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ECE710:

Wireless Communication Networks — Broadband Wireless Access Technology

Lin CaiBroadband Communications Research (BBCR) Group

June 8, 2010

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Wireless communication networks

Internet

Vehicle Networks

Wireless HotspotsSatellite Communication

Network

Medical sensor

TV

PC/PDA

Broadband Home Network

WiMAX/cellular Networks

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UWB

Whom is this tutorial for?

• Someone who– is interested in

knowing the research issues in last mile wireless broadband access technology

– expects to learn the objectives and specifications of IEEE 802 family

4G

WiFi

WiMAX

Mesh

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Agenda

• Introduction• Local/Personal Area Networking Technology

– Overview– WLAN PHY & MAC– UWB and mmWave WPAN

• WiMAX and Resource Management– WiMAX PHY & MAC– Resource Management

• Summary

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Wireless Network Classification

• Network scale or scope

Distance Location Network Abbre.

<2m Wireless Body area network WBAN

<10m Room WPAN

10-100m(1km) Building WLAN

1-10km city Wireless Metropolitan area network WMAN

100-100km country Wireless Wide area network WWAN

Wireless Personal area network

Wireless Local area network

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Global Wireless Standards

BAN

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Scope of 802 Standards

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Agenda

• Introduction• Local/Personal Area Networking Technology

– WLAN PHY & MAC– UWB and mmWave WPAN

• WiMAX and Resource Management– WiMAX PHY & MAC– Resource Management

• Summary

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Part I: WLAN/WPAN

• WLAN and WPAN:– wireless networks suitable for local short-distance

networking and compatible with existing LANs

• Benefits: open technology, easy deployment, expandability, cost efficiency, convenient, mobility, etc.

• Challenges: transmission range, reliability, data rate, QoS, security, etc.

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Historical perspective of WLAN standards

• WLAN Standards:– HiperLAN: European Telecommunications Standards

Institute (ETSI)– Wi-Fi: IEEE 802.11 Worldwide Standard Group

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Historical perspective of WPAN projects

• Started in 1997 as ‘ad hoc’ group within IEEE Portable Applications Standards Committee (PASC)

• In March 1998 a Study Group was formed within 802.11, and in March 1999, IEEE 802.15 Working Group for WPANs established

• In 2003, IEEE 802.15.3 specifies a MAC and PHY standard for high-rate WPANs– 3a: high speed UWB PHY – 3b: amendment– 3c: Millimeter Wave alternative PHY

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Part I: WLAN/WPAN--- WLAN Technology

• WLAN technology– Architecture– WLAN PHY & MAC protocols– Performance study – Other Issues

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WLAN Architecture

Infrastructure Mode Independent Mode (Ad Hoc)

Station

Station

Station

Station

Station

Station

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WLAN Architecture (Cont’d)

StationStation

Station

Station

BSS

Station

Station

Station

BSS

Distribution System

LAN (802.X)

Portal

Basic Service Set (BSS):

-Group of stations using the same radio frequency

Portal:

-Bridge to other networks

Distribution System:

-interconnection network to from one logical network, extended service set (ESS) based on several BSSs.

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WLAN PHY and MAC Layers

[5]

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DIFS

BO

DIFS DIFS

Busy

BO

t

Station1

Station2

Station3

Station4

BO

BO

Busy

BOr

BOr

BO Busy

Busy

BOrBO

DIFS

Station5

: Packet arrival; BO: Elapsed backoff time; BOr: Residual backoff time; : Collision occurs.

IEEE 802.11 MAC - Distributed Coordination Function (DCF)

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IEEE 802.11 MAC -Point Coordination Function (PCF)

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IEEE 802.11e MAC -Enhanced DCF (EDCF)

Traffic differentiation(TC); Transmission Opportunity( TXOP); PF

{AIFS ,CWmin, Cwmax}

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IEEE 802.11e MAC -Hybrid Coordination Function

Differences between hybrid coordinator (HC) and point coordinator (PC):HC can poll QSTAs in both CP and CFPHC grants a polled TXOP to one QSTA, which restricts the duration of the QSTA’s access to the medium.

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IEEE 802.11n

• PHY Key features –Bandwidth extension

• Using double channel (40 MHz) to achieve higher data rate

–MIMO• Enhance the PHY data rate of 802.11

– 2X2: 108Mbps (54Mbps X2)– 4X4: 216Mbps (54Mbps X4)

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MIMO Technolgoy: Diversity vs Multiplexing

IEEE 802.11n - MIMO

[2]V. Tarokh, N. Seshadri, and A. R. Calderbank. Space–time codes for high data rate wireless communication: Performance criterion and code construction. IEEE transaction on Information Theory. Vol 44. Iss. 2. 1998.

