Tonex RF Bootcamp

RF100 - 1November, 2014 RF Bootcamp - Course RF100 v10.0 - (c) 2014 Tonex

Tonex RF BootcampTonex RF Bootcamp


History of RF AndEarly Telecommunications

History of RF AndEarly Telecommunications


How Did We Get Here?

Days before radio..... 1680 Newton first suggested

concept of spectrum, but for visible light only

1831 Faraday demonstrated that light, electricity, and magnetism are related

1864 Maxwells Equations: spectrum includes more than light

1890s First successful demos of radio transmission

UN S

LF HF VHF UHF MW IR UV XRAY


Telegraphy Samuel F.B. Morse had the idea of the telegraph on a

sea cruise in the 1833. He studied physics for two years, and In 1835 demonstrated a working prototype, which he patented in 1837.

Derivatives of Morse binary code are still in use today The US Congress funded a demonstration line from

Washington to Baltimore, completed in 1844. 1844: the first commercial telegraph circuits were coming

into use. The railroads soon were using them for train dispatching, and the Western Union company resold idle time on railroad circuits for public telegrams, nationwide

1857: first trans-Atlantic submarine cable was installedSamuel F. B. Morse

at the peak of his career

Field Telegraphyduring the US Civil War, 1860s

Submarine Cable Installationnews sketch from the 1850s


Telephony By the 1870s, the telegraph was in use all over the world and largely taken for

granted by the public, government, and business. In 1876, Alexander Graham Bell patented his telephone, a device for carrying

actual voices over wires. Initial telephone demonstrations sparked intense public interest and by the late

1890s, telephone service was available in most towns and cities across the USA

Telephone Line Installation Crew1880s

Alexander Graham Bell and his phonefrom 1876 demonstration

electricfield

magneticfield

Propagationdirection

Electromagnetic Radiation

Interrelated electric and magnetic fields traveling through space

Electromagnetic radiation travels at about c = 3108 m/s in a vacuum the cosmic speed limit!

299792458.0 m/s, more exactly in cables, 82-95% speed in a vacuum In glass, about 66% speed in a vacuum

November, 2014 RF Bootcamp - Course RF100 v10.0 - (c) 2014 Tonex RF100 - 6


Radio Milestones 1888: Heinrich Hertz, German physicist, gives lab demo of

existance of electromagnetic waves at radio frequencies 1895: Guglielmo Marconi demonstrates a wireless radio

telegraph over a 3-km path near his home it Italy 1897: the British fund Marconis development of reliable

radio telegraphy over ranges of 100 kM 1902: Marconis successful trans-Atlantic demonstration 1902: Nathan Stubblefield demonstrates voice over radio 1906: Lee De Forest invents audion, triode vacuum tube

feasible now to make steady carriers, and to amplify signals

1914: Radio became valuable military tool in World War I 1920s: Radio used for commercial broadcasting 1940s: first application of RADAR - English detection of

incoming German planes during WW II 1950s: first public marriage of radio and telephony - MTS,

Mobile Telephone System 1961: transistor developed: portable radio now practical 1961: IMTS - Improved Mobile Telephone Service 1970s: Integrated circuit progress: MSI, LSI, VLSI, ASICs 1979, 1983: AMPS cellular demo, commercial deployment

Guglielmo Marconiradio pioneer, 1895

Lee De Forestvacuum tube inventor

MTS, IMTS

Prefixes for Large and Small Units


Wavelength, Frequency, and Energy Relationships

Wavelength (m) Frequency (Hz) Energy (J)

Radio > 1 x 10-1 < 3 x 109 < 2 x 10-24

Microwave 1 x 10-3 - 1 x 10-1 3 x 109 - 3 x 1011 2 x 10-24- 2 x 10-22

Infrared 7 x 10-7 - 1 x 10-3 3 x 1011 - 4 x 1014 2 x 10-22 - 3 x 10-19

Optical 4 x 10-7 - 7 x 10-7 4 x 1014 - 7.5 x 1014 3 x 10-19 - 5 x 10-19

UV 1 x 10-8 - 4 x 10-7 7.5 x 1014 - 3 x 1016 5 x 10-19 - 2 x 10-17

X-ray 1 x 10-11 - 1 x 10-8 3 x 1016 - 3 x 1019 2 x 10-17 - 2 x 10-14

Gamma-ray < 1 x 10-11 > 3 x 1019 > 2 x 10-14


Frequency vs. Wavelength


Radio Spectrum Designations

Designation Abbreviation Frequencies Free-space Wavelengths

Very Low Frequency VLF 9 kHz - 30 kHz 33 km - 10 km

Low Frequency LF 30 kHz - 300 kHz 10 km - 1 km

Medium Frequency MF 300 kHz - 3 MHz 1 km - 100 m

High Frequency HF 3 MHz - 30 MHz 100 m - 10 m

Very High Frequency VHF 30 MHz - 300 MHz 10 m - 1 m

Ultra High Frequency UHF 300 MHz - 3 GHz 1 m - 100 mm

Super High Frequency SHF 3 GHz - 30 GHz 100 mm - 10 mm

Extremely High Frequency EHF 30 GHz - 300 GHz 10 mm - 1 mm


Common Terms for US Frequency Bands

Band Frequency range

UHF ISM 902-928 MHz

S-Band 2-4 GHz

S-Band ISM 2.4-2.5 GHz

C-Band 4-8 GHz

C-Band satellite downlink 3.7-4.2 GHz

C-Band Radar (weather) 5.25-5.925 GHz

C-Band ISM 5.725-5.875 GHz

C-Band satellite uplink 5.925-6.425 GHz

X-Band 8-12 GHz

X-Band Radar (police/weather) 8.5-10.55 GHz

Ku-Band 12-18 GHz

Ku-Band Radar (police) 13.4-14 GHz 15.7-17.7 GHz


L band 1 to 2 GHz

S band 2 to 4 GHz

C band 4 to 8 GHz

X band 8 to 12 GHz

Ku band 12 to 18 GHz

K band 18 to 26.5 GHz

Ka band 26.5 to 40 GHz

Q band 30 to 50 GHz

U band 40 to 60 GHz

V band 50 to 75 GHz

E band 60 to 90 GHz

W band 75 to 110 GHz

F band 90 to 140 GHz

D band 110 to 170 GHz

Microwave Bands (complete list)


November, 2014 RF100 - 14RF Bootcamp - Course RF100 v10.0 - (c) 2014 Tonex

Frequencies Used by Wireless SystemsOverview of the Radio Spectrum

3 4 5 6 7 8 9 10 12 14 16 18 20 22 24 26 28 30 GHz30,000,000,000 i.e., 3x1010 Hz

Broadcasting Land-Mobile Aeronautical Mobile TelephonyTerrestrial Microwave Satellite

0.3 0.4 0.5 0/6 0.7 0.8 0.9 1.0 1.2 1.4 1.6 1.8 2.0 2.4 3.0 GHz3,000,000,000 i.e., 3x109 Hz

UHF TV 14-59UHF GPSDCS, PCS, AWS700 + Cellular

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.2 1.4 1.6 1.8 2.0 2.4 3.0 MHz3,000,000 i.e., 3x106 Hz

AM LORAN Marine

3 4 5 6 7 8 9 10 12 14 16 18 20 22 24 26 28 30 MHz30,000,000 i.e., 3x107 Hz

Short Wave -- International Broadcast -- Amateur CB

30 40 50 60 70 80 90 100 120 140 160 180 200 240 300 MHz300,000,000 i.e., 3x108 Hz

FM VHF TV 7-13VHF LOW Band VHFVHF TV 2-6


The Broadband Wireless Spectrum

Five differently-regulated ranges of spectrum are available for broadband: ISM - the Industrial, Scientific, and Medical band. Unlicensed, already used for Wi-Fi networking,

cordless phones, toys, and microwave ovens. Spread-spectrum transmission is required. In some localities this spectrum may be too cluttered to be useful for broadband.

U-NII Unlicensed National Information Infrastructure band. Unlicensed, and spread-spectrum transmission is not required. This spectrum has far fewer users at present than ISM.

BRS - Broadband Radio Service. (Earlier called the Multipoint Distribution Service (MDS)/MMDS), it was used as wireless cable to bring video to end-users.) Links are licensed, so the potential for interference is small. Sprint and Nextel both control large blocks which are now combined.

EBS Educational Broadband Service (formerly ITFS/Instructional Television Fixed Service) instructional video and data for education. Licensed spectrum; can be used for wireless broadband. Clearwire/Craig McCaw control large blocks.

WCS Wireless Communications Service. Licensed spectrum available for broadband. Bellsouth owns large blocks.

5700 5800 5900 MHz.

ISM

900800 1000 MHz.

ISM

2400 2500 2600 MHz. 2690

EBSISM

2300

WCSWCSSATELLITE

BCST. BRS EBS BRS

Sirius& XM

5300 540052005100

U-NII


Current Wireless/Cellular Spectrum in the US

Modern wireless began in the 800 MHz. range, when the US FCC reallocated UHF TV channels 70-83 for wireless use and AT&Ts Analog technology AMPS was chosen.

