601_602_603

Course 601

Intro Intro to to Wireless Wireless BDA, BDA, DAS, DAS, and and Repeater Repeater Technologies Technologies

June, 2011

Course 601-2-3 (c)2011 Scott Baxter

Page 1

601 Course Outline Specialized Coverage Expansion Techniques – The Family Tree Explained • Repeaters, Boosters, Cell Enhancers: broadband, narrowband, channelized, high power, frequency translating • Distributed Antenna Systems Bi-Directional Amplifiers: The engine inside most systems • Linearity and Power Output Requirements • The danger of oscillation/feedback • output-input coupling and stability considerations • modern DSP cancellation technologies Examples of common BDA/DAS Applications and Systems • Outdoor operator-licensed repeaters • Indoor One-Operator Systems • passive re-radiators • Frequency-specific, stand-alone solutions (one cellular operator, medical data, etc.) • Neutral Host (Multi Frequency, Multi-Cellular Operator, Local Wireless Systems)

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Specialized Specialized Coverage Coverage Expansion Expansion Techniques Techniques –– The The Family Family Tree Tree

June, 2011


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The Family Tree of Special RF Distribution Re-radiators (boosters, cell enhancers, repeaters) • Passive – Coax-fed • Active (bi-directional amplifiers, on-frequency) – Coax-fed – Fiber-fed • Active, Frequency-Converting Distributed Antenna Systems • Passive – Coax-fed – Fiber-fed • Active – Cable fed – Fiber fed with active remote nodes • Single User • Community/Co-operative These are just the major branches of the tree – there are many variations June, 2011


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Wireless Reradiators Reradiators (also called “boosters”, “repeaters”, “cell enhancers”) are amplifying devices intended to add coverage to a cell site Reradiators are transparent to the host Wireless system • A reradiator amplifies RF signals in both directions, uplink and downlink • The system does not control reradiators and has no knowledge of anything they do to the signals they amplify, on either uplink or downlink Careful attention is required when using reradiators to solve coverage problems • to achieve the desired coverage improvement • to avoid creating interference • to ensure the active search window is large enough to accommodate both donor signal and reradiator signal as seen by mobiles June, 2011


Cell

RR

Reradiators are a ‘“crutch” with definite application restrictions. Many operators prefer not to use re-radiators at all. However, reradiators are a cost-effective solution for some problems. Page 5

Home or Small Office Reradiator Setup Opposing Requirements: • Reradiator must have enough gain to deliver coverage to its whole intended coverage area • But the reradiator transmits on the same frequency it is receiving • To prevent oscillation, the gain of the reradiator must be at least 10 db less than the isolation (loss) between its serving and donor antennas

June, 2011


Isolation

Page 6

Wilson Electronics Signal Booster Wilson Electronics is probably the best-known consumer-level provider of bidirectional amplifiers for deployment by end-users. Wilson’s early models often oscillated and caused serious interference to wireless systems. • Customers often mounted the antennas close together, producing very low isolation • Wilson’s current products are better protected against oscillation, but non-technical end-users still make bad installation choices

June, 2011


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What is a DAS? A Distributed Antenna System, or DAS, is a network of spatially separated antenna nodes connected to a common source via a transport medium that provides wireless service within a geographic area or structure. 1.

2.

3. 4.

5.

June, 2011

Building-wide wireless services (cellular/PCS, 2-way radio, paging) connect to integrated access device (IAD) through either base stations or off-air repeaters IAD combines radio signals for applications and services, filters them and sends them into a single wired backbone or trunk running up the building riser The trunk (typ. 7/8”) distributes service to every floor of building WLAN, building automation, security, etc. are added on floor-by-floor basis via applications portals. Access points are in locked closets on each floor Antenna components, radiating cable, standard cables, and omni and directional antennas branch off the trunk on each floor.


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Types of Distributed Antenna Systems There are several kinds of Distributed Antenna Systems, each with their own characteristics : Passive DAS – where RF signals are combined using passive components such as filters, splitters and couplers. Great for multiple bands and small to medium size locations • no power consumed, just off-air pickup and redistribution Active DAS – RF signals are converted and distributed over fiber. Easy to serve larger installations but more costly since each band and operator must be filtered/amplified/processed individually. Hybrid DAS – combination of active and passive techniques DAS can be employed purely within a large building (In-building DAS) or across a large urban area (Street Level DAS). Street Level DAS can provide a very efficient solution for large urban regeneration projects which require dense coverage. They can also be provided in other busy areas such as Metros, Airports or Railway Stations

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A Cable-Distributed DAS

June, 2011


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Fiber-distributed DAS: Lake Nona, FL

Block flow diagram of an actual Neutral-Host DAS serving three wireless operators as well as public-safety systems June, 2011


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Detailed Functions: Lake Nona, FL

Device functional diagram showing hardware detail for Lake Nona DAS June, 2011


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Equipment List for Lake Nona DAS This list includes the major active RF devices in the Lake Nona DAS, broken out by project

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Elements of an In-Building DAS Installation

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Elements of an Outdoor DAS Installation

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Typical Equipment of Neutral-Host DAS With Operator’s BTSs On-Site

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Passive DAS System

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Off-Air vs. Direct Feed A DAS which connects with outside radio systems through antennas over the air is said to be in the “Off Air” mode A DAS which has actual base stations of outside radio systems located in its equipment rooms, and connects directly to them, is said to operate by “Direct Feed” Off-air operation is certainly less expensive, but the reliability and quality of the connection is affected by possible changes in propagation and interference. • Since an off-air DAS merely uses existing capacity from the wireless networks it carries, this places a practical limit on the amount of total traffic the DAS is able to handle Direct Feed brings more complicated and expensive Base Stations onto the DAS headend premises, but the DAS operator is usually not responsible for their cost. The connection is more reliable and the entire capacity of the base stations is available for use on the DAS system. • Most large DAS systems use Direct Feed mainly because of traffic considerations. June, 2011


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Bi-Directional Bi-Directional Amplifiers: Amplifiers: The The engine engine inside inside most most systems systems

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Bi-Directional Amplifiers Depending upon the size of the desired coverage and the expected traffic levels, most repeaters and DAS systems use some form of Bi-Directional Amplifiers (BDAs) to boost the signal level in both directions • If the external signals are picked up using antennas aimed at external cellsites, then the system is called “off-air” • If base stations of the external operators are actually placed at the DAS head end and connected directly to DAS equipment, we say the system is “direct feed”.

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Linearity and Power Output Requirements Power output of system amplifiers is determined by the needed coverage and the gains and losses of other system components • A formal link budget is used for design of the system Amplifier linearity is expressed by the following specifications • Third-order intercept • Noise floor • Levels of Intermodulation products

June, 2011


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Avoiding Oscillation and Feedback What is BDA oscillation? Oscillation is when the outside antenna hears the amplified signal from the indoor antenna or the indoor antenna hears the amplified signal from the outside antenna. This event is similar to microphone/speaker feedback in audio. Prior to about 2000, bidirectional amplifiers used automatic sensing to gauge the level of isolation between their input and output signal lines • The amplifiers would automatically reduce their gain to keep it below the point of oscillation Beginning around 2000, several manufacturers began using DSP technology to do RF sensing and automatically inject oppositely-phased RF energy into their input circuitry • This technique can provide roughly an additional 30 db of cancellation • For example, a reradiator with 100 db isolation between its antennas would have been able to use only about 90 db of gain • With the DSP cancellation, at the same 100 db isolation the advanced amplifier is able to operate stably with about 120 db gain

June, 2011


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Course 602

Wireless Wireless BDA/DAS BDA/DAS Application Application and and Design Design

June, 2011


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602 Course Outline Classes of BDA/DAS Devices and Systems Wireless Services and Frequencies Wireless Technologies: Signal Types carried by BDA/DAS Systems Quality Criteria For BDA/DAS Systems Basic BDA/DAS Coverage Requirements In-Building Propagation RF Propagation in BDA/DAS Systems Antennas for BDA/DAS Systems BDA/DAS System Link Budgets System design to satisfy link budget requirements BDA/DAS Equipment Manufacturers and Product Offerings BDA/DAS Installation Techniques and Practices BDA/DAS Example Case Studies June, 2011


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Classes Classes of of BDA/DAS BDA/DAS Devices Devices and and Systems Systems

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Experimental 40 km Fiber DAS

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A Unique Kind of DAS Cable Distribution: Using HVAC metal Ducting as Waveguide! Wireless RF Distribution in Buildings using Heating and Ventilation Ducts • http://citeseerx.ist.psu.edu/viewdoc /download?doi=10.1.1.81.368&rep =rep1&type=pdf

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Wireless Wireless Services Services and and Frequencies Frequencies

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Frequencies Used by Wireless Systems Overview of the Radio Spectrum AM

0.3

0.4

0.5

0.6

LORAN

0.7 0.8 0.9 1.0

1.2

Marine

1.4 1.6 1.8 2.0

2.4

Short Wave -- International Broadcast -- Amateur

3

4

5

6

VHF LOW Band

30

40

7

8

9

VHF TV 2-6

50

60

70

10

12

FM

80 90 100

30,000,000 i.e., 3x10 Hz

VHF VHF TV 7-13

120 140 160 180 200

0.5

3

4

5

Broadcasting June, 2011

0/6

6

300 MHz

2.4

3.0 GHz

GPS

0.7 0.8 0.9 1.0

7

240

300,000,000 i.e., 3x108 Hz DCS, PCS, AWS

UHF UHF TV 14-59

0.4

CB

14 16 18 20 22 24 26 28 30 MHz 7

700 + Cellular

0.3

3.0 MHz

3,000,000 i.e., 3x106 Hz

8

9

10

1.2

1.4 1.6 1.8 2.0

12

14 16 18 20 22 24 26 28 30 GHz 10

3,000,000,000 i.e., 3x109 Hz

30,000,000,000 i.e., 3x10 Hz

Land-Mobile Aeronautical Mobile Telephony Terrestrial Microwave Satellite Course 601-2-3 (c)2011 Scott Baxter

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700 MHz

800

900

PCS Uplink

PCS DownLink

1700 1800 1900 Frequency, MegaHertz

2000

AWS DownLink

2100

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. June, 2011


Page 30

SAT

AWS Uplink

AWS?

