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Fundamentals of 802.11n WLAN
John Scott Wells RCDD, WDBluestone Communications
Welcome to the Jungle!
History• IEEE 802• IEEE 802.11 a/b/g• IEEE 802.11n Working Group formed in
2003• 802.11n Ratified Sept 11, 2009• 802.11n Published Oct 29, 2009
WI FI Alliance
• Wi-Fi CERTIFIED for 802.11n Draft 2.0 • The Wi-Fi CERTIFIED for 802.11n
program tests and certifies products based upon IEEE 802.11n Draft 2.0 , WFA, WMM and WPA documents
• WFA• WMM• WPA
Wi Fi Certified 802.11n draft 2.0 Baseline Requirements
• Mandatory support for two spatial streams in transmit mode required for an AP device.
• Mandatory support for two spatial streams in receive mode required for an AP and a client device, except for handhelds.
• Mandatory support for A-MPDU and A-MSDU required for all devices
Continued• Mandatory for Block ACK required for all
devices.• Devices can be 2.4 GHz only, 5 GHz only
or dual band tested if implemented.• 5 GHz operation tested if implemented.• 40 MHz in the 5 GHz band, Wi Fi Alliance
only recognizes channel bonding in the 5 GHz band.
Continued• The Greenfield Preamble can not be
interpreted by legacy stations.• Must support the optional Short Guard
Interval of 400 ns.• Must support concurrent operations in the
2.4 GHz and 5 GHz bands.
802.11n Amendment• Defines High Throughput (HT)• Makes use of MIMO• Using OFDM• Enhancements to MAC sub layer• HT radios required to be backwards
compatible
MIMO• The heart and soul of 802.11n• Uses multiple radio and antennas which
provide better diversity and increase range• Spatial Multiplexing provides greater
throughput and with optional smart antennas can perform “beam steering”
• We now love Multipathing!
High Throughput Channels (HT)• 802.11n channels are larger in size
compared to 802.11 a/b/g channels• 802.11n can either use 20 MHz or 40 MHz
channel size• 40 MHz channels can only be effectively
used in the 5 GHz spectrum.
Some 802.11n MCS valuesMCS Index Type Coding Rate
Spatial Streams
Data Rate (Mbps) Data Rate (Mbps)
20 MHz 40 MHz
0 BPSK 1/2 1 6.5 7.2 13.5 15
1 QPSK 1/2 1 13 14.4 27 30
2 QPSK 3/4 1 19.5 21.7 40.5 45
3 16-QAM 1/2 1 26 28.9 54 60
4 16-QAM 3/4 1 39 43.3 81 90
5 64-QAM 2/3 1 52 57.8 108 120
6 64-QAM 3/4 1 58.5 65 121.5 135
7 64-QAM 5/6 1 65 72.2 135 150
8 BPSK 1/2 2 13 14.4 27 30
9 QPSK 1/2 2 26 28.9 54 60
10 QPSK 3/4 2 39 43.3 81 90
11 16-QAM 1/2 2 52 57.8 108 120
12 16-QAM 3/4 2 78 86.7 162 180
13 64-QAM 2/3 2 104 115.6 216 240
14 64-QAM 3/4 2 117 130 243 270
15 64-QAM 5/6 2 130 144.4 270 300
16 BPSK 1/2 3 19.5 21.7 40.5 45
... ... ... ... ... ... ... ...
31 64-QAM 5/6 4 260 288.9 540 600
Data Rate, in Mbps
20 MHz Channel 40 MHz Channel
1 stream 2 streams 1 stream 2 streams
802.11g 2.4 GHz 1, 2, 6, 9, 12, 18, 24, 36, 48, 54
802.11n GI1=800ns 2.4 GHz
6.5, 13, 19.5, 26, 39, 52, 58.5, 65
13, 26, 39, 52, 78, 104, 117, 130
802.11n GI2=800ns 5 GHz
6.5, 13, 19.5, 26, 39, 52, 58.5, 65
13, 26, 39, 52, 78, 104, 117, 130
13.5, 27, 40.5, 54, 81, 108, 121.5, 135
27, 54, 81, 108,162, 216, 243, 270
802.11n, GI=400ns2.4 and 5 GHz
7.2, 14.4, 21.7, 28.9, 43.3, 57.8, 65, 72.2
14.4, 28.9, 43.3, 57.8, 86.7, 115.6, 130, 144.4
15, 30, 45, 60, 90, 120, 135, 150
30, 60, 90, 120,180, 240, 270, 300
Physical Enhancements• Spatial Multiplexing (SM)• Space-Time Block Coding (STBC)• Transmit Beamforming (TxBF)• Shorter Guard Interval (SGI)• Maximum Radio Combining (MRC)• Forward Error Correction (FEC)
Transmit Beam forming (TxBF)• Used in Sonar / Radar systems for many
years• Uses “smart antenna” technology to
effectively focus the transmission in a coordinated method.
Greenfield Mode• Greenfield is the community buzzword to
describe a new 802.11 installation with no existing 2.4 GHZ or 5 GHz systems within the intended RF space.
• Greenfield is known as High Throughput (HT) mode, this is an optional mode.
Non HT (Legacy Mode)• 802.11n AP’s using Non – HT mode sends
all frames in the old 802.11a/g format so legacy stations can communicate with new stations.
HT Mixed Mode• Mandatory and will be the most common
mode over the next couple of years.• HT enhancements can be used
simultaneously with HT protection parameters that permit communication with legacy stations.
Deployment Challenges• Network Infrastructure Upgrades• Power• Density• Antenna Selection• RF Planning and Site Surveying
Be Careful!• Hybrid Installations• 802.11n can be unpredictable, lossy, and
bursty• Block ACK• Backwards Compatibility• Coverage
Security• 802.11n employs the same 802.11i
(WPA2) security measures used by legacy equipment.
• New wireless IPS alerts and reports are needed to spot and react to 802.11n rogue AP’s
Summary• There is much to be gained by upgrading
to 802.11n.• 802.11n can leverage options to
significantly improve WLAN range, throughput, and reliability.
Acknowledgements• BICSI WD Reference Manual 3rd Addition• Trapeze Networks• Airmagnet• Keith Parsons “The Wireless Road Warrior”• Wi Fi Alliance• CWNP• Airtight• Meru Networks
Contact Info• Scott Wells• 610-237-8800 wk• 610-500-4706 cell• [email protected]