Abstract
In this paper, we present a carrier phase recovery (CPR) algorithm using a modified superscalar parallelization based phase locked loop (M-SSP-PLL) combined with a maximum-likelihood (ML) phase estimation. Compared to the original SSP-PLL, M-SSP-PLL + ML reduces the required buffer size using a novel superscalar structure. In addition, by removing the differential coding/decoding and employing ML phase recovery it also improves the performance. In simulation, we show that the laser linewidth tolerance of M-SSP-PLL + ML is comparable to blind phase search (BPS) algorithm, which is known to be one of the best CPR algorithms in terms of performance for arbitrary QAM formats. In 28 Gbaud QPSK (112 Gb/s) and 16-QAM (224 Gb/s), and 7 Gbaud 64-QAM (84 Gb/s) experiments, it is also demonstrated that M-SSP-PLL + ML can increase the transmission distance by at least 12% compared to BPS for each of them. Finally, the computational complexity is discussed and a significant reduction is shown for our algorithm with respect to BPS.
Highlights
As the quadrature phase shift keying (QPSK) modulation based 100G products are being commercialized, research interests are moving on to the generation optical transport systems with spectrally efficient modulation formats such as 16-quadrature amplitude modulation (QAM) [1] and 64-QAM [2]
Carrier phase recovery (CPR) is an indispensible digital signal processing (DSP) procedure in coherent transmission systems to compensate for the random phase shifts induced by both the transmitter laser and the local oscillator (LO) [3,4,5]
Two digital-to-analog converters (DACs) each driven by a field-programmable gate array (FPGA) boards were used to generate non-return-to-zero (NRZ) two-level, four-level and eight-level electrical inphase and quadrature signals for QPSK, 16-QAM and 64-QAM, respectively
Summary
As the quadrature phase shift keying (QPSK) modulation based 100G products are being commercialized, research interests are moving on to the generation optical transport systems with spectrally efficient modulation formats such as 16-quadrature amplitude modulation (QAM) [1] and 64-QAM [2]. The Viterbi and Viterbi algorithm is well-established for QPSK systems attributed to its high laser linewidth tolerance and reasonable computational complexity [3, 5]. It is not suitable for higher order QAM unless modifications are made, e.g. QPSK partitioning for 16-QAM [6, 7]. We first numerically demonstrate that the proposed algorithm achieves a comparable linewidth tolerance to the BPS algorithm for QPSK, 16-QAM and 64-QAM, respectively. The complexity of our algorithm is discussed, showing a significant reduction compared to BPS algorithm
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