Proposed AWS-2

SAT

700 MHz.

IDEN CELL DNLNK

IDEN CELL UPLINK

Current Wireless Spectrum in the US

2200

North American Cellular Spectrum Uplink Frequencies (“Reverse Path”) 824

835

Downlink Frequencies (“Forward Path”) 845

849

Frequency, MHz

870

Paging, ESMR, etc. 825

846.5

Ownership and Licensing

890

880

A

B

869

891.5

Frequencies used by “A” Cellular Operator Initial ownership by Non-Wireline companies Frequencies used by “B” Cellular Operator Initial ownership by Wireline companies

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 June, 2011


894

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Development of North America PCS 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 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

51 MTAs 493 BTAs

PCS SPECTRUM ALLOCATIONS IN NORTH AMERICA A

D

B

E F

C

15

5

15

5

15

1850 MHz. June, 2011

5

unlic. unlic. data voice

1910 MHz.

A

D

B

E F

C

15

5

15

5

15

5

1930 MHz.


1990 MHz. Page 32

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. June, 2011


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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 introduce their service to new areas June, 2011


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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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Wireless Wireless Technologies: Technologies: Signal Signal Types Types carried carried by by BDA/DAS BDA/DAS

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Characteristics of a Radio Signal SIGNAL CHARACTERISTICS The complete, timevarying radio signal

Natural Frequency of the signal

S (t) = A cos [ ωc t + ϕ ] Amplitude (strength) of the signal

Phase of the signal

Compare these Signals: Different Amplitudes

Different Frequencies

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

Different Phases June, 2011


Page 37

Modulation and Occupied Bandwidth Time-Domain

Frequency-Domain

(as viewed on an Oscilloscope)

(as viewed on a Spectrum Analyzer)

Voltage

The bandwidth occupied by a signal depends on:

Voltage

Time

0

Frequency

Lower Sideband

fc

Upper Sideband

fc

fc

• 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

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 LSB USB June, 2011


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Frequency Modulation (“FM”) TIME-DOMAIN VIEW

t sFM(t) =A cos ωc t + mω m(x)dx+ϕ0 t0

[

]

where: A = signal amplitude (constant) ωc = radian carrier frequency mω = frequency deviation index m(x) = modulating signal ϕ0 = initial phase

Voltage

FREQUENCY-DOMAIN VIEW LOWER SIDEBANDS

0 Frequency June, 2011

UPPER SIDEBANDS

SFM(t)

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

fc


Page 40

The Digital Advantage

transmission

demodulation-remodulation

transmission


transmission


June, 2011

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


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Theory of Digital Modulation: Sampling m(t)

Sampling p(t)

m(t) Recovery

The Sampling Theorem: Two Parts •If 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 fM samples per second or higher. June, 2011

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 bandlimited (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 Shannon’s Theorem: at least one Hertz of bandwidth is required to convey one bit per second of data


Page 42

Sampling Example: the 64 kb/s DS-0 Band-Limiting C-Message Weighting

0 dB -10dB -20dB -30dB -40dB

100

10000

Companding

16

16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

300 1000 3000 Frequency, Hz

15

8

8 3

3

t

4 4

µ-Law

y = sgn(x)

ln(1+ µ| x|) ln(1 + µ)

(whereµ = 255)

1

A-LAW A|x| y = sgn(x)

1

for 0 ≤ x ≤ A ln(1+ A) 1 ln(1+ A|x)| y = sgn(x) for < x ≤1 A ln(1+ A) (where A = 87. 6)

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

June, 2011

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 – µ-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)


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Digital Digital Modulation Modulation

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Modulation by Digital Inputs 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

1

0 1 0

1

0 1 0

1

0 1 0

June, 2011

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


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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. Shannon died Feb. 24, 2001, at age 84. June, 2011


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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.

June, 2011

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


Page 47

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

June, 2011

Modulation Scheme

Shannon Limit, BitsHz

BPSK QPSK 8PSK 16 QAM 32 QAM 64 QAM 256 QAM

1 b/s/hz 2 b/s/hz 3 b/s/hz 4 b/s/hz 5 b/s/hz 6 b/s/hz 8 b/s/hz

SHANNON’S CAPACITY EQUATION

C = Bω log2 [

1+

S N

]

Bω = bandwidth in Hertz C = channel capacity in bits/second S = signal power N = noise 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 June, 2011


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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 June, 2011

Q Distortion

Q Normal 64QAM

(Gain Compression)

I

I

Q Noise

Q Interference

I


I

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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”) • typically 0.89-0.96

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Modulation used in IS-95 CDMA Systems Mobiles: OQPSK CDMA mobiles use offset QPSK modulation • the Q-sequence is delayed half a chip, so that I and Q never change simultaneously and the mobile TX never passes through (0,0) CDMA base stations use QPSK modulation • every signal (voice, pilot, sync, paging) has its own amplitude, so the transmitter is unavoidably going through (0,0) sometimes; no reason to include 1/2 chip delay June, 2011

Q Axis Short PN I

cos ωt

User’s chips Short PN Q

Σ

I Axis 1/2 chip sin ωt

Base Stations: QPSK Q Axis Short PN I

cos ωt

User’s chips Short PN Q

Σ

I Axis sin ωt


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CDMA Base Station Modulation Views The view at top right shows the actual measured QPSK phase constellation of a CDMA base station in normal service The view at bottom right shows the measured power in the code domain for each walsh code on a CDMA BTS in actual service • Notice that not all walsh codes are active • Pilot, Sync, Paging, and certain traffic channels are in use

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Multiple Access Methods FDMA

FDMA: AMPS & NAMPS

Power ue q e Fr

T im e

nc

y

•Each user occupies a private Frequency, protected from interference through physical separation from other users on the same frequency

TDMA: IS-136, GSM TDMA Power Ti m e

F re

e qu

nc

CDMA E D CO

Power Tim

e

June, 2011

F

ue req

nc

y

y

•Each user occupies a specific frequency but only during an assigned time slot. The frequency is used by other users during other time slots.

CDMA •Each user uses a signal on a particular frequency at the same time as many other users, but it can be separated out when receiving because it contains a special code of its own Course 601-2-3 (c)2011 Scott Baxter

Page 55

Multiple Access Methods OFDM, OFDMA Power

OFDM

Ti m e

Frequency

MIMO

•Orthogonal Frequency Division Multiplexing; Orthogonal Frequency Division Muliple Access •The signal consists of many (from dozens to thousands) of thin carriers carrying symbols •In OFDMA, the symbols are for multiple users •OFDM provides dense spectral efficiency and robust resistance to fading, with great flexibility of use

MIMO •Multiple Input Multiple Output •An ideal companion to OFDM, MIMO allows exploitation of multiple antennas at the base station and the mobile to effectively multiply the throughput for the base station and users

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Quality Quality Criteria Criteria For For BDA/DAS BDA/DAS Systems Systems

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Signal Quality Criteria C/I Carrier-to-Interference • Ratio of power of desired signal to power of undesired signals in the background S/N Signal-to-Noise Ratio • Ratio of power of desired signal to the noise in the background Linearity • Purity of the signal. Typically expressed as Rho or Error Vector Magnitude. • Typical specification: Rho >= 0.9, or EVM <0.1 Amplitude “tilt” over frequency • Variable frequency response causing some parts of the signal to be amplified more than others, distorting the waveform Intersymbol Interference (ISI) • The process of a 1 or 0 in the signal getting overlapped with adjoining 1’s or 0’s, potentially causing incorrect decoding • ISI can be caused by distortion in equipment and by external interference June, 2011


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Phase Constellation ‘Argand’ Diagram If a transmitter were perfect, it would transmit exactly the proper strength and phase and the diagram at right would have only clean little dots. Real transmitters have variable phase and amplitude errors and instead of precise dots, the diagram at right looks like a paintball target. If the error is large enough, the dots will splatter enough to cause mistakes in the decoding process. June, 2011


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Spectrum Display showing Noise Floor On this spectrum analyzer, the noise floor is below the specified maximum. If the amplifier were nonlinear, or there were corroded connections involved, locally-generated noise would drive the noise floor up above spec and potentially interfere with other communications.

