1. Small Cell Deployments: Impacts on the
Energy Efficiency
Rouzbeh Razavi

2. Traffic growth for communication networks
3
10
2
10
Traffic (Tb/s)
1
10
Wireless data
0
10 P2P grows fastest
-1
Wireless Voice
10
-2
10
2010 2015 2020
Year
Data from: RHK, McKinsey-JPMorgan, AT&T, MINTS, Arbor, ALU, and
Bell Labs Analysis: Linear regression on log(traffic growth rate) versus
log(time) with Bayesian learning to compute uncertainity.
Transition to LTE will increase capacity trough more spectrum, better
scheduling, and MIMO, but these gains are not sufficient.
Energy consumption of networks will become an increasing problem. “More of
the same” will not be good enough.
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3. How can we
address these
problems?
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4. Historic Capacity Gains in Wireless
Networks
Wireless Network Capacity
Gains 1950-2000
15x by using more spectrum (3 GHz vs 150 Mhz)
5x from better voice coding
5x from better MAC and modulation methods
2700x from smaller cells
Total gain 1 million fold
Source: William Webb, Ofcom.
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5. Small Cells - A Necessary Topology Evolution
for Future Data Growth
Moving to hierarchical cell structures with small cells can:
• Significantly increase the capacity in the same bandwidth
• Significantly reduce the energy consumption of networks
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6. How can
Small Cells
improve
Energy
Efficiency?
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7. Impact of femtocells on the network energy
consumption
• Telecommunications is a large consumer of
energy (e.g. Telecom Italia uses 1% of Italy’s
total energy consumption, NTT uses 0.7% of
Japan’s total energy consumption)
Opportunity:
Small cells have the potential to reduce the transmit
power required for serving a user by a factor in the
order of 103 compared to macrocells.
Small cells can provide significant capacity improvement
in hotzone areas where traffic demand is high and hence
can replace traditional cumbersome macrocells
Due to their reduced coverage, small cells normally
serves fewer users and hence enable significant
reduction of power consumption if efficient idle mode
procedures are enabled
Source: BBC News - How the world is changing
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8. Methodology & Model
Given the traffic demand map for an area, find out the optimal
network topology in terms of the number and the transmit
power of macrocell and small cell required
Consider variations of hourly traffic demand to enable
investigation of idle mode procedures
System Model:
PNo_Load PTotal
PNoLoad PTotal Macrocell
γ= α=
PTotal PTotal Smallcell
Typical Values :
PTotal Macro = 1350 [W ]
PTotal Smallcell = 14 . 7 [W ]
γ Macro = 0 . 55 , γ Macro = 0 . 60
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9. Energy Consumption Improvements
Factor of 45.7 Energy
4 Reduction
Observations 10
x 10
Macrocells Only
9 PIF Macrocells=15%, PIF Smallcells=15%, γm =0.4, γs =0.4
Significant power reduction gains as the traffic
PIF Macrocells=30%, PIF Smallcells=30%, γm =0.2, γs =0.3
demand increases (Small Cells can replace 8
PIF Macrocells=50%, PIF Smallcells=50%, γm =0.2, γs =0.05
macrocells) 7
Total Power [W]
6
Improving the idle mode energy efficiency of
small cells (γs) is significantly rewarding 5
4
Challenge 3
2
Maintaining high Quality of Service (QoS) while
enabling efficient idle mode procedures for 1
small cells
0
2010 2011 2012 2013 2014 2015 2016
Year
References:
[1] R. Razavi and H. Claussen, “Urban Small Cell Deployments: Impact on the Network Energy Consumption" in Proc. IEEE Wireless Communications and
Networking Conference (WCNC),Paris, France, Apr. 2012.
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10. Reducing energy consumption
Idle mode procedures for Small Cells
When femtocells become more widely
deployed, their energy consumption
becomes a concern.
Idle mode procedures can:
• Significantly reduce energy consumption
• Reduce power density in the home
• Reduce mobility procedures and associated
signalling
• Reduce interference caused by pilot
transmissions
Femtocell activation based on noise rise from active UE
allows to activate the femto only for serving a call
References:
[1] I. Ashraf, L. T. W. Ho, and H. Claussen, “Improving energy efficiency of femtocell base stations via user activity detection," in Proc. IEEE Wireless Communications
and Networking Conference (WCNC), Sydney, Australia, Apr. 2010.
[2] H. Claussen, I. Ashraf, and L. T. W. Ho, “Dynamic idle mode procedures for femtocells," Bell Labs Technical Journal, to be published in 2010.
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11. Challenges and Ongoing Research
Enabling idle mode for small cells requires
- Efficient algorithms to enable sleeping/ awaking
- Modular hardware design that allow independent
operation of components
- Hardware design that fulfil the time to
reconfigure requirements after awaking
- Self-configuration/Optimisation algorithms that
can swiftly adapt to the environment changes
after awaking
Femtocell energy consumption - Today Femtocell energy consumption – Optimized design
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12. What is the
future for
Macrocells?
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13. lightRadio Cube and Active Antenna Array
lightRadio
cube
Digital link
Active
Antenna
Array
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14. What Do We Mean By lightRadio AAA?
Part I: “Invisible infrastructure” co-locating the
RF with the antenna
X X ⌧
X X ⌧
Conventional X Distributed X Active ⌧
X X ⌧
Node B site X Node B site X Antenna ⌧
X X ⌧
X X ⌧
RF
AAA Node B site
Remote
Radio
Head
Move RF to
Integration
antenna CPRI
CPRI
OR Cloud
Reduces Energy consumption by ~50%
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15. What Do We Mean By lightRadio AAA?
Part II: Places a “lightRadio cube” transceiver behind
each antenna element
RF •Pico Cell
•Micro Cell (SNAP)
•Macrocell
upgrade
Ethernet
or CPRI
Innovative Designs
can result significant
additional reductions
of energy consumption
for macrocells
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16. Remarks & Conclusions
• Wireless data traffic is increasing significantly in the future.
– Energy consumption of networks becomes a major problem.
• Small cells are a necessary topology evolution for future data growth and for
reducing energy consumption.
– Compared to an architecture consisting of only macrocells a hybrid
deployment results in significant energy reduction gains
– Idle mode procedures in combination with a modular hardware design are
essential.
– Future research focuses on modular hardware and software design of
small cells that that can enable efficient idle mode procedures
• Light Radio can improve energy efficiency of base-stations.
– Removing cable losses by integrating RF part and antenna into the
“lightRadio Cube” reduces energy consumption by ~50%.
– Individual control of antenna elements enables large scale antenna
systems which can significantly reduce the energy consumption for
macrocells.
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