Electrical and Electronic Engineering - Theses
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ItemTechnologies for millimetre-wave fibre-radio systems( 1999)The recent advances in mobile wireless technology have increased the need for more transmission bandwidth to accommodate for future telecommunication services. The millimetre-wave (mm-wave) hybrid fibre-radio system is one of the potential technologies for provision of these broadband services. With the advent of low-loss and high bandwidth optical fibre in telecommunication networks, it is an ideal medium for distributing the broadband mm-wave information. In addition to the provision of broadband services and high capacity, the hybrid fibre-radio system also enables customer mobility. This thesis investigates the performance of different architectures for distributing radio signals over fibre in mm-wave fibre-radio applications. In particular, networks incorporating radio signal distribution as mm-wave frequency and as baseband data over fibre are investigated. There have been many different downlink implementations incorporating mm-wave radio signal distribution over fibre for mm-wave fibre-radio system, however there has been little focus on the uplink path. For the first time a simple mm-wave uplink path in a mm-wave fibre-radio system is presented in this thesis which incorporates direct modulation of a multi-section mode-locked distributed-Bragg reflector (DBR) laser at the base station. The performance of the multi-section laser as a mm-wave optical transmitter is presented, and a detailed characterisation of the multi-section laser stabilised via hybrid mode-locking at fundamental and subharmonic frequencies is carried out. The uplink path implementation using the multi-section laser is further extended to incorporate multi-channel transmission. Efficient multi-channel transmission incorporating the multi-section laser requires the separation of the stabilisation and modulation functions of the drive signal applied to the laser. Two different stabilisation techniques namely fundamental hybrid and subharmonic synchronous mode-locking are considered for multichannel operation, and their performance investigated. A detailed theoretical analysis is then presented that quantifies the impact of fibre chromatic dispersion-induced rf power penalties when using the multi-section laser to transmit mm-wave frequencies over fibre. The model is also used to study the performance of the laser as a function of its operating conditions. The thesis also presents a detailed investigation of the implementation and performance of a mm-wave hybrid fibre-radio system with baseband data delivery over optical fibre, a technique which has not been previously reported. The first realisation of a mm-wave fibre-radio system with baseband data delivery over the optical fibre network is presented. This system incorporates a novel modulation scheme for simultaneous transmission of baseband digital data and remote local oscillator (LO) signal delivery. The modulation scheme exhibits several unique features including the use of a single dual-electrode Mach-Zehnder modulator and the delivery of the LO signal is such a way that it is not affected by fibre dispersion. A full-duplex mm-wave fibre-radio system comprising broadband baseband data transmission is implemented with custom-designed mm-wave diplexers and antennas. A theoretical model is also developed to quantify the performance of the baseband data modulation scheme. The analysis is used to determine the sensitivity of the modulator input parameters on the system performance and good agreement is obtained between the model and measurements of the fibre-radio link incorporating baseband data modulation.
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ItemBroadband millimetre-wave fibre-radio access networks( 2000)Millimetre-wave (mm-wave) fibre-radio networks are emerging as a promising technology for providing customer access to future interactive broadband multimedia services. At mm-wave frequencies, propagation effects through air limit radio cell sizes so an implementation of a mm-wave fibre-radio network would require large numbers of simple, low-cost antenna base stations (BSs). To achieve this goal, it is advantageous to share some of the electronic functionality and processing at a central office (CO) rather than at each BS, with the connection between the CO and BSs provided by an optical fibre network The integration of the optical and radio technologies poses a new set of technical challenges. These include mm-wave generation schemes using optics, effects of fibre distribution on radio signals, implementation of low cost BSs, network architectures that provide lower cost links with improved system performance, and system modelling techniques. This thesis advances each of these areas. The optical chirp associated with modulation is shown to be able to improve fibre link performances that are usually limited by chromatic dispersion. Furthermore, a novel modulation scheme generating an optical single sideband- with-carrier (OSSB-WC) spectrum and a novel frequency tripling self-heterodyning scheme are shown to also significantly reduce the effects of fibre dispersion. These optical sources are also inc1uded in demonstrations of a number of novel bi-directional links. A descriptive analysis is used to determine the expected system performance using each technique. This same analysis is extended to predict component specifications and system algorithms that are necessary to achieve certain levels of system performance in a variety of mm-wave fibre-radio link scenarios. The thesis also examines the optical-radio interface and determines suitable techniques that can be used to transport different radio modulation formats, inc1uding multilevel QAM and spread spectrum signals. The physical optoelectronic interface is also considered and a novel system function and hybrid integrated circuit package design is described. A major contribution of this thesis is a detailed investigation into wavelength-division-multiplexing (WDM) based mm-wave fibre-radio networks. Simple uni-directional ring/bus and star-tree architectures are proposed and implemented and the deterioration effects of linear and homodyne crosstalk are also considered so that the limitations of each architecture can be determined. The final major contribution of this thesis is to examine the modelling of mm-wave fibre-radio systems, which is especially important for dimensioning networks. One critical parameter that does require consideration in the models is the deterioration of signal quality from intermodulation distortion in multi-carrier systems. This thesis extends conventional fixed load models that have been developed for low frequency fibre-radio networks and applied them to mm-wave systems. This fixed load model was the first attempt to link physical layer limitations to system performance. While the model derived is simple and fast to simulate, it does not model the behaviour of users in the system. In this thesis, the first model to link physical layer limitations and user behaviour has been implemented and the significant changes in the expected system performance are shown. The model can also be used to predict the required component specifications and for examining system algorithms that are necessary to achieve certain levels of system performance in a variety of mm-wave fibre-radio link scenarios.