Design and Analysis of Free-space Optical Communications Systems for Next Generation Short-range Wireless Networks

This dissertation focuses on indoor free-space optical communications systems for use in short range wireless networks. We propose that current radio frequency wireless links be augmented or replaced with optical frequency links due to overcrowding in the radio frequency spectrum. Optical frequencies contain hundreds of terahertz of unregulated bandwidth and offer a physical layer of protection due to the inherently line-of-sight nature of near infrared light. We first present a hybrid optical and radio frequency link based on inexpensive LEDs in which a downlink is established optically, while the uplink is routed through preexisting radio frequency channels. Second, an all optical dual channel laser-based communication system is implemented consisting of a medium bandwidth wide-angle optical femtocell and a high-speed line-of-sight optical attocell. This approach balances the diverse needs of end users by providing links optimized for both mobility and bandwidth. Lastly, we demonstrate a high-power vertical cavity surface emitting laser (VCSEL) array transmitter for use in optical femtocells. A complimentary design for a distributed current laser driver is also presented

Practical implementation of multiple-input multiple-output visible light communication systems

Wireless data transmission occurs everywhere and the global data traffic is growing rapidly. Current radio frequency (RF) spectrum resource is becoming saturated and our current RF based wireless communication system will not meet the demands for data traffic in the future. Research efforts have been put into increasing the spectral efficiency of existing RF networks. Techniques such as multiple-input multiple-output (MIMO), have been well studied. However, it is still insufficient for the rapid growth of the wireless data traffic. The visible light (VL) spectrum is over 1000 times wider than the size of the entire 300 GHz RF spectrum, therefore, it is a viable alternative resource. The spread of light emitting diode (LED) lighting infrastructures provides a good opportunity for visible light communication (VLC). VLC turns the LEDs into high speed wireless data transmitter while retaining their illumination function. VLC has drawn much attention in recent years. MIMO techniques have also been studied in VLC. However, there have only been a few studies that compared practical MIMO VLC systems with theoretical studies. In this thesis, several practical implementations of the MIMO VLC system have been presented. First, a generalised space shift keying (GSSK) system, which is a simple form of spatial modulation (SM), has been presented. The performance of the field programmable gate array (FPGA) based real-time system has been studied against different transmitter (Tx) and receiver (Rx) numbers. The performance against mobility has also been evaluated. Up to 16 transmitters have been used and the result shows high spectral efficiency is achievable with the low complexity implementation of GSSK. Second, an investigation of an ultra-high speed wavelength division multiplexing (WDM) VLC system using inexpensive, low-complexity front-end components has been developed. We have used ordinary off-the-shelf red, green, blue and yellow (RGBY) LEDs in surface-mount technology (SMT). The result shows that a data rate of over 15 Gbits/s can be achieved by using proper optimising procedures on the inexpensive commercially available components. This study has confirmed the potential of high achievable capacities of VLC systems. Third, the first MIMO VLC system using organic photovoltaics (OPVs) has been implemented featuring simultaneous data communication and energy harvesting. Record data rates of 102 Mbits/s for a single pixel and 146 Mbits/s for a 2-by-2 MIMO set-up have been presented. The first system model for MIMO OPV VLC system has been proposed. The model has been validated with experimental results. The scalability of the system has also been discussed

SPATIAL TRANSFORMATION PATTERN DUE TO COMMERCIAL ACTIVITY IN KAMPONG HOUSE

ABSTRACT Kampung houses are houses in kampung area of the city. Kampung House oftenly transformed into others use as urban dynamics. One of the transfomation is related to the commercial activities addition by the house owner. It make house with full private space become into mixused house with more public spaces or completely changed into full public commercial building. This study investigate the spatial transformation pattern of the kampung houses due to their commercial activities addition. Site observations, interviews and questionnaires were performed to study the spatial transformation. This study found that in kampung houses, the spatial transformation pattern was depend on type of commercial activities and owner perceptions, and there are several steps of the spatial transformation related the commercial activity addition. Keywords: spatial transformation pattern; commercial activity; owner perception, kampung house; adaptabilit

