Power line communication systems for industrial control applications

For almost as long as the electricity distribution industry itself has existed, so also has the idea of utilising the transmission grid, be it over a wide area or on a local basis, for the transmission of 'intelligence'. This might be in the form of voice transmissions, or for the purposes of monitoring or controlling electrical devices attached to the network. This thesis specifically concerns itself with the potential applications of power-line-carrier (PLC) communications technology within the field of industrial plant/equipment control, as it is within this field that the author works. We look at the entire subject area of industrial control, starting from a historical viewpoint, and consider the special needs and requirements that a proposed PLC solution must offer for this application, especially based on the noise conditions likely to be experienced on a `real' power line. A proposal is made for a `Power Bus', intended for use within certain areas of industrial control, and decisions are made based on the projected link response times for such applications. The experimental phase of the research is practical in nature and consists of a raft of tests and evaluations of the performance of power line modem technologies, under controlled and repeatable noise conditions. To complement these results, further tests are carried out under `real world' conditions, within an actual factory environment. Based on the results of all of these tests, the suitability of a PLC solution for this type of industrial control application is considered. The Thesis concludes with a look at recent developments in, as well as the future of, Power Line Communication techniques

A distributed control system for the St Andrews twin photometric telescope

Many astronomers require large amounts of observational data to solve astrophysical problems and to validate theoretical hypotheses. It is therefore imperative that both the observer and telescope work efficiently, maximising data collection whilst minimising object selection and acquisition time. One method in which this can be achieved is through telescope automation. The advent of cheap integrated process controllers enables the system designer to realise novel control system architectures which were previously prohibitive to all but the largest of sites. This thesis reviews the development of processor based control systems in the astronomical and industrial environment and compares distributed and centralised control system architecture. It describes the design and construction of one such distributed control system for the St Andrews Twin Photometric Telescope

Linearization techniques to suppress optical nonlinearity

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.This thesis is shown the implementation of the linearization techniques such as feedforward and pre-distortion feedback linearization to suppress the optical components nonlinearities caused by the fibre and semiconductor optical amplifier (SOA). The simulation verified these two linearization techniques for single tone direct modulation, two tone indirect modulation and ultra wideband input to the optical fibre. These techniques uses the amplified spontaneously emission (ASE) noise reduction in two loops of SOA by a feed-forward and predistortion linearizer and is shown more than 6dB improvement. Also it investigates linearization for the SOA amplifier to cancel out the third order harmonics or inter-modulation distortion (IMD) or four waves mixing. In this project, more than 20 dB reductions is seen in the spectral re-growth caused by the SOA. Amplifier non-linearity becomes more severe with two strong input channels leading to inter-channel distortion which can completely mask a third adjacent channel. The simulations detailed above were performed utilizing optimum settings for the variable gain, phase and delay components in the error correction loop of the feed forward and Predistortion systems and hence represent the ideal situation of a perfect feed-forward and Predistortion system. Therefore it should be consider that complexity of circuit will increase due to amplitude, phase and delay mismatches in practical design. Also it has describe the compatibility of Software Defined Radio with Hybrid Fibre Radio with simulation model of wired optical networks to be used for future research investigation, based on the star and ring topologies for different modulation schemes, and providing the performance for these configurations

