Download or read book A High Speed OFDM Long Reach Passive Optical Network System Employing PAPR Reduction Techniques written by and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A Novel Multi band CO OFDM Based Long Reach Passive Optical Network Architecture written by Mohamed Ben Zeglam and published by . This book was released on 2017 with total page 66 pages. Available in PDF, EPUB and Kindle. Book excerpt: The thesis investigates a new long-reach passive optical networks (LRPON) architecture based on multi-band coherent optical orthogonal frequency division multiplexing (CO-OFDM). The proposed CO-OFDM based LRPON system is characterized by a novel phase noise compensation mechanism aiming to deal with optical signal dispersion in long-range transmissions. By employing a dispersion compensating fiber (DCF) and local oscillator (LO) laser phase shifter for each end-to-end transmission between OLT and ONU, we will show the phase noise due to dispersion can be effectively mitigated. Simulation of the downlink traffic between one optical line terminal (OLT) and 12 optical network units (ONUs) is performed successfully at different fiber lengths, at the data rate of 10$Gbps$ per ONU. The required BER for the forward error correction (FEC) has been achieved for most ONUs, using a dispersion compensating fiber (DCF) and local oscillator (LO) laser phase shifter to compensate for the chromatic dispersion (CD) and the polarization mode dispersion (PMD), respectively.

Download or read book Bit Interleaved Coded Modulation written by Albert Guillén i Fàbregas and published by Now Publishers Inc. This book was released on 2008 with total page 170 pages. Available in PDF, EPUB and Kindle. Book excerpt: Bit-Interleaved Coded Modulation is a comprehensive study of the subject, providing a comprehensive review of one of the most important coding schemes in modern communication systems.

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 Optical Fiber Telecommunications Volume VIB written by Ivan Kaminow and published by Academic Press. This book was released on 2013-05-11 with total page 1139 pages. Available in PDF, EPUB and Kindle. Book excerpt: Optical Fiber Telecommunications VI (A&B) is the sixth in a series that has chronicled the progress in the R&D of lightwave communications since the early 1970s. Written by active authorities from academia and industry, this edition brings a fresh look to many essential topics, including devices, subsystems, systems and networks. A central theme is the enabling of high-bandwidth communications in a cost-effective manner for the development of customer applications. These volumes are an ideal reference for R&D engineers and managers, optical systems implementers, university researchers and students, network operators, and investors. Volume A is devoted to components and subsystems, including photonic integrated circuits, multicore and few-mode fibers, photonic crystals, silicon photonics, signal processing, and optical interconnections. Volume B is devoted to systems and networks, including advanced modulation formats, coherent detection, Tb/s channels, space-division multiplexing, reconfigurable networks, broadband access, undersea cable, satellite communications, and microwave photonics. - All the latest technologies and techniques for developing future components and systems - Edited by two winners of the highly prestigious OSA/IEEE John Tyndal award and a President of IEEE's Lasers & Electro-Optics Society (7,000 members) - Written by leading experts in the field, it is the most authoritative and comprehensive reference on optical engineering on the market

Download or read book Selective Mapping technique for PAPR reduction in LTE OFDM Systems written by Neelam Dewangan and published by GRIN Verlag. This book was released on 2012-11-22 with total page 100 pages. Available in PDF, EPUB and Kindle. Book excerpt: Master's Thesis from the year 2012 in the subject Engineering - Communication Technology, grade: none, , course: M.Tech, language: English, abstract: As a promising technique, OFDM has been widely used in emerging broadband communication systems, such as digital audio broadcasting (DAB), high-definition television (HDTV), wireless local area network (IEEE 802.11a and HIPERLAN/2). However, as the OFDM signals are the sum of signals with random amplitude and phase, they are likely to have large PAPR that requires a linear high-power- amplifier (HPA) with an extremely high dynamic range, which is expensive and inefficient. Furthermore, any amplifier nonlinearity causes intermodulation products resulting in unwanted out-of-band power. A number of approaches have been proposed to deal with the PAPR problem, including clipping, clipping-and-filtering (CF), coding, companding transform, active constellation extension (ACE), selected mapping (SLM), partial transmit sequence (PTS), and so on. This thesis proposes an improvement in Selected Mapping technique and Simulation results are compared to existing techniques namely Exponential Companding Transform, Repeated Clipping and Filtering and Adaptive Active Constellation Extension. The improvements which are proposed in classical Selective Mapping technique satisfies the PAPR Reduction criteria with reducing the computational complexity. Also this new scheme has an important advantage of avoiding the extra bits along with the transmitted OFDM signal .This scheme can also be applied to the multiple transmitting antenna cases.

