Download or read book OFDM Systems for Optical Communication with Intensity Modulation and Direct Detection written by Jian Dang and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Intensity modulation and direct detection (IM/DD) is a cost-effective optical communication strategy which finds wide applications in fiber communication, free-space optical communication, and indoor visible light communication. In IM/DD, orthogonal frequency division multiplexing (OFDM), originally employed in radio frequency communication, is considered as a strong candidate solution to combat with channel distortions. In this research, we investigate various potential OFDM forms that are suitable for IM/DD channel. We will elaborate the design principles of different OFDM transmitters and investigate different types of receivers including the proposed iterative receiver. In addition, we will analyze the spectral efficiency and decoding complexities of different OFDM systems to give a whole picture of their performance. Finally, simulation results are given to assess the detection performance of different receivers.

Download or read book Orthogonal Frequency division Multiplexing for Optical Communications written by Daniel Jose Fernandes Barros and published by Stanford University. This book was released on 2011 with total page 160 pages. Available in PDF, EPUB and Kindle. Book excerpt: The drive towards higher spectral efficiency and maximum power efficiency in optical systems has generated renewed interest in the optimization of optical transceivers. In this work, we study the different optical applications: Wide Area Networks (WANs), Metropolitan Area Networks (MANs), Local Area Networks (LANs) and Personal Area Networks (PANs). In WANs or long-haul systems, orthogonal frequency-division multiplexing (OFDM) can compensate for linear distortions, such as group-velocity dispersion (GVD) and polarization-mode dispersion (PMD), provided the cyclic prefix is sufficiently long. Typically, GVD is dominant, as it requires a longer cyclic prefix. Assuming coherent detection, we show how to analytically compute the minimum number of subcarriers and cyclic prefix length required to achieve a specified power penalty, trading off power penalties from the cyclic prefix and from residual inter-symbol interference (ISI) and inter-carrier interference (ICI). We derive an analytical expression for the power penalty from residual ISI and ICI. We also show that when nonlinear effects are present in the fiber, single-carrier with digital equalization outperforms OFDM for various dispersion maps. We also study the impairments of electrical to optical conversion when using Mach-Zehnder (MZ) modulators. OFDM has a high peak-to-average ratio (PAR), which can result in low optical power efficiency when modulated through a Mach-Zehnder (MZ) modulator. In addition, the nonlinear characteristic of the MZ can cause significant distortion on the OFDM signal, leading to in-band intermodulation products between subcarriers. We show that a quadrature MZ with digital pre-distortion and hard clipping is able to overcome the previous impairments. We consider quantization noise and compute the minimum number of bits required in the digital-to-analog converter (D/A). Finally, we discuss a dual-drive MZ as a simpler alternative for the OFDM modulator, but our results show that it requires a higher oversampling ratio to achieve the same performance as the quadrature MZ. In MANs, we discuss the use OFDM for combating GVD effects in amplified direct-detection (DD) systems using single-mode fiber. We review known direct-detection OFDM techniques, including asymmetrically clipped optical OFDM (ACO-OFDM), DC-clipped OFDM (DC-OFDM) and single-sideband OFDM (SSB-OFDM), and derive a linearized channel model for each technique. We present an iterative procedure to achieve optimum power allocation for each OFDM technique, since there is no closed-form solution for amplified DD systems. For each technique, we minimize the optical power required to transmit at a given bit rate and normalized GVD by iteratively adjusting the bias and optimizing the power allocation among the subcarriers. We verify that SSB-OFDM has the best optical power efficiency among the different OFDM techniques. We compare these OFDM techniques to on-off keying (OOK) with maximum-likelihood sequence detection (MLSD) and show that SSB-OFDM can achieve the same optical power efficiency as OOK with MLSD, but at the cost of requiring twice the electrical bandwidth and also a complex quadrature modulator. We compare the computational complexity of the different techniques and show that SSB-OFDM requires fewer operations per bit than OOK with MLSD. In LANs, we compare the performance of several OFDM schemes to that of OOK in combating modal dispersion in multimode fiber links. We review known OFDM techniques using intensity modulation with direct detection (IM/DD), including DC-OFDM, ACO-OFDM and pulse-amplitude modulated discrete multitone (PAM-DMT). We describe an iterative procedure to achieve optimal power allocation for DC-OFDM, and compare analytically the performance of ACO-OFDM and PAM-DMT. We also consider unipolar M-ary pulse-amplitude modulation (M-PAM) with minimum mean-square error decision-feedback equalization (MMSE-DFE). For each technique, we quantify the optical power required to transmit at a given bit rate in a variety of multimode fibers. For a given symbol rate, we find that unipolar M-PAM with MMSE-DFE has a better power performance than all OFDM formats. Furthermore, we observe that the difference in performance between M-PAM and OFDM increases as the spectral efficiency increases. We also find that at a spectral efficiency of 1 bit/symbol, OOK performs better than ACO-OFDM using a symbol rate twice that of OOK. At higher spectral efficiencies, M-PAM performs only slightly better than ACO-OFDM using twice the symbol rate, but requires less electrical bandwidth and can employ analog-to-digital converters at a speed only 81% of that required for ACO-OFDM. In PANs, we evaluate the performance of the three IM/DD OFDM schemes in combating multipath distortion in indoor optical wireless links, comparing them to unipolar M-PAM with MMSE-DFE. For each modulation method, we quantify the received electrical SNR required at a given bit rate on a given channel, considering an ensemble of 170 indoor wireless channels. When using the same symbol rate for all modulation methods, M-PAM with MMSE-DFE has better performance than any OFDM format over a range of spectral efficiencies, with the advantage of M-PAM increasing at high spectral efficiency. ACO-OFDM and PAM-DMT have practically identical performance at any spectral efficiency. They are the best OFDM formats at low spectral efficiency, whereas DC-OFDM is best at high spectral efficiency. When ACO-OFDM or PAM-DMT are allowed to use twice the symbol rate of M-PAM, these OFDM formats have better performance than M-PAM. When channel state information is unavailable at the transmitter, however, M-PAM significantly outperforms all OFDM formats. When using the same symbol rate for all modulation methods, M-PAM requires approximately three times more computational complexity per processor than all OFDM formats and 63% faster analog-to-digital converters, assuming oversampling ratios of 1.23 and 2 for ACO-OFDM and M-PAM, respectively. When OFDM uses twice the symbol rate of M-PAM, OFDM requires 23% faster analog-to-digital converters than M-PAM but OFDM requires approximately 40% less computational complexity than M-PAM per processor.

