Introduction to the IEEE
802.16e Power Saving
Mechanism
Advisor: Ho-Ting Wu
Speaker: Lei Yan
1
Outlines

Introduction to IEEE 802.16
Physical (PHY) Layer behavior
 Medium Access Control (MAC) Layer behavior


Introduction to the Power Saving
Mechanism (PSM) in IEEE 802.16e
MS aspect: Sleep interval adaption
 BS aspect: Packet scheduling


Future works
2
References
[1] IEEE 802.16d-2004 and IEEE 802.16e-2005 Std.
[2] Berlemann, C. Hoymann, G. R. Hiertz, and S. Mangold,
“Coexistence and Interworking of IEEE 802.16 and IEEE 802.11e,”
IEEE Vehicular Technology Conference, 2006. VTC 2006-Spring.
IEEE 63rd, Volume 1, 2006 Page(s):27 - 31
[3] Slides from Sih-Han Chen
[4] Slides from Chi-Fong Yang
[5] 張致恩. 無線都會網路系統與技術短期課程. 中原大學電子系.
2008
[6] 曾春亮, 張寧, 王旭瑩, 俞一鳴. WiMAX/802.16 原理與應用. 機械工
業出版社. 2006
[7] Min-Gom Kim, Minho Kang, and Jung Yul Choi, “Performance
Evaluation of the Sleep Mpde Operation in the IEEE 802.16e MAC,”
Advanced Communication Technology, The 9th International
Conference. Publication Date: 12-14 Feb. 2007 Vol. 1, pp. 602605
[8] Kwanghun Han and Sunghyun Choi, “Performance Analysis of
Sleep Mode Operation in IEEE 802.16e Mobile Broadband Wireless
Access Systems,” Vehicular Technology Conference, 2006. VTC 3
2006-Spring. IEEE 63rd Volume 3, 2006 Page(s):1141 – 1145
References (cont.)
[9] Shengqing Zhu, Xiaoyu Ma, and Lujian Wang, “A Delayaware Auto Sleep Mode Operation for Power Saving WiMAX,”
Computer Communications and Networks, 2007. ICCCN 2007.
Proceedings of 16th International Conference on 13-16 Aug.
2007 Page(s):997 - 1001
[10] Shengqing Zhu and Tianlei Wang, “Enhanced power
efficient sleep mode operation for IEEE 802.16e based
WiMAX,” Mobile WiMAX Symposium, 2007. IEEE 25-29 March
2007 Page(s):43 - 47
[11] Yan Zhang, “Performance Modeling of Energy Management
Mechanism in IEEE 802.16e Mobile WiMAX,” Wireless
Communications and Networking Conference, 2007.WCNC
2007. IEEE 11-15 March 2007 Page(s):3205 - 3209
[12] Dinh Thi Thuy Nga, Min-Gon Kim, and Minho Kang; “A
Delay Constraint Energy Saving algorithm in IEEE 802.16e
wireless man,” Wireless Telecommunications Symposium,
2007. WTS 2007 26-28 April 2007 Page(s):1 - 6
4
References (cont.)
[13] Min-Gon Kim, JungYul Choi, and Minho Kang; “Adaptive
power saving mechanism considering the request period of
each initiation of awakening in the IEEE 802.16e system,”
Communications Letters, IEEE Volume 12, Issue 2, February
2008 Page(s):106 - 108
[14] Jaehyuk Jang, Kwanghun Han, and Sunghyun Choi,
“Adaptive Power Saving Strategies for IEEE 802.16e Mobile
Broadband Wireless Access,” Communications, 2006. APCC
'06. Asia-Pacific Conference on Aug. 2006 Page(s):1 - 5
[15] Sanghvi, K., Jain, P.K., Lele, A., and Das, D., “Adaptive
waiting time threshold estimation algorithm for power saving
in sleep mode of IEEE 802.16e,” Communication Systems
Software and Middleware and Workshops, 2008. COMSWARE
2008. 3rd International Conference on 6-10 Jan. 2008
Page(s):334 - 340
[16] Woo Jin Jung, Hyung Joo Ki, Tae-Jin Lee, and Min Young
Chung; “Adaptive sleep mode algorithm in IEEE 802.16e,”
Communications, 2007. APCC 2007. Asia-Pacific Conference
5
on 18-20 Oct. 2007 Page(s):483 - 486
References (cont.)
[17] Jinglin Shi, Gengfa Fang, Yi Sun, Jihua Zhou, Zhongcheng
Li, and Eryk Dutkiewicz, “Improving Mobile Station Energy
Efficiency in IEEE 802.16e WMAN by Burst Scheduling,” in
Proc. GLOBECOM’06, pp.1-5, Nov. 2006
[18] 邱元甫. 應用於IEEE 802.16網路之整合性節能排程演算法
(IPSS: Integrated Power Saving Scheduling Algorithm for
IEEE 802.16 PMP Networks). 國立成功大學電腦與通信工程研
究所碩士論文. July, 2008
[19] Shih-Chang Huang, Rong-Jong Jan, and Chien Chen,
“Energy efficient scheduling with QoS guarantee for IEEE
802.16e broadband wireless access networks,” Proceedings
of the 2007 international conference on Wireless
communications and mobile computing, pp. 547-552
[20] Chia-Yen Lin and His-Lu Chao, “Energy-saving scheduling
in IEEE 802.16e networks,” 14-17 Oct. 2008 Page(s):130 135
6
A brief to IEEE 802.16

