Low-power sleep mode - Workshop Series on Green Communications

Bell Labs
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Low-power sleep mode
and out-of-band wake-up
for indoor Access Points
Ivaylo Haratcherev, Carine Balageas
and Michele Fiorito
2nd International Workshop on Green Communications - Honolulu, HI, USA, 4 December 2009
Current status
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“Your home Access Point is always on”
•  Today, the home Access Points (APs) are kept switched on 24/7 even if
there are no users that need connection (e.g. at night).
–  APs continuously listen in case of incoming terminals
–  APs periodically broadcast pilots/beacons to signal their presence
•  The massive adoption of home Access Points (+ Femtos, Boxes…) will
increase the overall power consumption.
–  36 Million femtocells will be sold by end 2012 (source: ABI Research report)
•  Home Access Points are increasingly underused.
–  A daily session = average length of 91 min. (source: iPass index for Wi-Fi).
–  Network densification trend = higher probability of temporary empty cells
Motivations to switch-off
Energy saving
Avoid useless radiation
Reduce interferences
Regulation
• European directives require
automatic switch-off to
standby mode for household
and office equipment with
power consumption
requirements, before 2012
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Increase security
The solution
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•  Energy efficient Standby mode on home Access Points.
–  at night or when users are away.
•  Innovative mechanisms to wake up the home Access Points.
–  rapidly restore connectivity to avoid any degradation of the user
experience
•  “Reverse idle mode” concept:
–  Roles are inverted: the home AP is in standby mode
–  the terminal is responsible to wake up remotely the AP when a user
needs connection
Wake-up
Standby
Energy efficient Standby mode
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•  Completely switch off the wireless interface (RF + baseband).
•  Entering standby mode on inactivity detection
Out-of-band wake-up
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•  As the primary radio of the home AP is switched off, a secondary
radio channel is used, dedicated to the transport of wake-up
messages from the Terminal to the home AP.
•  Thе secondary radio works on a different frequency (out-of-band).
•  ... and it is a low-power radio.
Terminal
Out-of-band wake-up
Low power
Radio module
Low power
Radio module
Access Point
Secondary Low Power Radio Module
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Why does it consume little power:
•  using narrow band channels and simple modulation schemes
(e.g. On-Off Keying, OOK)
•  radios specifically designed for sensor networks
•  short wake-up messages
Prototype design
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•  Wi-Fi technology to demonstrate the out-of-band wake-up concept
Access Point
Linksys WRT54G V3.1
Terminal
Lenovo T400
Core2Duo P8400
Low-power Radio Module
TinyNode 184
TinyNode advantages
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TinyNode 184
Power consumption
TX mode: 15/25 mA (0/10 dBm)
RX mode: 3 mA
Stand-by mode: 4 µA
Power supply
Transmission range
1.8 - 3.6 V
Outdoor 150 m @ 25 kbps +10dBm
Indoor 50 m @ 25 kbps +10dBm
Modulation
Frequency band
FSK, OOK
868-870 MHz
License free
frequency band
Simple CSMA MAC to
avoid contention
Transmission range
similar to the
coverage range of the
Wi-Fi Access Point
Wake-up message
contains an identifier
for authentication
Modification to the Access Point
Logical control
TinyNode
Serial connection
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Wi-Fi Radio
Module
Micro-controller
Electrical control
The low power module
at the AP operates in
RX mode only and
consumes around 10
mW
Power
Supply
Linksys WRT54G
Consumes 3 to 5 W
depending on conditions
Software implementation
Terminal
Access Point
•  Switch ON if serial message
received from the TinyNode
•  Switch OFF when no more
active connections
•  Need to send packets over
the 802.11 interface
•  Detection of kernel alarms
•  Delivery of serial message
User ID
TinyNode
•  Packet encapsulation
•  Radio forward
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User ID
Out-of-band
Wake-up
TinyNode
•  Packet decapsulation
•  Serial forward
Static results
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AP Power consumption in standby
Overall power consumption
ON components
OFF components
(currently the Wi-Fi interface)
P [W]
Wi-Fi interface ON
Wi-Fi interface OFF
3.36
2.48
26 %
More measurements …
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•  Emulation of user
behavior over an entire
day
•  Real-time power
measurements with a
NI acquisition module
and LabView
•  Results processed with
MATLAB
Power consumption over time
Wake-up delay
KERNEL
TX
DHCP
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Next generation switch-off
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•  Out-of-band wake-up
–  The secondary frequency to be used must be standardized to be
worldwide harmonized, as initiated by ETSI and IEEE 1900.4
–  Target = 90 % energy saving (all unnecessary modules
switched-off)
–  Shorter wake-up delay
•  In-band wake-up
–  Add low power receiver in primary radio frequency band of home
Access Points
–  No modification to the terminal
•  More future work
–  Extend the concepts to Femtos
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www.alcatel-lucent.com
www.alcatel-lucent.com
[email protected]
[email protected]
16 | Titre de la présentation | Mois 2009