MW Links Planning

Micro‐Wave Links Planning

01/12/2010/ /

RICHE ALI

Transmission Expert

LEO Burundi

[email protected]

MW Links Planning Transmission Design Department01‐ 12‐ 2010

i C i iMicrowave Communication

A communication system that utilizes the radio frequency band spanning 2 to 60 GHz. As per IEEE, electromagnetic waves between 30 and 300 GHz are called millimeter waves (MMW) instead of microwaves as their wavelengths are about 1 to 10mminstead of microwaves as their wavelengths are about 1 to 10mm.

Small capacity systems generally employ the frequencies less than 3 GHz while medium and large capacity systems utilize g p y yfrequencies ranging from 3 to 15 GHz. Frequencies > 15 GHz are essentially used for short‐haul transmission.

Microwave radio communication requires a clear line‐of‐sight (LOS) condition.

R di LOS k i h f F l lli id dRadio LOS takes into account the concept of Fresnel ellipsoids and their clearance criteria.


Available RF SpectrumAvailable RF Spectrum

Band AdvantageAdvantage DisadvantageWideband links are vulnerable to dispersive fading

2‐4 GHzBest propagation - no power fading (decoupling, ducting).Effective space diversity.

Best propagation - no power fading (decoupling, ducting).Effective space diversity.

Wideband links are vulnerable to dispersive fading. Reduced fade margins due to lower antenna gains. Higher interference levels. 2 GHz impacted by UMTS, FWA. High clearance paths are vulnerable to reflections. 4 GHz shared with satellites.

6‐8 GHzLowest outage in non-ducting areas. Best high capacity, long-haul performance Very effective space diversity. Good discrimination to interference and long-delayed reflections

Lowest outage in non-ducting areas. Best high capacity, long-haul performance Very effective space diversity. Good discrimination to interference and long-delayed reflections

Longer paths are vulnerable to power fades due to ducting and decoupling in an adverse climate, requiring higher path clearances in some areas. Bands are crowded in some areas.

10 GHz

delayed reflections.

Good longer path performance .Effective space diversity. Low rain outage in thunderstorm areas.

delayed reflections.

Good longer path performance .Effective space diversity. Low rain outage in thunderstorm areas.

Limited bandwidth (4‐16 T1/E1) RF channels.

Rain outage is a major factor in some areas. Shared with

11 GHzWide spectrum (1000 MHz) available Many high capacity channels available

Narrow and wideband channels available

Wide spectrum (1000 MHz) available Many high capacity channels available

Narrow and wideband channels available

satellite services 10.9‐12.75 GHz.

Outages are dominated by rain in thunderstorm areas, so path lengths are limited.

13‐18 GHz

23‐38 GHz

Narrow and wideband channels availableUncrowded bands (2000 MHz @ 18 GHz).

Few bandwidth constrictions .Uncrowded bands (e.g. 2400 MHz wide band at 23 GHz)

Narrow and wideband channels availableUncrowded bands (2000 MHz @ 18 GHz).

Few bandwidth constrictions .Uncrowded bands (e.g. 2400 MHz wide band at 23 GHz)

Very rain sensitive ‐ e.g. needs 12‐16 dB more fade margin (or 50% shorter paths) at 23 GHz than 18 GHz for equal outage in rain areas.


Microwave Link design methodologyMicrowave Link design methodology

Microwave Link Design is a methodical, systematic and sometimes lengthy process that includes :

Loss/attenuation calculations.

Fading and fade margins calculations.

Frequency planning and interference calculations.

Quality and availability calculations.


Microwave Link design ProcessMicrowave Link design Process

The whole process is iterative and may go through many redesign phases before the required quality and availability are achievedphases before the required quality and availability are achieved.

