http://hdl.handle.net/10230/16116 2013-05-24T01:16:38Z http://hdl.handle.net/10230/20555 Asymptotic capacity of static multiuser channels with an unknown number of users Biglieri, Ezio We examine a multiple-access communication system in which multiuser detection is performed without knowledge of the number of active interferers. Using a statistical-physics approach, we compute the single-user channel capacity and spectral efficiency in the large-system limit. Comunicació presentada al 11th International Symposium on Wireless Personal Multimedia Communications (WPMC '08), celebrat els dies 8, 9, 10 i 11 de setembre de 2008 a Lapland, Finlàndia, i organitzat pel Centre for Wireless Communications i el National Institute of Information and Communications Technology. 2008-01-01T00:00:00Z http://hdl.handle.net/10230/20510 Multiple target tracking using random sets Angelosante, Daniele; Biglieri, Ezio; Lops, Marco This paper presents several algorithms for joint estimation of the target number and state in a time-varying scenario. Building on the results presented in [1], which considers estimation of the target number only, we assume that not only the target number, but also their state evolution must be estimated. In this context, we extend to this new scenario the Rao-Blackwellization procedure of [1] to compute Bayes recursions, thus defining reduced-complexity solutions for the multi-target set estimator. A performance assessment is finally given both in terms of Circular Position Error Probability - aimed at evaluating the accuracy of the estimated track - and in terms of Cardinality Error Probability, aimed at evaluating the reliability of the target number estimates. Comunicació presentada en la 16th European Signal Processing Conference (EUSIPCO 2008), celebrada els dies 25, 26, 27, 28 i 29 d’agost de 2008 a Lausana (Suïssa), organitzada per la European Association for Signal Processing (EURASIP). 2008-01-01T00:00:00Z http://hdl.handle.net/10230/20509 Multiuser detection with an unknown number of active users: receiver design Angelosante, Daniele; Biglieri, Ezio; Lops, Marco In multiuser detection, the set of users active at any time may be unknown to the receiver. In these conditions, optimum reception consists of detecting simultaneously the set of active users and their data, problem that can be solved exactly by applying random-set theory (RST) and Bayesian recursions (BR). However, implementation of optimum receivers may be limited by their complexity, which grows exponentially with the number of potential users. In this paper we examine three strategies leading to reduced-complexity receivers. In particular, we show how a simple approximation of BRs enables the use of Sphere Detection (SD) algorithm, which exhibits satisfactory performance with limited complexity. Comunicació presentada en la 16th European Signal Processing Conference (EUSIPCO 2008), celebrada els dies 25, 26, 27, 28 i 29 d’agost de 2008 a Lausana (Suïssa), organitzada per la European Association for Signal Processing (EURASIP). 2008-01-01T00:00:00Z http://hdl.handle.net/10230/20508 Silver space-time trellis-coded modulation Biglieri, Ezio; Hong, Yi; Viterbo, Emanuele Silver Code (SilC) was originally discovered in [1–4] for 2×2 multiple-input multiple-output (MIMO) transmission. It has non-vanishing minimum determinant 1/7, slightly lower than Golden code, but is fast-decodable, i.e., it allows reduced-complexity maximum likelihood decoding [5–7]. In this paper, we present a multidimensional trellis-coded modulation scheme for MIMO systems [11] based on set partitioning of the Silver Code, named Silver Space-Time Trellis Coded Modulation (SST-TCM). This lattice set partitioning is designed specifically to increase the minimum determinant. The branches of the outer trellis code are labeled with these partitions. Viterbi algorithm is applied for trellis decoding, while the branch metrics are computed by using a sphere-decoding algorithm. It is shown that the proposed SST-TCM performs very closely to the Golden Space-Time Trellis Coded Modulation (GST-TCM) scheme, yet with a much reduced decoding complexity thanks to its fast-decoding property. Comunicació presentada en la 16th European Signal Processing Conference (EUSIPCO 2008), celebrada els dies 25, 26, 27, 28 i 29 d’agost de 2008 a Lausana (Suïssa), organitzada per la European Association for Signal Processing (EURASIP). 