Development of a dc-ac power conditioner for wind generator by using neural network

This project present of development single phase DC-AC converter for wind generator application. The mathematical model of the wind generator and Artificial Neural Network control for DC-AC converter is derived. The controller is designed to stabilize the output voltage of DC-AC converter. To verify the effectiveness of the proposal controller, both simulation and experimental are developed. The simulation and experimental result show that the amplitude of output voltage of the DC-AC converter can be controlled

Delta-Sigma Digitization and Optical Coherent Transmission of DOCSIS 3.1 Signals in Hybrid Fiber Coax Networks

We first demonstrate delta-sigma digitization and coherent transmission of data over cable system interface specification (DOCSIS) 3.1 signals in a hybrid fiber coax (HFC) network. Twenty 192-MHz DOCSIS 3.1 channels with modulation up to 16384QAM are digitized by a low-pass cascade resonator feedback (CRFB) delta-sigma analog-to-digital converter (ADC) and transmitted over 80 km fiber using coherent single-λ 128-Gb/s dual-polarization (DP)-QPSK and 256-Gb/s DP-16QAM optical links. Both one-bit and two-bit delta-sigma digitization are implemented and supported by the QPSK and 16QAM coherent transmission systems, respectively. To facilitate its practical application in access networks, the coherent system is built using a low-cost narrowband optical modulator and RF amplifiers. Modulation error ratio (MER) larger than 50 dB is successfully demonstrated for all 20 DOCSIS 3.1 channels, and high order modulation up to 16384QAM is delivered over fiber for the first time in HFC networks. The raw DOCSIS data capacity is 54 Gb/s with net user information ~45 Gb/s. Moreover, the bit error ratio (BER) tolerance is evaluated by measuring the MER performance as BER increases. Negligible MER degradation is observed for BER up to 1.5 × 10−6 and 1.7 × 10−4, for one-bit and two-bit digitization, respectively

Multicarrier communication over underwater acoustic channels with nonuniform Doppler shifts

Author Posting. © IEEE, 2008. This article is posted here by permission of IEEE for personal use, not for redistribution. The definitive version was published in IEEE Journal of Oceanic Engineering 33 (2008): 198-209, doi:10.1109/JOE.2008.920471.Underwater acoustic (UWA) channels are wideband in nature due to the small ratio of the carrier frequency to the signal bandwidth, which introduces frequency-dependent Doppler shifts. In this paper, we treat the channel as having a common Doppler scaling factor on all propagation paths, and propose a two-step approach to mitigating the Doppler effect: 1) nonuniform Doppler compensation via resampling that converts a "wideband" problem into a "narrowband" problem and 2) high-resolution uniform compensation of the residual Doppler. We focus on zero-padded orthogonal frequency-division multiplexing (OFDM) to minimize the transmission power. Null subcarriers are used to facilitate Doppler compensation, and pilot subcarriers are used for channel estimation. The receiver is based on block-by-block processing, and does not rely on channel dependence across OFDM blocks; thus, it is suitable for fast-varying UWA channels. The data from two shallow-water experiments near Woods Hole, MA, are used to demonstrate the receiver performance. Excellent performance results are obtained even when the transmitter and the receiver are moving at a relative speed of up to 10 kn, at which the Doppler shifts are greater than the OFDM subcarrier spacing. These results suggest that OFDM is a viable option for high-rate communications over wideband UWA channels with nonuniform Doppler shifts.B. Li and S. Zhou are supported by the ONR YIP grant N00014-07-1-0805 and the NSF grant ECCS-0725562. M. Stojanovic is supported by the ONR grant N00014-07-1-0202. L. Freitag is supported by the ONR grants N00014- 02-6-0201 and N00014-07-1-0229. P. Willett is supported by the ONR grant N00014-07-1-0055