FInterference

Frequency Planning

analysis

Propagation losses

h

RainattenuationFading

Link BudgetBranching losses

Diffraction‐refraction losses

gPredictions

QualityOther Losses

losses

Multipath

Qualityand

Availability


Micrwave Link DesignpropagationCalculations

Radio Path Link BudgetRadio Path Link Budget

Transmitter 1

Splitter Splitter

Transmitter 2waveguide

Receiver 1

Splitter Splitter

Receiver 2

OutputP (T )

Branching

pagatio

nesenna

n en

na

nPower (Tx) Losses

Prop

Loss

Ante

Gain

Ante

Gain

Branching Losses

Fade Margin


Receiver threshold Value

SDH Capacities

Line Rate SDH Signal PDH Signal Ch l T

SDH Capacities

Line Rate(Mbit/s)

SDH Signal PDH Signal# E1 (2048 kbit/s)

Channel Transport

2.048 VC ‐ 12 1 30

34 368 VC 3 16 480

Radio or Fiber

34.368 VC ‐ 3 16 480

51.84 Sub‐STM‐1* 21 630

139.264 VC ‐ 4 64 1,920

155.52 STM ‐ 1 63 1,890

622.08 STM ‐ 4 252 7,560

2488 32 STM ‐ 16 1 008 30 240

1:N Radioor Fiber2488.32 STM 16 1,008 30,240

9953.28 STM ‐ 64 4,032 120,960

Reference: ITU‐R Rec. F.750‐3 (1997)

Fiber

( )


SDH Frame StructureSDH Frame Structure

Frame Length: 125RSOH : Regenerator Section OverheadMSOH: Multiplexer Section Overhead

secµ


MSOH: Multiplexer Section OverheadBit rate: 155.520 Mbps

SDH Frame OverheadSDH Frame Overhead

X … Bytes reserved forynational usage

M … Bytes reserved for media specific usage

(empty) … Bytes reserved for future standardization


Typical Service RequirementsTypical Service Requirements

Bandwidth requirements for the applications listed are considered sufficient to provide adequate user


Bandwidth requirements for the applications listed are considered sufficient to provide adequate user experience on a single workstation.

Transmission Media

Copper or Fiberoptics Cable ‐ Leased Services

Transmission Media

Copper or Fiberoptics Cable ‐ Leased ServicesMonthly fee…operator never owns the network

Often long repair times ... customers are out of service

Limited availability...e.g. ~99.8% (~17 hr/yr traffic loss)

Fiberoptics Cable ‐ PurchaseHigh installing cost ($30k‐300k per km) favors very high capacity (2.5‐10 Gb/s, per “colour” with WDM) data transportVulnerable to route damage with long service interruptions

Wi l O i l (I f d L ) P hWireless Optical (Infrared, Laser, etc.) ‐ PurchaseVery short range ‐ affected by optical visibility (300 m – 3 km)Low to high capacity, now to ~10 Gbit/s (OC‐192/STM‐64)

Microwave Radio ‐ PurchaseLow life cycle costRapid deployment responsive service implementation and under full user control (sites


Rapid deployment, responsive service implementation, and under full user control (sites and routes are secure)

Terrestrial Radio‐relay linksInterference

Terrestrial Radio‐relay links

Antenna

Path

Antenna

RadioTx

RadioTx

Path

Feeder

Data Data

Feeder

MultiplexRx

MultiplexRx

Data

Terminal “A” Terminal “B”

Radio meets superior reliability, higher security, and more demanding performance andRadio meets superior reliability, higher security, and more demanding performance and quality standards.Radio user has total control over site access and restore time.Radio grows with the network: Easily expandable and accommodates future relocation.Radio has an operational life long after the leased line payback has passed (~2 yrs)


Radio has an operational life long after the leased‐line payback has passed ( 2 yrs).Radio provides clear channel and protection capabilities.