Nextel bought many existing 800 MHz. Enhanced Specialized Mobile Radio (ESMR) systems and converted to Motorolas IDEN technology

The FCC allocated 1900 MHz. spectrum for Personal Communications Services, PCS, auctioning the frequencies for over $20 billion dollars

With the end of Analog TV broadcasting in 2009, the FCC auctioned former TV channels 52-69 for wireless use, 700 MHz.

The FCC also auctioned spectrum near 1700 and 2100 MHz. for Advanced Wireless Services, AWS.

Technically speaking, any technology can operate in any band. The choice of technology is largely a business decision.

700 MHz 800 900 1700 1800 1900 2000 2100 2200

700 MHz.I

D

E

N

I

D

E

N

C

E

L

L

D

N

L

N

K

C

E

L

L

U

P

L

I

N

K

AWSUplink

AWSDown-Link

PCSUplink

PCSDown-Link

Proposed AWS-2

A

W

S

?

S

A

T

S

A

T

Frequency, MegaHertz

November, 2014 Page 17RF Bootcamp - Course RF100 v10.0 - (c) 2014 Tonex

North American Cellular Spectrum

In each MSA and RSA, eligibility for ownership was restricted A licenses awarded to non-telephone-company applicants only B licenses awarded to existing telephone companies only subsequent sales are unrestricted after system in actual operation

Downlink Frequencies(Forward Path)

Uplink Frequencies(Reverse Path)

Frequency, MHz824 835 845 870 880 894

869

849

846.5825

890

891.5

Paging, ESMR, etc. A B

Ownership andLicensing

Frequencies used by A Cellular OperatorInitial ownership by Non-Wireline companies

Frequencies used by B Cellular OperatorInitial ownership by Wireline companies

November, 2014 Page 18RF Bootcamp - Course RF100 v10.0 - (c) 2014 Tonex

By 1994, US cellular systems were seriously overloaded and looking for capacity relief

The FCC allocated 120 MHz. of spectrum around 1900 MHz. for new wireless telephony known as PCS (Personal Communications Systems), and 20 MHz. for unlicensed services

allocation was divided into 6 blocks; 10-year licenses were auctioned to highest bidders

Development of North America PCS

51 MTAs493 BTAs

PCS Licensing and Auction Details A & B spectrum blocks licensed in 51 MTAs (Major Trading Areas )

Revenue from auction: $7.2 billion (1995) C, D, E, F blocks were licensed in 493 BTAs (Basic Trading Areas)

C-block auction revenue: $10.2 B, D-E-F block auction: $2+ B (1996) Auction winners are free to choose any desired technology

A D B E F C data unlic.voice A D B E F C

1850 MHz.

1910 MHz.

1990 MHz.

1930 MHz.

15 15 155 5 5 15 15 155 5 5

PCS SPECTRUM ALLOCATIONS IN NORTH AMERICA

G G

November, 2014Page 19 RF Bootcamp - Course RF100 v10.0 - (c) 2014 Tonex

Advanced Wireless Services: The AWS Spectrum

To further satisfy growing demand for wireless data services as well as traditional voice, the FCC has also allocated more spectrum for wireless in the 1700 and 2100 MHz. ranges

The US AWS spectrum lines up with International wireless spectrum allocations, making world wireless handsets more practical than in the past

Many AWS licensees will simply use their AWS spectrum to add more capacity to their existing networks; some will use it to introduce their service to new areas


AWS Spectrum Blocks

The AWS spectrum is divided into blocks Different wireless operator companies are licensed to use specific

blocks in specific areas This is the same arrangement used in original 800 MHz. cellular,

1900 MHz. PCS, and the new 700 MHz. allocations


The US 700 MHz. Spectrum and Its Blocks

To satisfy growing demand for wireless data services as well as traditional voice, the FCC has also taken the spectrum formerly used as TV channels 52-69 and allocated them for wireless

The TV broadcasters will completely vacate these frequencies when analog television broadcasting ends in February, 2009

At that time, the winning wireless bidders may begin building and operating their networks

In many cases, 700 MHz. spectrum will be used as an extension of existing operators networks. In other cases, entirely new service will be provided.


Wireless Systems:Modulation and Signal Bandwidth

Wireless Systems:Modulation and Signal Bandwidth

fc

fc

Upper Sideband

Lower Sideband

fc

fc

I axis

Q axis

a

b

c

QPSK

I axis

Q axis

c

a

b

p

r

v/4 shifted DQPSK

1 0 1 0

1 0 1 0

1 0 1 0


Characteristics of a Radio Signal

The purpose of telecommunications is to send information from one place to another

Our civilization exploits the transmissible nature of radio signals, using them in a sense as our carrier pigeons

To convey information, some characteristic of the radio signal must be altered (I.e., modulated) to represent the information

The sender and receiver must have a consistent understanding of what the variations mean to each other

RF signal characteristics which can be varied for information transmission:

Amplitude Frequency Phase

SIGNAL CHARACTERISTICS

S (t) = A cos [ c t + ]The complete, time-varying radio signal

Amplitude (strength) of the signal

Natural Frequencyof the signal

Phase of the signal

Compare these Signals:

Different Amplitudes

Different Frequencies

Different Phases


Modulation and Occupied Bandwidth

The bandwidth occupied by a signal depends on:

input information bandwidth modulation method

Information to be transmitted, called input or baseband

bandwidth usually is small, much lower than frequency of carrier

Unmodulated carrier the carrier itself has Zero bandwidth!!

AM-modulated carrier Notice the upper & lower sidebands total bandwidth = 2 x baseband

FM-modulated carrier Many sidebands! bandwidth is a

complex mathematical function PM-modulated carrier

Many sidebands! bandwidth is a complex mathematical function

Voltage

Time

Time-Domain(as viewed on an

Oscilloscope)

Frequency-Domain(as viewed on a

Spectrum Analyzer)Voltage

Frequency0

fc

fc

Upper Sideband

Lower Sideband

fc

fc


The Emergence of AM: A bit of History

The early radio pioneers first used binary transmission, turning their crude transmitters on and off to form the dots and dashes of Morse code. The first successful demonstrations of radio occurred during the mid-1890s by experimenters in Italy, England, Kentucky, and elsewhere.

Amplitude modulation was the first method used to transmit voice over radio. The early experimenters couldnt foresee other methods (FM, etc.), or todays advanced digital devices and techniques.

Commercial AM broadcasting to the public began in the early 1920s.

Despite its disadvantages and antiquity, AM is still alive: AM broadcasting continues today in 540-1600 KHz. AM modulation remains the international civil aviation standard,

used by all commercial aircraft (108-132 MHz. band). AM modulation is used for the visual portion of commercial

television signals (sound portion carried by FM modulation) Citizens Band (CB) radios use AM modulation Special variations of AM featuring single or independent

sidebands, with carrier suppressed or attenuated, are used for marine, commercial, military, and amateur communicationsSSB

LSB USB


Frequency Modulation (FM) Frequency Modulation (FM) is a type of

angle modulation in FM, the instantaneous frequency

of the signal is varied by the modulating waveform

Advantages of FM the amplitude is constant

simple saturated amplifiers can be used

the signal is relatively immune to external noise

the signal is relatively robust; required C/I values are typically 17-18 dB. in wireless applications

Disadvantages of FM relatively complex detectors are

required a large number of sidebands are

produced, requiring even larger bandwidth than AM

TIME-DOMAIN VIEW

sFM(t) =A cos [c t + mm(x)dx+ ]t

t0

where:A = signal amplitude (constant)c = radian carrier frequency

mfrequency deviation indexm(x) = modulating signal

= initial phase

FREQUENCY-DOMAIN VIEW

V

o

l

t

a

g

e

Frequency0 fc

SFM(t)UPPERSIDEBANDS

LOWERSIDEBANDS


The Digital Advantage

The modulating signals shown in previous slides were all analog. It is also possible to quantize modulating signals, restricting them to discrete values, and use such signals to perform digital modulation. Digital modulation has several advantages over analog modulation:

Digital signals can be more easily regenerated than analog

in analog systems, the effects of noise and distortion are cumulative: each demodulation and remodulation introduces new noise and distortion, added to the noise and distortion from previous demodulations/remodulations.

in digital systems, each demodulation and remodulation produces a cleanoutput signal free of past noise and distortion

Digital bit streams are ideally suited to many flexible multiplexing schemes

transmission

demodulation-remodulation

transmission


transmission



Theory of Digital Modulation: Sampling

Voice and other analog signals first must be sampled (converted to digital form) for digital modulation and transmission

The sampling theorem gives the criteria necessary for successful sampling, digital modulation, and demodulation

The analog signal must be band-limited (low-pass filtered) to contain no frequencies higher than fM

Sampling must occur at least twice as fast as fM in the analog signal. This is called the Nyquist Rate

Required Bandwidth for p(t) If each sample p(t) is expressed as

an n-bit binary number, the bandwidth required to convey p(t) as a digital signal is at least N*2* fM

this follows Shannons Theorem: at least one Hertz of bandwidth is required to convey one bit per second of data

