IEEE 802.11 Wireless LANsIEEE 802.11 Wireless LANs

Sunghyun Choi Ph D Associate ProfessorSunghyun Choi, Ph.D., Associate ProfessorMultimedia & Wireless Networking Lab. (MWNL)

School of Electrical EngineeringSchool of Electrical EngineeringSeoul National UniversityEmail: schoi@snu.ac.kr

http://www.mwnl.snu.ac.kr

“Byeong Gi Lee and Sunghyun Choi, Broadband Wireless Access & Local Networks: Mobile WiMAX“Byeong Gi Lee and Sunghyun Choi, Broadband Wireless Access & Local Networks: Mobile WiMAXWireless Access & Local Networks: Mobile WiMAX and WiFi, Artech House, Norwood, USA, May 2008”Wireless Access & Local Networks: Mobile WiMAX and WiFi, Artech House, Norwood, USA, May 2008”

Talk OutlineTalk Outline

Introduction to IEEE 802.11 WLAN

Evolution of IEEE 802 11 WLAN Evolution of IEEE 802.11 WLAN

Baseline MAC of IEEE 802.11

IEEE 802.11e for QoS

IEEE 802.11n for high throughput

Conclusion

3

WLAN vs. Other SolutionsWLAN vs. Other Solutions

WLANV hi l

Mobility WAN

tdoo

r

Walk

Vehicle

808

Out

Fixed

aUMTSWideband Cellular

8

Wired LAN02.11a/g

802.11b

door Walk

Cellular

802.11ng

Mbps (Tx Rate)1 10 1000 1

Ind Fixed/

Desktop Bluetooth

Mbps (Tx Rate)1 10 1000.1

4

IEEE 802.11 Standard Overview IEEE 802.11 Standard Overview

Layers 1 and 2 One MAC and multiple PHYs

MAC

multiple PHYs

A li ti7

Layer

2.4 GHz 2.4 GHz

MAC

DS IRFH

Application

TCP4

7

.11a OFDM5 GHz

DS IRFH1 & 2 Mbps1 & 2 Mbps

IP3

.11a OFDM

.11b CCK

6~54 MbpsTook Off

Available since 2002 LLC

2802.2 5.5 & 11 Mbps

.11g OFDMT k ffMAC

PHY1802.11

6~54 Mbps Took off

O2.4 & 5 GHz

PHY1

5

.11n OFDM6.5~600 Mbps

Taking off

802.11 Standards802.11 Standards

6

Task Groups Finalized in 2008Task Groups Finalized in 2008

11k for Radio Resource11k for Radio Resource Measurement (RRM) enhancements provide mechanisms to higher layers for provide mechanisms to higher layers for

radio and network measurements.

11 f F t R i d f t BSS 11r for Fast Roaming and fast BSS transition Fast Roaming With QoS and security in mindQ y E.g.) fast handoff for VoIP hansets

7

Task Groups Finalized in 2008Task Groups Finalized in 2008

11y for 3650-3700 MHz Operation11y for 3650 3700 MHz Operation in the USA Support operation in licensed bands Support operation in licensed bands Cognitive radio functions (spectrum

sharing incumbent detection) forsharing, incumbent detection) for co-existence enhancements in non-exclusively licensed bandsnon exclusively licensed bands

8

Task Groups Finalized in 2009Task Groups Finalized in 2009

11n for Higher Throughput11n for Higher Throughput Provide much higher throughputs Maximum throughput of at least 100 Mb/s as Maximum throughput of at least 100 Mb/s, as

measured at MAC SAP Modifications to both PHY and MAC

11w for Protected Management FramesFrames Provide Advanced Security mechanisms

f d h Protect management frames to reduce the susceptibility of systems to attack

9

On-going StandardizationOn-going Standardization

802.11p / TGpWireless Access for the Vehicle Environment

ESS Mesh Networking 802.11s / TGs

Wireless Interworking with 802 11 / TGgExternal Networks 802.11u / TGu

Wireless Network Management 802.11v / TGv

Direct Link Setup 802.11z / TGz

Video Transport Streams 802.11aa / TGaa

Very High Throughput <6Ghz 802.11ac / TGac

Very High Throughput in 60 GHz 802.11ad / TGad

Prioritization of Management Frames 802.11ae / TGae

10

Wireless LAN in the TV White Space 802.11af / TGaf

11p for Vehicular Environments11p for Vehicular Environments

Wi l f hi l Wireless access for vehicular environments (WAVE)( ) Inter-car and car-to-road communications Extension of 11a for 5.9 GHz ITS bandExtension of 11a for 5.9 GHz ITS band 5.850-5.925GHz Dedicated Short-Range

Communication (DSRC) bandCommunication (DSRC) band Over line-of-sight distances within 1 km

11

DSRC Performance EnvelopesDSRC Performance Envelopes

54~

Dat

33

30

~

Data Transfer and Internet Access Servicesta R

ate (Mbp

27

24 5850 - 5925 MHz BandPerformance Envelope

(Approximate)

ps) 21

18

(Approximate)

12

9

6

Emergency Vehicle ServicesSafety Message Services

6

3

0 902 - 928 MHz Band Performance Envelope

Toll and Payment Services

Range (ft)

