13.5: R&D Challenges for Broadband Satcoms in 2020 Marinella Aloisio, Piero Angeletti, Francesco Coromina, Francois Deborgies, Riccardo De Gaudenzi, Alberto Ginesi European Space Agency European Space Research and Technology Centre (ESTEC) Keplerlaan 1, 2200 AG Noordwijk, The Netherlands e-mail: marinella.aloisio@esa.int, piero.angeletti@esa.int Abstract: The paper describes possible key challenges and critical techniques and technologies for broadband satellite communications which in the authors’ opinion show enough potential to justify their development in the coming years. Keywords: Satellite communications; satellite payloads; flexibility, TWTA; MPA. Introduction Despite the pessimistic view on the commercial satellite communications (satcom) already emerging in the ‘80s and the bankruptcies of several big satcom systems at the end of the ‘90s, telecommunications do still represent the most important commercial application of satellites. However, the past success should not relax the need for a continuous, yet strengthened innovation effort to guarantee a comparable role in the medium/long term. This is particularly true when we look at the fast pace at which terrestrial wireline and wireless technologies are developing and the extreme competition existing in this field that makes service quality constantly growing with reduced provisioning cost. In the coming years, the broadband market is expected to grow and, in particular, a large traffic growth will be related to the increased demand for video and multimedia content distribution. In the rich multimedia content provision to a large number of users, satellite systems are in a significantly favorable position for covering broadcasting/multicasting type of services as compared to terrestrial networks. Also the terrestrial broadband access capabilities, although constantly covering an increased percentage of the population, are leaving interesting niches to the satellite market. The identified key challenges for the satellite broadband interactive and broadcasting services are summarized as follows: • Traffic is developing in a very non uniform way – current payloads can cope with that inefficiently or with no flexibility. Can we have a flexible, yet efficient, payload? • Ka-band may be able to support both interactive and broadcast services – can we economically develop flexible multi-mission satellites? • Users will require enhanced interactive services for the same price (volume and peak rate increase). Can satellite communications cope with the evolving user demand? • Not all regions of the world can commercially exploit Ka-band (South America, Asia, Africa) because of too heavy atmospheric fading. There is a need for cost- effective Broadband solutions for rainy regions. • Video traffic is quickly growing. There is a need for cost-effective massive video (interactive) downloading to large communities (IPTV-like). • Need for increased security of satellite networks. As far as interactive services are concerned, multibeam payloads with small beam size allow for increased throughput and higher data rates. On the other hand, for a given coverage, the smaller the beam size the lower the traffic aggregation at beam level and the higher the load/beam variability in space and time. The uniform distribution of bandwidth and power is not an optimal solution, being incapable of serving the hot spots and resulting in wasted capacity/power/bandwidth in the cold spots (Fig. 1). Advanced techniques are therefore necessary to meet the need of flexible allocation of bandwidth and power to beams [1]. Figure 1. Example of Unbalance between Requested and Offered Traffic for a Non-flexible Payload For the example in Fig. 1, a relatively simple payload has been assumed based on a single-feed-per-beam antenna design (Fig. 2a) where a digital processor assigns bandwidth to beam in a flexible manner and the signals are amplified by 160 W 3 dB-flexible TWTAs (Fig. 2b). 978-1-4244-7099-0/10/$26.00 © 2010 IEEE 307