Partial Shift Mapping Decoding Algorithm to PAPR Reduction in OFDM Systems

Orthogonal Frequency Division Multiplexing (OFDM) is a kind of modulation technique which allows the transmission of high data rates over wideband radio channels subject to frequency selective fading by dividing it to several narrow band and flat fading channels. OFDM has high spectral efficiency and Robustness to multipath fading. In contrast high peak to average power ratio (PAPR) of the transmitted signals is a major drawback of multicarrier systems like OFDM. High PAPR causes the nonlinear distortion in the received data and reduces the efficiency of the high power amplifier in transmitter. To solve the problem many techniques such as SLM and PTS algorithms are proposed. Recently a new simple method with low complexity respected to the SLM and PTS as Partial Shift Mapping (PSM) is proposed by Xing et al. He showed that the PSM method can reduce the PAPR parameter respected the other mentioned methods, effectively. In this paper we will design the corresponding decoder to the PSM technique and will evaluate its robustness respected to the high power amplifier distortion and the AWGN channel. Simulation results will show that the PSM method has a better Power spectrum density and is less sensitive to the type of modulation and number of subcarriers

On the effects of memoryless nonlinearities on M-QAM and DQPSK OFDM signals

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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

Adjustable dynamic range for paper reduction schemes in large-scale MIMO-OFDM systems

In a multi-input-multi-output (MIMO) communication system there is a necessity to limit the power that the output antenna amplifiers can deliver. Their signal is a combination of many independent channels, so the demanded amplitude can peak to many times the average value. The orthogonal frequency division multiplexing (OFDM) system causes high peak signals to occur because many subcarrier components are added by an inverse discrete Fourier transformation process at the base station. This causes out-of-band spectral regrowth. If simple clipping of the input signal is used, there will be in-band distortions in the transmitted signals and the bit error rate will increase substantially. This work presents a novel technique that reduces the peak-to-average power ratio (PAPR). It is a combination of two main stages, a variable clipping level and an Adaptive Optimizer that takes advantage of the channel state information sent from all users in the cell. Simulation results show that the proposed method achieves a better overall system performance than that of conventional peak reduction systems in terms of the symbol error rate. As a result, the linear output of the power amplifiers can be minimized with a great saving in cost

Analytical Characterization and Optimum Detection of Nonlinear Multicarrier Schemes

It is widely recognized that multicarrier systems such as orthogonal frequency division multiplexing (OFDM) are suitable for severely time-dispersive channels. However, it is also recognized that multicarrier signals have high envelope fluctuations which make them especially sensitive to nonlinear distortion effects. In fact, it is almost unavoidable to have nonlinear distortion effects in the transmission chain. For this reason, it is essential to have a theoretical, accurate characterization of nonlinearly distorted signals not only to evaluate the corresponding impact of these distortion effects on the system’s performance, but also to develop mechanisms to combat them. One of the goals of this thesis is to address these challenges and involves a theoretical characterization of nonlinearly distorted multicarrier signals in a simple, accurate way. The other goal of this thesis is to study the optimum detection of nonlinearly distorted, multicarrier signals. Conventionally, nonlinear distortion is seen as a noise term that degrades the system’s performance, leading even to irreducible error floors. Even receivers that try to estimate and cancel it have a poor performance, comparatively to the performance associated to a linear transmission, even with perfect cancellation of nonlinear distortion effects. It is shown that the nonlinear distortion should not be considered as a noise term, but instead as something that contains useful information for detection purposes. The adequate receiver to take advantage of this information is the optimum receiver, since it makes a block-by-block detection, allowing us to exploit the nonlinear distortion which is spread along the signal’s band. Although the optimum receiver for nonlinear multicarrier schemes is too complex, due to its necessity to compare the received signal with all possible transmitted sequences, it is important to study its potential performance gains. In this thesis, it is shown that the optimum receiver outperforms the conventional detection, presenting gains not only relatively to conventional receivers that deal with nonlinear multicarrier signals, but also relatively to conventional receivers that deal with linear, multicarrier signals. We also present sub-optimum receivers which are able to approach the performance gains associated to the optimum detection and that can even outperform the conventional linear, multicarrier schemes

MIMO signal processing in offset-QAM based filter bank multicarrier systems

Next-generation communication systems have to comply with very strict requirements for increased flexibility in heterogeneous environments, high spectral efficiency, and agility of carrier aggregation. This fact motivates research in advanced multicarrier modulation (MCM) schemes, such as filter bank-based multicarrier (FBMC) modulation. This paper focuses on the offset quadrature amplitude modulation (OQAM)-based FBMC variant, known as FBMC/OQAM, which presents outstanding spectral efficiency and confinement in a number of channels and applications. Its special nature, however, generates a number of new signal processing challenges that are not present in other MCM schemes, notably, in orthogonal-frequency-division multiplexing (OFDM). In multiple-input multiple-output (MIMO) architectures, which are expected to play a primary role in future communication systems, these challenges are intensified, creating new interesting research problems and calling for new ideas and methods that are adapted to the particularities of the MIMO-FBMC/OQAM system. The goal of this paper is to focus on these signal processing problems and provide a concise yet comprehensive overview of the recent advances in this area. Open problems and associated directions for future research are also discussed.Peer ReviewedPostprint (author's final draft

Hardware Impairments Aware Transceiver Design for Bidirectional Full-Duplex MIMO OFDM Systems

In this paper we address the linear precoding and decoding design problem for a bidirectional orthogonal frequencydivision multiplexing (OFDM) communication system, between two multiple-input multiple-output (MIMO) full-duplex (FD) nodes. The effects of hardware distortion as well as the channel state information error are taken into account. In the first step, we transform the available time-domain characterization of the hardware distortions for FD MIMO transceivers to the frequency domain, via a linear Fourier transformation. As a result, the explicit impact of hardware inaccuracies on the residual selfinterference (RSI) and inter-carrier leakage (ICL) is formulated in relation to the intended transmit/received signals. Afterwards, linear precoding and decoding designs are proposed to enhance the system performance following the minimum-mean-squarederror (MMSE) and sum rate maximization strategies, assuming the availability of perfect or erroneous CSI. The proposed designs are based on the application of alternating optimization over the system parameters, leading to a necessary convergence. Numerical results indicate that the application of a distortionaware design is essential for a system with a high hardware distortion, or for a system with a low thermal noise variance.Comment: Submitted to IEEE for publicatio