Papers by Athanasios Panagopoulos
In-cabin aircraft channel temporal variations due to moving human bodies: Measurements and channel characterization
ABSTRACT In this paper in-cabin channel measurements are presented. The scenarios under investiga... more ABSTRACT In this paper in-cabin channel measurements are presented. The scenarios under investigation involve a passenger or passengers walking between the LoS path of the fixed terminals, along the hallway of the aircraft. Three different frequency bands of commercial radio networks and as well as various movement tests have been considered and presented in this paper. Slow and fast fading effects, of the in-cabin aircraft channel under the moving human presence, are examined and statistically characterized. Finally, a modeling approach in terms of a time series generator is also presented and compared with the measured data.
Communications - Scientific letters of the University of Zilina, 2012
A feasibility study of collaborative beamforming in satellite-based wireless sensor networks
Dynamic Properties of Rain Attenuation in Athens, Greece: Slant Path Rain Attenuation Synthesizer and Dynamic Diversity Gain
Progress In Electromagnetics Research M, 2015
Satellite-based sensor networks: M2M Sensor communications and connectivity analysis
2014 International Conference on Telecommunications and Multimedia (TEMU), 2014
ABSTRACT In this paper, we study the performance of satellite-based sensor networks. In particula... more ABSTRACT In this paper, we study the performance of satellite-based sensor networks. In particular, we consider dense networks of M2M sensor devices deployed in several geographical locations. The M2M sensor devices are locally grouped into clusters and communicate with a satellite gateway. The proposed network architecture is a potential solution for remote monitoring and surveillance networks usually deployed on border and non-habitable areas. We also consider the employment of Ka band for the broadband satellite connection. Consequently, an efficient clustering methodology is proposed for the M2M sensor devices while the feasibility of the proposed system in terms of connectivity of the satellite gateways using high data rate terrestrial links operating at frequencies above 10GHz, is investigated. Finally, we present realistic satellite link budget analysis using either GEO or LEO Ka band satellites.
Optimal iSINR-based power control for cognitive satellite terrestrial networks
Transactions on Emerging Telecommunications Technologies, 2015
ABSTRACT The incorporation of cognitive radio techniques in satellite communications has recently... more ABSTRACT The incorporation of cognitive radio techniques in satellite communications has recently become a significant research challenge leading to the proposal of a novel network infrastructure known as cognitive satellite terrestrial networks. However, efficient resource management mechanisms should be proposed to provide a complete system analysis for this promising architecture. Towards this direction, this article focuses on the problem of power management in cognitive satellite terrestrial systems, where the satellite system has the role of the cognitive system, while the terrestrial represents the primary one. Particularly, a power control scheme for the satellite terminal is proposed. Taking into account the peculiarities of both systems and considering the uplink case, the goal of the proposed scheme is to optimise the performance of the satellite link without deteriorating the communication quality of the terrestrial link. To safeguard the communication of the terrestrial system, we introduce a novel interference-based constraint, which ensures a specific level for the inverse signal-to-interference plus noise ratio of the terrestrial link. Both the cases of perfect and imperfect channel estimation of terrestrial link are considered in order to study a more realistic scenario. Furthermore, for the imperfect case, a protection mechanism is proposed to guarantee the communication quality of the primary link that offsets the uncertainty of channel estimation. Simulation results evaluate the performance of the proposed scheme for various system parameters and verify its superiority compared with the well-known water-filling based power control scheme for both cases of perfect and imperfect channel estimation. Copyright © 2015 John Wiley & Sons, Ltd.
Effects of spatial correlation on QoS-driven power allocation over Nakagami- m fading channels in cognitive radio systems
Transactions on Emerging Telecommunications Technologies, 2013
ABSTRACT Cognitive radio (CR) technology is a revolutionary wireless communication paradigm that ... more ABSTRACT Cognitive radio (CR) technology is a revolutionary wireless communication paradigm that targets at the efficient and flexible utilization of the limited radio spectrum resource. This paper considers a spectrum underlay CR system operating in a fading environment, where the secondary users (SUs) have specific communication quality requirements. In this system, the unlicenced SUs may coexist with the licenced primary users, as long as the average interference-power that they cause to the primary users does not exceed a threshold value.The concept of spatial correlation (cross-correlation) of Nakagami-m fading channels is introduced in the quality of service-driven CR system. Specifically, we present a power allocation scheme that aims at maximising the SU's effective capacity, and we study the effects of the spatial channel correlation on the performance of the proposed scheme. In order to investigate thoroughly the impact of fading correlation, two different scenarios are studied, depending on which links are considered correlated, the receive correlation model and the transmit correlation model. The performance of the proposed allocation scheme is evaluated through simulations. Finally, the effects of spatial channel correlation for different system requirements and scenarios are presented and discussed. Copyright © 2013 John Wiley & Sons, Ltd.
