A. Kocian

University of Rome Tor Vergata, Roma, Latium, Italy

Are you A. Kocian?

Claim your profile

Publications (20)6.31 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper proposes a novel, interactive telemedicine platform, providing real-time audio and video interactions among patients, physicians and health service provider. Such a system has been developed within the framework of the European Space Agency (ESA) project TElemedicine Services for HEALTH (TESHEALTH) in collaboration among industry, academia, and hospitals. In particular, in the framework of the project, all citizens from many different sites have the same opportunity to access services promoting disease prevention and healthy life style, and professional users (specialists, physicians, operators) can exploit the platform to accomplish clinical studies and medical research. In such a context, an IP-based heterogeneous network architecture, composed of both satellite and terrestrial components, is considered in order to provide properly the TESHEALTH services. The paper presents the network parameters, the user requirements, and the hybrid satellite/terrestrial network architecture of the TESHEALTH platform. In addition, the platform offers Quality-of-Service, tailored to the individual user profiles and services, as well.
    Aerospace Conference, 2011 IEEE; 04/2011
  • [Show abstract] [Hide abstract]
    ABSTRACT: The paper presents a solar sensor to be embarked as payload of a micro-satellite that can provide information on the attitude of the satellite in space. The solar sensor has been developed in the framework of the Italian project EDUSAT (Educational Satellite), managed by ASI (Italian Space Agency), aiming at educating pupils at high school. Class rooms all over Italy will be supplied by payload telemetry data from the earth station via internet. The micro-satellite EDUSAT will be launched in April 2010 by the Russian launcher vehicle Dnepr and operated by an earth station located in Rome, Italy. The satellite will be located in LEO circular orbit. The performance of the sensor is analysed theoretically and by means of field-experiments.
    IEEE Aerospace Conference Proceedings 01/2010;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents an iterative scheme for joint timing acquisition, multi-channel parameter estimation, and multiuser soft-data decoding. As an example, an asynchronous convolutionally coded direct-sequence code-division multiple-access system is considered. The proposed receiver is derived within the space-alternating generalized expectation-maximization framework, implying that convergence in likelihood is guaranteed under appropriate conditions in contrast to many other iterative receiver architectures. The proposed receiver iterates between joint posterior data estimation, interference cancellation, and single-user channel estimation and timing acquisition. A Markov Chain Monte Carlo technique, namely Gibbs sampling, is employed to compute the a posteriori probabilities of data symbols in a computationally efficient way. Computer simulations in flat Rayleigh fading show that the proposed algorithm is able to handle high system loads unlike many other iterative receivers.
    IEEE Transactions on Signal Processing 01/2010; 58:5756-5766. · 2.81 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Within the context of high-data rate transmissions over time varying multipath fading channels, this article presents a new receiver design for orthogonal frequency division multiplexing (OFDM) systems. The received signal is processed jointly in time and frequency domains. A Discrete Wavelet Transform is applied to the received signal before equalization which is based on the minimum mean square error (MMSE) principle. The paper shows that the proposed receiver is able to work also in highly time-variant channels where a traditional frequency domain equalizer gets very bad performance. Moreover, it is shown that this joint time-frequency equalization is able to exploit time diversity without coding. The performance of the proposed equalizer are shown both in case of perfect channel estimation and in presence of a MMSE linear channel estimator.
    Proceedings of the IEEE 21st International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC 2010, 26-29 September 2010, Istanbul, Turkey; 01/2010
  • [Show abstract] [Hide abstract]
    ABSTRACT: This paper is concerned with joint multiuser detection and multichannel estimation (JDE) for uplink multicarrier code-division multiple-access (MC-CDMA) systems in the presence of frequency selective channels. The detection and estimation, implemented at the receiver, are based on a version of the expectation maximization (EM) algorithm and the space-alternating generalized expectation–maximization (SAGE) which are very suitable for multicarrier signal formats. The EM-JDE receiver updates the data bit sequences in parallel, while the SAGE-JDE receiver reestimates them successively. The channel parameters are updated in parallel in both schemes. Application of the EM-based algorithm to the problem of iterative data detection and channel estimation leads to a receiver structure that also incorporates a partial interference cancelation. Computer simulations show that the proposed algorithms have excellent BER end estimation performance.
    Physical Communication 01/2010; 3(2):87-96.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: An efficient, joint transmission delay and channel parameter estimation algorithm is proposed for uplink asynchronous direct-sequence code-division multiple access (DS-CDMA) systems based on the space-alternating generalized expectation maximization (SAGE) framework. The marginal likelihood of the unknown parameters, averaged over the data sequence, as well as the expectation and maximization steps of the SAGE algorithm are derived analytically. To implement the proposed algorithm, a Markov chain Monte Carlo (MCMC) technique, called Gibbs sampling, is employed to compute the a posteriori probabilities of data symbols in a computationally efficient way. Computer simulations show that the proposed algorithm has excellent estimation performance. This so-called MCMC-SAGE receiver is guaranteed to converge in likelihood.
