Philip Constantinou

A UTD propagation model in urban microcellular environments

This paper presents a three-dimensional (3-D) propagation model for path-loss prediction in a typical urban site, based on geometrical optics (GO) and uniform theory of diffraction (UTD). The model takes into account numerous rays that undergo reflections from the ground and wall surfaces and diffraction from the corners or rooftops of buildings. The exact location of the reflection and diffraction points is essential in order to calculate the polarization components of the reflected and diffracted fields and their trajectories. This is accomplished by local ray-fixed coordinate systems in combination with appropriate dyadic reflection and diffraction coefficients. Finally, a vector addition of the received fields is carried out to obtain the total received field strength and, subsequently, the path loss along a predetermined route. The model computes the contributions of various categories of rays, as selected, in a flexible manner. Several results-path loss versus distance and power-delay profile-are given, and comparisons with measured data are presented.

Measurements and characterization of wideband indoor radio channel at 60 GHz

This paper presents the measurements, the statistical results and channel models extracted by impulse response measurements of an indoor 60 GHz radio channel. The measurements were based on the pulse sounding technique. Multipath parameters that characterize the channel have been extracted and analyzed statistically concerning corridors and offices locations. The mean excess delay is in the range of 3.84 to 8.18 ns for hallways and 3.52 to 14.69 ns for offices. Additionally, rms delay spread varies from 12.34 to 15.04 ns in corridors and from 12.56 to 21.09 ns inside the laboratory. The coherence bandwidth varies between 13.88 and 30.49 MHz in corridors with a mean value of 22.48 MHz. Inside offices the mean coherence bandwidth is 22.80 MHz for LoS locations and drops to 7.05 MHz for NLoS. Small-scale models for all the measured locations were developed using tapped delay lines. The maximum Doppler frequency of the modeled channel remains around 1 Hz, whereas the coherence time is calculated 1.04 s, which indicates that the channel remains, almost stationary, exhibiting very slow fading. Finally, from the models it is derived that the channel preserves WSS and US characteristics giving rise to a WSSUS representation.

Application of Fuzzy AHP and ELECTRE to Network Selection

In a heterogeneous wireless network environment services are ubiquitously delivered over multiple wireless access technologies. Ranking of the alternatives and selection of the most efficient and suitable access network to meet the QoS requirements of a specific service, as these are defined by the user, constitutes thus an important issue. Decisions on which network to connect to are however difficult to be reached, since multiple factors of different relative importance have to be taken into consideration. This paper addresses this difficulty by adopting Multi Attribute Decision Making (MADM) methods. Fuzzy AHP, a MADM method, is initially applied to determine the weights of certain Quality of Service indicators that act as the criteria impacting the decision process. The fuzzy extension of the method, and consequently the use of fuzzy numbers, is adopted in order to incorporate the existence of fuzziness as a result of subjective evaluations. Afterwards, ELECTRE, a ranking MADM method, is applied to rank the alternatives, in this case wireless networks, based on their overall performance.

Propagation measurements and comparison with EM techniques for in-cabin wireless networks

This paper presents results of a narrowband measurement campaign conducted inside a Boeing 737–400 aircraft, the objective being the development of a propagation prediction model which can be used in the deployment of in-cabin wireless networks. The measurements were conducted at three different frequency bands: 1.8, 2.1, and 2.45 GHz, representative of several wireless services. Both a simple, empirical, inverse distance power law and a deterministic, site-specific model were investigated. Parameters for the empirical model were extracted from the measurements at different locations inside the cabin: aisle and seats. Additionally, a statistical characterization of the multipath scenario created by the transmitted signal and the various cabin elements is presented. The deterministic model, based on Physical Optics (PO) techniques, provides a reasonable match with the empirical results. Finally, measurements and modeling results are provided for the penetration loss into the cabin (or out of the cabin), representative of interference scenarios.

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.

Capacity results from short range fixed MIMO measurements at 5.2 GHz in urban propagation environment

In this paper, wideband MIMO channel measurements conducted in Athens, Greece are described. Short range scenarios with fixed transmitter and receiver, in urban like environments under LOS propagation conditions have been measured, using an 8/spl times/8 vector channel sounder operating at 5.2 GHz. Based on the measured MIMO channel matrices, results of mean and outage normalized capacity calculations are presented. These results correspond to systems with various numbers of antenna elements and various ULA antenna configurations.

Performance Evaluation of an Enhanced Uplink 3.5G System for Mobile Healthcare Applications

The present paper studies the prospective and the performance of a forthcoming high-speed third generation (3.5G) networking technology, called enhanced uplink, for delivering mobile health (m-health) applications. The performance of 3.5G networks is a critical factor for successful development of m-health services perceived by end users. In this paper, we propose a methodology for performance assessment based on the joint uplink transmission of voice, real-time video, biological data (such as electrocardiogram, vital signals, and heart sounds), and healthcare records file transfer. Various scenarios were concerned in terms of real-time, nonreal-time, and emergency applications in random locations, where no other system but 3.5G is available. The accomplishment of quality of service (QoS) was explored through a step-by-step improvement of enhanced uplink systems parameters, attributing the network system for the best performance in the context of the desired m-health services.

Microcellular propagation measurements and simulation at 1.8 GHz in urban radio environment

This paper presents the results of measurements performed at 1.8 GHz in a microcellular environment in a city center (Athens, Greece). Studies have shown that the microcellular environment is dissimilar to the conventional macrocell area, therefore, accurate knowledge of propagation characteristics is essential. The aim of the measurement campaign is to provide a clear understanding of the propagation parameters affecting the design of a personal communication system (PCS) in a city center. Theoretical predictions developed using ray tracing techniques and measurement-based models are plotted versus distance for alternative configurations. The measurement procedure, data analysis, and comparison between theoretical and experimental results are given.

Interference Environment Between High Altitude Platform Networks (HAPN), Geostationary (GEO) Satellite and Wireless Terrestrial Systems

A new broadband telecommunication system has been recently proposed for provision of fixed, mobile and personal services adopting the use of high altitude platform stations placed in a fixed position in the stratospheric layer at heights from 15.5 to 30 km. The International Telecommunication Union (ITU) has allocated a pair of 300 MHz of spectrum in the V band for these services, which is already in use by geostationary satellite and wireless terrestrial systems as co-primary allocations. This paper addresses an in-depth co-channel interference analysis and proposes a C/I (carrier-to-interference) calculation model applicable to all the interference propagation paths as well as sharing criteria between HAPN, GEO satellite and wireless terrestrial systems extracted from simulations performed in urban, suburban and rural environments. By evaluating the interference density cumulative probability distribution functions, sufficient geographical separation distances between the ground stations are proposed which guarantee the harmonic co-existence between the three broadband systems. Maintaining the platform stable in the stratosphere is a key issue, and in this paper the effect of the three different stratospheric platform’s movement models (ITU, HELINET, HALO) appearing in the literature, on C/I levels is estimated.

Direction of arrival estimation using genetic algorithms

This paper presents an application of a genetic algorithm developed for extraction of the directions of arrival of several signals impinging on a linear array. The first part describes the specific genetic algorithms terms and formulation. The second part presents some illustrative simulation cases where the impact of changes in the receiving antenna structure and the influence of the main genetic algorithm parameters are examined. Results are statistically analyzed in order to conclude on the algorithms accuracy and reliability.