Theodoros E. Athanaileas

Parallel radio-wave propagation modeling with image-based ray tracing techniques

Ray tracing is a technique based on the numerical simulation of geometrical optics and the uniform theory of diffraction, two well-known approximate methods for estimating a high-frequency electromagnetic field, based on the ray theory of field propagation. Radio-wave propagation prediction models based on ray tracing play an important role in wireless network planning, as they take into account diverse physical phenomena such as reflection, diffraction and foliage attenuation and are considered critical for the analysis of long term evolution (LTE) systems, which requires a detailed description of the wireless channel. A major practical drawback of these models is that they can easily become very computationally expensive, as the required level of accuracy and the corresponding areas of study increase. In this paper, a parallel ray tracing algorithm for radio-wave propagation prediction based on the electromagnetic theory of images is presented. The implementation of the algorithm is based on the message passing interface (MPI). The decomposition of the problem is conducted by partitioning the image tree, while dynamic load balancing techniques are employed by means of the master-worker and the work-pool patterns. The performance of the parallel implementation is studied for different problems and task assignment schemes, showing that high speedups can be achieved.

An agent-based framework for integrating mobility into grid services

This paper presents an approach to integrating mobility into the originally static grid environment. The mobile agent paradigm has been exploited in order to facilitate the migration of grid services. The approach presented here separates each mobile grid service in a static part and a mobile part that can dynamically migrate across grid nodes as appropriate. In order to enable this approach, a framework based on a novel mobile agent system is proposed. The components of the framework consist exclusively of grid services conforming to the Web Services Resource Framework (WSRF) standards. The framework provides mechanisms to seamlessly integrate mobile agents and stateful grid services.

Implementation and Evaluation of a Web- Based Grid-Enabled Environment for WCDMA Multibeam System Simulations [Wireless Corner]

In the work presented in this paper, a Web-based, grid-enabled environment for wideband code-division multiple-access (WCDMA) system simulations has been implemented and evaluated. The increasing demands for computation times as the complexity of the simulation increases (e.g., increased sectorization order, smart antennas, etc., or combining system with link-level simulations) soon become prohibitively high. A WCDMA simulation is essentially a Monte Carlo simulation, consisting of a large number of identical and independent processes, which are viable for efficient and cost-effective distributed processing on a grid infrastructure. In the work presented herein, a problem-solving environment (PSE) has been implemented for grid-enabled execution of WCDMA simulations on the production grid infrastructure deployed by the Enabling Grids for E-sciencE (EGEE) project. The problem-solving environment provides a secure, Web-based portal for interacting with the grid middleware (e.g., job submission and monitoring, result retrieval, etc.). The grid-enabled simulator is presented, and implementation details are discussed. Simulation results and grid execution statistics are also shown, in order to demonstrate the validity of the approach.

A Grid Enabled Problem Solving Environment for Monte Carlo Matlab Simulations

This paper presents a problem solving environment (PSE) for the grid-enabled execution of Monte Carlo simulations. Our main concern during the design and development of the PSE was to hide the complexity of using the grid infrastructure from the actual users and simplify the way users run their application on grid resources. In order to assist non grid-expert users to execute their simulations on the grid, we have implemented transparent mechanisms that automatically create the appropriate scripts and components required for grid execution by taking as input plain Matlab files. The PSE sets up a temporary distributed Matlab environment on grid resources by using the Matlab compiler and allows the concurrent execution of standard Matlab code. The PSE has been used for several wideband code division multiple access (WCDMA) system simulation scenarios in the production grid provided by the EGEE infrastructure. Simulation results regarding performance of the PSE are presented.

Exploiting grid technologies for the simulation of clinical trials: the paradigm of in silico radiation oncology

In silico (on the computer) oncology is a complex and multiscale combination of sciences and technologies that focuses on the study and modelling of biological mechanisms related to the phenomenon of cancer at all levels of biocomplexity. In silico oncology simulation models may be used for evaluating and comparing different therapeutic schemes, while at the same time considering different values of critical parameters which present substantial inter-patient variability. As the number of the involved parameters characterizing both the complex tumour biosystem and possible treatment schemes increases, the resulting exponential increase in computational requirements makes the use of a grid environment for the execution of the simulations a particularly attractive solution. In this paper, a grid-enabled simulation environment for the execution of in silico oncology radiotherapy simulations on grid infrastructures is presented and implementation details are discussed. The environment provides a web portal as the end-user interface and contains advanced features that facilitate the execution of in silico oncology simulations in grid environments. Special consideration has been given during the development of the environment in order to simplify the maintenance and extension of the application, while additional services for Quality of Service provisioning have been applied. The simulation environment has been employed in order to perform several scenarios of glioblastoma multiforme radiotherapy simulations on the Enabling Grids for E-sciencE (EGEE) grid infrastructure. Indicative simulation results, as well as statistics regarding execution times on the grid, are presented.