Download or read book OFDM for Optical Communications written by William Shieh and published by Academic Press. This book was released on 2009-09-18 with total page 457 pages. Available in PDF, EPUB and Kindle. Book excerpt: - The first book on optical OFDM by the leading pioneers in the field - The only book to cover error correction codes for optical OFDM - Gives applications of OFDM to free-space communications, optical access networks, and metro and log haul transports show optical OFDM can be implemented - Contains introductions to signal processing for optical engineers and optical communication fundamentals for wireless engineers This book gives a coherent and comprehensive introduction to the fundamentals of OFDM signal processing, with a distinctive focus on its broad range of applications. It evaluates the architecture, design and performance of a number of OFDM variations, discusses coded OFDM, and gives a detailed study of error correction codes for access networks, 100 Gb/s Ethernet and future optical networks. The emerging applications of optical OFDM, including single-mode fiber transmission, multimode fiber transmission, free space optical systems, and optical access networks are examined, with particular attention paid to passive optical networks, radio-over-fiber, WiMAX and UWB communications. Written by two of the leading contributors to the field, this book will be a unique reference for optical communications engineers and scientists. Students, technical managers and telecom executives seeking to understand this new technology for future-generation optical networks will find the book invaluable. William Shieh is an associate professor and reader in the electrical and electronic engineering department, The University of Melbourne, Australia. He received his M.S. degree in electrical engineering and Ph.D. degree in physics both from University of Southern California. Ivan Djordjevic is an Assistant Professor of Electrical and Computer Engineering at the University of Arizona, Tucson, where he directs the Optical Communications Systems Laboratory (OCSL). His current research interests include optical networks, error control coding, constrained coding, coded modulation, turbo equalization, OFDM applications, and quantum error correction. "This wonderful book is the first one to address the rapidly emerging optical OFDM field. Written by two leading researchers in the field, the book is structured to comprehensively cover any optical OFDM aspect one could possibly think of, from the most fundamental to the most specialized. The book adopts a coherent line of presentation, while striking a thoughtful balance between the various topics, gradually developing the optical-physics and communication-theoretic concepts required for deep comprehension of the topic, eventually treating the multiple optical OFDM methods, variations and applications. In my view this book will remain relevant for many years to come, and will be increasingly accessed by graduate students, accomplished researchers as well as telecommunication engineers and managers keen to attain a perspective on the emerging role of OFDM in the evolution of photonic networks." -- Prof. Moshe Nazarathy, EE Dept., Technion, Israel Institute of Technology - The first book on optical OFDM by the leading pioneers in the field - The only book to cover error correction codes for optical OFDM - Applications of OFDM to free-space communications, optical access networks, and metro and log haul transports show optical OFDM can be implemented - An introduction to signal processing for optical communications - An introduction to optical communication fundamentals for the wireless engineer

