ABSTRACT
The abstract of the paper talks about how wireless communication
is dominating the present
communication scenario. It talks about how wireless will also
dominate our future connectivity
requirements, as we move towards speeds greater than
gigabits/second. In all of this wireless scenario
the authors stress that photonics can provide an energy
efficient, scalable and high speed front end and
back end technologies. The most important concern when it comes
to implementation of any new
technology is its commercial viability as at the end it all
comes down to making it cost friendly for the
consumer. This technology as claimed by the authors will provide
cost-effective network integration
approaches as well as competitive optical wireless connectivity
alternatives.
1) Gigabit Wireless
The first part of the paper starts off with the introduction of
the term Gigabit wireless. The later parts of
the paper speaks about how photonics can be used to achieve
this. Now coming back to gigabit wireless,
we know that how the capabilities of our computing and
communication devices continue to improve
on a daily basis. The display, camera and processors
technologies are being improving like never before.
The number of such devices will only grow exponentially in the
future and a majority of them will be
embedded into natural or built environments. With the Internet
of Things everything will be connected
in future and a lot of data will be generated and high data
rates would be required to handle them. For
all these devices the most efficient method of getting connected
is wireless as it provides most flexible
on demand connectivity anywhere with rapid convergence of fixed
and mobile wireless broadband
technologies. The mobile networks are going to the next era of
5G going beyond the 4G systems and this
would mean that there will be an increase in speeds and the data
rates will certainly exceed the Gigabits
per second rates. To accommodate these high data rates, wireless
networks will be required to deploy
large number of base stations and they will be deployed in a
hierarchical manner to balance the capacity
and bandwidth allocation. The adoption of millimeter wave
frequency bands have opened the possibility
of providing speeds greater than Gigabits/second over smaller
cells in the form of pico and femto cells.
Large number of devices being always connected means there will
be a lot of increase in wireless data
traffic and bandwidth accessed by them. This would mean that the
focus would shift to how base
stations are connected the network via front end and back end
technologies.
The authors have presented their works focusing on optical
backhaul technologies and optical backhaul
network planning for small cell deployment as well as optical
wireless options for the indoor
applications.
2. Photonics for wireless front-haul and back-haul.
The authors believe that from single antenna site to phased
array systems optical fiber links can provide
efficient connectivity. The normal way is to provide a microwave
point to point link, but the optical fiber
links can provide high performance, scalable and energy
efficient physical layer connectivity. Some of
the new functionalities needed in the next generation wireless
networks would be collaborative signal
processing, beam forming and interface mitigation these can be
achieved by bringing together signals
from a range of antenna sites, distributed antenna systems and
phased array systems. Optical fiber is
being significantly deployed and they have emerged as the most
cost effective way to realize wireless
backhaul.
3) Optical Transport of microwave and millimeter wave wireless
signals.
Fig1. Options for transporting microwave and millimeter wave
signals over an optical fibre links and
complexity trade-offs in the architecture of base stations.
The above figure shows the most popular approaches that had been
researched over the past two
decades. 1(i) represents direct transmission of radio frequency
signal over fiber and requires high speed
analog link with good spurious free dynamic range (SFDR) and
high speed transreceivers. Where as
digitized RF over fibre shown in 1(ii) removes the need to have
while maintaining the same advanages
and slightly imroving the energy efficiency.
4. Optical backhaul network planning and design.
Traditionally wireless networks were planned depending on the
network capacity considerations and
wireless propagation over a given terrain. As we are moving
towards Gb/s speeds, the base stations are
required to be near to the customers in a cpnstellation of small
cells thus creating a challenge of
achieving the a cost-effective backhaul. A alternate approach
has been proposed by the authors, as the
penetration of optical fiber has incerased the existing fiber
access points as a starting point in selection
of potential locations for small cell base-stations and then
ensured coverage map could meet the
capacity requirements.
5. Fiber-Fed Gigabit Optical Wireless
The authors have proposed an indoor optical wireless system,
that is a hybrid of LoS and diffused beam
system and fed by an optical fiber distribution network.
This system has a ceiling mounted transmitter which establishes
a cone of light, it comprises of a focusing lens on a sliding pair
arrangement and a pair of steering mirrors (MEMS) to control the
beam width and direction. The reciver uses a compound parabolic
concentrator (CPC) to collect light from a wide field of view and a
photo-detector to receive light. In the uplink direction it uses
the same arrangement. Depending on the bit rate of the optical
transmission, coverage zones with different beam waists [specified
for a bit error rate of -9] can achieved. The authors could achieve
an uplink data rate of 500 Mb/s in one of the experiments the
conducted. 6.Conclusion The authors by this paper have proposed
that for networks going into data rates of Gb/s, Optical fibers
will provide an efficient and cost-effective way of providing a
back haul and front haul connection.