MW advantages and Disadvantages

Advantages of MW wireless Disadvantages of MW wireless

MW advantages and Disadvantages

solution solution

Low fixed costs Line of sight (LOS) propagation Fast implementation (days)Focus deployment on best

opportunities

Weather affects availabilityAesthetics problems of customer

antenna community base stations andopportunitiesWinning cost profile in urbanand rural marketsS d ll t i t

antenna, community base stations and towersMMW technology is relatively new

t i l li ti (55 GH )Speed allows entry into newmarketsUnregulated at local levels

to commercial applications (55 GHz)

80% of cost is electronics(not labor and structures)


Radio Wave Propagation

GEO, MEO,

p g

and LEO Satellites

Sky Wave(HF only)

Ionosphere

REFRACTED WAVE

NON‐REFRACTED (k=1) WAVETransmitting Receiving

Troposphere

Antenna AntennaMULTIPATH RAYS

Ground Wave(LF/MF only)

True Earth’s Curvature


True Earth s Curvature

Logarithmic Units

P d i dB V l d i dB V

Logarithmic Units

⎟⎠⎞

⎜⎝⎛=

WPdBmP

1log10][ ⎟

⎠

⎞⎜⎜⎝

⎛=

VUVdBUµ

µ1

log20][

Power expressed in dBm: Voltage expressed in dBuV:

1pW = -90 dBmd

⎠⎝ mW1 ⎠⎝ Vµ1

1nW = -60 dBm1 W = -30 dBm1mW = 0 dBmµ

1mW 0 dBm1W = 1000 mW = 30 dBm2W = 2000 mW = 33 dBm4W 4000 W 36 dB4W = 4000 mW = 36 dBm10W = 40 dBm40W = 46 dBm


Antenna Center‐line Determination

The antenna height should be chosen in such a way that obstruction

Antenna Center line Determination

The antenna height should be chosen in such a way that obstruction losses during adverse propagation conditions are acceptable.Also, designer must consider the increased risk for ground reflections if too large a clearance is used.Antenna heights for a path can be obtained:

• Graphically from path profiles• By using mathematical formulae• Using Link planning software tools (e.g. Pathloss v.4.0, Enterprise

Connect, TEMS Link Planner, Ellipse, Harris Magic)


Path CalculationsPath Calculations

500 500

k = 4/3F = 0.6

1.9 GHz

440

m A

MSL

410

470

440

410

470

k=4/3

390

Elevation,

360

410

390

360

410

0.6F1

330

300

330

300

k=4/3

270 270

Site: Yates CenterLat.: 37‐51‐02.NLong : 095 43 53 W

Marmaton37‐49‐40. N

095 09 44 W

____

__ __ __ __ ____

__ __ __ __ ____

__ __ __ __ ____

__ __ __ __ ____

__ __ __ __ ____

__ __ __ __ ____

__

0 5 10 15 20 25 30

Distance, km


Long.: 095‐43‐53. W 095‐09‐44. W

Frequency Spectrum Allocation

Radio signals have to be frequency‐separated if neither antenna discrimination nor topographical shielding provides the necessary

i f i f i i lsuppression of interfering signals.Distinct segments of MW frequency spectrum exhibits different

propagation characteristics (mutli‐path effects rain attenuationpropagation characteristics (mutli path effects, rain attenuation, absorption).

Particular frequency bands differ by their spectral width hence can support different link capacities (channel separations range between 1.75 to 56 MHz).

All f i d i di l t k h ld ll bAll frequencies used in a radio‐relay network should normally be selected from an established frequency plan, generated either by international or national organization


international or national organization.

Receiver SensitivityReceiver Sensitivity

Receiver sensitivity of a digital radio, is a minimum signal level on thereceiver’s input terminals, that secures specified maximum allowable BER behind receivers detector (typically 10‐3 or 10‐6 ), including FEC.

Receiver sensitivity is affected by:

Type of modulation method employedType of carrier and clock recovery circuitsNoise figure of the receiver pathPhase noise level of the local oscillatorType of FEC and soft‐detection employedyp p y


Receiver Sensitivity and C/NReceiver Sensitivity and C/N

Sensitivity (minimum required Rx power) can be also expressed in terms of i i i d C i N i R i (C/N)minimum required Carrier‐to‐Noise Ratio (C/N).

