Direct sequence spectrum spreading techniques for next generation mobile broadband satellite services

The recently approved mobile version of the Digital Video Broadcasting Return Channel via Satellite (DVB-RCS+M) foresees the use of direct sequence spectrum spreading (DS-SS) in the forward link. The addition of a spreading mode, on top of the conventional time division signaling structure of the fixed DVB-S2, allows in fact for the efficient extension of DVB-S2 to mobile terminals with small aperture antennas operating in Ku (11-14 GHz) and Ka (20-30 GHz) bands. Spectrum spreading has been introduced to augment the received energy without increasing the transmitted power density, which is limited by regulatory constraints, and to enhance the waveform resilience to co-channel interference. In this paper, we report on the design and assessment of the DS-SS technique that we carried out for its inclusion in the DVB-RCS+M standard. In particular, by comparing the physical layer performance of the spread and nonspread modes in the specific DVB-RCS+M mobile scenarios, we show that the proposed DS-SS technique has no impact on the DVB-RCS+M data detection performance, while satisfying the requirements on interference resilience and received energy augmentation. In order to deal with the acquisition issues raised by the introduction of the DS-SS technique, we then propose and evaluate several synchronization sub-systems able to deal with the specific impairments of the mobile satellite scenarios, that is, large frequency offsets, phase noise, link obstructions, etc. Finally, a possible implementation of the DS-SS technique that fully accommodates the reuse of the specific hardware compatible with conventional DVB-S2 is also reported.