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See detailSensitivity Analysis of Multicarrier Digital Pre-distortion/ Equalization Techniques for Non-linear Satellite Channels
Piazza, Roberto UL; Shankar, Bhavani UL; Zenteno, Efrain et al

in Proceedings of 31st AIAA International Communications Satellite Systems Conference (ICSSC), (2013)

On-board joint power amplification of multiple-carrier DVB-S2 signals using a single High-Power Amplifier (HPA) is an emerging configuration that aims to reduce flight hardware and weight. However ... [more ▼]

On-board joint power amplification of multiple-carrier DVB-S2 signals using a single High-Power Amplifier (HPA) is an emerging configuration that aims to reduce flight hardware and weight. However, effects specific to such a scenario degrade power and spectral efficiencies with increased Adjacent Channel Interference caused by non-linear characteristic of the HPA and power efficiency loss due to the increased Peak to Average Power Ratio (PAPR). The paper studies signal processing techniques that counteract for both aspects enabling efficient multicarrier on board amplification. Digital pre-distortion (DPD) at the gateway and equalization (EQ) at the User Terminal are the designed avenues of attack to mitigate the non-linear effects and improve power as well as spectral efficiencies. This paper builds on our initial work in Ref.1 that performed a survey on the adaptability of various compensation techniques to the considered scenario and short-listed the most favourable ones. Preliminary performance analysis of these techniques was undertaken with Signal to Interference Ratio (SINR) as the figure of merit. The contribution of this work over Ref. 1 includes : (a) a full DVB-S2 chain is simulated with the chosen techniques with Total Degradation (TD) as the figure of merit and (b) a sensitivity analysis is performed to study the dependence of the pre-distortion/ equalization performance ( measured as TD) on the channel parameters. [less ▲]

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See detailLarge scale transmit diversity in Q/V band feeder link with multiple gateways
Gharanjik, Ahmad; Shankar, Bhavani UL; Arapoglou et al

in Personal Indoor and Mobile Radio Communications (PIMRC), 2013 IEEE 24th International Symposium on (2013)

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 ... [more ▼]

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. [less ▲]

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See detailSpace-Frequency Coding for Dual Polarized Hybrid Mobile Satellite Systems
Shankar, Bhavani UL; Arapoglou, Pantelis-Daniel UL; Ottersten, Björn UL

in IEEE Transactions on Wireless Communications (2012), 11(8), 2806-2814

An increasing number of hybrid mobile systems comprising a satellite and a terrestrial component are becoming standardized and realized. The next generation of these systems will employ higher dimensions ... [more ▼]

An increasing number of hybrid mobile systems comprising a satellite and a terrestrial component are becoming standardized and realized. The next generation of these systems will employ higher dimensions adopting multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) techniques. In this work, we build upon recent studies of dual polarization MIMO for each component and propose the use of full-rate full-diversity (FRFD) codes adopting a space-frequency paradigm. We also propose a scheme taking advantage of the separation between the subcarriers to enhance the coding gain. By critically assessing the different options for the 4 transmit, 2 receive hybrid scenario taking into account system and channel particularities, we demonstrate that the proposed scheme is a solution for enhancing the performance of next generation hybrid mobile satellite systems. [less ▲]

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See detailOperational Optimization of a Ku Multibeam Flexible Payload
Metzger, Nathalie; Morgues, Stephane; Morel, Coline et al

in Proceedings of 2nd ESA workshop on Advanced Flexible Telecom Payloads (2012, April)

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See detailPower allocation in Multibeam satellites - A hybrid-Genetic Algorithm approach
Aravanis, Alexis; Shankar, Bhavani UL; Danoy, Grégoire UL et al

in ESA Workshop on Advanced Flexible Telecom Payloads (2012)

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See detailMulticarrier Digital Pre-distortion/ Equalization Techniques for Non-linear Satellite Channels
Piazza, Roberto UL; Shankar, Bhavani UL; E, Zenteno et al

in Proceedings of 30th AIAA International Communications Satellite Systems Conference (ICSSC), (2012)

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See detailDetection of sparse random signals using compressive measurements
Shankar, Bhavani UL; Chatterjee, Saikat; Ottersten, Björn UL

in Acoustics, Speech and Signal Processing (ICASSP), 2012 IEEE International Conference on (2012)

We consider the problem of detecting a sparse random signal from the compressive measurements without reconstructing the signal. Using a subspace model for the sparse signal where the signal parameters ... [more ▼]

