Project
IEEE 802.16 Broadband Wireless Access Working Group <http://ieee802.org/16>
Title
Sleep Mode Considerations for a Device-Based Power Saving
Date
Submitted
2008-07-07
Source(s)
Mamadou Kone, Ming-Hung Tao, Ying-Chuan Hsiao,
Richard Li
ITRI
Re:
IEEE 802.16m-08/016r1 - Call for Contributions on Project 802.16m System Description
Document (SDD), shoot for “Upper MAC concepts and methods (limited to addressing, mobility
and power management)” topic.
Abstract
This contribution proposes a unique Power saving Class as a device based sleep mode.
Purpose
For discussion and approval by TGm.
Notice
Release
Patent
Policy
E-mail: 970031@itri.org.tw,
richard929@itri.org.tw
This document does not represent the agreed views of the IEEE 802.16 Working Group or any of its subgroups. It
represents only the views of the participants listed in the “Source(s)” field above. It is offered as a basis for
discussion. It is not binding on the contributor(s), who reserve(s) the right to add, amend or withdraw material
contained herein.
The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution,
and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name
any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole
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contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.16.
The contributor is familiar with the IEEE-SA Patent Policy and Procedures:
<http://standards.ieee.org/guides/bylaws/sect6-7.html#6> and
<http://standards.ieee.org/guides/opman/sect6.html#6.3>.
Further information is located at <http://standards.ieee.org/board/pat/pat-material.html> and
<http://standards.ieee.org/board/pat>.
IEEE C802.16m-08/580r1
Sleep Mode Considerations for a Device-based Power Saving
Mamadou Kone, Ming-Hung Tao, and Ying-Chuan Hsiao
ITRI
1-Introduction
In 802.16m there are three types of power saving class (PSC) defined according to the connections common
demand properties. The PSC type 1, based on BE and NRT-VR connections, starts with an Initial sleep window
and a fixed listen window to monitor MOB_TRF_IND for DL data. Whenever the received traffic indicator
does not signal incoming data and MS does not have any UL data to send, the next sleep window will be twice
the previous length. This process continues until reaching an upper bound of sleep window. The PSC type 2 is
usually representative of RTVR and UGS traffic; as so, it has a determined sleep and listen window length
alternating during the sleep mode period. PSC type 3 indicates management messages and multicast data and is
represented by a unique sleep window where MS awakes on next expected periodic ranging or data. The device
power saving mode will be decided based on the alignment of these three types of power saving class as
illustrated in figure 1 below.
It goes without saying that when the number of the different PSCs defined above increases, the overlapping of
their different windows may not necessarily produces good unavailability interval for power saving. This is
observed despite the alignment optimization used to improve the different PSCs windows overlapping.
Availability interval
Unavailability interval
PSC type 2 – listening window of constant size and sleep window of constant
size
PSC type 1 – listening window of constant size and doubling sleep window
PSC type 3 –No listening window, a constant sleep window is used
Device mode –unavailable (and may power down) when all PSCs are in sleep
windows
Figure 1. Three PSCs
produce the device power saving mode
The actual definition of power saving mode presents lot of complexities and overheads which are inefficient to
optimize the power saving for a device. Two important performance factors have to be considered for MS
operating in sleep mode:
1- MS power consumption
 Strongly depending on the number of PSCs in the power management mode
2- Signaling load generated by MS in sleep mode
 Traffic indications from the network, deactivation and handoffs signals from the network.
Therefore, an enhanced sleep mode should have these two factors optimize at the best to increase the power
saving and reduce the protocol overhead.
2. Issues related to the Power Saving Classes (PSCs)
2.1 Issue related to PSC type 2
Issue1: Possibly several PSCs type 2 might be defined which involves overlapping of listen and sleep windows
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from different PSCs, reducing the sleep interval.
Issue 1: The fixity of the listening window may be a drawback when we consider that its length be likely
defined longer to cover different cases (HARQ operations, etc).
