WiMAX

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11/07/200511/07/2005 IEEE Communications Society IEEE Communications Society -- Chicago Chicago ChapterChapter

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WiMAXWiMAXA Killer Technology orA Killer Technology or

Another HypeAnother Hype

James T. Yu, Ph.D.James T. Yu, [email protected]@cs.depaul.edu

School of CTISchool of CTIDePaul UniversityDePaul University


22

OutlineOutlineIntroduction Broadband Wireless Access Introduction Broadband Wireless Access (BWA)(BWA)WiMAXWiMAX Applications/MarketApplications/Market•• AnalysisAnalysis•• Service ProvidersService Providers•• Equipment VendorsEquipment Vendors

IEEE 802.16IEEE 802.16•• Physical LayerPhysical Layer•• MACMAC--CPSCPS•• MACMAC--SSCSSSCS•• QoS and SecurityQoS and Security

SummarySummary

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Wireless PuzzleWireless Puzzle

Mobile-Fi

WiMAXLMDS

MMDS

CDMA

VSAT

UMTS

Bluetooth®

802.11802.15

802.16

802.20 EVDO

3G

FSO

GPRS

HSD

PAWiFi


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Broadband Broadband Wireless Wireless

Access (BWA)Access (BWA)

Backbone

Base Station

CPE(modem)

AntennaSystem

LAN

3


55

WiMAXWiMAXWiMAXWiMAX -- Worldwide interoperability for Microwave AccessWorldwide interoperability for Microwave Access•• It is a forum of product certification for interoperability It is a forum of product certification for interoperability

Standard: IEEE 802.16Standard: IEEE 802.16--20042004Frequency Spectrum: Frequency Spectrum: •• 10 10 -- 66 GHz (LOS)66 GHz (LOS)•• 2 2 –– 11 GHz (NLOS) 11 GHz (NLOS) –– both licensed and unlicensedboth licensed and unlicensed

Last mile technology (MAN/WAN)Last mile technology (MAN/WAN)•• Support pointSupport point--toto--point communicationpoint communication•• Support Quality of Service (QoS)Support Quality of Service (QoS)

Backhaul technology for wireless LANs (802.11)Backhaul technology for wireless LANs (802.11)Up to 30 miles of range with cell radius: 4Up to 30 miles of range with cell radius: 4--6 miles6 milesShared data rate up to 75 Mbps.Shared data rate up to 75 Mbps.•• Support 50 customers with T1Support 50 customers with T1--rate wireless rate wireless

connectionsconnections

Los: line of sight


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http://www.wimaxforum.org/news/events/wca_jan_2005/RWG_WCA_Jan_2005.pdf

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Technologies vs. ProblemsTechnologies vs. ProblemsWiMAXWiMAX is a wonderful technology, is a wonderful technology, but what is the problem?but what is the problem?•• Internet: Internet: How do we use wireless (and How do we use wireless (and

which one?) to surf the Internet?which one?) to surf the Internet?•• Intranet: Intranet: Is wireless (and which one) a Is wireless (and which one) a

viable technology for the intranet viable technology for the intranet application?application?


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Technology ConsiderationTechnology ConsiderationPrice/performancePrice/performance•• Throughput/SpeedThroughput/Speed

max throughput = channel bandwidth (Hz) max throughput = channel bandwidth (Hz) ×× bits/Hzbits/Hz

WAN vs. LANWAN vs. LAN•• DistanceDistance

Licensed vs. UnlicensedLicensed vs. Unlicensed•• 2.5G (unlicensed), 5.8G (unlicensed), 3.5G (licensed)2.5G (unlicensed), 5.8G (unlicensed), 3.5G (licensed)

Line of Sight (LOS) vs. NonLine of Sight (LOS) vs. Non--LOS NLOS)LOS NLOS)HalfHalf--duplex vs. full duplexduplex vs. full duplexPoint to Point (P2P), Point to MultiPoint to Point (P2P), Point to Multi--Point (P2MP), Point (P2MP), and Meshand MeshFixed, portable (nomadic), and mobileFixed, portable (nomadic), and mobileCarrier, Enterprise, SOHO, ResidentialCarrier, Enterprise, SOHO, Residential

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WiMAXWiMAX ApplicationsApplications

Last Mile (T1 replacement)Last Mile (T1 replacement)Broadband Access for rural areas Broadband Access for rural areas where there is a lack of wired where there is a lack of wired infrastructureinfrastructureWiFiWiFi BackhaulBackhaulEvolution: 3G to 4GEvolution: 3G to 4G


