Flight Model Performance of 640-GHz Superconductor–Insulator–Superconductor Mixers for JEM/SMILES Mission

Performances of 640-GHz Superconductor–Insulator–Superconductor (SIS) mixers developed for the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) mission are described. SMILES, launched in September 2009, is the first mission to observe atmosphere from space using superconducting mixers. Ground test performances of the SIS mixers show very flat gain and noise characteristics in their observation bands in compliance with the specifications required for SMILES.     

Design of a laminated current cell relocation 12-bit CMOS D/A converter with a high output impedance technique and a merged switching logic

A compact and low power 12-bit 300 MS/s current steering CMOS D/A converter is presented. The architecture of the D/A converter is based on the current steering 6 + 6 segmented type with a laminated current cell relocation technique. In order to improve the linearity and glitch noise, a high output impedance analog current cell is designed. Furthermore, for the purpose of reducing the chip area and power dissipation, a noble merged switching logic and a compact layout technique are proposed. To verify its performance, the chip was fabricated with 0.13 μm thick-gate 1-poly 6-metal N-well Samsung CMOS technology. The effective chip area is 0.26 mm² (510 × 510 μm) with a power consumption of 100 mW. The measured INL and DNL are within ±3LSB and ±1LSB, respectively. The measured SFDR is about 70 dB, when the input frequency is 1 MHz at a clock frequency of 300 MHz.     

Modeling of Dynamic Effects in a Laser-Driven Semiconductor Switch of High-Power Microwaves

Problems of high-power microwaves penetrating into and reflecting from a semiconductor (silicon) plate with non-stationary processes are investigated. The plate is the basis of switches activated by laser-driven photoconductivity which changes its properties when heated by the switched microwave power. Analytical criteria for the stationary solutions of the activated (quasi-metallic) and deactivated (dielectric) states of the switch under the conditions of high-power microwave heating and external cooling are found. Results of numerical simulations are also given for the problems of the switch activation by microwave heating initiated by pulsed laser radiation, which increases the carrier density rapidly. Numerical simulations are carried out using the finite-difference time-domain method with the unsplit perfectly matched layer absorbing boundary conditions. We demonstrate various types of solutions depending on the basic parameters of the problems - microwave field intensity, laser pulse energy and semiconductor doping.     

A novel multicast routing algorithm in sparse splitting WDM network with power attenuation constraint

With the increasing requirement for communication bandwidth, all-optical network has been more and more important owning to its large traffic capability. Multicasting is an important technology in wavelength division multiplexing (WDM) optical network, and has been studied in many works. In this paper, we consider the multicasting technology on all-optical metropolitan area network (MAN) with maximum power attenuation constraint. The objective is to minimize total cost of a multicasting request. This problem is NP-hard. We propose a heuristic, named Power-Constraint Fix-Destination-Path (PC-FDP) algorithm, to solve this maximal power-loss constrained minimizing cost multicasting problem. It means that, during the process of building a multicasting tree, when a destination is reached and its power satisfies the constraint, the path from source to it would be fixed in the tree. Simulation results show that, all multicasting trees building the proposed algorithm satisfy the power constraint, with slight increasing of the total cost.     

Routing for disruption tolerant networks: taxonomy and design

Communication networks, whether they are wired or wireless, have traditionally been assumed to be connected at least most of the time. However, emerging applications such as emergency response, special operations, smart environments, VANETs, etc. coupled with node heterogeneity and volatile links (e.g. due to wireless propagation phenomena and node mobility) will likely change the typical conditions under which networks operate. In fact, in such scenarios, networks may be mostly disconnected, i.e., most of the time, end-to-end paths connecting every node pair do not exist. To cope with frequent, long-lived disconnections, opportunistic routing techniques have been proposed in which, at every hop, a node decides whether it should forward or store-and-carry a message. Despite a growing number of such proposals, there still exists little consensus on the most suitable routing algorithm(s) in this context. One of the reasons is the large diversity of emerging wireless applications and networks exhibiting such “episodic” connectivity. These networks often have very different characteristics and requirements, making it very difficult, if not impossible, to design a routing solution that fits all. In this paper, we first break up existing routing strategies into a small number of common and tunable routing modules (e.g. message replication, coding, etc.), and then show how and when a given routing module should be used, depending on the set of network characteristics exhibited by the wireless application. We further attempt to create a taxonomy for intermittently connected networks. We try to identify generic network characteristics that are relevant to the routing process (e.g., network density, node heterogeneity, mobility patterns) and dissect different “challenged” wireless networks or applications based on these characteristics. Our goal is to identify a set of useful design guidelines that will enable one to choose an appropriate routing protocol for the application or network in hand. Finally, to demonstrate the utility of our approach, we take up some case studies of challenged wireless networks, and validate some of our routing design principles using simulations.     

