Long Term Outcome of Severe Anaemia in Malawian Children

Severe anaemia is a common, frequently fatal, condition in African children admitted to hospital, but its long term outcome is unknown. Early reports that survivors may be at risk of additional late morbidity and mortality may have significant implications for child survival in Africa. We assessed the short and long term outcome of severe anaemia in Malawian children and identified potential risk factors for death and further severe anaemia. For 18 months, we followed up children (6-60 months old) presenting to hospital with severe anaemia (haemoglobin <or=5 g/dl) and their hospital and community controls with the aim to compare all cause mortality and severe anaemia recurrence rates between the groups, and to identify risk factors for these adverse outcomes. A total of 377 cases, 377 hospital controls and 380 community controls were recruited. Among cases, the in-hospital mortality was 6.4% and post-discharge all cause mortality was 12.6%, which was significantly greater than in hospital controls (2.9%) or community controls (1.4%) (Log rank test, p <0.001). The incidence of recurrence of severe anaemia among the cases was 0.102 per child-year (95% Confidence Interval 0.075-0.138), and was significantly higher than the 0.007 per child-year (95% CI 0.003-0.015) in the combined controls (p <0.0001). HIV was the most important risk factor both for post-discharge mortality (Hazard Ratio 10.5, 95% CI 4.0-27.2) and for recurrence of severe anaemia (HR 5.6, 95% CI 1.6-20.1). Severe anaemia carries a high 'hidden' morbidity and mortality occurring in the months after initial diagnosis and treatment. Because severe anaemia is very common, this is likely to contribute importantly to overall under-five mortality. If not adequately addressed, severe anaemia may be an obstacle to achievement of the Millennium development goal No.4 on child survival. Strategies to diagnose and properly treat HIV infected children early most likely will reduce the high post-discharge mortality in severe anaemi

Radio-over-fibre technology for broadband wireless communication systems

Wireless coverage of the end-user domain, be it outdoors or indoors (in-building), is poised to become an essential part of broadband communication networks. In order to offer integrated broadband services (combining voice, data, video, multimedia services, and new value added services), these systems will need to offer higher data transmission capacities well beyond the present-day standards of wireless systems. Wireless LAN (IEEE802.11a/b/g) offering up-to 54 Mbps and operating at 2.4 GHz and 5 GHz, and 3G mobile networks (IMT2000/UMTS) offering up-to 2 Mbps and operating around 2 GHz, are some of today’s main wireless standards. IEEE802.16 or WiMAX is another recent standard aiming to bridge the last mile through mobile and fixed wireless access to the end user at frequencies between 2 – 66 GHz. The need for increased capacity per unit area leads to higher operating frequencies (above 6 GHz) and smaller radio cells, especially in in-door applications where the high operating frequencies encounter tremendously high losses through the building walls. To reduce the system installation and maintenance costs of such systems, it is imperative to make the radio antenna units as simple as possible. This may be achieved by consolidating signal processing functions at a centralised headend, through radio-over-fibre technology. The research in this thesis focussed on the feasibility of using both single-mode and multimode fibres to distribute high-frequency microwave signals to simplified remote radio antenna units. An alternative radio-over-fibre technique, termed Optical Frequency Multiplication (OFM) has been investigated. OFM entails the periodic filtering of a swept optical signal at the headend followed by photodetection at the radio access unit. A low sweep frequency (e.g. 3 GHz) is used. After photodetection at the remote radio access unit, high-frequency (>21 GHz) harmonic components of the sweep signal are generated. The desired microwave signal is selected by means of bandpass filtering, amplified, and radiated by the antenna. Modulated microwave carriers are generated by intensity modulating the frequency-swept optical signal. Through modelling, simulations, and extensive experiments, the behaviour and performance of a radio-over-fibre downlink employing OFM was investigated. Simulation and comprehensive experimental results showed that OFM can be used to generate pure high-frequency microwave signals with very narrow linewidth and low SSB phase noise. This is because in the OFM process laser phase noise is inherently suppressed. The low-phase noise capability of OFM enables it to support the delivery of carriers modulated not only by the simple ASK data format, but also by complex multilevel modulation formats such as BPSK, QPSK, and x-level QAM. Multicarrier signals such as Subcarrier Multiplexed signals, and OFDM signals used in wireless LANs are also supported. Low Error Vector Magnitudes (below 5%) were obtained for x-QAM modulation formats, including 64-QAM. BER measurements showed a modal dispersion penalty of about 1 dB for a 4.4 km MMF link under restricted launch condition. It was established that OFM is chromatic dispersion tolerant and can support more than 10 times longer single-mode fibre transmission links (exceeding 50 km) than IMDD systems, which suffer from the chromatic-dispersion-induced amplitude suppression. OFM also enables the delivery of microwave carriers exceeding the modal bandwidth of MMFs, by using the higher transmission passbands of the fibre response. Silica glass MMF links of more than 4 km are feasible. The maximum link length, which can be bridged with Polymer Optical Fibre (POF) is significantly shorter, owing to its higher attenuation values. Thus POF may be more attractive for in-building applications where link lengths of 500m are often sufficient. Several different implementations of the Mach Zehnder Interferometer, and the Fabry Perot Interferometer filters were considered to determine their simplicity, performance, and applicability within the end-user environment. It was established that the wavelength of the optical FM source needs to be carefully aligned to the characteristics of the periodic optical filter. Therefore, it is preferred that both the source and the filter are co-located. This makes it easier to employ electronic tuning control of the filter (e.g. a fibre Fabry Perot Interferometer), so as to automatically track the alignment with the optical source, resulting in remarkable improvement of the OFM system stability. The ability to achieve high frequency multiplication factors, good phase noise performance, the support for all modulation formats, and the ability to operate on both single-mode and MMFs, all make OFM ideal for use in high-frequency (>5 GHz) broadband wireless system applications