June, 2011


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Working Working in in Decibels Decibels

June, 2011


Page 61

Decibels (DB) Calculations of transmitted and received power on radio links and many other electronic circuits always encounters very large and very small numbers • Multiplying and dividing these numbers is tedious Fortunately, there is a simpler way to perform the needed calculations: a logarithmic system which expresses the powers, gains and losses of the circuits in units called decibels (db) Decibels offer two big advantages over straight arithmetic: • in decibels, the numbers are never very large or small • working in arithmetic, power calculations always involve multiplying. Working in decibels, only addition or subtraction are needed. Working in decibels • can be performed using a calculator, or • by remembering two or three key values in a table and knowing how to apply them June, 2011


Page 62

Using Decibels In manual calculation of RF power levels, unwieldy large and small numbers occur as a product of painful multiplication and division. It is popular and much easier to work in Decibels (dB). • rather than multiply and divide RF power ratios, in dB we can just add & subtract Ratio to Decibels

db = 10 * Log ( X ) Decibels to Ratio

X = 10 (db/10) June, 2011

Decibel Examples Number N 1,000,000,000 100,000,000 10,000,000 1,000,000 100,000 10,000 1,000 100 10 4 2 1 0.5 0.25 0.1 0.01 0.001 0.0001 0.00001 0.000001 0.0000001 0.00000001 0.000000001


dB +90 +80 +70 +60 +50 +40 +30 +20 +10 +6 +3 0 -3 -6 -10 -20 -30 -40 -50 -60 -70 -80 -90 Page 63

Example Link Budget, NOT Using DB Why Use Decibels? For convenience and speed. Here’s an example of why, then we’ll see how. Transmitter

Trans. Line Antenna

Let’s track the power flow from transmitter to receiver in 20 Watts TX output a radio link. We’re going to use typical values that x 0.50 line efficiency = 10 watts to antenna commonly occur in real links. x 20 antenna gain = 200 watts ERP x 0.000,000,000,000,000,1585 path attenuation = 0.000,000,000,000,031,7 watts if intercepted by dipole antenna

Antenna Trans. Line

Receiver June, 2011

x 20 antenna gain = 0.000,000,000,000,634 watts into line x 0.50 line efficiency = 0.000,000,000,000,317 watts to receiver

Did you enjoy that arithmetic? (No!) Let’s go back and do it a better and less painful way. Course 601-2-3 (c)2011 Scott Baxter

Page 64

Example Link Budget Using DB Transmitter

Let’s track the power flow again, using decibels. +43

dBm TX output

Trans. Line

-3 = +40

dB line efficiency dBm to antenna

Antenna

+13 = +53

dB antenna gain dBm ERP

-158 = -105

dB path attenuation dBm if intercepted by dipole antenna

+13 = -92

dB antenna gain dBm into line

-3 = -95

dB line efficiency dBm to receiver

Antenna Trans. Line

Receiver June, 2011

Wasn’t that better?! How to do it -- next. Course 601-2-3 (c)2011 Scott Baxter

Page 65

Decibels - Relative and Absolute Decibels normally refer to power ratios -- in other words, the numbers we represent in dB usually are a ratio of two powers. Examples: • A certain amplifier amplifies its input by a factor of 1,000. (Pout/Pin = 1,000). That x 1000 amplifier has 30 dB gain. .001 w 1 watt • A certain transmission line has an efficiency 0 dBm 30 dBm of only 10 percent. (Pout/Pin = 0.1) The +30 dB transmission line has a loss of -10 dB. Often decibels are used to express an absolute x 0.10 number of watts, milliwatts, kilowatts, etc.... 100 w 10 w +40 dBm When used this way, we always append a letter +50 dBm -10 dB (W, m, or K) after “db” to show the unit we’re using. For example, • 20 dBK = 50 dBW = 80 dBm = 100,000 watts • 0 dBm = 1 milliwatt June, 2011


Page 66

Decibels Two Other Popular Absolute References dBrnc: a common telephone noise measurement • “db above reference noise, C-weighted” • “Reference Noise” is 1000 Hz. tone at -90 dBm • “C-weighting”, an arbitrary frequency response, matches the response best suited for intelligible toll quality speech • this standard measures through a “C-message” filter

C-Message Weighting

0 dB -10dB -20dB -30dB -40dB

100

300 1000 3000 Frequency, Hz

10000

dBu: a common electric field strength expression • dBu is “shorthand” for dBµV/m • “decibels above one microvolt per meter field strength” • often we must convert between E-field strength in dBu and the power recovered by a dipole antenna bathed in such a field strength:

FSdBu = 20 * Log10(FMHZ) + 75 + PwrDBM

Dipole Antenna Electromagnetic Field dBµV/m @ FMHZ

Pwr dBm

PwrDBM = FSdBu - 20 * Log10(FMHZ)-75 June, 2011


Page 67

Decibels referring to Voltage or Current By convention, decibels are based on power ratios. However, decibels are occasionally used to express to voltage or current ratios. When doing this, be sure to use these alternate formulas: db = 20 x Log10 (V or I) (V or I) = 10 ^ (db/20) • Example: a signal of 4 volts is 6 db. greater than a signal of 2 volts db = 20 x Log10 (4/2) = 20 x Log10 (2) = 20 x 0.3 = 6.0 db

June, 2011


Page 68

Prefixes for Large and Small Units Summary of Units Number N 1,000,000,000,000 1,000,000,000 1,000,000 1,000 100 10 1 0.1 0.01 0.001 0.000001 0.000000001 0.000000000001 0.000000000000001 June, 2011

x10y x1012 x109 x106 x103 x102 x101 x100 x10-1 x10-2 x10-3 x10-6 x10-9 x10-12 x10-15

Prefix Tera GigaMegaKilohectodecadecicentimillimicronanopicofemto-

Large and small quantities pop up all over telecommunications and the world in general. We like to work in units we can easily handle, both in math and in concept. So, when large or small numbers arise, we often use prefixes to scale them into something more comfortable: • Kilometers • Megahertz • Milliwatts – etc....


Page 69

Basic Basic BDA/DAS BDA/DAS Coverage Coverage Requirements Requirements

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Page 70

Coverage Tradeoffs

After the desired coverage area is known, the next step is to determine how many antennas will be required to serve it Alternatives will be available for antennas of different gains and transmitters of different power outputs In general, the solution with the maximum number of antennas will have the fewest significant coverage holes

June, 2011


Page 71

A Resource for Indoor Radio Planning A new version of the bestseller, updated with an introduction to LTE and treatments of modulation principle, DAS systems for MIMO/LTE , designing repeater systems and elevator coverage Addresses the challenge of providing coverage inside train, and high speed rail Outlines the key parameters and metrics for designing DAS for GSM, DCS, UMTS, HSPA & LTE Essential reading for engineering and planning personnel at mobile operators, also giving a sound grounding in indoor radio planning for equipment manufacturers Written by a leading practitioner in the field with more than 20 years of practical experience

June, 2011


Page 72

Radio Radio Propagation Propagation

June, 2011


Page 73

Some Physics: Wavelength of the Signal and Its Influence on Propagation

λ=C/F Frequency, GHz. 0.92 2.4 5.8

Radio signals in the atmosphere travel at the speed of light

Wavelength cm. in. 32.6 12.8 12.5 4.9 5.2 2.0

λ/2

June, 2011

λ = 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


Page 74

Propagation: Getting the Signal to the Customer AP

SM

“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

June, 2011


Page 75

The First Fresnel Zone and Free-Space Propagation AP

Frequency, Path, GHz. Miles 0.92 10 2.4 10 5.8 10

Mid-Pt Fresnel R, ft 119 74 47

SM

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 June, 2011


Page 76

Free-Space Propagation Technical Details r

Free Space “Spreading” Loss energy intercepted by receiving antenna is proportional to 1/r2

d A

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)

1st Fresnel Zone

D B

June, 2011

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


Page 77

Obstructions and their Effects AP

SM

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 June, 2011


Page 78

Severe Obstructions AP

SM

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 the link is likely to be usable anyway June, 2011


Page 79

Knife-Edge Diffraction

H

R1 ν = -H

R2 2 λ

(

1 R1

+

1 R2

)

0 -5 atten -10 dB -15 -20 -25 -5 -4 -3 -2 -1 0 1 2 3

ν

June, 2011

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 ν from the geometry of the path Next consult the table to obtain the obstruction loss in db Add this loss to the otherwisedetermined 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


Page 80

Foliage and Building Penetration Considerations AP Building

SM

AP SM Building

June, 2011

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.


