Simultaneous Users Research Articles

Performance analysis of AO‐OFDM‐CDMA with advanced 2D‐hybrid coding for amplifier‐free LR‐PONs

All-optical orthogonal frequency division multiplexing (AO-OFDM) and optical code-division multiple-access system (OCDMA) are combined in the first analytical model, which considers subcarrier hopping by means of advanced two-dimensional (2D) hybrid-coded (2D-HC) signature. The model incorporates probabilistic subcarrier overlapping, multiple-access interferences and is tested, for the first time, over amplifier-free long-reach passive optical networks (LR-PONs) using cost-effective intensity modulations and direct detection. For the upstream direction at 40 Gb/s, AO-OFDM-OCDMA outperforms a ‘classical’ multi-channel OCDMA system for low received powers and any number of simultaneous users. In comparison to conventional 1D Walsh–Hadamard, 1D prime code and 2D prime hop system, coding with 2D-HC can improve the performance of AO-OFDM-CDMA, thus allowing a higher number of simultaneous users in LR-PON without optical amplification. From numerical simulations, the authors show that 16-quadrature amplitude modulation (16-QAM) AO-OFDM-CDMA with 45 users has comparable performance to conventional multi-channel 16-QAM coherent optical OFDM in the downstream direction and up to 58 km with 1:45 split ratio, without employing complex coherent technology. Similarly, based on the feasibility of physical implementation configuration, a budget power calculation is performed showing 108 km as maximum reachability distance for 40 Gb/s QAM signal, 1:64 split ratio when considering standard forward-error-correction.

Efficiency and Reliability Performance's of the Bioinformatics Resource Portal

This paper discusses the resource portal of the analysis of the Borneo's Biodiversity Information System (BBIS) from the point of view of the characteristics of efficiency and reliability performance. Data collection methods and tools use the observation approach that simulates 100 simultaneous users, logging every 10 seconds between random clicks on the URL site. Efficiency testing results that measured 27 recommendations from PageSpeed measuring instruments and 19 recommendation parameters from YSlow, obtained average scores on grade A. However, there were still 6 parameters related to system resource issues with grade F scores, and these parameters were the significant effect the reliability value. Reliability test results referring to Jacob Nelson's equation approaches and Standard Telcordia reference. The result shows that the value of R = 0.988967 or the percentage of the reliability value is 98.89% and r = 0.011 or the error rate is 1.1%. and the user threshold test results are found when the number increases to 500 users. The success of efficiency testing parameters significantly affects the percentage of performance reliability.

Who diagnosed and prescribed what? Using provider details to inform observational research.

To describe how often patients with depression initiating antidepressants receive their depression diagnosis and prescriptions from the same provider and, when simultaneously initiating benzodiazepines, how often both prescriptions come from the same provider. Using a US healthcare claims database, we created a cohort of adults (18-64years) with a depression diagnosis who initiated antidepressants. We examined concordance by provider specialty and provider identifier between (a) the first antidepressant prescription fill and most proximal depression diagnosis, and (b) the initial antidepressant and benzodiazepine prescription fills among simultaneous benzodiazepine and antidepressant initiators. Among 245166 antidepressant initiators with a recent depression diagnosis (female=67%; median age=39), the specialty of the provider assigning the depression diagnosis matched the antidepressant prescriber's specialty in 94% of cases with known provider details (provider identifier concordance=93%). Concordance was higher for adults diagnosed by a general practitioner (98%) or psychiatrist (92%) than for those diagnosed by a psychologist (74%). In simultaneous new users of antidepressants and benzodiazepines (n=19371), both prescriptions were issued by the same provider specialty and provider identifier 94% and 93% of the time, respectively. The vast majority of patients who received antidepressant prescriptions and depression diagnoses appear to have received both diagnosis and antidepressants from the same provider, suggesting that when antidepressants are issued around the time a patient is diagnosed with depression, the antidepressant was likely prescribed for depression. In addition, the great majority of patients who simultaneously initiate benzodiazepines appear to do so under the direction of one provider.

