Alexandru Martian

Big Data, Internet of Things and Cloud Convergence --- An Architecture for Secure E-Health Applications

Big data storage and processing are considered as one of the main applications for cloud computing systems. Furthermore, the development of the Internet of Things (IoT) paradigm has advanced the research on Machine to Machine (M2M) communications and enabled novel tele-monitoring architectures for E-Health applications. However, there is a need for converging current decentralized cloud systems, general software for processing big data and IoT systems. The purpose of this paper is to analyze existing components and methods of securely integrating big data processing with cloud M2M systems based on Remote Telemetry Units (RTUs) and to propose a converged E-Health architecture built on Exalead CloudView, a search based application. Finally, we discuss the main findings of the proposed implementation and future directions.

A new ML detector for trellis-coded spatial modulation using hard and soft estimates

In this paper we propose a new detector for the spatial modulation (SM) receiver. In trellis coded spatial modulation (TCSM) schemes, the joint detection is used for identifying both the antenna index and the transmitted symbol. We define a hybrid maximum-likelihood (ML) SM detector, which determines the transmit antenna index soft estimate and the transmitted symbol hard estimate. The antenna indexes soft estimates are decoded using the logarithmic maximum a posteriori probability (log-MAP) algorithm. It is shown that for at least four receive antennas, the hybrid ML-SM detector offers a coding gain of at least 2 dB over the hard-output solutions in spatially correlated (SC) channels. The proposed detector is less complex than soft-output one, with a negligible bit error rate (BER) performance decrease. The BER is estimated by simulation for QPSK-TCSM transmissions over stationary Rayleigh and SC fading channels with additive white Gaussian noise (AWGN).

Analysis of frequency spectrum usage from a cognitive radio perspective

Inefficient usage of the radio frequency spectrum has been identified as one of the major problems to be solved, in a world where new communication systems appear more often lately than ever before. Cognitive Radio (CR) technology promises to be one possible solution to this problem, by allowing access of unlicensed users in licensed bands, based on an opportunistic approach and without interfering with the licensed (primary) user. A first step in order to identify the frequency bands that are more suitable for opportunistic usage is to evaluate the degree in which licensed bands are currently used. Although some measurement campaigns have already been carried out, most of them were done in the USA and only a few in other locations worldwide. This paper presents results of a measurement campaign conducted in Bucharest, Romania, covering the frequency range from 25 MHz up to 3.4 GHz. The measurement results are confronted with the frequency allocation table published by the national authority for communications and an analysis of the obtained data is being made.

Access to RF White Spaces in Romania: Present and Future

AbstractAs the demand for frequency resources increases because of the great number of new wireless technologies, the frequency spectrum becomes overcrowded and solutions have to be found in order to solve this problem. One possible solution would be to take advantage of the so called white spaces (WS), frequency bands that are actually not used by the primary (licensed) radio communication systems, by using a dynamic spectrum access (DSA) approach. In order to take advantage of these spaces, secondary (unlicensed) users have to perform a spectrum sensing process in order to accurately detect the presence of a primary system and avoid unwanted interference with it. This paper provides an overview of the status of WS in Romania by analysing the current regulations and the analogue switch-off that is planned to take place in the near future (2015). The current state of the art regarding several standards that incorporate DSA elements is being made, emphasizing the high interest in using this WS in upcoming communication systems. In order to prove the low degree in which the RF spectrum is currently used, the results of a measurement campaign performed in both urban and rural locations of Romania are discussed. A comparison with the results of other similar measurement campaigns conducted in several locations worldwide is performed as well. Several frequency bands are identified as possible WS for future opportunistic use.

