Analysis and design of a two-octave polarization rotator formicrowave frequency

The analysis and design of a 45° polarization rotator are presented. A two-octave frequency band is achieved with only three grids of strips, each rotated with respect to the previous one. Over this band the transmission loss is less than 0.5 dB, the circular polarization ratio is less than 2.0 dB, and the major axis of the polarization ellipse forms 45°±3° with respect to the linear polarization direction of the incident plane wave. The analysis method is an original scheme based upon the conjugate-gradient fast Fourier transform (CG-FFT) method to analyze periodic structures and the generalized scattering matrix method to study their connection. A comparison between numerical and measured data is presented     

Near-lossless and lossy compression of imaging spectrometer data: comparison of information extraction performance

We investigate the ability to derive meaningful information from decompressed imaging spectrometer data. Hyperspectral images are compressed with near-lossless and lossy coding methods. Linear prediction between the bands is used in both cases. Each band is predicted by a previously transmitted band. The residual is formed by subtracting the prediction from the original data and then is compressed either with a near-lossless bit-plane coder or with the lossy JPEG2000 algorithm. We study the effects of these two types of compression on hyperspectral image processing such as mineral and vegetation content classification using whole- and mixed pixel analysis techniques. The results presented in this paper indicate that an efficient lossy coder outperforms near-lossless method in terms of its impact on final hyperspectral data applications.     

Modern development methods and tools for embedded reconfigurable systems: A survey

Heterogeneous reconfigurable systems provide drastically higher performance and lower power consumption than traditional CPU-centric systems. Moreover, they do it at much lower costs and shorter times to market than non-reconfigurable hardware solutions. They also provide the flexibility that is often required for the engineering of modern robust and adaptive systems. Due to their heterogeneity, flexibility and potential for highly optimized application-specific instantiation, reconfigurable systems are adequate for a very broad class of applications across different industry sectors. What prevents the reconfigurable system paradigm from a broad proliferation is the lack of adequate development methodologies and electronics design tools for this kind of systems. The ideal would be a seamless compilation of a high-level computation process specification into an optimized mixture of machine code executed on traditional CPU-centric processors and on the application-specific decentralized parallel data-flow-dominated reconfigurable processors and hardware accelerators. Although much research and development in this direction was recently performed, the adequate methodologies and tools necessary to implement this compilation process as an effective and efficient hardware/software co-synthesis flow are unfortunately not yet in place. This paper focuses on the recent developments and development trends in the design methods and synthesis tools for reconfigurable systems. Reconfigurable system synthesis performs two basic tasks: system structure construction and application process mapping on the structure. It is thus more complex than standard (multi-)processor-based system synthesis for software-programmable systems that only involves application mapping. The system structure construction may involve the macro-architecture synthesis, the micro-architecture synthesis, and the actual hardware synthesis. Also, the application process mapping can be more complicated and dynamic in reconfigurable systems. This paper reviews the recent methods and tools for the macro- and micro-architecture synthesis, and for the application mapping of reconfigurable systems. It puts much attention to the relevant and currently hot topic of (re-)configurable application-specific instruction set processors (ASIP) synthesis, and specifically, ASIP instruction set extension. It also discusses the methods and tools for reconfigurable systems involving CPU-centric processors collaborating with reconfigurable hardware sub-systems, for which the main problem is to decide which computation processes should be implemented in software and which in hardware, but the hardware/software partitioning has to account for the hardware sharing by different computation processes and for the reconfiguration processes. The reconfigurable system area is a very promising, but quite a new field, with many open research and development topics. The paper reviews some of the future trends in the reconfigurable system development methods and tools. Finally, the discussion of the paper is summarized and concluded.     

Fast-polarization-hopping transmission diversity to mitigate prolonged deep fades in indoor wireless communications

Fast-polarization-hopping (FPH) transmission diversity is herein proposed to mitigate prolonged deep fades at the mobile receiver in, for example, the indoor propagation environment. Even if the individual multipaths are each sufficiently strong for detection, deep fades may occur due to the multipath signals' destructive summation at the receiver. The relative immobility of the transmitter, the propagation environment, and the receiver in the indoor environment means that a deep fade may last for a very long duration, dropping calls or severing links. By rapidly hopping the transmission polarization (say, alternating transmission between a vertically-polarized-dipole antenna and a horizontally-polarized-dipole antenna - or between two "X"-oriented dipoles), the effective propagation channel experiences consecutive polarization modes (each involving a different multipath summation), all within the duration allowed by the channel-coder's interleaving depth. This scheme is usable for either frequency-shift keying (with incoherent demodulation), or for channel-coded phase-shift keying (with differential coding, or with pilot-symbol phase synchronization). This scheme requires no change in the mobile receiver (which does not need to be dual polarized). The base station also needs no spatially separated antenna array, nor any other additional hardware, no mechanical movement of the transmitting antenna(s), and no sophisticated signal processing (such as channel estimation or closed-loop feedback) nor any additional software. The proposed scheme's cost - relative to using antenna arrays at the base station and/or the mobile - is a potentially doubling of the transmission bandwidth. The proposed scheme's potential is illustrated by limited computer simulations using CINDOOR, a polarization-sensitive indoor wireless-propagation ray-tracing simulation software package based on geometrical optics and the uniform theory of diffraction (GO/UTD).     

