Athanasios D. Marousis

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.

E-SPONDER system: A new communication infrastructure for future emergency networks

This paper describes a novel emergency communication network architecture implemented within the FP7 EU project E-SPONDER [1]. It is characterized by the deployment of heterogeneous wireless systems and also by its holistic approach achieving reliability, high performance, reconfigurability and standalone operation. It is a complete suite of real-time communication technologies built to support the first responders [1] with information services during disaster events. This work investigates the system architecture in an aircraft landing incident and describes a field test carried on at Schiphol airport in Amsterdam. More specifically, a scalable and adaptive telecommunication architecture that ensures voice, video and data between first responders and command centers at all times, even under extreme conditions, is presented. The structure and functionalities of the VoIP subsystem that operates above the proposed heterogeneous E-SPONDER network architecture is described, with a detailed scenario analysis. Finally, the paper presents how the recommended solutions are integrated into an implementable platform.

Radio Planning of Single-Frequency Networks for Broadcasting Digital TV in Mixed-Terrain Regions

This paper presents a design performed for the digital terrestrial television network in Greece. Based on the initial assumptions provided by the General Secretariat of Telecommunications, and the functional requirements of modern broadcasting networks, the authors analytically describe the design methodology followed for a successful service provision in demanding mixed-terrain country. The paper presents the calculation of the network planning values, as well as the step-by-step approach adopted for the radio coverage and the synchronization studies of the planned single-frequency networks (SFNs). The proposed DVB-T network was based on the system variant B3, and consisted of 35 single-frequency networks with a minimum of eight multiplexes in each single-frequency network. Despite the difficulties of the Greek terrain, the design proposed 191 stations, providing digital TV services to 95.9% of the population; with 84 more stations, the percentage climbed to 97.3%.

Performance of a full rate quasi-orthogonal extended MIMO MC-CDMA system with efficient channel estimator

Multi-carrier CDMA and multiple antennas are very promising candidates for simultaneous use in 4G systems, since they achieve robustness, high spectral efficiency, and high data rates in rich scattering environments. Especially, in this work an efficient extended multiple transmit antenna scheme with MT=4 elements and full rate mode for a downlink scenario has been designed and detailed evaluated. Its efficiency is enhanced by the use of an iterative architecture as a counterbalance of the quasi-orthogonal nature of the transmit diversity scheme, offering overall a higher degree of diversity gain. The evaluation has been performed in the framework of a realistic MC-CDMA system transmitting in a space-frequency format. Furthermore, the incorporation of an efficient pilot based MMSE channel identification, tracking and compensation scheme contribute resolutely to an accurate system design and evaluation. The evaluation has been performed over various spatial channel models according to IEEE 802.16e case of 3GPP.25.996 definition incorporating all IF/RF stages.

Channel Identification and Equalization for Multi-Transmit Antenna MC-CDMA Systems with Orthogonal Space-Frequency Coding

The combination of multi-carrier CDMA and multiple antennas is a very promising candidate for the downlink in 4G systems, since it achieves robustness, high spectral efficiency, and high data rates in rich scattering environments. This paper presents the design and evaluation of a channel identification scheme as a key factor for the overall performance of MC-CDMA systems. It is efficient by means of both the mean square error (MSE) and its incorporation in a real space-frequency coded MIMO system (BER). The evaluation has been performed over the spatial channel model according to 802.16e case of 3GPP.25.996, incorporating all IF/RF stages

An efficient channel estimation scheme for realistic SFBC MISO OFDM systems

This paper presents a channel estimation scheme that is efficiently designed for multiple transmit antennas, capable of operating in time varying and frequency selective propagation channels. The evaluation has been performed over the spatial channel model developed for MIMO simulations according to 802.16e case of 3GPP.25.996, taking also into account all IF and RF stages. Orthogonality has been applied in space-frequency dimension for preamble, pilot, as well as for the data symbols. In 4G multicarrier systems, multidimensional orthogonal coding design turns into a key factor for the performance of the system, something which is quite challenging in highly time-variant propagation channels. The proposed estimation approach is efficient in minimization of the processing requirements at the receiver by estimating only the time-varying channel properties. The presented results refer to MSE of the estimator, as well as to overall performance of the system (BER) in various propagation channels, data rates and FEC modes.

