Firefly algorithm (FA) is one of the newly developed nature inspired optimisation algorithm, inspired by the flashing behaviour of fireflies that a firefly tends to be attracted towards other fireflies with higher brightness. Thus FA has two advantages: local attractions and automatic regrouping. Based on these good properties, a novel image watermarking method based on FA in discrete wavelet transform (DWT)-QR transform domain is proposed in this study. Structural similarity index measure and bit error rate are used in the objective function to trade-off invisibility and robustness. The experiment results show that the proposed image watermarking method not only meet the need of invisibility, but also has better or comparable robustness as compared with some related methods.
It is well known that the domain of Fourier transform (FT) can be extended to the Schwartz space [Formula: see text] for convenience. As a generation of FT, it is necessary to detect the linear canonical transform (LCT) on a new space for obtaining the similar properties like FT on [Formula: see text]. Therefore, a space [Formula: see text] generalized from [Formula: see text] is introduced firstly, and further we prove that LCT is a homeomorphism from [Formula: see text] onto itself. The linear canonical wavelet transform (LCWT) is a newly proposed transform based on the convolution theorem in LCT domain. Moreover, we propose an equivalent definition of LCWT associated with LCT and further study some properties of LCWT on [Formula: see text]. Based on these properties, we finally prove that LCWT is a linear continuous operator on the spaces of [Formula: see text] and [Formula: see text].
High speed modulation based on bandwidth limited devices is desired for cost-effective PON capacity upgrade. In this paper, we investigate the equalization techniques for enabling 25-Gb/s transmission with 10G-class optics. A comparison between FFE and DFE based equalizer and MLSE based digital equalizer is made, where 13-tap FFE and 3-tap DFE are required to obtain similar performances with MLSE based detection. In addition, to verify the cost introduced by the ADC, the demand for the ADC parameters in the MLSE based detector, including the sampling rate, resolution, and timing jitter is investigated. Experimental results show that using a 25-GS/s ADC with 4-bit resolution, 25-Gb/s transmission is realized using 10-G TOSA and ROSA, and 28-/30-dB loss budget can be achieved in C-/O-band respectively.
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