Complex Field Modulation in Direct Detection Systems

Even though fiber optics communication provides a high bandwidth channel to achieve high-speed data transmission, there is still demand for higher spectral efficiency, faster data processing speeds with reduced resource requirements due to ever increasing data and media traffic. Also, lately the demand for online streaming because of remote working has increased significantly. Various multilevel modulation and demodulation techniques are used to improve spectral efficiency. Although spectral efficiency is improved, there are other challenges that arise. Such as requirements for high speed electronics, receiver sensitivity degradation, chromatic dispersion, operational flexibility, effects of nonlinearity impairments etc. Here, we investigate complex bandwidth efficient field modulation and coding techniques to improve spectral efficiency while reducing the digital signal processing (DSP) resources required for implementations using FPGAs or ASICs and compensation for linear and nonlinear impairments that appear in fiber optic communication systems. In this dissertation we investigated and developed solutions for various limitations and impairments in a direct-detection transmission system with complex field modulated optical signal. The solutions that we developed to compensate the fiber optical impairments can be implemented using DSP either at transmitter side or the receiver. By employing DSP based approach to mitigate the optical impairments and limitations we can achieve more flexibility in the optical transceivers while achieving higher spectral efficiency. We proposed and demonstrated digital-analog hybrid subcarrier multiplexing (SCM) technique which can reduce the speed requirement of high-speed digital electronics such as ADC and DAC, while providing wideband capability, high spectral efficiency, operational flexibility and controllable data-rate granularity. Hybrid SCM is a modular approach in which multiple digitally generated subcarriers are aggregated through RF oscillators and IQ mixers for frequency up- and down-conversions. Next, to achieve maximum spectral efficiency with conventional Quadrature Phase Shift Keying (QPSK) we need highly spectral efficient Nyquist filters which require large amount of FPGA resources for digital signal processing (DSP). Hence, we investigated Quadrature Duobinary (QDB) modulation as a solution to reduce the FPGA resources required for DSP while achieving spectral efficiency of 2bits/s/Hz. We compared QDB with QPSK in a digital-analog hybrid subcarrier multiplexing system and we show that with minor changes in transmitter design we can achieve 2bits/s/Hz spectral efficiency, which is same as the Nyquist QPSK with relaxed resource requirements for DSP. We investigated and developed a solution to digitally compensate the nonlinearities introduced by semiconductor optical amplifiers (SOA). In a field modulated direct-detection system, due to square-law detection of the photodiode, leads to an interference called signal-signal beat interference (SSBI). To eliminate SSBI we can use Kramers-Kronig (KK) receiver as we can retrieve the phase information from the direct detected optical signal for the class of signals called as minimum phase signals. However, it is under the assumption that the entire transfer function of our optical transmission system is linear except for photodiode. However, when the system transfer function is non-linear due to SOA nonlinearities when operated in gain saturation region. By using electrical forward propagation method for pre-compensation of nonlinearities caused by SOA we show that we can simultaneously restore the efficiency of KK receiver and as well achieve electronic dispersion post-compensation

Nonlinear Mixing in Optical Multicarrier Systems

Although optical fiber has a vast spectral bandwidth, efficient use of this bandwidth is still important in order to meet the ever increased capacity demand of optical networks. In addition to wavelength division multiplexing, it is possible to partition multiple low-rate subcarriers into each high speed wavelength channel. Multicarrier systems not only ensure efficient use of optical and electrical components, but also tolerate transmission impairments. The purpose of this research is to understand the impact of mixing among subcarriers in Radio-Over-Fiber (RoF) and high speed optical transmission systems, and experimentally demonstrate techniques to minimize this impact. We also analyze impact of clipping and quantization on multicarrier signals and compare bandwidth efficiency of two popular multiplexing techniques, namely, orthogonal frequency division multiplexing (OFDM) and Nyquist modulation. For an OFDM-RoF system, we present a novel technique that minimizes the RF domain signal-signal beat interference (SSBI), relaxes the phase noise limit on the RF carrier, realizes the full potential of optical heterodyne-based RF carrier generation, and increases the performance-to-cost ratio of RoF systems. We demonstrate a RoF network that shares the same RF carrier for both downlink and uplink, avoiding the need of an additional RF oscillator in the customer unit. For multi-carrier optical transmission, we first experimentally compare performance degradations of coherent optical OFDM and single-carrier Nyquist pulse modulated systems in a nonlinear environment. We then experimentally evaluate SSBI compensation techniques in the presence of semiconductor optical amplifier (SOA) induced nonlinearities for a multicarrier optical system with direct detection. We show that SSBI contamination can be significantly reduced from the data signal when the carrier-to-signal power ratio is sufficiently low