    Signal Processing Advances in Wireless Communications, 2009. SPAWC '09. IEEE 10th Workshop on; 07/2009
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, main single carrier (SC) and multicarrier (MC) systems with frequency domain equalization (FDE) are reviewed with the objective to identify key features of the evolution path of air interfaces towards 4G. In particular, this paper shows that the FFT/IFFT operation can be seen as the concatenation of two operations: S/P conversion and spreading. We show that the transmitter of an OFDMA system performs a S/P conversion and a multiplication with specific complex spreading codes. By replacing the orthogonal complex spreading codes of this equivalent OFDMA system, with traditional orthogonal spreading codes that are used in DS-CDMA systems, for instance Walsh-Hadamard codes, we achieve a novel multicode-CDMA system. The comparison of this novel SC transmission scheme with other SC and MC systems shows that the novel SC system has almost the same performance as OFDMA and also similar PAPR. On the other hand, it has a pretty different behavior wrt other SC systems such as IFDMA and DS-CDMA with FDE.
    Wireless Communication, Vehicular Technology, Information Theory and Aerospace & Electronic Systems Technology, 2009. Wireless VITAE 2009. 1st International Conference on; 06/2009
  • A. Kocian, B. Hu, B. H. Fleury
    [Show abstract] [Hide abstract]
    ABSTRACT: The paper presents an iterative scheme that incrementally minimizes the Kullback-Leibler divergence between joint posterior and nuisance parameter distribution, and directly minimizes the Kullback-Leibler divergence between joint posterior and parameter-of-interest distribution in alternating order. This so-called variational Bayes incremental expectation maximization (VB-IEM) algorithm has two virtues: first, it non-decreases an objective function at each iteration and secondly, it adopts the convergence properties of the exact EM algorithm if the parameter estimate is consistent and maximum a posteriori. When the VB-IEM algorithm is applied to joint multi-user decoding and multi-channel estimation in flat Rayleigh fading, Monte Carlo simulations show that the proposed scheme supports extremely high effective system loads.
    Circuits, Systems and Computers, 1977. Conference Record. 1977 11th Asilomar Conference on 01/2008;
  • A. Kocian, I. Land, B.H. Fleury
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper deals with the derivation and optimization of an iterative receiver architecture performing joint multiuser decoding and channel estimation. We consider an asynchronous multirate convolutional coded DS-CDMA system that communicates over quasi-static flat Rayleigh fading channels. The proposed receiver is derived within the space-alternating generalized expectation-maximization (SAGE) framework in connection with the noise-splitting approach. The used theoretical framework guarantees convergence of the receiver, as opposed to many other iterative receiver structures. Furthermore, the noise-splitting approach provides a set of noise-weighting coefficients that can be optimized under weak constraints. The inputs to the single-user decoders are linear combinations of two kinds of soft values with weights determined by the noise-weighting coefficients. These two kinds of soft values can be interpreted as a priori information and extrinsic information, respectively, if the channels are known. In the case of unknown channels, they are asymptotically a priori and asymptotically extrinsic, i.e., they become a priori and extrinsic when the length of the observed frame tends to infinity. In most cases, the optimum coefficients lead to extrinsic or asymptotically extrinsic values fed to the input of the single-user decoders. Monte Carlo simulations show that the proposed receiver is resistant to channel estimation errors and supports high system loads.
    IEEE Transactions on Communications 07/2007; · 1.75 Impact Factor
  • Alexander Kocian, Ingmar Land, Bernard H. Fleury
    IEEE Transactions on Communications. 01/2007; 55:1231-1241.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We derive a multi-user receiver that performs joint data de-tection and channel estimation (JDE) of DS-CDMA signals. The proposed sub-optimal receiver is formulated within the framework of the space-alternating generalized expectation-maximization (SAGE) algorithm. The time-varying channel is represented by discrete prolate spherical (DPS) sequences. The resulting receiver iterates between MMSE based channel estimation in the subspace spanned by the DPS sequences and successive interference cancellation at significantly less time complexity than previously proposed SAGE based JDE schemes. The reduction is in the order of 200 for the inves-tigated system parameters. Numerical examples show that the proposed receiver works efficiently in a wide range of velocities and system loads.
    01/2006;
  • A. Kocian, I. Land, B.H. Fleury
    [Show abstract] [Hide abstract]
    ABSTRACT: An iterative receiver for joint multiuser-decoding and channel-estimation of coded CDMA is derived by applying the noise-splitting approach within the space alternating generalized expectation-maximization (SAGE) framework. We consider asynchronous single-rate DS/CDMA over flat Rayleigh fading channels. The resulting receiver structure comprises partial successive interference-cancellation (SIC), channel estimation, and soft-input/hard-output maximum likelihood sequence decoding (MLSD) for each user. Additionally, one obtains a set of noise-weighting coefficients that can be freely chosen within weak constraints. These coefficients determine the amount of feedback from the decoder output to the decoder input in the subsequent iteration, and thus, "how extrinsic" the decoder output values are. The noise-weighting coefficients strongly influence the system performance. Their optimization within the SAGE framework leads to extrinsic output values in most of the cases. The proposed receiver is evaluated by Monte-Carlo simulations, and it shows two major advantages: high load is supported and convergence is guaranteed.