1000

1200

1400

1600

1800

2000

2200

2400

2600

2800

3000

3200

3400

3600200

400

600

800

0

0.5 Mbps

p

12

11s for ESS Mesh Networks 11s for ESS Mesh Networks

M h ki (M l i h i l ) Mesh networking (Multi-hop wireless) Define an 802.11 mesh using the MAC/PHY

layers Support auto-configuring paths between APs

lf fi i lti h t l iover self-configuring multi-hop topologies Layer-2 mesh path selection and forwarding

(routing at the link layer)(routing at the link layer) Advantageous properties of mesh networks

Robustness range extension and density Robustness, range extension and density Potential challenges such as power consumption and

security

13

Multi-Hop WirelessMulti-Hop Wireless

14

11ac & 11ad for VHT11ac & 11ad for VHT

V Hi h Th h Very High Throughput Wireless LAN Gigabit MAC and PHY

specifications Enable a maximum BSS throughput of at g p

least 1 Gbps, at MAC SAP The discussion of 802.11 VHT is divided

into two directions 11ac (Freq. < 6 GHz) 11ad (Freq. ≈ 60 GHz)

15

802.11ac (1)802.11ac (1)

E h f V Hi h Enhancements for Very High Throughput for operation in bands g p pbelow 6 GHz Below 6 GHz carrier frequency operationBelow 6 GHz carrier frequency operation

excluding 2.4 GHz operation Ensure backward compatibility andEnsure backward compatibility and

coexistence with legacy IEEE802.11a/n devices in the 5 GHz unlicensed band

16

802.11ac (2)802.11ac (2)

Ch l b di 80/100 MH Channel bonding – 80/100 MHz Advanced codingAdvanced coding FEC/ LDPC Network coding Network coding Interference cancellation coding

Advanced parallel communications Multi-user MIMO Cooperative wireless networking Single-hop relaySingle hop relay

17

802.11ad (1)802.11ad (1)

E h f V Hi h Enhancements for Very High Throughput in the 60 GHz Band g p(57 – 66GHz) Fast session transfer between 60 GHz andFast session transfer between 60 GHz and

2.4/5 GHz bands Maintain the 802 11 user experienceMaintain the 802.11 user experience Address coexistence with other systems in

the band (e g high-speed WPAN systemsthe band (e.g., high speed WPAN systems such as IEEE 802.15.3c, ECMA 387)

18

802.11ad (2)802.11ad (2)

U d l Usage model Desktop storage and display Video streaming High speed cable replacement (HDMI,High speed cable replacement (HDMI,

monitor) Wireless LAN and BackhaulWireless LAN and Backhaul To differentiate from 802.15.3c, VHT is

focusing its purpose on the core of 802 11focusing its purpose on the core of 802.11 which is data networking.

19

Other Task Groups (1)Other Task Groups (1)

11u for Wireless Interworking with11u for Wireless Interworking with External Network Interworking with 3G cellular Interworking with 3G cellular

11z for Extensions to Direct Link Setup(DLS) Does not require non-DLS capable access q p

point upgrades Supports power save modepp p Continues to allow operation of DLS in the

presence of existing DLS capable access p g ppoints

20

Other Task Groups (2)Other Task Groups (2)

11v for Network ManagementM t f AP STA t i Management of non-AP STAs to improve the overall performance.

11aa for Robust AV Transport Enhancing .11e for AV streamingg g

11ae for Prioritization of Management FramesManagement Frames Priority for latency and transmission

reliabilityreliability

11af for channel access and coexistence in the TV White Space

21

Baseline ProtocolBaseline Protocol

802.11 Reference Model802.11 Reference Model

23

Baseline Protocol Part I - PHYs

Baseline Protocol Part I - PHYsPart I - PHYsPart I - PHYs

Various PHYs of IEEE 802.11Various PHYs of IEEE 802.11

TransmissionSchemesPHY Frequency Bands

DSSS&FHSS- 2 4 GHz

Supported Transmission Rate (Mbps)

DSSS, FHSS and IRBaseline DSSS & FHSS 2.4 GHzIR - 850~950 nm wavelength 1, 2

OFDM802.11a 5 GHz (12 channels of 20 MHz width) 6, 9, 12, 18, 24, 36, 48, 54(12 channels of 20 MHz width)

CCK802.11b 2.4 GHz(11 channels of 22 MHz width

5.5, 11 + DSSS rates

(11 channels of 22 MHz width, overlapping)OFDM802.11g 6, 9, 12, 18, 24, 36, 48, 54 + 802.11b rates

OFDM MIMO802 11 2 4 &5 GH U t 600OFDM + MIMO802.11n 2.4 & 5 GHz Up to 600

25

802.11 (11a/b/g) Data Rates802.11 (11a/b/g) Data Rates

Rate, Mbps Single/Multi Carrier Mandatory Optional Mandatory Optional Mandatory Optional

802.11b @2.4GHz 802.11g @2.4GHz 802.11a @5GHz

1 Single Barker Barker

2 Single Barker Barker

5.5 Single CCK PBCC CCK PBCC

6 Multi OFDM CCK-OFDM OFDM6 Multi OFDM CCK-OFDM OFDM

9 Multi OFDM, CCK-OFDM OFDM

11 Single CCK PBCC CCK PBCC

12 Multi OFDM CCK-OFDM OFDM

18 Multi OFDM, CCK-OFDM OFDM

22 Single PBCC

24 Multi OFDM CCK-OFDM OFDM

33 Single PBCC33 Single PBCC

36 Multi OFDM, CCK-OFDM OFDM

48 Multi OFDM, CCK-OFDM OFDM

54 Multi OFDM, CCK-OFDM OFDM

26

802.11n Data Rates 802.11n Data Rates Data Rate (Mbps)

