Chapter 17: Green Broadband Access Networks

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Chapter 17 Green Broadband Access Networks
HANDBOOK ON GREEN INFORMATION AND COMMUNICATION
SYSTEMS

• Tao Han, Jingjing Zhang, and Nirwan Ansari
• Advanced Networking Laboratory,
• New Jersey Institute of Technology,
• Newark, NJ, United States

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Green Broadband Wireless Access Networks

• Techniques on greening cellular networks
• Power saving communication protocols
• Heterogeneous network deployment
• Enabling off-grid BSs
• Greening via cooperative networking
• Cooperation among BSs
• Cooperation between BSs and UEs

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Power saving communication protocols

• Idea Adjusting the transmit power of the
  transceivers according to the traffic intensity
• Traffic volumes variation
• Typical day-night behavior of users
• Mobility of users
• Users tend to range over their office districts
  during working hours and stay home in their
  residential area after work. This results in the
  surge of traffic in both areas at peak usage
  hours, but in the drop of traffic during the
  off-peak hours.
• Solutions
• Switching off the transceivers when the traffic
  load is below a certain threshold for a certain
  time period. When some base transceiver stations
  are switched off, radio coverage and service
  provisioning are taken care of by the remaining
  active devices.

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Heterogeneous Network Deployment

• Disadvantages of Homogeneous Network Deployment
• Optimization of the location of BSs is
  complicated
• Limited ability to adapt to the traffic load.
• Heterogeneous Network Deployment
• Utilizing a diverse set of base stations can be
  deployed to improve spectral and energy
  efficiency per unit area.

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Enabling Off-Grid BSs (1)

• Designing off-grid BSs and communication
  protocols to enable optimal utilization of
  renewable energy in cellular access networks
• Off-grid BSs

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Enabling Off-Grid BSs (2)

• Designing communication protocols to maximize the
  utilization of green energy
• Energy Source Aware Target Cell Selection (Ref.
  31)
• The proposed algorithm is to ease the mobile
  users to handover into the green cell and also to
  make the UE more difficult to leave the green
  cell. As a result, the coverage of the green cell
  is actually enlarged, therefore reducing the
  on-grid power consumption.

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Greening via Cooperative Networking Cooperation
among BSs

• Green opportunities
• Cooperation umbrella cell and the underlying
  cells in multi-layer cellular network
  architecture
• Cooperation among BSs in flat cellular network
  architecture
• Cooperation among BSs from different mobile
  service providers

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Greening via Cooperative Networking Cooperation
among BSs

• Green challenges
• When to cooperate determine the traffic
  threshold for cooperation
• If the threshold is too high, the coalition will
  break down in a short time period. In other
  words, some BSs that were turned into the sleep
  mode in the cooperation will restart soon. In
  this case, the energy consumed by restarting the
  BSs may be much higher than that of
  noncooperation.
• If the threshold is too low, the BSs may miss
  some cooperative opportunities.
• Who to cooperate determine the coalition among
  BSs
• Determine the size of the coalition
• Determine the members of the coalition

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Greening via Cooperative Networking Cooperation
between BSs and UEs

• Green opportunities
• Unified cellular and ad-hoc network architecture
  (ref. 33)
• Cooperation with beamforming
• Transmit beamforming provides incentives to the
  relay users to stimulate the cooperation
• One hop relay to attain largest performance
  improvement while consuming minimal relay energy

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Greening via Cooperative Networking Cooperation
between BSs and UEs

• Cooperation network protocols
• Channel measurement and data request
• Transmission strategy calculation
• Relay selection and cooperation negotiation
• Relay assignment and relay negotiations
• Relay assignment acknowledgement
• Data transmission

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Greening via Cooperative Networking Cooperation
between BSs and UEs

• Green challenges
• Channel state information
• New protocols to enable the measurements and
  updates of the channel state information among
  UEs
• How to efficiently feedback the channel state
  information to BSs
• Incentive mechanism
• Design incentive mechanism to avoid tragedy of
  common
• Hybrid handover scheme
• Design an efficient handoff scheme to address the
  handovers from BSs to BSs, from BSs to relay UEs,
  from relay UEs to relay UEs, and from relay UEs
  to BSs.

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Greening via Cooperative Networking Cooperation
between BSs and UEs

• Case study energy efficient wireless
  multicasting (ref. 34)
• The energy efficient wireless multicasting
  integrates multicast beamforming and cooperative
  networking. It contains two phases in phase 1,
  the base station (BS) transmits the signal to the
  subscribers using antenna arrays with multicast
  beamforming in Phase 2, the users who
  successfully received the signal in phase 1
  forward the signal to other users. The
• unsatisfied users combine
• the received signals in both
• phases to retrieve the infor
• -mation.

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Greening via Cooperative Networking Cooperation
between BSs and UEs

• Case study simulation results (1)

The simulation compares the minimal transmit
power of different multicasting strategies. With
transmit beamforming, BS saves more than 3dBm
transmit power. Lozano's algorithm is a multicast
beamforming algorithm that does not consider
cooperation. As the number of users increases,
the performance of the proposed algorithm becomes
better because there are more cooperative
opportunities. When the number of users is larger
than 40, the performance becomes steady, in which
it uses about 3.5dBm, 2dBm, and 1dBm less
transmit power than those of Lozano's algorithm,
respectively. It becomes steady because when the
number of users is large enough (40 in the
simulation), the cooperation gain is not limited
by the cooperative opportunities, and becomes
steady.
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Greening via Cooperative Networking Cooperation
between BSs and UEs

• Case study simulation results (2)

