31.38 Gb/s GaN-based LED array visible light communication system enhanced with V-pit and sidewall quantum well structure

Although the 5G wireless network has made significant advances,it is not enough to accommodate the rapidly rising requirement for broader bandwidth in post-5G and 6G eras.As a result,emerging technologies in higher frequencies including visible light communication(VLC),are becoming a hot topic.In particular,LED-based VLC is foreseen as a key enabler for achieving data rates at the Tb/s level in indoor scenarios using multi-color LED arrays with wavelength division multiplexing(WDM)technology.This paper proposes an optimized multi-color LED array chip for high-speed VLC systems.Its long-wavelength GaN-based LED units are remarkably enhanced by V-pit structure in their efficiency,especially in the“yellow gap”region,and it achieves significant improvement in data rate compared with earlier research.This work investigates the V-pit structure and tries to provide insight by introducing a new equivalent circuit model,which provides an explanation of the simulation and experiment results.In the final test using a laboratory communication system,the data rates of eight channels from short to long wavelength are 3.91 Gb/s,3.77 Gb/s,3.67 Gb/s,4.40 Gb/s,3.78 Gb/s,3.18 Gb/s,4.31 Gb/s,and 4.35 Gb/s(31.38 Gb/s in total),with advanced digital signal processing(DSP)techniques including digital equalization technique and bit-power loading discrete multitone(DMT)modulation format.

Wildfire Monitoring and Detection System Using Wireless Sensor Network: A Case Study of Tanzania

This paper proposes a wildfire monitoring and detection system based on wireless sensor network. This system detects fire by monitoring surrounding temperature, humidity and smoke. Once fire is detected, a warning message containing probable location of that fire is immediately sent to the responsible authority over cellular network. In order for the system to be more effective, communities living near forests or national parks can send warning messages through the same system to the responsible authority using their mobile handsets once they witness wildfire or illegal activities. For the system to be fully functional, the only requirement is the availability of cellular network coverage in forests or national parks to enable short message services to take place. The system prototype is developed using Arduino microcontroller, several sensors to detect temperature, relative humidity and smoke as well as wireless network connection modules. At the control center Telerivet messaging platform is used to design the messaging service. The experimental results justify the capability of the proposed system in detecting wildfire in real time.

DESIGN AND FABRICATION OF HIGH-PERFORMANCE INFRARED HOLLOW FIBER FOR MEDICAL LASER POWER DELIVERY

We proposed a method to evaluate the material dispersion of the dielectric film in dielectriccoated silver hollow fiber.By taking into consideration the derived material dispersion,the wavelengths of the loss peaks and valleys in the loss spectra of the hollow fiber can be predicted more accurately.Then,we fabricated the dielectric-coated silver hollow fiber according to the parameters obtained by using the improved design method.The measured data showed good agreement with the calculated results.The loss for medical laser of Er:YAG and CO_(2)was less than 0.3 dB/m.The loss for green or red pilot beams was around 5 dB/m,which is sufficiently low for the purpose of pilot beam transmission.The derived material dispersion plays an important role in the design and fabrication of the hollow fiber for multiwavelength delivery.

Design of an Interactive Mobile Application for Maternal, Neonatal and Infant Care Support for Tanzania

Reducing maternal and infant deaths’ rates in the developing countries, particularly in sub-Sahara Africa, remain a big challenge. Despite efforts by governments, the reductions have been unsatisfactory. To accelerate the reduction in maternal and infant deaths, m-health has been proposed as a viable, economical and effective intervention, able to reach the low income and disadvantaged groups. Mobile phone-based applications are among the m-health interventions that have been found to have positive outcomes for different healthcare challenges, such as improving clinical attendance and skilled delivery, and reducing perinatal mortality. However, the adoption of smartphone-based applications for health in Tanzania has been slow. Some of the likely contributing factors might be low technology exposure by the majority of the population and English language skills’ limitations. In this work, we developed a mobile application for providing interactive support to users, thus complementing other solutions available such as SMS and other smartphone apps. The main advantage of this app is the presence of interactive features that enable patient-provider communication. We adopted the Rapid application development (RAD) model for developing the application. We used UML modeling language tools for designing the application. The mobile application’s technical architecture uses various technologies and system development tools such as PHP programming language for the web application, MySQL database management system and Android Studio mobile application development platform.