2008-01-01T00:00:00Z http://hdl.handle.net/10230/20507 Fading models and metrics for contemporary wireless systems Jindal, Nihar; Lozano Solsona, Àngel The purpose of this paper is to examine (1) some of the models commonly used to represent fading, and (2) the information-theoretic metrics most commonly used to evaluate performance over those models. We raise the question of whether these models and metrics remain adequate in light of the advances that wireless systems have undergone over the last two decades. Weaknesses are pointed out, and ideas on possible fixes are put forth. Comunicació presentada en la 44th Asilomar Conference on Signals, Systems and Computers, celebrada els dies 7, 8, 9 i 10 de novembre de 2010 a Pacific Grove, Califòrnia (EUA), organitzada per la Naval Postgraduate School (Monterey, CA) i l’ATK Mission Research (Monterey, CA). 2010-01-01T00:00:00Z http://hdl.handle.net/10230/20506 On iterative performance of LDPC and Root-LDPC codes over block-fading channels Andriyanova, Iryna; Biglieri, Ezio; Boutros, Joseph Jean This paper presents our investigation on iterative decoding performances of some sparse-graph codes on block-fading Rayleigh channels. The considered code ensembles are standard LDPC codes and Root-LDPC codes, first proposed in and shown to be able to attain the full transmission diversity. We study the iterative threshold performance of those codes as a function of fading gains of the transmission channel and propose a numerical approximation of the iterative threshold versus fading gains, both both LDPC and Root-LDPC codes. Also, we show analytically that, in the case of 2 fading blocks, the iterative threshold root of Root-LDPC codes is proportional to (α1 α2)1, where α1 and α2 are corresponding fading gains. From this result, the full diversity property of Root-LDPC codes immediately follows. Comunicació presentada en la 48th Annual Allerton Conference on Communications, Control and Computing, celebrada els dies 29 i 30 de setembre i 1 d’octubre de 2010 a Monticello, Illinois (EUA), organitzada pel Coordinated Science Laboratory de l’University of Illinois at Urbana-Champaign. 2010-01-01T00:00:00Z http://hdl.handle.net/10230/20505 Optimum pilot overhead in wireless communication: a unified treatment of continuous and block-fading channels Lozano Solsona, Àngel; Jindal, Nihar The optimization of the pilot overhead in wireless fading channels is investigated, and the dependence of this overhead on various system parameters of interest (e.g., fading rate, signal-to-noise ratio) is quantified. The achievable pilot-based spectral efficiency is expanded with respect to the fading rate about the no-fading point, which leads to an accurate order expansion for the pilot overhead. This expansion identifies that the pilot overhead, as well as the spectral efficiency penalty with respect to a reference system with genie-aided CSI (channel state information) at the receiver, depend on the square root of the normalized Doppler frequency. It is also shown that the widely-used block fading model is a special case of more accurate continuous fading models in terms of the achievable pilot-based spectral efficiency. Furthermore, it is established that the overhead optimization for multiantenna systems is effectively the same as for single-antenna systems with the normalized Doppler frequency multiplied by the number of transmit antennas. Comunicació presentada en la 16th European Wireless Conference 2010 (EW '10), celebrada els dies 12, 13, 14 i 15 d’abril de 2010 a Lucca (Itàlia), organitzada per l’IMT Institute for Advanced Studies. 2010-01-01T00:00:00Z http://hdl.handle.net/10230/20504 Outage thresholds of LDPC codes over nonergodic block-fading channels Andriyanova, Iryna; Biglieri, Ezio; Boutros, Joseph Jean This paper derives approximations allowing the estimation of outage probability for standard irregular LDPC codes and full-diversity Root-LDPC codes used over nonergodic block-fading channels. Two separate approaches are discussed: a numerical approximation, obtained by curve fitting, for both code ensembles, and an analytical approximation for Root-LDPC codes, obtained under the assumption that the slope of the iterative threshold curve of a given code ensemble matches the slope of the outage capacity curve in the high-SNR regime. Comunicació presentada en la 16th European Wireless Conference 2010 (EW '10), celebrada els dies 12, 13, 14 i 15 d’abril de 2010 a Lucca (Itàlia), organitzada per l’IMT Institute for Advanced Studies. 2010-01-01T00:00:00Z http://hdl.handle.net/10230/20503 A systolic array for linear MIMO detection based on an all-swap lattice reduction algorithm Wang, Ni-Chun; Biglieri, Ezio; Yao, Kung A systolic array to implement lattice-reduction-aided linear detection is proposed for a MIMO receiver. The lattice reduction algorithm and the ensuing linear detections are operated in the same array, which can be hardware-efficient. All-swap lattice reduction algorithm (ASLR) is considered for the systolic design. ASLR is a variant of the LLL algorithm, which processes all lattice basis vectors within one iteration. Lattice-reduction-aided linear detection based on ASLR and LLL algorithms have very similar bit-error-rate performance, while ASLR is more time efficient in the systolic array, especially for systems with a large number of antennas. Comunicació presentada en la 34th IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP '09), celebrada els dies 19, 20, 21, 22, 23 i 24 d’abril de 2009 a Taipei, (Taiwan), organitzada per l’Institute of Electrical and Electronics Engineers (IEEE). 