The Sampling Theorem: Two PartsIf the signal contains no frequency higher than fM Hz., it is comletely described by specifying its samples taken at instants of time spaced 1/2 fM s.The signal can be completely recovered from its samples taken at the rate of 2 fMsamples per second or higher.

m(t)

Sampling

Recoverym(t)

p(t)


Sampling Example: the 64 kb/s DS-0 Telephony has adopted a world-wide PCM

standard digital signal employing a 64 kb/s stream derived from sampled voice data

Voice waveforms are band-limited upper cutoff between 3500-4000 Hz. to

avoid aliasing rolloff below 300 Hz. to minimize

vulnerability to hum from AC power mains Voice waveforms sampled at 8000/second rate

8000 samples x 1 byte = 64,000 bits/second A>D conversion is non-linear, one byte per

sample, thus 256 quantized levels are possible

Levels are defined logarithmically rather than linearly to accommodate a wider range of audio levels with minimum distortion

-law companding (popular in North America & Japan)

A-law companding (used in most other countries)

A>D and D>A functions are performed in a CODEC (coder-decoder) (see following figure)

-10dB

-20dB

-30dB

-40dB

0 dB

100 300 1000 3000 10000Frequency, Hz

C-Message Weighting

t

0123456879101112131415

16

4

16

13

15

8

3 48

A-LAWy sgn(x) A|x|

ln(1A) for 0 x1A

(where A 87.6)y sgn(x) ln(1A|x)|

ln(1A) for1A x 1

-Lawy sgn(x) ln(1 |x|)

ln(1 )(where 255)

Companding

Band-Limiting

x = analog audio voltagey = quantized level (digital)


Digital ModulationDigital Modulation


Modulation by Digital Inputs

For example, modulate a signal with this digital waveform. No more continuous analog variations, now were shifting between discrete levels. We call this shift keying.

The user gets to decide what levels mean 0 and 1 -- there are no inherent values

Steady Carrier without modulation Amplitude Shift Keying

ASK applications: digital microwave Frequency Shift Keying

FSK applications: control messages in AMPS cellular; TDMA cellular

Phase Shift KeyingPSK applications: TDMA cellular,

GSM & PCS-1900

Our previous modulation examples used continuously-variable analog inputs. If we quantize the inputs, restricting them to digital values, we will produce digital modulation.

Voltage

Time1 0 1 0

1 0 1 0

1 0 1 0

1 0 1 0


Claude Shannon: The Einstein of Information Theory and Signal Science

The core idea that makes CDMA possible was first explained by Claude Shannon, a Bell Labs research mathematician

Shannon's work relates amount of information carried, channel bandwidth, signal-to-noise-ratio, and detection error probability

It shows the theoretical upper limit attainable

In 1948 Claude Shannon published his landmark paper on information theory, A Mathematical Theory of Communication. He observed that "the fundamental problem of communication is that of reproducing at one point either exactly or approximately a message selected at another point." His paper so clearly established the foundations of information theory that his framework and terminology are standard today.Shannon died Feb. 24, 2001, at age 84.


Modulation Techniques of 1xEV Technologies

1xEV, 1x Evolution, is a family of alternative fast-data schemes that can be implemented on a 1x CDMA carrier.

1xEV DO means 1x Evolution, Data Only, originally proposed by Qualcomm as High Data Rates (HDR).

Up to 2.4576 Mbps forward, 153.6 kbps reverse

A 1xEV DO carrier holds only packet data, and does not support circuit-switched voice

Commercially available in 2003 1xEV DV means 1x Evolution, Data and Voice.

Max throughput of 5 Mbps forward, 307.2k reverse

Backward compatible with IS-95/1xRTT voice calls on the same carrier as the data

Not yet commercially available; work continues

All versions of 1xEV use advanced modulation techniques to achieve high throughputs.

QPSKCDMA IS-95,

IS-2000 1xRTT,and lower ratesof 1xEV-DO, DV

16QAM1xEV-DOat highest

rates

64QAM1xEV-DV

at highestrates


Digital Modulation Systems

Each symbol of a digitally modulated RF signal conveys a number of bits of information

determined by the number of degrees of modulation freedom

More complex modulation schemes can carry more bits per symbol in a given bandwidth, but require better signal-to-noise ratios

The actual number of bits per second which can be conveyed in a given bandwidth under given signal-to-noise conditions is described by Shannons equations

ModulationScheme

Shannon Limit,BitsHz

BPSK 1 b/s/hzQPSK 2 b/s/hz8PSK 3 b/s/hz

16 QAM 4 b/s/hz32 QAM 5 b/s/hz64 QAM 6 b/s/hz256 QAM 8 b/s/hz

SHANNONS CAPACITY EQUATION

C = B log2 [ 1 + ]S N B = bandwidth in HertzC = channel capacity in bits/secondS = signal powerN = noise power


Digital Modulation Schemes There are many different schemes for digital modulation, each a

compromise between complexity, immunity to errors in transmission, required channel bandwidth, and possible requirement for linear amplifiers

Linear Modulation Techniques BPSK Binary Phase Shift Keying DPSK Differential Phase Shift Keying QPSK Quadrature Phase Shift Keying IS-95 CDMA forward link

Offset QPSK IS-95 CDMA reverse link Pi/4 DQPSK IS-54, IS-136 control and traffic channels

Constant Envelope Modulation Schemes BFSK Binary Frequency Shift Keying AMPS control channels MSK Minimum Shift Keying GMSK Gaussian Minimum Shift Keying GSM systems, CDPD

Hybrid Combinations of Linear and Constant Envelope Modulation MPSK M-ary Phase Shift Keying QAM M-ary Quadrature Amplitude Modulation MFSK M-ary Frequency Shift Keying FLEX paging protocol

Spread Spectrum Multiple Access Techniques DSSS Direct-Sequence Spread Spectrum IS-95 CDMA FHSS Frequency-Hopping Spread Spectrum


Error Vulnerabilities ofHigher-Order Modulation Schemes

Higher-Order Modulation Schemes (16PSK, 32QAM, 64QAM...) are more vulnerable to transmission errors than the simpler, more rugged schemes (BPSK, QPSK)

Closely-packed constellations leave little room for vector error

Non-linearities (gain compression, clipping, reflections within antenna system) warp the constellation

Noise and long-delayed echoes cause scatter around constellation points

Interference blurs constellation points into rings of error

Q

I

Normal 64QAMQ

I

Distortion(Gain Compression)

Q

I

Noise Q

I

Interference


Error Vector Magnitude and (Rho)

A common measurement of overall error is Error Vector Magnitude EVM

usually a small fraction of total vector amplitude, ~0.1

EVM is usually averaged over a large number of symbols

Root-mean-square (RMS) Commercial test equipment

for BTS maintenance measures EVM

Signal quality is often expressed as 1-EVM

normally called (Rho) typically 0.89-0.96


RF Fundamentals: Noise

RF Fundamentals: Noise

Receiving Weak Signals:Noise, Unwelcome Guest Who Wont Go Home!

To hear a very weak signal, why cant we just add amplifier after amplifier until we get enough gain to hear it?

Unfortunately, theres always noise in the background free! The signal must be strong enough to hear despite the noise Signal-to-Noise Ratio SNR Different kinds of signals have different resistance to noise

The most common, ever-present kind of noise is thermal noise Electrons in metal are always randomly moving around,

propelled by free ambient heat Electron flow is the same thing as current noise current Thermal noise power is distributed evenly through the radio

spectrum a certain amount per hertz of bandwidth


How Strong is the Thermal Noise?

The strength of the noise we receive is determined by three things: Its proportional to absolute temperature (degrees Kelvin) Its proportional to the bandwidth were looking at (thermal noise

is uniformly distributed in watts per hertz) The exact amount of noise per degree kelvin per hertz is

determined by Boltzmanns constant In the world of radio, we usually express noise power in decibels

above a milliwatt (dbm). Heres the everyday formula for the amount of thermal noise in dbm:

Where P is the power in dbm Delta F is the bandwidth were watching, in hertz


the Noise Floor

Thermal Noise Strength in the Bandwidths of Common Signals



Physical Principles of Propagation

Physical Principles of Propagation

Working in Decibels

Amplifiers increase the power of electrical signals (an increase is called gain)

Cables, attenuators, or simple radiation through space decrease signal power (called loss)

Decibels are logarithmic units, so db values are never very big or very small db, even if the gains or losses are extremely big or small

Db are always small enough to allow doing the arithmetic in your head without needing a calculator


db = 10 * Log10 (Pout/Pin)

Ratio to Decibels

(Pout/Pin) = 10 (db/10)Decibels to Ratio

1 x

10 x

100 x

1,000 x

10,000 x

100,000 x

1,000,000 x

.1 x

.01 x

.001 x

.0001 x

.00001 x

.000001 x

+10 db

+20 db

+40 db

+50 db

+60 db

0 db

-10 db

-20 db

-30 db

-40 db

-50 db

-60 db

+30 db

2 x4 x +6 db

+3 db

GAIN and LOSSRatio vs. dB

Decibels can Express Relative Gains/Losses, or Absolute Amounts of Power,or Gains of Specific Antennas

dB - relative gain or loss When you see just a simple value 30 dB, this tells what happens to a

signal when it passes through a certain device or system If a device increases the signal power 1000x, that is 30 db gain. If signal power decreases 1000x, that is -30 db gain (thats loss).