Recent Development of Hybrid Renewable Energy Systems

Abstract: The use of renewable energies continues to increase. However, the energy obtained from renewable resources is variable over time. The amount of energy produced from the renewable energy sources (RES) over time depends on the meteorological conditions of the region chosen, the season, the relief, etc. So, variable power and nonguaranteed energy produced by renewable sources implies intermittence of the grid. The key lies in supply sources integrated to a hybrid system (HS)

Interference mitigation techniques for optical attocell networks

The amount of wireless data traffic has been increasing exponentially. This results in the shortage of radio frequency (RF) spectrum. In order to alleviate the looming spectrum crisis, visible light communication (VLC) has emerged as a supplement to RF techniques. VLC uses light emitting diodes (LEDs) for transmission and employs photodiodes (PDs) for detection. With the advancement of the LED technology, LEDs can now fulfil two functions at the same time: illumination and high-speed wireless communication. In a typical indoor scenario, each single light fixture can act as an access point (AP), and multiple light fixtures in a room can form a cellular wireless network. We refer to this type of networks as ‘optical attocell network’. This thesis focuses on interference mitigation in optical attocell networks. Firstly, the downlink inter-cell interference (ICI) model in optical attocell networks is investigated. The conventional ray-tracing channel model for non-line-of-sight (NLOS) path is studied. Although this model is accurate, it leads to time-consuming computer simulations. In order to reduce the computational complexity, a simplified channel model is proposed to accurately characterise NLOS ICI in optical attocell networks. Using the simplified model, the received signal-to-interference-plus-noise ratio (SINR) distribution in optical attocell networks can be derived in closed-form. This signifies that no Monte Carlo simulation is required to evaluate the user performance in optical attocell networks. Then, with the knowledge of simplified channel model, interference mitigation techniques using angle diversity receivers (ADRs) are investigated in optical attocell networks. An ADR typically consists of multiple PDs with different orientations. By using proper signal combining schemes, ICI in optical attocell networks can be significantly mitigated. Also, a novel double-source cell configuration is proposed. This configuration can further mitigate ICI in optical attocell networks in conjunction with ADRs. Moreover, an analytical framework is proposed to evaluate the user performance in optical attocell networks with ADRs. Finally, optical space division multiple access (SDMA) using angle diversity transmitters is proposed and investigated in optical attocell networks. Optical SDMA can exploit the available bandwidth resource in spatial dimension and mitigate ICI in optical attocell networks. Compared with optical time division multiple access (TDMA), optical SDMA can significantly improve the throughput of optical attocell networks. This improvement scales with the number of LED elements on each angle diversity transmitter. In addition, the upper bound and the lower bound of optical SDMA performance are derived analytically. These bounds can precisely evaluate the performance of optical SDMA systems. Furthermore, optical SDMA is shown to be robust against user position errors, and this makes optical SDMA suitable for practical implementations

Synthesis of new pyrazolium based tunable aryl alkyl ionic liquids and their use in removal of methylene blue from aqueous solution

In this study, two new pyrazolium based tunable aryl alkyl ionic liquids, 2-ethyl-1-(4-methylphenyl)-3,5- dimethylpyrazolium tetrafluoroborate (3a) and 1-(4-methylphenyl)-2-pentyl-3,5-dimethylpyrazolium tetrafluoroborate (3b), were synthesized via three-step reaction and characterized. The removal of methylene blue (MB) from aqueous solution has been investigated using the synthesized salts as an extractant and methylene chloride as a solvent. The obtained results show that MB was extracted from aqueous solution with high extraction efficiency up to 87 % at room temperature at the natural pH of MB solution. The influence of the alkyl chain length on the properties of the salts and their extraction efficiency of MB was investigated