2009-01-01T00:00:00Z http://hdl.handle.net/10230/20502 De-hyping transmit diversity in modern MIMO cellular systems Jindal, Nihar; Lozano Solsona, Àngel A contemporary perspective on the tradeoff between transmit antenna diversity and spatial multi-plexing is provided. It is argued that, in the context of modern cellular systems and for the operating points of interest, transmission techniques that utilize all available spatial degrees of freedom for multiplexing outperform techniques that explicitly sacrifice spatial multiplexing for diversity. Reaching this conclusion, however, requires that the channel and some key system features be adequately modeled; failure to do so may bring about starkly different conclusions. As a specific example, this contrast is illustrated using the 3GPP Long-Term Evolution system design. Comunicació presentada en la Global Telecommunications Conference (GLOBECOM '09), celebrada els dies 30 de novembre, 1, 2, 3 i 4 de desembre de 2009 a Honolulu, Hawaii (EUA), organitzada per l’Institute of Electrical and Electronics Engineers (IEEE). 2009-01-01T00:00:00Z http://hdl.handle.net/10230/20501 ClubADSL: When your neighbors are your friends Giustiniano, Domenico; Gomà Llairo, Eduard; Morillo Pozo, Julián; López Toledo, Alberto; Rodríguez, Pablo ADSL is becoming the standard form of residential and small-business broadband Internet access due to, primarily, its low deployment cost. These ADSL residential lines are often deployed with 802.11 Access Points (AP) that provide wireless connectivity. Given the density of ADSL deployment, it is often possible for a residential wireless client to be in range of several other APs, belonging to neighbors, with ADSL connectivity. While the ADSL technology has showed evident limits in terms of capacity (with speeds ranging 1-10 Mbps), the short-range wireless communication can guarantee a much higher capacity (up to 20 Mbps). Furthermore, the ADSL links in the neighborhood are generally under-utilized, since ADSL subscribers do not connect 100% of the time. Therefore, it is possible for a wireless client to simultaneously connect to several APs in range and effectively aggregate their available ADSL bandwidth. In this paper, we introduce ClubADSL, a wireless client that can simultaneously connect to several APs in range on different frequencies and aggregate both their downlink and uplink capacity. ClubADSL is a software that runs locally on the client-side, and it requires neither modification to the existing Internet infrastructure, nor any hardware/protocol upgrades to the 802.11 local area network. We show the feasibility of ClubADSL in seamlessly transmitting TCP traffic, and validate its implementation both in controlled scenarios and with current applications over real ADSL lines. In particular we show that a ClubADSL client can greatly benefit from the aggregated download bandwidth in the case of server-client applications such as video streaming, but can also take advantage of the increased upload bandwidth greatly reducing download times with incentive-based P2P applications such as BitTorrent. Comunicació presentada en el Symposium on Computers and Communications (ISCC '09), celebrat els dies 5, 6, 7 i 8 de juliol de 2009 a Sussa (Tunísia), organitzat per l’Institute of Electrical and Electronics Engineers (IEEE). 2009-01-01T00:00:00Z http://hdl.handle.net/10230/20500 Bit loading for MIMO with statistical channel information at the transmitter and ZF receivers García Armada, Ana; Hong, Li; Lozano Solsona, Àngel For single-user MIMO communication with uncoded and coded QAM signals, we propose bit and power loading schemes that rely only on channel distribution information at the transmitter. To that end, we develop the relationship between the average bit error probability at the output of a ZF linear receiver and the bit rates and powers allocated at the transmitter. This relationship, and the fact that a ZF receiver decouples the MIMO parallel channels, allow leveraging bit loading algorithms already existing in the literature. We solve dual bit rate maximization and power minimization problems and present performance results that illustrate the gains of the proposed scheme with respect to a non-optimized transmission. Comunicació presentada en la International Conference on Communications (ICC '09), celebrada els dies 14, 15, 16, 17 i 18 de juny de 2009 a Dresden (Alemanya), organitzat per l’Institute of Electrical and Electronics Engineers (IEEE). 