References of "Shankar, Bhavani 50002712"
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See detailJoint Predistortion and PAPR Reduction in Multibeam Satellite Systems
Mengali, Alberto UL; Shankar, Bhavani UL; Ottersten, Björn UL

in Proceedings of IEEE ICC 2016 (2016, May)

Precoding for multibeam satellites with aggressive frequency reuse has attracted interest of late towards enhancing system capacity. Most of the works on precoding mitigate the linear co-channel ... [more ▼]

Precoding for multibeam satellites with aggressive frequency reuse has attracted interest of late towards enhancing system capacity. Most of the works on precoding mitigate the linear co-channel interference between the beams caused by frequency reuse. How- ever, the high power amplifier (HPA), an integral part of the satellite payload, is inherently non linear. Non-linear amplification combined with the linear co-channel interference introduces non- linear co-channel distortions at the receiver. Further, signals with very high peak to average power ratios (PAPR), typical of spectrally efficient modulations, are sensitive to the non-linear characteristic of the HPA and necessitate large back-off to have manageable distortion levels. In this work, a novel architecture comprising multistream Crest Factor Reduction (signal pre-clipping) and Signal Predistortion (SPD) in cascade, is devised to counter the non- linearities and co-channel interference in multibeam satellite sys- tems. An iterative algorithm to optimize the parameters of the signal clipping and predistortion is devised taking recourse to analytical derivations. The proposed joint estimation paradigm is shown to compare favorably with state-of-art and provides a framework to combine predistortion and precoding. [less ▲]

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See detailGrab-n-Pull: An Optimization Framework for Fairness-Achieving Networks
Soltanalian, Mojtaba UL; Gharanjik, Ahmad UL; Shankar, Bhavani UL et al

in IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) 2016 (2016, March 20)

In this paper, we present an optimization framework for designing precoding (a.k.a. beamforming) signals that are instrumental in achieving a fair user performance through the networks. The precoding ... [more ▼]

In this paper, we present an optimization framework for designing precoding (a.k.a. beamforming) signals that are instrumental in achieving a fair user performance through the networks. The precoding design problem in such scenarios can typically be formulated as a non-convex max-min fractional quadratic program. Using a penalized version of the original design problem, we derive a simplified quadratic reformulation of the problem in terms of the signal (to be designed). Each iteration of the proposed design framework consists of a combination of power method-like iterations and the Gram-Schmidt process, and as a result, enjoys a low computational cost. Moreover, the suggested approach can handle various types of signal constraints such as total-power, per-antenna power, unimodularity, or discrete-phase requirements—an advantage which is not shared by other existing approaches in the literature. [less ▲]

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See detailCooperative Estimation of Power and Direction of Transmission for a Directive Source
Maleki, Sina UL; Ciblat, Philippe; Chatzinotas, Symeon UL et al

in IEEE Transactions on Cognitive Communications and Networking (2016)

Reliable spectrum cartography of directive sources depends on an accurate estimation of the direction of transmission (DoT) as well as the transmission power. Joint estimation of power and DoT of a ... [more ▼]

Reliable spectrum cartography of directive sources depends on an accurate estimation of the direction of transmission (DoT) as well as the transmission power. Joint estimation of power and DoT of a directive source using ML estimation techniques is considered in this paper. We further analyze the parametric identifiability conditions of the problem, develop the estimation algorithm, and derive the Cramer-Rao-Bound (CRB) for the two situations: a) where the source signal is known to the sensors, and b) where the sensors are not aware of the source signal but its distribution. Particularly, we devise a specific sensor placement/selection setup for the symmetric antenna patterned sources which leads to identifiability of the problem. Finally, numerical results verifies the efficiency and accuracy of the provided estimation algorithms in this paper. [less ▲]

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See detailPower and Direction of Transmission Estimation for a Directive Source: Identifiability Analysis and Estimation Algorithm
Maleki, Sina UL; Ciblat, Philippe; Shankar, Bhavani UL et al

in 2016 IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM) (2016)

Reliable spectrum cartography of directive sources depends on an accurate estimation of the direction of transmission (DoT) as well as the transmission power. Joint estimation of power and DoT of a ... [more ▼]

