Low complexity carrier-phase estimation based on sign-error modified CMA for 16-QAM coherent optical receivers

Carrier-phase estimation (CPE) is one of the key elements of the digital signal processing (DSP) unit of a coherent optical receiver. CPE is required to eliminate the effect phase noise, mainly stemming from transmitting laser and local oscillator (LO). In this paper, a simple CPE scheme for 16-QAM digital coherent receiver is proposed which is based on coordinate transformation and sign-error modified constant-modulus algorithm (CMA). Such CPE can be achieved with very low implementation complexity. Performance of the proposed CPE scheme is analyzed with intensive computer simulation. For a 32-Gbaud 16-QAM system, the combined laser linewidth tolerance of more than 2 MHz is found for 1-dB sensitivity penalty.