DVB (Digital Video Broadcasting) is the television digital system. It's however much more than a simple replacement for existing analogue television transmission, this system has many advantages such as picture quality and allows you a range of new features and services including subtitling, multiple audio tracks, interactive content, multimedia content. The system is based in the OFDM technology, which allows DVB system to exploit the spectrum frequencies in a better way, saving spectrum, but OFDM has an important drawback that is the peak to average power ratio problem. OFDM is based on the FFT algorithms generating orthogonal subcarriers. This thesis talks about the improvement of the PAPR problem using the soft compression method. The simulation has been developed in Simulink® and Matlab®. With all the information presented in this thesis, any user can simulate the system. Thus, this thesis can be improved using other techniques to solve the PAPR problem.

<p>DAB (Digital Audio Broadcasting) is the radio digital system developed as an european standard by the ETSI, EN 300 400, based on the Eureka-147 group works, to improve the performance of the analogue radio systems (AM and FM). The system is based on the OFDM technology which allows DAB to exploit the spectrum frequencies in a better way with a higher quality of sound for mobile receivers specially. The main part of the OFDM system is based on the FFT algorithms to spread the data flow over different orthogonal carriers. The simulation has been developed in Simulink^TMand Matlab^TMand the layout designed follows faithfully the standard for the transmission system. The simulation can be reloaded by the user with the information presented in this thesis. Thus, this work can be continued to complete the DAB whole system simulation. The results obtained running this simulation show the main DAB system characteristics.</p>

DAB (Digital Audio Broadcasting) is the radio digital system developed as an european standard by the ETSI, EN 300 400, based on the Eureka-147 group works, to improve the performance of the analogue radio systems (AM and FM). The system is based on the OFDM technology which allows DAB to exploit the spectrum frequencies in a better way with a higher quality of sound for mobile receivers specially. The main part of the OFDM system is based on the FFT algorithms to spread the data flow over different orthogonal carriers. The simulation has been developed in Simulink&lt;sup&gt;TM&lt;/sup&gt;and Matlab&lt;sup&gt;TM&lt;/sup&gt;and the layout designed follows faithfully the standard for the transmission system. The simulation can be reloaded by the user with the information presented in this thesis. Thus, this work can be continued to complete the DAB whole system simulation. The results obtained running this simulation show the main DAB system characteristics.

This thesis describing basic concepts and parts of OFDM modulator, showing their implementation in Matlab. It’s focused on how to use USRP with Matlab to create fully functional OFDM modulator.

This thesis describing basic concepts and parts of OFDM modulator, showing their implementation in Matlaba. It's also focusing on how to use USRP with Matlab and creating functional OFDM modulator. Main efford is forwarded to practical impelementation of OFDM using available hardware.

Approved for public release, distribution is unlimited / Synchronization of orthogonal frequency-division multiplexed (OFDM) signals is significantly more difficult than synchronization of a single-carrier system. The recently approved IEEE Standard 802.11g specifies a packet-based OFDM system that provides a basis for the discussion of OFDM synchronization in a packet-based environment. Algorithms that synchronize the receiver carrier demodulation frequency and phase, the data frame, the OFDM symbol timing, and the data symbol timing are discussed and analyzed in an AWGN channel. System View simulation is used to implement the frame and carrier frequency synchronization algorithms, where the performance of these algorithms is analyzed and they are shown to be useful detection algorithms for Standard 802.11g signal reception. / Lieutenant Commander, United States Navy

Approved for public release; distribution in unlimited. / OFDM is a modulation technique that achieves high data rates, increased bandwidth efficiency and robustness in multipath environments. However, OFDM has some disadvantages, such as sensitivity to channel fading, large peak to average ratio and sensitivity to frequency offset. The latter causes intercarrier interference (ICI) and a reduction in the amplitude of the desired subcarrier which results in loss of orthogonality. In this thesis, the effects of frequency offset are studied in terms of loss of orthogonality. A number of techniques for frequency offset estimation are presented and tested in computer simulations. / Lieutenant Junior Grade, Turkish Navy

Digital communication systems which use Orthogonal Frequency Division Multiplexing (OFDM) are now widely used and have many advantages. The main disadvantage is the requirement for highly linear analogue electronics including the high power amplifier (HPA). This requirement cannot be met in all circumstances because of the occurrence of symbols with high peak to average power ratio (PAPR). Such symbols may be non-linearly distorted by limiting. Approaches to solve this problem have been either to reduce the PAPR at the transmitter or to try to mitigate the effect of the non-linearity at the receiver. Soft-limiting, i.e. applying limiting in software prior to the HPA is a simple way to reduce the PAPR. It produces non-linear distortion which will cause an increase in the bit-error-rate (BER) at the receiver. This thesis surveys existing alternatives ways of reducing the effect of non-linearity and proposes some new ones. Two iterative receiver techniques, based on statistical analysis of the nature of the non-linearity, have been implemented and investigated. These are the ‘Bussgang Noise Cancellation’ (BNC) technique and the ‘Decision Aided Reconstruction’ (DAR) techniques. As these techniques are valid for any memory-less nonlinearity, an alternative form of limiting, named as Inverted-Wraparound (IWRAP) has been included in the BNC investigation. A new method is proposed which is capable of correcting the received time-domain samples that are clipped, once they have been identified. This is named the ‘Equation-Method’ and it works by identifying constellation symbols that are likely to be correct at the receiver. If there are a sufficient number of these and they are correctly identified, the FFT may be partitioned to produce a set of equations that may be solved for the clipped time-domain samples. The thesis proposes four enhancements to this new method which improve its effectiveness. It is shown that the best form of this method outperforms conventional techniques especially for severe clipping levels. The performance of these four enhancements is evaluated over channels with additive white Gaussian noise (AWGN) in addition to clipping distortion. A technique based on a ‘margin factor’ is designed to make these methods work more effectively in the presence of AWGN noise. A new combining algorithm referred as ‘HARQ for Clipping’ is presented where soft bit decisions are combined from multiple transmissions. ‘HARQ for Clipping’ has been combined with the best version of the Equation-Method, and the performance of this approach is evaluated in terms of the BER with different levels of AWGN. It has been compared to other approaches from the literature and was found to out-perform the BNC iterative receiver by 3dB at signal to noise ratios around 10dB. Without HARQ, the best version of the Equation-Method performs better than the BNC receiver, at signal-to-nose ratios above about 17dB.

Approved for public release, distribution is unlimited / Orthogonal frequency division multiplexing (OFDM) is being successfully used in numerous applications. It was chosen for IEEE 802.11a wireless local area network (WLAN) standard, and it is being considered for the fourthgeneration mobile communication systems. Along with its many attractive features, OFDM has some principal drawbacks. Sensitivity to frequency errors is the most dominant of these drawbacks. In this thesis, the frequency offset and phase noise effects on OFDM based communication systems are investigated under a variety of channel conditions covering both indoor and outdoor environments. The simulation performance results of the OFDM system for these channels are presented. / Lieutenant Junior Grade, Turkish Navy