Sincronização de quadro e frequência para OFDM no padrão IEEE 802.15.4g : algoritmos e implementação em hardware

Orientadores: Renato da Rocha Lopes, Eduardo Rodrigues de LimaDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: O objetivo deste trabalho é propor métodos de sincronização de quadro e de frequência de portadora para a camada física MR-OFDM do padrão IEEE 802.15.4g, começando pela pesquisa de algoritmos, passando pelas etapas de modelagem e simulação em alto nível, e finalmente implementando e avaliando os métodos propostos em hardware. A sincronização de quadro é o processo responsável por detectar o início do dado transmitido, ou seja, a primeira amostra válida do sinal de interesse. No caso de sistemas OFDM, onde o sinal transmitido é composto por um ou mais símbolos OFDM (cada símbolo sendo composto por uma quantidade fixa de amostras), o objetivo é detectar a borda ou janelamento de tais símbolos OFDM, ou seja, onde começa e termina cada um deles. A sincronização de frequência, por sua vez, consiste em estimar e compensar o erro de frequência de portadora, causado principalmente pelo descasamento dos osciladores do transmissor e do receptor. Com base em estudos preliminares, selecionamos o algoritmo de Minn para a detecção de quadro. Para a correção de erro de frequência, dividimos o processo em duas etapas, como é geralmente proposto na literatura: primeiro, o erro de frequência fracionário é estimado no domínio do tempo durante a detecção de quadro e compensado via rotação de sinal; após a conversão do domínio do tempo para o domínio da frequência, o erro de frequência inteiro é estimado e compensado utilizando um novo e simples algoritmo que será proposto e detalhado neste trabalho. Os algoritmos propostos foram implementados em hardware e uma plataforma de verificação baseada em FPGA foi criada para avaliar o seu desempenho. Os módulos implementados são parte de um projeto que está sendo desenvolvido no Instituto de Pesquisa Eldorado (Campinas) que tem como objetivo implementar em ASIC um transceptor compatível com o padrão IEEE 802.15.4gAbstract: The objective of this work is proposing methods of frame and frequency synchronization for the MR-OFDM PHY of IEEE 802.15.4g standard, starting with the research of state-of-the-art algorithms, passing through modeling, high-level simulations, and finally implementing and evaluating the proposed methods in hardware. Frame synchronization is the process responsible for detecting the beginning of transmitted data and, in the case of OFDM systems, the border of each OFDM symbol, while frequency synchronization consists of estimating and compensating the Carrier Frequency Offset (CFO) caused mainly by a mismatch between the transmitter and receiver oscillators. Based on the initial studies, we selected Minn¿s algorithm for frame detection. For the CFO correction, we split the process into two steps, as commonly proposed in the literature: first, the Fractional CFO is estimated in the time domain during the frame detection and compensated via signal rotation; after the conversion from time to frequency domain, the Integer CFO is estimated and compensated with a novel and simple algorithm that will be detailed in this work. The proposed algorithms were implemented in hardware and inserted in an FPGA-based verification platform for performance measurement. The implemented modules are part of a project that is under development at Eldorado Research Institute (Campinas) and aims to implement in ASIC a transceiver compliant to the IEEE 802.15.4g standardMestradoTelecomunicações e TelemáticaMestra em Engenharia Elétric

Waveform Advancements and Synchronization Techniques for Generalized Frequency Division Multiplexing

