Data transmission by frequency-hopped multilevel frequency shift keying

Spread spectrum systems make use of radio frequency bandwidths which far exceed the minimum bandwidth necessary to transmit the basic message information.These systems are designed to provide satisfactory communication of the message information under difficult transmission conditions. Frequency-hopped multilevel frequency shift keying (FH-MFSK) is one of the many techniques used in spread spectrum systems. It is a combination of frequency hopping and time hopping. In this system many users share a common frequency band using code division multiplexing. Each user is assigned an address and the message is modulated into the address. The receiver, knowing the address, decodes the received signal and extracts the message. This technique is suggested for digital mobile telephony. This thesis is concerned with an investigation of the possibility of utilising FH-MFSK for data transmission corrupted by additive white gaussian noise (A.W.G.N.). Work related to FH-MFSK has so far been mostly confined to its validity, and its performance in the presence of A.W.G.N. has not been reported before. An experimental system was therefore constructed which utilised combined hardware and software and operated under the supervision of a microprocessor system. The experimental system was used to develop an error-rate model for the system under investigation. The performance of FH-MFSK for data transmission was established in the presence of A.W.G.N. and with deleted and delayed sample effects. Its capability for multiuser applications was determined theoretically. The results show that FH-MFSK is a suitable technique for data transmission in the presence of A.W.G.N.

High-frequency fiber Bragg grating sensing interrogation system using Sagnac-loop-based microwave photonic filtering

A novel high-frequency fiber Bragg grating (FBG) sensing interrogation system by using fiber Sagnac-loop-based microwave photonic filtering is proposed and experimentally demonstrated. By adopting the microwave photonic filtering, the wavelength shift of sensing FBG can be converted into amplitude variation of the modulated electronic radio-frequency (RF) signal. In the experiment, the strain applied onto the sensing FBG has been demodulated by measuring the intensity of the recovered RF signal, and by modulating the RF signal with different frequencies, different interrogation sensitivities can be achieved.

Photonic processing for wideband cancellation and spectral discrimination of RF signals

Photonic signal processing is used to implement common mode signal cancellation across a very wide bandwidth utilising phase modulation of radio frequency (RF) signals onto a narrow linewidth laser carrier. RF spectra were observed using narrow-band, tunable optical filtering using a scanning Fabry Perot etalon. Thus functions conventionally performed using digital signal processing techniques in the electronic domain have been replaced by analog techniques in the photonic domain. This technique was able to observe simultaneous cancellation of signals across a bandwidth of 1400 MHz, limited only by the free spectral range of the etalon. © 2013 David M. Benton.

High-gain frequency reconfigurable Vivaldi antenna

This article proposes a frequency agile antenna whose operating frequency band can be switched. The design is based on a Vivaldi antenna. High-performance radio-frequency microelectromechanical system (RF-MEMS) switches are used to realize the 2.7 GHz and 3.9 GHz band switching. The low band starts from 2.33 GHz and works until 3.02 GHz and the high band ranges from 3.29 GHz up to 4.58 GHz. The average gains of the antenna at the low and high bands are 10.9 and 12.5 dBi, respectively. This high-gain frequency reconfigurable antenna could replace several narrowband antennas for reducing costs and space to support multiple communication systems, while maintaining good performance.

A high-power-factor, three-phase isolated AC-DC converter using high-frequency current injection

A single-stage, three-phase AC-to-DC converter topology is proposed for high-frequency power supply applications. The principal features of the circuit include continuous current operation of the three AC input inductors, inherent shaping of the input currents, resulting in high power factor, a transformer isolated output, and only two active devices are required, both soft-switched. Resonant conversion techniques are used, and a high power factor is achieved by injecting high-frequency currents into the three-phase rectifier, producing a high frequency modulation of the rectifier input voltages. The current injection principle is explained and the system operation is confirmed by a combination of simulation and experimental results.

