These developing technologies generate growth and support industry in Europe.
DVB-S2 is the second generation DVB system for broadband satellite communications, covering digital TV and HDTV broadcasting, interactive services and professional links by satellite. This standard for broadcasting, interactive and professional services was developed by the Digital Video Broadcasting organization in 2005. It enables delivery of a significantly higher data rate in a given transponder bandwidth.
DVB-S2 has been rapidly adopted worldwide as the new standard for broadcasting, interactive and professional applications. Of particular importance for the standard commercial take off is the availability of mass market chipsets supporting various profiles including ACM.
The ACM interactive service profile opens up a number of great opportunities for the design and development of satellite broadband networks. According to ESTEC representative Riccardo De Gaudenzi: “ACM is essential for economically supporting interactive services in the presence of propagation fading in particular at Ka-band or at Ku-band in tropical regions”.
ACM introduction in the satellite downlink enhances system performance and provides a profound impact on the way the system and some of the key system components are designed. The point-to-point nature of link connections enables the exploitation of spatial and temporal variability of end-user channel conditions to increase the average system throughput. This is achieved by adapting coding rate and modulation format (ACM) of the downlink time division multiplex (TDM) frame addressed to a specific user (or a subset of users experiencing the same signal-to-noise plus interference condition) to best match the current user link conditions.
Development and performance analysis have been conducted through internal work at ESTEC as well as research and development contracts in ESA Technology Research Program (TRP) and Telecom’s Advanced Research in Telecommunications Systems (ARTES) program, particularly the recently completed project entitled Adaptive Coding and Modulation Modem for Broadband Communications.
The purpose of this project was to develop a demonstrator for testing of ACM techniques for broadband satellite communications. These techniques were based on the DVB-S2 specification for the forward link, and the DVB-RCS specification for the return link.
The project was split into two phases. Phase 1 focused on system scenario definition, ACM modem demonstrator specification and high-level algorithm design, while Phase 2 dealt with the ACM modem demonstrator detailed design, implementation and testing.
Further work includes running tests by satellite and to record statistics especially on the ACM loop, in Ku and Ka-band, to get a feedback from operational use. This will be addressed in the on-going ESA ARTES project known as the DVB-S2 Satellite Experiment.
"The use of DVB-S2 in the new broadcast and broadband systems will help make the use of satellite much more competitive due to large gains in efficiency," explains Michele Le Saux, Head of Ground Segment Technology Section of ESA's Telecommunications and Integrated Applications Department. "The use of ACM will also allow operators to make the best use of their available space segment while offering their clients the highest throughput possible."
DVB-S2 Licensing campaign underway
A licensing campaign is underway for the DVB-S2 standard. Intellectual property rights holders of DVB-S2 include the DirectTV group, RAI (Radiotelevisione Italiana) and ESA. The holders launched the patent licensing campaign in June, 2008 in the United States. The US patent, granted in January, 2007, is called Coded Digital Modulation Method for Communication System. ESA also holds non essential patents related to DVB-S2 demodulator synchronisation.
The work ESA carried out by the ESTEC Technical Directorate engineers involved a new way of designing highly spectral efficient modulations to make them better than conventional squared Quadrature Amplitude Modulations such as 16QAM and 32QAM over satellite channels. The work focused on constellation optimisation, nonlinear channel pre-compensation techniques and digital demodular synchronisation.
The optimised Amplitude and Phase Shift Keying (APSK) modulation proposed by ESA outperforms QAM modulation over satellite nonlinear channels, allowing close to saturation operation of the on-board high power amplifiers. The concept of circular APSK modulation was already proposed 30 years ago but it was concluded that for single carrier operation over nonlinear channel APSK performs worse than PSK schemes. The work conducted at ESA shows that APSK modems for satellite channels can be easily implemented. Since the patent filing, articles on the APSK design have been published by ESA engineers in the IEEE Transactions of Wireless Communication and the Wiley International Journal of Satellite Communications and Networking.
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