All‐optical VPN platform for multisite VLC‐based networks

AbstractOptical networks and, in particular, visible light communication represent a very promising communication medium for future‐generation company networks. The establishment of virtual private networks (VPNs) in these specific distributed networks is a fundamental issue. In this paper, we present an all‐optical VPN platform based on visible light communication small cells on the access side and an optical fiber link on the backbone side. We exploited the security enhancement using the superposition of optical signals encoded using optical code‐division multiplexing codewords specific to each user. Two VPN modes are proposed: transport and tunnel. Even though the transport mode provides a much lower blocking rate as well as transmission performance (lower packet delay), the tunnel mode is advantageous from a security perspective due to the embedded optical code‐division multiple access encoding that it implements. Simulations are carried out for both modes to study the performance and security level provided by the proposed VPN architecture relatively to specific parameters (codeword size and number of simultaneous users).

Effect of atmospheric turbulence on the BER performance of an optical CDMA FSO link with SIK receiver

An analytical approach is presented to evaluate the effect of atmospheric turbulence on the bit error rate (BER) performance of an optical code division multiple access (OCDMA) free space optical (FSO) link using optical domain encoder and sequence inverse keying (SIK) balanced photodetector receiver. The analysis is presented to find the expression of the signal current and multi access interference (MAI) current at the output of the SIK receiver taking into account the effect of atmospheric turbulenceand the channel effect due to pointing error. The conditional BER conditioned on a given atmospheric turbulence is evaluated. The average BER is obtained by averaging the conditional BER over the probability density function (pdf) of the atmospheric turbulence. The results are evaluated for different code length, number of simultaneous user, link distances and other system parameters. It is found that, the performance of an OCDMA system with a SIK receiver is highly degraded due to turbulence effect and suffers significant power penalty at a given BERwhich can be substantially reduced by increasing the code length using SIK receiver. The penalty is found to be 9 dB and 11.5 dB for link distance 3000m with user number 2 and 16 respectively at BER=10−9. The allowable number of simultaneous user at a given BER is also determined for a given code length.

Enhanced Spectral Amplitude Coding OCDMA System Utilizing a Single Photodiode Detection

In this paper, the performance of a spectral amplitude coding-optical code division multiple access (SAC-OCDMA) system is investigated utilizing a single photodiode (SPD) detection technique. The proposed system uses enhanced double weight (EDW) codes as signature codes with three simultaneous users to overcome both phase-induced intensity noise (PIIN) and multiple access interference (MAI). In addition, a dispersion compensating fiber (DCF) is used in order to decrease the group velocity dispersion (GVD) caused in the single mode fiber. An erbium-doped fiber amplifier (EDFA) is used to overcome the attenuation. The use of both DCF and EDFA leads to an appreciable enhancement in the system performance. The system performance is evaluated through its bit error rate (BER), Q-factor, and received power. A comparison between the EDW codes and modified double weight (MDW) codes on the SAC-OCDMA system is demonstrated. Simulation is carried out through Optisystem ver. 7. The simulation results show that: (a) using an avalanche photodiode (APD) over PIN photodiode allows data transmission over longer distances; (b) the use of DCF improves the system BER;(c) using MDW codes gives better BER than using EDW codes.

Multiuser virtual reality environment for visualising neuroimaging data.

The recent advent of high-performance consumer virtual reality (VR) systems has opened new possibilities for immersive visualisation of numerous types of data. Medical imaging has long made use of advanced visualisation techniques, and VR offers exciting new opportunities for data exploration. The author presents a new framework for interacting with neuroimaging data, including MRI volumes, neuroanatomical surface models, diffusion tensors, and streamline tractography, as well as text-based annotations. The system was developed for the HTC Vive using C++, OpenGL, and the OpenVR software development kit. The author developed custom GLSL shaders for each type of data to provide high-performance real-time rendering suitable for use in a VR environment. These are integrated with an interface that enables the user to manipulate the scene through the Vive controllers and perform operations such as volume slicing, fibre track selection, and structural queries. The software can read data generated by existing automated brain MRI analysis packages, enabling the rapid development of subject-specific visualisations of multimodal data or annotated atlases. The system can also support multiple simultaneous users, placing them in the same virtual space to interact with each other while visualising the same datasets, opening new possibilities for teaching and for collaborative exploration of neuroimaging data.

