10-1©2010 Raj JainCSE574sWashington University in St. Louis

WiMAX WiMAX Part I: PHYPart I: PHY

Raj JainProfessor of Computer Science and Engineering

Washington University in Saint LouisSaint Louis, MO 63130

Jain@cse.wustl.edu

Audio/Video recordings of this lecture are available at:http://www.cse.wustl.edu/~jain/cse574-10/

10-2©2010 Raj JainCSE574sWashington University in St. Louis

What is WiMAXPrevious Broadband Wireless Access: LMDS, MMDSWiMAX PHY LayerFrequency ReuseSubchannelizationFrame structure

OverviewOverview

10-3©2010 Raj JainCSE574sWashington University in St. Louis

What is WiMAX?What is WiMAX?

Telco Core

Point to Multipoint

Point to Point

Base Stations (BSs)

Subscriber Station (SSs)

(Rural Areas)

(Congested Areas)

<50km

<70Mbps

Downlink (DL)Uplink (UL)

<120km/sec(Mobile Users)

10-4©2010 Raj JainCSE574sWashington University in St. Louis

Data rate vs. MobilityData rate vs. Mobility

0.1 1 10 100 ++

User/Link Bit Rate Mbits/second

WiFi

WiMAX

CellularMob

ility

Vehicular

Stationary

Nomadic

10-5©2010 Raj JainCSE574sWashington University in St. Louis

Key Features of WiMAXKey Features of WiMAXWorks on many bands: 2.3 GHz, 2.5 GHz, 3.5 GHz, …Scalable ⇒ Can use any available spectrum width: 1.25 MHz to 28 MHzStrong securityOpen technology like WiFiReach and mobility like Cellular but much higher data rates

High data rate, up to 70MbpsLong distance, up to 50kmsMobility, up to 120 to 150 km/hour

Data rate vs Distance trade off using adaptive modulation. 64QAM to BPSKOffers non-line of site (NLOS) operationStrong QoS ⇒ Guaranteed services for data, voice, and video

10-6©2010 Raj JainCSE574sWashington University in St. Louis

Prior Attempts: LMDS & MMDS Prior Attempts: LMDS & MMDS Local Multipoint Distribution Service (1998)1.3 GHz around 28 GHz band (Ka Band)28 GHz ⇒ Rain effectsMulti-channel Multipoint Distribution Services (1999-2001)2.1, 2.5-2.7 GHz Band ⇒ Not affected by rain

Issues: Equipment too expensive, Roof top LoS antennas, short range (LMDS) or too small capacity (MMDS)

Modem

PoP

10-7©2010 Raj JainCSE574sWashington University in St. Louis

WiMAXWiMAX

WiMAX ≠ IEEE 802.16Worldwide Interoperability for Microwave Access420+ members including Semiconductor companies, equipment vendors, integrators, service providers. Like Wi-Fi AllianceNarrows down the list of options in IEEE 802.16 Plugfests started November 2005WiMAX forum lists certified base stations and subscriber stations from many vendorshttp://www.wimaxforum.org

10-8©2010 Raj JainCSE574sWashington University in St. Louis

Spectrum OptionsSpectrum Options

10-9©2010 Raj JainCSE574sWashington University in St. Louis

Effect of FrequencyEffect of FrequencyHigher Frequencies have higher attenuation, e.g., 18 GHz has 20 dB/m more than 1.8 GHzHigher frequencies need smaller antennaAntenna > Wavelength/2, 800 MHz ⇒ 6”Higher frequencies are affected more by weatherHigher than 10 GHz affected by rainfall60 GHz affected by absorption of oxygen moleculesHigher frequencies have more bandwidth and higher data rateHigher frequencies allow more frequency reuseThey attenuate close to cell boundaries. Low frequencies propagate far.Mobility ⇒ Below 10 GHz

10-10©2010 Raj JainCSE574sWashington University in St. Louis

IEEE 802.16 PHYsIEEE 802.16 PHYsFunction LOS Freq.

