An Investigation of Orthogonal Wavelet Division Multiplexing Techniques as an Alternative to Orthogonal Frequency Division Multiplex Transmissions and Comparison of Wavelet Families and Their Children

Recently, issues surrounding wireless communications have risen to prominence because of the increase in the popularity of wireless applications. Bandwidth problems, and the difficulty of modulating signals across carriers, represent significant challenges. Every modulation scheme used to date has had limitations, and the use of the Discrete Fourier Transform in OFDM (Orthogonal Frequency Division Multiplex) is no exception. The restriction on further development of OFDM lies primarily within the type of transform it uses in the heart of its system, Fourier transform. OFDM suffers from sensitivity to Peak to Average Power Ratio, carrier frequency offset and wasting some bandwidth to guard successive OFDM symbols. The discovery of the wavelet transform has opened up a number of potential applications from image compression to watermarking and encryption. Very recently, work has been done to investigate the potential of using wavelet transforms within the communication space. This research will further investigate a recently proposed, innovative, modulation technique, Orthogonal Wavelet Division Multiplex, which utilises the wavelet transform opening a new avenue for an alternative modulation scheme with some interesting potential characteristics. Wavelet transform has many families and each of those families has children which each differ in filter length. This research consider comprehensively investigates the new modulation scheme, and proposes multi-level dynamic sub-banding as a tool to adapt variable signal bandwidths. Furthermore, all compactly supported wavelet families and their associated children of those families are investigated and evaluated against each other and compared with OFDM. The linear computational complexity of wavelet transform is less than the logarithmic complexity of Fourier in OFDM. The more important complexity is the operational complexity which is cost effectiveness, such as the time response of the system, the memory consumption and the number of iterative operations required for data processing. Those complexities are investigated for all available compactly supported wavelet families and their children and compared with OFDM. The evaluation reveals which wavelet families perform more effectively than OFDM, and for each wavelet family identifies which family children perform the best. Based on these results, it is concluded that the wavelet modulation scheme has some interesting advantages over OFDM, such as lower complexity and bandwidth conservation of up to 25%, due to the elimination of guard intervals and dynamic bandwidth allocation, which result in better cost effectiveness

Synchronization in OFDM communication systems

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Design and FPGA Implementation of OFDM System with Channel Estimation and Synchronization

In wireless and mobile communications, multipath fading severely degrades the quality of information exchange. The orthogonal frequency division multiplexing (OFDM) technology is able to provide a high transmission data rate with enhanced communication performance at a relatively small bandwidth cost, together with proper estimation and compensation of channel effects. Therefore, it has been widely applied in many wireless and mobile networks, especially for the state-of-the-art communication standards. The unique structure of OFDM signals and the application of discrete Fourier transform (DFT) algorithm have significantly simplified the digital implementation of OFDM system. Among different kinds of implementations, field programmable gate array (FPGA) is a very cost-effective and highly flexible solution, which provides superior system performance and enables easy system upgrade. In this thesis, a baseband OFDM system with channel estimation and timing synchronization is designed and implemented using the FPGA technology. The system is prototyped based on the IEEE 802.11a standard and the signals is transmitted and received using a bandwidth of 20 MHz. With the help of the quadrature phase shift keying (QPSK) modulation, the system can achieve a throughput of 24 Mbps. Moreover, the least squares (LS) algorithm is implemented and the estimation of a frequency-selective fading channel is demonstrated. For the coarse estimation of timing, a modified maximum-normalized correlation (MNC) scheme is investigated and implemented. Starting from theoretical study, this thesis in detail describes the system design and verification on the basis of both MATLAB simulation and hardware implementation. Bit error rate (BER) verses bit energy to noise spectral density (Eb/N0) is presented in the case of different channels. In the meanwhile, comparison is made between the simulation and implementation results, which verifies system performance from the system level to the register transfer level (RTL). First of all, the entire system is modeled in MATLAB and a floating-point model is established. Then, the fixed-point model is created with the help of Xilinx’s System Generator for DSP (XSG) and Simulink. Subsequently, the system is synthesized and implemented within Xilinx’s Integrated Software Environment (ISE) tools and targeted to Xilinx Virtex-5 board. What is more, a hardware co-simulation is devised to reduce the processing time while calculating the BER for the fixed-point model. The present thesis is an initial work on the implementation part of an collaborative research and development (CRD) project of the Natural Sciences and Engineering Research Council of Canada (NSERC) sponsored by the WiTel Technologies, Ontario. It is the first and foremost step for further investigation of designing innovative channel estimation techniques towards applications in the fourth generation (4G) mobile communication systems

Passive radar based on WiFi transmissions: signal processing schemes and experimental results

Aim of this work is to study innovative techniques and processing strategies for a new passive sensor for short range surveillance. The principle of work of the sensor will be based on the passive radar principle, and WiFi transmissions - which usually provide Internet access within local areas - will be exploited by the passive sensor to detect, localize and classify targets

Passive radar based on WiFi transmissions: signal processing schemes and experimental results

Aim of this work is to study innovative techniques and processing strategies for a new passive sensor for short range surveillance. The principle of work of the sensor will be based on the passive radar principle, and WiFi transmissions - which usually provide Internet access within local areas - will be exploited by the passive sensor to detect, localize and classify targets

Advanced signal processing techniques for WiFi-based Passive Radar for short-range surveillance

In this work, advanced signal processing techniques for a Passive Radar (PR) based on WiFi transmissions are considered. The possibility to exploit such a ubiquitous and accessible source is shown to be an appropriate choice for the detection, localization and imaging of vehicles, people and aircrafts within short ranges in both outdoor and indoor environments