The technology has been around on the U.K. network for some time. The earliest reference I can find to trials is 2012. SWT introduced it in fleet service in 2015. I found a thread on its introduction here:
https://www.railforums.co.uk/threads/444-450-asdo-introduction-into-passenger-service.121525/
(I hope I’ve linked that correctly, I’m still new here!).
One thing that does seem a little surprising is that it took so long for the Nova 3 sets to make their way over the core route. Whilst most of the train’s systems could be tested on any route, it would seem it is only possible to test ASDO on the intended route. I wonder when the beacons were installed?
Video below is less technical than the one posted earlier but it’s interesting from the point of view of daily operation from a guards perspective.
ASDO is way older than that. Part of the problem is that a lot of the older material has been lost "down the back of the internet" over time as website get updated.
The first use was Connex South Central / Porterbrooks 377 order. ASDO was one of the improvements over the Connex Southeastern specified 375s. The variation came from the Connex SC's fresh management team at the very end when they were trying to turn it around - the specifier was the later infamous Mr C Horton! (along with DOO cameras). The Porterbrook technical side was led by Ian Walmsley now Modern Railway Tech correspondent.
The initial system was GPS based and didn't work in areas with bad GPS signal leading to manual overrides and slow door opening e.g. at Victoria.
The second version of the then Southern system was an upgrade to improve the GPS issues in problem locations by using RFID beacons fitted between the rails (in a square section fibreglass yellow rod). The new equipment was supplied by Hima-Sella and called TrackLink II and has been fully operation on all 377s for the past 11+ years.
London Underground had been keeping an eye on the Southern ASDO work and for the 09 (Vic) and S (Met. Circ. Dist. + H&C) Stock specified ASDO and a new feature Correct Side Door Enabling - CSDE. The upgraded Hima-Sella system for LU became TrackLink III.
FCC then ordered Tracklink III for the 377/5s for use in the Thamelink core then being upgraded and TrackLink III was also later fitted to the 387s.
(NatEx Anglia 379 were only ordered with the original GPS only system that doesn't work...)
SWR then specified the TrackLink III system for the 458 5car mods (Windsor Line) and later other upgrades.
RSSB then wrote a standard to hopefully make all new implementation compatible and future proof. The main change was to swap from proprietary TrackLink III beacons to off the shelf passive Eurobalsies (lower cost and future proof).
The class 700 order for Thameslink was the first to implement the new RSSB method and Siemens had lots of fun with the software and testing positioning as they made a few bad assumption and took the standard too literally.
All new Siemens and Bombardier products (Desitro City and Aventra) comply with the RSSB standard - safe and relaible. The RSSB standard is become the defacto European way of doing ADSO in the ETCS era.
It appears First / CAF / Beacon all with no previous ASDO experience have gone cheap and ignored the carefully standard based on previous learning experience.