Democratizing assessment practices through multimodal critique in the design classroom

Critique is a primary method of assessment and feedback used in design education, yet is not well understood apart from traditional instructor-led activities in physical learning spaces. In this study, we analyze a series of group critiques in a human–computer interaction learning experience, focusing on an emergent instructional design for technologically-mediated critique created by experienced students serving as peer mentors. Peer mentors designed complex interactions that supported assessment in the design classroom, including multiple technology-supported modes of critique beyond the traditional oral critique. The modes of critique, and the ways in which they intertwined, included: (1) public oral critique led by the instructor, (2) a critique document authored by experienced students in real-time using Google Docs, and (3) backchannel chat used by experienced students in Google Docs to facilitate and organize their critique. Using this model of distributed assessment, which we refer to as multimodal critique, the amount of feedback and number of interlocutors increased dramatically, facilitating participation by students and peer mentors alike. These interactions indicate instructional affordances for including many simultaneous users within an existing assessment infrastructure using readily accessible technologies, and a means of activating student development at multiple levels of expertise.

The historic wooden model of Solomon’s Temple

PurposeRecent advances in contemporary virtual reality (VR) technologies are going to have a significant impact on everyday life. Through VR it is possible to virtually explore a computer-generated environment as a different reality, and to immerse oneself into the past or in a virtual museum without leaving the current real-life situation. For such an ultimate VR experience, the user should only see the virtual world. Currently, the user must wear a VR headset which fits around the head and over the eyes to visually separate himself from the physical world. Via the headset images are fed to the eyes through two small lenses. The purpose of this paper is to present the generation of a virtual 3D model of the wooden model of Solomon’s Temple, located at the Hamburg museum (Museum für Hamburgische Geschichte), and its processing for data integration into the two game engines Unity and Unreal.Design/methodology/approachCultural heritage (CH) monuments are ideally suited for both thorough multi-dimensional geometric documentation and realistic interactive visualisation in immersive VR applications. Additionally, the game industry offers tools for interactive visualisation of objects to motivate users to virtually visit objects and places.FindingsThe project has been carried out by the Photogrammetry & Laser Scanning Lab of the HafenCity University Hamburg, Germany to demonstrate an immersive and interactive visualisation using the VR System HTC Vive.Originality/valueThe workflow from data acquisition to VR visualisation, including the necessary programming for navigation and interaction, is described. Furthermore, the use (including simultaneous multiple users environments) of such a VR visualisation for a CH monument is discussed in this contribution.

Development of a novel two-dimensional-SWZCC – Code for spectral/spatial optical CDMA system

In order to overcome the effect of the Multiple Access Interference (MAI) and noises, and increase the number of the simultaneous users, the multiplexing capacity and data rate, this paper proposes a novel design of a two dimensional spectral/spatial code named Two Dimensional-Single Weight Zero Cross Correlation (2D-SWZCC) based on a single weight code which is characterized by a zero cross correlation and a high number of users. The proposed code is developed to be implemented in non-coherent Optical Code Division Multiple Access (OCDMA) systems. Numerical results of the design construction show that the proposed code enhances the system performance by improving its capacity, reducing the signal-to-noise ratio, and increasing the data rate. The system output performance for active user number is equal to 1.09, 1.54, 2.14, 2.215, 3.89 and 5.14 times than those of, Two Dimensional Multi-Diagonal (2D-MD), Two Dimensional Dynamic Cyclic Shift (2D-DCS), (1D-SWZCC), Two Dimension Perfect Difference (2D-PD), Two Dimensional Hybrid Flexible Cross Correlation- Modified Double Weight (FCC/MDW) and Two Dimensional Extended Enhanced Double Weight (2D-extended-EDW) codes, respectively. It can save an effective power around −3.2 dBm and −1.4 dBm at the level of the receiver compared to 2D-DCS and 2D-MD codes. Moreover, the system performance has been studied using Optisystem software. The simulation results show that the system respects the optical transmission property accommodating four users for a power of the source equal to −10 dBm, and the data rate is 1 Gbps.