However, the length of the listen window might be too long or too short for MS operations. These cases may
happen randomly so it may be hard to decide an adequate length for the listening window without excessive
power consumption, as in figure 2.
Possible enhancement for PSC type 2
1. Merge all the type 2 connections into a unique PSC based on the averaging of their constraints or based on
the most constraining connection.
2. Give to the PSC type 2 a minimum listen window which is enough to carry out normal operations of DL
and UL based on no error of transmission and by the use of timers/signals extend the listen window
according to traffic behaviors.
3. Use a HARQ traffic timer when a packet couldn’t be recovered. Thus, MS go to sleep on a limited listening
window if all operations went fine, otherwise the listening window covers the next sleep length if HARQ
operations were involved.
Main advantages of this design are:
 A unique PSC type 2 no matter different type of connections are grouped, eliminate the overlapping between
listen and sleep issue.
 Possible increase of the sleep interval when the default listening window is enough to cover the type 2
connections traffic operations.
 Adaptively could respond to type 2 connections traffic pattern for HARQ operations. This may increase the
power consumption but it is compensated by the use of a default listen window when all operations worked
fine.
Default listen window
Normal PSC type 2
HARQ operations could not be
completed in that case
Wasted interval
Default listen window
HARQ traffic timer expires
for each transmission
Sleep window
Enhanced PSC type 2
HARQ traffic timer expires
for each transmission
HARQ traffic timer stopped
because of erroneous data
The listening window is
extended to recover the data
Figure 2: Illustration of normal and enhanced PSC type 2
2.2 Issue related to PSC type 1
In case there are only type 1 connections:
Issue 1: Load of signaling: traffic indication at every listen window for incoming data burst or not, signaling for
reactivation of the power saving after any deactivation.
Issue 2: No matter the length of the sleep window before deactivation, after every reactivation, MS restarts the
power saving with the same Initial sleep window.
Possible enhancement for PSC type 1 as unique PSC for the device
The following enhancement can be applied if there is only one PSC type 1 to decide for the device power saving
as illustrated in figure 3 above.
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1.
2.
3.
4.
5.
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IEEE C802.16m-08/580r1
Produce only one PSC from all type 1 connections (to avoid overlapping of windows)
Use a traffic timer to monitor data burst or positive traffic indication signal from BS, if that timer expires,
MS returns to sleep. A trade-off is used to decide if the positive traffic indication is needed or not.
For any incoming traffic before the traffic timer expires, MS starts a data burst timer to monitor incoming
data burst ending (see figure 3, second illustration).
When MS restarts sleeping, after a data burst timer expires, instead of starting the sleep window at initial
sleep length, it could be possible to change the initial sleep window length (a multiple of the first initial
window length), according to when the incoming data burst happens in MS power saving cycle.
Match the start of every listening window with a super frame header, hence, the sleep window length could
be a multiple of super frame length. For 802.16m, the doubling sleep window should be well calculated so
that the listen period could match with the super frame header for synchronization to have the different
frames information.
Apply also the HARQ traffic timer, introduced in PSC 2 enhancement to handle erroneous data case.
Traffic indication
message=No
Traffic indication
message=No
Traffic timer starts and
Traffic timer starts and
ends no data burst received ends no data burst received
Traffic indication
message=Yes
Data burst/positive traffic
indication received before timer
ends
Message exchange
to return to sleep
Data burst timer
reached, MS sleeps
Data burst timer not expired
Figure 3: Illustration of the former PSC type 1 and the enhanced one
The main advantages of this design are:
 Reduce signaling load needed to trigger data reception by the use of traffic timer with/out positive traffic
indication.
 Gain in power saving for not waiting the end of the listen window to restart sleeping when the traffic timer
expires (no data burst from BS).
 Increase of power saving for not restarting by the same initial sleep window if the sleep window was long
enough before deactivation of the power saving mode.
In case type 1 connections coupled with type 2 connections:
There will be two kinds of PSC which have to be aligned so that the overlapping of their sleep windows
produces the device power saving mode as in figure 4.