    Global Telecommunications Conference, 2005. GLOBECOM '05. IEEE; 01/2005
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper we propose an extension of the space alternating generalized expectation maximization (SAGE) algorithm that accepts as input and provides as output soft information. This so-called soft-input soft-output (SISO) SAGE algorithm is applied to joint successive interference cancellation and channel estimation and combined with SISO single-user decoders in an iterative CDMA receiver. Monte Carlo simulations in flat Rayleigh fading channel show that this receiver is robust against channel estimation errors and can support a high system.
    Signals, Systems and Computers, 2004. Conference Record of the Thirty-Eighth Asilomar Conference on; 12/2004
  • A. Kocian, B.H. Fleury
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, we present an efficient iterative receiver architecture of tractable complexity for joint multiuser detection and channel estimation (JDE) in DS/CDMA based on the EM algorithm. The EM algorithm provides a set of free parameters called weight coefficients which can be selected to optimize its performance. Two optimality criteria are defined and analytical expressions for the corresponding optimized weight coefficients are given. Monte Carlo simulations of an asynchronous multi-rate system operating in flat Rayleigh fading channel show that the proposed receiver is near-far resistant and robust against errors in estimation of the channel parameters.
    Global Telecommunications Conference, 2003. GLOBECOM '03. IEEE; 01/2004
  • [Show abstract] [Hide abstract]
    ABSTRACT: The paper presents two iterative multiuser detection and channel estimation (JDE) receivers of tractable complexity for downlink transmission using beamforming. The receivers results from an application of the space-alternating generalized expectation-maximization (SAGE) algorithm and a modified version. The proposed JDE schemes update the channel parameters in parallel and re-estimates the users' symbols in successive order. Monte Carlo simulations in a frequency-selective scenario show that the JDE schemes are robust against errors in the estimation of the channel coefficients.
    Signals, Systems and Computers, 2003. Conference Record of the Thirty-Seventh Asilomar Conference on; 12/2003
  • A. Kocian, B.H. Fleury
    [Show abstract] [Hide abstract]
    ABSTRACT: We present two efficient iterative receiver structures of tractable complexity for joint multiuser detection and multichannel estimation (JDE) of direct-sequence code-division multiple-access signals. The schemes result from an application of the expectation-maximization (EM) and the space-alternating generalized expectation-maximization (SAGE) algorithms, respectively. The EM-JDE receiver updates the data bit sequences in parallel, while the SAGE-JDE receiver reestimates them successively. The channel parameters are updated in parallel in both schemes. The EM algorithm provides a set of free parameters, called weight coefficients, which can be selected to optimize its performance. Two optimality criteria are defined and analytical expressions for the corresponding optimized weight coefficients are given. Monte-Carlo simulations of a synchronous scenario show that the proposed JDE receivers have excellent multiuser efficiency and are robust against errors in the estimation of the channel parameters. Moreover, very short training sequences are required for the JDE schemes to converge. Simulation results further demonstrate that the SAGE-JDE receiver exhibits a better performance when the users' bit sequences are updated in the order of increasing signal strength, i.e., the bit sequence of the user with the weakest signal strength is updated first at each stage.
    IEEE Transactions on Communications 11/2003; · 1.75 Impact Factor
  • Alexander Kocian, Bernard H. Fleury
    IEEE Transactions on Communications. 01/2003; 51:1709-1720.
  • A. Kocian, B.H. Fleury
    [Show abstract] [Hide abstract]
    ABSTRACT: We present a method of tractable complexity for joint data detection and channel estimation of DS/CDMA signals. The scheme results from an application of the SAGE algorithm. Monte Carlo simulations of a synchronous scenario show that the method is near-far resistant and that it is robust against estimation errors of the channel parameters. Moreover, very short training sequences are required for the scheme to converge. Simulation results further demonstrate that a better performance is obtained when the users' bit sequences are cyclically updated in the order of increasing strength of the users' signals at the output of the whitening filter in the receiver
    Personal, Indoor and Mobile Radio Communications, 2000. PIMRC 2000. The 11th IEEE International Symposium on; 02/2000
  • A. Kocian, D. Dahlhaus
    [Show abstract] [Hide abstract]
    ABSTRACT: A concept of an air interface for the downlink of an indoor mobile radio system with code-division multiple access (CDMA) based on chirp modulation is presented. A homogenous occupation of the total available bandwidth can be guaranteed for arbitrary signature sequences of the different users. A cost-efficient noncoherent demodulation scheme is presented and analyzed in terms of the bit-error rates for both frequency-nonselective and frequency-selective transmission channels. The analog signal processing includes chirp matched filtering and a post-detection integration, while the code correlation is carried out in the digital domain. Monte-Carlo simulations of a typical application, like, for example, the auto-identification with active microwave tags in the car industry, indicate that the scheme is robust against multiple-access interference and able to overcome the problem of frequency-selective fading
    Vehicular Technology Conference, 1999 IEEE 49th; 08/1999