Also called WiMAX (Worldwide Interoperability for Microwave
Access) as the Wireless metropolis access network (MAN) solution
and an alternative to optic fibers and DSL for last-mile.

Supports both TDD (Time Division Duplex) and FDD (Frequency
Division Duplex) in Scalable-OFDMA scheme.

Supports point-to-multipoint (PMP) for line-of-sight (LOS) with 10
to 66GHz and Non-LOS with 2 to 11GHz; provide high
transmission rate and wide coverage (75 Mbps and 50km).

Supports MIMO (multiple input and multiple output) for a better
transmission quality.

Supports adaptive modulation coding (AMC).

Well-known versions:
 IEEE 802.16d-2004: Fixed subscriber station (SS)
7
 IEEE 802.16e-2005: Mobile (subscriber) station (MSS or MS)
IEEE 802.16 in comparison to other communication
schemes
8
IEEE 802.16 in comparison to the similar
communication schemes

Q: Does IEEE 802.11n contend with WiMAX?
A: No. Although both IEEE 802.11n and
WiMAX support MIMO-OFDM, there exists
tiny conflicts since WiMAX has a wider
coverage. Whereas they may co-work since
there exists some researches such as [2] for
linking the MAC interface between WiMAX
and IEEE 802.11e (MAC solution for IEEE
802.11n).
9
Outlines

Introduction to IEEE 802.16
Physical (PHY) Layer behavior
 Medium Access Control (MAC) Layer behavior


Introduction to the Power Saving
Mechanism (PSM) in IEEE 802.16e
MS aspect: Sleep interval adaption
 BS aspect: Packet scheduling


Future works
10
Physical structure of a WiMAX Frame

Base station (BS) is responsible for scheduling
the MAC PDUs (protocol data units) and DL/UL
MAP in frames and then broadcasts them to
the MSs it is responsible for.

DL subframe is always first because in this
way MSs can know how much BW they need
for the next bandwidth request (BR) in
comparison to their “previously received” BW.
11
Physical structure of a WiMAX Frame (cont.)
The length of a frame is fixed and formed in slots
 Always DL subframe first
 The length of DL/UL subframe is adaptive

12
How DL/UL subframes work

A DL subframe uses DL-MAP to define DL data burst profiles
for all MSs, and a UL subframe to define UL data burst profile
and channel access
13
How DL-MAP works
14
How UL-MAP works
15
Bandwidth request (BR) for connections

We use the transmission bandwidth (BW) in data
communications:

Spectral BW: The interval between two arbitrary
frequencies (for channels). Ex: An antenna works
between 1GHz and 3GHz, so its BW is 2GHz.

Transmission BW (also called bit rate, symbol rate,
data rate, or transmission rate):

Equals the data size (bits) / sampling duration (sec) =
data size (bits) * spectral BW (Hz) = BW (bps)
16
BR for connections (cont.)

BW stealing (not for UGS)
 MS
borrows partial BW from a best effort
connection A to perform BR for ANOTHER
connection B.

Piggyback (not for UGS)
 MS
piggybacks BR inside a MAC PDU for a given
connection ITSELF.

Polling (especially for UGS)
 MS
sends CID for a connection to ASK BS FOR
POLLING IT.
17
Outlines

Introduction to IEEE 802.16
Physical (PHY) Layer behavior
 Medium Access Control (MAC) Layer behavior


Introduction to the Power Saving
Mechanism (PSM) in IEEE 802.16e
MS aspect: Sleep interval adaption
 BS aspect: Packet scheduling


Future works
18
MAC layering: Convergence Sublayer (CS)

Functions:



Provide transmission or
mapping of external network
data into MAC SDU (service
data unit)
Classify external network
data and associate them (if
accepted by BS) to proper
service-flow ID (SFID) and
the mapped connection ID
(CID)
In any sublayer, SDU is the
unprocessed data and
been encapsulated to PDU.
So the PDU in upper layer
is the SDU in neighboring
lower layer.
19
MAC layering: Common Part Sublayer (CPS)

