Performance of Spectrum Sharing System in Gamma Shadowed Nakagami-<Emphasis Type="Italic">m</Emphasis> Fading Environment

In this paper, the performance of spectrum sharing system in composite Nakagami-m/gamma shadowed channels is analyzed. The environments (of primary and secondary users) corrupted only by noise or interference are considered in details. The novel analytical expressions for outage probability, moment generation function and ergodic capacity are derived in a form of fast-computable Meijer’s G functions, for both mentioned scenarios. Numerical results illustrate the impact of fading and shadowing phenomena on system performance, and appropriate comparison between noise- and interference-limited cases is presented.     

Performance Evaluation of Multiple-Cell DS-CDMA Systems Over Correlated Nakagami-<Emphasis Type="Italic">m</Emphasis> Fading Environments

In this paper, the impact of the branch correlation on the performance of multiple-cell DS-CDMA cellular systems over Nakagami-m fading channels with arbitrary branch correlation is investigated. The received multipath-faded signals are assumed to experience identical but non-independent correlated Nakagami-m channels within the reference cell. A new closed-form formula for the joint probability density function (joint pdf) of the diversity combiner with arbitrary correlation coefficients in terms of the generalized Laguerre polynomial and the new expressions of average bit-error rate (BER) for the DS-CDMA system are given in this paper. The results, which were also compared with the performance of the single cell environments, demonstrate that the BER is significantly dependent on the correlation characteristic of diversity branching for both single-cell and multiple-cell environments.Joy I. Z. Chen was born in Taiwan. He received his B.Sc degree in electronics engineering from the National Taiwan Technical University, Taipei, Taiwan, and M.Sc degree in electrical engineering from the Da Yeh University, Chung Hwa, Taiwan, in 1985 and 1995, respectively, and Ph.D. degree in electrical engineering from National Defense University, Tao-Yuan, Taiwan, in 2001.He is currently an assistant professor of Department of Communication Engineering, Da Yeh University at Chang-Hwa Taiwan. Prior to joining the Da Yeh University, he worked at the Control Data Company (Taiwan) as a technical manager since September 1985–September 1996. His research interests include wireless communications, communication theory, and spread spectrum technical.     

Capacity of Dual Branch MRC System Over Correlated Nakagami-<Emphasis Type="Italic">m</Emphasis> Fading Channels-A Review

Various papers on the channel capacity using different diversity combining techniques and/or adaptive transmission schemes are available to enhance channel capacity under fading environment without the necessity of increasing bandwidth and transmit powers. This paper provides the review on the channel capacity of MRC (Maximal ratio combining) over uncorrelated and correlated Nakagami-m fading channels with m = 1 (Rayleigh fading channel) under ORA (Optimum rate adaptation with constant transmit power), CIFR (Channel inversion with fixed rate) and OPRA (Optimum power and rate adaptation) schemes. We also highlight the effect of fade correlation on channel capacity and discuss the improvement of the system performance under the different adaptive techniques.     

Performance of massive MIMO uplink system over Nakagami-<Emphasis Type="Italic">m</Emphasis> fading channel

This paper studies the performance of massive MIMO uplink system over Nakagami-m fading channel. The performance is measured in terms of spectral efficiency versus the number of base station antennas with different values of the parameter m using two schemes of linear detection; maximum ratio combining (MRC) and zero forcing receiver (ZF). The simulation results show that as m increases, the spectral efficiency increases slowly, but it increases significantly with the rise of the number of base station antennas. It should be also noted that the spectral efficiency with ZF is better than that with MRC.     

Performance analysis of a MIMO-RFID system in Nakagami-<Emphasis Type="Italic">m</Emphasis> fading channels

We analyze the bit error rate (BER) performance of a multiple-input multiple-output (MIMO) radio-frequency-identification (RFID) system employing orthogonal space-time block codes when the forward and backward channels exhibit independent but not necessarily identically distributed Nakagami-m fading. A closed-form upper bound on the BER performance is derived, and the corresponding diversity order is quantified. Numerical results provide some insight into the impact of several different parameters on the system performance.     

