Section: Scientific Foundations

Agile Radio Resource Sharing

For current systems, the radio access reliability is guaranteed by the strict reservation of a band to a specific application. This band is further divided into multiple sub-bands, allocated to specific service providers, base stations or mobile users. Such resource reservation is really too restrictive and a less stringent approach is mandatory to improve the radio resource usage efficiency.

On the opposite, the total deregulation already effective in the $2.4$ GHz ISM band, already shows the inefficiency of actual uncoordinated resource sharing principles: the coexistence of more and more systems will quickly lead to unacceptable strong interference levels and hence major malfunctions. Therefore, the solutions will originate from a self-adaptive behavior. To achieve a true self-adaptive behavior, the radio nodes should be able to analyze their radio environment thanks to cognitive radio capabilities as mentioned in the previous challenge. Based on this knowledge, each radio node has to decide which resource it can use without impending the other (primary) users' performance. Both sensing scheduling followed by transmission scheduling necessitate the design of cognitive medium access procedures (C-MAC). If centralized approaches are possible, they however suffer from the lack of adaptability and strong algorithmic complexity. Promising approaches rather rely on distributed algorithms where nodes take decisions on their own knowledge. Specific mechanisms are required to ensure robustness and stability.

Complementarity, and beyond a simple decision of using a radio resource, cooperative approaches between heterogeneous radio nodes open still more perspectives to increase the system efficiency. An important issue relies on exploiting the relay channel concept introduced in 1971 by van der Meulen but mor recently extended to multiple sources and relays, while introducing simultaneously network coding capabilities. This problem is really open as the capacity bounds are not even known.

The second challenge consists in proposing distributed algorithms for resource sharing and cooperation, optimized with respect to our three common objectives (QoS, Energy consumption and Security) and exploiting cognitive radio.