Certified Wireless Network Administrator

Module 18 – High Throughput (HT)

Slide 1

Module Introduction

 802.11n-2009 amendment
 Wi-Fi Alliance certification
 MIMO
 HT channels
 HT MAC

_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Slide 2

802.11n-2009 Amendment

 The 802.11n-2009 amendment defines:

 High Throughput (HT) Clause
 20 radios that use multiple-input, multiple-output (MIMO)
technology in unison with Orthogonal Frequency Division
Multiplexing (OFDM) technology
 The benefits of using MIMO are increased throughput and
even greater range

_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Slide 3

Wi-Fi Alliance Certification

_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Slide 4

Wi-Fi Alliance Certification (Cont.)

_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Slide 5

MIMO

 The heart and soul of the 802.11n amendment exists at

the Physical (PHY) layer with the use of a technology
known as multiple-input, multiple-output (MIMO)
 MIMO requires the use of multiple radios and antennas, called
radio chains
 Transmitting multiple streams of data with a method called
spatial multiplexing (SM) provides for greater throughput and
takes advantage of the old enemy known as multipath
 MIMO systems can also use multiple antennas to provide for
better transmit and receive diversity, which can increase range
and reliability
 There are various transmit and receive diversity techniques
 Space-time block coding (STBC) and cyclic shift diversity (CSD)
are transmit diversity techniques where the same transmit data is
sent out of multiple antennas

_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Slide 6

MIMO (Cont.)

_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Slide 7

MIMO (Cont.)

 Conventional 802.11 radios transmit and receive RF

signals by using a single-input, single-output (SISO)
system
 SISO systems use a single radio chain
 A radio chain is defined as a single radio and all of its
supporting architecture, including mixers, amplifiers, and
analog/digital converters
 A MIMO system consists of multiple radio chains, with
each radio chain having its own antenna
 A MIMO system is characterized by the number of
transmitters and receivers used by the multiple radio
chains

_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Slide 8

MIMO (Cont.)

 The use of multiple transmitters in a MIMO

system provides for the transmission of more
data via spatial multiplexing
 The use of multiple receivers increases signal-to-
noise ratio (SNR) because of advanced MIMO
antenna diversity

_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Slide 9

Spatial Multiplexing (SM)

 You have already learned that MIMO radios will

transmit multiple signals
 A MIMO radio also has the ability to send
independent unique data streams
 Each independent data stream is known as a spatial
stream
 Each unique stream can contain data that is different
from the other streams transmitted by one or more of
the other radio chains

_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Slide 10

Spatial Multiplexing (SM) (Cont.)

 The benefit of sending multiple unique data

streams is that throughput is drastically
increased
 If a MIMO access point sends two unique data
streams to a MIMO client station that receives both
streams, the throughput is effectively doubled
 If a MIMO access point sends three unique data
streams to a MIMO client station that receives all
three streams, the throughput is effectively tripled

_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Slide 11

Spatial Multiplexing (SM) (Cont.)

 Do not confuse the independent unique streams

of data with the number of transmitters
 In fact, when referring to MIMO radios it is important
to also reference how many unique streams of data
are sent and received by MIMO radios

_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Slide 12

MIMO Diversity

 If you cover one of your ears with your hand, will

you hear better or worse with a single ear?
 Obviously, you will hear better with two ears
 Do you think you would be able to hear more clearly
if you had three or four ears instead of just two?
 Do you think you would be able to hear sounds from
greater distances if you had three or four ears
instead of just two?
 Yes, a human being would hear more clearly and with
greater range if equipped with more than two ears.
 MIMO systems employ advanced antenna diversity
capabilities that are analogous to having multiple
ears

_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Slide 13

MIMO Diversity (Cont.)

