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  • 1.
    Arapoglou, Pantelis-Daniel
    et al.
    University of Luxembourg, Luxembourg.
    Shankar, M. R. Bhavani
    University of Luxembourg, Luxembourg.
    Panagopoulos, Athanasios
    University of Luxembourg, Luxembourg.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Gateway Diversity Strategies in Q/V Band Feeder Links2011In: Proceedings 17th Ka and Broadband Communications Conference, 2011Conference paper (Refereed)
  • 2.
    Gharanjik, Ahmad
    et al.
    Interdisciplinary Cen tre for Security, Reliability and Tru st (SnT), University of Luxembourg.
    Rao, Bhavani Shankar Mysore Rama
    Interdisciplinary Cen tre for Security, Reliability and Tru st (SnT), University of Luxembourg.
    Arapoglou, Pantelis-Daniel
    Ottersten, Björn
    Interdisciplinary Cen tre for Security, Reliability and Tru st (SnT), University of Luxembourg.
    Large scale transmit diversity in Q/V band feeder link with multiple gateways2013In: 2013 IEEE 24th International Symposium on Personal Indoor and Mobile Radio Communications (PIMRC), 2013, p. 766-770Conference paper (Refereed)
    Abstract [en]

    Exploiting transmit diversity amid a high number of multiple gateways (GW) is a new research challenge in Q/V band satellite communication providing data rates of hundreds of Gbit/s. In this paper, we propose a practical switching strategy in a scenario with N+P GWs (N active and P redundant GWs) towards achieving GW transmit diversity. Differently from other works, the treatment in this paper is analytical and explores two key factors: outage performance and switching rate in detail. Further, the interplay between the number of redundant and active GWs on the availability is illustrated highlighting the contribution of the work towards system sizing.

  • 3.
    Shankar, M. R. Bhavani
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    A Novel Space-Time-Frequency Code for Multiband-OFDM UWB2008In: RadioVetenskap och Kommunikation (RVK), 2008, p. 12-16Conference paper (Other academic)
    Abstract [en]

    In this paper, we propose a novel STF (Space-Time-Frequency) code for use in MB-OFDM UWB (Multiband-Orthogonal Frequency Divvision Multiplexing based Ultra-WideBand) systems with multiple antennas. These codes guarantee a rate of one symbol per channel use and result in moderate decoding complexity. Further, in conjunction with hopping multiband OFDM modulation, these codes are shown to exploit the spatial and frequency divversities available in MIMO UWB systems for channels with arbitrary PDPs (Power Delay Profiles). A systematic procedure to enhance the coding gain of these codes in the absence of PDP information at transmitter is also presented. BER (Bit Error Rate) performance of these codes is shown to be better than those of existing codes due to the systematic coding gain enhancement.

  • 4.
    Shankar, M. R. Bhavani
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hari, K. V. S.
    Department of Electrical Communication Engineering, Indian Institute of Science , Bangalore 560012, India .
    Systematic Construction of Linear Transform based Full Divversity, Rate One Space-Time-Frequency Codes2009In: IEEE Transactions on Signal Processing, ISSN 1053-587X, Vol. 57, no 6, p. 2285-2298Article in journal (Refereed)
    Abstract [en]

    In this paper, we generalize the existing rate-one space frequency (SF) and space-time frequency (STF) code constructions. The objective of this exercise is to provide a systematic design of full-diversity STF codes with high coding gain. Under this generalization, STF codes are formulated as linear transformations of data. Conditions on these linear transforms are then derived so that the resulting STF codes achieve full diversity and high coding gain with a moderate decoding complexity. Many of these conditions involve channel parameters like delay profile (DP) and temporal correlation. When these quantities are not available at the transmitter, design of codes that exploit full diversity on channels with arbitrary DP and temporal correlation is considered. Complete characterization of a class of such robust codes is provided and their bit error rate (BER) performance is evaluated. On the other hand, when channel DP and temporal correlation are available at the transmitter, linear transforms are optimized to maximize the coding gain of full-diversity STF codes. BER performance of such optimized codes is shown to be better than those of existing codes.

