Study And Design Of Key Technologies For DVB-T COFDM Receiver Systems

Digital Video Broadcasting-Terrestrial (DVB-T) has been one of the most important standards for terrestrial transmission and undoubtedly been shown as a great success in delivering high quality digital television. DVB-T adopts coded orthogonal frequency division multiplexing (COFDM) as the modulation technique and is a typical OFDM system. OFDM has found its wide application in many scientific areas due to its high-spectrum efficiency, its robustness against both multi-path and pulse noises, etc. However, the OFDM system is vulnerable to synchronization errors and channel estimation errors. How to effectively do the synchronization and do the channel estimation at the OFDM receiver are important issues, which need be addressed in OFDM systems. Hence, the dissertation focuses on the timing synchronization, carrier frequency synchronization and channel estimation methods design for DVB-T. The main contribution of this dissertation can be concluded as following:Firstly, this dissertation gives a brief introduction about the characteristics of the terrestrial wireless channels and basic principles about OFDM technologies. A complete DVB-T transmission system model is established and the effects of non-ideal transmission conditions are thoroughly analyzed. A inner receiver scheme, consists of two-stage synchronization (acquisition and tracking) and two-dimension channel estimation, is adopted.Secondly, in this dissertation, a whole timing synchronization scheme including symbol synchronization and sampling clock synchronization is presented. Employing cyclic property of GI, the blind Mode/GI detection, coarse symbol synchronization and fractional frequency offset are exploited. For more accurate symbol timing, we will illustrate the pilot phase property. In sampling clock synchronization, an estimation based on least square algorithm with the multi-stage tracking loop is proposed which improved the conventional designs.Thirdly, a two-stage scheme is proposed for the integer carrier frequency offset acquisition to reduce the search range. Besides, two low complexity methods are also proposed to detect the accurate integer carrier frequency offset value and many multiplications can be saved without any performance loss to the overall system compared with the conventional approach.Fourthly, we propose the adaptive channel estimator for pilot signal which can average out the noise effects under portable environments. Furthermore, the channel response is estimated by means of two-dimension interpolation of scattered pilots. We analyze several polynomial interpolation methods under channels specified by standards.Fifthly, A novel mixed radix-16/8 FFT algorithm and architecture are presented. By using a single radix-16/8 butterfly processing element and reducing the number of multipliers, the proposed approach obtained significant hardware reduction. To achieve high speed processing, the "radix-4＋radix-4/2" cascade pipeline architecture is designed in radix-16/8 butterfly unit. Furthermore, a symmetry ping-pang RAM structure is adopted to increase the continuous computing capability of the butterfly core. Computing precision is also enhanced through a modified block floating point anti-overflow scheme.Finally, the problems requiring further studies are discussed.