SS=1 SS=2 SS=4

Modulation R

SS SS SS

20 MHz 40 MHz 20 MHz 40 MHz 20 MHz 40 MHz

800 400 800 400 800 400 800 400 800 400 800 400ns ns ns ns ns ns ns ns ns ns ns ns

BPSK 1/2 6.5 7.2 13.5 15.0 13.0 14.4 27.0 30.0 26.0 28.9 54.0 60.0

QPSK 1/2 13 0 14 4 27 0 30 0 26 0 28 9 54 0 60 0 52 0 57 8 108 0 120 0QPSK 1/2 13.0 14.4 27.0 30.0 26.0 28.9 54.0 60.0 52.0 57.8 108.0 120.0

QPSK 3/4 19.5 21.7 40.5 45.0 39.0 43.3 81.0 90.0 78.0 86.7 162.0 180.0

16-QAM 1/2 26.0 28.9 54.0 60.0 52.0 57.8 108.0 120.0 104.0 115.6 216.0 240.0

16-QAM 3/4 39.0 43.3 81.0 90.0 78.0 86.7 162.0 180.0 156.0 173.3 324.0 360.0

64-QAM 2/3 52.0 57.8 108.0 120.0 104.0 115.6 216.0 240.0 208.0 231.1 432.0 480.0

64-QAM 3/4 58.5 65.0 121.5 135.0 117.0 130.0 243.0 270.0 234.0 260.0 486.0 540.0

64-QAM 5/6 65.0 72.2 135.0 150.0 130.0 144.4 270.0 300.0 260.0 288.9 540.0 600.0

27* SS=Spatial Stream <= min(# Tx Antennas, # Rx Antennas)

PHY Evolution HistoryPHY Evolution History 11b

Published in 1999 Market introduction in 1999 WLAN became popular due to 11b

11a 11a Published in 1999 Market introduction in 2002 Never have been popular Likely to be more popular in the future, e.g., triple

mode (11a/b/g) devices( / /g) 11g

Published in 2003 Market introduction in 2003

11n Published in 2009 Published in 2009 Emerging as a dominating form

28

Baseline ProtocolPart II - MAC

Baseline ProtocolPart II - MACPart II - MACPart II - MAC

802.11 - Infrastructure Mode802.11 - Infrastructure Mode

802 x LAN802.11 LAN Station (STA)

802.x LAN

BSS

Wireless terminals Basic Service Area (BSA) Coverage area of one accessSTA1

PortalBSS1

AccessPoint

Coverage area of one access point (AP)

Basic Service Set (BSS) group of stations controlled by

1

Distribution System

AccessPoint

group of stations controlled by the same AP

Distribution System (DS)ESS Point

BSS2

Fixed infrastructure used to connect several BSSs to create an Extended Service Set (EES)

l

802.11 LAN

Portal bridge to other (wired) networks Every tx is via APSTA2 STA3 y

30

802.11 – Ad Hoc mode802.11 – Ad Hoc mode

Terminals communicate in a peer to peer basis802.11 LAN in a peer-to-peer basis

Independent BSS (IBSS) A STA can be a routerSTA1 A STA can be a router

to connect to the wireline network

BSS1

1STA3

STA2

BSS2

STA5

802.11 LANSTA4

5

31

Important ConceptsImportant Concepts Rate Sets BSS Basic Rate Set – shall by supported by allBSS Basic Rate Set shall by supported by all

stations Operational Rate Set – can be used by stations

b { } d { } l E.g., in 11b, {1,2} and {1,2,5.5,11}, respectively Control (ACK, RTS, CTS) and broadcast/multicast

frames (e.g., beacon) shall be transmitted withframes (e.g., beacon) shall be transmitted with one of the rates in BSS Basic Rate Set

Unicast vs. Broadcast In case of infrastructure BSS, uplink transmission

is always unicastS i S t ID (SSID) Service Set ID (SSID) A character set identifying each ESS Conveyed within beacon frames Conveyed within beacon frames Often called ESSID

32

Two Coordination FunctionsTwo Coordination Functions

Mandatory Distributed Coordination yFunction (DCF) For distributed contention-based channelFor distributed contention based channel

access

Optional Point Coordination Function Optional Point Coordination Function (PCF) For centralized contention-free channel

access

DCF only for most commercial 802.11 devices802.11 devices

33

802.11 MAC Architecture802.11 MAC Architecture

PCF sits on top of DCF PCF operation relies on DCF

Time-division-based packet-by-p ypacket transmission No transmission slots no control channels No transmission slots, no control channels,

no separate pilot channels, …

34

Distributed Coordination Function (DCF)Distributed Coordination Function (DCF)

Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) similar to IEEE 802 3 Ethernet CSMA/CD similar to IEEE 802.3 Ethernet CSMA/CD

