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Publications (6 of 6) Show all publications
Gharanjik, A., Shankar, B., Soltanalian, M. & Ottersten, B. (2016). An iterative approach to nonconvex QCQP with applications in signal processing. In: Proceedings of the IEEE Sensor Array and Multichannel Signal Processing Workshop: . Paper presented at 2016 IEEE Sensor Array and Multichannel Signal Processing Workshop, SAM 2016, 10 July 2016 through 13 July 2016. IEEE
Open this publication in new window or tab >>An iterative approach to nonconvex QCQP with applications in signal processing
2016 (English)In: Proceedings of the IEEE Sensor Array and Multichannel Signal Processing Workshop, IEEE, 2016Conference paper, Published paper (Refereed)
Abstract [en]

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.

Place, publisher, year, edition, pages
IEEE, 2016
Keywords
Constraint theory, Iterative methods, Quadratic programming, Constrained problem, Design problems, Iterative approach, Multi-group, Quadratically-constrained quadratic programs, Scalar function, Unconstrained problems, Upper Bound, Signal processing
National Category
Signal Processing
Identifiers
urn:nbn:se:kth:diva-202884 (URN)10.1109/SAM.2016.7569622 (DOI)2-s2.0-84990829369 (Scopus ID)9781509021031 (ISBN)
Conference
2016 IEEE Sensor Array and Multichannel Signal Processing Workshop, SAM 2016, 10 July 2016 through 13 July 2016
Note

QC 20170310

Available from: 2017-03-10 Created: 2017-03-10 Last updated: 2017-03-10Bibliographically approved
Gharanjik, A. (2016). Transmission Optimization for High Throughput Satellite Systems. (Doctoral dissertation). Stockholm: KTH Royal Institute of Technology
Open this publication in new window or tab >>Transmission Optimization for High Throughput Satellite Systems
2016 (English)Doctoral thesis, monograph (Other academic)
Abstract [en]

Demands on broadband data service are increasing dramatically each year. Following terrestrial trends, satellite communication systems have moved from the traditional TV broadcasting to provide interactive broadband services even to urban users. While cellular and land-line networks are mainly designed to deliver broadband services to metropolitan and large urban centers, satellite based solutions have the advantage of covering these demands over a wide geography including rural and remote users. However, to stay competitive with economical terrestrial solutions, it is necessary to reduce the cost per transmitted bit by increasing the capacity of the satellite systems. The objective of this thesis is to design and develop techniques capable of enhancing the capacity of next generation high throughput satellite systems. Specifically, the thesis focuses on three main topics: 1) Q/V band feeder link design, 2) robust precoding design for multibeam satellite systems, and 3) developing techniques for tackling related optimization problems. Design of high bandwidth and reliable feeder links is central towards provisioning new services on the user link of a multibeam SatCom system. Towards this, utilization of the Q/V band and an exploitation of multiple gateway as a transmit diversity measure for overcoming severe propagation effects are being considered. In this context, the thesis deals with the design of a feeder link comprising $N+P$ gateways (N active and P redundant gateways). Towards satisfying the desired availability, a novel switching scheme is analysed and practical aspects such as prediction based switching and switching rate are discussed. Building on this result, an analysis for the N+P scenario leading to a quantification of the end-to-end performance is provided. On the other hand, frequency reuse in multibeam satellite systems along with precoding techniques can increase the capacity at the user link. Similar to terrestrial communication channels, satellite based communication channels are time-varying and for typical precoding applications, the transmitter needs to know the channel state information (CSI) of the downlink channel. Due to fluctuations of the phase components, the channel is time-varying resulting in outdated CSI at the transmitter because of the long round trip delay. This thesis studies a robust precoder design framework considering requirements on availability and average signal to interference and noise ratio (SINR). Probabilistic and expectation based approaches are used to formulate the design criteria which are solved using convex optimization tools. The performance of the resulting precoder is evaluated through extensive simulations. Although a satellite channel is considered, the presented analysis is valid for any vector channel with phase uncertainty.

In general, the precoder design problem can be cast as power minimization problem or max-min fairness problem depending on the objectives and requirements of design. The power minimization problem can typically be formulated as a non-convex quadratically constrained quadratic programming (QCQP) problem and the max-min fairness problem as a fractional quadratic program. These problems are known to be NP-hard in general. In this thesis, the original design problem is transformed to an unconstrained optimization problem using the specialized penalty terms. The efficient iterative optimization frameworks are proposed based on a separate optimization of the penalized objective function over its partition of variables at each iteration. Various aspects of the proposed approach including performance of the algorithm and its implementation complexity are studied.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. p. 145
Series
TRITA-EE, ISSN 1653-5146 ; 2016:058
National Category
Signal Processing
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-185506 (URN)978-91-7595-954-2 (ISBN)
Public defence
2016-05-13, B001, 4 rue alphonse weicker, L-2721, Luxembourg, 16:54 (English)
Opponent
Supervisors
Available from: 2016-04-21 Created: 2016-04-20 Last updated: 2016-05-13Bibliographically approved
Gharanjik, A., Shankar, B. M. R., Arapoglou, P.-D. & Ottersten, B. (2015). Multiple Gateway Transmit Diversity in Q/V Band Feeder Links. IEEE Transactions on Communications, 63(3), 916-926
Open this publication in new window or tab >>Multiple Gateway Transmit Diversity in Q/V Band Feeder Links
2015 (English)In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 63, no 3, p. 916-926Article in journal (Refereed) Published
Abstract [en]

Design of high bandwidth and reliable feeder links are central toward provisioning new services on the user link of a multibeam satellite communication system. Toward this, utilization of the Q/V band and an exploitation of multiple gateways (GWs) 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). Toward provisioning the desired availability, a novel switching scheme is analyzed 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 analytically derive average outage probability in the fundamental 1 + 1 GW 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 GWs on the chosen metrics: average outage and average switching rate.

