Carrier Phase Recovery Estimation Algorithms in Optical Coherent QPSK Communication System

Abstract

Increased data rate demand, driven by various Internet applications & exponential growth of electronics processing speeds were drivers behind this coherent optical communication. Optical Fiber sends out pulses of light to transmit information from one place to another. When relaying signals over long distances, light is just meant to allow mechanically coded signals to be visible to one another. Pulses of light can carry information by modulating electromagnetic carriers. Presence of Laser phase noise (LPN), induced by the signal transmission as well as by the local oscillator (local oscillator phase noise), causes fluctuation in intensity and laser output electrical field deviations that leads to degraded Signal-to-Noise Ratio (SNR). In a Coherent transmission system, it is unavoidable to suffer from these phase noise problems which is quite common to experience. Thus, carrier phase recovery (CPR) method is used in coherent systems where LPN is present. In this research, evaluation of relationship between the symbol error rate (SER) and input power in two different carrier phase recovery estimate (CPE) algorithms in optical coherent QPSK optical communication system were studied. As a result, based on the simulations done we can conclude that pilot-aided feedforward recovery is the best algorithm in terms of SER over input power for the two algorithms.