Download or read book PAPR Reduction of Optical OFDM Systems with Exponential Companding Transform and Zero Padding written by Deyan Chen and published by . This book was released on 2016 with total page 75 pages. Available in PDF, EPUB and Kindle. Book excerpt: Optical wireless communication (OWC) is an alternative to radio frequency (RF)communication with a signi cantly larger and unregulated spectrum. In OWC systems, optical orthogonal frequency division multiplexing (O-OFDM) with intensity modulation and direct detection (IM/DD) is commonly used. There are two common signal structures in most OWC systems based on IM/DD OFDM. One is called DC-biased optical OFDM (DCO-OFDM) and the other one is called asymmetrically clipped optical OFDM (ACO-OFDM). One drawback of an OFDM signal is its high peak-to-average power ratio (PAPR), which requires the transmitter to operate in a large dynamic range to retain all desirable information. To reduce the PAPR,companding transform has been investigated. Because of the nonlinear operation of companding, a high electrical signal-to-noise ratio (SNR) is required. In this thesis, a combination of an exponential companding transform and a zero padding scheme is employed on both DCO-OFDM and ACO-OFDM systems to reduce PAPR and the required electrical SNR. Systems that employ quadrature amplitude modulation (QAM) with gray mapping are simulated. Results have shown that the optimized DCO-OFDM and ACO-OFDM reduced the PAPR by about 7dB and 11dB, respectively, through exponential companding. Meanwhile, the required SNR is decreased by approximately 10dB in the optimized DCO-OFDM and by approximately 13dB in the optimized ACO-OFDM by using zero padding.

Download or read book Next Generation Passive Optical Networks Based on Orthogonal Frequency Division Multiplexing Techniques written by Francesc Xavier Escayola Elias and published by . This book was released on 2016 with total page 257 pages. Available in PDF, EPUB and Kindle. Book excerpt: In recent decades, the industry of communications has acquired huge significance, and nowadays constitutes an essential tool for the society information. Thus, the exponential growth in demand of broadband services and the increasing amount of information to be transmitted have spurred the evolution of the access network infrastructure to effectively meet the user needs in an effective way in terms of costs of both installation and maintenance. Passive optical networks (PON) are currently considered the most efficient and least costly alternative to deploy fiber to the home environment. In order to allow many users simultaneously coexist PONs based on time multiplexing (TDMA) have been developed. Looking ahead, however, it is expected that these techniques do not meet the requirements on access networks. In consequence, other multiple access techniques such as Wavelength Division Multiplexing Access (WDMA) or Orthogonal Frequency Division Multiplexing Access (OFDMA) are currently under study and development for use in the next generation of PONs. Particularly, in recent years OFDM has stood out among the scientific community to be considered a solution with great potential on future implementation of PONs. This is especially true due to the capacity of OFDM to work with multilevel modulations, its high tolerance to chromatic dispersion, and its high flexibility and granularity in terms of bandwidth management. Given the above, the aim of this Thesis is to study deeply the advantages and challenges of implementing the standard OFDM as an access network solution; likewise, it offers solutions to improve its performance. In order to evaluate the main structures and strategies for OFDM-based PON, a comparative analysis of all of them is performed firstly, highlighting their sensitivity levels, maximum range and number of users. A key aspect for network providers is the cost of operation, deployment and maintenance of networks. As a low-cost solution, this Thesis proposes a network model called Statistical-OFDMA-PON based on intensity modulation and direct detection. In addition, dynamic bandwidth management strategies are applied into this model getting an improvement in the power balance which in turn, allows to increase the maximum range and the scalability in number of users. One of the main OFDM problems is the Peak-to-Average Power Ratio (PAPR) which increases with the number of carriers. This thesis proposes a new algorithm based on folding the signal and transmitting auxiliary information in order to compensate the PAPR effect and thus increase the sensitivity of the optical system. On the other hand, OFDMA requires a large number of operations in the digital domain resulting in a high computational effort, which in turn results in an increased cost. For this reason, this Thesis presents a study on the optimization of the required resolution in the Digital-to-Analog / Analog-to-Digital Converters (DAC/ADCs) maintaining the transmission quality. The optimization of the computation time may make the OFDMA-based optical network more attractive for future PONs. Finally, another problem concerning the OFDM optical networks is their sensitivity to Phase Noise (PN). In this regard, this Thesis presents a study of the effect of the laser linewidth and its dependence on signal bandwidth. A mitigation technique based on pilot tones is implemented and the limiting values for the laser linewidth are found to be within the reach of present low-cost light sources.

