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The efficiency of an AlGaN deep-ultraviolet light-emitting diode with peak emission wavelength of 285nm is investigated as a function of current over a wide range of temperatures (110K to 300K). We find that the efficiency-versus-current curve exhibits unique and distinct features over the entire temperature range including three points of inflection, a u-shape phenomenon which the efficiency increases again after the minimum, and higher low-temperature efficiency than room-temperature efficiency at high-current density regime.

An evident correlation between the high injection and the efficiency droop is demonstrated in GaInN light-emitting diodes (LEDs) for temperature ranging from 80K to 450K. For this temperature range, the efficiency droop has the same thermal tendency with the high injection, i.e. the onset shifts to lower voltage and higher current with increasing temperature. The voltage difference between two onsets mainly falls on the resistive p-type region and induces strong electric field to enable electron drift leakage and the resulting efficiency droop.

A planar loop antenna producing a uniform horizontal magnetic field to the antenna plane is presented. It consists of a pair of two turn spiral coils to which currents are supplied alternately. The antenna is suitable for an RFID reader antenna that is installed in a dealer's chip tray to monitor gaming chips in a casino.

A flexible, wideband antenna for radio frequency identification tags mountable on metallic surfaces is presented. A novel balanced feed structure, in which a longitudinal two-step staircase slit is inserted at one of the radiating edges of a patch and a tag chip feed is placed between the two steps, is proposed to perform simple and wideband impedance matching between an antenna and a tag chip. There is no via connection between the patch and ground plane. The measured 3-dB return loss bandwidth of the proposed antenna is about 84 MHz, and its read range is about 8.1 m.

A circularly polarized antenna with a wide beamwidth and high return loss is presented. The antenna consists of four U-shaped metal strips sequentially rotated and fed with a 90° phase difference. The antenna is designed for UHF RFID applications, and the experimental results show that it has a wide beamwidth of over 114° at 915 MHz and high return loss of over 34 dB in the 902–928 MHz range.

Ultra-high, omnidirectional transmittance through a coated glass window is demonstrated over the entire accessible portion of the solar spectrum. The average broadband transmittance has been increased to greater than 98.5% at normal incidence, and exceeds 97.8% at all wavelengths between 440 nm and 1800 nm, significantly outperforming conventional MgF 2 coated glass. The measured improvement in transmittance results from coating the window with a new class of materials consisting of porous SiO 2 nanorods. The step-graded antireflection structure also exhibits excellent omnidirectional performance, enabling average broadband transmittance in excess of 96% at incident angles as high as 70°.

With the rapid development of high-power white light-emitting diodes (LEDs), advances in packaging are required to further improve the device performance. In this work, an optimized packaging configuration for high power LED lamps with enhanced phosphorescence efficiency is presented based on ray-tracing simulations and experimental results

Enhancement of light extraction in a GaInN light-emitting diode employing a conductive omnidirectional reflector consisting of GaN, an indium-tin oxide nanorod low-refractive-index layer, and an Ag layer is presented.

We observed over two-fold enhancement in light extraction efficiency from GaN-based light emitters grown on a nano-patterned sapphire substrate. Nano-hole array patterns were generated by laser holography, which enabled a large area process with high throughput.

In this paper, three different integer frequency offset estimators for orthogonal frequency-division multiplexing systems are derived: maximum-likelihood, blind, and correlation estimators. These are based on one pilot symbol with adjacent subcarriers differentially modulated. Specially, the correlation estimator attains a good performance even if there exists residual symbol timing offset. We present the method used to compose the pilot symbol and derive three estimators based on it. Results from simulations are presented to verify the performance of the estimators.

This paper proposes a burst synchronization method with a preamble for high data rate wireless asynchronous transfer mode (WATM) systems that use orthogonal frequency division multiplexing (OFDM). The preamble for synchronization is composed of four identical periods. Using this signal repetition, the correlation for symbol timing detection and frequency offset estimation are calculated. The proposed method improves the performance of synchronization by increasing the size of data used in the correlation operation. The analytic results show that by using the proposed method a gain of 1 dB in SIR (signal to interference ratio) is possible.

The increase of the capacity of the digital magnetic recording systems inevitably causes severe intersymbol interference (ISI) and nonlinear distortions in the magnetic channel. Thus to achieve large capacity magnetic recording systems it is necessary to compensate these problems. In order to cope with the severe ISI and nonlinear distortions a neural decision feedback equalizer (NDFE) is applied to the digital magnetic recording channel. In the performance comparison between the NDFE and the conventional decision feedback equalizer (DFE) via simulations, it is found that as nonlinear distortions increase the NDFE has a greater SNR (signal to noise ratio) advantage over the DFE.

When convolution code is used in wireless coded orthogonal frequency division multiplexing (COFDM) systems, effective maximum likelihood (ML) decoding requires information on the frequency response of each subcarrier. This translates into increased hardware complexity, for instance, in the form of an additional deinterleaving block. We propose an optimal weighting scheme that combines the metrics for soft decision and channel influence into a single metric, can be performed before the deinterleaving block, and makes ML decoding possible. It shows comparable performance to ML decoding and better performance over suboptimal decoders.

An OFDM signal with large peak-to-average power ratio (PAPR) can cause power degradation (inband distortion) and spectral spreading (out-of-band radiation) by being clipped passing through a power amplifier. The PAPR characteristics are analyzed in two different aspects. From the foundation of the analysis, we propose Hadamard transform, which is ascribed to the relationship between the autocorrelation function and PAPR. Extensive computer simulations show that Hadamard transform is an effective technique to reduce PAPR.

A new coarse frequency offset estimation algorithm is proposed which performs robust operation in the presence of a symbol timing offset in an allowed range. The effect of a symbol timing offset on estimating a coarse frequency offset is analyzed and the coherence phase bandwidth according to the allowed symbol timing offset is introduced. In addition, a new technique for performing the coarse frequency estimation using the coherence phase bandwidth is described. Simulation results show that the proposed algorithm estimates a coarse frequency offset well under both AWGN and multipath channels even in the presence of the symbol timing offset within an allowed range.

The dependence of the polarization-induced electric field in GaInN/GaN multiple-quantum-well light-emitting diodes (LEDs) on the GaN quantum barrier (QB) thickness is investigated. Electrostatic arguments and simulations predict that a thin QB thickness reduces the electric field in the quantum wells (QWs) and also improves the LED efficiency. We experimentally demonstrate that the QW electric field decreases with decreasing QB thickness. The lower electric field results in a better overlap of electron and hole wave functions and better carrier confinement in the QWs. A reduced efficiency droop and enhanced internal quantum efficiency is demonstrated for GaInN/GaN LEDs when the QB thickness is reduced from 24.5 to 9.1 nm.