Time and frequency offsets in all optical OFDM systems

Ultra-high-speed data transmission (terabit-per-second per channel) is urgently required in optical communication systems to fulfill the emerging demands of 3D multimedia applications, cloud computing, and bandwidth-hungry applications. In one way by using singlecarrier optical communication systems for the data transmission rates 1 Tb/s, we need the high baud rate and/or the high-order modulation formats (i.e. 512-QAM, 1024-QAM). Another way is to group the data carrying subcarriers without a guard bands (tightly spaced) to form a superchannel which gives increase in channel capacity. In a superchannel, the requirements of high-order modulation formats and high baud rates are relaxed. In an alloptical orthogonal frequency division multiplexing (AO-OFDM) system, the subcarriers are orthogonal and closely packed which gives more suitability to form superchannel. This thesis focuses on the time and frequency offsets in AO-OFDM systems. A theoretical model to investigate the performance of on-off-keying (OOK) modulated AO-OFDM system is developed for analytical simulation. The analytical (statistical) model considers the random characteristics of time and frequency offsets in adjacent subcarriers as well as the common noise sources such as shot and thermal noises to calculate the interference variances for evaluating the BER performance. The effects of time and frequency offsets on the BER performance of AO-OFDM system is evaluated with the number of optical subcarriers (NSC), receiver bandwidth (BWRX), and cyclic prefix (CP) We further develop an analytical model to evaluate the performance of AO-OFDM system with advanced modulation format (M-QAM) in the presence of time and frequency offsets, and the performance is compared with numerical simulations of other emulation setups (oddand- even subcarriers and decorrelated systems). The performance is investigated with NSC, BWRX, and CP in AO-OFDM system. A delay-line interferometer based all-optical method to reduce the effects of time and frequency offsets is proposed and evaluated. Finally, performance of demultiplexed subcarriers from an optical discrete Fourier transform (O-DFT) in AO-OFDM system in the presence of chromatic dispersion and limited modulation bandwidth is evaluated. The fiber Bragg grating (FBG) based passive device is proposed to reduce the interference and the results are compared with existing method using sampling gates. The proposed method using FBG for interference reduction provides a cost-effective design of AO-OFDM system

New Design of SCM-SAC-OCDMA-FSO System by Using Gain Techniqe Based on MD Code

بصريات الفضاء الحرة (FSO) هو نظام اتصالات حديث وجديد حيث الفضاء الحر بمثابة وسيلة بين المرسل والمستلم، وينبغي أن تكون في خط البصر (LOS) لنجاح نقل شعاع الضوء. ونظرا لمتوسط ​​المساحة الحرة، فإنها تعاني من تداخلات مختلفة مثل [المطر والضباب والثلج] التي يمكن أن تؤثر على أداء الإشارة وتؤدي إلى تقليل توافر الاشارة، الموثوقية وصلة الاتصال. وبسبب المناخ الصحراوي العراقي، فإنه يتعرض للعواصف الترابية في معظم الوقت من السنة أكثر من مناطق أخرى، لذلك فمن المهم لدراسة تأثير الجو الترابي وإيجاد طريقة مناسبة للحد من هذا التأثير الجوي على شعاع الليزر عند السفر إلى النقطة النهائية للاشارة. ترميز الطيف الضوئي _ الشفرة الضوئية المتعددة المنافذ (SAC-OCDMA) أصبح مجالا رئيسيا للبحوث في نظام الاتصالات البصرية. OCDMA تسمح للمستخدم المتعدد للوصول إلى النظام دون أي خلاف، ترميز متعدد الاقطار (MD) يستخدم في النظام لدعم عدد كبير من المستخدمين مع ارتفاع معدل البيانات المرسلة. مكبر للموجة البصرية يضاف إلى النظام لتوفير المزيد من التحسين والسماح لإرسال شعاع الليزر لمسافات طويلة وانخفاض التدخل بين الموجات المرسلة. وتبين نتيجة الدراسة أن أداء النظام المقترح أفضل من النظام بدون مكبر الموجة البصرية. ويمكن ملاحظة أن معدل الخطأ في البتات (BER) في الحد الأدنى من الرؤية ( عند وجود عاصفة ترابية ) يصل إلى ، معدل الخطا في البتات في الرؤية المتوسطة بين ( & ) ، معدل الخطا في البتات  مع الوضوحية العالية ( )) مع 1.85 كم كمسافة انتقال البيانات  و 1 جيجا  بايت  كبيانات نقل للمستخدم.Free space optic (FSO) is a new modern communication system where free space acts as a medium between transverse and they should be in Line Of Sight (LOS) for successful transmission of optical beam. Due to free space medium , it suffer of various interference like [Rain , Fog/Haze , Snow] that can effect on signal performance and lead to reduce  the availability and reliability of the communication link .Because of Iraqi desert climate ,it exposed to dusty storm in most time of year more than other regions , so it is important to study the effect of Fog/Haze and find suitable method to reduce this atmospheric effect on the laser beam when it travel to its final point .Spectral Amplitude Coding Optical Code Division Multiple Access (SAC-OCDMA) has become a major area of research in optical communication system . OCDMA allows multiple user to access the system without any contention; Multi Diagonal (MD) code used in system to support large number of user with high data rate .Optical amplifier is added to the system to provide more enhancement and permit to send the laser beam in longer distance and decrease the interference on it. The result of the study shows that the performance of the proposed system is better than the system without amplifier. It can be seen that the BER with minimum visibility (strong Haze storm) reach to 8 , BER of medium visibility between (1 & 8 ), BER with high visibility (1 ) at 1.85 Km as a transmission distance and 1Gbps as a transmission data

