RF fundamentals

CONFIDENTIAL
© Copyright 2014. Aruba Networks, Inc. All rights reserved
Welcome to
The Technical Climb Webinar
On
RF Fundamentals

CONFIDENTIAL © Copyright 2014. Aruba Networks, Inc. All rights reserved
Welcome to the Technical Climb Webinar
Listen to this webinar using the
computer audio broadcasting or dial in
by phone.
The dial in number can be found in the
audio panel, click additional numbers to
view local dial in numbers.
If you experience any difficulties
accessing the webinar contact us
using the questions panel.

Housekeeping
This webinar will be recorded
All lines will be muted during the
webinar
How can you ask questions?
Use the question panel on your screen
The recorded presentation will be posted on arubapedia for partners
(afp.arubanetworks.com)
The TAC team will answer additional questions after the webinar on
Airheads Community

CONFIDENTIAL
Radio Frequency Fundamentals

Loss (Attenuation)
• Decrease of amplitude or signal strength
– On a wire due to impedance
– Over the air-Free Space Path Loss
• Loss depends on Wavelength of a Signals
• Short WL Signals will have more effect that long WL Signals
• Loss is more in 5 Ghz compared to 2.4 Ghz

CONFIDENTIAL
© Copyright 2010. Aruba Networks, Inc.
All rights reserved6
Frequency effect on attenuation
2.4 Ghz
5 Ghz

Multipath
•When multiple signals arrive at receiver due to
different obstructions/effects on RF signal
•Difference in arrival is delay spread.
Downfade
Upfade
Nulling

Demo on Multipath effect and Attenuation

RF Channel

Overlapping vs. Non-Overlapping

Effective Wireless deployment

2.4 Ghz channels

Throughput
2 Mbps
Throughput is actual data performance

Bandwidth
• Don’t confuse frequency Bandwidth (size of channels) and
data bandwidth (speeds for transmission)
• Bandwidth always effected by throughput

Floor noise
• Noise level is measured in -dBm format (0 to -100).
• The closer the value to 0, the greater the noise level.
• Sources of noise can include
• microwave ovens
• cordless phones
• Bluetooth devices
• wireless video cameras
• wireless game controllers
• fluorescent lights

What is SNR ?
• The signal-to-noise ratio (SNR) compares the level of the Wi-FI signal to the
level of background Floor noise (RF Noise)
• This value is represented as a +dBm value.
• When Floor noise increases, SNR Decreases.
• Always SNR between 20-25 is considered as good.
For example:
• If you have a -41dBm signal strength, and a -50dBm noise level, this results in a poor signal-to-noise
ratio of +9dBm.
• If you have a -41dBm signal strength, and a -96dBm noise level, this results in an excellent signal-to-
noise ratio of +55dBm.

Relation between SNR and Data rate
Rate (Mb/s) 1 2 5.5 11 6 9
SNR (dB) 4 6 8 10 4 5
Signal level (dBm) -81 -79 -77 -75 -81 -80
Rate (Mb/s) 12 18 24 36 48 54
SNR (dB) 7 9 12 16 20 21
Signal level (dBm) -78 -76 -73 -69 -65 -64

SNR VS Data rate

CONFIDENTIAL
Ask a Question

Techniques used for enhancing the performance
• Antenna Diversity
• MIMO
• Spatial Multiplexing
• Transmit beam formation
• Channel bonding
• Short guard interval

Antenna Diversity
• A technique where multiple antennas are strategically spaced
and connected to common receiving system.
• While one antenna sees a signal null, one of the other
antennas may see a signal peak, and the receiver is able to
select the antenna with the best signal at any time.
• Also avoids multipath down fading and nullify effect

MIMO
• A wireless technology that uses multiple transmitters and receivers to
transfer more data at the same time.
• MIMO technology takes advantage of a radio-wave phenomenon called
multipath.
• Single user MIMO
– All the data streams destined to the same user
• Multi User MIMO
– Data streams destined to different users

MIMO
Each MIMO system is defined with NxM antenna matrix
N – No of Tx antenna
M – No. of Rx antenna
E.g. 3x3 AP means physical presence of 3 transmit and 3 receive antenna.
Each Tx antenna transmits uniquely encoded data stream simultaneously. This
is called Spatial Stream (SS).

Spatial Multiplexing
• Each stream can use the same, or different modulation techniqus
A2
B2
B1
A1
A
B
1
2

Transmit Beamforming (TxBF)

Channel Bonding

Wide Channels

Bandwidth Total Subcarriers Subcarriers
for Data
Multiplier
20 MHz 56 52 1
40 MHz 114 108 (108/52) = 2.07
80 MHz 242 234 (234/52) = 4.5
160 MHz 484 468 (468/52) = 9.0
FCC Band
Channel
Number
Available
Bandwidth
Configurable
80 MHz
channels
Configurable
160 MHz
channels
UNII-1 36-48 5150-5250
2 1
UNII-2 52-64 5250-5350
UNII-2e 100-144 5470-5720 3 1
UNII-3 149-161 5745-5805
1 0
ISM 165 5825
Spectral efficiency and channel availability

Short guard interval
a
b
c
a
b
c
Receivedpowerlevel
time
A
B
1
2
N N+1 N+2
N N+1 N+2
N N+1 N+2
Guard
interval
Inter-symbol
interference
Previous 802.11 standards used a guard interval of 800nsec. 802.11n adds an option for
400nsec

Modulation Coding scheme (Set) ( MCS )
• New standards like, 11n and 11ac will use best combination of
Modulation and coding ( MCS ) to select the datarate ( 70 + in 11n and
10 in 11ac )
• MCS leads to a wide range of speeds depend on
• Channel condition,
• best combination of datarates,
• bonded channels,
• multiple spatial streams,
• different guard intervals
• modulation types and coding
• Modulation describes how many bits are contained within one
transmission time increment. Higher modulations pack more data into
the transmission, but they require much higher signal-to-noise ratios
• Error-correcting code adds redundant information in a proportion
described by the code rate.
• A code at rate R=1/2 transmits one user data bit (the numerator) for
every two bits (the denominator) on the channel.
• Higher code rates have more data and less redundancy at the cost of
not being able to recover from as many errors.

