A Closed Form Selected Mapping Algorithm for PAPR Reduction in OFDM Multicarrier Transmission

Nowadays, the demand for communication multi-carriers' channels, where the sub-channels are made mutually independent by using orthogonal frequency division multiplexing (OFDM), is widespread both for wireless and wired communication systems. Even if OFDM is a spectrally efficient modulation scheme, due to the allowed number of subcarriers, high data rate, and good coverage, the transmitted signal can present high peak values in the time domain, due to inverse fast Fourier transform operations. This gives rise to high peak-to-average power ratio (PAPR) with respect to single carrier systems. These peaks can saturate the transmitting amplifiers, modifying the shape of the OFDM symbol and affecting its information content, and they give rise to electromagnetic compatibility issues for the surrounding electric devices. In this paper, a closed form PAPR reduction algorithm is proposed, which belongs to selected mapping (SLM) methods. These methods consist in shifting the phases of the components to minimize the amplitude of the peaks. The determination of the optimal set of phase shifts is a very complex problem; therefore, the SLM approaches proposed in literature all resort to iterative algorithms. Moreover, as this calculation must be performed online, both the computational cost and the effect on the bit rate (BR) cannot be established a priori. The proposed analytic algorithm finds the optimal phase shifts of an approximated formulation of the PAPR. Simulation results outperform unprocessed conventional OFDM transmission by several dBs. Moreover, the complementary cumulative distribution function (CCDF) shows that, in most of the packets, the proposed algorithm reduces the PAPR if compared with randomly selected phase shifts. For example, with a number of shifted phases U=8, the CCFD curves corresponding to the analytical and random methods intersect at a probability value equal to 10(-2), which means that in 99% of cases the former method reduces the PAPR more than the latter one. This is also confirmed by the value of the gain, which, at the same number of shifted phases and at the probability value equal to 10(-1), changes from 2.09 dB for the analytical to 1.68 dB for the random SLM

Enhanced Next Generation Millimeter-Wave Multicarrier System with Generalized Frequency Division Multiplexing

Orthogonal Frequency Division Multiplexing (OFDM) is a popular multicarrier technique used to attain high spectral efficiencies. It also has other advantages such as multipath tolerance and ease of implementation. However, OFDM based systems suffer from high Peak-to-Average Power Ratio (PAPR) problem. Because of the nonlinearity of the power amplifiers, the high PAPR causes significant distortion in the transmitted signal for millimeter-wave (mmWave) systems. To alleviate the high PAPR problem, this paper utilizes Generalized Frequency Division Multiplexing (GFDM) which can achieve high spectral efficiency as well as low PAPR. In this paper, we show the performance of GFDM using the IEEE 802.11ad multicarrier frame structures. IEEE 802.11ad is considered one of the most successful industry standards utilizing unlicensed mmWave frequency band. In addition, this paper indicates the feasibility of using GFDM for the future standards such as IEEE 802.11ay. This paper studies the performance improvements in terms of PAPR reduction for GFDM. Based on the performance results, the optimal numbers of subcarriers and subsymbols are calculated for PAPR reduction while minimizing the Bit Error Rate (BER) performance degradation. Moreover, transmitter side ICI (Intercarrier Interference) reduction is introduced to reduce the receiver load

Uso de técnicas de combinação de diversidade e fatores de espalhamento estendidos para melhorar a performance e reduzir a complexidade do receptor OFDM em IEEE 802.15.4g