Issue 1: Same issues observed as when there is only PSC type 1.
Issue 2: Coupled with PSC type 2, the PSC type 1 may contribute to increase the power consumption of MS by
extending the availability period as observed in figure 4, due to overlapping sleep and listen windows.
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IEEE C802.16m-08/580r1
Traffic indication
Positive Traffic indication
Receive signal from BS
to reactivate PSC1
DL/ UL data burst
operations
Unavailability interval
Availability interval
The PSC type 2 could be still running, but
the device power saving is interrupted.
PSC type 2 – listening window of constant size and sleep window of constant
size
PSC type 1 – listening window of constant size and doubling sleep window
Device mode –unavailable (and may power down) when all PSCs are in sleep
windows
Figure 4: PSC type 1 influence on PSC type 2 during power saving
Possible enhancement for PSC type 1 coupled with PSC type 2
1. The power saving design will be based on only connections type 2 to create only one PSC and to define a
default sleep and listening windows as described previously.
2. Apply the same enhancement as when only PSC 1 decides for the device power saving: Data burst timer and
HARQ traffic timer are used as previously defined. The following changes will be applied to the protocol:
a. Traffic timer will start during the listening window and at the same time connections type 2
operations will be carried out.
b. If the traffic timer expires with no data burst / positive traffic indication, MS carries out only type 2
traffics and go to sleep.
c. The length of the window could be extensible to support the data reception operation if any data
burst/positive traffic indication is received.
d. When receiving data burst MS still carries out connections type 2 traffics simultaneously.
e. If the data burst operation covered one part of the following sleep window, then this length will be
subtracted from the sleep window length.
f. If the data burst operation covered the entire length of the next sleep window then MS will keep
listening corresponding to the next default listening window before restarting the sleep window, see
figure 5.
Thus, only one PSC can represent merging of type 1 and type 2 connections and either signaling and/or timers
can be used to adjust the sleep window restart time when data burst are sent / received.
Work as PSC type 2 connections
only, because no data burst
Traffic timer expires
without data burst
Data / positive traffic indication
before traffic timer expires
Data burst timer expires, MS sleeps
for the remaining of the sleep
Traffic timer expires
without data burst
Work as PSC type 2 connections
only, because no data burst
Data burst / Positive
traffic indication
Data Timer expires but coincides
with next listen window, still listen
Traffic timer expires
Figure 5: One PSC representing PSC type 1 and type 2 activities
Main advantages of this design:
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IEEE C802.16m-08/580r1
Simplicity in power saving class management. It will be based on a unique PSC design no matter what
type of connections involved.
Reduce greatly signaling load for traffic indication, the sleep mode works based on type 2 connections
traffics until a traffic timer is interrupted by incoming data /positive traffic indication from BS for type 1.
Reduce power consumption because of no more possible mismatch between different listening windows
from PSCs to increase the availability interval. The flexible listen window is still more appropriated than
the former deactivation period and possible overlapping windows.
Consistent power saving than before, because the system can benefit of a fix sleep length, with no
overlapping from different other power saving classes. Therefore, the only period of reduction of this
sleep length is when the flexible listen extend to cover some of its length.
2.3 Issue related to PSC type 3
In case there are only connections of type 3:
Issue 1: Possibly several PSCs type 3 might be defined which involves overlapping of sleep windows and
deactivation time from different PSCs, reducing the sleep interval
Issue2: The lack of listen window brings a burden of signaling to reactivate the power saving. While the events
involved during the activation can be somehow predictable. An example will be that for periodic ranging, there
is a minimum length of frames to succeed the process.
Receiving data
Signaling with BS to reactivate the PSC
Deactivate the PSC at the
end of sleep window
Figure 6: Representation of actual PSC type 3
Possible enhancement for a unique PSC type 3
1. Integrate all type 3 connections to define a unique PSC type 2 alike, with a default listen and the predicted
sleep window alternating.
