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High-Speed OpticalWireless Communication System for Indoor Applications
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Abstract
A novel high-speed optical wireless communication
system for indoor personal area networking applications is proposed
and studied. A proof-of-concept experiment at 12.5-Gb/s
wireless transmission has been successfully demonstrated with
limited mobility. When integrated with a WiFi-based localization
system, high-speed optical wireless communication with a mobility
feature can be achieved over the entire room. The performance
trade-offs between the maximum beam footprint and overall bit
rate have also been studied and quantified experimentally and the
results show that error-free BER reception can always
be achieved for a wide range of bit rates from 1 to 12.5 Gb/s.
Index Terms—Broadband communication, fiber-optics links
and subsystems, indoor optical wireless communications, personal
communication networks.
I. INTRODUCTION
WIRELESS communication systems are attractive because
of its capability to provide mobility to end users.
Compared with the traditional radio frequency (RF) technology
and millimeter-wave systems, optical wireless (OW) technology
has multiple advantages, such as the unregulated large
bandwidth available, immunity to electromagnetic interference,
and the possibility of frequency reuse and security at physical
layer where optical beam does not penetrate walls or opaque
objects [1]. Therefore, for over one decade OWcommunication
for indoor applications has attracted considerable attention
[2]–[7].
Optical wireless (OW) communications can be generalized
into two groups: the diffused system and the line-of-sight
(LOS) system [2]. The former utilizes totally diffused beam
that covers the entire service area and provides mobility functionality
to subscribers. However, the diffused system suffers
Manuscript received January 04, 2011; accepted February 02, 2011. Date of
publication February 10, 2011; date of current version March 30, 2011. This
work was supported in part by NICTA. NICTA is funded by the Austrailian
Government as represented by the Department of Broadband, Communications
and the Digital Economy and the Australian Research Concil through the ICT
Centre of Excellence Program.
K. Wang, A. Nirmalathas, and E. Skafidas are with the Department of
Electrical and Electronic Engineering, The University of Melbourne, Melbourne,
VIC 3010, Australia, and also with National ICT Australia-Victoria
Research Laboratory (NICTA-VRL), Department of Electric and Electrical
Engineering, The University of Melbourne, Melbourne, VIC 3010, Australia
(e-mail: KeDesmond.Wang[at]nicta.com.au; nirmalat[at]unimelb.edu.au;
sskaf[at]unimelb.edu.au).
C. Lim is with the Department of Electrical and Electronic Engineering,
The University of Melbourne, Melbourne, VIC 3010, Australia (e-mail:
chrislim[at]unimelb.edu.au).
Color versions of one or more of the figures in this letter are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/LPT.2011.2113331
from severe multipath dispersion which limits the transmission
bit rate and also it is not energy efficient [3]. On the other hand,
the direct LOS system employs a narrow laser beam to establish
a point-to-point transmission link between the transceivers;
thereby the transceivers must be spatially fixed to satisfy the
strict alignment requirement. Therefore no mobility can be
provided in this scheme in spite of its potential of providing
extreme high transmission bit rate.
To take advantage of both kinds of OW systems, we have
recently proposed a novel OW system for indoor personal area
networking applications and have experimentally demonstrated
error-free BER transmission of up to 2.5 Gb/s
[8]–[10]. The concept used by us is similar to the “hotspot”
proposed by D.C. O’Brien et al. [4], however instead of using
a separate light source in each “hotspot”, we proposed the
ceiling mounted fiber transmitter which is simply composed
by a fiber end, a lens and a steering mirror. All these fiber
transmitters are connected to a central office (CO) by a fiber
distribution network and multiple rooms can be served by a
single CO. All the complex functions and expensive devices
are located in the CO to reduce the cost. We also proposed
to incorporate WiFi-based localization function with the OW
system and it enables dynamic change of the beam position to
provide ubiquitous coverage of the entire room. It should also
be noted that recently a remarkable 1.25 Gb/s indoor cellular
OW communication has been experimentally demonstrated [5].
However, an angle-diversity receiver was used and three transmitters
and receivers were needed for each user. In this letter,
we further improve our system to 12.5 Gb/s communication.
We also experimentally investigate and quantify the trade-off
between the maximum beam footprint and achievable bit rate
of our proposed OW system.
II. SYSTEM STRUCTURE
Our proposed system consists of a COthat centrally processes
and distributes the optical signal to a number of access points via
an optical fiber feeder network. The CO also acts as a gateway
to the external network. In the access point, the fiber end is the
transmitter and it is incorporated with a localization function to
provide ubiquitous coverage over a m m m room.
With the localization information of the subscriber, comparatively
wider divergent beam is employed to cover that user’s
position and its surrounding areas. Therefore both high speed
data transmission using direct LOS link as well as limited mobility
can be provided. When the user moves out of that area,
which can be identified by the localization system, the signal
light is then directed to the new position, resulting in mobility
over the entire room. The redirection of signal is realized by the
proposed ceiling mounted fiber transmitter, as shown in Fig. 1.
1041-1135/$26.00 © 2011 IEEE
520 IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 23, NO. 8, APRIL 15, 2011
Fig. 1. System structure.
This fiber transmitter consists of a fiber end, a lens and a steering
mirror. The lens is used to increase the divergence of the signal
beam to cover a certain area and the steering mirror is used to
change its orientation according to the localization information.
At the receiver end, a compound parabolic concentrator (CPC)
pointed straight up is employed to collect the signal before detection
with a photodiode (PD) directly [9].
The localization function can be realized through a number
of different methods, such as WiFi-based [11], Zigbee-based
system [12] and infrared-sensor-based [13].We have chosen the
WiFi-based localization scheme in our system for its low-cost
and easily available nature. Furthermore our system does not
require precise location which is also more suited to the WiFibased
localization system.
The room considered is a realistic office scenario consisting
of two rectangular cubicles with strong background lamps. All
the partitions are opaque therefore the incident signals are either
absorbed or blocked. Furthermore, the cubicles are equipped
with tables, chairs and other office equipments. It is obvious
that in such a scenario, shadowing due to physical obstacles
result in the worst signal reception and strong lamps creates an
environment of worst case background light. However as the
fiber transmitter is located just above the interactions of the two
adjacent cubicles, direct line-of-sight (LOS) channel is always
available.