is adopted in order to overcome this uncertainty, resulting in different tests intimately related to familiar diversity combining techniques. The performance of the proposed detectors is analyzed and tested in different scenarios.2012-01-02T17:50:21ZAsymptotic and finite user PER analysis of successive interference cancellation in DS-CDMA
http://hdl.handle.net/2117/14040
Title: Asymptotic and finite user PER analysis of successive interference cancellation in DS-CDMA
Authors: Sala Álvarez, José; Villares Piera, Nemesio J.; Rey Micolau, Francesc
Abstract: An expression is derived for the average Packet Error Rate (PER) of a Successive Interference Canceller (SIC) for DS-CDMA when the number of users asymptotically tends to infinity. The asymptotic probability density function of the interference power is governed by a Fokker-Planck differential equation with drift and (asymptotically vanishing) diffusion depending on the PER function of the adopted forward error-correcting code (FEC). In addition to the asymptotic solution for the PER, a particle-based algorithm is also developed for computing efficiently the PER in the finite user case.2011-11-23T18:22:38ZOptimum power allocation and bit loading for BICM systems
http://hdl.handle.net/2117/12470
Title: Optimum power allocation and bit loading for BICM systems
Authors: Matas Navarro, David; Lamarca Orozco, M. Meritxell
Abstract: This paper introduces a joint bit loading and power allocation algorithm for systems combining bit-interleaved coded modulation (BICM) with multicarrier transmission. The proposed algorithm maximizes the mutual information, so it can be regarded as a generalization of mercury/waterfilling policy
that incorporates bit loading.
The followed approach relies on irregular modulation and power to cast the problem in the framework of convex optimization.
This allows to derive the optimum solution without resorting to greedy algorithms, embedding the bit loading in the definition of an equivalent constellation such that the complexity increase with respect to mercury/waterfilling is negligible. While irregular modulation plays a key role in algorithm definition, it is proved that only a few subcarriers employ it and it is shown that a practical low complexity algorithm can
be obtained with minimal losses that does not use irregular modulation.2011-05-05T08:18:12ZTechnoeconomic evaluation of cooperative relaying transmission techniques in OFDM cellular networks
http://hdl.handle.net/2117/11797
Title: Technoeconomic evaluation of cooperative relaying transmission techniques in OFDM cellular networks
Authors: Moral, Antolín; Vidal Manzano, José; Pérez, Jorge; Agustín de Dios, Adrián; Marina, Ninoslav; Host-Madsen, Anders
Abstract: We evaluate the costs in the deployment of a 4G relay-assisted network in the 2.6GHz band following a technoeconomic
methodology that departs fromcell dimensioning based on spectral efficiency and outage capacity requirements. Different decodeand-
forward relaying protocols are considered in the analysis, assuming a certain traffic load evolution over a period of ten years,
different geotypes, and a progressive deployment of base stations and relay stations. Results show significant benefits for operators
as well as reduction in the total radiated power.2011-03-14T09:44:17ZPulsar navigation
http://hdl.handle.net/2117/11565
Title: Pulsar navigation
Authors: Sala Álvarez, José; Urruela Planas, Andreu; Villares Piera, Nemesio J.; Romeu Robert, Jordi; Blanch Boris, Sebastián; Estalella Boadella, Robert; Paredes, J. M.
Abstract: This paper evaluates the fundamental performance
bounds, signal processing and technological complexity
associated with the synchronization to radio and X-ray
pulsars as well as its impact on the positioning accuracy
of an autonomous spacecraft navigation system. Performance
analysis of synchronization and location algorithms
builds on Maximum Likelihood (ML) estimation
which provides, asymptotically, unbiased minimum variance
estimates with mean square error strictly approaching
the Cramer-Rao Lower Bound (CRLB).2011-02-28T11:11:35ZMean square convergence of consensus algorithms in random WSNs
http://hdl.handle.net/2117/11008
Title: Mean square convergence of consensus algorithms in random WSNs
Authors: Silva Pereira, Silvana; Pagès Zamora, Alba Maria
Abstract: Distributed consensus algorithms for estimation of parameters or detection of events in wireless sensor networks have attracted considerable attention in recent years. A necessary condition to achieve a consensus on the average of the initial
values is that the topology of the underlying graph is balanced or symmetric at every time instant. However, communication
impairments can make the topology vary randomly in time, and instantaneous link symmetry between pairs of nodes is not
guaranteed unless an acknowledgment protocol or an equivalent approach is implemented. In this paper, we evaluate the convergence of the consensus algorithm in the mean square sense in wireless sensor networks with random asymmetric topologies. For the case of links with equal probability of connection, a closed form expression for the mean square error of the state along with
the dynamical range and the optimum value of the link weights that guarantee convergence are derived. For the case of links with
different probabilities of connection, an upper bound for the mean square error of the state is derived. This upper bound can be
computed for any time instant and can be employed to compute a link weight that reduces the convergence time of the algorithm.2011-01-13T11:39:07Z