Bidirectional relaying with energy harvesting capable relay: outage analysis for Nakagami-<Emphasis Type="Italic">m</Emphasis> fading

This paper analyzes outage probability of bidirectional relaying (BDR) where two power-unconstrained single-antenna sources communicate with each other under assistance of a self-powered half-duplex single-antenna relay capable of energy harvesting and amplify-and-forward implementation. The relay harvests radio energy from both sources to power its relaying operation with the power splitting method. For outage analysis of the BDR for Nakagami-m fading, an exact formula is first proposed in closed-form. Through this formula, influences of important specifications (time switching ratio, power splitting ratio, energy conversion efficiency, fading severity, target transmission rate, transmit power of each source, distances from sources to relay) on the outage probability are then evaluated. Finally, Monte-Carlo simulations are generated to corroborate the proposed formula.     

Outage Performance of OFDM-Based Selective Decode-and-Forward Cooperative Networks Over Nakagami-<Emphasis Type="Italic">m</Emphasis> Fading Channels

In this paper, we investigate the outage performance of OFDM-based selective decode-and-forward cooperative networks over independent but not necessarily identically distributed (i.n.i.d.) Nakagami-m fading channels, with integer values of parameter m. A unified closed-form expression for the outage probability is derived for three selective relaying schemes. The effect of the coherence bandwidth on the proposed scheme is also investigated. Monte Carlo simulations are carried out to validate our analysis.     

Exploiting cooperative relays to enhance the performance of energy-harvesting systems over Nakagami-<Emphasis Type="Italic">m</Emphasis> fading channels

This paper investigates a time-switching energy-harvesting system in which a source communicates with a destination via energy-constrained amplify-and-forward relays. To exploit the benefit of using multiple relays, we propose a relay scheduling called consecutive relay selection (CRS), which allows all relays to assist the source-to-destination communication, to improve the transmission efficiency of the time-switching policy. The partial relay selection (PRS) is examined for performance comparison. The selected relay in the PRS protocol is considered in two cases: in one, it is selected based on the first-hop channel gains (PRS-1 protocol), and in the other, it is selected based on the second-hop channel gains (PRS-2 protocol). For performance evaluation, the analytical expressions of the outage probability and throughput for Nakagami-m fading channel are derived. Our results show that the CRS protocol outperforms the PRS protocol in terms of throughput, the PRS-1 protocol achieves better performance than the PRS-2 protocol. Moreover, we discuss the effects of various key system parameters on system performance, such as the energy-harvesting ratio, source transmission rate, and locations of relays, to provide insights into the various design choices.     

An ultra-low-power CMOS symmetrical OTA for low-frequency <Emphasis Type="Italic">G</Emphasis><Subscript><Emphasis Type="Italic">m</Emphasis></Subscript>-<Emphasis Type="Italic">C</Emphasis> applications

In this paper an ultra-low-power CMOS symmetrical operational transconductance amplifier (OTA) for low-frequency G _m -C applications in weak inversion is presented. Its common mode input range and its linear input range can be made large using DC shifting and bulk-driven differential pair configuration (without using complex approaches). The symmetrical OTA was successfully verified in a standard CMOS 0.35-μm process. The measurements show an open loop gain of 61 dB and a unit gain frequency of 195 Hz with only 800 mV of power supply voltage and just 40 nW of power consumption. The transconductance is 66 nS, which is suitable for low-frequency G _m -C applications.     

Recombination of charge carriers in the GaAs-based <Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">i</Emphasis>-<Emphasis Type="Italic">n</Emphasis> diode

It is established that the radiative recombination of charge carriers plays a substantial role in the GaAs-based p-i-n diodes at high densities of the forward current. It is shown experimentally that the diodes operating in microwave integrated circuits intensely emit light in the IR range with wavelengths from 890 to 910 nm. The obtained results indicate the necessity of taking into account the features of recombination processes in the GaAs-based microwave p-i-n diodes.     

