Outage Performance of Energy Harvesting DF Relaying NOMA Networks

In this paper, we investigate energy harvesting decode-and-forward relaying non-orthogonal multiple access (NOMA) networks. We study two cases of single relay and multiple relays with partial relay selection strategy. Specifically, one source node wishes to transmit two symbols to two respective destinations directly and via the help of one selected intermediate energy constraint relay node, and the NOMA technique is applied in the transmission of both hops (from source to relay and from relay to destinations). For performance evaluation, we derive the closed-form expressions for the outage probability (OP) at D ₁ and D ₂ with both cases of single and multiple relays. Our analysis is substantiated via Monte Carlo simulation. The effect of several parameters, such as power allocation factors in both transmissions in two hops, power splitting ratio, energy harvesting efficiency, and the location of relay nodes to the outage performances at the two destinations is investigated.     

Analytic, Simulation, and Empirical Evaluation of Delay/Fault-Tolerant Mobile Sensor Networks

The delay/fault-tolerant mobile sensor network (DFT-MSN) has been proposed for pervasive information gathering. DFT-MSN distinguishes itself from conventional sensor networks by several unique characteristics such as sensor mobility, loose connectivity, and delay/fault tolerability. This paper focuses on the performance evaluation of DFT-MSN. We first introduce a queuing model by using Jackson network theory. While the queuing model is based on a few simplification assumptions for analytic tractability, it provides insights into the queuing behavior of the mobile sensors in DFT-MSN. Extensive simulations are performed under realistic environment and assumptions. Our simulation results show that the dynamic DFT-MSN data delivery scheme achieves the highest message delivery ratio with acceptable delay and transmission overhead, compared with simple schemes such as flooding and direct transmission or other approaches in the literature such as Zebranet. We have also implemented a DFT-MSN testbed by deploying crossbow motes for noise level monitoring in our university library. Though in a small scale, the testbed demonstrates the feasibility of DFT-MSN and provides guidance for future large scale deployment.     

Affine-permutation invariance of 2-D shapes.

Shapes provide a rich set of clues on the identity and topological properties of an object. In many imaging environments, however, the same object appears to have different shapes due to distortions such as translation, rotation, reflection, scaling, or skewing. Further, the order by which the object's feature points are scanned changes, i.e., the order of the pixels may be permuted. Relating two-dimensional shapes of the same object distorted by different affine and permutation transformations is a challenge. We introduce a shape invariant that we refer to as the intrinsic shape of an object and describe an algorithm, BLAISER, to recover it. The intrinsic shape is invariant to affine-permutation distortions. It is a uniquely defined representative of the equivalence class of all affine-permutation distortions of the same object. BLAISER computes the intrinsic shape from any arbitrarily affine-permutation distorted image of the object, without prior knowledge regarding the distortions or the undistorted shape of the object. The critical step of BLAISER is the determination of the shape orientation and we provide a detailed discussion on this topic. The operations of BLAISER are based on low-order moments of the input shape and, thus, robust to error and noise. Examples illustrate the performance of the algorithm.     

Long-wavelength GaInNAs(Sb) lasers on GaAs

The boom in fiber-optic communications has caused a high demand for GaAs-based lasers in the 1.3-1.6-μm range. This has led to the introduction of small amounts of nitrogen into InGaAs to reduce the bandgap sufficiently, resulting in a new material that is lattice matched to GaAs. More recently, the addition of Sb has allowed further reduction of the bandgap, leading to the first demonstration of 1.5-μm GaAs-based lasers by the authors. Additional work has focused on the use of GaAs, GaNAs, and now GaNAsSb barriers as cladding for GaInNAsSb quantum wells. We present the results of photoluminescence, as well as in-plane lasers studies, made with these combinations of materials. With GaNAs or GaNAsSb barriers, the blue shift due to post-growth annealing is suppressed, and longer wavelength laser emission is achieved. Long wavelength luminescence out to 1.6 μm from GaInNAsSb quantum wells, with GaNAsSb barriers, was observed. In-plane lasers from these samples yielded lasers operating out to 1.49 μm, a minimum threshold current density of 500 A/cm² per quantum well, a maximum differential quantum efficiency of 75%, and pulsed power up to 350 mW at room temperature     

Multiaxial and Transparent Strain Sensors Based on Synergetically Reinforced and Orthogonally Cracked Hetero‐Nanocrystal Solids

Wearable strain sensors are widely researched as core components in electronic skin. However, their limited capability of detecting only a single axial strain, and their low sensitivity, stability, opacity, and high production costs hinder their use in advanced applications. Herein, multiaxially highly sensitive, optically transparent, chemically stable, and solution‐processed strain sensors are demonstrated. Transparent indium tin oxide and zinc oxide nanocrystals serve as metallic and insulating components in a metal–insulator matrix and as active materials for strain gauges. Synergetic sensitivity‐ and stability‐reinforcing agents are developed using a transparent SU‐8 polymer to enhance the sensitivity and encapsulate the devices, elevating the gauge factor up to over 3000 by blocking the reconnection of cracks caused by the Poisson effect. Cross‐shaped patterns with an orthogonal crack strategy are developed to detect a complex multiaxial strain, efficiently distinguishing strains applied in various directions with high sensitivity and selectivity. Finally, all‐transparent wearable strain sensors with Ag nanowire electrodes are fabricated using an all‐solution process, which effectively measure not only the human motion or emotion, but also the multiaxial strains occurring during human motion in real time. The strategies can provide a pathway to realize cost‐effective and high‐performance wearable sensors for advanced applications such as bio‐integrated devices.     