Download or read book Fiber Nonlinearity Mitigation Using Mid span Spectral Inversion in Long haul Coherent Optical OFDM Systems written by Mohammad Monir Morshed and published by . This book was released on 2015 with total page 302 pages. Available in PDF, EPUB and Kindle. Book excerpt: Optical fiber communication systems have become the backbone of today's communication networks due to their enormous bandwidth, over several terahertz (THz), enabling capacities of 100 Tb/s and beyond. Almost all of world's long-haul internet traffic is carried by these optical backbone networks. Despite the fact that the internet bubble ended in the early 2000s, its traffic has been constantly increasing at an astounding rate of 75% per year. In addition to that, new emerging video-centric applications such as IPTV will continue to increase the demand on the underlying optical backbone networks.As a result, ten to twenty years from now, optical networks will have to carry vastly increased amounts of data. However, recent research shows that fundamental limits in optical backbone networks are being approached. These limits are imposed by noise generated from inline amplifiers used to boost up the signal and the intrinsic nonlinearity of conventional standard single mode fiber (S-SMF). In order to meet long-term needs and challenges, therefore, research in wideband optical subsystems enabling high capacity long-haul transmission must be urgently pursued. One approach to break through the current capacity limit is a combination of using advanced modulation formats like coherent optical Orthogonal Frequency Division Multiplexing (CO-OFDM) and fiber nonlinearity mitigation techniques. In OFDM, the orthogonal property of the sub-carriers allows formation of an almost rectangular spectrum, which increases spectral efficiency. However, at the high powers required for higher order modulation formats, the nonlinearity in the fiber causes nonlinear mixing between the subcarriers, restricting the maximum allowable power below nonlinear threshold, and hence constraining the total capacity and distance.The PhD thesis proposed using mid-span spectral inversion (MSSI) that uses optical phase conjugation (OPC) module to mitigate the fiber nonlinearity in CO-OFDM systems.Using MSSI, the spectrum of the first-half of the link (from the Tx to the OPC module) will be inverted by Four-Wave Mixing (FWM) of the OFDM signal with a pump wave. The spectrally inverted signal is then selected to pass through the second half of the link. Because the signal is spectrally inverted, the second half of the link should undo the dispersion and nonlinearity of the first half of the link.During the project, a detailed analytical formalism to describe the performance of the OPC module has been developed. This aids the design and improvement of fundamental performance of OPC module. The first experimental demonstration of using MSSI in a coherent system has been made using dual polarization CO-OFDM systems carrying 1.21-Tb/s over 800 km. A design outline for optimum performance using MSSI has been developed. Two novel methods for improving the fundamental performance of MSSI have been proposed. The first method splits the nonlinear element into two parts, inserting a notch filter to remove the pump and then reinserting the pump into the second part of the nonlinear element. The second method uses a phase shift filter between the two nonlinear elements, to improve robustness in practical implementation. Both methods offer 1 dB of maximum signal quality improvement in a 10 x 80-km 4-QAM 224-Gb/s CO-OFDM system.In summary, this work has demonstrated by simulation and experiments that MSSI offers benefits to coherent optical systems, including OFDM systems. It has developed analytical formalisms that identify the performance-limiting mechanisms in optical phase conjugators based on third order nonlinearity, and has introduced two methods of mitigating these mechanisms. MSSI fell from favour in the mid-2000s due to its complexity. However, after this successful demonstration of fiber nonlinearity compensation using MSSI in a coherent system, MSSI has now drawn considerable attention recently. Subsequently, there have been demonstrations of Raman-enhanced MSSI and multiple phase-conjugations based coherent systems at the 2014 conference on Optical Fiber Communications (OFC).

