Researchers in aviation usually test systems in simulated environments to find out the pros, cons, challenges, etc. Now ADS-B is a key component of NextGen and its European counterpart. And I've seen papers/researches on applications than utilize ADS-B.
For the US, even shortly before the current pandemic, the Office of Inspector General was not too thrilled with NextGen, with the latest in a series of audits being announced in Oct of 2019. Based on earlier audits, the benefits will not be realized before 2025, and that was before the pandemic, and the latest audit is currently questioning the benefits:
Given concerns over the progress and benefits of NextGen, the FAA Reauthorization Act of 2018 mandated that our office study the potential impacts of a significantly delayed, diminished, or completely failed delivery of FAA's NextGen initiative.
Two years ago I asked, What benefits does Automatic Dependent Surveillance bring to continental ATC over Mode S? Of the pros noted, there were these two relevant to my question here:
- ADS-B updates faster
- ADS-B is cheaper
Since one of NextGen's big aims is boosting the traffic capacity, which is mostly limited by separation in the terminal environment, were alternatives tested? For example:
- Sector limited radars (one per approach end) that would provide the faster update rates. (Radars that don't make complete revolutions.)
- Its relative cost, i.e. equipping thousands of planes versus tens of super busy airports.
If no, were there [then-valid] reasons?