A MULTI-RESOLUTION SPECTRUM SENSING （MRSS） SCHEME UNDER MEASUREMENT-BASED CHANNEL MODELS IN COGNITIVE RADIO

Spectrum sensing is one of the key technologies in Cognitive Radios (CRs). Previous works are accomplished under simple channel models, which may lead to unreliable results when it applied to the over-the-air systems. In this paper, we investigate the performance of a Multi-Resolution Spectrum Sensing (MRSS) algorithm under measurement-based channel models in China. MRSS is a wavelet based algorithm which is suitable for non-stationary, wideband signal analysis. Using statistical modeling, measurement-based channel models are presented under typical urban and suburban scenarios in Shanghai, China. Then, the performance of the MRSS algorithm is evaluated under the measurement-based channel models. Simulation results show that, using MRSS, the performance is always better in the scenarios where Line-Of-Sight (LOS) path exist; also, in LOS scenarios, rich scattering effect helps to increase the performance.     

Cyclostationarity-Based Modulation Classification of Linear Digital Modulations in Flat Fading Channels

Modulation classification is an intermediate step between signal detection and demodulation, and plays a key role in various civilian and military applications. In this correspondence, higher-order cyclic cumulants (CCs) are explored to discriminate linear digital modulations in flat fading channels. Single- and multi-antenna CC-based classifiers are investigated. These benefit from the robustness of the CC-based features to unknown phase and timing offset. Furthermore, the latter provides significant performance improvement due to spatial diversity used to combat the fading effect. Classifier performances are investigated under a variety of channel conditions. In addition, analytical closed-form expressions for the cyclic cumulant polyspectra of linearly digitally modulated signals affected by fading, carrier frequency and timing offsets, and additive Gaussian noise are derived, along with a condition for the oversampling factor to avoid aliasing in the cycle and spectral frequency domains.     

A power-adaptable A/D converter with integrated data compression

A novel adaptable analog/digital converter (ADC) that combines analog/digital conversion and entropy-coding for integrated data compression and low-power operation is reported. The converter has high flexibility of operation in terms of adaptable resolution, conversion rate and input signal statistics. This feature allows to adaptively react to changes of the situation and to put the device in each case into the optimum configuration. The ADC has been realized in a 0.6 μm CMOS technology with a peak resolution of 12 bit and 200 kS/s maximum sampling rate. A comprehensive power model of the converter is presented that reflects precisely the power consumption determined from experiments. The model is very useful for optimizing the converter configuration in the node of a wireless sensor network for specific situations. A feasible real-life application is demonstrated.     

Array-OL with delays,a domain specific specification language for multidimensional intensive signal processing

Intensive signal processing applications appear in many application domains such as video processing or detection systems. These applications handle multidimensional data structures (mainly arrays) to deal with the various dimensions of the data (space, time, frequency). A specification language allowing the direct manipulation of these different dimensions with a high level of abstraction is a key to handling the complexity of these applications and to benefit from their massive potential parallelism. The Array-OL specification language is designed to do just that. We introduce here an extension of Array-OL to deal with states or delays by the way of uniform inter-repetition dependences. We show that this specification language is able to express the main patterns of computation of the intensive signal processing domain.     

Structural Characterization of Doped GaSb Single Crystals by X-ray Topography

We characterized GaSb single crystals containing different dopants (Al, Cd, and Te), grown by the Czochralski method, using x-ray topography and high-angular-resolution x-ray diffraction. Lang topography revealed dislocations parallel and perpendicular to the crystal surface. Double-crystal GaSb 333 x-ray topography showed dislocations and vertical stripes that could be associated with circular growth bands. We compared our high-angular- resolution x-ray diffraction measurements (rocking curves) with findings predicted by the dynamical theory of x-ray diffraction. These measurements show that our GaSb single crystals have a relative variation in the lattice parameter (Δd/d) on the order of 10⁻⁵. This means that they can be used as electronic devices (e.g., detectors) and as x-ray monochromators.