Download or read book 10GB S Burst Mode Transmission in Long Reach Passive Optical Networks written by Cleitus Antony and published by . This book was released on 2010 with total page 224 pages. Available in PDF, EPUB and Kindle. Book excerpt: Long reach passive optical networks (PONs) are currently emerging as one of the leading candidates for the next generation of telecommunications access networks, which will provide end customers with future high bandwidth interactive and video-rich services. In order to satisfy future bandwidth demand in an economic fashion it is likely that PON technology will need to evolve dramatically from that which is commercially available today. In particular the reach of these networks will need to increase fivefold to around 100km and the supported data rates will jump by nearly an order of magnitude to around 10Gb/s. In this thesis a hybrid dense wavelength division multiplexed- time division multiple access passive optical network (DWDM-TDMA PON) suitable for use in next generation optical access networks is proposed and studied. In order to implement such challenging architectures new types of high speed, burst mode optical transmission techniques are required, which enable bandwidth sharing between users on the network. This project has developed these new burst mode techniques and sub-systems required to enable these new networks. The main aim of the investigations in this thesis are in overcoming all the physical layer challenges due to 10Gb/s burst mode nature of transmission in these types of networks. A range of investigations, both of a theoretical and experimental nature, such as the dynamics of optical amplifiers, interferometric noise mitigation, suppression of crosstalk from multiple sources, maximum transmission distance, etc., are carried out to optimise the performance of individual components as well as the fully integrated system. The suitability of hybrid DWDM-TDMA architectures as a cost effective solution for use in future optical access networks is verified through full-scale network demonstrations in an experimental long reach PON laboratory test-bed.

Download or read book Peak to Average Power Ration Reduction and Bit Error Rate Improvement in Wireless Orthogonal Frequency Division Multiplexing Communication Systems written by Wisam Fahmi Al-Azzo and published by . This book was released on 2009 with total page 390 pages. Available in PDF, EPUB and Kindle. Book excerpt: Orthogonal frequency division multiplexing (OFDM) offers high data rate transmission with high spectral efficiency, immunity to multipath fading, and simple implementation using fast Fourier transform (FFT). OFDM is readily implemented by present day processors in many high speed networks. However, one of the major drawbacks of OFDM systems is the high peak-to-average power ratio (PAPR); this can result in poor power efficiency, degradation in bit-error-rate (BER) performance, and spectral spreading. The effective PAPR reduction of OFDM signals by simple processing has been challenge for the limited power and processing capability of portable OFDM applications. This thesis investigates the problem of high PAPR in OFDM systems and presents many simple implementation PAPR reduction techniques, and one error-resilient technique. The first part of this thesis presents two time-domain PAPR reduction techniques, viz, square-rooting the envelope of the OFDM output signals, and the smoothing technique. The square-rooting process changes the statistical distribution of the OFDM output signals from Rayleigh to Gaussian-like distribution and reduces the differences between the value of peak and average power, which consequently reduces the PAPR significantly. About 6 dB reduction in PAPR is achieved with moderate degradation in BER performance. For the smoothing process, which is derived from the image enhancement technique, the smoothing applied on the OFDM signals mitigates the PAPR due to its averaging effect. Up to 2.5 dB reduction is achieved by smoothing. Two new probabilistic based non-iterative frequency-domain PAPR reduction techniques are introduced in the second part of the thesis. These techniques reduce PAPR by changing the statistical distribution of the OFDM modulated symbols from uniform distribution to Gaussian-like distribution. This task is performed by two different methods in two different PAPR techniques. The first method of PAPR reduction is done by the addition of complex Gaussian random signals, while the second one is done by insertion of dummy Gaussian subcarriers. The two techniques provide PAPR reduction in the order of 5 dB for PSK-OFDM systems with no out-of-band radiation. The adaptive operation of these techniques enhances significantly both the BER performance and reduce the transmission power. The last part of this thesis presents a new modulation-based error resilient technique referred to as multi-dimensional modulation technique (MDM). In this technique concatenation of digital modulators of decreasing modulation orders are employed. The MDM technique improves the BER performance linearly with increased size of modulation order; up to 12 dB improvement in Eb/No is achieved relative to the conventional OFDM systems at high modulation orders, M≥1024. Also, the MDM technique offers both error resilience and PAPR reduction when it is combined with the conventional OFDM systems in time domain. As a conclusion, the proposed techniques described above offer new solutions to the problem of high PAPR in OFDM systems, and for one of them offer improvement of BER performance at the same time. Besides, they can be applied for different systems parameters and applications requirement. Moreover, the PAPR reduction techniques proposed in this thesis are data-independent and can be implemented in one-shot; while the MDM technique uses only digital modulation and dc-offset signal processing, which can be implemented by simple circuits and/or processors.