BandCarrier Duplexing

WirelessMAN SC Pt-to-pt LOS 10-66 GHz

Single TDD, FDD

WirelessMAN SCa

Pt-to-pt LOS 2-11 GHzLicensed

Single TDD, FDD

WirelessMAN OFDM (16d)

Pt-to-mpt NLOS 2-11 GHzLicensed

256 TDD, FDD

WirelessMANOFDMA (16e)

Pt-to-mpt NLOS 2-11 GHzLicensed

2048 TDD, FDD

WirelessHUMAN(High-speed Unlicensed)

Pt-to-mpt NLOS 2-11 GHzLicense Exempt

1/256/ 2048

TDDDynamic Freq. Sel.

10-11©2010 Raj JainCSE574sWashington University in St. Louis

IEEE 802.16 PHY: FeaturesIEEE 802.16 PHY: Features

Features discussed previously:Scalable OFDMATDD and FDDAdaptive Modulation and CodingSpace Time Block Codes (STBC)Adaptive Antenna System

Other Features:Subchannelization and permutationSlots, tiles, and clusters, bursts

10-12©2010 Raj JainCSE574sWashington University in St. Louis

Frequency ReuseFrequency ReuseNxSxK frequency reuse patternN=Number of cells per clusterS= Number of sectors in a cellK = Number of frequency allocations per cell

1X3X3

10-13©2010 Raj JainCSE574sWashington University in St. Louis

Frequency Reuse (Cont)Frequency Reuse (Cont)

11

1 11

1 11

1

11

1

11

1

11

1

11

1

11

1

11

1

11

1

SS

21

32

1

3 21

3

21

3

21

3

21

3

21

3

21

3

21

3

21

3

SS

1

1

1

1

1

1

1

1

1

1

SS

1

3

2

3

1

2

3

2

3

1

SS

11

13

3

3 22

2

33

3

11

1

22

2

33

3

22

2

33

3

11

1

SS

21

38

7

9 54

6

87

9

21

3

54

6

87

9

54

6

87

9

21

3

SS

1x3x1 1x3x3 1x1x1

3x1x1 3x3x1 3x3x3

10-14©2010 Raj JainCSE574sWashington University in St. Louis

Fractional Frequency ReuseFractional Frequency ReuseUsers close to the BS use all frequency subchannelsUsers at the cell boundary use only a fraction of available subchannels

F1,F2,F3

F1

F2

F3

F1,F2,F3

F1,F2,F3

10-15©2010 Raj JainCSE574sWashington University in St. Louis

OFDM SubcarriersOFDM Subcarriers

Data subcarriersPilot Subcarriers: Used for channel estimationGuard subcarriers: At the edges. No powerDC subcarrier: At the center for frequency band. No power.

DC GuardGuardPilot Data

10-16©2010 Raj JainCSE574sWashington University in St. Louis

SubchannelizationSubchannelizationSubchannel = Group of subcarriersEach user is given one or more subchannel.Subcarriers of a subchannel can be contiguous or distributed

Contiguous ⇒ Subchannels allocated based on use's SINR ⇒ Band AMC ⇒ Not suitable for mobile applications

Subchannel 1

10-17©2010 Raj JainCSE574sWashington University in St. Louis

Subcarrier PermutationsSubcarrier Permutations

Subcarriers are randomly assigned to a channel and changed every symbol time ⇒ Frequency hoppingAll subcarriers are used ⇒ Full Usage of Subcarriers (FUSC) – Not in WiMAX Forum ProfilesPartial Usage of Subcarriers (PUSC) - in WiMAX Forum profiles ⇒ commonly used

10-18©2010 Raj JainCSE574sWashington University in St. Louis

Downlink Partial Usage of SubcarriersDownlink Partial Usage of SubcarriersSubcarriers are divided in to 6 groups and only some groups may be used in a sector or cellData and pilots are arranged in clusters of 14 subcarriers over 2 symbols = 24 data + 4 pilot Clusters are renumbered using a pseudo random numbering schemeThe clusters are then divided into 6 groups (segments 0 through 5)Subchannel = Two clusters from the same groupIt is possible to allocate some subset of groups to each transmitter in a cell, e.g., 2 groups per sector