To enable a new level of connectivity among machines as well as between people and machines, future wireless applications will demand higher requirements on data rates, response time, and reliability from the communication system. This will lead to a different system design, comprising a wide range of deployment scenarios. One important aspect is the evolution of physical layer (PHY), specifically the waveform modulation. The novel generalized frequency division multiplexing (GFDM) technique is a prominent proposal for a flexible block filtered multicarrier modulation. This thesis introduces an advanced GFDM concept that enables the emulation of other prominent waveform candidates in scenarios where they perform best. Hence, a unique modulation framework is presented that is capable of addressing a wide range of scenarios and to upgrade the PHY for 5G networks. In particular, for a subset of system parameters of the modulation framework, the problem of symbol time offset (STO) and carrier frequency offset (CFO) estimation is investigated and synchronization approaches, which can operate in burst and continuous transmissions, are designed. The first part of this work presents the modulation principles of prominent 5G candidate waveforms and then focuses on the GFDM basic and advanced attributes. The GFDM concept is extended towards the use of OQAM, introducing the novel frequency-shift OQAM-GFDM, and a new low complexity model based on signal processing carried out in the time domain. A new prototype filter proposal highlights the benefits obtained in terms of a reduced out-of-band (OOB) radiation and more attractive hardware implementation cost. With proper parameterization of the advanced GFDM, the achieved gains are applicable to other filtered OFDM waveforms. In the second part, a search approach for estimating STO and CFO in GFDM is evaluated. A self-interference metric is proposed to quantify the effective SNR penalty caused by the residual time and frequency misalignment or intrinsic inter-symbol interference (ISI) and inter-carrier interference (ICI) for arbitrary pulse shape design in GFDM. In particular, the ICI can be used as a non-data aided approach for frequency estimation. Then, GFDM training sequences, defined either as an isolated preamble or embedded as a midamble or pseudo-circular pre/post-amble, are designed. Simulations show better OOB emission and good estimation results, either comparable or superior, to state-of-the-art OFDM system in wireless channels

SYNCHRONIZATION AND RESOURCE ALLOCATION IN DOWNLINK OFDM SYSTEMS

The next generation (4G) wireless systems are expected to provide universal personal and multimedia communications with seamless connection and very high rate transmissions and without regard to the users’ mobility and location. OFDM technique is recognized as one of the leading candidates to provide the wireless signalling for 4G systems. The major challenges in downlink multiuser OFDM based 4G systems include the wireless channel, the synchronization and radio resource management. Thus algorithms are required to achieve accurate timing and frequency offset estimation and the efficient utilization of radio resources such as subcarrier, bit and power allocation. The objectives of the thesis are of two fields. Firstly, we presented the frequency offset estimation algorithms for OFDM systems. Building our work upon the classic single user OFDM architecture, we proposed two FFT-based frequency offset estimation algorithms with low computational complexity. The computer simulation results and comparisons show that the proposed algorithms provide smaller error variance than previous well-known algorithm. Secondly, we presented the resource allocation algorithms for OFDM systems. Building our work upon the downlink multiuser OFDM architecture, we aimed to minimize the total transmit power by exploiting the system diversity through the management of subcarrier allocation, adaptive modulation and power allocation. Particularly, we focused on the dynamic resource allocation algorithms for multiuser OFDM system and multiuser MIMO-OFDM system. For the multiuser OFDM system, we proposed a lowiv complexity channel gain difference based subcarrier allocation algorithm. For the multiuser MIMO-OFDM system, we proposed a unit-power based subcarrier allocation algorithm. These proposed algorithms are all combined with the optimal bit allocation algorithm to achieve the minimal total transmit power. The numerical results and comparisons with various conventional nonadaptive and adaptive algorithmic approaches are provided to show that the proposed resource allocation algorithms improve the system efficiencies and performance given that the Quality of Service (QoS) for each user is guaranteed. The simulation work of this project is based on hand written codes in the platform of the MATLAB R2007b

Timing and Carrier Synchronization in Wireless Communication Systems: A Survey and Classification of Research in the Last 5 Years

Timing and carrier synchronization is a fundamental requirement for any wireless communication system to work properly. Timing synchronization is the process by which a receiver node determines the correct instants of time at which to sample the incoming signal. Carrier synchronization is the process by which a receiver adapts the frequency and phase of its local carrier oscillator with those of the received signal. In this paper, we survey the literature over the last 5 years (2010–2014) and present a comprehensive literature review and classification of the recent research progress in achieving timing and carrier synchronization in single-input single-output (SISO), multiple-input multiple-output (MIMO), cooperative relaying, and multiuser/multicell interference networks. Considering both single-carrier and multi-carrier communication systems, we survey and categorize the timing and carrier synchronization techniques proposed for the different communication systems focusing on the system model assumptions for synchronization, the synchronization challenges, and the state-of-the-art synchronization solutions and their limitations. Finally, we envision some future research directions