Page 81

In-Building In-Building Propagation Propagation

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Page 82

iBWAVE: Common Commercial Software for Indoor Propagation Prediction

AWE Communications offers iBWAVE, a commercial indoor propagation prediction and design tool. This tool is a good example of the current state of the art. Large database of building material characteristics Import walls/floorplans from AutoCAD, images or PDF files. Propagation module offers dominant path and COST 321 multi-wall models. • accurate propagation results from antennas and radiating cables • can increase accuracy by calibrating the prediction model with survey data The Propagation module provides output maps giving a visual representation of propagation results, even for different technologies and different bands. • These include signal strength, field strength, best server and soft handoff maps. • evaluate different design configurations and instantly get a clear picture of the impact on coverage and cost. • The Propagation module delivers professional documentation about the project for effective communication with customers to facilitate agreements and approvals. June, 2011


Page 83

iBWAVE Examples

June, 2011


Page 84

iBWAVE Images

June, 2011


Page 85

iBWAVE Coverage Map

June, 2011


Page 86

Equipment List

June, 2011


Page 87

iBwave Documentation iBwave also provides documentation capabilities • Very useful in large projects

June, 2011


Page 88

iBwave System Detail Diagram

June, 2011


Page 89

Stadium Example Example of stadium detail and calculation of signal levels on each element

June, 2011


Page 90

Network Diagram on Floor Plan

June, 2011


Page 91

Network Diagram on Detailed Floor Plan

June, 2011


Page 92

Signal Strength on Floor Plan

June, 2011


Page 93

iBwave Configuration and Display Examples

June, 2011


Page 94

3-story DAS components

June, 2011


Page 95

Equipment Room of Neutral Host System

June, 2011


Page 96

June, 2011


Page 97

Indoor Best Server Plot

Example Indoor best server plot computed by iBWAVE June, 2011


Page 98

RF RF Propagation Propagation in in BDA/DAS BDA/DAS Systems Systems

June, 2011


Page 99

Antennas Antennas for for BDA/DAS BDA/DAS Systems Systems

June, 2011


Page 100

Understanding Antenna Radiation The Principle Of Current Moments An antenna is just a passive conductor carrying RF current

Zero current at each end each tiny imaginary “slice” of the antenna does its share of radiating

TX

RX Maximum current at the middle Current induced in receiving antenna is vector sum of contribution of every tiny “slice” of radiating antenna Width of band denotes current magnitude

June, 2011

• 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


Page 101

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”

Omni-directional Antenna

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 June, 2011


Directional Antenna Page 102

Reference Antennas Defining Gain And Effective Radiated Power Isotropic Radiator

• Truly non-directional -- in 3 dimensions • Difficult to build or approximate physically, Isotropic Antenna 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 Quantity Gain above Isotropic radiator Gain above Dipole reference Effective Radiated Power Vs. Isotropic Effective Radiated Power Vs. Dipole June, 2011

Units dBi dBd (watts or dBm) EIRP (watts or dBm) ERP


Dipole Antenna Notice that a dipole has 2.15 dB gain compared to an isotropic antenna. Page 103

Radiation Patterns Key Features And Terminology An antenna’s 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 Example

Horizontal Plane Pattern Notice -3 dB points 0 (N) 0 -10

10 dB points

-20 -30 dB 270 (W)

Main Lobe

nulls or a Minor minim Lobe Front-to-back Ratio

180 (S)

June, 2011


Page 104

90 (E)

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 June, 2011


In phase

Out of phase

Page 105

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

RF power

– one driven element, parasitic coupling to others

• Log-periodic – all elements driven – wide bandwidth

RF power

All of these types of antennas are used in wireless June, 2011


Page 106

Omni Antennas Collinear Vertical Arrays The family of omni-directional wireless antennas: Number of elements determines

Typical Collinear Arrays Number of Elements 1 2 3 4 5 6 7 8 9 10 11 12 13 14

• 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 June, 2011

Power Gain 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Gain, dB 0.00 3.01 4.77 6.02 6.99 7.78 8.45 9.03 9.54 10.00 10.41 10.79 11.14 11.46

Angle θ n/a 26.57° 18.43° 14.04° 11.31° 9.46° 8.13° 7.13° 6.34° 5.71° 5.19° 4.76° 4.40° 4.09°

Vertical Plane Pattern beamwidth -3

d B


θ Angle of first null

Page 107

Sector Antennas Reflectors 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 Up

• 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?)

June, 2011


Down Horizontal Plane Pattern N

W

E

S

Page 108

Pattern of Canopy AP Internal Patch Antenna

June, 2011


Page 109

Andrew Radiax

June, 2011


Page 110

Radiax Design Considerations System Architecture for a specific application will depend on overall objectives • dictated in large part by the geometry and area that is required for coverage. • For tunnel applications, the length, construction, and the size of the tunnel will establish the basic parameters. • Other key factors include the number of services, providers, and channels required to meet the objectives. For tunnel applications, the two primary architectures used are: • A series of cascaded amplifiers or • Using a T-feed configuration. In some implementations, it is smart to use a combination of these two techniques. • The T-feed structure is appropriate when feeding from multiple base stations or when using amplifiers that are connected to a common base station using fiber • The T-feed structure has the advantage that an amplifier can drive a longer length of cable than can be achieved with the cascaded architecture. • The T-feed structure generates less downlink intermodulation since the amplifiers are not cascaded. • The cascaded configuration has a higher dynamic range on the uplink and is useful for communication systems that do not use uplink power control. • The cascade configuration has been used effectively on tunnels where the communication system employs conventional or trunk radio techniques. • The T-feed configuration has been particularly well suited for cellular and PCS applications. June, 2011


Page 111

Radiax Applications

Cable Parameters • Insertion Loss • Coupling Loss • Fading Characteristic • Coherent Bandwidth • Launch Angle Insertion Loss • a measure of the attenuation in the coaxial cable, measured in dB per unit length. • primarily a result of the copper losses and the amount of power that is radiated from the cable. • The loss due to radiation is somewhat affected by the proximity of the cable to other surfaces. • This effect is more pronounced for cables having low coupling loss, however, significant changes will typically not occur until the spacing is less than 1 inch. Coupling Loss • Coupling loss is the ratio between the power in the cable and the amount of power received by a dipole antenna at a specified distance from the cable. • For example, if the power in the cable were 0 dBm and the power received by the antenna was -65 dBm, then the coupling loss would be 65 dB. • Typically Andrew will use distances of 2 meters (6.6 feet) or 6 meters (20 feet). • The value specified is the median value measured as the dipole travels parallel to the cable. • Typically, the radiated energy from the radiating cables is polarized. The degree of polarization is measured for all Andrew cables. The majority of the Andrew radiating cables have a dominant vertical polarization, however, this may be frequency dependent. Fading Characteristic • Radiating cables exhibit a fading characteristic that is a result of the multipath nature of the cable. • Typically, a fade will occur approximately every wavelength. • The depth of the fade is dependant not only on the design of the cable but also on the multipath environment. • Andrew quantifies the depth of fading by calculating the ratio between the median value of the coupling loss (50%) to the coupling loss that occurs at least 5%. • This produces a ratio of the 50 to 95% values. • For coupled mode RADIAX (RXL), the fading factor is typically 11 dB. • For RADIAX utilizing the array construction, radiating mode RADIAX (RCT), this value can be as low as 2 to 3 dB. • In a majority of systems applications, the low fading characteristic is somewhat negated by the environment

June, 2011


Page 112

Radiax - Tunnels Coherent Bandwidth • a measure of instantaneous bandwidth of the signal that can reliably be transmitted from the cable. • significant for wide bandwidth signals, especially third generation systems. • For applications involving wider bandwidths, the radiating mode cables (RCT) are designed to handle third generation signals. Launch Angle • For coupled mode RADIAX®, there is no dominant launch angle as RF energy emits from the cable at all angles. • For the radiating mode series of cables there is a dominant launch angle. • this dominant launch angle contributes to the low fading characteristic and the wider coherent bandwidth. The launch angle for any particular cable varies as a function of frequency and will typically be (45 degrees relative to a perpendicular line from the cable. Cable Orientation • For most cables, the orientation of the slots is not critical. • the dominant radiation is not directly from the slots, rather caused by current that flows in the outer jacket of the cable. • Directivity of the cable is related to the frequency and the size of the cable. That is, a 1-5/8 inch cable at 2400 MHz will be more directive than at 900 MHz, further the 1-5/8 inch cable will have a higher directivity than a 7/8" cable. Link Budget • basic elements of a link budget can be demonstrated by considering an example that involves a dual-bore road tunnel that is 800 meters (2620 feet) in length that is to be configured to handle cellular signals (824 MHz-894 MHz). The power per channel available for the downlink is 1 watt (+30 dBm). Following is an example link budget:

June, 2011


Page 113

Radiax – Tunnels (2) Downlink (Base to Mobile) Link Budget for 95% Coverage Available Power/Channel 30 dBm Distribution Loss, Power divider feeds both bores 3.5 dB Feeder Cable Loss, 30 m (100 ft) LDF5-50 1.6 dB Insertion Loss, 800 m (2620 ft) RCT7-TC-1 18.4 dB Coupling Loss @ 2 m 53.0 dB Antenna Loss, relative to dipole 3 dB Wide Tunnel Factor, tunnel width 10 m (33 ft), Wide Tunnel Factor = 20 Log (Width/2) 14 dB Vehicle Penetration Loss 6 dB Raleigh Fading, Z(Σ(σil2+σcl2+σant2+σ...)1/2 11 dB Statistical Variation 3 dB Tunnel Factors 0 dB Received Signal Power (Level that will be achieved at least 95% of the time at the terminated end of the cable) -83.5 dBm Uplink performance can be computed in a very similar manner.

