Overview and comparison of on-ground and on-board beamforming techniques in mobile satellite service applications J. Tronc 1, * ,† , P. Angeletti 2 , N. Song 3 , M. Haardt 3 , J. Arendt 4 and G. Gallinaro 5 1 ASTRIUM, 31, rue des Cosmonautes, 31 402 Toulouse, France 2 ESA/ESTEC, Keplerlaan 1—PO Box 299, 2200 AG Noordwijk, Zuid-Holland The Netherlands 3 Ilmenau University of Technology, Helmholtzplatz 2 PO Box 100565, 98 693 Ilmenau, Germany 4 Fraunhofer IIS, Am Wolfsmantel 33, 91 058 Erlangen, Germany 5 Space Engineering, Via dei Berio, 91, I-00155 Roma, Italy SUMMARY The objective of this paper is to review state-of-the-art techniques of beamforming in mobile satellite systems and evaluate the potential benefits/drawbacks of on-ground beamforming compared with on-board beamforming approach. The paper also provides a short analysis of beamforming error sources in on-ground beamforming such as propagation effects at feeder link level, on-board degradations at payload level, differential atmospheric perturbations, and Doppler shift effect. An investigation of signal processing techniques is also performed to provide a preliminary assessment of the interest for employing adaptive beamforming and precoding techniques in multi-spots mobile satellite systems. Copyright © 2013 John Wiley & Sons, Ltd. Received 31 October 2012; Revised 9 June 2013; Accepted 8 July 2013 KEY WORDS: beamforming; on-board beamforming; on-ground beamforming; ground based beamforming; spot beam 1. INTRODUCTION The modern geostationary mobile satellite service (MSS) systems aim at providing broadband and high- speed mobile services covering a large area. To accommodate numerous users while improving the spec- trum efficiency as well as providing enhanced quality of service, it is desired to adopt multi-spot beams, each of which serves one distinct cell within the whole service coverage area. Multiple beams can be generated by implementing smart antenna technologies on the satellite (e.g., an array-fed reflector), and beamforming can be carried out either on-board or on-ground to electronically steer the beams [1, 2]. From the algorithm implementation point of view, there are four main digital beamforming classes: fixed, programmable, adaptive, and dynamic. • In fixed beamforming, weights are designed in advance and kept constant [3]. • With programmable beamforming, weights are adjustable via command from ground. This weight adjustment is useful to meet antenna performance requirements such as beam pointing, sidelobe levels even in presence of changes such as satellite pointing errors (e.g., as consequence of operating with an inclined orbit) or some drift due to hardware aging, and so on. In this case, the programmable beamforming does not necessarily rely on the quality of the received signal [4]. • In adaptive beamforming, an array beam pattern is automatically optimized by adaptively calculating complex weighting coefficients until a certain optimization is achieved. To enhance *Correspondence to: J. Tronc, ASTRIUM, 31, rue des Cosmonautes, 31 402 Toulouse, France. † E-mail: jerome.tronc@astrium.eads.net INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING Int. J. Satell. Commun. Network. 2014; 32:291–308 Published online 23 October 2013 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/sat.1049 Copyright © 2013 John Wiley & Sons, Ltd.