title: Phase noise tolerance study in coherent optical circular QAM transmissions with Viterbi-Viterbi carrier phase estimation.
abstract: We present a performance evaluation of a non-conventional approach to implement phase noise tolerant optical systems with multilevel modulation formats. The performance of normalized Viterbi-Viterbi carrier phase estimation (V-V CPE) is investigated in detail for circular m-level quadrature amplitude modulation (C-mQAM) signals. The intrinsic property of C-mQAM constellation points with a uniform phase separation allows a straightforward employment of V-V CPE without the need to adapt constellation. Compared with conventional feed-forward CPE for square QAM signals, the simulated results show an enhanced tolerance of linewidth symbol duration product (ΔνTs) at a low sensitivity penalty by using feed-forward CPE structure with C-mQAM. This scheme can be easily upgraded to higher order modulations without inducing considerable complexity.
authors.forename: Sebastian Ortega
authors.initials: SO
authors.lastname: Zafra
authors.forename: Xiaodan
authors.initials: X
authors.lastname: Pang
authors.forename: Gunnar
authors.initials: G
authors.lastname: Jacobsen
authors.forename: Sergei
authors.initials: S
authors.lastname: Popov
authors.forename: Sergey
authors.initials: S
authors.lastname: Sergeyev