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• MAC Enhancement:– Aggregation of multiple frames => improve transmission

efficiency– Bi-directional transmission– One single medium access for one High Throughput

PHY (HTP) burst transmission; frames can be sent to different destinations

– Block ACK that improves the channel efficiency by aggregating several acknowledgements into one frame

IEEE 802.11n (Cont’d)

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• Saturated Station Scenario– Bi-dimensional Markov model [3]

• Non-saturated Station Scenario– M/M/1 and M/G/1 Model [4]– G/G/1 Model [5,6]

[3] G. Bianchi. Performance analysis of the IEEE 802.11 distributed coordination function. IEEE J. Select. Areas Commun., 18(3):535-547, March 2000.

[4] C. H. Foh and M. Zukerman. Performance analysis of the IEEE 802.11 MAC protocol. In European Wireless, Feburary 2002.[5] O. Tickoo and B. Sikdar. Queueing analysis and delay mitigation in IEEE 802.11 random access MAC based wireless

networks. In Proc. IEEE Infocom’04, volume 2, pages 1404-1413, March 2004.[6] L.X. Cai, X. Shen, J.W. Mark, L. Cai and Y. Xiao, "Voice Capacity Analysis of WLAN with Unbalanced Traffic'', IEEE Trans.

on Vehicular Techn ology, Vol. 55, No. 3, pp. 752-761, 2006.

MAC performance analysis

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CN1

CN2

AP

CN3

CNN-1

MNN-1

MN2

MN1

………… MN

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802.11 WLAN

Internet

A single hop WLAN; Ideal channel;

Conditional Collision Probability p is assumed constant;

Mean traffic arrival rate of MN i: frames per slot;

Mean frame service rate of MN i: frames per slot;

Traffic intensity/queue utilization ratio:

MAC performance analysis (Cont’d)

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The channel is busy due to the successful transmissions of the tagged node;The channel is busy due to the successful transmissions of the remaining nodes; The channel is busy due to the collisions;The channel is idle when the tagged node is in the backoff stage.

[6] L.X. Cai, X. Shen, J.W. Mark, L. Cai and Y. Xiao, "Voice Capacity Analysis of WLAN with Unbalanced Traffic'', IEEE Trans. on Vehicular Techn ology, Vol. 55, No. 3, pp. 752-761, 2006.

During the interval 1/ μ, one of the following events must occur[6]:

=

MAC performance analysis (Cont’d)

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Numerical results

Queue utilization ratio Voice capacity in IEEE 802.11b WLAN

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Number of Voice Connections

Que

ue U

tiliz

atio

n R

atio

AP-729-10ms(typical) MN-729-10ms(typical) AP-729-20msMN-729-20ms AP-729-30ms MN-729-30msAP-711-20ms(typical) MN-711-20ms(typical) AP-723-30ms(typical)MN-723-30ms(typical)

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Voice Capacity in IEEE 802.11n WLAN [7][7] Lin X. Cai et.al. Supporting voice and video in an IEEE 802.11n WLAN. Accepted in Wireness Networks

Numerical results (Cont’d)

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• Improve range: – farthest distance is 300 feet, and performance drops off rapidly

as an MN move farther from the access point

• Enhance data rate and throughput – 60GHz frequency bands (mmWave communication technology)– Higher throughput at a longer distance

• Provide QoS – Efficient Connection control and DiffServ mechanisms

• Security

Other issues in WLAN

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• IEEE 802.15.3– Standard for high-rate (20Mbit/s – Gbit/s) WPANs,

while still low-power/low-cost Short Range (at least 10m, up to 70m possible)

– 802.15-3a: UWB 400Mbit– 802.15-3c: mmWave 2-3Gbit

IEEE 802.11 WLAN vs IEEE 802.15 WPAN

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Part I: WLAN/WPAN--- WPAN Technology

• WPAN technology– Applications and design criteria– UWB and mmWave communication techniques– IEEE 802.15.3 MAC– Exclusive region based MAC protocol design and

capacity analysis

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Applications

Last-meter wireless access

– Support video streaming, broadband ad-hoc meeting,

high volume content distribution, etc.

