IEEE 802.16e/Mobile WiMAX
Gleneesha Johnson
CMSC 818Z, Spring 2007
March 06, 2007
Outline
• 802.16 Overview
• Physical Layer
• MAC Layer
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
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]
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
[2]
• MAC/Physical layer enhancements to support
subscribers moving at vehicular speeds
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
~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
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
Network Architecture
Source: WiMAX Nuts and Bolts – Steve Hilton [3]
Outline
• 802.16 Overview
• Physical Layer
• MAC Layer
Physical Layer
• Five physical layer modes
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
802.16d
802.16e
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
Conventional FDM and OFDM
Source: Broadband Wireless Access (W-PAN, W-LAN, WiMAX, Wi-Mob) (including
OFDM concepts) - A. K. Seth [4]
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
Other Physical Layer Features
• Adaptive modulation and coding (AMC)
• Fast Channel Feedback
[3]
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
HARQ
Nak
Hello
Hello
Ack
t
Base Station
1
2
H
Hello
3
4
Nak
Hello
Ack
Subscriber Station
H
Hello -> Jello
Source: WiMAX Nuts and Bolts – Steve Hilton [3]
H
H
Hello + Hello -> Hello
Outline
• 802.16 Overview
• Physical Layer
• MAC Layer
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)
[1]
MAC Layer
Service Specific Convergence
Sublayer
Interface to higher layer
protocols, classifies
incoming data, etc.
MAC Common Part Sublayer
Core MAC functions (i.e.,
scheduling, connection
maintenance,fragmentation),
QoS control
Privacy Sublayer
Encryption, authentication,
secure key exchange
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
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
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
Backup
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
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