On proportional fairness of uplink spectral efficiency in cell‐free massive MIMO systems

This paper is concerned with the proportional fairness (PF) of the spectral efficiency (SE) maximization of uplinks in a cell‐free (CF) massive multiple‐input multiple‐output (MIMO) system in which a large number of single‐antenna access points (APs) connected to a central processing unit (CPU) serve many single‐antenna users. To detect the user signals, the APs use matched filters based on the local channel state information while the CPU deploys receiver filters based on knowledge of channel statistics. We devise the maximization problem of the SE PF, which maximizes the sum of the logarithm of the achievable user rates, as a jointly nonconvex optimization problem of receiver filter coefficients and user power allocation subject to user power constraints. To handle the challenges associated with the nonconvexity of the formulated design problem, we develop an iterative algorithm by alternatively finding optimal filter coefficients at the CPU and transmit powers at the users. While the filter coefficient design is formulated as a generalized eigenvalue problem, the power allocation problem is addressed by a gradient projection (GP) approach. Simulation results show that the SE PF maximization not only offers approximately the achievable sum rates as compared to the sum‐rate maximization but also provides an improved trade‐off between the user rate fairness and the achievable sum rate.     

Variational models for image colorization via chromaticity and brightness decomposition.

Colorization refers to an image processing task which recovers color in grayscale images when only small regions with color are given. We propose a couple of variational models using chromaticity color components to colorize black and white images. We first consider total variation minimizing (TV) colorization which is an extension from TV inpainting to color using chromaticity model. Second, we further modify our model to weighted harmonic maps for colorization. This model adds edge information from the brightness data, while it reconstructs smooth color values for each homogeneous region. We introduce penalized versions of the variational models, we analyze their convergence properties, and we present numerical results including extension to texture colorization.     

Printed Sub‐2 V Gel‐Electrolyte‐Gated Polymer Transistors and Circuits

The fabrication and characterization of printed ion‐gel‐gated poly(3‐hexylthiophene) (P3HT) transistors and integrated circuits is reported, with emphasis on demonstrating both function and performance at supply voltages below 2 V. The key to achieving fast sub‐2 V operation is an unusual gel electrolyte based on an ionic liquid and a gelating block copolymer. This gel electrolyte serves as the gate dielectric and has both a short polarization response time (<1 ms) and a large specific capacitance (>10 µF cm^?2), which leads simultaneously to high output conductance (>2 mS mm^?1), low threshold voltage (<1 V) and high inverter switching frequencies (1–10 kHz). Aerosol‐jet‐printed inverters, ring oscillators, NAND gates, and flip‐flop circuits are demonstrated. The five‐stage ring oscillator operates at frequencies up to 150 Hz, corresponding to a propagation delay of 0.7 ms per stage. These printed gel electrolyte gated circuits compare favorably with other reported printed circuits that often require much larger operating voltages. Materials factors influencing the performance of the devices are discussed.     

Density‐adaptive network reprogramming protocol for wireless sensor networks

Network reprogramming is a process used to update program codes of sensor nodes that are already deployed. To deal with potentially unstable link conditions of wireless sensor networks, the epidemic approach based on 3‐way advertise‐request‐data handshaking is preferred for network reprogramming. Existing epidemic protocols, however, require a long completion period and high traffic overhead in high‐density networks, mainly due to the hidden terminal problem. In this paper, we address this problem by dynamically adjusting the frequency of advertisement messages in terms of the density of sensor nodes, which is the number of sensor nodes in a certain area. We compare the performance of the proposed scheme, called DANP (Density‐Adaptive Network Reprogramming Protocol), with a well‐known epidemic protocol, Deluge. Simulations indicate that, in the grid topologies, DANP outperforms Deluge by about 30% in terms of the completion time and about 50% in terms of the traffic overhead. Significant performance gain is observed in random topologies as well. The performance of DANP is further confirmed via measurements in an experimental test bed. Copyright © 2009 John Wiley & Sons, Ltd.     

Voltage Injection Method for Three-Phase Current Reconstruction in PWM Inverters Using a Single Sensor

This paper presents a voltage injection method for reconstructing phase currents from current signals measured on single current-shunt circuits with cost-effective and high-performance configurations in the pulsewidth modulation (PWM) inverters that are used for digital appliances. This method involves the injection of voltage signals at the carrier frequency for reconstructing the phase currents in PWM inverters using a single current sensor in the DC-link. It uses minimum signals to reduce the voltage and current harmonics caused by the injected signals. The vector of the injected voltage is at a minimum distance from the original reference to ensure the measurement time in the reconstruction of the phase currents. An injection sequence control method is also proposed to avoid an abrupt change in the injection signals. A PWM scheme for splitting phase voltages is proposed to reduce any audible noise, especially in low-speed operation. The proposed method reconstructs the phase currents with signals from a single current sensor and minimizes the amplitude of the injected signals to reduce the harmonics at audible noise frequencies in the injection signals. Experimental results showed the effectiveness of the proposed method.