A review of communication-oriented optical wireless systems

This article presents an overview of optical wireless (OW) communication systems that operate both in the short- (personal and indoor systems) and the long-range (outdoor and hybrid) regimes. Each of these areas is discussed in terms of (a) key requirements, (b) their application framework, (c) major impairments and applicable mitigation techniques, and (d) current and/or future trends. Personal communication systems are discussed within the context of point-to-point ultra-high speed data transfer. The most relevant application framework and related standards are presented, including the next generation Giga-IR standard that extends personal communication speeds to over 1 Gb/s. As far as indoor systems are concerned, emphasis is given on modeling the dispersive nature of indoor OW channels, on the limitations that dispersion imposes on user mobility and dispersion mitigation techniques. Visible light communication systems, which provide both illumination and communication over visible or hybrid visible/ infrared LEDs, are presented as the most important representative of future indoor OW systems. The discussion on outdoor systems focuses on the impact of atmospheric effects on the optical channel and associated mitigation techniques that extend the realizable link lengths and transfer rates. Currently, outdoor OW is commercially available at 10 Gb/s Ethernet speeds for Metro networks and Local-Area-Network interconnections and speeds are expected to increase as faster and more reliable optical components become available. This article concludes with hybrid optical wireless/radio-frequency (OW/RF) systems that employ an additional RF link to improve the overall system reliability. Emphasis is given on cooperation techniques between the reliable RF subsystem and the broadband OW system

100 Gbit/s optical wireless communication system link throughput

Novel results on the link layer protocol performance of future infrared personal communication links at a line rate of 100 Gbit/s are presented. The discussion aims to demonstrate the shortcomings of the currently standardised half-duplex mode of communications in the physical layer and details its negative impact on the link layer efficiency. Results of a non-standardised full-duplex mode of operation that is however suitable for application in future high capacity infrared links are also presented. The results predict that the migration to this full-duplex mode can prove advantageous for the link layer performance, as it not only yields a higher efficiency, but also requires significantly smaller frame and window sizes

Resource partitioning in the NEPHELE datacentre interconnect

We present heuristic algorithms for the efficient resource partitioning in the NEPHELE datacentre optical interconnect. The algorithms aim to segment the network into smaller and isolated virtual datacentres (VDCs), where all racks are able to communicate at full capacity irrespective of their placement. Since the NEPHELE architecture relies on shared optical rings, the isolation of VDC traffic is challenging. Observing its close resemblance to finding a bi-clique on a bipartite graph, which is NP-hard, we propose heuristic algorithms which find a solution by limiting either the spatial spread of racks that construct each VDC or their wavelength allocation. If a solution cannot be found, then the algorithms invoke a second de-fragmentation phase, where they re-allocate the racks of existing VDCs to concentrate them spatially and reduce traffic on the shared optical rings. It is demonstrated via simulation that the proposed heuristics can achieve very high utilization and also exhibit low VDC request blocking probability for typically expected VDC sizes

Accurate Evaluation of the Average Probability of Error of Pulse Position Modulation in Amplified Optical Wireless Communications under Turbulence

We present exact and approximate results on the average probability of error (PER) for pulse position modulation (PPM) in pre-amplified optical wireless communication systems with diversity. The approximate results are obtained by combining a new mathematical formula that we derive for binary PPM and an existing formula that associates higher-order PPM PERs with their binary PPM counterpart. The approximate results are compared with the exact in weak, moderate, and strong turbulence, and it is demonstrated that they are in good agreement under all fading conditions. Moreover, the accuracy of the approximation improves with the optical signal-to-noise ratio and the number of diversity branches that are used, which correspond to implementation scenarios that are typically anticipated in practice

Average Error Probability of an Optically Pre-Amplified Pulse-Position Modulation Multichannel Receiver under Malaga-ℳ Fading

We present analytical results on the average probability of error (PER) performance of an optically pre-amplified pulse-position modulation (PPM) receiver under Malaga- M fading. The results are in the form of a finite sum whose number of terms depends on the PPM modulation order and the noise modes of the amplifier, enabling the efficient calculation of the average PER. In addition, we utilized the presented analysis to evaluate the performance of a equal-gain-combining (EGC) diversity receiver that operates in conjunction with optical amplification and PPM. The results show that the utilization of diverse and relatively low PPM orders achieves a drastic reduction in the average PER

Generation of 40-GHz control signals from flag pulses for switching alloptical gates for use with optical packets

We demonstrate an all-optical circuit capable of generating 40-GHz control signals from f lag pulses that can be used to define the switching state of all-optical gates for use with optical packets. The circuit comprises a Fabry -Perot filter and a semiconductor optical amplifier, and with a single pulse it can generate 12 control pulses with 0.64-dB amplitude modulation. With two and three f lag pulses the number of control pulses becomes 36 and 54, respectively