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DSP-Based Coherent Optical Transmission Systems
Published in Le Nguyen Binh, Advanced Digital, 2017
Nyquist pulse shaping is one of the most efficient methods to pack adjacent subchannels into a super-channel. The timing recovery of such Nyquist subchannels is critical for sampling the data received and for improving the transmission performance. Timing recovery can be done either before or after the PMD compensator. The phase detector scheme is shown in Figure 13.28, a Godard type [13] that is a first-order linear scheme. After CD compensation (CD−1 blocks), the signal is sent to an SOP modifier to improve the clock extraction. The clock performance of NRZ-QPSK signal in the presence of a first-order PMD characterized by a DGD and azimuth is presented in Figure 13.3. The azimuth of 45° and DGD of a half-symbol/unit interval (UI) completely destroys the clock tone. Therefore, the SOP modifier is required for enabling the clock extraction. In practical systems, a raised-cosine filter is used to generate Nyquist pulses instead of the Sinc shape type. A filter pulse response is defined by two parameters, the roll-off factor β and the symbol period Ts, and described by taking the inverse Fourier transform of Equation 13.4. The Godard phase detector cannot recover the carrier phase even with small β, and thus the channel spectra is close to rectangular. A higher-order phase detector must be used to effectively recover the timing clock period, as shown in Ref. [14]. A quadratic-power law PD (4PDP) with prefiltering presented in Ref. [15], as shown in Figure 13.28b, can deal with small β values.
Analyzing image transmission quality using filter and C-QAM
Published in Debatosh Guha, Badal Chakraborty, Himadri Sekhar Dutta, Computer, Communication and Electrical Technology, 2017
Md. Khaliluzzaman, Deepak Kumar Chy, Kaushik Deb
A pair of raised cosine filter is used in both transmitter and receiver sites, which act as square root-raised cosine filter. In practice, ISI cannot be zero when both filters are implemented due to some numerical decision error in both the design phase and implementation phase.
Stair-type parallel digital predistorter for power amplifier linearisation and harmonic reduction
Published in International Journal of Electronics Letters, 2021
Eui-Rim Jeong, Hyukjun Oh, Jingon Joung
The proposed PD was initially examined through computer simulation. In the simulation, the transmitted signals were modulated using 16-quadrature amplitude modulation (16-QAM), and pulse-shaped using a square-root-raised-cosine filter with a roll-off factor of 0.25. The pulse-shaping filter output was oversampled ten times. We assumed to remove harmonics up to the third. Further interpolation of the PD output was performed by a factor of 20 to model the analog up/down-converter and analog PA in the digital domain. The carrier frequency was , where is the symbol rate. Fifth-order polynomials were used for the PA models:
Novel calibration algorithm of six-port receivers based on radial basis function network
Published in International Journal of Electronics, 2023
Qing Wang, Yongle Wu, Yue Qi, Weimin Wang, Qinghua Yang
As shown in Figure 3, it is necessary to use the Matlab software in the computer to generate an ideal 16-QAM signal, and then go through the raised cosine filter to become an ideal transmission symbol. This paper generates 16,393 random ideal signals. Modulate the 16-QAM signal to the RF signal generator, and set the carrier frequency and signal bandwidth. The RF signal and the local oscillator signal enter the six-port receiver together. Finally, the voltage signal output by the four-channel detector is received by the oscilloscope. Thus, in this way, the data can enter the digital signal processing part, and the operator can obtain an accurate received signal after processing the received data.
Frequency selective digital predistortion for harmonic rejection
Published in International Journal of Electronics, 2018
Xiaofang Wu, Xinshuo Cai, Jinfu Huang, Jianghong Shi
First, the performance of our proposed DPD method is examined through simulation. The transmitted signal is a 16-quadrature amplitude modulation signal which is pulse-shaped by a square root raised cosine filter with roll-off 0.25. The sampling clock of pulse shaping filter output is 10 times the symbol rate. The coefficients of PA model inEquation (1) are setting as as in Choi et al. (2011) which is extracted from a real solid-state PA. The carrier frequency is , where is the symbol rate.