Functional connectivity of gamma EEG activity is modulated at low frequency during conscious recollection

We examined two subjectively distinct memory states that are elicited during recognition memory in humans and compared them in terms of the gamma oscillations (20–60 Hz) in the electroencepahalogram (EEG) that they induced. These subjective states, ‘recollection’ and ‘familiarity’ both entail correct recognition but one involves a clear and conscious recollection of the event including memory for contextual detail whilst the other involves a sense of familiarity without clear recollection. Here we show that during a verbal recognition memory test, the subjective experience of ‘recollection’ induced higher amplitude gamma oscillations than the subjective experience of ‘familiarity’ in the time period 300–500 ms after stimulus presentation. Recollection, but not familiarity, was also associated with greater functional connectivity in the gamma frequency range between frontal and parietal sites. Furthermore, the magnitude of the gamma functional connectivity varied over time and was modulated at 3 Hz. Previous studies in animals have shown local theta frequency modulation (3–7 Hz) of gamma-oscillations but this is the first time that a similar effect has been reported in the human EEG.

Simultaneous interrogation of fiber Bragg grating sensors using an acoustooptic tunable filter

In this letter, we describe a novel technique to provide demultimplexing of fiber Bragg grating sensors, interrogated using interferometric wavelength shift detection. Amplitude modulation of multiple radio frequency driving signals allows au acoustooptic tunable filter to provide wavelength demultiplexing. We demonstrated a noise limited strain resolution of 150 nanostrain/√Hz and a crosstalk better than -50 dB.

Improving returnable transport equipment management with an autonomous approach

Challenges of returnable transport equipment (RTE) management continue to heighten as the popularity of their usage magnifies. Logistics companies are investigating the implementation of radio-frequency identification (RFID) technology to alleviate problems such as loss prevention and stock reduction. However, the research within this field is limited and fails to fully explore with depth, the wider network improvements that can be made to optimize the supply chain through efficient RTE management. This paper, investigates the nature of RTE network management building on current research and practices, filling a gap in the literature, through the investigation of a product-centric approach where the paradigms of “intelligent products” and “autonomous objects” are explored. A network optimizing approach with RTE management is explored, encouraging advanced research development of the RTE paradigm to align academic research with problematic areas in industry. Further research continues with the development of an agent-based software system, ready for application to a real-case study distribution network, producing quantitative results for further analysis. This is pivotal on the endeavor to developing agile support systems, fully utilizing an information-centric environment and encouraging RTE to be viewed as critical network optimizing tools rather than costly waste.

Exploring civil servant resistance to M-government:a story of transition and opportunities in Turkey

The concept of mobility, related to technology in particular, has evolved dramatically over the last two decades including: (i) hardware ranging from walkmans to Ipods, laptops to netbooks, PDAs to 3G mobile phone; (ii) software supporting multiple audio and video formats driven by ubiquitous mobile wireless access, WiMax, automations such as radio frequency ID tracking and location aware services. Against the background of increasing budget deficit, along with the imperative for efficiency gains, leveraging ICT and mobility promises for work related tasks, in a public administration context, in emerging markets, point to multiple possible paths. M-government transition involve both technological changes and adoption to deliver government services differently (e.g. 24/7, error free, anywhere to the same standards) but also the design of digital strategies including possibly competing m-government models, the re-shaping of cultural practices, the creation of m-policies and legislations, the structuring of m-services architecture, and progress regarding m-governance. While many emerging countries are already offering e-government services and are gearing-up for further m-government activities, little is actually known about the resistance that is encountered, as a reflection of civil servants' current standing, before any further macro-strategies are deployed. Drawing on the resistance and mobility literature, this chapter investigates how civil servants' behaviors, in an emerging country technological environment, through their everyday practice, react and resist the influence of m-government transition. The findings points to four main type of resistance namely: i) functional resistance; ii) ideological resistance; iii) market driven resistance and iv) geographical resistance. Policy implication are discussed in the specific context of emerging markets. © 2011, IGI Global.