Vehicle communication networks

– Safety, entertainment, location-based services, etc.

Other applications

– Imaging, real time location sensing (RTLS), etc.

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Design criteria for high rate WPAN

• Very low power consumption and low complexity wireless connection within personal operating space

• Co-existence with other standard devices such as 802.11, Bluetooth etc.

• Cost effective implementation in ad hoc networks– Fast connection– Dynamic membership– Efficient data transmission

• QoS provision for a variety of traffic classes • WPAN mesh networking

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WPAN PHY: Ultra-wideband (UWB)

Ultra-wideband (UWB) communication system:

FCC: BW>500MHz or (fH-fL)/fC >20%

• Large bandwidth: 3.1-10.6 Ghz

• Low emission power: < -41.3 dBm/MHz

• Adaptive data rate, interference-limited multiple access,

ranging capability

Narrowband (30kHz)

Wideband CDMA (5 MHz)

UWB (Several GHz)

Frequency

Part 15 Limit

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WPAN PHY: Millimeter Wave (mmWave)

IEEE 802.15.3c:

57-64 GHz unlicensed band

Principle characteristics:

High, variable data rate

Severe path loss

Small size of RF unit

⇒Directional antenna

High rate and efficient operation in dense environment

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IEEE 802.15.3 MAC

Piconet Coordinator manages piconet

Starting a Piconet

DEV uses passive scanning to detect piconet

DEV chooses the channel and broadcasts its

beacon

Managing a Piconet

Assign DEVID to devices requesting to

associate to a piconet

Scheduling peer to peer transmission among

devices

DEV DEV

DEV

DEVWPAN

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IEEE 802.15.3 MAC

• Channel time is divided into superframe– Beacon

– Contains piconet synchronization parameter and IE (Information Element)s

– CAP (Contention Access Period) Optional – For command frames and non-stream data. Using CSMA/CA with

backoff scheme– CFP (Contention Free Period)

– For data stream. PNC assigns to DEV with each CTA (Channel Time Allocation)

Distributed Reservation Protocol (DRP) for WPAN mesh networks

Distributed MAC without central controller

Reservation based DRP and random access based PCA

Disadvantages:

– Beacon period (BP)

synchronization

– Merging multiple BPs

– Beacon collision

(burst join)

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ER based MAC for UWB/mmWave WPANs

Narrow band collision model is no longer applicable in

UWB systems

Explore spatial capability to significantly improve

resource utilization

=> Exclusive Region (ER) [JSAC04] based MAC

protocol for appropriate concurrent transmissions

[JSAC04] B. Radunovic and J. Le Boudec. “Optimal Power Control, Scheduling, andRouting in UWB Networks”, IEEE J. Sele. A. in Comm., vol. 22, no, 7, pp. 1252-1270,Sept. 2004.

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ER based MAC design principle

Define an exclusive region around the receiver

Other senders outside of the ER can transmit

concurrently; otherwise, refrain their transmissions

Case 1: Omni-Omni Case2: Directional-Omni

Case 4: Directional-Directional

r0

r3r4

r8r6

r7

r5

r2r1

Case 3: Omni-Directional

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Central controller schedules concurrent transmissions

Key parameter: ER radius r

– Smaller r , higher spatial multiplexing

gain, higher interference;

– Vice versa.

Spatial multiplexing capacity of WPAN

To maximize the network spatial multiplexing capacity by fine

tuning ER size r [Cai_TWC10]

DEV

DEV

[Cai_TWC10] L. X. Cai, L. Cai, X. Shen, and J. W. Mark, “REX: a Randomized EXclusive region based scheduling scheme for mmWave WPANs with directional antenna,” IEEE Transactions on Wireless Communications, Jan. 2010.

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Numerical results: Spatial multiplexing gain

Omni-Omni Dir-Omni, Dir-Dir

WPAN mesh networks

Asynchronous distributed MAC:

– No central controller with global user information

– Avoid the need of synchronization, which is difficult

and costly

CSMA/CA based asynchronous MAC:

Hidden/exposed terminal problem

Flow starvation and unfairness problems

Distributed Exclusive region (DEX) based MAC42

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Distributed MAC design

DEX: Distributed EXclusive region based MAC

– Use RTS/CTS exchange to reserve small ERs for each pair of sender and receiver

– Other flows can initiate their transmission if they are outside the ERs of ongoing transmissions

Key parameters: transmission rate R and ER radius r

[Cai_TWC10] L. X. Cai, L. Cai, X. Shen, J. W. Mark, and Q. Zhang, “MAC protocol design and optimization for multi-hop Ultra-wideband networks,” IEEE Transactions on Wireless Communications, in press.