QAM
quadrature amplitude modulation (QAM) works by using the
combination of amplitude level and phase shift to select one of many
symbols
To identify each of the values, there will be a unique combination of phase
shift and quadrature (roughly speaking, the amplitude of a wave).
Ex : 16 QAM = 4 Phase shifts and 4 Quadrature
64 QAM = 8 Phase shifts and 8 Quadrature
256 QAM = 16 Phase shifts and 16 Quadrature
Each time a symbol is transmitted, it may take on one of the phase shifts
and one of amplitude levels combination.
With 256 QAM we can transmit 256 symbols at a time.

MCS Index
MCS index value Modulation Code rate (R)
0 BPSK 1/2
1 QPSK 1/2
2 QPSK 3/4
3 16-QAM 1/2
4 16-QAM 3/4
5 64-QAM 2/3
6 64-QAM 3/4
7 64-QAM 5/6
8 256-QAM 3/4
9 256-QAM 5/6

Speed with Combo of MCS, CH width and SS
MCS value
20 MHz data
rate (1SS,
short GI)
Spatial stream
multiplication factor
Channel width
multiplication
factor
Maximum 40
MHz rate (8 SS,
short GI)
Maximum 80
MHz rate (8
SS, short GI)
Maximum 160
MHz rate (8 SS,
short GI)
MCS 0 7.2 Mbps
x2 for 2 streams
x3 for 3 streams
x4 for 4 streams
x5 for 5 streams
x6 for 6 streams
x7 for 7 streams
x8 for 8 streams
x1.0 for 20 MHz
x2.1 for 40 MHz
x4.5 for 80 MHz
x9.0 for 160 MHz
120.0 Mbps 260.0 Mbps 520.0 Mbps
MCS 1 14.4 240.0 520.0 1040.0
MCS 2 21.7 360.0 780.0 1560.0
MCS 3 28.9 480.0 1040.0 2080.0
MCS 4 43.3 720.0 1560.0 3120.0
MCS 5 57.8 960.0 2080.0 4160.0
MCS 6 65.0 1080.0 2340.0 4680.0
MCS 7 72.2 1200.0 2600.0 5200.0
MCS 8 86.7 1440.0 3120.0 6240.0
MCS 9 96.3 1600.0 3466.7 6933.3

802.11 n
• 2.4 Ghz AND 5 Ghz
• High Throughput-HT
• Improved OFDM
– Instead of using 48 sub carriers, it uses 52 sub carriers
• MIMO technology with OFDM
– Increased throughput and greater range
– Radio Chains
• spatial multiplexing
• Transmit beam forming
– Can use max 4 SS
• Channel Bonding
– Uses (20 + 20) MHz in 2.4 GHz and 40MHz in 5 GHz channels
• Short god interval
– Uses 400 ns Guard interval
• Block acknowledgement

IEEE 802.11 n
300 Mbps with
2 Streams
600 Mbps with
4 Streams
450 Mbps with
3 Streams

802.11 ac
• Wide Channels
80 MHz channels (contiguous)
160 MHz channels (contiguous or two non-contiguous 80 MHz slices)
256-QAM (Quadrature amplitude modulation)
Provides a 33% increase in throughput over the 64-QAM used in 11n
• Short Guard Interval ( 400 ns )
• Up to 8 spatial streams
Compared to a maximum of 4 spatial streams in 11n
Up to 8 spatial streams in both single-user and multi-user modes
• Downlink Multi-user MIMO
Allows 1 AP to transmit unique data to multiple stations simultaneously
• Independent virtual carrier sense in sub-channels

Speed comparison
Technology 20 MHz[a]
40 MHz 80 MHz 160 MHz
802.11b 11 Mbps
802.11a/g 54 Mbps
802.11n (1 SS) 72 Mbps 150 Mbps
802.11ac (1 SS) 87 Mbps 200 Mbps 433 Mbps 867 Mbps
802.11n (2 SS) 144 Mbps 300 Mbps
802.11ac (2 SS) 173 Mbps 400 Mbps 867 Mbps 1.7 Gbps
802.11n (3 SS) 216 Mbps 450 Mbps
802.11ac (3 SS) 289 Mbps 600 Mbps 1.3 Gbps 2.3 Gbps[b]
802.11n (4 SS)[c]
289 Mbps 600 Mbps
802.11ac (4 SS) 347 Mbps 800 Mbps 1.7 Gbps 3.5 Gbps
802.11ac (8 SS) 693 Mbps 1.6 Gbps 3.4 Gbps 6.9 Gbps

RF fundamentals

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to RF fundamentals

Similar to RF fundamentals (20)

Recently uploaded

Recently uploaded (20)

RF fundamentals