We consider the problem of detecting a sparse random signal from the compressive measurements without reconstructing the signal. Using a subspace model for the sparse signal where the signal parameters are drawn according to Gaussian law, we obtain the detector based on Neyman-Pearson criterion and analytically determine its operating characteristics when the signal covariance is known. These results are extended to situations where the covariance cannot be estimated. The results can be used to determine the number of measurements needed for a particular detector performance and also illustrate the presence of an optimal support for a given number of measurements. [less ▲]

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See detailMulti-objective Optimization Approach to Power Allocation in Multibeam Systems
Aravanis, Alexis; Shankar, Bhavani UL; Danoy, Grégoire UL et al

in Proceedings of 30th AIAA International Communications Satellite Systems Conference (ICSSC), (2012)

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See detailMIMO Extension to DVB-SH
Shankar, Bhavani UL; Kyrolainen, Jukka; Arapoglou, Pantelis-Daniel UL et al

in 30th AIAA International Communications Satellite Systems Conference (ICSSC) (2012)

DVB-SH is a hybrid satellite-terrestrial system combining a satellite component and a complementary ground component to provide service in all types of environments, i.e., outdoor and indoor coverage in ... [more ▼]

DVB-SH is a hybrid satellite-terrestrial system combining a satellite component and a complementary ground component to provide service in all types of environments, i.e., outdoor and indoor coverage in urban, sub-urban and rural. This paper reports the studies on multiple-input multiple-output (MIMO) extension to the existing DVB-SH standard. MIMO techniques are considered in this paper for achieving increased spectral efficiency and reliability in the challenging satellite and hybrid channel environments [less ▲]

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See detailGolden Codes for Dual Polarized MIMO-OFDM Transmissions in Hybrid Satellite/Terrestrial Mobile Systems
Shankar, Bhavani UL; Arapoglou, Pantelis-Daniel UL; Ottersten, Björn UL

in Communications (ICC), 2011 IEEE International Conference on (2011)

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 ... [more ▼]

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. [less ▲]

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See detailConvergence of the Iterative Water-filling algorithm with Sequential Updates in Spectrum Sharing Scenarios
Shankar, Bhavani UL; von Wrycza, Peter; Bengtsson, Mats et al

in Communication Technologies Workshop (Swe-CTW), 2011 IEEE Swedish (2011)

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 ... [more ▼]

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. [less ▲]

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See detailOn the Diversity and Complexity of Zero Forcing Receivers for MIMO Zero Padded Systems
Shankar, Bhavani UL; K V S, Hari

in Proceedings of 2010 International Conference on Signal Processing and Communications (SPCOM), (2010)

Zero padded systems with linear receivers are shown to be robust and amenable to fast implementations in single antenna scenarios. In this paper, properties of such systems are investigated when multiple ... [more ▼]

Zero padded systems with linear receivers are shown to be robust and amenable to fast implementations in single antenna scenarios. In this paper, properties of such systems are investigated when multiple antennas are present at both ends of the communication link. In particular, their diversity and complexity are evaluated for precoded transmissions. The linear receivers are shown to exploit multipath and receive diversities, even in the absence of any coding at the transmitter. Use of additional redundancy to improve performance is considered and the effect of transmission rate on diversity order is analyzed. Low complexity implementations of Zero Forcing receivers are devised to further enhance their applicability. [less ▲]

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See detailSystematic Construction of Linear Transform based Full Diversity, Rate One Space-Time-Frequency Codes
Shankar, Bhavani UL; Hari, K. V. S.

in IEEE Transactions on Signal Processing (2009), 57(6), 2285-2298

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 ... [more ▼]

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. [less ▲]

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See detailConvergence of the Iterative Water-Filling Algorithm in Multiple User Spectrum Sharing Scenarios
Shankar, Bhavani UL; von Wrycza, Peter; Bengtsson, Mats et al

in Communication Technologies Workshop (Swe-CTW), 2011 IEEE Swedish (2009)

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 ... [more ▼]

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. [less ▲]

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See detailSpectrum Allocation for Decentralized Transmission Strategies: Properties of Nash Equilibria
von Wrycza, Peter; Shankar, Bhavani UL; Bengtsson, Mats et al

in EURASIP Journal on Advances in Signal Processing (2009)

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See detailA Game Theoretic Approach to Multi-User Spectrum Allocation
von Wrycza, Peter; Shankar, Bhavani UL; Bengtsson, Mats et al

in A Game Theoretic Approach to Multi-User Spectrum Allocation (2009)

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See detailOn the Variations in Mutual Information of MIMO Communication Systems Due to Perturbed Channel State Information at Transmitter
Shankar, Bhavani UL; Hari, K. V. S.

