HERALD Lab #7

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Interference Analysis

(Herald Professional only)

HERALD Functions

Exercise 7.1 : Search interference

Exercise 7.2 : Modify antennas

Exercise 7.3 : Modify power levels

Exercise 7.4 : Modify frequency/pol.

Exercise 7.5 : Test rain correlation model

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HERALD Functions

The following Herald functions are related to Interference Analysis :

· Prior to interference analysis, hop and equipment configuration must be suitably defined:

· RF channels and polarization used in the active hop are defined in the Frequency Arrangement dialog (displayed by clicking the "Frequency Arrangement / Define" button in the Hop Configuration dialog).

· Net Filter Discrimination (NFD) is defined in the "Interference - Net Filter Discrimination" dialog (displayed by the DataBase / Net Filter Discrim. command), where the interfering and interfered (victim) equipment and the relevant channel spacing are specified (interference analysis indicates if a potential interference cannot be evaluated because NFD is missing).

· Antenna diagram is defined in the "Modify Antenna Data" dialog (displayed by the DataBase / Antenna command).

· The Evaluate / Interference commands start the interference search process. Depending on the selected command, the interference received / produced by the active hop or interference produced in the whole radio network is considered. The "Search Interference" dialog allows the operator to set the search limits (max distance, max frequency spacing, max S/I ratio).

· The Interference Report gives a list of interference exposures, including all the radio and topological data useful to characterize each interference.

· The Customize / Propagation models command displays the "Propagation Models" dialog, where the Interference correlation model can be specified.

Exercise 7.1 : Search interference

Run Herald and open the Interference1_Sample.hpf" project (all the hops in this project operate at 15 GHz).

· Select the ALPHA-ZEBRA hop and display the Hop Report. Check that the channel arrangement is already defined (last lines in the Configuration section of the Hop Report).

· Execute the Evaluate / Interference / From Any Hop to Active Hop command. In the "Search Interference" dialog set the search limits:

· Max frequency spacing = 56 MHz;

· Max distance = 200 km;

· Max (faded) S/I = 100 dB.

Select the first visibility option (list on the right), so that line-of-sight conditions are assumed for all the interference sources.

· In the Interference Report (Useful Rx Site: ALPHA), check the various items in the list of interfering signals and in the interference sources table. Execute the Display / Interference / Toggle Site command to display the Interference Report, Useful Rx Site: ZEBRA ( Tip : Use the Herald Icon ).

· Similarly, test the other commands in the Evaluate / Interference menu. In particular, execute the From Any Hop to Any Hop command, do not modify the Search limits options, so that interference analysis is performed for all the radio hops in the present project.

· Select another hop as the Active Hop, then display the Interference Report using the Display / Interference / Received (or Produced) command.

Exercise 7.2 : Modify antennas

Run Herald and open the Interference2_Sample.hpf" project (the same project used in the previous example, interference search parameters are already initialized).

· Select the ALPHA-ZEBRA hop and display the Interference Report (command Display / Interference Report / Received). Take note of the results, in particular, interference degradation = 4.3dB (print the report to make comparison easier).

· Go to the Hop Configuration dialog ( Tip : Use the Herald Icon ). Modify the antenna at the ALPHA site; select the antenna with code DDD1-15/60/S (second item in the list). Note that this antenna has the same diameter and gain of the previous one, but a large 3dB beamwidth and a lower directivity.

· Display the Interference Report again and compare the new results with the previous ones (in particular, interference degradation has increased to 7.4dB).

· Similarly, open again the Interference2_Sample.hpf" project and select the CHARLIE-DELTA hop. In the Hop Configuration dialog, modify the antenna at the DELTA site; select the antenna with code DDD1-15/60/S (second item in the list). Then, select the ALPHA-ZEBRA hop and display the Interference Report. Compare the results with the ones computed at the first step in this exercise (in particular, interference degradation has increased to 6.9dB).

Exercise 7.3 : Modify power levels

Run Herald and open the Interference2_Sample.hpf" project. As in the previous exercise, select the ALPHA-ZEBRA hop and take note of the interference results, in particular, interference degradation = 4.3dB (print the interference report to make comparison easier).

· Select the CHARLIE-DELTA hop and go to the Hop Configuration dialog. Clicking the "Losses/Degrad. / Define" button, insert in the DELTA site a TX attenuator = 10dB. Check the Hop Report and in particular the Rain Unavailability prediction (increased to about 10 minutes, because of the lower Tx Power = lower Fade Margin, but still acceptable).

· Return to the ALPHA-ZEBRA hop and display the Interference Report. Note that the interference degradation has decreased to 1.4dB).

Exercise 7.4 : Modify frequency/pol.

Run Herald and open the Interference2_Sample.hpf" project. As in the previous exercise, select the ALPHA-ZEBRA hop and take note of the interference results. Display and print the Interference Reports, for both Received interference and Produced Interference (ALPHA and ZEBRA sites).

· Go to the Hop Configuration dialog. Click the "Freq. Arrangement / Define" button to display the Frequency Arrangement dialog. Modify the polarization setting, by clicking the "H<=>V Pol" button (below the table on the right).

· Display again all the Interference Reports (Received, Produced; ALPHA and ZEBRA sites) and compare them with the original ones (printed at the beginning of the present exercise). Note that a significant reduction in interference levels has been obtained with the new polarization in the ALPHA-ZEBRA hop.

Exercise 7.5 : Test rain correlation model

Run Herald and select the BETA-CHARLIE hop.

· Display the Interference Report and note that the interference to the BETA site, coming from the CHARLIE site (CHARLIE-DELTA hop) is labeled as "Correlated Interference" (both the useful and the interfering signals travel the same path and suffer the same rain attenuation).

· Select the ALPHA-ZEBRA hop and display the Interference Report. Note that the interference to the ALPHA site, coming from the DELTA site (CHARLIE-DELTA hop) is very high; the Rx angle, at the ALPHA site is about 2° only (see the Interference Sources table), so the interference path is very close to the useful path. However, this interference in NOT labeled as "Correlated Interference".

· Execute the Customize / Propagation Models command to display the Propagation Models dialog. Note that Correlation Distance (lower frame on the left) is zero, so that Interference Correlation requires that Useful and Interference paths are identical. Modify Correlation Distance to 0.5 km, so that Correlation is declared also if Useful and interference paths are not identical, but very close.

· Display again the ALPHA-ZEBRA Interference Report. Note that the interference to the ALPHA site, coming from the DELTA site (CHARLIE-DELTA hop) is now labeled as "Correlated Interference". (Correlation Distance in the range 0.5-1.0 km appears as the most realistic design choice).

End of HERALD Lab#7

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