Abstract
A new modulation scheme that improves the bandwidth efficiency of an optical access link is proposed in this paper. It is implemented using non-orthogonal frequency shift keying (FSK) and quadrature amplitude modulation (QAM) simultaneously. We call the proposed technique non-orthogonal frequency quadrature amplitude modulation (NOFQAM). Especially, non-orthogonal FSK based on digital signal processing (DSP) is proposed for the first time. DSP-aided non-orthogonal FSK allows us to select RF carrier frequency irrespective of the channel bandwidth to allocate FSK symbols, unlike the existing orthogonal FSK. The non-orthogonality is implemented using a sequential correlation, where a received NOFQAM signal is correlated with only one RF carrier at a time by using DSP. After the sequential correlation is completed, both the FSK and the QAM symbols are recovered successfully and merged to generate the NOFQAM symbols. For experimental verification, a 20-km optical access link, which can transmit a 64-NOFQAM signal sampled at 10 Gsample/s, is implemented. We observed no increase in occupied channel bandwidth and a power penalty <0.5 dB compared to the 16-QAM scheme. A bit error rate lower than 10−11 was obtained for the frequency spacing considered herein, which corresponds to 3% of the used RF carrier (1.5 GHz) when there are 50 sampling points per 64-NOFQAM symbol.
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Acknowledgements
This research was partly supported by the ICT program of MSIP/IITP, Republic of Korea [B0101-16-1347] and partly supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2016R1D1A1B01008748). Also, Sang Min Yoon was supported by the Institute for Information & Communications Technology Promotion (IITP) grant funded by the Korean government (MSIP) (No. R0115-15-1009).
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Won, YY., Yoon, S.M. & Seo, D. Optical access transmission with improved channel capacity using non-orthogonal frequency quadrature amplitude modulation. Opt Quant Electron 49, 78 (2017). https://doi.org/10.1007/s11082-017-0892-z
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DOI: https://doi.org/10.1007/s11082-017-0892-z