Radio over Fiber Transceiver's Architectures for Wireless and Satellite Communications
Date
2021-02-22
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Abstract
The development of the fifth-generation (5G), and beyond, of wireless communications motivates researchers to design innovative architectures in order to guarantee the delivery of data rate as high as 10 Gbps. The existing 4G wireless access architectures broadcast radio frequency (RF) signals below 6 GHz. This congestion in the available spectrum limits the data speed to a few hundred Mbps. Researchers investigated the option of using millimeter wave (mm-wave) between 30-300 GHz as wireless carriers to broadcast and transmit signals with data speed up to 10 Gbps and higher. The need for an efficient wire or wireless broadband link between base stations is vital to allow a variety of applications and services (like interactive HD TV, internet video, augmented reality, vehicle telematics, high-speed train, the wireless cloud office, etc.) to be delivered simultaneously and seamlessly. Using lasers in generating mm-wave carriers is still an active area of research since the 1990s, due to its overall design simplicity and efficiency. By modulating laser light, using a radio-frequency signal, it becomes possible to transmit the latter over standard optical fiber cables, for which the loss in the telecommunication band is as low as 0.2 dB/km. Radio-over- fiber (RoF) technology combines the advantages of radio and photonic devices. RoF technology, therefore, allows extending the distance between central stations and wireless end-users, thus maximizing the coverage of micro-cell and macro-cell based networks. In addition, photonics and RoF can be seen as enabling technologies to generate radio signals at mm-wave frequencies in a cost-effective manner. Hence, RoF technology will lead to reduced Capital Expenditure (CAPEX), and Operational Expenditure (OPEX), compared to traditional all-electronic networks. The electrical-optical-electrical conversion process in RoF links inevitably comes with impairments that degrade the signal quality. Simpler setups, using cheaper off-the-shelf components, can still lead to an acceptable performance by boosting the input RF signal power before optical modulation. Amplification of the RF signal carried by optical fiber is commonly adopted to minimize the impact of photo-detection noise on the dynamic range at the receiver. Unfortunately, this amplification causes the RoF system to behave non-linearly, leading to distortions during the electrical-optical-electrical conversion process that degrades the overall signal quality. To overcome this problem and linearize the RoF link, in this thesis, we propose a novel full-duplex RoF transceiver (TRx) architecture, augmented with an effective digital predistortion (DPD) technique to mitigate the non-linearities of the RoF TRx using a memory polynomial (MP) model. This thesis deals with the implementation of RoF TRx and provides solutions to some of the observed impairments in the electro-optical systems. In the first phase of the research project, the design of a single RoF fronthaul downlink transmitter is built and supported by experimental validation. The second phase of the project is conducted to enhance and upgrade the capability of RF signal generation and bandwidth of the RoF TRx. The third phase is focused on the establishment of a bidirectional link between central baseband unit (BBU) to remote radio head (RRH) and to integrate it with a free-space optics. The fourth phase is accomplished by building dynamic DPD models, which provide on-line feedback information from the RRHs through an established pre-calibrated observation path.
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Keywords
DSP, 5G, Radio over fiber, laser telecommunication, Digital predistortion, Satellite communications, free space optics, Linearization, Impairment mitigation, 4G, Wireless communication, millimeter wave
Citation
Noweir, M. (2021). Radio over Fiber Transceiver's Architectures for Wireless and Satellite Communications (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.