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Project Goals

Looking at the recent development of the wireless access networks, it is easy to clearly identify a new trend which leads from systems with single technology and few large-scale transmitting stations, located at strategic places, to pervasive systems characterized by many stations, many technologies and many actors. The large increase of the offered traffic and the need for broadband access networks led to a reduction in cell size. Moreover, the emergence of new technologies such as Wi-Fi and WiMax, in addition to the traditional cellular networks, increased the number of different wireless technologies. Those latter are often in overlap according to criteria laid down by market imperatives, rather than technical considerations. The great number of actors involved in the installation and management of wireless equipments further increases the complexity of those systems: telcos offer traditional services, new Internet Service Providers offer data connectivity in urban areas, local governments provide connectivity via hot spot, civic associations set up urban mesh networks sharing their equipment and so on. The above remarks show the high complexity of handling access networks with such heterogeneous actors and technologies. First of all the high number of device to be managed implies a great effort to configure, to monitor and to keep efficient both the devices and the whole network. Moreover, it is very difficult to find skilled personnel to operate on the network: while this issue is of no concerns for a telco operator, many other actors, such as local governments, citizen association, are forced to outsource the network management and therefore they try to limit the operation to be done on the network to the minimum possible. These factors pose considerable limitations on the exercise of the network.

To address these issues, from some time, the research and development community which works on wireless networks has focused on the idea of “Self-Organizing” devices. Devices which are capable to self-organizing, in fact, would allow to manage the network and modify its settings without the human intervention. The STEM-Net project is placed within the framework of “Self-Organization”. Its ultimate target is to study, to analyze, and to implement a new approach for wireless multi-hop networks which is based on the use “stem” devices. A stem device is able to reconfigure itself at many protocol layers depending on the situation, on the context, on the required service, on the information formerly learned and on its interaction with other analogous devices. The concept of “stemness” of a wireless communication device is accomplished, within STEM-Net following 4 main relevant research directions: protocol reconfiguration capability (intra-stack), multi-homing functioning capability (inter-stack protocol reconfiguration capability), learning capability and capability to cooperate/coordinate with other devices.

The project aims at the final goal by establishing specific objectives related to research directions mentioned specifically in what follows:

Protocol reconfiguration capability (intra-stack)

- To devise an agile, and flexible protocol stack which allows to include new functionalities, which behaves as a repository of the information learned during the lifetime of a stem device, which allows the information exchange between the layers of the protocol stack following a cross-layer approach, which enables control function across the protocol stack.

- To determine a set of parameters of the physical and MAC layer which may be modified depending on the characteristics of the environment and on the infrastructure where the device is operating.

- To determine the enabling technologies to reconfigure the lower levels (Physical and MAC) of the protocol stack (intra- stack reconfiguration capability). Those technologies should also enable to activate “on-the-fly” extensions/variants of the MAC protocol and should be based on the paradigms of dynamic spectrum access (DSA) and of cognitive radio (CR).

- To define a set of metrics to evaluate the impact of the mobility of the nodes on each layer of the protocol stack.

Multi-homing functioning capability (inter-stack reconfiguration)

- To determine network and transport level characteristics which allow to activate:

- routing functionality and also switching between different routing protocols;

- bridging functionality between different technologies (e.g. Wi-Fi and UMTS);

- on-the fly services such as DHCP, DNS, Proxy http, Proxy SIP;

- and deactivate interfaces.

- To analyze the case of multi-home stem nodes which own multiple radio interfaces operating on heterogeneous wireless access technologies. To determine, in that case, the enabling technologies for protocol reconfiguration at the upper levels of the protocol stack (i.e. session/application level).

- To determine methods for role assignment to every stem device in order to meet specific optimization criteria.

- To define transparent management policies to address vertical handover.

- To define systems to update on-the-fly device's software/firmware in order to implement new functions/protocols.


- To study decision making techniques by which stem units can dynamically learn the optimal configuration of their own physical and MAC transmission parameters. The concept of optimality, as it is meant in this context, refers to the quality of service requirements of the applications.

- To study the cognitive cycle and physical/MAC reconfiguration capability impact on the network and transport protocol levels.

- To define mathematical models for determining the role of topology in the process of stem unit's resource optimization in terms of energy, transmission band and propagation delays.


- To study solutions to support concurrent multi-homing, by allowing stem unit to use all available wireless access technologies in order to increase the aggregate transmission capability.

- To analyze the relationship between intra-stack and inter-stack reconfiguration capability and define coordination mechanisms by allowing stem units to select the most suitable reconfiguration capability approach to address both application's requirements and environment's constraints.

- To define the coordination and information exchange mechanisms between nodes in order to obtain a specific global behaviour.

- To define cooperation techniques among nodes which relay the same data stream through algebraic network coding.

- To introduce coordination techniques allowing distributed scheduling between nodes.

- To implement cooperation techniques allowing nodes to follow a common behaviour.


P.R.I.N. 2009


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