Essay On Modulation

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As data rate in communication system increases impairments like Phase Noise, Gaussian Noise and other system generated noises hinders the functioning of the communication system. The phase noise is due to the interference of non-coherent frequency at the local oscillator stage. Gaussian noise is the noise remaining in the system. Modulation format with
Digital Signal Processing is an important aspect in order to increase the bit rate. Multiplexing is another aspect with which bit rate can be increased. The literature survey of noise analysis and various modulation format discussed by various researchers in the past years is given below. Divya Sharma[] described DP-QPSK modulation scheme at 100 Gbps for the propagation length of 500
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Our results show that the FSE can compensate any arbitrary amount of CD and first- order PMD distortion, provided that the oversampling rate is at least 3/2 and that a sufficient number of equalizer taps are used. In contrast, the amount of CD and PMD that can be corrected by a symbol-rate equalizer only approaches an asymptotic limit, and increasing the number of taps has no effect on performance due to aliasing that causes signal cancellation and noise enhancement.

Yumin Liu[] presented the time-domain equalization method for compensation of chromatic dispersion (CD) using Wiener filter in digital coherent optical receivers. The Wiener filter can compensate CD, filter out the noise from the corrupted signal, and provide an optimal estimate of the signal of interest in the sense of minimum mean square error. The tap weights of the Wiener filter applied to a multirate system are determined by the channel impulse response and the signal-to-noise ratio. Numerical Results of 16-ary quadrature amplitude modulation coherent optical multirate transmission systems show that the proposed equalizer outperforms the existing ones.

Dany-Sebastien Ly-Gagnon[] describes a coherent optical receiver for demodulating optical quadrature phase-shift keying (QPSK) signals. At the receiver, a phase diversity homodyne detection scheme is employed without locking the phase of the local oscillator (LO). To handle the carrier phase drift, the carrier phase is estimated
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