Athanasios Iossifides | International Hellenic University - IHU (original) (raw)

Papers by Athanasios Iossifides

IEEE Journal on Selected Areas in Communications, 1999

In this paper, we derive an analytical framework for the performance evaluation of a recently pro... more In this paper, we derive an analytical framework for the performance evaluation of a recently proposed M-ary orthogonal scheme based on differential encoding/decoding of the Walsh/Hadamard chips prior/after spreading. This technique makes feasible nonpilot-assisted detection over fast fading environments such as the land mobile satellite (LMS) channel. Our results show that differential M-ary orthogonal signaling presents very good performance at Doppler frequency shifts much higher than the symbol rate. Amplitude statistics are considered to be Rayleigh, but may be easily extended to more general models based on the analytical derivation presented.

This work introduces a non-orthogonal multiple access (NOMA) downlink scheme, reinforced by a sim... more This work introduces a non-orthogonal multiple access (NOMA) downlink scheme, reinforced by a simple multiplexing technique of index modulation (IM) and quadrature amplitude modulation (QAM) signals, tailored to minimize their mutual interference. Integrated with orthogonal frequency division multiplexing (OFDM), this scheme achieves low bit error probability for the IM signal, at the cost of lower information rate, while practically affecting the performance of the QAM signal only due to power sharing. These characteristics, along with the provided wide range of power allocation possibilities, facilitate favorable user pairing strategies, which can be efficiently applied to multiplexing low-rate ultra-reliable low-latency communication (URLLC) and enhanced mobile broadband (eMBB) services, conveyed by the IM, and QAM signals, respectively. Aiming at providing a proof of concept of the proposed scheme, the bit error probability of both signals, the rate reduction of the eMBB service...

2016 23rd International Conference on Telecommunications (ICT), 2016

This paper investigates the performance of high rate IEEE 802.15.4 UWB PHY schemes. Evaluation ta... more This paper investigates the performance of high rate IEEE 802.15.4 UWB PHY schemes. Evaluation takes place over office, residential and outdoor IEEE channel models via Monte-Carlo simulation. Special attention is given to the highest rate (27.24 Mbps) scheme that suffers from intersymbol interference (ISI) over NLOS outdoor and residential channels. Optimum bit-to-symbol mapping (OBM), ISI cancellation and MLSE techniques are proposed and evaluated in conjunction with RAKE reception. Significant gains are attained with the proposed enhancements while keeping complexity low. On the other hand, the coverage range of high rate schemes is estimated for a given BEP. It is deduced that 27.24 Mbps and 6.81 Mbps schemes are well applicable to all LOS channels. However, the maximum allowable transmission power deteriorates range in NLOS cases. Overall, high rate schemes are shown to deserve more attention in the context of high rate sensor applications.

Proceedings of 8th International Symposium on Personal, Indoor and Mobile Radio Communications - PIMRC '97

... be used in the case of Rician fading (which is the most probable microcellular channel model ... more ... be used in the case of Rician fading (which is the most probable microcellular channel model ... Be-sides the performance gain by the use of M-ary signalling, RS codes ... should be considered in the future to complete the perspective of RS coded DS/CDMA systems with orthogonal ...

In this paper we study the statistics of the signal to noise-plus-interference ratio of a direct ... more In this paper we study the statistics of the signal to noise-plus-interference ratio of a direct sequence code division multiple access (DS/CDMA) system in a log-normal fading indoor channel. Based on the signal to noise-plus-interference ratio statistics we investigate the performance of the system in terms of the bit error probability when a maximal ratio combining RAKE receiver with either antipodal or orthogonal signalling, or square law combining RAKE receiver with orthogonal signalling is used.

2011 IEEE Symposium on Computers and Communications (ISCC), 2011

Page 1. Complex Orthogonal Coded Binary Transmission with Amicable Hadamard Matrices over Rayleig... more Page 1. Complex Orthogonal Coded Binary Transmission with Amicable Hadamard Matrices over Rayleigh Fading Channels Athanassios C. Iossifides Department of Electronics Alexander Technological Educational Institute ...