2. In case the default length of the listen window is not enough for ongoing operations, timers are used to
increase its length (e.g. as long as a timer is running, the device is in active mode).
3. The minimum listen window size could be a multiple of the longest timer used to monitor incoming data
traffic.
4. When data reception is over, use signaling to decide for the next incoming data (periodic ranging,
multicast…) otherwise use the same length of inactivity for the next wakeup after timers expires.
Main advantages of this design
 Flexible listening window by using timers could enhance the length of sleep period, and signaling could
speed the return to sleep
 Improve the power saving mode while at the same time eliminating long deactivation period.
Receiving data
Signal to sleep and for next
wakeup
Receiving data
All timers expire without any
data, MS goes to sleep
A timer didn’t expire, extend
listen window size
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IEEE C802.16m-08/580r1
Figure 7: PSC type 3 as unique PSC of a device power saving
In case there is type 3 connection coupled with other types of connection:
Issue 1: No matter how long is the PSC type 3 sleep windows, when coupled with different PSCs, the listening
window of these PSCs will still consume power for the device.
Issue 2: The same issue observed when there are only connections of type 3 could also increase the power
consumption because of the deactivation of the power saving mode even if other type of connections present
opportunity of saving power.
Possible enhancement for a PSC type 3 coupled with other types of connection
Type 2 and type 3 connections
1. Design a unique PSC integrating type 2 connections constraints and the type 3 connections predicted sleep
time. This means to satisfy the constraints of the real time traffic at first, and to integrate later the type 3
connections constraints.
2. Use the predictive activation of connections of type 3 (signaling or timer as defined above) to define the
scenarios of listen and sleep window, as illustrated in figure 8.
3. Adjust the default listen window according to the behavior of connections of type 3. The extension of the
listen will decrease the length of the following sleep as observed with type 1 and type 2 merging case, to
respect connections constraints.
All type of connections
1. Integrate type 1 connections to the merging of type 2 and type 3 connections. If any type 1 connection is
present, the listen period in figure 8 will be the appropriate time to receive or send the data burst. Hence, the
type 1 connections will be sent and received only during the listen period defined by type 2 or type 3 (having
QoS or predicted inactive time to respect).
2. Apply all the timers and operations of type 1 connections during the listening window length until
completion. Additionally, when the listen period extension covers a complete length of sleep window then
the device is active for the next listen window, this situation was described in figure 5.
Case 1: type 3 wakeup time matches with type 2 listening
Length of the predicted type 3
inactive time matches with listen
Traffic timers expires
Listen matches with type 3
connections data reception
Timers start
Case 2: type 3 wakeup time matches with type 2 sleep
Type 2 sleep matches with type
3 connections data reception
Length of the predicted type 3
inactive time matching with sleep
MS goes to sleep for the
remaining of the sleep window
All type 3 timers end without
any data burst reception
Continues with other types of
connection operations
Signal for next wakeup
Figure 8: Unique PSC representing type 3 and all connections behavior
Type 1 and type 3 connections
1. When coupled with PSC type 1 only, use the length of the type 3 connection inactive time as the default
sleep window. However, if the inactive time of type 3 is long enough to overflow BS buffer for type 1 data,
a much shorter length is used as default sleep window. This choice is a trade-off and is decided accordingly.
2. Integrate the traffic timer and traffic indication from type 1 connections with the other timers/signal from
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IEEE C802.16m-08/580r1
type 3 during listen window to either continue to receive data or to go to sleep for a length of the default
sleep after the timers expires.
Receiving type 3 data
Traffic indication positive
start with type 1 traffics
Length of the predicted type 3 inactive
time ok for BS to buffer data burst
Traffic indication positive
start with type 1 traffics
Type 3 data
Data burst timer expires without
any data, MS goes to sleep PSC
Signal to
sleep and or
next wakeup
Length of the predicted type 3 inactive
time is reduced to comply with BS buffer
Figure 9: Type 3 predicted inactive time too long for type 1 connections burst
Main advantages of this design
 Consistent power saving because no overlapping involved between listening and sleep windows of different
PSCs when different type of connections, but only one PSC produced.
