title: Low-complexity feed-forward carrier phase estimation for M-ary QAM based on phase search acceleration by quadratic approximation.
abstract: Blind phase search (BPS) algorithm for M-QAM has excellent tolerance to laser linewidth at the expense of rather high computation complexity (CC). Here, we first theoretically obtain the quadratic relationship between the test angle and corresponding distance matric during the BPS implementation. Afterwards, we propose a carrier phase estimation (CPE) based on a two-stage BPS with quadratic approximation (QA). Instead of searching the phase blindly with fixed step-size for the BPS algorithm, QA can significantly accelerate the speed of phase searching. As a result, a group factor of 2.96/3.05, 4.55/4.67 and 2.27/2.3 (in the form of multipliers/adders) reduction of CC is achieved for 16QAM, 64QAM and 256QAM, respectively, in comparison with the traditional BPS scheme. Meanwhile, a guideline for determining the summing filter block length is put forward during performance optimization. Under the condition of optimum filter block length, our proposed scheme shows similar performance as traditional BPS scheme. At 1 dB required E(S)/N(0) penalty @ BER = 10(-2), our proposed CPE scheme can tolerate a times symbol duration productΔf⋅T(S) of 1.7 × 10(-4), 6 × 10(-5) and 1.5 × 10(-5) for 16/64/256-QAM, respectively.
authors.forename: Meng
authors.initials: M
authors.lastname: Xiang
authors.forename: Songnian
authors.initials: S
authors.lastname: Fu
authors.forename: Lei
authors.initials: L
authors.lastname: Deng
authors.forename: Ming
authors.initials: M
authors.lastname: Tang
authors.forename: Perry
authors.initials: P
authors.lastname: Shum
authors.forename: Deming
authors.initials: D
authors.lastname: Liu