[Sls-slp] Satellites approach the Shannon limit

Adrian J. Hooke adrian.j.hooke at jpl.nasa.gov
Thu Oct 30 12:57:20 UTC 2008


28 October 2008

Satellites approach the Shannon limit

(PhysOrg.com) -- Satellites are achieving unparalleled efficiency 
with a new protocol, DVB-S2. The performance of DVB-S2 satellite 
systems is very close to the theoretical maximum, defined by the 
Shannon Limit. That efficiency could be pushed even further by 
network optimisation tools and equipment recently developed by 
European researchers.

European researchers have created network optimisation hardware and 
software tools that are able to manage satellite resources more 
efficiently. The developed tools are able to push the state of the 
art in satellite transmission technology even further. The increased 
efficiencies lead to cheap broadband, TV and voice access from anywhere.

But vast numbers of Europeans also live in rural or even isolated 
regions and providing broadband access for them is more complicated.

But not, perhaps, for much longer. Recent progress in satellite 
technology has led to vastly improved bandwidth efficiencies. The 
newly developed DVB-S2, which stands for digital video broadcast 
satellite second generation, improves on DVB-S by a purported 30%.

"Using satellite resource management tools, based on cross-layer 
techniques, the IMOSAN project is trying to push that technology even 
further, in order to make it more attractive not only from the 
technical aspects, but from the business point of view as well," 
explains Anastasios Kourtis, coordinator of the EU-funded project.

Cross-layer techniques work across the application, service and 
physical layers of a communication medium to maximise efficient usage 
of bandwidth.

Approaching the Shannon Limit

The Shannon Limit establishes the maximum capacity of any channel. A 
channel is subject to bandwidth and noise restrictions, but its 
capacity can be improved with clever modulation and multiplexing 
techniques. The theoretical ultimate limit of a channel for specific 
bandwidth and signal-to-noise ratio is called the Shannon Limit.

Like the speed of light, that limit cannot be overcome and, again 
like the speed of light, it is very difficult even to approach it.

The inherent feature of DVB-S2, called Adaptive Coding and Modulation 
(ACM), allows a satellite system to adapt, in real time, to various 
transmission conditions and service demands. In this respect, 
satellite channels are very close to their theoretical limit.

"The IMOSAN consortium developed innovative software and hardware 
modules and protocols, called the Satellite Resource Management 
System (SRMS) that apply ACM to voice, data and TV in a clever way, 
allowing the provision of cost-effective 'triple-play' satellite 
services to users in rural or isolated areas," Kourtis explains.

SRMS was a key advance, but only one of a series of innovations and 
improvements the team performed on the DVB-S2 system. They also 
developed hardware and software that supports MPEG-2 HDTV. They 
developed software that can use both the older Multiprotocol 
Encapsulation (MPE) scheme and the newer Ultra Light Encapsulation 
(ULE) one. Both have also been optimised for IPv4 or IPv6.

IPv4 is the current Internet Protocol (IP) that we mainly use for all 
data communications. But the unique IP addresses are running out 
rapidly, and the protocol is creaking under the strain of modern 
network demands. IPv6 will address this shortage and offer other new 
features to improve the internet.

It offers so many unique addresses that it would be possible to give 
an address to every individual grain of sand on earth and still have 
enough numbers left to give a unique one to every individual on the 
planet, any pets they have and all the devices they own. IPv6 also 
provides better security and error correction and it is the IP 
standard of the future. Including it in their system means that 
IMOSAN has future-proofed its work.

The work of IMOSAN is expected to have significant impact on 
satellite communications.

"The innovative tools and techniques that were developed in the frame 
of IMOSAN, gave [us] a great opportunity [for] efficient 
collaboration among private-sector companies and public academic 
organisations, with a common goal: to provide cost-effective 
broadband satellite services to rural and isolated areas," Kourtis 
concludes. This should help tackle the digital divide problem.

This is part one of a two-part feature on the IMOSAN project funded 
by the ICT strand of the EU's Sixth Framework Programme for research. 
Part two will appear on 4 November.  
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