This simulation compare the BS power consumptions
under different multicasting strategies. . The
blue line indicates the power consumption of the
standard LTE Macro BS, which can be considered as
the power constraint of BS. Note that simply
broadcasting without beamforming and cooperation
cannot satisfy the users' requirement under the
constraint. As compared to the Lozano's multicast
beamforming algorithm, our proposed algorithm can
save at least 100 Watts when the number of users
is larger than 60. The power savings are
benefited from the cooperation between BS and
users.
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Green Broadband Wireline Access Networks

• Why saving energy consumption of optical access
  network is important?
• Where and how much is the power consumed in
  Passive Optical Network?
• Where is the power wasted?
• Optical network unit (ONU) and optical line
  terminal (OLT)
• How to save? - proposals
• Vision and challenges
• Proposals

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Motivation

• Power consumption of FTTx networks

• Power consumption
• On average, each FTTx user consumes 15w (gt30w)
• In 2011, the total FTTx energy consumption is
  11 TWhr, equal to 7M tons of CO2, 3 extra 500MW
  power stations

Goals Save FTTx energy consumption!
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Background Passive Optical Network

• Passive optical network (PON) the major FTTx
  technology

• 1 OLT chassis
• contains 8 OLT line cards
• consumes 100w
• 1 OLT line card connects with 32 ONUs
• OLTs consume lt40 of FTTx energy (NTT)

• 1 ONU consumes 10w
• ONUs consumes gt60 FTTx energy

Question How to save energy at OLT and ONUs?
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Upstream and downstream scenarios

• Upstream scenario
• Pros the upstream traffic arrival triggers the
  wakeup of asleep ONUs
• Challenges physical layer implementation, fast
  wakeup and fast sleep
• Downstream scenario
• Owing to the broadcast nature, an ONU needs to be
  awake all the time to check the header of each
  packet!

upstream

• When the upstream buffer is empty for some time,
• ONU enters into sleep
• 2. Upon the upstream traffic arrival, ONU wakes up

ONU
ONU
user
Control scheme is needed to put an ONU into sleep
when it doesnt have downstream packets!
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How to put an ONU into sleep in the downstream
scenario?

• Existing proposal two-way or three-way handshake
• When the downstream queue of an ONU is empty for
  some time, OLT sends a message informing ONU to
  sleep
• ONU sends an ACK to confirm the sleep
• It addresses the problem, but
• At least one round trip time needs to be taken
  for negotiation
• EPON MPCP protocol needs to be extended to
  support the mechanism

ONU
OLT
Ref J. Mandin,10G-EPON task force meeting 2008,
R. Kubo et al., Globecom09, JOCN10 S. Wong, et
al. Greencom09, OFC10
Sleep notification
Sleep ack
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Our proposal main idea

• Main idea let ONU infer its downstream queue
  status instead of being explicitly notified by
  OLT
• Assume OLT schedule downstream traffic of ONUs
  with nonempty queues in order (e.g., 1, , N)
• If no traffic is destined to an ONU for some
  time, the ONU can infer that it doesnt have
  downstream traffic, and then go to sleep

Onu 1
onu2
onu2
OLT
ONU 1
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Our proposal

• Implement a sleep control algorithm at ONU
• How can an ONU avoid missing downstream packet
  when it is sleeping?
• Solution Implement a sleep control algorithm at
  OLT
• Pros easy implementable, compatible with current
  protocol

Sleep control algorithm If no traffic is sent to
me for time t_silent, then, I will go to sleep
for time t_sleep
OLT
ONU
Sleep control algorithm If I havent sent
traffic to ONU i for time t_silent, then, I will
buffer its traffic which arrives in the next
t_sleep time
OLT
ONU
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Energy-Efficient OLT

• Current status
• One OLT chassis contains multiple line cards
• All OLT line cards are power-on all the time
• OLT traffic profile
• Why not aggregate traffic of multiple line cards
  and power off some line cards in off-peak hour?

Typical daily traffic profile
Off-peak hour traffic rate is much less than peak
hour traffic
Peak hour
Off-Peak hour
Source Amsterdam Internet Exchange
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Energy-efficient OLT

• How to aggregate traffic of multiple PONs at OLT?
• Assume one OLT chassis contains 4 line cards

OLT chassis
Green OLT chassis
ONUs
OLT line card
ONUs
OLT line card
44 optical switch
ONUs
OLT line card
ONUs
OLT line card
ONUs
OLT line card
ONUs
OLT line card
ONUs
OLT line card
ONUs
OLT line card
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Energy-efficient OLT

• Assume the switching speed is fast (lt1 DBA
  cycle),
• i.e., the switch configuration can be rather
  dynamic

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Energy-efficient OLT

• Assume the switch speed is slow,
• i.e., the switch configuration is semi-static
• Further assume the traffic is uniform among all
  PONs

Case 3 Loadlt25
Case 1 Loadgt50
Case 2 Load 25 50
OLT line card
OLT line card
OLT line card
OLT line card
OLT line card
OLT line card
OLT line card
OLT line card
OLT line card
OLT line card
OLT line card
OLT line card
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Simulation results
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Conclusions

• Green broadband wireless networks
• Techniques on greening cellular networks
• Power saving communication protocols
• Heterogeneous network deployment
• Enabling off-grid BSs
• Greening via cooperative networking
• Cooperation among BSs
• Cooperation between BSs and Ues
• Case study energy efficient wireless
  multicasting
• Green broadband wireline networks
• Energy consumption measurement in Passive Optical
  Networks
• Energy waste in ONU
• Energy wast in OLT
• Energy efficient Passive Optical Networks
• Energy efficient ONU
• Energy efficient OLT

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Thanks for your attention!