Free space optical communication

Performance of 120 Gbps single channel coherent DP-16-QAM in terrestrial FSO link under different weather conditions

Optical wireless communication (OWC) covering an ultra-wide range of unlicensed spectrum has emerged as an extent efficient solution to mitigate conventional RF spectrum scarcity ranging from communication distances from nm to several kilometers. Free space optical (FSO) systems operating near IR (NIR) band in OWC links has received substantial attention for enormous data transmission between fixed transceivers covering few kilometers path distance due to high optical bandwidth and higher bit rate as well. Despite the potential benefits of FSO technology, its widespread link reliability suffers especially in the long-range deployment due to atmospheric turbulence, cloud induced fading, some other environmental factors such as fog, aerosol, temperature variations, storms, heavy rain, cloud, pointing error, and scintillation. FSO has the potential to offloading massive traffic demands from RF networks, consequently the combined application of FSO/RF and radio over FSO (RoFSO) systems is regarded as an excellent solution to support 5G and beyond for improving the limitations of an individual system. This survey presents the overview of several key technologies and implications of state-of-the-art criteria in terms of spectrum reuse, classification, architecture and applications are described for understanding FSO. This paper provides principle, significance, demonstration, and recent technological development of FSO technology among different appealing optical wireless technologies. The opportunities in the near future, the potential challenges that need to be addressed to realize the successful deployment of FSO schemes are outlined.

A Contemporary Survey on Free Space Optical Communication: Potential, Technical Challenges, Recent Advances and Research Direction.

A contemporary survey on free space optical communication: Potentials, technical challenges, recent advances and research direction

The reliability and efficiency of free space optics (FSO) systems is significantly degraded by attenuation caused by different climate conditions and atmospheric turbulence. In this work, an FSO transmission system with high-speed transmission capability is proposed by deploying orthogonal frequency division multiplexing (OFDM) to mitigate channel fading effects. Further, we propose the hybridization of polarization division multiplexing (PDM) with CO-OFDM to improve the system capacity. We perform the bit error rate (BER) and optical signal to noise ratio (OSNR) comparative analysis of multi-level quadrature amplitude modulation (QAM) schemes, i.e., 4-QAM, 16-QAM, 32-QAM, and 64-QAM at 100, 120, 360, and 480 Gbps transmission rates, respectively. The obtained results reveal that the 4-QAM modulation scheme achieves the highest transmission range and the least OSNR requirement. In terms of spectral efficiency, 64-QAM shows the best performance. Also, the impact of different climate conditions on the system performance has been investigated. Through simulations, we demonstrate a successful transmission of 100 Gbps 4-QAM information at 15 km. Furthermore, we numerically investigated the increasing scintillation effect on the BER system performance. The proposed system not only reduces the channel fading but also improves the information rate and maximum transmission distance. The reported work can be considered for future FSO systems even in adverse climate conditions.

A long-haul 100 Gbps hybrid PDM/CO-OFDM FSO transmission system: Impact of climate conditions and atmospheric turbulence

Design and analysis of a dense wavelength-division multiplexed integrated PON-FSO system using modified OOK/DPPM modulation schemes over atmospheric turbulences

A full-duplex optical fiber/wireless coherent communication system with digital signal processing at the receiver

A full-duplex optical fiber/wireless single-channel coherent communication system is presented for high-speed data center interconnections. In-phase and quadrature modulator (IQM)-based dual polarization 256 quadrature amplitude modulation (DP-256-QAM) is implemented to achieve a maximum data rate of 640 Gbps with 40 Gbaud symbol rate for both the single-mode fiber (SMF) and free-space optics (FSO) links. Advanced digital signal processing (DSP) algorithms have been implemented at the receiver to compensate for signal impairments during propagation. The system with optical IQM and DSP algorithms can be fabricated in the form of cost-efficient integrated circuits and possess a potential spectral efficiency of 15.2344 b/s/Hz. A maximum transmission distance of 160 km and 4 km is achieved in simulation platform for the SMF and FSO links, respectively. The system performance is evaluated regarding laser linewidth requirements, optical signal-to-noise ratio tolerance, receiver sensitivity and launched optical power. This transceiver system shall be useful in high-speed long-haul communications, and the FSO system provides the same data rate to the remote areas, and last mile connections where laying of an optical fiber is not possible or cost is a major concern.

A 640-Gbps, 15.2344-b/s/Hz full-duplex optical fiber/wireless single-channel coherent communication system using IQM-based DP-256-QAM and DSP techniques

In this article the performance of grey-coded advanced optical modulation formats is evaluated on a single-channel high-speed long-haul optical communication link and are compared to the respective differential-coded modulation formats. Polarisation division multiplexed optical in-phase quadrature modulator (IQM) structure and homodyne detection scheme are used to realise 100 Gbps quadrature phase-shift keying (QPSK), 120 Gbps 16-ary quadrature amplitude modulation (16-QAM), 360 Gbps 32-QAM and 480 Gbps 64-QAM modulation formats. Advanced digital signal processing unit with various pre-processing and recovery stages such as direct current blocking, normalisation, low-pass Bessel filter, resampling, quadrature imbalance compensation, chromatic dispersion compensation, non-linear compensation, timing recovery, adaptive equalisation, down-sampling, frequency offset estimation, and carrier phase estimation is used at the receiving end to compensate for signal impairments during propagation. Maximum transmission distances of 7200, 1050, 560, and 360 km have been achieved at an acceptable bit error rate for QPSK, 16-QAM, 32-QAM, and 64-QAM, respectively. The grey-coded systems outperformed the differential-coded systems regarding optical signal-to-noise ratio requirement, receiver sensitivity, and transmission distance.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-com.2019.0205

Dhiman Kakati

Papers

Performance of 120 Gbps single channel coherent DP-16-QAM in terrestrial FSO link under different weather conditions

Design and analysis of a dense wavelength-division multiplexed integrated PON-FSO system using modified OOK/DPPM modulation schemes over atmospheric turbulences

A full-duplex optical fiber/wireless coherent communication system with digital signal processing at the receiver

A 640-Gbps, 15.2344-b/s/Hz full-duplex optical fiber/wireless single-channel coherent communication system using IQM-based DP-256-QAM and DSP techniques

Performance of grey-coded IQM-based optical modulation formats on high-speed long-haul optical communication link