Nikos Fragoulis

Log-domain wave filters

A systematic method for designing log-domain wave filters is presented. Wave filters simulate topologically and functionally passive doubly terminated LC ladder prototype filters of low sensitivity. The design in the log-domain is based on a transposition of the signal flow graph (SFG) that corresponds to the wave equivalent of elementary two-port blocks in the linear domain, to the corresponding log-domain SFG. This is achieved by using an appropriate set of complementary operators, in order to preserve the linear operation of the whole circuit. Simulation results of a fifth-order low-pass and a fourth-order bandpass log-domain wave filter are given, using HSPICE. The proposed circuits are suitable for low-voltage operation and in high-frequency applications.

Modular log-domain filters realized using wave port terminators

Log-domain wave filters that simulate the passive LC ladder prototype filters are introduced in this paper. The proposed circuits are constructed from the wave equivalents of the reactive elements corresponding to those in the prototype circuit. The wave equivalent circuits are obtained by using a novel log-domain wave port terminator. The wave equivalent of a capacitor in a shunt branch was chosen as an elementary building block for creating high-order filters. The wave equivalent circuits of all other reactive elements in a shunt or in a series-branch connection can be readily obtained using the elementary building block plus some inverters. This way the derived high-order filter configurations are modular. A design example of a third-order elliptic low-pass filter is given, and the performance of the filter was verified by simulation.

Broadband Internet Access via Multi-Hop Wireless Mesh Networks: Design, Protocol and Experiments

While bandwidth for Internet access in urban areas is steadily increasing in recent years, many rural areas are still suffering from the effect of the digital divide. This paper presents a broadband Internet access paradigm developed in the context of the ADHOCSYS project, which was financed by the European Commission under the 6th Framework Program Information and Society Technologies, within the strategic objective of Broadband for All. Aiming at providing reliable Internet access in rural and mountainous regions where xDSL connections are not available due to coverage limit, the ADHOCSYS network provides a cost-effective solution based on multi-hop wireless mesh network technologies. Starting from a general description of the network architecture and application scenarios, this paper focuses on presenting the routing, QoS and network deployment aspects of the developed solution. Other aspects like reliability prediction, power supply, security and authentication, and auto-configuration, etc are discussed only briefly. In order to validate the developed broadband access solution, a real-life operational wireless mesh network has been deployed in a mountainous region in Northern Italy. The performance of the developed solution has been evaluated based on the deployed real-life network, and the obtained numerical experimental results, along with the practical lessons learnt through installations and experiments are also presented in this paper.

Performance Evaluation of Image Fusion Methods

The recent advances in sensor technology, microelectronics and multisensor systems have motivated researchers towards processing techniques that combine the information obtained from different sensors. For this purpose a large number of image fusion techniques [Mukhopadhyay & Chanda, 2001; Pohl & van Genderen, 1998, Tsagaris & Anastassopoulos, 2005; Piella, 2003] have been proposed in the fields of remote sensing, medical diagnostics, military applications, surveillance etc. The main goal of these image fusion techniques is to provide a compact representation of the multiple input images into a single grayscale one that contains all the important original features. Such an image provides improved interpretation capabilities but can also be used for further computer processing tasks, like feature extraction or classification. The performance of image fusion techniques is sometimes assessed subjectively by human visual inspection. The reproduction of subjective tests is often time-consuming and expensive, while the exact same conditions for the test cannot be guaranteed. This has led to a rising demand for objective measures in order to rapidly compare the results obtained with different algorithms or to obtain optimal settings for a specific fusion algorithm. The objective evaluation of the performance of pixel level fusion methods is addressed in this book chapter. The image fusion processes can be classified in grayscale or color methods depending on the resulting fused image. For this purpose the general framework of objective evaluation of image fusion is discussed and different fusion measures are discussed. Moreover, a global measure for grayscale image fusion schemes, IFPM, based on information theory is presented. The measure employs mutual and conditional mutual information in order to assess and represent the amount of information transferred from the source images to the final fused grayscale image. Accordingly, the common information contained in the source images is considered only once in the performance evaluation procedure. The experimental results clarify the applicability of the IFPM measure in comparing different fusion methods or in optimizing the parameters of a specific algorithm. Moreover, a measure for objectively assessing the performance of color image fusion methods, CIFM, is presented in this chapter. Two different aspects are considered in establishing the measure, namely the amount of common information between the source images and the final fused image as well as the distribution of color information in the final

Information Fusion in Ad hoc Wireless Sensor Networks for Aircraft Health Monitoring

In this paper the use of an ad hoc wireless sensor network for implementing a structural health monitoring system is discussed. The network is consisted of sensors deployed throughout the aircraft. These sensors being in the form of a microelectronic chip and consisted of sensing, data processing and communicating components could be easily embedded in any mechanical aircraft component. The established sensor network, due to its ad hoc nature is easily scalable, allowing adding or removing any number of sensors. The position of the sensor nodes need not necessarily to be engineered or predetermined, giving this way the ability to be deployed in inaccessible points. Information collected from various sensors of different modalities throughout the aircraft is then fused in order to provide a more comprehensive image of the aircraft structural health. Sensor level fusion along with decision quality information is used, in order to enhance detection performance.

Differential current-mode tunable wave active filters based on single-ended wave port terminators

A method for the design of differential current-mode wave active filters, which is based on the use of single-ended wave port terminators, is presented in this paper. The resulting filters are modular and very simple to design while their cutoff frequency is controlled by a dc current, giving them the ability of frequency tuning. As an example a wide-band bandpass filter is realized by cascading a low-pass and a highpass filter. The overall filter has been integrated using a standard 0.35-/spl mu/m CMOS technology.

An Integratable Chaotic Oscillator with Current Amplifiers

A current-mode chaotic oscillator based on current amplifiers is studied. The oscillator operates on high frequencies and is suitable for on chip implementation. Its chaotic behavior is controlled by means of a bias voltage. Various methods for detecting chaos, such as the Lyapunov exponents, the Lyapunov dimension, the spectrum and the phase portraits are used, in order to confirm the chaotic behavior of the circuit. Simulation results, using a typical 0.35 mum CMOS technology, fully coincide with theoretical results.

Leapfrog-type filters that retain the topology of the prototype ladder filters

New circuit topologies are proposed for obtaining lowpass all-pole and elliptic filters of any order. The derived circuits retain the attractive features of the leapfrog circuits and in addition they retain the topological equivalence with the prototype LC ladders. The formation of transmission zeros is straightforward. An example of 7 th-order elliptic filter including a sensitivity study is given.

Wave log-domain filters using lattice sections

In this paper, the design of log-domain filters with uncommon transfer functions is considered, using the wave log-domain design method. To this end, the concept of log-domain wave equivalent of a lattice section is introduced, as a new building block, in order to enable the design of filters with transfer functions dealing with amplitude and phase response at the same time. This building block is very useful when the phase and the group delay response of the filter is significant. The functionality of this design approach is verified through a design example and simulation results. Copyright

A LOG-DOMAIN WAVE POSITIVE IMPEDANCE INVERTER

A new log-domain building block for log-domain filter design is proposed in this paper. This block realizes a positive impedance inverter (gyrator) by using the log-domain wave method. A simple procedure for log-domain filter development, using the proposed block, is outlined. This method results in circuits, which are simple in structure and very easy to design. An example of a second-order bandpass filter is given and its functionality is verified through simulations.