rf characteristics and radio fundamentals
TRANSCRIPT
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
WattsdBm
P
PP
4 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
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
5 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
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
7 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
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
8 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
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 – Factors of 10 in distance are 20 dB
• Indoor Two Slope Model R2 to R3
– First Meter the same as Free Space– Factors of 2 in distance are 9 dB – Factors of 10 in distance are 30 dB
• 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
9 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
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
10 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
Reading Antenna Pattern Plots - Omni
Azimuth Elevation
Omnidirectional Antenna (Linear View)
-3 dB
Sidelobes
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Reading Antenna Pattern Plots - Sector
Azimuth Elevation
Sector Antenna (Logarithmic View)
-3 dB
-3 dB
SidelobesBacklobe
Front
Back
Side
13 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
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
14 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
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
15 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
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Building Arrays: 4 Elements
• By introducing additional antenna elements we can control the way that the energy radiates
• 4 elements excited in phase
– Equal amplitude
dB Plot
16 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
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Building Arrays: 4 Elements
• By shaping the amplitude we can control sidelobes
• 4 elements excited in phase
– Amplitude 1, 3, 3, 1
dB Plot
17 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
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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
19 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
• Model• Measured
Ant-2x2-5010 Antenna Patterns
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a
a 5 dB per division
20 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
Ant-2x2-5010 Simple projection
Assuming 20m install height
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a
a 5 dB per division
0m20m
50m100 m
200 m
21 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
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
22 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
Heat Map: Antenna at 5 m height
100 m 1000 m
23 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
Heat Map: Antenna at 10 m height
23
100 m 1000 m
24 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
C/I Contours
CI dBm
Heat Map: Antenna at 20 m height
24
C/I Contours
CI dBm
100 m 1000 m
25 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
Heat Map: Antenna at 40 m height
100 m 1000 m
26 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
prop( )
1.7 X 1.1 m window
Propagation through a window
27 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
Two1.7 X 1.1 m windows
Separated by 2.8 m
prop( )
Propagation through 2 windows
28 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
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
29 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
- 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
30 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
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
32 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
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
33 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
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)
34 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
Aruba MIMO Antennas – ANT-2x2-5005
0
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180
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Distance (km)
TCP
Thr
ough
put (
Mbp
s)
ANT-2x2-5005 (H+V) Result (Orange)
5 dBi V+V Result
(Blue)
35 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
Aruba MIMO Antennas – ANT-2x2-5010
0
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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)
TCP
Thr
ough
put (
Mbp
s)
10dBi V + 10 dBi H
10dBi V + 10 dBi V
36 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
3x3 Testing: 2x2 Laptop and Varying AP Antennas
38 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
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
39 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
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90 Sector 6 dBi Gain
39
Azimuth
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dBm
Elevation
40 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
Various Tilts: 45m install height
32 dBm EIRP:
C/I Contours
CI
C/I Contours
CI 15°Tilt0° Tilt
41 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
90 Sector 9 dBi Gain
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AzimuthElevation
42 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
Various Tilts: 45m install height
35 dBm EIRP:
C/I Contours
CI
C/I Contours
CI 20°Tilt0° Tilt
43 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
60 Sector 17 dBi Gain
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AzimuthElevation
44 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
Various Tilts: 45m install height
42 dBm EIRP:C/I Contours
CI
C/I Contours
CI 20°Tilt0° Tilt
45 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
Various Tilts: 45m install height
42 dBm EIRP:C/I Contours
CI
C/I Contours
CI 40°Tilt30° Tilt
47 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
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
49 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
Transmitter Line Up
DACSymbol
GenerationUp
ConvertPA
50 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
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
51 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
802.11 Symbol Stream
0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 6415-
11.25-
7.5-
3.75-
0
3.75
7.5
11.25
15
Time (symbols)
Line
ar A
mpl
itude
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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
53 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
0 5 10 15 20 25 30 35 4060-
50-
40-
30-
20-
10-
0
Frequency (MHz)
Am
pli
tude
(dB
)
051015202530354060 -
50 -
40 -
30 -
20 -
10 -
0
Frequency (MHz)
Amplitude (dB)
0 5 10 15 20 25 30 35 4060-
50-
40-
30-
20-
10-
0
a
051015202530354060 -
50 -
40 -
30 -
20 -
10 -
0
a
802.11n Signal Frequency Domain
Digital Domain
After DACPA Non Linearity
802.11 Mask
54 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
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
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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
56 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
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
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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
59 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
Receiver Line Up
59
ADCSymbol
DecodeDown
ConvertLNA
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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
61 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
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
62 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved#ATM15 |
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).