Orthogonal chirp division multiplexing for coherent optical fiber communications

In this paper, we propose an orthogonal chirp division multiplexing (OCDM) technique for coherent optical communication. OCDM is the principle of orthogonally multiplexing a group of linear chirped waveforms for high-speed data communication, achieving the maximum spectral efficiency (SE) for chirp spread spectrum, in a similar way as the orthogonal frequency division multiplexing (OFDM) does for frequency division multiplexing. In the coherent optical (CO)-OCDM, Fresnel transform formulates the synthesis of the orthogonal chirps; discrete Fresnel transform (DFnT) realizes the CO-OCDM in the digital domain. As both the Fresnel and Fourier transforms are trigonometric transforms, the CO-OCDM can be easily integrated into the existing CO-OFDM systems. Analyses and numerical results are provided to investigate the transmission of CO-OCDM signals over optical fibers. Moreover, experiments of 36-Gbit/s CO-OCDM signal are carried out to validate the feasibility and confirm the analyses. It is shown that the CO-OCDM can effectively compensate the dispersion and is more resilient to fading and noise impairment than OFDM

Coherent Optical OFDM Modem Employing Artificial Neural Networks for Dispersion and Nonlinearity Compensation in a Long-Haul Transmission System

In order to satisfy the ever increasing demand for the bandwidth requirement in broadband services the optical orthogonal frequency division multiplexing (OOFDM) scheme is being considered as a promising technique for future high-capacity optical networks. The aim of this thesis is to investigate, theoretically, the feasibility of implementing the coherent optical OFDM (CO-OOFDM) technique in long haul transmission networks. For CO-OOFDM and Fast-OFDM systems a set of modulation formats dependent analogue to digital converter (ADC) clipping ratio and the quantization bit have been identified, moreover, CO-OOFDM is more resilient to the chromatic dispersion (CD) when compared to the bandwidth efficient Fast-OFDM scheme. For CO-OOFDM systems numerical simulations are undertaken to investigate the effect of the number of sub-carriers, the cyclic prefix (CP), and ADC associated parameters such as the sampling speed, the clipping ratio, and the quantisation bit on the system performance over single mode fibre (SMF) links for data rates up to 80 Gb/s. The use of a large number of sub-carriers is more effective in combating the fibre CD compared to employing a long CP. Moreover, in the presence of fibre non-linearities identifying the optimum number of sub-carriers is a crucial factor in determining the modem performance. For a range of signal data rates up to 40 Gb/s, a set of data rate and transmission distance-dependent optimum ADC parameters are identified in this work. These parameters give rise to a negligible clipping and quantisation noise, moreover, ADC sampling speed can increase the dispersion tolerance while transmitting over SMF links. In addition, simulation results show that the use of adaptive modulation schemes improves the spectrum usage efficiency, thus resulting in higher tolerance to the CD when compared to the case where identical modulation formats are adopted across all sub-carriers. For a given transmission distance utilizing an artificial neural networks (ANN) equalizer improves the system bit error rate (BER) performance by a factor of 50% and 70%, respectively when considering SMF firstly CD and secondly nonlinear effects with CD. Moreover, for a fixed BER of 10-3 utilizing ANN increases the transmission distance by 1.87 times and 2 times, respectively while considering SMF CD and nonlinear effects. The proposed ANN equalizer performs more efficiently in combating SMF non-linearities than the previously published Kerr nonlinearity electrical compensation technique by a factor of 7

Engineering evaluations and studies. Volume 3: Exhibit C

High rate multiplexes asymmetry and jitter, data-dependent amplitude variations, and transition density are discussed