Zoltán Jakó

Chaotic communications with correlator receivers: theory and performance limits

This paper provides a review of the principles of chaotic digital communications using correlator receivers. Modulation schemes using one and two chaotic basis functions, as well as coherent and noncoherent correlation receivers, are discussed. The performance of differential chaos shift keying (DCSK) in multipath channels is characterized. Results are presented for DCSK with multiuser capability and multiple bits per symbol.

FM-DCSK: a novel method for chaotic communications

In binary Differential Chaos Shift Keying (DCSK), each information bit is mapped to the correlation between two pieces of a chaotic waveform. The receiver determines the correlation (which is proportional to the energy per bit) in order to demodulate the received signal. Since a chaotic signal is not periodic, the energy per bit is not constant and can only be estimated, even in the noise-free case. This estimation has a non-zero variance that limits the attainable data rate. This problem can be avoided if the energy per bit is kept constant. In this paper, the DCSK technique is combined with frequency modulation in order to achieve two properties: the excellent noise performance of DCSK is maintained; in addition, the energy per bit is kept constant in order not to limit the data rate. A low-pass equivalent model that significantly speeds up the simulation of an FM-DCSK system is also developed. Finally the noise performance of the proposed FM-DCSK system is given.

Enhanced versions of DCSK and FM-DCSK data transmission systems

Over the past five years many different modulation schemes have been proposed for chaotic communications. Of these, the DCSK and FM-DCSK techniques offer the best noise performance. However, even the noise performance of these schemes is a few dB worse than that of the conventional noncoherent FSK technique. The paper shows how the noise performance of DCSK and FM-DCSK systems can be improved considerably. Two solutions are considered: in the first version more than one information bit is sent using the same reference signal, while in the second version the received noisy sample functions are cleaned by averaging.

A survey of handover management in LTE-based multi-tier femtocell networks

Ubiquitous mobile communication requires increased capacity and appropriate quality guarantee for services. To meet these demands next-generation mobile network operators will deploy small cells next to conventional base station structure intensively to enhance capacity and service coverage for customers. Implementation of seamless handover between first tier (macrocell layer) and second tier (small cells) is one of the key challenges to fulfill the QoS requirements. In this paper we introduce the reader to the details of the handover procedure: information gathering, decision strategies and the base station exchange process. All these three phases face difficulties in multi-tier networks. High dense femtocell deployment makes handover related information gathering very hard, efficient handover decision mechanisms are vital to reduce the number of unnecessary handovers and avoid ping-pong effect. Last but not least base station exchange has to be accelerated to achieve appropriate system performance. Next a comprehensive survey of state of the art handover optimization solutions in 3GPP LTE/LTE-A Home eNodeB handover management is presented which includes the actual version of 3GPP LTE/LTE-A HeNB handover procedure.

On some recent developments of noise cleaning algorithms for chaotic signals

This brief deals with the design of noise cleaning algorithms aimed at the decontamination of chaotic signals having a priori known dynamics. It clarifies the derivation of two recently proposed methods by showing that they are related to noise cleaning methods based on simple standard optimization techniques. In addition, the optimality of the two methods is considered, proving that one of the methods is optimal in its optimization class while the other is suboptimal.

On the effectiveness of noise reduction methods in DCSK systems

Many different methods to decontaminate noisy chaotic signals have been proposed over the past few years. A possible application of these techniques is chaotic communications, where an unwanted additive channel noise has to be removed from the received chaotic signal. Until now, the noise performance of differential chaos shift keying (DCSK) could not be improved significantly using these noise reduction algorithms. Recent investigations suggest that noise reduction techniques can be used only if the signal-to-noise ratio (SNR) of the received signal exceeds a certain threshold. The objective of this work is to introduce an adequate performance measure based on correlation. Using this performance measure the reason for the threshold effect is explained.

Coverage Analysis of Matérn Cluster Based LTE Small Cell Networks

In next-generation mobile networks e.g., Long Term Evolution Advanced (LTE-A) the conventional macro cell structure is under laid with small cells in order to fulfill the strict QoS (Quality of Service) requirements. Smaller cells offer better receiving conditions for nearby users, thus the usage of small cells ensure throughput enhancement. On the other hand, small cells are considered as interference sources to users served by a macro cell. Therefore mobile service providers have to pay attention to the number of simultaneously operating small cells and encroach, if necessary, to provide appropriate service level to every mobile user. In this paper we provide a stochastic geometry based analytic framework to characterize the lower bound of coverage probability for a designated macro cell user. The spatial location femtocells is modelled with a two-dimension random spatial point process, namely Matérn Cluster process (MCP) and the radio channels are infected by Nakagami-m fading. The accuracy of the analytic form is verified with Monte Carlo simulations.

Analyzing LTE Small Cell Interference Distribution via Fading Factorial Moments

In LTE-A (LTE-Advanced) the macro base station structure will be augmented with outdoor and indoor small cells in order to increase the system data rate via providing better signal coverage for potential users. However, densely small cell deployment generates remarkable interference, especially operating in same spectra. This paper investigates the total interference power’s distribution generated by the small cells in the UE’s receiver. The location of the small cells is kept random and modelled as a spatial homogeneous Poisson Point Process (SPPP). The cumulative distribution function (c.d.f) of the interference is investigated in the power domain in case of Nakagami-m, Rician and Weibull faded channels. The contribution of this paper is that the interference’s cumulative distribution function follows a special symmetric alpha-stable distribution (SaS) distribution, namely Levy distribution. This kind of distribution is one the rare alpha-stable distributions, that can be characterized with a closed form c.d.f. Monte Carlo simulations confirmed the validity of the analytic forms.

Average system capacity in a two-tier LTE environment with random waypoint mobile users

Delivery of multimedia transmission in mobile networks requires appropriate coverage and enough capacity to provide Quality of Service. Femtocell systems can be suitable network components to handle these challenges. State of the art mobile and wireless networks introduce MIMO transmitters and receivers to increase available capacity significantly in exchange of very sophisticated signal processing algorithms. In this paper we present a new system model for OFDM-based femtocell systems which allows computing the average system capacity for mobile users using multimedia applications.

Downlink femtocell interference in WCDMA networks

With the usages of femtocells, users can achieve better coverage and QoS in home or office environment. But with this cheap solution in two-tier WCDMA systems the interference is increasing in the adjacent network. Because of interference the number of femtocells per macrocell is limited. This article analyse the downlink interference types in two-tier WCDMA network and sets up a simulation model for these femtocell generated downlink interferences. The simulation deals with the house/office wall penetration loss which is limiting the interference. The aim of this article to find out how many femtocells can be deployed to a macrocell, and which parameters vary this limit.