Functions:
QoS: BW allocation for
service classes (e.g.,
UGS, rtPS, ertPS, nrtPS,
and BE) (in some sense
the packet scheduling
since we can take a
specific frame as “a part
of” BW)
 Connection
establishment/maintenance with service flow
 BR: Dynamic DL/UL
modulation and coding
updates
 Support handover

20
MAC layering: Security Sublayer

Functions:
 Encryption
for data
 Privacy
key
management
protocol (PKM) that
describes how BS
distributes keys to
MSs
21
Service Flow and connection

Service Flow:




A unidirectional DL/UL flow of SDUs on a connection
Described by QoS parameters (e.g., delay, jitter, and
throughput)
Identified by a 32-bit Service Flow ID (SFID)
Connection:



A unidirectional DL/UL mapping between BS and MS
Provided as a “channel” for service flow traffic
Identified by a 16-bit Connection ID (CID), and as a
mapping from SFID, which happens when this service
flow is admitted or activated
22
QoS aspect: Service classes in IEEE
802.16e

The polling service is used as a method of BR
for MSs to request BS to poll them

For any service type (for example, Real-time
and variable bit rate):
 DL
case (Service class in power saving): RT-VR
 UL case (Scheduling class): rtPS
 rtPS and RT-VR share the SAME QoS parameters
23
QoS aspect: Service classes in IEEE 802.16e (cont.)
Feature
Application
DL/UL: Unsolicited
Grant Service (UGS)
1. Real-time
2. Constant bit rate (CBR)
1. T1/E1
2. VoIP
DL: Real-time Variable
Rate (RT-VR)
UL: Real-time Polling
Service (rtPS)
1. Real-time
2. Variable bit rate
MPEG video
DL: Extended Real-time
Variable Rate (ERT-VR)
UL: Extended Real-time
Polling Service (ertPS)
1. Real-time
2. Constant bit rate (CBR)
1. Ranging
2. VoIP with silencesuppression
DL: Non-real-time Variable
Rate (NRT-VR)
UL: Non-real-time Polling
Service (nrtPS)
1. Non-real-time
2. Variable bit rate
FTP
DL/UL: Best Effort (BE)
1. Non-real-time
2. No QoS guarantee
1. HTTP
2. E-mail
24
Outlines

Introduction to IEEE 802.16
Physical (PHY) Layer behavior
 Medium Access Control (MAC) Layer behavior


Introduction to the Power Saving
Mechanism (PSM) in IEEE 802.16e
MS aspect: Sleep interval adaption
 BS aspect: Packet scheduling


Future works
25
Why power saving (sleep mode) for
WiMAX?

For IEEE 802.16e, the MS terminal may be a PDA,
cell phone, or laptop, all of them are powered by
battery.

In MS circuitry, both CPU and antenna have to
consume more energy to guarantee the QoS (e.g.,
high quality of audio/video and multiplexing).
Consequently, the battery must run out very fast.

So, what can we do to prolong the life-cycle of
battery?
26
What happens to MS during sleep mode

Consider the power consumption during ONE frame:


Normal mode: PMS = Pcircuit + PRF
Sleep mode: PMS = Pcircuit

Pcircuit is the power consumption for LCD, CPU, or
memory…etc.

PRF is the power consumption for antenna and RF IC.

Goal of sleep mode: Turn off the RF devices to save power.
27
Definition for sleep mode

The 802.16e MS operation is alternated between:


Normal mode: Tx/Rx data (RF devices are “ON”)
Sleep mode: Only data processing (RF devices are “OFF”)

sleep interval Ts (in frames): The duration that the MS sleeps.

listening interval TL (in frames): The duration that the MS
listens to the broadcast from BS, so the power consumption
when listening equals that of normal mode.

The sleeping and listening operations alternate inside the
sleep mode.

sleep cycle: One complete period for (Ts + TL) for a PSC
during the sleep mode.
28
Definition for sleep mode (cont.)

There are three classes of power saving based on the different QoS
characteristics. Both 1st class and 2nd class are interleaved by sleep
duration (interval) and listening duration (interval).
29
Four sleep mode scenarios
Sleep initiation
Sleep termination
BS initiated
(shown in P.31)
MS initiated
(shown in P.31)
MS listens to the
DL messages
from BS (shown
in P.32)
UL transmission:
The MS awakes
IMMEDIATELY
anytime (shown
in P. 32)
30
31
32

Power Saving classes (PSCs)
PSC is a class that contains traffics with similar QoS
characteristics. Note: ALL PSCs are independent to others.
 PSC I (NRT-VR and BE): Binary-exponential sleep
interval
 PSC II (UGS and RT-VR): Constant sleep interval
 PSC III (ERT-VR): Sleep without listening

Once ONE PSC of a MS enters the sleep mode, we say this
PSC is ACTIVATED. However, now the MS still NOT enters
the sleep mode. We say this PSC is DEACTIVATED if it
returns to the normal mode (awakes).

