Performance and Complexity of Digital Clock Recovery for Nyquist UDWDM-PON in Real Time

We analyze the performance and the complexity of a real-time digital signal processing (DSP)-based optical network unit architecture for the digital detection of Nyquist-shaped signals in ultra-dense wavelength-division multiplexing passive optical network (UDWDM-PON) scenarios. Using field-programmable gate array-based 8-bit DSP, we experimentally demonstrate in a real-time mode operation the receiver performance in terms of Nyquist filter roll-off factor for 8×2.5 Gb/s quadrature phase-shift keying (QPSK) with 2.5 GHz of channel spacing. We analyze the performance of the linear and cubic interpolation for the clock recovery as well as the Gardner algorithm for the timing-error estimation, considering the amplitude and power formulations. The experimental evaluation shows that the linear interpolation along with the power formulation is an attractive solution for the QPSK-based UDWDM-PON, considering the tradeoff between the performance and the complexity.