How to decide the data transmission rate R to ensure

successful data transmissions [Cai_TWC10] ?

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Performance Analysis and Parameter Setting

Given ER radius r

maximum interference to a receiver

where

Considering the worst case scenario

of interference, we can determine the

transmission rate with guaranteed bit

error performance

)]()1([)3/(6 0 αςαςrPGI α −−−≤ −

.1∑∞

=k

xk=ς(x) r

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Performance study

• Given r and a saturated network in an area L*L, the upper bound of CT is(Circle packing problem)

• The lower bound of CT is(Circle covering problem)

• Optimal ER size that maximizes the expected network transport throughput

22 32Lmax CT r=

22 27min CT rL=

)1(log][ 22 I+NPd+ηWd

Dk=TRE

αα

r

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Hidden/Exposed Terminal and Fairness Problems

Hidden terminal problem:

– Reserve a relatively long TXOP -> less collisions

Exposed terminal problem:

– With smaller ERs, more flows transmit concurrently to

achieve a higher spatial multiplexing gain

Starvation and unfairness problems are mitigated

with the reduced contention level within the ER

4646

Simulation results: Transport throughput

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Transport throughput = Link throughput x Distance 47

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Compare Jain's Fairness Index

Simulation results: Fairness

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• WiMAX Overview– WiMAX objectives– WiMAX & IEEE 802.16

• WiMAX PHY & MAC • Resource Management

Part II: WiMAX*

* The WiMAX part of this talk are prepared by our bbcr former colleague Mehri Mehrjoo.

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WiMAX Overview

IEEE 802.16 is a standard for:

fixed and mobilebroadband Wireless systems

with a P2M and/or mesh technology

Objectives:

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IEEE 802.16: A standard forFixed and Mobile Application

Backhaul

Residential

Rural

Industrial

Business

Wired-line Network

Mobile users

Nomadic Application

802.16-2004

802.16e Hot spot

Last mile

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IEEE 802.16: A standard for Broadband Wireless Application

• Point-to-multipoint scenarios

Reference: http://www.wcai.com/pdf/2004/w_Krzywicki_John.pdf100 m

3-8 Km

2-8 Km NLOS

30-50 Km LOS

WiFi (80.11)

11-54 Mbps

2G, 2.5G, 3G

10-21 Kbps (2G)

30-130 Kbps (2.5G)

300-500 Kbps (3G)

802.16

1.5-70 Mbp

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Performance Comparison

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Where is WiMAX?

3G

WiMAX

WiFiLarge coverage

Full mobility

broadband

simplicity

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IEEE 802.16: A standard for PMP& mesh application

Mesh• SS to SS &/or BS communication

• Distributed &/or centralized coordination

• Only TDD is supported

PMP• No communication between SSs

• Centralized coordination

• Three channel access mechanisms:• Unsolicited bandwidth grants• Polling• Contention-based

P2P• BS to BS communications

• A fiber replacement

• Backhaul solutions

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IEEE 802.16 Family

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WiMAX & IEEE 802.16

Broadband Wireless product

IEEE 802.16: A standard for fixed and mobile broadband wireless systems with a point-to-multipoint design and/or mesh technology

WiMAX: Worldwide Interoperability for Microwave Access

WiMAX Forum WiMAX

WiMAX WiMAX

WiMA

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• WiMAX Overview– WiMAX objectives– WiMAX & IEEE 802.16

• WiMAX PHY & MAC • Resource Management

Part II: WiMAX

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WiMAX PHY Issues

• Spectrum• OFDM/OFDMA fundamentals• OFDMA sub-channelization• Antenna system• Power control & Adaptive modulation

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SpectrumLow frequency

Low energy

Long wavelength

High frequency

High energy

Short wavelength

WiM

AX

28-

29 U

n

WiM

AX

5.2

5-5.

85 U

n

802.

11 a

,e 5

.0 U

n

802.

