High level of security is essential in wireless communications multimedia applications. The last few years there has been an increase in research interest in the potential of the radio channel's physical properties to provide communications security. These research efforts investigate fading, interference, and path diversity to develop security techniques for implementation in wireless systems. In this paper, we propose an enhancement to existing physical layer security schemes, taking advantage of the characteristics of the OFDM technique. An OFDM symbol includes the pilot sub-carriers, essential for the pilot channel estimation process performed at the legitimate receiver. In this work we propose the positions of the sub-carriers to change on every OFDM symbol following a probability distribution known only to the legitimate transmitter and legitimate receiver. An eavesdropper receiver, does not have access to the information of the pilot sub-carriers positions so, it performs blind channel estimation. The theoretical analysis is based on the information theoretic problem formulation and is confirmed by simulations. The performance metrics used are the secrecy capacity, the outage probability, the channel mean square error and the bit error rate. The proposed scheme is very simple and robust, strengthening security in multimedia applications.

Critical characteristics of wireless sensor networks, as being autonomous and comprising small or miniature devices are achieved at the expense of very strict available energy related limitations. Therefore, it is apparent that optimal resource management is among the most important challenges in WSNs development and success. However, energy management requires in depth knowledge and detailed insight concerning the factors contributing to the overall power consumption of a WSN mote. To achieve such awareness, appropriate measuring test-beds and methodologies are needed, enabling reliable and accurate power consumption measurements of critical functionalities. Moving towards that direction, the contribution of this paper is twofold. On one hand, the design and implementation of a system is presented, capable of accurately measuring and displaying a wide range of power consumption thresholds. On the other hand, the elementary functionalities of a WSN platform are identified, isolated and measured with respect to their contribution to the overall mote power consumption. Valuable conclusions are extracted and analyzed.

The paper presents a new approach to the Volterra analysis of analog circuits. This kind of analysis is widely used for the calculation of distortion and intermodulation products. However, the analysis is limited to circuits with small signal excitations and becomes inaccurate when the input signal amplitude increases, especially when MOSFETs are involved. In this paper, the authors analyze the reasons of this drawback, which is no other than the Taylor series' convergence properties. Furthermore, the authors propose a solution, by calculating the nonlinearity coefficients using a different type of polynomial expansion, the Chebyshev series. The authors also present results comparing Chebyshev series performance with other types of polynomial expansions. Finally, the authors apply the proposed method to analyze the intermodulation distortion (IMD) of a CMOS RF power amplifier.

Analytical expressions concerning the capacity and bit error rate (BER) of multiple-input multiple-output systems with space-time block coding (STBC) are derived. Two fading environments are examined, log-normal and Rician channels. A tight closed-form upper bound is presented for the BER of systems operating in log-normal fading environments in addition to an upper bound for the capacity of this type of systems. The latter bound applies to systems that operate under Rician fading as well. The analytical results were validated against ample numerical simulations for three STBC schemes and three phase-shift-keying modulations. The proposed bounds proved to be a tractable way to evaluate the system performance when no closed-form expression for the probability density function or the moment generating function is known.

This paper presents an ad-hoc sensor network especially developed for a disaster relief application that provides the rescue teams with a quickly deployable, cost-effective, and reliable tool to collect information about the presence of people in a collapsed building space and the state of the ruins. The hardware/software architecture of the wireless sensor nodes is developed for a low-cost design implementation. Energy efficiency is another objective of this paper, achieved by the combination of a low-power-mode algorithm and a power-aware routing strategy. A selected set of simulation studies indicate a reduction in energy consumption and a significant increase in node lifetime whereas network performance is not affected significantly. Finally, a lightweight management architecture is presented to facilitate autonomous management of ad-hoc sensor networks

