Capacity Bounds under Imperfect Polarization Tracking
Journal article, 2022
In optical fiber communication, due to the random variation of the environment, the state of polarization (SOP) fluctuates randomly with time leading to distortion and performance degradation. The memory-less SOP fluctuations can be regarded as a two-by-two random unitary matrix. In this paper, for what we believe to be the first time, the capacity of the polarization drift channel under an average power constraint with imperfect channel knowledge is characterized. An achievable information rate (AIR) is derived when imperfect channel knowledge is available and is shown to be highly dependent on the channel estimation technique. It is also shown that a tighter lower bound can be achieved when a unitary estimation of the channel is available. However, the conventional estimation algorithms do not guarantee a unitary channel estimation. Therefore, by considering the unitary constraint of the channel, a data-aided channel estimator based on the Kabsch algorithm is proposed, and its performance is numerically evaluated in terms of AIR. Monte Carlo simulations show that Kabsch outperforms the least-square error algorithm. In particular, with complex, Gaussian inputs and eight pilot symbols per block, Kabsch improves the AIR by 0.20 to 0.30 bits/symbol throughout the range of studied signal-to-noise ratios.
multimode fiber
decision-directed least mean square
Achievable information rate
state of polarization
least square error
Channel estimation
Symbols
polarization-mode dispersion
Probability density function
capacity
Signal processing algorithms
channel estimation
mutual information
constant modulus algorithm
space-division multiplexing
lower bound
Optical fiber dispersion
Mutual information
multicore fiber
Optical fiber communication
Kabsch algorithm
Author
Mohammad Farsi
Chalmers, Electrical Engineering, Communication, Antennas and Optical Networks
Magnus Karlsson
Chalmers, Microtechnology and Nanoscience (MC2), Photonics
Erik Agrell
Chalmers, Electrical Engineering, Communication, Antennas and Optical Networks
IEEE Transactions on Communications
00906778 (ISSN) 15580857 (eISSN)
Vol. 70 11 7240-7249Unlocking the Full-dimensional Fiber Capacity
Knut and Alice Wallenberg Foundation (KAW 2018.0090), 2019-07-01 -- 2024-06-30.
Subject Categories
Telecommunications
Probability Theory and Statistics
Signal Processing
DOI
10.1109/TCOMM.2022.3206803