DIFSI di t h

Busy SIFSPIFS

DIFS

B k ffDIFS

Contention WindowImmediate access whenmedium is idle >= DIFS

BusyMedium

SIFS BackoffWindow

Slot Time

Next Frame

Defer Access Select Slot and decrement backoffas long as medium stays idle

35

Interframe Spaces (IFSs) (1)Interframe Spaces (IFSs) (1)

To give priority to different frame t i itransmissions Short IFS (SIFS)( ) Between a frame and an immediate

response Data-ACK, RTS-CTS-Data-ACK, …

PCF IFS (PIFS)( ) Before sending beacon under PCF; when

no response after a polling frame DCF IFS (DIFS) Before a backoff countdownBefore a backoff countdown

36

Interframe Spaces (IFSs) (2)Interframe Spaces (IFSs) (2)

Extended IFS (EIFS) SIFS + ACK_Transmission_Time + DIFS Used instead of DIFS after an erroneous

frame reception To protect the subsequent ACK transmissionp q

DataACKDestination station

DIFS

BackoffSource station

NAV

Destination station

SIFSBackoff

NAVOther stations receiving data frame correctly

Backoff

EIFS

Other stations receiving data frame incorrectly

37

Interframe Spaces (IFSs) (3)Interframe Spaces (IFSs) (3)

IFS l f i PHY IFS values for various PHYs

9 μsec

20 μsec

16 μsec

10 μsec

25 μsec

35 μsec

34 μsec

50 μsec

9 μsec

μ

10 μsec

μ

19 μsec

μ

28 μsec

μ

20 μsec 10 μsec 30 μsec 50 μsec

38

Carrier-Sense MechanismsCarrier-Sense Mechanisms

Physical carrier-sense Physical carrier-sense Provided by PHY, and depends on PHY Clear Channel Assessment (CCA) by PHY Clear Channel Assessment (CCA) by PHY

Virtual carrier-senseP id d b MAC i N t k All ti V t Provided by MAC via Network Allocation Vector (NAV) counter

Each frame carries Duration value in the header Each frame carries Duration value in the header Any correctly received frame updates NAV if the

new NAV is largernew NAV is larger Assumes busy channel if non-zero NAV

irrespective of CCA!p

39

Stop-and-Wait ARQStop-and-Wait ARQ

Receiver of a directed frame returns an ACK

If ACK not received, sender retransmits ,after another backoff

DATA

SIFS

DIFSSource

SIFS

DIFS

B k ff

ACKDestination

Backoff Next FrameOthers

Defer Access Backoff after Defer

40

Binary Exponential BackoffBinary Exponential Backoff

Backoff Counter is randomly selected from [0,CW],

For each unsuccessful

where CW is contention window

For each unsuccessful frame transmission, CW doubles (from

CWmax=255 255

250

300

Example

CW doubles (from CWmin to CWmax)

127150

200

250

CW 2 (CW+1)-1

Reduces the collision CWmin=15

3163

0

50

100

probability0

1 2 3 4 5 6

41

Hidden TerminalHidden Terminal

STA 1 and STA 2 can see STA 3 but STA 1 and STA 2 can see STA 3, but they do not see each other May result in more collisions due to

the failure of carrier-sensing!the failure of carrier sensing!

42

RTS/CTS ExchangeRTS/CTS Exchange

A way to handle hidden terminals! Request-To-Send / Clear-To-SendRequest To Send / Clear To Send

(RTS/CTS) to reserve medium Works with virtual carrier sense Works with virtual carrier-sense

43

FragmentationFragmentation

One MSDU can be fragmented into multiple MPDUsmultiple MPDUs All the fragments have virtually the same

MAC header (except for the fragmentMAC header (except for the fragment number) Theoretically up to 11 fragments from oneTheoretically up to 11 fragments from one

MSDU since Max MSDU size = 2304 octets Min Fragment Threshold = 256 octets

44

Fragmentation Burst Fragmentation Burst

Fragments are transmitted with SIFS gintervals Backoff if a fragment transmission Backoff if a fragment transmission

fails

45

RTS & Fragment ThresholdsRTS & Fragment Thresholds

RTS Threshold Use RTS/CTS if MPDU_size > threshold Depending on the size of MPDU relative to RTS

threshold, the max retransmission limit is determined differently!

L R t Li it ( h t) 4 (7) b d f lt LongRetryLimit (short) = 4 (7) by default

Fragment Threshold Use fragmentation if MPDU_size > threshold

Default values of both are large enough g gsuch that none of them is used! Max MSDU size = 2304 bytes in 802.11Max MSDU size 2304 bytes in 802.11

46

Power Management (1)Power Management (1)

Without power management, a STA always senses medium Lots of power consumption for channel p p

sensing/receiving Power management allows STAs to g

go to doze state as much as possible without losing incoming p g gdata Active mode (AM) – always awake stateActive mode (AM) always awake state Power Save (PS) mode – switch between

awake and doze states

47

Power Management (2)Power Management (2)

Switch between AM and PS mode is i f d i f l finformed via a successful frame transmission with Power Mgmt bit (re)set

In BSS, AP buffers downlink frames, and announce it via beacon frames (in TIM field)

In IBSS, each STA buffers frames, and , ,announce it via ATIM frames

Power-saving STAs wake up periodically!Power saving STAs wake up periodically!