 Reduced signaling with BS, as traffic activation can be predicted and timers exist to trigger sleep after
reception. The signaling is used to define some change in next traffic
 Efficient use of the listen window when all connections involved, because all traffics can be handled during
that period, to avoid isolated small active time reducing the power saving.
3-Toward a device based sleep mode
From the above section discussion on 802.16e it appears that the actual definition of power saving classes
present serious flaws and complexities to have an efficient power saving. This is due the loaded signaling
involved in each power saving design and decreased power saving gain from the overlapping of different PSCs.
That is, defining different power saving classes do not to produce consistent power saving for a device.
As the different analyses from the above section have proven already, these connections of different type can be
merged to create a unique power saving class. Such a unique power saving class is at the same time the actual
power saving mode of the device, without any overlapping of PSCs. Thus, it can produce more consistent power
saving and present a real flexibility according to the connections demand properties.
Therefore, to reduce the protocol complexity, it will more indicate to design a device-based power management
instead of different power saving classes. As so, a unique PSC is a possible solution as long as it can adapt itself
to the different connection behaviors and also keep the signaling level lower.
3.1 From connections-based PSCs to a unique Power saving class
Based on the actual power saving classes, a unique power saving class is designed by merging the different
PSCs into only one PSC according to specific cases. That unique power saving class still can react to the traffic
pattern of the different types of connections that it represents. Therefore, our approach has been specifically to
merge the different connections behaviors into one power saving class representation. That PSC has a default
listen and sleep windows which are flexible according to the behavior of the different types of connection by
using timers or signaling fashion.
According to the different cases the unique PSC design could be one of by these conditions:
If only connections of type 2
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IEEE C802.16m-08/580r1
 Define a unique PSC based on the enhancement of PSC type 2
If only connections of type 1
 Define a unique PSC based on the enhancement of PSC type 1
Else if only connection for PSC type 3
 Define a unique PSC based on the enhancement of PSC type 3
Else if connections coupled together
 Define a unique PSC based on the different enhancement proposed for <type 2-type 1> or <type 1-type
3> or <type 3-type 2> or < all>
When all the different types of connection are represented, the unique PSC definition is based on the behaviors
of type 2 connections, to determine a default sleep and listening windows. To support data burst transfer and
sending, at each default listen the PSC can offer an opportunity to send and receive data burst using timers
and/or signal to determine when to go back to sleep. Whenever, the other types of connections (type 1 and type
3) are not active, the unique PSC behave as our proposed enhanced PSC of type 2. Only when traffic exists for
type 3 or/and type 1 that the listen and sleep window may be flexible to satisfy their traffic patterns.
Because of the limited length of the default sleep window, it is possible not to give to MS at each listening
window an opportunity to receive/send data burst. Instead, it could be done after every n listening window as
illustrated in figure 10 (n= 2 listening windows). The choice of n may depend on the default sleep length of type
2 connections. The advantage of this design is to reduce the use of the traffic timer when the probability of
receiving such traffics is low, also to allow an efficient use of the listening window for type 2 traffics and still
having some sleep intervals. Thus, we propose a semi-deterministic unique PSC completely flexible which uses
timers and few signals to adjust the listen and sleep windows.
First opportunity for sending burst,
but no burst, works as PSC 2
No
opportunity
2nd opportunity: Data
burst for type 1
Data reception timer end without
any data burst reception
Data reception timer didn’t expire, data
incoming, extend listen window size
Extension of default listening to
satisfy type 2 traffics demand
Figure 10: Type 2 and type 3 connections merged in one PSC
2nd opportunity: Data
burst for type 1 traffics
Length of the predicted type 3 Listening matches with type 3
inactive time match with listen connections data reception
First opportunity for sending burst,
but no burst, then works as PSC 2
MS goes to sleep for the remaining of
the sleep window at the end of the timer
Extension for type 2
Type 1 data reception timer ends
without any data burst reception
Signal to stop data sending for
type 3 and define next wake up
time
Figure 11: All the connections merged into a unique PSC
3.2 Dynamic update of the unique PSC
After the design of the unique Power saving class, if some type of connections just come to end their traffic,
how will the PSC adapts itself?