Download or read book Optical Fiber and Wireless Communications written by Rastislav Róka and published by BoD – Books on Demand. This book was released on 2017-06-21 with total page 374 pages. Available in PDF, EPUB and Kindle. Book excerpt: The book Optical Fiber and Wireless Communications provides a platform for practicing researchers, academics, PhD students, and other scientists to review, plan, design, analyze, evaluate, intend, process, and implement diversiform issues of optical fiber and wireless systems and networks, optical technology components, optical signal processing, and security. The 17 chapters of the book demonstrate capabilities and potentialities of optical communication to solve scientific and engineering problems with varied degrees of complexity.

Download or read book Optimization of Optical OFDM Transmission Systems written by Cristóbal Manuel Romero Vidal and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Orthogonal frequency division multiplexing (OFDM) is a well-known modulation technique which is used in broadband wired and wireless communication systems, such as standard 802.11a/b/g/n, digital video broadcasting television (DVB-TV), and Long Term Evolution in the next mobile generation, due to its capacity in solving the problem of the Inter-symbol Interference caused by the effects of a dispersive channel. Since a few years ago, this technique has been used in optical communications which is the aim of this thesis. In this Master Thesis, the most relevant aspects of optical OFDM communication are described and implemented in optical simulation software called VPItransmissionMakerTM and VPIphotonicsAnalyzerTM, (VPI). We find out that the OFDM coder and decoder provided by this program cannot be upgraded. This handicap does not allow modifying the main work algorithm and therefore the system cannot be improved. To solve this problem, it has been designed a Matlab OFDM coder and decoder to study the behaviour of optical OFDM systems using Intensity Modulation (IM) and Direct Detection (DD). As it will be detailed along the thesis, two different optical OFDM simulation scenarios using IM/DD are developed: an IM/DD RF and Hermitian Symmetry demos. Both of them are optical OFDM systems with an intensity modulation transmission and direct detection. The focus has been set primarily in obtaining a flexible, efficient and user-friendly simulation platform allowing for straightforward setup of advanced simulation of optical OFDM systems. The performance of these two scenarios is studied, taking advantage from the Simulation Script which VPI software provided in a more manageable mode, specifically, scripts using Tcl/tk language have been developed to derive power budget plots at desired Bit Error Ratio (BER).

Download or read book System Design and Performance Analysis of Asymmetrically and Symmetrically Clipped Optical ASCO OFDM for IM DD Optical Wireless Communications written by Nan Wu and published by . This book was released on 2015 with total page 88 pages. Available in PDF, EPUB and Kindle. Book excerpt: As the quantity of mobile communication devices, such as cellphones, tablets, and laptops, dramatically increase, the demand for high speed wireless service has been growing. Optical wireless communications (OWCs), which offer unlimited transmission bandwidth, have received a lot of attention and been studied in recent decades. They can be an effective alternative to radio frequency communications (RFCs) for indoor high speed data transmission. Intensity modulation direct detection (IM/DD) is a simple way to realize the transmission of optical wireless signals in an indoor environment. Information data streams are modulated into the intensity of optical carriers and transmitted by light emitting diodes (LEDs). At the receiver, the instantaneous power of optical signals can be directly detected by photodiodes. Multipath distortion, especially in an indoor environment, caused by reflection from walls or furniture, severely affects the transmission quality of optical signals. Orthogonal frequency division multiplexing (OFDM) is a promising modulation technique and has been widely used to combat inter-symbol-interference (ISI) resulting from multipath propagation in RFCs. So far, the technique of OFDM has also been successfully applied into IM/DD optical wireless systems. In this dissertation, the author focuses on the system design and performance analysis of a novel power-efficient scheme based on OFDM for IM/DD OWCs. This dissertation is divided into four main sections. In the first part, a novel power-efficient scheme, called asymmetrically and symmetrically clipped optical (ASCO)-OFDM, for intensity modulation direct detection (IM/DD) optical wireless systems is proposed. The average bit rate versus (vs.) normalized bandwidth and the optical power per bit of this novel scheme are expressed by a closed form, respectively. The symbol error rate (SER) performance is investigated when optical signals are transmitted in a flat fading channel. Simulation results show that this proposed scheme can achieve better performances in terms of both power efficiency and symbol error rate (SER) when the optical power of transmitted signals is limited. In the second part, an improved receiving technique is applied into the conventional receiver of ASCO-OFDM to improve the SER performance. This technique can explore and reuse some useful information hidden in the received signals. The detection procedure is described in detail and the improved SER performances are presented for different constellation cases. In the third part, the information rates of ADO-OFDM and ASCO-OFDM are obtained for an additive white Gaussian noise (AWGN) channel with an average transmitted optical power constraint. In the last part, this novel power efficient scheme, ASCO-OFDM, is extended into two-dimensional (2D) IM/DD optical wireless systems. The theoretical analysis and simulation results show that this technique not only achieves high average bit rate, but reduces the Peak-to-average power ratio (PAPR) as well.

