RF characteristics and radio fundamentals

#ATM15 |
RF Characteristics and Radio Fundamentals
Onno Harms
March 2015
@ArubaNetworks

3 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
RF Power
• RF power of an is specified at the antenna ports
in a 50 ohm system
• RF power is measured in milliwatts or dBm
• dBm = dB relative to 1 milliwatt
• 0 dBm = 1 milliwatt
To convert power (watts) to dBm and back:














10
10
10001.0
001.
log10
dBmP
Watts
Watts
dBm
P
P
P

Why Use dBm Instead of Milliwatts?
• Due to Free Space Path Loss, signal attenuates quickly
• mW represents the data linearly
• dBm represents the data logarithmically
• The amount of power received from a 2.4 GHz, 100mW transmitted
signal
1 -20 .0098911
10 -40 .0000989
20 -46 .0000247
100 -60 .0000010
1000 (1km) -80 .0000000099
Distance(m) dBm Signal mW Signal
 dBm is much easier to work with

dBm and mW Relationships
+3 dBm = double the power
-3 dBm = half the power
+10 dBm = ten times the power
-10 dBm = one tenth the power
dBm mW
+20 100
+19 80
+16 40
+13 20
+10 10
+9 8
+6 4
+3 2
0 1
-3 0.5
-6 0.25
-9 0.125
-10 0.1
-13 0.05
-16 0.025
-19 0.0125
-20 0.01

66#ATM15 |
Antennas and Propagation
6

Basic Radio Wave Characteristics
Wavelength
Amplitude
One
Oscillation
f = c / λ
λ = wavelength, measured in meters
f = frequency, in hertz
c = speed of light, 299,792,458 m/s

Propagation
• Free Space Propagation
– -20*log(4*p/l)
• 2.4 GHz you lose -40 dB in the first meter
• 5.8 GHz you lose -48 dB in the first meter
– Factors of 2 in distance are 6 dB
• Indoor Two Slope Model R2 to R3
– First Meter the same as Free Space
• Outdoor Two Ray breakpoint model
– Propagation changes from R2 to R4 beyond this distance
• 4hthr/l
• ht: this is the height of the transmitter
• hr: this is the height of the receiver

Fresnel Zone
• This is a football shaped area between two antennas that define
the area needed to propagate the plane wave without excess
power loss
– It reaches a maximum half way across the link
2.4 GHz 5 GHz
Distance Fresnel 0.6 Fresnel Fresnel 0.6 Fresnel
Miles ft ft ft ft
0.25 11.6 7.0 7.5 4.5
0.5 16.5 9.9 10.7 6.4
1 23.3 14.0 15.0 9.0
2.5 36.8 22.1 23.7 14.2
5 52.0 31.2 33.5 20.1

Reading Antenna Pattern Plots - Omni
Azimuth Elevation
Omnidirectional Antenna (Linear View)
-3 dB
Sidelobes

Reading Antenna Pattern Plots - Sector
Azimuth Elevation
Sector Antenna (Logarithmic View)
-3 dB
-3 dB
SidelobesBacklobe
Front
Back
Side

1212#ATM15 |
BASIC BEAMFORMING

Antenna Basic Physics
• When the charges
oscillate the waves go
up and down with the
charges and radiate
away
• With a single element
the energy leaves
uniformly.
• Also known as omni-
directionally

Building Arrays: 2 Elements
• By introducing additional antenna elements we
can control the way that the energy radiates
• 2 elements excited in phase
l/2
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dB Plot

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• By introducing additional antenna elements we
can control the way that the energy radiates
– Equal amplitude
dB Plot

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• By shaping the amplitude we can control
sidelobes
– Amplitude 1, 3, 3, 1
dB Plot

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Building Arrays: 4 Elements Phase
• By altering phase we can alter the direction
that the energy travels
• 4 elements excited with phase slope
– Equal amplitude
dB Plot

1818#ATM15 |
ANT-3x3-5010 Heat Maps

• Model• Measured
Ant-2x2-5010 Antenna Patterns
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a
a
5 dB per division

Ant-2x2-5010 Simple projection
Assuming 20m install height
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a
a
5 dB per division
0m
20m
50m
100 m
200 m

Analysis
The heatmaps are shown across 100m by 100m
and 1000m by 1000m areas
These are flat earth models and the antenna is
straight up above the plane
Assume 0 dBi antenna on client

Heat Map: Antenna at 5 m height
100 m 1000 m

23
100 m 1000 m

C/I Contours
CI dBm
24
C/I Contours
CI dBm
100 m 1000 m

100 m 1000 m

prop( )
1.7 X 1.1 m window
Propagation through a window

Two1.7 X 1.1 m windows
Separated by 2.8 m
prop( )
Propagation through 2 windows

Practical Antenna Mounting
Most critical alignment is mounting antenna
vertical
– This can be accomplished with a simple spirit level
Some basic trigonometry
– Antenna beamwidth of 15 degrees (+/- 7.5°)
– At 1 km from the antenna this covers
• +/-1000 * tan(7.5°) = +/- 130 m ( +/- 40 floors of building)
– The narrowest horizontal beamwidth we support is 30°
• +/-1000 * tan(15°) = +/- 270 m
Slide 28