June, 2011


Page 114

Radiax – Tunnels (3) Tunnel Effects on Design Coupling loss is dependent on the construction and shape of the tunnel. Typically, steel tunnels will perform appreciably better than concrete tunnels. Another factor that modifies the performance of the system is the placement of the cable in the tunnel. The cable should be mounted in the manner, which provides the best line-ofsight and proximity to the mobile/portable antenna

June, 2011


Page 115

BDA/DAS BDA/DAS System System Link Link Budgets Budgets

June, 2011


Page 116

DAS Link Budgets

The Components and Calculations of the RF Link The Maximum Allowable Path Loss The Components in the Link Budget Link Budgets for Indoor Systems Passive DAS Link Budget Active DAS Link Budget The Free Space Loss The Modified Indoor Model The PLS Model Calculating the Antenna Service Radius

June, 2011


Page 117

Link Budgets

What is a link budget? A link budget is the calculation of signal strength on a Distributed Antenna System (DAS) at coax connection points. Example of a downlink link budget for one indoor antenna DAS; Roof RSSI(75dBm) + gain donor antenna (11dB) + loss coax to BDA (3dB) + gain BDA (62dB) + loss coax to indoor antenna (4.5dB) = -9.5dBm at indoor antenna port. June, 2011


Page 118

Coverage Area of An Antenna Antenna coverage is determined by • the building characteristic path loss, • frequency band(s), • signal strength at antenna port and antenna type. For example, in a typical office application, an omni antenna with an output signal of +9.5dBm will maintain a coverage area of +85dB or better for 22k square feet on the cellular frequency band, 16k square feet on the PCS frequency band.

June, 2011


Page 119

BDA/DAS BDA/DAS Equipment Equipment Manufacturers Manufacturers and and Products Products

June, 2011


Page 120

Mobile Access Hardware Selection

June, 2011


Page 121

Mobile Access Hardware (2)

June, 2011


Page 122

Mobile Access Hardware (3)

June, 2011


Page 123

BDA/DAS BDA/DAS Installation Installation Techniques Techniques and and Practices Practices

June, 2011


Page 124

How to Properly Design an In-Building Distributed Antenna System (DAS) A typical in-building coverage system consists of two major components, • a bi-directional amplifier relaying and amplifying the RF signals between the remote base station and portable or mobile radios, and • a network to distribute the signal to every corner of the desired coverage area. The most common type of distribution network is a system of coax cables and indoor antennas called a Distributed Antenna System or DAS. Most of the reference materials and application notes on in-building coverage solutions have focused on the booster technologies or system design architecture. One often overlooked aspect in the system design is the DAS implementation. • This includes connecting all the cables and antennas throughout the building and balancing the signal levels at each DAS node. • If ignored, an improperly designed DAS results in degraded performance and unnecessary cost increases.

June, 2011


Page 125

The DAS Design Process The first step of DAS design is to obtain an accurate and up-to-date blueprint of the building. • An architectural drawing is best, but even a fire exit map will suffice, if drawn to scale. Be careful when using the scale on any drawing to calculate the real dimensions; • the drawing may not be the same size as originally printed. . The second step is to gather all relevant physical information on building and DAS installation. • What kind of material was used for exterior construction? • Could some RF signals be present on upper floors and near exterior boundaries that will reduce the need for the in-building coverage? • What kind of material was used for interior construction, drywall or concrete? • Is the building designed for a special application that may result in RF blockage? • Many hospitals and power generating plants fall into this category. • Are there any restrictions on the cable runs and antennas installation? • Some buildings won’t allow any visible hardware for aesthetic reasons. • Where can the cables go between floors? Where will the head-end booster be located? • A quick word on another type of DAS: radiating cable. It is essentially a coax cable with lots of tiny slits cut along the length of the cable. Each slit functions as a tiny antenna with RF energy leaking out of it, hence the nickname “leaky cable”.

June, 2011


Page 126

Two Sets of Diagrams To make it easier to see, a DAS design is often drawn up with 2 sets of diagrams • one with direct marking on the building blueprint to indicate the location of the antennas and cable splits, • a second set of “abstract” drawings (typically in VisioTM or AutocadTM) showing the cable lengths and coupler models. how do you connect all the cable segments and antennas to make them into a network? • directional couplers are much better alternatives than splitters at this task. • They offer various power split ratios to allow the designer flexibility in balancing the power level at each DAS node. The main goal of using couplers is to offset the difference in cable losses by using the different loss ratios between the two outputs of the coupler. June, 2011


Page 127

Balancing Losses Using Couplers

With 15 dB loss in one branch vs. 5 dB loss in the other, let’s select a coupler that has 10 dB of difference in power split ratios. • Put the lower loss port on the higher loss branch, and the higher loss port on the lower loss branch • Most manufacturers provide products with different split ratios to allow matching the loss differentials as closely as possible. In the left Figure, we have a branch with 150 ft and about 3.3 dB of insertion loss, and a branch of 3 ft jumper cable with 0.5 dB of loss. • select a coupler that can make up the loss differential in the two cable runs. • Browsing, select a coupler with a 4.8/1.8 dB split ratio as Coupler #1. • connect the longer cable run to the port with 1.8 dB, and connect the shorter cable run to the 4.8 dB, the total losses from the input of the coupler to the antennas are 3.3 + 1.8 = 5.1 dB and 0.5 + 4.8 = 5.3 dB respectively. • If we had used a 3 dB splitter, the total losses would have been 3.3 + 3 = 6.3 dB and 0.5 + 3 = 3.5 dB. • see the benefit of using a coupler as it manages to balance the signal levels at the two antennas within 0.2 dB of each other. • Next, work backwards toward the booster. Take the worse number of the two above (5.1 and 5.3 dB, so we use 5.3 dB), and add the 0.5 dB cable loss between the two couplers, we get 5.8 dB, which is the loss from the output of Coupler #2 to either Antenna #1 or Antenna #2.

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Page 128

Balancing Losses Using Couplers

Assume there are more floors above this one. The DAS on the upper floor has been balanced using couplers in the same way as illustrated, and the total loss in the DAS on the upper floor is 10 dB. See the left figure as we “propagate” the loss in the DAS backwards toward the booster. We want to select a coupler that will offset the loss differential and balance the signal levels. we find a coupler with a 6/1.2 dB split ratio. If we connect the 6 dB coupled port to the lower loss DAS on this floor, and the 1.2 dB throughput port to the higher loss DAS on the upper floor, we get 5.8 + 6 = 11.8 dB and 10 + 1.2 = 11.2 dB. The total losses from the input of Coupler #2 to the cable runs on this floor and the cable runs on the upper floor are within 0.6 dB of each other. June, 2011


Page 129

Continuing Back to the Booster If there are more floors below it or more cable splits between this one and the booster, the same iteration is to be repeated until we work all the way back to the booster. A typical in-building coverage system can vary from 10,000 sq ft to 1,000,000 sq ft or more, with the number of couplers from a handful to hundreds. However, the rules of calculating the losses and selecting the couplers stay the same, allowing the designer to balance any DAS and achieve the optimal signal levels throughout the network. The total DAS loss should be limited to no more than 25~30 dB, in order to maintain a sufficient signal to noise ratio. working backwards toward the booster, eventually the system loss exceeds the limit. We know that we will need to insert an in-line booster at that point. The exact location depends on the practical constraints of the building, but wherever the in-line booster is, the cumulative loss ends at its output, and starts from zero again on the other side of the in-line booster. Another alternative is to use coax with larger diameters with lower insertion loss. But that option has high material and labor costs, as well as the physical limitations on bending radius and weight support issues.

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BDA/DAS BDA/DAS Example Example Case Case Studies Studies

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Page 131

Site Survey A site survey is performed prior to the final design. Objectives: • to characterize signal propagation within the building • investigate donor signal options and to • investigate equipment space and cable routing issues. Proper engineering and planning will minimize capital expenditures while ensuring that coverage goals for each of the mobile service providers are met. Several factors must be considered when designing a neutral hosts system. • characterize signal propagation within the target area. • test transmitters are placed at various locations within the building. • A receiver and mapping software are used to record the signal strength at various locations within the building. A sample transmitter test is shown on the next page.

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Page 132

Site Survey Results Map

June, 2011


Page 133

Site Survey Results Various transmitter tests are performed to get a thorough understanding of the building’s propagation characteristics In the test just shown, signal loss does not degrade in direct proportion to the distance from the transmitter but is largely dependant on the building structure. • Using the proper tools and procedures to characterize signal loss helps ensure that the system is not over designed and meets customer requirements. Suitable equipment room space and it’s proximity to the coverage objective strongly affect the type of system installed and its overall cost. • These issues are investigated at the time of the site survey. Potential donor signals are also investigated for neutral host opportunities that may not require dedicated base stations. • These measurements are generally performed at the roof level. • A receiver capable of measuring multiple technologies and frequencies is required for these measurements. • Alternatively phones from various carriers with an accessible diagnostic or debug mode can be used. Potential donor antenna locations and roof penetration issues also need to be investigated at this stage. June, 2011


Page 134

System Design The building characterization along with available equipment space determined during the site survey is the basis for system design. The propagation model is optimized for accuracy using the transmitter tests performed in the site survey. • Each wall type within a building affects signal propagation differently therefore each wall type must be identified in the propagation model and assigned attenuation values obtained from the information in the transmitter tests. • This allows for optimum transmitter location and minimizes required capital. The system design determines which OEM hardware solution is appropriate for the venue. A partial design (one floor of a multi story building) is shown in the next figure.

