IEEE 802.16e/Mobile WiMAX

1. IEEE 802.16e/Mobile WiMAX Gleneesha Johnson CMSC 818Z, Spring 2007 March 06, 2007

2. Outline • 802.16 Overview • Physical Layer • MAC Layer

3. IEEE 802.16 Overview • Family of standards for wireless metropolitan area networks (WMAN) • Provide broadband (i.e., voice, data, video) connectivity • Specifies the air interface, including the medium access control (MAC) layer and multiple physical layer specifications • 802.16e is an amendment to 802.16d (fixed or nomadic wireless broadband) to support mobility • Vehicular speeds up to 75 mph

4. WiMAX Forum • Formed in June 2001 to promote conformance and interoperability of the 802.16 standard • Develops “system profiles” that define mandatory and optional features of standard [1]

5. 802.16 Evolution 802.16 Dec 2001 • Original fixed wireless broadband air Interface for 10 – 66 GHz • Line-of-sight only • Point-to-Multi-Point applications 802.16a Jan 2003 • Extension for 2-11 GHz • Non-line-of-sight • Point-to-Multi-Point applications 802.16d Oct 2004 • Revised and replaced previous versions • WiMAX System Profiles 802.16e Dec 2005 • MAC/Physical layer enhancements to support subscribers moving at vehicular speeds [2]

6. Characteristics of 802.16 Frequency Ranges • 10 - 66 GHz • Short wavelength • Line-of-sight (LOS) required • Negligible multipath • 2 – 11 GHz • Longer wavelength • Improved range and in-building penetration • LOS not required • Multipath effects may be significant

7. ~Data Rates and Range

8. Why do we need broadband wireless access? • Fill the gap between high data rate wireless LAN and very mobile cellular networks. • Wireless alternative to cable and DSL for last-mile broadband access • Developing countries • Rural areas • Provide high-speed mobile data and telecommunications services

9. Network Architecture Source: WiMAX Nuts and Bolts – Steve Hilton [3]

10. Outline • 802.16 Overview • Physical Layer • MAC Layer

11. Physical Layer • Five physical layer modes 802.16d 802.16e

12. Orthogonal Frequency Division Multiplexing (OFDM) • Multiplexing technique that divides the channel into multiple orthogonal subchannels • Input data stream is divided into several substreams of a lower data rate (increased symbol duration) and each substream is modulated and simultaneously transmitted on a separate subchannel • High spectral efficiency, resilient to interference, and low multi-path distortion

13. Conventional FDM and OFDM Source: Broadband Wireless Access (W-PAN, W-LAN, WiMAX, Wi-Mob) (including OFDM concepts) - A. K. Seth [4]

14. Orthogonal Frequency Division Multiple Access (OFDMA) • Multiple-access/multiplexing scheme • multiplexing operation of data streams from multiple users • Dynamically assign a subset of subchannels to individual users • WirelessMAN-OFDMA based on scalable OFDMA (SOFDMA) • Support scalable channel bandwidths from 1.25 to 20 MHz

15. Other Physical Layer Features • Adaptive modulation and coding (AMC) • Fast Channel Feedback [3]

16. Other Physical Layer Features • Hybrid automatic repeat request (HARQ) • Adjusts automatically to channel conditions • Adds redundancy only when needed • Receiver saves failed transmission attempts to help future decoding • Every transmission helps increase probability of success • Multiple-in Multiple-out (MIMO) • Multiple antennas on sender and receivers • Increased spectral efficiency • Takes advantage of multipath

17. Ack Nak Ack Nak Hello Hello Hello H H Hello H H Hello -> Jello H H Hello + Hello -> Hello HARQ t Base Station 3 4 1 2 Subscriber Station Source: WiMAX Nuts and Bolts – Steve Hilton [3]

18. Outline • 802.16 Overview • Physical Layer • MAC Layer

19. MAC Layer • Connection-oriented • A fundamental premise of the MAC architecture is quality of service (QoS) • QoS provided via service flows • Unidirectional flow of packets provided with a set of QoS parameters • Applies to both downlink (DL) and uplink (UL)

20. [1]

21. Service Specific Convergence Sublayer MAC Common Part Sublayer Privacy Sublayer MAC Layer Interface to higher layer protocols, classifies incoming data, etc. Core MAC functions (i.e., scheduling, connection maintenance,fragmentation), QoS control Encryption, authentication, secure key exchange

22. Power Management • Sleep and Idle modes enable power-efficient MS operation • Sleep mode • MS conducts pre-negotiated periods of absence from air interface • Minimize MS power usage, and air interface resources • Allows scanning of other BSs to assist handoff • Idle mode • Allows MS to become periodically available for broadcast messages without registering at a BS

23. Handoff • 3 handoff methods supported • Hard Handoff (HHO) – required • “Break-before-make” • Optimized to keep handoff delays below 50 milliseconds • Fast Base Station Switching (FBSS) - optional • Macro Diversity Handover (MDHO) - optional

24. References [1 ] “Mobile WiMAX – Part 1: A Technical Overview and Performance Evaluation,” WiMAX Forum, August 2006 [2] Shyam Parekh, “802.16/WiMAX,” University of California, Berkeley, 2006 [3] Steve Hilton, “WiMAX Nuts and Bolts: An Introduction to the IEEE 802.16e Standard,” Motorola, Inc., March 2006 [4] A. K. Seth, “Broadband Wireless Access (W-PAN, W-LAN, WiMAX, Wi-Mob) (including OFDM concepts)” [5] “Air Interface for Fixed Broadband Wireless Access Systems,” IEEE STD 802.16 – 2004, October 2004 [6] “Air Interface for Fixed and Mobile Broadband Wireless Access Systems,” IEEE 802.16e – 2005, December 2005

25. Backup

26. WiMAX in the News • Sprint-Nextel announced in mid-2006 that it will be investing about $ 3 billion in a WiMAX technology buildout over the next few years. • Motorola plans to introduce a 802.16e WiMAX phone in 2007 • Reportedly announced that IEEE has begun working on 802.16m, which could push data transfer speeds up to 1Gbps while maintaining backwards compatibility

27. Network Working Group (NWG) • Developing higher-level networking specifications for Mobile WiMAX • Beyond air interface (PHY and MAC) specifications • End-to-end Mobile WiMAX network