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The Research of Synchronization Algorithm for OFDM Systems

Author: LiKai
Tutor: RenJunYan; YeFan
School: Fudan University
Course: Microelectronics and Solid State Electronics
Keywords: UWB OFDM carrier frequency offset sampling frequency offset
CLC: TN919.3
Type: Master's thesis
Year: 2012
Downloads: 121
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Abstract


The explosive growth of modern multimedia technology and its corresponding consumer-oriented electronic equipments, such as high-definition television (HDTV), digital home theater, high-fidelity digital audio, smart phone, lat-top, set-top boxes and gaming stations, have recently convinced and promoted a brand new market for wireless applications:the wireless personal area network (WPAN).Ultra-Wide Band (UWB) has become the preferred technical solution for the next generation of WPAN, due to its characteristics of high data rate, flexible spectrum utilization, low energy consumption, low cost, less interference and strong anti-interference fuction. Recently, Multi-Band OFDM based UWB technology proposed by WiMedia has been choosen for the international standard by ISO. Chinese government issued its UWB spectrum plan in2008, and subsequently started the standardization work. Chinese UWB standard introduces the dual-carrier OFDM (DC-OFDM) technology.However, OFDM has some inherent drawbacks, one drawback is the sensitivity to synchronization error. Because OFDM consists of many overlapped sub-carriers, when synchronization error occurs, the orthogonality between sub-carriers doesn’t be preserved, serious Inter-Carrier interference is introduced and demodulation performance will be degraded greatly. So fine synchronization is essential to OFDM systems.This thesis not only puts emphasis on synchronization issues mainly in DC-OFDM based UWB systems and proposes an algorithm for this system, but also gives some other synchronization algorithms for other OFDM systems. The thesis consists of symbol timing and frequency synchronization.Regarding on the symbol timing, I analyze the impact of several synchronization errors in OFDM system. After that, I divide the synchronization process into four modules by functionality:packet detection, coarse timing, TFC detection and fine timing. In the aspect of algorithm development, I adopt the joint auto-correlation and cross-correlation method to meet the requirements of UWB system in different indoor multi-path environments, and therefore achieve the robustness.Regarding on the frequency synchronization, I first investigate the multiple analog front-end imperfections in OFDM system, like CFO, SFO, and present an algorithm for DC-OFDM based UWB system. Frequency synchronization is divided into two parts:the carrier frequency synchronization and the sampling clock synchronization. The carrier frequency synchronization need to detect the carrier frequency offset, and then compensates it. The sampling clock synchronization need to eliminate the offset between the A/D sampling frequency and phase of the receiving side and the D/A clock frequency and phase of the sending side, which can impact the system performance. In the aspect of implementation, I present the structure of CFO estimation module catered for OFDM based UWB system, with the emphasis on CORDIC unit that is responsible for triangle calculations.Finally, I give a summary of this paper, and then list several issues deserved further research.

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