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Page 135

One Floor Design

June, 2011


Page 136

Construction Once the proposed design is approved for installation by the building manager, a preconstruction site visit is completed. • During this visit, equipment locations and cable routes are verified, as well as acceptable contractors to perform any electrical or roofing work that may be required. • If any of the locations proposed in the design are not acceptable to the building manager, the design is modified to allow for these changes. • Once final approval is obtained, the actual installation of equipment begins. Construction begins with the installation of cabling, typically both fiberoptic and coaxial. • Cabling is routed from the main equipment room throughout the building to all the antenna locations. A DAS system allows for the reuse of many network elements - trunking and hubbing minimize the amount of new cable required. Cable is run in existing cable trays or utility chases where available. The equipment deployment is fairly straight forward. The main equipment room typically needs dedicated electrical services to handle both the DAS equipment and the carrier equipment. The remote units and the antenna use minimal power and usually only involve a 110v outlet.

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Page 137

Optimization and Verification When the construction phase is complete, the system is tested and optimized. • Each coax and fiber optic cable is swept, • isolation tests are performed, • sources of interference are investigated, • donor signal levels are verified, and • a final coverage assessment is performed. • The results of the coverage analysis reflect both coverage provided by the external macro cell and enhanced coverage provided by the DAS. The next page show is a sample plot that can be used to measure the success of the installation.

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Page 138

Signal Levels After Activation

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Page 139

DAS Reduce Interference to Medical Devices Interference Concerns Much has been written about cellular devices interfering with medical equipment. Generally, the use of a DAS will greatly lower the power output of the mobile device, reducing the risk of interference. Poor coverage inside a building means that a mobile device has to transmit at a higher power setting to ensure that a connection with the cell site is made. Cellular devices can transmit at relatively high power levels (perhaps 1 W) for short periods of time such as during the ring cycle. However, if the cellular device is in a reasonably good coverage location, it will transmit at much lower levels (potentially under 5 mW), which is not a real concern. In addition if you have good coverage, the battery life of the device will be greatly enhanced. Essentially a DAS provides 5 bars all the time, thus less power is required to enable the up-link from the mobile devices. The use of DAS in healthcare will actually decrease electromagnetic interference and improve battery life of these devices.

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Page 140

Course 603

Wireless Wireless BDA BDA and and DAS DAS Advanced Advanced Topics Topics

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603 Course Outline

Traffic Capacity of BDA/DAS Systems Intermodulation Distortion and Interference External Interference Interference Sources MIMO – Multiple Input-Output Broadband Data Systems Femtocells • Comparison of function and performance against BDA/DAS technologies • Differences and advantages

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Page 142

Intermodulation Intermodulation Distortion Distortion and and Interference Interference

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Page 143

Modulation and Mixing vs. Intermodulation When two signals are intentionally combined in a nonlinear device we call the effect modulation • Amplitude modulator, or quad phase modulator • Mixer, down or up converter in superheterodyne When two (or more) signals are unintentionally combined in a non-linear device, we call the effect intermodulation (a pejorative term) An analogy: Botanists use soil to grow plants. But on your living room carpet, soil is just dirt.

IM signals increase system noise, or cause distinctive recognizable interference signals

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Intermod Basics Definition: Intermodulation (“IM”) is Non-linear device Input Output the unintended mixing of legitimate RF signals, producing undesired signals (‘intermodulation products’) on f f unrelated frequencies possibly f1 f2 3f1-2f2 f1 f2 3f2-2f1 already being used for other services 2f2-f1 2f1-f2 • IM can devastate reception on certain frequencies at base stations and other communication facilities Power transfer characteristics Intermodulation occurs because of typical amplifier or other device signals are passing through a nonlinear device, allowing each signal Predicted Third order to alter the waveshape of the others power intercept • the frequencies of the intermod point products are sums and differences of multiples of the Output original signal frequencies, and power Third order can be calculated exactly (dBm) intermodulation • the strength of the intermod products products depends on the degree Noise floor of nonlinearity of the circuits involved, and can be predicted with good accuracy using Input power (dBm) measured “intercept” levels June, 2011


Page 145

Intermodulation Interference Analysis There are three basic categories of Intermodulation (IM) interference: Transmitter produced IM is the result of one or more transmitters impressing a signal in the non-linear final output stage circuitry of another transmitter, usually via antenna coupling. The IM product frequency is then re-radiated from the transmitter's antenna. Receiver produced IM is the result of two or more transmitter signals mixing in a receiver RF amplifier or mixer stage when operating in a non-linear range. “Other" radiated IM is the result of transmitter signals mixing in other non-linear junctions. These junctions are usually metallic, such as rusty bolts on a tower, dissimilar metallic junctions, or other nonlinear metallic junctions in the area. IM products can also be caused by non-linearity in the transmission system such as antenna, transmission line, or connectors. June, 2011

Duplexer Duplexer


Comb

Comb Circ

BPF

Circ

TX

TX

Preamp

Splitter

RX

Page 146

Intermodulation Interference Analysis Communication sites with co-located transmitters, usually have RF coupling between each transmitter and antenna system. • This results in the signals of each transmitter entering the nonlinear final output (PA) circuitry of the other transmitters. When intermodulation (IM) products are created in the output circuitry and they fall within the passband of the final amplifier, the IM products are re-radiated and may interfere with receivers at the same site or at other nearby sites. Additionally, these strong transmitter signals may directly enter a receiver and drive the RF amplifier into a nonlinear operation, or • if not filtered effectively by the receiver input circuitry, these signals could mix in the nonlinear circuitry of the receiver frontend or mixer, creating IM products directly in the receiver.

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Page 147

Transmitter Noise Analysis Transmitter noise interference occurs because a transmitter radiates energy on its operating frequency as well as frequencies above and below the assigned frequency. The energy that is radiated above and below the assigned frequency is known as sideband noise energy and extends for several megahertz on either side of the operating frequency. This undesired noise energy can fall within the passband of a nearby receiver even if the receiver's operating frequency is several megahertz away. The transmitter noise appears as "on-channel" noise interference and cannot be filtered out at the receiver. • It is on the receiver's operating frequency and competes with the desired signal, which in effect, degrades the operational performance.

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Transmitter Noise Analysis The analysis predicts each transmitter’s noise signal level present at the input of each receiver. • It takes into account the transmitter’s noise characteristics, frequency separation, power output, transmission line losses, filters, duplexers, combiners, isolators, multi-couplers and other RF devices that are present in both systems. • Additionally, the analysis considers the antenna separation space loss, horizontal and vertical gain components of the antennas as well as how they are mounted on the structure. The gain components are derived from antenna pattern data published by each manufacturer.

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Transmitter Noise Analysis The analysis determines how much isolation is required, if any, to prevent receiver performance degradation caused by transmitter noise interference. The Table below depicts the results of this analysis. For each receiver, the transmitter that has the worst-case impact is displayed. The Signal Margin represents the margin in dB, before the receiver’s performance is degraded. A negative number indicates that the performance is degraded and the value indicates how much additional isolation is required to prevent receiver performance degradation

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Page 150

Receiver Desensitization Analysis Receiver desensitization interference occurs when an undesired signal from a nearby "off-frequency" transmitter is sufficiently close to a receiver's operating frequency. The signal may get through the RF selectivity of the receiver. If this undesired signal is of sufficient amplitude, the receiver's critical voltage and current levels are altered and the performance of the receiver is degraded at its operating frequency. The gain of the receiver is reduced, thereby reducing the performance of the receiver.

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Page 151

Receiver Desensitization Analysis A transmitter can be operating several megahertz away from the receiver frequency and/or its antenna can be located several thousand feet from the receiver's antenna and still cause interference. The analysis predicts each transmitter’s signal level present at the input of each receiver. It takes into account the transmitter’s power output, frequency separation, transmission line losses, filters, duplexers, combiners, isolators, multi-couplers and other RF devices that are present in both systems. Additionally, the analysis considers the antenna separation space loss, horizontal and vertical gain components of the antennas as well as how they are mounted on the structure. The gain components are derived from antenna pattern data published by each manufacturer.

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Page 152

Receiver Desensitization Analysis The analysis determines how much isolation is required, if any, to prevent receiver performance degradation caused by receiver desensitization interference. The Table provided separately depicts the results of this analysis. • For each receiver, the transmitter that has the worst-case impact is displayed. • The Signal Margin represents the margin in dB, before the receiver’s performance is degraded. • A negative number indicates that the performance is degraded and the value indicates how much additional isolation is required to prevent receiver performance degradation.

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Page 153

Intermodulation Interference Analysis The frequencies of IM products are derived from mathematical formulae. IM products are classified by their "order" (2nd, 3rd, 4th, ...Nth). Some of the more common forms of mixing are illustrated in the following examples. Note that The "A", "B", and "C" designations are the mixing frequencies. The numerical number assigned to the letter designation indicates the harmonic relationship of the frequency. Thus, 2A means the 2nd harmonic of frequency A. Order First Second Third Fourth Fifth Sixth Seventh Eighth Ninth

June, 2011

Mixing Formulae A=B, A=C, etc. A ± B, A ± C, etc. A + B - C, A ± 2B, 2A ± B, etc. A ± 3B, 2A ± 2B, 3A ± B, etc. A ± 4B, 2A ± 3B, 3A ± 2B, 4A ± B, etc. A ± 3B ± 2C, 2A ± 2B ± 2C, 3A ± 2B ± C, etc. A ± 6B, 2A ± 5B, 3A ± 4B, 4A ± 3B, 5A ± 2B, etc. A ± 7B, 2A ± 6B, 3A ± 5B, 4A ± 4B, 5A ± 3B, 6A ± 2B, A ± 8B, 2A ± 7B, 3A ± 6B, 4A ± 5B, 5A ± 4B, 6A ± 3B, c.


