Generalized data-aided multi-symbol phase estimation for improving receiver sensitivity in direct-detection optical m-ary DPSK

Abstract

We present a generalized framework of data-aided multi-symbol phase estimation (MSPE) for improving the receiver sensitivity of direct-detection optical m-ary differential phase-shift keying (DPSK) through the extraction of a more accurate phase reference. Derivations of the data-aided MSPE algorithms for quaternary DPSK (DQPSK), 8-ary DPSK, m-ary DPSK, and DPSK/ASK are provided. Simulations show that receiver sensitivity improvements of over 2 dB can be obtained with the data-aided MSPE, enabling the performances of direct-detection m-ary DPSK signals to approach those of coherent homodyne-detection without resorting to an optical local oscillator. Performance improvements in nonlinear transmission are briefly discussed, and an electronic nonlinear phase shift compensation scheme is introduced for DPSK/ASK. Also presented is a simple yet universal receiver platform for m-ary DPSK consisting of just one pair of optical I/Q demodulators and a digital signal processing unit.