Mobile wimax technology

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
• Extension for 2-11 GHz
• Non-line-of-sight
• Point-to-Multi-Point applications
• Original fixed wireless broadband air Interface
for 10 – 66 GHz
• Line-of-sight only
• Point-to-Multi-Point applications
• Revised and replaced previous versions
• WiMAX System Profiles
• MAC/Physical layer enhancements to support
subscribers moving at vehicular speeds
802.16
Dec 2001
802.16a
Jan 2003
802.16d
Oct 2004
802.16e
Dec 2005
[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
Standard Data Rate Range
802.16d Up to 75 Mbps
(20 Mhz channel)
4–10 miles
802.16e Up to 30 Mbps
(10 Mhz channel)
1-3 miles

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
Designation Applicability
WirelessMAN-SC 10 -66 GHz
WirelessMAN-SCa Below 11GHz
Licensed bands
WirelessMAN-OFDM Below 11GHz
Licensed bands
WirelessMAN-OFDMA Below 11GHz
Licensed bands
WirelessHUMAN Below 11GHz
Licensed-exempt bands

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. HARQ
t
Hello
Nak
Hello
HelloHelloHH
Hello -> JelloHH Hello + Hello -> HelloHH
Nak
Ack
Ack
Base Station
Subscriber Station
1 2 3 4
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. MAC Layer
Service Specific Convergence
Sublayer
MAC Common Part Sublayer
Privacy Sublayer
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