Hybrid Architecture and Beamforming Optimization for Millimeter Wave Systems

Hybrid beamforming(HBF)has become an attractive and important technology in massive multiple-input multiple-output(MIMO)millimeter-wave(mmWave)systems.There are different hybrid architectures in HBF depending on different connection strategies of the phase shifter network between antennas and radio frequency chains.This paper investigates HBF optimization with different hybrid architectures in broadband point-to-point mmWave MIMO systems.The joint hybrid architecture and beamforming optimization problem is divided into two sub-problems.First,we transform the spectral efficiency maximization problem into an equivalent weighted mean squared error minimization problem,and propose an algorithm based on the manifold optimization method for the hybrid beamformer with a fixed hybrid architecture.The overlapped subarray architecture which balances well between hardware costs and system performance is investigated.We further propose an algorithm to dynamically partition antenna subarrays and combine it with the HBF optimization algorithm.Simulation results are presented to demonstrate the performance improvement of our proposed algorithms.

A High-Speed Bi-Directional Visible Light Communication System Based on RGB-LED

In this paper,we propose and experimentally demonstrate a bi-directional indoor communication system based on visible light RGB-LED.Spectrally efficient modulation formats(QAM-OFDM),advanced digital signal processing,pre- and postequalization are adopted to compensate the severe frequency response of indoor channel.In this system,we utilize red-green-blue Light emitting diodes(LEDs),of which each color can be used to carry different signals.For downlink,the low frequencies of each color are used while for uplink,the high frequencies are used.The overall data rate of downlink and uplink are 1.15-Gb/s and 300-Mb/s.The bit error ratios(BERs) for all channels after0.7 m indoor delivery are below pre-forwarderror-correction(pre-FEC) threshold of3.8×l0^(-3) To the best of our knowledge,this is the highest data rate in bi-directional visible light communication system.

Maternal and Child Health Care Quality Assessment: An Improved Approach Using K-Means Clustering

High maternal and child deaths in developing countries are frequently linked to poor health services provided to pregnant women and children. To improve the quality of maternal, neonatal and child health (MNCH) services, the government and other stakeholders in MNCH emphasize the importance of quality assessment. However, effective quality assessment approaches are mostly lacking in most developing countries, particularly in Tanzania. This study, therefore, aimed at developing a quality assessment approach that can effectively assess and report on the quality of MNCH services. Due to the need for a good quality assessment approach that suits a resource-constrained environment, machine learning-based approach was proposed and developed. K-means algorithm was used to develop a clustering model that groups MNCH data and performs cluster summarization to discover the knowledge portrayed in each group on the quality of MNCH services. Results confirmed the clustering model’s ability to assign the data points into appropriate clusters;cluster analysis with the collaboration of MNCH experts successfully discovered insights on the quality of services portrayed by each group.

Design of an Interactive Geo-Location Mobile Application for Civil Societies in East Africa

This paper reports the developed mobile application through the use of advanced technologies such as mobile computing, cloud computing and Global Positioning System (GPS) in order to solve the challenges. The purpose of this study is to find out how the recent advances and mass adoption of ICT by the public can best be leveraged to enhance the performance of Civil Society Organizations (CSOs) in East Africa. The data collection techniques used are through questionnaires, observations and conducting interviews with different stakeholders in the civil society arena i.e., the donors, the CSOs and the people in society that are given a voice by civil societies. In the system development phase, agile development methodology was used. Analysis of the data collected showed that there is a gap in the availability of a single or a centralized platform which can be easily accessed, user-friendly and reliable where different actors can readily get reliable and up-to-date information about the available CSOs they are interested in. To address this problem, an interactive online directory of CSOs has been developed. The platform is mobile based and enables CSOs to register and fill up their current details, thus ensuring that there is always correct and updated information. The platform is equipped with, among other features, a geo-mapping facility which enables users of the system to correctly geo-locate their civil societies of interest on a map view. The results of system evaluation showed that 88.125% of users were satisfied with the system basing on the evaluation criteria.

