SUMMARYThe second-generation specification for Digital Video Broadcast over Satellite, DVB-S2, defines an improved and adaptive physical layer. A new framing structure at the link layer, known as the generic stream (GS), is introduced offering an alternative to the well-known MPEG transport stream (TS). This paper presents the requirements for and the design of an encapsulation protocol to transport IPv4 and IPv6 datagrams and other network protocol packets directly over DVB-S2 using this GS profile. The resulting generic stream encapsulation (GSE) is a novel method that provides flexible encapsulation with support for fragmentation. A flexible extension header format allows GSE to carry additional header information, suitable for enhanced features, such as link layer encryption and IP header compression. The paper assesses GSE performance by simulation using realistic traffic profiles and attenuation fading. This demonstrates considerable improvement in efficiency compared with the MPE/MPEG-2 TS, especially when used with adaptive coding and modulation (ACM). Although designed for DVB-S2 systems, the new encapsulation is suitable for other second-generation physical layer standards.

SUMMARYThis paper assesses the way error control is managed jointly by Forward Error Codes (FEC) and Cyclic Redundancy Checks (CRC) in the lower layers of today's Digital Video Broadcasting (DVB) satellites. Mathematical and simulation results clearly show that the outer block codes of the coding schemes used in DVB-S and DVB-S2 (Reed-Solomon and Bose-Chaudhuri-Hocquenghem, respectively) can provide very accurate error-detection information to the receiver in addition to their basic correction task at virtually no cost, making an uncorrected error after decoding an extremely improbable event. For this reason, the workload of CRCs can be ensured safely by the FEC subsystem if a dedicated function allowing the physical layer to share its decoding information with the adaptation layer is set. This particular cross-layer mechanism would allow freeing up the bandwidth currently used by CRCs}which adds up to 10% for more than 35% of the total number of IP packets}and pave the way for an enhanced transport of IP over DVB-S2.

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Since Kragh and Christie's 2002 seminal paper on repeatability, nrms and predictability (PRED) have been the most widely used metrics for analyzing 4D noise in time-lapse studies. However, their values and behavior are rather counterintuitive, and they invariably end up stagnating above 15% and 0.95, respectively, in repeated marine data of variable quality. Moreover, their respective variations with regards to measurable differences in data, acquisition, and processing are still poorly understood from a quantitative standpoint. With the objective of improving our assessment, interpretation, and understanding of time-lapse repeatability, this paper introduces an analytical formulation of the 4D problem from the perspective of perturbation theory, building on the preliminary works of Calvert and high-quality data from our latest time-lapse campaigns in Gulf of Guinea. This framework brings to light blatant problems with our current repeatability metrics, and proposes a complementary set of QCs and best practices to get more out of 4D data. The cornerstone of this effort is the introduction of the new signal-to-distortion ratio (SDR) attribute as a true, reliable indicator of time-lapse repeatability. It provides the essential common ground on which different acquisition technologies, deployment and processing strategies are to be compared.

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