Efficient DSP and Circuit Architectures for Massive MIMO: State of the Art and Future Directions

Massive MIMO is a compelling wireless access concept that relies on the use of an excess number of base-station antennas, relative to the number of active terminals. This technology is a main component of 5G New Radio (NR) and addresses all important requirements of future wireless standards: a great capacity increase, the support of many simultaneous users, and improvement in energy efficiency. Massive MIMO requires the simultaneous processing of signals from many antenna chains, and computational operations on large matrices. The complexity of the digital processing has been viewed as a fundamental obstacle to the feasibility of Massive MIMO in the past. Recent advances on system-algorithm-hardware co-design have led to extremely energy-efficient implementations. These exploit opportunities in deeply-scaled silicon technologies and perform partly distributed processing to cope with the bottlenecks encountered in the interconnection of many signals. For example, prototype ASIC implementations have demonstrated zero-forcing precoding in real time at a 55 mW power consumption (20 MHz bandwidth, 128 antennas, multiplexing of 8 terminals). Coarse and even error-prone digital processing in the antenna paths permits a reduction of consumption with a factor of 2 to 5. This article summarizes the fundamental technical contributions to efficient digital signal processing for Massive MIMO. The opportunities and constraints on operating on low-complexity RF and analog hardware chains are clarified. It illustrates how terminals can benefit from improved energy efficiency. The status of technology and real-life prototypes discussed. Open challenges and directions for future research are suggested.

Simultaneous Detection and Channel Estimation for Censoring-Based Spectrum Sensing in Cognitive Radio Networks

This letter considers simultaneous primary user (PU) detection and channel estimation for censoring-based spectrum sensing in cognitive radio networks over fading channels. We formulate the problem mathematically for Rician and Rayleigh fading channels. Closed-form expressions are derived for the critical performance metrics in low SNR regime. Further, we optimize the censoring parameter and the power allocation for throughput maximization under transmit and interference power constraints. Our results demonstrate that simultaneous PU detection and channel estimation substantially improve the throughput of cognitive radio networks over an approach where PU detection and channel estimation are treated independently.

A Comparison of Hybrid Beamforming and Digital Beamforming With Low-Resolution ADCs for Multiple Users and Imperfect CSI

For 5G it will be important to leverage the available millimeter wave spectrum. To achieve an approximately omni- directional coverage with a similar effective antenna aperture compared to state of the art cellular systems, an antenna array is required at both the mobile and basestation. Due to the large bandwidth and inefficient amplifiers available in CMOS for mmWave, the analog front-end of the receiver with a large number of antennas becomes especially power hungry. Two main solutions exist to reduce the power consumption: hybrid beam forming and digital beam forming with low resolution Analog to Digital Converters (ADCs). In this work we compare the spectral and energy efficiency of both systems under practical system constraints. We consider the effects of channel estimation, transmitter impairments and multiple simultaneous users. Our power consumption model considers components reported in literature at 60 GHz. In contrast to many other works we also consider the correlation of the quantization error, and generalize the modeling of it to non-uniform quantizers and different quantizers at each antenna. The result shows that as the SNR gets larger the ADC resolution achieving the optimal energy efficiency gets also larger. The energy efficiency peaks for 5 bit resolution at high SNR, since due to other limiting factors the achievable rate almost saturates at this resolution. We also show that in the multi-user scenario digital beamforming is in any case more energy efficient than hybrid beamforming. In addition we show that if different ADC resolutions are used we can achieve any desired trade-offs between power consumption and rate close to those achieved with only one ADC resolution.

