Abstract
A novel two-stage n-PSK partitioning carrier phase recovery (CPR) scheme for circular multilevel quadrature amplitude modulation (C-mQAM) constellations is presented. The first stage of the algorithm provides an initial rough estimation of the received constellation, which is utilized in the second stage for CPR. The performance of the proposed algorithm is studied through extensive simulations at the forward error correction bit error rate targets of 3.8 × 10−3 and 1 × 10−2 and is compared with different CPR algorithms. A significant improvement in the combined linewidth symbol duration product (ΔνTs) tolerance is achieved compared to the single-stage n-PSK partitioning scheme. Superior performance in the ΔνTs tolerance compared to the blind phase search algorithm is also reported. The relative improvements with respect to other CPR schemes are also validated experimentally for a 28-Gbaud C-16QAM back-to-back transmission system. The computational complexity of the proposed CPR scheme is studied, and reduction factors of 24.5 | 30.1 and 59.1 | 63.3 are achieved for C-16QAM and C-64QAM, respectively, compared to single-stage BPS in the form of multipliers | adders.
Highlights
High-order modulation formats together with coherent detection and digital signal processing (DSP) have attracted significant attention to increase spectral efficiency in coherent optical transmission systems [1]
Algorithm [2] and the N-th power approach [3] have typically been proposed for carrier phase recovery (CPR) in square multilevel quadrature amplitude modulations (Sq-mQAM) [4,5,6]
A novel two-stage CPR scheme for circular multilevel quadrature amplitude modulation (C-mQAM) constellations based on the n-PSK partitioning algorithm is presented
Summary
High-order modulation formats together with coherent detection and digital signal processing (DSP) have attracted significant attention to increase spectral efficiency in coherent optical transmission systems [1]. Carrier phase recovery (CPR) algorithms play a key role in these systems for the estimation and compensation of the phase noise induced by free running lasers. High-order modulation formats impose stringent requirements on the performance of these algorithms, as the distance between constellation points reduces with the increase in modulation order. The BPS algorithm achieves a high phase noise tolerance, it requires a large computational complexity especially for high-order modulations where the required number of test phases increases. The N-th power concept requires less hardware complexity but comes at the expense of a poorer phase noise tolerance, as the relative number of suitable constellation points for phase estimation decreases with
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