Unlike the scenario in traditional high-order QAM signals, viterbi and viterbi (V&V) algorithm becomes more powerful for carrier phase recovery (CPR) in probabilistically shaped (PS) signals. The reason relies on ...
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Unlike the scenario in traditional high-order QAM signals, viterbi and viterbi (V&V) algorithm becomes more powerful for carrier phase recovery (CPR) in probabilistically shaped (PS) signals. The reason relies on that the PS signals assign much higher probability to the innermost 4 constellation points, which are qualified for V&V algorithm. In this article, we compare the performance of V&V algorithm to that of blind phase search (BPS) algorithm for PS-64 QAM and PS-256 QAM in the aspects of window size and signal to noise ratio under the constraint of different laser linewidths. Besides, the impact of signal entropy on both algorithms is investigated. The computational complexity and running time for both algorithms are also summarized. Results show that the two algorithms perform similarly for PS-64 QAM signals when the linewidth is less than 1 MHz while the running time of BPS algorithm is at least 45 times longer than that of V&V algorithm. Finally, we conduct a coherent detection based optical back-to-back experiment where the laser linewidths of both transmitter laser and local oscillator are 100 kHz. For PS-64 QAM, both V&V and BPS algorithms show negligible penalty compared to the performance of homodyne detection, verifying the feasibility of applying V&V algorithm in the CPR of PS-64 QAM.
Two novel low-complexity multistage digital feedforward carrier phase estimation algorithms for 64-ary quadrature amplitude modulation (QAM) are proposed and analyzed by numerical simulations. The first stage is compo...
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Two novel low-complexity multistage digital feedforward carrier phase estimation algorithms for 64-ary quadrature amplitude modulation (QAM) are proposed and analyzed by numerical simulations. The first stage is composed of a viterbi and viterbi block, based on either the standard quadrature phase shift keying (QPSK) partitioning algorithm using only Class-1 symbols or amodified QPSK partitioning scheme utilizing both Class-1 and outer most triangle-edge symbols. The second stage applies the viterbi and viterbi algorithm after a 64-QAM-to-QPSK transformation, while the subsequent stages iterate a maximum likelihood estimation algorithm for phase estimation. All proposed techniques are characterized by a high tolerance to laser phase noise: with an optical signal-to-noise ratio penalty of 1 dB at bit error rate of 10(-2), the proposed schemes can tolerate a linewidth times symbol duration product (Delta nu.T-s) equal to 5.6 x 10(-5) and 7.1 x 10(-5), respectively. At 32 Gbaud, all of the above linewidth requirements can bemet using commercial tunable lasers. The proposed schemes achieve a similar linewidth tolerance with a reduced implementation complexitywith respect to algorithms based on the blind phase search method.
We propose a novel two-stage blind carrier phase recovery scheme tailored for probabilistically shaped QAM. Our algorithm is based on modifying the classic viterbi&viterbi (V&V) and maximum likelihood (ML) pha...
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We propose a novel two-stage blind carrier phase recovery scheme tailored for probabilistically shaped QAM. Our algorithm is based on modifying the classic viterbi&viterbi (V&V) and maximum likelihood (ML) phase estimators by optimizing the blind decisions over the received symbols taking into account the probability distribution of the received signal. Our technique improves the standard V&V + ML in all conditions and outperforms the state-of-the-art blind phase search (BPS) algorithm for a constellation entropy <= 4. At the same time our implementation preserves the low complexity of standard V&V + ML. This results in a remarkable reduction in complexity of up to a factor thirty compared to BPS.
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