Orientadores: Renato da Rocha Lopes, Eduardo Rodrigues de LimaDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: EEE 802.15.4g é um adendo da norma IEEE 802.15.4 focada em Smart Utility Network (SUN), e dedicada a requisitos de comunicação no contexto de Low Rate (LR) Wireless Personal Area Network (WPAN). Hoje em dia, devido às suas características, o adendo foca em apliações de Smart Ubiquitous Network, como cidades inteligentes e Internet das Coisas (IoT). Uma das três Camadas Físicas (PHYs) definidas na norma é a Multi-Rate and Multi-Regional Orthogonal Frequency Division Multiplexing (MR-OFDM). Além de outras características, o MR-OFDM emprega o método Frequency Spreading (FS) para reduzir a Peak-to-Average Power Ratio (PAPR) do símbolo OFDM. Sob algumas premissas do canal, este trabalho mostra que o FS também pode introduzir diversidade em frequência à camada física. Este trabalho propõe um método para reverter o espalhamento de frequência que explora diversidade em IEEE 802.15.4g MR-OFDM. O método segue duas abordagens: o uso de técnicas de combinação de diversidade e a proposta de novas configurações de Modulation and Coding Scheme (MCS) usando fatores de espalhamento estendidos. Em um canal com distribuição Rayleigh e assumindo subportadoras não correlacionadas, o método proposto mostra melhorias de até 10.35 dB quando comparado ao MR-OFDM, revertendo o espa-lhamento de frequência de forma direta, usando configurações originais. O método é válido mesmo na presença de erros na estimativa do canal e bandas de coerência largas. O trabalho faz parte de um projeto maior que visa a implementação de um circuito integrado capaz de suportar as três camadas físicas definias em IEEE 802.15.4g, não apenas o MR-OFDM. Devido a isso, o método deve ser totalmente compatível com a norma e focar na complexidade de implementação do receptor MR-OFDMAbstract: IEEE 802.15.4g is an amendment of the IEEE 802.15.4 standard focused on Smart Utility Networks (SUN), and devoted to the communication requirements of Low Rate Wireless Personal Area Network (LR-WPAN). Nowadays, due to its characteristics, the amendment focuses on Smart Ubiquitous Network applications, such as Smart City and Internet of Things (IoT). One of the three Physical Layers (PHYs) defined in the standard is the Multi-Rate and Multi-Regional Orthogonal Frequency Division Multiplexing (MR-OFDM). In addition to other features, the MR-OFDM employs frequency spreading to reduce the Peak-to-Average Power Ratio (PAPR) of the OFDM symbol. Under some channel assumptions, this frequency spreading can also introduce frequency diversity to the PHY. This work proposes a method to perform frequency despreading that exploits diversity in the IEEE 802.15.4g MR-OFDM PHY. The method follows two approaches: the use of diversity combining techniques and the proposal of new Modulation and Coding Scheme (MCS) configurations using extended spreading factors. In a channel with Rayleigh distribution and assuming uncorrelated subcarriers, the proposed method shows improvements up to 10.35 dB when compared to the MR-OFDM performing frequency despreading using original configurations. The method is valid even in the presence of channel estimation errors and large channel coherence bandwidths. The work is part of a larger project which aims at the implementation of an Integrated Circuit capable of handling the three PHYs defined in the IEEE802.15.4g, not only the MR-OFDM. Thus, the method must be fully compliant to the standard and focus on the MR-OFDM receiver implementation complexityMestradoTelecomunicações e TelemáticaMestre em Engenharia Elétric

Intelligent Processing in Wireless Communications Using Particle Swarm Based Methods

There are a lot of optimization needs in the research and design of wireless communica- tion systems. Many of these optimization problems are Nondeterministic Polynomial (NP) hard problems and could not be solved well. Many of other non-NP-hard optimization problems are combinatorial and do not have satisfying solutions either. This dissertation presents a series of Particle Swarm Optimization (PSO) based search and optimization algorithms that solve open research and design problems in wireless communications. These problems are either avoided or solved approximately before. PSO is a bottom-up approach for optimization problems. It imposes no conditions on the underlying problem. Its simple formulation makes it easy to implement, apply, extend and hybridize. The algorithm uses simple operators like adders, and multipliers to travel through the search space and the process requires just five simple steps. PSO is also easy to control because it has limited number of parameters and is less sensitive to parameters than other swarm intelligence algorithms. It is not dependent on initial points and converges very fast. Four types of PSO based approaches are proposed targeting four different kinds of problems in wireless communications. First, we use binary PSO and continuous PSO together to find optimal compositions of Gaussian derivative pulses to form several UWB pulses that not only comply with the FCC spectrum mask, but also best exploit the avail- able spectrum and power. Second, three different PSO based algorithms are developed to solve the NLOS/LOS channel differentiation, NLOS range error mitigation and multilateration problems respectively. Third, a PSO based search method is proposed to find optimal orthogonal code sets to reduce the inter carrier interference effects in an frequency redundant OFDM system. Fourth, a PSO based phase optimization technique is proposed in reducing the PAPR of an frequency redundant OFDM system. The PSO based approaches are compared with other canonical solutions for these communication problems and showed superior performance in many aspects. which are confirmed by analysis and simulation results provided respectively. Open questions and future Open questions and future works for the dissertation are proposed to serve as a guide for the future research efforts