dBm - absolute power A value 30 dBm expresses an actual amount of power. m stands for

milliwatts. Example: 1000 milliwatts is +30 dBm

dBi or dBd gain of test antenna compared to a reference antenna 12.1 dbi gain means the test antenna makes signals seem 12.1 db

stronger than if an isotropic antenna had been used 10 dbd gain means the test antenna makes signals seem 10 db

stronger than if a dipole antenna had been used



Introduction to Propagation

Propagation is a key process within every radio link. During propagation, many processes act on the radio signal.

attenuation the signal amplitude is reduced by various natural mechanisms; if there is

too much attenuation, the signal will fall below the reliable detection threshold at the receiver. Attenuation is the most important single factor in propagation.

multipath and group delay distortions the signal diffracts and reflects off irregularly shaped objects, producing a

host of components which arrive in random timings and random RF phases at the receiver. This blurs pulses and also produces intermittent signal cancellation and reinforcement. These effects are combatted through a variety of special techniques

time variability - signal strength and quality varies with time, often dramatically space variability - signal strength and quality varies with location and distance frequency variability - signal strength and quality differs on different

frequencies Effective mastery of propagation relies on

Physics: understand the basic propagation processes Measurement: obtain data on propagation behavior in area of interest Statistics: characterize what is known, extrapolate to predict the unknown Modelmaking: formalize all the above into useful models


Some Physics: Wavelength of the Signaland Its Influence on Propagation

Radio signals in the atmosphere travel at the speed of light

= wavelengthC = distance traveled in 1 secondF = frequency, Hertz

The wavelength of a radio signal determines many of its propagation characteristics

Internal antenna elements size are typically in the order of 1/4 to 1/2 wavelength

Objects bigger than a wavelength can reflect or obstruct RF energy

RF energy can penetrate into a building or vehicle if it has openings the size of a wavelength, or larger

C / FFrequency,

GHz.Wavelengthcm. in.

0.92 32.6 12.82.4 12.5 4.95.8 5.2 2.0

/2

Propagation Effects of Earths Atmosphere

Earths unique atmosphere supports life (ours included) and also introduces many propagation effects -- some useful, some troublesome

Skywave Propagation: reflection from Ionized Layers LF and HF frequencies (below roughly 50 MHz.) are

routinely reflected off layers of the upper atmosphere which become ionized by the sun

this phenomena produces intermittent world-wide propagation and occasional total outages

this phenomena is strongly correlated with frequency, day/night cycles, variations in earths magnetic field, 11-year sunspot cycle

these effects are negligible for wireless systems at their much-higher frequencies


More Atmospheric Propagation Effects

Attenuation at Microwave Frequencies rain droplets can substantially attenuate RF signals

whose wavelengths are comparable to, or smaller than, droplet size

rain attenuations of 20 dB. or more per km. are possible troublesome mainly above 10 GHz., and in tropical

areas must be considered in reliability calculations during path

design not major factor in wireless systems propagation

Diffraction, Wave Bending, Ducting signals 50-2000 MHz. can be bent or reflected at

boundaries of different air density or humidity phenomena: very sporadic unexpected long-distance

propagation beyond the horizon. May last minutes or hours

can occur in wireless systems

Refraction by air layers

Ducting by air layers

>100 mi.

Rain Fades onMIcrowave Links



Dominant Mechanisms of Mobile PropagationMost propagation in the mobile

environment is dominated by these three mechanisms:

Free space No reflections, no obstructions

first Fresnel Zone clear Signal spreading is only mechanism Signal decays 20 dB/decade

Reflection Reflected wave 180out of phase Reflected wave not attenuated much Signal decays 30-40 dB/decade

Knife-edge diffraction Direct path is blocked by obstruction Additional loss is introduced Formulae available for simple cases

Well explore each of these further...

Knife-edge Diffraction

Reflection with partial cancellation

B

A

d

D

Free Space


Propagation: Getting the Signal to the Customer

Propagation is the name for the general process of getting a radio signal from one place to another

During propagation, the signal gets weaker because of several natural processes. This weakening is called attenuation.

Point-to-point radio links work best when there is line-of-sight between the two antennas. This is the condition of least attenuation

nothing along the way to block the signal In mobile systems, line-of-sight only happens near base stations or from

high spots (hilltops, top floors of buildings and parking garages, etc.)

AP SM


The First Fresnel Zone and Free-Space Propagation

Most of the signal power sent from one antenna to another travels in an elliptical, football shape called the First Fresnel zone. the thickness of the zone depends on the signal frequency

If the First Fresnel zone is free of penetration or obstruction by any objects, we say free-space conditions apply this is the desirable condition providing highest received signal strength

Sometimes obstructions are unavoidable, and penetrate the first fresnel zone this attenuates the signal and reduces the signal strength received at the

other end of the link the amount of attenuation depends on the degree of penetration by the

obstruction, and its absorbing characteristics

Frequency,GHz.

Path,Miles

Mid-PtFresnel

R, ft0.92 10 1192.4 10 745.8 10 47

AP SM

LoS, nLoS, and NLoS Definitions

Line of Site(LoS)

Near Line of Site

(nLoS)

Non Line of Site

(NLoS)



Free-Space Propagation Technical Details

The simplest propagation mode Antenna radiates energy which spreads in space Path Loss, db (between two isotropic antennas)

= 36.58 +20*Log10(FMHZ)+20Log10(DistMILES ) Path Loss, db (between two dipole antennas)

= 32.26 +20*Log10(FMHZ)+20Log10(DistMILES ) Notice the rate of signal decay: 6 db per octave of distance change, which is

20 db per decade of distance change Free-Space propagation is applicable if:

there is only one signal path (no reflections) the path is unobstructed (i.e., first Fresnel zone

is not penetrated by obstacles)

First Fresnel Zone ={Points P where AP + PB - AB < }Fresnel Zone radius d = 1/2 (D)^(1/2)

1st Fresnel Zone

B

A

d

D

Free Space Spreading Lossenergy intercepted by receiving antenna is proportional to 1/r2

r


Path Profiles from Propagation Prediction Tools

Propagation models can also prepare automated path profiles From a path profile, you can quickly determine whether the path is

line-of-sight or obstructed


Reflection With Partial Cancellation

Mobile environment characteristics: Small angles of incidence and reflection Reflection is unattenuated (reflection coefficient =1) Reflection causes phase shift of 180 degrees

Analysis Physics of the reflection cancellation predicts signal

decay of 40 dB per decade of distance

Heights Exaggerated for Clarity

HTFTHTFT

DMILES

Comparison of Free-Space and Reflection Propagation ModesAssumptions: Flat earth, TX ERP = 50 dBm, @ 1950 MHz. Base Ht = 200 ft, Mobile Ht = 5 ft.

Received Signal in Free Space, DBMReceived Signal inReflection Mode

DistanceMILES-52.4-69.0

1-58.4-79.2

2-64.4-89.5

4-67.9-95.4

6-70.4-99.7

8-72.4-103.0

10-75.9-109.0

15-78.4-113.2

20

Path Loss [dB ]= 172 + 34 x Log (DMiles )- 20 x Log (Base Ant. HtFeet)

- 10 x Log (Mobile Ant. HtFeet)

SCALE PERSPECTIVE


Signal Decay Rates in Various Environments

Weve seen how the signal decays with distance in two basic modes of propagation:

Free-Space 20 dB per decade of distance 6 db per octave of distance

Reflection Cancellation 40 dB per decade of distance 12 db per octave of distance

Real-life wireless propagation decay rates are typically somewhere between 30 and 40 dB per decade of distance

Signal Level vs. Distance

-40

-30

-20

-10

0

Distance, Miles1 3.16 102 5 7 86

One Octaveof distance (2x)

One Decadeof distance (10x)


Obstructions and their Effects

When an obstruction penetrates the first fresnel zone, the signal is attenuated. The degree of attenuation depends on

how much of the first fresnel zone is obstructed the absorptive characteristics of the obstructing object(s) whether the signal is also reflecting off of other nearby objects,

possibly providing a degree of fill-in Depending on the length of the path, the transmitter power, and

the receiver sensitivity, the link may still work despite the obstruction

AP SM


Severe Obstructions

When the path is blocked by a major obstruction (large hill, downtown building, etc.) there will be substantial signal attenuation

Even under this undesirable condition, if the distance is small there may be enough signal to make the link usable

A very small amount of the signal will actually diffract (bend) over the obstruction

the extra attenuation caused by the obstruction can be calculated by the knife edge diffraction model

this diffraction loss can be considered in the link budget to see if the link is likely to be usable anyway

AP SM


Knife-Edge Diffraction Sometimes a single well-defined

obstruction blocks the path, introducing additional loss. This calculation is fairly easy and can be used as a manual tool to estimate the effects of individual obstructions.