2009-01-01T00:00:00Z http://hdl.handle.net/10230/20499 What is the value of joint processing of pilots and data in block-fading channels? Jindal, Nihar; Lozano Solsona, Àngel; Marzetta, Thomas L. The spectral efficiency achievable with joint processing of pilot and data symbol observations is compared with that achievable through the conventional (separate) approach of first estimating the channel on the basis of the pilot symbols alone, and subsequently detecting the data symbols. Studied on the basis of a mutual information lower bound, joint processing is found to provide a non-negligible advantage relative to separate processing, particularly for fast fading. It is shown that, regardless of the fading rate, only a very small number of pilot symbols (at most one per transmit antenna and per channel coherence interval) should be transmitted if joint processing is allowed. Comunicació presentada en el International Symposium on Information Theory (ISIT '09), celebrat els dies 28, 29 i 30 de juny i 1, 2 i 3 de juliol de 2009 a Seül (Corea del Sud), organitzat per l’Institute of Electrical and Electronics Engineers (IEEE). 2009-01-01T00:00:00Z http://hdl.handle.net/10230/20498 A comparison of full-rate full-diversity 2x2 space-time codes for WiMAX systems Sezginer, Serdar; Sari, Hikmet; Biglieri, Ezio Multiple-input multiple-output (MIMO) techniques have become an essential part of broadband wireless communications systems. For example, the recently developed IEEE 802.16e specifications for broadband wireless access include three MIMO profiles employing 2×2 space-time codes (STCs), and two of these MIMO schemes are mandatory on the downlink of Mobile WiMAX systems. One of these has full rate, and the other has full diversity, but neither of them has both of the desired features. The third profile, namely, Matrix C, which is not mandatory, is both a full rate and a full diversity code, but it has a high decoder complexity. Recently, the attention was turned to the decoder complexity issue and including this in the design criteria, several full-rate STCs were proposed as alternatives to Matrix C. In this paper, we review these different alternatives and compare them to Matrix C in terms of performances and the corresponding receiver complexities. Comunicació presentada en el 10th International Symposium on Spread Spectrum Techniques and Applications (ISSSTA '08), celebrat els dies 25, 26, 27, i 28 d’agost de 2008 a Bolonya (Itàlia), organitzat per l’Institute of Electrical and Electronics Engineers (IEEE). 2008-01-01T00:00:00Z http://hdl.handle.net/10230/20497 Full diversity product codes for block erasure and block fading channels Boutros, Joseph Jean; Zémor, Gilles; Guillén i Fàbregas, Albert; Biglieri, Ezio We show how to build full-diversity product codes under both iterative encoding and decoding over non-ergodic channels, in presence of block erasure and block fading. The concept of a rootcheck or a root subcode is introduced by generalizing the same principle recently invented for low-density parity-check codes. We also describe some channel related graphical properties of the new family of product codes, a family referred to as root product codes. Comunicació presentada en el Information Theory Workshop (ITW '08), celebrat els dies 5, 6, 7, 8 i 9 de maig de 2008 a Porto (Portugal), organitzat per l’Institute of Electrical and Electronics Engineers (IEEE). 2008-01-01T00:00:00Z http://hdl.handle.net/10230/20496 Generalized low-density codes with BCH constituents for full-diversity near-outage performance Boutros, Joseph Jean; Zémor, Gilles; Guillén i Fàbregas, Albert; Biglieri, Ezio A new graph-based construction of generalized low density codes (GLD-Tanner) with binary BCH constituents is described. The proposed family of GLD codes is optimal on block erasure channels and quasi-optimal on block fading channels. Optimality is considered in the outage probability sense. A classical GLD code for ergodic channels (e.g., the AWGN channel, the i.i.d. Rayleigh fading channel, and the i.i.d. binary erasure channel) is built by connecting bitnodes and subcode nodes via a unique random edge permutation. In the proposed construction of full-diversity GLD codes (referred to as root GLD), bitnodes are divided into 4 classes, subcodes are divided into 2 classes, and finally both sides of the Tanner graph are linked via 4 random edge permutations. The study focuses on non-ergodic channels with two states and can be easily extended to channels with 3 states or more. Comunicació presentada en el International Symposium on Information Theory (ISIT '08), celebrat els dies 6, 7, 8, 9, 10 i 11 de juliol de 2008 a Toronto (Ontario, Canadà), organitzat per Institute of Electrical and Electronics Engineers (IEEE). 