The muscle activation method: an approach to impedance control of brain-machine interfaces through a musculoskeletal model of the arm

Current demonstrations of brain-machine interfaces (BMIs) have shown the potential for controlling neuroprostheses under pure motion control. For interaction with objects, however, pure motion control lacks the information required for versatile manipulation. This paper investigates the idea of applying impedance control in a BMI system. An extraction algorithm incorporating a musculoskeletal arm model was developed for this purpose. The new algorithm, called the muscle activation method (MAM), was tested on cortical recordings from a behaving monkey. The MAM was found to predict motion parameters with as much accuracy as a linear filter. Furthermore, it successfully predicted limb interactions with novel force fields, which is a new and significant capability lacking in other algorithms.     

Efficient coding of homogeneous textures using stochastic vectorquantisation and linear prediction

Vector quantisation (VQ) has been extensively used as an effective image coding technique. One of the most important steps in the whole process is the design of the codebook. The codebook is generally designed using the LBG algorithm which uses a large training set of empirical data that is statistically representative of the images to be encoded. The LBG algorithm, although quite effective for practical applications, is computationally very expensive and the resulting codebook has to be recalculated each time the type of image to be encoded changes. Stochastic vector quantisation (SVQ) provides an alternative way for the generation of the codebook. In SVQ, a model for the image is computed first, and then the codewords are generated according to this model and not according to some specific training sequence. The SVQ approach presents good coding performance for moderate compression ratios and different type of images. On the other hand, in the context of synthetic and natural hybrid coding (SNHC), there is always need for techniques which may provide very high compression and high quality for homogeneous textures. A new stochastic vector quantisation approach using linear prediction which is able to provide very high compression ratios with graceful degradation for homogeneous textures is presented. Owing to the specific construction of the method, there is no block effect in the synthetised image. Results, implementation details, generation of the bit stream and comparisons with the verification model of MPEG-4 are presented which prove the validity of the approach. The technique has been proposed as a still image coding technique in the SNHC standardisation group of MPEG     

A novel CMOS exponential transconductor operating in weak inversion

A novel CMOS exponential transconductor which employs only three NMOS transistors operating in weak inversion, is presented. The main advantage of the proposed circuit is its wide range of exponential behaviour, which reaches up to five decades of current range, and above 10 μA to an input voltage range of 800 mV. The physical realisation is achieved in two forms: in the first one, the circuit is implemented with discrete MOS transistor arrays by CD4007 series; in the second one, the circuit is fully integrated in a 0.5 μm CMOS standard process. Simulated and experimental results of the proposed exponential transconductor are also presented.     

SMOS Calibration

The calibration of the Soil Moisture and Ocean Salinity (SMOS) payload instrument, known as Microwave Imaging Radiometer by Aperture Synthesis (MIRAS), is based on characterization measurements which are performed initially on-ground prior to launch and, subsequently, in-flight. A good calibration is a prerequisite to ensure the quality of the geophysical data. The calibration scheme encompasses both the spaceborne instrument and the ground data processing. Once the system has been calibrated, the instrument performance can be verified, and the higher level geophysical variables, soil moisture and ocean salinity, can be validated. In this paper, the overall calibration approach is presented, focusing on the main aspects relevant to the SMOS instrument design and mission requirements. The distributed instrument, comprising 72 receivers, leads to a distributed internal calibration approach supported by specific external calibration measurements. The relationship between the calibration data and the routine ground processing is summarized, demonstrating the inherent link between them. Finally, the approach to the in-flight commissioning activities is discussed.     

Properties and Printability of Inkjet and Screen-Printed Silver Patterns for RFID Antennas

We report the modeling, and geometrical and electrical characterization, of inkjet and screen-printed patterns on different polymeric substrates for use as antennas in radio-frequency identification (RFID) applications. We compared the physical and electrical characteristics of two silver nanoparticle-based commercial inkjet-printable inks and one screen-printable silver paste, when deposited on polyimide (PI), polyethylene terephthalate (PET), and polyetherimide (PEI) substrates. First, the thickness of the inkjet-printed patterns was predicted by use of an analytical model based on printing conditions and ink composition. The predicted thickness was confirmed experimentally, and geometrical characterization of the lines was completed by measuring the root-mean-square roughness of the patterns. Second, direct-current electrical characterization was performed to identify the printing conditions yielding the lowest resistivity and sheet resistance. The minimum resistivity for the inkjet-printing method was 8.6 ± 0.8 μΩ cm, obtained by printing four stacked layers of one of the commercial inks on PEI, whereas minimum resistivity of 44 ± 7 μΩ cm and 39 ± 4 μΩ cm were obtained for a single layer of screen-printed ink on polyimide (PI) with 140 threads/cm mesh and 90 threads/cm mesh, respectively. In every case, these minimum values of resistivity were obtained for the largest tested thickness. Coplanar waveguide transmission lines were then designed and characterized to analyze the radio-frequency (RF) performance of the printed patterns; minimum transmission losses of 0.0022 ± 0.0012 dB/mm and 0.0016 ± 0.0012 dB/mm measured at 13.56 MHz, in the high-frequency (HF) band, were achieved by inkjet printing on PEI and screen printing on PI, respectively. At 868 MHz, in the ultra-high-frequency band, the minimum values of transmission loss were 0.0130 ± 0.0014 dB/mm for inkjet printing on PEI and 0.0100 ± 0.0014 dB/mm for screen printing on PI. Although the resistivity achieved is lower for inkjet printing than for screen printing, RF losses for inkjetted patterns were larger than for screen-printed patterns, because thicker layers were obtained by screen printing. Finally, several coil inductors for the HF band were also fabricated by use of both printing techniques, and were used as antennas for semi-passive smart RFID tags on plastic foil capable of measuring temperature and humidity.