Download or read book Optical Communications written by Alberto Paradisi and published by Springer. This book was released on 2018-09-04 with total page 271 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book focuses on recent research and developments on optical communications. The chapters present different aspects of optical communication systems, comprising high capacity transmission over long distances, coherent and intensity modulated technologies, orthogonal frequency-division multiplexing, ultrafast switching techniques, and photonic integrated devices. Digital signal processing and error correction techniques are also addressed. The content is of interest to graduate students and researchers in optical communications.

Download or read book Performance Analysis of Optical Orthogonal Frequency Division Multiplexing O OFDM in Intensity Modulation and Direct Detection IM DD System written by Hardina Siswi and published by . This book was released on 2014 with total page 188 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Intensity Modulation and Direct Detection OFDM Dimensioning for Next generation Passive Optical Networks written by Bruno Alberto Calmels and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: [ANGLÈS] A cost-effective architecture for next-generation passive optical networks is designed and dimensioned, based on intensity modulation and direct detection optical orthogonal frequency division multiple access.

Download or read book Iterative Receiver for Flip OFDM in Optical Wireless Communication written by Shiva Shankar Reddy Borra and published by . This book was released on 2016 with total page 58 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: Intensity Modulation and Direct Detection (IM/DD) is a traditional technique commonly used in Optical Wireless Communication (OWC) systems. However, this detection technique being non-coherent, either partially or completely, suppresses the negative data segment resulting in signal distortions. Flip-OFDM handles the constraints of IM/DD in OWC systems. The conventional receivers for flip-OFDM subtracts the negative data segment from the positive segment. As the noise variance increases, the receiver performance degrades. The iterative receiver is a new receiver structure introduced for flip-OFDM systems where the negative signal segment is concatenated to the positive segment. The technique estimates transmitted data, which ensures an optimum detection receiver performance. This technique is implemented for QAM (16, 64, and 256), BPSK and QPSK modulation schemes and the results for Line-Of-Sight (LOS), Non Line-Of-Sight (NLOS) and Stanford University Interim (SUI) channels are produced. Simulations prove that the iterative receiver provided SNR improvement over a conventional receiver.

Download or read book Low complexity Direct detection Optical OFDM Systems for High Data Rate Communications written by Fatima Barrami and published by . This book was released on 2015 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: A possible approach to maximize the data rate per wavelength, is to employ the high spectral efficiency discrete multitone (DMT) modulation. The work presented in this thesis mainly focuses on optimizing the power consumption and cost of DMT, that are the major obstacles to its market development. Within this context, we have first developed novel techniques permitting to discard the use of Hermitian symmetry in DMT modulations, thus significantly reducing the power consumption and the system cost. We have next proposed an asymmetric linear companding algorithm permitting to reduce the optical power of conventional DCO-OFDM modulation with a moderate complexity. A new VCSEL behavioural model based on the use of the VCSEL quasi-static characteristic was also developed to accurately evaluate the VCSEL impact on DMT modulations. Finally, we have built an experimental system to experimentally validate our proposed techniques. Several simulations and measurement results are then provided.

