Page 119 - ITU Kaleidoscope 2016

ICTs for a Sustainable World

from the antenna. In this case however, the radio processing transceivers that can be manufactured in high volume and
delay requirements become the limitation. In LTE the Up- low cost [24].
Link Hybrid Automatic Repeat reQuest (UL-HARQ) has a
4 ms response time requirement that, given the processing
2.3. Data Centres
time requirements, translates into a maximum fibre distance
of 20 km. A small amount of additional headroom can signif-
Data centres are proliferating worldwide, but mostly in urban
icantly increase the optical reach. This would open the pos-
areas and developed countries, thus increasing the global dig-
sibility to distribute the low-cost, low-power, high-reliability 2
ital divide. The reason is that the conditions in rural and de-
radio heads across an area extending 20 km from a central-
veloping countries often exacerbate the challenges for oper-
ized processing location, where higher reliability, security,
ating data centres in addition to prohibitive acquisition costs.
and greater efficiency may be possible [18].
A part from the previously discussed connectivity problems,
When considering core transport networks (i.e., the ones energy provisioning raises several challenges. Specifically,
used to move data from/to access networks), renewable en- in developing countries electrification is often not com-
ergy such as solar will likely be important for many rural plete and especially rural areas lack access to the electric
areas with limited power availability. Their drawbacks is grid. To cope with energy variability and security, research
mainly in their lack of reliability. In this context, several on demand-response and emergency demand-response [25]
studies have looked at the operation of optical systems in tries to optimize the data centre operation based on the en-
the presence of a variable and renewable energy sources (see ergy costs and availability. For this, they exploited the large
e.g., [19]). body of research which went into power consumption flex-
Another way to reduce the cost and improve the resource ibility at data centres via capacity right-sizing [26], load
efficiency in a transport network is to introduce advanced shifting over time [27] and across geographies [28].
network functionalities (i.e., dynamic resource sharing and To overcome the lack of grid access and to green the impact
Network Function Virtualization (NFV)) [20]. This allows of data centres as well as to drive down the CAPEX costs,
for example the allocation of resources on-demand to sup- data centres are scaled down in size [29], powered via re-
port specific transport needs that may vary over time, with- newable energies [30] and rely on micro-servers with better
out the need of manually setting up the devices. Dynamic work done per joule and work done per dollar ratios [31].
resource sharing is based on the intuition that the same trans-
To reduce the energy consumption and OPEX costs, re-
port resource can be dynamically shared over time for dif-
search tries to optimize the three major pillars in data centre:
ferent transport purposes. NFV provides flexibility by dy-
IT, cooling and power (see e.g., [33]). The upcoming 5G
namically placing network functions in different locations
also promotes the use of softwarization and virtualization as
depending on the specific need of a service, e.g., close to the means to drive up efficiency [34], especially via cloud-based
users to exploit traffic locality. Examples of network func- radio access networks [35].
tions that can be virtualized include for instance Evolved
Packet Core (EPC) functionalities for local breakout, virtu-
alization of packet aggregation capabilities, and virtualiza- 3. CHALLENGES
tion of computing and storing functionalities, e.g., network
caching. We first review the challenges related to the exploitation of
These advanced functionalities required the presence of dis- 5G technologies iin rural and low-income zones the first step,
tributed (possibly small) Data Centre (DC). Therefore, the and then we consider the socio-economic aspects that need
possibility to have low-power low-cost DC solution is cru- also to be taken into account.
cial. In this respect optics can help again [21]. Small form 5G Technology Challenges The application of 5G in rural
factor optics for DCs use minimal electronics and trade per- and low-income areas is challenged by the peculiar features
formance for low cost. Long reach transceivers are available of such scenarios. Tab. 1 reports a comparison between a
up to 100 Gb/s and 80 km reach. Continued progress in classical 5G urban scenario [5] against 5G rural and low-
3
reducing the cost and form factor of these optics will be income ones (whose requirements may be inferred from
important for applications in rural and low-income areas. [36]). In contrast to 5G urban’s most advanced Internet
Integrated photonics is a promising approach to doing this services such as High-Definition (HD) streaming, tactile In-
[22]. In particular, silicon photonics integrates multiple ternet and Internet of Things, many rural and low-income
photonic devices on silicon chips, which are often Comple- regions are still disconnected from the rest of the world
mentary Metal Oxide Semiconductor (CMOS) compatible, and the lack of Internet coverage is the most critical prob-
with the potential for optical devices to share the same cost lem to be tackled. The state of several essential services
benefits of high-volume micro-electronics. Recently, single- such as e-Learning and e-Health have remained substan-
chip Wavelength Division Multiplexing (WDM) chips were dard. Therefore, the infrastructure is required to support the
manufactured with 500 Gb/s aggregate data rate and as many
2 Data centres requirements may be different than the ones of telecom-
as 1700 devices [23]. This Indium Phosphide (InP) based
munication networks, which are mainly based on central offices.
chip was designed for long-haul links. Intense research and 3 Low-income areas include both low density regions in terms of popula-
development are currently underway for silicon photonic tions as well as town and cities.

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