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See detailCoverage Extension via Side-Lobe Transmission in Multibeam Satellite System
Gharanjik, Ahmad UL; Kmieciak, Jarek; Shankar, Bhavani UL et al

in 23rd Ka and Broadband Communications Conference (2017, October 16)

In this paper, we study feasibility of coverage extension of a multibeam satellite network by providing low-rate communications to terminals located outside the coverage of main beams. Focusing on the MEO ... [more ▼]

In this paper, we study feasibility of coverage extension of a multibeam satellite network by providing low-rate communications to terminals located outside the coverage of main beams. Focusing on the MEO satellite network, and using realistic link budgets from O3b networks, we investigate the performance of both forward and return-links for terminals stationed in the side lobes of the main beams. Particularly, multi-carrier transmission for forward-link and single carrier transmission for return-link are examined and the resulting coverage and data rate for different setups are evaluated. Simulation results verifies that side-lobe transmission can extend the coverage area and provide considerable data rate, thereby providing a solution for enhancing capacity of existing networks. [less ▲]

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See detailOptical Feeder Links Study towards Future Generation MEO VHTS Systems
Mengali, Alberto UL; Lyras, Nikos K.; Shankar, Bhavani UL et al

in Proceedings of the 35th AIAA International Communications Satellite Systems Conference (ICSSC) (2017, October)

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See detailRandom Phase Center Motion Technique for Enhanced Angle-Doppler Discrimination Using MIMO Radars
Hammes, Christian UL; Shankar, Bhavani UL; Nijsure, Yogesh UL et al

in European Signal Processing Conference (EUSIPCO) 2017 (2017, August)

A random Phase Center Motion (PCM) technique is presented in this paper, based on Frequency Modulated Continuous Wave (FMCW) radar, in order to suppress the angle- Doppler coupling in Time Division ... [more ▼]

A random Phase Center Motion (PCM) technique is presented in this paper, based on Frequency Modulated Continuous Wave (FMCW) radar, in order to suppress the angle- Doppler coupling in Time Division Multiplex (TDM) Multiple- Input-Multiple-Output (MIMO) radar when employing sparse array structures. The presented approach exploits an apparently moving transmit platform or PCM due to spatio-temporal transmit array modulation. In particular, the work considers a framework utilizing a random PCM trajectory. The statistical characterization of the random PCM trajectory is devised, such that the PCM and the target motion coupling is minimal, while the angular resolution is increased by enabling the virtual MIMO concept. In more details, this paper discusses sidelobe suppression approaches within the angle-Doppler Ambiguity Function (AF) by introducing a phase center probability density function within the array. This allows for enhanced discrimination of multiple targets. Simulation results demonstrate the suppression angle- Doppler coupling by more than 30 dB, even though spatiotemporal transmit array modulation is done across chirps which leads usually to strong angle-Doppler coupling. [less ▲]

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See detailDiscrimination of Angle-Doppler Signatures using Arbitrary Phase Center Motion for MIMO Radars
Hammes, Christian UL; Nijsure, Yogesh UL; Shankar, Bhavani UL et al

in IEEE Radar Conf 2017 (2017, May)

A novel Phase Center Motion (PCM) based technique for discriminating angle-Doppler signatures within Multiple-Input-Multiple-Output (MIMO) radars using Frequency Modulated Continuous Wave (FMCW) has been ... [more ▼]

A novel Phase Center Motion (PCM) based technique for discriminating angle-Doppler signatures within Multiple-Input-Multiple-Output (MIMO) radars using Frequency Modulated Continuous Wave (FMCW) has been explored in this work. The PCM technique induces angle dependent Doppler shifts in the back-scattered signal, wherein a modified Doppler post processing for FMCW leads to joint angle-Doppler processing. Specifically, we intend to design unique spatialtemporal motion of the phase center on each individual MIMO radar channel in an effort to synthesize nearly orthogonal angle-Doppler signatures. Subsequently, we also develop a MIMO radar receiver design, which would be capable of discriminating between these induced angle-Doppler signatures. The asymptotic investigation provides a Bessel function characteristic. Simulation results demonstrate a significant side-lobe suppression of 8:5 dB for an individual PCM trajectory and 7 dB over distinct PCM trajectories, in an attempt towards realization of nearly orthogonal MIMO radar channels. [less ▲]

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See detailMax-min transmit beamforming via iterative regularization
Gharanjik, Ahmad UL; Shankar, Bhavani UL; Soltanalian, Mojtaba et al

in 50th Asilomar Conference on Signals, Systems and Computers, November 2016 (2016, November)

This paper introduces an iterative optimization framework to tackle the multi-group multicast Max-Min transmit beamforming problem. In each iteration, the optimization problem is decomposed into four sub ... [more ▼]

This paper introduces an iterative optimization framework to tackle the multi-group multicast Max-Min transmit beamforming problem. In each iteration, the optimization problem is decomposed into four sub-problems, all of which can be solved using computationally efficient algorithms. The advantage of proposed method lies in its ability to handle different types of signal constraints like total power and unimodularity; a feature not exhibited by other techniques. The proposed technique outperforms the well-known semidefinite relaxation method in terms of quality of solutions [less ▲]