Download or read book Study Analysis and Application of Optical OFDM Single Carrier SC and MIMO in Intensity Modulation Direct Detection IM DD written by Paul Fahamuel Mmbaga and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Orthogonal Frequency division Multiplexing for Optical Communications written by Daniel Jose Fernandes Barros and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The drive towards higher spectral efficiency and maximum power efficiency in optical systems has generated renewed interest in the optimization of optical transceivers. In this work, we study the different optical applications: Wide Area Networks (WANs), Metropolitan Area Networks (MANs), Local Area Networks (LANs) and Personal Area Networks (PANs). In WANs or long-haul systems, orthogonal frequency-division multiplexing (OFDM) can compensate for linear distortions, such as group-velocity dispersion (GVD) and polarization-mode dispersion (PMD), provided the cyclic prefix is sufficiently long. Typically, GVD is dominant, as it requires a longer cyclic prefix. Assuming coherent detection, we show how to analytically compute the minimum number of subcarriers and cyclic prefix length required to achieve a specified power penalty, trading off power penalties from the cyclic prefix and from residual inter-symbol interference (ISI) and inter-carrier interference (ICI). We derive an analytical expression for the power penalty from residual ISI and ICI. We also show that when nonlinear effects are present in the fiber, single-carrier with digital equalization outperforms OFDM for various dispersion maps. We also study the impairments of electrical to optical conversion when using Mach-Zehnder (MZ) modulators. OFDM has a high peak-to-average ratio (PAR), which can result in low optical power efficiency when modulated through a Mach-Zehnder (MZ) modulator. In addition, the nonlinear characteristic of the MZ can cause significant distortion on the OFDM signal, leading to in-band intermodulation products between subcarriers. We show that a quadrature MZ with digital pre-distortion and hard clipping is able to overcome the previous impairments. We consider quantization noise and compute the minimum number of bits required in the digital-to-analog converter (D/A). Finally, we discuss a dual-drive MZ as a simpler alternative for the OFDM modulator, but our results show that it requires a higher oversampling ratio to achieve the same performance as the quadrature MZ. In MANs, we discuss the use OFDM for combating GVD effects in amplified direct-detection (DD) systems using single-mode fiber. We review known direct-detection OFDM techniques, including asymmetrically clipped optical OFDM (ACO-OFDM), DC-clipped OFDM (DC-OFDM) and single-sideband OFDM (SSB-OFDM), and derive a linearized channel model for each technique. We present an iterative procedure to achieve optimum power allocation for each OFDM technique, since there is no closed-form solution for amplified DD systems. For each technique, we minimize the optical power required to transmit at a given bit rate and normalized GVD by iteratively adjusting the bias and optimizing the power allocation among the subcarriers. We verify that SSB-OFDM has the best optical power efficiency among the different OFDM techniques. We compare these OFDM techniques to on-off keying (OOK) with maximum-likelihood sequence detection (MLSD) and show that SSB-OFDM can achieve the same optical power efficiency as OOK with MLSD, but at the cost of requiring twice the electrical bandwidth and also a complex quadrature modulator. We compare the computational complexity of the different techniques and show that SSB-OFDM requires fewer operations per bit than OOK with MLSD. In LANs, we compare the performance of several OFDM schemes to that of OOK in combating modal dispersion in multimode fiber links. We review known OFDM techniques using intensity modulation with direct detection (IM/DD), including DC-OFDM, ACO-OFDM and pulse-amplitude modulated discrete multitone (PAM-DMT). We describe an iterative procedure to achieve optimal power allocation for DC-OFDM, and compare analytically the performance of ACO-OFDM and PAM-DMT. We also consider unipolar M-ary pulse-amplitude modulation (M-PAM) with minimum mean-square error decision-feedback equalization (MMSE-DFE). For each technique, we quantify the optical power required to transmit at a given bit rate in a variety of multimode fibers. For a given symbol rate, we find that unipolar M-PAM with MMSE-DFE has a better power performance than all OFDM formats. Furthermore, we observe that the difference in performance between M-PAM and OFDM increases as the spectral efficiency increases. We also find that at a spectral efficiency of 1 bit/symbol, OOK performs better than ACO-OFDM using a symbol rate twice that of OOK. At higher spectral efficiencies, M-PAM performs only slightly better than ACO-OFDM using twice the symbol rate, but requires less electrical bandwidth and can employ analog-to-digital converters at a speed only 81% of that required for ACO-OFDM. In PANs, we evaluate the performance of the three IM/DD OFDM schemes in combating multipath distortion in indoor optical wireless links, comparing them to unipolar M-PAM with MMSE-DFE. For each modulation method, we quantify the received electrical SNR required at a given bit rate on a given channel, considering an ensemble of 170 indoor wireless channels. When using the same symbol rate for all modulation methods, M-PAM with MMSE-DFE has better performance than any OFDM format over a range of spectral efficiencies, with the advantage of M-PAM increasing at high spectral efficiency. ACO-OFDM and PAM-DMT have practically identical performance at any spectral efficiency. They are the best OFDM formats at low spectral efficiency, whereas DC-OFDM is best at high spectral efficiency. When ACO-OFDM or PAM-DMT are allowed to use twice the symbol rate of M-PAM, these OFDM formats have better performance than M-PAM. When channel state information is unavailable at the transmitter, however, M-PAM significantly outperforms all OFDM formats. When using the same symbol rate for all modulation methods, M-PAM requires approximately three times more computational complexity per processor than all OFDM formats and 63% faster analog-to-digital converters, assuming oversampling ratios of 1.23 and 2 for ACO-OFDM and M-PAM, respectively. When OFDM uses twice the symbol rate of M-PAM, OFDM requires 23% faster analog-to-digital converters than M-PAM but OFDM requires approximately 40% less computational complexity than M-PAM per processor.

