Network Energy Saving Technologies For Green Wireless Network Access

3.  The energy consumption of cellular networks worldwide has become
a major obstacle to the continued future development of mobile data
services.
 It is very urgent need to reduce energy consumption both for
environmental protection and operational cost reduction reason.
 Recently, mobile telecommunication operators worldwide have been
becoming increasingly aware of these existing and upcoming energy
challenges and have begun to study and research an area that has now
been coined “Green Radio” - techniques and solutions which can be
employed to improve the energy efficiency of the Mobile Access
Network.

4.  Base stations contribute 60% of the whole network
energy consumption. Thus the efforts in the reduction
of energy consumption focus on the BS equipment,
which includes the minimization of BS energy
consumption.
Fig 1: Energy consumption composition of a mobile operator

5.  Energy efficiency through better
performance of BS hardware.
 Usage of system level and software
features .
 Usage of BS site solutions.

6.  Boosting the power efficiency of High Power
Amplifier by reducing the PAR of the transmitted
signal.

7.  If the system load is low, then energy can be saved by
switching off some of the transmit antennas.
 The energy efficiency of the base band unit (BBU) of
the base station can be further improved by introducing
power save modes to subunits.

8.  Underutilized cells are switched off whenever traffic load is
small.
 If switching off a cell creates uncovered areas, remaining
active cells need to increase their power to cover this area.
 Switching off cells may reduce the battery life of served UE
units as they have to connect with other cells far away.
Fig 2: Hexagonal and crossroad configurations

9.  With indoor sites the energy could be saved by utilizing
fresh air cooling systems instead of using air conditioner.
 With RF head or modular BS the RF transmitter is located
close to BS antenna.
 With outdoor sites, the cooling requirements can be
lowered by raising the allowable operating temperature
range for the BS site.

10.  TIME DOMAIN
• PA Off at Signal-Free Symbol
• MBSFN
• Extended Cell DTX
 FREQUENCY DOMAIN
• Bandwidth Reduction
• Carrier Aggregation
 SPATIAL DOMAIN
• Reduce Antenna Number
 HYBRID SOLUTIONS

11. Fig 3: Reduce RSs of LTE frame in idle and low traffic load conditions
 The time domain solutions in LTE temporally shutdown PAs in a
RBS when in given time there is no data traffic in the downlink.

12. PA Off at Signal-Free Symbol
• Turn off PAs in time periods of a slot where downlink symbols are
signal-free.
• Some symbols of each sub frame cannot be signal-free due to the
need to transmit RSs and control signals.
• At least 47% of the time in a frame, Pas has to be on due to the need
to transmit RSs and control signals.

13. MBSFN
• In an MBSFN frame, the symbols for RS in sub frames 1–4 and6–9
are reduced to 1.
• The PA operating time during a frame is then reduced 28% .
Extended Cell DTX
• It is currently under discussion in 3GPP Radio Access Network
Working Group.
• If there is no downlink traffic, in this mode there is no need to
have any transmission in sub frames 1–4 and 6–9 of a frame.
•The PA operating time in a frame is further reduced to 7.1%.

14. Bandwidth Reduction
• If the downlink traffic is low, the channel bandwidth can be shrunk
so that less power is required.
• Fewer RSs are needed for smaller bandwidth. This further reduces
the power budget.
Carrier Aggregation
• Shut down the associated PAs when the corresponding aggregated
carriers are not scheduled for the downlink traffic.
• It is only applicable to an RBS that has aggregated carriers and
separate PAs attached to each group of carriers.

15. Reduce Antenna Number
• If the branches of antennas are reduced energy consumption
of transceivers is reduced ,as the PAs associated with those
branches can be switched off.
• It can combine with the bandwidth reduction technique for
the low traffic mode of an RBS.
• Boost the power of RSs and control signals so as to maintain
the cell size.

16. • It combine solutions in different domains to adapt energy
consumption of an RBS in different traffic conditions.
• The challenge of hybrid solutions is the processing/interruption
time and signaling for system reconfiguration.

18.  Extended cell DTX and MBSFN for no load, achieve energy
saving gain less than 8%.
 Among three low load approaches, MBSFN for low load
shows highest performance.
 The bandwidth reduction solution outperforms the
antenna number reduction solution.
 Better energy saving gain can be achieved by the hybrid
solution.

19.  This thesis contributes to the mainstream discussion on the
importance of reduction in energy consumption to achieve
economic and environmental benefits.
 Particularly it has addressed the possible ways to minimize the
energy consumption on the BS sites.
 It is identified that the common energy consumption problem in
an RBS of a wireless access system is the energy scaling
traffic load problem. It can be tackled by solutions from the
time, frequency, and spatial domains.
 As most solutions only focus on a single RBS, we believe the
most promising solutions are those that apply hybrid techniques
cross multiple networks.