The communication Networks of the future will require signal switching in the optical domain to avoid the inherent speed bottleneck of optical-electronic-optical conversions. This has resulted in an intense research effort in this area. Of particular interest are wavelength division multiplexing (WDM) and optical time division multiplexing (OTDM). The latter offers the advantage that it operates over a single wavelength, removing the problems associated with dispersion in fibre systems whilst the former operates over a number of wavelengths. This thesis concentrates on the modelling and simulation of one particular system: the asymmetric semiconductor laser amplifier loop mirror (ASLALOM) for OTDM.Initially, a literature review looks at the theory of laser operation which complements the following chapter on laser amplifiers. A review of current optical switching devices will be examined next with regard to switching speeds, crosstalk and the possibility of integration. Also wavelength division multiplexing and time division multiplexing are reviewed, comparing the different systems in current use. At the present time, no complete models of an asymmetric semiconductor laser amplifier loop mirror have been developed. The intention of this work is to determine the equations necessary for a model to be developed and thus enable the system to be simulated. Computer modelling of a system prior to implementation is advantageous in all aspects of engineering. As this system is still confined to the laboratory a model would complement any practical work and identify critical design parameters. In this work the Travelling Wave Semiconductor Laser Amplifier (TWSLA) is first modelled in a form which is appropriate for the asymmetric semiconductor laser amplifier loop mirror architecture. The simulations are then used to demonstrate the switching speeds for different configurations and identify any areas needing further work, such as crosstalk, birefringence and polarisation, a method for multi-channel output is also presented. A further aim is to lay a foundation for future work to enable the system to be fully characterised with regard to noise, dispersion and integration.

Fingerprinting methods for positioning is an area of great interest, this thesis presents a study on the Adaptive Enhanced Cell Identity (AECID) fingerprinting method for positioning. By creating a map of the radio characteristics in a geographical region, the AECID method is able to locate a UE by gathering information of the radio conditions of its current location. By performing positioning in this manner, there is no need for additional signaling, which is a better usage of the radio resources. This thesis presents a new approach for the creation of fingerprints together with alternative methodology at each step proposed by the AECID method. These alternatives are implemented and evaluated for real and simulated scenarios. Accuracy performance metrics are discussed based on different formats supported for reporting position. The alternatives presented in this thesis will show not only an enhancement on the accuracy levels but most importantly, the impact of each step on the final performance of the method.

This thesis is concerned with a detailed study of laser nonlineanties and the implications for multichannel subcamer multiplexed fibre optic systems. In view of the limitations of previously reported analytic treatments of laser nonlinear distortion, a considerable part of the study is dedicated to the development of modelling and analytic tchniques suitable for practical system design and optimisation The single-mode rate equations provide an adequate basis for the analysis of laser intnnsic dynamic distortion and relative intensity noise and their dependence on device parameters and operating conditions. The Volterra series method of nonlinear system theory is then applied and an analytical model is obtained that describes the nonlineanty in the frequency domain by a set of nonlinear transfer functions This method provides a ngorous analytic nonlinear model that takes into account all the intermodulation products up to third-order as determined by the rate equations Moreover, the laser response to the important case of a sum of narrow-band signals is considered and under certain conditions, which are valid for the majority of systems of interest, the intermodulation power spectral density of the distortion products is determined This enables an accurate evaluation of the impact on the overall system performance of laser intrinsic distortion and optimum overall performance is identified after including the noise introduced in the detection process The relative importance of laser intnnsic distortion and clipping-istortion is also examined. Finally, the analytic model is used to investigate design constraints and the overall system performance of relevant SCM systems. Case studies are considered that demonstrate the applicability of the method devised.

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The aim of this project is to analyze a data log of wireless packet traffic, and to produce: (1) models for dynamic fluctuations in wireless channel and link quality, and, (2) a design for real-time communications over the given wireless channel. The models and designs are useful in setting up real-time communications in a vehicular test track (www.astazero.com). The data log came from experimental measurements at the test track. From this data, we fitted simple models for packet losses and retransmissions in the wireless communication system. These models took the form of a combination of a statistical model for the packet losses, with a deterministic model for retransmissions of lost packets. Such fitted models can be used to predict the average quality of vehicle position monitoring based on periodically transmitted position information. Such predictions help us decide the feasibility of safe and reliable conduct of testing with two or more moving test objects.

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