Reliable spectrum cartography of directive sources depends on an accurate estimation of the direction of transmission (DoT) as well as the transmission power. Joint estimation of power and DoT of a directive source using ML estimation techniques is considered in this paper. We further analyze the parametric identifiability conditions of the problem, develop the estimation algorithm, and derive the Cramer-Rao-Bound (CRB). [less ▲]

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See detailMulti-gateway Data Predistortion for Non-linear Satellite Channels
Piazza, Roberto UL; Shankar, Bhavani UL; Ottersten, Björn UL

in IEEE Transactions on Communications (2015), 63(10), 3789-3802

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See detailPrecoding Design and User Selection for Multibeam Satellite Channels
Gharanjik, Ahmad UL; Shankar, Bhavani UL; Arapoglou, Pantelis-Daniel UL et al

in 16th IEEE International Workshop on Signal Processing Advances in Wireless Communications, SPAWC 2015 (2015, June 28)

Precoding for the downlink of a multibeam satellite system has been recently shown, under ideal conditions, to be promising technique towards employing aggressive frequency reuse gainfully. However, time ... [more ▼]

Precoding for the downlink of a multibeam satellite system has been recently shown, under ideal conditions, to be promising technique towards employing aggressive frequency reuse gainfully. However, time varying phase uncertainties imposed by the components and the channel, combined with delayed feedback perturbs the channel state information at the transmitter (CSIT). In this paper, we consider a power constrained robust formulation of the downlink precoding problem to counter the phase uncertainties. In particular it considers imposing conditions on the average signal to interference plus noise ratio (SINR), to deal with imperfect CSIT. In addition to the robust formulation, the primacy of user selection is highlighted and a new approach exploiting the satellite system design is proposed. Performance of the derived robust precoder in conjunction with the proposed location based user selection is then evaluated and the gains are tabulated. [less ▲]

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See detailOn-board Signal Predistortion for Digital Transparent Satellites
Mazzali, Nicolò UL; Shankar, Bhavani UL; Ottersten, Björn UL

in Proceedings on IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC) (2015, June)

On-board processing (OBP), a paradigm that allows for manipulation of the signal at the satellite transponder, is being embraced by a large section of the satellite community. Exploiting OBP can lead to ... [more ▼]

On-board processing (OBP), a paradigm that allows for manipulation of the signal at the satellite transponder, is being embraced by a large section of the satellite community. Exploiting OBP can lead to efficient implementation, bandwidth saving, lower redundancy, and better performance. Enabling processing aboard a satellite necessitates re-assessing the implementation of a number of signal processing techniques which, so far, have been ground-centric. In this work, we investigate the possibility of implementing signal predistortion (SPD) aboard a satellite having digital transparent processor (DTP). Such satellites employ transponders that allow for the implementation of limited functionalities in the digital domain. On-board predistortion can then be performed on the digitized data and can provide better performance compared to on-ground techniques. However, the conversion to the digital domain performed by an analog-to-digital converter (ADC) introduces different types of noise. Among these, the clock jitter requires the implementation of estimation and compensation algorithms. In this paper we propose a reduced-complexity on-board signal predistortion algorithm capable of post-compensating the jitter introduced by the ADC, and pre-compensating the distortion generated by the amplifier. [less ▲]

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See detailRobust Precoding Design for Multibeam Downlink Satellite Channel with Phase Uncertainty
Gharanjik, Ahmad UL; Shankar, Bhavani UL; Arapoglou, Pantelis-Daniel UL et al

in 40th IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) 2015 (2015, April 19)

In this work, we study the design of a precoder on the user downlink of a multibeam satellite channel. The variations in channel due to phase noise introduced by on-board oscillators and the long round ... [more ▼]

In this work, we study the design of a precoder on the user downlink of a multibeam satellite channel. The variations in channel due to phase noise introduced by on-board oscillators and the long round trip delay result in outdated channel information at the transmitter. The phase uncertainty is modelled and a robust design framework is formulated based on availability and power constraints. The optimization problem is cast into the convex paradigm after approximations and the benefits of the resulting precoder are highlighted. [less ▲]