At a time the MS can enter the sleep mode (i.e., turn off its
RF devices) iff. {PSC I activated && PSC II activated &&
PSC III activated}, which is very difficult for MS to sleep.

That is, the MS is in the normal mode even if some of its 33
PSCs have slept.
Power Saving classes (cont.)

Plot for the three PSCs: The interval of unavailability is the time that the
MS REALLY enters the sleep mode.
34
Power Saving classes (cont.)

The binary-exponential sleep interval for PSC I:
Tn  2
n 1
 Tmin  Tmax
, where the exponent n (provided by BS) is the nth
sleep cycle in MS. Note: ALL the parameters for
sleep are given in MOB_SLP-RSP from BS

Note: Due to tight delay constraints for Real-time
data, in PSC II MS can BOTH Tx/Rx during the
listening interval.
35
Outlines

Introduction to IEEE 802.16
Physical (PHY) Layer behavior
 Medium Access Control (MAC) Layer behavior


Introduction to the Power Saving
Mechanism (PSM) in IEEE 802.16e
MS aspect: Sleep interval adaption
 BS aspect: Packet scheduling


Future works
36
About binary-exponential sleep interval in
PSC I

Pros:
Longer sleep time, more power saved

Cons:
 An
inherent problem for all PSCs: BS cannot wake
up the MS
 The frame response delay is very long especially
for the max. sleeping interval

The trade-off: Power vs. Delay
37
Related works in PSC I

Current researches in PSC I:


Criterions for balancing both power and delay [5,6]
Frame response delay concern [7-14]: To pull back the
max. sleep interval in the aspect of QoS, which is simply a
mathematically “GUESS” process in MS

However, the pull-back scheme does NOT touch the
heart of the matter that MS CANNOT guarantee
WHEN the DL frame arrives

Therefore, the best way to balance the trade-off
between power and delay is the QoS-based
scheduling controlled by BS.
38
Outlines

Introduction to IEEE 802.16
Physical (PHY) Layer behavior
 Medium Access Control (MAC) Layer behavior


Introduction to the Power Saving
Mechanism (PSM) in IEEE 802.16e
MS aspect: Sleep interval adaption
 BS aspect: Packet scheduling


Future works
39
Concepts about packet scheduling

BS broadcasts a frame with the “scheduled”
PDUs inside, however, the Std. does NOT
define a default algorithm for scheduling but
only service classes and their sustained jitters

The propose of packet scheduling is to
manage these PDUs with order to enhance
the system efficiency, such as QoS or power
saving…etc.
40
Related works

The slot-based LVBF scheduler proposed in [17]
monopolize most BW to the MS with the most BW
requirement and force it to sleep longer.

[18] schedules alternately between PSC I and II so
as to force them to sleep in turns (a QoS-based
consideration). However, this algorithm does NOT
really reduce the Tx/Rx power for MS since its PSC
I and II are NOT SIMULTANEOUSLY activated
(slept). Besides, [16] does not consider the effect
of multiple MSs.
41
Related works (cont.)

[19] provides a Round-Robin scheduler in
order not to waste BW for all MSs. However,
[19] ONLY considers PSC II.

[20] merges all normal mode frames for all
service classes to concentrate BW so as to
save power. As far as I know, [20] is the
FIRST which adds call admission control (CAC)
before the entire scheduling. However, [20]
supports ONLY one BS and one MS.
42
Outlines

Introduction to IEEE 802.16
Physical (PHY) Layer behavior
 Medium Access Control (MAC) Layer behavior


Introduction to the Power Saving
Mechanism (PSM) in IEEE 802.16e
MS aspect: Sleep interval adaption
 BS aspect: Packet scheduling


Future works
43
Requirements for a PSM scheduler in BS
1. Call admission control (CAC):


BS can filter some connections to serve more MSs.
BW (and the Tx power needed) of filtered connections are
saved
2. QoS-based scheduler

Schedule packets without violating their delay bounds
3. Power saving concept

Concentrate the normal mode frames to prolong the sleep
mode time.
4. General to all scenarios

Support multiple MSs; Integrate both Real-time and NonReal-time
44
A prediction curve for simulation metrics


CAC -> pkt. dropping rate rises -> sleep time rises -> more power saved
-> Avg. pkt. delay rises
So, how to trade off between power consumption and delay?
45
Thanks for your attention!!

Q&A
46