Security enhanced underwater visible light communication system based on chaotic phase scrambling and conjugate frequency hopping

We propose an encryption technique for underwater visible light communication[UVLC]based on chaotic phase scrambling[PS]and conjugate frequency hopping[CFH].The technique is experimentally tested using an 8-level pulse amplitude modulation[PAM-8]and a 1.2 m underwater link.The security key of the phase scrambling code is generated according to a logistic map,and the frequency hopping is achieved by adding the same zero frequency points to the signal spectrum.The maximum transmission rate of 2.1 Gbit/s is measured with bit-error-rate[BER]below 7%the hard-decision forward error correction[HD-FEC]threshold of 3.8×10^(-3).

Bandwidth-efficient visible light communication system based on faster-than-Nyquist pre-coded CAP modulation

With the rapid development of the light-emitting diode(LED) industry, interest in visible light communication(VLC) is growing. The limited bandwidth of commercial LEDs is one of the main challenges to achieve highspeed VLC. In this Letter, a kind of bandwidth-efficient VLC system based on carrierless amplitude and phase(CAP) modulation is proposed, where a simple differential faster-than-Nyquist(FTN) pre-coding scheme is employed to compress the spectrum and further improve the overall system baud rate. The system is experimentally demonstrated with a data rate of 1.47-Gb/s over 1.5 m free space transmission. The results indicate that an improvement of 80 Mbaud is achieved by FTN-CAP4 at 20% subband overlap and 40 Mbaud rate improvement by FTN-CAP16 at 7.5% subband overlap. Compared with traditional CAP, the FTN pre-coded CAP shows a better performance in spectral efficiency(SE) and intercarrier interference resistance. To the best of our knowledge, it is the first time to employ FTN pre-coded CAP in indoor high-data-rate VLC systems.

A novel OFDM-CPM modulation scheme and its application in WDM-PON

A novel scheme to generate, transmit, and receive an optical orthogonal frequency division multiplexing (OFDM) continuous phase modulation (CPM) signal, which is combining minimum shift keying (MSK) coding with OFDM optical modulation, for downlink application in a 4×2.5-Gb/s wavelength division multiplexing (WDM) passive optical access network, is proposed and experimentally validated. We also realize wavelength remodulation for carrying upstream on-off keying (OOK) data to reduce the cost budget at the optical network unit. The experimental results show that the power penalties for the downlink and the uplink data after transmission over 25-km SMF-28 fiber are 0.1 dB and smaller than 0.4 dB, respectively.

Investigation on performance of special-shaped 8-quadrature amplitude modulation constellations applied in visible light communication

Light-emitting diode(LED)-based visible light communication(VLC) has become a potential candidate for nextgeneration ultra-high-speed indoor wireless communication. In this paper, four special-shaped 8-quadrature amplitude modulation(QAM) constellations are investigated in a single-carrier VLC system. It is numerically verified and experimentally demonstrated that circular(7,1) shows obvious superiority in the performance of the dynamic range of signal voltage peak-to-peak(vpp) value and bit error rate(BER). Next best is rectangular, followed by triangular; circular(4,4) has the worst performance. A data rate of 1.515 Gbit/s is successfully achieved by circular(7,1) employing a red chip LED over 0.5 m indoor free space transmission below a BER threshold of3.8 × 10^(-3). Compared with circular(4,4), the traditional 8-QAM constellation, circular(7,1) provides a wider dynamic range of signal vpp, a higher data rate, and a longer transmission distance. To the best of our knowledge,this is the first investigation into the performance differences of special-shaped 8-QAM constellations in a highspeed, single-carrier VLC system, and the results comprehensively demonstrate that circular(7,1) is the optimal option.