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See detailGeneralized Direct Predistortion With Adaptive Crest Factor Reduction Control
Piazza, Roberto; Shankar, Bhavani UL; Ottersten, Björn UL

in Proceedings of 40th IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) 2015 (2015, April)

Efficient power amplification is inherently a non linear operation that introduces unwanted interference in the amplified signal. Strong inter-symbol interference is generated when the amplifier non ... [more ▼]

Efficient power amplification is inherently a non linear operation that introduces unwanted interference in the amplified signal. Strong inter-symbol interference is generated when the amplifier non linearity is combined with channel memory effects. Further, signals with very high peak to average power ratio, typical of multiple carrier systems, are even more sensitive to the non linearities resulting in severe distortion effects. Signal pre-clipping (crest factor reduction) and predistortion are conventional countermeasure techniques to reduce the generated non linear distortion and improve power and spectral efficiency. In this work, novel optimization methods for predistortion and pre-clipping are analytically derived for a general non-linear communication channel with memory. A combined architecture in which crest factor reduction is followed by signal predistortion is proposed and the parameters are estimated resorting to iterative algorithms based on least squares method. Performance evaluation of the estimation techniques shows the effectiveness of the derived algorithms and significant gain compared to previously known methods. [less ▲]

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See detailLow Complexity Predistortion and Equalization in Nonlinear Multicarrier Satellite Communications
Zenteno, Efrain; Piazza, Roberto UL; Shankar, Bhavani UL et al

in EURASIP Journal on Advances in Signal Processing (2015)

Aiming to reduce the power/mass requirements in satellite transponders and to reduce mission costs, joint amplification of multiple carriers using a single high-power amplifier (HPA) is being considered ... [more ▼]

Aiming to reduce the power/mass requirements in satellite transponders and to reduce mission costs, joint amplification of multiple carriers using a single high-power amplifier (HPA) is being considered. In this scenario, a careful investigation of the resulting power efficiency is essential as amplification is nonlinear, and multicarrier signals exhibit enlarged peak-to-average power ratio. Thus, operating the amplifier close to saturation vastly increases signal distortion resulting in a severe degradation of performance, especially for higher order modulations. This paper proposes a reduced-complexity digital predistortion (DPD) scheme at the transmitter and a corresponding equalizer (EQ) at the receiver to mitigate these nonlinear effects. Scenarios include both the forward as well as the return links. In particular, the paper exploits the MIMO Volterra representation and builds on a basis pursuit approach using a LASSO (least absolute shrinkage and selection operator) algorithm to achieve an efficient basis representation, avoiding large computational complexity, to describe the selection of predistorter/equalizer model. The work further compares and contrasts the two mitigation techniques taking various system aspects into consideration. The gains in performance and amplification efficiency demonstrated by the use of DPD/ EQ motivate their inclusion in next-generation satellite systems. [less ▲]

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See detailPerformance Analysis of Noncoherent Frame Synchronization in Satellite Communications with Frequency Uncertainty
Mazzali, Nicolò UL; Stante, Giulio; Shankar, Bhavani UL et al

in Proceedings on IEEE Symposium on Communications and Vehicular Technology in the Benelux (2015)

Emerging markets for satellite communications, such as maritime and aeronautical applications, require reliable communications in challenging conditions and low-cost, low-complexity user terminals. In ... [more ▼]

Emerging markets for satellite communications, such as maritime and aeronautical applications, require reliable communications in challenging conditions and low-cost, low-complexity user terminals. In this perspective, the synchronization chain is a fundamental part of the receiver and its design becomes critical. When a quadricorrelator is used as first stage of the synchronization chain so as to perform a coarse frequency estimation, then a noncoherent algorithm for frame synchronization can be employed as second stage. A popular algorithm for frame synchronization is the post-detection integration (PDI), whose noncoherent version (NCPDI) is quite robust to non-negligible residual frequency offsets. In this paper we will assess the performance of NCPDI in presence of a random uniformly-distributed residual frequency offset and will find a closed-form approximation for the probability of detection. Moreover, we will optimize the design parameters of NCPDI for a system operating at very low signal-to-noise ratio (VL-SNR) by minimizing the probability of missed detection for a given probability of false alarm. [less ▲]