2012 5th International Conference on New Technologies, Mobility and Security (NTMS), 2012

ABSTRACT This paper proposes a semi-analytical medium access control (MAC) layer model for the ma... more ABSTRACT This paper proposes a semi-analytical medium access control (MAC) layer model for the macroscopic analysis of long term evolution (LTE) uplink. The model takes into consideration the expected number of retransmissions arising from channel disturbances and the number of allocated resources so that to satisfy a required packet delay budget. The former is computed in terms of the mean bit error probability while the latter is calculated through a high order Markov chain incorporating cell traffic load conditions. The proposed model can be used as a macroscopic planning decision tool that poses the working limits of MAC schedulers for different packet delay budget requirements, in terms of the mean number of allocated resources, MAC packet length and maximum retransmission attempts according to the channel conditions. In this context, based on measured data, we investigate the impact of the MAC packet size on the total uplink delay budget of a single user aiming to set-up the basis for future multi-user analysis.

This paper investigates the application of Reed-Solomon coding on DS/CDMA systems with M-ary orth... more This paper investigates the application of Reed-Solomon coding on DS/CDMA systems with M-ary orthogonal signaling for the reverse link of a microcellular environment. The performance of voice and data communications are analytically evaluated for a Rician or Rayleigh faded channel with lognormal shadowing and a two-slope path loss model. The effects of sectorization and antenna diversity are also considered. Numerical results, in terms of bit error probability and throughput, show that with proper selection of the coding rate and spreading, the proposed system presents enhanced performance with moderate complexity.

ABSTRACT In contemporary and future mobile communication networks, variable services with differe... more ABSTRACT In contemporary and future mobile communication networks, variable services with different characteristics need to be served simultaneously. This paper proposes a novel mathematical model for the analysis of such cases based on a two-dimensional Markov approach. This model comprises higher order resource allocation and resource sharing with no packet traffic pre-emption priority and no buffers. The state probabilities of the model have been mathematically derived and can be used as a basis for the evaluation of performance metrics of modern high speed mobile networks supporting two different service classes. Based on the model developed the blocking probabilities of two resource allocation strategies are evaluated for two simultaneous services of different characteristics.

ABSTRACT Semiconductor devices have been used extensively in optoelectronics and communications. ... more ABSTRACT Semiconductor devices have been used extensively in optoelectronics and communications. Semiconductor lasers have been proved to be the most promising devices in nowadays-optical communication networks. However light emitting diodes (LED) are the counterparts with moderate bandwidth efficiency and bit rates compared to semiconductor lasers. Considering though the cost efficiency in integrated multi-optical networks (UMTS, B-ISDN in-building links), LED is still superior. Moreover, the use of Plastic Optical Fibers (POF) in recent years, mainly for short distance optical networks, increased the interest in LEDs as transmission device. This paper presents an optical network, designed for short distance optical links, using a LED as the transmitter, POF as the channel. The examination of the optical response of LEDs in applied electrical signals is important, and the optical-to-electrical current ratio is used as the parameter of evaluation. A presentation of POF and its transmission parameters is included in order to study the channel characteristics. Finally, a multiple access scheme, based on theoretical results of LED&#39;s optical response to an applied Return to Zero (RZ) digital signal, is proposed as a technique to increase the bit rate.

2013 IEEE 14th International Symposium on "A World of Wireless, Mobile and Multimedia Networks" (WoWMoM), 2013

This paper proposes a successive coordinated power allocation (SCPA) scheme for orthogonal freque... more This paper proposes a successive coordinated power allocation (SCPA) scheme for orthogonal frequency division multiple access (OFDMA) systems based on the water-filling algorithm. The model assumes two transmitters belonging to heterogeneous cells, i.e. a macro cell and a micro/pico cell with predefined different power capabilities that cover a common geographical area over a channel that includes path loss and shadowing. The main idea is the reduction of the computation complexity and the minimization of information exchange between the two transmitters while preserving similar performance with the optimal cooperative power allocation (OCPA) joint transmission algorithm, recently proposed in the literature. The algorithms are evaluated via extensive Monte-Carlo simulations. The results show that the proposed algorithm provides similar sum rate than OCPA and presents a higher mean number of serving mobile units while reducing, at the same time, the complexity by roughly to orders of magnitude.