Generation of coherent optical multi-carriers using concatenated,dual-drive Mach-Zehnder and phase modulators

The generation of coherent optical subcarriers based on a concatenated dual-drive Mach-Zehnder intensity modulator（IM） and two phase modulators（PMs） is proposed and experimentally demonstrated.The modulation index and DC bias of PM+IM modulation are theoretically investigated.Theoretical analysis and numerical study are also carried out to examine the proposed scheme.We use 25-GHz RF synchronous sinusoidal signals to drive cascaded two-stage PMs and IM,through which we generate 28 subcarriers with peak power fluctuations less than 4 dB.The measured tone-to-noise ratio of the subcarrier is higher than 40 dB.The experimental results show that for 100-Gb/s polarization multiplexing QPSK signal,the receiver sensitivity of the back-to-back signal is -28.6 dBm,and the power penalty is lower than 1 dB after 100-km transmission at the BER of 1×10-9.

Analysis of smooth phase modulation formats compared with conventional QPSK and BPSK using coherent detection

Novel optical offset quadrature phase shift keying (OQPSK) and improved minimum-shift keying (MSK) modulation schemes to smooth optical phase hopping for high speed fiber optics transmission are proposed. Simulations have been done among the MSK, OQPSK, quadrature phase shift keying (QPSK), and binary phase-shift keying (BPSK) modulation formats at 40 Gb/s over 100-km transmission link using coherent detection. Simulation results present good performances to elevate chromatic dispersion tolerance and reduce the influence of nonlinear effects by adopting the smooth phase modulation formats. Inter-symbol interference decreases for the fast side-lobe property and tight spectrum as a result of avoding the π phase shift and reducing envelop fluctuation.

Experimental verification of performance improvement for a gigabit wavelength division multiplexing visible light communication system utilizing asymmetrically clipped optical orthogonal frequency division multiplexing

Asymmetrically clipped optical orthogonal frequency division multiplexing(ACO-OFDM)has been a promising candidate in visible light communications(VLC)due to its improvement in power efficiency and reduction of nonlinearity based on previous simulation analysis.In this paper,for the first time as far as we know,we experimentally verify that ACO-OFDM would be an efficient scheme to improve the performance of a gigabit wavelength division multiplexing VLC system.Our theoretical investigations reveal that the advantages of ACO-OFDM can be attributed to the reduction of inter-carrier interference caused by signal–signal beating noise.An aggregate data rate of 1.05 Gb∕s is successfully achieved over 30 cm transmission below the 7%forwarderror-correction threshold of 3.8×10−3.The experimental results show that ACO-OFDM can outperform DC-biased optical OFDM by BER performance of 1.5 dB at the same data rate and 4 dB at the same bandwidth,which clearly demonstrates the benefit and feasibility of ACO-OFDM.

Improving performance of 750-Mb/s visible light communication system using adaptive Nyquist windowing

We propose a configuration of a wavelength division multiplexing(WDM)-visible light communication(VLC) system using orthogonal frequency division multiplexing(OFDM) modulation and an adaptive Nyquist windowing of the OFDM signal in the receiver.Based on this configuration,we demonstrate a 750-Mb/s WDM-VLC transmission based on RGB light-emitting diode(LED) with a distance of 70 cm.The measured bit error rate(BER) for all channels are under the pre-forward error correction limit of 3.8×10 3.The BER performances of all the channels of the proposed WDM-VLC system show considerable improvement compared with those of the system without Nyquist windowing.