Download or read book Long Reach Passive Optical Networks written by Huan Song and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: With the advances in optical technology, the span of a broadband access network using Passive Optical Network (PON) technology can be increased from today's standard of 20 km to 100 km or higher. Such an extended-reach PON is known as Long-Reach PON (LR-PON). This technology can enable broadband access for a large number of customers in the access/metro area, while decreasing capital and operational expenditures for the network operator. Therefore, it is very desirable to comprehensively investigate this technology for future broadband access. This dissertation is dedicated to the research of architecture, management, and reliability of LR-PON. This dissertation first reviews the evolutionary path of access networks and shows the drivers from technology and business perspectives for high bandwidth and low cost. A variety of research challenges in this field is reviewed, from optical components in the physical layer to the control and management issues in the upper layers. We discuss the requisites for optical sources, optical amplifiers, and optical receivers in optical access networks with high transmission rate (10 Gbps) and large power attenuation (due to large split, transmission over 100 km and beyond, and propagation). We analyze the key topological structures to guarantee physical protection (e.g., tree-and-branch, ring-and-spur). Then, some relevant demonstrations of Long-Reach optical access networks developed worldwide by different research institutes are presented. A major challenge in LR-PON is that the propagation delay (for data as well as control signals) between the telecom central office (CO) and the end user is increased by a very significant amount. Now, traditional PON algorithms for scheduling the upstream transmission, such as dynamic bandwidth allocation (DBA) algorithms, may not be sufficient; actually, they may lead to degraded performance because of the long delay of the CO-to-Users "control loop". This challenge motivates us to propose and study a multi-thread polling algorithm to effectively and fairly distribute the upstream bandwidth dynamically. This algorithm exploits the benefits of having multiple polling processes running simultaneously and enabling users to send bandwidth requests before receiving acknowledgement from the CO. We compare the proposed algorithm with traditional DBA, and show its advantage on average packet delay. With the increased bandwidth requests from the expanding base of users, LR-PON should utilize the network resource (e.g., wavelengths, lasers, etc.) more effectively. We propose a new and efficient protocol to achieve better utilization of tunable lasers, as well as wavelength resources across different user groups in LR-PON. In order to accommodate downstream bursty traffic and provide Quality of Service (QoS) in the user-specified Service-Level Agreements (SLA), the protocol integrates our proposed SLA-aware bandwidth allocation scheme based on flow scheduling. We show the protocol's advantage to support incremental upgrade of bandwidth with increasing user bandwidth requests, and to provide a user with a SLA which guarantees a number of streaming flows with average bandwidth and maximum delay guarantee (e.g., 5 ms), as well as data flows with average bandwidth specifications. Since LR-PON serves a lot more users, a network failure may lead to a huge amount of data loss and negative user experience. Thus, to understand the importance of LR-PON survivability, we propose hardware-accelerated protection schemes for the LR-PON, incorporating the "ring-and-spur" structure to achieve fast protection-switching time, and automatic failure location at the Optical Line Terminal (OLT), which is located at the head end of the optical access network. We design the protection schemes for multiple network environments, e.g., unidirectional transmission vs. bidirectional transmission, and 1+1 protection vs. 1:1 protection. The numerical examples demonstrate that protection paths can be established within a few tens of ms after a failure occurs. This dissertation makes important contributions by studying novel architectures, protocols, and algorithms of LR-PON that will help to improve the next-generation telecom access networks.

