IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, VOL. 10, NO. 9, SEPTEMBER 2011 2807 To MIMO or Not To MIMO in Mobile Satellite Broadcasting Systems Pantelis-Daniel Arapoglou, Member, IEEE, Paolo Burzigotti, Member, IEEE, Massimo Bertinelli, Member, IEEE, Ana Bolea Alamanac, and Riccardo De Gaudenzi, Senior Member, IEEE Abstract—This letter studies the potential capacity advantages of introducing a dual polarization per beam paradigm instead of the conventional single polarization per beam in mobile satellite broadcasting systems. This enables the application of MIMO techniques, not yet thoroughly investigated for mobile satellite systems. We engage in a fair system performance comparison between single polarization SISO and dual polarization non- MIMO and MIMO configurations based on the DVB-SH state- of-the-art mobile satellite standard. Along the course, the major advantages and pitfalls of a dual polarization per beam system from an interference, antenna, payload, and capacity perspective are highlighted. Index Terms—MIMO, dual polarization, mobile satellite broadcasting, LMS, outage capacity. I. I NTRODUCTION B ROADCASTING of multimedia services to mobile user terminals (UT) via geostationary satellites at L (1/2 GHz) and S (2/4 GHz) frequency bands is becoming increasingly attractive. Mobile satellite broadcasting (MSB) systems are now an integral part of hybrid broadcasting networks, where the ground component provides urban and indoor coverage and the satellite component is responsible for delivering a high QoS to open/rural environments and to less densely pop- ulated areas. Amid the standards competing in the mobile TV arena worldwide, DVB-SH 1 [1] represents the state-of-the-art, specifically designed to operate in hybrid satellite/terrestrial reception providing resistance against land mobile satellite (LMS) channel impairments [2]. Toward the optimal use of the narrow MSB spectrum available, the present letter aims at assessing the potential advantages of migrating from the conventional single polarization per beam (SPPB) to an ad- vanced dual polarization per beam (DPPB) MSB architecture. By itself, the reuse of two polarizations within the same satellite beam constitutes an important innovation in the MSB paradigm not investigated yet, allowing to double the available spectrum at the expense of increased inter-beam interference. Section II touches upon key system aspects of such a mi- gration demonstrating its feasibility in terms of UT receiver, Manuscript received September 8, 2010; revised May 25, 2011; accepted June 22, 2011. The associate editor coordinating the review of this paper and approving it for publication was F. Tufvesson. P.-D. M. Arapoglou is with the School of Electrical & Computer Engi- neering, National Technical University of Athens, Greece, GR15780 (e-mail: parap@central.ntua.gr). P. Burzigotti, M. Bertinelli, A. Bolea Alamanac, and R. De Gaudenzi are with the European Space Agency-ESTEC, Keplerlaan 1, 2200 AG, No- ordwijk ZH, The Netherlands (e-mail: {Paolo.Burzigotti, Massimo.Bertinelli, Ana.Bolea.Alamanac}@esa.int, rdegaude@xrsun0.estec.esa.nl). This work is supported by the joint ESA-NTUA NPI programme “MIMO Technology in Satellite Communications for Interference Exploitation and Capacity Enhancement.” Digital Object Identifier 10.1109/TWC.2011.071411.101599 1 Digital video broadcasting to satellite handhelds. payload and antenna. The concept of realizing two streams of information flow by simultaneously transmitting/receiving over two orthogonal polarizations naturally lends itself to the idea of applying MIMO techniques [3], which have been embraced by several wireless standards 2 . As concluded by previous review articles on satellite based MIMO alternatives [4], the more realistic near-term possibility for MSB to profit by MIMO is the polarization realm. However, given that the 2 × 2 dual polarization LMS channel [5] exhibits completely different characteristics compared to a spatial independent and identically distributed (i.i.d.) MIMO channel, it remains uncertain if applying MIMO in MSB systems is beneficial. Actually, the long time interleaver employed in the DVB- SH waveform coupled with very powerful FEC along with the limited fading decorrelation between the two polarizations renders the case in favor of MIMO in MSB more difficult. Therefore, to address the question raised in the title, we analyze: a) the capacity bounds of the dual polarization LMS channel in Section III, after defining appropriate capacity metrics; b) the FEC uncoded and coded performance of the most promising techniques after simulating them over the full DVB-SH transmission chain in Section IV. Note that, aside of the typical spatial MIMO Rayleigh fading channel, there is a lack of similar performance comparisons under more realistic channel and system assumptions 3 . II. SYSTEM ASPECTS A. Selecting Between Linear and Circular Dual Polarization The most common alternatives of dual polarization in wireless communication are: a) linear polarization (LP) ap- pearing as horizontal/vertical (HP/VP) with polarization tilt angles 0 ∘ /90 ∘ and b) circular polarization (CP) appearing as right/left hand (RHCP/LHCP) with polarization tilt angles ±45 ∘ . Terrestrial dual polarization MIMO systems usually opt for the linear pair due to the legacy from single polarization systems, although MIMO ergodic capacity has been shown to be equal for the two alternative polarization schemes [7]. On the other hand, in conventional single polarization SISO MSB systems operating at L- or S-band the use of CP instead of LP is preferred to counteract the effects of Faraday rotation. Taking into account that MSB systems will be typically complemented by terrestrial gap fillers, the complexity of the UT RF front-end can be reduced by maximizing the 2 Indicatively, MIMO techniques are now an integral part of the latest amendments of LTE, IEEE 802.11 and IEEE 802.16 wireless standards and recently adopted for the new DVB-NGH broadcasting standard. 3 For instance, the discussion on the choice between transmit diversity and spatial multiplexing under a more realistic channel and employing hybrid automatic repeat request (HARQ) was recently reopened in [6]. 1536-1276/11$25.00 c ⃝ 2011 IEEE