We already define a state of each case of integration during the different connections merging. That means for
each case, the default listen and sleep window are as proposed in our different enhancement. Therefore, when
any type of connections drops off, BS and MS will exchange signal messages during the following listen
window to define the next sleep and listening window of the new state. That is possible because BS like MS is
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IEEE C802.16m-08/580r1
award of the connection deletion. As so, we can dynamically update the unique power saving class to the
connections behavior without interrupting the sleep mode.
There are two levels of dynamism observed in a unique PSC:
 When a connection is updated /deleted but still exist other connections of same type
 When the entire type of a connection is deleted
In the first case, it is likely that type 2 and maybe type 3 connections may have an impact on the PSC design
than type 1 case. A type 1 connection update may have little impact on the previous defined PSC windows
pattern. A type 2 connection update/deletion may change the sleep and the listen window length. That update
can be effective after few sleep and listen windows using signaling during default listening window time when it
is for an increase of the sleep length. On the contrary, when the connection update/created might reduce the
sleep length of the default sleep, then BS and MS resolve the process during the default listening window and
the next sleep will be updated to the new parameter constraint. The same principle is applied to type 3
connections.
The second case involves the complete deletion of one type of connection included in the unique PSC design. In
that case the unique Power saving class will be defined based on the connections remaining and BS and MS
might exchange signals to decide for the effective start of the new definition. This case is illustrated in figure 12
with type 2 connections deletion in a unique PSC design
New parameters applied
Type 3 connections
data reception
traffic indication
Signal for for type 1 traffics
predicted type 3 inactive time next wakeup
Exchange new windows
definition for 2nd sleep
type 3 connections
data reception
Signal for next
wakeup time
…
……
1st opportunity for data burst, but
traffic timer expires, works as PSC 2
No traffic indication/ data burst
Type 1 connection
deletion indication
Type 3 connections
data reception
Signal for next
wakeup time
Type 3 connections
data reception
type 3 connections
data reception
Signal for next
wakeup time
Type 2 connection
deletion
indication
1st new opportunity: traffic
indication positive
Signal for next
wakeup time
Next predicted inactive time
…
No traffic indication/data burst
Define or not new windows
size for next sleep
No more traffic timer, works with
type 3 connections only
New parameters are applied
Figure 12: Dynamic update of a unique PSC after a type of connection is deleted
Main advantage of this design
 All the advantages related to each case already proposed
 Full dynamism of the power saving without any deactivation because of connection update or deletion
 Simplicity and consistent power saving with an integrated flexibility in managing sleep and listening
windows using less signaling loads.
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============================================================================
4-Proposed Text in SDD
X.xx Sleep mode operation
Sleep mode operation uses connection behaviors to design a unique device-based power saving framework.
A mechanism for adaptively adjusting sleep patterns (i.e. duration of sleep and listening windows) based on
traffic pattern without deactivating the sleep mode should be provided.
This unique power saving framework uses efficient timers with less signaling that enables maximum MS power
saving and reduces the air-link resource usage associated with sleep mode signaling
==================================================================
References
[1] IEEE Std. 802.16e-2005, IEEE Standard for Local and metropolitan area networks, Part 16: Air Interface for
Fixed and Mobile Broadband Wireless Access Systems, Amendment 2: Physical and Medium Access Control
Layers for Combined Fixed and Mobile Operation in Licensed Bands, and P802.16Rev2/D3 (February 2008).
[2] IEEE 802.16m-08/003r1, “The Draft IEEE 802.16m System Description Document”
.
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