Ioana Marcu

Multiuser Systems Implementations in Fading Environments

The theory of multiuser detection technique has been developed during the 90s [Verdu, 1998], but its application gained a high potential especially for large mobile networks when the base station has to demodulate the signals coming from all mobile users [Verdu, 1998; Sakrison, 1966]. The performances of multiuser detection systems are affected mostly by the multiple access interference, but also by the type of channel involved and the impairments it might introduce. Therefore, important roles for improving the detection processes are played by the type of noise and interferences affecting the signals transmitted by different users. Selection of spreading codes to differentiate the users plays an important role in the system performances and in the capacity of the system [Halunga & Vizireanu, 2009]. There are important conclusions when the signals of the users are not perfectly orthogonal and/or when they have unequal amplitude [Kadous& Sayeed, 2002], [Halunga & Vizireanu, 2010]. In a wireless mobile communication system, the transmitted signal is affected by multipath phenomenon, which causes fluctuations in the received signal’s amplitude, phase and angle of arrival, giving rise to the multipath fading. Small-scale fading is called Rayleigh fading if there are multiple reflective paths that are large in number and there is no line-of-sight component. The small-scale fading envelope is described by a Rician probability density function [Verdu, 1998], [Marcu, 2007]. Recent research [Halunga & Vizireanu, 2010] led us to several conclusions related to the performances of multiuser detectors in different conditions. These conditions include variation of amplitudes, selective choice of (non) orthogonal spreading sequences and analysis of coding/decoding techniques used for recovering the original signals the users transmit. It is very important to mention that the noise on the channel has been considered in all previous simulations as AWGN (Additive White Gaussian Noise). This chapter implies analysis of multiuser detection systems in the presence of Rayleigh and Rician fading with Doppler shift superimposed over the AWGN noise. The goal of our research is to illustrate the performances of different multiuser detectors such as conventional detector and MMSE (Minimum Mean-Square Error) synchronous linear detectors in the presence of selective fading. The evaluation criterion for multiuser systems performances is BER (Bit Error Rate) depending on SNR (Signal to Noise Ratio). Several conclusions will be withdrawn based on multiple simulations.

Orthogonality, amplitude and number of users efects on conventional multiuser detection using turbo decoding

This paper aims to present the results that can be obtained with a conventional multiuser detector used in conjunction with turbo encoding in order to improve its performance, evaluated in terms of Bit Error Rate (BER) as a function of Signal to Noise Ratio (SNR). We used extensive Monte Carlo simulations, taking into consideration different combinations with respect to the number of users, the cross-correlation between them, amplitude vectors but also turbo decoding algorithms.

A Comparison between Performances of QPSK and 16QAM Signals for a Underground Multiuser Scenario

We will present a security/disaster scenario for a communications system with multiple access and code division in direct sequence where a number of sources communicate concurrently over the same physical channel. Since the main difference between the underground communications and the terrestrial one is the communications medium, we have investigated the specific propagation problems in dielectric medium for 16QAM and QPSK modulated signals. We found that QPSK technique is a better choice for propagation at large distances (over 200m) while for short distance transmissions, the 16QAM has some clear advantages.

Building a Unified Middleware Architecture for Security in IoT

During the past few years, the concept Internet of Things (IoT) has seen a rapid evolution from the point of view of products developed for interconnection. Even if the trend is moving towards a more secure and reliable environment, where, even if people are surrounded by sensors, actuators of intelligent devices, their need for privacy and safety is the first priority. Yet, given that recent years had also revealed some major security breaches in the way networks are designed, the need of implementing security in every aspect of our daily lives is growing. The present paper introduces a middleware architecture with the purpose of empowering IoT applications, by having a better understanding of implementation and execution of proposed security mechanisms, through testing. The middleware is part of a larger platform based on an IoT gateway node that has 3 different hardware architectures (MCU, SDSoC, traditional CPU) integrated in the shape of a single testbed.

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.

Persons Counting and Monitoring System Based on Passive Infrared Sensors and Ultrasonic Sensors (PIRUS)

Counting systems are widely used for applications related to counting people within a certain area or traffic monitoring in a crowded commercial area, for automatic settings of air-conditioning systems depending on the number of the persons located in that space, etc. Persons counting and identification systems are useful in educational domain or in cultural and entertaining areas where resource allocation must treat differently every class of customers. Therefore the main goal of the paper is to present a sensor-based system that can be used either to monitor the presence of the students in a classroom or to differentially count adults and children that enter parks, museums, etc. The implemented system (PIRUS) comprises passive infrared sensors and ultrasonic sensors. Multiple scenarios have been depicted in order to analyze and improve the performances of the designed system.

Convolutional encoding effects on conventional multiuser decoding algorithm in imperfect decoding conditions

The present work aims to illustrate the improvement that turbo encoding / decoding algorithms can bring to a multiuser detection system, evaluated in terms of Bit Error Rate (BER). Extended simulations have been performed for conventional multiuser detection algorithms and are still under study for other algorithms, like the optimal, the MMSE and the classical MMSE ones. Simulations have been performed in both optimal conditions and imperfect ones, like non-equal power of users and non- zero correlations between them and for different number of users. Several interesting conclusions have been highlighted with respect to parameters influence on overall system performances.

LDPC encoding performances for fading suppression in MIMO-CDMA wireless networks

In multiuser wireless communication systems, signal recovery, even at low BER is a relevant factor for ensuring a safe and reliable communication. Efforts for interference minimization include multiple analysis of source coding/decoding techniques, channel coding/decoding techniques and multiuser detection algorithms. This paper illustrates the improvement brought by LDPC technique in SS systems when AWGN and Rayleigh/Nakagami-m fading occur on communication channel. Performances are evaluated for different sets of spreading sequences (Walsh-Hadamard, Kasami and PN) and based on the simulation results several conclusions are highlighted and further improvement will be proposed for fading effects reduction and interference minimization.

Considerations on Estimating the Minimal Level of Attenuation in TEMPEST Filtering for IT Equipments

The main purpose of this research is to improve the security of critical computer systems with minimal costs. One of the main problems in such cases is the secondary emissions generated by electronic equipment that, sometimes, might contain confidential information stored inside a secured computer network. The implementation of a set of measures necessary to prevent information leakage through compromising emissions is generally expensive. This paper analyzes some minimal requirements that have to be fulfilled by the filtering devices in order to protect the existing commercial IT equipment against compromising emissions.

SmartGreeting: A New Smart Home System Which Enables Context-Aware Services

Home automation systems are expected to develop a new trend, as they embed new technologies and low-cost devices making them suitable for any budget. Nowadays, the researching efforts are dedicated to designing low-power and low-cost smart home systems that offer personalized services considering multiple scenarios that cover usual daily activities. The main goal of the paper is to analyse the digital output signal of passive infrared sensors used in a configuration of smart home entrance called SmartGreeting. The system can be used to enable personalized services in an entire smart home environment.