CO2SAT – Cooperative and Cognitive Architectures for Satellite Networks
The demand for broadband access is ever increasing with various applications in business, education and entertainment. However, the available frequency resources are becoming scarce due to the spectrum segmentation and the dedicated frequency allocation of the standardized wireless systems. In addition, the power consumed by current communications systems has become a limiting factor in the face of global warming, leading to the concept of green radio. Therefore, it becomes crucial to define and investigate new network architectures which have the ability to support higher system throughput and energy efficiency, while providing large-scale coverage.
In this direction, cooperative and cognitive satellite systems constitute innovative and promising network architectures, which can combine all of the aforementioned characteristics. Cooperative satellite networks operate by jointly processing the spatially distributed users at the ground station. In this context, multiuser encoding and decoding techniques can be utilized to maximize the spectral and energy efficiency. This is achieved by minimizing the inter-beam interference in multi-spot-beam satellite systems. The additional signal processing required for those techniques can be transferred to the ground station in order to maximize the satellite lifetime. Moreover, cognitive satellite systems are based on hybrid networks which combine a ground and a satellite component operating over the same frequency bandwidth. Based on cognitive overlay and underlay techniques, both ground and satellite components can communicate simultaneously with the users without the need of orthogonalization (Frequency Division), minimizing the need of purchasing expensive bandwidth. In addition, this concept can lead to the integration of satellite and terrestrial services in order to support ubiquitous indoors and outdoors coverage.
The objective of this project is to evaluate the performance gain of the aforementioned satellite network architectures in comparison to the traditional satellite systems. Although cooperative and cognitive techniques have been investigated in the context of terrestrial networks, the application is not straightforward to satellite systems due to their inherent characteristics: distortion from payload relay, power constraint, strong line-of-sight, high path loss, long shadowing. In this direction, the following figures of merit will be employed in order to quantify the system performance: a) bits/sec/Hz/Km2 for the spectral efficiency, b) bits/sec/Hz/Joule/Km2 for the energy efficiency. In all examined scenarios, the optimal figures of merit will be calculated using information-theoretic concepts in order to maintain a fixed framework of reference. In order to crosscheck and verify the performance results, the following methodologies will be utilized: a) mathematical analysis based on matrix theory and optimization techniques, b) Monte Carlo simulations over multiple channel instances. In the context of cooperative satellite networks, linear and non-linear precoding and decoding techniques will be considered for optimizing the system. Regarding the cognitive satellite networks, the concepts of interference alignment, interference temperature and cognitive beamforming will be employed.