National Category
Telecommunications
Identifiers
urn:nbn:se:kth:diva-164469 (URN)10.1109/TCOMM.2014.2385703 (DOI)000351507600027 ()2-s2.0-84925071135 (Scopus ID)
Note

QC 20150422

Available from: 2015-04-22 Created: 2015-04-17 Last updated: 2017-12-04Bibliographically approved
Gharanjik, A., Bhavani Shankar, M. R., Arapoglou, P.-D., Bengtsson, M. & Ottersten, B. (2015). Precoding design and user selection for multibeam satellite channels. In: IEEE Workshop on Signal Processing Advances in Wireless Communications, SPAWC: . Paper presented at 16th IEEE International Workshop on Signal Processing Advances in Wireless Communications, SPAWC 2015, 28 June 2015 through 1 July 2015 (pp. 420-424). IEEE conference proceedings
Open this publication in new window or tab >>Precoding design and user selection for multibeam satellite channels
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2015 (English)In: IEEE Workshop on Signal Processing Advances in Wireless Communications, SPAWC, IEEE conference proceedings, 2015, p. 420-424Conference paper, Published paper (Refereed)
Abstract [en]

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.

Place, publisher, year, edition, pages
IEEE conference proceedings, 2015
Keywords
Downlink, Feeds, Interference, Robustness, Satellites, Signal to noise ratio, Uncertainty, Channel state information, Communication satellites, Feedback, Feeding, Robustness (control systems), Signal interference, Signal processing, Spurious signal noise, Wave interference, Wireless telecommunication systems, Channel state information at the transmitters, Multi-beam satellite systems, Phase uncertainties, Robust formulations, Satellite system design, Signal to interference plus noise ratio
National Category
Signal Processing
Identifiers
urn:nbn:se:kth:diva-181184 (URN)10.1109/SPAWC.2015.7227072 (DOI)000380547100085 ()2-s2.0-84953391841 (Scopus ID)9781479919307 (ISBN)
Conference
16th IEEE International Workshop on Signal Processing Advances in Wireless Communications, SPAWC 2015, 28 June 2015 through 1 July 2015
Note

QC 20160208

Available from: 2016-02-08 Created: 2016-01-29 Last updated: 2016-12-22Bibliographically approved
Gharanjik, A., Bhavani Shankar, M. R., Arapoglou, P. D., Bengtsson, M. & Ottersten, B. (2015). Robust precoding design for multibeam downlink satellite channel with phase uncertainty. In: ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings: . Paper presented at 40th IEEE International Conference on Acoustics, Speech, and Signal Processing, ICASSP 2015, 19 April 2014 through 24 April 2014 (pp. 3083-3087). IEEE conference proceedings
Open this publication in new window or tab >>Robust precoding design for multibeam downlink satellite channel with phase uncertainty
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2015 (English)In: ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings, IEEE conference proceedings, 2015, p. 3083-3087Conference paper, Published paper (Refereed)
Abstract [en]

n 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.

Place, publisher, year, edition, pages
IEEE conference proceedings, 2015
Keywords
Convex optimization, Phase Uncertainty, Robust Precoding, Satellite Channel, SDR
National Category
Signal Processing Telecommunications
Identifiers
urn:nbn:se:kth:diva-181633 (URN)10.1109/ICASSP.2015.7178538 (DOI)2-s2.0-84946080887 (Scopus ID)9781467369978 (ISBN)
Conference
40th IEEE International Conference on Acoustics, Speech, and Signal Processing, ICASSP 2015, 19 April 2014 through 24 April 2014
Note

QC 20160229

Available from: 2016-02-29 Created: 2016-02-02 Last updated: 2016-02-29Bibliographically approved
Gharanjik, A., Rao, B. S., Arapoglou, P.-D. & Ottersten, B. (2013). Large scale transmit diversity in Q/V band feeder link with multiple gateways. In: 2013 IEEE 24th International Symposium on Personal Indoor and Mobile Radio Communications (PIMRC): . Paper presented at IEEE 24th International Symposium on Personal Indoor and Mobile Radio Communications (PIMRC); London, United Kingdom, 8-11 September 2013 (pp. 766-770).
Open this publication in new window or tab >>Large scale transmit diversity in Q/V band feeder link with multiple gateways
2013 (English)In: 2013 IEEE 24th International Symposium on Personal Indoor and Mobile Radio Communications (PIMRC), 2013, p. 766-770Conference paper, Published 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.

Keywords
Attenuation, Availability, Logic gates, Rain, Satellites, Signal to noise ratio, Switches, Feeder Link, Gateway Diversity, Q/V Band, Satellite Communication, active and redundant gateways
National Category
Signal Processing
Identifiers
urn:nbn:se:kth:diva-138995 (URN)10.1109/PIMRC.2013.6666239 (DOI)2-s2.0-84893313553 (Scopus ID)
Conference
IEEE 24th International Symposium on Personal Indoor and Mobile Radio Communications (PIMRC); London, United Kingdom, 8-11 September 2013
Note

QC 20140203

Available from: 2013-12-23 Created: 2013-12-23 Last updated: 2014-02-03Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-3442-6566

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