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Case Studies Case Studies -- Wireless ISPWireless ISPTowerStreamTowerStream•• http://http://www.towerstream.comwww.towerstream.com//

WiMAXWiMAX services in Boston, Chicago, services in Boston, Chicago, LA, NYC, and bay area.LA, NYC, and bay area.Product vendor: Product vendor: ApertoAperto NetworksNetworksa profitable companya profitable company55--forfor--5 plan, 5M at $500/month5 plan, 5M at $500/month•• a better deal than T1 and DSL (today!)a better deal than T1 and DSL (today!)

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WISP Case Studies (others)WISP Case Studies (others)AT&T AT&T WiMAXWiMAX TrialTrial

•• Atlanta, June 2005Atlanta, June 2005•• 40 towers and 30 trial customers40 towers and 30 trial customers•• pretrial test at New Jersey and Alaskapretrial test at New Jersey and AlaskaBellSouth BellSouth WiMAXWiMAX TrialTrial

•• Athens, GA (targeting college students) and a Athens, GA (targeting college students) and a few rural sites in Floridafew rural sites in Florida

•• 1.5M (down) and 256K (up) for $39.95/mm1.5M (down) and 256K (up) for $39.95/mm•• Strategy: 100% coverage of service area with Strategy: 100% coverage of service area with

80% DSL and 20% 80% DSL and 20% WiMAXWiMAXSprint and British Telecom also showed Sprint and British Telecom also showed interests in interests in WiMAXWiMAX trialstrials


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WiMAXWiMAX –– a viable last mile solution?a viable last mile solution?

What is the price for T1 (internet) What is the price for T1 (internet) today? (~$600/month)today? (~$600/month)What is the cost of T1 for ILEC today?What is the cost of T1 for ILEC today?•• T1: 2T1: 2--wire (HDSL2) and 4wire (HDSL2) and 4--wire (HDSL)wire (HDSL)•• local loop: 2local loop: 2--wire, $10/monthwire, $10/month

If ILEC lowers the T1 price, how will it If ILEC lowers the T1 price, how will it change the landscape of the broadband change the landscape of the broadband access market?access market?

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WiMAXWiMAX for places w/o wired infrastructurefor places w/o wired infrastructure

Advantages over DSLAdvantages over DSL•• Much longer distanceMuch longer distance

Some suburban areasSome suburban areasRural areasRural areasdeveloping countriesdeveloping countriesNote: this is the same for other WBA Note: this is the same for other WBA technologies which all failed.technologies which all failed.


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WiMAXWiMAX for 802.11 Backhaulfor 802.11 Backhaul

*TROPOS Networks whitepaper

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WiMAXWiMAX vs. 3G vs. 3G (which one is a better wireless technology?)(which one is a better wireless technology?)

Some studies position Some studies position WiMAXWiMAX as a 4G as a 4G technology due to its higher speed technology due to its higher speed (throughput) than 3G. (throughput) than 3G. WiMAXWiMAX (w/ 802.16e) offers mobility and (w/ 802.16e) offers mobility and has some advantages over 3G (higher has some advantages over 3G (higher performance).performance).Is there any major Is there any major wirelesswireless carrier carrier considering? If not, what is migration considering? If not, what is migration path from 3G to 4G (if there is one)?path from 3G to 4G (if there is one)?


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WiMAXWiMAX Equipment and VendorsEquipment and VendorsBase Station: ~$50KBase Station: ~$50KCPE: ~$500CPE: ~$500Price is expected to go down significantly Price is expected to go down significantly after the interoperability certification in after the interoperability certification in 2006?2006?Vendors:Vendors:•• AirSpanAirSpan Networks (AS4030)Networks (AS4030)•• AlvarionAlvarion ((BreezaMAXBreezaMAX))•• TroposTropos NetworksNetworks•• ApertoAperto NetworksNetworks•• NaviniNavini NetworksNetworks•• Others (Motorola, Nokia, etc.)Others (Motorola, Nokia, etc.)

