| Summary: | 碩士 === 國立交通大學 === 照明與能源光電研究所 === 107 === While the advances in communication technology of wireless networks are rapidly developing, the requirements placed on these networks by the transportation of digital media tends to increase as well, due to rising consumer demand relating to high resolution images and better quality audio and video transmissions. Furthermore, convenience is important in the lives of consumers as well, so the adoption of mobile devices is becoming more and more common among the population. As, the demand for data traffic gradually increases, so does the need for increased speed and capacity of existing wireless networks. Therefore, there is an ever increasing need to develop novel technologies for wireless networks which improve upon their ability to transmit data faster and more reliably. Consequently, technologies tend to develop that utilize higher frequencies that can be found with wider bandwidth utilization to provide increased capacity. On the other hand, the need for increased spectral efficiency is ever present as well. These two aspects of communication technology can be used to enhance data traffic and may be the trend of the future. Inevitably, wireless communication systems will become a broadband system with high spectral efficiency, high capacity, reasonable cost, and energy efficiency.
The data capacity of broadband technologies is limited because some standards limit spectra which industries can utilize. The V-band (57–64 GHz) is license-free bandwidths which are released by the Federal Communications Commission (FCC). At the same time, industry dictates the development of 60-GHz wireless communication systems. Unfortunately, power attenuation is relatively large in some frequency bands including 60 GHz. To overcome natural limitations, the numbers of base stations or remote antenna units (RAUs) need to increase to provide the wireless coverage space where RAUs currently exist. Therefore, the technology of interfacing between radio equipment controllers (REC) and radio equipment (RE) needs to be developed.
Radio-over-Fiber (RoF) technology supports radio-frequency (RF) signals which are processed in a central station that transmit the desired signals to RAUs using low-loss optical fiber. Compared with conventional wireless systems, this technology can reduce the cost and complexity of RAUs. Furthermore, lower power consumption can reduce the number of components needed for RAUs. In this way, coverage can be effectively enhanced and satisfy data needs associated with future 5G communications.
Multiple-input Multiple-output (MIMO) is also proposed to enhance the spectral efficiency in limited bandwidth scenarios. This technology can be classified as optical MIMO and wireless MIMO. Additionally, the present technology of optical MIMO can be classified as polarization division multiplexing (PDM), wavelength division multiplexing (WDM) and mode division multiplexing (MDM). Because, the technology of PDM can only support a 22 wireless system, new development tends to focus on WDM and MDM. At present, the numbers of light amplification by stimulated emission of radiation (LASER) devices in WDM increases the cost which makes it impractical going forward. However, it is this very communication technology that this research is interested in, that is the technology of MDM. MDM communication offers high spectral efficiency in limited bandwidth space. As such, this thesis proposes a fiber/wireless MIMO system using optical MDM.
The feasibility of a fiber/wireless MIMO system using optical MDM has been investigated and discussed. The issues of the interactive influence of modes and wireless channels may induce signal mix that can improve the performance of the technology by introducing digital signal processing (DSP). To reduce complexity of systems, direct detection is adopted. However, direct detection may have power decay issues, so additional approaches using DSP are proposed to attempt to solve the problem.
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