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

• 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

802.16Dec 2001

802.16aJan 2003

802.16dOct 2004

802.16eDec 2005

[2]

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

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

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

t

Hello

Nak

Hello

Hello

HelloHH

Hello -> JelloH H Hello + Hello ->

Hello H H

Nak

Ack

Ack

Base Station

Subscriber Station

1 2 3 4

Source: WiMAX Nuts and Bolts – Steve Hilton [3]

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

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

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