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Title: High sensitivity optical digital pulse position modulation systems.
Author: Cryan, Robert Anthony.
Awarding Body: University of Huddersfield
Current Institution: University of Huddersfield
Date of Award: 1992
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Digital pulse position modulation (PPM) is a transmission format that can be used to exchange excess channel bandwidth for improved receiver sensitivity. This thesis is concerned with the performance of digital PPM for use in optical fibre systems such that increased single-span transmission distances can be achieved. It includes a literature survey and a thorough theoretical investigation into uncoded directly detected and coherently detected digital PPM, along with an evaluation of forward error correction coded PPM. Original contributions are described for digital PPM systems employing PIN-BJT transimpedance and PIN -FET high impedance pre-amplifiers. In the PIN -BJT case, a new analysis is presented that accounts for the band-limiting effect of the preamplifier and the non-white noise power spectral density, resulting from equalisation. For the PIN-FET, a causal noise-whitening filter is considered and the factors that limit the maximum bit-rate determined. By using an upper Chernoff Bound to the average binary error probability, results are calculated for APD-BJT and APD-FET PPM systems. The practical implementation of the optimal PPM filter is considered and two novel techniques are described for automating the realisation process. Coherent PPM is investigated and new work is presented for Reed-Solomon coded homodyne PPM. The influence of the Reed-Solomon code rate on receiver sensitivity is studied and it is shown that a 3/4 code rate leads to optimum sensitivity. Digital PPM employing soliton pulses is examined and it is shown that, under ideal conditions, a higher bit-rate than PCM can be achieved. The influence of timing jitter, associated with soliton pulse energy fluctuations and the Gordon-Haus effect, on the performance of digital PPM is investigated. The simplification of the PPM pre-detection filter is studied and a range of suboptimum filters investigated. The calculations demonstrate that the optimal predetection filter can be replaced by a simple 3rd order filter without incurring a severe sensitivity penalty. The sensitivity results of the various digital PPM systems investigated in this thesis are compared to those of equivalent PCM systems. It is illustrated that digital PPM offers an improvement of between 5-10 dB depending upon which coding format/ detection technique is employed. This represents an increase in transmission distance of 25-50 km and demonstrates that digital PPM is a promising modulation format and has potential for future high performance telecommunication routes.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Optical fibre communications Communication Optics