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Future of Future of WiMAXWiMAXHow is How is WiMAXWiMAX different from those failed different from those failed wireless technologieswireless technologies•• standards, interoperability (standards, interoperability (WiMAXWiMAX forum)forum)•• Wireless service providersWireless service providers•• Product vendorProduct vendor

INTEL (>$500M invested), more players, etcINTEL (>$500M invested), more players, etc

Broadband wireless access (BWA) market is Broadband wireless access (BWA) market is projected to reach $1.2B (worldwide) by 2007, projected to reach $1.2B (worldwide) by 2007, and and WiMAXWiMAX is expected to be a key player. (by is expected to be a key player. (by InIn--Stat/MDR, 2005).Stat/MDR, 2005).What is your projection?What is your projection?


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WiMAXWiMAX

TechnologyTechnology

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Wireless Frequency BandWireless Frequency Band

27.527.5--31.3GHz31.3GHz

22--11 and 1011 and 10--66 GHz66 GHz

5.7255.725--5.875G5.875G

2.42.4--2.48G2.48G

2.52.5--2.7G2.7G

1.8501.850--1.990G1.990G

824824--894M894M

Frequency BandFrequency Band

MAN/WANMAN/WAN

MAN/WANMAN/WAN

LANLAN

LANLAN

MAN/WANMAN/WAN

CellularCellular

CellularCellular

ApplicationsApplications

LMDSLMDS

802.16802.16--20042004

UU--NNI (802.11a)NNI (802.11a)

ISM (802.11b)ISM (802.11b)

MMDSMMDS

PCSPCS

CellularCellular

TechnologyTechnology

http://www.ntia.doc.gov/osmhome/allochrt.pdf


2020

WiFiWiFi and and WiMAXWiMAX

ConnectionConnection--orientedorientedConnectionlessConnectionlessConnection typeConnection type

TDD/FDDTDD/FDDNONOFull DuplexFull Duplex

TDM/TDMA/OFDMATDM/TDMA/OFDMACSMA/CACSMA/CAMultiple AccessMultiple AccessYESYESNONOQoSQoS

>10 miles>10 miles300 ft300 ftMax DistanceMax Distanceup to 75Mup to 75M11M/54M11M/54MSpeed (bps)Speed (bps)

22--11GHz*11GHz*(both)(both)

2.4GHz2.4GHz(unlicensed)(unlicensed)

Frequency bandFrequency band802.16802.16802.11b/g802.11b/gStandardStandardWiMAXWiMAXWiFiWiFi

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Performance vs. MobilityPerformance vs. Mobility

fixed nomadic mobile

10M

1M

20M

50M

802.1x

802.16WiMAX

802.16e

802.203G

EVDO/HSDPA


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IEEE StandardsIEEE Standards1. IEEE 802.161. IEEE 802.16--2001 (102001 (10--66GHz)66GHz)

Air Interface for Fixed Broadband Wireless Access Air Interface for Fixed Broadband Wireless Access SystemSystem

2. IEEE 820.16a2. IEEE 820.16a--2003 (22003 (2--11GHz) 11GHz) –– WiMAXWiMAX3. 3. IEEE 802.16IEEE 802.16--20042004: (1) + (2): (1) + (2)4. IEEE 802.16.2 4. IEEE 802.16.2 –– CoexistenceCoexistence5. IEEE 802.16c 5. IEEE 802.16c –– System Profile for 10System Profile for 10--

66GHz66GHz6. 6. IEEE 802.16e (draft) IEEE 802.16e (draft) -- mobilitymobility

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2323

WAN (Mobile)802.20

MAN (Metro)802.16

LAN (Local)802.11

IEEE Wireless StandardsIEEE Wireless Standards

PAN (personal)802.15

WiFi: 802.11b/gWiMAX: 802.16


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Reference Model of 802.16Reference Model of 802.16

Source: IEEE 802.16 (Figure 1)

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802.16 Physical Layer802.16 Physical Layer

Several Several PHYsPHYs are standardized: are standardized: •• SingleSingle--carrier (SC) for 10carrier (SC) for 10--66 GHz 66 GHz •• SingleSingle--carrier (SC2) for 2carrier (SC2) for 2--11 GHz 11 GHz •• OFDM for 2OFDM for 2--11 GHz 11 GHz –– 256 FFT256 FFT•• OFDMA for 2OFDMA for 2--11 GHz 11 GHz –– 2048 FFT2048 FFT

High degree of flexibility for cost, High degree of flexibility for cost, capability, services, capacitycapability, services, capacity