Page 154

Intermodulation Interference Analysis The IM product formulae are just a few of the many possible combinations. When there are four frequencies involved at one time, the mixing possibilities increase tremendously. Not all of the mixing possibilities are significant in creating interference signals. Some fall “out-of-band” of the receiver and the higher order IM products are usually weaker in signal strength.

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Page 155

Transmitter Spurious Output Interference Analysis Transmitter spurious output interference can be attributed to many different factors in a transmitter. The generation of spurious frequencies could be due to non-linear characteristics in a transmitter or possibly the physical placement of components and unwanted coupling. If a spurious signal falls within the passband of a nearby receiver and the signal level is of sufficient amplitude, it can degrade the performance of the receiver.

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Transmitter Spurious Output Interference Analysis The analysis takes into account a transmitter’s spurious output specification, output levels, transmission line losses, filters, duplexers, combiners, isolators, multi-couplers and other RF devices that are present in each system. Additionally, the analysis considers the antenna separation space loss, horizontal and vertical gain components of the antennas as well as how they are mounted on the structure. The gain components are derived from antenna pattern data published by each manufacturer. The analysis determines how much isolation is required to prevent receiver performance degradation for any transmitter spurious signals that fall within a receiver’s passband.

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Page 157

Non-linear Effects and Intermodulation

Almost “everything” is slightly (or extremely) non-linear. Only free space is theoretically a true linear medium. Particularly non-linear are: • all active semiconductor devices • corroded electrical connections, etc. When high RF current levels are present in non-linear devices, waveform distortion occurs • A distorted (clipped, peaked, etc.) non-sinusoidal waveform is equivalent to a sum of sine waves of several different frequencies (Fourier series) • Product waveforms can also occur when two frequencies are “mixed” due to the non-linearity • if the nonlinear device characteristics are accurately known (intercept point, etc.), IM amplitudes can be accurately computed. • If nonlinear device characteristics are unknown, the worst-case intermod mechanism will have a conversion loss of at least 6 dB. June, 2011


Page 158

What to do about IM Try to prevent or reduce the amplitude of strong RF signals reaching receivers in wireless systems • Reduce or eliminate at the source, if feasible (spurious emissions from electric lamps, signs, elevator motors, etc.) • Shielding, enclosure, modification of antenna directionality to reduce the penetration of electromagnetic waves • Identify and eliminate secondary non-linear radiators: parallel metal joints with conductive connections, ground all parts of metal fences, rain gutters, etc. (also improves lightning protection) • Conducted RF from wires, etc. entering receiver can be reduced via low pass or band pass filters, ferrite beads, etc. • Notch filters to remove source RF, or specific harmonics or products

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Page 159

Intermod Intermod “Forensics” “Forensics”

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Intermod “Forensics” and Detective Work “Detective” Work to identify • the likely creation paths for an observed intermod problem • methods of reducing the intermod production or delivery to non-problematic levels Identify source and victim destination • analyze each conceivable path – gains, isolations, line losses, conversion losses, bandpass filters in the path – compute the likely intermod amplitude at the victim due to that path – the path with the largest calculated amplitude at the victim is the most suspect and should be investigated or mitigated first

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Truth Serum for a Witchhunt: a lowly attenuator Often the source of intermod is unclear – it could be anywhere: • In the affected victim receiver • In a transmitter of one of the source signals • In some other nonlinear device nearby A simple attenuator (usually 3, 6 or 10 db “pad”) can be used to help isolate where the intermod is occuring • Place pad in front of the victim receiver – If the intermod decreases the same amount as the pad attenuation, it is coming in from outside, beyond the pad Keep looking elsewhere – If the intermod decreases by a multiple of the pad attenuation, it is being generated in the receiver Consider additional filtering for the receiver • Place high power pad in front of the transmitters, one by one – When the intermod is reduced by the maximum amount, the pad is on the transmitter producing most of the intermod

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Using an Attenuator for Intermodulation Location

IM -90 dbm

TX1

RX

Troublesome intermod is received on a product frequency of TX1 and TX2. Where is the source?

IM -102 dbm RX

TX2

IM -96 dbm

TX1

6 db RX TX2

June, 2011

A 6 db pad on the receiver merely reduces all signals including the intermod by 6 db. The intermod is originating outside this receiver.

IM -114 dbm RX


6 db With a 6 db pad on TX1, the intermod TX1 goes down 12 db. The intermod is reduced, but this does not prove where the IM is generated. TX2

With a 6 db pad on TX2, the intermod goes down TX1 lower than anywhere else. TX2 is an intermod 6 db generator.Now consider additional flitering for TX2 TX2 to suppress the IM.

Page 163

Working Working With With Repeaters Repeaters

AKA AKARe-Radiators, Re-Radiators,Cell CellEnhancers, Enhancers,Boosters Boosters

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Page 164

Wireless Reradiators Reradiators (also called “boosters”, “repeaters”, “cell enhancers”) are amplifying devices intended to add coverage to a cell site Reradiators are transparent to the host Wireless system • A reradiator amplifies RF signals in both directions, uplink and downlink • The system does not control reradiators and has no knowledge of anything they do to the signals they amplify, on either uplink or downlink Careful attention is required when using reradiators to solve coverage problems • to achieve the desired coverage improvement • to avoid creating interference • to ensure the active search window is large enough to accommodate both donor signal and reradiator signal as seen by mobiles June, 2011


Cell

RR

Reradiators are a ‘“crutch” with definite application restrictions. Many operators prefer not to use re-radiators at all. However, reradiators are a cost-effective solution for some problems. Page 165

Consideration Checklist for Reradiators Must not overdrive Repeater to output levels above max • Forward link case • Reverse link case Repeater gain must not exceed antenna isolation plus safety cushion • Forward link case • Reverse link case Repeater output noise floor must not raise BTS noise floor more than 1 db Repeater Donor must be dominant, so no other defacto donors appear Windows of mobile and BTS must span both the BTS-mobile direct signal and BTS-RR-mobile signal (see separate page and diagrams) Donor must have sufficient capacity to handle intercepted traffic Power budgets and levels must take into account maximum carriers maximum loading situation General: Don’t allow “foldback” coverage from RR in direction of donor BTS unless absolutely required by unavoidable situation • Life is so much better downrange – relatively narrow windows are adequate • Wide windows are needed if you get between donor and RR June, 2011


Page 166

Wireless Reradiators Propagation Path Loss Considerations To solve a coverage problem using a reradiator, path loss and link budget must be considered • how much reradiator gain is required? • how much reradiator output power is required? • what type of antennas would be best? • how much antenna isolation is needed? • how big will the reradiator footprint be? • how far can the reradiator be from the cell? • will the reradiator interfere with the cell in other areas? • What is the propagation delay through the reradiator, in chips? • Will search windows need to be adjusted for compensation? Path Loss Cell

Gain

RR Gain

(free space ERP usually applies) Line Loss

Path Loss (free space??)

RR Gain

June, 2011


Signal Level in target area Page 167

Design Limitations of Wireless Reradiators Input and output are on same frequency! • usable gain: must be less than isolation between antennas, or oscillation occurs • this gain restriction seriously limits available coverage • Typically achievable isolations: 80-100 dB Some reradiators use advanced internal DSP signal cancellation techniques to achieve an extra 20-30 db of equivalent isolation June, 2011

Broadband Reradiator Cell

Unavoidable Coupling C o m b i n e r

C o m b i n e r

BPF: Uplink BPF: Downlink

Wireless Spectrum


Frequency

Page 168

Reradiator Issues Amplification of Undesired Signals • The reradiator is a broadband device capable of amplifying other signals near the intended CDMA carrier, both on uplink and downlink. Will these signals capture unwanted traffic, cause unwanted interference, or overdrive CDMA handsets or the base station? Linearity • CDMA reradiators must be carefully adjusted to ensure they are not overdriven. Overdriving would produce clipping or other nonlinearities, resulting in code interference Traffic Capacity • Noise floor of reradiator’s output may raise noise floor at donor BTS receiver, reducing inherent capacity and coverage of the donor BTS!! Careful adjustment is necessary Alarms • Normal BTS faults are automatically reported through the system; reradiator faults must be monitored some other way June, 2011


Page 169

Search Search Window Window Considerations Considerations When When Using Using Repeaters Repeaters

June, 2011


Page 170

Dealing With Reradiator Srch/Acq Window Issues General Principle for Forward Link Survival: • All copies of the forward link signal MUST be inside the mobile’s active search window – Calculate the propagation delay of the direct BTS>Mobile signal in chips – Calculate the propagation delay of the BTS>Rerad>Mobile signal in chips (don’t forget delay inside Rerad, ~12 ch) – Make sure that the active search window is twice the difference between these two signals’ arrival delay (if 72 chips apart, make window 2 x 72 chips wide plus an allowance for scattering as observed from drive tests) General Principle for Reverse Link Survival: • All copies of the reverse link signal MUST arrive inside the channel element’s search windows • Hearing the ACH Preamble: On access channel: ACCacqSrchW must be wide enough to hear the most-delayed signal • Hearing the rest of the Access Probe: On access channel: ACCdemodSrchW must be wide enough to continue hearing ALL signal components – double the difference in their arrival times • Hearing the TCH Preamble: Traffic channel TCHacqSrchW must be wide enough to hear the most-delayed signal • Hearing the rest of the Call on Traffic channel: TCHdemodSrchW must be wide enough to continue hearing ALL signal components – double the difference in their arrival times Max ACQ or DEMOD SW, both ACC and TCH: 4096 eighthchips for orig; with XCEM effective width is X C Rings x 4096, June, 2011


Page 171

Mobile Rx (Fwd Link) Situation Donor PN244

Repeater Delay 12 chips

24 km = 4 x 24 = 96 chips

RR

RR 24-8 km 16 km 64 chips

8 km 32 chips Driving away from Donor

Srch_Win_A 40 chips Mobile

76 chips diff.

