Carrier phase estimation for optically coherent QPSK (Technion)
Carrier Recovery (CR) is a critical component in modern digital signal processing (DSP) oriented coherent receivers for 100-400G transmission and beyond. Multiple carrier phase estimation (CPE) methods have been heretofore considered for Quadrature Phase-Shift Keying (QPSK) transmission. One of the most popular CPE techniques for QPSK coherent detection is the Viterbi&Viterbi algorithm, which is conceptually elegant, yet suffers from phase wrap-around effects, cycle slips, noise enhancement and scaled argument extraction operations.Based on Wiener-optimal and using the adaptive Multi-Symbol Delay Detection (MSDD), the carrier phase estimation technique presented here is for optically coherent QPSK transmission. MSDD carrier recovery retains some of the advantages of Differential Phase-Shift Keying systems while overcoming its sensitivity disadvantages. This highly efficient non-optimal QPSK MSDD version, with uniform coefficients, requires just a single complex multiplication used for demodulation. This reduced complexity is preferred for certain QPSK low-cost applications, generating a cleaner demodulation reference relative to other carrier-recovery methods. Moreover, the MSDD features linear (time-varying) processing, freeing it of cycle-slips and other phase unwrapping impairments. In addition, this method is preferred due to its improved resilience in the lower optical signal to noise ratio.
Simplified hardware realizations
• Nearly optimal performance for linewidths up to ~0.5 MHz and optimal performance for wider linewidths
• Multiplier-free CPE realization with negligible performance penalty
• Provides uninterrupted operation, eliminating cycle-slips and other non-linear phase-wrapping artifacts common to other methods
QPSK coherent receivers
• Quadrature amplitude modulation (QAM) coherent receivers
• Carrier frequency offset (CFO) and phase estimation
COM-1400
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