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With precursor modification by regulating dianhydride hydrolysis degree, the viscosity of polyimide precursor solution, derived from 3,3',4,4'-biphenyl tetracarboxylic dianhydride (BPDA) and para-phenylenediamine (PDA), was facilely manipulated. The chemical structure of the precursor was characterized by infrared (IR) spectrometry and proton nuclear magnetic resonance (1H-NMR) spectrometry. The effects of dianhydride hydrolysis on the viscosity, imidization process and properties were investigated. The results show that the precursor can be formed from hydrolytic BPDA and PDA, with amide acid and carboxylic ammonium salt groups in the molecular structure. The viscosity of the precursor can be reduced by the introduction of carboxylic ammonium salt group, achieving the effective regulation of viscosity in the 10-105cP range. Importantly, the existence of carboxylic ammonium salt shows no influence on the complete imidization of the precursor, which guarantees the maintenance of mechanical property. Interestingly, the coefficient of thermal expansion (CTE) of this BPDA-PDA polyimide films can be reduced by this viscosity manipulation method.

The chaotic mapping enables the logo pixels rearrange randomly in the specified spatial domain, and the mixed bits of the logo were embedded in the image DCT coefficients. To lay the watermarking information in the notable areas of the features, an algorithm of fuzzy entropy estimation was proposed. The embedding strength was characteristic adaptability with the statistic of the local feature coefficients of the original image. The logo could be detected and reconstructed by a specifically Kalman filter without the original data from the watermarked image, and would provide indication of the copyright existence. Experimental results show that the proposed scheme gives good capability and turns out to be a reliable copyright authentication tool for the digital image.

Timing jitter, frequency offset, carrier phase jitter and sampling clock frequency offset are the main synchronization errors encountered by OFDM systems. As many literatures have proved, OFDM systems are very sensitive to frequency errors. In this paper, an improved method to do decimal frequency offset estimation in time domain is proposed. In addition, lots of simulations have proved that when the decimal frequency offset in data streams approaches to 0.5 of the subcarrier spacing, a wrong estimated frequency offset with inverse polarity will be presented, therefore, a novel adjusting model to deal with this problem is also proposed in this paper. Simulation results show that the mean square error (MSE) can be significantly improved by over three order of magnitude at high SNR with the proposed method compared with the conventional method [1], [2]. The correspondent Field Programmable Gate Array (FPGA) circuit through test in HDTV prototype in Team of Engineering Expert Group (TEEG) proves its feasibility and availability. Index Terms--COFDM, FPGA, frequency offset estimation, HDTV.