Introduction to the IEEE 802.16e Power Saving Mechanism

1. Introduction to the IEEE 802.16e Power Saving Mechanism Advisor: Ho-Ting Wu Speaker: Lei Yan

2. 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

3. 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. 602-605 [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 2006-Spring. IEEE 63rd Volume 3, 2006 Page(s):1141 – 1145

4. References (cont.) [9]Shengqing Zhu, Xiaoyu Ma, and Lujian Wang, “A Delay-aware 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

5. 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 on 18-20 Oct. 2007 Page(s):483 - 486

6. 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

7. 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) • IEEE 802.16e-2005: Mobile (subscriber) station (MSS or MS)

8. IEEE 802.16 in comparison to other communication schemes

9. 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).

10. 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

11. 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.

12. 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

13. 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

14. How DL-MAP works

15. How UL-MAP works

16. 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)

17. 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.

18. 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

19. 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.

20. 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/mainten-ance with service flow • BR: Dynamic DL/UL modulation and coding updates • Support handover

21. MAC layering: Security Sublayer • Functions: • Encryption for data • Privacy key management protocol (PKM) that describes how BS distributes keys to MSs

22. 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

23. 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

24. QoS aspect: Service classes in IEEE 802.16e (cont.)

25. 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

26. 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?

27. 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.

28. 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.

29. 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).

30. Four sleep mode scenarios

33. 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 PSCs have slept.

34. Power Saving classes (cont.) • Plot for the three PSCs: The interval of unavailability is the time that the MS REALLY enters the sleep mode.

35. Power Saving classes (cont.) • The binary-exponential sleep interval for PSC I: , 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.

36. 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

37. 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

38. 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.

39. 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

40. 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.

41. 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.

42. 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.

43. 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

44. 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 Non-Real-time

45. 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?

46. Thanks for your attention!! • Q&A