Performance Analysis of the Double-Antenna SDC System Over <Emphasis Type="Italic">N</Emphasis>-Nakagami Fading Channels

The performance of the double-antenna switched diversity combining (SDC) system over N-Nakagami fading channels is investigated in this paper. Based on the method of the probability density function of the signal-to-noise ratio, the exact expressions for the channel capacity and average symbol error probability (ASEP) are derived. Then the channel capacity and ASEP performance under different conditions is evaluated through numerical simulations to verify the analysis. The simulation results showed that the performance of the double-antenna SDC system is improved with the fading coefficient increased, but the level of improvement is declined as the number of cascaded components increased.     

High-efficiency LEDs based on <Emphasis Type="Italic">n</Emphasis>-GaSb/<Emphasis Type="Italic">p</Emphasis>-GaSb/<Emphasis Type="Italic">n</Emphasis>-GaInAsSb/<Emphasis Type="Italic">P</Emphasis>-AlGaAsSb type-II thyristor heterostructures

A new type of light-emitting diodes (LEDs), a high-efficiency device based on an n-GaSb/p-GaSb/n-GaInAsSb/P-AlGaAsSb thyristor heterostructure, with the maximum emission intensity at wavelength λ = 1.95 μm, has been suggested and its electrical and luminescent characteristics have been studied. It is shown that the effective radiative recombination in the thyristor structure in the n-type GaInAsSb active region is provided by double-sided injection of holes from the neighboring p-type regions. The maximum internal quantum efficiency of 77% was achieved in the structure under study in the pulsed mode. The average optical power was as high as 2.5 mW, and the peak power in the pulsed mode was 71 mW, which exceeded by a factor of 2.9 the power obtained with a standard n-GaSb/n-GaInAsSb/P-AlGaAsSb LED operating in the same spectral range. The approach suggested will make it possible to improve LED parameters in the entire mid-IR spectral range (2–5 μm).     

Implementation of a field programmable gate array for wireless control of a <Emphasis Type="Italic">lab</Emphasis>-<Emphasis Type="Italic">on</Emphasis>-<Emphasis Type="Italic">a</Emphasis>-<Emphasis Type="Italic">robot</Emphasis>

We report the design of a digital system to wirelessly control microchip capillary electrophoresis (CE) equipment and a mobile unit for chemical analysis. The digital system consists of an embedded processor designed for digital control, decoding and applying of wirelessly-transmitted test parameters, data acquisition, and mobility control. The design is implemented on a field programmable gate array (FPGA) and its development board interfaces with four digital-to-analog converters on a newly-designed 3-channel high voltage power supply, electrochemical detector, wireless modems for communications with a base unit, mobile platform motor controllers, GPS sensor, and an air micropump. The FPGA allows for all the interfacing hardware to perform CE and transmission of the data acquired from the interfacing electrochemical detector. The work described herein extends the utilization of microchip capillary electrophoresis to include remotely controlled field applications.     

3<Emphasis Type="Italic">C</Emphasis>-SiC <Emphasis Type="Italic">p-n</Emphasis> structures grown by sublimation on 6<Emphasis Type="Italic">H</Emphasis>-SiC substrates

Sublimation epitaxy in a vacuum has been employed to grow n-and p-type 3C-SiC layers on 6H-SiC substrates. Diodes have been fabricated on the basis of the p-n structure obtained, and their parameters have been studied by measuring their current-voltage and capacitance-voltage characteristics and by applying the DLTS and electroluminescence methods. It is shown that the characteristics of the diodes studied are close to those of diodes based on bulk 3C-SiC. A conclusion is made that sublimation epitaxy can be used to fabricate 3C-SiC p-n structures on substrates of other silicon carbide polytypes.     

Temperature dependence of the band structure of 3<Emphasis Type="Italic">C</Emphasis>, 2<Emphasis Type="Italic">H</Emphasis>, 4<Emphasis Type="Italic">H</Emphasis>, and 6<Emphasis Type="Italic">H</Emphasis> SiC polytypes

