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Introduction to indoor networking concepts and challenges in LiFi

Harald Haas, Liang Yin, Cheng Chen, Stefan Videv, Damian Parol, Enrique Poves, Hamada Alshaer, and Mohamed Sufyan Islim

Open Access Open Access

Abstract

LiFi is networked, bidirectional wireless communication with light. It is used to connect fixed and mobile devices at very high data rates by harnessing the visible light and infrared spectrum. Combined, these spectral resources are 2600 times larger than the entire radio frequency (RF) spectrum. This paper provides the motivation behind why LiFi is a very timely technology, especially for 6th generation (6G) cellular communications. It discusses and reviews essential networking technologies, such as interference mitigation and hybrid LiFi/Wi-Fi networking topologies. We also consider the seamless integration of LiFi into existing wireless networks to form heterogeneous networks across the optical and RF domains and discuss implications and solutions in terms of load balancing. Finally, we provide the results of a real-world hybrid LiFi/Wi-Fi network deployment in a software defined networking testbed. In addition, results from a LiFi deployment in a school classroom are provided, which show that Wi-Fi network performance can be improved significantly by offloading traffic to the LiFi.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

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Figures (13)
Fig. 1.
Fig. 1. Here we illustrate a LiFi network. Each light acts as an optical access point, which serves multiple user equipment within its illumination area/cell. Users can also move, and they will be served by different light bulbs as they roam. This change of serving access point happens seamlessly. Several cells form a cluster, UEs at the cell edges can be served by multiple access points to avoid interference. This technique is referred to as cooperative multipoint (CoMP) transmission.

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Fig. 2.
Fig. 2. (a) LiFi channel block diagram. (b) Illustration of the indoor free-space VLC channel.

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Fig. 3.
Fig. 3. LiFi network illustration. A complete LiFi network includes downlink, uplink, and backhaul connections. In addition, the system should provide a handover function, mobility support, and multiple access capability.

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Fig. 4.
Fig. 4. (a) Demonstration of CCI. (b) Static resource partitioning. (c) Fractional frequency reuse. (d) Interference coordination with angular diversity transmitters and receivers. (e) Cooperative multipoint joint transmission.

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Fig. 5.
Fig. 5. (a) Relationship between Shannon capacity upper bound and channel capacity in a LiFi network. (b) Various cell layouts in LiFi networks. (c) Example of downlink performance in a LiFi network with an average cell radius of 2.5 m, and a source half-power semiangle of 40°.

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Fig. 6.
Fig. 6. (a) Wi-Fi standalone network. (b) LiFi standalone network. (c) LiFi/Wi-Fi hybrid network. (d) Load balancing in LiFi/Wi-Fi hybrid network.

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Fig. 7.
Fig. 7. Experimental SDN-enabled LiFi/Wi-Fi network testbed diagram, LiFi R&D Centre, UoE.

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Fig. 8.
Fig. 8. Measured average data rate during handover of user device from LiFi to LiFi and LiFi to Wi-Fi.

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Fig. 9.
Fig. 9. Simulation-based and measured SNR under varying distance under a LiFi attocell.

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Fig. 10.
Fig. 10. Network topology of the LiFi APs in classroom 2 and the Wi-Fi AP serving both classrooms.

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Fig. 11.
Fig. 11. CDF of the data rate for the Wi-Fi and LiFi users based on the 1 Mbps and 3 Mbps data rate targets.

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Fig. 12.
Fig. 12. CDF of the data rate for the Wi-Fi and LiFi users assuming no data rate targets.

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Fig. 13.
Fig. 13. Surge in Wi-Fi aggregated data rate in neighboring classrooms.

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Tables (1)

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Table 1. Average Data Rates Achieved for the Wi-Fi and LiFi Networks

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Equations (1)

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c = 1 2 W   log 2 ( 1 + σ 0 2 ‖ H 0 ‖ 2 ∑ i ∈ I ⁡ σ i 2 ‖ H i ‖ 2 + W N 0 ) ,
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