Abstract
In this study, we demonstrated generation and transmission of 114 Gbaud and 126 Gbaud faster-than-Nyquist (FTN) discrete Fourier transform-spread (DFT-spread) quadrature phase shift keying orthogonal frequency division multiplexing (QPSK-OFDM) with 88-Gsa/s sampling rate digital-to-analog converters (DACs) experimentally. It is the first time to realize 400G FTN DFT-spread QPSK-OFDM signal per optical carrier for metro and regional applications, which will be a solution for network operators to address the issue of increasing bandwidth derived from the rapid popularization of mobile Internet and the wide application of IoT (Internet of Things technology). Delay-and-add filter (DAF) is adopted to realize frequency shaping at the transmitter to keep higher portions of energy of signal at low frequencies, which makes the OFDM much more robust to strong filtering effect. After pre-equalization, bit error rate (BER) performance of 114 GBaud and 126 GBaud FTN DFT-spread QPSK-OFDM has been significantly improved, and maximum-likelihood sequence estimation (MLSE) shows a better effect than binary decoding in the aspect of against the inter symbol interference (ISI) introduced by spectrum compression. The effective bit rate of dual polarization 126 Gbaud FTN DFT-spread QPSK-OFDM which is generated with 88 GSa/s sampling rate is 410.08 Gb/s, to the exclusion of all overhead including TSs, cyclic prefix (CP), and 20% forward error correction (FEC) coding. We successfully transmit 8 × 400 Gbit/s FTN DFT-spread QPSK-OFDM signal generated from 88 Gsa/s sampling rate DAC over 420 km single mode fiber (SMF) with the BER under 2.4 × 10−2.
Highlights
Faster-than-Nyquist (FTN) is extensively studied to improve the spectrum efficiency by transmitting symbols within a bandwidth less than the Nyquist bandwidth [1,2,3,4,5,6,7,8,9]
As can be seen from equation y(n) x(n) + x(n − 1), it is obvious that the input of the node y(1) is needed for the output x(0) at the first moment, and we can take any value in x(0) ∈ {1, −1} because the influence of the selection of the initial state on the maximum-likelihood sequence estimation (MLSE) algorithm in the long-distance transmission is negligible
As frequency offset estimation (FOE) and phase noise estimation is realized with radio frequency pilot (RF-pilot) scheme [17], another five subcarriers around zero frequency are reserved for RF-pilot insertion, and the rest L (L = N-6)
Summary
Faster-than-Nyquist (FTN) is extensively studied to improve the spectrum efficiency by transmitting symbols within a bandwidth less than the Nyquist bandwidth [1,2,3,4,5,6,7,8,9]. In order to further improve the spectral efficiency, we integrated wavelength division multiplexing (WDM) system with FTN DFT-spread system, and increased the single-channel pay-load bit rate to more than 400G by using 88 Gsa/s sampling rate DACs. In this study, generation and transmission of 400G FTN QPSK-OFDM signal are experimentally demonstrated with single DFT-spread band to avoid multi-band ISBI. The transmitted symbols of FTN DFT-spread OFDM signal are duo/poly-binary encoded in the transmitter. As can be seen from equation y(n) x(n) + x(n − 1), it is obvious that the input of the node y(1) is needed for the output x(0) at the first moment, and we can take any value in x(0) ∈ {1, −1} because the influence of the selection of the initial state on the MLSE algorithm in the long-distance transmission is negligible. For double/multiple binary signals with a memory length of one for M 2 and 4, the performance penalty for MLSE is almost negligible when the K value is above 20
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