WeC4 – Optical Communications

Wednesday, 19 June 2019, 14:00-15:30, Room 4


Session Chair:Konstantinos Stavropoulos (EXFO, United Kingdom (Great Britain))


Duobinary Modulation for Visible Light Communications

Petr Chvojka (Czech Technical University in Prague, Czech Republic); Paul Anthony Haigh (Newcastle University, United Kingdom (Great Britain)); Izzat Darwazeh (University College London, United Kingdom (Great Britain)); Zabih Ghassemlooy (Northumbria University, United Kingdom (Great Britain)); Stanislav Zvanovec (Czech Technical University in Prague, Czech Republic)
The paper proposes and experimentally investigates the performance of the duobinary transmission technique for a highly bandlimited VLC system. By adding a controlled amount of inter-symbol interference (ISI) into the transmit pulse shaping filters, the supported data rate can be doubled requiring the same signal bandwidth. To gain full insight into duobinary signalling, the so-called modified binary scheme is also tested. The bit error rate (BER) performance of both systems is measured for a range of data rates, before comparison with the ideal binary and traditional on-off keying non-return to zero (OOK-NRZ) formats across the same physical link. We show the duobinary system can support higher bit rates and lower BER than OOK-NRZ while requiring half the bandwidth of the binary scheme.


Modeling and Link Quality Assessment of THz Network Within Data Center

Boujnah Noureddine (Waterford Institute of Technology, TSSG, Tunisia & Faculty of Sciences of Gabes, unknown); Saim Ghafoor (Waterford Institute of Technology & TSSG, Ireland); Alan Davy (Waterford Institute of Technology, Ireland)
Terahertz band has gained enormous interest recently due to its wide bandwidth availability, and the data rate is reaching $100$ Gbps are nowadays achievable. The current advancement in Terahertz technology is aiming to achieve the data rate up to 1 Terabit per second. However, the unique band characteristics introduce some issues related to the propagation channel like high path and absorption loss which increases with distance. Such limitations at one hand can limit the coverage and throughput. But, on the other hand, suits indoor environment such as data center, a data center geometry is used in this paper to design and model a network of THz nodes placed on the top of the data center racks, to increase network connectivity, THz reflectors are positioned on ceiling and walls. Through simulations, we show that it is possible to reduce the average number of interferers in the system and minimize bit error probability by using specific waveforms and planar antenna array with active variable elements.


How, When and Where Can Fixed Wireless Access Compete with FTTH?

Szymon Piotr Izydorek (Aalborg University, Denmark); Annie Gravey (Institut Mines Telecom – Telecom Bretagne, France); Reza Tadayoni (Aalborg University Copenhagen, Denmark)
The following paper compares, from a techno-economic point of view, the deployment of different broadband access technologies in four types of geographical areas which differ in terms of surface, and number of households. The study concerns urban and rural areas and the rural areas are divided in homogeneous and heterogeneous scenarios to be able to come up with more realistic conclusions. In order to cover realistic scenarios, four engineering models have been considered: two of them based on Gigabit Passive Optical Network based (GPON-based): in the first one, poles and ducts are available and can be used to support fibre, whereas in the second one, civil engineering is required. The two other models are based on Fixed Wireless Access (FWA) provided respectively by 4G and 5G infrastructures. A tool has been designed to asses the profitability of these deployments in terms of payback period over a long period of time, taking explicitly into account investment costs, operational costs and take-up rates. The final results showcase the match between the topology and the deployment model, in regard to the network costs. A full data set is provided, which makes the study adaptable and replicable. The paper then provides some answers to the following question: which technology is better suited to provide broadband access in a specific area type?


Optical Interconnection of CDN Caches with Tb/s Sliceable Bandwidth-Variable Transceivers Featuring Dynamic Restoration

David Larrabeiti and Gabriel Otero Pérez (Universidad Carlos III de Madrid, Spain); Juan Pedro Fernández-Palacios (Telefónica I+D, Spain); Michela Svaluto Moreolo (Centre Tecnològic de Telecomunicacions de Catalunya (CTTC), Spain); José Alberto Hernández (Universidad Carlos III de Madrid, Spain); Pedro Reviriego (University Carlos III of Madrid, Spain); Josep M. Fabrega (Centre Tecnologic de Telecomunicacions de Catalunya, Spain); Victor Lopez (Telefonica, Spain); Laia Nadal (CTTC, Spain); Ricardo Martinez (Centre Tecnològic de Telecomunicacions de Catalunya (CTTC/CERCA), Spain)
A scalable cost-effective solution for high service availability featuring low latency CDN caching is making other MAN data centers at a distance within the latency budget backup other data centers of usually lesser reliability. Given the low latency target of caching, the optical layer is the preferred option to interconnect caches. However, carrying the backup traffic from one data center (DC) to another with a permanent optical circuit based on Fixed Transceivers (FT) features low utilization and no statistical multiplexing gain on the path, which makes the backup network resources costly. In this paper we compare several approaches to implement this scenario with dynamic circuits, considering both inter-cache and backup traffic with FTs featuring both permanent and switched optical circuits, and with the Tb/s sliceable bandwidth-variable transceivers (S-BVT) developed in the EU project PASSION. As we show, S-BVTs can be key devices to improve backup-network scalability in terms of IT resources and transceivers, thanks to their capability to adapt to the actual traffic demand and to obtain multiplexing gains at the optical layer.


Adaptive Unipolar MIMO-OFDM for Visible Light Communications

Mohamed Al-Nahhal (Ozyegin University, Turkey); Ertugrul Basar (Koc University, Turkey); Murat Uysal (Ozyegin University, Turkey)
Unipolar orthogonal frequency division multiplexing (U-OFDM) appears as an attractive optical OFDM solution for emerging visible light communication (VLC) systems. This paper proposes spectral efficiency improvement for U-OFDM systems by applying adaptive transmission over realistic VLC links. This adaptive transmission includes switching among a number of multiple-input multiple-output (MIMO) modes combined with appropriate modulation size selection. The considered MIMO modes are repetition coding, spatial modulation, and spatial multiplexing, where each mode supports different modulation sizes. The selection of the corresponding MIMO mode and its modulation size is based on the received signal-to-noise ratio and target bit error rate. The proposed U-OFDM system is applied over different VLC MIMO setups with realistic channel models for 8 × 8, 4 × 4 and 2 × 2 MIMO systems. Our simulation results show that the proposed adaptive system provides a significant spectral efficiency improvement over stand-alone U-OFDM MIMO modes/setups.