  • 5.
    Shankar, M. R. Bhavani
    et al.
    Interdisciplinary Centre for Security, Reliability and Trust (SnT), University of Luxembourg, Luxembourg.
    von Wrycza, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Convergence of the Iterative Water-Filling Algorithm with Sequential Updates in Spectrum Sharing Scenarios2011In: 2011 IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH, AND SIGNAL PROCESSING, 2011, p. 3216-3219Conference paper (Refereed)
    Abstract [en]

    Spectrum sharing between two independent, co-existing transmit-receive pairs (TRPs) is formulated as a non-cooperative game with the TRPs as players, their individual link rates as payoffs and power allocation over the utilized spectral bands as the strategy. A Nash Equilibrium (NE) corresponds to the outcome of such a game and TRPs iteratively use the water-filling algorithm according to an agreed order for achieving the NE. Dynamics of this distributed algorithm is studied to determine the conditions for convergence and characterize the resulting NE. A sufficient condition on global convergence is derived and is shown to be tighter than existing ones. Further, a novel characterization of the globally achievable NE based on necessary conditions is presented. Some of these results are also extended to multiple NE scenarios where local convergence is exhibited.

  • 6.
    Shankar, Mysore Rama Rao Bhavani
    et al.
    Interdisciplinary Centre for Security, Reliability and Trust (SnT), University of Luxembourg, Luxembourg.
    Arapoglou, Pantelis-Daniel
    School of Electrical & Computer Engineering, National Technical University of Athens, Greece.
    Ottersten, Björn
    Interdisciplinary Centre for Security, Reliability and Trust (SnT), University of Luxembourg, Luxembourg.
    Golden Codes for Dual Polarized MIMO-OFDM Transmissions in Hybrid Satellite/Terrestrial Mobile Systems2011In: 2011 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS (ICC), IEEE , 2011Conference paper (Refereed)
    Abstract [en]

    This paper discusses the performance of Golden codes in a hybrid satellite/terrestrial system framework employing dual polarized MIMO-OFDM transmissions. Although the use of Golden codes in satellite and terrestrial scenarios has been studied independently, a realistic performance assessment must involve both components taking into account the relative delay between their reception. In fact, this work exploits the relative delay to create a multipath scenario and further improve the coding gain of the Golden codes, which is otherwise fixed. This is made possible by utilizing the Golden code in a Space-Frequency coding framework instead of the traditional Space-Time paradigm. The separation between the subcarriers constituting a Golden code is shown to be central to the coding gain enhancement and an algorithm to choose this separation is provided.

  • 7.
    Shankar, Mysore Rama Rao Bhavani
    et al.
    Interdisciplinary Centre for Security, Reliability and Trust, University of Luxembourg, Luxembourg.
    von Wrycza, Peter
    Ericsson Research, Stockholm, Sweden.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    Convergence of the iterative water-filling algorithm in multiple user spectrum sharing scenarios2011In: IEEE Swedish Communication Technologies Workshop (Swe-CTW), 2011, 2011, p. 80-85Conference paper (Refereed)
    Abstract [en]

    Spectrum sharing between multiple independent, coexisting transmit-receive pairs (TRPs, also termed as users) is formulated as a non-cooperative game with the TRPs as players, their individual link rates as payoffs and the iterative water-filling algorithm (IWFA) as the strategy for each TRP. The dynamics of this distributed algorithm are studied for sequential and simultaneous update mechanisms to determine the nature of convergence. Global convergence to unique Nash Equilibrium (NE) is considered and sufficient conditions tighter than those in the literature are derived. Necessary conditions are also derived to complement the sufficient conditions. The necessary conditions serve as tools for characterizing the structure of NE and also highlight the sensitivity of convergence to update orders in sequential IWFA.