C / [dB dB dB]NCNP Th /min += [dBm; dBm, dB]

Where thermal noise:Where thermal noise:

dBTh NFkTBN ++= 30)log(10 [dBm; dBW, dB]

k… Boltzman’s constant = 1.38 x 10‐23 J/KT… Absolute temperature of the receiver in K (0 oC = 273.15 K)B … Noise bandwidth in HzB … Noise bandwidth in HzNF … Noise Figure of the receiver in dB

E.g. for BPSK minimum required C/N= 6 dB, for QPSK minimum


Required C/N=10 dB, for 16‐QAM minimum required C/N= 17 dB@10‐3

Receiver Thresholds

Three Digital Radio Thresholds: One for factory and field in‐service testingThree Digital Radio Thresholds: One for factory and field in service testing,and two for outage calculations, performance measurements, etc.

The 10‐6 BER (or other BER<10‐6) Static Threshold is for factory and in‐service field verification of receiver noise and interference levels, measured manually with attenuators

The 10‐3 BER Dynamic Threshold is for outage calculations and “hands‐off” field measurements in a normal fading environment with BER network managementmeasurements in a normal fading environment with BER network management, following ITU‐T G.821 performance definitions.

The BER‐SES Dynamic Threshold is the same as the above dynamic threshold, but is y yused for outage calculations following ITU‐T G. 826 performance definitions. Usual range of BER‐SES is 10‐3 – 10‐4.


Comparison of Modulation MethodsComparison of Modulation Methods

Receiver sensitivities for BER = 10‐6 (3.5, 10.5 GHz)

For the same input data rate, more crowded M‐QAM constellations use channel frequency band more effectively, but require higher C/IHigher level M QAM are susceptible to selective fading and other typesHigher level M‐QAM are susceptible to selective fading and other types

of linear distortion.M‐QAM schemes require linear RF power amplification.


Spectrum is expensive => Spectrum efficiency wins the battle

Free Space Loss and AbsorptionFree Space Loss and Absorption

A free space equation simply assumes that radio waves are transmitted equally in all directions Hence the power density is equal in every point of a sphere havingall directions. Hence the power density is equal in every point of a sphere having transmitter in its center. Receiver captures only small part of the power, which is proportional to the effective area of receiving antenna – isotropic radiator.

2⎞

⎜⎛=A λ

4 ⎠⎜⎝

=D

AFS π⎞

⎜⎛A λl20

⎠⎞

⎜⎝⎛−=

DAFSdB π

λ4

log20In decibels:

Where D distance between transmitter and receiverWhere D… distance between transmitter and receiver… wavelengthλ


Atmospheric Absorption CurvesAtmospheric Absorption Curves

Significant for frequency bands above 15Significant for frequency bands above 15 GHz.

Absorption on water vapor H2OAbsorption on oxygen molecules O2Absorption on other gasses:smog, exhaustions, etc.


Terrain Related EffectsTerrain Related Effects

Specular Reflection: For MW hops routed across large or medium sized bodies ofSpecular Reflection: For MW hops routed across large or medium sized bodies of water (see, lakes, rivers), part of the energy radiated by the transmitter can be almost totally reflected from the water level, then reach the receiver and add d i l i h di i l hi f d h d h f hi hdestructively with a direct signal. This causes a power fade, the depth of which changes nocturnally (K‐variation).

Diffraction effects: MW energy reaching an obstacle, the longitudinal dimension of which is comparable to the wavelength, is bent behind the obstacle. This bending is called diffraction. The rays behind the obstacle, that are bent under different angles, add up in a complex manner and cause cross‐sectional variation in power density. Common manifestation of such varying power density is an p y y g p yattenuation on the direct path between Tx and Rx. This attenuation is subjected to K‐variation and is closely coupled to Fresnel zones clearance.


Long High HopLong High Hop

K = ∞2400

0.25° Discriminationto the Reflection

0.543°Decoupling

Angle2000

2400(731m)

K = 4/3

1500

1000 AMSL, Ft

500 0.249°Grazing Angle

1150 ft(350 m)

Elevation

0

0 20 40 60 80 100(161 km)

Distance,Mi

Short delays (up to 5 nsec) must be tolerable if radio DFM is high enough (>50dB), since there is very little antenna discrimination on long paths. Coupling of the reflected ray can be sometimes controlled by up‐tilting the


antennae (0‐0.5 deg.)