48

TIM & Dedicated TIM (DTIM) BeaconsTIM & Dedicated TIM (DTIM) Beacons

Time-axis

Beacon Interval DTIM interval

TIM (in Beacon) TIM DTIM TIM TIM DTIM

AP activity

Downlinkbuffered frame

Buffered framefor other station

Downlinkbuffered frame Broadcast

PS StationPS-Poll

PS Station(extreme low power) PS-Poll( p )

Beacon Transmissions Busy MediumIn Active State

49

IEEE 802.11e for QoS Provisioning

IEEE 802.11e for QoS Provisioningfor QoS Provisioningfor QoS Provisioning

Backward Compatible with Legacy MAC(Based on IEEE 802.11e-2005)

Limitations of Baseline MAC Limitations of Baseline MAC No notion of QoS and related signaling

R t i t d lli h d li Restricted polling scheduling PCF mandates round-robin scheduling

Superframe with alternating CFP and CP need to be short for short delay bound

AP assuming the full control over the medium during CFPg overlapping WLANs?

Uncontrollable/unpredictable frame Uncontrollable/unpredictable frame transmission times Just one frame per being polled

51

Just one frame per being polled

Prioritized vs. Parameterized QoSPrioritized vs. Parameterized QoS

Prioritized QoS (like DiffServ)Q ( ) Differentiated channel access for frames with

different user prioritiesdifferent user priorities 8 different user priorities (UPs)

802 1d b id t i il t 802.1d bridge supports similar concept

Parameterized QoS (like IntServ)Q ( ) QoS is characterized by a set of parameters

A traffic stream (TS) is set up between A traffic stream (TS) is set up between transmitter and receiver (and QoS AP or QAP)

52

Hybrid Coordination Function (HCF)Hybrid Coordination Function (HCF) Two access mechanisms Contention-based channel access Contention-based channel access Enhanced Distributed Channel Access (EDCA) Variation of legacy DCF Variation of legacy DCF

Controlled channel access HCF Controlled Channel Access (HCCA) HCF Controlled Channel Access (HCCA) Polling mode plus HC’s prioritized channel access

mainly y Variation of legacy PCF

53

IEEE 802.11e Part I: IEEE 802 11e EDCA

IEEE 802.11e Part I: IEEE 802 11e EDCAPart I: IEEE 802.11e EDCA Part I: IEEE 802.11e EDCA

User Priority to Access Category MappingUser Priority to Access Category Mapping

Priority User Priority 802 1D Access DesignationPriority User Priority (UP - Same as 802.1D User Priority)

802.1D Designation

Access Category (AC)

Designation (Informative)

Priority)

Lowest 1 BK AC_BK Background

2 - AC BK Background2 AC_BK Background

0 BE AC_BE Best Effort

3 EE AC BE Best Effort3 EE AC_BE Best Effort

4 CL AC_VI Video

5 VI AC_VI Video

Highest 6 VO AC_VO Voice

7 NC AC_VO Voice

55

Four Channel Access FunctionsFour Channel Access Functions

Channel accessChannel access function for each AC as a virtual DCFas a virtual DCF

Multiple channel access functionsaccess functions contend independently

Back

AIFSB

C[

Back

AIFSB

C[

Back

AIFSB

C[

Back

AIFSB

C[independently

The winning channel access function

koff S[0] 0]

koff S[1] 1]

koff S[2] 2]

koff S[3] 3]

access function transmits a frame

56

Prioritized Channel AccessPrioritized Channel Access

Each channel access function contends with AIFS[AC] (instead of DIFS) and CW[AC] (instead of [ ] ( ) [ ] (

CW)

PIFS

AIFS[AC]

AIFS[AC]

Contention Windowfrom [0,CW[AC]]

Immediate access whenmedium is idle >= AIFS[AC]

BusyMedium

SIFS BackoffWindow

Sl t Ti

AIFS[AC]

Next Frame

Slot Time

Defer Access Select Slot and decrement backoffas long as medium stays idle

57

EDCA TXOPEDCA TXOP

Within an EDCA TXOP multiple MSDUs from the AC can be transmitted

with the limit of TXOPLimit[AC] Ends if a frame transmission fails! Ends if a frame transmission fails!

TXOP shall not extend across TBTTSh ld b t l t ti t t it 256 b t Should be at least time to transmit 256 byte MPDU at the lowest rate

58

EDCA Parameter Set ElementEDCA Parameter Set Element

In beacon and probe response frames The parameters should be updated within

a beacon intervala beacon interval Different parameters can be used for

AP’s downlink transmissions

59

Further on EDCA ParametersFurther on EDCA Parameters Management and control (except PS-poll

= AC BE) frames belongs to AC VO AC_BE) frames belongs to AC_VO Zero TXOP Limit means one MSDU Tx

ll d d i EDCA TXOPallowed during EDCA TXOP Default values:

60

IEEE 802.11ePart II: Traffic Stream Operation

IEEE 802.11ePart II: Traffic Stream OperationPart II: Traffic Stream Operation Part II: Traffic Stream Operation

Traffic ID & Traffic StreamTraffic ID & Traffic Stream

Each MSDU from LLC carries one of 16Each MSDU from LLC carries one of 16 Traffic ID (TID) values 0~7 identify user priorities (UPs) 0~7 identify user priorities (UPs) 8~15 identify (parameterized) traffic streams IDs

(TSIDs)(TSIDs)

Traffic Stream (TS) is set up after admission control by QAPadmission control by QAP Up to 8 TSs per STA per direction TS can be set up for prioritized QoS if QAP

mandates admission control for specific priority traffictraffic

62

TS LifecycleTS Lifecycle

63

Traffic Specification (TSPEC)Traffic Specification (TSPEC)

The QoS characteristics of a data flow to and from a non AP QSTAand from a non-AP QSTA.