Comparative study of Radio Mobile and ICS Telecom propagation prediction models for DVB-T

In this paper, a comparative study between the results of a measurement campaign conducted in northern Greece and simulations performed with Radio Mobile and ICS Telecom radio planning tools is performed. The DVB-T coverage of a transmitting station located near the city of Thessaloniki is estimated using three empirical propagation models (NTIA-ITS Longley Rice, ITU-R P.1546 and Okumura-Hata-Davidson) and one deterministic model (ITU-R 525/526). The best results in terms of minimum average error and standard deviation are obtained using the deterministic model and the NTIA-ITS Longley Rice empirical model. In order to improve the results, the tuning options available in the ICS Telecom software are used on the Okumura-Hata-Davidson model, leading to a significant increase in accuracy.

Transition from analog to digital broadcasting A spectral efficiency review

Conforming to european standards, starting with the 1st of January 2012 analog TV broadcasting should be completely replaced by digital broadcasting in Romania. In this paper we present a series of measurements done in the 470-790 MHz band, which for the moment still contains both old analog TV stations and new digital ones. An analysis is being made regarding spectral efficiency improvements brought by the new digital technologies, using sets of data collected from two different measurement locations.

Real-time spectrum sensing using software defined radio platforms

As the lack of frequency resources became a critical problem in recent years, solutions had to be found in order to use the available spectrum in a more efficient way. Cognitive radio (CR) technology is a possible answer to this, by proposing a dynamic spectrum access approach, which allows unlicensed users to access unused licensed frequency bands. In order to detect the presence of licensed users, any CR equipment has to perform a spectrum sensing process. This paper presents a practical solution for building this essential part of a frequency agile device. The implementation of the proposed real-time spectrum sensing solution is based on commercial software defined radio platforms. Hardware and software details regarding the described prototype are given, together with aspects related to the optimal configuration of the used platforms for such an application. Moreover, the performance that can be obtained using the proposed solution is evaluated through measurements performed in several different scenarios.

Erratum to: Big Data Processing for Renewable Energy Telemetry Using a Decentralized Cloud M2M System

Acknowledgments This work has been funded by the Sectoral Operational Programme Human Resources Development 2007–2013 of the Ministry of European Funds through the Financial Agreements POSDRU/ 159/1.5/S/134398 and POSDRU/159/1.5/S/132395, and supported by UEFISCDI Romania, under the Grant No. 20/2012 ‘‘SaRaT-IWSN’’. The authors are grateful to Adelina Ochian and Laura Ghenciu from Beia Consult International for the fruitful discussions that helped in the writing of this paper.

Spectrum Sensing Based on Energy Detection Algorithms Using GNU Radio and USRP for Cognitive Radio

Cognitive Radio technology focuses on the efficient use of the radio frequency spectrum. One of the challenging tasks for secondary users (SUs) is Spectrum Sensing., used to accurately detect primary users (PUs) and not to interfere with their signals. In this paper., we design a CR system in a real environment and test three spectrum sensing algorithms based on Energy Detection (ED). The capability of sensing the radio spectrum is implemented using two Universal Software Radio Peripheral (USRP) platforms combined with the GNU Radio software toolkit. The three ED algorithms are compared in terms of performance., taking into account the PU activity duty cycle in a low SNR scenario. We present the performance of these three algorithms for DPSK modulation as a primary signal to check the feasibility of these methods.

Relative orientation estimation in formation flying satellites

Satellite precision formation flying (PFF) is a concept in which multiple spacecraft communicate via an inter-satellite link (ISL) and cooperate to achieve the goal of a single, more complex satellite. This enables the creation of virtual scientific structures such as interferometers or imagers that would not be deployable in space because of their physical dimensions. PFF requires precise knowledge of the relative orientation and distance between the involved satellites. Determining the relative orientation is similar to estimating the angle of arrival (AoA) of the ISL. This paper presents an AoA estimation technique specific to Orthogonal Frequency-Division Multiplexing (OFDM) communications systems. The AoA is calculated using the preamble that is necessary to synchronize the ISL. It is estimated from the phase of the correlation at maximum. The AoA estimator is evaluated under various SNR conditions using MATLAB simulations. The results show that the estimator accuracy improves as the distance between the receiver antennas approaches the half-wavelength condition.