Carrier Phase Recovery for Coherent Optical Transmission Systems

This thesis presents studies concerned with the evaluation of the suitablility of an optical-phase-locked-loop (OPLL) as a component in a coherent optical transmission network. The performance of various binary optical transmission schemes, measured by the probability of error (Bit Error Rate), is presented. The linewidths of semiconductor diode lasers are, in general, not optimally suited to coherent transmission formats and therefore an additional power penalty must be paid if such sources are to be used. This power penalty is included in the analysis of a binary PSK transmission. The performance analysis of coherent transmission schemes is extended to encompass multi-level signalling formats. It is shown that, with the use of a sufficient number of signalling levels, these schemes can provide a receiver sensitivity which is better than a shot noise limited binary PSK transmission even when subject to the effects of high laser line width. A discussion on the properties of the laser diode, which are of interest in the design of a coherent optical transmission scheme (the source linewidth, modulation charateristics, wavelength tunablity and frequency and power stability), is provided. Measurements of these properties is given along with documentation of experimental attempts to reduce the linewidth of the laser emission. Linewidth reductions from between five and ten Megahertz down to tens of kilohertz were obtained. An analysis of the performance of an OPLL, taking into consideration the effect of phase instability of the laser diode source, is given. This analysis predicts that present day laser diodes can be used in the construction of the OPLL provided that the loop bandwidth is sufficiently large to account for the laser instability, while not being excessively large such that the performance is impaired by the influence of shot noise. This analysis is extended to describe the effect which the loop transport delay will have on such a loop, as the required loop bandwidth is extended. Similar calculations are performed to evaluate the effect of the loop receiver amplifier bandwidth. An evaluation of the OPLL response in the time domain, with the use of the Root Locus construction technique and a digital simulation, is presented. This analysis supports the findings of the analysis described above. The simulation of the loop dynamic response is found to be in reasonable agreement with the experimental findings of a previous worker. The components for the construction of an optical heterodyne-phase-locked-loop were assembled and attempts were made to lock both free running laser diodes and external cavity line-narrowed diodes. Reliable aquisition of lock was never achieved in any of the experiments performed despite the fact that beat notes of less than 50 kHz were achieved on a regular basis. The main factor which frustrated the succesful implenentation of the OPLL was deduced to have been mechanical disturbances, of the order of nanometers in magnitude, in the reflecting mirror of the external cavity sources. Hysteresis in the mechanical positioning equipment used to control the external reflector positioning was responsible for limiting the effectiveness of the frequency control loop. Experimentation was terminated by the deterioration of the laser sources, the suspected cause of which was the clustering of material defects within the active region of the device

A priority based routing protocol for wireless sensor networks

Recently, the demands on wireless sensor networks have switched from low traffic rate and static topology to more challenging requirements in order to meet the rapid expansion of WSN into various domain applications. This paper proposes a seamless cross layer solution that integrates network layer and medium access control to accommodate some of the new challenges. This new solution allows routing paths being generated dynamically to meet the requirement of potential mobile nodes. Higher data throughput and flow control are part of the new demands required to be addressed urgently. The proposed solution integrates a priority based MAC to handle congestion and packet loss problems which commonly happened in WSN when an occurrence of event spread into wide are

The use of UHF transponders as a potential replacement for cattle passports

Commercially available UHF RFID tags and interrogators (readers) are surveyed with a view to assessing their suitability as a replacement for cattle passports and preliminary laboratory trials for the tag read/write range are presente

On the interpretation of responses from hydrogel based distributed microbend fibre optic sensors

This contribution discuses the physicochemical aspects associated with the response of hydrogel based distributed fibre optic microbend sensors to different humidity conditions. We explain that the swelling of the hydrogel which leads to the observed change in the OTDR signal should be attributed to a change in the water potential of the hydrogel being at an equilibrium with the water potential of its immediate physicochemical environment. Since the water potential in the hydrogel matrix is the result of several equilibration processes from multiple species that are interacting in the immediate environment surrounding the sensor, the observed fibre deformation should be attributed to all of the components of the chemical potential. The work draws attention to the necessity to fully characterize the hydrogel system used in each sensing application. The analysis is of relevance to all types of fibre optic biosensors that utilize hydrogels in the measurement process

On the interpretation of responses from hydrogel based distributed microbend fibre optic sensors

This contribution discuses the physicochemical aspects associated with the response of hydrogel based distributed fibre optic microbend sensors to different humidity conditions. We explain that the swelling of the hydrogel which leads to the observed change in the OTDR signal should be attributed to a change in the water potential of the hydrogel being at an equilibrium with the water potential of its immediate physicochemical environment. Since the water potential in the hydrogel matrix is the result of several equilibration processes from multiple species that are interacting in the immediate environment surrounding the sensor, the observed fibre deformation should be attributed to all of the components of the chemical potential. The work draws attention to the necessity to fully characterize the hydrogel system used in each sensing application. The analysis is of relevance to all types of fibre optic biosensors that utilize hydrogels in the measurement process

