http://hdl.handle.net/2117/1256 2013-05-22T00:21:25Z 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. 2012-12-20T14:31:52Z 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. 2012-10-03T17:49:18Z 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. 2012-03-22T19:25:00Z 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. 2012-01-02T17:50:21Z 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. 2011-11-23T18:22:38Z 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. 2011-05-05T08:18:12Z 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. 2011-03-14T09:44:17Z 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). 2011-02-28T11:11:35Z 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 http://hdl.handle.net/2117/8322 Title: Stochastic and balanced distributed energy-efficient clustering (SBDEEC) for heterogeneous wireless sensor networks Authors: Brahim, Elbhiri; Rachid, Saadane; Pagès Zamora, Alba Maria; Aboutajdine, Driss Abstract: Typically, a wireless sensor network contains an important number of inexpensive power constrained sensors which collect data from the environment and transmit them towards the base station in a cooperative way. Saving energy and therefore, extending the wireless sensor networks lifetime, imposes a great challenge. Many new protocols are specifically designed for these raisons where energy awareness is an essential consideration. The clustering techniques are largely used for these purposes.In this paper, we present and evaluate a Stochastic and Balanced Developed Distributed Energy-Efficient Clustering (SBDEEC) scheme for heterogeneous wireless sensor networks. This protocol is based on dividing the network into dynamic clusters. The cluster’s nodes communicate with an elected node called cluster head, and then the cluster heads communicate the information to the base station. SBDEEC introduces a balanced and dynamic method where the cluster head election probability is more efficient. Moreover, it uses a stochastic scheme detection to extend the network lifetime. Simulation results show that our protocol performs better than the Stable Election Protocol (SEP) and than the Distributed Energy-Efficient Clustering (DEEC) in terms of network lifetime. In the proposed protocol the first node death occurs over 90% times longer than the first node death in DEEC protocol and by about 130% than SEP. 2010-07-21T13:04:47Z http://hdl.handle.net/2117/8075 Title: Compress-and-forward cooperative MIMO relaying with full channel state information Authors: Simoens, Sebastien; Muñoz Medina, Olga; Vidal Manzano, José; Coso, Aitor del 2010-07-08T11:27:44Z http://hdl.handle.net/2117/1959 Title: Detection of PPM-UWB random signals Authors: López Salcedo, José Antonio; Vázquez Grau, Gregorio Abstract: This paper focuses on the symbol detection problem of random pulse-position modulation (PPM) ultrawideband (UWB) signals in the absence of interframe interference. Particular attention is devoted to severely time-varying channels where optimal detectors are proposed for both uncorrelated and correlated scattering scenarios. This is done by assuming the received waveforms to be unknown parameters. In UWB communication systems, the assumption of unknown random waveforms is consistent with the fact that the received waveform has very little resemblance with the original transmitted pulse. In order to circumvent this limitation, a conditional approach is presented herein by compressing the likelihood ratio test with the information regarding the second-order moments of the end-to-end channel response. Both full-rank and rank-one detectors are derived. For the reduced complexity rank-one detector, an iterative procedure is presented that maximizes the J-divergence between the hypotheses to be tested. Finally, simulation results are provided to compare the performance of the proposed detectors in different propagation environments. 2008-04-25T10:52:42Z http://hdl.handle.net/2117/1610 Title: Space-time front-ends for RAKE receivers in the FDD mode of UTRA Authors: Vidal Manzano, José; Cabrera Beán, Margarita Asuncion; Agustín de Dios, Adrián Abstract: A unified and general vision of different space-time processors is presented. Many popular receivers can be accomodated, like V-RAKE receivers, weighted V-RAKE, or spatial narrowband beamforming. By making appropriate assumptions on the space/time characteristic of the interference it is possible to enhance the performance of the receiver through spatial/temporal pre-processors. These receivers will be tested in the FDD mode of UTRA. 2008-02-18T09:01:20Z http://hdl.handle.net/2117/1609 Title: A non-extensive maximum entropy based regulations method for bad conditioned inverse problems Authors: Rebollo Neira, Laura; Fernández Rubio, Juan Antonio; Plastino, Angel Luís Abstract: A regularization method based on the non-extensive maximum entropy principle is devised. Special emphasis is given to the q=1/2 case. We show that, when the residual principle is considered as constraint, the q=1/2 generalized distribution of Tsallis yields a regularized solution for bad-conditioned problems. The so devised regularized distribution is endowed with a component which corresponds to the well known regularized solution of Tikhonov (1977). 2008-02-18T08:40:46Z http://hdl.handle.net/2117/1608 Title: Frames: a maximum entropy statistical estimate of the inverse problem Authors: Rebollo Neira, Laura; Fernández Rubio, Juan Antonio; Plastino, Angel Luís Abstract: A maximum entropy statistical treatment of an inverse problem concerning frame theory is presented. The problem arises from the fact that a frame is an overcomplete set of vectors that defines a mapping with no unique inverse. Although any vector in the concomitant space can be expressed as a linear combination of frame elements, the coefficients of the expansion are not unique. Frame theory guarantees the existence of a set of coefficients which is “optimal” in a minimum norm sense. We show here that these coefficients are also “optimal” from a maximum entropy viewpoint. 2008-02-15T13:17:24Z