Tonex RF Bootcamp

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Tonex RF Bootcamp

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History of RF And

Early Telecommunications

History of RF And

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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 Maxwell’s Equations:

spectrum includes more than light • 1890’s First successful demos of

radio transmission

U

N S

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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 installed

Samuel F. B. Morse

at the peak of his career

Field Telegraphy

during the US Civil War, 1860’s

Submarine Cable Installation

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Telephony

 By the 1870’s, 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 1890’s, telephone service was available in most towns and cities across the USA

Telephone Line Installation Crew

1880’s

Alexander Graham Bell and his phone

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electric

field

magnetic

field

Propagation direction

Electromagnetic Radiation



Interrelated electric and magnetic fields

traveling through space



Electromagnetic radiation travels at about

c

= 310

8

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

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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 Marconi’s development of reliable radio telegraphy over ranges of 100 kM

 1902: Marconi’s 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 Marconi

radio pioneer, 1895

Lee De Forest

vacuum tube inventor MTS,

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Prefixes for Large and Small Units

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Wavelength, Frequency, and Energy Relationships

Wavelength (m) Frequency (Hz) Energy (J) Radio > 1 x 10-1 _{< 3 x 10}9 _{< 2 x 10}-24 Microwave 1 x 10-3 _{- 1 x 10}-1 _{3 x 10}9 _{- 3 x 10}11 _{2 x 10}-24_{- 2 x 10}-22 Infrared 7 x 10-7 _{- 1 x 10}-3 _{3 x 10}11 _{- 4 x 10}14 _{2 x 10}-22 _{- 3 x 10}-19 Optical 4 x 10-7 _{- 7 x 10}-7 _{4 x 10}14 _{- 7.5 x 10}14 _{3 x 10}-19 _{- 5 x 10}-19 UV 1 x 10-8 _{- 4 x 10}-7 _{7.5 x 10}14 _{- 3 x 10}16 _{5 x 10}-19 _{- 2 x 10}-17 X-ray 1 x 10-11 _{- 1 x 10}-8 _{3 x 10}16 _{- 3 x 10}19 _{2 x 10}-17 _{- 2 x 10}-14 Gamma-ray < 1 x 10-11 _{> 3 x 10}19 _{> 2 x 10}-14

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Frequency vs. Wavelength



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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

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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

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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)

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Frequencies Used by Wireless Systems

Overview of the Radio Spectrum

3 4 5 6 7 8 9 10 12 14 16 18 20 22 24 26 28 30 GHz

30,000,000,000 i.e., 3x1010_Hz

Broadcasting Land-Mobile Aeronautical Mobile Telephony

Terrestrial 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 GHz 3,000,000,000 i.e., 3x109_Hz UHF TV 14-59 UHF GPS DCS, PCS, AWS 700 + 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 MHz 3,000,000 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 MHz 30,000,000 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 MHz

300,000,000 i.e., 3x108_Hz

FM VHF TV 7-13

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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 900 800 1000 MHz. ISM 2400 2500 2600 MHz. 2690 EBS ISM 2300 WCS WCSSATELLITEBCST. BRS EBS BRS Sirius & XM 5300 5400 5200 5100 U-NII

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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&T’s Analog technology “AMPS” was chosen.

 Nextel bought many existing 800 MHz. Enhanced Specialized Mobile Radio (ESMR) systems and converted to Motorola’s “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. IDEN IDEN CELL DNLNK CELL U PLINK AWS Uplink AWS Down-Link PCS Uplink PCS Down-Link Proposed AWS-2 AW S ? SA T SA T Frequency, MegaHertz

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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, MHz 824 835 845 870 880 894 869 849 846.5 825 890 891.5 Paging, ESMR, etc. A B

Ownership and

Licensing

Frequencies used by “A” Cellular Operator

Initial ownership by Non-Wireline companies

Frequencies used by “B” Cellular Operator

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 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 MTAs

493 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 dataunlic.

voice A D B E F C

1850

MHz. 1910 MHz. 1930 MHz. 1990 MHz.

15 5 15 5 5 15 15 5 15 5 5 15

PCS SPECTRUM ALLOCATIONS IN NORTH AMERICA

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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

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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

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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.

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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

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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 Frequency

of the signal

Phaseof the signal

Compare these Signals:

Different Amplitudes Different Frequencies Different Phases

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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 Frequency 0 fc fc Upper Sideband Lower Sideband fc fc

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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-1890’s by experimenters in Italy, England, Kentucky, and elsewhere.

 Amplitude modulation was the first method used to transmit voice

over radio. The early experimenters couldn’t foresee other methods (FM, etc.), or today’s advanced digital devices and techniques.