Direct sequence spread spectrum techniques in local area networks

This thesis describes the application of a direct sequence spread spectrum modulation scheme to the physical layer of a local area networks subsequently named the SS-LAN. Most present day LANs employ erne form or another of time division multiplexing which performs well in many systems but which is limited by its very nature in real time, time critical and time demanding applications. The use of spread spectrum multiplexing removes these limitations by providing a simultaneous multiple user access capability to the channel which permits each and all nodes to utilise the channel independent of the activity being currently supported by that channel. The theory of spectral spreading is a consequence of the Shannon channel capacity in which the channel capacity may be maintained by the trading of signal to noise ratio for bandwidth. The increased bandwidth provides an increased signal dimensionality which can be utilised in providing noise immunity and/or a simultaneous multiple user environment: the effects of the simultaneous users can be considered as noise from the point of view of any particular constituent signal. The use of code sequences at the physical layer of a LAN permits a wide range of mapping alternatives which can be selected according to the particular application. Each of the mapping techniques possess the general spread spectrum properties but certain properties can be emphasised at the expense of others. The work has Involved the description of the properties of the SS-LAN coupled with the development of the mapping techniques for use In the distribution of the code sequences. This has been followed by an appraisal of a set of code sequences which has resulted in the definition of the ideal code properties and the selection of code families for particular types of applications. The top level design specification for the hardware required in the construction of the SS-LAN has also been presented and this has provided the basis for a simplified and idealised theoretical analysis of the performance parameters of the SS-LAN. A positive set of conclusions for the range of these parameters has been obtained and these have been further analysed by the use of a SS-LAN computer simulation program. This program can simulate any configuration of the SS-LAN and the results it has produced have been compared with those of the analysis and have been found to be in agreement. A tool for the further analysis of complex SS-LAN configurations has therefore been developed and this will form the basis for further work

Investigation of wavelength tunable laser modules for use in future optically switched dense wavelength division multiplexed networks

This thesis investigates the use of fast wavelength tunable laser modules in future optically switched dense wavelength division multiplexed networks (DWDM). The worldwide demand for increasingly greater broadband access has thus far been satisfied by the use of DWDM networks, enabled by the development of the erbium doped amplifier. However as this demand continues to grow electronic switching at network nodes will become a limiting factor, creating a potential bandwidth mismatch between the fibre capacities and switching capacity. Optical switching has been proposed to overcome this electronic bottleneck and fully utilize the enormous bandwidth offered by fibre. Fast tunable lasers (TLs) are a key technology in this area, enabling fast wavelength switching. Experimental work involving the fast wavelength switching of sampled grating distributed Bragg reflector TL modules is presented. Spurious mode generation during wavelength tuning is shown to cause severe cross-channel interference on other data channels in a DWDM test bed. Bit error rate (BER) results demonstrate that a integrated semiconductor optical amplifier can greatly reduce system degradation caused by asynchronous switching of multiple TLs. This is achieved by optically blanking the laser output during channel transition for a period of 60 ns. Immediately after the blanking period a wavelength drift due to the TL module wavelength locking is found to cause cross channel interference and introduce an error floor >1 e-4 on the BER performance characteristic of an adjacent channel in a 12.5 GHz spaced DWDM network. This drift is characterised, using a selfheterodyne and a filter based approach – Error free performance is subsequently demonstrated by using an extended blanking period of 260 ns or by using subcarrier multiplexing transmission and phase selective demodulation before detection. A DWDM optical label switching system, utilizing 40 Gbit/s payload data with low data rate labels placed on a 40 GHz sub-carrier and using TL transmitters is presented. Channel performance is monitored on a static channel as a second data channel is tuned into an adjacent channel on a 100 GHz spaced grid. Error free performance is demonstrated only for the channel payload – Time resolved BER results in agreement with the TL wavelength drift are measured and demonstrate a detrimental influence of the drift on the sub-carrier label performance

Practical free-space quantum key distribution

Within the last two decades, the world has seen an exponential increase in the quantity of data traffic exchanged electronically. Currently, the widespread use of classical encryption technology provides tolerable levels of security for data in day to day life. However, with one somewhat impractical exception these technologies are based on mathematical complexity and have never been proven to be secure. Significant advances in mathematics or new computer architectures could render these technologies obsolete in a very short timescale. By contrast, Quantum Key Distribution (or Quantum Cryptography as it is sometimes called) offers a theoretically secure method of cryptographic key generation and exchange which is guaranteed by physical laws. Moreover, the technique is capable of eavesdropper detection during the key exchange process. Much research and development work has been undertaken but most of this work has concentrated on the use of optical fibres as the transmission medium for the quantum channel. This thesis discusses the requirements, theoretical basis and practical development of a compact, free-space transmission quantum key distribution system from inception to system tests. Experiments conducted over several distances are outlined which verify the feasibility of quantum key distribution operating continuously over ranges from metres to intercity distances and finally to global reach via the use of satellites