Wireless networks - Lecture 42: IEEE 802.16

Wireless networks - Lecture 42: IEEE 802.16. The main topics covered in this chapter include: IEEE 802.16 overview; WiMAX forum; characteristics of 802.16 frequency ranges; provide high-speed mobile data and telecommunications services; orthogonal frequency division multiplexing (OFDM);...

Wireless Networks

Lecture 42 IEEE 802.16

Dr Ghalib A Shah

WiMAX Basics

standards based air interfaces for the licensed and

unlicensed radio frequencies from 2 to 66 GHz

MAC – Media Access Control sub layer of the data link layer

the needs of the different frequencies and regulatory environments

delivering wireless data services do have the potential

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 J une 2001 to promote conformance

and interoperability of the 802.16 standard

 Develops “system profiles” that define

mandatory and optional features of standard

IEEE® 802.16e Mobile Broadband Wireless Amendment

IEEE® 802.16-2004 Fixed Broadband Wireless Standard

Mobile WiMAX System Profile Release-1 Mandatory and

Optional Features

• Extension for 2­11 GHz

•  Non­line­of­sight

•  Point­to­Multi­Point applications

• Original fixed wireless broadband air Interface  for 10 – 66 GHz

•  Line­of­sight only

•  Point­to­Multi­Point 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

Characteristics of 802.16 Frequency Ranges

 10 - 66 GHz

► Short wavelength

► Line-of-sight (LOS) required

► Negligible multipath

► The commonly used frequencies in this range are

10.5, 25, 26, 31, 38, and 39 GHz

 2 – 11 GHz

► Longer wavelength

► LOS not required

► Improved range and in-building penetration

► Multipath effects may be significant

IEEE 802.16 Standard

802.16 802.16d/HiperMAN 802.16e Completed December 2001 June 2004 (802.16d) Es timate 2005

Spectrum 10 ­ 66 GHz < 11 GHz < 6 GHz

Channel 

Conditions

Bit Rate 32 – 134 Mbps  in 

28MHz channel  bandwidth

Up to 75 Mbps  in 20MHz  channel bandwidth Up to 15 Mbps  in 5MHz channel 

bandwidth

Modulation QPSK, 16QAM and 

64QAM OFDM 256 FFTQPSK, 16QAM, 64QAM Scalable OFDMA128 to 2048 FFT

Channel 

Bandwidth

s

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

802.11 v 802.16

► 802.11’s media access control protocol is optimized for

shorter-range topologies

► It also was not designed to serve a large number of users

► Wireless MAN, on the other hand, was designed to solve the

problems of delivering wireless broadband networks over longer distances and through more difficult environments, such as

heavily wooded areas

Comparison 802.11 and 802.16

802.11

< 300 feet

Optimized for  indoor short range 2.7 bps/Hz peak. 

 <= 54Mbps in 20MHz  1­10 CPE CSMA/CA

Technology

Range

Coverage

Data rate

Scalability

802.16

< 30 Mile ( typical 3~4) Outdoor LOS & NLOS

5bps/Hz peak, 

<100Mbps in 20 MHz 1­ hundreds CPE TDMA

Network Architecture

Physical Layer

 Five physical layer modes

802.16d

802.16e

Licensed bands

Licensed bands

Licensed bands

Orthogonal Frequency Division Multiplexing

(OFDM)

 Multiplexing technique that divides the channel

into multiple orthogonal sub channels

 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 sub channel

 High spectral efficiency, resilient to

interference, and low multi-path distortion

Conventional FDM and OFDM

Orthogonal Frequency Division Multiple Access

(OFDMA)

 Multiple-access/multiplexing scheme

► a multiple-access/multiplexing scheme that provides

multiplexing operation of data streams from multiple users onto the downlink sub-channels and uplink multiple access by means of uplink sub-channels.

► 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

► Adjusts automatically to channel conditions

► Receiver saves failed transmission attempts to help future

decoding

• Every transmission helps increase probability of success

► Multiple antennas on sender and receivers

► Takes advantage of multi-path

► Increased spectral efficiency

Half-Duplex FDD operation;

system-wide synchronization;

reasons:

► TDD enables adjustment of the downlink/uplink ratio to

efficiently support asymmetric downlink/uplink traffic,

► Unlike FDD, which requires a pair of channels, TDD only

requires a single channel for both downlink and uplink providing greater flexibility

► Transceiver designs for TDD implementations are less

MAC Layer

 Connection-oriented

 A fundamental premise of the MAC architecture

is quality of service (QoS)

 QoS provided via service flows

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,