- The plot on the right hand side
shows the antenna pattern impact
of an 2.4 GHz omni antenna in the
presence of a wooden pole
- As might be expected the impact
is reduced as the distance from
the pole is increased. The benefit
of increasing the distance levels
off as the distance gets to 18” or
larger
- At a 2” spacing the omni behaves
like a 180 degree sector antenna
Varied Distances from 12” Diameter Wooden Pole
Slide 29
Front of
Pole
Back of
Pole
Pole
Top View

Varied Distances from 8” Diameter Metal Pole
- The plot on the right hand side shows
the antenna pattern impact of an 2.4
GHz omni antenna in the presence of a
metal pole
- As might be expected the impact is
reduced as the distance from the pole
is increased. The benefit of increasing
the distance levels off as the distance
gets to 18” or larger
- With the metal pole the direction
opposite the pole increases and
decreases in gain as the antenna
interacts with it image.
Front of
Pole
Back of
Pole
Pole
Top View

3131#ATM15 |
Importance of Polarization
31

Polarization
• The horizontal or vertical orientation of a wave
• Red wave has vertical polarization, green wave has horizontal
polarization
• RSSI increases when the receiving antenna is polarized the same as
transmitting antenna
Red Wave
Green Wave

Open Air Range Testbed
AP-ANT-86 2x2 Array, Over/Under Mounting
Vertical Polarization (all elements)
AP-ANT-86 2x2 Array, Side by Side Mounting
Vertical Polarization (all elements)

Aruba MIMO Antennas – ANT-2x2-5005
0
20
40
60
80
100
120
140
160
180
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Distance (km)
TCPThroughput(Mbps)
ANT-2x2-5005 (H+V) Result (Orange)
5 dBi V+V Result
(Blue)

Aruba MIMO Antennas – ANT-2x2-5010
0
20
40
60
80
100
120
140
160
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3
Distance (km)
TCPThroughput(Mbps)
10dBi V + 10 dBi H
10dBi V + 10 dBi V

3x3 Testing: 2x2 Laptop and Varying AP Antennas

3737#ATM15 |
Coverage vs Gain
37

Notes
All plots done at 2.4 GHz
Adjusted for maximum available EIRP with a given
antenna gain
– Not necessarily in line with in country regulatory restrictions
38

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90 Sector 6 dBi Gain
39
Azimuth
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7590105
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dBm
Elevation

Various Tilts: 45m install height
32 dBm EIRP:
C/I Contours
CI
C/I Contours
CI
15°Tilt0° Tilt

41
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135
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a
a
5 dB per division
0
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30
45
60
7590105
120
135
150
165
180
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210
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255 270 285
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AzimuthElevation

35 dBm EIRP:
C/I Contours
CI
C/I Contours
CI 20°Tilt0° Tilt

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30
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60
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105
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135
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165
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a
a
5 dB per division
0
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30
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7590105
120
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165
180
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AzimuthElevation

42 dBm EIRP:
C/I Contours
CI
C/I Contours
CI 20°Tilt0° Tilt

42 dBm EIRP:
C/I Contours
CI
C/I Contours
CI 40°Tilt30° Tilt

10 dBi and 14 dBi antenna
Downlink 10 dBi Antenna Downlink 14 dBi Antenna
tx Power per Branch 18 dBm tx Power per Branch 18 dBm
2 branches 3 dB 2 branches 3 dB
antenna gain AP 10 dBi antenna gain AP 14 dBi
Cable losses -1 dB Cable losses -1 dB
Client antenna gain 0 dBi Client antenna gain 0 dBi
Net EIRP + Client Ant 30 dBm Net EIRP + Client Ant 34 dBm
Client rx noise floor -95 dBm Client rx noise floor -95 dBm
total downlink path loss 125 dB total downlink path loss 129 dB
Uplink 10 dBi Antenna Uplink 14 dBi Antenna
tx Power per Branch 14 dBm tx Power per Branch 14 dBm
1 branch 0 dB 1 branch 0 dB
antenna gain AP 10 dBi antenna gain AP 14 dBi
Cable losses -1 dB Cable losses -1 dB
2 branches 3 dBi 2 branches 3 dBi
Net EIRP + AP Ant 26 dBm Net EIRP + AP Ant 30 dBm
AP rx noise floor -99 dBm AP rx noise floor -99 dBm
total uplink path loss 125 dB total uplink path loss 129 dB

Transmitter Line Up
DAC
Symbol
Generation
Up
Convert PA

Transmitter Terms
Conducted Power
– This is the power that leaves the connectors
EIRP: Effective Isotropic Radiated Power
– This is the conducted power (dBm) + antenna gain (dBi) in the direction
of interest – cable losses (dB)
Peak EIRP
– This is what is regulated
– It is the conducted power + peak gain – cable losses
dBm: log power ratio to milliwatt
dBi: antenna gain relative to isotropic
dBr: relative power eg:used with describing transmit mask

