Carmen Voicu

Performances of conventional and MMSE detectors for image transmissions

This paper presents the results obtained by using conventional and MMSE (minimum mean square error) multiuser detectors structures when gray images are transmitted through the system. Three metrics are used to evaluate and compare the output images: the bit error rate, the peak signal-to-noise ratio and the structural similarity index. Several conclusions are highlighted, with respect to the level of performance achieved.

A comparison between the performances of CDMA multiuser detectors for binary image transmission

This article presents the results obtained by using CDMA multiuser detectors structures when binary images are transmitted. The performances are compared in terms of bit error rate as well as peak signal-to-noise ratio as functions of the channel signal-to-noise ratio and for different transmission scenarios. In the final section, several interesting conclusions are highlighted.

Performances of synchronous multiuser detectors for grey-type image transmissions

This article presents the results obtained by three multiuser detectors, namely the conventional, the minimum mean square error and the optimal maximum a posteriori one, when grey images are transmitted, as well as the inter-correlation between users and the amplitude imbalance effects on their performances. Three metrics are used to measure and compare the quality of the received images: the bit error rate, the peak signal-to-noise ratio and the mean structural similarity index. Based on the results obtained, we compared the performances achieved by the three detectors and their sensitivity to system imperfections. Several interesting conclusions are highlighted in the final section.

Conventional and optimum multiuser detectors performances for image transmissions

This paper presents the results obtained by using conventional and optimal multiuser detectors structures when gray images are transmitted. The bit error rate and peak signal-to-noise ratio performances are evaluated and compared, as functions of signal to noise ratio and the correlation coefficients between them. Finally, several conclusions are highlighted, with respect to the level of performance achieved and implementation complexity.

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.

Performance evaluation of subcarrier allocation methods for OFDMA

The purpose of this paper is to analyze performances of three subcarrier allocation methods used by orthogonal frequency-division multiple access (OFDMA). In OFDMA, before assigning subcarriers to users, they are first distributed into subchannels using three different subcarrier allocation methods. The results are compared in terms of bit error rate (BER) dependency on signal to noise ratio (SNR), for different multipath propagation channels, for a variable number of users and for different digital modulation schemes.

MMSE detector using space-time diversity coding over Rayleigh fading channels

The present paper investigates the impact of space-time diversity coding over Rayleigh fading channels when the Minimum Mean Square Error (MMSE) multiuser detector structure is used. The Bit Error Rate (BER) is used to evaluate and compare the system performances in several situations. In the final part, several conclusions are highlighted, with respect to the level of performance achieved.

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.

LDPC Coding Used in Massive-MIMO Systems.

This paper presents the importance of Massive-MIMO systems and the LDPC coding technique used to improve their performance. We will focus on LDPC coding used in the implementation of a Massive-MIMO system and the simulation results using Matlab. A comparison between the classical systems and the LDPC coded system will be made, in order to stress the improvements in particular cases. Starting with simple MIMO systems, the number of antennas at the receiver will be increased and the result will be discussed.

Estimation Algorithm for Large MIMO System

In multiuser Large MIMO communication systems, signal recovery is a relevant factor for ensuring a safe and reliable communication, especially when the users are intercorrelated. Solutions for interference minimization include analysis regarding source coding/decoding techniques, channel coding/decoding methods and multiuser detection algorithms. This paper illustrates the performance improvement brought by convex optimization technique in Large MIMO systems when the channel is affected by AWGN and Rice fading. The performance is evaluated for different sets of spreading sequences (Walsh-Hadamard 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.