http://hdl.handle.net/2117/1257 2013-05-20T03:03:12Z http://hdl.handle.net/2117/18932 Title: Day-ahead bidding strategies for demand-side expected cost minimization Authors: Atzeni, Italo; García Ordoñez, Luis; Scutari, Gesualdo; Palomar, D.P.; Rodríguez Fonollosa, Javier Abstract: Day-ahead DSM techniques in the smart grid allow the supply-side to know in advance an estimation of the amount of energy to be provided to the demand-side during the upcoming day. However, a pure day-ahead optimization process cannot accommodate potential real-time deviations from the expected energy consumption by the demand-side users, neither the randomness of their renewable sources. This paper proposes a day-ahead bidding system based on a pricing model that combines: i) a price per unit of energy depending on the day-ahead bid energy needs of the demand-side users, and ii) a penalty system that limits the real-time fluctuations around the bid energy loads. In this day-ahead bidding process, demand-side users, possibly having energy production and storage capabilities, are interested in minimizing their expected monetary expense. The resulting optimization problem is formulated as a noncooperative game and is solved by means of suitable distributed algorithms. Finally, the proposed procedure is tested in a realistic setup. 2013-04-22T17:41:14Z http://hdl.handle.net/2117/18566 Title: MCS and sub-band selection for downlink interference coordination in LTE-A Femtocells Authors: Muñoz Medina, Olga; Agustín de Dios, Adrián; Vidal Manzano, José Abstract: This paper proposes a decentralized algorithm for interference coordination in LTE-A networks, based on the exchange of information (pricing) at control plane level. In our approach, every user equipment (UE) report the maximum modulation and coding scheme (MCS) that can be used within several sets (sub-bands) of available resource blocks, along with a parameter (cost) that measures the MCS degradation due to the transmission from an interfering neighbor. Through the exchange of pricing messages, the higher costs are distributed to the dominant interferers; and the selection of the MCS and operational sub-band is based on the current link conditions along with the received pricing messages. We evaluate the algorithm in a cellular area covered by a macro base station (MBS) and multiple active femtocells. We also measure the degradation due to the quantization of the exchanged cost values. The results demonstrate significantly enhanced performance as compared to the non-coordinated case. 2013-04-03T10:56:22Z http://hdl.handle.net/2117/18421 Title: Adaptive sampling for fast sparsity pattern recovery Authors: Ramírez Javega, Francisco; Matas Navarro, David; Lamarca Orozco, M. Meritxell Abstract: In this paper we propose a low complexity adaptive algorithm for lossless compressive sampling and reconstruction of sparse signals. Consider a sparse non-negative real signal x containing only 𝑘 << 𝑛 non-zero values. The sampling process obtains 𝑚 measurements by a linear projection y = Ax and, in order to minimize the complexity, we quantize them to binary values. We also define the measurement matrix A to be binary and sparse, enabling the use of a simple message passing algorithm over a graph. We show how to adaptively construct this matrix in a multi-stage process that sequentially reduces the search space until the sparsity pattern is perfectly recovered. As verified by simulation results, the process requires 𝑂(𝑛) operations and 𝑂(𝑘 log(𝑛/𝑘)) samples 2013-03-19T17:03:52Z http://hdl.handle.net/2117/18420 Title: Binary graphs and message passing strategies for compressed sensing in the noiseless setting Authors: Ramírez Javega, Francisco; Lamarca Orozco, M. Meritxell; Villares Piera, Nemesio J. Abstract: We propose a scheme for Compressed Sensing in the noiseless setting that reconstructs the original signal operating on a binary graph where the samples are obtained sequentially. The proposed scheme has an affordable computational complexity and a large performance enhancement with respect to similar schemes in the literature, thanks to the proposed measurement matrix structure and enhanced decoding based on a message passing algorithm. 2013-03-19T16:59:00Z http://hdl.handle.net/2117/18373 Title: Optimal pilot design and power control in correlated MISO links Authors: Pastore, Adriano; Rodríguez Fonollosa, Javier Abstract: We study the maximization of an achievable ergodic rate expression of a multiple-input single-output (MISO) channel where both ends are cognizant of the same erroneous estimate of the current fading state, yet they have complete knowledge of channel statistics. A training procedure estimates each channel state by means of dedicated pilot symbols whose sum energy is fixed, while for data transmission a fixed average energy per channel access (i.e., average power) is available. The optimization consists, on one hand, in finding the optimal beamforming strategy and temporal power control policy, and on the other hand, in optimally constructing the pilot sequence according to the channel's correlation structure. 