OFDM Systems for Optical Communication with Intensity Modulation and Direct Detection

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

Power Line Communication (PLC) Impulsive Noise Mitigation: A Review

Power Line Communication (PLC) is a technology which transforms the power line into pathways for the conveyance of broadband data. It has the advantage for it can avoid new installation since the current installation used for electrical power can also be used for data transmission. However, this power line channel presents a harsh environment for data transmission owing to the challenges of impulsive noise, high attenuation, selective fading and etc. Impulsive noise poses a severe challenge as its Power Spectral Density (PSD) is between 10–15dB above background noise. For good performance of the PLC system, this noise must be mitigated.  This paper presents a review of the techniques for the mitigation of impulsive noise in PLC which is classified into four categories, namely time domain, time/frequency domain, error correction code and other techniques. Time domain technique is a memoryless nonlinear technique where the signal's amplitude only changes according to a specified threshold without changing the phase.  Mitigation of impulsive noise is carried out on the received time domain signal before the demodulation FFT operation of the OFDM. Time/Frequency technique is a method of mitigating impulsive noise on the received signal at both before FFT demodulation and after FFT demodulation of the OFDM system. Error correction code technique is the application of forward error correction code by adding redundancy bits to the useful data bits for detection and possibly correction of error occurring during transmission.  Identifying the best performing technique will enhance the deployment of the technique while exploring the PLC channel capacity enhancement in the future. The best performing scheme in each of the category were selected and their BER vs SNR curves were compared with respect to the impulsive noise + awgn curve. Amongst all of these techniques, the error correction code technique had a performance that presents almost an outright elimination of impulsive noise in power line channel. Keywords: Impulsive noise, time domain, time/frequency domain, error correction code, sparse Bayesian learning, recursive detection and modified PLC-DMT

Maximum likelihood detection for OFDM signals with strong nonlinear distortion effects

Dissertação para obtenção do Grau de Mestre em Engenharia Electrotécnica e de Computadore

Near-Instantaneously Adaptive HSDPA-Style OFDM Versus MC-CDMA Transceivers for WIFI, WIMAX, and Next-Generation Cellular Systems

Burts-by-burst (BbB) adaptive high-speed downlink packet access (HSDPA) style multicarrier systems are reviewed, identifying their most critical design aspects. These systems exhibit numerous attractive features, rendering them eminently eligible for employment in next-generation wireless systems. It is argued that BbB-adaptive or symbol-by-symbol adaptive orthogonal frequency division multiplex (OFDM) modems counteract the near instantaneous channel quality variations and hence attain an increased throughput or robustness in comparison to their fixed-mode counterparts. Although they act quite differently, various diversity techniques, such as Rake receivers and space-time block coding (STBC) are also capable of mitigating the channel quality variations in their effort to reduce the bit error ratio (BER), provided that the individual antenna elements experience independent fading. By contrast, in the presence of correlated fading imposed by shadowing or time-variant multiuser interference, the benefits of space-time coding erode and it is unrealistic to expect that a fixed-mode space-time coded system remains capable of maintaining a near-constant BER

Enhanced Receivers for OFDM signals with super-QAM constellations

Nowadays, there is a high demand for wireless communication systems with higher through- put. One popular technique widely used in current and developing wireless technologies is Orthogonal Frequency-Division Multiplexing (OFDM) due to its robustness against fre- quency selective fading and high spectral efficiency. To further extend OFDM capacity to meet the near future’s expected demanding needs, OFDM systems with very large Quadrature Amplitude Modulation (QAM) constellations, the so-called super-QAM, are being proposed. However, OFDM signals are prone to nonlinear distortion effects due to their high envelope fluctuations which reduces the system’s performance and this issue is aggravated by the increase in the size of the constellation. For the implementation of effective super-QAM OFDM systems, it is crucial to develop receivers that expect and mitigate the nonlinear distortion on the transmitted signal. In this work, nonlinear distortion on OFDM small QAM and super-QAM constellations signals is studied, along with distortion models and methods to estimate them solely from the transmitted signal, and application of Bussgang noise cancellation receivers and analysis of their performance over a wide range of scenarios.Nos dias de hoje, há uma grande necessidade de criar sistemas de telecomunicação com maior ritmo de dados. Uma técnica popular em tecnologias de telecomunicação atuais e em desenvolvimento é Ortogonal Frequency-Devision Multiplexing (OFDM) devido à sua robustez contra atenuação seletiva na frequência e alta eficiência espectral. Para aumentar ainda mais a capacidade do OFDM de forma a preparar para ritmos ainda mais altos que são expectáveis num futuro próximo, estão a ser propostos sistemas OFDM com enormes constelações de Quadrature Amplitude Modulation (QAM), o chamado super-QAM. O problema é que sinais OFDM são suscetíveis a efeitos de distorção não linear devido às altas flutuações de envolvente e que traz pior desempenho do sistema, sendo esse problema agravado pelo aumento do tamanho da constelação. Para a implementação de sistemas super-QAM OFDM eficazes é crucial desenvolver recetores que mitiguem a distorção não linear no sinal transmitido. Neste trabalho, estuda-se a distorção não linear em sinais OFDM de pequenas cons- telações QAM e super-QAM, modelos de distorção e métodos para estimá-los a partir do sinal transmitido, aplicação de recetores de cancelamento de ruído Bussgang e análise de seu desempenho em diversos cenários

Convergence Analysis of BNC Turbo Detection for Clipped OFDM Signalling

Abstract-All communication systems in which Orthogonal Frequency Division Multiplexing (OFDM) is applied suffer from a well-known problem: the high Peak-to-Average Power Ratio (PAPR) of the time domain OFDM signal. From many PAPR reduction techniques clipping is one of the simplest: although the PAPR can be easily limited, it also introduces strong nonlinearities, reducing the bit error performance of the system unless it is not compensated at the receiver. In this paper we will investigate one of the receiver oriented iterative (turbo) clipping mitigation methods, the so-called Bussgang Noise Cancellation (BNC). We show that with small modifications to this algorithm, the performance of the system can be further improved

Fifty Years of Noise Modeling and Mitigation in Power-Line Communications.

Building on the ubiquity of electric power infrastructure, power line communications (PLC) has been successfully used in diverse application scenarios, including the smart grid and in-home broadband communications systems as well as industrial and home automation. However, the power line channel exhibits deleterious properties, one of which is its hostile noise environment. This article aims for providing a review of noise modeling and mitigation techniques in PLC. Specifically, a comprehensive review of representative noise models developed over the past fifty years is presented, including both the empirical models based on measurement campaigns and simplified mathematical models. Following this, we provide an extensive survey of the suite of noise mitigation schemes, categorizing them into mitigation at the transmitter as well as parametric and non-parametric techniques employed at the receiver. Furthermore, since the accuracy of channel estimation in PLC is affected by noise, we review the literature of joint noise mitigation and channel estimation solutions. Finally, a number of directions are outlined for future research on both noise modeling and mitigation in PLC