Rake Fingers

The mobile Active search window is internally administered, constantly recentered on the earliest observed multipath component in the window noticed during each scan by the pilot searcher

Bad!!

24-8 km 16 km = 64 chips

The BTS>RR>Mobile signal isn’t even noticed by the mobile since it falls outside the mobile’s active search window!!

PN244+ 96+12+32 = 140 chips

Reference PN June, 2011


Page 172



24 km = 4 x 24 = 96 chips

RR


8 km 32 chips Driving away from Donor

Srch_Win_A 160 chips

Mobile Rake Fingers

76 chips diff. Mobile Rake Fingers

Good!!

24-8 km 16 km = 64 chips

The BTS>RR>Mobile signal is safely used by the mobile since it falls already inside the mobile’s active search window!!

PN244+ 96+12+32 = 140 chips



Page 173



24 km = 4 x 24 = 96 chips

RR


8 km 32 chips Driving toward Donor

76 chips diff. The BTS>Mobile direct signal isn’t even noticed by the mobile since it falls outside the mobile’s active search window!!

Bad!!

24-8 km 16 km = 64 chips

Srch_Win_A 40 chips

PN244+ 96+12+32 = 140 chips



Page 174


24 km = 4 x 24 = 96 chips

Repeater Delay 12 chips RR


8 km 32 chips Driving toward Donor

76 chips diff. The BTS>Mobile direct signal is safely used by the mobile since it falls already inside the mobile’s active search window!!

Good!!

24-8 km 16 km = 64 chips

Srch_Win_A 160 chips

PN244+ 96+12+32 = 140 chips



Page 175

BTS Rx (Rev Link) Situation


Donor 24 km = 4 x 24 = 96 chips

RR


8 km 32 chips Driving either Direction

Maximum RTD delay, chips = 2 x 140 = 280 chips AchAcqSW and TCHacqSW

True LC PN Offset Intended for Mobile to TX June, 2011

24-8 km 16 km = 64 chips late

280 chips = 2240 eighthchips

PN244+ 96+12+32 = 140 chips late


Page 176

BTS Rx (Rev Link) Situation


Donor 24 km = 4 x 24 = 96 chips

RR


8 km 32 chips Driving either Direction

Offset RTD delay, chips = 2 x 76 = 152 chips AchDemodSW And TCHDemodSW

76 chips diff. one side

24-8 km True LC PN Offset Intended for Mobile to TX 16 km

152 chips = 856 eighthchips

PN244+ 96+12+32 = 140 chips late

= 64 chips late June, 2011


Page 177

Femtocells Femtocells

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Page 178

What do you mean, “Femtocell”?! Summary of Units Number N 1,000,000,000,000 1,000,000,000 1,000,000 1,000 100 10 1 0.1 0.01 0.001 0.000001 0.000000001 0.000000000001 0.000000000000001 June, 2011

x10y x1012 x109 x106 x103 x102 x101 x100 x10-1 x10-2 x10-3 x10-6 x10-9 x10-12 x10-15

Prefix Tera GigaMegaKilohectodecadecicentimillimicronanopicofemto-

We use big and small units every day to quantify how big things are. • Kilograms (cocaine) • Megahertz (frequency) • Milliwatts (power) A Femtogram is 10-15 gram, 1/1000000000000000 gram. Over the years there’s been talk about microcells, nanocells, picocells, and femtocells. All of these are tiny cells covering just a small building, room, or parking area, etc.


Page 179

Sprint Femtocell Public Article Sprint has begun offering femtocells for its customers that have reception problems in their homes. If you have reception problems in your house, your cell phones will connect to the femtocell rather than struggle to connect to towers. The femtocell is then connected to your home network and your voice and data signals are routed through your internet provider and ultimately to Sprint's network. You must qualify by having low reception issues. If you do qualify though, the device is free, but you must return it if you drop Sprint as your carrier, so basically consider it a loaner. Sprint charges your monthly allotments as well for voice, data and texts, but they don't charge you for the device or a monthly fee. Worst case scenario with Sprint's femtocell might be it just doesn't work. You are not out any money. Best case scenario though is you can use your Sprint phone in the house without dropping calls or losing your internet connection during a download. June, 2011


Page 180

Sprint Femtocell Article (continued) As wireless data traffic grows, many operators have started deploying femtocells for their 2G and 3G networks. Others are incorporating femtocells and in-building coverage solutions into their 4G network plans. Last month AT&T made its first foray into the femtocell arena by offering a 3G Microcell femtocell for $150 with a $100 rebate if customers sign up for a monthly $20 plan that offers unlimited calling for subscribers within the femtocell's range. And in July Sprint Nextel inked a deal with Airvana for 3G CDMA femtocells. Sprint currently offers CDMA femtocells from Samsung, which are designed to boost

June, 2011


Page 181

Sprint JV with GE Healthcare This week, Sprint has gone ahead, working with GE Healthcare to provide a platform for patient data sharing. This move is important not only for healthcare readers, but also for wireless users generally. To offer the service, Sprint is using GE's CARESCAPE Enterprise Access platform, a single, universal wireless platform powered by MobileAccess. Sprint is adding the voice and data transmission layer, along with handsets. Hospitals will be able to use the wireless platform to offer voice and data communications over secure cellular, WiFi and telemetry. When FierceHealthIT met with Sprint representatives at HIMSS '07 earlier this year, they said they were planning to develop inbuilding wireless service not only to serve hospitals, but to establish a model for providing broader wireless services to business campuses in varied industries. In other words, this launch is important not only for HIT, but for Sprint's strategy for oncampus wireless. So if you're interested in wireless generally, keep an eye on how this launch pans out. June, 2011


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Sprint 3G Femtocell Project Sprint will be launching a 3G femtocell, a mini cell phone tower like device that helps you get a better voice and data signal in your home or office. It will be a faster version of the wireless carrier’s 2G Airave product, according to documents filed with the U.S. Federal Communications Commission. The new Sprint femtocell will include a radio for the 3G service and a port for a VoIP (voice-over-IP) line. A release date for the new femtocell is unknown, but expected very soon considering the FCC filing. It may cost the same $100 as the current product, and is also likely to carry a $5 monthly fee. When users make calls connected to the Airave, however, the time spent won't count towards plan minutes. A femtocell operates like your personal mini cell phone tower. You connect the router-like device to your existing broadband landline service (cable or fiber) and it provides better indoor coverage for your phone. Sprint, who has reportedly partnered with Femtocell manufacturer Airvana to deliver the new product. Airave, their $100 femtocell device made by Samsung, has been available nationwide since August 2008. However, Airave doesn’t support 3G - merely Sprint’s CDMA network with speeds of about 150 kilobits per second. Femtocells could help numerous customers with coverage issues when it comes to phone calls, but most require an additional monthly fee of $5-$20 per month. In addition, vendors such as Ubiquisys recently announced that the wholesale price of a femtocell has dropped to below $100. Its usefulness is less obvious when it comes to data transfer, since most customers who own broadband lines already use the much-faster Wi-Fi at home.

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Metro Femtocells and Distributed Antenna Systems (DAS) Compared There’s been a lot of hype recently proposing femtocells as a low cost means of rolling out mobile network capacity (specifically for LTE). • Femtocells could be a low cost way of providing hotspot capacity in public areas. • But in some situations, it will compete with existing techniques. Here we compare and contrast femtocells with DAS. Pros and Cons The benefits of this approach include: • Operator equipment is located in one place – simpler maintenance and upgrade procedures • Supports multiple network operators, allowing sharing of costs and resources • RF coverage can be tailored to meet the needs of specific buildings and use cases • Easily upgraded to handle new frequencies, transmission technologies, capacity • Allows capacity uplift by offloading in-building traffic from Macro layer • Supports rollout of bandwidth hungry, low latency applications But the downsides include: • High capital investment – only justified for large airports, businesses, campuses, centres Complexity - Needs specialist RF expertise to design and maintain Large Business Premises June, 2011


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