This study proposes a new dynamic threshold model to detect keyframes for the coding of a video sequence. The proposed detection threshold is content adaptive which dynamically updates its value at each frame by taking into consideration both the statistical properties of the video sequence and the resolution as well as the quantisation parameters. The content variation metric used in the proposed detection method utilises the information that is already generated by the encoder during the encoding process and thus it makes the detection process fast. By applying the proposed scheme to rate control, the sizes of group of pictures are now adapted to the video content and it removes the temporal redundancy among different frames better, which transforms to the improvements on coding efficiency. The experimental results have shown that the proposed method achieves peak signal-to-noise ratio (PSNR) improvement.
We have demonstrated a novel modulation-pulse-pre-shaping technique to improve the transmission performance of constant amplitude NRZ-DPSK signal. Transmission distance is doubled using this method together with the optimization of phase modulation depth. 02005 Optical Society of America, OCIS codes: (060.2330) Fiber optics communication, (060.4080) Modulaiion
I, TntroductionDifferential-phase-shift-keying (DPSK) moduIation format has attracted intensive research interests for its good performance in long haul optical transmission system and ultra-high speed packet switching network [1,2]. It features high receiver sensitivity and high tolerance to nonlinearities due to its constant envelope. 0.9dS improvement in Q performance for 32*IOGb/s transmission system over 450km NZDSF has been calculated [3].However, for a pure phase-modulation based NRZ-DPSK signal, the phase modulation will induce amplitude modulation in the form of ampIitude ripples in the waveform when it propagates through a dispersive element. Therefore, ampIitude modulation (AM) based NRZ-DPSK were suggested to be used in transmission systems such as 4* I OGbls over 2400 DSF [4] and 40*40Gb/s over 300km N D S F [5]. In these applications, instantaneous optical power at the position where phase experience sudden change, is completely suppressed by push-pull Mach-Zehnder modulator biasd at transmission null point, However, by doing this, the optical intensity is not constant anymore. In addition, to generate such signals, 2Vn: broadband RF signal amplifier or dual drive modulator together with two modulator drivers are required, which inevitably increase the symmetric requirement and cost of the overall setup.In this paper, a novel modulation-pulse-pre-shaping (MPPS) method is suggested to generate constant amplitude
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