TSPEC Element The combination of TSID and Direction identify the

traffic streamoctets: 1 3 2 42 44 41

Elenent ID(13)

Length(55) TS Info

NominalMSDU Size

InactivityInterval

MaximumMSDU Size

MaximumServiceInterval

MinimumServiceInterval

SuspensionInterval

4 4 4 4 24 44 2

Service StartTime

MinimumData Rate

MeanData Rate

Peak DataRate

SurplusBandwidthAllowance

Burst Size MinimumPHY Rate

DelayBound

MediumTime

Traffic TSID Direction Access ScheduleAggregation UserAPSD ResrevedTSInfo Ack

B0 B1 B4 B5 B6 B7 B8 B16B9 B11 B13B10 B17 B23B14 B15

Type TSID Direction Policy ScheduleAggregation PriorityAPSD ResrevedPolicy

bits: 4 2 2 11 31 721

64

An example of the operation during a TS lifetimeAn example of the operation during a TS lifetime

Non-APQoS Station QoS AP

ADDTS Response (TSPEC, TCLAS, Schedule)

ADDTS Request (TSPEC, TCLAS)TS

setup

QoS CF-Poll

QoS DATA

QoS CF-Ack

Schedule(Schedule) Schedule

QoS CF-Poll

change

QoS DATA

QoS CF-Ack

65

DELTS (TS Info) TS deletion

IEEE 802 11eIEEE 802 11eIEEE 802.11e Part III: 11e Automatic Power

IEEE 802.11e Part III: 11e Automatic Power

Save Delivery (APSD)Save Delivery (APSD)

What APSD is about?What APSD is about?

A mechanism to deliver unicast d li k f idownlink frames to power-saving stations Still rely on Power Mgmt bit of Frame

Control field to switch between AM and PS modes

Same goal as TIM & PS-poll ofSame goal as TIM & PS poll of legacy MAC

PS poll me h ni m o ld be lo nd PS-poll mechanism could be a slow and uncontrolled process for downlink delivery

67

APSD SetupAPSD Setup APSD is a capability of a QAP APSD bit in Capability Information Field in p y

beacon, probe response, and (re)association response

N AP QSTA t t APSD Non-AP QSTA can request to use APSD APSD bit in TS info field of TSPEC element

TSPEC i ADDTS f ( ) i ti TSPEC in ADDTS frame or (re)association frame

APSD is set up for a TS APSD is set up for a TS

68

Two Types of APSD MechanismsTwo Types of APSD Mechanisms

Depending on schedule bit in TSPECScheduled APSD (S APSD) Scheduled APSD (S-APSD) Schedule delivery of frames during scheduled Service

Periods (SPs) Unscheduled APSD (U-APSD)

Deliver frames during unscheduled SPs triggered by non-AP QSTAQS

When access policy = EDCA Schedule bit is reserved, otherwise

APSD Schedule Usage0 0 No Schedule1 0 Unscheduled APSD0 1 Reserved (Scheduled PSMP)

h d l d1 1 Scheduled APSD

69

Unscheduled SPUnscheduled SP

Begins when QAP receives a “trigger” g Q ggframe Trigger frame = uplink QoS data or NullTrigger frame = uplink QoS data or Null

frame associated with an admitted uplink or bidirectional TSPEC (with APSD=1 &or bidirectional TSPEC (with APSD 1 & Schedule=0)

Ends when QAP has attempted to Ends when QAP has attempted to transmit at least one buffered MPDU t AP QSTAto non-AP QSTA

70

Scheduled SPScheduled SP Non-AP QSTA wakes up to receive

frames during scheduled SPsframes during scheduled SPs Schedule element in ADDTS responseFi t h d l d SP t t First scheduled SP starts Lower 4 bytes of TSF timer = Service Start

TimeTime Subsequent scheduled SP starts Every Service Interval

71

IEEE 802.11e Part IV: Block ACK

IEEE 802.11e Part IV: Block ACKPart IV: Block ACK Part IV: Block ACK

Other Features of 802.11eOther Features of 802.11e

Block ACK Group of frames are ACKed with a single BlockACK frame A key mechanism to improve MAC efficiency (further

evolution expected as part of 11n) No ACK policy is also supported

Direct Link Protocol (DLP) Direct communication between non-AP STAs in

infrastructure mode

Both will enhance the efficiency of 802.11 Both requires a priori agreement between

communicating partiescommunicating parties

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Two Types of Block AckTwo Types of Block Ack

Immediate Block Ack Suitable for high-bandwidth, low latency traffic

Delayed Block Ack Suitable for applications tolerant of moderate

latencyWith i i l HW h With minimal HW changes

Depends on whether BlockAck is t itt d i di t l fttransmitted immediately after BlockAckRequest frame Both of them are optional in 11e Usage of one type is agreed between

communicating partiescommunicating parties

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Immediate Block Ack PolicyImmediate Block Ack Policy