Download or read book Physical Layer Monitoring of Passive Optical Networks written by Maged A. Esmail and published by LAP Lambert Academic Publishing. This book was released on 2013 with total page 120 pages. Available in PDF, EPUB and Kindle. Book excerpt: In order to enable new services that require high data rates over longer distances, the optical ber substitutes the copper cable step by step in the access network area. Time division multiplexed-Passive optical network (TDM-PON) is a fast emerging architecture that uses only passive components between the customer and the central office. PON operators need a monitoring system for the physical layer to guarantee high service quality. This monitoring system is necessary during the ber installation, final network installation testing, regular operation of the network, and for fault localization. In this book, we present the motivations, requirements and challenges of TDM-PON monitoring. We made an exhaustive review and comparison of the monitoring techniques and systems for TDM-PON, mostly proposed within the last five years. We have discussed the open issues and future research perspectives in physical layer PON monitoring that may target higher performance, lower cost, or scalability to next generation PON architectures. This includes wavelength division multiplexing (WDM), TDM over WDM or long-reach PONs intended to extend the reach from 20 up to 100 km distances and beyond.

Download or read book New Peak to average Power Ratio Reduction Schemes for OFDM Systems written by Peng Liu and published by . This book was released on 2004 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: It is known that the orthogonal frequency division multiplexing (OFDM) modulation is very suitable for high-speed wireless transmission systems due to its bandwidth efficiency and ability in coping with multipath fading. However, the large peak-to-average power ratio (PAPR) of an OFDM signal limits the application of OFDM to a certain degree. The research focus of this thesis is on the study of some new PAPR reduction schemes for OFDM systems. In the first part of the thesis, we investigate the peak windowing method, the clipping method, and a combination of the two techniques with an emphasis on the performance assessment of the transmitted OFDM signal using the combination scheme. We start with the review of the two typical signal distortion techniques and point out their advantages and shortcomings. We then propose a combination scheme for the two techniques in order to overcome their drawbacks. In the proposed combination scheme, a weighting function is used to remove instantaneous signal peaks and then a hard-limiting is utilized for the reduction of the overall peak powers. A modified IDFT interpolation is developed and employed in the combination scheme to improve the interpolation precision of the time-domain OFDM signal. (Abstract shortened by UMI.).

Download or read book Wireless OFDM and MIMO OFDM Communications written by P. Mukunthan and published by LAP Lambert Academic Publishing. This book was released on 2014-06-14 with total page 140 pages. Available in PDF, EPUB and Kindle. Book excerpt: The present wireless systems aim for two conflicting goals, viz., providing quality of service such as delay, fairness to users, and maximizing the throughput of the system. Several techniques have been developed for increasing bandwidth with high data rate. Among these techniques, Orthogonal Frequency Division Multiplexing (OFDM) is a special form of multicarrier technique where all the subcarriers are orthogonal to each other. OFDM offers higher data rate and high immunity to the multipath fading channel without degrading the Bit Error Rate (BER) performance. It has gained popularity for broadband communication system because of its high spectral efficiency and capacity to combat multipath fading. At the same time, it has some limitations such as Inter-Symbol Interference (ISI), Inter-Carrier Interference (ICI) and high Peak-to-Average Power Ratio (PAPR). This book contain seven chapters and an attempt has been made in this research work to enhance the power amplifier efficiency and reduce the high PAPR of the OFDM and MIMO-OFDM systems through modified PTS approach combined with some PAPR reduction techniques.

