DSP techniques for optical coherent receivers.
Doctoral thesis, UCL (University College London).
The design of modern optical communication systems seeks a solution to the optimisation of bandwidth utilisation. Despite the inherent simplicity offered by intensity modulation direct detection (IM-DD), it is evident that this conventional binary scheme cannot fully explore in full the theoretical achievable capacity of optical systems. A lot of research activity is directing towards coherent detection techniques, already investigated in the early nineties, but then abandoned because of IM-DD cost efficiency and technological ease with erbium-doped fibre amplifiers. Coherent techniques require a more complex receiver architecture, but allow higher receiver sensitivity and more spectrally efficient modulation formats. With these advanced modulation formats it is possible to better exploit the wide bandwidth offered by the optical channel so that the total bit rate can be increased keeping affordable baud rates. Coherent detection is therefore a promising candidate that will most likely represent the future of optical communication systems. The aim of this thesis is to investigate coherent detection algorithms empowered by advanced digital signal processing (DSP) techniques for multilevel modulation formats to improve the performance of coherent systems. We first review the basic concepts of coherent detection. Algorithms for the compensation of imperfections in the receiver front-end are investigated. Characterisation of time-interleaved ADCs is presented and it is shown that the imperfections can be mitigated using DSP. The digital compensation of quadrature imbalance due to imperfections in a digital coherent receiver is then discussed. Blind equalisation techniques for the 16-QAM modulation format are also presented. Next, algorithms to compensate for frequency offset and laser phase noise for a 16-QAM coherent system are discussed. We consider a second-order recursive digital loop to track frequency offset from the transmitter laser and the LO. Finally, the thesis examines the interaction between the LO phase noise and electronically-compensated chromatic dispersion.
|Title:||DSP techniques for optical coherent receivers|
|Additional information:||Permission for digitisation not received|
|UCL classification:||UCL > School of BEAMS > Faculty of Engineering Science > Electronic and Electrical Engineering|
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