Data-aided adaptive weighted channel equalizer for coherent optical OFDM

Abstract

We report an adaptive weighted channel equalizer (AWCE) for orthogonal frequency division multiplexing (OFDM) and study its performance for long-haul coherent optical OFDM (CO-OFDM) transmission systems. This equalizer updates the equalization parameters on a symbol-by-symbol basis thus can track slight drifts of the optical channel. This is suitable to combat polarization mode dispersion (PMD) degradation while increasing the periodicity of pilot symbols which can be translated into a significant overhead reduction. Furthermore, AWCE can increase the precision of RF-pilot enabled phase noise estimation in the presence of noise, using data-aided phase noise estimation. Simulation results corroborate the capability of AWCE in both overhead reduction and improving the quality of the phase noise compensation (PNC).

A Blind Channel Estimation for 100+ Gb/s Optical IM-DD DMT Over 100-km SMF in 1550 nm

“…The difference between the proposed DF-LS CE here and ADDCE of [9], [10] can be summarized as follows: 1-DF-LS is implemented on every L C E symbols, while ADDCE is symbol-by-symbol. 2-DF-LS is based on decision feedback as opposed to ADDCE that is decision directed.…”

“…The authors of [9], [10] proposed an adaptive decisiondirected CE (ADDCE) for coherent optical OFDM applications. In ADDCE, the channel coefficients are updated symbol-by-symbol relying on the equalized signal and its decision.…”

Experimental Demonstration of Data-dependent Pilot-aided Phase Noise Estimation for CO-OFDM

“…Existing CO-OFDM phase noise compensation (PNC) may be divided into three groups, data aided (DA) [3][4][5], pilot subcarrier aided (PA) [6], and radio frequency (RF)-pilot enabled estimation [7]. RF-pilot enabled estimation is realized by inserting a RF-pilot tone in the middle of the OFDM band that can be used at the receiver to revert phase noise related impairments [7].…”

Experimental Study of a novel adaptive decision-directed channel equalizer in 28 GBaud RGI-DP-CO-OFDM transport systems

“…Following the recent surge of interest in digital signal processing (DSP) for optical fiber communications, coherent-optical orthogonal-frequency-division-multiplexing (CO-OFDM) has been intensively investigated as a possible modulation format for future uncompensated fiber optic transmission links. One of the key attributes of using DSP is the capability to send training symbols (TSs) and pilot subcarriers (PSCs) which are known to the receiver to provide data-aided channel estimation [1][2][3]. To combat dynamic changes in channel characteristics, i.e.…”

“…polarization mode dispersion (PMD), and to provide synchronization, the TSs are periodically inserted into the OFDM data symbol sequence. TSs have to be sent at a speed that is much faster than the speed of significant channel fluctuations [3,4]. TS overheads of 2% to 5% are often reported for CO-OFDM transport systems [1][2][3][4][5].…”