Development and Performance Improvement of a New Two-Dimensional Spectral/Spatial Code Using the Pascal Triangle Rule for OCDMA System

Abstract This paper introduces a novel code called two dimensional Pascal’s triangle zero cross correlation (2D-PTZCC) for spectral/spatial coding with its structure of the corresponding system to implement in spectral amplitude coding optical code division multiple access (SAC-OCDMA) systems The novel code is derived from a one dimensional zero cross correlation (1D-ZCC) code using Pascal’s triangle rule. The analytical results prove that the proposed code has totally removed the multiple access interference (MAI), in addition the phase induced intensity noise (PIIN) influence is highly reduced due to the zero cross correlation (ZCC) property. Comparing with the recent developed two-dimensional codes like 2D multi diagonal (2D-MD), 2D dynamic cyclic shift (2D-DCS), 2D diluted perfect difference (2D-DPD) and 2D perfect difference (2D-PD) codes for the same code length. The results of simulation show that the suggested code improve the system capacity and increase the number of simultaneous users reaches 29 % and 64 % comparing to 2D-DPD and 2D-PD codes, respectively. As well, it supplies higher signal power and data bit rates whereas it saves effective source power around −0.81dBm for 2D-DCS and 2D-DPD codes and consumes minor light spectral width. The passage from 1D to 2D ameliorated 1.68 times the system capacity and saved around − 4.27 d B m $ - 4.27{\rm{ dBm}}$ the effective power for each user.

Performance analysis and optimization of wavelength routed (WR) and wavelength selected (WS) hybrid optical distributed network (ODN) for next generation passive optical network stage 2 (NG-PON2)

Next-generation passive optical network stage 2 (NG-PON2) supports the wavelength routed optical distributed network (WR-ODN), power splitter optical distributed network or wavelength-selected optical distributed network (WS-ODN) and hybrid of both the architecture configuration. NG-PON2 is world’s first multi-wavelength passive optical network (PON) standard. The fiber dispersion and nonlinearity degrades the performance of NG-PON2 severely. Fiber nonlinearity depends on the optical launch power and fiber reach. This paper focuses on maximizing the network performance and maximizing the number of simultaneous users with error-free performance by optimizing the optical launch power respectively at dynamic reach and differential reach. The optical launch power is optimized to abate the fiber nonlinearity and significantly enhances the performance of NG-PON2 at dynamic fiber reach for Alcatel 6912 Teralight Ultra 1625 commercial fiber specification. Furthermore, precise values of the optimum launch power for the dynamic fiber reach, for different NG-PON2 architecture, under industrial fiber specification is meticulously obtained. It is identified that irrespective of both, WR-ODN and WS-ODN architecture configuration, optimum launch power remains constant. Power budget is calculated for both, maximizing the performance and maximizing the simultaneous number of users at differential reach and dynamic reach of the NG-PON2.

Application of Semiconductor Optical Amplifier (SOA) in Managing Chirp of Optical Code Division Multiple Access (OCDMA) Code Carriers in Temperature Affected Fibre Link

Chromatic and temperature induced dispersion can both severely affect incoherent high data rate communications in optical fibre. This is certainly also true for incoherent optical code division multiple access (OCDMA) systems with multi-wavelength picosecond code carriers. Here, even a relatively small deviation from a fully dispersion compensated transmission link can strongly impact the overall system performance, the number of simultaneous users, and the system cardinality due to the recovered OCDMA auto-correlation being strongly distorted, time-skewed, and having its full width at half maximum (FWHM) value changed. It is therefore imperative to have a simple tunable means for controlling fibre chromatic or temperature induced dispersion with high sub-picosecond accuracy. To help address this issue, we have investigated experimentally and by simulations the use of a semiconductor optical amplifier (SOA) for its ability to control the chirp of the passing optical signal (OCDMA codes) and to exploit the SOA ability for dispersion management of a fibre link in an incoherent OCDMA system. Our investigation is done using a 19.5 km long fibre transmission link that is exposed to different temperatures (20 °C and 50 °C) using an environmental chamber. By placing the SOA on a transmission site and using it to manipulate the code carrier’s chirp via SOA bias adjustments, we have shown that this approach can successfully control the overall fibre link dispersion, and it can also mitigate the impact on the received OCDMA auto-correlation and its FWHM. The experimental data obtained are in a very good agreement with our simulation results.