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See detailPushing for higher rates and efficiency in Satcom: the different perspectives within SatNExIV
Vazquez, Miguel-Angel; Neira, Ana-Perez; Mosquera, Carlos et al

in Proceedings of the 11th International Symposium on Wireless Communication Systems (ISWCS 2015) (2015)

SatNEx IV project aims at studying medium and long term directions of satellite telecommunication systems for any of the commercial or institutional applications that can be considered appealing by key ... [more ▼]

SatNEx IV project aims at studying medium and long term directions of satellite telecommunication systems for any of the commercial or institutional applications that can be considered appealing by key players although still not mature enough for attracting industry or initiating dedicated ESA R&D activities. This paper summarizes the first year activities identified as very promising techniques for next generation satellite communication systems. Concretely, very high throughput satellite trunking, physical layer advances for fullduplex and multipolarization systems, network coding applications and multiple access schemes for information centric networking are briefly presented. For all the activities, we identify the scenarios under study so as the preliminary technical solutions to be further investigated. [less ▲]

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See detailPower Allocation in Multibeam Satellite Systems: A Two-Stage Multi-Objective Optimization
Aravanis, Alexis; Shankar, Bhavani UL; Arapoglou, Pantelis-Daniel et al

in IEEE Transactions on Wireless Communications (2015)

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See detailMultiple Gateway Transmit Diversity in Q/V Band Feeder Links
Gharanjik, Ahmad UL; Shankar, Bhavani UL; Arapoglou, Pantelis-Daniel et al

in IEEE Transactions on Communications (2015)

Design of high bandwidth and reliable feeder links is central towards provisioning new services on the user link of a multibeam satellite communication (SatCom) system. Towards this, utilization of the Q ... [more ▼]

Design of high bandwidth and reliable feeder links is central towards provisioning new services on the user link of a multibeam satellite communication (SatCom) system. Towards this, utilization of the Q/V band and an exploitation of multiple gateways (GW) as a transmit diversity measure for overcoming severe propagation effects are being considered. In this context, this contribution deals with the design of a feeder link comprising N + P GWs (N active and P redundant GWs). Towards provisioning the desired availability, a novel switching scheme is analysed and practical aspects such as prediction based switching and switching rate are discussed. Unlike most relevant works, a dynamic rain attenuation model is used to derive analytically average outage probability in the fundamental 1 + 1 gateway case. Building on this result, an analysis for the N +P scenario leading to a quantification of the end􀀀to􀀀end performance is provided. This analysis aids system sizing by illustrating the interplay between the number of active and redundant gateways on the chosen metrics : average outage and average switching rate. [less ▲]

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See detailFeasibility Study of Full-duplex Relaying in Satellite Networks
Shankar, Bhavani UL; Zheng, Gan; Maleki, Sina UL et al

in The 16th IEEE International Workshop on Signal Processing Advances in Wireless Communications, SPAWC 2015 (2015)

With the successful implementation of full-duplex radio prototypes, traditional orthogonal half-duplex communications is deemed to be inefficient in certain terrestrial applications. While full-duplex ... [more ▼]

With the successful implementation of full-duplex radio prototypes, traditional orthogonal half-duplex communications is deemed to be inefficient in certain terrestrial applications. While full-duplex techniques are gaining interest in terrestrial communications, thanks to the trend of short-distance and low-power transmissions, their application to satellite communications has drawn little attention. Motivated by this, the paper explores the use of the full-duplex relaying operation on-board the satellite in a DVB-S2 compliant network. Self-interference, whose management is the key component of a full-duplex communication, is the focus of study in this paper. Modelling the effects of self-interference and power amplifier nonlinearities on the quality of the received signal in undertaken. Subsequently, closed-form expressions for the various interference components are derived. The numerical evaluations of derived expressions rely on realistic link budgets and indicate substantial gains in spectral efficiency when self-interference can be well calibrated and measured. This confirms that the satellite full-duplex communications could be a promising solution for the efficient use of satellite spectrum, at least from a technical point of view. [less ▲]