FSK Modulation Scheme for High-Speed Optical Transmission

In this paper,we describe the generation,detection,and performance of frequency-shift keying (FSK) for high-speed optical transmission and label switching.A non-return-to-zero (NRZ) FSK signal is generated by using two continuous-wave (CW) lasers,one Mach-Zehnder modulator (MZM),and one Mach-Zehnder delay interferometer (MZDI).An RZ-FSK signal is generated by cascading a dual-arm MZM,which is driven by a sinusoidal voltage at half the bit rate.Demodulation can be achieved on 1 bit rate through one MZDI or an array waveguide grating (AWG) demultiplexer with balanced detection.We perform numerical simulation on two types of frequency modulation schemes using MZM or PM,and we determine the effect of frequency tone spacing (FTS) on the generated FSK signal.In the proposed scheme,a novel frequency modulation format has transmission advantages compared with traditional modulation formats such as RZ and differential phase-shift keying (DPSK),under varying dispersion management.The performance of an RZ-FSK signal in a 4 × 40 Gb/s WDM transmission system is discussed.We experiment on transparent wavelength conversion based on four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) and in a highly nonlinear dispersion shifted fiber (HNDSF) for a 40 Gb/s RZ-FSK signal.The feasibility of all-optical signal processing of a high-speed RZ-FSK signal is confirmed.We also determine the receiver power penalty for the RZ-FSK signal after a 100 km standard single-mode fiber (SMF) transmission link with matching dispersion compensating fiber (DCF),under the post-compensation management scheme.Because the frequency modulation format is orthogonal to intensity modulation and vector modulation (polarization shift keying),it can be used in the context of the combined modulation format to decrease the data rate or enhance the symbol rate.It can also be used in orthogonal label-switching as the modulation format for the payload or the label.As an example,we propose a simple orthogonal optical label switching technique based on 40 Gb/s FSK payload and 2.5 Gb/s intensity modulated (IM) label.

SVM for Constellation Shaped 8QAM PON System

Nonlinearity impairments and distortions have been bothering the bandwidth constrained passive optical network(PON)system for a long time and limiting the develop-ment of capacity in the PON system.Unlike other works concentrating on the exploration of the complex equalization algorithm,we investigate the potential of constellation shap-ing joint support vector machine(SVM)classification scheme.At the transmitter side,the 8 quadrature amplitude modulation(8QAM)constellation is shaped into three designs to mitigate the influence of noise and distortions in the PON channel.On the receiver side,simple multi-class linear SVM classifiers are utilized to replace complex equalization methods.Simulation results show that with the bandwidth of 25 GHz and overall bitrate of 50 Gbit/s,at 10 dBm input optical power of a 20 km standard single mode fiber(SSMF),and under a hard-decision forward error correction(FEC)threshold,transmission can be realized by employing Circular(4,4)shaped 8QAM joint SVM classifier at the maximal power budget of 37.5 dB.

Experimental demonstration for 40-km fiber and 2-m wireless transmission of 4-Gb/s OOK signals at 100-GHz carrier

We experimentally demonstrate a 4-Gb/s radio-over-fiber (RoF) system with 40-km fiber and 2-m wireless distance downstream at 100-GHz carrier. To the best of our knowledge, this is for the first time in China to realize optical wireless link at 100 GHz. In this letter, simple intensity modulator with direct detector (IM-DD) modulation is employed and optical power penalty after 40-km single mode fiber (SMF)-28 and 2-m air link is 3.2 dB with bit-error-rate (BER) at 1×10 9 .

Carrier-less amplitude and phase modulated visible light communication system based on a constellation-shaping scheme

In this Letter,we propose a novel constellation-shaping carrier-less amplitude and phase(CAP) modulation scheme to alleviate the systematic nonlinearity in visible light communication(VLC) systems.A simple geometric transformation shaping method is employed to convert the normal square lattice constellation into multiple circular constellations.The feasibility and performance are investigated and experimentally demonstrated by a 1.25 Gb/s CAP-modulated VLC system.The results indicate that the circular constellation has better resistance to systematic nonlinearity compared with a rectangular constellation.The dynamic range of input signal peak-to-peak values promotes 20% at a low bias voltage nonlinear area and 50% at a high bias voltage nonlinear area.To the best of our knowledge,this is the first time constellation-shaping CAP has ever been reported in indoor high data rate VLC systems.