Snjezana Gligorevic and Michael SchnellGerman Aerospace Center - DLR

Channel Occupancy and Capacity Analysis

2Authors: Gligorevic and Schnell – DLR

Overview

B-VHF in Current VHF Band Situation

NavSim Simulations

Channel Occupancy Measurements

B-VHF System Design

Conclusion

3Authors: Gligorevic and Schnell – DLR

Current VHF Band Situation – Theoretical

8.33 kHz VHF AM-Channel

25 kHz VHF AM-Channel

25 kHz VHF VDL-Channel

25 kHzFrequency

Power

Analog

Digital

25 / 8.33 kHz channel spacingAll channels continuously allocated & used

4Authors: Gligorevic and Schnell – DLR

Current VHF Band Situation – Practical

8.33 kHz VHF AM-Channel

25 kHz VHF AM-Channel

25 kHz VHF VDL-Channel

Analog

Digital

25 kHzFrequency

Power

25 / 8.33 kHz channel spacingOnly a part of the allocated channels are used

Not all channels are ‘seen’ with full power all the time

5Authors: Gligorevic and Schnell – DLR

B-VHF Overlay System

8.33 kHz VHF AM-Channel

25 kHz VHF AM-ChannelAnalog

25 kHzFrequency

Power

25 / 8.33 kHz channel spacingOnly a part of the allocated channels are used

Not all channels are ‘seen’ with full power all the time

25 kHz VHF VDL-ChannelDigital

B-VHF Channel

6Authors: Gligorevic and Schnell – DLR

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).

7Authors: Gligorevic and Schnell – DLR

B-VHF A/C DSB-AM A/C

Cell Radius

B-VHF Cell

Cell Center

NavSim Simulations – Worst Case Interfering A/C

ATC Sector

8Authors: Gligorevic and Schnell – DLR

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

9Authors: Gligorevic and Schnell – DLR

B-VHF A/C DSB-AM A/C

Cell Radius

B-VHF Cell

Cell Center

NavSim Simulations – Multiple Observation Points

ATC Sector

10Authors: Gligorevic and Schnell – DLR

NavSim Simulations – Results

11Authors: Gligorevic and Schnell – DLR

12Authors: Gligorevic and Schnell – DLR

13Authors: Gligorevic and Schnell – DLR

NavSim Simulations – Results

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%

14Authors: Gligorevic and Schnell – DLR

NavSim Simulations – Results

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%

15Authors: Gligorevic and Schnell – DLR

Results of Measurements

Bovingdon VOR

Radius of Orbit

Flight Level

Interference PowerThreshold

Available VHF Band

Segment Half OrbitWhole 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%

67.2% / 79.1%

6.4% / 17.6%

Worst case Simulations

EBBR / EDDM

16Authors: Gligorevic and Schnell – DLR

B-VHF A/C DSB-AM A/C

Cell Radius

B-VHF Cell

Cell Center

Distance?

-95.0 dBmMax. Interference

B-VHF System Design – Link Budget Analysis

Power?

ATC Sector

41.0 dBm

17Authors: Gligorevic and Schnell – DLR

Example – Link Budget Analysis

B-VHF CellInterference Power

10.2 dBabove Signal Level

B-VHF A/C DSB-AM A/C

Cell Radius20 nm

41.0 dBm-75.0 dBm

21.0 dBm -95.0 dBm

-78.4 dBm

Cell Center

-88.6 dBm

24.4 dBm -95.0 dBm-85.2 dBm

42 nm

Threshold: -75 dBm (65% VHF band available @ EDDM)

Interference Power10.2 dB

above Signal Level

18Authors: Gligorevic and Schnell – DLR

Conclusions

Interference towards DSB-AM can be avoided! B-VHF Tx power < 21 dBm (A/C) and < 24.4 dBm (GS) With respect to SNR, small B-VHF Tx power no problem

(SNR > 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