Optical fiber is capable of providing the solution to the need of high bandwidth communication. The main degradation to the optical signal integrity in single mode fibers (SMFs) is chromatic dispersion (CD). The effect of CD is pulse spreading which in turn leads to inter-symbol interference (ISI), thus increasing the bit error rate (BER) of the system. This paper presents a CD compensation technique that utilizes a parallel optical all pass filter (p-OAPF), where the design is based on the inverse phase response of the SMF. The p-OAPF is based on a class of all-pass filter. Simulation results of the proposed technique show an increase in the repeater-less length of a point-to-point optical communication system by 3 times with Gaussian pulses at 10 Gb/s and BER of 10-9. A passive infinite impulse response filter structure is proposed for the implementation of the p-OAPF.

This paper analyses the merits of adaptive threshold detection (ATD) over fixed threshold detection (FTD) as a means to reduce the impact of ambient shot noise on wireless infrared communication links. Original analytic details are provided to allow for an accurate sensitivity account of an optical wireless receiver that employs either ATD or FTD. Proposals towards the implementation of adaptive threshold detection are outlined with considerations on their respective benefits and drawbacks.

This paper proposes new divergence detection techniques for implementation within in-service non-intrusive measurement devices (INMDs) in public switched telephone networks (PSTNs). The in-service non-intrusive measurement system of interest is used to monitor the delivered quality of speech (QoS) by monitoring the echoes in the telephony network. INMDs are usually based on a class of least mean square (LMS) digital adaptive filters (DAFs). The performance criterion is defined by the modelling convergence rate derived from the optimal Wiener weights, and the excitation for the DAFs is conversational speech. Four types of divergence detectors (DD) are proposed. These are energy divergence detectors (EDD), log energy divergence detectors (LDD), zero crossing divergence detectors (ZDD) and autocorrelation coefficient divergence detectors (ADD). The proposed DDs are based on the detection of voiced/unvoiced/silence periods and as such act as pattern classifiers. Experimental observations have shown that divergence occurs during the low energy unvoiced segments in high-noise environments. The tap-weight coefficients of the DAF are updated with the new value during the voiced segment while the update of the tap-weight coefficients during unvoiced segments of the speech is frozen. This result is then compared with the perfect divergence detector, which employs the Wiener weight theory. The DD techniques reported produce a significant improvement in the system's performance in a noise-impaired environment. Over one second adaptation (8000 samples) the energy divergence detector, the log energy divergence detector, the autocorrelation divergence detector and the zero crossing divergence detector gave model improvements of 16.93 dB, 15.81 db, 12.48 dB and 11.62 dB respectively at echo to noise ratio (e/N) of 0 dB. The proposed DDs compare well with the ideal (nonimplementable) Wiener DD which gives an improvement of 20.92 dB.

Code division multiple access (CDMA) allows simultaneous access to network facilities and enables independent and concurrent communication among the users. We propose a hybrid pulse position modulation (PPM) with CDMA. The hybrid can usefully be exploited in optical wireless and optical fibre networks. Original results are presented for the scheme under various coding schemes (optical orthogonal codes, prime codes and extended prime codes). The implications of using each coding scheme are evaluated in terms of error rate, number of users and bandwidth requirements.

Digital pulse position modulation (PPM) has been shown to be attractive for implementation over the optical fibre channel when the laser transmitters are average power limited and the channel bandwidth is abundant. The synchronization requirements for optical fibre PPM however have not yet been addressed. We present an original mathematical formulation for the problem of spectral prediction and synchronization in PPM based on the cyclostationary properties of the format. Further we predict the conditions required to achieve and optimize both slot and frame synchronization. The major system parameters including the modulation index, data probability distribution and pulse shape are catered for and used in the analysis. A novel technique, capable of coping with the different PPM word sizes, is presented and used to achieve frame phase extraction directly from the PPM stream. Appropriate mathematical models are developed and used to predict the spectral properties at the output of the frame phase synchronizer. Original practical results measured on a PPM system are presented and shown to agree with the theoretical models and predictions to within 1 dB.>

The optimum pre-detection filter for a PPM signal comprises a matched filter in cascade with a proportional-derivative-delay network. This paper addresses the problem of realising such a filter and in particular, describes a technique for synthesising the matched filter on microstrip.>

An optimum pre-synchronisation filtering strategy is proposed and analysed in the context of optical fibre pulse position modulation (PPM). Under Ideal synchronisation, the PPM system is shown to outperform the equivalent PCM system sensitivity. The PPM system performance penalty due to jitter is evaluated and an original expression is presented for the jittered PPM format power spectral density (PSD). The performance improvement obtained by using the proposed filtering is ascertained and the system parameters are specified for optimum performance.>

An original implementation for a PPM correlator-synchroniser is reported. The PPM frame synchronisation is achieved on both the frequency and phase levels. The proposed technique does not suffer any of the limitations of the previous methods such as the bit rate and sensitivity penalties. Original theoretical and practical results are reported for the synchroniser while a performance evaluation is carried out. An original method for pattern dependency elimination is proposed, implemented and characterised.>