First calculate the diffraction parameter from the geometry of the path

Next consult the table to obtain the obstruction loss in db

Add this loss to the otherwise-determined path loss to obtain the total path loss.

Other losses such as free space and reflection cancellation still apply, but computed independently for the path as if the obstruction did not exist

H

R1 R2

attendB

0-5

-10-15-20-25

-4 -3 -2 -1 0 1 2 3-5

= -H R1 R22 ( R1 + R2)


Foliage and Building Penetration Considerations

At broadband wireless frequencies, the penetration loss entering a building often exceeds 35 db.

this restricts range so greatly that antennas are almost never located inside a building

At broadband wireless frequencies, trees and other vegetation effectively block and absorb the signal

typical attenuation for just one mature tree can be 20 db or more

Unfortunately, neither building nor vegetation loss can be predicted accurately. Measurement is the only way to know accurately what is happening.

Building

SM

AP

BuildingSM

AP


Combating Rayleigh Fading: Space Diversity

Fortunately, Rayleigh fades are very short and last a small percentage of the time

Two antennas separated by several wavelengths will not generally experience fades at the same time

Space Diversity can be obtained by using two receiving antennas and switching instant-by-instant to whichever is best

Required separation D for good decorrelation is 10-20

12-24 ft. @ 800 MHz. 5-10 ft. @ 1900 MHz.

Signal received by Antenna 1

Signal received by Antenna 2

Combined Signal

D


Types Of Propagation Models And Their Uses

Simple Analytical models Used for understanding and

predicting individual paths and specific obstruction cases

General Area models Primary drivers: statistical Used for early system

dimensioning (cell counts, etc.) Point-to-Point models

Primary drivers: analytical Used for detailed coverage

analysis and cell planning Local Variability models

Primary drivers: statistical Characterizes microscopic level

fluctuations in a given locale, confidence-of-service probability

Simple Analytical Free space (Friis formula) Reflection cancellation Knife-edge diffraction

Area Okumura-Hata Euro/Cost-231 Walfisch-Betroni/Ikegami

Point-to-Point Ray Tracing

- Lees Method, others Tech-Note 101 Longley-Rice, Biby-C

Local Variability Rayleigh Distribution Normal Distribution Joint Probability Techniques

Examples of various model types


General Principles Of Area Models

Area models mimic an averagepath in a defined area

Theyre based on measured data alone, with no consideration of individual path features or physical mechanisms

Typical inputs used by model: Frequency Distance from transmitter to

receiver Actual or effective base

station & mobile heights Average terrain elevation Morphology correction loss

(Urban, Suburban, Rural, etc.) Results may be quite different

than observed on individual paths in the area

RSSI, dBm

-120

-110

-100

-90

-80

-70

-60

-50

0 3 6 9 12 15 18 21 24 27 30 33

Distance from Cell Site, km

FieldStrength,dBV/m

+90

+80

+70

+60

+50

+40

+30

+20

Green Trace shows actual measured signal strengths on a drive test radial, as determined by real-world physics.

Red Trace shows the Okumura-Hata prediction for the same radial. The smooth curve is a good fit for real data. However, the signal strength at a specific location on the radial may be much higher or much lower than the simple prediction.


The Okumura Model: General Concept

The Okumura model is based on detailed analysis of exhaustive drive-test measurements made in Tokyo and its suburbs during the late 1960s and early 1970s. The collected date included measurements on numerous VHF, UHF, and microwave signal sources, both horizontally and vertically polarized, at a wide range of heights.

The measurements were statistically processed and analyzed with respect to almost every imaginable variable. This analysis was distilled into the curves above, showing a median attenuation relative to free space loss Amu (f,d) and correlation factor Garea (f,area), for BS antenna height ht = 200 m and MS antenna height hr = 3 m.

Okumura has served as the basis for high-level design of many existing wireless systems, and has spawned a number of newer models adapted from its basic concepts and numerical parameters.

M

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d

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n

A

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A

(

f

,

d

)

,

d

B

1

2

5

40

70

80

100

100 3000500Frequency f, MHz

10

50

70 Urban Area

d

,

k

m

30

850

26

35

100 200 300 500 700 1000 2000 3000Frequency f, (MHz)

5

10

15

20

25

30

C

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,

G

a

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(

d

B

)

9 dB

850 MHz


Structure of the Okumura Model

The Okumura Model uses a combination of terms from basic physical mechanisms and arbitrary factors to fit 1960-1970 Tokyo drive test data

Later researchers (HATA, COST231, others) have expressed Okumuras curves as formulas and automated the computation

Path Loss [dB] = LFS + Amu(f,d) - G(Hb) - G(Hm) - Garea

Free-Space Path Loss

Base StationHeight Gain

= 20 x Log (Hb/200)

Mobile StationHeight Gain

= 10 x Log (Hm/3)

Amu(f,d) Additional Median Loss

from Okumuras Curves

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A

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(

f

,

d

)

,

d

B

1

2

5

40

70

80

100

100 3000500

Frequency f, MHz10

50

70Urban Area

d

,

k

m

30

850

26

Morphology Gain0 dense urban5 urban10 suburban17 rural

35

100 200 300 500 700 1000 2000 3000Frequency f, (MHz)

5

10

15

20

25

30

C

o

r

r

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f

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c

t

o

r

,

G

a

r

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(

d

B

)

850 MHz


Examples of Morphological Zones Suburban: Mix of

residential and business communities. Structures include 1-2 story houses 50 feet apart and 2-5 story shops and offices.

Urban: Urban residential and office areas (Typical structures are 5-10 story buildings, hotels, hospitals, etc.)

Dense Urban: Dense business districts with skyscrapers (10-20 stories and above) and high-rise apartments

Suburban Suburban

UrbanUrban

Dense Urban Dense Urban

Although zone definitions are arbitrary, the examples and definitions illustrated above are typical of practice in North American PCS designs.


Example Morphological Zones

Rural - Highway: Highways near open farm land, large open spaces, and sparsely populated residential areas. Typical structures are 1-2 story houses, barns, etc.

Rural - In-town: Open farm land, large open spaces, and sparsely populated residential areas. Typical structures are 1-2 story houses, barns, etc.Suburban

Rural

Suburban

Rural

Rural - HighwayRural - Highway

Notice how different zones may abruptly adjoin one another. In the case immediately above, farm land (rural) adjoins built-up subdivisions (suburban) -- same terrain, but different land use, penetration requirements, and anticipated traffic densities.

Radio Network Planning Tools -Basics



Rough Planning with Propagation Prediction Tools

Access Point locations can be compared using commercial propagation prediction tools

Tools include terrain databases and land-use or land-cover data to predict the signal levels between the AP and neighborhoods needing service

the AP antenna patterns can also be included in the model

Actual field test measurements should be used to tune the model parameters for best agreement with the field data

Such models are especially valuable for analyzing effects of terrain obstructions


Typical Model Results Including Environmental Correction

TowerHeight,

mEIRP

(watts)C,dB

Range,kmf = 870 MHz.

Dense UrbanUrban

SuburbanRural

30303050

200200200200

-2-5-10-26

4.04.96.726.8

Okumura/Hata

TowerHeight,

mEIRP

(watts)C,dB

Range,kmf =1900 MHz.

Dense UrbanUrban

SuburbanRural

30303050

200200200200

0-5-10-17

2.523.504.810.3

COST-231/Hata


Propagation at 1900 MHz. vs. 800 MHz.

Propagation at 1900 MHz. is similar to 800 MHz., but all effects are more pronounced.

Reflections are more effective Shadows from obstructions are deeper Foliage absorption is more attenuative Penetration into buildings through openings is more effective,

but absorbing materials within buildings and their walls attenuate the signal more severely than at 800 MHz.

The net result of all these effects is to increase the contrast of hot and cold signal areas throughout a 1900 MHz. system, compared to what would have been obtained at 800 MHz.

Overall, coverage radius of a 1900 MHz. BTS is approximately two-thirds the distance which would be obtained with the same ERP, same antenna height, at 800 MHz.


