Luca Simone Ronga

A dynamic channel allocation technique based on Hopfield neural networks

The interest in global spectrum allocation techniques is growing with the always increasing spectrum demand for mobile communications. This paper deals with a dynamic channel allocation (DCA) technique based on an energy function whose minimization can be performed by a Hopfield neural network. The performance of the proposed DCA technique is derived by computer simulations. Comparisons with a classical FCA technique and a previously proposed DCA technique are given to highlight the better performance of our DCA technique.<<ETX>>

Emergency satellite communications: research and standardization activities

Space communications is an ideal candidate to handle critical and emergency situations arising on a regional to global scale, provided there is effective integration among them. The article presents a review of solutions offered by space communication systems for early warning and emergency communication services. It includes an up-to-date review of public research and standardization activity in the field, with a specific focus on mass alert. The main technical issues and challenges are also discussed along with the cutting-edge research from the scientific community.

A Game Theory Approach for DVB-RCS Resource Allocation

A DVB-RCS based, hierarchical satellite network model is presented. The network is constituted by two levels for the allocation of the resources, i.e. beam level and terminal level. For each level will be studied two different approaches, in particular the second level resource allocation has been developed according two different game theoretical approaches, based on both non-cooperative and cooperative game theory.

Communications and networking over satellites: SatNEx experimental activities and testbeds

One of the aims of the SatNEx (Satellite Network of Excellence, http://www.satnex.de) European project is to provide the scientific community that operates on satellite communications with measurement campaign results and evaluation tools, in order to support research activities that investigate problems in satellite communications at different levels of the OSI stack. In fact, the research activities developed in SatNEx address the most relevant aspects of satellite communications, such as channel modulation and coding schemes, access strategies, advanced networking, end-to-end quality of service, transport performance, delay tolerant networks, and new applications. Even if SatNEx is mainly devoted to satellite communications, integration of satellite and terrestrial wireless segments has also been taken into account. This paper presents the results obtained in the specific research activity devoted to trials and testbeds developed during the SatNEx project. The high number of authors of this paper is an indication of the strong collaborative work sustained, the numerous measurement campaigns, and the complexity in developing integrated testbeds. Copyright

Flexible heterogeneous satellite-based architecture for enhanced quality of life applications

The future pervasive communication ecosystem can improve and enhance the quality of our everyday lives by increasing comfort and safety perception, and improving interaction and conditions of activities: remarkable quality and performance will be afforded by the synergistic use of communication, positioning, and monitoring techniques, provided by means of meshed heterogeneous architectures based on satellite and terrestrial segments. In such a scenario satellite communication will represent the missing link of the evolution of services. This article aims to describe a flexible architecture that could be adopted in the future system and discussing the open points in the development of the system as well as of its single building blocks.

Cooperative Strategies for Satellite Access

Satellite communications have become an important node of the global telecommunication infrastructure. Satellite capacity request is growing quickly, driven not only by broadcast applications but, mainly, by broadband services, in particular by the expectation of “always-on” broadband services available everywhere. Thus, new “killer” applications such as HDTV (High Definition Digital Television) and broadband Internet access, provided through satellites, can help to face the growth of capacity demand foreseen in the near future. Moreover, in addition to the provision of satellite multimedia services to fixed terminals, there is an increasing demand for broadband communications on the move (i.e. on ships, trains, aircrafts, vans, cars). Analysing such an increasing demand of satellite communications, the work reported in this chapter is focused on the study of different techniques which allow the improvement of the performance of satellite users displaced in severe environments. The analysis of this context, in fact, has revealed the need to adopt adequate advanced techniques to achieve a sufficient quality in satellite links, especially in those scenarios where the link budget is tighter, such as, for example, the mobile satellite one. These considerations havemotivated the study of cooperative strategies which allow the mitigation of the deleterious effects of fading. This is obtained thanks to a new form of spatial diversity in which the diversity gain can be achieved through the cooperation of different users which generate a virtual MIMO (Multiple-Input MultipleOutput) system. The adoption of these methodologies can be very helpful in those scenarios characterised by continuous occurrences of NLOS (Non-line-of-sight) and LOS (Line-of-sight) channel conditions and, therefore, it is interesting to assess their implementation in critical satellite contexts. Considering such a context, the chapter will investigate the adoption of different cooperative techniques in some satellite access scenarios, pointing out its advantages and drawbacks. The chapter is organised as follows. Starting from the identification of critical issues in different satellite access scenarios, reported in Section 2, a general overview on cooperative strategies and, in particular, on the selected cooperative approaches, is provided in Section 3. Then, Section 4 and Section 5 report some different satellite case studies in order to show the advantages of using this kind of approach in uplink and in downlink satellite access, respectively. Finally, Section 6 provides some concluding remarks. 3

Asymptotic multiuser efficiency for a two-states CDMA system

The use of CDMA makes third generation wireless systems interference limited rather than noise limited. The research for new methods to reduce interference and increase efficiency lead us to formulate a signaling method where fast impulsive silence states are mapped on zero-energy symbols. The theoretical formulation of the optimum receiver is reported and the asymptotic multiuser efficiency has been derived and applied to the optimum two-states receiver. Numerical comparisons have been performed to show the advantages of the proposed scheme over the traditional single state CDMA transmission. Several operating scenarios have been numerically analyzed and the results are reported in the paper.

Dynamic resource allocation for LEO satellite systems with QoS provision for an IPv6 network

The approach presented in this paper aims to obtain a QoS for IPv6 protocol over LEO satellites. Most of the switching and access operations in the proposed system will require the intelligent functions to be located on Earth. We can allocate links at different bit-rates and no particular assumptions have been made as concerns the access protocol in order to maintain the presented work at a general level. Both controlled load and not-controlled load traffic have been considered. The behavior of the proposed system shows that the utilization and the delays are strictly related. The simulations show that large delays correspond to small values of utilization while short delays have the drawbacks of bandwidth wastage. The results point out that, as concerns the privileged traffic classes of NCL are subject to delays very close to those obtained by the CL traffic while maintaining high link utilizations.

Resource allocation mechanisms in satellite cooperative systems

This paper reports a study concerning the assessment of cooperation effects at MAC layer in DVB-RCS systems. In particular, a modified resource allocation mechanism has been considered in order to implement a Selective Forwarding cooperation scheme within a group of sources working in a land-vehicular scenario. The achieved results are presented in terms of aggregated average throughput for different source loads. The use of cooperation can allow improving system performance depending on the number of cooperators considered and the different channel conditions which they are subject to, and increasing the number of scenarios characterized by different propagation conditions wherein the system can transmit data packets compared to the case of absence of cooperation.

Reconfigurability for Satellite Terminals: Feasibility and Convenience

The reasons for the growing interest in reconfigurability is motivated and supported by a technology evolution of signal processing components, such as analog-to-digital and digital-to-analog converters, signal processors and FPGAs, available in the market with ever increasing performances and lower power consumptions. Reconfigurability however is expensive, in terms of development costs, power consumption, computational efficiency of devices, so not all radio systems may benefit from this innovative design. The selection of convenience areas is a tough task. Each communication context, satellites being one, has to be properly analyzed before making the decisions. We try in this paper to analyze the potentials of Software Radio for space applications, where large investments but also large