Download or read book Performance Analysis of Optical OFDM Transmission Systems Using PAPR Mitigation Techniques and Alternative Transforms written by Laia Nadal Reixats and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: [ANGLÈS] Optical orthogonal division multiplexing (OFDM) has recently been introduced in optical communications because of its robustness against channel dispersion and its high spectral efficiency. OFDM is based on the fast Fourier transform (FFT). In this thesis, we study alternative transforms to create the OFDM symbols: the fast Hartley transform (FHT) and the discrete Wavelet packet transform (DWPT). Besides the advantages of using optical OFDM (O-OFDM), there are also some disadvantages that must be taken into account. High peak-to-average power ratio (PAPR) is one of the major drawbacks of OFDM-based systems that can cause intermodulation among the subcarriers due to the nonlinearities of the fiber and devices such as analog-to-digital converters (ADC) and external modulators. Here, PAPR reduction techniques are studied to mitigate the effects of the PAPR. Finally, we demonstrate that applying PAPR reduction techniques to O-OFDM systems using intensity modulation and direct detection (IM/DD) the effects of the clipping noise are mitigated without the need of adding a higher bias to the signal.

Download or read book OFDM Based RF and Optical Wireless Systems written by Bilal Ranjha and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Orthogonal frequency division multiplexing (OFDM) is currently being used predominantly in radio frequency (RF) mobile broadband communication systems because of its ability to combat inter-symbol interference (ISI) and robustness against frequency selective fading caused by multipath wireless channel. Wireless mobile standards like 3G and 4G long term evolution (LTE) use orthogonal frequency division multiple access (OFDMA) as a multiplexing/modulation scheme. Despite its many advantages like single tap frequency domain equalization and fast discrete time implementation, OFDM suffers from certain disadvantages like high peak-to-average power ratio (PAPR) and high sensitivity to carrier frequency offset (CFO). Although OFDM has solved problems like multipath fading but it cannot solve the emerging problems like scarcity of RF spectrum for mobile wireless broadband applications. Optical wireless (OW) communication has recently gained a lot of attention as a candidate to complement RF communication. It offers advantages like virtually infinite bandwidth, data security and use of low cost transmitters and receivers like solid state light emitting diodes (LEDs) and optical detectors. OFDM is also being considered as a candidate for visible light communication (VLC) as it offers robustness against multipath caused by diffuse indoor OW channel. One way to realize VLC is intensity modulation direct detection (IM/DD). Although the major difference between RF and OW based OFDM lies in the front end of transmitter and receiver, but due to the unipolar nature of optical intensity in IM/DD system, methods of generating baseband OFDM signal, techniques to reduce PAPR and timing synchronization schemes for RF cannot be directly applied to optical OFDM systems and therefore must be revisited. Therefore, in this thesis, we will first look into the interference caused by CFO in RF based OFDMA system and will analyze the characteristics of this interference for two mapping subcarrier strategies. We will explicitly calculate SINR expression for OFDMA based systems and analyze two types of symbol mapping strategies and characterize interferences due to CFO for each scheme. We will also develop some techniques to reduce high PAPR in OFDM based OW systems since the non-linear characteristics of LED transmitters can severely affect system performance. We will look into various precoding based PAPR reduction techniques. We will then analyze performance of various OFDM based OW schemes in multipath diffuse indoor wireless channel. We will compare performance of conventional schemes with a precoded version. We will then describe in detail our newly proposed power and spectrally efficient hybrid asymmetrically clipped optical orthogonal frequency division multiplexing (HACO-OFDM) system and compare its performance with previously proposed schemes. Finally, we will present details of our newly proposed timing synchronization scheme for power efficient asymmetrically clipped (AC) OW OFDM systems. Detailed performance analysis will be presented and a comparison will be developed. Simulation results show that our proposed scheme outperforms all other timing synchronization techniques and exhibits perfect accuracy even at very low signal-to-noise ratio (SNR). Besides performance, our scheme works perfectly for multiple AC OW which proves its high versatility.