 Commercial AM broadcasting to the public began in the early

1920’s.

 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 communications

SSB

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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

s

_FM(t) =A cos

[

_c t + m_m(x)dx+_

]

t t₀ where:

A = signal amplitude (constant)

_c= radian carrier frequency

m_frequency deviation index

m(x) = modulating signal _{}= initial phase FREQUENCY-DOMAIN VIEW V oltage Frequency 0 f_c S_FM(t) UPPER SIDEBANDS LOWER SIDEBANDS

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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 clean output signal free of past noise and distortion

 Digital bit streams are ideally suited to many flexible multiplexing schemes

transmission demodulation-remodulation transmission demodulation-remodulation transmission demodulation-remodulation

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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 f_M

• Sampling must occur at least twice

as fast as f_M 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* f_M

• this follows Shannon’s Theorem: at

least one Hertz of bandwidth is required to convey one bit per second of data

The Sampling Theorem: Two Parts

•If the signal contains no frequency higher than f_M Hz., it is comletely described by specifying its samples taken at instants of time spaced 1/2 f_M s.

•The signal can be completely recovered from its samples taken at the rate of 2 f_M samples per second or higher.

m(t)

Sampling

Recoverym(t)

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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 10000 Frequency, Hz C-Message Weighting t 0 1 2 3 4 56 87 9 10 11 12 13 14 15 16 4 16 1 3 15 8 3 4 8 A-LAW y sgn(x) A|x|_{ln(1 A)} for 0 x 1 A (where A 87.6) y sgn(x)ln(1 A|x)|_ln(1_{ A)} for 1 A x 1 µ-Law y sgn(x)ln(1 | x|) ln(1 ) (where 255) Companding Band-Limiting

x = analog audio voltage y = quantized level (digital)

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Digital Modulation

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Modulation by Digital Inputs

 For example, modulate a signal with this

digital waveform. No more continuous

analog variations, now we’re “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 Keying

PSK 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

Time

1 0 1 0

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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.

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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.

QPSK

CDMA IS-95, IS-2000 1xRTT, and lower rates of 1xEV-DO, DV

16QAM

1xEV-DO at highest rates

64QAM

1xEV-DV at highest rates

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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

Shannon’s equations

Modulation

Scheme Shannon Limit,BitsHz

BPSK 1 b/s/hz QPSK 2 b/s/hz 8PSK 3 b/s/hz 16 QAM 4 b/s/hz 32 QAM 5 b/s/hz 64 QAM 6 b/s/hz 256 QAM 8 b/s/hz

SHANNON’S

CAPACITY EQUATION

C

=

B

_ log₂

[

1 + S

]

N B_ = bandwidth in Hertz

C = channel capacity in bits/second S = signal power

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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

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Error Vulnerabilities of

Higher-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 64QAM

Q

I

Distortion (Gain Compression)

Q

I

Noise

Q

I

Interference

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Error Vector Magnitude and ρ (“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 ρ (“Rho”)

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RF Fundamentals:

Noise

RF Fundamentals:

Noise

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Receiving Weak Signals:

Noise, Unwelcome Guest Who Won’t Go Home!



To hear a very weak signal, why can’t we just add amplifier after

amplifier until we get enough gain to hear it?

• Unfortunately, there’s 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

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How Strong is the Thermal Noise?



The strength of the noise we receive is determined by three things:

• It’s proportional to absolute temperature (degrees Kelvin)

• It’s proportional to the bandwidth we’re looking at (thermal noise

is uniformly distributed in watts per hertz)

• The exact amount of noise per degree kelvin per hertz is

determined by Boltzmann’s constant



In the world of radio, we usually express noise power in decibels

above a milliwatt (dbm). Here’s the everyday formula for the amount

of thermal noise in dbm:



Where

• P is the power in dbm

• Delta F is the bandwidth we’re watching, in hertz

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Thermal Noise Strength

in the Bandwidths of Common Signals

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Physical Principles of

Propagation

Physical Principles of

Propagation

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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 * Log**

₁₀

(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 x 4 x +6 db +3 db

GAIN and LOSS

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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 (that’s 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

(46)

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

(47)

Some Physics: Wavelength of the Signal

and Its Influence on Propagation



Radio signals in the atmosphere

travel at the speed of light

 = wavelength

C = distance traveled in 1 second F = 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 / F

Frequency, GHz. Wavelength cm. in. 0.92 32.6 12.8 2.4 12.5 4.9 5.8 5.2 2.0 /2

(48)

Propagation Effects of Earth’s Atmosphere

 Earth’s 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 earth’s magnetic field, 11-year sunspot cycle

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

(49)

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” on MIcrowave Links

(50)

Dominant Mechanisms of Mobile Propagation

Most 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 180out 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  We’ll explore each of these further...

