Peak-to-Average-Power-Ratio (PAPR) Reduction Techniques for Orthogonal-Frequency-Division- Multiplexing (OFDM) Transmission

Wireless communication has experienced an incredible growth in the last decade. Two decades ago,the number of mobile subscribers was less than 1% of the world\u27s population. As of 2011, the number of mobile subscribers has increased tremendously to 79.86% of the world\u27s population. Robust and high-rate data transmission in mobile environments faces severe problems due to the time-variant channel conditions, multipath fading and shadow fading. Fading is the main limitation on wireless communication channels. Frequency selective interference and fading, such as multipath fading, is a bandwidth bottleneck in the last mile which runs from the access point to the user. The last mile problem in wireless communication networks is caused by the environment of free space channels through which the signal propagates. Orthogonal Frequency Division Multiplexing (OFDM) is a promising modulation and multiplexing technique due to its robustness against multipath fading. Nevertheless, OFDM suffers from high Peak-to-Average- Power-Ratio (PAPR), which results in a complex OFDM signal. In this research, reduction of PAPR considering the out-of-band radiation and the regeneration of the time-domain signal peaks caused by filtering has been studied and is presented. Our PAPR reduction was 30% of the Discrete Fourier Transform (DFT) with Interleaved Frequency Division Multiple Access (IFDMA) utilizing Quadrature Phase Shift Keying (QPSK) and varying the roll-off factor. We show that pulse shaping does not affect the PAPR of Localized Frequency Division Multiple Access (LFDMA) as much as it affects the PAPR of IFDMA. Therefore, IFDMA has an important trade-off relationship between excess bandwidth and PAPR performance, since excess bandwidth increases as the roll-off factor increases. In addition, we studied a low complexity clipping scheme, applicable to IFDMA uplink and OFDM downlink systems for PAPR reduction. We show that the performance of the PAPR of the Interleaved-FDMA scheme is better than traditional OFDMA for the uplink transmission system. Our reduction of PAPR is 53% when IFDMA is used instead of OFDMA in the uplink direction. Furthermore, we also examined an important trade-off relationship between clipping distortion and quantization noise when the clipping scheme is used for OFDM downlink systems. Our results show a significant reduction in the PAPR and the out-of-band radiation caused by clipping for OFDM downlink transmission system

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

Channel Estimation in Uplink of Long Term Evolution

Long Term Evolution is considered to be the fastest spreading communication standard in the world.To live up to the increasing demands of higher data rates day by day and higher multimedia services,the existing UMTS system was further upgraded to LTE.To meet their requirements novel technologies are employed in the downlink as well as uplink like Orthogonal Frequency Division Multiple Access (OFDMA) and Single Carrier- Frequency Division Multiple Access (SC-FDMA).For the receiver to perform properly it should be able to recover athe transmittedadata accurately and this is done through channel estimation.Channel Estimation in LTE engages Coherent Detection where a prior knowledge of the channel is required,often known as Channel State Information (CSI).This thesis aims at studying the channel estimation methods used in LTE and evaluate their performance in various multipath models specified by ITU like Pedestrian and Vehicular.The most commonly used channel estimation algorithms are Least Squarea(LS) and Minimum MeanaSquare error (MMSE) algorithms.The performance of these estimators are evaluated in both uplink as well as Downlink in terms of the Bit Error Rate (BER).It was evaluated for OFDMA and then for SC-FDMA,further the performance was assessed in SC-FDMA at first without subcarrier Mapping and after that with subcarrier mapping schemes like Interleaved SC-FDMA (IFDMA) and Localized SC-FDMA (lFDMA).It was found from the results that the MMSE estimator performs better than the LS estimator in both the environments.And the IFDMA has a lower PAPR than LFDMA but LFDMA has a better BER performance

Synchronization in wireless communications

The last decade has witnessed an immense increase of wireless communications services in order to keep pace with the ever increasing demand for higher data rates combined with higher mobility. To satisfy this demand for higher data rates, the throughput over the existing transmission media had to be increased. Several techniques were proposed to boost up the data rate: multicarrier systems to combat selective fading, ultra wide band (UWB) communications systems to share the spectrum with other users, MIMO transmissions to increase the capacity of wireless links, iteratively decodable codes (e.g., turbo codes and LDPC codes) to improve the quality of the link, cognitive radios, and so forth

Parameters of Communication Systems Based on OFDM-CDMA

Cíl disertační práce leží v oblasti modelování a vyhodnocení bezdrátových komunikačních systémů s dvojrozměrným rozprostíráním signálu a jejich klíčových parametrů v závislosti na vybraných vlastnostech moderního bezdrátového komunikačního řetězce. Výzkumné metody použité v této práci spočívají především ve vývoji softwarového simulátoru pro prostředí Matlab, s jehož pomocí, a s využitím statistického přístupu, jsou navržené algoritmy ověřeny. Dále je použit simulátor fyzické vrstvy dle 3rd Generation Partnership Project Long Term Evolution (3GPP LTE), vyvinutý na Technické univerzitě ve Vídni. Tento představuje ideální platformu pro implementaci metody dvojrozměrného (2D) rozprostírání a její vyhodnocení s přihlédnutím k současným bezdrátovým komunikačním systémům. Zjištění prezentovaná v této práci představují především ověření účinnosti systému nazvaného jako Variable Spreading Factor - Orthogonal Code Frequency Division Multiplex (VSF-OFCDM), který využívá principu 2D rozprostírání signálu a zjištění, že VSF-OFCDM systém překonává systémy využívající Orthogonal Division Frequency Multiplex (OFDM), nebo Code Division Multiple Access (CDMA). Dále byla navržena metoda 2D rozprostírání signálu v systému LTE, kde se též potvrdila její účinnost. Díky účinnějšímu potlačení vlivu rychlé variace přenosového kanálu v závislosti na frekvenci a čase, dosahuje systém VSF-OFCDM znatelně vyšší datové prostupnosti.The focus of this research is in the area of modeling and evaluating of the wireless systems with two dimensional signal spreading, it’s key parameters and dependencies on other features in modern wireless communication chain. The research method adopted in this dissertation includes a development of Matlab based simulators which exploits a statistical approach to show a contribution of proposed algorithms. Furthermore, a model of physical layer of the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE), developed by the Vienna University of Technology, was utilized as a simulation environment suitable for implementation of a two dimensional (2D) signal spreading method and its evaluation as well as comparison of achieved results with the state-of-the-art systems. The findings from this research provide evidence that the Variable Spreading Factor - Orthogonal Code Frequency Division Multiplex (hereafter VSF-OFCDM) employing a 2D spreading is a promising wireless access scheme superior to Orthogonal Division Frequency Multiplex (OFDM) or Code Division Multiple Access (CDMA) and is capable to significantly increase the data rates in wireless transmission due to the capability of such system to effectively cope with fast time and frequency fluctuations in the wireless transmission channel.