11 b

,g 2

.4 U

n

CD

MA

2000

460,

800

,1.7

, 1.9

, 2.1

GSM

800

, 1.8

Lice

nsed

1 2 3 5 11 29 66GHz

WiM

AX

3.3

-3.8

Li

WiM

AX

2.5

-2.6

9 L

i

802.16a Licensed+ Un 802.16-2004 Licensed+ Un

Radio microwave IR visible UV X-Ray Gamma

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Spectrum (Cont’d)

Licensed Band advantages:

• Relatively high max power level• Better quality of service

Unlicensed Band advantages: • Fast rollout, more worldwide options• Low administrative/regulatory costs• Promote spectrum efficiency

Licensed Unlicensed

Unlicensed WiMAX applications:

• Point to point, or point to multipoint in scarcely populated environments

• Where interference in the unlicensed band can be controlled. Such as campuses, large enterprise

• Where cost is the major factor

Licensed WiMAX applications:

• large coverage• When controlling the interference is needed• When cost is not the primary issue (3G data

overlays will cost more and have worse performance)

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OFDM Fundamentals

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OFDMA

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• Power saving methods for portable and mobile user devices

• Sub-channelization is an optional feature in OFDM 256 that is generating a lot of interest from operators. It allows a subscriber station to concentrate its transmit power on a subset (sub-channel) of the total OFDM subcarriers, leading to link budget improvements in the uplink

WiMAX uses subchannelization

Sub-channelization

BS- downlink

SS- uplink without subchannelization

SS- uplink with subchannelization

Power level of sub-carrier

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Antenna Systems

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Adaptive Modulation

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MAC Issues

• Service scheduling• Admission control

& bandwidth request/grant

• Link Initiation• Ranging• Moblity• Power

Management• Fragmentation• Retransmission• Security

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Service Flows

• Unsolicited Grant Service (UGS)– Supports real-time service flows that generate fixed size data

packets on a periodic basis, such as T1/E1 and Voice over IP

• Real-time Polling Service (rtPS)– Supports real-time service flows that generate variable size data

packets on a periodic basis, such as MPEG video

• Non-real-time Polling Service (nrtPS)– Supports non real-time service flows that generate variable size

data packets on a regular basis, such as high bandwidth FTP.

• Best Effort (BE)– Supports data streams with no minimum service level

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Bandwidth Allocation and Request Mechanisms

• UGS : – The BS provides fixed size bandwidth at periodic intervals to the UGS.– The SS is prohibited from using any contention request opportunities.– The BS shall not provide any unicastrequest opportunities.

• rtPS– The BS provides periodic unicastrequest opportunities.– The SS is prohibited from using any contention request opportunities.

• nrtPS– The BS provides timely unicastrequest opportunities.– The SS is allowed to use contention request opportunities.

• BE– The SS is allowed to use contention request opportunities.

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Mandatory QoS Service Flow Parameters

• Radio resources have to be scheduled according to the QoS(Quality of Service) parameters.

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Downlink/Uplink Transmissions

• IEEE 802.16 supports both TDD and FDD.• TDD allows flexible allocation of BW between UL & DL. Downlink tx needs

higher throughput.• TDD transceiver design is cheaper and less complex.

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Mobility

• Real-time handoff: – portable applications with simple mobility provide adequate

handover performance for latency tolerant applications such as TCP , but not VoIP. Obviously considering full mobility as well as real-time multimedia scenarios makes a quite challenging hand over.

• Security & Authentication: – portable & mobile applications need enhanced security than

fixed wireless application. Re-authentication at a new place after movement needs a centralized authentication method.

• Power management:– sleep and idle modes

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• WiMAX Overview– WiMAX objectives– WiMAX & IEEE 802.16

• WiMAX PHY & MAC• Resource Management

Part II: WiMAX

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Resource Management

• Scheduling Heterogeneous traffic in OFDMA WiMAX

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Utility based Resource Management

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Problem Description

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Opportunistic Fair Scheduling

• Opportunistic fairscheduling is between the two extremes of pure opportunistic scheduling and fair scheduling.

• Proposed opportunistic fair scheduling jointly considers:

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Opportunistic Fair Scheduling

• To achieve all in one and reduce the complexity, we propose a modular scheduler design and use decomposition algorithms to exploit parallel processing and achieve a real-time scheduling scheme

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Opportunistic Fair Scheduling

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Numerical Results

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Numerical Results (Cont’d)

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Summary

PHY & MAC research issues in broadband

wireless access networks

IEEE 802.11WLAN

IEEE 802.15 WPAN

IEEE 802.16 WiMAX

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Final Comment

• WLAN, WPAN, and WiMAX are complementary wireless networks of each other, none of which will entirely replace the others

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Thank You!