Abstract
This paper presents a novel digital feedforward carrier recovery algorithm
for arbitrary $M$-ary quadrature amplitude modulation ($M$-QAM) constellations in an intradyne
coherent optical receiver. The approach does not contain any feedback loop
and is therefore highly tolerant against laser phase noise. This is crucial,
especially for higher order QAM constellations, which inherently have a smaller
phase noise tolerance due to the lower spacing between adjacent constellation
points. In addition to the mathematical description of the proposed carrier
recovery algorithm also a possible hardware-efficient implementation in a
parallelized system is presented and the performance of the algorithm is evaluated
by Monte Carlo simulations for square 4-QAM (QPSK), 16-QAM, 64-QAM, and 256-QAM.
For the simulations ASE noise and laser phase noise are considered as well
as analog-to-digital converter (ADC) and internal resolution effects. For
a 1 dB penalty at ${\rm
BER} = 10^{- 3}$, linewidth times symbol duration products
of $4.1\times 10^{- 4}$ (4-QAM), $1.4\times
10^{- 4}$ (16-QAM), $4.0\times
10^{- 5}$ (64-QAM) and $8.0\times 10^{- 6}$ (256-QAM) are tolerable.
© 2009 IEEE
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