Receiver synchronisation based on a single dummy frame for DVB-S2/S2X beam hopping systems Xavier Giraud Cabinet NOVACOM Email: giraud.novacom@wanadoo.fr Guy Lesthievent CNES Email: guy.lesthievent@cnes.fr Hugo M´ eric CNES Email: hugo.meric@cnes.fr Abstract—We study the receiver synchronisation in a DVB- S2/S2X beam hopping system. In such a scenario, each beam is illuminated during defined temporal windows. As a consequence, the receivers do not receive a continuous signal which strongly disturbs their synchronisation. To tackle this problem without using a specific format, we introduce a dedicated dummy frame with a synchronisation field that enables the receiver to lock with one frame even with poor channel conditions (a signal-to- noise ratio down to -10 dB). This solution is fully compliant with the existing standards. Through simulations, we present the performance of our scheme and demonstrate its effectiveness for DVB-S2/S2X systems. I. I NTRODUCTION Very high throughput satellites combined with multi-beams systems provide a significant increase of the available capacity. However on-board resources (especially high power ampli- fiers) are limited due to consumption, mass and dissipation. Moreover, the traffic demand is time varying and differs between beams. One solution to properly allocate the resources and solve previous constraints is beam hopping. To that end, beam hopping proposes a temporal allocation of the resources by illuminating the beams in various temporal windows (thus avoiding a complicated frequency allocation). First studies regarding beam hopping dated back to 2006 [1]. Since then, the literature has been growing [2]–[9]. Previous works cover the payload architecture [1]–[4], [6], the system performance combined with resource allocation algorithms [1], [3]–[7] and the receiver synchronisation [8], [9]. In this work, we study the receiver synchronisation. This means the frame, frequency, phase and timing synchronisations as the receiver needs to lock after a period without signal. All previous works studying synchronisation for beam hop- ping systems rely on the super-frame format introduced in DVB-S2X [10, Annex E] and depicted in Fig. 1a (we also remind the DVB-S2/S2X framing in Fig. 1b). In [8], [9], the authors use this new framing as a solution to synchronisation issues in beam hopping and very-low signal-to-noise ratio (VL-SNR) modes. They present synchronisation performance such as false alarm and missed detection probabilities. Even if the super-frame presents some benefits, its adoption by the satellite community is not that simple as it has many impacts on the transmitter and the receiver: special header (not backward-compatible with DVB-S2), long and fixed framing size (the super-frame lasts more than 6 ms for R s < 100 MBauds), limited granularity, insufficient guard symbols for switching and system uncertainty, hardware complexity, etc. Before going any further, we shortly discuss the impact of the super-frame (or any possible framing) length in a beam hopping system. Even at 500 MBauds, the super-frame lasts more than 1 ms as shown in Fig. 1c. Thus the gap between two consecutive illuminations may be quite long. A long period SOSF 611 820 symb. 450 symb. 270 symb. Ressource allocation (format specific) SFFI 612 540 symb. (a) Super-frame (optionnal) format composed of: start of super-frame, super-frame format indicator and the resource (several PLFRAMES as depicted in Fig. 1b and pilots) Data field BB header LDPC BCH FEC FEC BBFRAME BBFRAME FECFRAME FEC encoding Bit mapping to symbols Slot S Slot 1 Slot 2 Slot 16 Slot S header PL XFECFRAME PLFRAME Pilot block 36 symb. 90 symb. 90 symb. Slot 1 PL framing Bits Symbols 80 bits -K BCH bits bits BCH K N LDPC (b) DVB-S2/S2X framing (mandatory) 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 50 100 150 200 250 300 350 400 450 500 Frame duration [s] R s [MBaud] Dummy Super QPSK 8PSK 16APSK 32APSK (c) Duration of normal frame (64 800 encoded bits) with pilots Fig. 1: DVB-S2/S2X framing