Satellite Communications

In 1945 Arthur C Clarke suggested that artificial satellites could be employed for communications. In 1957 the Soviet Union successfully launched Sputnik. Since then thousands of satellites have been built and are now used for numerous applications including surveillance, mobile communications, navigation, broadcasting, point to point communications, disaster monitoring, space science, exploration of other planets and earth observation.

Figure 3 from Clarke, 1945

Satellite systems provide a key part of our communications infrastructure. Despite the advances in terrestrial communications, satellites are still able to provide unique services for broadcasting, remote areas and mobile users. During the last four decades satellite communication has made huge process. Modern systems can perform "on board" processing (rather than just shift frequency and amplify weak signals) and handle packet data (including storage and routing functions). In addition they often employ multiple transponders, sophisticated multi-beam antenna systems (such as the 12m ACeS antennas in the figure below) and may operate to 30 GHz carrier frequencies. Since bandwidth is a non-renewable commodity, and small portable terminals require low power consumption, two key objectives are better spectral efficiency (to allow move bit/s per Hz) and better power efficiency (to allow lower transmit power for the same bit error rate).

Australian CRCSS research satellite Fedsat being released from Japanese H-IIA rocket in December 2002

Key Research Challenges

Some specific areas of research in satellite communication systems are:

dealing with transponder non-linearities, especially when high spectral efficiencies are required
mitigating the effects of interference to/from adjacent satellites or terrestrial systems
moving to IP-based satellite networks, including better integration with terrestrial networks
optimizing the performance of mobile satellite systems, given the poor channel conditions
devising optimum access and modulation/coding methods for satellite links
designing efficient signal processing architectures, both for space and ground segments.