Estimation of aircraft distances using transponder signal strength information

Figures & data

Table 1. Mode S downlink formats

Downlink Format	Length (Bytes)	Squittered	Content
DF0	56	No	Air-to-Air (Traffic Collision Avoidance)
DF4	56	No	Surveillance, Altitude
DF5	56	No	Surveillance, Identity
DF11	56	Yes	Mode S All-Call Reply (Identification Squitter)
DF16	112	No	Air-to-Air (Traffic Collision Avoidance)
DF17	112	Yes	1090 Extended Squitter
DF20	112	No	Address, Flight Status, Altitude
DF21	112	No	Address, Flight Status, Identity
DF24	Up to 224	No	Address, Flight Status, Identity, Extended Message

Figure 1. Flowchart depiction of the distance estimation process.

Figure 2. Mode S data vector.

Figure 3. Departure, N170TH, KLAF, April 1, 2016.

Figure 4. Signal strength and altitude, N170TH, KLAF, April 1, 2016.

Figure 5. Noiseless signal channel.

Figure 6. Noisy signal channel.

Figure 7. Geometry for Aulin’s short-term fading model.

Figure 8. Doppler power density spectrum with overlay of first-order Butterworth filter (f _c  = 220 Hz).

Figure 9. Signal excursions and distance estimation errors, N170TH, KLAF, April 1, 2016.

Figure 10. TERM distance estimation error with Pearson Type VII distribution overlay.

Figure 11. NISW distance estimation error with Pearson Type VII distribution overlay.

Table 2. Distance estimation errors

Distance estimation method	Median absolute deviation (nm), KLAF-TERM	Median absolute deviation (nm), KLAF-NISW
Adaptive Butterworth Filter + Rayleigh MLE	0.92	1.12