Prospects of the 3G Mobile Networks in Greece (Proc. IST Mobile & Wireless Telecommunications Summit 2002, pp 557-561 16-19 June, Thessaloniki, Greece)

This paper analyses the financial impact of the deployment and operation of the UMTS networks on Greek mobile operators. A Greek incumbent operator with market share 30% throughout the ten-year period of the study has been examined. The methodology and the tool developed in ACTS- TERA and IST-TONIC projects have been utilized for this case study. Initial economic conclusions have been derived, presented and discussed using key profitability factors such us Net Present Value (NPV), Internal Rate of Return (IRR) and payback period. The techno-economic evaluation is followed by a sensitivity analysis in order to identify the impact of the most important parameters such us UMTS penetration, market share, tariff level and usage level.telecommunications, 3G mobile networks, UMTS, technoeconomics

Matching theory as enabler of efficient spectrum management in 5G networks

This is the peer reviewed version of the following article: Tsirakis, C, Lopez‐Aguilera, E, Agapiou, G, Varoutas, D. Matching theory as enabler of efficient spectrum management in 5G networks. Trans Emerging Tel Tech. 2020; 31:e3769., which has been published in final form at https://doi.org/10.1002/ett.3769. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.This paper analyzes the spectrum trading problem in virtualized fifth generation (5G) networks in order to enhance the network performance with respect to the spectrum utilization. The problem is modeled as a Many-to-Many Matching (M2MM) game with utility-based preferences and determines the matching between mobile network operators and mobile virtual network operators. The two proposed versions of utility functions for each set aim at maximizing the satisfaction of both sets with conflicting interests and improving the overall spectrum efficiency. In the simulation evaluation, the proposed scheme is compared with three different schemes in terms of the system utility, individual and pair matching satisfaction. We also investigate the scalability aspects, the strategy plan impact on the matching performance of our proposed scheme, and, at the same time, we attempt to make appropriate assumptions closer to reality. Our proposed scheme shows much better performance than the other schemes achieving a quite high level of satisfaction for the matching result on both sets.Postprint (author's final draft

Spectrum trading in virtualized multi-tenant 5G networks

© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.In this research work, we analyze the problem of spectrum trading in virtualized multi-tenant 5G networks using principles from matching theory. More specifically, we deal with the matching problem among the Mobile Network Operators (MNOs) and the Mobile Virtual Network Operators (MVNOs) and we propose a matching scheme that takes into account the preferences of each entity in terms of different utility variables. Our proposal includes a many-to-many matching scheme, that is an extension of the deferred acceptance algorithm, where each MNO and MVNO can cooperate with one or more MVNOs and MNOs, respectively. The performance of our proposed scheme is finally investigated by comparing it with various schemes and some useful conclusions are drawn.Postprint (author's final draft

Incorporating Gabriel graph model for FTTx dimensioning

For the realistic generation of synthetic street configurations, used in fiber-to-the-x (FTTx) dimensioning, the Gabriel graph model is proposed. Commencing the analysis with the Primal approach for 100 samples of urban street networks, a great heterogeneity is empirically discovered in their structural properties. Due to the observed morphological complexity, the necessity of a fast abstraction model capturing the complex street patterns is justified. The case study supports the sufficiency of Gabriel graphs for the reproduction of the street networks’ basic structural properties such as the average shortest path, the diameter or the average street segment length. The results also demonstrate the sheer superiority of Gabriel graphs for the early estimation of the trenching length of FTTx networks with more than 48 % better accuracy in comparison with the conventional geometric models. Particularly in dense urban areas, the geometric models suffer more serious accuracy shortcomings, whereas the suggested model performs even better. © 2015, Springer Science+Business Media New York

On the relation between organizational culture and leadership: An empirical analysis

Leadership and organizational culture are considered to be two of the most crucial organizational elements in order for firms to compete successfully and to gain sustainable advantage. We examine the interconnection between the aforementioned elements and create an empirical link based on data drawn from a competitive industry. The results indicate a strong relationship between these two operational factors, while factors’ coordination (identical cultural type and leadership style) enforces this relationship. Moreover, it is investigated whether market conditions, such as strength of competition and “operational age and size,” can determine the extent and the direction of the relationship. Market competition seems to affect the direction of the relationship, while operational age and size affect the relevant extent. © 2015 The Author(s). This open access article is distributed under a Creative Commons Attribution (CC-BY) 4.0 license

Investments in next generation access infrastructures under regulatory uncertainty

This article studies the impact of regulatory uncertainty on an incumbent's incentives to undertake the socially optimal investments in NGA networks. Thus, a regulatory non-commitment setting in which the regulator sets the access price after the deployment of the NGA network is used. In particular, it is assumed that the regulator sets the access price at the marginal cost of providing the access with some probability and gives an access markup, which equals the average cost of the investments, with the complementary probability. It is found that when the slope of the marginal investment cost function is not particularly steep in relation to the impact of investments on demand, the incumbent underinvests compared to the socially optimal investment level. On the contrary, in a more realistic case when the impact of investments on demand is low in relation to the slope of the marginal investment cost function, the incumbent may overinvest or underinvest depending on the probability of incorporating an access markup into the access price. © 2013 Elsevier Ltd

Connectivity issues for ultraviolet UV-C networks

This paper focuses on the connectivity issues of a non-line-of-sight (NLOS) optical wireless network operating in the ultraviolet UV-C spectral region. NLOS UV-C transmitters have a limited effective coverage and, hence, a dense node distribution is required in order to efficiently cover a large geographical area. Under this assumption, the concept of connectivity is more than important since it provides a strong indication of the network reliability and robustness. In the present study, we consider transmission with onoff keying and pulse position modulation schemes assuming both Gaussian and Poisson noise and adopt an effective experimental path loss model. Then, we evaluate the k-connectivity properties in terms of several network parameters. More precisely, we present and analyze the trade-off between node density and the degree of k-connectivity against other parameters (i.e.,transmitted power, supported data rate, and error probability). The derived results are depicted using appropriate figures and tables and constitute the theoretical basis for the design and implementation of a reliable UV-C network in practice. © 2011 Optical Society of America