ADS-B data latency refers to the delay between the moment an aircraft's onboard GPS system determines its position and other relevant information, and when this information is displayed or utilized by air traffic control (ATC) systems or other users. This latency represents the time it takes for the ADS-B data to be transmitted from the aircraft, received by ground receivers, processed, and then displayed on ATC screens or other monitoring devices. A latency of 2 seconds would mean that the displayed aircraft position is actually from 2 seconds ago. Minimizing data latency is crucial for ensuring real-time situational awareness and making timely decisions in air traffic management and surveillance.
Indeed, the latency of ADS-B data can vary depending on the specific information being transmitted. For instance, GPS position and velocity data may have different latencies. However, to simplify, let's focus on the latency associated with GPS position data in the context of ADS-B ground-to-air surveillance applications.
I’ll list all the latencies below.
1.GPS receiver catches aircraft position, time T0;
2.GPS receiver output position to onboard data bus, time T1;
3.Position data from GPS receiver arrives at ADS-B transmitter via onboard data bus, time T2;
4.ADS-B transmitter transmit the position data, time T3;
5.ADS-B position data arrives at ADS-B ground receiver, time T4;
6.ADS-B ground receiver output ADS-B position data, time T5;
7.ADS-B position data arrives at ADS-B display system, time T6.
The whole latency is T6 minus T0.
Please keep in mind that this is a very simple explanation of ADS-B latency. The real situation is far more complicated.