FFT: Fast Fourier Transform


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Physical Layer (cont.)Physical Layer (cont.)PHY is pointPHY is point--toto--multipoint and mesh multipoint and mesh topology topology LOS and NLOSLOS and NLOS•• Multipath may be significant (NLOS) Multipath may be significant (NLOS)

Channel BW Channel BW –– 1.5 to 14 MHz1.5 to 14 MHzAdvanced power managementAdvanced power managementInterference mitigation Interference mitigation AAS and sectored AntennaAAS and sectored AntennaARQ on a perARQ on a per--connection basis connection basis

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WiMAXWiMAX Architecture (P2MP)Architecture (P2MP)BS: Base StationSS: Subscriber StationRS: Repeater StationTE: Terminal Equipment

Source: GWEC


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PointPoint--toto--Multipoint (P2MP)Multipoint (P2MP)Wireless MAN: not a LANBase Station (BS) connected to public networks BS serves Subscriber Stations (SS)• BS and SS are stationary• SS typically serves a building (business or

residence)Provide SS with first-mile access to public networksMultiple services, with different QoS priority, simultaneously

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Mesh ArchitectureMesh Architectureoptional architecture for WiMAX

Source: GWECc.f. 802.11s


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LOS vs. NLOSLOS vs. NLOS

Ref: WiMAX Forum

In general, >10GHz is LOS, and <10G can be either LOS or NLOS.

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MultipathMultipath SignalSignal

Multipath is the composition of a primary signal plus duplicate or echoed images caused by reflections of signals off objects between the transmitter and the receiver.The echoed signal is delayed in time and reduced in power, and it causes intersymbol interference (ISI) or distortion of the received signal. Not an issue for LOS, but a major issue for NLOS.What are the solutions to Multipath signal in NLOS?


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NLOS Technology SolutionsNLOS Technology Solutions(to address the issue of (to address the issue of multipathmultipath))

Adaptive modulationError correction techniques•• Forward Error Correction (FEC)Forward Error Correction (FEC)Spread SpectrumSpread Spectrum•• Orthogonal Frequency Division Multiplexing Orthogonal Frequency Division Multiplexing

(OFDM)(OFDM)• Sub-Channelization – divide into many

subchannels and mux them together for a bigger pipe

Advanced antenna System Power control.

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Adaptive ModulationAdaptive ModulationAdjust the signal modulation scheme depending on the signal to noise ratio (SNR) condition of the radio link. • a fixed scheme that is budgeted for the worst case

conditions. • Qadrature Amplitude modulation (QAM)• Phase Shift Keying (PSK)

Binary Phase Shift Keying (BPSK): 1 bit/Hz• for reference, not used

Quadrature PSK (QPSK): 2 bits/Hz, low SNR16-QAM (4 phases × 4 amplitudes): 4 bit/Hz64-QAM: 6 bit/Hz256-QAM: 8 bit/Hz, high SNRQ: In a very noisy channel, which modulation scheme is selected?


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Adaptive Physical Layer Adaptive Physical Layer

64-QAM

256-QAM

16-QAM

QPSK

distance

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3535

Modulation and BER (Bit Error Rate)Modulation and BER (Bit Error Rate)

SNR (dB)

256-QAMrequireshigh SNR

QPSKachieves

same BER atlower SNR

QPSK

Ref: Cisco Interoworking book


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Error Correction TechniquesError Correction TechniquesError correction techniques have been incorporated into WiMAX to reduce the system signal to noise ratio (SNR) requirements. Forward Error Correction (FEC): Advanced algorithms to detect and recover from erroneous frames. Automatic repeat request (ARQ) to request frame retransmission for frames that cannot be corrected by FEC. Improve the bit error rate (BER) performance for a similar threshold level.

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Orthogonal Frequency Orthogonal Frequency Division Multiplexing (OFDM)Division Multiplexing (OFDM)

It is a technique to increase transmission It is a technique to increase transmission speed by multiplexing.speed by multiplexing.It uses one wide frequency channel by It uses one wide frequency channel by breaking it up into several subbreaking it up into several sub--channels. channels. All small subAll small sub--channels are multiplexed channels are multiplexed into one “fat” channel. into one “fat” channel. Orthogonal: overlapping but Orthogonal: overlapping but distinguishabledistinguishable


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OFDMOFDM

Ref. http://www.iec.org/online/tutorials/ofdm/

When A is at the peak, B, C, D and E are all zero.