Using Java Mobile Agents and PSO for Implementing a Distributed Antenna-Optimization Platform [EM Programmer's Notebook]

Various techniques and platforms have been introduced for the effective use of distributed computational resources when using specialized computational electromagnetics (CEM) simulation software for designing antennas. These techniques usually impose significant entry barriers to researchers, in the form of a steep learning curve for specialized application programming interfaces (APIs), or limited access to resources such as clusters or computational grids. The current paper discusses a sophisticated approach for alleviating these barriers, with the fusion of the programming paradigms of object-oriented programming and mobile agents. A case study concerning the development of a distributed Particle Swarm Optimization (PSO) platform - an increasingly popular algorithm within the antenna-research community - is thoroughly analyzed and presented as an example of data-level parallelism. Various aspects of computational efficiency in terms of scaling have been examined, in order to estimate the merits of the proposed approach. The aim of the analysis is to stress the advantages of the above-mentioned techniques for the effective loose coupling of CEM programs with distributed resources, demonstrating ease of application, improved scalability, and future expandability.

Performance of WCDMA in a Multicellular Network for different Multiuser Detection Strategies

The purpose of the study presented in this paper is to investigate the performance of a multicelluar Wideband Code Division Multiple Access (WCDMA) network for different multiuser detection (MUD) strategies in terms of maximum achievable capacity. Capacity is evaluated both with system level simulations for different loading, as well as with link level simulations for different MUD techniques. Due to the increased complexity of the problem, a grid-enabled problem solving environment is developed in order to reduce execution time and make feasible the Monte Carlo (MC) simulation of scenarios with up to 4 tiers of cells and increased number of users. Hence, this Grid enabled WCDMA simulator now allows for detailed consideration of the multi-cell multi-user interference with complex techniques like MUD, previously not possible. Results indicate that the parallel interference cancellation (PIC) technique with one stage detection has the best performance in a multicellular network with ideal power control.

Adaptive Beam-Centric Admission Control for WCDMA Multicell/Multiservice Scenarios with Non-Uniform Traffic

The goal of the study presented in this paper is the accurate performance evaluation of adaptive beam-centric admission control (AC) for wideband code-division multiple access (WCDMA) multicell networks with non-uniform traffic requirements. Each NodeB employs antenna arrays (AAs), used either to form fixed grids of beams (FGoBs), or to steer and shape multiple beams towards directions of increased traffic, in an adaptive manner. The adaptive beam-centric AC maximizes the cell throughput in a multirate/multicell environment by grouping as many users as possible under a common beam formed by the AA, taking into account their spatial distribution and overall interference. Due to the increased complexity of the Monte Carlo (MC) simulations, a novel grid-enabled problem solving environment has been developed in order to reduce execution times considerably and make feasible full scale extensive simulations of complex operational scenarios (up to 4 tiers of cells, multiple beams per cell, non-uniform traffic distributions with different spatial characteristics). Results show that the network with the adaptive beam-centric AC can achieve significantly higher throughput per beam in multirate/multicell environments with hotspots. In particular, it is shown that the throughput per beam gain depends exponentially on the number of hotspots per cell and their angular width, and gains up to 200/350/700% can be achieved with 1/2/3 hotspots, respectively. Moreover, it is shown that the adaptive beam-centric AC provides significant reduction in interbeam handovers, which leads to more available resources in downlink, reduced signaling requirements and easier network planning.

A grid-enabled toolkit for in silico oncology simulations

In silico (on the computer) oncology is a multi-disciplinary field that focuses on the examination and modeling of biological mechanisms related to the phenomenon of cancer. In silico oncology simulation model may be used for evaluating and comparing different therapeutic schemes while at the same time considering different values of critical parameters which present substantial inter-patient variability. As the number of the involved parameters and of the considered radiotherapeutic schemes increases, the resulting exponential increase in computational requirements makes the use of a grid environment for the execution of the simulations both a necessity for the involved researchers and an opportunity to make in silico oncology applications available to a wider biomedical and research community. In this paper, we describe a toolkit that enables the execution of in silico oncology simulations on grid infrastructures. This toolkit is designed and developed as a web portal with advanced features that facilitates the execution of in silico oncology simulations in grid environments. Several scenarios of radiotherapy simulations have been performed on the EGEE grid and indicative simulation results, as well as execution times are presented.

Using multiple communication channels in a mobile agent platform

This paper describes a flexible architecture that enables the adoption of additional communication channels in a mobile agent platform. The architecture extends an already implemented Web Service [1] based mobile agent platform by replacing communication mechanisms with more advanced components, and without modifying the platforms core components. The proposed architecture uses well-known design patterns to better define its distinguishing parts. Sockets are used as the first alternate to SOAP communication. Finally, the two different communication channels are compared and benchmarked.