Short High HopShort High Hop

K =0.109O Decoupling

Angle

K = 4/31.25O Discriminationto the Reflection

1200(365m)

1000

K = Angle

1150 ft (351m) 750

500 AMSL, Ft

500

250 1.248O

Grazing Angle levation

A

0

0 4 8 12 16 20(32 km)

Distance,Mi

E

For high grazing angles (1‐5 deg.), vertical polarization shall be preferred. Decoupling of the reflected ray is difficult to control and


p p g ydelays can be high (up to 25 ns).

Basic of Fresnel ZoneBasic of Fresnel Zone

Fresnel Zone ‐ Areas of constructive and destructive interference created when electromagnetic wave propagation in free space is reflected (multipath) orelectromagnetic wave propagation in free space is reflected (multipath) or diffracted as the wave intersects obstacles. Fresnel zones are specified employing ordinal numbers that correspond to the number of half wavelength multiples that represent the difference in radio wave propagation path frommultiples that represent the difference in radio wave propagation path from the direct path.

The Fresnel Zone must be clear of all obstructions.

Typically the first Fresnel zone (N=1) is used to determine obstruction loss.

The direct path between the transmitter and the receiver needs a clearance above ground of at least 60% of the radius of the first Fresnel zone to achieveabove ground of at least 60% of the radius of the first Fresnel zone to achieve free space propagation conditions.

Earth‐radius factor k compensates the refraction in the atmosphere.

Clearance is described as any criterion to ensure sufficient antenna heights so that, in the worst case of refraction the receiver antenna is not placed in the diffraction region.


g

Fresnel Zones ConceptpElectromagnetic energy directed by the transmitting antenna needs 3D unobstructed space to travel to the particular receiver. p pMore then 90% of the energy radiated in particular direction is concentrated in so called 1‐st Fresnel zone. 1‐st Fresnel zone must remain unobstructed to avoid diffraction losses Even Fresnel zone

Radius of the n th Fresnel zone

remain unobstructed to avoid diffraction losses. Even Fresnel zone are important to judge upon reflection points.

Radius of the n‐th Fresnel zone:

21

ddddnr+

= λ21 dd +

Where … wavelengthλ


Fade MarginFade Margin

4PSK 8PSK 16QAM 32QAM225QPR 128QAM256QAM

–10‐2—‐‐‐‐

–10‐3—

—‐‐‐‐—‐‐‐‐—‐‐‐‐—‐‐‐‐—‐‐‐‐—‐‐‐‐—‐‐‐‐—

4PSK4QAMQPSK

9QPR

8 S 32QAM

49QPR 64QAM128QAM32PSK

Q

512QAM25QPR

Fade Margin is a difference between median received signal level, calculated from Power

‐‐‐‐

–10‐4—‐‐‐‐

–10‐5—‐‐

(OUTAGE) Excludes FEC Coding Gains

Budget equation, and BER=10‐3 threshold of the receiver system.This difference has to account for stochastic

i h h‐‐

–10‐6—‐‐‐‐

–10‐7—‐‐‐

BER

(STATIC)

propagation phenomena, that can compromise system reliability.

Th h‐–10‐8—

‐‐‐‐

–10‐9—‐‐‐‐

10‐10

These phenomena are:Attenuation due to rain.Intersystem interference.

–10‐10—‐‐‐‐

–10‐11—‐‐‐‐

–10‐12— — ‐ ‐ ‐ ‐ — ‐ ‐ ‐ ‐ — ‐ ‐ ‐ ‐ — ‐ ‐ ‐ ‐ — ‐ ‐ ‐ ‐ — ‐ ‐ ‐ ‐ — ‐ ‐ ‐ ‐ —

BPSK Multipath fading.K‐factor variation.Ducting.


5 10 15 20 25 30 35 40

C/N or C/I Ratio, dB

Ducting.

END!


MW Links Planning

Documents

effective space diversity

branching losses

uncrowded bands

decoupling

ducting

dbm

distance

10 log