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See detailConstellation Design in Four Dimensions under Average Power Constraint
Kayhan, Farbod UL; Mazzali, Nicolò UL; Shankar, Bhavani UL

in Proceedings on IEEE Symposium on Communications and Vehicular Technology in the Benelux (2015)

In this paper we address the problem of constellation design in four dimensional space (4D) under average power constraint. We compare the performance of best lattice constellations with those optimized ... [more ▼]

In this paper we address the problem of constellation design in four dimensional space (4D) under average power constraint. We compare the performance of best lattice constellations with those optimized without any constraint on their structure. Even though the lattice based constellations provide the best minimum distance, usually they do not allow for a good binary labelling. Therefore, in more realistic system scenarios, up to a 2 dB gain can be obtained by properly optimizing the constellation and the corresponding binary labelling. We also investigate the performance of 4D constellations obtained by the Cartesian product of two 2D constellations. [less ▲]

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See detailA MIMO Symbol Rate Signal Digital Predistorter for Nonlinear Multicarrier Satellite Channels
Zenteno, Efrain; Piazza, Roberto UL; Shankar, Bhavani UL et al

in IET Communications (2015), 9(15), 20532059

A digital predistortion (DPD) scheme is presented for non-linear distortion mitigation in multi-carrier satellite communication channels. The proposed DPD has a multiple-input multiple-output architecture ... [more ▼]

A digital predistortion (DPD) scheme is presented for non-linear distortion mitigation in multi-carrier satellite communication channels. The proposed DPD has a multiple-input multiple-output architecture similar to data DPD schemes. However, it enhances the mitigation performance of data DPDs using a multi-rate processing algorithm to achieve spectrum broadening of non-linear operators. Compared to single carrier (single-input single-output) signal (waveform) DPD schemes, the proposed DPD has lower digital processing rate reducing the required hardware cost of the predistorter. The proposed DPD outperforms, in total degradation, both data and signal DPD schemes. Further, it performs closest to a channel bound described by an ideally mitigated channel with limited maximum output power. [less ▲]

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See detailSpatial Multiplexing in Optical Feeder Links for High Throughput Satellites
Gharanjik, Ahmad UL; Liolis, Konstantinos; Shankar, Bhavani UL et al

in Spatial Multiplexing in Optical Feeder Links for High Throughput Satellites (2014, December 02)

Optical feeder links are an attractive alternative to the RF feeder links in satellite communications (SatCom). In this paper, we present initial results from an optical feeder link study. We discuss the ... [more ▼]

Optical feeder links are an attractive alternative to the RF feeder links in satellite communications (SatCom). In this paper, we present initial results from an optical feeder link study. We discuss the architecture of a geostationary earth orbit (GEO) satellite system based on optical feeder links. To mitigate the effects of cloud coverage, which is the main availability-limiting factor, Optical Ground Station (OGS) diversity is employed. Moreover, a spatial multiplexing scheme is considered. Assuming an ON-OFF channel model, the number of required OGSs to ensure availability and throughput requirements is analyzed [less ▲]

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See detailData Predistortion for Multicarrier Satellite Channels Based on Direct Learning
Piazza, Roberto UL; Shankar, Bhavani UL; Ottersten, Björn UL

in IEEE Transactions on Signal Processing (2014), 62(22),

Satellite communication is facing the urgent need of improving data rate and efficiency to compete with the quality of service offered by terrestrial communication systems. An imminent gain, achievable ... [more ▼]

Satellite communication is facing the urgent need of improving data rate and efficiency to compete with the quality of service offered by terrestrial communication systems. An imminent gain, achievable without the need of upgrading current satellite technology, can be obtained by exploiting multicarrier operation at the transponder and using highly efficient modulation schemes. However, on-board multicarrier joint amplification of high order modulation schemes is a critical operation as it brings severe non-linear distortion effects. These distortions increase as the on-board High Power Amplifier (HPA) is operated to yield higher power efficiencies. In this work, we propose novel techniques to implement on ground predistortion that enable multicarrier transmission of highly efficient modulation schemes over satellite channels without impacting infrastructure on the downlink. [less ▲]

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