  • 8.
    von Wrycza, Peter
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Shankar, M. R. Bhavani
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    A Game Theoretic Approach to Multi-User Spectrum Allocation2009In: GLOBECOM 2009 - 2009 IEEE Global Telecommunications Conference / [ed] Ulema M, IEEE , 2009, p. 5425963-Conference paper (Refereed)
    Abstract [en]

    We consider the interaction of several transmit-receive pairs coexisting in the same area and communicating using the same portion of the spectrum. Using a game theoretic framework, each pair is regarded as a player whose payoff function is the individual link rate and power is allocated using the iterative water-filling algorithm. We find properties of the resulting Nash equilibria and derive conditions for when various operating points are achievable. The analysis presented herein extends previous work by characterizing the set of stable solutions for a multi-user system. Also, we show how the game can be modified to obtain better operating points in terms of sum rate compared to the iterative water-filling algorithm. The increase in performance corresponding to one such modification is evaluated and compared to the iterative water-filling algorithm by numerical simulations.

  • 9.
    von Wrycza, Peter
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Shankar, M. R. Bhavani
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Game Theoretic Approach to Spectrum Allocation for Weak Interference Systems2008In: GLOBECOM 2008 - 2008 IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE, 2008, p. 1-5Conference paper (Refereed)
    Abstract [en]

    A scenario consisting of two transmitter-receiver pairs coexisting in the same area and communicating using the same portion of the spectrum is considered. Decentralized coding strategies are employed at the transmitter side and no cooperation is assumed between the two systems. We investigate the structure of Nash equilibria corresponding to simultaneous water-filling solutions and propose a scheme that improves overall performance of systems with weak mutual interference. The resulting scheme provides a spectrum sharing rule in the form of a modified utility function. The conditions for optimality are presented and a numerical example illustrates the performance compared to a scheme employing the link rate as utility function.

  • 10.
    von Wrycza, Peter
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Shankar, M. R. Bhavani
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    Properties of Iterative Water-Filling Algorithm for Flat-Fading Multi-User Environments2010In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476Article in journal (Other academic)
  • 11.
    von Wrycza, Peter
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Shankar, M. R. Bhavani
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Spectrum Allocation from a Game Theoretic Perspective: Properties of Nash Equilibria2008In: 2008 42ND ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS AND COMPUTERS, VOLS 1-4 / [ed] Matthews MB, New York: IEEE , 2008, p. 1542-1546Conference paper (Refereed)
    Abstract [en]

    We consider a scenario consisting of two transmit-receive pairs coexisting in the same area and communicating using the same portion of the spectrum. Applying a game theoretic framework, each pair is regarded as a player whose payoff function is the individual link rate and power is allocated using the iterative water-filling algorithm. We study the dynamics of such a game and find properties of the resulting Nash equilibria. For high interference scenarios, operating points admitting complete, partial or no overlap are possible and we present conditions under which the different Nash equilibria are achievable. Based on this analysis, a modified water-filling algorithm is designed to increase the sum-rate of the communication links. Its performance is compared to that of the iterative water-filling algorithm by numerical simulations. Although we restrict the analysis to a two player game, analogous concepts can be used to design decentralized algorithms for scenarios with more players.

  • 12.
    von Wrycza, Peter
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Shankar, Mysore Rama Rao Bhavani
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Bengtsson, Mats
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Spectrum Allocation for Decentralized Transmission Strategies: Properties of Nash Equilibria2009In: EURASIP Journal on Advances in Signal Processing, ISSN 1687-6172Article in journal (Refereed)
    Abstract [en]

    The interaction of two transmit-receive pairs coexisting in the same area and communicating using the same portion of the spectrum is analyzed from a game theoretic perspective. Each pair utilizes a decentralized iterative water-filling scheme to greedily maximize the individual rate. We study the dynamics of such a game and find properties of the resulting Nash equilibria. The region of achievable operating points is characterized for both low-and high-interference systems, and the dependence on the various system parameters is explicitly shown. We derive the region of possible signal space partitioning for the iterative water-filling scheme and show how the individual utility functions can be modified to alter its range. Utilizing global system knowledge, we design a modified game encouraging better operating points in terms of sum rate compared to those obtained using the iterative water-filling algorithm and show how such a game can be imitated in a decentralized noncooperative setting. Although we restrict the analysis to a two player game, analogous concepts can be used to design decentralized algorithms for scenarios with more players. The performance of the modified decentralized game is evaluated and compared to the iterative water-filling algorithm by numerical simulations.

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