in IEEE Transactions on Communications (2006), 54(9), 1593-1603

In this paper, we address the issue of perturbed information at the transmitter in a multiple-input multiple-output (MIMO) system. Two schemes, correlation matrix feedback and channel information feedback ... [more ▼]

In this paper, we address the issue of perturbed information at the transmitter in a multiple-input multiple-output (MIMO) system. Two schemes, correlation matrix feedback and channel information feedback, are proposed to convey information necessary for achieving capacity to the transmitter. This information is perturbed due to various impairments. A perturbation analysis is carried out to study the variations in mutual information for each of the proposed schemes. For ergodic channels, this analysis is used to design a MIMO system with a limited rate feedback. Using a codebook-based approach, vector quantizers are designed to minimize the loss in ergodic capacity for each of the proposed schemes, and their performance is studied. A non-codebook method, parameter-based feedback, is also presented, and the underlying rate-performance tradeoff is highlighted [less ▲]

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See detailReduced Complexity Equalization schemes for Zero Padded OFDM Systems
Shankar, Bhavani UL; Hari, K. V. S.

in IEEE Signal Processing Letters (2004), 11(9), 752-755

Three reduced complexity equalization schemes for Zero-padded OFDM systems are described. These schemes guarantee Zero-Forcing (ZF) equalization irrespective of the channel s. Two of these schemes ... [more ▼]

Three reduced complexity equalization schemes for Zero-padded OFDM systems are described. These schemes guarantee Zero-Forcing (ZF) equalization irrespective of the channel s. Two of these schemes implement the minimum-norm ZF equalizer efficiently using QR decomposition. In the third scheme, the channel zeros are grouped as being inside or outside or on the unit circle. These groups are then equalized sequentially in a manner so as to tackle excess noise amplification. The three schemes are compared for their computational complexity and Bit Error Rate (BER) performance. It is shown that the attractive scheme depends on the system specifications. The BERComputations trade off occurring in the choice of the right algorithm is also highlighted. [less ▲]

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See detailAllpass Delay Chain-Based IIR PR Filterbank and Its Application to Multiple Description Subband Coding
Shankar, Bhavani UL; Makur, Anamitra

in IEEE Transactions on Signal Processing (2002), (4), 814-823

A class of infinite impulse response (IIR) perfect reconstruction (PR) filterbank is obtained with an allpass delay chain and finite impulse response (FIR) matrices at the analysis side. Such a ... [more ▼]

A class of infinite impulse response (IIR) perfect reconstruction (PR) filterbank is obtained with an allpass delay chain and finite impulse response (FIR) matrices at the analysis side. Such a formulation leads to a filterbank that can be optimized to any desired response. For a first-order allpass, the synthesis bank becomes FIR. Design examples showing warping of the frequency scale and filters with unequal passband widths are presented. The latter part of the work deals with designing a filterbank for a multiple description coding scenario. This is achieved in two parts: by obtaining the MMSE synthesis bank for a given analysis bank and channel state and by optimizing the analysis response to minimize the average distortion in the presence of channel erasures and quantization. The proposed IIR filterbank, as well as the well-known FIR paraunitary filterbank, are optimized for various channels, and their performances for the two-channel case have been compared with the derived optimal performance [less ▲]

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See detailOn the Variations in Capacity of MIMO Communication Systems to Channel Perturbations
Shankar, Bhavani UL; Hari, K. V. S.

in Proceedings of IEEE ICPWC (2002)

It is known that the capacity of a multi-antenna flat non-fading Gaussian channels (MIMO capacity) can be improved if the transmitter has perfect knowledge of channel. The channel information affects the ... [more ▼]

It is known that the capacity of a multi-antenna flat non-fading Gaussian channels (MIMO capacity) can be improved if the transmitter has perfect knowledge of channel. The channel information affects the input allocation and hence there is capacity degradation when the transmitter does not know the channel perfectly. In this work variation in MIMO capacity due to small perturbations that do not change the rank of the channel is studied. The need for the analysis is highlighted by the fact that at high SNR, most channel estimation algorithms give small errors. Expressions and bounds for capacity are derived using first order perturbation analysis. Further to this, the dependence of capacity on the channel parameters and total power is studied. It is shown that the upper bound on degradation in capacity for small errors varies as the square of the spectral norm of perturbation. Further the degradation has an approximate inverse square relation with total power used and channel singular values. These results are extended to a general class of communication systems and results for MIMO-OFDM systems over frequency selective channels are presented. [less ▲]

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