2013-03-18T15:20:32Z http://hdl.handle.net/2117/18258 Title: Improved capacity lower bounds for fading channels with imperfect CSI using rate splitting Authors: Pastore, Adriano; Koch, Tobias; Rodríguez Fonollosa, Javier Abstract: As shown by Medard (“The effect upon channel capacity in wireless communications of perfect and imperfect knowledge of the channel,” IEEE Trans. Inform. Theory, May 2000), the capacity of fading channels with imperfect channel-state information (CSI) can be lower-bounded by assuming a Gaussian channel input X, and by upper-bounding the conditional entropy h(XY, Ĥ), conditioned on the channel output Y and the CSI Ĥ, by the entropy of a Gaussian random variable with variance equal to the linear minimum mean-square error in estimating X from (Y, Ĥ). We demonstrate that, by using a rate-splitting approach, this lower bound can be sharpened: we show that by expressing the Gaussian input X as as the sum of two independent Gaussian variables X(1) and X(2), and by applying Medard's lower bound first to analyze the mutual information between X(1) and Y conditioned on Ĥ while treating X(2) as noise, and by applying the lower bound then to analyze the mutual information between X(2) and Y conditioned on (X(1), Ĥ), we obtain a lower bound on the capacity that is larger than Medard's lower bound. 2013-03-13T12:58:42Z http://hdl.handle.net/2117/18157 Title: Asymptotic error exponents in energy-detector and estimator-correlator signal detection Authors: Font Segura, Josep; Vázquez Grau, Gregorio; Riba Sagarra, Jaume Abstract: The performance in signal detection is evaluated by the error (false-alarm and missed-detection) probabilities. However, calculating these probabilities is a difficult task in practice. This paper studies the asymptotic behavior of the energy-detector and the estimator-correlator by means of the Stein's lemma. The Stein's lemma is an information-theory result that provides the best achievable error exponent in the error probabilities when the number of observations goes to infinity. The derived closed-form expressions explain how detection performance is driven by the detector parameters and the second-order statistics of the problem. More specifically, it is shown that the error exponents depend on the signal-to-noise ratio (SNR) and the observation size. The prime focus is to establish a link between the required observation size for a fixed error probability as a function of the SNR. Numerical results show the tightness of the lemma. 2013-03-08T19:32:42Z http://hdl.handle.net/2117/16314 Title: Decentralized weighted sum rate maximization in MIMO-OFDMA femtocell networks Authors: Agustín de Dios, Adrián; Vidal Manzano, José; Muñoz Medina, Olga; Rodríguez Fonollosa, Javier Abstract: We propose a decentralized strategy for downlink interference management in overlaid MIMO femtocell-macrocell deployments operating in the same band under OFDMA access. The resource allocation, consisting of MIMO precoders at the macro base station (MBS) and femto access points (FAPs) and possibly the resource block (RB) assignment, is designed to maximize the Weighted Sum Rate (WSR) of the system. Being the overall problem non-convex, we propose to solve it in a decentralized way where each transmitter designs its resource allocation using interference prices exchanged with other transmitters (FAPs and MBS) by exploiting the wired backhaul connection. The problem includes a rate restriction per FAP that accounts for the limited bitrate provided by the Internet Service Provider (ISP) wired backhaul. Two efficient algorithms are provided for: 1) optimizing MIMO precoders and 2) optimizing both MIMO precoders and RB assignment. Numerical results compare decentralized strategies based on pricing exchange and on pure competition in dense FAP deployments. 2012-07-23T10:07:30Z http://hdl.handle.net/2117/16313 Title: Improved interference alignment precoding for the MIMO X channel Authors: Agustín de Dios, Adrián; Vidal Manzano, José Abstract: We derive a linear transmit precoding scheme based on interference alignment at the transmitters and zero-forcing at the receivers, for the MIMO X channel based on the Generalized Singular Value Decomposition (GSVD) that is able to attain the outer bound on the degrees of freedom (DoF) region for any antenna configuration, except when all terminals have one antenna. Additionally, the proposed scheme is able to enhance the transmission rate in terms of high SNR offset. 