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14 Journal of Communications and Information Networks
rection) under different device positions and orienta-
tions in an array of luminaires in order to maximize
achievable signal strength while improving both cov-
erage and reliability through AP redundancy. The
proposed solutions for adaptive transmitters and re-
ceivers successfully address common VLC network
challenges related to light occlusion and dynamic en-
vironments.
Related work falls into categories of (a) beam
steering using SLMs, (b) the impacts of receiver de-
sign, and (c) small-cell array-based VLC analysis.
Prior work in VLC beam steering includes MEMS
SLMs such as mirrors
[2-5]
and piezioelectric
[6]
de-
vices. Efforts in beam steering apply primarily to
an indoor FSO model with narrow beams or match-
ing receivers
[7]
; but includes use of static steering
with gratings
[8,9]
or holographic techniques
[10]
. Cov-
erage and lighting are considered in Ref. [11]; but
with fixed-orientation sources and without experi-
mental validation. Ref. [12] considers how spatial
layout can improve coverage and SNR while consid-
ering lighting goals. Regarding receiver orientation,
it is well known that mobile UEs such as smart-
phones have existing limitations on data rate when
a phone camera is used. But with future enhance-
ments, smartphones will adopt VLC receivers that
must account for rotation and tilt with respect to
VLC sources. Mobile device orientation has been
studied generally
[13]
and for VLC in a number of
works
[14,15]
. Lastly, there is much work on small cell
VLC networks – including the incorporation of alter-
native media such as RF
[7,16,17]
.
Our work is distinguished by dynamic steering
and focus, the use of multiple beams to extend
data coverage, and the incorporation of the light-
ing specification in the system design. We also pro-
vide experimental data supporting our simulations.
The remainder of this paper is organized as follows.
Section 2 introduces ultra-dense wireless networks,
OWC, and directional VLC. Section 3 describes new
models, predicted performance, and characterization
of AP coverage with respect to a single VLC AP. Sec-
tion 4 shows experimental results in the evaluation
of a MEMS-based directional VLC transmitter. Sec-
tion 5 introduces hybrid approaches considering nar-
row beams in lighting and evaluates multi-coverage
in networks with multiple VLC APs. Section 6 con-
cludes the paper.
2 Background and assumptions
In this work, we explore the impact of dynamic
OWC devices on network performance. We first pro-
vide background in relation to (1) ultra-dense wire-
less networks with multiple APs and UEs; (2) static
OWC networks and requirements of dual-use VLC
systems; and (3) dynamic VLC systems with ad-
justable emission profile. We also introduce assump-
tions related to the device capabilities along with
models for the operating environment and the opti-
cal channel.
2.1 Ultra-dense wireless networks
Next generation wireless networks will need to ac-
commodate an increasing density of wireless devices
along with increasing data demand per device. Given
the high percentage of traffic occurring in indoor en-
vironments, strategically placed ultra-dense wireless
networks have been proposed in order to provide ad-
ditional wireless capacity where it is needed most.
In addition to the growing data demand, wireless
devices are becoming increasingly diverse (e.g., IoT
devices, wearables, mobiles, laptops/tablets, etc.).
This diversity implies that future wireless networks
must also accommodate a broad range of operating
conditions (e.g., rate requirements, mobility, etc.).
In the case of ultra-dense wireless networks, sim-
ply moving through a room or changing a UEs ori-
entation implies multiple changes in the potential
network connections. Accordingly, practical imple-
mentation must account for coverage and reliability
in multi-cell/multi-user networks with mobile and
quasi-static devices. Multi-tier HetNet (Heteroge-
neous Network) integration is one technique to pro-
vide the coverage of larger cells along with the aggre-
gate capacity of ultra-dense wireless networks. Al-
ternatively, redundancy in the AP deployment can