First experimental demonstration of 6Gb/s real-time optical OFDM transceivers incorporating channel estimation and variable power loading

Abstract

The fastest ever 6Gb/s real-time FPGA-based optical orthogonal frequency division multiplexing (OOFDM) transceivers utilizing channel estimation are experimentally demonstrated, for the first time, with variable power loading being incorporated to effectively compensate for the rapid system frequency response roll-off effect. The implemented transceivers are constructed entirely from off-the-shelf components and incorporate crucial functionalities of on-line performance monitoring and live optimization of key parameters including signal clipping, subcarrier power and operating conditions of directly modulated DFB lasers (DMLs). Real-time end-to-end transmission of a 6Gb/s 16-QAM-encoded OOFDM signal over 300m OM1 multi-mode fiber with a power penalty of 0.5dB is successfully achieved in an intensity-modulation and direct-detection system employing a DML.

Simple all-optical FFT scheme enabling Tbit/s real-time signal processing

“…They almost exclusively perform the FFT/STFT on the time-sampled signal in the electronic domain [17]. Such electronic real-time implementations are currently restricted to OFDM symbol rates of a few MBd due to speed limitations of the digital signal processor [18,19]. These symbol rates correspond to total bitrates of several Gb/s as a large number of subcarriers and higher order modulation formats are used.…”

Real-time experimental demonstration of low-cost VCSEL intensity-modulated 1125Gb/s optical OFDM signal transmission over 25km PON systems

“…It should be noted that the OOFDM transceiver architecture adopted here is very similar to those reported in [4,11,13], with real-time DSP being employed to perform functionalities such as IFFT/FFT algorithms, channel estimation, on-line performance monitoring and live parameter optimization. In comparison with the system setups reported in [4,11,13], the major differences in the current system are: (1) the use of a low-cost VCSEL for intensity modulation, (2) signal encoding in the transmitter and decoding in the receiver are performed using 32-QAM or 64-QAM. The use of these two signal modulation formats is to examine the highest achievable system performance and identify the dominant physical mechanisms limiting the maximum achievable transmission performance.…”

“…The electrical output signal from the PIN is amplified to an optimum level to provide a suitable amplitude prior to digitization by an ADC. Similar to procedures reported in [4,10,11,13,14], only 15 data-carrying subcarriers are chosen for channel estimation and data recovery.…”

Real-Time Data Transfer Based on Software Defined Radio Technique using Gnu radio/USRP

“…The reliability of OFDM systems depends on the decoder's method for obtaining channel state information (CSI) of the dispersive fading channels and compensating for channel effects like less delay spread and less Doppler spread. Several authors have tested real-time implementations of OFDM using various channel-estimation schemes [2][3][4][5]. The physical layer-capture effect, carrier sensing, and preamble detection have been studied experimentally, focusing on signal capture and the Least-Square (LS) scheme for channel estimation [2].…”

“…The physical layer-capture effect, carrier sensing, and preamble detection have been studied experimentally, focusing on signal capture and the Least-Square (LS) scheme for channel estimation [2]. Another group proposed and tested a channel-estimation scheme with pilot subcarriers and achieved low complexity, buffer-free data flow, high accuracy, small pilot bandwidth usage, and excellent stability [3][4]. These tests were implemented in real-time optical OFDM transceivers based on Field-Programmable Gate Arrays (FPGAs), which allow a three-level variable-power loading scheme.…”