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RRM for CDMA networks

In Third Generation Cellular Networks, the capacity is not fixed a priori, but it is soft, which means that no-trivial relation-ship exists between the users. On the other hand, power feasibility constraints have to be solved to find the system operating point. Various Radio Resource Management (RRM) techniques, in particular Call Admission Control (CAC), are necessary to guarantee an efficient management of multiple access to the CDMA channel. For example, when the vector of users requesting admission has no feasible solution, CAC must be performed by trying to have the best possible Quality of Service (QoS), i.e., admission decision has to be taken in the most efficient way. Research performed by Leonardo Badia in this field has dealt with performance evaluation of existing CAC policies and analysis in presence of mobility of the terminals.

Economic aspects of Radio Resource Allocation

Another field has been investigated with the goal of determining a joint-venture between micro-economic instruments, like utility-functions, often applied by telecommunication researchers for analytical approaches, and economic goals of the Radio Resource Management, like maximisation of the profit for the resource assignment, and other criteria of efficiency. This work, which has been partially developed in co-operation with the Wireless Telecommunication Group at the Royal Institute of Technology (Stockholm, Sweden), has involved the formulation of an original model, called MEDUSA (Micro-economic Elastic Decentralised Users' Service Acceptance) which has been applied to different cases of Resource Management. In particular, the model proposes a way to evaluate the probability of accepting the service for each users, based on technical criterion, and employs this value to determine estimates of useful metrics, like the number of admitted users or the achieved revenue, which can be used both as a design guidelines and operative means of driving algorithms for efficiency improvement. The strong point of the MEDUSA model is the tunability of the users' reaction, achieved by means of the setting of very few parameters, whose meaning can be connected with similar economic factors. In this way, it is emphasised that a joint economic and technical analysis done at a preliminar level by the provider can be useful for estimating the behaviour of the users and gain useful insights. From a general point of view, the MEDUSA model can be applied for everyone of the following Radio Resource Management levels: Scheduling, Power Control, Rate Assignement, Admission Control. Adaptations by means of different time-scale have been proposed to distinguish between different layers, and for every case several tests have been conducted to prove the effectiveness of the approach. Several proposals have been developed in which the MEDUSA model has been applied to case studies. In particular the following studies have been completed or are under development:

  • Rate assignment for CDMA cellular networks
  • Scheduling strategies for Third Generation Networks High Speed Channels
  • WLAN management with micro-economic issues
  • Revenue-based Admission Control

Transmission protocol modelling and other studies

As a complementar topic of research, the issue of transmission protocol modelling by means of Markov chains has been studied by Leonardo Badia together with other researchers of the group at the University of Ferrara. As a side research topic, different aspects of modern communication systems have also been investigated, like the impact of mobility on Ad Hoc networks and the convergence between WLAN and 3G systems.