2008-01-01T00:00:00Z http://hdl.handle.net/10230/20495 Opportunities for a cultural specific approach in the computational description of music Serra, Xavier The current research in Music Information Retrieval (MIR) is showing the potential that the Information Technologies can have in music related applications. A major research challenge in that direction is how to automatically describe/annotate audio recordings and how to use the resulting descriptions to discover and appreciate music in new ways. But music is a complex phenomenon and the description of an audio recording has to deal with this complexity. For example, each music culture has specificities and emphasizes different musical and communication aspects, thus the musical recordings of each culture should be described differently. At the same time these cultural specificities give us the opportunity to pay attention to musical concepts and facets that, despite being present in most world musics, are not easily noticed by listeners. In this paper we present some of the work done in the CompMusic project, including ideas and specific examples on how to take advantage of the cultural specificities of different musical repertoires. We will use examples from the art music traditions of India, Turkey and China. Comunicació presentada al 2nd CompMusic Workshop, celebrat els dies 12 i 13 de juliol de 2012 a Istanbul (Turquia), organitzat per CompMusic. 2012-01-01T00:00:00Z http://hdl.handle.net/10230/20494 Carnatic music: Svara, Gamaka, Motif and Raga identity Krishna, T. M.; Ishwar, Vignesh Over the last century in Karnatik music, the method of understanding raga has been to break it down into its various components, svara, scale, gamaka, and phrases. In this paper, an attempt is made to define the abstract concept of raga in its entirety within the aesthetics of Karnatik music considering the various components and their symbiotic relationship. This paper also attempts to prove that the identity of a raga exists as a whole. Section 2 explains the concept of a fundamental musical note or svara. Section 3 illustrates the concept of gamaka or inflections. Section 4 delves into the concept of raga in detail and then flows into Section 5 which enunciates the identity of a raga in terms of svara, gamaka, and phraseology. The paper concludes in Section 6, and Section 7 gives the references. Comunicació presentada al 2nd CompMusic Workshop, celebrat els dies 12 i 13 de juliol de 2012 a Istanbul (Turquia), organitzat per CompMusic. 2012-01-01T00:00:00Z http://hdl.handle.net/10230/20493 A Musically aware system for browsing and interacting with audio music collections Sordo, Mohamed; Koduri, Gopala Krishna; Sentürk, Sertan; Gulati, Sankalp; Serra, Xavier In the context of the CompMusic project we are developing methods to automatically describe/annotate audio music recordings pertaining to various music cultures. As a way to demonstrate the usefulness of the methods we are also developing a system to browse and interact with specific audio collections. The system is an online web application that interfaces with all the data gathered (audio, scores plus contextual information) and all the descriptions that are automatically generated with the developed methods. In this paper we present the basic architecture of the proposed system, the types of data sources that it includes, and we mention some of the culture specific issues that we are working on for its development. The system is in a preliminary stage but it shows the potential that MIR technologies can have in browsing and interacting with music collections of various cultures. Comunicació presentada al 2nd CompMusic Workshop, celebrat els dies 12 i 13 de juliol de 2012 a Istanbul (Turquia), organitzat per CompMusic. 2012-01-01T00:00:00Z http://hdl.handle.net/10230/20492 Incorporating features of distribution and progression for automatic Makam classification Ünal, Erdem; Bozkurt, Baris; Karaosmanoğlu, M. Kemal Automatic classification of makams from symbolic data is a rarely studied topic. In this paper, first a review of an n-gram based approach is presented using various representations of the symbolic data. While a high degree of precision can be obtained, confusion happens mainly for makams using (almost) the same scale and pitch hierarchy but differ in overall melodic progression, seyir. To further improve the system, first n-gram based classification is tested for various sections of the piece to take into account a feature of the seyir that melodic progression starts in a certain region of the scale. In a second test, a hierarchical classification structure is designed which uses n-grams and seyir features in different levels to further improve the system. Comunicació presentada al 2nd CompMusic Workshop, celebrat els dies 12 i 13 de juliol de 2012 a Istanbul (Turquia), organitzat per CompMusic. 2012-01-01T00:00:00Z