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See detailReturn Link Optimized Resource Allocation for Satellite Communications in the Ku/Ka-Band
Pranjic, Vanja; Mazzali, Nicolò UL; Emiliani, Luis et al

in Proceedings on the 22nd Ka and Broadband Communications Conference and the 34th AIAA International Communications Satellite Systems Conference (ICSSC) (2016, October)

Broadband satellite networks play an important role in today’s worldwide telecommunication infrastructure, providing services to an increasing number of users. Therefore, an efficient management of the ... [more ▼]

Broadband satellite networks play an important role in today’s worldwide telecommunication infrastructure, providing services to an increasing number of users. Therefore, an efficient management of the spectrum resources is required in order to meet the fast-growing service demand. To this purpose, this paper addresses the optimization of the return carrier frequency plan for a broadband network benefiting from adaptive return channel selection (ARCS). The optimization problem is formulated as a multiobjective instance aiming at minimizing the total bandwidth and the unused throughput by using integer linear programming techniques. So as to capture events in which multiple terminals experience fade simultaneously, the spatial correlation of the attenuation fields has been incorporated in the optimization process. Moreover, physical layer characteristics and a minimum guaranteed throughput per user have been included as optimization constraints. Hence, the final outcome of this paper is a general technique providing an optimized carrier allocation plan, i.e., the number of carriers required to cover a certain area and guarantee a given throughput to each user. [less ▲]

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See detailLow Complexity Transmit Processing for Multibeam Satellite Systems with Non-Linear Channels
Mengali, Alberto UL; Kayhan, Farbod UL; Shankar, Bhavani UL et al

in Proceedings of ASMS Conference (2016, September)

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See detailAn Iterative Approach to Nonconvex QCQP with Applications in Signal Processing
Gharanjik, Ahmad UL; Shankar, Bhavani UL; Soltanalian, Mojtaba et al

in 2016 IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM) (2016, July 10)

This paper introduces a new iterative approach to solve or to approximate the solutions of the nonconvex quadratically constrained quadratic programs (QCQP). First, this constrained problem is transformed ... [more ▼]

This paper introduces a new iterative approach to solve or to approximate the solutions of the nonconvex quadratically constrained quadratic programs (QCQP). First, this constrained problem is transformed to an unconstrained problem using a specialized penalty-based method. A tight upper-bound for the alternative unconstrained objective is introduced. Then an efficient minimization approach to the alternative unconstrained objective is proposed and further studied. The proposed approach involves power iterations and minimization of a convex scalar function in each iteration, which are computationally fast. The important design problem of multigroup multicast beamforming is formulated as a nonconvex QCQP and solved using the proposed method. [less ▲]

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See detailFour-Dimensional Constellations for Dual-Polarized Satellite Communications
Mazzali, Nicolò UL; Kayhan, Farbod UL; Shankar, Bhavani UL

in Proceedings on IEEE International Conference on Communications (2016, May)

In this paper, we investigate the performance of constellations optimized for transmissions in dual-polar mobile satellite applications. These four-dimensional constellations (inphase and quadrature per ... [more ▼]

In this paper, we investigate the performance of constellations optimized for transmissions in dual-polar mobile satellite applications. These four-dimensional constellations (inphase and quadrature per polarization) are designed for joint transmission over the two polarizations. Such constellations enhance the reliability of the system by providing certain redundancy into their design. Their performance is compared with transmission of independent 2D constellations over each polarization. As performance metrics, the pragmatic achievable mutual information and the bit error rate have been considered. The gains serve to indicate the need to further investigate 4D constellation design and its application in dual-polar MIMO systems. [less ▲]

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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 detailGEO Satellite Feeder links and Terrestrial Full-Duplex Small Cells: A case for Coexistence
Shankar, Bhavani UL; Maleki, Sina UL; Zheng, Gan et al

in Proceedings of 83rd IEEE VTC (Spring 2016) (2016, May)

The demand for wider bandwidths has motivated the need for wireless systems to migrate to higher frequency bands. In line with this trend is an envisaged deployment of Ka-band (or mmWave) cellular ... [more ▼]

The demand for wider bandwidths has motivated the need for wireless systems to migrate to higher frequency bands. In line with this trend is an envisaged deployment of Ka-band (or mmWave) cellular infrastructure. Further, to improve the spectral efficiency, developing full-duplex radio transceivers is gaining momentum. In view of this move, the paper proposes the possibility of reusing the satellite feeder uplink band in the full-duplex small cells. The motivation for such a reuse is two-fold :(a) there is virtually no interference from the small cells to the incumbent in-orbit satellite receiver, and (b) directive feeder antennas, with possibly additional isolation and processing causing negligible interference to the small cells. The presented interference analysis clearly supports the proposed coexistence. [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 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 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 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 ▲]

Detailed reference viewed: 78 (1 UL)