pathloss training nec.ppt

NEC Internal Use Only

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INTRODUCTIONTo

PATHLOSS

March 17, 2009 NEC Corporation Islamabad

PATHLOSS TRAINING COURSE


NEC Internal Use OnlyNEC Internal Use Only

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Path Loss program is organized into the 8 following modules: Module 01: SummaryModule 02: Terrain DataModule 03: Antenna HeightsModule 04: WorksheetsModule 05: DiffractionModule 06: ReflectionModule 07: MultipathModule 08: Network

GENERAL PROGRAME OUTLINE



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• Module 01: Summary• Module 02: Terrain Data• Module 03: Antenna Heights• Module 04: Worksheet• Q&A

COURSE OUTLINE



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Module 1: SUMMARY MODULE



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Module 2: Terrain Data Module

• Basic procedures to create a Terrain Profiles• Survey Angle calculation• Global 30 ARC Second Database• SRTM Database. • Profile Generation



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Module 2: Terrain Data Module (cont’d)



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Module 2: Terrain Data Module GTOPO30

• GTOPO30 is a global digital elevation model (DEM) with a horizontal grid spacing of 30 arc seconds (approximately 1 kilometer).

• GTOPO30, completed in late 1996, was developed over a three year period .

• The absolute vertical accuracy of GTOPO30 varies by location according to the source data.

• The full resolution have a vertical accuracy of + or - 30 meters.



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Module 2: Terrain Data Module SRTM

• SRTM is a 90m Digital Elevation Data for the entire world. • Originally produced by NASA, is a major breakthrough in

digital mapping of the world, and provides a major advance in the accessibility of high quality elevation data for large portions of the tropics and other areas of the developing world.

• The NASA Shuttle Radar Topographic Mission (SRTM) has provided digital elevation data (DEMs) for over 80% of the globe.

• The SRTM data is available as 3 arc second (approx. 90m resolution) DEMs.

• A 1 arc second data product was also produced, but is not available for all countries.



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Module 3: Antenna Height Module

• Basic Operations, • Setting Clearance Criteria,• Clearance Calculation at a point, • Antenna height Considerations,• Setting Antenna Heights, • Optimizing Antenna heights, • Report Generations



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Module 3:Antenna Height Module (cont’d)



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Module 4: Worksheet Module

• Overview• Antenna Configurations• Reliability Options • Diversity options• Microwave Worksheet Options• Look up Tables



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Module 4: Worksheet Module (cont’d)



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Module 5: Diffraction Module

• Overview, • Diffraction loss variation with K-factor• Diffraction loss variation with different algorithms• Diffraction loss variation with height variation



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Module 5: Diffraction Module (cont’d)

• Diffraction of microwave beam occurs when the beam center line grazes over an obstacle and RF energy reaching the far antenna is attenuated.

• Diffraction creates a small shadow region where some energy is re directed in a narrow and rapidly diminishing wedge toward total shadow.



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Fresnel ZonesFresnel Zones

• The actual amount of diffraction is dependent upon:• The Fresnel Zone Radius of the wave front at the

obstruction point• The Size and Shape of the obstruction and• The Reflectivity of the obstruction.



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Module 6: Reflection Module

• Reflective Plan Definition, • Terrain Roughness,• Variable Parameters, • Dispersion Analysis,



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Module 6: Reflection Module

•Reflection occurs when radio waves strike:• A smooth surface such as water,

sheet of Ice in winter• A smooth earth • The boundary between the adjacent

atmospheric layers of different densities.



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Module 6: Reflection Module (cont’d)

Depending on the length of the reflected path, the reflected wave may arrive at the receive antenna either:

• In phase,• Out of phase or• Partially out of phase



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Module 7: Multipath Module

• Overview, • Constant Gradient Method• Variable Gradient Method



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Module 7: Multipath Module



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Module 7: Multipath Module (Cont’d)



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Module 8: Network Module

• Overview, • Interference calculation procedure, • Interference Calculations



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Module 8: Network Module (Cont’d)



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The simplified RL networks are used to illustrate the calculation procedure.

RECTANGULAR NETWORK TRIANGULAR NETWORK



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Obtain the following information to determine where interference analysis is needed in the network:

Frequency Bands

If the network frequency plan uses different frequencies then there is no need to analyze these links for interference. For example use of 7 and 13 GHz bands together.

Available Frequency Pairs

For example a two frequency plan as opposed to a four frequency plan. Number of pairs determine how often the frequencies are repeated.

System Layout ( to scale)

This will indicate possible cases of interferences in the network

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Distance between paths

Distances over 150 Km an be ignored, however short distances or co located sites must be analyzed for interference.

Terrain

Mountains between sites will block an interfering signal, however sites located on mountain tops must be investigated for possible interference.

Exaggerated Azimuths

90 – 180 degrees may not require interference analysis.



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Antenna Patterns

These should be based on polarizations schemes such as HH, VV, HV, VH used in the network and shall be available for both, the victim receiver and the interfering transmitter.

Path Calculations

These should include: Victim Path, Interfering Path and interfering path to victim receiver.



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• Consider any of the following options to meet the required interference objectives:

• Antenna Changes:

• Adjust Power Output

• Use other frequency assignments

• Re route the link

• Use larger diameter antenna to increase gain

• Use High performance antennas to achieve higher levels of discrimination

• X pole discrimination



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THANK YOU

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