Advanced physical and MAC layer techniques for DVB based interactive satellite terminals

Abstract

With their tremendous success in broadcasting entertainment services, interactive broadband satellite systems are now also being viewed as viable service delivery vehicles. Many network operators seriously consider satellite-based networks to offer broadband and multimedia services to supplement and enhance their existing terrestrial networks. High speed user terminal interactivity via satellite requires the presence of a satellite return link with broadband capability. Such connectivity is typically offered nowadays via different solutions, some of which proprietary. DVB-RCS 1 is the well known standard concerning the air interface of the return link of interactive satellite terminals. It defines the end-to-end connectivity link between the satellite operator hub and the user terminal. To this end, it embraces the DVB-S and the DVB-S2 2 standards as the forward link specifications, while it describes in more details the physical and MAC layer aspects of the return channel. Although there is certainly a market for two ways satellite-based interactive systems, a number of issues will influence the rate of uptake, financing of systems, and ultimately, the number of subscribers. Among these, the cost of the terminal and service (cost per bit delivered to the end user) has to be effective in order to support the financial case for the satellite and ground segments. To this end, the system spectral and energy efficiency has to be improved by using state-of-the art techniques and solutions. The newly defined DVB-S2 2 standard implements a number of innovative techniques to dramatically improve the forward link system throughput for interactive systems. These techniques comprise an enhanced FEC code (LDPC), interference cancellation techniques, use of satellite-optimized higher order modulations with ACM (Adaptive Coding and Modulation), an efficient framing scheme, transmit signal pre-distortion techniques and direct mapping of variable length packets into the DVB-S2 physical layer. This paper presents some enhanced techniques that can be successfully applied to the return link of interactive satellite terminals with some estimated performance gains. In particular the following techniques are presented: i) an enhanced Forward Error Correction (FEC) scheme with improved performance with respect to the current turbo code, ii) a novel framing and layer 2 encapsulation scheme optimized for adaptive physical layer and matching traffic characteristics, iii) adjacent and co-channel interference cancellation techniques, iv) high order modulation schemes (i.e. 8PSK and possibly 16APSK) with adaptive coding and modulation and a variety of code rates; v) optimized contention-based access.