Snjezana Gligorevic and Michael Schnell

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B-VHF System Concept
Channel Occupancy and Capacity Analysis

• Snjezana Gligorevic and Michael Schnell
• German Aerospace Center - DLR

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Overview

• B-VHF in Current VHF Band Situation
• NavSim Simulations
• Channel Occupancy Measurements
• B-VHF System Design
• Conclusion

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Current VHF Band Situation Theoretical
25 / 8.33 kHz channel spacing All channels
continuously allocated used
Power
Frequency
25 kHz
25 kHz VHF AM-Channel
Analog
8.33 kHz VHF AM-Channel
Digital
25 kHz VHF VDL-Channel
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Current VHF Band Situation Practical
25 / 8.33 kHz channel spacing Only a part of the
allocated channels are used Not all channels are
seen with full power all the time
25 kHz VHF AM-Channel
Analog
8.33 kHz VHF AM-Channel
Digital
25 kHz VHF VDL-Channel
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B-VHF Overlay System
25 / 8.33 kHz channel spacing Only a part of the
allocated channels are used Not all channels are
seen with full power all the time
25 kHz VHF AM-Channel
Analog
8.33 kHz VHF AM-Channel
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NavSim Simulations

• Worst Case Simulation
• Considerable more occupied VHF channels expected
  than in measurement flights!

• All ground stations (100 duty cycle) and ATC
  sectors within radio horizon considered.

• Each ATC sector is represented by a worst-case
  interfering A/C, i.e. interfering A/C (100 duty
  cycle) is located at the border of ATC sector
  next to victim receiver (observation point).

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NavSim Simulations Worst Case Interfering A/C
ATC Sector
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NavSim Simulations

• Worst Case Simulation
• Considerable more occupied VHF channels expected
  than in measurement flights!
• All ground stations (100 duty cycle) and ATC
  sectors within radio horizon considered.
• Each ATC sector is represented by a worst-case
  interfering A/C, i.e. interfering A/C (100 duty
  cycle) is located at the border of ATC sector
  next to victim receiver (observation point).

• Multiple observation points 12 points on a
  circle representing a fictitious B-VHF boundary

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NavSim Simulations Multiple Observation Points
ATC Sector
B-VHF Cell
Cell Center
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NavSim Simulations Results
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NavSim Simulations Results
Munich Airport (EDDM) Munich Airport (EDDM) Munich Airport (EDDM) Munich Airport (EDDM)
Cell Size Flight Level Interference Power Threshold Available VHF Band
20 nm FL 50 -85 dBm 35.7
20 nm FL 250 -85 dBm 17.6
20 nm FL 50 -80 dBm 50.0
20 nm FL 250 -80 dBm 38.8
20 nm FL 50 -75 dBm 65.5
20 nm FL 250 -75 dBm 65.7
20 nm FL 50 -70 dBm 80.8
20 nm FL 250 -70 dBm 79.1
60 nm FL 50 -85 dBm 19.7
60 nm FL 250 -85 dBm 8.4
60 nm FL 50 -80 dBm 33.0
60 nm FL 250 -80 dBm 23.6
60 nm FL 50 -75 dBm 47.0
60 nm FL 250 -75 dBm 47.1
60 nm FL 50 -70 dBm 55.4
60 nm FL 250 -70 dBm 55.0
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NavSim Simulations Results
Brussels Airport (EBBR) Brussels Airport (EBBR) Brussels Airport (EBBR) Brussels Airport (EBBR)
Cell Size Flight Level Interference Power Threshold Available VHF Band
20 nm FL 50 -85 dBm 24.7
20 nm FL 250 -85 dBm 6.4
20 nm FL 50 -80 dBm 39.6
20 nm FL 250 -80 dBm 24.7
20 nm FL 50 -75 dBm 50.3
20 nm FL 250 -75 dBm 50.4
20 nm FL 50 -70 dBm 67.2
20 nm FL 250 -70 dBm 67.2
60 nm FL 50 -85 dBm 12.2
60 nm FL 250 -85 dBm 3.8
60 nm FL 50 -80 dBm 19.3
60 nm FL 250 -80 dBm 9.1
60 nm FL 50 -75 dBm 34.9
60 nm FL 250 -75 dBm 34.9
60 nm FL 50 -70 dBm 46.3
60 nm FL 250 -70 dBm 46.1
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Results of Measurements
Worst case Simulations EBBR / EDDM
Bovingdon VOR Bovingdon VOR Bovingdon VOR Bovingdon VOR Bovingdon VOR Bovingdon VOR
Radius of Orbit Flight Level Interference PowerThreshold Available VHF Band Available VHF Band Available VHF Band
Radius of Orbit Flight Level Interference PowerThreshold Segment Half Orbit Whole Orbit
10 nm FL 340 -86 dBm 60.58 60.58 48.30
10 nm FL 340 -82 dBm 69.78 69.78 59.33
10 nm FL 340 -78 dBm 78.84 78.84 69.45
10 nm FL 340 -74 dBm 84.10 84.10 79.50
10 nm FL 340 -70 dBm 89.36 89.36 85.61
20 nm FL 260 -86 dBm 66.80 55.52 44.24
20 nm FL 260 -82 dBm 74.87 65.70 56.53
20 nm FL 260 -78 dBm 80.82 74.16 67.50
20 nm FL 260 -74 dBm 85.68 80.93 76.18
20 nm FL 260 -70 dBm 89.71 86.32 82.93
30 nm FL 160 -86 dBm 72.68 58.54 44.40
30 nm FL 160 -82 dBm 78.55 68.26 57.97
30 nm FL 160 -78 dBm 82.98 75.09 67.20
30 nm FL 160 -74 dBm 87.16 81.35 75.54
30 nm FL 160 -70 dBm 90.39 86.41 82.43
6.4 / 17.6
67.2 / 79.1
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B-VHF System Design Link Budget Analysis
B-VHF Cell
ATC Sector
Distance?
B-VHF A/C
Cell Center
Power?
41.0 dBm
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Example Link Budget Analysis
Threshold -75 dBm (65 VHF band available _at_
EDDM)
B-VHF Cell
Interference Power10.2 dBabove Signal Level
42 nm
Cell Center
41.0 dBm
-75.0 dBm
-78.4 dBm
21.0 dBm
-95.0 dBm
-88.6 dBm
-85.2 dBm
24.4 dBm
-95.0 dBm
Interference Power10.2 dBabove Signal Level
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Conclusions

• Interference towards DSB-AM can be avoided!
• B-VHF Tx power lt 21 dBm (A/C) and lt 24.4 dBm (GS)
• With respect to SNR, small B-VHF Tx power no
  problem(SNR gt 64 dB for 25 kbit/s transmission
  per 25 kHz)
• This holds even for the -75 dBm threshold
  (worst case)
• Large interference from DSB-AM towards B-VHF
• Worst case interference on used subcarriers
  within B-VHF system is10.2 dB above B-VHF signal
  level
• Actual interference is much lower then the
  simulated worst case
• Actual interference is not present all the time
  (duty cycle!)
• B-VHF overlay system able to cope with large
  interference power levels
• Spread-spectrum system
• Interference reduction by spreading (diversity)
  and coding
• Final verification of B-VHF system concept with
  simulations