Adaptive optical feedforward linearization of optical transceiver for radio over fiber communication link

With the tremendous growth in numbers of mobile data subscribers and explosive demand for mobile data, the current wireless access network need to be augmented in order to keep up with the data speed promised by the future generation mobile network standards. Radio over fiber technology (RoF) is a cost effective solution because of its ability to support numerous numbers of simple structured base stations by consolidating the signal processing functions at the central station. RoF systems are analog systems where noise figure and spurious free dynamic range (SFDR) are important parameters in an RoF link. The nonlinearity of a laser transmitter is a major limiting factor to the performance of an RoF link, as it generates spurious spectral components, leading to intermodulation distortions (IMD), which limit the achievable SFDR of the analog RF wave transmissions. The device nonlinearity can be mitigated through various linearization schemes. The feedforward linearization technique offers a number of advantages compared to other techniques, as it offers good suppression of distortion products over a large bandwidth and supports high operating frequencies. On the other hand, feedforward linearization is a relatively sensitive scheme, where its performance is highly influenced by changing operating conditions such as laser aging, temperature effect, and input signal variations. Therefore, for practical implementations the feedforward system has to be real-time adaptive. This thesis aims to develop an adaptive optical feedforward linearization system for radio over fiber links. Mathematical analyses and computer simulations are performed to determine the most efficient algorithm for the adaptive controller for laser transmitter feedforward linearization system. Experimental setup and practical measurement are performed for an adaptive feedforward linearized laser transmitter and its performance is optimized. The adaptive optical feedforward linearization system has been modeled and simulated in MATLAB Simulink. The performances of two adaptive algorithms, which are related to the gradient signal method, such as least mean square (LMS) and recursive least square (RLS) have been compared. The LMS algorithm has been selected because of its robustness and simplicity. Finally, the adaptive optical feedforward linearization system has been set up with digital signal processor (DSP) as the control device, and practical measurement has been performed. The system has achieved a suppression of 14 dB in the third order IMD products over a bandwidth of 30 MHz, in a two-tone measurement at 1.7 GHz

Análise de redes de rádio sobre fibra óptica

Mestrado em Engenharia Electrónica e TelecomunicaçõesEste trabalho teve como objectivo a implementação e simulação de dois sistemas óptico-analógicos possíveis para a transmissão de sinais rádio sobre fibra óptica. O primeiro utilizando modulação externa, e o segundo modulação directa. Foram implementados modelos necessários para a modelação/transmissão de sinais rádio, bem como a sua desmodulação/recepção. Estes modelos foram adaptados ao software de simulação óptica OSIP, de modo a permitir a simulação de Rádio sobre Fibra. Para validar os resultados, foram utilizados valores obtidos de simulações com o software VPI, assim como medidas experimentais. ABSTRACT: The objective of the presented work was to implement and simulate two different analog optical systems for the transmission of radio signals over optical fiber. The first one with external modulation, and the second with direct modulation. In order to make this possible, were implemented necessary models to the modulation/transmission of radio signals, as well as the respective demodulator/receiver. Those models were adapted to the optical simulation software OSIP, to allow the Radio over Fiber simulation. To validate the results were used experimental measurements, as well as results from VPI, another simulation software

Studies on Optical Components and Radio Over Fibre Systems

In the modern era good communication systems are the need of the hour. This project includes the study of optical components and Radio over Fibre systems. Various Optical components are used in optical systems and those optical components have different characteristics. Various optical components have been studied in this project and in addition to that there is a study of components using S-matrix. The use of S-matrix in analyising the directional coupler. Optical networks can be analysed with the same methods as microwave networks in theory of microwave networks, components are generally represented by complex scattering parameters which form the S- matrix. we adopted this formalism to fibre optic coupler used in optical network taking the polarization dependence into account. There is the study of Fabry- perot filter in which the study of free spectral range (FSR) and the Transfer function was determined through Matlab simulation. The results thus obtained are studied. For the future provisions of broadband, multimedia the radio over fibre systems are a good alternative. RoF systems are used basically because of their low loss and extremely wide bandwidth and robustness. Radio over fibre can use millimeter waves and serve as a high speed wireless local or personal area network. In this project various parts of the Radio over fibre systems are studied, The power spectrum measurements of a millimeter wave Radio over Fibre under different single mode fibre length is done with a Matlab simulation it is found that the fading occurs at some values of length of fibre in the power spectrum. In radio over fibre systems the two subcarrier modulations (SCMs) i.e., single sideband and tandem single sideband have been widely used both SSB and TSSB SCMs can be obtained by using optical mach Zehnder modulator. In this project we investigate the impact of the impact of the harmonic distortion and inter modulation distortion in RoF systems for one wavelength carrying two radio frequency signals with either SSB or TSSB SCM. It is found that non linear distortion can be reduced when the frequency difference ~ 1 GHz. It was found that non linear distortion strongly depends on the modulation index. The source of these results was a mat lab simulation and calculations. For the different values of the signal frequencies the NSR was calculated

Exploring the Unknown: Selected Documents in the History of the US Civilian Space Program

One of the most important developments of the twentieth century has been the movement of humanity into space with machines and people. The underpinnings of that movement -why it took the shape it did; which individuals and organizations were involved; what factors drove a particular choice of scientific objectives and technologies to be used; and the political, economic, managerial, and international contexts in which the events of the space age unfolded- are all important ingredients of this epoch transition from an earthbound to spacefaring people. This desire to understand the development of spaceflight in the United States sparked this documentary history series. 'Exploring the Unknown' is a multi-volume series containing a selection of key documents in history of the U.S. civil space program. This current volume, Volume III, focusing on the use of space for practical applications, prints 112 key documents on the history of satellite communications, remote sensing of earth, and space as an investment in economic growth, edited for ease of use. Each is introduced by a headnote providing context, bibliographical information, and background information necessary to understanding the document