Development of indoor wireless optical CDMA system for local-area networks (LANs) and health-care continuous monitoring

Optical wireless communication (OWC) is an important area of research that offers a number of advantages over radio frequency based systems. These advantages include high bandwidth, free licensed spectrum band, high security, ease of installation, immunity to induced electromagnetic interference (EMI), and low-cost subsystems. The focus of this thesis is on indoor owe channels and systems. The main limitations ofindoor owe systems include Inter-Symbol Interference (lSI) due to multi path dispersion, background noise, and Multiple Access Interference (MAl) and Phase-Induced Intensity Noise (PUN) associated with simultaneous multi-user systems. The former degrades the signal-to-noise ratio (SNR), while the latter limits the maximum achievable data rate. This thesis investigates the use of an optimised divergence angle of the transmitter in a room structure of 1-cell and 4-cell configurations to achieve a higher transmission bandwidth and a more uniform optical power distribution, resulting in lower IS I. This work also investigates the use of Optical Code Division Multiple Access (OCDMA) technology based on a Zero Cross Correlation (ZCC) code in optical wireless networks to reduce the impairments such as MAl and PIIN that exist in the system and thus improve the overall system performance. The obtained results are compared with a Flexible Cross Correlation CFCC) based system. As a result, the indoor wireless OCDMA (W-OCDMA) system based on 4-celJ configuration and using the ZCC code can accommodate a large number of users with less transmission power and a higher data rate compared to the 1-cell configuration or using the FCC code. The 4-cell configuration system based on the ZCC code offered 42% and 150% larger cardinality at the edges, and the comers of the room respectively, compared to the 1-cell configuration. In addition, this system also offered 55%, 47%, 51% larger cardinality at the centre, the edges, and the comers of the room, respectively, in contrast to the FCC code. Furthermore, this research also investigates the use of infrared technology in healthcare monitoring to develop a mobile medical system. This is because existing technology is generally based on radio frequency (RF) systems, which might suffer from electromagnetic interference (EMI). Additionally, the effect of the radiation field on medical equipment may lead to misdiagnosis. In answer to these issues, optical wireless links between the medical sensors and the receiver in the middle of the ceiling in a hospital room was examined. From the results, the power efficiency of the mobile optical wireless system to ensure the communication between medical sensors and the receiving point was established. Furthermore, the minimum required transmitted power for the required performance was determined, so as to achieve a higher power autonomy. The results also show that the requirements of a healthcare monitoring application for medical nodes of up to 10 nodes, considering a data rate lower than 1 Mbps, can be achieved using infrared technology. The results prove the superiority of the optical wireless technology over the conventional radio-based communication network in healthcare monitoring systems.