Download or read book Papr Reduction in Ofdm System Using Pulse Shaping Technique written by Prakash Shahi and published by LAP Lambert Academic Publishing. This book was released on 2011-02 with total page 76 pages. Available in PDF, EPUB and Kindle. Book excerpt: Orthogonal Frequency Division Multiplexing (OFDM) techniques allow the transmission of high data rates over broadband radio channels subject to multipath fading without the need for powerful channel equalization. However, they are very sensitive to nonlinear effects owing to high peak-to-average power ratio (PAPR) owned by their transmitted signals. This thesis proposes an efficient technique for reducing the PAPR of OFDM signals.The proposed technique is data-independent and, thus, does not require new processing and optimization for each transmitted OFDM block. The reduction in PAPR of the OFDM signal is obtained through a proper selection of a pulse shaping scheme that distributes the power of each modulated symbol over the OFDM block such that the average power of OFDM signal will not be far from individual symbol power. It is shown, through computer simulations, that the PAPR of pulse shaped OFDM signals approaches that of single-carrier signals.The pulse shaping schemes also take advantage of the frequency variations of the communication channel and can provide considerable performance gain in multipath fading channels

Download or read book Energy efficient Long reach Passive Optical Networks written by Lei Shi and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: To bring the high capacity of the optical fiber closer to the end users with affordable costs, passive optical network (PON) was introduced and developed as a promising access network technology over the past decade. Long-reach PON (LR-PON) extends the coverage span of PONs from the traditional 20 km range to 100 km, consolidates the multiple active sites and thus lowers the costs. Besides extending the reach, energy conservation, which is of growing concern today, gives LR-PON a brand new advantage over its competitors. In this dissertation, we focus on the intersection of these two topics, namely Energy-Efficient LR-PON. We present several distinct schemes with the potential for substantial energy savings under practical settings, while not significantly affecting the network's performance. We develop and evaluate novel architectures, protocols, and algorithms for a LR-PON to will help to improve the performance of next-generation telecom access networks. One major component of LR-PON is the optical line terminal (OLT), which is deployed in central offices. Specifically for energy savings in OLT, we propose a centralized network planning approach based on user behaviors. By considering the different network usage behaviors of different kinds of users, we develop an efficient user-assignment scheme in which users with complementary behaviors are assigned to the same network segment to share the bandwidth. This achieves high bandwidth utilization at all times, and reduces the number of wavelengths needed, thus lowing cost and energy usage. Heuristic searches can provide such assignments, and their approximate solutions are very close to the lower bound. We then extend our work to the network operation (i.e., traffic engineering) stage, where an energy-efficient dynamic wavelength allocation scheme is developed on the "ring-and-spur" LR-PON. This scheme enables a wavelength to be dropped dynamically at multiple remote nodes, making it possible for users in different network segments to share downstream capacity in a statistical multiplexing fashion. The wavelength allocation may also be dynamically changed according to the network traffic so that the OLT can efficiently utilize all operational wavelengths. The other major component of LR-PON is the optical network unit (ONU), a remote unit close to the users. We propose a service-level agreement (SLA)-based scheduling scheme, in which the sleep time of an ONU can be adjusted and the ONU can quit sleep mode to send high-priority packets. Our proposal solves the problems of slow transition of power from active mode to sleep mode in an ONU and the relatively large recovery and synchronization time needed during the wakeup process. The tradeoff in energy savings vs. delay performance is evaluated using simulations under practical power-consumption settings. We also study the effects of arrayed-waveguide grating (AWG) and erbium-doped-fiber amplifier (EDFA) on bit-error rate (BER) in LR-PON, and propose both short-term and long-term distance-aware wavelength allocation schemes to balance the BER among ONUs at different distances. Simulation results show that average BER improves and the relative standard deviation decreases.