The temperature dependences of significant energy extrema at the high-symmetry points Γ, X, L, K, M, A, and H of the Brillouin zone in the cubic and hexagonal modifications of SiC, as well as the energies of the main interband transitions at these points, were calculated for the first time by the empirical-pseudopotential method. The effect of the temperature dependence of the electron-phonon interaction on the crystal band structure was taken into account via the Debye-Waller factors, and the contribution of the linear expansion of the lattice was accounted for via the temperature dependence of the linear-expansion coefficient. The special features of the temperature dependences of the energy levels and of energies of the interband and intraband transitions are analyzed in detail. The results of the calculations are in good agreement with the known experimental data on the characteristics of SiC-based p-n structures operating in the breakdown mode. For example, the temperature coefficient of the energy of the X_1c–X_3c transition, which is responsible for the narrow violet band in the breakdown-electroluminescence spectra of reverse-biased p-n junctions, was found to be significantly smaller than the temperature coefficients for the interband transitions (from the conduction to valence band). This fact is quite consistent with the experimental curve of the temperature coefficient of the emission spectrum, which has a minimum in the same wavelength range.     

Depolarization in a metal-<Emphasis Type="Italic">p</Emphasis>-ferroelectric-<Emphasis Type="Italic">n</Emphasis>-semiconductor structure

The depolarization in a metal-p-ferroelectric-n-semiconductor structure is calculated based on an analysis of the experimental parameters of a ferroelectric hysteresis loop in a metal-ferroelectric-metal structure. For a semiconductor, the Poisson equation is solved using a standard method, while, for a ferroelectric, a numerical integration is applied. Two variants of semiconductor parameters are considered: (i) a thick n-type region (there is a region of electrical neutrality beyond a space-charge region), and (ii) a thin n-type region (an electric field penetrates all the way through this region). It is shown that depolarization significantly reduces ferroelectric polarization, and this reduction is stronger in the case of a semiconductor with lower doping. If the electric field penetrates all the way through the n-type region, depolarization decreases as the n-type region becomes thinner.     

Low-Power FPGA-Implementation of <Emphasis Type="Italic">atan</Emphasis>(<Emphasis Type="Italic">Y</Emphasis>/<Emphasis Type="Italic">X</Emphasis>) Using Look-Up Table Methods for Communication Applications

This paper presents an architecture for the computation of the atan(Y/X) operation suitable for broadband communication applications where a throughput of 20 MHz is required. The architecture takes advantage of embedded hard-cores of the FPGA device to achieve lower power consumption with respect to an atan(Y/X) operator based on CORDIC algorithm or conventional LUT-based methods. The proposed architecture can compute the atan(Y/X) with a latency of two clock cycles and its power consumption is 49% lower than a CORDIC or 46% lower than multipartite approach.

Analysis of Asynchronous Band-Limited DS-CDMA with MMSE Multiuser Detector over Generalized-<Emphasis Type="Italic">k</Emphasis> Fading Channels

In this paper, we investigate bit-error-rate (BER) performance of a minimum mean-squared error (MMSE) multiuser receiver for asynchronous band-limited direct- sequence code-division multiple-access (DS-CDMA) systems. We focus on the BER performance in the presence of multitone jamming (MTJ) over frequency-selective multipath fading channels. We consider the generalized-K fading model in our analysis, as it can model a large spectrum of fading-channel characteristics. We also analyze the effects of band- limited pulse shape on the BER performance of the system. Multipath diversity based on the maximal-ratio combining (MRC) scheme is employed to combat fading effects. Our analytical expressions are valid for arbitrary diversity levels and fading parameters. Spectrum raised cosine (SRC) and Beaulieu–Tan–Damen (BTD) pulse shapes are employed for numerical analysis. Numerical results show that in the presence of MTJ and under various channel conditions, the MMSE based receiver gives better BER performance than the one without it. Moreover, the system with BTD pulses outperforms the one with SRC pulses.     

A DLTS study of 4<Emphasis Type="Italic">H</Emphasis>-SiC-based <Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">n</Emphasis> junctions fabricated by boron implantation

Deep-level transient spectroscopy (DLTS) has been used to study p-n junctions fabricated by implantation of boron into epitaxial 4H-SiC films with n-type conductivity and the donor concentration (8–9) × 10¹⁴ cm⁻³. A DLTS signal anomalous in sign is observed; this signal is related to recharging of deep compensating boron-involved centers in the n-type region near the metallurgical boundary of the p-n junction.