Walfisch-Betroni/Walfisch-Ikegami Models

Ordinary Okumura-type models do work in this environment, but the Walfisch models attempt to improve accuracy by exploiting the actual propagation mechanisms involved

Path Loss = LFS + LRT + LMS

LFS = free space path loss (Friis formula)LRT = rooftop diffraction lossLMS = multiscreen reflection loss Propagation in built-up portions of cities is

dominated by ray diffraction over the tops of buildings and by ray channeling through multiple reflections down the street canyons

-20 dBm-30 dBm-40 dBm-50 dBm-60 dBm-70 dBm-80 dBm-90 dBm-100 dBm-110 dBm-120 dBm

Signal Level

Legend

Area View


Elements of Propagation Measurement Systems

WirelessReceiver

PC or Collector

GPSReceiver

DeadReckoning

Main Features Field strength measurement

Accurate collection in real-time Multi-channel, averaging

capability Location Data Collection Methods:

Global Positioning System (GPS) Dead reckoning on digitized map

database using on-board compass and wheel revolutions sensor

A combination of both methods is recommended for the best results

Ideally, a system should be calibrated in absolute units, not just raw received power level indications

Record normalized antenna gain, measured line loss


Typical Test Transmitter Operations

Typical Characteristics portable, low power needs weatherproof or weather resistant regulated power output frequency-agile: synthesized

Operational Concerns spectrum coordination and proper

authorization to radiate test signal antenna unobstructed stable AC power SAFETY:

people/equipment falling due to wind, or tripping on obstacles

electric shock damage to rooftop

Statistical TechniquesDistribution Statistics Concept

An area model predicts signal strength Vs. distance over an area

This is the median or most probable signal strength at every distance from the cell

The actual signal strength at any real location is determined by local physical effects, and will be higher or lower

It is feasible to measure the observed median signal strength M and standard deviation

M and can be applied to find probability of receiving an arbitrary signal level at a given distance

Median Signal Strength

,dB

Occurrences

RSSI

Normal Distribution

RSSI,dBm

Distance

Signal Strength predictedby area model

Signal Strength Predicted Vs. Observed

Observed Signal Strength


Statistical TechniquesPractical Application Of Distribution Statistics

General Approach: Use a model to predict RSSI Compare measurements with model

obtain median signal strength M obtain standard deviation now apply correction factor to obtain field

strength required for desired probability of service

Applications: Given A desired outdoor signal level (dbm) The observed standard deviation from signal

strength measurements A desired percentage of locations which must

receive that signal level Compute a cushion in dB which will give us

that % coverage confidence

RSSI,dBm

Distance

10% of locations exceed this RSSI

50%

90%

Percentage of locations where observed RSSI exceeds predicted

RSSI

Median Signal Strength ,

dB

Occurrences

RSSI

Normal Distribution


Cell Edge Area Availability And Probability Of Service

Overall probability of service is best close to the BTS, and decreases with increasing distance away from BTS

For overall 90% location probability within cell coverage area, probability will be 75% at cell edge

Result derived theoretically, confirmed in modeling with propagation tools, and observed from measurements

True if path loss variations are log-normally distributed around predicted median values, as in mobile environment

90%/75% is a commonly-used wireless numerical coverage objective

Recent publications by Nortels Dr. Pete Bernardin describe the relationship between area and edge reliability, and the field measurement techniques necessary to demonstrate an arbitrary degree of coverage reliability

Statistical View ofCell Coverage

Area Availability:90% overall within area

75%at edge of area

90%

75%


Application Of Distribution Statistics: Example

Lets design a cell to deliver at least -95 dBm to at least 75% of the locations at the cell edge (This will provide coverage to 90% of total locations within the cell)

Assume that measurements you have made show a 10 dB standard deviation

On the chart: To serve 75% of locations at the cell edge , we

must deliver a median signal strength which is.675 times stronger than -95 dBm

Calculate:- 95 dBm + ( .675 x 10 dB ) = - 88 dBm

So, design for a median signal strength of -88 dBm!

Standard Deviations from Median (Average) Signal Strength

Cumulative Normal Distribution

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

-3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3

75%

0.675


Statistical Techniques:Normal Distribution Graph & Table For Convenient

ReferenceCumulative Normal Distribution

Standard Deviation from Mean Signal Strength

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

-3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3

CumulativeProbability

0.1%

1%

5%

10%

StandardDeviation

-3.09

-2.32

-1.65

-1.28

-0.84 20%

-0.52 30%

0.675 75%

0 50%

0.52 70%

0.84 80%

1.28 90%

1.65 95%

2.35 99%

3.09 99.9%

3.72 99.99%

4.27 99.999%


Composite Probability Of ServiceAdding Multiple Attenuating Mechanisms

For an in-building user, the actual signal level includes regular outdoor path attenuation plus building penetration loss

Both outdoor and penetration losses have their own variabilities with their own standard deviations

The users overall composite probability of service must include composite median and standard deviation factors

COMPOSITE = ((OUTDOOR)2+(PENETRATION)2)1/2LOSSCOMPOSITE = LOSSOUTDOOR+LOSSPENETRATION

Building

Outdoor Loss + Penetration Loss


Composite Probability of ServiceCalculating Fade Margin For Link Budget

Example Case: Outdoor attenuation is 8 dB., and penetration loss is 8 dB. Desired probability of service is 75% at the cell edge

What is the composite ? How much fade margin is required?

Composite Probability of ServiceCalculating Required Fade Margin

EnvironmentType

(morphology)MedianLoss,

dB

Std.Dev., dB

Urban Bldg. 15 8

Suburban Bldg. 10 8

Rural Bldg. 10 8

8 4Typical Vehicle

Dense Urban Bldg. 20 8

BuildingPenetration

Out-Door

Std.Dev., dB

8

8

8

8

8

CompositeTotal

AreaAvailabilityTarget, %

90%/75% @edge

90%/75% @edge

90%/75% @edge

90%/75% @edge

90%/75% @edge

FadeMargin

dB

7.6

7.6

7.6

6.0

7.6

COMPOSITE = ((OUTDOOR)2+(PENETRATION)2)1/2= ((8)2+(8)2)1/2 =(64+64)1/2 =(128)1/2 = 11.31 dB

On cumulative normal distribution curve, 75%

probability is 0.675 above median. Fade Margin required =

(11.31) (0.675) = 7.63 dB.Cumulative Normal Distribution

Standard Deviations from Median (Average) Signal Strength

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

-3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3

75%

.675


RF propagationPropagation loss in non free space

For outdoor usage models have been created that include

path loss coefficient up to a measured breakpoint (

path loss coefficient beyond measured breakpoint (

breakpoint depend on antenna height (dbr)

L(2.4GHz) = 40 +10 * * log(dbr) + 10 * * log(d/dbr)November, 2014 RF Bootcamp - Course RF100 v10.0 - (c) 2014 Tonex RF100 - 83

Link Budget Analysis

Since each bit rate requires a specific receive sensitivity for a given radio, any wireless network (simply referred to as link for the purpose of this discussion) design must estimate the available link budget in dB to make sure that that the link budget is at least 0 dB for the highest bit rate desired.

It is also a good practice to leave some reasonable margin (e.g., 10 dB) in the link budget to accommodate any variations in signal strength caused by interferers or reflectors and to increase the reliability of the link.

The link budget analysis can be used to estimate the range or capacity or to select an antenna.


Link Budget Calculation

The first step in the calculation of the link budget is to calculate the received power at the receiver.

The Received Power is given as: Received Power = Radiated Power/EIRP Path Loss + Receiver Gain

The radiated power (EIRP or Effective Isotropic Radiated Power is the correct technical term) in dBm is given as:

EIRP (dBm) = Radio Transmit Power (dBm) Cable/Connector/Switch Loss (dB) at Transmitter + Transmit Antenna Gain (dBi)

The Path Loss can be calculated using the appropriate path loss exponent, as discussed earlier, and may include attenuations caused by other objects in the path, if known. The Receiver Gain is given as:

Receiver Gain = Receive Antenna Gain (dBi) - Cable/Connector/Switch Loss (dB) at Receiver


Link Budget

One important point to note here is that the antenna gain is reciprocal, i.e., the antenna gain can be added to the wireless device at either end to increase the overall link budget. For example, a wireless system with a 10 dBi antenna on the transmitter and a 2 dBi antenna on the receiver will have the same range as a system with a 4 dBi antenna the transmitter and an 8 dBi antenna on the receiver, everything else being equal. Therefore, adding a high gain antenna allows a device not only to transmit signals farther, but also to receive weaker signals.

Once the received power (or signal strength) is known, the link budget can be calculated by subtracting the receive sensitivity of the receiver from the received power, i.e.,

Link Budget = Received Power Receive Sensitivity

The Noise Floor at the receiver can be subtracted from the received power to calculate the SNR. If the noise is lower than the Rx sensitivity, the link will be limited by the Rx sensitivity. Otherwise, the link will be limited by the Noise Floor.


An Example

For example, with 30 dB EIRP (e.g., 23 dBm Transmit Power, 10 dBi antenna gain and 3 dB cable/connector loss) in 2.4 GHz, the signal attenuates to -50 dBm at 100 meters in free space. For a receiver with Receive Gain of 0 dB (e.g., 2 dBi Receiver antenna and 2 dB cable/connector loss), the received power is -50 dBm.

If the receive sensitivity is -91 dBm for 1 Mbps, then the link margin is 41 dB. However, if the Noise Floor is -85 dBm, then the SNR is 35 dB. In either case, the signal is more than enough to decode 1 Mbps. However, as the distance increases the Noise Floor will be the limiting factor in this specific example.