Dat

a

Dat

a

Dat

a

Ack

Req

Dat

a

QoS

QoS

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Delayed Block Ack PolicyDelayed Block Ack Policy

OriginatorData Block

E h

Block Ackg

for NAV Protection

Frame-exchange

Exchange

NAV due to recipient

Recipient

Ack Policy = Block AckAck Policy = Normal Ack

NAV at other STAs

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IEEE 802.11n for Higher-Throughput

IEEE 802.11n for Higher-ThroughputThroughputThroughput

802.11n for Higher Throughput802.11n for Higher Throughput

To provide higher throughput, i e > 100 Mbps at MAC SAPi.e., > 100 Mbps, at MAC SAP By Task Group n (TGn)

Enhance both OFDM PHY and MAC Make the current MAC (based on .11

and .11e) more efficient Add MIMO (SDM, STBC, beamforming),

h l b di t t PHYchannel bonding, etc. to PHY

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11n PHY Candidate Techniques11n PHY Candidate Techniques

Channel bonding E.g., using 40MHz instead of 20MHz (of

11a) Multi-Input Multi-Output (MIMO) Spatial channels of different antenna pairs

are often uncorrelated Data rate or reliability can be improved

TX RXInput OutputTX

TX

RX

RX

MIM

O

Processor

p p

TX RX r

MIMO Channel

Source: [Insider04] 79

Scalable PHY ArchitectureScalable PHY Architecture

Mandatory Optional

Open Loop SDM

Robustness Enhancement

Closed Loop Tx BF

C C di LDPC

Robustness Enhancement

STBC

Throughput

Conv. Coding LDPC

1or 2 Spatial Streams 4 Spatial Streams

ThroughputEnhancement

Throughput

20 MHz 40 MHz

ThroughputEnhancement

∼150 Mbps ∼ 600 Mbps

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802.11n MAC Overview802.11n MAC Overview

Note: 802 11n MAC is based on 802 11 & 802 11e MACNote: 802.11n MAC is based on 802.11 & 802.11e MAC

802.11n MAC Features802.11n MAC Features

82

MAC OverviewMAC Overview

83

MAC Frame FormatMAC Frame Format

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QoS Control FieldQoS Control Field

Bit Bit 4 Bit 5 6 Bit 7 Bit 8 15Bits0-3

Bit 4 Bit 5-6 Bit 7 Bits 8-15

TID EOSPTXOP /

Ack Policy

A-MSDUPresent

TXOP limitTXOP duration/

QueueSize

yQAP PS Buffer size

Queue Size

QOS Control field bit 7 Indicates the presence/absence of A-MSDU

Bit 7 is formerly reserved Bit 7 is formerly reserved Valid in DATA type/QOS Subtype frames:

QoS Data QoS Data+CF-Ack QoS Data+CF-Poll QoS Data+CF Ack+CF Poll QoS Data+CF-Ack+CF-Poll

Aggregate MSDU (A-MSDU)Aggregate MSDU (A-MSDU) A-MSDU operation Mechanism to provide enhanced efficiency atMechanism to provide enhanced efficiency at

the top of the MAC layer Support for A-MSDU is mandatory at the

receiver where the A MSDU is carried in areceiver, where the A-MSDU is carried in a single (i.e., non A-MPDU) QoS Data MPDU under Normal Ack policy

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A-MSDUA-MSDU

An A-MSDU is composed of MSDUs with the same TID valueTID value.

All the MSDUs are intended to be received by a single receiver, and necessarily they are allsingle receiver, and necessarily they are all transmitted by the same transmitter.

Maximum A-MSDU length Indicates maximum A-MSDU length.

Set to 0 for 3839 octets Set to 1 for 7935 octets

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Aggregate MPDU (A-MPDU)Aggregate MPDU (A-MPDU) Robust Structure A-MPDU Aggregation is a purely-MAC function gg g p y

Architecturally at the “Bottom of MAC” PHY has no knowledge of MPDU boundaries

Control and data MPDUs can be aggregated The A-MPDU maximum length is 65535 octets

All h MPDU i hi A MPDU dd d h All the MPDUs within an A-MPDU are addressed to the same receiver address.

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Basic A-MPDU ExchangeBasic A-MPDU Exchange

U UU U UUU UU U UUU U

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Implicit Block Ack Protocol

RTS/CTSProtocol

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89

Value of A-MPDUValue of A-MPDU

RTS/CTS/A MPDU/BA sequence is typically RTS/CTS/A-MPDU/BA sequence is typically 2.5x more efficient than Data/Ack

RTS/CTS/A-MPDU/BA is 30% more efficient RTS/CTS/A MPDU/BA is 30% more efficient than A-MSDU/Ack

Enables BA and Data to be aggregatedEnables BA and Data to be aggregated (few % can be gained)

Conditions: •Control rate 24Mbpsp•Data rate 243Mpbs•500B MSDUs500B MSDUs

90

A-MSDU & A-MPDUA-MSDU & A-MPDU

Pros. and Cons.

