User-centric visible light networking

Abstract

In this thesis, we propose a suite of schemes for indoor visible light communications (VLC), where multiple light emitting diode (LED) based access points (APs) serve multiple photo diode (PD) aided user equipment (UE). A novel user-centric (UC) VLC network is conceived, relying on user-clustering, resource allocation and sophisticated multiple access (MA) design. Our objective is to improve both the throughput and outage probability of the proposed UC-VLC network under practical indoor positioning and backhaul network design.

Specifically, instead of relying on the conventional network-centric (NC) design, we conceive the novel concept of UC-VLC supported by amorphous cells exhibiting extra benefits. By beneficially clustering multiple attocells based on the location information of UEs, a centre-shifting UC-clustering strategy is proposed, leading to a multi-AP multi-UE scenario within each cluster. Upon employing the potent transmit pre-coding (TPC) concept, the multi-user interference (MUI) within each cluster can be completely eliminated, where multiple APs simultaneously serve the clustered UEs. Since the construction of the UC-clusters relies on the knowledge of the UEs' positions, the amalgamation of indoor positioning with the VLC network becomes important. Upon combining the benefits of triangulation and fingerprinting based positioning techniques, we propose a novel hybrid solution exhibiting a high accuracy, robustness and scalability.

This is achieved by beneficially combining the low-complexity triangulation based positioning with high-accuracy fingerprinting, in order to efficiently support UC-clustering.
Since the improvement of the UC-VLC over NC-VLC has in the past been quantified based on a number of idealized simplifying assumptions, such as operating exactly at the Shannon capacity, our motivation is to quantify the performance of the UC-VLC under more practical considerations. Therefore, adaptive modulation is invoked, which allows the individual UEs to be assigned various modulation-modes. Since the different modulation-modes require different power, the transmit power allocated to each AP is therefore dependent and dynamic. Furthermore, instead of greedily supporting all the UEs in the network, a dynamic scheduling scheme is advocated. To obtain the maximum throughput of the constructed UC-VLC under practical constraints, an efficient resource allocation strategy is required for dealing with the modulation-mode assignment, power allocation and the scheduling. To solve this complex maximization problem, a heuristic RA algorithm based on dynamic-programming is proposed. Aided by it, we will show under a range of scenarios that the achievable throughput and the outage probability of the proposed UC-VLC system are better than that of the conventional NC-VLC system.

Then, we study the MA of VLC, when the APs are densely deployed, leading to an ultra-dense VLC network, where the inter-cell interference (ICI) amongst the densely-deployed APs is severe. To handle this challenge, both orthogonal MA (OMA) and non-orthogonal MA (NOMA) are considered. In order to cope with the grave ICI of our UC-VLC network, a hybrid NOMA and OMA scheme is proposed for enhancing the performance, where the frequency reuse (FR) technique and the TDMA-based scheduling may be dynamically invoked, which are further amalgamated with the spectrum-efficient NOMA scheme. We will show that the proposed MA scheme is more robust against the ICI, keeping the outage probability as low as possible, at a price of modestly degrading the achievable throughput.

Finally, we consider the realistic backhaul issue of our VLC network. Since the ubiquitous mains power line constitutes a natural backbone feed for VLC, a combined power line communication (PLC) and VLC (PLC-VLC) network is conceived. More specifically, the source data arriving from the Ethernet is fed by a power line into the VLC network through the alternating current (AC) power supply, hence combining the power supply and data communication relying on PLC. In this PLC-VLC network, the power line connects the LEDs without requiring a duplicated fibre-backbone, which is implementationally convenient. To cope with the harsh impulse noise of the PLC channel, broadband OFDM PLC is used. The information gleaned from PLC is then forwarded to multiple UEs via visible light. To increase the downlink bit rate, the NOMA principle is invoked in our VLC network. For the sake of maximizing the sum-throughput of the PLC-VLC network, we conceive an optimal joint power allocation (JPA) strategy for each subcarrier in PLC and for each UE in VLC, which will be demonstrated to outperform the benchmarkers.

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Identifiers

ORCID for Lajos Hanzo: orcid.org/0000-0002-2636-5214

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