Cellular base Station and its Greening Issues

Abstract

Minimizing of energy consumption in cellular system is becoming a major or growing concern for cellular operators not only to meet profitability, but also to reduce the impact on the environment. Since base stations consume a maximum portion of the total energy used in a cellular system, achieving energy efficiency has motivate some of the authorities and network operators to explore future technologies in the entire network infrastructures. This article put emphasis on the brief research of methods to improve the power efficiency of cellular networks, techniques to obtain energy saving in base stations.

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INTERNATIONAL JOURNAL OF ADVANCED ELECTRONICS & COMMUNICATION SYSTEMS
Approved by CSIR-NISCAIR ISSN NO: 2277-7318
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ISSUE 2 VOL 3, APR-MAY-2014 PAPER ID 86-221-SM
Cellular Base Station and its Greening Issues
Janmoni Borah 1, Sandeep Kumar Singh2, , Amlan Deep Borah3
Dept of CSE
National Institute of Technology,
Arunachal Pradesh-791112, India1, 2, 3
borah1989@gmail.com1
sandeeps177@gmail.com2
amlan20deep@gmail.com3
Abstract- Minimizing of energy consumption in cellular system
is becoming a major or growing concern for cellular operators
not only to meet profitability, but also to reduce the impact on
the environment. Since base stations consume a maximum
portion of the total energy used in a cellular system, achieving
energy efficiency has motivate some of the authorities and
network operators to explore future technologies in the entire
network infrastructures. This article put emphasis on the brief
research of methods to improve the power efficiency of cellular
networks, techniques to obtain energy saving in base stations.
Index terms- Smart grids, Off-grid, Power amplifier, Cognitive
radio, PAPR, Cell zooming, DRX, DTX, SON.
I. INTRODUCTION
Due to the frequently scaling of number of subscribers
and demand for cellular networks, there is a tremendous
growth in cellular system in the last few decades. Cellular
industries because of these issues relating to providing some
social networking giants to large number of users, has pushed
the limits of energy consumption in wireless network.
Currently more than 4 million BSs consuming an average of
25mwp per year, and the number of BSs in developing region
expected to double each coming year. And if is found that 2%
of total carbon emission by ICT (Information and
Communication Technology) nearly about 0.2% represents
mobile networks. Consuming about environmental aspects,
additionally energy cost also plays a vital role for network
operators. Since , BSs runs through off grid in remote areas
using diesel power generator cost nearly ten times more than
BSs running through electrical grid, which cost approx 3000$
per year.
Some of the regulatory bodies such that as 3GPP and ITU
[1][2], because of energy costs and carbon footprint have led
to an emerging trend of energy efficiency among of network
operators and innovate some green cellular networks. In this
regard, the European communication has recently started
some projects for power savings in multi-standard wireless
devices viz. EARTH (Energy Aware Radio and Network
Technologies), TREND (Towards Real Energy-efficient
Network Design) and C2POWER (Cognitive Radio and
Cooperative for power saving) [3][4][5]. Some authors [6]
identified key trade-off for between network performance with
energy efficiency deployment efficiency, spectrum efficiency,
bandwidth and delay. And some of the paradigm–shifting
technologies such as BS redesign, smart grids, heterogeneous
network deployment and efficient wireless protocols were
address to meet the increasing power efficiency in future
wireless networks and thereby maintaining profitability. Thus
reducing energy consumption has become a vital issue for
cellular industries, maintaining economical, environmental
and marketing conditions. In recent years, a valuable effort
has been done towards to reducing unnecessary energy
expenditure, which is called as a greening of the networking
technologies.
II. GREENING THE BASE STATION
In recent years, the number of cellular BSs has increased
from a few hundreds to many million on worldwide, due to
the rapidly growing demand for mobile communication
technology. Such a large growth in the number of BSs causes
the sudden increase in population and greenhouse gases and to
higher energy costs to operate them. The radio network
consumes up to 80% of operators entire energy consumption.
With the development of some intensive cellular standards, it
is found that power consume by BS increases up to 1400 watts
and energy costs per BS reaches up to $3200 per annum with
a carbon footprint of 12 ton of CO2 [7].
Fig.1 Power utilization in a cellular system [15] (ref. therein)