2012-07-23T08:52:34Z http://hdl.handle.net/2117/15633 Title: Network MIMO for downlink in-band relay transmissions with relaying phases of fixed duration Authors: Agustín de Dios, Adrián; Vidal Manzano, José; Lagen, Sandra; Valera, Eduard Abstract: A half-duplex relay station (RS)-based cellular system deployment is considered, where multiple base stations (BS) cooperate in the BS-RS in-band transmission for the downlink. The duration of the relay-receive and the relay-transmit phases are fixed beforehand, so that the interference induced by other cells is stationary during a transmission interval. With the optimization of the precoders and powers allocated to the wireless backhaul (relay-receive phase)and to the RS-MS access (relay-transmit phase), it is possible to exploit the benefits of network-MIMO (N-MIMO) along with combating the pathloss and shadowing effects thanks to the RSs. Consequently, an appealing significant enhanced spectral efficiency, power efficiency and coverage homogeneity are obtained. Results are benchmarked to the case where the relay phases are optimized. 2012-03-21T11:50:07Z http://hdl.handle.net/2117/15370 Title: Consensus in random WSNs with correlated symmetric links Authors: Silva Pereira, Silvana; Pagès Zamora, Alba Maria Abstract: In this paper we study the convergence of consensus algorithms in wireless sensor networks with random topologies and instantaneous symmetric links which exist with different probabilities independently in time but correlated in space. Aiming at minimizing the convergence time of the algorithm, we adopt an optimization criterion based on the spectral radius of a positive semidefinite matrix for which we derive a closed-form expression, and propose a general formulation for the spatial correlation among the links that allows us to compute the optimum parameters ensuring almost sure convergence. We show that our general formulation can be particularized for existing protocols found in literature, and derive additionally closed-form expressions for the optimal parameters in two particular cases of equal probability of connection for all the links. 2012-02-26T11:51:05Z http://hdl.handle.net/2117/15369 Title: When gossip meets consensus : convergence in correlated random WSNs Authors: Silva Pereira, Silvana; Pagès Zamora, Alba Maria 2012-02-26T11:38:20Z http://hdl.handle.net/2117/15118 Title: Fundamental diversity, multiplexing, and array gain tradeoff under different MIMO channel models Authors: García Ordoñez, Luis; Pérez Palomar, Daniel; Rodríguez Fonollosa, Javier Abstract: Following the seminal work of Zheng and Tse on the diversity and multiplexing tradeoff (DMT) of MIMO channels, in this paper we introduce the array gain to investigate the fundamental relation between transmission rate and reliability in MIMO 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 can be directly translated into a parameterized characterization of its associated outage probability performance. In this paper we derive the fundamental DMA tradeoff achievable by any scheme in uncorrelated Rayleigh, semicorrelated Rayleigh, and uncorrelated Rician block-fading MIMO channels. We use these results to analyze the effect of important channel parameters in the outage performance at different points of the DMT curve. 2012-02-14T11:08:22Z http://hdl.handle.net/2117/15117 Title: DMA tradeoff for the MIMO static half-duplex relay Authors: García Ordoñez, Luis; Pérez Palomar, Daniel; Rodríguez Fonollosa, Javier Abstract: The diversity and multiplexing tradeoff (DMT) has been extensively applied in the literature to compare the high-SNR outage performance of relaying techniques and to propose new design guidelines. The problem with this approach is that the DMT provides only a coarse measure of performance and, hence, it is more convenient to adopt the diversity, multiplexing, and array gain (DMA) framework, in which the error probability is characterized by two parameters: the diversity gain (associated with the SNR exponent) and the array gain (related to the SNR offset). In this paper, we derive the DMA tradeoff associated with the cut-set bound outage probability of the static half-duplex MIMO relay under uncorrelated/semicorrelated Rayleigh fading and uncorrelated Rician fading. This provides an upper bound to the DMA tradeoff achievable by any relaying scheme. 2012-02-14T11:00:06Z http://hdl.handle.net/2117/15099 Title: Multi-frequency GLRT spectrum sensing for wideband cognitive radio Authors: Font Segura, Josep; Vázquez Grau, Gregorio; Riba Sagarra, Jaume Abstract: The problem of spectrum sensing in multi-frequency cognitive radio systems is addressed. We show that as the sensed bandwidth increases, the primary user detection is governed by a low signal-to-noise ratio (low-SNR) regime. By means of low-SNR approximations, we show that the optimal generalized likelihood ratio test (GLRT) only depends on the second order statistics of the observations and on a shaping kernel that highlights the relevant parameters required for detection. Furthermore, the ML estimates of the unknown model parameters are derived for multi-frequency systems, which allow closed-form expressions for the GLRT statistic. The detection performance and the kernel interpretation are supported with simulation results. 2012-02-13T13:12:13Z