Design and simulation of a vector channel sounder for UMTS

The purpose of this paper is to present a design and an accurate system simulation of a dynamic vector channel sounder that will allow the spatio-temporal characterization of multi-dispersive wideband radio channels. The operating frequency is in the region of 2 GHz with switchable bandwidth up to 200 MHz, which is close to future UMTS applications. The key point of the reliability of the simulations is the use of measured component-level characterization data. Simulation results are given for different type of propagation environments.

Design of microstrip antennas for channel characterization receiver system

Summary form only given. The paper presents the design methodology and simulation results of various microstrip antennas intended to be used in the vector channel sounder under development in the Mobile Radiocommunications Laboratory. Extraction of multipath signal direction of arrival (DoA) information during wideband channel characterization requires spatially diversified reception of impinging waves. Sampling of the incident field in several locations enables one to resolve the direction of arrival of multipath signals by considering the phase difference between samples. In order to determine the DoA in three dimensions (when both azimuth and elevation angle are essential), the measurement system requires samples from non-collinear points. In this case, incident field sampling is performed by a three-dimensional (spherical) or by a two-dimensional (planar or circular) antenna array. On the other hand, for DoA resolving in two dimensions (thus, when just the azimuth angle is adequate for channel characterization) the points can be placed in a straight line, as in a linear array. In order to conclude on the type and the exact shape of the elementary antenna that will be used in the channel sounders receiving array, several design scenarios are considered based on the properties of the specific channel characterization application. The scenarios include single layered and multi layered microstrip patch antennas, experimentation on parasitic element influence, and investigation of different feeding and bandwidth enhancement techniques. Finally, an estimation of mutual coupling influence is presented by simulating. neighboring elementary antennas in patterns similar to those that would be encountered in either a linear or a two-dimensional array.

An Enhanced Embedded-Pilot Channel Estimation Architecture for MIMO MC-CDMA Systems

In this work an enhanced semi-blind channel estimator is presented for multicarrier CDMA systems with multiple transmit and receive antennas. The novel scheme is based on embedded pilots that are characterized as virtual users and their number is determined in a dynamic fashion according to the propagation channel conditions. The superimposed code-multiplexed pilots are used initially for channel estimation before the despreading operation, thus achieving per subcarrier estimation using the known unique multi-layer pattern of the virtual users. Afterwards, the estimation is enhanced by using the despread pilots. Furthermore, an iterative scheme is incorporated in channel estimation process minimizing the effect of multiuser interference and operates either in interference cancellation, or in virtual user mode. The proposed architecture is evaluated for spatial diversity systems (space- frequency block coded) with two transmit and up to four receive antennas operating in realistic propagation channels for various modulation and coding schemes. The results demonstrate a significant performance improvement especially as the channel is dominated by its time variant characteristics. The dynamic assignment of spreading codes in the payload and the pilots offers to the system realistic flexibility and adaptivity in demanding channels achieving concurrently maximization of the real overall system throughput, while maintaining low overhead and complexity burden.

Performance evaluation of a channel estimator applied in SFBC MIMO systems for W-MANs

This paper presents a channel estimation scheme that is designed for time variant propagation channels and it is efficient by means of mean square error (MSE) of channel estimation and tracking and its incorporation in a real MIMO system. Such schemes target in demanding applications with minimum data rates well above the conventional standards under pedestrian level of mobility. The evaluation has been performed over the spatial channel model developed for MIMO simulations according to 802.16e case of 3GPP.25.996. Orthogonality has been applied in space-frequency dimension for both preamble and pilot symbols, as well as for the data symbols, with the application of Alamoutis coding. The estimation scheme is efficient in minimization the processing requirements at the receiver by estimating only the time-varying channel properties, and the presented results refer to MSE of the estimator, as well as to overall performance of the system (BER) in various propagation channels, data rates and FEC modes.