Knife-edge

Diffraction

Reflection

with partial cancellation

B A

d D

(51)

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.)

(52)

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-Pt Fresnel R, ft 0.92 10 119 2.4 10 74 5.8 10 47 AP _SM

(53)

LoS, nLoS, and NLoS Definitions

Line of Site

(

LoS

)

Near Line of

Site

(

nLoS

)

Non Line of

Site

(

NLoS

)

(54)

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(F_MHZ)+20Log₁₀(Dist_MILES)

• Path Loss, db (between two dipole antennas)

= 32.26 +20*Log₁₀(F_MHZ)+20Log₁₀(Dist_MILES)

• 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” Loss energy intercepted by receiving antenna is proportional to 1/r2 r

(55)

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

(56)

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

HT_FT HTFT

D_MILES

Comparison of Free-Space and Reflection Propagation Modes

Assumptions: Flat earth, TX ERP = 50 dBm, @ 1950 MHz. Base Ht = 200 ft, Mobile Ht = 5 ft.

Received Signal in Free Space, DBM Received Signal in Reflection Mode Distance_MILES -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 (D_Miles)

- 20 x Log (Base Ant. Ht_Feet) - 10 x Log (Mobile Ant. Ht_Feet)

(57)

Signal Decay Rates in Various Environments

We’ve 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, Miles 1 2 3.16 5 6 7 8 10 One Octave of distance (2x) One Decade of distance(10x)

(58)

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

(59)

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

(60)

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

R

₁

R

₂



atten dB 0 -5 -10 -15 -20 -25 -4 -3 -2 -1 0 1 2 3 -5 = -H R1 R2 2 ( R1 + R2)

(61)

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 Building SM AP

(62)

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

(63)

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

- Lee’s Method, others

• Tech-Note 101

• Longley-Rice, Biby-C

 Local Variability

• Rayleigh Distribution

• Normal Distribution

• Joint Probability Techniques

(64)

General Principles Of Area Models

 Area models mimic an average

path in a defined area

 They’re 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

Field Strength, dBµV/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.

(65)

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 1960’s and early 1970’s. 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.

Median A ttenu atio n A (f,d), dB 1 2 5 40 70 80 100 100 500 3000 Frequency f, MHz 10 50 70 Urban Area d, km 30 850 26 35 100 200 300 500 700 1000 2000 3000 Frequency f, (MHz) 5 10 15 20 25 30 Correct ion fa ct or, Garea (dB) 9 dB 850 MHz

(66)

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 Okumura’s

curves as formulas and automated the computation

Path Loss [dB] =

L

_FS

+ A

_mu

(f,d)

- G(H

_b

)

- G(H

_m

)

-

G

_area

Free-Space Path Loss Base Station Height Gain = 20 x Log (H_b/200) Mobile Station Height Gain = 10 x Log (H_m/3) A_mu(f,d) Additional Median Loss from Okumura’s Curves M edian A tt e n u a ti on A (f ,d ), dB 1 2 5 40 70 80 100 100 500 3000 Frequency f, MHz 10 50 70 _{Urban Area} d, km 30 850 26 Morphology Gain 0 dense urban 5 urban 10 suburban 17 rural 35 100 200_{Frequency f, (MHz)}300 500 700 1000 2000 3000 5 10 15 20 25 30 Correcti on factor, Garea (dB) 850 MHz

(67)

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

Urban

Urban

Dense Urban _{Dense Urban}

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

(68)

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 - Highway Rural - 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.

(69)

Radio Network Planning Tools

-Basics

(70)

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

(71)

Typical Model Results

Including Environmental Correction

Tower Height, m EIRP (watts) dBC, Range,km f = 870 MHz. Dense Urban Urban Suburban Rural 30 30 30 50 200 200 200 200 -2 -5 -10 -26 4.0 4.9 6.7 26.8

Okumura/Hata

Tower Height, m EIRP (watts) dBC, Range,km f =1900 MHz. Dense Urban Urban Suburban Rural 30 30 30 50 200 200 200 200 0 -5 -10 -17 2.52 3.50 4.8 10.3

COST-231/Hata

(72)

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.

(73)

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 = L

_FS

+ L

_RT

+ L

_MS

L

_FS = free space path loss (Friis formula

)

L

_RT

=

rooftop diffraction loss

L

_MS

=

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

(74)

Elements of Propagation Measurement Systems

Wireless Receiver PC or Collector GPS Receiver Dead Reckoning

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

(75)

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

(76)

Statistical Techniques

Distribution 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 predicted by area model

Signal Strength Predicted Vs. Observed

Observed Signal Strength