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: [email protected]
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
QoS
Blo
ckA
QoS
K kAck
AC
Blo
ck
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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
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MAC OverviewMAC Overview
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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
Dat
a M
PDU
eD
ata
MPD
U
Dat
a M
PDU
r Tx
Act
ivity
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AC
Tx
RTS
Dat
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PDU
Dat
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PDU
Dat
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PDU
Dat
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PDU
Dat
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PDU
Dat
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PDU
Dat
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PDU
Dat
a M
PDU
Dat
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PDU
Dat
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PDU
Dat
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PDU
e
Agg
rega
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T P
PDU
Initi
ator
PHY
Tx
Lega
cy
PP
DU
Agg
rega
teH
T P
PDU
ity x ckck
Implicit Block Ack Protocol
RTS/CTSProtocol
nder
Tx
Act
ivi
TxM
AC
T
Blo
ck A
c
y UC
TS
Blo
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cy U y U
Res
pon
PH
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Lega
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PD
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Lega
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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
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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
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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
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PSMP Frame FormatPSMP Frame Format
A PSMP sequence with a duration of up to 8.184 ms
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MTBA Frame FormatMTBA Frame Format
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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
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PSMP BurstPSMP Burst Retransmission and resource allocation
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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
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RD Example ExchangeRD Example Exchange
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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
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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)
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Example of L-SIG TXOP ProtectionExample of L-SIG TXOP Protection
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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
eaco
n
-to-s
elf
chan
ge
uest
F-E
nd
anne
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sy
rol C
han.
Be
CTS
elf
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End
Fram
e E
xc
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d z yC
h B
Con
trha
n.
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-to-s
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Cha
nne
Bus
y
40M
Hz
F
PC
O P
CF-
End
20M
Hz
OB
SS
A
ctiv
it y
Ext
ensi
on C
hE
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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
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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