Fibre-based devices for next generation photonics communication systems

The future broadband information network will undoubtedly integrate the mobility and flexibility of wireless access systems with the huge bandwidth capacity of photonics solutions to enable a communication system capable of handling the anticipated demand for interactive services. Towards wide coverage and low cost implementations of such broadband wireless photonics communication networks, various aspects of the enabling technologies are continuingly generating intense research interest. Among the core technologies, the optical generation and distribution of radio frequency signals over fibres, and the fibre optic signal processing of optical and radio frequency signals, have been the subjects for study in this thesis. Based on the intrinsic properties of single-mode optical fibres, and in conjunction with the concepts of optical fibre delay line filters and fibre Bragg gratings, a number of novel fibre-based devices, potentially suitable for applications in the future wireless photonics communication systems, have been realised. Special single-mode fibres, namely, the high birefringence (Hi-Bi) fibre and the Er/Yb doped fibre have been employed so as to exploit their merits to achieve practical and cost-effective all-fibre architectures. A number of fibre-based complex signal processors for optical and radio frequencies using novel Hi-Bi fibre delay line filter architectures have been illustrated. In particular, operations such as multichannel flattop bandpass filtering, simultaneous complementary outputs and bidirectional nonreciprocal wavelength interleaving, have been demonstrated. The proposed configurations featured greatly reduced environmental sensitivity typical of coherent fibre delay line filter schemes, reconfigurable transfer functions, negligible chromatic dispersions, and ease of implementation, not easily achievable based on other techniques. A number of unique fibre grating devices for signal filtering and fibre laser applications have been realised. The concept of the superimposed fibre Bragg gratings has been extended to non-uniform grating structures and into Hi-Bi fibres to achieve highly useful grating devices such as overwritten phase-shifted fibre grating structure and widely/narrowly spaced polarization-discriminating filters that are not limited by the intrinsic fibre properties. In terms of the-fibre-based optical millimetre wave transmitters, unique approaches based on fibre laser configurations have been proposed and demonstrated. The ability of the dual-mode distributed feedback (DFB) fibre lasers to generate high spectral purity, narrow linewidth heterodyne signals without complex feedback mechanisms has been illustrated. A novel co-located dual DFB fibre laser configuration, based on the proposed superimposed phase-shifted fibre grating structure, has been further realised with highly desired operation characteristics without the need for costly high frequency synthesizers and complex feedback controls. Lastly, a novel cavity mode condition monitoring and optimisation scheme for short length, linear-cavity fibre lasers has been proposed and achieved. Based on the concept and simplicity of the superimposed fibre laser cavities structure, in conjunction with feedback controls, enhanced output performances from the fibre lasers have been achieved. The importance of such cavity mode assessment and feedback control for optimised fibre laser output performance has been illustrated.

Extended-range fiber polarimetric strain sensor

We describe a frequency-modulation technique that is applicable to two-beam interferometric systems illuminated by semiconductor diode lasers. The technique permits a determination of the optical path difference between the two arms of the interferometer and is used here to extend the range of a fiber polarimetric strain sensor by determining the order of the particular polarimetric fringe under consideration.

Impact of RFID in reverse logistics

This paper aims to discuss the recent literature on Radio Frequency Identification (RFID) and reverse logistics (RL). Particular attention is applied to the bullwhip effect and its increase as RL activities are integrated into the supply chain. RFID is investigated as a tool to assist with integrating reverse and forward logistics into a seamless supply chain and reduce the bullwhip effect. However, further research is required within this area and in particular the return on investment for RFID-enabled integrated systems.

270-km ultralong raman fiber laser

We analyze the physical mechanisms limiting optical fiber resonator length and report on the longest ever laser cavity, reaching 270 km, which shows a clearly resolvable mode structure with a width of ~120??Hz and peak separation of ~380Hz in the radio-frequency spectrum.

Using RFID-RTE to increase efficiency in the supply chain

This paper aims to explore the application of Radio Frequency Identification (RFID) to Returnable transit equipment (RTE) in the supply chain. Particular attention is applied to the current structures of RTE networks as formulated by RTE providers. The problems related to RTE usage are described and the effect to the network analyzed. RFID is investigated as a tool to assist with the movement of the RTE both from the client’s and RTE provider’s point of view.

RFID adoption issues in the warehouse

In recent years the increased interest in introducing radio frequency technology (RFID) in warehousing was observed. First adopters of RFID reported numerous benefits, which included: reduced shrinkage, real-time tracking and better accuracy of data collection. Along with the academic and industrial discussion on benefits which can be achieved in RFID enabled warehouses there are reports on issues related to adoption of RFID technology in warehousing. This paper reviews results of scientific reports of RFID implementation in warehouses and discusses the adoption barriers and causes of not achieving full potential of the technology. Following adoption barriers are identified and set in warehousing context: lack of forseeable return on investment (ROI), unreliable performance of RFID systems, standarisation, integration with legacy systems and privacy/security concerns. As more studies will address these challenges, the realisation of RFID benefits for warehouses will become reality.