802.11 Symbol Stream
0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64
15-
11.25-
7.5-
3.75-
0
3.75
7.5
11.25
15
Time (symbols)
LinearAmplitude

Transmitter Non-Idealities
DAC Quantization: this is due to the limited number of bits in
a practical Digital to Analog Converter
– This noise source is not affected when the power is reduced
PA Non Linearity: OFDM has a high Peak to Average Ratio.
The peaks in the OFDM signal cause distortions which
manifest as noise like shoulders
– Known as spectral regrowth
– For every one 1 dB drop in tx power the regrowth drops by 3 dB
• 2 dB net
The in channel noise is referred to as EVM
– Error Vector Magnitude
The out of channel noise interferes with other Wi-Fi channels
and determines how close we can space antennas

0 5 10 15 20 25 30 35 40
60-
50-
40-
30-
20-
10-
0
Frequency (MHz)
Amplitude(dB)
0510152025303540
60 -
50 -
40 -
30 -
20 -
10 -
0
Frequency(MHz)
Amplitude(dB)
0 5 10 15 20 25 30 35 40
60-
50-
40-
30-
20-
10-
0
a
0510152025303540
60 -
50 -
40 -
30 -
20 -
10 -
0
a
802.11n Signal Frequency Domain
Digital Domain
After DAC
PA Non Linearity
802.11 Mask

Wideband Noise
• The quantization noise is present from DC to daylight
• Since the radios may be tuned over the entire 2.4 or 5
GHz band no filtering may be applied
• If the radio is transmitting 16 dBm conducted from 802.11
spec the wideband noise could be as high as -29 dBm
• Our noise floor is at -98 dBm
• To operate with no impact radios in the same band need
to be isolated by 69 dB
• In reality out radios are about 10 dB better on wideband
noise so the isolation requirement drops to 59 dB

Practical isolation example: ANT-2x2-5314
Front to side
27 dB
Net side gain
-13 dBi
How much space is required to completely isolate two radios looking at wide band noise?
Conducted power 23 dBm
Wideband noise -22 dBm
Cable loss 1 dB
Net Antenna gain -13 dBi
Net EIRP -36 dBm
Gain on rx side -13 dBi
Zero space power -49 dBm
With 1 m of spacing FSL is 48 dB
Net rx power is -97 dBm @ 1m
Note 2.4 GHz would be -89

EVM
• As the depth of modulation increase the
number of bits per symbol increases
• The in-band noise introduces uncertainty
wrt to the actual symbol position
• Higher order modulations decrease the
space between code points
• To make higher order modulations work
the tx power needs to be reduced
• The EVM noise will add with interference
and background noise
16 QAM

BPSK 1/2 -5 -5
QPSK 1/2 -10 -10
QPSK 3/4 -13 -13
16QAM 1/2 -16 -16
16QAM 3/4 -19 -19
64QAM 2/3 -22 -22
64QAM 3/4 -25 -25
64QAM 5/6 -28 -27
256QAM 3/4 N/A -30
256QAM 5/6 N/A -32
802.11n
EVM (dB)
802.11ac
EVM (dB)
Modulation Coding Rate
EVM Specification and 22x tx table

Receiver Line Up
59
ADC
Symbol
Decode
Down
Convert
LNA

Receiver Impairments
• Analog Compression
– Modern LNAs have very effective input power tolerance
• Digital Compression
– This is where a high power signal hits the Automatic Gain
Control (AGC) Circuit. Gain drops and receiver sensitivity
degrades
– The radio can be totally blocked if the power hits the Analog
to Digital Converter (ADC) and consumes all the bits
• Intermodulation
– Again, the effective linearity of modern LNAs reduces the
impact of this

DAS Interference: Example
• Without filtering any signal that hits the receiver
above -45 dBm will cause a reduction of sensitivity
• The degradation continues until about -15 dBm at
which point the signal is totally blocked
• With a 100 mW (20 dBm) DAS system at 2100 MHz
– Tx 20 dBm
– Effective rx antenna gain 3 dBi
– 1st meter at 2100 MHz -39 dB
• Power at 1m -19 dBm
– No impact distance 40 meters

Advanced Cellular Coexistence
• Proliferation of DAS and new LTE bands at 2.6
GHz are creating issue for Wi-Fi solution
• All new APs introduced by Aruba in the last 12
months and going forward have implemented
significant filtering into the 2.4 GHz radio portion
to combat this
• Design solution
– Use high-linear LNA followed with a high-rejection filter to achieve
rejection target and little sensitivity degradation;
– Design target: Minimal Sensitivity degradation with -10dBm interference
from 3G/4G networks (theoretical analysis).

THANK YOU
63#ATM15 | @ArubaNetworks

RF characteristics and radio fundamentals

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