Section: Scientific Foundations
Future wireless networks will have to be adaptive, self-organized and possibly cooperative. These features can be referred to as smart wireless networking. To address this challenging topic, three main research fields are investigated by SWING: flexible radio node, agile resource sharing, and autonomous radio networking. Moreover, with the new development optimization security
Flexible radio node design – Designing a radio node is definitely not an all-analogue process. Since software defined radio principles were established, some new features such as adaptability and auto-reconfiguration are becoming mandatory for the terminal to adapt to its environment and to the application in use. This relies on doing an important part of the radio coding/decoding process in the digital world. Because a full software radio node is still an utopia, future architectures will have to cope with analogue and digital constraints and their co-design is a real challenge. New computation models are emerging, such as for instance, the concept of radio virtual machine or new hardware abstraction layers permitting to develop separately the radio protocols, the strategies for resource sharing, the operating systems and top-level applications.
Agile radio resource sharing – Radio resource sharing is very important in autonomous and spontaneous networks. This problem covers several research fields including signal processing and protocols. In various contexts from wireless sensor networks (WSNs) to cellular wireless networks, the problem of sharing the radio resource remains a challenging issue. Mitigating interference for multi-system environments, optimizing energy and capacity for high data rate access networks or increasing the life-time of WSNs all strongly rely on the resource sharing strategy. The complexity of this problem originates from the inherent properties of the radio channel which is subject to highly variable propagation phenomena and interference. Since the radio environments are dynamic, as well as the users' and QoS needs, future systems will have to integrate self-adaptive, real-time and distributed algorithms. More recently, a tremendous interest for cooperative techniques appeared which allow the nodes to do more than just coexist: they can cooperate. This is a very competitive issue especially for heterogeneous systems where nodes only have a partial view of their radio environment. This cooperation can be considered at the signal level (virtual MIMO) or at the coding level (network coding), in a strong relationship with the data link layer to ensure robustness of end-to-end communications.
Autonomous wireless networking – The previously described mechanisms allow to manage efficiently the radio resource in the neighborhood of a node by taking into account the different wireless interactions. Next, the objective is to route a data from a source to a destination. This well-known problem should be revisited in the context of distributed wireless networks, particularly if we want to take benefit from agile radio, opportunistic radio links, non-symmetric neighbors and so on. Because of the large-scale dimension of the networks we consider, centralized approaches should be dismissed to the benefit of the development of distributed and localized protocols: based on local information and local interactions, the aim is to synthesize a global behavior in terms of routing, data gathering, etc. The most important issues deal with activity scheduling, topology control and protocols adaptability to the evolution of the network topology. Because such features need to be human-free, they are often referred to as the self- * paradigm which will drive our research effort. Hence, cooperation among nodes is also a tool that can be considered at the networking layer. However, such cooperative techniques will be carefully designed since they can trigger additional overhead in the network and reduce the benefits of adaptability. Furthermore, since network topologies are constantly evolving due to the mobility of the nodes and the variability of the radio links properties, fault-tolerant protocols are needed to guarantee robustness and self-stabilization.
Performance and optimization Performance evaluation and global optimization define a cross-layer axis of our project. In this action, we will be able to merge our contributions on smart wireless networks modeling using combinatorial and stochastic modeling tools. Global optimization is meant to describe system-wide behaviors and provide theoretical bounds on its performance, both by benchmarking the existing solutions and by guiding their improvement which will foster new developments. Our global optimization framework will progressively account for the software radio capabilities of the radio nodes, the properties of resource sharing algorithms and new self-* protocols. Realistic models of the wireless medium will be included, as well as refined models of adaptive protocols. This action will lead to three results : realistic models of smart wireless networks properties, global optimization and performance bounds derivation as well as distributed sub-optimal but feasible algorithms. This cross-layer axis on optimization is a necessity for developing new approaches and tools that are both efficient, provably reliable and relevant to the inherent cross-layer, dynamic and statistical nature of the systems under study.
Security – Security is one of the main cross-layer challenges of the SWING project. Security must be envisioned at each level, from hardware to routing protocols, in order to guarantee an end-to-end comprehensive security strategy. Moreover, in the context of embedded architectures, security related processing must be maintained to the least acceptable energy cost. The main challenges will then be the design of new energy efficient cryptographic primitives (in hardware and in software), the design of security mechanisms for routing protocols in order to preserve the networks from some specific attacks. The band deregulation and the on-the-fly adaptation reduces dangerously the access security. If cooperative mechanisms have to be used, the security of the various applications must be simultaneously guaranteed. Thus, security must be considered from a cross-layer perspective to allow cooperation at the physical layer while still protecting from malicious data access.
Prototyping – In SWING, we aim at addressing the challenges of smart wireless networks not only from a theoretical point of view, but also from a practical one, using simulations and prototypes. From our past experience, we acquired and developed several simulation tools. The CITI laboratory is also equipped with up-to-date radio design platforms allowing to test the embedded software radio systems, evaluate MIMO communications and perform real radio channel measurements. These skills have been acquired thanks to strong partnerships with the industrial community, which we plan to expand via new cooperations with Orange Labs, Alcatel-Lucent and other partners.