10-19©2010 Raj JainCSE574sWashington University in St. Louis

Symbols, Clusters, and Slots (PUSC DL)Symbols, Clusters, and Slots (PUSC DL)10 MHz = 1024 FFT = 840 subcarriers + 1 DC + 183 GuardTotal 30 subchannels = 30×28 = 840 subcarriers

PilotData

Cluster=2 symbols× 14 subcarriers

Slot=2 Clusters

Time

Frequency

Symbols

Subcarriers

Subchannel=28 subcarriers

10-20©2010 Raj JainCSE574sWashington University in St. Louis

PilotData

Tile=3 symbols× 4 subcarriers

Slot=6 Tiles

Time

Frequency

Symbols

Subcarriers

Subchannel=24 subcarriers

Symbols, Tiles, and Slots (PUSC UL)Symbols, Tiles, and Slots (PUSC UL)10 MHz = 1024 FFT = 840 subcarriers + 1 DC +183 GuardTotal 35 subchannels = 35X24 = 840 subcarriers

10-21©2010 Raj JainCSE574sWashington University in St. Louis

802.16 Frame Structure802.16 Frame Structure

TDD = Time Division DuplexingDL = Downlink (Base to subscriber)FCH = Frame control header:

Preamble FCH Burst 1 Burst n

Burst1

Burstm

Preamble UL Burst

DL Subframe UL Subframe DL Subframe UL SubframeTDD

…

…

FDD = Freq Div DuplexingUL = Uplink

Contention forInitial Ranging

Contention forBandwidth Req.

Burst2

Burst Profile, Down-link map, Uplink map, DL channel descriptor, etc.

10-22©2010 Raj JainCSE574sWashington University in St. Louis

Mobile WiMAX FrameMobile WiMAX FramePr

eam

ble

DL-

MA

PU

L-M

AP

FCH

UL-

MA

P (C

ont)

Ran

ging

Fast Feedback (CQICH)A

ck-C

HBurst 1

Burst 3

Burst 2

Burst 5

Burst 4Burst 1

Burst 2

Burst 3

Burst 4

Time

Freq

uenc

y

10-23©2010 Raj JainCSE574sWashington University in St. Louis

Frame StructureFrame StructureDL Preamble: Time and frequency synchronizationFrame Control Header (FCH): MAPs lengths, modulation and coding, usable subcarriersDownlink MAP: Burst profile (time, freq., modulation, coding)Uplink MAP: Burst profile for transmission from each user. MAPs can be compressedContention-based region: Ranging, bandwidth request, best-effort dataRanging Channel:

Closed loop frequency, time, and power adjustmentsChannel quality indicator channel (CQICH) CINR measurementAck Channel: subscriber stations

Initially, 5 ms frames only.

10-24©2010 Raj JainCSE574sWashington University in St. Louis

Subscriber InitializationSubscriber Initialization

Subscriber scans pre-set frequencies for base stationSubscriber finds base transmissions and synchronizes to it

Subscriber sends a ranging-request to BS at low powerSubscriber resends a ranging-request to BS at higher powersBase sends ranging response giving management conn IDs

Subscriber reports its PHY capabilities (modulation, coding, xDD)Base accepts subscriber or rejects some PHY capabilitiesBase-Subscriber Authentication using X.509 Certificates

10-25©2010 Raj JainCSE574sWashington University in St. Louis

SummarySummary

WiMAX supports non-line of sight using scalable OFDMAAny band any bandwidthSophisticated frequency reuse2D frame structure

10-26©2010 Raj JainCSE574sWashington University in St. Louis

References: BooksReferences: Books1. Cal Eklund, Roger B. Marks, Subbu Ponnuswamy, Kenneth

L. Stanwoood, Noco J.M. van Waes, "WirelessMAN: Inside the IEEE 802.16 Standard for Wireless Metropolitan Area Networks," IEEE, May-06, ISBN:0738148423.