An auction-based mechanism for spectrum leasing in overlay cognitive radio networks
2013 IEEE 24th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC), 2013
ABSTRACT Spectrum leasing in cognitive radio networks has recently started to draw the attention ... more ABSTRACT Spectrum leasing in cognitive radio networks has recently started to draw the attention of the researchers. According to this concept, the primary users own specific spectral resources and they decide how to lease them to the secondary users so as to optimize their performance. In this paper, we consider an overlay cognitive radio network where the secondary users are allowed to transmit simultaneously with the primary user in exchange for devoting a part of their power to relay the primary signal. Focusing on the distributed nature of cognitive radio networks, we propose an auction-based mechanism for the leasing process. The secondary users, who represent the bidders, decide the power that are willing to employ for relaying PU's data whereas the primary user has the role of the auctioneer deciding the duration of the leasing process as well as the leasing time allocated to each secondary user. Furthermore, three different scenarios are studied, depending on the channel state information available to the secondary users. The performance of the proposed mechanism is investigated through the numerical analysis and the advantages of complete knowledge of channel state information are highlighted.
QoS-Driven Power Allocation Under Peak and Average Interference Constraints in Cognitive Radio Networks
Wireless Personal Communications, 2014
ABSTRACT Efficient radio spectrum utilization can be improved using cognitive radio technology. I... more ABSTRACT Efficient radio spectrum utilization can be improved using cognitive radio technology. In this work, we consider a spectrum underlay cognitive radio system operating in a fading environment. We propose an efficient power control scheme that maximizes the effective capacity of the secondary user, provisioning quality of service while on the same time the communication of the primary user is guaranteed through interference constraints. The specific power allocation scheme uses a policy in which the outage events of the primary user are exploited leading to a significant increase of the secondary user’s effective capacity. Moreover, the interference of the primary link to the secondary is taken into account so as to study a more realistic scenario. In order to safeguard primary user’s communication, two types of restrictions are considered: the traditional interference power constraint and the proposed inverse signal to interference plus noise ratio constraint. Different scenarios depending on the nature of the constraints (peak/average) are studied and their impact on the performance of the primary and secondary users is investigated. The superiority of the proposed schemes is demonstrated through their comparison with two reference power control schemes. Finally, numerical calculations, validated with simulation results, confirm the theoretical analysis and evaluate the performance of the proposed scheme for all the different scenarios.
Advanced Energy Efficient Communication Techniques for Wireless Ad Hoc and Sensor Networks
Advances and Applications in Mobile Computing, 2012
Cooperation Incentives in 4G Networks
Wireless Networks and Mobile Communications, 2011
Game-theoretic Spectrum Trading Mechanism for Cognitive Radio Networks
Satellite-based wireless sensor networks: Radio communication link design
ABSTRACT This paper focuses on the application of Collaborative Beamforming (CB) technique to a s... more ABSTRACT This paper focuses on the application of Collaborative Beamforming (CB) technique to a satellite-based environmental monitoring and surveillance scenario, where wireless sensor nodes communicate directly with a satellite, without the need of a gateway. We consider Geostationary (GEO) and Low Earth Orbit (LEO) satellite networks scenarios that operate at the frequency range of S-band and a typical wireless sensor network (WSN) (e.g. Zigbee). The analytical link budget is presented. Moreover, the effect of different system parameters on the number of nodes required for direct link communication is examined. Significant conclusions are drawn.
QoS-driven spectrum sharing game in cognitive radio systems: a variational inequality approach
Transactions on Emerging Telecommunications Technologies, 2014
ABSTRACT Cognitive radio (CR) technology aspires to the efficient usage of the limited and underu... more ABSTRACT Cognitive radio (CR) technology aspires to the efficient usage of the limited and underutilised radio spectrum resources. Constituting a flexible and intelligent network, the unlicensed secondary users (SUs) may coexist with the licensed primary users (PUs), under the prerequisite not to disturb their communication. A spectrum interweave CR system is considered, where SUs coexist with a single PU pair in a fading environment. The SUs are allowed to transmit their data ‘peacefully’, only with the absence of PU's transmission, by exploiting spectrum holes of the licensed band. A quality of service (QoS)-driven spectrum sharing scheme is proposed. Specifically, the problem of licensed spectrum sharing among SUs is formulated as a novel non-cooperative game with a view of maximising the effective capacity of each SU that has specific delay QoS requirements, subject to the coupled constraint of the available bandwidth. Because this game constitutes a generalised Nash equilibrium problem, we apply the variational inequality framework to solve it. The variational solution is proven to be unique, and it is obtained through a distributed iterative algorithm. The performance of the proposed scheme is evaluated through numerical simulations, and the results confirm the importance of incorporating the delay QoS factor in spectrum sharing studies. Copyright © 2014 John Wiley & Sons, Ltd.