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Some manufactures related to production of BS
equipments has offer a number of eco and cost effective
solution to reduce BS power and to support off-grid technique
in BSs with renewable in nature [8][9][10]. Figure 1 above
provides an idea related to power utilization in a typical BS
and other components such as switching center, data center,
and BS core material of a cellular system. The various
methods presented by some of the authors in [11] such as
related to improved transmitter efficiency, system features,
cooling, renewable energy sources and energy saving during
low traffic. Most typical cellular system comprises mainly
three components-A core network for switching, BSs for radio
interface and mobile terminals for connecting voice and data.
So with the increasing in BSs, it is necessary to point out their
energy consumption in the system or network. Related to
above issues, the below points address or discuss about
different ways in reducing BSs energy consumption.
A. BS-HARDWARE AND SOFTWARE MANAGEMENT.
The improvement in the hardware design and inclusion of
some system featured software in a typical BS can balance
proper energy consumption and performance. Additionally to
improve or redesign hardware of BS related to energy
consumption, the power amplifier (PA) dominates a lot. So
energy efficiency of PA is a great concern and it depends on
the frequency band, modulation and operation environment
[11]. Some feature related to improving energy efficiency of
BS during low traffic or cell zooming and in addition, RF
heads and modular BS design can be helpful to reduce power
loss in feeder cables were discussed in [11].
Fig. 2 Utilization of power in cellular base stations [16] (ref.
therein)
Some steps towards BS redesign includes -
1) Power amplifier modification
Figure 2 above shows power utilization by cellular BSs
during amplification, cooling mechanism, and data processing
and supplied power needed by a BS. The most essential
components of a BS include radio, baseband and feeder. It is
found that radio part of BS consumes more than 80% of the
total BSs energy and PA consumes almost 50% of its [12].
Also it is to be noted that 80-90% of that is wasted as heat in
PA, which is then requires air-conditions, results in more
energy cost. Depending on the standards deployed viz. GSM,
UMTS, CDMA and the equipments used, the currently
deployed amplifier provides a ratio of AC power input to
generated RF output power of range from 5% to 20% [13]. In
order to have PA linearity and high peak-to-average power
ratio (PAPR) maintaining the quality of the radio signals, PAs
have to operate well below saturation, which results in poor
power efficiency. Since some technologies related to level
efficiency of modern amplifiers have reached their limits, PAs
based on some special architecture such as digital pre-
distorted, Doherty architecture and GaN (Aluminium Gallium
Nitride) based amplifiers seems to be more efficient by
pushing the power efficiency levels to over 50% [13]. In
addition to this, we need to investigate more efficient
modulation schemes, because modulation also affects the PA
efficiency. Also using some different linearization techniques
like Cartesian feedback, feed-forward with different kind of
DSP methods is suggested [11].
2) Using power saving protocols.
For high speed data networks and energy conservation
both in the hardware and protocols, BSs and mobile units
employ new hardware such as MIMO antennas that increases
spectral efficiency and allows transmitting more data with
same power. Also LTE standards deal with the developing of
some power saving protocols such as Discontinuous reception
(DRX) and Discontinuous transmission (DTX) for mobile
handsets which provides a power saving by switching off the
Transceiver whenever there is no need to transmit or receive.
Unfortunately such power saving protocols for BSs have not
been considered in the current wireless standards. In future
wireless standards, energy saving protocols of BSs needs to be
exploited by designing protocols to enable sleep nodes in BSs.
B. ADOPTING RENEWABLE ENERGY RESOURCES.
Most of the remote locations in the world such as Africa
and Northern Canada rely on off-grid i.e. diesel powered
generators rather than electrical grid to run BSs, which is not
only expensive, but also generate huge amount of CO2. Such
generator consumes an average of 1500 litres of diesel per
month, resulting in a cost of approximately $30,000 per year
to the network operator and also adds transportation cost.
Figure 3 shown below gives an overview related to
increase in the on-grid base stations compared to off-grid one
in developing regions of the world. The fig.3 also provides a
statistical data related to development of base stations from
2007 to 2012. Thus adopting resources such as sustainable
bio-fuels, solar and wind energy seem to be more viable to
reduce network expenses and CO2 emission.
Recently, under the association of GSM program named
“Green Power for Mobile” has been started by 25 leading

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telecoms including MTN Uganda and Zain to renewable
energy resources for BSs [14]. Powering that many BSs on
renewable energy would save up to 2.5 billion litres of diesel
per annum and cut annual carbon emissions by up to 6.8
million tonnes.
Fig. 3 On-grid BSs compared to Off-grid BSs in developing
region [17] (ref. therein).
C. ALTERNATIVE METHODS.
The total energy consumption of a cellular network
includes the summation of energy used by each BS. So some
features such as 2-way and 4-way diversity, feeder less site,
extended cell, low frequency band, 6-sector site and smart
antenna can be used to minimize the number of BS sites [11].
By bringing some architectural changes to the BS, the power
efficiency of a BS can be improved. Currently, long coaxial
cables are used as connection between the RF-transmitter and
antenna which add almost 3dB to the losses in power
transmission and therefore, low power RF-cables should be
used and RF-amplifier has to be kept closer to the antenna
[13]. Also a concept of self organizing networks (SON) have
been introduced in 3GPP standard (3GP Ts 32.521) to add
network management and intelligence features and heal itself
in order to reduce costs and improve network performance and
flexibility.
III. CONCLUSIONS
This paper presented a brief research of methods that have
been currently adopted or will be adopted in near future in
order to obtain energy efficiency in base stations (BSs), since
BSs consumes a major portion of the total energy in the
cellular communication. Also we addresses some of the recent
improvements in power amplifier (PA) technology which will
not only bring energy savings in BSs, but will also make BSs
less dependent on cooling mechanism. We also put emphasis
on power saving protocols for next generation wireless
systems, energy aware cooperative BS power management,
cell zooming, using of renewable energy resources at the off-
grid sites, minimizing the number of BSs and changes in the
network design which can be beneficial in achieving energy
efficiency in cellular systems.
ACKNOWLEDGEMENTS
On the very outset of this report, we would like to extend
our sincere & heartiest obligation towards all the personages
who have helped us in this Endeavour. Without their active
guidance, help, co-operation & encouragement, we would not
have made headway in the research.
We would also like to thank Mr. Swarnendu Kr.
Chakraborty (HoD i/c, Dept of CSE, NIT Arunachal
Pradesh), to give us the chance to do this paper work and all
the staff members of CSE dept. for their motivation, guidance
and support throughout the research. First and foremost, we
would like to thank Mr. Anish Kr. Saha (Asst. professor,
Dept of CSE, NIT Arunachal Pradesh) who instead of his
busy schedule, always guided us in the right direction. We
were privileged to experience a sustained enthusiastic and
involved interest from his side. This fuelled our enthusiasm
even further and encouraged us to boldly step into what was a
totally dark and unexplored expanse before us. He always
fuelled our thoughts to think broad and out of the box.
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