Link BudgetsLink Budgets


Link Budget Example: Usage Model and Service Assumptions

This section outlines the number of subscribers and amount of traffic by year

This section shows the variability of outdoor and indoor signals, and the building penetration loss

Interactive Initial System Design Example v1.2fill in GREEN fieldsYELLOW fields calculate automatically

Step 1. Basic Business Plan Details

Year Launch 1 2 3 4 5Population 3,886,000 3,949,350 4,012,700 4,076,050 4,139,400 4,202,750Penetration, % 0.05% 1.85% 3.72% 5.64% 7.60% 9.57%#Customers 1,781 72,933 149,453 229,941 314,451 402,360BH Erl/Cust 0.1 0.05 0.045 0.05 0.05 0.05Total BH erl 178.1 3,646.7 6,725.4 11,497.0 15,722.6 20,118.0

2. Enter building penetration loss and standard deviations from measurements.

Composite Probability Of Service & Required Fade MarginEnvironment

Type ("morphology")

Building Median

Loss, dB

Building Std. Dev,

dB

Outdoor Std. Dev,

dB.

Composite Standard Deviation

Desired Reliability at Cell Edge, %

Fade Margin,

dB.Dense Urban 20 8 8 11.31 75.0% 7.63Urban 15 8 8 11.31 75.0% 7.63Suburban 15 8 8 11.31 75.0% 7.63Rural 10 8 8 11.31 75.0% 7.63Highway 8 6 8 10.00 75.0% 6.74


Reverse Link Budget Example

The Reverse Link Budget describes how the energy from the phone is distributed to the base station, including the major components of loss and gain within the system

3. Construct Link Budgets

Reverse Link Budget

Term or Factor GivenDense Urb. Urban Suburban Rural Highway Formula

MS TX Power (dbm) (+) 23MS antenna gain and body loss (+/-) 0MS EIRP (dBm) (+) 23.00 23.00 23.00 23.00 23.00 AFade Margin, (dB) (-) -7.63 -7.63 -7.63 -7.63 -6.74 BSoft Handoff Gain (dB) (+) 4 4 4 4 4 CReceiver Interf. Margin (dB) (-) -3 -3 -3 -3 -3 DBuilding Penetration Loss (dB) (-) -20.00 -15.00 -15.00 -10.00 -8.00 EBTS RX antenna gain (dBi) (+) 17 17 17 17 17 FBTS cable loss (dB) (-) -3 -3 -3 -3 -3 G

kTB (dBm/14.4 KHz.) -132.4 HBTS noise figure (dB) 6.5 I

Eb/Nt (dB) 5.9 JBTS RX sensitivity (dBm) (-) -120.0 -120.0 -120.0 -120.0 -120.0 H+I+J

Survivable Uplink Path Loss (dB) (+) 130.4 135.4 135.4 140.4 143.3

A+B+C+D+E+F+G-(H+I+J)


Forward Link Budget Example

This section shows the forward link power distribution, and compares the relative balance of the forward and reverse links

Forward Link Budget

Term or Factor GivenDense Urb. Urban Suburban Rural Highway Formula

BTS TX power (dBm) (+) 45 45 45 45 45BTS TX power (watts) 31.62 31.62 31.62 31.62 31.62% Power for traffic channels 74.0% 74.0% 74.0% 74.0% 74.0%Number of Traffic Channels in use 19 19 19 19 19BTS cable loss (dB) (-) -3 -3 -3 -3 -3BTS TX antenna gain (dBi) (+) 17 17 17 17 17BTS EIRP/traffic channel (dBm) (+,-) 44.9 44.9 44.9 44.9 44.9 AFade margin (dB) (-) -7.63 -7.63 -7.63 -7.63 -6.74 BReceiver interference margin (db) (-) -3 -3 -3 -3 -3 CBuilding Penetration Loss (dB) (-) -20.0 -15.0 -15.0 -10.0 -8.0 DMS antenna gain & body loss (dB) (+,-) 0 0 0 0 0 E

kTB (dBm/14.4 KHz.) -132.4Subscriber RX noise figure (dB) 10.5

Eb/Nt (dB) 6Subscriber RX sensitivity (dBm) (-) -115.9 -115.9 -115.9 -115.9 -115.9 F

Survivable Downlink Path Loss, dB (+) 130.2 135.2 135.2 140.2 143.1A+B+C+D

+E-F

Forward/Reverse Link Balance DenseUrban Urban Suburban Rural Highway

Which link is dominant? Reverse Reverse Reverse Reverse ReverseWhat advantage, dB? 0.2 0.2 0.2 0.2 0.2


Link Budgets: What is the Radius of a Cell?

This section uses the Okumura-Hata/Cost-231 model to describe the frequency, antenna heights, and environmental factors, and their relationship on the cells coverage distance

4. Explore propagation model to figure coverage radius of cell.

Frequency, MHz. 870Subscriber Antenna Height, M 1.5

DenseUrban Urban Suburban Rural Highway

Base Station Antenna Height, M 20 20 30 50 50

DenseUrban Urban Suburban Rural Highway

Environmental Correction, dB -2 -5 -10 -17 -17

Coverage Radius, kM 1.30 2.17 6.87 20.86 25.40Coverage Radius, Miles 0.81 1.35 4.27 12.96 15.78


Link Budgets: Putting It All Together

Step 4 estimates the number of cells required to serve each distinct environment within the system

Steps 5, 6, and 7 estimate the RF coverage from each cell, and the number of cells required

5. Calculate number of cells required for coverage, ignoring traffic considerations.

Dense TotalUrban Urban Suburban Rural Highway # Cells

Covered Area of this type, kM^2 55 450 1700 3400 1400 RequiredOne cell's coverage in this zone, kM^2 5.35 14.73 148.46 1367.34 2026.72 for System

# Cells required to cover zone 10.3 30.6 11.5 2.5 0.7 55.5

6. What is the traffic capacity (in erlangs) of your chosen BTS configuration, year-by-year?

Year Launch 1 2 3 4 5Erlangs which one BTS can carry 18.3 18.3 90 90 450 450

7, 8. What is the total busy-hour erlang traffic on your system? How many BTS are required?

Year Launch 1 2 3 4 5Total System Busy-Hour Erlangs 178.1 3,646.7 6,725.4 11,497.0 15,722.6 20,118.0

Capacity of One BTS, erlangs 18.3 18.3 90 90 450 450# BTS required to handle all the traffic 9.7 199.3 74.7 127.7 34.9 44.7

9. Examine your market, #BTS required for coverage and capacity; estimate totalnumber of BTS required.

Year Launch 1 2 3 4 5#BTS req'd just to achieve coverage 55.5 55.5 55.5 55.5 55.5 55.5

#BTS required just to carry traffic 9.7 199.3 74.7 127.7 34.9 44.7Estimated total #BTS required 56.3 206.8 206.8 206.8 206.8 206.8

Radio Link - Simplified Model

Tx Rx

Attenuator

Lt LrPt Pr

Gt Gr

Lp

free space path obstruction atmospheric gases multipath beam spreading variation of angle of arrival and launch Precipitation (rainfall) sand and dust storms


Link Budget Calculations

TxTx RxRxd = 12 km

f = 18 GHz

Pt = 23 dBm

Lt = 1.5 dB

Gt = 38 dBiGr = 38 dBi

Lr = 1.5 dB

Pr = ? dBm

Pr = Pt - Lt + Gt - Lp + Gr - Lr dBm

Lp = 92.45 + 20 log(18) + 20 log(12) = 119.11 dBm

Pr = 23 - 1.5 + 38 119.11 + 38 - 1.5 = -23dBm


Path Loss Calculations

The simplest propagation mode Antenna radiates energy which spreads in space

Lp or Path Loss, db (between two isotropic antennas) = 36.56 +20*Log10(F MHZ)+20Log10(Dist MILES )

Lp or Path Loss, db (between two dipole antennas) = 32.26 +20*Log10(F MHZ)+20Log10(Dist MILES )

Lp = Path Loss, db (between two isotropic antennas) = 92.45 (30+62.45) + 20 log(FGHz) + 20 log( Distance km)


Passive Repeater Configuration

TxTx

RxRx

d = 0.8 km

f = 18 GHzPt = 23 dBm

Lt = 1.5 dB

Gt = 38 dBi

Gr = 38 dBi

Lr = 1.5 dB

Pr = ? dBm

d = 12 km

Gt = 42 dBi

Gt = 42 dBi

1 dB


RF propagation Simple Path Analysis Concept (alternative)

WP II

PC Card

pigtail cable

Lightning Protector

RF Cable Antenna

WP II

PC Card

pigtail cable

Lightning Protector

RF CableAntenna

+ Transmit Power

- LOSS Cable/connectors

+ Antenna Gain + Antenna Gain

- LOSS Cable/connectors

RSL (receive signal level) or P r> sensitivity + Fade Margin

- Path Loss over link distance

Calculate signal in one direction if Antennas and active components are equal


RF propagation FADE MARGIN

WP II

Tx =15 dBm

1.3 dB

.7 dB

50 ft.LMR 400

3.4 dB 24 dBi

WP II

Rx = -82 dBm

1.3 dB

.7 dB

50 ft.LMR 400

3.4 dB24 dBi parabolic

For a Reliable link - the signal arriving at the receiver - should be greater than the Sensitivity of the Radio (-82dBm for 11 Mbit)