2. Jeffrey G. Andrews, Arunabha Ghosh, Rias Muhamed, "Fundamentals of WiMAX: Understanding Broadband Wireless Networking," Prentice-Hall, ISBN:0132225522.

3. Loutfi Nuaymi, "WiMAX: Technology for Broadband Wireless Access," Wiley, Mar-07, 310 pp., ISBN:0470028087.

Note: These are the best 3 of 12+ books on WiMAX.

10-27©2010 Raj JainCSE574sWashington University in St. Louis

Reading ListReading ListJ. Thiel, “Metropolitan and Regional Wireless Networking: 802.16, 802.20 and 802.22,” http://www.cse.wustl.edu/~jain/cse574-06/wimax.htmM. Wood, “An Analysis of the Design and Implementation of QoS over IEEE 802.16,” http://www.cse.wustl.edu/~jain/cse574-06/wimax_qos.htm

10-28©2010 Raj JainCSE574sWashington University in St. Louis

Related Wikipedia PagesRelated Wikipedia Pageshttp://en.wikipedia.org/wiki/WiMAXhttp://en.wikipedia.org/wiki/IEEE_802.16http://en.wikipedia.org/wiki/Orthogonal_frequency-division_multiple_accesshttp://en.wikipedia.org/wiki/Orthogonal_frequency-division_multiplexinghttp://en.wikipedia.org/wiki/Symbol_ratehttp://en.wikipedia.org/wiki/WiBrohttp://en.wikipedia.org/wiki/WiMAX_MIMOhttp://en.wikipedia.org/wiki/Wireless_broadbandhttp://en.wikipedia.org/wiki/Wireless_local_loop

10-29©2010 Raj JainCSE574sWashington University in St. Louis

Related Wikipedia Pages (Cont)Related Wikipedia Pages (Cont)http://en.wikipedia.org/wiki/Local_Multipoint_Distribution_Servicehttp://en.wikipedia.org/wiki/Multichannel_Multipoint_Distribution_Servicehttp://en.wikipedia.org/wiki/Cellular_networkhttp://en.wikipedia.org/wiki/Cellular_network#Frequency_reusehttp://en.wikipedia.org/wiki/Xohmhttp://en.wikipedia.org/wiki/Clearwirehttp://en.wikipedia.org/wiki/List_of_deployed_WiMAX_networks

10-30©2010 Raj JainCSE574sWashington University in St. Louis

List of AcronymsList of AcronymsAAS Adaptive Antenna SystemAPAC Asia PacificBS Base StationBTC Block Turbo CodesCC Convolutional CodingRS-CC Reed-Solomon Convolutional CodesCINR Carrier to Interference and Noise RatioCQICH Channel quality indicator channelCTC Convolutional Turbo CodesDC Direct CurrentDIUC Downlink Interval Usage CodeDL DownlinkGHz Giga HertzIEEE Institution of Electrical and Electronics EngineersLMDS Local Multipoint Distribution Service

10-31©2010 Raj JainCSE574sWashington University in St. Louis

List of Acronyms (Cont)List of Acronyms (Cont)MAC Media Access ControlMAP Media Access Profile?MCS Modulation and Coding schemeMHz Mega HertzMIB Management Information BaseMIMO Multiple Input Multiple OutputMMR Mobile Multihop RelayOFDM Orthogonal Frequency Division MultiplexingOFDMA Orthogonal Frequency Division Multiple AccessPCMCIA Personal Computer Memory Card International AssociationPHY Physical LayerPUSC Partial Usage of SubcarriersQAM Quadrature Amplitude ModulationRSSI Received Signal Strength IndicatorSINR Signal to Interference and Noise RatioSTBC Space Time Block Codes