Evolution of Cognitive Networks and Self-Adaptive Communication Systems
The rapid growth of spectral resources' demands, as well as the increasing Quality of Service (Qo... more The rapid growth of spectral resources' demands, as well as the increasing Quality of Service (QoS) requirements of wireless users have led to the necessity for new resource allocation schemes which will take into account the differentiated QoS needs of each wireless user. Towards this direction, the researchers have introduced the concept of effective capacity, which is defined as the maximum rate that the channel can support in order to guarantee a specified QoS requirement. This concept has been considered as a "bridge" among the physical layer characteristics and the upper-layer metrics of QoS. During the last years, it has been widely employed for resource allocation problems in various wireless networks leading to efficient mechanisms. This chapter focuses on the employment of the effective capacity theory in Cognitive Radio (CR) systems, presenting an extensive survey on QoS-driven resource allocation schemes proposed in the literature. Some useful conclusions are presented and future research directions on this subject are highlighted and discussed.
Optimal power allocation under QoS constraints in cognitive radio systems
2011 8th International Symposium on Wireless Communication Systems, 2011
ABSTRACT Cognitive radio technology aims at the efficient utilization of the limited radio resour... more ABSTRACT Cognitive radio technology aims at the efficient utilization of the limited radio resources and the improvement of flexibility of spectrum usage in wireless networks. The main idea of this technology is the development of intelligent networks where the unlicensed secondary users may coexist with the licensed primary users, always limited by the obligation not to affect their communication. In this paper, we consider a spectrum underlay cognitive radio system operating in fading environment. Guaranteeing that the average interference limit constraint to primary users is satisfied, we propose a quality of service (QoS)-driven power allocation scheme, with a view to maximizing the effective capacity of the secondary users. The proposed scheme takes into consideration the interference of primary user to the secondary user, in order to accomplish the optimal allocation more realistically. Finally, the proposed allocation scheme has been evaluated through numerical simulations that confirm the presented theoretical analysis.
Time diversity prediction modeling using Copula functions for satellite communication systems operating above 10GHz
2014 XXXIth URSI General Assembly and Scientific Symposium (URSI GASS), 2014
2012 6th European Conference on Antennas and Propagation (EUCAP), 2012
The Inverse Gaussian (IG) distribution is examined for modeling the rainfall rate and slant path ... more The Inverse Gaussian (IG) distribution is examined for modeling the rainfall rate and slant path and terrestrial link rain attenuation. The long-term statistics of rain rate and rain attenuation are modeled using the IG distribution. The method is validated using the recommendation of International Telecommunication Union (ITU) recommendation ITU-R. P. 837 and rain rate data from the ITU Study Group 3 database (DBSG3) database for the case of rain rate. For the modeling of rain attenuation, data which are derived from two databases of DBSG3, these of Earth-space links and line-of-sight terrestrial links are used for validating the model. The results are compared to the one using the lognormal distribution. It has been shown that IG distribution could be more appropriate for modeling rainfall rate and slant path and terrestrial link rain attenuation. Finally, some useful conclusions are derived and presented in this paper.
On the Outage Probability Prediction of Time Diversity Scheme in Broadband Satellite Communication Systems
Progress In Electromagnetics Research C, 2013
Wireless Personal Communications, 2009
A number of research works have suggested a possible capacity advantage when employing direct seq... more A number of research works have suggested a possible capacity advantage when employing direct sequence-code division multiple access (DS-CDMA) instead of the more common time division multiple access option for fixed broadband wireless access networks operating at millimeter-waves. The choice of this multiple access scheme, which, up to now, has not been foreseen by recent WiMax (worldwide interoperability for microwave access) standards, exhibits an improved performance in terms of cochannel interference in the upstream, even though it experiences higher interference in the downstream. The present paper focuses on enhancing the bottleneck downstream performance of fixed wireless networks by proposing a methodology for controlling the signal-to-interference ratio throughout the cell, so that all subscribers meet the given interference quality-of-service specifications. This is accomplished by exploiting the properties of a combination of multirate CDMA techniques. The paper describes a simple policy for code assignment, which is proved to be optimal, incorporating the effect of rain fading over multiple paths. The performance of the algorithm is tested against single code DS-CDMA both under long term channel statistics (static code assignment) and under dynamic channel effects (dynamic code assignment). The first test verifies the compliance of all sector subscribers with more demanding SIR specifications, while the second yields a significant improvement in terms of resource utilization.
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Papers by Athanasios Panagopoulos