Analytical study of DWDM optical long haul network with symmetrical dispersion compensation

Objective: To design 40 Gbps ultra-dense wavelength division multiplexed (DWDM) optical network for 32 and 64 channels. Methods: Proposed DWDM architecture supports three different advance modulation schemes with symmetrical dispersion compensation unit. Performance of proposed work has been investigated using parameters bit error rate (BER) and quality factor. For efficient analysis, we employ variation in channel spacing, transmission length of fiber and input laser power, which is resulted into some significant observations. Findings: Carrier Suppressed Return to Zero (CSRZ) scheme exhibits a good quality factor with maximum achievable distance up to 4250 km due to highest tolerance to nonlinear effects. Modified Duobinary Return to Zero (MDRZ) modulation scheme also provides a good quality factor with laser power variation due to high receiver sensitivity, but with limited reach upto 2750 km. While Duobinary Return to Zero (DRZ) scheme provides moderate transmission coverage up to 3750 km in comparison to CSRZ and MDRZ, with a lesser quality factor due to effect of Inter Symbol Interference (ISI). We observe that an increase in number of simultaneous users through the channels results into performance degradation. Application: This work delivers very huge data rate and good spectral efficiency to sustain the current high traffic growth. Keywords: Dispersion, Long Haul System, Optical Network, Symmetrical Compensation, DWDM

Experiment of wireless optical communication applied to hybrid SAC/PDM OCDMA scheme with FBG-based fiber lasers

In this study, hybrid spectral amplitude coding and polarization division multiplexing based optical code-division multiple access (SAC/PDM-based OCDMA) was proposed for transmitting an optical-coded and polarized signal over a wireless transmission channel. The experimental results showed that the desired signal easily identifies either a horizontal or a vertical polarized state and then extracts the M-sequence of the signature address code correctly. Hence, compared with SAC-OCDMA schemes, the spectral efficiency and number of simultaneous active users of the proposed hybrid SAC/PDM-based OCDMA scheme are twice those of the conventional SAC-OCDMA scheme.

Concurrent and Simultaneous Use of Cannabis and Tobacco and Its Relationship with Academic Achievement amongst University Students.

The combined use of cannabis and tobacco is frequent in Europe. Few studies have nonetheless explored this pattern of consumption and its relationship with academic achievement in Spanish population. The aim of the present study was to analyze (1) the frequency of four patterns of polydrug use the last year (non-dual users of cannabis and tobacco; concurrent users: cannabis and tobacco separately; simultaneous users: tobacco in cannabis “joints”; simultaneous users: tobacco in cannabis joints alongside alcohol) by gender and age; (2) grade point average (GPA) by gender and age; (3) the association between the frequency of the four patterns of use and the GPA amongst a sample of 477 Spanish university students. The use of cannabis and tobacco (concurrent and simultaneous) and GPA were assessed by means of self-reported questionnaires. Statistically significant differences were found for the GPA with respect to gender. The GPA by the non-dual users of cannabis and tobacco was significantly higher than the GPA corresponding to the concurrent and simultaneous users. The combined use of cannabis and tobacco, regardless of the type of use (concurrent or simultaneous), is moderately related to poor academic achievement amongst university students.

Design and performance analysis of modified two dimensional Golomb code for optical code division multiple access networks

In this work, a two dimensional (2D) wavelength/time code is developed. The 64 bit 2D code is constructed by a technique based on folding of Golomb rulers referred in this work as modified Golomb code (2D MGC) and the proposed 2D code is generated using Java 8.1 software. The performance of the proposed 2D MGC is evaluated in terms of bit error rate (BER), received signal power, and time domain analysis of multiple users. In this experiment, it is found that the BER increases with multiple numbers of simultaneous users due to multiple access interference. The proposed 2D code yields better network performance in terms of BER compared to that of different existing 2D OCDMA codes. In this work, mathematical analysis is also carried out to prove that the proposed 64 bit code is optimal satisfying auto and cross correlation properties. Furthermore, the complexity analysis of the proposed 64 bit optical code division multiple access (OCDMA) code is analysed. The OCDMA model is validated using the optisystem software.