Download or read book Optical Orthogonal Frequency Division Systems with Direct Detection Receivers written by Juan Miguel Pérez Rosas and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: [ANGLÈS] The new generation of Pasive Optical Networks (PONs) to cover the last-mile to the user, is today a hot topic of research. Stringent performance requirements are both capacity and reach; these, together with reduced cost lead to consideration of a new paradigm. In this context, Optical OFDM (O-OFDM) is regarded as a promising candidate. From the many architectures being proposed for O-OFDM, the use of Direct Detection is particularly interesting for the downlink of Passive Optical Networks as cost-efficient Optical Network Units (ONUs) are required. In this line, this work encompasses a general study of Direct Detection Optical OFDM (DD O-OFDM) communications systems with emphasis on applications to optical Access Networks. It proposes designs for the downstream links of three different access network topologies differentiated by the optical modulation used: an Intensity Modulation (IM) with a Directly Modulated Laser (DML) an IM with a Mach-Zehnder Modulator (MZM) and an Amplitude modulation also with a MZM. All systems are based on Direct Detection receivers and the transmission of O-OFDM signals. The architectures, establish a wavelength agnostic link by transmitting Double Side Band signals. The impairments of a DSB transmission are studied and parting from them an optimization on the network?s parameters of frequency Guard Band and Carrier to Signal Power Ratio is performed. In order to test the architectures and optimize the parameters, simulations were executed using the commercial software VPI Transmission Maker TM. The testing of the architectures was done by minimizing receiver sensitivity at a BER 10-3 for data rates of 10Gbps and 40Gbps using 4-QAM and 16-QAM respectively, as digital modulation formats. Results show that spectral occupancy of the O-OFDM signal and the CSPR can be optimized while at the same time compensating for DSB impairments such as amplitude fading. Also the advantages and disadvantages of each optical modulation format depending on data rates and link?s distances required as well as cost-effectiveness are tested and described.

Download or read book High Spectral Density Optical Communication Technologies written by Masataka Nakazawa and published by Springer Science & Business Media. This book was released on 2010-08-12 with total page 337 pages. Available in PDF, EPUB and Kindle. Book excerpt: The growth of Internet traf?c in recent years surpassed the prediction of one decade ago. Data stream in individual countries already reached terabit/s level. To cope with the petabit class demands of traf?c in coming years the communication engineers are required to go beyond the incremental improvement of today’s technology. A most promising breakthrough would be the introduction of modulation f- mats enabling higher spectral ef?ciency than that of binary on–off keying scheme, virtually the global standard of ?ber-optic communication systems. In wireless communication systems, techniques of high spectral density modulation have been well developed, but the required techniques in optical frequency domain are much more complicated because of the heavier ?uctuation levels. Therefore the past trials of coherent optical modulation/detection schemes were not successful. However, the addition of high-speed digital signal processing technology is the fundam- tal difference between now and two decades ago, when trials of optical coherent communication systems were investigated very seriously. This approach of digital coherent technology has attracted keen interest among communication specialists, as indicated by the rapid increase in the pioneering presentations at the post-deadline sessions of major international conferences. For example, 32 terabit/s transmission in a ?ber experiment based on this technology was reported in post-deadline session of Optical Fiber Communication Conference (OFC) 2009. The advancement of the digital coherent technologies will inevitably affect the network architecture in terms of the network resource management for the new generation photonic networks, rather than will simply provide with huge transmission capacity.