A phase frequency detector (PFD) with wide linear operating range and the ability to saturate beyond that range is presented in this paper. Its use in phase locked loops (PLLs) implies elimination of cycle slipping, which results in an analytically predictable transient behavior and a possible improvement in acquisition speed, depending on the PLL design. Simulation results confirm these advantages. Moreover, a detailed study on the applicability of this PFD is conducted in this paper

This paper proposes a new methodology for the system design and development of wireless network protocols. The proposed methodology used UML and its real-time extensions at its basis. This system design methodology formalizes the system specification and validation phases. Furthermore, wireless system design is enhanced by the concept of high-level system codesign, which can be achieved by the use of UML in the system design. The presented methodology has been applied to the design of the industrial prototype implementation of a wireless network node based on the HIPERLAN/2 standard. The system design of the HIPERLAN/2 prototype is presented in details, with special information given on the system architecture and the implementation of the hardware and software parts of the system. The application of the presented system methodology helped in the reduction of the development time and effort for the HIPERLAN/2 prototype

In this paper, the architecture and the operation of a cut-through forwarding device to be used in broadcasting, hybrid wired/wireless fieldbus systems are described. Analytical models of the delay overhead introduced due to frame forwarding are presented. It is shown that the usage of cut-through forwarding devices relaxes the bit-rate requirements in the radio segments, while it drastically improves the inherent advantages and reduces the drawbacks of hybrid transmission media architectures which are based on a single MAC domain.

Abstract In recent years, wireless access networks offer an alternative method for connecting subscribers to the global communication network. Several high‐speed Wireless LAN's (WLAN) standards have emerged and among them the ETSI BRAN HiperLAN II standard is distinguished for its performance and QoS support. This paper, starting with a short overview of HiperLAN II main features and Medium Access (MAC) protocol, presents the architecture of an implemented high‐speed Frame Processor that realizes the medium access control (MAC) protocol of the HiperLAN II standard. The main goal of the Frame Processor is the real‐time management of the air interface as well as to bridge the upper network layers with the wireless world, relieving the data link control (DLC) layer of time‐consuming tasks such as slot map allocation extraction, bit‐by‐bit processing of data units, framing and synchronization. Copyright © 2003 John Wiley & Sons, Ltd.

The benefits of wireless extensions in industrial networks are well recognized as long as the integration of the wireless and fieldbus domains will be capable to offer the realtime and dependability quality of the current wired industrial networking solutions. This paper presents a study, from a performance point of view, for the possible integration of the most popular 3G and WLAN radio technologies with fieldbus technologies. A brief examination of a number of dominant wireless protocols against the basic wireless fieldbus requirements is presented. For the case study, Profibus is used, on which, the basic message cycle performance is calculated for each of the UNITS, 802.11b and HIPERLAN protocols, under different integration approaches.

This paper presents a machine vision methodology for automated quality inspection of wood boards. A pilot real-time system has been developed. It performs four-face inspection and detects and classifies the main biological and mechanical defects using standard area-scan cameras and a PC with an off-the-shelf frame grabber.

The design and joint simulation of the heterogeneous parts of a system in a unified environment offers many advantages including reduced system design and debug times as well as increased simulation accuracy. This paper presents a couple of flexible interfaces that have been implemented for bridging VHDL with electromechanical systems simulators (EMSS) and VHDL simulators with the application programs that control the digital circuit simulated in VHDL correspondingly. These interfaces are based on the use of VHDL interface components with generic structure that simplify the whole simulation procedure. The basic concepts and features used for these implementations are characterized by increased portability while other significant advantages of the proposed schemes are their speed, their flexibility in supporting various communication protocols and the simplified and fully automated simulation procedure which is transparent to the user.

The adaptive reservation protocol, referred to as ATP-2, uses two frequency separated subchannels, the request and information subchannels, for the request and information packets. The nature of the accessing algorithms for these two subchannels characterizes the overall ATP-2 protocol quality. Extended ATP-2 performance results are presented and a comparison is made between the ATP-2 and some other well-known multiple-access protocols.>