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Adaptive Antenna System (AAS)Adaptive Antenna System (AAS)

Optional in 802.16Use multiple antennas to improve the coverage and the system capacity. The spectral efficiency is increased linearly with the number of antenna elements. AAS is able to improve the SNR gain by combining multiple signals. AAS also reduces the frequency interference between users.


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Power ControlPower ControlPower control is used to improve the overall performance of the system. It is implemented by the base station (BS) sending power control information to subscriber stations (SS) to regulate the transmit power level so that the level received at the base station is at a pre-determined level.The SS transmits only enough power (as specified by the BS). The power control reduces the overall power consumption of the SS and the potential interference with other co-located base stations. For LOS the transmit power of the SS is approximately proportional to it’s distance (square) from the base station. For NLOS it is heavily dependant on the interference.

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4141

Dynamic Frequency Selection (DFS) Dynamic Frequency Selection (DFS) Optional procedure, but required in Optional procedure, but required in unlicensed bands unlicensed bands DFS consists of DFS consists of •• Requesting and reporting measurementsRequesting and reporting measurements•• Testing channels for the presence of Testing channels for the presence of

primary usersprimary users•• Detecting primary usersDetecting primary users•• Ceasing operation on a channel after Ceasing operation on a channel after

primary users have been foundprimary users have been found•• Selecting and advertising a new channelSelecting and advertising a new channel


4242

MAC Common Part MAC Common Part SublayerSublayerSupporting multiple accessSupporting multiple accessIn the downlink, BS does not have to coordinate its In the downlink, BS does not have to coordinate its transmissions, except for TDD (Time Division transmissions, except for TDD (Time Division Duplex).Duplex).The uplink is shared on a demand basis.The uplink is shared on a demand basis.The multipleThe multiple--access procedure in the uplink is access procedure in the uplink is implemented using implemented using •• unsolicited bandwidth grants, unsolicited bandwidth grants, •• polling, and polling, and •• contention procedures. contention procedures.

Vendors can have different implementations to Vendors can have different implementations to optimize system performanceoptimize system performance

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4343

MACMAC--CPS: Duplex Scheme SupportCPS: Duplex Scheme SupportOn downlink, SS is associated with a specific burst.On uplink, SS is allotted a variable length time slot , for their transmissionsMAC support for duplex schemesTime-Division Duplex (TDD)• Downlink & Uplink time share the same RF channel• Dynamic asymmetry

Frequency-Division Duplex (FDD)• Downlink & Uplink on separate RF channels• Static asymmetry


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FrequencyFrequency--division duplexing (FDD)division duplexing (FDD)Separated frequency channel for DL and UL.Separated frequency channel for DL and UL.Unframed FDD for fullUnframed FDD for full--duplex SS duplex SS

Framed FDD Framed FDD -- downlink in burstsdownlink in bursts

IEEE 802.16(Figure 37)

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4545

TDD FrameTDD Frame

Source: IEEE 802.16 (Figure 38)

(physical slot) asymmetric DL/UL


4646

Service Specific Service Specific Convergence Convergence SublayerSublayer (SSCS)(SSCS)Accepting higherAccepting higher--layer data layer data Classification (and processing) of data Classification (and processing) of data Delivering data to the MAC layerDelivering data to the MAC layerReceiving data from the peer entityReceiving data from the peer entityTwo convergence Two convergence sublayerssublayers::•• ATM CSATM CS•• Packet CS (Ethernet and IP)Packet CS (Ethernet and IP)

QoSQoS

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4747

Medium Access Control (MAC)Medium Access Control (MAC)

A MAC frame consists of header, A MAC frame consists of header, payload, and CRC payload, and CRC Frames can be concatenated, Frames can be concatenated, fragmented, or packedfragmented, or packedOne SS may serve multiple tenantsOne SS may serve multiple tenants


4848

MAC AddressingMAC AddressingSS has 48SS has 48--bit 802.3 MAC addressbit 802.3 MAC addressBS has 48BS has 48--bit base station IDbit base station ID•• Not a MAC addressNot a MAC address

Connection ID (CID)Connection ID (CID)•• 16 bit16 bit•• Used in MAC PDUUsed in MAC PDU•• Note that MAC PDU does not have SS Note that MAC PDU does not have SS

MAC address or BS IDMAC address or BS IDwhy? connectionwhy? connection--oriented serviceoriented service

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4949

Generic MAC Header Generic MAC Header

Q: do you see source and destination MAC address?Q: How does SS and BS accept MAC frames sent to them?


