Bassant Selim

Optimal cooperative spectrum sensing over composite fading channels

In this paper, we study cooperative spectrum sensing over composite fading channels. First, we consider the Mixture of Gaussian distribution to model the composite channel statistics and derive a simple generic approximation for the average probability of detection which can be efficiently applied to any composite fading channel. Second, we derive the optimal voting rule for hard combining in cooperative spectrum sensing over composite fading channels. In particular, we derive an exact closed form expression for the optimal decision fusion rule (k-out-of-N) that minimizes the total sensing error in cognitive radio networks (CRNs). This expression enjoys both simplicity and generality, making it applicable to any CRN, regardless of the channel considered. Numerical results validate the proposed analysis and show that the proposed combining rule efficiently minimizes the CRNs total error and significantly outperforms the AND, OR and majority rules that are usually considered.

Modeling and Analysis of Wireless Channels via the Mixture of Gaussian Distribution

In this paper, we consider a unified approach to model wireless channels by the mixture of Gaussian (MoG) distribution. The proposed approach provides an accurate approximation for the envelope and the signal-to-noise ratio (SNR) distributions of wireless fading channels. Simulation results have shown that the proposed model can accurately characterize multipath and composite fading channels. We utilize the well-known expectation-maximization (EM) algorithm to estimate the parameters of the MoG distribution and further utilize the Bayesian information criterion (BIC) to determine the number of mixture components automatically. We employ the Kullback-Leibler (KL) divergence and the mean-square-error (MSE) criteria to demonstrate that the proposed distribution provides both high accuracy and low computational complexity. Additionally, we provide closed-form expressions or approximations for several performance metrics used in wireless communication systems, including the moment generating function (MGF), the raw moments, the amount of fading (AF), the outage probability, the average channel capacity, and the probability of energy detection for cognitive radio (CR). Numerical analysis and Monte Carlo simulation results are presented to corroborate the analytical results.

A Generalized Mixture of Gaussians for Fading Channels

The analysis of composite fading channels, which are typically encountered in wireless channels due to multipath and shadowing is quite involved, as the underlying fading distributions do not lend themselves to analysis. An example of such channels are the Nakagami/Rayleigh-Lognormal fading channels. Several simplified expressions have been proposed in the literature. In this paper, a generalized fading model for composite and non-composite fading models, based on the so-called Mixture of Gaussians (MoG) distribution, is proposed. The well-known expectation-maximization algorithm is utilized to estimate the parameters of the MoG model. Furthermore, relying on the proposed MoG model, we derive closed form expressions for several performance metrics used in wireless communication systems, including the raw moments, the amount of fading, the outage probability, the average channel capacity, and the moment generating function. In addition, the symbol error rate of L-branch maximum ratio combining diversity receiver is studied for linear coherent signaling schemes. Monte Carlo simulations are presented to corroborate the analytical results and to assess the accuracy of the MoG model.

The effects of I/Q imbalance on wireless communications: A survey

Radio frequency front-ends constitute a core part of both conventional and emerging communication systems. Yet, although hardware realizations practically suffer from several types of impairments that degrade the overall system performance, the corresponding effects are often neglected and transceivers are assumed ideal. This typically refers to effects that are typically related to amplier nonlinearities, phase noise and in phase and quadrature imbalance (IQI), with the latter being among the most critical ones. In this context, this work provides a thorough survey on the effects of IQI, aiming to highlight their important manifestations which depending on the considered scenario can result to destructive and occasionally constructive effects.

An interoperable multi-sensor system for healthcare

Pervasive healthcare systems, enabled by information and communication technology (ICT), can allow the elderly and chronically ill to stay at home while being constantly monitored. Patient monitoring can be achieved by sensors and sensor systems that are both worn by the patient and installed in his home environment. There is a large variety of sensors available on the market that can all serve to this purpose. In order to have a system that is independent of the sensors that are used, standardization is the key requirement. This work aims to present a framework for healthcare monitoring systems based on heterogeneous sensors. In order to achieve interoperability, standards are considered in the system design.

Outage probability under I/Q imbalance and cascaded fading effects

Direct-conversion architectures (DCA) can offer highly integrated low-cost hardware solutions to communication transceivers. However, DCA devices are sensitive to radio frequency (RF) imperfections such as amplifier non-linearities, phase noise and in-phase/quadrature-phase imbalances (IQI), which typically lead to a severe degradation of the performance of such systems. Motivated by this, we quantify and evaluate the impact of RF IQI on wireless communications in the context of cascaded fading channels. Novel closed form expressions are derived for the corresponding outage probability for the case of ideal transmitter (TX) and receiver (RX), ideal TX and I/Q imbalanced RX, I/Q imbalanced TX and ideal RX, and joint I/Q imbalanced TX/RX. The offered analytic results have a relatively convenient algebraic representation and their validity is extensively justified through simulations. Based on these, it is shown that cascaded fading leads to considerable degradation in the system performance and that assuming ideal RF front-ends at the TX and RX induces non-negligible errors in the outage probability that can exceed 20% in several communication scenarios. We further demonstrate that the effects by cascaded multipath fading conditions are particularly severe, as they typically result to considerable performance losses of around or over an order of magnitude.

Key management for the MANET: A survey

Mobile Ad Hoc Networks (MANETs) are a spontaneous network of mobile devices that do not rely on any kind of fixed infrastructure. In these networks, all the network operations are carried out by nodes themselves. The self-organizing nature of MANETs makes them suitable for many applications and hence, considerable effort has been put into securing this type of networks. Secure communication in a network is determined by the reliability of the key management scheme, which is responsible for generating, distributing and maintaining encryption/decryption keys among the nodes. In this paper we investigate key management schemes for MANETs. We give an overview of available key management schemes for symmetric key, asymmetric key, group key and hybrid key cryptography.

Performance of differential modulation under rf impairments

Coherent detection requires exact knowledge of the channel state information, which is often a challenging task in demanding practical applications. Based on this, non-coherent detection of differentially modulated signals can be considered as an alternative method. The present paper investigates the effects of in-phase/quadrature-phase imbalance (IQI), which are known to degrade the performance of wireless communication systems. Specifically, we evaluate the effects of IQI on the bit error rate (BER) performance of differential quadrature phase shift keying (dQPSK) for ideal receiver (RX) with transmitter (TX) IQI, ideal TX with RX IQI and joint TX/RX IQI. Explicit analytic expressions are derived for the BER of both single-carrier and multi-carrier systems suffering from IQI at the TX and/or RX. Extensive Monte-Carlo simulation as well as offered analytic results show that realistic TX/RX IQI values can degrade the corresponding BER by over 30%. Likewise, it is shown that the detrimental effects of IQI are more considerable on DQPSK than on QPSK.

Optimal cooperative primary user localization in Cognitive Radio networks

Spectrum sensing is an essential feature of Cognitive Radio (CR) that enables the nodes to determine the availability of the spectrum to be exploited. Recent work on CR propose localization of Primary Users (PUs) which enables CR nodes, also called Secondary Users (SUs), to utilize gray spectrum (occupied by PUs) by limiting their transmission power and hence not causing interference to PUs. Techniques for cooperative localization of PU are inspired from localization in Wireless Sensor Networks. There are a number of algorithms for the enhancement of these techniques in the context of CR. The intended work, presented in this paper, aims to define an algorithm for cooperative PU localization in Cognitive Radio Networks based on an optimal tolerated error. This approach would minimize cooperation overhead while maximizing the probability of detection. The overhead refers to any extra sensing time, delay, energy and operations devoted to cooperative sensing and any performance degradation caused by cooperative sensing [1].