Pros Cons

A-MSDU Lower overhead Good for low error

environment

Cannot support selective retransmission

environment

A-MPDU Support selective retransmission using MPDU delimiter

Higher overhead

Good for high error environment

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Enhanced BA MechanismEnhanced BA Mechanism Implicit BAR: The originator may omit the inclusion of a BAR fr

ame in an aggregated frame and set QoS ack policy to “Normal Ack”.

Compressed BA: Defines a compressed variant of the 802.11e BA MPDUBA MPDU.

Partial State for Immediate BA reduces complexity of recipient

Aggregation frame

D1 D2 D3 D4InitiatorSIFS

Initiator

ResponderCompressed

BA

8 octetsFrame Control

Duration/ID RA TA BA Con

trolBA Starting Seq. Control BlockAckBitmap FCS

92

PSMP/MTBAPSMP/MTBA

Power-save Multi-Poll (PSMP)Power save Multi Poll (PSMP) PSMP sequence allows the AP to create effective service

periods Benefits from statistical multiplexing of retries, activity

cycles and rate variations In the VoIP application, benefit is up to 2x resulting from

sharing an allocation for retries within the current aggregate SP

Multi-TID Block Ack (MTBA)Multi TID Block Ack (MTBA) Allows for single frame to respond to (implicit) BAR for

multiple TID Shall be used within PSMP sequences instead of BA

93

PSMP Frame FormatPSMP Frame Format

A PSMP sequence with a duration of up to 8.184 ms

94

MTBA Frame FormatMTBA Frame Format

95

PSMP with MTBAPSMP with MTBA

Frames of different TID may be transmitted within a PSMP Frames of different TID may be transmitted within a PSMP-DTT or PSMP-UTT allocation of a (Scheduled or Unscheduled) PSMP sequence without regard to Access Category. MTBA efficiently carries BA for multiple TIDse c e t y ca es o u t p e s

PSMP schedules when a STA receives and when it may transmit.

DL Acknowledgement scheduled in the uplink & vice versag p UL data acknowledged by following PSMP sequence

96

PSMP BurstPSMP Burst Retransmission and resource allocation

97

Reverse Direction (RD)Reverse Direction (RD)

Allows a STA to share its TXOP with another STAanother STA The most significant benefit is obtained if this

reduces the number of channel access attempts

Some benefit from aggregating BA and Data t thtogether

Signalled by:D ti /ID fi ld hi h i th i i Duration/ID field, which carries the remaining duration of the TXOP

HT control Field which carries: RDG / More HT control Field, which carries: RDG / More PPDU, AC constraint

QoS Control field, which carries TID of traffic Q ,allowed in this RD

98

RD Example ExchangeRD Example Exchange

99

MCS Request / Feedback ProtocolMCS Request / Feedback Protocol

HTC Description Signalled in HTC Timing of response

d

Fieldp

MRQ MCS requestis unconstrained Unsolicited

response permitted

MRQ MCS request

MSI Sequence Identifier of MCS 000 110response permitted

Sequence Identifier to pair MRQ and

MCS request 000-110

MFSI Seq. Identifier of MFB p QMFB response (feedback) or

“unsolicited” (111)

MFB MCS feedback and Antenna SelectionCommand/ Data

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Coexistence (Protection for HT transmission)Coexistence (Protection for HT transmission)

Greenfield & RIFS protection L-SIG TXOP Protection L SIG TXOP Protection PCO 20/40 Operation Dual Beacon & Dual CTS protection Channel selection rules Channel selection rules Channel width Management

101

L-SIG TXOP ProtectionL-SIG TXOP Protection Optional Feature Establishes PHY-layer protection using HT Mixed mode (MM) y p g ( )

PPDUs AP indicates if all STAs in its BSS support it Duration implied by legacy length value in MM PPDU

dg g

conveys a duration > current PPDU Value protected also indicated in MAC duration field and all

PPDUs (except RTS) locate the same protection end pointd d f d f RTS protection extends to end of CTS to avoid unfairness

problems when comparing CCA (legacy) to NAV (HT)

102

Example of L-SIG TXOP ProtectionExample of L-SIG TXOP Protection

103

PCO 20/40PCO 20/40

Phased Coexistence Operation (PCO) Optional feature AP Establishes separate 20MHz and 40MHz

operating phases 20MHz phase: allows independent BSS activity on

control channel and OBSS on extension channelcontrol channel and OBSS on extension channel 40MHz phase: 40MHz transmissions across 40MHz

channel with no 20MHz interference Allows AP to switch PCO-capable STA between

20 & 40 operation 20MHz STA can only communicate during the 20MHz

phase

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PCO 20/40 OperationPCO 20/40 Operation

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105

Performance SummaryPerformance Summary

Feature Value

A-MPDU About 2.5 × Data/Ack

A-MSDU About 20% on top of A-MPDUp

Reverse Direction Roughly 25%

Enhanced BA Roughly 5-10%

PSMP / MTBA VoIP call density increase of up toPSMP / MTBA VoIP call density increase of up to 2 × non-PSMP

106

ConclusionConclusion

IEEE 802.11 is evolving today!IEEE 802.11 is evolving today! Emerging 802.11n on top of 802.11e

makes the 802 11 even faster!makes the 802.11 even faster! Will be interesting to see how this

technology evolves in the futuretechnology evolves in the future Along with IMT-Advanced standardization

activityactivity

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Thank you!!Thank you!!yy