 Antenna diversity often is mistaken for the spatial

multiplexing capabilities that are utilized by MIMO
 Antenna diversity (both receive and transmit) is a
method of using multiple antennas to survive the
negative effects of multipath
 As you just learned, MIMO takes advantage of multipath
with spatial multiplexing to increase data capacity
 Simple antenna diversity is a method of compensating
for multipath as opposed to utilizing multipath
 Multipath produces multiple copies of the same signal
that arrive at the receiver with different amplitudes

_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Slide 14

Space-Time Block Coding (STBC)

 Space-time block coding (STBC) is a method

where the same information is transmitted on
two or more antennas
 It is a type of transmit diversity
 STBC can be used when the number of radio chains
exceeds the number of spatial streams
 By sending copies of the same information on multiple
antennas, the actual rate of the data transmitted does
not increase as transmit antennas are added

_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Slide 15

Cyclic Shift Diversity (CSD)

 Cyclic shift diversity (CSD) is another transmit

diversity technique specified in the 802.11n
standard
 Unlike STBC, a signal from a transmitter that uses
CSD can be received by legacy 802.11g and 802.11a
devices
 For mixed mode deployments, where 802.11n
coexists with 802.11g and 802.11a devices, there is a
need to have a way of transmitting the symbols in the
legacy OFDM preamble over multiple transmit
antennas

_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Slide 16

Transmit Beamforming (TxBF)

 The 802.11n amendment also proposes an optional

PHY capability called transmit beamforming (TxBF),
which uses phase adjustments
 Can be used when there are more transmitting antennas
than there are spatial data streams
 Allows a MIMO transmitter using multiple antennas to
adjust the phase and amplitude of the outgoing
transmissions in a coordinated method
 Results in constructive multipath communication, the result
is a higher signal-to-noise ratio and greater received
amplitude
 Therefore, transmit beamforming will result in greater
range for individual clients communicating with an access
point

_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Slide 17

Transmit Beamforming (TxBF) (Cont.)

 Transmit beamforming relies on implicit feedback or

explicit feedback from both the transmitter and receiver.
 Any frame can be used as a sounding frame
 Null function data frames can be used if another frame is not used
 When using implicit feedback, the beamformer sends a sounding
frame and then receives long training symbols transmitted by the
beamformee, which allows the MIMO channel between the
beamformee and beamformer to be estimated by the beamformer

_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Slide 18

20 MHz Non-HT and HT Channels

 802.11a and 802.11g radios use 20 MHz OFDM channels

 Each channel consists of 64 subcarriers
 Forty-eight of the subcarriers transmit data
 Four of the subcarriers are used as pilot tones for dynamic calibration
between the transmitter and receiver
 The remaining subcarriers are not used
 OFDM technology also employs the use of convolutional coding and
forward error correction
 802.11n (HT) radios also use the same OFDM technology and have
the capability of using either 20 MHz channels or 40 MHz channels
 The 20 MHz channels used by HT radios have four extra subcarriers and can
carry a little more data than a non-HT OFDM channel
 As a result, the HT 20 MHz channel with a single spatial stream can
provide greater aggregate throughput for the same frequency space

_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Slide 19

20 MHz Non-HT and HT Channels (Cont.)

_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Slide 20

40 MHz Channels

 802.11n (HT) radios also

have the capability of using
40 MHz OFDM channels
 The 40 MHz channels used
by HT radios are essentially
two 20 MHz OFDM channels
that are bonded together
 Each 40 MHz channel
consists of a primary and
secondary 20 MHz channel
 The primary and secondary
20 MHz channels must be
adjacent 20 MHz channels in
the frequency in which they
operate

_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Slide 21

Module Review

 802.11n-2009 amendment
 Wi-Fi Alliance certification
 MIMO
 HT channels
 HT MAC

_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Review Questions:
1. True or False: SISO systems use a double radio chain.
A. True
B. False

2. True or False: Space-time block coding (STBC) is a method where the same
information is transmitted on two or more antennas.
A. True
B. False

3. True or False: A MIMO radio has the ability to send dependent unique data
streams.
A. True
B. False

4. True or False: Antenna diversity often is mistaken for the spatial multiplexing
capabilities that are utilized by MIMO.
A. True
B. False

5. True or False: 802.11n (HT) radios have the capability of using 40 MHz OFDM
channels.
A. True
B. False
Answer Key:
1. B
False. SISO systems use a single radio chain.

2. A
True. Space-time block coding (STBC) is a method where the same information
is transmitted on two or more antennas.

3. B
False. A MIMO radio has the ability to send independent unique data streams.

4. A
True. Antenna diversity often is mistaken for the spatial multiplexing capabilities
that are utilized by MIMO.

5. A
True. 802.11n (HT) radios do have the capability of using 40 MHz OFDM
channels.