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

Benefits• Increased Range• Improved Capacity• Increased Data Rates• Improved Quality of Service

What are the differences between 802.11 a/b/g and 802.11n

• Throughput• MIMO• OFDM• Multiplexing

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.

Channel Bonding

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.

Sonar / Radar Basics

802.11n Modes• Greenfield• Non HT (Legacy)• HT Mixed Mode

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

Engineering Tools• RF Analyzers• Design Software• Capabilities and Limitations

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.

Questions?

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• s.wells@bluestonecomm.com