International Journal of Satellite Communications, 1998

This paper presents a coded modulation scheme based on M-ary orthogonal modulation by means of Wa... more This paper presents a coded modulation scheme based on M-ary orthogonal modulation by means of Walsh-Hadamard (WH) sequences, suitable for low-earth-orbit (LEO) direct sequence/code division multiple access (DS/CDMA) satellite communication systems. Based on the IS-95 scheme, we consider Reed-Solomon (RS)-coded M-ary orthogonal modulation with error or erasures decoding, which presents good performance enhancement with low complexity. LEO satellite links are characterized by large Doppler frequency shifts caused by the difference in velocity between the satellite and the earth mobile terminal, which make conventional non-coherent detection ineffective. In order to overcome the phase shift variations during the symbol period, which result in orthogonality loss of the WH sequences, we applied a differential encoding process to the spreading sequences or the WH chips prior to transmission. A special diversity process suitable for the environment under consideration is also applied. Simulation results show that the proposed diversity/coding/modulation scheme attains very good performance at low transmitter/receiver complexity.

This paper addresses the problem of calculating the number of active users in a cell on time t, g... more This paper addresses the problem of calculating the number of active users in a cell on time t, given the total number of users entering the system from the beginning of the counting process. This calculation is especially useful for estimating the active users after a certain period of time, in order to optimize scheduling decisions. In applied wireless networks, the service time most usually follows a general distribution which for some simplified models can be considered as negative exponential. This paper proposes a technique to approximate a general distribution by a Gaussian like distribution based on Hermitian polynomial expansion.

Lecture Notes in Computer Science, 2018

This paper presents and analyses a set of data that reveal secondary education students' stance o... more This paper presents and analyses a set of data that reveal secondary education students' stance on the educational activities that were realised during a UMI (ubiquitous, mobile computing and the Internet of Things) Summer School. This Summer School deals with an IoT based recycling management application development and is part of UMI-Sci-Ed project that provides a training framework on UMI learning, for students aged between 14-16, with the use of properly designed educational scenarios and communities of practice (CoP) by setting UMI technologies as learning means and learning outcomes, simultaneously. The analysis focuses on the students' satisfaction and engagement (observed through a set of questionnaires) in relation with students' potential to follow the activities, the perceived, by the students, easiness, enjoyment and usefulness while setting as parameters the student gender and age. The results clearly show high student acceptability and engagement with the designed IoT-driven activities and reveal certain differentiations with respect to gender and age in these aspects. These findings, together with the observations that high student satisfaction does not translate to equally high engagement and that enjoyment is a critical factor, provide a basis for future adjustment of the educational scenarios and activities scope and design in order to enhance the UMI-Sci-Ed impact on student preference for a future career in the UMI technologies domain.

The development of mobile communication systems started immediately after the end of world war tw... more The development of mobile communication systems started immediately after the end of world war two, with increasingly significant and global impact. The available systems faced various challenges, enforcing the development of new practices and the introduction of emerging technologies. An important aspect of those systems is security, due to their widespread use, the significance of the transmitted information and possible service abuse. Through this study, the identified security vulnerabilities of digital mobile communication systems are examined, in parallel to the emerging threats. This will provide a valuable understanding on the historical efficiency of the deployed security mechanisms and guidelines for the security requirements of future generation systems.

