Oluwajobi, Festus Idowu
(2020)
Novel binary/multilevel Manchester based modulation technique for high-speed communication systems.
PhD thesis, University of Nottingham.
Abstract
A new advanced modulation format based on Manchester signalling was proposed and assessed for high-speed optical communication systems. This new advanced modulation format called Modified Manchester (MM) was derived from the combination of Manchester and Vestigial-Sideband (VSB) techniques. Its performance was assessed and compared in terms of spectral efficiency, chromatic dispersion tolerance and receiver sensitivity against Conventional Manchester (CM), Return-to-Zero (RZ) and Non-Return-to-Zero (NRZ). The spectral efficiency of the MM was enhanced by 31.3% due to the optimisation of the optical filter employed for VSB filtering. Therefore, the dispersion tolerance of MM is140 ps/nm, which is three times more than that of CM of 44 ps/nm and twice more than that of NRZ of 51.8 ps/nm and better than RZ with dispersion tolerance of 109 ps/nm at the BER of 10-9. The improvement performance was achieved without the utilisation of any dispersion compensation module or electronic equalisation. The research also examined the transmission performance of the MM modulation scheme over wavelength division multiplexing (WDM) system and compared with the CM format at the bitrate of 10 Gb/s per channel. Where MM has a better performance compared to CM in terms of tolerance against narrow optical filtering, spectral efficiency (improved by 32%) and chromatic dispersion tolerance (improved by +100 ps/nm). Sixteen wavelength channels (16 x 10 Gb/s) are modulated to provide 160 Gb/s data capacity which was successfully transmitted over 224 km standard single mode fibre (SSMF) using MM while the CM range is approximately 157 km.
Furthermore, the new multilevel Manchester-based signalling referred to as four-level Modified Manchester (4-MM) modulation and four-level Manchester Coding (4-MC) formats are proposed and demonstrated numerically for high-speed optical communication systems. Using the developed bit error rate (BER) estimation model, the performance of 4-MC and 4-MM were compared against CM modulation, binary MM and four-level amplitude modulation (4-PAM) formats in terms of receiver sensitivity, spectral efficiency and chromatic dispersion tolerance at the total bitrate of 40 Gb/s. The receiver sensitivity and the chromatic dispersion tolerance at the BER of 10-9 of the 4-MC scheme are -22 dBm and 67.5 ps/nm, respectively while for the 4-MM scheme are -21.5 dBm and 95 ps/nm, respectively. Therefore, 4-MC and 4-MM are superior to 4-PAM by 3.5 dB and 3 dB, respectively in terms of receiver sensitivity. Similarly, the results also indicate that 4-MC and 4-MM techniques are better compared with CM and binary MM in terms of spectral efficiency and chromatic dispersion tolerance. Therefore, the proposed schemes can be considered as alternatives to 4-PAM in high-speed optical access and short-reach networks where power efficiency is of critical important.
Lastly, the numerical results indicate that optical equalisation method is capable of improving the formats performance considerably. The MM format with optical equaliser at 10 Gb/s can reach 40 km with the receiver sensitivity of -18 dBm whereas at 25 Gb/s it has a receiver sensitivity of -14 dBm over 7.5 km in optical simplified access networks. Although without optical equaliser, the maximum distance realised at bitrate of 10 and 25 Gb/s are 20 km and 4 km, respectively. Moreover, the transmission distance of 4-MC and 4-MM were increased to 25 km and 27 km, respectively with the corresponding receiver sensitivity of -17 dBm and -15 dBm at 20 Gb/s. However, at the bitrate of 40 Gb/s, the 4-MC and 4-MM reached transmission distance of 6.5 km and 7.5 km, respectively while equivalent receiver sensitivity of -10 dBm and -18 dBm were observed. Whereas, the maximum distance realised by 4-MC and 4-MM without optical equaliser at 20 Gb/s are 15 km and 18 km respectively, and at 40 Gb/s, 4-MC and 4-MM are able to reach 4 km and 5.5 km, respectively for high-speed optical short-reach and access networks.
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