Onno Harms - Home - Airheads Community · PDF fileOnno Harms March 2015 ... Antenna Basic Physics ... Practical Antenna Mounting Most critical alignment is mounting antenna

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RF Characteristics and Radio Fundamentals Onno Harms

March 2015

@ArubaNetworks

2 2 #ATM15 |

RF Power

3 CONFIDENTIAL © Copyright 2015. Aruba Networks, Inc. All rights reserved

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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: !

"

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&

×=

!"

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&=

10

10

10001.0

001.log10

dBmP

Watts

WattsdBm

P

PP


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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


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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

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Antennas and Propagation

6


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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


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Propagation

•  Free Space Propagation –  -20*log(4*π/λ)

•  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/λ•  ht: this is the height of the transmitter •  hr: this is the height of the receiver


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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 GHzDistance Fresnel 0.6 Fresnel Fresnel 0.6 Fresnel

Miles ft ft ft ft0.25 11.6 7.0 7.5 4.50.5 16.5 9.9 10.7 6.41 23.3 14.0 15.0 9.0

2.5 36.8 22.1 23.7 14.25 52.0 31.2 33.5 20.1


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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

Sidelobes Backlobe

Front

Back Side

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BASIC BEAMFORMING


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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


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Building Arrays: 2 Elements

•  By introducing additional antenna elements we can control the way that the energy radiates

•  2 elements excited in phase

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dB Plot


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•  By introducing additional antenna elements we can control the way that the energy radiates

•  4 elements excited in phase –  Equal amplitude

dB Plot


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•  By shaping the amplitude we can control sidelobes

•  4 elements excited in phase –  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

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ANT-3x3-5010 Heat Maps


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•  Model •  Measured

Ant-2x2-5010 Antenna Patterns

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a,

a,5,dB ,per,divis ion


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Ant-2x2-5010 Simple projection

Assuming 20m install height

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0m 20m

50m 100 m 200 m


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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


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Heat Map: Antenna at 5 m height

100 m 1000 m


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23

100 m 1000 m


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C/I Contours

CI dBm


24

C/I Contours

CI dBm

100 m 1000 m


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100 m 1000 m


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prop( )

1.7 X 1.1 m window

Propagation through a window


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Two1.7 X 1.1 m windows Separated by 2.8 m

prop( )

Propagation through 2 windows


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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


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-  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


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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

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Importance of Polarization

31


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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


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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)


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Aruba MIMO Antennas – ANT-2x2-5005

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0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

Distance (km)

TCP

Thro

ughp

ut (M

bps)

ANT-2x2-5005 (H+V) Result (Orange)

5 dBi V+V Result(Blue)


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Aruba MIMO Antennas – ANT-2x2-5010

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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

Thro

ughp

ut (M

bps)

10dBi V + 10 dBi H

10dBi V + 10 dBi V


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3x3 Testing: 2x2 Laptop and Varying AP Antennas

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Coverage vs Gain

37


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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

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Azimuth

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dBm

Elevation


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Various Tilts: 45m install height 32 dBm EIRP:

C/I Contours

CI

C/I Contours

CI 15°Tilt 0° Tilt


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Azimuth Elevation


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C/I Contours

CI

C/I Contours



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Azimuth Elevation


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C/I Contours

CI

C/I Contours



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C/I Contours

CI

C/I Contours


46 46 #ATM15 |

Link Balance


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10 dBi and 14 dBi antenna Downlink(10(dBi(Antenna Downlink(14(dBi(Antennatx#Power#per#Branch 18 dBm tx#Power#per#Branch 18 dBm2#branches 3 dB 2#branches 3 dBantenna#gain#AP 10 dBi antenna#gain#AP 14 dBiCable#losses >1 dB Cable#losses >1 dBClient#antenna#gain 0 dBi Client#antenna#gain 0 dBiNet#EIRP#+#Client#Ant 30 dBm Net#EIRP#+#Client#Ant 34 dBmClient#rx#noise#floor >95 dBm Client#rx#noise#floor >95 dBmtotal#downlink#path#loss 125 dB total#downlink#path#loss 129 dB

Uplink(10(dBi(Antenna Uplink(14(dBi(Antennatx#Power#per#Branch 14 dBm tx#Power#per#Branch 14 dBm1#branch 0 dB 1#branch 0 dBantenna#gain#AP 10 dBi antenna#gain#AP 14 dBiCable#losses >1 dB Cable#losses >1 dB2#branches 3 dBi 2#branches 3 dBiNet#EIRP#+#AP#Ant 26 dBm Net#EIRP#+#AP#Ant 30 dBmAP#rx#noise#floor >99 dBm AP#rx#noise#floor >99 dBmtotal#uplink#path#loss 125 dB total#uplink#path#loss 129 dB

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Transmitters


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Transmitter Line Up

DAC Symbol Generation

Up Convert PA


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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


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802.11 Symbol Stream

0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 6415−

11.25−

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3.75−

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15

Time (symbols)

Line

ar Am

plitud

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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


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0 5 10 15 20 25 30 35 4060−

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Frequency (MHz)

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plitu

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B)

051015202530354060 −

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802.11n Signal Frequency Domain

Digital Domain

After DAC PA Non Linearity

802.11 Mask


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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


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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 (5QPSK 1/2 (10 (10QPSK 3/4 (13 (1316QAM 1/2 (16 (1616QAM 3/4 (19 (1964QAM 2/3 (22 (2264QAM 3/4 (25 (2564QAM 5/6 (28 (27256QAM 3/4 N/A (30256QAM 5/6 N/A (32

802.11n7EVM7(dB)

802.11ac7EVM7(dB)

Modulation Coding7Rate

EVM Specification and 22x tx table

58 58 #ATM15 |

Receivers

58


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Receiver Line Up

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ADC Symbol Decode

Down Convert LNA


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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


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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


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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

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Onno Harms - Home - Airheads Community · PDF fileOnno Harms March 2015 ... Antenna Basic Physics ... Practical Antenna Mounting Most critical alignment is mounting antenna