A High-speed Reconfigurable Free Space Optical Communication System Utilizing Software Defined Radio Environment

Free space optical (FSO) communication allows for high-speed data transmissions while also being extremely cost-effective by using visible or infrared wavelengths to transmit and receive data wirelessly through the free space channel. However, FSO links are highly susceptible to the effects of the atmosphere, particularly turbulence, smoke, and fog. On the other hand, FSO itself does not provide enough flexibility to address the issue of such blockage and obstruction caused by objects and atmospheric conditions. This research investigates, proposes, and evaluates a software defined multiple input multiple output (MIMO) FSO system to ensure link availability and reliability under weather conditions as part of the last mile access in the 5th generation, 6th generation, and beyond. Software defined radio (SDR) technology is adopted in order to provide a certain degree of flexibility to the optical wireless communications system. The scope of this research focuses on the design, validation, implementation, and evaluation of a novel adaptive switching algorithm i.e., activating additional transmitters of a MIMO FSO system using a software defined ecosystem. The main issues are the compactness of the experimental design; the limitation of software-oriented signal generation; robustness; reliability; and the quality of service. As part of the system design, the thresholding method, a decision-making process via the feedback link, and a spatial diversity technique is adopted to carry out the adaptive switching. The adaptive switching is performed via a feedback link in which the atmospheric loss and scintillation index are calculated for fog and turbulence respectively. The initial design is implemented in SDR/ GNURadio for a real-time emulation of the proposed system to enhance the system flexibility of a traditional MIMO FSO system. A bit-by-bit comparison is performed with the GNURadio signal processing block and BERT for a real-time BER estimation. However, based on the initial results, the switching mechanism can only overcome the effect of turbulence at a certain level. A new design to mainly mitigate the varying fog conditions is proposed based on the SDR-based adaptive switching for a gigabit ethernet (GbE) MIMO FSO system and tested in a 5 m dedicated atmospheric chamber. The proposed system is implemented using off-the-shelf components such as a media converter, small form pluggable transceivers, optical switch, and power meter to estimate the channel state information. A new Schmitt trigger-based thresholding method is also introduced. The proposed software defined GbE MIMO FSO with an adaptive switching algorithm is fabricated, implemented, and investigated. The results are also compared with the real-time simulated data. Since the purpose of this Ph.D. is to explain and demonstrate the proof of concept for the proposed SDR-MIMO FSO system, the emphasis has been on the design, evaluation, and minimal performance requirements rather than maximizing the data rate. The outcome of the thesis will be a huge degree of flexibility and mitigation property MIMO FSO can offer with the help of SDR. It will be shown that the designed system has the capability to provide data transmission with 99.999% availability with a packet error rate and data rate of 7.2 ×10−2 and ~120 Mbps respectively, under extremely harsh fog conditions with visibility V of < 11 m

Scaling of the Number of Modes in Mode Division Multiplexing Systems

We review our recent advances on the design of multimode fibres with hundreds of spatial pathways for reduced differential mode delay in the C-band and on the development of adaptable spatial multiplexing techniques to enable scalability of all data pathways

Performance Analysis and Software-Defined Implementation of Real-Time MIMO FSO with Adaptive Switching in GNU Radio Platform

In this paper, we provide the first software-based implementation of multiple-input multiple-output (MIMO) free space optical (FSO) link with the adaptive switching based on the software defined radio developed by GNU Radio software system, which emulates the real-time capability of the proposed scheme. We propose a switching mechanism to independently configure each transmitter and receiver, based on the channel state information provided at the transmitter via a feedback link and evaluate the link performance under atmospheric conditions such as fog and turbulence. We also validate the advantages of mitigating both the turbulence and fog in the proposed MIMO FSO system by means of numerical simulations and the developed GNU Radio software platform

Implementation and Evaluation of a 10 Gbps Real-time FSO Link

In this paper, we present and experimentally evaluate a real-time 10 Gbps free-space optical (FSO) link under varying atmospheric conditions. In bandwidth-craving wireless technologies due to the ubiquitous consumption by internet of things devices and requiring high data rate online services, unlicensed FSO systems can be a promising candidate to satisfy the network capacity of the existing data communications technologies. In this work, we verify the experiment using small form-factor pluggable transceivers mounted FPGA as a FSO transmitter and receiver. Here, a high-speed single FSO link is proposed and its performance under turbulence and fog conditions using the dedicated indoor atmospheric chamber is evaluated. We show that the proposed system under the turbulence condition with a scintillation index of 0.35 offers the same data rate as the link under a clear channel, while the bit error rate increases from 10-12 to 5 × 10-4

The BER Performance of a FSO System with Polar Codes Under Weak Turbulence

The key challenge in free space optical (FSO) communications is combating the turbulence induced fading. As the channel fading in FSO is quasi-static, the transmission parameters such as the code rates, transmit power and modulation schemes can be modified with respect to the channel state information transmitted via the feedback path. As a result, adaptive channel coding is considered as one of the practical approaches to improve the FSO link performance. In this paper we investigate the FSO system with polar codes and analyse its performance by determining the optimum code-rate required to achieve a bit error rate of 10-9 under weak turbulence. We show that, using Monte-Carlo simulations for the scintillation indices of 0.12 and 0.2, the successive cancellation list (SCL) decoder offers coding gains of 2.5 and 0.3 dB, respectively as compared with SC decoder, and for scintillation index of 0.31, the SC decoder offers a coding gain of 2.5 dB compared to SCL decoder for the code rate

Experimental real-time GbE MIMO FSO under fog conditions with software defined GNU Radio platform-based adaptive switching

In this paper, we demonstrate the first, to our knowledge, experimental implementation of a gigabit Ethernet multiple input single output free space optical (FSO) communications link using adaptive switching implemented in the software defined open-source software, GNU Radio, and analyze its performance. A fully functional FSO link with a feedback path is implemented using cost effective off-the-shelf components, i.e., media converters and small form-factor pluggable modules. We propose a switching mechanism at the transmitter to improve the link performance under different fog conditions and provide results for the proposed FSO system compared with a single FSO link. The real-time channel estimation is demonstrated and, based on the channel state information, adaptive switching is carried out in GNU Radio. We show that the proposed system under the heavy fog condition offers almost the same packet error rate under the clear channel but with a reduced data rate by about 100 Mbps (i.e., 600 Mbps)

Demonstration of Optical Wireless Communications System using a Software Defined Ecosystem

In this paper, we experimentally demonstrate the implementation of an optical wireless communication system in a software defined radio platform using GNU radio ecosystem and verify the link performance in terms of the bandwidth and jitter by changing the interpolation parameters in the software domain. We show that, the software defined optical system provides high reconfigurability and can be easily implemented without the need to change the architecture of the hardware, providing a real-time signal based system, which is highly desirable