Antonis G. Gotsis

Non-ionizing electromagnetic radiation monitoring in Greece

The design, development, and operation of a network for the monitoring of the non-ionizing electromagnetic radiation in Greece is presented in this paper. Two independent sub-networks, called “Hermes” and “pedion24” have been operating since November 2002 in many areas, and more than 4,000,000 electric field strength measurements have been conducted to date. The measurement results indicate that the non-ionizing electromagnetic radiation levels are several times below the European Commission Recommendation 1999/519/EC and the Hellenic Republic Law no. 3431 reference levels.

Linear modeling and performance evaluation of resource allocation and user scheduling for LTE-like OFDMA networks

A linear model for evaluating the performance of adaptive resource allocation and user scheduling regarding a single-cell downlink SISO-OFDMA packet data network like LTE is developed in this paper. Based on this model several power, bit, frequency block and frame allocation approaches are examined and the corresponding performance upper bounds are numerically extracted. We put a special emphasis on equal power allocation and single modulation mode per user approaches, since they are proposed by the 3GPP standardization body. The individual and joint effect of each system degree of freedom to the overall performance is thoroughly discussed. The merit of the specific model is that it provides us with the performance upper bounds spending polynomial execution time.

On user association and multiple access optimisation in 5G massive MIMO empowered ultra dense networks

Ultra network densification and massive multiple-input and multiple-output are considered major 5th generation technology enablers, promising huge capacity gains as they offer proximity, spectral and spatial reuse benefits. Towards succeeding in harnessing the anticipated gains, a systematic treatment of radio resources management challenges encountered in such network deployments is of utmost importance. In this respect, we introduce and study in detail the user-association and multiple-access optimisation aspects of massive multiple-input and multiple-output ultra dense networks. We derive for the first time to the best of our knowledge a series of mathematical programming models for computing the optimal user-association decisions and assessing the impact of two multiple access candidate approaches, namely, frequency domain and spatial domain multiple access. We support the work with an extensive performance evaluation study, which reveals the rate scaling performance trends of the different approaches, considering various network operation conditions, as well as obtain useful design insights for future setups employing the particular technologies. Copyright

Adaptive Power and Subchannel Allocation for Dual-Class OFDMA Packet Data Networks

Adaptive Radio Resource Allocation exploiting the inherent frequency selectivity of the wireless medium as well as the multi-user diversity effect is expected to play a crucial role in providing high QoS on emerging OFDMA-based wireless networks. Although a plethora of studies concerning exclusively constant bit rate (CBR) or variable bit rate/best effort (BE) traffic has been published to date, limited amount of work has been devoted to the more practical mixed CBR-BE data traffic scenario over OFDM radio access networks. In this paper we attempt to deal with the specific heterogeneous allocation problem, namely the maximization of elastic users’ sum-throughput while providing minimum data rate service to a subset of non-elastic users. The contribution of this work is twofold. First, due to the high complexity of the resource allocation problem, we propose a relaxation method based on the prioritization of CBR- over BE-class users during the subchannel allocation procedure. We devise a method for obtaining the exact performance penalty induced by the specific hypothesis when compared to the optimal (unprioritized) decision. Secondly, we develop a polynomial complexity approximation algorithm for allocating power and bandwidth, that employs the CBR-prioritization idea. The scheme is shown to experience a relatively low performance penalty compared to its upper bound and to outperform two representative algorithms from the literature.

PHY- and MAC-aware Resource Allocation and Packet Scheduling for Single-Cell OFDMA Packet Networks

Radio resource management mechanisms such as PHY-centric Radio Resource Allocation and MAC-centric Packet Scheduling are expected to play a substantial role in the performance of future OFDMA-based wireless networks. Inevitably, efficient resource allocation strategies have to exploit information laying in different OSI layers, allowing for a cross-layer design. In the literature adaptive allocation schemes have been proposed for optimum or suboptimum resource distribution in the frequency domain under static individual user rate constraints. The contribution of this work is twofold: First, we evaluate current allocation schemes under realistic traffic and channel conditions, in order to acquire the upper performance bounds on a real time evolving network. Then we extend them to incorporate MAC-layer information, as well as opportunistic packet scheduling in the time-domain. The key factors that affect the overall system performance in terms of system average throughput and delay are identified, evaluated and discussed. The presented ideas are accompanied with extensive system level Monte-Carlo simulations.