This EXTRA signal strength is FADE MARGIN

FADE MARGIN can be equated to UPTIME

Minimum Fade Margin = 10 dB

Links subject to interference (city) = 15dB

Links with Adverse Weather = 20dB

Calculate RSL > -82 + 10 = -72dBm


RF propagation Sample Calculation

WP II

Tx =15 dBm

1.3 dB

.7 dB

50 ft.LMR 400

3.4 dB 24 dBi

WP II

Rx = -82 dBm

1.3 dB

.7 dB

50 ft.LMR 400

3.4 dB24 dBi parabolic

RSL > PTx - Cable Loss + Antenna Gain - Path loss + Antenna Gain - Cable Loss

16 Km = - 124 dB

+ 15 dBm

- 2 dB

- 3.4 dB

+ 24 dBi

- 124 dB

+ 24 dBi

- 3.4 dB

- 2 dB

- 71.8 dB > -72

This lets us know that if the Fresnel zone is clear, the Link should work. If RSL < than -72 then MORE GAIN is needed, using Higher Gain Antennas or Lower loss Cables or Amplifiers (not a Agere Systems provided option)


Earth Curvature

Obstacle Clearance

Fresnel Zone Clearance Antenna

HeightAntenna Height

Midpoint clearance = 0.6F + Earth curvature + 10' when K=1First Fresnel Distance (meters) F1= 17.3 [(d1*d2)/(f*D)]1/2 where D=path length Km, f=frequency (GHz) , d1= distance from Antenna1(Km) , d2 = distance from Antenna 2 (Km)Earth Curvature h = (d1*d2) /2 where h = change in vertical distance from Horizontal line (meters), d1&d2 distance from antennas 1&2 respectively

Clearance for Earths Curvature 13 feet for 10 Km path200 feet for 40 Km path

Fresnel Zone Clearance = 0.6 first Fresnel distance (Clear Path for Signal at mid point) 30 feet for 10 Km path

57 feet for 40 Km path

RF PropagationAntenna Height requirements


RF Propagation Reflections

Signals arrive 180 out of phase ( 1/2 ) from reflective surface Cancel at antenna - Try moving Antenna to change geometry of link - 6cm is the

difference in-phase to out of phase



Elements of Typical Measurement Systems

WirelessReceiver

PC or Collector

GPSReceiver

DeadReckoning

Main Features Field strength measurement

Accurate collection in real-time Multi-channel, averaging

capability Location Data Collection Methods:

Global Positioning System (GPS) Dead reckoning on digitized map

database using on-board compass and wheel revolutions sensor

A combination of both methods is recommended for the best results

Ideally, a system should be calibrated in absolute units, not just raw received power level indications

Record normalized antenna gain, measured line loss


Typical Test Transmitter Operations

Typical Characteristics portable, low power needs weatherproof or weather resistant regulated power output frequency-agile: synthesized

Operational Concerns spectrum coordination and proper

authorization to radiate test signal antenna unobstructed stable AC power SAFETY:

people/equipment falling due to wind, or tripping on obstacles

electric shock damage to rooftop


Antennas for Wireless Systems

Antennas for Wireless Systems

Dipole

Typical WirelessOmni Antenna

Isotropic


Understanding Antenna RadiationThe Principle Of Current Moments

An antenna is just a passive conductor carrying RF current

RF power causes the current flow

Current flowing radiates electromagnetic fields

Electromagnetic fields cause current in receiving antennas

The effect of the total antenna is the sum of what every tiny slice of the antenna is doing

Radiation of a tiny slice is proportional to its length times the magnitude of the current in it, at the phase of the current

TX RX

Width of banddenotes current

magnitude

Zero currentat each end

Maximum currentat the middle

Current induced inreceiving antennais vector sum of

contribution of everytiny slice of

radiating antenna

each tiny imaginary sliceof the antennadoes its share

of radiating

Polarization of an Antenna and its Effects

To intercept significant energy, a receiving antenna must be oriented parallel to the transmitting antenna

A receiving antenna oriented at right angles to the transmitting antenna is cross-polarized; will have very little current induced

Vertical polarization is the default convention in wireless telephony In the cluttered urban environment, energy becomes scattered and de-

polarized during propagation, so polarization is not as critical Handset users hold the antennas at seemingly random angles..

TX

ElectromagneticField

currentalmost

nocurrent

Antenna 1VerticallyPolarized

Antenna 2Horizontally

Polarized

RX

RF current in a conductor causes electromagnetic fields that seek to induce current flowing in the same directionin other conductors.

The orientation of the antenna is called its polarization.



Antenna Gain

Antennas are passive devices: they do not produce power

Can only receive power in one form and pass it on in another, minus incidental losses

Cannot generate power or amplify However, an antenna can appear to have gain

compared against another antenna or condition. This gain can be expressed in dB or as a power ratio. It applies both to radiating and receiving

A directional antenna, in its direction of maximum radiation, appears to have gain compared against a non-directional antenna

Gain in one direction comes at the expense of less radiation in other directions

Antenna Gain is RELATIVE, not ABSOLUTE When describing antenna gain, the

comparison condition must be stated or implied

Omni-directionalAntenna

DirectionalAntenna


Reference AntennasDefining Gain And Effective Radiated Power

Isotropic Radiator Truly non-directional -- in 3 dimensions Difficult to build or approximate physically,

but mathematically very simple to describe A popular reference: 1000 MHz and above

PCS, microwave, etc. Dipole Antenna

Non-directional in 2-dimensional plane only Can be easily constructed, physically

practical A popular reference: below 1000 MHz

800 MHz. cellular, land mobile, TV & FM

IsotropicAntenna

(watts or dBm) ERP Effective Radiated Power Vs. DipoleEffective Radiated Power Vs. Isotropic

Gain above Dipole referenceGain above Isotropic radiator

(watts or dBm) EIRP dBddBi

Quantity Units Dipole Antenna

Notice that a dipolehas 2.15 dB gaincompared to an isotropic antenna.


Radiation PatternsKey Features And Terminology

An antennas directivity is expressed as a series of patterns

The Horizontal Plane Pattern graphs the radiation as a function of azimuth (i.e..,direction N-E-S-W)

The Vertical Plane Pattern graphs the radiation as a function of elevation (i.e.., up, down, horizontal)

Antennas are often compared by noting specific landmark points on their patterns:

-3 dB (HPBW), -6 dB, -10 dB points

Front-to-back ratio Angles of nulls, minor lobes, etc.

Typical ExampleHorizontal Plane Pattern

0 (N)

90(E)

180 (S)

270(W)

0

-10

-20

-30 dB

Notice -3 dB points

Front-to-back Ratio

10 dBpoints

MainLobe

a MinorLobe

nulls orminima


In phase

Out of phase

How Antennas Achieve Their Gain

Quasi-Optical Techniques (reflection, focusing) Reflectors can be used to concentrate

radiation technique works best at microwave frequencies,

where reflectors are small Examples:

corner reflector used at cellular or higher frequencies

parabolic reflector used at microwave frequencies

grid or single pipe reflector for cellular

Array techniques (discrete elements) Power is fed or coupled to multiple

antenna elements; each element radiates Elements radiation in phase in some

directions In other directions, a phase delay for each

element creates pattern lobes and nulls


Types Of Arrays

Collinear vertical arrays Essentially omnidirectional in

horizontal plane Power gain approximately

equal to the number of elements

Nulls exist in vertical pattern, unless deliberately filled

Arrays in horizontal plane Directional in horizontal

plane: useful for sectorization Yagi

one driven element, parasitic coupling to others

Log-periodic all elements driven wide bandwidth

All of these types of antennas are used in wireless

RF power

RF power


Omni AntennasCollinear Vertical Arrays

The family of omni-directional wireless antennas:

Number of elements determines Physical size Gain Beamwidth, first null angle

Models with many elements have very narrow beamwidths

Require stable mounting and careful alignment

Watch out: be sure nulls do not fall in important coverage areas

Rod and grid reflectors are sometimes added for mild directivity

Examples: 800 MHz.: dB803, PD10017, BCR-10O, Kathrein 740-198

1900 MHz.: dB-910, ASPP2933

beamwidth

Angleof

firstnull

-3

dB

Vertical Plane Pattern

Number ofElements

PowerGain

Gain,dB

Angle

0.00 n/a3.01 26.574.77 18.436.02 14.046.99 11.317.78 9.468.45 8.139.03 7.139.54 6.3410.00 5.7110.41 5.1910.79 4.7611.14 4.40

1234567891011121314

1234567891011121314 11.46 4.09

Typical Collinear Arrays


Sector AntennasReflectors And Vertical Arrays

Typical commercial sector antennas are vertical combinations of dipoles, yagis, or log-periodic elements with reflector (panel or grid) backing

Vertical plane pattern is determined by number of vertically-separated elements

varies from 1 to 8, affecting mainly gain and vertical plane beamwidth

Horizontal plane pattern is determined by:

number of horizontally-spaced elements

shape of reflectors (is reflector folded?)

Vertical Plane PatternUp

Down

Horizontal Plane PatternN

E

S

W

Cassegrain a

Documents

Tonex RF Bootcamp