5050

MAC PDU TransmissionMAC PDU Transmission

P

PDU 2 PDU 3 PDU 4 PDU 5

FEC 1 FEC 2 FEC 3

PDU 1

P: Preamble

Burst

FEC Block: MAC PDUs + FEC Code

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5151

SS Operation: SS Operation: Network Entry and InitializationNetwork Entry and Initialization

1.1. Scan for downlink channel; synchronize Scan for downlink channel; synchronize with BSwith BS

2.2. Obtain uplink transmission parametersObtain uplink transmission parameters3.3. Perform ranging (acquire timing offset)Perform ranging (acquire timing offset)4.4. Negotiate capabilitiesNegotiate capabilities5.5. Establish connectivity (for upper layer)Establish connectivity (for upper layer)6.6. Establish time of dayEstablish time of day7.7. Transfer operational parametersTransfer operational parameters8.8. Set up connections Set up connections


5252

Channel Access and QoSChannel Access and QoSPackets are associated with a Packets are associated with a service service flowflowA service A service flowflow has associated QoS has associated QoS parameters: bandwidth, latency, jitter, parameters: bandwidth, latency, jitter, and throughput and throughput Service flows can be static (preService flows can be static (pre--configured) or dynamically establishedconfigured) or dynamically establishedThe BS includes authorization module that The BS includes authorization module that approves or denies every change to the approves or denies every change to the QoS parameters QoS parameters

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5353

QoS MechanismQoS MechanismScheduling services Scheduling services •• Unsolicited grant service (UGS) Unsolicited grant service (UGS) -- for for

realreal--time fixedtime fixed--size packets (VOIP, size packets (VOIP, T1/E1)T1/E1)

•• RealReal--time polling service (rtPS) time polling service (rtPS) -- for for variablevariable--size packets (MPEG video) size packets (MPEG video)

•• NonNon--realreal--time polling service (nrtPS) time polling service (nrtPS) ––nonnon--realreal--time data with variabletime data with variable--sized sized packets (FTP) packets (FTP)

•• Best effort service Best effort service


5454

Requests and GrantsRequests and GrantsSSs can request bandwidth SSs can request bandwidth During these requests, collisions During these requests, collisions can happen (CSMA).can happen (CSMA).If the request is successful, the SS If the request is successful, the SS will receive a data grant.will receive a data grant.There are incremental and There are incremental and aggregated requests.aggregated requests.Requests are per connections, but Requests are per connections, but grants are per SS only.grants are per SS only.

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5555

Privacy Privacy SublayerSublayerPrivacy Privacy -- encrypting connections encrypting connections SS/BSSS/BSEncryption has two component Encryption has two component protocolsprotocols•• Encapsulation protocol for encrypting Encapsulation protocol for encrypting

packet data packet data •• Privacy key management (PKM) Privacy key management (PKM)

protocol. protocol.

Protection from theft of servicesProtection from theft of services


5656

Privacy key management Privacy key management (PKM) protocol(PKM) protocol

AuthorizationAuthorizationPeriodic rePeriodic re--authorization is authorization is required. (why?)required. (why?)X.509 digital certificates.X.509 digital certificates.Keys and age must be refreshed. Keys and age must be refreshed. Two sets of keys are always Two sets of keys are always active.active.

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5757

Current projects within 802.16Current projects within 802.16

802.16e 802.16e –– mobilitymobilityPhysical layer below 2 GHz Physical layer below 2 GHz MAC modification to support pointMAC modification to support point--toto--point (P2P) systemspoint (P2P) systems


5858

SummarySummaryFixed wireless does NOT have a successful Fixed wireless does NOT have a successful story in US, yet.story in US, yet.WiMAXWiMAX is a very complex protocol.is a very complex protocol.•• No analogy between No analogy between WiFiWiFi and and WiMAXWiMAX, except , except

for wirelessfor wirelessWiMAXWiMAX is great for T1 users today, but …is great for T1 users today, but …WiMAXWiMAX is better than 3G, but …is better than 3G, but …WiMAXWiMAX can be used for can be used for WiFiWiFi backhaul, but …backhaul, but …WiMAXWiMAX is attractive in urban and developing is attractive in urban and developing countries.countries.There are market windows for There are market windows for WiMAXWiMAX, but …, but …There are more questions than answers.There are more questions than answers.

WiMAX

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