This paper presents and analyses a set of data that reveal secondary education students’ stance o... more This paper presents and analyses a set of data that reveal secondary education students’ stance on the educational activities that were realised during a UMI (ubiquitous, mobile computing and the Internet of Things) Summer School. This Summer School deals with an IoT based recycling management application development and is part of UMI-Sci-Ed project that provides a training framework on UMI learning, for students aged between 14–16, with the use of properly designed educational scenarios and communities of practice (CoP) by setting UMI technologies as learning means and learning outcomes, simultaneously. The analysis focuses on the students’ satisfaction and engagement (observed through a set of questionnaires) in relation with students’ potential to follow the activities, the perceived, by the students, easiness, enjoyment and usefulness while setting as parameters the student gender and age. The results clearly show high student acceptability and engagement with the designed IoT-...

2017 Panhellenic Conference on Electronics and Telecommunications (PACET), 2017

One of the major challenges that Wireless Local Area Networks (WLANs) are facing is to address de... more One of the major challenges that Wireless Local Area Networks (WLANs) are facing is to address dense scenarios, a case that is motivated by the continuous deployment of new Access Points (APs) to cover new areas and, thus, provide higher data rates. To address this challenge, which existing protocols cannot meet, the High-Efficiency WLAN (HEW) group is currently working on a new high throughput amendment named IEEE 802.11ax. In this paper, we introduce an Interference Based Dynamic Channel Access (IB-DCA) algorithm that enhances spatial reuse. We then evaluate our algorithm against the existing channel access algorithm as well as the Dynamic Sensitivity Control (DSC) and Adaptive Transmit Power Control (ATPC) algorithms that are proposed by the HEW group for various density WLAN scenarios.

IFIP Advances in Information and Communication Technology

The increase of the adoption of IoT devices and the contemporary problem of food production have ... more The increase of the adoption of IoT devices and the contemporary problem of food production have given rise to numerous applications of IoT in agriculture. These applications typically comprise a set of sensors that are installed in open fields and measure metrics, such as temperature or humidity, which are used for irrigation control systems. Though useful, most contemporary systems have high installation and maintenance costs, and they do not offer automated control or, if they do, they are usually not interpretable, and thus cannot be trusted for such critical applications. In this work, we design Vital, a system that incorporates a set of low-cost sensors, a robust data store, and most importantly an explainable AI decision support system. Our system outputs a fuzzy rule-base, which is interpretable and allows fully automating the irrigation of the fields. Upon evaluating Vital in two pilot cases, we conclude that it can be effective for monitoring open-field installations.

2019 IEEE International Conference on Pervasive Computing and Communications Workshops (PerCom Workshops), Mar 1, 2019

This work studies the influence of IoT-driven educational activities and tools (software, hardwar... more This work studies the influence of IoT-driven educational activities and tools (software, hardware and educational material) in STEM education as well as their role as STEM related career enablers to young boys and girls. The study builds on previous related results and applies to over 60 young students that are involved in hands-on learning activities in the context of a summer school. The analysis is based on especially designed close-ended and open-ended questionnaires as well as in-class observations and focuses on age and gender aspects. The results confirm the overall positive stance of the students on the educational activities and show that the provided tools under consideration are well accepted and effectively used. Furthermore, students' choices regarding prospective future careers reveal that their views on STEM fields and related professions have significantly been enriched through their participation in the summer school.

Computer Supported Education, 2019

Internet of Things and other state-of-the-art technologies like mobile and ubiquitous computing p... more Internet of Things and other state-of-the-art technologies like mobile and ubiquitous computing present ample opportunities for developing novel solutions almost in every domain of modern life. The research work presented here aims to leverage on the potential of such technologies in the direction of enhancing learning practices in secondary level education and promoting positive attitudes towards the corresponding scientific and engineering disciplines. The originality of the proposed approach lies on the provision of an educational platform, framed by contemporary pedagogical principles, and with an aim to stimulate collaboration between the relevant stakeholders in the form of operational communities of practice. Such communities are brought together on the basis of participating in on line activities, problem solving, exchanging reflections and experiences in the context of educational scenarios that incorporate modern technologies. The platform development is discussed in terms of the underlined conceptual models, the defined stakeholders' requirements, the online services developed, the software tools integrated and the data management supported. An example educational scenario, the corresponding IoT application developed and preliminary evaluation results of this approach are also reported.