RF characteristics and radio fundamentals

#ATM15 |

RF Characteristics and Radio FundamentalsOnno Harms

March 2015

@ArubaNetworks

22#ATM15 |

RF Power

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


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 – 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


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

0m20m

50m100 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

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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)


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)

TCP

Thr

ough

put (

Mbp

s)

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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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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AzimuthElevation



35 dBm EIRP:

C/I Contours

CI

C/I Contours

CI 20°Tilt0° Tilt



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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

4646#ATM15 |

Link Balance


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

4848#ATM15 |

Transmitters


Transmitter Line Up

DACSymbol

GenerationUp

ConvertPA


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 6415-

11.25-

7.5-

3.75-

0

3.75

7.5

11.25

15

Time (symbols)

Line

ar A

mpl

itude


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 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


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

5858#ATM15 |

Receivers

58


Receiver Line Up

59

ADCSymbol

DecodeDown

ConvertLNA


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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