Wide area cyclic blackout mitigation by supply-demand matching of HVAC counterpart loads

Many countries around the world are challenged to meet the escalating demand for power often resulting in frequent blackouts. Domestic standby generation and associated running costs are prohibitive and novel strategies to provision measures that manage blackouts are becoming much sought after. Almost all installed standby generation is not fully utilized and certain amounts of surplus power can be identified. The paper presents a strategy that harnesses the aggregated standby superfluous power to fulfil essential demand in residential areas during cyclic blackouts covering wide areas. The solution has at its foundation, a multiagent distributed demand management system with a supply-demand matching capability. Environmental conditions are monitored periodically and power is distributed accordingly to each sub-district. Customers at sub-districts receive a share of power according to two different distribution criteria and although their immediate allocated power is not the same, their overall daily power ration is equal. Air conditioners are backed up with less power demanding counterparts and a group of options is adaptively clustered. Their usage rights are distributed among customers according to available superfluous power. The approach is evaluated through an extensive emulation framework and results show that the proposed system is capable of providing an acceptable Quality-of-Service (QoS) level during cyclic blackout periods

Detailed theoretical model for adjustable gain clamped semiconductor optical amplifier (AGC-SOA)

The adjustable gain-clamped semiconductor optical amplifier (AGC-SOA) uses two SOAs in a ring-cavity topology: one to amplify the signal and the other to control the gain. The device was designed to maximize the output saturated power while adjusting gain to regulate power differences between packets without loss of linearity. This type of subsystem can be used for power equalisation and linear amplification in packet-based dynamic systems such as passive optical networks (PONs). A detailed theoretical model is presented in this paper to simulate the operation of the AGC-SOA, which gives a better understanding of the underlying gain clamping mechanics. Simulations and comparisons with steady-state and dynamic gain modulation experimental performance are given which validate the model

From lists of behaviour change techniques (BCTs) to structured hierarchies: comparison of two methods of developing a hierarchy of BCTs

Objectives Behaviour change technique (BCT) Taxonomy v1 is a hierarchically grouped, consensus-based taxonomy of 93 BCTs for reporting intervention content. To enhance the use and understanding of BCTs, the aims of the present study were to (1) quantitatively examine the ‘bottom-up’ hierarchical structure of Taxonomy v1, (2) identify whether BCTs can be reliably mapped to theoretical domains using a ‘top-down’ theoretically driven approach, and (3) identify any overlap between the ‘bottom-up’ and ‘top-down’ groupings. Methods and design The ‘bottom-up’ structure was examined for higher-order groupings using a dendrogram derived from hierarchical cluster analysis. For the theory-based ‘top-down’ structure, 18 experts sorted BCTs into 14 theoretical domains. Discriminant Content Validity was used to identify groupings, and chi-square tests and Pearson's residuals were used to examine the overlap between groupings. Results Behaviour change techniques relating to ‘Reward and Punishment’ and ‘Cues and Cue Responses’ were perceived as markedly different to other BCTs. Fifty-nine of the BCTs were reliably allocated to 12 of the 14 theoretical domains; 47 were significant and 12 were of borderline significance. Thirty-four of 208 ‘bottom-up’ × ‘top-down’ pairings showed greater overlap than expected by chance. However, only six combinations achieved satisfactory evidence of similarity. Conclusions The moderate overlap between the groupings indicates some tendency to implicitly conceptualize BCTs in terms of the same theoretical domains. Understanding the nature of the overlap will aid the conceptualization of BCTs in terms of theory and application. Further research into different methods of developing a hierarchical taxonomic structure of BCTs for international, interdisciplinary work is now required. Statement of contribution What is already known on this subject? * Behaviour change interventions are effective in improving health care and health outcomes

Detecting heat stress in dairy cattle using neck-mounted activity collars

Collar based activity sensors are in common use as a means of detecting oestrus to optimise farm fertility and hence productivity. More recently the same acceleration-derived signals have been processed to detect the time spent ruminating and eating which together give an insight into animal welfare. Here the use of neck-mounted accelerometers to provide a quantifiable measure of the time period that an individual animal exhibits signs of heat stress is reported. Heat stress has a significant impact on both animal welfare and productivity. Cattle studied during elevated temperatures were found to exhibit signs of exaggerated breathing motions, an indicator of heat stress, for 8 hours on average per day. This exceeds the time that cattle spend feeding and is similar to daily rumination times which could impact on both animal welfare and production. No similar cases were recorded on the cooler conditions of a Scottish winter. The approach offers a cost effective measure of heat stress and a potential tool to quantify its impact more generally

On models and approaches for human vital signs extraction from short range radar signals

The paper centres on an assessment of the modelling approaches for the processing of signals in CW and FMCW radar-based systems for the detection of vital signs. It is shown that the use of the widely adopted phase extraction method, which relies on the approximation of the target as a single point scatterer, has limitations in respect of the simultaneous estimation of both respiratory and heart rates. A method based on a velocity spectrum is proposed as an alternative with the ability to treat a wider range of application scenarios